Patent Publication Number: US-8109598-B2

Title: Image recording device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2008-104137, filed on Apr. 11, 2008. The entire subject matter of the application is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     Aspects of the present invention relate to an image recording device provided with a switch mechanism which switches a driving force between transmission gears connected to drive mechanisms by changing positions of switch gears connected to a motor. 
     2. Related Art 
     Conventionally, image recording devices, such as an inkjet printer, have been widely used. The inkjet printer records an image on a recording medium by ejecting ink in accordance with an input signal. More specifically, in the inkjet printer, ink is introduced to actuators in a recording head, and the ink is pressurized and ejected through the effect of deformation of the actuators or the effect of locally boiled ink by heating elements. 
     The inkjet printer ejects ink selectively from nozzles to form an image on the sheet of paper during a carrying process for carrying the sheet of paper from a paper supply tray to an output tray. The supply of the sheet of paper from the paper supply tray and the carrying of the sheet of paper along a sheet carrying path are performed by providing rollers, such as a supply roller and a carrying roller, to rotate while closely contacting the sheet of paper. In general, a motor, such as a DC motor or a stepping motor, is used as a driving source, and transmission of the driving force from the motor to the rollers is achieved through a transmission mechanism, such as a pinion gear or a timing belt. 
     There is a possibility that a faulty ejection condition occurs in the ejecting motion of the nozzles, for example, due to air bubbles caused in the nozzles or foreign material lodging in the nozzles. To prevent such a faulty ejection condition, a purge motion is executed in the printer. A maintenance unit for executing the purge motion includes a cap for covering the nozzles of the recording head, and a pump to depressurize the inside of the cap. The motor is also used for driving the pump and a cam for switching the status of an exhaust valve, and the above described transmission mechanism is used for transmitting the drive force from the motor to driving units. 
     Japanese Patent Provisional Publication No. 2007-90761 (hereafter, referred to as JP2007-90761A) discloses an image recording device provided with a driving force transmission switch unit for switching the driving force from a motor to driving units. The driving force transmission switch unit is configured to selectively transmit the driving force to the driving units. By this structure, it becomes possible to transmit the driving force from a single motor to a supply roller or a carrying roller during image formation, and to transmit the driving force to a maintenance unit during the purge operation. 
     More specifically, the image recording device disclosed JP2007-90761A is configured as follows. In the following, reference numbers in parentheses correspond to those indicated in JP2007-90761A. In the image recording device disclosed JP2007-90761A, a driving force from a single LF motor ( 42 ) is transmitted to a plurality of driving units through the driving force transmission switch unit ( 100 ). The driving force transmission switch unit ( 100 ) includes a single switch gear ( 102 ) and four types of transmission gears including an intermittent supply transmission gear ( 113 ), a continuous supply transmission gear ( 114 ), a lower stage supply transmission gear ( 121 ) and a maintenance transmission gear ( 115 ). By positioning a lever part ( 104   a ) to one of setting portions  111 ,  112  and  108 , the switch gear ( 102 ) engages with corresponding one of the transmission gears to transmit the driving force. The position of the lever part ( 104   a ) is set by movement of a carriage ( 13 ) in a main scanning direction in accordance with an operation mode. 
     Japanese Patent Provisional Publication No. HEI 8-174958 (hereafter, referred to as JP HEI 8-174958A) discloses an image recording device configured to have a switch gear, a transmission gear connected to a carrying driving unit, and a transmission gear connected to a purge driving unit. More specifically, in order to smoothly switch the switch gear between the transmission gear connected to the carrying driving unit and the transmission gear connected to the carrying driving unit, the motor is controlled to reciprocate and the switch gear is controlled to reciprocate in the same direction. By this structure, the switch gear is smoothly detached from one of the transmission gear and is smoothly engaged with another transmission gear. 
     SUMMARY 
     Among various types of image recording devices such as an inkjet printer, an image recording deice provided with a plurality of paper supply trays for convenience of uses are also widely used. In such an image recording device, the user is allowed to set a large amount of sheets of paper in one paper supply tray and to set another type of paper having a desired size in the other paper supply tray. In the image recording device provided with the plurality of paper supply trays, a plurality of supply rollers respectively corresponding to the plurality of paper supply trays are provided. 
     Image recording devices are provided with multiple functions particularly in recent years. Therefore, various types of driving units are provided for an image recoding device. If a plurality of driving units are provided in the image recoding device, a structure of a transmission mechanism for transmitting a driving force from a single motor to the plurality of driving units becomes inevitably complicated. Furthermore, the sequence of switch timing between the driving units becomes complicated. This might cause a problem that a time for switching a transmission gear to another desired transmission gear becomes too long. 
     If a plurality of motors are used, it is possible to form the transmission mechanism in a relatively simple structure. For example, the transmission mechanism may be configured such that a first switch gear connected to a first motor is positioned to be able to selectively engage with transmission gears of respective supply rollers, and that a second switch gear connected to a second motor is positioned to be able to selectively engage with transmission gears of carrying rollers and a pump of a maintenance unit. However, the switch gears and the transmission gears are not always located at positions where the switch gears are able to engage with respective transmission gears. For this reason, even if the switch gears are moved concurrently in a moving direction, each switch gear might not be able to properly engage with the transmission gear. 
     Furthermore, due to a surface pressure between gears provided between the driving unit and the transmission gear, the switch gear might become unable to move in the axial direction, and thereby the switch gear and the transmission gear might become unable to engage with each other. In these cases, the switch gear and the transmission gear may become able to engage with each other by controlling each motor to reciprocate as described in JP HEI 8-174958A. 
     However, if the plurality of motors are controlled to reciprocate in a careless way, each switch gear can not be switched between the transmission gears. For example, if a pair of gears are brought to a state of being able to engage with each other, the other pair of gears might become unable to engage with each other due to excessively increased rotation speed of the motor. Furthermore, even if the plurality of motors are alternatively driven in the state where switch gears engage with respective transmission gears, both of the switch gears are not able to move concurrently due to the surface pressure when one of the switch gears is stopped. In this case, each switch gear becomes unable to engage with the transmission gear. 
     Aspects of the present invention are advantageous in that an image recording device capable of engaging a plurality of switch gears with transmission gears quickly and reliably is provided. 
     According to an aspect of the invention, there is provided an image recording device, comprising: a first motor configured to be able to rotate in a first rotational direction and a second rotational direction different from the first rotational direction; a second motor configured to be able to rotate in the first rotational direction and the second rotational direction; a first switch gear that is rotated by receiving a driving force from the first motor; a second switch gear that is rotated by receiving a driving force from the second motor and is supported coaxially with respect to the first switch gear; a first transmission gear that is located to be able to engage with the first switch gear and transmits a driving force to a first driving unit; and a second transmission gear that is located to be able to engage with the second switch gear and transmits a driving force to a second driving unit. The first switch gear and the second switch gear are provided to engage with corresponding ones of the first transmission gear and the second transmission gear in accordance with movement of the first and second switch gears in an axial direction. The image recording device further comprises a control unit configured such that when the first switch gear and the second switch gear are moved in the axial direction, the control unit rotates one of the first and second motors by a first predetermined rotation amount, and starts the other of the first and second motors while the one of the first and second motors is rotated. The control unit rotates the other of the first and second motors by a second predetermined rotation amount. 
     In the above described configuration, an overlapping drive period in which the first and the second motors are driven concurrently can be secure. Therefore, it is possible to release a surface pressure acting on gears and, for at least one of the motors, it is possible to move the switch gear and the transmission gear to the state of being able to engage with each other at a low speed period of the corresponding motor (i.e., a state immediately after activation of the motor). Consequently, it becomes possible to engage each switch gear to a corresponding transmission gear rapidly and securely before the speed of each motor increases. 
     It is noted that various connections are set forth between elements in the following description. It is noted that these connections in general and unless specified otherwise, may be direct or indirect and that this specification is not intended to be limiting in this respect. Aspects of the invention may be implemented in computer software as programs storable on computer-readable media including but not limited to RAMs, ROMs, flash memory, EEPROMs, CD-media, DVD-media, temporary storage, hard disk drives, floppy drives, permanent storage, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
         FIG. 1  is a perspective view illustrating an outer appearance of an MFP (Multifunction Peripheral) according to an embodiment. 
         FIG. 2  is a cross sectional view illustrating an internal structure of a print unit provided in the MFP. 
         FIG. 3  is a perspective view of the internal structure of the print unit when viewed from the rear side. 
         FIG. 4  is a perspective view illustrating a drive switch mechanism provided in the MFP. 
         FIG. 5  schematically illustrates a structure of a gear unit and a transmission path. 
         FIGS. 6A to 6C  are explanatory illustrations for explaining positions of an input lever and motion of the gear unit. 
