Abstract:
A print head is provided in a casing of a printing apparatus having a housing section which houses continuous paper therein, to perform printing on the continuous paper. A platen roller has a platen shaft rotatably supported on a cover of the printing apparatus which is pivotably supported on the casing to open or close the housing section. The platen roller being abutted against the print head through the continuous paper situated therebetween and rotating to feed the continuous paper, when the cover is closed. A head support member is disposed in the casing and has a head shaft which pivotably supports the print head so as to vary a distance with respect to the platen roller. A lock lever is pivotable about the platen shaft. The lock lever is engaged with the head shaft to determine a position of the platen roller with respect to the print head when the cover is closed.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a printer unit which effects printing on continuous paper such as rolled paper and a printing apparatus incorporating such a printer unit. 
     In the related art, one type of printing apparatus includes a housing section for housing continuous paper, such as rolled paper, and effects printing by drawing the continuous paper from the housing section. Printing apparatus of this type has an opening section that is opened and closed by a cover. The continuous paper is replaced and the inside of the printing apparatus is maintained through this opening section. When installing or replacing the continuous paper, the printing apparatus entails a necessity of manually drawing the continuous paper from the housing section and setting the thus-drawn continuous paper along a predetermined paper path. It is therefore preferable to locate a print head on the side of the housing and a platen roller disposed in a position opposite to the print head on the side of the cover for opening and closing the opening section of the housing. This configuration assures that the continuous paper can be easily aligned in the paper path when the cover is opened to replace the continuous paper because the platen roller retracts with the cover and thus opens the paper path. 
     If a thermal print head is used in a printing apparatus, securing of print quality requires accurate positioning of a platen roller with a print line of a print head and pressing of continuous paper against the print line of the print head (with the platen roller). To this end, such a cover of an ordinary thermal printing apparatus is equipped with a pivotable lock lever. The platen roller is positioned by causing the lock lever to engage with the housing. 
     However, in the related-art printing apparatus, the lock lever is pivotally supported by a lever shaft projecting from the platen frame. The lock lever is engaged with a locking shaft projecting from a head frame. Hence, there is a potential risk of accuracy of positioning of the platen roller with the print head being deteriorated by an error in machining of the platen frame, an error in attachment of the lever shaft to the platen frame, an error in machining of the head frame, and an error in attachment of the locking shaft to the head frame. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a printer unit, which enables an improvement in the accuracy of positioning of a platen roller with respect to a print head by minimizing error factors existing between the platen roller and the print head, which obviates a necessity for special lever axis (shaft) or locking axis (shaft), and which enables an attempt for reducing the number of parts and simplifying the structure thereof. 
     It is also an object of the invention to provide a printing apparatus incorporating such a printer unit. 
     In order to achieve the above objects, according to the present invention, there is provided a printer unit, comprising: 
     a print head, provided in a casing of a printing apparatus having a housing section which houses continuous paper therein, and operable to perform printing on the continuous paper; 
     a platen roller, having a platen shaft rotatably supported on a cover of the printing apparatus which is pivotably supported on the casing to open or close the housing section, the platen roller being abutted against the print head with the continuous paper therebetween and rotated to feed the continuous paper, when the cover is closed; 
     a head support member, disposed in the casing and pivotably supporting the print head around a head shaft so as to move the print head toward the platen roller; and 
     a lock lever, which is pivotable about the platen shaft and is engaged with the head shaft to determine a position of the platen roller with respect to the print head when the cover is closed. 
     Preferably, the head shaft is disposed closer to a pivot of the cover than a printing face of the print head. In such a configuration, since the lock lever is arranged so as not to project from the extremity of the cover, the lock lever is prevented from interfering with opening and closing of the cover, and designing of the cover can be facilitated. 
     Preferably, an imaginary line passing through an axis of the platen shaft and an axis of the head shaft is substantially parallel with a printing face of the print head when the cover is closed. In such a configuration, positioning of the platen roller with respect to the print head is facilitated, and printing accuracy can be improved by suppressing displacement of the platen roller resulting from driving reaction force. 
