Spindle encoder shot.. I am going to repair it

[SSMrob]

Ok, have an older spindle encoder, the type that is on top of the motor under a little cover, and is basically a toothed gear with a pickup that reads the teeth as they go by..

Now, it originally worked, but not well. At high speeds in the CW direction it would lose counts.. In reverse, it worked great..

Well, I went up there to reset the gap to try to get a bit more sensitivity out of the pickup, and I started it up and it turns about a quarter turn, then shuts off. No tacho signal is present at all now according to the control panel in either direction.

I noticed that there is an adjuster screw that seems to move the pickup sensor back and forth in very small increments. I still get nothing.

I know that the pickup has to have an excitation voltage (similiar to the pickup on a guitar)

I guess I will start there and see. I would suspect that there is a bad connection somewhere between the pickup and the main processor.

My most important question is, anyone know where the connection is made within the panel for the tacho pickup? I am thinking about just rewiring it with high quality shielded multiconductor wire and seeing if that helps. From the pedestrian schemos that are provided with the owners manual, I can't really tell.

Thanks in advance for any help anyone can throw my way!

[Eurisko]

Check for physical damage to the sensor. If the sensor came in contact with the gear teeth, it will have to be replaced.

Your setup sounds similar to the one used on our Okuma lathe live tool spindle. The gap between sensor and gear was very small, probably about .020.
Had to replace a few sensors due to careless installation.

[SSMrob]

Wow, the sensor is that sensitive that touching it off on the gear will destroy it??!?!

Incredible.. Well, when I first took it off to look at it, it had a rub mark on it before I even tried to adjust it so maybe thats what went on with it and why it was acting up.

I really dislike pickups like that.

Now I see why later they moved to the gear driven optical or hall effect tachos.. These types of sensors go out on cars quite a bit more than I like also. The biggest problem is when they go out, they do it in a way that its hard to diagnose exactly what the problem may be.

I think there is a company that makes a conversion for this that I may look into later..

Next step: where do I get the pickup sensor? And how much are they usually?

[One of Many]

Sounds like a typical prox switch application. Although prox switches are far from typical in specifications and characteristics

Depending on the configuration of the body, there may be numbers on it to reference. If not, you'd need to know the voltage, frequency limits and field sensitivity to save a few bucks on a cross referenced part.

Calling any online Fanuc supporting parts supplier with a Manufacturer, model and serial number could save some time. If you have the part number out of the manual, do a search and see what pops up.

DC

[Al_The_Man]

Many manufacturers use a similar PWG for spindle rpm detection, both Fanuc and Mitsubishi tend to use Matsu****a and Tamagawa made components for these kind of detectors and tachs etc, these are often custom made for each of their OEM's.
Al.

I forgot about the automatic editing, the Manuf in question sound like Matsusheeta!

[SSMrob]

If I could find the complete schematic of the in and out of this thing, or if I could see what the signals look like I could make something that would replace this..

Anybody got schemos of this bugger?

I know everyone will say "oh just buy another one will ya" but thats not how I work nor do I have that kind of cash.. $400 for a new one is just not possible..

[fanucman]

ok you are missing some steps here..

1) what control is on this machine
2) how do you know that its missing the "tacho" signal? You have a scope?
3) what alarm is this thing giving you?
4) are you sure that this sensor is the problem and not a separate position coder?
5) this ring and magnetic sensor arent old technology.. new ones use them too..
the motors that have a magnetic drum and a sensor are high resolution ones..
6) if you believe that this is the problem you need to adjust the sensor to the gear it needs to be 6 thousands away from the gear.. use a feeler gauge..
7) are there any marks or scratches in the senor?
8) have you checked the feedback cable yet?

[SSMrob]

1) what control is on this machine

Its a 3m

2) how do you know that its missing the "tacho" signal? You have a scope?

Yep. Got a really nice Fluke that does it all.. Saw some irregularity in the signal when CW.. I readjusted it and it worked ok for a bit, then it simply stopped working.. First sign was that it would *miss* pulses in CW and act up. I would have to warm it up for about 3 hours before it would smooth out and allow me to cut anything..

3) what alarm is this thing giving you?

8... Pretty generic..

4) are you sure that this sensor is the problem and not a separate position coder?

Its most likely the tach sensor.. Thats what I am going after now.. The spindle worked *great* in CCW, but not in CW. I don't think the position encoder would cause that..

5) this ring and magnetic sensor arent old technology.. new ones use them too..
the motors that have a magnetic drum and a sensor are high resolution ones..

Well, for some reason Kitamura swapped them over for the little gear type later on..

6) if you believe that this is the problem you need to adjust the sensor to the gear it needs to be 6 thousands away from the gear.. use a feeler gauge..
I tried everything from 10 thou to around 2 thou and couldn't get it to fire back up..

7) are there any marks or scratches in the senor?
That was the FIRST thing I noticed.. The tacho gear had rubbed it.. I saw it before I even adjusted it by shining an led flashlight in there.. It had been hit before I even got at it..

8) have you checked the feedback cable yet?
Yep, it rings out solid.. I even contemplated rewiring it from the spindle controller to the pickup just because I figure its prlly some old wiring and may need some help

One thing I *did* notice is the shielding on the cable isn't grounded on either end (!?). Sorta strange, but, I do know that sometimes you leave it floating depending on the app. right now I am not getting anything out of it from what I can tell..

I need to play around with it some more.. Another thing that gets me is, the sensor may be out, however, there really isn't *much* to break? I wonder if its possible just to rebias the circuit to deal with what looks like a decrease in output from the sensor?

At any rate, I got a bit more to look at before I figure out how to get this thing running again..

[fanucman]

Originally Posted by SSMrob 1) At any rate, I got a bit more to look at before I figure out how to get this thing running again..

ok good so this is a dc spindle or ac?


as far as the sensor goes.. i have replaced a ton of these.... if there is scratches on it just replace it... call fanuc and give them the part number off the motor and they will be able to give you a price on the sensor..

if the senor is having a problem you will usually see someting like 5volts or more on Pa and Pb check pins on the spindle board..

but alarm 8 is overvoltage usually on the 24 volt check pins.. check that..
i would also check incoming power to drive...

the other thing to try is to swap the board if you have a spare or another machine.. on the spindle drive you might have a board problem since its going in 1 direction..

i would honestly call fanuc their advice over the phone is great i bust their balls all the time with questions they are good for it.. lol

[SSMrob]

Spindle is DC..

the alarm 8 isn't at the spindle controller, it is at the panel...

on the PIL it lights up the 2 in the 8421 output..

Well, so far, we pretty much know the sensor is toast with all the scratches it had on it. It was rubbed up pretty badly..

If that doesn't do it, then, its on to start trying to route it back to something else..

[fanucman]

Originally Posted by SSMrob Spindle is DC.. the alarm 8 isn't at the spindle controller, it is at the panel... on the PIL it lights up the 2 in the 8421 output.. Well, so far, we pretty much know the sensor is toast with all the scratches it had on it. It was rubbed up pretty badly.. If that doesn't do it, then, its on to start trying to route it back to something else..

ok then perfect.. alarm 2 is speed deviation or signal loss..

check PA and PB with a meter on ac and if you see something like 5 volts the sensor is definitely bad..

[broby]

mean while... back at the ranch... well over $400 of lost production has flown out the window!
Are you really sure you can NOT afford the measly amount i would cost to do this job as stated earlier?
Seems like you must be charging only a few dollars per day for your time if it is okay to spend this amount of time fixing this problem.