Patent GB-917851-A (GB)
Title: Improvements in or relating to projectors
IPC: G03B21/00
Filed: 1959-02-13
Abstract: 917,851. Optical projection apparatus. PHILIPS ELECTRICAL INDUSTRIES Ltd. Feb. 13, 1959 [Feb. 17, 1958; April 12, 1958], No. 5078/59. Class 97 (1). [Also in Group XXXVIII] A stationary projector arranged for continued and enlarged projection of a stationary mark such as an arrow on a screen preferably cornprises as shown (Figs. 1 and 2) a lamp 1, a condenser 5, a mark 8 (see also Fig. 8) a double prism 13, a projection lens 28 and a movable mirror 26 for directing the projected mark on to any part of the screen (not shown). A spring 41 holds the mirror 26 in contact with three supports 27, 30, 35, one of which, 27, is fixed and the other two being adjustable longitudinally by co-operation of relays 31, 32, 36, 37 with oppositely directed ratchet-wheels 33, 34, 38, 39. The three supports will usually be arranged at the corners of a right-angled isosceles triangle, but in special cases other apex angles may be chosen. In a modified arrangement (Fig. 9, not shown) a second and rigidly mounted mirror is provided in the path of the image forming rays so that the optical axis of the projector lies parallel to the direction of projection. In order that the attitude of the mark may be altered on the screen the double prism 13 (or an equivalent system of mirrors) is rotatably mounted in bearings 10 and 11, the rotation being controlled by relays 16, 17 co-operating with ratchetwheels 14, 15. An arrow may, for example, be projected on to a chart of a particular district, either alone or together with other arrows from similar projectors to convey information relating to traffic conditions. For such a purpose, the projector may include one or more coloured filters 20, pivoted at 21 and controlled by relays 22. Also for the same purpose, a number of index marks are provided in the arrow 8 (Fig. 7) some or all of which may be covered by pivoted masks 64, 67, pulled together by springs 72 and controlled by relays 76-79 or by a slide 75 controlled by a relay 80, all the marks and relays being accommodated in the space A (Fig. 1). The arrow 8 may be formed in a disc of thin opaque material with a space 91 (Fig. 11) at its tail for an index. In order that this index may remain upright on the screen when the attitude of the projected arrow is changed, a plurality of indices 99 (Fig. 12) any one of which may correspond with the space 71, are provided on a second disc which may be fixed to the lower end of the sleeve 12 enclosing the double prism 13. Alternatively the second disc may either have a single central index number (Fig. 13, not shown) and be rotatable about an axis passing through the centre of space 91 or may have its axis of rotation outside the projector and have a plurality of index marks round its perimeter (Fig.14, not shown ). In a further modification (Fig. 15, not shown) a disc is provided with one central index mark lying on the optical axis and the arrow is arranged to rotate around this mark. In any of these arrangements, a step-by-step mechanism may be included so that the indices move quickly into and out of correspondence with the space 91 in dependence on the adjustment of the double prism or equivalent system of mirrors. In modifications the projected mark and/or index may be dark instead of luminous. The projector may be remotely controlled and when a number of them are combined as mentioned above to indicate traffic conditions, it may be arranged for example, by having contacts on supports 30 35 that when a mark reaches the edge of the chart, control circuits are energized to return the mark to its central position.