Patent Publication Number: US-9849601-B2

Title: Cutting apparatus and printing apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a cutting apparatus that cuts a cut medium and a printing apparatus with the cutting apparatus mounted therein. 
     Description of the Related Art 
     A cutting apparatus that cuts a cut medium using a pair of blades is conventionally known. The cutting apparatus is mounted in, for example, a printing apparatus that cuts a rolled print medium, and is used as a device that cuts and separates a print medium with image data printed thereon into pages. 
     A configuration is known in which one of the blades is brought into contact with the other blade under pressure to prevent inappropriate cutting. 
     However, when cut media with different cutting resistances are cut, the configuration disadvantageously fails to deal with the respective cutting resistances, resulting in inappropriate cutting. 
     To solve this problem, Japanese Patent Laid-Open No. H06-155372 (1994) discloses a configuration in which a rotary blade fixing member is moved to change the spring pressure of a spring that biases the rotary blade to change the pressing force of the blade according to the cutting resistance, thus improving the cutting performance. 
     However, when cutting is continued with the increased pressing force, cutting edges are significantly worn off, and the lives of the blades are shortened. When cutting is carried out with the pressing force of the blade increased to enhance the cutting performance as in Japanese Patent Laid-Open No. H06-155372(1994), the blades appropriately bite into the cut medium at the start of the cutting, preventing inappropriate cutting. However, the blades are significantly worn off during the cutting, and the lives of the blades are shortened. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention provides a cutting apparatus and a printing apparatus that enhance cutting performance at the start of cutting, while suppressing wear of cutting edges. 
     Thus, a cutting apparatus comprising: a cutting unit including a first blade member and a second blade member that cooperates with the first blade member in cutting an object, configured to cut the object by relatively moving the object and at least one of the first blade member and the second blade member to each other to cut the object; and a changing unit configured to change a pressing force between the first blade member and the second blade member during an operation of cutting the object; wherein the changing unit sets the pressing force during the initial cutting operation from a time when cutting of the object is started until the object has been cut by a predetermined length higher than the pressing force during the subsequent cutting operation. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view depicting an ink jet printing apparatus according to a first embodiment; 
         FIG. 2  is a schematic block diagram depicting an embodiment of a control configuration; 
         FIG. 3  is a perspective view of a cutting apparatus according to the first embodiment; 
         FIG. 4  is a top view of an ink jet printing apparatus according to the first embodiment; 
         FIG. 5  is a schematic sectional view of a cutter unit according to the first embodiment as seen from above; 
         FIG. 6  is a schematic sectional view of the cutter unit according to the first embodiment as seen from behind; 
         FIG. 7  is a schematic sectional view of the cutter unit according to the first embodiment as seen from behind during cutting; 
         FIG. 8  is a schematic sectional view illustrating the cutter unit according to the first embodiment, when the cutter unit is in a cutting start point position; 
         FIG. 9  is a diagram illustrating the cutter unit according to the first embodiment, when the cutter unit has moved further in a cutting direction; 
         FIG. 10  is a graph illustrating a relation between a wear state of cutting edges and a cutting distance; 
         FIG. 11A  is a schematic diagram illustrating the displacement of a pressing spring; 
         FIG. 11B  is a schematic diagram illustrating the displacement of the pressing spring; 
         FIG. 12  is a schematic sectional view of the cutter unit of the present embodiment when viewed from above; 
         FIG. 13  is a top view illustrating a state where the cutter unit is in the cutting start point position; 
         FIG. 14  is a top view illustrating a state where the cutter unit is performing cutting; 
         FIG. 15A  is a schematic diagram illustrating the displacement of the pressing spring; 
         FIG. 15B  is a schematic diagram illustrating the displacement of the pressing spring; 
         FIG. 16A  is a diagram depicting a pressing force changing device; 
         FIG. 16B  is a diagram depicting the pressing force changing device; 
         FIG. 17A  is a diagram depicting a pressing force changing device; 
         FIG. 17B  is a diagram depicting the pressing force changing device; 
         FIG. 18A  is a diagram depicting a pressing force changing device; and 
         FIG. 18B  is a diagram depicting the pressing force changing device. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     A first embodiment of the present invention will be described with reference to the drawings. The same reference numerals denote the same or corresponding components throughout the drawings. 
       FIG. 1  is a schematic sectional view depicting an ink jet printing apparatus according to the first embodiment of the present invention. With reference to  FIG. 1 , a general configuration of the ink jet printing apparatus according to the present embodiment will be described. Rolled paper  1  held in an ink jet printing apparatus  100  is fed downstream through a conveying path including an upper guide  6  and a lower guide  7 . When a leading end of the rolled paper  1  reaches a nip portion between a conveying roller  8  and a pinch roller  9 , the rolled paper  1  is sandwiched between the conveying roller  8  and the pinch roller  9  and conveyed onto a platen  99  (image printing section) arranged opposite to a print head  2 . 
     The image printing section includes the print head  2 , a carriage  3  on which the print head  2  is mounted, and the platen  99  arranged opposite to the print head  2 . The carriage  3  is slidably supported by the main body of the ink jet printing apparatus  100  along a carriage shaft  4  and a guide rail (not depicted in the drawings) arranged parallel to each other. The carriage  3  is configured to be able to reciprocate. Printing is performed by reciprocating the carriage  3  with the print head  2  mounted thereon and allowing the print head  2  to eject ink onto the rolled paper  1 . 
     In the image printing section, when an image is printed by moving the carriage  3  forward or backward to scan one line, the conveying roller  8  and the pinch roller  9  feed the rolled paper  1  by a predetermined pitch in a conveying direction. The carriage  3  is then moved again to print the next line of the image. A printed portion of the rolled paper  1  is conveyed toward a sheet discharging guide  11 . Such an operation is repeated to print an image on the rolled paper  1 . When the image printing ends, the rolled paper  1  is conveyed to a predetermined cutting position where the rolled paper  1  is cut using a cutting apparatus  5 . The cut rolled paper  1  is discharged to the exterior of the ink jet printing apparatus  100  through the sheet discharging guide  11 . 
       FIG. 2  is a schematic block diagram depicting an embodiment of a control configuration of the ink jet printing apparatus  100 . With reference to  FIG. 2 , the control configuration according to the present invention will be described in brief. A control section  400  is provided on the ink jet printing apparatus  100 . The control section  400  achieves control of a conveying motor  51 , a cutter motor  52 , a carriage motor  53 , and a print head  54 . 
     The control section  400  also includes a CPU, a ROM, a RAM, and a motor driver not depicted in the drawings, and further includes a main control section  410 , a conveyance control section  420 , and an image formation control section  430 . The main control section  410  gives instructions to the conveyance control section  420  and the image formation control section  430 . Based on a determination by the main control section  410 , the conveyance control section  420  drives the conveying motor  51  to operate conveying devices, such as the conveying roller  8 , to convey the rolled paper  1 , and drives the cutter motor  52  to cut the rolled paper  1 . The image formation control section  430  allows the carriage motor  53  and the print head  2  to cooperate with each other in forming an image at an appropriate position on the rolled paper  1 . 
       FIG. 3  is a perspective view depicting the cutting apparatus according to the present invention.  FIG. 4  is a top view of the ink jet printing apparatus according to the present invention.  FIG. 5  is a schematic sectional view of a cutter unit according to the present invention as seen from above.  FIG. 6  is a schematic sectional view of the cutter unit according to the present invention as seen from behind, depicting a rotary-blade rotating device that rotates a lower movable blade when the cutter unit is in a cutting start point position. 
     Now, the cutting apparatus according to the present invention will be described with reference to  FIG. 3 ,  FIG. 4 ,  FIG. 5 , and  FIG. 6 . 
