View Full Version : Sanity check my understanding of estop and MPG

16-11-2023, 02:03 AM
Hello, looking to sanity check what I'm doing.

Little bit of background, feel free to skip.
I purchased a Chinese CNC router (Forsun if anyone is interested) and I'm pulling out the ncstuido card it came with and replacing it with the massively overkill CMSMIO/IP-S and MPG.

So I've pulled out the dodgy card, avoided touching the 240v side any more than required and added a Meanwell 24v PSU. I have connected up the sensors and tested them, the steppers are connected up but not powered or tested and the spindle is disconnected. My intention is to connect up the MPG module I'm a little unsure when it comes to the estop on that which has now made me question the estop on the rest of the machine.

The machine has a estop and a power button, when plugged in you press the power button which activates a contactor and turns everything on and the estop will cause that to deactivate and turn everything off including the 24v and the IP-S. This seems ok to me so far. For the estop on the MPG, I understand that this would act as a switch for a 24v signal into one of the digital inputs on the IP-S and the IP-S would then use this to trigger a 24v contactor to disable just the spindle and axis motors whilst keeping itself powered on?

17-11-2023, 01:21 AM
For this setup, I'd keep the 24V PSU alive, and kill only the motor/spindle power with all E-stops.
I wouldn't involve anything other than a safety relay in the E-stop actuation process, as relying on the controller has the potential to cause an issue if it's because of the controller that you want to e-stop.

17-11-2023, 09:19 AM
On my own router I have three e-stop buttons around the machine, wired in series. They supply power to a relay with multiple contacts which switch the "enable" signal to the stepper drivers, switch power to the relay which supplies power to the stepper driver supply, and send a signal to the estop input on the motion controller. I should also switch an enable signal to the VFD but I ran out of control wires to the VFD... This is a big advantage of using the estop button(s) to switch a relay - a relay with multiple contacts can then switch multiple different items. Essentially using the estop as a mains switch is a bit brutal - but easy, which is why it's done. However, you are now relying on the reliability of a single component, the relay, to guarantee safe operation. That is why a safety relay is recommended - these are designed to be as reliable as you can practicably achieve and are used for things like safety gate operation. They are not cheap (although I was lucky enough to pick up one as obsolete and damaged packaging which is why I use one). If I were doing it again, I would use a pair of standard relays arranged with coils in parallel and contacts in series or parallel (depending on what they are switching) to give a poor-man's safety relay equivalent. The commercial safety relays include quite a lot of internal complication that is not really required for a machine like this (such as supporting duplicated estop wiring).