Abstract:
A magnetic recording and reproduction apparatus includes a tape loading mechanism including a driving ring gear member, first and second ring gear members for shifting first and second tape guide posts, respectively, and first, second, and third gear members engaging the driving ring gear member and the first and second ring gear members, respectively. Each of the first through third gear members includes a gear part and a cam part in the same plane. The cam part of the first gear member has an arcuate shape. The cam part of the second gear member engages the cam part of the third gear member so as to transmit rotation during the operation of the tape loading mechanism, and is pressed against the circumferential surface of the arcuate cam part of the first gear member in a state where the operation of the tape loading mechanism is completed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to magnetic recording and reproduction apparatuses, and more particularly to a magnetic recording and reproduction apparatus including a tape loading mechanism.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 1 is an exploded view of a tape loading mechanism  10  of a conventional magnetic recording and reproduction apparatus. The tape loading mechanism  10  includes a driving ring gear member  11 , an L ring gear member  20  having a tape guide pole  21 , an R ring gear member  30  having a tape guide pole  31 , and a gear mechanism  40 . The driving ring gear member  11 , the L ring gear member  20 , and the R ring gear member  30  are superimposed and supported so as to be rotatable independent of one another. Referring to FIGS. 2A through 2C, the gear mechanism  40  includes a gear member  41  that engages the driving ring gear member  11  shown in FIG. 1, a first gear member  50  that engages the gear member  41 , and a second gear member  60  that engages the first gear member  50 . The first gear member  50  engages the L ring gear member  20 , and the second gear member  60  engages the R ring gear member  30 .  
           [0005]    When the driving ring .gear member  11  is rotated counterclockwise by a motor, the gear member  41  is rotated. The rotation of the gear member  41  is transmitted to the first gear member  50  and further to the second gear member  60 . The rotation of the first gear member  50  is transmitted to the L ring gear member  20 , so that the L ring gear member  20 , together with the tape guide pole  21 , is rotated clockwise. The rotation of the second gear member  60  is transmitted to the R ring gear member  30 , so that the R ring gear member, together with the tape guide pole  31 , is rotated counterclockwise. As a result, a magnetic tape is pulled out to be wound around a rotary drum, thereby terminating tape loading.  
           [0006]    While the driving ring gear member  11  is rotated a predetermined angle, the rotation is transmitted to the gear member  41 , so that the gear member  41  is rotated. When the driving ring gear member  11  is rotated more than the predetermined angle, the rotation is prevented from being transmitted, so that the gear member  41  remains in a stationary state. While the gear member  41  is rotated a predetermined angle, the rotation is transmitted to the first gear member  50 , so that the first gear member  50  is rotated. When the gear member  41  is rotated more than the predetermined angle, the rotation is prevented from being transmitted, so that the first gear member  50  remains in a stationary state. The first and second gear members  50  and  60  are always engaged.  
           [0007]    As shown in FIGS. 2A through 2C, the gear member  41  has a cam part  41   a  disposed on a gear part  41   b . The first gear member  50  has a convex cam part  51   a  formed to project upward (as viewed in FIG. 2B) from a gear tooth  51   b   −1  of a gear part  51   b . The gear part  41   b  engages the gear part  51   b , and the cam part  41   a  and the cam part  51   a  are positioned at the same level.  
           [0008]    When tape loading is terminated, the gear mechanism  40  enters the state shown in FIG. 3A. In this state, as shown enlarged in FIG. 3B, the cam part  41   a  of the gear member  41  comes into contact with the convex cam part  51   a  of the first gear member  50 . A spring member (not shown in the drawings) exerts a turning force in the A 1  direction on the gear member  41  with the cam part  51   a  being pressed against the cam part  41   a  with a force f 1 .  
         SUMMARY OF THE INVENTION  
         [0009]    The demand for downsizing magnetic recording and reproduction apparatuses has brought about a demand that the gear mechanism  40  should have as thin a configuration as possible. In order to reduce the thickness of the gear mechanism  40 , it is required to reduce the gear member  41  and the first gear member  50  in thickness.  
