CN113561061A

CN113561061A - Dressing device

Info

Publication number: CN113561061A
Application number: CN202110463429.4A
Authority: CN
Inventors: 增田祐生; 河原彻; 村上慎二; 野野山真; 斋藤明
Original assignee: JTEKT Corp
Current assignee: JTEKT Corp
Priority date: 2020-04-28
Filing date: 2021-04-25
Publication date: 2021-10-29
Also published as: DE102021110566A1; JP2021171888A

Abstract

A dressing device is provided with: a detector that detects at least one of a surface property evaluation value indicating a surface property of the workpiece in an axial direction and an outer diameter evaluation value regarding an outer diameter at a plurality of axial positions; a calculation section that calculates a degree of shape damage on the grinding stone from a reference surface state based on the evaluation value corresponding to the surface state of the workpiece detected by the detector; a determination unit that determines whether or not dressing of the grinding stone can be performed and whether or not dressing conditions can be changed, based on the degree of shape damage; and an execution unit that executes dressing of the grinding stone based on the determination result of the determination unit.

Description

Dressing device

Technical Field

The present invention relates to a dressing apparatus.

Background

In a grinding machine that grinds a workpiece by a grinding wheel while rotating the workpiece, dressing of the grinding wheel is performed to restore the shape damage of the grinding wheel. Dressing is generally performed when a predetermined number of abrasions of the workpiece have been reached. The shape damage of the grindstone depends on the grinding amount of the workpiece, but is set to have a margin in the grinding amount in order not to produce an unqualified workpiece. Therefore, it is an important factor to reduce the life of the grinding stone, and therefore, to stabilize the quality of the workpiece, it is desired to increase the life of the grinding stone.

Jp 10-000556 a describes that a specific frequency which is an integral multiple of the rotational frequency of a grinding wheel in the vibration of a grinding machine is obtained, and the dressing timing and the dressing quality are determined based on the amplitude of the vibration. Further, japanese patent application laid-open No. 2000-263437 discloses that when the current value of a motor for rotationally driving a grinding stone exceeds a threshold value, it is determined that the sharpness of the grinding stone is deteriorated, and the grinding stone is dressed.

Disclosure of Invention

The invention provides a dressing device which can realize the stabilization of a workpiece and the long service life of a grinding stone by different methods.

The dressing device is provided with: a detector that detects, as an evaluation value indicating a surface state of a workpiece having a center axis, at least one evaluation value of a surface property evaluation value indicating a surface property of the workpiece in an axial direction and an outer diameter evaluation value regarding an outer diameter at a plurality of axial positions; a calculation unit that calculates a degree of shape damage from a reference surface state on a grinding stone configured to grind the workpiece, based on the at least one evaluation value corresponding to the surface state of the workpiece detected by the detector; a determination unit that determines whether or not dressing of the grinding stone is to be performed and whether or not the dressing condition is to be changed, based on the degree of shape damage; and an execution unit that executes the dressing of the grinding stone based on a determination result of the determination unit.

At least one of the surface texture evaluation value and the outer diameter evaluation value is used as the evaluation value indicating the surface state of the workpiece. The evaluation value represents the surface state of the workpiece itself. Further, the surface condition of the grinding stone is transferred to the surface of the workpiece, and therefore the evaluation value indicates the surface condition of the grinding stone.

Therefore, the calculation section calculates the degree of shape damage of the grinding stone using the evaluation value indirectly representing the surface state of the grinding stone. Then, based on the calculated shape damage degree, the determination unit determines whether or not the trimming can be executed and/or whether or not the trimming conditions can be changed. Therefore, by performing dressing based on the degree of shape damage of the grinding stone indirectly evaluated using the surface state of the workpiece, stabilization of the quality of the workpiece and a long life of the grinding stone can be achieved.

Drawings

Fig. 1 is a plan view showing an example of a grinding machine.

Fig. 2 is a functional block diagram of the trimming device.

Fig. 3 is a diagram showing changes in the grinding stone state grade with respect to the number of grindings of the workpiece W in the first example processing by the determination unit and the execution unit.

Fig. 4 is a flowchart showing a first example of the process of the determination unit.

Fig. 5 is a diagram showing transition of the grinding stone state grade with respect to the number of grindings of the workpiece W in the second example processing of the determination section and the execution section.

Fig. 6 is a flowchart showing a second example process of the determination section.

Fig. 7 is a diagram showing transition of the grinding stone state grade with respect to the number of grindings of the workpiece W in the third example processing of the determination section and the execution section.

Fig. 8 is a flowchart showing a third example of the process of the determination unit.

Fig. 9 is a view showing a workpiece.

Fig. 10 is a diagram showing a plurality of circumferential chatter data used for calculating the first surface property evaluation value.

Fig. 11 is a diagram showing the surface roughness data.

Fig. 12 is a diagram showing the chatter amounts at a plurality of axial positions used for calculation of the first surface property evaluation value.

Fig. 13 is a diagram showing outer diameter data used for calculation of the outer diameter evaluation value.

Fig. 14 is a diagram showing corrected surface roughness data used for calculating the third surface shape evaluation value.