     Preferably, the printer unit further comprises: a platen frame, fixed on the cover, and formed with supporting holes elongated in a direction substantially perpendicular to a printing face of the print head when the cover is closed; and bearing members, through which both ends of the platen shaft is rotatably supported on the platen frame, each of the bearing members being supported by each of the supporting holes movably in an elongating direction of the supporting holes. In such a configuration, since the platen roller (platen shaft) is movable back and forth along with the lock lever, the platen roller can be positioned accurately with respect to the print head without being affected by an error in attachment of the head support member (or a head frame described below) to the casing or the platen frame to the cover. 
     Here, it is preferable that: the lock lever includes a first engagement member and a first stopper; the platen frame includes a second engagement member and a second stopper; the printer unit further comprises an urging member interposed between the first engagement member and the second engagement member so as to pivot the lock lever in a first direction such that the lock lever engages with the head shaft; and a pivotal movement of the lock lever in the first direction is restricted when the first stopper and the second stopper come in contact with each other. 
     It is also preferable that the lock lever is formed with a tapered portion which is brought into contact with the head shaft to pivot, for example, temporarily, the lock lever in a second direction opposite to the first direction during a closing operation of the cover. 
     Further, it is preferable that the head support member is formed with grooves into which the bearing members are respectively fitted when the cover is closed. 
     Still further, it is preferable that the head support member is formed with projections onto which the bearing members are respectively brought into contact during a closing operation of the cover, so that the print head is temporarily moved away from the platen roller. 
     Still further, it is preferable that the printer unit as set forth above, further comprises: a head frame, fixed to the casing while pivotably supporting the head support member, the head frame including a first stopper; and an urging member, interposed between the head frame and the head support member so as to pivot the head support member toward the platen roller. The head support member may also further include a second stopper so as to restrict a pivotal movement of the head support member when the first stopper and the second stopper come in contact with each other. 
     Here, it is preferable that the head frame is formed with grooves into which the bearing members are respectively fitted when the cover is closed. 
     Further, it is preferable that the head frame includes a guide member which guides the continuous paper into a space between the print head and the platen roller. 
     Still further, it is preferable that a dimension of each of the bearing members in an axial direction of the platen shaft is greater than an additional thickness of the head frame and the head support member. 
     Preferably, the lock lever includes a lock releaser which disengages the lock lever from the head shaft. 
     According to the present invention, there is also provided a printing apparatus incorporating the above described printer unit. 
     According to the present invention, there is also provided a printing apparatus, comprising: 
     a print head unit; 
     a platen unit; 
     a print head, provided in the print head unit, and operable to perform printing on continuous paper; 
     a platen roller, provided in the platen unit, having a platen shaft, the platen roller being abutted against the print head with the continuous paper therebetween and rotated to feed the continuous paper; 
     a head support member, provided in the print head unit, the head support member pivotably supporting the print head around a head shaft so as to move the print head toward the platen roller; and 
     a lock lever, provided in the platen unit, the lock lever being pivotable about the platen shaft and engaged with the head shaft to determine a position of the platen roller with respect to the print head. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a printing apparatus when a cover is closed; 
     FIG. 2 is a perspective view of the printing apparatus when the cover is opened; 
     FIG. 3 is a schematic cross-sectional view of the printing apparatus; 
     FIG. 4 is a fragmentary side view of a printer unit when the cover is closed; 
     FIG. 5 is a perspective view of the printer unit when the cover is closed; 
     FIG. 6 is a perspective view of the printer unit when the cover is opened; 
     FIG. 7 is a perspective view of the printer unit shown in FIG. 6 when viewed from another angle; 
     FIG. 8 is a perspective view of a platen frame; 
     FIG. 9 is a perspective view of a lock member; 
     FIG. 10 is a perspective view of a head support member; 
     FIG. 11 is a perspective view of the head support member provided with a print head; 
     FIGS. 12A to  12 C are descriptive views showing temporary retracting action of the print head; 
     FIG. 13 is a descriptive view showing positioning action of a platen roller when the cover is opened; and 
     FIG. 14 is a descriptive view showing positioning action of the platen roller when the cover is closed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the invention will be described hereinbelow by reference to the accompanying drawings. As will be known from FIGS. 1 to  3 , the printing apparatus  10  comprises a housing section  12  for housing rolled paper P as a type of continuous paper is provided in a casing  11 . An opening section  13  is formed above the housing section  12 , and rolled paper P is replaced through the opening section  13 . The opening section  13  is opened and closed by a cover  14  which is pivotable up and down while a rear end of the cover  14  is taken as a pivot. A slit-shaped discharging port  15  is formed between an front end of the cover  14  and a front edge of the opening section  13 . One end of the rolled paper P rotatably retained in the housing section  12  is withdrawn from the discharging port  15  by way of a paper path  16 . 
