Abstract:
A printing unit includes a thermal head, a platen roller, a head support member and a guide member. The platen roller is abutted against the thermal head with the recording sheet therebetween and rotated to feed the recording sheet. The head support member pivotably supports the thermal head around a pivot shaft so as to move the thermal head toward the platen roller. The head frame supports the head support member via the pivot shaft. The guide member guides the recording sheet between the thermal head and the platen roller. The thermal head and the guide member are positioned with respect to the head frame through the pivot shaft.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a printing unit and a thermal printer. 
         [0003]    2. Description of the Related Art 
         [0004]    Hitherto, a thermal printer has been known as a printer configured to perform printing on a recording sheet (heat-sensitive paper). The thermal printer includes a printing unit that can be reduced in size and weight, and has a simple configuration without using toner or ink. Therefore, the thermal printer is employed for cash registers or mobile terminal devices to be widely used to print various labels, receipts, and tickets. 
         [0005]    As the above-mentioned printing unit, there has been known a separate-type printing unit including a head unit and a platen unit mounted to the head unit separably. The head unit mainly includes a head frame, a pivot shaft supported on the head frame, a thermal head supported on the pivot shaft so as to be pivotable, and a guide member configured to guide the recording sheet to the thermal head. The platen unit includes a platen roller configured to feed the recording sheet. 
         [0006]    Incidentally, in the printing unit, the guide member is mounted to the head frame with fastening members, such as screws or dowels. Therefore, it may be difficult to position the thermal head and the guide member relative to each other with high accuracy depending on the dimension accuracy of the head frame or the like. Further, it is necessary to form mounting portions for the fastening members in each of the head frame and the guide member, thereby also causing a problem of leading to complication of the configuration and increase in the number of components. 
         [0007]    In view of the above-mentioned matters, in this technical field, there have been demanded a printing unit and a thermal printer, which are capable of positioning a guide member and a thermal head with high accuracy as well as simplifying their configurations and reducing the number of components. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one embodiment of the present invention, there is provided a printing unit, including: a thermal head operable to perform printing on a recording sheet; a platen roller abutted against the thermal head with the recording sheet therebetween and rotated to feed the recording sheet; a head support member pivotably supporting the thermal head around a pivot shaft so as to move the thermal head toward the platen roller; a head frame supporting the head support member via the pivot shaft; and a guide member configured to guide the recording sheet between the thermal head and the platen roller, wherein the thermal head and the guide member are positioned with respect to the head frame through the pivot shaft. 
         [0009]    In the above-mentioned printing unit according to the one embodiment of the present invention, the head support member includes: a head support wall having the thermal head fixed thereto; a pair of stays formed by respectively bending rearward both ends of the head support wall; and a coupling concave portion formed in the stays and configured to receive the pivot shaft therein. 
         [0010]    In the above-mentioned printing unit according to the one embodiment of the present invention, the head frame has a receiving concave portion configured to receive the platen roller rotatably. 
         [0011]    In the above-mentioned printing unit according to the one embodiment of the present invention, the pivot shaft has a release lever mounted thereto so as to be pivotable and configured to press the platen roller in a direction of removing the platen roller from the receiving concave portion. 
         [0012]    In the above-mentioned printing unit according to the one embodiment of the present invention, the guide member has a sheet detection sensor configured to detect one of presence and absence of the recording sheet passing through the guide member. 
         [0013]    According to one embodiment of the present invention, there is provided a thermal printer including: the printing unit; and a casing having the printing unit mounted therein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a sectional view of a thermal printer, for illustrating a state in which a printer cover is located at an opened position. 
           [0015]      FIG. 2  is a sectional view of the thermal printer, for illustrating a state in which the printer cover is located at a closed position. 
           [0016]      FIG. 3  is a side view of a printing unit. 
           [0017]      FIG. 4  is an exploded perspective view of the printing unit. 
           [0018]      FIG. 5  is a sectional view taken along the line V-V in  FIG. 4 . 
           [0019]      FIG. 6  is a sectional view taken along the line VI-VI in  FIG. 4 . 
           [0020]      FIG. 7  is an exploded perspective view of a head unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Embodiments of the present invention are now described referring to the accompanying drawings. 
