Re: Announcing the ORDuino !
Posted: Mon Jun 11, 2012 7:08 pm
I realize that it's way late for the safety circuit and E-Stop conversation in this thread, relative to the initial design and boards, but here's my current take on it.
The 3D printers are quickly becoming more mainstream. More like real machines and less like hobby hardware hacker devices. The ORDuino is part of that progression, with more integration and more features. It's probably time for some more attention to safety.
Many of the earlier comments about E-Stop circuits were more akin to stop or reset circuits. Similarly, a true E-Stop is completely independent of any software or firmware.
Here are some other concerns expressed about hot parts getting too hot and run away code:
viewtopic.php?f=33&t=1352&p=11955#p11945
You might consider a separate safety circuit on future ORDuino boards. It could work in a similar manner to a true E-Stop circuit, and people who didn't want it could simply not use it. The circuit I envision would interface with the rest of the ORDuino via three lines - GND, +V and Vmotor. The +V would be +12V for most of us, and the Vmotor would be +V after the E-Stop circuit. The E-Stop would interrupt the voltage to anything that makes motion or heat. The E-Stop circuit would be the electronic version of a latching E-Stop relay in bigger industrial machines. When power is initially applied (analogous to pressing the START button on a big machine), if the E-Stop circuit is in the ready state with all switches closed, the E-Stop circuit latches itself in the ON state. The E-Stop circuit is a series of switches, as many as the builder wants to install, wired in series. As soon as any one of these switches is opened, the E-Stop circuit is no longer latched and the +V signal is no longer supplied to the motors and heaters via Vmotor. To reset the E-Stop circuit, the fault is cleared and the printer power is cycled. Alternatively, there could be a START or FAULT RESET button that reengages the E-Stop circuit.
Or, even simpler, the +V could be supplied to Vmotor any time the E-Stop circuit is in the ready state. Press the E-stop button and all motion stops. Fix the problem, restart the software to start building another part, and deactivate the E-Stop push button. The non-latching E-Stop would allow power cycling if a thermal switch is used to detect a runaway heater, but a thermal fuse would stay blown so it wouldn't cycle the power. The simpler non-latching E-Stop wouldn't need any ORDuino board space. We could simply wire our ORD Bots that way, as I'm thinking of doing.
And yes, an E-Stop is not a pause button. It immediately stops errant software that can't stop itself. As such, there is no ordered shutdown that allows a graceful restart. There should be other provisions for that. E-Stop is an EMERGENCY Stop!
The 3D printers are quickly becoming more mainstream. More like real machines and less like hobby hardware hacker devices. The ORDuino is part of that progression, with more integration and more features. It's probably time for some more attention to safety.
Many of the earlier comments about E-Stop circuits were more akin to stop or reset circuits. Similarly, a true E-Stop is completely independent of any software or firmware.
Here are some other concerns expressed about hot parts getting too hot and run away code:
viewtopic.php?f=33&t=1352&p=11955#p11945
You might consider a separate safety circuit on future ORDuino boards. It could work in a similar manner to a true E-Stop circuit, and people who didn't want it could simply not use it. The circuit I envision would interface with the rest of the ORDuino via three lines - GND, +V and Vmotor. The +V would be +12V for most of us, and the Vmotor would be +V after the E-Stop circuit. The E-Stop would interrupt the voltage to anything that makes motion or heat. The E-Stop circuit would be the electronic version of a latching E-Stop relay in bigger industrial machines. When power is initially applied (analogous to pressing the START button on a big machine), if the E-Stop circuit is in the ready state with all switches closed, the E-Stop circuit latches itself in the ON state. The E-Stop circuit is a series of switches, as many as the builder wants to install, wired in series. As soon as any one of these switches is opened, the E-Stop circuit is no longer latched and the +V signal is no longer supplied to the motors and heaters via Vmotor. To reset the E-Stop circuit, the fault is cleared and the printer power is cycled. Alternatively, there could be a START or FAULT RESET button that reengages the E-Stop circuit.
Or, even simpler, the +V could be supplied to Vmotor any time the E-Stop circuit is in the ready state. Press the E-stop button and all motion stops. Fix the problem, restart the software to start building another part, and deactivate the E-Stop push button. The non-latching E-Stop would allow power cycling if a thermal switch is used to detect a runaway heater, but a thermal fuse would stay blown so it wouldn't cycle the power. The simpler non-latching E-Stop wouldn't need any ORDuino board space. We could simply wire our ORD Bots that way, as I'm thinking of doing.
And yes, an E-Stop is not a pause button. It immediately stops errant software that can't stop itself. As such, there is no ordered shutdown that allows a graceful restart. There should be other provisions for that. E-Stop is an EMERGENCY Stop!