Patent Publication Number: US-2004055435-A1

Title: Rotary cutting device and printer incorporating the same

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a rotary cutting device for cutting a recording paper and a printer incorporating the rotary cutting device.  
       [0003] 2. Description of Related Art  
       [0004] In general, many receipt printers and facsimile machines using a lengthy recording paper such as a receipt paper are provided with a cutting device for cutting a printed paper into a sheet of an appropriate length downstream from a printing section in a paper advancing direction. One example of such a cutting device is a rotary cutting device  103 , as shown in FIG. 9, which is designed to cut a cutting object (for example, a receipt paper) positioned between cutting edges  101   a  and  102   a  of blades by rotating a platy movable blade  101  having a length across a full width of the recording paper in respect to a stationary blade  102  and making the blades to engage with each other as in a pair of scissors. Such a rotary cutting device  103  provides reliable cutting despite of its simple structure.  
       [0005] The movable blade  101  of such rotary cutting device  103  includes the cutting edge  101   a  at one edge of a base  101   b  and supporting axes  101   c  at both ends of the base  101   b , and is formed by cutting one piece of metal cutting material. The movable blade  101  is rotatably supported by a frame  104  on the supporting axes  101   c , being connected to a drive section, not shown, and is provided to rotate by a driving power from the drive section.  
       [0006] However, cost of such rotary cutting device  103  is raised due to necessity of cutting of the movable blade  101  having the supporting axes  101   c . Also, in mass-production of the rotary cutting device  103 , because the movable blade  101  must be individually processed for cutting, there is expected little cost margin in mass-production of the rotary cutting device  103  despite of a large amount of production of the movable blade  101 .  
       SUMMARY OF THE INVENTION  
       [0007] An object of the present invention is to reduce a cost of a rotary cutting device. This object can be accomplished by providing a rotary cutting device comprising a stationary blade having a cutting edge, a movable blade having a cutting edge, a movable-blade holding section of a resin that holds the movable blade, the cutting edge of the stationary blade and the cutting edge of the movable blade being positioned at a slight angle in respect to their parallel arrangement so as for the two cutting edges to engage each other, a supporting section for rotatably supporting the movable-blade holding section enabling the engaging position of the cutting edges to move as the movable-blade holding section rotates, and a driving section for driving to rotate the movable-blade holding section supported by the supporting section.  
       [0008] Thus, a cutting object, which is interposed between the cutting edge of the stationary blade and the cutting edge of the movable blade that are positioned at a slight angle in respect to their parallel arrangement, is cut as the engaging position of the movable blade cutting edge and stationary blade cutting edge moves in line with rotation of the movable blade. Because the movable blade is held by the movable-blade holding section, it needs no longer to form supporting axes as provided in conventional movable blades. Besides, because the movable-blade holding section for holding the movable blade is made of a resin, it can be die-formed. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a longitudinal cross sectional side view that generally displays a receipt printer incorporating a rotary cutting device as an embodiment according to the present invention.  
     [0010]FIG. 2 is a general prospective front view of a structure of the rotary cutting device.  
     [0011]FIG. 3 is a general prospective rear view of the movable-blade holding member in the rotary cutting device and the movable blade that is dismounted from this movable-blade holding member.  
     [0012]FIG. 4 is a general plan view of the movable-blade holding member in a state that the movable blade is mounted in the rotary cutting device.  
     [0013]FIG. 5 is a side view that generally displays a structure of a drive force transmitting mechanism in the rotary cutting device  
     [0014]FIG. 6 is a longitudinal side view that generally displays the receipt printer in a state that the upper unit and lower unit are separated from each other.  
     [0015]FIG. 7 is a perspective view that generally displays the receipt printer in a state that the upper unit and lower unit are assembled.  
     [0016]FIG. 8 is a longitudinal sectional side view that shows a structure in which a thermal printer and a hook member are mounted.  
     [0017]FIG. 9 is a perspective view of a conventional rotary cutting device. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION  
     [0018] An embodiment according to the present invention will be described in reference to FIGS. 1 through 8. This embodiment is an example of a receipt printer to which the present invention is applied. This printer is provided with a rotary cutting device as a cutter device and is incorporated into a POS terminal or ECR.  
