Flexure Hinges Research Articles

A novel ball-screw-driven rigid–flexible coupling stage with active disturbance rejection control to compensate for friction dead zone

The conventional ball-screw-driven high-speed precision motion stage, which is often referred to as rigid stage, usually employs mechanical bearings to achieve superior stiffness and rapid response. Despite these advantages, a high-stiffness design of the rigid stage can limit the positioning precision owing to the friction dead zone. In this study, we propose a ball-screw-driven rigid–flexible coupling (RFC) stage to compensate for the friction dead zone through flexure hinges. The frequency response functions indicate that friction is converted into elastic deformation of the flexure hinges. In addition, active disturbance rejection control (ADRC) is implemented to cancel the flexure hinge vibration and maximize the RFC stage performance. Preliminary simulation results confirmed the effectiveness of the proposed mechanical control scheme. This effectiveness was further demonstrated through three comparative experiments. First, in five repeated long-stroke point-to-point motion experiments, the RFC stage with ADRC exhibited excellent consistency in both transient and steady-state responses, achieving a positioning precision of ±0.1μm. Second, the RFC stage with ADRC was able to track a ladder-like step reference with fast transients and positioning precision of ±0.1μm. Finally, in a sinusoidal tracking experiment, the maximum and root-mean-square tracking errors of the RFC stage with ADRC were reduced by 88.85% and 43.32%, respectively, compared to the rigid stage with PID control.

A Bionic Piezoelectric Robotic Jellyfish With a Large Deformation Flexure Hinge

Jellyfish are one of the underwater creatures that have been imitated by underwater bionic robots, but a current challenge to create a bionic jellyfish is with the use of piezoelectric ceramic sheets as the driving element, due to their small output displacement. Here, a bionic robotic jellyfish with three tentacles is presented that is driven by three piezoelectric beams, and to transmit power, a large deformation composite flexure hinge is created which employs fishing line embedded in a 3D printed structure. In addition, the structure design and fabrication of the drive system are described. A dynamic model of the drive system is established to solve for the working mode, forced displacement responses, and swimming lift. A series of experiments are carried out to verify the theoretical analysis and validate the design of the robotic jellyfish. The proposed robotic jellyfish has a total mass of 29.4 g, tentacle spread of about 150 mm, and an overall height of 100 mm. The robotic jellyfish can exhibit swimming performance with drive frequencies of 0.7-1.1 Hz, and the best achieved swimming speed was 10 mm/s. These design, modeling, and fabrication methods may be beneficial and inspiring for the future development of the micro soft robot.

Design, optimization, and characterization of an XY nanopositioning stage with multi-level spatial flexure hinges for high-precision large-stroke motion guidance.

Establishing a novel design and accurate analytical models for XY nanopositioning stages based on voice coil motor (VCM) actuators is critical to achieving an optimal working performance. To overcome the existing design challenges of 2-degree-of-freedom guiding mechanisms, a four-layer structure composed of L-shaped spatial double parallelogram flexure mechanisms was proposed for the magnetic stage, which exhibits light weight and inhibits parasitic and decoupled motions. The guiding mechanisms were modeled by the compliance matrix method. Thereafter, by combining an electromagnetic model for the VCMs with the equivalent magnetic network method, an electromagnetic-mechanical coupling optimization method with multiple constraints was proposed for the stage to achieve a millimeter-range motion with a maximized natural frequency. The mechanical and electromagnetic performances were then verified by finite element analysis software. The optimized prototype was tested with a stroke of ±3.41 and ±3.08mm for X axis and Y axis, respectively, a closed-loop resolution of 100nm for X axis and 150nm for Y axis, and a resonant frequency of 11.75Hz for both axes. The tracking of a 0.1Hz spiral of Archimedes achieved a maximum tracking error of 2.9%.

