Grinding device and grinding method

Abstract

This grinding device comprises: a grindstone base having a grindstone; a support part that supports a cylindrical workpiece so as to be capable of rotating about an axis of the workpiece; a drive device configured to be capable of moving the grindstone base relative to the workpiece; and a control unit that controls the drive device while rotating the workpiece about the axis, and causes the rotating grindstone to approach the workpiece in a cutting direction intersecting the axis, thereby grinding the outer peripheral surface of the workpiece. The control unit continuously reduces the speed at which the grindstone cuts into the workpiece as the cutting of the grindstone into the workpiece progresses, and reduces the amount of reduction in the cutting speed as the cutting progresses.

Description

Grinding device and grinding method

[0001] The present disclosure relates to a grinding device and a grinding method.

[0002] Regarding a grinding device, Patent Document 1 discloses that each process is executed in the order of a rough grinding process, a finish grinding process, a fine grinding process, and a spark-out process to grind a workpiece.

[0003] Japanese Unexamined Patent Application Publication No. 2023-158578

[0004] Conventionally, when executing each of the rough grinding process, the finish grinding process, and the fine grinding process, the feed rate of the grinding wheel to the workpiece is made constant during the execution of each process, and in order to ensure the machining quality of the workpiece, the feed rate is made smaller for the later process. As a result, in the fine grinding process, the feed rate is kept constant at a relatively slow speed, resulting in a longer grinding time.

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

[0006] (1) According to a first embodiment of the present disclosure, a grinding apparatus is provided. This grinding apparatus comprises a grinding wheel holder having a grinding wheel, a support unit that rotatably supports a cylindrical workpiece around an axis of the workpiece, a drive unit configured to move the grinding wheel holder relative to the workpiece, and a control unit that grinds the outer surface of the workpiece by controlling the drive unit while rotating the workpiece around the axis, thereby bringing the rotating grinding wheel closer to the workpiece in a cutting direction intersecting the axis. The control unit continuously decreases the cutting speed of the grinding wheel into the workpiece as the cutting progresses, and reduces the amount of decrease in the cutting speed as the cutting progresses. According to this embodiment, as grinding progresses, the cutting speed is continuously decreased and the amount of decrease in the cutting speed is reduced, so that the cutting speed is not kept constant at a relatively slow speed in the relatively later stages of grinding, while suppressing a relatively rapid decrease in the cutting speed. As a result, the grinding time can be kept from being prolonged while ensuring the processing quality of the workpiece. (2) In the above embodiment, the support part has a shoe that supports the outer peripheral surface from the opposite side of the grinding wheel in a direction along the cutting direction of the grinding wheel into the workpiece, and is configured to support the workpiece in a centerless state by the shoe, and the control unit grinds the outer peripheral surface of the workpiece supported by the shoe in the centerless state, and the period during which the workpiece is cut at a first cutting speed is defined as the first period, and the second period following the first period is defined as the period during which the workpiece is cut at a second cutting speed smaller than the first cutting speed, and when the first cutting speed and the second cutting speed are defined as the amount of cutting of the workpiece by the grinding wheel per unit rotation of the workpiece, the difference between the second cutting speed and the first cutting speed may be less than or equal to the dimension by which the workpiece is removed in the second period. According to this configuration, when grinding a workpiece in a centerless state while supporting the workpiece with a shoe, it is possible to suppress a decrease in the machining quality of the workpiece due to changes in the position of the workpiece axis as grinding progresses. (3) In the above configuration, the control unit may continuously decrease the cutting speed according to a sine function.According to this configuration, the cutting speed can be continuously reduced by a simple method. (4) In the above configuration, the control unit may continuously reduce the cutting speed from the start of cutting the workpiece to the completion of cutting according to a curve of the sine function that represents from the inflection point to the next valley after the inflection point. According to this configuration, the cutting speed can be continuously reduced in a simple and effective manner. (5) In the above configuration, the control unit may receive a specification from the user of cutting conditions including an initial speed representing the cutting speed at the start of cutting the workpiece, a final speed representing the cutting speed at the completion of cutting the workpiece, and a cutting time from the start of cutting to the completion of cutting, and continuously reduce the cutting speed according to the sine function based on the specified cutting conditions. According to this configuration, the cutting speed can be continuously reduced by a simple method while reflecting the user's requirements regarding grinding. This disclosure can also be implemented in various forms other than grinding apparatus. For example, it can be implemented in the form of a grinding method, a control method for a grinding apparatus, a computer program for implementing the control method, and a non-temporary recording medium on which the computer program is stored.

