as) United States
`a2) Patent Application Publication (0) Pub. No.: US 2006/0145547 Al
`
` Kraus (43) Pub. Date: Jul. 6, 2006
`
`
`US 20060145547A1
`
`(54) CONTROLLING AN ELECTRIC MOTOR
`HAVING MULTIPLE OSCILLATORY
`ELEMENTS
`
`(76)
`
`Inventor: Bernhard Kraus, Braunfels (DE)
`
`Correspondence Address:
`FISH & RICHARDSON PC
`P.O. BOX 1022
`
`(30)
`
`Foreign Application Priority Data
`
`Jul. 9, 2003)
`Jul. 3, 2003)
`
`(DE)... eeeeeseeeeees 103 30 979.0
`(DE). ee eesceeceecseesseeseeeenees 103 30 205.0
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`HO2K 33/00
`(52) US. Che
`cressscssssssssssesssesestesssenseene 310/36; 318/114
`
`MINNEAPOLIS, MN 55440-1022 (US)
`
`(57)
`
`ABSTRACT
`
`(21) Appl. No.:
`
`—-11/327,916
`
`(22)
`
`Filed:
`
`Jan. 9, 2006
`
`Related U.S. Application Data
`
`(63) Continuation of application No. PCT/EP04/06198,
`filed on Jun. 9, 2004.
`
`Amethod of controlling an electric motor includes providing
`an electric motor having a plurality of magnetically driven
`oscillatory elements having differing oscillatory character-
`istics, and an electromagnet having a coil arranged to drive
`all of the oscillatory elements. The method includes supply-
`ing an electric signal to the electromagnet, which creates a
`magnetic field that drives the oscillatory elements. The
`method also includes varying a frequency of the electric
`signal for individual control of oscillatory movements of the
`oscillatory elements.
`
`8
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`10
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`APPLE 1042
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`APPLE 1042
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`Patent Application Publication
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`Patent Application Publication
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`Jul. 6, 2006 Sheet 2 of 3
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`Fig. 4
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`6
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`J 2
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`Slt €
`Td
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`SS
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`Patent Application Publication
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`US 2006/0145547 Al
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`Fig. 8
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`aaaAET?
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`US 2006/0145547 Al
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`Jul. 6, 2006
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`CONTROLLING AN ELECTRIC MOTOR HAVING
`MULTIPLE OSCILLATORY ELEMENTS
`
`REFERENCE TO RELATED APPLICATIONS
`
`[0001] This application is a continuation of PCT applica-
`tion PCT/EP2004/0061 98, filed Jun. 9, 2004 and designating
`the United States, and claimspriority under 35 USC § 119(a)
`from German patent application 103 30 979.9, filed Jul. 9,
`2003. The complete disclosures of both priority applications
`are incorporated herein by reference.
`
`
`
`TECHNICAL FIELD
`
`[0002] This invention relates to a method of controlling an
`electric motor having a plurality of magnetically driven
`oscillatory elements and devices having such motors.
`
`BACKGROUND
`
`[0003] Electric motors having a multitude of oscillatory
`motor components are known in the art. Furthermore, it is
`known in the art to employ electric motors of this type in
`electric appliances, such as electric shavers and electric
`toothbrushes.
`
`[0004] For example, an electric motor of this type is
`described in German patent publication 1 151 307 A which
`discloses an oscillating armature drive for a dry shaving
`apparatus. The oscillating armature drive includes a recip-
`rocating shaving cutter and a U-shaped electromagnet
`formed fast with a housing of the shaving apparatus. A
`working armature and compensating armatures, adjacent the
`work armature on opposing sides, are arranged in an oscil-
`latory mannernear the poles of the electromagnet. In opera-
`tion, the working armature, which drives the shaving cutter,
`oscillates in parallel with the pole faces of the electromag-
`net, and the compensating armatures oscillate in opposite
`phase with the working armature to prevent the transmission
`of oscillations from the working armature to the housing of
`the shaving apparatus.
`
`[0005] As another example, U.S. Pat. No. 5,632,087 dis-
`closes a dry shaver with a linear motor. The linear motor has
`a stator coil and several rotors equipped with permanent
`magnets which are excited into a state of linear oscillation by
`the stator coil. The displacements of the rotors are detected
`by means of detectors associated with the rotors and are
`further processed in the form of an average value. In the
`process, the supply of current to the stator coil is controlled
`as a function of the average value in such a way that the
`oscillation amplitudes of all rotors are maintained as con-
`stant as possible. The detectors each comprise one perma-
`nent magnet which is positioned on the respective rotor and
`one positionally fixed sensor coil in which an induction
`voltage dependent on the velocity of the respective rotor is
`generated as a result of the effect of the permanent magnet.
