Systems with variable stiffness

Abstract

The present invention relates to variable stiffness systems, which are used both as vibration isolation and vibration absorption systems in industrial applications, in systems that reliably protect vibration-sensitive mechanical, optical and electronic devices from vibration, and also as variable stiffness springs or joints in the robotics and biomedical fields.

Description

[Technical field]

[0001] The present invention relates to variable stiffness systems, which are used both as vibration isolation and vibration absorption systems in industrial applications, in systems that reliably protect vibration-sensitive mechanical, optical and electronic devices from vibration, and also as variable stiffness springs or joints in the robotics and biomedical fields. [Background technology]

[0002] Currently, variable stiffness systems can be used both as vibration isolation and vibration absorption systems. These variable stiffness systems can be used in industrial activities. In robotics and biomedical systems, the systems ensure protection of vibration-sensitive mechanical, optical and electronic devices from vibration. Variable stiffness systems are often encountered in the field of robotics, especially robot arms, and biomedical prosthetics technology.

[0003] In the prior art, variable stiffness systems are widely used in various fields. Variable stiffness systems have some unfavorable issues in the performance and excitation level of nonlinear isolators. When the performance of the isolator in question and the level of excitation are small, the isolator and therefore the stiffness system works well. However, it has been found that the performance of the isolator decreases when the excitation level increases.

[0004] It is noted that the prior art stiffness systems include vibration damping elements. These vibration damping devices are known to operate in a narrow range of 6.3 to 7 Hz. The operation of the vibration damping devices in a narrow range limits the use of the stiffness systems. This situation prevents the variable stiffness systems described above from being used in all embodiments.

[0005] In another known prior art, there are variable stiffness systems used in various fields. In these variable stiffness systems, the response time of the stiffness change of the system is very long. The long response time of the stiffness change leads to the ineffectiveness of the system. Additionally, in the current technology, there is a need for an external energy source from outside the stiffness system.

[0006] There is a known document with the application number CN105179587. This invention provides a multi-degree-of-freedom, all-metal, low-frequency passive vibration isolator with heavy load. The vibration isolator is composed of a load mounting table, a horizontal vibration isolation pressing bar, a bottom support table, a vertical main support shaft, a vertical guide rail, an upper auxiliary platform, a vertical support beam, a negative stiffness adjuster, and a roller support. The bottom plate is supported by the foot of the machine, etc. It provides a three-way non-linear vibration isolator with heavy load and low natural frequency based on Euler buckled beam and negative stiffness mechanism. The vibration isolation frequency can be realized as low as 1.5Hz.

[0007] As a result, all the above problems are unavoidable for innovation in the related art. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] China Patent Publication No. 105179587 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention relates to a variable stiffness system with a very short response time, which can be adjusted with very small forces over a wide operating frequency range, to eliminate the above-mentioned drawbacks and to bring new advantages to the related technical field.

[0010] It is an object of the present invention to provide a variable stiffness system, the stiffness of which can be varied, thereby changing the natural frequency.

[0011] Another object of the present invention is to provide a variable stiffness system in which the stiffness of the system can be varied with very little adjustment force by a near zero stiffness adjustment mechanism.

[0012] Another object of the present invention is to provide a variable stiffness system in which the tensioning mechanism in the embodiment allows for fast response time in changing the stiffness of the system. [Means for solving the problem]