     A cutting apparatus  5  has a cutter unit  12 , a guide rail  10 , and a belt  14 . The guide rail  10  is configured to guide the cutter unit  12  in a direction orthogonal to the conveying direction of the rolled paper  1 . The cutter unit  12  can be reciprocated along the guide rail  10  in the direction X 1  and the direction X 2  of arrow X by a driving force transmitted from the cutter motor  52 , which is a driving section, via the belt  14 . The cutter unit  12  stands by in a standby position P 1  (see  FIG. 4 ) where the cutter unit  12  is away from an end of the rolled paper  1  while image formation is being performed on the rolled paper  1 . When the rolled paper  1  is cut, the cutter unit  12  moves in the cutting direction X 1 , which is the direction for cutting, from the standby position P 1  to cut the rolled paper  1  (object). After the rolled paper  1  is cut, the cutter unit  12  moves in the direction X 2  without performing a cutting operation and stands by in the standby position P 1  until the next cutting operation. 
     As depicted in  FIG. 5  and  FIG. 6 , the cutter unit  12  includes an upper movable blade  13   a , a lower movable blade  13   b , a crossing angle changing device  61 , a pressing force changing device  62 , and a rotary-blade rotating device  63 . The upper movable blade  13   a  is a rotatable disc-like (circular) blade disposed above a surface of the rolled paper  1  on which an image is formed and including a peripheral blade. The lower movable blade  13   b  is a rotatable disc-like circular blade disposed below a back surface of the rolled paper  1 , that is opposite to the surface on which the image is formed, and includes a peripheral blade. The lower movable blade  13   b  cooperates with the upper movable blade  13   a  in cutting the object. The lower movable blade  13   b  has a surface substantially parallel to the cutting direction. On the other hand, the blade of the upper movable blade  13   a  has a surface inclined to the cutting direction and subtends a predetermined angle θ (crossing angle θ) to the cutting direction X 1 . 
     Specifically, a standby position P 1  side of the upper movable blade  13   a  is disposed on a downstream side with respect to the lower movable blade  13   b  in the conveying direction of the rolled paper  1 . The side of the upper movable blade  13   a  opposite to the standby position P 1  side is partly disposed on an upstream side with respect to the lower movable blade  13   b  in the conveying direction of the rolled paper  1 . The upper movable blade  13   a  is pressed against the lower movable blade  13   b  at a predetermined angle θ (crossing angle θ) to the cutting direction X 1 . The upper movable blade  13   a  thus comes into point contact with the lower movable blade  13   b  and is rotatably held. In other words, the upper movable blade  13   a  is pressed against the lower movable blade  13   b  at the predetermined angle θ (crossing angle θ). The contact point between the upper movable blade  13   a  and the lower movable blade  13   b  corresponds to a cutting point  15 . The upper movable blade  13   a  and the lower movable blade  13   b  rotate while in contact with each other at the cutting point  15 . Consequently, the cutter unit  12  moves in the cutting direction X 1  with the rolled paper  1  held, cutting the rolled paper  1 . 
     When the rolled paper  1  is cut, the cutter unit  12  moves in the cutting direction X 1  to rotate the upper movable blade  13   a  and the lower movable blade  13   b  in a direction in which the rolled paper  1  is drawn into the cutting point  15 , and moves in the direction X 1  as depicted in  FIG. 6 . 
     A bearing  18   a  and a bearing  18   b  are fixed with an adhesive or the like to the vicinities of the centers of rotation of the upper movable blade  13   a  and the lower movable blade  13   b , respectively. The bearings reduce rotating loads on the upper movable blade  13   a  and the lower movable blade  13   b . The upper movable blade  13   a  and the lower movable blade  13   b  rotate around an upper movable blade rotating shaft  19   a  and a lower movable blade rotating shaft  19   b , respectively, via the bearings. 
     As depicted in  FIG. 5 , the crossing angle changing device  61  includes an upstream side holding portion  20 , a downstream side holding portion  21 , a slide member  22 , a slide pressing spring  23 , and a slide rail shaft  30 . The crossing angle changing device  61  allows the crossing angle θ of the upper movable blade  13   a  to be changed. A groove portion  22   a  is formed in the slide member  22  to pivotally support one side of the upper movable blade rotating shaft  19   a . A groove portion  21   b  is formed in the downstream side holding portion  21  to pivotally support the other side of the upper movable blade rotating shaft  19   a.    
     That is, the groove portion  22   a  formed in the slide member  22  and the groove portion  21   b  formed in the downstream side holding portion  21  pivotally support the upper movable blade rotating shaft  19   a . The groove portion  22   a  in the slide member  22  is arranged behind and at a predetermined distance from the groove portion  21   b  in the downstream side holding portion  21  such that the upper movable blade rotating shaft  19   a  is inclined to a direction orthogonal to the cutting direction X 1 . Thus, the upper movable blade  13   a  is inclined at the predetermined angle (crossing angle) θ to the cutting direction X 1 . That is, the upper movable blade rotating shaft  19   a , the groove portion  21   b  in the downstream side holding portion  21 , and the groove portion  22   a  in the slide member  22  set the crossing angle θ. 
     A thrust suppressing portion  29  is attached to an end of the downstream side holding portion  21  of the upper movable blade rotating shaft  19   a  to prevent the upper movable blade rotating shaft  19   a  from slipping out from the downstream side holding portion  21 . The slide rail shaft  30  is pivotally supported in a direction substantially orthogonal to the cutting direction X 1  by the upstream side holding portion  20  and the downstream side holding portion  21 . The slide member  22  includes an abutting contact portion  22   c  arranged in a slide area L 1  sandwiched between a retaining portion  20   a  of the upstream side holding portion  20  and a sliding suppressing portion  21   a  of the downstream side holding portion  21 . In the above-described arrangement, the slide member  22  can slide on the slide rail shaft  30  within the slide area L 1 . 
     The slide member  22  is biased, by the slide pressing spring  23  held by the slide member  22 , in a direction in which the slide member  22  presses the abutting contact portion  22   c  against the retaining portion  20   a  of the upstream side holding portion  20 . The slide member  22  also has a contact portion  22   b  that partly protrudes from the upstream side holding portion  20  and in which the protruding part is shaped like a circular arc at a leading end of thereof. Pushing in the contact portion  22   b  in the direction of arrow a moves the slide member  22  within the slide area L 1 . When the slide member  22  moves within the slide area L 1 , the upper movable blade rotating shaft  19   a  is tilted around the groove portion  21   b  in the downstream side holding portion  21  so as to change the inclination of the upper movable blade rotating shaft  19   a  to the direction orthogonal to the cutting direction X 1 . This changes the crossing angle θ of the upper movable blade  13   a . When the cutter unit  12  reciprocates, the upstream side holding portion  20  and the downstream side holding portion  21  are guided with respect to the guide rail  10  depicted in  FIG. 3 . 
     When the abutting contact portion  22   c  of the slide member  22  maximally approaches the sliding preventing portion  21   a  of the downstream side holding portion  21  (as depicted in  FIG. 5 ), the crossing angle θ is maximized. In contrast, when the abutting contact portion  22   c  of the slide member  22  maximally approaches the retaining portion  20   a  of the upstream side holding portion  20 , the crossing angle θ is minimized. Thus, moving the slide member  22  enables a change in the crossing angle, which is the angle of the upper movable blade  13   a  to the cutting direction X 1 . In other words, while the rolled paper  1  is being cut, moving the slide member  22  enables the crossing angle θ to be changed even while the rolled paper  1  is being cut. 
     The crossing angle θ is an element related to a cutting property, and an increase in crossing angle θ allows the blades to appropriately bite into a sheet at the start of cutting (cutting performance). However, an increase in crossing angle θ leads to degraded cutting quality, such as a large amount of paper dust from a cutting surface of the rolled paper  1  being cut, or deteriorated durability of the blades. Thus, the quality of cutting surface of the paper (cutting quality) is enhanced by reducing the crossing angle at a predetermined timing after the start of the cutting. 
     The pressing force changing device  62  includes a spring holder  24 , a pressing spring  25 , an external holder  27 , and a pressing device  28 . The pressing force changing device  62  enables a change in a pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a . The spring holder  24  is attached around the upper movable blade rotating shaft  19   a  so as to contact an inner ring portion of the bearing  18   a  of the upper movable blade  13   a . The pressing spring  25  is held by the external holder at one end of the pressing spring  25  and by the spring holder  24  at the other end of the pressing spring  25 . The pressing spring  25  presses the upper movable blade  13   a  against the lower movable blade  13   b  via the spring holder  24  and the bearing  18   a  of the upper movable blade  13   a.    
