CN112930247A

CN112930247A - Polishing jig, polishing apparatus and polishing method

Info

Publication number: CN112930247A
Application number: CN201980071521.7A
Authority: CN
Inventors: 若林亮太
Original assignee: Yamaha Motor Co Ltd
Current assignee: Yamaha Motor Co Ltd
Priority date: 2019-02-08
Filing date: 2019-02-08
Publication date: 2021-06-08
Also published as: WO2020161881A1; TW202030037A; JP7017651B2; TWI726333B; JPWO2020161881A1

Abstract

Provided is a polishing technique capable of flexibly adjusting the holding posture of a ball screw nut and performing polishing finish by a forming tool satisfactorily. The disclosed device is provided with: a jig base fixedly disposed on the rotation center shaft; and a profile-maintaining section attached to the jig base and configured to maintain the ball screw nut while changing a posture of the ball screw nut with respect to the jig base in accordance with a machining region of the outer surface of the forming tool, the machining region being in sliding contact with the threaded groove and grinding the threaded groove.

Description

Polishing jig, polishing apparatus and polishing method

Technical Field

The present invention relates to holding of a ball screw nut during grinding and finishing of a thread groove of the ball screw nut by a forming tool.

Background

Conventionally, a ball screw mechanism is known as one of drive mechanisms provided in an industrial robot. A ball screw nut used in this ball screw mechanism has a spiral thread groove formed therein, in which balls roll. The thread groove is formed into a predetermined shape by cutting, and then finished to a final dimension by grinding with a forming tool, so-called lapping.

This polishing process is performed using a polishing apparatus shown in patent document 1, for example. In the device described in patent document 1, the ball screw nut is held by a chuck unit (corresponding to the "polishing jig" of the present invention) having three chuck jaws. Further, at a position above the chuck unit, a polishing rod having a shaft body structure (corresponding to a "forming tool" of the present invention) is provided so as to be capable of reciprocating in the vertical direction while rotating, in a state in which the axial center of the polishing rod coincides with a rotation center axis extending in the vertical direction. The rotating grinding rod is screwed into the ball screw nut held by the chuck unit at a predetermined rotational speed and a predetermined feed speed, thereby performing grinding.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-292520 (FIG. 7)

Disclosure of Invention

Problems to be solved by the invention

In this way, in the polishing apparatus of patent document 1, the ball screw nut is fixedly held by the chuck unit, and the polishing rod is moved up and down along a rail extending in the vertical direction. That is, in this polishing apparatus, polishing is performed on the premise that the axis of the ball screw nut held by the chuck unit coincides with the axis (rotation center axis) of the polishing rod. Therefore, for example, when at least one of the holding posture of the chuck unit with respect to the ball screw nut and the installation posture of the polishing rod is inappropriate, the axial centers of the two are not aligned with each other, and it is difficult to perform polishing with sufficient processing accuracy. In particular, if the ball screw nut is deformed by the heat treatment performed between the cutting and the grinding, the holding posture of the chuck unit with respect to the ball screw nut becomes poor, and the conventional apparatus cannot cope with this.

The present invention has been made in view of the above problems, and an object thereof is to provide a polishing technique capable of flexibly adjusting the holding posture of a ball screw nut and performing polishing finishing with a forming tool in a satisfactory manner.

Means for solving the problems

A first aspect of the present invention is a grinding jig for holding a ball screw nut in which a threaded groove is ground by a forming tool and finish grinding is performed, the forming tool being reciprocated in a first direction while being rotated around a rotation center axis extending in the first direction, the grinding jig including: a jig base fixedly disposed on the rotation center shaft; and a profile-maintaining section attached to the jig base and configured to maintain the ball screw nut while changing a posture of the ball screw nut with respect to the jig base in accordance with a machining region of the outer surface of the forming tool, the machining region being in sliding contact with the threaded groove and grinding the threaded groove.

A second aspect of the present invention is a polishing apparatus for performing polishing finish by grinding a thread groove of a ball screw nut with a forming tool having a shaft structure extending in a first direction, the polishing apparatus including: the above-mentioned grinding jig; and a tool driving unit configured to reciprocate the forming tool in the first direction with respect to the ball screw nut held by the polishing jig while rotating the forming tool about a rotation center axis extending in the first direction.

A third aspect of the present invention is a polishing method for performing finish polishing by grinding a thread groove of a ball screw nut with a forming tool having a shaft structure extending in a first direction, the polishing method including: a first step of holding the ball screw nut by the grinding jig; and a second step of reciprocating the forming tool in the first direction relative to the ball screw nut held by the polishing jig while rotating the forming tool about a rotation center axis extending in the first direction.

In the invention thus constituted, the grinding process is performed on the thread groove of the ball screw nut by reciprocating the forming tool in the first direction relative to the ball screw nut while rotating the forming tool about the rotation center axis extending in the first direction, thereby performing the polishing finish. In the polishing finish, the ball screw nut is held while changing the posture of the ball screw nut in accordance with a processing region of the outer surface of the forming tool, which is in sliding contact with the thread groove and grinds the thread groove. Therefore, the polishing finish is performed in a state where the axial center of the forming tool coincides with the axial center of the ball screw nut.

