Planetary Roller Screw Device

Abstract

The rotation of a plurality of planetary rollers in a planetary roller screw device is synchronized without using a gear transmission mechanism. [Solution] A planetary roller screw device 1 has eight planetary rollers 30 arranged around a central screw shaft 2, and these planetary rollers 30 are rotatably held inside a nut 10. A ring member 40 is arranged inside the nut 10, and the ring member 40 has multiple tapered convex portions 41 protruding from its inner peripheral surface. Each planetary roller 30 has concave portions 50, 51, into which the convex portions 41 fit, on its outer peripheral surface facing the inner peripheral surface of the ring member 40. As each planetary roller 30 rotates with its convex portions 41 fitting into the concave portions 50, 51, the rotation of each planetary roller 30 is restricted in the same way, and the rotation is synchronized without the use of a gear transmission mechanism.

Description

[Technical Field]

[0001] The present invention relates to a planetary roller screw device that moves a nut containing multiple planetary rollers arranged around a screw shaft linearly along the screw shaft, and in particular to one that allows multiple planetary rollers to rotate synchronously without using a rotation transmission mechanism using gears. [Background technology]

[0002] Conventionally, there has been known a device (planetary differential screw type rotation-to-linear motion conversion device) that includes a screw shaft, a plurality of planetary rollers arranged around the screw shaft, and a nut that contains the planetary rollers, and that converts the rotation of the screw shaft into linear motion of the nut (see, for example, Figures 1-10 and the like of Patent Document 1 below).

[0003] Furthermore, in the device described above, the rotation of the screw shaft is transmitted to the multiple planetary rollers, causing them to rotate individually. However, if the rotation of each of these planetary rollers is not synchronized, a twisted state will occur in each planetary roller, hindering the movement of the nut.

[0004] To prevent the above-described situation from occurring, there is a device having a gear transmission mechanism in which gears are provided on multiple planetary rollers, and a ring gear (with a gear wheel formed on the ring-shaped inner peripheral surface) that meshes with the gears is precisely assembled and press-fitted into the nut, allowing the multiple planetary rollers to rotate synchronously (see, for example, Figures 11-22 and the like in Patent Document 1, Figures 1-6 and the like in Patent Document 2, and Figures 1-7 and the like in Patent Document 3 below). Note that, as disclosed in Patent Document 2, when a ring gear is precisely assembled and press-fitted into the nut, it is usually required that the ratio of the numerical values ​​relating to the diameter of the screw shaft and the diameter of the planetary rollers be constant, due to the strict meshing condition between the gears.

[0005] The linearly moving nut is basically cylindrical, with donut-shaped retainers attached to both ends of the nut, and the retainer has through holes formed at specified intervals on the same circumference. The ends of the planetary rollers are inserted into these through holes, so that the planetary rollers are rotatably held.

[0006] Incidentally, Patent Document 4 below discloses that, in order to ensure the strength of the cage and reduce noise, the shape of the through holes formed in the cage is an elongated hole with the radial direction of the cage as the longitudinal direction. Such planetary roller screw devices are often used as units that constitute mechanisms that convert rotational motion into linear motion in various automatic machines in production facilities, etc., and are also sometimes incorporated into electric brake devices for use, as shown in Patent Document 5 below. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4289513 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-75804 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-133052 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-56993 [Patent Document 5] Japanese Patent Application Laid-Open No. 2013-223301 Summary of the Invention [Problem to be solved by the invention]

[0008] As described above, conventional planetary roller screw devices use a gear transmission mechanism to rotate multiple planetary rollers synchronously, but gears generally need to have unique tooth profiles, such as involute curves. Therefore, to form the gear tooth profiles, required cutting processing is required using a special cutting tool, such as a hob cutter, which increases the cost of gear production. In particular, since multiple metal planetary rollers are used in one planetary roller screw device, cutting processing is required for the gears in the number equal to the number of planetary rollers, which cumulatively increases the cost issue.

[0009] Furthermore, in the device described in Patent Document 2, the ring gear provided on the nut is precisely assembled into the nut, but in order to assemble it with such precision, the ring gear and nut must be manufactured with precision, which also increases costs.

[0010] Furthermore, when assembling the ring gear incorporated in the nut and the gears attached to the multiple planetary rollers by meshing them together, it is necessary to align the gears with each other, which requires a certain level of skill and effort, increasing the number of labor hours, and this also contributes to increasing the manufacturing costs of the planetary roller screw device.

[0011] The present invention has been made in view of the above circumstances, and has as its object to provide a planetary roller screw device that ensures synchronous rotation of multiple planetary rollers without using a rotation transmission mechanism using gears, thereby reducing manufacturing costs and improving ease of assembly. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a planetary roller screw device comprising a screw shaft, a plurality of planetary rollers arranged around the screw shaft and screwed onto the screw shaft, and a nut rotatably containing the plurality of planetary rollers, wherein the rotation of the screw shaft is transmitted to the plurality of planetary rollers, thereby causing the nut to move linearly along the screw shaft; the device further comprises a ring member arranged inside the nut so as to surround the plurality of planetary rollers, and the ring member has a plurality of tapered convex portions formed on its inner peripheral surface along the circumferential direction, the convex portions having a shape different from that of gear teeth, and the plurality of planetary rollers have a plurality of concave portions formed on their outer peripheral surfaces facing the inner peripheral surface of the ring member, into which the convex portions can be fitted, and the plurality of planetary rollers rotate while the convex portions of the ring member fit into the concave portions of the plurality of planetary rollers, thereby synchronizing the rotation of the plurality of planetary rollers.

[0013] In this invention, tapered convex portions different from the gear tooth shape are formed on the inner peripheral surface of a ring member placed inside the nut, and concave portions are formed by recessing the outer peripheral surfaces of multiple planetary rollers. When these convex portions are fitted into the concave portions and each planetary roller is rotated, the fit of the convex portions and the concave portions synchronizes the rotation of each planetary roller without using a rotation transmission mechanism using gears. The concave portions of such planetary rollers can be formed by processing methods such as rolling or form rolling rather than cutting, which allows for reduction in manufacturing costs.

[0014] Furthermore, the recesses recessed into the outer peripheral surface of the planetary roller make it easier to bring the tip of the mating convex portion into contact with the outer peripheral surface of the planetary roller and then guide it into the recess, compared to conventional gears. This makes it easier to fit the convex portion into the recess, compared to the alignment of gears required in conventional gear transmission mechanisms, and therefore makes the device easier to assemble.

[0015] The present invention is also characterized in that a plurality of the ring members are arranged inside the nut, and the plurality of planetary rollers have the recesses formed on their outer surfaces at locations facing the inner surfaces of the plurality of ring members.

[0016] In the present invention, multiple ring members are arranged inside the nut, and each planetary roller has a recess formed on its outer surface facing the inner surface of each ring member. This causes the convex and concave portions to fit together at each location where a ring member is provided, improving the accuracy of synchronizing the rotation of the multiple planetary rollers and further stabilizing the operation of the planetary roller screw device, making it particularly suitable when the device is made larger.

[0017] Furthermore, the present invention is characterized in that two ring members are arranged inside the nut, each of the plurality of planetary rollers has a first area, a second area, and a third area from one end to the other, the second area has a larger diameter than the first area and the third area, and has a thread groove formed on its outer surface to threadably engage with the screw shaft, the first area is arranged to face the inner peripheral surface of one of the two ring members, and the recess is formed on the outer peripheral surface at a location facing the inner peripheral surface of that one ring member, and the third area is arranged to face the inner peripheral surface of the other of the two ring members, and the recess is formed on the outer peripheral surface at a location facing the inner peripheral surface of the other ring member.

[0018] In the present invention, recesses into which the protrusions of the two ring members fit are formed in the first and third regions, which are on one and the other side of the planetary rollers, and these first and third regions are made smaller in diameter than the central second region, so that when assembling the device, the protrusions of the ring members fit into the recesses at the narrow parts of the planetary rollers, ensuring a situation where the protrusions can be easily fitted into the recesses, contributing to ease of assembly of the device. Furthermore, because the second region, in which the thread grooves are formed, has a large diameter, it can be reliably screwed along the screw shaft, ensuring ease of assembly and ensuring reliably screwing each planetary roller into the screw shaft.

[0019] The present invention is characterized in that the convex portion is formed in a hemispherical convex shape, and the concave portion is formed in an inverted trapezoidal concave shape in a cross section perpendicular to the rotational axis direction of the planetary roller.

