A low-complexity method for authoring an interactive virtual maintenance training system of hydroelectric generating equipment

Computers in Industry 100 (2018) 159–172

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A low-complexity method for authoring an interactive virtual maintenance training system of hydroelectric generating equipment

T

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Bailin Lia, , Yaxiong Bib, Qiang Hec, Jie Renc, Zhaohui Lid a

College of Hydropower and Information Engineering, Huazhong University of Science and Technology, Wuhan 430074, China China Three Gorges Corporation, Beijing 100000, China c China Yangtze Power Co., Ltd, Yichang 443002, China d State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Interactive industrial training Interactive virtual scenario authoring Modelling maintenance instructions Hydroelectric generating equipment

In heavy industry, an interactive maintenance training system is the most effective way to acquire maintenance knowledge while it is the most difficult to be achieved. To reduce the difficulty in authoring and improve the consistency between the virtual maintenance system and the site, a low-complexity method is proposed to author an interactive virtual maintenance training system of hydroelectric generating equipment in this paper. This method decomposes the complex equipment into a set of parts and components. Based upon the interactive operation of each part and component, an interactive virtual maintenance system of the entire equipment is established. First, the relationship among the component actions is quickly and clearly expressed through the overall modeling. Second, the component models, simulation classes of the motion characteristics, simulation classes of the interactive operation, and other auxiliary classes are created based on object-oriented thinking, and are then encapsulated together as standardized interactive virtual elements. Finally, a virtual environment system with an interactive operation response is created through the interactive virtual elements. An interactive maintenance system of hydroelectric generating equipment based on this method is currently being applied to the training of new employees in a hydropower station, which enhances the training experience and effectiveness.

1. Introduction Maintenance plays an important role in the life cycle of a mechanical equipment system [1–3], especially for heavy industry, such as aircraft [4], Electrical Power Engineering [5–7], Vehicle Engineering [8]. To improve the skills of the maintenance engineers/technicians, which the maintenance quality depends on [9–11], it needs a lot of hand-on maintenance training. Particularly for hydroelectric generating equipment (HGE), however, which is bulky, heavy, and undergoes longterm operation, it is generally impossible to provide adequate prototypes for maintenance training. Therefore, virtual maintenance training system (VMTS) which has the advantages such as low-cost, safe and repeatable training has become an important auxiliary means for skills training. Due to the user's active participation, interactive VMTS which is the most difficult to be achieved becomes the most effective medium to quickly master maintenance skills. Virtual reality (VR) technology with more interactive experience [2], such as immersive VR [12,13], has also been widely developed. However, compared with the desktop VR,

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Corresponding author. E-mail address: [email protected] (B. Li).

https://doi.org/10.1016/j.compind.2018.04.018 Received 24 April 2017; Received in revised form 25 April 2018; Accepted 30 April 2018 Available online 09 May 2018 0166-3615/ © 2018 Elsevier B.V. All rights reserved.

immersed VR hardware is expensive and the penetration rate is low. Therefore, the desktop VR technology which was chosen to develop the training system is still more practical. An interactive VMTS based upon desktop VR includes the following works. i) Visualization – A reconstruction of the maintenance environment should be realized on a computer, including the equipment, tools, and plant structure. ii) Simulation of human-computer interaction – The system should provide users with an interactive interface for controlling the virtual models. The system needs to understand the actions of the users through the detection of mouse and keyboard events, achieve the model selection, tool operation, and other factors. iii) Simulation of virtual model – The system performs the necessary physics simulation and boundary condition judgment. Based on the action of a user interaction and the results of the conditional judgment, the virtual models should show a reasonable response in position and orientation. iv) Check of maintenance knowledge – When the users operate in an

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near optimal disassembly sequence is selected based on the optimal technique. The system then uses a near optimal disassembly sequence to control the display of the disassembly process. The user can trigger the entire maintenance process using a GUI module. In other fields, A. Çetin et al. [17] and M. Grazia, et al. [18] developed 3D Web-based interactive medical devices for educational purposes and distance training. A.Z. Sampaio et al. [19] applied VR technology in civil engineering and architecture courses. S. Borsci [8] et al. used VR-based systems for the training of automotive assembly tasks. J. Osterlund et al. [20] applied VR technology to spacecraft assembly and training. In addition, some virtual training software are commercially available, such as Virtual Maintenance Trainers (VMT) developed by DiSTI Corporation [4]. The VMT consist of three main components: virtual environment, simulation model, lesson engine. It can be used as a vetting process for new hires, testing basic knowledge of mechanics and safety awareness. Through which the trainees can be guided to avoid unsafe work environments and damaged equipment. In order to adapt to different trainees with different knowledge and experience levels, researchers have classified the functions of a training system. B. Arendarski et al. [7] provided users with the choice of three degrees of model interactivity: presentation, guided, and free. M.P.A. De Sousa et al. [5,6] divided a maintenance course into three modes: automatic, guided, and exploratory. The system developed by A.A. Garcia et al. [9] also provides three operation modes: learning, practice, and evaluation. In these different functions, the interactive operation training becomes the most useful way to grasp the maintenance skills. Meanwhile, it is also the difficulty of system implementation. The key to developing an interactive system is the expression of the operation information and the recognition of input and the execution of response. Y.A.O. Lili et al. [21] use XML to describe the assembly process, interactive tasks, and a state diagram. Over the years, researchers divide the assembly process into three layers: scene, model, and operation. The operation mode is realized by mouse clicks, drags, and movements, as well as keyboard events. The basic operation is as follows: The type of operation and model are selected, and the assembly animation is played back if the selected model can be operated. L.Pengyuan et al. [22] realized an interaction process using a mouse pickup, drag, and release in three steps. A. Çetin [17] realized rotating, panning, and zooming motions by dragging and rolling the mouse. M.P.A. de Sousa et al. [5,6] control the maintenance procedure using a button on a GUI. T. Ma et al. [23] designed a file data type called DAR (.dat extension) to meet the freedom required to customize the training equipment. The data stored in a .dat file includes the equipment name, total number of parts, total number of operation steps, the number of disorderly dismantling parts and their corresponding index within the same group, and the number of un-demolition parts and their corresponding index. For the assembly and disassembly operations, the DAR data also include the assembly position, starting position, disassembly sequence, operation type, torque/result range, and name of the part. When starting an operation, if the part is selected by directly clicking on it, and if the operating sequence is correct, the system will finish the dismantling operation automatically. Similarly, other researchers have also studied a simulation method to realize interactive operations. To reduce the complexity of modeling and analysis, F. Lin et al. [24] used the Petri nets to model the operation process. In the system, the complex training goals are decomposed by goal trees and then Petri nets are used as a process control tool to control the VR simulation. The conditions, that the last step is completed and the trainee triggers the current process by interacting operation such as pressing, pushing, grasping, pointing and so on, are used to control the execution of the simulated operation process. To avoid a complex judgment of the operation details, T.L. Sun et al. [25] also described a Petri net-based approach to realize an interactive virtual maintenance operation. The user behaviors of trainees interacting with virtual objects are programmed into every component model. Disassembly of a part is

