Motion Control using Stepper Motors: cRIO vs. PCI/PXI

[Jack_W]

Hello everyone.

Firstly I want to introduce my problem for which I am looking for a solution:

I want to control 2 separate stepper motors, both with encoder feedback in a closed loop system.

Additionally, I need to be able to measure analog voltage signals (4-6 total) and 2 rotational frequencies from a generator's encoder (ttl signal).

I solved similar tasks using DAQ devices, but as I want to expand the project, I thought about different solutions.

After gathering some information, the question is rather to use compactRIO systems or PCI/PXI.

I am not very familiar with applications in compactRIO. However, I find the motion control using PXI very handy.

Any thoughts about the best/most handy way to solve the issue is highly appreciated.

Cheers,
J W

[MoviJOHN]

With cRIO, you can use SoftMotion.  This will require two pieces of hardware.  The first is a module on the cRIO, and the other is a stepper driver.  I've only seen this configuration used with servos, but I'm sure it works with steppers also.

Recently, I worked on a system using steppers, encoders, and an NI motion controller.  Trying to run the steppers in closed loop did not behave in the same way as a stepper.  Instead, the stepper moved its commanded counts, and then at the end of the move, there was a noticeable correction move.  Removing the closed loop requirement, and setting proper ramp and speed values, I was able to move the stepper precisely, and then use the encoder for verification.

The moral of the story:  If you want closed loop control during the move profile, go with servos.

[J_Priya]

Hi,

I have a similar dilemma between cRIO Vs PCI/PXI. I am working on a project on simultaneous motion control of 6 axes in real time. I am using 6 DC servos for this. I have gone through the NI 7350 PXI controller and it looked suitable for my application. Recently only I came across cRIO. I am new to this and not sure how it'll work. Which system will be more effecient and apt for my application - cRIO or PXI. Any suggestions would be deeply appreciated.

J_Priya

[MoviJOHN]

You know the saying "There's more than one way to skin a cat"?  It applies to motion very much so.

You should start with a budget in mind, and performance requirements, of course.

If you need to control 6 axes simultaneously, the cRIO and SoftMotion may not be the best fit.  PXI chassis, and a couple of 4 axis controllers will do the job nicely, but the price will be high, especially if you are using servos/encoders.

The middle of the road solution would be to use steppers, without feedback encoders if you can get away with it.

It all depends.

[J_Priya]

Thanks for the reply. I already have  DC motors and encoders. I think I'll go with PXI motion controller itself.