Actuator and method for manufacturing actuator

Abstract

To suppress misalignment between a ball screw shaft and a linear motion member.SOLUTION: An actuator comprises: a ball nut that is rotated around a first central axial line by a hollow motor; a ball screw shaft that is linearly moved along a second central axial line by rotation of the ball nut; a linear motion member that is linearly moved together with the ball screw shaft; and a reference member fixed to an end part of the ball screw shaft. The reference member is fixed by being pressed against a part of the linear motion member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an actuator and a method for manufacturing the actuator. [Background technology]

[0002] Patent Document 1 discloses an electric actuator in which a nut of a ball screw is rotated by a hollow motor to move the ball screw shaft forward in one axial direction or backward in the other axial direction. Patent Document 2 discloses a robot including a parallel link equipped with multiple drive units. The drive units include an actuator that drives a rod forward and backward, and a slider to which the tip of the rod is fixed and which guides the rod in one axial direction.

[0003] The robot disclosed in Patent Document 2 has multiple degrees of freedom due to the parallel link mechanisms connected in series, and its configuration including parallel links gives it superior accuracy and strength compared to general serial link robots, and it has been made smaller.

[0004] On the other hand, in a robot in which parallel links are connected in series, the tip working point is located at a distance from each actuator, so misalignment in each actuator has a significant effect on the positioning accuracy of the tip operation of the robot. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6632909 [Patent Document 2] Patent No. 7088440 Summary of the Invention [Problem to be solved by the invention]

[0006] In an actuator having a linearly moving member that can be linearly moved together with a ball screw shaft, it is desirable to make the center axis of the ball screw shaft and the moving direction of the linearly moving member parallel with high precision so that the linearly moving member can move linearly with high precision. However, even if alignment adjustment is performed to make the central axis of the ball screw shaft parallel to the moving direction of the linear moving member, if even a slight force is applied to the ball screw shaft or the linear moving member when fixing the linear moving member to the ball screw shaft, misalignment between the ball screw shaft and the linear moving member (the moving direction of the linear moving member being inclined with respect to the central axis of the ball screw shaft) may occur. Misalignment between the ball screw shaft and the linear moving member significantly affects the positional accuracy of the linear moving member.

[0007] Therefore, an object of the present invention is to provide a technique for suppressing misalignment between a ball screw shaft and a linear motion member. [Means for solving the problem]

[0008] One aspect of the actuator according to the present invention includes a hollow motor, a ball nut having a first central axis and rotated about the first central axis by the hollow motor, a ball screw shaft having a second central axis that coincides with or is parallel to the first central axis and engaged with the ball nut so as to be linearly moved along the second central axis by rotation of the ball nut, the ball screw shaft having an end, a linearly moving member that is linearly moved together with the ball screw shaft along the second central axis, and a reference member fixed to the end of the ball screw shaft. The reference member is fixed by being pressed against a part of the linearly moving member.

[0009] To manufacture such an actuator, a reference member fixed to the end of the ball screw shaft is pressed against a portion of the linear motion member. In this state, the second central axis of the ball screw shaft and the moving direction of the linear motion member can be made parallel with high accuracy while monitoring the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis of the ball screw shaft. By fixing the reference member and a portion of the linear motion member in this aligned state, the aligned state can be maintained. By fixing the reference member and a portion of the linear motion member in this state, the second central axis and the moving direction of the linear motion member can be made parallel with high accuracy. Misalignment between the ball screw shaft and the linear motion member can be suppressed after fixing.

[0010] Preferably, a male thread portion is formed on the end of the ball screw shaft. The linear motion member may have an attachment portion attached to the ball screw shaft, and the attachment portion may have a through hole through which the end of the ball screw shaft passes. The attachment portion may have a first flat surface perpendicular to the second central axis of the ball screw shaft. The reference member may have a second flat surface perpendicular to the second central axis of the ball screw shaft. The actuator includes a fastening nut that is threaded onto the male thread portion of the end of the ball screw shaft, with the second flat surface of the reference member overlapping the first flat surface of the attachment portion in parallel and the attachment portion being interposed between the reference member and the fastening nut, and an adhesive portion made of an adhesive that bonds the reference member to the attachment portion of the linear motion member. may further be provided.

[0011] To manufacture such an actuator, the mounting portion of the linear motion member is fastened to the ball screw shaft by threading the fastening nut onto the male thread of the ball screw shaft with the second flat surface of the reference member overlapping the first flat surface of the mounting portion of the linear motion member in parallel and with the mounting portion of the linear motion member interposed between the reference member and the fastening nut. Because the second flat surface of the reference member is perpendicular to the second central axis of the ball screw shaft, if the first flat surface of the mounting portion of the linear motion member can be made substantially parallel to the second flat surface before fastening the mounting portion to the ball screw shaft, the movement direction of the linear motion member will be substantially parallel to the second central axis of the ball screw shaft. Prior to this fastening, the second central axis of the ball screw shaft and the movement direction of the linear motion member can be made parallel with high precision while monitoring the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis of the ball screw shaft. With the alignment adjusted in this manner, the fastening nut can be threaded onto the male thread of the ball screw shaft and the mounting portion fastened to the ball screw shaft, thereby maintaining the aligned state. By fixing the reference member to the mounting portion with an adhesive before fastening the mounting portion to the ball screw shaft, the aligned state can be maintained even when a force for fastening the mounting portion to the ball screw shaft is applied to the mounting portion and the ball screw shaft. For example, when a fastening nut is threaded onto the male thread of the ball screw shaft, the torque applied to the ball screw shaft prevents the linear motion member and the ball screw shaft from twisting, thereby preventing the movement direction of the linear motion member from tilting with respect to the second central axis of the ball screw shaft. In this way, by fastening the mounting portion of the linear motion member to the ball screw shaft with the second central axis and the movement direction of the linear motion member being parallel with high precision, misalignment between the ball screw shaft and the linear motion member can be suppressed after fastening.

