Experimental Physics and
Industrial Control System

"Pearson, Matthew R." <[email protected]> · Wed, 16 Sep 2015 18:51:39 +0000

Hi,

I've had a number of requests recently for a setpoint deadband on the motor record. This seems to be an issue where we use encoder readback, and so the readback is almost never equal to the last demand position. So if there is backlash correction setup, the motor performs a move when it doesn't really need to. At the very least there is a amplifier enable/disable cycle even with no backlash correction.

Do other people have this issue?

It seems to be general enough that it should be a feature of the motor record, or at least the Asyn driver base classes.

I initially thought about re-using the retry deadband field for this, but that may break too many existing systems. So a new field sounds appropriate (say .SPDB).

So the logic would be something like:

If abs(pmr->dval - pmr->drbv) < pmr->spdb:
	return
else:
	continue

with SPDB defaulting to 0.

Cheers,
Matt

Data Acquisition and Control Engineer
Spallation Neutron Source
Oak Ridge National Lab

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System