Abstract:
Power toothbrushes are provided having toothbrush heads that move in a substantially random manner when in use and in contact with a user&#39;s teeth.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of and claims priority to U.S. Ser. No. 10/445,103, filed on May 23, 2003, now U.S. Pat. No. 7,302,726 which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to toothbrushes, and more particularly to power toothbrushes. 
     BACKGROUND 
     Power toothbrushes are well known and have been on the market for years. In typical power toothbrushes, tufts of bristles on the brush head extend generally perpendicularly from the top surface of the head. The head is oscillated, rotated and/or translated in order to provide enhanced tooth cleaning capability. Generally, the head moves in a substantially fixed path over the surface of the user&#39;s teeth. 
     SUMMARY 
     In one aspect, the invention features a power toothbrush including a handle, a toothbrush head that extends from the handle and carries a plurality of cleaning elements, and a drive mechanism constructed to cause motion of the toothbrush head. The toothbrush head is configured to move in a substantially random path when the drive mechanism is actuated and the cleaning elements are brought into contact with a user&#39;s teeth. 
     In some embodiments, the drive mechanism drives the toothbrush head in an orbital motion about an axis that is spaced from the axis of the toothbrush head. 
     In some cases, the drive mechanism includes a bevel gear. The toothbrush head can be mounted on the bevel gear. The toothbrush head can be mounted on a shaft that extends through a bore in the bevel gear, the shaft being mounted to spin freely within the bore. In some embodiments, the shaft is disposed at an angle (e.g., from about 2° to about 7°) with respect to a center axis of the bevel gear. In some cases, the bore is offset from a center axis of the bevel gear. The bore can be offset from the center axis by about 1 mm to about 3 mm. The bevel gear can include an O-ring disposed between a lower surface of the toothbrush head and an upper surface of the bevel gear. The upper surface of the bevel gear can include a counterbore that is configured so that the O-ring rests on a plane that is perpendicular to a center axis of the bore. In some cases, there is sufficient clearance between the bore and the shaft to allow the shaft to move radially within the bore. 
     In some embodiments, the toothbrush is configured so that when the toothbrush is in use, the motion of the toothbrush head is determined by a fluctuating sticking and slipping of a surface of the toothbrush head on a surface of the drive mechanism. 
     In some cases, the cleaning elements include bristles. In some embodiments, the cleaning elements include bristle tufts. 
     In another aspect, the invention features a method of brushing the teeth of a mammal. The method includes providing a power toothbrush that has a handle, a toothbrush head extending from the handle and carrying a plurality of cleaning elements, and a drive mechanism that causes the toothbrush head to move. The toothbrush is configured so that the toothbrush head will move in a substantially random path when the drive mechanism is actuated and the cleaning elements are brought into contact with a user&#39;s teeth. The method further includes contacting the teeth with the cleaning elements while the drive mechanism is actuated. 
     In another aspect, the invention features a power toothbrush including a handle, a toothbrush head extending from the handle and carrying a plurality of cleaning elements, and a drive mechanism. The drive mechanism is constructed to drive the toothbrush head in an orbital motion about an axis spaced from the axis of the toothbrush head. The drive mechanism includes a bevel gear. The toothbrush head is mounted on a shaft that extends through a bore defined by the bevel gear. The shaft is mounted to spin freely within the bore. 
     In some embodiments, the shaft is disposed at an angle with respect to a center axis of the bevel gear. In some cases, the bore is offset from a center axis of the bevel gear. 
     In another aspect, the invention features a power toothbrush including a handle, a toothbrush head extending from the handle and carrying a plurality of cleaning elements, and a drive mechanism that is constructed to cause the toothbrush head to move. The drive mechanism drives the toothbrush head in an orbital motion. 
     In some embodiments, the orbital motion is about an axis spaced from the axis of the toothbrush head. The drive mechanism can include a bevel gear. 
     In some cases, the toothbrush head is configured to move in a substantially random path when the drive mechanism is actuated and the cleaning elements are brought into contact with a user&#39;s teeth. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view in partial cross-section, with a portion of the housing removed, of an embodiment of a power toothbrush. 
         FIG. 2  is a side view in partial cross-section of an embodiment of a brush head of the power toothbrush shown in  FIG. 1 . 