     The external holder  27  is coupled to the pressing member  28  on a side thereof opposite to a side thereof that holds the pressing spring  25 . The downstream side holding portion  21  is sandwiched between a thrust suppressing portion  27   a  of the external holder  27  and a thrust suppressing portion  28   a  of the pressing member  28 . The external holder  27  is slidable with respect to the downstream side holding portion  21 . The external holder  27  moves via the pressing member  28  to change an operating length of the pressing spring  25 , thus changing the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a.    
     When the thrust suppressing portion  28   a  of the pressing member  28  maximally approaches the downstream side holding portion  21  (as depicted in  FIG. 5 ), the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  is maximized. In contrast, when the thrust suppressing portion  27   a  of the external holder  27  maximally approaches the downstream side holding portion  21 , the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  is minimized. Thus, moving the external holder  27  via the pressing member  28  enables a change in the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a . In other words, moving the external holder  27  via the pressing member  28  during the cutting of the rolled paper  1  enables a change in the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  even during the cutting of the rolled paper  1 . 
     The pressing force F is an element related to the cutting property. An increase in pressing force F allows suppression of inappropriate cutting resulting from separation of the blades caused by cutting resistance from the sheet; the inappropriate cutting is likely to occur near the end of the rolled paper  1  at the start of the cutting. However, increasing the pressing force F causes the blades to be worn off, degrading the durability of the upper movable blade  13   a  and the lower movable blade  13   b . Thus, at a predetermined timing after the start of the cutting, the pressing force is reduced to suppress degraded durability of the blades. 
     As depicted in  FIG. 6 , the rotary-blade rotating device  63  is provided in the cutter unit  12  and includes a rotation input gear  40   a , a driven gear  40   b , and a rotary blade rotating gear  40   c . In the rotary-blade rotating device  63 , the rotation input gear  40   a  meshes with a rack member  41  provided on the guide rail  10  to move relative to the guide rail  10 , thus forcibly rotating the lower movable blade  13   b . The rotation input gear  40   a  meshes with the rack member  41  provided on the guide rail  10  and is thus forcibly rotated in conjunction with movement of the cutter unit  12 . 
     The rotation input gear  40   a  meshes with the rack member  41  provided on the guide rail  10  so as to be forcibly rotated in conjunction with movement of the cutter unit  12 . The driven gear  40   b  transmits rotation of the rotation input gear  40   a  to the rotary blade rotating gear  40   c . The rotary blade rotating gear  40   c  is integrally attached to the lower movable blade  13   b  such that the lower movable blade rotating shaft  19   b  corresponds to a central axis, so that the rotary blade rotating gear  40   c  can rotate integrally with the lower movable blade  13   b . Forcibly rotating the rotary blade rotating gear  40   c  also rotates the lower movable blade  13   b.    
     In an area where the rack member  41  is not provided, the rotary blade rotating gear  40   c  does not mesh with the rack member  41  and thus does not rotate. That is, within a movement area of the cutter unit  12 , different areas are provided: the area where the rotation input gear  40   a  meshes with the rack member  41  and the area where the rotation input gear  40   a  does not mesh with the rack member  41 . Consequently, the rotary-blade rotating device  63  enables switching between an area where the lower movable blade  13   b  is forcibly rotated and an area where the lower movable blade  13   b  is not rotated. 
     A moving speed of the cutter unit  12  is represented as a cutting speed V 1 . A peripheral speed of the lower movable blade  13   b  is represented as a peripheral speed V 2 . As the cutter unit  12  moves, the rotation input gear  40   a , the driven gear  40   b , and the rotary blade rotating gear  40   c  are forcibly rotated at a peripheral speed equal to the cutting speed V 1  in the direction of an arrow in  FIG. 6 . Rotation of the rotary blade rotating gear  40   c  rotates the lower movable blade  13   b , which rotates integrally with the rotary blade rotating gear  40   c.    
     The pitch circle diameter of the rotary blade rotating gear  40   c &lt;the diameter of the lower movable blade  13   b , and thus, the peripheral speed V 2  of the lower movable blade  13   b  is higher than the cutting speed V 1 . In the present embodiment, the lower movable blade  13   b  has a diameter of 24 mm, and the rotary blade rotating gear  40   c  has a pitch circle diameter of 12 mm. Thus, the peripheral speed V 2  of the lower movable blade  13   b  is approximately 2×V 1 , that is, approximately twice as high as the cutting speed V 1 , that is, the moving speed of the cutter unit  12 . The speed of a cutting edge relative to the rolled paper  1  is approximately 2×V 1 , which is equal to the peripheral speed V 2  of the lower movable blade  13   b.    
     On the other hand, in the area where the rack member  41  is not provided, the lower movable blade  13   b  is not rotated by the rack member  41 . However, when the rolled paper  1  is cut, the upper movable blade  13   a  and the lower movable blade  13   b  are moved at the cutting speed V 1  equal to the moving speed of the cutter unit  12 , while cutting the rolled paper  1 . Thus, the upper movable blade  13   a  and the lower movable blade  13   b  rotate as a result of a frictional force between the rolled paper  1  and the blades. Consequently, when the rolled paper  1  is cut in the area where the rack member  41  is not provided, the upper movable blade  13   a  and the lower movable blade  13   b  rotate at the peripheral speed V 2  approximately equal to the cutting speed V 1  corresponding to the moving speed of the cutter unit  12 . The speed of the cutting edge relative to the rolled paper  1  is approximately equal to the cutting speed V 1 , which is in turn equal to the peripheral speed V 2  of the lower movable blade  13   b.    
     On the other hand, when the rolled paper  1  is not being cut in the area where the rack member  41  is not provided, no force that rotates the lower movable blade  13   b  is obtained, and thus, the peripheral speed V 2  of the lower movable blade  13   b  is zero. Consequently, the upper movable blade  13   a  and the lower movable blade  13   b  do not rotate. The speed of the cutting edge relative to the rolled paper  1  is zero, which is equal to the peripheral speed V 2  of the lower movable blade  13   b.    
     The case where the rolled paper  1  is not being cut occurs during a moving operation in the cutting direction X 1  after the cutting of the rolled paper  1  ends and during a moving operation in the direction X 2  when the cutter unit  12  returns to the standby position P 1 . While the rolled paper  1  is not being cut, the upper movable blade  13   a  is rotated in conjunction with rotation of the lower movable blade  13   b  as a result of friction between the upper movable blade  13   a  and the lower movable blade  13   b . The upper movable blade  13   a  rotates at a speed lower than the peripheral speed V 2  of the lower movable blade  13   b . As described above, when a cutting path for the rolled paper  1  includes different parts: the part where the rack member  41  is provided and the part where the rack member  41  is not provided, the peripheral speed V 2  of the lower movable blade  13   b  can be switched during cutting of the rolled paper  1 . 
     In cutting using a disc-like circular blade, the peripheral speed, which is equal to the speed of the cutting edge relative to the rolled paper  1 , is an element related to the cutting property. An increase in peripheral speed allows the blades to appropriately bite into the sheet. On the other hand, increasing the peripheral speed leads to degraded cutting quality such as a large amount of paper dust from the cutting surface or degraded durability of the blades. When the peripheral speed V 2  of the lower movable blade  13   b  is increased with respect to the moving speed, an effect is enhanced which causes the rolled paper  1  to be drawn into the cutting point  15  between the upper movable blade  13   a  and the lower movable blade  13   b . This is effective for enabling the blades to more appropriately bite into the sheet. 
       FIG. 7  is a schematic sectional view of the cutter unit  12  according to the present invention during cutting as seen from behind, illustrating that the cutter unit  12  in the state illustrated in  FIG. 6  has moved in the cutting direction X 1  and depicting the rotary-blade rotating device rotating the lower movable blade  13   b  while the cutter unit is in the position of cutting.  FIG. 8  is a schematic sectional view of the cutter unit according to the present invention in a cutting start point position as seen from above.  FIG. 9  is a schematic sectional view depicting a state where the cutter unit in the state illustrated in  FIG. 8  has further moved in the cutting direction X 1  and where the cutter unit according to the present invention is in the position of cutting, as seen from above. 
