Patent ID: 8041534

Claim:
A sensor device which detects a positional relationship between an insulating first member and second member of which the surfaces face each other in coming close to each other, comprising: a first signal source generating an electrical signal; a first electrode disposed at a first part on a surface of the first member to receive the electrical signal and store an electrical charge at the first part; a second electrode which is disposed at a second part on a surface of the second member and is electrically floated so that the second electrode is directly connected to no voltage source, wherein the second electrode induces an electrical charge, corresponding to the electrical charge stored in the first part, at the second part when the first electrode approaches; a third electrode which is disposed at a third part on a surface of the second member, is electrically connected to the second electrode and is electrically floated so that the third electrode is also directly connected to no voltage source, wherein the third electrode induces an electrical charge, corresponding to the electrical charge induced at the second part, at the third part; a fourth electrode disposed at a fourth part on a surface of the first member and inducing an electrical charge, corresponding to the electrical charge induced at the third part, at the fourth part when the third electrode approaches; a reference electrode disposed at a fifth part on a surface of the second member to be connected to a reference voltage point; a fifth electrode disposed at a sixth part on a surface of the first member, and inducing an electrical charge, corresponding to the electrical charge to be stored in the fifth part, at the sixth part when the reference electrode approaches; and a differential amplifier amplifying a voltage difference between the fourth electrode and the fifth electrode and outputting a difference signal corresponding to the positional relationship.