Linear actuator

Abstract

To reduce a pressure change in an internal space of a guide sleeve caused by reciprocating motion of a linear motion rod, and to protect the internal space from foreign matter.SOLUTION: The linear motion actuator includes a nut member which is linearly moved in accordance with rotation of the feed screw, a cylindrical linear motion rod which is linearly moved together with the nut member, a guide sleeve which guides the linear motion of the linear motion rod, and a piston which is linearly moved together with the linear motion rod. The rectilinearly movable rod has a first space. The internal space of the guide sleeve has a second space in which the rectilinearly movable rod and the nut member are not located. When the rectilinearly movable rod is in the retracted state, the volumes of the first space and the second space decrease, and when the rectilinearly movable rod is in the extended state, the volumes of the first space and the second space increase. When the rectilinearly movable rod is in the retracted state, the volume of the third space of the piston chamber increases, and when the rectilinearly movable rod is in the extended state, the volume of the third space decreases. The third space of the piston chamber communicates with the first space and the second space.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a linear actuator. [Background technology]

[0002] A linear actuator has been developed that includes a rotating feed screw, a linear motion member that moves linearly back and forth along the axial direction of the feed screw as the feed screw rotates, and a cylindrical member that surrounds the linear motion member (Patent Document 1). In such a linear motion actuator, the volume of the internal space of the cylindrical member changes as the linear motion member moves back and forth, and the pressure in the internal space also changes. If the pressure in the internal space decreases, there is a risk that moisture may enter the internal space from the outside.

[0003] In the technology described in Patent Document 1, through-holes are formed in the peripheral wall of a cylindrical member, and the through-holes allow air to flow in the internal space of the cylindrical member. When the through-holes are formed in the peripheral wall of the cylindrical member and are open to the atmosphere, the pressure in the internal space does not change. However, in this case, there is a risk that foreign matter (including water) may enter the internal space.

[0004] Therefore, in one technique described in Patent Document 1, a hose is attached to the through-hole via an air nipple. Another technology described in Patent Document 1 further includes a bellows that surrounds a cylindrical member including the periphery of the through hole, so that the internal volume of the bellows changes when the volume of the internal space changes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Utility Model Application Publication No. 05-004749 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a hose is attached to a through-hole formed in the peripheral wall of a cylindrical member via an air nipple, the internal space of the cylindrical member is protected from foreign matter, but the pressure in the internal space still changes.

[0007] Furthermore, if a bellows is provided surrounding the cylindrical member, when the linear motion member extends from the cylindrical member and the volume of the internal space increases, the bellows also extends, increasing the internal volume of the bellows, and when the linear motion member retracts into the cylindrical member and the volume of the internal space decreases, the bellows also contracts, decreasing the internal volume of the bellows. Therefore, the pressure in the internal space changes more significantly than if there were no bellows.

[0008] Changes in pressure in the internal space of a cylindrical member affect the thrust force that moves a linearly moving member. In other words, when the pressure in the internal space changes, the required thrust (required acceleration) to be applied to the linearly moving member becomes unstable. For example, in a control system that commands the thrust to be applied to the linearly moving member, the commanded thrust and the required thrust differ, and the actual movement amount of the linearly moving member differs from the target movement amount. Also, in a control system that commands the movement amount to be applied to the linearly moving member, the thrust that achieves the commanded movement amount differs from the required thrust, and the actual movement amount of the linearly moving member differs from the commanded movement amount.

[0009] Therefore, the present invention provides a linear motion actuator that can reduce pressure changes in the internal space of the guide sleeve caused by the reciprocating motion of the linear motion rod and can protect the internal space from foreign matter. [Means for solving the problem]

[0010] One aspect of the present invention provides a linear actuator. The linear actuator includes a rotatable lead screw, a nut member that is caused to reciprocate linearly along the axial direction of the lead screw as the lead screw rotates, a cylindrical linear rod that has a cylindrical first space into which at least a portion of the nut member is inserted and is fixed to the nut member and caused to reciprocate linearly together with the nut member, a guide sleeve that has a cylindrical internal space into which the linear rod is inserted and that guides the reciprocating linear motion of the linear rod, a piston that is connected to the linear rod and caused to reciprocate linearly together with the linear rod, and a piston chamber in which the piston is disposed. The linear rod is caused to reciprocate linearly between an extended state in which it is extended from the guide sleeve and a retracted state in which it is retracted within the guide sleeve as the nut member reciprocates linearly. When the linear rod is in the retracted state, the lead screw protrudes into the first space, thereby reducing the volume of the first space, and when the linear rod is in the extended state, the lead screw retracts from the first space, thereby increasing the volume of the first space. The internal space of the guide sleeve has a second space where the linear rod and the nut member are not located. When the linear rod is in the retracted state, the volume of the second space decreases, and when the linear rod is in the extended state, the volume of the second space increases. The piston chamber is divided into a third space and a fourth space by the piston. When the linear rod is in the retracted state, the volume of the third space increases, and when the linear rod is in the extended state, the volume of the third space decreases. When the linear rod is in the retracted state, the volume of the fourth space decreases, and when the linear rod is in the extended state, the volume of the fourth space increases. The fourth space of the piston chamber communicates with the atmospheric space outside the piston chamber. The third space of the piston chamber communicates with at least one of the first space of the direct acting rod and the second space of the guide sleeve, and the first space of the direct acting rod communicates with the second space of the guide sleeve. [Effects of the Invention]