         [0022]      FIG. 1  and  FIG. 2  are sectional views of a thermal printer  1 .  FIG. 1  is an illustration of a state in which a printer cover  6  is located at an opened position, whereas  FIG. 2  is an illustration of a state in which the printer cover  6  is located at a closed position. In the drawings, FR represents a forward direction, LH represents a leftward direction, and UP represents an upward direction. As illustrated in  FIG. 1  and  FIG. 2 , the thermal printer  1  of this embodiment includes a casing  4  and a printing unit  9  incorporated into the casing  4 . 
         [0023]    The casing  4  includes a casing main body  5  and the printer cover  6 . The casing main body  5  includes a roll sheet receiving portion  5   a  configured to receive a roll sheet R therein. The printer cover  6  opens and closes the roll sheet receiving portion  5   a.  The roll sheet R is formed by rolling a recording sheet P. The printer cover  6  is coupled to the casing main body  5  through intermediation of a hinge portion  7  so as to be pivotable. Further, as illustrated in  FIG. 2 , a discharge port  8  configured to discharge the recording sheet P, which is pulled out from the roll sheet R, externally (upward) is formed between an opening edge of the roll sheet receiving portion  5   a  and a distal end of the printer cover  6  when the printer cover  6  is located at the closed position. 
         [0024]    The printing unit  9  includes a platen unit  2  and a head unit  3  combined with each other separably. The platen unit  2  is mounted to a distal end of an inner surface of the printer cover  6 . The platen unit  2  is a unit having a platen roller  10  and a fixed blade  13  mainly incorporated therein. Meanwhile, the head unit  3  is mounted in the casing main body  5 . Therefore, along with an opening and closing operation of the printer cover  6 , the head unit  3  is combined with the platen unit  2  separably. The head unit  3  is, for example, a unit having a thermal head  12  and a movable blade  11  mainly incorporated therein. In the example of  FIG. 1 , the head unit  3  is fixed to an inner plate  5   b  arranged so as to be adjacent to the roll sheet receiving portion  5   a  so that the thermal head  12  is oriented toward the roll sheet receiving portion  5   a.    
         [0025]    As illustrated in  FIG. 2 , when the printer cover  6  is closed to combine the platen unit  2  and the head unit  3  with each other, the thermal head  12  is pressed against the platen roller  10 . At the same time, the movable blade  11  and the fixed blade  13  are located at a predetermined position. 
         [0026]      FIG. 3  is a side view of the printing unit  9 , and  FIG. 4  is an exploded perspective view of the printing unit  9 .  FIG. 5  is a sectional view taken along the line V-V in  FIG. 4 .  FIG. 6  is a sectional view taken along the line VI-VI in  FIG. 4 . As illustrated in  FIG. 3  to  FIG. 6 , the platen unit  2  includes the platen roller  10  and the fixed blade  13 , which are described above, a platen frame  21 , and a subframe  22 . The platen frame  21  supports the platen roller  10  and the fixed blade  13 . The subframe  22  supports the platen frame  21 . 
         [0027]    The platen frame  21  is formed by bending a plate material made of a metal or the like, and is formed into a U-like shape that is open downward in front view as viewed in a front-back direction. Specifically, the platen frame  21  includes a pair of shaft support portions  24  and a coupling portion  25 . The shaft support portions  24  are respectively located on both ends in a horizontal direction. The coupling portion  25  extends along the horizontal direction and bridges the shaft support portions  24 . A bearing  29  for the platen roller  10 , which is described later, is held in a rear end of each of the shaft support portions  24 . A projecting piece  26  that projects outward in the horizontal direction is formed on a lower end of one of the shaft support portions  24 , which is located on one end side (left side in the illustrated example) in the horizontal direction. 
         [0028]    The platen roller  10  is arranged so that an outer peripheral surface thereof is brought into contact with the thermal head  12  under a state in which the recording sheet P is nipped between the platen unit  2  and the head unit  3  when the platen unit  2  and the head unit  3  are combined with each other while the printer cover  6  is located at the closed position. Specifically, the platen roller  10  includes a platen shaft  27  and a roller main body  28 . The platen shaft  27  extends along the horizontal direction. The roller main body  28  is made of a rubber or the like, and is mounted to the platen shaft  27 . 
         [0029]    As illustrated in  FIG. 3 , the bearings  29  are respectively mounted to both ends of the platen shaft  27 . Each of the bearings  29  is held by the shaft support portion  24  of the above-mentioned platen frame  21 . Through intermediation of the bearings  29 , the platen roller  10  is rotatably supported on the platen frame  21 . As illustrated in  FIG. 4 , a platen gear  31  is mounted to the other end (right end) of the platen shaft  27 . 
