Load limiting device

Abstract

To prove a load limiting device capable of effectively limiting a shock load without causing lowering of stiffness.SOLUTION: A load limiting device 10 limits a load F to be input to a protection target O from the external environment, and includes: a first member to which the load F is input; a second member attached to the protection target O; a connection member which connects the first member and the second member so that the first member can be displaced only in a direction (Z-direction) of the load F with respect to the second member; and a first gas spring and a second gas spring which are disposed in a space between the first member and the second member and to which a force corresponding to the load F is input via the connection member. The first gas spring is displaced only when the load F is a compressive load and the input force is equal to or more than a preset first initial load. The second gas spring is displaced only when the load F is a tensile load and the input force is equal to or more than a preset second initial load.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a load limiting device that limits compressive loads and tensile loads input to a protection target within a preset range.

Background Art

[0002] In recent years, the use of electric cylinders in place of hydraulic cylinders as linear actuators has been studied in various fields. Electric cylinders are expected to enable more precise position control than hydraulic cylinders. On the other hand, electric cylinders are composed of mechanical structures where metals come into contact and slide or roll, such as speed reducers (gears) that reduce the rotation of the electric motor, and rotation-linear motion conversion mechanisms such as ball screws that perform linear motion (extension and retraction) by receiving the reduced rotation. Therefore, there is a problem that electric cylinders are more vulnerable to large loads input from the external environment compared to hydraulic cylinders.

[0003] As a conventional device capable of solving the above problem, for example, the device described in Patent Document 1 is known. According to this device, when the force input from one member to the other member reaches or exceeds a predetermined threshold value, the magnetic plate detaches from the magnet, thereby preventing a force equal to or greater than the threshold value from being input to the other member. In this device, the threshold value for limiting the force input from one member to the other member is determined by magnetic force. That is, the settable threshold value is limited by the strength of the magnetic force. For electric cylinders with large output thrust (large load input from the external environment), it is expected that the transmittable thrust will be insufficient with the threshold value that can be set by magnetic force.

[0004] The above problems can also be solved by methods such as (1) installing an elastic body between the load input and the electric cylinder, (2) using an electric cylinder with a sliding screw that is more resistant to impact than a typical ball screw, (3) providing a mechanical clutch mechanism between the load input and the electric cylinder, or (4) providing a software clutch in the electric motor's control system. However, method (1) reduces the rigidity related to high-precision position control, method (2) reduces efficiency, and method (3) increases weight. Furthermore, method (4) cannot adequately limit rapidly changing loads (i.e., impact loads) because there is a response delay in software control. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2001-3951 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above circumstances, and aims to provide a load limiting device that can effectively limit impact loads without causing a decrease in rigidity. [Means for solving the problem]

[0007] To solve the above problems, the load limiting device according to the present invention limits the load that the external environment inputs to the object to be protected, and comprises a first member to which the load is input, a second member attached to the object to be protected, a connecting member that connects the first member and the second member such that the first member can be displaced with respect to the second member only in the direction of the expected load, and a first gas spring and a second gas spring arranged in the space between the first member and the second member, to which a force corresponding to the load is input via the connecting member, wherein the first gas spring displaces and limits the load only when the load is a compressive load that brings the first member closer to the second member and the force input via the connecting member is greater than or equal to a preset first initial load, and the second gas spring displaces and limits the load only when the load is a tensile load that moves the first member away from the second member and the force input via the connecting member is greater than or equal to a preset second initial load.

[0008] The above load limiting device comprises, for example, a first member, a second member, and a connecting member. Saralink It may constitute a mechanism.

[0009] The load limiting device may further include, for example, a first force transmission member connected to a first link mechanism constituting a connecting member and the input end of a first gas spring, which is displaceable in a direction perpendicular to the direction of the load; a second force transmission member connected to a second link mechanism constituting a connecting member and the input end of a second gas spring, which is displaceable in a direction perpendicular to the direction of the load; and a gas spring support member connected to the base end of the first gas spring and the base end of the second gas spring, wherein the first link mechanism and the second link mechanism are opposite to each other.

