Grinding equipment

Abstract

To determine that grinding is performed unstably, when the ongoing grinding is performed unstably.SOLUTION: A grinding device comprises: a chuck table on which a work-piece is held; a grinding unit having a spindle and a spindle motor connected to an upper end of the spindle, in which a grinding wheel having a grinding stone arranged annularly therein is fitted to a lower end side of the spindle and which grinds the work-piece by rotating the spindle and contacting the grinding stone being rotationally moved to the work-piece held on the chuck table; a grinding / feeding unit that moves the chuck table and the grinding unit relatively so that the table and the unit approach and separate from each other; a load current value measuring unit that measures a load current value of the spindle motor that rises when the grinding stone contacts the work-piece; and a control unit. When variations per unit time of the load current value measured by the load current value measuring unit exceed a preset threshold, the control unit determines that the load current value is unstable.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a grinding apparatus for grinding and thinning a plate-shaped workpiece such as a semiconductor wafer. [Background technology]

[0002] Device chips used in electronic devices such as mobile phones and computers are formed by grinding a wafer, on which multiple devices are arranged on the front surface, from the back surface to thin the wafer and then dividing the wafer into individual devices. Grinding of workpieces such as wafers is performed using a grinding machine. The grinding machine includes a chuck table that holds the workpieces and a grinding unit that grinds the workpieces held by the chuck table.

[0003] The grinding unit is fitted with a grinding wheel having grinding stones arranged in an annular pattern on its underside. The grinding unit has a spindle with a wheel mount at its bottom end that holds the grinding wheel, and a spindle motor connected to the top end of the spindle for rotating the spindle. When the spindle motor is operated to rotate the spindle, the grinding wheel rotates, causing the grinding stones to rotate and move along the annular orbit.

[0004] In a grinding machine, a workpiece is held on a chuck table with its backside exposed upward, and a rotating grinding wheel is brought into contact with the backside of the workpiece to grind the workpiece. However, in a grinding machine, problems such as clogging or glazing of the grinding wheel can occur during the grinding process, making it impossible to grind the workpiece properly. To address this issue, a grinding machine has been developed that takes advantage of the fact that the load current value of the spindle motor increases when this occurs, and issues an alarm to notify workers, managers, etc. when the load current value exceeds an allowable upper limit (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-157383 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even if the load current value of the spindle motor does not exceed the allowable upper limit, if the workpiece is ground under inappropriate grinding conditions, the grinding may not proceed stably and the finished quality may be low. For example, when starting to grind a new, unprecedented workpiece, it is necessary to prepare multiple workpieces, grind each under various grinding conditions, evaluate the state of each workpiece after grinding, evaluate the quality of each grinding condition, and select the grinding conditions, i.e., perform test grinding.

[0007] In test machining, the condition of the workpiece was evaluated after grinding was completed, and it was sometimes discovered later that the grinding was proceeding unstably. However, if it was discovered while grinding was in progress that there was no need to continue grinding, and there was no need to inspect the workpiece after grinding. In this case, if the grinding conditions could be changed while grinding was in progress, it would be possible to evaluate the next grinding conditions early and reduce the number of workpieces lost during test machining.

[0008] Furthermore, if it were possible to determine whether the grinding of a workpiece being processed by a grinding device is unstable while the grinding is in progress, it would also be useful for detecting abnormalities in normal grinding processes other than test grinding. That is, there is a demand for detecting whether the grinding is unstable not only in test grinding but also when the load current value of the spindle motor does not exceed the allowable upper limit.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide a grinding device that can determine that grinding is unstable when the grinding in progress is unstable. [Means for solving the problem]

[0010] According to one aspect of the present invention, there is provided a grinding unit having a chuck table for holding a workpiece, a spindle, and a spindle motor connected to the upper end of the spindle, wherein a grinding wheel having grinding stones arranged in an annular shape is attached to the lower end side of the spindle, and which rotates the spindle to bring the grinding stone, which rotates and moves, into contact with the workpiece held on the chuck table, thereby grinding the workpiece; a grinding feed unit which moves the chuck table and the grinding unit in directions to move closer to and farther away from each other; a load current value measurement unit which measures the load current value of the spindle motor which rises when the grinding stone comes into contact with the workpiece; and a control unit which controls each component, wherein the control unit is configured to measure the load current value measured by the load current value measurement unit. When the load current value does not exceed the allowable upper limit and grinding proceeds normally, When the fluctuation amount of the load current value per unit time exceeds a preset threshold, the load current value is determined to be unstable. The grinding process is unstable. The grinding device is characterized by determining that the grinding force is too large.

[0011] Preferably, the control unit further comprises a display unit for displaying information, and when the control unit determines that the load current value is unstable, the control unit displays a message indicating that the load current value is unstable on the display unit.

