Author Topic: stepper motor stalling in x axis only problem  (Read 5698 times)

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Offline alex850

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stepper motor stalling in x axis only problem
« on: August 16, 2010, 11:30:44 AM »
i am haveing problems with a drillingcode moveing in the x axis. it is stalling , wineing, and lossing position before going to the 3rd line of code. the motors are nema 42 and  motor ouput is identical settings. the screen in mach shows the program to move correctly and the code is fine. when i uncheck the backlash compensation box it works fine. but then the profile program does not profile the part correctly. there is nothing wrong mechanical in the mill that i can see. any help would be great.
thanks alex

Offline monty62

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Re: stepper motor stalling in x axis only problem
« Reply #1 on: September 10, 2010, 06:50:17 AM »
i seem to have the same problem do you have a solution
regards les

Offline Stupidspencer

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Re: stepper motor stalling in x axis only problem
« Reply #2 on: April 12, 2014, 08:40:02 PM »
My Harbor-Freight mini-mill had the same issue. Does your machine use stepper motors or servos? If it has steppers (and it sounds like it does), then read on.

My setup uses Keling 4042d drives and 425oz-in motors. All three axes are the same and use the same settings, but only the X-axis was stalling... and only when commanded to move the table at 38-41ipm. Above and below this feedrate, no problems. I solved my problem by putting the drives in software controlled mode and running the compatible tuning software that was available. I found that only the X-axis had the problem because it moves the least amount of mass out of the 3 axes and has the least rigid ballscrew and motor mount. The mass (weight) of the Y-axis saddle and the Z-axis head provide enough dynamic dampening and resistance that the problem is avoided. The X-axis motor only has to move the table which weighs a lot less comparatively. Now you are probably thinking: less weight= shouldn't stall as easily. But you would be wrong.

Your X-axis stalls because you are experiencing stepper resonance. Step motors typically move 1 step at a time, even during long rapid moves. It appears to be a continuous movement but it is actually a series of really fast steps. At the end of each step, the motor's rotor over-shoots the stop point a bit due to inertia and then rocks back and forth around the step point before coming to rest. When the rate of the rocking motion equals a multiple of the step rate, the motor resonates causing it to lose almost all of its torque. If the mechanical resistance is greater than the motor's reduced torque, it loses sync with the control pulses and stalls.

There are ways to combat resonance, but it cannot be completely eliminated from a stepper system.

1)
If your motor drives support microstepping, using it will greatly help. Also, increasing the number of microsteps can help. This is because the motor arrives at the end of each step more smoothly instead of jumping from step to step. This means it overshoots the end point less which results in less rocking of the rotor and thus less resonance effects.

2)
Change the motor coupling. "Springy" motor couplers allow the previously mentioned rocking motion to become amplified and actually increase the resonance effect. Change to a coupler that doesn't have urethane cushions. Or use a different type of coupler. If your machine setup allows, using a sleeve with set-screws to hard drive the lead-screw may do the trick. Note that you cannot have any motor to lead-screw mis-alignment to do this. If this doesn't seem feasible, you could possibly put some kind of a harmonic balancer or flywheel on the motor. If your motors have shafts that extend from both ends, this could be an easy thing to implement.

3) Use tuning software. If your stepper drives have tuning software, use it. Once tuned, the resonance RPMs of the motor are avoided internally by the stepper drive regardless of the commanded step speed.

4) Lower your max rapid speed to just below the resonance speed on that axis so the motor never hits the resonance RPMs. For me this was only a temporary solution because I couldn't stand having 37 ipm be the fastest it could move along the longest axis. Especially since my motors can now rapid at 245ipm which is scary-fast for such a small machine.