CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation application of and claims priority under 35 U.S.C. §120 to PCT/EP2005/005892, filed on Jun. 1, 2005, and claims priority under 35 U.S.C. §119 from German application DE 10 2004 028 064.9, filed Jun. 9, 2004, both of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to an electric shaving apparatus. More specifically, in one configuration, the present invention relates to an electric shaving apparatus having a pivotal shaving head.  
       BACKGROUND  
       [0003]     As most people are aware, electric shaving apparatuses are a popular way to perform any one of a number of personal grooming tasks. A typically shaving apparatus may have a housing serving as a handle and a shaving head assembly that is adapted to pivot relative to the housing about a pivot axis. Furthermore, typical shaving apparatuses may also include an outer cutter and an undercutter. Moreover, as a large majority of the locations on the human body amenable to shaving are sloped, it is advantageous for an electric shaving apparatus to be capable of pivoting or tilting the shaving head. To provide this functionality, conventional tilting shaving systems typically employ a shaving head that includes an integral motor. However, a shaving head of this type is usually relatively heavy due to the presence of the motor.  
         [0004]     An improved electric shaving system would be desirable.  
       SUMMARY  
       [0005]     In one configuration, there is provided an electric shaving apparatus including a housing, a shaving head pivotal relative to the housing and including at least one shaving system, and an electric drive mechanism for driving at least one component of the shaving system. The drive mechanism may also include a stationary stator and at least one rotor movable relative to the stator, wherein the stator is disposed in the housing and the rotor in the shaving head.  
         [0006]     Advantageously, this configuration provides a driven component of the shaving system that is excitable into oscillations of high frequency, thereby enabling a thorough shave. Another advantage is the efficiency of the drive concept employed. Furthermore, it is an advantage that the stator is not located in the shaving head, thereby enabling the shaving head to be of small size and light weight. This allows the shaving apparatus to be handled comfortably, with the shaving head adjusting itself to a favorable pivot position.  
         [0007]     In one configuration, a gap may be formed between the stator and the rotor. In this configuration, the stator and the rotor may be shaped such that the drive mechanism continues to be operable even though the shaving head inclusive of the rotor are pivoted relative to the housing. In particular, the stator and the rotor can be shaped in the region adjoining the gap in such manner that the magnetically effective width of the gap is maintained substantially constant as the shaving head is being pivoted. This design may enable consistently high efficiency of the drive mechanism over wide parts of the pivotable range. For example, the stator could be curved to a concave configuration in the region adjoining the gap and/or the rotor could be curved to a convex configuration in the region adjoining the gap.  
         [0008]     In another embodiment, the rotor is connected fast (e.g. rigidly) with the driven component of the shaving system. This configuration enables a precise control of the driven component of the shaving system. In particular, the oscillation amplitude and the oscillation frequency of the driven component of the shaving system can be maintained constant during the shave to avoid sudden drops in oscillation.  
         [0009]     In still another example, the rotor may be movably suspended on the shaving head so as to be moveable linearly. In particular, the rotor may be coupled to at least one element that is resilient parallel to the direction of movement of the rotor, whereby an oscillatory system is created which can be driven very efficiently. Parallel to the pivoting direction of the shaving head, the rotor is preferably rigidly connected with the shaving head, thereby causing it to be pivoted uniformly with the shaving head. For example, in one embodiment, the rotor is fastened to the shaving head by means of oscillating bridges.  
         [0010]     In yet another embodiment, the shaving system includes at least one permanent magnet. Further, a pole shoe may also be disposed on a side of the permanent magnet facing the stator in order to obtain a desired geometry with little effort. In a further aspect of the shaving apparatus, a plurality of rotors which drive a plurality of components of the same shaving system and/or different shaving systems may be employed. In this configuration, complex shaving systems can be driven with low outlay.  
