A double inverted pendulum control system based on SPCE061A single chip microcomputer

1. Introduction

High-voltage transmission lines and tower accessories are exposed to the wild for a long time. Due to the continuous mechanical tension, electrical flashover, and material aging, they are damaged by broken strands, wear, corrosion, etc. If they are not repaired and replaced in time, the originally small damage and defects may expand, eventually leading to serious accidents. Therefore, power companies need to regularly inspect line equipment, promptly detect early damage and defects and evaluate them, and arrange necessary maintenance and repairs based on the evaluation results to ensure the safety and reliability of power supply. The traditional manual inspection method is not only labor-intensive but also difficult. In particular, it is very difficult to inspect transmission lines in mountainous areas and large rivers. Even some inspection projects are difficult to complete by conventional methods. Therefore, the use of robots for automatic line inspection has become a necessary means to ensure the safe operation of high-voltage transmission lines.

High-voltage transmission line patrol robots belong to the research scope of special robots. They mainly complete high-altitude operations such as non-destructive testing of high-voltage power supply cables, insulation property testing of suspension insulators, transmission performance testing of transmission line accessories, mechanical connection firmness inspection, and cable foreign body removal. Foreign countries started early in the field of patrol robots and have a high level of research. In 1988, Sawada and others from Tokyo Electric Power Company of Japan developed a fiber-optic composite overhead ground wire patrol mobile robot. The robot can crawl along the ground wire and can assist in crossing obstacles with arc arms. Montambault and others from the Quebec Hydropower Research Institute of Canada successfully developed a transmission line remote control robot in 2000. The remote control robot can eliminate ice accumulation on power transmission lines and can be used as a line inspection platform. Domestic research on transmission line patrol robots is still in its infancy. Only Wuhan University of Water Resources, Shandong University, and the Chinese Academy of Sciences have conducted some research.

2. Robots Overview

Since the cable accessories of high-voltage transmission lines are of many types and complex shapes, obstacle crossing has become the primary function that line inspection robots must have. The robot described in this article uses three freely swinging booms to cross the cable accessories. When encountering obstacles, the three booms are swung so that the three booms pass through the obstacles in sequence. The robot body is shown in Figure 1. The robot can crawl on four-split, two-split, single-strand and other high-voltage transmission cables, and can autonomously cross over cable accessories such as suspension insulators, isolation rods, vibration dampers, and wire clamps, and has the function of detecting transmission cables. The comprehensive performance indicators of the robot are as follows: 1) Body shape: 850×300×700 mm ; 2) Body weight 45 Kg ; 3) Cable diameter adaptability Ф10~Ф25 mm ; 4) Moving speed 0~25 m /min ; 5) Climbing angle 0~30 ° ; 6) Control mode: autonomous operation and master-slave remote control operation; 7) Fault handling: manual/automatic.

3. Design of control system

The robot control system is divided into two parts: the main control system and the ground monitoring system, as shown in Figure 2. The main 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 manual/automatic control of the robot and monitors the stable operation of the robot. Designing two sets of automatic and manual control systems for the robot increases the flexibility and reliability of the robot. When one of the systems fails, the other control system can be started. In addition, in some special occasions, only the manual system can be used, which reduces the difficulty of the robot's field operation and increases the applicability of the robot.

3.1 Design of robot control system

The robot control system is based on an embedded PC104 industrial computer, and is equipped with an input and output expansion board HT-750 and an A/D acquisition expansion board PM-516. Using PC104 as the core module allows the main focus to be placed on software and interface design, and 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 meets the special requirements of embedded control and provides a standard system platform for embedded applications ^{[ 1 ]} .

3.1.1 Fault Detection

Transmission cable accessories are of many types and complex shapes, which makes it extremely difficult for robots to judge the type of obstacles. Therefore, it is necessary to carry multiple sensors, integrate multiple line fault detectors into the mobile platform of the line patrol robot, and use multi-sensor information fusion technology to improve the efficiency, precision and accuracy of fault detection. The main sensors include CCD vision modules, infrared temperature sensors, ultrasonic sensors, etc.