interactive VMTS, the system should check the correctness of the operation in real time and give a prompt, such as whether the disassembly sequence is correct, whether the tool selection is appropriate and whether the maintenance record is correct. As for the large mechanical equipment in heavy industry sectors, the maintenance process is complex, which hinders the authoring of interactive VMTS. It is mainly reflected in the following aspects: First, the number of parts is large and many are repeated, which led to a large number of operational sequences are reasonable. Thus, enumerating all possible sequences will greatly increase the workload and using fixed disassembly order will affect the user experience. Second, during operation, each part/component interacts with others and produces associated motion based on conditions. Even worse, conditions and movement may be constantly changing. Third, besides the disassembly/ assembly of a large number of components, it also contains adjustment of equipment technical parameters. This process includes the use of instrumentation and repeated adjustment operations. What is more, the operation varies from person to person and the operation order is unpredictable. The above complexities make it quite difficult for the developers to simulate the actual maintenance processes of large mechanical equipment, especially for hydroelectric generating equipment (HGE). To reduce such complexities, this paper proposes a novel method of developing the interactive virtual maintenance training system (IVMTS) for HGE that can effectively and efficiently simulate the actual HGE maintenance processes. This method applies modularization techniques to construct the IVMTS that consists of many devices. Every device is decomposed into the modularized and standardized interactive virtual elements. Interactive virtual element encapsulates the component models, motion characteristics, interactive operation, and other auxiliary cautions. In such a way, this method simplifies complex action relationship, reduces persons’ repeated authoring work and better reproduces engineering spot. The rest of this paper is organized as follows. Section 2 reviews the application of different methods for the interactive maintenance training system. Section 3 describes the analysis and modeling of maintenance process. The implementation method of the interactive virtual element (IVE) is elaborated upon in Section 4. Section 5 describes the authoring of the interactive virtual equipment scenario (IVES). Section 6 presents the effect of the method application on the interactive virtual maintenance for the main shaft center adjustment. The last section, Section 7, provides a discussion and concluding remarks regarding the proposed work. 2. Related work This work draws knowledge from two main areas of research: applications of VMTS based on desktop VR technology in industry and the implementation method of interactive maintenance operation simulation. For power system equipment, M.P.A. De Sousa et al. [5,6] presented a 3D learning tool for a hydroelectric unit, through which the staff members can learn the maintenance and operational processes. B. Arendarski et al. [7] developed an interactive visualizing system for virtual development and training platform used for the maintenance of complex machines in electric power systems. A.A. Garcia et al. [9] also developed a 3D workforce training system for maintenance of energized high-voltage power lines. A. Cardoso, et al. [14] proposed a VR approach for the simulation, training, and control of electric substations, which reduces the operators’ mental effort and increases the human performance when operating an electrical system. For the centrifugal pump system, J.R. Li et al. [1,15,16] developed a low-cost VMTS, called V-REALISM, that is applied to the maintenance training. The authors provide a method to generate all possible disassembly sequences using disassembly constraint graph, in which the 160

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represented using a petri net, in which place the nodes represent the disassembly states and transition nodes define rules to move a token between locations. The part disassembly operations for maintenance training are controlled using mouse-sensing and mapping-control nodes. According to the work presented above, it shows that VR technology in the industrial maintenance training has a great potential advantage. These methods are effective for the simulation of linear sequences or relatively simple non-linear sequence operations. However, as TL Sun et al. [25] summarized, more in-depth research is needed to adapt to simulations of more complex operations, such as hundreds of disassembly states, complicated logic operations, and components that interact with each other during a maintenance operation. In view of the limitation of these methods, we propose the novel method in this paper. Three are the main novelties of the presented work: an approach of implementing an interactive VMTS based on the simulation of each component is presented, a method of constructing a common and instantiable interactive three-dimensional simulation element is proposed and the method is effectively applied to the simulation of complex main shaft center adjustment maintenance at the water guide bearing.

Fig. 2. Representation of IVE.

of an object, the following five basic aspects are to be analyzed: direct external action, direct action on the other objects, the movement condition, the movement characteristic, and the interaction function. A direct external action and the conditional information are expressed as input variables I, the direct action on the other components and the output conditions are expressed as output variables O, the motion is expressed as motion simulation function M, and the operation of the user is expressed as the interactive interface II. The indirect boundary conditions are not considered when the component is modeled. However, they cannot be ignored. They are finally expressed through a multi-level transmission of the direct boundary conditions. To achieve the effect of the indirect conditions in this way, the operational and movement conditions of every component need to be detected in real time. The condition detecting is expressed as function C. The results of the detection are cached into memory and passed to the directly affected components as output variables. Thus, each IVE can be represented as shown in Fig. 2. The composition of IVE includes two parts: three dimensional geometric model and simulation classes which are used to define the input and output variables, interactive interface, motion simulation and condition detecting.

3. Analysis and modeling of maintenance process Modeling the relationship between the objects in the maintenance environment is the basis for implementing an interactive VMTS. It includes modeling of basic objects such as part, component, tool, and modeling of the entire equipment system. In this paper, the simulated virtual basic object which contains properties, motion simulation, interactive functions, and maintenance knowledge check, is called interactive virtual element (IVE). The virtual equipment system built by IVE is called interactive virtual equipment scenario (IVES).

