Digital Training Devices

Digital Training Devices CHARLES R. WICKMAN Haneywwll. Inc.,

West Covino, Corifornia

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1. Introduction 2. TrminingRequirementa 2.1 Introduction . 2.2 Definitions 2.3 Training Problem and Requirementa . 2.4 Training Concept 2.6 Trmining Retionale . 3. Training Simulators Using General Purpose Digital Computers 3.1 Introduction . 3.2 Student Environment . 3.3 Instructor'e Console . 3.4 Red-World Simulator 4. Programming Considerations . 5. Non-Training Uses of a Training Simulator . 8. Future Training Device Requirementa Aaknowledgmenta

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1. Introduction

The advent of complex manlmachine systems has resulted in an increasing emphasis being placed on the adequate training of personnel required for system operation and control. This training requirement has, in turn, led to the development of manlmaohine systems, especially designed for training, that effectively duplicate the functional environment to whioh the trainee will be exposed in the operational system. These systems, generally called training devices, have evolved in complexity and sophistication so that at times they rival the complexity of the operational systems. "mining devices are defined for the purpose of this article as equipment especially designed or configured for the purpose of instructing either individuals or groups. For the most part the present article is concerned with a restricted type of training device, namely, a training simulator. A training simulator is a device that effectively reproducea 89

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certain aspects of a given system so that training may be obtained. The aspects reproduced depend upon the particular training problem and include not only external appearance, but also simulation of the operation of parts of the system and selected characteristics of the environment in which the system operates. Examples are many and varied including operational flight trainers for instructing of aircraft pilots and flight crews; submarine attack teachers for coordinated training of complete teams associated with certain aspects of submarine operation; driving simulators for driver education programs; and missile procedure trainers for training launch crews for ballistic missile operation. I n each of these devices the intent is to enable instruction by providing some replica of the operational, real system. These devices have increasingly used digital techniques, including large general purpose computers. It is the purpose of this article to discuss the use of digital techniques in training devices and, in particular, training simulators. The article is neither a complete text nor a highly technical treatise, but rather an introduction and survey of the application of digital techniques, directed towmd readers generally familiar with digital computers and associated techniques. The emphasis is on training aspects of the devices and ways in which digital techniques are used to enhance training. I n order to do this effectively, it is first necessary to explain the nature of training devices, from the standpoint of not only end use, but also the process and considerations underlying the eventual system implementation. I n an article of this length, it is impossible to exhaustively treat digital aspects of training devices. Therefore, it is assumed that the reader has a knowledge of not only digital computers and related techniques, but also the rudiments of systems design and analysis. For completeness, the problem of analysis is discussed, but only as a vehicle to clarify the concepts underlying the use of digital techniques. Similarly, certain aspects of general purpose computers are discussed in order to clarify their particular use in training devices, 2. Training Requirements

2.1 Introduction

As man/machine systems have become more complex, the role of man in systems has changed. One aspect of most complex systems is that fewer individuals are required for performance of given functions. Automatic equipment has replaced many man functions resulting in a 90

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significant reduction in the number of personnel required to implement complex operations. Paradoxically, this does not always result in a reduction of total personnel since the complexity or quantity of the operation may have increased significantly. A case in point would be the large number of operators employed by telephone companies. The original function of manually completing all phone calls has been replaced by a higher order function; yet the total number of operators employed is still very large since the volume of telephone calls and hence the need for the higher order operator function has had a manifold increase. At the same time, and as a result of both the reduction of personnel required for given functions and the performance of simple tasks by automatic equipment, the contribution of the remaining personnel as part of a system has become more complex and critical. Thus, the need for effective training has become increasingly important. Any machine, equipment, or system requires some degree of training or instruction of personnel for either operation or use. Completely automatic systems require minimal instruction. For example, an automatic elevator system requires no operators per se and requires only that passengers select the desired floor and push the correct button. Instruction is satisfactorily conveyed by means of simple printed directions. As the function of man in the system becomes more complex the need for training increases. Even equipment apparently as simple to operate as a telephone requires some training. In fact, industry expends a great deal of effort in improving telephone procedures so as to maximize the effectiveness of telephone use. The importance of adequate training is a function not only of complexity of operation and use by man, but also of the critical nature of the role of man in the effectiveness of system operation. For example, a bank may install an expensive, sophisticated machine bookkeeping system, relatively simple to operate. But, unless the personnel involved in its use are properly trained, errors will occur in these simple operations, both of commission and omission, and as a result the system will not be used to maximum effectiveness. This inefficiency implies a relatively poor return on the investment in the system. In the same way, unless personnel are adequately trained in correct use of a modern weapon system, the system effectiveness may be seriously compromised, Thus, complex man/machine systems require effective training of personnel involved in the use and operation of the system. As the importance and complexity of man’s function in modern systems has increased, training requirements have become increasingly 91

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important. This,however, does not imply that training must in turn be complex. Many critical manual functions in a system are simple and, hence, adequate training can be provided by verbal instruction or simple treining. For example, the role of man in the bank bookkeeping system is important and critical but the individual tasks are by themselves simple. Therefore, a combination of classroom instruction and on-thejob training oan satisfrtotorily fulfill the training requirement. However, in many man/machine systems in existence today the role of man is of critical importance and complex to perform. This l e d to training requirements that in turn are important and complex, For the cams of important and complex training requirements that cannot be satisfied effectively by instruction, on-the-job training, or both, sophisticated training devices have been developed. Typical of the use of oomplex and sophisticated training simulators is the Fleet Ballistic Missile trainer produced by Honeywell for the Navy Training Device Center and installed at the U.S. Submarine Btlee at New London, Connecticut. This simulator mlistically reproduces the functional environment experienced by the attack team of a modern submarine to such an extent that the team may be exercised and trained in all critical tmks whose performance will be required in the operational environment aboard the actual submarine. This simulator is in itself a complex and sophisticated man/maohine system, and is required as a training device because of the critical and complex functions that must be performed by the submarine team. Thus, a complex man/machine system with important and complex functions assigned to operating personnel leads to the development of a sophisticated training device in which the personnel can gain the necessary proficiency in the performance of their assigned t d s . The use of digital techniques in training simulators can be explained only in the context of training problems. Digital techniques are used in the implementation of training simulators only because these techniques aid in the solution of particular training problems. The problems in implementation we seldom unique to training simulators. Only the application is unique. Thus, this section of the article discusses training requirements and serves as the framework for understanding the unique application of digital techniques to training simulators. 2.2 Definitions

Prerequisite to any detailed discussion of training requirements is an understanding of the terminology used. The terminology employed herein is not necessarily at odds with colloquial umge. However, many 92

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terms are used in a restrictive and somewhat narrow sense and thus can cause confusion if not properly explained. “Operational system” or simply “system” will in this article mean the functional manlmachine system or complex. Thus, the actual bank bookkeeping system or the real submarine are “operational systems.” “Training requirement” refers to the need to impart knowledge and skills, not possessed by the personnel assigned to operate the system and essential to successful operation of the system. I n the case of the bank bookkeeping system, the tasks that the operators are unable to perform properly, rapidly, or efficiently and that are essential to the effective use of the system constitute a training requirement, For example, keypunch operators may possess the usual skills required to operate a keypunch, but might not understand the function of the punched cards in the particular bank system. If this understanding is essential to effective use of the total bank system, then this constitutes a training requirement. “Training concept” means the method or methods used to satisfy a particular training requirement for a particular operational system. “On-the-jobtraining” means training effected by using the operational system to provide training while the system is in use. “Training device” denotes any mechanical aid used in training. “Trainer” will denote any training device that exercises the student in the performance of a task or function. “Training simulator” means a trainer that simulates or attempts to duplicate desired aspects of the operational system and is designed exclusively for training purposes. (Sometraining simulators are used for purposes other than training. Rather than confuse the issue, it will be assumed in this article that a training simulator is at least designed for the sole purpose of giving training. An example of a dual purpose device is given below.) “Task trainer” will mean a trainer that exercises a student in the performance of a particular task. A training simulator generally is concerned with a complete set of tasks and provides for training by providing a simulation of the operating environment. A task trainer, on the other hand, is concerned with one or a t the most a few tasks and does not necessarily provide simulation of the environment. “Training rationale” is the logical justification for the assumption that a particular training simulator will solve part or all of a particular training problem. The training rationale, thus, is an analysis and evaluation of a particular training simulator system design insofar as that design fulfills the training requirements. 93

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2.3 Training Problems and Requirements