           [0010]    The cam part  41   a  and the gear part  41   b  of the gear member  41  are disposed. at different levels, and the cam part  51   a  and the gear part  51   b  of the first gear member  50  are also disposed at different levels. Under the condition where there is limitation on the thickness of the gear member  41  and the first gear member  50 , the thickness (height) a of each of the cam parts  41   a  and  51 a is limited to small values. Further, the cam part  51   a  is pressed against the cam part  41   a  with the force f 1 . Therefore, there is a problem that the cam parts  41   a  and  51   a  are worn easily so as to shorten the useful life of the gear mechanism  40 . There is another problem that the cam part  51   a  easily disengages the cam part  41   a.    
           [0011]    Accordingly, it is a general object of the present invention to provide a magnetic recording and reproduction apparatus in which the above-described disadvantages are eliminated.  
           [0012]    A more specific object of the present invention is to provide a magnetic recording and reproduction apparatus including a gear mechanism having a longer useful life and increased reliability.  
           [0013]    The above objects of the present invention are achieved by a magnetic recording and reproduction apparatus, including: a tape loading mechanism including: a driving ring gear member; first and second ring gear members for shifting first and second tape guide posts, respectively; and first, second, and third gear members, the first gear member being rotatable by rotation transmitted from the driving ring gear member, and including a first gear part and a first cam part in a first single plane, the first cam part having an arcuate shape, the second gear member being rotatable by rotation transmitted from the first gear member to rotate the first ring gear member, and including a second gear part and a second cam part in a second single plane, the third gear member being rotatable by rotation transmitted from the second gear member to rotate the second ring gear member, and including a third gear part and a third cam part in a third single plane, the third cam part being shaped so as to be engageable with the second cam part of the second gear member, the first, second, and third single planes forming substantially a single plane, wherein the second cam part engages the third cam part so as to transmit rotation during an operation of the tape loading mechanism, and is pressed against a circumferential surface of the first cam part in a state where the operation of the tape loading mechanism is completed.  
           [0014]    According to the above-described magnetic recording and reproduction apparatus, the first gear member rotatable by rotation transmitted from the driving ring gear member includes a gear part and an arcuate cam part in the same plane. Further, the second gear member, which is rotated by rotation transmitted from the first gear member so as to rotate the first ring gear member, includes a gear part and a cam part in the same plane, and the third gear member, which is rotated by rotation transmitted from the second gear member so as to rotate the second ring gear member, includes a gear part and a cam part in the same plane, the cam part being shaped so as to be engageable with the cam part of the second gear member. Therefore, compared with the conventional configuration, in which the gear part and the cam part of the second gear member are disposed in different planes, the thickness of the cam part of the second gear member and the arcuate cam part of the first gear member against which the cam part of the second gear member is pressed may be increased. This may delay the development of frictional wear in the arcuate cam part of the first gear member and the cam part of the second gear member, so that the useful life of a gear mechanism incorporating such gear members can be extended. Further, the cam part of the second gear member does not disengage the arcuate cam part of the first gear member as easily as the conventional configuration, so that the reliability of the gear mechanism may be increased.  
