Abstract:
A glass cutter is provided which can form, using a wheel, a uniform crack in glass even when a projection or an earlier-formed scribe line is present on the glass. When the wheel is moved on the glass, a fracture layer is formed causing a rib mark to be formed below the fracture layer and a crack to be formed below the rib mark. To cut the glass, the crack is required to be formed uniformly. Applying a force to resist the rotating force of the wheel makes it possible to form a uniform crack even when a projection is present on the glass. This improves glass cutting yield.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese Patent Application JP 2010-142876 filed on Jun. 23, 2010, the content of which is hereby incorporated by reference into this application. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to technology which, when separating, for example, liquid crystal display (LCD) panels from a mother substrate by scribing, enables vertical cracks to be formed stably to achieve stable scribing. 
       BACKGROUND OF THE INVENTION 
       [0003]    In LCD panel production, to improve production efficiency, plural LCD panels are formed on a large mother panel, then they are separated from the mother panel by scribing. Generally, for glass cutting, a wheel made of, for example, sintered diamond or cemented carbide with a diameter of several millimeters is used. The wheel has a circumferential edge and is moved on a glass surface while applying a certain pressure to the glass surface. The wheel moves on the glass surface cutting into the glass by several micrometers thereby forming a linear score measuring several micrometers both in depth and in width. Such a linear score may hereinafter be referred to as a “fracture layer.” 
         [0004]    At the same time as the linear score is formed, a crack with a depth vertical to the glass surface of several tens of micrometers to several hundred micrometers is formed immediately below the linear score. The formation of such a vertical crack propagates, as the wheel advances, ahead of the advancing wheel position with a front angle of several degrees with respect to the vertical direction extending right below the wheel. That the formation of the vertical crack propagates with such an angle can be known by observing a mark called a rib mark which is generated on the cut surface of the glass. The depth of the vertical crack is the depth of the rib mark plus the depth of a crack formed to further extend depthwise beyond the rib mark. As far as the present invention is concerned, the rib mark depth and the depth of the vertical crack may be regarded, for the sake of convenience, as being identical. Generally, the operation and what is caused by the operation described above are collectively referred to as scribing. To separate a sheet of glass into multiple parts, one side of a sheet of glass is scribed, and the scribed portion is pressed from the other side causing the vertical crack formed in the scribed portion to extend deeper. This glass separation may be referred to as breaking. 
         [0005]      FIG. 22  shows a glass cutter  1 . As shown, the glass cutter  1  includes a wheel  10  used for scribing, a wheel pin  11  serving as a shaft of the wheel  10 , and a holder  12  supporting the wheel  10  and the wheel pin  11 . 
         [0006]      FIG. 23  is a sectional view of the wheel  10  used for scribing. Referring to  FIG. 23 , the wheel  10  has a ridge, i.e. a cutting edge  101 , bevels  102 , and sides  103 . The wheel  10  has thickness t ranging from 0.5 to 1.0 mm, edge angle θ ranging from 100 to 130 degrees, and diameter d ranging from 2 to 3 mm. The wheel  10  is formed of, for example, sintered diamond or cemented carbide. 
         [0007]      FIGS. 24A and 24B  are a plan view and a sectional view, respectively, showing scribing of glass performed using the wheel  10  shown in  FIG. 23 . Referring to  FIG. 24A , a fracture layer  201  formed by the wheel  10  has width w which is about several micrometers. 
         [0008]    Referring to  FIG. 24B , the fracture layer  201  formed by the wheel  10  has depth d 1 , and a rib mark  202  is formed below the fracture layer  201  with a crack  203  further extending from the rib mark  202 . Depth d 1  of the fracture layer  201  is several micrometers. Depth d 2  from the glass surface to the bottom of the crack ranges from several tens of micrometers to several hundred micrometers. 
         [0009]    In  FIG. 24B , a white arrow MD denotes the moving direction of the wheel  10 , “FF” denotes a force moving the wheel  10 , and “RF” denotes a rotating force generated as the wheel  10  moves. Also, “F 1 ” denotes a force the wheel  10  applies, in its moving direction, to the glass  300 ; “F 2 ” denotes a force the wheel  10  vertically applies to the glass  300 ; and “F 3 ” denotes a resultant force of F 1  and F 2 . As the wheel  10  moves, while rotating, in the direction MD, the crack  203  is formed in the glass  300 . 
