Y axis drift

I have a cnc router. It used to be multicam, but we retrofit the unit, with camsoft software, and a galil motion card. The software runs well, and has plenty of options. The problem I am having is: when I run a series of holes using only the x axis, the gantry moves toward the home position, .00085" per cycle, and doesn't show up on the y axis display. In the program, the y is set at the same at the start, as at the finish, but the gantry drifts over, even though the display says it is not. Any ideas? help.:confused::idea::drowning:

I see this is a very old post, hope you got it fixed...

Is the machine closed loop (encoder or Glass Scale)

Servo or stepper ??

If it is Stepper it is probably open loop, it is most likely losing steps check for excess drag on Y axis. You may need to slow the acceleration rate to fix.

If it is Servo closed loop, check that there is no slippage between the encoder and ballscrew. Check for lose electrical connections and/or noise on encoder signals.

If you got it fixed what was to problem ???



I am having similar problems on a big Vertical Machining center with the Z axis losing position about 0.020" over 4 to 6 hrs of running a program (production)

I am rewiring the Z axis encoder with new shielded cable and going to see if that fixes it.

I have a servo motor system, with motor mounted encoders. The x axis is gantry type, with master/slave motors. The y and z axis are both driven by servo motors with timing belts, and ball screws. I still have the problem. I had a yaskawa tech here last week, and he thought, that it was possible that there was noise in the system, and pulses were being picked up in the drives, and not showing up in the displays. I took apart one of the cables, we had retrofit, and the soldering job was deplorable. I am currently looking for factory made cables, that I can plug into the drives, and wire the other end into my terminal blocks.

japco43,

How many signal wires come out of the Encoder ??

single ended has a,b,z V+ and Common (0V)

Differential has a, a-not, b, b-not, z, z-not, V+ and Common (0V)

If the encoder is not a Differential type (6 signals) (8 wire total)

be sure that the cable is a Shielded type either way.

and use twisted pair for Differential to further help reduce noise. and Ground Shield ONLY at the Control end, leave the encoder end "floating"

The encoder has 6 wires. The cable is factory made, with a molded end, that plugs directly into the yaskawa amp. We recently had the router retrofit, and some of the wiring, runs along with, or near some of the power wires. I have a feeling, I am going to have to rewire it myself, to correct any noise issues.

That would most likely mean that it is single ended:

a, b, z, V+, V0 and probably a voltage sense line.

the voltage sense feeds your V+ back to the power supply so it can adjust its output voltage up or down for line drop. This is used only if your power supply has this capability.


Again with Single Ended encoder output it is most important to shield and do it properly, and stay away from running parallel to power conductors.

that should solve your problem. :D