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Mach4 General Discussion / Jerky dual axis movement
« on: April 08, 2018, 04:28:55 PM »
Hi guys,
I have a problem with a jerky axis movement on my home built machine (with PoKeys 57CNC controller) and don't quite know where it comes from.
The only affected axis is the Y. It is a dual axis (two ball screws, two 8Nm closed loop steppers). Both bearings on the Y axis are quite preloaded but this shouldn't be a problem for the stepper motors.
During the milling cycle the Y axis starts to bang when it accelerates. At first I expected the worst, that both axis motors didn't move synchronously and the gantry is put under heavy stress. But turned out not to be the case, I measured the flatness of my X axis and it was just fine. If both Y motors would have moved different from one another, the gantry would bent. This shouldn't even happen though, because both stepper motors do have encoders and the same input signal. If they wouldn't move in sync, an alarm would be triggered.
So I watched both motors during a job and noticed that both seem to jerk simultaneously.
I don't think this comes from overload of the motors, they have plenty of power and in general they aren't equally strained during a job so a simultaneous jerking movement is quite unlikely.
Additionally these jerky movements don't appear when I jog the Y axis. This leads me to the assumption that there must be something wrong with Mach4 or the way I set it up.
I already thought this may come from too many steps per unit, but according to my calculations it should be ok and Mach4 (PoKeys plugin) didn't complain.
But I don't know how these step frequency calculations apply to a dual axis or when more than one axis is moving.
In order to give you an impression of what I mean I uploaded a short mp3 file where I face off my slot table. From 2,5 - 4 seconds you can clearly hear the banging of both motors in the background. AudioYaxismotors.m4a
I hope you have some ideas and can help me out!
Many thanks and best regards,
cncnc
I have a problem with a jerky axis movement on my home built machine (with PoKeys 57CNC controller) and don't quite know where it comes from.
The only affected axis is the Y. It is a dual axis (two ball screws, two 8Nm closed loop steppers). Both bearings on the Y axis are quite preloaded but this shouldn't be a problem for the stepper motors.
During the milling cycle the Y axis starts to bang when it accelerates. At first I expected the worst, that both axis motors didn't move synchronously and the gantry is put under heavy stress. But turned out not to be the case, I measured the flatness of my X axis and it was just fine. If both Y motors would have moved different from one another, the gantry would bent. This shouldn't even happen though, because both stepper motors do have encoders and the same input signal. If they wouldn't move in sync, an alarm would be triggered.
So I watched both motors during a job and noticed that both seem to jerk simultaneously.
I don't think this comes from overload of the motors, they have plenty of power and in general they aren't equally strained during a job so a simultaneous jerking movement is quite unlikely.
Additionally these jerky movements don't appear when I jog the Y axis. This leads me to the assumption that there must be something wrong with Mach4 or the way I set it up.
I already thought this may come from too many steps per unit, but according to my calculations it should be ok and Mach4 (PoKeys plugin) didn't complain.
But I don't know how these step frequency calculations apply to a dual axis or when more than one axis is moving.
In order to give you an impression of what I mean I uploaded a short mp3 file where I face off my slot table. From 2,5 - 4 seconds you can clearly hear the banging of both motors in the background. AudioYaxismotors.m4a
I hope you have some ideas and can help me out!
Many thanks and best regards,
cncnc