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Why Install Encoders on Motors?

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Why Install Encoders on Motors?

2024-01-30 10:17:51

Encoders are used to monitor various parameters, such as current, speed, and the relative position of the rotor in real-time during the operation of a motor. This information is used to determine the status of the motor and any connected devices, allowing for real-time control of their operation. By using encoders as front-end measurement components, the measurement system is greatly simplified, while also providing precise, reliable, and powerful functionality.

Encoders are rotary sensors that convert physical quantities, such as position or displacement, into a series of digital pulses. These pulses are collected and processed by the control system, which then sends commands to adjust or change the operating state of the device. Encoders can also be used to measure the position or displacement of linear motion components when combined with gears or lead screws.

Types of Encoders

Encoders are precision measurement devices that combine mechanical and electronic components to encode or convert signals or data for communication, transmission, and storage. Encoders are classified based on different characteristics, as follows:

  • Linear encoders and rotary encoders: Linear encoders convert linear motion into electrical signals, while rotary encoders convert rotary motion into electrical signals.
  • Absolute and incremental encoders: Absolute encoders provide absolute position information, while incremental encoders provide relative position information.
  • Absolute and hybrid encoders: Hybrid encoders provide both absolute and incremental position information.

Common Types of Encoders Used in Motors

  • Incremental encoders: Incremental encoders use optical principles to output three square wave pulses, A, B, and Z. The A and B pulses are 90 degrees out of phase, allowing for the determination of rotation direction. The Z pulse is used for reference positioning. The advantages of incremental encoders include simple construction, long mechanical lifespan, strong anti-interference ability, high reliability, and suitability for long-distance transmission. The disadvantage is that they cannot output the absolute position information of the rotating shaft.
  • Absolute encoders: Absolute encoders directly output digital quantities. The sensor disc on an absolute encoder has multiple concentric code tracks, each consisting of alternating transparent and opaque sectors. Adjacent code tracks are in a double relationship with each other. The number of code tracks on the disc determines the binary resolution of the encoder. The more code tracks, the higher the resolution. The advantages of absolute encoders include no need for a counter, the ability to read out a fixed numerical code corresponding to the position at any rotor position, and high resolution.

Encoder Working Principle

Encoders work by using a central shaft with a circular optical encoder disc that has annular light and dark lines. These lines are read by optical emitters and receivers to obtain four sinusoidal wave signals that are combined into A, B, C, and D signals. Each sinusoidal wave is 90 degrees out of phase with respect to one full cycle of 360 degrees. The C and D signals are reversed and added to the A and B signals to enhance the stability of the signal. Each rotation also outputs one Z pulse to represent the zero position reference.

Encoder Structure

Because the A and B phases are 90 degrees out of phase, the direction of rotation of the encoder can be determined by comparing whether the A phase is ahead or the B phase is ahead. The zero position pulse can be used to obtain the zero position reference of the encoder.

Encoder discs can be made of glass, metal, or plastic. Glass discs have very thin lines deposited on the surface, providing good thermal stability and high precision. Metal discs have lines that are directly etched, providing good durability but lower precision due to the thickness of the metal. Plastic discs are economical, but their precision, thermal stability, and lifespan are lower than those of glass discs.

Encoder Resolution

Encoder resolution refers to the number of light or dark lines provided by the encoder per 360-degree rotation, also known as the resolution or number of lines. Typical encoder resolutions range from 5 to 10,000 lines per rotation.

Position Measurement and Feedback Control Principle

Encoders play a crucial role in elevators, machine tools, material processing, electric motor feedback systems, and measurement and control devices. Encoders use optical grating and infrared light sources to convert optical signals into TTL (HTL) electrical signals. By analyzing the frequency and number of high levels of the TTL signal, the rotational angle and position of the motor can be directly reflected.

Because both the angle and position can be accurately measured, encoders and inverters can be combined to form a closed-loop control system, making the control more precise. This is why elevators and machine tools can operate with such precision.

In summary, encoders can be classified into incremental and absolute types based on their structure. Both types convert other signals, such as optical signals, into electrical signals that can be analyzed and controlled. In everyday life, devices such as elevators and machine tools rely on precise control of motors through electrical signal feedback closed-loop control, and encoders combined with inverters make precise control possible.

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