Patent Publication Number: US-6334725-B1

Title: Drive transmitting apparatus and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive transmitting apparatus for selectively transmitting a driving force from a drive source to a driving member through clutch means and an image forming apparatus using such a drive transmitting apparatus. 
     2. Related Background Art 
     Among drive transmitting mechanisms for image forming apparatuses, there is a mechanism in which a partially non-toothed gear having a non-toothed portion is used as clutch means for effecting connection and disconnection of a driving force, as disclosed in Japanese Patent Application Laid-open No. 10-274312. According to this mechanism, in a normal condition, the non-toothed portion is opposed to a drive gear to block transmission of the driving force to the partially non-toothed gear, and, when the partially non-toothed gear is slightly rotated by trigger means such as a solenoid, the drive gear is engaged by the partially non-toothed gear, thereby transmitting the driving force to the partially non-toothed gear. When the partially non-toothed gear is rotated by one revolution, since the transmission of the driving force is blocked again by the non-toothed portion, this mechanism acts as a one revolution controlling clutch. 
     On the other hand, as disclosed in Japanese Patent Application Laid-open No. 9-141966, there is an apparatus in which a driving force is switched by connecting a disconnecting clutch means of a driving system by utilizing a movement of a carriage. In this apparatus, a pair of clutch gears having triangular teeth (ratchets) formed on opposed side surfaces and engageable with each other are provided, and, when one of the clutch gears is pushed toward the other clutch gear by the carriage, the triangular teeth are engaged by each other, thereby transmitting a driving force. According to this arrangement, a construction in which one of the clutch gears is pushed by using a solenoid is not required, and trigger for transmitting the driving force can be achieved by using the movement of the carriage itself, thereby reducing the cost. 
     However, in the above-mentioned conventional technique, when the drive gear begins to be engaged by the partially non-toothed gear, the tops of the teeth may abut against each other to cause poor engagement, with the result that noise may be generated or an out-of-phase condition of a motor may be caused. In the technique disclosed in Japanese Patent Application Laid-open No. 10-274312, although special tooth configurations in which inclined surfaces are formed on the teeth are adopted to avoid such inconvenience, it is difficult to set the optimum tooth configurations. 
     On the other hand, in the technique disclosed in Japanese Patent Application Laid-open No. 9-141966, as shown in FIG. 9, a trigger tooth portion  901   b  complementary to the non-toothed portion is provided aside the non-toothed portion  901   a  of the partially non-toothed gear  901 , and the drive gear  902  is opposed to the non-toothed portion  901   a  and a driven gear  903  is disposed in an engagement relationship to the trigger tooth portion  901   b.    
     The driven gear  903  has no self-driving ability and can be moved in a thrust direction so as to contact with and separate from the drive gear  902 . When the driven gear  903  is urged against the drive gear  902 , the opposed triangular teeth (not shown) engageable with each other are meshed with each other, thereby transmitting the driving force of the drive gear  902  to the driven gear  903 . As a result, the driving force from the drive gear  902  is transmitted to the partially non-toothed gear  901  through the driven gear  903 , thereby starting rotation of the partially non-toothed gear  901 . When the partially non-toothed gear  901  is rotated by a predetermined amount, the drive gear  902  is engaged by a toothed portion  901   c  of the partially non-toothed gear  901 , with the result that, even when the urging of the driven gear  903  against the drive gear  902  is released, the driving force can be transmitted. In this case, so long as the phases of the gear portions of the gears  902 ,  903  in a condition that the triangular teeth are engaged by each other are aligned with each other, since the tooth of the drive gear  902  is smoothly engaged by the toothed portion  901   c  of the partially non-toothed gear  901 , the tops of the teeth of both gears are prevented from abutting against each other to cause the poor engagement. 
