Patent ID: 8299806

Claim:
A sensor apparatus for detecting a positional relationship between first and second members having first and second surfaces, respectively, comprising: a first electrode provided on the first surface of the first member; an applying unit configure to apply a charging signal periodically with a first cycle period to the first electrode so that first charges are induced on the first surface of the first member; a second electrode provided on the second surface of the second member to generate electrical detecting signals with the first cycle periods depending on second charges which are induced on the second surface due to the first charges held on the first surface and are changed with the first cycle period depending on a distance between the first and second surfaces; a selecting unit configured to select one of the first cycle period and a second cycle period which is different from the first cycle period, the first and second cycle periods being partially overlapped in respective segment periods; an output unit which periodically receives the electrical detecting signals from the second electrode, which allows parts of the electrical detecting signals to be output from the output unit during the segment periods, if the second cycle period is selected, and allows the electrical detecting signals to be output from the output unit with the first cycle in synchronized with the charging signals, if the first cycle period is selected; a comparator configure to compare an amplitude of the part of the electrical detecting signal or the electrical detecting signal from the output unit with a predetermined threshold value and generate a first comparison signal when the amplitude is not less than the predetermined threshold value and a second comparison signal when the amplitude is less than the predetermined threshold value, respectively; and a controller configure to generate, in response to the first comparison signal, a proximity signal which indicates the proximity of the first and second members, and to generate, in response to the second comparison signal, a non-proximity signal which indicates the non-proximity of the first and second members, wherein the selecting unit selects the second cycle period in response to the non-proximity signal, and selects the first cycle period in response to the proximity signal so that the proximity signal is continuously generated depending on the successive generation of the first comparison signals.