[0011] In one embodiment of the present invention, the volumes of the first space in the linear rod inserted into the internal space of the guide sleeve and the second space, which is part of the internal space of the guide sleeve, change as the linear rod reciprocates. However, the third space in the piston chamber, in which the piston reciprocating linearly with the linear rod is disposed, is connected to at least one of the first space in the linear rod and the second space in the guide sleeve, and the first space is connected to the second space. Therefore, the volume of the third space changes simultaneously with the change in the volumes of the first and second spaces. The change in the volume of the third space is negatively correlated with the change in the volumes of the first and second spaces, reducing the change in pressure in the first and second spaces. This stabilizes the required thrust to be applied to the linear rod and improves the accuracy of the linear rod's movement. The first space, which is part of the internal space of the guide sleeve, and the second space, which is also part of the internal space of the guide sleeve, are connected to the third space of the piston chamber, but the first space and the second space are not directly connected to the atmosphere. Therefore, the first space and the second space can be sealed and protected from foreign matter. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing a linear motion actuator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the linear actuator of FIG. 1 in a retracted state. [Figure 3] FIG. 3 is a cross-sectional view showing the linear actuator of FIG. 1 in an extended state. [Figure 4] FIG. 4 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 5] FIG. 5 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 6] FIG. 6 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 7]FIG. 7 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 8] FIG. 8 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 9] FIG. 9 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 11] FIG. 11 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. [Figure 12] FIG. 12 is a cross-sectional view showing a linear motion actuator according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The drawings are not necessarily drawn to scale, and some features may be exaggerated or omitted.

[0014] As shown in Fig. 1, a linear motion actuator 1 according to an embodiment of the present invention has a gear transmission mechanism 2. The gear transmission mechanism 2 is driven by a motor 3. The motor 3 is, for example, a servo motor or a stepping motor.

[0015] The motor 3 has a rotating shaft 3a. The motor 3 is fixed to a bracket 6, and the rotating shaft 3a passes through a hole formed in an end wall 6a of the bracket 6. The bracket 6 is made of a rigid material such as metal or resin. The end wall 6a of the bracket 6 is fixed to a bottom wall 31a and a central wall 31b of a housing 31 of the linear motion actuator 1 with screws.

[0016] The gear transmission mechanism 2 is driven by a rotating shaft 3a of a motor 3. The gear transmission mechanism 2 has a first gear 7, a second gear 8, and a third gear 9. The first gear 7 is fixed to the rotating shaft 3a and rotates together with the rotating shaft 3a. For example, the first gear 7 is fixed to the rotating shaft 3a by a key 3b.

[0017] The second gear 8 meshes with the first gear 7 and is driven to rotate by the first gear 7. The second gear 8 is fixed to a rotating shaft 8a and rotates together with the rotating shaft 8a. For example, the second gear 8 is fixed to the rotating shaft 8a by a key 8b.

[0018] The rotating shaft 8a is rotatably supported by rolling bearings 10 and 11. The rolling bearing 10 is fixed to a central wall 31b of a housing 31 of the linear motion actuator 1, and the rolling bearing 11 is fixed to a cover 32.

[0019] The third gear 9 meshes with the second gear 8 and is driven to rotate by the second gear 8. The third gear 9 is fixed to a rotating shaft 9a and rotates together with the rotating shaft 9a. For example, the third gear 9 is fixed to the rotating shaft 9a by a key 9b.

[0020] In this embodiment, the rotary shaft 9a is the output shaft of the gear transmission mechanism 2, and the feed screw 34 of the linear motion actuator 1 is formed on an extension of the rotary shaft 9a.

[0021] The rotating shaft 9a is rotatably supported by rolling bearings 13 and 14. The rolling bearings 13 and 14 are supported by a bearing housing 15, which is fixed with screws to a central wall 31b and an upper wall 31c of a housing 31 of the linear motion actuator 1. The rolling bearings 13 and 14 are enclosed by the bearing housing 15 and a bearing cover 16. The bearing cover 16 is fixed to the bearing housing 15 with screws.

[0022] The linear motion actuator 1 includes the above-mentioned gear transmission mechanism 2, a housing 31, a cover 32, an end attachment portion 33, a feed screw 34, a nut member 35, a linear motion rod 36, and an end attachment portion 37.

[0023] The housing 31 is formed from a rigid material such as metal or resin, and has, in addition to the lower wall 31a, central wall 31b, and upper wall 31c, a cylindrical guide sleeve 38 that guides the linear motion of the linear motion rod 36, and a piston chamber wall 39. The guide sleeve 38 is integrally connected to the central wall 31b and the upper wall 31c. The piston chamber wall 39 is integrally connected to the guide sleeve 38 and the upper wall 31c. In this specification, the terms "lower wall 31a," "central wall 31b," and "upper wall 31c" are merely names used to facilitate understanding from the drawings, and are not intended to limit the orientation of the linear motion actuator 1 during use.

[0024] The cover 32 is made of a rigid material such as metal or resin and is fixed to the lower wall 31a and upper wall 31c of the housing 31 with screws, and together with the housing 31 and the bearing cover 16, defines a gear space 41 that surrounds the gear transmission mechanism 2. The cover 32 protects the spur gears 7, 8, 9 and other mechanical parts from foreign matter such as dust and water.

[0025] The end attachment portion 33 is integrally connected to the cover 32. The end attachment portion 33 is formed with a circular through-hole 33a.