[0012] Furthermore, preferably, the control unit includes a graph conversion unit that creates a graph showing the change in the load current value measured by the load current value measurement unit, and the graph showing the change in the load current value created by the graph conversion unit can be displayed on the display unit.

[0013] Preferably, the control unit further comprises an input unit used to input information to the control unit, and the control unit can accept input of information relating to the grinding of the workpiece by the input unit while the grinding of the workpiece by the grinding unit is in progress, and when it determines that the load current value is unstable, it can change the grinding conditions based on the information relating to the grinding of the workpiece input while the grinding of the workpiece is in progress and continue grinding. [Effects of the Invention]

[0014] A grinding machine according to one aspect of the present invention includes a load current measurement unit that measures a load current value of a spindle motor connected to the upper end of a spindle having a grinding wheel attached to the lower end thereof, and a control unit of the grinding machine calculates a fluctuation amount per unit time of the load current value measured by the load current measurement unit, and determines that the load current value is unstable if this amount exceeds a preset threshold value.

[0015] Therefore, even if the load current value does not exceed the allowable upper limit, it is possible to detect if the load current value is unstable. If it is determined that the load current value is unstable, it means that grinding of the workpiece is not progressing stably, and an operator who knows this can determine whether grinding needs to continue and change the grinding conditions. Unlike conventional methods that wait until grinding of the workpiece is completed before checking the state of the workpiece, the grinding device according to one aspect of the present invention can make a determination without waiting for grinding to be completed.

[0016] Therefore, according to one aspect of the present invention, there is provided a grinding device that can determine that grinding is unstable when ongoing grinding is unstable. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 2 is a perspective view schematically showing a grinding device. [Figure 2] 1 is a cross-sectional view schematically showing a grinding device that grinds a workpiece. [Figure 3] FIG. 3(A) is a graph showing a schematic diagram of the change in the load current value when grinding is proceeding stably, and FIG. 3(B) is a graph showing a schematic diagram of the change in the load current value when grinding is proceeding unstably. [Figure 4] FIG. 4(A) is a flowchart showing the operation flow of the grinding device when determining whether the load current value is unstable, and FIG. 4(B) is a flowchart showing the operation flow of the grinding device when changing the grinding conditions while grinding is in progress. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. A grinding device according to this embodiment grinds a plate-shaped workpiece to a predetermined thickness. FIG. 1 is a perspective view showing a grinding device 2 according to this embodiment. FIG. 2 is a cross-sectional view showing a grinding device 2 that grinds a workpiece 1.

[0019] First, the workpiece 1 to be ground by the grinding device 2 will be described. The workpiece 1 is a disk-shaped wafer made of a material such as silicon, and has a front surface 1a and a back surface 1b that are generally parallel to each other. A plurality of planned dividing lines (not shown) are set on the front surface 1a of the workpiece 1, and are arranged in a grid pattern so as to intersect with each other. Devices (not shown), such as ICs and LSIs, are formed in each of the areas defined by the planned dividing lines on the front surface 1a of the workpiece 1.

[0020] There are no limitations on the material, structure, size, shape, etc. of the workpiece 1. For example, the workpiece 1 may be a substrate made of a semiconductor other than silicon (GaAs, InP, GaN, SiC, etc.), sapphire, glass (quartz glass, borosilicate glass, etc.), etc. There are also no limitations on the type, number, shape, structure, size, arrangement, etc. of devices, and the workpiece 1 does not necessarily have to have any devices formed thereon.

[0021] When the back surface 1b side of the workpiece 1 is ground, a tape-like protective member 3 having a diameter approximately the same as that of the workpiece 1 is attached to the front surface 1a side of the workpiece 1 in order to protect the front surface 1a side. The workpiece 1 is ground from the back surface 1b side to be thinned, and then divided along the planned division lines to produce a plurality of thin chips (device chips) each equipped with a device.

[0022] Next, the grinding device 2 will be described. The grinding device 2 has a substantially rectangular parallelepiped base 4 that supports each component. A recess 4a is formed on the top surface of the base 4 along the Y-axis direction. The recess 4a is provided with a chuck table 6 that is movable in the Y-axis direction and can hold a workpiece, and a dustproof and drip-proof cover 4b that covers the opening of the recess 4a while exposing the chuck table 6.

[0023] The dustproof and drip-proof cover 4b is omitted in Fig. 2. A Y-axis movement mechanism 8 that movably supports the chuck table 6 is disposed inside the recess 4a. The Y-axis movement mechanism 8 includes a pair of guide rails 10 extending along the Y-axis direction, a moving table 12 slidably supported on the guide rails 10, and a ball screw 16 that extends along the Y-axis direction and is threadedly engaged with a nut portion 14 provided on the underside of the moving table 12. A pulse motor 18 that rotates the ball screw 16 is connected to one end of the ball screw 16.