     Now, with reference to  FIG. 6 ,  FIG. 7 ,  FIG. 8 , and  FIG. 9 , the operation of the cutter unit  12  changing cutting conditions during cutting by the cutting apparatus according to the present invention will be described in conjunction with effects of an upstream support member  16 , effects of a downstream support member  17 , and effects of the rack member  41 . 
     The upstream support member changes the crossing angle θ of the upper movable blade  13   a  to the lower movable blade  13   b . As depicted in  FIG. 7 , the upstream support member  16  is arranged above a surface of the rolled paper  1  on which the image is printed. The upstream support member  16  controls the position of the slide member  22  via the contact portion  22   b  of the cutter unit  12  to change the crossing angle θ of the upper movable blade  13   a  to the lower movable blade  13   b . As depicted in  FIG. 8 , the upstream support member  16  includes a first flat surface (protruding portion)  16   a  that is a surface protruding in the conveying direction, which is orthogonal to the cutting direction X 1 , a second flat surface  16   b  that is a surface retracted at a predetermined distance from the first flat surface  16   a  in the conveying direction, and a slope portion  16   c  that joins the first flat surface  16   a  and the second flat surface  16   b  together. 
     The first flat surface  16   a  protrudes to the degree that the contact portion  22   b  is pushed to bring the abutting contact portion  22   c  of the slide member  22  nearly into contact with the sliding suppressing portion of the downstream side holding portion  21 . As depicted in  FIG. 8 , when the contact portion  22   b  is in a position corresponding to the first flat surface  16   a  in the cutting direction, that is, when the cutter unit  12  is in a position where the contact portion  22   b  is pushed in by the first flat surface  16   a , the crossing angle θ of the upper movable blade  13   a  to the cutting direction X 1  is maximized (crossing angle θ=θ 2 ). At a crossing angle θ=θ 2  where the crossing angle θ is maximized, the blades appropriately bite into the sheet. This prevents a situation where, when the cutting point  15  between the upper movable blade  13   a  and the lower movable blade  13   b  passes through a cutting start point P 2  for the rolled paper  1 , the blades fail to bite into the sheet, which is then deformed. 
     The second flat surface  16   b  is provided on a traveling direction side (opposite to the standby position P 1 ) in the cutting direction during cutting with respect to the first flat surface  16   a . The second flat surface  16   b  is retracted to the degree that, with the abutting contact portion  22   c  of the slide member  22  in contact with the retaining portion  20   a  of the upstream side holding portion  20 , the contact portion  22   b  of the slide member  22  does not contact the second flat surface  16   b . That is, as depicted in  FIG. 9 , when the contact portion  22   b  is in the position corresponding to the second flat surface  16   b  in the cutting direction, the cutter unit  12  is not pushed in because the contact portion  22   b  of the slide member  22  does not contact the second flat surface  16   b.    
     At this time, the spring bias force of the slide pressing spring  23  brings the abutting contact portion  22   c  of the slide member  22  into contact with the retaining portion  20   a  of the upstream side holding portion  20 . Thus, the crossing angle θ of the upper movable blade  13   a  to the lower movable blade  13   b  is minimized (crossing angle θ=θ 1 ). At a crossing angle θ=θ 1  where the crossing angle θ is minimized, cutting can be achieved such that the cutting surface of the rolled paper  1  being cut exhibits high quality, suppressing possible paper dust during the cutting. 
     In connection with movement of the cutter unit  12  in the cutting direction X 1 , the first flat surface  16   a  is arranged such that at least when the cutting point  15  of the cutter unit  12  is positioned at the cutting start point P 2  where the cutting of the rolled paper  1  is started, the contact portion  22   b  comes into contact with the first flat surface  16   a . Specifically, the first flat surface  16   a  is formed to extend from a position closer to the standby position P 1  than the cutting start point P 2  in the cutting direction to a position on the traveling direction side in the cutting direction with respect to the end of the rolled paper  1 . Thus, the contact portion  22   b  remains in contact with the first flat surface  16   a  until the cutting point  15  reaches the cutting start point P 2 . 
     The slope portion  16   c  is arranged so as to extend from a position to which, during the cutting, the cutting point  15  of the cutter unit  12  moves a predetermined distance after passing through the cutting start point P 2 . In this regard, the predetermined distance is determined with a variation in the sheet end position of the rolled paper  1  taken into account and, for example, corresponds to one rotation of the upper movable blade  13   a  following the start of the cutting of the rolled paper  1 . In the present embodiment, the predetermined distance is 5 to 80 mm from the cutting start point P 2 . 
     The slope portion  16   c  smoothly joins the first flat surface  16   a  and the second flat surface  16   b  together to suppress a rapid change in the position of the slide member  22 , thus restraining damage to the upper movable blade  13   a  and the lower movable blade  13   b  caused by a rapid change in the crossing angle θ of the upper movable blade  13   a . The slope portion  16   c  may be a flat surface or a curved surface as long as the slope portion  16   c  allows the first flat surface  16   a  and the second flat surface  16   b  to be smoothly joined together. In the above description, the second flat surface  16   b  is retracted to the degree that, with the abutting contact portion  22   c  of the slide member  22  in contact with the retaining portion  20   a  of the upstream side holding portion  20 , the contact portion  22   b  of the slide member  22  does not contact the second flat surface  16   b . However, the present embodiment is not limited to this configuration. For example, the second flat surface  16   b  may be positioned to the degree that the abutting contact portion  22   c  of the slide member  22  contacts the second flat surface  16   b , and, more specifically, to the degree that the abutting contact portion  22   c  of the slide member  22  contacts the retaining portion  20   a  of the upstream side holding portion  20 . 
     As described above, in the present embodiment, the crossing angle changing device  61  and the upstream support member  16  provided in the cutting apparatus  5  enable the crossing angle θ of the upper movable blade  13   a  to be changed while the rolled paper  1  is being cut. When the cutting of the rolled paper  1  is started (cutting start point P 2 ), the crossing angle θ of the upper movable blade  13   a  is set to a large value because the blades have difficulty biting into the sheet. This allows the blades to appropriately bite into the sheet to prevent a situation where the sheet starts to be deformed at the position of abutting contact with the blades and is thus pushed in the cutting direction X 1 , resulting in inappropriate cutting. On the other hand, in the area corresponding to a time following the start of the cutting, the inappropriate cutting resulting from the pushing of the sheet in the cutting direction X 1  is unlikely to occur. Thus, the crossing angle θ of the upper movable blade  13   a  is set to a small value to suppress degraded cutting quality such as a large amount of paper dust from the cutting surface or degraded durability of the blades. 
     As described above, the cutting apparatus of the present embodiment includes the crossing angle changing device that changes the crossing angle θ, which is the angle of the upper movable blade  13   a  to the lower movable blade  13   b , while the cut medium is being cut. In the crossing angle changing device, the upstream support member  16  includes the first flat surface  16   a  and the second flat surface  16   b . Before the cutter unit  12  performs cutting and when the cutter unit  12  is in the cutting start point P 2 , the slide member  22  contacts the first flat surface  16   a  and is pushed downstream in the conveying direction to tilt the upper movable blade rotating shaft  19   a , increasing the crossing angle θ. Thus, at the start of the cutting, the blades appropriately bite into the sheet to allow the cutting performance to be enhanced. During the cutting, the slide member  22  reaches the second flat surface  16   b  through the slope portion  16   c  and is slid toward the upstream side holding portion  20 . Consequently, the crossing angle θ decreases to allow the quality of the cutting surface to be restrained from being degraded. 
