Optical design of a variable view imaging system with the combination of a telecentric scanner and double wedge prisms.

Recent developments in micro-electro-mechanical systems and biotechnology have presented an emerging need for observation of dynamic targets in three-dimensional space. Unfortunately, conventional microscopes with fixed optical parameters have difficulty supplying sufficient vision information because of occlusion, small field of view, and low depth resolution. This paper introduces the design of a variable view imaging system that can supply a flexible view with a relatively large zenith angle and simple kinematics. Because of several performance factors, a multiobjective optimization process is applied to achieve an appropriate design. A prototype system is developed and used to verify the proposed design.

Sensor fusion of phase measuring profilometry and stereo vision for three-dimensional inspection of electronic components assembled on printed circuit boards.

Automatic optical inspection (AOI) for printed circuit board (PCB) assembly plays a very important role in modern electronics manufacturing industries. Well-developed inspection machines in each assembly process are required to ensure the manufacturing quality of the electronics products. However, generally almost all AOI machines are based on 2D image-analysis technology. In this paper, a 3D-measurement-method-based AOI system is proposed consisting of a phase shifting profilometer and a stereo vision system for assembled electronic components on a PCB after component mounting and the reflow process. In this system information from two visual systems is fused to extend the shape measurement range limited by 2pi phase ambiguity of the phase shifting profilometer, and finally to maintain fine measurement resolution and high accuracy of the phase shifting profilometer with the measurement range extended by the stereo vision. The main purpose is to overcome the low inspection reliability problem of 2D-based inspection machines by using 3D information of components. The 3D shape measurement results on PCB-mounted electronic components are shown and compared with results from contact and noncontact 3D measuring machines. Based on a series of experiments, the usefulness of the proposed sensor system and its fusion technique are discussed and analyzed in detail.

Active optical system for variable view imaging of micro objects with emphasis on kinematic analysis.

Insufficient vision information, such as occlusion, low resolvability, and a small field of view, represent important issues in microassembly and micromanipulation. We propose an active optical system to solve problems related to insufficient vision information through the integration of robotics and optics technologies. The proposed system integrates a double-prism system and a scanning mirror system to supply a compact flexible view. The kinematics of the imaging system is analyzed based on a simplified model initially to investigate the workspace and identify the kinematic performance. A more rigorous analysis of kinematics of the system is then made based on the ray tracing method. The simulation results based on the preliminary design are provided for investigating the workspace and demonstrating the capability of the system in imaging with variable views.

Dense range map reconstruction from a versatile robotic sensor system with an active trinocular vision and a passive binocular vision.

One major research issue associated with 3D perception by robotic systems is the creation of efficient sensor systems that can generate dense range maps reliably. A visual sensor system for robotic applications is developed that is inherently equipped with two types of sensor, an active trinocular vision and a passive stereo vision. Unlike in conventional active vision systems that use a large number of images with variations of projected patterns for dense range map acquisition or from conventional passive vision systems that work well on specific environments with sufficient feature information, a cooperative bidirectional sensor fusion method for this visual sensor system enables us to acquire a reliable dense range map using active and passive information simultaneously. The fusion algorithms are composed of two parts, one in which the passive stereo vision helps active vision and the other in which the active trinocular vision helps the passive one. The first part matches the laser patterns in stereo laser images with the help of intensity images; the second part utilizes an information fusion technique using the dynamic programming method in which image regions between laser patterns are matched pixel-by-pixel with help of the fusion results obtained in the first part. To determine how the proposed sensor system and fusion algorithms can work in real applications, the sensor system is implemented on a robotic system, and the proposed algorithms are applied. A series of experimental tests is performed for a variety of configurations of robot and environments. The performance of the sensor system is discussed in detail.

Flexible depth-of-field imaging system using a spatial light modulator.

A major problem of optical microscopes is their small depth-of-field (DOF), which hinders automation of micro object manipulation using visual feedback. Wavefront coding, a well-known method for extending DOF, is not suitable for direct application to micro object manipulation systems based on visual feedback owing to its expensive computational cost and due to a trade-off between the DOF and the image resolution properties. To solve such inherent problems, a flexible DOF imaging system using a spatial light modulator in the pupil plane is proposed. Especially, the trade-off relationship is quantitatively analyzed by experiments. Experimental results show that, for low criterion resolution, the DOF increases as the strength of the mask increases, while such a trend was not found for high criterion resolution. With high criterion resolution, the DOF decreases as the mask strength increases when high-resolution images are required. The results obtained can be used effectively to find the optimum mask strength given the desired image resolution.