[0024] The chuck table 6 is disposed on the moving table 12. When the Y-axis moving mechanism 8 is operated, the chuck table 6 can be moved along the Y-axis direction. The nozzle has a ceramic frame 6a. A flow path (not shown) is provided inside the frame 6a, and one end of the flow path is connected to a suction source (not shown) such as an ejector.

[0025] The frame 6a has a recess on its upper surface, which is a disk-shaped space. A roughly disk-shaped porous plate 6b is fixed in this recess. The porous plate 6b has flat, circular upper and lower surfaces. The diameter of the porous plate 6b is roughly the same as the diameter of the workpiece 1. The other end of the flow path of the frame 6a is connected to the lower surface of the porous plate 6b. When the suction source is operated, negative pressure is generated on the upper surface of the porous plate 6b, and the workpiece 1 is sucked and held by this upper surface. Therefore, the upper surface of the chuck table 6 functions as a holding surface 6c.

[0026] A disk-shaped table base 6d is connected to the underside of the frame 6a of the chuck table 6. The upper end of a spindle 20 is connected to the center of the underside of the table base 6d, and the lower end of the spindle 20 is rotatably housed in a spindle housing 20a. A rotational drive source (not shown), such as a motor, that rotates the spindle 20 is provided in the spindle housing 20a. By operating this rotational drive source, the chuck table 6 rotates around a rotation axis perpendicular to the holding surface 6c.

[0027] The grinding device 2 includes a grinding unit 22 that grinds the workpiece 1 held by the chuck table 6, and a grinding feed unit (elevating mechanism) 24 that raises and lowers the grinding unit 22. The grinding feed unit 24 may raise and lower the chuck table 6 instead of the grinding unit 22. In other words, the grinding feed unit 24 moves the chuck table 6 and the grinding unit 22 in directions that move them closer to and away from each other.

[0028] A support part 26 is erected on the rear side of the grinding device 2, and this support part 26 supports the grinding unit 22 via the grinding feed unit 24. A pair of guide rails 28 along the Z-axis direction (vertical direction) are provided on the front surface of the support part 26. A moving plate 30 is slidably attached to each guide rail 28.

[0029] A nut portion 32 is provided on the back side (rear side) of the moving plate 30, and a ball screw 34 parallel to the guide rail 28 is threadedly engaged with this nut portion 32. A pulse motor 36 is connected to one end of the ball screw 34. When the ball screw 34 is rotated by the pulse motor 36, the moving plate 30 moves in the Z-axis direction along the guide rail 28.

[0030] The grinding unit 22 is fixed to the front side of the movable plate 30. By moving the movable plate 30, the grinding unit 22 can move in the Z-axis direction (grinding feed direction). The grinding unit 22 has a cut cylindrical holding member 38. The holding member 38 is fixed to the surface on the front side of the movable plate 30.

[0031] A spindle housing 40 is provided inside the holding member 38. An annular buffer member 42 made of rubber or the like is provided at the bottom of the spindle housing 40. The spindle housing 40 is supported on the bottom plate of the holding member 38 via the buffer member 42.

[0032] A portion of a spindle 44 is rotatably housed in the spindle housing 40. A spindle motor 41 is connected to the upper end of the spindle 44. When the spindle motor 41 is operated, the spindle 44 rotates around a rotation axis 46.

[0033] The lower end of the spindle 44 is located below the bottom plate of the holding member 38. The upper surface of a disk-shaped wheel mount 48 is connected to the lower end of the spindle 44. An annular grinding wheel 50 is attached to the lower end of the spindle 44 via the wheel mount 48.

[0034] The grinding wheel 50 has an annular wheel base 52. The wheel base 52 is made of a metal such as aluminum, and has a diameter corresponding to the diameter of the workpiece 1. The upper surface side of this wheel base 52 is connected to the lower surface side of the wheel mount 48. In other words, the grinding wheel 50 is attached to the spindle 44 via the wheel mount 48.

[0035] A circularly arranged grinding wheel 54 is provided on the underside of the wheel base 52. The grinding wheel 54 is formed by mixing abrasive grains such as diamond or cBN (cubic boron nitride) with a binder such as vitrified or resinoid, and then sintering the mixture. When the spindle motor 41 is operated to rotate the spindle 44 around the rotation axis 46 and thus rotate the grinding wheel 50, the grinding wheel 54 rotates on a circular orbit.

[0036] When grinding the workpiece 1 with the grinding device 2, the workpiece 1 is placed on the holding surface 6c of the chuck table 6 via the protective member 3, and the workpiece 1 is held by suction on the chuck table 6, with the back surface 1b of the workpiece 1, which will be the surface to be ground, exposed upward. Then, the Y-axis movement mechanism 8 is operated to move the chuck table 6 below the grinding unit 22.

