Quick Guide to Precision Measuring Instruments

PG50Measurement along Multiple Portions of an ImageLarge features that cannot be contained on one screen have to be measured by precisely controlling the position of the sensor and stage so as to locate each reference point within individual images. By this means the system can measure even a large circle, as shown below, by detecting the edge while moving the stage across various parts of the periphery.Composite Coordinates of a PointMeasuring machine stage position M = (Mx, My, Mz)Detected edge position (from the center of vision) V = (Vx, Vy)Actual coordinates are given by X = (Mx + Vx), Y = (My + Vy), and Z = Mz, respectively.Machine coordinate systemVision coordinate systemSince measurement is performed while individual measured positions are stored, the system can measure dimensions that cannot be included in one screen, without problems.Principle of Auto FocusingThe system can perform XY-plane measurement, but cannot perform height measurement using only the camera image. The system is commonly provided with the Auto Focus (AF) mechanism for height measurement. The following explains the AF mechanism that uses a common image, although some systems may use an AF laser.The AF system analyzes an image while moving the Camera up and down in the Z axis. In the analysis of image contrast, an image in sharp focus will show a peak contrast and one out of focus will show a low contrast. Therefore, the height at which the image contrast peaks is the just-in-focus height.Variation in Contrast Depending on the Focus ConditionEdge contrast is low due to out-of-focus edges.Edge contrast is high due to sharp, in-focus edges.MMzMyMxVxVyVMachine coordinate systemVision coordinate systemMMzMyMxVxVyVCameraZ coordinateIn-focus heightContrastHighHighLowLowContrast in the scanning directionHighHighLowLowContrast in the scanning directionContrast in the scanning directionVision Measuring MachinesMMzMyMxVxVyVMachine coordinate systemVision coordinate systemMMzMyMxVxVyV

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