Effects of the invention

As described above, the finish grinding is performed using the grinding jig that holds the ball screw nut while changing the posture of the ball screw nut in conformity with the machining region of the outer surface of the forming tool that is in sliding contact with the thread groove and grinds the thread groove. Therefore, the holding posture of the ball screw nut can be flexibly adjusted, and the grinding and finishing by the forming tool can be favorably performed.

Drawings

Fig. 1 is a diagram showing a first embodiment of a polishing apparatus according to the present invention.

Fig. 2 is a perspective view showing a polishing jig used in the polishing apparatus shown in fig. 1.

Fig. 3 is a block diagram showing an electrical configuration of the polishing apparatus shown in fig. 1.

Fig. 4A is a diagram schematically showing the operation of the polishing jig during polishing finishing.

Fig. 4B is a diagram schematically showing the operation of the polishing jig 2 before and after polishing finishing.

Fig. 5 is a flowchart showing a procedure of polishing finishing by the polishing apparatus shown in fig. 1.

Fig. 6 is a view schematically showing a polishing finishing process performed by the polishing apparatus shown in fig. 1.

Fig. 7 is a diagram schematically showing an additional step of polishing finishing by the polishing apparatus according to the second embodiment of the present invention.

Detailed Description

Fig. 1 is a diagram showing a first embodiment of a polishing apparatus according to the present invention. Fig. 2 is a perspective view showing a polishing jig used in the polishing apparatus shown in fig. 1. Fig. 3 is a block diagram showing an electrical configuration of the polishing apparatus shown in fig. 1. The polishing apparatus 1 performs polishing finishing by grinding a thread groove 201 of a ball screw nut 200 (hereinafter, simply referred to as a "nut 200") held by a polishing jig 2 by a machining tool 100 by reciprocating the machining tool 100 in a Z direction while rotating the machining tool 100 about a rotation center axis AR in a state where the axis AX1 of the forming machining tool (hereinafter, simply referred to as a "machining tool") 100 having a shaft body structure extending in a vertical direction Z coincides with the rotation center axis AR. In fig. 1 and 2, XYZ rectangular coordinate axes are shown to clarify the directional relationship of the respective drawings. In these figures, the vertical direction Z corresponds to an example of the "first direction" of the present invention, and the arrow Z1 in the Z direction is directed toward the forward direction of the processing tool 100, and the arrow Z2 in the Z direction is directed toward the backward direction of the processing tool 100. The XYZ rectangular coordinate axes are shown in fig. 1 and 2 by the vertical direction Z and the horizontal directions X and Y orthogonal to the Z direction. The Y direction corresponds to an example of the "second direction" of the present invention, and arrow Y1 in the Y direction faces the left side of the polishing apparatus 1 when viewed from the front side, and arrow Y2 in the Y direction faces the right side of the polishing apparatus 1. The X direction corresponds to an example of the "third direction" of the present invention, and arrow X1 in the X direction faces the front side of the polishing apparatus 1, and arrow X2 in the X direction faces the back side of the polishing apparatus 1. Further, an arrow R in fig. 1 indicates a rotation direction of the machining tool 100.

As shown in fig. 1, the polishing apparatus 1 includes: a base table 3; a ball screw nut support device 4 attached to the upper portion of the front surface side of the base 3; an upper support base 5 erected on the upper portion of the back side of the base 3; an elevating head 7 supported by the upper support base 5 via an elevating device 6; and a rotation driving device 8 provided in the lift head 7. In the ball screw nut support device 4, the table 42 is configured to be moved up and down in the vertical direction Z by operating the operation lever 41. A polishing jig 2 is fixed to the upper surface of the table 42, and the nut 200 is detachably held by the polishing jig 2. The detailed structure and operation of the polishing jig 2 will be described later.

As shown in fig. 1, the lifting head 7 is provided above the polishing jig 2 holding the nut 200 so as to be capable of reciprocating in the vertical direction Z and is driven to be lifted by the lifting device 6. As shown in fig. 1, the lifting device 6 includes: a pair of left and right slide rails 61, 61 (only the Y2 direction side is illustrated in fig. 1) attached to the front surface (the X1 direction side) of the upper support base 5 extending in the vertical direction Z; a slider 62 supported by the

slide rails

61, 61 so as to be able to ascend and descend; a ball screw nut 63 attached to a central portion of the slider 62 in the left-right direction Y; a ball screw shaft 64 penetrating the ball screw nut 63 and extending in the vertical direction Z; and an elevating motor 65 connected to an upper end portion of the ball screw shaft 64. In response to a command from the control device 9 that controls the entire polishing apparatus 1, the lifting motor 65 is rotated in the normal direction, and the lifting head 7 configured as described below can be moved in the forward direction (Z1 direction side), while the lifting motor 65 is rotated in the reverse direction, and the lifting head 7 can be moved in the backward direction (Z2 direction side).

As shown in fig. 1, the lift head 7 includes: a spindle housing 71 mounted on the front surface of the slider 62; a cylindrical main shaft 72 rotatably supported by a bearing (not shown) in the main shaft housing 71; and a tap chuck 73 attached to the spindle 72. A weight balance 75 for weight compensation is connected to both sides of the upper end of the spindle case 71 via a wire 74. The wire 74 is routed over

pulleys

76, 76 provided at the upper end of the upper support base 5, and connects a counterweight 75 housed in the upper support base 5 to the spindle case 71.

