Patent Publication Number: US-8533960-B1

Title: Electrical devices, particularly electrical shavers, having magnetically coupled drives, and adapters therefor

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to electrical devices having magnetically coupled drives, and particularly to electrical shavers of the type described in my U.S. patent application Ser. No. 09/312,765, filed May 17, 1999, which application issued as U.S. Pat. No. 6,226,870, which application claims the benefit of Provisional Patent Application Ser. No. 60/164,771 filed Nov. 12, 1999, Provisional Patent Application Ser. No. 60/154,034 filed Sep. 16, 1999, Provisional Patent Application Ser. No. 60/145,803, filed Jul. 27, 1999, and Provisional Patent Application Ser. No. 60/142,943, filed Jul. 12, 1999. The invention also relates to adapters for use with existing electrical devices, particularly electrical shavers, to provide a magnetic coupling enabling the motor housing of such devices to be sealed against the entry of water or other foreign substances. 
    
    
     My above-identified patent application describes an electrical shaver comprising a housing including a rotary electrical motor and at least one drive magnet within the housing and mechanically coupled to the electrical motor to be rotated thereby; a cutter holder externally of the motor housing and including a cutter head (preferably three); and a driven magnet externally of the housing for each drive magnet within the motor housing. The driven magnet is magnetically coupled to the respective drive magnet within the housing so as to be rotated thereby, and is mechanically coupled to the cutter heads so as to rotate them when the driven magnet is rotated by the drive magnet. As described in that patent application, the electrical motor within the housing is completely sealed from exposure to water, and therefore such an electrical shaver may be used not only for conventional dry shaving, but also for wet shaving (with soap and water) in order to produce a close shave and a clean after-feeling as when wet shaving with a blade. The contents of that patent application are incorporated herein by reference. 
     In the embodiments of the invention described in that patent application, the driven magnet is included in the cutter holder unit. While such a construction is capable of producing a more compact arrangement, it requires redesign of the existing cutter holder units, and therefore can not easily accommodate the many existing designs of cutter holder units. 
     OBJECTS AND BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electrical shaver particularly of the type described in the above-identified patent application but having a number of advantages, as will be described more particularly below, particularly enabling the electrical shaver to accommodate existing designs of cutter holder units. 
     Another object of the invention is to provide similar advantages to other types of electrical devices, such as electrically driven pumps and valves. 
     A further object of the invention is to provide an adapter which may be used with existing electrical shavers, or other electrical devices, to enable such devices to be sealed against the entry of water or other foreign substances. 
     According to one aspect of the present invention, there is provided an electrical device, comprising: a housing shaped and dimensioned for hand-gripping by a user for manipulating the electrical device; an electrical drive motor and a drive magnet mechanically coupled thereto located within said housing; a sealing end wall carried by one end of said housing and sealing the motor and magnet within said housing; and a load device magnetically coupled to said drive magnet through said sealing end wall; characterized in that said load device is magnetically coupled to said drive magnet by a driven magnet included within a separate magnetic coupling unit clamped against separation to said one end of said housing and mechanically coupled to said load device, said magnetic coupling unit being releasably clamped to said housing against a force tending to pull apart the magnetic coupling unit from said housing during normal use of the electrical device. 
     According to another aspect of the present invention, there is provided an electrical shaver, comprising: a housing shaped and dimensioned for hand-grasping by a user, an electrical drive motor located within said housing; a drive magnet mechanically coupled to the drive motor through one end of said housing; a driven magnet magnetically coupled to the drive magnet; a cutter holder including a cutter head mechanically coupled to the driven magnet; and a sealing end wall between said drive magnet and the driven magnet; the driven magnet being within a separate magnetic coupling unit attachable to and detachable from said one end of the housing. 
     According to a still further aspect of the present invention, there is provided an adapter for use with an electrical device including a housing having an electrical motor and a drive spindle projecting through one end of the housing, and a load device to be driven by the drive spindle; the adapter being attachable between the one end of the housing and the load device and comprising: a body member attachable at one end to the one end of the housing, with the load device being attachable to the opposite end of the body member; a transverse wall extending transversely of and within the body member; a drive magnet rotatably mounted at one side of the transverse wall to be mechanically coupled to the motor drive spindle after the body member is attached to the housing; and a driven magnet rotatably mounted at the opposite side of the transverse wall to be mechanically coupled to the load device when attached to the body member. The driven magnet is thus magnetically coupled to the drive spindle by a magnetic field passing through the transverse wall to couple the load device to the motor, while the transverse wall serves as a sealing end wall with respect to the housing and the electrical motor therein. 
