Polishing tool, polishing head, polishing device and polishing method

Abstract

To achieve high-accuracy polishing with a simple structure.SOLUTION: A polishing tool 200, which polishes a work-piece while holding a polishing material between a polishing surface 230 thereof and the work-piece, comprises: a main shaft part 210 that has the polishing surface at a tip thereof and extends along a polishing shaft J; a plurality of elastic parts 310, 320 and 330 extending continuously from the main shaft part toward outside in a radial direction; and a plurality of seat parts 410, 420 and 430 arranged continuously outside in the radial direction of the plurality of elastic parts. In the elastic parts, positions leading to the main shaft part and positions leading to the seat parts are set different from each other in a shaft direction of the polishing shaft J. Therefore, when an external tool driving mechanism acts to displace the seat parts in the radial direction by same distances, the plurality of elastic parts elastically deform and the main shaft part is displaced along the polishing shaft. Further, when the external tool driving mechanism acts to displace the seat parts toward the radial direction by different distances, the main shaft part is displaced along the radial direction of the polishing shaft J.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a polishing tool and a polishing method for precisely polishing the surface of a workpiece such as a lens or an optical element. [Background technology]

[0002] Optical elements such as aspherical lenses that are incorporated into electronic devices and optical devices are manufactured by molding, grinding, polishing, etc. These optical elements require high accuracy in shape.

[0003] Methods for polishing optical elements include polishing, lapping, and magnetic polishing. For example, in the magnetic polishing method, as shown in Patent Document 1, a magnetic polishing fluid is used, either a magnetic fluid alone or one in which fine abrasive particles are suspended and dispersed. The magnetic polishing fluid is supplied between the polishing surface at the tip of the polishing tool and the workpiece to perform polishing. During this process, a Z-direction actuator made of an electrostrictive element is used to minutely move the polishing surface and the workpiece (by minutely moving them closer to or further away from each other) in the Z-axis direction. At the same time, an X-direction actuator and a Y-direction actuator made of an electrostrictive (piezo) element are used to minutely move the polishing surface and the workpiece in the XY plane, which is perpendicular to the Z-axis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 2682260 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of the polishing device of Patent Document 1, a block of polishing tools (polishing block) including an X-direction actuator and a Y-direction actuator is suspended further forward (toward the polishing surface) than the Z-axis actuator. As a result, the polishing block becomes larger, increasing its inertia and its structure becoming more complex, which poses the problem that various adjustments are required to control the polishing surface with high precision.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a polishing tool or the like that is capable of realizing high-precision polishing while simplifying the structure.

[0007] To achieve the above object, the present invention provides a grinding tool for grinding a workpiece by holding an abrasive between its grinding surface and the workpiece, wherein when a virtual grinding axis is defined as the direction in which the center of the grinding surface approaches or moves away from the workpiece, the grinding tool has the grinding surface facing the workpiece at its tip, and comprises a main shaft portion extending along the grinding axis, a plurality of elastic portions continuing from the main shaft portion and extending radially outward from the grinding axis, and a plurality of seats continuing radially outward from the plurality of elastic portions, wherein the positions of the elastic portions continuing from the main shaft portion and the positions of the elastic portions continuing from the seat portions are different in the direction of the grinding axis, and when the tool drive mechanism applies the same amount of displacement in the radial direction to each of the plurality of seats, the plurality of elastic portions elastically deform and the main shaft portion is displaced so as to include an axial component of the grinding shaft, and when the tool drive mechanism applies different amounts of displacement in the radial direction to each of the plurality of seats, the main shaft portion is displaced so as to include a radial component of the grinding shaft.

[0008] The above grinding tool may be characterized in that a plurality of the elastic portions and the seat portions are arranged at equal intervals in the circumferential direction of the grinding shaft.

[0009] The grinding tool may be characterized in that it includes three of the elastic portions and the seat portions.

[0010] The present invention, which achieves the above-mentioned object, is a polishing head having the above-mentioned polishing tool, characterized in that it comprises a tool base and a tool driving mechanism that is arranged on the tool base and displaces or elastically deforms the polishing tool, and the tool driving mechanism comprises a plurality of driving units that are arranged on a plurality of the seat portions and displace the seat portions in the radial direction.

[0011] The polishing head may include a tool control device that controls the tool drive mechanism, and the control device may include a first frequency signal generating unit that generates a plurality of first frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the periods of increase and decrease in displacement amount match each other, a second frequency signal generating unit that generates a plurality of second frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the periods of increase and decrease in displacement amount match each other, and a signal superimposing unit that generates a drive signal for each of the plurality of drive units by superimposing the plurality of first frequency signals and the plurality of second frequency signals.

[0012] In relation to the above-mentioned polishing head, the plurality of first frequency signals generated by the first frequency signal generating unit may be characterized in that the increase and decrease phases are the same, and the plurality of second frequency signals generated by the second frequency signal generating unit are characterized in that the increase and decrease phases are different.

[0013] In relation to the polishing head, the frequency of the first frequency signal may be greater than the frequency of the second frequency signal.

[0014] The polishing head may further include a bias signal generating section that generates a bias signal to be superimposed on at least one of the plurality of drive signals.

[0015] The polishing head may be characterized by including a polishing head setting calculation unit that changes the bias signal generated by the bias signal generation unit by referring to scanning path information of the polishing head relative to the workpiece and / or shape information of the workpiece.

[0016] In relation to the polishing head, the polishing surface may be vibrated along a spiral movement locus by the tool driving mechanism.

[0017] In relation to the polishing head, the tool driving mechanism may be characterized in that the helical axis of the helical movement locus on the polishing surface is displaced.

[0018] To achieve the above object, the present invention provides a polishing head comprising: a polishing tool for holding an abrasive between its polishing surface and a workpiece to polish the workpiece; a tool base; a tool drive mechanism disposed on the tool base and displacing the polishing tool; and a control device for controlling the tool drive mechanism, wherein, when a virtual polishing axis is defined as a direction in which the center of the polishing surface approaches or moves away from the workpiece, the tool drive mechanisms are disposed in a circumferential direction of the polishing axis, and each tool drive mechanism has a drive unit for displacing the polishing tool in a radial direction of the polishing axis, and the control device comprises: a first frequency signal generation unit that generates a plurality of first frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the increase and decrease periods of the displacement amount match each other; a second frequency signal generation unit that generates a plurality of second frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the increase and decrease periods of the displacement amount match each other; and a signal superposition unit that generates a drive signal for each of the plurality of drive units by superimposing the plurality of first frequency signals and the plurality of second frequency signals.

[0019] In relation to the polishing head, the plurality of first frequency signals generated by the first frequency signal generating unit may have the same increase / decrease phase, and the plurality of second frequency signals generated by the second frequency signal generating unit may have different increase / decrease phases.

[0020] In relation to the polishing head, the frequency of the first frequency signal may be greater than the frequency of the second frequency signal.

[0021] To achieve the above object, the present invention provides a polishing apparatus comprising: a base; the above-mentioned polishing head; a polishing head holding mechanism provided on the base and holding the polishing head; a workpiece holding mechanism provided on the base and holding the workpiece; and a relative movement mechanism for moving the workpiece and the polishing head relative to each other in the axial direction of the polishing shaft and in the radial direction of the polishing shaft.

[0022] To achieve the above object, the present invention provides a polishing method for polishing a workpiece by holding an abrasive, which is composed of a fluid having abrasive grains dispersed therein, between the polishing surface of a polishing tool and the workpiece, the method comprising: defining a virtual polishing axis as the direction in which the center of the polishing surface approaches or moves away from the workpiece; arranging a plurality of drive units circumferentially around the polishing axis; displacing a point of contact with the polishing tool in a radial direction of the polishing axis by each of the drive units; generating synchronous frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the increase / decrease periods and increase / decrease phases of the displacement amounts coincide with each other; generating a plurality of first frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the increase / decrease periods of the displacement amounts coincide with each other; generating a plurality of second frequency signals for periodically reciprocatingly displacing the plurality of drive units so that the increase / decrease periods of the displacement amounts coincide with each other; superimposing the plurality of first frequency signals and the plurality of second frequency signals to generate drive signals for each of the plurality of drive units; and displacing the plurality of drive units using the plurality of drive signals to displace the polishing surface of the polishing tool in the axial and radial directions of the polishing axis.

[0023] In the above-described polishing method, the first frequency signals may have the same increase and decrease phase, and the second frequency signals may have different increase and decrease phases.

[0024] In relation to the above polishing method, the polishing surface may be displaced in the radial and / or axial directions of the polishing shaft by superimposing a bias signal on at least one of the plurality of drive signals.

[0025] In the above polishing method, the bias signal may be changed with reference to scanning path information of the polishing surface relative to the workpiece and / or shape information of the workpiece.

[0026] In the above polishing method, the polishing surface may be vibrated along a spiral movement locus.

