Measure
Encoder
You might say: joint angle sensor
An encoder reports shaft angle or position from pulses or an absolute coded scale. It may be mounted on the motor side or directly on the joint output.
- What it does
- It closes the position and velocity feedback path for a joint.
- Ask
- What resolution, latency and accuracy are available at the load after gearing and backlash?
- Typical
- Renishaw RESOLUTE angle encoders offer absolute position immediately at switch-on and high-resolution rotary versions; Blue used a 14-bit absolute magnetic encoder.
- Trouble
- Low resolution produces quantization and velocity noise; a motor-side encoder cannot see gearbox backlash or elastic error at the load.
What to look for
- Phase-shifted pulses or coded angle
- Shaft or joint-output position reading
- Reference needed after incremental startup
Catalogue: Encoder
- Incremental: An incremental encoder emits phase-shifted pulses; the controller counts edges and normally needs a known reference after startup.
- Absolute: An absolute encoder reports a coded angle immediately at switch-on; Renishaw RESOLUTE needs no battery backup.
Sources
- Kevin M. Lynch and Frank C. Park, Modern Robotics: Mechanics, Planning, and Control, Ch. 1, sensors
For both revolute and prismatic joints, encoders, potentiometers, or resolvers measure the displacement and sometimes tachometers are used to measure velocity.
- Renishaw, RESOLUTE absolute optical encoder system, pp. 1–2 and 8, system features
Patented RESOLUTE encoder technology combines 1 nm resolution with exceptionally high speed, reading from a range of high-accuracy linear tape and spar scales or angle encoder rings.
- David V. Gealy et al., Quasi-Direct Drive for Low-Cost Compliant Robotic Manipulation, p. 4, 14-bit absolute magnetic encoder
14-bit absolute on-axis magnetic encoding for motor commutation and robot position sensing
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