         [0010]    The above glass cutting mechanism is described, for example, in literature by Toshihiko Ono and Yuko Ishida, “Cuttability of AMLCD Glass Substrate” in SID 02 DIGEST, pages 45-47 (2002) and also in literature by T. Murata, S. Miwa, H. Yamazaki, S. Yamamoto, “Suitable Scribing Conditions for AMLCD Glass Substrate” in SID Digest, pages 374-377. Also, a configuration for stably forming a crack when forming a scribe line crossing an existing scribe line on a glass surface is described, for example, in Japanese Patent Laid-Open No. 2009-93051. Furthermore, a wheel  10  with notches formed on its cutting edge so that it may securely rotate on the glass surface is described in WO2007/004700. Still furthermore, a configuration in which a wheel  10  and a rotary shaft for rotating the wheel  10  are united is described in Japanese Patent Laid-Open No. 2001-246616. 
       SUMMARY OF THE INVENTION 
       [0011]      FIGS. 25A to 25D  show operation of the wheel  10  in a case where a microprojection (hereinafter also referred to simply as a “projection”)  301  is present on the surface of the glass  300 .  FIG. 25A  shows the wheel  10  moving on a flat surface portion of the glass  300 . In  FIG. 25B , the wheel  10  is shown having ridden on the projection  301  present on the glass  300 . In the state shown in  FIG. 25B  with the wheel  10  over the projection  301 , the wheel  10  applies, in its moving direction, no force to the glass  300 . In this state, the force applied from the wheel  10  to the glass  300  is F 2  only. As a result, formation of the crack  203  that has been continued until before the wheel  10  has ridden on the projection  301  is once discontinued. 
         [0012]      FIG. 25C  shows the wheel  10  that is, having passed the projection  301 , about to start moving on a flat surface portion of the glass  300  again. As shown in  FIG. 25C , the wheel  10 , after passing the projection  301 , starts applying forces F 1 , F 2 , and F 3  to the glass  300  again to cause formation of the crack  203  to be resumed.  FIG. 25D  shows a state in which the wheel  10  passed the projection  301  and the crack  203  is formed in the glass  300  in a normal manner. 
         [0013]      FIGS. 25C and 25D  show that no crack  203  is formed in portion Y below the projection  301  present on the glass surface. Thus, with the glass  300  having a portion where the crack  203  required for subsequent glass breaking operation is not formed, there is a large risk that the portion causes, by preventing the glass  300  from being stably broken into plural parts, generation of defective parts in the subsequent glass breaking operation. This problem cannot be adequately dealt with by the configurations described in Japanese Patent Laid-Open No. 2009-93051 and WO2007/004700. 
         [0014]    In many cases of LCD cell cutting, particularly, where plural LCD cells are cut out from a single LCD sheet, first, plural first scribe lines are formed on the LCD sheet, then plural second scribe lines are formed perpendicularly to the first scribe lines, so that the first scribe lines and the second scribe lines have intersections where they cross. 
         [0015]    When a second scribe line is formed using a wheel  10  to cross a first scribe line already formed, formation of a vertical crack along the second scribe line to propagate ahead of the position of the wheel  10  may be once discontinued at the intersection of the first and second scribe lines, requiring the wheel  10  to move several hundred micrometers past the intersection before the vertical crack formation can be resumed. Namely, the vertical crack formed along the second scribe line is not formed over a range of several hundred micrometers from the intersection. Such a scribe line intersection with no vertical crack formed along the second scribe line makes glass breaking difficult and possibly causes glass edge chipping in the subsequent glass breaking operation. Such discontinuation of vertical crack formation is referred to as “intersection skipping.” Intersection skipping is assumed to occur when formation of a vertical crack propagating ahead of the position of the wheel  10  is discontinued at a scribe line intersection causing the wheel  10  to temporarily ride on the glass surface thereby preventing formation of a fracture layer and, hence, preventing formation of a vertical crack. 
         [0016]    The above process is schematically illustrated in  FIGS. 26A to 26D .  FIG. 26A  shows the wheel  10  moving, while rotating, toward an existing scribe line  302 . The crack  203  is formed in the glass  300  in the manner as described above with reference to  FIGS. 25A to 25D .  FIG. 26B  shows a state in which formation of the crack  203  by the wheel  10  has been discontinued by the presence of the scribe line  302 . 
         [0017]    Namely, when the wheel  10  passes the scribe line  302 , it enters a state similar to riding on a new glass edge. In such a state, F 2  is the only force applied from the wheel  10  to the glass  300  with no force applied to the glass  300  in the moving direction of the wheel  10 . As a result, formation of the crack  203  in the glass  300  is discontinued. 
         [0018]      FIG. 26C  shows a state in which, with the wheel  10  having crossed the scribe line  302 , formation of a vertical crack in the glass  300  is being resumed.  FIG. 26D  shows a state in which the wheel  10  passed the scribe line  302  and the crack  203  is formed in the glass  300  in a normal manner. 
