Superfinishing apparatus for screw shaft of ball screw

Abstract

To provide a superfinishing device of a screw shaft of a ball screw capable of sufficiently enhancing machining accuracy of superfinishing of an inner surface of a groove of a screw shaft.SOLUTION: At the time of superfinishing an inner surface of a groove of a screw shaft W, grinding wheel swinging units 4A and 4B are fixed on a sub-base table B2, and a work head 2 is moved in a direction along an axial center of the screw shaft W by a work head moving unit 3 in accordance with rotation of the screw shaft W by screw shaft rotating units 21A and 21B while swinging the grinding wheel by a grinding wheel swinging mechanism 44 in a state where the grinding wheel is in contact with the inside of the groove of the screw shaft W. As a result, machining accuracy of superfinishing of the inner surface of the groove of the screw shaft W can be sufficiently enhanced.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a superfinishing device for a screw shaft of a ball screw. In particular, the present invention relates to an improvement in a device for superfinishing the inner surface of a groove of a screw shaft.

Background Art

[0002] A ball screw is a mechanical element for converting a rotational motion received from a power source such as a motor into a linear motion, or conversely, converting a linear motion received from a power source into a rotational motion, and is applied to power transmission parts of various devices such as semiconductor manufacturing devices, machine tools, and industrial robots. Further, this ball screw has a configuration including a screw shaft, a nut, balls, and a ball circulation mechanism, and has characteristics such as a very small friction coefficient and high energy efficiency due to the circulation of the balls between the screw shaft and the nut.

[0003] Also, in a ball screw, in order to improve the accuracy of motion conversion and reduce the operating noise, it is required to reduce the surface roughness of the inner surface of the groove formed on the outer peripheral surface of the screw shaft (generally, to increase the smoothness of the inner surface of the groove having a Gothic arc-shaped cross section). Therefore, for example, as disclosed in Patent Document 1, a superfinishing device for superfinishing the inner surface of the groove of the screw shaft has been proposed.

[0004] The superfinishing device disclosed in this Patent Document 1 includes a screw shaft rotating device and a grinding wheel head moving device supported on a base, and a grinding wheel swinging device supported by the grinding wheel head moving device. The screw shaft rotating device includes a main spindle base and a center rest that respectively support both ends of the screw shaft. The main spindle base is provided with a servo motor for rotating the screw shaft. The grinding wheel head moving device includes a linear guide extending in the arrangement direction of the main spindle base and the center rest, a moving body movable along the linear guide, and a servo motor for moving the moving body along the linear guide. By the operation of this servo motor, the moving body moves along the linear guide, whereby the grinding wheel swinging device can move in the direction along the axis of the screw shaft. Then, during the superfinishing process of superfinishing the inner surface of the groove of the screw shaft, the screw shaft is rotated around its axis by the screw shaft rotating device, and the grinding wheel supported by the grinding wheel swinging device is swung in a state of being in contact with the inner surface of the groove of the screw shaft, and in this state, the moving body of the grinding wheel head moving device is moved (moved in the direction along the axis of the screw shaft). As a result, while moving the grinding wheel swinging device in the direction along the axis, the inner surface of the groove of the screw shaft is superfinished from one end side to the other end side of the screw shaft.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the superfinishing device disclosed in Patent Document 1, the grinding wheel swinging device swings the grinding wheel and moves in the direction along the axis of the screw shaft along with the operation of the grinding wheel head moving device to superfinish the inner surface of the groove of the screw shaft. Therefore, when there is play inside the grinding wheel head moving device, it becomes difficult to make the surface of the swinging grinding wheel come into good contact with the inner surface of the groove of the screw shaft.

[0007] In addition, there was also a concern that the vibration generated by the grinding wheel swing device might have an adverse effect on the movement (the movement of the grinding wheel along the axial center of the screw shaft), or that the influence of this vibration acting on the linear guide might cause poor accuracy.

[0008] Therefore, there was room for improvement to sufficiently enhance the machining accuracy of the superfinishing of the inner surface of the groove of the screw shaft.

[0009] The present invention has been made in view of such points, and an object thereof is to provide a superfinishing device for a screw shaft of a ball screw that can sufficiently enhance the machining accuracy of the superfinishing of the inner surface of the groove of the screw shaft.

Means for Solving the Problem

[0010] The solution means of the present invention for achieving the above object is premised on a superfinishing device for a screw shaft of a ball screw that superfinishes the inner surface of the groove by rotating the screw shaft while bringing a grinding wheel into contact with the groove of the screw shaft of the ball screw. And for this superfinishing device for the screw shaft of the ball screw, a grinding wheel swing unit mounted on a base table and having a grinding wheel support portion for supporting the grinding wheel and a grinding wheel swing mechanism for swinging the grinding wheel, a work head having a screw shaft rotation unit for supporting both ends of the screw shaft and rotating the screw shaft around its axial center, and a work head movement unit for moving the work head in a direction along the axial center of the screw shaft on the base table are provided. During the superfinishing of the inner surface of the groove, the grinding wheel swing unit is fixed on the base table, and while the grinding wheel is swung by the grinding wheel swing mechanism in a state where the grinding wheel is in contact with the groove of the screw shaft, the work head is moved in a direction along the axial center of the screw shaft by the work head movement unit according to the rotation of the screw shaft by the screw shaft rotation unit.