[0020] In the present invention, a hemispherical convex portion is formed on the inner peripheral surface of the ring member, and a concave portion having an inverted trapezoidal cross section that narrows toward the bottom is formed on the outer peripheral surface of the planetary roller, so that the required meshing force is ensured while using a shape that is easy to manufacture, and the rotation of multiple planetary rollers can be reliably synchronized. In other words, since a hemispherical shape is generally easy to manufacture, the convex portion can be easily manufactured, and further, if the hemispherical convex portion and the concave portion having an inverted trapezoidal cross section are in local contact with the hemispherical curved surface of the convex portion and the slope of the inverted trapezoidal shape of the concave portion, the required contact pressure is ensured, resulting in a sufficient meshing state and obtaining the torque (driving force) necessary for the multiple planetary rollers to rotate synchronously.

[0021] In addition, the present invention is characterized in that the convex portion is formed in a hemispherical convex shape, and the concave portion is formed in a concave shape equivalent to the hemispherical shape.

[0022] In the present invention, the shape of the convex portion projecting from the inner peripheral surface of the ring member and the shape of the concave portion formed on the outer peripheral surface of the planetary roller are both hemispherical, which makes it easy to manufacture the convex portion and the concave portion, and the convex portion and the concave portion mesh perfectly, ensuring a predetermined meshing force and ensuring that the multiple planetary rollers rotate in sync. In particular, the hemispherical concave portion is a shape that is suitable for forming by processing methods such as rolling or form rolling.

[0023] Furthermore, the present invention is characterized in that the convex portion is formed in a quadrangular pyramidal convex shape, and the concave portion is formed in an inverted trapezoidal concave shape in a cross section perpendicular to the rotational axis direction of the planetary roller.

[0024] In the present invention, the convex portion protruding from the inner peripheral surface of the ring member is made into a quadrangular pyramid shape, and the concave portion recessed into the outer peripheral surface of the planetary roller is made into a shape whose cross section is an inverted trapezoid. Therefore, the convex portion and the concave portion fit together with the sloping surface of the quadrangular pyramid-shaped convex portion and the sloping surface of the inverted trapezoid-shaped concave portion facing each other and in contact, generating the required fitting force and improving the accuracy with which the rotation of each planetary roller is synchronized, ensuring smoother and more stable operation of the device.

[0025] Furthermore, the present invention is characterized in that the convex portion is formed in a quadrangular pyramidal convex shape, and the concave portion is formed in a hemispherical concave shape.

[0026] In the present invention, since the inner peripheral surface of the ring member is provided with a quadrangular pyramidal convex portion and the outer peripheral surface of the planetary roller is provided with a hemispherical concave portion, the required meshing force is ensured while using a shape that is easy to manufacture, thereby achieving a good balance between reduced manufacturing costs and synchronous rotation of the planetary rollers. In other words, since the hemispherical shape is easy to manufacture, the manufacture of the concave portion is also easy, and the inclined surfaces of the quadrangular pyramidal convex portion and the curved surfaces of the hemispherical concave portion come into local contact with each other, ensuring the required contact pressure and generating sufficient meshing force, so that the multiple planetary rollers rotate reliably in synchronization.

[0027] The present invention is characterized in that a disk-shaped retainer having a plurality of through holes formed therein is attached to both ends of the nut, and each of the plurality of planetary rollers is rotatably held on the nut by inserting the shaft portions at both ends of the planetary roller into the respective through holes of the retainer, and the through holes are elongated with the radial direction of the retainer as the longitudinal direction, and the outer part of the retainer that is on the outer side when attached to the nut has a smaller diameter in its thickness direction than the inner part of the retainer that is on the inner side when attached to the nut, and the hole depth of the range including the outer hole end of the through hole is a dimension that corresponds to the thickness of the inner part.

[0028] In the present invention, the shafts at both ends of the planetary rollers are inserted into through-holes in a retainer (cage). The through-holes are elongated, with the radial direction of the retainer as the longitudinal direction, as in Patent Document 4, and the outer portion of the retainer is stepped with a smaller diameter. This allows the depth of the elongated through-holes at the end portions closer to the outer peripheral contour of the retainer to be smaller than at other portions. As a result, during device assembly, the planetary rollers can be displaced more obliquely relative to the central screw axis than in the case of the elongated holes described in Patent Document 4. This makes it easier to fit the convex portions into the concave portions, contributing to easier assembly. Furthermore, because the planetary rollers have play along the longitudinal direction of the through-holes, even if a load is applied to the planetary rollers for some reason, the play in the longitudinal direction allows the planetary rollers to displace to relieve the load. This facilitates stable rotation of each planetary roller and reduces noise.

[0029] In addition, the present invention is characterized in that the ring member is made of a flexible synthetic resin and is rotatable inside the nut.

[0030] In the present invention, the ring member is made of a flexible synthetic resin, allowing the ring member itself to bend. During assembly, for example, when fitting the convex portions of the ring member into the concave portions of the planetary rollers, bending the ring member makes it easier to fit the convex portions into the concave portions. This, combined with the ring member's ability to rotate within the nut, improves ease of assembly. Furthermore, since the ring member is made of a synthetic resin, it can be manufactured using an injection molding machine, which helps reduce manufacturing costs for the ring member and contributes to reduced device costs. Furthermore, by allowing the ring member to rotate within the nut, flexibility is achieved in the engagement between the convex portions and the concave portions, eliminating the need to maintain a constant ratio between the diameter of the screw shaft and the diameter of the planetary rollers, thereby increasing device design flexibility. Furthermore, using a synthetic resin material for the ring member to rotate within the nut is preferable because it also improves the sliding properties of the parts that come into contact with the nut. [Effects of the Invention]

[0031] In the present invention, each planetary roller rotates with the convex portions protruding from the inner surface of the ring member fitted into the concave portions formed in the outer surfaces of the multiple planetary rollers. As a result, the rotational state of each planetary roller is regulated by the fitting of the convex portions and the concave portions, and therefore synchronization of the rotation of each planetary roller can be achieved without using a gear transmission mechanism, and the recesses, etc. can be easily manufactured, reducing manufacturing costs while ensuring the specified performance of the planetary roller screw device.

[0032] Furthermore, in the present invention, the convex portions formed on the multiple ring members are fitted into the concave portions formed in multiple locations on each planetary roller, thereby increasing the degree of fit between the convex portions and the concave portions and stabilizing the synchronization of the rotation of each planetary roller.

[0033] Furthermore, in the present invention, the points where the convex portions of the two ring members fit into the concave portions of the planetary rollers are located within the small diameter range of the planetary rollers, making it easier to fit the convex portions of the ring members into the concave portions of the planetary rollers, ensuring ease of assembly of the device, and the two ring members also make the rotational synchronization of each planetary roller more stable.

[0034] In the present invention, a hemispherical convex portion is provided on the ring member, and a concave portion having an inverted trapezoidal cross section is provided on the outer peripheral surface of each planetary roller, so that a shape that is easy to manufacture can be used while also generating the required meshing force, thereby synchronizing the rotation of each planetary roller.

[0035] Furthermore, in the present invention, the shape of the convex portion of the ring member and the shape of the concave portion of the planetary roller are both hemispherical, which makes it easy to manufacture the convex portion and concave portion, and the convex portion and concave portion have the same shape so that they fit together perfectly, ensuring a predetermined meshing force and allowing multiple planetary rollers to rotate reliably in sync, thereby stabilizing the operation of the device.

[0036] Furthermore, in the present invention, the convex portion of the ring member is formed in a quadrangular pyramid shape, and the concave portion of the planetary roller has an inverted trapezoidal cross section, so that the convex portion and the concave portion can be fitted together with the sloping surface of the quadrangular pyramid-shaped convex portion facing and contacting the sloping surface of the inverted trapezoid-shaped concave portion, thereby exerting the necessary fitting force and improving the accuracy of synchronizing the rotation of each planetary roller.

[0037] Furthermore, in the present invention, the convex portion of the ring member is made into a quadrangular pyramid shape and the concave portion of the planetary roller is made into a hemispherical shape, so that a shape that is easy to manufacture by rolling or the like is used, while also generating the required meshing force, making it easy to synchronize the rotation of each planetary roller, and achieving stable operation of the planetary roller screw device.

[0038] In the present invention, the retainer has an elongated through-hole shape, and the retainer is stepped in the thickness direction so that the hole depth of the hole end portion on the outer peripheral contour side of the retainer is reduced. This makes it easy to position the planetary rollers at an angle to the screw shaft when assembling the device, making it easier to fit the convex portions of the ring member into the concave portions of each planetary roller, contributing to easier device assembly and also helping to stabilize the device and reduce noise when it is operating.

