JPH1044031A - Grinding method for work - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a grinding wheel for a long time by correcting the relative position between the grinding wheel and a work so that a sizing device faces a plunge grinding surface when the grinding wheel width becomes smaller due to modification of it, and then by measuring some diameters of a cylindrical component of the work during grinding the work. SOLUTION: Feed per revolution of a table are corrected by one modification of a grinding wheel so that the right end surface 21a of the grinding wheel is positioned to a nominal position (P), and the contact 32a of a sizing device is set so that it measures diameters of a cylindrical component Wa at the fixed position facing a plunge grinding surface 21a. Then a wheel spindle stock is moved with rapid traverse, a intermediate part Wd of the cylindrical component W a is provided with the plunge grinding by the grinding surface 21a of a grinding wheel 21. This plunge grinding is direct sizing grinding for which measurement signal from a measuring head for outer diameters of the intermediate part Wd is timely sent to a device control unit. Thus, even if the width of the grinding wheel changes due to its modification, the sizing device is always set to the position facing the plunge grinding surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding machine provided with a grinding wheel which moves relative to a workpiece in a direction parallel to the axis of the workpiece and in a direction intersecting with the axis of the workpiece. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grinding method and apparatus for contour grinding adjacent arc corners.

[0002]

2. Description of the Related Art Conventionally, as a processing technique for rapidly grinding a workpiece W having a pair of arc-shaped corner portions Wb and a pair of shoulder portions Wc adjacent to a cylindrical portion Wa as shown in FIG. There is one disclosed in the official gazette of Kaihei 8-90408. The technique disclosed in this publication discloses, as shown in FIG. 11, a grindstone composed of a plunge ground surface Gs parallel to the rotation axis of a workpiece W and arcuate ground surfaces Gr formed on both sides of the plunge ground surface Gs. Using the wheel G, plunge grinding is performed while measuring a part Wd of the cylindrical portion Wa of the workpiece W by the measuring device (sizing device) 30. The diameter of the part Wd of the plunge-ground cylindrical portion Wa is predetermined. When the output measuring device 30 outputs a signal indicating that the target value with the finishing allowance has been left, the output of the measuring device 30 is the machine coordinate system in the direction intersecting the rotation axis of the workpiece W of the grinding wheel G. The shoulder Wc, the corner Wb, and the cylindrical portion Wa of the workpiece W are successively ground based on the reset machine coordinate system based on the signal.

A workpiece W shown in FIG. 11 shows an engine crankshaft, and an oil hole O is formed substantially at the center of a cylindrical portion Wa of the crankshaft W. An arc-shaped corner portion Wb adjacent to the cylindrical portion Wa of the crankshaft W
And Japanese Patent Application Laid-Open No. 8-904 described above for grinding the shoulder portion Wc.
When the grinding method of No. 08 is used, the sizing device 30
And need to be inserted at a position T facing the cylindrical portion Wa.

[0004]

In the case where the arc-shaped corner portion Wb and the shoulder portion Wc adjacent to the cylindrical portion Wa are continuously ground, the grinding wheel G is deteriorated when the sharpness of the grinding wheel G of the shoulder portion Wc becomes poor. It is necessary to modify the entire G wheel. However, while the grinding wheel is being modified, the end surface of the grinding wheel G is scraped off, and the width of the grinding wheel G is reduced as indicated by a dashed line, and the insertion position T of the sizing device 30 is changed to the plunge grinding surface G.
s.

For this reason, conventionally, the grinding wheel G is replaced when the insertion position T of the sizing device 30 deviates from the plunge grinding surface Gs, and the grinding wheel G is replaced even though the grinding wheel G is still usable. There was a problem that had to be.

[0006]

According to a first aspect of the present invention, there is provided a grinding method for machining a grinding wheel having a plunge grinding surface parallel to a rotation axis of a workpiece and an arc grinding surface adjacent to the plunge grinding surface. With a grinding machine relatively moving with respect to the workpiece in a direction parallel to and orthogonal to the rotation axis of the workpiece, one end face of the grinding wheel is positioned at a predetermined reference position, and is moved together with the workpiece. In the method of grinding a workpiece, wherein the grinding wheel is modified and the width of the grinding wheel is narrowed, the grinding wheel is modified while measuring a part of the cylindrical portion of the workpiece by a sizing device for measuring an outer diameter of the cylindrical portion of the workpiece. When the above, the relative position between the grinding wheel and the workpiece is corrected so that the sizing device is located at a position facing the plunge grinding surface,
Thereafter, the grinding is performed while measuring the diameter of a part of the cylindrical portion of the workpiece.

