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Old 12-20-2016, 12:23 PM   #1
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Default (dual) motor rotation monitoring relay

Different situation here. A friend asked me for help with their CNC table.

The X axis has a master/slave motor setup. He recently fat fingered something and wound up spinning master and slave in different directions - breaking a significant chunk of the machine.

Due to the way it's setup there's no sort of interlock he can wire up. Both motors can spin forward and backward - but they MUST spin the same direction as the other.

My original back of the napkin diagram tells me that a pair of motor rotation monitoring relays could do the trick. The panel housing all of his controls is already pretty packed. It also got me to thinking - is there anything already existing for this purpose?
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Old 12-20-2016, 01:02 PM   #2
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Old 12-20-2016, 01:51 PM   #3
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Old 12-20-2016, 03:31 PM   #4
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what controls the motors? vfd, servo drives, contactors?
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Old 12-20-2016, 03:59 PM   #5
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Default Not from CNC program

It sounds more like a machine malfunction then a fat finger. If he was just writing a CNC program it would not of caused a master/slave motor screw up. The CNC program sends a command to the drive and the drive controls the matching of the motors.

NOW if he was in the drive setup and this happened it is his fault for changing something he should not of. If you fix this on X how about Y and Z or C or A or......

There should already be an error signal in the CNC machine. I know you can't add anything external such as your suggesting due to the speed of the changes in direction. If this is on a rack and pinion drive they use it for anti-backlash / static stiffness and at times run them in opposite directions to hold a axis in place.
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Old 12-20-2016, 04:30 PM   #6
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Controller is a HiCon Integra

Macmikeman: Unfortunately when this program is running (via Mach 4) their programming is not available. He also wants something hardware independent.

oliquir: Motors have their own controllers. This shouldn't happen but due to a bug it did. The motors and controllers are Yaskawa high end servo motors.

just the cowboy: This is a 100% custom CNC machine. Every piece in it that isn't bosch unistrut (Rexroth?) is custom milled out of aluminium. He's a machinist by trade. Much of what you have said does not apply. There is a error signal for the drives - but that would only occur if the drive had an actual error. The drives for the X axis should never run in opposite directions in this unit. If ones running clockwise the other needs to run clockwise. I know my solution should work. Each COM connected to one of the inputs to which I can flag a "error enable". The NC from one connected to the NO from the other and vice versa. At least from a quick sketch this seems to work.

The bug was in either the software that converted the 3d drawing to G code or the G code transition to the controller (hicon integra). For some reason it treated the spindle as a motor. This "overwrote" the commands to the slaved motor and caused the problem. We still aren't 100% positive about the exact cause and how it happened, but we have been able to repeat it with a test program. He has been dealing with the Software manufacturer and the hardware manufacturer.

He was asking me to help him design a independent system to prevent this from happening again.
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Old 12-20-2016, 04:35 PM   #7
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Default Encoder and PLC

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Originally Posted by fttank85 View Post

He was asking me to help him design a independent system to prevent this from happening again.
Use two encoders into a PLC automation direct under $1000 in parts.
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Old 12-21-2016, 04:14 AM   #8
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Use two encoders into a PLC automation direct under $1000 in parts.
Would it still be quick enough to react ???..

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Old 12-21-2016, 09:26 AM   #9
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maybe you can program the servo drives to output a contact when in forward direction so you could check the status of those contact
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Old 12-21-2016, 09:49 AM   #10
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Default It should

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Would it still be quick enough to react ???..
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If you used it as a dedicated PLC with a dual channel high-speed inputs, you can be in the high micro seconds. Even at 1ms I don't think it is going to do any damage, it takes longer than that for a E-stop relay to disengage.
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