[0012] The linear motion member may have a mounting hole used to mount a jig supporting two sensors that measure the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis when the second central axis is parallel to the movement direction of the linear motion member. By using the mounting hole of the linear motion member to attach a jig to the linear motion member before fastening the mounting portion to the ball screw shaft, it is possible to monitor the position of the ball screw shaft or the reference member in two directions perpendicular to the second center axis of the ball screw shaft, while making it possible to align the second center axis of the ball screw shaft with the movement direction of the linear motion member with high precision.

[0013] The second plane of the reference member may have an overlapping portion that overlaps the mounting portion of the linear motion member, and an exposed portion that does not overlap the mounting portion and is exposed. In this case, because the entire second flat surface of the reference member does not overlap the mounting portion, the amount of adhesive used to fix the reference member to the mounting portion can be minimized. Therefore, after supplying the adhesive to the reference member and the mounting portion, the second central axis of the ball screw shaft and the moving direction of the linear motion member can be made parallel with high accuracy while monitoring the position of the ball screw shaft or the reference member before the adhesive hardens. For example, even if the moving direction of the linear motion member is tilted with respect to the second central axis of the ball screw shaft before the adhesive hardens, the second central axis of the ball screw shaft and the moving direction of the linear motion member can be made parallel with high accuracy while monitoring the position of the ball screw shaft or the reference member.

[0014] One aspect of the present invention provides a method for manufacturing the actuator, the method including: preparing an assembly including the hollow motor, the ball nut, the ball screw shaft, and the reference member; disposing the linear motion member in a state in which the end of the ball screw shaft passes through the through hole of the mounting portion and the first flat surface of the mounting portion overlaps the second flat surface of the reference member; supplying an adhesive to bond the reference member to the mounting portion of the linear motion member; aligning the second central axis of the ball screw shaft and a moving direction of the linear motion member while monitoring the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis of the ball screw shaft; waiting for the adhesive to harden; and, after the adhesive has hardened, fastening the mounting portion to the ball screw shaft by threading the fastening nut onto a male thread of the ball screw shaft with the mounting portion interposed between the reference member and the fastening nut.

[0015] If the first plane of the mounting portion of the linear motion member can be made substantially parallel to the second plane before fastening the mounting portion to the ball screw shaft, the movement direction of the linear motion member will be substantially parallel to the second central axis of the ball screw shaft. Before this fastening, the second central axis of the ball screw shaft and the movement direction of the linear motion member can be made parallel with high precision while monitoring the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis of the ball screw shaft. With the alignment adjusted in this state, the fastening nut can be threaded onto the male thread of the ball screw shaft to fasten the mounting portion to the ball screw shaft, thereby maintaining the aligned state. By adhesively fixing the reference member to the mounting portion before fastening the mounting portion to the ball screw shaft, the aligned state can be maintained even when force is applied to the mounting portion and the ball screw shaft to fasten the mounting portion to the ball screw shaft. For example, when the fastening nut is threaded onto the male thread portion of the ball screw shaft, the torque applied to the ball screw shaft prevents the linear motion member and the ball screw shaft from twisting, and prevents the moving direction of the linear motion member from tilting with respect to the second central axis of the ball screw shaft. In this way, by fastening the mounting portion of the linear motion member to the ball screw shaft with the second central axis and the moving direction of the linear motion member being parallel with high precision, it is possible to prevent misalignment between the ball screw shaft and the linear motion member after fastening.

[0016] Preparing the assembly may include fixing the reference member to the end of the ball screw shaft such that the second plane of the reference member is perpendicular to the second central axis of the ball screw shaft. In this case, since the second plane of the reference member is perpendicular to the second central axis of the ball screw shaft, it becomes easy to make the second central axis of the ball screw shaft and the moving direction of the linear moving member parallel with high precision before fastening the mounting portion to the ball screw shaft. [Effects of the Invention]

[0017] According to the aspects of the present invention, misalignment between the ball screw shaft and the linearly moving member can be suppressed. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a front view of an actuator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of FIG. [Figure 3] FIG. 3 is a left side view of the actuator of FIG. [Figure 4] FIG. 4 is an enlarged bottom view of a portion of the actuator of FIG. [Figure 5] FIG. 5 is an enlarged bottom view of a portion of an actuator according to a modified example. [Figure 6] FIG. 6 is a cross-sectional view including the central axis of the ball screw mechanism of the actuator. [Figure 7] 7 is a cross-sectional view perpendicular to the central axis of the ball screw mechanism of FIG. [Figure 8] 8 is a schematic cross-sectional view of the ball screw mechanism in the case where the ball screw shaft of the ball screw mechanism is inclined with respect to the central axis of the ball nut in the cross section taken along the line VIII-VIII in FIG. [Figure 9] 9 is a schematic cross-sectional view of the ball screw mechanism when the ball screw shaft of the ball screw mechanism is inclined with respect to the central axis of the ball nut in the cross section taken along the line IX-IX of FIG. [Figure 10] FIG. 10 is a front cross-sectional view showing a step in a method of manufacturing the actuator. [Figure 11] FIG. 11 is a perspective view of a jig used in the method for manufacturing the actuator. [Figure 12] FIG. 12 is a front view of the actuator of FIG. 1 with the fixture of FIG. 11 and two sensors attached. [Figure 13] FIG. 13 is a left side view of the actuator with the jig and two sensors attached. [Figure 14] FIG. 14 is a perspective view of the actuator to which the jig and two sensors are attached. [Figure 15]FIG. 15 is a perspective view of the actuator to which the jig and two sensors are attached, seen from a different direction from that of FIG. [Figure 16] FIG. 16 is a front view of a portion of an actuator according to a modified example of the embodiment of the present invention. [Figure 17] FIG. 17 is a front view of a portion of an actuator according to another modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The drawings are not necessarily drawn to scale, and some features may be exaggerated or omitted.

