Need Help!- SQT 10MS WILL NOT FIND HOME ON Z AXIS

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MACHINE WILL NOT FIND Z HOME ON START UP.
Z SWITCH DOESN'T SEEM TO BE STUCK
Z AXIS MOVES BACK AND FORTH FINE IN JOG.
JUST WILL NOT ZERO.

ANY HELP WOULD BE APPRECIATED
ALL OTHER FUNCTIONS SEEM TO WORK
TURRET, SPINDLE, X AXIS AND SUB SPINDLE
AND NO ALARMS...

[onthebumper]

What exactly is the axis doing? Does it slow down when it hits the switch and continue to move on it's own? If so does it keep going until it hits the hard over travel switch?

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Yes it keeps going on to hit the hard stop.
it seems as if it is stuck on the slow speed
travel looking for the home point but just keeps
on going.

[onthebumper]

And you are sure the switch is coming back up? If so then the encoder is probably faulty. Once the switch comes back up then there is a pulse in the encoder that the CNC is looking for. I would try to swap the encoders and see if the problem follows.

You should also be able to check the switch state on the IF Diagnosis page if you know what the address is.

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not sure what the address is. The switch snaps up so I think it's
working. I have had this machine off for a couple of months is
it possible there is a battery that has run down?

[onthebumper]

It's not likely that a battery has run down. You would have more problems with the machine then this. What type of control do you have on this machine? This will help to determine what style of encoder you have. Again I would try to swap the encoder with another motor to see if the problem stays on Z. I can tell you more about swapping the encoders once I know what type of control you have. Most of the encoders are pretty easy to swap out though.

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T-PLUS CONTROL

[onthebumper]

Depending on the year you will have one of two encoders.

OS type encoder
Very easy to swap. Most of the older styles had an outside large cover that needs to be removed (four screws) then the encoder is on the inside which also removes with four screws. When removing make sure to pay attention to the T handle on the end of the encoder shaft. There is a mark on one side. Make sure when swapping the encoder that the swapped encoder's mark points in the same direction.

OH type encoder
A little more difficult but not impossible to do. Remove the outside larger cover (four screws). Remove the three screws holding the encoder on. Remove the sticker to expose the hole on the end of the encoder. Remove the Hex screw inside the hole. Once removed you will need to thread a larger longer bolt into the same middle hole (not sure of the size but it is metric). This longer larger bolt will push the encoder off of the shaft of the motor. It's a tapered fit so as soon as it releases it will pull right off. When reinstalling the encoder make sure to align the groove in the encoder shaft with the pin in the motor shaft. There is also a small hole in one of the tabs on the encoder that needs to align to the small pin sticking out of the motor end plate. This sounds like a lot of steps but once you get the encoder off it will make more sense when you see it.

If you have any questions just post them up here. If you would like to talk to someone on the phone about swapping it you can call Mitsubishi at 847-478-2100 and talk to a CNC service tech.

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build date is 1997, and as far as I can see looks like
an OS. I'll try the swap this weekend.

have you ever used a rebuilt encoder?
any ideas on the cost of rebuilt or new?



Thank you very much for all of your help.

[girishdk]

Hi,

From your feedback the Encoder seems to be Incremental, because it slows down after Home Limit switch is released.

Normally for Absolute Encoder, the home return is high speed, but of course with parameter you can make it search for Marker Pulse in slow speed, for every Homing.

The details of encoder should also be available in the Diagnosis->> Servo Diagnosis/Monitor screen, it will have OSAxxx or OSExxx or OHExxx or OHAxxx type for T-PLUS control with MDS-A or B type drives.

Normally the Home Limit Switch for this control is X001A for Z-axis. But some MTBs change it & assign to some other input.

if it is not changed, you can check for the Z-Home input in PLC Diagnosis as below.

X0018 00000a00 ---> check if a changes from 1 --> 0 --> 1

If above change in a is happening ok, please check if the Hard Limit happens after at least 1 rotation of motor.

If the hard limit happens before 1 rotation of motor, then the Limit Switch or the Dog need to be adjusted.

If the Hard Limit happens after 1 or more rotations, then the encoder or Cable could be faulty.

Chances of faulty cable exists, only if the encoder if OHExxx / OHAxxx because it is ABZ type. It cannot happen with Serial encoders OSExxx/OSAxxx.

Ref. attached for approx. layout.

Best Regards,


Girish

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it does not slow down after hitting switch in Z...
the z axis will run to the hard stop. not stop after hitting switch.
the part that i don't understand is it is stuck in slow motion looking for the
switch when I hit home to the right (or z +). if I hit home to the left (or z-) it travels faster with out slowing down.

[girishdk]

Hi,

Normally the +ve side is the Home position, so if the axis slows down during +ve direction seems ok.

If you can find the PLC Diagnosis Monitor, check for X001A input for Z-axis Home L.S.

if L.S. is pressed, a below should be 0. When released it should be 1, as below.

X0018 00000a00 ---> check if a changes from 1 --> 0 --> 1

If it does not change, need to check as below.

1) Confirm from Electrical dwg. Z-Home L.S. is X001A only.

2) Check this L.S. Cable.

Best Regards,

Girish