Why Should an Encoder Be Installed on the Motor? How Does the Encoder Work?

What is an encoder?

During motor operation, real-time monitoring of parameters such as current, speed, and relative position of the rotating shaft is essential to control the motor and its driven equipment effectively. An encoder, as a front-end measurement component, simplifies measurement systems while providing precision, reliability, and robust functionality.

An encoder is a rotary sensor that converts the position or displacement of rotating components into a series of digital pulse signals. These signals are collected and processed by control systems, issuing commands to adjust and change the operating status of equipment. When combined with gear racks or screw threads, encoders can also measure the position or displacement of linear motion components.

Encoder Classification:

Basic encoder categories include:

- Shaft encoders: Convert linear displacement to electrical signals (linear encoders) or angular displacement to electrical signals (rotary encoders).

- Absolute encoders: Provide position, angle, and rotation count information in incremental steps, with each step assigned a unique code.

- Hybrid absolute encoders: Output two sets of information - one for detecting pole positions with absolute information functionality, and the other similar to incremental encoders' output.

Commonly Used Encoders:

- Incremental encoders: Utilize optical-electric conversion principles to output three sets of square wave pulses (A, B, Z phases). A and B phases have a 90-degree phase difference, aiding in determining rotation direction, while the Z phase serves for reference point positioning. Advantages include simple construction, long mechanical lifespan, strong anti-interference capability, high reliability, and suitability for long-distance transmission. Disadvantages include the inability to output absolute position information.

- Absolute encoders: Directly output digital signals, with concentric code tracks on the circular encoder disc. Each track consists of alternating transparent and opaque sectors, with adjacent tracks having a double relationship. The number of tracks on the disc determines its binary code digits. This type of encoder requires no counter, providing a fixed digital code corresponding to the position at any shaft location.

Working Principle:

An optical-electric code disc with central shaft generates four sets of sinusoidal waveforms (A, B, C, D) with a 90-degree phase difference (relative to a 360-degree cycle). By comparing the phases of A and B signals, rotation direction can be determined. Additionally, a Z phase pulse is output once per rotation to represent the zero reference position.

Encoder Structure:

Code discs can be made of glass, metal, or plastic, each with different characteristics regarding precision, thermal stability, and lifespan. Resolution, measured as the number of lines per 360 degrees of rotation, ranges typically from 5 to 10,000 lines.

Encoder Applications:

Encoders are crucial in elevators, machine tools, material processing, motor feedback systems, and measurement/control devices. By converting light signals into TTL (HTL) electrical signals, encoders provide precise feedback on motor rotation angle and position. This feedback allows for closed-loop control systems, enabling precise control in various applications.

In conclusion, encoders play a vital role in precision control systems, categorizing into incremental and absolute types based on structure. They convert non-electrical signals, like light, into analyzable and controllable electrical signals. Encoders, in conjunction with frequency converters, facilitate precise control in motor-driven systems like elevators and machine tools through feedback loops.