Development of the hottest portable joint type arc

2022-08-11
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Development of portable joint type arc welding robot

welding is one of the basic production means in the mechanical manufacturing industry. It is very important to improve the stability and reliability of welding quality. Limited to economic and technical reasons, welding production operations in China are basically manual. Using manual operation, not only the welding workload is large, the welding productivity is low, and the welding quality fluctuates greatly; Moreover, the working environment is poor, the working conditions are poor, and the labor intensity is high. Arc, noise and smoke during welding directly endanger the health of workers. With China's entry into WTO and international integration, it is very urgent to vigorously implement "health, safety and environmental protection" or "HSE" management in industrial enterprises to improve the working environment of workers in welding. Adopting automatic welding technology is the only way to change the above situation. As the extension of human limbs, industrial robots can tirelessly engage in hard and heavy work in an environment where production personnel cannot operate, so that production workers can get rid of dangerous and harmful working environment and reduce the labor intensity of production workers [1], which is the best automatic tool to replace workers in welding operations. The universal arc welding robot is composed of mechanical system, control system and drive system, as shown in Figure 1. At present, the wide use of general-purpose arc welding robots is still subject to certain restrictions: general-purpose arc welding robots are expensive, and the risk of one-time investment is large; The structure is a split structure, which is large in volume, heavy in weight and inconvenient to move flexibly. It is suitable for use on the fixed welding station of the flow production line; Most control programs are developed by teaching programming or robot language programming. Due to the limited knowledge structure of production workers in China, it is not enough to master teaching programming or robot language programming to develop control programs

Figure 1 universal arc welding robot

the price, structure and development mode of control program of universal arc welding robot restrict the application and promotion of universal arc welding robot to a great extent. Therefore, under the current conditions of our country, whether the arc welding robot can be used in the non fixed welding station or field welding is a topic worthy of exploration. The author believes that by combining electromechanical integration technology with computer hardware and software, a portable arc welding robot with low price, small volume, light weight, compact structure and easy to move flexibly should be developed; Developing control software by graphic simulation and simplifying the development method of control software can use arc welding robot in non fixed welding station or field welding. The portable arc welding robot introduced in this paper takes the MC68HC908GP32 microprocessor as the core and the solidified control software to control the portable arc welding robot to complete the welding production operation, which provides a valuable reference for the application and promotion of arc welding robot. This paper briefly introduces the mechanical structure, control system hardware and control software development of portable arc welding robot

the biggest feature of the application of arc welding robot is that the change of control software replaces the change of complex mechanical structure and electrical structure, making the arc welding robot flexible in completing arc welding production operations. Therefore, according to the viewpoint of flexible manufacturing, the hardware of the arc welding robot - boom, jib, wrist, body, together with the electrical hardware of the control, as well as the robot controller are designed and manufactured as an electromechanical functional module structure [2]. According to the needs of enterprises to complete specific welding production operations, users of arc welding robots purchase electromechanical integrated function modules and assemble them into a special portable arc welding robot, which avoids redundant degrees of freedom, making the portable arc welding robot compact in structure, light in weight, cheap in price and easy to move flexibly. Figure 2 is a prototype of a portable arc welding robot assembled with electromechanical integration function modules

Figure 2 portable arc welding robot prototype

2 portable arc welding robot control hardware

in order to adapt to the use of electromechanical integration function modules and assemble various portable arc welding robots in the form of "building blocks", the portable arc welding robot control hardware uses microprocessors as the control core. Obviously, in order to meet the needs of increasing and reducing electromechanical integration modules to expand the functions of portable arc welding robots, The hardware of the control system must be expandable, including:

a. the microprocessor provides more i/o ports. Without expanding the programmable input and output interface, multiple arm modules can be "connected", and multiple arm modules can be driven at the same time, and the i/o ports are reserved, so as to facilitate the function expansion of the portable robot (expanded into a portable detection robot, etc.)

B. the servo system of the mechatronic arm function module is embedded in the arm, The microprocessor must have a large capacity of on-chip flash memory and ram, which can be expanded to reduce the size of the servo system

the MC68HC908GP32 microprocessor chip, the core of the portable arc welding robot control system, can form five i/o ports, and use three ports to control three arm modules. One i/o port controls the wrist direct current motor, and one i/o port controls the wrist stepper motor

