Patent Publication Number: US-11389920-B2

Title: Cutting apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a cutting apparatus provided with a blade monitor that monitors a cutting blade. 
     Description of the Related Art 
     A wafer with a plurality of devices such as integrated circuits (ICs) or large scale integrations (LSIs) formed on its surface divided by planned dividing lines is divided into individual device chips by a cutting apparatus, and the divided device chips are used in electrical equipment such as mobile phones or personal computers. 
     A cutting apparatus is configured from at least a chuck table that holds a workpiece, a cutting unit that subjects the workpiece, which is held on the chuck table, to cutting by rotating a cutting blade provided with a cutting edge on a periphery thereof while supplying cutting water to the workpiece, and a machining feed unit that subjects the chuck table and the cutting unit to machining feed relative to each other, and can accurately divide the workpiece, for example, a semiconductor wafer into individual device chips. 
     More sophisticated types of cutting apparatus have also been proposed including those which have a function to interrupt cutting if a cutting blade develops chipping or wearing at a cutting edge thereof. These more sophisticated types of cutting apparatus include a light-emitting end face, which emits light of a light-emitting element, and a light-receiving end face, which receives the light emitted from the light-emitting end face and guides it to a light-receiving element, arranged with the cutting edge interposed therebetween and detect changes in the quantity of received light to monitor the conditions of the cutting edge; or include an image capture camera to monitor the conditions of the cutting edge (see, for example, Japanese Patent Laid-Open No. 2009-083077 and Japanese Patent No. 2627913). 
     SUMMARY OF THE INVENTION 
     According to the cutting apparatus described in Japanese Patent Laid-Open No. 2009-083077 or Japanese Patent No. 2627913, the conditions of the cutting edge of the cutting blade can be monitored based on the quantity of light received at the light-receiving element or an image captured by the image capture camera, whereby chipping or wearing can be detected to achieve the interruption of the cutting as needed. However, swarf occurs during the cutting, and mixes in cutting water scattered subsequent to its supply in a vicinity of the cutting edge. As the light-emitting end face of the light-emitting element and the light-receiving end face of the light-receiving element or an end face of the image capture camera are arranged close to the cutting edge, the swarf contained in the cutting water scattered from the cutting edge adheres the respective end faces. If swarf adheres as described above, the detection of an accurate quantity of light based on the light-emitting element and the light-receiving element or the capture of an image of the cutting edge by the image capture camera is interfered. Even if the cutting edge of the cutting blade undergoes chipping or wearing, the cutting cannot be interrupted as needed, thereby developing a problem that the quality of the cutting may be affected. 
     Therefore, the present invention has as an object thereof the provision of a cutting apparatus that can suppress adhesion of swarf, which is mixed in cutting water, on an end face of at least one of a light-emitting element and a light-receiving element, an image capture camera, or the like. 
     In accordance with an aspect of the present invention, there is provided a cutting apparatus including a chuck table that holds a workpiece, a cutting unit that subjects the workpiece, which is held on the chuck table, to cutting by rotating a cutting blade while supplying cutting water to the workpiece, and a machining feed unit that subjects the chuck table and the cutting unit to machining feed relative to each other. The cutting unit includes a spindle with a cutting blade mounted thereon for rotation, a spindle housing that rotatably supports the spindle, a blade cover that is attached to the spindle housing and covers the cutting blade, a cutting water supply nozzle that supplies cutting water to the cutting blade, and a blade monitor that has an end face configured to monitor a cutting edge of the cutting blade. The end face of the blade monitor has a recessed portion to which rinsing water is supplied to rinse the end face. 
     Preferably, the rinsing water may be supplied when rotation of the cutting blade is stopped. Preferably, the rinsing water may include one of diluted fluoric acid and a surfactant. 
     According to the present invention, it is configured that the end face of the blade monitor has the recessed portion and the rinsing water, which rinses the end face, is supplied to the recessed portion, and therefore it is possible to suppress the adhesion of swarf, which is mixed in the cutting water through rinsing of the end face of the blade monitor, and to prevent such swarf from impeding the monitoring of the cutting edge of the cutting blade. 