     Further features and advantages of the invention will be apparent from the description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIG. 1  is an exploded perspective view illustrating the three main units in one form of electrical shaver constructed in accordance with the present invention; 
         FIG. 2  is another exploded perspective view better illustrating the manner in which the main components of the three units coact; 
         FIG. 3  is a sectional view particularly illustrating the magnetic coupling unit attached to the housing; 
         FIG. 4  is a view of the magnetic coupling unit from the end facing the housing; 
         FIG. 5  is an end view of the magnetic coupling unit from the end facing the cutter holder, with the outer wall of the magnetic coupling unit removed to show the internal structure; 
         FIG. 6  is a view similar to that of  FIG. 5 , but illustrating a modification in the construction of the magnetic coupling unit to minimize variations in speed with variations in load; 
         FIG. 7  is a sectional view corresponding to that of  FIG. 3  but illustrating another embodiment of the invention; 
         FIG. 8  illustrates an electrical shaver, such as that of  FIG. 1 , provided with an oscillatory-type trimmer device, which device is shown in broken lines in its operative position; 
         FIG. 9  is a sectional view corresponding to that of  FIG. 7  but illustrating one manner of coupling the trimmer device to the electrical motor in a manner which enables the trimmer device in that embodiment also to be used during a wet shave; 
         FIG. 10  is a view along line X-X of  FIG. 9  more particularly illustrating the coupling of the trimmer device to the electrical motor; 
         FIG. 11  is a view, similar to that of  FIG. 7 , but illustrating coupling the vibratory-type trimmer device via mechanism within the magnetic coupling unit, thereby enabling the motor housing to be completely sealed; 
         FIG. 12  is a view illustrating the oscillatory mechanism within the magnetic coupling unit of  FIG. 11 ; and 
         FIG. 13  illustrates the face of each of the rotary gears in  FIG. 11  cooperable with the oscillatory mechanism of  FIG. 12 ; and 
         FIGS. 14   a - 14   f  diagrammatically illustrate a number of adapter implementations of the invention for use with existing electrical shavers or other electrical devices driving other types of loads. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The electrical shaver illustrated in  FIGS. 1-5  of the drawings includes a motor housing  10  constructed as a separate unit; a cutter holder  20  also constructed as a separate unit; and a magnetic coupling unit  30  attachable to and detachable from one end of the motor housing  10  and, in turn, attachably and detachably receiving the cutter holder  20 . When the three units  10 ,  20 ,  30  are assembled together, the magnetic coupling unit  30  effects a magnetic coupling between the electrical motor M within housing  10  and the cutter heads carried by the cutter holder  20 . 
     Housing  10  is shaped and dimensioned for hand-grasping by a user for manipulating the electrical device and is hermetically sealed so as to protect the motor M and the rechargeable battery B within the housing from penetration of water, dirt, etc. The housing end receiving the magnetic coupling unit  30  is closed by a sealing end wall  11 . End wall  11  is provided with a pair of inturned flanges  12  for receiving the magnetic coupling unit  30 , and with a resilient clip  13 , cooperable with a recess on the underside of the magnetic coupling unit  30  for releasably retaining the magnetic coupling unit attached to the housing  10 . 
     The two inturned flanges  12  converge towards one end  12   a , normally the end facing the user when using the shaver. Each flange is formed with a pair of parallel longitudinal slots  12   b ,  12   c  extending for a part of its length from its end  12   a  to impart elasticity to the respective end  12   a  of the flanges. As will be described below, such an arrangement facilitates the attachment and detachment of the magnetic coupling unit  30  with respect to the housing  10 . 
     The cutter holder  20  has three cutter heads. In the construction of  FIGS. 1-5 , motor M within housing  10  is coupled by mechanical gearing, generally designated  14 , to three disc-type drive magnets  15  located close to the inner face of end wall  11 . As shown in  FIG. 3 , gearing  14 , which may be basically the same as in the present commercial three-head electrical shaver of this type, includes a drive gear  14   a  coupled to the motor M and meshing with three driven gears  14   b , each coupled by a spindle  14   c  to its respective drive magnet  15 . Since the cutter holder  20  includes three cutter heads, each to be rotated by the motor M, the housing  10  would similarly include three gears  14   b  and three drive magnets  15  (only two of which are seen in  FIG. 3 ). 
