Interfacing a piezioelectric actuator with Labview

[biomems]

im looking at controlling a Melles Griot piezoelectirc actuator with Labview to obtain real time data of voltage vs displacement. However, i do not know how to write the program for a closed loop function block. Ie, i need to ask the actuator to move a distance by applying a suitable voltage when there is resistance to motion.

[Jochen]

Unless you are using LabVIEW RT on a PXI system it's not a good idea to do control loops in LabVIEW or any other Windows based software. On Windows the timing behavior is not deterministic. That means the loop cycle time varies. The loop cycle time directly influences the control algorithm. The faster a PID loop runs, the lower your Kp, Kd, Ki values need to be. Thus on a system like Windows without deterministic timing it's hard or even impossible to get a stable system.

A much better choice is the use of a motion control board, e. g. the PCI-7344 or PCI-7342 board. These devices run the PID loop onboard in realtime and you only need to set parameters like travel distance, speed and acceleration. You can use quadrature encoders or analog signals as feedback signals and
with the latest release of the driver software, NI-Motion 6.0 there is also an assistant included that helps you to eliminate the effects caused by static friction that are immanent to piezo systems.

Please visit the following link to get more information:

http://www.ni.com/motion

Best regards,

Jochen Klier
Applications Engineering Group Leader
National Instruments GERmany GMbH

[algames]

I agree with Jochen. There is, however, another alternative. You could use the NI-Motion controllers and drivers to do the motion control interface from LabVIEW to your piezo actuator. All you need to do is connect the servo output for the 734x or 735x controller to the piezomotor command aomplifier and user the encoder or analog feedback from you actuator to close the PID loop for position control that you have. The NI-Motion controllers also implement static friction compensation that allows you to tune the PID loop on the controller to compensate for the resistance intrinsecal to piezo motors and actuators.