     [0019]FIG. 1 is a side view of a longitudinal cross section that generally displays a receipt printer of the present embodiment. As shown in FIG. 1, the receipt printer is composed of a main frame  2 , paper compartment  3 , paper guide  4 , printing section  5 , rotary cutting device  6 , and others. In this receipt printer  1 , the paper travel path  7  is formed through paper compartment  3 , printing section  5 , and rotary cutting device  6 . The paper compartment  3  having a hyperbolic bottom contains a lengthy rolled recording paper  8  as a cutting object. The paper guide  4 , which is formed en route from a leading edge of the paper compartment  3  to the printing section  5 , supports the recording paper  8  on the surface of the paper.  
     [0020] The printing section  5  is composed of a platen  9  and a thermal head  10  as a recording head facing the platen  9 . The platen  9  is driven to rotate by a motor, not shown, intervened by lined gears, not shown. The thermal head  10  is mounted on a flat head holding member  11 . This head holding member  11  is provided so as to freely pivot on a fulcrum  12  towards or apart from the platen  9 , and is biased towards the platen  9  by a force of a coil spring  13  that is provided between the head holding member  11  and a hooking member  43 . The coil spring  13  serves as a compression spring, which will be described later. The thermal head  10  thereby abuts to the platen  9 . The printing part  5  performs printing by the thermal head  10  on a recording paper  8  interposed between the platen  9  and the thermal head  10 . The recording paper  8  is conveyed along the paper travel path  7  by the platen  9  driven to rotate by the motor. The printing section  5  functions also as a paper transport section for transporting the recording paper  8 .  
     [0021] The rotary cutting device  6 , which is provided downstream from the printing section  5  in a paper advancing direction, is structured in combination of the stationary blade  14  and the movable blade  15 , both of which are formed nearly flat.  
     [0022]FIG. 2 is a perspective view that generally shows a structure of the rotary cutting device  6  from the front. FIG. 3 is a perspective view that generally shows from rear the movable-blade holding member and the movable blade  15  dismounted from this movable-blade holding member in the rotary cutting device  6 . FIG. 4 is a plane view that generally shows the movable-blade holding member in a state that the movable blade  15  is mounted back in the rotary cutting device  6 . FIG. 5 is a side view that generally shows a structure of the drive force transmitting mechanism in the rotary cutting device  6 .  
     [0023] As shown in FIG. 2, in the stationary blade  14 , one edge of the nearly flat body  14   a  forms the cutting edge  14   b . On the edge opposite to the cutting edge  14   b  in the shorter direction of the stationary blade  14 , a support axis  14   c  is provided. This support axis is movably mounted to an upper unit frame  31 , which will be described later. Between the stationary blade  14  and the upper unit frame  31  a spring  16  (refer to FIG. 1) is provided, by which the stationary blade  14  is biased towards the movable blade  15 . Also, in the stationary blade  14 , a guiding part  14   d  is formed for guiding the cutting edge  15   a  to a position where it engages with the cutting edge  14   b  of the stationary blade  14 . To be more specific, this guiding part  14   d  is formed continuing from the cutting edge  14   b  and protruding on the outskirts of the cutting edge  14   b . This stationary blade  14  is held nearly on the level in a state that the stationary blade  14  and the movable blade  15  are engaged each other, as shown in FIG. 1.  
     [0024] On the other hand, on the nearly flat base  15   b  of the movable blade  15  is formed a surface  15   c , which provides the paper travel path  7 . At an edge of the surface  15   c  is formed the cutting edge  15   a  of the movable blade  15 . This movable blade  15  can be readily mounted or dismounted to/from the movable-blade holding member  17  as a movable-blade holding section, as shown in FIGS. 3 and 4.  
     [0025] The movable-blade holding member  17  is of a resilient resin, formed in a rod, and positioned so that its axis parallels with an axis of the platen  9 . At the both ends of the movable-blade holding member  17  are formed support axes  18 ,  19 , which are rotatably supported by a lower unit frame  29 , which will be described later. In the middle of the movable-blade holding member  17  between the both support axes  17  and  18 , there is provided a plane  20  for holding the movable blade  15 , whose cross section forms a near semicircle. At both ends of this plane  20  inside the support axes  17  and  18 , there are formed grooves, respectively, to which the ends of the movable blade  15  can slidably engage. At bottom of each groove  21 , position-determining parts  22  for supporting and determining positions of low end of the movable blade  15 , which is inserted into the grooves  21 , are provided.  