[0007] This is an explanatory diagram showing the schematic configuration of a grinding machine. This is a block diagram showing the schematic configuration of a control device. This is an explanatory diagram showing an example of cutting speed data. This is a schematic cross-sectional view illustrating how a workpiece is ground during shoe grinding. This is a flowchart of the machining process in the first embodiment. This is a flowchart of the machining process in the second embodiment.

[0008] A. First Embodiment: Figure 1 is an explanatory diagram showing the schematic configuration of the grinding apparatus 100. Figure 1 shows arrows representing the three coordinate axes, X, Y, and Z, which are mutually orthogonal. The Z axis and X axis are coordinate axes parallel to the horizontal plane. The Y axis is a coordinate axis parallel to the vertical direction. The arrows representing the X, Y, and Z axes in Figure 1 and the arrows representing the X, Y, and Z axes in other figures point in the same direction. When specifying the direction, the positive direction, which is the direction pointed to by the arrow, is denoted as "+", and the negative direction, which is the direction opposite to the direction pointed to by the arrow, is denoted as "-", and both positive and negative signs are used in the direction notation. Hereafter, the +Y direction will also be referred to as "up", and the -Y direction will also be referred to as "down".

[0009] In this embodiment, the grinding apparatus 100 is configured as a centerless type cylindrical grinding machine. The grinding apparatus 100 grinds the outer surface WS of the workpiece W by rotating the cylindrical workpiece W around the axis RX of the workpiece W and bringing the rotating grinding wheel 31 closer in the cutting direction intersecting the axis RX. More specifically, the grinding apparatus 100 grinds the outer surface WS by bringing the grinding wheel 31 into contact with the workpiece W and moving the workpiece W and the grinding wheel 31 relatively in the cutting direction. Hereinafter, the relative movement of the grinding wheel 31 with respect to the workpiece W will also be simply referred to as the movement of the grinding wheel 31. In this embodiment, the cutting direction is the -X direction. The axis RX is along the Z axis. The direction along the axis RX will also be called the axis RX direction. The axis RX direction includes both the direction along the axis RX and the opposite direction.

[0010] The workpiece W is any cylindrical workpiece, such as various rolls like rolling press rolls or conveying rolls, or bearings. In this embodiment, the workpiece W is a rolling press roll. In this embodiment, the journal portion of the workpiece W into which the inner ring of the bearing is fitted is ground by the grinding device 100. The workpiece W is made of metal, carbon fiber reinforced plastic (CFRP), carbon, ceramic, etc. In this embodiment, the workpiece W is made of steel.

[0011] The grinding apparatus 100 comprises a bed 10, a support unit 20, a grinding wheel base 30, a table moving device 40, a drive unit 50, a rest device 70, and a control device 200.

[0012] The bed 10 supports the support portion 20, the grinding wheel base 30, the table moving device 40, and the drive device 50. The bed 10 is made of, for example, cast iron. The upper surface of the bed 10 has a sliding surface for the support portion 20 to move along the Z-axis direction and a sliding surface for the grinding wheel base 30 to move along the X-axis direction.

[0013] The support unit 20 comprises a table 21, a spindle device 22, and a rest device 70. The support unit 20 supports the workpiece W so that the workpiece W can rotate around the axis RX. In this embodiment, the workpiece W is supported so as to be rotatable around the axis RX by a holding member 26 of the spindle device 22 (described later) and a shoe 71 of the rest device 70.