Further, in the grinding method according to the present invention, the grinding wheel is positioned such that the sizing device faces the plunge grinding surface every time the grinding wheel of the grinding wheel is corrected a predetermined number of times. The plunge grinding may be performed after correcting the relative position of the workpiece and the workpiece. Further, the grinding method according to the present invention relates to a grinding wheel provided with a plunge grinding surface parallel to the rotation axis of the workpiece and an arc grinding surface adjacent to the plunge grinding surface in a direction parallel to the rotation axis of the workpiece. A sizing method for positioning one end face of the grinding wheel at a predetermined reference position by a grinder relatively moving with respect to the workpiece in a direction intersecting with the workpiece, and measuring an outer diameter of a cylindrical portion of the workpiece. In the method for grinding a workpiece, which grinds while measuring a part of the cylindrical portion of the workpiece by the apparatus, the sizing device faces the plunge grinding surface when the grinding wheel is modified and the grinding wheel width is reduced. The relative position between the grinding wheel, the workpiece and the sizing device is corrected so as to be a position, and then the grinding is performed while measuring the diameter of a part of the cylindrical portion of the workpiece.

Further, in the grinding method according to the present invention, the grinding wheel is positioned such that the sizing device is located at a position facing the plunge grinding surface every time the grinding wheel is corrected a predetermined number of times. The plunge grinding may be performed after correcting the relative positions of the workpiece and the sizing device.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where a grinding method according to the present invention is applied to grinding of an intermediate journal portion of a crankshaft of an automobile engine according to a first embodiment shown in FIGS. 1 to 7 will be described below. . First, a grinding device used in the first embodiment will be described with reference to FIGS.

A work table 12 guided and supported on a bed 11 of a grinding device 10 so as to be movable in the left-right direction (Z direction).
A headstock 14 for supporting the spindle 15 and a tailstock 16 are coaxially provided on the upper side in opposition in the left-right direction, and a workpiece (crankshaft) W is a center 15a provided on the spindle 15 and the tailstock 16. , 16a at both ends. Spindle 15
The workpiece W is rotated by a motor 14 a provided on the headstock 14, and the workpiece W is engaged with a drive pin 17 projecting from the main shaft 15 at the left end and rotated with the main shaft 15. The servo motor 25 provided on the bed 11 has a drive circuit 25 that operates based on a position command given from the numerical controller 50.
a, and feeds the workpiece table 12 in the Z direction via a feed screw mechanism (not shown). The Z-direction position of the workpiece table 12 is detected by the encoder 25b and input to the drive circuit 25a.

The headstock 14 has a grinding wheel 21 described later.
A grindstone correcting device 40 for performing the grindstone correction is mounted. The grindstone correcting device 40 includes a grindstone correcting spindle 41 that rotates around an axis parallel to the spindle 15.
, A grinding wheel correction roll 42 is attached to one end, and a motor 43 is attached to the other end. Whetstone correction roll 4
A plurality of diamond wheels 2 have a plurality of diamonds adhered to the circumferential surface and the vicinity of the tip side surface, and are driven to rotate by the rotation of the motor 43 to correct the grinding wheel 21.

A grinding wheel base 13 is guided and supported on the bed 11 so as to be movable in a horizontal X direction perpendicular to the Z direction. A grinding wheel 21 has a grinding wheel shaft 20 parallel to the main shaft 15 on the grinding wheel base 13. , And is rotationally driven by a motor 22 via a rotation transmission mechanism. The grinding wheel 21 is provided with a grinding wheel layer of a predetermined thickness formed by bonding CBN abrasive grains by vitrified bond on the outer periphery of a metal disk-shaped grinding wheel core. The servo motor 26 provided on the bed 11 is provided with the numerical controller 5
The drive is controlled by a drive circuit 26a that operates based on a position command given from 0, and feeds the grindstone table 13 in the X direction via a feed screw mechanism (not shown). The position in the X direction of the wheel head 13 is detected by the encoder 26b and input to the drive circuit 26a. As shown in FIGS. 3 and 4, at both ends of a plunge grinding surface 21 a on the outer periphery of the grinding wheel 21, an arc grinding surface 21 b for grinding an arc portion is formed. The vertical end face 21c is continuous.

