Grinding method and grinding machine

Abstract

To provide a technique that can suppress elongation of a shaft grinding time.SOLUTION: A grinding method comprises a process in which a reference journal is rotated around a rotation axis so as to decenter a reference center axis of the reference journal from the rotation axis by only an eccentricity, and an abrasive wheel feed operation is controlled on the basis of the eccentricity and a phase to perform grinding of the reference journal.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to grinding methods and grinding machine technology. [Background technology]

[0002] A conventional technique for grinding crankshafts using a grinding wheel of a grinding machine is known (Patent Document 1). In the technique of Patent Document 1, the amount of eccentricity of the rotation axis of the crankpin journal caused by pressure support of the center and the phase of the eccentricity are determined, and the feed operation of the grinding wheel is controlled taking the determined amount of eccentricity into consideration to grind the crankpin and crankpin journal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-76961 Summary of the Invention [Problem to be solved by the invention]

[0004] In the past, when the degree of bending of a crankshaft due to the release of residual stress is so great that the central axes of multiple crank journals are significantly misaligned with each other, it may be necessary to perform rough machining on the crank journals using a grinding machine to release the residual stress and then perform finish machining to prevent the misalignment of the central axes. This requires two grinding stages, which can lengthen the grinding time for the crankshaft. This issue is not limited to crankshafts, but is common to any shaft with multiple journals. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to a first aspect of the present disclosure, there is provided a grinding method for grinding a shaft having multiple journals using a grinding machine. The multiple journals are arranged side by side in the axial direction of the shaft and include a reference journal and other journals. The grinding machine includes a headstock having a main spindle that supports the shaft and is driven to rotate about a rotation axis, a grinding wheel head that rotatably supports a disk-shaped grinding wheel, a drive unit that performs a feed operation of the grinding wheel to move the grinding wheel relatively toward or away from the shaft in a direction intersecting the rotation axis, and a control unit that controls the position of the grinding wheel relative to the shaft in accordance with the angular position of the headstock, thereby grinding the journals with the grinding wheel to have a circular cross-sectional shape. This grinding method includes the steps of: (a) receiving an input of an eccentricity amount of the reference central axis in the grinding process, the eccentricity amount being set so that the reference central axis, which is the central axis of a reference journal, is closer to the other central axes, which are the central axes of the other journals, than when the grinding process is performed so that the center axes of the plurality of journals are positioned on the rotation axis; (b) receiving an input of a phase of the reference journal with respect to the rotation axis; and (c) rotating the reference journal in a whirling manner about the rotation axis so that the reference central axis of the reference journal is eccentric from the rotation axis by the eccentricity amount, and controlling the feed operation of the grinding wheel based on the eccentricity amount and the phase, thereby grinding the reference journal. According to this embodiment, the reference central axis of the reference journal is eccentric from the rotation axis by the eccentricity amount set so that the reference central axis approaches the other central axes, and controlling the feed operation of the grinding wheel based on the eccentricity amount and the phase, thereby grinding the reference journal. This makes it possible to prevent the central axes of multiple journals from becoming significantly misaligned with one another through a single grinding step, without having to perform rough grinding on the journals to release residual stress and then finish grinding them, thereby shortening the grinding time for the shaft. (2) The above-described embodiment may further include a step (d) of rotating the other journal about the rotation axis so that the other central axis of the other journal is positioned on the rotation axis, and then performing the grinding process on the other journal. According to this embodiment, the other journal is ground without being eccentric, so that the central axis of the reference journal can be brought closer to the central axis of the other journal. (3) In the above embodiment, the plurality of journals may include a one-end journal located on one end side, an other-end journal located on the other end side, and one or more intermediate journals located between the one-end journal and the other-end journal, and steps (a) to (c) may be performed with the one-end journal and the other-end journal as the reference journals and the intermediate journal as the other journal. According to this embodiment, the central axes of the one-end journal and the other-end journal can be brought closer to the central axis of the intermediate journal. (4) In the above embodiment, the plurality of journals may include a one-end journal located on one end side, an other-end journal located on the other end side, and one or more intermediate journals located between the one-end journal and the other-end journal, and steps (a) to (c) may be performed with the intermediate journal as the reference journal. According to this embodiment, the central axis of the intermediate journal can be brought closer to the central axis of the one-end journal and the central axis of the other-end journal. (5) According to a second aspect of the present disclosure, there is provided a grinding machine for grinding a shaft having a plurality of journals. The plurality of journals are arranged in a line in the axial direction of the shaft and include a reference journal and other journals. The grinding machine includes a headstock for supporting the shaft, the headstock having a spindle that is driven to rotate about a predetermined rotation axis, a grinding wheel head for rotatably supporting a disk-shaped grinding wheel, a drive unit for executing a feed operation of the grinding wheel to move the grinding wheel relatively toward or away from the shaft in a direction intersecting the rotation axis, and a control unit for controlling the position of the grinding wheel relative to the shaft in accordance with the angular position of the spindle, thereby grinding the journals with the grinding wheel so that their cross-sectional shapes are circular, and the control unit controls the grinding of the plurality of journals so that the central axes of the plurality of journals are aligned on the rotation axis. The grinding device receives an input of an eccentricity amount of the reference central axis in the grinding process from the rotation axis, which is set so that the reference central axis, which is the central axis of the reference journal, is closer to the other central axis, which is the central axis of the other journal, than when grinding is performed, receives an input of a phase of the reference journal with respect to the rotation axis, rotates the main spindle in a state in which the reference central axis of the reference journal is eccentric from the rotation axis by the eccentricity amount, thereby causing the reference journal to whirl and rotate about the rotation axis, and controls the feed operation of the grinding wheel based on the eccentricity amount and the phase of the reference journal to grind the reference journal. According to this embodiment, the reference central axis is eccentric from the rotation axis by the eccentricity amount set so that the reference central axis of the reference journal is closer to the other central axis, and controls the feed operation of the grinding wheel based on the eccentricity amount and the phase to grind the reference journal. This makes it possible to prevent the central axes of multiple journals from becoming significantly misaligned with one another through a single grinding step, without having to perform rough grinding on the journals to release residual stress and then finish grinding them, thereby shortening the grinding time for the shaft. The present disclosure can be realized in various forms, and in addition to the grinding method and grinding machine described above, it can also be realized in the form of, for example, a computer program for causing a computer to execute the grinding method. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a diagram showing a grinding machine according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a crankshaft ground by a grinding machine. [Figure 3] A diagram illustrating bending of the crankshaft due to stress relief. [Figure 4] 10 is a flowchart showing a process for calculating an amount of eccentricity and an initial phase. [Figure 5] FIG. 4 is a diagram for explaining the amount of eccentricity and the initial phase. [Figure 6] 4 is a flowchart showing a process for grinding a crank journal. [Figure 7] FIG. 10 is a diagram showing control of the feed operation of the grinding wheel. [Figure 8] FIG. 10 is a diagram showing control of the feed operation of the grinding wheel. [Figure 9] FIG. 10 is a diagram showing control of the feed operation of the grinding wheel. [Figure 10] FIG. 10 is a diagram showing control of the feed operation of the grinding wheel. [Figure 11] FIG. 10 is a diagram showing control of the feed operation of the grinding wheel. [Figure 12] Figure 1 shows the crankshaft evaluation. [Figure 13] Figure 2 shows the crankshaft evaluation. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Implementation: FIG. 1 is a diagram showing a grinding machine 10 according to an embodiment. FIG. 1 shows X, Y, and Z axes that are orthogonal to each other. Other figures also show X, Y, and Z axes corresponding to FIG. 1 as necessary. The grinding machine 10 grinds a crankshaft W, which is an example of a shaft that is a workpiece. Note that grinding by the grinding machine 10 according to this embodiment is not limited to crankshafts W, but can also be applied to other types of shafts having multiple journals, such as camshafts.