The need for a trainer is indicated when the man cannot acquire a necessary level of skill by on-the-job experience, “dry run” practice, or verbal instruction or written directions. A trainer can provide the opportunity for practice that may not be present on the job. For example, emergency situations can be set up on the trainer and responses practiced without hazard to the trainee. If he makes a mistake on the trainer, i t is not fatal. The situation on the trainer can be modified to permit learning by simplifying the task. An easy problem oan be set up first and practiced and then the difficulty level can be increased in gradual steps. As examples, a trainee pilot can practice control of each axis separately and then altogether; the sonar echo can be clear and distinct at first and then gradually obscured; the target can be moved in a straight line at first and evasive maneuvers gradually added. This problem control from simple to difficult is one of the main advantages of the use of a trainer, since practice in the real-world situation in gradual steps may not be possible. The trainer may also be necessary to sense and record trainee aotions for evaluation and critique. This is important where detection of errors or mistakes with the operational equipment is not possible. Comparative scores and measured skill levels are also obtainable in a trainer and may not be available with the operational equipment. These and other considerations determine whether a training problem exists in a given situation. The scope of this article is limited to those training problems requiring a trainer of sufficient complexity to use digital techniques. To a great extent, the article is concerned with an even more restrictive set of training problems, namely, those requiring training simulators. I n general, a training problem requiring use of a training simulator involves complex functions of the man in the system. For example, the functions performed by the pilot of a modern high-performance aircraft are very complex. This complexity is inherent because of the multitude of pilot tasks and is compounded because of the extremely short response times involved. An error can have very serious consequences. Thus, the complexity and criticality of the functions of the pilot indicate a training requirement that in turn indicates a sophistioated fiight simulator. Similarly, the functions of the submarine team involved in a complex torpedo attack problem are complex and important. I n this case individual tmks may be well understood, but what is required is that the total team effort be very smoothly coordinated. Individual tasks 94

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must not only be performed proficiently but the total set of tmks must be integrated successfully. Thus, the complexity and importance of team activity in a complex manlmachine system again result in a training requirement that indicates the need for a complex team-training simulator. The two examples given above are illustrative of the two principal types of training problem encountered. The first is characterized by complex individual functions. Successful operation depends to a great extent on the individual; he must be proficient in the execution of his assigned tasks. This type of simulator will be called an individual skill trainer. The second type is characterized by the complexity of interaction of many individuals. The individual tasks may be simple, but the coordinated functions of the team are not. This type of simulator will be called a team trainer. Complex team activities may and generally do involve complex individual functions. For example, the flight simulator is designed to solve an individual training problem. Once the pilot is proficient in operation of the aircraft he must become proficient in use of his aircraft as part of a team, such m a hunter-killer anti-submarine group. Thus, simultaneously, there is a training requirement for an individual skill trainer and a team trainer. Although many skill trainers are also useful for some aspects of team training and team trainers may incorporate features that allow use for skill training, this article will separate the two categories for simplicity of discussion. This categorization is somewhat artificial but clarifies some of the considerations underlying the implementation problems. As has been emphasized, one of the characteristics of a man function that may indicate the need for a training simulator is the complexity of the function. This is not a sufficient condition, since many complex functions require skill and knowledge already possessed by the operating personnel. Furthermore, in some cases the complex functions can best be learned with training devices other than simulators. However, complexity of function and interaction of many simple functions are generally a necessary condition indicating the possible need for a training simulator. An important consideration in understanding training simulators is the scope of training obtained by their use. No training simulator satisfies the complete training problem. Other training methods must also be used. For example, the Apollo Mission Simulator is being constructed for the training of the crew for the manned lunar mission. This simulator by itself is not sufficient to impart all the training 95

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required, It will be supplemented by clwsroom instruction, physical conditioning, and p a r t - t d training on other trainers. The complete mission simulator serves an important role in training but is not the only training technique to be used.

2.3. I lndlvldual Skill Tralners An individual skill trainer is a device used by one man at a time, and on whioh he learns and practices specific individual skills. These skills can be conveniently categorized into the following five groupings. (a) Perceptual Skill Qroup: A perceptual skill involves the ability of the man or trainee to see, hear, feel, or otherwise recognize nuances within the stimulus signal and to detect signals under confusing conditions, If the input signal or other informational input is likely to be missed, confused, or misinterpreted, perceptual training is required. The sensory organs of the man must be “trained,” so to speak, to detect the fine shadings and discriminatethe significant cues from the background noise. In engineering terms the sensitivity of the perception organ is increctsed so the man can respond when the signal-to-noiseratio is small. With appropriate training this sensitivity can be increased to the threshhold of detectability inherent in the man. The man’s discriminatory threshold is in certain caaes lower than can be achieved with present state-of-the-& equipment. Sonar, radar, and photo interpretation &ills are examples of tasks requiring perceptual training. A training simulator must provide cues with sufficient realism so the man can learn these perceptual skills. (b) Motor Skills: Motor skills involve muscles. If a tmk requires a degree of accuracy, timing, rhythm, or strength, motor skill training is indicated. Typing, weight lifting, and sending Morse code are typical examples of motor skills requiring training. A motor skill trainer must provide the equipment on which these motor skills are praoticed. (c) Pwcepto-Motor Skill.8: Percepto-motor skills characterize those tcleks in which perception is directly related to the motor skill. Tracking tasks such aa vehicle control and moving target marksmanship are percepto-motor skills that require training. Other skills such as stationary target marksmanship, surgery, and the playing of most musical instruments involve a motor skill with perception and are also called percepto-motor skills even though the motor fask is significantly more pronounced than the perception involved. These skills also require training. A percepto-motor skill trainer must provide both the perceptual cues and the equipment for making the skilled motor responses. 96

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(d) Procedural Skills: A procedural skill is the ability to perform a sequence of tasks in appropriate order and at the appropriate time. Even though each ta& is simple, the multiplicity of tasks and their performance on cue can create a training problem. The astronaut tasks in Project Mercury are a good example of a series of simple tasks in which an orderly and timely procedure was of significant importance in mission success. A procedural skill trainer must present all cues to action present in the actual situation. Since motor skill is not involved, the response equipment is less important unless it provides additional procedural cues. (e) dlental Skills: Other skills are characterized as mental skills and include decision making tasks, mental processing tasks, and memorization tasks. These skills may require a trainer but the rationale for equipment is beyond the scope of this paper.

2.3.2 Team Trainers One of the purposes of any operational Navy submarine is to carry out conventional torpedo attacks, against either surface targets or other submarines. The torpedo attack has several phases culminating in the launch of the weapon and destruction o i the target. This attack may take several hours and requires the use of many submarine subsystems including the submarine itself. There is little opportunity to effect sufficient training aboard a real submarine. Dry run or dry firing practices help, but do not solve the training requirement for assured peak performance. The training requirement for a submarine attack team is the provision of a situation in which all relevant cues are provided and tasks can be practiced so that the desired level of skill is attained. The training situation must be so designed that the practiced tada will transfer to the operational tasks. If the operational hardware is used and stimulated with realistic signals, the transfer is almost certain to occur because the inputs affecting the man are equivalent to the actual inputs and his responses are the same as the actual responses. The first step in establishing the training requirements is to determine those elements or tasks that cannot be practiced effectively in the aotual submarine on the open ocean. Immediately, it can be seen that submarine operation, engine operation, housekeeping tasks, etc., can be practiced to any desired skill level. Thus, their inclusion in an attack trainer is not warranted. The actual detection, closure, and attack on a target, however, cannot be practiced from beginning to end. If the attack cannot be practiced in total, elements of the attack procedure and integrated task 97

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performance cannot be performed until an actual attack is in process. Mistakes here can result in serious consequences. To assure peak performance a series of practice situations are required, The trtlining requirement is the provision of sufficient practice of a complete attack or attack phases so that in the actual attack all manual tasks or man functions will be performed effectively. Each man who contributes to the success of the attack is important and his performance must be added to the total team effort. The first area of concern is thus to identify the man functions that are directly related to the attack. In the submarine this includes the sonar operator, fire control personnel, launch personnel, and conning station personnel. Engine room, stores, and mess personnel and others not directly involved do not contribute to the success of the attack and can be safely eliminated. Second, the equipment that is used by these personnel in an attack must be identified and those equipment features which contribute directly or affect the attack or relate to the man’s performance should be determined and specified. This includes the weapons to be employed. Third, the probable target and ocean environment characteristics that affect the attack must be ascertained. These three areas constitute the basis for the training requirement. Each area must be studied to determine specific details that relate to problem success and these details listed as necessary to fulfill the training requirement. For example, the sonar operator position is studied to determine the relevant cues which must be provided on his displays. The cues he uses during an attack must be provided in the trainer so he can practice responding to these cues. The fire-control equipment must be analyzed to determine the part it plays in the attack problem and what effect the team members can have on its function. Equipment should be provided in the trainer that plays a similar part and can be affected in a similar way by the trainee operators. The targets in the problem should have the same characteristics as real targets. They should move, maneuver, hide, and otherwise act as real targets would act when under attack. Those aspects of the ocean environment such as thermal layers, sea state, and signal attenuation should be included in the trainer because they affect the team performance. Ocean and target characteristics should be simulated on the equipment with which the men come in contact. To be an effective trainer other features are required to enable learning to take place. Simple attacks must be provided EM well as more complex and difficult problems. Emergency situations and degraded equipment situations should also be provided because an actual attack may occur under these conditions. 98

