I. Overview of Encoders
An encoder is a sensor that converts displacement into digital signals, primarily used to measure parameters such as rotation angle and linear displacement. The working principle of an encoder is to utilize photoelectric and magnetoelectric effects to convert physical quantities into electrical signals, process these signals, and output digital signals directly related to the physical quantities.
Based on the type of output signal, encoders can be divided into two types: absolute encoders and incremental encoders. The signal output by an absolute encoder represents a unique set of position information, while the signal output by an incremental encoder only represents the relative change in position.
II. Application of Encoders in Motor Control
1. Motor position control
In motor position control, the encoder, as a position feedback element, provides real-time position information of the motor rotor. By comparing the encoder output signal with the target position signal, the controller...
2. Motor speed control
In motor speed control, encoders can provide real-time feedback information on motor speed. By comparing the encoder output signal with the target speed signal, the controller can...
3. Motor acceleration control
In motor acceleration control, the encoder can provide information on the rate of change of motor speed. By comparing the encoder output signal with the target acceleration signal, the rate of change of the motor's output torque and speed can be matched with the target values.
III. How to use an encoder to control motor speed
The basic steps for controlling motor speed using an encoder are as follows:
1. Encoder Installation
Install the encoder on the motor shaft and connect the encoder's output signal line to the motor controller's input signal line.
2. Encoder signal processing
The encoder output signal is processed, including signal filtering, amplification, and digitization, in order to match it with the motor controller.
3. Motor controller settings
Configure the parameters of the motor controller as needed, including speed range, speed accuracy, and speed curve.
4. Target speed setting
Set the target speed of the motor as needed and input the target speed signal into the motor controller.
5. Comparison of controller and encoder signals
The encoder output signal is compared with the target speed signal, and the motor controller output signal is adjusted according to the comparison result.
6. Motor controller output adjustment
Based on the output signal from the motor controller, the motor's output torque and speed are adjusted. The encoder, as a crucial component in motor control, provides real-time feedback information such as motor position, speed, and acceleration, enabling precise motor control. Using encoders to control motor speed improves motor accuracy and stability, thereby increasing production efficiency and product quality.
The type of encoder output signal directly affects the design of the motor control system, and can be mainly divided into the following three types:
Open set output
This circuit uses a transistor output. When the input signal is high, the transistor's collector is open; when it's low, it's directly grounded. An external pull-up resistor is required to maintain the logic high level, but this increases power dissipation and reduces signal slewing rate, making it suitable for low-speed or low-power applications.
Push-pull output
Signal output is achieved through the alternating operation of two transistors, eliminating the need for external pull-up resistors, resulting in fast conversion speeds and low power consumption. Suitable for high-speed motor control, it can significantly improve encoder resolution.
Differential line drive output
This system enhances signal immunity through differential amplifiers, making it suitable for long-distance transmission or environments with high electromagnetic interference. It requires the use of a differential receiver circuit to effectively suppress common-mode noise.
When selecting, motor speed, system voltage, and anti-interference requirements should be considered: push-pull output is preferred for low-speed or low-power scenarios; differential output is recommended for high-speed or long-distance transmission; and open-collector or push-pull output can be selected based on cost for general applications.
01 The Importance of Encoders During motor operation, real-time monitoring of key parameters such as current, speed, and the relative position of the shaft in the circumferential direction is crucial. Accurate acquisition of these parameters is decisive for judging the state of the motor itself and the equipment it drives, as well as for real-time control of the motor's operation. The realization of advanced functions such as servo control and speed regulation also depends on the precise measurement of these parameters. In this process, the application of encoders as front-end measurement elements not only greatly simplifies the measurement system but is also highly regarded for its precision, reliability, and comprehensive functionality.
【The function and application of encoders】
An encoder is essentially a rotary sensor that converts the position and displacement of rotating parts into digital pulse signals. These pulse signals are then captured and processed by the control system to issue commands, enabling precise adjustments to the equipment's operating status. Notably, encoders combined with racks and pinions or lead screws can also be used to measure the position and displacement of linear motion components.