[0013] The present invention is a variable stiffness system used in industrial activities as both a vibration isolation system and a vibration absorption system. In order to achieve all the objectives that may arise from the above and the following "Description of the Preferred Embodiments", the system provides for protecting vibration-sensitive mechanical devices from vibrations in robotics and biomedical fields. Accordingly, the variable stiffness system includes at least one body located in the negative stiffness section and extending in the y-axis direction; two opposing plates at both ends of the body, perpendicular to the body; at least one stud extending between the two plates in the y-axis direction and parallel to the body; at least one upper beam and at least one lower beam extending opposite each other, extending at equal distances from each other between the upper and lower beams and connected to the plates at both ends; at the positive stiffness section, located at the point where the central axis intersects the upper beam, one side of which is connected to the upper beam and the other side of which is connected to a compression spring; The variable stiffness system includes at least one spring bottom plate, at least one compression spring located at a point where the central axis intersects the spring bottom plate and connected to the spring bottom plate, at least one spring top plate located above the compression spring and parallel to the spring bottom plate, a beam group located opposite each other in the bottom section and provided by a group of beams, at least one wire connected to a wire compression channel at a free end of the beam group and connected to the spring top plate located on the compression spring, the positive stiffness section of the wire is provided through the negative stiffness section and the central axis of the bottom section and along the x-axis. Thus, a variable stiffness system is provided with the intention of providing stiffness changes to the beam group, making the response time of the variable stiffness system faster than existing systems with almost zero effort, and providing large tension changes in the wires connected to the beam group and therefore a wide range of stiffness and natural frequency adjustments in the beam group.

[0014] A possible embodiment of the invention is characterized in that the stiffness of the positive and negative stiffness sections is provided to be equal, thus providing a variable stiffness system that can be activated by applying very small adjustment forces.

[0015] A possible embodiment of the invention features at least one wire passing through a hole in the stud, thus providing a variable stiffness system with maximum effectiveness, by preventing the wire passing through the central axis from hitting the stud, for example when using the system to adjust stiffness in the system.

[0016] Another possible embodiment of the invention is characterized in that at least one nut positioned on the stud is used to buckle the top and bottom beams, thus ensuring that the top and bottom beams are fixed to maintain their current shape after buckling.

[0017] Another possible embodiment of the invention is characterized in that at least one bolt is used to buckle the top and bottom beams, and that the at least one bolt is connected by passing through a hole, thus ensuring that the top and bottom beams are fixed to maintain their current shape after buckling.

[0018] Another possible embodiment of the invention is characterized in that the centering element in the screw bottom plate and the compression spring are connected, which therefore serves to maintain the compression spring in an upright position during the application of force.

[0019] Another possible embodiment of the present invention is characterized in that there is at least one wire holder bottom part located in the positive stiffness section, and one end of the wire is connected and at least one wire holder top part is connected to said wire holder bottom part, thus helping to achieve the adjustment force with almost zero effort.

[0020] Another possible embodiment of the invention is characterized in that the pins are connected to the pin slots of the spring top plate through the pin holes of the spring top plate, thus providing a system that prevents the wire holder from rotating the bottom part when the top part rotates. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 is a representative overall view of a variable stiffness system according to the present invention. [Diagram 2] FIG. 1 illustrates a representative bottom section of a system of the present invention with variable stiffness and elements of the bottom section. [Diagram 3] FIG. 1 illustrates a representative group of beams of a variable stiffness system of the present invention buckling laterally towards two different sides. [Figure 4] FIG. 2 is a representative diagram of a variable stiffness system of the present invention with maximum natural frequency and stiffness. [Diagram 5] FIG. 2 is a representative diagram of a variable stiffness system of the present invention where the natural frequency and stiffness are below their maximum levels. [Figure 6] FIG. 2 is a diagram showing a typical negative stiffness section and a positive stiffness section connected in the variable stiffness system of the present invention. [Figure 7] FIG. 2 is a representative diagram of a variable stiffness system of the present invention in which a negative stiffness section buckles with the aid of a compression stud. [Figure 8] FIG. 2 is a generalized view of a spring in a representative upper section of a variable stiffness system of the present invention. [Figure 9]FIG. 2 is an exploded view of the elements of an exemplary upper section of a variable stiffness system of the present invention. [Figure 10] FIG. 2 is a representative diagram of a variable stiffness system of the present invention showing studs, wire through holes, and wires. [Figure 11] 13 is a graph showing the change in natural frequency of a free end of a representative beam group of a variable stiffness system of the present invention due to tension in the wire. [Figure 12] 1 is a representative force-displacement graph of a variable stiffness system according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] In this "Description of the Preferred Embodiments" the present invention is described by way of examples without any limiting effect in order to make it better understandable.

