Patent GB-618420-A (GB)
Title: Improvements in scanning apparatus
IPC: H01Q3/08
Filed: 1945-09-14
Abstract: 618,420. Directive radio systems. SPERRY GYROSCOPE CO., Inc. Sept. 14, 1945, No. 23837. Convention date, Sept. 14, 1944. [Class 40 (vii)] A scanning apparatus comprises means for causing a line in fixed relation to a scanning member to describe a conical spiral by nodding said scanning member about an axis fixed in a second supporting member which is spun about an axis normal to the nod axis, and means for decreasing the rate of spin for large nod angles so that the field of view is more uniformly scanned. A spiral scan aerial system has its aerial and reflector mounted on a unit 112 pivoted in bearings 113, 114 mounted on arms 33, 34 which are attached to unit 32 bolted to extension 38 of sleeve 31. Sleeve 31 is capable of rapid rotation, rotating the aerial system with it and at the same time the unit 112 may be oscillated in bearings 113, 114 to give the spiral scan. A motor 42 (Fig. 9) is used to drive the scanner through gear train 43, 45, 46 and 47; gear 47 is fixed to its shaft and turns the driving member of clutch 50 which is normally engaged with a facing on loose gear 51 which is meshed with gear 40 (Fig. 3) attached to sleeve 31. Gear 47 also drives gear 56 mounted on a cam sleeve 57 free to rotate on sleeve 31. Cam sleeve 57 has an extended portion sliding between the outer and inner portions 69 and 61 of an annular member which is driven by sleeve 31 through key 63, but which is free to slide along the sleeve laterally. A roller mounted on member 69 engages with a cam groove 65 (Fig. 14) cut in sleeve 57. The difference in speed of sleeves 31 and 57 thus causes members 61, 69 to oscillate laterally and an adjustable rod (Fig. 4, not shown) transfers this motion to " nod " aerial mounting 112. In a preferred system an overrunning clutch is introduced between members 40 and 56 so that they may be coupled together, in which case the aerial will sweep round a cone of small vertical angle, a condition suitable for use in tracking a given object. A casing 78 on the side of gear 56, Figs. 3 and 6, carries a spring-loaded pawl 75 co-operating with a single tooth 79 formed on an extended portion 60 of gear 40. Normally, gear 40 is turning more rapidly than gear 56 and the tooth 79 passes pawl 75 periodically; if, however, clutch 50 (Fig. 9) is released by energizing solenoid 54, which works through lever 52 against a spring loading, gear 40 is not driven, pawl 75 catches up and drives tooth 79, and so sleeves 31 and 57 rotate at the same speed producing no nod motion. As there is only one tooth 79, the aerial always reaches the same position relative to the axis and traces out the same preset cone. High-frequency feed to the antenna is through input member 130, joint 131, member 132, bent wave-guide 133 and joint 105. This is fed through tube 103 within sleeve 31 and rotary joint 104 attached to the rear casing of the mechanism. Fig. 2 shows a front view of the scanner mounting; the body of the scanner is supported so that it can turn about a horizontal axis through bearings carried by the arms 22 and 23 of yoke 24 which is mounted for rotary azimuth movement in suitable bearings on the base-plate. A wave-guide 134 connects rotary joint 104 with a special hollow joint 135 fed by guide 136 from another rotary joint 137; connection to the external circuits is made through this joint. In order to scan the outer areas of the spiral more closely, cam 65 (Fig. 14) may have areas 179 shaped to provide a more gradual change. In addition, the outer areas may be scanned more slowly either by having continuously variable motor control or by arranging a switch which, when the nod angle exceeds 45 degrees, serves to actuate a relay introducing additional resistance into the motor circuit (Figs. 12 and 13, not shown). Two phase generators may be driven by the spin and nod movements to provide reference currents corresponding to the instantaneous position of the scanner.