Stepper Idiosyncrasy

[Me2]

I have a question on Stepper Motor performance.
I have been running my machine for a number of years now with steppers driven by Gecko 201’s. The controller is Mach3.
When I run a cut on a diagonal the X and Y-axis work in sink and in a smooth action.
When I cut a circle the X and Y run togeter and then seem to stop momentarily, then run again and stopping momentarily continuing until the circle is complete
Watching servo motors the movement on the X and Y is smooth and fluid when cutting a circle.
Is this type of stop start, stop start motion in circle cutting an idiosyncrasy of steppers or is there a way of smoothing the motion to act more like a servo?

Cam

[neilw20]

How fast is your computer.

XP goes off into the weeds occasionally and the queue gets emptied by the low level driver, as it should. Because the operating system is busy, Mach3 doesn't get a look in to feed the queue in a timely manner.
I have the same problem using a 600MHz HP running XP.
Haven't tracked down what it is, but it's not the network. Maybe IDE hard disk being serviced. I will trap it one day! (or get another faster computer).

It is obvious during cutting circles, but can happen while cutting a straight line even at very low feed rates.
During rapid feeds, you can get a 'clunk' as the stepper(s) decelerate(s) too quickly, because it is not being fed pulses continuously. My temporary fix is to detune the maximum speed of the motors, by about 50%. At least it never loses steps when going 'clunk'! Normally Mach3 controls the deceleration, but not when XP has stolen the CPU. Watch the diagnostics screen. You will eventually see it happen.

Make sure you no anti-virus software running, especially Norton. I have AVG installed and running, and have not ruled it out yet.

Make sure your AGP window (BIOS Setting) is not larger than your video card.

and so it goes....

Wher in Aus are you. I am Melbourne.

Neil

[Me2]

G'Day Neil,
Thanks for the quick reply. Live just down the road in Geelong.
The PC I'm running is a pentium 4 2.0 running win 2000 with 256 meg ram. The machine is dedicated to Mach 3 only, no internet or virus scanners etc.
Just curious to know if others have this behavior with their steppers when cutting circles

Cam

[neilw20]

Originally Posted by Me2 G'Day Neil, Thanks for the quick reply. Live just down the road in Geelong. The PC I'm running is a pentium 4 2.0 running win 2000 with 256 meg ram. The machine is dedicated to Mach 3 only, no internet or virus scanners etc. Just curious to know if others have this behavior with their steppers when cutting circles Cam

Cam.

I'm in Deer Park.
We should touch base one day.
I've got 384 Meg memory, and that is not enough.
You have to make sure it doesn't try to use virtual memory
In you system.ini file try this:
[386Enh]
ConservativeSwapfileUsage=1

This may stop it hitting the disk until it's used about 80% of ram.
Harmless if it doesn't work.

Also, make sure nothing is in the system scheduler.
I have not found simple (turn off the monitor) screensaver to be a problem.


Neil

[ger21]

Do you have backlash comp turned on?

[Pres]

How much slop (backlash) do you have in the axis reversal?

It usually shows up most in cutting circular tool paths.

Pres

[Me2]

Thanks for the replies,
Backlash elimination is turned off.
There is no backlash in the screws, they are as tight as a drum.
I'm wondering if it has something to do with the computors memory having difficulty with computation speed while cutting a circle.

Cam

[ger21]

How is the circle coded? Full Circle G2/G3, or in quadrants? Do you have CV turned on? If you run the Mach3 Driver Test (drivertest.exe in the Mach folder) and get a clean, flat line, the problem is probably not the PC.