An integrated bevel gears manufacturing system

Mechanismand Mechine TheoryVol. 14, pp. 11-23 © Pergamon Press Ltd., 1979. Printed in Great Britain

0094-113X/79/0101-00111502.0010

An Integrated Bevel Gears Manufacturing System M. S. Konstsntlnovt

and N. V. DJsmdjlev

Received 17 December 1976 Abstract Wholly automated forging systems are still comparatively rare. This paper summarizes the principles of integrated manufacturing systems and reviews the state-of-the-art. The problems associated with the application of automatic loading equipment to the handling of forgings to insure continuous operation of the integrated manufacturing system, object of this research study, are examined by arguments and various types of handling devices are considered. The manufacturing system is under direct numerical control (DNC) and is centered on chipless forming which, as a final product, yield bevel gears and similar parts with ready-to-mount teeth. However, the ultimate solution to automation in such systems seems to lie neither in copying of human skills nor in applying sophisticated industrial robots. Therefore, the synthesis technique of a simple manipulator which is adaptable to transfer/handling tasks in this billet stock metering, forming, cutting, and measuring integrated system aimed at the production of ready-tomount parts is discussed. The manipulator can be adjusted to handle forgings from the last engraving stage of the installed multistage forging press, attended by a multipositions inter press transfer manipulator for hot components, to the cutting machine, and then to the conveyor of the automatic measuring line. A hot machining technique is considered as an interesting possibility to increase the cutting operation rates.

1. Introduction TH~ FIRST known gear cutting by a machine was that developed by Juanelo Torriano in constructing, more than four centuries ago, a great clockwork for Charles V of Spain[l]. The whole clockwork had more than 1800 wheels. The inventor got up to a production rate of three wheels per day using his homemade, hand powered gear cutting machine (approx. date 1540). In the period 1800-1916, most of the gear cutting machines which we know to-day got started. Thus, the first practical bevel gear making machine was built by William Gleason of the United States in 1874. After more than 40 years of successful operation, this original machine was presented to the Ford Museum at Dearborn, Michigan. Gears of any sort and size are now being made by conventional metal cutting processes. The time-honoured machining process is to use a tool that is tougher and harder than the metal to be cut. There are, however, 2 basic limitations. One is due to the increase in mechanical strength of the material relative to that of the cutting tool, the other is geometrical. Naturally, the manufacturing cost of such gears is rarely comparable to that of conventional drop forgings. It is well known that very powerful new forging machines can make hot steel flow into a die like molten metal, thus forming gear teeth. The advantages of metal forming are: material conservation, substantial reduction in cost of machining, and possibly an improved product because of beneficial grain flow. In fact, the deciding factor over metal cutting is the quantity required, since the cost of design and manufacture of dies has to be justified. Besides the vast improvements made in the field of drop forging, one of the main weak spots of the process is that generally the forging needs to be machined before it can be fitted. But there are a number of process combinations about chipless forming, such as precision forging, tCentral Laboratory for Manipulators and Robots, P.O. Box 97, Sofia 1000, Bulgaria. 11

12 power forging or sinter forging, which as a final product yield a ready-to-mount part[2]. Precision forged parts produced on a multistage press are serious competitors for the power or sinter forged parts. In the case of precision forging of bevel gears, only the difficult to machine surfaces are forged to finished dimensions. The seat surfaces, which are cheap to be turned, will be machined further. This already hints at a manufacturing system integrating these operations. The manufacturing system concept originated with Brunel[3]. At the beginning of the 19th century, the then novel system, which is believed to have comprised 45 machines of 22 varieties, was set up in the Royal Dockyard at Portsmouth, England. Integrated manufacturing means coordination of all functions that go into turning out a product into an efficient, economical process. Assuming a given level of automation, to design the appropriate integrated manufacturing system it is necessary to know the range of size, the material, and the distribution of machining operation times and cycle times. Completely integrated manufacturing systems involve computer control and numerically controlled machine tools. Commonly, they intermix metal working, material handling, and measuring operations in sequences that optimize work flow and that bring all operations into close proximity. In some cases other operations than conventional metal cutting are integrated into the system such as welding, broaching, cleaning, heat treatment and automatic assembly. Integrated operations eliminate unnecessary handling between machines and pieces of equipment and especially handling operations are more easily automated. Product quality is improved because handling is reduced, less capital is tied up in in-process inventory, less floor space is required, and visual surveillance is improved. This work is a part of a wider programme of research aiming at the application of the integrated manufacturing concept to the production of bevel gears and similar parts with ready-to-mount teeth. The manufacturing system contains a multistage press, a NC lathe, and automatic measuring, plus billet stock metering and numerous pieces of material handling devices, comprising a multiposition interpress transfer manipulator and a multimachine transfer manipulator. The fundamental objective is to optimise and maintain strict control over the production process. DNC is envisaged to this end. Attempts will be made to increase the cutting rates by a hot machining technique. Indeed, this paper is concerned with the automatic handling equipment used in the integrated manufacturing system of the present project. The difficulties in robot handling of multistage presses have been discussed elsewhere[4], and a novel multiposition interpress transfer manipulator[5] has been disclosed therein. Below is a description of a specially designed manipulator. It sequences the work pieces not in circular arcs, as an industrial robot of the known types, but in the form of an algebraic curve with cusps and through the press, the NC lathe and the conveyor of the measuring line. The synthesis of a 6-1ink mechanism having three cusps is discussed.

