Linear motion unit and electric actuator

Abstract

To provide an electric actuator capable of effectively sliding a load by a ball by using a bearing for a linear motion member, and capable of inexpensively improving rigidity of a table.SOLUTION: An electric actuator of the present invention includes a slider 50 including a base portion having two linear bush shafts 40, and a slider main body having left and right linear bushes 60 attached to the two linear bush shafts 40, wherein one of the linear bushes 60 is attached to a linear bush attachment hole without a gap in a horizontal direction and a vertical direction, and the other linear bush 60 is provided to be movable in the horizontal direction without a gap in the vertical direction with respect to the linear bush attachment hole.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a linear motion unit and an electric actuator. [Background technology]

[0002] Conventionally, linear motion units of linear motion rolling guides having one row of balls on each side have been proposed that have a structure in which rolling elements contact each raceway groove on both sides of the casing and track rail.Furthermore, there is also a structure in which rolling elements contact the raceway surface on one side at four points and the raceway surface on the other side at two points (Patent Document 1).

[0003] In this structure, by setting the number of surfaces where the rolling elements come into contact with the raceway surface according to the direction of the load applied to the slider, it is possible to allow for machining errors in the raceway grooves and ensure a margin of machining accuracy. Another advantage is that the slider can slide smoothly on the track rail even when the slider slides on the track rail with an unbalanced load applied to the casing.

[0004] However, with the above-mentioned sliding structure, the load input to the table is held by the balls that contact the raceway surface at a 45-degree angle, so if a load is applied to the table from above or below or from the left or right, the load cannot be efficiently received. Also, assembly is difficult because the slider, casing, and balls must be assembled separately, and the need to ensure dimensional precision for each part increases the cost. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-141416 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] The present invention has been made in light of these problems, and aims to provide a linear motion unit and an electric actuator that can efficiently receive the balls that slide against the load applied to the table using a bearing for a linear motion component (hereinafter referred to as a "linear bushing"), and that can reduce the occurrence of rattle that occurs in the horizontal direction of the slider in particular. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention employs the following means.

[0008] The linear motion unit according to the present invention comprises: a base portion formed in a cylindrical shape with an open top, having a screw shaft for a feed screw or ball screw connected to an electric motor, and two linear bushing shafts each having a connecting portion connected to a left wall surface or a right wall surface; a slider having left and right linear bushings attached to the two linear bushing shafts, and a slider body having left and right linear bushing attachment holes to which the linear bushings are respectively attached; Equipped with the linear bushings include a left linear bushing having an opening portion disposed so that the left side thereof is open relative to the slider, and a right linear bushing having an opening portion disposed so that the right side thereof is open, One of the linear bushings is attached to the linear bushing attachment hole without gaps in the horizontal and vertical directions, and has at least three rows of balls, one on each side of the linear bushing, arranged in a range of 15° to 25° from the center vertical direction of the linear bushing on the wall surface side to which the linear bushing shaft is attached, and one on each side of the linear bushing within 20° above the center horizontal, The other linear bushing is characterized in that it is provided with no gap in the vertical direction relative to the linear bushing mounting hole and is movable in the horizontal direction.

[0009] The linear motion unit of the present invention uses commercially available linear bushings in a linear motion guide, with ball contact points at two upper, two lower, one right, and one left. This allows the sliding balls to efficiently support the load applied to the table, thereby increasing the rigidity of the table. However, in a linear motion unit with a slider in which linear bushings are attached to two linear bushing shafts with connecting parts connected to the left or right wall of the base, it is easy to ensure accuracy in the vertical direction, but it is difficult to ensure accuracy in the pitch between the left and right linear bushing shafts of the base. As a result, gaps may occur between the balls of the left and right linear bushings and the linear bushing shafts, or they may interfere with each other, causing sliding resistance. Therefore, the present invention eliminates pitch misalignment and prevents rattle by adjusting the arrangement of the ball rows serving as rolling elements in the linear bushings, moving one linear bushing and the linear bushing shaft horizontally without rattle, and changing the relative horizontal position between the other linear bushing and the linear bushing mounting hole.

