Absolute Position for Incremental Systems

In linear motion applications, it is often desirable to eliminate the need to make a homing run to re-acquire the reference position for an incremental linear encoder. The homing routine may need to be eliminated to save processing time, or it may not be practical…for example, if the machine can’t be moved following a loss of power due to some mechanical consideration. Additionally, to reduce costs and simplify system design, it would also be helpful to eliminate the need for home and limit switches.

Absolute linear encoders offer an upgrade path, however they also require changes on the controller side to more costly and difficult-to-implement serial interfaces like Biss C, EnDat®, SSI, and others.  These obstacles have limited the use of absolute encoders in the majority of linear motion applications.

Recently, an innovative encoder interface called Absolute Quadrature brings absolute encoder functionality to systems with controllers designed to accept a simple and commonly used A-B quadrature incremental interface.

This demonstration video from In-Position Technologies highlights the functionality and advantages of upgrading incremental positioning systems with an Absolute Quadrature encoder.

To learn more about our Absolute Quadrature encoder, visit www.balluff.com.

2 Replies to “Absolute Position for Incremental Systems”

  1. Henry Menke says:

    Thank you and thanks for your questions. I can’t comment authoritatively about interfacing to specific servo controllers, but I can tell you more about the operation of this new encoder technology. In the default operating mode, upon power-up the stationary encoder head reads its absolute position from the magnetic tape. It then delivers a Z-pulse to the high-speed counter to reset the count back to the reference or home position value. Then the encoder delivers a burst of A-B quadrature pulses to the high-speed counter input. The counter sees the burst of pulses as ordinary position counts, as if the encoder was physically moving. When the burst is completed, the counter has re-acquired the absolute position. A simple way to implement this functionality is to power the encoder through a controller output, so that power can be interrupted and re-applied to the encoder once it has been confirmed that the controller is awake and ready to receive position inputs.

    A second way to acquire absolute position is through the burst request function. A 5V differential input on the encoder is used to trigger a Z pulse followed by a burst of A-B quadrature pulses corresponding to the absolute position of the encoder.

    More information is available here: http://www.balluff.com/local/us/news/product-news/bml-absolute-quadrature/

  2. controlsgirl says:

    Great summary of the old and new technology. How much manual configuration needs to be done in the servo controllers to set this up? We could use Siemens CU320 for example. Would it already know to treat it as an absolute encoder or is it going to fault by default upon startup if the drive is not homed?

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