JP2015040576A - Linear actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear actuator capable of reducing a load applied on force for rotation-driving a screw shaft when the excessive load is supplied on the screw shaft.SOLUTION: A thread portion 26 of a screw shaft 24 has a first inclined surface 26a disposed on a side toward a first direction, and inclined to an axial direction of the screw shaft 24 by a first angle, and a second inclined surface 26b disposed on a side toward a second direction, and inclined to the axial direction of the screw shaft 24 by a second angle smaller than the first angle. A nut member 22 has a plurality of nut portions 30 aligned in a circumferential direction of the screw shaft 24, and capable of displacing between a first position engaged with the thread portion 26 and a second position releasing the engagement to the thread portion 26; and a plurality of springs 32 for elastically deviating the plurality of nut portions 30 from the second position to the first position.

Description

  The present invention relates to a linear actuator that converts rotational motion into linear motion.

  For example, a linear actuator that converts rotational motion into linear motion is used for an electric bed or the like having a reclining function (see, for example, Patent Document 1).

  A conventional linear actuator includes an electric motor, a screw shaft that is rotationally driven by the electric motor, a nut that is engaged with a screw thread portion of the screw shaft, and a rod portion that can move integrally with the nut. The rod part is connected to the backrest part of the electric bed, for example.

  When the screw shaft rotates in the positive direction, the nut moves linearly in the first direction with respect to the screw shaft. At this time, for example, when the rod portion moves in the extending direction, the backrest portion of the electric bed moves in the direction to be raised. On the other hand, when the screw shaft rotates in the opposite direction, the nut moves linearly in a second direction opposite to the first direction with respect to the screw shaft. At this time, for example, when the rod portion moves in the contraction direction, the backrest portion of the electric bed operates in the direction in which it is laid down.

  The conventional linear actuator further includes a one-way clutch mechanism. The one-way clutch mechanism is a mechanism for restricting rotation of the screw shaft in the reverse direction. For example, when a foreign object gets caught between the bed body and the backrest while the backrest of the electric bed is operating in the direction to lie down, the screw shaft is excessive in the thrust direction (that is, the axial direction). Load will be applied. At this time, when the one-way clutch mechanism is operated, the rotation of the screw shaft in the reverse direction is forcibly stopped, and the operation of the backrest portion is stopped.

JP 2011-153635 A

  However, the conventional linear actuator described above has the following problems. As described above, when the one-way clutch mechanism is operated, the rotation of the screw shaft in the reverse direction is forcibly stopped, so that a large load acts on the electric motor that is drivingly connected to the screw shaft. Challenges arise.

  The present invention is intended to solve the above-described problem, and its purpose is to reduce the load acting on the force for rotationally driving the screw shaft when an excessive load is applied to the screw shaft. An actuator is provided.

  In order to achieve the above object, a linear actuator according to an aspect of the present invention is a linear actuator that converts rotational motion into linear motion, and has a helical thread portion on an outer peripheral surface, and is rotationally driven. And a second direction in the first direction or the opposite direction to the first direction with respect to the screw shaft as the screw shaft rotates. A nut member that linearly moves in the direction of the screw thread, and the screw thread portion is disposed on the side toward the first direction, and is inclined at a first angle with respect to the axial direction of the screw shaft. A second inclined surface that is disposed on a side toward the second direction and is inclined at a second angle smaller than the first angle with respect to the axial direction of the screw shaft. An inclined surface, and the nut member is in a circumferential direction of the screw shaft. A plurality of nut portions arranged side by side and displaceable between a first position engaged with the screw thread portion and a second position where engagement with the screw thread portion is released; and A plurality of elastic members that elastically bias each of the plurality of nut portions in a direction from the second position toward the first position, and each of the plurality of nut portions includes the screw When an excessive load is applied to the shaft in the second direction, the shaft is pressed by the second inclined surface to be displaced from the first position to the second position.

  According to this aspect, when an excessive load is applied to the screw shaft in the second direction, each of the plurality of nut portions is displaced from the first position to the second position. To come. Thereby, the load which acts on the force which rotationally drives a screw shaft can be reduced.

