How to move motor one step

[ochensati]

I have a stepper motor connected to the MID-7604 driver.  I am trying to drive the motor in a linear manner.  I can do runs of 5000 steps with no problem, even runs of 500 steps are fine, but what I need is to move the motor is steps of 1 - 4.  The small steps just do not happen.  I have been playing with all the settings, changing the max currents and all the rest and have not had any luck so far.  I have both tried using the motion assistant and the example programs, and it is always the same.  The motor will run over long ranges, but not for these single steps that I need. 

Thanks

Brian

[Brian_Beal]

Are you using an encoder?  Are you using microstepping?  What controller are you using?

[ochensati]

I am using the MID-7604 which is the controller and has a encoder, which I am using. 

[ochensati]

I am also using 250 microsteps.

[Brian_Beal]

The MID-7604 is a drive, not a controller.

[ochensati]

Ok, I was confused.  I send commands from the computer to the MID-7604 and then it moves the motor, but it will only move over large ranges.  Is there something missing?

[Rodj]

The MID 7604 is the drive, in the computer connected to the drive is the motion controller card.  Is this a 7330, 7340, or 7350 motion controller card?  If not a motion controller card, then how have you connected from the computer to the drive?

Thanks

[Rodj]

How many quadrature counts per revolution does your encoder have?  Does counts equal steps per revolution or is there a mismatch?

[BCho]

Hey ochensati,

How many steps per revolution is your stepper motor? Some typical stepper motor have 200 steps per revolution, and with 250 microsteps per step that becomes 50,000 microsteps per revolution. Are you trying to move one step, or one micro step? If you are trying to move one step, in my example 1.8 degrees, this should be very attainable. However, if you are interested in moving one microstep, in my case 0.0072 degrees, a single step may not even be noticeable. Weather or not this step is noticeable or not is completely dependent on your system. But it does raise the question of are you trying to attain 1 step or 1/250 of a step? As it is, what is the smallest number of steps that you can successfully move?

In regards to moving your motor in a linear manner, there is a Knowledgebase that addresses this issue that you may be interested in.

Hope this helps.

-Ben

[Jochen]

Just a little addition from my own experience:

I have been working with a customer with a similar issue and we found that at very high microstepping rates (and 250 IS very high) the distance the motor travels at each step is not exactly equally distributed between the full steps. That means, that some microsteps might be even much shorter than in Ben's calculation. This behavior is caused by limitations of the mechanical accuracy of the motor and by the physical limits of the current resolution of the drive. So typically you can rely on the fact that if your controller outputs a step, a microstep is performed by the motor, but the move distance may vary and sometimes it even might not be noticeable.

High real-world position resolution can't be reached with high microstepping rates but only with high quality motors and gears.

Regards,

Jochen