Internal surface grinder maintenance method, grinding system, and ring-shaped member manufacturing method

Abstract

The present application provides a maintenance method for an internal surface grinder capable of properly determining a replacement time of a grinding wheel. The maintenance method for the internal surface grinder of the present application includes: a process of measuring a drive current of a motor that moves a rotating grinding wheel in a cutting-in direction during sparkless grinding, and collecting drive current data during the sparkless grinding; and a process of determining a replacement time of the grinding wheel based on a temporal change in the drive current data during the sparkless grinding.

Description

Technical Field

[0001] This application relates to a method for maintaining an internal surface grinding machine, an internal surface grinding system, and a method for manufacturing a ring-shaped component. Background Technology

[0002] Internal surface grinding is a machining method that uses a chuck or similar device mounted on the spindle table of a grinding machine to hold the workpiece, and grinds the inner surface of a workpiece with a hollow cylindrical shape (including annular shape) by means of the rotational motion of the grinding wheel, the reciprocating motion of the table, and the rotational motion of the workpiece. In this specification, a grinding machine capable of performing such internal surface grinding is referred to as an "internal surface grinding machine".

[0003] In the past, grinding wheels in internal surface grinding machines were replaced when changing the type of workpiece or when a grinding malfunction occurred. Examples of grinding malfunctions include increased deviations in workpiece dimensions, chipping of the grinding edge, and abnormal noises during grinding. Furthermore, there were also cases where grinding wheels were replaced regardless of whether a malfunction actually occurred, simply because the grinding wheel's service life or the number of workpieces processed reached specified values.

[0004] For example, in the manufacture of rare-earth sintered toroidal magnets, the hollow cylindrical magnet undergoes circumferential grinding, longitudinal grinding, and internal surface grinding. During internal surface grinding, the radial dimension of the grinding wheel needs to be smaller than the inner diameter of the toroidal magnet. When rare-earth sintered toroidal magnets are miniaturized, a large load is applied to the finer grinding wheel during internal surface grinding, leading to increased wheel wear. As the wear and deterioration of the grinding wheel increase, the aforementioned defects are more likely to occur during grinding. Furthermore, wheel wear and deterioration can lead to further processing instability.

[0005] Patent Documents 1 and 2 disclose techniques for monitoring vibrations during internal surface grinding and for estimating wear and deterioration of grinding tools based on vibration conditions.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-171871

[0009] Patent Document 2: Japanese Patent Application Publication No. 2008-290203 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] Monitoring vibrations during internal surface grinding requires installing vibration sensors on the internal surface grinding machine. Since vibrations have three degrees of freedom in three directions within three-dimensional space, multi-axis accelerometers (e.g., three or more axes) are needed for detection, making data analysis complex.

[0012] The applicant explored measuring the drive current (load current) of the motor used to rotate the grinding wheel and judging the degree of wear (deterioration) of the grinding wheel based on the measured change in drive current over time. However, it was found that the current of the motor that rotates the grinding wheel rarely changes over time, even when the grinding wheel is worn or deteriorated, making it difficult to use for judging the replacement time of the grinding wheel.

[0013] This invention provides a method for maintaining an internal surface grinding machine, an internal surface grinding system, and a method for manufacturing a ring-shaped component that can solve such problems.

[0014] Technical solutions for solving the problem

[0015] In an exemplary, non-limiting embodiment, the maintenance method for an internal surface grinding machine disclosed herein includes: a step of measuring the drive current of a motor that moves a rotating grinding wheel along the cutting direction during sparkless grinding and collecting drive current data during sparkless grinding; and a step of determining the replacement time of the grinding wheel based on the time-dependent changes in the drive current data during sparkless grinding.

[0016] In one embodiment, the process includes a step of reciprocating the grinding wheel along a rotating axis, and the replacement time of the grinding wheel is determined based on the characteristic quantity of the vibration waveform of the drive current generated by the reciprocating motion of the grinding wheel during sparkless grinding.

[0017] In one embodiment, the characteristic quantity includes at least one of the amplitude, average value, and maximum value of the vibration waveform of the drive current.

[0018] In one embodiment, the grinding tool is replaced when the value of the characteristic quantity exceeds a predetermined value.

[0019] In one embodiment, the relationship between the feature quantity and the change time of the grinding wheel is defined by a learned model, which is generated by machine learning using drive current data collected from multiple grinding wheels during sparkless grinding as learning data.

[0020] In one embodiment, in addition to the time-varying drive current data during sparkless grinding, the grinding wheel replacement time is determined based on at least one of several parameters, including the number of workpieces being ground on the inner surface by the grinding wheel and the total time of the inner surface grinding.

[0021] In one embodiment, the grinding tool has diamond abrasive grains on its surface.

[0022] In a non-limiting, exemplary embodiment, the internal surface grinding system of the present invention is an internal surface grinding system for grinding the internal surface of a workpiece that is a hollow cylinder extending along a central axis, comprising: a first motor that rotates a grinding wheel about a rotation axis parallel to the central axis; a second motor that moves the grinding wheel along a tangential direction orthogonal to the rotation axis; a third motor that moves the grinding wheel along a lateral direction parallel to the rotation axis; a control device that controls the operation of the first, second, and third motors; and a galvanometer that measures the drive current of the second motor during sparkless grinding, in which the movement of the grinding wheel based on the second motor stops and the inner surface of the hollow portion of the workpiece is ground by the rotating grinding wheel, and the control device stores the drive current of the second motor during sparkless grinding in a storage device.

[0023] In one embodiment, a maintenance information providing device is also included, which provides the user with information related to the replacement time of the grinding wheel based on the drive current of the second motor during sparkless grinding.

[0024] In one embodiment, the maintenance information providing device prompts the user with characteristic quantities of the vibration waveform of the drive current data generated by the reciprocating motion of the grinding wheel along the traverse direction during sparkless grinding.