`
`SUMMARY
`
`[0006] Various aspectsof this invention includean electric
`motor having a plurality of oscillatory elements, wherein the
`oscillatory movements of the oscillatory elements are indi-
`vidually controlled.
`
`[0007] According to one aspectof the invention, a method
`of controlling an electric motor includes providing an elec-
`tric motor having a plurality of magnetically driven oscil-
`
`latory elements having differing oscillatory characteristics,
`and an electromagnet having a coil arranged to drive all of
`the oscillatory elements. The method includes supplying an
`electric signal to the electromagnet, which creates a mag-
`netic field that drives the oscillatory elements. The method
`also includes varying a frequency ofthe electric signal for
`individual control of oscillatory movements of the oscilla-
`tory elements. According to this aspect, all drive motions
`(1.e., oscillatory movements) can be generated by means of
`a shared electromagnet, the magnetic field of which acts
`upon the magnetically driven oscillatory elements, and thus
`drives the oscillatory elements directly. Therefore, a variety
`of drive functions can be made available by means of a
`single motor having a simple mechanical and magnetic
`layout. A gearing or other auxiliary meansof influencing the
`drive motions is not required, and, as a result, cost and
`attendant frictional losses can be minimized. The electric
`signal can enable the magnetic field to unfold a different
`effect on each of the individual oscillatory elements. There-
`fore, with comparatively low outlay, several individually
`controllable drive motions can be made available.
`
`In somecases varying the frequencyofthe electric
`[0008]
`signal can include presetting the frequency of the electric
`signal. The effect that the magnetic field has on the oscil-
`latory elements depends upon the oscillatory characteristics
`ofthe latter, therefore, the magnetic field unfolds a different
`effect on each oscillatory element. Therefore, by setting the
`frequencyofthe electric signal it is possible to individually
`control the oscillatory movements of the oscillatory ele-
`ments.
`
`In some embodiments, the electric signal includes
`[0009]
`a plurality of individual frequencies. Preferably, the oscil-
`latory movements of the oscillatory motor components are
`individually controlled by weighting the individual frequen-
`cies in the electric signal. More preferably, the differing
`oscillatory characteristics of the oscillatory elements include
`differing resonant frequencies. In somecases, the individual
`frequencies correspond to the resonant frequencies of the
`oscillatory elements. Depending on the magnitude by which
`the signal frequency deviates from the individual resonant
`frequencies, the oscillatory movements of the oscillatory
`elements are influenced differently by the magnetic field
`generated using the signal.
`In this way the oscillatory
`movements of the oscillatory elements can be varied almost
`independently of each other and through wide control
`ranges.
`
`In someinstances, the electric signal can be sup-
`[0010]
`plied to the electromagnet in the form ofpulses. In this case,
`the oscillatory movements of the oscillatory elements can be
`individually controlled by presetting a pulse pattern for the
`electric signal which is supplied to the electromagnet. The
`use of pulses provides for signal generation with very little
`outlay, and, therefore, the method can also be used to control
`electric motors for small electric appliances, e.g., electric
`shavers and electric toothbrushes, which do not have a mains
`supply connection and are operated by means of recharge-
`able batteries or non-rechargeable batteries.
`
`the oscillation ampli-
`In some implementations,
`[0011]
`tudes of the oscillatory elements can be individually con-
`trolled by the electric signal. In some cases, the oscillation
`amplitudes of the oscillatory elements can be reduced down
`to zero so that the oscillatory elements are switched onoroff
`
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`individually by the electric signal. In this way, an automated
`means of switching individual drive functions on and off can
`be achieved without additional outlay in terms of apparatus.
`
`In some embodiments, the method includes detect-
`[0012]
`ing characteristic data of the oscillatory movements of the
`individual oscillatory elements. In this case, the character-
`istic data can be detected by one or more sensors. Preferably,
`the detected characteristic data is delivered from the sensors
`
`to a microcontroller. More preferably, the microcontroller
`controls the frequency of the electric signal. Even more
`preferably, the microcontroller compares the detected char-
`acteristic data with setpoint data values and controls the
`frequencyofthe electric signal such that any deviation from
`the setpoint data values is minimized. In somecases, the
`amplitude and/or frequency and/or phase of the oscillatory
`movements of the individual oscillatory elements can serve
`as the characteristic data. In some cases, the electric signal
`is generated as a function of the detected characteristic data,
`preferably, the electric signal is generated in a closed control
`loop. This approach makes it possible to achieve more
`precise control of the oscillatory movement.
