Aug 2026· Journal of Mechanisms and Robotics· 0 citations
Abstract
Passive stiffness modulation is essential for compliant robotic systems in dynamic and uncertain environments, where rigid actuators or constant stiffness designs are often insufficient to ensure safety and adaptability. This paper presents the design, modeling, optimization, and experimental validation of a Load-Dependent Contact-Aided Compliant Joint (LCCJ) that passively modulates stiffness in response to external torque. An integrated design pipeline is established, which bridges a high-fidelity analytical framework with a physically-motivated optimization strategy. The framework combines a chained pseudo-rigid-body model (CPRBM) with Karush-Kuhn-Tucker (KKT) conditions to describe the complex beam-boundary interactions. Using the distinct deformation regimes of the mechanism, the pipeline employs a two-stage optimization strategy to precisely map the desired stiffness modulation back to the physical geometric parameters. Simulation results demonstrate that, across the benchmark and optimized-design validation cases, the model predictions agree closely with finite element analysis (FEA), with maximum relative errors in the torque–deformation response of 4.02% and 3.18% in the pre- and post-contact regions, respectively. Experimental validation confirms the effectiveness of the proposed design; compared to the FEA predictions, the experimental results exhibit relative errors below 2.6% in the pre-contact region and 5.22%–6.21% in the post-contact region. The LCCJ offers a compact and monolithic solution for passive stiffness modulation in compliant joint applications.
Pneumatic soft actuators are widely used in soft robotic systems because of their inherent compliance and smooth deformation. However, their practical application is often limited by low structural stiffness, restricted load-bearing capability, and insufficient tip output force. These limitations become more pronounced in tasks that require stable force transmission or precise interaction with the environment. In response to these limitations, this study proposes a stiffness-enhanced pneumatic soft actuator based on a modified multilayer structural configuration. The actuator integrates chamber layers, a constraint layer, and periodically distributed rigid reinforcement elements. This structural arrangement improves the way internal pressure is converted into bending deformation and external force output, while avoiding excessive local expansion of the chambers. Based on this actuator, a coupled theoretical model is developed to describe the relationship between internal pressure, bending angle, and tip force. The model considers both the hyperelastic behavior of the silicone material and the geometric constraints introduced by chamber deformation. Finite element simulations are performed to examine the actuator’s mechanical response under different pressure inputs. This effect becomes evident at higher pressure levels. Both free-bending behavior and tip contact force generation are analyzed. The simulation results follow the same trends as the theoretical predictions, and the overall deviation remains below 10% across the investigated pressure range. The agreement shows that the model reflects the main mechanical response. Compared with a conventional pneumatic soft actuator, the proposed design achieves higher stiffness and larger tip output force, while maintaining compliant motion and smooth bending behavior. The actuator structure and model may serve as a useful basis for pneumatic actuator design in force-demanding tasks.
Wenjing Zhou, Rui Ma, Mingyue Lu et al.· SAE technical paper series· 0 citations
Modular steel construction offers significant advantages in fabrication efficiency, installation speed, and structural adaptability; however, the performance of inter-module connections remains a critical concern, particularly under lateral loading conditions. This study aimed to evaluate the mechanical behavior and stiffness characteristics of a modified plug-in device connection incorporating a U-shaped stiffener with bolted stiffener-to-column connections. The research employed finite element analysis using ANSYS Mechanical. Numerical models were first validated against previous experimental studies using two reference connections, SC1 and SC2, before analyzing the modified model, SC_Mod. The validation results showed differences of 7% and 9% between the numerical and experimental results, confirming the acceptable accuracy of the developed models. The SC_Mod connection achieved an initial translational stiffness of 21,500.46 kN/m and rotational stiffness of 26,739.38 kNm/rad. Compared with SC1, the translational and rotational stiffness increased by 243% and 163%, respectively, while increases of 127% and 82% were observed relative to SC2. The modified connection reached a maximum load of 633.5 kN, with yielding occurring at approximately 22.6 mm deformation and failure occurring at 120.39 mm. These findings demonstrated that the bolted U-shaped stiffener configuration substantially improved connection stiffness, load transfer capacity, ductility, and constructability, making it a promising alternative for steel modular building connections while preserving the practical advantages of modular construction systems.