           [0015]    The above objects of the present invention are also achieved by a magnetic recording and reproduction apparatus provided with a tape loading mechanism, including: first, second, and third gear members engaging first, second, and third ring gear members, respectively, so that rotation of the first ring gear member is transmitted to the second and third ring gear members via rotation of the first, second, and third gear members, whereby a tape may be selectively loaded and unloaded, the first ring gear member being a driving gear member, wherein: each of the first, second, and third gear members includes a gear part and a cam part formed in a single plane, the cam part of the first gear member having an arcuate shape; and the cam part of the second gear member engages the cam part of the third gear member while loading or unloading the tape, and is pressed against a circumferential surface of the cam part of the first gear member when the tape is loaded. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:  
         [0017]    [0017]FIG. 1 is an exploded view of a tape loading mechanism of a conventional magnetic recording and reproduction apparatus;  
         [0018]    [0018]FIGS. 2A through 2C are a top plan view, a front view, and a bottom plan view, respectively, of a gear mechanism of the tape loading mechanism of FIG. 1;  
         [0019]    [0019]FIGS. 3A and 3B are diagrams showing a state of the gear mechanism after tape loading has been completed;  
         [0020]    [0020]FIG. 4 is a perspective view of a magnetic recording and reproduction apparatus according to an embodiment of the present invention;  
         [0021]    [0021]FIG. 5 is a plan view of the magnetic recording and reproduction apparatus according to the embodiment of the present invention;  
         [0022]    [0022]FIG. 6 is a plan view of the magnetic recording and reproduction apparatus according to the embodiment of the present invention, showing a state in which tape loading has been completed;  
         [0023]    [0023]FIG. 7 is a perspective view of a tape loading mechanism and its peripheral support structure of the magnetic recording and reproduction apparatus according to the embodiment of the present invention;  
         [0024]    [0024]FIG. 8 is a front view of the tape loading mechanism of FIG. 7 according to the embodiment of the present invention;  
         [0025]    [0025]FIG. 9 is an exploded perspective view of the tape loading mechanism of FIG. 7 according to the embodiment of the present invention;  
         [0026]    [0026]FIGS. 10A through 10C are a top plan view, a front view, and a bottom plan view, respectively, of a gear mechanism of the magnetic recording and reproduction apparatus according to the embodiment of the present invention;  
         [0027]    [0027]FIG. 11 is an enlarged bottom plan view of the gear mechanism according to the embodiment of the present invention;  
         [0028]    [0028]FIGS. 12A through 12C are a perspective view of a gear member, an exploded perspective view of a first gear assembly, and an exploded perspective view of a second gear assembly, respectively, of the gear mechanism according to the embodiment of the present invention;  
         [0029]    [0029]FIGS. 13A through 15B are diagrams showing a series of rotation transmitting movements of the gear mechanism according to the embodiment of the present invention; and  
         [0030]    [0030]FIGS. 16A and 16B are diagrams showing a final state of rotation transmission of the gear mechanism according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    A description will now be given, with reference to the accompanying drawings, of an embodiment of the present invention.  
         [0032]    [0032]FIGS. 4 and 5 are diagrams showing the state of a magnetic recording and reproduction apparatus  100  according to the embodiment of the present invention in a stop mode. FIG. 6 is a diagram showing the state of the magnetic recording and reproduction apparatus  100  where tape loading is completed. The magnetic recording and reproduction apparatus  100  is a streamer employed, for instance, as external storage for a computer The magnetic recording and reproduction apparatus  100  includes: a holder  101  in which a tape cassette (not shown in the drawings) is inserted; a holder transporting mechanism  102  for transporting the holder  101  to a loading position; a tape loading mechanism  103  for pulling out a magnetic tape (not shown in the drawings) wound around the reels of the tape cassette; a rotary drum unit  104  around which the magnetic tape is wound a predetermined angle by the tape loading mechanism  103 ; reel driving mechanisms  105  and  106  for rotating the reels of the tape cassette; a pinch roller mechanism  107 ; and a main chassis  108  supporting these mechanisms.  
         [0033]    A description will be given of the tape loading mechanism  103 .  
         [0034]    Referring to FIGS. 7 through 9, a ring guide member  110 - 1  and guide shafts  110 - 2  and  110 - 3  are fixed to the center of the main chassis  108 . A driving ring gear member  111 , an L ring gear member  112 , and an R ring gear member  113  are superimposed on and supported by the ring guide member  110 - 1  and the guide shafts  110 - 2  and  110 - 3  so as to be rotatable independent of one another. A tape guide post unit  114  is attached to the R ring gear member  113 , and a tape guide post unit  115  is attached to the L ring gear member  112 .  
