Introduction Welding is one of the basic production methods in the machinery manufacturing industry. Improving the stability and reliability of welding quality is of paramount importance. Due to economic and technical reasons, welding production in China is still mainly done manually. Manual operation not only results in a large workload, low welding productivity, and large fluctuations in welding quality, but also a harsh working environment, poor working conditions, and high labor intensity. The electric arc, noise, and fumes during the welding process directly harm the health of workers. With China's accession to the WTO and integration with the international community, the "Health, Safety, and Environmental Protection" (HSE) management is being vigorously promoted in industrial enterprises. Improving the working environment of workers in welding is very urgent. The adoption of automatic welding technology is the only way to change the above situation. As an extension of human limbs, industrial robots can tirelessly perform arduous and heavy labor in environments where production personnel cannot operate, freeing production workers from dangerous and harmful working environments and reducing the labor intensity of production workers [1]. They are the best automated tools to replace workers in welding operations. The general-purpose arc welding robot consists of a mechanical system, a control system, and a drive system, as shown in Figure 1. Currently, the widespread use of general-purpose arc welding robots is still limited by certain factors: they are expensive, with high initial investment risks; their modular structure results in large size, heavy weight, and inconvenient mobility, making them suitable only for use at fixed welding stations on assembly lines; and the control program development methods mostly employ teach-in programming or robot language programming, which, due to the limited knowledge structure of Chinese production workers, is insufficient for developing control programs using these methods. [align=center]Figure 1 General-purpose arc welding robot[/align] The price, structure, and control program development methods of general-purpose arc welding robots significantly restrict their application and promotion. Therefore, under current conditions in my country, whether arc welding robots can be used in non-fixed welding stations or field welding is a topic worth exploring. The author believes that by combining mechatronics technology with computer hardware and software to develop inexpensive, small, lightweight, compact, and easily movable portable arc welding robots; and by developing control software using graphical simulation to simplify the development process, it is possible to use arc welding robots in non-fixed welding stations or field welding. The portable arc welding robot introduced in this article uses the MC68HC908GP32 microprocessor as its core and solidified control software to control the portable arc welding robot to complete welding production operations, providing a valuable reference for the application and promotion of arc welding robots. This article briefly introduces several key technical issues such as the mechanical structure, control system hardware, and control software development of portable arc welding robots. 1. Portable arc welding robot mechanical hardware The biggest feature of arc welding robot application is that the change of control software replaces the change of complex mechanical and electrical structures, making the arc welding robot flexible in completing arc welding production operations. Therefore, according to the concept of flexible manufacturing, the hardware of the arc welding robot—the upper arm, forearm, wrist, and body, together with the control electrical hardware and the robot controller—are designed and manufactured as mechatronic functional module structures [2]. According to the needs of enterprises to complete specific welding production operations, users of arc welding robots purchase arc welding robot mechatronic functional modules and assemble them into dedicated portable arc welding robots, avoiding redundant degrees of freedom, making the portable arc welding robot compact, lightweight, inexpensive, and easy to move flexibly. Figure 2 shows a prototype of a portable arc welding robot assembled using mechatronics functional modules. [align=center] Figure 2 Portable Arc Welding Robot Prototype[/align] 2. Portable Arc Welding Robot Control Hardware To adapt to the use of mechatronics functional modules and the assembly of various portable arc welding robots in a "building block" manner, the control hardware of the portable arc welding robot uses a microprocessor as the control core. Obviously, to adapt to the need to expand the functions of the portable arc welding robot by adding or removing mechatronics modules, the control system hardware must be scalable. This includes: a) The microprocessor provides a large number of I/O ports, and without expanding the programmable input/output interface, it can "connect" multiple arm modules and drive multiple arm modules simultaneously, and reserve I/O ports to facilitate the expansion of portable robot functions (expanding into portable inspection robots, etc.). b) The servo system of the mechatronics arm functional module is embedded in the arm body. The microprocessor must have a large capacity on-chip Flash memory and RAM, so that the memory does not need to be expanded externally, thereby reducing the size of the servo system. The core MC68HC908GP32 microprocessor chip of the portable arc welding robot control system can form 5 I/O ports. Three ports control three arm modules, one I/O port controls the wrist DC motor, and one I/O port controls the wrist stepper motor. 