     Disposed along the paper path  16  are a thermal print head  17 , a platen roller  18  for transporting the rolled paper P at a position opposite the print head  17 , and a cutter unit  19  for cutting the rolled paper P at a position downstream of the platen roller  18 . When the printing apparatus  10  has received a print instruction, the print head  17  effects printing on the rolled paper P while the platen roller  18  feeds the rolled paper P. Subsequently, the printed portion of the paper is further advanced toward the discharging port  15 . When the trailing end of the printed portion reaches a particular position relative to the cutter unit  19 , the cutter unit  19  cuts the paper to separate the printed portion from the paper unwound from the rolled paper P. The separated portion is then supplied from the discharging port  15  as a single cut sheet to a user. 
     As shown in FIGS. 4 to  7 , a printing mechanism of the printing apparatus  10  is assembled into a unit such as a printer unit  20 . The printer unit  20  comprises a head unit  21  to be provided on a main body of the printing apparatus (i.e., the casing  11 ), and a platen unit  22  to be provided on the cover  14 . As a result, in a state in which the cover  14  is opened, the platen roller  18  to be built into the platen unit  22  retracts from the print head  17  to be built in the head unit  21 , thereby opening a paper path  16 . When the rolled paper P is replaced, the cover  14  is opened, and the rolled paper P is housed in the housing section  12 . Subsequently, one end of the rolled paper P is drawn to the outside of the casing  11 . In this state, the cover  14  is closed, whereby the rolled paper P is set along the paper path  16 . 
     The platen unit  22  comprises a platen frame  23  to be fixed on a lower face of the front end of the cover  14 ; a platen shaft  24  rotatably supported by the platen frame  23 ; a lock member  25  which pivots back and forth around the platen shaft  24 ; and springs  26  for urging the lock member  25  backward. As shown in FIG. 8, the platen frame  23  is formed so as to assume the shape of a gate when viewed from the front. Elongated platen support holes  23   b  are formed in respective side plates  23   a . The platen roller  18  is provided integrally in an intermediate portion of the platen shaft  24 . A platen gear  27  is provided integrally on the left end of the platen shaft  24 . Both ends of the platen shaft  24  penetrate through corresponding platen support holes  23   b  and are supported by the platen frame  23  via bearing members  28 . An inner side edge of each bearing member  28  extends toward the platen roller  18  so as to have a width wider than an additional thickness of a head frame  29  and a head support member  30  (described later) in an axial direction of the platen shaft  24 . 
     As shown in FIG. 9, the lock member  25  is formed so as to assume the shape of a gate when viewed from the front. A lock lever  25   a  is provided on either side of the lock member  25 . Integrally formed in the lock lever  25   a  are an engagement hook  25   b , a stopper piece  25   c , a spring engagement piece  25   d , a lock release piece  25   e , and a support hole  25   f . The support hole  25   f  is pivotably fitted around a corresponding bearing member  28 . The lock member  25  is supported so as to be pivotable back and forth around the platen shaft  24 . 
     Each of the springs  26  is interposed in a pulled state between a spring engagement piece  23   c  formed at the rear end of the platen frame  23  and the spring engagement piece  25   d  of the lock lever  25   a . Further backward pivotal movement of the lock levers  25   a , which are urged backward by the springs  26 , is restricted as a result of the stopper pieces  25   c  coming into contact with stopper pieces  23   d  of the platen frame  23 . At this time, the lock levers  25   a  are oriented in a direction substantially perpendicular to the cover  14 , thereby avoiding projection of the lock levers  25   a  from the extremity of the cover  14 . In place of the stopper pieces  23   d  of the platen frame  23 , projections projecting outside from side plates  23   a  may be formed. 
