Grinding device and method for grinding a workpiece

Abstract

To provide a grinding device which can grind a workpiece at a proper processing feed speed.SOLUTION: A grinding device grinds a workpiece and includes: a chuck table having a holding surface which holds the workpiece; a grinding unit which has a spindle and grinds the workpiece held by the chuck table with a grinding wheel attached to a tip of the spindle; a moving mechanism which relatively moves the chuck table and the grinding unit along a processing feed direction parallel to the holding surface at a predetermined processing feed speed; a processing load measuring unit which measures a value corresponding to a load exerted on the grinding wheel during grinding of the workpiece; and a control unit which adjusts the processing feed speed according to the value measured by the processing load measuring unit.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a grinding device for grinding a workpiece, and a method for grinding a workpiece using the grinding device to grind the workpiece.

Background Art

[0002] In the manufacturing process of device chips, a wafer in which devices are formed in a plurality of regions partitioned by a plurality of streets (lines to be divided) intersecting each other is used. By dividing this wafer along the streets, a plurality of device chips each having a device can be obtained. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] In recent years, with the miniaturization of electronic devices, there has been a demand for thinning of device chips. Therefore, a process of grinding and thinning the wafer before division may be performed using a grinding device. The grinding device includes a chuck table having a holding surface for holding a workpiece, and a grinding unit for grinding the workpiece, and a grinding wheel including a grinding stone is mounted on the grinding unit. The grinding device grinds the workpiece by rotating the grinding wheel and bringing the grinding stone into contact with the workpiece.

[0004] When grinding a workpiece such as a wafer using a grinding device, the positional relationship between the chuck table and the grinding unit is adjusted so that the center of the workpiece held by the chuck table overlaps the locus of the grinding stone. Then, while rotating the chuck table and the grinding wheel respectively, when the grinding wheel is lowered toward the holding surface of the chuck table, the lower surface of the grinding stone contacts the upper surface side of the workpiece and the workpiece is ground. Such a grinding method is called infeed grinding.

[0005] On the other hand, for grinding a workpiece, a grinding method called creep feed grinding may be used. In creep feed grinding, the positional relationship between the chuck table and the grinding unit is adjusted such that the grinding wheel is positioned outside the workpiece and the lower surface of the grinding wheel is positioned below the upper surface of the workpiece. Then, while rotating the grinding wheel, the chuck table is moved along the machining feed direction (horizontal direction) parallel to the holding surface. As a result, the upper surface side of the workpiece is cut off in an arc shape from the side surface of the workpiece by the grinding wheel, and the workpiece is ground (see Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In creep feed grinding, since the grinding wheel collides with the side surface of the workpiece, a lateral force (lateral load) parallel to the machining feed direction is applied to the grinding wheel. When a large lateral load acts on the grinding wheel during grinding of the workpiece, breakage (such as cracking) of the grinding wheel may occur.

[0008] Also, for example, when performing creep feed grinding on a disk-shaped workpiece such as a silicon wafer, as the machining feed progresses, the area of the region of the workpiece in contact with the grinding wheel gradually increases, and the magnitude of the lateral load applied to the grinding wheel changes. Therefore, it is difficult to grind the entire workpiece under the same conditions, and machining marks (scratches) having an irregular pattern (shading) are likely to remain on the surface to be ground of the workpiece. As a result, the surface roughness of the workpiece after grinding tends to become non-uniform.

[0009] Note that the lateral load acting on the grinding wheel increases as the machining feed rate increases. Therefore, if the machining feed rate is set low to reduce the lateral load acting on the grinding wheel, the grinding wheel is less likely to be damaged, and irregular machining marks are less likely to be formed on the surface to be ground of the workpiece. However, if the machining feed rate is maintained at a low speed, the time required for grinding the workpiece increases, and the machining efficiency decreases.

[0010] The present invention has been made in view of such problems, and an object thereof is to provide a grinding apparatus capable of grinding a workpiece at an appropriate machining feed rate, and a method for grinding a workpiece using the grinding apparatus.

Means for Solving the Problems

[0011] According to one aspect of the present invention, there is provided a grinding apparatus for grinding a workpiece, including a chuck table having a holding surface for holding the workpiece, a grinding unit having a spindle and a grinding wheel attached to the tip of the spindle for grinding the workpiece held by the chuck table, a moving mechanism for relatively moving the chuck table and the grinding unit along a machining feed direction parallel to the holding surface at a predetermined machining feed rate, and a machining load measurement unit for measuring a value corresponding to the load applied to the grinding wheel during grinding of the workpiece. A control unit, and the control unit adjusts the positional relationship between the chuck table and the grinding unit such that the workpiece held by the holding surface and the grinding wheel included in the grinding wheel are separated from each other in the machining feed direction parallel to the holding surface, and the lower surface of the grinding wheel is positioned a predetermined distance below the upper surface of the workpiece. While rotating the grinding wheel, the workpiece and the grinding wheel are relatively moved at a predetermined machining feed rate along the machining feed direction, so that the workpiece is ground from one end side to the other end side by the grinding wheel. The control unit, during the grinding of the workpiece A grinding apparatus is provided that adjusts the machining feed rate according to the value measured by the machining load measurement unit. during grinding

[0012] Preferably, the control unit decreases the machining feed rate when the value measured by the machining load measurement unit exceeds the upper limit value of the allowable range. Also preferably, the control unit increases the machining feed rate when the value measured by the machining load measurement unit is less than the lower limit value of the allowable range.