[0026] The lead screw 34 is a part of the rotating shaft 9a of the third gear 9. The lead screw 34 is arranged coaxially with the guide sleeve 38. The lead screw 34 may be a trapezoidal screw, a ball screw (e.g., a circulating ball screw), or any of various roller screws. The roller screw may be, for example, a planetary roller screw, a circulating roller screw, or any other roller screw.

[0027] The nut member 35 is engaged with the feed screw 34. A part of the nut member 35 (body portion 35b) is inserted into the internal space of the linear motion rod 36. The head portion 35a of the nut member 35 is not inserted into the linear motion rod 36, but is fixed to the linear motion rod 36 with a screw.

[0028] The linear motion rod 36 is a cylindrical pipe made of a rigid material such as metal or resin. The linear motion rod 36 is arranged coaxially with the lead screw 34 and the guide sleeve 38. The linear motion rod 36 is inserted into the cylindrical internal space of the guide sleeve 38 and is capable of reciprocating movement along the axial direction of the linear motion rod 36. The lead screw 34 is arranged in the cylindrical internal space of the linear motion rod 36.

[0029] As will be described later, the linear motion rod 36 is restricted from rotating relative to the guide sleeve 38. Therefore, when the feed screw 34 rotates, the nut member 35 engaged with the feed screw 34 and the linear motion rod 36 fixed to the nut member 35 are moved linearly along the axial direction of the feed screw 34.

[0030] 2 shows the retracted state of the linear motion actuator 1 (more precisely, the retracted state of the linear motion rod 36). In this manner, the feed screw 34, which is an extension of the rotary shaft 9a, is rotated by the gear transmission mechanism 2, and the nut member 35 and the linear motion rod 36 are moved linearly in accordance with the rotation of the feed screw 34. In the retracted state, the linear motion rod 36 is retracted into the guide sleeve 38.

[0031] If the gear transmission mechanism 2 is rotated in the reverse direction, the linear motion rod 36 is extended, as opposed to the state shown in Figure 2. Figure 3 shows the linear motion actuator 1 in an extended state (more precisely, the extended state of the linear motion rod 36). In this way, as the feed screw 34 rotates, the linear motion rod 36 is caused to move back and forth linearly along the axial direction of the feed screw 34. In the extended state, the linear motion rod 36 extends from the guide sleeve 38.

[0032] The linear motion range (stroke) of the linear motion rod 36 is finite. Therefore, the motor 3 is controlled by a motor driver (not shown) so as to rotate within a finite angular range. In this way, the motor 3 is rotated within a finite angular range, and the gears 7, 8, and 9 of the gear transmission mechanism 2 also rotate within a limited angular range.

[0033] The linear motion rod 36, which is a cylindrical pipe, has an end wall 36a. The end mounting portion 37 is integrally connected to the end wall 36a of the linear motion rod 36. Therefore, the end mounting portion 37 can be considered to be part of the linear motion rod 36. A circular through hole 37a is formed in the end mounting portion 37.

[0034] The end mounting portion 33 and the end mounting portion 37 are attached to the equipment or structure (not shown) in which the linear actuator 1 is used. For example, the linear actuator 1 can be used for lateral vibration control of railway vehicles or other transportation equipment, or for lateral vibration control of buildings. In this case, one of the end mounting portions 33, 37 is attached to one side of the equipment or structure, and the other is attached to the other side of the equipment or structure.

[0035] Alternatively, the linear actuator 1 can be used as an electromagnetic suspension for transportation equipment or buildings, in which case one of the end mounting portions 33, 37 is attached to the top of the equipment or building and the other is attached to the bottom of the equipment or building.

[0036] By attaching the end attachment portion 37 to a device or a structure, the linear motion rod 36 to which the end attachment portion 37 is connected is restricted from rotating relative to the guide sleeve 38.

[0037] To facilitate the linear motion of the linear motion rod 36, a first plain bearing 42 and a second plain bearing 43 are interposed between the outer circumferential surface of the linear motion rod 36 and the inner circumferential surface of the guide sleeve 38. The plain bearings 42, 43 are, for example, cylindrical bushings. However, each of the plain bearings 42, 43 may also be a split plain bearing having multiple arc-shaped pieces. In either case, each of the plain bearings 42, 43 has a sealing function that seals the annular gap 49 between the inner circumferential surface of the guide sleeve 38 and the outer circumferential surface of the linear motion rod 36.

[0038] The first plain bearing 42 is disposed in a circumferential groove formed in the inner peripheral surface of the guide sleeve 38 and is stationary relative to the guide sleeve 38. The inner peripheral surface of the first plain bearing 42 is in slidable contact with the outer peripheral surface of the linear motion rod 36.

[0039] The second plain bearing 43 is disposed in a circumferential groove formed on the outer circumferential surface of the linear motion rod 36 and is stationary relative to the linear motion rod 36. The outer circumferential surface of the second plain bearing 43 is in slidable contact with the inner circumferential surface of the guide sleeve 38.

[0040] Next, a description will be given of the multiple spaces inside the guide sleeve 38. The volumes of these spaces change as the nut member 35 and the linear motion rod 36 move back and forth linearly.

[0041] First, the cylindrical linear motion rod 36 has a columnar space (first space) 46. The first space 46 is closed by an end wall 36a. A part of the nut member 35 is inserted into the first space 46.

[0042] Furthermore, a portion of the lead screw 34 engaged with the nut member 35 may be located within the first space 46. As shown in Fig. 2, when the linear motion rod 36 is in a retracted state, the lead screw 34 protrudes into the first space 46, thereby reducing the volume of the first space 46. As shown in Fig. 3, when the linear motion rod 36 is in an extended state, the lead screw 34 retracts from the first space 46, thereby increasing the volume of the first space 46.