[0011] Due to this specific matter, when superfinishing (superfinishing process) the inner surface of the groove of the screw shaft of the ball screw, while the grinding wheel oscillation unit is fixed on the base table, the work head moves in the direction along the axis of the screw shaft (while moving the screw shaft in the same direction). Therefore, the grinding wheel oscillation unit is not designed to move in the direction along the axis of the screw shaft while oscillating the grinding wheel. When the grinding wheel oscillation unit moves in the direction along the axis of the screw shaft while oscillating the grinding wheel (in the case of the prior art), if there is play in the mechanism for this movement, it becomes difficult to make the surface of the oscillating grinding wheel contact well with the inner surface of the groove of the screw shaft. Also, the vibration generated by the grinding wheel oscillation unit may adversely affect the movement of the grinding wheel in the direction along the axis of the screw shaft, making it difficult to sufficiently improve the machining accuracy of the superfinishing of the inner surface of the groove of the screw shaft. However, in this solution, the work head moves in the direction along the axis of the screw shaft to relatively move the grinding wheel and the screw shaft (relatively move in the direction along the axis of the screw shaft). Since the grinding wheel oscillation unit does not move in the direction along the axis of the screw shaft, it becomes possible to make the surface of the oscillating grinding wheel contact well with the inner surface of the groove of the screw shaft. Thereby, the machining accuracy of the superfinishing of the inner surface of the groove of the screw shaft can be sufficiently improved.

[0012] Further, the grinding wheel oscillation units are respectively disposed on one side and the other side sandwiching the screw shaft in a direction intersecting the axis of the screw shaft supported by the screw shaft rotation unit.

[0013] According to this, it becomes possible to simultaneously superfinish the inner surface of the groove of the screw shaft by each grinding wheel oscillation unit at a plurality of locations, and efficient superfinishing can be performed. Thereby, it is possible to shorten the time required for superfinishing and improve the machining accuracy of superfinishing.

[0014] Further, the screw shaft rotation unit includes a first screw shaft rotation unit that supports one end of the screw shaft and a second screw shaft rotation unit that supports the other end of the screw shaft, and a power source for applying a rotational force to the screw shaft is provided in each of the screw shaft rotation units.

[0015] Generally, since the contact area between each screw shaft rotation unit and the end of the screw shaft is small, if a power source (a power source for applying a rotational force to the screw shaft) is provided only in one of the first screw shaft rotation unit and the second screw shaft rotation unit, there is a possibility that the rotational force cannot be properly transmitted to the screw shaft. In this case, the rotation of the screw shaft may become unstable, and it becomes difficult to sufficiently increase the machining accuracy of the inner surface of the groove of the screw shaft. On the other hand, in this solution, since the rotational force is applied to the screw shaft from both sides of the first screw shaft rotation unit and the second screw shaft rotation unit, it becomes possible to stably obtain the rotation of the screw shaft, and it becomes possible to sufficiently increase the machining accuracy of the inner surface of the groove of the screw shaft.

[0016] Also, one of the screw shaft rotation units is a movable screw shaft rotation unit supported by a moving unit and movable in a direction along the axis of the screw shaft by the operation of the moving unit. The moving unit includes a plurality of moving devices, and the movable screw shaft rotation unit can move forward and backward with respect to the screw shaft rotation unit on the other side by these moving devices.

[0017] In this way, since the movable screw shaft rotation unit can move forward and backward with respect to the screw shaft rotation unit on the other side by each of the plurality of moving devices, the positional accuracy of the movable screw shaft rotation unit can be obtained highly. That is, the interval between the screw shaft rotation units can be managed with high accuracy. As a result, the support state of the screw shaft supported between the screw shaft rotation units can be appropriately obtained, and also by this, the machining accuracy of the inner surface of the groove of the screw shaft can be sufficiently increased.

[0018] In this case, it is preferable that the plurality of moving devices include at least one electric moving device and at least one hydraulic moving device.

[0019] According to this, it is possible to realize a moving unit that effectively utilizes the advantages (such as moving speed, accuracy of moving position, cost, etc.) of each of the electric moving device and the hydraulic moving device.

Effects of the Invention

[0020] In the present invention, during the superfinishing of the inner surface of the groove of the screw shaft, a grinding wheel swing unit is fixed on the base table, and while the grinding wheel is swung by the grinding wheel swing mechanism in a state where the grinding wheel is in contact with the groove of the screw shaft, the work head is moved in the direction along the axis of the screw shaft by the work head moving unit according to the rotation of the screw shaft by the screw shaft rotation unit. For this reason, the processing accuracy of the superfinishing of the inner surface of the groove of the screw shaft can be sufficiently improved.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0023] FIG. 1 is a plan view showing the overall schematic configuration of the superfinishing apparatus 1 according to the present embodiment. Further, FIG. 2 is a front view showing the overall schematic configuration of the superfinishing apparatus 1 according to the present embodiment.

[0024] As shown in these figures, the superfinishing apparatus 1 includes a work head 2 that supports both ends of a screw shaft W and rotates the screw shaft W around its axis, a work head moving unit 3 that is placed on a main base table B1 (see FIG. 2) and moves the work head 2 in a direction along the axis of the screw shaft W, and a pair of grindstone swing units 4A and 4B that support a grindstone 45a (see FIG. 3, which is a view seen from the direction of arrow III in FIG. 1) for superfinishing the inner surface of the groove of the screw shaft W and swing the grindstone 45a.

