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Decoupling Torque and Stiffness: A Unified Modeling and Control Framework for Antagonistic Artificial Muscles

Kazemipour, Amirhossein, Katzschmann, Robert K.

arXiv.org Artificial Intelligence

Antagonistic soft actuators built from artificial muscles (PAMs, HASELs, DEAs) promise plant-level torque-stiffness decoupling, yet existing controllers for soft muscles struggle to maintain independent control through dynamic contact transients. We present a unified framework enabling independent torque and stiffness commands in real-time for diverse soft actuator types. Our unified force law captures diverse soft muscle physics in a single model with sub-ms computation, while our cascaded controller with analytical inverse dynamics maintains decoupling despite model errors and disturbances. Using co-contraction/bias coordinates, the controller independently modulates torque via bias and stiffness via co-contraction-replicating biological impedance strategies. Simulation-based validation through contact experiments demonstrates maintained independence: 200x faster settling on soft surfaces, 81% force reduction on rigid surfaces, and stable interaction vs 22-54% stability for fixed policies. This framework provides a foundation for enabling musculoskeletal antagonistic systems to execute adaptive impedance control for safe human-robot interaction.


A Machine Learning Pipeline for Multiple Sclerosis Biomarker Discovery: Comparing explainable AI and Traditional Statistical Approaches

Punzo, Samuele, Galfrè, Silvia Giulia, Massafra, Francesco, Maglione, Alessandro, Priami, Corrado, Sîrbu, Alina

arXiv.org Artificial Intelligence

We present a machine learning pipeline for biomarker discovery in Multiple Sclerosis (MS), integrating eight publicly available microarray datasets from Peripheral Blood Mononuclear Cells (PBMC). After robust preprocessing we trained an XGBoost classifier optimized via Bayesian search. SHapley Additive exPlanations (SHAP) were used to identify key features for model prediction, indicating thus possible biomarkers. These were compared with genes identified through classical Differential Expression Analysis (DEA). Our comparison revealed both overlapping and unique biomarkers between SHAP and DEA, suggesting complementary strengths. Enrichment analysis confirmed the biological relevance of SHAP-selected genes, linking them to pathways such as sphingolipid signaling, Th1/Th2/Th17 cell differentiation, and Epstein-Barr virus infection--all known to be associated with MS. This study highlights the value of combining explainable AI (xAI) with traditional statistical methods to gain deeper insights into disease mechanism.


Directional Ensemble Aggregation for Actor-Critics

Werge, Nicklas, Wu, Yi-Shan, Tasdighi, Bahareh, Kandemir, Melih

arXiv.org Machine Learning

Off-policy reinforcement learning in continuous control tasks depends critically on accurate $Q$-value estimates. Conservative aggregation over ensembles, such as taking the minimum, is commonly used to mitigate overestimation bias. However, these static rules are coarse, discard valuable information from the ensemble, and cannot adapt to task-specific needs or different learning regimes. We propose Directional Ensemble Aggregation (DEA), an aggregation method that adaptively combines $Q$-value estimates in actor-critic frameworks. DEA introduces two fully learnable directional parameters: one that modulates critic-side conservatism and another that guides actor-side policy exploration. Both parameters are learned using ensemble disagreement-weighted Bellman errors, which weight each sample solely by the direction of its Bellman error. This directional learning mechanism allows DEA to adjust conservatism and exploration in a data-driven way, adapting aggregation to both uncertainty levels and the phase of training. We evaluate DEA across continuous control benchmarks and learning regimes - from interactive to sample-efficient - and demonstrate its effectiveness over static ensemble strategies.


From Idea to CAD: A Language Model-Driven Multi-Agent System for Collaborative Design

Ocker, Felix, Menzel, Stefan, Sadik, Ahmed, Rios, Thiago

arXiv.org Artificial Intelligence

In modern product development, Computer Aided Design and Engineering (CAD/E) plays a key role to turn innovative ideas and visions into tangible and manufacturable designs. Digital 2D and 3D geometry representations of objects on different levels of granularity are required in various intermediate development steps, for example aesthetic discussions, design quality evaluations based on simulation tools, and design feasibility checks. For these steps, development teams include various roles such as requirement engineers, style designers, Computer-Aided Design (CAD) experts, simulation domain experts, and quality assurance teams who create a product cooperatively. Stakeholders in these roles utilize software tools to implement digital representations of products, also referred to as digital twins. This process receives an increasing amount of support in the form of Artificial Intelligence (AI) methods. For example, data science methods provide efficient ways to improve the problem understanding, e.g., by calculating design sensitivities towards a certain performance aspect [Gräning and Sendhoff, 2014], or displaying the distribution of design variations in the solution space using clustering [Lanfermann et al., 2020].


Portable, High-Frequency, and High-Voltage Control Circuits for Untethered Miniature Robots Driven by Dielectric Elastomer Actuators

Shao, Qi, Liu, Xin-Jun, Zhao, Huichan

arXiv.org Artificial Intelligence

In this work, we propose a high-voltage, high-frequency control circuit for the untethered applications of dielectric elastomer actuators (DEAs). The circuit board leverages low-voltage resistive components connected in series to control voltages of up to 1.8 kV within a compact size, suitable for frequencies ranging from 0 to 1 kHz. A single-channel control board weighs only 2.5 g. We tested the performance of the control circuit under different load conditions and power supplies. Based on this control circuit, along with a commercial miniature high-voltage power converter, we construct an untethered crawling robot driven by a cylindrical DEA. The 42-g untethered robots successfully obtained crawling locomotion on a bench and within a pipeline at a driving frequency of 15 Hz, while simultaneously transmitting real-time video data via an onboard camera and antenna. Our work provides a practical way to use low-voltage control electronics to achieve the untethered driving of DEAs, and therefore portable and wearable devices.