[0027] The polishing method may be characterized in that the helical axis of the helical movement locus on the polishing surface is displaced. [Effects of the Invention]

[0028] According to the present invention, it is possible to obtain the excellent effect of polishing the surface of a workpiece with high precision using a simple structure. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a side view of a polishing apparatus according to an embodiment of the present invention; [Figure 2] 2A and 2B are a front view and a side view, respectively, of a polishing head applied to the polishing apparatus. [Figure 3] 3 is a partial cross-sectional view of the polishing head taken along the line III-III of FIG. 2(A). [Figure 4] 1A is a perspective view of a polishing tool applied to the polishing head, and FIG. 1B is a perspective view showing a modified example of the polishing surface. [Figure 5] 2A is a front view of the grinding tool, and FIG. 2B is a side view of the grinding tool. [Figure 6] 1A is a front view of the grinding tool, FIG. 1B is a side view thereof, and FIG. 1C is a diagram showing the resultant vector of each displacement vector. [Figure 7] 1(A) and 1(B) are perspective views showing the steps of manufacturing the grinding tool. [Figure 8] FIG. 2A is a block diagram showing the function of a movement control device of the polishing device, and FIG. 2B is a block diagram showing the function of a tool control device of the polishing device. [Figure 9](A) is a diagram showing the first to third synchronized frequency signals DA, DB, DC of the tool control device, (B) is a diagram showing the first to third phase difference frequency signals QA, QB, QC, (C) is a diagram showing the first to third drive signals KA, KB, KC, and (D) is a front view showing the operation of the grinding surface 230 by the first to third drive signals KA, KB, KC. [Figure 10] 10A and 10B are side and front views showing the operation of the polishing surface 230 in response to the first to third drive signals KA, KB, and KC. [Figure 11] (A) is a diagram showing the first to third bias signals EA, EB, EC of the tool control device, (B) is a diagram showing the first to third drive signals KA(t1), KB(t1), KC(t1), (C) is a front view showing the operation of the grinding surface at elapsed time t1, (D) is a front view showing the operation of the grinding surface at elapsed time t2, and (E) is a front view showing the operation of the grinding surface at elapsed time t3. [Figure 12] (A) is a diagram showing the first to third bias signals EA, EB, EC of the tool control device, (B) is a diagram showing the first to third drive signals KA(t1), KB(t1), KC(t1), (C) is a side view showing the operation of the grinding surface at elapsed time t1, (D) is a side view showing the operation of the grinding surface at elapsed time t2, and (E) is a side view showing the operation of the grinding surface at elapsed time t3. [Figure 13] 4(A) to 4(C) are cross-sectional views showing the steps of polishing a workpiece using the polishing tool. [Figure 14] (A) is the vibration waveform of the same grinding tool in the Z-axis direction, and (B) is the vibration waveform of the same grinding tool in the radial direction. [Figure 15] (A) Micrograph and (B) three-dimensional profile of the verification workpiece in its initial state. [Figure 16] (A) Micrograph and (B) three-dimensional profile of a verification workpiece after polishing with this polishing device. [Figure 17] (A) Micrograph and (B) three-dimensional profile of a verification workpiece after polishing using a polishing device serving as a comparative example. [Figure 18]10 is a diagram showing modified examples of the first to third synchronized frequency signals DA, DB, DC, the first to third phase difference frequency signals QA, QB, QC, and the first to third drive signals KA, KB, KC of the tool control device. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0031] FIG. 1 shows the overall configuration of a polishing apparatus 1 according to this embodiment. The polishing apparatus 1 includes a base 10, a polishing head 100, a polishing head holding mechanism 20 mounted on the base 10 and holding the polishing head 100, a workpiece holding mechanism 30 mounted on the base 10 and holding a workpiece W, a relative rotation mechanism 33 for relatively rotating the workpiece W and the polishing head 100, a relative movement mechanism 40 for relatively moving the workpiece W and the polishing head 100 in the axial direction of the polishing axis J and the radial direction R, and an abrasive supply device 35 for supplying a fluid abrasive between the workpiece W and the polishing head 100. The polishing apparatus 1 further includes a tool control device 50 for controlling a tool drive mechanism 140 in the polishing head 100 and a movement control device 60 for controlling the relative movement mechanism 40. The tool control device 50 and the movement control device 60 are configured to operate in conjunction with each other.

[0032] For ease of explanation, the direction in which the center of the polishing surface of the polishing head 100 approaches or moves away from the workpiece W (the left-right direction in FIG. 1) is defined as the Z-axis direction. In FIG. 1, a line passing through the center of the polishing surface 230 of the polishing head 100 and parallel to the Z-axis direction is defined as a virtual polishing axis J. The vertical direction perpendicular to the Z-axis direction (the up-down direction in FIG. 1) is defined as the Y-axis direction, and the direction perpendicular to both the Z-axis direction and the Y-axis direction (the direction perpendicular to the plane of FIG. 1) is defined as the X-axis direction. The direction perpendicular to the polishing axis J (or Z-axis) is defined as the polishing axis radial direction R, and the circumferential direction centered on the polishing axis J (or Z-axis) is defined as the polishing axis circumferential direction S.

[0033] <Work holding mechanism> The workpiece holding mechanism 30 holds the workpiece W to be polished. Although not specifically shown, the workpiece holding mechanism 30 includes a chuck that holds the workpiece W so that the surface to be polished of the workpiece W faces the Z-axis direction.

[0034] <Polishing head holding mechanism> The polishing head holding mechanism 20 serves as a base for holding the polishing head 100. The polishing head holding mechanism 20 holds the polishing head 100 so that the polishing axis J of the polishing head 100 is parallel to the Z-axis direction. Although not specifically shown, the polishing head holding mechanism 20 preferably includes a chuck that detachably holds the polishing head 100 so that the polishing surface faces the Z-axis direction. By using the chuck to replace the polishing head 100 held by the polishing head holding mechanism 20 with a regular cutting tool, the entire polishing apparatus 1 can be switched into a general-purpose cutting apparatus.

[0035] <Relative rotation mechanism> The relative rotation mechanism 33 is a rotation mechanism that rotates the workpiece W and the polishing surface 230 relative to each other around the Z axis. Here, it is a rotation main shaft that is fixed to the base 10, and rotates the workpiece holding mechanism 30 around the Z axis.

[0036] <Relative movement mechanism> The relative movement mechanism 40 moves the workpiece W and the polishing head 100 relative to each other in the X-, Y-, and Z-axes. In this embodiment, the mechanism includes a Y-axis linear motion device 42 that moves the polishing head holding mechanism 20 in the Y-axis direction relative to the base 10, a Z-axis linear motion device 44 that moves the Y-axis linear motion device 42 in the Z-axis direction, an X-axis linear motion device 46 that moves the Z-axis linear motion device 44 in the X-axis direction, and a tilt mechanism 48 that tilts the polishing axis J of the polishing head holding mechanism 20 relative to the Z-axis direction. While this embodiment illustrates a structure that moves the polishing head 100 relative to the base 10 in the X-, Y-, and Z-axes and in the tilt direction, the present invention is not limited to this. Some or all of the functions in the X-, Y-, and Z-axes and the tilt direction may be provided on the workpiece holding mechanism 30. If the surface to be polished of the workpiece W is flat, the tilt mechanism 48 can be omitted. On the other hand, when the surface to be polished of the workpiece W has a three-dimensional shape, it is preferable to tilt the polishing head 100 by the tilt mechanism 48 so that the polishing axis J coincides with the direction perpendicular to the surface to be polished.

[0037] <Abrasive supply device> The abrasive supply device 35 continuously supplies a fluid abrasive between the workpiece W and the polishing surface of the polishing head 100. Specifically, it has a pump (not shown), a pipe 36 that guides the abrasive discharged from the pump, a nozzle 37 that is attached to the tip of the pipe 36 and discharges the abrasive, and a nozzle holding mechanism 38 that holds the nozzle 37 in a predetermined position.

[0038] <Polishing head> As shown enlarged in Figure 2, the polishing head 100 includes a tool base 110, a tool driving mechanism 140 arranged on the tool base 110, a polishing tool 200 held by the tool driving mechanism 140, and a tool control device 50 that controls the tool driving mechanism 140.

[0039] (Tool base) The tool base 110 is a plate-like member extending in the X-axis and Y-axis directions.

[0040] (polishing tool) The grinding tool 200 is a tool that grinds the workpiece W by holding an abrasive between its grinding surface 230 and the workpiece W. For ease of explanation, the side of the grinding tool 200 that approaches the workpiece W along the grinding axis J (or Z axis) will be referred to as the tip side, and the side that moves away from the workpiece W will be referred to as the base side. As shown enlarged in FIGS. 4 to 6, the grinding tool 200 has a main shaft portion 210, a first elastic portion 310, a second elastic portion 320, a third elastic portion 330, a first seat portion 410, a second seat portion 420, and a third seat portion 430.

[0041] The spindle portion 210 is a rod-shaped member extending along the grinding axis J (or Z-axis) and has a grinding surface 230 at its tip that faces the workpiece W. More specifically, the spindle portion 210 has a central axis 210A extending along the grinding axis J, a first rib 211 extending from the central axis 210A in a first radial direction R1 and extending toward the grinding axis J, a second rib 212 extending from the central axis 210A in a second radial direction R2 and extending toward the grinding axis J, and a third rib 213 extending from the central axis 210A in a third radial direction R3 and extending toward the grinding axis J. These first to third ribs 211 to 213 enhance the rigidity of the spindle portion 210. The grinding surface 230 is provided at the tip of the central axis 210A. Note that the grinding surface 230 is not limited to a flat surface. As shown in FIG. 4(B), the grinding surface 230 may be a three-dimensional flat surface (for example, a convex surface such as a part of a sphere).

[0042] The first elastic portion 310 is a member that continues from the base end side of the main shaft portion 210 and extends outward in the first radial direction (R1 direction) from the grinding axis J. The first elastic portion 310 is elastically deformed in the grinding axis J direction and / or the first radial direction R1 by an external force. The first seat portion 410 is a portion provided on the radially outer side of the first elastic portion 310, and provides a structural portion (here, a seat surface 410A) such as a surface for being supported by the tool driving mechanism 140 described later.