[0009] The grinding machine 10 includes a bed 1, a workpiece table 2, a pair of guide surfaces 22, a table movement motor 21, a grinding wheel head 5, a V-shaped guide surface 57, a flat guide surface 56, a grinding wheel head drive motor 51, a control device 8, and drive circuits 97, 98, and 99.

[0010] The workpiece table 2 is mounted on the bed 1 so as to be movable in the Z-axis direction along a pair of guide surfaces 22. The table movement motor 21 is computer numerically controlled (CNC) by the control device 8, and moves the workpiece table 2 in the Z-axis direction by rotating a feed screw (not shown). The table movement motor 21 has a table encoder 21a, and a signal from the table encoder 21a is fed back to the drive circuit 97.

[0011] The grinding machine 10 further has a first headstock 3 and a tailstock 4 arranged on the workpiece table 2. The first headstock 3 has a spindle center 33, a drive fitting 34, a drive pin 36, a spindle rotation motor 31, and a spindle encoder 38. The tailstock 4 has a tailstock spindle 42, a tailstock center 43, and a tailstock movement motor 41.

[0012] The first headstock 3 has a spindle 32 having a rotation axis Rj parallel to the Z axis. The spindle 32 supports a crankshaft W and is driven to rotate about the rotation axis Rj. A spindle rotation motor 31 drives the spindle 32 to rotate. A spindle encoder 38 is disposed on the spindle rotation motor 31 and detects the phase of the spindle 32 (angular position about the rotation axis Rj). The first headstock 3 is disposed on one end side of the work table 2 in the axial direction along the rotation axis Rj of the spindle 32.