[0014] The table 21 is positioned on the upper surface of the bed 10. The spindle unit 22 is mounted on the upper surface of the table 21. Furthermore, in this embodiment, a rest device 70 is fixed to the upper surface of the table 21. In other embodiments, the rest device 70 may be fixed to the bed 10, for example.

[0015] The rest device 70 includes a shoe 71, a shoe feed device 80, and a rest base 90. In this embodiment, the shoe 71 and the shoe feed device 80 are mounted on a rest base 90 which is fixed to the table 21 so as to be adjustable in the Z direction. In this embodiment, the rest device 70 is used with its position in the Z direction adjusted so that the grinding position of the workpiece W, which will be described later, is supported by the shoe 71.

[0016] The rest device 70 supports the workpiece W so that it can rotate around the axis RX by a shoe 71. The shoe 71 has a contact portion 72 for supporting the outer circumferential surface WS of the workpiece W. The contact portion 72 supports the outer circumferential surface WS of the workpiece W from the opposite side of the grinding wheel 31 in the X direction along the cutting direction, i.e., from the -X direction. The shoe feed device 80 is configured as a drive mechanism having a motor and a transmission mechanism for operating the shoe 71, and under the control of the control device 200, moves the shoe 71 forward or backward relative to the workpiece W in a direction perpendicular to the axis RX. Note that "moving forward relative to the workpiece W" means moving closer to the workpiece W, and "moving backward relative to the workpiece W" means moving away from the workpiece W. Note that the number of shoes 71 and shoe feed devices 80 in the rest device 70 is not limited to one, but may be two or more. Furthermore, the shoe 71 only needs to be configured to support the outer surface WS from the opposite side of the grinding wheel 31 in the direction along the cutting direction, and may have multiple contact parts, such as a contact part that supports the outer surface WS from below.

[0017] The spindle unit 22 is positioned on the -Z direction side of the workpiece W. The spindle unit 22 includes a headstock 23, a spindle motor 24, and a holding member 26.

[0018] The headstock 23 is fixed on the table 21 and supports the holding member 26 so that it can rotate around the axis of rotation (not shown) of the holding member 26. The spindle motor 24 is supported by the headstock 23. The spindle motor 24 rotates under the control of the control device 200 and rotates the holding member 26.

[0019] The holding member 26 is configured to hold the end of the workpiece W in the axial direction RX. In this embodiment, the holding member 26 is configured as a magnetic chuck that holds the end of the workpiece W on the -Z direction side by magnetic force. The rotation axis of the holding member 26 is configured to be located between the axis RX and the shoe 71 in the X direction along the cutting direction. With this configuration, the holding member 26 presses the workpiece W against the shoe 71 in the cutting direction while transmitting the rotational driving force of the spindle motor 24 to the workpiece W without restricting the axis RX of the workpiece W. As a result, the workpiece W rotates around the axis RX while being supported by the shoe 71 in a centerless state. This method of grinding the workpiece W while supporting it with the shoe 71 in a centerless state is also called "shoe grinding". Note that the configuration of the spindle device 22 is not limited to the above. For example, the spindle device 22 may be configured to support the workpiece W in a centerless state using a turner (also called a spool) or a universal joint, while transmitting rotational driving force to the workpiece W.

[0020] The grinding wheel holder 30 is positioned on the upper surface of the bed 10. The grinding wheel holder 30 includes a grinding wheel 31, a grinding wheel shaft 32, and a grinding wheel rotation motor 33.

[0021] The grinding wheel 31 grinds the outer surface WS of the workpiece W by rotating around the grinding wheel rotation axis BX, which is the axis of the grinding wheel 31. In this embodiment, the grinding wheel rotation axis BX is parallel to the axis RX, that is, parallel to the Z axis. The grinding wheel 31 has a core and a grinding layer. The core is disc-shaped and made of a metal such as iron. The core is detachably connected to the grinding wheel axis 32 by bolts or the like. The grinding layer is provided in a disc shape on the outer circumference of the core. The grinding layer is formed by mixing abrasive grains and a binder and firing them together. As abrasive grains, for example, CBN (Cubic Boron Nitride) or diamond is used. The outer surface WS of the workpiece W is ground when the grinding layer comes into contact with the workpiece W. Hereinafter, the point at which the grinding wheel 31 grinds the workpiece W will be called the grinding point. Furthermore, the position of the grinding point in the axial RX direction is also called the grinding position.