  For example, in the linear actuator according to one aspect of the present invention, the nut member is further disposed so as to surround the outer peripheral surface of the screw shaft, and each of the plurality of nut portions is disposed at the first position. It may be configured to have a holder portion that is supported so as to be displaceable between the first position and the second position.

  According to this aspect, since the nut member has the holder portion, the holder portion can support each of the plurality of nut portions so as to be displaceable between the first position and the second position. it can.

  For example, in the linear actuator according to one aspect of the present invention, the holder portion is disposed corresponding to each of the plurality of nut portions, and includes a plurality of guide surfaces that are inclined with respect to the radial direction of the holder portion. Each of the plurality of nut portions from the first position while sliding on the corresponding guide surface when an excessive load is applied to the screw shaft in the second direction. You may comprise so that it may displace to the said 2nd position.

  According to this aspect, since the holder portion has a plurality of guide surfaces, when an excessive load in the second direction acts on the screw shaft, each of the plurality of nut portions corresponds to the corresponding guide surface. Slide Thus, each of the plurality of nut portions can be guided from the first position to the second position.

  For example, in the linear actuator according to an aspect of the present invention, each of the plurality of elastic members may be configured to be disposed between the corresponding nut portion and the holder.

  According to this aspect, since each of the plurality of elastic members is disposed between the corresponding nut portion and the holder portion, each of the plurality of elastic members can be stored compactly inside the holder portion.

  For example, in the linear actuator according to one aspect of the present invention, the plurality of nut portions may be arranged at equal intervals in the circumferential direction of the screw shaft.

  According to this aspect, since the plurality of nut portions are arranged at equal intervals in the circumferential direction of the screw shaft, the nut member can be stably meshed with the thread portion of the screw shaft.

  According to the linear actuator which concerns on 1 aspect of this invention, when an excessive load acts on a screw shaft, the load which acts on the force which rotationally drives a screw shaft can be reduced.

It is a perspective view which shows the external appearance of the linear actuator which concerns on embodiment. It is the sectional view on the AA line in FIG. It is principal part sectional drawing which expands and shows the structure of the nut member of FIG. 2, and its periphery. It is a perspective view which shows a nut member. It is a principal part perspective view which shows the state in which the nut member was meshed | engaged with the thread part of the screw shaft. FIG. 6 is a cross-sectional view taken along line B-B in FIG. 5, showing a state where each of a plurality of nut portions is displaced to a first position. It is a figure which expands and shows the guide surface of FIG. FIG. 6 is a cross-sectional view taken along line B-B in FIG. 5, showing a state where each of a plurality of nut portions is displaced to a second position. It is CC sectional view taken on the line in FIG. 6 which shows the state which a nut member moves to a 1st direction with respect to a screw shaft. It is CC sectional view taken on the line in FIG. 6 which shows the state which a nut member moves to a 2nd direction with respect to a screw shaft. It is the DD sectional view taken on the line in FIG. 8 which shows the state which each of the several nut part displaced to the 2nd position. It is a perspective view which shows the electric bed in which the linear actuator of embodiment was mounted. It is a principal part cross-section perspective view which shows the internal mechanism of the electric bed of FIG. It is a principal part perspective view which shows the state which the foreign material pinched | interposed between the backrest part and bed main body of the electric bed of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each of the embodiments described below shows a preferred specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connecting forms of the constituent elements shown in the following embodiments are merely examples, and are not intended to limit the present invention. The invention is specified by the claims. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims are not necessarily required to achieve the object of the present invention, but are described as constituting more preferable embodiments. Is done.

(Embodiment)
[Overall configuration of linear actuator]
First, the overall configuration of the linear actuator according to the embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view illustrating an appearance of a linear actuator according to an embodiment. FIG. 2 is a cross-sectional view taken along the line AA in FIG.

  As shown in FIGS. 1 and 2, the linear actuator 2 is an actuator for converting rotational motion into linear motion. The linear actuator 2 includes a housing 4 and a rod portion 6.

