Linear motor Accuracy

Dear All,
We are using a ultra precision lathe with linear motor and dual V groove pin roller guideways. The machine performance in terms of surface roughness during a facing operation is consistent with nanometer range, but the form and the Pt value is in terms of sub-micron (around 300nm). The surface seems to have some circular markings(as shown in image - image not that clear) along the faced surface. The positioning of the slides seems to in nm level which is measured using laser interferometer. Also the squareness of the stages is also measure and compensated in the m/c controller. We are unable to find the reason for the ripple mark on the surface which spoils both the optical characteristics of the w/p and also the profile of the machined surface. If anyone an help me in this regards, your efforts would be appreciated. I have doubt whether the resolution of the motor or the controllers plays a role in this? If so, can we calculate the resolution of the linear motor and the controller.

Thank you all.

Regards,
Rag

I've no direct experience but...

Is the problem area at a consistent diameter ? if so I'd suspect linear guide way. (e.g. contamination)

If the problem areas are spaced at similar distances, is that distance consistent with the pin roller diameter (circumference) i.e. a faulty roller bearing

If the problem is completely random, perhaps it is caused by external vibration ? (could it be acoustically coupled ?)

Bill

First, I would measure the peak to peak radial distance of the aberration. Then in order to help, we would need some info:
Pin roller diameter
If the roller diameter * pi is equivalent to the period of the aberration, then
that can be a smoking gun.
Is the motor amplifier sinusoidally commutated?
This would tell if it is torque ripple
What amplifiers are used?
What is the resolution of the linear encoder in both cross-slide and bed?
Does it do the same thing every time?
Are you able to look at a plot of the bed axis encoder position while the cut is being made? Do you see this period on the encoder plot?
If you push on the carriage away from the spindle with something near the cutting force, do you feel the servo loop vibrate?

Quote:

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Originally Posted by raghav2984

dual V groove pin roller guideways.

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Not the best setup for Nano type work. Hydrostatic tend to be much better. Your also not saying what type of spindle your using, or if it's simply a flat surface or convex/concave. Resolution does come in to play if it's not a flat surface. Is your lag/servo error staying consistent across the cut?