3.2. Modeling of IVES The entire equipment maintenance process can be considered as a collection of these basic operations and organized under certain rules and constraints. As shown in Fig. 3, the entire model of the equipment system is built by connecting the components that directly act on each other. Specific variables, flags and interfaces are then defined to express the interaction between each other. This method does not need to take a large number of components into account at a time, which reduces the mental workload. Meanwhile, the operation is more in line with the actual overhaul. It is able to easily solve the following three complex problems: disassembly sequence planning of components, simulation of a complex action relationship, and simulation of a complex adjustment process. i) Disassembly sequence planning of components – Fixed sequence of maintenance operations are easy to be simulated. However, it is difficult to program maintenance operations without sequence constraints. For example, for the maintenance of a component fixed by 24 bolts, each bolt has an equal probability of being demolished. Thus, there are 24! (24*23*…*2*1) types of disassembly orders, which are all legitimate. The modeling can be quickly and easily completed through this method, and can avoid massive judgments of the sequence. As shown in Fig. 4, each component is an independent object which can be operated. There is no direct relationship between each bolt, and thus there is no need to consider the order of their mutual disassembly. As long as the demolition conditions are met, each bolt can be removed in any order. This is in line with the on-site demolition of the 24 bolts.

3.1. Modeling of IVE 3.1.1. Analysis of a basic virtual operation In a maintenance process, a basic operation of an object is expressed as shown in Fig. 1. In Fig. 1, the process sequence is “A – B – C – D – E”. A maintenance technician determines a part or component to be disassembled and selects the maintenance tool from the tool base. Then, the maintenance technician controls the selected tool to complete the maintenance operation through the interactions between the selected tool and part. In this process, the user is the driving force and actively controls the execution of the whole process. The tool, part or component is the important IVEs. 3.1.2. Composition of IVE To realize an interaction and motion simulation for the maintenance

Fig. 1. Model of maintenance operation in a virtual system.

Fig. 3. Modeling of virtual equipment. 161

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Fig. 4. Modeling of a bolt operation.

Fig. 5. Modeling of the complex action relationship.

ii) Modeling the complex action relationship – As shown in Fig. 5(a), the equipment contains six rigid parts: Part1–Part6. A Tool is used to push the parts at the Part1. The distance between PartM and PartN is defined dMN. The frX which is Boolean is defined as the flag whether the PartX can be pushed towards the right. If frX = =true, the PartX can be pushed, otherwise it can not be pushed. Similarly, the flx is defined as the flag whether the PartX can be pushed towards the left and the ft is defined the Tool whether can be operated. F(dMN) is defined to check whether the PartM touches the PartN. If they touch each other, the F (dMN) will return true, otherwise it returns false. So, the ft is determined by the Eq. (3.1). This equation is complex and will become more complicated as the number of parts increases. In this paper, each component only considers a direct relationship. Eq. (3.1) can be decomposed into Eq. (3.2). Since every part performs self-checking and updates frX in real time. The result of the ft can be calculated by “ft = F (dt1)||fr1” which is not affected by the number of parts. According to Eq. (3.2), the model of this equipment can be quickly represented as shown in Fig. 5(b).

⎧ ft = F (dt1) fr1 ⎪ fr1 = (F (d12) fr 2 )&(F (d13) fr 3 ) ⎪ f = F (d24 ) fr 4 ⎨ r2 ⎪ fr 3 = F (d34 ) fr 4 ⎪ f = (F (d ) f )&(F (d ) f ) 45 46 r5 r6 ⎩ r4

(3.2)

iii） Modeling of adjustment process – An adjustment process is repeated and unpredictable which poses a great challenge for the simulation. As shown in Fig. 6(a), the Tool1 and the Tool2 are used to adjust the position of the Component. The user needs to operate the two tools repeatedly until the position of the Component meets the requirement. Each part, component and tool needs produce the correct movement based on user real-time actions and physical conditions. The model of the system can be easily expressed as shown in Fig. 6(b) by the method in this paper. Since each object is simulated in real time in the model, the user can repeatedly adjust the Component from a different direction as long as the physical conditions permit. This is consistent with the actual operation.

ft = F (dt1) {{F (d12) {F (d24 ) {{F (d45) fr 5 }&{F (d46) fr 6 }}}} &{F (d13) {F (d34 ) {{F (d45) fr 5 }&{F (d46) fr 6 }}}}}

4. Implementation of IVE (3.1)

According to the above modeling in the Section 3, constructing the IVE of each object is the key to system implementation. The following defines the rules of making IVE and describes the implementation of the IVE in detail. 162

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Fig. 6. Modeling of the adjustment process.

iv) Each IVE is encapsulated as a standard template which is editable to adapt to build different scenes. v) Only one human-computer interaction component is activated at a time in the virtual maintenance environment. 4.2. Standardized implementation of IVE The standardized implementation of IVE mainly includes seven aspects: geometric modeling, attribute abstraction, motion simulation, simulation of the maintenance operation, conditional judgment and operation prompts, other auxiliary functions improving the experience of the interactive maintenance operation, and encapsulation of the all elements as a standard IVE. All of these simulation classes are programmed via C # in Unity3D [26]. The content of the simulation not only contains interactive operations, but also embeds inspection of maintenance process knowledge, which comes from the actual maintenance operation manual.

Fig. 7. Modeling workflow.

4.1. Rules of making IVE IVE's characteristics will determine the feasibility of the system and the difficulty of development. In order to quickly build an efficient virtual training environment, it needs to meet the following basic requirements.

4.2.1. Geometric modeling Geometric modeling is the foundation of IVE. It describes the geometric properties of the hydropower equipment. A 3D virtual hydropower equipment maintenance system mainly includes hydropower unit equipment models, maintenance tool models, and environment models. The workflow of a geometric model is described in Fig. 7, and the implementation steps are as follows. Step 1: Understanding the actual physical system and equipment structure, collecting corresponding pictures and CAD/CAE drawings. Step 2: Converting 2D information into 3D information. The components are then assembled into equipment to ensure the completeness and correctness of the modeling components. Step 3: To achieve a better display effect, the material is given to the geometric model. A shader is created to make the material, texture, and gloss of the equipment in a virtual environment similar with those of a real environment. Step 4: The component models are imported into the Unity3D project in .FBX file form. Generally, a device contains many duplicate parts while Unity3D can not maintain the constraint and array relationship of the assembly. So, to avoid unnecessary resource redundancy, each type part models are imported only one. Then, they are simulated, packaged, instantiated and re-assembled into a device, which will be described in detail later.

i) An IVE should be universal – An IVE should be adapted to build different virtual device environments. The virtual objects cloned from the same IVE have the same characteristics at different position and orientation. For example, a wrench can not only be used to twist the someone jack, and other same jacks which have different position and attitude, but also should be used for operating all the components which need use this type and size wrench, such as bolts, nuts. ii) Simulation should be independent – Each IVE has an independent and complete function that satisfies all interactive operations and motion simulations that are relevant to it and are not affected by external changes. iii) The simulation should run efficiently – According to the method of this article, we can see that all the components are in real-time simulation state, which will consume a large amount of system resources. Therefore, each IVE should be optimized to ensure the system efficiently running. iv) It should be easy to be updated – Developers can quickly update objects in virtual scenes, such as adding new operating hints, upgrading new operating tools, and modifying simulation details.

