GB716346A - A method and a device or a machine for driving one or more elements in synchronism with a magnetic field - Google Patents

Abstract

716,346. Electric motors. TRIGGS, W. W. (Pestarini, J. M.). March 21, 1952, No. 7387/52. Class 35 A rotary or linear synchronous motor has a short-circuited moving member and its stator is energized by polyphase alternating current whose amplitude is modulated in accordance with a frequency w. different from the phase frequency W 1 . The phase' currents for a three-phase machine are thus given by: I 1 =A sin w.t, sin W 1 t; I,=A sin w.t, sin (W 1 t-2/ 3 #) I 3 =A sin w o t, sin(W 1 t-<SP>4</SP>/ 3 #). In a simple four-pole rotary form, Figs. 1 and 2, the rotor element 12 comprises a pair of coaxial rings 16 interconnected by mutually insulated groups of bars 17 spaced by a pole-pitch. Inside the rotor is a freely revolving core 11 for completing the flux path to the stator 13. The stator windings 25 are energized with three-phase current from a generator 41 which is in turn excited by a single-phase generator 40 to produce the modulated supply. In a modification, the freely rotating core 11 carries a further polyphase winding fed, like the stator winding, from an A.C. excited alternator, the rate of modulation being w o as before but the phase frequency w, of the current being different. By this arrangement, the internal rotor 11 may drive an external load at a speed and direction depending on the difference between the frequencies of the two supplies. In a further modification, the shortcircuited bars 17 on the rotor 12 are replaced by a polyphase winding connected to a variable starting resistance, one phase only being short-circuited, leaving the others disconnected during running. The machine may operate as a frequency changer from w 1 to w, and vice versa. The principle of the invention may also be applied to the propulsion of groups of spaced shuttles along a circular or longitudinal path as shown in Fig. 10, The shuttles 71 comprise an insulating body carrying a short-circuited conducting ring. The rectilinear stator parts, 66, 67 carry three-phase windings 69, 70 energized with modulated current as described. Direct current energized braking windings 72, 73, 74, 75 are situated at each end of the shuttle travel.