[gbowne1]

copied from other thread post.. "As an aside, Can scales be used as a backup for the other positioning system, ie encoders, etc, in case something happens to it?", just sorta wondered if it could be at least semi redundancy for failures as a backup system.

I do have several FANUC controls, and beyond what is described in the manual, I don't really know much about the scale interface(s), especially when it comes to the 16M and 18i, much as some of the others I have (6M, 0MC, 10T, 15MA, etc.

I would like to understand more about the use(s) of scales in the FANUC system.

-Greg

[drdos]

The scale feedback is used for positioning the axis. This is done to improve accuracy. Rather than position to the motor's feedback you position to the scale. The motor's feedback is used for velocity (Speed) So when scales are used BOTH the motor feedback and the scale feedback must be operable. Servo motors are usually mounted on the end of the ball screw while the scales are mounted to the slide. Therefore when using only the motor feedback you are only as accurate as the motor shaft so any slop between the motor and slide is lost. When you add a scale to the slide you are now position to the slide and any slop between motor and slide don't matter as you are positioning to the slide.

[gbowne1]

Yeah, figured that the motor feedback wasn't gonna be able to do it alone for accuracy. Even though the slides I have are installed pretty accurately through X and Y. I have pretty good ballscrews and couplings.

I had some great results with the bar testing I had done a year ago.

greg

[underthetire]

I've laser comped machines with std fanuc 10k count encoders to < .0001 over 30 inches. Scales can be a pia on some machines. What kind of accuracy are you trying to achieve? All scales will get you is high positional accuracy, and hide mechanical backlash to some extent. Will not help squareness or roundness issues.

[gbowne1]

All parts have to be pretty much 0.003" or better on position, dia., // etc. etc. Some I can fudge a bit but not much.

display is .0001" resolution.

[underthetire]

.003 is easy with encoders alone, as long as the mechanics are reasonably good. I don't recommend scales till your down in the .0005 or less, or, using low count encoders on the motor.

[FanFan]

Hello,
As a troubleshooting technique and sometime a temporary method ( to keep a machine running) on some fanuc control you can disable the scale input thru setting some parameters. Essential you are using the motor encoder for axis postioning instead of the scales. That can be helpful. But you will have to sacrifice accuracy. Fanfan

PS, Not sure if Fanuc would recommend doing what I suggest above. Maybe some else could let us know.