PURPOSE: To elevate the reliability of the results in the measurement while facilitating the assembly of the equipment by detecting the differential rotation between the rotational speed and the reference rotational speed of an object to be measured utilizing the phase difference cycle of a polarized wave.
CONSTITUTION: When passed through a polarization plate 40, a light from a light source 32 makes a reference polarized wave whose polarization plane rotates at the same speed as a reference motor 22. This reference polarized wave is made to transmit a polarization plate 14a and the quantity of light received with a light receiving element 28 varies according to a phase difference between the phase in the polarization plane of the reference polarized wave and the phase in the polarization plane of a polarizor 14a. When the phase difference reaches 90°, the quantity of light received is zero. Therefore, measurement of the cycle, at which the quantity of light received with the light receiving element 28 is zero, enables the computation of the rotational speed of an object 12 to be measured. This eliminates the need for coincidence of the axis between a synchronous rotor and a rotor of a known speed thereby improving the measuring accuracy with an easy assembly.
KAWASAKI HIROTAKA
INOUE MASAHIRO