As shown in FIGS. 1 and 2, a sizing device 30 is mounted on the work table 12. FIG.
As shown in the figure, the sizing device 30 can advance and retreat the measuring head 31 by a predetermined distance in the X direction by a built-in cylinder device, and the measuring head 31 is a pair of contacts 32 facing each other.
a and a pair of measuring arms 32 and 3 provided with 33a, respectively.
Three. The forward and backward movement of the measuring head 31 in the X direction is command-controlled by the numerical controller 50, and is normally at the non-operation position indicated by the two-dot chain line A in FIG. 2, but in the state of the forward position indicated by the solid line, each contact 32a , 33a engage with an intermediate portion Wd (see FIG. 3) of a cylindrical portion (intermediate journal portion) Wa, which is a surface to be ground of a workpiece (crankshaft) W being ground, so that the outer diameter thereof is continuous. And the measurement signal (analog signal) is input to the numerical controller 50 via an A / D converter (not shown).

At this time, the contacts 32a, 33a of the measuring arms 32, 33 are moved relative to a reference position P, which is L away from one crank arm We of the workpiece W in the Z direction as shown in FIG. At a position further apart by a distance H. As shown in FIG. 1, a numerical control device 50 displays a CRT for displaying data such as a grinding state of the grinding device 10.
And an input / output device 51 composed of a keyboard for inputting control data, operation commands and the like.

The numerical controller 50 mainly stores various data such as a grinding program, the diameter and width of the grinding wheel 21, the number of times of grinding wheel correction, and the allowance for each grinding wheel repair, and the like. And an interface 54 for executing a grinding program. The numerical controller 50 receives a command from the input / output device 51, a grinding program and various data stored in the memory 52, and an input signal from the sizing device 30, and the like.
The operation of the workpiece table 12, the grindstone table 13, the sizing device 30, the grindstone correcting device 40, and the like is controlled to operate the grinding device 10.

Next, a first embodiment of the grinding method executed by the grinding apparatus configured as described above will be described with reference to FIGS. 3 to 5 and FIGS. explain. 3 to 5 show only the cylindrical portion Wa of the workpiece W and the crank arms We on both sides thereof, and the other portions are omitted. When a grinding start command is given from the input / output device 51 in a state where the grinding wheel 21 is rotating and the grinding wheel base 13 is at the original processing position shown in FIG. 1, the numerical controller 50 sets various variables to predetermined values. Is reset to the initial value, the workpiece W supported by the headstock 14 and the tailstock 16 is rotated (step 100).
Next, the numerical controller 50 moves the workpiece table 12, and the crank arm We of the workpiece W as shown in FIG.
One end face 21c of the grinding wheel 21 is positioned at a reference position P separated by L from. (Step 101) Next, the numerical controller 50 activates the built-in cylinder device, advances the measuring head 31 from the position indicated by the two-dot chain line A to the position indicated by the solid line, and contacts the contacts 32a, 32a of the measuring arms 32, 33. The tip of 33a is engaged with the intermediate portion Wd of the cylindrical portion Wa of the workpiece W (Step 102).

Next, the numerical controller 50 controls the servo motor 2
6, the grinding surface 21a of the grinding wheel 21 is moved to the intermediate portion Wd.
After the grindstone table 13 is rapidly advanced and advanced to a point short of contact with the workpiece (step 103), the grindstone table 13 is advanced by coarse grinding feed to perform plunge grinding of the intermediate portion Wd of the cylindrical portion Wa (step 1).
04). The plunge grinding is performed by direct dimensional grinding in which a measurement signal (analog signal) of the outer diameter of the intermediate portion Wd obtained from the measurement head 31 is input to the numerical controller 50 every moment. The engagement of the sizing device 30 with the intermediate portion Wd of the cylindrical portion Wa may be performed in the course of the rough grinding feed in which the pre-processed surface of the intermediate portion Wa is removed.

