PLC is a general industrial automatic control device based on a microprocessor, which integrates computer technology, semiconductor integration technology, automatic control technology, digital technology and communication network technology. In industrial production, PLC and industrial robots often form a complete automation system. Through the excellent performance of PLC, the functions of the automation control system can be further improved. As PLC is a digital operation electronic system specially designed for application in the industrial environment, it adopts user-oriented instructions, so it is convenient to write programs, and it has strong expansibility when combined with industrial control systems.
 
An industrial manipulator is a device that combines mechanical technology and automation to meet the needs of industrial production. Generally, it is composed of execution, driving and control systems, and can perform movements such as moving and grabbing. The application of industrial manipulators in industrial production has solved the problems of a hard-working environment and high labor intensity. The combination of PLC and industrial robot automation control systems can complete more complex actions, and the operation is simpler and more accurate, and it can complete the operation according to the preset trajectory, greatly improving the quality and efficiency of industrial production.
 
Characteristics of PLC and automatic control of industrial manipulators
 
Good input/output interface. The input/output function modules of PLC are relatively complete, which is one of the greatest advantages of PLC, and also an important foundation for industrial robots to achieve high automation. In the input/output modules of PLC, there are corresponding templates that are directly connected with the industrial field devices to control the field signals. With the improvement of industrial production level, there is a higher requirement for the operation speed and accuracy of the manipulator, and the action instruction of the manipulator is issued by a written program, and the transmission speed of the instruction is related to the operational efficiency and accuracy of the manipulator. Combined with the PLC manipulator, PLC sends control instructions to the manipulator, and the input/output interface of PLC responds quickly. For industrial manipulators with high production efficiency, it can realize the efficient transmission of control and feedback signals, and provide a basic guarantee for the precise action and fast operation of the manipulator.
 
Modular structure design. In order to meet the needs of industrial production, the performance and functions of PLC are constantly adjusted and improved, and small PLC systems are constantly integrated, gradually changing to a modular structure with powerful functions. At present, PLC systems are comparable to those of microcomputers to some extent. The modular structure design of the PLC system is designed into different structural modules according to different functions, and then a brand-new system can be formed by connecting these functional modules. In the process of practical application, we can choose or adjust each function module of PLC according to the demand of automatic control of the manipulator, so as to achieve the goal of automatic control.
 
High reliability. In industrial production, the safe and reliable operation of the industrial manipulator is an important guarantee for safe production. The application of PLC in the automatic control of industrial manipulators can effectively improve the stability of manipulator operation. PLC system has a self-diagnosis function. When the controlled manipulator fails, the system can quickly locate the fault point according to the self-diagnosis function, and take corresponding actions for specific faults to avoid the occurrence of safety accidents. The PLC system also has a good circuit protection function, which can realize on-off operation by switching the power supply. In the complex industrial production environment, the anti-interference ability and shielding ability of PLC can improve the reliability of system operation.
 
PLC system programming is easy. In order to meet the needs of the industrial production environment, the manipulator needs to change the corresponding program according to the production requirements. Most of the programs are written with vivid and simple ladder diagrams. The manipulator program design is relatively simple and can be programmed without professional knowledge, which is very suitable for the flexible control requirements of the manipulator.
 