     However, immediately before the partially non-toothed gear  901  is rotated by one revolution to return to its initial position again, when the driven gear  903  freely rotatable without transmission of the driving force due to disconnection of the triangular tooth from the triangular tooth of the drive gear  903  is engaged by the trigger tooth portion  901   b  again, the tops of the teeth of the driven gear  903  and the trigger tooth portion  901   b  may abut against each other to cause poor engagement. 
     In this case, so long as a condition that the driven gear  903  is urged against the drive gear  902  is maintained while the partially non-toothed gear  901  is rotated by one revolution, since the phases of the gears can be aligned even when the driven gear  903  and the trigger tooth portion  901   b  are engaged by each other again, this problem can be solved. However, meanwhile, the carriage must be retained in a predetermined position for urging the driven gear  903  against the drive gear  902 , thereby delaying the further recording operation. 
     SUMMARY OF THE INVENTION 
     The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a drive transmitting apparatus in which a positive switching operation can be achieved without noise and/or poor drive transmission from a drive source, and an image forming apparatus using such a drive transmitting apparatus. 
     Another object of the present invention is to provide a drive transmitting apparatus comprising an output gear having a non-toothed portion not including a predetermined number of teeth and an entirely toothed portion having no non-toothed portion in a tooth width-wise direction, an input gear disposed at a position where it can be opposed to the non-toothed portion of the output gear and rotated by a driving force from a drive source, a trigger gear meshed with the entirely toothed portion of the output gear and rotatable with respect to a rotary shaft and movable in a thrust direction so as to contact with and separate from the output gear, and engagement portions provided on opposed side surfaces of the input gear and the trigger gear and engageable with each other, and wherein, when the input gear and the trigger gear are engaged by each other through the engagement portions, the driving force from the drive source is selectively transmitted to a driving member through clutch means for synchronizing phases of the input gear and the trigger gear, and an image forming apparatus using such a drive transmitting apparatus. 
     A further object of the present invention is to provide a drive transmitting apparatus in which a positive switching operation can be achieved without noise and/or poor drive transmission from a drive source by providing a construction in which tops of teeth of an input gear and an output gear do not abut against each other by aligning phases of engagement portions of the input gear and a trigger gear, and an image forming apparatus using such a drive transmitting apparatus. 
     A still further object of the present invention is to provide a drive transmitting apparatus in which engagement portions of two gears are constituted by ratchets having relative symmetrical configurations and engageable with each other so that, when phases of two gears are aligned, a gap is created between the ratchets. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an ink jet printer according to a first embodiment of the present invention; 
     FIG. 2 is a schematic plan view of a sheet feeding mechanism; 
     FIGS. 3A,  3 B and  3 C are explanatory views for explaining a drive transmitting system of clutch means; 
     FIGS. 4A and 4B are development views of a gear train; 
     FIG. 5 is a schematic perspective view of a partially non-toothed gear; 
     FIGS. 6A,  6 B,  6 C and  6 D are explanatory views showing ON/OFF conditions of a clutch depending upon positions of a slider; 
     FIGS. 7A and 7B are explanatory views showing a relationship between an ASF-system output gear and an ASF-system clutch gear and an ASF-system clutch trigger gear; 
     FIG. 8 is a development view of a ratchet portion according to a second embodiment of the present invention; and 
     FIG. 9 is an explanatory view showing a conventional technique. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, an image forming apparatus using a drive transmitting apparatus according to an embodiment of the present invention will be explained with reference to the accompanying drawings. 
     [First Embodiment] 
     Here, an entire construction of the image forming apparatus will first be described, and then, the drive transmitting apparatus will be described. (Construction of image forming apparatus) 
     FIG. 1 is a perspective view showing an ink jet printer according to the first embodiment of the present invention, and FIG. 2 is a schematic plan view of a sheet feeding mechanism. 