     [0026] Also, as shown in FIG. 4, the grooves  21  of the movable-blade holding member  17  are formed so that the movable blade  15  inserted is slightly inclined from a line parallel with the axis of the movable-blade holding member  17 . Accordingly, the cutting edge  14   b  of the stationary blade  14  and the cutting edge  15   a  of the movable blade  15  are disposed as slightly inclined from the imaginary parallel line. Therefore, a cutting object passage A between the cutting edge  14   b  of the stationary blade  14  and the cutting edge  15   a  of the movable blade  15  is provided in a V-shape, as indicated in FIG. 2. This cutting object passage A forms a part of the paper travel path  7 . In a state that the stationary blade  14  and the movable blade  15  are engaged with each other, this movable blade  15  is held vertically, as shown in FIG. 1.  
     [0027] In the base  15   b  of the movable blade  15 , there are provided two apertures  15   d  as engaging parts, as shown in FIG. 3. On the other hand, on the plane  20  of the movable-blade holding member  17 , two hemicycle-protrusions  20   a  that engage with the above apertures are formed. To make the movable blade  15  to engage with the grooves  21 , the movable blade  15  is moved so that the cutting edge  15   a  of the movable blade  15  and the opposite lower edge slide into the grooves. As the movable-blade holding member  17  having a resilient property bends, the protrusions  20   a  are allowed to engage into the apertures  15   d . The movable blade  15  now engaged in the grooves  21  are in a state of being interposed between the resilient grooves  21 . By these engagements, movement of the movable blade  15  is restrained, and so the movable blade  15  is secured into the grooves  21 .  
     [0028] In this state, the cutting edge  15   a  of the movable blade  15  protrudes in a direction normal to the periphery of the movable-blade holding member  17 , while the base  15   b  of the movable blade  15  reaches near the periphery of the movable-blade holding member  17  opposite to the cutting edge  15   a  of the movable blade  15 . That is, the movable blade  15  has a length nearly the same as the diameter of the movable-blade holding member  17 . Thus, the movable-blade holding member  17  is reinforced by the movable blade  15 , as it is fixed thereto, with the whole strength, even though the movable-blade holding member  17  is made of a resin.  
     [0029] To detach the movable blade  15  from the grooves  21  of the movable-blade holding member  17 , the movable blade  15  is withdrawn from the grooves  21 , so that the movable-blade holding member  17  is bent so as to release the engagement of the protrusions  20   a  and the apertures  15   d , and the movable blade  15  comes off. Herein, the apertures  15   d  and the protrusions  20   a  constitute a securing section  23 .  
     [0030] As shown in FIGS. 3 and 4, inside both fulcrum shafts  18  and  19  of the movable-blade holding member  17  that detachably holds the movable blade  15  in this manner, paper guides  18   a  and  19   a , which face to each other interposing the plane  20 , are formed. An interval between these paper guide surfaces  18   a  and  19   a  is set to be almost the same as a width of the recording paper  8  perpendicular to the paper directing direction. The paper guide surfaces  18   a  and  19   a  serve to position ends of the recording paper  8 , in the paper advancing direction, which is conveyed along the paper traveling path  7 . The paper traveling path  7  is formed by one surface  15   c  of the movable blade  15  now fixed to the movable-blade holding member  17 .  
     [0031] The fulcrum shaft  19  of the movable blade  15  as such is coupled to the driving force transmitting mechanism  24  (refer to FIG. 5) that transmits a drive force of a motor (not shown). Herein, this motor and the driving force transmitting mechanism  24  constitute a drive section  25 .  
