This paper presents an investigation into the structural characterization of tensegrity systems for potential use as aircraft structures, especially for morphing aircraft. Morphing aircraft provide multi-role and multi-mission capabilities by adapting their performance to different in-flight requirements. Flexible elements must be included within the structure to permit morphing capabilities compared to conventional single mission aircraft, which are designed for high rigidity and not ideal for shape morphing applications. Tensegrity systems are structures that consist of a series of connected cables, in tension, and struts, in compression, that exist in a self-equilibrium state. Since the struts and cables are loaded axially, external loads are efficiently distributed throughout the tensegrity components resulting in a strong and stiff structure. Adjusting the pretension of the tensegrity will tailor the structural characteristics as needed without a basic configuration change. By changing the length of the cables or struts, tensegrity systems are capable of movement while maintaining their inherent strength and rigidity. This makes tensegrity systems an attractive candidate for morphing aircraft structures. This paper quantifies the strength and rigidity of a single module of various tensegrity systems along with traditional structures to assess their ability to serve as aircraft wings. Those properties are evaluated after boundary conditions are carefully selected to avoid adding unnecessary stiffness. Lastly, a concept for a tensegrity morphing aircraft wing is presented.

Industrial robots need motors with high-precision positioning, large torque output, and small size. However, the conventional motors combined with reducers tend to be large. To solve the problem, we proposed the motor integrated with reducer that could output reduced rotation directly by using the strain wave gearing system. The proposed motor is thought to have advantages not only in downsizing but also in high load-supporting capacity and high stiffness because of the simultaneous engagement of three gear pairs. In this paper, we derive the theoretical input-output relation in the proposed motor with a focus on the deformation of the elastic gear in the motor. The result gives the pushing force of the linear actuators at an arbitrary output rotation angle of the motor. We conduct the experiments to clarify the optimal input pattern for the accurate rotation by using the prototype of the proposed motor. Through the observation and measurement, the optimal input pattern is suggested.

This paper deals with the design of a robust control scheme for a suspended Cable-Driven Parallel Robot (CDPR), composed of eight cables and a moving platform (MP), suitable for pick-and-place operations of heterogeneous objects with different shapes, sizes and masses, up to a total load of 700 kg. Dynamometers measure the force applied by each cable onto the moving-platform and are used to assess the payload mass at any time. In the proposed control solution, each motor of the CDPR is directly driven by a PD torque controller, which takes benefit of the real-time payload estimation in a feedforward term. In order to evaluate its performance, experiments on a typical pick and place trajectory are realized for different payloads. As a result, three control schemes: (i) a Proportional-Derivative (PD) torque controller; (ii) a PD controller with compensation of the MP mass only and (iii) a PD controller with real-time mass estimation and compensation are experimentally compared with respect to their positioning accuracy. It turns out that a good estimation of the payload is obtained in real-time thanks to the dynamometers. Moreover, the higher the payload mass, the more accurate the proposed controller with respect to its two counterparts.

This paper presents trajectory planning methods for a kinematically redundant parallel mechanism. The architecture of the mechanism is similar to the well-known Gough-Stewart platform and it retains its advantages, i.e., the members connecting the base to the moving platform are only subjected to tensile/compressive loads. The kinematic redundancy is exploited to avoid singularities and extend the rotational workspace. The architecture is described and the associated kinematic relationships are presented. Solutions for the inverse kinematics are given, as well as strategies to take into account the limitations of the mechanism such as mechanical interferences and velocity limits of the actuators while controlling the redundant degrees of freedom.

MEMS diaphragms utilizing an embedded cantilever array to sense pressure were investigated in an effort to detect blast-induced loads that potentially cause mild traumatic brain injury (mTBI). Overhanging cantilever beams of varying length sequentially contacted convexly deformed diaphragms during pressure loading to enable binned binary threshold pressure sensing. Diaphragms and overhanging cantilever beam arrays photolithographically defined using double-layer SOI-DRIE processes were designed to minimize footprint and maximize sensing resolution while avoiding diaphragm fracture. Analytic models based on classical plate theory were correlated with a FEA model to guide design decisions by predicting deflection behavior of circular diaphragms under uniformly distributed pressure loads. Fabricated sensors experimentally tested under static conditions revealed good agreement with modeling, and indicated such a sensor may be well-suited for integration into a future wearable device capable of sensing potentially mTBI-causing blasts using minimal power.

