GB745919A - Improvements in and relating to screw-actuated scale-dividing or angular adjusting apparatus - Google Patents

Abstract

745,919. Dividing-engines. NATIONAL RESEAHCH DEVELOPMENT CORPORATION. June 8, 1954 [March 6, 1953], No. 6332/53. Class 97 (3). In apparatus for dividing a linear scale a continuously rotating screw 11 moves a nut 23, 24 of the kind described in Specifications 684,846 or 708,539, [both in Group XXIX], endwise movement of the screw is prevented by means of a bearing 13 of similar construction to the nut, the journal running in the bearing having a series of parallel circumferential grooves 17, and the nut is used to produce relative movement between a photographic plate 28 or the like and a projecting system 29 which projects an image of a fine slit 32 on to the plate, this system being momentarily illuminated at regular intervals determined by the rotation of the screw. In apparatus for effecting an angular adjustment, an arm carried by the member to be adjusted is engaged by a peg or the like on a nut coacting with a screw, the peg projecting transversely to the screw axis and the nut being of the kind described in Specifications 684,846 or 708,539, [both in Group XXIV]. As shown, the screw 11 is supported in bearings 12, 13 with strips 14 of cork or similar resilient material engaging the journals in three regions. The journal in bearing 13 has a large number of shallow parallel grooves inscribed thereon, e.g. in the manner described in Specification 717,678, [Group XIV], while the journal in bearing 12 may be similarly grooved, or smooth as shown. Driving means 18 rotates the screw 11 evenly and continuously through a fork 19 engaging a cross-pin 21. A fine helix 22 is inscribed on the greater part of the length of screw 11 and is engaged by a nut with hinged jaws 23, 24 provided with cork or like strips 25 and urged together by springs 26. The upper jaw 23.carries a frame 27 for the photographic plate 28, the frame 27 engaging a fixed roller 31 which prevents the nut from rotating. A xenon flash tube 33, when triggered, illuminates a slit 32, an image of which is formed on plate 28 by a lens system 29. A cam on the driving mechanism 18 closes a switch to trigger tube 33 accurately at the same phase of each revolution of the screw 11, so that a scale of equallyspaced lines is formed on plate 28. If desired, a second switch in series with the first may be operated by a second cam driven at a slower speed so as to close the switch just before each of a periodic series of closures of the first switch, so that the line interval is a multiple of the basic interval. Part of the slit 32 may be covered by a shutter 34 operated periodically by an electromagnet 35 so that some of the lines are prolonged. Apparatus wherein the nut engages an arm rotating a turntable carrying a circular plate is also described. The total angular movement is small and may be restricted by limit switches. The angular position of the plate on the table may be adjusted.