Abstract: A starting-process controller for starting a piezomotor, having a voltage-controlled oscillator, a power output stage, and a resonant converter. The oscillator generates the control signals required for the power output stage and the resonance converter converts the stepped output voltage from the power output stage into a sinusoidal voltage at the output. The resonance converter drives the piezomotor with the voltage. The motor current that flows when the piezomotor is driven is measured and compared with the phase of the drive voltage in a phase comparator. The comparison output signal is a measure of the phase difference at the time between current and voltage. A phase-locked loop filter smoothes the phase-difference signal for controling the oscillator. The controller includes a start-assisting circuit element that fixes the output voltage from the phase-locked loop filter at start-up and thus applies a constant voltage to the input of the voltage-controlled oscillator.

Abstract: A starting-process controller for starting a piezomotor, having a voltage-controlled oscillator, a power output stage, and a resonant converter. The oscillator generates the control signals required for the power output stage and the resonance converter converts the stepped output voltage from the power output stage into a sinusoidal voltage at the output. The resonance converter drives the piezomotor with the voltage. The motor current that flows when the piezomotor is driven is measured and compared with the phase of the drive voltage in a phase comparator. The comparison output signal is a measure of the phase difference at the time between current and voltage. A phase-locked loop filter smoothes the phase-difference signal for controling the oscillator. The controller includes a start-assisting circuit element that fixes the output voltage from the phase-locked loop filter at start-up and thus applies a constant voltage to the input of the voltage-controlled oscillator.

Abstract: A piezoelectric driving device and a regulation method for a piezoelectric driving device are proposed. Piezoelectric driving devices known so far show a characteristic with which the electric power applied to the motor drops when the load increases. This behavior, which leads to a strong reduction of the range of use of such motors, is counteracted by predefining the amplitude of the excitation voltage so that the effective power does not drop with increasing load. For this purpose the electrical effective power is determined from the excitation voltage and the current flowing through the piezoelectric resonator. Alternatively, with a predefined fixed phase angle between excitation voltage and current a regulation may also be effected in the way that the current is kept to the constant value. A further aspect of the invention relates to a unit for limiting the current flowing through the piezoelectric resonator, so as to avoid this component being damaged.

Abstract: A piezoelectric driving device and a regulation method for a piezoelectric driving device are proposed. Piezoelectric driving devices known so far show a characteristic with which the electric power applied to the motor drops when the load increases. This behavior, which leads to a strong reduction of the range of use of such motors, is counteracted by predefining the amplitude of the excitation voltage so that the effective power does not drop with increasing load. For this purpose the electrical effective power is determined from the excitation voltage and the current flowing through the piezoelectric resonator. Alternatively, with a predefined fixed phase angle between excitation voltage and current a regulation may also be effected in the way that the current is kept to the constant value. A further aspect of the invention relates to a unit for limiting the current flowing through the piezoelectric resonator, so as to avoid this component being damaged.

Abstract: The invention relates to a starting-process controller for starting a piezomotor (4), having a voltage-controlled oscillator (1)(VCO), a power output stage (2), and a resonant converter (3), wherein the oscillator (VCO) generates the control signals required for the power output stage (2), and the resonance converter (3) converts the stepped output voltage from the power output stage (2) into a sinusoidal voltage at the output of the resonance converter (3), with which voltage the resonance converter (3) drives the piezomotor (4). The motor current that flows when the piezomotor (4) is driven is measured and compared with the phase of the drive voltage in a phase comparator (6). The output signal from the phase comparator (6) then is a measure for the phase difference at the time between current and voltage. A phase-locked loop filter (8) smoothes the phase-difference signal, which in turn controls the oscillator (1)(VCO).

Abstract: The invention relates to a piezoelectric actuator (1) for driving a movable part (2), for example a rotor, having an elongate piezoelectric resonator (3), which serves to perform longitudinal vibrations and which is acted upon by elastic means (10), for example a spring (10). The elastic means (10) acts upon the piezoelectric resonator (3) mainly in the longitudinal direction (11) and serves to exert a force on the resonator (3) in a direction towards the movable part (2), the resonant frequency of the elastic means (10) being substantially smaller than the resonant frequency of the piezoelectric resonator (3), and the piezoelectric resonator (3) is guided by at least one guide element (4, 5) in a direction perpendicular to its longitudinal direction (11). This enables the resonator (3) to vibrate as freely as possible, which leads to a higher efficiency.

Abstract: The invention relates to a motor having a cuboid piezoelectric element (1) which carries an actuating member (2) for transmitting a force in an actuating direction (x). In known motors the piezoelectric element (1) is restrained by four restraining elements which are disposed in the plane of vibration (x/y plane) and which exert a preloading force on the piezoelectric element (1) in a direction perpendicular to the actuating direction (x). However, this gives rise to a frictional force between the restraining elements and the piezoelectric element, which reduces the vibration quality and, as a consequence, the motor power. This is avoided by means of the invention, where the piezoelectric element (1) is restrained by means of restraining elements (20, 21, 22, 23) without preloading, i.e. with maximal slidability in the directions (y, z) perpendicular to the actuating direction (x).

Abstract: The invention relates to a piezoelectric actuator (1) for driving a movable part (2), for example a rotor, having an elongate piezoelectric resonator (3), which serves to perform longitudinal vibrations and which is acted upon by elastic means (10), for example a spring (10). The elastic means (10) acts upon the piezoelectric resonator (3) mainly in the longitudinal direction (11) and serves to exert a force on the resonator (3) in a direction towards the movable part (2), the resonant frequency of the elastic means (10) being substantially smaller than the resonant frequency of the piezoelectric resonator (3), and the piezoelectric resonator (3) is guided by at least one guide element (4, 5) in a direction perpendicular to its longitudinal direction (11). This enables the resonator (3) to vibrate as freely as possible, which leads to a higher efficiency.