[0037] Thereafter, the grinding wheel 50 and the chuck table 6 are rotated around their respective rotation axes, and the grinding feed unit 24 is operated to start the downward movement of the grinding unit 22. Then, when the lower surface of the grinding stone 54 moving on the circular orbit comes into contact with the back surface 1b of the workpiece 1, grinding of the workpiece 1 begins. The grinding device 2 is equipped with a thickness measurement unit (not shown) that can measure the thickness of the workpiece 1, and the grinding unit 22 continues to move downward while monitoring the thickness of the workpiece 1 with the thickness measurement unit.

[0038] Thereafter, when the thickness of the workpiece 1 reaches a predetermined finishing thickness, the lowering of the grinding unit 22 is stopped and the grinding unit 22 is raised, thereby obtaining the workpiece 1 thinned to the finishing thickness.

[0039] During grinding of the workpiece 1, friction between the workpiece 1 and the grinding wheel 54 generates frictional heat. If the temperatures of the workpiece 1, the grinding wheel 54, etc. change due to the frictional heat, they may thermally expand, and the desired grinding results may not be obtained. During grinding, the workpiece 1 and the grinding wheel 54 are worn out, generating chips. Therefore, during grinding of the workpiece 1, a grinding fluid such as pure water is supplied to the workpiece 1 and the grinding wheel 54, and the chips and frictional heat are removed by the grinding fluid.

[0040] The grinding device 2 is equipped on its exterior with a touch panel display 58. The touch panel display 58 is composed of a touch panel that serves as an input unit (input interface) and a display unit such as a liquid crystal panel that is placed on the touch panel. The touch panel display 58 functions as a display unit that can display various types of information, and also functions as an input unit that is used to input various commands and information to a control unit 60, which will be described later.

[0041] A moderate amount of abrasive grains are exposed from the binder on the surface of the grinding wheel 54. While the workpiece 1 is being ground with the grinding wheel 54, it is conceivable that the grinding ability of the grinding wheel 54 would decrease as the abrasive grains wear out or fall off the binder. However, the binder also gradually wears out, and new abrasive grains are successively exposed on the surface, so the grinding ability of the grinding wheel 54 is maintained. This effect is called self-sharpening.

[0042] However, problems such as clogging, where processing debris gets stuck between the abrasive grains, or glazing, where the binder is not worn down as expected and the exposed abrasive grains are worn away, can occur, reducing the grinding ability of the grinding wheel 54 and making it unable to properly grind the workpiece 1. When the grinding ability of the grinding wheel 54 begins to decrease, the load current value of the spindle motor 41, which is the rotation drive source for the grinding wheel 54, increases.

[0043] Therefore, the grinding apparatus 2 is provided with a load current value measuring unit 56 that measures the load current value of the spindle motor 41. The load current value measuring unit 56 is, for example, an ammeter provided in a power supply system connected to the spindle motor 41. In the grinding apparatus 2, the load current value of the spindle motor 41 is monitored by the load current value measuring unit 56.

[0044] First, when the grinding wheel 54 comes into contact with the workpiece 1 and begins to bite into it, the load current value measured by the load current value measuring unit 56 increases, and then the load current value reaches a steady state. Then, when the load current value of the spindle motor 41 exceeds the allowable upper limit, it is determined that the grinding wheel 54 is not in a state where it can continue appropriate grinding, and grinding is automatically stopped.

[0045] However, even if the load current value of the spindle motor 41 does not exceed the allowable upper limit, if grinding of the workpiece 1 is carried out under inappropriate grinding conditions, grinding may not proceed stably and the finished quality may be low.

[0046] Furthermore, when starting to grind a new workpiece 1 that has never been ground by the grinding device 2, it is necessary to perform test grinding of the workpiece 1 under various grinding conditions, evaluate the state of the workpiece 1 after grinding, evaluate the quality of each grinding condition, and identify grinding conditions that allow stable grinding. In other words, test grinding is required.

[0047] In the test machining, the condition of the workpiece 1 was evaluated after grinding of the workpiece 1 was completed, and it was sometimes discovered later that the grinding was proceeding unstably. However, if it could be determined while grinding was in progress that the grinding was unstable, there would be no need to continue grinding or inspect the workpiece 1 after grinding. In this case, if it were possible to switch the grinding conditions for the grinding in progress on the grinding device 2, it would be possible to evaluate new grinding conditions early and reduce the number of workpieces lost in the test machining.

[0048] Furthermore, being able to determine whether the grinding of the workpiece 1 being performed by the grinding device 2 is unstable while the grinding is in progress is also useful for detecting abnormalities in normal grinding processes other than test grinding. There is a demand for detecting whether the grinding is unstable even when the load current value of the spindle motor 41 does not exceed the allowable upper limit.

[0049] Therefore, in the grinding device 2 according to this embodiment, whether or not grinding is progressing stably is determined using the load current value of the spindle motor 41 measured by the load current value measuring unit 56. Below, the grinding device 2 will be further described, focusing on the configuration that contributes to the determination.