The intermediate portion Wd detected by the sizing device 30
If the outer diameter detection signal reaches D + 2t (D is the finishing diameter of the cylindrical portion Wa, t is the finishing allowance) in diameter (see FIG. 3),
The numerical controller 50 stops the feed of the grindstone table 13, ends the rough grinding, and resets the machine coordinate system (step 10).
5), the wheel head 13 and the sizing device 30 are retracted to predetermined positions (Step 106). The resetting of the machine coordinate system includes the nominal outer diameter of the intermediate portion Wd of the workpiece W determined by the distance from the tip position of the grinding wheel 21 to the axis of the spindle 15 at the end of the rough grinding, and the sizing device 30. The deviation amount of the actual outer diameter of the intermediate portion Wd detected by the above is obtained, and the tip position of the grinding wheel 21 is reset so as to correspond to the actual outer diameter. As a result, the distance from the tip position of the grinding wheel 21 to the axis of the main shaft 15 coincides with the actual outer diameter of the intermediate portion Wd, and in the subsequent indirect sizing performed without using the sizing device 30. , Highly accurate cylindrical part W
a can be processed.

Next, the numerical controller 50 positions the workpiece table 12 at a contouring grinding start position where the workpiece W and the grinding wheel 21 have a relationship shown by a solid line in FIG. 4 (step 107). Based on the plurality of contouring grinding program blocks included in the above, the position of the grindstone table 13 is controlled in the reset machine coordinate system, thereby performing contouring grinding by indirect sizing (step 108).

In the contour grinding, the numerical controller 50 first cuts the grinding wheel base 13 in the X direction, moves the grinding wheel 21 with respect to the workpiece W as shown by an arrow F1 in FIG. Finish grinding of Wc is performed, and then, the Z direction feed of the work table 12 and the X direction feed of the grindstone table 13 are combined to move the grinding wheel 21 in an arc shape with respect to the work W as shown by an arrow F2. The corner Wb is finished and ground in an arc shape. In the state where the finish grinding of the corner Wb is completed, about half of the cylindrical portion Wa is finish ground by the grinding wheel 21 and the diameter thereof becomes the finish diameter D. Next, the numerical controller 50 sends the workpiece table 12 in the Z direction (traverse direction), moves the grinding wheel 21 with respect to the workpiece W as shown by an arrow F3, and finish-grinds the cylindrical portion Wa to the center portion. Then, as shown by an arrow F4, the grindstone table 13 is once retracted to a predetermined position. Subsequently, the numerical controller 50 sends the workpiece table 12 in the Z direction, moves the grinding wheel 21 with respect to the workpiece W as shown by an arrow F5, and moves the grinding wheel 21 to the right shoulder portion Wc.
And the grinding wheel 21 is moved with respect to the workpiece W as shown by arrows F6, F7, and F8 to finish the right shoulder Wc, corner Wb, and cylindrical Wa. Grind.

When the above-described contouring grinding is completed, the numerical controller 50 retracts the grindstone table 13, stops the workpiece W, and terminates the processing of the workpiece W. (Step 109) When the machining of the workpiece W is completed, the numerical controller 50 increases the number of machining stored in the memory 52 by 1 (step 110), and then determines whether the number of machining has reached a value for performing the grinding wheel correction. It is checked whether or not it is (step 111).

As a result of this check, if the number of processed pieces has not reached the number to perform the grinding wheel correction, the operation is stopped until a grinding start command for a new workpiece or a processed portion is input from the input / output device 51. On the other hand, when the number of processing has reached the number of grindstones to be modified, a grindstone modification operation shown in detail in FIG. 7 is executed (step 112). In the grinding wheel correcting operation, the numerical controller 50 controls the motor 43 of the grinding wheel correcting device 40.
Is started, the grindstone correction roll 42 is rotated, the workpiece table 12 and the grindstone table 13 are moved, and a cut of half of the allowance S is made from one end face 21c of the grindstone wheel 21 as shown in FIG. After the application, the grinding wheel 21 is fed in the X direction to perform the grinding wheel correction. Then, return the grinding wheel 21,
The numerical controller 50 simultaneously moves the grindstone table 13 and the workpiece table 12, and moves the end surface 21 as shown in FIG.
arc grinding surface 21b and plunge grinding surface 21 continuous with c
After removing a by half of the allowance S, as shown in FIG. 7 (a), the plunge grinding surface 21a, the arcuate grinding surface 21b continuous with the plunge grinding surface 21b, and the other end surface 21c are subjected to grinding wheel modification.

Further, this time, as shown in FIG. 7 (b), a cut is made from the other end face 21c of the grinding wheel 21 by half of the allowance S, and the plunge is operated in the reverse manner as above. The grindstone of the grinding surface 21a, the arcuate grinding surface 21b continuous with the grinding surface 21a, and the one end surface 21c is corrected. As a result, the plunge ground surface 21a, both arc ground surfaces 21b, and both end surfaces 21C are cut off by the allowance S.

