Axial inhaul cable variable stiffness system for slender truss structure

Abstract

The invention relates to an axial inhaul cable variable stiffness system for a long and thin truss structure. The axial inhaul cable variable stiffness system comprises a tension actuating mechanism, a tension measurement feedback mechanism and a control system. The tension actuating mechanism is used for applying tension to the inhaul cable according to a real-time driving instruction of the control system; the tension measurement feedback mechanism measures the tension on the inhaul cable in real time and feeds back the tension to the control system; the control system adopts a PID closed-loop control method, and sends a real-time driving instruction to the tension actuating mechanism according to the real-time tension on the inhaul cable. The structure installation requirement is low, no extra structure is needed for installation, and only the axial inhaul cable, used for eliminating the pre-tightening force, of the original truss needs to be used; the control method is simple, the physical characteristics of the structure can be greatly changed, the rigidity of the truss structure in the bending direction can be greatly changed by simply adjusting the tensile force on the axial inhaul cable, and therefore vibration suppression and dynamic performance optimization are achieved.

Description

Technical Field

[0001] This invention belongs to the field of spacecraft truss structure design and relates to an axial cable variable stiffness system for slender truss structures. Background Technology

[0002] In spacecraft structures, slender trusses are widely used in systems such as satellite deployable mechanisms and space station support frames. These structures offer advantages such as lightweight and high rigidity, playing a crucial role in ensuring the on-orbit performance of spacecraft. However, during launch and on-orbit operation, truss structures are often subjected to complex dynamic excitation environments, and their natural frequencies are prone to coupling with the control system frequencies, leading to resonance phenomena. This amplifies vibrations and consequently affects attitude stability and payload performance.

[0003] Currently, the aerospace field has various technical approaches for vibration control of truss structures. Passive damping methods offer advantages such as simple structure and high reliability, effectively suppressing vibrations within a certain frequency band. However, their suppression bandwidth is typically limited, making them unsuitable for wide-frequency vibration environments. Active control schemes, such as piezoelectric actuator-based systems, feature fast response and high control precision, making them suitable for suppressing small-amplitude vibrations. However, their output displacement is usually small, limiting their ability to significantly adjust the overall stiffness and frequency of the truss. Furthermore, some research has explored ground-based cable systems arranged perpendicular to the truss, using lateral tension adjustment to control stiffness. While this method extends the actuation stroke to some extent, it typically requires a support structure of similar size to the truss, potentially introducing additional complexity and mass, making it unsuitable for on-orbit applications.

[0004] It is worth noting that many existing aerospace truss structures already include cables for enhancing stiffness or maintaining morphological stability. If active stiffness control can be achieved based on these existing cables, it can not only avoid a significant increase in system complexity and weight, but also effectively solve vibration problems caused by frequency coupling, thereby improving the spacecraft's adaptability to the dynamic environment in orbit. Summary of the Invention

[0005] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose an axial cable variable stiffness system for slender truss structures.

[0006] The solution of the present invention is: An axial cable variable stiffness system for slender truss structures includes a tension actuation mechanism, a tension measurement feedback mechanism, and a control system; The tension actuation mechanism applies tension to the cable according to the real-time drive commands from the control system; The tension measurement and feedback mechanism measures the tension on the cable in real time and feeds it back to the control system. The control system adopts the PID closed-loop control method, which sends real-time drive commands to the tension actuator based on the real-time tension on the cable.

[0007] Preferably, the cables are arranged along the axis of the main truss.

[0008] Preferably, the cable reuses the original truss structure to eliminate the preload of the axial cable.

[0009] Preferably, the stiffness matrix of the truss is related to the cable tension. The relationship satisfies:

[0010] in Let be the stiffness matrix of the truss without axial cable tension. The axial tensile force is The stiffness matrix of the time truss, and The axial tensile force is The truss stiffness change matrix at time,

[0011] in

[0012] L is the length of the cable.

[0013] Preferably, the tension actuation mechanism includes, but is not limited to, linear motors, articulated motors, voice coil motors, and piezoelectric ceramic actuators.

[0014] Preferably, the tensile force measurement feedback mechanism includes, but is not limited to, tensile and compressive force sensors, spring balances, and piezoelectric strain sensors.

[0015] Preferably, the cable includes, but is not limited to, carbon fiber or aramid fiber.

[0016] Preferably, the axial cable variable stiffness system is installed at the root of the truss structure.

[0017] The advantages of this invention compared to the prior art are: (1) It can be directly integrated into existing aerospace platforms and is easy to modify: This invention directly utilizes the axial cable structure originally designed on the spacecraft truss to eliminate preload or enhance stability. It does not require the addition of large external support masts or complex actuation mechanisms, which greatly reduces system complexity, extra weight and installation difficulty. It is particularly suitable for on-orbit spacecraft structures that are sensitive to weight and space.

[0018] (2) It can effectively solve the problem of vibration amplification caused by frequency coupling: By adjusting the axial tension of the cable, the present invention can change the bending stiffness of the truss structure in real time and continuously, thereby quickly adjusting its overall dynamic characteristics and natural frequency, effectively avoiding resonance caused by frequency coupling with the control system, and significantly improving the on-orbit attitude stability and load pointing accuracy of the spacecraft. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall axial cable variable stiffness system for slender truss structures according to the present invention; Figure 2 This is a schematic diagram of an embodiment of the present invention; Figure 3 This is a schematic diagram of an axial cable system according to an embodiment of the present invention. Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] The main truss structure of this invention includes, but is not limited to, a slender truss structure composed of repeating units connected end to end, generally as follows: Figure 1 As shown in Figure 1. There are no restrictions on the internal structure of its repeating units, the constituent materials, or the cross-sectional shape along the extension direction; only the slender characteristics of the overall structure need to be satisfied.

