Abstract: A concrete vibrator is disclosed in which a sensorless semiconductor motor is employed for driving an exciter. The sensorless semiconductor motor has an arrangement in which the rotational position of the permanent magnet rotor is sensed through utilization of a voltage which is induced from three-phase stator windings, i.e. a voltage which is induced according to the magnetic flux distribution in the gap and varies its frequency with the rotation speed alone instead of by using the Hall element which is readily damaged by vibration and heat, that is, seriously poor in environmental resistance. Further, the sensorless semiconductor motor is arranged so that the current supply to the stator winding is placed under control of a semiconductor inverter which is controlled by a PWM or PAM system.

Abstract: As opening/closing device to be provided at a mouth of a container such as a paper container, a bottle, a can, etc., in which a lid is provided via a hinge on the inside of a cylindrical pouring mouth made of synthetic resin and a gap space is formed between the pouring mouth and the lid. A metallic film consisting of a metal foil having synthetic resin layers coated on its both surfaces is bonded so as to straddle both the upper surface of the lid and the upper surface of the pouring mouth. Opening of the lid is effected by peeling of the metallic film, and upon closing the lid, the metallic film is pressed from its outer surface so that it may be stuffed in the gap space between the lid and the pouring mouth. Upon making the opening/closing device, an annular protrusion is formed on the top end surface of the pouring mouth, the metallic film is bonded to this annular protrusion and the lid so that the metallic film may be easily peeled off.