Jovana Jovanova | Searcharxiv

arXiv2026

Off-Axis Compliant RCM Joint with Near-Isotropic Stiffness and Minimal Parasitic Error

This paper presents an off-axis, monolithic compliant Remote Center of Motion (RCM) joint for neuroendoscopic manipulation, combining near-isotropic stiffness with minimal parasitic motion. Based on the Tetra II concept, the end-effector is placed outside the tetrahedral flexure to improve line of sight, facilitate sterilization, and allow rapid tool release. Design proceeds in two stages: mobility panels are sized with a compliance-based isotropy objective, then constraining panels are synthesized through finite-element feasibility exploration to trade stiffness isotropy against RCM drift. The joint is modeled with beam elements and validated via detailed finite-element analyses, including fatigue-bounded stress constraints. A PA12 prototype is fabricated by selective laser sintering and characterized on a benchtop: a 2 N radial load is applied at the end-effector while a 6-DOF electromagnetic sensor records pose. The selected configuration produces a stiffness-ellipse principal axis ratio (PAR) of 1.37 and a parasitic-to-useful rotation ratio (PRR) of 0.63%. Under a 4.5° commanded rotation, the predicted RCM drift remains sub-millimetric (0.015-0.172 mm). Fatigue analysis predicts a usable rotational workspace of 12.1°-34.4° depending on direction. Experiments reproduce the simulated directional stiffness trend with typical deviations of 6-30%, demonstrating a compact, fabrication-ready RCM module for constrained surgical access.

cs.RO↗

arXiv2025

Piezoelectric truss metamaterials: data-driven design and additive manufacturing

In the development of active animate materials, electromechanical coupling is highly attractive to realize mechanoresponsive functionality. Piezoelectricity is the most utilized electromechanical phenomenon due to the wide availability of materials that display precise and reliable coupling. However, the inherent directionality of these materials is constrained by the symmetry of their crystal structure, which limits the choice of available properties in natural piezoelectric materials. A solution to alleviate this limitation could be to leverage geometry or architecture at the mesoscale. Here, we present an integrated framework to design and 3D-print piezoelectric truss metamaterials with customizable anisotropic responses. To explore the vast design space of truss metamaterials, we employ generative machine learning to optimize the topology and geometry of truss lattices and achieve target piezoelectricity. Then, we develop an in-gel-3D printing method to fabricate polymer-ceramic piezoelectric truss metamaterial structures using a composite slurry of photo-curable resin and lead-free piezoelectric particles. The ML framework discovers designs exhibiting unconventional behaviors, including auxetic, unidirectional, and omnidirectional piezoelectricity, while the additive manufacturing technique ensures shaping freedom and precision in fabricating these metamaterials at small scales. Our results show an improvement of over 48% in the specific hydrostatic piezoelectric coefficient in optimized metamaterials over bulk lead zirconate titanate (PZT). We successfully achieved metamaterials with higher transverse piezoelectric coupling coefficient than its longitudinal coefficient, which is a phenomenon that is rare in bulk materials. Our approach enables customizable piezoelectric responses and paves the way towards the development of a new generation of electro-active animate materials.

physics.app-ph↗