Shopbot with Mach3 Proxmity switch hookup

[Helicopterjohn]

Hi,

I have just purchased a Shopbot CNC router that was setup to run on Mach3 in lieu of the Shopbot operating software.  The previous owner disconnected all the homing and limit switches on the machine when he converted it to Mach3.

I have watched the videos on the Mach3 support on limit switches, homing etc.

If I hook up couple of wires to one of the inputs of the CNC4PC C-10 Breakout board it works as one would expect (i.e. normally open or normally closed) getting the desired lights on the Mach3 diagnostics screen.  However, if I hook up the Proxmity switches that came with the Shopbot router the LED on the Proxmity switch lights up when the switch comes with the designated gap of the proxmity plate but does not send a signal to the control to disable the axis movement.  My assumption??? is that being the LED light on the Proxmity switch comes on they are working correctly.  Maybe, they need a different activation voltage etc.?

Any of you guys out their with converted Shopbots that may have already encountered this issue and found the solution.

Also, my pulse frequency on the diagnostics page is reading around 45K instead of 25K.  Any ideas on how to correct this?  I ran the Driver test and got an excellent report but got a message saying that the pluse rate was too fast.

The machine is running but just wanted to fix this issue.

Any help would be appreciated.

Thanks,

John

[Tweakie.CNC]

John,

I would suggest you contact Shopbot regarding the proximity switch wiring for the type of switch you have fitted as some may require a pullup or bias resistor connected to operate correctly with the Mach input. If they don't know, or are uninterested, then if you have the make and type number for your prox. switch I should be able to identify the wiring requirements.

If you change the kernal speed to reduce your pulsing frequency you will also need to re-tune your stepper motors, unless you are happy doing this (not difficult really) then my advice is if it ain't broke.....

Tweakie.

[Helicopterjohn]

Hi Tweakie,

First, thanks for your valued input.

I spoke to Shopbot yesterday and they informed my that my proximity switches are the normally open type.

I did a little experimenting today.  I changed the jumper on the CNC4PC.com C10 breakout board as it pertains to Pull Up or Pull down selection.  It was set for Pull Down and I switched it to Pull Up.  Now my proximity switches work GREAT on both the X and Y axis.  That's all for the good news. 

When I changed to that configuration then my Emergency Stop button will not work.  I tried changing the active low settings etc. but it was of no help.  Would I need to put some type of resistor on that circuit to get it to work as expected?

Any ideas?

[Tweakie.CNC]

Hi John,

I think you have just discovered the reason your proximity switches were disconnected in the first place.  

The C10 pull up / pull down unfortunately applies to all input pins and adding a resistor will not solve the problem.
As I see it you could either.........
1) Do a bit of sugery on the BoB to remove the pull up resistor which is associated with the pin you use for the estop or possibly.........
2) Swap the estop switch from one with normally closed contacts to one with normally open contacts and reconfigure your active hi / low within Mach (incidentally I use normally open contacts on my estop and limits).

Given the choice I think I would go for the surgery but then electronics is my thing.  

Tweakie.

[Hood]

Dont know much about electronics or prox switches in particular but could a NOR gate be used? I seem to recall I had a similar issue on the Bridgeport when I did it (5 or 6 yrs ago) and used a NOR.

Hood

[Tweakie.CNC]

You are quite right Hood, it doesn't necessarily have to be a NOR though as any inverting logic gate would do. In effect it would turn the logic of a normally closed contact into a normally open contact. (quicker to snip off the pull up resistor but it depends on personal courage  )

Tweakie.

[Hood]

Yes snipping the resistor would likely be the easiest. I cant remember why exactly I had to use one but dont think it was so much the pullup issue, think it was more to do with the limits I used actually had two optos in them and wanting to connect them to one input required the gate, it was a long time ago though so memory is hazy.

Hood

[Helicopterjohn]

Hi,

Thank you guys for your valued input.  My weak suite is electronics.  I have a friend of mine stopping by on Friday to take a look at the situation.  Actually, the Emergency Stop button has 4 wires and I tried different configurations but probably not the one I needed for success.

In talking with the guy from Shopbot he says that all their new proximity switches are normally closed.  The reason is that if there is a failure in any of the switches or wiring the the router will stop.  With a normally open proximity switch if you have a broken wire or other simiilar failure the router will just cruise right by the proximity switch and crash!!!!!!

My goal is to get all the limit and homing setup on the machine working properly prior to moving on to get the tool setter working.

John

[Hood]

That is definitely the best way, all safety switches (limits/E-Stop) should be wired NC  for the very reaons you mention.
Hood

[Helicopterjohn]

Hi Hood,

Funny thing,  I was reading some more posts here on the forum about homing, proximity switches, etc. and found an answer you submitted that was also verbatim of the information I received from Shopbot.

I guess I need to look into the availability and cost of some new N/C proximity switches.   Currently my configuration is that I have (1) each proximity switch on both the X and Y Axis and none on the Z axis.  From what I understand I should have (1) on the X, Y and Z axis.

Can anyone recommend a brand and associated reseller here in the USA that can provide these N/C Proximity switches and associated cabling.  I believe I read that the cables should be shielded to give proper noise rejection.

I will also contact Shopbot and see what they get for the new style N/C Proximity switches that are currently supplied with their new machines.

John