1 Introduction
The flourishing development of modern life, production and construction has greatly promoted the development of elevator technology, and thus put forward higher and higher requirements for elevator control systems.
The elevator control system which combines programmable logic controller (PLC) and variable frequency (VVVF) speed control technology is widely used by small and medium sized elevator manufacturers for its characteristics of reliable operation, convenient use and maintenance, strong anti-interference, and excellent speed control performance. The control of elevator running curve of this type of system mostly uses the multi-speed control mode of the speed terminal combination to output the fixed elevator running curve, and there is a slow crawling process before the elevator leveling.
The giants of the international elevator industry mostly use self-developed elevator-specific controllers and use direct control of distance control. However, due to limitations of its own programming instructions and program scanning time, it is difficult to program a distance control PLC. The EV3100 elevator-specific frequency converter introduced by Emerson CT not only has the speed-regulating function of a general-purpose inverter, but also the common elevator-specific function. The unique layer height data register can achieve distance control through parameter setting.
2 basic principles of distance control
The running curve of the traditional control method of given deceleration distance is shown in Fig.1 [1], the x-axis is the time of the elevator running process, and the y-axis is the running speed. When the elevator receives the start signal of the system, after the system accelerates to the rated speed, it runs at a uniform speed. When the system receives the deceleration signal, it begins to decelerate. After reaching the gate area, it begins to crawl and stops after reaching the leveling floor. The entire running curve shows the S type.
Figure 1 Running curve for given deceleration distance
The above operating curve is preset by the control system. When the rated speed is generally 1m/s, a single curve is run. When the speed is 1.5m/s, two curves are run. The control method that the control system automatically generates the elevator running curve according to the parking distance is generally called “distance controlâ€, and the running curve thereof is shown in FIG. 2 .
Figure 2 Distance Control Running Curve
3 control system hardware design
3.1 The composition of the control system
Figure 3 System composition
As can be seen from Figure 3, the system is mainly composed of the following components: PLC, inverter, traction machine, door machine and so on. PLC is the core of the control system. [2]PLC automatically determines the elevator's running direction and speed based on the incoming call signal and the current position of the elevator. The inverter controls the speed of the traction motor according to the PLC speed command. After reaching the destination floor, the automatic leveling and parking , Switch door, in the course of the operation, output elevator floor position and running direction, at the same time complete the call signal registration, save and eliminate the work. Some special conditions in the elevator operation (such as emergency stop, overload, top, bottom, etc.) are automatically processed and alarmed.
3.2 hardware selection
Taking a 15-storey building as an example, the elevator control system actually needs to input 60 points and output 62 points. Mitsubishi's FX2N-128MR PLC was selected. This model has more than 100 programming instructions, built-in 8K step RAM registers, and is equipped with the corresponding programming software GX Developer, not only can programming PLC by handheld programmer, but also can be programmed on personal PC [3]. During the operation of the elevator, the elevator operation status can be monitored through the status of the internal auxiliary relays in the program, and on-site debugging is very convenient.
The frequency converter selects Emerson CT's EV3100 elevator-specific frequency converter. In addition to vector control, slip compensation, and load torque adaptive functions, it also has elevator-specific functions such as brake control and detection, and elevator overspeed detection. In order to achieve closed-loop vector control, improve the dynamic performance of the system and realize zero-speed brake control, a rotary encoder is installed at the shaft end of the traction motor. The encoder signal not only serves as the speed feedback of the traction motor, but also utilizes the frequency division function of the EV3100 inverter, and it can also realize the digital displacement control of the elevator. System hardware circuit shown in Figure 4. [4]
Figure 4 system hardware circuit
4 distance control operation principle
(1) The inverter outputs the contactor pull-in command (CR) when it receives the operation command (FWD) and floor setting command (FLE, F1~F6) sent by the controller;
(2) After the frequency converter detects the contactor pull-in (CSM), it passes the delay, opens the inverter, outputs the brake release command (BR), and the inverter running signal (Y2);
(3) After the brake opening delay time T2, the brake is fully opened, and the inverter starts to accelerate according to the S curve;
(4) The elevator can continuously respond to other set floor instructions (FLE, F1 ~ F6) during the elevator running, and the inverter will select the optimal floor stop according to whether it can stop normally;
(5) After reaching the curve deceleration point, the inverter starts to decelerate to stop. After entering a certain distance from the leveling layer (F4.07 leveling distance adjustment), the speed is reduced to 0. After the delay, the inverter outputs the brake closing command (BR) and the elevator stop signal (Y1) is output at the same time. Run command (FWD);
(6) After the controller receives the elevator stop signal, it cuts off the running command (FWD) after the time delay, and the inverter blocks the PWM and outputs a shutdown status signal (Y2);
(7) After the shutdown state (Y2) is valid, the output current is 0 after the time delay. The inverter output releases the contactor command (CR), and the one-time operation process ends.
5 Conclusion
Practice has proved that the control system based on distance control technology developed on the basis of EV3100 elevator special-purpose inverter has been adopted by a certain elevator company in batches, and the system is stable and reliable. There are also elevator control products developed for medium and small-scale elevator manufacturers. Learn from value.
references
[1] Gu Deren, Xu Huigang, Guo Wenhua. PLC-based elevator high-precision position control implementation. "Microcomputer Computer Information". P.61-62.
[2] Gu Deren, Lu Zhanqiu. PLC-based home hydraulic elevator control system. China Elevator. P45-56.
[3] Mitsubishi FX Series PLC User Manual. Mitsubishi Electric Corporation, 1998.2.
[4] EV3100 Series Elevator Inverter User Manual. Emerson CT, 2005.3.
About the Author
Gu Deren Male, Engineer, currently working at Suzhou Yuanzhi Technology Co., Ltd.