[0050] The grinding machine 2 includes a control unit 60. The control unit 60 is connected to each component of the grinding machine 2 and has the function of controlling each component. The control unit 60 is configured by a computer including, for example, a processing device such as a CPU (Central Processing Unit), a main storage device such as a DRAM (Dynamic Random Access Memory), and an auxiliary storage device such as a flash memory. The functions of the control unit 60 are realized by operating the processing device and the like in accordance with software stored in the auxiliary storage device.

[0051] Grinding conditions for processing the workpiece 1 are input and registered in advance in the control unit 60. The control unit 60 then controls each component in accordance with the grinding conditions. The grinding conditions are set appropriately depending on the type of workpiece and the desired processing results. The control unit 60 then controls each component while referring to the information sent from each component, and causes the grinding of the workpiece 1 to proceed in a predetermined procedure.

[0052] In other words, the control unit 60 includes a memory section 62 in which grinding conditions, etc. are input and registered in advance, and a grinding control section 64 that controls each component in accordance with the grinding conditions registered in the memory section 62 to perform grinding of the workpiece 1.

[0053] Furthermore, the control unit 60 of the grinding device 2 according to this embodiment has the function of determining whether the load current value measured by the load current value measuring unit 56 is unstable, and determining whether grinding of the workpiece 1 is progressing stably. In other words, the control unit 60 includes a determination section 66 that determines whether the load current value is unstable, and determines whether grinding of the workpiece 1 is progressing stably.

[0054] For example, the control unit 60 (determination unit 66) evaluates the amount of change in the load current value per unit time, and if this exceeds a preset threshold, determines that the load current value is unstable. Here, we will explain the transition of the load current value measured by the load current value measurement unit 56 as grinding of the workpiece 1 progresses.

[0055] 3(A) is a graph showing an example of a change in the load current value observed while grinding of the workpiece 1 proceeds stably. In this graph, the horizontal axis represents the elapsed time since grinding started, and the vertical axis represents the load current value of the spindle motor 41 measured by the load current value measuring unit 56.

[0056] When grinding the workpiece 1, first, the spindle motor 41 is operated to rotate the spindle 44, and the grinding wheel 54 begins to rotate on the circular orbit. Thereafter, the grinding feed unit 24 is operated to start the downward movement of the grinding unit 22. Then, when the grinding wheel 54 comes into contact with the back surface 1b of the workpiece 1, the load current value of the spindle motor 41 begins to increase. In the graph shown in FIG. 3(A), the time when the grinding wheel 54 comes into contact with the workpiece 1 is designated as T0, and the load current value up to this time is designated as I0.

[0057] When the grinding wheel 54 comes into contact with the workpiece 1 and begins to bite into it, the load current value continues to rise for a dozen seconds. Then, just before grinding transitions to a stable state, the increase in the load current value ends, after which the load current value drops slightly and grinding transitions to a stable state. When grinding then progresses stably, a gradual increase in the load current value is observed, but no large fluctuations are observed.

[0058] The load current value shown in the graph of FIG. 3A becomes stable after time T1. Therefore, in the grinding device 2, the load current value is monitored after time T1, and the control unit 60 (determining unit 66) starts making a determination. For example, the load current value has an allowable upper limit (I MAX ) is set. When the load current value exceeds this upper limit, the control unit 60 determines that the grinding wheel 54 is not in a normal state and that grinding of the workpiece 1 is proceeding improperly, and stops grinding of the workpiece 1.

[0059] In addition, the upper limit of the load current value of the spindle motor 41 (I MAX ), the control unit 60 (determination unit 66) determines whether the load current value is unstable. Here, whether the load current value is unstable is evaluated based on the amount of fluctuation in the load current value per unit time.

[0060] For example, the load current value measuring unit 56 measures the load current value of the spindle motor 41 every 0.1 seconds and transmits the measured value to the control unit 60. The control unit 60 then calculates the average value of the load current value every second and records it in the memory unit 62, and determines that the load current value is unstable when the difference between the previous and next average values ​​exceeds a predetermined threshold value.

[0061] More specifically, when the grinding wheel 54 comes into contact with the workpiece 1, the load current value rises to about 8.0 A and then stabilizes at 7.5 A. When the load current value reaches the upper limit (I MAX ) is set to about 15 A. At this time, for example, a fluctuation in the load current value of between 0.1 A and 0.3 A per second is allowed. On the other hand, when the fluctuation in the load current value per second is 0.5 A or more, the control unit 60 determines that the load current value is unstable. In other words, the threshold value set for the fluctuation in the load current value per unit time is, for example, 0.5 A.

[0062] Here, the threshold does not need to be set to the amount of fluctuation in the load current value per second. That is, a threshold that is acceptable for the amount of fluctuation in the load current value of the spindle motor 41 observed over several seconds may be set. For example, 1.0 A may be set as the threshold for the amount of fluctuation in the load current value per 5 seconds. That is, even if the amount of fluctuation in the load current value per second is within the acceptable range, if the load current value fluctuates by more than 1.0 A over 5 seconds, the control unit 60 determines that the load current value is unstable.