[0013] The tailstock 4 is disposed on the other end of the workpiece table 2 in the axial direction. The tailstock 4 is movable along the axial direction by being driven by a tailstock movement motor 41. The tailstock shaft 42 is driven to rotate in synchronization with the main spindle 32. The tailstock center 43 is attached to the tailstock shaft 42. The main spindle center 33 and the tailstock center 43 face each other on the rotation axis Rj of the main spindle 32. When a second headstock is used instead of the tailstock 4, the second headstock has a motor that drives the tailstock center 43 and an encoder that detects the phase of the motor. The main spindle center 33 supports one end of the crankshaft W. One end of the drive pin 36 is attached to the main spindle 32, and the other end is rotationally engaged with the drive fitting 34. The drive fitting 34 is fixed to one end of the crankshaft W. The drive pin 36 and the drive fitting 34, together with the spindle center 33, transmit the rotational force around the rotation axis Rj to the crankshaft W. The tailstock center 43 supports the other end of the crankshaft W. The tailstock center 43 applies a force to the crankshaft W that pushes the crankshaft W toward the spindle center 33.

[0014] The wheel head 5 is mounted on the bed 1. The wheel head 5 is movable in the X-axis direction, which is perpendicular to the axial direction of the crankshaft W, along a V-shaped guideway 57 and a flat guideway 56. The wheel head drive motor 51, which serves as a drive device, is computer numerically controlled (CNC) by a control device 8 and rotates a feed screw (not shown) to move the wheel head 5 in the X-axis direction. In other words, the wheel head drive motor 51 performs a feed operation of the grinding wheel 55, moving the grinding wheel 55 toward or away from the crankshaft W in the X-axis direction, which intersects with the rotation axis Rj of the main spindle 32. An encoder 58 is attached to the wheel head drive motor 51. The wheel head 5 includes a disk-shaped grinding wheel 55 that grinds the crankshaft W, a grinding wheel spindle 54 that rotatably supports the grinding wheel 55, and a grinding wheel rotation motor 52 that rotates the grinding wheel spindle 54 via a belt 53.

[0015] The control device 8 includes a storage unit 82 configured with ROM and RAM, and a processor 84 that executes the programs stored in the storage unit 82. The storage unit 82 stores a standard machining program 85, an eccentricity machining program 86, workpiece information 87, and grinding wheel information 88.

[0016] The standard machining program 85 is a program for rotating the crank journal J about the rotation axis Rj to grind the crank journal J without controlling the feed operation of the grinding wheel 55 according to the phase of the crank journal J to be ground. In the standard machining program, the target position of the center axis Lj of the crank journal J is on the rotation axis Rj. Strictly speaking, in the standard machining program, the position of the center axis Lj is slightly offset from the rotation axis Rj of the main spindle 32, so the crank journal J to be ground rotates in a whirling manner relative to the rotation axis Rj. In the standard machining program 85, grinding conditions such as the cutting speed and cutting amount of the grinding wheel 55 are set.

[0017] The eccentricity machining program 86 is a program for rotating the crank journal J in a whirling manner about the rotation axis Rj so that the central axis Lj of the crank journal J to be ground is eccentric from the rotation axis Rj by a predetermined eccentricity amount d (described later), and for controlling the feed operation of the grinding wheel 55 based on the eccentricity amount d and the rotation phase α (also simply referred to as "phase α") of the crank journal J to be ground, thereby grinding the crank journal J. The eccentricity machining program 86 has set grinding conditions such as the cutting speed of the grinding wheel 55, the cutting amount of the grinding wheel 55, the previously calculated eccentricity amount d, and an initial phase αi (described later).

[0018] The workpiece information 87 stores information about the crank journals J, which are the workpieces to be ground. The workpiece information 87 includes the diameters of the crank journals J1 to J5 before grinding, the target diameters of the crank journals J1 to J5 after grinding, etc. The grinding wheel information 88 stores information about the grinding wheel 55. The grinding wheel information 88 includes the diameter of the grinding wheel 55, etc.

[0019] The control device 8 controls the operation of the grinding machine 10 based on operation commands from the processor 84. Specifically, the control device 8 numerically controls the motors 21, 41, 51, and 52 in accordance with a grinding program. For example, the control device 8 controls the position of the grinding wheel 55 relative to the crankshaft W in accordance with the rotational phase (angular position) of the main spindle 32, thereby grinding the crank journal of the crankshaft W with the grinding wheel 55 so that its cross section has a circular shape. The control device 8 acquires the phase of the main spindle 32 from the main spindle encoder 38 and outputs drive commands generated by the processor 84 to drive circuits 97, 98, and 99. The processor 84 of the control device 8 includes a grinding wheel position calculation unit 89. The grinding wheel position calculation unit 89 calculates the position of the grinding wheel 55 when executing the eccentricity processing program. The grinding wheel position calculation unit 89 calculates the distance X between the rotation axis Og of the grinding wheel 55 and the rotation axis Rj of the spindle 32 using the eccentricity d set in the eccentricity machining program 86, the radius ra of the crank journal J before grinding stored in the workpiece information 87, the radius Ra of the grinding wheel 55 stored in the grinding wheel information 88, and the phase α given as a drive command to the spindle rotation motor 31. The control device 8 controls the feed operation of the grinding wheel 55 according to the calculated distance X. The method of calculating the distance X and the feed operation of the grinding wheel 55 will be described later.