[0043] As shown in FIG. 5, the position of the first elastic portion 310 that is continuous with the spindle portion 210 (grinding axis J) is defined as the spindle-side continuous point 310A, and the portion of the first elastic portion 310 that is continuous with the first seat portion 410 (seat surface 410A) is defined as the seat-side continuous point 310B. The seat-side continuous point 310B is located at a position offset along the grinding axis J from the spindle-side continuous point 310A, specifically, toward the base end. If the central axis of the first elastic portion 310 in the direction of extension is defined as the first arm axis 310J, this first arm axis 310J becomes an inclined member that displaces from the tip of the grinding axis J toward the base end as it moves from the inside to the outside in the radial direction R1 of the grinding axis J. The first arm axis 310J may also be defined as a straight line connecting the spindle-side continuous point 310A and the seat-side continuous point 310B. As shown in FIG. 5(B), a constricted portion 310K is formed in the first elastic portion 310 proximal to the main shaft-side continuous point 310A. A dimension 310Kw of this constricted portion 310K in a direction perpendicular to the first arm axis 310J is smaller than a dimension 310Ew of an arbitrary point distal thereto. As a result, the rigidity of the constricted portion 310K in the first elastic portion 310 is reduced, and this constricted portion 310K actively deforms elastically. A first relief space 410K is formed on the inside of the first seat portion 410 in the radial direction R1.

[0044] In this embodiment, the case where the spindle side continuous point 310A is located at the tip end side and the seat side continuous point 310B is located at the base end side is illustrated, but the present invention is not limited to this, and a structure in which the spindle side continuous point 310A is located at the rear end side and the seat side continuous point 310B is located at the tip end side may be adopted.

[0045] The first seat portion 410 provides a surface facing the outside in the first radial direction R1. The first seat portion 410 receives a first external force F1 directed from the outside to the inside in the first radial direction R1. A first seating surface 410A provided on the first seat portion 410 is a partially spherical recessed portion in this case. When the tool driving mechanism 140, which will be described later, engages with the first seating surface 410A, the first seat portion 410 is supported and pressed from the outside to the inside in the first radial direction R1. The initial pressure applied to the first seat portion 410 serves as a holding pressure (pre-pressure) for maintaining the holding posture of the grinding tool 200.

[0046] The second elastic portion 320 is a member that continues from the base end side of the main shaft portion 210 and extends outward from the grinding axis J in the second radial direction (R2 direction). The second elastic portion 320 is elastically deformed in the grinding axis J direction and / or the second radial direction by an external force. The second seat portion 420 is a portion provided on the radially outer side of the second elastic portion 320, and provides a structural portion (here, seat surface 420A) such as a surface for being supported by the tool driving mechanism 140 described later.

[0047] As shown in FIG. 5, the position of the second elastic portion 320 that is continuous with the main shaft portion 210 (grinding shaft J) is defined as the main shaft-side continuous point 320A, and the portion of the second elastic portion 320 that is continuous with the second seat portion 420 (seat surface 420A) is defined as the seat-side continuous point 320B. The seat-side continuous point 320B is located closer to the rear end of the grinding shaft J than the main shaft-side continuous point 320A. In other words, the main shaft-side continuous point 320A and the seat-side continuous point 320B are located at different positions along the grinding shaft J. If the central axis of the second elastic portion 320 in the extending direction is defined as the second arm axis 320J, the second arm axis 320J is an inclined member that displaces from the tip to the base end of the grinding shaft J as it moves from the inside to the outside in the second radial direction R2 of the grinding shaft J. A constricted portion 320K is formed in the second elastic portion 320 proximal to the main shaft-side continuous point 320A. As a result, the rigidity of the constricted portion 320K is reduced, and the constricted portion 320K is actively elastically deformed. A second relief space 420K is formed on the inside of the second seat portion 420 in the second radial direction R2.

[0048] In this embodiment, the case where the spindle side continuous point 320A is located at the tip end side and the seat side continuous point 320B is located at the base end side is exemplified, but the present invention is not limited to this, and a structure in which the spindle side continuous point 320A is located at the rear end side and the seat side continuous point 320B is located at the tip end side may be adopted.

[0049] The second seat portion 420 provides a surface facing the outside in the second radial direction R2. The second seat portion 420 receives a second external force F2 directed from the outside to the inside in the second radial direction R2. Here, a second seating surface 420A provided on this second seat portion 420 is a partially spherical recess. When the tool driving mechanism 140, which will be described later, engages with this second seating surface 420A, the second seat portion 420 is supported and pressed from the outside to the inside in the second radial direction R2. The initial pressure applied to the second seat portion 420 serves as a holding pressure (pre-pressure) for maintaining the holding posture of the grinding tool 200.

[0050] The third elastic portion 330 is a member that continues from the base end side of the main shaft portion 210 and extends outward from the grinding axis J in the third radial direction (direction R3). The third elastic portion 330 is elastically deformed in the grinding axis J direction and / or the third radial direction by an external force. The third seat portion 430 is a portion provided on the radially outer side of the third elastic portion 330, and provides a structural portion (here, seat surface 430A) such as a surface for being supported by the tool driving mechanism 140 described later.

[0051] As shown in FIG. 5, the position of the third elastic portion 330 that connects to the main shaft portion 210 (grinding shaft J) is defined as the main shaft-side continuous point 330A, and the portion of the third elastic portion 330 that connects to the third seat portion 430 (seat surface 430A) is defined as the seat-side continuous point 330B. The seat-side continuous point 330B is located closer to the rear end of the grinding shaft J than the main shaft-side continuous point 330A. In other words, the main shaft-side continuous point 330A and the seat-side continuous point 330B are located at different positions along the grinding shaft J. If the central axis of the third elastic portion 330 extending from the member is defined as the third arm axis 330J, the third arm axis 330J is an inclined member that displaces from the tip to the base end of the grinding shaft J as it moves from the inside to the outside in the third radial direction R3 of the grinding shaft J. A constricted portion 330K is formed in the third elastic portion 330 proximal to the main shaft-side continuous point 330A. As a result, the rigidity of the constricted portion 330K is reduced, and the constricted portion 330K is actively elastically deformed. A third relief space 430K is formed on the inside of the third seat portion 430 in the third radial direction R3.

[0052] In this embodiment, the case where the spindle side continuous point 330A is located at the tip end side and the seat side continuous point 330B is located at the base end side is illustrated, but the present invention is not limited to this, and a structure in which the spindle side continuous point 330A is located at the rear end side and the seat side continuous point 330B is located at the tip end side may also be adopted.

[0053] The third seat 430 provides a surface facing the outside in the third radial direction R3. The third seat 430 receives a third external force F3 directed from the outside to the inside in the third radial direction R3. A third seating surface 430A provided on the third seat 430 is a partially spherical recessed portion in this case. When the tool driving mechanism 140 (described later) engages with the third seating surface 430A, the third seat 430 is supported and pressed from the outside to the inside in the third radial direction R3. The initial pressure applied to the third seat 430 serves as a holding pressure (pre-pressure) for maintaining the holding posture of the grinding tool 200.

[0054] Furthermore, in this embodiment, the first radial direction R1, the second radial direction R2, and the third radial direction R3 have an angular difference of 120 degrees along the circumferential direction S. That is, the first elastic portion 310, the second elastic portion 320, and the third elastic portion 330 are arranged at equal intervals in the circumferential direction S. Similarly, the first seat portion 410, the second seat portion 420, and the third seat portion 430 are arranged at equal intervals in the circumferential direction S. The first elastic portion 310, the second elastic portion 320, and the third elastic portion 330 have a rotationally symmetric structure with respect to the grinding axis J. Similarly, the first seat portion 410, the second seat portion 420, and the third seat portion 430 have a rotationally symmetric structure with respect to the grinding axis J.

[0055] (Method of manufacturing abrasive tool) FIG. 7 shows a manufacturing method for the grinding tool 200. As shown in FIG. 7(A), a columnar (cylindrical) base material B is machined using, for example, a wire cutting device to form a precursor Z having first to third planes B1, B2, and B3 extending radially from a central axis C, as shown in FIG. 7(B). The first plane B1, second plane B2, and third plane B3 of the precursor Z are further machined using a wire cutting device or the like to cut out the first rib 211, first elastic portion 310, and first seat portion 410 from the first plane B1, the second rib 212, second elastic portion 320, and second seat portion 420 from the second plane B2, and the third rib 213, third elastic portion 330, and third seat portion 430 from the third plane B3. Through these steps, a precision grinding tool 200 can be manufactured.

[0056] (Tool drive mechanism) As shown in FIGS. 2 and 3, the tool driving mechanism 140 includes a first driving unit 510, a second driving unit 520, and a third driving unit 530.

[0057] The first driving unit 510 is a member that supports and displaces the first seat portion 410 from the outside toward the inside in the first radial direction R1. The first driving unit 510 includes a first contact body 510A, a first displacement shaft 510B that holds the first contact body 510A and displaces it in the first radial direction R1, a first driving source 510C that reciprocates the first displacement shaft 510B in the axial direction (first radial direction R1), a first bracket 510D that is fixed to the tool base 110 and holds the first driving source 510C movably in the first radial direction R1, and a first position adjusting unit 510E that adjusts the position of the first driving source 510C in the first radial direction R1.

