Commonly used encoder classification and various types of encoder working principle

Absolute encoder is a kind of sensor, mainly plays the role of detecting the speed, position, angle, distance and other parameters of mechanical movement. The encoder as a signal detection method has been widely used in various industries.

The working principle of absolute encoder is like this: when the absolute encoder shaft drives the grating disk to rotate, the light emitted by the light-emitting element is cut into intermittent light by the slit of the grating disk and is received by the receiving element to produce the initial signal. The signal is processed by the relay circuit and outputs a pulse or code signal.

The advantages of absolute encoder are small size, light weight, more varieties, full function, high frequency response, high resolution, small torque, low energy consumption, stable performance, reliable long service life. Incremental encoder encoder is an angular displacement or linear displacement into an electrical signal device. Absolute encoder common types of incremental encoder, absolute encoder, binary encoder, these three kinds of encoder and what is the difference between it!

1、Incremental encoder

The incremental encoder shaft rotates with a corresponding phase output. The direction of rotation and the increase or decrease of the number of pulses are realized with the help of the rear orientation circuit and the counter. The starting point of counting can be set arbitrarily and unlimited accumulation and measurement of multiple revolutions can be realized. It is also possible to use the Z signal of one pulse per revolution 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 utilized to multiply the original pulse number.

2、Absolute encoder

Absolute encoder shaft rotator, there is a one-to-one correspondence with the position of the code output, from the change in code size can be judged from the positive and negative direction and displacement of the position, without the need to judge the direction of the circuit. Encoder installed in the power motor shaft end, this method has the advantage of high resolution, due to the multi-turn encoder has 4096 turns, the number of motor turns in this range, can be fully utilized in the full range and improve the resolution, the disadvantage is that the movement of the object through the deceleration gears, the back and forth with the gear lash error, generally used for unidirectional high-precision control and positioning, such as steel rolling roll gap control. In addition, the encoder is directly installed in the high-speed end, the motor jitter must be small, or easy to damage the encoder. It has an absolute zero code, when the power outage or shutdown and then power on re-measurement, can still accurately read out the power outage or shutdown position code, and accurately find the zero code. Generally the measuring range of the absolute encoder is 0 to 360 degrees, but special models can also realize multi-turn measurement.

3、Sine wave encoder

Sine wave encoders also belong to the category of incremental encoders, the main difference being that the output signal is a sine wave analog signal instead of a digital one. This type of encoder can be used when one needs to improve the dynamic characteristics on the basis of comparison with other systems.

So how do you choose an absolute encoder in practice?

In order to ensure good motor control performance, the encoder feedback signal must be capable of delivering a large number of pulses, especially at very low rotational speeds.The use of conventional incremental encoders to generate a large number of pulses is problematic from many points of view.Transmitting and processing digital signals is difficult when the motor is rotating at high speeds. In this case, the bandwidth required to process the given, signal will easily exceed the MHz threshold; while on the other hand the use of analog signals greatly reduces the above mentioned troubles and has the ability to simulate a large number of pulses from the encoder. This is possible thanks to the interpolation of sine and cosine signals, which provides a calculation method for the angle of rotation. This method allows high multiplications of the fundamental sine to be obtained, e.g. more than 1,000,000 pulses per revolution can be obtained from a sine wave encoder with 1,024 pulses per revolution. The bandwidth required to accept this signal is only slightly greater than 100 KHz. Interpolated frequency doubling is done by a secondary system.