Position detector

Abstract

A detector for checking the symmetry of a helicopter rotor while it is rotating has a scanner (11) which scans vertically a field of view (15) and the view is interrupted by a vertical strip on the blade tip (16). A slot (18) in the strip gives a characteristic signal as at (L 2 ). The position of the signal (L 2 ) in a scanning cycle gives an indication of the height of the blade tip and also the circumferential spacing between blades.

I claim: .[.1. A position detector comprising means defining an elongate field of view, for viewing a target which is arranged to cross the field of view in any of a range of positions along the length of the field of view and having a reference part, a sensor in the form of a line of sensitive elements extending parallel with the field of view and positioned to receive an image of the field of view, and electronic means for repeatedly scanning the elements in scanning cycles and for detecting the particular sensitive element which receives the image of the reference part of the target as the target crosses the field of view..]. .[.2. A detector as claimed in claim 1, in which the target is fixed to a rotor blade, whose position is to be detected..]. .[.3. A detector as claimed in claim 1, in which the target comprises a blade of a helicopter rotor and 
     
        the reference part is the edge of the blade..]. 4. .[.A detector as claimed in claim 1, in which the.]. .Iadd.A position detector comprising means defining an elongate field of view, for viewing a target which is arranged to cross the field of view in any of a range of positions along the length of the field of view and which has a reference part, which said .Iaddend.reference part is a slot extending perpendicularly to the length of elongation of the field of view.Iadd., a sensor in the form of a line of sensitive elements extending parallel with the field of view and positioned to receive an image of the field of view, and electronic means for repeatedly scanning the elements in scanning cycles and for detecting the particular sensitive element which receives the image of the reference 
     
     
        part of the target as the target crosses the field of view.Iaddend.. 5. .[.A detector as claimed in claim 4, in which.]. .Iadd.A position detector comprising means defining an elongate field of view, for viewing a target which is arranged to cross the field of view in any of a range of positions along the length of the field of view and which has a reference part, which .Iaddend.said reference part is a reflecting line and further including a source of radiation to which the sensor is sensitive for illuminating the reflecting line when the target is in the field of view.Iadd., a sensor in the form of a line of sensitive elements extending parallel with the field of view and positioned to receive an image of the field of view, and electronic means for repeatedly scanning the elements in scanning cycles and for detecting the particular sensitive element which receives the image of the reference part of the target as the target 
     
     
        crosses the field of view.Iaddend.. 6. .[.A detector as claimed in claim 1, in which the.]. .Iadd.A position detector comprising means defining an elongate field of view, for viewing a target which is arranged to cross the field of view in any of a range of positions along the length of the field of view and having a reference part, in which said .Iaddend.means defining the elongate field of view comprises an elongate lens.Iadd., and said reference part is a slot extending perpendicularly to the length of elongation of the field of view, and further comprising a sensor in the form of a line of sensitive elements extending parallel with the field of view and positioned to receive an image of the field of view, and electronic means for repeatedly scanning the elements in scanning cycles and for detecting the particular sensitive element which receives the image of the reference part of the target as the target crosses the field of view.Iaddend.. .[.7. A detector as claimed in claim 1, further including computer means connected to receive the output from the sensor and including means for computing the position of the reference part in 
     
     
        the field of view..]. 8. .[.A detector as claimed in claim 7 in combination with.]. .Iadd.A position detector comprising means defining an elongate field of view, for viewing a target which is arranged to cross the field of view in any of a range of positions along the length of the field of view and which has a reference part, .Iaddend.a helicopter rotor .Iadd.having blades constituting the target, .Iaddend..[.and having.]. .Iadd.a sensor in the form of a line of sensitive elements extending parallel with the field of view and positioned to receive an image of the field of view, and electronic means for repeatedly scanning the elements in scanning cycles and for detecting the particular sensitive element which receives the image of the reference part of the target as the target crosses the field of view, computer means connected to receive the output from the sensor and including means for computing the position of the reference part in the field of view, and .Iaddend.means for generating a reference signal once per rotor revolution, and in which the computer means includes means for computing the circumferential position of each 
     
     
        rotor blade in relation to the reference signal. 9. A method of testing a helicopter rotor having blades in which a thin, generally vertical elongate field of view is defined, the rotor is rotated so that the blades in turn cross the vertical field of view, a multi-element sensor extending parallel with the field of view is repeatedly scanned in scanning cycles, and the position of the various blades in the field of view are computed 
     
     
        from signals derived during the scanning cycles. 10. A method as claimed in claim 9, in which the scanning cycle is fast in relation to the time 
     
     
        taken for a blade to cross the field of view. .Iadd.11.  The method of claim 10 wherein said elements are scanned several times each time the helicopter blade crosses said field of view. .Iaddend. .Iadd.12. The method of claim 11 wherein the computation involves measuring the ratio of the time between the beginning of the scanning of said elements and the instant when the first of the sensor elements upon which the image of a rotor blade is projected is scanned and the time it takes to scan all of the sensor elements involved. .Iaddend. .Iadd.13. The method of claim 9 wherein said ratio is indicated by the position of a pointer moving over a scale. .Iaddend. .Iadd.14. The position detector of claim 8 wherein said computer means includes means for computing the ratio of the time between the beginning of the scanning of said elements and the instant when the first of the sensor elements upon which the image of a rotor blade is projected is scanned and the time it takes to scan all of the sensor 
     
     
        elements involved. .Iaddend. .Iadd.15.  The position detector of claim 14 combined with means for displaying said computed ratio, in which the reference part is a slot in an opaque target secured to a rotor blade between the opposite ends of the target so that the projection of said field of view on said sensor elements when the target comes into the said field of view includes a light area outside said target, followed by the opaque area of said target in advance of said slot, the slot area, and an opaque area of said target beyond the slot, each area being projected onto different elements in the line of elements. .Iaddend. .Iadd.16. The position detector of claim 15 wherein said last mentioned means is a meter movement where said ratio is displayed by the position of a movable 
     
     
        pointer on a scale. .Iaddend. .Iadd.17.  The position detector of claim 16 wherein there is provided means responsive to the peak output of the sensing elements corresponding to the peak value of a number of measured values of the said ratio for varying the amount of light projected by said light source upon said field of view to keep the said peak output constant. .Iaddend. .Iadd.18. The method of claim 9 or 12 wherein said signals derived from successive scannings of said elements are averaged. .Iaddend.