[0058] The first position adjustment unit 510E has a first female-threaded seat 510E1 fixed to the tool base 110 and a first adjustment male screw 510E2 that threads into the female thread of the first female-threaded seat 510E1. By adjusting the amount of threading of the first adjustment male screw 510E2 into the first female-threaded seat 510E1, the first adjustment male screw 510E2 is movable in the first radial direction R1. By engaging the tip of the first adjustment male screw 510E2 with the first drive source 510C, the position of the first drive source 510C in the first radial direction R1 is adjusted.

[0059] The first contact body 510A is a spherical convex portion having the same diameter as the spherical concave portion of the first seating surface 410A. As a result, the first contact body 510A engages with the first seating surface 410A, thereby functioning as a so-called spherical seat. The first contact body 510A supports the first seating portion 410 in all directions, including the grinding axis J direction, the circumferential direction S, and the first radial direction R1. Note that, although the example shown here shows a case where the first contact body 510A is a spherical convex portion and the first seating surface 410A is a spherical concave portion, these structures may be reversed. Furthermore, the structure is not limited to a spherical seat structure, and other structures may be used for mutual engagement.

[0060] The first drive source 510C is a stacked piezoelectric actuator, and is held by the first bracket 510D so that the first radial direction R1 is its displacement axis. The stacked piezoelectric actuator can control the position of the first displacement axis 510B (first contact body 510A) relative to itself (actuator body) with high precision and high speed by using a voltage supplied from the tool control device 50.

[0061] When the first driving source 510C displaces the first contact body 510A from the outside toward the inside in the first radial direction R1, the first seat portion 410 moves in the same direction. At this time, the first elastic portion 310 elastically deforms in the first radial direction R1, so that a first external force F1 acts between the first contact body 510A and the first seating surface 410A. The first external force F1 becomes larger as the first contact body 510A is displaced from the outside toward the inside in the first radial direction R1. The first position adjustment portion 510E serves to apply pressure between the first contact body 510A and the first seating surface 410A.

[0062] The second driving unit 520 is a member that supports and displaces the second seat portion 420 from the outside toward the inside in the second radial direction R2. The second driving unit 520 includes a second contact body 520A, a second displacement shaft 520B that holds the second contact body 520A and displaces it in the second radial direction R2, a second driving source 520C that reciprocates the second displacement shaft 520B in the axial direction (second radial direction R2), a second bracket 520D that is fixed to the tool base 110 and holds the second driving source 520C movably in the second radial direction R2, and a second position adjusting unit 520E that adjusts the position of the second driving source 520C in the second radial direction R2.

[0063] The second position adjustment unit 520E has a second female-threaded seat 520E1 fixed to the tool base 110 and a second adjustment male screw 520E2 that threads into the female thread of the second female-threaded seat 520E1. By adjusting the amount of threading of the second adjustment male screw 520E2 into the second female-threaded seat 520E1, the second adjustment male screw 520E2 is movable in the second radial direction R2. By engaging the tip of the second adjustment male screw 520E2 with the second drive source 520C, the position of the second drive source 520C in the second radial direction R2 is adjusted.

[0064] The second contact body 520A is a spherical convex portion having the same diameter as the spherical concave portion of the second seating surface 420A. As a result, the second contact body 520A engages with the second seating surface 420A, thereby functioning as a so-called spherical seat. The second contact body 520A supports the second seating portion 420 in all directions, including the grinding axis J direction, the circumferential direction S, and the second radial direction R2. While the example shown here illustrates a case in which the second contact body 520A is a spherical convex portion and the second seating surface 420A is a spherical concave portion, these structures may be reversed. Furthermore, the structure is not limited to a spherical seat structure, and other structures may be used for mutual engagement.

[0065] The second drive source 520C is a stacked piezoelectric actuator, and is held by the second bracket 520D so that the second radial direction R2 is its displacement axis. The stacked piezoelectric actuator can control the position of the second displacement axis 520B (second contact body 520A) relative to itself (actuator body) with high precision and high speed by using a voltage supplied from the tool control device 50.

[0066] When the second contact body 520A is displaced from the outside toward the inside in the second radial direction R2 by the second driving source 520C, the second seat portion 420 moves in the same direction. At this time, the second elastic portion 320 is elastically deformed in the second radial direction R2, and a second external force F2 acts between the second contact body 520A and the second seating surface 420A. The second external force F2 becomes larger as the second contact body 520A is displaced from the outside toward the inside in the second radial direction R2. The second position adjustment portion 520E serves to apply pressure between the second contact body 520A and the second seating surface 420A.

[0067] The third driving unit 530 is a member that supports and displaces the third seat 430 from the outside toward the inside in the third radial direction R3. The third driving unit 530 includes a third contact body 530A, a third displacement shaft 530B that holds the third contact body 530A and displaces it in the third radial direction R3, a third driving source 530C that reciprocates the third displacement shaft 530B in the axial direction (the third radial direction R3), a third bracket 530D that is fixed to the tool base 110 and holds the third driving source 530C movably in the third radial direction R3, and a third position adjustment unit 530E that adjusts the position of the third driving source 530C in the third radial direction R3.

[0068] The third position adjustment part 530E has a third female-threaded pedestal 530E1 fixed to the tool base 110 and a third adjustment male screw 530E2 that threads into the female thread of the third female-threaded pedestal 530E1. By adjusting the amount of threading of the third adjustment male screw 530E2 into the third female-threaded pedestal 530E1, the third adjustment male screw 530E2 is movable in the third radial direction R3. By engaging the tip of the third adjustment male screw 530E2 with the third drive source 530C, the position of the third drive source 530C in the third radial direction R3 is adjusted.

[0069] The third contact body 530A is a spherical convex portion having the same diameter as the spherical concave portion of the third seating surface 430A. As a result, the third contact body 530A engages with the third seating surface 430A, thereby functioning as a so-called spherical seat. The third contact body 530A supports the third seating portion 430 in all directions, including the grinding axis J direction, the circumferential direction S, and the third radial direction R3. While the third contact body 530A is a spherical convex portion and the third seating surface 430A is a spherical concave portion, these structures may be reversed. Furthermore, the engagement is not limited to a spherical seat structure, and other structures may be used.

[0070] The third drive source 530C is a stacked piezoelectric actuator, and is held by the third bracket 530D so that the third radial direction R3 is its displacement axis. The stacked piezoelectric actuator can control the position of the third displacement axis 530B (third contact body 530A) relative to itself (actuator body) with high precision and high speed by using a voltage supplied from the tool control device 50.

[0071] When the third contact body 530A is displaced from the outside toward the inside in the third radial direction R3 by the third driving source 530C, the third seat portion 430 moves in the same direction. At this time, the third elastic portion 330 is elastically deformed in the third radial direction R3, and a third external force F3 acts between the third contact body 530A and the third seating surface 430A. The third external force F3 becomes larger as the third contact body 530A is displaced from the outside toward the inside in the third radial direction R3. The third position adjustment portion 530E serves to apply pressure between the third contact body 530A and the third seating surface 430A.

[0072] <Explanation of the polishing head function> Next, the operation of the grinding head will be described. For ease of illustration, the displacements U1, U2, and U3 are exaggerated. As shown in FIG. 5, the tool drive mechanism 140 generates a first displacement (movement) U1, a second displacement U2, and a third displacement U3, each of which is equal inward in the radial directions R1, R2, and R3, for the first seat portion 410, the second seat portion 420, and the third seat portion 430. For example, as shown in FIG. 5(B), a first external force F1 acts on the seat-side continuation point 310B of the first elastic portion 310 based on the first displacement (movement) U1. A resultant force FG in the first radial direction R1 of the second external force F2 and the third external force F3 based on the second displacement U2 and the third displacement U3 acts on the spindle-side continuation point 310A. Because the first external force F1 and the resultant force FG have the same magnitude and parallel vectors, the first elastic portion 310 elastically deforms like an elastic hinge, reducing the inclination angle θ relative to the grinding axis J. Because the first bearing surface 410 engages in the direction of the grinding axis J, the spindle-side continuation point 310A displaces toward the tip of the grinding axis J, as indicated by the transition from the chain line to the dotted line. The elastic deformation of the first elastic portion 310 described above also occurs in the second elastic portion 320 and the third elastic portion 330. Therefore, the spindle portion 210 displaces toward the tip along the grinding axis J, and the grinding surface 230 approaches the workpiece W. The displacement (distance) of the grinding surface 230 can be adjusted by the amount of depression of the first seat portion 410, the second seat portion 420, and the third seat portion 430. In other words, the displacement (distance) of the grinding surface 230 can be adjusted by the magnitude of the first external force F1, the second external force F2, and the third external force F3. For example, if the first displacement amount (movement amount) U1, the second displacement amount U2, and the third displacement amount U3 are operated so that their increase / decrease amplitude (displacement width), increase / decrease period, and increase / decrease phase are all matched, the polishing surface 230 will vibrate back and forth along the polishing axis J. Note that by making the displacement amounts U1, U2, and U3 unbalanced (unequal), the vibration direction (vibration axis) of the polishing surface 230 can also be tilted with respect to the Z axis.

