Browse Prior Art Database

MINIMUM SETUP TIME ROBOTIC ACCURACY MEASUREMENT SYSTEM

IP.com Disclosure Number: IPCOM000006832D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-06
Document File: 2 page(s) / 156K

Publishing Venue

Motorola

Related People

Barry Groman: AUTHOR [+2]

Abstract

Robot accuracy is becoming increasingly important as factory automation moves towards CAD data driven systems and component placement requires tighter tol- erances. In order to insure that a robot performs within specitlcations, a qu&liable measurement of the mechan- ical accuracy as the robot travels through the work enve- lope must be made. The most precise instrument avail- able to measure robot accuracy is a laser interferometer system. The laser interferometer system measures positional accuracy via the use of a laser head and a set of two optics, the retro-reflector and the reflecting mir- ror. Traditionally robot characterization with this equip- ment would entail complicated alignment of the laser beam and optics to the robot's travel. The current pro- cedure for measurement of robot accuracy is the foUowing: Setup: 1) Assemble tripod and mounting bracket for laser head. 2) Mount laser head to tripod. 3) Remove robot end-effector and mount reflecting mirror.

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INC. Technical Developments Volume 19 June 1993

MINIMUM SETUP TIME ROBOTIC ACCURACY MEASUREMENT SYSTEM

by Barry Groman and Scott Potter

   Robot accuracy is becoming increasingly important as factory automation moves towards CAD data driven systems and component placement requires tighter tol- erances. In order to insure that a robot performs within specitlcations, a qu&liable measurement of the mechan- ical accuracy as the robot travels through the work enve- lope must be made. The most precise instrument avail- able to measure robot accuracy is a laser interferometer system. The laser interferometer system measures positional accuracy via the use of a laser head and a set of two optics, the retro-reflector and the reflecting mir- ror. Traditionally robot characterization with this equip- ment would entail complicated alignment of the laser beam and optics to the robot's travel. The current pro- cedure for measurement of robot accuracy is the foUowing:

Setup:

1) Assemble tripod and mounting bracket for laser head.
2) Mount laser head to tripod.
3) Remove robot end-effector and mount reflecting mirror.

Alignment:

4) Roughly align laser with robot axis by manually moving tripod.
5) Place alignment target on reflecting mirror.
6) Jog robot and observe where beam hits the alignment target.
7) Adjust tripod height, and laser head angle in both the horizontal and vertical planes.
8) Repeat steps 6 and 7 until aligned properly.
9) Mount retro-reflector and align with laser beam. Data Collection:

10) Manually record accuracy measurement data.

  The problem with the above laser interferometer methods is that setup is very tedious, alignment is time consuming, and data collection requires an experienced engineer to take measurements. All these could be elimi- nated by dedicating and integrating a laser measurement system into each robotic cell, however, the system is prohibitively expensive. Also, since the laser interfer-

e Motorola. Inc. ,993

ometer measurement technique is a relative measure- ment method, where the measurement is made with respect to the physical position of the laser beam gener- ator, it is almost impossible to exactly reproduce meas- urement data once a setup is disturbed. This introduces a source of variation in the robot accuracy measure- ment since data taken at two different setup configura- tions do not exactly correspond. AU of the constraints of this measurement method has made this method unadaptable to the manufacturing environment.

  The purpose of this invention is to simplify the setup time, automate the data collection procedure, and pro- vide means for a repeatable measurement strategy for using the laser interferometer system to measure robot accuracy and repeatability.

  The new method reduces the setup time by fixing the laser head and retro-reflector to a plate. (see attach- ment A). The plate is...