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REAL TIME WORKSPACE MONITORING SYSTEM: FIRST RESULTS 
Martin Rechsteiner, Markus Thaler, Gerhard Troester 
Electronics Laboratory ETH Zurich 
Gloriastrasse 35, 8092 Zurich, Switzerland 
Phone: +41 1 632 5167 Fax: +41 1 632 1210 
email: rechsteiner@ife.ee.ethz.ch 
KEY WORDS: cooperation, correlation, robot, stereo, texture, workspace 
ABSTRACT 
To provide advanced robotic systems with the capability to share their workspace with humans, they must be equipped 
with an adequate security system. For lack of sophisticated monitoring systems, the workspace of robots has at the time 
to be strictly separated from the workspace of humans. We propose a vision based security system that monitors an 
invisible but clearly defined dynamical safety zone around the robot for intruding objects. À texture based stereo vision 
method is used, not requiring a time consuming correspondence search. Objects are detected when they enter the safety 
zone and the system only has to detect if an object is in the separation surface. To detect objects in the separation 
surface, one camera image is transformed with respect to the separation surface, as if it would have been taken by the 
other camera, then both images are compared. Corresponding regions belong to objects on the separation surface. 
In the following we present results of a prototype software implementation. In addition we investigated the influences of 
texture intensity on correlation results, different texture measures and the achievable thickness of the separation surface. 
1. INTRODUCTION 
A robot not only doing simple repetitive handling of objects cannot do such a task unassisted and depends on human 
interaction (Vischer, 1992). Cooperation between humans and robots is indispensable for complex tasks. Thus advanced 
robotic systems must be capable to share their workspace with humans and therefore must be equipped with an adequate 
security system. Today such cooperation is still in its infancy. This is mainly due to the fact that robots without an 
adequate security system are a great danger for humans working in the same area. 
For lack of sophisticated monitoring systems, the workspace of robots must at the time be strictly separated from the 
workspace of humans. Using hardware- or light-barriers the two workspaces are split up at a predefined location, called 
'separation surface'. Thus, cooperative work between humans and robots as well as dynamic change of their workspace 
according to time-varying needs are made almost impossible. 
A security system is needed that monitors the workspace and prevents the robot from hurting humans. A flexible, 
Baseline 
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Figure 1: Workspace of a cooperating robot Figure 2: Experimental setup 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop "From Pixels to Sequences", Zurich, March 22-24 1995