Incremental encoder

Incremental encoder is also called incremental encoder, incremental encoder, which is an encoder that generates signals according to rotation movement, and its scale method is that each pulse is incremented. Incremental encoders are often used with mechanical conversion devices (such as rack-pinion, measuring wheels or spindles) to measure linear motion. Incremental encoders are often used for position control and motor speed feedback, including servo, industrial applications or heavy-duty applications. It can provide excellent speed and position feedback, with a simple system architecture and low cost. Since incremental encoders can only provide signals for position changes, a reference point is generally required to establish the zero position of the current system in practical applications.

Incremental encoder structure and working principle

The incremental encoder can output a specific number of pulses per revolution. The output signal can be a single A signal or a dual AB signal, and the direction of rotation is detected by the phase difference. We call this AB signal a quadrature signal. Incremental encoder is mainly composed of shaft, PCB and housing. The PCB contains sensors and signal processing circuits to generate two main AB signals. In addition, it can also provide a Z signal generated once per revolution for origin detection or AB signal correction.

Incremental photoelectric encoder is mainly composed of light source, code disc, detection grating, photoelectric detection device and conversion circuit, as shown in the figure below.

The code disc is engraved with radial light-transmitting slits of equal pitch, and the adjacent two light-transmitting slits represent an incremental period; the detection grating is engraved with two groups of A and B corresponding to the code disc. Used to pass or block the light between the light source and the photoelectric detection device. Their pitch is equal to the pitch on the code disc, and the two sets of light-transmitting gaps are staggered by 1/4 pitch, so that the signals output by the photoelectric detection device are different in phase by 90 degrees in electrical degrees. When the code disc rotates with the measured shaft, the detection grating does not move, and the light passes through the gaps on the code disc and the detection grating to irradiate the photoelectric detection device, and the photoelectric detection device outputs two sets of phase difference 90° electrical degrees. The electrical signal is similar to a sine wave. The electrical signal is processed by the conversion circuit to obtain the rotation angle or speed information of the measured shaft. The output signal waveform of the incremental photoelectric encoder is shown in the figure below.

Features of incremental encoder

The advantages of the incremental photoelectric encoder are: the principle structure is simple and easy to realize; the average mechanical life is long, which can reach more than tens of thousands of hours; the resolution is high; the anti-interference ability is strong, the signal transmission distance is long, and the reliability is high. The disadvantage is that it cannot directly read the absolute position information of the rotating shaft.

Alternative products for incremental encoders

•Resolver

The basic principle of the resolver is that the current flowing through the coil generates a magnetic field. The resolver consists of two sets of mutually perpendicular coils. One set of coils is fixed, and the other set of coils rotates with the shaft. The movement of the object can be detected by detecting the strength and phase of the two sets of mutual inductance magnetic fields.

The simple design of the resolver makes it adapt to very extreme environments, such as high temperature, low temperature, radiation environment and even severe mechanical vibration. But the disadvantage of the resolver is that it can't provide very accurate signals, and its output signal is an analog signal, which must be processed by an additional AD chip.

• Absolute encoder

Absolute encoders are used in occasions that require very precise position and speed. We can know the actual position of the current axis without relying on external sensors. The ultra-high precision of the absolute encoder helps to improve the overall performance of the system, and is widely used in CNC, medical and robotics industries.

Application of incremental encoder

The design of incremental encoder considers a very wide range of applications, mainly used in three industries:

Heavy-duty industry: it can resist moisture, high temperature, vibration and impact in extreme environments, such as papermaking, metallurgy and woodworking machinery

General industry: general industrial environment, meet the standard IP level

Light load/servo: high-precision robot control, electronic semiconductor industry.