Fig. 15 is a diagram showing a plurality of linear surface properties used for calculating the third surface property evaluation value.

Detailed Description

(1. outline of dressing apparatus)

The dressing device is a device for dressing a grinding stone mounted on a grinding machine. The dressing device may be a device incorporated in the grinding machine, or may be a device different from the grinding machine. In this example, the dressing apparatus is assembled to the grinding machine.

(2. example of grinding machine 10)

An example of a grinding machine 10 to which a dressing apparatus is applied will be described with reference to fig. 1. The grinding machine 10 is a machine tool for grinding a workpiece W, and has a structure for relatively moving the workpiece W and a grinding wheel 16. The workpiece W has a central axis, and the workpiece W is polished by bringing the grinding stone 16 into contact with the workpiece W while rotating the workpiece W around the central axis.

The grinding machine 10 can be a cylindrical grinding machine, a cam grinding machine, or any other grinding machine. In this example, a grinding machine 10 is exemplified by a grinding stone bed traversing type cylinder grinding machine. However, the grinding machine 10 can also employ a table traversing type. In addition, although the grinding machine 10 is exemplified as a structure for grinding the outer peripheral surface of the workpiece W, a structure for grinding the inner peripheral surface of the workpiece W may also be applied.

The grinding machine 10 mainly includes a bed 11, a headstock 12, a tailstock 13, a traverse base 14, a grindstone bed 15, a grindstone 16, a size determination device 17, a grindstone correction device 18, and a coolant device 19. The grinding machine 10 further includes a detector 21 and a control device 22. In the figure, the Z-axis direction is a direction that coincides with the central axis direction of the workpiece W, the X-axis direction is a direction orthogonal to the Z-axis, and the Y-axis direction is a direction orthogonal to the X-axis direction and the Z-axis direction.

The base 11 is fixed on the setting surface. The spindle base 12 is provided on the upper surface of the bed 11 on the near side (lower side in fig. 1) in the X-axis direction and on one end side (left side in fig. 1) in the Z-axis direction. The spindle base 12 supports the workpiece W rotatably about the Z axis. The workpiece W is rotated around the central axis of the workpiece W by driving of a motor 12a provided in the spindle stock 12. The tailstock 13 is provided on the upper surface of the bed 11 at a position facing the spindle stock 12 in the Z-axis direction, that is, on the front side in the X-axis direction (the lower side in fig. 1) and on the other end side in the Z-axis direction (the right side in fig. 1). That is, the headstock 12 and the tailstock 13 support both ends of the workpiece W so as to be able to rotate the workpiece W. When the grinding machine 10 is configured to grind the inner peripheral surface of the workpiece W, the workpiece W is supported only by the spindle base 12.

The traverse base 14 is provided on the upper surface of the base 11 so as to be movable in the Z-axis direction. The traverse base 14 is moved by driving a motor 14a provided in the bed 11. The grindstone holder 15 is provided on the upper surface of the traverse base 14 so as to be movable in the X-axis direction. The grinding stone holder 15 is moved by driving a motor 15a provided in the traverse base 14.

The grindstone 16 is a tool for grinding the workpiece W. In this example, a grinding wheel formed in a disk shape is used as the grinding stone 16. The grinding stone 16 is rotatably supported by the grinding stone holder 15. The grinding stone 16 is rotated by driving a motor 16a provided in the grinding stone holder 15. The grinding stone 16 includes a cylindrical core and an abrasive particle portion configured to fix a plurality of abrasive particles to an outer peripheral surface of the cylindrical core with a binder. As the binder, various materials such as resin and metal can be used.

The size determining device 17 measures the size (diameter) of the workpiece W. The size determining device 17 is provided on the upper surface of the housing 11 so as to be movable in the Z-axis direction. The position of the dimension determining device 17 in the Z-axis direction is controlled by a feed mechanism 17a provided in the housing 11. The size determination device 17 includes a detection measurement feeler 17b that contacts the polished surface of the workpiece W. The detection measurement feeler 17b is always in contact with the polishing surface of the workpiece W rotating during polishing.

The grinding stone correction device 18 corrects the shape of the grinding stone 16. The grinding stone dresser 18 is a device for dressing (including dressing) the grinding stone 16. The grinding stone correction device 18 also has a function of measuring the size (diameter) of the grinding stone 16.

Here, the dressing is a reshaping operation, and is an operation of shaping the grinding stone 16 in accordance with the shape of the workpiece W when the grinding stone 16 is worn by grinding, an operation of removing the wobbling of the grinding stone 16 caused by one-side wear, or the like. The modification is a modification (eye し, eye て) operation, and is an operation of adjusting the protruding amount of abrasive grains or creating a cutting edge of abrasive grains. The modification is usually performed after the modification, in order to correct the operations such as the inactivation, clogging, and falling-off of the abrasive grains. However, since trimming and modification may be carried out without particular distinction, the term "trimming" is used in the present specification to include modification.

The coolant device 19 supplies coolant to a polishing point of the workpiece W by the polishing stone 16. The coolant device 19 cools the recovered coolant to a predetermined temperature, and supplies the cooled coolant to the polishing point again.

