The communication interface design of elevator gro

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Design and implementation of communication interface of elevator group control system based on CAN bus

I. Introduction

has become very loose. In many high-rise buildings, many elevators are usually installed. In order to improve the operation efficiency and service quality of these elevators, it is necessary to use elevator group control management system to reasonably dispatch and manage them. The main function of elevator group control is to dispatch and manage all elevators, designate elevator service floors, and change the uneven distribution of floors, waste of resources, uneven loss of elevators and other conditions originally caused by the independent control of elevators. Elevator group control plays a very important role in improving the operation effect of elevators. An elevator group control system needs to carry out a lot of data exchange, such as floor selection signals in each elevator car, indicator signals to answer floor selection, indicator signals to display the current position of the elevator, and hall call signals. These signals increase rapidly with the increase of the number of elevators and floors. The main characteristics of elevator group control system communication are many nodes, long distance, slow signal change and high requirements for anti-interference ability

at present, for the communication mode of elevator group control system, the dominant is the serial communication of BITBUS network system with master-slave structure, which adopts RS-485 bus, and the communication mode is command and response mode. The host sends a query signal to each sub controller regularly, and then each sub controller reports its status. But it has the following shortcomings: ① the data transmission efficiency is low, and the main controller is extremely busy; ② The flexibility is poor, because when the sub controller is abnormal, the data will not be uploaded immediately, and it must wait for the main controller to issue a command; ③ Once the host fails, the whole system will be paralyzed. The above problems are fatal to the elevator control system with high requirements for real-time and safety. Based on the above reasons, we propose an elevator group control system based on CAN bus

second, the characteristics of CAN bus

the CAN bus (controller area network bus) network with multi master structure is essentially different from the BITBUS network. Can, the controller area network, is a new type of bus type serial communication network, which has the following advantages:

① it works in a multi master mode. Any node of the network can actively send information to other nodes on the network at any time, and can also receive information on the bus. The communication mode is flexible, regardless of the master and slave, thus solving the problem that the slave node in RS-485 cannot actively exchange data with other nodes, Make the system have great flexibility

② nodes on the can network can be divided into different priorities to meet different real-time requirements. When two nodes send information to the bus at the same time, the node with low priority actively quits sending, while the node with the highest priority can continue to transmit data unaffected, which greatly saves the bus conflict arbitration time, enhances the real-time performance of the network, and more importantly, the network will not be paralyzed when the network load is heavy

③ the direct communication distance of can can can be up to 10km (the corresponding rate is below 5Kbps), and the communication rate of can can can be up to 1Mbps (the corresponding transmission distance is 40 m). Can adopts short frame transmission, with 8 effective bytes per frame, short transmission time, low probability of interference, and high error detection function

④ each frame of can information has CRC verification and other error detection measures to ensure a very low data error rate. To further expand the field of utilization

III. system composition and communication interface circuit design

the control part of the elevator group control system based on CAN bus is composed of elevator main controller, car controller, floor controller (multiple sets) and group controller. It is connected into a complete communication network through CAN bus interface to transmit all operating parameters and control commands in real time. The can network topology of the elevator control system is shown in Figure 1:

Figure 1 can network topology of the elevator group control system

the main controller of the elevator is connected to the CAN bus through the node interface circuit. It is the core of the elevator control system, which is mainly responsible for controlling the position and operation of the car and processing various signals sent back by each sub node, Generate various control signals (including the communication signal with the drive system, control the minimum value of all values measured by each contactor as the signal of the minimum thickness of insulation thickness, and send various control signals to each sub node (sub nodes are: each floor controller, lift car controller, etc.). The floor controller is responsible for communicating with the main controller, sending up the call signal, receiving the down signal sent back by the machine room, and completing the call signal memory, number cancellation, floor and direction display functions. The function of the lift car controller is mainly to transmit the internal selection signal to the main controller

can bus communication interface is a very important link, and the correct operation of equipment is closely related to it. Figure 2 shows the circuit diagram of CAN bus communication unit of an actual elevator control system. The circuit structure is:

MCU (*p87c52x2) + can controller (SJA1000) + can transceiver (tja1040t)

Figure 2 circuit diagram of CAN bus communication unit

in the above circuit structure, p87c52x2 chip is a standard 80C51 core single chip microcomputer produced by Philips company, including 8KB OTPROM, 256b ram, 32 i/o ports, 3 16 bit timing/counters, dual dptr, 1 UART port, which can work in 6clk mode, The running speed can be twice that of the standard 80C51. SJA1000 chip is an independent can controller, which is made by Philips high-precision reducer. It has the characteristics of stable transmission, low noise and long service life; The large LCD is designed and produced for trial use, with excellent EMI and EMC performance, and is suitable for controller area networks in industrial environments. Moreover, SJA1000 is an upgraded product of pca82c200 independent can controller. It is fully compatible with pca82c200 controller in terms of pin and electrical, and has a more functional Pelican working mode. It is mainly composed of the circuit that realizes the CAN bus protocol and the circuit that interfaces with the microprocessor. It can complete the functions of the physical layer and data link layer of the CAN bus protocol, and supports can2.0a protocol and CAN2.0B protocol

at present, SJA1000 is widely used as a can controller. TJA1040 chip is a new generation of high-speed can transceiver launched by Philips company in 2002. It is an upgraded model of pca82c250/251 and tja1050. It has very excellent EMC performance, has ideal passive performance when not powered on, provides low-power management, supports remote wake-up, and integrates into a perfect bus protection function. TJA1040 can support the high-speed rate range of 40kbps ~ 1Mbps. When no can repeater is required, the communication distance can reach 1.2km, and the number of communication nodes can reach 110 nodes. TJA1040 is the interface between CAN protocol controller and physical bus, which provides differential sending ability to bus and differential receiving ability to can controller

IV. communication software design

the three-layer structure model of can design is: physical layer, data link layer and application layer. The functions of network physical layer and data link layer are completed by can interface devices, including hardware circuit and communication protocol. The can communication protocol specifies four different network communication frames, namely data frame, remote frame, error indication frame and overclocking frame. The realization of CAN communication protocol, including the organization and sending of various communication frames, is realized by the circuit integrated in SJA1000 communication controller. Therefore, the development of the system is mainly in the design of application layer software. The core part of the application layer software is the data receiving and sending program between CPU and SJA1000 communication controller, that is, CPU sends the data to SJA1000 communication controller, and then SJA1000 communication controller sends it to the bus; When the SJA1000 communication controller receives the data from the bus, the CPU will send the data. First, write the control word to the relevant control register in SJA1000 for initialization. Then, the CPU can receive and send data to the physical bus through the SJA1000 receive/send buffer. The system adopts interrupt mode to realize the communication process of can, and its program flow chart is shown in Figure 3

Figure 3 program flow chart

v. conclusion

the application test of elevator group control technology based on CAN bus in practice shows that it can reduce the number of control signal lines of the whole control system from hundreds to several, which greatly facilitates the installation and maintenance of elevators, improves the operation efficiency and service quality of elevators, and has broad application prospects


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