Abstract: This paper introduces a high-voltage transmission line inspection robot control system, which realizes the robot's functions of obstacle crossing, line detection, and real-time monitoring. Experimental results show that the system operates well and has good reliability and practical value. Keywords: PC104; inspection robot; control system; high-voltage transmission line 1. Introduction High-voltage transmission lines and tower accessories are exposed to the outdoors for a long time. Due to continuous mechanical tension, electrical flashover, and material aging, they suffer damage such as strand breakage, wear, and corrosion. If not repaired or replaced in time, even minor damage and defects may expand and eventually lead to serious accidents. Therefore, power companies need to regularly inspect line equipment to detect and assess early damage and defects, and arrange necessary maintenance and repairs based on the assessment results to ensure the safety and reliability of power supply. Traditional manual inspection methods are not only labor-intensive but also arduous, especially for transmission lines in mountainous areas and along major rivers, where inspections are very difficult, and some inspection items are even difficult to complete using conventional methods. Therefore, the use of robotic automated line inspection has become a necessary means to ensure the safe operation of high-voltage transmission lines. High-voltage transmission line inspection robots fall under the research scope of special robots. They primarily perform high-altitude operations such as non-destructive testing of high-voltage power cables, insulation characteristic testing of suspension insulators, transmission performance testing of transmission line accessories, mechanical connection stability inspection, and removal of foreign objects from cables. Research on inspection robots began earlier and at a higher level abroad. In 1988, Sawada et al. of Tokyo Electric Power Company (TEPCO) developed a fiber optic composite overhead ground wire inspection mobile robot. This robot can crawl along the ground wire and use its curved arm to assist in crossing obstacles. In 2000, Montambault et al. of Hydro-Quebec in Canada successfully developed a remote-controlled transmission line robot. This remote-controlled robot can remove ice accumulation on power transmission lines and can be used as a line inspection platform. Domestic research on transmission line inspection robots is still in its early stages, with only Wuhan University of Hydraulic Engineering, Shandong University, and the Chinese Academy of Sciences conducting some research. 2. Robot Overview Due to the variety and complex shapes of cable accessories on high-voltage transmission lines, obstacle crossing is the primary function that inspection robots must possess. The robot described in this paper uses three freely swinging booms to traverse cable accessories. When encountering obstacles, the three booms swing sequentially to pass through the obstacles. The robot body is shown in Figure 1. This robot can crawl on high-voltage transmission cables of various types, including four-split, two-split, and single-strand cables. It can autonomously cross cable accessories such as suspension insulators, isolation rods, vibration dampers, and clamps, and has the function of detecting transmission cables. The robot's comprehensive performance indicators are as follows: 1) Body dimensions: 850×300×700mm; 2) Body weight: 45Kg; 3) Cable diameter adaptability: Ф10～Ф25mm; 4) Moving speed: 0～25m/min; 5) Climbing angle: 0～30°; 6) Control mode: autonomous operation and master-slave remote control; 7) Fault handling: manual/automatic. Figure 1 Schematic diagram of the robot body. 3. Design of the control system The robot's control system consists of two parts: the body control system and the ground monitoring system, as shown in Figure 2. The robot body control system is used to plan the robot's motion trajectory, control the robot's moving components, ensure that the robot can reliably and quickly cross obstacles, and realize the long-distance transmission of commands and data with the ground base station; the ground monitoring system realizes the robot's manual/automatic control and monitors the robot's stable operation. Designing two sets of control systems for the robot, one automatic and one manual, increases the robot's flexibility and reliability. When one set of systems fails, the other set of control systems can be started. In addition, in some special situations, only the manual system can be used, which reduces the difficulty of the robot's field operation and increases the robot's applicability. 