Glossary · Sensors and measurement
Resolver
Also known as: Rotary resolver
German: Resolver
In motion control, a resolver is an electromagnetic rotary position sensor that works like a rotating transformer: an excited rotor winding induces sine and cosine signals in two stator windings, from which the evaluation electronics compute the absolute angle within one revolution.
- Sensors
In one sentence
A resolver is a robust electromagnetic rotary sensor that outputs sine and cosine signals for the absolute angle within one revolution.
Example
Servo motors in a hot, vibrating forming press use resolvers for rotor position feedback because optical encoders would not last.
How it applies
- Engineering: Resolvers contain no electronics or optics in the sensor, so they tolerate high temperatures, shock and vibration. Resolution and accuracy are generally lower than with high-end optical encoders, and a resolver-to-digital converter is needed in the drive.
- Commissioning: The resolver offset relative to the motor's magnetic poles must be correct for servo motors; drives usually determine it automatically or it is set at the factory.
- Maintenance: Replacing a resolver or motor may require re-determining the commutation offset. Follow the drive manufacturer's procedure.
- Documentation: State the feedback type for each axis in the drive configuration documentation and describe the steps after replacement.
Resolver vs. absolute encoder
Both give the absolute angle within one revolution. A resolver provides analog signals and is very robust; an Absolute encoder provides a digital position, usually with higher resolution and optionally multi-turn information.