Dynamic behavior of a cantilever type nano-switch actuated by pure Casimir force is investigated. Residual surface stress, surface elasticity and intermolecular forces are included in Euler–Bernoulli beam model. Knudsen number dependent squeeze-film air damping model and an asperity-based contact model are incorporated. The proposed model is inherently nonlinear due to interactions between the different nonlinear physics. An approximate analytical approach based on Galerkin’s method has been employed for predicting transient dynamic responses, since no exact solutions are available. Predicted responses show that the beam tip hits the substrate and bounces before making a permanent contact. Actuation of the switch via pure Casimir force is demonstrated for certain length and gap combinations. Initial contact time which governs the switch performance, and the deflections under non-closure condition are also quantified. This study is envisaged to provide useful insights for the future design of Casimir actuated NEM switches.

Ocean wave power is a promising renewable energy source for future energy production. It has however been difficult to find a cost-effective solution to convert the wave energy into electricity. The harsh marine environment and the fact that wave power is delivered with high forces at low speeds makes design of durable mechanical structures and efficient energy conversion challenging. The dimensioning forces strongly depend on the wave power concept, the Wave Energy Converter (WEC) implementation and the actual Power Take-Off (PTO) system. A WEC using a winch as a Power Take-Off system, i.e. a Winch Based Point Absorber (WBPA), could potentially accomplish a low Levelized Cost Of Energy (LCOE) if a key component — a low-cost, durable and efficient winch that can deal with high loads — can be developed. A key problem for achieving a durable winch is to find a force transmitting solution that can deal with these high loads and handle up to 80 million cycles. In this article we propose a design solution for a force transmitting chain in a WBPA system where elastomeric bearings are used as a means to achieve the relative motion between the links in the chain. With this solution no sliding is present and the angular motion is achieved as a deformation in the elastomeric bearing when the chain is winded on a drum. The link was designed primarily to minimize the number of joints in the chain: Thereby the maximum allowed relative angle between the links when rolled up over the drum should be as large as possible within practical limits. The angle is to be handled by the elastomeric bearing. A detailed strength analysis of the link has been performed as well as topology optimization to increase the strength to weight ratio. A test rig for a first proof of concept testing has been developed and the first preliminary test results indicate that this concept with using elastomeric bearings can be a potential solution for a durable chain and should be analyzed further for fatigue conditions and under water operations.

In this paper, the sling load dynamics of an aerial vehicle carrying a payload are investigated by employing three formulations of the governing equations. They are the hybrid formulation where the system exists in either a taut cable or slack cable configuration, with appropriate treatment of the transition between the two; the linear complementarity problem (LCP) formulation where the cable constraints are imposed as linear complementarity conditions and finally, the lumped parameter formulation where the cable is modelled with a series of spring-mass elements. The hybrid and LCP formulations neglect the elasticity of the cable while the lumped parameter model explicitly accounts for the elastic properties of the cable, albeit in a discrete way. The importance of the incorporation of elastic properties of the cable on the system is investigated for the variation in solution space of the payload. The three formulations are compared numerically, for information on the computational cost, motion of the payload, and tension profile, for several aerial maneuvers, including an aggressive obstacle avoidance with a window clearance flight.

In order to study dynamics response of a launch vehicle under ground wind loads, the dynamics model of a launch vehicle erected on the pad is developed based on transfer matrix method for multibody systems and the theory of structural wind engineering. The overall transfer equation, overall transfer matrix, and characteristics equation of the system are deduced based on the automatic deduction theorem of overall transfer equation of multibody system. The equation governing the motion of the launch vehicle is obtained by using the orthogonality of augmented eigenvector. The vibration characteristics, and frequency domain and time domain dynamics response under ground wind loads of the launch vehicle are simulated. The simulation results show that the eigenfrequencies obtained by the proposed method and ordinary dynamics method have good agreements. The paper provides an effective approach to compute the dynamics response of the launch vehicle under ground wind loads.

