Electric actuator

Abstract

We provide an electric actuator that can maintain the quick-release speed at a safe speed. [Solution] A disc 35 is fixed to a screw shaft 6. A support pin 36 is fixed to the disc 35. A brake weight 39 is rotatably attached to the support pin 36 and housed in a cylindrical sliding ring 38. During quick release, the rotation of the screw shaft 6 causes the brake weight 39 to rotate around the support pin 36 fixed to the disc 35, and the braking member 46 comes into contact with the inner surface of the sliding ring 38. This applies a braking force corresponding to the rotational speed of the screw shaft 6.

Description

Technical Field

[0001] The present invention relates to an electric actuator, and relates to a technology for realizing a quick release function for flattening the back of an electric bed or the like in an emergency, and a technology for keeping the operating speed of the quick release function at a safe speed.

Background Art

[0002] As an operating means for adjusting the angle of a backrest of a medical or nursing care bed or the like, an electric actuator that converts the forward and reverse rotational movements of a motor into a linear movement of a rod is widely used (see Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] The configuration of the electric actuator described in Patent Document 1 will be briefly described. The electric actuator described in Patent Document 1 includes an electric motor as a drive source and a speed reduction means for reducing and converting the rotational output of the electric motor from the vertical direction to the horizontal direction. The speed reduction means is composed of a worm attached to the tip of the rotor shaft of the electric motor and a worm wheel meshing with the worm, and reduces the rotation of the electric motor.

[0005] A screw shaft is fixed concentrically on the worm wheel of the speed reduction means, and the screw shaft rotates together with the worm wheel. A trapezoidal screw is formed on the screw shaft, a driving force connecting means is screwed onto the trapezoidal screw, and a driving rod is fixed to the driving force connecting means. The screw shaft and the driving rod constitute a motion conversion means.

[0006] By rotating the screw shaft of the motion conversion means in a predetermined direction, the drive rod moves back and forth in a linear direction due to the screw action of the drive force coupling means. This back and forth movement of the drive rod moves various parts (such as the backrest) of the bed or other equipment that are fixed to the end of the drive rod.

[0007] Furthermore, a one-way clutch is attached to the screw shaft. When the drive rod rotates the screw shaft in the forward direction, the one-way clutch does not act, allowing the screw shaft to rotate freely. When rotating in the reverse direction, the one-way clutch rotates together with the screw shaft. Since a holder is fixed to the one-way clutch, when the one-way clutch rotates together with the screw shaft, a braking force is generated between the brake shoe, which is fixed to the holder, and the brake disc opposite it. [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, electric actuators equipped with a so-called quick-release function have been developed for medical and nursing care beds, etc., to quickly flatten the bed backrest in emergencies (such as during cardiopulmonary resuscitation). The electric actuator described in Patent Document 1 does not have such a quick-release function, but as long as it is equipped with a mechanism to release the connection between the electric motor and the screw shaft as described in Patent Document 1, the screw shaft will be able to rotate freely, making it possible to quickly flatten the bed backrest by utilizing the load applied to the drive rod.

[0009] One possible method for disengaging the connection between the electric motor and the screw shaft is for the operator to operate a lever or similar device on the electric actuator, thereby disengaging the connection between the electric motor and the screw shaft, as well as the connection between the one-way clutch and the screw shaft. When the above connection is disengaged, the braking force via the screw shaft is completely lost, causing the drive rod to retract at a speed corresponding to the applied load. This could result in the bed user experiencing an impact when the bed's backrest becomes flat, causing significant physical and mental strain.

[0010] The present invention can solve these problems and provides an electric actuator that, when the angle of the bed backrest etc. is flattened in an emergency using a quick-release function, can flatten the backrest etc. at a constant (including nearly constant) safe speed regardless of the load on the bed, thereby mitigating the impact on the user and preventing mental and physical burden. [Means for solving the problem]

