JP7295670B2 - Grinding equipment - Google Patents

Description

The present invention relates to grinding equipment.

Grinding equipment that grinds a workpiece with a grinding wheel grinds the workpiece to a predetermined thickness. Grinding is performed at a slow speed to the finish thickness (Patent Documents 1, 2, and 3). In this way, in the grinding process in the thickness region from a thickness slightly thicker than the finish thickness to the finish thickness, grinding at a slow grinding feed rate reduces the load that presses the grinding wheel against the workpiece, thereby reducing mechanical strain. The workpiece is finished to have a uniform thickness by grinding in this state.

In addition, in order to prevent the grinding wheel from clogging or becoming blocked during grinding, the workpiece cannot be ground normally. When the load current value of the spindle motor during machining exceeds the upper limit value, an alarm is issued to notify the operator.

JP 2012-151409 A JP 2013-226625 A JP 2014-024145 A

As described above, when the load current value measured during grinding exceeds the upper limit of the load current value that is set regardless of the grinding feed rate, it is recognized. . However, the load current value of each spindle motor is different when the grinding feed speed is fast and when the feed speed is slow. There is a problem that it is insufficient to implement
Therefore, in the grinding apparatus, there is a problem to be solved in that the load current value of the spindle motor is monitored according to each grinding feed rate and the occurrence of an abnormality in the grinding process is detected.

The present invention comprises holding means for holding a workpiece, and grinding means for grinding the workpiece held by the holding means with the grinding wheel by rotating a spindle equipped with a grinding wheel in which grinding wheels are arranged in an annular shape. , a grinding feeding means for moving the holding means and the grinding means in directions toward and away from each other; a thickness measuring means for measuring the thickness of the workpiece; A grinding and polishing apparatus comprising a load current value detection means for detecting a load current value of a spindle motor which is moved in a direction to approach a workpiece and rises when the grinding wheel comes into contact with the workpiece, and a control means. The grinding feed means includes a first grinding feed section that grinds the workpiece to a first thickness that is thicker than a preset finish thickness at a first grinding feed rate, and a second grinding feed section that is slower than the first grinding feed rate. and a second grinding feed unit that grinds to the finish thickness at a grinding feed rate of , and the control means controls when grinding at the first grinding feed rate and during grinding based on the measurement results measured in the past grinding process. 2. An upper limit value setting unit for setting an upper limit value of the load current value detected by the load current value detection means for each grinding feed speed when grinding at two grinding feed speeds, and the load current value detection means detects a lower limit value setting unit for setting a lower limit value of the load current value; a recognition unit for recognizing that the grinding wheel is clogged or blocked when the load current value detected by the load current value detection means exceeds the respective upper limits; When the load current value detected by the load current value detection means between the upper limit value and the lower limit value exceeds the respective lower limit values during grinding at the second grinding feed rate, the and a second recognition unit that recognizes that the grinding wheel is chipped or abnormally worn .

Further, the present invention is a grinding method in which a holding means for holding a workpiece and a spindle equipped with a grinding wheel having grinding wheels arranged in an annular shape are rotated to grind the workpiece held by the holding means with the grinding wheel. means, grinding feeding means for relatively moving the holding means and the grinding means in directions toward and away from each other, and top surface height measuring means for measuring the top surface height of the workpiece held by the holding means. Then, the grinding wheel moves in the direction of approaching the workpiece held by the holding means, and the load current value of the spindle motor which rises when the grinding wheel comes into contact with the workpiece is detected. and a control means, wherein the grinding feeding means measures the top surface height until the surface to be ground reaches the top surface height lowered by a preset first grinding amount. A first grinding feed unit that grinds the workpiece at the first grinding feed rate, and while measuring the top surface height, the ground surface is lowered by the preset second grinding amount until the finished height is reached. a second grinding feed section for grinding the workpiece at a second grinding feed rate slower than the first grinding feed rate, wherein the control means controls the first grinding feed based on the measurement result measured in the past grinding process; an upper limit value setting unit for setting an upper limit value of the load current value detected by the load current value detection means for each of the grinding feed speed when grinding at the feed speed and when grinding at the second grinding feed speed; a lower limit value setting unit for setting a lower limit value of the load current value detected by the load current value detection means ; A recognition unit that recognizes that the grinding wheel is clogged or blocked when the load current value detected by the load current value detection means between the lower limit value and the upper limit value exceeds the respective upper limit value. and the load current values detected by the load current value detecting means between the upper limit value and the lower limit value during grinding at the first grinding feed rate and the second grinding feed rate, respectively. a second recognizing unit that recognizes that the grinding wheel is chipped or abnormally worn when the lower limit of is exceeded .