         [0035]    A gear mechanism  120  is provided on the main chassis  108 . The gear mechanism  120  includes a gear member  121  engaging the driving ring gear member  111 , a first gear assembly  130  engaging the gear member  121 , and a second gear assembly  140  engaging the first gear assembly  130 . The first gear assembly  130  engages the L ring gear member  112 , and the second gear assembly  140  engages the R ring gear member  113 .  
         [0036]    In addition to the gear assembly  120 , a gear member  150 , an intermittent gear member  151 , and an intermittent gear member  152  are disposed around the driving ring gear member  111  (FIG. 7).  
         [0037]    When a motor  260  is started, its rotation is transmitted through the gear member  150  to the driving ring gear member  111  so that the driving ring gear member  111  is rotated counterclockwise (in the B direction in FIG. 9). During the transmission, the rotation is decelerated. The rotation of the driving ring gear member  111  is transmitted to the intermittent gear member  151 , the gear member  121 , and the intermittent gear member  152  according to predetermined timing, so that the intermittent gear member  151 , the gear member  121 , and the intermittent gear member  152  are intermittently rotated. Rotating the intermittent gear member  151  causes the holder transporting mechanism  102  to operate to load the cassette tape. The gear member  121  is rotated in the C direction (FIG. 9). When the gear member  121  is rotated in the C direction, the first gear assembly  130  is rotated in the D direction (FIG. 9), so that the L ring gear member  112  is rotated in the F direction (FIG. 9) through the first gear assembly  130 . Simultaneously, the second gear assembly  140  is rotated in the E direction (FIG. 9), so that the R ring gear member  112  is rotated in the G direction (FIG. 9) through the second gear assembly  140 . As a result, the tape guide post units  115  and  114  are shifted as shown in FIG. 6 so as to pull out the magnetic tape from the tape cassette, and later-described torsion coil springs  135  and  145  (see FIGS. 12B and 12C) are twisted so as to fix the tape guide post units  115  and  114  to their respective final positions. Thus, the magnetic tape is loaded, wound over an angular range of approximately 220° around the rotary drum unit  104 . Rotating the intermittent gear member  152  causes the pinch roller mechanism  107  to operate so that a pinch roller  107   a  presses the magnetic tape against a capstan  107   b , thereby pinching the magnetic tape. The magnetic tape is driven, pinched and held by the pinch roller  107   a  and the capstan  107   b , so as to run back and forth along the rotary drum unit  104  so that information may be recorded on the magnetic tape.  
         [0038]    Next, a description will be given of the gear mechanism  120 .  
         [0039]    [0039]FIGS. 10A through 10C are a top plan view, a front view, and a bottom plan view, respectively, of the gear mechanism  120 . FIG. 11 is an enlarged version of FIG. 10C. FIG. 12A is a perspective view of the gear member  121 , FIG. 12B is an exploded perspective view of the first gear assembly  130 , and FIG. 12C is an exploded perspective view of the second gear assembly  140 . In FIGS. 10A and 10B, for convenience of description, the upper parts of the first and second gear assemblies  130  and  140  are omitted, and only the relevant parts thereof according to the present invention are shown.  
         [0040]    The gear mechanism  120  is provided for operating the tape loading mechanism  103 . Therefore, it is required that the rotation of the gear member  121  be intermittently transmitted to a later-described input-side gear member  132  of the first gear assembly  130 . That is, there should be a state where the gear member  121  rotates while the input-side gear member  132  is stopped. Further, it is also necessary that the rotation of the input-side gear member  132  be constantly transmitted to a later-described input-side gear member  142  of the second gear assembly  140 . Since the rotation of the gear member  121  should be transmitted intermittently to the input-side gear member  132 , the input-side gear member  132  preferably includes a cam part of some kind. In the illustrated embodiment, the input-side gear member  132  includes a cam part  132   b  (FIG. 11), which is disposed in the same plane as a gear part  132   a  thereof. This prevents the gear part  132   a  from being formed circumferentially over an angular range of 360°. In order to have the rotation of the input-side gear member  132  transmitted constantly to the input-side gear member  142  in this situation, a special device should be provided to the input-side gear member  142 . In consideration of the above-described situation, the gear mechanism  120  is configured as follows.  
