Enable pins on Stepper driver, are they required?

[Robin Hewitt]

I had forgotten that you write your own control code and don't use Mach or Linuxcnc

That was unexpected. I thought the only person who listened to me was my wife, one word out of place and her jaw starts to flap.

[Neale]

Editing a post because of a missing gerund was pretty unexpected!

But back to topic - in an emergency (about to smash cutter into clamp, body part in imminent danger...) you want the machine to stop with 100% certainty and as quickly as possible. So you won't trust motion controller firmware, cutting power to driver power supply probably won't stop the machine immediately as you need to wait for output caps to discharge, and removing driver enable might not brake motors. Could cut power to drivers on output side of PSU but need chunky and reliable relay as you are switching high DC currents (possible contact welding?) and still lose braking. Could put something (TTL gates? Another relay?) in line with step signals - four of them, in my case.

This is getting a bit silly! In my case, the Pilz device sends e-stop to CSMIO (manual says this has very fast response) and cuts mains to driver PSU (via secondary relay). These use high-reliability n/o Pilz contacts. I am also using the auxiliary n/c contact (not high-reliability) to switch the enable signal. This is for convenience as the drivers are effectively active-low on the enable input so I need to put +5V on them to disable. So, I have two not-absolutely-reliable stopping mechanisms but which are independent so one should work when needed with cutting driver power as a slower-acting backup, but not clear at the moment if I shall get motor braking. Safety is such a compromise...

[Clive S]

In my experience cutting power to the power supply does not make the machine run on more than a few m/s before the caps run out of juice

[magicniner]

Safety is such a compromise...

One of your primary E-Stop circuits should reliably control the spindle and effect an E-Stop with braking (if available) using it's controller. ;-)

[Neale]

The Huanyang VFD is controlled by the CSMIO and I have been assuming that this will stop on e-stop although I have not checked this. However, I do have a primary Pilz contact going spare and I could wire the VFD run signal via that for belt-and-braces. I have more-or-less finished the control box, apart from some small odds and ends, but the machine isn't quite at the same state. Once I have limit and e-stop switches fitted and wired, I shall be going through the safety functionality that I have. For example, I haven't yet checked the VFD braking characteristics and tuned things like deceleration.

When I say that safety is a compromise this is, obviously, I hope, tongue-in-cheek but we do have to be sensible about this. I am building a hobby machine for a home workshop, and not expecting idiot bystanders to wander by and poke fingers in it. However, I am also moving from the mark 1 built from MDF which is just about strong enough to stand up to its own weight(*) but would self-destruct in the case of any foul-up, to the mark 2 which is all welded steel, including gantry, and could do itself and anyone in its path serious damage. So, for example, accessible e-stops and limit switches all round, but no "open door" detector for the control box. Just trying to steer a sensible course between extremes.

(*) I exaggerate - in fact, it is not quite strong enough to stand up to its own weight...

[cropwell]

(*) I exaggerate - in fact, it is not quite strong enough to stand up to its own weight...

I hope to start a steel gantry build soon - I hope it will stand up to my weight, but I am not light.

Serious question - does anybody use braking resistors on VFD's ?

Cheers,

Rob

[Clive S]

Rob I am sure they do but for the ones we tend to use I personally don't think they are a necessary. But you can alway connect it to the 3 bar fire under the bench

[magicniner]

The Huanyang VFD is controlled by the CSMIO and I have been assuming

My Siemens VFDs have Stop and E-Stop wired inputs, it's this input and not a peripheral device which should be relied upon to implement the E-Stop.
Most good E-Stop switches have at least two circuits to facilitate direct control of the nastiest component of a machine, if it's all nasty then it usually operates a mains cut off but for most lathes and mills killing the spindle removes the most risk, the motor cannot start while the wired E-Stop to the VFD is active.

[njhussey]

I thought I read somewhere in a discussion that cutting power to the VFD whilst it was running was not a good idea and that the best thing to do was fit a timer to then switch off the power after it has been told to stop by the controller?

[magicniner]

I thought I read somewhere in a discussion that cutting power to the VFD whilst it was running was not a good idea and that the best thing to do was fit a timer to then switch off the power after it has been told to stop by the controller?

That's why the decent manufacturers have an E-Stop input on the VFD, you can configure different ramp down and braking for Stop and E-Stop, if you have a braking resistor the E-Stop can be startlingly fast.

An electrical engineer I used to talk to was discussing ramp down time for a circular saw E-Stop with his boss and was instructed to make it stop as fast as possible, his boss arrived later that day for official commissioning and a demo an was surprised to find Chris outside the workshop door with the E-Stop on a long lead, his boss paid for the replacement blade and the floor, wall and ceiling repairs.