Re: 3D printer progress

Well I got the control board mounted onto the gantry and the paper
detect sensor mounted and re-rigged the cable drive ready or more
experiments.

It turns out the gantry has enough movement for all of the start up
procedure but not the preprint dancing.

This is a problem and has inspired a new train of thought. I'm going
to change the cable drive to a continous belt drive. The thing about
a belt is that if you grab the upper part of the loop you go one way
and if you grab the lower part you go the other. So the idea is to
have an electrically operated means of gripping the belt, which side
of the loop is gripped depends on if you are printing or returning the
gantry to the start. The grip will be latched when the print head is
in the paper area but otherwise loose, the grip will be initialized by
the high feed motor voltage seen when paper is fed.

I like this idea because with very simple electronics it creates a
flat bed printer that prints in alternate directions without
interfering with the printer's own electronics. Returning the gantry
is of course done by printing a blank page!

I've come up with lots of ways to do this, here is my possible final
choice, chosen for ease of building and low weight.

The two sides of the loop of toothed belt pass within a U shaped
channel, the flat side of the belt is very close to the rubberized
(glued on strip) sides of this channel but don't touch. In the centre
of the channel is an RC servo, chosen because of the high torque
available in a small package at low weight (8g servo has about 1kg.cm
stall torque). On the shaft of the servo is an eccentric disk. In
the neutral position the belts pass freely and the gantry does not
move but turn the cam and one of the two sides of the belt are clamped
against the side walls of the channel. In one direction you even get
a slight cam-action clamping effect, this should be the printing
direction!.

Its possible to get the cam clamping action in both directions but
only at the expense of complexity.

I'd like to hear peoples thoughts and ideas.

Graham