[0013] ​Preferably, the moving mechanism includes a ball screw connected to the chuck table and a ball screw motor that rotates the ball screw. The machining load measurement unit measures the current value of the ball screw motor, and the control unit adjusts the machining feed rate according to the current value of the ball screw motor. Preferably, the grinding unit includes a spindle motor that rotates the spindle. The machining load measurement unit measures the current value of the spindle motor, and the control unit adjusts the machining feed rate according to the current value of the spindle motor.

[0014] According to another aspect of the present invention, there is provided a method for grinding a workpiece using a grinding apparatus. The grinding apparatus includes a chuck table having a holding surface for holding the workpiece, and a grinding unit having a spindle and a grinding wheel attached to the tip of the spindle for grinding the workpiece held by the chuck table. The method includes a holding step of holding the workpiece on the holding surface, a preparation step of adjusting the positional relationship between the chuck table and the grinding unit such that the workpiece and the grinding wheel included in the grinding unit are separated from each other in a machining feed direction parallel to the holding surface, and the lower surface of the grinding wheel is positioned a predetermined distance below the upper surface of the workpiece, and a grinding step of relatively moving the workpiece and the grinding wheel along the machining feed direction at a predetermined machining feed rate while rotating the grinding wheel, and grinding the workpiece from one end side to the other end side with the grinding wheel. In the grinding step, a value corresponding to the load applied to the grinding wheel during grinding of the workpiece is measured, and a method for grinding a workpiece is provided in which the machining feed rate is adjusted according to the value.

[0015] Preferably, in the grinding step, the machining feed rate is decreased when the value exceeds the upper limit value of the allowable range. Preferably, in the grinding step, the machining feed rate is increased when the value is less than the lower limit value of the allowable range.

Advantages of the Invention

[0016] A grinding apparatus according to an aspect of the present invention includes a machining load measurement unit that measures a value corresponding to a load applied to a grinding wheel during grinding of a workpiece, and a control unit that adjusts a machining feed rate according to the value measured by the machining load measurement unit. Thereby, it becomes possible to appropriately increase or decrease the machining feed rate according to the load applied to the grinding wheel, and it is possible to prevent an excessive machining load from being applied to the grinding wheel without making the machining feed rate lower than necessary.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0018] Hereinafter, an embodiment according to an aspect of the present invention will be described with reference to the accompanying drawings. First, a configuration example of the grinding apparatus according to the present embodiment will be described. FIG. 1 is a partial cross-sectional side view showing a grinding apparatus 2. In FIG. 1, the X-axis direction (machining feed direction, first horizontal direction, front-rear direction) and the Y-axis direction (second horizontal direction, left-right direction) are perpendicular to each other. The Z-axis direction (vertical direction, up-down direction, height direction) is perpendicular to the X-axis direction and the Y-axis direction.

[0019] The grinding apparatus 2 includes a base 4 that supports or houses each component constituting the grinding apparatus 2. On the upper surface side of the base 4, a rectangular parallelepiped-shaped opening 4a is provided. And inside the opening 4a, a chuck table (holding table) 6 for holding a workpiece 11 to be machined by the grinding apparatus 2 is provided.

[0020] The upper surface of the chuck table 6 is a flat surface generally parallel to the horizontal direction (XY plane direction), and constitutes a holding surface 6a for holding the workpiece 11. The holding surface 6a is connected to a suction source (not shown) such as an ejector via a flow path (not shown), a valve (not shown), etc. formed inside the chuck table 6.

[0021] Also, inside the base 4, a moving mechanism (moving unit) 8 for moving the chuck table 6 along the X-axis direction is provided. The moving mechanism 8 includes a ball screw 10 connected to the chuck table 6. The ball screw 10 is arranged along the X-axis direction and is screwed into a nut portion (not shown) provided on the chuck table 6 or a moving plate (not shown) that supports the chuck table 6. Further, at the end of the ball screw 10, a ball screw motor 12 for rotating the ball screw 10 is connected. As the ball screw motor 12, for example, a pulse motor is used.

[0022] When the ball screw 10 is rotated at a predetermined rotational speed by the ball screw motor 12, the chuck table 6 moves along the X-axis direction at a machining feed speed corresponding to the rotational speed of the ball screw 10. Thereby, the chuck table 6 and a grinding unit 28 described later relatively move at a predetermined machining feed speed along the machining feed direction parallel to the holding surface 6a.