[0011] The electric actuator according to the present invention is an actuator that converts the rotational drive of a screw shaft by a motor into linear motion of a rod, and comprises a transmission mechanism that transmits the rotational motion of the motor to the screw shaft, and a component of the transmission mechanism And, due to the rotation of the rotor shaft of the motor, it rotates A first clutch mechanism and a first brake mechanism that apply braking force only to the rotation of the cylindrical part in one direction, and a second clutch mechanism that switches between fixing and releasing the cylindrical part and the screw shaft. Furthermore, a second braking mechanism applies a braking force to the rotation of the screw shaft when the fixing between the cylindrical part and the screw shaft is released. Equipped with, The aforementioned The second clutch mechanism includes a clutch pin located in a shaft hole drilled axially from the base end of the screw shaft and moving within the shaft hole by operation of a clutch lever; a sphere positioned in an opening of the screw shaft communicating with the shaft hole and fixing the transmission mechanism and the screw shaft together by contacting the larger diameter portion of the clutch pin; and a diameter reduction portion formed on the clutch pin, which, when the clutch pin advances into the shaft hole, causes the sphere to disengage from the opening and fit into place, thereby releasing the fixation between the screw shaft and the transmission mechanism. The second brake mechanism comprises a disc that rotates with the screw shaft, a support pin fixed to the disc, a driven pin not fixed to the disc, a spring member connecting the support pin and the driven pin, a cylindrical sliding ring housing the support pin, the driven pin and the disc, and a brake weight supported by the support pin, which rotates with the driven pin around the support pin as the disc rotates, and applies braking force to the screw shaft via the disc by contacting the inner surface of the sliding ring. It is composed of the following features.

[0013] Also, The electric actuator according to the present invention includes a transmission mechanism that transmits the rotational motion of a motor to the screw shaft, and components that constitute the transmission mechanism. And, due to the rotation of the rotor shaft of the motor, it rotates The device comprises a first clutch mechanism and a first brake mechanism that apply braking force only to the rotation of the cylindrical portion in one direction, a second clutch mechanism that switches between fixing and releasing the cylindrical portion and the screw shaft, and a second brake mechanism that applies braking force to the rotation of the screw shaft when the fixing between the cylindrical portion and the screw shaft is released. The second clutch mechanism includes a clutch pin located in a shaft hole drilled axially from the base end of the screw shaft and moving within the shaft hole by operation of a clutch lever, a sphere positioned in an opening of the screw shaft communicating with the shaft hole and fixing the transmission mechanism and the screw shaft together by contacting the larger diameter portion of the clutch pin, and a diameter reduction portion formed on the clutch pin, which releases the fixing between the screw shaft and the transmission mechanism when the clutch pin advances into the shaft hole and the sphere disengages from the opening and fits into it. The second brake mechanism comprises a disc that rotates with the screw shaft, a support pin fixed to the disc, a driven pin not fixed to the disc, a spring member connecting the driven pins, a cylindrical sliding ring housing the support pin, the driven pin and the disc, and a brake weight supported by the support pin, which rotates with the driven pin around the support pin as the disc rotates and contacts the inner surface of the sliding ring, thereby applying braking force to the screw shaft via the disc.

[0014] Furthermore, the brake weight of the electric actuator according to the present invention contacts the inner circumferential surface of the sliding ring against the tensile force of the spring member at a rotational speed greater than or equal to that of the screw shaft when the fixing between the screw shaft and the transmission mechanism and the first clutch mechanism is released, thereby applying a braking force to the screw shaft via the disc. [Effects of the Invention]

[0015] According to the electric actuator of the present invention, a braking force corresponding to the load applied to the bed can be applied to the screw shaft, thereby preventing the bed's backrest, etc., from flattening at an excessive speed. As a result, the impact when the backrest, etc., flattens can be mitigated, preventing mental and physical strain on the user of the bed, etc.

[0016] Furthermore, the backrest and other components can be flattened at a constant (including nearly constant) speed, regardless of the load on the bed. Since this speed is set to a safe speed, the impact on the user when the inclination angle of the backrest and other components becomes flat can be mitigated, thereby ensuring the user's safety. [Brief explanation of the drawing]

