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Heft 4.
nna 1996
OBJECT RECOGNITION USING MULTI-SENSOR FUSION AND ACTIVE EXPLORATION
Claus Brenner and Michael Hahn
Institute of Photogrammetry
Stuttgart University
P.O.B. 106037
70049 Stuttgart / Germany
ISPRS Commission V, Working Group |
KEY WORDS: Active exploration, object recognition, multi-sensor fusion, free-form surfaces
ABSTRACT
This paper presents a concept for the recognition and localization of objects which relies on multi-sensor-fusion and active
exploration. Today research in photogrammetry generally agrees that the use of complementary sensors, e.g. ranging and
imaging cameras, is important for simplifying interpretation related tasks. But no notice has been taken so far on the role of
active exploration. Our work is part of a research program where five institutes of Stuttgart University cooperate to develop
an experimental measuring system for flexible inspection and gauging. The system will be capable of determining auto-
matically the shape, form and class attributes of an industrial object. It then solves in a self-acting manner the measuring
task associated with that object. The paper briefly describes the experimental measuring system and the used sensors. It
then focuses on the object recognition concept. With first results a number of subsequent processing steps of the whole
procedure is illustrated.
1 INTRODUCTION
For years, the production of many plastic and metal parts,
for example in the automobile industry, has been auto-
mated. While at the same time the complexity of the parts
increases, often the production lots get smaller. This has
led in many areas to a more flexible assembly of the pro-
ducts. Quality assurance in this case is often performed
with individually prepared gauges or specialized measur-
ing systems, which is a very unflexible solution. Addition-
ally, the need for a 10096 quality control has grown in areas
such as automobile production, since more and more com-
plicated parts are assembled by suppliers.
Optical measurement techniques have several properties
that make them interesting for flexible gauging and inspec-
tion tasks: they are able to carry out quickly measurements
and are applicable to a wide range of materials including
deformable objects. When used in conjunction with pho-
togrammetric techniques, optical measurement can yield
very accurate results.
Despite those advantages, optical measurement tech-
niques are not well accepted in the industry (Grün 1994).
One reason for this is that traditional measurement tech-
niques, such as coordinate measuring machines (CMM),
are very well established whilst optical systems with com-
parable performance have not been commercially available
until recently. This may change now with new very high
resolution sensors and projectors. Another drawback is that
optical techniques are often considered to be too compli-
cated to be operated under factory conditions. Testing of
geometric specifications is simply solved by an unskilled
worker by placing a part on a part-specific gauge. Further,
59
optical measurements often give accuracies which depend
on the specific object. In unfavourable cases, e.g. if an ob-
ject's surface is soiled, measurement may become impossi-
ble using fixed sensor and lighting positions. But changing
this conditions (e.g. by changing the sensor, lighting or ob-
ject positions) usually requires some skilled person familiar
with that particular measuring system.
To overcome these difficulties, two key components of in-
spection and measurement systems will be
1. multi-sensor-fusion and
2. active exploration.
Multi-sensor fusion gives a system the opportunity to se-
lect another measurement technique if the measurement
task can not be performed with the currently used tech-
nique. Thus, sensor-specific flaws can be avoided. More-
over, combining sensors with different resolutions allows
for precise measurements with the accuracy of the fine-
resolution sensor whilst the field of view is that of the
coarse-resolution sensor.
Active exploration is the process of choosing sensors and
sensor positions automatically when capturing the object
under consideration. Ideally, this is some hierarchical pro-
cess, much like humans proceed when they examine some
object: first an overall view of the object is taken which re-
veals some general properties and hints on interesting fea-
tures of this object. Then those features are inspected in
detail. For a measurement system this means that different
sensors are used for different levels of detail. Active explo-
ration also allows to change sensor and lighting positions
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