[0039] Furthermore, in the present invention, the ring member is made of a flexible synthetic resin and is rotatable. Therefore, when assembling the device, for example, when fitting the convex portion of the ring member into the concave portion of the planetary roller, the ring member can be bent to make it easier to fit the convex portion into the concave portion, improving the ease of assembling the device. Furthermore, if the ring member is made of synthetic resin, it is easier to keep down the manufacturing costs of the ring member, reducing the cost of the device and also improving the freedom of device design. [Brief explanation of the drawings]

[0040] [Figure 1] 1 is a schematic perspective view showing an external appearance of a planetary roller screw device according to an embodiment of the present invention; [Figure 2] FIG. 1 is a cutaway perspective view of a main part of a planetary roller screw device according to an embodiment, showing the inside of the device. [Figure 3]FIG. 1 is a cutaway front view of a main portion of a planetary roller screw device according to an embodiment, showing the inside of the device. [Figure 4] FIG. [Figure 5] FIG. 2 is a perspective view showing the appearance of a planetary roller. [Figure 6] 1A shows a planetary roller, where (a) is a front view, (b) is a cross-sectional view taken along line AA in the front view of (a), and (c) is an enlarged view of one of the recesses in the cross-sectional view of line AA in (b). [Figure 7] 1A is a front view of the retainer, FIG. 1B is a side view seen from the thickness direction, and FIG. 1C is an enlarged view of one of the plurality of holding through holes. [Figure 8] 1A is a perspective view of a ring member, FIG. 1B is a front view thereof, and FIG. 1C is an enlarged view of a main part including a protrusion. [Figure 9] 10 is an enlarged perspective cutaway view of a main portion showing a state in which the convex portion of the ring member is fitted into the concave portion of the planetary roller; FIG. [Figure 10] FIG. 2 is a schematic diagram illustrating the rotation of a screw shaft, planetary rollers, etc. [Figure 11] FIG. 10 is a perspective view showing the appearance of a planetary roller according to a modified example. [Figure 12] 10 is an enlarged perspective cutaway view of a main part showing a state in which a convex portion of a ring member is fitted into a concave portion of a planetary roller according to a modified example. FIG. [Figure 13] 1A and 1B show a modified ring member, in which (a) is a perspective view, (b) is an enlarged perspective view of the main part including the convex part, (c) is a front view, and (d) is an enlarged front view of the main part including the convex part. [Figure 14] FIG. 10 is an enlarged perspective cutaway view of a main part showing a state in which a convex portion of a ring member of a modified example is fitted into a concave portion of a planetary roller. [Figure 15] FIG. 10 is an enlarged perspective cutaway view of a main part showing a state in which a convex portion of a ring member of a modified example is fitted into a concave portion of a planetary roller of a modified example. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0041] 1 shows the appearance of a planetary roller screw device 1 according to an embodiment of the present invention. The planetary roller screw device 1 has a plurality of planetary rollers 30 (eight in this embodiment) arranged around a screw shaft 2, which serves as the central axis of the device. The rotation of the screw shaft 2 is transmitted to the plurality of planetary rollers 30, causing a cylindrical nut 10, which rotatably houses the planetary rollers 30, to move linearly (in a straight line) along the axial direction of the screw shaft 2. In particular, the present invention is characterized by the use of a rotation transmission mechanism inside the nut 10 that is different in shape from gears, which synchronizes the rotation of the planetary rollers 30 to ensure stable operation, while also making the device easier to assemble and reducing costs.

[0042] The planetary roller screw device 1 can be manufactured in various sizes depending on the application. As an example of the size of the planetary roller screw device 1 of this embodiment, a screw shaft 2 (made of metal) with a screw groove 2a (spiral groove) formed on its outer surface has a diameter (diameter at the screw apex) of approximately 22.5 mm and a length (axial length) of approximately 400 mm (the screw pitch is approximately 1 mm), and a cylindrical nut 10 (made of metal) has a length of approximately 70 mm and an outer diameter of approximately 53 mm. Note that the X-axis shown in FIG. 1 indicates a direction parallel to the axial direction of the screw shaft 2 at the center of the device, the Y-axis indicates a direction perpendicular to the X-axis on the same plane, and the Z-axis indicates a direction perpendicular to both the X-axis and the Y-axis (the directions of these axes are the same in other figures).

[0043] 2 and 3 show the internal structure of the planetary roller screw device 1, with a portion of the nut 10 and other components cut away. Each planetary roller 30 contained within the nut 10 is rotatably held by a donut-shaped disk-shaped retainer 20 attached to both ends 10a and 10b of the nut 10 (note that the retainer 20 is prevented from falling off the nut 10 by a snap ring 5).

[0044] Each planetary roller 30 has a screw groove 37 (spiral groove) formed on the outer periphery in the central range in the longitudinal direction, which screws onto the central screw shaft 1, and a first groove portion 36 and a second groove portion 38 (non-spiral parallel grooves, straight grooves) formed on the outer periphery in both end ranges in the longitudinal direction (X-axis direction). Furthermore, each planetary roller 30 has a number of recesses 50, 51 (see Figure 3) formed in the ranges where the grooves 36, 38 are formed, at locations (two locations) adjacent to the range where the screw groove 37 is formed.

[0045] A ring member 40 is disposed inside the nut 10 facing the two recessed portions 50, 51 of the planetary rollers 30 (only one of the two ring members 40 is shown in FIGS. 2 and 3). When disposed inside the nut 10, the ring member 40 surrounds the eight planetary rollers 30 contained within the nut 10. The ring member 40 has a plurality of protrusions 41 (see FIG. 2) protruding in the circumferential direction on its inner peripheral surface, and these protrusions 41 fit into and mesh with the recessed portions 50, 51 of each planetary roller 30. The meshing of the protrusions 41 with the recessed portions 50, 51 regulates the rotation of each planetary roller 30 so that the rotation of each planetary roller 30 is synchronized. Below, the various components (nut 10, planetary rollers 30, retainer 20, etc.) that make up the planetary roller screw device 1 will be described in detail.

[0046] 4 is a cross-sectional view of the nut 10 cut in half parallel to the X-axis, showing the interior 10c of the nut 10. Because the nut 10 is cylindrical as a whole, the interior 10c is also a cylindrical cavity, but the inner circumferential surface 10d of the cavity has a somewhat complex shape. First, the inner circumferential surface 10d of the cavity is divided into three areas from one end 10a of the nut 10 to the other end 10b: a first inner circumferential area 11, a second inner circumferential area 12, and a third inner circumferential area 13. These first inner circumferential area 11, second inner circumferential area 12, and third inner circumferential area 13 correspond to the areas in which the first groove portion 36, the thread groove 37, and the second groove portion 38 of the planetary roller 30 described above are formed, respectively.

[0047] A one-end fitting recess 14 for fitting the retainer 20 is formed in a portion of the first inner circumferential range 11 that is on the one end 10a side of the nut 10, and a one-end groove 14a for fitting a snap ring 5 (see FIG. 1, etc.) that functions to prevent the retainer 20 from coming off is formed in a portion of the one-end fitting recess 14 closer to the one end 10a. The inner diameter of the one-end fitting recess 14 is sized according to the outer diameter of the retainer 20, and in this embodiment, in terms of precision, a loose-fitting value (a clearance fit value, a plus tolerance value) is set, making it easy to fit the retainer 20 and also to adjust the planetary rollers 30 (in this embodiment, the inner diameter of the one-end fitting recess 14 is set to about 45 mm with a plus tolerance).

[0048] The length of the one-end fitting recess 14 along the X-axis direction is sized according to the thickness of a large-diameter portion 22 of the retainer 20, which will be described later. The one-end groove 14a has a size suitable for fitting a snap ring 5, and its inner diameter is slightly larger than the inner diameter of the one-end fitting recess 14 (in this embodiment, the inner diameter of the one-end groove 14a is set to about 47.2 mm).

