On 13.05.14 15:55, Viesturs Lācis wrote:
> The task is to build a machine which would process side edges of wood
> boards. The thing is that board width varies in range of 80 to 300 mm
> in a random, unpredictable order. There are 2 motors - one for each
> side. What I have in mind - boards are based along a fixed slide, so
> one motor is firmly mounted, the other motor is supposed to be
> repositioned for the width of particular board by stepper motor.
> The problem is how to measure the width of board in most simple way.
What about backing the moving motor/cutter-head well out of the way
until the end of the board has arrived, as detected by a microswitch or
light beam, then just running the head in on a straight rail
perpendicular to the board axis, perhaps just by simple DC motor,
stopping when a microswitch bumps into the board edge, e.g. as part of a
compliant sole plate? I.e:
||
|| Head runs on this rail.
||
||
| --------
| | Head |
V | | == - Sole plate
&=#==@==== # - Opto-transistor
! ! - Photons
----------------------- * - IR LED
Board --> | & - Bump switch (infeed stop)
----------------------- @ - Cutter/whatever
!
Fixed Side *
If no side pressure roller is provided, to keep the incoming board snug
against the fixed side, then the Bump switch could also be omitted,
being replaced with current sensing on the (DC) head infeed motor. When
the motor is pushing with xyz amps of torque, then the board has been
pushed hard enough against the fixed side. Use a leadscrew for head
feed, and there'll be enough push, without cooking the motor. (And the
current sense reduces power after the infeed/board-alignment)
It would be better, though, to use a stepper motor (as you intend), then
just pulse away long enough to snug the thinnest board, then drop the
coil current to a lower holding value, if the stepper driver does that.
(But board width need not be known. It is handled by the stepper's lost
steps, once the board is snug.)
... [original concept details]
> The problem with this is that once the board passes through, the spring
> will return that lever to starting position very quickly and the motor
> might not manage to follow, so I cannot think of a nice way to adjust, how
> fast it returns back.
If you have an Arduino in there, then the retrace speed can easily be
damped in your design. In this one, retrace speed is whatever is chosen.
(The light beam detects the board's passing, triggering retrace.)
OK, the edge processing very likely produces sawdust which would
necessitate frequent cleaning of a light beam transmitter and receiver.
A row of fingers protruding through the table, each with a microswitch,
all wired in parallel, could instead detect the board ends.
There are probably considerations which are not fully taken into
account, but these suggestion might at least serve as food for thought.
It sounds like a fun project.
Erik
--
"What we found was, in fact, about half of that observed warming over Greenland
since 1979 can be attributed to natural variations actually stemming from the
Pacific Ocean."
-
http://www.abc.net.au/news/2014-05-12/climate-change-hot-spot-in-pacific-ocean/5446786
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