         [0030]    The fixed blade  13  is formed into a plate-like shape extending along the horizontal direction. The fixed blade  13  is fixed to the coupling portion  25  of the platen frame  21  under a state in which a cutting edge of the fixed blade  13  is oriented to the rear side. 
         [0031]    The subframe  22  is slightly larger than the platen frame  21 . That is, the subframe  22  surrounds the platen frame  21  on an upper side and both sides in the horizontal direction. Specifically, the subframe  22  includes side wall portions  33  and a base portion  34 . The side wall portions  33  are located on both sides in the horizontal direction. The base portion  34  couples the side wall portions  33 . The bearings  29  for the platen roller  10  are respectively inserted freely into rear ends of the side wall portions  33 . The platen unit  2  is mounted to the printer cover  6  through intermediation of the subframe  22 . 
         [0032]    Between the platen frame  21  and the subframe  22 , a pressure-applying mechanism  37  configured to urge (apply a pressure to) the platen frame  21  about the platen shaft  27  in a direction away from the subframe  22  (downward) is interposed. The pressure-applying mechanism  37  is formed of, for example, a coil spring extending in a vertical direction. The pressure-applying mechanism  37  is arranged at a left end of the platen unit  2 . Specifically, a lower end of the pressure-applying mechanism  37  is coupled to the subframe  22 , and an upper end thereof is coupled to the coupling portion  25  of the platen frame  21 . It is only necessary that the pressure-applying mechanism  37  be arranged in at least one of right and left ends of the platen unit  2 . 
         [0033]      FIG. 7  is an exploded perspective view of the head unit  3 . The illustration of the movable blade  11  and a support member  47  is omitted in  FIG. 7 . As illustrated in  FIG. 4  to  FIG. 7 , the head unit  3  includes the movable blade  11 , a head block  38 , a head frame  41  configured to support the head block  38  and the movable blade  11 , and a guide member  43  configured to guide the recording sheet P to the thermal head  12 . 
         [0034]    The head frame  41  is formed into a U-like shape that is open upward in front view as viewed in the front-back direction. Receiving concave portions  44  are formed in a pair of side wall portions  41   a  and  41   b  of the head frame  41 , which are located on both sides in the horizontal direction. The receiving concave portions  44  are open upward, and have a width along the front-back direction, which gradually decreases in a downward direction. The bearings  29  for the platen roller  10  are respectively engaged with the receiving concave portions  44 . Stopper portions  45  (see  FIG. 4 ) are formed on inner peripheral edges of the receiving concave portions  44  so as to project rearward. The stopper portions  45  are engaged with the bearings  29  for the platen roller  10  from above when the printer cover  6  is located at the closed position. As illustrated in  FIG. 4  and  FIG. 7 , positioning concave portions  46  that are recessed rearward are respectively formed in front end edges of the side wall portions  41   a  and  41   b.    
         [0035]    As illustrated in  FIG. 4  to  FIG. 6 , the support member  47  is arranged at rear parts of the side wall portions  41   a  and  41   b  (part located on the rear side with respect to the head block  38 ). The support member  47  has its thickness direction corresponding to the vertical direction and is arranged so as to extend in the horizontal direction. The support member  47  bridges the side wall portions  41   a  and  41   b.  The support member  47  supports the head block  38  from the rear side, and connects the movable blade  11  and the head frame  41  to each other. 
         [0036]    As illustrated in  FIG. 4 , a platen gear train mechanism  53  is arranged on the side wall portion  41   a  on the right side of the side wall portions  41   a  and  41   b.  The platen gear train mechanism  53  is brought into meshing engagement with the platen gear  31  of the platen unit  2  when the platen unit  2  and the head unit  3  are combined with each other. As illustrated in  FIG. 7 , the platen gear train mechanism  53  is connected to a platen motor  54  mounted to the head frame  41 . Through appropriate rotation of the platen motor  54 , a rotating force of the platen motor  54  is transmitted to the platen gear  31  through intermediation of the platen gear train mechanism  53 . As a result, the platen roller  10  is rotated. 