The detector 21 detects an evaluation value indicating a surface state of the workpiece W being polished. The evaluation value indicating the surface state of the workpiece W is at least one of a surface property evaluation value indicating the surface property of the workpiece W in the axial direction and an outer diameter evaluation value regarding the outer diameter at a plurality of axial positions. The detector 21 is used to determine whether or not dressing of the grinding stone 16 can be performed, whether or not dressing conditions can be changed, and the like.

The detector 21 can be applied to any one of a type of contact with the workpiece W and a type of non-contact with the workpiece W. For example, the detector 21 may be an acceleration sensor that detects acceleration generated by relative movement with respect to the workpiece W in a state of contact with the surface of the workpiece W in the case of a type of contact with the workpiece W. The detector 21 may be a displacement sensor capable of detecting the distance to the surface of the workpiece W with reference to a predetermined position. When the detector 21 is a displacement sensor, any one of a type of contact with the workpiece W and a type of non-contact can be applied.

In this example, the detector 21 uses the size determining device 17 as a type of contact with the workpiece W. The detector 21 is an acceleration sensor provided on an arm supporting the detection measurement probe 17b of the size determination device 17. The detector 21, which is an acceleration sensor, outputs acceleration data indicating the acceleration detected in a state where the center of the measurement probe 17b is detected to be in contact with the polished surface of the rotating workpiece W. Instead of the acceleration sensor, the detector 21 may be a displacement sensor that outputs displacement data indicating a displacement value detected in a state where the center of the measurement probe 17b is in contact with the polishing surface of the rotating workpiece W.

The control device 22 controls the respective drive devices based on an NC program generated based on operation command data such as the shape of the workpiece W, machining conditions, the shape of the grinding stone 16, and supply timing information of the coolant. That is, the control device 22 receives the operation command data and generates an NC program based on the operation command data.

The controller 22 controls the

motors

12a, 14a, 15a, and 16a, the coolant device 19, and the like based on the NC program, thereby polishing the workpiece W. In particular, the control device 22 polishes the workpiece W until the workpiece W has a finished shape based on the diameter of the workpiece W measured by the size determination device 17. The controller 22 controls the

motors

14a, 15a, and 16a, the grinding wheel correction device 18, and the like at the timing of correcting the grinding wheel 16, thereby correcting (dressing and dressing) the grinding wheel 16.

(3. Structure of dressing device 30)

The structure of the dressing apparatus 30 will be explained with reference to fig. 2. As shown in fig. 2, the trimming device 30 includes a detector 31, a calculating unit 32, a determining unit 33, and an executing unit 34. The calculation unit 32, the determination unit 33, and the execution unit 34 are configured by a processor, a storage device, and the like, and are realized by executing a program in the processor.

The detector 21 constituting the grinding machine 10 is used as the detector 31. That is, the detector 31 detects an evaluation value indicating a surface state of the workpiece W being polished. The evaluation value indicating the surface state of the workpiece W is at least one of a surface property evaluation value indicating the surface property of the workpiece W in the axial direction and an outer diameter evaluation value regarding the outer diameter at a plurality of axial positions.

The calculation section 32 calculates the degree of shape damage on the grinding stone 16 grinding the workpiece W from the reference surface state based on the evaluation value as the surface state of the workpiece W detected by the detector 31. For example, in the case where the reference surface state of the grinding stone 16 is a straight line parallel to the central axis of the grinding stone 16, the degree of shape collapse is a degree of deviation in the radial direction from the straight line parallel to the central axis of the grinding stone 16.

The determination unit 33 determines whether or not at least one of dressing of the grinding stone 16 is executable and whether or not the dressing condition is changeable, based on the degree of shape damage calculated by the calculation unit 32. The execution unit 34 executes dressing of the grinding stone 16 based on the determination result of the determination unit 33. The execution unit 34 uses the control device 22 constituting the grinding machine 10. That is, the actuator 34 functions as a part of the control device 22, and controls the

motors

14a, 15a, and 16a and the grinding wheel correction device 18 to perform dressing of the grinding wheel 16.

(4. examples of the judgment unit 33 and the execution unit 34)

An example of the determination unit 33 and the execution unit 34 constituting the finisher device 30 will be described. In the following description, the degree of shape damage on the grinding stone 16 from the reference surface state calculated by the calculation unit 32 is referred to as a grinding stone state grade. The higher the grade of the state of the grindstone, the greater the degree of shape damage, i.e., the greater the amount of deviation from the reference shape. Therefore, the grade of the state of the grinding stone immediately after the normal dressing is the lowest, and the grinding work W becomes gradually higher as it goes.

(4-1. first example)

The determination unit 33 and the execution unit 34 of the first example will be described with reference to fig. 3 and 4. As shown in fig. 3, as the grinding number of the workpiece W increases, the grindstone condition grade L becomes higher. The grindstone condition of the first workpiece W was rated L1 (1). The nth stone condition was rated as L1 (N).

In fig. 3, the maximum value of the grinding stone state grade is Lmax, and the grinding stone state grade L is required not to exceed the maximum value Lmax. In addition, in the case where dressing is normally performed, the grade of the state of the grinding stone immediately after dressing is less than the minimum threshold value Lmin.