[0025] In one embodiment, the maintenance information providing device determines the replacement time of the grinding wheel based on the characteristic quantity.

[0026] In one embodiment, the characteristic quantity includes at least one of the amplitude, average value, and maximum value of the vibration waveform of the drive current.

[0027] In one embodiment, the maintenance information providing device prompts the user with information related to the replacement of the grinding wheel when the value of the characteristic quantity exceeds a predetermined value.

[0028] In one embodiment, the maintenance information providing device determines the content of information related to the replacement time of the grinding wheel or the timing of prompting the user based on a learned model generated through machine learning. The machine learning uses drive current data collected from multiple grinding wheels during sparkless grinding as learning data to study the relationship between the feature quantity and the replacement time of the grinding wheel.

[0029] In one embodiment, the grinding tool has diamond abrasive grains on its surface.

[0030] In a non-limiting, exemplary embodiment, the method for manufacturing the annular component of the present invention includes: a step of preparing a workpiece of a hollow cylinder extending along a central axis; an inner surface grinding step of machining the inner surface of the hollow portion of the workpiece using a grinding wheel; and a step of obtaining the annular component from the workpiece, wherein in the inner surface grinding step, the grinding wheel is rotated about a rotation axis parallel to the central axis using a first motor, the grinding wheel is moved along a tangential direction intersecting the rotation axis using a second motor, the inner surface of the hollow portion is pressed with the rotating grinding wheel, and the drive current of the second motor is measured during sparkless grinding of the inner surface of the hollow portion using the rotating grinding wheel when the movement of the grinding wheel based on the second motor stops.

[0031] In one embodiment, the replacement time of the grinding tool is determined based on the measured value of the drive current.

[0032] In one embodiment, the workpiece is a rare-earth sintered ring magnet.

[0033] In one embodiment, the grinding tool has diamond abrasive grains on its surface.

[0034] Invention Effects

[0035] According to embodiments of the present invention, a maintenance method for an internal surface grinding machine, an internal surface grinding system, and a method for manufacturing a ring-shaped component can be provided. Specifically, the replacement time of the grinding wheel can be appropriately determined based on the current flowing through the infeed motor during sparkless grinding in the internal surface grinding process. Attached Figure Description

[0036] Figure 1 This is a perspective view showing an example of the configuration relationship between the hollow cylindrical workpiece 10 and the grinding wheel 20 during internal surface grinding.

[0037] Figure 2A This is a top view schematic diagram showing an example of the configuration of the internal surface grinding machine 100 in this embodiment.

[0038] Figure 2BThis is a side view schematic diagram showing an example of the configuration of the internal surface grinding machine 100 in this embodiment.

[0039] Figure 3 (a) to (d) are schematic cross-sectional views representing the various stages of the internal surface grinding process.

[0040] Figure 4 (a) to (d) are other schematic cross-sectional views representing the various stages of the internal surface grinding process.

[0041] Figure 5 (a) is a schematic cross-sectional view showing the beginning stage of sparkless grinding in the internal surface grinding process, and (b) is a schematic cross-sectional view showing the completion stage of sparkless grinding.

[0042] Figure 6 (a) is a graph schematically showing the relationship between lateral momentum and time, and (b) is a graph schematically showing the relationship between the amount of cutting and time.

[0043] Figure 7 This is a graph showing an example of the drive current of the second motor M2 when grinding the inner surface of a workpiece using a grinding wheel.

[0044] Figure 8 (a), (b), (c), and (d) are graphs showing examples of the drive current flowing through the second motor M2 when the number of workpieces being ground on the inner surface using a grinding wheel is the 1st, 200th, 5000th, and 17000th.

[0045] Figure 9 (a), (b), (c), and (d) are respectively... Figure 8 The graphs (a), (b), (c) and (d) show the amplified driving current flowing through the second motor M2 during sparkless grinding.

[0046] Figure 10A This is a graph showing the correlation coefficient between the number of internal surface grinding operations and the drive current of the infeed axis motor (second motor M2) and the statistics (maximum, range, σ).

[0047] Figure 10B This is a graph showing the correlation coefficient between the number of internal surface grinding operations and the drive current of the grinding wheel shaft motor (motor M2, number 1) (maximum value, range, σ).

[0048] Figure 11 (a), (b), (c) and (d) are graphs showing examples of the drive current flowing through the first motor M1 when the number of workpieces being ground on the inner surface using a grinding wheel is the 1st, 200th, 5000th and 17000th respectively.

[0049] Figure 12 (a), (b), (c) and (d) are graphs showing examples of the drive current flowing through the third motor M3 when the number of workpieces being ground on the internal surface using a grinding wheel is the 1st, 200th, 5000th and 17000th.

[0050] Figure 13 This is a block diagram illustrating an example of the hardware configuration of a control device. Detailed Implementation

[0051] The embodiments of the present invention will now be described. However, there are instances where detailed descriptions that exceed the necessary scope are omitted. For example, detailed descriptions of known matters and repetitive descriptions of substantially the same components may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the inventors have provided the drawings and the following description to enable those skilled in the art to fully understand this disclosure, but it is not intended that the drawings and description limit the subject matter of the claims. In the following description, the same reference numerals are used to denote constituent elements having the same or similar functions.

[0052] The following embodiments are examples, and the technology disclosed herein is not limited to these embodiments. For example, the values, shapes, materials, steps, order of steps, and layout of the display screen shown in the following embodiments are merely examples, and various changes can be made without causing technical inconsistencies. Furthermore, one solution can be combined with other solutions without causing technical inconsistencies.

[0053] First, refer to Figure 1 , Figure 2A and Figure 2B The basic description of internal surface grinding is given first, followed by an explanation of the maintenance method for the internal surface grinding machine and the implementation of the internal surface grinding system according to the present invention. Finally, an example of internal surface grinding of a rare earth sintered ring magnet will be used as an example to illustrate an implementation of the method for manufacturing the ring-shaped component according to the present invention.