[0025] In the following description, the left-right direction (the direction along the axis of the screw shaft W supported by the work head 2) in FIGS. 1 and 2 is defined as the X direction. In this direction, the left direction in FIGS. 1 and 2 may be referred to as the X1 direction, and the right direction may be referred to as the X2 direction. Further, the horizontal direction orthogonal to the X direction is defined as the Y direction. In this direction, the upward direction in FIG. 1 and the back direction of the paper surface in FIG. 2 may be referred to as the Y1 direction, and the downward direction in FIG. 1 and the front direction of the paper surface in FIG. 2 may be referred to as the Y2 direction. Also, the height direction in the superfinishing apparatus 1 is defined as the Z direction. In this direction, the front direction of the paper surface in FIG. 1 and the upward direction in FIG. 2 may be referred to as the Z1 direction, and the back direction of the paper surface in FIG. 1 and the downward direction in FIG. 2 may be referred to as the Z2 direction.

[0026] Hereinafter, the configurations of the work head moving unit 3, the work head 2, and the grindstone swing units 4A and 4B will be described respectively.

[0027] -Configuration of Work Head Moving Unit- The work head moving unit 3 includes a slide rail 31, a spindle base table 32 placed on the slide rail 31, and a first servo motor (slide movement power source) 33 for moving the spindle base table 32.

[0028] The slide rail 31 is composed of two rail members extending along the X direction on the main base table (the base table that supports the work head moving unit in the present invention) B1. The length of this slide rail 31 is preset according to the length of the screw shaft W to be processed. For example, when the superfinishing device 1 is used for processing a plurality of types of screw shafts W with different lengths, the length of the slide rail 31 is set according to the length of the longest screw shaft W (according to the moving distance of this screw shaft W required for processing this screw shaft W).

[0029] The spindle head table 32 is made of a rectangular plate material in plan view (when viewed from the direction along the Z direction), and a plurality of sliders 32a, 32a,... provided on the lower surface are placed on the slide rail 31, whereby it can slide freely along the horizontal direction (X direction). In the present embodiment, the length dimension of the spindle head table 32 in the X direction is set to about 1 / 2 of the length dimension of the main base table B1 in the X direction. This ratio of lengths is not limited to this. Also, the configuration that enables the spindle head table 32 to slide freely on the main base table B1 is not limited to the one described above.

[0030] The first servo motor 33 is disposed at a position closer to the X1 direction on the main base table B1, and a ball screw 34 for converting the rotational movement of the drive shaft into a linear movement, which is the sliding movement of the spindle head table 32, is connected to the drive shaft thereof. That is, the screw shaft 34a of this ball screw 34 is connected to the drive shaft of the first servo motor 33, and the nut 34b of the ball screw 34 is connected to the spindle head table 32. Thus, the spindle head table 32 can slide on the slide rail 31 by the operation of the first servo motor 33. The sliding movement direction of the spindle head table 32 is determined by the rotational direction of the first servo motor 33, and the sliding movement speed of the spindle head table 32 is determined by the rotational speed of the first servo motor 33. The rotational direction and rotational speed of this first servo motor 33 are adjusted (controlled) according to a control signal from a controller (not shown). Note that the configuration of the power source for sliding the spindle head table 32 is not limited to this.

[0031] -Configuration of the work head- The work head 2 is placed on the spindle head table 32 and includes a pair of screw shaft rotation units 21A and 21B, and a movement unit 22 for moving the screw shaft rotation unit 21B on one side (X2 direction side).

[0032] The screw shaft rotation units 21A and 21B are composed of a first screw shaft rotation unit 21A arranged at a position closer to the X1 direction and a second screw shaft rotation unit 21B arranged at a position closer to the X2 direction.

[0033] The first screw shaft rotation unit 21A is fixed on a support block 21a fixed on the spindle head table 32. Further, this first screw shaft rotation unit 21A includes a second servo motor (drive servo motor: a power source for applying a rotational force to the screw shaft in the present invention) 21b and a screw shaft support shaft 21c connected to the drive shaft of the second servo motor 21b and extending along the X direction (toward the X2 direction). The screw shaft support shaft 21c is rotatably supported by a radial bearing inside the first screw shaft rotation unit 21A. This screw shaft support shaft 21c is inserted into a recess provided at the center of one end (the end on the X1 direction side) of the screw shaft W to support (clamp) one end of the screw shaft W.

[0034] The second screw shaft rotation unit 21B is mounted on the moving unit 22 placed on the spindle head table 32 and is movable in the X direction along with the operation of this moving unit 22. Similarly to the first screw shaft rotation unit 21A, the second screw shaft rotation unit 21B also includes a third servo motor (drive servo motor: a power source for applying a rotational force to the screw shaft in the present invention) 21d and a screw shaft support shaft 21e connected to the drive shaft of the third servo motor 21d and extending along the X direction (toward the X1 direction). The screw shaft support shaft 21e is rotatably supported by a radial bearing inside the second screw shaft rotation unit 21B. This screw shaft support shaft 21e is inserted into a recess provided at the center of the other end (the end on the X2 direction side) of the screw shaft W to support (clamp) the other end of the screw shaft W.

[0035] The moving unit 22 includes a first table 22a, a second table 22b, a fourth servo motor (an electric moving device in the present invention) 22c, and an air cylinder (a fluid pressure type moving device in the present invention) 22d.

[0036] The first table 22a is supported so as to be slidable (slidable along the X direction) on a table support block 22e fixed on the spindle head table 32. For example, the first table 22a is inserted into a groove formed on the table support block 22e and extending along the X direction, or placed on a slide rail provided on the table support block 22e, so as to be slidable along the X direction.