         [0041]    The gear member  121  includes a gear part  121   a  and a cam part  121   b  disposed in the same plane S 1  and a gear part  121   c  and an arcuate cam part  121   d  disposed in the same plane S 2  below (in FIG. 10B) the plane S 1 . As shown in FIG. 10A, the gear part  121   a  is formed over an angular range of α1 and the cam part  121   b  is formed over an angular range of α2. As shown in FIG. 11, the gear part  121   c  is formed over an angular range of α3 and the arcuate cam part  121   d  is formed over an angular range of α4. The gear part  121   a  and the cam part  121   b  work with the driving ring gear member  111 . The gear part  121   c  and the arcuate cam part  121   d  work with the first gear assembly  130 . Since the gear part  121   c  and the arcuate cam part  121   d  are positioned in the same plane S 2 , the gear part  121   c  and the arcuate cam part  121   d  each have a thickness b (FIG. 10B), which is approximately twice the thickness a of each of the cam parts  41   a  and  51   a  of the prior-art gear mechanism  40  shown in FIG. 2B. The arcuate cam part  121   d  is shaped so as to extend along a tip circle  160  (FIGS. 10C and 11) of the gear part  121   c.    
         [0042]    Further, the gear member  121  includes a concave cam part  121   e  (FIGS. 10C and 11) formed between the gear part  121   c  and the arcuate cam part  121   d . The concave cam part  121   e  is shaped so as to correspond to a later-described first cam part  163  of the cam part  132   b  of the input-side gear member  132 . An end face  121   f  (FIG. 11) of the arcuate cam part  121   d  opposes the concave cam part  121   e.    
         [0043]    Referring to FIG. 12B, the first gear assembly  130  includes an output-side gear member  134 , a bushing  131  caulked thereto, the input-side gear member  132 , a flange member  133 , and the aforementioned torsion coil spring  135 . The input-side gear member  132  and the flange member  133  are superimposed to be fitted with the bushing  131 . The torsion coil spring  135  is provided between the input-side gear member  132  and the output-side gear member  134 . The input-side gear member  132  has substantially the same thickness b (FIG. 10B) as the gear part  121   c.    
         [0044]    As shown in FIG. 11, the input-side gear member  132  includes the gear part  132   a  formed over an angular range of α10 and the cam part  132   b  formed over an angular range of α11. The gear part  132   a  and the cam part  132   b  are disposed in a single plane that is substantially the same as the plane S 2  (see FIG. 10B). Reference numeral  161  denotes the tip circle of the gear part  132   a  and reference numeral  162  denotes the root circle of the gear part  132   a . The cam part  132   b  includes the projecting first cam part  163  formed over an angular range of α12 and a concave second cam part  164  formed over an angular range of α13. The first and second cam parts  163  and  164  are adjacent to each other. The first cam part  163  includes a convex cam part  163   a  projecting from the tip circle  161  and a cam part  163   b  formed along the tip circle  161 . The second cam part  164  includes a recess formed between the gear part  132   a  and the first cam part  163 . The second cam part  164  further includes a concave cam part  164   a , a convex cam part  164   c , and a concave cam part  164   b  that are formed at the bottom of the recess. The concave cam parts  164   a  and  164   b  are formed inside the root circle  162 . The crest part of the convex cam part  164   c  is formed along the root circle  162 .  