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Contingencies of reinforcement and realistic outcomes should be included so that each man can recognize the results of his and the team’s action. Means of evaluation of each man’s performance as well as overall team performance should be provided to insure that faulty or erroneous performance is detected and corrected. I n this type of team trainer, it may not be necessary to include all of the tasks performed by each man. Only those relating to team performance are pertinent to a team trainer. On the other hand, in an individual skill trainer, all tasks the man performs should be included if total training is necessary. If all tasks are not included, then parttask training results and the man must learn to coordinate and integrate the total tasks in a different trainer or on the job. 2.4 Training Concept

Once the training requirement is known, a concept must be developed for satisfying the requirement. This concept will suggest the various ways by which all of the requirements are met. If a training simulator is indicated, the training concept will specify the training to be given in the simulator and will further specify the types of simulation required and the degree of fidelity desired. The training concept serves as the basis for the system design of the training simulator. The training concept should ideally be independent of implementation considerations. If, in the context of the training requirement, certain training can best be satisfied or can only be satisfied with a simulator, then the training concept would so indicate. However, it is pointless to specify training simulator characteristics that are impossible or impractical of attainment. For example, i t is currently impossible to attain a zero-g environment in a training simulator and therefore it would be of little value for a training concept to specify that a training simulator provide a zero-g environment. However, if a real need for a particular feature is indicated, it may serve to direct development of new techniques to enable the feature to be included, With regard to zero-g environment, there has been serious discussion for inclusion of a training simulator in an orbiting vehicle so this aspect of environment can be obtained. Thus, although the particular effect is impossible of attainment today, thoughts have been directed toward its eventual realization because the requirement exists. The scientist developing a training concept is generally a human factors specialist and may not be technically competent to judge the femilibity of a particular implementation feature. Thus, without assistance from competent engineers, there is a danger of not obtaining optimal features in a trainer. I n owes of doubt, the human factors 99

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apecialist should request a particular feature and leave the implementation decision to the engineers for realkation. If the engineers cannot provide the feature within the state-of-theart, reliability, or economic limitations, they should discuss the difficulty with the human factors specialist so that the best possible compromise can be obtained. The human factors specialist should be consulted so that the compromise feature will provide the most training value short of the optimum. Thus, the lack of realism of an approximate solution may not have a critioal effeot on training. The training concept thus specifies the manner and degree in which the training requirement will be met with a training device. It is the result of numerous trade-offs and compromises between training requirements and equipment capabilities. A TV view from a camera descending onto a model and shown on a screen ahead of the pilot in a flight trainer to simulate the view of an aircraft landing is one concept for providing an out-the-window view. Obviously the TV picture is not realistic but it provides selected cues for the pilot and enhances training. Another concept for the same purpose is the use of a filmed view on an actual wrap-around screen. The former has the advantage of a dynamic display that responds to pilot actions, while the latter provides better depth effects. However, neither meets the full training requirement, which is for the pilot to lemn to land an aircraft. The selection of one of these or another technique must be baaed on the training concept. The TV presentation is better if the trainer is designed with internal cues for the pilot’s action. The filmed view is better if the pilot must observe ground cues to initiate action and if the problem can be stopped when an action is not initiated at the correct time. 2.5 Training Rationale

Once the training concept has been developed and a system design for a training simulator formulated, it is then required to analyze and evaluata the efficacy of the system design of the simulator in satisfying the training concept requirements. T w o results may be expected from this training rationale analysis. First, if deficiencies or excesses in a training simulator system design are noted, the simulator design may be modified. If the deficiencies or excesses are minor this is practical. Slight ohanges in the problem setup provision may add additional realism or permit simpler problems to be set up to enhance early atages of training. Additional sound tracks may be added for realism or to provide an overlooked auditory cue, or additional recording oapacity may be added for measurement and evaluation of responses. Excesses that may be removed are those that have proved to be costly to provide and are not sufficiently realistic to fulfill their intent. 100

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These excesses occur mostly in the inability to provide sufficient realism in displays. Simulated views of the real world and realistic sounds are frequent CMS where excessivecosts occur and do not provide sufficient training value. The second result of the training rationale analysis is the determination of additional training devices or programs to satisfy requirements that are not or cannot be met with the simulator. This may result in changes to the basic training concept for the simulator, which in turn could lead to changes in the simulator design. For example, if the trainer concept includes navigational training, some provision for navigation will be included in the simulator design. If the training rationale analysis shows that the navigation capability provided in the simulator is not effective and is too costly to improve, a separate navigation trainer may be indicated. If this trainer will provide effective navigation training, then the concept of the original trainer can be modified and the provision for navigation removed. The training rationale is thus the analysis of the resulting implementation of the training concept with logical assumptions to demonstrate its effectiveness or the need for modification. 3. Training Simulators Using General Purpose Digital Computers

3.1 Introduction

The use of general purpose digital computers is probably the most dramatic use of digital techniques for training of people. It is also a restricted application since the majority of training devices currently in existence do not employ general purpose digital computers. There are several reasons for emphasis of the general purpose computer application. First, since training simulators employing general purpose computers also use many other digital techniques, they are illustrative of the general application of digital techniques. Second, the discussion is timely since the use of general purpose computers for training devices is of very recent advent. For these reaaons and because training problems requiring the use of general purpose computers are generally more complex, and hence more interesting from the engineer’s viewpoint, this article stresses the application of computers. Digital computers are used in a training simulator only if appropriate to the training system concept. There is seldom an absolute training requirement for use of a computer. In the following discussion, the dependency of the computer on the system concept is very important, A statement made here cannot be considered as a general and inviolate rule, but must be considered applicable only if it is suitable for a specific system concept. lOl

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General purpose digital computers are generally suitable for application within a training device only when an economic advantage results from their use. I n a training device, the total system and system costs are usually definable and, therefore, a valid cost comparison can be determined. The total functions implemented within the computer can be specified; and the total computer cost, including programming, can be compared with the cost of non-computer implementation. Everything else being equal, the method having the lowest total cost is selected. Other factors do intrude, such as flexibility and growth, and it is difficult to assign costs and value to these factors; but in general, a close approximation of alternative mats can be realized. The application of general purpose computers, therefore, must be considered with regard to both total system concept and overall economic advantage. A training simulator consists of three conceptually distinct parts, namely, the student environment, the instructor console, and the realworld sirnulator. These distinct parts will be discussed separately in the following sections. 3.2 Student Environment

The first distinct part of any training simulator is the student environment. The student environment is intended to duplicate all aspects of the operational system environment that are significant to the training requirement. The student environment contains all instruments, controls, and other effects indicated by the training requirement, For example, in a trainer designed to teach a student how to effect the landing of an aircraft in a thick fog, the student’s environment must contain the instruments normally located on the panel of his airplane; a method of communicating with the (simulated) ground station; and the controls that he normally uses to maneuver the aircraft, such as the elevator, rudder, and aileron controls. I n this particular application, the simlation of the view out of the aircraft’s window serves no useful purpose and therefore need not be simulated. It is desired to provide an environment with sufficient realism that the student engrossed in a problem will forget that he is in a simulator and act and function as he must within the operational environment. If this realism is achieved, maximum transfer of training will more probably ocour. This does not necessarily imply that every feature of the operational environment be present in the training simulator; only those that affect the function being t r h e d need be reproduced. It is always possible for a disinterested observer to discern many differences between the training simulator and the operational system. 102

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The submarine attack trainer will not have all physical appurtenaxices existing in the real submarine. The view out of the window of a flight simulator will not duplicate the view from a real aircraft. These are not important to training. (If they are, they must be provided.) The trainee soon forgets these nonessential discrepancies and believes he actually is aboard the real submarine or is flying the real aircraft. A flight simulator that almost “crashes” causes real anxiety. Just as the ardent concert attendee automatically compensates for the minor deficiencies of the auditorium, so does the professional pilot compensate for the nonessential deficiencies of the flight simulator. If this were not the case, training simulators would have little value since it is impossible to design a training simulator that exactly duplicates an operational environment. The problem of designing the student environment, then, is to provide that realism indicated by the training requirement. Other aspects of the environment can be ignored. For convenience, the environment can be separated into three parts, the physical appearance, the dynamic similarity (or static similarity), and the motivational similarity. The physical appearance or static similarity includes the shape, texture, color, feel, and placement of objects within the environment. The fidelity of physical appearance varies greatly with the training problem. I n an operational Aight trainer, essentially every internal physical aspect of the aircraft is duplicated. All controls, instruments, and obstructions are duplicated. I n fact, many portions of the operational aircraft are used. At the other extreme, a tactics trainer used by fleet commanders has almost nothing that duplicates the appearance of real equipment. Only the information used in the problem is required. The training situation and the training problem are the determining factors. Physical appearance is reproduced only if it is required for training. The dynamic similarity of the environment includes all student dynamic simulation and response mechanisms required for training. This includes not only controls and displays, but also such simulation aa background noise, out-of-window views and temperature effects if these are important to training, time varying displays, and changing visual environments. Again, only the essential features are included in the training problem. Dynamic similarity can be divided into two categories, open loop similarity and operational similarity. (a) Open Loop Similarity (programmed cues): Open loop similarity describes the kind of dynamism that generally occurs in the absence of pilot or operator. Uniform aircraft motion which might include 103