[0020] As shown in FIGS. 1 and 2, an actuator 1 according to an embodiment of the present invention includes a drive assembly 10 and a slider assembly 30.

[0021] Drive Assembly Configuration The drive assembly 10 includes a housing 11 , a hollow motor 12 , a ball nut 13 , a ball screw shaft 14 , and a reference member 15 .

[0022] The housing 11 is a housing for the hollow motor 12 and the ball nut 13. In Fig. 2, the housing 11 is shown as an integral part having a hollow rectangular parallelepiped shape, for example. However, in reality, the housing 11 is made up of multiple pieces.

[0023] As shown in FIG. 2, the hollow motor 12 has a stator 12a, a rotor 12b, and a hollow rotating shaft 12c. The hollow motor 12 is, for example, a stepping motor. The stator 12a is substantially annular, disposed in the interior space of the housing 11, and fixed to the housing 11. The rotor 12b is disposed radially inside the stator 12a and surrounded by the stator 12a. The hollow rotating shaft 12c is a circular tube with a uniform thickness, and the rotor 12b is disposed around the hollow rotating shaft 12c. The rotor 12b is fixed to the hollow rotating shaft 12c, and when the rotor 12b is rotated about its central axis, the hollow rotating shaft 12c is also rotated about the central axis of the rotor 12b.

[0024] A bearing 16 that rotatably supports the hollow rotary shaft 12c is disposed in the interior space of the housing 11 and fixed to the housing 11. Although a single bearing 16 is shown in Figure 2, multiple bearings 16 may be provided. A handle 12d is fixed to one end of the hollow rotary shaft 12c. The handle 12d is disposed outside the housing 11. A worker manufacturing the actuator 1 can grasp the handle 12d and rotate the hollow rotary shaft 12c around the central axis of the rotor 12b.

[0025] The ball nut 13 is disposed inside the housing 11 and is concentrically connected to the hollow rotary shaft 12c of the hollow motor 12. A bearing 17 that rotatably supports the ball nut 13 is disposed in the interior space of the housing 11 and fixed to the housing 11. Although two bearings 17 are shown in FIG. 2, the number of bearings 17 may be one. The ball nut 13 has a central axis (first central axis) Ax1, is rotatably supported relative to the housing 11 by a bearing 17, and is rotated around the central axis Ax1 together with the rotor 12b and the hollow rotating shaft 12c by the hollow motor 12. The ball nut 13 is restricted so as not to move in a direction along the central axis Ax1.

[0026] The ball screw shaft 14 is disposed radially inside the ball nut 13. The ball screw shaft 14 has a central axis (second central axis) Ax2, is engaged with the ball nut 13, and is caused to move linearly along the central axis Ax2 by rotation of the ball nut 13. Therefore, the ball screw shaft 14 is advanced in a forward direction in which it protrudes from the housing 11, and is retracted in a backward direction in which it retreats toward the interior of the housing 11. In this embodiment, a ball screw mechanism having a ball screw shaft 14 and a ball nut 13 is arranged concentrically with the hollow motor 12, thereby making the actuator 1 compact. 2, the central axis Ax2 of the ball screw shaft 14 coincides with the central axis Ax1 of the ball nut 13. This is because, during the manufacture of the actuator 1, alignment adjustment is performed to make the central axis Ax2 parallel to the moving direction of the slider 32 with high precision, and as a result of the alignment adjustment, the central axis Ax2 coincides with the central axis Ax1.

[0027] As described above, a worker manufacturing the actuator 1 can grasp the handle 12d fixed to the hollow rotary shaft 12c and rotate the hollow rotary shaft 12c around the central axis of the rotor 12b. Because the hollow rotary shaft 12c is fixed to the ball nut 13, the ball screw shaft 14 moves linearly along its own central axis Ax2 as the handle 12d and the hollow rotary shaft 12c rotate. In addition, a worker can grasp the hollow motor 12 and transport the drive assembly 10.

[0028] The ball screw shaft 14 has a ball screw portion 14a, an end portion 14b, and a small diameter portion 14c, which are concentric with one another. The ball screw portion 14a is engaged with the ball nut 13. The ball screw portion 14a can enter the internal space of the hollow rotary shaft 12c of the hollow motor 12. A male thread portion 14d is formed at the tip of the end portion 14b. A retaining ring 18 made of a rigid material (e.g., metal) is fixed to the end portion 14b. The fixing method is not limited, but for example, the retaining ring 18 may be fixed to the end portion 14b by press-fitting the end portion 14b into a through-hole in the center of the retaining ring 18. The retaining ring 18 is used to position the reference member 15, which will be described later. The small diameter portion 14c is located between the ball screw portion 14a and the end portion 14b. The small diameter portion 14c has a diameter smaller than the outer diameter of the ball screw portion 14a and the diameter of the end portion 14b. A limiter ring 19 is fixed to the small diameter portion 14c by a plurality of screws 20. The limiter ring 19 is made of a rigid material (e.g., metal). When the ball screw shaft 14 is retracted toward the inside of the housing 11, the limiter ring 19 comes into contact with the ball nut 13, preventing the ball screw shaft 14 from retracting. In this way, the limiter ring 19 restricts movement of the ball screw shaft 14 in the direction of the central axis Ax2.

[0029] The reference member 15 is made of a rigid material (e.g., metal) and is fixed to the end 14b of the ball screw shaft 14. As will be described later, when fastening the mounting portion 34 of the slider 32 to the ball screw shaft 14, the reference member 15 is used as a reference for orthogonally ... In this embodiment, the reference member 15 is annular and has a flat surface 15a and an opposite flat surface 15b, which are parallel to each other. The flat surfaces 15a and 15b are machined to have high surface accuracy and high parallelism. The end 14b of the ball screw shaft 14 is inserted into a through hole in the center of the reference member 15.

