BMC20 / ULTIMAX 2 PROBLEM

[theexhaustman]

As pre title. I have a problem that after the machine has run for approx an hour I get a X or Y axis MOTION ERROR and the machine stops. If I switch it all off and on again it will run again for maybe 10-15 minutes then stop again.

The problem doesn't originate from the motors or drives ( FANUC ) as I have swapped them from axis to axis and rewired them on the drive.

Does anyone know how I might access the service page that will allow me to diagnose what causes the servos to shut down ?

Many thanks,

Andy.

[fasto]

I think you and I must be the only BMC-20 owners out there with the Fanuc triple servo.

When you get the MOTION ERROR, are there any lights lit up on the triple servo? There's a vertical row of led's on the top right corner of the servo drive board. The top green led should be lit. If any other led's are lit there's a problem with the servo, motor, or most likely the encoder cable.

I think MOTION ERROR means that control missed some encoder counts, or received encoder counts when they were not expected. On my machine I can cause a MOTION ERROR by turning the ballscrews by hand with the servo power off. Missing or spurious encoder counts are most likely caused by a faulty encoder cable.

Have you done any testing or repairs? I would disconnect the encoder cables from the X and Y motors and make sure ther pins are not corroded or covered by oil. Use contact cleaner, if needed. Then, I'd unplug and replug the blue Honda connectors on the triple servo and CRP board. Then, I'd unplug and replug the DB25 connectors on the dual axis board, and the CRP board.
Sometimes a bit of corrosion on these connector pins can cause intermittent trouble. Remaking the connections wipes the corrosion off.

[theexhaustman]

Thanks for the reply. When I bought the machine many years back, I specifically wanted Fanuc motors / drives as they are in my opinion very reliable.

Have done all the normal unplugging, cleaning connectors etc. The green LED goes out when the m/c trips out but no red LED's are shown on either the axis or spindle drive. The machine resets after 5-10 mins and will run for 15-20 mins afterwards before repeating fault. Will run for approx 1hr from cold.

[fasto]

I thought that one of the red led's would light up if the green light went out. (Just to be sure, you do have the triple servo drive?)

There is a "drive ready" signal for each section of the triple servo. From the machine schematics it looks like Hurco looped all of these together. The drive itself has a 4-bit status output but I don't think it's hooked up to anything, and I don't know what the status means. I think the status output is only available from the drive if it faults, in which case the status replaces the A !A B !B quadature outputs to the control (if I recall). I do not have any manuals or any other information on the drive.
For information, I am not certain that the control does a good job of identifying drive trouble. I had a faulty part on the Y axis in my drive, and the control showed Z AXIS SERVO ERROR even though the Y axis was actually giving trouble.

Did you check the fans and such to see if you're getting enough airflow? You could even put a thermometer in each cabinet. Your description of 1 hour running, then fault, then after a bit running again for 15 minutes sounds very much like a thermal problem.

You said that you're getting X and Y MOTION ERROR alarms. Do you get both at the same time? Do you get mainly X but sometimes Y? When you changed cables around did you then get different alarms?

[theexhaustman]

Definitely 3 axis, and definitely no red LED when the green one goes out ! I had also come to the conclusion it was a heat related issue. All the fans are good and have even tried airconditioning the cabinet, but to no avail ! The alarms are x, y, or occasionally z, but not altogether. I think the alarms are as a result of the servos being shut down during motion because of another issue rather than servo related. If I remove the 100vac from the servo's during operation I get exactly the same symptoms. I have jury rigged the 100vac supply directly from the transformer to the drives to eliminate the control circuit that it passes through, but the fault remains the same leading me to think that the motion error / servo issue is a symptom rather than the actual fault.

[fasto]

I believe the trouble is in the triple servo drive. You're right about the MOTION ERROR. This error happens because the control wants to move the axis, and the axis won't move if the servo drive trips out. Thus, the MOTION ERROR. If the servo drive was properly telling the control that it had faulted, you'd get a SERVO ERROR so this points the finger at the servo drive. I considered that the X/Y dual axis board might be causing trouble, with your saying that you have had Z axis MOTION ERROR alarms I no longer think the dual axis board is likely.

When you jumpered the 100VAC into the drive, that makes the two contactors in the drive pull in. The contactors (1) release the brake on the servo motors and (2) apply 180VAC 3-phase to the rectifiers to make the drive's DC bus voltage and (3) signal the drive that it is supposed to start working.

This triple servo is essentially three servo drives that share a common DC power supply, and a fourth, common circuit that gives the "drive ready" signal - the green light.
Each servo drive watches itself, and if it is in trouble it lights a red led (either TG or OVC) and simultaneously signals the common circuit that it's "not ready" The common circuit shuts off the green led and opens that small relay near the led's.
The common circuit also watches some other items that are used by all 3 servo drives. The main DC bus voltage, if it goes high or low the common circuit will shut off the green led, turn on a red led (HV or LV), and open that small relay. The main power supply input current, if this goes too high it lights the HC led. And what is important to us, the +15, +5, and -15V power supplies, if any fails it should light the DC led but this is not guaranteed.
There is no condition that's supposed to have the green led out and no red led lit. This leads me to believe that perhaps the power supplies on the servo drive that make +5V are not working when the MOTION ERROR happens.

Do you have a volt meter? Next time the MOTION ERROR happens, leave everything "as-is", get your meter, and check the voltages on the servo drive. There's a vertical line of test pins on the left-hand bottom side of the drive. Check voltages between the pin labeled "0V" and the pins labeled "+15V", "-15V", and "+5V". You will need the right-hand cabinet open while the machine is working in order to do this, and you'll have to turn on the main switch without using the handle on the cabinet door, since you can't open the door with the switch on! Be triple careful as there's voltages up to 600V on some terminals in that cabinet.

[theexhaustman]

Thanks for that, but unfortunately all the 3 voltages are present when the machine trips out.

[fasto]

Ok then! This one's a puzzler for sure.

To clear this error, do you have to turn off the main switch, or does "Reset Servos and Spindle" clear it? Does it clear immediately, or as you said, do you actually need to wait to clear it? If you wait with the power on will it eventually clear? If you leave the right-hand cabinet open does it run longer before faulting? What if you set up a portable fan blowing right onto the drive's card?

I believe that you've got a thermal intermittent connection or component on the drive card. I'm not certain that you would want to troubleshoot this further, or have a local tech in to look it over, this would depend on your needs. If you need the machine for production you'd probably be ahead by calling in a tech. In my case I decided to look it over myself, because these drive cards are nigh impossible to find used, and Fanuc wanted $5,000 for one. I also considered installing three new separate servo drives, as I recall I costed this out at around $2400 total, plus installation (which I was going to do myself).

If you've got time to spare I'd be happy to help.

[theexhaustman]

If you switch the m/c off and back on it clears immediately. If you go on the 'servo reset' soft key it will reset but only after 5-10 minutes. I have tried an air conditioning unit blowing cold air onto it but makes no obvious difference.

[bloke]

What's the serial number of your machine? (If you don't mind me asking...).

[theexhaustman]

BH2-002-048

Why ?

[bloke]

It gives an idea of location...

BH8-002-048