  The housing 4 is configured in a substantially cylindrical shape. An electric motor 8 is disposed inside the housing 4. The electric motor 8 has an output shaft 10. When the electric motor 8 is driven, the output shaft 10 rotates in the forward direction or the reverse direction. A bearing portion 12 is further provided inside the housing 4. A pair of bracket portions 14 for attaching the linear actuator 2 to, for example, an electric bed 50 (see FIG. 12 described later) or the like is provided on the side surface of the housing 4. Each of the pair of bracket portions 14 is provided with an insertion hole 16 for inserting a bolt or the like (not shown).

  The rod part 6 has a fixed rod part 18 and a movable rod part 20, and extends substantially perpendicular to the output shaft 10 of the electric motor 8. As will be described later, the rod portion 6 is configured to be extendable and contractible as a whole.

  The fixed rod portion 18 is configured in a substantially cylindrical shape. The fixed rod portion 18 is fixed to the side surface of the housing 4 and extends from the side surface of the housing 4 toward the side. A guide recess (not shown) extending in the axial direction of the fixed rod portion 18 is provided on the inner peripheral surface of the fixed rod portion 18.

  The movable rod portion 20 is configured in a substantially cylindrical shape. The movable rod portion 20 is disposed inside the fixed rod portion 18 and is slidable relative to the fixed rod portion 18. The movable rod portion 20 is slidable between a storage position stored inside the fixed rod portion 18 and a protruding position protruding from the fixed rod portion 18. A nut member 22 is attached to the inner peripheral surface of the movable rod portion 20. The linear actuator 2 according to the present embodiment is characterized by the configuration of the nut member 22. The configuration of the nut member 22 will be described later. On the outer peripheral surface of the movable rod portion 20, a guide protrusion (not shown) that protrudes in the radial direction of the movable rod portion 20 is provided. When the guide protrusion of the movable rod portion 20 is guided along the guide recess of the fixed rod portion 18, the movable rod portion 20 is prevented from rotating with respect to the fixed rod portion 18, while being stored in the storage position and the protruding position. The slide is moved between.

  A screw shaft 24 is disposed inside the housing 4 and the rod portion 6. The screw shaft 24 extends linearly along the axial direction of the rod portion 6. One end portion of the screw shaft 24 is rotatably supported by a bearing portion 12 provided inside the housing 4. The screw shaft 24 is drivingly connected to the output shaft 10 of the electric motor 8 via a speed reduction mechanism (not shown). The rotation of the output shaft 10 of the electric motor 8 is transmitted to the screw shaft 24 after being decelerated by the speed reduction mechanism. Thereby, the screw shaft 24 is rotated in the forward direction (that is, the direction indicated by the arrow X in FIG. 2) or in the reverse direction (that is, the direction indicated by the arrow Y in FIG. 2). On the outer peripheral surface of the screw shaft 24, a screw thread portion 26 extending in a spiral shape along the axial direction of the screw shaft 24 is provided. The nut member 22 described above is meshed with the thread portion 26 of the screw shaft 24. The linear actuator 2 according to the present embodiment is characterized by the configuration of the thread portion 26. The configuration of the thread portion 26 will be described later.

  When the screw shaft 24 rotates in the forward direction, the nut member 22 moves linearly in the first direction (that is, the direction indicated by the arrow S in FIG. 2) with respect to the screw shaft 24. As the nut member 22 moves, the movable rod portion 20 slides in a direction from the storage position toward the protruding position, as indicated by an arrow P in FIGS. At this time, the rod part 6 extends as a whole.

  On the other hand, when the screw shaft 24 rotates in the reverse direction, the nut member 22 has a second direction opposite to the first direction with respect to the screw shaft 24 (that is, the arrow T in FIG. 2). Move linearly in the direction shown). As the nut member 22 moves, the movable rod portion 20 slides in the direction from the protruding position toward the storage position, as indicated by an arrow Q in FIG. At this time, the rod part 6 contracts as a whole.

[Configuration of threaded part]
Next, the configuration of the screw thread portion 26 described above will be described with reference to FIG. FIG. 3 is an essential part cross-sectional view showing an enlarged configuration of the nut member in FIG. 2 and its surroundings.

  As shown in FIG. 3 and FIG. 9, which will be described later, the thread portion 26 has a first inclined surface 26a and a second inclined surface 26b.