         FIGS. 7A and 7B  are explanatory illustrations for explaining malfunctions of the gear unit. 
         FIG. 8  is a block diagram of a motor control unit. 
         FIG. 9  is a flowchart illustrating a motor control process executed by the motor control unit. 
         FIG. 10  is a timing chart illustrating an operation state of an ASF motor and an LF motor. 
         FIG. 11  is a flowchart illustrating a first variation of the motor control process executed by the motor control unit. 
         FIG. 12  is a timing chart illustrating an operation state of the ASF motor and the LF motor during the motor control process shown in  FIG. 11 . 
         FIG. 13  is a flowchart illustrating a second variation of the motor control process executed by the motor control unit. 
         FIG. 14  is a timing chart illustrating an operation state of the ASF motor and the LF motor during the motor control process shown in  FIG. 13 . 
         FIG. 15  is a flowchart illustrating a third variation of the motor control process executed by the motor control unit. 
         FIG. 16  is a timing chart illustrating an operation state of the ASF motor and the LF motor during the motor control process shown in  FIG. 15 . 
         FIGS. 17A and 17B  are flowcharts illustrating a fourth variation of the motor control process executed by the motor control unit. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, an embodiment according to the invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a perspective view illustrating an outer appearance of an MFP (Multifunction Peripheral)  10  according to an embodiment.  FIG. 2  is a cross sectional view illustrating an internal structure of a print unit  11  provided in the MFP  10 .  FIG. 3  is a perspective view of the internal structure of the print unit  11  when viewed from the rear side. 
       FIG. 4  is a perspective view illustrating a drive switch mechanism  70 .  FIG. 5  schematically illustrates a structure of a gear unit  110  and a transmission path.  FIGS. 6A to 6C  are explanatory illustrations for explaining positions of an input lever  74  and motion of the gear unit  110 .  FIGS. 7A and 7B  are explanatory illustrations for explaining malfunctions of the gear unit  110 . 
       FIG. 8  is a block diagram of a motor control unit  130 .  FIG. 9  is a flowchart illustrating a motor control process executed by the motor control unit  130 .  FIG. 10  is a timing chart illustrating an operation state of an ASF motor  65  and an LF motor  66 . 
       FIG. 11  is a flowchart illustrating a first variation of the motor control process executed by the motor control unit  130 .  FIG. 12  is a timing chart illustrating an operation state of the ASF motor  65  and the LF motor  66  during the motor control process shown in  FIG. 11 . 
       FIG. 13  is a flowchart illustrating a second variation of the motor control process executed by the motor control unit  130 .  FIG. 14  is a timing chart illustrating an operation state of the ASF motor  65  and the LF motor  66  during the motor control process shown in  FIG. 13 . 
       FIG. 15  is a flowchart illustrating a third variation of the motor control process executed by the motor control unit  130 .  FIG. 16  is a timing chart illustrating an operation state of the ASF motor  65  and the LF motor  66  during the motor control process shown in  FIG. 15 . 
       FIGS. 17A and 17B  are flowcharts illustrating a fourth variation of the motor control process executed by the motor control unit  130 . 
     As shown in  FIGS. 1 and 2 , the MFP  10  includes the print unit  11  and a scanner unit  12  which are integrally formed. The MFP  10  has a print function, a scanner function, a copying function, and a facsimile function. The MFP  10  may be configured not to have the scanner function, the copying function and the facsimile function. For example, if the MFP  10  is configured not to have the scanner unit  12 , the MFP  10  is formed as a single-function device having only the print function. 
     In the MFP  10 , the print unit  11  is located on the lower side and the scanner unit  12  is located on the upper side. The print unit  11  records an image (including text) on a sheet of recording medium (e.g., a sheet of paper) in accordance with print data (including image data and text data) transmitted from an external computer. In this embodiment, the scanner unit  12  is formed as a flat bed scanner. 
     As shown in  FIG. 1 , the MFP  10  has a box shape whose width (indicated by an arrow  101 ) and the depth (indicated by an arrow  103 ) are larger than the height (indicated by an arrow  102 ). That is, the MFP  10  has a low-profile box shape. The outer shape of the MFP  10  is formed principally by a casing  15  of the printer unit  11  and a casing  16  of the scanner unit  16 . 
     The casing  15  of the printer unit  11  has an opening  13  on the front side. In the inside of the opening  13 , a first paper supply cassette  20  and a second paper supply cassette  21  are provided. The first and second paper supply cassettes  20  and  21  are mounted in a two layer structure in a vertical direction such that the first paper supply cassette  20  is located on the upper side and the second paper supply cassette  21  is located on the lower side. A top surface  22  of the first paper supply cassette  21  serves as an output tray. In this configuration, a sheet of paper supplied from the first paper supply cassette  21  or the second paper supply cassette  21  is subjected to an image formation process, and thereafter is ejected to the top surface  22  of the first paper supply cassette  20 . 
     On the upper front portion of the casing  15  of the print unit  11 , an operation panel  14  is provided. Through the operation panel  14 , a user is able to input various commands such as a command for controlling the print unit  11  or the scanner unit  12  to execute a desired operation. On the operation panel  14 , various types of buttons for user operations and a display for displaying various types of information including error information are provided. When the MFP  10  is connected to an external device, the MFP  10  is also able to operate in accordance with commands transmitted from the external device via communication software, such as a printer driver or a scanner driver. 
     As shown in  FIG. 2 , the print unit  11  is provided with the first and second paper supply cassettes  20  and  21 . The second paper supply cassette  21  is located at the bottom of the print unit  11 . The first paper supply cassette  20  is located on the upper side of the second paper supply cassette  21 . Each of the first and second paper supply cassettes  20  and  21  is connected to the top surface  22  of the first paper supply cassette  20  via a first paper carrying path  23  and a second paper carrying path  24 . The sheets of paper accommodated in the first paper supply cassette  20  are supplied one by one by a first supply roller  25 . The sheet of paper supplied from the first paper supply cassette  20  is guided, from the lower side to the upper side, through the first paper carrying path  23  in a form of a horizontally-oriented letter U, toward an image recordation unit  41 . After the image formation is executed on the sheet of paper at the image recordation unit  41 , the sheet of paper is ejected to the top surface  22  of the first paper supply cassette  20 . 
     The sheets of paper accommodated in the second paper supply cassette  21  are supplied one by one by a second supply roller  30 . The sheet of paper supplied from the second paper supply cassette  21  is guided, from the lower side to the upper side, through the second paper carrying path  24  in a form of a horizontally-oriented letter U, toward the image recordation unit  41 . After the image formation is executed on the sheet of paper at the image recordation unit  41 , the sheet of paper is ejected to the top surface  22  of the first paper supply cassette  20 . 
     The first paper supply cassette  20  is configured such that a rear part of a case thereof is opened (i.e., a rear side opening is formed) and a stack of sheets is accommodated in the inside thereof. In this embodiment, the first supply roller  25  contacts the top of the stacked sheets while being inserted into the inside of the first paper supply cassette  20  through the rear side opening. The first paper supply cassette  20  is able to accommodate various types of sheets of paper smaller than or equal to A3 size paper, such as A4 size, B5 size, and post card size. The top surface  22  of the first paper supply cassette  20  serving as an output tray on which the sheet of paper is ejected is located on the front side of the MFP  10 . 
     The second paper supply cassette  21  is configured such that a rear part of a case thereof is opened (i.e., a rear side opening is formed) and a stack of sheets is accommodated in the inside thereof. In this embodiment, the second supply roller  30  contacts the top of the stacked sheets while being inserted into the inside of the second paper supply cassette  21  through the rear side opening. The second paper supply cassette  21  is able to accommodate various types of sheets of paper smaller than or equal to A3 size paper, such as A4 size, B5 size, and post card size. 
     If an image recording device is configured to have a single paper supply cassette, in order to form an image on a sheet of paper having a size different from the size of a sheet of paper being accommodated in a paper supply cassette, the user is required to replace the sheet of paper accommodated in the cassette with a new sheet of paper having the different size. By contrast, since the MFP  10  according to the embodiment has two paper supply cassettes, the user is allowed to set sheets of paper having a certain size in one of the first and second paper supply cassettes  20  and  21  and sets sheets of paper having a different size in the other of the first and second paper supply cassettes  20  and  21 . Therefore, according to the embodiment, the above described problem can be solved. That is, the user is able to execute the image formation selectively on one of two types of sheets of paper without conducting troublesome work for replacing sheets of paper in a cassette with new sheets of paper. 