2. Automated Material Handling 2.1 Loading and unloading machine tools On account of fully automatic operation, a machine tool can enable a sequence of machining operations to be completed quickly, so that in some instances, parts loading and unloading can occupy a significant part of the material handling time. In addition, an operator can become fatigued quickly when parts are to be handled at frequent intervals, with the result that the efficiency of the machine is reduced. In order to overcome these problems, automated handling equipment is introduced. Before the handling device can be selected, the job size must be analysed. A division between the groups which differ according to the size of similar parts in series production presents a first group noted by its large job size, a further group marked by its very small job size, and the group lying between these two groups, noted by its middle size job lots. For the first group automated handling equipment is available which is assembled onto the machine or integrated therein[6]. Very small job size commonly does not make the automation thereof worthwhile, whilst the automated handling equipment necessary for the third group must be quickly changed over or modified. The most sensational aspect of automated handling of small quantities of discrete parts is

13 undoubtedly the current development of industrial robots, which is starting to get into the area of tactile and visual cognition in addition to pickup and placement[7]. There is, however, no basic reason why the operation of a robot should approximate to that of a human. But in certain instances--for the handling operation in an assembly line for example--it is desirable that the handling function of the robot should approach that of the human being replaced. However, industrial robots have come under criticism recently in many instances. The more complex the robot becomes, to embrace more of men's capabilities, the more expensive it is and will be. Evidence shows that it will be some years before the labour rates will reach equilibrium with the more advanced industrial robot. Taking this problem into consideration, together with many others of less significance, production engineers are turning to simple industrial robot-type automation. Simple manipulators of the pick-and-place type with a fixed programme operate at their optimum rate whilst being fail-safe in operation. A survey paper by Tassel [8] shows that the manipulators' family forms by far the largest proportion of the world's automatic handling equipment population. It is to note that according to Tassel, the population of simple manipulators will grow in Japan to 21,500 units for 1978, and to 15,000 units in the U.S.A and Europe for the same year. 2.2 Handling in integrated manufacturing systems In an integrated manufacturing system handling and the machining systems are inseparable functions. The material handling system would have to be designed so that workpieces could move not only between the machines and pieces of equipment, but also within the tooling room of the machines and through the pieces of equipment, in order to ensure continuous work flow. It is technically possible to divide the work flow through an integrated manufacturing system into four main areas. Referring to Fig. 1, in which the layout of the bevel gears manufacturing system of our research project is illustrated, the journey of the workpieces through the system is broken down into 4 basic areas. Area (A) represents material handling from the main storage through the billet stock metering equipment to the major machine (multistage forging press). Area (B) comprises the movement of the work in the tooling room of the major machine. Movement between the first major machine and the further major machine or machines (multi-machine handling) represents the third area (C). And the fourth area (D) is the sector through the automatic measuring line to the storage for finished workpieces. Automatic handling equipment for integrated manufacturing systems can be classified as follows: Feeding, orienting mechanisms and escapements. Basic machines (fixed-position-machines, indexing rotary tables, linear transfer and fixed indexing machines, power and free lines). Automatic loaders (automanipulators). Simple manipulators.

billet

I

stock metering

forging

monipuloto¢2 J ~ ' ~

,i I I

,,o,

storage

monipulotorI

Figure 1. Layout of the manufacturing system.

cuffing

14 Programmable manipulators or industrial robots. It appears possible to introduce the robots to all four areas of an integrated manufacturing system. But regard should be paid not only to the question of economy, the shape of the workpieces and the job size should be considered also. The question of economy moves favorably to the side of simple manipulators in the second (B) and third (C) areas. For areas (A) and (D) it is more advisable to use standard automatic handling equipment. A few words about so-called flexible manufacturing systems are appropriate in this context. The concept of flexibility applied to manufacturing technology means that the manufacturing system should have the capability of producing several workpieces in random sequence without the need for resetting the installed machine tools. The most important pre-requisite that an industrial robot must fulfill in handling operations being that it could be quickly changed over from one workpiece to the other, demonstrates that robots are best suited for manufacturing systems of this type. Clearly, the concept of flexibility can not be applied to our manufacturing system, since retooling of the multistage forging press is impossible during machining time. It must be stressed now, that the change-over from one forging to another is dearer in automation, even considerably dearer than in manual operations. Therefore, our system is economically dependent upon a fixed job size. This factor is decisive also in first observations as to whether the introduction of an industrial robot is at all worthwhile.

