Patent Publication Number: US-9410593-B2

Title: Nodal spring assembly for an electronic toothbrush

Description:
This application is a continuation of U.S. patent application Ser. No. 12/303,162, filed 25 Jun. 2007 now U.S. Pat. No. 8,413,969, which is a national phase application of international application PCT/IB2007/052455, filed 25 Jun. 2007, which claims priority to U.S. provisional patent application 60/817,959, filed 30 Jun. 2006. 
    
    
     This invention relates generally to drive train assemblies for an electronic toothbrush, and more specifically concerns a nodal spring arrangement for such a drive train. 
     Various drive train arrangements are known for electronic toothbrushes. The drive train portion of the toothbrush is responsive to a motor action, including mechanical, electromechanical, magnetic or other action, to drive a brushhead in a reciprocating manner. One type of drive train arrangement uses a spring which is fixedly mounted at both ends as well as at a node point, wherein the node point is between the two ends of the spring, typically mid-length. When the drive action excites the spring in its desired out-of-phase torsion mode, it produces a desired reciprocating brushhead action through a selected angle. 
     In one arrangement, the nodally mounted torsion spring is V-shaped, having a node point which is connected to the housing by a mounting plate. In such arrangements, the mounting plate, which acts as a ground connection for the V-shaped torsion spring bar, is connected to the handle frame/housing, reducing vibrations which would otherwise be transferred to the handle. The V-shaped torsion bar, which acts as a node spring, has several important functions, including returning the brushhead, or other workpiece, to a center position and to clearly separate the in-phase rotational mode from the desired out-of-phase rotational mode sufficiently to avoid interaction between the two modes. Such a V-spring arrangement is described in U.S. Pat. No. 6,859,968 the contents of which are hereby incorporated by reference. That patent is owned by the assignee of the present invention. 
     In the above-described nodal spring arrangement, there are several structural challenges to achieving a desired and reliable operation. It is important that the node spring be arranged so that the desired dynamic response of the torsion spring is achieved and to reduce the high stresses and the potential for wear in the area of contact between the V-spring and the mounting plate. It is also important that the response of the V-spring be as linear as possible along the length thereof, as opposed to a non-linear response. 
    
    
     
       Accordingly, the present invention is a spring assembly for a drive train used in an electronic toothbrush, comprising: a V-shaped spring member which is secured at both ends so that it can be excited in a torsion mode about a node point along the axial dimension of the V-shaped spring member; an insert member for closely supporting a lower surface portion of the V-shaped spring member; a shim member positioned between the V-shaped spring member and a node spring member which is connected to the housing of the toothbrush; and an attachment member for securing the node spring member, the shim, the V-shaped spring member and the insert tightly together. 
         FIG. 1  is a perspective view of a portion of an electronic toothbrush showing a V-spring with an integrated node spring function and mounting plate drive train arrangement for an electronic toothbrush. 
         FIG. 2  is a perspective view showing the V-spring portion of the arrangement of  FIG. 1  in more detail. 
         FIG. 3  is an exploded view showing another V-spring and node spring arrangement in an electronic toothbrush. 
         FIG. 4  is a cross-section view showing one variation of the embodiment of  FIG. 3  in more detail. 
         FIG. 5  is a perspective view showing a portion of the variation of  FIG. 4  in detail. 
         FIGS. 6A and 6B  show another portion of the variation of  FIG. 4 . 
         FIG. 7  is an elevational view of another variation of the embodiment of  FIG. 3 . 
         FIGS. 8A and 8B  are perspective views of portions of the variation of  FIGS. 7A and 7B . 
     
    
    
