Industrial robot simulation manufacturing based on big data and virtual reality technology

1 Introduction

With the transformation of traditional factories to intelligent factories, industrial robot workstations, an important component of intelligent manufacturing, are paid more and more attention. The intelligent production line is generally composed of industrial robot workstations or multiple workstations, with complex process, large equipment investment, and difficult on-site debugging. In order to solve the problem of difficult on-site debugging, virtual simulation debugging technology has been gradually applied to the debugging of industrial robot workstations and intelligent production lines. With the development of computer science, electromechanical engineering, information technology, and control theory, industrial robot technology has gradually become standard equipment widely used in various fields such as welding, assembly, handling, polishing, and gluing. Industrial robots not only improve the level of industrial production automation, but also significantly reduce labor costs and improve production efficiency. In addition, with the high attention paid by the country to the manufacturing industry and the transformation and upgrading of traditional industries, while promoting the construction of new infrastructure, the demand for high-quality industrial robot application talents is becoming more urgent [1]. At present, more and more vocational colleges are offering industrial robot technology majors. In the teaching of industrial robot related courses, students need to rely on specific industrial robot workstations, and the prices of related equipment are relatively high, the required space is relatively large, and due to constraints such as funding and space, the number of practical training equipment in the school is relatively small; hence, in the classroom, 5–6 students share a set of equipment, and the average operating time for each student is very limited [2]. In response to the limitations of the number of training equipment and student operation time, virtual simulation software was used to simulate and debug workstations during the teaching process, and then verified on physical devices, reducing training costs and improving training efficiency, significantly improving the teaching effectiveness, and also to some extent, solving the problem of students not having the opportunity to engage in physical operations during the pre-class self-learning and post-class expansion stages [3]. For enterprises with rapidly changing production tasks, using traditional online teaching methods to program robots can take up a lot of production time and seriously affect the efficiency of the entire production line. The robot virtual simulation software, with its built-in virtual teaching panel and related motion control modules, provides users with a “virtual teaching” method to complete the programming work of the robot. This new teaching method does not require production time and does not affect the normal operation of the robot, greatly reducing the teaching cost [4]. In addition, robot virtual simulation software provides a fully virtual environment for robots to work in, which can be used for trajectory and related verification of programmed programs. Verifying the correctness of a program in a virtual environment can significantly reduce the probability of damaging robots and other devices due to programming errors, and can improve the safety and reliability of the entire programming process. Industrial robot simulation system involves a series of problems such as robot kinematics analysis, trajectory planning, motion control, and program interpretation, and it is a comprehensive embodiment of industrial robot technology and a powerful tool for studying robots and their applications. According to the applicability of robot simulation systems, the mainstream industrial robot simulation systems in the current market can be divided into two categories: The first type is general-purpose software, which is generally developed and maintained by third-party companies and can support simulation, trajectory programming, and other aspects of multi brand robots. Due to the varying technical parameters of various robot manufacturers, the development of universal simulation systems is difficult and the development cost is relatively high [5]. However, general-purpose simulation software generally has good openness and scalability, and is currently a hot research direction. The second type is specialized, and most of this software is developed by robot manufacturers themselves, so it can generally only support their company’s brand of robots. The compatibility of specialized robot simulation systems is poor and does not support secondary development. However, the development difficulty of such software is relatively low, and the support for specific brand robots is relatively complete. With the widespread application of robots in various industries, domestic research institutions have also conducted extensive research on robot simulation systems. However, compared to foreign countries, domestic simulation software still has a significant gap in terms of multi robot simulation, trajectory optimization, and interactive experience. In fact, due to the limitation of the number of I/O ports of industrial robots, programmable logic controller (PLC) is mostly used to control other equipment of industrial robot workstations. Generally, industrial robots directly control their terminal equipment only, and there is an inconsistency between the simulation and the actual equipment. In order to solve this research problem, the authors propose a joint virtual simulation debugging method of industrial robot workstation and Siemens PLC based on simulation software OCTOPUZ [6,7]. This work discusses a dynamic simulation model with industrial robot assembly workstation in the production line. The simulation workstation is controlled by the external PLC to simulate the field equipment, predict the real production, and guide the site debugging, so as to improve the efficiency of the equipment debugging.