[0054] Figure 1 This is a perspective view showing an example of the arrangement of a hollow cylindrical workpiece 10 and a grinding wheel 20 in an internal surface grinding process. For reference, the X, Y, and Z axes, which are orthogonal to each other, are shown in the figure.

[0055] In the illustrated example, the hollow cylindrical workpiece 10 is configured with its central axis parallel to the Z-axis direction. As described later, the workpiece 10 is held on the spindle of an internal surface grinding machine. The grinding wheel 20 has an abrasive wheel 20A on which numerous abrasive grains formed of a high-hardness material such as diamond are electrodeposited by electroplating or the like, and a rigid shaft 20B supporting the abrasive wheel 20A. With the grinding wheel 20 inserted into the interior of the hollow cylinder of the workpiece 10, it rotates while pressing against the inner surface 12 of the hollow cylinder to perform internal surface grinding. The rotation axis of the grinding wheel 20 moves a predetermined amount little by little in the "cut-in" direction (X-axis direction) as the internal surface grinding progresses. During internal surface grinding, grinding fluid is supplied to the machined surface for cooling and to reduce the machining load by improving chip removal and lubrication.

[0056] The radial dimension of the grinding wheel 20 needs to be smaller than the radial dimension (inner diameter) of the hollow cylinder of the workpiece 10. For example, when the inner diameter of the workpiece 10 is 20 mm, an abrasive wheel 20A with an outer diameter of about 16 mm can be used. In this case, the outer diameter and length of the rigid shaft 20B can be, for example, about 15 mm and 100 mm, respectively. If the inner diameter of the workpiece 10 becomes smaller, a thinner rigid shaft 20B needs to be used. For example, when grinding the inner surface of hard workpieces such as rare earth sintered toroidal magnets, the force (machining load) acting on the grinding wheel 20 during inner surface grinding is large, causing deflection of the thinner rigid shaft 20B.

[0057] In internal surface grinding, the grinding wheel 20 can also perform a reciprocating "traverse" motion in a direction parallel to its rotation axis (Z-axis direction). This traverse motion achieves uniformity of the grinding amount in the Z-axis direction. Additionally, the workpiece 10 itself also rotates around its central axis. Preferably, the rotation direction of the workpiece 10 and the rotation direction of the grinding wheel 20 are opposite to each other.

[0058] The depth of cut (cut-in amount) of the grinding wheel 20, i.e., the amount of movement of the grinding wheel 20 in the X-axis direction, is defined as the thickness of the area removed from the inner surface of the hollow cylinder of the workpiece 10. The position of the grinding wheel 20 in the X-axis direction when the cutting stops is determined according to the target inner diameter of the workpiece 10 after the inner surface is ground.

[0059] Figure 2A This is a top view schematic diagram showing an example of the configuration of the internal surface grinding machine 100 in this embodiment. Figure 2B This is a side view of the internal surface grinding machine 100. The internal surface grinding machine 100 is included in the internal surface grinding system 1000 disclosed herein. The internal surface grinding system 1000 may also include the maintenance information providing device described below, in addition to the internal surface grinding machine 1000.

[0060] A hollow cylindrical workpiece 10 is set as the workpiece (machining object) in the internal surface grinding machine 100. In the illustrated example, the hollow cylindrical workpiece 10 is mounted on the internal surface grinding machine 100 with its central axis parallel to the Z-axis direction.

[0061] The internal surface grinding machine 100 includes a first motor M1, a second motor M2, and a third motor M3. The first motor M1 rotates the grinding wheel 20 about a rotational axis R1 parallel to the Z-axis. The second motor M2 moves the grinding wheel 20 along a tangential direction (X-axis direction) orthogonal to the rotational axis R1. The third motor M3 moves the grinding wheel 20 along a transverse direction (Z-axis direction) parallel to the rotational axis R1. The rotational motion of the output shafts of the second motor M2 and the third motor M3 is converted into linear motion, for example, by a device such as a ball screw. The position and number of these motors M1 to M3 are not limited to the example shown. In particular, the second motor M2 and the third motor M3 can be arranged in positions different from the example shown, depending on the structure of the device that converts the rotational motion into linear motion.

[0062] The first motor M1, the second motor M2, and the third motor M3 are sometimes referred to as the "grinding axis motor," the "cut-in axis motor," and the "transverse axis motor," respectively. Furthermore, the internal surface grinding machine 100 includes a fourth motor M4 capable of rotating the workpiece 10 about a rotational axis parallel to the Z-axis. The workpiece 10 is fixed to the output shaft of the fourth motor M4 by means of a workpiece holding member (workpiece holding device) 42, such as a collet chuck.

[0063] These motors M1 to M4 can be, for example, servo motors. A servo motor is, for example, an AC synchronous motor that includes a rotational position detection sensor such as a rotary encoder. A motor typically includes a stator and a rotor. The torque of the motor is controlled by adjusting the magnitude of the current (drive current) flowing through the coils of the stator. In this embodiment, the rotational position, speed, and torque of each of the motors M1 to M4 can be controlled to the desired values ​​using known control methods by obtaining feedback from measured, estimated, or commanded values ​​of the drive current, rotational position, and rotational speed of each motor.

[0064] The internal surface grinding machine 100 includes a control device 60 for controlling the movements of the first motor M1, the second motor M2, the third motor M3, and the fourth motor M4 (see reference). Figure 2B The control device 60 includes a computer, described later, and is electrically connected to actuators other than motors M1 to M4, and various sensors (ammeters, position sensors). Figure 2BFor convenience, the control device 60 is described as being located within the base 50, but the location of the control device 60 is not limited to the example shown. Furthermore, some or all of the functions of the control device 60 can also be performed by a computer or other device located elsewhere outside the internal surface grinding machine 100. In particular, operations such as storing the current measurement values ​​described later and performing calculations required for maintenance can be performed by a computer (a control device located outside the grinding apparatus) other than the computer used to perform the normal grinding operations of the internal surface grinding machine 100 (the control device for grinding operations).

