Electrical generator or motor structure – Dynamoelectric – Oscillating
Reexamination Certificate
2001-06-21
2002-08-27
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Oscillating
C310S036000, C030S045000
Reexamination Certificate
active
06441517
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a drive mechanism for driving a working unit, movable in an oscillating manner, of electric products of personal use, particularly dry shavers.
BACKGROUND
Dry shavers which cut off beard hairs with a reciprocating cutter block are known examples of household appliances with an oscillating working unit. Oscillating dry shavers are traditionally driven by a rotary electric motor, for example a direct current motor. The rotary motion of the motor shaft is transformed into a linear oscillatory motion through suitable eccentric gearing.
Unlike gear solutions of this type, the linear oscillatory motion of the working unit may also be generated directly by a direct drive. This obviates the need to provide the eccentric gearing for transforming the rotary motor motion into a linear oscillation.
One form of a quasi linear direct drive is, for example, the so-called oscillating armature motor (cf., for example, DE 31 39 523 A1). Such oscillating armature motors are disadvantageous, however, on the one hand in that they can only be operated with a 220 volt line voltage, which makes them unsuitable for battery-powered appliances, and on the other hand in that they produce very large stray magnetic fields.
A vibratory drive for dry shavers is also known in which a rotor arrangement capable of performing rotary oscillations is connected to the cutter block by a cable control via deflection pulleys and drives said cutter block (cf. DE 41 17 225 A1) This vibratory drive which is operated with line voltage has a relatively low level of efficiency and is unsatisfactory with regard to its size and dimensions. The yieldability of the drive mechanism limits its efficiency.
A linear permanent magnet motor is also known as a direct drive for a dry shaver, in which a motion unit with permanent magnets is suspended from leaf springs in the manner of a suspension bridge above a stator with an exciter winding and drives a coupled cutter block (cf. WO 95/26261). A sensor monitors the speed of the motion unit, in dependence on which a controller modifies the electric power fed to the motor in such a way that the amplitude of oscillation of the motion unit is maintained constant. However, this known direct drive for dry shavers is complicated and less compact in design. The precision necessary for a good level of efficiency can only be achieved with a great outlay.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved drive mechanism of the type initially referred to which avoids the disadvantages of known drives. In particular it is desirable for the drive mechanism to be of simple design and achieve stable operation with a high level of efficiency.
This object is accomplished according to the invention by a drive mechanism of the type initially referred to, with a permanent magnet motor which has a stator with an exciter winding and a rotor with at least one permanent magnet positioned in the stator field and rotatably mounted on a shaft, with a reset device for returning the rotor to a position of rest in such a way as to enable the rotor to oscillate about the position of rest, with a coupling device for coupling the rotor to the working unit, wherein the coupling device is connected to the rotor in spaced relationship to the rotor shaft, with a detecting device for detecting the oscillatory motion of the rotor, and with an actuating unit for actuating the permanent magnet motor in response to the detected oscillatory motion, provision being made for frequency control elements for actuating the permanent magnet motor with a frequency corresponding approximately to the resonant frequency of the rotor.
The rotary bearing arrangement of the permanent magnetic motion unit configured as a rotor affords the advantages of high stability and rigidity. Unlike a spring suspension in the manner of a suspension bridge in the case of the linear motor, the rotor with a rotary oscillating motor does not undergo any rocking motion. The rotary oscillating motor leads in a dry shaver to reduced foil wear and permits a smaller distance to be maintained between the foil and the cutter blocks. Advantageously, the air gap between the rotor and the stator can be very small, in particular around0.5 mm or less. On account of the rotary bearing arrangement there is no risk of contact between the rotor and the stator. This results in a high level of efficiency.
The working unit is not coupled to the rotor shaft but is eccentrically connected directly to the body of the rotor by the coupling device. Favorable leverage ratios and a high level of rigidity are thus achieved. The rigid and direct transmission of the rotor's rotary motion to the working unit displays a high level of efficiency, particularly for oscillations of high frequency far in excess of the line frequency, and is the reason for such high-frequency oscillations being at all possible.
The actuating unit, to which the oscillatory motion of the rotor is fed back via the detecting device connected thereto, actuates the exciter winding of the stator such that the rotor oscillates with a frequency corresponding approximately to the resonant frequency of the system comprised of the rotor and the reset device. Operation at resonance achieves a very high degree of efficiency. Unlike weighty line-operated appliances with a low level of efficiency it is possible, on account of the actuating unit, to achieve very high operating frequencies in the range of 10
4
min
−1
, thus enabling the shaving time to be shortened. In conjunction with the rigid coupling of the working unit it is possible to compensate for load peaks, such as occur during shaving, very quickly, particularly from one half cycle to the next. This leads to a higher quality and speed of processing. As a result of the high level of efficiency the drive mechanism can be built to small dimensions. Together with the motion element's configuration as a rotor it is thus possible to achieve a highly compact design.
According to a preferred embodiment of the invention the rotor has various sections made of various materials. In particular the rotor may have an inner lying core made of a soft magnetic material of high permeability and poles made of a permanent magnetic material. Conversely, it is also possible for the rotor to have an inner lying core of permanent magnetic material and poles made of a soft magnetic material of high permeability. On account of smaller stray losses of the poles made of permanent magnets, the air-gap field and hence the output power and efficiency of the drive are greater than with the second arrangement. Furthermore, the inductance of the motor viewed from the terminals of the exciter winding is smaller. Consequently the current is allowed to increase more quickly, which again raises the output power. The rotor is advantageously configured so that the inductance is independent of the rotor's position. This simplifies the electronic actuation of the motor. It is also an advantage for the rotor shaft to be worked into the soft magnetic material and not into the magnet material, which is relatively hard to machine. This simplifies production substantially.
It is also possible for the rotor to be comprised completely of permanent magnetic material. In this case the rotor shaft is preferably not made of permanent magnetic material. The embodiment in which the rotor is made completely of permanent magnetic material is particularly advantageous with regard to the level of efficiency. However, the previously mentioned embodiment has advantages with regard to production and machining.
According to a preferred embodiment of the invention the reset device is connected to the rotor in spaced relationship to the rotor shaft. Hence the reset device does not engage the rotor shaft. Precise oscillation of the rotor is effected using a lever arm acting on the rotor. It will be understood that the reset device can also act on the working unit. The resetting force is preferably transferred to t
Brum Thomas
Klös Alexander
Port Holger
Port Werner
Schaaf Uwe
Braun GmbH
Jones Judson H.
Podszus Edward S.
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