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Quasi-Absolute Encoders Homing Procedure

Requesting AKD implementation for Quasi-absolute encoders:

Quasi-absolute or distance-coded encoders are available from several manufacturers and incorporate high resolution incremental encoder track and a low resolution absolute encoder track that wires to the index pulse channel.  These are used to minimize homing motion on startup and work well in cost sensitive applications, long travel situations, or in some high speed applications where an absolute encoder has limited data transmission speed.

The distance coded marks have unique spacing between meaning traveling past 3 indexes in a constant direction can allow absolute position value to be known (from table lookup) or moving to two indexes in known direction can provide absolute position.

This can prevent driving all the way to the end in a long linear application or minimize angle traveled in rotary (this is advantageous for homing large load with changing moment of inertia/changing tuning gains)

See attached documentation from Renishaw regarding DCRM and position algorithm





mechatron's picture
Interesting. It seems like a homing mode would be needed on startup to pass several marks and then make the determination of starting position based on the table. At that point, the controller/drive keeps track of absolute position, so essentially this would be a type of homing mode, but normal operation would be like any other encoder.