[0020] The drive circuit 97 controls the operation of the table moving motor 21 in response to a drive command from the processor 84. The drive circuit 98 controls the operation of the wheel head drive motor 51 in response to a drive command from the processor 84. The drive circuit 99 controls the operation of the spindle rotation motor 31 in response to a drive command from the processor 84.

[0021] The grinding machine 10 further has a dial gauge 62 that can advance and retreat relative to the crankshaft W. In this embodiment, the dial gauge 64 is of a lever type. The dial gauge 62 is used to measure the eccentricity d of the central axis Lj of the crank journal J from the rotation axis Rj. When measuring the eccentricity d, the spindle 61, which is the measuring point of the dial gauge 64, comes into contact with the uppermost part of the outer circumferential surface of the crank journal J.

[0022] FIG. 2 is a diagram showing an example of a crankshaft W ground by the grinding machine 10. The crankshaft W shown in FIG. 2 is a single-plane crankshaft for an in-line four-cylinder engine. The crankshaft W has four crank pins P1 to P4 and five crank journals J1 to J5. The crank journals J1 to J5 are cylindrical. The crank pins P1 to P4 are cylindrical, each having a central axis Lp that is radially eccentric from the central axis Lj of the crank journals J1 to J5. Here, when distinguishing between the crank journals J1 to J5, the following terms will be used: first crank journal J1, second crank journal J2, third crank journal J3, fourth crank journal J4, and fifth crank journal J5. The first crank journal J1 is a one-end crank journal located at one end of the crankshaft W. The fifth crank journal J5 is an other-end crank journal located at the other end of the crankshaft W. The second to fourth crank journals J2 to J4 are intermediate crank journals located between the first crank journal J1 and the fifth crank journal J5. The center axis of the first crank journal J1 is referred to as the first center axis Lj1, the center axis of the second crank journal J2 is referred to as the second center axis Lj2, the center axis of the third crank journal J3 is referred to as the third center axis Lj3, the center axis of the fourth crank journal J4 is referred to as the fourth center axis Lj4, and the center axis of the fifth crank journal J5 is referred to as the fifth center axis Lj5. The center axis Lj of the crank journals J1 to J5 is the center axis when the first center axis Lj1 to the fifth center axis Lj5 are aligned.

[0023] FIG. 3 is a diagram illustrating bending of a crankshaft W due to stress relief. A crankshaft W before grinding (also simply referred to as the "unprocessed crankshaft W") undergoes forging and other processes in the manufacturing process prior to grinding, which generates residual stress. If a crankshaft W with residual stress before grinding is ground using a grinding machine 10 so that the first center axis Lj1 to the fifth center axis Lj5 are aligned with the rotation axis Rj, bending of the crankshaft W may occur due to stress relief. Therefore, in conventional technology, if the bending of the crankshaft W due to stress relief is significant, a two-stage grinding process, consisting of rough grinding and finish grinding, is performed as described below. Specifically, the crank journals J1 to J5 of the unprocessed crankshaft W are rough-processed using the grinding machine 10 to release stress and straighten the bending. Then, the crank journals J1 to J5 of the stress-released crankshaft W are finish-processed again using the grinding machine 10. The crank pins P1 to P5 are ground before stress release, for example, before the crank journals are roughly ground. In this embodiment, however, taking into consideration bending due to the release of residual stress, the crank journals J1 to J5 are ground in a single step by eccentrically positioning the center axis Lj of one of the crank journals J1 to J5 relative to the rotation axis Rj. This process is described in detail below.

[0024] 4 is a flowchart showing the process of calculating the eccentricity d and the initial phase αi. In the following example, a first crank journal J1, which is a one-end journal located on one end side of the plurality of crank journals J1 to J5, and a fifth crank journal J5, which is an other-end journal located on the other end side, are set as reference journals (reference crank journals), and an example will be described in which grinding is performed by making these reference journals eccentric.

[0025] First, using a standard machining program stored in the control device 8, the first to fifth crank journals J1 to J5 of a test unmachined crankshaft Wt are ground (test grinding) by the grinding machine 10 (step S10). The test crankshaft Wt and the crankshaft w have the same shape and are made of the same material. In the standard machining program, the crank journals J1 to J5 are ground by the grinding wheel 55 so that the target positions of the first center axis Lj1 to the fifth center axis Lj5 are located on the rotation axis Rj of the main spindle 32.