[0010] Furthermore, in the linear motion unit according to the present invention, the arrangement of the three ball rows of the other linear bushing may be such that one is disposed on each of the upper and lower sides of the linear bushing on the wall surface side where the linear bushing shaft is attached within a range of 15° to 25° relative to the vertical direction at the center of the linear bushing, and one is disposed within 20° above the horizontal center.By preventing rattle between the other linear bushing and the linear bushing shaft, horizontal rattle can be absorbed only by horizontal movement of the other linear bushing and the linear bushing attachment hole, making it possible to prevent rattle even more efficiently.

[0011] Furthermore, in the linear motion unit according to the present invention, the other linear bushing may be characterized by having gaps on the left and right sides with respect to the linear bushing mounting hole. By providing gaps on the left and right sides in advance, even if the pitch misalignment between the two linear bushing shafts is in either the direction of narrowing or widening relative to each other, the pitch misalignment can be effectively absorbed and horizontal rattle can be prevented.

[0012] Furthermore, in the linear motion unit according to the present invention, the cross section of the linear bushing mounting hole may be formed into an ellipse so that the linear bushing can move horizontally by 0.1 mm to 0.4 mm.

[0013] The present invention also provides an electric actuator comprising the linear motion unit described above and an electric motor as a drive source, thereby providing the above-described effects. [Effects of the Invention]

[0014] The linear motion unit and electric actuator of the present invention can provide an electric actuator that can use linear bushings to effectively slide a load with balls and inexpensively improve the rigidity of the table. Also, by making it possible to change the relative horizontal position between the other linear bushing and the linear bushing mounting hole, pitch deviation can be eliminated and rattle can be prevented. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing an electric actuator 100 according to an embodiment. [Figure 2] FIG. 2 is a perspective view showing the internal structure of the electric actuator 100 according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the electric actuator 100 according to the embodiment taken along line AA. [Figure 4] FIG. 4 is a cross-sectional view of the base frame 26 according to the embodiment. [Figure 5] FIG. 5 is a perspective view of a slider 50 according to the embodiment. [Figure 6] FIG. 6 is a perspective view of a slider body 59 according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments and drawings described below exemplify some of the embodiments of the present invention and are not intended to limit the configurations of these embodiments. Corresponding components in each drawing are denoted by the same or similar reference numerals. Note that in the present invention, "up and down," "front and back," and "left and right" refer to the directions shown in FIG. 1.

[0017] FIG. 1 shows a perspective view of an electric actuator 100 according to this embodiment. FIG. 2 shows a perspective view illustrating the internal structure of the electric actuator 100. FIG. 3 shows a cross-sectional view of the electric actuator 100 taken along line AA (the cross-sectional line has been omitted to ensure visibility). As shown in FIG. 2, the electric actuator 100 mainly comprises an electric motor 10 and a linear motion unit comprising a screw shaft 30, a linear bushing shaft 40, and a slider 50, which are arranged within a base portion 20. The linear motion unit is a mechanical element that converts the rotational motion of the electric actuator 100 into linear motion, and the difference lies in whether or not its operation can be directly controlled by the electric motor 10. Therefore, the description of the linear motion unit will be replaced by the description of the electric actuator 100.

[0018] The electric motor 10 is a motor that rotates the screw shaft 30 of a feed screw or ball screw. There are no particular limitations on the type of motor, but it is preferable to use a stepping motor or servo motor that can precisely control the angle and rotation speed.

[0019] The base portion 20 is made of a long member having a hollow portion 25 inside, and has a base frame 26 (see Figure 4) having a linear bushing shaft 40, and a screw shaft 30 connected to an electric motor 10 arranged inside this base frame 26, with a slider 50 arranged inside.

