Fanuc 6M-B on old Okuma...how to get axis off hard limit?

[greenbuggy]

Trying to learn myself about this old control, of course that naturally means screwing things up and trying to figure out how to undo the screw up.

Machine is a ~1984-85 Okuma Millac MC-4VA with a Fanuc 6M-B control

Was trying to get machine to home all axis and I went too far on X and hit the hard limit, the hard limit must be part of the E-stop circuit because when it tapped that limit switch my "machine ready" light immediately shut off as if I'd hit the E-stop. If I hold the "machine ready" button that normally turns all the subsystems (servo amps, lube pump, hydraulics, spindle drive) the light comes on but "servo error 401" shows up on the alarm screen. With error 401 up, the servo amps will not reset (and hitting the "reset" button causes the alarm to disappear for a couple seconds then immediately reappear) as such I can't jog the table in the opposite direction so that it gets off the hard limit switch.

Some googling suggests restarting the control while holding P+cancel buttons down which didn't appear to do anything. I have to wonder if the hard limit switches are somehow tied into the servo amps, unfortunately this machine didn't come with wiring diagrams to tell me if or how.

Is there an easier way to do this than unbolting and disconnecting the axis servo motor and rotating it until its off the limit switch? Or disconnecting the hard limit long enough to jog it back to center? I can do either if necessary but it seems like more work than it ought to be.

Last question, is there a procedure or call to make the machine automatically home itself? I'm a fanuc n00b.

 

[ewlsey]

There should be an override button somewhere. Hold it down. You will here a contact pull in after a second or two. Then you can jog off the limit while holding this button.

 

[mkd]

or turn screw with power off.

okuma controls have the override switch, not fanuc, right?

 

[aj]

There 'should' be an over-travel button on the controller somewhere. It'll be off by itself somewhere, maybe on one of the sides of the controller. Turn the controller on and hold that button in and you should be able to jog your machine off the hard stop.

As far as homing the machine, all our Fanucs will home with G28 U0 W0 with U0 being for X and W0 being for Z. On our older machines you have to home it manually after a cold start first though. Not sure about your particular model.

The "P-Cancel" trick is for another problem entirely.

 

[atex57]

If I hit the limit on my 6T I have to hold jog switch for a moment to re-engage the servo amp and jog away from the limit. Rehome after that.

Ed.

 

[Ox]

Every machine and brand will have it's own processes. This is not a "Fanuc" thing.

If you cannot find an O/T button nearby, just turn the screw by hand with the machine in E-stop.


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I am Ox and I approve this h'yah post!

 

[greenbuggy]

Every machine and brand will have it's own processes. This is not a "Fanuc" thing.

If you cannot find an O/T button nearby, just turn the screw by hand with the machine in E-stop.

I don't see an O/T button and can't find much in the (admittedly dated) 6M manual that the local Okuma dealer gave me. Will keep looking though.

I'm not so worried about the X/Y axis as those are pretty easy to move with power off, my bigger concern was with the Z-axis which has a servo brake and will not move without either applying power to loose the brake or unbolting and disconnecting the servo and spinning it down manually.

 

[Larry Dickman]

or, if getting to the motor is inconvenient, just unbolt the OT dog, and then jog it back. (and make dam sure you jog it back the right way)

 

[Heavey Metal]

On the z you can generally slide the brake

You can also hot wire the brake but be ready cause you prolly don't have a counterbalance and it will come off the

Limit fast.

 

[triumph406]

or, if getting to the motor is inconvenient, just unbolt the OT dog, and then jog it back. (and make dam sure you jog it back the right way)

I have a Makino with a Fanuc 0M control, that's how I have to get the Z-axis to move after a hard overtravel.

 

[Oldwrench]

When you have the dog out from under the switch (or vice versa) actuate the limit switch manually and if it shows signs of sticking, free it up with WD-40. If it's solidified coolant that's got it stuck, Windex will dissolve it. Because of water-soluble coolant, I'd swear stuck limit switches are more common on modern CNC machines than in the days of cutting oil. At least that stuff would lubricate the moving parts.

 

[Vancbiker]

I don't see an O/T button and can't find much in the (admittedly dated) 6M manual that the local Okuma dealer gave me. Will keep looking though.

The presence or not of a hard OT release button and if there is one, how it works, is the machine builders decision, not Fanuc. You will not find anything about it in a Fanuc manual. You will need the Okuma Howa machine operators manual to see how they handle this.