`
`[0013] According to another aspect, an electric appliance
`includes a housing and an electric motor contained within
`the housing. The electric motor includes a plurality of
`magnetically driven oscillatory elements, and an electro-
`magnet having a coil arrangedto driveall of the oscillatory
`elements. The electric appliance also includes a control
`device configured to deliver an electric signal to the elec-
`tromagnet for generating a magnetic field that influences
`oscillatory movements of the oscillatory elements. Notably,
`the oscillatory elements have differing oscillatory character-
`istics, and the control device is arranged to control different
`aspects of the electric signal to control different ones of the
`oscillatory elements.
`
`In somecases, the differing oscillatory character-
`[0014]
`istics include differing resonant frequencies, and the differ-
`ent aspects of the electric signal include signal components
`of differing frequencies.
`
`In some embodiments, each oscillatory element
`[0015]
`includes a plurality of permanent magnets secured to a
`carrier plate. In this case, the permanent magnets of each
`oscillatory element can be arranged adjacent each other in an
`anti-parallel configuration. Preferably, the carrier plate has a
`first end connected to the housing bya first spring element,
`and a second end, opposite the first end, connected to the
`housing by a second spring element.
`
`In some embodiments, the oscillatory elements are
`[0016]
`configured for linear oscillatory movement. For example,
`this could be the case with an electric shaver.
`
`Insomecases, the control device includes a micro-
`[0017]
`controller. Preferably, the electric appliance also includes
`one or more sensors for measuring characteristic data of the
`motor and supplying the measured data to the microcontrol-
`ler. More preferably, the microcontroller compares the mea-
`sured characteristic data with setpoint data values and
`adjusts the electric signal to minimize deviation from the
`setpoint data values.
`
`In some examples, the electromagnet includes a
`[0018]
`magnetizable core and a coil wound about the magnetizable
`core, wherein the magnetizalbe core includes one of the
`oscillatory elements. Therefore, the magnetizable core can
`
`perform the function of a conventionalstator, albeit without
`being stationary. This allows the magnetizable core to per-
`form a drive function, and the transmission of unwanted
`vibrations from the electric motor to the housing can be
`minimized. Preferably, the magnetizable core is configured
`for movementrelative to the coil. This means that the coil
`
`can be arranged in a stationary mannerandcan therefore be
`contacted more easily than a movable coil. Furthermore, the
`oscillating mass can be kept relatively low, as the coil does
`not co-oscillate.
`
`In some implementations, the oscillatory elements
`[0019]
`are configured for
`rotary oscillatory movement. For
`example, this could be the case with an electric toothbrush.
`
`[0020] Other features and advantagesofthe invention will
`be apparent from the following detailed descript, and from
`the claims.
`
`DESCRIPTION OF DRAWINGS
`
`[0021] FIG.1 is a schematic side view of an embodiment
`of a linear oscillation motor;
`
`[0022] FIG. 2 is a schematic plan view of oscillatory
`elements of the embodiment of FIG.1;
`
`[0023] FIG. 3 is a diagram illustrating the oscillatory
`action of the linear oscillation motor illustrated in FIGS. 1
`and 2;
`
`[0024] FIG.4 is a block diagram illustrating the control
`method of the invention;
`
`[0025] FIGS. 5, 6, 7 are diagrams illustrating the indi-
`vidual control of two oscillatory elements of a linear motor;
`
`[0026] FIG.8 is a schematic side view of an embodiment
`of a statorless linear oscillation motor; and
`
`[0027] FIG.9 is a schematic side view of an embodiment
`of a statorless rotary oscillation motor.
`
`DETAILED DESCRIPTION
`
`[0028] FIG. 1 shows an embodimentofa linearoscillation
`motor in a schematic side view. The linear motor has a
`
`stationary stator (i.e., electromagnet) 1 and three oscillatory
`elements or rotors 2 each capable of performing a linear
`oscillatory movement. As the three oscillatory elements 2
`are arranged one behind the other, only the foremostoscil-
`latory element 2 can be seen in the representation of FIG.1.