3. The Computer in Metalworking Manufacture The use of the computer in metalworking manufacture, whenever it was used in conjuction with numerical control, proceeded slowly till 1973 when computer controls were heavily emphasized at the Machine Tools Conference of the IEEE (U.S.A.). Now, the trend in control is more and more to computers, smaller ones and simpler minded, plugged into modular hierarchical systems. The question is not whether computerized control systems would be used in metalworking plants, but rather how--and very specifically. DNC (direct numerical control) is strongly favoured as an hierarchic approach to computerization of manufacturing facilities, whilst the trend to CNC (computerized numerical control) appears almost irresistible. 4. The Present State-of-the-Art A complete panorama of the state of the art throughout the world cannot be discussed here, and therefore only very brief notes are given.

4.1 Automated forging production Wholly automated forging production systems are still comparatively rare. Typical examples were described in [4]. Automatic forging of gear blanks was reported recently by Croom[9]. The forgings, with little or no flash and only small draft angles, are made to close dimensional tolerances at production speed of up to 4200 per hr. It is to note that the process render feasible a nearer approximation of the forging to the finished shape, not however, the production of ready-to-mount part shape. 4.2 Muitiposition transfer of forgings The possibilities and economic limits in the automation of forging on crank presses were studied by Beuscher[10]. He notes that three different tools are generally introduced with success in area (B), see Fig. 1, viz. (a) Rotary table. Here the forgings are placed in a drum where the periphery of the drum moves through the tooling room. (b) Swivel pincers. Here the drum is replaced by a pincer which carries out a turning movement. (c) Moving beam. This construction is used most. It was described and illustrated in our[4]. Briefly, gripping fingers mounted on 2 parallel beams line up with each die. The beams (and fingers) move in and out, up and down, left and right, to transfer the forgings from one die station to the next. New possibilities offered by industrial robots for the automation of symmetrically rotating parts in a l0 MN Maxipress were reported by Boije [11]. An interesting alternative is in this case

15

the utilisation of two Electrolux robots, one on either side of the press. Two workpieces can be forged simultaneously, one in each position. Multiposition transfer of forgings up to 5 kp by simple manipulators is described by Dietrich[12]. A press with a row of progressive dies equipped with grippers is disclosed in[13]. Each gripper and the jaws of each gripper of the press are movable independently of the other gripper or grippers. The latter may be disposed at one or both sides of the row of dies and are movable radially of the dies, either at right angles to the common plane of the axes of dies or at an acute angle to such plane. Another U.S. Patent[14] deals with a conveyor for transporting a workpiece from one die to another in a multistage press, so that succesive pressing operations can be performed on the workpiece. 4.3 Industrial robots applied in manufacturing systems For investigating handling systems, a manufacturing system consisting of 2 numerically controlled machine tools and an industrial robot linked to a DNC-computer has been built up at the Institute fiir Werkzeugmaschinen und Fertigungstechnik der Technischen Universit~it Berlin[15]. This fleible system comprises a milling machine, a lathe, NC-milling control, CNC-lathe control, DNC-adaptor, industrial robot, display, magazine. A significant recent step in robots is in Sweden, where Electrolux has organized machining centres and production lines based on robot mechanics. Some of the existing applications, both simple and more complex ones, are described by Ryott[16]. In Japan, a robot has been developed in order to load and unload workpieces of eight NC-lathes in the FANUC DNC system for improved automatic operation[17]. A concept for a completely automatic, computer controlled factory is presented by McLay and von Turkovich in[18].

5. The Research Project The manufacturing system of our research project is for medium batch sizes and the principles of integrated manufacturing are involved therein. By combining the normally diverse operations of cropping, heating, precision forging, cutting, and automatic measuring (Fig. 1), this computer controlled system does all the work of a small jobbing forge, supplying the engineering industries with ready-to-mount bevel gears (Fig. 2). Comparing the precision produced by the system with that usual in general drop forging, it will be noted that tolerances after maching and grinding in the range of IT6 are equaled by the precision forged bevel gears, and that therewith the requirements set by the designer for a ready-to-mount gear are met. Precision forging opens, furthermore, new possibilities to the designer, such as having two different toothings forged in one part or the like. This offers him the possibility of optimum design. As the subject dealt with in this work is so large, it is not intended that details of the billet stock metering, automatic measuring and computer control systems, the multistage press and

fl Figure 2. Bevel gears, (a) forged surfaces; (b) machined surfaces. MMT Vol. 14, No. 1--B.

16 NC lathe, used should be covered. We will concentrate our discussion on the application of manipulator mechanics in attending the multistage forging press and in serving the 2 major machines and the automatic measuring line.

