Z axis full power no motion

[glbreil]

I have learned a few things here this evening. First the I do not have enough cable to swap the wires at the motor, but it does have connectors that would allow it.

I was able to get the machine to home even though the Z axis encoder quit reading at anout 12" instead of the usual 17". Once it homed and my DRO got some numbers on it I was able to see what was happening.

When you Jog the Z axis the encoder reading did not change so the motor took off wild at full speed. It has 1/2 second to prove motion and when that doesn't happen even though it is really moving it stops and gives the Full Power No Motion alarm.

I did swap the motor and encoder wires in the control panel and the problem stays with the Z axis. I have to assume since I can find no wire damage that it is the encoder. Oh and when you diconnect the encoder wire it does give you an error message that lets you know the connection is lost.

So the question is do I have to get a whole new motor? Is it repairable? I will of course look for bad connections in the motor and hope that is what I find.

If I have to get a motor or even parts do I go back to Centroid or will that come from somewhere else? Do all the motors have to be a like or will any motor of the same power and such work?

As you can tell I am new at this and this is the first problem I have had. I guess that is good luck.

Thanks for your help! Gary

[glbreil]

I got the motor off and don't see any visible problems. Here is the motor information.

SEM Made in England
Type: MTS30M4-48 NO: T18913
C. Stall Current: 6.8
Max. 3000 RPM 140 V 37 AMP
IP 54 IC 400
S/N E97-62154

The Encoder has the Following information.

SEM Made in England
7557HV 747-1-47811
PPR: 2000 V+ 5-24
NO: 740148


Thanks Again any information would be appreciated.

Gary

[MarcL]

With the motor off the machine, you could plug it into one of the other cables easily enough, just to confirm the problem is in the motor and not the external Z cable.

Cheapest solution is to just replace the encoder. You need to match shaft diameter (this one will be hollow shaft with flex mount) and output type (5V differential line driver). Ideally you also want to match cycles per revolution (2000) and connector type (9-pin black Waldom C-Grid?).

The shaft diameter could be 3/8", 1/4" or 6mm. I am thinking the "-1-" in the part number says it is 1/4".

Presuming it is one of those three sizes, is on a flex mount, and has the flat black connector on it, I have replacements in stock, for $160. Give me a call at 360-738-4829 if you want one. Centroid would have them too, perhaps for a few dollars less.

If you ever do need to replace a motor, any of several models from SEM, Baldor, Glentech or others would serve. You just need suitable voltage rating (preferably 140V); comparable current ratings (e.g. 6.8A continuous, 37A peak); and a suitable encoder (lines and output type). The connector pinout seems to be pretty standard, but may not be universal.

- Marc Leonard

[glbreil]

I got my hands on an encoder. I actually tried to call you Marc and got an answering machine and wanted to get it shipped so I would get it before the weekend.

I got it from Centroid and it is of course different than the one I had.

This one is a Danaher and the wiring all seems to be the same but the mounting is somewhat different. The old on had a spring mount and locked on the shaft with two set screws that tightened to two flats on the motor shaft.

The new one has a collar with ttwo set screws that fits over a hollow shaft that fits over the motor shaft which will all work fine, but there is no definate alignment as with the other one there was only two possibilties. Theis one has infinte possibilties. the directions talk about aligning with an Osciliscope which is not avaiable in my shop. Is this all necessary or can I just mount it and go?

Thanks again Gary

[glbreil]

Well I went a head and gave the encoder a try and it seems to work alright. One thing I do notice without have the motor mounted yet is that it seems to be kind fighting itself.

When you move the motor say .001 it will sit and sound like it is having trouble holding that position, like it is trying to rock back and forth but it is not moving then it will quit after a moment as sit quietly. You can move it another and it might just move and sit quiet and then it mightmake that noise for a while and sometimes it is sitting quiet and will start making the noise without being moved.

I think I have heard that even before the encoder problem and didn't really know what it was.

I think I might hear the Y axis doing that also once in awhile, but I don't think the Xaxis is doing it at all.

Sound like a problem?

Thanks Gary

[MarcL]

I am pretty sure that alignment using an oscilloscope is only necessary for commutation encoders on AC servo motors: not applicable here.

Originally Posted by glbreil When you move the motor say .001 it will sit and sound like it is having trouble holding that position, like it is trying to rock back and forth but it is not moving then it will quit after a moment as sit quietly. ... I think I might hear the Y axis doing that also once in awhile, but I don't think the Xaxis is doing it at all.

Not a problem. If you want to try to quiet it down, then rotating the encoder on the shaft (spring mount encoders) or rotating the encoder body around the hub (Danaher encoders) very slightly in either direction might make a difference.

Also, you can sometimes quiet an axis down by reducing Kd on your PID configuration. If you have Kd = 15 or 20, try cutting it back to 8 or 10.

[MarcL]

Regarding the Danaher encoders, be very careful inserting the wrench to tighten the collar, and don't forget the step of unclamping the disk. These encoders are easy to damage.

[glbreil]

Marc thanks for all your help. You seem to be very knowledgeable about this stuff. Are you a parts dealer or repair business or just someone who knows a lot about this stuff?

It does seem to be working good. If the noise is not a problem then I won't worry about it. I did try yesterday rotating the encoder a little and could tell no difference. I am pretty sure it did thia prior to the encoder problem, but with the motor laying out on the ladder you can here it good.

I will install the motor this morning and I have a gunstock waiting to be modified.

Thanks Again Gary

[MarcL]

Are you a parts dealer or repair business or just someone who knows a lot about this stuff?

All of the above: control dealer, retrofitter, service tech, trainer, programmer etc.. See www.cncsnw.com.

Unfortunately, "knowing a lot" in this business does not always add up to "knowing enough". :-)