         [0037]    The head block  38  includes a head support member  56  and the above-mentioned thermal head  12 . The head support member  56  is supported on a pivot shaft  55  arranged in the head frame  41  so as to be pivotable about the pivot shaft  55 . The thermal head  12  is fixed to the head support member  56 . The pivot shaft  55  is arranged so as to extend along the horizontal direction, and both ends of the pivot shaft  55  are respectively supported in through holes  48   a  and  48   b  of the side wall portions  41   a  and  41   b.  As illustrated in  FIG. 3 , a release lever  61  configured to release the combination of the platen unit  2  and the head unit  3  is arranged at a portion of the pivot shaft  55 , which is located on the outer side with respect to the side wall portion  41   b  on the left side. 
         [0038]    The release lever  61  is formed into a V-like shape in side view as viewed in the horizontal direction. A corner portion of the release lever  61  is supported so as to be pivotable about the pivot shaft  55 . A lever member (not shown) provided to the casing main body  5  is locked to a portion of the release lever  61 , which is located on one end side with respect to the corner portion. On the other hand, a portion of the release lever  61 , which is located on the other end side with respect to the corner portion, is brought into abutment against the above-mentioned projecting piece  26  of the platen frame  21  from below. In this manner, the release lever  61  pivots in conjunction with the operation of the lever member to push up the platen unit  2  through intermediation of the projecting piece  26 , thereby separating the platen unit  2  from the head unit  3 . An urging member  60  configured to urge the release lever  61  in a direction away from the projecting piece  26  is interposed between the release lever  61  and the side wall portion  41   b.    
         [0039]    As illustrated in  FIG. 5  to  FIG. 7 , the head support member  56  is formed by bending a plate member made of a metal or the like. The head support member  56  is arranged inside the head frame  41 . Specifically, the head support member  56  includes a head support wall  62  having the thermal head  12  fixed thereto, and a pair of stays  63  formed by respectively bending rearward both ends of the head support wall  62  in the horizontal direction. 
         [0040]    The head support wall  62  has its thickness direction corresponding to the front-back direction and is arranged so as to extend in the horizontal direction. A lower end of each of the stays  63  is located at a position lower than the head support wall  62 . In the lower end of each of the stays  63 , a coupling concave portion  64  configured to receive the above-mentioned pivot shaft  55  therein is formed. The coupling concave portion  64  is formed into a C-like shape that is open forward in side view as viewed in the horizontal direction. With this, the head support member  56  is pivotable about the pivot shaft  55  in the front-back direction (in a direction toward and away from the platen roller  10 ), and is mounted to the pivot shaft  55  in a removable manner. In the illustrated example, a lower end edge of each of the stays  63  (portion located lower than the coupling concave portion  64 ) is tapered to be inclined downward in a rearward direction. Note that, the pivot shaft  55  may be inserted into through holes instead of the coupling concave portions  64 . 
         [0041]    A stopper engagement portion  66  is formed on each of both ends of the head support wall  62  in the horizontal direction at a portion located above each of the above-mentioned stays  63  so as to project rearward. The stopper engagement portion  66  is locked to a regulating portion  67  of the head frame  41  to restrict a pivot range of the head block  38 . As illustrated in  FIG. 5  and  FIG. 6 , a head urging member  65  is interposed between the head support wall  62  and the above-mentioned support member  47  in the front-back direction. The head urging member  65  is configured to urge the head block  38  (thermal head  12 ) toward the platen roller  10  (to the front side). 
         [0042]    As illustrated in  FIG. 7 , the thermal head  12  is fixed to a front surface of the head support wall  62 . The thermal head  12  is formed into a plate-like shape extending along the horizontal direction (sheet width direction of the recording sheet P). A plurality of heating elements  12   a  are arranged linearly on a front surface of the thermal head  12 . 
         [0043]    As illustrated in  FIG. 4  to  FIG. 6 , the movable blade  11  is mounted to an upper part of the head frame  41  (each of the side wall portions  41   a  and  41   b ) through intermediation of the above-mentioned support member  47 . Specifically, the movable blade  11  includes a movable blade frame  81 , a movable-blade main body  82  supported on the movable blade frame  81  so as to be slidable, and a driving mechanism  83  configured to drive the movable-blade main body  82 . 
         [0044]    The movable blade frame  81  is formed by bending a metal plate or the like. The movable blade frame  81  is mounted on the above-mentioned support member  47  in a removable manner. A cutting edge of the movable-blade main body  82  is formed into a V-like shape in plan view as viewed in the vertical direction. That is, the movable-blade main body  82  is formed so that a length from a bottom to the cutting edge of the movable-blade main body  82  gradually decreases from both ends toward the center in the horizontal direction. The driving mechanism  83  includes a cutter motor mounted on the movable blade frame  81  so as to be rotatable in a forward direction and a reverse direction, and a gear train mechanism connected between the cutter motor and the movable-blade main body  82 . When a driving force of the cutter motor is transmitted to the movable-blade main body  82  through intermediation of the gear train mechanism, the movable-blade main body  82  is slid. 