[0023] Also, a rotational drive source (not shown) such as a motor for rotating the chuck table 6 around a rotational axis (a rotational axis generally parallel to the Z-axis direction) substantially perpendicular to the holding surface 6a is connected to the chuck table 6. That is, the rotational axis of the chuck table 6 is set along a direction perpendicular to the holding surface 6a.

[0024] A rectangular parallelepiped-shaped support structure 14 is provided behind the chuck table 6 and the moving mechanism 8 (on the right side of the paper surface in FIG. 1). And a moving mechanism (moving unit) 16 is provided on the surface side (front side) of the support structure 14.

[0025] The moving mechanism 16 includes a pair of guide rails 18 fixed to the surface side of the support structure 14. The pair of guide rails 18 are arranged along the Z-axis direction while being spaced apart from each other in the Y-axis direction. Further, a flat plate-shaped moving plate 20 is slidably mounted on the pair of guide rails 18 along the guide rails 18.

[0026] A nut portion 22 is provided on the back surface side (rear surface side) of the moving plate 20. Further, a ball screw 24 is provided between the pair of guide rails 18 along the Z-axis direction, and the ball screw 24 is screwed into the nut portion 22. And a ball screw motor 26 for rotating the ball screw 24 is connected to an end portion of the ball screw 24. As the ball screw motor 26, for example, a pulse motor is used.

[0027] A grinding unit 28 for grinding the workpiece 11 is mounted on the surface side (front surface side) of the moving plate 20. The grinding unit 28 includes a hollow columnar support member 30 fixed to the surface side of the moving plate 20. A columnar housing 32 is accommodated in the support member 30. The lower surface side of the housing 32 is supported by the bottom surface of the support member 30 via a buffer member 34 made of rubber or the like.

[0028] A columnar spindle 36 arranged along the Z-axis direction is accommodated in the housing 32. The tip end portion (lower end portion, one end portion) of the spindle 36 is exposed from the housing 32 and protrudes downward from the lower surface of the support member 30 through an opening provided at the bottom of the support member 30. Further, a spindle motor 38 for rotating the spindle 36 is connected to the base end portion (upper end portion, the other end portion) of the spindle 36.

[0029] A disk-shaped mount 40 made of metal or the like is fixed to the tip end portion of the spindle 36. And an annular grinding wheel 42 for grinding the workpiece 11 is mounted on the lower surface side of the mount 40. For example, the grinding wheel 42 is fixed to the mount 40 by a fixture (not shown) such as a bolt. Thereby, the grinding wheel 42 is mounted on the tip end portion of the spindle 36.

[0030] The grinding wheel 42 is made of a metal such as aluminum or stainless steel and has an annular base 44 formed to have approximately the same diameter as the mount 40. The upper surface side of the base 44 is fixed to the lower surface side of the mount 40. A plurality of grinding wheels 46 are fixed to the lower surface side of the base 44. For example, a plurality of rectangular parallelepiped grinding wheels 46 are arranged in an annular shape at approximately equal intervals along the circumferential direction of the base 44. The grinding wheel 46 is formed by fixing abrasive grains made of diamond, cBN (cubic Boron Nitride), etc. with a binder (bonding material) such as a metal bond, a resin bond, or a vitrified bond. However, there are no restrictions on the material, shape, structure, size, etc. of the grinding wheel 46. Also, the number of the grinding wheels 46 can be arbitrarily set.

[0031] When the ball screw 24 is rotated at a predetermined rotational speed by the ball screw motor 26, the moving plate 20 moves (ascends and descends) along the guide rail 18 at a speed corresponding to the rotational speed of the ball screw 24. Thereby, the chuck table 6 and the grinding unit 28 relatively move at a predetermined speed along the direction (Z-axis direction) perpendicular to the holding surface 6a.

[0032] Also, the grinding wheel 42 rotates around a rotation axis (a rotation axis substantially parallel to the Z-axis direction) substantially perpendicular to the holding surface 6a of the chuck table 6 by the power transmitted from the spindle motor 38 via the spindle 36 and the mount 40. That is, the rotation axis of the grinding wheel 42 is set along the direction perpendicular to the holding surface 6a.

[0033] When the rotating grinding wheel 46 is brought into contact with the upper surface side of the workpiece 11 held by the chuck table 6, the upper surface side of the workpiece 11 is scraped off. Thereby, the workpiece 11 is subjected to a grinding process and thinned.

[0034] Further, the grinding apparatus 2 includes a machining load measurement unit that measures a value (load corresponding value) corresponding to the load (machining load) applied to the grinding wheel 42 during the grinding of the workpiece 11. FIG. 1 shows a machining load measurement unit 48 connected to the moving mechanism 8 and a machining load measurement unit 50 connected to the grinding unit 28.

[0035] For example, the machining load measurement unit 48 is an ammeter that measures the current value of the ball screw motor 12, and the machining load measurement unit 50 is an ammeter that measures the current value of the spindle motor 38. Note that the machining load measurement unit 48 may be built into the ball screw motor 12, and the machining load measurement unit 50 may be built into the spindle motor 38.