`FIG. 2 showsthe oscillatory elements 2 in a schematic plan
`view, with all three oscillatory elements 2 being visible in
`FIG. 2. The oscillatory movements of the oscillatory ele-
`ments 2 are illustrated in FIGS. 1 and 2 by means of a
`double arrow 3. The stator 1 is comprised of an iron core 4
`which is formed in a “U” shape and has two legs 5, around
`each of which part of a coil 6 is wound. The coil 6 is shown
`in a sectional view to offer a view ofthe iron core 4. The two
`parts of the coil 6 are electrically connected to each other
`and can also be spatially arranged together, for example by
`being wound around the crossbar which connects the two
`legs 5 of the iron core 4. The oscillatory elements 2 each
`have three permanent magnets 7 resting with one of their
`poles against a carrier plate 8, said three permanent magnets
`being arranged closely next to each other in an anti-parallel
`layout. The permanent magnets 7 are positioned close to the
`ends of the legs 5 of the iron core 4 leaving only an air gap
`
`6
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`9. The carrier pates 8 are made of an iron material just like
`the iron core 4, and they are each connected at two opposing
`sides with one end of a spring 10 each. The other ends of the
`springs 10 are fixedly suspended, for example on a housing
`of an electric appliance not shownin the illustration,
`in
`which the linear motor is installed such that the oscillatory
`elements 2 can execute the linear oscillatory movement
`described by the double arrow 3.
`
`using multiple excitation frequencies f. For example, three
`excitation frequencies can be used corresponding to the
`three resonant frequencies fl, f2 and f3 of the oscillatory
`elements 2. The oscillation amplitudes A thereby achievedat
`the oscillatory elements 2 depend in each case on the
`amplitudes of the excitation signals. Depending on the
`sharpness of resonance, each excitation signal may also
`effect a small influence onthe other two oscillatory elements
`2. The concrete application of the above described principles
`[0029] With the linear motor in operating mode, an elec-
`for individual control of the oscillatory movement of the
`tric signal is supplied to the coil 6, as a result of whichaflow
`oscillatory elements 2 will be explained with reference to
`FIG.4.
`of current is generated through the coil 6 and a magnetic
`field develops in the iron core 4. Particularly in the area of
`the ends of the legs 5 of the iron core 4, the magnetic field
`acts upon the permanent magnets 7 and effects,
`in the
`geometry shown in FIG.1, a lateral displacement of the
`oscillatory elements 2 in relation to the stator 1. The
`direction of the displacement depends upon the direction of
`the current in the coil 6. By means of a variation of the
`current flow through the coil 6, during which as a rule the
`current direction is also varied, and also under assistance
`from the springs 10,
`the oscillatory elements 2 can be
`excited into linear oscillatory movement. The oscillatory
`action of the oscillatory elements 2 is shown in FIG.3.
`
`[0033] FIG. 4 showsa simplified block diagram for illus-
`tration of the control principle of the invention. The electric
`signal required to drive the coil 6 of the stator 1 is generated
`by a microcontroller 11. To do this, measuring data is
`supplied from three sensors 12 to the microcontroller 11.
`Instantaneous values for oscillation amplitude, frequency
`and phaseposition ofthe oscillatory elements 2 are detected
`by the sensors 12. The microcontroller 11 compares each of
`these instantaneous values with preset setpoint values and
`drives the coil 6 such that for each of the three oscillatory
`elements 2 deviation from the setpoint values can be
`reduced. To do this, the microcontroller 11 generates three
`[0030] FIG. 3 shows a diagram which illustrates the
`electric oscillation signals, the frequencies of which match
`oscillatory action of the linear oscillation motor shown in
`the resonant frequencies of the three oscillatory elements 2.
`
`FIGS. 1 and 2. In this Figure, the excitation frequencyfis The amplitudesof the electric oscillation signals depend on
`assigned to the abscissa and the amplitude A ofthe oscilla-
`the previously detected deviations of the instantaneous val-
`tion movement is assigned to the ordinate, and one curve
`ues detected by the sensors 12 from the setpoint values. The
`showing the frequency responseofthe oscillation amplitude
`electric oscillation signals are superimposed to form a
`Ais entered for each of the three oscillatory elements 2. The
`composite signal which is fed into the coil 6 by meansof a
`three curves all have a similar shape characterized by a
`power amplifier 13. The coil 6 thus receives an electric
`maximum oscillation amplitude A at the resonant frequency
`signal with three frequency components, each of which may
`fl, f2 and £3, respectively, and a decrease in amplitude A
`have a different amplitude, and generates a corresponding
`with increasing distance of the resonant frequencyf1, f2 and
`magnetic field which acts upon the three oscillatory ele-
`f3 to low and high excitation frequencies f. The three curves
`ments 2. The three oscillatory elements 2 are influenced
`are offset relative to each other due to the different resonant
`differently depending on the frequency components con-
`frequency f1, f2 and £3 of the three oscillatory elements 2.
