How can I set the direction of motion before number of steps?

[caswell]

Hi all,

There's probably some really obvious answer to this that I'm just missing, but I need to separate (delay) the signal for direction change from the clock pulse train when driving a stepper motor. I'm using Labview 6.1 (oldish system) and PCI-7334 motion control card and basically need a way to set the direction for the motion before the number of steps using the motion library.

Thanks.

[MikeS81]

duplicate post -- continue here

[Eric_R]

Hi Caswell,

Let me make sure I understand correctly, you want to take the TTL pulse train for direction and separate/delay this from the TTL movement pulse? I don't know if this is possible using the 7334 and am unsure as to the effect of this on the stepper motors microcontroller if the pulses did not synch properly. You could delay the direct pulse train using one of our DAQ boards, but I'm afraid this would greatly complicate your application. Can you go into further details as to the end objective of this and describe your project further?

Thank You,

Eric Reid

Applications Engineer

Message Edited by Eric_R on 06-18-2008 10:43 AM

[Eric_R]

I think I understand better now, your drive needs extra time to settle and since the commands to move from the 7334 are both instantaneous you are seeing an incorrect servo movement at the beginning. Are you basically looking for a way to settle out the direction line before you send steps?

Thank you,

Eric Reid

[caswell]

Hi Eric,

That's more or less what I want to do, yes. I'm using the 7334 card to drive what I'm told is a fairly unique set of stepper motors (3). An engineer had designed and built an interface between the NI card and the motors to 'properly' drive them (I don't know much about the interface). The motors are being used on a goniometer for an Ion Beam Analysis experiment using an alpha particle beam, so accurate movement is essential. We noticed that the movement was not accurate, and after putting a scope on card outputs saw that the direction signal and the first clock  pulse arrives at the same time, which his circuitry does not cater for, so that what is happening is that on a direction change (there are several) the motor will sometimes take that first step before changing direction. The cummulative effect is noticeable in the exeriment.

So my query is really on whether there is a way to issue that direction change in software.

[Eric_R]

Hi Caswell,

I tried testing a stepper motor on hand here by setting the steps =0 and doing an increment, this did not update the direction line. Unfortunately, JB was right in the other thread and the only option you have is to make one step and wait for a time before continuing or use another DAQ device to set the direction. I will fill out a product suggestion to add this functionality.

Thank You

Eric Reid

Applications Engineer

[caswell]

Hi Eric,

Thanks for the effort (everybody else who posted too). I'll try setting the direction another way as you suggested and post back on how it went.

Cheers