[0023] The present invention relates to a variable stiffness system, used in both vibration isolation and vibration absorption systems in industrial applications, providing protection against vibrations for mechanical devices sensitive to vibrations, in robotics and biomedical fields. The variable stiffness system of the present invention basically comprises a positive stiffness section (10), a negative stiffness section (20) and a bottom section (30) containing an axially loaded beam. A structure is provided in which the stiffness of the positive stiffness section (10) and the negative stiffness section (20) are equal.

[0024] There is at least one body (24) located in the negative stiffness section (20) and extending in the direction of the y-axis (Y), and two opposing plates (25) located on either side of the body (24) and perpendicular to the body (24). There is at least one top beam (21) and at least one bottom beam (22) extending parallel to the body (24) between the two plates (25) in the y-axis (Y) direction. There is at least one stud (28) extending along the y-axis (Y) and between the top beam (21) and the bottom beam (22) at equal distances from each other and connected at both ends to the plates (25).

[0025] There is at least one spring bottom plate (12) connected to the upper beam (21) at the point where the positive stiffness section (10) and central axis (O) intersect the upper beam (21), and at least one compression spring (15) located at the point where the central axis (O) intersects the spring bottom plate (12) and connected to the spring bottom plate (12). At least one spring top plate (11) is mounted on the compression spring (15) and parallel to the spring bottom plate (12).

[0026] The beam group (32) is located in the bottom section (30) and is provided by the combination of many beams (31). At least one wire (40) is provided in contact with the wire compression channel (34) with one end located in the free end (33) of the beam group (32) and the other end located in the spring top plate (11) which is located in the compression spring (15).

[0027] A wire (40) is disposed through the central axis (O) of the positive stiffness section (10), the negative stiffness section (20), and the bottom section (30) and along the x-axis (X).

[0028] The overall structure of the variable stiffness system is shown in FIG. 1. In the bottom section (30), there is a beam group (32), which is located opposite each other and is provided by a group of multiple beams (31). The beam group (32) bears an axial load, such as on a central axis (O). A wire (40) passing through the central axis (O) of this embodiment is used to transmit the axial load to the beam group (32). One end of the wire (40) is connected to a wire compression channel (34) located at the free end (33) of the axially loaded beam group (32). In this way, the force in the wire (40) can be transmitted evenly to all the beams (31) forming the beam group (32). The other end of the wire (40) is connected to a spring top plate (11) located on a compression coil spring (15).

[0029] Additionally, there is at least one spring bottom plate (12) connected to the upper beam (21) at the point where the central axis (O) intersects the upper beam (21). When the spring bottom plate (12) rises between the compression spring (15) and the upper beam (21), the compression spring (15) pushes against the spring top plate (11), causing the wires (40) to go taut. If the wire tension (T) in the wire (40) element exceeds the total buckling force (B) of the beams (31) in the beam group (32), the beam (31) will buckle to one side, as seen in FIG. 3.

[0030] When the tension in the wires (40) approaches but does not exceed the buckling force (B), the lateral stiffness of the beams (31) in the beam group (32) decreases, and as a result, the natural frequency (W) at the free end (33) of the beam group (32) decreases, as can be seen in the graph of FIG.

[0031] The position of the spring bottom plate (12) on the x-axis (X) can be changed by moving the spring housing (16) in the opposite direction of the x-axis (X) and in the x-axis (X) direction. As a result, both the stiffness of the beams (31) in the beam group (32) and the natural frequency (W) at the free end (33) of the beam group (32) can be adjusted by increasing or decreasing the tension of the wires (40). As can be seen in FIG. 4, when the spring bottom plate (3) is at the lowest position, the stiffness and natural frequency (W) of the free end (33) of the beam group (32) in the z-axis (Z) direction are at the highest level. If the spring bottom plate (12) moves in the opposite direction of the x-axis (X), the stiffness and natural frequency (W) of the free end (33) of the beam group (32) in the z-axis (Z) direction will decrease, as shown in FIG. 5.

[0032] Figure 2 shows the elements that form the bottom section (30) of the variable stiffness system. The number of beams (31) in the beam groups (32) in Figure 2 can be increased or decreased depending on the amount of stiffness desired and the mass desired to be held. However, in order for the variable stiffness system to work, it is necessary to have at least two beams (31) in the two beam groups (32) located on either side. Additionally, in order for the system to work in a balanced manner, the number of beams (31) in both beam groups (32) must be equal and the dimensions of the beams (31) must be the same.