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buffeting, vibration, and soundand programmed changes on the environment are principal cues for open loop similarity. An example of dynamic similarity is motion pictures of the flight environment that provide programmed cues. (b) Operational Similarity (unprogrammed cues): This is the more important variety of dynamic similarity because it concerns the response or behavior of the simulator as a result of what the operator does. It can be termed “closed loop,’’ since most sequences of cues are dependent on what the operator does and therefore cannot be programmed in advance. Only the simulator providing unprogrammed cues or cue sequences c m provide operational similarity. Operational similarity is the key aspect of the flight trainer, the factor most directly responsible for learning. However, in many aspects it is very difficult and in some respeota impossible to completely simulate all things flight vehicles can do. I n most cases the principal concern of the simulator designer is a design that incorporates a high degree of operational similarity with some real aircraft. Motivational similarity deals with similarity in feeling or attitude on the part of those trained in the simulator as compared to the feeling experienced in the actual vehicles, whether ship, aircraft, submarine, or tank. This can be only partially achieved, because of its intangible nature. Although it forms a critical aspect of the training simulator it is often ignored. Unless the operators being trained capture some of the feeling associafed with the events simulated, much of the value of even the finest operational simulator may be lost. Naturally the attitudes of the crew in the sirnulator will differ in many respects from what they would feel on a real mission. I n the simulator, the attitudes should be such that they motivate good performance. The pilot in the simulated aircraft will not feel in danger when he performs poorly, as he might on a combat mission, but he should feel disturbed. The submariner will have difficulty experiencing the same urgency he would experience when pitted against an enemy submarine. The sonar operator will not get the same experience he would if a real torpedo were fired at his ship. The esprit de corps of the weapon system team will be evident to a different degree in the simulator, but if training is to be effective it must be present. The motivation to learn and to perform well on the simulator muet be strong, even though it will be different in both quality and intensity from the motivation for performing well on the real mission,

3.3 Instructor’s Console The seoond distinct part of any training simulator is the instructor’s console. The instructor’s console contains all the controls required to 104

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set up and control a given training problem, as well m all displays required to monitor the problem progress and student’s activity. I n addition to the functions of problem setup and control, the instructor will provide some of the capability not present in the training simulator. I n particular he usually provides any required voice communications from outside the training simulator. The design of an instructor’s console depends upon the information and control requirements of the instructor operator. These requirements are based upon the nature of the operational problems to be conducted on the simulator, the variation in the problems required, and the functions of the console operator-instructor. I n general, the instructor’s console will intedace directly with the computer and for the most part will control the problem by setting values within the computer. I n some cases, problem control will be accomplished by direct connection with the operational or simulation equipment. Communication links generally do not involve the computer. However, if automatic control of propagation characteristics is desired, these may be convenient for computer implementation. To perform these many functions, a carefully designed console is required. The minimum number of displays and controls should be used in order to minimize the complexity of the instructor’s twk. As many functions as possible should be handled automatically by the computer to relieve the instructor of routine noncritical functions. Those displays that are essential should be emily read and provide the specific information required by the instructor to eliminate complex mental tasks. The controls should be easily reached and tw simple tw possible to operate. Thus, design of the instructor’s console must be based on a number of interrelated factors. The role of digital techniques in the design of the instructor’s console includes not only standard displays and controls but also the intimate relation between the console and the computer. An operator using a properly designed instructor’s console in a training simulator need have no knowledge of computer operation. I n fact, there is no requirement that he even be aware that a computer is part of the system. A properly designed instructor’s console is the best example known to the author of a problem-oriented computer console. As such, it is instructive to examine the design and use of a typical console. Similar techniques are applicable to the design of any problem-oriented console. An excellent example of such an instructor’s console is that provided for the operation of the Submarine Attack Center Trainer at New London. 105

CHARLES R. WICKMAN

Operation of the Submasine Attack Center Trainer is controlled by means of Honeywell-designed and -developed consoles located in each of the three attack centers and in the tactical display room. Consoles me designated Master Instructor’s Console, located in the tactical display room, Program Operator’s Console, and Assistant Program Operator’s Console, one each installed in each attack center. The Master Instructor’s Console (Fig. 1) is the control and monitoring instrument for the entire Submarine Attack Center Trainer, and controls problems, assigns vehicle designation and control, and designates the modes of operation for all attack centers, &B well as the tactical display room. I n addition the operator may select any attack center problem for monitoring, either by digital display of problem parameters and status, or by optical projection of problem tracks on the tactical display room screen. I n all, except independent attack center problems, the Master Instructor may override the Program Operator or the Command Center for instructions or critiques or for insertion of d d i t i o n d information. In order to set up a typical tactical problem on the trainer, a minimum of input directives must be inserted into the computer. The input directives me called “commands.” The commands or input words establish the parameters of the problem. The parameters include the initial location of the attacking submarines and targets, motion of the targets, and other features of the simulation. In order to exert overall control of the problem, the Mmter Instructor has 18 “words” or computer command entries for use at his discretion. Computer command entries and their functions are given in the accompanying tabulation. The console operational requirements are in five me-: (a) Establishment of problem relationships between vehicles (b) Initiation or cessation of operations (0) Insertion of data into the system (d) Obtaining information from the system (e) Control of services All of these operations except the service controls have a similar sequence of procedures. The services are controls that do not directly involve the computer system. The service controls provided include: console illumination intensity, projector power and lamp controls, communications, radar and sonar monitoring, and maintenance mode aontrols. The sequence of procedures for constructing and entering words to the computer system basically calls for: (a) The selection of the vehicle 106

DIGITAL TRAINING DEVICES

(b) The selection of the order type (function) (0) The entering of order value (by Keyboard) (d) The introduction of this data to the system (by Execute switch). Logical interlocks in the consoles and computer program checks 1 07

CHARLES R. WICKMAN

will prevent the input of impossible or incomplete information

to the system for the protection of the aomputer program

(e) The operator is furnished information concerning the suitability

of his selection by the status display of the Execute switch; thus, the system will be safeguarded and the operator informed if his entry is acceptable

Computer command entry Type eseignment Problem essignment

Taxget mode Order poeition and motion Position and motion readout Convoy mode Convoy order Problem select Relative position reedout Stert

Freeze Deactivate Hit c l w Soreen scale offset Start clock

Time rate Delete time merks Reeotivate time mmka

Function Establishing the type of ship for targeta Establishing the Master Instructor’s Console or Atteok Center as target controller, and ability to sense Assigning targeta to a mode of operation, i.e., Independent or Convoy Eetebliahing psrametere for eaoh target Check geographical location of target Provide sinuous course for taxgeta in convoy Entering course, speed, and turn rate of convoy Display of problem on Tactical Display Room Screen Obtain dsta on target relative to an operating submarine (08)’ 0 8 to another 08, and 0 5 to weapon Start the problem Stopping the problem (problem can be reeumed

after hem) Removing target from problem Clew hit light from target if oontrolled by Mae Size of simulated 008811 to be used, centered

about selected vehicle Starting problem time Real time or other time rate Removing time maxka from vehicle projector

treoke Resume time marks for vehicle projector traoke

A typioal entry to the computer using the Mmter Instructor’s Console would be as follows: To order target 2 to make 20 knots, the instruotor would press target 2 button, press the speed button, set in 20 on the keyboard, verify that 20 r e d s out on keyboard, verify that the execute button is m e d , and then press the execute button. Target 2 would then come to 20 knots at the prescribed acceleration or deceleration rate established for the type of ship that target 2 represents. It is estimated that the Instructor has 1048 control variations over the vehioles and weapons at his command. 108

DIGITAL TRAINING DEVICES

3.4 Real-World Simulator

The third distinct part of any training simulator is the red-world simulator. The red-world simulator must generate all the effects required in the student environment. For example, the real-world simulator might be required to generate the aircrdt’s air speed. The air speed is a function of the aircraft being simulated, the throttle position set by the trainee, and the wind gusts set by the instructor. The relationship between the aircraft’s air speed and all of the parameters controlling it is usually given in terms of mathematical equations. A computer is most reasonably employed in fulfillment of this function of ml-world simulation, but it is also intimately associated with the other functions and often provides for the display of quantities to the instructor that are not otherwise available. In providing real-world simulation, the computer is, in essence, taking account of all significant effects that occur in the operational environment but are not capable of exact duplication within the training simulator. Any necessary characteristic of the training problem that concerns the physical world external to the duplicated environment must be simulated. Motion simulation is a prime example of such an effect. In an operational flight trainer, it is intended that the pilot “fly” the trainer. Since the trainer does not actually fly, some means must be provided to simulate the aircraft flight motion. In a training simulator this is accomplished by solving motion equations that provided for proper activation of all indicators available to the pilot. Hence, the solution of the motion equations substitutes for the real-world environment of the actual aircraft motion. The adequacy of these equations and their solution determines in large part the efficaoy of the simulator. The Fleet Ballistic Missile attack trainer, installed at New London, Connecticut, uses a Honeywell 800 digital computer to provide many of the real-world simulations required by the tr*g problem. The principal computations performed within the digital computer are: Own 8hip m o t h