[0022] The grinding wheel 31 is fixedly supported at one end of the grinding wheel shaft 32 on the grinding wheel rotation axis BX. The grinding wheel shaft 32 is supported on the grinding wheel base 30 so as to be rotatable around the grinding wheel rotation axis BX via a bearing (not shown).

[0023] The grinding wheel rotation motor 33 is positioned coaxially with the grinding wheel shaft 32 within the grinding wheel base 30. The grinding wheel rotation motor 33 rotates the grinding wheel shaft 32 around the grinding wheel rotation axis BX at a predetermined rotational speed. The on / off operation of the grinding wheel rotation motor 33 is controlled by the control device 200. As the grinding wheel shaft 32 rotates, the grinding wheel 31 rotates around the grinding wheel rotation axis BX.

[0024] The table moving device 40 is connected to the table 21 and moves the table 21 along the Z-axis. The table moving device 40 has a table moving motor 41. The table moving motor 41 generates a driving force to move the table 21 under the control of the control device 200 and controls the position of the table 21. With this configuration, the table 21 is configured to be able to move relative to the bed 10 in the axial RX direction together with the workpiece W placed on the table 21.

[0025] The drive unit 50 is connected to the grinding wheel base 30 and moves the grinding wheel base 30 along the X-axis. The drive unit 50 has a grinding wheel base moving motor 51. Under the control of the control device 200, the grinding wheel base moving motor 51 generates a driving force to move the grinding wheel base 30 and controls the position of the grinding wheel base 30.

[0026] The control device 200 controls the operation of the grinding machine 100 by controlling various parts of the grinding machine 100, such as the grinding wheel rotation motor 33, the spindle motor 24, the table movement motor 41, the drive unit 50, and the rest unit 70.

[0027] Figure 2 is a block diagram showing the schematic configuration of the control device 200. The control device 200 comprises a CPU 201, a memory 202 including RAM and ROM, an input / output interface 203, and an internal bus 204. The CPU 201, the memory 202, and the input / output interface 203 are connected bidirectionally via the internal bus 204. In addition to the drive units of the grinding machine 100 described above, a display device 206 and an input device 207 are connected to the input / output interface 203. The memory 202 stores various information, including a program PG and a database DB. The CPU 201 realizes various functions, including the functions of a control unit 210, by executing the program PG stored in the memory 202. The database DB stores cutting speed data, which will be described later. The display device 206 is configured as, for example, a liquid crystal display and displays various information related to the grinding machine 100. The input device 207 is, for example, a keyboard or mouse. The display device 206 may be configured as, for example, a touch-type display and function as an input device 207.

[0028] The control unit 210 grinds the workpiece W by controlling the grinding wheel rotation motor 33, the spindle motor 24, and the grinding wheel base movement motor 51. More specifically, the control unit 210 grinds the outer surface WS of the workpiece W by rotating the workpiece W around the axis RX and bringing the rotating grinding wheel 31 closer to the workpiece W in the cutting direction. In this embodiment, the control unit 210 performs plunge grinding of the workpiece W in this manner. That is, in the grinding apparatus 100 in this embodiment, the outer surface WS of the workpiece W is ground by plunge grinding while being supported by the shoe 71 in a centerless state.

[0029] The control unit 210 controls the cutting speed so that, in grinding, the cutting speed of the grinding wheel 31 to the workpiece W is continuously reduced as the cutting process progresses, that is, as the cutting process progresses. The control unit 210 also reduces the amount of reduction in the cutting speed as the cutting process of the grinding wheel 31 to the workpiece W progresses. The point at which the cutting process begins, that is, the point at which the grinding wheel 31 begins to cut into the workpiece W, is also called the "cutting start point." The point at which the cutting process is completed, that is, the point at which the grinding wheel 31 has finished cutting into the workpiece W, is also called the "cutting completion point." Note that "cutting" and "cutting process" as used here do not include the spark-out process (also called the zero-cut process). That is, if the spark-out process is performed in grinding, the spark-out process is performed after the cutting completion point in time.