[0030] The flat surface (second flat surface) 15a faces the flat surface (first flat surface) 34a of the mounting portion 34 of the slider 32 and is superimposed on the flat surface 34a in parallel. Preferably, an adhesive layer (adhesive portion) 21 made of an adhesive is provided between the flat surfaces 15a and 34a. The adhesive layer 21 bonds the reference member 15 to the mounting portion 34 of the slider 32. Meanwhile, the flat surface 15b is in contact with the retaining ring 18, which is used to position the reference member 15.

[0031] When preparing the drive assembly 10, the reference member 15 is fixed to the end 14b of the ball screw shaft 14 so that the flat surface 15a of the reference member 15 is orthogonal to the central axis Ax2 of the ball screw shaft 14 with high accuracy. The fixing method is not limited, and for example, the reference member 15 may be fixed to the end 14b by press-fitting the end 14b into a through-hole in the center of the reference member 15. Instead of or in addition to press-fitting, the reference member 15 may be fixed to the end 14b with a screw, or the reference member 15 may be fixed to the end 14b with an adhesive.

[0032] A through hole 34b and a recess 34c are formed in the mounting portion 34 of the slider 32. The male thread portion 14d at the tip of the end portion 14b of the ball screw shaft 14 is inserted into the through hole 34b. A fastening nut 22 is disposed inside the recess 34c, and the fastening nut 22 is screwed onto the male thread portion 14d. Therefore, with the flat surface 15a of the reference member 15 overlapping and parallel to the first flat surface of the mounting portion 34 and with the mounting portion 34 interposed between the reference member 15 and the fastening nut 22, the fastening nut 22 fastens the mounting portion 34 to the ball screw shaft 14.

[0033] Slider Assembly Configuration The slider assembly 30 includes a housing 31, a slider (linearly moving member) 32, a cover 35, and a plurality of linear guides 36. The housing 31 has an elongated rectangular cylindrical shape extending parallel to the axes Ax1 and Ax2, and is fixed to the housing 11 of the drive assembly 10 by screws 37.

[0034] The slider 32 is formed from a rigid material (e.g., metal) and has a bar portion 33 in the shape of an elongated rectangular parallelepiped and an attachment portion 34 formed to protrude in one direction from one end of the bar portion 33, forming an overall L-shape as shown in FIGS. 1 and 2. The attachment portion 34 is attached to the ball screw shaft 14 of the drive assembly 10 and is formed integrally with the bar portion 33. The bar portion 33 extends parallel to the axes Ax1 and Ax2, is partially disposed inside the housing 31, and is supported by the housing 31. As shown in FIG. 3, the attachment portion 34 has a width greater than that of the bar portion 33. The lid 35 closes the upper opening of the housing 31 in the drawing.

[0035] As shown in Fig. 3, guide rails 38 are attached to both side surfaces of the bar portion 33 of the slider 32. As shown in Figs. 1 and 2, each guide rail 38 extends parallel to the longitudinal direction of the bar portion 33 and is fixed to the bar portion 33 by, for example, screws 39. Each guide rail 38 is positioned so that it extends highly parallel to the longitudinal direction of the bar portion 33. A plurality of linear guides 36 are arranged inside the housing 31. The linear guides 36 are fixed to the housing 31 by, for example, screws 40. As shown in FIG. 3, the linear guides 36 support guide rails 38, which allow the slider 32 to move linearly along the longitudinal direction of the bar portion 33.

[0036] As described above, the mounting portion 34 of the slider 32 is attached to the end portion 14b of the ball screw shaft 14. Therefore, when the ball screw shaft 14 is moved linearly along its central axis Ax2 as the rotor 12b and ball nut 13 of the hollow motor 12 rotate, the slider 32 is also moved linearly together with the ball screw shaft 14. That is, as shown by imaginary lines in FIGS. 1 and 2 , when the ball screw shaft 14 is moved forward in the direction indicated by arrow A so that it protrudes from the housing 11, the slider 32 is also moved forward in the direction so that it protrudes from the housing 31. When the ball screw shaft 14 is moved backward in the direction opposite to arrow A so that it retracts toward the inside of the housing 11 as the rotor 12b and ball nut 13 of the hollow motor 12 rotate in the reverse direction, the slider 32 is also moved backward in the direction so that it retracts toward the inside of the housing 31.

[0037] A plurality of through holes 33a are formed at the end of the bar portion 33. The through holes 33a are, for example, screw holes, and an end effector (not shown) is attached to the bar portion 33 by the through holes 33a and screws (not shown). Therefore, the end effector, together with the slider 32, is moved linearly along the central axis Ax2 of the ball screw shaft 14. The housing 31 incorporating the linear guide 36 is positioned with high precision and fixed to the housing 11 of the drive assembly 10, so that the longitudinal direction (movement direction) of the slider 32 is adjusted to be parallel with the central axis Ax1 of the ball nut 13 with high precision. Furthermore, it is desirable that the central axis Ax2 of the ball screw shaft 14 and the direction of movement of the slider 32 are parallel to each other. In this case, the amount of movement of the slider 32 and the end effector when the ball nut 13 makes one rotation is equal to the lead of the ball screw shaft 14. However, if the direction of movement of the slider 32 is inclined with respect to the central axis Ax2, the amount of movement of the slider 32 and the end effector when the ball nut 13 makes one rotation is shorter than the lead of the ball screw shaft 14. In other words, a lead error occurs. If a lead error exists, the amount of movement of the slider 32 and the end effector cannot be controlled by controlling the rotation angle of the hollow motor 12.

