Recent advances in the fields of MEMS and MOEMS often require precise assembly of very small parts with an accuracy of a few microns. In order to meet this demand, a new approach using a robot based on parallel mechanisms in combination with a novel 3D-vision system has been chosen. The planar parallel robot structure with 2 DOF provides a high resolution in the XY-plane. It carries two additional serial axes for linear and rotational movement in/about z direction. In order to achieve high precision as well as good dynamic capabilities, the drive concept for the parallel (main) axes incorporates air bearings in combination with a linear electric servo motors. High accuracy position feedback is provided by optical encoders with a resolution of 0.1 µm. To allow for visualization and visual control of assembly processes, a camera module fits into the hollow tool head. It consists of a miniature CCD camera and a light source. In addition a modular gripper support is integrated into the tool head.To increase the accuracy a control loop based on an optoelectronic sensor will be implemented. As a result of an indepth analysis of different approaches a photogrammetric system using one single camera and special beam-splitting optics was chosen. A pattern of elliptical marks is applied to the surfaces of workpiece and gripper. Using a modelbased recognition algorithm the image processing software identifies the gripper and the workpiece and determines their relative position. A deviation vector is calculated and fed into the robot control to guide the gripper.
In photogrammetry several images of an object taken from different positions in space, are combined to calculate 3D geometrical data. This concept can be scaled down to dimensions in the mm or sub-mm regime. In this paper the application of microphotogrammetry for the measurement of strain fields in material testing is presented. The working principle and an experimental measurement setup are described and results of two application examples are given. Microphotogrammetry is compared with speckle-interferometry as an alternative approach for strain field measurement. As an additional implementation of the microphotogrammetric approach the current state of development of a precision assembly system with a positioning control using CCD-cameras is discussed.
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