[0065] In this embodiment, the control device 60 includes a servo amplifier for driving motors M1 to M4. Although not shown, motor drive circuits that supply current to motors M1 to M4 are connected to motors M1 to M4 respectively, and control motors M1 to M4 according to command values ​​from the control device 60. Motors M1 to M4 may also be motor modules that have built-in motor drivers, DC-DC converters, inverters, and other circuits.

[0066] A first motor M1, which rotates the grinding wheel 20 about a rotation axis R1 parallel to the Z-axis, is mounted on a cutting-in moving stage 24. In the illustrated example, the cutting-in moving stage 24 is supported on a transverse moving stage 32 so as to be able to move along the cutting-in axis track 26X in the X-axis direction. The position of the cutting-in moving stage 24 in the X-axis direction is controlled by a second motor M2 on the transverse moving stage 32. The position, moving speed, and pressing force on the inner surface of the hollow cylinder of the workpiece 10 in the X-axis direction of the grinding wheel 20 can be controlled by the drive current of the second motor M2. In addition, the drive current of the second motor M2 can also be referred to as the "cutting-in axis current".

[0067] The traverse moving stage 32 is supported on the base 50 in a manner that allows it to move along the traverse axis track 34Z in the Z-axis direction (traverse axis direction). The position of the traverse moving stage 32 in the Z-axis direction is controlled, for example, by a third motor M3 mounted on the base 50. The position and movement speed of the grinding wheel 20 in the Z-axis direction can be controlled by the drive current of the third motor M3. Figure 2A In this diagram, there are two third motors, M3, but there can also be only one third motor, M3. The driving current of the third motor, M3, can also be called the "transverse shaft current".

[0068] A fourth motor M4, capable of rotating workpiece 10 about a rotation axis parallel to the Z-axis, is supported by a workpiece stand 44 on a base 50. During internal surface grinding, the fourth motor M4 rotates workpiece 10, causing the position of the area in contact with the grinding wheel 20 to move along the inner surface of the hollow cylinder of workpiece 10, thus enabling the circumferential grinding of the entire inner surface of the hollow cylinder of workpiece 10. When workpiece 10 is not rotated, a planetary motion is performed to rotate the rotation axis R1 of the grinding wheel 20 about the central axis of workpiece 10.

[0069] As described later, in the internal surface grinding process performed using the aforementioned internal surface grinding machine 100, the grinding wheel 20 is rotated about a rotation axis R1 parallel to the central axis using the first motor M1, and the grinding wheel 20 is moved along a tangential direction (X-axis direction) intersecting the rotation axis R1 using the second motor M2. The rotating grinding wheel 20 then presses against the inner surface of the hollow portion of the workpiece 10. After stopping the movement of the grinding wheel 20 based on the second motor M2, "spark-free grinding" (spark out, clean grinding, finishing grinding) is performed on the inner surface of the hollow portion using the rotating grinding wheel 20. Details of "spark-free grinding" will be described later.

[0070] The internal surface grinding machine 100 or internal surface grinding system 1000 in this embodiment includes a galvanometer 28 that measures the drive current (cut-in shaft current) of the second motor M2 during the internal surface grinding process, specifically during "sparkless grinding" where the grinding wheel 20 based on the second motor M2 stops moving and the rotating grinding wheel 20 grinds the inner surface of the hollow portion of the workpiece 10. Furthermore, the control device 60 is configured to store the drive current of the second motor M2 during sparkless grinding in a storage device 240. The display device 220 displays information such as changes in drive current and grinding wheel replacements as needed.

[0071] Alternatively, the storage device 240 and the display device 220 may also be located within the maintenance information providing device described later.

[0072] In the embodiments of this disclosure, the reason for measuring the drive current of the second motor M2 during sparkless grinding is not only to obtain the feedback required for the aforementioned motor control, but also to obtain the data or information required for the maintenance of the grinding wheel 20. Details of this point will be described later.

[0073] Next, refer to Figures 3 to 6 The internal surface grinding process is described in detail.

[0074] Figure 3 (a) to (d) and Figure 4 (a) through (d) are other schematic cross-sectional views representing the various stages of the internal surface grinding process.

[0075] First, such as Figure 3 As shown in (a), the grinding wheel 20 is inserted into the position where it contacts the inner surface 12 of the workpiece 10. Figure 3 (b) to Figure 3 As shown in (d), the grinding wheel 20, rotating about a rotation axis parallel to the Z-axis, performs a reciprocating (lateral) motion along the Z-axis while moving along the X-axis. As mentioned earlier, the movement of the grinding wheel 20 in the X-axis direction is called "cut-in," and the amount of movement defines the cut-in amount. The cut-in amount increases as the internal surface grinding progresses, and the inner diameter of the workpiece 10 expands.

[0076] like Figure 4 (a) to Figure 4 As shown in (d), when the rigid shaft 20B deflects due to the machining load acting on the grinding wheel 20 during internal surface grinding, the amount of grinding on the inner surface of the workpiece 10 varies depending on its position (Z coordinate value) in the Z-axis direction. Figure 4 (c) and Figure 4 As emphasized in (d), when the rigid body axis 20B deflects, the larger the Z coordinate value, the smaller the inner diameter of the workpiece 10.