In the present invention, in order to monitor the load current value of the spindle motor in relation to the upper limits of the respective grinding feed speeds of the first grinding feed speed and the second grinding feed speed during grinding, It is possible to prevent excessive load from being applied to the grinding wheel. Further, the upper limit of the load current value of the spindle motor when the grinding feed rate is the second grinding feed rate can be set to a lower value than in the conventional art, and the occurrence of defective grinding can be detected.

Moreover, by setting the lower limit of the load current value, it is possible to detect the occurrence of an abnormality such as chipping of the grinding wheel or abnormal wear of the grinding wheel.

It is a perspective view showing the whole grinding device. It is a side view showing a mode that a to-be-processed object is ground. (a) is a graph showing the value of the load current value of the motor when grinding the workpiece at each of the first grinding feed speed and the second grinding feed speed; , (c) is a graph in which the upper limit value of the load current value is further drawn on the time characteristic graph of the load current value shown in (a); and (c) is a graph in which the lower limit value of the load current value is further drawn. be.

1 Configuration of Grinding Apparatus A grinding apparatus 1 shown in FIG. The configuration of the grinding apparatus 1 will be described below.

The grinding machine 1 is provided with a control means 8 having a CPU or the like for electrically controlling various mechanisms provided in the grinding machine 1 . Various mechanisms of the grinding apparatus 1 are connected to a power source (not shown) and operate using power supplied from the power source as a power source.

As shown in FIG. 1, the grinding apparatus 1 includes a base 10 extending in the Y-axis direction and a column 11 standing on the base 10 in the +Y direction.

As shown in FIG. 1, a holding means 2 is provided on a base 10 of the grinding device 1 . The holding unit 2 is a disc-shaped table that holds the workpiece W, and includes, for example, a suction unit 20 having a holding surface 20 a and a frame 21 that surrounds the suction unit 20 . The holding means 2 is also connected to a suction source 23 via a suction path 22 . For example, as shown in FIGS. 1 and 2, a tape T for protecting the back surface Wb of the workpiece W is attached to the back surface Wb of the workpiece W, and the workpiece W is held on the holding surface 20a. By transmitting the suction force exerted by the suction source 23 to the holding surface 20a through the suction path 22 in the state of being placed on the workpiece W, the workpiece W can be held by suction on the holding surface 20a.
In addition, the holding means 2 is provided with a rotating means 24 for rotating the holding means 2 around a rotating shaft 25 in the Z-axis direction.
Further, a cover 12 is arranged around the holding means 2, and a bellows 13 is connected to the cover 12 so as to be extendable. During grinding of the workpiece W, the cover 12 and the holding means 2 are driven by means of movement in the Y-axis direction (not shown) disposed inside the base 10, and are integrated in the Y-axis direction. move back and forth to At this time, the bellows 13 expands and contracts as the cover 12 moves in the Y-axis direction.

Grinding means 3 and grinding feeding means 4 are provided on the side surface of the column 11 in the -Y direction.
The grinding means 3 includes a spindle 30 having a rotation axis 35 in the Z-axis direction, a spindle motor 32 for rotating the spindle 30 around the rotation axis 35, and a housing 31 for rotatably supporting the spindle 30. ing. A mount 33 is connected to the lower end of the spindle 30 , and a grinding wheel 34 is detachably attached to the lower surface of the mount 33 . The grinding wheel 34 is composed of a base 341 and a plurality of rectangular parallelepiped grinding wheels 340 annularly arranged on the lower surface of the base 341 . The grinding wheel 340 is made of, for example, diamond abrasive grains fixed by resin bond, metal bond, or the like, and its lower surface 340a serves as a grinding surface for grinding the workpiece W. As shown in FIG.

The spindle motor 32 is electrically connected to load current value detection means 6 for measuring the value of the load current flowing through the spindle motor 32 .

The grinding feed means 4 includes a ball screw 40 having a rotation axis 45 in the Z-axis direction, a pair of guide rails 41 arranged parallel to the ball screw 40, and connected to the upper end of the ball screw 40 to rotate the ball screw 40 as a rotation axis. A Z-axis motor 42 that rotates around 45, an elevating plate 43 that has an internal nut screwed onto a ball screw 40 and whose side portion is in sliding contact with the guide rail 41, and is connected to the elevating plate 43 to hold the grinding means 3. A holder 44 is provided.
When the ball screw 40 is driven by the Z-axis motor 42 and rotates around the rotary shaft 45 , the elevating plate 43 is guided by the guide rail 41 to move up and down in the Z-axis direction, and is held by the holder 44 . Grinding means 3 attached to it is configured to move up and down in the Z-axis direction. By driving the grinding means 3 using the grinding feed means 4 , the grinding wheel 340 can be moved toward and away from the workpiece W held by the holding means 2 .