[0010] The load limiting device may further include a force sensor provided between the gas spring support member and the base end of the first gas spring, or between the gas spring support member and the base end of the second gas spring.

[0011] Furthermore, the "first gas spring" and "second gas spring" described above include mechanical elements equivalent to gas springs that have a relatively large initial load (for example, an initial load of several kgf to tens of tons or more) and whose load change in response to stroke changes is slower than other springs such as coil springs, rubber springs, and leaf springs (preferably, the load hardly changes in response to stroke changes) (see Figure 8). The slow change in load in response to stroke changes is important for accurately limiting the load with the preset first load F1 and second load F2 (see Figure 2). [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a load limiting device that can effectively limit impact loads without causing a decrease in rigidity. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view showing a load limiting device according to an embodiment of the present invention. [Figure 2] This graph shows the effects of the load limiting device according to the embodiment. [Figure 3] This figure shows the components of a load limiting device according to an embodiment, where (A) is a perspective view showing the load conversion section and (B) is a perspective view showing the load limiting section. [Figure 4] This figure shows the load limiting section in the embodiment, where (A) is a plan view and (B) is a front view. [Figure 5] A simplified diagram of a load limiting device according to an embodiment, where (A) is a simplified diagram when the load F is greater than or equal to the first load F1, (B) is a simplified diagram when the load F is greater than the second load F2 and less than the first load F1, and (C) is a simplified diagram when the load F is less than or equal to the second load F2. [Figure 6]A front view showing the load limiting device according to the embodiment, wherein (A) is a front view when the load F is equal to or greater than the first load F1, (B) is a front view when the load F is greater than the second load F2 and smaller than the first load F1, and (C) is a front view when the load F is equal to or less than the second load F2. [Figure 7] A plan view showing the load limiting portion in the embodiment, wherein (A) is a plan view when the load F is equal to or greater than the first load F1, (B) is a plan view when the load F is greater than the second load F2 and smaller than the first load F1, and (C) is a plan view when the load F is equal to or less than the second load F2. [Figure 8] It is a graph showing the characteristics of a gas spring and other springs. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] Hereinafter, embodiments of the load limiting device according to the present invention will be described with reference to the accompanying drawings. Note that in the present specification, a left-handed system is used as the coordinate system instead of a (general) right-handed system, which has no particular significance, and the operational effects will not change at all even if the description is made using a right-handed system.

[0015] [Embodiment] FIG. 1 shows a load limiting device 10 according to an embodiment of the present invention. As shown in the figure, the load limiting device 10 is used by being attached to the distal end portion of a protection target O constituted by an electric cylinder or the like, and limits the load F that the external environment inputs to the protection target O. More specifically, as shown in FIG. 2, the load limiting device 10 cuts off the portion of the compressive load which is a positive load F that exceeds a preset first load F1, and the portion of the tensile load which is a negative load F that falls below a preset second load F2, so that only the hatched portion is input to the protection target O.

[0016] Note that in the present embodiment, the distal end portion of the protection target O has a mounting surface parallel to the XY plane. Further, in the present embodiment, the load F in the Z direction is input to the load limiting device 10.

[0017] The load limiting device 10 includes a load conversion unit 20 shown in Figure 3(A) and a load limiting unit 30 shown in Figure 3(B).

[0018] The load conversion unit 20 is configured to convert a load F in the Z direction into a force in the X direction, and includes a top plate 21 to which the load F is input, a bottom plate 22 attached to the mounting surface of the protection target O, and four link mechanisms 23, 24, 25, 26. The terms "top plate" and "bottom plate" do not mean that the member indicated by reference numeral 21 is located above the member indicated by reference numeral 22. Further, the link mechanisms 23, 24, 25, 26 correspond to the "connecting member" of the present invention.

[0019] The top plate 21 corresponds to the "first member" of the present invention. The top plate 21 has connecting portions 21a, 21d formed of through holes extending in the Y direction, and connecting portions 21c, 21d formed of through holes extending in the X direction. In this embodiment, the connecting portions 21a, 21b are provided at opposite edge portions of the top plate 21 that are spaced apart in the X direction, and the connecting portions 21c, 21d are provided at opposite edge portions of the top plate 21 that are spaced apart in the Y direction.