[0020] The screw shaft 30 is a threaded shaft that is used to move the slider 50 via a nut portion 52 provided on the slider 50. The screw shaft 30 is connected to the electric motor 10 and is provided over the entire length of the base portion 20 of the electric actuator 100 in the longitudinal direction (front-rear direction). By rotating this screw shaft 30, the slider 50 can be moved in the front-rear direction.

[0021] The linear bushing shafts 40 are shafts arranged inside the linear bushing 60, and two are provided along the longitudinal direction of the base portion 20. As shown in FIG. 3, these linear bushing shafts 40 are formed in a substantially cylindrical shape, and each side surface is connected over its entire length to the right inner wall 21 or left inner wall 22 of the base frame 26 by connecting portions 45. This ensures high rigidity, unlike when the linear bushing shafts 40 do not have connecting portions 45 and are arranged in a hollow rod shape.

[0022] As shown in FIG. 3, the slider 50 is disposed so as to form a gap with the inner wall of the hollow portion 25 of the base frame 26, and is disposed so as to be slidable back and forth within the hollow portion 25. As shown in FIG. 5, the slider 50 includes a nut portion 52 (threading grooves are omitted) that screws onto the screw shaft 30, left and right linear bushings 60 formed so as to insert the linear bushing shafts 40 described above, and a table mounting portion 80 formed on the upper surface of the base frame 26 and connected to the slider 50. As shown in FIG. 6, a linear bushing mounting hole 54 into which the linear bushing 60 can be inserted is provided in the slider body 59, and the linear bushing 60 is mounted in this linear bushing mounting hole 54. The relationship between the linear bushing mounting hole 54 and the linear bushing 60 will be described later. As shown in FIG. 3, the slider 50 is disposed in the hollow portion 25, with the screw shaft 30 inserted through the nut portion 52 and the linear bushing shaft 40 inserted through the linear bushing 60.

[0023] The nut portion 52 is threadedly engaged with the screw shaft 30 and constitutes a feed screw or ball screw mechanism together with the screw shaft 30. When the screw shaft 30 is rotated by the electric motor 10, the nut portion 52 converts the rotation into linear motion in the longitudinal direction of the base portion 20, moving the slider 50 over the entire length of the base portion 20.

[0024] The linear bushing 60 is a bearing for a linear motion member, and in this embodiment, an open-type linear bushing 60 having at least three rows of balls is used. The linear bushing 60 has a cylindrical cross section with an open portion 64 for passing the connecting portion 45 of the linear bushing shaft 40. As shown in FIG. 5 , the linear bushing 60 includes a left linear bushing 60a arranged so that the open portion 64 is open to the left relative to the slider 50, and a right linear bushing 60b arranged so that the open portion 64 is open to the right. Furthermore, the linear bushing shaft 40 is inserted into each linear bushing 60, and the connecting portion 45 that connects the linear bushing shaft 40 and the base portion 20 is provided so that it is positioned in the open portion 64.

[0025] As shown in Fig. 3, at least three rows of balls 61 are arranged in the linear bushing 60. At least one or both of the three rows of balls 61 in the left linear bushing 60a or the right linear bushing 60b are arranged as follows. 1. The three rows of balls in the left linear bushing 60a are arranged as follows: A position above the center of the cross section of the linear bushing 60 where the angle A1 between the vertical direction V1 of the cross section center and the center of the ball 61 is within a range of 15° to 25° (upper ball row 61a). A position below the center of the cross section of the linear bushing 60, where the angle A2 between the vertical direction V1 of the cross section center and the center of the ball 61 is within a range of 15° to 25° (lower ball row 61b). A position to the right of the center of the cross section of the linear bushing 60, where the angle A3 between the horizontal direction H1 of the center of the cross section of the linear bushing 60 and the center of the ball 61 is in the range of 0° to 25° upward (the central ball row 61c). 2. The three rows of balls in the right linear bushing 60b are arranged symmetrically with respect to the center perpendicular line V3 of the slider cross section in the case of the left linear bushing. Specifically, they are arranged as follows: A position above the center of the cross section of the linear bushing 60 where the angle A4 between the vertical direction V2 of the cross section center and the center of the ball 61 is within the range of 15° to 25° (upper ball row). A position below the center of the cross section of the linear bushing 60 where the angle A5 between the vertical direction V2 of the cross section center and the center of the ball 61 is within a range of 15° to 25° (lower ball row). A position to the left of the center of the cross section of the linear bushing, where the angle A6 between the horizontal direction H1 of the center of the cross section of the linear bushing 60 and the center of the ball 61 is in the range of 0° to 25° upward (the central ball row).

