On Wednesday 23 August 2017 12:33:37 Chris Albertson wrote: > Yes, you absolutely need that, not implementing something like that > would a liability issue. Systems like this need an integrated E-stop > they is trigged independently of the motion controller. I'm imagine a > layered system where the controller can issue a "stop" or the operator > or some sensors or as a last resort a bumper presses a microswitch > with cuts power to the motors. Like a few switches in parallel and > if any one of them get tripped the power is cut to the relays that > connect power to the motor and the motor lead short putting the motor > in "brake mode" This would also have the effect of stopping the > motors after a power failure. Using energy in the motors coils to > brake motion. > > None of this is rocket science. Hire an engineer with experience in > factory automation. Or just skim through some text books > > Half of the design of such a system, is self monitoring. You need a > design that remains safe even after a component failure. Some times > it is easy, like using normally open relays so power is disconnected > if control signal sops. > > We are talking about a system that will cost many millions of dollars > and will need a full time engineering staff to design and build. > What he said...
> On Wed, Aug 23, 2017 at 9:19 AM, Rick Gresham > <[email protected]> > > wrote: > > The building will likely typical concrete tilt-up or something > > similar. The system will have to track/control position in real > > time. Collisions will be very expensive so redundant systems are > > easily justified. It may need some sort of collision avoidance > > system as a back up, too. If the crosses some boundary, everything > > stops. Stoppages are not a big problem, bumps in the dark are. > > > > I've wondered about redundant control systems but haven't come > > across any information yet. Anyone remember the triple Tandem > > non-stop systems NASA used? Three fault-tolerant systems running in > > parallel. If they came up with different results, it was > > odd-man-out. Probably don't need to go that far for this > > application unless something available off the shelf affordably. > > > > > On Aug 23, 2017, at 8:56 AM, Chris Albertson > > > <[email protected]> > > > > wrote: > > > There are many ways to measure position. With something this big > > > and expensive I would suggest some redundancy. The cost of > > > measuring is tiny computer t the cost of a 100f gantry. > > > > > > One of the bigger problems I see is flex in the system and thermal > > > expansion. If the goal is 1/8th inch over a 100 foot run then > > > their > > > > needs > > > > > to be some design margin so you'd be designing for something like > > > 1/16th inches. > > > > > > I doubt that simply measuring how for you are along a steel bed > > > will > > > > work. > > > > > Yes you could try but the beam itself will bend and change it's > > > length. You would have to measure absolute position relative to > > > fixed locations > > > > on > > > > > the floor. > > > > > > I don't think I've ever seen a building made to close tolerances > > > either. The sports are not going to be square to each other or > > > level or vertical. > > > > > > I't not hard to compensate for the not-perfect mechanics. You can > > > also continuously calibrate the sensors from know references > > > inthewtork space > > > > > >> On Wed, Aug 23, 2017 at 2:21 AM, andy pugh <[email protected]> wrote: > > >>> On 23 August 2017 at 05:17, Dave Cole <[email protected]> > > >>> wrote: > > >>> > > >>> A 3D laser tracker was part of the control scheme to track the > > >>> actual > > >> > > >> tool > > >> > > >>> head location. > > >>> That way standard rack could be used for the positioning > > >>> mechanism and > > >> > > >> the > > >> > > >>> position could be corrected on the fly via the laser tracker. > > >> > > >> That might still be a good idea, because it seems that such a > > >> machine might need to be modular, so units that are > > >> friction-drive on standard rolled steel sections seems like a > > >> likely solution. > > >> There will be some tyre-creep, but the laser (or acoustic) > > >> feedback could correct it. > > >> I heard of a system where you have a microphone in each corner of > > >> the room and a "clicker" that is localised in space by clever > > >> acoustic processing. > > >> The application was measuring accelerometer positions when > > >> instrumenting a car or van body. If you have ever "walked" a Faro > > >> arm round a van body you would know why the system seemed > > >> attractive. > > >> > > >> > > >> -- > > >> atp > > >> "A motorcycle is a bicycle with a pandemonium attachment and is > > >> designed for the especial use of mechanical geniuses, daredevils > > >> and lunatics." > > >> — George Fitch, Atlanta Constitution Newspaper, 1916 > > >> > > >> ------------------------------------------------------------ > > >> ------------- > > > > ------------------------------------------------------------ > > ------------------ > > Check out the vibrant tech community on one of the world's most > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