Amplification Ratio of a Recycled Plastics-Compliant Mechanism Flexure Hinge

This research focuses on the fabrication of plastic flexure hinges from diverse plastics such as ABS, PP, HDPE, and LDPE. To enhance hinge efficiency, the recycling ratios are also investigated. The amplification ratio of different recycle ratios and plastic types are measured. The results show that the input and output displacements of all PP, ABS, and HDPE hinges are linear. The presence of recycled plastics has no impact on this basis. The pure PP, ABS, and HDPE flexure hinges achieve the highest amplification ratios of 5.728, 8.249, and 5.668. The addition of recycled plastics reduces the amplification ratio. This decrease in the amplification ratio, however, is small. At a 25% recycle ratio, the PP, ABS, and HDPE flexure hinges have 12%, 13.3%, and 21.7% lower amplification ratios than the pure plastic hinges. Furthermore, the utilization of recycled plastics may lessen the need for new plastic made from raw materials. With the PP flexure hinge, a maximum input value of 157 µm could result in an output value of 886 µm. At a maximum input value of 115 µm, the ABS flexure hinge could achieve an output value of 833 µm. Finally, a maximum input value of 175 µm might result in an output value of 857 µm when using the HDPE flexure hinge. The average amplification ratio values for all recycling ratios for PP, ABS, and HDPE flexure hinges are, respectively, 5.35, 7.60, and 5.02. The ABS flexure hinge frequently outperforms the PP and HDPE flexure hinge in terms of amplification ratios. Among these plastics, HDPE flexure hinges have the lowest amplification ratio. In general, increasing the thermoplastic polyurethane (TPU) content of the LDPE/TPU blend increases the amplification ratio. The cause could be the TPU’s high compatibility with the LDPE polymer. The LDPE/TPU blend hinge offers a broader range of the amplification ratio of 2.85–10.504 than the PP, ABS, and HDPE flexure hinges. It is interesting that changing the blend percentage has a much greater impact on the amplification ratio than changing the recycling ratio. The findings broaden the range of applications for plastic flexure hinges by identifying optimal plastic types. The impact of the hinge shape on the performance of the injected plastic flexure hinge might be studied in further research.

Bandgap tunability in pantographic metamaterials via flexure-based mechanisms

Inspired by flexure-based compliant mechanisms, we propose a novel pantographic system with broad, multiple bandgaps for wave and vibration control. This compliant mechanism embeds local inhomogeneities, such as flexure hinges, to achieve tunable bandgap properties. Using finite element analysis and Bloch’s theorem, we systematically study the bandgap properties of the pantographic lattice, including band structure diagrams, flexure hinge geometry effects, and vibration isolation in finite pantographic beam.

A medium-high frequency FBG accelerometer based on a V-shaped flexible hinge

Acquiring medium- and high-frequency acceleration signals is vital for broad infrastructure health monitoring, such as bridges, railways, and tunnels. This article introduces an innovative fiber Bragg grating (FBG) accelerometer featuring a V-shaped flexure hinge structure with enhanced sensitivity. Theoretical calculation and simulation analysis software were employed to evaluate the proposed structure's parameters. Experimental results show a sensitivity of approximately 67.9 pm/G under a working bandwidth of 400–900 Hz and a resonant frequency of 1250 Hz. The influence of temperature at 8.4 pm/°C and transverse interference validate 3.5%. These findings align with simulations, affirming the sensor's performance. This innovation holds promise for enhancing structural integrity monitoring in large-scale structures by detecting medium- and high-frequency vibration measurements.