     In FIGS. 1 and 2, sheet feeding means  100  serve to separate and feed sheets stacked on a stacking tray  101  one by one by rotating a sheet feeding roller  102 . The sheet fed by the sheet feeding means  100  is conveyed onto a platen  301  by a conveying roller  302  forming a part of conveying means. After recording is effected on the sheet by recording means  200 , the sheet is discharged out of the printer. 
     The recording means  200  according to the illustrated embodiment are of serial ink jet recording type in which a carriage  201  is reciprocally movable along a guide shaft  202  and an ink cartridge  203  integrally including a recording head and an ink tank is mounted on the carriage  201 . By discharging ink from the recording head in response to a shifting movement of the carriage  201 , an ink image is formed on the sheet (recording medium) conveyed to a recording area defined between the opposed carriage  201  and platen  301 . Incidentally, at an end of a shifting range of the carriage  201 , recovery means  500  for recovering an ink discharging function of the recording head are disposed in a confronting relation to the recording head. The recovery means  500  serve to maintain a good recording condition of the recording head by recovering ink clogging and have a cap and pumping means. Further, in place of the ink cartridge  203 , a recording head and an ink tank may be provided independently. 
     Incidentally, according to the illustrated embodiment, in an ink discharging arrangement, an electrical/thermal converter is energized in response to a recording signal to generate thermal energy by which film boiling is generated in the ink, and the recording is effected by discharging the ink from a discharge port of the recording head by growth and contraction of a bubble generated by the film boiling. Regarding representative construction and principle, it is preferable that a fundamental principle is used, for example, as disclosed in U.S. Pat. No. 4,723,129 or No. 4,740,796. Although this system can be applied to both so-called on-demand type and continuous type, particularly, the on-demand type is effective because, by applying at least one drive signal for giving abrupt temperature increase exceeding nucleate boiling and corresponding to recording information to the electrical/thermal converter opposed to the sheet and a liquid flow path holding liquid (ink), thermal energy is generated in the electrical/thermal converter to generate the film boiling on an acting surface of the recording head, thereby forming a bubble corresponding to the drive signal in the liquid. Due to the growth and contraction of the bubble, the liquid is discharged from the discharge port, thereby forming at least one liquid droplet. When the drive signal has a pulse shape, since the growth and contraction of the bubble can be effected promptly and properly, particularly excellent liquid discharging can be achieved. This is more preferable. 
     (Driving Force Transmitting Arrangement) 
     Next, a driving force transmitting arrangement for transmitting a driving force to the sheet feeding means  100  and the conveying means such as the conveying roller  302  will be described. 
     In the illustrated embodiment, a driving force from a pulse motor  305  as a drive source is selectively transmitted to the sheet feeding means  100 , conveying roller  302  and recovery means  500  through clutch means  600 . 
     As shown in FIG. 2, the driving force from the pulse motor  305  is transmitted to a conveying gear  303  secured to one end of the conveying roller  302  through a speed reduction gear  306 , thereby rotating the conveying roller  302 . Further, the driving force can be transmitted to the sheet feeding means  100  and the recovery means  500  by an LF-system output gear  304  secured to the other end of the conveying roller  302 . 
     Now, a construction of the clutch means  600  will be fully explained. FIGS. 3A to  3 C are explanatory views for explaining a drive transmitting system of the clutch means  600 , where FIG. 3A is a plan view, FIG. 3B is a schematic right side view and FIG. 3C is a schematic left side view. 
     A drive base  601  is provided with an LF-system transmission gear  602  for receiving a driving force from the LF-system output gear  304 , an ASF-system output gear  603  for transmitting the driving force to the sheet feeding means  100 , and a pump-type output gear  604  for transmitting the driving force to the pump means  503 , so that the driving force from the LF-system transmission gear  602  is appropriately connected to or disconnected from the sheet feeding means  100  and the pump means  503  through a clutch mechanism which will be described later. 