[0037] The fourth servo motor 22c is disposed on the side surface on the X2 direction side of the table support block 22e, and a ball screw 23 for converting the rotational movement of the drive shaft into a linear movement which is the sliding movement of the first table 22a is connected to the drive shaft thereof. That is, the screw shaft 23a of this ball screw 23 is connected to the drive shaft of the fourth servo motor 22c, and the nut 23b of the ball screw 23 is connected to the first table 22a, whereby the first table 22a can slide on the table support block 22e (can slide along the X direction) by the operation of the fourth servo motor 22c. The position of the first table 22a in the sliding movement direction will be determined by the rotational angle position of the fourth servo motor 22c. The rotational angle position of this fourth servo motor 22c is adjusted according to a control signal from a controller (not shown). The configuration for making the first table 22a slidable is not limited to this.

[0038] The second table 22b is supported so as to be slidable (slidable along the X direction) on the first table 22a. For example, the second table 22b is inserted into a groove formed on the first table 22a and extending along the X direction, or placed on a slide rail provided on the first table 22a, so as to be slidable along the X direction.

[0039] The air cylinder 22d is disposed on the side surface on the X2 direction side of the first table 22a, and the second table 22b is connected to the tip of the piston rod 22f of this air cylinder 22d. That is, the second table 22b can slide on the first table 22a (slide along the X direction) by the reciprocating motion of the piston rod 22f due to the operation of the air cylinder 22d. The position of the second table 22b in the sliding direction is determined by the protruding amount of the piston rod 22f of the air cylinder 22d. The protruding amount of the piston rod 22f of this air cylinder 22d is adjusted according to a control signal from a controller (not shown). The configuration for making the second table 22b slidable is not limited to this.

[0040] Since the second screw shaft rotation unit 21B is supported by such a configured moving unit 22, the second screw shaft rotation unit 21B is configured as the "movable screw shaft rotation unit" in the present invention.

[0041] The height position of the upper surface of the support block 21a that supports the first screw shaft rotation unit 21A (the surface on which the first screw shaft rotation unit 21A is placed) and the height position of the upper surface of the moving unit 22 that supports the second screw shaft rotation unit 21B (specifically, the upper surface of the second table 22b on which the second screw shaft rotation unit 21B is placed) are the same. Thereby, the height position (position in the Z direction) of the screw shaft support shaft 21c of the first screw shaft rotation unit 21A and the height position (position in the Z direction) of the screw shaft support shaft 21e of the second screw shaft rotation unit 21B are the same. Also, the position in the Y direction of the screw shaft support shaft 21c of the first screw shaft rotation unit 21A and the position in the Y direction of the screw shaft support shaft 21e of the second screw shaft rotation unit 21B are the same. Thereby, each screw shaft rotation unit 21A, 21B can support the screw shaft W so that its axis extends in the horizontal direction.

[0042] -Configuration of the grinding wheel swing unit- The grinding wheel swing units 4A and 4B are arranged on both sides in the Y direction with the spindle head table 32 interposed therebetween. That is, the grinding wheel swing units 4A and 4B are arranged on one side and the other side with the screw shaft W interposed therebetween in a direction intersecting the axis of the screw shaft W supported by each screw shaft rotation unit 21A and 21B. Since the configurations of the grinding wheel swing units 4A and 4B are substantially the same, one of the grinding wheel swing units 4A will be described here as a representative. In each drawing, the same members in each of the grinding wheel swing units 4A and 4B are denoted by the same reference numerals.

[0043] As shown in FIG. 1, the grinding wheel swing unit 4A is placed on a sub-base table (the base table on which the grinding wheel swing unit according to the present invention is placed) B2. A slide rail 41 extending along the X direction is provided on the sub-base table B2, and the grinding wheel swing unit 4A is placed on this slide rail 41 so that the mounting position in the X direction can be adjusted.

[0044] The grinding wheel swing unit 4A includes a slide plate 42 placed on the slide rail 41 and a unit body 43 placed on the slide plate 42, and a grinding wheel swing mechanism 44 is provided in the unit body 43. In FIG. 1, a part of this grinding wheel swing mechanism 44 is shown by a virtual line.

[0045] In this way, the position of the grinding wheel swing unit 4A can be adjusted on the sub-base table B2, but during the superfinishing process of superfinishing the inner surface of the groove of the screw shaft W, it is fixed on the sub-base table B2. For example, the grinding wheel swing unit 4A is fixed on the sub-base table B2 by using a fastener such as a bolt or a well-known locking mechanism.

[0046] The unit body 43 is movable on the slide plate 42 along a predetermined arc locus (refer to the posture shown by the solid line and the posture shown by the virtual line in FIG. 1). The center of the arc of this arc locus is the position of a grinding wheel 45a described later. This is for adjusting the direction of the grinding wheel 45a according to the lead angle of the groove of the screw shaft W.

[0047] In this way, the unit body 43 is movable on the slide plate 42 along a predetermined arc trajectory. However, during the finish machining for finishing the inner surface of the groove of the screw shaft W, it is fixed on the slide plate 42 (fixed on the slide plate 42 so that the orientation of the grinding wheel 45a set according to the lead angle of the groove of the screw shaft W is maintained). Also in this case, for example, it is fixed on the slide plate 42 by using fasteners such as bolts and well-known locking mechanisms.