In this example, a predetermined period of dressing is set. For example, as the predetermined period of dressing, the number N of workpieces W from the last dressing is set. That is, when the number of workpieces W from the previous dressing is N, it is determined that the predetermined time for dressing has been reached.

When the number of workpieces W reaches N, whether or not a delay with respect to a predetermined period of dressing is allowed is determined based on the grindstone condition level L1 (N). In fig. 3, the grindstone condition level L1(N) does not exceed the level threshold Lth for determination, and therefore a delay is made with respect to the predetermined period of dressing.

Thereafter, when the number of workpieces W becomes Na, the after-lapse grindstone state level L1(E) exceeds the level threshold Lth, and therefore dressing is performed (T1 of fig. 3). After the trimming, when the number of workpieces W from the trimming reaches N, it is determined whether or not a delay of the trimming is allowed, as described above. That is, when the total number of the works W reaches "Na + N", it is determined whether or not the dressing is allowed to be postponed.

In fig. 3, the grindstone condition level L2(N) does not exceed the level threshold Lth for determination, and therefore a delay is made with respect to the predetermined period of dressing. Thereafter, when the number of workpieces W becomes "Na + Nb", the grinding stone state level L2(E) after the delay exceeds the level threshold Lth, and therefore dressing is performed (T2 of fig. 3).

That is, the number of the postponed workpieces W is different corresponding to the grindstone state levels L1(N), L2(N) when the predetermined period of dressing is reached. The number of the delayed workpieces W may be determined in accordance with the grinding stone state levels L1(N) and L2(N) for a predetermined period.

A first example of the determination process by the determination unit 33 will be described with reference to fig. 4. First, the determination unit 33 acquires the number Np of trimmed workpieces W (S1). Next, it is determined whether or not the acquired number Np of the works W has reached the number N (set number N) corresponding to the set scheduled time of trimming (S2). If not (S2: NO), the process returns to S1.

On the other hand, when the set number N is reached (YES in S2), the grinding stone state grade L (N) of the N-th workpiece W after dressing is obtained (S3). Next, based on the obtained grinding stone state level l (n), it is determined whether or not a delay is allowed for a predetermined period of the set dressing (S4). In the case of determining the extension, the extension amount Δ N is determined. The extension amount Δ N is determined corresponding to the set number N of grinding stone condition levels l (N). For example, the extension amount Δ N may be determined based on the difference between the set number N of grinding stone state levels l (N) and the maximum value Lmax. The extension amount Δ N may be determined based on the difference between the set number N of grinding stone state levels l (N) and the level threshold Lth used for determination.

Next, it is determined whether or not the number Np of trimmed workpieces W has reached "N + Δ N" (S5). If not (S5: No), the workpiece W is continuously ground until it is reached. On the other hand, if it is reached (S5: YES), the grinding stone state grade L (Np) of the number Np of the works W is acquired (S6).

Next, it is determined whether or not the obtained grinding stone state level l (np) exceeds a level threshold Lth for determination (S7). If not (S7: No), return is made to S6. That is, the polishing of the workpiece W is continued until the level threshold Lth is exceeded. When the level threshold Lth is exceeded, the execution of trimming is determined (S8).

Here, when the determination unit 33 determines to perform dressing, the execution unit 34 performs dressing of the grinding stone 16. That is, the execution unit 34 executes the dressing of the grinding stone 16 when the time of the deferred dressing is reached.

In the above description, the extension amount Δ N is determined when the dressing timing is extended, and the dressing execution timing is determined by comparing the grinding stone state level l (np) with the level threshold Lth after the extension amount Δ N is reached. In addition, when the timing for extending the dressing is determined, the dressing execution timing may be determined by comparing the obtained grindstone state level l (np) with the level threshold Lth every time the workpiece W is polished. In addition, when the timing for extending the trimming is determined, the trimming may be performed when the determined extension amount Δ N is reached.

In summary, based on the calculated grindstone state level L (degree of shape damage), the determination section 33 determines whether or not dressing can be performed. Therefore, the dressing is performed based on the degree of shape damage of the grinding stone 16 indirectly evaluated using the surface state of the workpiece W, whereby stabilization of the quality of the workpiece W and a long life of the grinding stone 16 can be achieved.

(4-2. second example)

The determination unit 33 and the execution unit 34 of the second example will be described with reference to fig. 5 and 6. In fig. 5, the maximum value of the grinding stone state grade is Lmax, and the grinding stone state grade L is required not to exceed the maximum value Lmax. As the grinding stone state grade ranges, for example, Lev1, Lev2, Lev3, and Lev4 are set. The grindstone state grade was increased in the order Lev1, Lev2, Lev3, Lev 4. The maximum value of Lev4 corresponds to Lmax.

When the number of the works W reaches N, the determination unit 33 determines to perform dressing of the grinding stone 16. At this time, the dressing condition is determined in accordance with the grinding stone state level l (n) immediately before dressing is performed. In this example, the condition for dressing corresponding to the grinding stone state grade range is changed by determining the grinding stone state grade range to which the immediately-before grinding stone state grade l (n) belongs among the grinding stone state grade ranges Lev1, Lev2, Lev3, and Lev 4. For example, the radial cutting amount of the grinding stone 16 is changed as a condition for dressing. Then, the execution unit 34 executes the trimming based on the modified trimming condition.