[0020] The bottom plate 22 corresponds to the "second member" of the present invention. The bottom plate 22 has connecting portions 22a, 22b formed of through holes extending in the Y direction, and connecting portions 22c, 22d formed of through holes extending in the X direction. In this embodiment, the connecting portions 22a, 22b are provided at opposite edge portions of the bottom plate 22 that are spaced apart in the X direction, and the connecting portions 22c, 22d are provided at opposite edge portions of the bottom plate 22 that are spaced apart in the Y direction.

[0021] The first link mechanism 23 is composed of a top plate side link member 231 and a bottom plate side link member 232. The top plate side link member 231 is rotatably connected to the connecting portion 21a of the top plate 21 at its upper end. The bottom plate side link member 232 is rotatably connected to the connecting portion 22a of the bottom plate 22 at its lower end. The lower end of the top plate side link member 231 and the upper end of the bottom plate side link member 232 are also rotatably connected.

[0022] The second link mechanism 24 consists of a top plate side link member 241 and a bottom plate side link member 242. The top plate side link member 241 is rotatably connected at its upper end to the connecting portion 21b of the top plate 21. The bottom plate side link member 242 is rotatably connected at its lower end to the connecting portion 22b of the bottom plate 22. The lower end of the top plate side link member 241 and the upper end of the bottom plate side link member 242 are also rotatably connected.

[0023] The third link mechanism 25 consists of a top plate side link member 251 and a bottom plate side link member 252. The top plate side link member 251 is rotatably connected at its upper end to the connecting portion 21c of the top plate 21. The bottom plate side link member 252 is rotatably connected at its lower end to the connecting portion 22c of the bottom plate 22. The lower end of the top plate side link member 251 and the upper end of the bottom plate side link member 252 are also rotatably connected.

[0024] The fourth link mechanism 26 consists of a top plate side link member 261 and a bottom plate side link member 262. The top plate side link member 261 is rotatably connected at its upper end to the connecting portion 21d of the top plate 21. The bottom plate side link member 262 is rotatably connected at its lower end to the connecting portion 22d of the bottom plate 22. The lower end of the top plate side link member 261 and the upper end of the bottom plate side link member 262 are also rotatably connected.

[0025] The top plate 21, the bottom plate 22, and the four link mechanisms 23, 24, 25, 26 are a type of parallel link. Saralink This constitutes the mechanism. Therefore, when a positive load F (compressive load) is applied to the top plate 21, the top plate 21 moves closer to the bottom plate 22 while remaining directly facing it. On the other hand, when a negative load F (tensile load) is applied to the top plate 21, the top plate 21 moves away from the bottom plate 22 while remaining directly facing it. The link mechanisms 23, 24, 25, and 26 can be said to connect the top plate 21 to the bottom plate 22 in such a way that the top plate 21 is displaced only in the Y direction relative to the bottom plate 22.

[0026] In this embodiment, the top plate 21 and the link mechanisms 23, 24, 25, 26, the bottom plate 22 and the link mechanisms 23, 24, 25, 26, and the top plate side link member 231 and the bottom plate side link member 232 in each link mechanism (for example, the first link mechanism 23) are rotatably connected by a combination of bolts and nuts, but this is merely one example. In the present invention, in order to enable the movement of each part of the load conversion section 20, a mechanism with play equivalent to or less than that of a combination of bolts and nuts may be employed. For example, a combination of a rotating shaft and a ball bearing, or a rotating shaft and a bush, etc., may be employed.

[0027] As shown in Figures 3(B) and 4, the load limiting section 30 includes a first force transmission member 31, a second force transmission member 32, a gas spring support member 33, one first gas spring 40, two second gas springs 50, 50, and a force sensor 60.