     The first supply roller  25  is located on the rear side of the first paper supply cassette  20  (i.e., on the left side on  FIG. 2 ). The first supply roller  25  feeds the sheet of paper stacked on the first paper supply cassette  20  to the first paper carrying path  23 . The first supply roller  25  is rotated while being applied a driving force in a clockwise (CW) direction from an ASF (Auto Sheet Feed) motor  65  provided in the print unit  11  (see  FIG. 5 ) via a gear transmission mechanism (not shown). The first supply roller  25  is pivotally supported at a tip of a first arm  26 . A proximal end of the first arm  26  is pivotally attached to a driving shaft  28  installed on the upper side of the first paper supply cassette  20 . Therefore, the first supply roller  25  is able to move in a vertical direction to contact or detach from the first paper supply cassette  20 . 
     The first arm  26  is rotated downward through its own weight or a spring (not shown) so that the first arm  26  is able to move upward or downward depending on the amount of the staked sheets of paper accommodated in the first paper supply cassette  20 . Consequently, the first supply roller  25  contacts the top of the sheets of paper stacked on the first paper supply cassette  20 . When the first supply roller  25  is rotated in this state, at least a sheet of paper on the top of the stacked sheets is supplied toward the first paper carrying path  23  due to friction between a surface of the first supply roller  25  and the sheet of paper. Even if a plurality of sheets of paper are supplied by the first supply roller  25  toward the first paper carrying path  23 , only one sheet of paper is sent out to the first paper carrying path  23  by the effect of a separation member provided on a tilting separation surface  20 A provided on the left side of the first paper supply cassette  20  (see  FIG. 2 ). 
     The second supply roller  30  is located on the rear side of the second paper supply cassette  21  (i.e., on the left side on  FIG. 2 ). The second supply roller  30  feeds the sheet of paper stacked on the second paper supply cassette  21  to the second paper carrying path  24 . The second supply roller  30  is rotated while being applied a driving force in a counterclockwise (CCW) direction from the ASF motor  65  (see  FIG. 5 ) via a gear transmission mechanism (not shown). The second supply roller  30  is pivotally supported at a tip of a second arm  31 . A proximal end of the second arm  31  is pivotally attached to a driving shaft  33  installed on the upper side of the second paper supply cassette  21 . Therefore, the second supply roller  30  is able to move in a vertical direction to contact or detach from the second paper supply cassette  21 . 
     The second arm  31  is rotated downward through its own weight or a spring (not shown) so that the second arm  31  is able to move upward or downward depending on the amount of the staked sheets of paper accommodated in the second paper supply cassette  21 . Consequently, the second supply roller  30  contacts the top of the sheets of paper stacked on the second paper supply cassette  21 . When the second supply roller  30  is rotated in this state, at least a sheet of paper on the top of the stacked sheets is supplied toward the second paper carrying path  24  due to friction between a surface of the second supply roller  30  and the sheet of paper. Even if a plurality of sheets of paper are supplied by the second supply roller  30  toward the second paper carrying path  24 , only one sheet of paper is sent out to the second paper carrying path  24  by the effect of a separation member provided on a tilting separation surface  21 A provided on the left side of the second paper supply cassette  21  (see  FIG. 2 ). 
     In this embodiment, the first supply roller  25  or the second supply roller  30  is rotated while being applied a driving force in a clockwise direction or in a counterclockwise direction transmitted form the ASF motor  65 . On a transmission path between the ASF motor  65  and the first supply roller  25  or the second supply roller  30 , a transmission switch mechanism, such as a one-way clutch or a planet gear, is provided. Therefore, when the ASF motor  65  is rotated in the clockwise direction, the driving force is transmitted only to the first supply roller  25  and transmission of the driving force to the second supply roller  30  is cut off. On the other hand, when the ASF motor  65  is rotated in the counterclockwise direction, the driving force is transmitted only to the second supply roller  30  and transmission of the driving force to the first supply roller  25  is cut off. 
     The first paper carrying path  23  is formed on the upper side at the tip of the first paper supply cassette  20 . The first paper carrying path  23  extends upward from the rear end of the first paper supply cassette  20 , turns toward the front side, extends from the rear side to the front side of the MFP  10  (i.e., toward the right side on  FIG. 2 ), and finally connects to the top surface  22  of the first paper supply cassette  20  via the image recordation unit  41 . That is, the first paper carrying path  23  is formed to have a shape of a horizontally-oriented letter U (see  FIG. 2 ). The first paper carrying path  23  is formed of an outer guide face and an inner guide face located to face with each other to have a predetermined interval, excepting a portion around the image recordation unit  41 . 
     The second paper carrying path  24  is formed on the upper side at the tip of the second paper supply cassette  21 . Similarly to the first paper carrying path  23 , the second paper carrying path  24  is formed to have a shape of a horizontally-oriented letter U (see  FIG. 2 ) so that the second paper carrying path  24  connects to the top surface  22  of the first paper supply cassette  20 . The second paper carrying path  24  is merged with the first paper carrying path  23  on the upstream side with respect to the image recordation unit  41 , and a single carrying path is formed on the downstream side with respect to a merging point. Similarly to the first paper carrying path  23 , the second paper carrying path  24  is formed of an outer guide face and an inner guide face located to face with each other to have a predetermined interval, excepting a portion around the image recordation unit  41 . 
     As shown in  FIG. 2 , the image recordation unit  41  is provided on the first paper carrying path  23 . The image recordation unit  41  forms an image on the sheet of paper being carrying along the first paper carrying path  23 . More specifically, the image recordation unit  41  includes a carriage  38  and a recording head  39  forming an image in an inkjet printing manner. 
     As shown in  FIG. 3 , a pair of guide rails  43  and  44  are installed on the upper side of the first paper carrying path  23 . On the upper side of the first paper carrying path  23 , the pair of guide rails  43  and  44  are positioned to have a predetermined interval in a paper carrying direction, and each of the guide rails  43  and  44  extends in a direction (indicated by an arrow  101  in  FIG. 3 ) perpendicular to the paper carrying direction. The guide rails  43  and  44  are installed in the casing  15  of the print unit  11 , and form a part of a frame supporting various components in the print unit  11 . The carriage  38  is provided to bridge the guide rails  43  and  44 , and is able to reciprocate in the direction perpendicular to the paper carrying direction. 
     The guide rail  43  located on the upstream side in the paper carrying direction has a plate-like shape having the size in the direction of the width of the first paper carrying path  23  (i.e., the size in the direction indicated by the arrow  101 ) longer than a reciprocating motion range of the carriage  38 . The guide rail  44  located on the downstream side in the paper carrying direction has a plate-like shape having the size in the direction of the width of the first paper carrying path  23  substantially equal to that of the guide rail  43 . 
     An edge of the carriage  38  on the upstream side in the paper carrying direction is mounted on the guide rail  43 , and an edge of the carriage  38  on the downstream side is mounted on the guide rail  44  so that the carriage  38  is able to slide along the lengthwise direction of the guide rails  43  and  44 . An edge  45  of the guide rail  44  on the upstream side in the paper carrying direction is formed to bend upward at substantially the right angle. The carriage  38  supported by the guide rails  43  and  44  slidably holds the edge  45  with a holding member, such as a pair of rollers. In this structure, the carriage  3   8  is positioned with respect to the paper carrying direction and is able to slide in the direction perpendicular to the paper carrying direction. 
     On the top surface of the guide rail  44 , a belt drive mechanism  46  is provided. In the belt drive mechanism  46 , a drive pulley (not shown) and a driven pulley  48  are provided at respective ends in the width direction of the first paper carrying path  23  (i.e., in the direction indicated by the arrow  101 ). A ring-shaped endless belt  49  provided with a teeth on its inner surface is hung to the drive pulley and the driven pulley  48 . It should be noted that the drive pulley hides behind the carriage  38 . 
     A driving force is applied to a shaft of the drive pulley from a CR motor (not shown), and the belt  49  rotates through rotations of the drive pulley. Although in this embodiment the endless belt  49  is used, a belt having ends configured such that the carriage  38  is fixed to the ends may be used in place of the endless belt  49 . 
     The guide rail  43  is provided with a lever guide  91 . It should be noted that the lever guide  91  is omitted in  FIG. 4  for the sake of simplicity. The lever guide  91  is fitted into a fitting hole (not shown) formed in the guide rail  43  on the side of a maintenance mechanism  55  to be fixed with respect to the guide rail  43 . The drive switch mechanism  70  is located under the lever guide  91 . The lever guide  91  is a plate-like member in which guide holes  95  are formed on its inner surface (see  FIG. 5 ). An input part  77  of an input lever  74  is inserted into the guide hole  95  from the lower side to protrude on the upper side of the guide rail  43 . The input part  77  inserted into the guide hole  95  is kept at a first drive transmission position PI at the inside edge of the guide hole  95  when no external force is applied to the input part  77 . 