[0049] Furthermore, a first inner circumferential groove portion 16 that fits into the first groove portion 36 of the planetary roller 30 is formed on the first inner circumferential surface 11a, which is located inside the one-end fitting recess 14 in the first inner circumferential range 11. This first inner circumferential groove portion 16 is formed by forming multiple grooves (straight grooves) in parallel on the first inner circumferential surface 11a in the first inner circumferential range 11. The pitch between adjacent grooves in the first inner circumferential groove portion 16 is a value that matches the first groove portion 36 of the planetary roller 30, and in this embodiment is set to 1 mm, but is not limited to this value and can be set to various values ​​in the range of approximately 0.3 to 3 mm according to the size of the planetary roller screw device 1, etc. Furthermore, the first inner diameter D1 at the groove top of the first inner groove portion 16 is slightly smaller than the inner diameter of the one-end fitting recess 14 (for example, it is possible to set the inner diameter dimension to be approximately 1.5 mm smaller), and the dimension of the first inner groove portion 16 parallel to the X-axis direction is set to a value corresponding to the length in the X-axis direction of the range in which the first groove portion 36 of the planetary roller 30 is formed.

[0050] Furthermore, the first inner circumferential region 11 has a first ring groove 15 formed adjacent to the second inner circumferential region 12 for fitting a ring member 40 (see FIGS. 2 and 3). The dimensions of this first ring groove 15 are also appropriate for fitting the ring member 40, and in this embodiment, the inner diameter and length dimension according to the X-axis direction are set to values ​​that allow the ring member 40 to fit with a loose fit (a clearance fit is set, with a plus tolerance value). The inner diameter of the first ring groove 15 is larger than the first inner diameter D1 of the first inner circumferential groove portion 16 and the second inner diameter D2 of the second inner circumferential region 12, so that the ring member 40 fitted in the first ring groove 15 will not slip out.

[0051] The second inner circumferential range 12 of the nut 10 corresponds to the screw grooves 37 of the planetary rollers 30, but because the nut 10 does not thread into the screw grooves 37 of the planetary rollers 30, the second inner diameter D2 of the second inner circumferential range 12 is set to a dimension that creates a gap (clearance) with the screw grooves 37 of each planetary roller 30 when the nut 10 is contained within the nut 10 (in this embodiment, the second inner diameter D2 is set to a value of about 45.5 mm). Note that the second inner circumferential surface 12a in the second inner circumferential range 12 is simply a curved surface, and no grooves or the like are formed thereon.

[0052] The third inner circumferential range 13 on the other end 10b side of the nut 10 is formed symmetrically to the first inner circumferential range 11 with the second inner circumferential range 12 in between. An other-end fitting recess 17 for fitting a retainer 20 is formed on the other end 10b side, and an other-end groove 17a for fitting a snap ring 5 is formed in a portion of the other-end fitting recess 17 closer to the other end 10b. A second inner circumferential groove 18 that fits with the second groove 38 of the planetary roller 30 is formed on the third inner circumferential surface 13a, which is located deeper than the other-end fitting recess 17 in the third inner circumferential range 11. The third inner diameter D3 at the groove apex of the second inner circumferential groove 18 is the same as the first inner diameter D1 of the first inner circumferential groove 16. The dimension of the second inner circumferential groove 18 parallel to the X-axis direction is set to a value corresponding to the length in the X-axis direction of the range in which the second groove 38 of the planetary roller 30 is formed.

[0053] Furthermore, a second ring groove 19 for fitting a second ring member 40 is also formed in a location of the third inner circumferential region 13 adjacent to the second inner circumferential region 12. This second ring groove 19 is also set to the same dimensions as the first ring groove 15 described above.

[0054] 5 and 6(a) show the entire planetary roller 30. The planetary roller 30 is formed from a round bar-shaped metal member, with a one-end shaft portion 30c formed on one end 30a and a other-end shaft portion 30d formed on the opposite end 30b. These one-end shaft portion 30c and other-end shaft portion 30d function as rotation axes of the planetary roller 30, and therefore their outer peripheral surfaces are smoothly curved.

[0055] Furthermore, the outer peripheral range of the planetary roller 30 from the one end shaft portion 30c to the other end shaft portion 30d is divided from the one end 30a to the other end 30b into a first range 31, a second range 32, and a third range 33. The overall length (dimension parallel to the X-axis direction) of the planetary roller 30 of this embodiment is set to the same value (for example, approximately 70 mm) as that of the nut 10 described above. All of the planetary rollers 30 used in this embodiment have the same specifications.

[0056] The first region 31 of the planetary roller 30 has a first groove portion 36 formed on its outer circumferential surface 31a. This first groove portion 36 is a plurality of parallel grooves (straight grooves) having the same shape as the first inner circumferential groove portion 16 of the nut 10 described above, and is adapted to fit with the first inner circumferential groove portion 16. In this embodiment, the first outer diameter d1 of the first region 31 (diameter dimension at the groove top) is set to approximately 11 mm, and the dimension of the first region 31 along the X-axis direction is set to approximately 18.5 mm.

[0057] Furthermore, a plurality of recesses 50 are formed at predetermined intervals in the circumferential direction on the outer peripheral surface 34a (the outer peripheral surface forming the entire circumference) of the one-side region 34, which is a partial region of the first region 31 adjacent to the second region 32. The one-side region 34 does not have the straight groove of the first groove portion 36 described above, but has a cylindrically curved outer peripheral surface 34a, and the plurality of recesses 50 are recessed in this outer peripheral surface 34a. The dimension of this one-side region 34 along the X-axis direction is approximately the same as the thickness of the ring member 40 in this embodiment, which is set to approximately 2 mm in this embodiment. Note that, when the planetary roller 30 is properly positioned in the interior 10c of the nut 10, the one-side region 34 in the first region 31 is positioned opposite the first ring groove 15 formed in the inner peripheral surface 10d of the nut 10. Accordingly, the one-side region 34 also faces the inner peripheral surface 40a of the first (one of two) ring member 40 that is positioned in the first ring groove 15 of the nut 10.

[0058] FIG. 6(b) shows a cross section of the one-side region 34 cut along a plane perpendicular to the X-axis, and FIG. 6(c) shows an enlarged view of one of the recesses 50 (or recesses 51) formed in the one-side region 34 (or the other-side region 35). As shown in FIG. 6(b), in this embodiment, a total of 20 recesses 50 are formed at required intervals in the circumferential direction (in this embodiment, multiple recesses are formed at a pitch such that the central angle from the center of the cross section is 18 degrees). Furthermore, as described above, the diameter (first outer diameter d1) of the one-side region 34 is approximately 11 mm, and the radius from the center of the cross section to the bottom surface 50a of the recess 50 is approximately 5 mm in this embodiment. Therefore, the depth of the recess 50 is approximately 0.5 mm.

[0059] The recesses 50 have a shape that allows the protrusions 41 of the ring member 40 to fit into them. In this embodiment, as shown in FIG. 6(b), the recesses 50 have an inverted trapezoidal shape recessed from the outer peripheral surface 34a of the one-side region 34 in a cross section perpendicular to the rotational axis direction (X-axis direction) of the planetary roller 30. The slopes 50b, 50c on both sides of the recess 50 are inclined so that the angle between them is approximately 60 degrees, thereby ensuring a width W of the opening 50d of the recess 50 of approximately 1.2 mm in this embodiment. The recesses 50 are evenly spaced in the X-axis direction, centered on the center of the width of the one-side region 34 along the X-axis direction, and the width of the recesses 50 (the dimension along the X-axis direction) is set to approximately 1 mm in this embodiment.

[0060] The second region 32 of the planetary roller 30 is a region that threads with the screw shaft 2 located at the center of the device, and therefore the diameter (second outer diameter d2) of the second region 32 is larger (larger) than the first outer diameter d1 of the first region 31, and a screw groove 37 (spiral groove) is formed on the outer peripheral surface 32a thereof. The pitch of this screw groove 37 is set to a value corresponding to the screw groove 2a of the screw shaft 2. In this embodiment, the second outer diameter d2 (diameter at the groove apex) of the second region 32 is set to about 12 mm, and as will be described later, the second region 32 also has a larger diameter than the third region 33.

[0061] As shown in Figure 6(a), the third area 33 of the planetary roller 30 is formed symmetrically to the first area 31 described above, with the second area 32 sandwiched between them, and a second groove portion 38 is formed on its outer peripheral surface 33a, and a plurality of recesses 51 are formed at predetermined intervals in the circumferential direction on the outer peripheral surface 35a (the surface that forms one circumference around the outside) of the other side area 35, which is a partial area of ​​the third area 33 adjacent to the second area 32.

[0062] The specifications of the second groove portion 38, the other-side portion 35, and the recess 51 are the same as those of the first groove portion 36, the one-side portion 34, and the recess 50 of the first region 31 described above. Therefore, the other-side portion 35 of the third region 33 is also positioned opposite the second ring groove 19 formed in the inner circumferential surface 10d of the nut 10 when the planetary roller 30 is properly positioned inside 10c of the nut 10 (the other-side portion 35 in the third region 33 is the portion that faces the inner circumferential surface 40a of the second (the other of the two) ring member 40 that is positioned in the second ring groove 19 of the nut 10).