[0017] [Figure 1] This is a longitudinal cross-sectional view showing the configuration of the electric actuator according to the present invention. [Figure 2] This is a longitudinal cross-sectional view showing the state of the second clutch mechanism, which constitutes the electric actuator of the present invention, before operation. [Figure 3] It is a longitudinal sectional view showing the state after the operation of the second clutch mechanism constituting the electric actuator of the present invention. [Figure 4] It is a longitudinal sectional view showing the second brake mechanism constituting the electric actuator of the present invention. [Figure 5] It is a longitudinal sectional view showing the mounting state of the support pin and the driven pin of the second brake mechanism constituting the electric actuator of the present invention. [Figure 6] It is a front view showing the second brake mechanism constituting the electric actuator of the present invention. [Figure 7] It is a front view showing another embodiment of the second brake mechanism constituting the electric actuator of the present invention.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described. FIG. 1 is a longitudinal sectional view showing an electric actuator A according to the present invention. The electric actuator A of the present invention includes a motor 3, a transmission mechanism 4, a trapezoidal nut 5, a screw shaft 6, a rod 7, a first clutch mechanism 8, a second clutch mechanism 9, and a first brake mechanism 10 in a case 2 to which an outer pipe 1 is fixed, and a second brake mechanism 11 and an operation mechanism 12 are attached to an end portion (the left end portion in FIG. 1) of the case 1 to form a schematic configuration.

[0019] 13 indicates the rotor shaft of the motor 3, and 14 indicates a worm wheel that meshes with the rotor shaft 13 and converts the rotation direction of the rotor shaft 13 into the vertical direction. 15 is a fitting portion fixed to the inner diameter side of the worm wheel 14 and rotates together with the worm wheel 14 by a bearing 16, and 17 indicates a cylindrical portion fixed to the fitting portion 15 or integrally formed and rotates together with the fitting portion 15 by a bearing 18.

[0020] The transmission mechanism 4 consists of a worm wheel 14, a fitting portion 15, and a cylindrical portion 17. A fitting groove 19 is formed at the base end (left end in Figure 2) of the cylindrical portion 17 for accommodating a part (upper part) of a sphere (steel ball) which will be described later and constitute the second clutch mechanism 9.

[0021] The cylindrical portion 17 rotates the screw shaft 6 located on its inner diameter side via a second clutch mechanism 9. A threaded portion 20 is formed on the tip side of the screw shaft 6 (right side in Figure 1), and a trapezoidal nut 5 having a trapezoidal or similar threaded portion 21 that screws onto the threaded portion 20 is attached to the outer surface of the screw shaft 6.

[0022] The trapezoidal nut 5 is attached to the rod 7 so as to close the opening 22 at the base end of the hollow cylindrical rod 7, and a fixing member 23 is attached to the trapezoidal nut 5 and the rod 7 so as to rotate together. Although the rod 7 is subjected to a rotational force as the screw shaft 6 rotates, the tip of the screw shaft 6 is connected to each floor plate (bottom) via a connecting member (not shown) using the mounting hole 24, so the rod 7 does not rotate.

[0023] As the screw shaft 6 rotates, the trapezoidal nut 5, which is screwed onto the screw shaft 6, moves back and forth along the guide piece 23 inside the outer pipe 1 together with the rod 7. In this embodiment, when the rotor shaft 13 of the motor 3 rotates in the forward direction, the rod 7 moves forward in the direction extending outward from the case 2, and when the rotor shaft 13 rotates in the reverse direction, the rod 7 moves backward so that it is housed inside the case 2.

[0024] The first clutch mechanism 8 is a roller clutch fitted into a clutch holder 25 and installed on the outer circumference of the cylindrical portion 17. When the cylindrical portion 17 rotates in the direction in which the rod 7 extends outward from the case 2, there is no clutch action, and the clutch holder 25 does not rotate in conjunction with the rotation of the cylindrical portion 17. Therefore, the braking force of the first brake mechanism 10 is not applied to the clutch holder 25, and the cylindrical portion 17 rotates smoothly.

[0025] When the cylindrical portion 17 rotates in a direction that houses the rod 7 inside the case 2, the clutch of the first clutch mechanism 8 engages, and the braking force of the first brake mechanism 10 is applied to the clutch holder 25. This braking force from the first brake mechanism 10 is transmitted to the cylindrical portion 17, suppressing the rotational speed of the cylindrical portion 17.

[0026] The first brake mechanism 10 consists of a brake shoe 26 that applies braking force to the brake sliding surface 25a of the clutch holder 25. When the clutch of the first clutch mechanism 8 is engaged, the clutch holder 25 rotates together with the cylindrical portion 17, thereby applying braking force to the rotation of the cylindrical portion 17.