[0038] The mounting portion 34 has a flat surface 34a that is superimposed parallel to the flat surface 15a of the reference member 15, and a flat surface 34d on the opposite side of the flat surface 34a. The flat surface 34a is machined to have high surface precision and a high perpendicularity with respect to the bar portion 33. Therefore, by making the flat surface 34a parallel to the flat surface 15a, the flat surface 34a is perpendicular to the central axis Ax2 of the ball screw shaft 14, and the movement direction of the slider 32 is parallel to the central axis Ax2 of the ball screw shaft 14.

[0039] The flat surface 34d is formed with a recess 34c in which the fastening nut 22 is placed, and the recess 34c communicates with the through hole 34b into which the male thread portion 14d at the tip of the end 14b of the ball screw shaft 14 is inserted. Furthermore, mounting holes 34e are formed in the portions of the flat surface 34d where the recesses 34c are not formed. In this embodiment, the mounting holes 34e are formed in two locations, but more mounting holes 34e may be formed. As will be described later, the mounting holes 34e are used to mount a jig that supports a sensor that is used to align the central axis Ax2 of the ball screw shaft 14 with the longitudinal direction (movement direction) of the slider 32 with high precision.

[0040] Adhesion of the reference member and mounting part 3 and 4, the flat surface 15a of the reference member 15 has an overlapping portion 23 that overlaps the mounting portion 34 of the slider 32, and two exposed portions 24 that do not overlap the mounting portion 34. In this embodiment, the outer diameter of the reference member 15 is greater than the width of the mounting portion 34, so when the flat surface 15a is overlapped with the flat surface 34a of the mounting portion 34, the overlapping portion 23 and the exposed portions 24 are created on the flat surface 15a.

[0041] The adhesive layer 21 that bonds the reference member 15 to the mounting portion 34 of the slider 32 is interposed between the overlapping portion 23 and the flat surface 34a. Because the entire flat surface 15a of the reference member 15 does not overlap the mounting portion 34, the amount of adhesive that bonds the reference member 15 to the mounting portion 34 can be minimized.

[0042] 5, the flat surface 34a of the mounting portion 34 may be in direct surface contact with the overlapping portion 23 of the flat surface 15a. In this case, adhesive is applied to the periphery of the overlapping portion 23 so as to surround a part of the mounting portion 34, forming an adhesive portion 21A. In this case as well, the flat surface 15a of the reference member 15 does not entirely overlap the mounting portion 34, so the amount of adhesive used to bond the reference member 15 to the mounting portion 34 can be minimized.

[0043] Ball screw mechanism details 6 and 7 show the ball screw mechanism in detail. 6 and 7 show a state in which the alignment adjustment has been completed and the central axis Ax2 of the ball screw shaft 14 coincides with the central axis Ax1 of the ball nut 13. FIG. The ball circulation system of the ball screw mechanism is exemplified by the flop-over system (top system), but the ball circulation system of the ball screw mechanism may also be an end cap system, a return tube system, a return plate system, or an end deflector system.

[0044] Ball nut 13 has a plurality of pieces joined together, and these pieces cooperate to form a hole on the inner peripheral surface of which a spiral thread groove 13a is formed. A spiral thread groove 14e is formed on the outer peripheral surface of ball screw shaft 14. A large number of balls 25 circulate while rolling between thread groove 14e and thread groove 13a.

[0045] Each of the bearings has a bearing groove 26. The bearing groove 26 allows the balls 25 to ride over the threads of the ball screw shaft 14. As is well known, as each ball 25 rides over the threads of the ball screw shaft 14 via the bearing groove 26, each ball 25 moves from one lead with a screw groove 14e to the adjacent lead, and the balls 25 circulate within the ball nut 13.

[0046] 6, it is desirable that the central axis Ax2 of the ball screw shaft 14 coincides with the central axis Ax1 of the ball nut 13. In this case, the amount of movement of the ball screw shaft 14 when the ball nut 13 makes one rotation is equal to the lead of the ball screw shaft 14.

[0047] However, as shown in Figure 8, when the central axis Ax2 is inclined with respect to the central axis Ax1, the amount of movement of the ball screw shaft 14 when the ball nut 13 rotates once is shorter than the lead of the ball screw shaft 14. In other words, a lead error occurs due to the ball screw mechanism. When a lead error exists, the amount of movement of the slider 32 and the end effector becomes uncontrollable by controlling the rotation angle of the hollow motor 12. This problem is common to ball screw mechanisms, regardless of the ball circulation method.

[0048] In particular, in the case of the top system, as shown in Figure 9, in a cross section intersecting with the top groove 26, the balls 25 in the top groove 26 are located radially outward of the ball nut 13 relative to the other balls 25. Because these balls 25 do not restrict the inclination of the ball screw shaft 14, the inclination angle of the ball screw shaft 14 tends to be larger than in the case of Figure 8. However, in Figures 8 and 9, the inclination angle of the ball screw shaft 14 is exaggerated. In this embodiment, alignment adjustment is performed to make the central axis Ax2 of the ball screw shaft 14 parallel to the longitudinal direction (movement direction) of the slider 32. The longitudinal direction (movement direction) of the slider 32 is adjusted to be parallel to the central axis Ax1 of the ball nut 13 with high precision, and as a result of the alignment adjustment, the central axis Ax2 of the ball screw shaft 14 coincides with or is parallel to the central axis Ax1 of the ball nut 13 with high precision. Therefore, it is possible to suppress both a lead error caused by the movement direction of the slider 32 being inclined with respect to the central axis Ax2 and a lead error caused by the central axis Ax2 being inclined with respect to the central axis Ax1.