[0036] When the grinding wheel 46 contacts the workpiece 11 while the ball screw motor 12 rotates the ball screw 10 to move the chuck table 6 along the X-axis direction, a load is applied to the workpiece 11 and the grinding wheel 42. Then, the torque and current value of the ball screw motor 12 required to maintain the moving speed of the chuck table 6 increase. As a result, the current value of the ball screw motor 12 measured by the machining load measurement unit 48 changes.

[0037] Also, when the grinding wheel 46 contacts the workpiece 11 while the spindle motor 38 rotates the spindle 36, a load is applied to the workpiece 11 and the grinding wheel 42. Then, the torque and current value of the spindle motor 38 required to maintain the rotational speed of the spindle 36 increase. As a result, the current value of the spindle motor 38 measured by the machining load measurement unit 50 changes.

[0038] As described above, the change in the load applied to the grinding wheel 42 during the grinding of the workpiece 11 is reflected in the current values of the ball screw motor 12 and the spindle motor 38. Therefore, the current values measured by the machining load measurement units 48 and 50 correspond to the load corresponding values of the grinding wheel 42.

[0039] Note that there is no restriction on the type of the machining load measurement unit mounted on the grinding device 2. For example, the grinding device 2 may have a load measuring device (load cell) that measures the load applied to the chuck table 6, or a load measuring device (load cell) that measures the load applied to the spindle 36. In this case, the load value measured by the load measuring device corresponds to the load corresponding value. Also, an ammeter connected to the ball screw motor 26 can be used as the machining load measurement unit.

[0040] Each component of the grinding device 2 (such as the chuck table 6, the moving mechanism 8, the moving mechanism 16, the grinding unit 28, the machining load measurement units 48 and 50) is connected to a control unit (control section, control device) 52 that controls the grinding device 2. The control unit 52 generates a control signal for controlling the operation of the components of the grinding device 2 and controls the operation of the grinding device 2.

[0041] For example, the control unit 52 is constituted by a computer and includes an arithmetic unit that performs arithmetic operations necessary for the operation of the grinding device 2 and a storage unit that stores various types of information (data, programs, etc.) used for the operation of the grinding device 2. The arithmetic unit is constituted by including a processor such as a CPU (Central Processing Unit). Also, the storage unit is constituted by including memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory).

[0042] The workpiece 11 is ground by the above-described grinding apparatus 2. For example, the workpiece 11 is a disk-shaped wafer made of a semiconductor such as silicon, and includes surfaces (first surface) 11a and back surfaces (second surface) 11b that are generally parallel to each other. The workpiece 11 is partitioned into a plurality of rectangular regions by a plurality of streets (division planned lines) arranged in a lattice pattern so as to intersect each other. And on the surface 11a side of the plurality of regions partitioned by the streets, devices (not shown) such as IC (Integrated Circuit), LSI (Large Scale Integration), LED (Light Emitting Diode), and MEMS (Micro Electro Mechanical Systems) devices are formed.

[0043] By dividing the workpiece 11 along the streets, a plurality of device chips each including a device can be obtained. Further, before dividing the workpiece 11, by grinding the back surface 11b side of the workpiece 11 with the grinding apparatus 2 to thin the workpiece 11, a thinned device chip can be obtained.

[0044] Note that there are no restrictions on the type, material, size, shape, structure, etc. of the workpiece 11. For example, the workpiece 11 may be a disk-shaped wafer (substrate) made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), glass, ceramics, resin, metal, etc. Further, the workpiece 11 may be a package substrate such as a CSP (Chip Size Package) substrate or a QFN (Quad Flat Non-leaded package) substrate.

[0045] In the present embodiment, the workpiece 11 is thinned by performing creep feed grinding in which the chuck table 6 and the grinding wheel 42 are relatively moved along the machining feed direction parallel to the holding surface 6a to grind the workpiece 11. Hereinafter, a specific example of a method for grinding a workpiece using the grinding apparatus 2 will be described.

[0046] First, the workpiece 11 is held by the holding surface 6a of the chuck table 6 (holding step). For example, the workpiece 11 is placed on the chuck table 6 such that the surface 11a side faces the holding surface 6a and the back surface 11b side is exposed upward. When the suction force (negative pressure) of the suction source is applied to the holding surface 6a in this state, the workpiece 11 is suction-held by the chuck table 6. Note that a protective sheet made of resin or the like may be attached to the surface 11a side of the workpiece 11 to protect the surface 11a side (device, etc.) of the workpiece 11. In this case, the workpiece 11 is held by the holding surface 6a of the chuck table 6 via the protective sheet.

[0047] Next, the positional relationship between the chuck table 6 and the grinding unit 28 is adjusted (preparation step). FIG. 2(A) is a side view showing the chuck table 6 and the grinding unit 28 in the preparation step.

