Patent Publication Number: US-2023158817-A1

Title: Recording apparatus

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-189890, filed Nov. 24, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure relate to a recording apparatus that performs recording on a medium. 
     2. Related Art 
     A structure of an ink-jet recording apparatus in which a recording head configured to eject ink moves rotatably between a maintenance position and a recording position is disclosed in JP-A-2020-026071. A head holder that holds the recording head has three pins in a side view. These pins are guided along rails, thereby causing the recording head to move rotatably between the maintenance position and the recording position. One of the three pins is in engagement with a slide member. The slide member is coupled to a slide rack gear via a spring. The slide rack gear is in mesh with a drive gear. The rotation of the drive gear causes the slide gear and the slide rack gear to move up and down. 
     When the head holder is located at the recording position, the head holder tends to rotate due to the own weight of the head holder, and the positional orientation of the head holder is prone to be unstable. However, the urging force of the above-mentioned spring, which is provided between the slide member and the slide rack gear, acts to cancel the rotation. This action makes the positional orientation of the head holder stable. 
     In the above structure disclosed in JP-A-2020-026071, in a case where an increase in the own weight of the head holder makes its positional orientation more unstable, it is possible to stabilize the positional orientation by increasing the magnitude of the urging force of the spring. However, the urging force of the spring acts in a direction that is exactly the opposite of a direction in which the drive gear drives the slide rack gear. For this reason, if the magnitude of the urging force of the spring is increased, the rated output of a motor for driving the drive gear also needs to be increased. This will result in an increase in cost and an increase in power consumption. 
     SUMMARY 
     A recording apparatus according to a certain aspect of the present disclosure includes: a medium transportation path along which a medium is transported; a recording head that performs recording on the medium transported along the medium transportation path; a head unit including the recording head and configured to move between a recording position where the recording is performed on the medium and a retraction position away from the medium transportation path; a movement mechanism that moves the head unit by applying, to the head unit, a force acting in a moving direction of the head unit; a positioning portion with which a part of the head unit moving from the retraction position toward the recording position comes into contact for positioning the head unit at the recording position; and a unit pusher that applies, to the head unit, a force acting in a direction of canceling rotation of the head unit when the head unit is located at the recording position, wherein a moment for rotating the head unit as viewed in a medium width direction intersecting with a medium transportation direction is produced by the force applied by the movement mechanism to the head unit and by a reaction force received by the head unit from the positioning portion, and the unit pusher pushes the head unit in a direction intersecting with the moving direction of the head unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating a medium transportation path of a printer in a state in which a head unit is located at a recording position. 
         FIG.  2    is a diagram illustrating the medium transportation path of the printer in a state in which the head unit is located at a retraction position. 
         FIG.  3    is a perspective view illustrating the head unit and a movement mechanism in the state in which the head unit is located at the recording position. 
         FIG.  4    is a cross-sectional view illustrating the head unit and the movement mechanism in the state in which the head unit is located at the recording position. 
         FIG.  5    is a cross-sectional view illustrating the head unit and the movement mechanism in the state in which the head unit is located at the retraction position. 
         FIG.  6    is a perspective view illustrating the head unit. 
         FIG.  7    is a cross-sectional perspective view illustrating a right guide member in the state in which the head unit is located at the recording position. 
         FIG.  8    is a cross-sectional perspective view illustrating a first left guide member and a second left guide member in the state in which the head unit is located at the recording position. 
         FIG.  9    is a diagram schematically illustrating a movement area and positions of the head unit. 
         FIG.  10    is a side view illustrating the head unit and a unit pusher in a state in which the head unit is located before the recording position. 
         FIG.  11    is a side view illustrating the head unit and the unit pusher in the state in which the head unit is located at the recording position. 
         FIG.  12    is a perspective view illustrating the head unit and the unit pusher in the state in which the head unit is located at the recording position. 
         FIG.  13 A  is a side view illustrating a part of the head unit and the unit pusher in a state in which the head unit is located before the recording position. 
         FIG.  13 B  is a side view illustrating a part of the head unit and the unit pusher in the state in which the head unit is located at the recording position. 
         FIG.  14    is a plan view illustrating the head unit and the unit pusher in the state in which the head unit is located at the recording position. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First, a brief overview of the present disclosure is presented below. 
     A recording apparatus according to a first exemplary mode of the present disclosure includes: a medium transportation path along which a medium is transported; a recording head that performs recording on the medium transported along the medium transportation path; a head unit including the recording head and configured to move between a recording position where the recording is performed on the medium and a retraction position away from the medium transportation path; a movement mechanism that moves the head unit by applying, to the head unit, a force acting in a moving direction of the head unit; a positioning portion with which a part of the head unit moving from the retraction position toward the recording position comes into contact for positioning the head unit at the recording position; and a unit pusher that applies, to the head unit, a force acting in a direction of canceling rotation of the head unit when the head unit is located at the recording position, wherein a moment for rotating the head unit as viewed in a medium width direction intersecting with a medium transportation direction is produced by the force applied by the movement mechanism to the head unit and by a reaction force received by the head unit from the positioning portion, and the unit pusher pushes the head unit in a direction intersecting with the moving direction of the head unit. 
     In this exemplary mode, the recording apparatus includes a unit pusher that applies, to the head unit, a force acting in a direction of canceling rotation of the head unit when the head unit is located at the recording position. This makes it possible to suppress the instability in the positional orientation of the head unit due to the moment of force and thus obtain good recording quality. 
     Since the unit pusher behaves to cancel the rotation of the head unit by pushing the head unit in a direction intersecting with the moving direction of the head unit, it is possible to prevent the unit pusher from being obstructive to the movement of the head unit in the V-axis direction. Consequently, it is possible to prevent an increase in cost and an increase in power consumption resulting from increasing the rated output of a motor that is the power source for movement of the head unit. 
     A second exemplary mode is that, in the first exemplary mode, the head unit includes a first guided portion on one end portion in the medium width direction and a second guided portion and a third guided portion on an other end portion in the medium width direction with a space therebetween in the moving direction of the head unit, the first guided portion is guided in the moving direction while being supported by a first guide surface extending in the moving direction of the head unit, the second guided portion and the third guided portion are guided in the moving direction while being supported by a second guide surface extending in the moving direction, and at least in a state of being located at the recording position, the head unit is supported at three points via the first guided portion, the second guided portion, and the third guided portion. 
     In this exemplary mode, the head unit is supported at three points via the first guided portion, the second guided portion, and the third guided portion. Because of this structure, the positional orientation of the head unit is stable, and it is possible to obtain good recording quality. 
     A third exemplary mode is that, in the second exemplary mode, a position where the unit pusher applies the force to the head unit is located inside an area of a triangle having vertices at a first position, a second position, and a third position as viewed in a direction orthogonal to a plane including the first position, the second position, and the third position, the first position is a position where the first guided portion is in contact with the first guide surface, the second position is a position where the second guided portion is in contact with the second guide surface, and the third position is a position where the third guided portion is in contact with the second guide surface. 
     In this exemplary mode, the position where the unit pusher applies the force to the head unit is located inside an area of a triangle having vertices at the first position, the second position, and the third position. Because of this structure, the first guided portion is properly pushed against the first guide surface, the second guided portion is properly pushed against the second guide surface, and the third guided portion is properly pushed against the second guide surface. This makes the positional orientation of the head unit stable, resulting in good recording quality. 
