Motion control with labview

[Ycano]

Hello, everyone.

I'm working on the force feedback control with labview.

Two stepper motors are controlled by force feedback of Load cells (target force input by operator).

In terms of control the system,

can I use "velocity control" to control stepper motor?

    - I've tried that stepper motors have linear motion to get target force.

      But, I programmed it with repeatation of move&stop motion. 

      Two motors check the target force from load cell after every short movement.

     The problem is that the delay of signal responses caused with the contol loop.

Could you show me any idea for my force feedback control? 

[VGA_CD-ROM]

Hi Ycano,
Yes, you can operate your motor in velocity mode by using the Set Operation Mode VI to change it from position mode to velocity.

As for your control feedback loop, are you bringing in the feedback from the load cell via a separate DAQ card? If the load cell outputs a voltage in the +/- 10V range (if it's not a current transducer or doesn't require an excitation voltage), you could connect it straight to the analog input on your motion controller and directly implement it in your control loop for your motion controller. That feedback could then be operated upon at a faster rate than if you brought it in separately from a DAQ card (a closed loop stepper system).

Also keep in mind that load cells generally have a slow update rate, so they may be the limiting factor in how fast your system can respond to changes.

[2photonGuy]

how do i change operation mode from relative to velocity during runtime.

I need to switch between the 2 modes during the experiment.

[VGA_CD-ROM]

As I mentioned above, the Set Operation Mode VI, found in your NI-Motion » Trajectory palette, can be used to change the operation mode fo the motion controller. See the detailed help on the VI for more information. Note that you should only set a new operation mode when you intitialize the controller or when all current moves have been completed and trajectory generation is done. You shouldn't set a new operation while a move is in progress, or you could get unpredictable behavior.

[2photonGuy]

I have two sets of code for the same axis
one runs in position control the other in velocity control

now i need to combine both the codes so that during experiment i could switch between the 2 modes. This requirement is necessary for my operation.

Thanks

[VGA_CD-ROM]

The best way to do it essentially on the fly would be through a set of case structures all tied to the same boolean control or enum control. This way all the velocity-specific code will run together or all the position-specific code will run together but not both at the same time. You shouldn't need to have any special extra cases to handle switching between modes since if you are already in position mode and you tell it to go to position mode again, nothing bad will happen in your program (especially since your code needs to always wait until a move completes before switching modes).