     A driving force switching operation is effected by the shifting movement of the carriage  201 . That is to say, normally, although the driving force of the pulse motor  305  is transmitted to only the conveying roller  302 , when the pulse motor  305  is driven in a condition that the carriage  201  is in a predetermined position, the driving force is transmitted to the sheet feeding means  100  or the pump means  503 , thereby driving the sheet feeding means or the pump means. 
     Next, a gear train for transmitting the driving force will be explained with reference to FIGS. 4A and 4B. Incidentally, FIGS. 4A and 4B are development views of the gear train. In FIGS. 4A and 4B, both ends of a transmission shaft  605  having a key way  605   a  are rotatably supported by the drive base  601 , and the LF-system transmission gear  602  and a pump transmission gear  606  are mounted on the both ends through key portions  602   a ,  606   a  (FIGS. 3B and 3C) so that these gears cannot be rotated and are fixed with respect to a thrust direction. 
     Further, a slide gear  607  is mounted on the transmission shaft  605  at a central portion thereof for movement in the thrust direction, and the slide gear cannot be rotated with respect to the transmission shaft  605  by the presence of a key portion but can be rotated together with the transmission shaft. When the slide gear  607  is in a predetermined position, the slide gear is engaged by an idle gear  608  which is attached to the drive base  601  through an idle gear shaft  609 . 
     Further, both ends of an ASF-system clutch shaft  610  having a key way  610 a are rotatably supported by the drive base  601 , and there are provided a switching gear  611  having two gear portions  611 a,  611 b, an ASF-system clutch trigger gear  612 , an ASF-system clutch gear  613  as an input gear, and a biasing lever  614  (FIGS.  3 A and  3 C). The switching gear  611  is rotated together with the ASF-system clutch shaft  610  by the presence of a key portion, and two gear portions  611   a ,  611   b  have the same module and the same number of teeth. The gear  611   a  is meshed with the idle gear  608 , and, as shown in FIG. 4B, the gear  611   b  is engaged by the slide gear  607  when the latter is shifted. 
     The ASF-system clutch gear  613  is also rotated together with the ASF-system clutch shaft  610  by the presence of a key portion. On the other hand, the ASF-system clutch trigger gear  612  can freely be rotated with respect to the ASF-system clutch shaft  610  and can be shifted in the thrust direction. The biasing lever  614  is also rotatably mounted on the clutch shaft to regulate the position of the ASF-system clutch gear  613  in the thrust direction (In FIGS. 4A and 4B, the ASF-system clutch gear  613  abuts against the biasing lever  614  (not shown) to further leftward movement of the clutch gear). 
     An ASF-system output gear  603  having two gear portions and a cam portion is rotatably supported by the drive base  601 . A gear  603   a  serves to transmit a driving force to the sheet feeding means  100  and is meshed with an ASF-system input gear  103  (FIG. 2) to serve to transmit the driving force to the sheet feeding roller  102  through  104 ,  105  (FIG.  2 ). A gear  603   b  is an output gear meshed with the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612 . 
     FIG. 5 is a schematic perspective view of the partially non-toothed gear. The gear  603   b  has a non-toothed portion  603   d  opposed to the ASF-system clutch gear  613  and obtained by cutting away several teeth with leaving a tooth width w′ with respect to an entire tooth width W. That is to say, the gear  603   b  has the non-toothed portion  603   d  obtained by cutting away several teeth in the tooth width-wise direction, and an entirely toothed portion  603   e  having no non-toothed portion. 
     The biasing lever  614  biased by a spring is engaged by a cam portion  603   c  to regulate the phase of the non-toothed portion  603   d  of the ASF-system output gear  603 . 