Target motion weapon m o t h Weapon-target hit evaluation O m ehip-target relative mmh

f?O?lUr8

i m a h

Each of these is critical to the training problem and represents characteristics of the real world that cannot be duplicated within the

109

CHARLES

R. WICKMAN

trainer but must be simulated. The net result of these simulations is to provide an environment for the trainee that has no significant training difference from the real world. It will be noted that five of the six real-world simulations listed above involve motion or effects of motion. This is typical of training simulators that concern moving vehicles of any type. Since the training simulator does not move, simulation must be provided to substitute for the vehicle motion. Even so-called moving base simulators have only restricted motion artificially induced, and require simulation of the real vehicle motion. The sixth item listed, sonar simulation, does not involve motion as such, but does involve propagation of acoustic energy in water, which cannot be duplicated within the training simulator. Hence simulation of the propagation and return of the sonar energy are required. Three types of vehicle motion are indicated, namely, own ship, target, and weapon. These m separate and distinct simulations, not because the vehicles are different, but because the detailed training requirements are different. The trainees are “aboard” the own ship. Hence, own ship motion simulation must have detailed and precise characteristics. Target motion is perceived by the trainees only aa it appears on various sensor equipment. Therefore, simulation of target motion can be gross, since the trainee cannot peroeive extremely debiled motion perturbations. Although detailed simulation of target motion would not detract from training, detail is not required since it is costly to provide and adds no value to the training. Not all real-world simulation is provided by the computer. Some effects a m better simulated in special computing elements, and some are essentially impossible to implement within the computer. Voice communication from the attack center to other stations of own ship is simulated by letting the instructor represent the other stations. In this role, the instructor is effecting real-world simulation. I n addition to real-world simulation, the computer may also perform oomputations that effectively simulate equipment within the trainee environment. For example, consider a sonar simulation. The real-world simulation consists of computing the position and timing of the indicated sonar return, taking into account the necessary propagation and target reflecttion characteristics appropriate to the training problem. If operational sonar equipment is used in the training simulator, the output of the real-world simulation will be compatible with the physical characteristics of the sonar. No simulation of the prooessing characteristics of the sonar system is required. If a simulated sonar is used, further computationsmust be performed, which effectively duplicate the internal characteristics of the opera110

DIGITAL TRAINING DEVICES

tional equipment. Many times i t is simpler and more economical to simulate equipment rather than to use operational hardware. No general rule can be given. Only by study of each given problem can it be determined whether the operational equipment should be stimulated by a real-world simulation or whether a complete simulation of the equipment should be undertaken. Because of the critical nature of motion simulation, i t is of value to explore the problem in more detail. The following is a detailed discussion of the own ship motion simulation provided in the FBM attack trainer at New London, It is typical of the considerations underlying motion simulation. 3.4. I Own Ship Motion Simulation

(a)Introduction: The attack center in the New London FBM Trainer is stationary as opposed to moving base simulators. Therefore, the trainees receive no physical sensation of motion, Instead, an illusion of motion is created by activating the various repeaters in the attack center, which imply that the own ship is moving, such as the speed indicator, course indicator, and depth indicator. The motion of the own ship is also displayed to the instructor or program operator in the form of digital displays and position graphs. The program operator must not only monitor these displays from the standpoint of an instructor, but also act as a helmsman and msure that various orders pertaining to the motion of the submarine are properly executed. The purpose of the own ship motion mathematical model is to accept orders from the program operator and to subsequently generate and display the motion of the ship consistent with physical laws and the characteristics of the particular submarine being simulated. The perceivable quantities that must be displayed are:

(a) Components of horizontal position (X,Y ) (b) Speed (4 (c) Course angle (C) (d) Rate of change of course angle (el Depth (2) (f) Depth rate (2) (g) Rudder angle (Sr)

(c)

There are four major aspects involved in the own ship mathematical model : (a) Selection of a general set of equations that describe the dynamic motion of a submarine 111

CHARLES R. WICKMAN

(b) Construction of helmsmen algorithms to simplify the orders of the program operator (0) Development of a numerical integration method that can be used to solve the dynamic equations of motion (d) Determination of coefficients in the general equations of motion to simulate a particular submarine (b) E q w t i m of Motion: It is necessary to obtain a set of equations representing the dynamic motion of a submarine under the action of propellor thrust and hydrodynamic forces against both hull and movable members, such as the rudder and stern planes. To completely describe a submarine’s motion, six degrees of freedom are required. Three variables are normally used to locate the submarine’s center of gravity (0.g.) with respect to a fixed coordinate system, and three variables are used to describe the orientation of the submarine body axis with respect to the fixed coordinate system. The variables usually chosen are the X , Y, and 2 components of the c.g. position vector and the roll, pitch, and yaw Euler angles. I n this training simulator, the six output quantities corresponding to the six degrees of freedom are not required since the roll, pitch, and yaw of the submarine are not displayed to the trainees. Therefore equations, which correctly desoribe the motion of the submarine’s c.g. as a function of tactical decisions and are consistent with hydrodynamic effects, are completely adequate for the training purposes of this attack center. A major consideration in the construction of these equations was that it should be possible to evaluate the coefficients for a particular ship on the basis of tactical data memured a t sea rather than of data obtained from experiments on reduced scale models representing the ships. The coordinate system used in this trainer is the left-handed system shown in Fig. 2. North is taken as the Y axis and East as +X axis. ; The course Depth is taken as positive downward along the +Iaxis. angle (0) is measured as the clockwise angle from the Y axis to the projection of the velocity vector of the ship onto the X-Y plane. The dive angle (D) is measured as the elevation angle from the X- Y plane to the velocity vector. In Fig. 2, D is negative since the velocity vector has a downward component.

+

The empirically constructed equations of motion to be used for advancing the own ship are the following second-order differential equations:

fi =Ai{J’-(1+Aa

I Sr I )S){J’+(l+Aa

I

Sr I )d+AsS)

(3.1)

DIGITAL TRAINING DEVICES

D

=

-{A,SB+A,B

I b I +A~D+A,@+A,~P~,}

(3.3) where 6, is the rudder angle; 8. the stern plane angle; d3 the ordered speed; and A,, A,, ., A,, are coefficients to be determined for each particular ship. Unless otherwise stated, the units employed in this report are: for distance-yards ; for angles4egrees; and for time-seconds. Equations (3.1), (3.2), and (3.3) permit the calculation of the submarine's velocity vector m a function of time. However, the coordinates of the velocity vector will be given in terms of spherical coordinates (8,C, D). In order to transform the velocity vector into rectangular coordinates, the following transformation equations become necessary:

..

S =800sDsinC

P

=

2

=

(3.4)

8 COB D OOSC

(3.5) (3.6)

-8sinD

x (EAST)

FIG.2. Coordinate system.

For the sake of convenience,it is postulated that the longitudinal ctxis of the submarine is tangent to the motion versus time curve ( i a , pardel to the velocity of the submarine). This may be interpreted m 113

CHARLES R. WICKMAN

using equations of motion with five degrees of freedom with a constraint on the pitch and yaw of the submarine. The postulate permits the use of the quantities course angle (0) and dive angle ( D ) ae angles describing the yaw and pitch of the submarine, as well as referring to the orientation of the velocity vector. Roll must, however, remain indeterminate in the problem. It would be desirable to have equations of motion that would yield the dependent variables, X, Y,and 2 directly in terms of the independent variables #, s, s,, and time (t). However, since the forces acting on the submarine m velocity dependent and position independent, it is necessary to first solve for the submarine’s velocity. Equation (3.1) represents the acceleration of the submarine ae a function of speed (S), ordered speed (,S), and rudder angle (8,). If 8, = 0, then the acceleration becomes a quadratic function in both S and ,,S, Equation (3.1) is a modification of 8 = (08p-Sa) in which the thrust is proportional to ,,#a. When a rudder angle is inserted, the effect is to essentially decelerate the ship as though the present speed were raised to (1 A , I 6 I )S and the ordered speed remained as before, Since 1 is equal to zero if and only i€ {,,S-(l A , I 6, I )S}= 0, the ratio of final speed in a turn to ordered speed (usually the same ae initial speed in a turn) is a constant for a fixed rudder angle. Equation (3.1) was formerly written with a rudder term ( 1 - A p 1 8, I ) multiplying ,,S instead of 8.Conceptually, this is simpler since then a rudder angle can be interpreted m an ordered reduction of speed, Difficultiesarose, however, if at the same time that a rudder wm being applied, an ordered speed of zero was entered, thereby completely eliminating the rudder dependence in the speed equation. It would perhaps have been preferable to incorporate the effect of speed loss in a turn by making Eq. (3.1) a function of 6 instead of a function of 8,. However, since experimental data usually relate speed loss in a turn to rudder angle, this latter course waa not pursued, and it is doubtful that any improvement resulting from this change would be noticed by the trainees in the attack center. Equation (3.1) as it stands wm found not to be completely satisfactory. The acceleration of the ship became too large if ,,S were greatly different from S . A limit was therefore placed on 8 so that 8 would always remain less than 8 maximum, depending on the particular ship. It was also decided that the maximum acceleration should not be attained at once. Therefore, the acceleration is not permitted to change by more than a fixed constant each iteration cycle. However, a different constant is chosen for acceleration than for deceleration. Equation (3.2) represents the course angle acceleration of the submarine. 0 hae the usual dependence on s,6, and 8,. In a steady turn

