Application of static magnetic grating displacement sensor in elevator control system

1 Introduction to Elevator Control

Elevators are important means of transportation in modern buildings that are related to the safety of people's lives and property. How to improve the operating efficiency of elevators, reduce elevator energy consumption, reduce mechanical wear, and extend the service life of elevators are all very important research topics. Elevators are complete sets of equipment used for fixed lifting of floors. They are safe and reliable, comfortable to ride, accurate in stopping, easy to operate, and high in transportation efficiency. It consists of a lifting and traction system, a guidance system, a safety device, and an electric control system.

At present, two methods are commonly used for elevator control. One is to use a microcomputer as a signal control unit to complete the acquisition of elevator signals, the setting of operating status and functions, and the automatic scheduling and collective operation functions of the elevator. The traction control is completed by the frequency converter ; the second control method uses a programmable controller ( PLC ) to replace the microcomputer to realize signal collective control. In terms of control method and performance, there is not much difference between the two methods. Most domestic manufacturers choose the second method because the production scale is small and the cost of designing and manufacturing microcomputer control devices by themselves is high; while PLC has high reliability and convenient and flexible program design. This design uses Mitsubishi FX2 series PLC to control the static magnetic grid displacement sensor to realize the elevator leveling control. The role of the static magnetic grid displacement sensor in the elevator control system is to adjust the elevator leveling control. The electronic control system is the "central nervous system" of the elevator, and its quality directly affects the quality of the elevator. Passenger elevators and medical elevators are both comfortable to ride, and the comfort is related to the running time. To ride comfortably, the acceleration and deceleration time must be extended, which will extend the running time and reduce the elevator's operating efficiency. Therefore, in order to make the elevator have a higher operating efficiency, the acceleration and deceleration should have a suitable limit, and the change should be smooth, which puts forward the following requirements for the electronic control system: 1) Safe and reliable, easy to troubleshoot, and the simpler the circuit is, the better under the premise of meeting the use requirements. 2) Low noise and vibration, reasonable selection of components, not large electromagnetic sound, the structural parts of the installation parts must have sufficient rigidity, and there are anti-loosening measures. 3) Able to adapt to the working requirements of frequent starting, stopping, adjustment and reversing, good speed regulation performance, and easy conversion of working mode. Acceleration, deceleration and constant speed should be smooth, speed curve should be smooth, and there should be no micro movement before reaching the station. 4) Automatic leveling can be achieved, and the leveling must be accurate. 5) It can adapt to the load lifting in a large range and can start with heavy load. According to the characteristics of elevator operation and the above requirements, the operating speed of the elevator should comply with the curve shown in Figure 1. The leveling error should comply with the provisions of Table 1.

Elevator running speed curve 1
Vm elevator running rated speed Vp parallel climbing slow speed

Table 1 Leveling error range mm

2 Introduction to static magnetic grating displacement sensor

The static magnetic grating displacement sensor is a combination of "static magnetic grating source" and "static magnetic scale". The "static magnetic grating source" uses aluminum alloy pressure-sealed passive NdFeB magnetic grating to form a magnetic grating encoding array; the "static magnetic scale" is encapsulated with a special high-strength aluminum alloy tube with an embedded microprocessor system, and uses switch-type Hall sensor devices to form a Hall encoding array. The exterior of the aluminum alloy tube is treated with anti-oxidation plastic plating. When the "static magnetic grating source" moves relative to the axis of the "static magnetic scale" without contact (relative gap tolerance and relative posture tolerance up to 50mm), the "static magnetic scale" parses the digital displacement information and directly generates a digital signal of displacement higher than the order of millimeters. Make full use of the resources of the embedded microprocessor to increase the data update speed to the order of milliseconds, so as to adapt to the displacement response of movement speeds below 5m/S.

3 Comprehensive features of the product

1) Long service life: non-contact detection of position and angle, avoiding mechanical damage, theoretically no life limit;
2) Resistance to harsh environment: -40℃ to +100℃ working temperature range, continuous high dust, mud, underwater and high impact, strong vibration working environment;
3) Direct absolute measurement: directly indicate the displacement in millimeters or the rotation angle, no need for conversion, no fear of power failure, arbitrary positioning control;
4) Extremely long range, moderate resolution: 260mm-2000m length range, resolution 0.2mm-1mm;
5) Very rich data interface: 4-20mA, 1-5V and other analog outputs, various serial and parallel data interfaces and various field buses such as PROFIBUS;
6) Easy installation and maintenance: under the condition of maintaining a moderate gap, unconstrained installation and operation.

4 PLC controlled static magnetic grating displacement sensor to realize elevator leveling control

In order for the elevator to automatically level after reaching the leveling area, there must be an automatic control system, that is, the automatic control device of the elevator. The control part of the device is a static magnetic grid displacement sensor. Taking a 30-story elevator as an example, the installation diagram is shown in the figure below.

As shown in the figure above, the car is on the first floor above the underground floor. The static magnetic grating source is installed in parallel with the elevator shaft and the outdoor layer, one on each floor. The static magnetic scale is installed on the car with a length of 1.2 meters. Two static magnetic grating sources are installed on the underground floor to detect whether the car has reached the bottom position and the direction of movement.