[0028] The first force transmission member 31 has a gas spring connection portion 31b extending in the Y direction and a link connection portion 31a extending in the -X direction from the center of the gas spring connection portion 31b. The gas spring connection portion 31b is connected to the input end of the second gas springs 50, 50 (the tip of the piston rods 50a, 50a). The link connection portion 31a is rotatably connected to the movable part of the first link mechanism 23, that is, the connecting portion of the top plate side link member 231 and the bottom plate side link member 232. When the movable part of the first link mechanism 23 is displaced in the ±X direction, the first force transmission member 31 is also displaced by the same amount in the ±X direction.

[0029] The second force transmission member 32 has a link connection portion 32a extending in the X direction, a gas spring connection portion 32b located spaced apart from the link connection portion 32a in the -X direction, and guide portions 32c and 32d extending in the X direction so as to sandwich the gas spring support member 33 from above and below (Z direction) with a small gap between them, and connecting the link connection portion 32a and the gas spring connection portion 32b. The link connection portion 32a is rotatably connected to the movable part of the second link mechanism 24, that is, the connecting portion of the top plate side link member 241 and the bottom plate side link member 242. The gas spring connection portion 32b is connected to the input end of the first gas spring 40 (the tip of the piston rod 40a). When the movable part of the second link mechanism 24 is displaced in the ±X direction, the second force transmission member 32 is also displaced by the same amount in the ±X direction.

[0030] The gas spring support member 33 has a first support portion 33a connected to one of the base ends (end of tube 50b) of the second gas springs 50, 50 and extending in the X direction, a second support portion 33b connected to the other base end (end of tube 50b) and extending in the X direction, and a third support portion 33c that is continuous with both the first support portion 33a and the second support portion 33b and connected to the base end (end of tube 40b) of the first gas spring 40 via a force sensor 60. In particular, as shown in Figure 4(A), the gas spring support member 33 has a U-shape or a V-shape.

[0031] The gas spring support member 33 can slide non-contact with respect to the second force transmission member 32 only in the X direction.

[0032] The first gas spring 40 is a compression-type gas spring in which the fully extended state is the initial unloaded state and a reaction force is generated when it is compressed. It has a cylindrical tube 40b filled with gas and a piston rod 40a that is slidable relative to the tube 40b. When the force input to the piston rod 40a as the input end is less than the first initial load Fth1 (Fth1 = F1 × α, where α is the conversion coefficient of the load conversion section 20 including the first link mechanism 23 and the second link mechanism 24) corresponding to the first load F1 (see Figure 2), the piston rod 40a takes a state in which most of it is extended out of the tube 40b (initial state) (see Figures 7(B) and (C)). Furthermore, when a force of the first initial load Fth1 or greater is input to the piston rod 40a, it is retracted into the tube 40b, and finally takes a state in which most of it is retracted into the tube 40b (full stroke state) (see Figure 7(A)).

[0033] The second gas springs 50, 50 are compression-type gas springs similar to the first gas spring 40, and each has a cylindrical tube 50b filled with gas and a piston rod 50a that is slidable relative to the tube 50b. When the force applied to the piston rod 50a as the input end is less than the second initial load Fth2 (Fth2 = -F2 × 0.5 × α) corresponding to the second load F2 (see Figure 2), the piston rod 50a is in a state where most of it is extended out of the tube 50b (initial state) (see Figures 7(A) and (B)). When a force of Fth2 or greater is applied to the piston rod 50a, it is retracted into the tube 50b, and finally, it is in a state where most of it is retracted into the tube 50b (full stroke state) (see Figure 7(C)).

[0034] As mentioned above, the first force transmission member 31, the second force transmission member 32, and the gas spring support member 33 are displaced only in the ±X direction. Therefore, no force in any direction other than the X direction is applied to the first gas spring 40 and the second gas springs 50, 50. It can be said that the first gas spring 40 and the second gas springs 50, 50 are mechanically protected from being subjected to forces in any direction other than the X direction.

[0035] In this embodiment, the second initial load Fth2 is set to 25 kgf, which is half of the first initial load Fth1 (for example, 50 kgf), so that the absolute values ​​of the first load F1 and the second load F2 are equal.