     In the present embodiment, the first flat surface  16   a  extends from the position corresponding to a time preceding the start of the cutting to the position where the cutting point  15  of the cutter unit  12  reaches the cutting start point P 2 . However, the present embodiment is not limited to this configuration. For example, the first flat surface  16   a  may be formed at a position corresponding to a time immediately before the end of the cutting to increase the crossing angle θ to enhance the cutting performance. This configuration prevents a situation where the sheet above the sheet discharge guide  11  falls obliquely starting with a cutting start side of the sheet, to raise an uncut part of the sheet, resulting in inappropriate cutting. Alternatively, a flat surface with a protruding distance equivalent to the protruding distance of the first flat surface  16   a  may be provided in two areas including an area corresponding to an initial period of the cutting and an area corresponding to a time immediately before the end of the cutting. Thus, the protruding distance of the upstream support member  16  and the location of the upstream support member  16  are not limited to those in the present embodiment but may be freely set in order both to enhance the cutting performance and to ensure the cutting quality. 
     The downstream support member changes the pressing force exerted on the lower movable blade  13   b  by the upper movable blade  13   a . The downstream support member  17  is arranged above the surface of the rolled paper  1  on which the image is printed. The downstream support member  17  controls the position of the external holder  27  via the pressing member  28  of the cutter unit  12  to change the pressing force exerted on the lower movable blade  13   b  by the upper movable blade  13   a  as depicted in  FIG. 8 . The downstream support member  17  has undulating surfaces, and has a first flat surface  17   a  that is a surface protruding in a direction opposite to the conveying direction orthogonal to the cutting direction X 1 , a second flat surface  17   b  retracted at a predetermined distance from the first flat surface  17   a , and a slope portion  17   c  that joins the first flat surface  17   a  and the second flat surface  17   b  together. 
     The first flat surface  17   a , which is a part of the undulating portion, protrudes to the degree that the thrust suppressing portion  28   a  of the pressing member  28  is pushed in and brought nearly into contact with the downstream side holding portion  21 . That is, when the cutter unit  12  is in a position where the pressing member  28  is pushed in by the first flat surface  16   a , the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  is maximized (pressing force F=F 2 ). At the start of the cutting, inappropriate cutting is likely to result from separation of the blades caused by cutting resistance from the sheet. Thus, near the end of the rolled paper  1 , the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  is maximized in order to suppress inappropriate cutting. That is, at the start of the cutting, the upper movable blade  13   a  and the lower movable blade  13   b  are brought into contact with each other by a strong force near the end of the rolled paper  1 . 
     The second flat surface  17   b  is retracted to the degree that, with the thrust suppressing portion  27   a  of the external holder  27  in contact with the downstream side holding portion  21 , the pressing member  28  does not contact the second flat surface  17   b . As depicted in  FIG. 9 , when the pressing member  28  is in a position corresponding to the second flat surface  17   b  in the cutting direction, the pressing member  28  does not contact the second flat surface  17   b  and is thus not pushed in. When the cutter unit  12  is in this position, the pressing force F exerted on the lower movable blade  13   b  is minimized (pressing force F=F 1 ). The minimized pressing force F exerted on the lower movable blade  13   b  restrains the durability of the upper movable blade  13   a  and the lower movable blade  13   b  from being degraded as a result of the wear of the blades. 
     In connection with movement of the cutter unit  12  in the cutting direction X 1 , the first flat surface  17   a  is arranged such that at least when the cutting point  15  of the cutter unit  12  reaches the cutting start point P 2  where the cutting of the rolled paper  1  is started, the pressing member  28  comes into contact with the first flat surface  17   a  and is pushed a predetermined distance by the first flat surface  17   a . The slope portion  17   c  is arranged so as to extend from a position to which, during the cutting, the cutter unit  12  moves predetermined distance after the cutting point  15  of the cutter unit  12  passes through the cutting start point P 2 . Specifically, the first flat surface  17   a  is provided so as to extend from a position closer to the standby position P 1  than the cutting start point P 2  in the cutting direction, to a position slightly closer to the standby position than the end of the rolled paper  1  in the cutting direction. Thus, the pressing member  28  remains in contact with the first flat surface  17   a  until the cutting point  15  reaches the cutting start point P 2 . 
     The slope portion  17   c  smoothly joins the first flat surface  17   a  and the second flat surface  17   b  together to suppress a rapid change in the position of the external holder  27  via the pressing member  28 , thus restraining damage to the upper movable blade  13   a  and the lower movable blade  13   b  caused by a rapid change in the pressing force F. The slope portion  17   c  may be a flat surface or a curved surface as long as the slope portion  17   c  allows the first flat surface  17   a  and the second flat surface  17   b  to be smoothly joined together. In the above description, the second flat surface  17   b  is retracted to the degree that, with the thrust suppressing portion  27   a  of the external holder  27  in contact with the downstream side holding portion  21 , the pressing member  28  does not contact the second flat surface  17   b . However, the present embodiment is not limited to this configuration. For example, the second flat surface  17   b  may be positioned to the degree that the thrust suppressing portion  27   a  of the external holder  27  contacts the downstream side holding portion  21 . 
     As described above, the pressing force changing device  62  and the downstream support member  17  provided in the cutting apparatus  5  enable the pressing force F exerted on the lower movable blade  13   b  to be changed while the rolled paper  1  is being cut. That is, near the cutting start point of the rolled paper  1  where the blades have difficulty biting into the sheet, the pressing force exerted on the lower movable blade  13   b  is set to a large value. This allows the blades to more reliably contact each other, suppressing possible inappropriate cutting resulting from separation of the blades caused by cutting resistance from the sheet. On the other hand, in an area corresponding to a time following the start of the cutting, the inappropriate cutting resulting from separation of the blades is unlikely to occur. Thus, the pressing force F exerted on the lower movable blade  13   b  is set to a small value to suppress degraded durability resulting from the wear of the blades. 
     In connection with movement of the cutter unit  12  in the cutting direction X 1 , the first flat surface  17   a  is arranged such that the pressing member  28  comes into contact with the first flat surface  17   a  at least at the cutting start point P 2  where the cutter unit  12  starts cutting the rolled paper  1 . The slope portion  17   c  is arranged so as to extend from a position to which, during the cutting, the cutter unit  12  moves a predetermined distance after passing through the cutting start point P 2 . In this regard, the predetermined distance is determined with a variation in the sheet end position of the rolled paper  1  taken into account and, for example, corresponds to one rotation of the upper movable blade  13   a  following the start of the cutting of the rolled paper  1 . In the present embodiment, the predetermined distance is 5 to 80 mm from the cutting start point P 2 . 
     In the present embodiment, the first flat surface  17   a  extends from a position corresponding to a time preceding the start of the cutting, to a position where the cutting point  15  reaches the cutting start point P 2 . The first flat surface  17   a  may be formed at a position corresponding to a time immediately before the end of the cutting to increase the pressing force F to enhance the cutting performance. This configuration prevents a situation where the sheet above the sheet discharge guide  11  falls obliquely starting with the cutting start side of the sheet, to raise the uncut part of the sheet, resulting in inappropriate cutting. 
     The rack member changes the peripheral speed of the lower movable blade  13   b . The rack member  41  is provided on the guide rail  10 , and meshes with and forcibly rotates the lower movable blade  13   b  to change the peripheral speed of the lower movable blade  13   b  as depicted in  FIG. 6 . The rack member  41  is arranged such that at least at the cutting start point P 2  where the cutter unit  12  starts cutting the rolled paper  1 , the rotation input gear  40   a  meshes with the rack member  41  to forcibly rotate the lower movable blade  13   b  as depicted in  FIG. 6 . 
     That is, at the cutting start point P 2  where cutting is started, the rotation input gear  40   a  (pinion gear) meshes with the rack member  41  to make the peripheral speed V 2  of the lower movable blade  13   b  higher than the cutting speed V 1  corresponding to the moving speed of the cutter unit  12 . The peripheral speed V 2  of the lower movable blade  13   b  is increased to allow the blades to appropriately bite into the sheet at the start of the cutting. This suppresses a situation where the sheet starts to be deformed at the position of abutting contact with the blades and is thus pushed in the cutting direction X 1 , resulting in inappropriate cutting. 
