Patent GB-593231-A (GB)
Title: Improvements in apparatus for testing the balance of rotating bodies
IPC: G01M1/22
Filed: 1945-07-11
Abstract: 593,231. Testing balance of rotating bodies. REID & SIGRIST, Ltd., and CANTLE, L. G. H. July 11, 1945, No. 17749. [Class 106 (ii)] [Also in Groups XXXVIII and XL] In apparatus for testing the balance of a rotating body, such as a gyroscope rotor 26, the oscillations of the body due to unbalance produce an electric current by operating on an occulting-member, such as a wire 27, which controls the amount of light directed from a light source on to a photo-electric cell. A second electric current is generated by the' rotor 26 or by a separately driven wheel whereby an indication of the speed of the rotor is given and further to provide a reference current to enable the position of the correcting weight to be ascertained. The apparatus comprises a ring 21, attached to a base 10 by studs, supporting a circular carrier 23 adapted to receive the rotor 26 complete with gimbal 25. The carrier 23 is connected to the ring 21 by three radial spring strips 24 whereby it can rock circularwise if the rotor 26 is unbalanced. The wire 27 is secured at one end to the carrier 23 and extends at the other end through an aperture 28, Fig. 3, into a finder unit 29 where it can occult a beam of'light from a lamp 56 focussed by a lens objective 65 at a position adjacent the wire 27, the light falling on to a photo-electric cell 77. Arrangements for adjusting the lamp and lens are described. The position of the wire 27 and the light beam can be seen through the tube 76 co-operating with a right-angled prism 75 inside the unit 29. The casing 50 of the unit 29 has a socket 51 secured to a tubular spindle 13 mounted in a bearing 12 carried by a rigid bracket 11. A knob 15 and pointer 16 move relatively to a scale plate 14 secured to the bracket 11. A pivoted stop 80 co-operates with an arm 79 to allow rather more than one complete rotation of the spindle 13, which rotates the casing 50 about the wire 27. The rotor 26 is driven by an air jet device having two nozzles either of which can be supplied with compressed air according to the direction of rotation of the rotor desired. To determine the speed of the rotor 26 the latter is provided with a dark spot or polished portion, and a beam of light from a lamp 41 on a universally adjustable bracket 42 is directed on the rotor and reflected on to a photo-electric cell, whereby a datum of reference current is generated: Interchangeable rings 21 are provided, each holding the air jet device, lamp 41, and cell. The phase of the current due to the action of the wire 27 in relation to the reference current produced by the rotor can be adjusted by turning the knob 15 to adjust the finder unit 29. Each current is fed to an oscillograph through an amplifier. The screen for the reference current indicates the speed of the rotor by comparison with some standard frequency such as ordinary A.C. supply ; the other screen is fed with both generated currents so that phase difference can be seen and adjusted by rotating the knob 15. In a modification, a mirror is mounted on the end of the'wire 27 which reflects an incident light beam on to a cell when in a certain position in its orbit. The datum or reference current can be generated by providing a brass or other non-magnetic wheel having a soft iron plug on its periphery which co-operates with electromagnetic polepieces, or a steel wheel having a non-magnetic plug and driven by an air jet may be used.