[0048] Next, the grinding wheel swing mechanism 44 will be described. FIG. 3 is a view of each grinding wheel swing unit 4A, 4B as seen from the direction of arrow III in FIG. 1. Also, FIG. 4 is a diagram for explaining the outline of the principle of swinging the grinding wheel 45a in the grinding wheel swing mechanism 44. This FIG. 4 is a view of the grinding wheel swing mechanism 44 of the grinding wheel swing unit 4A as seen in the Y1 direction (a view as seen from the arrow IV direction in FIG. 3).

[0049] As shown in FIGS. 1, 3, and 4, the grinding wheel swing mechanism 44 includes a swing motor 44a, a crankshaft 44b, a crank buckle 44c, and a swing spindle 44d. Also, the position of the grinding wheel swing mechanism 44 in the vertical direction (Z direction) can be adjusted by a servo motor 46 (see FIG. 3) disposed at the upper end portion of the unit body 43.

[0050] The swing motor 44a is disposed at a position closer to the X1 direction in the unit body 43 and includes a drive shaft 44e extending substantially in the Y direction. A pulley 44f is attached to the tip end portion of this drive shaft 44e (the tip end portion closer to the Y2 side in the grinding wheel swing unit 4A).

[0051] The crankshaft 44b is disposed at a position closer to the X2 direction with respect to the swing motor 44a and extends parallel to the drive shaft 44e of the swing motor 44a. A pulley 44g is attached to the tip of this crankshaft 44b (the tip closer to the Y2 direction). A belt 44h is stretched between the pulley 44f attached to the drive shaft 44e of the swing motor 44a and the pulley 44g attached to the crankshaft 44b, and the rotational force (rotational driving force) of the swing motor 44a is transmitted to the crankshaft 44b by the belt 44h so that the crankshaft 44b rotates.

[0052] The swing spindle 44d is disposed at a position closer to the X2 direction with respect to the crankshaft 44b and extends parallel to the crankshaft 44b. The crankshaft 44b and the swing spindle 44d are connected by the crank buckle 44c. The connection position of the crank buckle 44c with respect to the crankshaft 44b is a position eccentric by a predetermined amount with respect to the axis of the crankshaft 44b. Also, the connection position of the crank buckle 44c with respect to the swing spindle 44d is a position eccentric by a predetermined amount with respect to the axis of the swing spindle 44d. For this reason, when the rotational force of the swing motor 44a is transmitted to the crankshaft 44b and the crankshaft 44b rotates, accordingly, the crank buckle 44c reciprocates substantially along the X direction, and accordingly, the swing spindle 44d is configured to swing (an operation of repeating rotation in one direction and rotation in the other direction) within a predetermined angle range (see arrow A in FIG. 4).

[0053] A grindstone head (a grindstone support part for supporting a grindstone in the present invention) 45 is attached to the tip of the swing spindle 44d (the tip on the Y2 direction side in the grindstone swing unit 4A, and the tip on the Y1 direction side in the grindstone swing unit 4B). A grindstone 45a having a predetermined shape is supported by this grindstone head 45. Specifically, as shown in FIG. 3, a through hole 45b penetrating in the vertical direction is provided at the tip of the grindstone head 45, and the grindstone 45a is inserted into this through hole 45b, and a support plate (not shown) is pressed against the side of the grindstone 45a (pressed in the Y direction), thereby supporting the grindstone 45a while preventing it from falling out of the through hole 45b. In this embodiment, the lower surface of the grindstone 45a in the grindstone oscillating unit 4A located on the Y1 direction side contacts the upper surface of the groove of the screw shaft W, and the upper surface of the grindstone 45a in the grindstone oscillating unit 4B located on the Y2 direction side contacts the lower surface of the groove of the screw shaft W, so that the positions of the grindstone heads 45 and the support state of the grindstone 45a are specified so that the grindstones 45a, 45a face each other across the screw shaft W. The support structure of the grindstone 45a is not limited to this. As described above, in the grindstone oscillating mechanism 44, the oscillating spindle 44d oscillates with the operation of the oscillating motor 44a, so that the grindstone head 45 attached to the oscillating spindle 44d also oscillates around the oscillating center of the oscillating spindle 44d (around an axis extending in the direction along the extension direction of the groove of the screw shaft W (extension direction according to the lead angle)). The support state of the grindstone 45a in the grindstone head 45 is specified such that when the grindstone 45a oscillates in conjunction with the oscillation of the grindstone head 45, the surface of the grindstone 45a describes a trajectory along the inner surface of the groove of the screw shaft W.

[0054] Further, a cylinder support bracket 45c is provided on the grinding wheel head 45, and an air cylinder 45d for pressing the grinding wheel 45a toward the inside of the groove of the screw shaft W is supported on the cylinder support bracket 45c. That is, the piston rod of this air cylinder 45d abuts against the back surface of the grinding wheel 45a, and by pressing the back surface of the grinding wheel 45a with the piston rod, the pressing force of the grinding wheel 45a against the inner surface of the groove of the screw shaft W is adjusted. The configuration for pressing the grinding wheel 45a is not limited to this.

[0055] -Ultra-finishing- Next, the ultra-finishing of the inner surface of the groove of the screw shaft W by the ultra-finishing device 1 configured as described above will be described. Incidentally, this ultra-finishing is performed after the groove of the screw shaft W is processed by forging and the inner surface of the groove is polished.