[0063] 3(B) is a graph showing an example of the transition of the load current value when the load current value measured by the load current value measuring unit 56 is unstable. For example, while grinding progresses after time T1, the amount of fluctuation in the load current value per relatively short time (ΔT1) and the amount of fluctuation in the load current value per relatively long time (ΔT2) are simultaneously evaluated. Then, when it is confirmed that the fluctuation in the load current value exceeds either of the threshold values ​​set for each, the control unit 60 may determine that the load current value is unstable.

[0064] In this way, the grinding device 2 is configured to set the upper limit (I MAX ), it is possible to determine whether the ongoing grinding of the workpiece 1 is unstable by evaluating the amount of fluctuation in the load current value. Therefore, for example, when performing test machining to find appropriate grinding conditions, if it is determined that the load current value is unstable, there is no need to continue grinding as is, and grinding can be performed by switching to other grinding conditions to be verified.

[0065] When the control unit 60 determines that the load current value of the spindle motor 41 is unstable, the control unit 60 may communicate the result of the determination to a user or manager of the grinding device 2 in a predetermined manner. For example, as shown in FIG. 1 , the control unit 60 includes a display control unit 68 that controls the display unit, and the display control unit 68 causes the touch panel display 58 to display the result of the determination. That is, the control unit 60 may display a message indicating that the load current value is unstable on the touch panel display 58 that functions as the display unit.

[0066] Furthermore, the control unit 60 may communicate the result of the determination by the determination unit 66 to the user or the like by other methods. For example, if the grinding device 2 has a speaker that emits an alarm sound, the control unit 60 causes the speaker to emit an alarm sound indicating the result of the determination. Also, for example, if the grinding device 2 has an alarm lamp, the control unit 60 causes the alarm lamp to emit light indicating the result of the determination. That is, in the grinding device 2 according to this embodiment, the method of notifying the result of the determination by the determination unit 66 is not particularly limited.

[0067] Furthermore, the display control section 68 of the control unit 60 may display not only the result of the determination by the determination section 66 but also information about the load current value of the spindle motor 41 on the touch panel display 58 that functions as a display unit.

[0068] The control unit 60 preferably further includes a graph conversion unit 72 that creates a graph showing the transition of the load current value of the spindle motor 41 measured by the load current value measurement unit 56. The display control unit 68 of the control unit 60 may then display the graph showing the transition of the load current value created by the graph conversion unit 72 on the display unit.

[0069] The graph shown in Figure 3(A) or 3(B) is an example of a graph showing the transition of the load current value, and it is preferable that a graph such as that shown in Figure 3(A) or 3(B) is displayed on touch panel display 58. In this case, it is preferable that the graph displayed on touch panel display 58 successively reflects the load current value of spindle motor 41, which changes as grinding of workpiece 1 progresses, and it is preferable that the graph be updated almost in real time.

[0070] Here, in the grinding apparatus 2, when test machining is being performed under various conditions to select appropriate grinding conditions for the workpiece 1, if the judgment unit 66 judges that the load current value of the spindle motor 41 is unstable, there is no need to continue grinding any further without changing the grinding conditions. In the grinding apparatus 2 according to this embodiment, the grinding conditions can be abandoned based on the judgment result of the judgment unit 66 without waiting for the grinding of the workpiece 1 to be completed and for the workpiece 1 to be inspected. In this case, it is desirable to immediately perform test machining under different grinding conditions.

[0071] Therefore, in the grinding device 2 according to this embodiment, the control unit 60 is capable of accepting input of a command to change the grinding conditions while the workpiece 1 is being ground under certain grinding conditions. For example, the control unit 60 includes an input control unit 70 that accepts commands input using the touch panel display 58 that functions as an input unit. The input control unit 70 is capable of accepting input of information related to the grinding of the workpiece 1, such as the grinding conditions, and can accept input of this information while the grinding of the workpiece 1 by the grinding unit 22 is in progress.

[0072] Then, when the determination section 66 of the control unit 60 determines that the load current value of the spindle motor 41 is unstable, the user or manager of the grinding device 2 uses the touch panel display 58 to input new grinding conditions as information related to the grinding of the workpiece 1. At this time, the control unit 60 records the new grinding conditions based on the input information in the memory section 62, and controls the grinding unit 22 and the like using the grinding control section 64 under the new grinding conditions to continue grinding while changing the grinding conditions.

[0073] Furthermore, if the determination unit 66 determines again that the load current value of the spindle motor 41 is unstable while grinding of the workpiece 1 is proceeding under the changed grinding conditions, it is possible to immediately switch to new grinding conditions and continue grinding of the workpiece 1. That is, with the grinding device 2 according to this embodiment, when test machining of the workpiece 1 is carried out to find the optimum machining conditions, it is possible to early abandon unpromising machining conditions and verify the machining conditions to be verified one after another.