A sub-millinewton resolution biaxial force sensor with temperature self-compensation for vascular intervention

This article presents a fiber Bragg grating (FBG)-based highly sensitive micro-biaxial force sensor for vascular intervention surgery. It features a 3D-printed integrated structure incorporating an FBG- embedded cavity at its front end for temperature decoupling and an elliptical arc ball hinge to improve lateral sensitivity. Four FBG-embedded fibers are suspended in a circular array within the flexible hinge to minimize lateral strain crosstalk and increase measurement accuracy. Finite-element analysis has been implemented to validate the flexure performance, while both static and dynamic loading experiments have been performed to validate the sensor performance. The experiments revealed resolutions of 0.761 and 0.765 mN, respectively for the two lateral forces within a range of −1 to 1 N, and dynamic measurement error lower than 0.67 % of full scale. Temperature compensation experiments are conducted under loaded conditions for both axes, showing errors of lower than 1.6 % and 1.2 %. The ability to decouple force and temperature will benefit its broad application for vascular intervention surgery.

Providing a strategy to restore damaged RC beam-column joints with the combination of CFRP and HPFRCC

This paper endeavors to assess the seismic performance of 3D reinforced concrete (RC) beam-column joints situated on the exterior of buildings, but lacking special ductility requirements. The joints have been rehabilitated by High-Performance Fiber-Reinforced Cement Composites (HPFRCC) and retrofitted using Carbon Fiber Reinforced Polymer (CFRP) wrap methodology. In this context, five beam-column joints located on the exterior of a structure have been subjected to cyclic lateral loading, while being scaled down to half their original size. The present study entailed an investigation into the cyclic behavior of three control specimens in its initial stage. Following the initial examination, it was observed that the control specimens, lacking any designated ductility standards, experienced significant core damage. During the subsequent phase of experimentation, the impaired concrete sections of the control samples were remediated through substitution with HPFRCC matter. Additionally, CFRP sheets were implemented for retrofit purposes. The modified specimens were then exposed to comparable cycles of loading. An analysis is conducted on the empirical findings of the specimens under investigation. The findings of this study indicate that the utilization of HPFRCC materials and CFRP sheets in the restoration and enhancement of deteriorated joints has led to a notable enhancement of their strength and displacement capacity. Specifically, this approach has facilitated the creation of a flexural plastic hinge and impeded the occurrence of shear failure within the core, leading to an improved overall behavior of the repaired damaged joint, which is comparable to that of undamaged seismic joints. The application of this technique demonstrates a high degree of efficacy in the rehabilitation and enhancement of edifices with deficient seismic details that have sustained damage subsequent to an earthquake event.

Assessing the mechanical and static aeroelastic performance of cellular Kirigami wingbox designs

Adaptive wings configurations have been evaluated for morphing airframe applications during the last two decades. Constructions with flexible hinges can be in particular a solution for small top medium-scale air vehicles, while novel Kirigami technologies help to produce flexible and complex structures by enabling novel geometric paradigms. In this study, a cellular Kirigami wingbox with an adaptive hinge is designed and manufactured. The mechanical properties of the wingbox are numerically evaluated, considering the shear modulus of the cellular elements patterning the wingbox. Thus, the equivalent torsional, flexural stiffness, as well as the shear center location of the whole wingbox structure are calculated. The analysis is parametrized against various possible internal cell angles and cell thickness values that define the Kirigami cellular tessellation of the wingbox. The static divergence speed is also evaluated by means of the same parametrization. This study shows the feasibility of using a Kirigami wingbox concept for morphing/adaptive small to medium-scale from a structural and aeroelastic perspective.

Modelling and performance analysis of a curvature-adjustable multiple-axis flexure hinge based on Bézier curve

In order to solve the uniqueness of the compliance equations and each notch profile, a curvature-adjustable multiple-axis flexure hinge with complex notch profiles is designed and investigated based on Bézier curve in this paper. The hinge can evolve into multiple-axis flexure hinges with single and hybrid, symmetric and asymmetric notch profiles composed of the ellipse, circle, hyperbola and parabola. In addition, analytical compliance equations in six degrees of freedom based on the Castigliano’s Second Theorem are proposed. Then, a simplified notch profile classification method based on a binary quadratic implicit equation is proposed. Moreover, analytical compliance equations are validated by finite element analysis. The maximum relative error between the finite element analysis and the analytical results is 6.07%. Finally, the compliance, precision of rotation and stress are investigated based on structural parameters. The results show that the change in the rotation centre does not significantly affect the axial and bending compliance for the flexure hinge with a specific single and flush Bézier curve notch profile. Moreover, the flexure hinge with a notch profile consisting of ellipse and hyperbola has the highest rotational precision. The proposed curvature-adjustable multiple-axis flexure hinge can provide more compliance options for the design of compliant mechanisms.