[0048] In the preparation step, the positional relationship between the chuck table 6 and the grinding unit 28 is adjusted such that the workpiece 11 and the grinding wheel 46 are separated from each other in the machining feed direction (X-axis direction) parallel to the holding surface 6a, and the lower surface of the grinding wheel 46 is positioned a predetermined distance below the upper surface (back surface 11b) of the workpiece 11.

[0049] Specifically, first, the position of the chuck table 6 in the X-axis direction is adjusted by the moving mechanism 8 (see FIG. 1) such that the workpiece 11 does not overlap with the grinding wheel 42 and is disposed in front of the grinding wheel 42 (left side of the paper in FIG. 2(A)). Also, the position of the grinding unit 28 in the Z-axis direction is adjusted by the moving mechanism 16 (see FIG. 1) such that the lower surface of the grinding wheel 46 is positioned below the upper surface of the workpiece 11. The difference ΔH in the height position (position in the Z-axis direction) between the upper surface of the workpiece 11 and the lower surface of the grinding wheel 46 at this time corresponds to the target value of the grinding amount of the workpiece 11 (the difference in the thickness of the workpiece 11 before and after grinding) in the subsequent grinding step.

[0050] Next, while rotating the grinding wheel 42, the chuck table 6 and the grinding unit 28 are relatively moved along the machining feed direction (X-axis direction), and the workpiece 11 is ground from one end side to the other end side by the grinding wheel 46 (grinding step). FIG. 2(B) is a side view showing the chuck table 6 and the grinding unit 28 in the grinding step.

[0051] In the grinding step, the workpiece 11 is ground by creep feed grinding. Specifically, first, the spindle 36 is rotated by the spindle motor 38 (see FIG. 1), so that the grinding wheel 42 is rotated around a rotation axis substantially perpendicular to the holding surface 6a of the chuck table 6. The rotation speed of the grinding wheel 42 is set, for example, to be 1000 rpm or more and 3000 rpm or less.

[0052] Then, with the grinding wheel 42 rotating and the chuck table 6 not rotating, the chuck table 6 is moved by the moving mechanism 8 (see FIG. 1). Specifically, the ball screw 10 is rotated at a predetermined rotation speed by the ball screw motor 12, so that the chuck table 6 is moved along the X-axis direction at a predetermined speed. As a result, the chuck table 6 and the grinding wheel 42 relatively move and approach each other at a predetermined machining feed speed along the machining feed direction. The machining feed speed (the moving speed of the chuck table 6) is set, for example, to be 1 mm / s or more and 20 mm / s or less.

[0053] When the chuck table 6 moves and one end of the workpiece 11 (the front end in the moving direction of the workpiece 11, the right end of the paper surface in FIG. 2(B)) reaches the orbit of the grinding wheel 46, one end portion of the workpiece 11 is cut off by the grinding wheel 46. Then, the chuck table 6 moves along the X-axis direction until the other end of the workpiece 11 (the rear end in the moving direction of the workpiece 11, the left end of the paper surface in FIG. 2(B)) is positioned at a position overlapping the locus of the grinding wheel 46. As a result, the workpiece 11 is ground from one end side to the other end side by the grinding wheel 46, and the whole of the workpiece 11 is thinned.

[0054] Note that a grinding fluid supply path (not shown) for supplying a liquid such as pure water (grinding fluid) is provided inside or near the grinding unit 28. When the workpiece 11 is ground by the grinding wheel 46, the grinding fluid is supplied to the workpiece 11 and the grinding wheel 46. As a result, the workpiece 11 and the grinding wheel 46 are cooled, and the chips (grinding chips) generated by the grinding process are washed away.

[0055] As described above, in creep feed grinding, the chuck table 6 moves along the machining feed direction (horizontal direction) parallel to the holding surface 6a, and the grinding wheel 46 collides with the side surface of the workpiece 11. Therefore, a lateral force (lateral load) parallel to the machining feed direction is applied to the grinding wheel 46. When a large lateral load acts on the grinding wheel 46 during grinding of the workpiece 11, the grinding wheel 46 may be damaged (broken, etc.).

[0056] Also, when performing creep feed grinding on a disk-shaped workpiece 11 such as a silicon wafer, as the machining feed progresses, the area of the region of the workpiece 11 that contacts the grinding wheel 46 gradually increases, and the magnitude of the lateral load applied to the grinding wheel 46 changes. Therefore, it is difficult to grind the entire workpiece 11 under the same conditions, and machining marks (somer marks) having an irregular pattern (shading) are likely to remain on the ground surface (back surface 11b) of the workpiece 11. As a result, the surface roughness of the workpiece 11 after grinding is likely to become non-uniform.

[0057] The lateral load acting on the workpiece 11 increases as the machining feed speed increases. Therefore, if the machining feed speed is set low to reduce the lateral load applied to the grinding wheel 46, the grinding wheel 46 is less likely to be damaged, and irregular machining marks are less likely to be formed on the workpiece 11. However, if the machining feed speed is maintained at a low speed, the time required to grind the workpiece 11 increases, and the machining efficiency decreases.

