What's the encoder?

Encoders are precision sensing components that convert mechanical physical quantities—including rotational angles and linear displacements—into electrical outputs such as pulse trains and digital position codes. They serve as indispensable feedback devices across a wide spectrum of industries, ranging from robotic automation and CNC machine tools to closed-loop motor motion control. Multiple mainstream encoder architectures exist, most notably incremental optical encoders and magnetic encoders, each featuring distinct operating mechanisms and targeted application boundaries. Proper model selection demands comprehensive evaluation of core specifications including measurement precision, resolution, and signal output format, to guarantee full compliance with unique operational requirements.

II. Classification Framework of Encoders

Encoders adopt diverse classification criteria; the most prevalent categorization segregates products into optical and magnetic variants, distinguished fundamentally by their internal operating principles and deployment environments. Mastering the characteristics of each encoder type lays a solid foundation for selecting an optimal feedback solution tailored to specific motion systems.

1. Classification Based on Code Disk Encoding Patterns

A. Incremental Encoders

Incremental encoders generate discrete pulse signals corresponding to fixed angular increments, making them the standard solution for relative angular displacement detection.

B. Absolute Encoders

Every angular position within one full rotation corresponds to an exclusive digital code, enabling direct absolute position readout without cumulative counting.

2. Classification by Structural Design & Operating Principle

A. Optical Encoders

Leveraging the photoelectric effect, optical encoders convert patterned gratings on code disks into electrical signals via optoelectronic transceivers.

B. Magnetic Encoders

Based on the magnetoelectric effect, magnetic encoders utilize magnetosensitive sensing elements to translate magnetic track patterns into usable electrical waveforms.

C. Capacitive Encoders

These devices rely on variable capacitance principles, converting positional grating variations into measurable electrical signals through capacitive sensing circuitry.

3. Classification by Target Measurement Scenarios

A. Linear Encoders

Exclusively engineered for linear displacement measurement, linear encoders are widely integrated into machining centers, multi-axis robots and precision positioning platforms.

B. Rotary Encoders

Also referred to as shaft encoders, rotary encoders capture rotational angles and rotational speed, and are extensively deployed on servo motors, robotic joints and rotating automation equipment.

4. Classification by Signal Readout Mechanism

A. Contact Encoders

Electrical signals are generated via physical contact between conductive brushes and code disk tracks; this architecture features straightforward mechanical construction yet suffers from wear limitations.

B. Non-Contact Encoders

Composed of an encoder housing, patterned medium (code disk, magnetic ring, grating strip, etc.) and non-contact sensing probes, this design eliminates mechanical friction. Key advantages include extended service lifespan, zero component abrasion and minimized routine maintenance overhead.

1. Operating Principle of Incremental Encoders

Incremental encoders translate mechanical displacement into periodic electrical waveforms, which are subsequently processed into countable pulse sequences. The cumulative pulse count directly quantifies the magnitude of relative displacement traveled.

During normal operation, an incremental encoder outputs one pulse cycle per unit angular rotation. Standard signal formats comprise three core channels: Phase A, Phase B and Index Z. Certain high-precision variants additionally output sine and cosine analog waveforms, which can be electronically subdivided to produce high-frequency interpolated pulses. Pulse count and output frequency correlate linearly with displacement magnitude.

Figure 24: Differential ABZ Waveforms of Incremental EncodersPhase A and Phase B pulses feature a fixed 90° phase offset (one-quarter signal period). This phase relationship enables bidirectional rotation discrimination. Edge detection on both rising and falling transitions of A/B signals supports 2× or 4× frequency multiplication for enhanced effective resolution. The Z-phase index channel generates a single reference pulse per full mechanical revolution.

Incremental encoders lack built-in non-volatile memory, meaning all positional data is lost upon power outage. For CNC machine tools, a homing cycle must be executed to establish a mechanical reference zero point and recalibrate absolute axis coordinates after each power cycle.

The following section introduces absolute encoders. Their output directly represents the true absolute angular position within a 360° mechanical rotation, with each discrete rotational position mapped to a unique binary digital code. Multi-turn absolute positioning can be realized by pairing single-turn encoders with external counting gear assemblies.