A symmetrical dual-mass block fiber Bragg grating vibration sensor based on a V-shaped flexible hinge

Real-time monitoring of vibration properties in micro-seismic applications, such as petroleum exploration, physical oceanography, and perimeter security, is important for deep exploration and the prediction of geological disasters and other fields. The fiber Bragg grating (FBG) vibration sensor with symmetrical V-shaped flexible hinges and a dual mass block is proposed. Utilizing formula derivation and simulation software, the sensor's structural parameters are optimized and subjected to analysis. These simulations inform the fabrication of the actual sensor, and subsequently, the sensor's performance is empirically tested. The results show an average sensitivity of 73.86 pm/G and a natural frequency of 800 Hz, with a working range of 20–340 Hz. Its exhibits anti-interference in the transverse direction is less than 5 % during vibration measurement. The research outcomes offer a point of guidance for the progress of FBG accelerometer development within applications that involve measuring low- to medium-frequency accelerations.

Development and evaluation of a light-weight flexure-based lockable joint for morphing wings

Single degree of freedom (single-DOF) morphing wings have the advantages of light-weight and multiple morphing shapes, which can enable aircraft to adapt to uncertain flight environments and various mission types. A single-DOF morphing wing with four morphing shapes designed based on the reconfigurable mechanism is introduced firstly in this paper. Then, a light-weight compliant locking mechanism (CLM) based on flexure hinges is proposed for lockable joints in the reconfigurable mechanism. The CLM has two types depending on the locking method, namely the “plug-in” compliant locking mechanism (PCLM) and the “friction” compliant locking mechanism (FCLM). The working principles of the two CLMs are described. The mathematical models are established to assess the static and dynamic characteristics of the proposed CLM, which are also verified by the finite element simulation. The influence of the flexure hinge dimensions on the working performance of the CLM is analyzed, and its dimensions are optimized considering both the locking performance and the maximum stress. Finally, a PCLM and a FCLM actuated by SMA wires are fabricated based on the optimized dimensions. The experiment is conducted to assess the locking torque of the CLM and the feasibility of the proposed CLM used for morphing wings is confirmed.

Strong attachment as an adaptation of flightless weevils on windy oceanic islands.

Enhanced attachment ability is common in plants on islands to avoid potential fatal passive dispersal. However, whether island insects also have increased attachment ability remains unclear. Here we measured the attachment of a flightless weevil, Pachyrhynchus sarcitis kotoensis, from tropical islands, and compared it with documented arthropods from the mainland. We examined the morphology and material gradient of its attachment devices to identify the specific adaptive modifications for attachment. We find that the weevil has much stronger attachment force and higher safety factor than previously studied arthropods, regardless of body size and substrate roughness. This probably results from the specific flexible bases of the adhesive setae on the third footpad of the legs. This softer material on the setal base has not been reported hitherto and we suggest that it acts as a flexible hinge to form intimate contact to substrate more effectively. By contrast, no morphological difference in tarsomeres and setae between the weevil and other beetles is observed. Our results show the remarkably strong attachment of an island insect and highlights the potential adaptive benefits of strong attachment in windy island environment. The unique soft bases of the adhesive hairs may inspire the development of strong biomimetic adhesives.

