Abstract:The paper describes the development of a micro-parallel-SCARA robot adapted in size to MEMS products. The degree of miniaturization is optimized concerning a smaller structure but high accuracy in a workspace dimensioned to chip card size. The robot supports the mostly used four degrees of freedom with a base area of less than 150 x 150 mm2. It is the result of a cooperative project between the Institute of Machine Tools and Production Technology at the Technical University of Braunschweig and Micromotion GmbH. This company is an innovative manufacturer of miniaturized zero-backlash gears and actors, which are used as main drives of the robot.
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.
This paper presents a planar parallel robot, built of spread-band elements. The robot has a workspace that exceeds its original size by far. The mass of the mechanical structure is extremely low, allowing accelerations up to 120 m/s2. A spread-band element consists of a roll with flanges and a cambered metal tape. The arch form of the cambered band allows the transmission of tensile and compressive forces and of one moment. The flange of the roll changes the orientation of the bending radius axis by 90°. Nevertheless the combination of roll and cambered band retains the bands flexural rigidity against a moment around an axis perpendicular to the longitudinal axis of the cambered band and the axis of the roll. This leads to the possibility of transforming rotation into translation and vice versa using spread-band elements. The combination of several spread-band elements performed in the presented robot results in a rigid mechanical system.
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