     The carriage  38  is fixed to the endless belt  49  at the bottom surface of the carriage  38 . In this structure, in accordance with rotational motion of the endless belt  49  by the CR motor (not shown), the carriage  38  reciprocates on the guide rails  43  and  44  with respect to the edge  45 . Therefore, the recording head  39  mounted on the carriage  38  also reciprocates in the width direction of the paper carrying path  23  (i.e., in the direction indicated by the arrow  101 ). 
     As shown in  FIG. 3 , at an upstream edge of the carriage  38 , a guide member  92  is formed to protrude upward. The guide member  92  reciprocates in the lengthwise direction of the guide rail  43  together with the carriage  38 . In accordance with movement of the carriage  38 , the guide member  92  contacts the input part  77  (see  FIG. 4 ) protruding upward from the guide hole  95  (see  FIG. 5 ) of the guide rail  43 . Thus, the position of the input lever  74  can be changed. The position of the input lever  74  can be changed to a desired position by controlling the reciprocating motion of the carriage  38 . When the input lever  74  is set to a certain position (i.e., one of first to third drive transmission positions P 1 -P 3 ), a first switch gear  71  and a second switch gear  72  of the gear unit  110  are also set to respective positions. 
     As shown in  FIGS. 2 and 3 , under the first paper carrying path  23 , a platen  42  is provided to face the recording head  39 . The platen  42  is installed, within the reciprocating motion range of the carriage  38 , to extend over a central portion where the sheet of paper passes. The width (i.e., the length in the direction indicated by the arrow  101  in  FIG. 2 ) of the platen  42  is sufficiently larger than the maximum available paper size of the MFP  10 . The sheet of paper is held on the platen  42  to have a constant interval with respect to the recording head  39 . In this state, drops of ink ejected from the recording head  39  fall on the sheet of paper. 
     As shown in  FIG. 2 , on the upstream side of the image recordation unit  41  in the paper carrying direction  104 , a pair of rollers  60  and  61  (i.e., a carrying roller  60  and a pinch roller  61 ) are provided. The pinch roller  61  is positioned under the carrying roller  60  to contact and press the outer surface of the carrying roller  60 . The carrying roller is rotated continuously while being applied a driving force from a LF (Line Feed) motor  66  provided in the print unit  11 , or is driven intermittently at predetermined line feed widths. When the sheet of paper enters between the carrying roller  61  and the pinch roller  60 , the sheet of paper is carried to the platen  42  while being sandwiched between the carrying roller  60  and the pinch roller  61 . 
     On the downstream side of the image recordation unit  41  in the paper carrying direction  104 , an ejection roller  62  and a wheel  63  are provided. The wheel  63  is located on the upper side of the ejection roller  62  to contact and press the outer surface of the ejection roller  62 . Between the carrying roller  60  and the ejection roller  62 , a drive transmission mechanism, such as a gear, is provided. The ejection roller  62  is continuously rotated concurrently with the carrying roller  60  while being applied the driving force from the LF motor  66  via the drive transmission mechanism or is driven intermittently at predetermined line feed widths. The ejection roller  62  and the wheel  63  carry the sheet of paper to the top surface  22  of the first paper supply cassette  20  while sandwiching the sheet of paper therebetween. 
     As shown in  FIG. 3 , the maintenance mechanism  53  is positioned at one end in the width direction (the direction indicated by the arrow  101 ) of the platen  42 , and a flushing unit  56  is positioned at the other end in the width direction of the platen  42 . On  FIG. 3 , the maintenance mechanism  53  is provided at the left end portion, and the flushing unit  56  is provided at the right end portion. The flushing unit  56  is configured to receive waste ink ejected from the recording head  39  in the flushing ejection motion. In the flushing unit  56 , an ink absorption body, such as a sponge or felt, is provided. The ink ejected in the flushing ejection motion is absorbed by the ink absorption body, such as a sponge or felt. 
     The maintenance mechanism  55  is configured to keep the recording head  39  to constantly achieve optimum performance. More specifically, the maintenance mechanism  55  has a function of executing a negative-pressure purge motion to suck air bubbles or foreign material from nozzles of the recording head  39 , a function of executing a wiping motion of cleaning the nuzzle surface of the recording head  39  with a wiper, and a function of executing an evacuation motion of removing air bubbles in a sub-tank provided in the recording head  39 . The maintenance mechanism  55  has a cap  57  for covering the nuzzles of the recording head  39  or an exhaust hole of the recording head  39 . The cap  57  is moved up and down by a lift up mechanism  51  (see  FIG. 3 ) to contact or detach from the surface of the exhaust hole or the nozzle surface of the recording head  39 . The maintenance mechanism  55  has a suction pump  52  (see  FIG. 5 ), although it is not shown in  FIG. 3 . The suction pump  52  communicates with the cap  57  so that when the suction pump  52  is activated, the inside of the cap  57  is kept in a negative pressure state. When the suction pump  52  is activated in a state where the cap  57  contacts and covers the nozzles and the exhaust hole, air bubbles or foreign material is sucked and removed from the recording head. The suction pump  52  of the maintenance mechanism  55  is activated while being applied the driving force transmitted from the LF motor  66 . The lift up mechanism  51  is activated while being applied the driving force transmitted from the ASF motor  65 . That is, each of the suction pump  52  and the lift up mechanism  51  serves as a driving unit. As describe above, the maintenance motion for removing air bubbles and mixed ink from the recording head  39  and for preventing the recording unit  39  from drying is performed. 
     Hereafter, the drive switch mechanism  70  is described. The drive switch mechanism  70  serves to switch the driving force from the ASF motor  65  and the LF motor  66  between driving units including the first supply roller  25 , the second supply roller  30 , the suction pump  52 , and the lift up mechanism  51 . The drive switch mechanism  70  is located on the right side (i.e., on the left side on  FIG. 3 ) of the frame formed by the guide rails  44  and  45 . The drive switch mechanism  70  transmits the driving forces transmitted separately in two routs from the ASF motor  65  and the LF motor  66 , to the driving units selectively. 
     As shown in  FIGS. 4 and 5 , the drive switch mechanism  70  includes a gear unit  110  and a support frame  120  supporting the gear unit  110 . The gear unit  110  includes a first switch gear  71  and a second switch  72 . In the gear unit  110 , each of the first and second switch gears  71  and  72  is supported on a single support shaft  74  to be rotatable about a support shaft  73  and slidable on the support shaft  73  in the axial direction. It should be noted that the left side on  FIG. 5  corresponds to the inside of the MFP  10 . 
     As shown in  FIG. 5 , the driving force of the ASF motor  65  is transmitted to the first switch gear  71 . Therefore, the first switch gear  71  is rotated by the rotational driving force received from the ASF motor  65 . A series of gears may be used as a transmission mechanism for transmitting the driving force form the ASP motor  65  to the first switch gear  71 . In this case, the series of gears are provided between an output gear  75  and the first switch gear  71  to transmit the rotational driving force from the ASf motor  65  to the first switch gear  71 . Since the thickness (i.e., the length in the axial direction) of a transmission gear  67  in the series of gears is sufficiently larger than the sliding range of the first switch gear  71  along the support axis  73 , the first switch gear  71  and the transmission gear  67  are able to constantly engage with each other within the sliding range of the first switch gear  71 . That is, the first switch gear  71  is able to move along the axial direction of the support haft  73  while engaging with the transmission gear  67 . 
     The driving force of the LF motor  66  is transmitted to the second switch gear  72 . The second switch gear  72  is rotated by the driving force received from the LF motor  66 . As an example of a transmission mechanism for transmitting the driving force from the LF motor  66  to the second switch gear  72 , a transmission gear may be provided on a side of the carrying motor  60  to have a common axis with respect to the carrying roller  60  and to rotate concurrently with the carrying roller  60  (i.e., the transmission gear may be formed integrally with the carrying roller  60 ), and a series of gears including a plurality of gears may be provided to connect the transmission gear with the second switch gear  72 . An output gear  76  of he LF motor  66  engages with the other side of the carrying motor with a gear mechanism. When the driving force from the LF motor  66  is applied to the other side of the carrying roller  60 , the carrying roller  60  is rotated and the second switch gear  72  is rotated in accordance with the driving force of the LF motor  66 . Since the thickness (i.e., the length in the axial direction) of the transmission gear  68  in the series of gears is sufficiently larger than the sliding range of the second switch gear  72  along the support axis  73 , the second switch gear  72  and the transmission gear  68  are able to constantly engage with each other within the sliding range of the second switch gear  72 . That is, the second switch gear  72  is able to move along the axial direction of the support haft  73  while engaging with the transmission gear  68 . 
     Hereafter, the gear unit  110  is described. 