5.1 The multi-grippers hot forge manipulator The engineering design of a multipositions inter press transfer manipulator for hot components was reported originally elsewhere[4]. A list of criterional conditions for such a manipulator was set forth therein. Analysis showed that only two of the structures generated by the used permutation algorithm fulfil the conditions of the mentioned list. These structures are discussed and finally, two improved structures for the modular design of a multigrippers manipulator were considered. These are shown in Figs. 3(a and b). The manipulator shown in Fig. 3(a) comprises a cradle arm attached to consoles on the press, in a manner that a swing motion is possible. The manipulator illustrated in Fig. 3(b) is floor mounted. Both manipulators are featured by parallelogram mechanisms. The grippers for picking up and depositing the billet and the forgings are fixed on a parallelogram linkage for

Y

Figure 3(a). Cradle arm inter press manipulator.

Figure 3(b). Floor mounted inter press manipulator.

17

movement toward the dies, workpieces lift, transfer, drop, and away from the dies under the action of reciprocable control hydraulic cylinders. When the billet is ready for transfer and the forgings are partially expelled from the dies (by press ejector pins). The billet and the thus exposed portions of forgings are grasped by the jaws of the grippers, which are moving now axially of the dies to fully extract the forgings and to lift the billet, and then transversally forth to move the billet into registry with the first die, the fully extracted forgings from registry with preceding dies into registry with the next-following dies, and the fully extracted forging from registry with the last die to the discharge mechanism. The stroke of any movement can be varied by infinitesimal values by means of mechanical arresters which can be adjusted by hand whenever it is necessary to change the stroke between minimum and maximum. Gripper rotation could be provided if necessary, both manipulators are patented [5]. 5.2 Multimachine handling in area (C) A survey on robotic type handling devices shows that almost 80% of all floor mounted industrial robots are available with cylindrical or spherical co-ordinates. Consequently, the arm's movement of an industrial robot with such co-ordinates installed in area (C) to attend the multistage press, the NC lathe, and the conveyor of the automatic measuring line (Fig. 1) is a circle. However, to accomplish roughly parallel feeding and unloading the robot's hand should move on the path shown in Fig. 4(a). Therefore, the positioning of an industrial robot, which seryes working area (C) and the first sector of working area (D), is dependent on the degrees of freedom, which are available from the gripping device. If a robot is to economically serve working area (C) and partially working area (D) a number of factors should be considered, such as the costs of a suitable robot (mainly dependent on the degrees of freedom available), grippers, control, annual maintenance, and the reliability of the robot. An important technical consideration is the comparative cycle time of the machine vs other robotic type handling devices. In addition, there are a host of environmental and technical factors which are difficult to quantify and which are heavily influenced by the manufacturing system. Thus, industrial robots are not normally expected to compete with the high production rates of the multistage press. Comparative low-cost robots available currently handle the pick and place problem by operating only one actuator at a time, so that the path movements of its hand (gripper) take the configuration shown in Fig. 4(a). In these circumstances the handling device is required to repeatedly go through the following sequence: (a) grip the forging from the press, (b) retract the arm, (c) transfer the forging from registry with the press to registry with the chuck of the lathe, (d) extend the arm, (e) release the forging in the chuck, (f) retract the arm and wait with open jaws, (g) extend the arm, (h) grip the finished part, (i) retract the arm, (j) transfer the part from registry with the chuck to registry with the conveyor, (k) extend the arm, (l) release the part,

press ~

conveyor

J

cutting the

(o)

Rgure 4(a). Circular path of a robot's hand.

18

(m) retract the arm with open jaws, (n) move the hand from registry with the conveyor to registry with the press, and (o) extend the arm. Clearly, the problem of reducing this considerable handling time should be attacked. Under the given circumstances there are two possible ways to reduce the handling time: (I) minimization of machining time in order to avoid any waiting time loss during event (f~ above. and (2) improvements relative to the robot dynamics. 5.2.1 Minimization of machining time. This approach could be achieved by (a) the use of a special 2-grippers device which cooperates with an automatic loader which is assembled onto the cutting machine, (b) hot machining technique, and (c) the combination of a further circular application where a robot handles the forged parts to and from surrounding cutting machines[16]. At this level, it is possible to synchronize and adjust the handling time of both circular applications by the use of a special 2-grippers device. Hot machining has long be considered an interesting possibility to increase machining rates, and thus to reduce machining time, particularly in turning. The objective is to heat the workpiece to a temperature at which it loses strength and thus can be cut more easily. A new technique was developed by Britain's PERA, in which the workpiece is heated by a plasma torch about 90° ahead of the cutting tool. Depending on the workpiece material, machining rates could be increased by factors as high as 30. 5.2.2 Improvements in robot's dynamics. Unlike "rotating" and "floating" machinery, the industrial robots are mechanical systems with "articulated links" in which all details are driven to move in various combinations of prescribed positions with reference to a fixed link or base plane. Thus, the system undergoes continually changes of configuration. Engineers do usually attempt to solve the handling time problem by dynamic synthesis techniques. Such techniques have been used in two ways, by positional changes of the configuration in minimum time [19], or by simultaneous movements of several joints[20]. Concepts about another technique for reducing cycle time, by pitching the workpieces are discussed by Birk and Franklin[21]. A control method is developed. It can be implemented by a computer program technique which calculates the minimum time that a robot must hold a workpiece before it is pitched to a target. The above techniques show various levels of complication in terms of programming the robot functions and positions in terms of coordinate geometry. Clearly, they would not compete with the situation in area (CI on purely economic grounds.