[0063] In this embodiment, the outer peripheral surface of the planetary roller 30 configured as described above is processed (processing to form the first groove portion 36, the screw groove 37, the second groove portion 38, and the recesses 50, 51) not by cutting, but by rolling. By using rolling in this way, it is possible to reduce manufacturing costs compared to cutting, and in particular, since eight planetary rollers 30 are used in this embodiment, the cumulative reduction in manufacturing costs is large, which in turn contributes to reducing the cost of the planetary roller screw device 1 itself.

[0064] 7(a) and (b) show the appearance of the donut-shaped disk-shaped retainer 20 that rotatably holds the planetary roller 30 described above. The retainer 20 has different outer diameters (diameters) in its thickness direction (the X-axis direction when attached to the nut 10) between an outer portion 21 (the outer portion 21 including the area on the side of one end face 20a) that is on the outer side when attached to the nut 10 and an inner portion 22 (the inner portion 22 including the area on the side of the other end face 20b) that is on the inner side when attached to the nut 10, and the outer diameter of the outer portion 21 is smaller than that of the inner portion 22. The contours of the outer periphery 21a of the outer portion 21 and the outer periphery 22a of the inner portion 22 are concentric.

[0065] 7(b), retainer 20 has a stepped shape when viewed in the thickness direction, and in this embodiment, outer diameter d10 of outer portion 21 is set to approximately 39 mm, and outer diameter d11 of inner portion 22 is set to approximately 45 mm (set to a negative tolerance). Because retainer 20 has one outer end face 20a with a stepped shape, the periphery of one end face 20a is recessed, which makes it easier to fit snap ring 5, which is attached to nut 20 and prevents retainer 20 from falling off, onto nut 10 during device assembly.

[0066] 7(a), the retainer 20 has a circular central through-hole 23 formed in its center for passing the screw shaft 2. The inner diameter of this central through-hole 23 is larger than the outer diameter of the screw shaft 2 (set to approximately 23 mm in this embodiment).

[0067] Furthermore, the retainer 20 is formed so that the retaining through-holes 24 are arranged on the same circumference. The retaining through-holes 24 are formed at positions corresponding to the locations where the eight planetary rollers 30 are arranged in the nut 10 at their normal design positions. Specifically, the eight planetary rollers 30 are arranged at equal circumferential intervals around the screw shaft 2, and when the screw grooves 2a of the screw shaft 2 and the screw grooves 37 of each planetary roller 30 are properly threadedly engaged, the centers (hole centers) of the retaining through-holes 24 are located on a circumference connecting the axial centers of the planetary rollers 30 and at points spaced apart at 22.5-degree angles in the circumferential direction. These retaining through-holes 24 are elongated holes whose longitudinal direction is the radial direction (normal direction) of the retainer 20, and extend both toward the center and outward from the above-mentioned hole center position.

[0068] As shown in Figure 7(c), the area including the outer hole ends 24a on the outer side (the outer peripheral contour side of the retainer 20) of these retaining through holes 24 is located at a point that protrudes outward from the outer periphery 21a of the outer portion 21 described above, and therefore the hole depth of the area including the outer hole ends 24a of the retaining through holes 24 is a dimension that corresponds to the thickness of only the inner portion 22.

[0069] In the present embodiment, the retaining through-hole 24 has a hole width L1 of approximately 6 mm (plus a tolerance), a hole length L2 corresponding to the elongated hole shape of approximately 7 mm (length from outer hole end 24a to inner hole end 24b), a hole depth of the retaining through-hole 24 in the range including the outer hole end 24a that protrudes outward from the outer portion 21 is approximately 3.5 mm (corresponding to a dimension corresponding to the thickness of the inner portion 22), and a hole depth of the retaining through-hole 24 in the range that does not protrude from the outer portion 21 (range including the inner hole end 24b) is approximately 6 mm (corresponding to a dimension corresponding to the overall thickness of the retainer 20 including the inner portion 22 and the outer portion 21). Note that the corner 21b of the outer portion 21 where the retaining through-hole 24 intersects with the protruding range is formed in a rounded shape, like a chamfer.

[0070] By forming the retaining through-holes 24 as described above, when assembling the planetary roller screw device 1, each planetary roller 30 can be positioned inside the nut 10 at an angle relative to the screw shaft 2, making it easier to assemble multiple planetary rollers 30. Note that the ability to position each planetary roller 30 at an angle during assembly is due to the fact that the retaining through-holes 24 are elongated and also because the depth of the retaining through-holes 24 in the range including the outer hole ends 24a is shallower (smaller) than in other hole ranges, and the width for holding each planetary roller 30 is smaller in the range including the outer hole ends 24 of each retaining through-hole 24, making it easier to change the planetary furnace rollers 30 to a tilted position.

[0071] 8(a) and (b) show the appearance of the ring members 40 respectively placed in the first ring groove 15 and the second ring groove 19 inside the nut 10. The ring member 40 of this embodiment is a member molded into a ring shape from a flexible synthetic resin material, and has a plurality of protrusions 41 (tapered protrusions) protruding from its inner peripheral surface 40a at predetermined intervals. The outer peripheral surface 40b of the ring member 40 has a smoothly curved surface.

[0072] As shown in FIG. 8(c), the convex portions 41 extending from the inner peripheral surface 40a of the ring member 40 have a shape different from that of gear teeth. In this embodiment, the convex portions 41 are tapered to a hemispherical shape, with a radius of approximately 0.5 mm. (The height of the convex portions 41 is preferably approximately 1 / 80 to 1 / 90 of the inner diameter of the ring member 40, and in this embodiment, it is set to approximately 1 / 89.) Note that, in this invention, the term "tapered shape" refers to a shape in which the width gradually decreases from the base (protrusion base or protrusion root) extending from the inner peripheral surface 40a of the ring member 40 toward the tip. The multiple convex portions 41 are spaced apart at a central angle of approximately 4.4 degrees from the center of the ring member 40, and the center of each convex portion 41 is located exactly in the middle of the thickness of the ring member 40 in the thickness direction (along the X-axis direction). In this embodiment, the ring member 40 has a ring outer diameter d20 of approximately 46.5 mm, an inner diameter of approximately 44.5 mm, and a thickness (dimension along the X-axis direction) of approximately 2 mm.The ring outer diameter d20 and thickness (dimension along the X-axis direction) are set to negative tolerance values ​​so that when the ring member 40 is fitted into the ring grooves 15, 19 of the nut 10, it is in a loosely attached state.

[0073] Next, we will explain how to assemble the planetary roller screw device 1. First, the ring members 40 are fitted into the first ring groove 15 and the second ring groove 19 formed in the interior 10c of the nut 10.

[0074] Specifically, one ring member 40 is inserted from one end 10a of the nut 10 into the interior 10c of the nut 10. At this time, since the outer diameter of the ring member 40 is larger than the first inner diameter D1 (inner diameter of the groove top) of the first inner circumferential groove portion 16 in the first inner circumferential range 11 of the nut 10, the ring member 40 is pushed into the first ring groove 15 in an oblique position and in a bent state so that the opposing portions are pressed and the diameter is reduced in the radial direction, and then the reduced diameter is released, thereby fitting the ring member into the first ring groove 15.

[0075] As described above, the ring member 40 is bent during assembly. However, because it is made of a flexible synthetic resin, it can be easily bent and smoothly return to its original ring shape, contributing to ease of assembly. From the other end 10b of the nut 10, the other ring member 40 is inserted into the interior 10c of the nut 10 and fitted into the second ring groove 19, similar to the case of the first end 10a. As described above, the outer dimensions of the ring members 40 fitted into the ring grooves 15, 19 are set smaller than the dimensions of the ring grooves 15, 19 (negative tolerance), allowing the ring members 40 to slide and rotate within the ring grooves 15, 19. Furthermore, because the ring members 40 are made of synthetic resin, the outer peripheral surface 40b has good sliding properties, which helps the ring members 40 to rotate smoothly within the ring grooves 15, 19.

