constant load control feedback control

[kingsgambit1943]

Ive been given the task of altering an already exsisting program.   Ive attached the program manual written by the program author.  He based his program on constant displacements for testing.  We now would like to alter it so that we will be using constant loads.  Hence the PZT actuator will be moving only to keep the load constant at specified loads. Ive been reading about feedback control, open loop control, and PID control.  I would just like to know if there are any tips to doing something like this.  I have a simple logic chart drawn out but I understand that feedback control is difficult.  My initial plan was to compare wanted load to actual load then check the magnitude of the difference- then by if possible a displacement to Load ratio - decide to tell the PZT to move that displacement then check again.  with several ranges of displacements chosen by the magnitude calculated earlier; to prevent overshoot.  e.g big difference bigger displacement and as we near the wanted load we move very minimally.   

I have labview 8.5, do I need to purchase the control design and simulation module ? if so is the 8.5 version availible anywhere?   

Any suggestions on how to accomplish this task?

thanks for the input 

[Vivek_N]

It will be a bit of a challenge modifying the current piece of code, but you could definitely use the Control Design and Simulation Module to implement the control algorithm. There is quite a bit of information for me to suggest a specific way of going about this - you would have to choose the feedback signals that suit your application and accordingly choose to send the required control signal.

You would need version 8.5 of the Control Design and Simulation Module to work with LabVIEW 8.5. If you are interested in purchasing it, please call NI Sales at (888) 280-7645. I hope this helps.