Optical Encoder: Working Principle
The optical encoder is the most widespread type in industrial automation. It uses light to detect the angular position of the shaft with very high precision and without physical contact.
Main Components
- Light source (LED): an infrared LED emits a collimated light beam towards the disk. The infrared choice reduces ambient light interference.
- Code disk: a glass or plastic disk with a pattern of opaque and transparent marks. The pattern determines the encoding type (incremental with equidistant lines, absolute with Gray or binary code).
- Photodetectors: photodiodes or phototransistors positioned behind the disk detect light passing through transparent zones. They generate an electrical signal proportional to light intensity.
- Conditioning electronics: an ASIC circuit amplifies the analog photodetector signals, converts them to digital square waves with precise thresholds, and formats them into the desired output (TTL, Line Driver, Push-Pull).
- High resolution: up to 65,536 ppr (16 bits) for single-turn
- No mechanical contact: no wear, virtually unlimited life
- Excellent linearity: error < ±0.01° on precision encoders
- High frequency response: up to 300 kHz
- Sensitivity to contamination (dust on the disk)
- Limited temperature range compared to magnetic
- Greater construction complexity
The Reading Process
When the shaft rotates, the disk rotates with it. Opaque zones block light, transparent zones let it pass. Photodetectors generate a sinusoidal signal that is converted to digital pulses. Two sensors with 90° phase shift (quadrature) allow determining the rotation direction.
Advantages of Optical Technology
Limitations
Ideal Applications
CNC machine tools, robots, precision measuring instruments, vision systems, motorized cameras, satellite dishes.
