An automatic focusing visual inspection system for die inspection

Automatic focusing of a visual inspection system is described. A vidicon camera was mounted on top of a high powered microscope to capture an image, process it and send an appropriate signal to a stepper motor which controls the movements of the microscope. The method used is based on the acutance of the video signal waveform. Acutance is a measure of the steepness of the video signal waveform. It implies that a sharp image will have a sharp gradient of the gray level across the image. This is measured vertically and horizontally and used to control the movements of a stepper motor to achieve an optimal focusing state. On achieving it a signal from the control circuitry of the automatic focusing system will be sent to the control circuitry of the die inspection machine to determine whether the die is good or a reject