     The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a cutting apparatus according to an embodiment of the present invention; 
         FIG. 2A  is an exploded perspective view of a cutting unit disposed in the cutting apparatus depicted in  FIG. 1 ; 
         FIG. 2B  is a perspective view of the cutting unit; 
         FIG. 3  is a schematic diagram illustrating a mechanism of a blade monitor in the cutting apparatus depicted in  FIG. 1 ; 
         FIG. 4  is a perspective view illustrating the mechanism of the blade monitor as depicted in  FIG. 3 ; and 
         FIG. 5  is a perspective view illustrating a state that rinsing water has been supplied to recessed portions of the blade monitor as depicted in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     About a cutting apparatus according to an embodiment of the present invention, a detailed description will hereinafter be made with reference to the drawings.  FIG. 1  depicts an overall perspective view of a cutting apparatus  2  that can perform dicing of a wafer to divide the wafer into individual device chips. 
     On a front side of the cutting apparatus  2 , operation means (operation control panel)  4  is disposed to allow an operator to input instructions such as machining conditions and the like for the apparatus. As depicted in the figure, a wafer W as a workpiece is bonded on a dicing tape T, and the dicing tape T is bonded at a peripheral edge portion thereof on a frame F. As a consequence, the wafer W is in a state of being supported on the frame F via the dicing tape T, and a plurality of wafers (for example, 25 wafers) are placed in a wafer cassette  8  depicted in  FIG. 1 . On a surface of the wafer W, planned dividing lines which are set to intersect at right angles are formed, and devices D are formed in plural regions divided by the planned dividing lines. The wafer cassette  8  is mounted on a cassette elevator  9  that is movable upward and downward. 
     Behind the wafer cassette  8 , a transfer in/out unit  10  is arranged to transfer each wafer W out of the wafer cassette  8  before cutting and to transfer it back into the wafer cassette  8  after cutting. Between the wafer cassette  8  and the transfer in/out unit  10 , a temporary placing region  12  is arranged, where each wafer transferred out or to be transferred in is temporarily placed. At the temporary placing region  12 , registration units  14  are arranged to bring the wafer W into registration with a predetermined location. 
     In a vicinity of the temporary placing region  12 , a transfer unit  16  is arranged with a swing arm that holds the frame F integrated with the wafer W under suction and transfers them. The wafer W transferred out to the temporary placing region  12  is held under suction by the transfer unit  16 , and is transferred onto a chuck table  18  configured as holding means. The wafer W is then sucked on the chuck table  18  and the frame F is fixed by a plurality of clamps  19 , whereby the wafer W is held on the chuck table  18 . 
     The chuck table  18  is configured to be rotatable and also to be reciprocally movable by a processing feed unit (not depicted) in an X-axis direction, that is, a processing feed direction. Above a moving path for the chuck table  18  in the X-axis direction, an alignment unit  20  is arranged to detect planned dividing lines along which the wafer W should be cut. 
     The alignment unit  20  includes an image capture unit  22  that captures an image of a surface of the wafer W, and based on the image captured by the image capture unit  22 , the planned dividing lines along which cutting should be conducted can be detected by processing such as pattern matching. The image captured by the image capture unit  22  is displayed on undepicted display means. 
     On a left side of the alignment unit  20 , a cutting unit  24  is arranged. The cutting unit  24  subjects the wafer W, which is held on the chuck table  18 , to cutting. The cutting unit  24  is configured integrally with the alignment unit  20 , and both of these units move together in a Y-axis direction and a Z-axis direction. 
     The cutting unit  24  is configured with a cutting blade  28  mounted on a free end of a rotatable spindle  26 , and is movable in the Y-axis direction and the Z-axis direction. The cutting blade  28  is located on an extension of the image capture unit  22  in the X-axis direction. 
       FIG. 2A  depicts an exploded perspective view of the cutting unit  24 .  FIG. 2B  is a perspective view of the cutting unit  24  assembled from a state depicted in  FIG. 2A . The cutting unit  24  includes a spindle housing  25 , in which the spindle  26  rotationally drivable by an undepicted servomotor is rotatably supported. The cutting blade  28  is, for example, an electroformed blade, and has on a peripheral portion thereof a cutting edge  28   a  with diamond abrasive grains distributed in a nickel matrix. 
     The cutting unit  24  includes a blade cover  30  that covers the cutting blade  28 , and a detachable cover  40  and a blade monitor  50  that are detachably attached to the blade cover  30 . 