         [0045]    Referring to FIG. 12C, the second gear assembly  140  includes an output-side gear member  144 , a bushing  141  caulked thereto, the input-side gear member  142 , a flange member  143 , and the aforementioned torsion coil spring  145 . The input-side gear member  142  and the flange member  143  are fitted with the bushing  141 . The torsion coil spring  145  is provided between the input-side gear member  142  and the output-side gear member  144 . The input-side gear member  142  has substantially the same thickness b (FIG. 10B) as the gear part  132   a.    
         [0046]    As shown in FIG. 11, the input-side gear member  142  includes a gear part  142   a , a cam part  142   b , and a gear part  142   c  formed successively-over an angular range of α20, an angular range of α21, and an angular range of α22, respectively. The gear part  142   a , the cam part  142   b , and the gear part  142   c  are disposed in a single plane that is substantially the same as the plane S 2  (see FIG. 10B) Reference numeral  171  denotes the tip circle of the gear parts  142   a  and  142   c , and reference numeral  172  denotes the root circle of the gear parts  142   a  and  142   c . The cam part  142   b  includes a concave first cam part  173  formed over an angular range of α23 and a projecting second cam part  174  formed over an angular range of α24. The first and second cam parts  173  and  174  are adjacent to each other. The first cam part  173  is shaped so as to correspond to the first cam part  163  of the cam part  132   b  of the input-side gear member  132 . The first cam part  173  includes a recess formed between the gear part  142   a  and the second cam part  174 . The first cam part  173  further includes a concave cam part  173   a  formed inside the root circle  172  and a cam part  173   b  formed along the root circle  172 . The second cam part  174  is shaped so as to correspond to the second cam part  164  of the cam part  132   b  of the input-side gear member  132 . The second cam part  174  includes a convex cam part  174   b , a concave cam part  174   c , a convex cam part  174   d , and a concave cam part  174   e  that are formed circumferentially in sequence. The convex cam parts  174   b  and  174   d  project outward from the tip circle  171 . The bottoms of the concave cam parts  174   c  and  174   e  are formed along the tip circle  171 .  
         [0047]    The input-side gear member  132  of the first gear assembly  130  engages the intermittent gear member  121 , and the input-side gear member  142  of the second gear assembly engages the input-side gear member  132 .  
         [0048]    Referring again to FIGS. 10A through 10C, the rotation of the gear member  121  of 360° or less in the C direction is transmitted to the input-side gear member  132  and the rotation of the input-side gear member  132  of 360° or less in the D direction is transmitted to the input-side gear member  142 , so that the input-side gear member  142  rotates 360° or less in the E direction. Next, a description will be given of this operation. For convenience of the following description, the gear mechanism  120  is viewed from its bottom side.  
         [0049]    Initially, the gear mechanism  120  is in the state shown in FIG. 11 (or FIGS. 10A through 10C). The gear part  121   c  of the gear member  121  engages the gear part  132   a  of the input-side gear member  132  of the first gear assembly  130 . The gear part  132   a  of the input-side gear member  132  engages the gear part  142   a  of the input-side gear member  142  of the second gear assembly  140 .  
         [0050]    The rotation of the driving ring gear member  111  causes the gear member  121  to rotate approximately 270° in the C direction to the position shown in FIG. 16A via the states shown in FIGS. 13A through 15B, and is stopped at the position shown in FIG. 16A.  
         [0051]    [Transmission of Rotation from the Gear Member  121  to the Input-Side Gear Member  132 ] 
         [0052]    As shown in FIGS. 13A through 14B, the gear part  121   c  of the gear member  121  and the gear part  132   a  of the input-side gear member  132  engage each other so that the rotation of the gear member  121  is transmitted to the input-side gear member  132 . At the final stage, as shown in FIGS. 15A through 16A, the concave cam part  121   e  of the gear member  121  and the first cam part  163  of the cam part  132   b  of the input-side gear member  132  engage each other, and then, the end face  121   f  of the arcuate cam part  121   d  of the gear member  121  pushes the first cam part  163  out of the concave cam part  121   e . The rotation is thus transmitted.  