Further, the grinding feed means 4 is provided with a first grinding feed section 46 and a second grinding feed section 47 . The first grinding feeder 46 has a function of lowering the grinding means 3 in the -Z direction at a constant first grinding feedrate, and the second grinder feeder 47 has a constant speed as well. Also, it has a function of lowering the grinding means 3 in the -Z direction at a second grinding feed rate that is slower than the first grinding feed rate.

Based on the load current value flowing through the spindle motor 32 measured in the past grinding process, the control means 8 lowers the grinding means 3 in the -Z direction at the first grinding feed rate to cause the workpiece to be machined. The upper limit of the load current value flowing to the spindle motor 32 when grinding the workpiece W, and the spindle when similarly lowering the grinding means 3 in the -Z direction at the second grinding feed rate to grind the workpiece W An upper limit value setting unit 80 is provided for setting the upper limit value of the load current value flowing through the motor 32 . Also, in the control means 8, the load current value detected by the load current value detection means 6 during grinding at the first grinding feed speed or the second grinding feed speed is set by the upper limit setting unit 80. A recognition unit 81 is provided for recognizing when the upper limit value set above is exceeded.

Similarly, the control means 8 causes the grinding means 3 to descend in the -Z direction at the first grinding feed rate based on the measurement result of the load current value applied to the spindle motor 32 measured in the past grinding process. The lower limit of the load current value flowing to the spindle motor 32 when grinding the workpiece W, and when grinding the workpiece W by lowering the grinding means 3 in the -Z direction at the second grinding feed rate. A lower limit value setting unit 82 is provided for setting the lower limit value of the load current value flowing through the spindle motor 32 . Further, when grinding is performed at the first grinding feed speed or the second grinding feed speed, the load current value detected by the load current value detection means 6 is below the lower limit value set by the lower limit value setting unit 82. A second recognition unit 83 is provided for recognizing the fact.

As shown in FIGS. 1 and 2, on the base 10 of the grinding apparatus 1, a wafer top surface height gauge 50, a holding surface height gauge 51, and a thickness measuring means 5 having a calculating means 52 are arranged. During the grinding process, the wafer upper surface height gauge 50 is brought into contact with the surface Wa of the workpiece W, and the holding surface height gauge 51 is brought into contact with the holding surface 20a of the holding means 2. By measuring the height of the holding surface 20a of the means 2, the thickness of the workpiece W can be calculated by the calculation means 52 based on the measured height values of both.

2 Operation of Grinding Device The operation of the grinding device 1 when grinding the workpiece W using the grinding device 1 configured as described above will be described with reference to FIGS. 1 to 3. FIG.

Before performing the grinding process, the first grinding feed rate and the second grinding feed rate are determined based on the load current value flowing through the spindle motor 32, which was previously measured using the load current value detection means 6 in the past grinding process. The upper limit setting unit 80 sets the upper limit value of the load current value flowing to the spindle motor 32 when the workpiece W is ground, and the workpiece W is ground at the two types of grinding feed rates. The lower limit value of the load current value flowing through the spindle motor 32 is set by the lower limit value setting unit 82 .

As a method of setting the upper limit and the lower limit, for example, the measurement data of the load current value when grinding 25 workpieces W are arranged in order of magnitude, and the median value of the measurement data is set in advance. Among the measurement data included in the range (for example, statistical interquartile range), the largest value is set as the upper limit, and the smallest value is set as the lower limit. As a result, the upper and lower limits can be set from useful measurement data excluding data greatly deviating from the median.

After setting the upper limit value and the lower limit value as described above, the grinding process is started. First, as shown in FIGS. 1 and 2, the workpiece W to which the tape T is adhered is placed on the holding surface 20a of the holding means 2 so that the surface Wa of the workpiece W faces upward. do.
The suction force generated by the suction source 23 is transmitted to the holding surface 20a of the holding means 2 through the suction path 22, and the workpiece W is held on the holding surface 20a of the holding means 2 by suction.