         [0019]      FIGS. 26C and 26D  show that no crack  203  is formed in portion Z, i.e. in the vicinity of the scribe line  302 . Thus, with the glass  300  having a portion where the crack  203  required for subsequent glass breaking operation is not formed, there is a large risk that the portion causes, by preventing the glass  300  from being stably broken into plural parts, generation of defective parts in the subsequent glass breaking operation. This problem cannot be adequately dealt with by the configurations described in Japanese Patent Laid-Open No. 2009-93051 and in WO2007/004700. 
         [0020]    An object of the present invention is to enable continuous formation of a crack and stable scribing by the wheel  10  so as to improve the yield in the process of breaking a mother substrate into plural LCD panels even in cases where there is a microprojection on the glass surface or there is a scribe line already formed on the glass surface. 
         [0021]    According to the present invention made in view of the above problem, when moving a wheel on a glass surface while rotating the wheel, a force to oppose, as if braking, the wheel rotation is applied. This makes it possible to stably form a vertical crack on the glass surface even in cases where a microprojection is present on the glass surface. Furthermore, it is also made possible to inhibit intersection skipping which causes the crack formation to be discontinued when the wheel moves crossing an earlier-formed scribe line. 
         [0022]    In other words, it is a principle of the present invention to restrain generation, due to rotation of a wheel, of an upward force by applying, to the wheel, a force to oppose the rotation of the wheel. Namely, the wheel is prevented from riding on a glass surface even when the glass surface includes projections, depressions, or otherwise non-flat portions or even when the wheel moves crossing an earlier-formed scribe line. In this way, it is easier for the wheel to keep applying a force, in its moving direction, to the glass in a stable manner so as to stably continue scribing. 
         [0023]    According to the present invention, in glass cutting operation, a wheel moving on a glass surface does not ride on the glass surface even when microdepressions and microprojections are present on the glass surface. Also, the wheel is prevented from riding on the glass surface when it finishes crossing an earlier-formed scribe line. This can prevent vertical crack formation in the glass from becoming unstable or from being discontinued. 
         [0024]    Since, in a process to scribe a mother substrate and separate LCD panels from the mother substrate, scribe lines can be continuously and stably formed, the yield of the scribe and break process can be improved. Since such a scribe and break process for separating display panels from a mother substrate is also used to manufacture organic EL display panels, the present invention can also be effectively applied to the manufacture of organic EL display panels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIGS. 1A to 1D  are schematic diagrams illustrating the principle of the present invention; 
           [0026]      FIGS. 2A to 2D  are schematic diagrams illustrating the principle of the present invention; 
           [0027]      FIG. 3  is a diagram illustrating a first embodiment of the present invention; 
           [0028]      FIG. 4  is a diagram illustrating a second embodiment of the present invention; 
           [0029]      FIG. 5  is a diagram illustrating a third embodiment of the present invention; 
           [0030]      FIG. 6  is a diagram illustrating a fourth embodiment of the present invention; 
           [0031]      FIG. 7  is a diagram illustrating a fifth embodiment of the present invention; 
           [0032]      FIG. 8  is a diagram illustrating a sixth embodiment of the present invention; 
           [0033]      FIG. 9  is a diagram illustrating a seventh embodiment of the present invention; 
           [0034]      FIG. 10  is a diagram illustrating an eighth embodiment of the present invention; 
           [0035]      FIG. 11  is a diagram illustrating a ninth embodiment of the present invention; 
           [0036]      FIG. 12  is a diagram illustrating a tenth embodiment of the present invention; 
           [0037]      FIG. 13  is a diagram illustrating an eleventh embodiment of the present invention; 
           [0038]      FIG. 14  is a diagram illustrating a twelfth embodiment of the present invention; 
           [0039]      FIG. 15  is a diagram illustrating a thirteenth embodiment of the present invention; 
           [0040]      FIG. 16  is a diagram illustrating a fourteenth embodiment of the present invention; 
           [0041]      FIG. 17  is a diagram illustrating a fifteenth embodiment of the present invention; 
           [0042]      FIG. 18  is a diagram illustrating a sixteenth embodiment of the present invention; 
           [0043]      FIG. 19  is a diagram illustrating a seventeenth embodiment of the present invention; 
           [0044]      FIG. 20  is a diagram illustrating an eighteenth embodiment of the present invention; 
           [0045]      FIG. 21  is a diagram illustrating a nineteenth embodiment of the present invention; 
           [0046]      FIG. 22  is a diagram illustrating an existing glass cutter; 
           [0047]      FIG. 23  is a sectional view of a wheel  10 ; 
           [0048]      FIGS. 24A and 24B  are diagrams illustrating scribing by the wheel  10 ; 
           [0049]      FIG. 25A to 25D  are diagrams illustrating a problem with scribing performed using prior-art technology; and 
           [0050]      FIG. 26A to 26D  are diagrams illustrating another problem with scribing performed using prior-art technology. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0051]      FIGS. 1A to 1D  are schematic diagrams illustrating the principle of the present invention based on an example case in which a wheel  10  moves across a microprojection  301  present on a glass  300 . For  FIGS. 1A to 1D , description already provided in the foregoing with reference to  FIGS. 25A to 25D  and other drawings will be omitted. Referring to  FIG. 1A  showing the wheel  10  moving toward the projection  301  present on the glass surface, the wheel  10 , when moving in the direction denoted by a white arrow MD, rotates with a rotating force RF. According to the present invention, a force RRF to oppose the rotating force RF is applied. Mechanisms used to generate the force RRF will be described in connection with the following embodiments. Namely, the present invention provides a configuration for braking the rotation of the wheel  10 . 