Abstract: The invention relates to an actuator having a plurality of piezoelectric drives (1a, 1b, 1c) and a sphere (2) which is rotatable about at least two axes of rotation (7a, 7b, 7c), and to an arrangement for transmitting pictures and sound, including an actuator. The actuator should be flexible in use and is to be realized at minimal cost. For this purpose, at least two piezoelectric drives (1a, 1b, 1c) have been provided which can rotate the sphere (2) arbitrarily, the piezoelectric drives (1a, 1b, 1c) being capable of transmitting their power to the sphere (2) in order to rotate this sphere about a respective axis of rotation by friction with the aid of vibrations in a tangential direction relative to the surface of the sphere (2).

Abstract: The invention relates to a motor having a cuboid piezoelectric element (1) which carries an actuating member (2) for transmitting a force in an actuating direction (x). In known motors the piezoelectric element (1) is restrained by four restraining elements which are disposed in the plane of vibration (x/y plane) and which exert a preloading force on the piezoelectric element (1) in a direction perpendicular to the actuating direction (x). However, this gives rise to a frictional force between the restraining elements and the piezoelectric element, which reduces the vibration quality and, as a consequence, the motor power. This is avoided by means of the invention, where the piezoelectric element (1) is restrained by means of restraining elements (20, 21, 22, 23) without preloading, i.e. with maximal slidability in the directions (y, z) perpendicular to the actuating direction (x).

Abstract: The invention relates to a driving device for at least two rotation elements, which device comprises at least one piezoelectric driving element. The object of the invention is to provide such a driving device having a high efficiency and allowing a more flexible positioning of the rotation elements.The invention is characterized in that the piezoelectric driving element comprises a piezoelectric resonator and at least two friction elements arranged on the piezoelectric resonator and disposed opposite one another, the piezoelectric resonator with the friction elements is arranged between the two rotation elements and is restrained by means of a pre-loading force, each one of the friction elements acts upon one of the rotation elements, and electrical means for the excitation of a vibration mode of the piezoelectric resonator have been provided.

Abstract: An electrically driven vibrating apparatus such as a dry shaver comprises a single-phase synchronous motor having a drive shaft, together with a part to be reciprocated. A cam is rotated by the motor drive shaft, and a lever is journalled about a pivot and is in contact with the part to be reciprocated. A pressure roller is mounted on the lever and is in constant contact with the cam profile. A compression spring acts on the lever to urge the pressure roller towards the cam.

Abstract: The invention relates to a device for improving the stability of rotation of the rotor of a single-phase synchronous motor mounted in an apparatus housing. The motor exhibits an average motor torque on which strong alternating torques are superimposed and which drives a preferably rotating load. The rotating load may be a small domestic appliance such as a citrus-juice extractor, a knife sharpener, or a dry-shaver with rotatary cutters.

Abstract: A single-phase synchronous motor with a two-pole permanent-magnet rotor of a magnet material having a remanence B.sub.r, a specific density .rho., a rotor diameter d, a resulting detent torque of an amplitude M.sub.k1, and a mass moment of inertia J. In the single-phase synchronous motor, high-energy magnet materials are used for the rotor, which rotor material is characterized by the constant ##EQU1## The moment of inertia J and/or the detent torque M.sub.k1 should be influenced in such a way that the natural frequency ##EQU2## of the low-amplitude freely oscillating system comprising the rotor and the load is unequal to the mains frequency .omega..sub.e. In the design of a single-phase synchronous motor this may result in, for example, the air gap at the narrowest point being enlarged in comparison with the dimensions of conventional motors having rotors with conventional permanent magnet materials.

Abstract: A drive mechanism for a dry shaver comprising a shear foil and a cutter reciprocatory relative to the shear foil includes a single-phase synchronous motor having a drive shaft. A cam is mounted on the drive shaft, and a transmission roller is constantly in contact with the cam. The surface of at least one of the cam and the transmission roller is provided with a layer approximately 1 mm in thickness of an elastic material.

Abstract: An electrically driven appliance such as a citrus press comprises a drivable tool; a self-starting single-phase synchronous motor including a diametrically magnetized permanent-magnet rotor forming a rotor field and positioned between two stator poles forming a stator field; and a drive mechanism arranged between the motor and the tool, for driving the latter, such mechanism including a plurality of drive elements each engaging the adjacent element or elements. A stalling device coacts with one drive element having a pair of stops, the stalling device including a member alternately engageable with such stops after a specific number of revolutions of the rotor in either direction of rotation, such engagement effecting stalling of the rotor and automatic reversal of the direction of the rotation of the rotor.

Abstract: A reversing device for a two-pole single-phase synchronous motor (3) without a starting coil. The motor comprises a diametrically magnetized permanent-magnet rotor having a shaft that runs against elastic stops for reversing the direction of rotation, and a capacitor arranged in series with the stator exciter coil. The capacitor serves for improving the reversing operation and is dimensioned so that its reactance at the AC supply frequency is greater than the reactance of the exciter coil of the synchronous motor.

Abstract: Disclosed is a shaving apparatus having a shear plate provided with hair-entry apertures and a cutting member drivable relative to the shear plate. The cutting member is formed with cutters each having an associated lead cutter slidingly engaging the guide wall of its respective cutter. The end of each lead cutter has a projection terminating in a cutting edge for penetration into a hair, the thickness of such projection permitting only partial penetration of the lead cutter into the hair. Such penetration is advantageously further limited by forming the front wall of the lead cutter perpendicular to the end wall of its associated cutter.