In brief
A rotary encoder is a sensor that converts the rotation of a shaft into electrical signals for position, angle or speed.
Contents
What is Rotary encoder?
Rotary encoders detect how far and how fast a shaft rotates. They provide controllers and drive controllers with feedback for positioning, synchronisation or speed control, for example on machine tools, conveyor belts or printing machines. A distinction is made between incremental encoders, which output pulses per revolution, and absolute encoders, which assign a unique value to each angular position.
Absolute encoders are available as single-turn for one revolution and as multi-turn, which also counts complete revolutions. Scanning is optical or magnetic. Key ratings are resolution (pulses or steps per revolution), interface (such as TTL, HTL, sine/cosine, SSI or fieldbus), supply voltage, shaft design (solid shaft or hollow shaft), flange type and degree of protection. There are also bearingless encoders and versions for potentially explosive atmospheres. In servo drives, the encoder is often integrated into the motor and matched to the relevant drive controller.
Failures are frequently caused by bearing wear, shaft misalignment, vibration, moisture or damaged cables. A replacement unit must fit both electrically and mechanically; with absolute encoders, the axis often has to be referenced after replacement. A flexible shaft coupling or torque arm prevents shaft misalignment from overloading the bearings.
In practice: maintenance and procurement
For an enquiry, the manufacturer part number, resolution, interface, supply voltage, shaft or hollow shaft diameter, flange type and connector pin assignment are needed. Allow time after the replacement for setting the zero point or reference.
Synonyms and abbreviations: encoder · incremental encoder · absolute encoder · shaft encoder · angle encoder
Frequently asked questions
What is the difference between an incremental encoder and an absolute encoder?
An incremental encoder outputs pulses when it rotates, from which the controller calculates distance and speed. After a power failure, the position is unknown and must be referenced again. An absolute encoder provides a unique value for every position, so the position is known immediately after switching on.
What information is needed to replace a rotary encoder?
Important are the manufacturer part number, encoder type, resolution, output or interface signal, supply voltage, shaft design with diameter, flange or mounting type, connector type and degree of protection. For multi-turn absolute encoders, the number of detectable revolutions also counts. If the nameplate is missing, photos of the mechanics and the connection help.
What does the resolution of a rotary encoder mean?
The resolution indicates how many pulses or measuring steps an encoder delivers per revolution. The higher it is, the more finely position or speed can be detected. When replacing, the resolution must match the parameter settings of the controller or inverter, otherwise distances and speeds will no longer be correct.