In fig. 5, the nth stone condition grade L1(N) belongs to the stone condition grade range Lev2, and thus dressing is performed with a radial cutting amount corresponding to Lev2 (T1 of fig. 5). The 2N-th stone condition grade L2(N) belongs to the stone condition grade range Lev4, and therefore dressing is performed with a radial cut amount corresponding to Lev4 (T2 of fig. 5). Thus, neither the grade of the state of the grinding stone immediately after the dressing T1 or T2 is sufficient for the minimum threshold value Lmin.

A second example of the determination process of the determination unit 33 will be described with reference to fig. 6. First, the determination unit 33 acquires the number Np of trimmed workpieces W (S11). Next, it is determined whether or not the acquired number Np of the works W has reached the number N (set number N) corresponding to the set scheduled time of trimming (S12). If not (S12: NO), the process returns to S11.

On the other hand, when the set number N is reached (YES in S12), the grinding stone state grade L (N) of the N-th workpiece W after dressing is obtained (S13). Here, in this example, after the nth workpiece W is polished, dressing of the grinding stone 16 is performed. Therefore, the grinding stone state level l (N) of the nth workpiece W becomes the grinding stone state level immediately before dressing is performed.

Next, the obtained grinding stone state grade l (n) is determined to belong to the grade range among the grinding stone state grade ranges Lev1, Lev2, Lev3, and Lev4 (S14). Next, the dressing condition corresponding to the associated grinding stone condition grade range is determined (S15). For example, the initial set value of the condition for trimming is the case of Lev 1. Therefore, it is determined that the trimming condition is changed when the trimming condition belongs to Lev2, Lev3, and Lev 4. In this example, the radial cutting amount of the grinding stone 16 is changed as a dressing condition.

Then, trimming is determined to be performed based on the modified trimming conditions (S16). Here, when the determination unit 33 determines to perform dressing, the execution unit 34 performs dressing of the grinding stone 16. That is, the execution unit 34 executes the dressing of the grinding stone 16 under the condition corresponding to the grinding stone state level l (n) immediately before the dressing. This makes it possible to form the trimming intervals as many as the number of workpieces W to be trimmed next as desired.

(4-3. third example)

The determination unit 33 and the execution unit 34 of the third example will be described with reference to fig. 7 and 8. In fig. 7, the maximum value of the grinding stone state grade is Lmax, and the grinding stone state grade L is required not to exceed the maximum value Lmax. In addition, in the case where dressing is normally performed, the grade of the state of the grinding stone immediately after dressing is less than the minimum threshold value Lmin.

When the number of the trimmed workpieces W reaches N, the determination unit 33 determines to perform the trimming of the grinding stone 16. Also, the stone condition grade L2(1) immediately after dressing at T1 of fig. 7 is not less than the minimum threshold value Lmin. That is, it means that trimming is not normally performed.

For this reason, the grindstone condition level L2(1) immediately after the dressing of T1 is not less than the minimum threshold value Lmin, and therefore re-dressing is performed (T2 of fig. 7). Thus, the grindstone condition level L3(1) immediately after the refinishing is insufficient by the minimum threshold value Lmin. Further, if the number of the trimmed workpieces W reaches N, trimming is performed (T3 of fig. 7). The stone condition level L4(1) immediately after this dressing is less than the minimum threshold value Lmin, and therefore no re-dressing is performed.

A third example of the determination process of the determination unit 33 will be described with reference to fig. 8. First, the determination unit 33 acquires the number Np of trimmed workpieces W (S21). Next, it is determined whether or not the acquired number Np of the works W has reached the number N (set number N) corresponding to the set scheduled time of trimming (S22). If not (S22: NO), the process returns to S21.

On the other hand, when the set number N is reached (yes in S22), the determination unit 33 determines to execute trimming (S23). In this way, the dressing of the grinding stone 16 is performed by the execution unit 34.

Next, the determination unit 33 acquires the polished grindstone condition level L (1) (S24). That is, the workpiece W is polished after dressing, and the grinding stone condition level L (1) relating to the workpiece W after polishing is acquired. Then, it is determined whether the obtained grinding stone state level L (1) is less than the minimum threshold value Lmin (S25). That is, the determination unit 33 determines whether or not the refinishing is executable. When the minimum threshold value Lmin is less than this (YES in S25), the judgment process by the judgment unit 33 is ended.

On the other hand, when the minimum threshold value Lmin is not less (S25: no), the determination unit 33 determines to execute the re-trimming (S26). In this way, the execution unit 34 executes refinishing.

Here, the condition of the refinishing may be set to a condition different from that of the normal trimming. For example, the radial cutting amount as the condition for the re-dressing is set to be smaller than the radial cutting amount of the normal dressing. Further, the condition of refinishing may be determined in accordance with the grindstone condition grade L (1) after polishing. For example, the condition for refinishing may be determined in accordance with the difference between the grindstone condition level L (1) after grinding and the minimum threshold value Lmin.