     The head unit  21  comprises a head frame  29  to be mounted on the main body of the printing apparatus; a head support member  30  to be provided on the head frame  29  so as to be pivotable back and forth; springs  31  for urging the head support member  30  to the platen roller  18 ; and a platen drive mechanism  32  for transmitting driving force to the platen roller  18 . The head frame  29  is formed so as to assume the shape of the letter U when viewed from the front. A step-shaped paper guide  29   a  (see FIG. 3) is formed at the rear end of the head frame  29  for guiding the rolled paper P drawn from the housing section  12  into a space defined between the print head  17  and the platen roller  18 . A fitting groove  29   c  is formed in each of side plate sections  29   b  of the head frame  29 . When the cover  14  is closed, the bearing members  28  are fitted into the fitting grooves  29   c  from above. 
     As shown in FIGS. 10 and 11, the head support member  30  is formed so as to assume the shape of the letter U when viewed from the top. The print head  17  is bonded integrally to a supporting face  30   a  opposing the platen roller  18 . The thermal print head  17  has the shape of a flat plate of specified thickness. A print line (heating element)  17   a  is formed at an upper front end so as to extend from side to side. In order to ensure print quality, the print head  17  of this type is required to press the rolled paper P against the print line  17   a . In order to satisfy this requirement, the head support member  30  is disposed to rotate freely back and forth on the head frame  29  by way of the rotary shaft  33 , and is urged to the platen roller  18  side by the springs  31 . 
     An arm section  30   b  is provided on either side of the head support member  30  so as to extend backward. A fitting groove  30   c  is formed in each of the arm sections  30   b  such that the respective bearing members  28  fit into the grooves  30   c  from above when the cover  14  is closed. Further, a contact projection  30   d  is formed integrally on each arm section  30   b  so as to come into contact with a corresponding bearing member  28  and to cause the head support member  30  (print head  17 ) to temporarily retract from the platen roller  18 . A support hole  30   e  is formed proximally below the fitting groove  30   c  on each of the arm sections  30   b . The rotary shaft  33  penetrating through the support holes  30   e  is offset backward with reference to a printing face of the print head  17  (i.e., close to a pivot  14   a  of the cover  14 ). Both ends of the rotary shaft  33  also serve as locking shafts which engage the engagement hooks  25   b  of the lock levers  25   a.    
     The springs  31  are interposed in a compressed state between the pair of spring support pieces  29   d  standing on the head frame  29  and the head support member  30  to be urged backward. As a result of stopper pieces  30   f  projecting from both ends of the head support member  30  coming into contact with the stopper pieces  29   e  of the head frame  29 , further backward pivotal movement of the head support member  30  is restricted. 
     Since the rotary shaft  33  is offset closer to the pivot  14   a  of the cover  14  than to the printing face of the print head  17 , the lock levers  25   a  can be arranged so as not to project from the extremity of the cover  14 . Consequently, elimination of an inconvenience, such as interference in opening and closing action of the cover  14  by the lock lever  25   a  can be achieved, along with facilitation of designing of the casing  11 . 
     Further, the necessity for special lever shaft or locking shaft is obviated, thereby enabling reduction of the number of components and simplifying the structure of a printing apparatus. 
     A platen drive mechanism  32  comprises a motor  34  disposed at a left inner part on the head frame  29 ; and a gear train  35  which transmits driving force of the motor  34  to the platen gear  27 . The gear train  35  comprises a drive gear  36  provided on a motor shaft  34   a  of the motor  34 ; a first transmission gear  37  meshing with the drive gear  36 ; a second transmission gear  37   a  formed integrally with the first transmission gear  37 ; a third transmission gear  38  meshing with the second transmission gear  37   a ; and a fourth transmission gear  38   a  formed integrally with the third transmission gear  38 . The gear train  35  is disposed along the left outside surface of the head frame  29 . When the cover  14  is closed, the platen gear  27  engages the fourth transmission gear  38   a . When the motor  34  is rotated in a predetermined direction in this state, the platen roller  18  performs a paper feeding operation. 
     Next, the temporary retracting action of the print head  17  to be performed at the time of closing of the cover  14  will be described by reference to FIGS. 12A to  12 C. As shown in FIG. 12A, when the cover  14  is opened, the platen roller  18  retracts with the cover  14  from the print head  17 , thereby opening the paper path  16 . At this time, the head support member  30  is rotated backward by pressing action of the springs  31 . In association with backward rotation, the print head  17  enters the path of movement of the platen roller  18 . 
