Abstract: A three-phase induction motor is subjected to countermeasure for the rotor and the stator in order to remove two harmonic components of the orders causing a torque ripple, among a plurality of harmonic components included in a magnetic flux generated in an air gap between a stator core and a rotor core. In the three-phase induction motor, conductor grooves of the rotor core are skewed by an electrical angle of 2.pi./n where n is the order of one of the harmonic components to be removed. In the stator, the number of slots (N) is selected so that an equation N=l.times.m.times.q is satisfied, where l=the number of poles, m=the number of phase, and q is a non integer number representing the number of slots per pole per phase, and the stator winding pitch is determined according to the order of another harmonic component to be removed.

Abstract: A thermal head which is reduced in restriction in dimension of a substrate to allow reduction in size thereof and wherein the contacting characteristic of the substrate with a platen is improved to assure a high quality of printing. The thermal head has a heat generating resistor element and a driving circuit therefor both formed on a substrate, and a suppporting heat radiating member joined to one face of the substrate on which the resistor element is located. The substrate is ground at least at a portion of the opposite face thereof corresponding to a heat generating portion of the resistor element to make the thickness smaller than the other portion of the substrate. Thermal recording is effected by the ground portion of the substrate. The substrate may be made of a transparent or translucent inexpensive material such as quartz or glass. Various forms of supporting heat radiating plate to be incorporated in the thermal printers are also disclosed.

Abstract: A three-phase induction motor includes winding slots and a stator winding. The number of winding slots per pole per phase is a noninteger. The stator winding is a three-phase balanced winding. A pitch s of the winding satisfies s=(r-t)/r or s=r/(r+t) (where t is an odd number and r is the order of a harmonic wave to be suppressed).