2010/4/20 Slavko Kocjancic <esla...@gmail.com>
> Alexey Starikovskiy pravi:
> > 20.04.2010 18:07, Slavko Kocjancic пишет:
> >
> >> Alexey Starikovskiy pravi:
> >>
> >>
> >>> Main problem seems to be that you need to make sure you don't increase
> skew
> >>> between linked axis while homing or working.
> >>>
> >>>
> >>>
> >> Just that.! The homing as is doesn't increase the skew (if parameters
> >> are correct)
> >>
> >>
> > Bold statement, do you have any proof for it? Or can you list
> > all parameter mistakes, which could lead to increase in skew?
> >
>
> Not yet. I have gantry machine as buid in progress.
>
> >>
> >>
> >>> Hoping that it's small enough and machine can cope with it could be
> >>> expensive.
> >>>
> >>>
> >>>
> >> The skew itself is problem. If appears then something is already very
> >> bad. As I tested on my unfinished machine if I fix the one side rock
> >> solid and pull another side with 500N force the gantry is skewed les
> >> than 1mm. So if I assume than my stepper can put max 500N force on
> >> gantry the max skew is 1mm. If My gantry hit some obstacles and is
> >> skewed more than 1mm then there are NO WAY to unskew that with homming
> >> procedure alone. As motors are NOT STRONG ENOUGHT to move such skewed
> >> gantry at all. So the home procedure can make unskew only if it's small.
> >> (and to do proper the gantry should move slow and home switch must have
> >> short "backlash".
> >>
> >>
> > This might be true for your one gantry. What about all other gantries?
> >
>
> In general if gantry is twisted to much the motor will stall! And if
> gantry is twisted there are something wrong in system and need user
> attention!
>
> >> Not so long ago I want to have report on (re)homming how far from home
> >> axis was. That's should be just fine here too. If Home is not same then
> >> you have gantry skew. And gantry skew can be removed in most cases only
> >> by hand intervention as skewed gantry make big force and stall mottors.
> >>
> >>
> >>
> >>> Second problem, it should still look as one axis to interpreter and
> gui.
> >>>
> >>>
> >>>
> >> I was thinking that gantry kins already do that.
> >> Wasnt?!?
> >>
> >>
> > No, there is some experimental setup with unapplied patch if I'm not
> > mistaken.
> > IMHO, all axis are independent, and all home switches too.
> >
> That's bad. I was thinking that this is already done.
>
> Long ago I solve problem like this (it's TurboCNC based) but that'
> doesn't matter.
>
> The both motor's uses same Step/Dir (whatever).
> There are one relay DPDT.
> The relay coil is under program control. (can be manual too)
>
> So when Home is applied the both motors goes to home position but in
> reality only motor1 limit is wired to computer.
> When home sequence is finished the relay is switched and home procedure
> repeated.
> But when relay is switched the one contact dissable motion of motor1
> (can use drive enable or just cut step pin) and the other contact rewire
> limit switch of motor2 to be used.
> That thing work's well. Of course when motor2 alone is homed the twist
> is introduced in lenght of limit switch 'backlash'. All switches I use
> have les than 1mm backlash so twist is not big. (and that machine is big
> oxy/acitelene (4 meters by 8 meters) and the gantry is very easy twised
> by 2 cm)
>
> if gantry kins doesn't do the job then this approach can be implemented
> entirely by hal. (not needs relay) just both limits (separated) and
> enable output (can be gated in hal too)
>
> Slavko.
>
> Forgot to say. That works for stepper driver. for servo are muc better
choices.
Slavko.
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