| 摘要 |
1,222,661. Photo-electric position measurements. ITEK CORP. Feb. 21, 1968 [March 29, 1967], No.8423/68. Heading G1A. In a photo-electric apparatus for measuring the position of a surface, which may be diffuse, two spots of light are projected upon the surface which are superimposed when the surface is at a desired position but separate as the surface moves away, two photodetectors view the surface to detect when and by how much the spots separate. Each spot moves in opposite directions for the forward and backward movement of the surface and by differently modulating the two beams creating the spots each spot can be identified and so reveal the direction in which the surface moved. A servo system may reposition the apparatus to restore the surface to its nominal position relative to the apparatus. The angular position of the surface is determined by comparing the intensities of the two spots. In Fig. 3 two beams 12 and 13 are produced by apertured plate 35 from a tungsten or xenon lamp 30 and are projected by lens 47 as two spots on the surface which are superimposed if the surface is at the focal point of the lens 47, that is its nominal position. Two detectors 44 and 45 view via reflecting truncated prism 40 different portions of the surface, either side of the optical axis 11. The two beams 12 and 13 are alternately interrupted by chopper 31 and beam 12 provides via photodetector 38 a reference signal to phase sensitive rectifier 23. As the surface moves away from position the two spots separate and pass into the field of view of the detectors 44 and 45. The detector outputs are fed to a differential amplifier whose output signal is an alternating one having an amplitude dependent upon the extent of surface movement from and a phase dependance upon the direction. The signal is synchronously rectified at 23. Fig. 7 shows a modified arrangement when the two detectors 51 and 52 view the surface via a reflecting prism 53 and partially reflecting mirror 50. Both spots are viewed via mirror 49 by a photo-detector 54, whose output is an A.C. signal of amplitude dependent upon the angular position of the surface. The reference signal in this instance is provided by two detectors 55 and 56 receiving parts of the transmitted beams via mirror 49. Instead of a chopper two light sources may be alternately energised. |