[0026] As described above, by arranging the three rows of balls 61, for example, when the left linear bushing 60a side is arranged as described above, the linear bushing shaft 40 is pressed toward the center perpendicular V3 of the slider cross section (the right side in FIG. 3) by the upper ball row 61a and the lower ball row 61b, and is pressed toward the opposite wall surface (the left wall surface in FIG. 3) by the central ball row 61c. This prevents horizontal wobble between the left linear bushing 60a and the linear bushing shaft 40.

[0027] Furthermore, by arranging at least three rows of balls 61 in one linear bushing 60, two above and two below, and one in the horizontal direction, the four rows of balls 61 above and below the two linear bushings 60 can withstand a load in the vertical direction at an angle of 25° or less from the vertical, and in the horizontal direction, all three rows of balls (61a, 61b, and 61c) on the right and left linear bushings 60 can withstand a load in the center horizontal direction. Therefore, it has high rigidity against loads.

[0028] As described above, the linear bushing 60 on one side on which the three rows of balls 61 are arranged is press-fitted into the linear bushing mounting hole 54 so that there is no rattle in either the vertical or horizontal direction. Therefore, the linear bushing 60 is fixed to the slider 50 without moving up, down, left, or right.

[0029] The linear bushing 60 on the other side has a cross-sectional circle of the linear bushing mounting hole 54 into which it is mounted, which is made as an ellipse that is slightly longer in the horizontal direction, and when the linear bushing 60 is inserted, there is no gap in the vertical direction, but a gap α is provided so that it can move horizontally by approximately 0.1 mm to 0.4 mm in both directions toward the right wall surface and the left wall surface.

[0030] The electric actuator 100 and linear motion unit configured as described above absorb rattle and pitch deviation as follows. This example describes an example in which the left linear bushing 60a is one of the linear bushings, equipped with the aforementioned ball rows, and press-fitted with no gaps at all vertically or horizontally. The right linear bushing is the other linear bushing, with gaps on both horizontal sides, allowing for horizontal movement. Assuming the base frame 26 is manufactured by extrusion molding, as shown in FIG. 4, the vertical pitch E of the left linear bushing shaft 40 and the vertical pitch F of the right linear bushing shaft 40 are short, making it easy to achieve precision. However, the pitch G between the linear bushing shafts 40 is long, and because the extrusion molding results in a shape where the metal wraps around, even slight distortion can make it difficult to achieve precision. If the pitch G between the linear bushing shafts 40 is too wide, rattle will occur. If it is too narrow, the linear bushing 60 may not fit or significant friction may occur.

[0031] The left linear bushing 60a of the present invention moves according to the manufacturing precision of the linear bushing shaft 40 while the slider 50 moves back and forth, without changing its relative left-right position with respect to the left linear bushing shaft 40. On the other hand, for example, if the pitch G of the right linear bushing 60 becomes shorter, the linear bushing 60 moves to the left with respect to the linear bushing mounting hole 54 to eliminate pitch misalignment, and if the pitch G becomes longer, the linear bushing 60 moves to the right with respect to the linear bushing mounting hole 54 to eliminate pitch misalignment. In this way, the movement of the linear bushing 60 on the other side prevents gaps and interference, and prevents rattling.

[0032] In this embodiment, the above-mentioned three-row ball row arrangement can be achieved on only one of the linear bushings 60, but in order to more effectively absorb rattle and pitch deviation, it is preferable to arrange the above-mentioned three-row ball rows on both the left and right linear bushings 60.

