>I'd spend some time looking at a DC motor approach
>with shaft encoder positional feedback.
Just like those fooling around with toner transfer now will someday
move on to photoetching so will those on steppers now move on to DC
servos. Seems to be a natural progression, at least it was for me.
--- In Homebrew_PCBs@yahoogroups.com, uhmgawa <uhmgawa@m...> wrote:
> Robert Hedan wrote:
> > Problem is now I have to reconsider a totally new driver
circuit 'cause
> > these are bipolar steppers. Can I modify my schematic without
TOO much
> > trouble? Or am I better using a new design?
>
> IMHO steppers are a rather brute-force way to
> address a limited set of applications. If all
> you need are simple open-loop indexed positioning,
> minimal/moderate static holding torque for gratis,
> but without much of a velocity/torque range,
> steppers will fit the bill.
>
> I'd spend some time looking at a DC motor approach
> with shaft encoder positional feedback. As a
> back of the envelope estimate a 28TPI lead screw
> combined with the optical encoder scavenged from
> a $3 mouse can give you positional accuracy in
> the 0.001" range. Physical drive requirements
> take the form of a simple H-bridge without the
> gyrations needed by steppers.
>
> You aren't likely to find anything off the shelf
> to address the drive and closed loop control but
> nearly any uC controller will due. Direction and
> velocity of the motor are proportional to the average
> energy seen by the motor and is driven via PWM.
> As with all but trivial stepper designs you'll need
> to address velocity ramp up/down. And if needed,
> an algorithm to emulate static hold of the motor
> position. Though with a lead screw of sufficient
> pitch and its inherent friction this may be
> unneeded or at least trivial.
>
> --
> uhmgawa@m... www.gnu.org