GB573989A - Improvements in or relating to apparatus for comparing the natural frequency of a mechanical oscillatory system with a standard frequency - Google Patents

Abstract

573,989. Testing balances of watches &c. SMITH & SONS (ENGLAND), Ltd., S., [formerly SMITH & SONS (MOTOR ACCESSORIES), Ltd., S.], and MEREDITH, F. W. June 30, 1943, No. 10648. [Class 139] [Also in Group XIX] An apparatus for comparing the natural frequency of mechanical oscillatory systems with a standard frequency comprises means for forcing the system to oscillate at the standard frequency and means for detecting or indicating the phase displacement between the forced oscillations and those of the force producing them. As shown applied to the testing of hairsprings and balance wheels for watches and clocks, the apparatus comprises a vibratory table 10, Fig. 1, mounted on a stand 11 and forced into oscillation by a master balance wheel 12 and a spring 13 having a natural frequency equal to the standard frequency. The mass of the table is such that its amplitude is small compared with that of the wheel 12. The oscillations of the wheel are maintained constant by a pair of electromagnets 14, 15 energized on the rise and fall of the wheel during oscillation. The table has supported thereon a standard hairspring and balance wheel 7 and one or more balance wheels and spring 24, 25 to be tested. To illuminate the table, a beam of light is directed from a lamp 17 through an aperture 18 in the master wheel 12 to a photo-electric cell 20. A shutter 21 operates to close the aperture alternate half-cycles so that the light passes once per cycle and the resulting impulse is amplified by an amplifier 22 to flash a neon lamp 123 once per cycle. A phase-adjusting means 23 may be provided to adjust the flashes to illuminate the table at any desired point of the cycle ; alternatively, the lamp 7 may be adjustably secured to the table 10 by a support 6. An adjustable holder for the balance 24 and spring 25 to be tested is shown in Fig. 6 and comprises a supporting plug 54 rotatable in a sleeve 56 itself rotatable in a bracket 58 with a supporting pillar 59. To adjust the periodicity of the balance wheel 24, the effective length'of the spring is arranged to be gripped between a roller 60 on an arm 61 attached to the plug 54 and a roller 62 secured to a shaft 63 having a pinion 64 engaging an arcuate rack 67 on the .sleeve 56. In an alternative form of construction, a number of balance wheels and springs are mounted individually on small oscillating tables driven in synchronism by an oscillating frame from an electric motor.