6. A Simple Multi-Machine Handling Arm 6.1 The "path generation" problem Ideally, a "simultaneous movements" handling time minimization technique reduces the length of the path followed by the robot hand, Fig. 4(a), and the generated path could correspond exactly with the path desirable in an effort to obtain the global minimum handling time, Fig. 4(b). In contrast to the path obtained by sequential control techniques, a proper way to generate the reduced path shown in Fig. 4(b) is by tape control, so that the continuous path movement is programmed by the "teach-in method". However, the dilemma in continuous path control is the accuracy of the generated path in relation to the joint forces, torques, link lengths, degrees of freedom, velocities, accelerations, load capacity, positioning accuracy, etc. of the installed robot. Clearly, in order that a useful solution is achieved it is necessary to use a sophisticated electronically controlled robot. However, such a robot would be not viable in our case. The problem of path-generation could be solved by other modern techniques capable of yielding truly practical solutions. 6.2 Planar path-generators The conventional industrial robot acts as an ordinary servomechanism which follows the given reference position. Ideally, the servomechanism could be replaced by a kinematic chain which generates a path close to the path imposed on the robot by preprogrammed schedules and data. As a reasonable solution for such an interchange let us examine one of the "classical" problems, which are studied in kinematic synthesis. In the problem of "path generation", one attempts to find a mechanism such that one point on its coupler or couplers, follows a given path (coupler curve).

19

This problem was attacked both by geometrical and by analytical methods, the latter making efficient use of the capabilities of digital computers [22]. Evidently, the few parameters of a 4-bar linkage, the lengths and the angular position of the 4 links, can not specify the parameters necessary for satisfying a complex coupler curve. Since 6-1ink mechanisms have more free parameters they can be synthesized either to satisfy more complex motion specifications for a moving point or plane in the system or to satisfy simultaneously the motion required of combinations of moving links. Thus, planar 6-1ink path-generating mechanisms or path-generators appear sufficiently complex to be used as elementary manipulators [23, 24]. Despite the increasing interest in path-synthesis techniques for plane mechanisms, a literature study made by Thompson[25] reveals a surprisingly small volume of papers devoted to the problem of coupler curve generation. Only Lewis and Gyory[26] precisely indicate how the coupler curve may be generated. In a study for the cusps on coupler curves Primrose et al. [27] obtain the number of cusps with respect to special types of 6-1ink mechanisms, but the continuity of the coupler courve is not taken into consideration. It should be noted, however, that only continuous coupler curves with cusps are applicable to the work positions of an automatic handling system (manipulator). The coordination of coupler point displacement with the swing of the driving link of a 6-1ink mechanism results in an open continuous coupler curve, whilst the correlation of the motion of the coupler point of this mechanism with the rotation of both the input and output links results in a closed coupler curve, as shown in Fig. 4(b). Path-generators having closed coupler curve with 3 cusps have not yet been synthesized. Some comments concerning this problem are made by Shimojima and Ogawa in[24]. The problem must be subjected to a detailed investigation before any further conclusions may be deduced.

6.3 The 6-bar path-generator There are two distinct forms for the 6-1ink kinematic chain, namely the Watt and Stephenson chains. The Watt mechanism exists in 2 modifications known as the so called 2 pivot Watt mechanism, and the Watt 2 mechanism. Three types of Stephenson mechanisms are known, but only the Stephenson 1 mechanism (Fig, 5) is well suited for automatic handling systems. As shown in Fig. 5, the Stephenson 1 mechanism contains 2 ternary links 5 and 6, joined by 2 binary links 1 and 2 to form a 4-1ink loop and by a dyad 3 and 4 to form a 5-1ink loop. Link 1 is fixed to form the mechanism, 6 is the driving link, 2, 3 and 4 are the couplers, 5 is the driven link, and the generating point is the pivot P34. Note that the coupler curve C~, C2, C3 is drawn only stylistically. The necessary and sufficient condition that the locus of P34 becomes a cusp C is

VP-LPa4P46,

V(5 0

(1a)

=

press

/

I L p l \F\ , \ \

co.,°°

conveyor

(b)

Rgure 4(b). Reduced path of a robot's hand (curve with cusps).