     Housing  10  may otherwise be constructed as in any of the commercial versions of this type of electrical shaver, to include a switch  16  for energizing the electrical motor M, and a display  17  for indicating the charge status, etc. of the rechargeable batteries B. 
     An important feature of the present invention is that the cutter holder  20  may be any one of the constructions presently available in the rotary type electrical shaver. For purposes of example, the illustrated cutter holder  20  includes a body member  21  of generally triangular configuration formed with three large openings  22  for receiving the three cutter heads  23 . Each cutter head  23  is constituted of a fixed shear member  23   a  ( FIG. 2 ) formed with hair-receiving slots, and a rotary shear member  23   b  rotatable within the fixed shear member  23   a . The three cutter heads  23  are retained within the body member  21  by a retainer  24  having three lobes each engageable with an annular flange formed in the fixed shear member  23   a  to press it against the end wall of the body member  21 . Retainer  24  includes a rotatable knob  25 , having a shaped bore  25   a  receiving the notched end  26   a  of an upstanding pin  26  on body member  21 , for releasably retaining the retainer member, and thereby the cutter heads  23 , within body member  21 . A spring  27 , between knob  25  and the end wall of body member  21 , permits each cutter head  23  to move within its respective opening  22  to more closely conform to the outer contour of the surface being shaved. Ribs  28  formed in the hub of each rotary cutter member  23   b  serve to couple each rotary cutter member to the electrical drive. 
     While one particular construction of cutter holder  2  is illustrated in the drawings, it will be appreciated that this is set forth merely for purposes of example, and that other cutter holder constructions could be used. 
     Whereas in the conventional electrical shaver, each rotary cutter member  23   b  is mechanically coupled via its hub ribs  28  to the electrical drive, in the electrical shavers described in the above-identified Patent Application, as well as in the present application, the coupling of the rotary cutter members  23   b  is effected via a magnetic coupling to the electrical drive, rather than a mechanical coupling, to thereby enable the interior of the motor housing  10  to be hermetically sealed against the penetration of water, soap, cut hairs, or other substances. In the above-identified Patent Application, this magnetic coupling is effected by permanent magnets mounted within the cutter holder  20 ; in the constructions described in the present application, the magnetic coupling is effected by the separate magnetic coupling unit  30  which is provided between the housing  10  and the cutter holder  20 , and which thereby enables conventional cutter holders to be used. 
     The magnetic coupling unit  30  also includes a body member  31  of the same triangular configuration as body member  21  of cutter holder  20 . In addition, it is formed with a peripheral ledge  31   a  ( FIG. 1 ) for receiving the inturned flanges  12  of the housing  10  when attaching the magnetic coupling unit  30  to the housing. 
     As shown particularly in  FIG. 3 , body member  31  of the magnetic coupling unit is formed with a transverse wall  32  having three openings therein for rotatably receiving three pins  33 . On one side of transverse wall  32 , each pin  33  is fixed to a magnetic disc  34  magnetically coupled to a magnetic disc  15  within the motor housing  10 . The opposite side of each pin  33  is formed with a socket  35  telescopically receiving a coupling pin  36  formed at its outer end with teeth  36   a  to engage ribs  28  of the respective rotary cutter member  23   b  ( FIG. 2 ) for rotating the cutter member. 
     A second transverse wall  37  in body member  31  is formed with three openings  37   a  ( FIG. 2 ) for accommodating the coupling pins  36 . Openings  37   a  are of slightly larger diameter than pins  36  to provide clearances permitting some axial and lateral movements of the pins with respect to wall  37 . Wall  37  is removably attached to wall  32  in any suitable manner, e.g., by studs  37   b  in wall  37  force-fitted within sockets  32   a  in wall  32 , or by screws (not shown). A spring  38  between each pair of pins  36  and  33  urges the coupling pin  36  outwardly of wall  37 . 
     Body member  31  further includes a button  39  ( FIG. 1 ) facing the user while using the electrical shaver. Button  39  is movable in a first direction (e.g., inwardly as shown by arrow a) to release a catch  39   a  in order to permit detachment of the cutter holder  20 , and in a second direction, (e.g., downwardly as shown by arrow b) to depress retainer clip  13  of the housing  10  in order to permit detachment of the magnetic coupling unit  30  from the housing. 
