I. Functions to be achieved by industrial robot control system
Robot control system is an important part of the robot, used to control the operator to complete a specific work task, its basic functions are as follows:
1.Memory function: store the order of operation, movement path, movement mode, movement speed and information related to the production process.
2.Demonstration function: offline programming, online demonstration, indirect demonstration. Online teaching includes two kinds of teaching boxes and guided teaching.
3.Contact function with peripheral equipment: input and output interface, communication interface, network interface, synchronization interface.
4.coordinate setting function: joint, absolute, tool, user-defined four kinds of coordinate system.
5.Human-machine interface: demonstration box, operation panel, display.
6.Sensor interface: position detection, vision, touch, force, etc..
7.position servo function: robot multi-axis linkage, motion control, speed and acceleration control, dynamic compensation, etc..
8.Failure diagnosis and safety protection function: system status monitoring during operation, safety protection under fault condition and fault self-diagnosis.
II. the composition of industrial robot control system
1. control computer: control system scheduling command organization. Generally microcomputer, microprocessor 32-bit, 64-bit, etc. such as Pentium series CPU and other types of CPU.
2. teaching box: teaching robot trajectory and parameter settings, as well as all human-computer interaction operations, with its own independent CPU and storage unit, and the main computer to serial communication to achieve information interaction.
3. Operation panel: It consists of various operation buttons and status indicator lights, and it only accomplishes the basic function operation.
4. Hard disk and floppy disk storage: the peripheral memory for storing the working program of the robot.
5. Digital and analog input and output: input or output of various status and control commands.
6. printer interface: record the need to output a variety of information.
7. the sensor interface: for the automatic detection of information to achieve smooth control of the robot, generally for the force, touch and vision sensors.
8. axis controller: complete the robot joints position, speed and acceleration control.
9. auxiliary equipment control: used with the robot with the control of auxiliary equipment, such as hand claw variators and so on.
10. Communication interface: realize the robot and other equipment information exchange, generally serial interface, parallel interface, etc..
11. network interface
(1) Ethernet interface: through the Ethernet to achieve a number of or a single robot direct PC communication, data transfer rate of up to 10Mbit / s, can be directly on the PC with the windows library function for application programming after the support of the TCP / IP communication protocol, through the Ethernet interface will be loaded into the data and programs in each robot controller.
(2) Fieldbus interface: support for a variety of popular fieldbus specifications, such as Devicenet, ABRemoteI/O, Interbus-s, profibus-DP, M-NET and so on.
III, industrial robot control system classification
1.program control system: to each degree of freedom to impose a certain regularity of the control role, the robot can achieve the required spatial trajectory.
2.adaptive control system: when the external conditions change, in order to ensure the required quality or in order to improve the quality of control with the accumulation of experience on their own, the process is based on the state of the operating machine and servo error observation, and then adjust the parameters of the nonlinear model, until the error disappears. The structure and parameters of such a system can change automatically with time and conditions.
3.Artificial intelligence system: It is impossible to prepare the motion program beforehand, but requires the control role to be determined in real time during the motion process according to the obtained information about the surrounding state.
4.Point type: the robot is required to accurately control the position of the end-effector, independent of the path.
5.Trajectory type: the robot is required to move according to the trajectory and speed taught.
6.Control bus: international standard bus control system. Adopt international standard bus as the control bus of the control system, such as VME, MULTI-bus, STD-bus, PC-bus.
7.Customized bus control system: the manufacturer defines its own use of the bus as the control system bus.
8.Programming method: physical setting programming system. Setting fixed limit switches by the operator to realize the program operation of starting and stopping, which can only be used for simple picking up and placing operations.
9.Online programming: through the human teaching to complete the operation of the information memory process programming methods, including direct teaching simulation teaching and teaching box teaching.
10.offline programming: not to the actual operation of the robot direct teaching, but detached from the actual operating environment.