[0056] First, the screw shaft W is supported by the work head 2. As an operation for this support, the main spindle table 32 is slid to the position closest to the X2 direction by the operation of the first servo motor 33. Further, the first table 22a is slid to the position closest to the X2 direction by the operation of the fourth servo motor 22c, and the second table 22b is slid to the position closest to the X2 direction by the operation of the air cylinder 22d. Incidentally, when the length of the screw shaft W to be used is relatively short, it is not necessary to slide the first table 22a to the position closest to the X2 direction. Further, the servo motors 46, 46 of the respective grinding wheel swing units 4A, 4B are operated, the grinding wheel swing mechanism 44 of the grinding wheel swing unit 4A is raised, and the grinding wheel swing mechanism 44 of the grinding wheel swing unit 4B is lowered.

[0057] In this state, one end of the screw shaft W (the end on the X1 direction side) is supported by the screw shaft support shaft 21c of the first screw shaft rotation unit 21A, and the first table 22a is moved in the X1 direction by the operation of the fourth servo motor 22c to support the other end of the screw shaft W (the end on the X2 direction side) by the screw shaft support shaft 21e of the second screw shaft rotation unit 21B. In this state, the air cylinder 22d is operated to move the second table 22b, thereby adjusting the clamping force obtained by the screw shaft support shaft 21e pressing the other end of the screw shaft W to a predetermined value. Thereby, an appropriate support state of the screw shaft W between the screw shaft rotation units 21A and 21B is obtained, and the rotational force during the operation of each of the second servo motor 21b and the third servo motor 21d is transmitted evenly from both sides of the screw shaft W.

[0058] Thereafter, as shown in FIG. 5, the servo motors 46, 46 of the respective grindstone swing units 4A, 4B are operated to bring the grindstone 45a into contact with the inner surface of the groove of the screw shaft W. That is, in the grindstone swing unit 4A, the grindstone swing mechanism 44 is moved downward to bring the grindstone 45a into contact with the inner surface of the groove located above the screw shaft W, and in the grindstone swing unit 4B, the grindstone swing mechanism 44 is moved upward to bring the grindstone 45a into contact with the inner surface of the groove located below the screw shaft W. Further, by operating the air cylinders 45d, 45d of the grindstone heads 45, 45, the pressing force of the grindstones 45a, 45a against the inner surface of the groove of the screw shaft W is adjusted.

[0059] In this way, the screw shaft W is supported and superfinishing is started with the grindstones 45a, 45a in contact with the inner surface of the groove of the screw shaft W. In the superfinishing process, rotation around the axis of the screw shaft W by synchronous rotation of the second servo motor 21b of the first screw shaft rotation unit 21A and the third servo motor 21d of the second screw shaft rotation unit 21B, sliding movement in the X1 direction on the slide rail 31 of the spindle head table 32 by the operation of the first servo motor 33, and swinging of the grindstones 45a, 45a by the grindstone swinging mechanisms 44, 44 (see the arrows shown by the broken lines in FIG. 5) are performed simultaneously. The sliding movement of the spindle head table 32 is performed while adjusting the moving speed of the spindle head table 32 by controlling the rotational speed of the first servo motor 33 according to the lead angle of the groove of the screw shaft W and the rotational speed of the screw shaft W. That is, the larger the lead angle of the groove of the screw shaft W and the higher the rotational speed of the screw shaft W, the larger the lead (the amount of movement in the direction along the axis per rotation). That is, the moving speed of the screw shaft W becomes higher. For this reason, in the present embodiment, the moving speed of the spindle head table 32 is adjusted by the control of the first servo motor 33 according to the lead angle of the groove of the screw shaft W and the rotational speed of the screw shaft W. More specifically, the control of the first servo motor 33 is performed so as to obtain the same amount of movement of the spindle head table 32 as the lead of the groove (the amount of movement in the direction along the axis per rotation of the screw shaft W).

[0060] Then, after superfinishing by the grindstone 45a is completed from one end side to the other end side of the groove along with the movement of the screw shaft W (see the position of the first screw shaft rotation unit 21A shown by the broken line in FIG. 2), the first servo motor 33, the second servo motor 21b, and the third servo motor 21d are each reversely rotated, and superfinishing similar to the above is performed while sliding the spindle head table 32 in the X2 direction. In this way, superfinishing is performed a plurality of times while moving the spindle head table 32.

[0061] -Effects of the Embodiment- As described above, in this embodiment, when finish - machining the inner surface of the groove of the screw shaft W, while the grinding - wheel rocking units 4A and 4B are fixed on the sub - base B2, the work head 2 moves in the direction along the axis of the screw shaft W (while moving the screw shaft W in the same direction) to perform the finish - machining. That is, the grinding - wheel rocking units 4A and 4B are not configured to move in the direction along the axis of the screw shaft W while rocking the grinding wheel 45a. When the grinding - wheel rocking unit moves in the direction along the axis of the screw shaft while rocking the grinding wheel (in the case of the prior art), if there is play in the mechanism for this movement, it becomes difficult to bring the surface of the rocking grinding wheel into good contact with the inner surface of the groove of the screw shaft. Also, the vibration generated by the grinding - wheel rocking unit may adversely affect the movement of the grinding wheel in the direction along the axis of the screw shaft, making it difficult to sufficiently improve the machining accuracy of the finish - machining of the inner surface of the groove of the screw shaft. In particular, when a plurality of grinding - wheel rocking units are installed and these are moved in the direction along the axis of the screw shaft, since each grinding - wheel rocking unit moves individually, this problem becomes prominent. In this embodiment, the work head 2 moves in the direction along the axis of the screw shaft W to relatively move the grinding wheels 45a and 45a and the screw shaft W (relatively move in the direction along the axis of the screw shaft W). Since the grinding - wheel rocking units 4A and 4B do not move in the direction along the axis of the screw shaft W, the machining accuracy of the finish - machining of the inner surface of the groove of the screw shaft W can be sufficiently improved.