[0073] Next, as shown in FIG. 6, consider a case in which the tool driving mechanism 140 generates first, second, and third displacements U1, U2, and U3, each of which is different from one another, for the first seat portion 410, the second seat portion 420, and the third seat portion 430. Here, we assume that the first displacement U1 is large, and the second and third displacements U2 and U3 are equal but smaller than the first displacement U1. In this case, due to the difference in these displacements, a resultant vector UF of the displacement vectors of the first displacement U1, the second displacement U2, and the third displacement U3 remains in the first radial direction R1, as shown in FIG. 6(C). As a result, as shown in FIG. 6(B), the entire grinding tool 200 is offset in the first radial direction R1 (the direction of the resultant vector UF) while the first elastic portion 310, the second elastic portion 320, and the third elastic portion 330 are elastically deformed. As a result, the main shaft portion 210 and the grinding surface 230 move in the first radial direction R1. The radial displacement of the polishing surface 230 can be adjusted appropriately by adjusting the overall balance of the first displacement amount U1, the second displacement amount U2, and the third displacement amount U3. For example, if the first displacement amount (movement amount) U1, the second displacement amount U2, and the third displacement amount U3 are adjusted so that their increase / decrease amplitudes (displacement widths) and increase / decrease periods are matched and their increase / decrease phases are shifted at equal intervals (here, 120-degree phase intervals), the polishing surface 230 will revolve in the circumferential direction S around a predetermined rotation center axis (Z-axis). The rotation radius can be controlled by adjusting the amplitudes (maximum displacement amounts) of the first displacement amount U1, the second displacement amount U2, and the third displacement amount U3.

[0074] <Movement control device> The movement control device 60 incorporates a driver and a computer for the relative rotation mechanism 33 and the relative movement mechanism 40. As shown in FIG. 8(A), the movement control device 60 has a movement control unit 62, a scanning path setting unit 64, and a polishing head setting calculation unit 65. Work shape information 300, which is three-dimensional shape data of the surface (surface to be polished) of the workpiece W, is loaded into the movement control device 60. Note that all or part of the movement control device 60 may be incorporated into the polishing head 100.

[0075] The scan path setting unit 64 sets scan path information for the polishing surface 230 of the polishing head 100 relative to the surface (surface to be polished) of the workpiece W. This scan path information is a change over time (t) in three-dimensional relative coordinates (Xw, Yw, Xw) based on the workpiece W, and is defined here as N(t). In other words, the scan path information N(t) can be expressed as position information in the relative coordinates (Xw(t), Yw(t), Xw(t)). The scan path setting unit 64 references the workpiece shape information 300 when setting the scan path information N(t). For example, if the surface to be polished of the workpiece W has a three-dimensional shape that includes irregularities, grooves, etc., the scan path information N(t) will also be information that follows the irregularities, etc. Note that when polishing is performed while rotating the relative rotation mechanism 33, it is preferable that the scan path setting unit 64 set spiral scan path information N(t) for the surface of the workpiece W.

[0076] The movement control unit 62 controls the relative rotation mechanism 33 and the relative movement mechanism 40 based on the scanning path information N(t) set by the scanning path setting unit 64. As a result, the polishing surface 230, whose position is controlled by the relative movement mechanism 40, moves along the scanning path information N(t) relative to the polished surface of the workpiece W, which is rotated by the relative rotation mechanism 33. At this time, it is desirable to control the distance between the workpiece W and the polishing surface 230 to be constant (this "constant" concept excludes minute vibrations / minute displacements of the polishing surface 230 caused by the tool driving mechanism 140). The movement control unit 62 can also use the relative movement mechanism 40 to tilt the polishing head 100 so that the polishing axis J is perpendicular to the polished surface of the workpiece W.

[0077] The polishing head setting calculation unit 65 generates polishing head setting information V, which is a target value for the micro-vibration and / or micro-displacement of the polishing surface 230, in conjunction with the scanning path information N(t). This polishing head setting information V is stored in the polishing head setting information storage unit 66. For example, the polishing head setting information V preferably stores the amplitude value of the polishing surface 230 in the Z-axis direction, the turning radius of the polishing surface 230 about the Z-axis direction, and instruction information regarding the amount of micro-displacement of the vibration reference position of the polishing surface 230 using a bias voltage. This makes it possible to change the vibration amount, vibration period, and vibration reference position of the polishing surface 230 in conjunction with the location (scanning path) of the polishing surface 230 relative to the workpiece W.

[0078] For example, the polishing head setting information V is preferably information on how to micro-vibrate and / or micro-displace the polishing surface 230 of the polishing head 100 depending on the position of the polishing surface 230 on the relative coordinates (Xw, Yw, Xw) on the surface to be polished of the workpiece W. In this case, the polishing head setting information V is position function information V(Xw, Yw, Xw) based on the relative coordinates (Xw, Yw, Xw).

[0079] On the other hand, for example, the polishing head setting information V is preferably information on how to micro-vibrate and / or micro-displace the polishing surface 230 of the polishing head 100 in accordance with the elapsed time (t) of the scanning path information N(t). In this case, the polishing head setting information V is time function information V(t) that depends on the elapsed time (t).

[0080] Specifically, the polishing head setting information V can be instruction information regarding the frequency, phase, and voltage (amplitude) of each signal generated by the first frequency signal generating unit 53, the second frequency signal generating unit 55, and the bias signal generating unit 56, which will be described in detail later. In other words, the polishing head setting information 66 is instruction information regarding the frequency, phase, and voltage (amplitude) of each of the first synchronized frequency signal DA, the second synchronized frequency signal DB, the third synchronized frequency signal DC, the first phase difference frequency signal QA, the second phase difference frequency signal QB, the third phase difference frequency signal QC, the first bias signal EA, the second bias signal EB, and the third bias signal EC. As a result, all signals DA, DB, DC, QA, QB, QC, EA, EB, EC become position function signals DA(Xw, Yw, Xw), DB(Xw, Yw, Xw), DC(Xw, Yw, Xw), QA(Xw, Yw, Xw), QB(Xw, Yw, Xw), QC(Xw, Yw, Xw), EA(Xw, Yw, Xw), EB(Xw, Yw, Xw), EC(Xw, Yw, Xw), or time function signals DA(t), DB(t), DC(t), QA(t), QB(t), QC(t), EA(t), EB(t), EC(t) depending on elapsed time. Here, the case where relative coordinates (Xw, Yw, Xw) are used is illustrated, but they can also be converted to absolute coordinates (X, Y, X).

[0081] The polishing head setting calculation unit 65 may receive real-time position information of the polishing head 100 from the movement control unit 62 of the movement control device 60 and calculate the polishing head setting information V in real time. The polishing head setting information V is transmitted to the tool control device 50 in real time, and the polishing head 100 is micro-vibrated.

[0082] <Tool control device> 8(B), the tool control device 50 includes an amplifier-type power supply (driver) for controlling the displacement and vibration of the stacked piezoelectric actuators serving as a first drive source 510C, a second drive source 520C, and a third drive source 530C, and a computer. Specifically, the tool driving mechanism 140 includes a first driver 51A for controlling the first drive source 510C, a second driver 51B for controlling the second drive source 520C, and a third driver 51C for controlling the third drive source 530C. Furthermore, the tool control device 50 includes a first frequency signal generator 53, a second frequency signal generator 55, a bias signal generator 56, and a signal superimposing unit 57.

[0083] The first frequency signal generating unit 53 generates a plurality of frequency signals by referring to the polishing head setting and holding unit 66. In particular, in this embodiment, the first frequency signal generating unit 53 generates a plurality of synchronous frequency signals whose increase / decrease periods and increase / decrease phases are the same. In detail, the first frequency signal generating unit 53 includes a first first frequency signal generating unit 53A that generates a first synchronous frequency signal DA for the first drive source 510C, a first second frequency signal generating unit 53B that generates a second synchronous frequency signal DB for the second drive source 520C, and a first second frequency signal generating unit 53C that generates a third synchronous frequency signal DC for the third drive source 530C. The first to third synchronous frequency signals DA, DB, and DC are all signals with the same increase / decrease amplitude, increase / decrease period, and increase / decrease phase.

[0084] The second frequency signal generator 55 generates multiple frequency signals by referring to the polishing head setting and holding unit 66. In this embodiment, the second frequency signal generator 55 generates multiple synchronous frequency signals whose increase / decrease periods are the same but whose increase / decrease phases are different from each other. Specifically, the second frequency signal generator 55 includes a second first frequency signal generator 55A that generates a first phase difference frequency signal QA for the first drive source 510C, a second second frequency signal generator 55B that generates a second phase difference frequency signal QB for the second drive source 520C, and a second third frequency signal generator 55C that generates a third phase difference frequency signal QC for the third drive source 530C. The first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC have the same increase / decrease amplitudes and increase / decrease periods, but have a 120-degree phase difference between each other. The amplitudes and periods of these signals are determined based on the information on the turning radius and turning period of the polishing surface 230 stored in the polishing head setting and holding unit 66. The frequencies of the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC are preferably set to be smaller than the frequencies of the first to third synchronization frequency signals DA, DB, and DC. The amplitudes of the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC are preferably set to be larger than the frequencies of the first to third synchronization frequency signals DA, DB, and DC.

[0085] The bias signal generating unit 56 generates multiple bias signals by referring to the polishing head setting and holding unit 66. Specifically, the bias signal generating unit 56 includes a first bias signal generating unit 56A that generates a first bias signal EA for the first drive source 510C, a second bias signal generating unit 56B that generates a second bias signal EB for the second drive source 520C, and a third bias signal generating unit 56C that generates a third bias signal EC for the third drive source 530C. As shown in FIG. 11A, the first to third bias signals EA, EB, and EC may have pulsed (linear) waveforms or periodic waveforms such as sine waves. Note that the units (e.g., seconds) on the horizontal axis (time) of the first to third bias signals EA, EB, and EC in FIG. 11A are significantly larger than the units (e.g., milliseconds) on the horizontal axis in FIGS. 9A and 9B. When a periodic waveform is used, its frequency is preferably smaller than those of the first to third synchronization frequency signals DA, DB, and DC and the first to third phase difference frequency signals QA, QB, and QC.