     To the blade cover  30 , a cutting water supply nozzle  32  is attached extending along a rear side wall of the cutting blade  28 . Cutting water is supplied to the cutting water supply nozzle  32  from above the blade cover  30  via a pipe  34 . The blade cover  30  has screw holes  36  and  38 . 
     The detachable cover  40  has another cutting water supply nozzle  42 , which extends along a front side wall of the cutting blade  28  when the detachable cover  40  has been attached to the blade cover  30 . Cutting water is supplied to the cutting water supply nozzle  42  from above via a pipe  44 . 
     The detachable cover  40  is fixed on the blade cover  30  by inserting a screw  48  into a round hole  46  of the detachable cover  40  and bringing it into threaded engagement with the screw hole  36  of the blade cover  30 . As a consequence, the cutting blade  28  is covered at a substantially upper half thereof by the blade cover  30  and detachable cover  40  as depicted in  FIG. 2B . 
     Referring to  FIGS. 2A through 5 , a description will be made about the configuration of the blade monitor  50 . The blade monitor  50  includes a fixed block  58  fixedly secured on the blade cover  30 , and a moving block  60  movable upward and downward relative to the fixed block  58  (see  FIG. 3 ). The blade monitor  50  is attached to the blade cover  30  by inserting a screw  54  into a round hole  52  of the fixed block  58  and bringing it into threaded engagement with the screw hole  38  of the blade cover  30 . 
     An adjustment screw  56  is mounted on the fixed block  58 , and is in threaded engagement with an undepicted, internally-threaded portion formed in the moving block  60 . When the adjustment screw  56  is rotated, the moving block  60  moves upward or downward relative to the fixed block  58  according to the turning direction. 
     As depicted in  FIGS. 3 and 4 , the blade monitor  50  includes a light-emitting section  70  and a light-receiving section  80 . The light-emitting section  70  is configured of a light-emitting element  71  formed from a light-emitting diode (LED), a laser diode (LD) or the like, an optical fiber  72  connected to the light-emitting element  71 , a right-angle prism  73  attached to the moving block  60  for reflecting, at a right angle, light from the optical fiber  72 , a light-emitting end face  74  constructed of a plate of sapphire or the like and bonded on a light-emitting surface of the right-angle prism  73 , and a first ring member  75  defining a recessed portion  75   a  in a surface of the light-emitting end face  74 . On the other hand, the light-receiving section  80  is configured of a light-receiving element  81  such as a photodiode (PD), an optical fiber  82  connected to the light-receiving element  81 , a right-angle prism  83  with the optical fiber  82  connected thereto, the right-angle prism  83  being attached to the moving block  60 , a light-receiving end face  84  constructed of a plate of sapphire or the like and bonded on a light-receiving surface of the right-angle prism  83 , and a second ring member  85  defining a recessed portion  85   a  in a surface of the light-receiving end face  84 . 
     The light entered from the light-receiving end face  84  is reflected by a reflecting surface of the right-angle prism  83 , and is guided to the light-receiving element  81  via the optical fiber  82 . The light-receiving element  81  is connected to the control unit  100 , and the quantity of light (current value) detected by the light-receiving element  81  is transmitted to the control unit  100  and is stored in a storage section. The recessed portions  75   a  and  85   a  are formed with a diameter dimensioned at 1 to 3 mm or so. In  FIG. 4 , the right-angle prism  73  and the right-angle prism  83  are arranged at angles different from actual angles for the convenience of description. Actually, the light-emitting end face  74  as an end face on the side of the light-emitting section  70  and the light-receiving end face  84  as an end face on the side of the light-receiving section  80  are arranged in parallel to each other such that they oppose each other with the cutting blade  28  interposed therebetween. 
     Further, the blade monitor  50  includes a rinsing water supply mechanism  90  for supplying rinsing water R to the recessed portion  75   a  formed by the first ring member  75  and the recessed portion  85   a  formed by the second ring member  85 . 