The first inclined surface 26a is disposed on the side toward the first direction. The first inclined surface 26a is inclined at a first angle θ1 with respect to the axial direction of the screw shaft 24 (that is, with respect to the central axis C0 of the screw shaft 24). For example, when the lead of the screw shaft 24 is L and the center diameter of the screw shaft 24 is d, the first angle θ1 is represented by θ1 = tan ⁻¹ (L / πd). In a normal actuator (for example, L = 100 to 250, d = 20 to 40), the first angle θ1 is, for example, 40 ° to 70 °.

  The second inclined surface 26b is disposed on the side facing the second direction, that is, on the opposite side to the first inclined surface 26a described above. The second inclined surface 26b is inclined with respect to the axial direction of the screw shaft 24 at a second angle θ2 smaller than the first angle θ1. The second angle θ2 is, for example, an angle having a difference of 5 ° to 10 ° with respect to the first angle θ1.

[Configuration of nut member]
Next, the configuration of the nut member 22 described above will be described with reference to FIGS. FIG. 4 is a perspective view showing a nut member. FIG. 5 is a main part perspective view showing a state in which the nut member is engaged with the thread portion of the screw shaft. FIG. 6 is a cross-sectional view taken along line BB in FIG. 5, showing a state where each of the plurality of nut portions is displaced to the first position. FIG. 7 is an enlarged view of the guide surface of FIG. FIG. 8 is a cross-sectional view taken along line BB in FIG. 5 showing a state where each of the plurality of nut portions is displaced to the second position.

  As shown in FIGS. 4 and 5, the nut member 22 includes a holder portion 28, a plurality of nut portions 30, and a plurality of springs 32 (each of the plurality of springs 32 constitutes an elastic member). In the present embodiment, three nut portions 30 and three springs 32 are provided.

  The holder portion 28 is configured in a substantially cylindrical shape, and is disposed so as to surround the outer peripheral surface of the screw shaft 24. A plurality of protrusions 34 are provided on the outer peripheral surface of the holder portion 28 so as to protrude in the radial direction of the holder portion 28. The plurality of protrusions 34 are arranged at equal intervals in the circumferential direction of the holder portion 28. Corresponding to the plurality of protrusions 34, a plurality of fixing recesses (not shown) are provided on the inner peripheral surface of the movable rod portion 20. The holder portion 28 is fixed to the inner peripheral surface of the movable rod portion 20 by inserting each of the plurality of protrusions 34 into the corresponding fixing concave portion.

  The inner peripheral surface of the holder portion 28 has a shape corresponding to the shape of each outer peripheral surface of the plurality of nut portions 30. A plurality of guide surfaces 36 are provided on the inner peripheral surface of the holder portion 28 so as to correspond to the plurality of nut portions 30. As shown in FIGS. 6 and 7, each of the plurality of guide surfaces 36 is a plane inclined with respect to the radial direction of the holder portion 28 (that is, with respect to a straight line L passing through the center C of the holder portion 28). . A plurality of mounting recesses 38 corresponding to the plurality of springs 32 are further provided on the inner peripheral surface of the holder portion 28.

  The plurality of nut portions 30 are disposed between the holder portion 28 and the screw shaft 24, and are disposed at equal intervals in the circumferential direction of the screw shaft 24. Each of the plurality of nut portions 30 is supported inside the holder portion 28 so as to be displaceable between the first position and the second position.

  As shown in FIG. 6, the first position is a position where each of the plurality of nut portions 30 is engaged with the screw thread portion 26 of the screw shaft 24. In a state where each of the plurality of nut portions 30 is displaced to the first position, the rotation of the screw shaft 24 is transmitted to each of the plurality of nut portions 30. On the other hand, as shown in FIG. 8, the second position is a position where the meshing of the plurality of nut portions 30 with the thread portions 26 is released. In a state where each of the plurality of nut portions 30 is displaced to the second position, the rotation of the screw shaft 24 is not transmitted to each of the plurality of nut portions 30. In the state where each of the plurality of nut portions 30 is displaced to the second position, the outer peripheral surface of each of the plurality of nut portions 30 is in contact with the inner peripheral surface of the holder portion 28. The operation in which each of the plurality of nut portions 30 is displaced from the first position to the second position will be described later.