     A fourth exemplary mode is that, in the third exemplary mode, the second guided portion is located at a position where the second guided portion gets lifted away from the second guide surface due to the rotation of the head unit, the third guided portion is located at a position where the third guided portion is pushed against the second guide surface due to the rotation of the head unit, and the position where the unit pusher applies the force to the head unit is located on a side closer to the second position with respect to a halfway position located between the first position and the second position in the medium width direction, and is located on a side closer to the second position with respect to a halfway position located between the second position and the third position in the moving direction. 
     In this exemplary mode, in a structure in which the second guided portion is located at a position where the second guided portion gets lifted away from the second guide surface due to the rotation of the head unit, the position where the unit pusher applies the force to the head unit is located on a side closer to the second position with respect to a halfway position located between the first position and the second position in the medium width direction, and is located on a side closer to the second position with respect to a halfway position located between the second position and the third position in the moving direction. Because of this structure, the head unit is pushed at the position closer to the second guided portion. Therefore, the rotation of the head unit is suppressed properly. 
     A fifth exemplary mode is that, in any of the first to fourth exemplary modes, the unit pusher includes a rotary member provided rotatably on the head unit and having a free end, a spring provided on the head unit and configured to push the rotary member in a direction in which the free end goes away from the head unit, and a contact member provided independently of the head unit and configured to come into contact with the rotary member when the head unit is located at the recording position, and the force acting in the direction of canceling the rotation of the head unit is applied to the head unit by a force of the spring. 
     In this exemplary mode, the unit pusher includes the rotary member, the spring, and the contact member. Therefore, it is possible to make the structure of the unit pusher simple. 
     A sixth exemplary mode is that, in the fifth exemplary mode, a centerline of a rotation shaft of the rotary member extends in the medium width direction, the free end is located on a side closer to the retraction position with respect to the rotation shaft in the moving direction of the head unit, and the contact member moves in relation to the rotary member from the rotation shaft toward the free end when the head unit moves from the retraction position to the recording position. 
     In this exemplary mode, the contact member moves in relation to the rotary member from the rotation shaft toward the free end when the head unit moves from the retraction position to the recording position. Because of this structure, the magnitude of the force applied by the unit pusher to the head unit increases gradually when the head unit moves from the retraction position to the recording position. Such a gradual increase in the magnitude of the pushing force makes it possible to avoid a heavy load from being applied suddenly when the head unit moves to the recording position, thereby ensuring smooth movement of the head unit to the recording position. 
     A seventh exemplary mode is that, in the sixth exemplary mode, the recording apparatus further includes a rotation restriction portion that restricts rotation of the rotary member in the direction in which the free end of the rotary member goes away from the head unit. 
     In this exemplary mode, the recording apparatus further includes a rotation restriction portion that restricts rotation of the rotary member in the direction in which the free end of the rotary member goes away from the head unit. Because of this structure, it is possible to make a contact angle smaller when the contact member comes into contact with the rotary member. The smaller contact angle further enhances the effect of avoiding a heavy load from being applied suddenly when the head unit moves to the recording position. 
     An eighth exemplary mode is that, in any of the first to seventh exemplary modes, the head unit includes a unit body including the recording head and configured to come into contact with the positioning portion, a displacement member whose relative position in relation to the unit body is configured to be changed in the moving direction of the head unit, and a pushing member provided between the unit body and the displacement member and configured to push the unit body toward the positioning portion when the head unit is located at the recording position, and the movement mechanism applies, to the displacement member, an external force for moving the head unit. 
     In this exemplary mode, the movement mechanism indirectly causes the head unit to move via the displacement member. Because of this structure, high stop precision is not required when stopping the head unit moved to the recording position by the movement mechanism in a state in which the unit body has come into contact with the positioning portion. This makes the position control of the head unit easier. 
     Next, embodiments of the present disclosure will now be explained with specific examples. 
     An ink-jet printer  1  that performs recording by ejecting ink, which is an example of liquid, onto a medium such as recording paper will be described below as an example of a recording apparatus. In the description below, a shorter term “printer  1 ” will be used for the ink-jet printer  1 . 
     The X-Y-Z coordinate system shown in each of the accompanying drawings is an orthogonal coordinate system. The Y-axis direction of the coordinate system represents a medium width direction intersecting with a medium transportation direction. The medium width direction is the same as an apparatus depth direction. The direction from the front toward the rear of the apparatus is defined as the +Y direction, which is one of the Y-axis direction. The direction from the rear toward the front of the apparatus is defined as the −Y direction, which is the other of the Y-axis direction. In the present embodiment, the Y-axis direction is an example of a width direction intersecting with the V-axis direction, in which a head unit  50  to be described later is configured to move. 
     The X-axis direction represents an apparatus width direction. As viewed from an operator of the printer  1 , the +X direction is the direction toward the left-hand side, and the −X direction is the direction toward the right-hand side. The Z-axis direction represents a vertical direction and is normal to a surface G on which the printer  1  is installed. Namely, the Z-axis direction represents an apparatus height direction. The +Z direction, one of Z-axis direction, is the direction going upward. The −Z direction, the other, is the direction going downward. 
     In the description below, the direction in which a medium is transported may be referred to as “downstream”. The opposite direction may be referred to as “upstream”. In  FIGS.  1  and  2   , a medium transportation path are indicated by broken-line curves. In the printer  1 , the medium is transported along the medium transportation path indicated by the broken-line curves in  FIGS.  1  and  2   . 
     The F-axis direction represents the medium transportation direction at a space between a line head  51  to be described later and a transportation belt  13  to be described later, that is, at a recording region. The +F direction goes downstream in the transportation direction. The −F direction, the opposite of the +F direction, goes upstream in the transportation direction. The V-axis direction, in which the head unit  50  to be described later is configured to move, is orthogonal to the F-axis direction. The +V direction, one of the V-axis direction, is the direction in which the head unit  50  goes away from a “during-recording” transportation path T 1 . The −V direction, the other, is the direction in which the head unit  50  comes toward the during-recording transportation path T 1 . 
     In some of the accompanying drawings, the F-V-Y coordinate system will be used instead of the X-Y-Z coordinate system. 
     With reference to  FIG.  1   , the medium transportation path in the printer  1  will now be explained. The printer  1  is configured such that an add-on unit  6  can be coupled thereto under its body  2 . A state in which the add-on unit  6  is coupled is illustrated in  FIGS.  1  and  2   . 
     The printer body  2  has, at its lower portion, a first medium cassette  3  configured to contain sheets of a medium. When the add-on unit  6  is coupled under the printer body  2 , a second medium cassette  4  and a third medium cassette  5  are provided under the first medium cassette  3 . 
     Each of these medium cassettes is provided with a pick roller that feeds out the medium contained in it in the −X direction. Pick rollers  21 ,  22 , and  23  are provided respectively for the first medium cassette  3 , the second medium cassette  4 , and the third medium cassette  5 . 
     For each of these medium cassettes, a corresponding pair of feed rollers configured to feed, obliquely upward, the medium having been fed in the −X direction is provided. Pairs of feed rollers  25 ,  26 , and  27  are these corresponding pairs of feed rollers provided respectively for the first medium cassette  3 , the second medium cassette  4 , and the third medium cassette  5 . 
     The term “pair of rollers” used below means a pair that is made up of a driving roller and a driven roller, wherein the driving roller is driven by a motor that is not illustrated, and the driven roller is in contact with the driving roller and rotates as a slave by receiving a driving force for rotation from the driving roller when the driving roller rotates, unless otherwise described. 
     The medium fed out of the third medium cassette  5  is sent to a pair of transportation rollers  38  by a pair of transportation rollers  29  and then by a pair of transportation rollers  28 . The medium fed out of the second medium cassette  4  is sent to the pair of transportation rollers  38  by the pair of transportation rollers  28 . The medium is nipped by the pair of transportation rollers  38  and is then sent to a pair of transportation rollers  31 . 