     [0032] Now, the drive force transmitting mechanism  24  of a drive section  25  will be briefly explained in reference to FIG. 5. The drive force transmitting mechanism  24  is composed of a cutter arm  26  that is coupled to the fulcrum shaft  19  of the movable blade  15  and swung with and on this fulcrum shaft  19 , a train of gears  27  that is mounted to the lower unit frame  29  and coupled to a motor, and a drive crank  28  that is rotatably mounted to the lower unit frame  29 . The drive crank  28  constitutes a cum mechanism along with the cutter arm  26  being connected to the gear train  27 . In the cutter arm  26 , a vertically long slot  26   a  is formed, into which an eccentric pin  28   a  of the drive crank  28  is engaged. Accordingly, the eccentric pin  28   a  of the drive crank  28  comes to move within the slot  26   a  of the cutter arm  26  in line with rotation of the drive crank  28 , which rotates by a drive force of the motor transmitted via the gear train  27 . By such a motion of this eccentric pin  28   a  on the drive crank  28  within the slot  26   a  of the cutter arm  26 , the cutter arm  26  can be swung on this fulcrum shaft  19 .  
     [0033] As the cutter arm  26  swings in this manner, the movable blade  15  is made to rotate on the fulcrum shaft  19 . In line with this rotation, the movable blade  15  presses itself onto the guiding part  14   d  of the stationary blade  14 . In this instance, the stationary blade  14  produces a reactive force in a direction opposite to the rotating direction by the restoring force of the spring  16  connecting the stationary blade  14  and the upper unit frame  31 . Namely, because the cutting edge  14   b  of the stationary blade  14  and the cutting edge  15   a  of the movable blade  15  are positioned at a slightly angle in respect to the assumed parallel line, the respective cutting edges  14   b  and  15   a  are to engage each other like a pair of scissors. As the cutting object passage A in a V-shape is gradually moved to become narrowed down by rotation of the movable blade  15  and the reactive force of the stationary blade  14 , that is, by shifting an engaging position between the cutting edge  14   b  of the stationary blade  14  and the cutting edge  15   a  of the movable blade  15 , the rotary cutting device  6  cuts a recording paper as a cutting object in the cutting object passage A, which is a part of the paper traveling passage  7 .  
     [0034]FIG. 6 is a side view of the longitudinal section that generally shows the receipt printer  1  in which the upper unit and the lower unit are separated. FIG. 7 is a perspective view that generally shows the receipt printer  1  in which the upper unit and the lower unit are united.  
     [0035] As shown in FIGS. 1, 5,  6 , and  7 , the paper guide  4 , thermal head  10 , movable blade  15 , and drive force transmitting mechanism  24 , described above, are provided in the lower unit frame  29  as a supporting section. These components constitute the lower unit  30 . On the other hand, the platen  9  and stationary blade  14  are provided in the upper unit frame  31  of a horseshoe shape, which is provided independently of the lower unit frame  29 . They constitute the upper unit  32 . The paper compartment  3  is provided in a main frame  2 . The motor for driving the movable blade  15  and the motor for driving the platen  9  are mounted on the lower unit frame  29 .  
     [0036] The lower unit  30  is screwed with screws  33  on the main frame  2  so as to be fixed and detached to/from the main frame  2 . The upper unit  32  is mounted to the lower unit  30  so as to be fixed and detached to/from it by a connecting mechanism  34 .  
     [0037] The connecting mechanism  34  comprises a connection rod  35  and platen  9  installed in the upper unit frame  31  of the upper unit  32 , cuts  36  that are formed in the lower unit frame  29  of the lower unit  30  to allow the connection rod  35  to engage therein, and cuts  37  that are formed in the lower unit frame  29  of the lower unit  30  to allow the both fulcrum shafts  9   a  to engage therein.  
     [0038] The connection rod  35  is provided upstream from the platen  9  in the paper advancing direction so that its axis parallels an axis of the platen  9  whose axis is oriented in a paper width direction. The cuts  36  are vertically formed in both sidewalls  38   a  and  38   b  of the lower unit frame  29  with their upper ends open. The cuts  37  are vertically formed in a pair of sidewalls  39   a  and  39   b , which stand inside sidewalls  38   a  and  38   b  of the lower unit frame  29 , with their upper ends open. As the connection rod  35  and the fulcrum shafts  9   a  fit in the cuts  36  and  37 , respectively, position of the upper unit  32  is determined in respect to the lower unit  30 , and the upper unit  32  and the lower unit  30  are coupled together. In this state, the upper unit  32  is fixed to the lower unit  30  so as to prevent the upper unit  32  from rotating apart from the lower unit  30 . Under this connection, the platen  9  faces the thermal head  10 , and the movable blade  15  and the stationary blade  14  are positioned so as to able to cut the recording paper  8 . An interval between the pair of internal walls  39   a  and  39   b  is provided to be narrower than that between the both sidewalls  40   a  and  40   b  of the upper unit frame  31 . This setting constitutes a guide in sideway for positioning the upper unit  32  in respect to the lower unit  30 , when the pair of internal walls  39   a  and  39   b  is inserted between the both sidewalls  40   a  and  40   b  of the upper unit frame  31  in jointing the upper unit  32  to the lower unit  30 .  
