Z axis home problem

[EliseoMonteverd]

Hi.

I have a probbem with Z axis home.
On the screen, when it is supposed that Z home has finished, it appears alarm # 126 Z AXIS NOT COMPLETED. in blue, or # 272 Z AXIS ORIGIN RETURN UNFINISH . in yellow.

Can someone give any idea where to check, to find the problem?.

Thanks in advance.

[onthebumper]

I believe this problem occurs when the control does not see the Z pulse coming from the encoder after it hits the dog switch. Does the axis slow down when it hits the zero return dog switch? If so try to swap the encoder on the end of the motor with another motor.

[EliseoMonteverd]

Opps!. I forgot to mention this machine is a 1990 VQC 15/40.

Yes,the Z axis slow down when it hits the zero return dog switch.

I wil try to swap the encoder on the end of the motor with another motor.

Thanks you.

[EliseoMonteverd]

The problem I think is the encoder, because I have opened it, and found a plastic scratched disc and some plastic chips inside...

The encoder can be repaired, polishing that plastic disc?

Thank you.

[onthebumper]

You can try to clean the disc but usually the encoder must be replaced.

[EliseoMonteverd]

Originally Posted by onthebumper You can try to clean the disc but usually the encoder must be replaced.

I have cleaned the disc, but no polishing.
At least something works because , turning by hand the encoder´s shaft , (wich is conected to the machine) I have readings on the screen.

So I am wondering if the encoder is Ok ..how can I chek it?

Thank you!

[MTSS Service]

HI There;

Go to your machine parameters for the axis soft limits. Positive and negative limits.
Record the numbers for both parameters. For the Neagtive type in
(Negative) -9999999 and for the (Positive) type in 9999999. Do not turn the machine off. Try and home the Z axis. If it will home then change the values back to the original values. Power the machine off then back on and try homing again.
If the Z axis continues to move slow all the time when trying to home then your delcelaration limit switch may be bad. You may also try doing a grid shift according to instructions in the maintenance manual that came with your machine.


Larry (MTSS)

[onthebumper]

By rotating the encoder and seeing the readings change on the screen only means your A and B phases are working properly. It does not mean the Z phase is working. The Z phase is used for home position return and only outputs a signal once per revolution. The fact that you can move the axis without alarming also says the A and B phase are good.

When you are zeroing out the machine the axis hits the dog switch which decelerates the axis and starts to look for the Z phase and stops once it finds Z and marks off home position. I suspect in your case the control/drive is not seeing the Z phase and that is why it is alarming.

[Leelund]

It's been a while, but you hit the dog at speed, then decel and travel at creep speed across the dog but it doesn't look for Z phase until the switch comes off the other end of the dog. After the switch extends it stops at the next Z phase plus offset. My experience has been if the limit swich is stuck in the axis will creep until it servo lags out or hits a hard limit and never stops until then. His machine sounds like it decels and does eventually stop which don't make sense. If it doesn't see the Z phase it should keep on rotating looking for it correct?

[onthebumper]

I believe the control or drive knows how many pules per revolution the encoder is (set by parameter). So for instance if it is a 25,000 pulse per revolution encoder and the control or drive sees that it has gone a full 360 degrees or 25,000 pulses without seeing a Z pulse then it alarms out. This of course is a guess but I'm pretty sure I've seen this problem fixed by encoder in the past.

By the way I agree with your explanation of the dog switch that is does wait for the dog to come off the switch before looking for Z.

[EliseoMonteverd]

Ok, too much work around here. But I promise that as soon as possible, I will follow yours recommendations.

Also, as I have Z + /- readings on the screen , I could check with a dial indicator the Z axis position going up an down.

Thank you for your interest in help me.

[Leelund]

This machine is not equiped with Sony Magnascales is it?