An upper end of the main shaft 72 protrudes upward from an upper end of the main shaft housing 71, and a lower end of the main shaft 72 protrudes downward from a lower end of the main shaft housing 71. A rotary drive device 8 for rotating the machining tool 100 is connected to an upper end portion of the spindle 72. The rotation driving device 8 includes: a speed reducer 82 attached to a support plate 81 extending forward (toward the X1 direction) from the upper end of the spindle housing 71; a rotation driving motor 83 provided in the speed reducer 82; a belt transmission 84 for transmitting power from the speed reducer 82 to the upper end of the main shaft 72. Therefore, the main shaft 72 can be rotated about the rotation center axis AR by operating the rotation driving motor 83 in response to a command from the control device 9.

Although not shown in fig. 1, a tapered sleeve is formed at the lower end of the spindle 72 so as to open downward, and a tapered shank of a tap chuck 73 is attached thereto. The tap chuck 73 holds the upper end of the machining tool 100, and the machining tool 100 is attached to the tap chuck 73 in a state where the axial center AX1 coincides with the rotation center axis AR. Then, in response to a command from the control device 9, the rotation driving motor 83 is operated to rotate the machining tool 100 about the rotation center axis AR, and the elevation motor 65 is operated to reciprocate the machining tool 100 in the vertical direction Z, that is, to perform Z-axis movement. As described above, by reciprocating the machining tool 100 in the vertical direction Z while rotating about the rotation center axis AR, the thread groove 201 of the nut 200 is ground by abrasive grains attached to the outer surface of the machining tool 100 by electrodeposition, adhesion, or the like. In this way, the grinding finish of the nut 200 can be performed. During the finish grinding, as will be described later, the nut 200 can be adjusted in posture so that the axis AX2 (see fig. 2 and 6) of the nut 200 coincides with the rotation center axis AR (the axis AX1 of the machining tool 100) in conformity with the outer side surface of the machining tool 100. On the other hand, before and after the finish polishing, the nut 200 is held in a predetermined initial posture by the polishing jig 2. The structure and operation of the polishing jig 2 holding the nut 200 in this manner will be described with reference to fig. 2, 4A, and 4B.

Fig. 4A and 4B are partial cross-sectional views of the polishing jig shown in fig. 2, in which fig. 4A schematically shows the operation of the polishing jig 2 during polishing, and fig. 4B schematically shows the operation of the polishing jig 2 before and after polishing. As shown in fig. 2, 4A, and 4B, the polishing jig 2 includes: a jig base 21 fixedly disposed on the upper surface of the table 42 on an extension of the rotation center axis AR of the machining tool 100; and a profile holding portion 22 for holding the nut 200 while changing the posture of the nut 200 with respect to the jig base 21 in accordance with the shape of the outer surface of the machining tool 100, as will be described later in detail.

The jig base 21 is a frame having a frame shape in a plan view from vertically above (the Z2 direction side), and the nut 200 is held by the nut holding member 23 in a central space thereof. In the present embodiment, the nut holding member 23 includes the jig base 231 and the support frame 232, and the jig base 231 holding the nut 200 is supported by the support frame 232 in a state of being surrounded from the horizontal direction. In order to adjust the posture of the nut 200 by displacing the nut holding member 23, the profile holding portion 22 is configured to have both a tilt adjustment function of adjusting the tilt posture of the nut 200 with respect to the rotation center axis AR and a horizontal adjustment function of adjusting the horizontal position of the nut 200 with respect to the rotation center axis AR.

The profile holding portion 22 includes a universal joint mechanism 24 including a movable frame 240, a first swing support shaft 241, and a second swing support shaft 242. More specifically, the movable frame 240 is a frame having a frame shape similar to the jig base 21, and is disposed so as to surround the nut holding member 23 from the horizontal direction in the central space of the jig base 21. First pivot shafts 241 are provided between the movable frame 240 and the jig base 21 at two positions separated in the Y direction. As shown in fig. 4A and 4B, the two swing support shafts 241 each have an inner bushing 241a, a slide shaft 241B, and a connecting pin 241c, and are symmetrically arranged with the nut 200 held by the nut holding member 23 interposed therebetween. Therefore, the structure of the first pivot shaft 241 on the Y2 direction side will be described here, and the description of the Y1 direction side will be omitted.

A through hole is provided in the Y direction at a substantially central position in the X direction in the side wall on the Y2 direction side of the jig base 21, and a cylindrical inner bushing 241a is inserted in the Y direction in the through hole. In the hollow portion of the inner hub 241a, a slide shaft 241b is slidably inserted in the Y direction with respect to the inner hub 241 a. A through hole is formed in the slide shaft 241b in the Y direction. The coupling pin 241c is inserted through the through hole from the Y2 direction side toward the Y1 direction side, and its tip end is coupled to the side wall of the movable frame 240 on the Y2 direction side. Further, the first swing support shaft 241 is also provided on the Y1 direction side in the same manner as the Y2 direction side. Therefore, the movable frame 240 is swingable in the Y direction with respect to the jig base 21 via the two first swing support shafts 241, and the movable frame 240, the slide shaft 241b, and the connection pin 241c are integrally slidable in the Y direction.

