KM-1 losing position?

[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.

[Radius]

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

Okay, thank you! I will work on it tonight.

Michael

[Radius]

Ok, so here's my results so far:

I took the covers off all the axis drives and looked inside. I cleaned the encoder discs with rubbing alcohol and q-tips.

I did find that the bottom opto limit switch for the Z axis was not working. Turns out the spindle had somehow flung grease into it. So I cleaned that out and now the opto seems to work.

However, now that I've cleaned that out something else kinda strange is going on. When I start the machine I put the knobs in auto, then press "table zero" so the table moves to the zero position. Afterwards, I press "Tool Cal" to zero the Z axis. Well now, after the Z returns to the "retract" position and then moves back down a little like it's supposed to, the Z axis does not read "0.00" It now reads "32.768"

The interesting thing here is that 32768 is the exact number that results from 32K of memory. 1024 x 32 = 32768. I find this to be extremely suspicious, especially since most of the problems I have been having with the machine losing position is on the Z axis.

Now I'm wondering if I actually have a corrupted bit in the data block 0 portion of the memory, or a problem with a memory board, or whatever. When I bought this machine it had a CMC systems tape emulator board and a 64K upgraded memory board. Except I've been running the 33a1 master which is for 32K machines. I don't know of another master that can take advantage of the full 64k on the board. Doesn't make any sense to me.

So my thought was to press the reset switch on the memory board to clear everything. The only problem with that is that the DOS laptop I used to save and load programs, along with the master, died. So I didn't press it.

BUT.. In the process of poking around in there, the servos suddenly went out of control and bottomed out in the zero position. That made me have to clean out my underwear! I hit the E stop and then shut down the power. Once I turned it back on the CRT simply said "Load Master"

So now I'm screwed. I have to find an old computer to put DOS on, get the emulator software and get a master. I know that Buddy at AMTS has masters available for download, along with DOS and windows emulator software. Unfortunately the emulator board that's in the computer doesn't seem to work with the windows version of the software I got from CMC before they went under. I don't know if the windows emulator software from AMTS will work either. Otherwise I could just do it from this computer I am using now. Assuming it ran ok under XP.

On a side note: Buddy at AMTS is a good guy. He's helped me before and I think he's a valuable resource for helping keep these old Hurco machines alive. If I ever do have to spend any $$ on stuff to keep her running, he will be the first place I go. Hopefully everyone else does too.

Anyway, on the bright side, it really looks like my problem with losing positions has nothing to do with the hardware. It's probably a poor connection at one of the boards or the ribbon cable, and/or some corrupted memory.

I have had trouble in the past with the little 16pin IC to IC ribbon cable before, maybe it's time to just make a new one.

Unfortunately I didn't get to try tuning the servo boards yet. Now I have to get the master reloaded, etc. Sigh.

Oh, and for what it's worth, it looks like the machine has Westamp servo boards in it.

Thanks,
Michael

[bloke]

If the axes jumped madly and you lost the master, it's likely you'll need to clean the ribbon cable that connects all the boards together. When you get the master back in, give it a tap with the servos on. I bet the axes jump.

If you have Westamps fitted, ignore the above advice on setting up the amps - that's for Randtronics servos. I'll dig out the setups for your amps in a while.

As for the number that appears on the display after tool cal, you'll need to have a "tool in spindle" set and a tool programmed in data block 0 to make this figure disappear.

[bloke]

WESTAMP SERVO AMP SET-UP

Test Equipment Required: Digital Volt Ohm Meter (DVM)
Procedure for Adjustment:
Verify all amplifier board mounting screws have star washers installed. Install if necessary.
Preset Pots as follows:

WEST AMP
a.) AUX Full CCW
b.) SIG Full CCW Then CW (8) turns.
c.) TACH Full CW.
d.) TC Full CW Then CCW (4) turns.
e.) CLM Full CW.
f). BAL Full CW then 8 Turns CCW.

Measure with a DVM at SJ2, SJ3, or SJ4, pins 8 & 9, of the Servo Control
PCB.
With no command, adjust the BAL Pot to yield minimum steady DAC voltage of (+/-.009 to .000vdc)
Adjust BAL by continuing to turn CCW. Look for the lowest steady voltage possible.

Command 25 IPM feedrate as displayed on CRT. Adjust SIG Pot for 0.900 VDC at J2, J3, J4, pins 8 & 9.

Check while jogging in both directions, then adjust if necessary, so both
directions are within .90 VDC to .92 VDC.
The TC Pot adjustment may interact with the SIG Pot adjustment. The BAL adjustment will minimize the difference in voltage measured in this step when comparing movement in one direction to the other direction. It may be necessary to repeat the above to get good readings.
Axis Connector + Pins -
X SJ-2 8-9
Y SJ-3 8-9
Z SJ-4 8-9
Adjust the Sig Pot to achieve 0.900 VDC out of the DAC while jogging the axis at 25 IPM.
If an imbalance of voltage occurs, adjust the Balance Pot to get both directional ± voltages within
.050 VDC of each other.

DAC is measured at pins 8 & 9 of the relevant channel on the servo control PCB in the card rack. Normally, the wires will be coloured clear and black.

[Radius]

WESTAMP SERVO AMP SET-UP

Test Equipment Required: Digital Volt Ohm Meter (DVM)
Procedure for Adjustment:
Verify all amplifier board mounting screws have star washers installed. Install if necessary.
Preset Pots as follows:

Thank you for that information. Buddy at AMTS has a Westamp servo tuning guide online, but I don't think it's as detailed as that.

It would not surprise me in the least if the bottom ribbon cable has developed a poor connection. Those edge style of connectors are notorious for that. Really poor design decision, especially for something that will be susceptible to vibration. I used to collect classic arcade games and these things were always giving trouble.

Oh, and another thing I forgot to mention. I was unable to get access to data block 0.1 to change the rapid speed. Does such a block exist on my ancient B control?

Thank you for your help and time!
Michael

[bloke]

Data block 0.1 was available right from the beginning of B series controls. it contains program parameters.