This paper proposes a novel method to achieve pose
measurement in 3-D space using a microscopic camera. For
an object with flange on its surface, there is a shadow region
around the flange in the image if the camera is equipped with
a ring light source. The flange’s shadow distribution caused by
the ring light source is deduced based on imaging principle.
An optimal model used to estimate object’s pose is designed
based on the flange’s shadow distribution. Take the objects with
circle flange, which are commonly used in precision assembly
as an example, the shadow-forming model and the relation
between the rotation angle and the shadow width deviation are
presented. The rotation axis is determined on the basis of two
particular rays on the shadow. Then the object’s orientation is
computed based on the rotation axis and the rotation angle.
A series of simulations and experiments are conducted to verify
the high precision of the proposed pose measurement method.
The root-mean-square (rms) errors of position and orientation
measurement are 6.26 μm and 0.19◦, respectively.