Bruce, Thanks for the information. You gave me quite a bit to chew on. Having a computer and electronic background I tend to think of logic being implemented via discreetly or through a micro-controller. I never really thought about relay logic. I have never tried to implement a logic circuit with relays, so would have to look at some samples. Off the top of my head it would seem that driving coils in series would be an AND and the same coils in parallel would be an OR. But beyond that no clue really.
You said I shouldn't use IC to implement logic, but aside from the Y and !Y (NO and NC contacts) output logic why do you recommend against it? Currently, I have 5Vdc, 36Vdc and 110Vac that I am dealing with. Seeing that the 5Vdc power supply supplies my BOB, and other future devices, TTL logic just seemed natural. I agree with you about the software E-Stop versus the Hard E-Stops. I will insist to my Boys and wife that if SHTF, ALWAY hit the big red buttons! Thanks again for all the support, advice, direction and resources. I appreciate it. I see I have a little reading on the subject to catch up on. Regards, Joe ----- On Nov 7, 2014, at 4:34 PM, Bruce Layne linux...@thinkingdevices.com wrote: > You shouldn't use integrated circuits to implement the AND logic. > Instead, use relay logic. > > The output from the BOB that represents the internal E-stop state in > LinuxCNC is wired to a relay. If the BOB can't source enough current to > drive the relay, you might need to use a small relay to operate a larger > relay, but you don't need a high current relay for the relay logic. You > only need a small "ice cube" relay and the BOB output should be able to > drive it directly. If you select a relay with normally open and > normally closed (NO and NC) contacts, you can select the correct set of > contacts as you wire it to negate any signals that may be an opposite > logic state than you assumed. That's a handy feature for flexibility and > can come in handy for future add-ons. It's easy to make one wrong > assumption about signal polarity and have the opposite of what you need > at the final relay in the circuit, and having NO and NC contacts on your > relay is never having to say DOH! > > The logic relay that represents the LinuxCNC internal E-stop state is > wired in series with any E-stop switches you installed. That way, if > you push any E-stop switch, or click the E-stop button in LinuxCNC, the > machine goes into an E-stop state and all motion stops. The signal that > passes through the E-stop switches and your small relay contacts then > operates a larger power relay that supplies power to all motion control > (spindle, steppers, etc.). This power relay can have multiple sets of > contacts, so each motion producing device can be controlled separately > if they use different voltages. A set of contacts can be used to > control your Hitachi router. Another can control the stepper motor > powers supply or power supplies. > > You can also include a set of contacts to control a digital signal that > feeds back as an input to the BOB so LinuxCNC can determine that you > pressed an E-stop switch, although for my simple machines like routers, > I generally don't bother because that takes a bit of messing around in > HAL, and I like being able to install a new copy of LinuxCNC, select a > generic stepper gantry router configuration, tweak the machine limits > and steps per inch, and Bob's your uncle. I don't plan on pushing the > E-stop switch, and if I do, I don't mind if the program keeps running as > long as the motion stops. I'm going to reset everything, anyway. > > Similarly, for a simple machine, you might skip the relay that > externalizes the internal LinuxCNC E-stop state. You'll probably press > a physical E-stop switch on the machine, but clicking the E-stop button > in LinuxCNC would still stop the motion even if it didn't generate a > real E-stop. The difference is, the motors would still be powered and > would be holding position, potentially keeping the operator pinned. If > you trained everyone to ignore the E-stop button in LinuxCNC and push > the E-stop mushroom head switch on the machine, it wouldn't be too much > of a safety problem IMO. If it's an emergency, the operator shouldn't > be mouse clicking or trying to press hot keys on the keyboard, and I > don't think they should be trusting any PC software, even if LinuxCNC is > very robust. I don't believe in software E-stops. > > If I was wiring it, I'd probably use a solid state relay ($6 each or > less on eBay) for each motion device I needed to control and use the > E-stop signal to control them all. I know they'd work for the 120VAC > power for your Hitachi router and the DC power supplies that dive the > stepper motors. If I had any three phase devices, I'd use