Design and application of a distributed control system in a tracking vehicle

This paper will introduce a design method of a distributed control system for a tracking car. The system can perform distributed control on the motor module, sensor module and light control module. This design is to facilitate the transplantation of the system from the tracking car to the real car in the future.

This tracking car model is driven by a 7.5V battery and the speed is adjusted by changing the PWM duty cycle. The car can detect the surrounding environment through self-judgment in an uncertain road environment and make corresponding responses (such as turning left, turning right and changing speed, etc.). Currently, most of the expensive ultrasonic sensors and infrared sensors are used in robots. This design uses cheap reflective optical coupling sensors to complete the perception of the surrounding environment. In addition, the car also has a good navigation system.

System structure

This system adopts a distributed structure, as shown in Figure 1. Because there are many and scattered control objects in the body control system, if a point-to-point centralized control method is adopted, a large number of connecting cables are required between the control module and the controlled object, which will lead to complex wiring in the car and difficult manufacturing and installation, and there are hidden dangers of failure. The distributed system structure can design the control module according to the location of the control object, thereby shortening the distance between the control object and the control module. Each module communicates through the LIN bus, which only requires one line as a communication line. In addition, the distributed system structure can also reduce the static current of the single board and increase the stability of the single board.

Figure 1 Distributed body control system structure diagram

1 Design of the main control module

According to the system functional requirements and structural characteristics, this control system is divided into a main control module and three sub-modules (sensor module, motor control module and light control module). The main control module mainly detects the status of the control switches of the main body of the vehicle, and implements the corresponding control strategy according to the status of these control switches. Then, the control command is sent to the corresponding sub-module through the CAN bus and the LIN bus. After that, it is judged whether there is a fault according to the load status fed back by each sub-module. If there is a fault, an alarm is displayed. At the same time, the CAN bus receives certain information from the upper CAN network. The microcontroller of the main control module adopts the automotive-specific chip XC164CS with high reliability and strong anti-interference ability, which integrates the CAN controller. Figure 2 is the hardware schematic diagram of the main control module.

Figure 2 Main controller module hardware schematic diagram

2 Design of DC motor drive and control module

The microcontroller in the motor control module also uses XC164CS, because there are corresponding units in this series of microcontrollers to realize the control of the motor, which is quite convenient. This design uses two motors to control the rear wheel drive and front wheel steering of the car. The motor control interface chip TLE6209 is used to drive and control the DC motor. It integrates an H-bridge circuit inside to drive the motor and realize the four-quadrant operation of the motor, corresponding to forward rotation, forward braking, reverse rotation and reverse braking. The 16-bit microcontroller XC164CS generates a 10kHz PWM signal to TLE6209 through the internal CAPCOM module to trigger the H-bridge circuit.

3 Design of sensor module The

microcontroller XC866 is used in the sensor module, which is mainly used to collect the values ​​of 8 sensors, transmit them to the XC164CS of the main control board for processing, and then generate corresponding strategies to change the PWM duty cycle to control the drive and steering motors accordingly. At the same time, the communication module data must be sent and received. Its hardware block diagram is shown in Figure 3.

Figure 3 Sensor module hardware block diagram

When the reflective photoelectric switch CNY70 detects a given white (or black) route, it generates a corresponding level signal, which is collected by XC866 and then transmitted to the main controller through the LIN bus. [page] The various electronic control units of

the system communication

car are connected through the LIN bus and the CAN bus.

In this system, the CAN transceiver uses TLE6250G, and the transmission of motor information requires a high-speed data transmission rate (200Kb/s) to meet the requirements of real-time motor control. The data transmission rate of CAN is as high as 1Mb/s, and it can work in receive-only mode and idle mode. It has excellent EMC characteristics and various protection functions; while the LIN bus is not suitable because of its low data transmission rate and from the perspective of ensuring high safety performance.

The network structure that uses CAN and LIN can take into account the characteristics of strong real-time performance, high reliability, fast communication rate, good interoperability, high flexibility of the CAN bus and the simple and low-cost LIN network structure, so as to better build the network system of the car.

This system uses the TLE6258 series LIN bus transceiver, which serves as an interface between the protocol controller and the physical bus. It is particularly suitable for driving the bus in LIN systems for automotive and industrial applications, and can be used in standard ISO9141 systems. TLE6258 provides an idle mode to reduce current consumption. By sending a wake-up frame on the bus, the host or slave can be awakened from the idle mode and returned to the normal operating mode. Figure 4 is the LIN bus hardware circuit diagram of this system.

Figure 4 Serial communication/LIN bus hardware circuit

As shown in Figure 4, the system selects between serial communication and LIN bus communication through connector K1, and the TXD0 (serial transmission) and RXD0 (serial reception) signals come from the microcontroller. When TXD0 and RXD0 are connected to TLE6258, the system is connected to the LIN bus, and when connected to MAX232, the system performs serial communication functions. In Figure 4, INH is a disable input pin, which is valid at high level. The transceiver pin TxD receives data from the microcontroller pin TXD0 and sends the data to the bus. It receives the data while sending it, and feeds back the self-received data to the microcontroller through the pin RxD. After receiving the feedback data, the microcontroller calls the receive interrupt, which continuously sends and receives data, thereby realizing the communication of the LIN bus. In this system, data communication mainly involves the main module sending control commands to the three modules and the three submodules feeding back status data to the main module. In the

software design

system, each ECU sends and receives commands through the CAN bus to communicate with each other, thereby realizing data sharing, etc. The software design is based on DAVE and KEIL software. The program mainly consists of three parts: CAN initialization, sending data and receiving data, as shown in Figure 5.

Figure 5 Main program flow chart

Conclusion

This design can realize the basic functions of the distributed body control system, and it has a simple structure and low cost. In addition, this design concept is also applicable to the control of real cars. The continuous advancement of automotive electronic technology will promote the organic combination of CAN, LIN and the developing higher-speed, fault-tolerant bus technology to form a safe, comfortable and more satisfying automotive network. (end)