Acorn Losing Steps

[Marik]

Hey Folks,

My gang tooling Mazak Q8 with Acorn and Dyn4 DMM 750W AC motors worked well for a few years. Last week it developed a problem--every time I run a program next cycle the X is about .004"--.007" off. If I keep running the cycles the error keeps accumulating. After re-homing the first cycle is fine and then it does the same. I tried a couple different programs--the same. All the programs I tried are well proof with years of running hundreds of parts. When I run dry it keeps doing the same.

Where should I start?

Please find a fresh report.

Thanks, M

report_F8369B953F85-0503203223_2024-03-05_16-51-52.zip

(796.08 KiB) Not downloaded yet

[tblough]

My guess is something mechanical. Increased drag, loose couplings, etc.

[lavrgs]

My DMMs were subject to noise - when I added a differential board it stopped losing steps. There have been various solutions to fix the problem. If you use the DMM app to move the servos and they don't return to zero it can help ID the problem, Obviously mechanicals must be checked first for relative motion.

[cnckeith]

Acorn doesn't lose steps

[cnckeith]

My guess is something mechanical. Increased drag, loose couplings, etc.

i second that.

[Marik]

Thank you! I checked and cannot see any loose coupling. How do I check a drug? When trying to rotate the ballscrew I cannot feel any particular friction beyond "it feels normal".

My understanding the DMM motor+DYN4 is a close loop system, so the drug should not affect it, or the system at least would show an error, no?

Also, if I home the machine it makes a good part within a couple tenths at the most. But the problem is for the next part the zero is moved.

Best, M

[ShawnM]

You would have to disconnect the motor from the ball screw and turn it by hand through its entire range of motion on the axis and see if there is any drag or binding. Do you have a keyway on the ballscrew and shaft coupling to mate with the motor? Did you use Loctite on the coupling?

[tblough]

The fact that it makes the first part ok and is then offset for the next implies that something is happening during the rapid moves back to the home position.

The fact that you had been running for two plus years prior to this without problems implies that something mechanical has happened. Assuming, you made no control changes prior to the problem appearing.

For drag issues, you need to manually move the machine (by hand by turning pulleys or belts) from one end of travel to the other and back noting if the effort increases at any point. This checks the ways, gibs, screws, and lubrication. "And back" is important because a loose gib will tighten up in one direction and loosen in the other.

"Seeing" a loose coupling is not very effective. You need to clamp the ball screw and try to turn the motor (or vise versa) and note any relative movement. 0.004" is only 0.29 degrees assuming a 5 TPI screw, so you will probably need an indicator to see movement.