[jon1982]

I know this has been discussed before, but I am just having a hell of a time. I believe the encoders to be 250ppr . I know that they recommend higher ppr , but these came with the mill and I have had them close it seems but not there. The calculator I am using says 10,000 steps per inch. When I do that they are off. The only way I could get close is by putting the step multiplier at 1. If I put it at 2500 and step multiplier at 4 its close. It will be spot on one measurement , but Then it will be .002 short on a smaller measurement. Sometimes it seems like it will be over on one and under on another. What am I missing.

2:1 ratio
250 encoder lines per revolution
5 pitch (.2000 inches per revolution )
Calculator says 10,000 steps per.

I am using an edgefinder and calipers.

The x and y motors and encoders were replaced about 10 years ago. I am going from the manual with the encoder count. I would only assume that they would use the same as the book so that it matched the other encoders .

I have the chance to get a big job, this is urgent. lol

[Louis_Cannell]

Try the Mach3 auto calibration feature if you are close you should be able to get the adjustment required very quickly and double check mechanical connections and backlash. Just google Mach3 Auto calibration a few videos available.

[jon1982]

Try the Mach3 auto calibration feature if you are close you should be able to get the adjustment required very quickly and double check mechanical connections and backlash. Just google Mach3 Auto calibration a few videos available.

I am familiar with the auto calibration. Its just weird. I did that and it was like it made it worse

[jon1982]

I dont know if that last one went through, but its like autocalibration made it worse.

[Louis_Cannell]

I would check the backlash and all mechanical connections also disable backlash correction if it is enabled prior to calibration, the fact that you say "Sometimes it seems like it will be over on one and under on another" leads me to think more likely a mechanical fault loose ballnut connection, damaged ballnut or bearing, or a slipping coupling than a tuning fault.

[ger21]

The calculator I am using says 10,000 steps per inch. When I do that they are off. The only way I could get close is by putting the step multiplier at 1. If I put it at 2500 and step multiplier at 4 its close.

10,000 steps is what you have.
setting it to 2500 with a 4x multiplier is basically the same thing, but I would think that setting it to 10,000 with the 1x multiplier should be more accurate, although I may be mistaken.

t will be spot on one measurement , but Then it will be .002 short on a smaller measurement. Sometimes it seems like it will be over on one and under on another.

Backlash, or ballscrew pitch error?

[jon1982]

I dont know, maybe the encoder count is to small for the viper drives . They look brand new. Maybe i shouldnt assume that they are 250 as well. It will be .017 off in a long distance and .005 in another and maybe .0005 in another. I can get it autocalibrated at 11. inches and then it will be dead on in the y when its a circle and .007 when it is a square. Its really messing with me . This shouldn't be that hard. I have messed with encoders before. I have some 500 line count encoders that will fit. They are from a different machine. I know for a fact those are 500 encoder lines per rev. I will just have to make up a cord and attach them to the viper.

[Larken]

Yes, its 10,000 cts/turn
Setting the step multiplier to 1 or 4 doesn't change the accuracy, because the drive is resolving motor counts either way.

have the viper tune connected to see at the end of a move how close it is to target pos (whats the error count ?)

20 motor counts would be 0.002" so im sure its much below that.. or it should be at the end of a move. It should be below 4 counts when holding.

Table friction, belt tension, backlash all affect positioning accuracy.

Larry

edit: sure they aren't 256 counts.. or dirty ?

[jon1982]

I will try the steps for 256 counts tonight and check them to see if they are dirty.

[jon1982]

ok I tried the 256 ppr , it cam out to 10240. That was not right. What is with hysteresis? I guess I dont understand what it does.

[ger21]

Setting the step multiplier to 1 or 4 doesn't change the accuracy, because the drive is resolving motor counts either way.

Not at the motor end, but the control is sending out fewer steps per inch (by a factor of 4), so your commanded resolution will be lower.

[jon1982]

so , I retuned the motors and while running the movements from mach3 there is very little error at the end of the movement. like 1 or 2 counts and then it goes right to 0 very quickly.
When doing circle pockets, I will have it calibrated at 1 inch. X is actuacly 1.002 and y is spot on at 1.000. x grows as the circles get bigger but y does not. I guess that is why I am shying away from mechanical problems and going with software or hardware problems. I went from a 1 inch circle to a 1.5 inch circle and x grew y .002.

1 inch circle = X,1.002 Y,1.000
1.5 inch circle = X,1.504 Y 1.5

My Y axis and Z axis have pretty well been tight since I got the drives, but my x seems to be out and grows by .002 or at some point shrinks little by little.

[jon1982]

So I believed I have tracked down a problem.

When I pulled the x servo and hooked it up to viper tune It holds in the CCW direction, but will not hold in the CW direction. Basically the servo wants to fight me when I try to move it to -1. I can move it to 25 or 30 counts the other direction without any fighting.

Is it possible that I have one of the encoder pin backwards or something?

[Larken]

This is a different problem. Email me. [email protected]

Larry