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Controlling servo with a set current
ED4
Member
10-22-2014 04:21 PM
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I have a servo motor hooked up to a UMI-7772 interface and an AKD servo drive. I need to set the motor at a specific torque while logging values from the motor's encoder. An outside force will be applied to the motor while it maintains its set force. It seems the easiest way to do this would just be to send a user-defined current to the motor. Is there a way to do this in labview? Setting a voltage is easy enough with the Load DAC VI, but I haven't found a way to specify a current value. If this isn't possible, what's the easiest way to set a constant torque? To be clear, I do not have a torque sensor in the system, so the torque control examples provided by national instruments don't do me any good.
Any input on the matter would be greatly appreciated.
Karl-G
NI Employee (retired)
10-23-2014 02:30 PM
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Commanding a constant torque setting used to require custom access to the AKD drive, but as of LabVIEW and SoftMotion 2013 SP1 there is a direct axis property to control the drive in torque mode. I have copied links to a KB describing to properties, as well as the LabVIEW help for the torque setpoint. You should be able to set a constant torque through this property, and the drive will close the necessary loops until a torque of 0 is commanded.
http://zone.ni.com/reference/en-XX/help/371093T-01/nimclvfb/mwrite.torquesetpoint_00a20009/
http://digital.ni.com/public.nsf/allkb/5EF2E51A9724674B86257D3C007E773B?OpenDocument
10-24-2014 01:13 PM - edited 10-24-2014 01:27 PM
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This seems to be exactly what I'm looking for. Thanks, Karl.
EDIT: Ah, I failed to read that this was for Softmotion only. I do not have access to that module, unfortunately. I'm only able to use the functions in the normal NI-motion package. Is there some kind of workaround, or am I out of luck?
Karl-G
NI Employee (retired)
10-27-2014 09:35 AM
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Sorry about that first link. I totally forgot to factor in the fact you are using NI-Motion and the 7772. The AKD's actual operation mode is torque control mode when using the analog connections to the 7772, so it may still be possible to command a constant torque using analog feedback. I'm not sure if this is doable for the AKD, but the NI-Motion manual does mention torque control moves.