[0086] The signal superimposing unit 57 has a first signal superimposing unit 57A, a second signal superimposing unit 57B, and a third signal superimposing unit 57C. The first signal superimposing unit 57A generates a first drive signal KA by superimposing a first synchronization frequency signal DA, a first phase difference frequency signal QA, and a first bias signal EA. The first signal superimposing unit 57A transmits the first drive signal KA to the first driver 51A. As a result, the first driver 51A displaces the first drive source 510C based on this first drive signal KA.

[0087] The second signal superimposing unit 57B generates a second drive signal KB by superimposing the second synchronization frequency signal DB, the second phase difference frequency signal QB, and the second bias signal EB. The second signal superimposing unit 57B transmits the second drive signal KB to the second driver 51B. As a result, the second driver 51B displaces the second drive source 520C based on this second drive signal KB.

[0088] The third signal superimposing unit 57C generates a third drive signal KC by superimposing the third synchronization frequency signal DC, the third phase difference frequency signal QC, and the third bias signal EC. The third signal superimposing unit 57C transmits the third drive signal KC to the third driver 51C. As a result, the third driver 51C displaces the third drive source 530C based on this third drive signal KC.

[0089] (Tool control device action) Fig. 9(C) schematically shows first to third drive signals KA, KB, KC obtained by superimposing the first to third synchronization frequency signals DA to DC of Fig. 9(A) and the first to third phase difference frequency signals QA, QB, QC of Fig. 9(B). The frequencies of the first to third synchronization frequency signals DA to DC of Fig. 9(A) are set to 200 Hz. The frequencies of the first phase difference frequency signal QA, second phase difference frequency signal QB, and third phase difference frequency signal QC of Fig. 9(B) are set to 99 Hz, and their reference phases are set to have a phase difference of 120 degrees.

[0090] The first to third synchronous frequency signals DA, DB, and DC contained in the first to third drive signals KA, KB, and KC in FIG. 9(C) have the same amplitude and period. As a result, as shown in FIG. 5(B), the polishing surface 230 vibrates back and forth along the polishing axis J at 200 Hz. At the same time, the first to third phase difference frequency signals QA, QB, and QC contained in the first to third drive signals KA, KB, and KC in FIG. 9(C) have a phase difference of 120 degrees. As a result, the state shown in FIG. 6(B) periodically changes in the circumferential direction, and as shown in FIG. 9(D), the polishing surface 230 slightly rotates around the Z-axis at 99 Hz (5960 rpm) with respect to the rotation center L, which serves as the vibration reference position. By providing a difference in the amplitude of the first to third synchronous frequency signals DA, DB, and DC, it is possible to rotate the polishing surface 230 in an elliptical orbit, for example. This allows the polishing surface 230 to vibrate back and forth along a spiral movement trajectory with the Z-axis direction as the spiral axis.

[0091] While FIG. 9 illustrates a case in which the polishing surface 230 is slightly rotated by the first to third phase difference frequency signals QA, QB, and QC, the present invention is not limited thereto. For example, by appropriately setting the amplitude (voltage) and phase difference of the first to third phase difference frequency signals QA, QB, and QC, as shown in FIG. 10, the first to third phase difference frequency signals QA, QB, and QC can be used to linearly vibrate back and forth in the Y-axis direction (or XY plane) (see arrow QM) without rotating the polishing surface 230. By matching the vibration period of this vibrating motion (see arrow QM) with the vibration period of the vibrating motion in the Z-axis direction (see arrow KM) caused by the first to third synchronous frequency signals DA, DB, and DC, the polishing surface 230 can be vibrated back and forth in a direction inclined relative to the Z-axis (see arrow RM). This allows the vibration direction of the polishing surface 230 (see arrow RM) to be aligned with the normal direction of the workpiece W, for example, when the normal direction to the surface of the workpiece W is inclined relative to the Z-axis.

[0092] The first to third drive signals KA(t1), KB(t1), and KC(t1) in FIG. 11(B) are obtained by superimposing the first to third synchronization frequency signals DA to DC in FIG. 9(A), the first to third phase difference frequency signals QA, QB, and QC in FIG. 9(B), and the first to third bias signals EA, EB, and EC in FIG. 11(A), and schematically illustrate the state around elapsed time t1 in FIG. 11(A). At elapsed time t1, the first bias signal EA has a bias value Ba1. As a result, the first drive signal KA(t1) has a higher value (higher voltage) than the second and third drive signals KB(t1) and KC(t1) by the bias value Ba1. As shown in FIG. 11(C), the first external force F1(KA(t1)) increases by an amount corresponding to this bias value Ba1, so the vibration reference position (swing center) L1 is offset by a distance O1 from the vibration reference position (swing center) L0 when there is no bias. At elapsed time t2 in Figure 11(A), because the bias value Bb2 of the second bias signal EB is present, the force of the second external force F2 (KB(t2)) increases, as shown in Figure 11(D), and the vibration reference position (turning center) L2 is offset by a distance O2 compared to the turning center L when there is no bias. At elapsed time t3 in Figure 11(A), because the bias value Bc3 of the third bias signal EC is present, the force of the third external force F3 (KC(t3)) increases, as shown in Figure 11(E), and the vibration reference position (turning center) L3 is offset by a distance O3 compared to the turning center L when there is no bias.

[0093] As can be seen from these examples, when the first to third bias signals EA, EB, and EC are sinusoidal signals (frequency signals) having a phase difference of 120 degrees from one another, the vibration reference position (rotation center) L of the polishing surface 230 itself can be rotated around the Z axis. Similarly, when the first to third bias signals EA, EB, and EC are appropriately combined, the rotation center L can be offset in any direction and by any amount. In other words, by controlling the first to third bias signals EA, EB, and EC, the spiral axis itself in the spiral movement locus of the polishing surface 230 can be rotated around the Z axis or moved in any direction within the XY plane.

[0094] The first to third drive signals KA(t1), KB(t1), KC(t1) in Figure 12(B) are obtained by superimposing the first to third synchronization frequency signals DA to DC in Figure 9(A), the first to third phase difference frequency signals QA, QB, QC in Figure 9(B), and the first to third bias signals EA, EB, EC in Figure 12(A), and schematically show the state near the elapsed time t1 in Figure 12(A).

[0095] As shown in Figure 12(A), at elapsed time t1, the bias value Ba1 of the first bias signal EA, the bias value Bb1 of the second bias signal EB, and the bias value Bc1 of the third bias signal EC simultaneously exist and are all the same value. As a result, the first drive signal KA(t1) and the second and third drive signals KB(t1) become higher (higher voltages) by the bias values ​​Ba1, Bb1, and Bc1, respectively. As shown in Figure 12(C), the Z-axis coordinate Z(t1) of the vibration reference position L1 of the polishing surface 230 is displaced in the Z-axis direction compared to the Z-axis coordinate Z(0) of the vibration reference position L0 of the polishing surface 230 when no bias is applied. At elapsed time t2 in Figure 12(A), the bias value Ba2 of the first bias signal EA, the bias value Bb2 of the second bias signal EB, and the bias value Bc2 of the third bias signal EC exist and are all the same value and are greater than the bias values ​​at elapsed time t1. As a result, as shown in FIG. 12(D), the Z-axis coordinate Z(t2) of the vibration reference position L2 of the polishing surface 230 is displaced in the Z-axis direction by an amount corresponding to this bias value, compared to the Z-axis coordinate Z(0) of the vibration reference position L0 of the polishing surface 230 when no bias is applied, and the amount of displacement is greater than the Z-axis coordinate Z(t1). At elapsed time t3 in FIG. 12(A), the bias value Ba3 of the first bias signal EA, the bias value Bb3 of the second bias signal EB, and the bias value Bc3 of the third bias signal EC exist, and these are all equal and greater than the bias values ​​at elapsed time t2. As a result, as shown in FIG. 12(E), the Z-axis coordinate Z(t3) of the vibration reference position L3 of the polishing surface 230 is displaced in the Z-axis direction, compared to the Z-axis coordinate Z(0) of the vibration reference position L0 of the polishing surface 230 when no bias is applied, and the amount of displacement is greater than the Z-axis coordinate Z(t2).

[0096] As can be seen from these examples, when the first to third bias signals EA, EB, and EC are applied simultaneously, the vibration reference position L of the polishing surface 230 can be displaced in the Z-axis direction. By combining the technical concepts of Figures 11 and 12, the first to third bias signals EA, EB, and EC can freely control the vibration reference position L of the polishing surface 230 in both the axial and radial directions.

[0097] The setting values ​​of the amplitude or voltage, frequency, reference phase, etc. of the first to third synchronized frequency signals DA, DB, DC, the first to third phase difference frequency signals QA, QB, QC, and the first to third bias signals EA, EB, EC can be automatically changed along the scanning path by the polishing head setting and holding unit 66 of the tool control device 50.