[0022] Cable 3 is arranged along the axis of the main truss, and the tension on the axial cable can be adjusted in real time via control. The cable material includes, but is not limited to, carbon fiber or aramid fiber. The cable reuses the original truss structure to eliminate preload.

[0023] The axial cable variable stiffness system 2 of this invention is located at the root of the main truss structure and includes a tension actuation mechanism, a tension measurement and feedback mechanism, and a control system. The tension actuation mechanism can directly act on the cable, changing its tension in an open-loop manner, and includes, but is not limited to, linear motors, articulated motors, voice coil motors, piezoelectric ceramic actuators, etc. The tension measurement and feedback mechanism can measure the tension on the cable in real time, providing feedback for closed-loop tension control, and includes, but is not limited to, tension / compression sensors, spring balances, piezoelectric strain sensors, etc. The control system can use the tension measured in real time by the tension measurement and feedback mechanism as feedback, calculate the final output signal according to PID control, and control the tension actuation mechanism to perform closed-loop control of the tension on the cable, and includes, but is not limited to, a computer host, such as... Figure 1 As shown in Figure 4.

[0024] The stiffness adjustment principle of the axial cable variable stiffness system for slender truss structures is as follows: When the axial cable undergoes vertical displacement, the change in cable length is proportional to the linear combination of the squares of the vertical displacements of each node. This characteristic allows the effect of axial tension on the truss structure to be equivalently modeled as applying a series of negative stiffness spring elements in the vertical direction at each node, thus substantially altering the overall stiffness characteristics of the truss in the vertical direction. This equivalent modeling method is called the negative stiffness equivalent method in structural mechanics. The overall stiffness matrix change is shown in the following equation.

[0025] in Let be the stiffness matrix of the truss without axial cable tension. The total axial tensile force is The stiffness matrix of the structure at that time, and The total axial tensile force is The structural stiffness change matrix over time can be written as:

[0026] in

[0027] n is the number of truss segments, which is an integer. All elements on the diagonal, except the last one, are zero. The last diagonal element is .

[0028] It can be seen that the vertical stiffness of the truss structure exhibits a linear relationship with the axial tensile force. This indicates that under axial cable tension... Under the influence of axial tension, the slender truss structure can actually be regarded as a variable stiffness unit. By controlling the axial tension, the stiffness of the truss structure in the vertical direction can be adjusted.

[0029] Example: Figure 2 The main truss 1 is a triangular prism truss structure. The main truss uses carbon fiber hollow members as its structural core, with the members directly connected using aluminum alloy connectors and screws. The entire truss has an equilateral triangle cross-section with one side length of 1000mm and an axial length of 6m. The cables are 2mm diameter double-strand Kevlar ropes, balancing strength and elasticity. The axial cable variable stiffness system is as follows... Figure 3 As shown, the tension actuation mechanism uses a joint motor, which is directly connected to the controller via a cable and directly controlled by the control system. Figure 3 As shown in Figure 31, the tensile force measurement feedback mechanism 32 selects a strain tensile sensor, which is directly connected to the data acquisition unit via a cable, and the control system directly acquires the feedback signal. Figure 33 represents the cable, and 34 represents the mounting plate for the articulated motor. The control system receives signals from the strain and tension sensors and achieves closed-loop adjustment of the cable tension by controlling the articulated motor. By providing axial tension, the stiffness in the bending direction of the structure is changed, giving the truss active variable stiffness characteristics. Its final stiffness matrix... With axial cable tension The interrelationship is as follows:

[0030]

[0031] in

[0032] This invention proposes an axial cable variable stiffness system for slender truss structures. The system has low installation requirements and does not require additional structures for installation. Only the original truss is needed to eliminate the preload of the axial cables. The control method is simple and can significantly change the physical properties of the structure. By simply adjusting the tension on the axial cables, the stiffness of the truss structure in the bending direction can be significantly changed, thereby achieving vibration suppression and dynamic performance optimization.

[0033] This invention achieves active stiffness control based on existing cables, which can avoid a significant increase in system complexity and weight, effectively solve the vibration problem caused by frequency coupling, and improve the spacecraft's adaptability to the dynamic environment in orbit.

[0034] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. An axial cable variable stiffness system for slender truss structures, characterized in that: This includes a tension actuation mechanism, a tension measurement and feedback mechanism, and a control system; The tension actuation mechanism applies tension to the cable according to the real-time drive commands from the control system; The tension measurement and feedback mechanism measures the tension on the cable in real time and feeds it back to the control system. The control system adopts the PID closed-loop control method, which sends real-time drive commands to the tension actuator based on the real-time tension on the cable.

2. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: The cables are arranged along the axis of the main truss.

3. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: The cable reuses the original truss structure to eliminate the preload of the axial cable.

4. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: The stiffness matrix of the truss and the tension of the cables The relationship satisfies: in Let be the stiffness matrix of the truss without axial cable tension. The axial tensile force is The stiffness matrix of the time truss, and The axial tensile force is The truss stiffness change matrix at time, in L is the length of the cable.

5. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: Pull-type actuators include, but are not limited to, linear motors, articulated motors, voice coil motors, and piezoelectric ceramic actuators.

6. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: Tension measurement feedback mechanisms, including but not limited to tension and compression sensors, spring balances, and piezoelectric strain sensors.

7. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: Cables include, but are not limited to, carbon fiber or aramid fiber.

8. The axial cable variable stiffness system for slender truss structures according to claim 1, characterized in that: The axial cable variable stiffness system is installed at the root of the truss structure.

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