  As shown in FIG. 4, the inner peripheral surface of each of the plurality of nut portions 30 is configured in a concave shape corresponding to the outer peripheral surface of the screw shaft 24. A plurality of screw groove portions 40 that are meshed with the thread portions 26 of the screw shaft 24 are provided on the inner peripheral surfaces of the plurality of nut portions 30. Each of the plurality of screw groove portions 40 has a shape corresponding to the screw thread portion 26. As shown in FIGS. 6 and 7, a guided surface 42 is provided on the outer peripheral surface of each of the plurality of nut portions 30. The guided surface 42 is a flat surface that slidably contacts the guide surface 36 of the corresponding holder portion 28. Each of the plurality of nut portions 30 is displaced between the first position and the second position while sliding on the corresponding guide surface 36. Thereby, each of the plurality of nut portions 30 is guided between the first position and the second position in a direction inclined with respect to the radial direction of the holder portion 28.

  Each of the plurality of springs 32 is constituted by, for example, a coil spring. Each of the plurality of springs 32 is disposed between the corresponding nut portion 30 and the holder portion 28. One end of the spring 32 is attached to the outer peripheral surface of the corresponding nut portion 30, and the other end of the spring 32 is attached to the mounting recess 38 of the holder portion 28. Each of the plurality of springs 32 elastically biases the corresponding nut portion 30 in the direction from the second position toward the first position. Thereby, each of the plurality of nut portions 30 is pressed against the thread portion 26 of the screw shaft 24 by the elastic restoring force of the corresponding spring 32.

[Operation of nut member]
Next, the operation of the nut member 22 described above will be described with reference to FIGS. 9 is a cross-sectional view taken along the line CC in FIG. 6 showing a state in which the nut member moves in the first direction with respect to the screw shaft. FIG. 10 is a cross-sectional view taken along the line CC in FIG. 6 showing a state in which the nut member moves in the second direction with respect to the screw shaft. FIG. 11 is a cross-sectional view taken along line DD in FIG. 8, showing a state where each of the plurality of nut portions is displaced to the second position.

  When the screw shaft 24 is rotating in the forward direction, as shown in FIG. 9, each of the plurality of nut portions 30 is displaced to the first position. Thereby, the rotation of the screw shaft 24 is transmitted to each of the plurality of nut portions 30, and the nut member 22 moves in the first direction (that is, the direction indicated by the arrow S in FIG. 9) with respect to the screw shaft 24. . At this time, the first inclined surface 26a of the thread portion 26 presses the nut portion 30 with the force F1. The horizontal component of the force F1 (that is, the component in the axial direction of the screw shaft 24) is Fx1, and the vertical component (that is, the component in the radial direction of the screw shaft 24) is Fy1. The horizontal component Fx1 is a force that presses the nut portion 30 in the first direction, and the vertical component Fy1 is a force that presses the nut portion 30 in the direction from the first position toward the second position.

  When the screw shaft 24 rotates in the reverse direction, as shown in FIG. 10, each of the plurality of nut portions 30 is displaced to the first position. Thereby, the rotation of the screw shaft 24 is transmitted to each of the plurality of nut portions 30, and the nut member 22 moves in the second direction (that is, the direction indicated by the arrow T in FIG. 10) with respect to the screw shaft 24. . At this time, the second inclined surface 26b of the thread portion 26 presses the nut portion 30 with the force F2. The horizontal component of the force F2 is Fx2, and the vertical component is Fy2. The horizontal component Fx2 is a force that presses the nut portion 30 in the second direction, and the vertical component Fy2 is a force that presses the nut portion 30 in the direction from the first position toward the second position. At this time, since the magnitude of the vertical component Fy2 is smaller than the magnitude of the elastic restoring force of the spring 32, the nut portion 30 is not displaced from the first position to the second position.

  Since the second angle θ2 is smaller than the first angle θ1 as described above, when the magnitude of the force F1 is equal to the magnitude of the force F2, the magnitude of the horizontal component Fx2 is the magnitude of the horizontal component Fx1. The vertical component Fy2 is smaller than the vertical component Fy1.