[0098] For example, as shown in FIG. 13(A), if a portion of the workpiece W's surface to be polished along the scanning path is flat or convex, the turning radius r1 of the polishing surface 230 can be set large. This improves polishing efficiency. On the other hand, as shown in FIG. 13(B), if a portion of the workpiece W's surface to be polished along the scanning path is grooved or concave, the turning radius r2 of the polishing surface 230 can be set small to suppress interference between the polishing surface 230 and the surface to be polished. For example, if the workpiece W is a Diffractive Optics lens or a microlens array, the surface will be uneven, so it is preferable to control the turning radius according to the scanning path. Furthermore, as shown in FIG. 13(C), if the workpiece W has a convex or concave curved surface, the vibration reference position L of the polishing surface 230 can be moved both axially and radially using the first to third bias signals EA, EB, and EC, thereby enabling high-precision and high-speed control of the distance (polishing gap) between the curved surface of the workpiece W and the polishing surface 230. For example, when the workpiece W is rotated at high speed by the relative rotation mechanism 33, the polishing gap may not be maintained constant in response to the uneven shape of the polished surface of the workpiece W due to the response speed limit of the relative movement mechanism 40. In such cases, the polishing gap can be maintained constant by the first to third bias signals EA, EB, and EC. To achieve this control, the polishing head setting calculation unit 65 in FIG. 8(A) controls the first to third bias signals EA, EB, and EC based on the scanning path information N(t) and the workpiece shape information 300.

[0099] (Introduction of variations) 9 and 10 illustrate an example in which the first frequency signal generating unit 53 of the tool control device 50 generates first to third synchronized frequency signals DA, DB, DC having the same increase / decrease cycles and increase / decrease phases, but the present invention is not limited to this, and the first to third phase difference frequency signals GA, GB, GC having different increase / decrease phases may be generated. By freely controlling the phase, frequency, and amplitude of a total of six signals, namely the first to third phase difference frequency signals GA, GB, GC generated by the first frequency signal generating unit 53 and the first to third phase difference frequency signals QA, QB, QC generated by the second frequency signal generating unit 55, the polishing surface 230 can be minutely vibrated in any direction or minutely rotated.

[0100] <Demonstration experiment 1: Verification of polishing head operation> The displacement of the polishing surface 230 of the polishing head 100 alone was examined. Specifically, the first to third synchronization frequency signals DA to DC were set to a frequency of 200 Hz and their reference phases were all set to 0. The frequencies of the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC were set to 99 Hz, with a phase difference of 120 degrees between their reference phases. The amplitudes of these signals were appropriately set within the range of 0 to 4 (V). The input of the first to third bias signals EA, EB, and EC was omitted. Under these settings, the polishing tool 200 was vibrated by the tool driving mechanism 140, and the displacement of the polishing surface 230 in the Z-axis direction and the radial direction R was measured using a confocal chromatic sensor. The results are shown in Figure 14.

[0101] 14(A), the polishing surface 230 could be reciprocated in the Z-axis direction with a movement distance of 0.025 mm or less (for example, 0.015 mm). The waveform of this reciprocating vibration was a smooth sine wave of 200 Hz, and the displacement normalized by the voltage of the drive signal was 4 μm / V.

[0102] As shown in FIG. 14(B), the polishing surface 230 was able to be revolved in the radial direction R (XY plane direction) with a travel distance of 0.025 mm or less (e.g., 0.015 mm) by superimposing the vibration in the Z-axis direction on the vibration in the Z-axis direction. The waveform of this reciprocating vibration approximated a seesaw function shape at 99 Hz, and the normalized displacement was 5 μm / V. A notable feature is that there was almost no crosstalk between the minute vibration in the Z-axis direction and the minute vibration in the radial direction R. In other words, even when the polishing tool 200 was displaced in a superimposed manner using the tool drive mechanism 140 with the first drive signal KA, the second drive signal KB, and the third drive signal KC, the minute vibration in the Z-axis direction and the minute vibration in the radial direction R of the polishing surface 230 could be independently controlled.

[0103] This verification procedure can be used as a method for calibrating the polishing head 100 alone. That is, the set values ​​of the first to third synchronization frequency signals DA to DC, the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC can be adjusted until the desired micro-vibrations in the Z-axis direction and the desired micro-vibrations in the radial direction R are obtained.

[0104] <Demonstration experiment 2: Polishing verification using a polishing device> Next, a verification was conducted on polishing a workpiece W using the polishing apparatus 1 shown in FIG. 1. For example, in the case of molding using a mold, hairline-shaped cutting marks (tool marks) are formed on the surface of the metal mold as the movement trajectory of the processing tool used in mold production, and these tool marks are transferred to the optical element. Similarly, even when an optical element is directly processed by cutting, hairline-shaped cutting marks (tool marks) as the movement trajectory of the cutting tool remain on the optical element. A verification was conducted on whether the polishing apparatus 1 can erase these tool marks by polishing the surface of the workpiece W.

[0105] (Preparing the abrasive) As the abrasive, a non-Newtonian fluid was prepared by adjusting the water and starch ratio to the desired viscosity within the range of 50:50 to 50:30, and alumina particles of #30000 (particle size 0.3 to 0.39 μm) were mixed at a concentration of 40 g / L.

[0106] (Work preparation) A circular (cylindrical) workpiece W with electroless nickel plating was prepared, and its circular surface (the surface to be polished) was cut using a diamond turning machine with a hairline path. The resulting surface condition is shown in Figure 15. As shown in the optical microscope photograph in Figure 15(A), hairline-like irregularities (grooves or ridges) were confirmed to have been formed on the surface to be polished. Furthermore, as shown in the three-dimensional profile measured with a three-dimensional scanner in Figure 15(B), hairline-like irregularities (grooves or ridges) were confirmed to have been formed on the surface to be polished. The surface roughness was measured using the three-dimensional profile and found to be 0.24 nmRa. Furthermore, the line pitch (distance) of the hairline-like irregularities (grooves or ridges) averaged approximately 20 μm.

[0107] (Polishing equipment settings) In the polishing apparatus 1, the polishing surface 230 was a circular plane with a diameter of 2 mm. The frequencies of the first to third synchronization frequency signals DA to DC were set to 1000 Hz, and the reference phases were all set to 0. The frequencies of the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC were set to 100 Hz, with a phase difference of 120 degrees between their respective reference phases. Calibration confirmed that the polishing surface 230 vibrated minutely in the Z-axis direction at 1000 Hz with an amplitude of 10 μm. It was also confirmed that the polishing surface 230 orbited around the Z-axis at 100 Hz with a rotation radius of 20 μm (micro-oscillation in the radial direction R with an amplitude of 40 μm). Using this polishing apparatus 1, the polished surface of the workpiece W was scanned with the polishing surface 230 while the workpiece W was rotated at 100 rpm while the above-mentioned abrasive was supplied, and polishing was performed to a material removal depth of approximately 10 nm. During polishing, the gap distance between the workpiece W and the polishing surface 230 was controlled to be 50 to 100 μm. Experiments by the inventors have revealed that within this gap distance range, micro-vibrations (pressure) at 1000 Hz with an amplitude of 10 μm in the Z-axis direction locally increase the viscosity of the abrasive.

[0108] The surface condition after polishing is shown in FIG. 16. As shown in the optical microscope photograph in FIG. 16(A) and the three-dimensional profile in FIG. 16(B), it was confirmed that the hairline irregularities (grooves or ridges) on the polished surface were almost completely eliminated. This confirmed that it was possible to reduce the surface roughness (PV value) of the polished surface to 100 nm or less. Furthermore, when the surface roughness was measured using the three-dimensional profile in FIG. 16(B), it was found to be 0.37 nmRa, confirming that the increase in surface roughness during the polishing process could also be suppressed. In other words, it can be seen that the polishing apparatus 1 of this embodiment can flatten the hairline irregularities to a PV value of 100 nm or less while suppressing the increase in surface roughness to, for example, 0.50 nmRa or less.

[0109] <Comparative experiment: Polishing verification using a polishing device> Next, the workpiece W was polished in the polishing apparatus 1 under the same conditions as in Experiment 2, except that the rotational motion (micro-vibration in the radial direction R) of the polishing surface 230 around the Z axis was stopped. The surface condition after polishing is shown in Figure 17. As shown in the optical microscope photograph in Figure 17(A) and the three-dimensional profile in Figure 17(B), it was confirmed that some hairline-like irregularities (grooves or ridges) remained on the polished surface. At the same time, it was confirmed that localized pits (depressions) were formed on the polished surface. The surface roughness was measured using the three-dimensional profile in Figure 17(B) and found to be 0.51 nmRa, confirming that the surface roughness increased during the polishing process.

[0110] As described above, according to the polishing apparatus 1 of this embodiment, by displacing the multiple bearing surfaces 410, 420, 430 of a single polishing tool 200, it is possible to elastically deform the polishing tool 200 and simultaneously micro-vibrate the polishing surface 230 in the polishing axis J direction and the radial direction R. Furthermore, since crosstalk is unlikely to occur between the micro-vibrations in the polishing axis J direction and the radial direction R, it is possible to independently control the micro-vibrations of the polishing surface 230 in the polishing axis J direction and the radial direction R of the polishing surface 230. Similarly, the multiple drive units 510, 520, 530 of the tool drive mechanism 140 work together to simultaneously realize micro-vibrations of the polishing surface 230 in the polishing axis J direction and the radial direction R, which allows the structure of the polishing head 100 to be simplified.

[0111] In the above-described polishing apparatus 1, the polishing tool 200 is illustrated as having a total of three elastic portions, namely, the first elastic portion 310, the second elastic portion 320, and the third elastic portion 330, arranged along the first to third radial directions R1 to R3, each having a phase difference of 120 degrees. However, the present invention is not limited to this. A total of two elastic portions may be provided with a phase difference of 180 degrees, or a total of four or more elastic portions may be provided with a phase difference at equal intervals in the circumferential direction. In order to realize the pivoting motion of the polishing surface 230, it is preferable to provide at least three elastic portions.

