Messages

101

General Mach Discussion / Re: Another lost steps post...

« on: May 26, 2010, 03:19:33 AM »

If I keep going positive I don't accumulate errors, the DTI will stay at 0.004" adrift. If I reset the DTI to "zero" after the first positive move, then any subsequent positive moves will not add to te error. The error is only introduced when I change direction.

102

General Mach Discussion / Re: Another lost steps post...

« on: May 26, 2010, 03:13:04 AM »

If I zero the DRO and DTI after a G0 X12.7 move, then do a G0 X-12.7 move the DRO will read 0.00 and the DTI will read -0.4996" (0.004" adrift by eye but probably will be 0.00039 due to my metric machine).

...Sweep

103

General Mach Discussion / Re: Another lost steps post...

« on: May 25, 2010, 05:16:35 PM »

oh, by the way, pushing the acceleration right up to 500mm/s^2, dropping the step pulse down to 5us still disn't cause a problem if i'd already taken out the 'electronic' backlash.
I was just playing with these silly high accelerations just to see what would happen and have returned them to a sensible figure.

104

General Mach Discussion / Re: Another lost steps post...

« on: May 25, 2010, 05:11:03 PM »

ok, the results of tonight's futile experiments!

As mentioned earlier, I am pretty limited to the range of accurate measurement by the 1" capacity of my DTI.
Taking on board what Mr Hood said earlier and adapting it to my limited range I thought would smaller diatances result in smaller errors being recorded.

For anyone who hasn't picked it up, the reason for all the odd figures like 12.7 and 2.54 etc is because i'm operating in mm but have an imperial (inch) DTI.

So starting with the DTI zeroed I drove the table G0 X12.7 (1/2") and the result was 4thou short.
Then driving the table G0 X0 the DTI returned to zero, therefore the error is apparent in both directions.
Next I thought what about "electronic" backlash so I first drove the table from zero to G0 X-2.54 and the same 4 thou error appeared. Driving the table back to G0 X0 returned it to zero on the DTI.
Now the intresting bit. When I now drove G0 X12.7 the needle hit the 1/2" mark right in the middle. Brilliant.
When I drove the table back, i.e. introduced a direction change, to zero the 4thou error reappeared.
Next, because i had just sorted my nice big fat pro MPG I set it to single step mode with a step of 0.1mm (0.0039") and did the same experiment. This gave exactly the same results; take up the electronic backlash and the DTI would read true, change direction and i'd lose some distance, well if I moved 0.1mm (0.0039") whilst changing direction I would only move half that distance.
Now I know that i'm only losing, say, 2thou on the shortest of distances and twice that on long distances but I think we can see the problem.
Question is, is there a cure?

...Sweep

105

General Mach Discussion / Re: Another lost steps post...

« on: May 25, 2010, 04:49:30 PM »

I have only tried the measurements over 12.7mm as my Imperial DTI is limited to around 1" range. I could experiment with larger distances but would have no way to accuratley measure them. For example at 127mm I wouldn't be able to get 0.030" accuracy. I suppose I could fasten my digital caliper to the table and have a go with that.

106

General Mach Discussion / Re: Another lost steps post...

« on: May 25, 2010, 12:43:46 PM »

No luck.
I have dropped the acceration right down, increased the step and direction pulse width from 5us to 20us, besides trying other settings in-between, I've tried changing from active high to active low on the step, but still i'm coming up short everytime by exactly the same amount. I even increased the acceleration to see if I could lose more distance but it performed the same.
I stripped off the X motor and counted the teeth on the timing pulleys and they are as expected 2.5:1 (12x30).
I measured the ballscrews with a rule and they are 5mm pitch and identified the ballscrew nuts as Warner RM1605 UF.
I have tried in Sherline mode (restating Mach3 as instructed) but nothing changes

 

107

General Mach Discussion / Re: Another lost steps post...

« on: May 24, 2010, 06:31:01 PM »

Appreciate your assistance Hood.
I will try this out tomorrow night, but according to my manual, and what I recall on the screen, the range of step pulse is only 1 to 5us ?

108

General Mach Discussion / Re: Another lost steps post...

« 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

109

General Mach Discussion / Re: Another lost steps post...

« 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?

110

General Mach Discussion / Re: Another lost steps post...

« 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.