IV. the structure of the robot control system
Robot control system can be divided into three categories according to its control mode.
(1) centralized control system (CentralizedControlSystem): a computer to achieve all the control functions, simple structure, low cost, but poor real-time, difficult to expand, in the early robot is often used in this structure.
PC-based centralized control system, taking full advantage of the characteristics of the PC resource openness can be achieved: a variety of control cards, sensor devices, etc. can be integrated into the control system through the standard PCI slot or through the standard serial port, parallel port. The advantages of the centralized control system are: lower hardware costs, easy to collect and analyze information, easy to realize the optimal control of the system, better integrity and coordination, PC-based system hardware expansion is more convenient. Its shortcomings are also obvious: the lack of flexibility in system control, control hazards are easy to concentrate, once the failure, its impact on a wide range of serious consequences; due to the high real-time requirements of industrial robots, when the system carries out a large number of data calculations, it will reduce the real-time nature of the system, the system's responsiveness to multi-tasking will also be in conflict with the real-time nature of the system; in addition, the system connects the complexity of the system, which will reduce the reliability of the system.
(2) Master-slave control system: the master and slave processors are used to realize all the control functions of the system. The master CPU realizes the management, coordinate transformation, trajectory generation and system self-diagnosis, etc.: the slave CPU realizes the action control of all joints. Its composition block diagram. Master-slave control mode system real-time is better, suitable for high-precision, high-speed control, but its system scalability is poor, maintenance difficulties.
(3) decentralized control system (DistributeControlSystem): according to the nature of the system and the way the system control is divided into several modules, each module has a different control task and control strategy, the modes can be master-slave relationship, can also be equal. This way of real-time is good, easy to realize high-speed, high-precision control, easy to expand, intelligent control can be realized, is the current popular way.
The main idea is "decentralized control, centralized management", that is, the system of its overall objectives and tasks can be integrated coordination and distribution, and through the coordination of sub-systems to complete the control task, the entire system in the functional, logical and physical aspects are decentralized, so the DCS system is also known as a centralized control system or decentralized control system. . In this structure, the subsystems are composed of controllers and different controlled objects or devices, and the subsystems communicate with each other through networks and so on. The distributed control structure provides an open, real-time, and accurate robot control system. Two levels of control are often used in distributed systems.
A two-level distributed control system usually consists of an upper machine, a lower machine, and a network. The upper machine can carry out different trajectory planning and control algorithms, and the lower machine carries out the research and implementation of interpolation subdivision and control optimization. The upper and lower machines work in coordination with each other via a communication bus, which here can be in the form of RS-232, RS-485, EEE-488, and USB buses.
Nowadays, the development of Ethernet and fieldbus technology provides faster, stable and effective communication services for robots. Especially fieldbus, which is applied to the production site, in the microcomputerization of measurement and control equipment to achieve bidirectional multi-node digital communication between the formation of a new type of network-integrated fully distributed control system - fieldbus control system FCS (FiledbusControlSystem). In the factory production network, the devices that can be connected through the fieldbus are collectively referred to as "field devices/instruments". From a system theory point of view, industrial robots, as one of the production equipment in a factory, can also be categorized as field devices. The introduction of fieldbus technology in robot systems facilitates the integration of robots in industrial production environments.
The advantages of the distributed control system are: good system flexibility, reduced danger of the control system, decentralized control with multiprocessors, which is conducive to the parallel execution of system functions, improves the processing efficiency of the system, and shortens the response time.
For industrial robots with multiple degrees of freedom, the centralized control handles the coupling relationship between the individual control axes well and can be compensated very simply. However, when the number of axes increases to the point where it makes the control algorithm complex, its control performance deteriorates. Moreover, when the number of axes or the control algorithm in the system becomes complex, it may lead to a redesign of the system. In contrast, the distributed structure has each motion axis handled by a single controller, which means that the system has less inter-axis bogey and higher system reconfigurability.