02 Encoder Functions and Principles [Encoder Working Mechanism]
Encoders play a crucial role in motor output signal feedback systems and measurement and control equipment. Their internal structure mainly consists of two components: a code disk and a receiver. The optical parameters generated by the rotation of the code disk are converted into corresponding electrical parameters. These electrical parameters are then amplified and processed by the frequency converter's preamplifier and signal processing system, ultimately outputting a signal to drive the power devices. Typically, rotary encoders can independently feed back a speed signal. This signal is compared with a set value and fed back to the frequency converter's execution unit, thereby achieving precise adjustment of the motor speed.
[Encoder Classification]
Based on different detection principles, encoders can be divided into four main categories: optical, magnetic, inductive, and capacitive. Furthermore, based on their scaling method and signal output method, encoders can be classified into three types: incremental, absolute, and hybrid. Incremental encoders determine position by calculating the number of pulses starting from the zero mark. They convert displacement into periodic electrical signals, then convert these signals into counting pulses, thus using the number of pulses to reflect the magnitude of the displacement. Absolute encoders, on the other hand, determine their position by the reading of their output code. Within each revolution, the output code reading for each position is unique, and even when the power is off, the correspondence with the actual position is not lost. Therefore, when an incremental encoder is powered on again after a power outage, its position reading returns to the current position. In contrast, each position of an absolute encoder corresponds to a specific digital code, and its indication value is only related to the start and end positions of the measurement, and is independent of the intermediate measurement process.
03 Practical Applications of Encoders Encoders, as key information acquisition components for motor operating status, are typically tightly connected to the motor via mechanical mounting. In practical applications, encoder mounts and termination shafts are often added to the motor to ensure stable signal transmission. Precise control of coaxiality is crucial during manufacturing, as it directly affects the smooth and safe operation of both the motor and the data acquisition system.
core role
During motor operation, encoders monitor critical parameters, enabling precise control and complex functions. As a rotary sensor, the encoder's unique feature is its ability to convert the position and displacement of rotating components into digital pulse signals. These pulse signals are efficiently acquired and processed by the control system, which then issues commands to precisely adjust the equipment's operating state.
▍ Working Principle
An encoder works by converting rotational or linear motion into digital signals. Using a grating and an infrared light source, along with a receiver, the optical signal is efficiently converted into a TTL (HTL) electrical signal. In-depth analysis of the frequency and number of high-level signals at these TTL levels can intuitively reveal the motor's rotation angle and position information. Through photoelectric conversion, the encoder achieves accurate control of the equipment's operating status.
02 Encoder Classification Encoders, a precise combination of mechanical and electronic components, are responsible for the efficient encoding and conversion of signals or data, and are a key link in communication, transmission, and storage. They can be classified in various ways, mainly based on different characteristics. Specifically, encoders can be divided into two main categories: code disks and code scales. The former converts linear displacement into electrical signals, while the latter is responsible for converting angular displacement into electrical signals.
▍ Code disk and code ruler
The code disk converts linear displacement into an electrical signal, while the code scale converts angular displacement into an electrical signal. This classification allows the encoder to perform its signal conversion function in a variety of scenarios.
▍ Incremental Encoder
Incremental encoders are a type of encoder that provides detailed information such as position, angle, and revolutions. They are based on optical pulses and are well-suited for long-distance transmission. They output three sets of square wave pulses: A, B, and Z phases.
▍ Absolute Encoder
An absolute encoder is a sensor that directly outputs a digital value. It can directly read the digital code corresponding to the position without the need for a counter. Its sensor has a circular code disk with several concentric code tracks distributed radially, and these code tracks have alternating light-transmitting and light-blocking sector areas.
03 Commonly Used Encoders for Motors
▍ Features of Incremental Encoders
Incremental encoders are one of the most commonly used encoder types in motors. They are simple in construction, have a long mechanical life, and possess excellent anti-interference capabilities and reliability. Although they cannot directly output the absolute position information of shaft rotation, their practicality and cost-effectiveness make them important in motor control.
▍ Features of Absolute Encoders
Absolute encoders greatly simplify system complexity by allowing direct reading without the need for counters. The number of code tracks determines the encoder's resolution; with current technology, 16-bit resolution has been achieved. Their high accuracy and stability meet various high-precision control requirements.