         [0045]    As illustrated in  FIG. 4  and  FIG. 7 , the guide member  43  is arranged between the side wall portions  41   a  and  41   b  in a front part of the head frame  41 . The guide member  43  includes a pair of side blocks  85  located on both right and left sides thereof, and a guide block  86  that bridges the side blocks  85 . The side blocks  85  are arranged on the inner side in the horizontal direction with respect to the side wall portions  41   a  and  41   b  of the head frame  41 . Positioning protrusions  87  are formed on front ends of the side blocks  85  so as to project outward in the horizontal direction. The positioning protrusions  87  are respectively received in the positioning concave portions  46  of the above-mentioned head frame  41  from the front side. The positioning protrusions  87  are surrounded by the positioning concave portions  46  at upper, lower, and rear parts thereof. 
         [0046]    As illustrated in  FIG. 5  and  FIG. 7 , positioning wall portions  88  are formed on rear parts of the side blocks  85  so as to extend rearward. The positioning wall portions  88  are formed so as to extend to positions overlapping with the stays  63  of the above-mentioned head block  38 , the pivot shaft  55 , and the through holes  48   a  and  48   b  as viewed in the horizontal direction. The positioning wall portions  88  are located on the inner side with respect to both end surfaces of the side blocks  85  in the horizontal direction. In this case, the stays  63  of the head block  38 ′are arranged respectively at portions located between the positioning wall portions  88  and the side wall portions  41   a  and  41   b  of the head frame  41  in the horizontal direction. 
         [0047]    Engagement portions  89  with which the above-mentioned pivot shaft  55  is to be engaged are formed in the positioning wall portions  88  at portions overlapping with the through holes  48   a  and  48   b  of the head frame  41  as viewed in the horizontal direction. The engagement portions  89  are each formed into a groove shape extending in the vertical direction. The engagement portions  89  are open upward at upper end edges of the positioning wall portions  88 . Lower end edges of the engagement portions  89  are each formed into an arc shape that projects downward. The above-mentioned pivot shaft  55  is received inside the engagement portions  89  under a state of being brought closer to or into abutment against the lower end edges of the engagement portions  89  from above. In the positioning wall portions  88 , portions located on the rear side with respect to the engagement portions  89  are lower in height than portions located on the front side with respect to the engagement portions  89 . Further, tapered surfaces  90  that are inclined inward in the horizontal direction as approaching the upper side are formed on upper ends of the positioning wall portions  88 . 
         [0048]    An upper surface and a front surface of the guide block  86  are recessed downward and rearward with respect to the side blocks  85 . A guide passage  91  is defined in the guide member  43  by the upper surface and the front surface of the guide block  86  and surfaces of the side blocks  85 , which are located on the inner side in the horizontal direction. The recording sheet P passes through the guide passage  91  toward the thermal head  12 , and the roller main body  28  of the above-mentioned platen roller  10  is received in the guide passage  91  from above when the printer cover  6  is located at the closed position. The heating elements  12   a  of the above-mentioned thermal head  12  are exposed to the inside of the guide passage  91  from the rear side. 
         [0049]    As illustrated in  FIG. 7 , concave portions  92  that are recessed downward are formed in a front part of the guide block  86 . The concave portions  92  are formed in both ends of the guide block  86  in the horizontal direction. In bottom wall portions of the concave portions  92 , through holes  93  passing therethrough in the vertical direction are formed. The through holes  93  are overlapped with through holes  95  (see  FIG. 7 ) formed in a bottom wall portion  41   c  of the above-mentioned head frame  41  as viewed in the vertical direction. Fastening members such as screws (not shown) are inserted through the through holes  93  and  95 . The fastening members are fastened to the above-mentioned casing main body  5 . Specifically, the guide member  43  is fastened to the casing main body  5  together with the head frame  41 . 
         [0050]    As illustrated in  FIG. 4  and  FIG. 7 , in the guide block  86 , there is arranged a sheet detection sensor  97  configured to detect presence or absence of the recording sheet P passing through the guide passage  91 . The sheet detection sensor  97  is, for example, a reflection-type photo sensor. The sheet detection sensor  97  is exposed to the inside of the guide passage  91  through a detection window  98  formed on the guide block  86 . 
