Automatic Control Algorithms For The White Light Interference System And Their Implementations In Measuring Diamond Grinding Wheels

The grinding wheel is widely used in grinding and its surface topographyparameters can not only influence the machinability of grinding wheel butalso the quality of workpiece surface. It will help improve the quality ofproducts and optimize the grinding process if the3D surface topographyinformation of the grinding wheel can be obtained. As a non-contact method,the white light interferometry has advantages of high precision, largearrangement and non-fuzzy phase among all the methods.The white light interferometers almost focus manually, that is, adjustingthe distance between the lens and the measured object so that the instrumentcan collect interference images. Since the poor coherence of the white light,the manual focus is time-consuming and laborious. In order to improve thework efficiency, the automatic acquisition method based on framedifferentiation is proposed to realize automationThe main contents are as follows:(1)Recount the white light vertical scanning interferometry and othermeasurement techniques for the grinding wheel topography measurement.Introduce the automatic focusing technique and its application in the whitelight Interferometry.(2)The principle of white light interferometry is introduced, and theVertical scanning white light interferometer system is built. The systemcontains the interference microscopy group, the CCD, the motor, thepiezoelectric ceramic actuator, the grating, the three-dimensional workbenchand the grinding wheel positioning device. The motions are vertical directionmotion of the len, horizontal translational motion of the workbench and rotarymotion of the grinding wheels. The fitting hysteresis curve of the piezoelectricceramic can be got by translating，rotating and zooming the limit rise curveand the limit down curve. (3)Two methods, the gray variance method and the Sobel operatorgradient method, that most commonly used for auto focus are introduced.Point out the distinction between the autofocus in cameras and the autocollection in the white light interferometer. A method based on framedifferentiation is proposed to get the interference area. First, the intensitychange of each pixel among two adjacent images in a series of imagescaptured by the white light interferometer was calculated to get a new seriesof grayscale images. A threshold was obtained by calculating the mean andthe extreme value of nonzero pixels of each new image. According to thisthreshold, the interference area could be found to realize the automaticscanning. Experiments show that, compared to the gray variance method andthe Sobel operator gradient method, it is more sensitive to local interferencearea to get a more accurate interference range at a fast rate using thisalgorithm.(4)In order to expand the vertical scanning scale, using the PZT and thestep motor to realize the relay control; In order to improve the efficiency,adopting the Sobel operator gradient method to reduce the scanning range sothat the instrument can search the interference area in a small range; In orderto solve the problem of small field of view, driving the wheel horizontaltranslation and rotation to collect images from the different locations on thesurface topography of grinding wheel.(5)The software of measurement and control is written; its mainfunctions include the image acquisition, the motor control procedures, gratingreal-time reading and the control of the piezoelectric ceramic micropositioning stage. The software interface, use method and matters needingattention are introduced.