     Pins  33 ,  36  for each of the cutter heads  23 , thus serve as a two-part drive spindle, or rotatable coupling, between the respective driven magnet  34  and the cutter head, which coupling is yieldable in the axial direction to permit inward and outward displacement of the cutter head within the cutter body member  21 . The rotary coupling is effected by teeth  36   b  in each coupling pin  36  receivable within axial slots  35   a  formed in the respective socket  35 ; whereas the axial yieldability is permitted by spring  38 , as in the existing electrical shaver coupling between the electrical motor and the cutter heads. 
     As indicated earlier,  FIG. 4  illustrates the end of the magnetic coupling unit  30  facing the housing  10 ; whereas  FIG. 5  illustrates the end of the magnetic coupling unit facing the cutter holder  20  but with the outer wall  32  removed to better show the internal structure. Thus, the end of the magnetic coupling unit  30  facing the cutter holder  20  (with wall  37  present) has the same “footprint” as the respective end of the shaver housing facing the cutter unit  20 , so that the commercially-available cutter units  20  presently used for conventional dry shaving can also be used in an electrical shaver equipped with the magnetic coupling unit  30  in accordance with the present invention for wet or dry shaving. 
     As shown in  FIGS. 3 and 4 , the transverse wall  32 , rotatably mounting the three magnetic discs  34  and their respective pins  33 ,  36 , is formed with a peripheral wall  32   b  circumscribing the three magnetic discs and projecting slightly past the outer faces of those discs wall  32   b  is dimensioned to engage the end wall  11  of the housing  10 , when the magnetic coupling unit  30  is applied thereto and to closely space the magnetic discs from that end wall. Peripheral wall  32   b , which thus defines a recess for the three magnetic discs  34 , has a flat outer surface enabling it to be slid over the housing end wall  11  when attaching the magnetic coupling unit  30  to the housing. At the end of the sliding movement of unit  30  when being attached to the housing, the apex portion  32   c  ( FIG. 4 ) of peripheral wall  32   b  engages and depresses the retainer clip  13  and permits that clip to snap into the recess  32   d  ( FIG. 4 ) inwardly of apex portion  32   c  to retain the magnetic coupling unit attached to the housing. 
     The electrical shaver illustrated in  FIGS. 1-5  is used in the following manner. 
     The magnetic coupling unit  30  may first be attached to the motor housing  10  by aligning the apex end of the coupling unit carrying the release button  39 , with the center of the opposite end of housing  10 , as shown in  FIG. 1 , and sliding the coupling unit  30  transversely with respect to the housing to cause the inturned flanges  12  of the housing to seat on the annular ledge  31   a  of the magnetic coupling unit. The peripheral wall  32   b  closely spaces the magnet discs  34  from the housing end wall  11  when the magnetic coupling unit  30  is thus applied. The two inturned flanges  12 , and particularly the elastic end portions  12   a  defined by the slots  12   b ,  12   c , are slightly stressed during the final insertion movement of the magnetic coupling disc  20 . As the magnetic coupling unit is moved into full alignment with housing  10 , retainer clip  13  of the housing snaps into the recess  32   d  ( FIG. 4 ) in the underside of the magnetic coupling unit  30  and engages shoulder  32   e  defined by the apex portion  32   c  of wall  32   b , to firmly retain the unit attached to the housing. 
     The magnetic coupling unit  30  may be detached from the housing by reversing this transverse movement. Thus, depressing button  39  releases clip  13 , thereby permitting the prestressed elastic portions  12   a  of the inturned flanges  12  to move the magnetic coupling unit  20  slightly away from clip  13 , such that the magnetic coupling unit may then be grasped and slid outwardly of the housing  10  from between the inturned flanges  12 . 
     This manner of attaching and detaching the magnetic coupling unit  30  to the housing  10  thus produces a transverse movement of the magnetic discs  34  of the coupling unit with respect to magnetic discs  15  within the housing. Such a transverse movement is less resisted by the magnetic force produced between these magnets than an axial movement as would be involved in pulling off the magnetic coupling unit from the housing by an outward movement rather than a transverse movement. 