     On the other hand, the drive transmission to the pump means  503  is similar to the drive transmission to the sheet feeding means. Namely, the driving force from the LF-system transmission gear  602  is transmitted to the coaxial pump-system transmission gear  606 , and a pump-system clutch gear  630  is disposed to mesh with the pump-system transmission gear  606 . The pump-system clutch gear  630  is rotatably supported on a pump-system clutch shaft  631  having both ends supported by the drive base  601 , and, adjacent to the pump-system clutch gear  630 , a pump-system clutch trigger gear  632  is rotatably supported on the pump-system clutch shaft  631  for a shifting movement in the thrust direction. Similar to the ASF-system output gear  603 , the pump-system output gear  604  has a non-toothed portion  604   a  and an entirely toothed portion  604   c , and the non-toothed portion  604   a  is opposed to the pump-system clutch gear  630 . Further, a cam portion  604   b  of the pump-system output gear is engaged by biasing means (not shown) to regulate the phase of the non-toothed portion  604   a.    
     The slide gear  607  is positioned between regulating walls  616   a  and  616   b  of a slide holder  616  and is always biased toward the regulating wall  616   a  by a spring  617 . The slide holder  616  can be shifted along the transmission shaft  605  and the pump-system clutch shaft  631  so that a boss  616   c  can be engaged by a slider  619  (FIGS.  3 A and  3 B). That is to say, when the slider  619  is shifted, the slide holder  616  is also shifted, thereby shifting the slide gear  607 . 
     The shifting movement of the slider  619  is effected by the shifted carriage  201  abutting and pushing the slider. During the recording operation, the slider  619  and the carriage  201  are not engaged by each other, but, when the sheet feeding operation or the recovery operation is required, the slider  619  is shifted to a predetermined position by the shifting movement of the carriage. 
     FIGS. 6A to  6 D show ON/OFF conditions of the clutch depending upon positions of the slider, and particularly FIG. 6A shows a normal conveying position. In this case, the clutch of the sheet feeding means and the clutch of the pump are both in an OFF condition, and only the conveying roller  302  is driven by the pulse motor  305 . 
     In a first feeding position, as the slider  619  is shifted to a position shown in FIG. 6B, a boss  620   a  of a first trigger lever  620  is rotated along a cam portion  619   a  of the slider  619 . The rotation of the first trigger lever  620  acts on a second trigger lever  622  through a trigger spring  621 , with the result that the ASF-system clutch trigger gear  612  is pushed by a boss  622   a  of the second trigger lever  622 . 
     A compression spring  623  is disposed between the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  to bias these gears away from each other. However, since a spring force of the trigger spring  621  is greater than a spring force of the compression spring  623 , the ASF-system clutch trigger gear  612  is shifted toward the ASF-system clutch gear  613  in the thrust direction, with the result that a ratchet portion  612   a  as an engagement portion formed on a side surface of the ASF-system clutch trigger gear  612  is engaged by a ratchet portion  613   a  as an engagement portion formed on a side surface of the ASF-system clutch gear  613 . 
     A displacement amount of the second trigger lever  622  is set to be greater than a displacement amount of the ASF-system clutch trigger gear  612 , and a difference in displacement amount is absorbed by the trigger spring  621 . Thus, even if the position of the slider  619  is slightly changed due to dimensional errors of parts, the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  can positively be engaged by each other. 
     In a second feeding position, the slider  619  is shifted to a position shown in FIG. 6C, and, similar to the first feeding position, the ratchet portions  613   a ,  612   a  of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are maintained in the engaged condition. However, the slide gear  607  is shifted by the shifting movement of the slide holder  616 , with the result that, as shown in FIG. 4B, the slide gear is disengaged from the idle gear  608  and is engaged by the gear portion  611   b  of the switching gear  611 . As a result, in the drive transmitting system, since the idle gear  608  is skipped, the rotational direction of the sheet feeding roller with respect to the conveying roller  302  is reversed in comparison with the first feeding position. That is to say, in the first feeding position, when the conveying roller  302  is rotated to feed the sheet in the normal or forward direction, the sheet feeding roller  102  is also rotated to feed the sheet in the normal direction; whereas, in the second feeding position, when the conveying roller  302  is rotated to feed the sheet in the reverse direction, the sheet feeding roller  102  is rotated to feed the sheet in the normal direction. 
