Encoder Types

Encoders are the “eyes” of industrial automation and precision motion control systems, converting mechanical movement into electrical signals with pinpoint accuracy. Depending on application requirements and implementation technology, encoders can be classified by output signal type, measurement form, and detection principle. Below is a professional, detailed breakdown.

I. Classification by Output Signal Type

1. Incremental Encoder

• Principle of Operation: Generates quadrature A/B pulses via optical or magnetic sensing, plus a single Z pulse for zero reference.
• Key Specifications:
  • Resolution: Typically 500–10 000 PPR; interpolation (4×, 16×) can boost this into the tens of thousands or millions of PPR.
  • Signal Quality: Phase error < 5°, jitter < ±1 LSB.
• Output Standards: TTL (0–5 V), HTL (10–30 V), RS‑422 differential.
• Pros & Cons:
  • Pros: Low cost, fast response—ideal for closed‑loop speed/position control.
  • Cons: Loses position on power loss; requires external counter and homing routine.
• Typical Applications: Servo drives, motor speed feedback, reciprocating‑motion monitoring.

2. Absolute Encoder

• Principle of Operation: Assigns each position a unique binary or Gray code, allowing immediate absolute position readout without homing; multi‑turn versions use gears or electronic counters.
• Key Specifications:
  • Single‑turn Resolution: 8–20 bit; Multi‑turn Range: 16–32 bit.
  • Code Formats: Gray, Binary, BCD, Excess‑3, etc.
• Interface Types: SSI, BiSS‑C, EnDat 2.2 (synchronous), CANopen, Profinet (networked).
• Pros & Cons:
  • Pros: Retains position on power loss; suited for high‑reliability multi‑axis systems; supports online parameterization.
  • Cons: Higher cost; serial interfaces demand high‑bandwidth controllers.
• Typical Applications: Robot joints, multi‑axis CNC machines, safety‑critical systems.

3. Hybrid Encoder

• Definition: Combines incremental and absolute outputs in one device, delivering both high‑speed pulses and absolute position data.
• Features: Provides redundant feedback for safety‑critical applications.
• Typical Applications: SIL‑rated safety systems, aerospace parachute monitoring, AGVs in smart logistics.

II. Classification by Measurement Form

1. Rotary Encoder

• Construction: Solid, hollow or semi‑hollow shaft; flange or panel mount.
• Mechanical Specs: Shaft diameter φ3–φ20 mm; radial load 10–50 N; axial load 5–20 N; bearing life L₁₀ ≥ 10⁷ h.
• Installation Tips: Maintain concentricity < 0.05 mm; avoid side loads and high vibration.
• Examples: Servo motor feedback, rotary table control, valve positioning.

2. Linear Encoder

• Types: Optical scale, magnetic scale, capacitive scale; keep 0.1–1 mm gap between read head and scale.
• Accuracy: Resolution 0.01–1 µm; linearity error < ±1 µm/m.
• Environment: Optical requires dust‑free conditions; magnetic works in oil and dust.
• Examples: CNC machine slides, CMM arms, semiconductor lithography stages.

3. Draw‑Wire Encoder

• Construction: Steel cable on a spring‑loaded spool; measurement range up to several meters.
• Accuracy: Resolution 0.1 mm; repeatability < ±0.5 mm.
• Use Cases: Lift height measurement, roller shutter position detection, tunnel profiling.
• Installation Advice: Keep cable vertical and taut; avoid side pull and bending.

III. Classification by Detection Principle

1. Optical Encoder

• Detection Method: Light source → code disc → photodetector; pulses generated by light transmission/reflection changes.
• Resolution Advantage: Up to millions of PPR; jitter < ±0.1 arcsec.
• Drawbacks: Sensitive to dust, oil and temperature variations.
• Standard: ISO 23125 for optical encoders.

2. Magnetic Encoder

• Detection Method: Hall effect or magnetoresistive sensors detect magnetic field changes.
• Reliability: Resistant to contamination, vibration and thermal drift; typical accuracy 0.1–0.5°.
• Applications: Elevator cabin positioning, heavy‑duty machinery angle monitoring.
• Standard: DIN 32701 for magnetic encoders.

3. Capacitive Encoder

• Detection Method: Changes in capacitance between plates with displacement, measured via AC excitation.
• Characteristics: Low power, compact, vibration‑resistant; accuracy up to ±1 µm.
• Drawbacks: Sensitive to metallic environments and static electricity.
• Applications: Micro‑robots, medical robotic arms, micro/nano‑motion platforms.

4. Inductive Encoder

• Detection Method: Changes in inductive coupling between coil and metal target measure distance.
• Advantages: High temperature, high pressure and EMI resistance.
• Accuracy: Typically ±10 µm; suited for heavy industry and rail applications.
• Standard: IEC 62130 for inductive position sensors.

IV. Selection Recommendations

1. Define Requirements: Motion type (rotary/linear), signal type (incremental/absolute).
2. Match Accuracy & Speed: High resolution demands sufficient controller bandwidth and interpolation capability.
3. Consider Environment: Optical for cleanrooms; magnetic/inductive for harsh conditions.
4. Mechanical Reliability: Check bearing loads, lifespan and proper alignment.
5. Interface Compatibility: Ensure protocol and interface support for system integration and diagnostics.

By applying these three classification dimensions and performance comparisons, you can quickly identify the ideal encoder type to optimize equipment performance and minimize development and maintenance costs.