[0077] To ensure that the inner diameter of workpiece 10 has a fixed value independent of the Z-coordinate, in this embodiment, after stopping the cutting, "spark-free grinding" is performed while maintaining the position of the grinding wheel 20 in the X-axis direction. "Spark-free grinding" refers to the state where the cutting of the grinding wheel 20 stops when the inner diameter of workpiece 10 reaches or approaches the target size. However, strictly speaking, although the inner diameter reaches the target size at a position closer to the second motor M2 that rotates the grinding wheel 20 within the hollow cylinder of workpiece 10, it does not reach the target size at the other end, which is farther from the second motor M2. Here, at a position closer to the second motor M2, there is a situation where, as the sharpness of the grinding wheel decreases, the inner diameter approaches the target size but does not reach it. In other words, this means that the inner diameter size differs between the positions closer to and farther from the second motor M2. This is because at the root of the grinding wheel 20, grinding corresponding to the depth of cut occurs relatively early, while at a position closer to the tip of the grinding wheel 20, grinding occurs later due to the elastic deflection of the rigid shaft 20B. However, if the infeed is stopped during sparkless grinding and the remaining cutting material is ground, the inner diameter of the workpiece 10 becomes uniform within tolerances regardless of its location. Therefore, sparkless grinding is sometimes also referred to as "zero cut".

[0078] Figure 5 (a) is a schematic cross-sectional view showing the stage at the beginning of sparkless grinding in the internal surface grinding process. Figure 5(b) is a schematic cross-sectional view showing the stage after sparkless grinding is completed. Utilizing the elastic force of the rigid shaft 20B, the rigid shaft 20B resists the machining load and attempts to return to a straight state. The machining residue (the area with a relatively small inner diameter) remaining in the workpiece 10 is ground away in sparkless grinding, achieving uniformity of the inner diameter dimension. Figure 5 In stage (b) shown, the deflection of rigid body axis 20B is essentially eliminated. Figure 5 The stage of (a) and Figure 5 In stage (b), the position of the root of rigid body axis 20B in the X direction is the same.

[0079] Figure 6 (a) is a graph schematically illustrating an example of the relationship between traverse motion (Z-axis coordinate value) and time in internal surface grinding. Figure 6 (b) is a graph schematically showing the relationship between the cutting depth (X-axis coordinate value) and time. Figure 6 In example (a), the transverse momentum changes into a triangular wave shape over time, but the transverse momentum is not limited to this example. The transverse momentum can also change into a rectangular wave, a sine wave, or any other arbitrary shape over time.

[0080] Depend on Figure 6 As shown in (b), the depth of cut (X-axis coordinate value) remains constant during sparkless grinding. Furthermore, in the illustrated example, traverse motion is also performed during sparkless grinding.

[0081] In this embodiment, the drive current of the second motor M2 is measured from the start to the end of sparkless grinding. To maintain the depth of cut (X-axis coordinate value) of the rotating grinding wheel at a certain position, the second motor M2 needs to generate a torque that counteracts the machining load of the internal surface grinding. Therefore, the magnitude of the drive current of the second motor M2 varies in response to changes in the machining load of the internal surface grinding. The inventors have discovered that when the grinding wheel 20 deflects from... Figure 5 The stage change of (a) is as follows Figure 5 The change in machining load during stage (b) depends on the degree of wear and deterioration of the grinding wheel 20. It was also thought that the degree of wear and deterioration of the grinding wheel 20 could be estimated by measuring the drive current of the second motor M2 during sparkless grinding, thereby determining the replacement time of the grinding wheel 20.

[0082] Figure 7This is a graph illustrating an example of the drive current of the second motor M2 during the internal surface grinding of a workpiece using a specific grinding wheel. The horizontal axis represents the elapsed time of the internal surface grinding process from start to finish, and the vertical axis represents the magnitude (measured value) of the drive current of the second motor M2. In this example, the infeed time for the internal surface grinding process is approximately 26 seconds, and the sparkless grinding time is approximately 15 seconds. The reason for the fluctuation in the current magnitude is as follows: Figure 6 As shown in (a), the grinding wheel undergoes traverse motion. More specifically, the magnitude of the force (load) on the grinding wheel along the entry axis from the workpiece changes according to the amount of traverse motion. Figure 5 As shown in (a), because the grinding wheel 20 deflects, the inner diameter of the workpiece 10 tends to decrease as its coordinate position in the Z-axis direction increases. As a result, the load on the grinding wheel 20 from the workpiece 10 increases at positions with relatively large traverse movement. During sparkless grinding, the depth of cut needs to be maintained at a constant value; therefore, the second motor M2 needs to generate a torque corresponding to the load on the grinding wheel 20 from the workpiece 10. Since traverse movement also occurs during sparkless grinding, the current flowing through the second motor M2 during sparkless grinding also increases or decreases according to the vibration of the traverse movement.

[0083] Figure 8 (a), (b), (c) and (d) are graphs showing examples of the drive current flowing through the second motor M2 when the number of workpieces being ground on the inner surface using the grinding wheel 20 is the 1st, 200th, 5000th and 17000th workpieces, respectively.

[0084] Figure 9 (a), (b), (c), and (d) are respectively... Figure 8 The graphs show the amplified drive current flowing through the second motor M2 during sparkless grinding in (a), (b), (c), and (d).

[0085] like Figure 8 and Figure 9 As shown, the current flowing through the second motor M2 during sparkless grinding depends on the degree of wear and deterioration of the grinding wheel 20. For example, the more severe the wear and deterioration of the grinding wheel 20, the higher the average and maximum values ​​(the envelope on the highest side) of the current flowing through the second motor M2 during sparkless grinding become as the grinding time progresses. Figure 9 The time (as shown in the figure) is reduced. The reason is believed to be that the grinding load during sparkless grinding varies sensitively depending on the wear and deterioration state of the grinding wheel 20. As mentioned earlier, during sparkless grinding, the second motor M2, acting as the infeed axis motor, also performs position control while pressing the workpiece 10 with the grinding wheel 20. Therefore, the second motor M2 needs to generate torque. The magnitude of this torque is proportional to the magnitude of the drive current of the second motor M2.