     When the magnetic coupling unit  30  has been attached to housing  10 , the cutter holder  20  may be attached to unit  30  in the same manner as in the conventional commercial construction, by merely pressing the cutter holder against the coupling unit  30 , which causes the catches  39   a  of the magnetic coupling unit to engage shoulders (not shown) in the cutter holder. To detach the cutter holder, button  39  is pressed inwardly to release the catches  39   a , also as in the conventional commercial construction. 
     After use, both the magnetic coupling unit  30 , and the cutter holder  20  attached to it, can be released together (e.g., for water rinsing after a wet shave) by merely pressing down on button  39  to depress clip  13 , which thereby permits the two units to be moved together transversely of the housing  10  and to be removed in the manner described above. If it is desired, however, only to remove the cutter holder, without removing the magnetic coupling unit  30 , this may be done by merely pressing button  39  inwardly, which releases the catches  39   a  to permit removal of the cutter holder  20  as in the conventional construction. 
     The electrical shaver illustrated in  FIGS. 1-5  thus permits conventional cutter holders  20  to be used in an electrical shaver having a sealed housing so that the shaver can be used for wet shaving as well as for dry shaving. The transverse walls  32  and  37  may be formed with additional openings to facilitate air cleaning, rinsing and/or drying. 
       FIG. 6  is a view similar to that of  FIG. 5  but illustrates a modification in the construction of the magnetic coupling unit, therein designated  40 . In this modification, the body member  41  of the magnetic coupling unit also includes a transverse wall  42  for rotatably mounting the three magnetic discs  44  on one side (to face the housing unit  10 ), and the sockets  45  and pins  46  on the opposite side, corresponding to sockets  35  and pins  36  in  FIG. 5 , to face the cutter unit  20 . In this case, however, each socket  45  has a circular gear  47  fixed to it so as to be rotated with the respective magnetic disc  44 , socket  45  and pin  46 . The gears  47  for the three magnetic discs  44  all mesh with a center gear  48  rotatably mounted on transverse wall  42 . Such an arrangement thus provides a gear assembly, similar to gear assembly  14  within the housing  10 , mechanically coupling together all the driven magnetic discs  44 , their drive pins  46 , and the cutter heads driven by those pins. This arrangement thereby increases the flywheel inertia of the cutter heads to produce a more uniform rotation of each cutter head and to make its rotation less sensitive to changing loads on the respective cutter head. 
       FIG. 7  illustrates another embodiment of the invention in which the magnetic coupling unit, therein designated  50 , is of a slightly different construction to accommodate only a single disc-type driven magnet  51  cooperable with a single disc-type drive magnet  52  coupled to the motor M within the housing  10 . 
     Thus, in  FIG. 7 , the gearing, corresponding to gearing  14  in  FIG. 1 , coupling the motor M to the three cutter heads in the cutter holder  20 , is located not within housing  10  as in  FIG. 3 , but rather is rotatably mounted to a transverse wall  54  within the magnetic coupling unit  50 . This gearing includes a center drive gear  54   a  fixed to the driven magnet  51 , and three driven gears  54   b  each fixed to one of the coupling pins  53  and meshing with gear  54   a  to provide the rotary, yieldable coupling to the respective shaver head. In substantially all other respects, the construction illustrated in  FIG. 7  is the same as described above with respect to  FIGS. 1-5  and provides the same advantages. 
     The construction illustrated in  FIG. 7  thus: reduces the number of parts by requiring only two large-diameter magnetic discs ( 51 ,  52 ) rather than six small-diameter discs; permits maximizing the coupling force with minimum magnetic material; and increases the “flywheel” inertia of the cutter heads to produce a more uniform rotational speed of each cutter head despite variations in their respective loads. 
     Electrical shavers of the rotary type described herein are frequently provided with trimmer devices in the form of oscillatory-type cutters for trimming side burns, mustaches, beards, and the like.  FIG. 8  illustrates such a trimmer device, therein generally designated  60 , included in the Philips “Philishave” Model 930. Such a trimmer device is pivotally mounted to the housing  10  to a non-operative position received within a recess (not shown) in the housing, or to an operative position shown in the broken lines in  FIG. 8 . The trimmer device is driven by a drive stem (shown schematically at  61  which is oscillated by the motor M within housing  10 , and which transmits its oscillations to a toothed cutter member  62  to oscillate that member with respect to a toothed shear member  63 . Since the structure of such trimmer devices is well known, further details of its construction and operation are not set forth except to describe how the magnetic coupling arrangements described herein can be used for driving the drive stem  61 , and for sealing it against the entry of water, when the electrical shaver is used in a wet shaving process. 