High-precision phase-shift method for heavy-load reference mirror based on capacitance sensor monitoring

To address the problems associated with the high-precision phase shift of heavily loaded reference mirrors in large-aperture interferometry, this study proposes a high-precision phase-shifting method based on capacitance sensor monitoring. This method achieves spatial nanoscale phase shifting for a heavy-load reference mirror via spatial three-point synchronous driving of piezoelectric ceramics combined with flexible hinges. The highly sensitive spatial translation of a heavy-load reference mirror is achieved through the gravitational loading of air-floating support and the spatial translation motion modeling of the reference mirror. Nano precision phase-shifting feeds are achieved through spatial in-situ monitoring by combining capacitive sensors and piezoelectric ceramics with a proportion integration differentiation closed-loop drive. Finally, high-precision and high-stability mechanical phase shifting in large-aperture interferometry circumvent the principal shortcomings of existing large-aperture wavelength-tuned phase shifting. The experimental results reveal that the established heavy-load reference mirror mechanical phase shift system has a resolving power of 1.1 nm, frequency response of 120 Hz, and synchronization accuracy of 2° for three-phase shift quantities. This method provides a novel phase-shifting technique for constructing large-aperture phase-shifting interferometers.

Mathematical modelling and experimental study of a novel planar micro-positioning stage using shape memory alloy actuators

The application of smart materials as actuators in precise positioning systems has witnessed significant growth in recent years. However, the use of shape memory alloy (SMA) materials in this context is hindered by their slow response and complex nonlinear behaviour. To overcome these limitations, this paper introduces a novel approach that incorporates two opposite SMA actuators into a flexure hinge type micro-positioning stage, aiming to enhance the system speed. A semi-analytical modelling approach is employed to model the nonlinear behaviour of the SMA actuator. Using the available material models for SMA materials and the nonlinear curved beam theory, the governing equations of the proposed SMA actuator are derived and the resulted partial differential equations are reduced to an algebraic equation based on the Galerkin method. The resulting equations are then solved using the return map method. To validate the accuracy and effectiveness of the proposed model, an experimental setup is constructed. The experimental results demonstrate the model ability to accurately predict the behaviour of the system. Additionally, the developed model allows for the extraction of stress and strain profiles of the SMA actuators for designing the actuator. The study highlights the potential of integrating the proposed model with robust control methods for future works, aiming to effectively control micro-positioning systems and further enhance their performance.

High-precision phase shift method for heavy-load reference mirrors based on nano-precision grating sensor monitoring

In large-aperture interferometry, achieving high-precision phase shifting for heavy-load reference mirrors is challenging. This study introduces a method based on nano-precision grating sensor monitoring. The technique utilizes spatial three-point synchronous driving by piezoelectric ceramics, combined with flexible hinges, to enable nanoscale phase shifting of heavy-load reference mirrors. Additionally, it integrates in-situ PID closed-loop drive monitoring at these three points, using nano-precision grating sensors and piezoelectric ceramics. To ensure nanoscale resolved spatial translation, the mirrors are supported by air-bearings that counteract gravity, coupled with a phase shift error calibration model. The final realization of high-precision and high-stability mechanical phase shifting in large-aperture interferometry circumvents the principle defects of existing large-aperture wavelength-tuned phase shifting. The experiments show that the established mechanical phase shifting system with heavy-load reference mirror has a resolution of 1.5 nm, a frequency response of 116 Hz, and a synchronization accuracy of 2° for the three phase shifting quantities, and the method provides a new method and means of phase shifting for the construction of large-aperture phase shifting interferometer.

Solution NMR assignments and structure for the dimeric kinesin neck domain.