[0027] Next, the second clutch mechanism 9 will be described. As shown in Figure 1, the second clutch mechanism 9 includes a clutch pin 28 positioned in a shaft hole 27 drilled axially (longitudinally) from the base end of the screw shaft 6 located on the operating mechanism 12 side, and a push pin 29 (see Figure 1) that pushes the clutch pin 28 into the shaft hole 27. As shown in Figure 2, the clutch pin 28 has a large diameter portion 30 and a continuous small diameter portion 31 at its tip located at the deepest part of the shaft hole 27.

[0028] 32 is a spherical object (steel ball) that is positioned in the opening 33 of the screw shaft 6 which communicates with the shaft hole 27 and in the fitting groove 19 formed in the cylindrical portion 17 of the transmission mechanism 4, and normally contacts the larger diameter portion 30 of the clutch pin 28, and together with the clutch pin 28 and the push pin 29, constitutes the second clutch mechanism 9.

[0029] When the sphere 32 is not advanced in the direction of the depth of the clutch pin 28 shaft hole 27 (normal state), it is positioned within the fitting groove 19 formed in the cylindrical portion 17 of the transmission mechanism 4 within the opening 33, thereby fixing the transmission mechanism 4 and the screw shaft 6 as shown in Figure 2. On the other hand, when the clutch pin 28 is advanced in the direction of the depth of the shaft hole 27 (quick release), it sinks into the opening 33, disengaging from the fitting groove 19 and moving onto the diameter reduction portion 31, releasing the fixed state between the transmission mechanism 4 and the screw shaft 6 as shown in Figure 3. As a result, the screw shaft 6 can rotate independently of the motor 3 while being supported by the bearing 34.

[0030] Next, the second brake mechanism 11 will be described. As shown in Figures 1 and 4, the second brake mechanism 11 is configured to include a disc 35 fixed to the base end of the screw shaft 6 and rotating together with the screw shaft 6, a support pin 36 and a driven pin 37 attached to the disc 35, a cylindrical sliding ring 38 housing the disc 35, the support pin 36 and the driven pin 37, and a brake weight 39 supported by the disc 35 via the support pin 36, which rotates around the support pin 36 as the disc 35 rotates and contacts a braking member, which will be described later, with the inner surface of the sliding ring 38.

[0031] The brake weight 39 may be constructed by stacking the required number of thin, plate-shaped segmented weights 39a. By using segmented weights 39a, it is possible to adjust the braking force generated between the brake weight and the sliding ring 38. Each segmented weight 39a can be connected to each other to be used as a single brake weight 39.

[0032] As shown in Figure 4, 40 is a sleeve positioned on the outer circumference of the screw shaft 6 to determine the mounting position of the disc 35 and the rotational position of the brake weight 39, and 41 is a push nut for fixing the disc 35 between itself and the sleeve 40.

[0033] Figure 5 shows the mounting structure of the disc 35, the support pin 36, and the brake weight 39 (split weight 39a) and the driven pin 37. The support pin 36 is fixed to the disc 35 by a tightening nut 42 so as not to swing when the brake weight 39 is attached.

[0034] The driven pin 37 is mounted in a through hole 43 (described later) of the brake weight 39, which is positioned on the disc 35, and is not fixed to the disc 35.

[0035] The support pin 36 and the driven pin 37 are connected by a spring pin, which will be described later.

[0036] Figure 6 shows an example of the arrangement of the brake weights 39. As shown in Figure 6, the brake weights 39 have, for example, a roughly crescent shape in plan view and are positioned opposite each other, with the screw shaft 6 and sleeve 40 in between. A support pin 36 passes through a 43 (see Figure 5) formed in each brake weight 39, and each brake weight 39 is pivotally supported on the disc 35 so as to be rotatable around the support pin 36.

[0037] Each brake weight 39 has a through hole 43 into which a driven pin 37 is attached. Each driven pin 37 is connected to a support pin 36 attached to the opposing brake weight 39 by a spring member 44. Under normal conditions, each brake weight 39 is pressed towards the sleeve 40 by the tensile force of the spring member 44, with the support pin 36 as the center.

[0038] If the brake weight 39 is composed of multiple segmented weights 39a, each segmented weight 39a can be connected, for example, by a spring pin 45 as shown in Figure 6.