4.2.2. Attribute abstraction All of the properties used to describe the device virtualization are abstracted as attributes. This mainly includes basic identification attributes, physical attributes, simulation attributes, and operation attributes. Basic identification attributes – These are used to mark the component object and its basic properties such as the name, component ID, component size, component position, and spatial orientation. Physical attributes – These are used to identify the physical properties of a component, such as the weight and material. In addition, to avoid the phenomenon of anti-physics appearing in a virtual environment, each IVE is given a collision body. Simulation attributes – These are used for the simulation of motion

In the production of each IVE, the following rules are prescribed based on the above basic requirements. i) The model local coordinate system is used as the reference coordinate system for motion simulation of an IVE. ii) The location and orientation of all the components loaded dynamically are determined by relative position and relative orientation based on world coordinate system. iii) The interaction of components in the system and human-computer interaction are all implemented through the encapsulated interface. For example, when to operate a tool, function buttons for operations are provided for users. 163

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operation item using the left mouse button, the tool conducts the corresponding operation action and acts on the component. In a 3D virtual maintenance environment, the specific details of the movement are automatically completed. This design comes from the on-site maintenance engineer's advice: For maintenance training, they are not concerned about how the tools and parts are moving and interrelated during the operation. The system only needs to provide them with an interactive access to operate the tools.

Table 1 Operation definitions. User Action

Definition

Press W/w key Press S/s key Press D/d key Press A/a key Hold down the left mouse button and drag Scroll the mouse wheel forward Scroll the mouse wheel backward Space key Click the left mouse button

The camera view moves forward The camera view moves backward The camera view moves to the right The camera view moves to the left Adjust camera view orientation

Click the right mouse button Double-click the left mouse button Press X/x key

Zoom in camera view Zoom out camera view Vertical jump Select the components, select the tool, trigger a repair operation Pop up the list of operations Trigger a special repair operation

4.2.5. Conditional judgment and operation prompts As the important part of virtual operation manual, the conditional judgment and the operation prompts are essential. They are present throughout the interactive maintenance operation to guide trainees to better use the interactive training system and improve the maintenance skills and knowledge. The contents mainly include the following:

Accelerates execution of actions

i) Stating important safety precautions and handling precautions – All the texts of precautions are saved using the TXT file and the corresponding audios are synthesized by the text to speech software. If a precaution is required before the equipment is maintained, the trainee is prompted with texts and sounds. ii) Checking whether the tool is properly selected and giving a prompt when the selected tool is wrong – As shown in Fig. 10(a), according to the set attribute values: tool type and tool size, the system judges the correctness of the selected tool and gives the prompt. iii) Checking whether the operation is physically allowed and giving a prompt when subject to physical limitations – For example, a component fixed by multiple bolts can be disassembled only after all the bolts have been removed. iv) Checking whether the instrument is used correctly and giving a prompt when the operation is incorrect – For example, after the dial indicator is installed, the first operation is to zero it. If the zero setting is not successful, as long as a trainee clicks other object, the system will prompt “Dial indicator is not zero. Please zero it!”. The program workflow is shown in Fig. 10(b). v) Checking whether the maintenance process is correct and giving a prompt when it is wrong – During the maintenance operation, although the above conditions check and prompts have been completed, the operation may still be wrong, because it does not meet the strict maintenance process. For example, the initial parameters need to be measured and recorded before the device parameters are adjusted. If the initial parameters are not processed, the adjustment operation will lose the reference.

and action characteristics such as the rotational angle, translation distance, and condition flag. Operation attributes – These are used for a representation of the variables in an interactive maintenance operation process, such as the tool name, tool type, and operation actions of the mouse and keyboard. 4.2.3. Motion simulation A 3D model is made up of three-dimensional data that do not have the motion characteristics of the actual components. A motion simulation transforms a virtual system model into a component system with motion characteristics and an operational response. According to the characteristics of the components, a virtual component motion, which is the same as in a real component, is simulated, such as the motion mode or motion form. 4.2.4. Simulation of the maintenance operation 4.2.4.1. User action definition. In the system, the basic actions of the user mouse and keyboard operations are defined, as shown in Table 1. The input device transforms the user operation behavior into command data. The program completes the operation action in a virtual environment according to the data obtained. 4.2.4.2. Object selection. Some researchers use a model tree or dropdown list to choose the equipment in a 3D virtual environment [1,5]. This paper uses 3D ray cast through the mouse click, as shown in Fig. 8. The user moves the mouse over the widget and selects it by clicking the left mouse button.

4.2.6. Auxiliary function In order to improve the user experience, discoloration prompt is used to notify the user of the operation result. A material ball with a green glow is attached to each component. The system has a standard mouse motion detection function. When the mouse enters the scope of the device, the model shows a green glow, and in contrast, returns to

4.2.4.3. Tool operation. As previously stated, the operable actions of the tool are fixed. When we click on the loaded tool, the system interface will automatically pop up the operation panel of the tool that has the operation buttons, as shown in Fig. 9. After the user clicks the

Fig. 8. Object selection. 164

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Fig. 9. The operation panel of tools.