3.1 Design of the robot body control system The robot body control system is based on the embedded PC104 industrial computer, and is equipped with the input/output expansion board HT-750 and the A/D acquisition expansion board PM-516. Using PC104 as the core module, the main focus can be placed on the design of software and interfaces. Moreover, the development, maintenance and expansion of PC104 are very convenient. PC104 is fully compatible with general PC and PC/AT standards (IEEE P996), and its software and hardware can be quickly mastered. It also has the special requirements of embedded control and provides a standard system platform for embedded applications [1]. 3.1.1 Fault detection There are many types of power transmission cable accessories and their shapes are complex, which makes it very difficult for robots to judge the type of obstacles. Therefore, it is necessary to carry multiple sensors and integrate multiple line fault detectors into the mobile platform of the line inspection robot, and use multi-sensor information fusion technology to improve the efficiency, accuracy and precision of fault detection. The main sensors include CCD vision module, infrared temperature sensor, ultrasonic sensor and so on. The vision detection CCD module uses the COM2 serial port on PC104 to identify various accessories of high voltage power transmission lines, find the target (vibration hammer, insulator, connecting hardware, isolation rod and other accessories) in the original image, use image processing technology to extract the feature size of the obstacle, automatically judge the type and distance of the obstacle on the power transmission line, and provide obstacle crossing information to the robot motion control unit [2] to form the next obstacle crossing strategy. In addition, visual inspection can generally find the surface fault phenomenon of overhead line, such as damage to the surface of the power transmission line, loose connecting hardware, etc.; the infrared temperature sensor uses the characteristic that the high voltage power transmission line will generate abnormal temperature rise at the fault point to detect the abnormal temperature rise of the cable. This paper uses the PerkinElmer A2TPMI-334 sensor to detect abnormal temperature rise in cables, thereby detecting cable faults. 3.1.2 Motion Control Due to the complexity of robot movements, most boom-type line-following robots employ a multi-motor drive scheme, using six motors to drive the swinging boom and rotating wheels. This scheme makes the robot more flexible, but the multiple motors increase the robot's weight, which is detrimental to its balance. This paper uses two motors to achieve the required movements. Three electromagnetic clutches, in conjunction with motor 1 in Figure 2, control the swinging of the three booms, while motor 2 controls the robot's movement. To increase the flexibility of detection, two liftable sensor brackets are added to the robot, driven by motors 3 and 4 respectively. The drive block diagram is shown in Figure 3, using a high-performance microcontroller C8051F047 from Silicon Labs and an H-bridge assembly LMD18200T to drive the motors. LMD18200T is a motion control H-bridge component launched by National Semiconductor (NS) of the United States. It integrates CMOS control circuit and DMOS drive circuit. The peak output current is up to 6A, the continuous output current is 3A, the working voltage is up to 55V, and it has temperature alarm and overheat and short circuit protection functions. The continuous stall current of the motor selected in this paper is about 3A, so the LMD18200T chip can meet the requirements. Motor 1 and Motor 2 use digital PID algorithm for speed regulation. Digital PID algorithm is a commonly used control algorithm. It compares the value of the photoelectric encoder at equal intervals with the given speed value. Through the PID algorithm, the duty cycle of the PWM of C8051F047 is changed to realize the closed-loop control of the motor, that is: (1) where K[sub]p[/sub] is the proportional coefficient, K[sub]i[/sub] is the integral coefficient, K[sub]d[/sub] is the derivative coefficient, and T is the sampling period[3]. Motor 3 and Motor 4 are only used to control the lifting of the bracket. There is no specific requirement for speed, so only the encoder pulse count needs to be collected. 3.1.3 Data transmission When the robot crawls, it needs to send its own status information, collected data, captured pictures and other information to the monitoring system; in special cases, the monitoring system also needs to send instructions to the robot, which requires data transmission between the two. The designed transmission distance is <2Km. This paper uses a pair of wireless data transmission modules SRWF-108 to complete this function. The SRWF-108 of the robot body occupies the COM1 port on PC104[4], with a baud rate of 9600bps and 8 data bits. There are three formats: status frame, instruction frame and file frame. 