[0074] Conventionally, test machining was repeated by preparing workpieces 1 for each machining condition to be verified. In contrast, the grinding device 2 according to this embodiment can evaluate multiple machining conditions to be verified using a single workpiece 1, thereby significantly reducing the number of workpieces 1 consumed in test machining. Furthermore, the quality of each machining condition can be evaluated without inspecting the workpiece 1 after grinding of the workpiece 1 is complete. Therefore, the time required to evaluate the machining results can also be reduced.

[0075] Finally, the operation flow of the grinding device 2 according to this embodiment will be described. Fig. 4(A) is a flowchart showing the operation flow of the grinding device 2 that grinds the workpiece 1 while determining whether the load current value of the spindle motor 41 is stable.

[0076] In the grinding device 2, first, the workpiece 1 is placed on the chuck table 6, which then sucks and holds the workpiece 1. Then, the chuck table 6 is moved below the grinding unit 22. Next, the spindle motor 41 is operated to rotate the grinding wheel 54 on a circular orbit. At this time, the load current value measuring unit 56 begins measuring the load current value of the spindle motor 41.

[0077] Then, the supply of grinding fluid from a supply nozzle (not shown) to the workpiece 1 or grinding wheel 54 is started, and the grinding feed unit 24 is operated to start the downward movement of the grinding unit 22 (S10). When the lower surface of the rotating grinding wheel 54 comes into contact with the rear surface 1b of the workpiece 1 exposed upward, grinding of the workpiece 1 is started (S20).

[0078] At this time, as explained with reference to the graphs in Figure 3(A) and elsewhere, the load current value of the spindle motor 41 measured by the load current value measuring unit 56 increases as the grinding wheel 54 bites into the workpiece 1. After that, the load current value passes its peak, decreases slightly, and reaches a steady state. At this time, monitoring of the load current value of the spindle motor 41 begins using the load current value measuring unit 56 (S30).

[0079] Then, the determination section 66 of the control unit 60 of the grinding device 2 determines whether the measured load current value is unstable (S40). More specifically, if the amount of fluctuation per unit time of the measured load current value does not exceed a predetermined threshold, it is determined that the load current value is not unstable and grinding of the workpiece 1 is proceeding appropriately. In this case, the grinding device 2 continues grinding the workpiece 1 as is.

[0080] In response to this, the determination section 66 of the control unit 60 determines that the load current value is unstable if the amount of fluctuation per unit time of the measured load current value exceeds a predetermined threshold. In this case, the display control section 68 of the control unit 60 causes the touch panel display 58, which functions as a display unit, to display a message indicating that the load current value is unstable (S50). Note that even in this case, stopping grinding is not necessarily desired, so the grinding control section 64 may cause the grinding unit 22 to continue grinding unless a special command is input.

[0081] When the thickness of the workpiece 1 measured by a thickness measuring unit (not shown) has not reached the predetermined thickness, the control unit 60 continues to monitor the load current value of the spindle motor 41 while continuing grinding of the workpiece 1. When the thickness of the workpiece 1 reaches the predetermined thickness, the control unit 60 stops the descent of the grinding unit 22 by the grinding feed unit 24, and ends the grinding of the workpiece 1 by the grinding wheel 54 (S80).

[0082] Here, in the grinding device 2 according to this embodiment, the grinding conditions can be changed after the grinding unit 22 starts to descend and the grinding wheel 54 comes into contact with the back surface 1b of the workpiece 1 to start grinding of the workpiece 1. Fig. 4(B) is a flowchart showing the operation flow of the grinding device 2, in which information related to grinding is input while grinding of the workpiece 1 is in progress and the grinding conditions are changed while continuing to grind the workpiece 1.

[0083] When information about grinding is input using the touch panel display 58 while grinding of the workpiece 1 is in progress (S90), the control unit 60 records the information in the storage unit 62, and changes the grinding conditions to continue grinding of the workpiece 1 (S60, S100).In addition, when no information about grinding is input, the control unit 60 continues grinding of the workpiece 1 under the same grinding conditions (S60).

[0084] Here, the grinding conditions mainly include the lowering speed (grinding feed speed) of the grinding unit 22 by the grinding feed unit 24, the rotation speed of the grinding wheel 54 rotated by the spindle motor 41, and the rotation speed of the chuck table 6. The grinding conditions may also include the amount of grinding fluid supplied, the tilt angle of the rotation axis of the chuck table 6, and the tilt angle of the spindle 44. However, the grinding conditions are not limited to these.

[0085] Then, when the thickness of the workpiece 1 has not reached the predetermined thickness, the control unit 60 continues grinding the workpiece 1 while accepting input of information. Thereafter, when the thickness of the workpiece 1 reaches the predetermined thickness, the control unit 60 stops the descent of the grinding unit 22 by the grinding feed unit 24, and ends the grinding of the workpiece 1 by the grinding wheel 54 (S80).

