Feedback from glass slide DRO

I currently am using an open loop system with stepper motors and occassionally may develop a difference between the system DRO and the glass slide DRO (Accurite). The glass slide DRO should be more accurate than the system DRO since the the system doesn't know anything about lost steps that may happen occasionally. The setup is on a 3 axis Bridgeport milling machine.

I think if a way of feeding back the glss slide DRO position via optical couplers and create a servo loop would improve accuracy.

Is it reasonable to do this?

Has anyone configured and setup a system using feedback from a glass slide DRO as could be setup on a milling machine?

jensor

Hi

If you search 'glass scale' on the forum, there is quite a lot of discussion on it, some Bridgeport specific

regards

Tbanks

I just found the search tab.

jensor

from what i understand the PID loop outputs velocity to catch up so stepgen needs to be configured for velocity not position. also there is the issue that when the motor is above the corner speed adding velocity reduces torque so the motor may just plain stall. the machine will error and stop more often than it helps with lost steps. but at least you'll know about it. i think there are still more reasons to do it such as the fact that steppers act as a kinda like a detent. it draws the motor to a position so when there is counter pressure it never actually reaches the position. often this doesn't matter much as the motors should have a large surplus of torque and a full step may be a small measurement so as long as the motor is never pushed to the point of a lost step the inaccuracy is either well within accepted tolerances or can be tuned out with cutter comp. still ther ecould be leadscrew or microstep nonlinearity. it would be especially useful for a machine that is driven by belts or low tpi leadscrews and has a high microstep count and a big full step increment. perhaps a gantry style home built cnc or plasma cutter. most people recommend dc servos instead of adding a feedback loop to steppers.