Further, the second swing support shaft 242 is provided at two locations separated in the X direction between the movable frame 240 and the nut holding member 23. As shown in fig. 4A and 4B, the two swing support shafts 242 each have an inner bush 242a, a slide shaft 242B, and a connecting pin 242c, and are arranged symmetrically with respect to the nut 200 held by the nut holding member 23. Therefore, the structure of the second swing support shaft 242 on the X2 direction side will be described, and the description of the X1 direction side will be omitted.

A through hole is provided in the X direction at a substantially central position in the Y direction in the side wall of the movable frame 240 on the X2 direction side, and a cylindrical inner bush 242a is fitted in the X direction in the through hole. In the hollow portion of the inner liner 242a, a slide shaft 242b is inserted slidably in the X direction with respect to the inner liner 242 a. A through hole is formed in the slide shaft 242b in the X direction, and a connecting pin 242c is inserted through the through hole from the X2 direction side toward the X1 direction side, and the tip end portion thereof is connected to the side wall of the support frame 232 on the X2 direction side. Further, the second swing support shaft 242 is also provided on the side of the X1 direction in the same manner as on the side of the X2 direction. Therefore, the support frame 232 is swingable in the X direction with respect to the movable frame 240 via the two second swing support shafts 242, and the support frame 232, the slide shaft 242b, and the coupling pin 242c are integrally slidable in the X direction.

In this way, in the present embodiment, by providing the universal joint mechanism 24, the nut holding member 23 can be tilted with respect to the rotation center axis AR, and the tilt posture of the nut 200 can be changed. The first swing support shaft 241 and the second swing support shaft 242 have slide bearing structures in the Y direction and the X direction, respectively, and function as a "moving mechanism" of the present invention, and can move the nut holding member 23 in the Y direction and the X direction. That is, the horizontal position of the nut 200 with respect to the rotation center axis AR can be changed by the moving mechanism. Therefore, as shown in fig. 4A, when the movable frame 240 and the support frame 232 are freely displaceable, when the outer side surface of the machining tool 100 is brought into sliding contact with the thread groove 201 of the nut 200 to perform grinding finishing, the nut 200 is tilted or horizontally moved in conformity with the outer side surface of the machining tool 100. Therefore, as shown in fig. 6 to be described later, the posture of the nut 200 can be adjusted so that the axis AX2 of the nut 200 coincides with the rotation center axis AR (the axis AX1 of the machining tool 100). In the present specification, a mode in which the posture of the nut 200 can be changed in accordance with the machining tool 100 is referred to as a "profile setting mode".

Here, it is also considered that the grinding jig 2 is always set to the profile setting mode when only the finish grinding is considered. However, considering workability when the nut 200 is attached to the polishing jig 2, workability when the nut 200 is removed after completion of polishing finish, and phase assurance when the machining tool 100 is inserted into the thread groove 201 of the nut 200 to perform polishing finish, and the like, it is preferable to position the nut 200 at an initial position suitable for phase assurance or the like before and after polishing finish, and to restrict displacement of the nut 200 from the initial position. Therefore, in the present embodiment, in addition to the above-described profile setting mode, an "initial setting mode" is provided in which the nut 200 is positioned at the initial position and the displacement from the initial position is restricted, and a mode switching mechanism 25 for switching these modes is provided.

The mode switching mechanism 25 includes: a cylinder 251 for positioning and fixing the nut 200 at an initial position in the X direction; and a cylinder 252 for positioning and fixing the nut 200 at the initial position in the Y direction. The through

holes

211, 2401 and the recess 2321 are provided in the wall portions on the Y1 direction side of the jig base 21, the movable frame 240 and the support frame 232, respectively, corresponding to the piston portion 251p of the cylinder 251, and are linearly arranged in the Y direction when the nut 200 is at the initial position. Therefore, even if the movable frame 240 and the support frame 232 are displaced in the X direction with respect to the jig base 21 following the machining tool 100, the piston portion 251p of the air cylinder 251 is extended in the Y2 direction side in response to a command from the control device 9, and the movable frame 240 and the support frame 232 are returned to the initial positions in the X direction. That is, the piston portion 251p enters the through

holes

211 and 2401 and the recess 2321, whereby the jig base 21, the movable frame 240, and the support frame 232 are pierced in the Y direction by the piston portion 251p, and in the process, the state shown in fig. 4A is shifted to the state shown in fig. 4B, whereby the nut 200 is positioned at the initial position in the X direction.

In addition, the positioning in the Y direction is also the same as in the X direction. That is, the through hole 212 and the recess 2402 are provided in the wall portions on the X2 direction side of the jig base 21 and the movable frame 240, respectively, corresponding to the piston portion 252p of the cylinder 252, and are linearly arranged in the X direction when the nut 200 is at the initial position. Therefore, even if the movable frame 240 and the support frame 232 are displaced in the Y direction with respect to the jig base 21 following the machining tool 100, the piston portion 252p of the air cylinder 252 is extended in the X1 direction in response to a command from the control device 9, and the movable frame 240 and the support frame 232 are returned to the initial positions in the Y direction. That is, the piston portion 252p enters the through hole 212 and the recess 2402, whereby the jig base 21 and the movable frame 240 are pierced in the X direction by the piston portion 252p, and in the process, the state shown in fig. 4A is shifted to the state shown in fig. 4B, whereby the nut 200 is positioned at the initial position in the Y direction.

