Hi all,
Just wondering if it is necessary to use the enable pins, I notice a lot of setups do not use them. What is the purpose of them? Any drawbacks to not using them?
Thanks
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Hi all,
Just wondering if it is necessary to use the enable pins, I notice a lot of setups do not use them. What is the purpose of them? Any drawbacks to not using them?
Thanks
They are not generally necessary to use them but they can be used to halt the drives from the motion controller via the BOB.Quote:
Originally Posted by ROBCNCAU
So it would be a good idea to use them then? It is only an one extra wire to hook up.
Yes but stall detect would be a better option for me especially if you have a slaved axisQuote:
Originally Posted by ROBCNCAU
I use a Pilz safety relay which sends an e-mail stop signal to the motion controller, takes power off the driver power supply, and also removes the enable signal from the drivers. One of those should stop the machine! The safety relay is tripped by the e-stop switches and the driver fault signals which are all wired in series. There are enough relay contacts on the safety relay to do that so, as you say, for the sake of a piece of wire it's easy enough to do. I wanted to make sure that the stall detect would stop the machine as I am using slaved motors for the X axis.
[Posted twice]
Doesn't the EN pin free the motor so you can do a bit of manual positioning? If so it makes for a crummy emergency stop because there is no braking. OTOH if your drivers have no pattern memory and revert to a set home pattern when you switch on, then EN would be a good option if you wanted everything to cool down while you replaced a broken tool, went out to buy milk, fags etc.
I hadn't thought of the possibility that the driver might remove motor voltage if not enabled. I can't see anything specific about this in the manual - going to have to actually test the hardware. I take the point about motor braking but I was influenced by a number of comments on this forum that you should not trust motion controller firmware for safety-critical functions like e-stop. Not entirely sure why not as we trust it to move each axis correctly and recognise limit switch inputs but there we are. So IF you don't trust the firmware and IF chopping power to the drivers will not have immediate effect, how do you stop the machine quickly? I'm particularly interested in avoiding damage if one of the slaved axis motors stalls. The manual does say that on stall detect, power is removed from the motor.
I agree Neale the beauty of stall detect is that you have all the drives connected together so that if any one drive stalls they all stop and that will stop the gantry from destroying itself.
We assume it will and we hope it does and that is usually the case but the E-Stop is there purely because we should be aware that the worst can happen and the way to make sure everything is guaranteed stop if we want it to is to have the best failsafe we can devise, and that is not the systems which will have failed in the worst case scenario.Quote:
Originally Posted by Neale
On the actual function of enable pins, a useful way to use them is to position work on the machine, jog the tool to your desired reference point, hit the disable switch and jog the controller to the matching position on the path display without moving the steppers. You could manually position the machine while the steppers are off if it has handwheels,
- Nick
There is a big difference between PAUSE and emergency STOP. If everything goes to hell in a handbasket I usually retreat to the safety of the mains socket and kill the power there. This does preclude braking the spindle at the VFD but it is comforting to know everything will soon come to a halt without removing any more fingers.
Pause OTOH implies a restart so it is purely a software driven thing which involves looking in to the G code future and creating a plan to get everything back up to speed. A well written pause is a joy to behold and well worth playing with :chuncky:
Why should a pause require a restart as you should just be able to do a resume with no problems. A pause is generally a controlled stop as apposed to an emergency stop which always requires a rehome etc.Quote:
Pause OTOH implies a restart so it is purely a software driven thing which involves looking in to the G code future and creating a plan to get everything back up to speed.
Sorry I should have said UNPAUSE. I award stepper motors a speed at which I can start or stop them without losing steps. Once beyond that speed pausing and unpausing become interesting. It's tricky keeping everyone in synch. I have written it twice, once in Z80 assembler and once in C.Quote:
Originally Posted by Clive S
I had forgotten that you write your own control code and don't use Mach or LinuxcncQuote:
Originally Posted by Robin Hewitt
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.Quote:
Originally Posted by Clive S
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...
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
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. ;-)Quote:
Originally Posted by 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...
I hope to start a steel gantry build soon - I hope it will stand up to my weight, but I am not light.Quote:
Originally Posted by Neale
Serious question - does anybody use braking resistors on VFD's ?
Cheers,
Rob
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:yahoo:
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.Quote:
Originally Posted by Neale
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.
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.Quote:
Originally Posted by njhussey
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.
I've found a reference to e-stop in the HY VFD manual - it seems that it's possible to define one of the digital input pins to accept an e-stop signal. I need to go through the manual in more detail to find out which of the many parameters will control things like e-stop ramp-down time, or if it just chops output and uses DC braking. I also assume (I'm doing a lot of assuming at the moment) that it will need an external braking resistor to give best results. More research...
My current e-stop switches are built from modular components and are single pole at the moment but could easily have a second pole added, wired either as an independent mechanism or via the second channel of the safety relay. But again, I have to come back to the appropriate level of protection. But then, I'm the guy who removed the chuck guard from his vertical mill as the first action after installing. Instead, I bear in mind that it would be an error to insert finger into revolving cutter.
This thread has drifted some way from the original question about enable pins on drivers, but I don't think that there has been a definitive answer to that one yet...
Been there, done that, lost a fingernail (but it has regrown, albeit lumpy). This is why I asked about braking resistors, as my little trip to the world of pain was taken while the cutter was on run-down.Quote:
Originally Posted by Neale
Cheers,
Rob
I've done a bit of googling of HY VFDs and braking resistors and there doesn't seem to be much folk wisdom out there. Plenty on how to make it spin up but very little on how to stop it again. The standard HY stop mechanism (if you just remove "run" signal) is to run down from current frequency to some pre-defined stop frequency at a rate given by a specified parameter, and then either coast to a stop or use "DC braking" according to another parameter. I can't find any specific description of how emergency braking works, but I haven't been through the manual word by word yet. I would have expected "cut power to motor and use DC braking", but in any case it sounds like there is a need for an external braking resistor. The manual does give recommended values for this, and it looks as if they are available from eBay or AliExpress for £20 or so.Quote:
Originally Posted by cropwell
Rob you should see this then https://www.youtube.com/watch?v=eiYoBbEZwlk they are made commercially they wreck the saw though I think there are types that clamp the blade with an explosive charge like a air bag.Quote:
Originally Posted by cropwell
My lathe has an electro-magnetic brake. I was worried that it might not work with the VFD I use to generate three-phase power but it actually works very well and brings a heavy chuck to a halt from 2K rpm in a surprisingly short time. Don't think I'll bother with trying to fit one to my 24K rpm spindle, though...
Quote:
Originally Posted by Neale
You don't have to use them, they are automatically pulled to the enable state by internal circuitry in the drive, if you connect the appropriate external circuit for your drive to pull the enable pin to the disable state the drive is disabled.Quote:
Originally Posted by ROBCNCAU
It's down to you to decide if you need this function and what for, if you don't need to disable the drives ignore it as enabled is the default state for common drives,
- Nick
I know this is an old thread, but for folks searching for information about using the enable pin: Check the current requirements of your driver input and the current capability of your BOB/controller before you hook multiple enables to a single output on your BOB. A lot of the drivers draw 12+ MA. on their input pin and some BOB/Controllers can only source as little as 24mA.