`tained in the magnetic field, and their oscillation states are
`individually adjusted in this way. The achieved result is
`monitored in each case by means of the sensors 12, and,
`depending on the requirements, further correcting interven-
`tions are made by suitably driving the coil 6. A notable
`feature of the described approachliesin the fact that all three
`oscillatory elements 2 can be controlled via the same coil6,
`yet the individual oscillatory elements 2 can be controlled
`individually. Ultimately,
`this is enabled by the different
`oscillation properties,
`in particular the different resonant
`frequencies, of the oscillatory elements 2. Details relating to
`the driving of the coil 6 will be explained with reference to
`FIGS. 5, 6 and 7.
`[0034] FIGS. 5, 6 and 7 show diagrams whichillustrate
`the individual control of two oscillatory elements 2 of a
`linear motor. The time t is plotted on the abscissa and the
`velocity v of the oscillatory elements 2 and the voltage U of
`the signal generated by the microcontroller 11 are plotted on
`the ordinate. Thefirst oscillatory element 2 oscillates with a
`high amplitude and a low frequency. The associated varia-
`tion of velocity v with time is shownin each case as a solid
`line. The second oscillatory element 2 oscillates with a
`significantly lower amplitude and a frequency whichis three
`times the frequency of the first oscillatory element 2. The
`variation of velocity v with time of the second oscillatory
`element 2 is shown as a dashedline. The signal generated by
`the microcontroller 11 comprises a sequence of square-wave
`
`[0031] As becomes directly apparent from FIG. 3, the
`degree to which the individual oscillatory elements 2 are set
`in an oscillatory motion dependsin each case on the selected
`excitation frequency f. For example, whicheveroscillatory
`element2 has a resonant frequencyf1, f2, £3 which is closest
`to the selected excitation frequency [is broughtto oscillate
`the most. At the same excitation, the other two oscillatory
`elements 2 develop only a loweroscillation amplitude A or
`are possibly not excited to oscillate at all. If, for example, the
`excitation frequency f is exactly in the mid-position of the
`resonant frequencies f1 and f2 or f2 and f3 of two oscillatory
`elements 2, then these oscillatory elements 2 are excited to
`oscillate with the same amplitude A. Through appropriate
`choice of the excitation frequencyf it is therefore possible
`to individually adjust the oscillation amplitudes A of the
`three oscillatory elements 2. However,
`these oscillation
`amplitudes A cannot be adjusted at will by meansofa single
`excitation frequency f, as only those combinations of oscil-
`lation amplitudesA ofthe three oscillatory elements 2 can be
`set up which result as intersections between the curves
`shown in FIG. 3 and a vertical line drawn at the excitation
`
`frequency f.
`
`[0032] Within the framework of the limits set by the
`system parameters,
`it is possible to adjust the oscillation
`amplitudes A of the three oscillatory elements 2 at will by
`
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`pulses. The square-wave pulses are easier to generate than
`for example sinusoidal signals.
`
`[0035] FIG. 5 showsa situation in which positive square-
`wave pulses each coincide with the maxima, and negative
`square-wave pulses each coincide with the minimaof the
`curve shown with a dashed line. This meansthat the electric
`
`signal effects a continual acceleration of the oscillatory
`element 2 which is oscillating at a higher frequency, and
`consequently the oscillation movement of this oscillatory
`element2 is intensified. In relation to the curve shown with
`a solid line, some of the square-wave pulses have the same
`sign and some havethe opposite sign, as a result of which
`the accelerating and decelerating effects of the electric signal
`are approximately cancelled out in the caseofthe oscillatory
`element 2 which is oscillating at a lower frequency, which
`means that
`the oscillation movement of this oscillatory
`element 2 is not significantly affected by the electric signal.