[0026] Next, in step S20, the eccentricity d and initial phase αi of the first crank journal J1 and the fifth crank journal J5 are measured. In step S20, the pressing force applied to the crankshaft W by the first headstock 3 and the tailstock 4 is released for the test crankshaft Wt, whose residual stress has been released by grinding. As a result, the crankshaft Wt bends due to the release of residual stress, as shown in FIG. 3 . Then, with the spindle 61 of the dial gauge 62 in contact with the top of the outer circumferential surface of the crank journal J, the main shaft 32 is rotated to rotate the crankshaft Wt once around the rotation axis Rj. When the measurement values ​​of the dial gauge 62 for each phase α of the crank journal J of the crankshaft Wt are measured as the runout, the control device 8 determines the maximum runout, which is the measurement value with the largest positive value, as the eccentricity d, and inputs the phase α at the maximum runout as the initial phase αi into the memory unit 82. The phase α is detected by the spindle encoder 38 and transmitted to the control device 8. In this embodiment, the eccentricity amount d and the initial phase α are measured for each of the first crank journal J1 and the fifth crank journal J5 to be ground by the eccentricity machining program, and input to the memory unit 82. The phase α is the angle formed between the Y axis and a line connecting the central axis Lp of the crank pin P1 and the central axis Lp of the crank pin P2. In the phase α, the crank pin P1 is positioned directly above, the crank pin P2 is positioned directly below, and the line connecting the central axis Lp of the crank pin P1 and the central axis Lp of the crank pin P2 is positioned on the Y axis, which is defined as 0°. In this embodiment, the maximum runout occurs when the phase α is 0°.

[0027] FIG. 5 is a diagram illustrating the eccentricity d and initial phase αi of the first crank journal J1 and the fifth crank journal J5. As described above, the measured eccentricity d and initial phase αi are input and stored in the memory unit 82. The eccentricity d represents the distance between the rotation axis Rj and the central axis Lj. When the first crank journal J1 and the fifth crank journal J5 are eccentrically machined, the eccentricity d, which is a machining condition, is set to a value such that the reference central axis, which is the central axis of the reference crank journal, is closer to the other central axes, which are the central axes of the other crank journals, than when the crank journals J1 to J5 are ground so that their respective central axes Lj1 to Lj5 are aligned on the rotation axis Rj. The initial phase αi is the rotational angle position of the central axis Lj relative to the rotation axis Rj. In this way, the degree of misalignment between the rotation axis Rj and the central axes Lj1 and Lj5 is measured based on the eccentricity d and the initial phase αi.

[0028] 6 is a flowchart showing the steps of grinding the crank journals. The control device 8 grinds the first crank journal J1 and the fifth crank journal J5, which are reference crank journals, by sequentially executing an eccentricity machining program on the first crank journal J1 and the fifth crank journal J5 (step S50). When the eccentricity machining program is executed, the phases α of the first crank journal J1 and the fifth crank journal J5 are detected by the spindle encoder 38 and input to the control device 8. In step S60, the control device 8 grinds the second to fourth crank journals J2 to J4, which are the other crank journals, by sequentially executing a standard machining program on the second to fourth crank journals J2 to J4 (step S60). In the standard machining program, the target positions of the center axes Lj2 to Lj4 of the second to fourth crank journals J2 to J4 are set on the rotation axis Rj, and the second to fourth crank journals J2 to J4 are ground by whirling and rotating about the rotation axis Rj. Note that the order of steps S50 and S60 is not limited to this.

[0029] 7 to 11 are diagrams illustrating control of the feed operation of the grinding wheel 55 by the eccentricity machining program. FIGS. 7 to 11 are schematic diagrams of the grinding wheel 55 and the crankshaft W projected onto an XY plane perpendicular to the rotation axis Rj. FIGS. 7 to 11 illustrate an example in which the first crank journal J1 is ground using the eccentricity machining program. When the first crank journal J1 is ground using the eccentricity machining program so that the first central axis Lj1 is positioned at a position displaced from the rotation axis Rj by the eccentricity amount d, the control device 8 controls the feed operation of advancing or retracting the grinding wheel 55 based on the eccentricity amount d1 and the phase α of the first crank journal J1 relative to the rotation axis Rj.