[0033] The negative stiffness section (20) shown in FIG. 1 is used to minimize the tuning force (F) required to change the stiffness of the beams (31) in the beam group (32) and therefore the natural frequency (W) at the free end (33) of the beam group (32). The tuning force (F) is a force applied to the spring housing (16) in the direction of the x-axis (X) or in the direction opposite to the x-axis (X). The positive stiffness of the compression springs (15) in the positive stiffness section (10) and the negative stiffness in the negative stiffness section (20) are equal, resulting in a system with a stiffness of approximately zero. The resulting tuning force-displacement graph is shown in FIG. 12. When the variable stiffness system is in the equilibrium position, the slope of the tuning force-displacement graph around the tuning force (F) corresponding to the displacement (D) value approaches zero. It is thus confirmed that the tuning force (F) does not change, while the displacement (D) changes around the equilibrium position.

[0034] When the adjustment force (F) is set close to zero and the spring housing (16) is moved in the x-axis (X) direction, the tension in the wire (40) changes significantly. However, this change takes effort to approach zero. The positive stiffness section (10) and the negative stiffness section (20) shown in FIG. 1 are used together to adjust the adjustment force (F) to approach zero.

[0035] In Fig. 9 the elements of the positive stiffness section (10) are shown in detail. On the wire holder bottom part (14) there is a screw thread. The inner surface of the wire holder top part (13) also has a screw thread. By rotating the wire holder top part (13), its height in the direction of the x-axis (X) changes and the adjustment force (F) can be made close to zero. The wire holder bottom part (14) should not rotate, while the wire holder top part (13) does. The non-rotation of the wire holder bottom part (14) is provided by a pin (50) passing through a pin hole (17) in the wire holder top part (13). The pin (50) fits into a pin slot (18) located in the spring top plate (11).

[0036] When the tension in the wires (40) used in the variable stiffness system changes, the compression force in the compression springs (15) also changes. In order to keep the compression springs (15) in an upright position while under force, the compression springs (15) and wires (40) must be concentric, i.e., located on a central axis (O). Positioning the compression springs (15) and wires (40) on the central axis (O) and concentric with each other is provided by the spring centering element (19). Figure 9 shows the spring centering element (19) used to center the compression springs (15) and ensure that they are positioned vertically under force.

[0037] The maximum force applied to the beams (31) in the beam group (32) should not exceed the maximum buckling force (B) of the beams (31). In this way, the natural frequency (W) at the free end (33) of the beam group (32) can be stably adjusted. If the maximum buckling force (B) of the beams (31) in the beam group (32) is exceeded, the free end (33) of the beam group (32) will tilt to one side as shown in FIG. 3. In order to adjust the tension to the maximum value, it is necessary to adjust the amount of buckling of the upper beams (21) and the lower beams (22) located in the negative stiffness section (20). Although one upper beam (21) and one bottom beam (22) are visible in FIG. 1, in another embodiment of the system, multiple upper beams (21) and multiple bottom beams (22) can be positioned parallel to each other.

[0038] FIG. 7 shows the appearance of the upper beam (21) and the lower beam (22) in the negative stiffness section (20) being distorted with the help of the stud (28). In order to buckle the upper beam (21) and the lower beam (22), the nut (26) on the stud (28) element needs to be tightened. During the buckling of the upper beam (21) and the lower beam (22), the bolt (27) passing through the bolt adjustment groove (29) of the body (24) in the negative stiffness section (20) is loosened, and both ends of the upper beam (21) and the lower beam (22) are attached to the opposing plates (25). After adjusting the buckling amount of the upper beam (21) and the lower beam (22), the nut (26) and the bolt (27) are tightened.

[0039] The upper beams (21) and lower beams (22) in the negative stiffness section (20) exhibit negative stiffness behavior in the x-axis (X) direction while the wires (40) pass through the middle, or central axis (O), of the upper beams (21) and lower beams (22), thereby ensuring that they do not bend in the y-axis (Y) or z-axis (Z). Additionally, there are wire through holes (23) in the studs (28) so that the wires (40) passing beyond the centers, or central axis (O), of the upper beams (21) and lower beams (22) do not strike the studs (28).

