if i use 'analog input' as the primary feedback, is the PID in MAX still in effect?

[langtian]

1,if i use 'analog input' as the primary feedback, is the PID in MAX still in effect?

2,if i programme the PID using labview by myself, how do if know the sampling time corresponding to 250*10^-6s appear in the node.

how many times does it take one loop in the while loop?if i use "waits until next..." to decide the time, what's the min time?

waiting for your suggestions! Thanks a lot!!

[Jochen]

Please provide more specific information. What do you try to accomplish? What hardware are you using? What are your driver versions?

It looks like you mix up several things here. If you are using a motion control board you can't run the PID loop in LabVIEW. If you want to do software based motion control this is also possible with LabVIEW but you will have to use other hardware platforms than a motion control board. 

Regards,

Jochen Klier
National Instruments Germany

P. S.: the PID loop on a motion control board like the PCI-7344 runs also with analog feedback

[langtian]

Thanks for your help first.

I am using a 7344 (MAX 3.1.1,ni motion 7.0)to control 3 voice coil actuators.The drive is just a PWM style amplifier.

you have tell me the answer of the first one.The key is the second one. Now I am debuging the 2-D table.

In MAX there are PID settings I counld use.However I think it is not enough. For example, I wound like to convert PD to PID when the motors are running to get less setting time and quicker reponse time.

So I plan to come true it using read encoder ,DAC output, and the like.

I have done some programmes. Today I have debugged them on my table. I failed  to finish it.

"this is also possible with LabVIEW but you will have to use other hardware platforms than a motion control board."

I thought if ni can programme the MAX ,why I can't programme it using labview on the basis of  7344.

Maybe this thought is facetiosity, please tell me why. I really hope your suggestion.Thank you very much.

The programme and the result are given as follow

帖子被langtian在03-22-2006 08:42 AM时编辑过了

[Jochen]

There are multiple reasons why your software PID control approach won't work:

1. When you exchange data between the 7344 and the PC the maximum update rate will be 5 ms. This is typically too slow for a motion control application.
2. Even if 5 ms update rate was enough this rate can't be synchronized with your loop in LabVIEW. This will result in a high amount of jitter and you won't be able to get a stable control system.
3. If you try to run the control loop under Windows you also won't get a stable system behavior as Windows is not a real-time operating system.

The simplest system setup for a software based motion control system contains these components:

• LabVIEW Real-Time
• LabVIEW Real-Time target (e. g. PXI controller)
• Multifunction DAQ device (e. g. PXI-6221)

Please read the information about the NI SoftMotion Development Module that I have linked to my first reply. This document should give you a good idea  how to proceed.

Jochen Klier
National Instruments Germany

[langtian]

hi,jochen.
I have read all the links you have provided,but I also have some uncertainty.Please help me to make sure it.
1, I have one 7344,It can't be used in the real-time module,right? Its best performance such as setting time,reponse time,and orientation accuracy should be got if I make the parameter of MAX suitable enough.No other way to improve its performance if I don't add (or change ) some hardware and software.

2,   a,  LabVIEW Real-Time
      b,  LabVIEW Real-Time target (e. g. PXI controller)
      c,  Multifunction DAQ device (e. g. PXI-6221)
I am not sure the relationship between b and c.  I guessed Multifunction DAQ device could be used as the device receiving the feedback from the encoder or analog input,right? you don't list the softmotion module? is it a optional?

3,If I would like to ignore the cost of the XYZ table,The best performance  shoule be got through Labview Real-time, R series reconfigurable I/O,NI softmotion module, right?

Thanks for your answer again

帖子被langtian在03-22-2006 09:40 PM时编辑过了

[Jochen]

Langtian,

1. The 7344 runs the PID loop onboard so there is no real added value if you run this board under LabVIEW real-time. Still this is possible to allow users to integrate these boards with other components into a real-time environment. The PID algorithm on the 7344 and it's performance are well suited for a wide range of motion control applications. 
   
   
2. The DAQ device is the I/O board but you need a CPU to do your calculations. A PXI controller is a modular PC that can run your application under LabVIEW RT.
   Of course you can program the trajectory generation the spline and PID algorithms and so on by your own but these features are already implemented in Softmotion.
   
   
3. An R-Series board provides extremely high control loop rates so yes, this configuration yields the highest performance. Please note that high speed PID loop rates don't result necessarily in an especially good system behavior. E. g. if your feedback signal changes slower than your PID loop rate (at slow moves) the system won't behave very stable.

In general as long as you don't have very special needs like feedback signals that can't be used with a 7344 or extremly high performance requirements the 7344 will do the job.

Jochen