An encoder is a sensor that converts mechanical motion into digital electrical signals. When the driver wants to control the motor's rotation, the U, V, and W three-phase electrical outputs drive the motor. To rotate the motor to a certain position or angle, we call this position the target value. We need to know the amplitude and position of the motor's rotation at this time; otherwise, the motor will just rotate blindly. In this process, the encoder plays a feedback role. The encoder separates the different positions of the rotor's rotation circle and then rotates with the rotor. The current position of the rotor is fed back to the driver in real time so that the driver knows whether the current position has reached the target value. Once the target value is reached, the output of the U, V, and W three-phase electrical signals is controlled, causing the rotor to stop at this position, thus controlling any position or angle. A brief introduction to the components of an encoder follows.
1. Encoder Introduction
In short, an encoder is a sensor that provides feedback signals. It is a device used to provide feedback on the motion information of a device. An encoder can determine the speed or position information of a motor or other mobile device and convert the motion information into electrical signals, which can be read by the corresponding type of interface module in the motion control system.
Because encoders can provide feedback signals to determine position, speed, or direction, they are a crucial component for the high-precision and accurate operation of small servo motors, and even for large motors used to improve heavy-duty operation, such as those in cranes. In fact, encoders can be found in almost every industry, from petrochemicals to pulp and paper, from precision electronics to automotive manufacturing.
2. Encoder Principle
Encoders can use different types of techniques to generate signals, including mechanical, magnetic, resistive, and optical signals. In optical sensing, encoders provide feedback based on interruptions in light, that is, by scanning a code disk using the principle of light transmission.
The pulse is generated by the mechanical movement of the slotted plate. Light is transmitted to the photosensitive element, and the light generates a voltage through the code disk aperture. The voltage is processed as a binary signal by the electronic system.
3. Encoder type
In terms of the type of signal generated, digital encoders typically measure changes in position and motion over time. However, sometimes it is necessary to consider environmental factors and use other measurement components. For example, in harsh environments or under vibration conditions, a rotary transformer or tachogenerator (speed measurement) must be used for measurement.
In terms of hardware structure, it is mainly divided into linear encoders and rotary encoders. A linear encoder is a encoder that moves along the motion path. A rotary encoder rotates with the motor to detect rotational motion information.
Encoders can be classified as incremental or absolute, depending on the technology used, the type of power supply, or the ability to remember the current position.
Incremental encoders do not provide absolute position information, but only position changes. Because they do not offer any information about absolute position, the drive loses its position value after power is cut off when using an incremental encoder to detect position. Upon power-up, the operator cannot determine the relationship between the motor shaft position and the machine position. Therefore, before achieving absolute positioning, the operator needs to actively return to a reference point (using different descriptors such as zero, reference, and origin) before re-establishing the relationship between the electrical zero point and the machine zero point. Incremental encoders are widely used in industrial applications of asynchronous induction motors.
4. Overview of Incremental Encoders
An incremental encoder (also known as an incremental or pulse encoder) is a transducer that generates electrical pulses to determine the increment of angle in rotational motion. One characteristic of incremental encoders is that the number of output pulses remains constant, which determines the accuracy of the measurement system. Besides requiring zeroing for absolute positioning, incremental encoders also feature low cost, high resolution, small size, easy replacement, strong anti-interference capability, reliable operation, and fast data transmission speed. Below are some commonly used incremental encoders.
5. HTL/TTL Incremental Encoder
When an HTL/TTL encoder changes the position of its rotary motion, it generates an electrical signal and sends it to the monitoring system (drive or controller). HTL/TTL encoders use digital signals that rise along the transmitted value. In use, enc
The difference between a rotary transformer and other encoders lies in its output: analog sine and cosine signals, rather than square wave pulse signals. Therefore, when applied to servo systems, it requires a specific interface circuit, or a resolver-to-digital converter, to convert the analog signal into a digital signal for the control system. A resolver is another name for a rotary transformer because its output of sine and cosine signals represents a form of orthogonal signal decomposition.