     Referring now to  FIGS. 1 and 2 , a nodal drive train assembly portion of an electronic toothbrush is shown which incorporates one embodiment of the nodal mount assembly disclosed herein. The nodal drive train assembly shown at  10  includes a front end portion  14  of an electromagnetic motor, driving a V-configured torsional bar spring  15 . The remainder of the motor is in a handle portion of the toothbrush (not shown). Such an electromagnetic motor arrangement is disclosed in U.S. Pat. No. 5,378,153, which is owned by the assignee of the present invention, the contents of which are hereby incorporated by reference. At the other end of drive train  10  is a portion of a toothbrush head assembly  16 . In one arrangement, the entire drive train assembly, including the head assembly, is removable from a handle portion of the toothbrush and replaceable as a unit, while in another arrangement, a brushhead is removable by itself from a mounting member at the distal end  17  of drive train  10 . 
     The V-shaped solid torsion member  15 , also referred to as a torsion spring, extends between the two portions  14  and  16  and is fixedly supported by two end mount assemblies  20  and  22 , which can be of various configurations. In a particular embodiment, the torsion member  15  is approximately 35 mm long, and comprises two identical plate portions  21  and  23 , which are approximately 4.25 mm wide and 0.30 mm thick, made from spring steel. The assembly shown in  FIG. 1  is typically supported to the housing of the toothbrush by spaced bearing assemblies (not shown) at the opposing ends thereof. A detailed example of such an arrangement of a nodal mounted drive train is shown and described in the &#39;968 patent. 
     In operation, the drive motor action excites the torsion bar spring  15  in its out-of-phase mode, such that rotation of the proximal half  27  of the torsion spring in one direction results in a rotation of the distal half  29  in the opposite direction. The frequency of the out-of-phase mode is approximately 270 Hz in the embodiment shown. 
     In this embodiment, a mounting plate  26  is fixedly connected to the node point  30  of the V-shaped torsion spring by welding or similar fixed connection. The node point is located approximately midway of the V-shaped member, along the ridge line  31  of the V-shaped member. The mounting plate is also connected fixedly to the housing of the toothbrush. This arrangement reduces the vibration of the handle. 
     In the embodiment of  FIGS. 1-2 , the stresses typically present at the node joint are reduced by a pair of slots in the V-shaped member. The slots, which result in the V-shaped torsion spring member functioning as a torsion bar node spring,  32  and  34  in the embodiment shown, are substantially identical and are located close to the ridge line, on opposite sides of the node point  28  in the respective plate portions  21 , of the V-shaped bar member. The slots  32 ,  34  extend longitudinally of the V-shaped member and are approximately 8 mm long and 2.4 mm wide. The effect of the slots is to more evenly distribute the stresses along the V-shaped member and reduce the stress in the vicinity of the node point  28 , as well as integrating a node spring function into a torsion bar  15 . The slots, while generally being uniform in width along their length, may include small tab portions which decrease the slot width at those points. 
       FIGS. 3-7  show another embodiment of the present invention.  FIG. 3  shows a nodal drive train arrangement  40  which includes a V-shaped bar spring member  50  which is fixedly mounted at the respective ends thereof to end mount assembles  42  and  44 . End mount assembly  42  is driven by a motor (not shown); extending from end mount  44  is a mount  48  for a brushhead assembly. As with the first embodiment, the entire drive train can be made replaceable relative to a handle portion of a toothbrush, or the structure can be arranged so that the brushhead assembly alone is replaceable. 
     V-shaped bar spring member  50 , shown in  FIG. 3  includes two extended end regions  501  and  502 , which extend below the longitudinal edges  503  of the middle portion of the V-spring. The width of the end regions is wide enough to accommodate the size and configuration of the portion of the end attachment assemblies which contact the spring. The free ends of the extended portions are joined by a flat cross-piece  504 . This “closed end” region is present at both ends of the V-spring. Preferably, the cross-piece  504  is integral, i.e. unitary, with the remainder of the spring, with the ends of the extended regions of the spring and the cross-piece having curved joints  505  for a smooth transition, referred to as closed end regions. The cross-piece could also, however, be a separate piece of material, attached by welding or other means, for some applications. The V-spring includes three openings along the peak of the V-spring one at either end to accommodate bolts for clamping the V-spring in a particular assembly and another at the center to accommodate a bolt for a nodal attachment member. 