Robotics is an advanced technology integrating multiple disciplines. It has a wide range of fields and new research results, including electrical, machinery, automation, communication, computer, and so on. In the 1960s, since the birth of the first robot, through continuous exploration and research at home and abroad, the robot technology has become more and more mature and has made a qualitative leap. It is precisely because the robot technology covers more knowledge of subjects and the development speed is fast, and its increasing functions and emerging models are far beyond people’s initial cognition of robot, so there is no exact definition of robot in the world. The American Robot Industry Association defined robot as a mechanical arm capable of realizing various functions. The mechanical arm has a programmability to meet different needs, and is suitable for handling materials and moving specific equipment. Countries have different definitions of robots, but they are all much the same.

In 1989, Jaron Lanier, known as the “father of virtual VR,” first proposed the concept of virtual reality (VR). VR is a comprehensive subject integrating computer system and sensing technology by creating a 3D virtual environment. It aims to simulate and mobilize the visual, touch, hearing, smell, and other senses to communicate and interact with the scene and create an immersive feeling. Therefore, VR has the following three characteristics: immersion, interactivity, and imagination.

At present, the research of VR technology is divided into four categories: desktop VR, immersive VR, augmented reality VR, and distributed VR.

2 Methods

2.1 Industrial robot assembly workstation

OCTOPUZ is a software solution for creating programming and simulation software for digital chemical plants and industrial robots. It can perform three-dimensional virtual simulation of industrial robots, electrical and peripheral equipment, quickly establish simulation of intelligent production lines according to user needs, and carry out engineering planning, engineering verification, process analysis, logic verification, and other work. It integrates logistics, human-machine engineering, and physical simulation functions, helping enterprises conduct debugging analysis, production capacity confirmation, and enhance industry competitiveness in the early stage of research and development [8].

The Fidget spinner production line uses industrial robots, CNC machine tools, and CNC milling machines in the software model library. Other models (speed multiplying chain, press mounting device, etc.) are first created in the 3D software SolidWorks, then guided to OCTOPUZ to set the attributes, and the PnP function is used to arrange each model to complete the layout of the Fidget spinner production line model, as shown in Figure 1. The model and structure of the industrial robot assembly workstation are shown in Figures 2 and 3, which mainly include industrial robots, press mounting devices, speed chain machine controllers, finished material trays, and various virtual sensors. The task of the assembly workstation is to transport the end cover and body of the Fidget spinner from the industrial robot to the press mounting device, press mount the Fidget spinner, and then transport it to the finished material tray using the industrial robot, and the whole process is controlled by PLC [9].

Figure 1

Fidget spinner production line model.

Figure 2

Simulation model of industrial robot assembly workstation.

Figure 3

Overall structure of industrial robot assembly workstation.

Robot simulation demand analysis: The display of the robot's motion process and the machining process of tools and workpieces should include: accurate robot motion control and trajectory planning; interactive specified trajectory welding; simulate material removal processes such as grinding and cutting; Realistic robot models and robot scenes; same or similar treatment effect as actual treatment.