[0086] As described above, the control unit 60 of the grinding device 2 according to this embodiment calculates the amount of fluctuation per unit time of the load current value of the spindle motor 41 measured by the load current value measuring unit 56. If this amount exceeds a preset threshold, it is determined that the load current value is unstable.

[0087] Therefore, even if the load current value does not exceed the allowable upper limit, it can be detected that the load current value is unstable. If it is determined that the load current value is unstable, it means that grinding of the workpiece 1 is not progressing stably, and an operator who knows this can determine whether grinding needs to be continued and can change the grinding conditions.

[0088] The present invention is not limited to the above-described embodiment, and various modifications can be made to the present invention. For example, in the above-described embodiment, the grinding device 2 includes one grinding unit 22 and one chuck table 6, and grinds one workpiece 1. However, the grinding device 2 according to the present embodiment is not limited to this.

[0089] That is, the grinding device 2 according to one aspect of the present invention may include two or more grinding units 22 and chuck tables 6, and may simultaneously grind two or more workpieces 1. In this case, a load current value measuring unit 56 is connected to the spindle motor 41 of each grinding unit 22, and each load current value is monitored to see if it becomes unstable.

[0090] Furthermore, in the above embodiment, a case has been described in which a user of the grinding device 2 inputs grinding-related information into the control unit 60 to change the grinding conditions when the load current value of the spindle motor 41 is unstable, but one aspect of the present invention is not limited to this. That is, in the grinding device 2 according to one aspect of the present invention, the control unit 60 may be able to accept input of the information and may be able to change the grinding conditions even when it is not determined that the load current value of the spindle motor 41 is unstable.

[0091] For example, when the determining unit 66 does not determine that the load current value is unstable, an operator or the like may wish to change the grinding conditions while looking at a graph showing the transition of the load current value of the spindle motor 41 displayed on the touch panel display 58. When an operator recognizes the need to change the grinding conditions based on experience or the like, the grinding device 2 according to one aspect of the present invention may be capable of changing the grinding conditions.

[0092] In addition, the structures, methods, etc. according to the above-described embodiments and modifications can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0093] 1 Workpiece 1a surface 1b back side 3 Protective materials 2 Grinding equipment 4 Foundation 4a Recess 4b Dustproof / waterproof cover 6 Chuck table 6a Frame 6b Porous plate 6c Holding surface 6d Table base 8 Y-axis movement mechanism 10 Guide rail 12 Mobile Table 14 Nut part 16 Ball screw 18 Pulse motor 20 spindles 20a spindle housing 22 Grinding unit 24 Grinding feed unit 26 Support part 28 Guide rail 30 Moving Plate 32 Nut part 34 Ball screw 36 Pulse motor 38 Retaining member 40 Spindle housing 41 Spindle motor 42 Cushioning material 44 Spindle 46 Rotation axis 48 Wheel Mount 50 grinding wheels 52 Wheel base 54 Grinding Wheel 56 Load current measurement unit 58 Touch panel display 60 Control Unit 62 Storage section 64 Grinding control section 66 Judgment section 68 Display control unit 70 Input control section 72 Graph transformation unit

Claims

1. a chuck table for holding the workpiece; a grinding unit having a spindle and a spindle motor connected to the upper end of the spindle, a grinding wheel having grinding stones arranged in a ring shape attached to the lower end side of the spindle, and rotating the spindle to bring the grinding stones, which are rotated and moved, into contact with the workpiece held on the chuck table, thereby grinding the workpiece; a grinding feed unit that moves the chuck table and the grinding unit in directions in which they approach and move away from each other; a load current value measuring unit for measuring a load current value of the spindle motor that increases when the grinding wheel comes into contact with the workpiece; a control unit for controlling each component; The control unit determines that the load current value is unstable and the grinding is proceeding unstably when the load current value measured by the load current value measuring unit does not exceed an allowable upper limit value and the grinding is proceeding normally, and when the fluctuation amount of the load current value per unit time exceeds a preset threshold value.

2. Further comprising a display unit for displaying information; 2. The grinding apparatus according to claim 1, wherein the control unit, when determining that the load current value is unstable, displays a message on the display unit indicating that the load current value is unstable.

3. 3. The grinding device according to claim 2, wherein the control unit includes a graph conversion unit that creates a graph showing the change in the load current value measured by the load current value measurement unit, and the graph showing the change in the load current value created by the graph conversion unit can be displayed on the display unit.

4. further comprising an input unit for inputting information to said control unit; 4. The grinding device according to claim 1, wherein the control unit is capable of accepting input of information relating to the grinding of the workpiece by the input unit while the grinding of the workpiece by the grinding unit is in progress, and when it determines that the load current value is unstable, the control unit is capable of changing the grinding conditions based on the information relating to the grinding of the workpiece input while the grinding of the workpiece is in progress and continuing the grinding.

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