Flagella and cilia are examples of actively oscillating, whiplike biological filaments that are crucial to processes as diverse as locomotion, mucus clearance, embryogenesis and cell motility. Elastic driven rod-like filaments subjected to compressive follower forces provide a way to mimic oscillatory beating in synthetic settings. In the continuum limit, this spatiotemporal response is an emergent phenomenon resulting from the interplay between the structural elastic instability of the slender rods subjected to the non-conservative follower forces, geometric constraints that control the onset of this instability, and viscous dissipation due to fluid drag by ambient media. In this paper, we use an elastic rod model to characterize beating frequencies, the critical follower forces and the non-linear rod shapes, for pre-stressed, clamped rods subject to two types of fluid drag forces, namely, linear Stokes drag and non-linear Morrison drag. We find that the critical follower force depends strongly on the initial slack and weakly on the nature of the drag force. The emergent frequencies however, depend strongly on both the extent of pre-stress as well as the nature of the fluid drag.

The paper presents the dynamic response of an Euler-Bernoulli beam supported by an elastic foundation and subjected to a moving step load. The Riccati transfer matrix method for linear multibody systems (Riccati MSTMM) is employed to find eigenfrequencies and mode shapes of the supported beam. A comparison of results obtained with the finite element method (FEM) indicates that the Riccati MSTMM is more accurate when using the same number segments. Based on these results, the dynamic response of the beam with moving step load is investigated for different propagation velocities by mode superposition, and the effect of loads is discussed.

This paper investigates the design of an electrostatic discharge protection device made of single-layer graphene nanoribbons. The device is meant to trigger electrostatic discharge at a target voltage of 1.5V. Other design requirements include the minimization of parasitic capacitance, electrical response time and mechanical response time. The device is designed to discharge static electricity by being pulled to ground through electrostatic forces, then making contact with ground before returning to its original position. Previous designs experienced repeatability issues due to a lack of securing the ribbon and mechanical failure due to high stresses at the boundary conditions. New designs are presented and optimized to maintain a high effective spring constant for the device while reducing stress during electrostatic pull-in. A single-degree of freedom model is used in conjunction with the Bernoulli-Euler beam equations and Castigliano’s method to guide the design process. Behavior of each design is validated, and repeatability is assessed using finite-element simulations. The new designs are to be fabricated using a low pressure chemical vapor deposition process.

This paper presents optimal design for nonlinear compliant cellular structures with bi- and multi-stable states via topology optimization. Based on the principle of virtual work, formulations for displacements and forces are derived and expressed in terms of stress and strain in all load steps in nonlinear finite element analysis. Optimization for compliant structures with bi-stable states is then formulated as: 1) to maximize the displacement under specified force larger than its critical one; and 2) to minimize the reaction force for the prescribed displacement larger than its critical one. Algorithms are developed using the present formulations and the moving iso-surface threshold method. Optimal design for a unit cell with bi-stable states is studied first, and then designs of multi-stable compliant cellular structures are discussed.

A displacement amplifier based on the bridge-lever-type hinge mechanisms is developed and optimized in this paper. The proposed design not only maintains a compact and symmetrical structure, but also features a high amplification ratio. To reduce the displacement loss and enhance the load capacity of the amplifier, the hybrid flexure hinges are employed in the novel design. The analyzed models for the amplification ratio and resonance frequency calculation are established based on the matrix method and Lagrangian method respectively, which are verified by finite-element analysis (FEA) and displacement experiment. Based on the established model, an optimization via the NSGA-II algorithm is performed to estimate the performance of the hinge mechanism.