Robot teaching requirement analysis: The robot teaching in the text takes lightweight and virtualization as the core, which is convenient for users to conduct the robot teaching operation anytime and anywhere, and should meet the following requirements:

1. Virtualized robots and virtual demonstrators, separated from the constraints of physical objects;

2. The robot language interpretation ability to meet the analysis and editing of a specific robot language;

3. Convenient and stable connection and communication between the virtual robot and the virtual trainer.

2.2 Design of workstation simulation system

2.2.1 Workstation workflow analysis

In the workstation, PLC is the core and the control center of the entire system. The working status of equipment such as material trays, industrial robots, and pressing devices will be sent to the PLC [10,11]. PLC can monitor the position, status, and other information of various components in the workstation in real time, and issue control commands based on the current status information of the equipment and preset control logic, achieving collaborative work among various devices in the workstation. After the simulation system is started, the PLC detects the status of the industrial robot and sends a start signal after passing the inspection. After receiving the handling signal, the simulation industrial robot sequentially transports the end caps and body on the pallet to the designated assembly position of the pressing device. After the press mounting of the Fidget spinner is completed, the industrial robot will transport the assembled Fidget spinner to the finished material tray. In this example, Siemens PLCS7-1200 (1212C) and Botu TIAV16 are used. The workflow of the simulation workstation is shown in Figure 4 [12].

Figure 4

Simple workflow diagram of industrial robot assembly workstation.

2.2.2 Simulation program writing

According to the requirements of work tasks and workflow, PLC control programs and simulation programs for robot assembly workstations are written in OCTOPUZ. A PLC control program based on the workstation workflow and control requirements are shown in Figure 4. The control program mainly includes several functional modules: Robot loading and unloading detection control module, pressing control module, tray conveying, lifting module, etc. After the program is written, it is compiled and downloaded to the PLC first, and separate testing is conducted without errors before proceeding to the next step of joint testing [13].

OCTOPUZ simulation industrial robot program writing assigns detailed work tasks to industrial robots according to the workstation workflow, and then writes industrial robot programs based on this. When starting, the industrial robot is at the working origin and receives the handling signal from the PLC; moves the front cover, rotating wing, and rear cover on the tray to the pressing station in sequence; exits to a safe position; and sends a pressing signal to the PLC. After receiving the signal that the robot can take materials, the industrial robot will put the assembled Fidget spinner in the finished product warehouse and return to the working origin, to wait for the next transportation order [14].

2.2.3 Establish communication between PLC and OCTOPUZ

In order to achieve the above functions, it is also necessary to solve the communication between the PLC and the simulation software OCTOPUZ, on the premise of having the respective programs of PLC and industrial robots. The authors adopt the OPC (OLE for process control) protocol. The OPC protocol is a security standard used in the automation industry and other industries for data security exchange. It can be independent of the platform and ensure seamless transmission of information between multiple manufacturers’ devices, solving the problem of data exchange between data source control systems and data sources. Siemens S7-1200PLC (firmware version V4.0 or above) supports OPC server function, by setting its internal OPCUA communication, and data communication using OPC technology as a communication bridge can be achieved, and OCTOPUZ also provides OPC additional function plugins that support reading and writing of OPC data. Therefore, using PLC as the OPC server and OCT0PUZ as the OPC client, data exchange between PLC and OCTOPUZ can be achieved without developing specific programs, as shown in Figure 5 [15].

Figure 5

Data exchange between PLC and OCTOPUZ based on OPC technology.

First, activate the OPCUA server in the device configuration of the Botu software, and then create an OPC server (named SIEMENS-PLC) in the OPCUA column. Finally, add all variables that need to interact with OCTOPUZ in the server interface to complete the creation of the OPC server in the PLC.

First, activate the “Connectivity” plugin in the software options, and then enable the server in OPCUA under “Connectivity.” Among them, simulation to server refers to the transmission of signals from OCTOPUZ to PLC, while server to simulation refers to the reception of signals from PLC by OCTOPUZ. By using the signal mapping command in the OCTOPUZ simulation server (select the correct one), a mapping relationship can be established between the output signal of the OCTOPUZ industrial robot workstation and the PLC input signal transmitted by the OPC server. If the sensor signal detected by the press station in the OCTOPUZ industrial robot workstation is mapped to the input signal detected by the PLC press station (select pair), after pairing is completed, a symbol that has already been paired will appear next to the variable in the virtual structure. It is also possible to establish a mapping relationship between the input signals of the OCTOPUZ industrial robot workstation and the PLC output signals transmitted by the OPC server, so that the input and output signals of the industrial robot workstation in OCTOPUZ are connected to the input and output signals of the PLC, achieving real-time information exchange [16].