[0049] Misalignment suppression Even if alignment adjustment is performed to make the central axis Ax2 of the ball screw shaft 14 parallel to the longitudinal direction (movement direction) of the slider 32, misalignment between the ball screw shaft 14 and the slider 32 may occur if even a slight force is applied to the ball screw shaft 14 or the slider 32 when fixing the slider (linear motion member) 32 to the ball screw shaft 14. For example, when the fastening nut 22 is screwed onto the male thread portion 14d of the ball screw shaft 14, torque B (see FIG. 3) applied to the ball screw shaft 14 may twist the slider 32 and the ball screw shaft 14, and the movement direction of the slider 32 may become inclined with respect to the central axis Ax2 of the ball screw shaft 14. A high level of skill is required from the worker to fix the mounting portion 34 of the slider 32 to the ball screw shaft 14 while preventing misalignment. Even if the worker has high skill, the fixing work takes a long time.

[0050] Therefore, the inventors have created an embodiment of a technique for suppressing misalignment between the ball screw shaft 14 and the slider 32. The actuator 1 according to this embodiment has a reference member 15 having a flat surface 15a with high surface precision that is perpendicular to the central axis Ax2 of the ball screw shaft 14. Furthermore, in the actuator 1 according to this embodiment, the mounting portion 34 of the slider 32 has a flat surface 34a with high surface precision. The flat surface 15a of the reference member 15 is pressed against and fixed to the flat surface 34a of the mounting portion 34. To manufacture the actuator 1, the flat surface 15a of the reference member 15 is aligned parallel to the flat surface 34a of the mounting portion 34 of the slider 32, and the mounting portion 34 of the slider 32 is interposed between the reference member 15 and the fastening nut 22. Then, the fastening nut 22 is threaded onto the male thread portion 14d of the ball screw shaft 14, thereby fastening the mounting portion 34 of the slider 32 to the ball screw shaft 14.

[0051] Since the flat surface 15a of the reference member 15 is perpendicular to the central axis Ax2 of the ball screw shaft 14, if the flat surface 34a of the mounting portion 34 of the slider 32 can be made substantially parallel to the flat surface 15a before fastening the mounting portion 34 to the ball screw shaft 14, the movement direction of the slider 32 will be substantially parallel to the central axis Ax2 of the ball screw shaft 14. Before this fastening, the central axis Ax2 of the ball screw shaft 14 and the longitudinal direction (movement direction) of the slider 32 can be made parallel with high precision while monitoring the position of the ball screw shaft 14 or the reference member 15 in two directions perpendicular to the central axis Ax2 of the ball screw shaft 14. With the alignment adjusted in this way, the fastening nut 22 can be threaded onto the male thread portion 14d of the ball screw shaft 14 to maintain the aligned state. In this way, by fastening the mounting portion 34 of the slider 32 to the ball screw shaft 14 while aligning the central axis Ax2 with the longitudinal direction (movement direction) of the slider 32 with high precision, misalignment of the ball screw shaft 14 and misalignment in the movement direction of the slider 32 can be suppressed after fastening.

[0052] Actuator manufacturing method Next, a method for manufacturing the actuator 1 that embodies the suppression of misalignment will be described. 10, the drive assembly 10 and the slider assembly 30 are prepared. Then, the housing 31 of the slider assembly 30 is fixed to the housing 11 of the drive assembly 10 with screws 37. In the process of preparing the drive assembly 10, the reference member 15 is fixed to the end 14b of the ball screw shaft 14 so that the flat surface 15a of the reference member 15 is perpendicular to the central axis Ax2 of the ball screw shaft 14. Because the flat surface 15a of the reference member 15 is perpendicular to the central axis Ax2 of the ball screw shaft 14, it becomes easy to align the central axis Ax2 of the ball screw shaft 14 and the longitudinal direction (movement direction) of the slider 32 with high precision before fastening the mounting part 34 to the ball screw shaft 14.

[0053] Next, the end 14b of the ball screw shaft 14 passes through the through hole 34b of the mounting portion 34 of the slider 32, and the slider 32 is arranged so that the flat surface 34a of the mounting portion 34 overlaps the flat surface 15a of the reference member 15.

[0054] At this time, an adhesive is supplied to bond the reference member 15 to the mounting portion 34 of the slider 32. As described above, the adhesive may be interposed as adhesive layer 21 between the overlapping portion 23 of the flat surface 15a and the flat surface 34a (see FIG. 4). Alternatively, the adhesive may be applied as adhesive portion 21A to the periphery of the overlapping portion 23 so as to surround a part of the mounting portion 34 (see FIG. 5). In either case, the flat surface 34a of the mounting portion 34 is supported by the flat surface 15a of the reference member 15. Therefore, the reference member 15 is used as a reference for orthogonally orthogonally orthogonalizing the ball screw shaft 14 to the mounting portion 34 and aligning the central axis Ax2 of the ball screw shaft 14 with the moving direction of the slider 32.

[0055] 10, a jig 50 for supporting two sensors is attached to the attachment portion 34 using two attachment holes 34e formed in the attachment portion 34. The attachment holes 34e are screw holes. 11, the jig 50 has three walls 51, 52, and 53 that are perpendicular to one another, and two guide blocks 54. The jig 50 is made of a rigid material (for example, metal or resin).

[0056] Two through holes 51a of the same shape and size and a through hole 51b larger than through hole 51a are formed in wall 51. A through hole 52a is formed in wall 52. A through hole 53a is formed in wall 53. Two guide blocks 54 are arranged parallel to each other in positions contacting walls 51 and 53.

