An 'E-Stop' is a very specific type of circuit, a safety circuit. It's job is to stop a machine when things go wrong it can be initiated by an operator or by a control sensing an error condition, like a limit switch being triggered. Think of an E-Stop as a several NC switches wired in series. Each switch as to be in its normal unswitched state (closed) for the circuit to completed and things to work. Even a wire in this circuit is damaged it will break the circuit and cause an E-Stop condition.
The problem comes about when folks think they can use Mach and the charge pump to be the instigator of all things E-Stop. In other-words you have a switch hooked up to an input in Mach and set up in Ports & Pins as the E-Stop input. THEN you depend on Mach to quit outputting the chargepump signal in order for your BOB or other chargepump receiver to remove power from the drives. That is a very dangerous condition as the entire E-Stop system relies on a PC and a piece of software to always function properly in order for the E-Stop to work.
An E-Stop circuit should be able to do its job no matter what is going wrong. That is why I suggest using the Charge Pump signal as an Enable not as a safety device.
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Jeff Birt |