     When the slider  619  is shifted to a position shown in FIG. 6D, a pump position is obtained. In this position, since the boss  620   a  of the first trigger lever  620  is dropped along the cam portion  619   a , the ASF-type clutch trigger gear  612  is separated from the ASF-system clutch gear  613  by the compression spring  623 , thereby achieving the clutch OFF condition. On the other hand, by the shifting movement of the slide holder  616 , a pump-system trigger rod  635  pushes the pump-type clutch trigger gear  632  through a spring  634 . As a result, ratchet portions  630   a ,  632   a  as engagement portions of the pump-system clutch gear  630  and the pump-system clutch trigger gear  632  are engaged by each other, thereby achieving the clutch ON condition. Also in this case, a pushing amount of the pump-system trigger rod  635  is set to be greater than a displacement amount of the pump-system clutch trigger gear  632 , and a difference therebetween is absorbed by the spring  634 . Thus, even if the position of the slider  619  is slightly changed due to dimensional errors of parts, the pump-system clutch gear  630  and the pump-system clutch trigger gear  632  can positively be engaged by each other. 
     Now, further detailed explanation is made with reference to the clutch means (first clutch means) of the sheet feeding means as an example. Incidentally, since the clutch means (second clutch means) of the pump is similar, explanation thereof will be omitted here. 
     As shown in FIG. 7A, since the ASF-system clutch gear  613  is opposed to the non-toothed portion  603   d  of the ASF-system output gear  603 , even when the ASF-system clutch gear  613  is rotated together with the ASF-system clutch shaft  610 , the driving force is not transmitted to the ASF-system output gear  603 . On the other hand, as shown in FIG. 7B, although the ASF-system clutch trigger gear  612  is always engaged by the ASF-system output gear  603 , since the ASF-system clutch trigger gear  612  can freely be rotated with respect to the ASF-system clutch shaft  610 , even when the ASF-system clutch shaft  610  is rotated, the ASF-system clutch trigger gear  612  is maintained in the stopped condition. In this case, the cam surface  603   c  of the ASF-system output gear  603  is pushed by the biasing lever  614 , thereby preventing inadvertent rotation of the gear (refer to FIG.  3 C). 
     Further, the ratchet portions  613   a ,  612   a  engageable with each other are symmetrically formed on inner surfaces of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  (the ratchet portion  613   a  is formed on a rear surface of the ASF-system clutch gear  613  shown in FIG. 7A) so that, in the condition (clutch ON condition) that the ratchet portions are engaged by each other, when the ASF-system clutch shaft  610  is rotated, the ASF-system clutch gear  613  is rotated to rotate the ASF-system clutch trigger gear  612  through the ratchet portions. As a result, since the ASF-system output gear  603  starts to be rotated, the phase of the non-toothed portion is deviated, thereby engaging the gear  603   b  and the ASF-system clutch gear  613  with each other. Thereafter, if the ASF-system clutch trigger gear  612  is separated, the driving force can be transmitted to the ASF-system output gear  603  only by the ASF-system clutch gear  613 . And, when the ASF-system output gear  603  is rotated by one revolution to return the non-toothed portion to the initial phase, the drive transmission is automatically disconnected. 
     According to this, so long as the phases of the gears and ratchet portions  613   a ,  612   a  of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are aligned (i.e., so long as the phases of teeth of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are synchronized when the ratchet portions  613   a ,  612   a  are engaged by each other), since the ASF-system clutch gear  613  and the ASF-system output gear  603  start to be engaged by being guided by the entirely toothed portion  603   e  (having the tooth width W′) of the ASF-system output gear  603  (i.e., by rotating the ASF-system output gear  603  by transmitting the driving force to the entirely toothed portion  603   e  engaged by the ASF-system clutch trigger gear  612  ratchet-connected to the ASF-system clutch gear  613 ), a problem that tops of the teeth of the gears abut against each other to cause poor engagement can be eliminated, and, further, since the ASF-system clutch trigger gear  612  is always engaged by the ASF-system output gear  603 , the tops of the teeth do not, of course, abut against each other. 
