Moving two motors together.

[cosmund]

Hi all,

I'm using MID-7604 motion controller that is driving a set of motors.

I wish to move 2 motors in tandem.

Can anyone suggest links to how this is done in Labview?

Does the hardware actually implement this in parallel, or does it internally serialize it?

Is there a performance issue with doing this vs moving the motors sequentially?

Thanks,

cosmund

[Jochen]

cosmund,

there are several ways to move two motors together. One option is to configure a vector space that contains both axes and  configure your moves for a vector space. Please refer to the shipping examples (e. g. Two-Axis Vector Move with Position Monitor.vi). Axes in a vector space always start and stop at the same time.

Another option is to configure the move constraints for both axes independently and use a single instance of Start Motion.flx to start both axes at the same time. You will have to use the Axis/VS map parameter and set the Axis or Vector Space parameter to Axis Control.

The third option is to use electronic gearing. In this mode you only have to control one axis and the other one will follow with the gear ratio specified by you. Please refer to the shipping examples (e. g. Master Axis - Slave Axis Gearing.vi).

I hope that helps,

Jochen Klier

National Instruments

P. S.: If you need further information, please add the NI-Motion device type (e. g. PCI-7340) to your next post.

[Jochen]

cosmund,

I have just realized, that my first answer was not complete. As all motion control tasks are done onboard, there is no difference in terms of performance, if you run two motors sequentially or in parallel.

Jochen

[cosmund]

Thanks Jochen,  I will look at these techniques.

At the hardware end, are the moves really being done in parallel, or does the hardware use time-sharing to execute parallel moves?

[Jochen]

cosmund,

internally the DSP on the board of course works with a time slice model to generate the trajectory data for each axis, but it outputs the trajectory data in a synchronized way to the step generators. The step generators run on an FPGA in parallel, so the outcome is parallel execution for all axes.

Jochen

[cosmund]

Thanks Jochen,  Good to know that the hardware actually moves the motors in parallel.

ie. we should achieve both moves in a shorter time than the sequential method, right?

[Jochen]

To make things not more complicated than they are: Each axis can be controlled seperately and independently from the others. That means, that you can move all axes in parallel or sequentially according to the requirements of your application.