         [0052]      FIG. 1B  shows the wheel  10  passing the projection  301  on the glass surface. With the force to oppose the rotation of the wheel  10  applied, the wheel  10  is prevented from riding on the projection  301 . As a result, the wheel  10  is allowed to form the fracture layer  201  even where the projection  301  is present, so that the crack  203  is formed to be continuous in the glass  300 . With the force RRF to oppose rotation of the wheel  10  applied, the wheel  10  cannot easily rotate where the projection  301  is present, so that the wheel  10  is caused to pass the projection  301  sliding without riding thereon. This allows the wheel  10  to continue formation of the crack  203 . Note that, for the sake of simplification, the projection  301  on the glass surface is not shown in  FIG. 1B . 
         [0053]      FIG. 10  shows a state in which the wheel  10  has passed the projection  301 . In  FIG. 10 , it is shown that a crack is formed also in portion W below the projection  301  of the glass.  FIG. 1D  shows a state in which the wheel  10  having passed the projection  301  is moving in the direction of arrow MD. As shown in  FIG. 1D , even though the projection  301  is present on the glass surface, the crack  203  is continuously formed in the glass by the wheel  10 . 
         [0054]      FIGS. 2A to 2D  schematically show the wheel  10  moving across an existing scribe line  302 . For  FIGS. 2A to 2D , description already provided in the foregoing with reference to  FIGS. 26A to 26D  and other drawings will be omitted. Referring to  FIG. 2A  showing the wheel  10  moving toward the scribe line  302 , a force RRF to oppose a rotating force RF of the wheel  10  is applied like in the case shown in  FIGS. 1A to 1D . 
         [0055]    Referring to  FIG. 2B , when the wheel  10  reaches the scribe line  302 , a crack  203  formed by the wheel  10  is discontinued.  FIG. 2C  shows that, immediately after the wheel  10  passes the scribe line  302 , formation of a crack starts. Namely, with the force RRF to oppose rotation of the wheel  10  applied, the wheel  10  does not ride on the surface of the glass  300  even when crossing the scribe line  302 , so that it can continuously form a fracture layer  201 , a rib mark  202 , and a crack  203 . 
         [0056]      FIG. 2D  shows the wheel  10  further moving in the direction of arrow MD after crossing the scribe line  302 .  FIGS. 2C and 2D  show that formation of the fracture layer  201 , rib mark  202  and crack  203  is started in portion X immediately after the wheel  10  passes the scribe line. 
         [0057]    As described above, according to the present invention, the crack  203  can be formed in a stable manner even when the wheel  10  passes the projection  301  present on the glass surface or the existing scribe line  302 . Thus, plural parts such as LCD panels can be separated from a mother substrate in a stable manner. The effects similar to those described above can also be obtained by applying the present invention to cases in which organic EL display panels are separated from a mother substrate. 
         [0058]    The concrete configuration of the present invention will be described in the following based on embodiments. For each embodiment, a glass cutter  1  according to the present invention will be described. Each embodiment provides a configuration for generating a force to oppose rotation of a wheel  10  included in the glass cutter  1 . 