     Accordingly, problems regarding noise and out-of-phase of motor can be eliminated, and the positive switching operation can be achieved. Further, since the pushing of the ASF-system clutch trigger gear  612  by means of the carriage  201  only requires a minimum time until the ASF-system clutch gear  613  and the ASF-system output gear  603  are engaged by each other, it is not required that the carriage  201  remains in the trigger position until the ASF-system output gear  603  is rotated by one revolution. Thus, the recording operation is not delayed. 
     [Second Embodiment] 
     Next, as a second embodiment of the present invention, a construction of the drive transmitting apparatus for effecting the drive switching more positively will be explained. Incidentally, here, only constructions different from those in the first embodiment will be explained and the same constructions will be omitted from explanation. 
     In the first embodiment, an example that the ASF-system clutch gear  613  and the ASF-system output gear  603  start to be engaged smoothly by aligning the phase of the gears in the condition that the ratchets of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are engaged by each other was explained. 
     However, immediately after, there is a duration in which both the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are engaged by the gear  603   b  of the ASF-system output gear. In this case, if the phases of the gears and ratchets of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are deviated and the deviated amount is greater than backlash, three gears may be strongly urged against each other to increase rotational load extremely or three gears may be strongly engaged by each other to prevent rotations thereof. Furthermore, the ASF-system clutch trigger gear  612  may not be separated only by the force of the compression spring  623 . 
     Thus, it is required that a dimensional relationship between the gears and the ratchets be governed severely. However, in the second embodiment, as shown in FIG. 8 which is a development view of the ratchets, by setting so that a gap is created between the ratchets when tooth tips (marking portions) of the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are aligned, the above-mentioned problems can be eliminated. 
     That is to say, even if the phases of the ratchets and the tooth tips are slightly deviated due to the dimensional errors of parts, since such deviation can be absorbed by the gap, the gears do not abut against each other. On the other hand, however, when the ASF-system clutch gear  613  and the ASF-system clutch trigger gear  612  are operated in the condition that they are engaged by each other, the tooth tips thereof are deviated by an amount corresponding to the gap due to the set gap. Thus, when the ASF-system clutch gear  613  and the ASF-system output gear  603  start to be engaged by each other, deviation will occur. However, so long as the deviation amount is smaller than about ¼ of the circular pitch of the gear (dimension corresponding to ¼ of circumference of one gear), the tooth tips do not abut against each other to achieve the positive engagement. With this arrangement, without governing of the several dimensional errors of parts, since the positive switching operation can be effected, the manufacturing cost can be reduced. 
     [Third Embodiment] 
     In the above-mentioned embodiments, while an example that the ink jet recording system is used as the recording system of the image forming apparatus was explained, the recording system of the image forming apparatus using the above-mentioned drive transmitting apparatus is not limited to the ink jet recording system, but a thermal transfer recording system, a heat-sensitive transfer recording system or an impact recording system may be used. 
     Further, the above-mentioned drive transmitting system can be applied to other apparatus such as an image reading apparatus in which an original is fed to a reading position and information on the original is read by reciprocally shifting a carriage having a reading sensor thereon, as well as the image forming apparatus. 
     According to the above-mentioned embodiments explained in detail, by aligning the phases of the gears and the engagement portions of the input gear and the trigger gear, the tooth tips do not abut against each other in engagement between the input gear and the output gear. Thus, the positive switching of the driving force can be achieved without the noise and the poor drive transmission from the drive source (for example, out-of-phase of the motor). 
     Further, when the trigger gear is operated by the shifting movement of the carriage, since the pushing time of the trigger gear is minimum, the recording operation is not delayed.