[0036] The first load F1 (first initial load Fth1) and the second load F2 (second initial load Fth2) roughly correspond to predetermined thresholds in the device described in Patent Document 1. In the device described in Patent Document 1, due to limitations in magnetic force strength, it is not possible to achieve thresholds of several tens of kgf or more without arranging a large number of relatively strong magnets. On the other hand, since gas springs generally have an initial load of several tens of kgf or more on their own, the present invention avoids such inconveniences and makes it possible to realize a small and lightweight load limiting device.

[0037] The force sensor 60 detects the force in the X direction acting between the tube 40b of the first gas spring 40 and the third support portion 33c of the gas spring support member 33, and outputs the detected result as an appropriate electrical signal. As described above, the gas spring support member 33 slides only in the X direction relative to the second force transmission member 32. Therefore, no force in any direction other than the X direction is input to the force sensor 60. It can be said that the force sensor 60 is mechanically protected from input of forces in directions other than the X direction.

[0038] Figure 5 shows a simplified diagram of the load limiting device 10 with the force sensor 60 omitted. As shown in the figure, the first link mechanism 23 is connected to the input ends of the second gas springs 50, 50 (the tips of the piston rods 50a, 50a) via the first force transmission member 31. The second link mechanism 24 is connected to the input end of the first gas spring 40 (the tip of the piston rod 40a) via the second force transmission member 32. In addition, the base end of the first gas spring 40 (the end of the tube 40b) and the base ends of the second gas springs 50, 50 (the ends of the tubes 50b, 50b) are interconnected via the gas spring support member 33.

[0039] Therefore, when a positive load F smaller than the first load F1, i.e., a compressive load that does not require restriction, is input to the load limiting device 10, and a force in the -X direction is applied to the movable part of the first link mechanism 23 (the connecting part of the top plate side link member 231 and the bottom plate side link member 232), and a force in the +X direction is applied to the movable part of the second link mechanism 24 (the connecting part of the top plate side link member 241 and the bottom plate side link member 242), a force is input to the first gas spring 40 that attempts to compress it (see Figure (B)). Then, when the input load F becomes equal to or greater than the first load F1, and the force attempting to compress the first gas spring 40 becomes equal to or greater than the first initial load Fth1, the first gas spring 40 compresses (see Figure (A)).

[0040] On the other hand, when a negative load F greater than the second load F2, i.e., a tensile load that does not require restriction, is input to the load limiting device 10, and a force in the +X direction is applied to the movable part of the first link mechanism 23 and a force in the -X direction is applied to the movable part of the second link mechanism 24, an equal force is applied to each of the second gas springs 50, 50 that attempts to compress them (see Figure (B)). Then, when the input load F becomes less than or equal to the second load F2, and the force attempting to compress the second gas springs 50, 50 becomes greater than or equal to the second initial load Fth2, the second gas springs 50, 50 compress (see Figure (C)).

[0041] The movement (deformation) of the load limiting device 10 when a load F is applied will be explained in more detail with reference to Figures 6 and 7. Note that the third link mechanism 25 and the fourth link mechanism 26 are omitted from Figure 6, and the load conversion unit 20 is omitted from Figure 7.

[0042] When the load F is greater than the second load F2 and less than the first load F1, that is, when the load F is zero, a relatively small compressive load, or a relatively small tensile load, the load limiting device 10 takes the state in which the first gas spring 40 and the second gas springs 50,50 are not compressed (initial state) (see Figures 6(B) and 7(B)). The reason the first gas spring 40 does not compress is that the force in the X direction (= load F × conversion coefficient α) that the load conversion unit 20, including the first link mechanism 23 and the second link mechanism 24, inputs to the first gas spring 40 has not reached the first initial load Fth1. Similarly, the reason the second gas springs 50,50 do not compress is that the force in the X direction (= 0.5 × load F × conversion coefficient α) that the load conversion unit 20 inputs to each of the second gas springs 50,50 has not reached the second initial load Fth2.

[0043] At this time, the force sensor 60 outputs an electrical signal relating to the force in the X direction output by the load conversion unit 20, that is, a force proportional to the load F.

[0044] Furthermore, at this time, the load F is directly input to the protected object O.