[0030] In this disclosure, the cutting speed is defined as the amount of cutting the grinding wheel 31 into the workpiece W per unit rotation of the workpiece W. Furthermore, "continuously decreasing the cutting speed" means continuously decreasing the cutting speed in a stepless manner or in four or more steps. In particular, when the cutting speed is continuously decreased in multiple steps, the cutting speed is reduced so that the difference in cutting speed from the start of cutting to the completion of cutting is one-tenth or less of the maximum cutting speed. The difference in cutting speed represents the difference in cutting speed between one period and the next, when the period during which the cutting speed is kept constant in the cutting process is defined as one period. The maximum cutting speed represents the maximum cutting speed in the cutting process and corresponds to the cutting speed at the start of cutting.

[0031] Figure 3 is an explanatory diagram showing an example of a cutting speed data CD. Figure 3 shows a graph with the degree of cutting progress on the horizontal axis and the cutting speed on the vertical axis. The degree of cutting progress is represented, for example, by the outer diameter of the workpiece W, the amount of workpiece W removed, or the elapsed time from the start of machining. The cutting speed data CD defines the cutting speed according to the degree of cutting progress in the cutting process. In this embodiment, the control unit 210 shown in Figure 2 controls the cutting speed in the cutting process using the cutting speed data CD. In addition, the cutting speed data CD may be prepared in the database DB according to, for example, the type and specifications of the workpiece W and the machining conditions.

[0032] As shown in Figure 3, in this embodiment, the cutting speed in the cutting speed data CD is defined to decrease continuously according to a sine function. More specifically, the cutting speed data CD is defined to decrease the cutting speed from the start time ts to the completion time te of cutting the workpiece W according to the curve Sc which represents the point from the inflection point IP to the next trough Pv of the sine function. The inflection point IP is the inflection point located between the peak (not shown) and the next trough Pv of the sine function. In the cutting speed data CD, the initial speed VF, which represents the cutting speed at the start time ts, is defined as the value corresponding to the inflection point IP of the sine function. Also, in the cutting speed data CD, the final speed VL, which represents the cutting speed at the completion time te, is defined as the value corresponding to the trough Pv of the sine function.

[0033] Figure 4 is a schematic cross-sectional view illustrating how the workpiece W is ground during shoe grinding. Figure 4 schematically shows the shoe 71 of the rest device 70, the grinding wheel 31, and the workpiece W. In Figure 4, time t2 is later than time t1. Time t3 is later than time t2. Time t4 is later than time t3. If the rotation angle of the workpiece W around axis RX at time t1 is 0 degrees, then the rotation angles at times t2, t3, and t4 are 90 degrees, 180 degrees, and 270 degrees, respectively. Also, for times t1, t2, t3, and t4, the angle by which the workpiece W rotates around axis RX from one time to the next is 90 degrees.

[0034] In Figure 4, from time t1 to time t2, the workpiece W is being cut by the grinding wheel 31 at a constant cutting speed. From time t1 to time t2, the grinding wheel 31 moves in the -X direction from position P1 to position P2. Also in Figure 4, at time t2, the grinding wheel 31 stops cutting into the workpiece W. This stopping of the grinding wheel 31's cutting is also called "stopping the feed of the grinding wheel 31" or "feed stop". Furthermore, in Figure 4, from time t2 to time t4, the workpiece W and the grinding wheel 31 are rotating with the grinding wheel 31's cutting stopped.

[0035] In Figure 4, the trajectory CT1 of the change in the contour of the workpiece W from time t1 to time t2 is schematically shown by a thick line. Also in Figure 4, the trajectory CT2 of the change in the contour of the workpiece W from time t2 to time t3 is schematically shown by a thick line. Furthermore, in Figure 4, a virtual circle CR is schematically shown by a dashed line. The virtual circle CR represents a circle when the workpiece W is viewed in cross-section along the Z direction. More specifically, the virtual circle CR is a circle that is tangent to position Pt1 of the workpiece W when the workpiece W is viewed in cross-section along the Z direction, and is centered at the position of the axis RX of the workpiece W. Position Pt1 represents the final position of the workpiece W that is cut by the grinding wheel 31, that is, the position that is in contact with the grinding wheel 31 when the feed stop is executed.

