Precision Pose Measurement of an Object with Flange based on Shadow Distribution

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 $\mu \text{m}$ and 0.19°, respectively.