Setting steps using Clearpath sdsk servos on emco 120p

[benscale160]

As the conversion continues I'm at the point where im fine tuning the motion on my emco 120p axises

The calculation:
Machine units are inch
Ball screws have a 5mm pitch
Motor to screw pully is 2:1
Steps per rev on the sdsk servo is 800 (1600 steps per screw revolution)
The math suggests that my turn ratio 10.16

Any thoughts on perhaps switching to DMM TECH servos? I selected Clearpath mainly for their hard stop homing feature thus allowing me to reserving the valuable inputs on acorn for other things like an atc and tailstock inputs.

When I put a 2" travel dial indicator and test accuracy with traveling in the z direction say 1 inch it seems pretty accurate. Within .0005"

I do the same test with a feeler or finger indicator with a 1-2-3 block, I get the same results. When command to move from 0 to 1" in z it is right on the money. 1-2" same thing. 2-3" off about .0005". Close enough to call good.

The issue:

When I select incremental mode and move .001, the axis moves more than .001". Four steps registers about .005". Dro says .004". I move .025" on the dial, dro says .020"

Any idea what is going on?

Do I need to run the servos through the Clearpath tuning process before I can expect to get accurate results in this manner?

It's poses the old question of which came first, the chicken or the egg.

I also need to adjust the gibbs to minimize lost motion, but as I understand, this too may affect the motor tuning.

Any suggestions welcome.

Also, any good suggestions how to measure the x axis for accurate movement?

Thanks,
Ben

[AMHKnives]

I recomend running the clearpath servo tuning first, put your vice/ whatever your going to keep on your table for a weight reference for the tuning and let the clearpath software auto tune, make sure your gibs are where you want them first. Them for you steps you can do the indicator method for small movements, but if your looking for accuracy over the full length you really need to do ballscrew mapping, there are a few videos on youtube about this, i show using a dro from my lathe and a laser interferometer. Hope this helps.
Alan

[ScotY]

I don’t think you need to change out your motors. I have had great results with Clearpath...simple to set up and they just work. Sounds like backlash and/or gib adjustment is needed for your lathe. You don’t need to run the autotune to expect accurate results. You do need to have your machine set up properly to expect the best results though.

As to why you’re seeing more movement than commanded in incremental mode...that’s a bit puzzling. However, it sounds like you have your settings close enough to work with.

There is one setting on the Clearpath motor that may help. I’m away from home and can’t remember what it’s called but it basically changes how “rigidly” the motor will hold a given position, or perhaps, how aggressively it will attempt to move to its final commanded position. When I got my motors, I put a coupler on the shaft and tried to twist the shaft. I noticed that it was easily possible to move it a few degrees before the motor started to resist. The setting I’m talking about will make the motor resist more, to the point where it almost feels like the shaft is locked. Rambling now but I hope that makes sense?

[agsweeney1972]

You should turn up your steps per rev on the servos to a much higher number. The lower steps per rev that the servo is set for the lower the accuracy of the machine will be. Centroid suggests 6400 steps per rev on the Clearpath's if I recall correctly. The only reason to set it lower would be if you need the machine to move faster than the Acorn can pulse at the higher step frequency.

As for the turns per rev math; you are correct.
(5/25.4) / 2 = 0.09842519685039370078740157480315
1/0.09842519685039370078740157480315 = 10.16

You should definitely run the tuning software before you worry if the machine is accurate.

[Dave_C]

Centroid suggests 6400 steps per rev on the Clearpath's if I recall correctly

The OP is using the lower grade servos so 800 steps per rev is all the encoders on the servo give.

The higher more expensive servos are 6400 steps per rev.

You need to match your motor steps per rev to the motor encoder steps per rev! (there are some exceptions but we don't normally need to go there)

Dave C.

[Gary Campbell]

The ClearPath RLN have 800 encoder counts per rev, but can be set higher. Of course you don't really gain anything, but you can set them higher.

[Dave_C]

Gary is correct, you can do "step gearing" but I purposely left that out so it would not be confusing! The encoder would still only give you the 800 steps.

The OP is using the lower grade servos so 800 steps per rev is all the encoders on the servo give.

Just trying to keep it simple.

Dave C.

[agsweeney1972]

Centroid suggests 6400 steps per rev on the Clearpath's if I recall correctly

The OP is using the lower grade servos so 800 steps per rev is all the encoders on the servo give.

The higher more expensive servos are 6400 steps per rev.

You need to match your motor steps per rev to the motor encoder steps per rev! (there are some exceptions but we don't normally need to go there)

Dave C.

Opps... I wasn't thinking about the fact that he would have them without the enhanced option. I have 3 SDHP's and 1 SDSK ( Z axis) with the enhanced option on my plasma table. I forgot that I ordered the SDSK that way.

[cnckeith]

fyi... you can run the 800 encoder count per rev units with acorn set to 6400 steps per rev (or 3200) as long as you have the clearpath software setup to accept 6400 as the input ..then the clearpath takes care of converting 6400 steps per rev with its 800 step encoder.

[Gary Campbell]

" ..then the clearpath takes care of converting 6400 steps per rev with its 800 step encoder."

True. At the 6400 steps per rev setting the motor will move one encoder count for each 8 steps it receives. Any more of less than an increment divisible by eight,.... let the rounding begin. In most cases a rack and pinion router will have between 1.25 and 2 revs per inch. At the average of 1.625 that's around 1300 steps per inch. sub 1/1000th. If you feel you need higher resolution than that for some reason, purchase the "ELN" version with 6400 counts per rev native.