     The medium fed out of the first medium cassette  3  is sent to the pair of transportation rollers  31  by the pair of feed rollers  25  without going through the pair of transportation rollers  38 . 
     A supply roller  19  and a separation roller  20 , which are provided near the pair of transportation rollers  38 , make up a roller pair configured to feed a medium from a supply tray that is not illustrated in  FIGS.  1  and  2   . 
     The medium that receives a transportation force from the pair of transportation rollers  31  is sent to the space between the line head  51 , which is an example of a recording head, and the transportation belt  13 . That is, the medium is sent to the position where it faces the line head  51 . The medium transportation path from the pair of transportation rollers  31  to a pair of transportation rollers  32  is herein referred to as the during-recording transportation path T 1 . 
     The line head  51  is a component of the head unit  50 . The line head  51  performs recording by ejecting ink, which is an example of liquid, onto a surface of the medium. The line head  51  is an ink ejecting head configured such that nozzles for ejecting ink are arranged throughout the entire area in the medium width direction. The line head  51 , as an ink ejecting head having such a structure, is capable of performing recording throughout the entire area in the medium width direction without moving in the medium width direction. However, the ink ejecting head is not limited to a line head. The ink ejecting head may be a serial-type head that is mounted on a carriage and ejects ink while moving in the medium width direction. 
     The head unit  50  is provided in such a way as to be able to advance toward and retract from the during-recording transportation path T 1 . Accordingly, the head unit  50  is movable between a recording position, at which the head unit  50  having advanced toward the during-recording transportation path T 1  performs recording, and a retraction position, which is away from the during-recording transportation path T 1 . 
       FIG.  1    illustrates a state in which the head unit  50  is located at the recording position. In this state, the head unit  50  performs recording on the medium.  FIG.  2    illustrates a state in which the head unit  50  is located at the retraction position. The head position illustrated in  FIG.  2    is a position where the head unit  50  is located when operation for wiping an ink ejecting surface  51   a  of the line head  51  is performed. 
     With reference to  FIG.  9   , a range of movement of the head unit  50  will now be explained.  FIG.  9    schematically illustrates the range of movement of the head unit  50 . In  FIG.  9   , each position of the head unit  50  in the V-axis direction is illustrated based on the position of its ink ejecting surface  51   a  in the V-axis direction. 
     In  FIG.  9   , the position V 1  is the most-advanced position of the head unit  50  when located closest to the during-recording transportation path T 1 . The position V 1  is an example of the recording position and corresponds to the position of the head unit  50  illustrated in  FIG.  1   . The recording position is adjustable by adjustment cams  80  to be described later (see  FIG.  10   ). The position V 1   b  is the most +V-directional-side position within an adjustable range of the recording position. In  FIG.  9   , the illustration of the line head  51  when at the position V 1   b  is omitted. Recording is performed on the medium when the head unit  50  is located at the position V 1 , the position V 1   b , or somewhere between the position V 1  and the position V 1   b.    
     The position V 4  is the farthest position, most distant from the during-recording transportation path T 1  in the +V direction, of the head unit  50 . The position V 4  is an example of the retraction position. The head unit  50  is attachable and detachable when at the position V 4 . The attachment of detachment of the head unit  50  will be described later. 
     The position V 2  is a position for wiping the ink ejecting surface  51   a  of the line head  51 . The position V 2  is another example of the retraction position.  FIG.  2    illustrates a state in which the head unit  50  is located at the position V 2 . In  FIG.  2   , the reference numeral  43  denotes a wiper unit, and the reference numeral  44  denotes a wiper provided on the wiper unit  43 . The wiper  44  is made of an elastic material such as a rubber, elastomer, or the like. The wiper  44  is able to be held in contact with, while being pressed against, the ink ejecting surface  51   a  due to its elasticity. 
     The wiper unit  43  is movable in the Y-axis direction, which is the direction along the ink ejecting surface  51   a , by being driven by a motor that is not illustrated. The wiper unit  43  has its home position at the +Y-side end of its movable area. Except for during wiping, the wiper unit  43  is located at the home position. Due to the movement of the wiper unit  43  in the Y-axis direction, the ink ejecting surface  51   a  is wiped by the wiper  44 . 
     The position V 3  is a position for capping the ink ejecting surface  51   a  by means of a cap that is not illustrated. The position V 3  is another example of the retraction position. The position V 3   b  is a position for performing flushing operation into the non-illustrated cap, that is, a position for ejecting ink from all of ink ejecting nozzles (not illustrated) of the line head  51 . The position V 3   b  is another example of the retraction position. In  FIG.  9   , the illustration of the line head  51  when at the position V 3   b  is omitted. 
     Referring back to  FIGS.  1  and  2   , reference signs  10 A,  10 B,  10 C, and  10 D denote ink containers as an example of “liquid container”. Ink to be ejected from the line head  51  is supplied to the line head  51  from each ink container through a corresponding tube that is not illustrated. The ink containers  10 A,  10 B,  10 C, and  10 D are provided detachably on attachment portions  11 A,  11 B,  11 C, and  11 D respectively. 
     The reference numeral  12  denotes a waste liquid container for serving as a reservoir for, as an example of waste liquid, ink having been ejected from the line head  51  into the non-illustrated flushing cap for the purpose of maintenance. 
     The transportation belt  13  is an endless belt wound around pulleys  14  and  15 . Either one of the pulleys  14  and  15  is, or both are, driven by a motor that is not illustrated. The transportation belt  13  turns due to this drive force. The medium is transported through a position where it faces the line head  51  while being held by adsorption on the belt surface of the transportation belt  13 . Known methods such as an air vacuuming method, an electrostatic chuck method, and the like can be used for holding the medium by adsorption on the belt surface of the transportation belt  13 . 
     The during-recording transportation path T 1 , which goes through the position where the medium is to face the line head  51 , intersects with both the horizontal direction and the vertical direction. The medium is transported upward along the during-recording transportation path T 1 . Therefore, the V-axis direction, in which the head unit  50  is configured to move, also intersects with both the horizontal direction and the vertical direction. The angle of inclination a of the V-axis direction with respect to the horizontal direction is less than 45°, more specifically, approximately 15°. 
     This structure makes it possible to strike a good balance between horizontal size and vertical size of a space required for movement of the head unit  50  and thus makes it possible to prevent the size of the apparatus from being extremely large in the horizontal direction and the vertical direction. 
     The scope of the present disclosure is not limited to the above example. The V-axis direction may be parallel to the horizontal direction. 
     An ejection tray  8  forming a supporting surface  8   b  configured to support the supporting surface  8   b  ejected from the medium transportation path is provided over the head unit  50 . The supporting surface  8   b  extends in the V-axis direction, in which the head unit  50  is configured to move. Because of this structure, a dead space is not formed in a relationship between the ejection tray  8  and the movement area of the head unit  50 . 
     Moreover, since a part of the head unit  50  overlaps with the ink containers  10 A,  10 B,  10 C, and  10 D in the Z-axis direction, it is possible to reduce the apparatus size in the Z-axis direction. 
     Next, after recording on the first side of the sheet of the medium by the line head  51 , the medium is transported by a pair of transportation rollers  32  located downstream of the transportation belt  13 . 
     A flap  41  is provided downstream of the pair of transportation rollers  32 . The medium transportation direction is switched by the flap  41 . When the medium is to be ejected without any further recording, the medium transportation path is switched by the flap  41  toward the pair of transportation rollers  35  located above it. In this case, the medium is ejected onto the ejection tray  8  by the pair of transportation rollers  35 . 
