Pose measurement method with six parameters for microassembly based on an optical micrometer

This paper presents a new pose measurement method of microminiature parts that is capable of transforming one dimension (1D) contour size obtained by optical micrometer to three dimension (3D) data with six parameters for microassembly. Pose measurement is one of the most important processes for microminiature parts' alignment and insertion in microassembly. During the past few years, researchers have developed their microassembly systems focusing on visual identification to obtain two or three dimension data with no more than three parameters. Scanning electronic microscope (SEM), optical microscope, and stereomicroscope are applied in their systems. However, as structures of microminiature parts become increasingly complex, six parameters to represent their position and orientation are specifically needed. Firstly, The pose measurement model is established based on the introduction of measuring objects and measuring principle of optical micrometer. The measuring objects are microminiature parts with complex 3D structure. Two groups of two dimension (2D) data are gathered at two different measurement positions. Then part pose with 6 parameters is calculated, including 3 position parameters of feature point of the part and 3 orientation parameters of the part axis. Secondly, pose measurement process for a small shaft, vertical orientation determination, and position parameters obtaining are presented. 2D data is gathered by scanning the generatrix of the part, and valid data is extracted and saved in arrays. A vertical orientation criterion is proposed to determine whether the part is parallel to the Z-axis of the coordinate. If not, 2D data will be fixed into a linear equation using least square algorithm. Then orientation parameters are calculated. Center of Part End (CPE) is selected as feature point of the part, and its position parameters are extracted form two group of 2D data. Finally, a fast pose measurement device is developed and representative experiments are carried out. Results show that the measurement method could obtain pose of complex 3D micro parts fast and accurately, and can meet the demand of microassembly system. 2009 SPIE.