     When using three drive magnets and three driven magnets ( FIGS. 1-6 ), the same type of mechanism may be used for driving the stem  61  as in the present commercial version of the electrical shaver, it only being necessary to seal the stem  61  with respect to its opening in housing  10 . This is not a difficult sealing problem because of the short reciprocatory movements of the drive stem  61  (as compared to the sealing problem involved with respect to the rotary movements of the cutter heads). 
       FIGS. 9 and 10  illustrate how the drive stem  61  may be driven in the  FIG. 7  construction wherein the magnetic coupling includes a single drive magnet  52  and a single driven magnet  51 . As shown, the drive stem  61  passes through a slot-type opening  64  within housing  10  for coupling to the vibratory cutter member  62  of the trimmer device  60 . Drive stem  61  is integrally formed as one arm of a lever  65  pivotally mounted at  66  to a wall  67  within housing  10 . The opposite end of lever  65  carries a pin  68  movable within a circular slot  69  formed in a plastic hub  70  fixed to the drive magnet  52 . Hub  70  is fixed to the motor drive spindle  71  which defines the axis of rotation of the drive magnet. 
     As seen particularly in  FIG. 10 , the circular slot  69  formed in hub  70  is eccentric with respect to the axis of rotation RA defined by the drive spindle  71 . Accordingly, as the drive magnet  52  is rotated, pin  68  received within the circular slot  69  will oscillate the drive stem  61  back and forth, as shown by the limit positions  61 ,  61 ′, about pivot  66 , and thereby rapidly reciprocate the drive cutter member  62  ( FIG. 8 ) of the trimmer device  60  with respect to the shear member  63 . 
     Since the movements of drive stem  61  with respect to the housing  10  are short oscillating movements, the sealing of the drive stem with respect to the housing may use a relatively simple type of seal, such as shown at  75  in  FIG. 10 . Other sealing arrangements are known and can be used. 
     For purposes of symmetry and weight reduction, the driven magnetic disc  51  may also be provided with a plastic center hub  72  corresponding to hub  70  in the drive magnetic disc  52 . Alternatively, the circular slot  69  may be formed directly in the drive magnetic disc  52 . 
       FIGS. 11-13  illustrate a further embodiment of the invention wherein the oscillatory cutter device is driven by an oscillatory mechanism within the magnetic coupling unit, rather than within the motor housing, thereby enabling the motor housing to be completely sealed against the penetration of water, dirt, etc. The oscillatory mechanism illustrated in  FIGS. 11-13  is basically the same as that now included in the Philips “Philishave” Model 930 referred to above, except that instead of being provided in the motor housing  10 , it is provided within the magnetic coupling unit. 
     As shown in  FIG. 11 , the magnetic coupling unit illustrated therein is very similar to magnetic coupling unit  50  illustrated in  FIG. 7 , and therefore corresponding parts are identified by the same reference numerals except increased by “100”. Thus, the magnetic coupling unit illustrated in  FIG. 11 , therein generally designated  150 , is removably attachable to the motor housing  110  in the same manner as described above, and rotatably mounts a driven magnet  151  magnetically coupled to the drive magnet  152  within the motor housing. Driven magnet  151  is mounted on one side of wall  154  and rotates a center gear  154   a  mounted on the opposite side of wall  154 . Gear  154   a  meshes with three gears  154   b  each driving, via the two-part drive spindles  155 ,  156  and teeth  156   a , one of the cutter heads ( 23 ,  FIG. 1 ) of the cutter holder ( 20 ,  FIG. 1 ) in an axially-yieldable manner as described above. 
     In the embodiment illustrated in  FIGS. 11-13 , the oscillatory cutter device, schematically indicated by broken lines  160  in  FIG. 12 , is driven by a drive stem  161  within the magnetic coupling unit  150 , rather than within the motor housing  110  as in the present commercial version referred to above. Thus, whereas in the commercial version, this mechanism is driven by one of the output gears driven by the center gear coupled to the motor drive spindle, in the embodiment illustrated in  FIGS. 11-13  the drive stem  161  is oscillated within a slot  161 ′ in the magnetic coupling unit  150  by one of the gears  154   b  driven via center gear  154   a  by the driven magnet  151 . 