After the refinishing, the process returns to S24 to continue the process. Therefore, if the grinding stone condition level L (1) after grinding is not less than the minimum threshold value Lmin due to the failed dressing again, the dressing is repeatedly performed.

(4-4. other)

The determination unit 33 can also perform a process in which the first and third example determination processes are combined. The determination unit 33 may perform a process in which the second and third example determination processes are combined. In other words, the timing of execution of the trimming can be determined in the first or second example determination process, and whether or not the re-trimming immediately after the trimming can be executed can be determined in the third example determination process.

(5. evaluation value)

Next, the evaluation value detected by the detector 31 will be described. As described above, the evaluation value is at least one of the surface property evaluation value and the outer diameter evaluation value.

(5-1. first surface texture evaluation value)

The first surface property evaluation value is a value for evaluating the surface condition of the workpiece W due to chatter vibration. Specifically, the first surface property evaluation value is a value obtained using circumferential chatter indicating a circumferential chatter state. In more detail, the first surface property evaluation value uses a plurality of vibration amounts respectively obtained from circumferential vibrations at a plurality of axial positions. A method of calculating the first surface property evaluation value will be described below.

Acceleration data or displacement data detected by the detector 31 is acquired in time series. For example, when the detection measuring stylus 17b of the size determination device 17 is moved spirally to the contact position on the polished surface of the workpiece W, time series data is acquired regarding the spiral position of the rotating workpiece W at predetermined angular intervals. That is, a plurality of time-series data are acquired.

That is, the detection measuring stylus 17b of the size determining apparatus 17 is moved in the Z-axis direction, which is the axial direction of the workpiece W, by the feeding mechanism 17a in a state where the workpiece W is rotated along with the polishing. In this case, since the detection measurement feeler 17b of the size determiner 17 is in contact with the polished surface of the workpiece W, the contact position of the center of the detection measurement feeler 17b with the workpiece W moves on the polished surface of the workpiece W while tracing a spiral trajectory. Therefore, the plurality of acceleration data obtained are acceleration data detected while the detection measurement probe 17b is relatively moved in a spiral shape on the polishing surface, and are data that are separated at predetermined angular intervals in a spiral shape.

For example, in the workpiece W shown in fig. 9, acceleration data of the workpiece W for one cycle is acquired. In this case, the data acquisition position moves spirally from the circumferential position Pa, passes through the circumferential position Pb, and returns to the circumferential position Pa again. The acceleration data of the workpiece W for one round is divided into a plurality of pieces at predetermined angular intervals, thereby generating the plurality of pieces of acceleration data. By moving in a spiral shape, time-series data at different axial positions can be acquired in a short time.

Next, FFT (fast fourier transform) is performed on a plurality of pieces of acceleration data obtained in time series from the detector 31 (acceleration sensor), and data on acceleration having a rotational frequency component (specific frequency component) corresponding to the number of revolutions of the grinding stone 16 is extracted. Then, the data on the acceleration having the extracted specific frequency component is subjected to inverse FFT. Thereby, the displacement value of the detection measurement probe 17b of the size determination device 17 having the specific frequency component, that is, displacement data (circumferential chatter data) relating to the irregularities (surface roughness) caused by the grinding stone on the polished surface of the workpiece W is converted. The specific frequency component is a frequency component of the rotation number of the grinding stone 16 and an integral multiple of the rotation number.

In this way, a plurality of circumferential chatter data caused by the grinding stone is generated. As shown in fig. 10, the plurality of circumferential chatter data caused by the grindstone is, for example, a1-a 6. Since the acquired acceleration data is data on a spiral trajectory, the circumferential positions of the circumferential chatter data a1-a6 are different from each other as shown in fig. 10.

Here, the workpiece W is polished while rotating the grinding stone 16. Therefore, the surface shape of the grinding stone 16 is transferred every rotation period of the grinding stone 16, that is, every rotation number to appear on the grinding surface of the workpiece W. Specifically, when abrasive grains protruding largely exist on the surface of the grinding stone 16, a concave portion is formed on the grinding surface of the workpiece W by cutting off a position abutting against the abrasive grains largely. In this case, the recesses formed in the workpiece W are formed at equal intervals in the rotational direction, and the intervals of the recesses in the circumferential direction of the workpiece W coincide with the rotational period (every revolution) of the grinding stone 16. Therefore, by extracting the data on the acceleration having the specific frequency component, it is possible to extract the unevenness due to the grinding stone on the grinding surface of the workpiece W.

Next, a series of surface roughness data is generated using the circumferential chatter data (displacement data) on the polished surface of the workpiece W. As described above, the plurality of pieces of circumferential runout data generated are generated at angles different from each other with respect to the angle of the rotation axis of the workpiece W. Therefore, as shown in fig. 10, the circumferential chatter data at adjacent axial positions are data at positions that are offset from each other in the circumferential direction of the workpiece W.

