Help with BiSS encoders and Galil controller

[Jesse Hopkins via Tech-talk <tech-talk at aps.anl.gov>]

Hi folks,

 

I have several motors with BiSS encoders (RL26BVE050D15V from Renishaw) that I would like to use with a Galil 4183 motor controller. The Galil controller is configured for absolute encoders with the -SER option for axes 1-8.

 

I’m using EPICS base 7.0.8, motor 7.3.1, and GALIL 4.0.02.

 

I’ve attempted to configure the motor and encoder appropriately. I’ve attached a screenshot of the various configuration screens. When I move the motor with the ‘Use Encoder’ option set to No, everything seems to work fine. The motor moves and the encoder counts change by roughly the expected amount. For example, I move the motor a nominal 0.4 mm, which is a full turn, and the encoder increments by 8008 counts, with the 50 nm per count resolution that is a total motion or 0.4004 mm. The nominal resolution is 0.5 um per step with the present microstepping settings, so this is an expected/acceptable level of accuracy.

 

However, if I turn on the Use Encoder setting, the motor moves in the wrong direction. So, for example, if I try to move the motor positive the motor moves negative as indicated by the encoder readback. If I try to move the motor negative the motor moves positive as indicated by the readback. This persists whether I set the calibration direction as Positive or Negative. In practical terms, this results in the motor getting stalled out with a controller message “Encoder stall stop motor C” unless the duration of the move is less than the encoder stall time.

 

As a side note, I encountered similar behavior when setting up quadrature encoders for different motors, but was able to fix the issue by changing from normal quadrature to reverse quadrature, which flipped the direction of the encoder count relative to the motor. However, there doesn’t seem to be any such option for the BISS inputs. So I’m currently wondering if this is related to these motors being configured as Rev HA Stepper, and the encoder counts coming in in the opposite direction of the expected motor motion and the GALIL driver not accounting for that.

 

Another possible concern, if I turn on the BiSS status poll the timeout, crc, warn, and error in the BiSS status all stay red/high, so maybe there’s an issue there? However, since I’m getting the right number of encoder counts with a given motion it feels like maybe this is an error on the driver side? Also, if I send the command MG _SSC0 to the controller I get a return value of 0.000, which would indicate no errors, so it seems likely the BiSS status display isn’t correct.

 

I did double check and SSC=? and SY? return the expected values (1,27,0,0,9 and 0 respectively), so it seems like the control settings and level are set correctly on the controller side.

 

Any advice/help would be greatly appreciated.

 

All the best.

- Jesse

 

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Jesse Hopkins, PhD (he/him)
Director, BioCAT

Sector 18, Advanced Photon Source

Research Associate Professor, Illinois Tech

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