20

Figure 5. Stephenson 1 mechanism. or

V~-J-P34P46,

V~sLP35P34

(lb)

where Ve and V~ are the velocities of the pivots P46 and P35, respectively. When conditions (la) or (lb) are satisfied the pivot P u coincides with the fixed pole of the coupler 4 or of the coupler 3, respectively, to define a singular point C where 2 branches of the generated coupler curve contact tangentially. Evidently, a cusp among singular positions on a coupler curve is a dwell point, which is applicable to a work position of an automatic handling system. In the general case of a plane curve f(x, y)= 0, generated by a pivot Pu,v of a multi-link mechanism, will have a number k of cusps when, according to Ganguli[28], the following three conditions are fulfilled

f(xi, yi) = 0

oZ= a/= o c~xi 0yi

(2)

02f2 _ a2f c~2f OxiOy l - -~Xi " -~Yi

where i = 1, 2, 3 . . . k. As conditions (2) are necessary in order to have a cusp, and since the number of parameters of all types of Watt and Stephenson mechanisms is 14, wherein one of the linear parameters is always specified, not more than 4 cusps can be satisfied by any of these 6-1ink mechanisms. There is also a relationship between the number and positions of cusps, and the mechanism parameters. 6.4 Six-bar path-generators for practical purposes Two examples have been selected with a view to demonstrate the adaptability of the Stephenson 1 mechanism to handling tasks. Example 1. The design of a Stephenson 1 mechanism well suited to the manipulation of an object having two rigid planes joined by a pin joint is considered by Myklebust and Tesar [23]. Analytical coplanar synthesis technique is utilized to coordinate 5 multiply separated positions of the coupler point path with the angles of the ternary links. Thus, the number of ordinary precision points being 5, the coupler curve has 2 cusps, the number of independent parameters

21

is 7, and the number of tangents at cusps is 2. It is to note that this manipulator can perform a required function during the handling operation. Thus, the coupler dyad (3, 4 in Fig. 5) is used to control the box opening problem when the manipulator picks up a folded box from a hopper and release it in an open configuration on a conveyor system. Example 2. For the purpose of manipulating 3 kinds of bodies on 3 conveyors into 2 positions, Shimojima and Ogawa [24] suggest a simple manipulator. A open coupler curve with three cusps of a Stephenson 1 path-generator is synthesized and then a new method is applied for the optimum synthesis by use of the last-square method. The number of parameters of the mechanism for satisfying the cusps is 12, four of them being independent ones. Under these circumstances it was not possible to generate a closed curve, as the driving link of the mechanism swings, and the path-generator has change points at the edges of swinging. Concluding, Shimojima and Ogawa discuss an example of application of closed curve, for the purpose of handling a body on a belt conveyor into a first machine tool, and further into a second machine tool, and transfering it back to the belt conveyor. They explain that in order to generate the closed curve, the Grashof's conditions should be taken into consideration. This is, however, a very hard problem [29]. Therefore, we will concentrate now our efforts on this section of the problem, and we suggest below a synthesis technique dependent upon an optimization procedure considering the Grashof criterion [30] and a defined quality index. By the way, the Grashof criterion, expressed as a simple inequality in terms of given link lengths, is often used to predict whether or not the input link in a plane four bar linkage is capable of continuous 360° rotation. The defined quality index removes from consideration those linkages that may be considered of poor proportions. 6.5 Computer-aided synthesis o[ plane mechanisms "The creation of automatic machine systems will require the development of methods for their probalilistic and structural-logical analysis and synthesis, taking into account their output, efficiency, reliability, quality of articles, economy, and precise operation", said Acad. Artobolevskii in his address before the 13th Mechanisms Con[erence. And he went on: "The analysis and synthesis of such systems will require the creation and development of special formal languages, oriented to solve problems of synthesis, to develop new mathematical methods for solving structural synthesis problems, using widely the system approach to the theory of operation investigation" [31]. Reverting again to [25] by Thompson, we note that he cites 10 references dealing with analytical path synthesis techniques for planar mechanisms. Three of the techniques represent precisionpoint approaches, the remainder of the techniques considered in this review are dependent upon an optimization procedure. Almost all of these are computer oriented. But despite this fact, and of the fact that these analytical path-synthesis techniques accomodate the practical aspects of mechanism design, they can not be termed as computer aided design techniques in the narrow sense of this notation. Broadly speaking, design calculations by a digital computer constitute c.a.d. in so far as the user is achieving desired results in a much reduced time. Alternatively, the narrower connotation of c.a.d, is understood to have at least provision for rapid and preferably visual means of assessing the effect of modifying design parameters. A computer-aided design procedure using an interactive graphics system, that allows the designer to simulate operation of planar 4-bar linkages is described by Peterson[32]. Linkages are selected from dimensional synthesis loci curves, and after the links are completed, the mechanism is rotated, using an algorithm developed by Suh and Radcliffe [33]. The linkage must be tested since all positions may not be obtainable without breaking the linkage past an immovable dead center position. A drafting capability is included to allow immediate assessment of interferences, impractilities, and specific geometric constraints. Parts of the configuration can be erased and new linkages substituted in seconds in an attempt to keep pace with the thinking process of the designer. The interactive graphics system used was the CDC 274 coupled to a 6400 central processor. 6.6 Computer-aided synthesis o[ Stephenson 1 handling arms No doubt that our problem relative to the synthesis of a 6-1ink mechanism to be applied as a multi-machine handling arm, can be solved by the computer-aided design procedure described [32], when appropriate dimensional synthesis loci curves are available, Evidently, the program used

