| 摘要 |
PURPOSE:To prevent the contact of the magnetic head, by forming a cam shaped notch at a specified position of the moving body so that the gap between the notch and a detecting element facing said moving body is slowly increased or decreased, and forming a so that the gap between the step part and said detecting element is quickly increased or decreased. CONSTITUTION:At the specified position of a magnetic disk 1, the cam shaped notch 8a whch has an arc shape whose radius gradually varies is provided, so that the gap between the notch and the detecting element 7 facing said disc 1 is slowly increased or decreased. The step part 8b is also provided so that the gap between the part 8b and said detecting element 7. When said magnetic disk 1 is rotated in the normal direction shown by an arrow or in the reverse direction, the gap with the detecting element 7 is quickly or slowly increased and decreased at first and then slowly or quickly increased or decreased. Thus the number of rotation of the moving body can be detected, and the contact of the magnetic head with the surface of the recording medium of the magnetic disk which is the moving body can be prevented. |