In this way, by the extending operation of the

air cylinders

251, 252, as shown in fig. 4B, the

piston portions

251p, 252p enter, whereby the nut holding member 23 is positioned at the initial position in the horizontal direction. Thus, in terms of design, the axial center (reference numeral AX2 in fig. 2 and 6) of the nut 200 held by the nut holding member 23 coincides with the rotation center axis AR of the machining tool 100 within a certain range. Simultaneously with such positioning operation, the horizontal movement and inclination of the nut 200 with respect to the rotation center axis AR are regulated at this position, that is, the universal joint mechanism 24 is locked (initial setting mode).

Conversely, by the contraction operation of the

air cylinders

251 and 252, as shown in fig. 4A, the

piston portions

251p and 252p are retracted into the through

holes

211 and 212 of the jig base 21, respectively, and the lock of the universal joint mechanism 24 is released. In this state, when the machining tool 100 is inserted into the thread groove 201 of the nut 200 and reciprocated to perform the finish grinding, the nut 200 is tilted while being horizontally moved with respect to the rotation center axis AR in accordance with the machining tool 100, and the outer side surface of the machining tool 100 is appropriately brought into sliding contact with the thread groove 201 in a state where the axis AX2 of the nut 200 coincides with the rotation center axis AR (the axis AX1 of the machining tool 100) (a copying setting mode). In addition, the threaded groove 201 is ground satisfactorily by the abrasive grains attached to the outer surface of the machining tool 100 as the machining tool 100 reciprocates.

A control device 9 is provided for controlling the polishing apparatus 1 configured as described above. The control device 9 includes an arithmetic Processing Unit 91 including a CPU (Central Processing Unit). The storage unit 92, the motor control unit 93, the cylinder control unit 94, the external input/output unit 95, the display unit 96, and the input unit 97 are connected to the arithmetic processing unit 91. The arithmetic processing unit 91 executes polishing finishing in accordance with each unit of the program control device stored in advance in the storage unit 92.

The motor control unit 93 drives the lifting motor (Z-axis motor) 65 to lift the machining tool 100, and drives the rotation driving motor (R-axis motor) 83 to rotate the machining tool 100 around the rotation center axis AR. The motor control unit 93 supplies the current value at the time of drive control of the

motors

65 and 83 to the arithmetic processing unit 91 as information related to the motor torque. Therefore, the arithmetic processing unit 91 can detect with high accuracy whether or not the rotation of the machining tool 100 is abnormal based on the information.

The cylinder control unit 94 controls the compressed air supplied to the

cylinders

251 and 252 to expand and contract the

piston units

251p and 252p, thereby switching the mode between the initial setting mode and the profile setting mode.

The external input/output unit 95 is a so-called interface configured to receive detection signals output from various sensors 951 provided in the polishing apparatus 1. These detection signals include signals from the proximity sensor 951a that detects the position of the tap chuck 73, and the arithmetic processing unit 91 can detect the presence or absence of a floating abnormality of the tap chuck 73 based on the signals.

The display unit 96 is constituted by a liquid crystal display device or the like having a display screen, and displays the state of the polishing apparatus 1 on the display screen. The input unit 97 is constituted by a keyboard or the like, and receives an input from the outside by a manual operation of an operator.

In the polishing apparatus 1 configured as described above, the program stored in the storage unit 92 is read out to the arithmetic processing unit 91, and the arithmetic processing unit 91 controls the respective units of the apparatus as follows to perform the polishing finishing of the nut 200. Next, the polishing finish by the polishing apparatus 1 will be described with reference to fig. 4A, 4B, 5, and 6.

Fig. 5 is a flowchart showing a procedure of polishing finishing by the polishing apparatus shown in fig. 1. Fig. 6 is a view schematically showing a polishing finishing process performed by the polishing apparatus shown in fig. 1. The open arrows in columns (a), (b), and (d) of the drawing indicate a state in which the lock is applied to the universal joint mechanism 24 by the expansion operation of the

cylinders

251 and 252, and the broken lines in column (c) of the drawing indicate a state in which the lock of the universal joint mechanism 24 is released by the contraction operation of the

cylinders

251 and 252, and the nut 200 is free from the horizontal movement operation and the tilting operation with respect to the rotation center axis AR.

The operator sets the nut 200 to the polishing jig 2 with the one end surface 202 of the nut 200 before polishing and finishing facing the machining tool 100 (corresponding to an example of the "first step" of the present invention). At this time, each part of the polishing apparatus 1 is located at the home position. That is, as shown in fig. 1, the machining tool 100 attached to the elevator head 7 is positioned at the origin position P1 (fig. 6) spaced vertically upward from the polishing jig 2, i.e., in the Z2 direction, while being stopped from rotating. In the polishing jig 2, the

air cylinders

251 and 252 are extended (fig. 4B), and the universal joint mechanism 24 is locked. This prevents the horizontal movement and inclination of the nut holding member 23 with respect to the rotation center axis AR, and facilitates the attachment of the nut 200 to the nut holding member 23 by the operator.