[0086] Compare Figure 9 (a) and Figure 9 In (b), no significant difference was observed in the current waveform. In contrast, a comparison... Figure 9 (b) and Figure 9 As shown in (c), the average and maximum values ​​of the current waveform (the envelope on the higher side) decrease with the elapsed time since the start of machining on the inner surface. Further comparison... Figure 9 (c) and Figure 9 (d) shows an increase in the amplitude of the current waveform vibration. This increase is due to the increased load on the motor during traverse caused by the deterioration of the grinding wheel. In this experimental example, it was confirmed that the wear and deterioration of the grinding wheel were significant when the number of workpieces ground on the inner surface was approximately 17,000. Therefore, it is preferable to use a grinding wheel with a high internal surface wear rate. Figure 9 The current waveform of (c) changes to Figure 9 The grinding tool is changed based on the time of the current waveform of (d).

[0087] Figure 10A This is a graph showing the correlation coefficients (maximum, range, σ) between the number of internal surface grinding operations and the drive current of the infeed axis motor (motor M2, second motor). "Maximum" is the maximum value of the drive current of motor M2, "Range" is the difference between the maximum and minimum values, and "σ" is the standard deviation. The correlation coefficients are calculated using known statistical analysis for both infeed (between 2.5 and 25 seconds after machining begins) and sparkless grinding (between 27 and 40 seconds after machining begins). Figure 10B This is a graph showing the same correlation coefficients obtained for the drive current of the motor (motor M1) for the mold shaft.

[0088] like Figure 10A As shown, the correlation coefficient between the maximum current flowing through the motor (second motor M2) on the infeed axis during sparkless grinding and the number of machining operations is approximately 0.72, which is a relatively large value. Furthermore, the standard deviation σ does not exceed 0.5. This indicates that the maximum current flowing through the motor (second motor M2) on the infeed axis during sparkless grinding is a parameter reflecting an increase in the number of machining operations, and is suitable as an indicator for determining changeover time. On the other hand, as... Figure 10BAs shown, the maximum current flowing through the grinding wheel shaft motor (motor M1) during sparkless grinding has a correlation coefficient of 0.62 with the number of machining operations, which is considered to be a high correlation. However, in the case of the grinding wheel shaft motor, the standard deviation σ of the current flowing through the grinding wheel shaft during sparkless grinding also shows a high correlation coefficient of approximately 0.75 with the number of machining operations. This means that the variation and deviation of the current flowing through the grinding wheel shaft motor (motor M1) during sparkless grinding increases with the increase of the number of machining operations. Therefore, it is difficult to determine the timing of grinding wheel replacement based on the change in the current flowing through the grinding wheel shaft motor (motor M1) during sparkless grinding.

[0089] Figure 11 (a), (b), (c) and (d) are graphs showing examples of the drive current flowing through the first motor M1 that rotates the grinding wheel 20 when the number of workpieces being ground on the inner surface using the grinding wheel 20 is the 1st, 200th, 5000th and 17000th workpieces.

[0090] from Figure 11 It can be observed that the waveform of the current flowing through the first motor M1 changes according to the wear and deterioration state of the grinding wheel 20. However, according to the inventor's research, it is difficult to find an effective characteristic quantity for determining the replacement time of the grinding wheel 20.

[0091] Figure 12 (a), (b), (c) and (d) are graphs showing examples of the drive current flowing through the third motor M3, which performs lateral movement, when the number of workpieces being ground on the inner surface by the grinding wheel 20 is the 1st, 200th, 5000th and 17000th workpieces.

[0092] Depend on Figure 12 It can be seen that the waveform of the current flowing through the third motor M3 does not depend on the wear and deterioration state of the grinding wheel 20.

[0093] The above experiments clearly show that the current flowing through the second motor M2, which is the infeed axis motor, during sparkless grinding can extract a characteristic quantity representing the wear and deterioration state of the grinding wheel. Based on this characteristic quantity, the replacement time of the grinding wheel can be determined or estimated.

[0094] The maintenance method for the internal surface grinding machine in this embodiment of the invention includes: a step of measuring the drive current flowing through a motor that moves the rotating grinding wheel in the cutting direction during sparkless grinding and collecting drive current data during sparkless grinding; and a step of determining the replacement time of the grinding wheel based on the time-varying changes in the drive current data during sparkless grinding.

[0095] As described above, in the maintenance method of this disclosure, characteristic quantities such as the amplitude of the waveform are easily extracted in the process of causing the grinding wheel to reciprocate (traverse) along the rotation axis. It is believed that the replacement time of the grinding wheel can be easily determined based on the characteristic quantities of the vibration waveform of the drive current generated by the reciprocating motion of the grinding wheel during sparkless grinding. As mentioned above, examples of the characteristic quantities preferably include at least one of the amplitude, average value, and maximum value of the vibration waveform of the drive current; in this case, for example, the grinding wheel can be replaced when the value of the characteristic quantity exceeds a predetermined value.

[0096] The relationship between the aforementioned characteristic quantities and the grinding wheel changeover time can be defined by a learned model generated through machine learning using drive current data collected from multiple sparkless grinding wheels as learning data. The learned model generated by machine learning includes a general-purpose computer, a computer program defining the machine learning model, and a set of parameter values ​​acquired through learning. Such a learned model uses characteristic quantities extracted from the current during sparkless grinding to perform predictive maintenance.

[0097] In addition to the time-varying changes in drive current data during sparkless grinding, the grinding wheel replacement time can also be determined based on at least one of several parameters, including the number of workpieces being ground on the internal surface by the grinding wheel and the total time of internal surface grinding. For example, the user can be notified of the grinding wheel replacement time when both conditions are met: the number of workpieces being ground on the internal surface exceeds 15,000 and the amplitude of the drive current data during sparkless grinding increases beyond a specified value.