[0043] The guide sleeve 38, which guides the reciprocating linear motion of the linear motion rod 36, has a cylindrical internal space. The cylindrical linear motion rod 36 and the nut member 35 fixed to the linear motion rod 36 are disposed in this internal space. The portion of the cylindrical internal space of the guide sleeve 38 where the linear motion rod 36 and the nut member 35 are not located is referred to as a second space 48.

[0044] The volume of the second space 48 increases or decreases with the reciprocating linear motion of the linear acting rod 36 and the nut member 35. Specifically, as shown in Figure 2, when the linear acting rod 36 is in a retracted state, the volume of the second space 48 decreases. As shown in Figure 3, when the linear acting rod 36 is in an extended state, the volume of the second space 48 increases.

[0045] An annular gap 49 is provided between the inner peripheral surface of the guide sleeve 38 and the outer peripheral surface of the linear motion rod 36. Slide bearings 42 and 43 are disposed in the annular gap 49. The distance between the first slide bearing 42 and the second slide bearing 43 changes as the linear motion of the linear motion rod 36 progresses. Specifically, as shown in FIG. 2, when the linear motion rod 36 is in a retracted state, the distance between the slide bearings 42 and 43 increases, and the volume of a space 49a between the slide bearings 42 and 43 in the annular gap 49 increases. As shown in FIG. 3, when the linear motion rod 36 is in an extended state, the movement of the second slide bearing 43 decreases the distance between the slide bearings 42 and 43, and the volume of a space 49a between the slide bearings 42 and 43 in the annular gap 49 decreases.

[0046] The second space 48 is part of the internal space of the guide sleeve 38. The space 49a is also part of the internal space of the guide sleeve 38. The first space 46 of the linear motion rod 36 inserted into the internal space of the guide sleeve 38 can also be considered to be part of the internal space of the guide sleeve 38. These spaces 46, 48, 49a inside the guide sleeve 38 are sealed to protect them from foreign matter such as dust and water. If the volume of the sealed space increases or decreases, the pressure in the space changes, and the required thrust to be applied to the linear motion rod 36 also changes.

[0047] Therefore, the linear motion actuator 1 has a mechanism for reducing the pressure change in the spaces 46, 48, 49a inside the guide sleeve .

[0048] This mechanism includes a piston 50, a connecting member 51, and a piston chamber 52. The piston 50 is connected to the linear acting rod 36 via the connecting member 51 and is caused to move back and forth linearly together with the linear acting rod 36. The connecting member 51 is an L-shaped rod, and one end of the connecting member 51 is connected to the linear acting rod 36 and the other end is connected to the piston 50. In this embodiment, one end of the connecting member 51 is connected to the end mounting portion 37, but it may also be connected to, for example, the end wall 36a of the linear acting rod 36.

[0049] The piston chamber 52 is provided in the piston chamber wall 39 of the housing 31. As described above, the piston chamber wall 39 is integrally connected to the guide sleeve 38 and the upper wall 31c. The piston chamber wall 39 has a peripheral wall 39a that surrounds the piston 50, a front end wall 39b, and a rear end wall 39c, and the peripheral wall 39a, the front end wall 39b, and the rear end wall 39c define the piston chamber 52.

[0050] A hole is formed in the front end wall 39b, and a plain bearing 53 is disposed in this hole. The connecting member 51 passes through the plain bearing 53. The plain bearing 53 has a sealing function that seals the gap between the inner peripheral surface of the hole and the outer peripheral surface of the connecting member 51. A ventilation hole 54 is formed in the rear end wall 39c.

[0051] A seal 55 is disposed on the periphery of the piston 50, and seals the gap between the piston 50 and the peripheral wall 39a.

[0052] The piston chamber 52 is divided into two spaces, a third space 52a and a fourth space 52b, by the piston 50. The third space 52a is located between the piston 50 and the front end wall 39b, and the fourth space 52b is located between the piston 50 and the rear end wall 39c. The fourth space 52b is in communication with the atmospheric space outside the piston chamber 52 through a vent hole 54.

[0053] As shown in Fig. 2, when the linear acting rod 36 connected to the piston 50 is in a retracted state, the volume of the third space 52a increases and the volume of the fourth space 52b decreases due to the movement of the piston 50. As shown in Fig. 3, when the linear acting rod 36 is in an extended state, the volume of the third space 52a decreases and the volume of the fourth space 52b increases due to the movement of the piston 50.

[0054] The third space 52 a communicates with both the first space 46 of the linear-acting rod 36 and the second space 48 of the guide sleeve 38 .

[0055] Specifically, the third space 52a communicates with the annular space 49a between the plain bearings 42, 43 via an air vent 57 that passes through the front end wall 39b and the guide sleeve 38. The piston chamber wall 39 has an extension 58 that is formed integrally with the guide sleeve 38. The air vent 57 is formed in the extension 58 of the piston chamber wall 39 that is formed integrally with the guide sleeve 38, and one end of the air vent 57 opens to the third space 52a and the other end opens to the space 49a.

[0056] The first space 46 of the linear motion rod 36 and the second space 48 of the guide sleeve 38 communicate with the space 49a of the annular gap 49 and then with the third space 52a. In this embodiment, a plurality of holes 60 are formed in the nut member 35. The holes 60 extend along the axial direction of the nut member 35 and penetrate the nut member 35. Therefore, each hole 60 communicates with the first space 46 and also with the second space 48. In other words, the first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 via the holes 60 of the nut member 35.

