Intensity Modulated Fiber Optic Sensors For Robot Feedback Control In Precision Assembly

摘要

Fiber optic reflectance sensors, mounted on a gripper, have been constructed for a scara-type robot in the insertion of electronic components. The position of the gripper fingers, the distance to the object component, the edges, the orientation and the pin images are meas-ured and determined during the assembly process. The sensor consists of a transmitter (LED, 850 nm) and a receiver, (PIN-photodiode), which are equipped with different fiber optic measurement heads according the kind of application. The emitters and detectors are con-nected to optical fibers using mounts and SMA connectors. The position sensors of the gripper fingers are used to measure the distance between the gripper body and the fingers. The measurement range of the position sensor is 17 mm and the resolution is better than 50 pm using 100 Hz bandwidth. The measured position information is used to control the gripper dc-motor drive via a I/O controller. Proximity sensors mounted on the ejector are used to measure the distance to the object component and detect the edges. Based on measured scan profiles of components (capacitor, inductor) the edges can be determined. A typical transition range of an edge is < 2 mm giving a position resolution better than 50 pm. This edge information is used for orientation calculations. The separate pin image sensor station is used to measure the reflectance scan profiles of the pins of the component to determine the span of the component pin relative to the robot gripper. The xy-motion of the robot is used for scanning at a constant velocity. The position of the tip of the pin can be determined in the xy-plane to an accuracy greater than ± 50 μm. The realization of the sensors together with experimental results are presented.