+

114

+

e

DIGITAL TRAINING DEVICES

when = 0, Eq. (3.2) can be rewritten so that Slbecomes a quadratic function of 01s. Since C/fl is equal to a constant divided by the steady turn diameter, 6, becomes a qudratic function in the reciprocal of the steady turn diameter. The relationship between t?/S and the reciprocal of the steady turn diameter can easily be seen from the fact that the ship traverses a distance of 27rR, while moving with speed 8,in the same time that it turns 360". Therefore,

0

360

s --2nR

(3.7)

The b equation resembles the 0 equation with the exception of the Cgand D terms. The dependence of D on the roll angle haa been included through the d2term. It is msumed that the ship will not roll unless it also turns and that, in this caae, the roll will be a function of the course rate. The D term causes the ship to return to a horizontal position in the absence of other forces. The depth of a submarine is to a large extent controlled through ballasting. This factor is not included in Eq. (3.3) wherein depth is controlled exclusively by stern plane movement. It is, therefore, assumed that the ship is always in neutral equilibrium with its environment and that there exists no net buoyant force acting on the vessel. (0) H e l m Algorithms: Given the thrust and the positions of the movable members (rudder and stern planes), the submarine will change its position in accordance with the equations of motion. Normally, ship conning orders are translated into rudder and stern plane angle changes by the ship's helmsmen. In this trainer, no helmsman exists; consequently, i t is the responsibility of the program operator to perform this task. However, it is impossible for the program operator, together with his other tasks, to continuously manipulate the rudder and stern planes to effect a desired maneuver. It is therefore necessary to develop mathematical helmsmen algorithms that will take conning orders and translate them into rudder and stern plane angle changes, thereby simulating the actions of the real-world helmsmen. The ship conning orders that must be implemented are: (a) Ordered speed (b) Ordered course angle (c) Ordered rate of change of course angle (d) Ordered rudder angle (e) Ordered depth (f) Ordered depth rate Since o8 appears directly in Eq. (3.1), no algorithm is needed to

115

CHARLES R. WICKMAN

simulate this order. If, in faot, an ordered number of turns were an allowable input, then an algorithm that converts turns to ordered speed would have been required. Actually, an ,,8of zero is interpreted by the program as a rapid deceleration order involving the reversal of the screws. In this case the ship decelerates at the maximum permissible value of 8. The other ship conning orders that must be implemented control either course or depth maneuvers. It is desirable to discuss these separately. (d) Courae Control: The course of the submarine is computed by using Eq. (3.2).Since the only independent variable in that equation is the rudder angle, all conning orders affecting course must eventually be interpreted in terms of the rudder angle. Of the three conning orders affecting course, .C, $, $, the ordered course rate and the ordered rudder cannot be ordered simultaneously, since 6 is a function of 6,. Figure 3 shows the course control program flow chart. Initial tests are first conducted to ascertain if the subroutine need be performed. It is possible to order a new course, in which w e the vessel will proceed to the new ordered course, or it is poseible to select an ordered rudder or ordered course rate without specifying a course, in which case the ship will continue to “orbit” until a new command is issued. If the orbit switch is on, the rudderlcourse switch determines whether the ship is following an ordered rudder command or an ordered course rate command. Both rudder and course rate cannot be ordered simultaneously. If the ship is controlled by an ordered rudder angle, then the ordered rudder is used as the value for the rudder angle term in the equations of motion. However, if the ship is controlled by an ordered course rate, then the course rate helmsman performs the helmsman function and calculates a rudder change. In either case, the new rudder angle must undergo a series of rudder limit t a t s to make certain that the magnitude of the rudder angle and its rate of change do not exceed physical limitations. A proximity test is performed each iteration cycle to determine whether the course of the vessel is near the prescribed course, and whether the course rate is such that a deorease in rudder angle will take place by the steady-up helmsman. If the proximity test is not paseed, the submarine is advanced by either the ordered rudder control or ordered course rate control as before. If the steady-up switch is equal to zero, which condition means that a proximity test was passed during the previous iteration cycle, a new rudder angle is calculated by the shady-up helmsman algorithm. A t high speeds, the steady-up helmsman algorithm causes the ship to 116

I---1

0 l~iT,4c1zfNbFOR

r-

?CC.(lMlN

I

--_PROXI W I T Y T E S T

Fra. 3. Course control,

T C I T

CHARLES R. WICKMAN

oscillate about the ordered course with damped oscillations; eventually the ordered course is attained. Unfortunately, at low speeds the algorithm becomes unstable and the ship never attains the ordered course. In order to eliminate this difficulty the program was modified so that once the ordered course is pmsed, the c o m e is set equal to the ordered course and is not permitted to change until a new order is given, (e) Depth Control: Depth control is given by Eq. (3.3) wherein the independent variable is the stern plane angle. The stern plane angle is not an allowable conning order; consequently, planesman algorithms are necessasy to execute depth maneuvers. The depth control subroutine (Fig. 4) is similar to the courae control subroutine. However, since a stern plane angle may not be ordered, it is simpler. The submarine will move to an ordered depth according to an ordered dive rate. If no dive rate is prescribed, then the vessel will

118

FIG.4. Depth control.

DIGITAL TRAINING DEVICES

prooeed along a standard dive rate which is inserted in $. The dive rate limit test ~ s u r e sthat the submarine will not Msume a pitch angle greater than the maximum permissible pitch angle for that specific submarine. It also prohibits dive rates greater than the velocity of the submarine. The steady-up'planesman, dive rate control, proximity test, steady-up setup, and the stern plane limit tests are analogous to their counterparts in the course control subroutine. At low speeds, the steady-up planesman algorithm becomes unstable in a similar manner to the stectdy-up helmsman algorithm in the course uontrol. This problem haa been eliminated by setting the depth equal to the ordered depth once the depth pmses the ordered depth. (f) Integration Method: The equations of motion together with the helmsmen algorithms determine the motion of a submarine. It is now necessary to determine a numerical solution method for these equations that is compatible with the speed and memory limitations of the Honeywell 800 coiuputer. The method used in integrating the equations of motion is shown in Fig. 6. First the equations of motion are evaluated at time t = n. Acceleration limit tests are performed to make certain that the magnitude of the acceleration or its rate of change does not exceed allowable values. The forward integration formula

+

(3.8) fn+l =fn idt (3f, -fn - l > together with the equations of motion are used to calculate the speed, course rate, and pitch angle rate at time t = n 1. Since the constants A, and A, in the equation of motion may be negative, i t is possible, by inserting absurd initial conditions, to blow up the solution of the equations of motion. I n order to protect against this, stability tests have been inserted. The stability tests are actually very weak when orders of magnitude are considered. and The values for Cn+land Dn+l are obtained by integrating l)n+l by the trapezoidal formula: (3.9) ~ n + l= Bn idt (Bn+I+ ri,) The velocity vector can then be transformed from spherical coordinates into rectangular coordinates by the standard transformation equations. The Cartesian components of velocity are then integrated by the trapezoidal formula to obtain the new position components. The method just described, using a forward integration formula followed by the corrective formula (i.e., trapezoidal formula), is discussed by W. E. Milne in Numerical Solution of Diflerential Equations (Wiley, New York, 1953). Figures 2,3,and 4 represent a complete flow diagram for the own ship motion equations.

+

+

119

CHARLES R. WICKMAN

r-

Q

T 1 1

e 8 8F

3

a

o-. Admittedly, errors exist in the equations of motion and in the integration method employed for their solution. However, in most cmes the errors are compensated for, and in all caw8 the errors are bounded. 120

DIGITAL TRAINING DEVICES

No errors exist for the w e of isovelocity motion; both the equations of motion and the integration method are exact. The motion of the submarine normally consists of isovelocity motion intermittently mixed with sequences of maneuvers such aa changes in speed, course, or depth. At the completion of a maneuver, the conning officer reevaluates his location and motion before ordering a new maneuver. Consequently, errors must be considered in terms of a definite maneuver, and the cumulative error for a complete problem becomes meaningless. The following maneuvers are possible: (a) A change from present speed to a new speed. (b) A change from present course to a new ordered course utilizing a preassigned rudder angle. This rudder angle may be the ordered rudder angle or a standard rudder angle if no rudder angle is ordered. (c) A change from a present c o m e to a new ordered course utilizing an ordered time rate of change of c o m e angle. (d) A continuous change in c o m e from a present course by utilizing an ordered rudder angle. (e) A continuous change in course from a present course utilizing an ordered time rate of change of course angle. (f) A change from the present depth to an ordered depth utilizing a preassigned depth rate. This depth rate may be the ordered depth rate or a standard depth rate. (g) Permissible combinations of the previous maneuvers.

