[larspeed]

Hello everyone!

I've been searching around here for answers regarding a foldback situation on a BDS4 drive. Could not quite find what I was searching for, so here is my cry for help;

The machine has got a brand new hard drive with fresh software, which might be of a slightly newer kind that the machine originally (1996) was delivered with.
However, It boots up fine - no diagnostic errors, except for Touchscreen (but I've read that's quite common). Readings from X and Y axes seems ok when pushing the table manually.

It's when powering on the fun begins. Instantly after pushing the green button, I get Alarm 31-56. In short terms "Z axis drive in foldback due to overcurrent on the servo output for over 2 seconds". Yup - foldback on BDS4 for Z-axis is lit.
I read on here about servo brakes beeing stuck, so I got to dismantle, clean and mount it back on - No luck!
I then tried to remove the brake disc assembly and power up the machine again - same result. Also I checked if the solenoid at the bottom of the brake assembly is working by holding a screwdriver to it, indicating it's magnetic when powered up and will release the brake.
I'm not able to turn the servo without the brake by hand - should this be possible, or are they having a severly reduced gear ratio perhaps?

I'm wondering if it might be some MAI-settings that needs to be corrected, before I go ahead and dig deeper into the servomotor. Any suggestions appreciated!


Regards

-larspeed-

[meckardt55]

Shut the machine off, block up the head, take the 3 - Z axis wires off the Z axis drive ( Ma, Mb, Mc) ( make sure you label them) turn on the machine all the way. With the motor load removed, if you get a fold back alarm you may have a shorted IGBT unit (power transistor). If you don't get the alarm and you should be able to move the X and Y axis then the problem is up in the motor, brake or the wires to the motor.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Hi, Sir meckardt55

Clever suggestion - thank you! Almost obvious to rule out the motor, so to say... revealing my lack of experience right there.
Will try this when home from work.

If it should turn out to be the drive failing; are the IGBTs situated in a module/cartridge or are they possible to solder of for replacement? I have not been looking too much into the BDS4's entrails. e.g. "If it works, don't fix it"


Thanks again!

[larspeed]

Okay! Disconnected Ma/b/c on Z-axis drive and powered up. Green lights on drive and No error until trying to run Z-axis retract - which ofcourse(?) gave an alarm.

Seems right to take a closer look at the servo motor then, I guess.

[meckardt55]

I would think that the Z axis brake may not be releasing, check for about 100VDC on the brake coil and the fuse.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Yes, I thought about that too and tried to run without it - i physically removed the brake discs and pressure plates over the solenoid/brake coil.
Maybe the whole motor shaft has seized, because i can turn the axis screw by spinning the whole motor after removing the 4 allen screws that fixes it to the coupling box. The shaft/rotor of the motor won't move freely in the stator housing at all - brake removed...

[meckardt55]

Yes, it sounds like the motor bearings may be seized, remove the motor and check it out. Block up the head first as it will fall down when the motor is removed.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Attachment 280240

Well... this guy in the screw end was seized.

Think I will put in some SKF replacements.

[larspeed]

Yes!

Fresh bearings did it! I can now home Z, Y and X. But when the spindle has done one rotation, I get this message;

Attachment 280256
Attachment 280258
Attachment 280260

Y axis seems safe and sound so it's odd that this show up, or...?

[meckardt55]

Go into program ware and check the input. Adjust the Y axis parameters but first write down any value before you change it. You may try to slow down the feed rate when aligning. Pull back the Y covers and clean out the chips first.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Figured out that I probably should make the Z-axis brake work. Had a head drop when overtravelling the Y-axis... spooky!
When the brake issue was settled, I could move the Y-axis all in and out to get out the chips as suggested. Brushed the switches and tried homing again. Same result - "Y-axis not on tpa".

NB! I have shorted the air pressure switch in the back to avoid having my noisy compressor rattling about during troubleshooting, but does that interfere with anything else rather than the tool carousel not being clamped in? I have secured it but there might perhaps be other pressure switches that I'm not aware of...

Back to the homing; do these parameters make any sense?

Attachment 280718
Attachment 280720
Attachment 280722


Again; Thank you for supporting me.
I should probably rename the thread topic to "Another a2100 back to life. Hopefully..." or such.

[meckardt55]

You can adjust the align trim that will keep the switch on at the end of alignment. you can also look at the "move to align zone" and " align switch clearance". Check out the inputs on the X and Z axis.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Tried same Window and trim for Y-axis as was set for x-axis without any success.
Here are the settings for the other enabled axes. I have no a-axis head present however the machine is delivered with a drive for it which seems healthy - green lights as the other drives.

Here are the other axes parameters;

Attachment 280736
Attachment 280738
Attachment 280742
Attachment 280744
Attachment 280746
Attachment 280748
Attachment 280750
Attachment 280752

Should I tick off/disable the A-axis maybe?

Also the display is showing coordinates in inches not mm, if that could be of concern.

There are several spindles delivered with these machines, and this is configured with a "High Torque spindle". Not sure if that is correct, but I know for sure it is a 8000 rpm spindle.
Is there anything I can look after on the machine to determine the correct spindle setting?

[larspeed]

Thought school was over, but...

Attachment 280820

... former owner had all(?) documentation for the machine laying around!
This should be juicy stuff :S

[larspeed]

Allright! Progress, finally!
I set the InPosition Window on Y-axis to 0.2 mm and voilá - all axes at TPA.

Alligned the mech aswell and tried a tool change. MDI : M06 T2 *play* Z up, tools in, carousell spin, air blast, pressure low alarm...

Time to get a bigger pressure tank sorted, I guess.
Anyway! I am thrilled!

Does anyone know how to change display from inch to metric?

[meckardt55]

I would not have adjusted that parameter because it determines when the control sees that the axis is in position. I would have adjusted MOVE TO ALIGN ZONE, ALIGN SWITCH CLEARANCE or REFERENCE MARK SEEK in the Machine Application page. G70 is inch and G71 is metric.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Yes!

Perfect, Mike!
I notched the Align Switch Clearance down from 5 to 4.5 mm - that did the trick.
MDI:G71 - metric display.

Thanks, a lot, again - superb!

Attachment 281632

[meckardt55]

Did you put the in position window for Y axis parameter back to the original value??

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services

[larspeed]

Almost - it was set to zero before i changed it, but when I tried to change it back I was not allowed to set it below 0.01 mm. So I went with that.

[meckardt55]

Yes, I think that is the default amount. I don't think you would want zero in this parameter.

Mike CNC Machine Services INC | Cincinnati Milacron MachinesCNC Machine Services