     As shown in  FIG. 5 , the gear unit  110  is configured such that a first coil spring  111  and a second coil spring  112  as well as the fist and second gears  71  and  72  and the input lever  74  are supported on the support shaft  73 . The first and second coil springs  111  and  112 , the first and second gears  71  and  72  and the input lever  74  are supported on the support shaft  73  to be slidable on the support shaft  73 . The support shaft  73  is supported horizontally by the support frame  120 . 
     The first switch gear  71  is positioned on the outer side (i.e., on the right side on  FIG. 5 ), and the second switch gear  72  is positioned on the inner side (i.e., on the left side on  FIG. 5 ). The axial direction of the support shaft  73  is equivalent to the reciprocating direction of the carriage  38 . By sliding the first switch gear  71  and the second switch gear  72 , the first switch ear  71  is selectively engaged with one of a first transmission gear  171  and a second transmission gear  172 . The second switch gear  72  is selectively set to one of a free state and an engaged state of being engaged with a third transmission gear  173 . 
     As shown in  FIG. 4 , each of the first and second switch gears  71  and  72  is configured such that an edge part in a radial direction is chamfered. Further, each of the transmission gears  171  to  173  is configured such that an edge part in a radial direction is chamfered, although they are not illustrated. The chamfering of these gears aims to ease the engagement between the first and second switch gear  71  and  72  and the transmission gears  171  to  173 . 
     The second switch gear  72  is provided with a cylinder part  79  extending toward the side of the first switch gear  71 . The cylinder part  79  is formed such that a tip end thereof contacts the first switch gear  71  so as to serve to keep the distance between the first switch gear  71  and the second switch gear  72  at a constant value. The cylinder part  79  further serves to transmit the pressing force of the second coil spring  112  to the first switch gear  71 . The size of the cylinder part  79  may be determined in accordance with the thicknesses of the transmission gears  171  to  173  and the number of transmission gears. 
     The input lever  74  is positioned on the outer side of the first switch gear  71  (i.e., on the right side on  FIG. 5 ). Through the effect of the input lever  74  and the lever guide  91 , the position of the first switch gear  71  is set to one of positions to be engaged with the first transmission gear  171  and the second transmission gear  172 , and the position of the second switch gear  72  is set to one of the free position and the position to be engaged with the third transmission gear  173 . That is, the input lever  74  and the lever guide  91  serve as a positioning unit. 
     As shown in  FIG. 5 , the input lever  74  has a cylindrical part  78  into which the support shaft  73  is fitted, and an input part  77  formed to protrude from the cylindrical part  78 . In a state where the gear unit  110  is mounted on the support frame  120 , the input part  77  of the input lever  74  is inserted into the guide hole  95  of the lever guide  95  through an opening  122  (which is described later). The cylindrical part  78  into which the support shaft  73  is fitted is able to slide in the axial direction and is rotatable about the support shaft  73 . When the cylindrical part  78  slides, the input part  77  slides in the axial direction. When the cylindrical part  78  rotates, the input part  77  rotates in the same rotational direction. 
     The first coil spring  111  is positioned on the outer side of the input lever  74  (i.e., on the right side on  FIG. 5 ). The second coil spring  112  is positioned on the inner side of the second switch gear  72  (i.e., on the left side on  FIG. 5 ). 
     In the sate where the gear unit  110  is mounted on the support frame  120 , each of the first coil spring  111  and the second coil spring  112  is in a compressed state. That is, each of the first and second coil spring  111  and  112  serves as a compression spring. 
     Each of the first and second coil springs  111  and  112  is provided to be able to expand and contract in the axial direction of the support shaft  73 . The input lever  74  is pressed by the first coil spring  111  toward the side of the first switch gear  71  (i.e., in the direction indicated by an arrow  85  in  FIG. 5 ). The second switch gear  72  is pressed by the second coil spring  112  toward the side of the first switch gear  71  (i.e., in the direction indicated by an arrow  86  in  FIG. 5 ). That is, the first switch gear  71  and the second switch gear  72  are pressed to approach with respect to each other by the two coil springs  111  and  112  which produce pressing forces in directions opposite to each other. In the state where the first switch gear  71  and the second switch gear  72  contact with each other by the pressing forces from the two coil springs  111  and  112 , the first and second switch gears  71  and  72  are able to rotate separately with respect to each other. 
     In this embodiment, the pressing force of the first coil spring  111  (i.e., the pressing force indicated by the arrow  85 ) is larger than the pressing force of the second coil spring  112  (i.e., the pressing force indicated by the arrow  86 ). Therefore, when no external force is applied, the second switch gear  72 , the first switch gear  71  and the input lever  74  are pressed toward the first coil spring  111  to compress the second coil spring  112  and to slide along the support shaft  73  in the direction indicated by the arrow  85 . When the input part  77  of the input lever  74  contacts the inner edge part of the guide hole  95  (i.e., the left edge part in  FIG. 5 ), the sliding of the members in the direction of the arrow  85  stopped. In this state, the input part  77  is positioned at the first drive transmission position P 1 . At the first drive transmission position P 1 , the first switch gear  71  engages with the second transmission gear  172 , and the second switch gear  72  is in the free state. When the guide member  92  contacts the input part  77  and the input part  77  is pressed by the guide member  92 , the input part  77  moves to the second drive transmission position P 2  or the third drive transmission position P 3  to switch the transmission state of the driving force. 
     As shown in  FIG. 4 , on the top surface  121  of the support frame  120 , the opening  122  is formed. The opening  122  has a shape elongated in the axial direction of the support shaft  73 . In the state where the gear unit  110  is mounted on the support frame  120 , the input part  77  of the input lever  74  is inserted into the opening  122 . The width of the opening  122  (i.e., the size in the axial direction of the support shaft  73 ) is set to have a value larger than the moving range of the input lever  74 . Therefore, movement of the input lever  74  is not limited by the opening  122 . 
     Hereafter, the transmission gears  171  to  173  are explained. 
     As shown in  FIG. 5 , under the first and second switch gears  171  and  172 , the first to third transmission gears  171  to  173  are provided in parallel with the support shaft  73  so that the first to third transmission gears  171  to  173  are supported on a support shaft  180  which is in parallel with the support shaft  73 . 
     The first and second transmission gears  171  and  172  are positioned to be able to engage with the first switch gear  71 . The third transmission gear  173  is positioned to be able to engage with the second switch gear  72 . The first, second and third transmission gears  171 ,  172  and  173  have thicknesses different from each other, and have the same outer diameter. The first, second and third transmission gears  171 ,  172  and  173  are arranged in this order from the outside on the support shaft  180 . 
     Each of the first to third transmission gears  171 - 173  serves to transmit the driving force to the corresponding drive mechanism. As shown in  FIG. 5 , the first transmission gear  171  transmits the driving force to the lift up mechanism for moving vertically the cap  57 . The second transmission gear  172  transmits the driving force to the first supply roller  25  and the second supply roller  30 . The third transmission gear  173  transmits the driving force, for example, to the suction pump  52  of the maintenance mechanism  5 . As described above, the first to third transmission gears  171 - 173  are assigned to respective driving mechanisms. Various types of transmission mechanisms, such as a series of gears or a belt, may be used as a transmission mechanism between each of the first to third transmission gears  171 - 173  and the corresponding drive mechanisms. 
       FIG. 6A  illustrates a state where the input part  77  of the input lever  74  is positioned at the first drive transmission position P 1 . In the state shown in  FIG. 6A , the first switch gear  71  engages with the second transmission gear  172 , and the second switch gear  72  is in the free state. When the input part  77  of the input lever  74  is moved to the second drive transmission position P 2  as shown in  FIG. 6B , the first switch gear  71  moves away from the second transmission gear  172 , and engages with the first transmission gear  171 . In this case, the second switch gear  72  stays in the free state. When the input part  77  of the input lever is moved to the third drive transmission position P 3 , the first switch gear  71  slides while engaging with the first transmission gear  171 . In this case, the second switch gear  72  moves from the free state to the state of being engaged with the third transmission gear  173 . 
     As shown in  FIG. 7A , when the first switch gear  71  moves away from the second transmission gear  172  and engages with the first transmission gear  171 , a possibility that the first switch gear  71  does not properly engage with the first transmission gear  171  arises. Further, by the effect of a surface pressure acting between the first switch gear  71  and the first transmission gear  171  may cause a phenomenon that the first switch gear  71  does not properly move away from the second transmission gear  172 . In this case, even if the input part  77  of the input lever  74  is moved to the second drive transmission position P 2 , the first switch gear  71  is not properly engaged with the first transmission gear  171 . Furthermore, as shown in  FIG. 7B , when the second switch gear  72  is driven to move to the free state to the state of being engaged with the third transmission gear  173 , a possibility that the second switch gear  72  does not properly engage with the third transmission gear  173 . For this reason, in this embodiment, each of the first and second switch gears  71  and  72  is rotated by a predetermined rotational amount when the drive transmission state of the first and second switch gears  71  and  72  is switched in accordance with a motor control process of the motor control unit  130  shown in  FIG. 9 . Consequently, the surface pressure between surfaces of engaged gears is released, and teeth of gears to be engaged are arranged to be able to properly engage with each other. Therefore, switching of the drive transmission state of the first and second switch gears  71  and  72  can be properly performed. 