When the setting of the nut 200 to the grinding jig 2 is completed, a start instruction for finishing grinding is given to the control device 9 by the operator via the input portion 97. Upon receiving the signal, the arithmetic processing unit 91 of the control device 9 controls the respective units of the device as follows to perform the polishing finishing of the nut 200. First, the lifting motor (Z-axis motor) 65 is operated to lower the machining tool 100 from the origin position P1 to the position P2 directly above the nut 200 as shown in the column (a) of fig. 6 (step S1). The lowering of the processing tool 100 is performed at a relatively high speed, and on the other hand, the rotation of the processing tool 100 is stopped.

When the lowering to the directly-upper position P2 is completed, the raising/lowering motor 65 lowers the rotation speed, and the lowering speed of the machining tool 100 is switched to a low speed. The rotation driving motor (R-axis motor) 83 operates in synchronization with the low-speed lowering to start the normal rotation of the machining tool 100 (step S2). Here, "normal rotation" means a direction in which the thread groove 201 is ground by abrasive grains attached to the outer side surface of the machining tool 100 while the machining tool 100 is lowered, and "reverse rotation" which is the opposite of "normal rotation" means a direction in which the thread groove 201 is ground by abrasive grains attached to the outer side surface of the machining tool 100 while the machining tool 100 is raised.

When the machining tool 100 is lowered while rotating in the normal direction in this way, as shown in the column (b) of fig. 6, the tip of the machining tool 100 enters in phase with the thread groove 201 while sliding on the end of the nut 200 on the Z2 direction side. At this time, when the axial center AX1 of the machining tool 100 is greatly offset from the axial center AX2 of the nut 200 or when the phase of the tip of the machining tool 100 with respect to the thread groove 201 is not matched, there occurs a problem that a large torque is applied to the machining tool 100 in the rotational direction (R-axis direction) (R-axis torque abnormality) or a problem that the tap chuck 73 connected to the machining tool 100 expands and contracts more than expected (floating abnormality). When the operation is performed in a state where such a problem occurs, a failure in polishing finish, a reduction in the life of the machining tool 100, a device failure, and the like may occur. Therefore, in the present embodiment, as shown in the column (b) of fig. 6, before the machining tool 100 is lowered to the preset initial insertion position P3 and inserted into the nut 200 by the initial insertion amount (for example, by about 1/3 with respect to the nut 200), the R-axis torque abnormality is monitored by monitoring the current value of the lifting motor 65, and the floating abnormality is monitored by the proximity sensor 951a (steps S3 and S4). Here, in order to detect the R-axis torque abnormality, the torque applied to the machining tool 100 may be directly measured by a torque sensor. The sensor for detecting the abnormal floating is not limited to the proximity sensor 951a, and any position detection sensor may be used.

When at least one of the R-axis torque abnormality and the float abnormality is detected in step S3, the control device 9 stops the lifting motor 65 and the rotation driving motor 83, and notifies the display unit 96 of the device stop due to the occurrence of the abnormality (step S5). The operator who has confirmed the alarm report operates the lifting motor 65, the rotation driving motor 83, and the like via the input unit 97 to eliminate the above-described abnormality, and returns the machining tool 100 to the origin position P1 and the like to return the apparatus to the origin. Then, when the abnormality is eliminated and preparation for retrying of finish grinding is completed, the operator operates the input unit 97 to provide a restart command to the control device 9. When receiving the restart instruction (yes in step S6), the control device 9 returns to step S1 to try the finish grinding again.

On the other hand, when the R-axis torque abnormality and the floating abnormality do not occur and the initial insertion of the machining tool 100 is completed (yes in step S4), the

cylinders

251 and 252 contract (fig. 4A) to unlock the universal joint mechanism 24 (step S7). At this time, when the axial center AX2 of the nut 200 held by the nut holding member 23 coincides with the rotation center axis AR of the machining tool 100, the nut holding member 23 does not move and maintains its position. On the other hand, in the case of the mismatch, the nut holding member 23 is horizontally moved and/or tilted with respect to the rotation center axis AR following the outer side surface of the machining tool 100, and as a result, the axis AX2 of the nut 200 held by the nut holding member 23 coincides with the rotation center axis AR of the machining tool 100.

After the lock of the universal joint mechanism 24 is released, the rotation and the reciprocating movement in the Z direction of the machining tool 100 (hereinafter referred to as "rotational reciprocating movement of the machining tool 100") are started at a rotation speed and a movement speed suitable for finishing (step S8). That is, the machining tool 100 is rotated in the normal direction and lowered in the Z1 direction at a speed suitable for finish polishing, whereby the central region 101 (column (c) of fig. 6) in the Z direction of the outer surface of the machining tool 100 is brought into sliding contact with the thread groove 201 as the "machining region" of the present invention, and the thread groove 201 is ground by the abrasive grains adhering to the central region 101. Conversely, when the machining tool 100 is raised in the Z2 direction while rotating in reverse, the central region 101 slides in contact with the thread groove 201, and the thread groove 201 is ground by the abrasive grains adhering to the central region 101. As described above, when the machining tool 100 that is rotating in the forward and reverse directions reciprocates, the thread groove 201 of the nut 200 appropriately performs horizontal movement and inclination with respect to the rotation center axis AR following the outer side surface of the machining tool 100, and polishing finishing is performed in a state where the axial center AX2 of the nut 200 coincides with the rotation center axis AR of the machining tool 100 (corresponding to an example of the "second step" in the present invention).