     The oscillatory mechanism is more particularly illustrated in  FIG. 12 . It includes a bell crank lever  162  pivotally mounted at  163  to wall  154  of the magnetic coupling unit  150 . One arm of lever  162  is defined by the drive stem  161 , whereas its arm  164  on the opposite side of pivot  163  is formed with an elongated slot  165 . This slot receives a cylindrical pin  166  ( FIG. 13 ) formed in the confronting face of one of the three rotatably mounted gears  154   b . As shown particularly in  FIG. 13 , cylindrical pin  166  in gear  154   b  is eccentric with respect to the rotary axis of gear  154   b  as defined by pin  167  of the gear received within bore  153  of wall  154 . Slot  165  in lever  162  has a width equal to the outer diameter of the cylindrical pin  166  on gear  154   b , and a length larger than its width. The arrangement is such that when the gear rotates about its axis defined by its pin  167  and bore  153  of wall  154 , cylindrical pin  166  moves along the inner surface of slot  165  to oscillate lever  162 , and thereby to drive stem  161 , through a forward stroke and a return stroke with each rotation of gear  154   b.    
     The oscillatory cutter device, schematically shown by broken lines  160  in  FIG. 12  (and  60  in  FIG. 8 ), is pivotally mounted to the motor housing  110  such that in the operative position of the cutter device (as shown in  FIG. 8 ), its movable cutter member (corresponding to  63 ,  FIG. 8 ) would be coupled to drive stem  161  so as to be oscillated thereby with respect to its shear member ( 63 ,  FIG. 8 ), as in the above-referenced commercial model of electrical shaver, except that the oscillating mechanism is provided in the magnetic coupling unit  150 , rather than in the motor housing  110 . Accordingly, the embodiment illustrated in  FIGS. 11-13  includes basically the same parts as in the above-referenced commercial shaver, requiring substantially only the addition of the drive magnet, the driven magnet, their mountings and the hermetically sealed end wall of the motor housing, to enable the shaver to be used for both wet shaving and dry shaving. 
     The above-described embodiments of the invention thus enable existing cutter holders to be used; however, they require some modification of the motor housing in the existing designs.  FIGS. 14   a - 14   f  diagrammatically illustrate a number of embodiments of the invention in the form of adapters for use with existing electrical shavers, in which the adapter is attachable between the housing and the cutter holder and does not require any modification in either. 
     Thus,  FIG. 14   a  illustrates a commercial electrical shaver including a housing  200  carrying an electrical motor and a transmission for driving three spindles  201 ,  202 ,  203  projecting through an end wall  204  circumscribed by a peripheral wall  205  of the housing; and a cutter holder  210  removable attachable to housing  200  and provided with three hubs in the form of sockets  211 ,  212 ,  213 , each carried by a rotary cutter member  214 ,  215 ,  216  to be driven by the spindles  201 - 203  when the cutter holder  210  is attached to the end of the housing  200 .  FIG. 14   a  also illustrates an adapter, constituted of two units  220   a ,  230   a , releasably attachable to each other, and also releasably attachable between the housing  200  and the cutter holder  210 , to enable the electrical shaver also to be used for wet shaving (i.e., with soap and water) without the danger of the water penetrating into the housing  200  and wetting the motor or the electrical circuitry therein. 
     Unit  220   a  of the two-unit adapter illustrated in  FIG. 14   a  is in the form of a cap to be attached to the end of motor housing  200 . One side has the same “footprint” as the cutter holder  210  facing housing end wall  204 . Thus, unit  220   a  includes hubs  221   a - 223   a  to be mechanically coupled to the spindles  201 - 203  of the motor housing  200  instead of hubs  211 - 213 . Each hub  221   a - 223   a  is fixed to a magnetic disc  224   a - 226   a  rotatably mounted within a body member  227   a  on one side of a wall  228   a  extending transversely of the body member. The arrangement is such that when body member  227   a  is attached to peripheral wall  205  of the motor housing  200 , spindles  201 - 203  are received within hubs  221   a - 223   a , respectively, to rotate the magnet discs  224   a - 227   a , while the transverse wall  228   a  serves as a sealing end wall with respect to the housing  200  and the electrical motor therein. 