     Extending between support members  42   a ,  44   a , which are mounted in end mount assemblies  42 ,  44 , is a V-shaped torsion member  50 , which functions as a spring. Mounted to the center point node point)  48  of torsion spring  50  is a separate node spring  52 , in the form of a mounting plate, unlike the embodiment of  FIGS. 1 and 2  in which the nodal spring function is integrated into the V-shaped bar member. The mounting plate (node spring)  52  is fixedly attached to the housing of the toothbrush at its outer edges thereof. In this arrangement, mounting plate  52  is secured to the V-shaped torsion spring  50  (V-spring) by a mounting assembly, which includes generally a base insert member  54  which fits within the trough portion  56  of the V-shaped torsion spring  50 , a shim member  56  which is positioned between the torsion spring  50  and the node spring  52 , configured to provide a stable connection therebetween, and an attachment member combination  58 ,  59  which secures the entire assembly firmly together. 
     There can be several structural variations of the general arrangement shown in  FIG. 3 . In all of the variations, however, there are several common functions of the assembly. First, the axis of rotation of the node spring (i.e. mounting plate)  52  should be as close as possible to the axis of rotation of the V-spring  50 , in order to achieve the desired dynamic response. Second, the mounting assembly, specifically the insert, shim and the attachment member combination, must provide a stable, strong connection between the V-shaped torsion spring and the node spring (mounting plate) at the node point, in such a manner as to withstand the particular stress at the node point connection for an extended period of time, while also reducing the stresses at that point. Third, the joint must be strong and fixed, so that the out-of-phase response of the V-shaped torsion spring is as linear as possible. 
     In a first variation, shown in  FIGS. 4, 5 and 6A, 6B , the insert member  62  is a diamond-shaped assembly. Referring to  FIGS. 4 and 5 , shoulder (side) portions  64  are flat, configured generally to provide a good extended clamping surface between the insert  62  and the V-spring  63 . The edges  64   a  of the insert round downwardly to avoid stress concentrations. The curve of the upper surface portions  66 ,  67  is such as to correctly mate the insert relative to the inner surface of the V-spring where the two plate portions thereof meet. The upper surface portions of the insert must have a slightly larger radius than the corresponding internal surface area  68  of the V-shaped torsion spring so that the torsion spring will sit flush on the flat shoulder portions  64  when the assembly is clamped together. An opening  69  extends through the insert member  62  for the attachment member. 
     A first shim member  56  for the first variation is shown in  FIGS. 6A and 6B . Referring to  FIG. 3 , shim member  56  is in the general form of a V-shaped block and is configured to fit on the top surface of the V-shaped torsion spring  50 , providing a stable clamping surface for the node spring  52 . Flat side shoulder portions  70 ,  71  provide a clamping surface to the V-spring  50 , while surface portions  72 ,  73  mate with the corresponding joint area (the upper surface of the bend) between the two plate portions of the V-spring  63  ( FIG. 4 ). Outer edges  74  and  76  of surfaces  70 - 73  of the shim curve outwardly, avoiding the stress concentrations. Surface portions  72 ,  73  have a smaller radius than the radius of the mating surfaces of the V-spring, so that the V-spring will contact flush the flat shoulder surface portions  70 ,  71  of the shim. An opening  80  through the shim is provided for the attachment member. 
     The opposing side of the V-block shim  56  includes a raised surface portion  82  which provides a keying function for positioning of the node spring (mounting plate)  81  thereon, while an adjacent flat surface  84  portion provides a clamping surface between node spring  81  and shim  56 . The raised surface  82  extends into a mating opening in the node spring  81 . The keying function can be accomplished by many different surface configurations, as long as the structure can react the torque loads on the joint. 
     Both the diamond-shaped insert and the V-block shim are shaped generally to allow the V-spring to deform in a manner as close to its natural state as possible, and to minimize stress increases, while at the same time providing substantial clamping surfaces between the assembly elements. The shim aligns the V-spring to the node spring and sets the gap between the node spring and the V-spring to prevent rubbing movement during operation. 
     The entire assembly ( FIG. 3 ) is clamped together with a screw and nut combination  58  and  59 , but it should be understood that other mechanical attachment means, such as a rivet, can also be used. The clamping surfaces of both the shim and the insert mate with the joining angle of the V-spring and sit flush on that portion of the V-spring, so as to prevent play in the assembly during operation. The actual area of contact between the insert, the V-spring and the shim must be small enough, however, to not significantly affect the overall stiffness of the V-spring member, but still great enough to provide an adequate clamping surface that the assembly lasts for the desired life of the product. 