     [0039] Also, as shown in FIG. 8, the lower unit  30  is provided with hooking members  43 , in which two hooking parts  41  for engaging and disengaging the both fulcrum shafts  9   a  of the platen  9  now fitted in the cuts  37  are formed. Each of these hooking members  43  comprises the hooking part  41  and a plane part  44 , which is formed integral with the hooking part  41 . The members  43  are provided so that the hooking parts  41  can freely rotate on a center of the fulcrums  12  in directions of engaging and disengaging the both fulcrum shafts  9   a  of the platen  9 . Also, the members  43  are biased by the coil spring  13 , which is provided between the head holding member  11  and the members  43 , in the direction (as indicated by the arrow a in FIG. 8) of engaging the both fulcrum shafts  9   a  of the platen  9 .  
     [0040] In the hooking parts  41 , there are formed slant parts  42   a  for escaping interference by the fulcrum shafts  9   a  associating with rotation of the hooking members  43  while the hooking parts  41  abut to the fulcrum shafts  9   a  of the platen  9  when mounting the upper unit  32  to the lower unit  30 , and slant parts  42   b  for escaping interference by the fulcrum shafts  9   a  associating with rotation of the hooking members  43  while the hooking parts  41  abut the fulcrum shafts  9   a  of the platen  9  when dismounting the upper unit  32  from the lower unit  30 . When the upper unit  32  is made to conjoin the lower unit  30 , the interference by the hooking members  43  to the fulcrum shafts  9   a  of the platen  9  is escaped against the biasing force of the coil spring  13  by rotation of the hooking members  43 , so that the hooking parts  41  eventually engage the fulcrum shafts  9   a  of the platen  9  and the upper unit  32  is locked against its upward movement from the lower unit  30 . To the contrary, when the upper unit  32  is made to separate from the lower unit  30 , the interference by the hooking members  43  to the fulcrum shafts  9   a  of the platen  9  is escaped against the biasing force of the coil spring  13  by rotation of the hooking members  43 , so that engagement between the hooking parts  41  and the fulcrum shafts  9   a  of the platen  9  is eventually released, enabling the upper unit  32  to be removed from the lower unit  30 .  
     [0041] In a state that the upper unit  32  is not conjoined with the lower unit  30 , the hooking members  43  that is biased by the coil spring  13  and the head holding member  11  are so positioned, abutting to positioning surfaces  45  and  46 , respectively, which are formed in the lower unit frame  29 .  
     [0042] To load the recording paper  8  in the receipt printer  1  in this state, the upper unit  32  is dismounted. To be more specific, the upper unit  32  is pulled upward so as to relieve locking of the platen  9  by the hooking members  43  and release coupling of the connecting mechanism  34 . Then, the upper unit  32  can be detached from the lower unit  30 . Alternately, locking of the platen  9  by the hooking members  43  can be also released by rotating the hooking members  43  in the lock-releasing direction (as indicated by the arrow b in FIG. 8). In this state, the recording paper  8  is loaded into the paper compartment  3 . Then, the recording paper  8  is pulled downstream from the movable blade  15  in the paper advancing direction, and the upper unit  32  is pushed down towards the lower unit  30  so that the connection rod  35  and the platen  9  in the upper unit  32  fit into cuts  36  and  37 , respectively, and the upper unit  32  and the lower unit  30  are coupled to each other. In this instance, the platen  9  is locked by the hooking members  43 . As the upper unit  32  and the lower unit  30  are coupled together in such a manner, the recording paper  8  is in a path between the connection rod  35  and the paper guide  4 , between the thermal head  10  and the platen  9 , and between the stationary blade  14  and the movable blade  15 . Thus, in the present embodiment, because the upper unit  32  is provided so as to be readily mounted and dismounted to/from the lower unit  30 , setting of the recording paper  8  in the receipt printer  1  can be easily made.  