of a M24 ´ 18 bolt is made as shown in Fig. 11. Step 1: The bolt is modeled with SolidWorks. Then its material is rendered through 3Dmax and it is transformed into. FBX format. After it is imported into the Unity3D platform, a minimal cylindrical collision body which can wrap it is given to the model. To support a friendly operation, the bolt is bound three displaying functions OriginalShow(), OverShow() and ClickedShow() which are used to control the different display when the bolt is loaded, mouse moving over it and mouse clicking it. Step 2: The basic properties of the bolt are defined as Name, bolt size Sb, thread distance PAS, thread number N, collision body Boltcollision, weight Boltweight, material Material, rotation angle θb, translation distance Db. The other properties include the maintenance wrench name Toolname and size Toolsize, the wrench loaded position Relativeposition and orientation Relativeorientation relative to the bolt, the bolt following rotation part Followpart. Step 3: The conditional checks are simulated. There are four check functions: OperationCondition(), Tool(name,size), Range(θb), BoltNumberDetection(). The first function is used to check bolt whether can be operated. The second function is used to check the selection of the tool is correct or not according to the Toolname and Toolsize. If they are correct, the system will call the function ToolLoad(name,size) to load tool. Meanwhile, the function DynamicInitialize() is executed to

the original display. The green glow is superimposed on the original device, which does not affect the original display quality. In addition, quickly disassembling a large number of repetitive parts is also necessary to improve the user experience. In this paper, if some one of these repetitive parts has been disassembled, the others can be quickly removed with the user double-clicking the left mouse button. 4.2.7. Encapsulation In order to fast instantiate object, it is necessary to encapsulate the models and simulation classes into an independent standard part/ component, similar to the encapsulation in the object-oriented programming [27]. The encapsulation is implemented via the function Prefab [28] of the Unity3D. The Prefab, like a template, is a collection of predefined object/component that is re-usable throughout project. Developers can fast instantiate the corresponding object by dragging the created prefab into the edit window [28]. When a prefab is updated, all the objects instantiated from the prefab will be updated simultaneously. This research makes full use of these advantages of Prefab. After a model and its associated simulation classes are completed, they are dragged into an empty prefab to be encapsulated as a standard IVE. 4.2.8. Example Bolt is the most common component in mechanical system. An IVE

Fig. 10. Some checks during the interactive maintenance operation. 165

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Fig. 11. The IVE of a bolt.

named Bolt_M24 × 18 in Unity3D.

initialize Followpart. The third function is used to check whether the bolt is screwed into or out a screw hole. The last function is used to check whether a bolt has been d, which the result is used as the condition to allow the same components to be removed once by double clicking the mouse left button. Step 4: The bolt motion characteristics are simulated. Bolt has two types of movement: Rotate(θw) and Translate(θw). It rotates following the wrench which is acting on it. Meanwhile, the bolt translates along the bolt center line as it rotates. The translation of the bolt will lead to the translation of the wrench in turn. The attributes of the wrench are defined the type as Sw, rotation angle as θw, translational distance as Dw. The relationship between them can be represented as the following equations.

5. IVES authoring based on IVE 5.1. Building of IVES The IVES is built through the parts/components IVEs in the Unity3D platform. The three basic steps are as follows. First, developers instantiate each part/component by dragging its IVE prefab from the prefabs library to the virtual scene editing window. Then, the parts/ components are assembled by setting the values of position and attitude. Finally, the parameters of the interactive simulation are initialized. The instantiation of a large number of same parts/components such as bolts is implemented by the following two steps. The first step is that the first part/component is instantiated as mentioned above. The second step is that the instantiated part is copied, and organized according to the parts/components distributing law such as linear-distributed law or circular-distributed law. As shown in Fig. 12, the distribution of bolts is a circular-distributed law that the symmetric center is O and the angle of the adjacent bolts is β. The other copied bolts need to be rotated to the corresponding position and the center of rotation is O. Because the parameters such as its operation tool are same for the all copied bolts, the relationship between the operation view and tool is as the bolt 2 shown in the figure, otherwise the relationship will be the bolt 3 as shown in the figure if the copied bolt is panned to the bolt 3 position. Obviously, the bolt 3 is unreasonable. Building IVES based on IVEs has many advantages in developing an IVMTS. As shown in Fig. 13, the same components in a virtual environment require only one IVE and all common classes and functions, such as the display class and input detection, only need to be implemented once. With the development of technology, actual maintenance way is constantly changing, such as the use of new maintenance tools. In this system, it only needs to do the following simple work to upgrade the corresponding virtual interactive operation: implementing the interactive operating simulation of the new tool and changing the tool name and tool size in the IVE simulation class. So, all of the parts/components instantiated from the IVE in the entire IVES

n

θb =

∑

θw n

i=1

(4.1)

Db = PAS * θb/360, (0 ≤ θb/360 ≤ N)

(4.2)

Dw = Db

(4.3)

Eq. (4.1) shows that the rotation angle of the bolt is the sum of the wrench rotation angles. Eq. (4.2) shows that the displacement of the bolt translating is equal to the number of twist cycles multiplied by the thread distance. If the number of twist cycles is equal to the number of thread, the bolt is removed from the screw hole. The last equation shows that the displacement of the wrench is the same as the displacement of the bolt. Step 5: The interactive interfaces are implemented. It contains three aspects: user interface (UI), input detection and data receiving. For the bolt, OperationUI() is used to provide operation buttons about maintenance content to users. PromptUI(str) is used to provide operation tips to guide the user to do the maintenance task. The functions MouseOver (), MouseClick() and KeyboardClick() is used to detect the user operation in real time. The function ReceiveData(θw) is used to receive the wrench rotation angle, which provides data for function Rotate(θw) and Translate(θw). Step 6: The bolt model, material ball, property class, simulation class, interface class and display class are all packaged into a prefab 166

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operation of a hydroelectric generator. During an operation, the turbine bearing bushes will gradually loosen with the friction between the turbine bearing bushes and the main shaft. This will result in the main shaft rotation center deviating from the geometric center, which will lead to an excessive main shaft vibration. Therefore, adjusting the main shaft center is a common and important maintenance task when the distance of the deviation is beyond the normal range. This section comprehensively introduces the maintenance operation for the main shaft center adjustment, and elaborates on the application effect of the method proposed in this paper.

