Scanning Optical Mosaic Scope for Micro-Manipulation

Conventional microscopes with high magnification are limited by the size of the field of view. For precision assembly tasks in a large work volume, a common solution is to move either the camera or the platform, which typically has limited bandwidth. This paper presents an alternate approach of combining high speed scanners and a high speed camera to create a mosaic view over a large field of view at high refresh rates. We state the design problem of the optical, motion, and image processing subsystems and discuss the initial experimental setup and results. For micro-assembly and micro-manipulation, a microscope is an indispensable tool (1). However, conventional microscopes suffer from the limitation that high magnification reduces the size of the field of view. As a result, many micro-assembly tasks that requires micron to sub-microns precision over millimeter work volume are beyond the capability of fixed optical microscopes. A common solution is to move the platform supporting the sample or move the microscope itself. The bandwidth of the motion is limited by the inertia of the platform or microscope, and the vibration resulting from the motion can blur the image or even modify the scene. This paper introduces a new approach to optical microscopy, which we call scanning optical mosaic scope (SOMS), that addresses the limitation of the field of vision. The key idea is to use high-speed scanners and a high- speed camera to scan the workspace, and combine the individual frames together to create an effective enlarged view. Since scanners can be precisely controlled and have superior dynamic characteristics, it is conceivable that a large field of view may be achieved at high refresh rates. In addition, if timing is less critical, the scanner motion can also be chosen to produce a higher effective resolution than the CCD array. Forming a larger image through mosaicking is an old idea, from NASA planetary fly- bys to the photo-stitching software in some consumer digital cameras. The challenge here is to attain high enough refresh rate to allow dynamic tasks in assembly and manipulation to be performed with real-time vision guidance. Confocal microscopes also employ high speed scanning to form images but only a single pixel data is obtained at each scan (2). Since our approach acquires a complete image in each scan, we are faced with a large amount of data as well as intensive computation to merge the images. To be specific, the following technical issues need to be addressed in order to realize the stated objective:  The optical system needs to be carefully designed so the images are focused and undistorted over the full range of the scanner motion.  Image processing needs to be performed to stitch the individually scanned images together on the fly. The amount of image processing depends on the scanner posi- tion sensor resolution.