     [0043] In printing, the recording paper  8  contained and supported in the paper compartment  3  is conveyed through the paper travel path  7  towards the printing part  5  and the rotary cutting device  6 , driven by the platen  9 , and a given receipt information can be sequentially printed on it by the thermal head  10 . When printing is finished, the recording paper  8  is cut at a tail of the printed part by driving the movable blade  15  in the cutting device. The cut recording paper  8  is issued as a receipt.  
     [0044] Because a force that the movable blade  15  receives from the stationary blade  14  during this cutting operation effects in the direction where the movable blade  15  is caused to engage further into the grooves  21  in the movable-blade holding member  17 , it can be prevented that the movable blade  15  runs out of the grooves  21 .  
     [0045] In the rotary cutting device  6  according to this embodiment, since the movable blade  15  is held by the movable-blade holding member  17 , to form support axes in the movable blade  15  is no longer needed, as needed in conventional movable blades. Also, because the movable-blade holding member  17  supporting the movable blade  15  is of a resin, it can be manufactured by die-forming. Thus, cost of the rotary cutting device  6  can be reduced, comparing to conventional rotary cutting devices whose movable blade having a supporting axis is formed through cutting process. Particularly, since die-forming the movable blade  15  of a resin yields a cost merit in mass-production, the cost of the rotary cutting device  6  can be further reduced.  
     [0046] When lifetime of the movable blade  15  is reached, the movable blade  15  can be changed by removing the movable blade  15  that reached the lifetime from the movable-blade holding member  17  and installing a new one to the movable-blade holding member  17 .  
     [0047] In conventional rotary cutting device, when the movable blade  15  reaches its lifetime and the movable blade needs to be replaced, a member that supports the movable blade and a member that imparts a drive force to the movable blade need to be disassembled. Whereas, in the present embodiment, because the movable-blade holding member  17  as a movable-blade holding section holds the movable blade  15  such that the movable blade  15  can be readily mounted and dismounted thereto/therefrom by the grooves that allow at least one edge side and the other edge side of the movable blade  15  to engage therein, such disassembling is no longer needed. Thus, replacement of the movable blade  15  can be readily made. Herein, a fear may be assumed when changing the movable blade  15 , since one holds a side of the cutting edge  15   a  of the movable blade  15  by the hand. However, even if the hand contacts the cutting edge, it is safe because there should be no danger of injuring the hand. Also, deformation of the movable-blade holding member  17  during the cutting operation can be prevented, since the movable-blade holding member  17  has been reinforced with the movable blade  15  such that the movable blade  15  engages into the grooves  21  of the movable-blade holding member  17  of a resin.  
     [0048] Furthermore, in the rotary cutting device  6  according to this embodiment, as the grooves  21  is provided such that the movable blade  15  is oriented at a slight angle in respect to a line parallel with an axis of the movable-blade holding member  17  as a movable-lade supporting section, the cutting edge  15   a  of the movable blade  15  and the cutting edge  14   b  of the stationary blade  14  are to become arranged at a slight angle in respect to the assumed parallel line according to the position of the groove  21 . Therefore, the axis of the movable-blade holding member  17  needs not to be positioned at a slant in respect to a paper width direction (direction of the axis of the platen  9 ), as needed so in conventional cutters. Instead, the axis of the movable-blade holding member  17  can now be provided in parallel with the width direction of the recording paper  8 . This facilitates to manufacture the movable-blade holding member  17  and the mounting part of the member  17 .  
     [0049] Still furthermore, the rotary cutting device  6  of this embodiment is structured such that: the movable-blade holding member  17  as a movable-blade supporting section is resilient; either one of the movable-blade holding member  17  or the movable blade  15  is provided with the protrusions  20   a , and the other of either the movable-blade holding member  17  or the movable blade  15  is provided with the apertures  15   d  as an engaging part; and there is provided the securing section  23  for securing in the grooves  21  the movable blade  15 , which is engaged in the grooves  21 , by engaging the protrusions  20   a  into the apertures  15   d  while the movable-blade holding member  17  being bent along with movement to engage the movable blade  15  into the grooves  21 . This structure can prevent the movable blade  15  engaged in the grooves  21  of the movable-blade holding member  17  from being coming off from the grooves  21 .