[0057] Each hole 60 has a branched portion extending radially outward from the nut member 35. A vent hole 62 communicating with the branched portion of the hole 60 of the nut member 35 is formed in the cylindrical peripheral wall of the linear motion rod 36. The first space 46 and the second space 48 communicate with the annular space 49a between the plain bearings 42, 43 via the hole 60 of the nut member 35 and the vent hole 62 of the linear motion rod 36.

[0058] Therefore, both the first space 46 of the linear motion rod 36 and the second space 48 of the guide sleeve 38 communicate with the third space 52a of the piston chamber 52 via the space 49a. As shown in Fig. 2, when the linear motion rod 36 is in the retracted state, the volumes of the first space 46 and the second space 48 decrease, but air flows from the first space 46 and the second space 48 into the third space 52a through the space 49a. Therefore, even if the volumes of the first space 46 and the second space 48 decrease, the third space 52a of the piston chamber 52 offsets the increase in pressure in the first space 46 and the second space 48.

[0059] Furthermore, when the linear motion rod 36 is in a retracted state, the volume of the annular space 49a between the plain bearings 42 and 43 increases, but air flows into the space 49a from the first space 46 and the second space 48. Therefore, even if the volume of the space 49a increases, the decrease in pressure in the space 49a is reduced.

[0060] 3, when the linear acting rod 36 is in an extended state, the volumes of the first space 46 and the second space 48 increase, but air flows from the third space 52a through the space 49a into the first space 46 and the second space 48. Therefore, even if the volumes of the first space 46 and the second space 48 increase, the third space 52a of the piston chamber 52 offsets the decrease in pressure in the first space 46 and the second space 48.

[0061] Furthermore, when the linear motion rod 36 is in an extended state, the volume of the annular space 49a between the plain bearings 42, 43 decreases, but air flows from the space 49a into the first space 46 and the second space 48. Therefore, even if the volume of the space 49a decreases, the increase in pressure in the space 49a is reduced.

[0062] As described above, the volume of the third space 52a changes simultaneously with the change in the volumes of the first space 46 and the second space 48. The change in the volume of the third space 52a has a negative correlation with the change in the volumes of the first space 46 and the second space 48, and reduces the change in pressure in the first space 46 and the second space 48. This stabilizes the required thrust to be applied to the linear acting rod 36, and improves the accuracy of the amount of movement of the linear acting rod 36.

[0063] Furthermore, the first space 46 and the second space 48 communicate with the third space 52a via the annular space 49a between the plain bearings 42 and 43, so that pressure changes in the space 49a are also reduced.

[0064] The stroke of the piston 50 is the same as the stroke of the linear acting rod 36. The variable volume of the third space 52a can be appropriately designed by appropriately designing the area of ​​the piston 50. For example, it is possible to completely offset the change in the total volume of the first space 46 and the second space 48 with the change in the volume of the third space 52a.

[0065] The fourth space 52b of the piston chamber 52 is connected to the atmosphere outside the piston chamber 52 through a vent hole 54 formed in the rear end wall 39c. When the volume of the third space 52a increases, air flows out of the fourth space 52b through the vent hole 54. When the volume of the third space 52a decreases, air flows from the atmosphere into the fourth space 52b through the vent hole 54. The air in the fourth space 52b provides almost no resistance to the reciprocating movement of the piston 50. The resistance to the reciprocating movement of the piston 50 is essentially the frictional resistance between the seal 55 provided on the outer periphery of the piston 50 and the peripheral wall 39a. Therefore, the volume of the third space 52a changes smoothly in response to changes in the volumes of the first space 46 and the second space 48.

[0066] The first space 46, which is a part of the internal space of the guide sleeve 38, and the second space 48, which is also a part of the internal space of the guide sleeve 38, are in communication with the third space 52a of the piston chamber 52, but the first space 46 and the second space 48 are not in direct communication with the atmosphere. Therefore, the first space 46 and the second space 48 can be sealed and protected from foreign matter. In particular, the third space 52a, through which the first space 46 and the second space 48 are in communication, is isolated from the atmosphere by the piston 50 and the seal 55 around it, so that foreign matter does not enter the first space 46 and the second space 48.

[0067] 4 shows a linear motion actuator 1A according to another embodiment of the present invention. In the linear motion actuator 1A, a pipe 68 is provided instead of the vent hole 57 formed in the extension portion 58 of the piston chamber wall portion 39.

[0068] The third space 52a of the piston chamber 52 communicates with the annular space 49a between the plain bearings 42, 43 via a pipe 68 arranged outside the piston chamber 52 and the guide sleeve 38. The pipe 68 may be a pipe made of a highly rigid material such as metal or resin, or may be a hose made of a highly flexible material such as elastomer.

[0069] In the linear motion actuator 1A in which the tube 68 is used, the extension portion 58 of the piston chamber wall portion 39 is not necessary, and the weight of the housing 31 can be reduced.

[0070] 5 shows a linear motion actuator 1B according to another embodiment of the present invention. In the linear motion actuator 1B, instead of the multiple holes 60, multiple grooves 70 and multiple holes 71 are formed in the nut member 35. The grooves 70 are formed in the outer peripheral surface of the body portion 35b of the nut member 35 and extend along the axial direction of the nut member 35. The head portion 35a of the nut member 35 is formed with holes 71 that are aligned with the grooves 70.

[0071] Each groove 70 communicates with the first space 46 and also communicates with the second space 48 through the hole 71. In other words, the first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 through the grooves 70 and holes 71 of the nut member 35.