     When recording is to be performed on the second side of the medium in addition to the first side, the medium transportation direction is switched by the flap  41  toward a branch position K 1 . The medium passes through the branch position K 1  to enter a switchback path T 2 . In the present embodiment, the switchback path T 2  is a medium transportation path located above the branch position K 1 . Pairs of transportation rollers  36  and  37  are provided on the switchback path T 2 . The medium having entered the switchback path T 2  is transported upward by the pairs of transportation rollers  36  and  37 . Upon the passing of the trailing edge of the medium through the branch position K 1 , the rotating direction of the pairs of transportation rollers  36  and  37  is switched, thereby changing the medium transportation direction to a downward direction. 
     A turnover path T 3  is connected to the switchback path T 2 . In the present embodiment, the turnover path T 3  is a medium transportation path leading from the branch position K 1  to the pair of transportation rollers  38  through pairs of transportation rollers  33  and  34 . 
     The medium transported downward from the branch position K 1  receives a transportation force from the pairs of transportation rollers  33  and  34  to reach the pair of transportation rollers  38 , and is then turned over along the curve to be sent to the pair of transportation rollers  31 . 
     The medium is sent to the position where it faces the line head  51  again. At this position, the second side, which is the opposite of the already-recorded first side, of the medium faces the line head  51 . This makes it possible to perform recording on the second side of the medium by means of the line head  51 . 
     Next, a movement mechanism  60  configured to move the head unit  50  in the V-axis direction will now be explained. 
     The movement mechanism  60  includes a right guide member  61 A, a second left guide member  61 B- 2 , a second member  63 , and first pinions  65 , which are illustrated in  FIGS.  4  and  5   , and third rack forming members  64 , and second pinions  67 , which are illustrated in  FIG.  3   . The movement mechanism  60  is configured such that the first pinions  65  apply an external force in a moving direction to second rack forming members  62 , a component of the head unit  50 . 
     The second rack forming member  62  is an example of a displacement member. The second rack forming members  62  and a unit body  50   a  constitute the head unit  50 . The head unit  50  includes the unit body  50   a , which includes the line head  51 , and the second rack forming members  62 . 
     A relative position between the second rack forming members  62  and the unit body  50   a  is changeable in the V-axis direction. This will be described later. 
     A first left guide member  61 B- 1  illustrated in  FIG.  8    is provided on the −V-directional side with respect to the second left guide member  61 B- 2 . In the description below, the right guide member  61 A, the first left guide member  61 B- 1 , and the second left guide member  61 B- 2  may be hereinafter referred to as “guide member  61 ” when there is no need to distinguish them from one another. 
     The guide member  61  is provided in a fixed manner on the frame of the apparatus (not illustrated). 
     First, a structure for guiding the head unit  50  in the V-axis direction will now be explained. 
     On the −Y-side lateral portion of the head unit  50  in the Y-axis direction, that is, on the side portion facing the right guide member  61 A, a second guided roller  52 B and a third guided roller  52 C are provided as illustrated in  FIG.  3   . Each of the second guided roller  52 B and the third guided roller  52 C is provided on a corresponding shaft  49  protruding in the −Y direction. Each of the second guided roller  52 B and the third guided roller  52 C is a bearing provided on the shaft  49  in such a way as to be able to rotate freely. The second guided roller  52 B and the third guided roller  52 C are spaced apart from each other in the V-axis direction. The second guided roller  52 B is located on the −V-directional side with respect to the third guided roller  52 C. 
     The second guided roller  52 B is an example of a second guided portion. The third guided roller  52 C is an example of a third guided portion. 
     On the +Y-side lateral portion of the head unit  50  in the Y-axis direction, that is, on the side portion facing the first left guide member  61 B- 1  and the second left guide member  61 B- 2 , a first guided roller  52 A and a fourth guided roller  52 D are provided as illustrated in  FIG.  6   . In  FIG.  6   , the head unit  50  only is illustrated with omission of the movement mechanism  60  illustrated in  FIG.  3   . 
     Each of the first guided roller  52 A and the fourth guided roller  52 D is provided on a corresponding shaft  49  protruding in the +Y direction. Each of the first guided roller  52 A and the fourth guided roller  52 D is a bearing provided on the shaft  49  in such a way as to be able to rotate freely. The first guided roller  52 A and the fourth guided roller  52 D are spaced apart from each other in the V-axis direction. The first guided roller  52 A is located on the −V-directional side with respect to the fourth guided roller  52 D. 
     The first guided roller  52 A is an example of a first guided portion. 
     As illustrated in  FIG.  7   , a first right guide groove  61   b  is formed in the V-axis direction in the right guide member  61 A disposed to face the −Y-side lateral portion of the head unit  50 . The second guided roller  52 B and the third guided roller  52 C, which are provided on the −Y-side lateral portion of the head unit  50  as described above, are inserted in the first right guide groove  61   b , and, because of this structure, the −Y-side lateral portion of the head unit  50  is guided by the first right guide groove  61   b  in the V-axis direction. 
     The reference sign S 2  denotes the lower surface of the first right guide groove  61   b . This surface will be hereinafter referred to as “second guide surface”. The second guided roller  52 B and the third guided roller  52 C are supported by the second guide surface S 2  and receive a reaction force from the second guide surface S 2 . 
     A normal force which the second guided roller  52 B receives from the second guide surface S 2  is indicated by an arrow with the reference sign H 2  in  FIG.  10   . A normal force which the third guided roller  52 C receives from the second guide surface S 2  is indicated by an arrow with the reference sign H 3  in  FIG.  10   . In addition, an arrow with the reference sign W 2  in  FIG.  10    indicates a force of contact of the second guided roller  52 B with the second guide surface S 2 , perpendicularly thereto, due to the own weight of the head unit  50 , and an arrow with the reference sign W 3  in  FIG.  10    indicates a force of contact of the third guided roller  52 C with the second guide surface S 2 , perpendicularly thereto, due to the own weight of the head unit  50 . 
     The greater the angle of inclination a of the V-axis direction with respect to the horizontal direction is, the less the magnitude of the normal force H 2 , the normal force H 3 , the force W 2 , and the force W 3  is. 
     Next, as illustrated in  FIG.  8   , a first left guide groove  61   d  is formed in the V-axis direction in the first left guide member  61 B- 1  and the second left guide member  61 B- 2 , which are disposed to face the +Y-side lateral portion of the head unit  50 . The first left guide member  61 B- 1  is located on the −V-directional side with respect to the second left guide member  61 B- 2 , and there is a gap G 1  between the first left guide member  61 B- 1  and the second left guide member  61 B- 2  in the V-axis direction. Therefore, the first left guide groove  61   d  is in a state of being split in a range of the gap G 1 . In  FIG.  8   , the first left guide groove formed in the first left guide member  61 B- 1  is denoted as  61   d - 1 , and the first left guide groove formed in the second left guide member  61 B- 2  is denoted as  61   d - 2 . However, they may be hereinafter collectively referred to as the first left guide groove  61   d.    
     The gap G 1  is a clearance for allowing the wiper unit  43  described earlier with reference to  FIG.  2    to move in the Y-axis direction while passing between the first left guide member  61 B- 1  and the second left guide member  61 B- 2 . 
     The first guided roller  52 A and the fourth guided roller  52 D, which are provided on the +Y-side lateral portion of the head unit  50 , are inserted in the first left guide groove  61   d , and, because of this structure, the +Y-side lateral portion of the head unit  50  is guided by the first left guide groove  61   d  in the V-axis direction. 
