Patent Publication Number: US-2006005331-A1

Title: Stroke transmission gear mechanism, and electric toothbrush having such a gear mechanism

Description:
The invention relates to a stroke transmission gear mechanism, in particular for an electric toothbrush, to translate an oscillating stroke motion of a drive rod into an oscillating amplitude-modified stroke motion of an output rod, with a transmission lever which is pivotable about a swivel bearing being provided between the two rods, both of which are linked to the transmission lever at different distances from the swivel bearing.  
      In such gear mechanisms, the problem lies in implementing the gear mechanism with as few articulating joints as possible to minimize susceptibility to malfunction. The gear mechanisms should also be extremely easy to manufacture to ensure suitability for mass production.  
      This problem is solved according to the invention by connecting the drive rod to the end of the transmission lever opposite from the swivel bearing via a hinge, and by holding the other end of the transmission lever in the swivel bearing in a displaceable manner.  
      Such a solution enables at least one of the rods to be directly connected to the transmission lever in an articulated manner, since the displaceable arrangement of the transmission lever allows it to yield when, in addition to the pivoting motion, a longitudinal motion is imposed on it by the stroke of the drive rod.  
      In particular, the drive rod may have a laterally stepped projection on its front end to which the transmission lever is pivotably mounted in a hinge. This also allows a configuration in the smallest possible space, since the transmission lever may be aligned approximately perpendicular to the drive rod and during its pivoting motion is therefore able to swing over the projection.  
      The displaceable bearing of the transmission lever may be implemented relatively easily by providing the other end of the transmission lever with a slot through which a pin projects which is stationarily mounted to the gear mechanism and which forms the pivot axis of the transmission lever. In this configuration the end of the transmission lever is thus designed as a fork which encloses the pin, so that during its pivoting motion the transmission lever can simultaneously undergo a longitudinal motion.  
      The output rod together with the drive rod is located in a stationary guide which allows only longitudinal motion but no transverse motion. For this reason a transmission rod connected to the output rod must be linked to the transmission lever via a hinge, and the transmission rod performs a pivoting motion corresponding to the up and down motions of the transmission lever.  
      In order to place the output rod in an oscillating rotational motion about its longitudinal axis, the invention provides that the transmission rod is connected to the output rod via a ball joint, and the output rod is guided into a slot running obliquely to the longitudinal axis of the output rod.  
      Provided that the load on the gear mechanism is not too great, as is the case for an electric toothbrush, for example, at least the transmission lever, the projection, and the transmission rod may be fabricated from plastic, and the hinges may be designed as film hinges.  
      The invention further relates to an electric toothbrush having a hand part provided with a drive, a drive pin which performs at least one axial stroke motion projecting at the slip-on end of the hand part, and a head part, which can be pushed onto the slip-on end of the hand part, in which a brush head which bears bristle tufts is mounted so that it can perform at least one back-and-forth stroke motion in the longitudinal direction of the head part, for which purpose the brush head is connected to the drive pin when the head part is pushed onto the hand part.  
      It is problematic that conventional drives which are intended to produce a rotational motion of the brush head about its vertical axis, for example, require a relatively large stroke of the drive pin. Therefore, such a hand part could not be readily combined with a head part, the brush head of which is intended to perform only a small stroke motion. Although it is conceivable that a separate hand part could be provided for such a head part, it is disadvantageous that the user would need several hand parts if the user wanted to use different brush heads for brushing the teeth.  
      This problem is solved according to the invention by providing a stroke transmission gear mechanism in the head part in the mechanical linkage between the drive pin and the brush head, the drive rod of the stroke transmission gear mechanism being connected to the drive pin, and by installing the stroke transmission gear mechanism in particular in such a way that a stroke reduction occurs.  
      This solution also has the advantage that the head part having a brush head which moves back and forth can be matched to existing hand parts having a specified stroke of the drive pins by merely adjusting the multiplication or reduction ratio of the stroke transmission gear mechanism, which is possible with minimal design engineering measures.  
      In principle, the stroke transmission gear mechanism may also be provided in an adapter which is first attached to the hand part.  
      Such toothbrushes are frequently provided with a replaceable head part to enable the toothbrush head to be exchanged from time to time for hygienic reasons. The invention therefore provides that the toothbrush comprises a hand part and a head part, an electric drive for the drive rod being furnished in the hand part, and that the gear mechanism in the head part is housed and mounted in the head part. Consequently, the gear mechanism described above is an integral component of the head part and is substituted by same. For this reason, everything must have a relatively simple design and be economical to manufacture. On the other hand, the requirements for durability of the gear mechanism are not very great, since it is assumed that the head part must be replaced after approximately 500 to 1000 tooth brushing operations. 
    
