Improvements in or relating to apparatus for tracking remote objects radiating more or less energy than the field of their background

摘要

664,092. Photo-electric control of tracking apparatus. SPERRY CORPORATION. May 11, 1949 [May 26, 1948], No. 12568/49. Class 40 (iii). [Also in Group XXXV] An object, such as a star or an aeroplane in a bright sky, which radiates more or less energy than its background is automatically tracked by a telescope. In one arrangement, Fig. 2, a rotary shutter 28, driven by a constant-speed motor 31, divides the image field in two so that when the disc of light 38 from, e.g., a star is not central in the field, as shown in Fig. 3A, the photo-cell 35 will receive more light than when the shutter is turned through 180 degrees, and thereby provide an alternating output. The amplified photo-cell output is compared in phase-sensitive amplifiers 62, 63, with referencevoltages from a two-phase generator 46 driven from the shutter, to control up-down, and leftright tracking servomotors 18, 19. When the telescope is correctly tracking a circular image the photo-cell output will be unmodulated. To track a dark object on a light background, the error signals are reversed. In an alternative arrangement, Fig. 5, a reversion prism 51 is rotated about the focal axis 17 by a constantspeed motor 52, causing the image to rotate (at twice the prism speed) before it reaches a splitting prism 54 reflecting on to two photocells 55, 56. The cells are connected to a push-pull amplifier, and the output is compared with reference voltages from a two-phase generator 57 as before.