         [0051]    In the thermal printer  1  configured as described above, as illustrated in  FIG. 2  and  FIG. 3 , under a state in which the printer cover  6  is located at the closed position and the units  2  and  3  are combined with each other, the movable blade  11  and the fixed blade  13  are arranged at a desired position, and the recording sheet P is nipped between the platen roller  10  and the thermal head  12 . After passing between the movable blade  11  and the fixed blade  13 , the recording sheet P is pulled out of the casing  4  through the discharge port  8 . Further, the platen gear  31  on the platen unit  2  side is brought into meshing engagement with the platen gear train mechanism  53  on the head unit  3  side. 
         [0052]    Thereafter, the platen motor  54  is driven so that the rotating force of the platen motor  54  is transmitted to the platen gear  31  of the platen unit  2 . As a result, the platen roller  10  can be rotated so that the recording sheet P can be fed while the recording sheet P is nipped between the platen roller  10  and the thermal head  12 . Simultaneously with the sheet feeding, various letters and figures can be clearly printed on the recording sheet P that is being fed, by appropriately allowing the heating elements  12   a  of the thermal head  12  to generate heat. 
         [0053]    The printed recording sheet P passes between the fixed blade  13  and the movable blade  11 . Then, after the passage of the recording sheet P by a predetermined length, the driving mechanism  83  is driven to slide the movable-blade main body  82  toward the fixed blade  13 . In this manner, the recording sheet P can be cut between the fixed blade  13  and the movable blade  11 . As a result, the recording sheet P thus cut can be used as a receipt or a ticket. 
         [0054]    Next, as an action of the above-mentioned thermal printer  1 , a method for assembling the head unit  3  is described. As illustrated in  FIG. 7 , first, the guide member  43  is mounted to the head frame  41 . Specifically, the head frame  41  and the guide member  43  are moved so as to be closer to each other in the front-back direction under a state in which the head frame  41  and the guide member  43  are opposed to each other in the front-back direction. Then, the guide member  43  is caused to enter a part between the side wall portions  41   a  and  41   b  from the front side, and the positioning protrusions  87  of the guide member  43  are caused to enter the positioning concave portions  46  of the head frame  41 . Under a state in which the guide member  43  is mounted to the head frame  41 , the engagement portions  89  of the guide member  43  and the through holes  48   a  and  48   b  of the head frame  41  are overlapped with each other as viewed in the horizontal direction. 
         [0055]    Subsequently, the pivot shaft  55  is mounted to the side wall portions  41   a  and  41   b  of the head frame  41 . For example, the pivot shaft  55  is inserted through the through hole  48   b  of the side wall portion  41   b  on the left side from a right end of the pivot shaft  55 , and the right end of the pivot shaft  55  is pulled out through the through hole  48   a  of the side wall portion  41   a  on the right side. As a result, the pivot shaft  55  bridges the side wall portions  41   a  and  41   b.  Stopper rings or the like (not shown) are mounted to both ends of the pivot shaft  55  at the outside of the head frame  41 . Further, the pivot shaft  55  may be mounted to the head frame  41  from the right side. 
         [0056]    While the pivot shaft  55  is being mounted, the pivot shaft  55  is caused to enter each of the engagement portions  89  of the guide member  43  from the left side. Then, after passing through the engagement portions  89  in the horizontal direction, the right end of the pivot shaft  55  is pulled out to the outside of the head frame  41  through the through hole  48   a  of the side wall portion  41   a  on the right side. As a result, the pivot shaft  55  is engaged with the engagement portions  89 . Specifically, the guide member  43  is positioned with respect to the head frame  41  through intermediation of the pivot shaft  55 . 
         [0057]    Next, the release lever  61  is mounted to a left end of the pivot shaft  55 . Subsequently, the head block  38  is mounted to the pivot shaft  55 . Specifically, the head block  38  is inserted between the side wall portions  41   a  and  41   b  of the head frame  41  from above. At this time, the pivot shaft  55  is caused to enter the coupling concave portions  64  of the head support member  56 , and the stopper engagement portions  66  are locked to the regulating portions  67  of the head frame  41 . As a result, the head block  38  is supported on the head frame  41  through intermediation of the pivot shaft  55 . In this embodiment, the tapered surfaces  90  are formed on the positioning wall portions  88  of the guide member  43 . Therefore, widths between the positioning wall portions  88  and the side wall portions  41   a  and  41   b  of the head frame  41  gradually increase as approaching the upper side. Accordingly, the stays  63  of the head block  38  can be caused to smoothly enter clearances between the positioning wall portions  88  and the side wall portions  41   a  and  41   b  of the head frame  41 . 