The visual inspection CCD module uses the COM2 serial port on PC104 to identify various accessories of high-voltage transmission lines, find the target (anti-vibration hammer, insulator, connection hardware, isolation rod and other accessories) in the original image, and use image processing technology to extract the characteristic size of obstacles, automatically determine the type and distance of obstacles on the 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 detect surface faults of overhead lines, such as damage to the surface of transmission lines, loose connection hardware, etc.; infrared temperature sensors use the characteristics of abnormal temperature rise of high-voltage transmission lines at the fault point to detect abnormal temperature rise of cables. This paper uses PerkinElmer's A2TPMI-334 sensor to detect abnormal temperature rise of cables to achieve the purpose of detecting cable faults.

3.1.2 Motion Control

Due to the complex movements of the robot, most boom-type line patrol robots use a multi-motor drive solution, that is, 6 motors are used to swing the boom and rotate the walking wheels. This solution makes the robot more flexible, but the multiple motors increase the weight of the robot, which is not conducive to the robot's own balance. This paper uses 2 motors to achieve the required movements, and controls the swing of the three booms through 3 electromagnetic clutches and motor 1 in Figure 2, and uses motor 2 to control the robot's walking. In order to increase the flexibility of detection, two liftable sensor brackets are added to the robot, which are driven by motor 3 and motor 4 respectively. The drive block diagram is shown in Figure 3. The high-performance microcontroller C8051F047 and H-bridge component LMD18200T of Silicon Lab are used to drive the motor. LMD18200T is a motion control dedicated H-bridge component launched by National Semiconductor (NS) of the United States. It integrates CMOS control circuit and DMOS drive circuit, with a peak output current of up to 6 A , a continuous output current of 3 A , an operating voltage of up to 55 V , and has temperature alarm and overheating and short circuit protection functions. The continuous stall current of the motor selected in this article is about 3 A , so the LMD18200T chip can meet the usage requirements.

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Motor 1 and Motor 2 use digital PID algorithm for speed control. 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 achieve closed-loop control of the motor, that is:

(1)

(1) Where is the proportional coefficient, is the integral coefficient, is the differential coefficient, and 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 the speed, so only the encoder pulse number 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 <2 km . 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 9600 bps and 8 data bits. There are three formats: status frame, command frame and file frame.

3.1.4 Power Supply Design

The line patrol robot can only use its own power supply when working at high altitude. This article uses 4 12 V lead-acid batteries, and the +12V, ±5V and other levels required by the system are obtained by power conversion chips such as B1205S, B1212S, and LM2678. In order to ensure that the robot has sufficient energy, it is necessary to monitor the battery power. This article uses the DS2438Z chip. The DS2438Z chip is a new generation of intelligent battery monitoring chip launched by DALLAS. It has the advantages of powerful functions, small size, and low price. It uses the 1-Wire bus to transmit data, and the hardware wiring is simple. It can be used to detect battery temperature, voltage, remaining power and other parameters. When the battery power is low, the robot body will send an alarm to the monitoring system to prompt the replacement of the battery.

3.1.5 Control system software

The software of the PC104 control system is programmed in C language, with a short development cycle and high efficiency. The program needs to realize functions such as data acquisition, system status detection, serial communication, action output, fault handling, abnormal situation handling, power monitoring, etc. Its program flow chart is shown in Figure 4. Data transmission with the monitoring system can be carried out in query or interrupt mode. The advantage of the query mode is that it is easy to program, but it will occupy more system resources, while the interrupt mode is the opposite. In addition to serial communication, the robot must also complete motor control, fault handling and other functions. Therefore, the query mode is not suitable for use. This article uses the interrupt mode. Initialize COM1 and COM1 interrupt handler [5] 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 check*/

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 monitoring system

The monitoring system was developed with Visual Basic 6.0 software. VB has advantages such as object-oriented visual design tools, event-driven programming mechanism, powerful database manipulation function, Active technology and application integrated development environment. According to the requirements of the robot system, a relatively complete monitoring system was developed using modular thinking. It has strong scalability and has functions such as battery power monitoring, motion status monitoring, cable fault database query, manual and automatic switching, etc. The fault information of the transmission line can be saved in the Access database, and the fault type and time can be queried.

4. Conclusion

This paper proposes a robot control system with PC104 module as the core, which solves the problem of autonomous obstacle crossing of the robot, and can identify some cable accessories, perform wireless data transmission, check cable status, etc., providing convenience for the automatic detection of high-voltage transmission lines.

References

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