`
`[0036] FIG. 6 showsa situation in which some of the
`square-wave pulses coincide with someofthe zero crossings
`of the curve shown with a dashed line, as a result of which
`the accelerating and decelerating componentsofthe electric
`signal cancel each other out exactly for the oscillatory
`element 2 which is oscillating at a higher frequency. In
`relation to the curve shown with a solid line, the positive
`square-wave pulses are positioned close to the maxima and
`the negative square-wave pulses are positioned close to the
`minima. Consequently, the oscillatory element 2 which is
`oscillating with the lower frequency experiences in each
`case an acceleration by the electric signal.
`
`[0037] As shown in FIG. 7, both oscillatory elements 2
`are accelerated, as the positive square-wave pulses coincide
`with the maxima and the negative square-wave pulses
`coincide with the minima of both curves. Therefore, by
`choosing the phase position of the square-wave pulses in
`relation to the oscillation movements of the two oscillatory
`elements 2, it is possible to act on the oscillatory elements
`2 individually.
`
`[0038] The control method of the invention may also be
`used for the control ofa linear oscillation motor which does
`not have a stationarystator 1, but instead has an additional
`rotor which is constructed in the same design as the stator 1
`but is movable. Such a statorless linear oscillation motor is
`shown in FIG. 8.
`
`[0039] FIG. 8 shows an embodimentofa statorless linear
`oscillation motor in a schematic side view. Instead of the
`stator 1 of the embodiment shown in FIG. 1, the embodi-
`ment shown in FIG. 8 has a component whichis referred to
`in the following as the active rotor 14. The active rotor 14
`is constructed in the same design as the stator 1 of the
`embodiment shown in FIG. 1 and serves in analogous
`fashion to generate a magnetic field, with the aid of which
`the oscillatory element 2 is driven. However, the special
`feature of the active rotor 14 is that, unlike stator 1, it is not
`stationary, being instead suspended for movementvia oscil-
`lating bridges 15 on a housing 16 ofthe electric appliance.
`The oscillating bridges 15 can be leaf springs which have a
`relatively low spring constant and therefore only form a
`weak coupling to the housing 16. Furthermore, the active
`rotor 14 is connected via a spring 10 to the housing 16 in
`order to obtain an oscillatory system. The oscillatory ele-
`ment 2, which is constructed identically to the embodiment
`shown in FIG.1, is connected in corresponding fashion via
`
`oscillating bridges 15 and a spring 10 to the housing 16. In
`this arrangement, provision can be madefor a single oscil-
`latory element 2 or several oscillatory elements 2.
`
`In termsof its mode of operation, the embodiment
`[0040]
`shownin FIG.8 differs from the embodiment of FIG. 1 in
`that the active rotor 14 is likewise set in an oscillatory
`motion. As this occurs, the oscillatory motion of the active
`rotor 14 is in phase opposition to the oscillatory motion of
`the oscillatory element 2. With regard to the individual
`control ofthe oscillatory movements, the statements made in
`relation to the embodiment of the linear motor shown in
`
`FIG.1 with the stator 1 also apply to the present embodi-
`ment with the active rotor 14, with the active rotor 14 acting
`in the manner of an oscillatory element 2 in terms ofits
`oscillatory motion.
`
`[0041] The embodiments of a linear oscillation motor
`described above can for example find application in an
`electric shaver. This applies to both the embodiment shown
`in FIG. 1 with the stator 1 and the embodiment shown in
`
`FIG. 8 with the active rotor 14. For example, in the case of
`the embodiment shown in FIG.1, two oscillatory elements
`2 can each be connected to a shaving cutter and drive the
`latter with the same frequency and the same constant ampli-
`tude. Unless further componentsofthe electric shaver are to
`be driven, unlike the rotor arrangement shown for this
`embodimentin FIG. 2, only two oscillatory elements 2 are
`required. In this case the embodiment shown in FIG.8 can
`be used in corresponding fashion. In this arrangement, the
`oscillatory element 2 and the active rotor 14 are each
`connected to one of the two shaving cutters. In both embodi-
`ments, the resonant frequencies of the two oscillatory sys-
`tems, 1.e., of the two oscillatory elements 2 or of the active
`rotor 14 and the oscillatory element 2 as well as the
`respective connected shaving cutters and the associated
`springs 10, are chosento be slightly different. For driving the
`coil 6 an electric signal is generated containing only one
`frequency which lies between the two resonant frequencies.