a three pole > relay (actually, a motor starter) to ensure that all three phases were > switch on and off at the same time. > > If you do an online search for E-stop circuit, I'm sure you can find a > lot of circuit diagrams that are wired as I'm describing. There will be > minor differences depending on the specifics of the machine hardware, > but the basic concept is the same. Use those as examples and draw > something similar for your machine. > > Good luck! > > > Bruce > > > > > On 11/07/2014 04:30 PM, Joe Hildreth wrote: >> Bruce, >> >> Thanks for taking the time to explain it to me. >> >> So I can take this approach then: >> >> 1) Use the internal E-Stop as an output on the BOB (Use this as in input to >> my >> AND gate) >> 2) Use the external E-stop which is normally closed as the second input to my >> AND gate) >> 3) Use the output of the Charge pump signal from the BOB as the third input >> to >> the AND gate. >> >> 4) The output of the AND gate to drive the TTL inputs of my AC Relays to >> enable/disable power to the motors. >> >> This way, I still have both E-Stops (Or additional ones by cascading E-stops) >> and the charge pump signal to rely on? >> >> I could make a PC board for an AND gate with Vcc and ground in with a >> decoupling >> cap and just bring the inputs and out puts to screw terminals. This way, it >> would be nice and modular, cheap and fit in any corner of my electronics >> drawer >> that slides in the computer rack. >> >> My spindle is a Hitachi router, so not sure if it is even possible to brake. >> It >> will get wired to a SuperPID so that I can control on/off and motor speed via >> software. I need to look at the documentation and see what I have available >> in >> terms of E-Stop control. It may be that I have to treat it like the stepper >> driver power supplies. I am just not there yet. I still consider myself a >> newbie so am trying to take it in digestible BYTES. >> >> As far as the external charge pump. I am thinking that LinuxCNC will only >> generate the carrier frequency (charge pump signal) when it has control. >> This >> way if the computer hangs or crashed I would at least have an additional >> level >> of safety. Or am I just over thinking it? >> >> One more question. If I wired it like my last email, then LinuxCNC would not >> have any clue that I hit the external E-Stop. Would it be benifitial to >> bring >> the signal back in anyway, just to let the software know we killed it >> externally? Otherwise, I imagine that the software will continue to send >> motion information and continue to plot like nothing ever happened. >> >> >> Thanks again for your help. >> >> Joe >> >> ----- On Nov 7, 2014, at 2:35 PM, Bruce Layne linux...@thinkingdevices.com >> wrote: >> >>> Hi Joe, >>> >>> The industry preferred method of implementing an E-stop would be the >>> opposite of what you propose. Rather than using the mechanical E-Stop >>> switch as an input and logically ANDing the external E-stop switch and >>> the internal E-stop machine state, you should use the internal E-stop >>> machine state as an output and use electronic hardware (relay logic) to >>> AND the E-stop switch and the E-stop machine state to enable the spindle >>> motion and the X/Y/Z motion. To be clear, you're actually ANDing the >>> non-E-stop conditions, or NANDing two E-stop signals. However you want >>> to say it, motion should only be possible when the PC based controller >>> says it's OK to run, and when the E-stop switch says it's OK to run. >>> >>> The issue is the reliability of computer hardware and software. These >>> have greatly improved, but are still not up to the reliability standards >>> of relays. >>> >>> I like solid state relays, although E-Stop relays are usually clackity >>> relays with mechanical contacts. >>> >>> Consider using multiple E-stop switches if someone could be pinned by >>> part of the machine. Try think of all of the things that could go wrong >>> and make sure someone could quickly reach an E-stop. >>> >>> When wiring your E-stop circuit, make sure the E-stop switch contacts >>> are closed when you want the machine to run, and open when the E-stop >>> switch is activated. That way, if there is any loose connection in your >>> E-stop circuit, the wiring fault causes the machine to fail in the >>> E-stopped condition. >>> >>> The simplest E-stop wiring would cut power to the spindle motor and all >>> of your stepper motor power supplies, even though the spindle could >>> probably be actively stopped faster if left under power and commanded to >>> stop rather than coasting to a stop. >>> >>> Bruce >> ------------------------------------------------------------------------------ >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> > > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