     As depicted in  FIG. 4 , the rinsing water supply mechanism  90  is configured of a rinsing water storage tank  91  that stores the rinsing water R, tubes  92  that guide the rinsing water R from the rinsing water storage tank  91  to the recessed portions  75   a  and  85   a , and on/off valves  93  and  94  that are arranged on the tubes  92 . As depicted in  FIG. 5 , the tubes  92  are connected to the first ring member  75  and second ring member  85  that define the recessed portions  75   a  and  85   a , and open/closure operation of the on/off valves  93  and  94  is controlled by a control unit  100  configured of a computer so that the rinsing water R is supplied to the recessed portions  75   a  and  85   a . The supply of the rinsing water R is basically conducted when the rotation of the cutting blade  28  is stopped. When the rinsing water R is supplied, the rinsing water R is retained under the action of surface tension in the recessed portions  75   a  and  85   a  as depicted in  FIG. 5 . The rinsing water R may preferably contain diluted fluoric acid. Even if swarf of silicon (Si) which forms the wafer W adheres, the use of diluted fluoric acid as the rising water R makes it possible to dissolve it. 
     As depicted in  FIGS. 3 and 4 , the light-emitting end face  75   a  of the light-emitting section  70  and the light-receiving end face  85   a  of the light-receiving section  80  are arranged such that they flank a perimeter portion of the cutting edge  28   a  of the cutting blade  28 . Moreover, it is set that light irradiated from the light-emitting end face  75   a  passes close to the perimeter portion of the cutting edge  28   a . If chipping or wearing occurs on the cutting edge  28   a , the quantity of light that passes close to the perimeter portion of the cutting edge  28   a  increases, and therefore the chipping or wearing can be detected. Upon detection of the chipping or wearing of the cutting edge  28   a , an alarm is issued by alarm means included in the control unit  100 , and the operator replaces the cutting blade  28  by a new cutting blade. 
     The positions of the light-emitting end face  74  and the light-receiving end face  84  relative to the cutting edge  28   a  of the cutting blade can be adjusted by turning the adjustment screw  56 . Upon replacement of the cutting blade  28 , the operator removes the detachable cover  40  from the blade cover  30  as illustrated in  FIG. 2A , and in this state, replaces the cutting blade  28 . The cutting apparatus  2  according to the present embodiment is configured basically as described above. A description will next be made about basic operation and functions of the cutting apparatus  2 , first with reference to  FIG. 1 . 
     Each wafer W placed in the wafer cassette  8  is grasped at the frame F thereof by the transfer in/out unit  10 , the transfer in/out unit  10  is moved to rear of the apparatus (in the Y-axis direction), and its grasp is then released at the temporary placing region  12 , whereby the wafer W is placed on the temporary placing region  12 . The registration units  14  are then moved in directions coming close to each other so that the wafer W is positioned at the predetermined location. 
     Then, the frame F is held under suction by the transfer unit  16 , and the transfer unit  16  is turned so that the wafer W which is integral with the frame F is transferred to the chuck table  18  and is held by the chuck table  18 . Thereafter, the chuck table  18  is moved in the X-axis direction and the wafer W is positioned right underneath the alignment unit  20 . When the wafer W has been positioned right underneath the alignment unit  20 , the image capture unit  22  captures an image of the surface of the wafer W. The captured image is displayed on the undepicted display means to perform retrieval for key patterns to be used as targets in pattern matching. These key patterns use, for example, characteristic parts in circuits of the devices D formed on the wafer W, individually. 
     Upon determination of the key patterns by the operator, the image including the key patterns is stored in the storage section included in the control unit  100  of the cutting apparatus  2 . Further, the distance between desired one of the key patterns and a center line of the two planned dividing lines on opposite sides of the desired key pattern is determined based on coordinate values or the like, and the value of the distance is also stored beforehand. After preparations for pattern matching from the captured image have been completed as described above, the chuck table  18  is moved in the X-axis direction, followed by pattern matching between two points which are substantially apart from each other in the X-axis direction on desire one of the planned dividing lines. 
     Upon completion of the pattern matching between the two points, a straight line that connects desired two of the key patterns to each other is now in parallel to all the planned dividing lines. The cutting unit  24  is then moved in the Y-axis direction by the distance between the desired one key pattern and the center line of the two planned dividing lines, whereby the alignment between the planned dividing line, along which cutting is about to be performed, and the cutting blade  28  is completed. 
     In the state that the alignment between the planned dividing line, along which cutting is about to be performed, and the cutting blade  28  has been performed, the chuck table  18  is moved in the X-axis direction and the cutting unit  24  is lowered while rotating the cutting blade  28  at high speed. As a consequence, cutting is performed along the planned dividing line the alignment of which has been completed. 
