Problem- Intermittent Steppers

[MX725]

Hello All
I'm new here and new to stepper drives. Our company recently purchased a used Foamlinx FC5555 hot wire foam cutting machine, which I have set up. It appears to be in very good condition and has had very little use.
I am having an intermittent issue with the steppers oscillating instead of stepping at various times at various motors. At first I thought they were stalling and I lubricated and aligned everything. (the screws, bearings and bearing rods). This didn't solve the issue.
I had been able to give the motor shafts a spin by hand and they would take off again. Now they seem to be going back and forth (at a high rate) between steps and they just vibrate without traveling in a direction.
I am running Mach3 software and was previously running FoamWorks, with the same or similar results.
All four steppers have voltage and hold their position when not being driven.
I can manually stop the screws from turning, but I have to use a rag and both hands to do so and this is while the carriage is being moved.
I have one motor that runs warmer than the other three and when I checked the voltage at the driver, the one had 7 volts while the others were 2.7 volts.
At the moment I'm not sure how to troubleshoot the system, other than changing components.

The motors were made in China and there are no specifications on the label.
The Driver is from Foamlinx, or at least that's what I believe.

Thanks in advance
BH

[vger]

BH,

Does the oscillation/stalling seem to happen only at high feed rates?
What parameters do you have set up in Mach3?

It sounds as if you may have a midband resonance issue. Stepper systems have a speed at which they resonate due to their nature. Atemting to run them at or very near this speed will cause erratic movement.

If you drasticly decrese the acceleration rate of one axis and run it manually, you may see that it accelerates up to a given speed and then stalls in oscillation.

Give it a try... (nice machine by the way)

Steve

[MX725]

Thanks Steve
Right now I have the speed set in Mach3 at 20 ipm. During cutting or simulated cutting I am running at around 8.5 imp.
I have noticed that the cutting speed (default I think) would start around 5 or 6 imp and it sounded horrible, so I would override it and get above 6 to let it smooth out. I had also tried the main setting at 40 ipm on the motor/tuning setup, but when I would hit "return to zero" it would sound really bad as well. The jog screen that comes up by hitting tab is set to run at 65% of the maximum.
I have noticed that there seems to be several harmonic resonance ranges (my description) where the whole unit sounds bad. I couldn't determine what was resonating, screw, bearings & rods or the motors.
I have tried to adjust the speed in the "motor tuning" window, while jogging the unit using the keyboard arrows. For some reason the arrows aren't working. When I first set up the software, I did use the arrows, but not with the tuning screen open.
Unfortunately I am trying to sort this out as well as figure out what speed and power level to run the hot wire at. Currently I am trying to cut a 48" wide section of 2 pound eps.
The whole process of steppers, cnc and foam cutting are brand new to me.
I will try adjusting the acceleration and see what I get.
Thanks again.
BH

[vger]

BH,

I looked at a manual on the Foamlinx site and it appears the stepper drivers are fractional drivers set at 1/20 step. From the pictures, it looks like the screws are 1/2" 10 TPI acme thread. With those screws you should be able to move much faster than 20 IPM.

What kind of computer are you using? If it's a notebook/laptop, that may be your problem. To run at 1/20 step the computer has to put out 20 pulses for every full step or 4000 per revolution. With 10 TPI that makes it 40,000 pulses per inch (which is what the manual shows for steps/inch). 20 IPM means the printer port must put out over 13 Khz when moving just one axis. With the overhead (things running in the background) on laptops, that would be difficult to do smoothly.

With 1/20 step fractional drive, things should run very smoothly unless the computer is not able to put out a smooth pulse stream because it is busy doing other things like checking battery level, additional buttons, etc.

