Abstract:
An exemplary gear transmission device includes a driving assembly including a driving shaft, a shaft coupling, a circular driving gear, a resilient mechanism and a driven gear engaging with the driving gear. The shaft coupling is fixed to the driving shaft and rotatable in unison with rotation of the driving shaft. The circular driving gear substantially surrounds and is operatively coupled to the shaft coupling and rotatable under urging of the shaft coupling. The resilient mechanism is held between the driving gear and the shaft coupling and is elastically deformable in circumferential directions of the shaft coupling. When the driving gear moves axially and collides with the driven gear without meshing with the driven gear, the driving gear rotates slightly relative to the shaft coupling thereby elastically deforming the resilient mechanism and the driving gear reaches a position where it can mesh with the driven gear.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure generally relates to gear transmission devices, and particularly to a gear transmission device with a resilient connection between a driving gear and a driving shaft. 
     2. Description of Related Art 
     In order to adjust a camera of a video capturing device such as a video camera or camcorder, a driving gear of the video capturing device moves along a driving shaft of a driving assembly to engage with one or more driven gears. Generally, the driving gear is fixed to the driving shaft of the driving assembly, so that the driving gear cannot rotate relative to the driving shaft. When the driving gear engages with one of the driven gears, teeth of the driving gear are prone to interfere with teeth of the driven gear, which leads to the teeth of the driving gear striking against the teeth of the driven gear and can result in the teeth of the driving gear and/or the driven gear getting damaged or even destroyed. 
     Therefore, a need exists in the industry to overcome the described problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, all the views are schematic, and like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a perspective view of a gear transmission device of an exemplary embodiment of the disclosure. 
         FIG. 2  is a disassembled view of the gear transmission device of  FIG. 1 , but not showing a driven gear thereof. 
         FIG. 3  is an enlarged, perspective view of a driving gear of the gear transmission device of  FIG. 2 . 
         FIG. 4  is an enlarged, perspective view of a shaft coupling of the gear transmission device of  FIG. 2 . 
         FIG. 5  is an enlarged, assembled, front plan view of the driving gear, the shaft coupling and a resilient mechanism of  FIG. 2 , showing the resilient mechanism comprising a pair of bent, cylindrical helical springs. 
         FIG. 6  is a front plan view of the gear transmission device of  FIG. 1 , showing a state before engagement of the driving gear and the driven gear. 
         FIG. 7  is similar to  FIG. 6 , but showing a counterclockwise engagement state of the driving gear and the driven gear, with the driving gear having rotated counterclockwise relative to the shaft coupling to become engaged with the driven gear. 
         FIG. 8  is similar to  FIG. 6 , but showing a clockwise engagement state of the driving gear and the driven gear, with the driving gear having rotated clockwise relative to the shaft coupling to become engaged with the driven gear. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like reference numerals indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one” embodiment. 
     With reference to  FIGS. 1-2 , a gear transmission device  100  comprises a driving assembly  50  configured with a driving shaft  51 , a shaft coupling  30  secured to the driving shaft  51 , a circular driving gear  20  positioned around the shaft coupling  30 , a resilient mechanism  40  urged between the shaft coupling  30  and the driving gear  20 , and an arc-shaped driven gear  10 . The driving assembly  50  drives the driving gear  20  to move axially along the driving shaft  51  to engage with or disengage from the driven gear  10 , and drives the driving gear  20  to rotate and thus cause the driven gear  10  to move. The driving gear  20  comprises a plurality driving teeth  23 , and the driven gear  10  comprises a plurality of driven teeth  11 . When one of the driving teeth  23  contacts one of the driven teeth  11 , a resisting force generated between the driving teeth  23  and the driven teeth  11  compels the driving gear  20  to rotate a tiny angle relative to the shaft coupling  30 . As a result, the driving teeth  23  of the driving gear  20  do not strike against the driven teeth  11  of the driven gear  10 , and the driving gear  20  meshes with the driven gear  10  smoothly. 