     The reference sign S 1 - 1  denotes the lower surface of the first left guide groove  61   d - 1 . The reference sign S 1 - 2  denotes the lower surface of the first left guide groove  61   d - 2 . Both the surface S 1 - 1  and the surface S 1 - 2  will be hereinafter referred to as “first guide surface”. The first guide surface S 1 - 1 , S 1 - 2  is a surface parallel to the second guide surface S 2 . 
     The first guided roller  52 A and the fourth guided roller  52 D are supported by the first guide surface S 1 - 1  or the first guide surface S 1 - 2  and receive a reaction force from the first guide surface S 1 - 1  or the first guide surface S 1 - 2 . 
       FIG.  8    illustrates a state in which the head unit  50  is located at the recording position. In this state, as illustrated therein, the first guided roller  52 A is located inside the first left guide groove  61   d - 1  and is supported by the first guide surface S 1 - 1 , whereas the fourth guided roller  52 D is located inside the gap G 1  and is supported neither by the first guide surface S 1 - 1  nor by the first guide surface S 1 - 2 . 
     Therefore, when the head unit  50  is located at the recording position, the head unit  50  is supported at one point via the first guided roller  52 A on its +Y-side lateral portion and at two points via the second guided roller  52 B and the third guided roller  52 C on its −Y-side lateral portion, namely, at three points in total. 
     As is clear from  FIG.  8   , when the head unit  50  moves from the recording position to the retraction position, the first guided roller  52 A and the fourth guided roller  52 D enter the first left guide groove  61   d - 2  and are supported by the first guide surface S 1 - 2 . 
     Since the gap G 1  is narrower than the interval between the first guided roller  52 A and the fourth guided roller  52 D in the V-axis direction, on the +Y-side lateral portion of the head unit  50 , either one of the first guided roller  52 A and the fourth guided roller  52 D is, or both are, supported by the first guide surface S 1 - 1  or the first guide surface S 1 - 2 . 
     A third guide groove  61   j  and a fourth guide groove  61   k  are formed in the second left guide member  61 B- 2  in a direction intersecting with the first left guide groove  61   d . When the head unit  50  moves to the most-retracted position in the +V direction, the first guided roller  52 A faces the third guide groove  61   j , and the fourth guided roller  52 D faces the fourth guide groove  61   k . In this state, the first guided roller  52 A can be moved upward along the third guide groove  61   j , and the fourth guided roller  52 D can be moved upward along the fourth guide groove  61   k.    
     Similarly, in the right guide member  61 A described earlier with reference to  FIG.  7   , a third guide groove  61   j  and a fourth guide groove  61   k  are formed in a direction intersecting with the first right guide groove  61   b . When the head unit  50  moves to the most-retracted position in the +V direction, the second guided roller  52 B faces the third guide groove  61   j , and the third guided roller  52 C faces the fourth guide groove  61   k . In this state, the second guided roller  52 B can be moved upward along the third guide groove  61   j , and the third guided roller  52 C can be moved upward along the fourth guide groove  61   k.    
     The third guide groove  61   j  and the fourth guide groove  61   k  are formed almost in the F-axis direction, though slightly at an angle with respect to the F-axis direction. 
     With the above structure, the head unit  50  having been moved to the most-retracted position in the +V direction can be detached upward. Moreover, at this position, the head unit  50  can be mounted onto the printer body  2  by going through procedures opposite of the case of detachment. The third guide groove  61   j  and the fourth guide groove  61   k  serve as guides for guiding the head unit  50  in the attachment/detachment direction. 
     Since the head unit  5   o  is configured to be detachably attached to the printer body  2 , the maintenance/replacement of the head unit  50  is easy. 
     Next, as illustrated in  FIGS.  4  and  5   , on the guide member  61 , a first rack  61   a  is formed in the V-axis direction on its side facing the head unit  50 . 
     The second rack forming member  62  is provided on each of the two ends of the head unit  50  in the Y-axis direction. A second rack  62   a  is formed on the second rack forming member  62  in the V-axis direction. The first rack  61   a  and the second rack  62   a  face each other. The first pinion  65  is disposed between the first rack  61   a  and the second rack  62   a . The first pinion  65  is in mesh with both the first rack  61   a  and the second rack  62   a.    
     The face-width direction of all of the first rack  61   a , the second rack  62   a , and the first pinion  65  is along the F-axis direction, which is orthogonal to the moving direction of the head unit  50 . 
     The first pinion  65  is provided rotatably on the second member  63 . As illustrated in  FIG.  3   , a lower-roller support member  54  is provided on each of the two ends of the second member  63  in the Y-axis direction. Two lower rollers  53  are provided on the lower-roller support member  54 , with a space therebetween in the V-axis direction. The lower roller  53  is a driven roller supported by the lower-roller support member  54  in such a way as to be able to rotate freely. 
     The two lower rollers  53  provided on the −Y-side lateral portion of the head unit  50  are inserted in a second right guide groove  61   c  formed in the V-axis direction in the right guide member  61 A as illustrated in  FIG.  7    and is guided by the second right guide groove  61   c  in the V-axis direction. 
     The two lower rollers  53  provided on the +Y-side lateral portion of the head unit  50  are inserted in a second left guide groove  61   e  formed in the V-axis direction in the second left guide member  61 B- 2  as illustrated in  FIG.  8    and is guided by the second left guide groove  61   e  in the V-axis direction. 
     As illustrated in  FIG.  3   , the third rack forming members  64  are provided under the second member  63 . A third rack  64   a  is formed on the bottom of the third rack forming member  64  in the V-axis direction. The face-width direction of the third rack  64   a  is along the Y-axis direction. The second pinion  67  is in mesh with the third rack  64   a.    
     The third rack forming member  64  is provided on the bottom of the second member  63  at each of the two ends in the Y-axis direction. On a rotation shaft  68  having its rotational axis parallel to the Y-axis direction, the second pinion  67  is provided at a position where it faces the third rack  64   a . The two second pinions  67  are configured to rotate simultaneously due to the rotation of the rotation shaft  68 . The power of a motor  59  is transmitted to the rotation shaft  68  via a gear mechanism that is not illustrated in  FIG.  3   . 
     In  FIG.  3   , the reference numeral  58  denotes a control unit that controls the motor  59 . Based on a signal received from a reference position sensor that is not illustrated and based on a drive amount of the motor  59 , the control unit  58  is able to obtain information on the position of the head unit  50  in the V-axis direction. 
     In the structure described above, when the second pinions  67  rotate by being driven by the motor  59 , the second member  63  moves in the V-axis direction. Since the guide member  61  illustrated in  FIGS.  4  and  5   , that is, the first rack  61   a , is provided in a fixed manner, the first pinion  65  provided on the second member  63  moving in the V-axis direction rotates due to meshing engagement with the first rack  61   a.    
     Since the first pinion  65  is in mesh with the second rack  62   a  provided on the head unit  50 , due to the rotation of the first pinion  65 , the head unit  50  moves in such a way as to be pushed in the V-axis direction. 
     For example, when the second member  63  moves in the +V direction by being driven by the motor  59  in a state in which the head unit  50  is located at the recording position illustrated in  FIG.  4   , the first pinion  65  located on the right side in  FIG.  4    rotates counterclockwise in  FIG.  4   , and the first pinion  65  located on the left side in  FIG.  4    rotates clockwise in  FIG.  4   . This causes the head unit  50  to move in the +V direction. 
     When the second member  63  moves in the −V direction by being driven by the motor  59  in a state in which the head unit  50  is located at the retraction position illustrated in  FIG.  5   , the first pinion  65  located on the right side in  FIG.  5    rotates clockwise in  FIG.  5   , and the first pinion  65  located on the left side in  FIG.  5    rotates counterclockwise in  FIG.  5   . This causes the head unit  50  to move in the −V direction. 
