A Novel Sensor for Dimensional Measurement Combining Laser, Image Processing, Focus Variation and Tactile-Optical Probing

摘要

A new sensor will be presented, being capable to realize optical and tactile 3D measurements on workpieces by combining several measuring principles in one sensor head. An image processing sensor enables lateral measurements of edges and margins of objects. To determine the objects surface shape, a laser distance sensor and alternatively a focus variation sensor, both operating thru the same telecentric optic, are used for vertical measurements. A third measuring method is realized by detachably mounting a flexible fiber including a tiny probing sphere in front of the optic to enable tactile probing (Figure 2a). As the deflection of the probing sphere has to be transmitted to a detection circuit via the stylus, all conventional tactile touch probes suffer from the limitations to the stylus diameter. Bending of the stylus does not have to be considered by using image processing for the direct determination of the probing spheres deflection. Existing commercially available fiber probe sensors are using this advantage for the lateral deflection with image processing (Figure 2b). The vertical position of the probing element is defined by the vertical position of the coordinate measuring machine that is used for the probing process as the stylus element is vertically stiffen. Probing spheres are available down to 20 (mu)m in diameter. A new approach for the vertical deflection determination uses a laser distance sensor operating on the upper fiber end (Figure 4c). Lateral and vertical measurement are now combined to determine the three dimensional deflection of the fiber resulting from object contact. Image processing and distance sensing are provided by the same optical system applied above the fiber (Figure 4a). The vertical deflection of the fiber is enabled by a flexible stylus fixation that additionally ensures isotropic probing forces. The new assembly will be presented as well as the current state of development. The target parameter for 1D probing error is below 0.15 (mu)m using unidirectional probing. The specification for the 3D probing error is below 0.25 (mu)m. It will be shown, how these values have been reached using special correction and calibration methods.