         FIG. 2A  is similar to  FIG. 2 , but shows the brush head in operation without a load (i.e., not contacting the teeth). 
         FIG. 3  is similar to  FIG. 2 , but shows the brush head in operation with a load applied (i.e., contacting the teeth). 
         FIG. 4  is similar to  FIG. 3 , but shows movement of the brush head (indicated by phantom lines). 
         FIG. 4A  is similar to  FIG. 4 , but shows the position of the brush head when the bevel gear has rotated 180° relative to its position in  FIG. 3  (shown in solid lines in  FIG. 4 ). 
     
    
    
     Other features and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a power toothbrush  10  includes a housing  12 , and a brushing portion  14  extending from the housing. The brushing portion  14  includes a shroud  13  and a toothbrush head  30  mounted within the shroud  13 . A drive shaft (not shown) is disposed within the housing, and is driven by a driving mechanism (e.g., an electric motor) to turn a gear  20 . Gear  20  in turn drives a bevel gear  22  which causes the toothbrush head  30  to orbitally rotate, as will be discussed below. Bevel gear  22  typically rotates at a velocity of about 750-2000 rotations per minute (RPM). 
     The toothbrush head  30  includes a spinning shaft  28 . One end of spinning shaft  28  is mounted to spin freely within a bore  202  in bevel gear  22 , and includes a cap  27  of greater diameter than the bore  202  to retain the spinning shaft  28  in the bore. Cap  27  is seated in a recess  29 . 
     The toothbrush head  30  includes a plurality of bristle tufts  32  mounted on a support member  34 , which is fixedly mounted on the other end of spinning shaft  28 . Although each tuft is shown as a solid mass in the drawings, the tufts are actually each made up of a great mass of individual plastic bristles. The bristles may be made of any desired polymer, e.g., nylon 6.12 or 6.10, and may have any desired diameter, e.g., 4-8 mil. The tufts are supported at their bases by the support member  34 , and may be held in place by any desired tufting technique as is well known in the art, e.g., hot tufting or a stapling process. The tufts have a length of between about 4 mm and about 12 mm, and preferably have a length of about 8 mm. 
     The support member  34  includes a lower portion  36 . The lower portion  36  has a diameter of between about 6 mm and about 18 mm, and preferably has a diameter of about 14 mm. One end of spinning shaft  28  is disposed within a bore  37  in lower portion  36 . 
     Referring also to  FIG. 2 , the brushing portion  14  further includes a resilient O-ring  38 , disposed between lower portion  36  and bevel gear  22 . The O-ring has a diameter that is approximately the same as that of lower portion  36 , for reasons that will be discussed below. Spinning shaft  28  is tilted at an angle  208  (e.g., five degrees) relative to a gear axis of rotation  210 . Because spinning shaft  28  is tilted at an angle, toothbrush head  30  is also tilted at an angle. The bevel gear  22  includes a counterbore  212 . The counterbore  212  is designed to cause O-ring  38  to be seated with its center axis disposed at the same angle as the center axes  207  of bore  202  and spinning shaft  28 . 
     Spinning shaft  28  is also located at an offset distance  200  relative to the center of bevel gear  22 . When toothbrush  10  is in operation, spinning shaft  28  and, therefore, toothbrush head  30  (which is mounted on spinning shaft  28 ), orbits about the axis of rotation  210  of bevel gear  22 . When a load is applied to the toothbrush head  30 , e.g., when the bristles contact a user&#39;s teeth, toothbrush head  30  will spin about axis  207  of spinning shaft  28 , as will be discussed below. As a result, when it is in use and under load, toothbrush head  30  moves in a path that includes both orbital and spinning motion. 
     Spinning shaft  28  extends through and spins freely within bore  202  in bevel gear  22 . The spinning shaft  28  does not fit tightly within bore  202 ; instead, there is clearance between spinning shaft  28  and the wall of bore  202 . Moreover, the cap  27  of shaft  28  can move freely within recess  29 . Because of the clearance between spinning shaft  28  and bore  202 , the shaft can move axially in response to pressure exerted on the upper surface  213  of tufts  32 , displacing cap  27  axially. These clearances also allow the toothbrush head  30  to pivot about the bore  202 . 