     To be exact, a force for movement in the −V direction acts on the head unit  50  due to the action of gravity. This is because the −V direction includes a −Z-directional component. Therefore, when the head unit  50  moves in the −V direction, the movement mechanism  60  applies a +V-directional force to the head unit  50  and is thus in a state of restricting the gravitational movement of the head unit  50  in the −V direction. However, the movement mechanism  60  applies a −V-directional force to the head unit  50  after the head unit  50  comes into contact with the adjustment cams  80  to be described later (see  FIG.  10   ). This will be described later. 
     When the head unit  50  moves in the +V direction, the movement mechanism  60  applies a +V-directional force to the head unit  50 . 
     The range, in the V-axis direction, denoted as M 1  in  FIGS.  4  and  5    is a moving range of the second member  63 , with the center of rotation of the first pinion  65  taken as a reference. The range, in the V-axis direction, denoted as M 2  in  FIGS.  4  and  5    is a moving range of the head unit  50 , with the position of the −V-side end of the second rack forming member  62  taken as a reference. 
     As described above, though the head unit  50  is configured to move in the V-axis direction due to the rotation of the first pinions  65 , the first pinions  65  themselves also are configured to move in the V-axis direction. For this reason, the moving range M 2  of the head unit  50  is wider than the moving range M 1  of the second member  63 . In the present embodiment, the moving range M 2  is approximately twice as wide as the moving range M 1 . 
     As described above, the movement mechanism  60  includes the guide member  61  on which the first rack  61   a  is formed in the moving direction of the head unit  50 , the first pinion  65  which is in mesh with the first rack  61   a , the second rack  62   a  which is provided on the head unit  50  at a position where it faces the first rack  61   a  and is formed in the V-axis direction, that is, the moving direction of the head unit  50 , and is in mesh with the first pinion  65 , and the second member  63 , on which the first pinion  65  is provided rotatably and which is able to move in the V-axis direction by receiving the power of the motor  59 . Due to the rotation of the first pinion  65  configured to move in the V-axis direction, a moving amount of the head unit  50  is larger than a moving amount of the second member  63 . In other words, it is possible to secure a sufficient moving amount of the head unit  50  while suppressing a moving amount of the second member  63 . Therefore, it is possible to prevent an increase in size of a mechanism configured to move the second member  63 . Specifically, in the present embodiment, it is possible to reduce the length of the third rack  64   a  in the V-axis direction. Consequently, it is possible to prevent an increase in size of the printer  1 . 
     Moreover, since the movement mechanism  60  is provided on each of the two sides of the head unit  50  in the Y-axis direction, it is possible to make a V-directional moving amount on one end side of the head unit  50  in the Y-axis direction equal to a V-directional moving amount on the other end side of the head unit  50  in the Y-axis direction. By this means, it is possible to move the head unit  50  in the V-axis direction while keeping the positional orientation of the head unit  50  properly. 
     The face-width direction of the first rack  61   a , the second rack  62   a , and the first pinion  65  is along the F-axis direction. The F-axis direction is substantially along the direction in which the head unit  50  is attachable and detachable. Because of this structure, when the head unit  50  is attached/detached, the meshing engagement of the first rack  61   a  with the first pinion  65  and the meshing engagement of the first pinion  65  with the second rack  62   a  do not obstruct the attachment/detachment work. Therefore, it is possible to attach/detach the head unit  50  easily. 
     In addition, even if vibration of the first pinion  65  in the face-width direction occurs when the second member  63  moves, it is hard for the vibration to be transmitted to the second rack  62   a , that is, to the head unit  50 ; therefore, it is possible to protect the head unit  50  from the vibration and thus prevent the head unit  50  from breaking down. 
     The face-width direction of the first rack  61   a , the second rack  62   a , and the first pinion  65  is along the F-axis direction, and is, in the present embodiment, slightly at an angle with respect to the direction in which the head unit  50  is attachable and detachable. However, it may be parallel to the direction in which the head unit  50  is attachable and detachable. 
     Furthermore, it is possible to move the second member  63  in the V-axis direction while keeping the positional orientation of the second member  63  properly because a plurality of third racks  64   a  and a plurality of second pinions  67  are provided in the Y-axis direction as illustrated in  FIG.  3   . This makes it also possible to move the head unit  50  while keeping the positional orientation of the head unit  50  properly. 
     Next, the structure of the head unit  50  will now be further explained. 
     As described earlier, the head unit  50  includes the unit body  50   a , which includes the line head  51 , and the second rack forming members  62  as an example of a displacement member. 
     The unit body  50   a  has engagement pins  50   d  (see  FIG.  10   ), as portions for engagement with the second rack forming member  62 , on each of the two sides in the Y-axis direction. Specifically, two engagement pins  50   d  are provided on each of the two sides of the unit body  50   a  in the Y-axis direction, with a space therebetween in the V-axis direction. Two guide holes  62   b  extending in the V-axis direction are provided in the second rack forming member  62 , with a space therebetween in the V-axis direction. The engagement pins  50   d  are inserted in the guide holes  62   b . This structure makes a relative position between the unit body  50   a  and the second rack forming member  62  changeable while coupling them to each other. 
     A spring  55 , which is an example of a pushing member, is provided between the unit body  50   a  and the second rack forming member  62  (see  FIG.  6   , too). In the present embodiment, the spring  55  is a helical compression spring. However, the spring  55  is not limited to a helical compression spring. It may be a helical tension spring or a helical torsion spring, etc. as long as it is able to exert a force F 3  to be described later (see  FIG.  11   ) between the unit body  50   a  and the second rack forming member  62 . 
     In  FIG.  10   , the reference sign  50   c  denotes a spring bearing portion of the unit body  50   a , and the reference sign  62   c  denotes a spring bearing portion of the second rack forming member  62 . The spring  55  exerts a pushing force between the spring bearing portion  50   c  and the spring bearing portion  62   c . The pushing force acts to increase the interval between the spring bearing portion  50   c  and the spring bearing portion  62   c.    
     When the head unit  50  is not in contact with the adjustment cams  80  to be described below, the spring  55  is in a most-expanded state between the spring bearing portion  50   c  and the spring bearing portion  62   c , and the engagement pins  50   d  are located at the −V-side end of the guide holes  62   b.    
     Next, the adjustment cams  80 , which are provided on the −V-directional side with respect to the head unit  50 , will now be described. The adjustment cam  80  is able to rotate on an eccentric shaft  81  by receiving power from a motor that is not illustrated. As illustrated in  FIG.  14   , the adjustment cam  80  is provided for each of the two side portions of the head unit  50  in the Y-axis direction. In  FIG.  14   , the adjustment cams  80  are hatched for illustrative purpose. 
     The head unit  50  has a cam contact surface  50   b  for contact with the adjustment cam  80 . As illustrated in  FIG.  14   , the cam contact surface  50   b  is provided on each of the two side portions of the head unit  50  in the Y-axis direction. 
     The cam contact surface  50   b  comes into contact with the adjustment cam  80 , thereby defining the recording position of the head unit  50 . That is, the adjustment cam  80  serves as a positioning portion with which a part of the head unit  50  moving from the retraction position toward the recording position comes into contact for positioning the head unit  50  at the recording position. 
     Since the adjustment cam  80  is configured to rotate on the eccentric shaft  81 , it is possible to adjust the position of the cam contact surface  50   b  in the V-axis direction, that is, the recording position, by the rotation of the adjustment cam  80 . The adjustment of the recording position is made based on, for example, the thickness of the medium on which recording is to be performed. 