Since definite maneuvers me completed in finite time, the errors are automatically bounded in a loose sense. Some errors are, however, bounded in a stronger sense. In each maneuver, the final value of a dominant variable is assigned. For example, in a dive the depth is the dominant variable and the ordered depth is the final assigned value. In dl cams the dominant variable attains its final value. Therefore, the only quantities that may be in error are stable (i.e., a small change in an initial condition will have a small effect on the solution) and sinoe the initial and h a 1 values of the dominant variable axe fixed, the error in time for that variable is bounded in the stronger sense. Test calculations have shown that the errors in all the variables are small, even over large ranges of parameters. In those maneuvers wherein helmsman algorithms are used (e.g., ohange in course to a new ordered course), it is difficult to evaluate errors sinm actual ship’s helmsmen differ in their characteristics. Therefore, small errors occurring in these maneuvers can be considered unimpo~t. The coefficients A,, A,, ., A,, in the equations of motion have been

..

121

CHARLES R. WICKMAN

determined utilizing the integration technique discussed. Therefore, the errors in the equations of motion and the errors in the integration technique tend to cancel each other. For example, the constant A, controls the tactical diameter. Therefore, A, was chosen so that a true solution of the equations of motion would yield a tactical diameter smaller than the true hctical diameter by the same amount that it is increased by the integration method. This ww accomplished by adjusting A, so that the tactical diameter obtained by utilizing the present integration method has the desired value. It is mentioned that the coefficients derived for simulating the attack centers are dependent upon the integration method employed. If the integration method is in any way changed, for example by changing the iteration cycle, then it would become necessary to redetermine values of these coefficients. 4. Programming Considerations

The programming considerations attendant upon a training simulator do not differ significantly from other real time programming considerations. Fundamentally the program must implement the mathematical model within the specified time constraints and within the constraints imposed by the computer inputloutput characteristics. Ideally the mathematical model should be a complete statement of the functions of the computer including all necessary problem constraints. This, together with a complete statement of the pmticular computer characteristics including input/output characteristics of the external hardware, should enable the program to be developed and coded. Seldom in real life does such a pure division of labor obtain. The problem of concurrent development of mathematical model, external htwdware, and program, compounded by less than perfect documentation of both mathematical model and external hardwtwe, makes the task of the progranuuer very difficult. These are practical problems. The theoretical problems are generally not profound. The function of the program is to provide implementation of the mathematical model and thus effectively provide correct stimuli to the training device. Because of the external equipment consideratione and the man/maahine relationship embodied in the device, the programming of a training simulator is similar to any other real-time programming problem. However, there is one important difference: the universe that the training device encompasses is closed. Also the bounds and conditions of this universe me amenable to change by the programmer. Thus, he can sometimes solve difficult programming problems by changing the characteristics of the problem. Since the programmer is generally involved in the systems design phase, he can influence the design to 122

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prevent impractical or impossible demands on the computer. The result is generally a more balanced design than will necessarily exist in a realtime system that is not a closed universe and where most of the system bounds and characteristics are dictated by invariant constraints. A training device program can be thought of as a mapping function that transforms a set of inputs, according to the dictates of the mathematical model, to produce a set of outputs. This process is cyclic and continues for the duration of the training problem. The entire training simulator can be analyzed as a closed loop function in which the total training program is a single loop entity. Internal aspects of the program may also be closed loop functions. A characteristic of training device programming is the requirement that the program be amenable to change as the training device itself is changed. This occurs not only during the device construction, but will occur on a continuing basis after the device is installed due to changes in the training problem and/or changes in the operational systems being simulated. This requirement imposes a demand on the programmer to clearly and exhaustively document the program, and also prevents him from using shortcuts or tricks that would create difficulties at some later time. For example, it is seldom allowed to have the program modify itself during execution. Address modification is permissible but command modification per se is generally inadvisable. Furthermore, the program must generally be prepared in self-contained segments, which implies that some optimizing techniques are not available to the programmer. To some extent these same considerations apply to any real-time program and should be considered by any programmer preparing a large complex program intended for extended use outside the control of the present programmer. These considerations are omnipresent in training device programming. Another consideration in training device programming, that also obtains to some extent in any real-time program, is the necessity of constructing a program to function within a system which is itself not completely defined. This creates difficulties not only in the detailed construction of the program, but makes the program checkout or debugging with the actual system extremely difficult. If an error occurs during system checkout, it is natural for the programmer to suspect the terminal equipment and the design engineer to suspect the program. If a stalemate exists, both will suspect the computer, and the computer maintenance personnel will have a low opinion of everyone. Only by mutual regard and understanding of each other’s problems can a system checkout be satisfactorily accomplished. 123

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Since a large-scale training device will generally involve several programmers, and also because of the requirement for exhaustive documentation, it is critical that conventions and standards of docud mentation be agreed on at the onset of a program. Again, this should be standard practice for any large programming effort, but is extremely important for training simulator programming. Assuming that these are dehed, the programming effort can be subdivided into a set of tasks, which are definitely not independent nor even necessarily sequential. Program testing consists essentially of two phases: testing independent of the training device, which is similar to any program checkout, and testing with the complete training device. After all checks of the program independent of the training device have been executed, it can be assumed that the program will at least cycle and perform computstions close to those originally desired. However, it is almost axiomatic that the system will not perform satisfactorily. Three types of difficulty will be experienced. First, although great care may have been taken in constantly reviewing the interactions of the mathematical model, progmm, and external equipment, differences will be uncovered between how the program waa intended to perform and how in reality it does perform. For example, the mathematical model may be correct over most of its range but, due to a combination of implicit wumptions and computation approximations, singularities will be uncovered. These hopefully will require only minor changes, but in any c m they do require extensive and detailed analyais with the added factor of severe pressure due to the ever present project schedule. It is true that theoretically all of these interactions could be predicted and errors therefore prevented. In actual practice, however, errors will occur. A second type of error is that caused by an incomplete understanding of the desired responae. Generally this type of error includes some detail of external equipment operation. After the device hm been installed and actual training use has been experienced, many changes will be suggested. These are not errors in the usual sense. Rather they are indications of less than perfect understanding of the entire training problem and are due in large part to the subjective and qualitative determination of the training problem. The proof of the training system is simply the quality of training imparted. This can be obtained only by actual use of the device and hence only after the complete installation of the airnulator. The power of the general purpose digital computer now becomes very apparent. Many changes can be incorporated without modification of external hardware, Further, if a change involves only the computer, no lost time in use of the trainer need occur. Thus the use of a central 124

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oomputer enables modification of the training problem simply and without interference with the training schedule. The program itself has some unique characteristics. Probably foremost is the extreme variability in execution time. Generally, a real-time training program is constructed with a major invariant cycle time. A convenient cycle time for submarine attack trainers is 1 sec. For flight simulators it may be much smaller, perhaps 100 msec. I n any cme, the major cycle will be an integral multiple of the integration interval. Within the major cycle all computations are executable at least once. Minor cycles, if required, will become integral fractions of the major cycle and for convenience may be a power of 2, such aa 4, A, etc., although this is by no means required or universal. The major cycle is so chosen that all time-dependent calculations, euch as integration, are performed correctly, and so that no response delays that affect training will occur. If a student actuates a control, the aomputer response to that control must have the same temporal oharacteristics as the real control. I n a complex training simulator, it is possible for many controls to be wtuated simultaneously. The major cycle of the program must be such that all possible computations can be performed within the cycle. Queuing of student inputs is not permissible. Queuing of some instructor inputs is possible, but generally these are insignificant calculations. The major cycle therefore must be able to satisfactorily handle a worst case condition of many simultaneous events. However, the normal situation is that the worst case will not occur very often. Usually very few events occur simultaneously. Thus, the average computation load is much less than the worst cme. During that portion of the major cycle not required by the computation load the computer will generally idle, waiting for a synchronizing signal indicating the start of the next major cycle. (If minor cycles are umd, some idling will occur during each minor cycle as well.) I n a worst case condition this idle time will be minimal, amounting to only a very small percentage of the cycle. Under average loads the idle time may be SO-SO% of the total cycle. Thus during normal training exercises the oomputer may be idle over half the time. There is generally no practical way to reduce the ratio of worst case to average execution time. Queuing of inputs cannot be done without compromising training. Diagnostic testing could be programmed, but seldom will the effectiveness of such diagnostic techniques justify the cost of programming and adaptation of the hardware. Thus it is a characteristic of training simulators using a general

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purpose computer that the computer will be idle for m appreciable portion of each training exercise. Another unique program characteristic apparent in the physical layout of the computer is the absence of normal inputloutput processing. A training program does not require any of the standard peripheral equipment. Once the program is loaded, the only input/output processing required is that which concerns the unique terminal devices associated with the simulator itself. Magnetic tape, high speed printers, and other adjuncts to the modern computer are not required. They are sometimes used for recording of problem progress, but seldom is such use sufficient to justify purchase of the equipment. In most other respects the program evidences no significant uniqueness. The sophistication it represents is a product of the total system concept and in particular the mathematical model. Nevertheless, it is a formidable undertaking to prepare a training simulator program, and competent programming techniques must be employed. The result is a complex and very specialized program, which is essential to successful use of the training device. 5. Non-Training Uses of a Training Simulator