22

gives the designer easy access to a selection of these curves. But incidentally, the question arises: how to define the set of loci curves (coupler curves) of a Stephenson 1 linkage having three or four cusps, the sole practicable in our case! Shimojima and Ogawa[24] are developing an optimum synthesis method that utilizes the tangent at each cusp, but the results obtained are not satisfying the rotatability conditions of the driving link. An analytical method for defining closed loci curves with three or four cusps is not yet known. The problem could be resolved by a path-synthesis technique involving the construction of an error function, expressing the error between the desired and generated positions of the cusps as well as the deviation of the tangents at the cusps, and dependent on the mechanism parameters. This error (or deviation) function is minimized in applying physical constraints using, for example, a rapidly-convergent descent method [34].

7. In Conclusion The demands of modern technology require a corresponding development of manufacturing methods which have served well in the past are in many cases no longer adequate. This is true for the field of gears, just as it is true in so many other fields. For example, gears are formed by rolling, and toothed gears are formed by high energy forging. Incidentally, forged gears have to have the "flash" trimmed off the ends of the teeth and the bores or journals finish ground. For very high accuracy gears, the high energy forging of gear teeth could be teamed up, as in our case, with a finishing operation only of shaving or grinding to get high accuracy. Some of the background to the design considerations of an integrated manufacturing system for forged gears, as they will affect the production of such bevel gears has been presented. The overall control of the system as an integrated machine, and the setting of tempo, is achieved in a link-up of the material-handling equipment with the manufacturing objectives. However, capital cost of the system is high, as well as costing in the present stage of research and development. The difi]culties of this important stage must not be minimised.

References 1. R. S. Woodbury, History of the gear cutting machine, pp. 45--46. M.I.T. Press, Massachusetts Institute of Technology, Cambridge, Massachusetts (1959). 2. O. Voigtlaender, Limitations of drop forging• 8e Congr~s International de l'Estampage et de la Forge. Com. No. 19. Nice, France (1974). 3. K. R. Gilbert, The Portsmouth Blockmaking Machinery. H.M.S.O., London (1965)• 4. M. S. Konstantinov and Z. I. Zankov, Multi-grippers hot forge manipulators. The Ind. Robot 2(2), 47-55 (1975). 5. M. S. Konstantinov and Z. I. Zankov, Manipulator with Parallelogram Mechanism• Bulgarian Authorship Certificate (priority 17.10.74), granted (1975)• 6. L. I. Voltshkevitsh and B. A. Usov, Autooperators (in Russian), 2nd Edn, 216pp. Mashinostroenie, Moscow (1974). 7. K. Matsushima and K. Hasegawa, Study on the Industrial Robot with Adaptability• Bulletin of the Tokyo Institute of Technology, No. 123, pp. 115-129 (1974). 8. M. Tassel, Etat actuel et evolution h court et moyen terme des manipulations automatiques programmables. 2~'~ Journ~e d'entretiens organis~e par le GAMIet I'ADEPA. Automatisation par Manipulateurs--Robots Industriels (1975), 9. E. A. G. Croom, The significance of mechanisation and automation in forging production. 8e Congr~s International de l'Estampage et de la Forge. Com. No. 5 (1974). 10. K. Beuscher, The possibilities and economic limits in the automation of forging on crank presses. 8e Congr~s International de l'Estampage et de la Forge. Com. No. 2. (1974). I1. P. Boije, The environment inside the forges can be improved. 8e Congr~s International de l'Estampage et de la Forge. Com. No. 3 (1974). 12. B. Dietrich, Caract~ristiques des manipulateurs programm~s utilis~s en estampage et en forge. Recueil des Communications Les Manipulateurs Programmables et leurs Applications dans l'Estampage. R6f. C. (1973). 13. R. Schulte and M. Daniels, Press. U.S. Patent No. 3,525,248, granted (1970). 14. F. K. Koch and O. Rahn, Workpiece Conveyor [or Multistage Press. U.S. Patent No. 3,809,255, granted (1974). 15. B. H. Auer, Industrial robot feeds numerical controlled machine tools. The Ind. Robot 1(4), 173--177 (1974). 16. J. P. Ryott, Some industrial robot applications in Swedish industry. The Ind. Robot 1(5) 207-210 (1974). 17. K. Kobayashi and Y. Kohzai, DNC System with Robot. Proc. 4th Int. Syrup. Ind. Robots• pp. 455--464 (1974). 18. R. W. McLay and B. F. v. Turkovich, An automatic factory concept. S.M.E. Paper No. AD74-420, p. 14 (1974). 19. J. T. Beckett, A Computer-Aided control Technique [or a Remote Manipulator. Ph.D. Thesis. Case Institute of Technology (1970). 20. D. L. Pieper and B. Roth, The kinematics of manipulators under computer control. Proc. 2rid Int. Congr. Theory of Machines and Mechanisms. 2, pp. 15%169 (1%9)•