     When the head unit  50  is moved to the recording position by driving the motor  59 , the control unit  58  (see  FIG.  3   ) further drives the motor  59  from a state in which the cam contact surface  50   b  has come into contact with the adjustment cam  80 , thereby moving the second rack forming member  62  in the −V direction. The unit body  50   a  does not move in the −V direction in this process because of the contact of the cam contact surface  50   b  with the adjustment cam  80 , and, therefore, the second rack forming member  62  alone moves in the −V direction as depicted by a change from  FIG.  10    to  FIG.  11   . The spring  55  contracts due to this relative movement of the second rack forming member  62  in relation to the unit body  50   a , thereby exerting the force F 3  illustrated in  FIG.  11    on the unit body  50   a.    
     As described above, the head unit  50  includes: the unit body  50   a  having the line head  51 , the second rack forming member  62  whose relative position in relation to the unit body  50   a  is changeable in the moving direction of the head unit  50 , and the spring  55  provided between the unit body  50   a  and the second rack forming member  62  and serving as a pushing member configured to push the unit body  50   a  toward the adjustment cam  80  when the head unit  50  is located at the recording position. The movement mechanism  60  is configured to apply, to the second rack forming member  62 , a force for moving the head unit  50 . Because of this structure, high stop precision is not required when stopping the head unit  50  moved to the recording position by the movement mechanism  60  in a state in which the unit body  50   a  has come into contact with the adjustment cam  80 . This makes the position control of the head unit  50  easier. 
     In a state illustrated in  FIG.  11   , the first pinion  65  exerts a force F 1  in the −V direction on the second rack forming member  62 . For the purpose of keeping this state, the control unit  58  (see  FIG.  3   ) may perform the hold control of the motor  59 . 
     Moreover, in this state, the unit body  50   a  receives a reaction force F 2  in the +V direction from the adjustment cam  80  at the position of the cam contact surface  50   b.    
     The direction of the reaction force F 2  is the opposite of the direction of the force F 1 . In addition, the position where the reaction force F 2  acts is away from the position where the force F 1  acts. Therefore, a moment of force Ma for counterclockwise rotation in  FIG.  11    acts on the head unit  50 . 
     Both the force F 1  and the reaction force F 2  act at the +Y-side lateral portion and the −Y-side lateral portion. In the present embodiment, the magnitude of the force F 1  acting at the +Y-side lateral portion is almost the same as the magnitude of the force F 1  acting at the −Y-side lateral portion. In addition, the magnitude of the reaction force F 2  acting at the +Y-side lateral portion is almost the same as the magnitude of the reaction force F 2  acting at the −Y-side lateral portion. Therefore, the magnitude of the moment of force Ma acting at the +Y-side lateral portion is also almost the same as the magnitude of the moment of force Ma acting at the −Y-side lateral portion. 
     The moment of force Ma acts on the third guided roller  52 C as a pushing force R 3  to push it against the second guide surface S 2 . In addition, the moment of force Ma acts on the second guided roller  52 B as a lifting force R 2  to lift it away from the second guide surface S 2 . 
     The pushing force R 3  assists the force of contact W 3  of the third guided roller  52 C with the second guide surface S 2  due to the own weight of the head unit  50 . Therefore, the third guided roller  52 C does not get lifted away from the second guide surface S 2 . By contrast, the lifting force R 2  acts in such orientation that cancels the force of contact W 2  of the second guided roller  52 B with the second guide surface S 2  due to the own weight of the head unit  50 . Therefore, if the lifting force R 2  surpasses the force W 2 , the second guided roller  52 B gets lifted away from the second guide surface S 2 . Since this will make the positional orientation of the head unit  50  improper, there is a risk that the quality of recording might be affected. 
     Since the head unit  50  is supported at one point via the first guided roller  52 A on its +Y-side lateral portion, the first guided roller  52 A does not get lifted away from the first guide surface S 1 - 1  of the first guided roller  52 A; however, because of susceptibility to rotation around the first guided roller  52 A, the positional orientation of the head unit  50  is unstable due to the effect of the moment of force Ma. 
     The greater the magnitude of the force F 1  is, the greater the magnitude of the moment of force Ma is. The greater the magnitude of the force F 3  is, the greater the magnitude of the moment of force Ma is. The greater the distance between the position where the force F 1  acts and the position where the reaction force F 2  acts in the F-axis direction, the greater the magnitude of the moment of force Ma is. 
     In the present embodiment, in order to suppress the instability in the positional orientation of the head unit  50  due to the moment of force Ma, a unit pusher  70  configured to exert, on the head unit  50 , a pushing force F 4  acting in a direction of canceling the rotation caused by the moment of force Ma is provided. In the present embodiment, the unit pusher  70  is provided near the −Y-side end portion of the head unit  50  in the Y-axis direction as illustrated in  FIG.  14   . 
     As illustrated in  FIG.  12   , the unit pusher  70  includes: a rotary member  71  provided rotatably on the head unit  50  and having a free end  71   d , a spring  73  (see  FIG.  13   ) provided on the head unit  50  and configured to push the rotary member  71  in a direction in which the free end  71   d  goes away from the head unit  50  (the +F direction), and a driven roller  76  provided independently of the head unit  50  and configured to come into contact with the rotary member  71  when the head unit  50  is located at the recording position. The driven roller  76  is an example of a contact member configured to come into contact with the rotary member  71 . 
     Since the unit pusher  70  includes the rotary member  71 , the spring  73 , and the driven roller  76  as described above, it is possible to make the structure of the unit pusher  70  simple. 
     More specifically, the driven roller  76  is provided rotatably on a support member  75  via a rotation shaft  77 . In the present embodiment, a single driven roller  76  is provided at a position where it interacts with the rotary member  71  in the Y-axis direction. 
     In  FIGS.  10  to  13   , the rotary member  71  is provided on the unit body  50   a  in such a way as to be able to rotate on a rotation shaft  72 . The axial centerline of the rotation shaft  72  extends in the Y-axis direction, and the free end  71   d  is located on the +V-directional side with respect to the rotation shaft  72 . 
     As illustrated in  FIG.  13   , the spring  73  is provided under the rotary member  71  and pushes the rotary member  71  in the direction in which the free end  71   d  goes away from the head unit  50  (the +F direction). Due to the urging force of the spring  73 , the rotary member  71  is pushed clockwise in  FIG.  13   . In the present embodiment, the spring  73  is a helical compression spring. However, the spring  73  is not limited to a helical compression spring. It may be a helical tension spring or a helical torsion spring, etc. as long as it is able to push the rotary member  71  clockwise in  FIG.  13   . 
     As illustrated in  FIG.  13   , the unit body  50   a  includes a rotation restriction member  78 . The rotation restriction member  78  includes a rotation restriction portion  78   a  having a protrusion shape. The rotation restriction portion  78   a  is inserted in a window hole  71   c  formed in the rotary member  71 . Because of this structure, in a state in which the rotary member  71  is away from the driven roller  76 , as illustrated in  FIG.  13 A , the lower edge of the window hole  71   c  is in contact with the rotation restriction portion  78   a  so as to restrict the clockwise rotation of the rotary member  71  in  FIG.  13   . 
     When the head unit  50  moves from this state toward the recording position, the rotary member  71  comes into contact with the driven roller  76  and rotates counterclockwise as depicted by a change from  FIG.  13 A  to  FIG.  13 B . This causes the contraction of the spring  73 , and the urging force of the spring  73  acts on a spring bearing  50   e  provided for the spring  73 . This urging force serves as the pushing force F 4  illustrated in  FIG.  11   . 
