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Servo Control, step & direction control hazards

garyhlucas

Stainless
Joined
Oct 17, 2013
Location
New Jersey
I am building this automated drilling machine that has Yaskawa servo drives and using Step & Direction control from a PLC. Suddenly the X axis stopped responding to the reverse signal and runs just one direction. Imagine that happening when it is running in auto!

Checked all wiring right to the input pins on the drive. Definitely the drive, confirmed by installing the spare with parameters loaded from the previous file which works perfectly. Second drive to do this already.

So are people using quadrature inputs to drives? I believe this would be much safer as a loss of one channel would cause the motor to stall I think. I am working on getting the encoder signals back to the PLC where I could detect this problem. So far haven’t managed to get that working.

1000 lbs of moving mass and grippers reaching in and out between clamps. An oops of any kind could be a real disaster. I do have sensors up the wazoo,
more than 30. They don’t help with motion errors.
 

ViktorS

Aluminum
Joined
Apr 26, 2021
Never had that issue with the machines we build, but then again I can count the times I have used step/dir on one hand. Probably with a few fingers to spare.
But I have not used differential (I guess you mean that) inputs to the ones where step/dir have been used. You are sure that the drive is actually the problem?
Just thinking out loud, a regular PLC probably would have some problem outputting the signals fast enough if one does not use outputs that are meant to go in at least the kHz range.
But I don't know.

We usually prefer to go with CAN bus or any form of serial connection due to several reasons:
1) Easier when doing diagnostics and preforming updates to parameters. Usually only required to connect PC to the PLC to get all the data. When swapping drives parameters can automatically upload to the drives. Almost plug-and-play!
2) If trouble occurs one can display more accurate fault codes to the operator (if a display is present that is).
3) Easier to scale. Add/remove drives depending on system requirements. Often times, at least when we make machines, the requirements change in late stage.
4) Retrieve position data "automatically", among other things. Also torque data have become something we use quite often to detect a shitstorm in the making.


But for your problem I strongly suggest you get the encoder data in to the PLC, there are so many errors one can prevent with that.
 

Vancbiker

Diamond
Joined
Jan 5, 2014
Location
Vancouver, WA. USA
I’m going to echo Victor’s advice to get your feedback working and get some kind or position error scheme working. That is really basic stuff for motion controllers. Depending on what the capabilities the PLC you are using has this may not be so easy.
 

garyhlucas

Stainless
Joined
Oct 17, 2013
Location
New Jersey
PLC is definitely capable. 250khz in and out for three drives. However this is my first servo project and while I have lots of control experience I have been tripping over some things.
 








 
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