An encoder is a device that converts angular or linear displacement into electrical signals. The former is called a code disk, and the latter a code scale. According to the readout method, encoders can be divided into contact and non-contact types. Contact encoders use brushes for output; a brush contacts a conductive or insulating area to indicate whether the code state is "1" or "0". Non-contact encoders use photosensitive or magnetic sensitive elements; when using photosensitive elements, the light-transmitting and opaque areas indicate whether the code state is "1" or "0". Encoders can also be divided into incremental encoders and absolute encoders based on the type of output data.
Incremental type: It emits a pulse signal for every unit angle rotated (some emit sine and cosine signals, which are then subdivided and chopped to produce higher frequency pulses). It is usually output in phase A, phase B and phase Z. Phase A and phase B are pulse outputs with a 1/4 cycle delay between each other. The forward and reverse directions can be distinguished according to the delay relationship. Moreover, the frequency can be multiplied by 2 or 4 by taking the rising and falling edges of phase A and phase B. Phase Z is a single-turn pulse, that is, one pulse is emitted per revolution. Generally speaking, incremental encoders do not have internal storage devices, so they do not have the function of retaining data after power failure. CNC machine tools must use the "return to reference point" operation to determine the counting reference and perform the actual position "zeroing". [4]
Absolute encoders: For each revolution, each reference angle emits a unique binary value corresponding to that angle. Multiple positions can be recorded and measured using an external revolution counting device. The output of an absolute encoder can directly reflect the absolute angle within a 360° range. The absolute position can be identified by the amplitude of the output signal or the physical encoding scale of the grating. The former is called a rotating transformer; the latter is called an absolute encoder.
Encoders can also be classified into optical, magnetic, inductive, and capacitive types based on their detection principle. The most common are photoelectric encoders (optical) and Hall effect encoders (magnetic).
An optical encoder is a sensor that converts the mechanical geometric displacement on an output shaft into pulses or digital signals through photoelectric conversion. An optical encoder consists of a code disk and a photoelectric detection device. The code disk is a disc with a certain diameter and several rectangular holes evenly spaced. Because the optical encoder is coaxial with the motor, when the motor rotates, the detection device detects and outputs several pulse signals. To determine the direction of rotation, it typically outputs two sets of square wave signals with a certain phase difference.
A Hall encoder is a sensor that converts the mechanical geometric displacement on an output shaft into pulses or digital signals through magneto-electric conversion. A Hall encoder consists of a Hall code disk and Hall elements. The Hall code disk is arranged with different magnetic poles at equal intervals on a disk of a certain diameter. The Hall code disk is coaxial with the motor. When the motor rotates, the Hall elements detect and output several pulse signals. To determine the direction of rotation, two sets of square wave signals with a certain phase difference are typically output.
Encoders are crucial feedback actuators in industrial automation control. Position encoders are classified into absolute and incremental types based on their operating mode. Absolute position encoders typically use serial communication for data output. Due to their high accuracy, they can directly feedback the absolute position, angle, and motion state of moving parts within the system. Furthermore, they do not require counting circuits or power-off retention functions, making them highly reliable. They are commonly used in high-precision servo motion control systems and precision CNC machine tools. The communication speed of a position encoder affects the time constant of the closed-loop system to some extent, thus impacting the reliability of the system's feedback data. This makes absolute encoders the primary product promoted by many technically advanced encoder manufacturers. Consequently, many manufacturers on the market use high-speed synchronous serial output as their encoder position signal output method, each employing different signal transmission protocols.
Encoders are widely used in the steel industry, automated production lines, conveying equipment, textile machinery, port machinery, plastic machinery, hoisting machinery, pressure machinery, glass machinery, printing machinery, woodworking machinery, packaging machinery, machine tools, logistics machinery, tire machinery, elevator automation, cement plant industrial robots, inkjet printers, construction machinery, etc. for reliable/accurate measurement of height, stroke, angle and speed.