         [0053]    [Transmission of Rotation from the Input-Side Gear Member  132  to the Input-Side Gear Member  142 ] 
         [0054]    Initially, the gear part  132   a  of the input-side gear member  132  and the gear part  142   a  of the input-side gear member  142  engage each other so that the rotation of the input-side gear member  132  is transmitted to the input-side gear member  142 . Next, as shown in FIGS. 13A and 13B, the first cam part  163  engages the first cam part  173  so as to be fitted in and pulled out of the first cam part  173  so that the transmission of rotation from the input-side gear member  132  to the input-side gear member  142  continues. Next, as shown in FIGS. 14A and 14B, the second cam part  174  engages the second cam part  164  so as to be fitted in and pulled out of the second cam part  164  so that the transmission of rotation continues. Thereafter, as shown in FIGS. 15A through 16A, the gear part  132   a  and the gear part  142   c  engage each other so that the rotation of the input-side gear member  132  is transmitted to the input-side gear member  142 .  
         [0055]    Following is a description of the transmission of rotation by the first cam part  163  and the first cam part  173  and of the transmission of rotation by the second cam part  164  and the second cam part  174 . The rotation of the input-side gear member  132  is transmitted first by the first cam part  163  pushing the first cam part  173  first at the point P 1  shown in FIG. 13A and next at the point P 2  shown in FIG. 13B and then by the second cam part  164  pushing the second cam part  174  first at the point P 3  shown in FIG. 14A and next at the point P 4  shown in FIG. 14B.  
         [0056]    The formation of the projecting convex cam part  163   a  and the concave cam part  173   a  (see FIG. 11) ensures the formation of (or the engagement at) point P 2  (FIG. 13B). Further, the formation of the projecting convex cam part  174   b  and the concave cam part  164   a  (see FIG. 11) ensures the formation of (or the engagement at) point P 3  (FIG. 14A). Accordingly, the stable transmission of rotation using the first cam parts  163  and  173  and the second cam parts  164  and  174 , which have special tooth shapes, is ensured.  
         [0057]    At the final stage of the transmission of rotation, the torsion coil springs  135  and  145  are twisted, so that the rotational force in the reverse direction of D is generated in the input-side gear member  132 . As a result, as shown in FIG. 16B, the convex cam part  163   a  of the first cam part  163  is pressed against the arcuate cam part  121   d  of the gear member  121  with a force f 10 .  
         [0058]    The thickness b of the convex cam part  163   a  and the arcuate cam part  121   d  is larger than the thickness a of the cam parts  41   a  and  51   a  of the prior-art gear mechanism  40  shown in FIG. 2B. Therefore, the convex cam part  163   a  and the arcuate cam part  121   d  are less subject to frictional wear than conventionally, so that the gear mechanisms  120  may enjoy a longer useful life than conventionally. Further, the convex cam part  163   a  disengages the arcuate cam part  121   d  less easily than conventionally.  
         [0059]    In the case of tape unloading, the gear member  121  is rotated in the reverse direction of arrow C from the state shown in FIG. 16A, and the rotation of the gear member  121  and the rotation of the input-side gear member  132  are transmitted to the input-side gear member  132  and the input-side gear member  142 , respectively, in the reverse order of the above-described sequence in the case of tape loading through the states shown in FIGS. 15B, 15A,  14 B,  14 A,  13 B, and  13 A.  
         [0060]    The transmission of rotation from the input-side gear member  132  to the input-side gear member  142  using the first cam parts  163  and  173  and the second cam parts  164  and  174  is performed first by the second cam part  164  engaging and fitting with the second cam part  174  and next by the first cam part  163  fitting in and engaging the first cam part  173 .  
         [0061]    The present invention is not limited to the specifically disclosed embodiment, and variations and modifications may be made without departing from the scope of the present invention.  
         [0062]    The present application is based on Japanese priority application No. 2002-178242, filed on Jun. 19, 2002, the entire contents of which are hereby incorporated by reference.