Justice Department halts DEA's random searches of airport travelers after report finds 'serious concerns'

FOX News

Video recorded by a passenger at the Cincinnati/Northern Kentucky International Airport this year shows a federal agent seizing a traveler's bag. The Justice Department has now ordered the DEA to halt random searches at transit hubs. The Drug Enforcement Administration is no longer allowed to randomly search travelers at airports and other transit hubs after a scathing report from the Justice Department found "serious concerns" with the practice. DEA agents failed to properly document searches, may have illegally targeted minorities and, in at least one case, paid an airline employee tens of thousands of dollars over several years to suggest targets for searches, according to the report released Thursday by Justice Department Inspector General Michael Horowitz. The deputy attorney general ordered the DEA to suspend the random searches Nov. 12 after seeing a draft of the memo.


Design, manufacturing, and inverse dynamic modeling of soft parallel robots actuated by dielectric elastomer actuators

Chang, Jung-Che, Wang, Xi, Axinte, Dragos, Dong, Xin

arXiv.org Artificial Intelligence

Soft parallel robots with their manipulation safety and low commercial cost show a promising future for delicate operations and safe human-robot interactions. However, promoting the use of electroactive polymers (EAPs) is still challenging due to the under-improving quality of the product and the dynamic modelling of the collaborations between multiple actuators. This article presents the design, fabrication, modelling and control of a parallel kinematics Delta robot actuated by dielectric elastomer actuators (DEAs). The trade-off between the actuation force and stroke is retaken by an angular stroke amplification mechanism, and the weight of the robot frame is reduced by utilizing 3D puzzling strip structures. A generic way of constructing a high-stability conductive paint on a silicon-based film has been achieved by laser scanning the DE-film and then sandwiching a conductive particle-based electrode with a paint which is mixed by the particles and photosensitive resin. Compared to the wildly used carbon grease, the fabricated electrode shows a higher consistency in its dynamic behaviour before and after the on-stand test. Finally, to predict the output force and inverse motion of the robot end effector, we constructed the inverse dynamic model by introducing an expanded Bergstrom-Boyce model to the constitutive behavior of the dielectric film. The experimental results show a prediction of robot output force with RSME of 12.4% when the end effector remains stationary, and a well-followed trajectory with less than RSME 2.5%.


Underwater and Surface Aquatic Locomotion of Soft Biomimetic Robot Based on Bending Rolled Dielectric Elastomer Actuators

Zhang, Chenyu, Zhang, Chen, Qu, Juntian, Qian, Xiang

arXiv.org Artificial Intelligence

Abstract-- All-around, real-time navigation and sensing across the water environments by miniature soft robotics are promising, for their merits of small size, high agility and good compliance to the unstructured surroundings. In this paper, we propose and demonstrate a mantas-like soft aquatic robot which propels itself by flapping-fins using rolled dielectric elastomer actuators (DEAs) with bending motions. This robot exhibits fast-moving capabilities of swimming at 57mm/s or 1.25 body length per second (BL/s), skating on water surface at 64 mm/s (1.36 BL/s) and vertical ascending at 38mm/s (0.82 BL/s) at 1300 V, 17 Hz of the power supply. These results show the feasibility of adopting rolled DEAs for mesoscale aquatic robots with high motion performance in various water-related scenarios. Inspired by natural animals, which evolved optimal body shapes along with strong motion propulsion methods, DEAs appeared to be promising in the abilities in various space, researchers introduced delicate field of centimeter scale robots in free water space for their structures and mechanisms to robots to realize multimodal large strain and fast response abilities [14].


Modelling and simulation of a commercially available dielectric elastomer actuator

Sohlbach, Lukas, Hobbani, Hamza, Blase, Chistopher, Perez-Peña, Fernando, Schmidt, Karsten

arXiv.org Artificial Intelligence

In order to fully harness the potential of dielectric elastomer actu-ators (DEAs) in soft robots, advanced control methods are need-ed. An important groundwork for this is the development of a control-oriented model that can adequately describe the underly-ing dynamics of a DEA. A common feature of existing models is that always custom-made DEAs were investigated. This makes the modelling process easier, as all specifications and the struc-ture of the actuator are well known. In the case of a commercial actuator, however, only the information from the manufacturer is available and must be checked or completed during the modelling process. The aim of this paper is to explore how a commercial stacked silicone-based DEA can be modelled and how complex the model should be to properly replicate the features of the actu-ator. The static description has demonstrated the suitability of Hooke's law. In the case of dynamic description, it is shown that no viscoelastic model is needed for control-oriented modelling. However, if all features of the DEA are considered, the general-ized Kelvin-Maxwell model with three Maxwell elements shows good results, stability and computational efficiency.


Resilient bug-sized robots keep flying even after wing damage

Robohub

MIT researchers have developed resilient artificial muscles that can enable insect-scale aerial robots to effectively recover flight performance after suffering severe damage. It is estimated that a foraging bee bumps into a flower about once per second, which damages its wings over time. Yet despite having many tiny rips or holes in their wings, bumblebees can still fly. Aerial robots, on the other hand, are not so resilient. Poke holes in the robot's wing motors or chop off part of its propellor, and odds are pretty good it will be grounded.