Servo Amp Errors

Okay, I decided to move this to the forums, as to quit filling up Bloke's (roooster on here, bloke at the 'zone) PM-box (sorry!) and also so someone can be helped, if they have the same problem. Additionally, I know this is on the 'zone too, http://www.(site which will remain nameless).com/forums/hurco/120674-motion_control_problem_servo_amp.html#post885809 there are lots of people who don't cross over, and it's seeming that I need all the help I can get...


Okay, I have a problem where when I put power to the servo drives, my x-axis takes off about an inch and a half, then faults out the drive. The encoder reads correctly when I turn the ballscrew by hand, and it is wired normally.

Here are the clues:
If you switch the A+ to B+, B+ to A+, A- to B-, and B- to A- on the encoder, the x axis runs correctly, but in reverse. (when you hit the + jog it goes in the - direction)

When the encoder is correctly wired, and the three plugs are in the original Max400 servo drive, the table jumps to the right (negative in cartesian coordinates) for an inch or two, then faults the 'X-axis Servo Amp' when the start button is pressed upon startup to power the drives

When the encoder is correctly wired, and the three plugs are in the Y-axis Max400 servo drive, the table jumps to the left (positive in cartesian coordinates) for an inch or two, then faults the 'X-axis Servo Amp' when the start button is pressed upon startup to power the drives

When the encoder is wired up with A and B swapped, so you can give power to the drives without faulting out, the Y and Z axis both work correctly.

Given these symptoms, what might a person think that it can be?

Are you using Z channel? If so, have you tried inverting that signal as well?

I don't know what a Z-channel is, is that the index pulse? It's an 8-wire encoder, A,B,Index, and power

Sounds like an axis runaway. The polarity of the encoders and the axis are reversed.
Since you have verified that the encoder is wired correctly, the axis itself appears to be "backwards".

Is this a case where the you want it to jog right, it starts going left, the controller thinks OMG! I need MORE right signal, which drives it harder left, until it gives up and faults out after an inch or so?

I don't anything about what sort of drive you have, or if you can reverse the direction of the drive in the parameters, but that sounds like what you are describing.

Is it a DC motor? Does it have a tach?

With a tach wired backwards, the drive tries to move, ever so slightly, and the tach tells the amp it is moving the Wrong way, so the drive gives it more juice which gives it more wrong information from the backwards wired tach, until it gives up and faults out.

So, brush type drive/motor?
Tach?

Parameters to reverse the axis direction?

Motor connections are wrong!

Connect up the encoder as it should be. Then look at the motor on the servo. If DC simply swap the 2 wires over will probably solve this. If Ac its a bit more involved but is again just a case of swapping wires. If there's a tach that's just a added complication.

Easiest options just to leave the encoder connected opposite and swap the control outputs direction signal in whatever parameters. This may also be a dip switch - jumper setting on the drive too but i am not familiar with that one.

+1, Motor connections are backwards

You asked how this could happen. Do you have a practical joker at work? an enemy? sounds like they simply swapped your +/-10v speed command to the both drives.

If dc motors and NO tachs, you CAN swap the two motor armature leads and it will 'fix' this. If dc motor with tach, you cannot swap motor leads or your tach will then be backwards. If dc motor and drive, simply wire the encoders back 'correctly' and simply swap your command input to the drives as i said above. that will reverse the direction of the motor and encoder and correct the position loop incorrect phasing.

If ac drive, if you do try to swap motor leads to fix it, be sure to carefully write down all the terminal numbers and colors of wires before hand because you will likely 3 hours later have to put them all back to get back to a semi-running machine. Ie., dont go there. simply wire encoders 'correctly' and swap the drive analog input command signal again.

In either case, just swap the command input and the 'backwards' but wired 'correctly'. encoders will be correct again.

Show the practical joker you can fix this easily this way. Ie., what you describe is not possible without someone changing some direction parameter or signal polarity on you. Two drives will not 'fail' this way on their own without help

The backstory:
Firstly, this is a '91 hurco 40slv, with ultimax 2 controls, brushed dc servos, max400 servo drives.

This machine had been giving me a servo amp error upon startup for probably a couple months, off and on. it will also give me a z fault when i would switch from auto or manual toolchanger control.

More and more i would begin to get z, x, and i think there was even one y axis fault, almost entirely during programming, though running 30-40 hour weeks i think there were only maybe one or two faults during a running program.

Last tuesday when i started the machine, it started jittering on the x when calibrating. it faulted out. i then jogged the x back and forth to see if it would go away... it did, but jittered realllly badly for 10-15 seconds firs

I had previously seen green sea creatures growing in the junction box on the x servo, so i decided i would clean things all up, take the connectors apart, and if i couuldn't get it back together, i'd just solder and heat shrink it.

When i got it back together it began this problem started, i originally thought i screwed up the encoder wiring, re-wired it half a dozen times until i finally traced the wires back to the board. i've swapped encoders and amps between axis, to no avail.

and here we are...


I had tried swapping motor leads, but that makes sense with the tach thing... When I get back to work, i'll try swapping the signal wires to the drive. The strange thing is that it's me and one other guy, so I don't think there was any foul play, but I really don't care how it ends up working, just as long as it does, so I'm all over the drive wires in the morning...

I'll keep you updated...


-Parker

New development...

I swapped the power wires, and the tach wires, and now the X works, but if it gets to the limit switch, it freezes the axis, and won't move it anymore. if you manually back it off by turning the screw, it takes off away from the limit switch for about five inches once it's off the switch. (scary as hell the first time it happens, with your hand in there!!!)

The machine says 'Axis Not Calibrated - Marker Not Found On X' Though, it shows an X- flag on the screen, and touching the limit switch stops the travel, though it doesn't stop it immediately like on the other axis, it coasts a little bit...

Anyway, what would be doing that?

Anybody have any ideas on this problem? I don't really know where to start...

Swapped the RAC and FAC on the drive, and it works! Thanks Roooster (and everybody else) for saving my life!!!

-Parker