3 control principle of portable arc welding robot

in welding production, through path planning, most of the welding production tasks completed by the arc welding robot are carried out in sequence, and the motion trajectory of completing the arc welding production operation is generally known, or the motion trajectory can be decomposed into a combination of multiple single motion trajectories, and the given motion trajectory can be synthesized by controlling each single motion trajectory. Therefore, by establishing a mathematical model and using mathematical methods to solve the inverse solution of the motion of the arc welding robot, the motion and path of the arc welding robot to complete the welding production operation can be transformed into a "predetermined" trajectory and attitude, and the control program can be developed by off-line programming, and real-time compensation can be made when controlling the motion of the arc welding robot. This control mode avoids the high requirements of computer performance for general-purpose arc welding robots to adopt real-time sampling and real-time calculation, so that low-cost control system can be used to control arc welding robots, which greatly reduces the price of arc welding robots

the portable robot, which adopts the arm function module of electromechanical integration and is assembled in the form of "building blocks", controls the position and posture of the welding tool when completing the welding production operation. In essence, it is the coordinated control of the rotation angle and rotation speed of the stepper motor shaft. The basic principle and formula of the stepper motor:

θ= 360/z

where: θ- The step angle

z- the number of teeth in the rotor of the stepping motor

it can be seen that each drive pulse is input, the motor shaft steps a step angle increment, so:

a, the rotation angle of the stepping motor shaft is directly proportional to the number of input pulses

b, the rotating speed of the stepper motor shaft depends on the frequency of the input pulse

stepper motor can convert input pulses into rotary motion. Its unique advantages of high precision, no drift, no cumulative error and so on make it the only servo and actuator that can use open-loop control technology in motor integrated products. Obviously, the motion control of portable arc welding robot is the coordinated control of the input pulse number and pulse frequency of stepping motor

4 development of portable robot control software

the development method of robot control software directly restricts the application and promotion of robots. A fast and simple development method not only promotes the application and promotion of robots, but also directly determines the flexibility of robots to complete production operations. Portable arc welding robot is for production workers to use as an intelligent tool, so the development method of control software must be simplified

in order to meet the requirements of real-time control, assembly language programming is adopted; In order to meet the needs of rapid development of control program after the structural change of portable arc welding robot or the improvement of production process, the software of "portable robot CAD system" is developed in Visual Basic language, so that the development of control software is carried out under the support of "portable robot CAD system" [3], and the development interface is shown in Figure 3. Input the relevant parameters of each function module in the visual human-machine interface, call the menus at all levels repeatedly, and optimize the structural parameters of the arc welding robot; Visually observe and compare the robot simulation graphics and various calculated data; In the way of graphic simulation, the production movement and trajectory of the arc welding robot are simulated, and the control program design is automatically completed at the same time of graphic simulation, which is downloaded to the robot controller, so as to simplify the development of the control program after judging the problems of the main swing bearing and disassembling it. The control program is developed with the support of "portable robot CAD system", and only the mouse clicks on the corresponding menu, and all robot professional knowledge and technology related to robot interpolation algorithm, inverse kinematics algorithm and so on are processed by the "portable robot CAD system" software. This way of developing control software through graphic simulation enables the portable arc welding robot to adapt to a variety of welding production operations and make the welding production operations flexible. Developing control software in the form of graphical simulation is just like using windows to operate microcomputers with graphical interfaces covering beverage bottles, lead-acid batteries, cars and other categories, so that people who are not familiar with robot hardware can quickly and easily develop robot control software to promote the application and promotion of robots

Figure 3 control program development interface

after the portable arc welding robot control system is powered on and reset, the solidified control software starts to run. After the system is initialized:

a, the control software reads the rotation angle values of the boom, jib and wrist, and calls the subroutines of forward rotation, reverse rotation, acceleration and deceleration of the stepping motor after calculation to output a continuous series of pulse signals to the corresponding i/o ports to control the rotation of the boom, jib and wrist

b, the control software reads the collected value of the marking operation state, compares the value with the target value read from the specified address, and calls the position and posture compensation subroutine of the boom, forearm and wrist according to the difference to compensate the rotation of the boom, forearm and wrist

c. Due to the external interference of a total of 413 extruders imported from Thailand from China from January to October this year, when the welding tool of the portable arc welding robot deviates or is far away from the predetermined track, the control software reads the collected value of the marked operation state, compares the value with the target value read from the specified address, and calls the boom, forearm, wrist acceleration and deceleration compensation subroutine according to the difference, and Wrist acceleration and deceleration compensation

4 conclusion

relying on the high performance of MC68HC908GP32 microprocessor chip, we have developed a portable arc welding robot with low price, small size, light weight, easy to move flexibly, and simple control software development. The prototype experiment shows that the motion function and control accuracy of the portable arc welding robot meet the requirements of automatic arc welding. The machine is compact in structure, light in weight, easy to carry and move flexibly. It is multi-purpose, developable, easy to develop control software, and low in production cost, which essentially makes the machine a smart automatic welding tool. Under the operation of the operator, carry out the function combination of the welding machine, control program development, positioning "reset" before automatic welding, etc. The machine only replaces people to complete heavy and harmful welding operations to improve welding quality, rather than completely replace human labor. In a country with a large population like China, reducing the cost of living

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