       First Embodiment 
       [0059]      FIG. 3  shows the glass cutter  1  of the first embodiment. As shown, the wheel  10  is supported by a wheel pin  11  and the wheel pin  11  is supported by a holder  12 . The wheel  10  is formed of sintered diamond added to by Co which is a magnetic material, so that the wheel  10  as a whole is a magnetic body. The holder  12  is formed of tool steel which is an ultrahard material, so that it is a magnetic body. Two magnets  20  are provided on outsides of the holder  12 . The magnets  20  generate a magnetic field of a prescribed magnetic flux density and, by having the magnetic field crossed by the wheel  10 , applies a force to press the wheel  10  against a side of the holder  12 . Pressing the wheel  10  against a side of the holder  12  generates a force RRF to oppose the rotating force RF of the wheel  10 , so that a fracture layer and a crack can be formed in the glass in a stable manner. 
         [0060]    Referring to  FIG. 3 , the magnets  20  sandwiching the holder  12  are disposed with the north pole of one of them facing the south pole of the other. According to the present embodiment, the magnets  20  each have a diameter of about 4 mm and a thickness of about 5 to 7 mm. The magnets  20  are most preferably made of neodymium-family material which is mechanically strong. Besides neodymium magnets, samarium-cobalt magnets which can generate strong magnetic fields may also be used as the magnets  20 . 
         [0061]    As shown in  FIG. 3 , the magnets  20  and the wheel  10  are not concentric. Therefore, when the wheel  10  rotates, it crosses a magnetic field with an uneven magnetic flux density. The wheel  10  containing a Co additive is conductive. When, in this configuration, the wheel  10  rotates, an eddy current is generated in the wheel  10 . The eddy current generates a force to oppose rotation of the wheel  10 . This results in allowing the wheel  10  to form a fracture layer and a crack in the glass in a stable manner. Thus, the wheel  10  can perform scribing in a stable manner. 
       Second Embodiment 
       [0062]      FIG. 4  is a diagram showing a second embodiment of the present invention. The wheel  10 , wheel pin  11 , holder  12 , and magnets  20  shown in  FIG. 4  are basically identical with those shown in  FIG. 3 . In the configuration shown in  FIG. 4 , the holder  12  and the magnets  20  are surrounded by a magnetic frame  21  with a high magnetic permeability with the magnetic frame  21  providing magnetic paths. In  FIG. 4 , broken-line arrows shown on the magnetic frame  21  represent a magnetic flux. With magnetic paths formed in the magnetic frame  21 , reluctance is reduced, so that the magnetic flux to flow through the wheel  10  becomes larger. This increases the force to oppose rotation of the wheel  10 . 
         [0063]    Since the magnetic flux passing through the wheel  10  becomes larger, the eddy current generated by the rotation of the wheel  10  becomes larger, so that the force generated by the eddy current to oppose rotation of the wheel  10  also becomes larger. The magnetic frame  21  is made of, for example, permalloy which has a high magnetic permeability. The magnetic frame  21  is, for example, squarely shaped measuring 15 mm in length of each side and 1 mm by 4 to 5 mm in cross-sectional area. 
       Third Embodiment 
       [0064]      FIG. 5  is a diagram showing a third embodiment of the present invention. As shown in  FIG. 5 , the magnets  20  are embedded in a gap inside the holder  12 . The magnets  20  of the third embodiment each measure 3 mm in diameter and 1.5 mm in thickness. Even though, the magnets  20  of the third embodiment are smaller than those of the first and second embodiments, the magnets  20  are disposed closer to the wheel  10  in the third embodiment than in the first and second embodiments, so that a magnetic flux required to be crossed by the wheel  10  can be secured. Referring to  FIG. 5 , the magnetic poles of the magnets  20  are arranged along the thickness direction of the holder  12  with the north and south poles oriented identically between the two magnets. This secures a magnetic flux perpendicular to the side surfaces of the wheel  10 . 
         [0065]    In the present embodiment, too, a force to press the wheel  10  against the holder  12  so as to oppose rotation of the wheel  10  can be generated by a magnetic field. As shown in  FIG. 5 , the magnetic flux is concentrated in an upper portion of the wheel  10 , so that the magnetic flux crossing the wheel  10  is uneven. Therefore, rotation of the wheel  10  generates an eddy current which also generates a force to oppose rotation of the wheel  10 . 
       Fourth Embodiment 
       [0066]      FIG. 6  is a diagram showing a fourth embodiment of the present invention. As shown in  FIG. 6 , the holder  12  is divided in two parts with each part holding an embedded magnet  20 . Namely, at least a portion of the region between the two holder parts includes the magnets  20 . The holder  12  need not necessarily include plural magnets, it may include only one magnet. When plural magnets  20  are used, they are arranged such that, between them, unlike poles mutually face. A force to press the wheel  10  against the holder  12  is generated by supplying a leakage flux from the magnets  20  to the wheel  10 . 
