Turntable apparatus

A turntable apparatus comprising a stationary substantially planar substrate having a shaft;

• a turntable rotatably supported by said shaft on said stationary substrate and superposed over said stationary substrate, said turntable and said substrate lying in registry one with the other and in spaced parallel planes normal to the axis of rotation of the turntable, said turntable having an outer peripheral edge and an annular inner surface, an annular metal plate secured to and dependent from said turntable adjacent said outer peripheral edge;
• a doughnut-shaped insulation member fixedly supported on said stationary substrate to overlie said stationary substrate in spaced relation thereto in the direction of the axis of rotation of the turntable;
• a plurality of coreless coils disposed on said insulation member;
• a plurality of first magnets disposed on said inner surface of said turntable facing said insulation member;
• a plurality of second magnets disposed on said annular metal plate, said coils facing said first magnets and said second magnets in the direction of the axis of rotation of the turntable;
• position detecting means provided on said insulation member for detecting the position of each said magnet relative to each said coil;
• an electric power source supplying an electric power to said coils;
• means operable upon receipt of output signals from said position detecting means to control supply of a current to each of said plurality of coils thereby to cause a rotating magnetic field to be produced in the coils;
• and speed regulating means comprising means for detecting the rotational speed of said turntable and producing an electric output signal corresponding to the rotational speed of said turntable, means for producing an electric reference signal corresponding to a predetermined rotational speed of said turntable, and means operative in response to said electric input signal from the rotational speed detecting means and said electric reference signal from the electric reference signal producing means thereby to control the amount of a current supplied to each coil from said power source.