         [0011]     In yet another aspect, control of the drive is accomplished by the stator including at least one winding adapted to be driven by a control device. In particular, the winding may be drivable by the control device such that the drive mechanism is operated at or close to its resonant frequency. The control device may be constructed such as to produce voltage pulses, (e.g., bipolar voltage pulses). For example, the control device may produce duration modulated voltage pulses that enable the power supplied to the winding to be controlled. In one embodiment of the control device, driving the winding may produce variations in the effective power of the drive mechanism that can be compensated for. Alternatively, the motion amplitude of the rotor can be adjusted to a constant value. This may enable a consistently good shaving result to be achieved despite changing outside influences.  
         [0012]     In still another configuration, there is provided an electric drive mechanism for driving at least one component of a shaving system of a shaving head pivotal relative to a housing of an electric shaving apparatus. The drive mechanism may include a stationary stator and at least one rotor movable relative to the stator, wherein the stator is configured to be mounted in the housing and the rotor is configured to be mounted in the shaving head of the shaving apparatus. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0013]     The present invention will be explained in greater detail in the following with reference to the embodiment illustrated in the accompanying drawings.  
         [0014]      FIG. 1  is a schematic sectional view of an embodiment of an electric shaving apparatus constructed in accordance with the present invention; and  
         [0015]      FIG. 2  is another schematic sectional view of the embodiment of the shaving apparatus illustrated in  FIG. 1 . 
     
    
       [0016]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0017]      FIG. 1  shows an electric shaving apparatus  1  constructed in accordance with one embodiment in a schematic sectional view. The shaving apparatus  1  has a housing  2  shaped to enable a user to hold the shaving apparatus  1  in his hand. Fitted to the housing  2  are two supporting arms  3  on which a shaving head  4  is suspended by means of two journals  5  for pivotal motion about a pivot axis  6 . The pivot axis  6  extends in the area of the shaving head  4  facing away from the housing  2 . The shaving apparatus  1  further includes a linear oscillation motor  7  comprised of a stator  8  and a rotor  9 . The stator  8  is disposed in the housing  2  which also may accommodate an electronic control unit  10  for controlling the linear motor  9 . In other configurations, further suitable components not illustrated in the Figure, such as batteries, may also be included in the housing  2 . The stator  8  includes an iron core  11 , (e.g., a stacked assembly of soft magnetic steel laminations) and a winding  12  which may be divided into a plurality of coil sets. The cross-sectional area of the iron core  11  shown in  FIG. 1  has the shape of an “E”, with the winding  12  embracing the center bar of the “E”. The winding  12  is connected to the electronic control unit  10  via connecting leads  13 .  
         [0018]     The rotor  9  is disposed in the shaving head  4  and includes a soft magnetic carrier plate  14  that mounts two permanent magnets  15  of anti-parallel polarity in a side-by-side arrangement. The directions of magnetization of the permanent magnets  15  are indicated by arrows and extend normal to the surface of the carrier plate  14  mounting the permanent magnets  15 , so that the carrier plate  14  serves as rotor return path. Arranged on the two permanent magnets  15  are two soft magnetic pole shoes  16  reaching close to the iron core  11  of the stator  8  so that a narrow gap  17  is maintained between the pole shoes  16  and the iron core  11  in which no magnetic material is arranged. The gap  17  may be filled in part with a non-magnetic material. For example, the adjacent areas of the pole shoes  16  and of the iron core  11  may be coated with a plastic. However, at least part of the gap  17 ′ remains as an air gap to enable the rotor  9  to move relative to the stator  8 .  
         [0019]     Another gap  18  which is likewise devoid of magnetic material is provided between the two pole shoes  16 . The gap  18  between the pole shoes  16  is wider than the gap  17  between the pole shoes  16  and the iron core  11 . For example, the gap  18  may be about twice to four times as wide as the gap  17 . The permanent magnets  15  are firmly connected with the carrier plate  14  and the pole shoes  16  using, for example, an adhesive material. The carrier plate  14  and the pole shoes  16  may be made of a soft magnetic sheet metal. As an alternative to the soft magnetic material, the pole shoes  16  could also be made from a permanent magnetic material or other suitable material. In this case, the permanent magnets  15  and the pole shoes  16  could be formed as a one-piece construction enabling the gap  18  between the pole shoes  16  to be omitted.  
