Remote motor group control based on GPRS and CAN bus

introduction

The application of motors in various fields has been quite extensive, and is developing in the direction of networking and intelligence. In complex control systems, multiple motors are often required to work at the same time, such as oil field motors, mining platforms, industrial cutting, elevator control, agricultural processing, etc. Motors are often installed in a dispersed manner and work in a complex working environment. Therefore, remote control is not only conducive to improving work efficiency and working environment, but also can greatly improve the safety factor. In many speed regulation processes, due to the complexity of the process (such as a large number of motors, high transmission requirements, complex timing, dispersed geographical distribution, etc.), the control equipment becomes huge, and it is particularly important to carry out network integrated management and control of the motor group transmission speed regulation system composed of a large number of motors.

Traditional motor control generally adopts a one-to-one control mode between the controller and the motor driver, which has the disadvantages of poor anti-interference ability, low reliability, complex control circuits, and poor maintainability. In recent years, there have been various studies on multi-motor group control technologies and methods, and the focus of multi-motor group control system improvement is generally to optimize the control method and control based on field bus or remote network. In combination with the actual production of oil fields, Zhang Yongjun designed a set of pumping motor group control system, which adopts a distributed structure and realizes the motor remote group control system through wireless transmission. It is used to detect, protect and control the motor to improve the reliability and work efficiency of the motor system. In 2006, the China Institute of Metrology proposed a control method based on a three-layer network for the motor group control system, which is the information layer, control layer and equipment layer from top to bottom. On this basis, Ying Huijuan et al. studied the motor group control system of the flour mill production line based on a three-layer network, realizing the remote monitoring of multiple motors on the equipment network.

At present, there are still many problems and shortcomings in the multi-motor group control technology, such as low reliability and accuracy of communication, lack of collection of motor working environment parameters, etc. The motor group control system based on GPRS and CAN bus studied in this paper applies microcontroller technology and CAN bus technology to the communication control of the motor group, and combines GPRS remote transceiver equipment and computer technology to form a remote motor group control system to achieve on-site and remote monitoring. The CAN bus has high security. When a node has a serious error, it can automatically disconnect from the bus, which can effectively improve the reliability and accuracy of communication; GPRS transceiver equipment can enable any mobile phone with SMS function and other GPRS transceiver equipment to monitor and remotely control the operation status of the motor group anytime and anywhere, which has high flexibility and convenience, and improves reliability and stability while ensuring remote communication function.

1 Overall design

Referring to the three-layer network control method proposed by the China Institute of Metrology, the information layer of this system uses GPRS wireless communication, the control layer uses CAN bus communication, and the device layer uses RS485 communication. Considering reliability and scalability, this system adopts a point-to-multipoint communication method, with the main control node as the main monitoring, regularly inspecting multiple slave control nodes, receiving motor information data sent by the slave control node, and storing it. Through this data information, the staff can make judgments and make corresponding processing in time, send control commands to the slave control node through the main control node, and the slave control node completes the direct control of the motor. The system structure is set as distributed control, that is, one master control node and multiple slave control nodes. When any slave control node fails, other slave control nodes are not affected, and real-time two-way data transmission is carried out between the master control node and the slave control node.

The system adopts modular design and consists of three parts: the main control part (including embedded touch PC and master node), the motor part (including multiple slave nodes) and the remote GPRS terminal (remote node). The overall effect of the system is shown in Figure 1.

2 Main control section

The main control part consists of two parts: the embedded touch PC and the master node. The embedded touch PC is the control terminal of the industrial site, which is used to display and control the running status of the motor in real time. The master node serves as the connection point between the embedded touch PC, the slave node and the remote GPRS terminal. It receives the motor status query and control instructions sent by the embedded touch PC and the remote GPRS terminal, sends them to the slave node, and then returns the motor status information sent by the slave node to the embedded touch PC and the remote GPRS terminal.

2.1 Embedded Touch PC

The embedded touch PC model is Blue Ocean Microchip LJD-eWin7000, which is a control platform based on WinCE operating system. It has a 32-bit ARM920T high-speed processor core and is mainly used for the human-machine interface on the system platform. Using C# language in VS2 005 as a development tool, it includes a monitoring interface (the control terminal of this motor group control system), which can display the motor speed and temperature and humidity in real time, record the alarm status, and set the motor speed and alarm parameters.

2.2 Master Node

The principle block diagram of the master node is shown in Figure 2. A master node can connect to multiple slave nodes, and can set parameters and start and stop control operations for the motors connected to each slave node. At the same time, it can realize the operation status monitoring, data storage, query and other functions of single and multiple motors, which is convenient for information storage and automatic management. The communication module of the master node connects to the GPRS wireless communication module and the embedded touch PC through the RS232 communication interface to realize information transmission. The GPRS wireless communication module is used to realize remote data transmission, receive query and control information sent by other GPRS modules or mobile phones with SMS sending function and other command request terminals. The GPRS wireless communication module sends the received information to the master node, which judges and analyzes it and makes corresponding replies, and finally returns the data information to the device terminal that sends the command request through the GPRS wireless module.