[0076] Then, the retainer 20 is fitted into a fitting recess (one-end fitting recess 14) formed on one end (one end 10a) of the nut 10. At this time, the retainer 20 is fitted so that its outer portion 21 faces outward. A snap ring 5 is then fitted into the groove on one side (one-end groove 14a) to prevent the retainer 20 from falling out. The snap ring 5 is a ring-shaped member with a notch in one part, and by fitting it into the one-end groove 14a in a reduced diameter state and then releasing the reduced diameter state to return it to its original state, it acts as a barrier to prevent the retainer 20 from falling outward. As described above, the outer one end face 20a of the retainer 20 has a stepped shape, making it easy to fit the snap ring 5.

[0077] Then, the eight planetary rollers 30 are inserted one by one into the interior 10c of the nut 10 from the other side (for example, the side of the other end 10b) of the nut 10, and the one-end shaft portions 30c of the planetary rollers 30 are inserted into the retaining through-holes 24 of the retainer 20 fitted in the one-end fitting recesses 14 until the end face 31b (see FIG. 5) of the first region 31 abuts against the other end face 20b of the retainer 20. With the one-end shaft portions 30c inserted into the retaining through-holes 24 in this manner, the one end of the planetary rollers 30 is held and regulated. Therefore, when the planetary rollers 30 are positioned parallel to the X-axis direction in this state, the one-side region 34 faces the inner circumferential surface 40a of the first ring member 40 fitted in the first ring groove 15, and the other-side region 35 faces the inner circumferential surface 40a of the second ring member 40 fitted in the second ring groove 19.

[0078] When the planetary rollers 30 are pressed against the inner peripheral surface 40a of the ring member 40 in the above state, the protrusions 41 of the first ring member 40 fitted in the first ring groove 15 can fit into the recesses 50 formed in the outer peripheral surface 34a of the one-side portion 34, and by appropriately rotating the planetary rollers 30 or by appropriately rotating the ring member 40 fitted in the first ring groove 15 in the circumferential direction, the recesses 50 and the protrusions 41 are aligned, and the protrusions 41 fit into the recesses 50. Similarly, the protrusions 41 of the second ring member 40 fitted in the second ring groove 19 are fitted into the recesses 51 formed in the outer peripheral surface of the other-side portion 35.

[0079] In this case, too, by appropriately rotating the planetary rollers 30 or by appropriately rotating the ring member 40 fitted into the second ring groove 19 in the circumferential direction, the recessed portions 51 and the protruding portions 41 are aligned and the protruding portions 41 are fitted into the recessed portions 51. Note that the ring member 40 is fitted into the first ring groove 15 and the second ring groove 19 with a clearance fit precision (negative tolerance), and therefore is rotatable in the circumferential direction, which also helps ensure ease of assembly.

[0080] Furthermore, in this embodiment, as shown in FIG. 6(c), each recess 50, 51 has a wide inverted trapezoidal opening 50d, 51d, and the protrusion 41 is formed in a hemispherical shape as shown in FIG. 8(c), so that the hemispherical curved surface of the protrusion 41 is guided into the wide opening 50d, 51d, making it easy for the protrusion 41 to slip into the recess 50, 51 even in a blind situation, thereby preventing the assembly of the planetary roller screw device 1 from becoming difficult.

[0081] The above-described insertion of the planetary rollers 30 into the interior 10c of the nut 10 is carried out for each of the eight planetary rollers 30 in turn, and the protrusions 41 of the two ring members 40 are fitted into the recesses 50, 51 of each planetary roller.

[0082] Then, in the same manner as for the one side described above, the retainer 20 is fitted into the fitting recess (other-end fitting recess 17) formed in the other end (other end 10b) of the nut 10. At this time, since the eight planetary rollers 30 are already inserted into the interior 10c of the nut 10, the other-end shaft portions 30d of the planetary rollers 30 are inserted into the respective holding through-holes 24 of the retainer 20 fitted into the other-end fitting recess 17.

[0083] As described above, each retaining through-hole 24 of the retainer 20 has an elliptical shape in the normal direction. Therefore, the opening area of ​​the retaining through-hole 24 is larger than the cross-sectional area of ​​the other-end shaft portion 30d of the planetary roller 30. Furthermore, even if the planetary roller 30 is tilted along the major axis of the elliptical shape, the other-end shaft portion 30d can be easily inserted into the retaining through-hole 24. Therefore, even if there are eight planetary rollers 80, a certain degree of ease in attaching the retainer 20 on the other end side can be ensured, which is also advantageous in terms of ease of assembly. When the retainer 20 is attached to the other-end fitting recess 17, a snap ring 5 is fitted into the groove on the other side (other-end groove 17a) in the same way as the side of the one end 10a described above, to prevent the retainer 20 fitted into the other-end fitting recess 17 from falling out.

[0084] Finally, the screw shaft 2 is inserted through the central through-hole 23 of the retainer 20 fitted into one end 10a of the nut 10 and is screwed in while rotating it clockwise. As the screwing is continued in this manner, the screw grooves 2a of the screw shaft 2 mesh with the screw grooves 37 of the eight planetary rollers 30 rotatably held in the nut 10. When the screw shaft 2 is further screwed in while being rotated, the screw shaft 2 comes outward from the through-hole 23 of the retainer 20 fitted into the other end 10b of the nut 10, and the planetary roller screw device 1 is thus completed.

[0085] 2 and 3, in the completed planetary roller screw device 1, the shaft portions 30c, 30d at both ends of each planetary roller 30 are inserted into the retaining through-holes 24 of the retainers 20 attached to both ends of the nut 10, and the planetary rollers 30 are rotatably held by the nut 10, and the screw grooves 37 of each planetary roller 30 are threadedly engaged with the screw grooves 2a of the screw shaft 2, but the first groove portions 36 and second groove portions 38 of each planetary roller 30 do not contact the screw shaft 2, and a gap is generated between them. This is because, as described above, the diameters (first outer diameter d1, third outer diameter d3) of the first region 31 and the third region 33 in which the first groove portions 36 and the second groove portions 38 are formed in the planetary roller 30 are smaller than the diameter (second outer diameter d2) of the second region 32 in which the screw groove 37 is formed.

[0086] On the other hand, the first groove portion 36 and the second groove portion 38 of each planetary roller 30 are in mesh with the first inner circumferential groove portion 16 and the second inner circumferential groove portion 18 of the nut 10, but the thread groove 37 of each planetary roller 30 is not in contact with the second inner circumferential surface 12a of the nut 10, and a gap is generated between them. This is because, as described above, in the interior 10c of the nut 10, the second inner diameter D2 of the second inner circumferential surface 12a is larger than the first inner diameter D1 and the third inner diameter D3 of the first inner circumferential range 11 and the third inner circumferential range 13 in which the first groove portion 36 and the second groove portion 38 are formed.

[0087] 9, the protrusions 41 of the ring member 40 fitted into the first ring groove 15 of the nut 10 fit into and mesh with the recesses 50 recessed in the outer peripheral surface 34a of the one-side portion 34 of each planetary roller 30. Although not shown in FIG. 9, the same is true for the recesses 51 of the other-side portion 35 of each planetary roller 30 and the protrusions 41 of the ring member 40 fitted into the second ring groove 19 of the nut 10, with the protrusions 41 fitting into and meshing with the recesses 51.

[0088] Next, the operation of the planetary roller screw device 1 completed as described above will be described with reference to Figure 10 etc. First, when the central screw shaft 2 is rotated in one direction (for example, clockwise rotation) by some kind of drive source (for example, a servo motor), the surrounding planetary rollers 30 that are threaded onto the screw shaft 2 rotate in the other direction (for example, counterclockwise rotation). In this way, the rotation of the screw shaft 2 is transmitted to the planetary rollers 30 arranged around the screw shaft 2, and with each rotation of the screw shaft 2, the positions of the screw shaft 2 and each planetary roller 30 in the X-axis direction are displaced relative to each other by the pitch of the screw groove 2a.

[0089] Furthermore, each planetary roller 30 and nut 10 has a first groove portion 36 and a second groove portion 38 meshed with the first inner circumferential groove portion 16 and the second inner circumferential groove portion 18, and since these are parallel grooves (straight grooves), even when each planetary roller 30 rotates, the relative positions of each planetary roller 30 and nut 10 in the X-axis direction do not change.

[0090] Therefore, as described above, when the relative positions of the screw shaft 2 and each planetary roller 30 in the X-axis direction are displaced due to rotation of the central screw shaft 2, the relative position of the nut 10 in the X-axis direction to the screw shaft 2 is also displaced, just like each planetary roller 30, and when viewed from the outside, the planetary roller screw device 1 can be operated in such a way that the rotation of the central screw shaft 2 causes the nut 10 to move linearly in the X-axis direction.