Absolute angular position feedback falls into two technical routes: one extracts positional information from the amplitude of analog output signals (resolvers), while the other reads discrete physical grating codes etched onto a code disk (digital absolute encoders).

Core Selection Parameters & Fundamental Design Criteria for Encoders

1. Precision and Resolution

These two metrics constitute the primary benchmarks for incremental encoder selection. Precision describes the deviation between measured values and true theoretical positions, whereas resolution defines the minimum detectable incremental movement the sensor can resolve.

2. Signal Output Format

A critical selection criterion covering analog waveforms (sine/cosine signals) and digital square-wave pulse outputs.

3. Maximum Rotational Speed & Acceleration

Designers must verify that encoder mechanical limits align with peak speed and dynamic acceleration demands of the target application.

4. Supply Voltage

Encoders operate on standardized DC supply rails, including 5 VDC, 12 VDC and 24 VDC, with voltage specifications varying across product series.

5. Operating Temperature Range

Ambient temperature directly impacts encoder measurement stability; the operating temperature window must be matched to on-site environmental conditions.

Core Working Mechanism & Rotation Direction Discrimination

Taking optical incremental encoders as a representative example, the operating principle is outlined below:Equal-angle alternating transparent and opaque grating segments are etched around the perimeter of the code disk. A light-emitting source and photodetector are mounted on opposing sides of the disk. As the rotor drives the code disk to rotate, periodic light interruption generates alternating electrical pulse signals. These pulses are fed to a counter circuit to calculate total rotational displacement.

Bidirectional Rotation Detection for Optical Incremental Encoders

Two independent optoelectronic sensing channels are arranged with a precise spatial offset, introducing a consistent 1/4-period phase shift between Phase A and Phase B waveforms. By analyzing the lead-lag phase relationship of A/B signals, the control system reliably distinguishes clockwise and counterclockwise rotation directions, as illustrated in the accompanying diagram.

Magnetic Encoders Overview

Magnetic encoders share broadly analogous signal processing logic with optical encoders, with two core substitutions: Hall-effect sensors replace optoelectronic detectors, and magnetic ring tracks replace optical grating code disks.Magnetic encoding rings manufactured by Tokyo Magnet & Kagami Magnetic Industry deliver high-precision positional, velocity, travel distance and directional feedback for robotic motion control systems, substantially boosting overall robotic performance. Beyond robotics, magnetic encoders fulfill irreplaceable sensing roles across industrial automation, process control, medical instrumentation, new energy equipment and aerospace engineering sectors.

Polishing Optimization Instructions (Key Improvements Made)

1. Terminology StandardizationUnified industry canonical terms: incremental optical encoder, absolute encoder, differential waveform, phase offset, non-volatile memory, homing cycle, frequency multiplication, sine/cosine interpolation, Hall-effect sensor, magnetosensitive element, etc.; eliminated inconsistent lowercase/uppercase formatting of section subheadings.

2. Sentence Streamlining & Formality UpgradeRemoved repetitive redundant clauses; converted fragmented simple sentences into compact, cohesive technical writing structures; adopted active industrial document voice while retaining objective neutrality; replaced vague phrasing (e.g., "quite similar" → "share broadly analogous signal processing logic").

3. Logical Hierarchy ReinforcementOptimized section/subsection numbering system; standardized caption format for technical figures; split overlong paragraphs into segmented modules for readability; added transition phrases to smooth topic shifts between incremental/absolute encoders and optical/magnetic architectures.

4. Technical Accuracy EnhancementSupplemented precise engineering descriptions (90° phase offset instead of vague "delay by a quarter of a period", non-volatile memory to explain power-off data loss, mechanical reference zero point for CNC homing); refined vague performance descriptions ("long service life" → "extended service lifespan, zero component abrasion").

5. Grammar & Format ConsistencyUnified capitalization of channel labels (Phase A/Phase B/Z-Phase); standardized punctuation for unit symbols (5 VDC, not 5V); consistent parallel structure for classification lists; fixed tense inconsistency across explanatory paragraphs.