This paper presents a new design concept for a morphing triangle-shaped compliant mechanism. The novel design is a bistable mechanism that has one changeable side. These morphing triangles may be arrayed to create shapemorphing structures. The mechanism was based on a six-bar dwell mechanism that can fit in a triangle shape and has stable positions at the motion-limit (dead-center) positions. An example of the triangle-shaped compliant mechanism was designed and prototyped: an isosceles triangle with a vertex that changes from 120 degrees to 90 degrees and vice versa. Three of these in the 120-degree configuration lie flat and when actuated to the 90-degree configuration become a cube corner. This design may be of use for folding and packaging assistance. The force analysis and the potential energy analysis were completed to verify the stability of the triangle-shaped compliant mechanism. Because of its dead-center motion limits the vertex angle cannot be extended past the range of 90 degrees to 120 degrees in spite of the mechanism’s compliant joints. Furthermore, because it is a dwell mechanism, the vertex angle is almost immobile near its stable configurations, although other links in the mechanism move. This makes the stable positions of the vertex angle robust against stress relaxation and manufacturing errors. We believe this is the first demonstration of this kind of robustness in bistable mechanisms.

Compliant shell mechanisms utilize spatially curved thin-walled structures to transfer or transmit force, motion or energy through elastic deformation. To design with spatial mechanisms designers need comprehensive characterization methods, while existing methods fall short of meaningful comparisons between rotational and translational degrees of freedom. This paper presents two approaches, both of which are based on the principle of virtual loads and potential energy, utilizing properties of screw theory, Plücker coordinates and an eigen-decomposition, leading to two unification lengths that can be used to compare and visualize all six degrees of freedom directions and magnitudes of compliant mechanisms in a non-arbitrary physically meaningful manner.

This paper outlines the design of a compliant crank slider with adjustable constant-force output. Constant-force mechanisms (CFM) are used to maintain a constant output reaction force throughout a large range of compressive motion. This novel design improves on existing CFM by introducing a second degree of freedom that adjusts the mechanism’s output without changing its kinematic structure. This second degree of freedom is the rotation of a compliant beam about its longitudinal axis as it is constrained to the initial plane of bending. The resulting change in the beam’s stiffness allows for adjustment to a specifiable range of constant-force outputs.

Due to the anisotropic nature of fibre-reinforced laminates, thermally-induced internal stresses can remain in the material after manufacture. Mismatches between coefficients of thermal expansion are especially prominent in thin shells with fewer plies or large angle variations. Such stresses cause out-of-plane warping and are therefore often deliberately avoided. Utilising their effects on structural behaviour however, can enable stiffness-tailored composite compliant mechanisms. Work detailed in this paper aims to exploit thermal prestress to reduce the torsional stiffness of cross-ply tape laminate springs. An extension of an analytical tape spring model with composite thermal analysis is presented, which shows that thermal effects cause significant changes to the energy landscapes of thin composite shells. Tape springs that would otherwise be monostable structures become bistable and exhibit greater ranges of low-energy twisting when thermally-induced prestress is present. Predicted shell geometries are compared with finite element models and manufactured samples, showing good agreement between all approaches. The limited feasibility of zero torsional stiffness composite tape springs is discussed, as well as wider challenges involved in manufacturing prestressed composite compliant mechanisms such as fibre misalignment and moisture ingress.

Parasitic motion is undesired in precision mechanisms, it causes unwanted kinematics. These erroneous motions are especially apparent in compliant mechanisms. Usually an analysis of parasitic motion is only valid for one type of mechanism. Kinematic information is imbedded in the compliance matrix of any mechanism; an eigenscrew decomposition expresses this kinematic information as screws. It uses screw theory to identify the lines along which a force yields a parallel translation and a rotation yields a parallel moment. These lines are called eigenwrenches and eigentwists. Any other load on the compliant mechanism will lead to parasitic motion. This article introduces two parasitic motion metrics using eigenscrew decomposition: the parasitic resultant from an applied screw and the deviation of an actual degree of freedom from a desired degree of freedom. These metrics are applicable to all compliant mechanism and allow comparison between two compliant mechanisms. These metrics are applied to some common compliant mechanisms as an example.

Two critical disadvantages of compliant mechanisms constructed of engineering plastics are poor creep and stress relaxation resistance. Metallic reinforcement is investigated as a method to improve the creep and stress relaxation behaviors of compliant mechanisms and compliant segments. The stress relaxation and creep behaviors of homogeneous compliant segments are compared to those of metallic reinforced compliant segments. Special specimens and fixtures were designed for conducting physical tests. Test results show that metallic reinforced compliant segments significantly outperform homogeneous compliant segments with respect to both creep and stress relaxation. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.