6.1. Modeling of main shaft center adjustment Fig. 15 shows the main shaft center adjustment of a hydroelectric generating unit. The user operates a jack using a wrench. The jack turns a rotary displacement into a horizontal displacement, and pushes the bearing bush to move toward the main shaft. When the bearing bush touches the main shaft, it will push the main shaft to move forward together. During the maintenance operation process, the motions of the wrenches, jacks, bearing bushes, and main shaft are associated. The condition of the association is whether the distance between them is zero. According to the method described in Section 2, the roles of the user and wrench are abstracted as the rotation angle θi. The relationship between the wrench and jack is abstracted as the rotation angle θ_WiToJi for the wrench acting on the jack, the translation distance S_JiToWi for the jack acting on the wrench, and the flag F_JiToWi for whether the jack can be rotated. The relationship between the jack and bearing bush is abstracted as the translation distance S_JiToBi for the wrench acting on the jack, the translation distance S_BiToJi for the bearing bush acting on the jack, and flag F_JiToBi for whether the bearing bush can be translated. The relationship between the bearing bush and the main shaft is abstracted as the translation distance S_BiToM for the bearing bush acting on the main shaft, flag F_BiToM for whether the bearing bush can be translated, the translation distance S_MToBi for the main shaft acting on the bearing, and flag F_MToBi for whether the main shaft can be pushed. Finally, as shown in Fig. 16, the entire model used to adjust the main shaft position in the X direction is quickly and clearly built by connecting all of the components through the interfaces.

Fig. 12. Instantiation of the same bolts.

will be upgraded to the new maintenance tool, which greatly reduces the workload. In addition, an IVE can be applied to building a different IVES. Therefore, when to develop an IVMTS of a new equipment, only the unique parts/components need to be simulated. 5.2. Management of IVES Effective management of IVES can not only help developers understand the composition of a hydropower unit, it can also significantly improve the efficiency of the system development. This paper uses an equipment tree to comprehensively and clearly manage the equipment components. According to the containment relationship of all the parts and components as shown in Fig. 14, each part and component of HGE is coded and the codes are stored in a table. Each time the system is run, the device tree information is dynamically loaded from the table. 6. Application notes A main shaft is an important part for maintaining the stable

Fig. 13. Process of building IVES. 167

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Fig. 14. Relationship of the parts/components.

Fig. 15. Adjusting the center of the main shaft in X direction.

and enrich the simulation details for a part, they only need to make changes to its simulation class without affecting other parts. Moreover, the IVEs in this project can be reused only need to import them into other projects. Therefore, the other projects are only need to make the unique IVEs, which is useful to efficiently develop an interactive VMTS of new equipment. With the richness of the IVE library, development work will become easier.

6.2. IVES of turbine bearing The composition of the turbine guide bearing is shown in Table 2. There are 197 components divided into 13 types in total. The NO. in the table corresponds to the numbers in Fig. 17(a). As shown in Fig. 17(a–d), a virtual maintenance environment is built according to the method described in Sections 3 and 4. Applying the method described in this paper, only 13 IVEs are made for the virtual maintenance of a turbine guide bearing. In addition, in these 13 IVEs, components 2, 3, 4, 11, and 12 share the same simulation class, of which the parameters are set differently during the initialization. To achieve the operation of the components, as shown in Table 2, five types of tool IVEs are made. In addition, a dial indicator and a micrometer IVE, which is used to measure the distance, are also made. Due to the independence of each IVE, if develops want to modify

6.3. Adjusting the main shaft center in an IVES The process of adjusting the main shaft center can be described ten main steps, as shown in Table 3. When a user chooses this maintenance task, the system loads the virtual interactive training environment and lets user select the order of maintenance steps (Fig. 18(a)). When the button “Sure” is clicked, if the selected step order is right, the system

Fig. 16. Modeling for adjusting the center of the main shaft in the X direction. 168

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Table 2 Composition of the turbine bearing.

Table 3 Steps of adjusting the main shaft center.

NO.

Name

Number

Tool

Step ID

Operation description

1 2 3

1 24 24

Chain hoist Wrench Wrench

24

Wrench

5 6 7

Bearing cap Bearing cap bolt Bolt between the bearing housing and supports the cover Bolt between oil pan and bearing housing Oil pan Epoxy board Turbine bearing bush

1 30 10

Learning the precautions Disassembling bolts from bearing cap Lifting bearing cap Installing the dial indicator Measuring the center of main shaft Installing the adjusting tool Adjusting the center Operating the screw of the bearing bush Removing the instrumentations and tools Reassemble the bearing cap

8 9 10 11 12 13

Oil barrel General hat Bearing housing Screw of the bearing bush General Cap Bolt Main Shaft

1 10 1 10 60 1

Chain hoist, Wrench Electric wrench Eyebolt, Chain hoist, Mechanical jack Wrench Wrench Chain hoist Wrench Wrench Dial indicator

1 2 3 4 5 6 7 8 9 10

4

wrench to disassemble the bolt. Although each bolt can be disassembled independently in turn, this is unfriendly to the user. Thus, if a bolt is disassembled and double clicking mouse left button, the remaining bearing cap bolts are removed at once. In the case where the 24 bolts are not completely removed, if the bearing cover is to be removed, the simulation program will pop up a prompt box because it is not physically removable (Fig. 20(b)). After the bearing cap is disassembled, the dial indicators and micrometers are installed in the + X and + Y directions (Fig. 20(c)). To easily observe the change in displacement of the main shaft, the dial indicator is set to zero by turning the dial before the other operation, otherwise the user will be alerted through the prompt box when to operate other object (Fig. 20(d)). Then, users measure the distance of the main shaft in the +X, −X, +Y, and −Y directions by adjusting micrometric screw (Fig. 20(e)). On the up-right corner of the main window, a measurement record child window is popped up when the micrometric screw is selected. After the value is entered, it is automatically calculates the offset values dX and dY between main shaft center and the turbine guide bearing body center in the X and Y direction. As the minimum scale of the dial indicator is 0.01 mm, the final values of dX and dY are converted to the values in 0.01 mm increments. Simultaneously, the measurement flag status of the main shaft is set

jumps to the next window to introduce precautions which are presented via text and sound (Fig. 18(b)). Otherwise it prompts the user with “Step order is wrong!” (Fig. 18(a)) Once the introduction is completed, the user can start the adjustment operation through the control method defined in Table 1. As shown in Fig. 19, the operation object can be selected by clicking the left mouse button. The selected object information is updated in real time in the upper area of the window. Then user can get the operation menu through the right mouse button. When an operation button is chosen, the tool selection panel will be automatically popped up in the right side of the main window. Tool type can be chosen according to the tool icon, and tool size can be chosen through the buttons. If the type and size of tool is chosen wrong, prompts will be popped up as described in Section 4. In this system, as long as the conditions allow, the user can disassemble any one part. As shown in Fig. 20(a), the user first removes the bearing cap bolts via a wrench. After users click the wrench, its operation panel is popped up, through which users can rotate the

Fig. 17. Work flow of making virtual maintenance environment for turbine guide bearing. 169

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Fig. 18. Learning maintenance knowledge before operation.