[0098] The internal surface grinding system 1000 in this embodiment may further include a maintenance information providing device that provides information to the user related to the replacement time of the grinding wheel 20 based on the drive current of the second motor M2 during sparkless grinding. This maintenance information providing device is preferably configured to provide the user with characteristic quantities of the vibration waveform of the drive current data generated by the reciprocating motion of the grinding wheel 20 along the lateral direction during sparkless grinding.

[0099] The maintenance information providing device can be configured to determine the replacement time of the grinding wheel based on a characteristic quantity. The characteristic quantity is preferably at least one of the amplitude, average value, and maximum value of a vibration waveform containing the drive current. The maintenance information providing device can be configured to prompt the user with information related to the replacement of the grinding wheel when the value of the characteristic quantity exceeds a predetermined value. Furthermore, the maintenance information providing device can be configured to determine the content of the information related to the replacement time of the grinding wheel or the timing of prompting the user based on a learned model generated through machine learning. For the relationship between the characteristic quantity and the replacement time of the grinding wheel, the machine learning uses drive current data collected from multiple grinding wheels during sparkless grinding as training data.

[0100] When the control device 60 is implemented by a computer, the maintenance information providing device can also be implemented through the control device 60. Furthermore, the maintenance information providing device can also be implemented by a server computer located in the cloud, and can also be configured to display maintenance information on a user's portable terminal.

[0101] Figure 13 This is a block diagram illustrating an example of the hardware configuration of the control device 60 in this embodiment.

[0102] The control device 60 includes an input device 210, a display device 220, a communication I / F 230, a storage device 240, a processor 250, a ROM (Read Only Memory) 260, and a RAM (Random Access Memory) 270. These components are interconnected via a bus 280.

[0103] Input device 210 is a device for converting instructions from a user into data and inputting it into a computer. Input device 210 may be, for example, a keyboard, mouse, or touch panel.

[0104] The Communication I / F230 is an interface for data communication between the control device 60 and external devices. For example, the Communication I / F230 can perform wired communication according to USB, IEEE 1394 (trademarked), or Ethernet (trademarked). The Communication I / F230 can also perform wireless communication according to the Bluetooth (trademarked) standard and / or the Wi-Fi (trademarked) standard. All standards include wireless communication standards using frequencies in the 2.4 GHz band.

[0105] 5. Storage device 240 is, for example, a semiconductor memory, a magnetic storage device, or an optical storage device.

[0106] Or combinations thereof. An example of an optical storage device is a CD-ROM drive. Examples of magnetic storage devices are hard disk drives (HDDs) or magnetic tape recording devices.

[0107] The processor 250 consists of one or more semiconductor integrated circuits, also known as the central processing unit.

[0108] Processing unit (CPU) or microprocessor. Processor 250 sequentially executes computer programs stored in ROM 260, which contain a set of commands necessary for grinding operations, including internal surface grinding.

[0109] The sequence is to achieve the desired processing.

[0110] In this embodiment, the processor 250 of the control device 60 functions as a maintenance information providing device by executing a predetermined algorithm based on a program. This maintenance information provides...

[0111] The device provides the user with information related to the replacement time of the grinding wheel 20 based on the drive current of the second motor M2 during sparkless grinding. Additionally, the device provides maintenance information.

[0112] This does not require the control device 60 of the internal surface grinding machine 100 to implement. For example, an external computer (e.g., a personal computer, portable terminal device, cloud computer) that obtains drive current data from the control device 60 via wired or wireless communication can also function as part or all of the maintenance information providing device.

[0113] 0. When the maintenance information providing device is implemented by an external computer, etc., the drive current data is preserved.

[0114] Storage can also be performed by a maintenance information providing device.

[0115] The term "processor 250" can be broadly interpreted as including FPGA (Field Programmable Gate Array), GPU (Graphics Processor Unit), ASIC (Application Specific Integrated Circuit), or ASSP (Application Specific Standard Product) which incorporates a CPU.

[0116] ROM 260 may be, for example, a writable memory (e.g., PROM (Programmable Read-Only Memory)), a rewritable memory (e.g., flash memory), or a dedicated read-out memory. ROM 260 stores a program that controls the operation of the processor. ROM 260 need not be a single recording medium; it can be a collection of multiple recording media. It can also be a removable part of a collection of multiple recording media.

[0117] RAM270 provides a working area that is temporarily expanded when booting the control program stored in ROM260. RAM270 does not need to be a single recording medium; it can be a collection of multiple recording media.

[0118] Utilizing references Figure 2A and Figure 2BThe internal surface grinding system 1000 described herein is capable of implementing a method for manufacturing a ring-shaped component. The method for manufacturing a ring-shaped component according to this disclosure includes: a step of preparing a workpiece consisting of a hollow cylinder extending along a central axis; an internal surface grinding step of machining the inner surface of the hollow portion of the workpiece using a grinding wheel; and a step of obtaining a ring-shaped component from the workpiece. In the internal surface grinding step, a first motor rotates the grinding wheel about a rotation axis parallel to the central axis, a second motor moves the grinding wheel along a tangential direction intersecting the rotation axis, the rotating grinding wheel presses against the inner surface of the hollow portion, and the drive current of the second motor is measured while the movement of the grinding wheel based on the second motor stops and the inner surface of the hollow portion is ground using the rotating grinding wheel in a sparkless grinding process. The replacement time of the grinding wheel can be determined based on the measured value of the drive current.

[0119] According to this method of manufacturing ring-shaped components, when the workpiece is a rare earth sintered ring magnet, a grinding wheel that has been changed at the appropriate time can be used to manufacture rare earth sintered ring magnets with good yield.

