Design and application of distributed control syst

The design and application of a distributed control system in a tracking car

this paper will introduce a design method of a distributed control system applied to the tracking car, which can control the motor module, sensor module and light control module in a distributed way. This design is convenient for the transplant of the system from the tracking car to the real car in the future

this tracking car model is driven by 7.5V battery and regulated by changing PWM duty cycle. Under the uncertain road environment, the trolley can detect the surrounding environment through self judgment and make corresponding responses (such as turning left, turning right, changing speed, etc.). At present, most of the sensors used in robots are expensive ultrasonic sensors and infrared sensors. This design uses the inexpensive reflective optocoupler sensor to realize the perception of the surrounding environment. In addition, the car also has a good navigation system

system structure

the system adopts a distributed structure, as shown in Figure 1. Because there are many and scattered control objects in the body control system, if the point-to-point centralized control mode is adopted, a large number of connecting cables will be required between the control module and the controlled object, which will lead to complex wiring in the vehicle, and the new Dow and new DuPont business layout will become increasingly difficult to manufacture and install, and there will be hidden trouble. The distributed system structure can design the control module according to the position of the control object, thus shortening the distance between the control object and the control module. Each module communicates with each other through LIN bus. This method only requires one wire as the communication line. In addition, the distributed system architecture can reduce the quiescent current of the board and increase the stability of the board

Figure 1 structure diagram of distributed body control system

1 design of main control module

according to the functional requirements and structural characteristics of the system, the control system is divided into main control module and three sub modules (sensor module, motor control module and lamp control module). The main control module mainly detects the status of the control switches of the body part, and realizes the corresponding control strategy according to the status of these control switches, then sends the control command to the corresponding sub modules through the CAN bus and LIN bus, and then judges whether there is a fault according to the load status fed back by each sub module. If there is a fault, the alarm will be displayed. At the same time, the CAN bus receives some information from the upper can network. The microcontroller of the main control module adopts XC164CS, a special chip for automobile with high reliability and strong anti-interference ability in petrochemical, chemical, automobile manufacturing, packaging and printing, automobile repair and other industries, and its internal controller is integrated with can. Figure 2 is the hardware schematic diagram of the main control module

Figure 2 hardware schematic diagram of main controller module

2 design of DC motor drive and control module

XC164CS is also used as the microcontroller in the motor control module, because there are corresponding units in this series of microcontrollers to control the motor, which is quite convenient. This design uses two-way motor to control the rear wheel drive and front wheel steering of the car. The motor control interface chip tle6209 is used for the drive and control of DC motor. An H-type bridge circuit is integrated in it to drive the motor and realize the four quadrant operation of the motor, corresponding to forward rotation, forward rotation braking, reverse rotation and reverse rotation braking respectively. 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 drive and control the steering motor accordingly. At the same time, the data transmission and reception of the communication module shall be completed. The hardware block diagram is shown in Figure 3

Figure 3 hardware block diagram of sensor module

when the reflective photoelectric switch cny70 of reflector detects the given white (or black) route, it generates the corresponding level signal, which is collected by xc866 and then transmitted to the main controller through LIN bus

system communication

each electronic control unit of the car is connected through LIN bus and can bus

the can transceiver in this system adopts tle6250g. The transmission of motor information requires 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, which can work in receive only mode and idle mode, and has excellent EMC characteristics and various protection functions; However, LIN bus is not suitable for low data transmission rate and high security performance

the network structure combining can and Lin can take into account the characteristics of strong real-time, high reliability, fast communication rate, good interoperability, high flexibility, simple Lin network structure and low cost of CAN bus, so as to better build the automobile network system

the system adopts the tle6258 series LIN bus transceiver, which is the interface between the protocol controller and the physical bus. It is especially suitable for driving the bus in the Lin system of automotive and industrial applications, and can be used in the standard ISO9141 system. The tle6258 provides an idle mode to reduce current loss. By sending a wake-up frame on the bus, the master or slave can wake up from the idle mode and return to the normal operation mode. Figure 4 is the LIN bus hardware circuit diagram of the 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 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 LIN bus. When MAX232 is connected and the recycling market prospect is promising, the system performs the serial communication function. In Figure 4, INH is the forbidden input pin, and the high level is valid. The transceiver pin TXD receives the data from the microcontroller pin txd0 and sends the data to the bus at the same time. China's plastic machinery enterprise market that sends the data will be more open and receive the data at the same time, and feed back the 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, so as to realize the communication of LIN bus. The data communication in this system is mainly that the main module sends control commands to three modules and the three sub modules feed back status data to the main module

software design

each ECU in the system sends and receives commands through the CAN bus to realize mutual communication, so as to realize data sharing, etc. The software design is based on Dave and keil software. The program is mainly composed of can initialization, sending data and receiving data, as shown in Figure 5

Figure 5 main program flow chart

conclusion

this design scheme can realize the basic functions of the distributed body control system, with simple structure and low cost. In addition, this design idea is also applicable to the control of real vehicles. The continuous progress of automotive electronic technology will promote the organic combination of can, Lin and the developing bus technology with higher speed and fault tolerance to form a safe, comfortable and more satisfying automotive network. (end)