Patent ID: 7705611

Claim:
A sensor device for detecting a positional relationship between a first member and a second member, comprising: a first charge-holding electrode provided on a surface of the first member and holding a charge; a second charge-holding electrode provided on the surface of the first member and holding a charge differing from the charge held by the first charge-holding electrode; a first charge-induced electrode provided on a surface of the second member, the first charge-induced electrode having a charge induced therein in accordance with the charge held by the first charge-holding electrode, when the positional relationship between the first and second members changes to cause the first charge-holding electrode to approach the first charge-induced electrode; a second charge-induced electrode provided on the surface of the second member, the second charge-induced electrode having a charge induced therein in accordance with the charge held by the second charge-holding electrode, when the positional relationship between the first and second members changes to cause the second charge-holding electrode to approach the second charge-induced electrode; and a difference detector which generates a difference detection signal indicative of the positional relationship when a difference between the charge induced in the first charge-induced electrode and the charge induced in the second charge-induced electrode is greater than a preset value.