Rack and Pinion positioning precision

[PaulRowntree]

Do any R&P users have measurements on the positioning precision that they could provide? Direct and backlash-corrected information would be very helpful.

Mike Everman's ServoBelt literature quotes +-0.0024" repeatability; it would be interesting to see how this compares to the R&P devices that are becoming popular.

Cheers!

[louieatienza]

Do any R&P users have measurements on the positioning precision that they could provide? Direct and backlash-corrected information would be very helpful.

Mike Everman's ServoBelt literature quotes +-0.0024" repeatability; it would be interesting to see how this compares to the R&P devices that are becoming popular.

Cheers!

I think it partially has to do with the r&p itself, which come in different degrees of accuracy, along with their cost.

[PaulRowntree]

I am sure you are right; high accuracy always costs more, for any drive system. That is why it would be interesting to know if the R&P builders have characterized this, to compare the accuracy vs price point for these two high-speed drive systems.

[louieatienza]

I am sure you are right; high accuracy always costs more, for any drive system. That is why it would be interesting to know if the R&P builders have characterized this, to compare the accuracy vs price point for these two high-speed drive systems.

I'm very interested in ths too. We must however distinguish accuracy and repeatabily. I wonder whether or not positional accuracy of r&p is cumulative. I also wonder of the positional repeatability, or is it dependant more on other factors?

From what I understand, helical r&p can achieve higher accuracy/precision due to the fact that there is more contact between the pinion and rack... I know that some of the larger gatry/portal style mills use helical r&p, with the higher end machines also incorporating linear encoders.

[mike_Kilroy]

I'm very interested in ths too. We must however distinguish accuracy and repeatabily. I wonder whether or not positional accuracy of r&p is cumulative. I also wonder of the positional repeatability, or is it dependant more on other factors?............

good points. to understand the specs one needs to realize repeatability and accuracy are totally different.

if u say to go to 12.003" position on the r&p but it goes to 12.004" and has 0 position error & sufficient resolution in the control system, that is accuracy (.001"). whether it is cummulative or not is a function of the particular units design - it can be either.

if u go to 12.004", no matter where you told it to go, go somewhere else, then command move back to 12.004 and it goes to 12.003 instead, that is repeatability.

repeatability is a function of the control system and feedback device (resolution & accuracy of say linear scale or encoder or resolver), not the r&p. only way r&p effects repeatability is if it has backlash that gets in the way.