Since the operation of the elevator is controlled according to the call signal and travel signal of the floor and car, and the call of the floor and car is random, the system control adopts random logic control. That is, on the basis of realizing the basic control requirements of the elevator with sequential logic control, the operation of the elevator is controlled in time according to the random input signal and the corresponding state of the elevator. In addition, the position of the car is determined by the static magnetic grating displacement sensor and sent to the PLC counter for control. At the same time, a static magnetic grating source is set on each floor to detect the floor signal of the system.

a. When the elevator is directional upward, the static magnetic scale detects the static magnetic grating source in the upward direction, the brake is opened, and the elevator goes up. When the car hits the upper forced speed change switch, the latching relay inside the PLC is energized and the timers Tim10 and Tim11 start timing. The length of the timing can be set according to the terminal station floor distance and the elevator speed. After the upper forced speed change switch is actuated, the elevator switches from express operation to slow operation. Under normal circumstances, the elevator should stop when going up to the leveling floor. If the car does not stop but continues to go up, when the setting value of Tim10 is reduced to zero, its normally closed point is disconnected, the slow contactor and the upward contactor lose power, and the elevator stops running. After the car hits the upper forced speed change switch, the elevator fails to switch to slow operation for some reason, and the express operation contactor fails to release. When the setting value of Tim11 is reduced to zero, its normally closed point is disconnected, the express operation contactor and the upward contactor both lose power, and the elevator stops running. Therefore, no matter whether it is slow or fast running, as long as the upper forced speed change switch sends a signal, regardless of whether other protection switches at the terminal station are activated, the elevator can be stopped with the help of Tim10 and Tim11, making the elevator terminal protection more reliable.

b. When the elevator needs to go down, as long as there is an elevator selection instruction, the down direction relay is energized and its normally open point is closed, the latch relay is reset, Tim10 and Tim11 are both de-energized, and their normally closed points are closed to prepare for the normal down of the elevator. The protection principle of the lower terminal station is similar to that of the upper terminal station and will not be repeated.

c. The floor counting adopts a relative counting method. Before running, the number of pulses of the corresponding floor height is measured by self-learning, and 30 memory units DM06~DM21 are stored in 30 corresponding to the 30 floors of elevators. The floor counter (CNT46) is a bidirectional counter. When it reaches the floor counting point of each floor, it counts by adding 1 or subtracting 1 according to the running direction. During operation, the accumulated value of the high-speed counter is compared with the number of pulses corresponding to the floor counting point in real time. When they are equal, a floor counting signal is issued, adding 1 for going up and subtracting 1 for going down. To prevent the counter from repeating counting during the high level of the counting pulse, the rising edge of the floor counting signal is used to trigger the floor counting.

d. When the high-speed counter value is equal to the number of pulses corresponding to the fast speed change point, if the elevator is in fast operation and there is a floor selection signal on this floor, a fast speed change signal is sent. If the elevator is running at medium speed or running at high speed but there is no floor selection signal on this floor, no speed change signal is sent.

e. Door zone signal; when the value of the high-speed counter CNT47 is within the range of the number of pulses corresponding to the door zone, a door zone signal is sent.

5 Software Design Features

According to the location and running direction of the elevator, four priority queues are used in programming, namely the up priority queue, the up sub-priority queue, the down priority queue, and the down sub-priority queue. Among them, the up priority queue is the call signal for upward operation issued by the floor above the elevator's location when the elevator is running upward, and the array composed of registers storing the static magnetic grating source of the floor corresponding to the call signal. The up-second priority queue is a queue composed of registers storing the static magnetic grid source of the floor corresponding to the upward call signal issued by the floor below the elevator when the elevator is running upward. The four priority arrays arranged in real time by the control system during the operation of the elevator provide the basis for the realization of random logic control.

Using a first-in-first-out queue, according to the running direction of the elevator, the non-zero unit (this unit is 70 units when there is a call, and this unit is zero when there is no call) in the priority queue of the same direction is sent to the register queue (first-in-first-out queue FIFO), and the data in the first unit of FIFO is sent to the comparison register using the first-in-first-out read instruction SFRDP.

Using random logic control, when the elevator approaches the deceleration position of a certain floor in a certain running direction, it is judged whether there is a call signal in the same direction on the floor (upward call flag register, downward call flag register, when there is a call request, the corresponding register is 1, otherwise it is 0). If so, the pulse number of the corresponding register is compared with the comparison register. If they are the same, the deceleration and stop are performed on the floor: if they are not the same, the register data is sent to the comparison register, and the original comparison register data is saved to execute the deceleration and stop of the floor. After the action is completed, the saved data is sent back to the comparison register to realize random logic control.

6 Conclusion

Use Mitsubishi FX2 series PLC to control static magnetic grid displacement sensor to realize elevator leveling control. It can realize intelligent elevator control, good elevator running comfort, and the comfort of starting, deceleration, and leveling does not change due to changes in car load, and a satisfactory effect has been achieved.

Statement: Part of the content comes from the application of Mitsubishi FX2 series PLC in elevator control system

Solution price: 19,800.00 yuan for 30 floors, replacing the original rotary encoder, proximity switch and inverter