Motion Control and Motor Drives

[ifc]

Hi there,

I'm trying to use a PXI-7350 to control a Stewart Platform using two UMI-7774 boards and LabVIEW's Vision & Motion tools. Everything works fine using axes 1-4, but I cannot figure out how to configure axes 5-8 for regular use and reading the documentation has been no help. When I try to make use of axes 5-8 in LabVIEW, I get an error -70006, indicating that the axis is improperly configured. This makes sense, because the axes do no show up in MAX.

The MAX documentation only explains how to add axes to a vector space, and axes 5-8 do not show up on the dropdown menu when I try this in any case. Can anyone explain how to enable these axes for motion control?

OS: Windows XP SP3

MAX version: 4.7.0f4

LabVIEW version: 2010

[Joseph-S]

Hi ifc,

Are you are using the PXI-7358? The 7350 refers to the family of controllers which can either drive 2,4,6 or 8 axes of motion. In MAX, under the "General Tab" of the motion card, how many axes of motion are listed? See the screenshot below. All 735x cards have enough ports to connect to 2 UMI boards, but the 2nd motion port is actually unused in the 7352 and 7354. Please see this document for an explanation.

[ifc]

I generally have the MAX window maximized, so I never even noticed the tabs at the bottom of the page. Yes, it turns out we are using a 7354. Thanks for the help!

[spitz]

Hi IFC, I'm also looking into building a small hexpod using the pci-7358 together with two MID-7654 servo drives. I was wondering if I could ask a few questions...?

- What kind of linear actuators are you using? I've had no luck in finding small actuators with built in optical encoders and limit switches.

- How do you plan to make a move? For a point in space I'm thinking of calculating the necessary motion tragectories for each of the six legs and then using a contour move.

- How do you plan to sync the motion of the 6 legs on the hexapod to avoid binding?

Best

[spitz]

Hi Joseph

You seem quite knowledgeable on the subject of motor control. I called NI tech support about this yesterday and they didn't have an answer. Basically, I have a motor (servo/stepper) undergoing a contour move based on a input trajectory file. I monitor this motor motion using an external IR optical tracking camera and I can read this motor motion back into Labview (this is all up and running already). Now, from the read in real-time feedback motion, I then calculate the necessary motion to cancel out the input motion or zero the motor. Do you know how I can merge/superimpose my calculated cancel motion onto the outgoing motion stream from the input trajectory file...?

[Joseph-S]

Hi spitz,

Just to clarify my understanding of your application, do you need to negate the motion in real-time (in other words implement some kind of control loop to regulate the position), or are you looking to perform the contour move first and then move the system back to its initial position based on the optical feedback?

[spitz]

It would be the first.

I plan to first perform a contour move based on an input file (will contain 6 trajectories for each of the Steward platform's motors). Next I will monitor the Steward platform motion using my real-time optical camera. Finally, in real-time, I will use the optically monitored motion, calculate it's inverse, and the add it to the outgoing contour motion for cancellation purposes.

Step 1 and 2 are complete. I do not know how to superimpose my real-time calculated cancellation motion on top of the in progress contour motion.

[spitz]

Just wondering if I can use my existing PCI-7344 and purchase a RTSI cable and a second PCI-7344 to get 8 axis of motion more cheaply than paying big bucks for a PCI-7358....? Can I perform 8 axis synchronized motion for my Steward platform?