Algorithms for On-line Monitoring of Components in an Optical Tweezers-based Assembly Cell

Optical tweezers have emerged as a powerful tool for micro and nanomanipulation. Using optical tweezers to perform automated assembly requires on-line monitoring of components in the assembly workspace. This paper presents algorithms for estimating positions and orientations of microscale and nanoscale components in the 3-Dimensional assembly workspace. Algorithms presented in this paper use images obtained by optical section microscopy. The images are first segmented to locate areas of interest and then image gradient information from the areas of interest is used to generate probable locations and orientations of components in the XY-plane. Finally, signature curves are computed and utilized to obtain component locations and orientations in 3-D space. We have tested these algorithms with silica micro-spheres as well as metallic nanowires. We believe that the algorithms described in this paper will provide the foundation for realizing automated assembly operations in optical tweezersbased assembly cells. INTRODUCTION Light beams exert small forces on objects, and for objects smaller than tens of micrometers the forces can be designed to “grasp” a particle in an optical beam and move it to a desired position. Using this property of light beams, optical tweezers have been developed to successfully trap and move nanoscale and microscale components of different sizes and shapes [1–10]. Optical tweezers do not make physical contact with the component being assembled and hence do not cause damage due to stiction or deformation, normally caused by contact forces. At the same time, optical tweezers provide a broad range of positioning and orienting capabilities to place components at the desired locations in the workspace. By utilizing multiple lasers beams, optical tweezers can perform several operations in parallel. These characteristics make optical tweezers a very promising technology for micro and nanomanipulation. Currently optical tweezers are operated by highly experienced human operators and performing a single successful assembly operation can take days of effort. In order to use optical tweezers in production processes, the following fundamental ad1 Copyright c © 2006 by ASME