     In the present embodiment, the rack member  41  is provided so as to extend from the standby position P 1  to a predetermined position at which the cutter unit  12  arrives after passing through the cutting start point P 2 . That is, the rack member  41  is arranged so as to extend from the cutting start point P 2  to a position where the rolled paper  1  has been cut by a predetermined length. In the present embodiment, the predetermined length is set with a variation in the sheet end position of the rolled paper  1  taken into account. In the present embodiment, for example, the predetermined length corresponds to an amount of time from the start of cutting of the rolled paper  1  by the upper movable blade  13   a  until the upper movable blade  13   a  has made one rotation, that is, 5 to 80 mm. The cutting over this distance is defined as an initial cutting operation. 
     As the cutter unit  12  further moves in the cutting direction X 1 , the cutter unit  12  encounters an area where the rack member  41  is not provided, as depicted in  FIG. 7 . That is, the rotation input gear  40   a  does not mesh with the rack member  41 . Thus, when the rolled paper  1  is cut, the lower movable blade  13   b  is rotated by the frictional force between the lower movable blade  13   b  and the rolled paper  1 . At this time, the peripheral speed V 2  is approximately equal to the cutting speed V 1  corresponding to the moving speed of the cutter unit  12 . When the rolled paper  1  is not cut (during a moving operation following the end of the cutting or the like), the peripheral speed V 2  of the lower movable blade  13   b  is zero. Consequently, the upper movable blade  13   a  and the lower movable blade  13   b  do not rotate relative to each other. 
     In the present embodiment, the rack member  41  rotates the lower movable blade  13   b . However, the present embodiment is not limited to this configuration. The upper movable blade  13   a  may be rotated or both the upper movable blade  13   a  and the lower movable blade  13   b  may be rotated. 
     As described above, when the rotary-blade rotating device installed in the cutting apparatus  5  is provided on a part of the guide rail  10 , it is possible to set the area where one of the movable blades is forcibly rotated while the rolled paper  1  is being cut and the area where neither of the movable blades are rotated while the rolled paper  1  is being cut. This enables the peripheral speed V 2  of the lower movable blade  13   b  to be changed. In the present embodiment, near the cutting start point of the rolled paper  1  where the blades have difficulty biting into the sheet, the rack member  41  is provided to set a high peripheral speed V 2  for the lower movable blade  13   b  to allow the blades to approximately bite into the sheet. This suppresses a situation where the sheet starts to be deformed at the position of abutting contact with the blades and is thus pushed in the cutting direction X 1 , resulting in inappropriate cutting. 
     On the other hand, in an area corresponding to a time following the start of the cutting, the inappropriate cutting resulting from pushing of the sheet in the cutting direction X 1  is unlikely to occur. Thus, the rack member  41  is omitted to make the peripheral speed V 2  approximately equal to the cutting speed to suppress degraded cutting quality such as a large amount of paper dust from the cutting surface or degraded durability of the blades. Moreover, in an area where the sheet is not cut, the peripheral speed V 2  of the lower movable blade  13   b  is zero, and the blades are protected from wear resulting from the relative rotation of the blades. This restrains the durability of the upper movable blade  13   a  and the lower movable blade  13   b  from being degraded. 
       FIG. 10  is a graph illustrating the results of experiments for verifying the relation between the wear state of the cutting edges and cutting distance for each pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a .  FIG. 11A  and  FIG. 11B  are a schematic diagram illustrating the displacement of the pressing spring. With reference to  FIG. 10 ,  FIG. 11A  and  FIG. 11B , the pressing force changing device  62  in the present embodiment will be described in detail. A cut material verified in  FIG. 10  was cloth paper with high cutting resistance. The verification was performed by repeatedly performing cutting operations with a given amount of rolled paper with a given width conveyed. 
     As depicted in  FIG. 10 , when (A) the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  was 3.92 N both for the start of the cutting and for the cutting in execution, the blades started to inappropriately bite, leading to inappropriate cutting, when a total cutting distance exceeded approximately 750 m. When the inappropriate cutting occurred, increasing the pressing force F up to 11.76 N allowed the blades to appropriately bite again, enabling the cutting to start (this is not depicted in the drawings). A cause of the inappropriate cutting in this case is the wear of the cutting edges, but the major cause is expected to be a weak pressing force F. 
     In contrast, when (B) the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  is initially set to 11.76 N both for the start of the cutting and for the cutting in execution, the wear state of the cutting edges is equivalent to the wear state observed when the inappropriate cutting occurred in the experiment (A). However, the weak pressing force F prevents the inappropriate cutting at this point in time. Then, when the cutting was subsequently continued, the inappropriate cutting occurred at the start of the cutting when the total cutting distance exceeded approximately 530 m. The cause of this inappropriate cutting is expected to be the wear of the cutting edges resulting from the increased pressing force F. 
     The experiments (A) and (B) indicate that, even when the wear state of the cutting edges is degraded to a given level, the cutting can be continued by increasing the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a . Furthermore, the experiments indicate that an excessive pressing force F causes the cutting edges to be quickly worn off and is unsuitable for long-distance cutting. Thus, when (C) the cutting was performed with the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  set to 11.76 N only for the start of the cutting and to 3.92 N for the cutting in execution, the cutting operation was successfully performed over a cutting distance approximately twice as long as the cutting distance in the experiment (A). 
     In the present embodiment, the elastic force of the pressing spring  25  is utilized to allow the upper movable blade  13   a  to exert the pressing force F on the lower movable blade  13   b  as depicted in  FIG. 11A  and  FIG. 11B . In the present embodiment, the displacement of the spring is 6.4 mm when the pressing force F is switched from 3.92 N to 11.76 N. In other words, with respect to the position of the second flat surface  17   b  of the downstream support member  17 , the first flat surface  17   b  is arranged at a position where the first flat surface  16   a  pushes in the pressing member by 6.4 mm. The thus arranged first flat surface  17   a  is placed at the cutting start point P 2  where the cutter unit  12  starts cutting the rolled paper  1 , to press the pressing member  28 . Then, after the cutter unit  12  passes through the cutting start point P 2 , the second flat surface  17   b  is placed at a position opposite to the pressing member  28 . This allows for a change in the pressing force F exerted by the upper movable blade  13   a  on the lower movable blade  13   b  in the process of the cutting. 
     As described above, the cutting apparatus of the present embodiment has the pressing force changing device that switches the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  while the cut medium is being cut. In the pressing force changing device, the downstream support member  17  includes the first flat surface  17   a  and the second flat surface  17   b  retracted downstream with respect to the first flat surface  16   a  by the predetermined distance in the conveying direction. Thus, before the start of cutting with the cutter unit  12  and at the cutting start point P 2 , the pressing member  28  contacts the first flat surface  17   a  and is pushed downstream in the conveying direction to press the upper movable blade  13   a , increasing the pressing force F. Thus, at the start of the cutting, the upper movable blade  13   a  is prevented from leaving the lower movable blade  13   b  to allow the lower movable blade  13   b  to bite into the cut medium, enabling the cutting performance to be enhanced. During the cutting, the pressing member  28  reaches the second flat surface  16   b  through the slope portion  16   c  to reduce the pressing force, allowing the wear of the cutting edges to be suppressed. 
     In the present embodiment, the pressing force F between the two blades is changed during the cutting operation to allow suppression of the wear of the cutting edges while enhancing the cutting performance at the start of the cutting as described above. 
     In the present embodiment, according to a change in the state of the contact between the pressing member  28  and the downstream support member  17 , the thrust suppressing portion  27   a  of the external holder  27  slides to allow for a change in the pressing force exerted on the upper movable blade  13   a  by the lower movable blade  13   b.    
     One blade of the pair of blades is changed to change the crossing angle between the two blades. At this time, with a shaft of the one blade (upper movable rotary blade  13   a ) unmoved, the slide member  22  supporting the shaft is moved in a direction crossing the cutting direction (in the present embodiment, the upper-movable-blade rotating shaft  19   a ). Then, the accuracy of a change in crossing angle can be improved regardless of the reaction force from the paper or the like. 
     In the present embodiment, the sliding distance of the slide member  22  pivotally supporting the upper-movable-blade rotating shaft  19   a  is adjusted using the groove portion  22   a  formed in the upstream side holding portion  20  and the groove portion  21   b  formed in the downstream side holding portion  21 . Thus, the sliding distance can be accurately managed. 
