A, photoelectric encoder and high-speed counter
1, the working principle of photoelectric encoder
Photoelectric encoder is a new type of speed and position control sensor, and its working principle can be explained by photoelectric encoder. The photoelectric code disk is a disk with uniform holes or teeth along the circumference, and a group of light-emitting elements and photosensitive elements are placed on both sides of the disk. When the disc rotates, light sometimes shines on the photosensitive element through holes or tooth gaps, and sometimes it is blocked by the disc, thus generating an electrical signal with pulse train waveform on the photosensitive element. The amplified and shaped signals can be used to measure speed and displacement. The photoelectric encoder can generate thousands or even tens of thousands of pulses in one rotation, which meets the requirements of high-precision rotation speed and positioning (the receiving frequency of the controller should also be considered when selecting the encoder that pursues high precision! )。 In the application of elevator, the resolution of encoder is not high, and it is enough that the car motion of 1mm can generate several pulses. We hope that the encoder can solve the problem of steering judgment while generating pulses. Therefore, the current encoders are generally equipped with two sets (or three sets-for zero measurement) of photoelectric devices, and the phases of the pulses generated by the two sets of photoelectric devices are different to a certain extent, which also produces direction signals. For example, when the pulse phase generated by device A is ahead of phase B, it is forward rotation. On the contrary, the opposite is true. For the convenience of discussion, we choose the trolley running 1mm, and the encoder generates 1 pulse.
2.PLC's high-speed counter and high-speed counting instruction (Mitsubishi FX series discussion)
High-speed counter is the programming soft element of PLC. Compared with ordinary counters, high-speed counters are used to count off-board pulses with a frequency higher than the internal scanning frequency (it is recommended to carefully understand the concept of PLC scanning period). Because of the high frequency of counting signal, counting is interrupted, and external signals are also used to start, reset or change the counting direction of the counter. There are three kinds of high-speed counters of PLC: 1, single-phase single-count input high-speed counter, 2, single-phase double-count input high-speed counter, 3 and dual-phase double-count input high-speed counter. For example, the single-phase single-count input high-speed counter C235 is an input signal for acquiring X0. (PLC has its own regulations, see the user manual for details. )
The high-speed counter has two working modes. The first one uses the action of his own contact as a signal. High-speed counters, like ordinary 32-bit up-down counters, move and hold the contacts when the up count reaches the set value, and reset the contacts when the down count reaches the set value (if the contacts are set). The disadvantage of this method is that the control is affected by the scanning period. The second working mode of the high-speed counter is interrupt mode, which requires the use of special instructions of the high-speed counter. FX2N has three instructions about high-speed counter: 1, high-speed counter setting instruction (HSCS), 2, high-speed counter resetting instruction (HSCR), 3 and high-speed counter interval comparison instruction (HSZ). These three instructions are all 32-bit instructions, and they are all executed in an interrupt mode.
Combined with the control of the five-story elevator, FX2N-64MRPLC is selected as the controller, and C254, a dual-phase double-counting input high-speed counter, is selected as the positioning counter of the car. Its A-phase pulse input terminal is X000, B-phase pulse input terminal is X000 1, reset terminal is X0002, and external start terminal is X0006.
Secondly, automobile position determination based on high-speed counter.
When the elevator is running, the photoelectric encoder drives the high-speed counter to complete the counting work. When the car rises, it counts up and down. The current value of the high-speed counter is the exact position of the car in the hoistway. For example, if the floor height is 5M and the counting range is 0-20000 during normal operation, the setting value of the high-speed counter can be set to 30000 or other values greater than 20000. Because this program does not intend to use events whose current value is equal to the preset value.
The determination of car position has many uses. One is to realize the digital indication of the floors in the lobby and car, the other is to orient the operation, and the third is to determine the braking time of the flat floor. The current position instruction switching interval of 200mm car is set up on each floor. When the car arrives at the interval, the current position data of the car will be sent to the floor current value storage unit for storage as the floor display data of the lobby and the car.
In order to correct the positioning error of the floor counter caused by mechanical reasons and architectural reasons during the debugging and maintenance of the elevator at the initial stage of operation, a positioning self-learning program can be set in the program. Accurate data of each layer can be obtained through maintenance operation.