[0030] First, when executing the eccentricity machining program, as shown in FIG. 9, the crankshaft W is set on the grinding machine 10 so that the phase α of the crank journal J1 to be ground is the initial phase αi. In this embodiment, the initial phase αi is 0°, so when grinding the first crank journal J1, the crankshaft W is set at a position where the phase α, which is the initial phase αi, is 0°. Then, regardless of the phase α, the control device 8 controls the feed operation of the grinding wheel 55 based on the eccentricity d and the phase α so that the grinding wheel passes through the grinding point Q and the distance (radius ra + radius Ra) between the first center axis Lj1 and the rotation axis Og is constant, thereby grinding the first crank journal J1. In this embodiment, the phase α is the same as the phase of the main spindle 32 and is the phase given as a drive command to the main spindle rotation motor 31 when execution of the eccentricity machining program is started.

[0031] 7, when the first crank journal J1 is at the phase α position, the control device 8 calculates the distance X between the rotation axis Rj of the main spindle 32 and the rotation axis Og of the grinding wheel 55, and performs a feeding operation of the grinding wheel 55 according to the distance X. The distance X is calculated using the following equations (1) and (2). d×sinαp=(ra+Ra)×sinβ...Equation (1) X=d×cosαp+(ra+Ra)×cosβ...Equation (2)

[0032] In the above formula (1), the angle αp can be calculated because the phase α is known. For example, in the state shown in FIG. 7, the angle αp can be calculated by subtracting 270° from the phase α. In addition, in the above formula (1), the eccentricity d, the radius ra of the crank journal J before grinding, and the radius Ra of the grinding wheel 55 are known, so β ​​can be calculated. The distance X can be calculated by substituting β calculated in formula (1) into formula (2).

[0033] 8, when the phase α of the spindle 32 is 270°, the first crank journal J1 and the grinding point Q of the grinding wheel 55 are located on a straight line connecting the rotation axis Rj and the rotation axis Og of the grinding wheel 55, and between the rotation axes Rj and Og. In this case, the distance X is maximized. In other words, when the phase α is 270°, the control device 8 performs numerical control so that the rotation axis Og of the grinding wheel 55 is located at the most retracted position in the reverse feed direction.

[0034] 9, when the phase α of the spindle 32 is 0°, the first center axis Lj1 is located directly above the rotation axis Rj. In this case, the distance X is smaller than when the phase α is 270°. In other words, the control device 8 performs numerical control so that the rotation axis Og of the grinding wheel 55 is positioned forward in the forward feed direction from when the phase α is 270°.

[0035] 10, when the phase α of the spindle 32 is 90°, the first crank journal J1 and the grinding point Q of the grinding wheel 55 are located on a line connecting the rotation axis Rj and the rotation axis Og of the grinding wheel 55, and on the opposite side of the rotation axis Og across the rotation axis Rj. In this case, the distance X is minimum. In other words, when the phase α is 90°, the control device 8 performs numerical control so that the rotation axis Og of the grinding wheel 55 is located at the most advanced position in the forward feed direction.

[0036] 11, when the phase α of the spindle 32 is 180°, the first center axis Lj1 is located directly below the rotation axis Rj. In this case, the distance X is greater than when the phase α is 90°. In other words, the control device 8 performs numerical control so that the rotation axis Og of the grinding wheel 55 is positioned at a position retracted in the reverse feed direction from when the phase α is 90°.

[0037] As described above, in the eccentricity processing program, the reference crank journal is rotated in a whirling manner relative to the rotation axis Rj so that the center axis of the reference crank journal is eccentric from the rotation axis Rj by the eccentricity amount d, and the feed operation of the grinding wheel 55 is controlled based on the eccentricity amount d and the phase α, thereby grinding the reference crank journal.

[0038] FIG. 12 is the first diagram showing the evaluation of the crankshaft W. FIG. 12 shows the runout of the crank journals J1 to J5 when the crankshaft W is rotated around the rotation axis Rj after stress relief by grinding. The black circles indicate the runout of the crank journals J1 to J5 when the crank journals J1 and J5 are ground using the eccentricity grinding program and the crank journals J2 to J4 are ground using the standard grinding program. The white circles indicate the runout of the crank journals J1 to J5 from the rotation axis Rj when all the crank journals J1 to J5 are ground using the standard grinding program. In FIG. 12, the black circles and white circles overlap for the crank journals J2 to J4. When the first and fifth crank journals J1, J5 are ground using an eccentricity machining program so that the first center axis Lj1 of the first crank journal J1 and the fifth center axis Lj5 of the fifth crank journal J5 approach the second to fourth center axes Lj2 to Lj4, the center axes Lj1, Lj5 of the first and fifth crank journals J1, J5 approach the center axes Lj2 to Lj4 of the second to fourth crank journals J2 to J4.

