Patent ID: 7894079

Claim:
A position sensing device comprising: a diffuse light source configured to radiate diffuse source light along an optical axis direction OA, the diffuse light source comprising at least a light generating portion; a position sensitive detector which is fixed relative to the light generating portion and aligned with its sensing surface opposing the diffuse light source and approximately normal to the optical axis direction OA, and with its sensing axis approximately aligned with the measuring axis; and a moving aperture arrangement located between the diffuse light source and the position sensitive detector, and attached to a movable member which is guided linearly over a measuring range that spans a dimension MR along a measuring axis direction which is transverse with the optical axis direction OA, the moving aperture arrangement configured to receive the diffuse source light and output a portion of the diffuse source light to form a measurement spot on the position sensitive detector, the sensed spot moving along the measuring axis direction corresponding to the position of the moving aperture arrangement along the measuring axis direction, wherein the position sensing device is configured such that: the moving aperture arrangement comprises a first limiting aperture having a dimension DP 1 along the measuring axis direction and a second limiting aperture having a dimension DP 2 along the measuring axis direction, wherein the first and second limiting apertures are spaced a distance LP from each other along the optical axis direction OA with the second limiting aperture closer to the position sensitive detector, and LP is at least 2 times the smaller of DP 1 and DP 2 ; the aperture arrangement angularly filters the diffuse source light such that the measurement spot consists of rays within a filtered angular range that is less than an unfiltered angular range of rays included in the diffuse source light, those rays originating from a portion of the diffuse light source spanning a light contribution dimension DLS along the measuring axis direction; an angular intensity distribution of the rays within the filtered angular range is more consistent as a function of position within the measuring range than the intensity distribution of the rays included in the unfiltered angular range as a function of position within the measuring range; and the position sensitive detector outputs at least one signal in response to the measurement spot, and the at least one signal is indicative of the position of the movable member along the measuring axis direction.