[0120] Symbol Explanation

[0121] 10…workpiece

[0122] 20… Grinding tools

[0123] 24…Switch into the mobile platform

[0124] 26X…cut-in axis rail

[0125] 28…Ammeter

[0126] 32… Horizontal Moving Platform

[0127] 34Z…Transverse axis track

[0128] 42…Workpiece retainer

[0129] 44…Workpiece stand

[0130] 50…Abutment

[0131] 60… control device

[0132] 220… display device

[0133] 240… storage devices

[0134] 100… Internal Surface Grinding Machine

[0135] 1000… Internal Surface Grinding System

[0136] R1…rotation axis

[0137] M1…First Motor

[0138] M2…Second Motor

[0139] M3…the third motor

[0140] M4…the fourth motor.

Claims

1. A maintenance method for an internal surface grinding machine, characterized in that, include: The process of measuring the drive current of a motor that moves a rotating grinding wheel along the cutting direction during sparkless grinding and collecting the drive current data during sparkless grinding. and The process of determining the replacement time of the grinding wheel based on the time-dependent changes in the drive current data during sparkless grinding.

2. The maintenance method for an internal surface grinding machine as described in claim 1, characterized in that, This includes the process of causing the grinding wheel to reciprocate along a rotation axis. The replacement time of the grinding wheel is determined based on the characteristic quantity of the vibration waveform of the drive current generated by the reciprocating motion of the grinding wheel during the sparkless grinding process.

3. The maintenance method for an internal surface grinding machine as described in claim 2, characterized in that, The characteristic quantity includes at least one of the amplitude, average value, and maximum value of the vibration waveform of the driving current.

4. The maintenance method for an internal surface grinding machine as described in claim 3, characterized in that, When the value of the characteristic quantity exceeds the specified value, the grinding tool shall be replaced.

5. The maintenance method for an internal surface grinding machine as described in any one of claims 2 to 4, characterized in that, The relationship between the feature quantity and the change time of the grinding wheel is defined by a learned model, which is generated by machine learning using drive current data collected from multiple grinding wheels during sparkless grinding as learning data.

6. The maintenance method for an internal surface grinding machine as described in any one of claims 1 to 4, characterized in that, In addition to the time-varying drive current data during sparkless grinding, the grinding wheel replacement time is determined based on at least one of several parameters, including the number of workpieces being ground on the inner surface using the grinding wheel and the total time of the inner surface grinding.

7. The maintenance method for an internal surface grinding machine as described in any one of claims 1 to 4, characterized in that, The grinding tool has diamond abrasive grains on its surface.

8. An internal surface grinding system, It is an internal surface grinding system for grinding the internal surface of a hollow cylindrical workpiece extending along its central axis, characterized in that, include: The first motor rotates the grinding wheel about a rotation axis parallel to the central axis; The second motor moves the grinding wheel along a tangential direction orthogonal to the rotation axis; The third motor moves the grinding wheel in a transverse direction parallel to the rotation axis; A control device that controls the operation of the first motor, the second motor, and the third motor; and A galvanometer measures the drive current of the second motor during sparkless grinding of the inner surface of the hollow portion of a workpiece using the rotating grinding wheel, when the movement of the grinding wheel based on the second motor stops. The control device stores the drive current of the second motor during sparkless grinding in a storage device, and determines the replacement time of the grinding tool based on the time-varying changes of the drive current.

9. The internal surface grinding system as described in claim 8, characterized in that, It also includes a maintenance information providing device that provides the user with information related to the replacement time of the grinding wheel based on the drive current of the second motor during the sparkless grinding.

10. The internal surface grinding system as described in claim 9, characterized in that, The maintenance information providing device prompts the user with characteristic quantities of the vibration waveform of the drive current data generated by the reciprocating motion of the grinding wheel along the lateral direction during the sparkless grinding.

11. The internal surface grinding system as claimed in claim 10, characterized in that, The maintenance information providing device determines the replacement time of the grinding wheel based on the characteristic quantity.

12. The internal surface grinding system as described in claim 10 or 11, characterized in that, The characteristic quantity includes at least one of the amplitude, average value, and maximum value of the vibration waveform of the driving current.

13. The internal surface grinding system as claimed in claim 12, characterized in that, When the value of the characteristic quantity exceeds a predetermined value, the maintenance information providing device prompts the user with information related to the replacement of the grinding wheel.

14. The internal surface grinding system as described in claim 10 or 11, characterized in that, The maintenance information providing device determines the content of information related to the replacement time of the grinding wheel or the timing of prompting the user based on a learned model generated through machine learning. The machine learning uses drive current data collected from multiple grinding wheels during sparkless grinding as learning data to study the relationship between the feature quantity and the replacement time of the grinding wheel.

15. The internal surface grinding system as described in any one of claims 8 to 11, characterized in that, The grinding tool has diamond abrasive grains on its surface.

16. A method for manufacturing a ring-shaped component, characterized in that, Include: The process of preparing a hollow cylindrical workpiece that extends along the central axis. An internal surface grinding process that uses a grinding wheel to process the inner surface of the hollow portion of the workpiece; and The process of obtaining a ring-shaped component from the workpiece. In the internal surface grinding process. The grinding wheel is rotated about an axis parallel to the central axis using a first motor. The second motor moves the grinding wheel along a cutting direction intersecting the rotation axis, and the rotating grinding wheel presses against the inner surface of the hollow portion. When the movement of the grinding wheel based on the second motor is stopped, and sparkless grinding is performed on the inner surface of the hollow part by the rotating grinding wheel, the drive current of the second motor is measured, and the replacement time of the grinding wheel is determined based on the time change of the drive current.

17. The method for manufacturing a ring-shaped component as described in claim 16, characterized in that, The replacement time of the grinding wheel is determined based on the measured value of the drive current.

18. The method for manufacturing a ring-shaped component as described in claim 16 or 17, characterized in that, The workpiece is a rare earth sintered ring magnet.

19. The method for manufacturing a ring-shaped component as described in claim 18, characterized in that, The grinding tool has diamond abrasive grains on its surface.

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