Next, the holding means 2 holding the workpiece W is moved in the Y-axis direction using a moving means (not shown). Thereby, as shown in FIG. 2, the grinding wheel 340 is positioned so as to pass through the center of the workpiece W. As shown in FIG. After that, the rotating means 24 is used to rotate the holding means 2 and the workpiece W held on the holding surface 20 a of the holding means 2 around the rotating shaft 25 .

Next, the spindle 30 is driven using the spindle motor 32 to rotate the spindle motor 32 about the rotating shaft 35 . As a result, the mount 33 provided at the lower end of the spindle 30 and the grinding wheel 34 attached to the lower surface of the mount 33 rotate.

Then, when an electric signal is sent from the control means 8 to the first grinding feeder 46, the rotation of the Z-axis motor 42 is controlled by the first grinder feeder 46 that has received the electric signal. As a result, the grinding means 3 descends in the -Z direction at the first grinding feed rate, and the grinding wheel 340 approaches the workpiece W. As shown in FIG. Specifically, the Z-axis motor 42 of the grinding feed means 4 that receives an electric signal from the first grinding feed section 46 rotates the ball screw 40 about the rotary shaft 45 at a rotation speed corresponding to the first grinding feed speed. As a result, the elevating plate 43 descends in the -Z direction at the first grinding feed rate while being guided by the guide rail 41, and along with this, the grinding wheel supported by the elevating plate 43 via the holder 44. 340 also descends in the -Z direction at the first grinding feed rate and approaches the workpiece W held on the holding means 2 . When the grinding wheel 340 descends in the -Z direction while rotating about the rotary shaft 35, it eventually comes into contact with the surface Wa of the workpiece W as shown in FIG. is ground.

During the grinding process, the thickness of the workpiece W is measured using the thickness measuring means 5 . While the wafer top surface height gauge 50 is in contact with the surface Wa of the workpiece W, the holding surface height gauge 51 is brought into contact with the holding surface 20a. The thickness of object W is measured. Grinding is performed at the first grinding feed rate until the thickness of the workpiece W reaches a first thickness that is thicker than the preset finish thickness. This control is performed by the first grinding feeder 46 .

After the workpiece W is ground to the first thickness, an electric signal for changing the grinding feed rate is sent from the control means 8 to the second grinding feed section 47 . The rotation speed of the Z-axis motor 42 is controlled by the second grinding feed section 47 which receives the electric signal, and the descending speed of the grinding means 3 is reduced from the first grinding feed speed to the second grinding feed slower than the first grinding feed speed. switch to speed. After switching the descending speed of the grinding means 3 to the second grinding feed speed, the grinding wheel 340 in contact with the surface Wa of the workpiece W is further pushed down in the -Z direction, and the workpiece is moved at the second grinding feed speed. The workpiece W is ground to the finish thickness. This control is performed by the second grinding feed section 47 .
In addition, the first grinding feed section 46 may grind at the first grinding feed rate until the surface to be ground of the workpiece reaches the upper surface height lowered by the preset first grinding amount. Similarly, the second grinding feed section 47 may grind at the second grinding feed rate until the surface to be ground of the workpiece reaches the upper surface finished height that is lowered by the preset second grinding amount. good.

During the grinding process of the workpiece W, grinding debris generated by the contact between the rotating lower surface 340a of the grinding wheel 340 and the surface Wa of the workpiece W adheres to the grinding wheel 340, and as the processing time elapses, the spindle motor is There is a possibility that the rotation speed of 32 will be decelerated compared to when grinding is started. Therefore, during the grinding process, the rotation speed of the spindle motor 32 is measured using an encoder or the like (not shown), and feedback control is performed to control the power supplied to the spindle motor 32 based on the measurement result. The rotation speed of the motor 32 may be kept constant.
In the feedback control of the rotational speed of the spindle motor 32, the load changes in the rotational direction according to changes in the frictional force acting on the contact portion between the surface Wa of the workpiece W and the lower surface 340a of the grinding wheel 340. The load current value flowing through the motor 32 changes.
For example, when the grinding wheel 340 is clogged or blocked, the workpiece W is not ground, so the force of the grinding wheel 340 pushing the workpiece W increases, and the lower surface 340a of the grinding wheel 340 and the workpiece W are separated from each other. The frictional force acting on the contact portion with the surface Wa increases, and the rotation speed of the spindle motor 32 is further reduced. be done. As a result, the load current value flowing through the spindle motor 32 increases.
On the other hand, for example, when chipping or abnormal wear occurs in the grinding wheel 340, the area where the lower surface 340a of the grinding wheel 340 is in contact with the surface Wa of the workpiece W becomes smaller. Since the frictional force acting on the contact portion between the lower surface 340a of the workpiece 340 and the surface Wa of the workpiece W becomes smaller, the load current value of the spindle motor 32 becomes smaller than that during normal grinding.
Thus, the load current value flowing through the spindle motor 32 serves as an index indicating the state of the lower surface 340 a of the grinding wheel 340 .

