GB1511265A - Apparatus for sensing the relative position of two object - Google Patents

Abstract

1511265 Optical position sensing NATIONAL AERONAUTICS & SPACE ADMINISTRATION 12 May 1975 [31 May 1974] 19849/75 Heading H4D The Specification describes apparatus for optically sensing the position of an article having mounted thereon a reflective target at a predetermined position, by a sensor mounted on a movable arm which is moved to a position above the article whereby the arm may be lowered and mechanically grasp, or make suitable connection with a cooperating portion of the article. The apparatus includes a photo electric sensor comprising a silicon quadrant detector 14 and three associated light emitteing diodes LED 1 , 2 , 3 , Fig. 7. The article 10 has mounted thereon reflective target 15 comprising a cube corner reflector 30, Fig. 4, and disposed on opposite sides thereof planar mirrors 31 and 32. In operation, the arm is moved under control of the operator, aided by, for example television, to a position as close as possible to one wherein the co-ordinate axes X, Y of the detector 14 are parallel to the co-ordinate axes X m , Y m of the target 15 on handle 11 and the respective Z and Z m axes are approximately aligned. The final accurate predetermined mutual positioning of the two coordinated systems obtains as a result of the action of servo motors (not shown) which are respectively arranged to move the apparatus in directions a x , α y , # x , # y , # and R (Fig. 1), in the appropriate sense until these respective deviation signals are nulled, and movement ceases when alignment is achieved. The actuator 12 may then be moved automatically, or controlled by the operator through a predetermined distance in the Z-direction whereupon fingers 13 are operated to correctly grasp handle 11. Diodes LED 1 , LED 2 , LED 3 are switched on successively, controlled by three phase clock signals # 1 , # 2 , # 3 from the pulse generator (Fig. 8). The quadrant detector output signals are fed to subtractors 51, 52 from which are respectively obtained signals V xn = A - B and V yn = C - D where n = 1, 2, 3 corresponding to the clock phase. Sample and hold circuits 58, 59, 60, 66, 67, 68 select the values signals V xn , V yn during the appropriate phase and from which the deviation signals are obtained according to the relationships: In another embodiment, telescopic sections 83, 85 and track 81 which produce translational movement may be replaced by angularly displaceable means when the displacements are small (see Fig. 9, not shown).