     Unit  230   a  in  FIG. 14   a  generally corresponds to the magnetic coupling unit, (e.g.,  30 ,  FIG. 1 ), of the above-described embodiments and has the same “footprint” as housing end wall  204  facing cutter holder  210 . Thus, unit  230   a  includes three magnetic discs  231   a - 233   a  adapted to be located on the outer side of the transverse wall  228   a , when unit  230   a  is attached to unit  220   a , with each magnetic disc having a spindle  234   a - 236   a  to be received within the hubs  211 - 213  of the cutter holder  210  when attached to the magnetic coupling unit  230   a.    
     Unit  230   a  may be attached to unit  220   a  by inturned flanges corresponding to flanges  12  in  FIG. 1 . However, other attachments may be used, e.g., a threaded attachment, a partial-turn, bayonet-type pin-and-slot attachment, etc. 
     It will thus be seen that when the two units  220   a  and  230   a  are attached together between the motor housing  200  and the cutter holder  210 , transverse wall  228   a  serves as a sealing end wall preventing water or other foreign substances from entering the interior of the motor housing  200 , while the magnets  224   a - 226   a  and  234   a - 236   a  serve as magnetic couplings for coupling the drive motor within housing  200  to the rotary cutter members  214 - 216  of the cutter holder  210 . Making the adapter in the two-unit form illustrated in  FIG. 14   a  enables the magnetic coupling unit  230   a  to be conveniently separated with the cutter holder  210  from housing  200  for cleaning, e.g., by rinsing under water, while the cap unit  220   a  is retained on the housing end. 
       FIG. 14   b  illustrates an arrangement wherein the adapter is constituted of a single unit  230   b  including a single body member  227   b  having a transverse wall  228   b  serving as the sealing end wall when the adapter is applied to the motor housing. Thus, three magnetic discs  224   b - 226   b  mounted at one side of the transverse wall  228   b , with each disc having a hub  221   b - 223   b  for receiving the spindles  201 - 203  of the motor housing  200 . Unit  230   b  further includes three magnetic discs  231   b - 233   b  rotatably mounted on the opposite side of the transverse wall  228   b , each carrying a spindle  234   b - 236   b  receivable within the hubs  211 - 213  of the cutter holder  210 , when unit  220   b  is attached between the motor housing  200  and the cutter holder  210 . 
       FIG. 14   c  illustrates an arrangement similar to that of  FIG. 14   a , except that in the magnetic coupling unit, therein designated  230   c , the drive magnets  231   c - 233   c  are coupled together by gears  237  and  237   a - 237   c , so as to increase the “flywheel” inertia of the cutter heads to produce a more uniform rotational speed of each cutter head during the variations in the load. The adapter in  FIG. 14   c  may otherwise be of the same construction as described above with respect to  14   a , and therefore the remaining parts have been correspondingly numbered to facilitate understanding. 
       FIG. 14   d  illustrates a single-unit adapter  230   d  similar to that of  FIG. 14   b , but including the gearing generally designated  237   d , coupled to the driven magnets  231   d - 233   d , to increase the flywheel inertia of the cutter heads as in  FIG. 14   c.    
       FIG. 14   e  illustrates a two-unit adapter, similar to  FIGS. 14   a  and  14   c , but including a single drive disc  224   e  on one side of the sealing end wall  228   e  in the cap unit  220   e , and a single driven disc  234   e  in the magnetic coupling unit  230   e  to be located on the opposite side of the sealing end wall. In this case, the drive magnet  224   e  in unit  220   e  is coupled via gearing  227   e  to the three spindles ( 201 - 203 ,  FIG. 14   a ); and the single driven disc  234   e  in unit  230   e  is coupled, via gearing  237   e , to the three rotary cutter members ( 214 - 216 ,  FIG. 14   a ). 
       FIG. 14   f  illustrates an arrangement similar to  FIG. 14   e , except in a one-unit construction  230   f , similar to that of  FIG. 14   d , in that it includes a single drive disc  224   f  on one side of the transverse wall  228   f , and a single driven disc  234   f  on the opposite side of the transverse wall. Drive disc  224   f  is driven, via gearing  227   f , by the three spindles ( 201 - 203 ,  FIG. 14   a ) of the motor housing; and the three rotary cutter members ( 214 - 216 ,  FIG. 14   a ) of the cutter holder are driven by the driven disc  234   f  via gearing  237   f.    
     While the invention has been described with respect to several preferred embodiments, it will be appreciated that these are set forth merely for purposes of example, and that many other variations, modifications and applications of the invention may be made.