     The insert and the shim portions of the node assembly should comprise a bearing-type material with a low friction, less than that of the V-spring, which is typically made from steel, in order to avoid wear between the V-spring, the insert and the shim, and to maintain a gradual stress introduction zone in the V-spring. Furthermore, the material must have a high enough yield strength to strongly hold the attachment member (rivet or screw), and yet must resist wear and loosening of the joint over the life of the product. Brass and bronze have shown to fulfill these requirements. Both have good bearing properties and high yield strength. Other materials, such as aluminum and zinc, could also be used. 
     The entire node assembly must be clamped tightly to maintain a tight joint therebetween, without play or movement between them, for the desired life of the product. The overall geometry of the insert and the shim minimize the clamping pressure produced by the approximately 500 N clamping force required to produce the desired tight arrangement, while the particular material of the insert and the shim creates a good friction/high wear tolerance surface between the V-spring, shim and insert elements. 
     A variation of the second embodiment includes different insert and shim configurations, shown in  FIGS. 7A, 7B and 8A, 8B , which provide the required clamping surfaces for attachment and alignment of the V-spring member, with different insert and shim configurations, which also provide a low friction bearing surface between the V-spring and the node spring (mounting plate). 
     Referring now to  FIG. 7 , insert  98  is round in general configuration and includes opposing flat side shoulder surfaces  104  and  105 , which provide the required clamping surfaces between insert  98  and the V-spring  100 , and positions the insert correctly relative to the V-spring. Again, the outer edges  106  of the flat side shoulder surfaces are rounded to avoid stress concentrations. The insert  98  also includes an upper raised portion  108  which functions as a keying element, extending upward through an opening in the V-spring. Upper surface portions  107  of the insert have a slightly larger radius than the lower surface of the V-spring member and the joint thereof, so that the V-spring will sit flush on the flat shoulder portions of the insert when the assembly is clamped together. 
     Intermediate between the keying portion  108  and the flat shoulder surfaces  104 ,  105  is a bearing boss  109  which provides a bearing surface for the node opening in the V-spring. The height of the bearing boss  109  must not interfere with the clamping action for the assembly, but is designed for an interference fit with an opening in the V-spring. 
     A groove  116  between the bearing boss  109  and the flat shoulder surfaces  104 ,  105  of the insert allows the V-spring to sit flush on those flat shoulder portions. The keying element  108  is configured to provide a slight interference fit with the corresponding opening in the V-spring. Opening  110  through element  108  is adapted to receive an attachment member therethrough. The base surface  111  of insert  108  provides support for a nut in the case of a screw and nut assembly or a clamping surface for the deformed end of a rivet connector. 
     A flat shim portion  118  is circular, with a diameter of approximately 4 mm, approximately 0.5 mm thick, with a central opening  112  which matches the raised keying portion  108  of the insert. The flat shim supports the mounting plate  121 , as shown in  FIG. 7 . An attachment member  120  secures the existing assembly together firmly. 
     The above two variations can be in turn varied. For instance, the bearing boss portion of the insert of  FIG. 8A  can be used with the insert of  FIG. 4  for an interference fit with an opening in the V-spring. 
     In a further variation, the arrangement of  FIGS. 7, 8A, 8B  can be modified so that the shim of  FIG. 8B  is replaced with the shim of  FIGS. 6A, 6B ; and still further, the insert of  FIG. 8A  can be modified to eliminate the bearing boss and then used with the shim of  FIGS. 6A, 6B . 
     Still further, the insert of  FIG. 5  can be used with the shim of  FIG. 8B , and in yet another variation, the insert of  FIG. 5  can be modified to include a bearing boss portion and used with the shim of  FIG. 8B . 
     Hence, a nodal spring arrangement has been described in which a V-shaped torsion member (spring) is secured at its node point to the handle housing by a mounting plate. In one embodiment, the mounting plate is welded to the V-shaped spring at the node point; slots provided in the V-shaped spring are located on opposing sides of the node point. These slots create a torsion bar node spring while also reducing stresses around the node point connection zone. Another embodiment includes a node point assembly which includes an insert supporting the V-shaped torsion spring and a shim member located between the V-shaped torsion spring and the mounting plate node spring, the assembly being held tightly together by an attachment member combination, such as a screw or a rivet. 
     Although a preferred embodiment of the invention has been disclosed for purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention which is defined by the claims which follow.