     As depicted in  FIG. 3 , upon cutting by the cutting blade  28  along the planned dividing line, the cutting along the planned dividing line is performed while ejecting cutting water toward the cutting blade  28  and wafer W from the cutting water supply nozzles  32  and  42 . The cutting blade  28  is cooled by ejecting cutting water against the cutting blade  28 . 
     By repeatedly performing cutting while subjecting the cutting unit  24  to index feeding in the Y-axis direction by the pitch of the planned dividing lines as stored in the storage section, cutting is completed along all the planned dividing lines in the same direction. When the chuck table  18  is turned by 90 degrees and cutting is then performed in a similar manner as described above, cutting is completed along all the planned dividing lines orthogonal to the planned dividing lines along which cutting has been completed before, so that the wafer W is divided into chips having the individual devices D. 
     After the completion of the cutting, the chuck table  18  is moved in the X-axis direction. Then, the wafer W is grasped by the transfer unit  25  that is movable in the Y-direction, and is transferred to a rinsing apparatus  27 . At the rinsing apparatus  27 , the wafer W is rinsed by rotating it at low speed (for example, 300 rpm) while spraying water from a rinsing nozzle. 
     After the rinsing, the wafer W is dried by blowing air from an air nozzle while rotating the wafer W at high speed (for example, 3,000 rpm). Subsequently, the wafer W is held under suction by the transfer unit  16  and is returned to the temporary placing region  12 , and is then returned to the original placing location in the wafer cassette  8  by the transfer in/out unit  10 . 
     Referring to  FIGS. 3 to 5 , a more specific description will next be made about operation and functions of the blade monitor  50  in the present embodiment. Upon operating the cutting apparatus  2  for the first time after setting the new cutting blade  28 , initial setting of the blade monitor  50  is first performed by moving the moving block  60  in the direction of an axis of rotation of the cutting blade  28  to position the light-emitting end face  74  of the light-emitting section  70  and the light-receiving end face  84  of the light-receiving section  80  at locations where they oppose each other with the perimeter portion of the cutting edge  28   a  being interposed therebetween. Specifically, the moving block  60  is moved in the direction of the axis of rotation of the cutting blade  28  to position the light-emitting end face  74  of the light-emitting section  70  and the light-receiving end face  84  of the light-receiving section  80  at locations close to the cutting edge  28   a.    
     Light is then emitted from the light-emitting element  71 , and the value of the quantity of light received by the light-receiving element  81  is transmitted to the control unit  100 . In the storage section of the control unit  100 , the value of a quantity of light as an initial criterion for light to be received at the light-receiving element  81  is stored, and a comparison is made between the value of the quantity of light received at the light-receiving element  81  and the value of the quantity of light as the initial criterion. Here, the quantity of light which is to pass close to the perimeter portion of the cutting edge  28   a  can be controlled by turning the adjustment screw  56  to adjust the positions of the light-emitting end face  74  and the light-receiving end face  84  in the upward/downward direction. When the quantity of light detected at the light-receiving element  81  is determined to coincide with the quantity of light as the initial criterion, in other words, if the blade monitor  50  is determined to be in a desired state that allows light, which is irradiated from the light-emitting element  71 , to slightly pass close to the perimeter portion of the cutting edge  28   a  and to reach the light-receiving element  81 , the blade monitor  50  is determined to have been set in a predetermined initial state. In the present embodiment, the adjustment screw  56  is described to be turned manually. It may, however, be configured to electrically drive the adjustment screw  56  by a pulse motor or the like and to control it by the control unit  100 . 
     In the present embodiment, the rinsing water supply mechanism  90  is actuated to supply the rinsing water R to the recessed portions  75   a  and  85   a  in the state that rotation of the cutting blade  28  is stopped. Specifically, an instruction signal is fed from the control unit  100  to the on/off valves  93  and  94  so that the rinsing water R is supplied in amounts sufficient to fill up the volumes of the recessed portions  75   a  and  85   a . The amounts of the rinsing water R to be fed to the recessed portions  75   a  and  85   a  by the rinsing water supply mechanism  90  may preferably be the amounts sufficient to exactly fill up the recessed portions  75   a  and  85   a , and the rinsing water R is retained under the action of surface tension in the recessed portions  75   a  and  85   a . If the rinsing water R is supplied as described above, the light-emitting end face  74  and the light-receiving end face  84  located in the recessed portions  75   a  and  85   a  are rinsed. As the timing of supplying the rinsing water R, it is preferred to conduct the supply of the rinsing water R when the cutting apparatus  2  is stopped after finishing cutting work for the day and/or when the cutting apparatus  2  is stopped for a temporary period of time because of a lunch break or the like. In this manner, the washing water R can be retained for a long period of time in the recessed portions  75   a  and  85   a , and swarf adhered on the light-emitting end face  74  and the light-receiving end face  84  can be eliminated. Especially when swarf is composed of Si, Si is dissolved and eliminated with diluted fluoric acid. In the present embodiment, the plates of sapphire, which is resistant to diluted fluoric acid, are adopted as the light-emitting end face  74  and the light-receiving end face  84 , and therefore the light-emitting end face  74  and the light-receiving end face  84  are not dissolved with diluted fluoric acid. 
