Absolute encoder

Absolute encoders share the same core assembly as incremental models, comprising five key components: optical code disk, light source, lens, photodetector and signal conversion circuit. Their differences lie in code disk layout and signal definition.

An absolute encoder’s code disk features multiple concentric grating tracks (code channels), each with slits of distinct quantity and length. Each track corresponds to one binary data bit; the outermost track represents the least significant bit (LSB), while the innermost stands for the most significant bit (MSB). N code channels deliver N-bit binary codes, supporting 2ᴺ unique position values. Every mechanical shaft angle maps to an exclusive fixed binary code independent of external counting. Unlike incremental encoders, absolute encoders retain valid position readings after power cycling and require no homing routine.

Operating Principle

At each rotational angle, photodetectors generate distinct electrical levels based on light transmission through the gratings, which are processed into unique binary position codes for direct output.

Absolute encoders fall into two categories: single-turn and multi-turn.Single-turn variants only deliver unique codes within a 360° rotation; position codes repeat once rotation exceeds one full circle, failing full-range absolute positioning requirements. Multi-turn absolute encoders solve this limitation with extended measuring ranges far beyond 360°, despite more intricate internal mechanics, while retaining the same fundamental encoding logic.

Multi-turn encoders adopt a clock-style gear transmission mechanism. The primary code disk drives auxiliary code disks via gear trains. On top of single-turn angular encoding, extra tracks record total rotation turns to extend the measurable range. All positions carry non-repeating mechanically encoded values without external memory.

An additional merit of multi-turn absolute encoders is ample redundant measuring range. Operators may set any intermediate position as the origin during installation, eliminating tedious zero-point alignment and drastically simplifying setup and commissioning.