Patent GB-853707-A (GB)
Title: Improvements in or relating to periodically displaced or rotatable elements
Inventor: HARRIES JOHN HENRY OWEN
IPC: G02B7/182
Filed: 1956-06-15
Abstract: 853,707. Television. HARRIES TELEVISION RESEARCH Ltd. June 6, 1957 [June 15, 1956(6)], Nos. 18574/56, 18575/56, 18576/56, 18578/56, 18580/56 and 18581/56. Class 40(3). [Also in Groups XL(c) and XXXV] In an arrangement employing an electrical driving means for imparting a periodic movement to an element, e.g. to effect scanning in television radar or oscilloscope systems, the element is subjected, at the end of each scanning period, to a restoring drive (additional to any restoration provided by the element suspension system) comprising a first pulse which drives the element in the "fly-back" direction followed by a second pulse of opposite polarity to the first pulse and which arrests the movement of the element when it has reached its initial position. With this arrangement the moving element may be much larger, (with a consequent increase in reflection efficiency) and the scanning frequencies higher than in arrangements in which restoration is effected by the suspension system alone. Fig. 2 shows at a the relationship between the displacement # of the element with respect to time and at b, the shape of the waveform supplied to the driving means to produce such motion. The latter waveform is generated, as shown in Fig. 1, by combining, via transformers 24, 25, the outputs of generators 33-36 the sequence of the operation of which is controlled by synchronising pulses derived from a source 45. Such waveform is then supplied to the electromagnetic drive coil 17 associated with the element 15 which, in this case, comprises a light-reflecting surface supported by a suspension system 16 providing one component of scan on a viewing screen 22, of a light source 21 which may be part of an oscilloscope or may consist of a television picture tube scanned in the other co-ordinate direction only. A preferred constructional form of the element 15 and driving arrangement 17 is shown in Fig. 3A (with associated sectional views in Figs. 5 and 6) and Fig. 4A. As shown, the element 15 comprising a mirror plate is suspended between supports 61, 62 by means of rectangular section springs 16 pivotally secured at 51 to clamps 54, 55 bolted at 58 to projections 59, 60 of the mirror plate and secured at further pivoted points 51 to clamps 56, 57 carried by the supports 61, 62. The drive coil 17 is wound on a frame 68 supported by three stiffened struts 69 cemented to the mirror the whole assembly being positioned, by adjustment of the nuts 63, 65, so that the coil is freely rotatable in the gaps 77 between the pole pieces 76, 76a of a magnet 75. For supplying driving current to the coil one end 71 of the latter is connected to the mirror (which has a metallic base) so that a conducting path exists between it and connection 73 whilst the other end, 72, is connected to the lower suspension spring 16 to establish a conducting path to connection 74 the clamp 55 being of insulating material and the clamp 57 insulated from the (conducting) support 62 by means of a bush 67. The whole assembly is contained in a housing 18 provided with a glass window 19 forming a gas-tight enclosure which is evacuated via a pipe 78 (subsequently sealed by pinching at 79) to reduce both air damping on the moving parts and to reduce any noise output when the device is operated. In a modified construction employing the same suspension arrangement 16 as described above the coil 17 carrying the mirror plate 15 is arranged with respect to the magnetic circuit 81 as shown in Fig. 7. Other arrangements described include; the production of an approximately piston-like motion of the mirror by means of a solenoid during coil (Fig. 8, not shown); the operation of an electromagnetic relay (Fig. 9, not shown); a radar scanner in which a feeder 100 (Fig. 10) is oscillated in the direction of arrow 101 inside a horn 98 provided with a dielectric lens 99; a radar scanner in which the direction of a microwave beam travelling along a waveguide 106 (shown in section in Fig. 11) is varied by variation of a metal vane 107 and the production of an approximately piston-like motion of mirror 15 (Fig. 13) by means of the electrostatic force between plates 126, 127 when the driving waveform is supplied thereto. An arrangement similar to the system of Fig. 7 but in which the mirror 15 is non-symmetrical about an axis at right angles to the axis of the suspension and in which, in order to avoid the production of a twisting moment in the suspension due to the difference in the moment of inertia of the mirror about the axis of non-symmetry, the magnetic system is arranged in two parts of appropriate moments.