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Article 1: Servo Motor Encoders – Core Classifications, Working Principles and Structural Characteristics
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Knowledge
Release Time：
2026-03-03
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Abstract
Servo motors are the core power source of modern industrial automation systems, and servo encoders, known as the "eyes" of servo systems, are crucial feedback components that determine the precision, stability and response speed of motion control. This article focuses on the core classifications of servo motor encoders, elaborating on the working principles, structural features, advantages and disadvantages of five mainstream types: integrated photoelectric encoders, separated photoelectric encoders, integrated magnetic encoders, separated magnetic encoders, and opto-magnetic hybrid servo motor encoders. It also highlights their key characteristics of high precision and small size, laying a foundation for understanding their application scenarios and parameter selection, and providing a comprehensive reference for engineers and system integrators.
1. Introduction
With the rapid development of industrial automation, intelligent manufacturing, robotics, and new energy equipment, the demand for high-performance servo systems is growing exponentially. As a key component that converts mechanical angular displacement or rotational speed into electrical signals, servo encoders are essential for closed-loop control of servo systems. They provide real-time position, speed and direction data to the servo drive, enabling precise positioning, stable speed regulation and high-dynamic response, which are indispensable for improving the automation level and production efficiency of equipment.
In the early stage, incremental encoders were widely used but had obvious limitations: they required homing after power-on and were prone to cumulative errors. Today, absolute encoders with multi-turn memory have become mainstream, retaining position data after power failure and improving system safety and efficiency. Technological innovation has driven encoders toward miniaturization, high precision, intelligence and hybrid sensing, making products that balance high precision, small size, strong environmental adaptability and standardized communication the first choice for high-end servo matching. This article focuses on encoder classification and working principles to help readers understand their technical characteristics and applicable boundaries.
2. Core Classification and Working Principles of Servo Motor Encoders
According to sensing principle and mechanical structure, industrial servo encoders are divided into five major categories, each with unique technical characteristics and application scenarios. Below is a detailed introduction.
2.1 Integrated Photoelectric Encoder
Integrated photoelectric encoders adopt a highly integrated built-in structure, with the code disk, light-emitting component, light-receiving component and signal processing circuit packaged in one shell, directly installed on the servo motor shaft. Working on the photoelectric effect, the LED emits light through a precision coded disc, and the phototube receives the modulated light, converts it into an electrical signal, and processes it into a digital position signal recognizable by the servo drive.
Their biggest advantage is ultra-high precision (up to 10 arcseconds) and excellent linearity, with strong anti-magnetic interference, mature technology and stable output. However, they are slightly sensitive to oil, dust and severe vibration, suitable for clean industrial environments. In terms of size and compatibility, they have a compact structure and small size, with outer diameters of 35, 46, 47, 48, 50, 56 mm optional, compatible with 40, 60, 80, 110 mm frame servo motors. They support single-turn 17/23/25/26 bit and multi-turn 16 bit resolution, widely used in high-end CNC machine tools, precision rotary tables, chip processing equipment and high-precision robots.
2.2 Separated Photoelectric Encoder
Different from integrated photoelectric encoders, separated photoelectric encoders split the stator and rotor into two independent parts without mechanical connection: the rotor is mounted on the motor shaft, and the stator on the end cover or housing. Their working principle is the same as integrated types, but the split structure makes installation more flexible, avoids shaft wear, improves vibration resistance and service life, and is suitable for high-speed motors.
They retain the high precision of photoelectric technology (up to 10 arcseconds) and have a more compact axial size (small dimension), suitable for equipment with limited installation space. They support single-turn 17/23/25/26 bit and multi-turn 16 bit resolution, with outer diameters of 35, 46, 47, 48, 50, 56 mm, compatible with 40, 60, 80, 110 mm servo motors. Typical applications include high-speed spindles, packaging machinery, textile machines, injection molding machines and automated assembly lines.
2.3 Integrated Magnetic Encoder
Integrated magnetic encoders adopt an integrated structure, with a small magnet on the motor shaft and a magnetoresistive or Hall effect chip in the encoder shell. The chip detects magnetic field changes caused by magnet rotation and converts them into electrical signals to detect angular displacement. Compared with photoelectric encoders, they have extremely strong environmental adaptability, insensitive to dust, oil, humidity and vibration, with low power consumption, low cost, high reliability and long service life.
Their disadvantage is slightly lower absolute precision (20-60 arcseconds) than photoelectric types under the same resolution, but sufficient for most general industrial applications. They are sensitive to strong external magnetic fields, which can be solved by adding a magnetic shield. They support single-turn 17/23 bit, multi-turn 16 bit resolution, adopt RS485 NRZ protocol, with outer diameters of 35, 46, 48, 50 mm, compatible with 40, 60, 80, 110 mm servo motors. Applications include AGVs, logistics robots, new energy vehicles, logistics equipment and harsh-environment automation.
2.4 Separated Magnetic Encoder
Separated magnetic encoders have a split structure similar to separated photoelectric types, with a non-contact gap between the magnet rotor and sensor stator, no mechanical contact or wear, and high reliability. Working on magnetic sensing technology, the split structure gives them ultra-high speed resistance, ultra-long service life, easy installation and strong anti-pollution ability, suitable for harsh environments with dust, oil and vibration.
They also have small dimension, compact structure and high cost-performance, suitable for large-scale industrial applications with moderate precision requirements. They support single-turn 17/23 bit, multi-turn 16 bit resolution, with outer diameters of 35, 46, 47, 48, 50, 56 mm, compatible with 40, 60, 80, 110 mm servo motors. Typical applications include logistics servo, textile machinery, winding machines, packaging equipment, pumps, fans and low-voltage servo drives.
2.5 Opto-Magnetic Hybrid Servo Motor Encoder
Opto-magnetic hybrid encoders integrate the advantages of photoelectric and magnetic technologies, using photoelectric sensing for high-precision single-turn absolute position and magnetic induction for multi-turn counting, complementing each other. They have ultra-high precision (single-turn up to 10 arcseconds), strong robustness (shock-proof, dust-proof, oil-proof), small size (outer diameter 35-56 mm), high reliability (no battery backup for multi-turn, maintenance-free), solving the contradiction between precision and environmental resistance.
Due to excellent comprehensive performance, they are widely used in high-end industrial fields, such as collaborative robots, surgical robots, aerospace actuators, high-end CNC and precision measuring instruments, becoming core components of high-end servo systems.
3. Summary of Article 1
The five types of servo encoders each have unique technical characteristics and application boundaries: integrated photoelectric encoders for high-precision clean environments; separated photoelectric encoders for high-speed and vibration scenarios; integrated magnetic encoders for harsh environments with high cost-performance; separated magnetic encoders for large-scale harsh-environment applications; opto-magnetic hybrid encoders for high-end equipment requiring both precision and robustness. All have high precision and small size, compatible with 40, 60, 80, 110 mm servo motors through 35, 46, 47, 48, 50, 56 mm outer diameters. The next article will focus on key parameters, communication protocols and applications to provide a comprehensive selection guide.
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