GB1420774A - Electromagnetically driven balance systems - Google Patents

Abstract

1420774 Electronic clocks and watches ITT INDUSTRIES Inc 2 March 1973 [4 March 1972] 10230/73 Heading G3T A timepiece balance is maintained oscillating by a drive circuit, Fig.1, and in synchronizm with synchronizing pulses applied at a terminal E. A drive transistor T 1 controlled by a transistor T 2 passes drive pulses through a coil L which cooperates with magnets (e.g. three pairs) on the balance and functions both as a drive coil and control coil. T 1 is turned ON and OFF by a transistor T 4 which is controlled by the synch. signals. Figs.3b to 3c illustrate the voltage waveform composed of drive pulses superimposed on induced voltage across the coil L while Fig.3a illustrates the synch. signal. The induced voltage pulses are synchronized with the synch. signal. The natural frequency f o of the balance is chosen to be slightly less than half the frequency f s of the synch-pulses so that without the synch. signal the timepiece would run fast. At synchronism, Fig.3b, one negative drive pulse only per half cycle of oscillation, is produced. In the Fig.3c case the balance is running too fast and a primary drive pulse I and secondary drive pulse II are produced each half cycle. With even greater excess over the synchronous speed condition of the balance, Fig.3d, the width of the primary drive pulse is automatically reduced and the secondary pulse II is made correspondingly wider in response to the charge in a capacitor C, which changes in dependence on the energy content of the primary drive pulse I. The total energy content of the pulses I, II remains substantially constant. The synch. signal may be derived from a crystal oscillator via a frequency divider chain of flip-flops. M.O.S. integrated circuit techniques may be employed throughout, or alternatively the drive circuit may use bipolar techniques while the synch. signal circuit may use M.O.S. techniques. In an alternative embodiment Fig.5 (not shown) separate drive and control coils are used.