Patent ID: 7238931
Filing Date: 2007-07-03
Classification: G01D,G03F,G05B

Abstract:
1. A displacement detection apparatus comprising: a scale having graduations arranged at a predetermined pitch; a first head adapted to detect periodic analog signals corresponding to the predetermined pitch; a second head adapted to detect periodic analog signals corresponding to the predetermined pitch; first processing means for detecting a first differential value between an immediately preceding positional data and a current positional data obtained by sampling the periodic analog signals detected by the first head; second processing means for detecting a second differential value between an immediately preceding positional data and a current positional data obtained by sampling the periodic analog signals detected by the second head; switching means for selectively providing an output corresponding to the first differential value detected by the first processing means or the second differential value detected by the second processing means; scale position detection means for detecting when the scale reaches a predetermined position relative to the first head or a predetermined position relative to the second head; switching control means for causing the switching means to switch in response to a signal received from the scale position detection means; and means for outputting positional information based on the provided output.