 

[andrewmawson]

On my 6M controlled Fanuc wire EDM machine, if you pass the hard limit, pressing reset clears the error message and allows you to jog only away from the error, not further towards it.

 

[greenbuggy]

An update: I don't have a proper wiring diagram for this machine so I did some tracing (BTW, if anyone has a proper wiring diagram for a 1984 Okuma Millac 4VA with a Mitsubishi PLC and a Fanuc 6M-B I'd pay dearly for it).

Turns out the top switch in the Omron switch packs on each axis is the "overtravel limit" for both +/- sides of an axis and is connected into the E-stop circuit. There's at least 3 (that I know of) Millac 4VA maintenance and operations manuals, the ones for the 11M have different (and wrong for this machine) switch diagrams and wire numbers.

The one I found with the correct wire numbers shows that the E-stop chain runs from wire 200 (at the E-stop switch on the panel) thru all of the limit switches (LS1 LS2 LS3) which have wires 211-212-213-214.

When there's continuity between 200 thru the E-stop mushroom switch on the panel and LS1 LS2 LS3 thru wire 214 then the cube relay on the top left of the panel by the contactors will close and illuminate the LED, when that LED is lit then pressing the "machine ready" button will close the 5-position contactor, start the hydraulic pump and servo drives, at which point you can jog the various axis around. Holding down the "machine ready" button will illuminate the green light above it but doesn't appear to energize the servo drives unless the cube relay is pulled in.

I looked all over and didn't see any sort of overtravel button or switch or bypass. Looking at the wires I traced there doesn't appear to be any relay or switch to bypass switches LS1 LS2 LS3, so in order to jog it off the overtraveled axis I put a jumper between wires 211 and 214 and was then able to get the machine ready light to stay on and servo drives energized so that I could jog it off of the overtravel switch, once off of the OT switch I could remove my jumper and use the machine as normal.

 

[Vancbiker]

Something that may help while looking for info would be to state Okuma Howa.. Until fairly recently (last 6-8 years) Okuma and Okuma Howa were two separate, distinct companies.

 

[greenbuggy]

Something that may help while looking for info would be to state Okuma Howa.. Until fairly recently (last 6-8 years) Okuma and Okuma Howa were two separate, distinct companies.

Anymore they're all under the Okuma umbrella but as I understand it Okuma & Howa Millacs are nearly if not identical iron as Okuma Millacs though they could be fitted with any number of Okuma or Fanuc controls. I also have a Howa Sangyo manual lathe, Howa/Howa Sangyo was bought/absorbed into Okuma & Howa which then became Okuma and the dealers (in my area Hartwig) are all the same regardless.

 

[Mickey_D]

A lot of older Okumas have an overtravel release switch in the rear cabinet. Takes one person to hold the button down and one to jog the machine.

 

[greenbuggy]

A lot of older Okumas have an overtravel release switch in the rear cabinet. Takes one person to hold the button down and one to jog the machine.

A small update:
This machine has no overtravel release/bypass switch, but if you hold down the "machine ready" button long enough it will engage the whole E-stop circuit (actuating the hydraulic pump, spindle lube pump and servo amps) for as long as you hold the "machine ready" button down, you can then flip mode switch to "jog" or "handle" and move the axis off the OT switch, at which point you can release the "machine ready" button and the machine ready light will stay lit.

I think I was getting the 401 servo alarm because this machine is running on an RPC and if it doesn't come on in just the perfect timing the 401 alarm will come on for the Y-axis (can tell by flipping open velocity unit door and looking for red error LED's). Bought an 200v Omron on-delay timer that I'm going to splice into that circuit to space the servo amp off for a half second and see if that doesn't get rid of the hassles I've had with the 401 alarm.

I did discover that my Y-axis home switch was out of adjustment by a bit so that Y-axis home would only happen past the OT switch (You can test this by flipping mode switch to "zero return" and pushing jog+ on whatever axis you want to test while holding down the "machine ready" button, if when the home light goes on you release the "machine ready" button and the "machine ready" light goes dark either your axis OT limit or zero return bump stops are spaced wrong). I moved the Y-axis home stop over by 1/16" and it homes without tripping the E-stop chain now.

I also discovered that my ATC and a couple of other zero lights were burnt out - I found odd because they are LED but wouldn't power on after being removed and hooked to a 24VDC regulated supply either. Going to test every one in the control panel and replace any others that are bad as well.

Now, on to figuring out how to configure and use the toolchanger!