Interpret the composition and typical structure of industrial robot control system
“For industrial robots with multiple degrees of freedom, centralized control handles the coupling relationship between each control axis very well and can be easily compensated. However, when the number of axes increases so that the control algorithm becomes complex, its control performance deteriorates. Also, when the number of axes in the system or the control algorithm becomes complex, it may lead to a redesign of the system. In contrast, each motion axis of the distributed structure is handled by a controller, which means that the system has less inter-axis coupling and higher system reconfigurability.
1. Functions to be achieved by the industrial robot control system
The robot control system is an important part of the robot, which is used to control the manipulator to complete specific work tasks. Its basic functions are as follows:
1. Memory function: store the job sequence, movement path, movement mode, movement speed and information related to the production process.
2. Teaching function: offline programming, online teaching, indirect teaching. Online teaching includes teaching box and guided teaching.
3. Contact with peripheral equipment: input and output interface, communication interface, network interface, synchronization interface.
4. Coordinate setting function: There are four coordinate systems: joint, absolute, tool and user-defined.
5. Human-machine interface: teaching box, operation panel, Display screen.
6. Sensor interface: position detection, vision, touch, force sense, etc.
7. Position servo function: robot multi-axis linkage, motion control, speed and acceleration control, dynamic compensation, etc.
8. Fault diagnosis and safety protection function: system state monitoring during operation, safety protection in fault state and fault self-diagnosis.
Second, the composition of the industrial robot control system
1. Control computer: the dispatching command organization of the control system. Generally, microcomputers and microprocessors include 32-bit and 64-bit CPUs such as Pentium series CPUs and other types of CPUs.
2. Teaching box: It teaches the working track and parameter setting of the teaching robot, as well as all human-machine interactive operations. It has its own independent CPU and storage unit, and realizes information exchange with the host computer through serial communication.
3. Operation panel: It is composed of various operation buttons and status indicators, and only completes basic function operations.
4. Hard disk and floppy disk storage: peripheral memory for storing robot working programs.
5. Digital and analog input and output: input or output of various states and control commands.
6. Printer interface: record various information that needs to be output.
7. Sensor interface: It is used for automatic detection of information and realizes the robot’s compliance control, generally force sense, tactile and visual sensors.
8. Axis controller: complete the position, speed and acceleration control of each joint of the robot.
9. Auxiliary equipment control: It is used to control the auxiliary equipment that cooperates with the robot, such as the gripper positioner.
10. Communication interface: realize the exchange of information between robots and other equipment, generally there are serial interfaces, parallel interfaces, etc.
11. Network interface
1) Ethernet interface: It can realize direct PC communication between several or single robots through Ethernet, and the data transmission rate is up to 10Mbit/s. After programming the application program directly on the PC with the windows library function, it supports the TCP/IP communication protocol , and load data and programs into each robot controller through the Ethernet interface.
2) Fieldbus interface: supports a variety of popular fieldbus specifications, such as Devicenet, ABRemoteI/O, Interbus-s, profibus-DP, M-NET, etc.
3. Classification of industrial robot control systems
1. Program control system: By applying a certain regular control effect to each degree of freedom, the robot can achieve the required space trajectory.
2. Adaptive control system: When the external conditions change, in order to ensure the required quality or to improve the control quality with the accumulation of experience, the process is based on the observation of the state of the operating machine and the servo error, and then adjust the nonlinearity. parameters of the model until the error disappears. The structure and parameters of such a system can change automatically with time and conditions.
3. Artificial intelligence system: The motion program cannot be programmed in advance, but it is required to determine the control effect in real time according to the obtained surrounding state information during the motion process.
4. Point type: The robot is required to accurately control the pose of the end effector regardless of the path.
5. Trajectory type: The robot is required to move according to the taught trajectory and speed.
6. Control bus: international standard bus control system. The international standard bus is used as the control bus of the control system, such as VME, MULTI-bus, STD-bus, PC-bus.
7. Custom bus control system: The bus used by the manufacturer is defined as the control system bus.
8. Programming method: physical setting programming system. The fixed limit switch is set by the operator to realize the program operation of starting and stopping, and can only be used for simple pick-up and place operations.
