[Radius]

Ok so after over a year of sitting idle I fired up my old Hurco KM-1 to work on a project.

Everything seemed ok to start with, but once in a while it would seem to lose it's position. I scrapped a couple of parts I was making and really couldn't find a reason why.

Well tonight it happened right before my eyes. The X shifted position to the + direction by approx .125" and the Z shifted in the - position (yikes!) by almost .200"!

It mainly seems to happen after the machine has moved to a different position during a rapid.

If I remember right I think these machines have optical encoders on them with hall effect sensors.

I'm going to pull the covers off the servo drives tomorrow night after I get off work and take a look see. Other than possibly blowing out any dust/debris out of the encoders and checking the wiring to make sure nothing is loose, is there anything else I should check? Any common problems with these encoders?

The servos definitely need to be tuned as they are slightly erratic and rough sounding at times - kinda like just a little tiny "hiccup" that really doesn't seem to do anything other than affect the surface finish a little bit. They seem to be that way especially on slow movement.

Oh, and on that note, I swear it seems like the erratic motion in the Y axis is affected by whether or not the coolant is turned on. Coolant on, servo seems smoother.

I don't think that the erratic movement has anything to do with my current encoder problem since they've been doing that since I got the machine almost 3 years ago.

Then again, maybe it does. I'm still way new at this stuff, so maybe I am missing something. How do you tune the servos on these things anyway?

Thanks,
Michael

[bloke]

It may be you have dirty glass on the encoder. If you take off the little cover, you should be able to clean the glass with a cotton bud.
Try to slow the rapids to see if the fault improves.

Set up the amps as follows (assuming you have a BX 0.0001" control):

Start by powering up the servos and winding the gain pot CW until the axis oscillates, then wind it back until the oscillation stops plus a further three turns.
Wind the Tach. pot fully CW then back eight turns. wind the Sig. pot fully CW then back about five turns. Put your meter on DC volts and measure the voltage at the brown and orange wires on the edge of the amp being checked (or between pins 8 & 9 on the relevant channel on the servo board).
Jog the axis forward and backwards at 25IPM and adjust the Sig. pot for 0.65v in both directions (use the Bal. pot to even things up about centre i.e 0.64v one way and 0.66v the other can be balanced to get 0.65v both directions).
If there is not enough adjustment on the Sig. pot, wind the Tach. pot CW one turn and try again. When you have 0.65v in both directions, wind the Gan. pot CW until the axis just becomes unstable then back it off 3 turns.

[Radius]

It may be you have dirty glass on the encoder. If you take off the little cover, you should be able to clean the glass with a cotton bud.
Try to slow the rapids to see if the fault improves.

Set up the amps as follows (assuming you have a BX 0.0001" control):

Start by powering up the servos and winding the gain pot CW until the axis oscillates, then wind it back until the oscillation stops plus a further three turns.
Wind the Tach. pot fully CW then back eight turns. wind the Sig. pot fully CW then back about five turns. Put your meter on DC volts and measure the voltage at the brown and orange wires on the edge of the amp being checked (or between pins 8 & 9 on the relevant channel on the servo board).
Jog the axis forward and backwards at 25IPM and adjust the Sig. pot for 0.65v in both directions (use the Bal. pot to even things up about centre i.e 0.64v one way and 0.66v the other can be balanced to get 0.65v both directions).
If there is not enough adjustment on the Sig. pot, wind the Tach. pot CW one turn and try again. When you have 0.65v in both directions, wind the Gan. pot CW until the axis just becomes unstable then back it off 3 turns.

Hi Bloke..

This is a KM-1, so it has a B control. Is it the same procedure or something different?

How do you slow down the rapids? I know how to do this when jogging the machine around, but when running a program the machine rapids on it's own. The table program knob has no effect during rapids.

Thanks,
Michael

[bloke]

For a B control, set the amps to 0.9v (900mv) at 25IPM.
go to data block 0.1 and look for the rapid traverse parameter. It should currently be 250IPM. Try reducing it to 50IPM and run the program again.

[Radius]

For a B control, set the amps to 0.9v (900mv) at 25IPM.
go to data block 0.1 and look for the rapid traverse parameter. It should currently be 250IPM. Try reducing it to 50IPM and run the program again.

Okay, I'll give it a shot. I've never accessed data block 0.1 before, but I think I know how to get into it.

As for the voltage measurement, I am assuming I measure the voltage across the same pins as the BX boardset?

Are all of the rest of the instructions you gave for the BX control the same as the B?

Thanks very much for the advice.

Michael

[bloke]

Yes. They are the same for both except for the signal voltage.

[bloke]

You should be able to access it in the same way as data block 0 but by pressing 0.1 instead of 0.

[Radius]

You should be able to access it in the same way as data block 0 but by pressing 0.1 instead of 0.

Hmmm.. That's exactly what I tried. I wonder why it didn't work?

Michael