     Hereafter, the configuration of the motor control unit  130  is explained with reference to  FIG. 8 .  FIG. 8  is a block diagram illustrating a configuration of the motor control unit  130 . in  FIG. 8 , a transmission oath from each of the motors  65  and  66  is surrounded by a box indicated by a dashed line. As described below, the motor control unit  130  serves to control the ASF motor  65  and the LF motor  66 . The motor control unit  130  may be configured as a separate control unit provided separately from a main controller for controlling totally the functions of the MFP  10 , or may be embedded in such a main controller. The CR motor for driving the carriage  38  is also controlled by the motor control unit  130  although a configuration for controlling the CR motor is omitted from  FIG. 8  for the sake of simplicity. 
     As shown in  FIG. 8 , the motor control unit  130  includes a CPU  131 , a ROM  132 , a RAM  133 , an ASIC  136 , a driving circuit  137 , which are connected to each other via a bus  135 . 
     The ROM  132  stores a program for executing the motor control process for controlling the ASF motor  65  and the LF motor  66 .  FIG. 9  is a flowchart illustrating the motor control process. The ROM  132  further stores a program for controlling switching of the ASF motor  65  and the LF motor  66  in accordance with detection signals from sensors, such as rotary encoders  81  and  82  and for controlling the rotation amount of the ASF motor  65  and the LF motor  66 . 
     The RAM  133  is used by the CPU  131  as a work memory for storing temporarily various types of data used for the above described programs. In the RAM  133 , a memory area for storing the number of counts of the motor control executed by the CPU  131  is secured. 
     In accordance with instructions from the CPU  131 , the ASIC  136  generates various control signals, such as a PWM signal, to be applied to the ASF motor  65  and the LF motor  66 , and sends the signals to the driving circuits  137  and  138 . By applying the driving signal to the ASF motor  65  via the driving circuit  137 , control of rotations of the ASF motor  65  is performed under control of the motor control unit  130 . By applying the driving signal to the LF motor  66  via the driving circuit  138 , control of rotations of the LF motor  66  is performed under control of the motor control unit  130 . 
     The driving circuit  137  serves to drive the ASF motor  65  connected to the first and second supply rollers  25  and  30 . By receiving the output signal from the ASIC  136 , the driving circuit  137  generates the drive signal to rotate the ASF motor  65  in the clockwise direction or in the counterclockwise direction. By receiving the drive signal from the driving circuit  137 , the ASF motor  65  rotates in a certain rotational direction. The rotation of the ASF motor  65  is transmitted to the first and second supply rollers  25  and  30  via the drive transmission mechanism, such as a gear provided on the transmission path between the ASF motor  65  and each of the first and second supply rollers  25  and  30 . 
     The driving circuit  138  serves to drive the LF motor  66  connected to the carrying roller  60 . By receiving the output signal from the ASIC  136 , the driving circuit  138  generates the drive signal to rotate the LF motor  66  in a certain rotational direction. By receiving the drive signal from the driving circuit  138 , the LF motor  66  rotates in a certain rotational direction. The rotation of the LF motor  66  is transmitted to the carrying roller  60  via the drive transmission mechanism, such as a gear provided on the transmission path between the LF motor  66  and the carrying motor  60 . 
     To the ASIC  136 , the rotary encoders  81  and  82  are connected. The rotary encoder  81  serves to detect the rotation amount of the ASF motor  65 , and is attached to the ASF motor  65 . The rotary encoder  82  serves to detect the rotation amount of the carrying roller  60  and the LF motor  66 , and is attached to the carrying roller  60 . 
     Each of the rotary encoders  81  and  82  includes an encoder disk and an optical sensor which are provided to have a common axis with respect to a rotational axis. When the encoder disk rotates together with the rotational axis, the optical sensor outputs pulses. The signal (pulses) detected by the rotary encoders  81  and  82  is sent to the CPU  131  via the ASIC  136  and the bus  135 . Based on the detection signal from the rotary encoders  81  and  82 , the CPU  131  measures the rotation amount of each of the motors  65  and  66  or detects a malfunction of the rotational motion of each of the motors  65  and  66 . 
     The drive control of the ASF motor  65  and the LF motor  66  executed under control of the CPU  131  will now be explained with reference to the flowchart of the motor control process shown in  FIG. 9  and a timing chart shown in  FIG. 10 . The motor control process is executed when the input lever  74  is moved from the first drive transmission position P 1  to the second drive transmission position P 3  or when the input lever  74  is moved from the first drive transmission position P 2  to the third drive transmission position P 3 . 
     When the motor control process is started, the CPU  131  resets the count C stored in a count memory area in the RAM  133 . Then, an ASF motor control process in steps S 10  to S 13  and an LF motor control process in steps S 20  to S 21  are executed concurrently. Although  FIG. 9  is illustrated such that the control flow is branched from step S 1  to steps S 10  and S 20  for convenience of explanation, actually the ASF motor control and the LF motor control are executed as separate processes. 
     In the ASF motor control process (steps S 10  to S 13 ), the ASF motor  65  is rotated by a certain rotation amount in the clockwise direction, and is then rotated by a certain rotation amount in the counterclockwise direction, and thereafter the ASF motor  65  is stopped. First, the CPU  131  activates the ASF motor  65  to rotate the ASF motor  65  by a certain rotation amount in the clockwise direction (step S 10 ). More specifically, the CPU  131  rotates the ASF motor  65  by a rotation amount corresponding to 1154 pulses (hereafter, frequently referred to as “1154ENC”) with reference to the pulse signal from the rotary encoder  81 . The 1154 pulses correspond to the rotation amount for rotating the first switch gear  71  by 2.7 teeth of the transmission gears  171  and  172 . That is, if the ASF motor  65  is rotated by the rotation amount of 1154 pulses when the first switch gear  71  and the first transmission gear  171  (or the second transmission gear  172 ) engage with each other, the first transmission gear  171  rotates by the rotation amount corresponding to 2.7 teeth. 
     When the ASF motor  65  is started from the stopped state, the ASP motor  65  is accelerated until a predetermined rotational speed is reached (729 min −1  in this embodiment). Thereafter, the ASF motor  65  is controlled to keep constantly the predetermined speed, and is decelerated to be stopped again (see the upper timing chart in  FIG. 10 ). When the driving finishes in step S 10 , the CPU  131  waits 100 ms (step S 11 ). Then, the CPU  131  rotates the ASF motor  65  in a predetermined rotation amount in the counterclockwise direction (step S 12 ). After the driving is finished in step S 12 , the CPU  131  waits 200 ms (step S 13 ). After waiting of 200 ms is finished, the CPU  131  sets an end flag for ASF motor control. Then, control proceeds to step S 14 . 
     In this embodiment, the ASF motor  65  is rotated by the rotation amount corresponding to 2.7 teeth of the transmission gears  171  and  172  in steps S 10  and S 12 . It should be noted that the rotation amount is determined in consideration of loss of rotation, such as backlash and a stopping error of gears. Therefore, for proper engagement between the first switch gear  71  and the first and second transmission gears  171  and  172 , the rotation amount of the first switch gear  71  may be one tooth of the first and second transmission gears  171  and  172  at the minimum. That is, even if the loss of rotation, such as backlash and a stopping error of gears, is taken into consideration, the ASF motor  65  may be rotated by the rotation amount for rotating the first switch gear  71  by an amount corresponding to one tooth of the first and second transmission gears  171  and  172 . 
     In step S 14 , the CPU  131  judges whether the LF motor control is finished. In step S 14 , the judgment may be made by setting the end flag to a register of the CPU  131  or to the RAM  133  when the LF motor control is finished, and checking the status of the end flag. 
     As described below, in the LF motor control in steps S 20  to S 21 , the LF motor  66  is rotated in the counterclockwise direction by a predetermined rotation amount, and thereafter the LF motor  66  is stopped. First, the CPU  131  activates the LF motor  66  at the same timing when the ASF motor  66  is activated, and rotates the LF motor  66  in the clockwise direction by the predetermined amount (step S 20 ). More specifically, the CPU  131  rotates the LF motor  66  by 1024 pulses (1024ENC) with reference the pulse signal from the rotary encoder  82 . The 1024 pulses correspond to the rotation amount for rotating the second switch gear  72  by 2.25 teeth with reference to teeth of the third transmission gear  173 . That is, if the LF motor  66  is rotated by the rotation amount of 1.24 pulses when the second switch gear  72  and the third transmission gear  173  engage with each other, the third transmission gear  173  rotates by the rotation amount of 2.25 teeth. 
