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Messages - brw0513

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21
General Mach Discussion / Re: What would cause my limit switches to trip?
« on: November 20, 2012, 06:43:51 AM »
I chased false limit switch triggers for weeks with no success.  My solution was to introduce a 12V DC relay - the six limit switches were wired in series and were in the 12V supply circuit to the relay coil.  The normally closed circuit in the relay was wired to the limit input of my controller.

Works well.  Not the best solution, but for the life of me I couldn't work out what was causing my limit switches to trip - and I tried to be very diagnostic.


22
General Mach Discussion / Re: Limit Switches and Interference
« on: November 20, 2012, 06:37:32 AM »
I am pleased to say I have a solution to my limit switch problem :)  Not really the way I was hoping to solve it, but trying to find the source of the false tripping turned into a 2 week saga that was doing my head in.

I'm now using a 12V DC SPDT relay.  The six limit switches are in the 12V power circuit to the relay coil and the normally open switch is connected to the limit input to the PROMiCA IC3A controller.  It works wonderfully :) but I do have a 12V power supply and circuit that I never thought I'd need. 

23
General Mach Discussion / Could Windows XP be Twiddling the PP Pins
« on: November 07, 2012, 05:13:23 PM »
I've had no success in trying to solve my nuisance limit switch tripping.

I'm at the point of clutching at straws now.

Is it possible Windows XP is twiddling the parallel port pins?

Any tips for me?

Thanks.

24
General Mach Discussion / Re: Stepper Motor Cables - Shielded or Not?
« on: October 30, 2012, 09:11:57 AM »
Thanks for the replies.  I just wish an earthing/grounding problem would leak a benign purple die to help identify the exact location of the problem!

Hood,

I have two questions for you:

1.  When you say shielding of "all wires" do you mean "only the stepper motor wires" or "absolutely all wires" i.e. stepper supply cables, cable between VFD and spindle, limit switch cables, home switch cables, earthing wire to case of PC, earthing jumper wire to VFD body, earthing wire to body of machine?

2.  If you were to put an "X" at the location where all these wires meet, would it be on the frame of the machine, PC case, controller case or elsehwere.

Picengraver,

Could you post a photo or two, or a specific description, of exactly where your capacitors are installed?  I have 4 wire stepper motors, so I assume the capacitors would be soldered between the supply wires to each phase.  The limit switch circuit has only two wires to the controller, but my opto home switches have three wires. 

When I do resolve my problem, I'm going to post about lessons learned and include a schematic of my solution to hopefully help others on this topic.   

25
General Mach Discussion / Stepper Motor Cables - Shielded or Not?
« on: October 30, 2012, 06:53:44 AM »
I started a previous thread about limit switches and interference - still haven't solved that one, but when I do I'll update with what I've found.

My questions now are:

1.  Do you use shielded or unshielded cable to supply your stepper motors?
2.  If shielded, where do you ground your shields?

IIRC, I have seen a few cnc hardware suppliers that sell 4 core unshielded cable, pressumably for stepper motors.  And from my current experience :) if I used unshielded stepper motor cable, then I may be blissfully unaware of my likely earth loop problem.

Thanks.

Ian B
 

26
General Mach Discussion / Re: Limit Switches and Interference
« on: October 28, 2012, 07:05:13 AM »
After another hour or so of trials and tribulations, I think I've found a potential solution (pun intended :) ) although what I've found to work still seems a bit odd.

My stepper motors are wired with 4 core insulated (braided shield) cables.  At the motor end, the braid is not connected to the stepper motor body.  At the controller end, the braid is exposed and twisted together and soldered within a female bullet connector.  My intention was to use a mating male bullet for ease of connection of a fly lead to an earthing point.  I now wonder if the "proper" thing to do was to expose the braid of the stepper cable at the motor end and connect it to the stepper motor body?  But anyway..................   

When the stepper motors are energised, the un-grounded braided shield around each 4 core supply cable shows a small AC voltage.  Between the stepper cable braid and ground:

The Z axis gives 2.25V
The Y axis 2.0V
The X axis 1.75V

If I don't ground the stepper motor bodies, then each develops 1.5V AC between its body and ground.

When I leave these stepper braid sheilds ungrounded, but ground the body of the stepper motor and the braided shield of the limit switch cable runs, then the router operates perfectly.

Alternatively, if I ground the stepper motor braided shields and stepper bodies, but do not ground the limit switch cables, then the router operates perfectly too.

It is only when I connect the braided shields of the stepper motor cables and the braided shields of the limit switch cables that the controller trips out - and it happens instantly.  The PROMiCA controller is just not happy when I earth both the stepper cable braids and the limits switch braids.

Happy to receive any further comments.

     

27
General Mach Discussion / Re: Limit Switches and Interference
« on: October 28, 2012, 12:09:22 AM »
The pics below show some details of my router.



X axis drive:


Y axis drive:


Z axis drive:


Typical limit switch and e-stop:


The spindle (not installed yet) is a TecknoMotor:


Plate used to connect the braided shields of all the limit switches:


The controller is from PROMiCA (Australian company).  It includes the axis driver cards, power supply, and limit and e-stop functionality:





Suprisingly, it did not include any grounding/earthing point so I made some.  The posts just loop to the earth pin on the incoming power supply fitting:


In the bottom two pictures, I do not have my limit switches or the e-stop button connected.  The bottom most green socket has two small loops of wire installed - the blue jumper is just a "dummy" limit switch circuit; the grey is the jumper for the e-stop.

When the stepper motors are energised and not grounded, I measure around 0.75V AC between stepper body and ground for the Y axis; 1.25V for the Z axis; 0V for the X axis.  This makes me wonder whether there is an insulation breakdown on the Y and Z motors.

I can get my controller to "limit switch" trip when I ground a motor during running, so highly suspect some grounding issue.

The odd thing is when I ground all the stepper motors, limit switches and e-stop switch the controller is constantly tripped so I can't do anything.

There is a few more things I can do, like disassemble the two leaky motors to have a look see - but would appreciate help.  
 

28
General Mach Discussion / Re: Limit Switches and Interference
« on: October 27, 2012, 11:48:20 PM »
Here's a general pic of the router.

Hmmm.  Seems I can post one pic at a time provided it's small enough.

29
General Mach Discussion / Re: Limit Switches and Interference
« on: October 27, 2012, 10:14:24 PM »
Grounding may well be the issue.  I've got lots to learn in this area, and having let the magic smoke out of one or two things in the past has me cautious  :-[

I'll post a few pics of my router on the next few posts - seems I can only post 4 pics at a time and getting some odd naming convention error at the moment trying to do it.

The frame is made out of aluminium extrusions bolted together with aluminium cast brackets or pieces of angle.  The frame is not grounded.

The stepper motors are mounted to pieces of aluminium angle.

30
General Mach Discussion / Re: Limit Switches and Interference
« on: October 27, 2012, 03:13:47 AM »
After much head scratching, I'm close to going to watch TV for the rest of the evening then sleeping on the problem.  Pity I can't get the World Series baseball on free to air TV here!

My router is made of aluminium extrusions.  I've measured a 1.2V AC voltage between the frame and earth when the stepper motors are energised.  I can't imagine that is normal but also can't really see where it is coming from.

More detective work ahead.

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