[0062] Also, in this embodiment, the grinding - wheel rocking units 4A and 4B are respectively disposed on one side and the other side sandwiching the screw shaft W in a direction intersecting the axis of the screw shaft W. For this reason, it becomes possible to simultaneously finish - machine the inner surface of the groove of the screw shaft W by the respective grinding - wheel rocking units 4A and 4B at a plurality of locations (two locations), and efficient finish - machining can be performed. Thereby, it is possible to shorten the time required for the finish - machining and improve the machining accuracy of the finish - machining.

[0063] In addition, in the present embodiment, servo motors (the second servo motor 21b and the third servo motor 21d) are provided for each of the screw shaft rotation units 21A and 21B. Since the contact areas between the screw shaft support shafts 21c and 21e of the screw shaft rotation units 21A and 21B and the ends of the screw shaft W are small, if a servo motor is provided only for one of the screw shaft rotation units, there is a possibility that the rotational force cannot be properly transmitted to the screw shaft, and it becomes difficult to sufficiently improve the machining accuracy of the finish machining of the inner surface of the groove of the screw shaft. In the present embodiment, since the rotational force is applied to the screw shaft W from both sides of the first screw shaft rotation unit 21A and the second screw shaft rotation unit 21B, it is possible to stably obtain the rotation of the screw shaft W, and it is possible to sufficiently improve the machining accuracy of the finish machining of the inner surface of the groove of the screw shaft W.

[0064] In addition, in the present embodiment, the second screw shaft rotation unit 21B is mounted on the moving unit 22. And the moving unit 22 is provided with a fourth servo motor 22c and an air cylinder 22d, and the moving position of the second screw shaft rotation unit 21B is adjusted by these. For this reason, the position accuracy of the second screw shaft rotation unit 21B can be obtained highly. That is, the interval between the screw shaft rotation units 21A and 21B can be managed with high accuracy. As a result, the support state of the screw shaft W supported between the screw shaft rotation units 21A and 21B can be appropriately obtained, and also by this, the machining accuracy of the finish machining of the inner surface of the groove of the screw shaft W can be sufficiently improved.

[0065] In addition, in the present embodiment, the work head 2 is supported by the spindle head table 32. For this reason, with the slide movement of the spindle head table 32 accompanying the operation of the first servo motor 33, the screw shaft rotation units 21A and 21B on the work head 2 move integrally in the direction along the axis of the screw shaft W. That is, it becomes possible to move the screw shaft W in the direction along its axis without changing the support state of the screw shaft W by the screw shaft rotation units 21A and 21B. Also by this, the machining accuracy of the finish machining of the inner surface of the groove of the screw shaft W can be sufficiently improved.

[0066] Further, in the present embodiment, the moving speed of the spindle table 32 is adjusted by the control of the first servo motor 33 according to the lead angle of the groove of the screw shaft W and the rotational speed of the screw shaft W. Thereby, the surface of the oscillating grindstone 45a can be brought into good contact with the inner surface of the groove of the screw shaft W, and also by this, the machining accuracy of the super finishing of the inner surface of the groove of the screw shaft W can be sufficiently enhanced.

[0067] -Modification Example- Next, the modification example will be described. In this modification example, the contact state of each of the grindstones 45a, 45a with respect to the groove of the screw shaft W is different from that of the above-described embodiment. Since the other configurations and operations are the same as those of the above-described embodiment, only the differences from the above-described embodiment will be described here.

[0068] FIG. 6 is a diagram for explaining the contact state between the inner surface of the groove of the screw shaft W and each of the grindstones 45a-1, 45a-2 in this modification example. As described above, since the grindstone swing units 4A, 4B are respectively disposed on one side and the other side sandwiching the screw shaft W in a direction intersecting the axis of the screw shaft W, it is possible to individually set the positions of the grindstones 45a-1, 45a-2 supported by the grindstone heads 45, 45 of each of the grindstone swing units 4A, 4B.

[0069] In this modified example, the inner surfaces of the groove of the screw shaft W, namely the inner surface closer to the X1 direction and the inner surface closer to the X2 direction, are each subjected to superfinishing by individual grindstones 45a-1 and 45a-2. In the case shown in FIG. 6, the upper grindstone 45a-1 is brought into contact with the inner surface of the groove of the screw shaft W closer to the X1 direction, and the lower grindstone 45a-2 is brought into contact with the inner surface of the groove of the screw shaft W closer to the X2 direction for superfinishing. As is well known, the groove of the screw shaft W has a cross-section in the shape of a Gothic arc. That is, the cross-section of the inner surface closer to the X1 direction and the cross-section of the inner surface closer to the X2 direction are each in the shape of an arc centered at a different position. In this modified example, the grindstones 45a-1 and 45a-2 are individually brought into contact with each of these inner surfaces having different shapes. Thereby, the processing accuracy of the superfinishing of the inner surface of the groove of the screw shaft W can be further enhanced.