In this way, there is a possibility that an R-axis torque abnormality occurs during the finish grinding. Therefore, in the present embodiment, while the value instructed by the operator in advance is repeated for the number of times of the rotational reciprocating movement, the arithmetic processing unit 91 monitors the occurrence of the R-axis torque abnormality based on the current value of the elevating motor 65 (steps S9, S10). When the R-axis torque abnormality occurs (yes in step S9), the arithmetic processing unit 91 temporarily stops the driving of the lifting motor 65 and the rotation driving motor 83, interrupts the rotational reciprocating movement of the machining tool 100, and then reversely drives the machining tool at a low speed by a predetermined amount. For example, if an R-axis torque abnormality occurs when the machining tool 100 is lowered in the Z1 direction while rotating in the normal direction, the machining tool 100 is raised in the Z2 direction while rotating in the reverse direction by a predetermined amount. On the other hand, when the R-axis torque abnormality occurs when the machining tool 100 is raised in the Z2 direction while being rotated in the reverse direction, the machining tool 100 is lowered in the Z1 direction while being rotated in the normal direction by a predetermined amount. Thereafter, the process returns to step S8, and the rotational reciprocation of the machining tool 100 is started again.

When the number of rotational reciprocating movements of the machining tool 100 reaches a predetermined value and the finish grinding of the nut 200 is completed (yes in step S10), the machining tool 100 is raised in the Z2 direction while being reversed, and after returning to the origin position P1 (step S12), the rotation and movement of the machining tool 100 are stopped. In the polishing jig 2, the

air cylinders

251 and 252 are extended (fig. 4B), and the universal joint mechanism 24 is locked. Thus, a series of processes for one nut 200 is completed.

As described above, in the present embodiment, the nut holding member 23 is horizontally moved and tilted with respect to the rotation center axis AR in conformity with the central region 101 (corresponding to the "machining region" of the present invention) of the outer surface of the machining tool 100 in which the grinding of the thread groove 201 is performed. Thus, during the finish grinding, the posture of the nut 200 is adjusted so that the axial center AX2 of the nut 200 coincides with the rotation center axis AR of the machining tool 100. Therefore, the threaded groove 201 can be ground in a state where the axial center of the machining tool 100 coincides with the axial center of the nut 200, whereby the finish grinding of the nut 200 by the machining tool 100 can be performed with high accuracy.

Further, since the finish grinding is performed in a state where the axial center AX1 of the machining tool 100 coincides with the axial center AX2 of the nut 200, it is possible to prevent an excessive external force, for example, a bending stress from being applied to the machining tool 100 during the finish grinding, and thus it is possible to extend the life of the machining tool 100.

When the nut 200 is set in the polishing jig 2, the mode is switched to the initial setting mode by the mode switching mechanism 25. That is, the nut 200 held by the nut holding member 23 is positioned at the initial position by locking the universal joint mechanism 24, and in this state, the nut 200 can be stably set in the polishing jig 2.

Before performing the polishing finish by the rotational reciprocating movement of the machining tool 100, the tip end portion of the machining tool 100 needs to be inserted into the nut 200 while aligning the phase with the thread groove 201, but in the present embodiment, the initial insertion is performed while maintaining the initial setting mode. Therefore, the initial insertion can be stably performed while the displacement of the nut 200 is restricted.

After finishing the polishing, the mode switching mechanism 25 returns the mode from the profile setting mode to the initial setting mode. Therefore, the finish-ground nut 200 can be stably removed from the grinding jig 2.

In the above-described embodiment, the rotation center axis AR corresponds to an example of the "rotation center axis extending in the first direction" in the present invention. The combination of the lifting device 6 and the rotation driving device 8 functions as a "tool driving unit" of the present invention. The end surface 202 on the Z2 direction side of the nut 200 corresponds to an example of "one end surface of the ball screw nut" in the present invention, and the end surface 203 on the Z1 direction side of the nut 200 corresponds to an example of "the other end surface of the ball screw nut" in the present invention.

The present invention is not limited to the above-described embodiments, and various modifications may be made to the above-described embodiments without departing from the spirit of the invention. For example, in the above-described embodiment, the polishing finish is performed by performing the rotational reciprocating movement a predetermined number of times, for example, 2N times, only in a state where the one end surface 202 of the nut 200 is directed to the machining tool 100, but, similarly to the first embodiment, after the polishing finish is performed, the polishing jig 2 may be turned upside down, and, for example, as shown in fig. 7, the polishing finish may be performed in a state where the other end surface 203 of the nut 200 is directed to the machining tool 100 (second embodiment). By performing the polishing finishing in two different modes, the finishing accuracy can be further improved. The number of times of the rotational reciprocating movement in the second embodiment may be configured to be N times in a state where one end surface 202 of the nut 200 is directed to the machining tool 100, and N times in a state where the other end surface 203 of the nut 200 is directed to the machining tool 100.

In the above embodiment, the profile modeling holding portion 22 has an additional function of moving the nut holding member 23 in the Y direction and the X direction to horizontally displace with respect to the rotation center axis AR and change the horizontal posture of the nut 200, in addition to the tilting function of tilting the nut holding member 23 with respect to the rotation center axis AR and changing the tilting posture of the nut 200. As this modification, only a moving mechanism for displacing and moving the nut holding member 23 in the X direction may be added, or conversely, only a moving mechanism for displacing and moving the nut holding member 23 in the Y direction may be added.