Therefore, in order to check the state of the lower surface 340a of the grinding wheel 340, the load current value flowing through the spindle motor 32 is measured using the load current value detection means 6 during the grinding process. FIG. 3(a) is an example of a graph showing changes over time in the value of the load current flowing through the spindle motor 32. The left part shows changes over time in the value of the load current flowing through the spindle motor 32 during grinding at the first grinding speed. , and the right part shows the change over time of the load current value flowing to the spindle motor 32 during grinding at the second grinding speed.

For example, assume that the upper limit value and the lower limit value of the load current value flowing to the spindle motor 32 in the grinding process at the first grinding feed speed are I1 and I2, respectively. Assume that the upper limit and lower limit of the load current value flowing through the spindle motor 32 during grinding are I3 and I4, respectively.
FIG. 3(b) is a graph of the time change of the load current value drawn in FIG. 3(a). It is the graph which drew the upper limit I1 of a load current value, and I3, respectively. As shown in FIG. 3B, the value of the load current flowing through the spindle motor 32 measured during grinding at the first grinding feed rate exceeds the upper limit value I1 at P1, and the recognition unit 81 recognizes this. Recognized.

FIG. 3C shows the graph shown in FIG. It is the graph which drew I4 respectively. As shown in FIG. 3(c), the value of the load current flowing through the spindle motor 32 measured during grinding at the second grinding feed rate is below the lower limit value I4 at P2, and the second recognition unit 83 is recognized.

As described above, the load current value measured by the load current value detection means 6 exceeds (belows) the preset upper limit value (lower limit value), and the fact is recognized by the recognition unit 81 (second recognition unit 83). In this case, for example, an alarm is issued by a notification means (not shown) provided in the grinding apparatus 1, thereby notifying the operator that an abnormality has occurred in the grinding process. Alternatively, for example, a display notifying the occurrence of the grinding abnormality is displayed on a display or the like (not shown), thereby notifying the operator of the occurrence.
After that, for example, an electric signal is transmitted from the control means 8 to the grinding feed means 4, and the grinding means 3 is driven by the grinding feed means 4 that received the electric signal, thereby lowering the grinding means 3 in the -Z direction. stops, and is further raised in the +Z direction, the grinding wheel 340 that has been in contact with the workpiece W is once retracted upward, and the machining is interrupted.

As described above, by operating the grinding device 1, the upper limit and lower limit of the load current value in the grinding process at the first grinding feed speed and the upper limit of the load current value in the grinding process at the second grinding feed speed It is possible to monitor the load current value by setting a value and a lower limit value respectively, thereby enabling more accurate detection of abnormalities occurring in the grinding process.
That is, since the second grinding feed speed is slower than the first grinding feed speed, the upper limit value and the lower limit value set for the second grinding feed speed are lower than the upper limit value and the lower limit value set for the first grinding feed speed. A small value is set.

In the embodiment for carrying out the present invention, the upper limit value and the lower limit value of the load current value corresponding to the two grinding feed speeds consisting of the first grinding feed speed and the second grinding feed speed are set to It is not limited to the configuration in which an abnormality occurring in the grinding process is detected using the set upper limit value and the set lower limit value.
For example, the third grinding feed rate, the fourth grinding feed rate, and so on, when grinding one workpiece W, the grinding process is performed by combining more types of grinding feed rates. In this case, similarly, the upper limit and lower limit of the load current value corresponding to each grinding feed rate are set based on the past machining experience, and the load current value flowing to the spindle motor during grinding is monitored. Thereby, it becomes possible to detect an abnormality that occurs in the grinding process at each grinding feed speed.