     After rotation of the LF motor  66  is started from the stopped state, the LF motor  66  is accelerated until a predetermined rotational speed is reached (140 min −1  in this embodiment). Thereafter, the LF motor  66  is controlled to keep constantly the predetermined speed, and is decelerated to be stopped again (see the lower timing chart in  FIG. 10 ). When the driving finishes in step S 20 , the CPU  131  waits 200 ms (step S 21 ). After waiting of 200 ms is finished, the CPU  131  sets an end flag for LF motor control. Then, control proceeds to step S 22 . 
     In this embodiment, the LF motor  66  is rotated by the rotation amount corresponding to 2.25 teeth of the third transmission gear  173  and  172  in step S 20 . It should be noted that the rotation amount is determined in consideration of loss of rotation, such as backlash and a stopping error of gears. Therefore, for proper engagement between the second switch gear  72  and the third transmission gear  173 , the rotation amount of the second switch gear  72  may be one tooth of the third transmission gear  173  at the minimum. That is, even if the loss of rotation, such as backlash and a stopping error of gears, is taken into consideration, the LF motor  66  may be rotated by the rotation amount for rotating the second switch gear  72  by an amount corresponding to one tooth of the third transmission gear  173 . 
     In step S 20 , the CPU  131  judges whether the ASF motor control is finished. In step S 20 , the judgment may be made by setting the end flag to a register of the CPU  131  or to the RAM  133  when the ASF motor control is finished, and checking the status of the end flag. 
     When the CPU  131  judges that the motor control is finished in step S 14  or S 22  (S 14 : YES or S 22 : YES), control proceeds to step S 30  where the count C is incremented. 
     In step S 31 , the CPU  131  judges whether the count C is equal to a predetermined count n. In this embodiment, the predetermined count n has been set to 3. In is understood that various numbers may be assigned to the predetermined number n. If the CPU  131  judges that that the count C is equal to n (C=n), the motor control process terminates. On the other hand, if the CPU  131  judges that the count C is not equal to n (C≠n), the ASF motor control (steps S 10 -S 13 ) and the LF motor control (steps S 20 - 21 ) are executed concurrently again. The ASF motor control and the LF motor control are executed until the condition C=n is satisfied in step S 14 . 
     According to the embodiment, the ASF motor control and the LF motor control are executed as described above. Therefore, as shown in  FIG. 10 , an acceleration timing of the ASF motor  65  and an acceleration timing of the LF motor  65  can be overlapped (see a time T 10 ). Although the acceleration timing of the ASF motor and the acceleration timing of the LF motor  65  do not completely overlap with each other, at least parts of the acceleration timing of the motors  65  and  66  overlap with each other in a time period between the activation of the motors and the time when one of the motors  65  and  66  reaches a constant speed. Immediately after activation of the motors  65  and  66 , each of the motors  65  and  66  rotates at a low speed. Therefore, in this low speed state, engagement of each of the first and second switch gears  71  and  72  is easily switched. That is, the first switch gear  71  is easily switched from the second transmission gear  172  to the first transmission gear  171 , and the second switch gear  72  is easily switched from the free state to the engaged state of being engaged with the third transmission gear  173 . Consequently, it is possible to engage each of the switch gears  71  and  72  to the corresponding one of the first to third transmission gears  171 - 173  quickly and reliably. 
     As shown in  FIG. 10 , a deceleration timing T 11  is defined for the driving control of the ASF motor  65  in the clockwise direction. Therefore, even if the switching can not be achieved in the acceleration timing T 10  immediately after the activation of each motor, at least the first switch gear  71  moves to the state of being able to easily switch from the second transmission gear  172  to the first transmission gear  171  in the deceleration timing T 11 . In this timing, although the LF motor  66  is rotated at the constant speed (see the lower timing chart in  FIG. 10 ), the first switch gear  71  is in the state of being able to switch easily in comparison with the case where the LF motor  66  is stopped because the phase of the gear  71  shifts (with respect to the transmission gear) as long as the LF motor  66  is rotated. The same holds true for the rotation of the ASF motor  65  in the counterclockwise direction because the acceleration timing T 12  is secured. 
     In the ASF motor control (steps S 10 -S 13 ) and the LF motor control (steps S 20 -S 22 ), the motors  65  and  66  may be controlled such that the stop timing in the drive control in step S 12  and the stop timing in the drive control in step S 20  substantially match with each other. In other words, the ASF motor control may be finished at substantially the same timing when the LF motor control is finished. In this case, as shown in  FIG. 10 , the deceleration timing (T 13 ) of the AF motor  65  can be overlapped with the deceleration timing (T 13 ) of the LF motor  66 . Therefore, even in the condition immediately before the stop of the motor, each of the first and second switch gears  71  and  72  is in the state of being easily switched. 
     In the motor control process shown in  FIG. 9 , the ASF motor  65  is rotated in the clockwise direction when the ASF motor  65  is activated, and the LF motor  66  is rotated in the clockwise direction when the LF motor  66  is activated. However, as shown by a thick dashed line in  FIG. 10 , the ASF motor  65  may be rotated in the counterclockwise direction when the ASF motor  65  is activated, and the LF motor  66  may be rotated in the counterclockwise direction when the LF motor  66  is activated. 
     In the motor control process shown in  FIG. 9 , the ASF motor  65  and the LF motor  66  are activated at the same timing. However, the timing of activating the ASF motor  65  and the timing of activating the LF motor  66  may be different from each other. That is, as long as at least the ASF motor is activated while the LF motor  66  rotates, the timing of activating the ASF motor  65  and the timing of activating the LF motor  66  may be different from each other. In this case, even if the acceleration timings of the ASF motor  65  and the LF motor  66  do not overlap with each other, the first switch gear  71  rotates at a low speed in the state where the surface pressure between gears is released because the ASF motor  65  is reversely accelerated while the LF motor  66  is rotated. Consequently, the first switch gear  71  is in the sate of being easily switched in comparison with the case where the LF motor  66  is stopped. 
     In the following, variations of the motor control process and the timing chart of control of the motors are explained. 
     (First Variation) 
     As a first variation of the motor control process and timing chart,  FIG. 11  illustrates a flowchart of a motor control process, and  FIG. 12  illustrates timing chart of control of motors. The motor control process is executed when the input lever  74  is moved from the first drive transmission position P 1  to the second drive transmission position P 3  or when the input lever  74  is moved from the first drive transmission position P 2  to the third drive transmission position P 3 . In  FIG. 11 , to steps which are substantially the same as those of  FIG. 9 , the same step numbers are assigned, and explanations thereof will not be repeated for the sake of simplicity. 
     When the count C is reset in step S 1 , ASF motor control in steps S 110  to S 113  and LF motor control in steps S 120  to S 124  are executed concurrently. Although  FIG. 11  is illustrated such that the control flow is branched from step S 1  to steps S 110  and S 120  for convenience of explanation, actually the ASF motor control and the LF motor control are executed as separate processes. 
     In the ASF motor control process (steps S 110  to S 112 ), the drive control where the ASF motor  65  is rotated by a certain rotation amount in the clockwise direction, and is then rotated by a certain rotation amount in the counterclockwise direction, and thereafter the ASF motor  65  is stopped is executed two times repeatedly (see the upper timing chart in  FIG. 12 ). First, in step S 110 , the same steps as steps S 10  to S 13  in  FIG. 9  are executed (step S 110 ). Then, the CPU  131  judges whether the first waiting time of 200 ms for the LF motor control has elapsed (step S 111 ). The CPU  131  waits until the first waiting time elapses (S 111 : NO). 
     If the CPU  131  judges that the first waiting time has elapsed (S 111 : YES), control proceeds to step S 112  where the same steps S 10 -S 13  as those in step S 110  are executed at the same timing as step S 122 . Next, in step S 113 , the CPU  113  judges whether the LF motor control is finished as in the case of step S 14 . 
     In the LF motor control process (steps S 120  to S 123 ), the LF motor  66  is rotated by a certain rotation amount in the clockwise direction, and is then rotated by a certain rotation amount in the counterclockwise direction, and thereafter the LF motor  66  is stopped. First, in step S 120 , the same steps as steps S 20  to S 21  in  FIG. 9  are executed. Then, the CPU  131  judges whether the first waiting time of 100 ms for the ASF moor control elapses (step S 121 ). The CPU  131  waits until the waiting time elapses (S 121 : NO). When the waiting time elapses (S 121 : YES 9 , control proceeds to step S 122  where the CPU  131  rotates the LF motor  66  in the counterclockwise direction by the predetermined amount at the same timing as step S 112  as in the case of step S 20 . After the drive control of step S 122  is finished, the CPU  131  waits 200 ms (step S 123 ). Then, the CPU  131  judges whether the ASF motor control is finished as in the case of step S 14 . 