         [0020]     In the area of the carrier plate  14 , the rotor  9  is rigidly connected with a cutter supporting member  19  mounting two undercutters  20 . Fastened to a shaving head frame  22  adjacent to each undercutter  20  is a respective shaving foil  21  bent to conform to the shape of the associated undercutter  20 . The cutter supporting member  19  is suspended on the shaving head frame  22  by means of a respective S-shaped oscillating bridge  24  disposed at either end so as to be movable linearly in the direction of movement of the rotor  9 , which is indicated by a double arrow  23 , and extends parallel to the section plane. The areas of the oscillating bridges  24  oriented transversely to the direction of movement of the rotor  9  are each made of a thin, high-vibration-resistant material as, for example, spring steel. Formed approximately in the center of these areas is a respective aperture through which resonant spring  25  is passed. The resonant spring  25  is held in tension between the cutter supporting member  19  and the shaving head frame  22  and in combination with the rotor  9 , the cutter supporting member  19  and the undercutters  20 , form an oscillatory system with a defined resonant frequency.  
         [0021]     Furthermore, a sensor  26  may be arranged in the shaving head  4  in close proximity to the rotor  9  and is connected to the electronic control unit  10  through a signal line  27 . In one configuration, the sensor  26  detects a variable indicative of the state of motion of the rotor  9  (e.g., the rotor velocity or oscillation amplitude). In still other configurations, the sensor  26  detects a variable that is indicative of the state of motion of one of the oscillating bridges  24 , the cutter supporting member  19 , or one of the undercutters  20 .  
         [0022]     With the shaving apparatus  1  in operation, the rotor  9  executes linear oscillations with a frequency that corresponds or is close to the resonant frequency of the oscillatory system. In one configuration the linear motor  7  operates very efficiently enabling relatively low power to be used. To set the rotor  9  and hence also the undercutters  20  in an oscillatory motion, the winding  12  of the stator  8  is driven by the electronic control unit  10  via bipolar voltage pulses of variable pulse width, that produce a short-time magnetic field in the iron core  11  that acts on the pole shoes  16  of the rotor  9 . The geometry of the magnetic field is determined by the shape of the iron core  11 . Depending on the direction of the magnetic field, which is in turn dependent on the direction of the current in the winding  12  and hence on the polarity of the voltage pulses produced by the electronic control unit  10 , the rotor  9  is deflected from the mid-position shown in  FIG. 1  to either the left or to the right. The repeated application of voltage pulses to the winding  12  at appropriate instants of time results in a linear oscillation parallel to the pivot axis  6  of the shaving head  4  with a frequency corresponding or close to the resonant frequency of the oscillatory system.  
         [0023]     The generation of the voltage pulses applied to the winding  12  at the proper instants of time can be achieved in a variety of suitable ways. In a first variant, the electronic control unit  10  produces voltage pulses of a predetermined frequency which correspond or are close to the resonant frequency of the oscillatory system. These pulses excite the rotor  9  into executing corresponding oscillations synchronously with the voltage pulses of the electronic control unit  10 . In a second variant, a self-oscillating loop is formed by feeding a signal dependent on the oscillation of the rotor  9  back to the electronic control unit  10 . For example, the signal could be generated by the sensor  26 . Due to the feedback, the winding  12  is driven by the electronic control unit  10  such that the oscillation frequency of the rotor  9  corresponds to the resonant frequency of the oscillatory system or is close to the resonant frequency.  
         [0024]     The oscillation amplitude of the rotor  9  may be adjusted to a constant value by the electronic control unit  10  during the shave. To this effect, the oscillation amplitude or the velocity of the rotor  9  is detected as an actual value and compared to a desired value. The deviation determined by the comparison is fed to a filter exhibiting, for example, a proportional-integral characteristic, which generates an actuating signal. A power unit then uses the actuating signal to produce bipolar voltage pulses for driving the winding  12  of the stator  8 . In the process, the power unit varies the drive power in response to the actuating signal, for example, by pulse duration modulation of the voltage pulses delivered to the winding  12 . The actual values necessary for control of the oscillation amplitude may be detected by the sensor  26  which is arranged in the shaving head  4 .  