Unknown authors· Journal of social research· 0 citations
Semi-rigid connections play a critical role in steel structures; however, most existing component-based approaches do not explicitly account for stiffness degradation and post-yield residual stiffness, which may reduce the accuracy of moment–rotation predictions. To address this limitation, direct numerical simulations (DNSs) of representative T-stub beam-to-column joints were conducted to investigate their nonlinear rotational behavior. Based on the observed joint response, a Joint Component Model (JCM) capable of representing sequential yielding, stiffness evolution, and residual rotational stiffness was developed. Constitutive relationships were derived, and a parameter identification procedure directly relating joint geometry and component mechanical properties to the model parameters was established. The proposed model was subsequently implemented in ANSYS and validated through analyses of T-stub joints and steel frames subjected to static and dynamic loading. The results showed good agreement between the JCM and DNS in terms of moment–rotation relationships, force–displacement responses, and dynamic time-history responses. Compared with DNS, the proposed model significantly reduced computational time while maintaining satisfactory prediction accuracy. The proposed JCM therefore provides an efficient and reliable component-based modeling framework for modeling semi-rigid steel connections and capturing stiffness evolution throughout the entire joint rotation process.
Xiao Liu, Yilun Li, Haiwei Yao et al.· Buildings· 0 citations
Robotic systems operating in unstructured environments face a conflicting requirement: they must be manoeuvrable to easily navigate tight and unstructured environments, yet stiff enough to perform precise, heavy-duty tasks. Tendon-driven hyper-redundant manipulators offer a compelling solution due to their lightweight and slender designs. In this work, a novel stiffness-adjusting strategy for a tendon-driven manipulator is presented. It goes beyond complex antagonistic drives, joint-level added components, and passive high-pretension schemes. This approach utilises a single active tensioning system to modulate a global reference tension, providing on-demand stiffness adjustment on the robot. Through a systematic experimental campaign involving varying payloads and tension levels, the behaviour of a five-degree-of-freedom prototype is characterised using high-precision motion capture. The results demonstrate that this mechanically simple input can amplify tip stiffness by a factor of three to four. Furthermore, the presented compliance model validates the efficiency of the global tensioning strategy in modulating the system’s overall stiffness.
A. Poka, Federico Manara, D. Ludovico et al.· 2026 IEEE/ASME International...· 0 citations
Piezoelectric-actuated nanopositioning stages commonly employ flexure amplification mechanisms to enlarge output displacement and are widely used in optical measurement, micro and nano manufacturing, and other precision engineering fields. However, existing methods still have limitations in computational efficiency, hinge modeling accuracy, and displacement prediction under external loading. To address these limitations, this paper proposes a generalized compliant-chain modeling method in which flexure hinges are treated as compliant units connected by rigid elements, improving computational efficiency relative to repeated finite element modeling. A multi-configuration hinge model (MCH model) is established to analyze the effects of hinge configurations and mechanism parameters on key performance indices, thereby improving prediction accuracy and extending the design space. A load-induced displacement loss model (LDL model) is further developed to characterize output displacement loss under external loading and improve the applicability of the method to loaded conditions and integrated systems involving multiple flexure mechanisms. Finite element simulations and experiments are conducted to validate the proposed models. The results show that the prediction errors of the amplification ratio and stiffness are both within 5%, while the designed mechanism achieves a high amplification ratio of 17.55. These results indicate that the proposed method provides competitive prediction accuracy and displacement amplification performance among similar flexure amplification mechanisms. The proposed method provides an effective modeling and design tool for amplification mechanisms requiring large stroke and high load capacity.
Hou-Wen Fu, Wen-Xi Zhang, Zi-Qi Wang et al.· Micromachines· 0 citations
The design freedom of additive manufacturing has potential to increase the complexity, functionality, and mechanical behavior of compliant mechanisms compared to conventional manufacturing methods. However, this same design freedom can result in “trial-and-error” design iteration when designing compliant mechanisms for target behaviors. Trial-and-error design iteration is undesirable and inefficient, particularly when designing compliant mechanisms with nonlinear-elastic materials and large deformations. To address this problem, we develop a synthesis method for the inverse design of compliant mechanisms that uses numerical optimization and a library of building blocks that incorporate nonlinear-elastic materials, and large deformations as geometric nonlinearity. The synthesis method works by selecting the type and geometry of the building blocks that will deflect to a target shape under a given load, or achieve a target stiffness response. The method's ability to use different building block geometries and incorporate nonlinear behaviors, such as the superelasticity of shape memory alloys, is shown to enhance the design of compliant mechanisms to reach target shapes or stiffness responses.
Brianne Hargrove, Taylor E. Greenwood, Mary X. Frecker et al.· Journal of Mechanisms and Ro...· 0 citations
