[ninjabika]

hi all

i'm just in the process of starting to build a cnc router, i've got the controller and motors , am just about to get the estop and home limit switches and this is where my problems begin, i have no idea how to wire these in, can somebody please shed some light on this for me please, i will be using mach3 if that's any help, i shouldn't have any problems building the unit as was a machinist / fitter for 26 years on millers/lathes can also weld pretty good aswell tig mig stick.
it's just the electrics never was my strong point


martin

[irving2008]

Hi there...

How they are wired in depends on which 6560 board you have and what controller software you are using. However one critical point... despite what some user guides say, the e-stop should be independent of the controller board and should kill all power to the controller/motor. It is unsafe to apply e-stop to the software and rely on it to stop the motors...

The usual way to do this is to power the motor power supply through a relay which is itself held on by the e-stop switch. The attached shows one configuration. By using the PC or breakout board 5v supply (or could be +12v from PC) the motors are automatically disabled when the PC is switched off.

When the e-stop switch is closed, pressing 'Start' energises RLB which in turn energises RLA and applies main power to the motor supply. RLB-1 contacts also bypass the start switch maintaining the power to RLB. Hitting e-stop de-energises both relays and cuts the power to the motors. The spare contacts on RLB (RLB-2) can be used to inform the controller software via the breakout or controller boards that e-stop has been actioned.

[MrWild]

I can see the thought behind a E stop that controls all power for a servo derived system. Looking at how stepper motors are energized, and need a for a computer control in the drive so that each phase of the stepper motor is turned on/off correctly, how is a software Estop such a bad thing? If the pulse stream is stopped, how would the drive get input to move the motor?

It is conceivable that a servo drive ciould short across the mosfets/busses, and the full power of the PS would go straight to the servo. As a (most) servo is just a DC motor, this could cause a run away and the use of an Estop would stop it in it's tracks.

If you're worried about an internal short caused fire in your control box and want the security of a mains power switch, then use one.

Here one last thought. Machine builders do NOT want a full power loss in their controls a full power Estop induces. Often times shutting down all power disengages the brake(s), and in an estop situation, you WANT that brake!

[irving2008]

I can see the thought behind a E stop that controls all power for a servo derived system. Looking at how stepper motors are energized, and need a for a computer control in the drive so that each phase of the stepper motor is turned on/off correctly, how is a software Estop such a bad thing? If the pulse stream is stopped, how would the drive get input to move the motor?

So your cutter is wandering off into the sunset and you hit e-stop.... but the reason its wandering off is the software isnt thinking any more, just doing... and its certainly NOT listening to that estop signal...!

Having written software for avionics systems the one thing you never ever do is rely on it in a critical situation unless you are sure there is some compensating solution (e.g. multiple voting systems or similar - and even then as one major aircraft manufacturer found out, it doesnt always cater for every eventuality)

Trust me, when you hit that e-stop, which i hope is never, you want to know its going to stop...

Here one last thought. Machine builders do NOT want a full power loss in their controls a full power Estop induces. Often times shutting down all power disengages the brake(s), and in an estop situation, you WANT that brake!

That may well be true. However in most systems where a brake is integral to safety it requires power to disengage brake, so killing power automatically engages the brake. If that is not the case (and I'd like to see the positive arguement for that) you'd create a safety first mechanism and put the brake supply on a seperate feed, actuated by a second set of contacts so e-stop kills power and applies brake. But for 99% of hobby or small workshop machines killing the power is the #1 solution.

[MrWild]

So your cutter is wandering off into the sunset and you hit e-stop.... but the reason its wandering off is the software isnt thinking any more, just doing... and its certainly NOT listening to that estop signal...!




Trust me, when you hit that e-stop, which i hope is never, you want to know its going to stop...




But for 99% of hobby or small workshop machines killing the power is the #1 solution.

Oh MY! Mach does this? EMC sure don't.

I have a E-stop that hooks directly to my G540 controller. I believe it shuts down the buffer power supply. Signals can't get through the BOB. The Chinese ~~65 boards do much the same. Even if your Windows based control system goes nuts, the signal doesn't get through. A Mains E-stop just isn't needed with most Stepper systems.


I don't think the figure is that high. While i agree it works and is fool proof, it just isn't needed with a properly designed BOB and low voltage E-stop circuit