Next, the numerical controller 50 retracts the grindstone table 13 and the workpiece table 12, and subtracts the diameter and width of the grinding wheel 21 stored in the memory 52 by twice the margin S, that is, 2S (step 114). ). When the above-described grinding wheel correction cycle is completed, the grinding device stops its operation until a grinding start command is input from the input / output device 51.

Next, the next time a grinding start command is input from the input / output device 51 to the numerical controller 50, the flowchart shown in FIG. 6 is executed again. At this time, the grinding wheel 2
As shown in FIG. 5 (a), the width of No. 1 is 2 of the allowance S from the previous time.
2S times smaller, and the grinding wheel 21
When positioning at the same position as the previous position of d, the contacts 32a, 3
3a is inserted at a position that does not face the plunge grinding surface 21a.

However, in this embodiment, the workpiece 12 is corrected by adjusting the feed amount of the tape 12 by the above-mentioned 2S so that the right end face 21c of the grinding wheel 21 coincides with the reference position P as shown in step 101 of FIG. The table 12 is positioned (FIG. 5B), and thereafter, plunge grinding is performed as shown in FIG. 5C. As described above, in the present embodiment, the feed amount of the tape 12 is corrected by twice the stock removal S by the grindstone correction, that is, 2S so that the right end surface 21a of the grindstone is positioned at the reference position P each time the grindstone is corrected. As a result, the diameter of the cylindrical portion Wa can be measured at the fixed position of the contacts 32a and 33a facing the plunge grinding surface 21a, and stable processing accuracy can always be obtained.

Next, a second embodiment shown in FIG. 8 will be described. The grinding apparatus used in the second embodiment is different from the first embodiment in that the function and the mounting position of the sizing device 30 are different from those of the first embodiment shown in FIG. . In FIG. 8, a sizing device 30 is attached so as to be movable on the bed 11 in the Z direction. The servomotor 34 provided on the bed 11 is driven and controlled by a drive circuit 34a that operates based on a position command given from a numerical controller 50, and has a feed screw 35 and a sizing device having the same configuration as that of the first embodiment. 30 in the Z direction.

The second embodiment of the grinding method executed by the grinding apparatus configured as described above will be described with reference to the flowchart shown in FIG. Note that the flowchart shown in FIG. 9 only partially differs from the flowchart used to describe the first embodiment shown in FIG. 6, and therefore only this difference is shown. In the second embodiment, the grinding wheel 21 is corrected and is twice as large as the allowance S, that is, 2 times.
In a state where the width of the grinding wheel 21 is reduced by S, FIG.
The operation of the grinding device when the flowchart shown in FIG.

As shown in step 101, the workpiece table 12 is positioned by correcting the feed amount of the tape 12 by the above 2S so that the right end face 21c of the grinding wheel 21 coincides with the reference position P (step 101). FIG. 10A). In the second embodiment, unlike the first embodiment, since the sizing device 30 is attached to the bed 11, only the workpiece W moves when executing up to step 101, and the sizing device 30 and the grinding wheel The positional relationship of the car 21 is unchanged. For this reason, after positioning the work table 12, as shown in FIG.
2a and 33a move to a position separated by a distance h from a reference position P facing the plunge grinding surface 21a (step 101a).

Thereafter, the plunge grinding and contouring grinding operations similar to those of the first embodiment are performed in step 102 for moving the fixed size head forward and thereafter. Note that the distance h is a value determined by the following equation.

[0031]

H = H + (S * n) where H is the reference position P when the grinding wheel 21 is replaced and the contact 3
The initial value of the distance between 2a, S is the allowance of the grinding wheel by the grinding wheel correction, and n is the number of times the grinding wheel is corrected. As described above, even when the sizing device 30 is mounted on the bed 11, the same effects as those of the first embodiment can be obtained.