The embedded touch PC serves as the human-machine interaction interface for the operator to operate on site, and displays the operating status of each motor in real time, including speed, direction, alarm parameters, etc. The interactive interface contains parameter settings and control buttons, which can facilitate the operator to monitor the motor status on site and effectively start and stop and control the speed.

2.2.1 Masternode Hardware Design

The core component of the main node circuit is the STM32F103VET microcontroller, which is convenient for digital, intelligent, networked and other field bus connection monitoring. It has strong anti-interference ability, high precision, stable and reliable working performance. The STM32 microcontroller is added to the original motor control link, and the CAN bus interface for external communication is added to achieve stable data transmission, upload motor operation status information and receive control commands from the embedded touch PC. The CAN bus controller uses CTM8 251T, which is a universal CAN transceiver chip with isolation. The CANG pin is the isolated power output ground. Therefore, isolation devices such as optocouplers and DC/DC isolators are no longer needed in the circuit.

2.2.2 Masternode Software Design

The master node receives the motor information uploaded by the slave node and the control information sent by the embedded touch PC through three external interfaces. At the same time, it sends status information to the embedded touch PC and sends inquiry, control and other information from the controller. Figure 3 is the program flow chart of the master node.

The GPRS interrupt function is used to send and receive GPRS remote commands and status information; the host computer interrupt function is used to receive control commands issued by the embedded touch PC; the CAN interrupt function is used to receive motor status information uploaded from the board and the response after the control command; the TIM2 timing interrupt function is used to centrally process commands issued by GPRS and embedded touch PC, including parsing and sending corresponding control commands to the destination slave node.

2.2.3 Masternode application layer data format definition

Through the analysis of system functions, it is found that the variables that need to be transmitted in system communication mainly include slave node address, motor status, motor speed, temperature value and humidity value. According to the function, the data type can be divided into inquiry command, motor setting command, system parameter setting command, emergency stop command, response information and alarm information. Taking the RS 232 communication between the embedded touch PC and the main control board as an example, its communication data format is listed in Table 1, which mainly includes start, end, variable value and CRC check. The RS 232 communication between the master node and the GPRS remote transceiver module, the SMS communication between the GPRS remote transceiver modules and the CAN bus communication between the master node and the slave node have basically the same data type and communication protocol, which will not be repeated here. [page]

3 Motor part

The motor part contains multiple slave nodes. Next, the design of the slave nodes is explained from the hardware and software aspects.

3.1 Slave Node Hardware Design

Similar to the master node, the microcontroller of the slave node also uses STM32F103VET6. The schematic diagram of the slave node is shown in Figure 4. The temperature and humidity sensor collects information about the temperature and humidity at the work site, and its serial data communication interface is directly connected to the I/O pin of the microcontroller. The slave node sends a motor status query command to the inverter through the RS485 bus at regular intervals, and stores the motor's operating status (direction and speed) in the Flash chip after receiving the inverter's reply. If an inquiry request is received from the master node on the CAN bus, the motor status information is returned. If a control command is received from the master node, the set speed and direction are sent to the inverter, and the control command of the master node is responded to at the same time.

3.2 Slave Node Software Design

The slave node controls the motor speed and direction by communicating with the inverter, receives the control commands issued by the main board through the CAN bus and returns status information (including motor direction, speed, temperature, humidity, and alarm status). Figure 5 is a flowchart of the slave node program.

4 System Debugging

Through the test of two three-phase asynchronous motors Y80L-2, it is found that this solution can realize the collection of multi-motor information (including motor direction, speed, on-site temperature, humidity) and on-site and remote monitoring and control of motor direction, speed, alarm temperature, and alarm humidity through the software interface of the on-site embedded touch PC terminal, the host computer connected to the GPRS communication module, and any mobile phone that can send text messages. Figure 6 is the display interface of the embedded touch PC control terminal, and Figure 7 is the host computer interface of the remote GPRS device terminal.

Conclusion

This article designs a remote motor group control system based on GPRS and CAN bus technology. Combined with actual production conditions, it adopts a distributed structure and wireless data transmission to achieve a low-cost, high-efficiency control system. Whether it is at the industrial site where the motor is working, or in the staff's office or any other place, the staff can obtain the parameters of the motor's operating status in real time and control it. This greatly improves the convenience of operation and reduces the complexity of control.

In order to obtain better control effects, advanced control algorithms can also be added. This system is open and flexible, easy to expand and transform, and can be widely used in actual industrial occasions to solve many related problems on industrial sites, with high application value.