Common industrial robot applications mainly have welding operations, handling, stacking work, glue operations, etc., in manufacturing. Due to differences in operating objects and production processes, there are significant differences in the programming of industrial robots. For example, welding robots need to use welding instructions with accurate tool data, while handling robot programs need to strictly follow the logical sequence of peripheral signals, etc.

3 Joint virtual simulation and result analysis of PLC and workstation

Download the edited and debugged PLC program to the PLC hardware on the computer and start it, while also starting the workstation simulation of OCTOPUZ. After the system simulation starts, the PLC first detects whether the industrial robot is at the working origin. If it is at the working origin, it sends a forward rotation signal of the double speed chain motor, after the PLC detects that there are virtual sensor signals for materials in the tray, upper end cover, rotating wing, and lower end cover, it sends a robot start signal to the industrial robot in the simulation software. After receiving the start signal, the industrial robot executes the handling program, as shown in Figure 6. The upper end cover, rotating wing, and lower end cover are all transported to the pressing station, and after exiting to a safe position, a request for pressing is sent to the PLC [17].

Figure 6

Robot grasping materials.

After receiving the information from the industrial robot requesting press mounting, PLC sends the start signal of press mounting to the press mounting device, as shown in Figure 7. After receiving the virtual sensor signal of press mounting cylinder and rising to the position, PLC sends the signal of Fidget spinner press mounting completion to the industrial robot. After receiving the signal, the industrial robot executes the procedure of transporting the Fidget spinner to the finished product silo, as shown in Figure 8. At this time, the simulation of the working process of a Fidget spinner assembly ends, and the next working cycle starts until the simulation stops [18].

Figure 7

Press mounting of Fidget spinner.

Figure 8

Fidget spinner Placing Finished Product Silo.

The industrial robot simulation workstation utilizes OPC for data exchange between PLC and simulation software, achieving joint virtual debugging of industrial robot programs and PLC programs in OCTOPUZ. Each unit of the workstation runs normally, verifying the effectiveness of the OCTOPUZ-based industrial robot workstation virtual debugging scheme and the correctness of the industrial robot program and PLC program. In practice, conducting simulation debugging before equipment construction can identify and solve program problems in advance, improving the efficiency of workstation design programming and debugging [19,20]. For the industrial robot automatic production line controlled by PLC, its equipment is more complex and the control is more difficult. This simulation debugging method can verify the correctness of the component design, PLC control program, and robot control program of the automatic production line faster and safer.

4 Conclusion

This work discusses a dynamic simulation model with industrial robot assembly workstation in the production line. The authors developed a virtual simulation debugging method for industrial robot assembly workstations based on the simulation software OCTOPUZ. Through OPC, the signal interaction between Siemens PLC control signals and workstation signals in the simulation software was achieved, achieving the simulation of robot assembly workstations under PLC integrated control. During the simulation process, the virtual debugging of the OCTOPUZ industrial robot assembly workstation based on OPC technology can detect problems in the design of industrial robot control programs, PLC control programs, and other electromechanical components during the assembly process in advance. In the virtual debugging stage, problems are solved to save the cost of actual equipment debugging and improve the efficiency and safety of engineering debugging. For industrial robot automation production lines controlled by PLC, the equipment is more complex and the control difficulty is greater. This simulation debugging method can verify the correctness of the component design, PLC control program, robot control program, etc., of the automation production line faster and safer. In the future, the functions of the virtual simulation platform of the industrial robot application system can be enriched. Teaching programming can only control the simple actions of industrial robots. According to the current research situation, we can further explore the five applications of Unity 3D control, including stacking, grinding, vision, assembly, and storage.