     If it is judged that the motor control is finished in step S 113  or S 123 , the count C is incremented. In step S 131 , the CPU  131  judges whether the count C is equal to a predetermined count n. If the CPU  131  judges that that the count C is equal to n (C=n), the motor control process terminates. On the other hand, if the CPU  131  judges that the count C is not equal to n (C≠n), the ASF motor control (steps S 110 -S 113 ) and the LF motor control (steps S 120 -S 124 ) are executed again. 
     (Second Variation) 
     As a second variation of the motor control process and timing chart,  FIG. 13  illustrates a flowchart of a motor control process, and  FIG. 14  illustrates timing chart of control of motors. The motor control process is executed when the input lever  74  is moved from the third drive transmission position P 3  to the first drive transmission position P 1 . In the following, explanations of steps which are substantially the same as those of  FIG. 9  will not be repeated for the sake of simplicity. 
     When the count C is reset in step S 201 , ASF motor control in steps S 210  to S 211  and LF motor control in steps S 220  to S 221  are executed concurrently. Although  FIG. 13  is illustrated such that the control flow is branched from step S 201  to steps S 210  and S 220  for convenience of explanation, actually the ASF motor control and the LF motor control are executed as separate processes. 
     In the ASF motor control process (steps S 210  to S 211 ), the ASF motor  65  is rotated by a predetermined rotation amount in the clockwise direction. First, in step S 210 , the same step as step S 10  in  FIG. 9  is executed. After the drive control in step S 210  is finished, the CPU  131  waits 200 ms (step S 211 ). After the waiting time of 200 ms has elapsed, the CPU  131  sets the end flag of the ASF motor control, and control proceeds to step S 212 . In step S 212 , the CPU  131  judges whether the LF motor control is finished as in the case of step S 14  in  FIG. 9 . 
     In the LF motor control process in steps S 220  to S 221 , the LF motor  66  is rotated by a predetermined rotation amount in the clockwise direction. First, in step S 220 , the same step as step S 20  in  FIG. 9  is executed. After the drive control in step S 220  is finished, the CPU  131  waits 200 ms (step S 221 ). After the waiting time of 200 ms has elapsed, the CPU  131  sets the end flag of the LF motor control. Then, control proceeds to step S 222 . In step S 222 , the same step as step S 22  in  FIG. 9  is executed. That is, in step S 222 , the CPU  131  judges whether the ASF motor control is finished. 
     If it is judged that the motor control is finished in step S 212  or S 222 , the count C is incremented. In step S 231 , the CPU  131  judges whether the count C is equal to a predetermined count n. If the CPU  131  judges that that the count C is equal to n (C=n), the motor control process terminates. On the other hand, if the CPU  131  judges that the count C is not equal to n (C≠n), the ASF motor control (steps S 210 -S 211 ) and the LF motor control (steps S 220 -S 221 ) are executed again. 
     (Third Variation) 
     As a third variation of the motor control process and timing chart,  FIG. 15  illustrates a flowchart of a motor control process, and  FIG. 16  illustrates timing chart of control of motors. The motor control process is executed when the input lever  74  is moved from the third drive transmission position P 3  to the first drive transmission position P 1 . In the following, explanations of steps which are substantially the same as those of  FIG. 9  will not be repeated for the sake of simplicity. 
     When the count C is reset in step S 301 , ASF motor control in steps S 310  to S 314  and LF motor control in steps S 320  to S 324  are executed concurrently. Although  FIG. 15  is illustrated such that the control flow is branched from step S 301  to steps S 310  and S 320  for convenience of explanation, actually the ASF motor control and the LF motor control are executed as separate processes. 
     As shown in the upper timing chart in  FIG. 16 , in the ASF motor control process (steps S 310  to S 314 ), the ASF motor  65  is rotated by a predetermined rotation amount in the clockwise direction, and is rotated by a predetermined rotation amount in the counterclockwise direction, and thereafter is stopped. First, in step S 310 , the CPU  131  rotates the ASF motor  65  by the predetermined amount in the clockwise direction as in the case of S 10  in  FIG. 9 . After the drive control in step S 310  is finished, the CPU  131  waits 200 ms (step S 311 ). After the waiting time of 200 ms has elapsed, the CPU  131  judges whether the first waiting time of the LF motor control has elapsed as in the case of step S 111  in  FIG. 11 . If the waiting time has elapsed, the CPU  131  rotates the ASF motor  65  by the predetermined amount in the counterclockwise direction at the same timing as steps S 323  as in the case of step S 12  in  FIG. 9  (step S 313 ). After the drive control in step S 313  is finished, the CPU  131  waits 200 ms (step S 314 ). After the waiting time of 200 ms has elapsed, the CPU  131  judges whether the LF motor control is finished as in the case of step S 14  in  FIG. 9  (step S 315 ). 
     As shown in the lower timing chart in  FIG. 16 , in the LF motor control process (steps S 320  to S 324 ), the LF motor  66  is rotated by a predetermined rotation amount in the clockwise direction, and is rotated by a predetermined rotation amount in the counterclockwise direction, and thereafter is stopped. First, in step S 320 , the CPU  131  rotates the LF motor  66  by the predetermined amount in the clockwise direction as in the case of S 10  in  FIG. 9 . After the drive control in step S 320  is finished, the CPU  131  waits 200 ms (step S 321 ). After the waiting time of 200 ms has elapsed, the CPU  131  judges whether the first waiting time of the ASF motor control has elapsed as in the case of step S 121  in  FIG. 11 . If the waiting time has elapsed, the CPU  131  rotates the LF motor  66  by the predetermined amount in the counterclockwise direction at the same timing as step S 313  as in the case of step S 122  in  FIG. 11  (step S 323 ). After the drive control in step S 323  is finished, the CPU  131  waits 200 ms (step S 324 ). After the waiting time of 200 ms has elapsed, the CPU  131  judges whether the ASF motor control is finished as in the case of step S 22  in  FIG. 9  (step S 325 ). 
     If it is judged that the motor control is finished in step S 315  or S 325 , the count C is incremented in step S 330 . In step S 331 , the CPU  131  judges whether the count C is equal to a predetermined count n. If the CPU  131  judges that that the count C is equal to n (C=n), the motor control process terminates. On the other hand, if the CPU  131  judges that the count C is not equal to n (C≠n), the ASF motor control (steps S 310 -S 314 ) and the LF motor control (steps S 320 -S 324 ) are executed again. 
     (Fourth Variation) 
     As a fourth variation of the motor control process and timing chart,  FIGS. 17A and 17B  illustrate parts of flowcharts of the motor control process. 
     There is a possibility that even if the driving signal is supplied to the motor  65  or  66 , the motor  65  or  66  does not rotate due to a load caused by the surface pressure between gears or an unexpected torque. There is also a possibility that due to the surface pressure or the unexpected torque, the rotation amount of the motor  65  or  66  gets lower than a predetermined rotation amount. Inversely, the rotation amount of the motor  65  or  66  might get larger than or equal to the predetermined rotation amount due to an excessively light load. Because both of the rotation amount larger than or equal to the predetermined rotation amount and the rotation amount smaller than the predetermined rotation amount is the abnormal condition for the ASF motor control and the LF motor control. Therefore, if the drive control is executed in such an abnormal condition, it is undesirable to count the number of times of drive control. 
     In the fourth variation, when it is judged that the motor control is finished in step S 14  or S 22  in  FIG. 9 , the CPU  131  judges whether an abnormal driving condition occurs during the ASF motor control or the LF motor control (step S 6 ). The judgment in step S 6  may be made based on the number of pulses from the rotary encoder  81  or  82 . For example, if the number of pulses corresponding to the predetermined rotation amount is not detected within a predetermined time range, the CPU  131  may judge that the abnormal driving condition occurs. 
     If the CPU  131  judges that the abnormal driving condition occurs, the CPU  131  may execute the judgment in step S 31  without incrementing the count C. On the other hand, if the abnormal condition does not occur, the count C is incremented in step S 30 . Since the number of times of motor control is not counted when the abnormal drive condition occurs, the motor control is properly executed for the predetermined number of times larger than or equal to the predetermined number n. As shown in  FIG. 17B , when it is judged that the abnormal drive condition occurs, control may proceed to step S 1  in  FIG. 9  to reset the counter C. 
     Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible.