Changeable Stiffness Research Articles

Deployment behavior and mechanical property analysis of Kresling origami structure

Kresling origami, a representative variant of origami, exhibits several distinctive features such as multistable states, changeable stiffness, and compression-torsion coupling deformation. The first focus of this study involves examining the mechanical properties of origami structures, specifically, the equivalent modulus and critical buckling stress during the deployment process are evaluated. Subsequently, the collapsibility of the Kresling origami structure is explicated with regard to energy and strain. In the folding process, when the Kresling angle is 0.0135 rad, the maximum torque is 959 Nmm, and the structure will occur snap-through instability, which is the nonlinear critical buckling load of the failure. After that, the torque decreases rapidly, and then gradually increases slowly. The mechanical model is developed and subsequently evaluated in terms of its flexibility and adjustment of stiffness. The present study investigates the buckling modes and vibration properties of Kresling origami structures, as well as their combination structures. For the buckling of Kresling origami structure, the critical buckling load of Euler buckling is 0.023 N and that of local buckling is 0.67 N. In short, the critical buckling load of the column shell is greater than that of the Kresling origami structure, which is due to the small local stiffness of structure.

A novel design of capacitive MEMS multi-range accelerometer; FEM and numerical approach

Sensing the acceleration with high dynamic range follows space and size limitations and many errors and inconveniences caused by using multiple accelerometers on a single structure. A novel MEMS capacitive accelerometer with a dual-spring system has been proposed to address this issue. Such a design is a single device with two sensitivities in different sensing ranges. It increases the dynamic range of the sensing by incorporating the supporting springs at high accelerations. Therefore, the sensor can sense a more comprehensive dynamic range while maintaining the required resolution in different ranges. The design parameters of the sensor, such as the thickness of the structural layer, the size of the sensor, and the width of the spring beams, have been investigated. The mechanical sensitivity in the first range is 0.082 μm g−1. For the second range, it is 0.0015 to 0.0091 μm g−1 depending on the supportive springs’ width. Moreover, the natural frequency of the device is 1740 Hz. The capacitance change of the proposed sensor is 7 fF g−1 on average for the first range and 0.08 to 0. 48 fF g−1 for different configurations in the second range. Utilizing such sensors with changeable stiffness in different ranges can reduce the sensor footprint and fabrication cost and increase reliability.

Liquid-Metal Magnetic Soft Robot With Reprogrammable Magnetization and Stiffness

Magneto-actuated soft robots have broad prospects for biomedical applications, such as cell manipulation, drug delivery, and noninvasive intervention. However, the single function and unchangeable stiffness restrict their practicality. Therefore, the work presented a functionally reconfigurable soft robot based on Gallium/NdFeB/PDMS composites. A heating-free reprogrammable magnetization technique was proposed to regulate the robot's response actions through re-patterning the magnetic domains. Moreover, a stiffness programming technique in terms of the liquid-metal thermotropic phase transition was employed to regulate the robot's stiffness. Four robot prototypes were constructed and tested. Experimental results showed that the robot performed variable responses and changeable stiffness, which satisfied different manipulation tasks. Therefore, the soft robot was endowed with variable functions and reusable characteristics. The proposed technique is expected to be applied to the batch manufacturing of intelligent soft machines.

Coupling Effect of Nonlinear Stiffness of Tape Spring Hinges and Flexible Deformation of Panels during Orbit Maneuvers

Many solar panels for spacecrafts are deployed by Tape Spring Hinges (TSHs) which have changeable stiffness. The stiffness of TSH is small when panels are folded, and it becomes large quickly in its deployed status. Since the solar panel is a thin sheet, flexible deformation is easily generated by orbit maneuvers. The coupling effect between the nonlinear TSHs and the flexible panels generates obvious vibration which affects the operational stability of the satellite. To investigate this coupling effect, non-deformable, linear deformable and nonlinear deformable panels were modelled by rigid body, modal order reduction method (MORM) and finite element method (FEM), respectively. The driving torque of TSH was described as a function of the rotation angle and angular velocity. The nonlinear properties of the TSH were reflected by one angle-stiffness spline multiplied by one stiffness coefficient. Dynamic responses of a satellite in deployment and orbit steering were analyzed by numerical simulations. Analysis results indicate the local deformation of panels keeps the stiffness of the TSH within a large range which accelerates the orbit maneuvers. However, much vibration is generated by the coupling effect if the luck-up status is broken up. The coupling effect affects the sequence of deployment, overshoot phenomenon and acceleration magnitude of the panels. Although the MORM is more efficient than FEM in computation, we propose FEM is better suited in the design of TSH and in studying the precise control of spacecraft with flexible solar panels and TSHs.

Topology optimization of degradable composite structures with time‐changeable stiffness

AbstractFor effective bone healing, the stiffness of the bone plate should be adjusted to different bone‐healing processes. Thus, the design of stiffness‐changeable structures that take into account the time effect is of importance. To this end, this study introduces a novel topological optimization approach for the composite structural layout design considering material degradation to realize structures with changeable stiffness over time. In this approach, two sets of variables are used: a density field that defines the material layout, and a time field that determines the effect of material degradation on mechanical performance. The continuous degradation update formula is proposed by integrating the Heaviside projected function and Kreisselmeier–Steinhauser function to guarantee its derivability. The objective is to minimize the summed compliance in some specified time steps subject to the constraints of volume fraction. The sensitivity of the aforementioned objective with respect to the design variable is deduced by considering the material degradation over time. The proposed design formulation is general and is demonstrated with several design analyses, considering different fix and degradable interface boundary conditions. Moreover, the results are compared with the results of not considering material degradation and demonstrate the effectiveness of the proposed method.

Design and modeling analysis of a changeable stiffness robotic leg working with magnetorheological technology

Since animals can adjust the stiffness of their bodies and/or appendages to adapt to changing environments and internal states and tasks, a robotic leg with changeable stiffness would be of assistance in developing mobile terrestrial robots. In this article, we present an improved model of a robotic leg that can alter its stiffness in real time by changing the characteristics of magnetorheological fluid. This particular robotic leg has a changeable stiffness module, which consists of a rotating magnetorheological fluid damper, a torsional spring, and a linear spring. The rotary magnetorheological fluid damper is used to control the deformation of a torsional spring, which alters the stiffness of the leg. To describe the mechanical features of the leg, a simplified mechanical model was built and then various experiments were carried out to verify the changeable stiffness characteristics. The simulation experiments of dual-leg locomotion were carried out to investigate the locomotive performance, including walking speed, maximum torque of motor, height variants, and mechanical cost of transport. These results demonstrate the adaptability and advantages of this changeable stiffness robotic leg and also indicated that developing a terrestrial robot which can adapt to various complex environments and tasks would be a worthwhile exercise.

Shape Memory Alloy-Based Soft Gripper with Variable Stiffness for Compliant and Effective Grasping.

Soft pneumatic actuators and motor-based mechanisms being concomitant with the cumbersome appendages have many challenges to making the independent robotic system with compact and lightweight configuration. Meanwhile, shape memory actuators have shown a promising alternative solution in many engineering applications ranging from artificial muscle to aerospace industry. However, one of the main limitations of such systems is their inherent softness resulting in a small actuation force, which prevents them from more effective applications. This issue can be solved by combining shape memory actuators and the mechanism of stiffness modulation. As a first, this study describes a shape memory alloy-based soft gripper composed of three identical fingers with variable stiffness for adaptive grasping in low stiffness state and effective holding in high stiffness state. Each finger with two hinges is fabricated through integrating soft composite actuator with stiffness changeable material where each hinge can approximately achieve a 55-fold changeable stiffness independently. Besides, each finger with two hinges can actively achieve multiple postures by both selectively changing the stiffness of hinges and actuating the relevant SMA wire. Based on these principles, the gripper is applicable for grasping objects with deformable shapes and varying shapes with a large range of weight where its maximum grasping force is increased to ∼10 times through integrating with the stiffness changeable mechanism. The final demonstration shows that the finger with desired shape-retained configurations enables the gripper to successfully pick up a frustum-shaped object.

Upheaval buckling of in-service cased insulated flowline

ABSTRACTAn upheaval buckling prediction approach is proposed for a high-temperature cased insulated flowline (CIF). Based on the tensile cracking and compression crushing analyses of the CIF concrete-weighted coats, the curvature-related nonlinear bending stiffnesses of CIF systems are discussed. A changeable stiffness is included in this buckling prediction approach developed using a transfer matrix method. Due to a relatively low bending stiffness, greater curvature and higher bending stress would be induced in the carrier pipe at field-joint positions in the buckling response of CIF systems, while the shear force change would be induced in the five pipe coats of CIF systems. Using the approach developed in this paper, the field-joint stress of a CIF carrier pipe and the interlayer shear forces of the CIF pipe coats can be obtained along the buckling path of the CIF systems by plotting the relationship curves between the carrier pipe axial forces and the CIF buckle lengths.

Dynamic bending of bionic flexible body driven by pneumatic artificial muscles(PAMs) for spinning gait of quadruped robot

The body of quadruped robot is generally developed with the rigid structure. The mobility of quadruped robot depends on the mechanical properties of the body mechanism. It is difficult for quadruped robot with rigid structure to achieve better mobility walking or running in the unstructured environment. A kind of bionic flexible body mechanism for quadruped robot is proposed, which is composed of one bionic spine and four pneumatic artificial muscles(PAMs). This kind of body imitates the four-legged creatures’ kinematical structure and physical properties, which has the characteristic of changeable stiffness, lightweight, flexible and better bionics. The kinematics of body bending is derived, and the coordinated movement between the flexible body and legs is analyzed. The relationship between the body bending angle and the PAM length is obtained. The dynamics of the body bending is derived by the floating coordinate method and Lagrangian method, and the driving force of PAM is determined. The experiment of body bending is conducted, and the dynamic bending characteristic of bionic flexible body is evaluated. Experimental results show that the bending angle of the bionic flexible body can reach 18°. An innovation body mechanism for quadruped robot is proposed, which has the characteristic of flexibility and achieve bending by changing gas pressure of PAMs. The coordinated movement of the body and legs can achieve spinning gait in order to improve the mobility of quadruped robot.

Experimental Research on Vibrating Head Elastomer Elements Supported with Magnetorheological Elastomer for the Purpose of its Regulation

Magnetorheological elastomers (MREs) belong to the group of so-called smart materials, which respond to an external stimulus by changing their viscoelastic properties.The vibration head will be modified with the MRE regulation system. The elastomer pillows will be enhanced with MRE and the regulation system (coils).The main idea of the modification is to increase an effectiveness of the vibrator work by the regulation that will stable the vibrations in the resonance frequency. It will be caused by the changeable stiffness of MRE elements under magnetic field.The aim of presented study is to research the influence of MREs cured under the magnetic fields on the strength properties of the elastomer pillow.

CHAOTIC VIBRATIONS OF TWO-LAYERED BEAMS AND PLATES WITH GEOMETRIC, PHYSICAL AND DESIGN NONLINEARITIES

In this paper, the theory of nonlinear interaction of two-layered beams and plates taking into account design, geometric and physical nonlinearities is developed. The theory is mainly developed relying on the first approximation of the Euler–Bernoulli hypothesis. Winkler type relation between clamping and contact pressure is applied allowing the contact pressure to be removed from the quantities being sought. Strongly nonlinear partial differential equations are solved using the finite difference method regarding space and time coordinates. On each time step the iteration procedure, which improves the contact area between the beams is applied and also the method of changeable stiffness parameters is used. A computational example regarding dynamic interaction of two beams depending on a gap between the beams is given. Each beam is subjected to transversal sign-changeable load, and the upper beam is hinged, whereas the bottom beam is clamped. It has been shown that for some fixed system parameters and with an increase of the external load amplitude, synchronization between two beams occurs with the upper beam vibration frequency. Qualitative analysis of the interaction of two noncoupled beams is also extended to the study of noncoupled plates. Charts of beam vibration types versus control parameters {q0, ωp}, i.e. the frequency and amplitude of excitation are constructed. Similar and previously described competitions have been reported in the case of two-layered plates.

2P2-K06 四脚型筋骨格歩行ロボットを用いた体幹剛性と安定歩行パターンに関する考察(移動知とその新展開)

This article treats development of a musculoskeletal quadruped locomotion robot, having pneumatic artificial muscles at the trunk changeable stiffness. Pneumatic artificial muscles have variable elastic characteristics. The robot has a multi joint structure in its spine and has a changeable elasticity and viscosity. Using the musculoskeletal quadruped robot, we investigated relationships between the stiffness of the musculoskeletal system and gait stability in locomotion. The results show there are some appropriate conditions for the stiffness at the trunk for each gait in the meanings of stability.

A semi-continuum finite element approach to evaluate the Young’s modulus of single-walled carbon nanotube reinforced composites

This paper describes a micromechanical finite element approach for the estimation of the effective Young’s modulus of single-walled carbon nanotube reinforced composites. These composite materials consist of aligned carbon nanotubes that are uniformly distributed within the matrix. Based on micromechanical theory, the Young’s modulus of the nanocomposite is estimated by considering a representative cylindrical volume element. Within the representative volume element, the reinforcement is modeled according to its atomistic microstructure while the matrix is modeled as a continuum medium. Spring-based finite elements are employed to simulate the discrete geometric structure and behavior of each single-walled carbon nanotube. The load transfer conditions between the carbon nanotubes and the matrix are modeled using joint elements of changeable stiffness that connect the two materials, simulating the interfacial region. The proposed model has been tested numerically and yields reasonable results for variable stiffness values of the joint elements. The effect of the interface on the performance of the composite is investigated for various volume fractions. The numerical results are compared with experimental and analytical predictions.