As described above, the circumferential irregularities (surface roughness) on the polished surface of the workpiece W repeatedly appear on the polished surface of the workpiece W every rotation cycle of the grinding wheel 16. Therefore, the respective circumferential chatter data at different angles are moved in the circumferential direction (the direction of the arrow shown in fig. 11). As a result, as shown in fig. 11, the circumferential chatter data at different angles is formed at the same angle as the angle of the workpiece W, and a series of planar roughness data aligned in parallel in the axial direction is generated.

Here, when dividing the circumferential direction chatter data (displacement data) converted from the acceleration data acquired in the spiral shape, the irregularities indicated by the respective divided roughness data may be deviated. Therefore, when generating the planar roughness data, the relative positions of the circumferential chatter data may be corrected so that the irregularities at the end points of the circumferential chatter data are continuous in the axial direction (Z-axis direction) of the workpiece W. In this case, the respective circumferential chatter data after the position correction are arranged in the axial direction to generate planar roughness data as state data.

Next, as shown in fig. 12, the generated surface roughness data is used to calculate the amount of chatter at a plurality of axial positions. The wobble amount here is the difference between the maximum value and the minimum value in each circumferential wobble data. For example, the respective amounts of judder in the circumferential judder data a1-a6 in fig. 11 are calculated. In practice, the circumferential chatter data is divided at every minute angle in the circumferential direction of the workpiece W, and therefore the amount of chatter at axial positions more than the illustrated number is calculated.

Also, the first surface property evaluation value can be formed as at least one of an average value of the amounts of chatter at a plurality of axial positions, a degree of difference (variance, average deviation, or the like) of the amounts of chatter, and a difference between a maximum value and a minimum value of the amounts of chatter. The first surface texture evaluation value may be any of an average value, a degree of difference, and a difference of the amount of chatter, or may be a composite value obtained by combining these values. In the above description, the planar roughness data is generated using a plurality of circumferential direction jitter data in order to relate to the following, but the planar roughness data need not be generated.

(5-2. evaluation value of outer diameter)

The outer diameter evaluation value is a value that evaluates a change in the outer diameter of the workpiece W at the axial position. Hereinafter, a method of calculating the outer diameter evaluation value will be described.

Based on the signal from the size determination device 17, the outer diameter data of the workpiece W is acquired. First, based on a signal from the size determination device 17, outer diameter data, which is time-series data of displacement with the outer diameter on the vertical axis, is acquired.

Next, FFT is performed on the acquired outer diameter data to extract a specific frequency region component. Specifically, a component corresponding to the rotational frequency of the workpiece W, i.e., a 1-mountain/cycle component is removed. A strong 1 mountain/week component is detected when the rotation axis of the workpiece W is deviated. Since it is sufficient to obtain the change in the outer diameter of the workpiece W in the axial direction as the outer diameter data, 1 mountain/circumference component is removed here.

Then, on the high frequency side of the acquired outer diameter data, vibration due to circumferential chatter of the workpiece W is detected. The circumferential chatter is information included in the circumferential chatter data in the calculation of the first surface property evaluation value. The range of the low frequency component extracted here may be appropriately determined depending on the number of revolutions of the grinding stone 16 and the workpiece W, and may be set to 50Hz or less, for example. In this way, by extracting low frequency components other than the 1 mountain/circumference component as specific frequency region components, the outer diameter variation in the axial direction of the workpiece W is extracted.

Then, the outer diameter data having the extracted specific frequency component is subjected to inverse FFT. Thereby, time-series data on the displacement of the outer diameter having the specific frequency component is converted. For example, the generated outer diameter data is shown in fig. 13.

The outer diameter evaluation value can be formed as at least one of an average deviation of the outer diameters, a degree of difference of the outer diameters, and a difference between a maximum value and a minimum value of the outer diameters at a plurality of axial positions. The outer diameter evaluation value may be any of the average deviation, the degree of difference, and the difference of the outer diameters, or may be a composite value obtained by combining these values.

(5-3. second surface texture evaluation value)

The second surface property evaluation value is a value for evaluating the surface state of the workpiece W using a planar surface property representing the surface property of the workpiece W as a planar surface property. Specifically, the second surface property evaluation value is a value obtained by acquiring linear surface properties indicating the relationship between the circumferential position, the axial position, and the surface properties using planar surface properties, and using a representative value of the linear surface properties.

More specifically, corrected planar roughness data as the planar surface property is generated using the planar roughness data generated in the calculation of the first surface property evaluation value and the outer diameter data generated in the calculation of the outer diameter evaluation value. The second surface property evaluation value uses corrected surface roughness data.

First, surface roughness data (shown in fig. 11) generated in the calculation process of the first surface property evaluation value is acquired. Then, the outer diameter data (shown in fig. 13) generated in the calculation process of the outer diameter evaluation value is acquired. Then, the surface roughness data and the outer diameter data are combined to generate corrected surface roughness data as shown in fig. 14. The corrected surface roughness data corresponds to the surface shape used for the second surface shape evaluation value.

Next, as shown in fig. 14, in the corrected planar roughness data, linear surface properties indicating the relationship between the axial position and the surface properties as shown in fig. 15 are obtained for each of the circumferential positions θ a and θ b. A plurality of linear surface features are generated for each circumferential position. Next, representative values of the respective linear surface properties are obtained. The representative value can be arithmetic average roughness Ra, maximum height roughness Rz, ten-point average roughness, or the like.