The profile modeling holding portion 22 may be configured to have only a movement function of moving the nut holding member 23 in the Y direction and the X direction and horizontally displacing the nut holding member with respect to the rotation center axis AR to change the horizontal posture of the nut 200.

In the above-described embodiment, the Z direction, the Y direction, and the X direction which are orthogonal to each other are set as the "first direction", the "second direction", and the "third direction" of the present invention, but the Y direction or the X direction may be set as the "first direction" of the present invention, and the remaining two directions may be set as the "second direction" and the "third direction", respectively. In the present invention, the "first direction", "second direction", and "third direction" are not necessarily orthogonal to each other, and may be set so as to intersect with each other.

Industrial applicability

The present invention can be applied to all polishing techniques in which a thread groove of a ball screw nut is ground by a forming tool to perform finish polishing.

Description of the reference symbols

1 … grinding device

2 … grinding clamp

6 … lifting device (tool driving part)

8 … Rotary drive device (tool drive part)

21 … clamp base

22 … profile modeling holder

23 … nut holding member

24 … universal joint mechanism

25 … mode switching mechanism

100 … (Forming) tool

101 … center area (machining area)

200 … (ball screw) nut

201 … thread groove

202 … (one) end face

203 … (other) end face

240 … Movable frame

241 … first swing fulcrum

242 … second pivot axle

AR … center axis of rotation

Axial center of AX1 … (of machining tool)

Axis of AX2 … (of ball screw nut)

X … horizontal direction (third direction)

Y … left-right direction (second direction)

Z … vertical direction (first direction)

Claims

1. A grinding jig that holds a ball screw nut that is finished by grinding a threaded groove with a forming tool that reciprocates in a first direction while rotating about a rotation center axis extending in the first direction, the grinding jig comprising:

a jig base fixedly disposed on the rotation center shaft; and

and a profile holding portion that is attached to the jig base and holds the ball screw nut while changing a posture of the ball screw nut with respect to the jig base in accordance with a machining region of an outer surface of the forming tool that is in sliding contact with the thread groove and that grinds the thread groove.

2. The lapping fixture of claim 1,

the profile-maintaining section includes: a nut holding member that holds the ball screw nut; and a universal joint mechanism that changes the inclination of the ball screw nut with respect to the rotation center axis by swinging the nut holding member about a second direction intersecting the first direction and about a third direction intersecting the first direction and the second direction.

3. The lapping fixture of claim 2,

the universal joint mechanism includes:

a movable frame;

a first swing support shaft provided at two locations separated in the second direction between the jig base and the movable frame, and supporting the movable frame to be swingable about the second direction with respect to the jig base; and

and a second pivot support shaft provided at two locations separated in the third direction between the movable frame and the nut holding member, and supporting the nut holding member to be pivotable in the third direction with respect to the movable frame.

4. The lapping fixture of claim 3,

the first pivot support shaft is provided integrally with the movable frame so as to be slidable in the second direction with respect to the jig base.

5. The grinding jig of claim 3 or 4,

the second pivot support shaft is provided integrally with the nut holding member so as to be slidable in the third direction with respect to the movable frame.

6. The lapping fixture of claim 1,

the profile-maintaining section includes: a nut holding member that holds the ball screw nut; and a moving mechanism that moves the nut holding member in a second direction intersecting the first direction and a third direction intersecting the first direction and the second direction, and displaces the position of the ball screw nut within a plane including the second direction and the third direction.

7. The grinding jig of any one of claims 2 to 6,

the second direction is a direction orthogonal to the first direction,

the third direction is a direction orthogonal to the first direction and the second direction.

8. The grinding jig of any one of claims 1 to 7,

the polishing jig further includes a mode switching mechanism that switches between an initial setting mode in which the ball screw nut held by the profile holding portion is positioned at a preset initial position with respect to the jig base and displacement of the ball screw nut is restricted, and a profile setting mode in which the restriction of the displacement of the ball screw nut is released and a change in the posture of the ball screw nut is allowed.

9. A polishing device for performing finish polishing by grinding a thread groove of a ball screw nut with a forming tool having a shaft structure extending in a first direction, the polishing device comprising:

the grinding fixture of any one of claims 1 to 8; and

and a tool driving unit configured to reciprocate the shaping tool in the first direction with respect to the ball screw nut held by the polishing jig while rotating the shaping tool about a rotation center axis extending in the first direction.

10. A polishing method for performing finish polishing by grinding a thread groove of a ball screw nut with a forming tool having a shaft structure extending in a first direction, the polishing method comprising:

a first step of holding the ball screw nut by the grinding jig according to any one of claims 1 to 8; and

a second step of reciprocating the shaping tool in the first direction with respect to the ball screw nut held by the polishing jig while rotating the shaping tool about a rotation center axis extending in the first direction.

11. The grinding method according to claim 10,

the first step is a step of holding the ball screw nut in a state where one end surface of the ball screw nut in the first direction faces the forming tool,

the second step includes:

reciprocating the forming tool with one end surface of the ball screw nut facing the forming tool;

a step of positioning the polishing jig so that the other end surface of the ball screw nut in the first direction faces the forming tool by turning the polishing jig; and

and a step of reciprocating the forming tool in a state where the other end surface of the ball screw nut faces the forming tool.