23 21. J. R. Birk and D. E. Franklin, Pitching workpieces to minimize the cycling time of industrial robots. The Ind. Robot 1(5) 217-222 (1974). 22. G. N. Sandor and F. Freudenstein, Kinematic Synthesis of Path-Generating Mechanisms by Means of the IBM 650. IBM 650 Program Library, File No. 9.5.003 Columbia University, New-York. 23. A. Myklebust and D. Tesar, Five position synthesis of six-link mechanisms coordinating up to four motion parameters. Proc. 3rd World Congress for the Theory of Machines and Mechanisms H, Paper H-28, 387--424 (1971). 24. H. Shimojima and K. Ogawa, Synthesis of planar six-link path-generator (Part 1, On the Cusps of Stephenson I Mechanism). Bulletin JSME, 15(90) 1617-1624 (1972). 25. B. S. Thompson, A survey of analytical path-synthesis techniques for plane mechanism. Mechanism and Machine Theory 10, Nos (2/3), 197-205 (1975). 26. D. W. Lewis and C. K. Gyory, Kinematic synthesis of plane curves. Trans. ASME $9B, 173-176 (1967). 27. E. J. F. Primrose, F. Freudenstein and B. Roth, Six-bar motion. Arch. for Rational Mechanics and Anal. 24(1) 22 (1967). 28. S. Ganguli, Theory of Plane Curves 1, 54 (1925). 29. J. Odeffeld, Generalization of the Grashof inequality (in Polish). 6(4) 521-529 (1959). 30. F. Grashof, Theoretische Maschinenlehre, Bd. 2, Theorie der Getriebe (1875). 31. I. I. Artobolevskii, General Problems in the Theory of Machines and Mechanisms. Address of the President of IFToMM Before the 13th ASME Mechanisms Conference. New-York, 8 October 1974. Mechanism and Machine Theory, 10 (2/3) 125-130 (1970). 32. D. W. Petersou, Design of four-bar linkages using interactive computer graphics and synthesis curves. ASME Paper No. 70-Mech-45 (1970). 33. C. H. Suh and C. W. Radcliffe, Synthesis of plane linkages with use of the displacement matrix. ASME Paper No. 66-Mech-19 (1966). 34. R. Fletcher and M. J. D. Powell, A rapidly convergent descent method for minimization. The Computer Journal6, 163-168 (1963).

EIN INTEGRIERTES FERTIGUNGSSYST~M F~R KEGELZAHNR~DER

M. S. Konstantlnov und N. V. Djamdjiev

Kurzfassung - Hobelmaschlnen f~r Kegelzahnr~der werden seit mehr als 100 Jahre gebaut und erfolgreich angewendet. Kegelzahnr~dern ben~tzt.

Heutigentags wird auch die Schmiedetechnik fur die Erzeugung yon Die Sitzfl~chen der geschmiedeten Zahnr~der m~ssen abet auf einer

spenabhebenden Maschine bearbeitet werden. Es wird ein integriertes Fertigungssystem f~r Kegelzahnr~der besprochen, Schmiedepresse mit einem Parallelograrmn-Manlpulator bedient wird. der spanabhebenden Maschlne und der Enderzeugnis-Transportanlage

in dem elne mehrstufige

Die Schmiedepresse ist mit (FSderband) dutch einem

Handhabungsger~t integriert, d.h. zu einer Fertigungseinheit zusammengefasst.

Des letzt-

genannte Handhabungsger~t besteht aus einem 6 g liedriegen Koppelgetriebe in der Form des Stephensonschen Mechanismus,

Typ i, der 4 Zweigelenkglieder und 2 Dreigelenkglieder aufweist.

Die Eigenschaften des Stephensonschen Mechanismus, Typ i, sind erforscht und seine Einsatzm~lichkeiten

als Integrationsglled des besprochenen Fertigungssystems gepr~ft.

Folglich,

um eine geschlossene Koppelkurve mit drei Spitzpunkten, die der Arbeitsstellungen des Handhabungsger~tes

ensprechen,

zu bilden, muss unbedingt einer der beiden Dreigelenkglieder

des 6 gliedriegen Koppelgetriebes um 360 ° drehbar sein.

Zu dem Zweck, m~ssen b e s t i ~ t e

Verh~itnisse der kinematischen Abmessungen des Mechanismus erf~llt werden. Koppelgetriebe dieses Typs sind als Handhabungsger~te dort berechtigt wo Forderungen zu er~dllen sind, die Fdr Industrie-Roboter geradezu einfach sind, d.h. wenn der Einsatz eines Roboters, wegen seiner ~berfl~ssigen Arbeitsm~glichkeiten, Ein guter Einsatzbeispiel ist das besprochene Fertigungssystem.

nicht rentabel ist.