[0045] When the load F is greater than or equal to the first load F1, that is, when the load F is a relatively large compressive load that should be limited, the load limiting device 10 takes a state in which the first gas spring 40 is compressed but the second gas springs 50, 50 are not compressed (see Figures 6(A) and 7(A)). The first gas spring 40 is compressed (displaced) because the force in the X direction that the load conversion unit 20 inputs to the first gas spring 40 has reached the first initial load Fth1.

[0046] At this time, the force sensor 60 outputs an electrical signal relating to the force in the X direction, i.e., the first initial load Fth1, which is limited by the load limiting unit 30, which is composed of the first gas spring 40 and the like.

[0047] At this time, the first load F1 is input to the protected object O.

[0048] When the load F is less than or equal to the second load F2, that is, when the load F is a relatively large tensile load that should be limited, the load limiting device 10 takes a state in which the first gas spring 40 is not compressed, but the second gas springs 50, 50 are each compressed (see Figures 6(C) and 7(C)). The reason why the second gas springs 50, 50 are compressed (displaced) is that the force in the X direction that the load conversion unit 20 inputs to each of the second gas springs 50, 50 has reached the second initial load Fth2.

[0049] At this time, the force sensor 60 outputs an electrical signal corresponding to the force in the X direction, i.e., the second initial load Fth2, which is limited by the load limiting section 30 composed of the second gas springs 50, 50, etc.

[0050] At this time, a second load F2 is input to the protected object O.

[0051] Thus, according to the load limiting device 10 of this embodiment, the portion of the compressive load (positive load F) that exceeds a preset first load F1 and the portion of the tensile load (negative load F) that falls below a preset second load F2 are cut off, and only the hatched portion is input to the protected object O (see Figure 2).

[0052] Furthermore, the load limiting device 10 according to this embodiment does not use an elastic body like the one used in the conventional method (1). Therefore, the load limiting device 10 can prevent an excessive load F from being input to the protected object O without causing a decrease in rigidity.

[0053] However, the load limiting device 10 according to this embodiment cannot continuously limit the large compressive load applied after the first gas spring 40 has fully compressed (full stroke state), nor the large tensile load applied after the second gas springs 50, 50 have fully compressed (full stroke state). However, this problem can be easily resolved by using a software-based clutch (conventional method (4)) that starts operating slowly but continues to operate indefinitely.

[0054] Conversely, by using the conventional method (4) in combination, the gas springs 40, 50, and 50 can focus solely on rapidly changing loads (impact loads) (i.e., only the high-frequency components of the load), making it possible to design a smaller required stroke. This enables further miniaturization and weight reduction of the load limiting device 10.

[0055] [Differentiation] While embodiments of the load limiting device according to the present invention have been described above, the configuration of the present invention is not limited thereto.

[0056] For example, in the present invention, instead of the load conversion unit 20, any parallel link can be used that includes a first member to which a load F is input, a second member attached to the object to be protected O, and a connecting member that connects the two such that the first member can be displaced relative to the second member only in the direction of the load F (Z direction). As an example, in the present invention, a load conversion unit 20 can be used in which the third link mechanism 25 or the fourth link mechanism 26 is omitted.

[0057] Furthermore, in this invention, the first gas spring 40 and the second gas spring 50 can be tensile-type gas springs, in which the fully compressed state is the initial unloaded state and a reaction force is generated when stretched. However, compression-type gas springs are more common as mechanical elements and offer a wider variety of product variations.

[0058] Furthermore, in this invention, one of the first gas spring 40 and the second gas spring 50 can be a compression type and the other a tension type. In this case, the first force transmission member 31, the second gas spring 50, the force sensor 60, the first gas spring 40, and the second force transmission member 32 can be mechanically connected in series in this order.

[0059] Furthermore, in this invention, the number of first gas springs 40 and second gas springs 50 can be changed to any number of 1 or more. For example, the number of first gas springs 40 may be 1 and the number of second gas springs 50 may be 1, or the number of first gas springs 40 may be 4 and the number of second gas springs 50 may be 2.

[0060] Furthermore, in this invention, a first initial load Fth1 corresponding to the first load F1 and a second initial load Fth2 corresponding to the second load F2 can be arbitrarily set according to the vulnerability of the protected object O.

