Losing steps

[tjs88yj]

I am having trouble with my mill, it seems that I am losing steps. The mill is set up as follows...

1986 Hurco SM1 Stock ElectroCraft Servos and encoders, Larkin Viper 200 drives, Smoothstepper, CNC4PC C23 BOB, Dura Pulse GS3 VFD, Mach 3

I am using an indicator mounted in the spindle, I zero out the indicator on a bar clamped to the table parallel to the Y axis. I then make a G1 move in the X axis of -1.000" and then insert a 1" Jo block. With the feed rate set to 4 IPM the indicator reads .000. I then rezero my indicator on the Jo block, remove the block and make a g1 move in the X axis back to 0. The indicator will read -.0015. I did this 3 time at this feed rate and had the same results. When I increase the feed rate to 6 IPM, I get an indicator reading of .001 on th first negative X axis move, but it is off -.035" on the move back to 0. If I increase the feedrate to 10 IPM I get .006" on the negative move and .067" on the move back to 0. If I do a G0 move it is off almost .185" on the move back to 0, sometimes the axis will error(red light flashing)on the G0 move.

I've done some testing in the Y and Z axis and don't seem to have any issue, the indicator reads within .0005" both directions.

Any idea what might be happening?

Thanks

Tom

[multiplex]

what count are your encoders? what voltage are your motors, and what are you powering them with?

that is quiet alot of error for such slow speeds!

[tjs88yj]

I have the stock 1000 count I believe, the voltage is ~80V dc, powered by the stock Hurco power supply

[multiplex]

are you able to jog at a decent speed without getting an axis fault?

[Larken]

You can read the internal counters (the 'm' command) in the drive to tell whether your loosing steps or encoder pulses

M= motor encoder counts S=step input counts.

-Clear the viper counts by turning it off then on. it should read M0000 S0000
-clear the Mach3 DRO to 0,0
-mark the shaft of the motor to a zero point or zero a dial indicator
-run a small program and send back to 0,0
-Use the m command to read the viper

you should get M0000 and S0000 or close to zero on M eg( MFFFF or M0001)
-If your S is not zero then you are loosing Step pulses.

-If the S is 0000 but the dial indicator is off, then your loosing encoder pulses.

Note: the PID will try to make S and M close , but what your looking for is to see if your loosing step pulses, if not your loosing encoder pulses.

Larry K

[tjs88yj]

Larry,
Thanks for the reply, it looks like I'm losing encoder pulses. How do I eliminate this problem? Thanks

Tom

[Larken]

Are they single ended or differential encoders?
Are you grounding the shield on one end only ?

[tjs88yj]

Larry,
Single end I believe, but I'm not sure. They're the stock encoders from my 1986 model Hurco. I am using the wiring that was on the mill, and tapping into the wiring harness in the power cabinet. I am only having trouble in the X axis, I have all 3 wired the same.

Tom

[Larken]

If your encoder uses 1 wire for each A and B channel then its single ended with a total of 4 wires.
If your encoder uses 2 wires for each A and B channel then its differential with a total of 6 wires.

I would suggest you run new twisted pair wires right from the encoder to the viper. Tapping into existing wireing can be a can of worms.

If the encoders are single ended, you may want to replace them with some US digital Differential encoders.

Larry

[tjs88yj]

If your encoder uses 1 wire for each A and B channel then its single ended with a total of 4 wires.
If your encoder uses 2 wires for each A and B channel then its differential with a total of 6 wires.

I would suggest you run new twisted pair wires right from the encoder to the viper. Tapping into existing wireing can be a can of worms.

If the encoders are single ended, you may want to replace them with some US digital Differential encoders.

Larry

Was looking at the US Digital site, which encoders would you recommend?

Tom

[springlakecnc]

Many times the problem is simply unschielded wire INCLUDING the 25 pin cable that goes between your computer and breakout board. Just because its a boughten cable, not a homemaid, it still could be your problem, as i found out once the hard way. I have used these drives on a few machines, and never lost steps because of the drive, its ALWAYS a wiring issue.

[tjs88yj]

Many times the problem is simply unschielded wire INCLUDING the 25 pin cable that goes between your computer and breakout board. Just because its a boughten cable, not a homemaid, it still could be your problem, as i found out once the hard way. I have used these drives on a few machines, and never lost steps because of the drive, its ALWAYS a wiring issue.

Thanks for the suggestion, I'll keep it in mind although I'm using a Smoothstepper so I'm using a USB cable between the computer and SS. I'll try some rewiring of the X axis when I get back to TN, I'm in MI right now.