[0039] As shown in Figure 6, 46 is a braking member attached to the outer circumference of each brake weight 39. When each brake weight 39 is pressed against the sleeve 40, a gap is formed between the braking member 46 and the inner surface of the sliding ring 38. The braking member 46 can be made of rubber, cork, resin, etc., but is not limited thereto.

[0040] The operating mechanism 12 shown in Figure 4 consists of a clutch lever 47 operated manually by the operator and a torsion spring (not shown) that returns the clutch lever 47 to its original position when manual force is released. The clutch lever 47 is operated in emergencies (quick release), and by operating the clutch lever 47, the push pin 29 shown in Figure 1 pushes the clutch pin 28 into the shaft hole 27 of the screw shaft 6, releasing the fixation between the transmission mechanism 4 and the screw shaft 6.

[0041] Next, the operation of the electric actuator A of the present invention will be described. The electric actuator A shown in Figure 1 can normally operate each floor plate (bottom) that makes up the electric bed to change the height of the bed and adjust the angles of the back and knees. Specifically, the tip of the rod 7 of the electric actuator A shown in Figure 1 is connected to each floor plate (bottom) by a connecting member (not shown), and the height and inclination of each floor plate (bottom) are adjusted by moving the rod 7 forward and backward.

[0042] Under normal conditions, the electric actuator A rotates the rotor shaft 13 of the motor 3 in either the forward or reverse direction according to the operator's remote control input. When the rotor shaft 13 rotates in the forward direction, the rotation of the rotor shaft 13 is transmitted to the worm wheel 14, and together with the worm wheel 14, the fitting portion 15 of the transmission mechanism 4 rotates in the forward direction using the bearing 16.

[0043] As a result, the cylindrical portion 17 fixed to (or integrally molded with) the fitting portion 15 rotates in the forward direction, and the sphere 32, which is partially housed in the fitting groove 19 of the cylindrical portion 17 and located inside the opening 33 of the screw shaft 6, transmits the rotation of the cylindrical portion 17 to the screw shaft 6, causing the screw shaft 6 to rotate in the forward direction.

[0044] The screw shaft 6 rotates via the cylindrical portion 17 on the bearing 18, and the trapezoidal nut 5, which has a threaded portion 21 that screws onto the threaded portion 20 of the screw shaft 6, moves along the inner surface of the outer pipe 1, causing the rod 7 to move from inside the outer pipe 1 to the outside.

[0045] As rod 7 extends, the linkage mechanism connected to it raises the height of the bed and adjusts the angles of the bottom parts, such as the knee area and backrest.

[0046] Furthermore, when the cylindrical portion 17 rotates due to the forward rotation of the rotor shaft 13 in this manner, the clutch action of the first clutch mechanism 8 is not performed, and the clutch holder 25 does not rotate in conjunction with the rotation of the cylindrical portion 17. Therefore, no braking force from the first brake mechanism 10 is applied to the clutch holder 25, and the cylindrical portion 17 and the screw shaft 6 rotate smoothly.

[0047] When the rotor shaft 13 of the motor 3 rotates in the reverse direction due to the operator's remote control operation, the rotation of the rotor shaft 13 is transmitted to the worm wheel 14, and the fitting portion 15 of the worm wheel 14 and the transmission mechanism 4 rotates in the reverse direction due to the bearing 16.

[0048] As a result, the cylindrical portion 17 fixed to (or integrally molded with) the fitting portion 15 rotates in the reverse direction, and the sphere 32, which is partially housed in the fitting groove 19 of the cylindrical portion 17 and located inside the opening 33 of the screw shaft 6, transmits the rotation of the cylindrical portion 17 to the screw shaft 6, causing the screw shaft 6 to rotate in the reverse direction.

[0049] The screw shaft 6 rotates via the cylindrical portion 17 on the bearing 18, and the trapezoidal nut 5, which has a threaded portion 21 that screws onto the threaded portion 20 of the screw shaft 6, moves along the inner surface of the outer pipe 1, causing the rod 7 to retract so that it is housed inside the outer pipe 1.

[0050] The retraction of rod 7 activates the linkage mechanism of the electric bed connected to it, lowering the height of the bed and adjusting the angles of the various bottom parts such as the knee rest and backrest.