[0040] The scope of protection of the present invention is set forth in the appended claims and may not be strictly limited to what has been described for illustrative purposes in this Detailed Description of the Invention. It is obvious that a person skilled in the art may provide similar embodiments in view of the above description without departing from the spirit of the present invention. [Explanation of symbols]

[0041] 10 Positive stiffness section 11 Spring upper plate 12 Spring bottom plate 13 Upper part of wire holder 14 Wire holder bottom part 15 Compression spring 16 Spring housing 17 Pin Hole 18 pin slot 19 Spring centering element 20 Negative Stiffness Section 21 Upper beam 22 Bottom beam 23 Wire Through Hole 24 Main Unit 25 Plate 26 Nut 27 Volts 28 Stud 29 Bolt adjustment groove 30 Bottom Section 31 Beam 32 Liang Group 33 Free end 34 Wire Compression Channel 40 Wire 50 pin XX axis YY axis ZZ axis O center axis D Displacement F Adjustment force W Natural frequency T Wire tension B Buckling force

Claims

1. A variable stiffness system used in both vibration isolation and vibration absorption systems in industrial applications, and in robotics and biomedical systems to provide protection from vibrations to vibration-sensitive mechanical devices, at least one body (24) located in the negative stiffness section (20) and extending in the y-axis (Y) direction; Two opposed plates (25) positioned at either end of said body (24) and perpendicular to said body (24); at least one top beam (21) and at least one bottom beam (22) extending parallel to the body (24) between the two plates (25) in the y-axis (Y) direction; at least one stud (28) extending equidistant from each other along the y-axis (Y) between said upper beam (21) and lower beam (22) and connected at both ends to said plate (25); at least one spring bottom plate (12) at the point where the central axis (O) intersects the upper beam (21) in the positive stiffness section (10), the at least one spring bottom plate (12) being connected on one side to the upper beam (21) and on the other side to a compression spring (15); at least one compression spring (15) located at the point where said central axis (O) intersects said spring bottom plate (12) and connected to said spring bottom plate (12); At least one spring top plate (11) located above the spring (15) and parallel to the spring bottom plate (12); a beam group (32) common to the bottom section (30) and provided by a combination of a plurality of beams (31); at least one wire (40), one end of which is connected to a wire compression channel (34) located at the free end (33) of said beam group (32) and the other end of which is connected to said spring top plate (11) located on said compression spring (15); and A variable stiffness system, characterized in that the wire (40) passes through the central axis (O) of the positive stiffness section (10), the negative stiffness section (20) and the bottom section (30) and ensures that it passes along the x-axis (X).

2. 2. A variable stiffness system according to claim 1, characterized in that the stiffness of said positive stiffness section (10) and said negative stiffness section (20) are equal.

3. 2. The variable stiffness system according to claim 1, characterized in that it comprises at least one wire through hole (23) provided in the stud (28) and through which the wire (40) passes.

4. 2. The variable stiffness system according to claim 1, characterized in that it comprises at least one nut (26) positioned on the stud (28) and used for buckling the top beam (21) and the bottom beam (22).

5. 2. The variable stiffness system according to claim 1, characterized in that it comprises at least one bolt (27) used to buckle the upper beam (21) and the lower beam (22) and connected by passing through a bolt adjustment groove (29).

6. 2. A variable stiffness system according to claim 1, characterized in that it comprises a spring centering element (19) located on said spring bottom plate (12) and to which said compression spring (15) is connected.

7. 2. The variable stiffness system according to claim 1, characterized in that it comprises at least one wire holder bottom part (14) located in the positive stiffness section (10) and to which one end of the wire (40) is connected, and at least one wire holder top part (13) connected to the wire holder bottom part (14).

8. 2. A variable stiffness system according to claim 1, characterized in that it comprises a pin (50) connected to a pin slot (18) in the spring upper plate (11) by passing through a pin hole (17).

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