Fig. 19. User interface of system.

information of each step in xml file and database. When the user performs maintenance training, the system invokes the corresponding motion information data to perform the motion demonstration according to the selected components. The second method is to adopt the Petri nets method in reference [25] to realize the interactive operation control of virtual maintenance process. The third method is to trigger the execution of the maintenance animation by users’ clicking or dragging operation. The animation of each component is completed in advance. It spends about three months to achieve basic disassembly operation interaction and process control through these common methods. Unfortunately, if there is a change in the maintenance operation, the first method is necessary to modify each component and control data one by one, which greatly limits the development efficiency. Moreover, all these methods cannot solve the simulation of the interactive adjustment operation. After careful consideration, we proposed the method in this paper and completed design and implementation of this important maintenance project interactive virtual training in about two months, and access to the acceptance of power plant engineers.

true. If simulation class detects that the status is false when the main shaft is pushed, it cannot be manipulated and prompts the users (Fig. 20(f)). Then, mechanical jacks, which are used to adjust the center of the main shaft are installed behind the turbine bearing bush in the +X, −X, +Y, and −Y directions (Fig. 20(g)). A wrench is used to turn the adjustment screw of the mechanical jacks. At the same time, the dial indicators are observed until the needle of the dial indicator in the +X direction indicates scale value dX, and the needle of the dial indicator in the +Y direction indicates scale value dY. If the axis meets the requirements, user need tight the screw of the bearing bush, remove the instrumentations and tools, reassemble the bearing cap. After all the operations are finished, the system prompts that adjusting the main shaft center is complete (Fig. 20(h)). If the users want to practice again, they can click the button “Sure” (Fig. 20(h)) and the IVES will be reset to the start state. This interactive maintenance training module is only part of a virtual training system project for a large runoff hydropower station. In the early period, we tried to implement this module through the following three common methods. The first method is to enumerate all possible disassembly sequences and store the component motion 170

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Fig. 20. The process of adjusting the main shaft center.

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7. Conclusion and future work

[12] S. Behdad, L. Berg, J. Vance, D. Thurston, Immersive computing technology to investigate tradeoffs under uncertainty in disassembly sequence planning, J. Mech. Des. 136 (2014) 71001, http://dx.doi.org/10.1115/1.4025021. [13] M. Slater, Enhancing Our Lives with Immersive Virtual Reality Vol. 3 (2016), pp. 1–47, http://dx.doi.org/10.3389/frobt.2016.00074. [14] A. Cardoso, P.R. Prado, G.F.M. Lima, E. Lamounier, A virtual reality based approach to improve human performance and to minimize safety risks when operating power electric systems, Adv. Intell. Syst. Comput. (AISC) 495 (2017) 171–182, http://dx. doi.org/10.1007/978-3-319-41950-3_15. [15] J.R. Li, L.P. Khoo, S.B. Tor, An object-oriented intelligent disassembly sequence planner for maintenance, Comput. Ind. 56 (2005) 699–718, http://dx.doi.org/10. 1016/j.compind.2005.03.005. [16] J.R. Li, L.P. Khoo, S.B. Tor, Generation of possible multiple components disassembly sequence for maintenance using a disassembly constraint graph, Int. J. Prod. Econ. 102 (2006) 51–65, http://dx.doi.org/10.1016/j.ijpe.2005.01.012. [17] A. Çetin, 3D web based learning of medical equipments employed in intensive care units, J. Med. Syst. 36 (2012) 167–174, http://dx.doi.org/10.1007/s10916-0109456-5. [18] M. Grazia, V. Enrico, Design and implementation of 3D Web-based interactive medical devices for educational purposes, Int. J. Interact. Des. Manuf. 11 (2017) 31–44, http://dx.doi.org/10.1007/s12008-015-0277-0. [19] A.Z. Sampaio, M.M. Ferreira, D.P. Rosário, O.P. Martins, 3D and VR models in Civil Engineering education: construction, rehabilitation and maintenance, Autom. Constr. 19 (2010) 819–828, http://dx.doi.org/10.1016/j.autcon.2010.05.006. [20] J. Osterlund, B. Lawrence, Virtual reality: avatars in human spaceflight training, Acta Astronaut. 71 (2012) 139–150, http://dx.doi.org/10.1016/j.actaastro.2011. 08.011. [21] Y.A.O. Lili, C. Jiayao, Research and implementation of virtual assembly training system, 2009 IEEE International Symposium on IT in Medicine & Education (ITME, (2009), pp. 641–647, http://dx.doi.org/10.1109/ITIME.2009.5236341. [22] L. Pengyuan, M. Long, Research on Interaction Technologies in Desktop Virtual Maintenance System of Certain Weapon, (2011), pp. 1–4, http://dx.doi.org/10. 1109/ICVRV.2011.27. [23] T. Ma, Z. Li, B. Ma, Disassembly and assembly relation data design in 3D VMT system, 2014 IEEE International Conference on Signal Processing, Communications and Computing (ICSPCC) (2014) 683–685, http://dx.doi.org/10.1109/ICSPCC. 2014.6986282. [24] F. Lin, L. Ye, V.G. Du, Developing virtual environments for industrial training, Inf. Sci. 140 (2002) 153–170, http://dx.doi.org/10.1016/S0020-0255(01)00185-2. [25] T.L. Sun, Petri net-based VR model interactive behaviour specification and control for maintaining training, Int. J. Comput. Integr. Manuf. 22 (2009) 129–137, http:// dx.doi.org/10.1080/09511920802199838. [26] J. Xie, Research on key technologies base Unity3D game engine, ICCSE 2012 – Proc. 2012 7th Int. Conf. Comput. Sci. Educ. (2012) 695–699, http://dx.doi.org/10. 1109/ICCSE.2012.6295169. [27] G. Bracha, D. Ungar, Mirrors: design principles for meta-level facilities of objectoriented programming languages, proc. 19textsuperscript{th} annu. {ACM} {SIGPLAN} conf. object-oriented program, Syst. Lang. Appl. (2004) 331–344, http://dx.doi.org/10.1145/1028976.1029004. [28] “Prefabs”. [Online] Available: https://docs.unity3d.com/Manual/Prefabs.html.