     When practicing cutting, cutting water is supplied to the cutting edge  28   a  and positions on the wafer W, where the wafer W is to be cut, from the cutting water supply nozzles  32  and  42  as described above. As the cutting blade  28  is rotating at high speed, the cutting water supplied to the cutting edge  28   a  is caused to scatter. The rinsing water R supplied to and retained in the recessed portions  75   a  and  85   a  is removed by the scattering cutting water. By periodically supplying the rinsing water R to the recessed portions  75   a  and  85   a , however, the rinsing of the light-emitting end face  74  and the light-receiving end face  84  is carried out so that they can retain a rinsed state. 
     If cutting is repeatedly performed and wearing of the cutting edge  28   a  proceeds, the quantity of light to be received at the light-receiving element  81  gradually increases, and hence the value of a current to be outputted from the light-receiving element  81  to the control unit  100  also increases gradually. If the wear of the cutting edge  28   a  reaches a limit value, the quantity of light detected by the light-receiving element  81  exceeds a threshold quantity of light stored beforehand for the determination of wearing in the control unit  100 , a display is made on the undepicted display means by the control unit  100  to indicate that the wearing of the cutting blade  28   a  has proceeded to its replacement time, and moreover an alarm is issued to the operator by alarming means such as a buzzer or lamp. 
     The output from the light-receiving element  81  is also used for the detection of damage to the cutting blade  28 . This damage detection is to detect chipping of the cutting edge  28   a . If chipping occurs on the cutting edge  28   a , the value of a current outputted from the light-receiving element  81  is detected to change in spike shape (suddenly increases and then decreases). If the value of a current outputted from the light-receiving element  81  is monitored by the control unit  100  and a spike-shaped change in the current value is detected, the cutting edge  28   a  is determined to have developed chipping, the cutting is interrupted immediately, and the occurrence of chipping is displayed on the undepicted display means. This display can urge the operator to replace the cutting blade  28  by a new cutting blade so that the productivity of cutting wafers W is improved. 
     In the embodiment described above, the use of diluted fluoric acid as the rinsing water R is described by way of example. However, the diluted fluoric acid used as the rinsing water R is in an extremely small amount, and moreover is diluted further with a large amount of cutting water. Its toxicity is, therefore, lowered significantly. Nonetheless, when disposing of waste water, it is preferred to dispose of the waste water by neutralizing fluoric acid, which is contained in the waste water, with lime milk, soda ash or the like, and then further diluting the neutralized waste water with water. 
     In the embodiment described above, it is described by way of example to use plates of sapphire, which is not dissolved even with diluted fluoric acid, or the like as the light-emitting end face  74  and the light-receiving end face  84  and also to use diluted fluoric acid as the rinsing water R. If these plates are formed from a general material such as glass, however, they may be dissolved with diluted fluoric acid so that the rinsing water R may preferably contain a surfactant instead of fluoric acid. 
     In the embodiment described above, the blade monitor  50  is configured to include the light-emitting element  71  in the light-emitting section  70  and the light-receiving element  81  in the light-receiving section  80  for the detection of a worn state or a chipped state of the cutting edge  28   a . However, the present invention is not restricted to this configuration, and an image capture camera may be adopted instead of the light-receiving element  81  and an image of conditions of the cutting edge  28   a  may be captured by the image capture camera. In this modification, a plate of sapphire may be arranged on the surface of a lens of the image capture camera, a recessed portion may be formed in an end face where the plate is arranged, and rinsing water R may be supplied to the recessed portion. 
     The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.