Patent GB-191512999-A (GB)
Title: Improvements in or relating to Searchlights.
Inventor: SPERRY ELMER AMBROSE
IPC: H05B31/00
Filed: 1915-09-10
Abstract: 12,999. Sperry, E. A. April 16, [Convention date]. Arc lamps.-Electrode-holders of a searchlight are strongly cooled by currents of air or other gas which do not come into contact with the arc. The holders may also protect the electrodes from the atmosphere and supply them with current close to the arc, so that high current densities are possible. The positive electrode is preferably rotated. Fig. 1 shows one form of positive electrode-holder, consisting of a block 10 carried by diverging legs 9. Towards the arc, the block is provided with cooling-ribs 13 of decreasing diameter. Air supplied from a fan blower through the hollow legs and passages 15, 16 in the block, is conducted by a slotted conical shield 18 around the ribs 13, which are cut away at the bottom and optionally also at the top. A silica or like sleeve 14 making an air-tight joint with the block and shield protects the electrode close to the arc. In a modification, the back end of the sleeve is flared to fit inside the conical shield, which is drawn against the ribs by a spring and may be coated with refractory material. In the upper part of the block 10, behind the ribs, is a recess taking a plug 124, through which pass three electric contact-pieces. These are pressed downwards by cross-bars 28, the ends of which are connected by systems of equalizing- levers to two springs, one on each side of the holder. The contact-pieces may be of copper, with detachable blocks of silver or the like at their lower ends. Mounted at the back of the holder is a worm-wheel 33 driven by a worm 34. Two brackets 36, 37, pivoted on the face of the worm-wheel and drawn together by a spring, carry rollers 39 geared together by wheels 45 and engaging opposite sides of the electrode, which is thus rotated with the wormwheel. One roller is knurled, and the other has flanges at its ends so that the electrode is held at three points. The latter roller is driven by worm gearing from a star-wheel 47, which at each revolution of the large wormwheel 33, strikes a finger 48 on a rod 55. Normally, the finger turns the star-wheel one tooth at a time, and thus feeds the positive electrode a little more slowly than it consumes. The finger is also adjustable by hand and by automatic mechanism so as to feed the starwheel through two or more teeth, when the crater is displaced from its proper position. To minimise resistance heating of the negative electrode, current is conveyed to it by contact springs within the ribbed part of the block, which is made in two or more parts to facilitate access to the springs, and is cooled by an air current similarly to the positive holder. The negative holder is pivoted to its legs to allow of the insertion of an electrode from below. As no rotation is here necessary, the electrode is fed by two rollers on spring-pressed brackets pivoted directly to the holder, the lower roller being driven through worm gear by a shaft extending down to the mechanism casing. The legs of the negative holder are tilted, to strike the arc, about a pivot below the search-light casing. A slide coupling and a universal joint are provided in the negative feeding-shaft. Shadows are reduced by arranging the feeding- shafts and the rod 55 directly behind the legs of the holders. Most of the light from the negative electrode is cut off by the positive holder, which also carries a shield 220 to arrest downward illumination. At the top of the projector barrel is an exhaust fan 201, Fig. 11, geared to a square vertical shaft 202, which fits within the worm driving the large wormwheel of the positive holder. A handle at the upper end of the square shaft allows it to be disengaged from the worm when the holder is to be removed. A single motor furnishes the power required by the feeding-mechanism and by the fan blower. The motor, mechanism, and fan blower are contained in a box 76, into which the legs of the holders extend. This box is mounted on a slide in grooves in the bottom of the search-light casing, and can be removed when the front of the search-light is open. Cored electrodes may be used. According to the Specification as open to inspection under Section 91 (3) (a), the finger 48 determining the amount of feed of the positive electrode is adjusted by an electromagnet, current through which is controlled by a bi-metallic switch arm 50, Fig. 7 (Cancelled). Part of the radiation from the crater is focused on to this switch arm by a mirror 49 on the opposite side of the projector, when the crater is in its proper position. The lower free end of the switch arm enters a slot in the upright arm of a lever connected to two dash-pots. The negative feed-shaft is bevel-geared to a wheel 99, Fig. 6 (Cancelled), rotated by a handle 106 or by oppositely-acting pawls 96, 97 pivoted to a slide 91, which is continuously reciprocated by a crank 92. Engagement of one or other of the pawls with the wheel 99 is determined by a three-armed lever 90 linked to the pawls and to the armature 87 of shunt electro-magnets 86. This subject-matter does not appear in the Specification as accepted.