     With reference to  FIG. 3  also, the driving gear  20  defines a hole  21  and comprises a pair of first positioning keys  22  respectively projecting from an inner surface  211  of the hole  21  toward a center of the hole  21 . In the embodiment, each of two opposite ends of each of the driving teeth  23  of the driving gear  20  comprises two half-portions of two corresponding chamfer edges  80 . That is, each of a plurality of the chamfer edges  80  is generally U-shaped, and forms one end of portions of two consecutive driving teeth  23 . Correspondingly, each of two opposite ends of each of the driven teeth  11  of the driven gear  10  comprises two half-portions of two corresponding chamfer edges  80 , as shown in  FIG. 1 . That is, each of a plurality of the chamfer edges  80  is generally U-shaped, and forms one end of portions of two consecutive driven teeth  11 . 
     With reference to  FIG. 4 , the shaft coupling  30  comprises a body  31  substantially in a shape of a hollow column (or hollow cylinder), a flange  32  located on one end of the body  31 , a second positioning key  33  projecting from an exterior surface  311  of the body  31 , and a stopper key  35  projecting from the exterior surface  311  of the body  31  and being opposite to the second positioning key  33 . In the embodiment, the flange  32  is substantially in the shape of a disk (or annulus) and has a common center with the body  31 . The stopper key  35  and the second positioning key  33  are located on a common diameter of the body  31 , at opposite sides of the exterior surface  311 . 
     In the embodiment, the shaft coupling  30  further comprises a pair of third positioning keys  34  respectively projecting from the exterior surface  311  of the body  31  and being opposite to each other. In assembly, the pair of third positioning keys  34  are respectively received in the hole  21  of the driving gear  20 , and abut the inner surface  211  of the hole  21 . This ensures stable radial positioning between the shaft coupling  30  and the driving gear  20 . 
     With reference to  FIG. 5  also, in the embodiment, the resilient mechanism  40  is a pair of bent, cylindrical helical springs. The driving gear  20  comprises a pair of first securing posts  221  respectively projecting from the pair of first positioning keys  22 , as shown in  FIG. 3 . Correspondingly, the shaft coupling  30  comprises a pair of second securing posts  331  projecting from two sides of the second positioning key  33 , as shown in  FIG. 3 . In assembly, the pair of cylindrical helical springs are bent and respectively received between the pair of first positioning keys  22  and the second positioning key  33 . Two ends of each bent, cylindrical helical spring are respectively coiled around a corresponding first securing post  221  and a corresponding second securing post  331 , as shown in  FIG. 5 . 
     In assembly of the gear transmission device  100 , the shaft coupling  30  is received in the hole  21  of the driving gear  20 . The pair of first positioning keys  22  respectively abut the exterior surface  311  of the body  31  of the shaft coupling  30 . The second positioning key  33  and the stopper key  35  of the shaft coupling  30  respectively abut the inner surface  211  of the hole  21  of the driving gear  20 . The flange  32  is stopped on one end of the driving gear  20 . With this assembled structure, a pair of arc-shaped positioning slots  60  are defined between the second positioning key  33  and the pair of the first positioning keys  22 . The pair of third positioning keys  34  are respectively received in the pair of positioning slots  60 . The resilient mechanism  40  is received in the pair of positioning slots  60 . That is, the pair of cylindrical helical springs are bent and respectively received in the pair of positioning slots  60 , and are urged between the pair of first positioning keys  22  of the driving gear  20  and the second positioning key  33  of the shaft coupling  30 , respectively. At same time, a pair of rotating gaps  70  are defined between the stopper key  35  and the pair of the first positioning keys  22 . Thereby, the driving gear  20  is elastically connected with the shaft coupling  30  along the circumferential direction, and spaces (i.e. circumferential widths) of the pair of rotating gaps  70  are held constant and cannot change without the application of an external force. The driving shaft  51  of the driving assembly  50  is inserted though the shaft coupling  30  and engages with the shaft coupling  30  firmly. 