     The urging force of the spring  73  counteracts the lifting force R 2 . The magnitude of the urging force of the spring  73  is set such that the second guided roller  52 B will never get lifted away from the second guide surface S 2 . 
     As described above, the printer  1  includes the unit pusher  70  configured to apply, to the head unit  50 , the pushing force F 4  (see  FIG.  11   ) acting in a direction of canceling the rotation of the head unit  50  when the head unit  50  is located at the recording position. The pushing force F 4  applied by the unit pusher  70  causes the second guided roller  52 B to be pushed against the second guide surface S 2  in spite of the lifting force R 2 . This makes it possible to suppress the instability in the positional orientation of the head unit  50  due to the moment of force Ma and thus obtain good recording quality. 
     Since the unit pusher  70  behaves to cancel the rotation of the head unit  50  by pushing the head unit  50  in a direction intersecting with the moving direction of the head unit  50 , it is possible to prevent the unit pusher  70  from being obstructive to the movement of the head unit  50  in the V-axis direction. Consequently, it is possible to prevent an increase in cost and an increase in power consumption resulting from increasing the rated output of the motor  59  (see  FIG.  3   ), which is the power source for movement of the head unit  50 . 
     In the present embodiment, the direction in which the head unit  50  is pushed by the unit pusher  70  is the −F direction, which is orthogonal to the V-axis direction, in which the head unit  50  is configured to move. However, the pushing direction of the unit pusher  70  is not limited to this direction but may be any direction intersecting with the V-axis direction, in which the head unit  50  is configured to move. 
     The head unit  50  includes the first guided roller  52 A on one end portion in the Y-axis direction (+Y-side end portion) and the second guided roller  52 B and the third guided roller  52 C on the other end portion in the Y-axis direction (−Y-side end portion) with a space therebetween in the moving direction of the head unit  50 . The first guided roller  52 A is guided in the moving direction of the head unit  50  while being supported by the first guide surface S 1 - 1 , S 1 - 2  (see  FIG.  8   ) extending in the moving direction of the head unit  50 . The second guided roller  52 B and the third guided roller  52 C are guided in the moving direction of the head unit  50  while being supported by the second guide surface S 2  (see  FIG.  7   ) extending in the moving direction of the head unit  50 . At least in a state of being located at the recording position, the head unit  50  is supported at three points via the first guided roller  52 A, the second guided roller  52 B, and the third guided roller  52 C. This makes the positional orientation of the head unit  50  at the recording position stable, resulting in good recording quality. 
     In  FIG.  14   , the reference sign Q 1  denotes a first position where the first guided roller  52 A is in contact with the first guide surface S 1 - 1 , the reference sign Q 2  denotes a second position where the second guided roller  52 B is in contact with the second guide surface S 2 , and the reference sign Q 3  denotes a third position where the third guided roller  52 C is in contact with the second guide surface S 2 . The reference sign Q 4  denotes a fourth position where the unit pusher  70  applies the pushing force F 4  to the head unit  50 . In the present embodiment, the fourth position Q 4  is located inside an area At of a triangle having vertices at the first position Q 1 , the second position Q 2 , and the third position Q 3  as viewed in a direction orthogonal to a plane including the first position Q 1 , the second position Q 2 , and the third position Q 3  (+F direction). 
     Because of this structure, the first guided roller  52 A is properly pushed against the first guide surface S 1 - 1 , the second guided roller  52 B is properly pushed against the second guide surface S 2 , and the third guided roller  52 C is properly pushed against the second guide surface S 2 . Consequently, the positional orientation of the head unit  50  is stable, and it is possible to obtain good recording quality. 
     However, the fourth position Q 4  may be located on an edge of the area At. Alternatively, the fourth position Q 4  may be located outside the area At. 
     In  FIG.  14   , the reference sign Q 5  denotes the position of the barycenter of the head unit  50  when viewed in a direction orthogonal to a plane including the first position Q 1 , the second position Q 2 , and the third position Q 3  (+F direction). The barycenter Q 5  is located inside the area At of the triangle having vertices at the first position Q 1 , the second position Q 2 , and the third position Q 3 . Because of this structure, the positional orientation of the head unit  50  is stable. 
     As described above, the second guided roller  52 B is located at a position where it gets lifted away from the second guide surface S 2  due to the rotation of the head unit  50  caused by the moment of force Ma, and the third guided roller  52 C is located at a position where it is pushed against the second guide surface S 2  due to the rotation of the head unit  50  caused by the moment of force Ma. The fourth position Q 4  where the unit pusher  70  applies the pushing force F 4  to the head unit  50  is located on the side closer to the second position Q 2  with respect to a halfway position Yc located between the first position Q 1  and the second position Q 2  in the Y-axis direction. In addition, the fourth position Q 4  is located on the side closer to the second position Q 2  with respect to a halfway position Vc located between the second position Q 2  and the third position Q 3  in the V-axis direction. 
     Because of this structure, the head unit  50  is pushed at the position closer to the second guided roller  52 B, and the rotation of the head unit  50  is suppressed properly. 
     Notwithstanding the above description, the fourth position Q 4  may be located at the halfway position Yc, or on the side closer to the first position Q 1  with respect to the halfway position Yc, in the Y-axis direction. Similarly, the fourth position Q 4  may be located at the halfway position Vc, or on the side closer to the third position Q 3  with respect to the halfway position Vc, in the V-axis direction. 
     The axial centerline of the rotation shaft  72  of the rotary member  71  extends in the Y-axis direction, and the free end  71   d  is located on the +V-directional side with respect to the rotation shaft  72  in the V-axis direction, namely, on the side closer to the retraction position. The driven roller  76  is configured to move in relation to the rotary member  71  from the rotation shaft  72  toward the free end  71   d  when the head unit  50  moves from the retraction position to the recording position. Because of this structure, the magnitude of the force applied by the unit pusher  70  to the head unit  50  increases gradually when the head unit  50  moves from the retraction position to the recording position. That is, such a gradual increase in the magnitude of the pushing force makes it possible to avoid a heavy load from being applied suddenly when the head unit  50  moves to the recording position, thereby ensuring smooth movement of the head unit  50  to the recording position. 
     As illustrated in  FIG.  13   , the surface of the rotary member  71  for contact with the driven roller  76  is made up of a first contact surface  71   a  and a second contact surface  71   b , which is at a predetermined angle with respect to the first contact surface  71   a . When the head unit  50  moves to the recording position, the first contact surface  71   a  comes into contact with the driven roller  76  first. The first contact surface  71   a  fulfills a function of guiding the driven roller  76  to the second contact surface  71   b  at the time of switching from a state illustrated in  FIG.  13 A  to a state illustrated in  FIG.  13 B , thereby enabling the head unit  50  to move to the recording position more smoothly. 
     The unit pusher  70  further includes the rotation restriction portion  78   a  that restricts the rotation of the rotary member  71  in the direction in which the free end  71   d  of the rotary member  71  goes away from the head unit  50 . Because of this structure, it is possible to make a contact angle smaller when the driven roller  76  comes into contact with the rotary member  71 . The smaller contact angle further enhances the effect of avoiding a heavy load from being applied suddenly when the head unit  50  moves to the recording position. 
     In the present embodiment, the load applied to the rotary member  71  is reduced by using the driven roller  76  as the contact member configured to come into contact with the rotary member  71 . However, any other kind of fixed member may be used as the contact member in place of the driven roller  76 . 
     The scope of the present disclosure is not limited to the foregoing embodiments. The present disclosure can be modified in various ways within the scope of the recitation of appended claims. Needless to say, such modifications are within the scope of the present disclosure.