[0033] 3, the upper and lower balls 61 arranged in the left linear bushing 60a and the upper and lower balls 61 arranged in the right linear bushing 60b are preferably arranged symmetrically with respect to the vertical center line V3 of the slider 50. By arranging them symmetrically in this way, a load applied to the table from above is more likely to be applied evenly to both sides, preventing uneven loads from being applied to one side. This prevents wear on only one side, and extends the life of the electric actuator 100.

[0034] The electric actuator 100 manufactured as described above can be manufactured easily and quickly by using a ready-made linear bushing 60 as the linear guide. Also, by using an open-type linear bushing 60 and connecting the linear bushing shaft 40 to the wall surface of the base portion 20, it is possible to effectively resist the load applied to the linear bushing shaft 40. Furthermore, by having the contact points of the balls 61 at two points above, two points below, one point to the right, and one point to the left, the load applied to the table can be efficiently supported by the sliding balls 61, thereby increasing the rigidity of the table.

[0035] Furthermore, even when a manufacturing method such as extrusion molding is used, which makes it more difficult to achieve dimensional accuracy compared to cutting, pitch deviations between the linear bushing shafts 40 can be effectively absorbed.

[0036] The electric actuator 100 as described above can be used not only in factories but also as a seat rail for vehicles. [Industrial Applicability]

[0037] As shown in the above-described embodiment, the present invention is industrially applicable as a seat rail device for a vehicle. [Explanation of symbols]

[0038] 10...electric motor, 20...base portion, 21...side wall, 22...left inner wall, 25...hollow portion, 26...base frame, 30...screw shaft, 40...linear bushing shaft, 45...connecting portion, 50...slider, 52...nut portion, 54...linear bushing mounting hole, 59...slider body, 60...linear bushing, 60a...left linear bushing, 60b...right linear bushing, 61...ball, 61a...ball row, 61b...ball row, 61c...ball row, 64...opening portion, 80...table mounting portion, 100...electric actuator

Claims

1. a base portion formed in a cylindrical shape with an open top, having a screw shaft for a feed screw or ball screw connected to an electric motor, and two linear bushing shafts each having a connecting portion connected to a left wall surface or a right wall surface; a slider including left and right linear bushings attached to the two linear bushing shafts, and a slider body having left and right linear bushing attachment holes to which the linear bushings are respectively attached; Equipped with the linear bushings include a left linear bushing that is disposed so that the left side of the opening portion is open relative to the slider, and a right linear bushing that is disposed so that the right side of the opening portion is open, one of the linear bushings is mounted in the linear bushing mounting hole without gaps in the horizontal and vertical directions, and has at least three rows of balls, one of which is disposed on the upper and lower sides of the linear bushing within a range of 15° to 25° on the wall surface side to which the linear bushing shaft is mounted relative to the vertical direction of the center of the linear bushing, and one of which is disposed in a range of 0° to 25° above the horizontal center; The linear motion unit is characterized in that the other linear bush is provided with no gap in the vertical direction relative to the linear bush mounting hole and is movable in the horizontal direction.

2. The linear motion unit described in claim 1, characterized in that the three ball rows of the other linear bush are arranged such that one is arranged on the upper and lower sides of the linear bush within a range of 15° to 25° on the wall surface side to which the linear bush shaft is attached relative to the center vertical direction of the linear bush, and one is arranged above the center horizontal within a range of 0° to 25°.

3. 3. The linear motion unit according to claim 2, wherein the other linear bushing has gaps on the left and right sides with respect to the linear bushing mounting hole.

4. 3. The linear motion unit according to claim 2, wherein the cross section of the linear bushing mounting hole is formed into an ellipse so that the linear bushing can move horizontally by 0.1 mm to 0.4 mm.

5. A linear motion unit according to any one of claims 1 to 3; An electric actuator comprising an electric motor as a drive source.

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