Kinesin is a motor protein, comprised of two heavy and two light chains that transports cargo along the cytoskeletal microtubule filament network. The heavy chain has a neck domain connecting the ATPase motor head responsible for walking along microtubules, with the stalk and subsequent tail domains that bind cargo. The neck domain consists of a coiled coli homodimer with about five heptad repeats, preceded by a linker region that joins to the ATPase head. Here we report 1H, 15N, and 13C NMR assignments and a solution structure for the kinesin neck domain from rat isoform Kif5c. The calculation of the NMR structure of the homodimer was facilitated by unambiguously assigning sidechain NOEs between heptad a and d positions to interchain contacts, since these positions are too far apart to give sidechain contacts in the monomers. The dimeric coiled coil NMR structure is similar to the previously described X-ray structure, whereas the linker region is disordered in solution but contains a short segment with β-strand propensity- the β-linker. Only the coiled coil is protected from solvent exchange, with ∆G values for hydrogen exchange on the order of 4-6kcal/mol. The high stability of the hydrogen-bonded α-helical structure makes it unlikely that unzippering of the coiled coil is involved in kinesin walking. Rather, the linker region serves as a flexible hinge between the kinesin head and neck.

A fast steering mirror with ultra-low geometric tilt-to-length coupling noise for space-borne gravitational wave detection

The misalignment between the geometric center and rotation center in fast steering mirrors (FSMs) poses a challenge for space-borne gravitational wave detection, as it results in geometric tilt-to-length (TTL) coupling noise. To address this issue, we have proposed a FSM structure that exhibits ultra-low geometric TTL coupling noise. The geometric TTL coupling noise is analyzed and evaluated strictly considering the FSM non-ideal tilt of the plane and the center shift characteristic of cartwheel flexure hinges under a small rotational angle. Compared to traditional FSM designs, our new design offers superior noise suppression capabilities and is capable of meeting the stringent piston effect noise requirements of 0.2 in the frequency band of under ideal conditions.

A novel quasi-intermittent vibration assisted swing cutting device: Design and experimental investigation

Elliptical vibration assisted cutting (EVAC) is gradually being one of the most potential machining methods for difficult to machine materials. However, the elliptical trajectory causes periodic residual traces on machined surface. A novel quasi-intermittent vibration assisted swing cutting (QVASC) device driven by two piezoelectric actuators is proposed to reduce the residual traces between adjacent paths and improve surface quality. An X-shaped flexure hinge was used to suppress the mutual interference between two driving shafts and realize kinematic decoupling. The mechanical configuration and geometric parameters of the proposed device were designed based on the analyzing of kinematics, dynamics, and flexible characteristics. The effectiveness of the proposed device was verified by finite element analysis and off-line performance test. Tests results show that the maximum coupling ratio of motion axis, maximum motion stroke, and minimum resolution of QVASC device are 1.65%, 19.943 μm, and 9.55 nm, which are satisfied with the design and machining requirements. Finally, systematic turning experiments were carried out to verify the effectiveness of the proposed device in restraining cutting residual traces. The experimental results indicate that the proposed device can effectively inhibit the generation of periodic residual traces, which validates the feasibility of the QVASC device.

Flexure Hinge Design and Optimization for Compact Anthropomorphic Grippers Made via Metal Additive Manufacturing

Abstract Flexure-based grippers offer an attractive alternative to conventional grippers used in robotics and automation. However, most existing designs appear to suffer from insufficient range of motion, loadability, and support stiffness. This article presents an approach to obtain well-performing flexure hinges for compact anthropomorphic grippers made via metal additive manufacturing. We propose a flexure hinge architecture that achieves a high range of motion despite the challenging combination of a small design space, high Young’s modulus, and limited minimum feature size. Furthermore, we present an optimization procedure to generate suitable tendon-driven designs with high loadability. Using this framework, a flexure hinge with an outer diameter of 21.5 mm and range of motion of ±30 deg is synthesized. For the range of 0–30 deg, simulations show a lateral loadability of 52.5–18.6 N and lateral support stiffness of 12,309–11,130 N/m, determined at a gripper interface located 41.2 mm from the hinge pivot axis. Experiments confirm a loadability of at least 15.4 N and determined a stiffness of 8982 to 9727 N/m for same conditions. The results show that the flexure hinge architecture has large potential for a wide range of applications, while in combination with the optimization procedure, superior designs for tendon-driven grippers can be obtained.