Non-training uses of a training simulator can be conveniently divided into two categories, applications using the complete simulator complex and applicationsusing only the computer. These alternate uses of the trainer are generally not planned for in the original concept of the system but are an outgrowthof the power and flexibilityof the computer. Since a training simulator reproduces the operating characteristics of a real, operational system, it can be used to develop and evaluate procedures and tactics applicable to the operational system. Within the limitations of the realism incorporated within the simulator, this use can be of great value and effect considerable economies. As an example, the submarine attack trainer can be used not only to train attack teams, but also to develop and improve the basic approach and attack tactics. If several attack centers are incorporated within the same trainer, mock battles can be staged between the various submarines. Since perfect data can be recorded as to the “true” situation, the tactics employed can be evaluated against what actually occurred. Also, replays can be conducted allowing the effects of perturbations in the tactics to be studied. The use of operational systems would require time-consuming deployment of complete submarines, and, unless expensive recording equipment is installed, a complete record of the exercise would not be available. Also, it would be very difficultto reconstruct and replay the 126

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exercise. Thus, the simulator can provide a very convenient means for improving the use of the operational system. To some extent, a training simulator can be used to evaluate operational equipment. For example, if a simulator incorporates an operational fire-control computer, new operational programs can be quickly evaluated. Thus the simulator is again valuable in improving the effectiveness of the real system. In order for a simulator to be useful in improving operational effectiveness, the limitations and departures from realism of the training simulator must be completely understood. The training device was originally designed to provide the realism required for training within the stated environment. If this environment changes or if new procedures or tactics require different realism reproduction, then the evaluation of the new equipment or tactics may be based on erroneous data. The limitations must be understood and considered in the evaluation. If the computer used in a training simulator is &generalpurpose device, then it may be used for any normal data processing function. Although this is not generally planned for in the original design of the sirnulator, it is seldom difficult to augment the computer with standard peripheral equipment and thus provide a standard data processing facility. Such use of the computer when training is not being conducted presents no problems. Normally, no special provisions are required. If protection against inadvertent access to the trainer equipment is required, a simple interlock could be provided. Otherwise the computer will function in a completely normal fashion. It is theoretically possible to time-share the computer between training problems and normal data processing. The attractiveness of such an idea is based on the average idle time of the computer, aa discussed in Section 3.3. I n theory the computer would be available about 60% of the time during a normal training problem. Thus, it would appear that considerable data processing could be accomplished without interfering with training. However, there are many practical difficulties in implementing such an arrangement. Since no interference with the training can be allowed, suitable absolute safeguards must be incorporated to protect the integrity of the training program. First, it would be required that the data processing program be prevented from halting the computer. Illegal commands, overflows, and any other condition that might normally stall the computer can usually be trapped. However, a HAIT command per se poses some difficulties. Again, this might be handled by trapping. Another problem is to assure that the data processing does not modify any storage location required by the training program. Memory 127

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barriers help somewhat but they generally me not foolproof. Because of the short time available in each cycle, it is impractical to use magnetic tape to store and retrieve either the training program or the data processing program. It is dso required that the data processing program be prevented from inadvertently accessing the trainer equipment 1/0 channels, Again this could be prevented by some form of trapping. It would likewise be necessary to prevent an inadvertent transfer of control to the training program. Perhaps memory barriers and trapping could prevent this. Since the execution time of the training program is variable, the time available for data processing is variable. It is also unpredictable. Thus an executive program would be required that could quickly and absolutely turn off the data processing. Generally the time synchronizing of the training program is accomplished by some form of priority interrupt. This conceivably could be absolute. However, if the data processing program is performing an 1/0function, it becomes difficult to wure safe and timely restart of the training program. None of these problems is impossible of satisfactory resolution, However, they do present serious practical problems and would require extensive analysis, a sophisticated executive program, and probably modification of the computer before simultaneous training and data processing could be undertaken. It hw not been done to date and probably will not be undertaken for quite some time, if at all. It is a very interesting programming problem and, if it could be solved, would make available to training simulator users considerable computer capacity. A modification of the concept is practical. During most training exercises some idle time occura due to intended interruptions of the training. These interruptions can vary from a few seconds to upwards of an hour. If a long interruption occurs, then it is practical to dump the training program on magnetic tape and load some data-processing program. When training is resumed, the revem transfer would take place. It is possible that interruptions w short w 10 sec would make such a procedure practical and attractive. However, the author knows of no instance where this has been accomplished. 6. Future Training Device Requirements

In one sense, any discussion of future training device requirements is presumptuous sinoe it must wume certctin training problems and further preempts detailed analysis of the suspected problems. However, in a broader sense, it is a necessary and desirable thing to be able to discuss the training needs of w yet undefined systems. Only by this 128

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tspe of planning can the tools be adequately developed to satisfy future training needs. Considering only the implementation of training devices, it is to be expected that training simulators will become more complex and sophisticated and make use of many advances in technology. Each generation of training devices has advanced in the use of techniques, and there is no reason why this trend will not continue. More importantly, however, there are good and sufficient reaaons why such advances me required. As has been stressed previously in this article, the underlying and paramount reason is the need to provide better training. The first consideration has to do with the role ,of man in future systems. It is expected that, aa systems become further automated, the remaining functions assigned to man will become increasingly critical. This trend has occurred in weapon systems, command-and-control systems, logistics systems, and nearly all system development. The rote function is automated, and only critical nonrote-type functions remain. Thus the expectation is that man’s role will become concerned to a much greater extent with decision processes that require judgment too complex or too little understood to automate. These types of system will in turn lead to the development of more sophisticated training simulators, and, since the decision process is amenable to logical manipulation,it is expected that the increased use of digital computers will result. This is an evolutionary process. More revolutionary changes are also expected. Today, reliability of training simulators is not of significant concern. Training problems either me of short duration or present no hazard in themselves to the trainee. Thus seldom is it economical to attempt to achieve reliabilities compatible with operational systems. However, some simulators have been designed where reliability is a very significant factor. I n space vehicle training, it is desirable to simulate mission profiles in their entirety for short missions and only the greater portion of the miasion profile for long missions.-Thus,it has become a requirement to effeot training problems of many hours’ or even many days’ duration. It then becomes important to assure that the training is not interrupted. This in turn pltwes a premium on the reliability of the training simulator. The Apollo Mission Simulator,for example, is required to operate over extended training periods. Thus the system design must reflect this requirement in the inherent system availability. The inherent capabilities of moving base simulators for modern airoraft or spaoe vehicles ctre such that injury could result to the trainee from erratic and hazardous behavior. Thus, reliability again becomes a factor to prevent the trainee from being exposed to such hazards. I n a more mundane vein, the ever increasing sophisticationof training I29

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simulators has resulted in increased cost. In order that the simulator aohieve a reasonable oost/effeotiveness,utilization of the devioe must be high. Utilization is a result of many factors, but one that is paramount is the availability of the simulator. Thus, to ensure a high utilization of the simulator, a premium is again plaoed on reliability. The result of all of these faotors will place an increasing and somewhat revolutionary emphasis on the reliability, maintainability, and availability of the training simulator. This will be aohieved by the use of many teohniques, suoh as fundamentally more reliable oomponents or redundanoy at either the oomponent or subsystem level. However, it is not expeoted that the trrtining simulator requirements will lead the advanoe of reliabilityteohniques.Rather, the training simulatorindustry will adapt teohniques developed in the design of operational system& One area of simulation that requires extensive advanoement is visual simulation. Today very few teohniques are available to generate dynamio, panoramio, visual displays. Suoh a display would be of great value for training situations requiring out-of-the-windowtype of simulation. Airoraft landing prooedures, spaoeoraft navigation and dooking, and other teeks requiring extensive visual oues are examples of training problems needing suoh a devioe. Although some techniques are available, muoh needs to be done. Sinoe the need exists, it is hoped that a solution will soon be forthooming. This is one area where true development is required striotly for simulator use. The use of digital teohniques, and in partioular large general purpose oomputers,has enabled very oomplex and sophistioated training devices to be oonstruoted. As oomputers become more refined it is expeoted that their power will enable many advanoes in simulation techniques, Many problems beoome praotioal of solution because the computer exists. Many more require still faster and larger oomputers. However, the oomputers will be available and the problem8 will be solved. The result will be better trained personnel, not only for oomplex weapon systems but for industrial systems as well. Through training, system effeotiveness oan be improved. Thus, many direot and indireot benefits will amrue. AOKNOWUCDQ~~~JT~

The author wiahea to expreaa hia appreaiation to the many people who have oontributed to thie article. Perticuler thenke me due to Mwara. Msurioe Bark, Stenley cfryde, and Be& Yeeger for their invaluable contributiona. Special mention end acknowledgment must a h be given to the U.S.Naval Training Devioe Center, Port Waahington, New York, under whoae eegia moat of the training simulators diaouseed in this articlehave been developed. The keenly perceptive foresight of Tminiig Devioe Center persome1 ia primarily reaponeible for the fmt that digital oomputera have oome into use in training aimulatora.

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