[0051] When the cylindrical portion 17 rotates due to the reverse rotation of the rotor shaft 13, the clutch of the first clutch mechanism 8 engages, and the braking force of the first brake mechanism 10 is applied to the clutch holder 25. This braking force from the first brake mechanism 10 is transmitted to the cylindrical portion 17, suppressing the rotational speed of the cylindrical portion 17 and the screw shaft 6.

[0052] In the normal operation described above, the second brake mechanism 11 shown in Figure 4 does not operate. This is because, although the brake weight 39 in Figure 6, which constitutes the second brake mechanism 11, rotates together with the screw shaft 6 via the disc 35 and support pin 36 due to the rotation of the screw shaft 6, the tensile force of the spring member 44 connecting the support pin 36 and the driven pin 37 is adjusted such that, at the normal rotational speed of the screw shaft 6, the brake weight 39 rotates outward around the support pin 36, preventing the braking member 46 from contacting the inner surface of the sliding ring 38.

[0053] Next, we will explain how to use the electric actuator A as a quick-release function in an emergency, such as when cardiopulmonary resuscitation is required, to adjust (flatten) the angle of the bed backrest. In this case, the rod 7 of the electric actuator A shown in Figure 1 moves backward, quickly flattening the angle of the bed backrest, which is connected to the tip of the rod 7 via a connecting member (not shown).

[0054] In the event of an emergency, such as those described above, if it is necessary to quickly release the bed backrest, the operator operates an operating lever (not shown) located on the bed side to rotate the clutch lever 47 shown in Figure 4 clockwise via a wire connected to the operating lever. This rotation is performed against the elastic force of a torsion spring (not shown) provided on the clutch lever 47.

[0055] The rotation of the clutch lever 47 pushes the push pin 29 shown in Figure 1, causing the clutch pin 28 to advance into the shaft hole 27 of the screw shaft 6. As the clutch pin 28 advances, the sphere 32, which was resting on the larger diameter portion 30 of the clutch pin 28 as shown in Figure 2, drops onto the smaller diameter portion 31 as shown in Figure 3, disengaging the engagement between the upper part of the sphere 32 and the fitting groove 19 formed in the cylindrical portion 17 of the transmission mechanism 4.

[0056] As a result, the screw shaft 6 is disconnected from the motor 3 via the transmission mechanism 4, and the braking action of the first brake mechanism 10 is also released, allowing it to rotate freely. A rod 7 is connected to the screw shaft 6 via a trapezoidal nut 5, and a load (such as the weight of the patient on the bed or the bed itself) is applied to the rod 7, causing the rod 7 to retract into the outer pipe 1 due to this load.

[0057] At this time, the screw shaft 6 rotates in the reverse direction, but the rotational speed of the screw shaft 6 at this time exceeds the normal rotational speed because the braking force of the first brake mechanism 10 is not acting.

[0058] The rotation of the screw shaft 6 rotates the disc 35 shown in Figure 6, which in turn rotates the brake weight 39 via a support pin 36 erected on the disc 35. The tensile force of the spring member 44 connecting the support pin 36 and the driven pin 37 is adjusted so that, at the normal rotation speed of the screw shaft 6, the brake weight 39 rotates outward around the support pin 36, preventing the braking member 46 from contacting the inner surface of the sliding ring 38. However, at rotation speeds exceeding the normal speed during quick release, the brake weight 39 rotates outward around the support pin 36 against the tensile force of the spring member 44, causing the braking member 46 to contact the inner surface of the sliding ring 38.

[0059] As a result, braking force is applied to the screw shaft 6 via the brake weight 39, support pin 36, and disc 35, reducing the rotational speed of the screw shaft 6. The magnitude of this braking force is proportional to the load applied to the rod 7. When the load applied to the rod 7 is large, the braking force applied to the screw shaft 6 is large, and when the load applied to the rod 7 is small, the braking force applied to the screw shaft 6 is small.

[0060] Therefore, the bed on which the patient is lying can be lowered at a constant (including nearly constant) speed for any patient, regardless of the patient's weight. This speed is set to a safe speed, which mitigates the impact on the patient when the backrest tilts to a flat position, thus ensuring the patient's safety. The speed at which the patient lies safe can be adjusted not only by changing the tensile force of the spring member 44 shown in Figure 4, but also by changing the number of segmented weights 39a.