  When an excessive load is applied to the screw shaft 24 in the second direction with the screw shaft 24 rotating in the opposite direction, the magnitude of the force F2 increases and the vertical component Fy2 increases. The magnitude increases by ΔFy2. At this time, the magnitude of the increased vertical component (Fy2 + ΔFy2) is larger than the magnitude of the elastic restoring force of the spring 32. Therefore, as shown in FIG. 11, each of the plurality of nut portions 30 is pressed in the direction from the first position toward the second position by the increased vertical component (Fy2 + ΔFy2). The peripheral surface runs on the screw thread portion 26. As a result, each of the plurality of nut portions 30 is displaced from the first position to the second position.

  Thereafter, when the screw shaft 24 further rotates in the opposite direction, the position of the thread portion 26 with respect to the plurality of screw groove portions 40 is displaced. Accordingly, as shown in FIG. 10, each of the plurality of nut portions 30 is displaced from the second position to the first position by the elastic restoring force of the corresponding spring 32. Thereafter, the nut member 22 does not move in the second direction with respect to the screw shaft 24, and each of the plurality of nut portions 30 is repeatedly displaced between the first position and the second position. . As a result, the rotation of the screw shaft 24 is not transmitted to each of the plurality of nut portions 30, and the screw shaft 24 idles.

  When an excessive load is applied to the screw shaft 24 in the first direction while the screw shaft 24 is rotating in the positive direction, the vertical component is increased as the magnitude of the force F1 increases. The magnitude of Fy1 increases by ΔFy1. Accordingly, each of the plurality of nut portions 30 is pressed in the direction from the first position toward the second position by the increased vertical component (Fy1 + ΔFy1). At this time, since the magnitude of the vertical component Fy1 is smaller than the magnitude of the vertical component Fy2, as described above, the magnitude of the increased vertical component (Fy1 + ΔFy1) is smaller than the magnitude of the elastic restoring force of the spring 32. As a result, each of the plurality of nut portions 30 is not displaced from the first position to the second position.

[Application example of linear actuator]
Next, application examples of the linear actuator 2 described above will be described with reference to FIGS. FIG. 12 is a perspective view showing an electric bed on which the linear actuator of the embodiment is mounted. 13 is a cross-sectional perspective view of a main part showing the internal mechanism of the electric bed shown in FIG. FIG. 14 is a main part perspective view showing a state in which foreign matter is sandwiched between the backrest part of the electric bed of FIG. 12 and the bed main body.

  As shown in FIG. 12, the linear actuator 2 mentioned above is mounted in the electric bed 50 which has a reclining function, for example. The electric bed 50 includes a bed body 52 and a mat-like bed 54 disposed on the upper surface of the bed body 52. The bed 54 has a backrest portion 56 and a seat portion 58. The backrest portion 56 is rotatably connected to the end portion of the seat portion 58.

  As shown in FIG. 13, a frame portion 60 extending in a substantially horizontal direction is disposed inside the bed main body 52. The linear actuator 2 described above is attached to the frame portion 60. The rod portion 6 extends in a substantially horizontal direction, and the distal end portion of the movable rod portion 20 is connected to a slider portion 62 disposed inside the bed main body 52. The slider portion 62 extends in a substantially horizontal direction, and both end portions thereof are slidably mounted on a pair of rail portions 64 attached to the inner surface of the bed main body 52. The slider portion 62 is further connected to the back surface of the backrest portion 56 via a pole portion 66.

  As shown in FIG. 13, when the rod portion 6 is extended, the slider portion 62 is slid in the direction indicated by the arrow P in FIG. 13 by the rod portion 6. Thereby, it operates in the direction in which the backrest portion 56 is raised (that is, the direction indicated by the arrow U in FIG. 13). On the other hand, when the rod portion 6 is contracted, the slider portion 62 is slid by the rod portion 6 in the direction indicated by the arrow Q in FIG. Thereby, it operates in the direction in which the backrest portion 56 is laid down (that is, the direction indicated by the arrow V in FIG. 13).