[0091] As each planetary roller 30 rotates, the ring member 40 rotates slowly in the same direction as the screw shaft 2 as the recesses 50, 51 of each planetary roller 30 engage with the protrusions 41, but the nut 10 does not generally rotate.

[0092] In the above operating conditions, each planetary roller 30 rotates while the protrusions 41 of the two ring members 40 fit into the recesses 50, 51 of each planetary roller 30, thereby restricting the rotational state of each planetary roller 30 to be similar and synchronizing the rotation of each planetary roller 30. This prevents the rotation of some of the eight planetary rollers 30 from shifting from the other planetary rollers 30, causing misalignment and other problems that could result in poor operation of the device.

[0093] In particular, in this embodiment, each planetary roller 30 is engaged with the convex portions 41 of the two ring members 40 attached to the nut 10 at two recesses 50, 51, one on one side 34 and the other on the other side 35, so that the rotational condition is regulated evenly and in a balanced manner along the X-axis direction, reliably preventing problems such as twisting.

[0094] Furthermore, as shown in Figure 6(c) etc., in this embodiment, each recess 50, 51 has a wide opening 50d, 51d of an inverted trapezoidal shape, and the protrusion 41 has a hemispherically curved surface, so that as the planetary roller 30 rotates, the protrusion 41 is smoothly guided into each recess 50, 51 and easily fits therein.

[0095] Furthermore, as the planetary rollers 30 rotate, the curved surfaces of the hemispherical convex portions 41 that have entered the concave portions 50, 51 successively come into contact with the slopes 50b, 51b on one side, the bases 50a, 51a, and the slopes 50c, 51c on the other side of the concave portions 50, 51. This contact is point contact due to the hemispherical shape of the convex portions 41, so the contact pressure is concentrated and a predetermined pressing force is generated, which serves as a restricting force sufficient to synchronize the rotation of the planetary rollers 30. As described above, the ring members 40 are rotatably arranged and attached within the ring grooves 15, 19 of the nut 10, and therefore the occurrence of a situation in which the meshing force between the convex portions 40 and the concave portions 50, 51 becomes too strong can be alleviated by rotating the ring members 40. This eliminates the need to keep the numerical ratio between the diameter of the screw shaft and the diameter of the planetary rollers constant, improving the degree of freedom in setting the dimensions of the screw shaft 2 and the planetary rollers 30 and making it easier to manufacture planetary roller screw devices 1 of various sizes.

[0096] In this way, the planetary roller screw device 1 of this embodiment can synchronize the rotation of each planetary roller 30 without using a strict transmission mechanism such as gears, and by not using gears, it is possible to introduce rolling or the like into the processing of each planetary roller 30, thereby reducing manufacturing costs. Another advantage is that the planetary roller screw device 1 can be made easier to assemble by devising the shapes of the retainer 20, the protrusions 41, the recesses 50, 51, etc.

[0097] The present invention is not limited to the above-described embodiment, and various modifications are contemplated. For example, in the above-described embodiment, the ring member 40 is made of a flexible synthetic resin, but the material is not limited to synthetic resin. Any other flexible material may be used. For example, the ring member 40 may be made of a metal material. If a metal material is used for the ring member 40, it is also conceivable that the ring member 40 is rigidly attached by fitting it into the interior 10c of the nut 10.

[0098] 11 shows a modified planetary roller 130. The planetary roller 130 of this modified example is characterized in that the recessed portion 150 recessed in the outer peripheral surface 134a of the one-side portion 134 and the recessed portion 151 recessed in the outer peripheral surface 135a of the other-side portion 135 are recessed and recessed in a hemispherical shape similar to the protruding portion 41 of the ring member 40. Note that this modified example is similar to the embodiment described above (the embodiment shown in FIGS. 1-10, etc.) in all respects except for the recessed portions 150 and 151.

[0099] As an example, these recesses 150, 151 are recessed in a hemispherical shape with a radius of approximately 0.5 mm, which gives them the same size as the protrusion 41 that protrudes from the inner surface 40a of the ring member 40 (strictly speaking, the recesses 150, 151 are made slightly larger than the protrusion 41 by approximately a plus tolerance), so that the protrusion 41 fits snugly into the recesses 150, 151 (see Figure 12).

[0100] As also shown in Figure 12, when the hemispherical convex portion 41 fits snugly into the hemispherical recessed portions 150, 151, the area over which the outer surface of the convex portion 41 comes into contact with the inner surface of the recessed portions 150, 151 is wider than in the case of the recessed portions 50, 51 in the above-mentioned embodiment, so that the contact pressure between the two can be dispersed when the convex portion 41 is fitted into the recessed portions 150, 151, thereby reducing wear mainly on the convex portion 41, making this modified example an ideal example for ensuring stable operation over a long period of time.

[0101] 13(a)-(d) show a modified ring member 140. The ring member 140 of this modified example is characterized in that the convex portion 141 is not hemispherical but tapered (a tapered shape different from the gear tooth shape) and has a quadrangular pyramidal shape projecting from the inner peripheral surface 140a. Note that this modified example is similar to the above-described embodiment (the embodiment shown in FIGS. 1-10, etc.) except for the convex portion 140.

[0102] As an example, this convex portion 141 has a square convex base 141a that protrudes from the inner surface 140a, with one side having a length of approximately 1.2 mm and a height of approximately 0.5 mm, and one pair of opposing sides of the square convex base 141a is provided with convex portion 141 that is oriented parallel to the X-axis when ring member 140 is attached to nut 10 (note that the other pair of opposing sides of convex base 141a becomes parallel to the Z-axis when ring member 140 is attached to nut 10).

[0103] The quadrangular pyramidal convex portion 141 has a tapered shape from the directions of the four sides of the convex base 141a toward the apex 141b, and therefore the outer peripheral surface of the convex portion 141 forms a slope that slopes from the four sides of the convex base 141a to the apex 141b. Therefore, when fitting each planetary roller 30 into the interior 10c of the nut 10 during device assembly, once the apex 141b of the convex portion 141 enters the openings 50d, 51d of the recesses 50, 51 of each planetary roller 30, the slope of the convex portion 141 slides smoothly into the recesses 50, 51, making it easier for the entire convex portion 141 to fit into the recesses 50, 51, which has the advantage of further improving ease of assembly.

[0104] Furthermore, as shown in Figure 14, when the device is in operation, as each planetary roller 30 rotates, the convex portions 141 that fit into the concave portions 50, 51 switch sequentially in the circumferential direction, and the inclined surfaces 50b, 50c (see Figure 6(c) etc.) of the inverted trapezoidal concave portions 50, 51 and the inclined surface of the outer circumferential surface of the convex portion 141 work together to smoothly switch the meshing between the two without interfering with each other, thereby ensuring good operating conditions.

[0105] In particular, in this modified example, as the convex portion 141 enters the concave portion 50, 51 due to the rotation of each planetary roller 30, one of the inclined surfaces of the convex portion 141 comes into contact with one of the inclined surfaces of the concave portion 50, 51 (e.g., inclined surface 50b, 51b), and a contact state between the surfaces is obtained depending on the rotation state of each planetary roller 30. Furthermore, as the rotation of each planetary roller 30 progresses, the top 141b of the convex portion 141 comes into contact with the bottom surface 50a, 51a of the concave portion 50, 51, and as the rotation of each planetary roller 30 continues, the other inclined surface on the opposite side of the convex portion 141 comes into contact with the other inclined surface of the concave portion 50 (e.g., inclined surface 50c, 51c). By ensuring such a contact state, even in this modified example, it is possible to exert the regulating force necessary to synchronize the rotation of each planetary roller 30.

[0106] Figure 15 shows yet another modified example, which is an example in which the modified planetary roller 130 (having hemispherical recesses 150, 151) shown in Figure 11 is combined with the modified ring member 141 (having quadrangular pyramidal protrusions 141) shown in Figure 13. Note that this modified example is similar to the above-described embodiment (the embodiment shown in Figures 1-10, etc.) except for using the modified planetary rollers 130 and ring member 141.

[0107] In this modified example, recesses 150, 151 have hemispherical inner surfaces, while pyramidal protrusion 141 has a slope. Therefore, when assembling the device, tapered top 141b of pyramidal protrusion 141 can easily fit smoothly into hemispherical recesses 150, 151, whose openings are wider than those near the bottom, and a certain degree of ease of assembly can be ensured even with this modified example.