[0058] Therefore, in the grinding step, a value (load corresponding value) corresponding to the load applied to the grinding wheel 42 during the grinding of the workpiece 11 is measured, and the machining feed rate is adjusted according to the load corresponding value. Thereby, the machining feed rate increases or decreases appropriately according to the load applied to the grinding wheel 42. As a result, it is possible to prevent an excessive machining load from being applied to the grinding wheel 42 without making the machining feed rate lower than necessary.

[0059] The machining feed rate in the grinding step is controlled by the control unit 52. FIG. 3 is a block diagram showing the control unit 52. FIG. 3 shows, in addition to the blocks indicating the functional configuration of the control unit 52, the blocks indicating the ball screw motor 12 of the moving mechanism 8 and the machining load measurement units 48 and 50.

[0060] The control unit 52 includes a speed adjustment unit 60 that adjusts the machining feed rate, and a storage unit 70 that stores information (data, programs, etc.) used for the adjustment of the machining feed rate by the speed adjustment unit 60. Then, a control signal is input from the control unit 52 to the ball screw motor 12 to control the rotational speed of the ball screw 10 (see FIG. 1), whereby the machining feed rate is adjusted.

[0061] The speed adjustment unit 60 includes a load comparison unit 62 that compares a value (load corresponding value) corresponding to the load applied to the grinding wheel 42 (see FIGS. 1, etc.) with a threshold value. The measured values measured by the machining load measurement units 48 and 50 are input to the load comparison unit 62 as the load corresponding values.

[0062] Specifically, when the machining load measurement unit 48 is an ammeter that measures the current value of the ball screw motor 12, the current value of the ball screw motor 12 is input from the machining load measurement unit 48 to the load comparison unit 62. Further, when the machining load measurement unit 50 is an ammeter that measures the current value of the spindle motor 38 (see FIG. 1), the current value of the spindle motor 38 is input from the machining load measurement unit 50 to the load comparison unit 62. Hereinafter, as a representative example, the operation of the control unit 52 when the load corresponding value (the current value of the ball screw motor 12) is input from the machining load measurement unit 48 to the load comparison unit 62 will be described.

[0063] Further, the storage unit 70 includes a threshold storage unit 72 that stores the threshold value of the load corresponding value. For example, in the threshold storage unit 72, the upper limit value and the lower limit value that define the allowable range of the load corresponding value are stored as threshold values. When the current value of the ball screw motor 12 is input from the machining load measurement unit 48 to the load comparison unit 62, the upper limit value and the lower limit value of the current value of the ball screw motor 12 are stored in the threshold storage unit 72 as threshold values.

[0064] When the load corresponding value is input from the machining load measurement unit 48 to the load comparison unit 62, the threshold values (the upper limit value and the lower limit value of the load corresponding value) are read from the threshold storage unit 72 and input to the load comparison unit 62. Then, the load comparison unit 62 compares the load corresponding value with the threshold values to determine whether the load corresponding value is within the allowable range, exceeds the upper limit value of the allowable range, or is less than the lower limit value of the allowable range.

[0065] Further, the feed rate adjustment unit 60 includes a feed rate determination unit 64 that determines the machining feed rate. The result of the determination by the load comparison unit 62 is input to the feed rate determination unit 64, and the feed rate determination unit 64 determines a machining feed rate suitable for grinding the workpiece 11 based on the determination result of the load comparison unit 62.

[0066] Specifically, the storage unit 70 includes a speed information storage unit 74 that stores information (speed information) used for determining the machining feed speed. For example, the speed information storage unit 74 stores the current machining feed speed and a correction value (increase / decrease value) of the machining feed speed. When the determination result is input from the load comparison unit 62 to the speed determination unit 64, the speed information is read from the speed information storage unit 74 and input to the speed determination unit 64. Then, the speed determination unit 64 determines the machining feed speed based on the determination result of the load comparison unit 62 and the speed information.

[0067] For example, when it is determined that the load response value exceeds the upper limit value of the allowable range, the speed determination unit 64 sets the value obtained by subtracting the correction value from the current machining feed speed as the changed machining feed speed. As a result, the machining feed speed decreases by the amount of the correction value. On the other hand, when it is determined that the load response value is less than the lower limit value of the allowable range, the speed determination unit 64 sets the value obtained by adding the correction value to the current machining feed speed as the changed machining feed speed. As a result, the machining feed speed increases by the amount of the correction value.

[0068] The correction value (increase / decrease value) of the machining feed speed is appropriately set within a range that does not interfere with the grinding of the workpiece 11. For example, the correction value of the machining feed speed can be set to be 1 / 10 or more and 1 / 2 or less of the current machining feed speed. Also, when the load response value is within the allowable range, the current machining feed speed is maintained.

[0069] Note that there is no limitation on the speed information stored in the speed information storage unit 74. For example, the speed information storage unit 74 may store, as speed information, a table including a plurality of data sets indicating the numerical range that the load response value can take and the machining feed speed suitable when the load response value is within that numerical range. In this case, the machining feed speed corresponding to the numerical range to which the measured load response value belongs is set as the changed machining feed speed.