1: Grinding Device 10: Base 11: Column 12: Cover 13: Accordion 2: Holding Means 20: Suction Part 20a: Holding Surface 21: Frame 22: Suction Path 23: Suction Source 24: Rotating Means 25: Rotating Axis 3: Grinding Means 30: Spindle 31: Housing 32: Spindle Motor 33: Mount 34: Grinding Wheel 340: Grinding Wheel 340a: Lower Surface of Grinding Wheel 341: Base 35: Rotating Axis 4: Grinding Feed Means 40: Ball Screw 41: Guide Rail 42 : Z-axis motor 43: Elevating plate 44: Holder 45: Rotating shaft 46: First grinding feed unit 47: Second grinding feed unit 5: Thickness measuring means 50: Wafer upper surface height gauge 51: Holding surface height gauge 52: Calculating means 6: Load current value detection unit 8: control means 80: upper limit value setting unit 81: recognition unit 82: lower limit value setting unit 83: second recognition unit W: workpiece Wa: front surface of workpiece Wb: back surface of workpiece T: tape I1: upper limit of load current value during grinding at the first grinding feed speed I2: lower limit of load current value during grinding at the first grinding feed speed I3: second grinding feed speed Upper limit of load current value during grinding I4: Lower limit of load current during grinding at the second grinding feed speed P1: Exceeded the upper limit of load current during grinding at the first grinding feed speed Point P2: The point where the load current fell below the lower limit during grinding at the second grinding feed rate.

Claims (2)

holding means for holding the workpiece;
Grinding means for rotating a spindle equipped with a grinding wheel having grinding wheels arranged in an annular shape and grinding the workpiece held by the holding means with the grinding wheels;
Grinding feed means for moving the holding means and the grinding means in directions toward and away from each other;
a thickness measuring means for measuring the thickness of the workpiece;
load current value detection means for detecting the load current value of the spindle motor which moves in a direction in which the grinding wheel approaches the workpiece held by the holding means and rises when the grinding wheel comes into contact with the workpiece; ,
A grinding apparatus comprising a control means,
The grinding feeding means is
A first grinding feed unit that grinds the workpiece to a first thickness thicker than a preset finishing thickness at a first grinding feed rate, and a second grinding feed rate that is slower than the first grinding feed rate to grind the workpiece to a finish thickness. and a second grinding feeder,
The control means
Based on the measurement result measured in the past grinding process, the load current value detection means for each grinding feed speed when grinding at the first grinding feed speed and when grinding at the second grinding feed speed. an upper limit setting unit for setting the upper limit of the load current value detected by the load current value detecting means; a lower limit setting unit for setting the lower limit of the load current value detected by the load current value detecting means;
When grinding at the first grinding feed rate and the second grinding feed rate, the load current values detected by the load current value detecting means between the upper limit value and the lower limit value are respectively a recognition unit that recognizes that the grinding wheel is clogged or blocked when the upper limit is exceeded;
When grinding at the first grinding feed rate and the second grinding feed rate, the load current values detected by the load current value detecting means between the upper limit value and the lower limit value are respectively a second recognition unit that recognizes that the grinding wheel is chipped or abnormally worn when the lower limit value is exceeded;
Grinding device with holding means for holding the workpiece;
Grinding means for rotating a spindle equipped with a grinding wheel having grinding wheels arranged in an annular shape and grinding the workpiece held by the holding means with the grinding wheels;
Grinding feed means for moving the holding means and the grinding means in directions toward and away from each other;
a top surface height measuring means for measuring the top surface height of the workpiece held by the holding means;
load current value detection means for detecting the load current value of the spindle motor which moves in a direction in which the grinding wheel approaches the workpiece held by the holding means and rises when the grinding wheel comes into contact with the workpiece; ,
A grinding apparatus comprising a control means,
The grinding feeding means is
a first grinding feed unit that grinds the workpiece at a first grinding feed rate until the surface to be ground reaches the top surface height that is lowered by a preset first grinding amount while measuring the top surface height; Second grinding, in which the workpiece is ground at a second grinding feed rate slower than the first grinding feed rate until the surface to be ground reaches a finished height that is lowered by a preset second grinding amount while measuring the height. a sending unit,
The control means
Based on the measurement result measured in the past grinding process, the load current value detection means for each grinding feed speed when grinding at the first grinding feed speed and when grinding at the second grinding feed speed. an upper limit setting unit for setting the upper limit of the load current value detected by the load current value detecting means; a lower limit setting unit for setting the lower limit of the load current value detected by the load current value detecting means;
When grinding at the first grinding feed rate and the second grinding feed rate, the load current values detected by the load current value detecting means between the upper limit value and the lower limit value are respectively a recognition unit that recognizes that the grinding wheel is clogged or blocked when the upper limit is exceeded;
When grinding at the first grinding feed rate and the second grinding feed rate, the load current values detected by the load current value detecting means between the upper limit value and the lower limit value are respectively a second recognition unit that recognizes that the grinding wheel is chipped or abnormally worn when the lower limit value is exceeded;
Grinding device with

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