    
      The invention is explained in greater detail below with reference to one exemplary embodiment. The figures show the following:  
       FIG. 1  shows a side view of the gear mechanism according to the invention;  
       FIG. 2  shows an exploded illustration of the head part of an electric toothbrush;  
       FIG. 3  shows a longitudinal section through this head part; and  
       FIG. 4  shows an exploded illustration of the gear mechanism in a cylinder composed of two half-shells. 
    
    
      Reference is first made to  FIG. 1 , which shows the gear mechanism  1  according to the invention. A drive rod  2  and an output rod  3  are situated in the coaxial direction inside a housing  19 , which in this exemplary embodiment is formed by the head part of an electric toothbrush. Between the two mutually facing ends of the rods  2 ,  3  a cylindrical transmission lever  4  is located in the vertical position, which on one end has the shape of a fork  5  which is pushed onto a pin  6 .  
      The other end of the transmission lever  4  is beveled, and merges into an edge  8  which is connected via a film hinge  9  to a projection  10  which laterally protrudes from the drive rod.  
      Below the fork  5  a bar  11  is located which projects laterally from the transmission lever  4  and which is connected to a short transmission rod  13  via an additional film hinge  12 . The other end of the transmission rod  13  has a ball head  14  which is inserted or snapped into a ball socket  15  at the end of the output rod  3 .  
      Two sliding blocks  16 , which are guided into slots (not illustrated here) in the housing  19 , are located on the side of the output rod  3  and simultaneously impart an oscillating rotational motion to the output rod  3  on account of their longitudinal motion.  
      The gear mechanism operates as follows: The drive rod  2  is placed in a back-and-forth motion by a drive, not illustrated here. This motion is transmitted via the film hinge  9  to the transmission lever  4 , which imparts a pivoting motion about the pin  6 . The pivoting motion is transmitted to the transmission rod  13  and thus to the output rod  3 , the stroke of the latter being shorter than that of the drive rod  2  since the transmission rod  13  engages with the transmission level with a shorter stroke path length than does the drive rod  2 .  
       FIG. 2  shows an exploded illustration of the head part  20  of an electric toothbrush. This head part comprises the previously mentioned housing  19  in which the above-described gear mechanism  1  is situated. The output rod  3  has a projection in the form of a plate  21 , situated below an opening  22  in the housing  19 , on the top side of which a brush bristle holder  23  is attached. The underside of the housing  19  is closed off by a shell-like cover  24 . As seen in  FIG. 3 , guides  25  for the rods  2 ,  3  and for the plate  21  are located in the housing  19 .  
      The gear mechanism  1  is housed in a two-part cylinder  30  which can be inserted into the head part  20 . This cylinder is composed of two interlocked half-shells  31   a ,  31   b.    
      The cylinder  30  forms a guide for both the drive rod  2  and the output rod  3 . In addition, a slot  33  for the sliding block  16  provided as a transverse rod  34  is embedded at one end.  
      The cylinder  30  has two oppositely-situated openings  35 ,  36  for the transmission lever  4  which are formed by open-edge recesses in the edges of the half-shells  31   a ,  31   b.    
      At one opening, enlarged areas  37 ,  38  having oppositely-situated flush blind holes are located in which the pin  6  for the transmission lever  4  is inserted.  
      On the exterior of the cylinder  30  are located additional longitudinal bars  39  which are introduced into corresponding grooves in the head part  20 , thereby preventing the cylinder  30  from rotating at that point.  
     List of Reference Numbers  
     
         
           1  Gear mechanism  
           2  Drive rod  
           3  Output rod  
           4  Transmission lever  
           5  Fork  
           6  Pin  
           8  Edge  
           9  Film hinge  
           10  Projection  
           11  Bar  
           12  Film hinge  
           13  Transmission rod  
           14  Ball head  
           15  Ball socket  
           16  Sliding block  
           19  Housing  
           20  Head part  
           21  Plate  
           22  Opening  
           23  Brush bristle holder  
           24  Cover  
           25  Guide  
           30  Cylinder  
           31   a  Half-shell  
           31   b  half-shell  
           33  Slot  
           34  Transverse rod  
           35  Opening  
           36  Opening  
           37  enlarged area  
           38  Enlarged area  
           39  Longitudinal bars