9. Online programming: The memory process programming method of operating information is completed through human teaching, including direct teaching simulation teaching and teaching box teaching.
10. Offline programming: It does not teach the actual robot directly, but separates it from the actual working environment.
Fourth, the robot control system structure
Robot control systems can be divided into three categories according to their control methods.
1) Centralized Control System: use one computer to realize all control functions, simple structure and low cost, but poor real-time performance and difficult to expand. This structure is often used in early robots, and its block diagram is shown in Figure 2. .
In the PC-based centralized control system, the characteristics of the openness of PC resources are fully utilized to achieve good openness: various control cards, sensor devices, etc. can be integrated into the control system through standard PCI slots or through standard serial ports and parallel ports. in the system. The advantages of the centralized control system are: low hardware cost, easy information collection and analysis, easy to realize the optimal control of the system, good integrity and coordination, and more convenient hardware expansion of the PC-based system. Its shortcomings are also obvious: the system control lacks flexibility, and the control risks are easy to concentrate. Once a fault occurs, its influence is wide and the consequences are serious; due to the high real-time requirements of industrial robots, when the system performs a large amount of data calculation, it will reduce the real-time performance of the system. , the system’s ability to respond to multitasking will also conflict with the system’s real-time performance; in addition, the system is complicated to connect, which will reduce the reliability of the system.
2) Master-slave control system: The master-slave two-level processor is used to realize all the control functions of the system. The main CPU realizes management, coordinate transformation, trajectory generation and system self-diagnosis, etc.: The control of all joints is realized from the CPU. Its block diagram is shown in Figure 3. The master-slave control system has good real-time performance and is suitable for high-precision and high-speed control, but its system scalability is poor and maintenance is difficult.
3) Distribute Control System: The system control is divided into several modules according to the nature and method of the system, each module has different control tasks and control strategies, and each mode can be a master-slave relationship or an equality relation. This method has good real-time performance, is easy to realize high-speed and high-precision control, is easy to expand, and can realize intelligent control. It is a popular method at present, and its control block diagram is shown in Figure 4.
Its main idea is “decentralized control, centralized management”, that is, the system can comprehensively coordinate and allocate its overall goals and tasks, and complete the control tasks through the coordination of subsystems. The entire system is functional, logical, and physical. It is decentralized, so the DCS system is also called a distributed control system or a distributed control system. In this structure, the subsystems are composed of controllers and different controlled objects or devices, and each subsystem communicates with each other through the network. The distributed control structure provides an open, real-time, and precise robot control system. A two-level control method is often used in distributed systems.
The two-level distributed control system usually consists of the upper computer, the lower computer and the network. The upper computer can carry out different trajectory planning and control algorithms, and the lower computer can carry out research and implementation of interpolation subdivision, control optimization, etc. The upper computer and the lower computer work in coordination with each other through the communication bus. The communication bus here can be in the form of RS-232, RS-485, EEE-488 and USB bus.
Now, the development of Ethernet and fieldbus technology provides faster, more stable and effective communication services for robots. Especially the field bus, it is used in the production field to realize the bidirectional multi-node digital communication between the computerized measurement and control equipment, thus forming a new type of network-integrated fully distributed control system – Fieldbus Control System (FCS). In the factory production network, the devices that can be connected through the field bus are collectively referred to as “field devices/instruments”. From the perspective of system theory, industrial robots, as one of the production equipment in factories, can also be classified as field equipment. After the introduction of fieldbus technology in the robot system, it is more conducive to the integration of robots in the industrial production environment.
The advantages of the distributed control system are: the system flexibility is good, the risk of the control system is reduced, the use of multi-processor distributed control is conducive to the parallel execution of system functions, the processing efficiency of the system is improved, and the response time is shortened.
For industrial robots with multiple degrees of freedom, centralized control handles the coupling relationship between each control axis very well and can be easily compensated. However, when the number of axes increases so that the control algorithm becomes complex, its control performance deteriorates. Also, when the number of axes in the system or the control algorithm becomes complex, it may lead to a redesign of the system. In contrast, each motion axis of the distributed structure is handled by a controller, which means that the system has less inter-axis coupling and higher system reconfigurability.