| 摘要 |
PURPOSE:To achieve a higher accuracy of measuring changes in the clearance between members removing effect of hysteresis of an electrostrictive element by controlling the difference in the optical path lengths with the application of a specified high frequency voltage to the electrostrictive element for adjusting the difference in the optical path length between reflected lights from two members. CONSTITUTION:A coherent light from a light source 1 irradiates a disc 14 and a head 15 and the reflected lights interfer with each other with optical systems 4 and 12. The strength of the resulting interference light is converted into an electrical signal with a detector 13 and based on the detection signal, a control signal is generated by the control system 16A to be applied to electrostrictive elements 8 and 9 with which the difference in the optical path length between the reflected lights to compensate the difference in the optical path length for the clearance between the disc 14 and the head 15. This keeps the optical path difference in the entire optical system invariably constant and enables measurement of dynamic changes in the clearance between the disc 14 and the head 15 by measuring the magnitude of a control signal applied to the elements 8 and 9. In this case, the control signal from the control system 16A employs a high frequency signal as modulated in the amplitude with a signal related to the dynamic changes in the clearance. |