[0061] Figure 7 is a front view showing another embodiment of the second brake mechanism 11. In Figure 7, a support pin 36 passes through a through hole 43 formed above the brake weights 39, which are positioned opposite each other across the screw shaft 6 and sleeve 40. Each brake weight 39 is pivotally supported on the disc 35 so as to be rotatable around the support pin 36.

[0062] Furthermore, a driven pin 37 is attached to a through hole 43 formed below each brake weight 39, and the driven pins 37 are connected to each other by a spring member 44. Under normal conditions, each brake weight 39 is pressed towards the sleeve 40 by the tensile force of the spring member 44, with the support pin 36 as the center.

[0063] Furthermore, as in the case of Figure 6, a braking member 46 is attached to the outer edge of each brake weight 39, and when each brake weight 39 is pressed against the sleeve 40, a gap is formed between the braking member 46 and the inner surface of the sliding ring 38.

[0064] When the screw shaft 6 rotates at a speed exceeding normal during quick release, the rotation of the screw shaft 6 rotates the disc 35 shown in Figure 7, and via the support pins 36 erected on the disc 35, the brake weight 39 rotates. The tensile force of the spring member 44 connecting the driven pins 37 is adjusted so that, at the normal rotation speed of the screw shaft 6, the brake weight 39 rotates outward around the support pins 36, preventing the braking member 46 from contacting the inner surface of the sliding ring 38. However, at a rotation speed exceeding normal during quick release, the brake weight 39 rotates outward around the support pins 36 against the tensile force of the spring member 44, causing the braking member 46 to contact the inner surface of the sliding ring 38.

[0065] As a result, braking force is applied to the screw shaft 6 via the brake weight 39, support pin 36, and disc 35, reducing the rotational speed of the screw shaft 6. The magnitude of this braking force is also proportional to the load applied to the rod 7; if the load applied to the rod 7 is large, the braking force applied to the screw shaft 6 will be large, and if the load applied to the rod 7 is small, the braking force applied to the screw shaft 6 will be small.

[0066] Therefore, the bed on which the patient is lying can be tilted down at a constant (including nearly constant) speed for any patient, regardless of the patient's weight. This speed is set to a safe speed, which can mitigate the impact on the patient when the tilt angle of the backrest becomes flat, thereby ensuring the patient's safety. In other words, the second brake mechanism 11 is not limited to the structure shown in Figure 6, but the objective of the present invention can also be achieved with the structure shown in Figure 7.

[0067] As described above, the electric actuator A of the present invention can apply a braking force to the screw shaft 6 in accordance with the load applied to the rod 7. For example, the backrest of the bed can always be lowered at the optimal speed, regardless of the weight of the user on the bed. This reduces the impact when the backrest or other parts are lowered, preventing mental and physical strain on the user of the bed.

[0068] In the above embodiment, the quick-release function of the electric actuator A was described in the case of eliminating (flattening) the tilt angle of the backrest of the electric bed. However, the quick-release function can also be used to eliminate the angle of the knee area of ​​the electric bed or to quickly lower the height of the electric bed. In any of these applications, the retraction speed of the rod 7 should be set to a safe speed that does not cause physical or psychological burden to the patient on the bed, as in the case of eliminating the backrest angle.

[0069] Furthermore, the applications of the electric actuator A according to the present invention are not limited to electric beds as described in the above embodiments, but can be applied to any equipment that can utilize the present invention.

[0070] Furthermore, the scope of the present invention is not limited to the structure of the electric actuator A described with reference to Figures 1 to 7, but naturally extends to structures modified without departing from the spirit of the present invention. For example, the brake weights 39 shown in Figures 6 and 7 are not limited to two opposing weights connected by a screw shaft 6, but may be three or more, and the present invention can also be established by swapping the vertical positions of the support pin 36 and the driven pin 37 (spring member 44) shown in Figure 7. [Industrial applicability]

[0071] This invention is applicable as an operating mechanism for any device that utilizes a quick-release function. [Explanation of Symbols]

