| 摘要 |
PURPOSE:To obtain a torque having high responsiveness over a wide range of rotational frequencies of a shaft, by projecting sine waves having a phase shift every 90 deg. to each other to each overlap part of two pairs of slit trains having a phase shift every 90 deg. to each other. CONSTITUTION:Slit trains 14 formed on a disk 13 have equal pitches; and slit trains 24 and 25 having a 1/4-pitch shift to each other and pitches equal to the trains 14 are formed at the circumference of an opposite disk 23. The sine and cosine waves having an angular speed omega decided by a time interval T with which a torque is obtained are oscillated by an oscillator 51 and supplied to driving circuits 54 and 55. If an output obtained when photodetecting elements 41 and 42 overlap perfectly with each other is set at 2B, a synthetic output (e) is shown as e=(B/2) [cos(omegat-alpha)+{2+sintheta+costheta}] with an electric angle alpha(=2pitheta/thetap) having a slit pitch thetap set at 2pi. This synthetic output (e) is compared with the phase of the oscillator 51 to obtain an angle displacement theta proportional to a change alpha of a phase, i.e., a torque with each fixed period T of the output (e). |