[0061] Furthermore, in the present invention, force sensors 60, 60 can be provided not between the third support portion 33c of the gas spring support member 33 and the base end (end of tube 40b) of the first gas spring 40, but between the first support portion 33a and the second support portion 33b of the gas spring support member 33 and the base end (end of tube 50b, 50b) of the second gas spring 50, 50. In this case, a separate processing unit provided at any location on the load limiting device 10 may calculate the electrical signal output by one force sensor 60 and the electrical signal output by the other force sensor 60 and output an electrical signal corresponding to the sum of the forces measured by each force sensor 60, 60, or an external processing unit may calculate the two electrical signals output from the load limiting device 10 (force sensors 60, 60) and find the sum of the forces measured by each force sensor 60, 60.

[0062] Furthermore, in the present invention, a force sensor 60 can be provided on the first force transmission member 31 (for example, in the middle of the link connecting portion 31a extending in the -X direction) or the second force transmission member 32 (for example, in the middle of the link connecting portion 32a extending in the X direction).

[0063] Furthermore, in this invention, the force sensor 60 can be omitted when it is not necessary to detect the load F. In this case, the base end of the first gas spring 40 (the end of the tube 40b) can be directly supported by the third support portion 33c of the gas spring support member 33.

[0064] Furthermore, in this invention, a first bottom plate, a first top plate (second bottom plate), a second top plate (third bottom plate), and a third top plate are arranged in order of proximity to the object to be protected O, and each is connected by a continuous member such as link mechanisms 23, 24, 25, and 26. A force sensor 60 is placed in the space between the first bottom plate and the first top plate (second bottom plate), at least one first gas spring 40 is placed in the space between the first top plate (second bottom plate) and the second top plate (third bottom plate), and at least one second gas spring 50 is placed in the space between the second top plate (third bottom plate) and the third top plate. The placement of the force sensor 60, the first gas spring 40, and the second gas spring 50 in the respective spaces can be arbitrarily changed.

[0065] Furthermore, the load limiting device according to the present invention may be used to protect something other than an electric cylinder. [Explanation of Symbols]

[0066] 10. Load limiting device 20 Load conversion section 21 Top plate 22 Bottom plate 23. First Link Mechanism 24. Second Link Mechanism 25. Third Link Mechanism 26. Fourth Link Mechanism 30 Load limiting section 31 First force transmission member 32 Second force transmission member 33 Gas spring support member 40. First Gas Spring 50 Second Gas Spring 60 Force Sensor

Claims

1. A load limiting device that limits the load that the external environment applies to the protected object, The first member to which the load is applied, A second member attached to the object to be protected, A connecting member that connects the first member and the second member such that the first member can be displaced relative to the second member only in the direction of the load that is assumed, A first gas spring and a second gas spring are arranged in the space between the first member and the second member, and a force corresponding to the load is input to them via the connecting member, Equipped with, The first gas spring displaces and limits the load only when the load is a compressive load that brings the first member closer to the second member, and the force input via the connecting member is greater than or equal to a preset first initial load. The second gas spring displaces and limits the load only when the load is a tensile load that moves the first member away from the second member, and the force input via the connecting member is equal to or greater than a preset second initial load. A load limiting device characterized by the following features.

2. The first member, the second member, and the connecting member constitute a Saras link mechanism. The load limiting device according to feature 1.

3. A first force transmission member, which is displaceable in a direction perpendicular to the direction of the load, is connected to the first link mechanism constituting the connecting member and the input end of the first gas spring. A second force transmission member, which is displaceable in a direction perpendicular to the direction of the load, is connected to the second link mechanism constituting the connecting member and the input end of the second gas spring. A gas spring support member connected to the base end of the first gas spring and the base end of the second gas spring, Furthermore, The first link mechanism and the second link mechanism are opposite each other. The load limiting device according to feature 2.

4. The system further includes a force sensor provided between the gas spring support member and the base end of the first gas spring, or between the gas spring support member and the base end of the second gas spring. The load limiting device according to feature 3.

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