[0072] The first space 46 and the second space 48 communicate with the annular space 49 a between the plain bearings 42 and 43 via the groove 70 and hole 71 of the nut member 35 and the vent hole 62 of the linear motion rod 36 .

[0073] The space 49a communicates with the third space 52a of the piston chamber 52 through a vent hole 57 formed in an extension portion 58 of the piston chamber wall portion 39. A pipe 68 (see FIG. 4) may be used to connect the space 49a and the third space 52a.

[0074] 6 shows a linear motion actuator 1C according to another embodiment of the present invention. In the linear motion actuator 1C, a plurality of grooves 70 and holes 71 are formed in the nut member 35. The first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 via the grooves 70 and holes 71 of the nut member 35.

[0075] Additionally, a plurality of grooves 72 are formed on the outer peripheral surface of the end portion of the cylindrical peripheral wall of the linear motion rod 36. Each groove 72 extends along the axial direction of the linear motion rod 36. These grooves 72 are provided to connect the second space 48 to the annular space 49a between the plain bearings 42, 43. Therefore, although the second plain bearing 43 overlaps these grooves 72, air flows from the space 48 to the space 49a and from the space 49a to the space 48 through the grooves 72.

[0076] The second space 48 communicates with the annular space 49 a between the plain bearings 42 and 43 via a plurality of grooves 72 in the linear motion rod 36 .

[0077] The space 49a communicates with the third space 52a of the piston chamber 52 through a vent hole 57 formed in an extension portion 58 of the piston chamber wall portion 39. A pipe 68 (see FIG. 4) may be used to connect the space 49a and the third space 52a.

[0078] 7 shows a linear motion actuator 1D according to another embodiment of the present invention. In this linear motion actuator 1D, a plurality of holes 60 are formed in the nut member 35. The first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 via the holes 60 in the nut member 35.

[0079] 6, a plurality of grooves 72 are formed on the outer peripheral surface of the end of the cylindrical peripheral wall of the linear motion rod 36. The second space 48 communicates with the annular space 49a between the plain bearings 42, 43 via the plurality of grooves 72 in the linear motion rod 36.

[0080] The space 49a communicates with the third space 52a of the piston chamber 52 through a vent hole 57 formed in an extension portion 58 of the piston chamber wall portion 39. A pipe 68 (see FIG. 4) may be used to connect the space 49a and the third space 52a.

[0081] FIG. 8 shows a linear motion actuator 1E according to another embodiment of the present invention. In the linear motion actuator 1E, a hole 74 is formed in the lead screw 34. The hole 74 has a central hole portion extending along the central axis of the lead screw 34 and a horizontal hole portion 75 extending radially outward from the central hole portion. The horizontal hole portion 75 opens on the outer peripheral surface of the lead screw 34. The horizontal hole portion 75 is located in the second space 48 of the guide sleeve 38. Therefore, the first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 via the hole 74 of the lead screw 34. However, instead of the hole 74 of the lead screw 34, the first space 46 may also communicate with the second space 48 via the hole 60 of the nut member 35 (see FIGS. 1 to 4 and 7) or the groove 70 and hole 71 of the nut member 35 (see FIGS. 5 and 6).

[0082] The peripheral wall 39a, which is the outer wall of the piston chamber 52, is formed integrally with the guide sleeve 38. The third space 52a of the piston chamber 52 communicates with the second space 48 of the guide sleeve 38 via an air vent 76. The wall portion in which the air vent 76 is formed is part of the peripheral wall 39a and also part of the guide sleeve 38.

[0083] Thus, in the linear actuator 1E, the first space 46 of the linear rod 36 is connected to the second space 48 of the guide sleeve 38, and the second space 48 is connected to the third space 52a via the air vent 76.

[0084] In the annular gap 49 between the guide sleeve 38 and the linear motion rod 36, a space 49a between the plain bearings 42, 43 does not communicate with either the first space 46 or the second space 48. However, when the linear motion rod 36 moves linearly, the second plain bearing 43 fitted to the linear motion rod 36 moves, changing the distance between the plain bearings 42, 43, and therefore the volume of the space 49a. Therefore, the space 49a communicates with the third space 52a of the piston chamber 52 via a vent hole 57 formed in an extension portion 58 of the piston chamber wall 39, thereby suppressing changes in pressure in the space 49a. A pipe 68 (see FIG. 4) may be used to connect the space 49a and the third space 52a.

[0085] 9 shows a linear motion actuator 1F according to another embodiment of the present invention. The structure of the linear motion actuator 1F is essentially the same as that of the linear motion actuator 1E of FIG.

[0086] The length of the connecting member 51 in the linear motion actuator 1F is greater than that in the linear motion actuator 1E in Fig. 8. Therefore, the position of the piston chamber 52 is different between Fig. 8 and Fig. 9, and the direction of the air hole 76 connecting the second space 48 and the third space 52a can be made perpendicular to the peripheral wall of the guide sleeve 38 (parallel to the piston 50).

[0087] 10 shows a linear motion actuator 1G according to another embodiment of the present invention. In the linear motion actuator 1G, the first space 46 of the linear motion rod 36 communicates with the second space 48 of the guide sleeve 38 via a hole 74 of the lead screw 34. However, instead of the hole 74 of the lead screw 34, the first space 46 may communicate with the second space 48 via a hole 60 of the nut member 35 (see FIGS. 1 to 4 and 7), or a groove 70 and a hole 71 of the nut member 35 (see FIGS. 5 and 6).

