Inductive position detection device

1. An inductive type position detection device comprising:

a coil section including a primary coil excitable by an AC signal and a secondary coil disposed to produce an induced output in response to excitation of the primary coil;

a self-oscillation circuit composed of the primary coil included in said coil section and a capacitor, said self-oscillation circuit having incorporated therein the primary coil as an inductance element for self-oscillation;

a target section disposed in such a manner that a position of the target section relative to said coil section varies in response to a position of a target of detection, said target section being formed of a magnetically responsive member constructed to vary inductance of the secondary coil in said coil section in response to the position of the target section relative to said coil section; and

output circuitry for outputting position data of the target of detection based on an amplitude level of an output signal of the secondary coil.

2. The inductive type position detection device as claimed in claim 1 , wherein said self-oscillation circuit has an oscillating frequency set at a high frequency band of hundreds of kHz or more.

3. The inductive type position detection device as claimed in claim 1 , wherein said output circuitry includes a rectifier circuit for rectifying the output signal of the secondary coil, and a circuit for offset-adjusting an output DC signal of the rectifier circuit and adjusting a gain of the output DC signal.

4. The inductive type position detection device as claimed in claim 1 , wherein the primary and secondary coils each comprise a flat coil formed in a spiral shape on a printed circuit board.

5. The inductive type position detection device as claimed in claim 4 , wherein the flat coil constituting the first or second coil includes a plurality of flat coil portions disposed in superposed multiple layers and connected in series with each other.

6. The inductive type position detection device as claimed in claim 1 , wherein the secondary coil comprises at least one pair of secondary coils that are disposed spaced from each other by a predetermined interval,

said target section is constructed in such a manner that inductance variation of individual ones of the pair of secondary coils presents mutually-opposite characteristics, and

output signals of the pair of secondary coils are differentially synthesized to generate a single synthesized output signal.

7. The inductive type position detection device as claimed in claim 6 , wherein the secondary coil comprises two pairs of secondary coils, and

wherein a synthesized output signal based on one of the pairs of secondary coils presents a sine function characteristic responsive to the position of the target of detection, and a synthesized output signal based on other of the pairs of secondary coils presents a cosine function characteristic responsive to the position of the target of detection.

8. The inductive type position detection device as claimed in claim 1 , which is constructed as a rotational position detection device where the target of detection moves in a rotational direction.

9. An inductive type multi-rotational position detection device comprising:

a first rotational position detection device constructed of an inductive type position detection device;

a second rotational position detection device constructed of an inductive type position detection device; and

transmission means for transmitting rotational displacement of the target of detection to said first rotational position detection device and said second rotational position detection device with different transmission ratios,

wherein the inductive type position detection device comprises:

a coil section including a primary coil excitable by an AC signal and a secondary coil disposed to produce an induced output in response to excitation of the primary coil;

a self-oscillation circuit composed of the primary coil included in said coil section and a capacitor, said self-oscillation circuit having incorporated therein the primary coil as an inductance element for self-oscillation;

a target section disposed in such a manner that a position of the target section relative to said coil section varies in response to a position of a target of detection, said target section being formed of a magnetically responsive member constructed to vary inductance of the secondary coil in said coil section in response to the position of the target section relative to said coil section; and

output circuitry for outputting position data of the target of detection based on an amplitude level of an output signal of the secondary coil,

said inductive type multi-rotational position detection device being capable of detecting absolute positions over a multiplicity of rotations through a combination of detection outputs of said first rotational position detection device and said second rotational position detection device.

10. The inductive type position detection device as claimed in claim 1 , which is constructed as a linear position detection device where the target of detection moves in a linear direction.

11. The inductive type position detection device as claimed in claim 1 , which is constructed as an inclination detection device where the target of detection moves in an arc.

12. The inductive type position detection device as claimed in claim 1 , wherein the magnetically responsive member of said target section is formed of a non-magnetic, good electrically conductive substance and has a curved or bent line shape.

13. The inductive type position detection device as claimed in claim 12 , wherein the magnetically responsive member, having the curved or bent line shape, forms a closed loop such that that an inductive current produced by a magnetic field of the primary coil flows therethrough.