arXiv subjects

Safvan Palathingal

Publications and source records attributed to Safvan Palathingal.

6 recordsLinked to original sources

arXiv2026

A passive universal grasping mechanism based on an everting shell

A passive monolithic compliant grasping mechanism that works based on the eversion of an elastically deformable bistable shell is conceptualized. It comprises grasping arms made of beam segments that work in conjunction with the everting shell. The grasper is capable of picking up a stiff object of any shape up to a maximum size and weight. The bistable shell everts upon contact with the object to enable the grasping arms envelop the object forming an enclosure. The mechanism then stays in that configuration until it is actuated again to turn the shell back to its original configuration and thereby opening the enclosure to release the object. The stiffness of the arms decides the payload of the mechanism. The size of the arms decides the largest object that can be grasped and held. The arms have distributed compliance so that they can conform to the shape of the object without applying undue force on it.

cs.RO↗

arXiv2026

Design and modelling of compliant mechanisms with invertible Poisson's ratio effect for growing biological cells

The behaviour of biological cells depends on the mechanical properties, such as Elastic Modulus and Poisson's ratio, of the substrate they adhere to. Tunable materials such as polyacrylamide gels and hydrogels were previously used as substrates to understand this dependence. However, these substrates do not facilitate changing their elastic properties in situ while cells are growing on them. This work presents an alternate approach that enables this--substrates based on tunable compliant micro mechanisms. In particular, the mechanism proposed here has an invertible Poisson's ratio effect. In the first configuration, the effect is positive, and in the second, it is negative, with any desired magnitude. We achieve this by changing the stiffness between two internal points of a mechanism with the shape of a re-entrant structure. An increase in stiffness causes the direction of deformation along the lateral axis to reverse for a given reference load along the horizontal axis. We derive analytical expressions that relate the geometric parameters to the ratio of input and output displacements for both mechanism configurations. The analytical modelling is verified with finite element analysis and experiments on mesoscale design prototypes of both configurations.

cond-mat.soft↗

arXiv2026

Bistability of midpoint-fused arches with pinned-pinned boundary conditions

Arranging multiple arches in a circular pattern and fusing them at their midpoint yields a three-dimensional configuration that we refer to as midpoint-fused arches (MFA). This study investigates the structural bistability of MFA, i.e., their ability to admit two distinct, force-free stable equilibrium states. Starting from an as-fabricated, stress-free configuration, MFA can invert into a stressed, toggled state reminiscent of an umbrella's ribs. We develop an analytical model for the response of a pinned-pinned MFA subjected to a concentrated mid-span load by minimizing the total potential energy. Individual arches are treated as spatially deforming, and kinematic compatibility relations are derived at the fusion point to couple their deformations. Various deformation symmetries are then exploited to simplify the problem. We demonstrate the model's utility by characterizing the force-displacement response of a two-arch MFA, identifying distinct deformation pathways and discussing the pathway transitions that occur during toggling. In particular, we show how the structure switches between symmetric and asymmetric deformation modes as it moves between stable configurations. The generality of the framework is further established through analysis of a three-arch MFA, which exhibits richer coupled deformation behaviour. Nonlinear finite-element simulations and table-top experiments corroborate the analytical predictions, showing close agreement in both equilibrium states and the associated transition responses.

cond-mat.soft↗

arXiv2025

Compliant Mechanisms for Invertible Poisson's Ratio and Tunable Stiffness in Cell Culture Substrates

The mechanical environment of a substrate plays a key role in influencing the behavior of adherent biological cells. Traditional tunable substrates have limitations as their mechanical properties cannot be dynamically altered in-situ during cell culture. We present an alternate approach by using compliant mechanisms that enable realization of tunable substrate properties, specifically, invertible Poisson's ratio and tunable stiffness. These mechanisms transition between positive and negative Poisson's effects with tunable magnitude through a bistable Engaging-Disengaging Compliant Mechanism (EDCM). EDCM allows stiffness between two points of the substrate to switch between zero and theoretically infinite. In the stiffened state, lateral deformation reverses under a constant axial load, while in the zero-stiffness state, the deformation direction remains outward as that of re-entrant structure. EDCM in conjunction with an offset mechanism also allows tuning of the effective stiffness of the entire mechanism. We present analytical models correlating geometric parameters to displacement ratios in both bistable states and through illustrative design cases, demonstrate their potential for designing dynamic and reconfigurable cell culture substrates.

cond-mat.soft↗

arXiv2025

Design of an engaging-disengaging compliant mechanism by using bistable arches

Compliant mechanisms utilise elastic deformation of their segments to transmit motion or force. The utility and behaviour of specific compliant mechanisms can be enhanced by introducing an engaging and disengaging ability with its elastic segments. Towards this, we present an engaging-disengaging compliant mechanism (EDCM) that can switch its stiffness between infinite and zero. The design of the EDCM is based on bistable arches and a locking mechanism. We describe its working, identify its design parameters, and use analytical expressions to arrive at its dimension. The design is verified by detailed finite element analysis and experiments on a 3D-printed prototype. Three alternate designs that lead us to the final mechanism are also briefly discussed.

cond-mat.soft↗

arXiv2024

Axisymmetric membrane nano-resonators: A comparison of nonlinear reduced-order models

The shift in the backbone of the frequency--response curve and the `jump-down' observed at a critical frequency observed in nano-resonators are caused by their nonlinear mechanical response. The shift and jump-down point are therefore often used to infer the mechanical properties that underlie the nonlinear response, particularly the resonator's stretching modulus. To facilitate this, the resonators's dynamics are often modelled using a Galerkin-type numerical approach or lumped ordinary differential equations like the Duffing equation, that incorporate an appropriate nonlinearity. To understand the source of the problem's nonlinearities, we first develop an axisymmetric but spatially-varying model of a membrane resonator subject to a uniform oscillatory load with linear damping. We then derive asymptotic solutions for the resulting partial differential equations (PDEs) using the Method of Multiple Scales (MS), which allows a systematic reduction to a Duffing-like equation with analytically determined coefficients. We also solve the PDEs numerically via the method of lines. By comparing the numerical solutions with the asymptotic results, we demonstrate that the numerical approach reveals a non-constant maximum compliance with increasing load, which contradicts the predictions of the MS analysis. In contrast, we show that combining a Galerkin decomposition with the Harmonic Balance Method accurately captures the non-constant maximum compliance and reliably predicts jump-down behaviour. We analyze the resulting frequency-response predictions derived from these methods. We also argue that fitting based on the jump-down point may be sensitive to noise and discuss strategies for fitting frequency-response curves from experimental data to theory that are robust to this.

cond-mat.mtrl-sci↗