Rotary Encoder In Elevator field
Principle and characteristics of rotary encoder:
The rotary encoder
is a speed and displacement sensor that integrates opto-electro-mechanical technology.
When the incremental encoder shaft rotates, there is corresponding phase output. The determination of the rotation direction and the increase or decrease of the number of pulses need to be realized with the aid of a direction determination circuit and a counter at the rear. The counting starting point can be set arbitrarily, and the infinite accumulation and measurement of multiple circles can be realized. The Z signal of one pulse per revolution can also be used as the reference mechanical zero position. When the pulse has been fixed and the resolution needs to be improved, the two signals with 90-degree phase difference A and B can be used to double the original pulse number.
When absolute value encoder shaft rotator is used, there are codes (binary, BCD code, etc.) corresponding to the position one by one. The positive and negative directions and the position of the displacement can be determined from the change of the code size, without the need for direction determination circuit. It has an absolute zero code, which can still accurately read the code of the power failure or shutdown position and accurately find the zero code when the power failure or shutdown is restarted and measured again. Generally, the measurement range of absolute value encoder is 0~360 degrees, but special models can also achieve multi-turn measurement.
The sine wave encoder also belongs to the incremental encoder. The main difference is that the output signal is a sine wave analog signal rather than a digital signal. Its appearance is mainly to meet the needs of the electrical field - as a feedback detection element of the motor. Compared with other systems, this kind of encoder can be used when people need to improve the dynamic characteristics.
In order to ensure good motor control performance, the feedback signal of the encoder must be able to provide a large number of pulses, especially when the speed is very low, the traditional incremental encoder generates a large number of pulses, which is problematic in many aspects. When the motor rotates at high speed (6000 rpm), it is difficult to transmit and process digital signals.
In this case, the bandwidth required to process the signal to the servo motor (for example, 10000 pulses per revolution of the encoder) will easily exceed the MHz threshold; On the other hand, the use of analog signals greatly reduces the above problems, and has the ability to simulate a large number of pulses of the encoder. This is thanks to the interpolation method of sine and cosine signals, which provides a calculation method for the rotation angle. This method can obtain a high power increase of the basic sine wave. For example, more than 1000000 pulses per revolution can be obtained from 1024 sine wave encoders per revolution. The bandwidth required to receive this signal is sufficient as long as it is slightly greater than 100KHz. Interpolation frequency doubling needs to be completed by the secondary system
Application of rotary encoder in elevator field
This system uses a relative counting method for position measurement. Before operation, the corresponding pulse number of each signal, such as the position of the speed change point, the position of the leveling point, and the position of the brake stop point, is stored in the corresponding memory unit by programming. During the operation of the elevator, the following signals are detected by the rotary encoder and calculated in real time by the software: the position of the elevator floor, the position of the speed change point, and the position of the leveling point, so as to count the floors and send the speed change signal and the leveling signal.
The calculation of displacement during elevator operation is as follows: H=SI
Where S: pulse equivalent I: cumulative pulse number H: elevator displacement
S=π λ D/P ρ
D: Diameter of traction wheel ρ: Frequency division ratio of PG card λ: Reduction ratio of reducer
P: Number of pulses per revolution of rotary encoder
In this system λ= 1/32 D=580mm
Ned=1450r/min P=1024 ρ= 1/18
Substitute S=π λ D/P ρ S=1.00 mm/pulse
If the height of the floor is 4m, the pulse number at the leveling point of each floor is: 0 for the first floor; 4000 on the second floor; 8000 on the third floor; 12000 on the fourth floor.
If the speed change point is 1.6 meters from the floor, the pulse number of the speed change point on each floor is: 2400 from the first floor to the second floor, 6400 from the second floor to the third floor, and 10400 from the third floor to the fourth floor; Descending: 9600 from the 4th floor to the 3rd floor, 5600 from the 3rd floor to the 2nd floor, 1600 from the 2nd floor to the 1st floor