[0036] As shown in Figure 4, from time t1 to time t2, as the grinding wheel 31 cuts into the workpiece W, the position of the axis RX of the workpiece W moves further in the -X direction. Hereafter, this movement of the axis RX in the direction along the cutting direction will also be referred to as "change in the position of axis RX" or "misalignment". Furthermore, at time t2, when the grinding wheel 31 stops cutting while in contact with position Pt1, that is, when the cutting speed of the grinding wheel 31 decreases, position Pt1 becomes a singularity in the workpiece W. A singularity here means a point where the curvature of the outer surface WS of the workpiece W changes abruptly compared to other positions on the workpiece W.

[0037] Subsequently, as the cut progresses from time t2 to time t4, the position of the axis RX of the workpiece W moves further in the -X direction. Also, at time t4, the singular point position Pt1 comes into contact with the contact portion 72 of the shoe 71, and a new singular point, position Pt2, also becomes a singular point. Position Pt2 is the position of the workpiece W where the angular position is 180 degrees when the angular position of position Pt1 around the axis RX is taken as 0 degrees.

[0038] As shown in Figure 4, when shoe grinding is performed by the grinding apparatus 100, the roundness of the workpiece W may deteriorate due to changes in the cutting speed. More specifically, the roundness of the workpiece W may deteriorate due to the change in position per unit rotation of the workpiece W and the appearance of singularities, as described above. The inventors of this application have found that by reducing the amount of change in the cutting speed when changing the cutting speed in the cutting process, the amount of change in position per unit rotation of the workpiece W and the amount of change in curvature at singularities can be reduced, thereby suppressing the deterioration of roundness. In this embodiment, this suppression of the amount of change in cutting speed is achieved by continuously changing the cutting speed in the cutting process.

[0039] Furthermore, when the cutting speed is changed during the cutting process, the change in cutting speed can cause irregularities in the shape of the outer surface WS of the workpiece W. The inventors of this application have found that by adjusting the cutting speed so that the difference in cutting speeds becomes smaller, the accumulation of such irregularities in shape during the cutting process can be suppressed. More specifically, as shown in Figure 3, when the period during which the workpiece W is cut at a constant first cutting speed V1 is defined as the first period Pd1, and the period during which the workpiece W is cut at a constant second cutting speed V2 that is smaller than the first cutting speed V1 is defined as the second period Pd2, the difference GP between the second cutting speed V2 and the first cutting speed V1 is adjusted to be less than or equal to the removal dimension in the second period Pd2. The removal dimension in a certain period means the dimension to which the workpiece W is removed by the grinding wheel 31 during that period. That is, the removal dimension in a certain period corresponds to the distance that the grinding wheel 31 cuts into the workpiece W during that period. In other embodiments, for example, depending on the required machining accuracy of the workpiece W, such adjustment of the cutting speed may not be necessary.

[0040] Figure 5 is a flowchart of the machining process for realizing the grinding method in this embodiment. The machining process is started, for example, when a predetermined operation is performed on the control device 200 via the input device 207 by the user, with the workpiece W supported by the holding member 26 and the shoe 71.

[0041] In step S105 of Figure 5, the control unit 210 obtains cutting speed data from the database DB stored in the memory 202. In step S110, the control unit 210 executes the cutting process. More specifically, in step S110, the control unit 210 grinds the workpiece W while controlling the cutting speed of the grinding wheel 31 according to the cutting speed data obtained in step S105. In step S115, the control unit 210 executes the spark-out process. The spark-out process may be omitted depending on the type, specifications, and processing conditions of the workpiece W, for example.