[0112] 5(B), the inclination angle θ between the first arm axis 310J of the first elastic part 310 and the grinding axis J is an acute angle, but the inclination angle θ may be an obtuse angle. When the inclination angle θ is an obtuse angle, the grinding surface 230 can be displaced in a direction away from the workpiece W by displacing the first seat part 410 inward in the first radial direction R1.

[0113] 2, the tool driving mechanism 140 has been described as displacing the first to third seats 410, 420, 430 radially inward toward the grinding axis J, but the present invention is not limited to this. For example, the first to third seats 410, 420, 430 may be displaced radially inward while the displacement vector is offset from the grinding axis J. The tool driving mechanism 140 may also displace the first to third seats 410, 420, 430 radially outward.

[0114] Furthermore, in the tool control device 50, the amplitudes of the first phase difference frequency signal QA, the second phase difference frequency signal QB, and the third phase difference frequency signal QC are greater than the synchronous frequency signal D, but the present invention is not limited to this. For example, as shown in Fig. 18, the first to third drive signals KA, KB, and KC may be generated by making the amplitudes of the first to third phase difference frequency signals QA, QB, and QC smaller than the amplitudes of the first to third synchronous frequency signals DA, DB, and DC.

[0115] Furthermore, in this embodiment, for convenience of explanation, the first to third synchronized frequency signals DA, DB, and DC, the first to third phase difference frequency signals QA, QB, and QC, and the first to third bias signals EA, EB, and EC are generated as independent waveforms, but the present invention is not limited to this. For example, setting the average voltage of the first synchronized frequency signal DA higher than the average voltages of the second and third synchronized frequency signals DB and DC is essentially equivalent to a state in which the first bias signal EA is superimposed. Similarly, setting the average voltage of the first phase difference frequency signal QA higher than the average voltages of the second and third phase difference frequency signals QB and QC is essentially equivalent to a state in which the first bias signal EA is superimposed.

[0116] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0117] 1 Polishing equipment 10 Foundations 20 Polishing head holding mechanism 30 Work holding mechanism 33 Relative rotation mechanism 35 Abrasive material supply device 40 Relative movement mechanism 50 Tool control device 60 Movement control device 62 Movement control unit 64 Scanning path setting unit 66 Polishing head setting holder 100 Polishing Heads 110 Tool Base 140 Tool drive mechanism 200 Polishing tools 210 Main shaft section 210A center axis 211 First Rib 212 Second Rib 213 Third Rib 230 Polished surface 310 First elastic part 320 Second elastic part 330 Third elastic part 410 First seat 420 Second seat 430 Third seat 510 First drive unit 520 Second Drive Unit 530 Third Drive Unit B Base material C center axis DA first synchronous frequency signal DB Second synchronous frequency signal DC third synchronous frequency signal IF setting interface J Polishing shaft KA First drive signal KB Second drive signal KC Third drive signal KC Second drive signal QA first phase difference frequency signal QB Second phase difference frequency signal QC third phase difference frequency signal R Radial direction S Polishing shaft circumferential direction U1 First displacement U2 Second displacement U3 Third displacement double work

Claims

1. A grinding tool for grinding a workpiece by holding an abrasive material between its grinding surface and the workpiece, When the direction in which the center of the polishing surface approaches or moves away from the workpiece is defined as a virtual polishing axis, a main shaft portion having the polishing surface facing the workpiece at its tip and extending along the polishing axis; a plurality of elastic portions extending radially outward from the grinding shaft, the elastic portions being continuous with the main shaft portion; a plurality of seat portions continuous with the radially outer sides of the plurality of elastic portions, a position where the elastic portion is continuous with the main shaft portion and a position where the elastic portion is continuous with the seat portion are different in the direction of the grinding axis, When the tool driving mechanism applies the same amount of displacement in the radial direction to each of the plurality of seats, the plurality of elastic portions are elastically deformed, and the spindle portion is displaced so as to include an axial component of the grinding shaft, when a tool driving mechanism applies different amounts of displacement in the radial direction to each of the plurality of seats, the spindle portion is displaced so as to include a radial component of the grinding shaft. Polishing tools.

2. a plurality of the elastic portions and the seat portions are arranged at equal intervals in the circumferential direction of the grinding shaft; The abrasive tool according to claim 1 .

3. The present invention is characterized in that it comprises three of the elastic portions and the seat portions. The abrasive tool according to claim 2.

4. A polishing head having the polishing tool of claim 1, Tool base and a tool driving mechanism disposed on the tool base for displacing or elastically deforming the grinding tool; The tool drive mechanism includes: The present invention is characterized in that it comprises a plurality of drive units arranged on a plurality of the seat portions and displacing the seat portions in the radial direction. Polishing head.

5. a tool control device that controls the tool driving mechanism; The control device a first frequency signal generating unit that generates a plurality of first frequency signals for periodically displacing the plurality of drive units back and forth so that periods of increase and decrease in the amount of displacement match each other; a second frequency signal generating unit that generates a plurality of second frequency signals for periodically displacing the plurality of drive units back and forth so that periods of increase and decrease in the amount of displacement match each other; a signal superimposing unit that generates drive signals for the plurality of drive units by superimposing the plurality of first frequency signals and the plurality of second frequency signals; characterized in that it has 5. The polishing head according to claim 4.

6. the first frequency signals generated by the first frequency signal generating unit have the same increase and decrease phases, The second frequency signals generated by the second frequency signal generating unit have different increase and decrease phases. The polishing head according to claim 5 .

7. The frequency of the first frequency signal is higher than the frequency of the second frequency signal.

7. The polishing head according to claim 5 or 6.

8. a bias signal generating unit that generates a bias signal to be superimposed on at least one of the plurality of drive signals, 7. The polishing head according to claim 5 or 6.

9. and a polishing head setting calculation unit that changes the bias signal generated by the bias signal generation unit by referring to scanning path information of the polishing head relative to the workpiece and / or shape information of the workpiece. The polishing head according to claim 8 .

10. The tool driving mechanism vibrates the polishing surface along a spiral movement locus. The polishing head according to claim 1 .

11. The tool driving mechanism displaces a helical axis of the helical movement locus on the polishing surface. The polishing head of claim 10.

12. a grinding tool for holding an abrasive material between its grinding surface and a workpiece to grind the workpiece; Tool base and a tool drive mechanism disposed on the tool base for displacing the grinding tool; a control device for controlling the tool driving mechanism, When the direction in which the center of the polishing surface approaches or moves away from the workpiece is defined as a virtual polishing axis, a plurality of the tool driving mechanisms are arranged in a circumferential direction of the grinding shaft, each of the tool driving mechanisms having a driving section for displacing the grinding tool in a radial direction of the grinding shaft; The control device a first frequency signal generating unit that generates a plurality of first frequency signals for periodically displacing the plurality of drive units back and forth so that periods of increase and decrease in the amount of displacement match each other; a second frequency signal generating unit that generates a plurality of second frequency signals for periodically displacing the plurality of drive units back and forth so that periods of increase and decrease in the amount of displacement match each other; a signal superimposing unit that generates drive signals for the plurality of drive units by superimposing the plurality of first frequency signals and the plurality of second frequency signals; characterized in that it has Polishing head.

13. the first frequency signals generated by the first frequency signal generating unit have the same increase and decrease phases, The second frequency signals generated by the second frequency signal generating unit have different increase and decrease phases. The polishing head of claim 11.

14. The frequency of the first frequency signal is higher than the frequency of the second frequency signal.

13. The polishing head according to claim 11 or 12.

15. The base and The polishing head according to any one of claims 4 to 14, a polishing head holding mechanism provided on the base and holding the polishing head; a workpiece holding mechanism provided on the base and holding the workpiece; a relative movement mechanism that moves the workpiece and the polishing head relatively in the axial direction of the polishing shaft and in the radial direction of the polishing shaft; A polishing apparatus comprising:

16. A polishing method for polishing a workpiece by holding an abrasive material, which is a fluid having abrasive grains dispersed therein, between a polishing surface of a polishing tool and the workpiece, comprising: When the direction in which the center of the polishing surface approaches or moves away from the workpiece is defined as a virtual polishing axis, a plurality of drive units are arranged in the circumferential direction of the grinding shaft, and each of the drive units displaces a contact point with the grinding tool in the radial direction of the grinding shaft; generating a synchronous frequency signal for periodically displacing the plurality of drive units back and forth so that the increase / decrease periods and increase / decrease phases of the displacement amounts coincide with each other; generating a plurality of first frequency signals for periodically displacing the plurality of drive units back and forth so that periods of increase and decrease in the displacement amount coincide with each other; generating a plurality of second frequency signals for periodically reciprocatingly displacing the plurality of drive units so that periods of increase and decrease in the displacement amount coincide with each other; generating drive signals for the plurality of drive units by superimposing the plurality of first frequency signals and the plurality of second frequency signals; The grinding surface of the grinding tool is displaced in the axial direction and the radial direction of the grinding shaft by displacing the plurality of drive units in response to the plurality of drive signals. Polishing method.

17. The first frequency signals have the same increase and decrease phases, The plurality of second frequency signals have different increase and decrease phases. The polishing method according to claim 16.

18. a bias signal is superimposed on at least one of the plurality of drive signals, thereby displacing the polishing surface in the radial direction and / or the axial direction of the polishing shaft; The polishing method according to claim 16 or 17.

19. The bias signal is changed by referring to scanning path information of the polishing surface relative to the workpiece and / or shape information of the workpiece. The polishing method according to claim 18.

20. The polishing surface is vibrated along a spiral movement locus. The polishing method according to claim 17.

21. a helical axis of the helical movement locus on the polishing surface is displaced; The polishing method according to claim 20.

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