[0070] Further, the feed rate adjustment unit 60 includes a motor control unit 66 that controls the ball screw motor 12. The machining feed rate determined by the feed rate determination unit 64 is input to the motor control unit 66. Then, the motor control unit 66 outputs a control signal to the ball screw motor 12, and controls the rotation speed of the ball screw motor 12 (the rotation speed of the ball screw 10) so that the moving speed of the chuck table 6 (see FIG. 1) matches the machining feed rate determined by the feed rate determination unit 64.

[0071] In this way, the machining feed rate is adjusted according to the load applied to the grinding wheel 42 (see FIG. 1 etc.). In the above description, the case where the load corresponding value (the current value of the ball screw motor 12) is input from the machining load measurement unit 48 to the feed rate adjustment unit 60 has been described. However, even when the load corresponding value (the current value of the spindle motor 38) is input from the machining load measurement unit 50 to the feed rate adjustment unit 60, the machining feed rate is similarly adjusted. In this case, the upper limit value and the lower limit value of the current value of the spindle motor 38 are stored as threshold values in the threshold value storage unit 72, and the load comparison unit 62 compares the current value of the spindle motor 38 with the threshold value.

[0072] Next, a specific example of the method for adjusting the machining feed rate in the grinding step will be described. FIG. 4 is a flowchart showing the method for adjusting the machining feed rate. Hereinafter, mainly with reference to FIGS. 3 and 4, the procedure for adjusting the machining feed rate will be described.

[0073] When grinding the workpiece 11 with the grinding apparatus 2 (see FIG. 1), first, the holding step and the preparation step are performed as described above. Thereafter, while rotating the grinding wheel 42, the chuck table 6 and the grinding unit 28 are relatively moved along the machining feed direction (see FIG. 2(B)). Thereby, the grinding of the workpiece 11 (grinding step) is started (step S1).

[0074] When the grinding of the workpiece 11 starts, the measurement of the load corresponding value by the machining load measurement unit also starts (step S2). For example, the current value of the ball screw motor 12 is measured by the machining load measurement unit 48. Or, the current value of the spindle motor 38 is measured by the machining load measurement unit 50. Then, the measured load corresponding value is input to the load comparison unit 62 of the control unit 52.

[0075] The load comparison unit 62 compares the load corresponding value input from the machining load measurement units 48 and 50 with the threshold value stored in the threshold value storage unit 72 (step S3). And when the load corresponding value is within the allowable range (YES in step S3), it is determined that the current machining feed rate is appropriate, and the machining feed rate is maintained (step S4). On the other hand, when the load corresponding value is outside the allowable range (NO in step S3), it is determined that the current machining feed rate is inappropriate, and the machining feed rate is changed.

[0076] Specifically, when the load corresponding value exceeds the upper limit value of the allowable range (YES in step S5), the changed machining feed rate smaller than the current machining feed rate is determined by the speed determination unit 64. Then, the motor control unit 66 controls the ball screw motor 12 to make the moving speed of the chuck table 6 coincide with the changed machining feed rate. Thereby, the machining feed rate decreases (step S6), and the machining load applied to the grinding wheel 42 (see FIG. 1 etc.) is reduced.

[0077] On the other hand, when the load corresponding value is less than the lower limit value of the allowable range (NO in step S5), the changed machining feed rate larger than the current machining feed rate is determined by the speed determination unit 64. Then, the motor control unit 66 controls the ball screw motor 12 to make the moving speed of the chuck table 6 coincide with the changed machining feed rate. Thereby, the machining feed rate increases (step S7), and the time required for grinding the workpiece 11 is shortened.

[0078] After adjusting the machining feed rate, machining of the workpiece 11 continues (NO in step S8), and the measurement of the load response value and the adjustment of the machining feed rate are continued. Then, when the grinding of the workpiece 11 is completed (YES in step S8), the machining feed is stopped.

[0079] The grinding of the workpiece 11 by the grinding apparatus 2 described above is realized by controlling the operations of the respective components of the grinding apparatus 2 (see FIG. 1 etc.) by the control unit 52. Specifically, in the memory (storage unit 70) of the control unit 52, a program is stored that describes a series of operations of the respective components of the grinding apparatus 2 necessary to sequentially perform the holding step, the preparation step, and the grinding step. Then, when executing the grinding of the workpiece 11, the control unit 52 executes the program and sequentially outputs control signals to the respective components of the grinding apparatus 2. Thereby, the operation of the grinding apparatus 2 is controlled, and the grinding method of the workpiece according to the present embodiment is automatically performed.

[0080] As described above, the grinding apparatus according to the present embodiment includes a machining load measurement unit 48, 50 that measures a value corresponding to the load applied to the grinding wheel 42 during the grinding of the workpiece 11, and a control unit 52 that adjusts the machining feed rate according to the value measured by the machining load measurement unit 48, 50. Thereby, it becomes possible to appropriately increase or decrease the machining feed rate according to the load applied to the grinding wheel 42, and it is possible to prevent an excessive machining load from being applied to the grinding wheel 42 without making the machining feed rate lower than necessary.