[0039] FIG. 13 is a second diagram showing the evaluation of the crankshaft W. FIG. 13 shows the coaxiality of the crankshaft W after stress release due to grinding. FIG. 13 shows the coaxiality of the second to fourth crank journals J2 to J4 based on the first crank journal J1 and the fifth crank journal J5. In FIG. 14, the open circles represent the coaxiality of all crank journals J1 to J5 when grinding is performed using the standard machining program. The closed circles represent the coaxiality when the crank journals J1 and J5 are ground using the eccentricity machining program and the crank journals J2 to J4 are ground using the standard machining program. As shown in FIG. 13, when the first and fifth crank journals J1 and J5 are ground eccentrically from the rotation axis Rj using the eccentricity machining program as in this embodiment, the coaxiality of the crank journals J2 to J4 is smaller than when grinding is performed using only the standard machining program. For example, when the crankshaft W is attached to a piston of an internal combustion engine, the crankshaft W rotates around the central axes Lj1 to Lj5 of the crank journals J. Therefore, the higher the concentricity of the first to fifth crank journals J1 to J5, the smaller the runout of the crankshaft W can be, and the more efficiently the reciprocating motion of the piston can be converted into rotational motion.

[0040] According to the above embodiment, after stress release, grinding is performed to eccentrically displace the first center axis Lj1 of the first crank journal J1 and the fifth center axis Lj5 of the fifth crank journal J5 from the rotation axis Rj so that the first center axis Lj1 and the fifth center axis Lj5 approach the second to fourth center axes Lj2 to Lj4. This prevents the center axes Lj1 to Lj5 of the first to fifth crank journals J1 to J5 from becoming significantly misaligned with each other through a single grinding step, without requiring finish machining after performing rough machining on the crank journals J1 to J5 to release residual stress. In other words, it is possible to improve the coaxiality of the crank journals J1 to J5 of the crankshaft W and reduce the degree of runout while shortening the grinding time for the crankshaft W.

[0041] Furthermore, according to the above embodiment, the first crank journal J1, which is a crank journal on one end, and the fifth crank journal J5, which is a crank journal on the other end, are used as reference crank journals, and the second to fourth crank journals J2 to J4, which are intermediate crank journals, are used as other crank journals, and the eccentricity machining program and the standard machining program are executed. This allows the center axis Lj1 of the first crank journal J1 and the center axis Lj5 of the fifth crank journal J5 to approach the center axes Lj2 to Lj4 of the second to fourth crank journals J2 to J4.

[0042] B. Other Embodiments: B-1. Alternative embodiment 1: In the above embodiment, the first crank journal J1 and the fifth crank journal J5, which are located at both ends of the crank journals J1 to J5, are used as reference journals, and grinding is performed on the reference journals according to the eccentricity machining program. However, grinding may be performed on the second to fourth crank journals J2 to J4, which are intermediate crank journals, as reference crank journals, and the first and fifth crank journals J1 and J5 as other crank journals according to the eccentricity machining program. In this case, the eccentricity amount d in the grinding process for each of the center axes Lj2 to Lj4 of the second to fourth crank journals J2 to J4 may be determined so that the center axes Lj2 to Lj4 of the second to fourth crank journals J2 to J4 approach the first center axis Lj1 and the fifth center axis Lj5 in the crankshaft W that has been stress-relieved after grinding. If there are multiple center axes (other center axes) of the other crank journals, a representative point, such as the average coordinate of the multiple other center axes, may be found, and the eccentricity amount d may be determined so that the center axes approach this representative point.

[0043] B-2. Alternative embodiment 2: In the above embodiment, as shown in FIG. 2, the crankshaft W has four crank pins P to P4 and five crank journals J1 to J5, but is not limited to this and may have, for example, six crank pins and seven crank journals.

[0044] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0045] 1...bed, 2...workpiece table, 3...first headstock, 4...tailstock, 5...grinding wheel head, 8...control device, 10...grinding machine, 21...table movement motor, 21a...table encoder, 22...guide surface, 31...spindle rotation motor, 32...spindle, 33...spindle center, 34...drive fitting, 36...drive pin, 38...spindle encoder, 41...tailstock movement motor, 42...tailstock spindle, 43...tailstock center, 51...grinding wheel head drive motor, 52...grinding wheel rotation motor, 53...belt, 54...grinding wheel spindle, 55...grinding wheel, 56...guide rail, 58...encoder Da, 62...dial gauge, 61...spindle, 82...storage unit, 84...processor, 85...standard machining program, 86...eccentric machining program, 87...workpiece information, 88...grinding wheel information, 89...grinding wheel position calculation unit, 97, 98, 99...drive circuit, J1 to J5...crank journal, Lj...center axis, Lj1...first center axis, Lj2...second center axis, Lj3...third center axis, Lj4...fourth center axis, Lj5...fifth center axis, Og...rotation axis, P1 to P5...crank pin, Q...grinding point, Rj...rotation axis, W, Wt...crankshaft

