Blowing driver fuse

[tesart]

I am retrofitting a large knee mill.  Mach3->Smooth Stepper->C23 cnc4pc bob->Larken viper 100 drives->baldor servos.(all latest rev)  Every thing is working fine but one thing.
 I have limits and then estops on all axises.  the X and Z work fine.  When I hit the limit on the Y it stops, then the fuse blows in the drive board.  Even hitting the switch at really slow speeds blows the fuse.  When this happens it jumps slightly in the oppisite direction.  Jogging>hit switch>machine stops>jumps back .01"> blows fuse.
The X and Z work fine,  hit switch>machine stops>press reset>jog off.

I'm tired of changing fuses  And am out of ideas.
Any here?

Tom

[Jeff_Birt]

Much more info needed. How do you have your limits wired? Are they wired to Mach only? So when mach/ss sees the limits it just stops sending motion commands? Do you have your limits wired to anything else, like a relay to kill power to something?

[tesart]

The limits are wired only to mach.  I have separate limits for X, Y, and Z axis.  They are active low.  Wired +5v>NC switch on the ++travel>NC switch on the --travel>mach pin.  In mach under Inputs I have the same pin assigned to both the ++ limit and the  -- limit.

Thanks

Tom

[Lucky13]

This is very odd for this to do this.

 When your E-stop or limit switchs are activated does it cut the power to the motors in anyway?    You DO NOT WANT to cut the power to the motors OR drives on the DC side of the circuit.  This will cause voltage to climb,  or have no place to go and burn drives.   When cutting the power it should be done on the A/C side of the power supply so that the DC circuit is still connected. 


What type power supply do you have?  It should have big capaitors and even some type of resistor that bleeds the capasitors after power is shut down.  These motors put voltage back into the system when they coast,  even if the power is shut down.  If there is no place for this voltage to go burning drives,  or even motors is what can happen.  Your every lucky blowing fuses is all that has happened no matter what the cause.  You need to fugure this out.  Of course I understand that is what your trying to do here but just to let you know this can cause big problems.     


The action that your system takes when the E-stop or limit switches are activated is very critical,  this is what the guys mean by needing more info on how you have your system wired and setup.  The complete system,  not just the limit switchs.  So a detialed description of your wiring of all systems might help the guys figure your problem out before something gets beyound repair.  The fact it only does this on some drives is bit odd.  WIthout knowing any wiring of system info I would say check all connections on the DC side of your motors and drives.  A connection that was lose and not making perfect contact could aid in causing this,  but expect something else to be the cause.


Good Luck
Jess

[tesart]

Thanks again for your help.   the switches are set up so that first the limit switch is tripped signaling Mach to stop motion.  If for some reason motion continues an Estop switch is tripped killing the AC power and applying the spindle brake and alerting Mach. 
When the problem happens on the Y it never gets to the Estop switch, just the limit.
I'll check the wiring connections. and swap drive boards today and see where the problem goes.
Thanks again,
Tom

[Jeff_Birt]

If for some reason motion continues an Estop switch is tripped killing the AC power and applying the spindle brake and alerting Mach. 

First I missed out that you are using a SS. It should be handeling the homing and limit switches, not Mach. I know Greg has been working on something related to homing (slaved axis I think), but you might want to dig around on the SS forum (warp9td.com) and see if you can find anything. The situation you describe above really concerns me. You should NEVER have switches in your EStop chain used as limits on the machine. That is a big NO-NO. Limit switches should be tied to your controller (the SS/Mach in this case) and it alone should be responsible for bringing things to a halt if you hit a limit. You can even set Mach to slow down as it approaches a limit, so in fact, you should never actually hit one hard.

I have seen machines wired as you describe and it makes for a very dangerous situation when servo power is removed all the sudden while the machine is in motion. On big gantry machines they will lurch and slaved axis will jump out of sync. Usually the same machines that did this also had the limits arranged so you could actually drive past them! Another big NO-NO. Limits should be arranged so that the machine hits them just before a hard stop, there should be just enough distance to allow the machine to decelerate enough to avoid banging into the hard stop. You should never be able to drive past the limit.

A limit is there to let the controller know that something has gone wrong and that it should quite trying to move.The controller should be smart enough to know that it is approaching a limit (a.k.a. soft limits) and not try to drive past it. EStop is there to protect the operator in case something goes wrong.

[tesart]

You should NEVER have switches in your EStop chain used as limits on the machine.

This isn't the case.  The limits are set up to signal the controller to stop motion(Mach is also set up to slow down near limits).  the Estop/hardlimit switches are are just for a secondary failsafe, A completely different circuit not connected to Mach.

Tom

[Jeff_Birt]

I understand that, but still maintain that it is not a wise idea. IMHO.

[arturod]

Tom,

So you are killing the AC power when you hit e-stop.  If you are using the C23 and have enabled the Safety Charge Pump, you can use pin 17 for that. This should not blow the fuse.  Have you talked to Larry?  I am sure he can suggest something.  This sounds like a problem with the power supply.

On large machines I always recommend users to not leave the limits and e-stop at software control.  Our boards come with an external enable terminal marked EN.  You can use that to connect e-stop and limits to have these disable the outputs and stop the machine at hardware level.

Arturo Duncan
http://cnc4pc.com