[0088] An air vent 78 is formed in the cylindrical peripheral wall of the linear motion rod 36, and communicates with the annular space 49a between the plain bearings 42, 43 and the first space 46. While the air vent 62 in FIGS. 1 to 4 overlaps with the nut member 35 in the radial direction, the air vent 78 does not overlap with the nut member 35 in the radial direction.

[0089] Thus, the second space 48 communicates with the first space 46, and the first space 46 communicates with the space 49a. The space 49a communicates with the third space 52a of the piston chamber 52 via a vent hole 57 formed in an extension portion 58 of the piston chamber wall portion 39. A pipe 68 (see FIG. 4) may be used to connect the space 49a and the third space 52a.

[0090] 11 shows a linear motion actuator 1H according to another embodiment of the present invention. In the linear motion actuator 1H, a connecting member 81 is connected to the piston 50 and the linear motion rod 36 instead of the connecting member 51. While the connecting member 51 is a solid rod, the connecting member 81 is a hollow rod and has an internal space, i.e., an air hole 82, in the center.

[0091] An air vent 83 communicating with the air vent 82 of the connecting member 81 is formed in the cylindrical peripheral wall of the linear acting rod 36. The third space 52a of the piston chamber 52 communicates with the first space 46 of the linear acting rod 36 via the air vent 82 of the connecting member 81 and the air vent 83 in the peripheral wall of the linear acting rod 36. An opening 81a opening into the third space 52a of the piston chamber 52 is formed in the connecting member 81, and the opening 81a communicates with the air vent 82.

[0092] The nut member 35 is formed with a plurality of holes 60 that communicate with the first space 46 and the second space 48, and the linear motion rod 36 is formed with a vent hole 62 that communicates with a branching portion of the hole 60 of the nut member 35. The first space 46 and the second space 48 communicate with the annular space 49a between the plain bearings 42, 43 via the holes 60 of the nut member 35 and the vent hole 62 of the linear motion rod 36. Therefore, the annular space 49a between the plain bearings 42, 43 and the second space 48 communicate with the third space 52a via the first space 46.

[0093] 12 shows a linear motion actuator 1I according to another embodiment of the present invention. In the linear motion actuator 1I, the air vent 54 of the piston chamber 52 is covered with a breathable waterproof filter 85. The waterproof filter 85 is a sheet with many pores that allows air to pass through but prevents liquid water from passing through. The waterproof filter 85 ensures air flow between the fourth space 52b of the piston chamber 52 and the atmospheric space, and also reduces the intrusion of foreign matter (including water) into the fourth space 52b of the piston chamber 52 and, ultimately, the third space 52a.

[0094] A stopper 86 is fixed by a screw to the end of the feed screw 34. The stopper 86 limits the range of linear movement of the linear acting rod 36. That is, when the linear acting rod 36 is maximally extended from the guide sleeve 38, the stopper 86 comes into contact with the nut member 35, preventing the nut member 35 from moving and, therefore, preventing further extension of the linear acting rod 36. When the linear acting rod 36 is maximally retracted within the guide sleeve 38, the stopper 86 comes into contact with the end wall 36a of the linear acting rod 36, preventing further retraction of the linear acting rod 36.

[0095] The linear motion actuator 1I in Figure 12 is a modification of the linear motion actuator 1 shown in Figures 1 to 3. However, a waterproof filter 85 and a stopper 86 may be provided in the linear motion actuators 1A, 1B, 1C, 1D, 1E, 1F, 1G, and 1H according to other embodiments.

[0096] Although the present invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the scope of the invention as set forth in the appended claims. Such changes, modifications and alterations are intended to be included within the scope of the invention.

[0097] For example, in the above embodiment, the gear transmission mechanism 2 has three gears 7, 8, and 9, but the number of gears provided in the gear transmission mechanism may be two, or four or more. Also, instead of the gear transmission mechanism 2, a belt mechanism or a chain mechanism may be used to rotate the feed screw 34, or the feed screw 34 may be directly rotated by a motor. [Explanation of symbols]

[0098] 1, 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I... Linear motion actuator, 2... Gear transmission mechanism, 3... Motor, 3a... Rotating shaft, 3b... Key, 6... Bracket, 6a... End wall, 7... First gear, 8... Second gear, 8a... Rotating shaft, 8b... Key, 9... Third gear, 9a... Rotating shaft, 9b... Key, 10, 11... Rolling bearing, 13, 14... Rolling bearing, 15... Bearing housing, 16... Bearing cover, 31... Housing, 31a... Lower wall, 31b... Center wall, 31c... Upper wall, 32... Cover, 33... End mounting portion, 33a... Through hole, 34... Lead screw, 35... Nut member, 35a... Head, 35b... Body, 36... Linear motion rod, 36a... End wall, 37... End mounting portion, 37a... Through hole, 38... Draft Inner sleeve, 39... piston chamber wall portion, 39a... peripheral wall, 39b... front end wall, 39c... rear end wall, 41... gear space, 42... first plain bearing, 43... second plain bearing, 46... first space, 48... second space, 49... annular gap, 49a... space between plain bearings in annular gap 49, 50... piston, 51... connecting member, 52... piston chamber, 52a... third Space, 52b...fourth space, 53...slide bearing, 54...vent hole, 55...seal, 57...vent hole, 58...extension portion, 60...hole, 62...vent hole, 68...pipe, 70...groove, 71...hole, 72...groove, 74...hole, 75...horizontal hole portion, 76...vent hole, 78...vent hole, 81...connecting member, 82...vent hole, 83...vent hole, 81a...opening, 85...waterproof filter, 86...stopper