Steve

[MX725]

Hi Steve
I will have to check the computer spec, but it isn't a laptop. So I guess we can't rule that in or out yet.
I really appreciate the legwork you did to try to help resolve this.
Yesterday I changed the acceleration values and speed values. At the moment I am having more issues with the one Y axis motor than the others, but they have all messed up at one time or another. I can run the X axis motors at the 100ipm that the Foamlinx website states for that model. On the Y axis, anything above 30ipm would stop the motor that was acting up. The other one would run most of the speeds, but maybe not up to 100ipm.
I was told my settings would be 4000 steps for the software, but after checking and calibrating, I settled on 2008 steps. That was from my calculations and the auto calculator in the Mach3 software. I'm not sure what that means for the motor specs as there weren't any specs on the motor plate. My screws are a 10 pitch thread.
When I slowed the acceleration way down, to .01, the motor would make almost one rev, before stopping and then it would just sit there and vibrate. This was using a velocity setting of 30 or higher.
By the way, the motor giving me the current headache is the one that is running hot and shows twice the voltage as the other three.
I don't understand why one driver output would be so different than the rest, but I'm not an electrical engineer.
I may not get time to play with the unit today as I have some production to get out the door. Thanks Again
Bill

[vger]

Bill,

I am wondering how you got the voltage measurements. One of the first rules for stepper drivers is NEVER disconnect the stepper from the driver while power is applied. This will damage most drivers because the driver senses the current through the motor in order to contol the power going to it.

It troubles me that the one motor is running hot. It could be a bad motor or a bad or mis-adjusted driver. Assuming all the motors are the same as I believe they are, the drivers should all be adjusted the same. Can you take some pictures of the drivers and post them? I'll bet Foamlinx used some off the shelf drivers rather than making their own, but anything is possible. How many wires connect to each stepper?

The motors are most likely 200 steps/rev. A setting of 2000 steps per inch with 10 TPI screws means the steppers are running full step mode. Is it possible someone changed the settings on the drivers?

If the electronics are in a blue box (or other color), please remove the cover and take closeup pics of the insides and post them here.

Steve

[Dorsal]

One of the distinct possibilities for that hot motor is that one of the windings is connected in reverse-phase, in other words the blue and blue-white wires (for example) are connected to the wrong pins on the board. That would definitely require greater voltage to run that stepper, as one winding is trying to go backwards.
Go back to the basics and double-check the wires from the steppers, whether you connected them or they are soldered into connectors.

[MX725]

Thanks for the input. I took a few pictures and I will try to post them. The wires attached to the board are green, black, white and red and all match connection wise. The wires at the motors are white with writing, which I couldn't check yet. I will buzz them all out (continuity test) to see if they are all connected properly. Tal at Foamlinx thought someone had extended the cables, after seeing a photo I sent him.
If there is a wire mismatch at the one motor, do you believe it could have an effect on all of the motors? Intermittent? Obviously I will check the wiring anyway, but I am just wondering if this may be a problem, but not the only problem.
I got my voltage reading inside the box, at the connection screws. I realize they actual value may not be correct, but the huge difference in one motor and the fact that it is running much warmer than the other three, at least gives me a clue to look further.
It is possible that someone adjusted the settings on the board, but I think it is unlikely. The original owner never really used the cutter. They set it up and played with it a bit, but I don't think they ever really used it much.
I have an electrical person familiar with steppers coming in today to look at the unit. I will post results.
As always, thanks so much for your input.
Bill

[MX725]

Continuity test results.

PC Board Motor Connector
Right X-axis Red White
White Long Blue dash
Black Blue X X X
Green Blue dash

Left X-axis Red Long Blue dash
White White
Black Blue X X X
Green Blue dash

Right Y-axis Red White
White Long Blue dash
Black Blue X X X
Green Blue dash

Left Y-axis Red Blue dash
White Blue X X X
Black Long Blue dash
Green White

As you can see, it's not consistent. I assume it should be, but I don't know.

We changed the Left Y-axis by reversing the order from top to bottom and and also by making it consistent with the Left X-axis. The total reversal showed 27 volts where it had been 9 and matching the Left X-axis was just like the original setup (only direction was reversed).

Bill