In each of the above embodiments, a description has been given of the grinding apparatus in which the work table 12 moves in the Z direction and the grindstone table 13 moves in the X direction, but the grindstone table 13 is moved in the X and Z directions. It is also applicable to possible grinding devices. Further, in the above embodiment, the positional relationship between the grinding wheel 21 and the sizing device 30 is corrected each time the grinding wheel is corrected, but the plunge grinding surface 21a and the contacts 32a, 3
If the only purpose is to make the 3a face each other, the grindstone correction is executed a plurality of times and the contacts 32a, 3
Numerical control unit 50 determines whether or not 3a no longer faces plunge grinding surface 21a of grinding wheel 21 or contacts 32
The number of times that the grinding wheels 21a and 33a no longer face the plunge grinding surface 21a of the grinding wheel 21 is experimentally determined in advance and stored in the memory 5
2, and the positional relationship between the grinding wheel 21 and the sizing device 30 may be corrected every several times the grinding wheel is corrected.

[0033]

As described above, according to the present invention, the sizing device is always positioned at the position facing the plunge grinding surface even after the grinding wheel is modified, so that the contact does not conventionally face the plunge grinding surface. While the grinding wheel had to be replaced when it reached the position, in the present invention the sizing device is always inserted at a position facing the plunge grinding surface even if the grinding wheel width changes due to grinding wheel correction, so the grinding wheel Can be used longer than before.

If the feed amount is corrected so that the end face of the grinding wheel is positioned at the reference position each time the grinding wheel is corrected, the sizing device always measures the diameter at the same position of the cylindrical portion facing the grinding surface. And stable processing accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a grinding device used in a first embodiment of the present invention.

FIG. 2 is a partial side view showing a main part of the sizing device.

FIG. 3 is an explanatory diagram showing a state at the time of finishing fine grinding by plunge grinding according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a finish grinding state by contouring grinding according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of an operation of positioning an end surface of the grinding wheel according to the first embodiment of the present invention at a reference position.

FIG. 6 is a flowchart showing the operation of the first embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating an operation of a grinding wheel correction cycle according to the first embodiment of the present invention.

FIG. 8 is a diagram showing an overall configuration of a grinding device used in a second embodiment of the present invention.

FIG. 9 is a flowchart showing the operation of the second embodiment of the present invention.

FIG. 10 is an explanatory diagram of an operation of positioning an end face of a grinding wheel at a reference position according to a second embodiment of the present invention.

FIG. 11 is an explanatory diagram of a conventional technique. 10: Grinding device, 12: Work table, 13: Grinding wheel stand, 21: Grinding wheel, 21a: Plunge grinding surface, 21b ...
Circular grinding surface, 21c: end face, 30: sizing device, 40: grinding wheel correction device, P: reference position, W: workpiece, Wa: cylindrical portion, Wb: corner portion.

Claims (4)

[Claims] 1. A grinding wheel having a plunge grinding surface parallel to a rotation axis of a workpiece and an arc grinding surface adjacent to the plunge grinding surface is machined in a direction parallel to the rotation axis of the workpiece and a direction crossing the same. A sizing method for positioning one end surface of the grinding wheel at a predetermined reference position by a grinder relatively moving with respect to the workpiece, and moving with the workpiece to measure an outer diameter of a cylindrical portion of the workpiece. In a workpiece grinding method for grinding while measuring a part of a cylindrical portion of the workpiece by an apparatus, a position where the sizing device faces the plunge grinding surface when the grinding wheel is modified and the grinding wheel width is reduced. Correct the relative position of the grinding wheel and the workpiece so that
Thereafter, the grinding is performed while measuring a diameter of a part of the cylindrical portion of the workpiece. 2. The method according to claim 1, wherein the correction of the relative position between the grinding wheel and the workpiece is performed every time the grinding wheel is corrected a predetermined number of times. 3. A grinding wheel having a plunge grinding surface parallel to a rotation axis of a workpiece and an arc grinding surface adjacent to the plunge grinding surface is machined in a direction parallel to the rotation axis of the workpiece and in a direction crossing the same. With a grinding machine that moves relative to the workpiece, one end face of the grinding wheel is positioned at a predetermined reference position, and a sizing device that measures an outer diameter of a cylindrical portion of the workpiece is used for the grinding of the workpiece. In a method of grinding a workpiece that grinds while measuring a part of a cylindrical portion, the grinding wheel is located at a position where the sizing device faces the plunge grinding surface when the grinding wheel is modified and the grinding wheel width is reduced. Wherein the relative position of the workpiece and the sizing device is corrected, and thereafter the grinding is performed while measuring the diameter of a part of the cylindrical portion of the workpiece. 4. The method of grinding a workpiece according to claim 3, wherein the correction of the relative positions of the grinding wheel, the workpiece and the sizing device is performed every time the grinding wheel is corrected a predetermined number of times.