         [0067]    In the above configuration, the holder  12  formed of tool steel which is a magnetic material allows a prescribed amount of magnetic flux to pass therethrough. Referring to  FIG. 6 , in the region not occupied by the magnets  20  between the two holder parts, a nonmagnetic spacer  25  is fitted. The nonmagnetic spacer  25  is, for example, about 1 mm thick. The presence of the nonmagnetic spacer  25  increases the amount of the magnetic flux reaching the wheel  10  so as to press the wheel  10  against the holder  12  by a larger force. Thus, a force to oppose rotation of the wheel  10  can be generated. 
         [0068]    In the present embodiment, too, the flux to pass through the wheel  10  is uneven. Therefore, rotation of the wheel  10  generates an eddy current which also generates a force to oppose rotation of the wheel  10 . 
       Fifth Embodiment 
       [0069]      FIG. 7  is a diagram showing a fifth embodiment of the present invention. As shown in  FIG. 7 , the magnets  20  are partly embedded in the holder  12  with their unlike poles facing each other. By being partly embedded in the holder  12 , the magnets  20  are positioned closer to the wheel  10 , so that the amount of the magnetic flux to pass through the wheel  10  is increased. This makes the force generated by the magnetic field to press the wheel  10  against the holder  12  larger, so that the force to oppose rotation of the wheel  10  becomes larger. 
         [0070]    In the present embodiment, too, the flux to pass through the wheel  10  is uneven. Therefore, rotation of the wheel  10  generates an eddy current which also generates a force to oppose rotation of the wheel  10 . 
       Sixth Embodiment 
       [0071]      FIG. 8  is a diagram showing a sixth embodiment of the present invention. As shown in  FIG. 8 , the magnets  20  are each disposed on a tilted surface  121  of the holder  12 . The two magnets  20  are arranged in parallel with their magnetic poles oriented identically. According to the configuration of the present embodiment, the magnets  20  can be disposed closely to the wheel  10  using the holder  12  as it is without any modification, so that a desired magnetic flux can be easily made to pass through the wheel  10 . Hence, a force to oppose rotation of the wheel  10  can be easily generated. In the present embodiment, too, a force to oppose rotation of the wheel  10  can also be generated by an eddy current. 
       Seventh Embodiment 
       [0072]      FIG. 9  is a diagram showing a seventh embodiment of the present invention. As shown in  FIG. 9 , the magnets  20  are embedded in the holder  12 . The two magnets  20  are arranged in parallel with their unlike poles facing each other. In the present embodiment unlike in the first to sixth embodiments, the portion where the magnets  20  are embedded of the holder  12  is smaller in width than the other portion thereof. This allows a magnetic flux from the magnets  20  to pass through the wheel  10  efficiently. Hence, a force to press the wheel  10  against the holder  12  so as to oppose rotation of the wheel  10  can be generated efficiently. In the present embodiment, too, a force to oppose rotation of the wheel  10  can also be generated by an eddy current. 
       Eighth Embodiment 
       [0073]      FIG. 10  is a diagram showing an eighth embodiment of the present invention. In the eighth embodiment unlike in the first to seventh embodiments, a magnetic flux to pass through the wheel  10  is generated using an electromagnet. As shown in  FIG. 10 , the holder  12  is wound with a coil  30 . A required magnetic flux can be made to pass through the wheel  10  by applying an appropriate electric current to the coil  30 . Like in the first to seventh embodiments, the magnetic flux generates a force to press the wheel  10  against the holder  12  so as to oppose rotation of the wheel  10 . 
         [0074]    Referring to  FIG. 10 , with a current applied to the coil  30 , the holder  12  serves as a horseshoe-shaped magnet. According to the present embodiment, a required magnetic flux is generated by the electromagnet, so that the magnetic flux can be controlled easily. Hence, the glass cutter  1  can be used to scribe various kinds of mother substrates. 
       Ninth Embodiment 
       [0075]      FIG. 11  is a diagram showing a ninth embodiment of the present invention. Referring to  FIG. 11 , a fabric member  43  is embedded inside the holder  12 . The fabric member  43  serves as a brake by pressing the bevels  102  of the wheel  10 . The fabric member  43  thus generates a force to oppose rotation of the wheel  10 , so that the wheel  10  can perform scribing in a stable manner. 
         [0076]    Referring to  FIG. 11 , inside the holder  12 , movement of the fabric member  43  is restrained by a holding pin  431 . The fabric member  43  may be made of, for example, nonwoven fabric like cotton. 