     When the brush is activated, centripetal force throws toothbrush head  30  outward to the greatest angle allowed by the clearances discussed above, i.e., an angle greater than angle  208 , typically about 7 degrees (angle A,  FIG. 2A ). In this position, the outer portion  37  of O-ring  38  is compressed by lower portion  36  of support member  34 . This compression results in friction which, in turn, effectively causes engagement of lower portion  36  with the surface of counterbore  212 . 
     Referring now to  FIG. 3 , when a toothbrush user places toothbrush  10  against her teeth, a force F is applied to toothbrush head  30 . Referring to  FIG. 2A , because it is tilted, toothbrush head  30  initially contacts the teeth at an angle. When a force F that is greater than the centripetal force is applied to toothbrush head  30 , toothbrush head  30  tries to right itself in response, and axis  207  of shaft  28  begins to move toward axis of rotation  210 , decreasing angle A. This movement of the shaft  28  disrupts the effective engagement between lower portion  36  and bevel gear  22 . The shaft  28  moves toward the axis of rotation  210  until shaft  28  is bound in bore  202 , and toothbrush head  30  is in the position shown in  FIG. 3 . In this position, the inner region  216  of O-ring  38  is compressed; i.e., the inner region  216  of the O-ring  38  is pinched between counterbore  212  and lower portion  36 . 
     The general motion of toothbrush head  30 , when it is contacting the teeth, is shown schematically in  FIG. 4 . The phantom lines in  FIG. 4  show the position of the head when the bevel gear has rotated 180 degrees, which is a mirror image about axis  210  of the initial position of the head, indicated by the solid lines in  FIG. 4 . The position of the entire brushing portion when the bevel gear has rotated 180 degrees from the position shown in  FIG. 3  is shown in solid lines in  FIG. 4A . Referring back to  FIG. 4 , because the toothbrush head  30  is tilted at an angle, as the toothbrush head  30  spins it rocks back and forth, so that the upper surface  213  of tufts  32  traces a cup-shaped pattern, indicated schematically by line C. Additionally, because the toothbrush head  30  rocks back and forth, the tufts  32  around the perimeter  31  of the toothbrush head move up and down over a distance D. 
     As long as no load is applied to toothbrush head  30 , the toothbrush head will orbit about axis  210  of bevel gear  22  at a constant velocity equal to that of bevel gear  22 . When an axial force is applied, toothbrush head  30  also begins to spin about its own axis  207 . Tilting of the toothbrush head toward the gear axis  210 , with constantly changing forces and binding of the O-ring, creates the effect of an eccentric weight, so that the head spins under load in a random motion. By “random”, we mean that during use of the toothbrush, toothbrush head  30  moves in a path that changes as a result of the changing force applied to the bristle tufts  32  when the tufts contact a user&#39;s teeth. Generally, the path changes constantly during brushing. This random motion allows the toothbrush user to more easily cover the surface of his teeth and the spaces in between his teeth, without having to intentionally exert an extra effort to achieve such coverage. A factor in the changing direction of the applied force is that the toothbrush  10  is not stationary in the user&#39;s hand. 
     The position of the force applied to the toothbrush head continuously changes during brushing, thus causing the binding and frictional forces to fluctuate. This fluctuation in turn causes a “stick and slip” contact between bevel gear  22  and lower portion  36  of support member  34 , transmitted by the O-ring  38 . This sticking and slipping occurs in a random, fluctuating manner, resulting in random motion of the toothbrush head  30 . 
     Referring back to  FIG. 2 , the randomness is increased by the offset distance  200  and the clearances discussed above, which cause spinning shaft  28  to exhibit a jiggling or wobbling motion when toothbrush  10  is in operation. If offset distance  200  were increased, the wobbliness of spinning shaft  28  would become more pronounced, since an increase in circumference of the orbit of rotation of toothbrush head  30  would lead to a corresponding increase in the velocity of toothbrush head  30 . 
     Other embodiments are possible within the scope of the invention. 
     In some cases, different bristle tufts  32  have a height differential. For example, the tufts around the perimeter of the toothbrush head may be shorter than the tufts at the center of the toothbrush head. 
     In some embodiments, the power toothbrush  10  does not have an O-ring. The O-ring could be replaced with a rubber flat washer or the bottom of  36  and/or top of  22  could be made of a material that has a rough surface or made of a molded elastomer. 
     Further embodiments are within the scope of the following claims.