Constant loss of position

Hi everyone, I have a strange problem, during processing the x axis constantly loses its position, always moving it to x+ as it works. I did a test, positioned the comparator in a fixed point and put the zero there. I made some moves in G1: X0 ->X350 X350 -> X0 10 times without ever changing the initial origin, every time I went back to X0 I found that 0.08mm was always missing... 0.08-0.16-0.24 etc etc.... After 10 times my origin was moved by 0.8mm. What could this absurd thing depend on? I have a Mesa 7i96s that moves jmc 180w servo motors set at 1000 steps/rev and 20mm screw pitch 5. Doing the graphic test on the jmc interface gives me a tracking error of 2/3 steps in the inversions which does not justify these 0.08mm of incremental error .

exactly, the origin moves to 350.08- 350.016 etc etc

There are multiple causes of lost position. It could be mechanical, electrical, or a configuration error.

Can you describe the mechanics of your system? What type of motor, stepper or servo?

Start by checking the easy things. Make sure all of your mechanics are sound. Nothing binding when moving, Nothing slipping, such as a belt, shaft coupling or pulley.

If your system is a stepper make sure that steps are not being lost due to timing problems, such as too short of a pulse length, or too fast acceleration, or too high velocity. If it is a servo make sure encoder feedback signals are clean and noise free, and that encoder couplings are not slipping.

Then that leaves electrical issues, which can be difficult to find, or diagnose, and if it is due to electrical noise, can be difficult to correct, unless it is due to an obvious mistake such as grounding issues or running un-shielded cables near noise sources.

You say you have step/dir commanded servos. Can you command the same test move only from your servo's software as a test leaving Linuxcnc and the command signals out of the equation?

If you can command the same moves without loss of motion from the servo software, that would verify that the problem is not mechanical or servo/drive/encoder related.

The Linuxcnc and Mesa hardware send step pulses at their minimum length set by the halpin hm2_7i96s.0.stepgen.NN.steplen. So if Linuxcnc is configured to move a a pulse rate of 1 pulse per second, it does not pulse on for a half second and off for a half second. it will pulse on for however many nanoseconds set by hm2_7i96s.0.stepgen.NN.steplen then wait off for the rest of the second. So it is best to calculate how ever long your maximum step rate might be and set hm2_7i96s.0.stepgen.NN.steplen to the largest number that you can and still achieve your desired max step rate.

If you can configure your drive to receive a quadrature command instead of step/dir, then the signals from the Mesa hardware would have the same on/off time.

Losing/gaining a fixed amount per reversal may indicate a a step timing issue
with direction (or inverted step polarity).

You can easily check this by setting long direction setup and hold times
(say 20000 ns) and seeing if the issue goes away.

Also in general unless it limits your maximum step rates I would set the
step time to double the manufacturers minimum step pulse width.

thanks for the answers, I'll start by saying that I'm not very good at configuring linuxcnc and what I came up with is the result of the guided procedure and many tests to make everything work. I do it as a hobby even though I am a milling machine by profession. I don't know if it is possible to move the motors via software but I don't think so, but mechanically everything runs well and everything is lubricated. I also tried inverting the axis motors and even loading the parameters of other axes but nothing changed. I add my .ini file configuration of the x and y axis but I don't see huge differences, but the x and z axis are perfect, the x gives me problems. I have a printnc that I upgraded myself with aluminum components that has a dual motor y-axis and all cables shielded. I attach the ini file and the hal file so you can see what I configured so you can tell me if I'm wrong. If I made a mistake, please tell me in detail what I did wrong so I can understand where to correct it. you wrote to me to try to put 2000 on the direction setting and holding times, but I don't really know which string you are referring to. thanks for your help.

This is what indicate the manual for the servomotors jmc

So the existing setup/hold times are marginal
I would set them both to 20000 (20 usec) as I
mentioned before.

exactly which items do you intend to set? 
 
[img]data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABQAAAAUCAQAAAAngNWGAAABDUlEQVR4AYXRgUZDYRjH4TegFTKgpEqiFJgoWAoMEQGBgBboChaaAKxLKAhAhQqAdAmpBIQolkCFqp2nITvNKXuA7+/Hhzey5OWjE4Nq3rzY1f9/NGHPB549492+8Ww060iCS2XdctZdI3GsECmb+HJoIX6x6EgDm+lURTH+YB7V9nAqE5WNme4YKuOiY6iMe6PaQxUUIuTbswgFVNJwA8sO3Bn6yR6bWZMSNtJwDtuWfHpQxaPx9C9zadil7jrCigbq6UXceNIVKTWUIqypm2ytJdTiNyNeXclF6GttOVfeDEc7qzjR23r3OMFqZKng1kw0mXGLrfibHTScOZWgGv9TdC6ROFeMTgwYiIxvJzMRWQbeGZUAAAAASUVORK5CYII=[/img]