[0057] 10 and 12 to 15, the wall 51 is in surface contact with the flat surface 34d of the mounting portion 34 of the slider 32. Two through holes 51a formed in the wall 51 are aligned with two mounting holes 34e of the mounting portion 34, respectively. Screws 60 passing through the through holes 51a are threaded into the mounting holes 34e, thereby fixing the jig 50 to the mounting portion 34. The mounting portion 34 of the slider 32 is sandwiched between the two guide blocks 54 of the jig 50. In this way, the guide blocks 54 guide the jig 50 so that the two through holes 51a of the wall 51 align with the two mounting holes 34e of the mounting portion 34. However, the guide blocks 54 may be omitted. When the jig 50 is fixed to the mounting portion 34, the through hole 51b of the wall 51 is aligned with the recess 34c of the mounting portion 34, and the male thread portion 14d of the ball screw shaft 14, which is positioned in the center of the recess 34c, is visible through the through hole 51b.

[0058] A sensor 61 is attached to the through-hole 52a of the wall 52, and a sensor 62 is attached to the through-hole 53a of the wall 53. The sensors 61 and 62 are non-contact sensors with a distance measurement function. The sensors 61 and 62 may be eddy current displacement sensors or laser distance sensors. The sensors 61 and 62 measure the position of the ball screw shaft 14 in two directions perpendicular to the central axis Ax2 of the ball screw shaft 14. Specifically, the sensor 61 has a function of measuring distance in a direction X (see FIG. 13) perpendicular to the central axis Ax2 of the ball screw shaft 14. The sensor 62 has a function of measuring distance in a direction Y perpendicular to the central axis Ax2 and also perpendicular to the direction X.

[0059] The position of the ball screw shaft 14 may be measured by measuring the position of the outer circumferential surface of a reference member 15 fixed to the ball screw shaft 14. That is, the sensor 61 may measure the distance between the sensor 61 and the outer circumferential surface of the reference member 15 in direction X, and the sensor 62 may measure the distance between the sensor 62 and the outer circumferential surface of the reference member 15 in direction Y. In this way, the outer circumferential surface of the annular reference member 15 is used as a reference for distance measurement. However, the outline of the reference member 15 does not have to be circular and may be, for example, polygonal.

[0060] Before the adhesive constituting the adhesive layer 21 or the adhesive portion 21A hardens, the worker aligns the central axis Ax2 of the ball screw shaft 14 with the longitudinal direction (movement direction) of the slider 32 while monitoring the distance measurements taken by the sensors 61 and 62. In this embodiment, the outer diameter of the reference member 15 is larger than the width of the mounting portion 34, and therefore the sensor 61 can be easily brought close to the reference member 15.

[0061] The worker fine-tunes the position of the ball screw shaft 14 (the tilt angle with respect to the slider 32) so that the central axis Ax2 of the ball screw shaft 14 is parallel to the longitudinal direction (movement direction) of the slider 32. In this manner, alignment adjustment using the sensors 61 and 62 is performed.

[0062] After confirming from the distance measurements taken by sensors 61 and 62 that the center axis Ax2 of the ball screw shaft 14 and the longitudinal direction (movement direction) of the slider 32 are parallel with high precision, the worker waits for the adhesive that constitutes the adhesive layer 21 or the adhesive portion 21A to solidify. Before fastening the mounting portion 34 to the ball screw shaft 14, the jig 50 is attached to the slider 32 using the mounting hole 34e of the slider 32, thereby making it possible to align the center axis Ax2 of the ball screw shaft 14 and the longitudinal direction (movement direction) of the slider 32 with high precision while monitoring the position of the ball screw shaft 14 or the reference member 15 in two directions perpendicular to the center axis Ax2 of the ball screw shaft 14.

[0063] After the adhesive constituting the adhesive layer 21 or the adhesive portion 21A has solidified, with the mounting portion 34 interposed between the reference member 15 and the fastening nut 22, the worker fastens the mounting portion 34 to the ball screw shaft 14 by screwing the fastening nut 22 into the male thread portion 14d of the ball screw shaft 14 (see Figures 12 to 15). In the jig 50, a through hole 51b is formed in the wall 51, and a socket wrench (not shown) for fastening the fastening nut 22 to the ball screw shaft 14 can be passed through the through hole 51b (see FIGS. 12 and 13).

[0064] Thereafter, the screw 60 is loosened and the jig 50 is removed from the mounting portion 34. In this manner, the actuator 1 shown in Figures 1 to 3 is obtained.

[0065] By fixing the reference member 15 to the mounting portion 34 with an adhesive before fastening the mounting portion 34 of the slider 32 to the ball screw shaft 14, even if a force for fastening the mounting portion 34 to the ball screw shaft 14 is applied to the slider 32 and the ball screw shaft 14, it is possible to maintain a state in which the central axis Ax2 of the ball screw shaft 14 and the moving direction of the slider 32 are parallel with each other with high precision. For example, when the fastening nut 22 is screwed onto the male thread portion 14d of the ball screw shaft 14, the torque applied to the ball screw shaft 14 prevents the slider 32 and the ball screw shaft 14 from twisting, and prevents the moving direction of the slider 32 from tilting with respect to the central axis Ax2.

[0066] As described above, the flat surface 15a of the reference member 15 has an overlapping portion 23 that overlaps the mounting portion 34 of the slider 32 and an exposed portion 24 that does not overlap the mounting portion 34 and is exposed. In this way, because the entire flat surface 15a of the reference member 15 does not overlap the mounting portion 34, the amount of adhesive used to fix the reference member 15 to the mounting portion 34 can be minimized. Therefore, after adhesive is supplied to the reference member 15 and the mounting portion 34, the central axis Ax2 of the ball screw shaft 14 and the movement direction of the slider 32 can be made parallel with high accuracy while monitoring the position of the ball screw shaft 14 or the reference member 15 before the adhesive hardens. For example, even if the longitudinal direction of the slider 32 is inclined with respect to the central axis Ax2 of the ball screw shaft 14 before the adhesive hardens, the central axis Ax2 of the ball screw shaft 14 and the movement direction of the slider 32 can be made parallel with high accuracy while monitoring the position of the ball screw shaft 14 or the reference member 15.