Claims

1. A grinding method for grinding a shaft having a plurality of journals using a grinding machine, comprising the steps of: The plurality of journals are arranged side by side in the axial direction of the shaft and include a reference journal and other journals, The grinding machine is a headstock having a main spindle that supports the shaft and is driven to rotate around a rotation axis; a grinding wheel head that rotatably supports a disc-shaped grinding wheel; a drive unit that performs a feed operation of the grinding wheel to move the grinding wheel relatively closer to or farther away from the shaft in a direction intersecting the rotation axis; a control device that controls the position of the grinding wheel relative to the shaft in accordance with the angular position of the spindle, thereby grinding the journal with the grinding wheel so that the cross section has a circular shape; The grinding method comprises: (a) receiving an input of an eccentricity amount of the reference central axis in the grinding process from the rotation axis, the eccentricity amount being set so that, in the shaft after the pressure is released, the reference central axis, which is the central axis of the reference journal, approaches another central axis, which is the central axis of the another journal, in comparison with a case in which the grinding process is performed by the grinding machine while applying a pressing force to the shaft from both sides in the axial direction of the shaft to position the central axes of the plurality of journals on the rotation axis, thereby releasing residual stress in the plurality of journals, and then the pressure is released, causing bending of the shaft due to the release of the residual stress; (b) receiving an input of a phase of the reference journal relative to the rotation shaft; (c) rotating the reference journal in a whirling motion about the rotation axis so that the reference center axis of the reference journal is eccentric from the rotation axis by the eccentricity amount, calculating a distance in the feed direction of the grinding wheel between the rotation axis of the grinding wheel and the rotation axis of the spindle based on the eccentricity amount and the phase so that the distance between the reference center axis passing through the grinding point of the reference journal by the grinding wheel and the rotation axis of the spindle becomes a predetermined constant value, and controlling the feed operation of the grinding wheel so that the calculated distance is obtained, thereby grinding the reference journal.

2. The grinding method according to claim 1, further comprising: (d) A grinding method comprising a step of rotating the other journal around the rotation axis so that the other center axis of the other journal is positioned on the rotation axis, and performing the grinding process on the other journal.

3. 3. The grinding method according to claim 1 or 2, the plurality of journals include a one-end journal located on one end side, an other-end journal located on the other end side, and one or more intermediate journals located between the one-end journal and the other-end journal, a grinding method in which the one end side journal and the other end side journal are set as the reference journals and the intermediate journal is set as the other journal, and steps (a) to (c) are carried out.

4. 3. The grinding method according to claim 1 or 2, the plurality of journals include a one-end journal located on one end side, an other-end journal located on the other end side, and one or more intermediate journals located between the one-end journal and the other-end journal, a grinding method in which the intermediate journal is used as the reference journal, and the steps (a) to (c) are performed using the intermediate journal as the reference journal.

5. A grinding machine for grinding a shaft having a plurality of journals, The plurality of journals are arranged side by side in the axial direction of the shaft and include a reference journal and other journals, The grinding machine is a headstock supporting the shaft, the headstock having a spindle that is driven to rotate around a predetermined rotation axis; a grinding wheel head that rotatably supports a disc-shaped grinding wheel; a drive unit that performs a feed operation of the grinding wheel to move the grinding wheel relatively closer to or farther away from the shaft in a direction intersecting the rotation axis; a control device that controls the position of the grinding wheel relative to the shaft in accordance with the angular position of the spindle, thereby grinding the journal with the grinding wheel so that the cross section has a circular shape; The control device an input of an eccentricity amount of the reference central axis in the grinding process from the rotation axis, the eccentricity amount being set so that, in the shaft in which the grinding process is performed while applying a pressing force to the shaft from both sides in the axial direction of the shaft by the grinding machine to release residual stresses in the plurality of journals and then the pressing force is released, the reference central axis, which is the central axis of the reference journal, approaches another central axis, which is the central axis of the another journal, rather than a case in which the grinding process is performed on the plurality of journals so that the central axes of the plurality of journals are positioned on the rotation axis while applying a pressing force to the shaft from both sides in the axial direction of the shaft by the grinding machine to release residual stresses in the plurality of journals and then the pressing force is released, causing bending of the shaft due to the release of the residual stress; Accepting an input of a phase of the reference journal relative to the rotation axis; a grinding machine that rotates the reference journal in a whirling motion relative to the rotation axis by rotating the main spindle so that the reference center axis of the reference journal is eccentric from the rotation axis by the eccentricity amount, calculates a distance in the feed direction of the grinding wheel between the rotation axis of the main spindle and the reference center axis of the reference journal based on the eccentricity amount and the phase of the reference journal so that the distance between the reference center axis passing through the grinding point of the reference journal and the rotation axis of the main spindle becomes a predetermined constant value, and controls the feed operation of the grinding wheel so that the calculated distance is obtained, thereby grinding the reference journal.

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