Optical 3D-sensors are useful tools for automatic inspection.
But frequently they are complex and expensive.
We introduce a simple 'point sensor' for the acquisition
of 3D object data, based on a modification of the
'confocal focus sensing'. This principle was described
by Shamir et ala, for sensing microscopic, mirrorlike
objects. Our modification works for macroscopic objects
with rough surfaces. Rough surfaces introduce problems,
because, with coherent illumination, we get speckled
spot images. To reduce speckle effects,often a very high
illumination aperture is used. But when measuring macroscopic
objects one needs small apertures to get enough depth
of field and to avoid shading. We reduce speckle by using a
broadband laser diode or a white light source. Fig.l
The sensor works as follows (Fig.l): a light spot is projected
onto the object surface. Two images of this light spot are created by
the lens L and two beamsplitters. Two pinholes are located on the optical
axis, at different distances. The flux l and 2 behind the pinholes
is measured. The ratio D1/D2 encodes the object distance. 41/b2 is independent
from the object reflectivity.