A low-complexity method is proposed in this paper for an interactive VMTS. It separates the complex equipment into independent IVEs, which has an operating response. The application indicates that the method greatly reduces the difficulty of a maintenance process analysis. Meanwhile, the method can quickly express the action of a complex interactive operation and avoid falling into a judgment regarding the operating conditions. Moreover, without increasing the difficulty of implementation, it improves the degree of freedom of the interoperability in a computer-simulated environment, and solves a problem in which there are too many combinations of an operation sequence for a large number of components with the same operation right. In addition, based on an object-oriented implementation method, it can quickly realize the modeling of the geometric characteristics and an interactive operation for large-scale components. The IVE, which includes a model, motion simulation characteristics, and interactive operating characteristics, can be shared by different projects, which avoids repeated development. With the continuous enrichment of the IVE library, the development of an interactive maintenance training system for other types of mechanical equipment will be simpler. Meanwhile, owing to the independence of each IVE, it shortens development time for the simulation of parts can be produced in parallel by different developers. Although the maintenance system provides users with a friendly interactive environment, the interaction capability still needs to be strengthened to directly operate the tools by intelligently recognizing the actions of a user operation. In addition, the intelligence of the perspective adjustment should be strengthened to improve the user experience. With the popularity of immersive virtual reality equipment, it will also be necessary to further develop an immersive interactive maintenance system. In addition, strengthening the application on the mobile platform to support real-time on-site maintenance will become an important application direction. References [1] J.R. Li, L.P. Khoo, S.B. Tor, Desktop virtual reality for maintenance training: an object oriented prototype system (V-REALISM), Comput. Ind. 52 (2003) 109–125, http://dx.doi.org/10.1016/S0166-3615(03)00103-9. [2] D. Pantf, B. Vogel-heuser, S. Member, D. Gramß, K. Schweizer, Supporting operators in process control tasks – benefits of interactive 3-D visualization, IEEE Trans. Hum.-Mach. Syst. 46 (2016) 895–907. [3] Michele Fiorentino, et al., Augmented reality on large screen for interactive maintenance instructions, Comput. Ind. 65.2 (2014) 270–278. [4] S.A. Vander Weide, J. Secretan, The Potential for Improving Maintainer, Equipment and Flight Safety Through Virtual Maintenance Training Vol. 4970 (2009), http:// dx.doi.org/10.4271/2009-01-3225. [5] M.P.A. De Sousa, M.R. Filho, M.V.A. Nunes, A. Da Costa Lopes, A 3D learning tool for a hydroelectric unit, Comput. Appl. Eng. Educ. 20 (2012) 269–279, http://dx. doi.org/10.1002/cae.20393. [6] M.P.A. De Sousa, M.R. Filho, M.V.A. Nunes, A.d.C. Lopes, Maintenance and operation of a hydroelectric unit of energy in a power system using virtual reality, Int. J. Electr. Power Energy Syst. 32 (2010) 599–606, http://dx.doi.org/10.1016/j. ijepes.2009.11.016. [7] B. Arendarski, W. Termath, P. Mecking, Maintenance of complex machines in electric power systems using virtual reality techniques, Conf. Rec. 2008 IEEE Int. Symp. Electr. Insul. (2008) 483–487, http://dx.doi.org/10.1109/ELINSL.2008. 4570378. [8] S. Borsci, G. Lawson, B. Jha, M. Burges, D. Salanitri, Effectiveness of a multidevice 3D virtual environment application to train car service maintenance procedures, Virtual Reality 20 (2016) 41–55, http://dx.doi.org/10.1007/s10055-015-0281-5. [9] A.A. Garcia, I.G. Bobadilla, G.A. Figueroa, M.P. Ramirez, J.M. Roman, Virtual reality training system for maintenance and operation of high-voltage overhead power lines, Virtual Reality 20 (2016) 27–40, http://dx.doi.org/10.1007/s10055015-0280-6. [10] T. Haase, W. Termath, ICTE in Regional Development A virtual interactive training application for supporting service technicians in the field of high voltage equipment, Procedia – Procedia Comput. Sci. 77 (2015) 207–214, http://dx.doi.org/10. 1016/j.procs.2015.12.372. [11] O. Usanmaz, Training of the maintenance personnel to prevent failures in aircraft systems, Eng. Fail. Anal. 18 (2011) 1683–1688, http://dx.doi.org/10.1016/j. engfailanal.2011.02.010.

Bailin Li (1987-) received his bachelor’s degree in the Huazhong University of Science and Technology (HUST), Wuhan, China, in 2012. He currently is a Ph.D. candidate from the College of Hydropower and Information Engineering, HUST. His current interests include condition monitoring and fault diagnosis of hydropower power station, and 3D visualization of electric power facilities. BI Yaxiong (1962-) is a senior engineer at the China Three Gorges Corporation and a professor at Huazhong University of Science and Technology. He got Bachelor in 1982 from South China University of Technology and got M. Sc. in 2001 from Chongqing University. He currently undertakes the job of the development, operation, and management of hydro electric enterprises. Qiang He (1989-) received bachelor’s degree in 2012, master’s degree in 2014, all from the Huazhong University of Science and Technology (HUST), Wuhan, China, in 2012. He currently is an assistant engineer and is engaged in maintenance work of electrical equipment in the Three Gorges Hydropower Plant. His interests include condition monitoring and fault diagnosis of hydropower power station, and 3D visualization of electric power facilities. Jie Ren (1990-) received bachelor’s degree in 2013, master’s degree in 2016, all from the Huazhong University of Science and Technology (HUST), Wuhan, China, in 2012. He currently is engaged in the operation and maintenance of power station monitoring systems and automation systems. His interests include condition monitoring and fault diagnosis of hydropower power station, and 3D visualization of electric power facilities. Zhaohui Li (1963-) is a Member of China National Standardization Technical Committee on Control of Hydraulic Turbines, IEEE senior Member, got Bachelor in 1983, M. Sc. in 1987 and Ph.D. in 1991, all from Huazhong University of Science and Technology (HUST). He has joined the faculty of HUST since 1987 and holds a rank of full professor and doctoral supervisor since 1997. His research interests include the process control of hydro-electric generation, and the condition monitoring and the fault diagnosis of the electric power facility.

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