Different pitch drive travel

[RBAT]

We have an in-house developed XYZ rig which we are driving via Motion Control / Assistant and the accuators have slightly different pitch screws in the X and Y axes (approx 2.5:1) meaning that if we try to draw a circle it comes out as an elipse (this was done deliberately since we needed the higher control/accuracy in the one axis for a specific project). So far we have only used simple patterns so it has not been a problem but we now want to do more complex designs.  My question is - is there a simple way to set the relative travel of the two axes at a high level so that we do not have to alter the shape of the path to compensate?  I know we could set the ecoder inputs to fool the system but this would loose some of the accuracy(?) Any help would be much appreciated!

[Jochen]

RBAT,

there are two options to compensate different pitch screws: 

1. Use Contouring. In this mode you can download position arrays to the motion control board. The motion controller steps through these position arrays with a fixed timing (e. g. 10 or 20 ms). In this mode you will have to do the pitch compensation when calculating the contouring data.
   
2. Use a dummy axis in your vector space and a second axis as a slave to this dummy axis. This mode is called electronic gearing and with the gear ratio you can compensate the pitch. The method is described here in more detail. You will need a spare axis for this option.

I hope this helps,

Jochen Klier

National Instruments 

[RBAT]

Thanks for your prompt reply Jochen.  I have already played around with contouring a little as it seemed a reasonably easy to understand solution (it's not just me using the rig) but I will definitely check out the electronic gearing as this sounds more like the kind of solution I want (i.e. 'invisible').  We do have a spare axis to play with (at the moment!). I will let you know how I get on.

rbat.

[RBAT]

Had a play with the contouring method and changing the co-ordinates seems straightforward and works OK but I would like to follow up on the electronic gearing solution but the vi you directed me to in flex004 unfortunately is version 5.0.1 and we get the error message "An error occurred loading VI Ellipse.vi.   LabVIEW load error code 10: VI version (5.0.1) is too old to convert to the current Labview version (8.5.1)".  Is it possible to get this vi updated so we can examine it?

RBAT

[Jochen]

This version of the vi should work for LabVIEW 8.5 and higher.

Jochen

[RBAT]

Thanks - this version loads OK ... all I need now is to study it!

RBAT