         [0025]     In some configurations a detector device which is arranged wholly or in part in the housing  2  of the shaving apparatus  1  may be employed. For example, the rotor  9  may have secured to it a permanent-magnetic pickup whose motion is detected by an inductive coil disposed in the housing  2 . Further, it will be understood by those of ordinary skill in the art that the permanent magnets  15  which are present anyway could also be used as pickups. In a further aspect, it is also possible to dispense with a concrete detector device altogether and to determine the actual values from the voltages and currents of the winding  12  of the stator  8 .  
         [0026]      FIG. 2  shows the embodiment of the shaving apparatus  1  illustrated in  FIG. 1  in a further schematic sectional view in which the section is taken along the line A-A drawn in  FIG. 1 . This means that the section is taken transversely to the direction of movement of the rotor  9  and parallel to the pivot direction of the shaving head  4 . The pivoting direction of the shaving head  4  is indicated by arrows  28 . In the representation of  FIG. 2 , the shaving foils  21  are removed from the shaving head  4  and hence not shown.  
         [0027]     To operate the rotor  9 , which is pivoted along with the shaving head  4 , also in a pivoted position of the shaving head  4 , which differs from the mid-position shown in  FIG. 2 , the gap  17  between the pole shoes  16  of the rotor  9  and the iron core  11  of the stator  8  may be of approximately like width for all the permitted pivot angles. In one configuration, this is accomplished by arranging the pivot axis  6  at a relatively large distance from this gap  17  and by conformability shaping the adjacent outer contours of the pole shoes  16  and of the iron core  11 . To this effect, the iron core  11  may be curved to a concave configuration in this area. Correspondingly, the pole shoes  16  may be curved to a convex configuration, with the curvature being the same or similar. For example, the curvature may be in particular of a circular-arc shape, with the center of the circle lying on or in close vicinity to the pivot axis  6 . It is also possible to provide for an intentional minor variation in the width of the gap  17 , dependent on the pivot angle of the shaving head  4 , in order to compensate for a dependence, if any, of the drive power of the linear motor  7  on the pivot angle.  
         [0028]     Furthermore, some configurations can compensate for the effects of an unwanted variation in the width of the gap  17  on the drive power of the linear motor  7  by appropriately driving the winding  12  of the stator  8 . In this way, dependences of the drive power of the linear motor  7  on the pivot angle of the shaving head  4  can be counteracted. In particular, the power loss which occurs in the presence of large pivot angles when the overlap between the pole shoes  16  and the iron core  11  decreases and can be balanced out to a certain degree. In this manner, a wide pivot angle range is accomplishable without little or no appreciable power losses of the linear motor  7 .  
         [0029]     The linear motor  7  may be used to drive not only the undercutters  20  but also the shaving foils  21  or a center cutting comb (not shown) for example. In this case, provision is made for several rotor units which, when taken in combination, have approximately the outer contour of the rotor  9  shown in  FIGS. 1 and 2 . For example, two rotor units could be provided, whereof one rotor unit is coupled to the undercutters  20  and the other rotor unit to the shaving foils  21 . The rotor units are each movably suspended via oscillating bridges  24  of their own and can all be driven by the stator  8  whose construction is maintained unchanged. In this arrangement, different oscillation amplitudes can be generated by equipping the rotor units with pole shoes  16  of different size. Similarly, the rotor units can be set in oscillations in phase opposition to each other by designing the rotor units to exhibit opposite magnetic polarity.  
         [0030]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, in other embodiments, other suitable shaving systems or motors may be employed. Accordingly, other embodiments are within the scope of the following claims.
There is provided an electric shaving apparatus including a pivotal shaving head. More specifically, in one embodiment, there is provided an electric shaving apparatus including a housing, a shaving head pivotal relative to the housing and including at least one shaving system, and an electric drive mechanism for driving at least one component of the shaving system. The drive mechanism includes a stationary stator and at least one rotor movable relative to the stator, wherein the stator is disposed in the housing and the rotor in the shaving head.