INSPECTION METHOD FOR SURFACE OF MAGNETIC DISK

PURPOSE:To improve product yield by deciding only a part except an unused area by a method which irradiates a magnetic disk with a light beam and inspecting the surface defect of the magnetic disk by using reflected or transmitted light. CONSTITUTION:A web type magnetic disk original plate 2 ground by a grinding device 1 is sent to an inspection roll 3. Then the surface of the original plate 2 is irradiated with laser light from a projector 4 and its reflected light is received by the photomultiplier tube of a photodetector 5. Then, the waveform of the signal of variation of the reflected light is processed by an inspecting device 6a to detect whether or not there is a defect. Further, web length is measured from rotations of the inspection roll 3, etc., and an inspection range is inputted to an inspection range controller 6. Then, only a range which is almost superposed upon the recording/reproduction area of the disk is inspected and the range is punched by punching devices 8 and 9. Thus, such a contradiction that a product is treated as a defective because there is a defect at an unused part is corrected, so that the yield is improved to begin with the original disk.