The second surface property evaluation value may be at least one of an average value of the plurality of representative values, a degree of difference between the plurality of representative values, and a difference between a maximum value and a minimum value of the plurality of representative values. The second surface property evaluation value may be any of an average value, a degree of difference, and a difference of a plurality of representative values, or may be a composite value obtained by combining these values.

(5-4. third surface character evaluation value)

The third surface property evaluation value is a value for evaluating the surface state of the workpiece W using a planar surface property representing the surface property of the workpiece W as a planar surface property. Specifically, the third surface property evaluation value is a representative value of the surface property as a whole. The representative values are an arithmetic average roughness Sa on the surface, a maximum height Sz on the surface, a root mean square height Sq on the surface, and the like.

If the planar surface property used for the third surface property evaluation value can be directly detected by the detector 31, the planar surface property used for the third surface property evaluation value can be formed as the detection data. The planar surface property may be planar roughness data generated in the calculation of the first surface property evaluation value, or may be corrected planar roughness data generated in the calculation of the second surface property evaluation value.

(6. summary)

As described above, the dresser 30 uses at least one of the surface property evaluation value and the outer diameter evaluation value as the evaluation value indicating the surface state of the workpiece W. The evaluation value indicates the surface state of the workpiece W itself. Further, since the surface condition of the grinding stone 16 is transferred to the surface of the workpiece W, the evaluation value indicates the surface condition of the grinding stone 16.

Therefore, the calculation section 32 calculates the degree of shape damage (stone state grade) of the grinding stone 16 using the evaluation value indirectly representing the surface state of the grinding stone 16. Then, based on the calculated shape damage degree (grinding stone state grade), the determination unit 33 determines whether or not the dressing can be executed and/or whether or not the dressing condition can be changed. Therefore, by performing dressing based on the degree of shape damage (grinding stone state grade) of the grinding stone 16 indirectly evaluated using the surface state of the workpiece W, stabilization of the quality of the workpiece W and a long life of the grinding stone 16 can be achieved.

Claims

1. A dressing apparatus is provided with:

a detector that detects, as an evaluation value indicating a surface state of a workpiece having a center axis, at least one of a surface property evaluation value indicating a surface property of the workpiece in an axial direction and an outer diameter evaluation value regarding an outer diameter at a plurality of axial positions;

a calculation section that calculates a degree of shape damage from a reference surface state on a grinding stone configured to grind the workpiece, based on the at least one evaluation value corresponding to the surface state of the workpiece detected by the detector;

a determination unit that determines whether or not dressing of the grinding stone can be performed and whether or not the dressing condition can be changed, based on the degree of shape damage; and

and an execution unit that executes the dressing of the grinding stone based on a determination result of the determination unit.

2. The finishing device of claim 1,

the determination unit determines whether or not a delay from a preset trimming time is allowed based on the degree of shape damage,

the execution unit executes the dressing of the grinding stone when a time of dressing delayed from a preset time has reached.

3. The finishing device of claim 1,

the determination section determines a condition for changing the dressing in correspondence with the degree of shape damage immediately before the dressing of the grinding stone is performed,

the execution unit executes the trimming based on the modified trimming condition.

4. The finishing device of claim 3,

the execution unit executes the dressing by changing a radial cutting amount of the grinding stone as a condition for the dressing.

5. The finishing device according to any one of claims 1 to 4,

the determination section determines whether or not re-dressing of the grinding stone can be performed based on the degree of shape damage immediately after the dressing of the grinding stone is performed,

the execution unit executes the refinishing when the determination unit determines that the refinishing is executed.

6. The finishing device according to any one of claims 1 to 5,

the detector detects at least one of an average value of a plurality of chatter amounts, a degree of difference between the plurality of chatter amounts, and a difference between a maximum value and a minimum value of the plurality of chatter amounts, using a plurality of chatter amounts obtained from circumferential chatter at the plurality of axial positions, respectively, as the surface property evaluation value representing the surface condition of the workpiece.

7. The finishing device according to any one of claims 1 to 5,

the detector detects at least one of an average deviation of outer diameters, a degree of difference in outer diameters, and a difference between a maximum value and a minimum value of outer diameters at a plurality of axial positions as the outer diameter evaluation value indicating the surface state.

8. The finishing device according to any one of claims 1 to 5,

the detector performs the following processing:

using a planar surface property representing the surface property of the workpiece as a planar surface property, acquiring a linear surface property representing a relationship between the axial position and the surface property for each circumferential position of the workpiece,

obtaining a plurality of representative values for each of the linear surface properties,

as the surface property evaluation value representing the surface state of the workpiece, at least one of an average value of the representative values, a degree of difference of the representative values, and a difference between a maximum value and a minimum value of the representative values is detected.

9. The finishing device according to any one of claims 1 to 5,

the detector detects a representative value of the entire surface as the surface property evaluation value indicating the surface state of the workpiece, using a planar surface property indicating the surface property as a planar surface property.