[0081] In addition, in the grinding method of the workpiece according to the present embodiment, the number of times of performing creep feed grinding (preparation step and grinding step) can be appropriately set according to the material of the workpiece 11, the grinding amount, etc. That is, the preparation step and the grinding step may be performed two or more times. Also, the number of times (frequency) of adjusting the machining feed rate in the grinding step can be freely set.

[0082] In addition, the structure, method, etc. according to the above embodiment can be appropriately changed and implemented without departing from the scope of the object of the present invention.

Explanation of Reference Numerals

[0083] 11 Workpiece 11a Surface (first surface) 11b Back surface (second surface) 2 Grinding device 4 Base 4a Opening 6 Chuck table (holding table) 6a Holding surface 8 Moving mechanism (moving unit) 10 Ball screw 12 Ball screw motor 14 Support structure 16 Moving mechanism (moving unit) 18 Guide rail 20 Moving plate 22 Nut part 24 Ball screw 26 Ball screw motor 28 Grinding unit 30 Support member 32 Housing 34 Buffer member 36 Spindle 38 Spindle motor 40 Mount 42 Grinding wheel 44 Base 46 Grinding stone 48, 50 Processing load measurement unit 52 Control unit (control part, control device) 60 Speed adjustment part 62 Load comparison part 64 Speed determination part 66 Motor control part 70 Memory part 72 Threshold memory part 74 Speed information memory part

Claims

1. A grinding apparatus for grinding a workpiece, a chuck table having a holding surface for holding the workpiece, a grinding unit having a spindle and a grinding wheel attached to the tip of the spindle for grinding the workpiece held by the chuck table, a moving mechanism for relatively moving the chuck table and the grinding unit along a machining feed direction parallel to the holding surface at a predetermined machining feed speed, a machining load measuring unit for measuring a value corresponding to the load applied to the grinding wheel during grinding of the workpiece, and a control unit, The control unit adjusts the positional relationship between the chuck table and the grinding unit so that the workpiece held by the holding surface and the grinding wheel included in the grinding wheel are separated from each other in the machining feed direction parallel to the holding surface, and the lower surface of the grinding wheel is positioned a predetermined distance below the upper surface of the workpiece. While rotating the grinding wheel, the workpiece and the grinding wheel are relatively moved along the machining feed direction at a predetermined machining feed speed, so that the workpiece is ground from one end side to the other end side by the grinding wheel, The control unit adjusts the machining feed speed according to the value measured by the machining load measuring unit during grinding of the workpiece. A grinding apparatus characterized by the above.

2. The grinding apparatus according to claim 1, wherein the control unit decreases the machining feed speed when the value measured by the machining load measuring unit exceeds the upper limit value of the allowable range.

3. The grinding apparatus according to claim 1 or 2, wherein the control unit increases the machining feed speed when the value measured by the machining load measuring unit is less than the lower limit value of the allowable range.

4. The moving mechanism includes a ball screw connected to the chuck table and a ball screw motor for rotating the ball screw, The machining load measurement unit measures the current value of the ball screw motor, The grinding apparatus according to any one of claims 1 to 3, wherein the control unit adjusts the machining feed rate according to the current value of the ball screw motor.

5. The grinding unit includes a spindle motor that rotates the spindle, The machining load measurement unit measures the current value of the spindle motor, The grinding apparatus according to any one of claims 1 to 3, wherein the control unit adjusts the machining feed rate according to the current value of the spindle motor.

6. A method for grinding a workpiece using a grinding apparatus, the method comprising: The grinding apparatus includes a chuck table having a holding surface for holding the workpiece, and a grinding unit having a spindle and a grinding wheel attached to a tip of the spindle for grinding the workpiece held by the chuck table. A holding step of holding the workpiece on the holding surface; A preparation step of adjusting a positional relationship between the chuck table and the grinding unit such that the workpiece and a grinding wheel included in the grinding wheel are separated from each other in a machining feed direction parallel to the holding surface, and a lower surface of the grinding wheel is positioned below an upper surface of the workpiece by a predetermined distance; A grinding step of relatively moving the workpiece and the grinding wheel along the machining feed direction at a predetermined machining feed rate while rotating the grinding wheel, and grinding the workpiece from one end side to the other end side with the grinding wheel; The method for grinding a workpiece, wherein in the grinding step, a value corresponding to a load applied to the grinding wheel during grinding of the workpiece is measured, and the machining feed rate is adjusted according to the value.

7. The method for grinding a workpiece according to claim 6, wherein in the grinding step, the machining feed rate is decreased when the value exceeds an upper limit value of an allowable range.

8. The grinding method of a workpiece according to claim 6 or 7, characterized in that in the grinding step, when the value is less than the lower limit value of the allowable range, the machining feed rate is increased.

Images