Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!well!nagle
From: nagle@well.sf.ca.us (John Nagle)
Newsgroups: comp.robotics
Subject: Re: Pizzabots (was: Robots applied in food preparation)
Message-ID: <24564@well.sf.ca.us>
Date: 3 May 91 05:59:23 GMT
References: <12476@qisoff.phx.mcd.mot.com>
Lines: 43

>I saw this system on some science television show, on the Discover
>channel I think. It was interesting but it got me wondering:
>Why do so many people/companies/universities try to throw robotic
>arms at every application, when a gantry style system would seem
>a better choice. I think this is the case with the pizza robot.

     Gantry style robots have their own set of problems.  I've
worked with IBM's effort in that direction, the RS-1 (also known
as the IBM 5640 Manufacturing System).  Fast, precise linear
actuators present problems.  There's nothing as clean as Adept's
electric direct drive system in the linear world.  The RS-1 used
multipiston walking hydraulic motors running on rails with wave-shaped
teeth for each axis, along with ultrasonic magnostrictive delay line linear
position transducers, connected via an analog servo system supervised
by a computer, and powered by a hydraulic pump in a box a cubic meter
on a side.  It required 3 phase 220 volt power, compressed air, and
chilled water.  This for a machine with a working load of 15 pounds.
It just took too much power to zoom that gantry around.  Didn't sell.

     On a smaller, scale, Automatix's Robotworld uses 4" square units
which translate in X and Y using two-dimensional linear stepping motors
and hanging magnetically from a flat surface above the work area.
The system is workable, but doesn't sell either.

     Neither of these systems offered force servoing or programmable
compliance.  For that you need a system with very little backlash and
one that's back-drivable.  There are good direct-drive electrical robots,
such as the Adept SCARA-type arms and the little Zero arm.  I don't know
of a comparable machine in the gantry form.

     For food processing applications you need a machine that can be
cleaned with boiling soapy water.  Gantry machines tend to have lots of
open track, complicated cabling and plumbing systems, and exposed
lubricated surfaces.  All these are unacceptable in a food processing
operation.  FDA-approved arms exist (the manufacturer is in Colorado
Springs, but the name escapes me.)  With arms, you can put the machinery
inside and out of the way, which is a big plus in many applications.

     SCARA-type arms tend to be the machine of choice today where a
gantry-type motion would be appropriate.  They're available, simple,
reliable, fast, and fully enclosed.  Adept is the big US vendor.

					John Nagle