Soft grippers are known for their ability to interact with objects that are fragile, soft or of an unknown shape, as well as humans in collaborative robotics applications. However, state-of-the-art soft grippers lack either payload capacity or durability, which limits their use in industrial applications. In fact, high force density pneumatic soft grippers require high strain and operating pressure, both of which impair their durability. This work presents a new sleeved bending actuator for soft grippers that is capable of high force density and durability. The proposed actuator is based on design principles previously proven to improve the life of pneumatic artificial muscles, where a sleeve provides a uniform reinforcement that reduces local stresses and strains in the inflated membrane. The sleeved bending actuator features a silicone membrane and an external two-material sleeve that can support high pressures while providing a flexible grip. The proposed sleeved bending actuators are validated through two grippers, sized according to foreseen soft gripper applications: A small gripper for drone perching and lightweight food manipulation, and a larger one for the manipulation of heavy material (>5 kg) of various weights and sizes. Performance assessment shows that these grippers have payloads up to 5.2 kg and 20 kg, respectively. Durability testing of the grippers demonstrates that the grippers have an expected lifetime ranging from 263,000 cycles to more than 700,000 cycles. The grippers are tested in various settings, including the integration of a gripper into a Phantom 2 quadcopter, a perching demonstration, as well as the gripping of light and heavy food items. Experiments show that sleeved bending actuators constitute a promising avenue for durable and strong soft grippers.

The fatigue life of pneumatic artificial muscles (PAMs) is a limitation to the development of reliability-intensive applications of soft robots in fields such as medical robotics, transportation, and industrial manufacturing. This article aims at improving the fatigue life of PAMs by (1) providing design principles for durable PAMs under high strains and (2) demonstrating these design principles by developing a representative optimal extensible pneumatic muscle (EPM) in the context of a soft surgical robot case study. Representative performance requirements are derived from an image-guided surgical robot taken as a case study. An experimental design study over relevant EPM geometries reveals three basic fatigue principles governing the failure of PAMs: fatigue limit, abrasion wear, and Hertz contact stress. Using these principles, a new extensible pneumatic muscle made of a silicone tube and a continuous orthotropic restraining sleeve is designed and characterized in terms of performance and fatigue life. Fatigue experiments confirm that the fatigue-optimized EPM can reach 50% elongation for 229,000 cycles, a 10 × improvement in fatigue life compared with currently available PAMs. Other than being optimized for fatigue, the proposed EPM also shows a linear force–displacement behavior and its hollow construction allows for easy integration of a position sensor as well as a telescopic guide that increases static force. The application of the proposed design principles offers a solution to the usual compromise between soft actuators' strain and durability. These principles can be applied to the design of any durable high-strain soft actuator or compliant structure.

This paper presents the design and experimental characterization of a binary jet valve, specifically developed to control an all-polymer needle manipulator during intramagnetic resonance imaging (MRI) prostate interventions (biopsies and brachytherapies). The key feature of the MRI-compatible valve is its compact dual-stage configuration. The first stage is composed of a low-friction jet nozzle, driven by a small rotary dielectric elastomer actuator (DEA). The second stage provides sufficient air flow and stability for the binary robotic application through an independent air supply, activated by a bistable spool. A hyperelastic stress-strain model is used to optimize the geometrical dimensions of the DEA jet assembly. Fully functional valve prototypes, made with 3M's VHB 4905 films, are monitored with a high-speed camera in order to quantify the system's shifting dynamics. The impact of nozzle clearance, dielectric elastomer film viscoelasticity, mechanical friction, and actuator torque generation on overall dynamic behavior of two different valve setups is discussed. Results show an overall shifting time of 200–300 ms when the friction of the nozzle and DEA actuation stretches are minimized. Low shifting time combined with compactness, simplicity, and low cost suggest that the low friction DEA-driven jet valves have great potential for switching a large number of pneumatic circuits in an MRI environment as well as in traditional pneumatic applications.