Patent GB-473977-A (GB)
Title: Magnetic rotary devices for generating, or comparing the frequencies of continuous oscillations
IPC: H03B5/30
Filed: 1936-04-22
Abstract: 473,977. Automatic control systems. RUSPOLI, E. April 22, 1936, No. 11536. [Classes 35 and 38 (iv)] [Also in Groups XVIII, XIX, XXXVI, and XXXVII] Relates to magnetic rotary devices for use either as generators of mechanical or electrical oscillations of substantially constant frequency (and lacking harmonics), or for determining the frequency of mechanical or electrical oscillations by a comparison with a standard frequency (which may be generated by the device). A magnetic circuit includes a driven toothed magnetic rotor, a second rotor bearing magnetic elements, any adjacent pair of which are separated by a distance integrally related to the tooth pitch of the first rotor, and a non- rotating polepiece or pieces with means (such as a vibrating fork or an electromagnet) for causing periodic variations in the flux distribution in the circuit. In Fig. 1, the circuit includes a bar-magnet 1 and arms 2, 3, a vibrating tuning- fork 4 with polepieces 16, a toothed rotor 5 driven by a motor 10, and, in the air-gap between the poles 16 and the teeth 6 of rotor 5, a free rotor 11 with magnetic elements 12 preferably in two staggered circumferential rows. If the rotor 5 is rotated at a speed greater or less than " synchronous " speed (i.e. a speed giving a one-tooth movement of the rotor 5 in the vibration period of the fork), the free rotor 11 rotates respectively in a positive or a negative direction at a speed equal to the difference between the actual speed of rotor 5 and its synchronous speed, the relative speeds of the rotors 11, 5, thus remaining constant since the frequency of the fork is constant. An initiating or sustaining effect, no effect, or a damping effect also is produced on the tuning- fork by rotor 11 according to the speed at which rotor 5 is rotated. The difference of phase which exists between the registration of the fork poles 16 and the rotor teeth 6, respectively, with the elements 12 corresponds to the state of equilibrium between the frictional resistance and the magnetic attractions of the free rotor 11 ; if the friction is extremely low when the fork is to be maintained in vibration, the rotor 11 may be braked to ensure the production of sufficient amplitude of vibration. Frequency variations of a current may be indicated by speed variations of rotor 11, the current being utilized to energize a synchronous motor driving toothed rotor 5. Regularly spaced current impulses may be produced by providing a contact on one rotor and a brush on the other, connected in a circuit. A watch may be regulated by transforming the oscillations of its balance-wheel into electric impulses, amplified and multiplied as necessary, which are utilized to control a synchronous motor 10, the fork 4 serving as the frequency standard. Or the motor 10 may be supplied with current of standard frequency, and a variable fork 4 maintained by, or synchronized with, a current derived from the balance-wheel, rotor 11 being provided with graduations for observation. The fork may be replaced by a vibrating strip maintained electromagnetically by a master fork in a thermostatically controlled enclosure. Fig. 8 (not shown) illustrates an electromagnetic device for frequency comparison, which is free from a damping action when the speed of the motor-driven rotor falls below synchronous speed. The fork shown in Fig. 1 is replaced by two fixed crowns formed of electromagnets energized by alternating current supplied, e.g. by a standard fork, coil, and amplifier. In order to measure the speed of the free rotor, further elements may be mounted thereon to co-operate with adjacent coil-carrying magnets to produce currents of corresponding intensity, Fig. 13 (not shown). In another method, Fig. 9 (not shown), for producing current impulses of a constant frequency equal to that of a fork, the peripheries of the two rotors arranged as in Fig. 1 or Fig. 8 (not shown), have rings of holes through which rays of light are reflected on to a photo-cell. In Fig. 10, the toothed rotor (not shown) is driven by a synchronous motor supplied with current of standard frequency, and the apparatus automatically maintains constant the frequency of a generator. Alternating current derived from the generator excites the magnetic circuit as in Fig. 8 (not shown), and one of two rods 62, 63 carried by arms 64, 65 and resting in a circumferential groove 66 in the spindle of the free rotor 23 is moved downwardly by rotation of the free rotor to close switch 68 or 69 to effect raising or lowering of the generator frequency by device 55 or 56. The switches of electric circuits may be opened and closed by variations in a driving frequency. For this purpose, a number of units, each for instance as in Fig. 8 (not shown), and having slightly different synchronous speeds, are actuated by a common synchronous motor. supplied with current, the frequency of which is carried at will. By varying this frequency, different free rotors may be made to reverse their rotation and thereby to actuate switches in the manner employed in Fig. 10. A rotating magnetic field, generated by a non-rotating member or by a rotor with alternate teeth of opposite permanent magnetization, Figs. 11, 12 (not shown), may be employed in lieu of the rotor 5, in which case the fork need not be separately magnetized. The use of the invention with radio apparatus for guiding aircraft, and with sound waves conducted through water, is referred to.