3. Portable Arc Welding Robot Control Principle In welding production, through path planning, the arc welding robot completes welding tasks mostly sequentially. Moreover, the motion trajectory for completing the arc welding operation is generally known, or the motion trajectory can be decomposed into a combination of multiple individual motion trajectories. A given motion trajectory can be synthesized by controlling each individual motion trajectory. Therefore, by establishing a mathematical model and solving the inverse kinematics of the arc welding robot using mathematical methods, the motion and path of the arc welding robot to complete the welding operation can be transformed into a "predetermined" trajectory and posture. A control program can be developed offline, and real-time compensation can be performed when controlling the arc welding robot's movement. This control method avoids the high demands on computer performance caused by real-time sampling and calculation in general-purpose arc welding robots, enabling the use of a low-cost control system to control the arc welding robot, significantly reducing the price of the arc welding robot. Portable robots, assembled like building blocks using mechatronic arm modules, control the position and posture of welding tools during welding operations. Essentially, this involves the coordinated control of the stepper motor shaft's rotation angle and speed. Based on the fundamental principles and formula of stepper motors: θ = 360/Z, where θ is the step angle and Z is the number of teeth on the stepper motor rotor, it can be seen that for each input drive pulse, the motor shaft advances by one step angle increment. Therefore: a) The rotation angle of the stepper motor shaft is directly proportional to the number of input pulses; b) The rotational speed of the stepper motor shaft is determined by the frequency of the input pulses. Stepper motors convert input pulses into rotational motion. Their inherent advantages, such as high precision, no drift, and no cumulative error, make them the only servo and actuator components in mechatronic products capable of using open-loop control technology. Clearly, the motion control of a portable arc welding robot is essentially the coordinated control of the number and frequency of input pulses to the stepper 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 in completing production operations. Portable arc welding robots are intended for use by production workers as intelligent tools, so the development method of control software must be simplified. To meet the requirements of real-time control, assembly language programming is used; to adapt to the need for rapid development of control programs after changes in the structure of portable arc welding robots or improvements in production processes, the "Portable Robot CAD System" software was developed using Visual Basic, so that the development of control software can be carried out under the support of the "Portable Robot CAD System" [3]. The development interface is shown in Figure 3. [align=center] Figure 3 Control Program Development Interface[/align] Input the relevant parameters of each functional module in the visual human-machine interface, repeatedly call the menus at all levels, and optimize the structural parameters of the arc welding robot; intuitively observe and compare the robot simulation graphics and various calculated data; simulate the production operation motion and trajectory of the arc welding robot in a graphic simulation mode, and automatically complete the control program design while performing graphic simulation, and download it into the robot controller, thereby simplifying the development of the control program. Developing control programs using a "Portable Robot CAD System" requires only clicking the corresponding menus with a mouse. All robot-related professional knowledge and technologies, such as robot interpolation algorithms and inverse kinematics algorithms, are handled by the "Portable Robot CAD System" software. This graphical simulation-based approach to developing control software enables portable arc welding robots to adapt to various welding production operations, making welding production more flexible. Developing control software using graphical simulation is similar to operating a microcomputer with a Windows graphical interface, allowing people unfamiliar with robot hardware to quickly and easily develop robot control software, thus promoting the application and widespread adoption of robots. After the portable arc welding robot control system is powered on and reset, the embedded control software starts running. After system initialization: a) The control software reads the rotation angle values ​​of the upper arm, forearm, and wrist, calculates them, and calls the stepper motor forward rotation, reverse rotation, acceleration, and deceleration subroutines to output a series of continuous pulse signals to the corresponding I/O ports to control the rotation of the upper arm, forearm, and wrist; b) The control software reads the collected values ​​of the characteristic working status and compares them with the target values ​​read from the specified address. Based on the difference, it calls the upper arm, forearm, and wrist position and posture compensation subroutines to compensate for the rotation of the upper arm, forearm, and wrist; c) When the welding tool of the portable arc welding robot deviates from or moves away from the predetermined trajectory due to external interference, the control software reads the collected values ​​of the characteristic working status and compares them with the target values ​​read from the specified address. Based on the difference, it calls the upper arm, forearm, and wrist acceleration and deceleration compensation subroutines to compensate for the acceleration and deceleration of the upper arm, forearm, and wrist. 5. Conclusion Based on the high performance of the MC68HC908GP32 microprocessor chip, a portable arc welding robot was developed that is inexpensive, small in size, lightweight, easy to move, and has simple control software development. Prototype experiments show that the portable arc welding robot's motion functions and control precision meet the requirements of automated arc welding. The robot's compact structure, light weight, portability, and versatility, along with its easy-to-develop control software and low production cost, essentially make it a clever automated welding tool. Under the operator's control, tasks such as welding function combination, control program development, and pre-welding positioning "zeroing" are performed. This allows the robot to replace humans in performing heavy and harmful welding operations, improving welding quality rather than completely replacing human labor. In a populous country like China, reducing labor intensity and improving work quality are the goals of automation and the guiding principles for developing portable arc welding robots. References: 1. Gao Delin, Wang Kanghua, Introduction to Robotics [M], Shanghai Jiaotong University Press, 1988, 3-6 2. Chen Jiong, An Articulated Arc Welding Robot [P], Chinese Patent, Patent No.: ZL 99115114.3, 2004 3. Chen Jiong, A Portable Robot Simulator Development Device [P], Chinese Patent, Application No.: ZL 01107364.0, 2001 Author Biography: Chen Jiong (1951-) Male, Senior Engineer of Sichuan Oil and Gas Field Construction Engineering Corporation, engaged in micro-robot research and design.