       Tenth Embodiment 
       [0077]      FIG. 12  is a diagram showing a tenth embodiment of the present invention. Referring to  FIG. 12 , a plate spring  41  is disposed inside the holder  12 . The plate spring  41  serves as a brake by pressing the bevels  102  of the wheel  10 . The plate spring  41  thus generates a force to oppose rotation of the wheel  10 , so that the wheel  10  can perform scribing in a stable manner. 
         [0078]    Referring to  FIG. 12 , the plate spring  41  is bent at a support pin  432 . The support pin  432  may be made unnecessary by appropriately changing the shape of the plate spring  41 . The plate spring  41  may be formed of, for example, stainless steel. The plate spring  41  presses the bevels  102  of the wheel  10 , so that the cutting edge  101  of the wheel  10  is not damaged. A different material, for example, resin may be interposed between the plate spring  41  and the bevels  102  of the wheel  10 . 
       Eleventh Embodiment 
       [0079]      FIG. 13  is a diagram showing an eleventh embodiment of the present invention. Referring to  FIG. 13 , washers  42  are disposed between the wheel  10  and the holder  12 . The washers  42  press the sides of the wheel  10  to serve as brakes. Namely, the friction between each of the washers  42  and the wheel  10  generates a force to oppose rotation of the wheel  10 , so that the wheel  10  can perform scribing in a stable manner. 
         [0080]    Each of the washers  42  is doughnut-shaped and measures, for example, 2 mm in outer diameter, 1 mm in inner diameter, and 5 to 10 micrometers in thickness. It may be made of either plastic or metal. 
       Twelfth Embodiment 
       [0081]      FIG. 14  is a diagram showing a twelfth embodiment of the present invention. Referring to  FIG. 14 , an elastic spacer  50  is sandwiched between the two holder parts. The holder  12  is formed by clamping the two holder parts, sandwiching the elastic spacer  50 , with a clamping screw  122 . 
         [0082]    The wheel  10  is disposed below the holder  12 . In the configuration shown in  FIG. 14 , clamping the two holder parts with the screw  122  causes the wheel  10  to be clamped by the holder  12 . Namely, a force to oppose rotation of the wheel  10  is generated by clamping the screw  122 . 
         [0083]    The presence of the elastic spacer  50  between the two parts of the holder  12  makes it possible to adjust the clamping force applied by the holder  12  to the wheel  10 . According to the present embodiment, a force to oppose rotation of the wheel  10  is generated to allow the wheel  10  to perform scribing in a stable manner and the force to oppose rotation of the wheel  10  can be arbitrarily controlled. 
       Thirteenth Embodiment 
       [0084]      FIG. 15  is a diagram showing a thirteenth embodiment of the present invention. Referring to  FIG. 15 , a rigid external member  55  is disposed outside the holder  12  with a spring member  52  disposed between the rigid external member  55  and the holder  12  on each side. The spring force of each of the spring members  52  causes the holder  12  to undergo elastic deformation causing the wheel  10  to be pressed by the holder  12 . This brakes rotation of the wheel  10 . In this configuration, a force to oppose rotation of the wheel  10  is thus generated. 
         [0085]    Even though the spring members  52  shown in  FIG. 15  are coil springs, they need not necessarily be coil springs. They may be replaced by other elastic bodies. The portion where the spring members (i.e. elastic bodies) are fitted of the holder  12  may be made, as shown in  FIG. 9 , smaller in width than the remaining portion of the holder  12  so as to make efficient use of the elasticity of the spring members. 
       Fourteenth Embodiment 
       [0086]      FIG. 16  is a diagram showing a fourteenth embodiment of the present invention. Referring to  FIG. 16 , the rigid external member  55  is disposed outside the holder  12  with a piezoelectric element  60  disposed between the rigid external member  55  and the holder  12  on each side. In other respects, the configuration of the present embodiment is the same as that of the thirteenth embodiment of the present invention. When a voltage is applied to each of the piezoelectric elements  60 , thickness p of each of the piezoelectric elements changes. For example, when a voltage is applied across each of the piezoelectric elements  60  causing thickness p of each of the piezoelectric elements  60  to increase, the holder  12  is pressed inwardly to brake the wheel  10 . 
         [0087]    Namely, applying a voltage across each of the piezoelectric elements  60  generates a force to oppose rotation of the wheel  10 , so that the wheel  10  can perform scribing in a stable manner. According to the present embodiment, the force to oppose rotation of the wheel  10  can be controlled by controlling the voltage applied to the piezoelectric elements  60 . This makes it easy to set conditions for scribing according to the condition of the mother substrate to be scribed. 
