Experimental Physics and
Industrial Control System

Hi

 

I am trying to implement a simple kinematics system for a standard slit motion, where we have the kinematics equation as:

 

Gap = A + B

Center = (A – B)/2

 

I used the motor record’s soft motor implementation which has an example here. The actual motor controller is Galil DMC based on the Galil EPICS driver, the kinematics is working fine but there might be some kind of a bug in the RBV value of the soft motors. If you were to move any motor whether actual or soft, the transform record starts calculating and updates the soft motor RBV accordingly, but the soft motor stops before reaching the actual calculated position due to the fact that the DINP field receives 1 if both motors are done moving (DMOV = 1). For example it is supposed to reach 5 mm but it reaches to 4.97 for example. The error might not be that much but it gets accumulated in each motion. I tried to investigate more and I found the following:

·         Removing the DINP link value “fixes” the behavior? I am not sure if it is fixed or not but the soft motors reach their corresponding values.

·         I remembered that we are configuring our Galil controllers on a 8 ms update rate. I set the update rate to slower values and the issue can be resolved.

·         I looked into the soft motor record’s source code and I noticed that the DINP value is mapped into 3 values: SOFTMOVE = 0, HARDMOVE = 1 and DONE = 2. I am not sure exactly what those mean, but I tried setting these values to the DINP field but it did not work, it seems there is a certain logic happening inside the record that behaves differently on each value.

 

This issue can problematic because the error in the position can be accumulated with each motion, also I am not sure how the SSCAN module will behave in this case. Any insight is really appreciated.

 

Best Regards,

 

Abdalla Al-Dalleh

Control Engineer

SESAME (Synchrotron-light for Experimental Science and Applications in the Middle East)
P.O. Box 7, Allan 19252, Jordan
Tel: +96253511348 , ext. 265

Fax: +96253511423

abdalla.ahmad at sesame.org.jo

www.sesame.org.jo