`By modifying the frequency ofthe electric signal towards
`the one or the other resonant frequency, the amplitudes of
`the two oscillatory elements 2 or of the oscillatory element
`2 and the active rotor 14 can be maintained constant even
`
`under load. Overall, the two oscillatory elements 2 or the
`oscillatory element 2 and the active rotor 14 are controlled
`in sucha waythat they oscillate with the same frequency, the
`same amplitude andin phase opposition to each other, which
`results in only relatively low housing vibrations. When using
`a linear motor in accordance with the embodiment shown in
`FIG.1, it should be noted that the polarity of the magnet
`arrangements of the two oscillatory elements 2 can be
`different in each case in order to generate oscillations of
`opposite phase.
`
`it is also possible to use the linear
`[0042] Furthermore,
`oscillation motor for driving a long-hair cutter and, as the
`case may be, also a middle cutter of the shaving apparatus.
`To do this, in the embodiment of the linear motor shown in
`FIG. 1 provision is made for a corresponding number of
`oscillatory elements 2, which drive the respective compo-
`nents of the shaving apparatus. In order to switch the long
`hair cutter or middle cutter on or off as required, the electric
`signal for driving the coil 6 is formed such that it addition-
`ally contains the resonant frequencies for the corresponding
`oscillatory systems, so that the oscillatory elements 2, which
`drive the long hair cutter or the middle cutter, can be
`
`8
`
`

`

`US 2006/0145547 Al
`
`Jul. 6, 2006
`
`selectively excited into a state of oscillation. In the process,
`those cutting devices where the resonant frequencies are not
`contained in the electric signal are not driven and are
`therefore in the off-state.
`
`[0043] As well as being applicable to linear oscillation
`motors, the control method described above can also be
`applied to rotary oscillation motors.
`
`[0044] FIG. 9 shows an embodimentofa statorless rotary
`oscillation motor in a schematic side view. The statorless
`rotary motor has functional components similar to the sta-
`torless linear motor shown in FIG. 8. However,
`these
`functional components are modified in such a way that a
`rotary oscillating motion is generated instead of a linear
`oscillating motion. Accordingly, the statorless rotary motor
`has an outer rotor 17 which is rotatably suspended and is
`made of an iron material. The outer rotor 17 extends in part
`within the coil 6, although without touching the latter, as a
`result of which the outer rotor 17 can be rotated in relation
`
`to the stationary coil 6. Arranged within the outer rotor 17
`is an innerrotor 18 that has a rotor core 19 made ofan iron
`
`material and permanent magnets 7 attached thereto. The
`inner rotor 18 is also rotatably suspended, with the outer
`rotor 17 and the inner rotor 18 having a shared axis of
`rotation 20. Furthermore, the rotary motoralso hasa series
`of spring elements which are arranged between the outer
`rotor 17 and the housing 16 and between the innerrotor 18
`and the housing 16 and are not shownin FIG.9 for reasons
`of clarity. The rotary motor therefore has two oscillatory
`systems. With regard to the control of the rotary motor, the
`above explanationsrelating to the control ofthe linear motor
`apply analogously.
`
`[0045] The rotary motor may be used for example as a
`drive for an electric toothbrush, with the embodimentof the
`rotary motor shown in FIG. 9 enabling two different brush-
`ing motions to be performed.
`Whatis claimed is:
`1. A method of controlling an electric motor, the method
`comprising:
`
`providing an electric motor comprising:
`
`a plurality of magnetically driven oscillatory elements
`having differing oscillatory characteristics, and
`
`an electromagnet having a coil arranged to driveall of the
`oscillatory elements;
`
`supplying an electric signal to the electromagnet, thereby
`creating a magnetic field to drive the oscillatory ele-
`ments;
`
`varying a frequency ofthe electric signal, thereby indi-
`vidually controlling oscillatory movementsoftheoscil-
`latory elements.
`2. The method according to claim 1, wherein varying the
`frequency of the electric signal comprises presetting the
`frequency ofthe electric signal.
`3. The method according to claim 1, wherein the electric
`signal comprises a plurality of individual frequencies.
`4. The method according to claim 3, wherein varying the
`frequency of the electrical signal comprises weighting the
`individual frequencies of the electric signal.
`5. The method according to claim 4, wherein the differing
`oscillatory characteristics comprise differing resonant fre-
`quencies.
`
`6. The method according to claim 5, wherein the indi-
`vidual frequencies of the electric signal correspond to the
`resonant frequencies of the oscillatory elements.
`7. The method according to