     As shown in FIG. 12B, when the cover  14  is closed, the bearing members  28  for supporting both sides of the platen shaft  24  come into contact with the contact projections  30   d  of the head support member  30  at a position before a closing position. In response to the contact, the head support member  30  temporarily retracts and rotates forward. In association with such a temporary retracting rotation, an upper edge of the print head  17  retracts from the locus of movement of the platen roller  18 . As a result, the cover  14  can be closed without causing the platen roller  18  to come into contact with the upper edge of the print head  17 . 
     As shown in FIG. 12C, when the cover  14  reaches a predetermined closing position, the head support member  30  that has temporarily retracted and moved forward is rotated backward under the force of the springs  31  in association with the contact projections  30   d  departing from the bearing members  28 . As a result, the print line  17   a  of the print head  17  is pressed against the platen roller  18  via the rolled paper P, thus entering a printable state. 
     Next, the positioning operation of the platen roller  18  (cover locking operation) will be described by reference to FIGS. 13 and 14. As shown in FIG. 13, the lock levers  25   a  are disposed freely rotatable back and forth about the platen shaft  24 . When the cover  14  is opened, the lock levers  25   a  are rotated backward under the force of the springs  26 . At this time, the lock levers  25   a  are oriented in a direction substantially perpendicular to the cover  14 , thus avoiding projection from the extremity of the cover  14 . When an operation for closing the cover  14  is performed, tapered sections  25   g  formed at the extremities of the respective engagement hooks  25   b  come into contact with respective ends of the rotary shaft  33  at a position before the closing position. In association with the contacting action, the lock levers  25   a  are rotated forward. 
     As shown in FIG. 14, when the cover  14  reaches the closing position, the lock levers  25   a  are rotated backward under the force of the springs  26 , whereby the engagement hooks  25   b  engage the respective ends of the rotary shaft  33 . As a result, the platen roller  18  is positioned relative to the print line  17   a  of the print head  17 , and the opening and closing actions of the cover  14  are locked. The accuracy of positioning of the platen roller  18  relative to the print line  17   a  of the print head  17  is determined by members interposed between the print head  17  and the platen roller  18 ; that is, the head support member  30 , the rotary shaft  33 , the lock lever  25   a  (lock member  25 ), the bearing members  28 , and the platen shaft  24 , therefore, the platen roller  18  can be positioned with high accuracy with respect to the print line  17   a  without affecting the accuracy of the head frame  29  or that of the platen frame  23 . Since the platen support holes  23   b  are elongated in the front and rear directions, the platen roller  18  (platen shaft  24 ) can move back and forth along with the lock levers  25   a  (lock member  25 ). As a result, the platen roller  18  can be positioned accurately with respect to the print line  17   a  without being affected by an error in attachment of the platen frame  23  to the cover  14  or an error in attachment of the head frame  29  to the casing  11 . 
     Namely, the accuracy of positioning of the platen roller  18  and the print head  17  can be improved by minimizing error factors existing between the platen roller  18  and the print head  17 . 
     As shown in FIG. 14, a imaginary line L passing through the platen shaft  24  and the rotary shaft  33  is substantially parallel to the printing face of the print head  17 . In short, the rotary shaft  33  is placed proximally right below the platen shaft  24 . Hence, positioning of the platen roller  18  with respect to the print head  17  in a longitudinal (vertical) direction is facilitated. Further, the drive reaction force acting on the platen roller  18  is received at a position located proximally right below the platen roller  18 . There is inhibited displacement of the platen roller  18 , which would otherwise be caused by the drive reaction force, thereby improving printing accuracy. 
     The lock lever  25   a  is unlocked in accordance with actuation of unlock buttons (not shown) engaging the lock release pieces  25   e  of the lock levers  25   a.    
     An embodiment of the invention has been described by reference to the accompanying drawings. However, the invention is not limited to items described in the embodiment. Persons skilled in the art can freely modify or apply the invention on the basis of claims, the description of the invention, and the known technology. For instance, the invention can be applied to a printing apparatus in which a print head (head unit) is provided on a cover and in which a platen roller (platen unit) is provided on a main body.