         [0058]    Thereafter, the support member  47  and the movable blade  11  are mounted to the head frame  41  from above so that the above-mentioned head unit  3  is assembled. Note that, the assembly procedure for the head unit  3  may be appropriately changed. 
         [0059]    As described above, in this embodiment, the engagement portions  89  that are engaged with the pivot shaft  55  configured to support the head block  38  are formed in the guide member  43 . According to this configuration, the head block  38  and the guide member  43  are positioned by the pivot shaft  55 , and hence the head block  38  and the guide member  43  can be positioned with high accuracy irrespective of the dimension accuracy of the head frame  41 . In this case, the recording sheet P can be smoothly guided to the thermal head  12 , thereby being capable of suppressing occurrence of paper jam or the like. Further, as compared to a configuration in which the guide member  43  is mounted to the head frame  41  using fastening members as in the related art, the number of components can be reduced. Further, as compared to a case where mounting portions for the fastening members are formed in each of the head frame  41  and the guide member  43 , the configuration can be simplified. 
         [0060]    Further, in this embodiment, the pivot shaft  55  is supported on the head frame  41 , and the receiving concave portions  44  configured to receive the platen roller  10  rotatably are formed in the head frame  41 . According to this configuration, the platen roller  10  and the thermal head  12  supported on the pivot shaft  55  can be positioned with high accuracy. As a result, misalignment of the platen roller  10  and the thermal head  12  can be suppressed so that the recording sheet P can be securely nipped between the platen roller  10  and the thermal head  12 . 
         [0061]    In addition, the release lever  61  is mounted to the pivot shaft  55 , and hence the platen unit  2  and the release lever  61  can be positioned with high accuracy. With this, along with the operation of the release lever  61 , the platen roller  10  can be securely removed from the receiving concave portions  44  so that the platen unit  2  and the head unit  3  can be easily separated from each other. As a result, excellent operability can be attained. 
         [0062]    Moreover, the sheet detection sensor  97  is mounted in the guide member  43 , and hence the sheet detection sensor  97  can be positioned with respect to the thermal head  12  with high accuracy. As a result, the detection accuracy for the recording sheet P can be enhanced. 
         [0063]    The thermal printer  1  of this embodiment includes the above-mentioned printing unit  9 , thereby being capable of providing the thermal printer  1  with high reliability, in which each of the components is positioned with high accuracy. 
         [0064]    Note that, the technical scope of the present invention is not limited to the above-mentioned embodiment, but various modifications may be made without departing from the gist of the present invention. 
         [0065]    For example, in the embodiment described above, the configuration in which the fixed blade  13  is provided to the platen frame  21  and the movable blade  11  is provided to the head frame  41  is described. However, the present invention is not limited thereto. Specifically, the configuration in which the movable blade  11  is provided to the platen frame  21  and the fixed blade  13  is provided to the head frame  41  may be employed. 
         [0066]    In the embodiment described above, the case where the engagement portions  89  are each formed into a groove shape that is open upward is described. However, the engagement portions  89  are not limited thereto, and through holes or the like may be appropriately employed as long as the pivot shaft  55  is engageable therewith. In the embodiment described above, the configuration in which the engagement portions  89  are formed in the both ends of the guide member  43  in the horizontal direction (side blocks  85 ) is described. However, the positions of the engagement portions  89  in the horizontal direction may be appropriately changed in design. In the embodiment described above, the configuration in which the head block  38 , the head frame  41 , the guide member  43 , and the release lever  61  are coupled to the pivot shaft  55  is described. However, the present invention is not limited thereto. Other configurations may be employed as long as at least the head block  38 , the head frame  41 , and the guide member  43  are coupled to the pivot shaft  55 . Further, the guide member  43  only needs to be engaged with at least the pivot shaft  55 , and may be supported on a portion other than the head frame  41 . 
         [0067]    Besides the above, the components in the above-mentioned embodiments may be replaced by well-known components as appropriate without departing from the gist of the present invention. The above-mentioned modified examples may be combined with each other as appropriate.