Abstract Portable robots, compared with general arc-welding robots, have unique characteristics due to their portability. Firstly, the mechanical architecture of the portable robot is introduced in this paper. Secondly , the hardware architecture of the robot controller is also introduced. Finally, the design of the software architecture is introduced in detail. Keywords: portable robot, robot controller Considering the structural characteristics and usage features of portable arc welding robots, they are small in size and light in weight, and trajectory planning does not require complex torque constraints. However, since portable arc welding robots are mainly used in confined spaces such as inside ship hulls and boilers, and the working environment is complex, the mobility requirements of the robot's end effector (welding torch) are high. Extensive research was conducted on domestic and international robot controllers during the controller design process. Taking into account the current development trend of robot controllers, we designed a robot controller with certain versatility and an open structure. 2. Portable Robot Body This robot is a six-degree-of-freedom articulated robot. All parts utilize rotary kinematic pairs. It is driven by an AC servo motor through a harmonic reducer. The mechanical body weighs approximately 30 kg, and the carrying capacity is approximately 5 kg. The physical structure diagram is simplified, and a coordinate system is established according to the DH rule, as shown in Figure 1. The structural parameters of each joint and link of the robot are shown in Table 1. [IMG]/uploadpic/THESIS/2008/3/2008032111414732596M.jpg[/IMG] 3 Controller Hardware Structure The hardware of the industrial robot controller mainly includes the host, teach pendant, motion motor, encoder, driver, and input/output expansion card. Based on the reference of domestic and foreign robot controllers, we designed the robot controller shown in Figure 2. The controller is mainly composed of the following hardware: [IMG]/uploadpic/THESIS/2008/3/2008032111424691662S.jpg[/IMG (1) The host adopts an industrial control computer based on the ISA bus, and the CPU is Pentium 166. (2) The communication card between the teach pendant and the host uses the MOXA C102 general-purpose RS-422/485 dual serial port communication card. The communication between the teach pendant and the host adopts the RS422 bus interface standard. This makes the communication anti-interference capability strong and the transmission distance long. The other end of the card is reserved as a spare. The communication between the driver and the host uses the M0XA C168P universal eight-serial E1 communication card. Its function is to transmit the motor position information fed back by the code disk to the host to determine the robot's initial precise position. (3) Teach pendant The teach pendant is a tool for human-machine interaction between the robot and the operator. The teach pendant consists of a box, keyboard, display screen, control circuit, etc. There are 55 keys on the teach pendant panel. The keys are lightweight and ultra-thin membrane switches. The operator inputs information through the keyboard. The display screen uses an MGLS240 X 128 dot matrix LCD screen. The LCD screen can display Chinese characters and the human-machine interface is user-friendly. (4) Motor This controller uses six AC servo motors. The motor itself is equipped with a code disk. A simple absolute code disk is selected. This code disk can only roughly record the absolute position of the robot. Therefore, when the robot is powered on, the joint motor needs to make a small rotation in order to determine the precise position of the motor in one revolution. This type of encoder combines the advantages of absolute encoders and incremental encoders to a certain extent. (5) Motion control board The motor motion control adopts a PMD-based motion control board. One board can control the linkage of 4 motors. Since there are 6 motors, two control boards are used. The control board outputs motor drive signals, servo ON, alarm clearing and other control signals to the driver. The driver's function is to amplify the control signals. (6) I/O expansion I/O expansion is mainly used for communication with external welding controllers and sensors, as well as the on/off of indicator lights on the robot controller panel and error alarms. Here, Weida Industrial Control's ICP-D10481/O expansion card is selected. 4 Controller software structure The robot controller software is a large system software. We adopted the process-oriented software design method for software design. In this way, the entire software is divided into relatively independent modules, making the software structure clear, easy to design and easy to read and understand. The overall structure of the portable robot controller software is shown in Figure 3. Figure 3 System software module structure diagram The part inside the dashed box above is the upper layer software of the controller software, which completes the task planning and monitoring of the controller. The dashed box below contains the lower-level software, including robot motion trajectory planning and servo motor control. Based on the working requirements of the portable arc welding robot and the principle of software module division, the entire control software is divided into the following relatively independent modules: (1) Initialization module: The main function of this module is to set the operating environment of the controller. (2) Monitoring module: This module provides communication functions between the teach pendant and the host, handles keystrokes, and takes measures to handle position over-limits during robot operation. The I/O module manages the controller panel lights and alarms. (3) Teaching Module: This module mainly performs teaching operations on the robot. It can teach in four coordinate systems: joint, Cartesian, tool, and user. The output of the teaching module is an instruction file that specifies the robot's motion reproduction mode and a position file that records the position information of the teaching points. (4) Reproduction Module: This module mainly performs the robot's reproduction operation. It calls the robot language interpretation module to form motion instructions that the machine can understand, and calls the lower-level software to drive the robot to complete the task according to different instructions. (5) File Management: There are various files in the robot controller, so the controller software has designed a module for file management, including renaming, deleting, and copying files. The file management module is similar to the file management function in the operating system. (6) Trajectory Planning: This module includes forward and inverse kinematics calculations and trajectory interpolation. (7) Servo Control: This module is the motor servo control software package of the PMD control board. This control package provides basic instructions for controlling the motion motor. The controller software uses DOS as the operating system and is programmed in C language. 5 Motion Control Simulation This controller was used to conduct motion control experiments on a portable robot. The data for circular motion were recorded in the table below. A graph was plotted using the second set of points (1, 1.4, 26), (1 1, 2, 4), and (1, 2, 5, 3), as shown below. The experiment shows that this controller can effectively and flexibly control the portable robot. 6. Conclusion Developing a "modular and standardized robot controller with an open structure" is a current development direction for robot controllers. The design and research of this project considered both the unique characteristics of portable arc welding robots and the current development direction of robot controllers. The controller was developed on a general-purpose hardware and software platform, using the powerful C language as the programming tool, giving the controller a certain degree of versatility and shortening the development cycle. References 1 Huang Tong et al., Design and Implementation of a General-Purpose Robot Control System, Proceedings of the 5th China Robotics Society Conference, 1997 2 Fan Yong, Tan Min. Current Status and Prospect of Robot Controllers, Machine, L. 1992 1 3 Hu Weilong, Theoretical Research and Software Development of Trajectory Planning for Six-Degree-of-Freedom Robots, Master's Thesis, Harbin Institute of Technology, 1999 4 Unimation. Unimate PUMA Mark _ 一VAL ll Robot 500Series (Models 552／562) Equipment Manual 398 AH1 AWestinghouse Company． January 1987 5 E Freund. JR Mangmann Sysllems Approach to Robotics and Automation IEEE Intemational Confefence on Robotics and Automation 0—7803—1965—6/950 1995 3 6 John Wiley Robot Analysis and Control1.1986 7 Moxa Teohnologies Co Ltd Moxa C1 02 Universal RS 一 422/485 2 Port Serial Boards User. S Manual 4th edition 1998 2 8 W indows—based PC Robot Controller YASKAWA NewsRelease 1997 10 9 Willian E Ford What is an Open Architecture Robot Controller?lEEE International Symposium on Intelligent Co nlr0l 1994