Application of PLC in automatic control of manipulators
 
PLC programming of the manipulator. In general, the manipulator is operated by stretching and moving up and down the arm, and the control of the manipulator is realized by PLC. The main workflow is as follows: meet the equipment opening conditions-determine the specific position of the workpiece by detecting elements-stretch the arm to grab the workpiece-grab the workpiece to rise or move left and right-the manipulator places the workpiece at the specified position-the manipulator is restored to the initial position, and the automatic operation of the manipulator can be realized through this process. In the specific application process, the models of PLC and electrical components should be selected according to the actual needs of production and the designed action control flow, and then the functions of PLC, the positions and numbers of input and output points should be determined, and on this basis, the PLC program should be written. In the automatic control system of the industrial manipulator, the input signals mainly include manual control and automatic control selection buttons, equipment start-stop buttons, signals for detecting the position of the manipulator and determining the specific position of the workpiece, etc., and the output signals mainly include the control of cylinder action and motor operation. The quality of programming is directly related to the accuracy and efficiency of the manipulator's operation. Therefore, before programming, we should take the manipulator's operation principle as the basis, analyze the actual production demand of the manipulator, and then compile the program. According to the operation principle of the manipulator, carry out requirement analysis. After understanding the operation principle of the manipulator, the key points needing attention in PLC programming can be analyzed. The mechanical movement of the manipulator mainly depends on the cylinder to provide driving force, and the action of the cylinder is controlled by the electromagnetic valve. When the manipulator performs grasping and relaxing actions, it is mainly controlled by the power-on and power-off of the solenoid valve. When the single coil is powered on, the manipulator can perform grasping actions, and when the single coil is powered off, the manipulator executes relaxing commands. In the automatic operation of industrial production, the same set of processes is repeatedly executed for a long time. In order to ensure the safety of production, it is necessary to strictly control the activation process of the manipulator. Only after a certain action is completely completed, the next action can be entered. Because the manipulator is engaged in a circular motion, it needs to return to the original point after completing one motion process to prepare for the cycle of the next task. The return of the manipulator to the original position can be controlled by a limit switch and an electromagnetic valve. In order to improve the reliability of manipulator control, the control system will be set to two modes: automatic mode and manual mode, and the control mode of the system will have corresponding indicator lights to show the state of the control mode. By analyzing the operation principle of the manipulator, the accuracy of PLC control can be improved, and then the safety and stability of manipulator operation can be ensured. Determine the initial position. The setting of the initial position is related to the accuracy of the manipulator control system. The manipulator must return to the initial position after each cycle, and the initial position can be determined according to the actual production needs. The initial position does not have to be fixed at a specific position, but can be set by the controller according to the production requirements. When setting the initial position, pay attention to the state of the manipulator. The manipulator should be in a normal stop state, and the cylinder piston should be in a retracted state. If the piston of the cylinder is in an extended state, oxidation and corrosion will occur due to external temperature and humidity, which will directly affect the air tightness of the cylinder and ultimately affect the operation control of the manipulator.
 
Software and hardware design of control system. The design of the hardware and software of the PLC manipulator control system is directly related to the control quality of the system, and the accuracy and stability of manipulator operation. In the hardware design of the control system, the automatic loop control device can be designed according to the PPL text content, the programmable control protocol can be selected, and the automatic controller of the manipulator can be designed in a closed loop. When selecting the data acquisition board, pay attention to the speed and overall performance of data acquisition. If the analog data collected by the selected data acquisition board does not meet the operation requirements of the system, an analog-to-digital converter can be designed to convert the collected data. In the software design of the control system, the data of the automatic operation of the manipulator can be collected based on PLC, and the selection of ports and the distribution of communication addresses can be designed according to the principle of corresponding design. After completing the data acquisition, use the corresponding communication network and follow the advanced protocol content to limit the number of cycles of the manipulator. Based on PLC control technology, the flat current is converted into alternating current according to the expression of signal filtering, and the terminal voltage data and signals are controlled by controlling the signal voltage value. By analyzing the acquired data, we can also analyze the energy consumption of the manipulator in different running states, and then optimize and adjust the control system to reduce the energy consumption of automatic control of the manipulator.
 
Conclusion

PLC has many advantages, such as high reliability, easy programming, flexible configuration, complete input/output function modules, convenient installation and fast running speed, so it has been widely used in industrial production. In some industrial production sites, there are many toxic and harmful substances, and the production environment is complicated. The manual operation will do great harm to the body, and industrial robots can effectively replace manual operation. An industrial manipulator is a kind of function that can imitate some actions of human hands and arms. It has the advantages of both human hands and manipulator machines in structure, and can perform operations according to the programmed trajectory, and can complete the tasks of grabbing and carrying. The combination of PLC and automatic control of an industrial manipulator can realize the start, stop, back and forth, left and right, and up and down movement of the manipulator through the program, and at the same time, it can automatically diagnose and deal with various faults in the grabbing process, which is of great significance to promote the improvement of industrial production level.