     With reference to  FIGS. 6-8 , in use, the driving assembly  50  drives the driving shaft  51  to move axially, and thus drives the shaft coupling  30  and the driving gear  20  to move along an axis of the driving shaft  51  so that the driving gear  20  can engage with the driven gear  10 . When the driving teeth  23  of the driving gear  20  contact the driven teeth  11  of the driven gear  10 , the resisting force generated between the driving teeth  23  and the driven teeth  11  enables the driving gear  20  to rotate a tiny angle relative to the shaft coupling  30 , due to the existence of the pair of rotating gaps  70 , which leads to the driving gear  20  meshing with the driven gear  10  easily and smoothly. 
     In detail, if the driving assembly  50  drives the driving gear  20  to counterclockwise engage with the driven gear  10 , as shown in  FIG. 7 , the driving assembly  50  drives the shaft coupling  30  and the driving gear  20  to move along the axial direction thereof; then when some of the driving teeth  23  of the driving gear  20  contact some of the driven teeth  11  of the driven gear  10 , the resisting force generated between the driving teeth  23  of the driving gear  20  and the driven teeth  11  of the driven gear  10  compels the driving gear  20  to overcome the elasticity of the resilient mechanism  40  and rotate the tiny angle counterclockwise. In this process, a rearward one of the pair of rotating gaps  70  closes up somewhat, and a forward one of the pair of rotating gaps  70  opens somewhat. As shown in  FIG. 7 , the rearward one of the rotating gaps  70  is nearer to the driven gear  10 , and the forward one of the rotating gaps  70  is farther away from the driven gear  10 . As a result, the driving teeth  23  of the driving gear  20  counterclockwise engage with the driven teeth  11  of the driven gear  10 . Subsequently, the shaft coupling  30  rotates counterclockwise to cause the stopper key  35  of the shaft coupling  30  to move relative to the driving gear  20  in the forward rotating gap  70 . When the stopper key  35  resists the corresponding forward one of the first positioning keys  22  of the driving gear  20  neighboring the forward rotating gap  70 , the shaft coupling  30  continues to rotate to make the driving gear  20  rotate correspondingly. 
     If the driving assembly  50  drives the driving gear  20  to clockwise engage with the driven gear  10 , as shown in  FIG. 8 , when some of the driving teeth  23  of the driving gear  20  contact some of the driven teeth  11  of the driven gear  10 , the resisting force generated between the driving teeth  23  of the driving gear  20  and the driven teeth  11  of the driven gear  10  compels the driving gear  20  to overcome the elasticity of the resilient mechanism  40  and rotate the tiny angle clockwise. In this process, a rearward one of the pair of rotating gaps  70  closes up somewhat, and a forward one of the pair of rotating gaps  70  opens somewhat. As shown in  FIG. 8 , the rearward one of the rotating gaps  70  is farther away from the driven gear  10 , and the forward one of the rotating gaps  70  is nearer to the driven gear  10 . As a result, the driving teeth  23  of the driving gear  20  clockwise engage with the driven teeth  11  of the driven gear  10 . Subsequently, the shaft coupling  30  rotates clockwise to cause the stopper key  35  of the shaft coupling  30  to move relative to the driving gear  20  in the forward rotating gap  70 . When the stopper key  35  resists the corresponding forward one of the first positioning keys  22  of the driving gear  20  neighboring the forward rotating gap  70 , the shaft coupling  30  continues to rotate to make the driving gear  20  rotate correspondingly. 
     In the embodiment, when no external force is applied on the driving gear  20 , the size (i.e. circumferential width) of each of the pair of rotating gaps  70  is greater than half a thickness of any one of the driving teeth  23  of the driving gear  20 . This ensures that the driving gear  20  is capable of rotating the tiny angle relative to the shaft coupling  30  to mesh with the driven gear  10  successfully. 
     Although the features and elements of the present disclosure are described as embodiments in particular combinations, each feature or element can be used alone or in other various combinations within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.