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Author Topic: Another lost steps post...  (Read 8243 times)

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Offline Sweep

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Another lost steps post...
« on: May 24, 2010, 05:05:13 PM »
After all the other niggling problems that I have encountered I now have a machine that is coupled and working with Mach3 and has a MPG controller. Great.
So, this weekend I thought I would do some axis tests to ensure that my programmed movements equated to the physical movements. Not great!
First of all my native and operating units are metric.
Using my Imperial (inch) DTI I positioned it on the X axis and moved the table left and right using MDI mode. The distance I moved was 12.7mm (1/2") to both keep the movement within the range of the DTI and to allow the DTI needle to fall on the same point of the scale.
Unfortunatley every time I moved from 0 to 12.7mm I was showing around 0.004" (0.1mm) short.
I have tried moving the table by hand and there is no play as witnessed by no movement of the DTI needle.
I have adjusted the axis acceleration down to single figures (5mm/s^2), have the velocity around 500mm/min, step and dir pulse as 5us but still i'm losing.
Tonight I double checked all the mechnicals and found 5mm pitch ballscrew (RM1605-UF), 2.5:1 timing belt drive (12x30T) and 400step/rev motors so I would expect that my steps per mm box is correct at 200.
I can solve the problem by 'tuning' the steps per mm to some spurious figure like 201.838 but that can't be correct as it has obviously been built to a round number and it should be 200, shouldn't it??

 ??? Sweep

Offline Hood

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Re: Another lost steps post...
« Reply #1 on: May 24, 2010, 05:26:30 PM »
Do you not use any microstepping in your drives?
Hood

Offline Sweep

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Re: Another lost steps post...
« Reply #2 on: May 24, 2010, 05:42:12 PM »
Sorry Hood, what do you mean?

Offline Hood

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Re: Another lost steps post...
« Reply #3 on: May 24, 2010, 05:47:54 PM »
What make of stepper drives do you have?
Hood

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Re: Another lost steps post...
« Reply #4 on: May 24, 2010, 05:51:16 PM »
The drives are Parker Digiplan SD2 units set to 400 steps/rev (half step) mode. I am just reading through the manual and cannot, as yet, see anything that relates to microstepping.
Earlier I did try setting the steps per mm on Mach3 to 100 and leaving the drives set at 400 steps/rev and the distance moved was have that indicated, but with missng distance, so I put it back to 200.

Offline Sweep

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Re: Another lost steps post...
« Reply #5 on: May 24, 2010, 05:57:46 PM »
Just a thought but I wonder how the direction signal is interpreted if it is received at exactly the same time as a step signal. Will the drive change direction first then move, or move then change direction therefore posibly losing 2 steps?

Offline Hood

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Re: Another lost steps post...
« Reply #6 on: May 24, 2010, 05:59:06 PM »
Ok thats fine, that ties in, your steppers are normal 1.8 degree steppers (200 steps per rev) and you are using half stepping so that gives you 400 steps per motor rev.

Can you set the stepping in the drive to 2000, that would be 10microsteps, ie 200 motor steps multiplied by 10 microsteps = 2000.
If you can do that then set your steps per unit to 1000 and see how it goes.
Hood

Offline Hood

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Re: Another lost steps post...
« Reply #7 on: May 24, 2010, 06:00:30 PM »
As to your last post, refer to the manual and see whether your step/dir signals should be active low or high, also see if it says  what the pulse width and Dir Prechange should be.
Hood

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Re: Another lost steps post...
« Reply #8 on: May 24, 2010, 06:13:36 PM »
Fancy having a quick browse as I am unsure what I am looking for...

http://www.denfordata.com/bb/files/sd2_179.pdf

Offline Hood

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Re: Another lost steps post...
« Reply #9 on: May 24, 2010, 06:26:53 PM »
Seems to be saying active High and a pulse width of 10uS min so in Ports and Pins try active High for your Step and Dir signals. In Motor Tuning set the Pulse Width to 10uS and Also the Dir Prechange to 10uS

You can only set the drive to full or half stepping according to the manual so you will not be able to set to 10 microsteps like I earlier suggested.

Another thing I noted is it says 20KHz is the max pulse rate, although with half stepping that will likely be plenty.

Hood