Build Log - Herbert

[Neale]

Just to be clear, opinions expressed below are not definitive or instructions to others, but are how I've built my own control cabinet.

Firstly, forget any idea that a fuse or MCB protects the thing that they feed. Any electronic engineer will tell you that a transistor is the fastest fuse known to man. If a driver's protection circuitry fails to protect against overload, it's probable that a fuse or MCB will still be scratching its head by the time that the driver has let out the magic smoke. What the MCB does do is protect against the effect on, usually, the wiring which is now carrying fault currents and where there is now a risk of fire. I have used a single 10A d-curve MCB to feed the whole cabinet; my hope is that this will protect the wiring against a major fault in any component. VFD is outside the cabinet, separately fused, by the way.

Power comes into the cabinet, then via MCB to two-pole isolating switch. Power then goes to auxiliary power supplies (5/12/24V for various things). I use a CSMIO motion controller which is powered at this point, together with "power on" panel LED. I use a Pilz safety relay (picked up cheap from eBay). A momentary push button turns on the safety relay which latches on. One set of contacts feeds the e-stop input on the motion controller, configured so that this enables the MC. A second contact feeds a 24V relay to provide mains to the linear PSU for the drivers, plus second panel LED. A third contact is used to enable the drivers. E-stop wiring connects to the safety relay; all switches wired in series and any switch will cause the relay to drop out so sending e-stop to motion controller, disabling drivers, and cutting mains power to drivers. That seems to cover most of the safety bases, at this kind of level. At the moment, the driver fault outputs are wired in parallel to the appropriate motion controller input so, for example, driver stall detect should stop motion. Limit switches do not trigger e-stop.

Using multiple contacts on the safety relay means reduced relay count (just one, for switching the linear power supply to keep mains off the safety relay contacts), while not relying on motion controller firmware alone for safety functions.

I haven't bothered talking about things like VFD connections to the motion controller, or coolant pump switching, as these are subject to individual designs, and I'm sorry that I don't have a wiring diagram as I've never drawn one... Don't know if there are any thoughts in there that might help - happy to discuss further if need be, or defend myself against other points of view!