Claims

1. a feed screw that can be rotated; a nut member that is caused to move linearly back and forth along the axial direction of the feed screw in accordance with the rotation of the feed screw; a cylindrical linear motion rod having a cylindrical first space into which at least a portion of the nut member is inserted, the cylindrical linear motion rod being fixed to the nut member and being moved in a reciprocating linear motion together with the nut member; a guide sleeve having a cylindrical internal space into which the linear motion rod is inserted and guiding the linear motion of the linear motion rod; a piston connected to the linear motion rod and adapted to reciprocate linearly together with the linear motion rod; a piston chamber in which the piston is disposed, The linear motion rod is caused to reciprocate linearly between an extended state in which it is extended from the guide sleeve and a retracted state in which it is retracted into the guide sleeve in accordance with the reciprocating linear motion of the nut member, When the linear acting rod is in the retracted state, the lead screw protrudes into the first space, thereby reducing the volume of the first space, and when the linear acting rod is in the extended state, the lead screw retracts from the first space, thereby increasing the volume of the first space; the internal space of the guide sleeve has a second space in which the linear motion rod and the nut member are not positioned; When the linear rod is in the contracted state, the volume of the second space decreases, and when the linear rod is in the extended state, the volume of the second space increases; The piston chamber is divided into a third space and a fourth space by the piston, When the linear rod is in the contracted state, the volume of the third space increases, and when the linear rod is in the extended state, the volume of the third space decreases; When the linear rod is in the contracted state, the volume of the fourth space decreases, and when the linear rod is in the extended state, the volume of the fourth space increases; the fourth space of the piston chamber is in communication with an atmospheric space outside the piston chamber, the third space of the piston chamber is in communication with at least one of the first space of the linear motion rod and the second space of the guide sleeve, The first space of the linear motion rod communicates with the second space of the guide sleeve. A linear actuator characterized by:

2. the third space of the piston chamber communicates with an annular gap between an inner peripheral surface of the guide sleeve and an outer peripheral surface of the linear motion rod, The first space of the linear motion rod communicates with the annular gap and then with the third space.

2. The linear actuator according to claim 1.

3. A first plain bearing that is stationary relative to the guide sleeve and in slidable contact with the outer circumferential surface of the linear motion rod, and a second plain bearing that is stationary relative to the linear motion rod and in slidable contact with the inner circumferential surface of the guide sleeve are disposed in the annular gap, and the distance between the first plain bearing and the second plain bearing changes in accordance with the reciprocating translatory motion of the linear motion rod.

3. The linear actuator according to claim 2.

4. an outer wall of the piston chamber has a portion integrally formed with the guide sleeve; The third space of the piston chamber communicates with the annular gap through a vent hole formed in the portion of the outer wall integrally formed with the guide sleeve.

4. The linear actuator according to claim 2 or 3.

5. The third space of the piston chamber communicates with the annular gap via a pipe disposed outside the piston chamber and the guide sleeve.

4. The linear actuator according to claim 2 or 3.

6. The nut member has a hole or a groove formed therein that communicates with the first space of the linear motion rod, a vent hole communicating with the hole or the groove of the nut member is formed in the cylindrical peripheral wall of the linear motion rod; The first space of the linear motion rod communicates with the annular gap via the hole or the groove of the nut member and the vent hole of the linear motion rod.

4. The linear actuator according to claim 2 or 3.

7. The first space of the linear motion rod communicates with the second space of the guide sleeve via the hole or the groove of the nut member.

7. The linear actuator according to claim 6.

8. The nut member has a hole or a groove formed therein that communicates with the first space of the linear motion rod, the first space of the linear motion rod communicates with the second space of the guide sleeve through the hole or the groove of the nut member, the third space of the piston chamber communicates with an annular gap between an inner peripheral surface of the guide sleeve and an outer peripheral surface of the linear motion rod, A groove communicating with the second space and the annular gap is formed on the outer circumferential surface of the cylindrical peripheral wall of the linear motion rod.

2. The linear actuator according to claim 1.

9. A first plain bearing that is stationary relative to the guide sleeve and in slidable contact with the outer circumferential surface of the linear motion rod, and a second plain bearing that is stationary relative to the linear motion rod and in slidable contact with the inner circumferential surface of the guide sleeve are disposed in the annular gap, and the distance between the first plain bearing and the second plain bearing changes in accordance with the reciprocating translatory motion of the linear motion rod.

9. The linear actuator according to claim 8.

10. The outer wall of the piston chamber is formed integrally with the guide sleeve, The third space of the piston chamber communicates with the second space of the guide sleeve through a vent hole formed in an outer wall of the piston chamber.

2. The linear actuator according to claim 1.

11. A hole is formed in the feed screw, and the first space of the linear motion rod communicates with the second space of the guide sleeve via the hole of the feed screw.

11. The linear actuator according to claim 1 or 10.

12. a vent hole is formed in a connecting member that connects the linear motion rod and the piston; an air hole communicating with the air hole of the connecting member is formed in a cylindrical peripheral wall of the linear motion rod; The third space of the piston chamber communicates with the first space of the linear motion rod via the vent hole of the connecting member and the vent hole of the peripheral wall of the linear motion rod.

2. The linear actuator according to claim 1.

13. The piston chamber is provided with a vent hole that connects the fourth space to the atmospheric space, and the vent hole is covered with a breathable waterproof filter.

2. The linear actuator according to claim 1.

Images