[0072] 1. Outer pipe 2 cases 3 motors 4. Transmission mechanism 5 trapezoidal nuts 6 Screw shaft 7 rods 8. First clutch mechanism 9. Second clutch mechanism 10. First braking mechanism 11. Second braking mechanism 12 Operating mechanism 13 Rotor shaft 14 Worm Wheel 15. Fitting part 16, 18, 34 bearings 17 Cylindrical section 19 Fitting groove 20,21 Screw part 22 Proximal opening 23 Fixing member 24 mounting holes 25 Clutch holder 26 Brake shoes 27 Shaft hole 28 Clutch pin 29 Push pins 30 Diameter Large Part 31 Reduced diameter part 32 Sphere (steel ball) 33 Aperture 35 discs 36 Support pins 37 Driven pin 38 Sliding ring 39 Brake weights 39a Split weights 40 sleeves 41 Pushnut 42 Tightening nuts 43 Through hole 44 Spring component 45 Spring Pins 46 Braking member 47 Clutch lever

Claims

1. In an actuator that converts the rotational drive of a screw shaft by a motor into the linear motion of a rod, the actuator comprises: a transmission mechanism that transmits the rotational motion of the motor to the screw shaft; a first clutch mechanism and a first brake mechanism that constitute the transmission mechanism and apply braking force only to the rotation in one direction of a cylindrical part that rotates due to the rotation of the rotor shaft of the motor; a second clutch mechanism that switches between fixing and releasing the cylindrical part and the screw shaft; and a second brake mechanism that applies braking force to the rotation of the screw shaft when the fixing between the cylindrical part and the screw shaft is released, wherein the second clutch mechanism is located in a shaft hole drilled axially from the base end of the screw shaft and moves within the shaft hole by operation of a clutch lever, and is located in an opening of the screw shaft that communicates with the shaft hole and contacts the larger diameter portion of the clutch pin to operate the transmission mechanism An electric actuator comprising a sphere that fixes the structure and the screw shaft, and a diameter reduction portion formed on the clutch pin, which releases the fixation between the screw shaft and the transmission mechanism when the clutch pin advances into the shaft hole and the sphere disengages from the opening and fits into place, the second brake mechanism comprising a disc that rotates together with the screw shaft, a support pin fixed to the disc, a driven pin not fixed to the disc, a spring member connecting the support pin and the driven pin, a cylindrical sliding ring housing the support pin, the driven pin and the disc, and a brake weight supported by the support pin, which rotates together with the driven pin around the support pin as the disc rotates and contacts the inner surface of the sliding ring, thereby applying braking force to the screw shaft via the disc.

2. In an actuator that converts the rotational drive of a screw shaft by a motor into linear motion of a rod, the actuator comprises: a transmission mechanism that transmits the rotational motion of the motor to the screw shaft; a first clutch mechanism and a first brake mechanism that constitute the transmission mechanism and apply braking force only to the rotation of a cylindrical part that rotates due to the rotation of the rotor shaft of the motor; a second clutch mechanism that switches between fixing and releasing the cylindrical part and the screw shaft; and a second brake mechanism that applies braking force to the rotation of the screw shaft when the fixing between the cylindrical part and the screw shaft is released, wherein the second clutch mechanism is located in a shaft hole drilled axially from the base end of the screw shaft and moves within the shaft hole by operation of a clutch lever, and is located in an opening of the screw shaft that communicates with the shaft hole and contacts the larger diameter portion of the clutch pin to transmit the An electric actuator comprising a sphere that fixes the drive mechanism and the screw shaft, and a diameter reduction portion formed on the clutch pin, which releases the fixation between the screw shaft and the drive mechanism when the clutch pin advances into the shaft hole and the sphere disengages from the opening and fits into place, the second brake mechanism comprising a disc that rotates together with the screw shaft, a support pin fixed to the disc, a driven pin not fixed to the disc, a spring member connecting the driven pins, a cylindrical sliding ring housing the support pin, the driven pin and the disc, and a brake weight supported by the support pin, which rotates together with the driven pin around the support pin as the disc rotates and contacts the inner surface of the sliding ring, thereby applying braking force to the screw shaft via the disc.

3. The electric actuator according to either Claim 1 or Claim 2, characterized in that the brake weight contacts the inner circumferential surface of the sliding ring against the tensile force of the spring member at a rotational speed greater than or equal to that of the screw shaft when the fixing between the screw shaft and the transmission mechanism is released, thereby applying a braking force to the screw shaft via the disc.

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