Is it possible to use software limits on 7354 board when switching control modes from open to closed or closed to open loop?

[Windserver]

Is it possible to use software limits on 7354 board when switching control modes from open to closed or closed to open loop?

[Vivek_N]

You can set software limits for both open loop and closed loop moves. I am not sure if this answers your question - please elaborate on what you are trying to do if you need more information.

[Windserver]

Thank you Vivek,

I am controlling a butterfly valve driven by a servo motor.  In open loop, I am seeking home (closing the valve).  In closed loop I am controlling pressure in a vessel by feeding compressed air through the butterfly and monitoring an analog pressure transducer.

I must not open the valve less than 90 degrees  so that failure would allow the air flow to close the valve.  I must not overdrive the valve into its seat and  fault the driver by exceeding current limits or damage the disc seal.

During operation the loop is switched from open loop to closed loop to open loop and the PID parameters are switched from primary to secondary.  I do not want to lose my software limits in this switching.

Hope that clarifies the task.

Richard

[Vivek_N]

Hello Richard,

Thanks for explaining your application. I'll have to check how to preserve software limits when switching between open loop and closed loop. Are you actually using the software limits in closed loop mode as well? 

I will let you know what I find out. 

[Vivek_N]

Hello Richard,

When you say 'open loop' and 'closed loop', are you referring to running the application in position and torque mode? If not, how exactly are your controlling a servo motor in open loop? 

In closed loop mode, the encoder values will be used as reference and the motion VIs can be used to configure the software limit as required. Are you currently losing the software limits? If so, how exactly are you losing these values? I am not sure I understood what exactly is happening with software limits in your program, so any more information on this would be useful. 

[Windserver]

Vivek,

As I said previously, the open loop usage is in fact position based and I have a proximity switch that I am using to mark Home so that the valve may be closed without overdriving the seat.

In the closed loop mode I am using torque control to regulate to a pressure monitored on the ADC input.  I must, however, limit the valve to an opening of less than 90 degrees (position) in order to protect from power loss, overcurrent fault, etc.

I guess my question is better stated by asking - When operating in closed loop configuration with feedback from the ADC, can I still read the encoder so as to limit the position of the valve?

Richard   

[Vivek_N]

Hello Robert,

I will post on this thread later today with what I find out. 

[Vivek_N]

Hello Richard,

It looks like you may have trouble using the encoder values to set software limits when running in torque mode, but the only way for me to verify this would be by testing it out. I am going to set up a test system to find this out. In the meantime, has it been possible for you to try this out as well? If so, how did you set your program up and what did you observe? 

[Windserver]

Vivek,

In short, the system seemed to disregard the software limit and run the butterfly open to it's physical limit (possibly resulting in damage) then trip the driver out on over-current.

Richard