  As shown in FIG. 14, in a state where the backrest portion 56 is laid down (that is, in a state where the screw shaft 24 rotates in the reverse direction), a foreign object is present between the bed main body 52 and the backrest portion 56. When 68 (for example, a user's arm) is pinched, an excessive load in the second direction acts on the screw shaft 24. At this time, as described above, each of the plurality of nut portions 30 is repeatedly displaced between the first position and the second position, and therefore, the rotation of the screw shaft 24 causes the rotation of the plurality of nut portions 30. Not transmitted to each. As a result, in the state where the screw shaft 24 is idle, the operation in the direction in which the backrest 56 is laid down stops.

[effect]
Next, the effect obtained by the linear actuator 2 of the present embodiment will be described. As described above, when an excessive load is applied to the screw shaft 24 in the second direction, each of the plurality of nut portions 30 is repeatedly displaced between the first position and the second position. The screw shaft 24 is idled. Thereby, the load which acts on the electric motor 8 drive-coupled to the screw shaft 24 can be reduced.

  The linear actuators according to the embodiments of the present invention have been described above, but the present invention is not limited to these embodiments.

  In the above embodiment, the screw shaft is driven to rotate by the electric motor, but the screw shaft can also be manually driven to rotate. In this case, the screw shaft can be rotationally driven by manually rotating a handle attached to the end of the screw shaft.

  In the above-described embodiment, the example in which the linear actuator is mounted on the electric bed has been described. However, the present invention is not limited to this. For example, the linear actuator can be mounted on an electric table or the like.

  In the above-described embodiment, three nut portions are provided on the nut member. However, the present invention is not limited to this. For example, two nut portions or four or more nut portions may be provided.

  The linear actuator of the present invention can be mounted on, for example, an electric bed.

2 Linear actuator 4 Housing 6 Rod portion 8 Electric motor 10 Output shaft 12 Bearing portion 14 Bracket portion 16 Insertion hole 18 Fixed rod portion 20 Movable rod portion 22 Nut member 24 Screw shaft 26 Screw thread portion 26a First inclined surface 26b Second Inclined surface 28 Holder portion 30 Nut portion 32 Spring 34 Protrusion 36 Guide surface 38 Mounting recess 40 Screw groove portion 42 Guide surface 50 Electric bed 52 Bed body 54 Bed 56 Backrest portion 58 Seat portion 60 Frame portion 62 Slider portion 64 Rail portion 66 Poles 68 Foreign object

Claims (5)

A linear actuator that converts rotational motion into linear motion,
A screw shaft having a helical thread portion on the outer peripheral surface and driven to rotate;
Meshed with the threaded portion of the screw shaft and linearly in a first direction or a second direction opposite to the first direction with respect to the screw shaft as the screw shaft rotates. A nut member that moves,
The thread portion is
A first inclined surface that is disposed on a side toward the first direction and is inclined at a first angle with respect to an axial direction of the screw shaft;
A second inclined surface that is disposed on the side toward the second direction and is inclined at a second angle smaller than the first angle with respect to the axial direction of the screw shaft,
The nut member is
The screw shaft is arranged side by side in the circumferential direction, and is displaceable between a first position engaged with the screw thread portion and a second position where the engagement with the screw thread portion is released. A plurality of nut portions;
A plurality of elastic members that elastically bias each of the plurality of nut portions in a direction from the second position toward the first position;
Each of the plurality of nut portions is pressed from the first position by the second inclined surface when an excessive load in the second direction is applied to the screw shaft. Linear actuator that is displaced to position 2. The nut member is further disposed so as to surround the outer peripheral surface of the screw shaft, and each of the plurality of nut portions can be displaced between the first position and the second position. The linear actuator according to claim 1, further comprising a holder portion that supports the linear actuator. The holder part is arranged corresponding to each of the plurality of nut parts, and has a plurality of guide surfaces inclined with respect to the radial direction of the holder part,
Each of the plurality of nut portions slides from the first position to the second position while sliding on the corresponding guide surface when an excessive load is applied to the screw shaft in the second direction. The linear actuator according to claim 2. The linear actuator according to claim 2, wherein each of the plurality of elastic members is disposed between the corresponding nut portion and the holder. The linear actuator according to claim 1, wherein the plurality of nut portions are arranged at equal intervals in a circumferential direction of the screw shaft.

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