[0070] -Other Embodiments- Note that the present invention is not limited to the above-described embodiments and modified examples, and all modifications and applications included within the scope of the claims and the scope equivalent thereto are possible.

[0071] For example, in the above-described embodiments and modified examples, superfinishing is performed by bringing the grindstones 45a and 45a into contact with the groove of the screw shaft W from both the upper and lower sides. The present invention is not limited to this, and superfinishing may be performed by bringing the grindstones 45a and 45a into contact with the groove of the screw shaft W from both horizontal sides. Also, superfinishing may be performed by bringing the grindstones 45a and 45a into contact with the groove of the screw shaft W from directions different from these directions. Also, the number of grindstone swing units 4A and 4B is not limited to two, and may be three or more, or may be only one.

[0072] Also, in the above-described embodiments and modified examples, the base table (main base table B1) that supports the workhead movement unit 3 and the base tables (sub-base tables B2) that support the respective grindstone swing units 4A and 4B are separate, but these workhead movement unit 3 and the respective grindstone swing units 4A and 4B may be supported on the same base table.

[0073] Also, in the above-described embodiment and the modification, only the second screw shaft rotation unit 21B out of the first screw shaft rotation unit 21A and the second screw shaft rotation unit 21B is supported on the moving unit 22, but the first screw shaft rotation unit 21A may also be supported on the moving unit 22. According to this, it becomes possible to manage the interval between the screw shaft rotation units 21A and 21B with higher accuracy.

[0074] Also, in the above-described embodiment and the modification, servo motors (power sources for applying rotational force to the screw shafts) 21b and 21d are provided for the first screw shaft rotation unit 21A and the second screw shaft rotation unit 21B, respectively. The present invention is not limited to this, and a servo motor 21b (21d) may be provided only for one of the rotation units 21A (21B).

[0075] Also, in the above-described embodiment and the modification, as the moving device of the moving unit 22, one servo motor (fourth servo motor 22c) and one air cylinder 22d are provided. The present invention is not limited to this, and the number of moving devices may be three or more. That is, as the moving device, at least one is an electric moving device such as a servo motor, and at least one is a fluid pressure type moving device such as an air cylinder. Also, all the moving devices may be electric moving devices, or all the moving devices may be fluid pressure type moving devices.

Industrial Applicability

[0076] The present invention is applicable to a superfinishing device that superfinishes the inner surface of a groove by rotating a screw shaft in a state where a grindstone is in contact with the groove of the screw shaft of a ball screw.

Explanation of Signs

[0077] 1 Superfinishing device 2 Work head 21A First screw shaft rotation unit 21B Second screw shaft rotation unit 21b Second servo motor (power source) 21d Third servo motor (power source) 22 Moving unit 22c Fourth servo motor (electric moving device) 22d Air cylinder (fluid pressure type moving device) 3 Workhead moving unit 32 Spindle head table 33 First servo motor (slide moving power source) 4A, 4B Grinding wheel swing unit 44 Grinding wheel swing mechanism 45 Grinding wheel head (grinding wheel support part) 45a Grinding wheel W Screw shaft B1 Main base table (base table) B2 Sub base table (base table)

Claims

1. In a superfinishing device for a screw shaft of a ball screw, the inner surface of a groove is superfinished by rotating the screw shaft while bringing a grindstone into contact with the groove in the screw shaft of the ball screw. A grindstone swing unit mounted on a base table, comprising a grindstone support portion for supporting the grindstone and a grindstone swing mechanism for swinging the grindstone. A work head having a screw shaft rotation unit for supporting both ends of the screw shaft and rotating the screw shaft around its axis. And a work head movement unit for moving the work head in a direction along the axis of the screw shaft on the base table. During the superfinishing process of the inner surface of the groove, the grindstone swing unit is fixed on the base table, and while the grindstone is brought into contact with the groove in the screw shaft and swung by the grindstone swing mechanism, the work head movement unit moves the work head in a direction along the axis of the screw shaft according to the rotation of the screw shaft by the screw shaft rotation unit. The superfinishing device for the screw shaft of a ball screw is characterized by this.

2. In the superfinishing device for the screw shaft of a ball screw according to Claim 1. The grindstone swing unit is disposed on one side and the other side sandwiching the screw shaft in a direction intersecting the axis of the screw shaft supported by the screw shaft rotation unit. The superfinishing device for the screw shaft of a ball screw is characterized by this.

3. In the superfinishing device for the screw shaft of a ball screw according to Claim 1 or 2. The screw shaft rotation unit is a first screw shaft rotation unit for supporting one end of the screw shaft and a second screw shaft rotation unit for supporting the other end of the screw shaft. A power source for applying a rotational force to the screw shaft is provided in each of the screw shaft rotation units. The superfinishing device for the screw shaft of a ball screw is characterized by this.

4. In the superfinishing device for the screw shaft of a ball screw according to Claim 3. One of the screw shaft rotation units is a movable screw shaft rotation unit supported by the moving unit and movable in the direction along the axis of the screw shaft by the operation of the moving unit. The moving unit includes a plurality of moving devices, and the movable screw shaft rotation unit is characterized in that it can move forward and backward with respect to the screw shaft rotation unit on the other side by these moving devices. A superfinishing device for the screw shaft of a ball screw.

5. In the superfinishing device for the screw shaft of a ball screw according to claim 4, The plurality of moving devices include at least one electric moving device and at least one fluid pressure moving device. A superfinishing device for the screw shaft of a ball screw.

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