Our CNC is in a communal woodshop and, as part of the rules of the shop, we need to implement some sort of safe lockout procedure during toolchanges. I know this is unorthodox but it’s the rules of the shop and we have to make it happen if we want to keep using the CNC. The goal is to add a switch that, when flipped, prevents the spindle from running even if the user were to accidentally resume their gcode program.
A pure hardware solution is preferred but it would be sufficient to add a switch that controlled some function within the VFD using its multi-function input terminals. Is this possible?
Machine details:
Altmill 4x4
SLB-ETX
1.5 kW spindle
The old, white, Sienci-branded unenclosed VFD. I think it’s an H-100?
@keglin I think that is an excellent safety feature to have. It’s something that has bothered me as well. When I change the blade on my table saw, I disconnect he power cable. When I change a bit on my router, I disconnect the power cable. I would expect something similar with the CNC. My current solution is to close the job within g-Sender. With no job configured to run, I figure the chances of the spindle starting by itself would be reduced. Another solution would be to get an ATC.
Maybe just an in-line switch on the cable to the spindle would work for existing systems.
That’s a good idea! I’d have to make a 3 relay setup to properly switch the spindle but that’s a pretty easy thing to implement.
I wonder how the VFD/gsender would react to that. If the user forgot to rearm their spindle and resumed their program, would it throw an error or would it start moving the gantry without the spindle running (causing your bit to crash into the work)
Edit, since I can’t post more than once on my first day I guess:
I’ve looked into it a little more and adding a relay inline with the cable is not recommended since it can damage the VFD if the switch is flipped while it’s running.
Everything is taking me back to finding a way to use a digital input as an interlock but it’s not clear to me how to best wire that up/configure the VFD to respect that interlock
@keglin Good point. One could disconnect the cable right now to see how it would behave. An interlock that kills power to all motors would be the best solution.
One could power off the SLB. But that then requires re-homing the machine. My tests show that the zeros are maintained within 0.01mm from one re-home to the next. I don’t know how well that works with a job that is paused for a tool change. Right now, I have different g-code files for each endmill.
Safety is the one thing that feels a wee wonkey on my machine too. I don’t allow people near my machine when it’s running. Children are forbidden to enter my shop at all time. People can bind them to the post outside or leave and return without their clones.
Since you are running the machine with safety in mind, I assume you have it inside an enclosure. This makes it a wee easier to implement foolproof safety features. Not only with tool changes in mind but simply at all time.
I think the safety can be implemented both on the software and hardware side. On the hardware side, I would simply use door switches to dissable the power from the vfd to the spindle and power to all stepper motors. When the door opens, the machine will no longer be able to do anything.
To prevent the doors from being able to be opened and abruptly stop everything it’s needed to tell the slb it is about to happen so it can enter a known state.
I would want a dual key switches with a single key that fits and operates both switches. One keyswitch is connected to the slb giving it a constant high signal when “working”. When the key is turned in it’s off position a low signal is given. A macro activates that moves the machine to a parking position and turns off the spindle. When the macro is done it signals one of the aux to switch on a relay. A power suply on the nc will be switched off. This power supply powers a magnet that prevents the door to be opened when the machine is running.
Both key switches need to have multiple contacts. The secundairy switch (nc) on the first switch bridges the relay contact that switches the power supply off. Keeping the magnet activated if the second key switch is used while the machine is still running. The secondairy switch (nc) on the second switch, switches the pulled down potential needed to activate the macro. When in the wrong position, the machine will not switch off, nor will the magnet be deactivated for there is no low signal to activate the parking macro.
This is a quick write-up without looking into availability of the imagined hardware. It is a functional wishlist for an ideal foolproof safety protocol, without looking into how realistic it is to implement it.
Just an idea, a brain fart so to speak. Can you smell it or do I need to spill more beans?
There is the door connector on the SLB. Does closing a switch attached to that connector kill power to all motors? Even without an enclosure, just a switch could be of use.
I only do tool changes between files so everything is stopped. I unload the last program, change the tool, zero everything, then load the new program and start the program. During the tool change, there is no program in gSender to cause anything to move and I can’t accidentally rerun the old program with a new tool. (Ask me how I know that’s important .)
I wonder what would happen if I hit the E-Stop when the first program is done, install the new tool, reset the E-Stop, zero everything and then load the new program.
.)