need advice from lego gurus

I'm thinking about the next version of my one-armed robot, Grabot. 
Presently he looks like this:

http://www.danbmil.com/lego/DSCN6131.JPG

what I want to do is have the claw go up and down but stay parallel to the
floor, rather than hoist itself up as in this picture.  Does anyone know of
a technique, used or just conceptual, for doing this?  I'll need some sort
of elevator construction, that can hold quite a bit of weight for the arm
assembly.  Here's a top-level view that shows how the arm looks now:

http://www.danbmil.com/lego/DSCN6128.JPG

Any thoughts will be greatly appreciated.  I am thinking of some sort of
worm gear + one of those toothed strips, but I can't really see how to make
it work efficiently with a good range of motion.

thanks in advance, this is a great group

- dan


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