[0042] As described above, the grinding apparatus 100 in this embodiment controls the cutting speed of the grinding wheel 31 to decrease continuously as the grinding process of the workpiece W progresses, and to minimize the amount of decrease in the cutting speed. As a result, unlike conventional methods where the cutting speed is kept constant in each of the rough grinding, fine grinding, and micro grinding processes, and then decreases in later processes, it is possible to avoid the cutting speed being kept constant at a relatively slow speed in the later stages of the cutting process. Furthermore, compared to, for example, a method in which the amount of decrease in the cutting speed is kept constant regardless of the progress of the cutting, it is possible to suppress a relatively rapid decrease in the cutting speed. As a result, it is possible to ensure the processing quality of the workpiece W while suppressing the prolongation of the grinding time.

[0043] Furthermore, in this embodiment, the outer surface WS of the workpiece W supported by the shoe 71 in a centerless state is ground, and the difference GP between the second cutting speed V2 in the second period Pd2 and the first cutting speed V1 in the first period Pd1 is less than or equal to the removal dimension of the workpiece W in the second period Pd2. In this way, when performing shoe grinding, it is possible to suppress a decrease in machining quality such as the roundness of the workpiece W due to the change in the position of the axis RX of the workpiece W as grinding progresses.

[0044] Also, in the present embodiment, the cutting speed in the cutting process is continuously decreased according to a sine function. Therefore, the cutting speed can be continuously decreased by a simple method. In particular, in the present embodiment, the cutting speed from the start point of cutting to the completion point of cutting is continuously decreased according to a curve representing from the inflection point IP of the sine function to the next valley Pv after the inflection point IP. Therefore, at a relatively early stage of the cutting process, the work W can be efficiently ground at a relatively high cutting speed, and immediately before the completion point of cutting, the work W can be finely ground at a cutting speed closer to zero. Thus, according to the present embodiment, the cutting speed can be continuously decreased simply and effectively.

[0045] B. Second Embodiment: FIG. 6 is a flowchart of a processing for realizing a grinding method in the second embodiment. In FIG. 6, the same steps as those in FIG. 5 are denoted by the same reference numerals as in FIG. 5. In the present embodiment, different from the first embodiment, the control unit 210 receives from the user a specification of cutting conditions including an initial speed, a final speed, and a cutting time. Further, the control unit 210 continuously decreases the cutting speed in the grinding process according to a sine function based on the specified cutting conditions. For the points not particularly described in the grinding apparatus 100 in the second embodiment, they are the same as those in the first embodiment.

[0046] In step S102, the control unit 210 receives a specification of cutting conditions from the user. In step S102, the control unit 210, for example, displays a message for requesting an input of cutting conditions on the display screen of the display device 206, and receives a specification of cutting conditions by the user via the input device 207.

[0047] In step S105b, the control unit 210 acquires the plunge feed rate data to be used in the plunge feed process based on the grinding conditions specified in step S102. In step S105b, for example, the control unit 210 may acquire the plunge feed rate data that continuously decreases the plunge feed rate according to a sine function and stored in advance in the memory 202, and correct the acquired plunge feed rate data based on the grinding conditions specified in step S102, thereby acquiring the plunge feed rate data to be used in the plunge feed process. Alternatively, in step S105b, the control unit 210 may acquire the plunge feed rate data to be used in the plunge feed process by generating the plunge feed rate data that continuously decreases the plunge feed rate according to a sine function using the grinding conditions specified in step S102. In step S110, the control unit 210 grinds the workpiece W while controlling the plunge feed rate according to the plunge feed rate data acquired in step S105b.

[0048] According to the grinding apparatus 100 in the second embodiment described above, the plunge feed rate in the grinding process is continuously decreased according to a sine function based on the grinding conditions specified by the user. Therefore, the plunge feed rate can be continuously decreased by a simple method while reflecting the user's requirements regarding the grinding conditions.