       Fifteenth Embodiment 
       [0088]    In the first to fourteenth embodiments, the wheel  10  is not restrained by the wheel pin  11  and is freely rotatable about the wheel pin  11 . In a fifteenth embodiment shown in  FIG. 17  of the present invention, the wheel  10  and the wheel pin  11  are united. As shown in  FIG. 17 , the wheel pin  11  extends to outside the holder  12 . The holder  12  has a support rod  123  with a plate spring  41  disposed between the wheel pin  11  extending to outside the holder  12  and the support rod  123 . 
         [0089]    A cylindrical member  111  is mounted on the portion outside the holder  12  of the wheel pin  11 . When the cylindrical member  111  is pressed by the plate spring  41 , the cylindrical member  111  presses the wheel pin  11  to brake rotation of the wheel pin  11 . Since, in the present embodiment, the wheel pin  11  and the wheel  10  are united, braking the wheel pin  11  brakes the wheel  10 . A force to oppose rotation of the wheel  10  is thus generated so as to allow the wheel  10  to perform scribing in a stable manner. 
       Sixteenth Embodiment 
       [0090]      FIG. 18  is a diagram showing a sixteenth embodiment of the present invention. In this embodiment, too, the wheel  10  and the wheel pin  11  are united. The configuration shown in  FIG. 18  differs from that shown in  FIG. 17  in that, instead of the plate spring  41 , a piezoelectric element  60  is disposed between the support rod  123  and the cylindrical member  111  of the wheel  11 . In other respects, the configuration shown in  FIG. 18  is the same as that shown in  FIG. 17 . 
         [0091]    In the configuration shown in  FIG. 18 , applying a voltage across the piezoelectric element  60  brakes the cylindrical member  111  and eventually the wheel pin  11 . Thus, a force to oppose rotation of the wheel  10  is generated in the configuration of the present embodiment with the wheel pin  11  and the wheel  10  united. In the present embodiment, the force to oppose rotation of the wheel  10  can be easily adjusted by adjusting the voltage applied across the piezoelectric element  60 . 
       Seventeenth Embodiment 
       [0092]      FIG. 19  is a diagram showing a seventeenth embodiment of the present invention. In this embodiment, too, the wheel  10  and the wheel pin  11  are united. Referring to  FIG. 19 , an electromagnetic brake  61  is attached to the portion extending outside the holder  12  of the wheel pin  11 . The electromagnetic brake  61  is controlled by a control power supply  62 . The electromagnetic brake  61  may be, for example, something like a motor. 
         [0093]    With the wheel  10  united with the wheel pin  11 , a force generated by the electromagnetic brake  61  to oppose rotation of the wheel  10  is directly applied to the wheel  10 . Thus, in the present embodiment, the wheel  10  is directly braked by the electromagnetic brake  61 , so that the force to oppose rotation of the wheel  10  can be accurately controlled. 
       Eighteenth Embodiment 
       [0094]      FIG. 20  is a drawing showing an eighteenth embodiment of the present invention. In this embodiment, too, the wheel  10  and the wheel pin  11  are united. Referring to  FIG. 20 , a fluid brake  65  is attached to the portion extending outside the holder  12  of the wheel pin  11 . The fluid brake  65  is internally filled with a fluid  67  such as oil. The wheel pin  11  extends, outside the holder  12 , through the fluid brake  65 . The portion extending inside the fluid brake  65  of the wheel pin  11  has a propeller  65  or something like that so as to brake rotation of the wheel pin  11 . 
         [0095]    Thus, a force to oppose rotation of the wheel  10  united with the wheel pin  11  is generated by the fluid brake  65  and is applied to the wheel  10 , so that the wheel  10  can perform scribing in a stable manner. 
       Nineteenth Embodiment 
       [0096]      FIG. 21  is a diagram showing a nineteen embodiment of the present invention. In this embodiment, the wheel  10  and the wheel pin  11  are not united. In this embodiment, a magnetized holder  12  is used to press the wheel  10  against a side of the holder  12  to thereby generate a force to oppose rotation of the wheel  10 . 
         [0097]    The holder  12  formed of tool steel which is a magnetic material can be magnetized. Referring to  FIG. 21 , the holder  12  serves as a horseshoe-shaped magnet  20  with one end being a north pole and the other end being a south pole. The wheel  10  and the wheel pin  11  are disposed between the north and south poles. The flux density between the north and south poles in  FIG. 21  is 3 mT (millitesla), i.e. not lower than 30 Gauss. This level of flux density is high enough to press the wheel  10  against the holder  12 . Thus, a force to oppose rotation of the wheel  10  can be generated. 
         [0098]    As described above, according to the present embodiment, the wheel  10  can scribe glass in a stable manner without requiring any additional part to be provided for the holder  12 .