[0108] Similarly, during operation of the device, as each planetary roller 130 of the modified example rotates, the protrusions 141 that fit into the recesses 150, 151 are guided sequentially by the hemispherical inner peripheral surfaces of the recesses 150, 151, and can be smoothly guided into the interior of the recesses, which helps the protrusions 141 to continuously mesh with the recesses 150, 151. Furthermore, in addition to guiding the recesses 150, 151 during the assembling and operation of the device as described above, the presence of an inclined surface on the quadrangular pyramidal protrusion 141 also helps to insert the protrusions 141 into the interior of the recesses 150, 151.

[0109] Furthermore, the tapered convex portions 41, 141 protruding from the inner peripheral surfaces 40a, 140a of the ring members 40, 140 may have the above-mentioned shapes (hemispherical, square pyramidal), or may have a truncated square pyramid shape with the apex of the pyramid parallel to the base, or a conical or truncated circular cone shape. Similarly, the concave portions 50, 51, 150, 151 recessed into the planetary rollers 30, 130 may have an inverted truncated square pyramid shape, an inverted cone shape, an inverted truncated circular cone shape, or the like.

[0110] Furthermore, although specific numerical values ​​are shown for the dimensions in the above-described embodiment shown in Figures 1 to 10 etc., it goes without saying that the present invention is not limited to such numerical values, and each numerical value can be changed as appropriate depending on the required size of the planetary roller screw device 1.

[0111] For example, when manufacturing a large planetary roller screw device 1, dimensions larger than the numerical values ​​of the above-described embodiment (the embodiment shown in FIGS. 1-10, etc.) will be used, and when the diameter of the central screw shaft 2 is increased, it is possible to use more than eight planetary rollers 30, 130. Furthermore, when the dimension of the nut 10 along the X-axis direction is increased, it is also possible to use more than two ring members 40, 140, and when the number of ring members 40 is increased in this way, recesses 50, 51, 150, 151 will be formed in the outer peripheral surfaces of the planetary rollers 30, 130 facing the locations where the ring members 40 are attached.

[0112] Specifically, when four ring members 40 are used, in addition to the recess 50 in the one-side portion 34 and the recess 51 in the other-side portion 35 shown in Figure 6(a), it is conceivable to form a third recess in the outer peripheral surface of a partial portion adjacent to the one-end shank portion 30c in the first region 31, and a fourth recess in the outer peripheral surface of a partial portion adjacent to the other-end shank portion 30d in the third region 33. In this case, in addition to the first ring groove 15 and the second ring groove 19 of the nut 10, two additional ring grooves are formed on the inner peripheral surface 10d thereof so that four ring members 40 can be attached so as to face the recessed portions.

[0113] On the other hand, when manufacturing a small-sized planetary roller screw device 1, dimensions smaller than the numerical values ​​of the above-described embodiment (the embodiment shown in FIGS. 1-10, etc.) will be used, and when the diameter of the central screw shaft 2 is reduced, it is possible to reduce the number of planetary rollers 30 to less than eight (when the diameter of the central screw shaft 1 is very small, it is possible to reduce the number of planetary rollers 30 to a minimum of two). Also, when shortening the dimension of the nut 10 along the X-axis direction, it is possible to use only one ring member 40, and when there is only one ring member 40, the planetary roller 30 will have a recess 50 only at the location of its outer circumferential surface facing the ring member 40.

[0114] Furthermore, the mechanism for synchronizing the rotation of the planetary rollers 30 by meshing the convex portions 41 protruding from the inner peripheral surface 40a of the ring member 40 with the concave portions 50 recessed in the outer peripheral surfaces of the planetary rollers 30 according to the present invention can also be applied to planetary roller screw devices of a conventional structure (planetary roller screw devices that include a screw shaft, a plurality of planetary rollers arranged parallel to the screw shaft and threadedly engaged with the screw shaft, and a nut rotatably enclosing the plurality of planetary rollers, such that rotation of the screw shaft is transmitted to the plurality of planetary rollers, causing the nut to move linearly along the screw shaft). For example, in the planetary roller screw devices shown in Patent Documents 1 to 5 mentioned above, it is also possible to use a rotation transmission mechanism in which the convex portions 41 of the ring member 40 according to the present invention mesh with the concave portions 50, 51 of the planetary rollers 30 instead of the gear transmission mechanism used in those devices. Note that the various modified examples described above can also be used in combination as appropriate. [Industrial Applicability]

[0115] The present invention can be suitably used to facilitate assembly and reduce manufacturing costs by eliminating the need to use a strict rotation mechanism such as a gear transmission mechanism to synchronize the rotation of each planetary roller in a planetary roller screw device. [Explanation of symbols]

[0116] 1 Planetary roller screw device 2 screw shaft 5 Retaining ring 10 nuts 11 First inner circumference range 12 Second inner circumference range 13 Third inner circumference range 15 First ring groove 16 First inner groove 18 Second inner groove 19 Second ring groove 20 retainer 21 Outer part 22 Inner part 23 Center through hole 24 Retention through hole 30, 130 Planetary roller 31 First Range 32 Second Range 33 Third Range 34 One side 35 Other side 36 First groove 37 Thread groove 38 Second groove 40, 140 Ring members 41, 141 convex part 50, 51, 150, 151 recesses

Claims

1. A planetary roller screw device comprising: a screw shaft; a plurality of planetary rollers arranged around the screw shaft and screwed with the screw shaft; and a nut rotatably containing the plurality of planetary rollers; wherein rotation of the screw shaft is transmitted to the plurality of planetary rollers, thereby causing the nut to move linearly along the screw shaft; a ring member disposed inside the nut so as to surround the plurality of planetary rollers; The ring member has a plurality of tapered projections formed on its inner peripheral surface along the circumferential direction, the projections having a shape different from that of gear teeth, The planetary rollers each have a plurality of recesses formed on their outer peripheral surfaces at locations facing the inner peripheral surface of the ring member, into which the protrusions can be fitted, a planetary roller screw device characterized in that the plurality of planetary rollers rotate while the convex portions of the ring member fit into the concave portions of the plurality of planetary rollers, thereby synchronizing the rotation of the plurality of planetary rollers.

2. A plurality of the ring members are disposed inside the nut, 2. The planetary roller screw device according to claim 1, wherein the recesses are formed on the outer peripheral surfaces of the plurality of planetary rollers at locations facing the inner peripheral surfaces of the plurality of ring members.

3. The two ring members are disposed inside the nut, Each of the plurality of planetary rollers has a first range, a second range, and a third range from one end to the other end, The second area has a larger diameter than the first area and the third area, and a screw groove that screws onto the screw shaft is formed on its outer circumferential surface, In the first region, the recess is formed so as to face the inner peripheral surface of one of the two ring members, and the recess is formed in the outer peripheral surface of the portion facing the inner peripheral surface of the one ring member, 2. The planetary roller screw device according to claim 1, wherein the third region faces the inner peripheral surface of the other of the two ring members, and the recess is formed on the outer peripheral surface at a location facing the inner peripheral surface of the other ring member.

4. The convex portion is formed in a hemispherical convex shape, 4. The planetary roller screw device according to claim 1, wherein the recessed portion is formed in an inverted trapezoidal shape in a cross section perpendicular to the rotational axis direction of the planetary roller.

5. The convex portion is formed in a hemispherical convex shape, 4. The planetary roller screw device according to claim 1, wherein the recess is recessed in a shape equivalent to the hemisphere.

6. The convex portion is formed in a quadrangular pyramidal shape, 4. The planetary roller screw device according to claim 1, wherein the recessed portion is formed in an inverted trapezoidal shape in a cross section perpendicular to the rotational axis direction of the planetary roller.

7. The convex portion is formed in a quadrangular pyramidal shape, 4. The planetary roller screw device according to claim 1, wherein the recess is formed in a hemispherical recess shape.

8. A disk-shaped retainer having a plurality of through holes formed therein is attached to both ends of the nut, each of the plurality of planetary rollers is rotatably held by the nut by inserting a shaft portion at each end of the planetary roller into a through hole of the retainer, The through hole has an elongated hole shape with a radial direction of the retainer as a longitudinal direction, 4. The planetary roller screw device according to claim 1, wherein an outer portion of the retainer that is on the outer side when attached to the nut has a smaller diameter in its thickness direction than an inner portion of the retainer that is on the inner side when attached to the nut, so that the depth of the through hole in a range that includes the outer hole end has a dimension that corresponds to the thickness of the inner portion.

9. 4. The planetary roller screw device according to claim 1, wherein the ring member is made of a flexible synthetic resin and is rotatable inside the nut.

Images