3.1.4 Power supply design The line-following robot can only use its own power supply when working at high altitudes. This paper uses 4 12V lead-acid batteries, and the +12V and ±5V levels required by the system are obtained by power conversion chips such as B1205S, B1212S and LM2678. To ensure the robot has sufficient energy, it is necessary to monitor battery power. This paper uses the DS2438Z chip, a new generation intelligent battery monitoring chip launched by Dallas Semiconductor. The DS2438Z chip boasts powerful functionality, small size, and low cost. It uses a 1-Wire bus for data transmission, simplifying hardware wiring. It can be used to detect parameters such as battery temperature, voltage, and remaining power. When insufficient battery power is detected, the robot will send an alarm to the monitoring system, prompting for battery replacement. 3.1.5 Control System Software The PC104 control system software is programmed in C language, resulting in a short development cycle and high efficiency. The program needs to implement functions such as data acquisition, system status detection, serial communication, action output, fault handling, abnormal situation handling, and power monitoring. Its program flowchart is shown in Figure 4. Data transmission with the monitoring system can be achieved using either polling or interrupt methods. The polling method is easier to program but consumes more system resources, while the interrupt method is the opposite. In addition to serial communication, the robot also needs to perform motor control and fault handling functions; therefore, the polling method is not suitable, and this paper uses the interrupt method. The initialization of COM1 and the COM1 interrupt handler[5] are as follows: void InitCOM() /* Initialize COM1 serial port and set serial port parameters */ { outportb(0x3fb,0x80); /* Set baud rate */ outportb(0x3f8,0x0c); /* Baud rate 9600 */ outportb(0x3f9,0x00); outportb(0x3fb,0x03); /* 8 data bits, 1 stop bit, no parity */ outportb(0x3fc,0x08|0x0b); /* Set MCR */ outportb(0x3f9,0x01); /* Enable interrupt */ } void interrupt far asyncint() { char ch; ch=inportb(0x3f8); /* ch is the received character data */ …… ……} 3.2 Design of the Monitoring System The monitoring system was developed using Visual Basic 6.0 software. VB has advantages such as object-oriented visual design tools, event-driven programming mechanism, powerful database manipulation functions, ActiveX technology, and application integrated development environment. Based on the requirements of the robot system, a relatively complete monitoring system was developed using a modular approach. It has strong scalability and functions such as battery power monitoring, motion status monitoring, cable fault database query, and manual/automatic switching. It can store transmission line fault information in an Access database and query by fault type and time. 4. Conclusion This paper proposes a robot control system based on the PC104 module, which solves the problem of autonomous obstacle crossing for robots and can identify some cable accessories, perform wireless data transmission, and check cable conditions, providing convenience for the automatic detection of high-voltage transmission lines. References [1] Qian Lujun, Shen Xi. Embedded temperature control system based on PC104 bus [J]. Modern Electronics Technology, 2004 (15): 87-91. [2] Xiong Xiaoming, Liang Zize, Tan Min. Automatic identification system for obstacles in power transmission lines [J]. High Technology Communications, 2005, 15 (2): 39-42. [3] Zhang Xiuli, Zheng Haojun, Zhao Liyao. A small pipeline inspection robot [J]. Robot, 2001, 7: 626-629. [4] Zhang Wenwen, Ouyang Xian, Bai Yonglin. Application of PC104 serial communication in engineering [J]. Microcomputer Information, 2006, 2: 57-59. [5] Gong Jianwei, Xiong Guangming. Visual C++/Turbo C Serial Communication Programming Practice [M]. Electronic Industry Press. 2004. About the Authors: Wu Junfei (1968-), male, Han nationality, PhD, Associate Professor. Research areas: Pressure vessel safety engineering, robotics. Wu Shuang (1982-), male, Han nationality, Master's student. Research area: Robotics, E-mail: [email protected] Jiang Shengyuan (1969-), male, Han nationality, PhD, Professor. Research areas: Robotics, virtual prototyping technology. Wang Xinzhi (1980-), male, Han nationality, Master's student. Research area: Robotics. Author introduction: WU Jun-fei, male, Doctor, Major: Safety Engineering for Pressure Vessels, Robot Technology. WU Shuang, male, Master graduate student, Qingdao University of Science and Technology, Major: Robot Technology, E-mail: [email protected] JIANG Sheng-yuan, male, Doctor, Major: Robot Technology, Virtual Prototyping Technology. WANG Xin-zhi, male, Master graduate student, Major: Robot Technology.