     The cutting apparatus in the present embodiment uses the circular blades, and thus compared to a cutting apparatus using knife-like blade, advantageously provides appropriate cutting surfaces, enables a variety of print media to cut, and has a long life. Furthermore, compared to a cutting apparatus in which one of the blades is an elongate fixed blade, the cutting apparatus in the present embodiment advantageously saves cost and space. 
     Second Embodiment 
     A second embodiment of the present invention will be described with reference to the drawings. A basic configuration of the present embodiment is similar to the basic configuration of the first embodiment, and only a characteristic part of the configuration will be described below. 
     The second embodiment of the present invention will be described with reference to  FIG. 12 ,  FIG. 13 ,  FIG. 14 ,  FIG. 15A , and  FIG. 15B . A variation of the pressure spring  25  serving as a pressing force changing device and a periphery of the pressure spring  25  are illustrated. However, the same components as those of the first embodiment are denoted by the same reference numerals and will not be described below. 
       FIG. 12  is a schematic sectional view of the cutter unit  12  of the present embodiment as seen from above. The upper movable blade  13   a  in the cutter unit  12  of the present embodiment is pressed against the lower movable blade  13   b  by two springs, a low-pressing-force spring  26   a  and a high-pressing-force spring  26   b . The low-pressing-force spring  26   a  and the high-pressing-force spring  26   b  are held by the spring holder  24  and the external holder  27 . The outer diameter of the high-pressing-force spring  26   b  is larger than the outer diameter of the low-pressing-force spring  26   a . The high-pressing-force spring  26   b  is arranged outside and coaxially with the low-pressing-force spring  26   a . The outer diameter of the low-pressing-force spring  26   a  may be set larger than the outer diameter of the high-pressing-force spring  26   b , with the outside arrangement and the inside arrangement reversed. 
     In the present embodiment, the two springs are used to allow the upper movable blade  13   a  to exert the pressing force F on the lower movable blade  13   b . However, the present invention is not limited to this configuration. For example, three or more springs may be used to apply the pressing force. Specifically, besides the high-pressing-force spring and the low-pressing-force spring, an intermediate-pressing-force spring may be used. 
       FIG. 13  is a top view illustrating that the cutter unit  12  is at the cutting start point position.  FIG. 14  is a top view depicting a state where the cutter unit  12  is performing cutting. 
     At the cutting start position, the pressing member  28  is pushed by the first flat area  17   a  to keep the thrust suppressing portion  27   a  in abutting contact with the downstream side holding portion  21  as depicted in  FIG. 13 . At this time, the pressing force F 3  of the low-pressing-force spring  26   a  is 3.92 N, and the pressing force F 4  of the high-pressing-force spring  26   b  is 7.84 N. In other words, at the cutting start position, the upper movable blade  13   a  presses the lower movable blade  13   b  by a force equal to the total of the pressing force F 3  of the low-pressing-force spring  26   a  and the pressing force F 4  of the high-pressing-force spring  26   b , that is, 11.76 N. 
     As depicted in  FIG. 14 , after the cutting start position is passed, when the pressing member  28  is at a position opposite to the second flat area  17   b , the pressing member  28  is not pressed by the second flat area  17   b . Thus, the thrust suppressing portion  27   a  is in abutting contact with the downstream side holding portion  21 . At this time, the pressing force F 3  of the low-pressing-force spring  26   a  is 3.92 N, and the pressing force F 4  of the high-pressing-force spring  26   b  is 0 N. 
     In other words, when the pressing member  28  is at a position opposite to the second flat area  17   b , the high-pressing-force spring  26   b  exerts no bias force. After the cutting start position is passed, the upper movable blade  13   a  presses the lower movable blade  13   b  by a force equal to the total of the pressing force F 3  of the low-pressing-force spring  26   a  (3.92 N) and the pressing force F 4  of the high-pressing-force spring  26   b  (0 N), that is, 3.92 N. After the cutting start position is passed, the pressing member  28  may or may not be in abutting contact with the second flat area  17   b  as long as the pressing force F 4  is 0 N. 
     As described above, the two springs, the high-pressing-force spring and the low-pressing-force spring, are used for the pressing, enabling a reduction in displacement at the time of pressing. Therefore, the apparatus can be miniaturized. 
       FIG. 15A  and  FIG. 15B  are schematic diagrams illustrating the displacement of the pressure spring. As depicted in  FIG. 15A  and  FIG. 15B , in the present embodiment, the displacement of the spring is 4.1 mm when the total of the low-pressing-force spring  26   a  and the high-pressing-force spring  26   b  is switched from 3.92 N to 11.76 N. In other words, the first flat area  17   a  is provided at a position where the first flat area  17   a  pushes in the pressing member  28  by 4.1 mm with respect to the position of the second flat area  17   b  of the downstream side support member  17 . In  FIG. 15A  and  FIG. 15B , the spring that affects the pressing force is represented by black circles, and the spring that does not affect the pressing force is represented by white circles. 
     That is, when the displacement is 4.1 mm, the pressing force F 4  of the high-pressing-force spring  26   b  is not exerted, and only the pressing force F 3  is exerted. Whereas the maximum displacement of the high-pressing-force spring  26   b  is 4.1 mm or less, the maximum displacement of the low-pressing-force spring  26   a  is more than 4.1 mm. Thus, the first flat area  17   a  is placed to press the pressing member  28  at the cutting start point P 2  where the cutter unit  12  starts cutting the rolled paper  1 . The second flat area  17   b  is placed at a position opposite to the pressing member  28  after the cutter unit  12  passes through the cutting start point P 2 . This enables a change in the pressing force F exerted by the upper movable blade  13   a  on the lower movable blade  13   b  in the process of the cutting. 
     As described above, the cutting apparatus of the present embodiment has the pressing force changing device that switches the pressing force F exerted on the lower movable blade  13   b  by the upper movable blade  13   a  while the cut medium is being cut. In the pressing force changing device, the downstream side support member  17  includes the first flat area  17   a  and the second flat area  17   b  retracted downstream in the paper conveying direction with respect to the first flat area  17   a . Thus, before the start of the cutting by the cutter unit  12  and at the cutting start point P 2 , the pressing member  28  contacts the first flat area  17   a  and is pushed upstream in the conveying direction to press the upper movable blade  13   a , leading to an increased pressing force F. Thus, at the start of the cutting, the upper movable blade  13   a  can be allowed to bite into the cut medium without being separated from the lower movable blade  13   b , enabling the cutting performance to be enhanced. During the cutting, when the pressing member  28  reaches the second flat area  17   b  through the slope portion  17   c , the pressing member  28  is slid downstream in the conveying direction to reduce the pressing force, allowing the wear of the cutting edges to be suppressed. 
     In the present embodiment, a plurality of springs is arranged to overlap concentrically to allow the pressing force to be changed with a small displacement of the springs. 
     Third Embodiment 
     A third embodiment will be described below with reference to the drawings. A basic configuration of the present embodiment is similar to the basic configuration of the first embodiment, and only a characteristic part of the configuration will be described below. In the present embodiment, the sliding distance of the pressing member  28 , which is the pressing force changing device for the start of the cutting, is freely switched to change the pressing force exerted at the start of the cutting, in stages. The same components as those of the first and second embodiments are denoted by the same reference numerals and will not be described below. 
       FIG. 16A  and  FIG. 16B  are diagrams depicting the pressing force changing device of the present embodiment.  FIG. 16A  is a schematic sectional view of the cutter unit exerting a pressing force at the first stage.  FIG. 16B  is a side view of a cam. 
     In the present embodiment, the pressing force exerted on the lower movable blade  13   b  by the upper movable blade  13   a  at the start of the cutting can be changed in stages. In other words, the wear of the cutting edges progresses as the cutting continues. Thus, the pressing force exerted at the start of the cutting is changed according to the degree of progress of the wear of the cutting edges to allow the cutting performance to be enhanced, while suppressing the wear of the cutting edges. The pressing force changing device that changes the pressing force in stages will be described. 