[0049] C. Other embodiments: (C-1) In each of the above embodiments, the support unit 20 is configured to support the workpiece W in a centerless state by the shoe 71, but the present invention is not limited to this. For example, the support unit 20 may be configured to support the workpiece W using a pair of centers. That is, in this case, the grinding apparatus 100 does not have to be configured as a centerless cylindrical grinding machine. In this case, the control unit 210 may grind the outer peripheral surface WS of the workpiece W with the grinding wheel 31 while supporting the workpiece W rotatable about the axis RX by, for example, a pair of centers and the shoe 71.

[0050] (C-2) In each of the above embodiments, the control unit 210 reduces the cutting speed in accordance with the curve Sc during the cutting process, but is not limited to this. For example, the control unit 210 may continuously reduce the cutting speed in accordance with a curve different from the curve Sc that represents the sine function. Alternatively, the control unit 210 may continuously reduce the cutting speed in accordance with a function different from the sine function, such as a curve function of order second or higher or an exponential function.

[0051] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in each embodiment corresponding to the technical features in the embodiments described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0052] 10...bed, 20...support unit, 21...table, 22...spindle unit, 23...headstock, 24...spindle motor, 26...holding member, 30...grinding wheel holder, 31...grinding wheel, 32...grinding wheel spindle, 33...grinding wheel rotation motor, 40...table moving device, 41...table moving motor, 50...drive unit, 51...grinding wheel holder moving motor, 70...rest device, 71...shoe, 72...contact part, 80...shoe feed device 80, 90...rest stand, 100...grinding machine, 200...control device, 201...CPU, 202...memory, 203...input / output interface, 204...internal bus, 206...display device, 207...input device, 210...control unit

Claims

1. A grinding apparatus comprising: a grinding wheel holder having a grinding wheel; a support portion that supports a cylindrical workpiece so as to be rotatable around the axis of the workpiece; a drive device configured to move the grinding wheel holder relative to the workpiece; and a control unit that grinds the outer surface of the workpiece by controlling the drive device while rotating the workpiece around the axis, thereby bringing the rotating grinding wheel closer to the workpiece in a cutting direction intersecting the axis, wherein the control unit continuously decreases the cutting speed of the grinding wheel into the workpiece as the cutting progresses, and reduces the amount of decrease in the cutting speed as the cutting progresses.

2. A grinding apparatus according to claim 1, wherein the support portion has a shoe that supports the outer circumferential surface of the grinding wheel from the opposite side of the grinding wheel in a direction along the cutting direction of the grinding wheel into the workpiece, and is configured to support the workpiece in a centerless state by the shoe, and the control unit grinds the outer circumferential surface of the workpiece supported by the shoe in the centerless state, and the period during which the workpiece is cut at a first cutting speed is defined as the first period, and the second period following the first period is defined as the period during which the workpiece is cut at a second cutting speed smaller than the first cutting speed, and when the first cutting speed and the second cutting speed are defined as the amount of cutting of the workpiece by the grinding wheel per unit rotation of the workpiece, the difference between the second cutting speed and the first cutting speed is less than or equal to the dimension by which the workpiece is removed in the second period.

3. A grinding apparatus according to claim 1 or 2, wherein the control unit continuously reduces the cutting speed according to a sine function.

4. A grinding apparatus according to claim 3, wherein the control unit continuously decreases the cutting speed from the start of cutting the workpiece to the completion of cutting, according to a curve of the sine function that represents from the inflection point to the next valley after the inflection point.

5. A grinding apparatus according to claim 3, wherein the control unit receives a specification from a user of cutting conditions including an initial speed representing the cutting speed at the start of cutting the workpiece, a final speed representing the cutting speed at the completion of cutting the workpiece, and a cutting time from the start of cutting to the completion of cutting, and continuously decreases the cutting speed according to the sine function based on the specified cutting conditions.

6. A grinding method comprising a grinding step of grinding the outer surface of a cylindrical workpiece by rotating the workpiece around its axis and bringing a rotating grinding wheel closer to the workpiece in a cutting direction intersecting the axis, wherein in the grinding step, the cutting speed of the grinding wheel into the workpiece is continuously reduced as the cutting progresses, and the cutting speed is controlled such that the amount of reduction in the cutting speed decreases as the cutting progresses.

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