[0067] However, adhesive may be supplied to the reference member 15 and the mounting portion 34 after alignment adjustment using the sensors 61 and 62. In particular, when adhesive is applied to the periphery of the overlapping portion 23 of the flat surface 15a of the reference member 15 so as to surround part of the mounting portion 34, as shown in Fig. 5, adhesive can be supplied to the reference member 15 and the mounting portion 34 after alignment adjustment.

[0068] Although the present invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the scope of the invention as set forth in the appended claims. Such changes, modifications and alterations are intended to be within the scope of the invention.

[0069] For example, as shown in Figure 16, the mounting portion 34 of the slider 32 may have a stepped surface 34f recessed from the flat surface 34a. When the flat surface 15a is in surface contact with the flat surface 34a, a gap is created between the flat surface 15a and the stepped surface 34f. An adhesive layer 21 can be provided in this gap. In this case, adhesive may be supplied to the reference member 15 and the mounting portion 34 after alignment adjustment using the sensors 61 and 62.

[0070] 17, a recess 34g may be formed in the flat surface 34a of the mounting portion 34 of the slider 32. When the flat surface 15a is in surface contact with the portion of the flat surface 34a other than the recess 34g, a gap is created between the flat surface 15a and the flat surface 34a due to the recess 34g. An adhesive layer 21 can be provided in this gap. In this case, adhesive may be supplied to the reference member 15 and the mounting portion 34 after alignment adjustment using the sensors 61 and 62.

[0071] If the reference member 15 and a portion of the slider 32 can be fixed together while the central axis Ax2 of the ball screw shaft 14 and the moving direction of the slider 32 are aligned parallel with high accuracy, the adhesive layer 21 or adhesive portion 21A may be eliminated, and the reference member 15 and a portion of the slider 32 (e.g., the mounting portion 34) may be fixed together by a fixing means other than the fastening nut 22. However, if the adhesive layer 21 or adhesive portion 21A is used as in the embodiment, twisting of the slider 32 and the ball screw shaft 14 due to torque applied to the ball screw shaft 14 when the fastening nut 22 is screwed onto the male thread portion 14d of the ball screw shaft 14 is suppressed, and the moving direction of the slider 32 is suppressed from tilting with respect to the central axis Ax2. [Explanation of symbols]

[0072] DESCRIPTION OF SYMBOLS 1...actuator, Ax1...central axis (first central axis), Ax2...central axis (second central axis), 10...drive assembly, 12...hollow motor, 13...ball nut, 14...ball screw shaft, 14b...end, 14d...male thread portion, 15...reference member, 15a...flat surface (second flat surface), 21...adhesive layer (adhesive portion), 21A...adhesive portion, 22...fastening nut, 23...overlapping portion, 24...exposed portion, 30...slider assembly, 31...housing, 32...slider (linearly moving member), 34...mounting portion, 34a...flat surface (first flat surface), 34b...through hole, 34e...mounting hole, 50...jig, 61, 62...sensor

Claims

1. A hollow motor; a ball nut having a first central axis and rotated about the first central axis by the hollow motor; a ball screw shaft having an end portion, the ball screw shaft having a second central axis that coincides with or is parallel to the first central axis, the ball screw shaft being engaged with the ball nut and being moved linearly along the second central axis by rotation of the ball nut; a linear motion member that is linearly moved together with the ball screw shaft along the second central axis; a reference member fixed to the end of the ball screw shaft, The reference member is pressed against and fixed to a part of the linearly moving member. An actuator characterized by:

2. a male thread portion is formed at the end of the ball screw shaft, the linear motion member has an attachment portion attached to the ball screw shaft, the attachment portion having a through hole through which the end portion of the ball screw shaft passes, and the attachment portion having a first plane perpendicular to the second central axis line of the ball screw shaft, the reference member has a second plane perpendicular to the second central axis of the ball screw shaft, The actuator is a fastening nut that is screwed onto the male thread portion at the end of the ball screw shaft, and fastens the mounting portion to the ball screw shaft in a state where the second flat surface of the reference member overlaps the first flat surface of the mounting portion in parallel, and the mounting portion is interposed between the reference member and the fastening nut; an adhesive portion made of an adhesive that adheres the reference member to the mounting portion of the linear motion member; The actuator of claim 1 further comprising:

3. The linear motion member has a mounting hole used to mount a jig supporting two sensors that measure the position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis when the second central axis is parallel to the moving direction of the linear motion member.

3. The actuator according to claim 1 or 2.

4. The second plane of the reference member has an overlapping portion that overlaps the mounting portion of the linear motion member and an exposed portion that does not overlap the mounting portion and is exposed.

3. The actuator according to claim 2.

5. 3. A method for manufacturing the actuator of claim 2, comprising the steps of: providing an assembly including the hollow motor, the ball nut, the ball screw shaft, and the reference member; disposing the linear motion member in a state in which the end of the ball screw shaft passes through the through hole of the mounting portion and the first flat surface of the mounting portion overlaps the second flat surface of the reference member; supplying an adhesive that bonds the reference member to the mounting portion of the linear motion member; While monitoring a position of the ball screw shaft or the reference member in two directions perpendicular to the second central axis of the ball screw shaft, the second central axis of the ball screw shaft is made parallel to a moving direction of the linearly moving member; Waiting for the adhesive to harden; After the adhesive has solidified, fastening the mounting portion to the ball screw shaft by threading the fastening nut onto the male thread portion of the ball screw shaft with the mounting portion interposed between the reference member and the fastening nut. A method for manufacturing an actuator having the above structure.

6. Preparing the assembly includes fixing the reference member to the end of the ball screw shaft such that the second plane of the reference member is perpendicular to the second central axis of the ball screw shaft. The method according to claim 5 .

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