     (Pressing Force in the First Stage) 
     In the present embodiment, a groove portion  17   d  is formed in the downstream side support member  17 , and a movable member  31  that is slidable in the sheet conveying direction is formed in the groove portion  17   d , as depicted in  FIG. 16A . The movable member  31  has a first flat area  31   a  and a slope portion  31   b . A tension spring  32  is provided between a bottom surface of the groove portion  17   d  and the movable member  31  and is held by the downstream side support member  17  and the movable member  31 . The movable member  31  is biased by the tension spring  32  so as to allow the first flat area  31   a  to protrude to the degree that the thrust suppressing portion  28   a  of the pressing member  28  is pushed close to a position where the thrust suppressing portion  28   a  comes into contact with the downstream side holding portion  21 .  FIG. 16A  depicts two tension springs  32 , but the number of tension springs  32  is not limited to this as long as the tension springs  32  can stably bias the movable member  31 . The tension spring  32  includes one or more springs. 
     The movable member  31  can be slid in the sheet conveying direction by rotational driving by a cam  33  that comes into contact with a protruding portion  31   c  of the movable member  31 . The cam  33  can be rotationally driven by transmitting a driving force from a driving motor  34  to the cam  33  via a first gear  35 , a second gear  36 , and a driving shaft  37 . At the start of the cutting or during the cutting, the driving motor  34  is excited to prevent a situation where the cam  33  is unintentionally rotated to slide the movable member  31  to switch the pressing force. 
     As depicted in  FIG. 16B , the cam  33 , which comes into contact with the protruding portion  31   c  of the movable member  31  is rotationally driven such that the thrust suppressing portion  28   a  of the pressing member  28  causes the first flat area  31   a  to push the pressing member  28  close to the position where the thrust suppressing portion  28   a  of the pressing member  28  comes into contact with the downstream side holding portion  21 . That is, as depicted in  FIG. 16B , the cam  33  acts to set the contact surface between the protruding portion  31   c  and the cam  33  at a position where the pressing force is 11.76 N. Thus, at the first stage, the first flat area  31   a  is placed at a position where the pressure spring  25  exerts a pressing force F 5  of 11.76 N. In other words, at the first stage, the upper movable blade  13   a  presses the lower movable blade  13   b  at a pressing force of 11.76 N at the cutting start position. 
     (Pressing Force at the Second Stage) 
       FIG. 17A  and  FIG. 17B  are diagrams of the pressing force changing device of the embodiment.  FIG. 17A  is a schematic sectional view of the cutter unit exerting a pressing force at the second stage as seen from above.  FIG. 17B  is a side view of the cam. As depicted in  FIG. 17B , the pressing force at the second stage causes the first flat area  31   a  to push the pressing member  28  to a position where the thrust suppressing portion  28   a  of the pressing member  28  does not come into in abutting contact with the downstream side holding portion  21  and the thrust suppressing portion  27   a  of the external holder  27  does not come in abutting contact with the downstream side holding portion  21 . The cam  33 , which comes into abutting contact with the protruding portion  31   c  of the movable member  31 , is rotationally driven to place the first flat area  31   a  at a position where the pressing member  28  is pushed in. 
     That is, as depicted in  FIG. 17B , the cam  33  acts to set the contact surface between the protruding portion  31   c  of the movable member  31  and the cam  33  at a position where the pressing force has any value between 3.92 N and 11.76 N. Thus, the first flat area  31   a  is placed at a position where the pressure spring  25  exerts a pressing force F 6  of any value between 3.92 N and 11.76 N. In other words, at the second stage, the upper movable blade  13   a  presses the lower movable blade  13   b  at a pressing force of any value between 3.92 N and 11.76 N at the cutting start position. 
     At this time, a step is formed between the slope portion  31   b  of the movable member  31  and the second flat area  17   b  of the downstream side support member  17  as depicted in  FIG. 17A . After the start of the cutting, the second flat area  17   b  is retracted such that, with the thrust suppressing portion  27   a  of the external holder  27  in contact with the downstream side holding portion  21 , the pressing member  28  does not to come into contact with the second flat area  17   b , preventing the pressing member  28  from being affected by the step. 
     (Pressing Force at the Third Stage) 
       FIG. 18A  and  FIG. 18B  are diagrams of the pressing force changing device of the embodiment.  FIG. 18A  is a schematic sectional view of the cutter unit exerting a pressing force at the third stage as seen from above.  FIG. 18B  is a side view of the cam. As depicted in  FIG. 18A , the cam  33 , which comes into abutting contact with the protruding portion  31   c  of the movable member  31 , is rotationally driven to move the first flat area  31   a  to a position where, with the thrust suppressing portion  27   a  of the external holder  27  in abutting contact with the downstream side holding portion  21 , the pressing member  28  does not come into contact with the first flat area  31   a.    
     That is, as depicted in  FIG. 18A  and  FIG. 18B , the cam  33  acts to set the contact surface between the protruding portion  31   c  of the movable member  31  and the cam  33  at a position where the pressing force is 3.92 N. Thus, the first flat area  31   a  is placed at a position where the pressure spring  25  exerts a pressing force F 7  of 3.92 N. In other words, at the third stage, the upper movable blade  13   a  presses the lower movable blade  13   b  at a pressing force of 3.92 N at the cutting start position. 
     In this manner, the present embodiment allows the pressing force exerted on the lower movable blade  13   b  by the upper movable blade  13   a  to be switched among the three stages. Thus, as the wear of the blades progresses, the pressing force was increased in stages to successfully enhance the cutting performance, while suppressing the wear of the cutting edges. 
     In the present embodiment, the configuration in which the pressing force is switched among the three stages has been described. However, the present embodiment is not limited to the configuration. For example, the pressing force may be switched among a plurality of stages according to the object to cut. 
     The cutting apparatus in the aspect of the present invention allows the cutting performance at the start of the cutting to be enhanced, while suppressing the wear of the cutting edges. 
     Other Embodiments 
     In the above-described embodiments, after the cutting point  15  of the cutter unit  12  passes through the cutting start point P 2  and then moves a predetermined distance (the distance corresponding to one rotation of the upper movable blade  13   a  following the start of the cutting), the contact portion  22   b  is placed in the position corresponding to the slope portion  16   c , and the pressing member  28  is placed in the position corresponding to the slope portion  16   c . However, the present invention is not limited to this embodiment. A timing when the contact portion  22   b  reaches the slope portion  16   c  may be different from a timing when the pressing member  28  reaches the slope portion  16   c.    
     For the configurations of the above-described embodiments, the serial ink jet printing apparatus has been described. However, the embodiments are applicable to what is called a line head printing apparatus in which nozzles in a print head are arranged in juxtaposition in a direction orthogonal to the sheet conveying direction (sheet width direction). Furthermore, the printing scheme is not limited to image printing based on the ink jet scheme using a liquid ink for image printing. A solid ink may be used as a print agent, and various schemes such as an electrophotographic scheme using toner and a sublimation scheme may be adopted. Additionally, the present invention is not limited to color printing using print agents in a plurality of colors, but monochrome printing using only black (including gray) may be performed. 
     In the above-described embodiments, the printing apparatus with the cutting apparatus has been described. However, the embodiments can also be applied to a configuration only with the cutting apparatus. 
     The cutter unit in which the upper movable blade and the lower movable blade are circular blades has been described. However, the present invention is applicable to a cutter unit including a circular blade and an elongate fixed blade and in which the peripheral speed of the circular blade is changed. 
     Even when the cutter unit uses knife-shaped blades, the pressing force exerted on the cut medium by the cutting edges of the blade members can be switched using a configuration that switches the pressing force of the cutter unit. 
     The configuration that cuts the cut medium by moving the cutter unit has been described. However, the present invention is applicable to a cutting apparatus configured to cut the cut medium by moving the cut medium instead of moving the cutter unit. 
     Besides paper, plastic sheets, photographic printing paper, cloths, and the like, a variety of sheet-like materials may be used as cut media. In the above description, the rolled paper has been taken as an example of the cut medium cut by the cutting apparatus. However, the present invention is not limited to rolled cut media. Continuous sheets that are not rolled and the like may be used, and any media that can be cut by the cutting apparatus may be used. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2014-183375, filed Sep. 9, 2014, which is hereby incorporated by reference herein in its entirety.