Robots with active variable stiffness (VS) capabilities can potentially achieve safer interactions with humans and better adaptabilities to uncertainties in complex environments. Currently, the conventional jamming or phase-change-based VS mechanisms simultaneously act on the stiffnesses of the robotic joint in all axes, making it difficult to achieve decoupled stiffness programming in different directions/axes. To overcome this challenge, a bio-inspired stiffness-programmable robotic flexible joint (SPRFJ) based on the electro-adhesive (EA) clutches is proposed. By programming the ON/OFF states of the EA clutches on different surfaces around the SPRFJ, customization of stiffness profiles in different directions/axes can be realized, and therefore, the load-bearing capacity and flexibility of the robotic arm can be adjusted. A SPRFJ prototype consisting of four EA clutch units is developed, and through extensive experiments, we demonstrate that it can achieve a stiffness change of 21 times and can withstand resisting forces up to 13.41 N at 1 kV. The reliable multi-directional stiffness programmability of the SPRFJ is shown via extensive tests. Demonstrations on stable position locking at different angles and free movements while carrying payloads are conducted to showcase its application in soft robotics. This SPRFJ developed in this work processes the potential in industrial robots, search-and-rescue missions, and space explorations.

Virtual reality (VR) technology has enormous applications in education, entertainment, and healthcare. Haptic feedback can significantly enhance the immersive experience in VR. However, most commercial hand/fingertip wearable VR haptic devices rely on bulky rigid structures, which are limited in the offered stimuli and cause fatigue. This study introduces a novel soft wearable fingertip device, T-Touch, that provides both thermal and multi-frequency haptic feedback for more realistic VR experiences. A flexible electrohydraulic actuator (EHA) is adopted for multi-frequency mechanical stimuli, and a flexible thermoelectric array (Flex-TEA) is utilized for distinct thermal stimuli. The EHA and Flex-TEA can be independently controlled to activate simultaneously or independently, thereby rendering ON/OFF contact stimuli, vibrations, controlled temperature stimuli, or any combination of the three modalities. Our T-Touch device features a compact form factor of 35 mm × 25 mm × 22 mm and weighs only ∼8 g. It can generate mechanical stimuli with the maximum stroke of ∼1 mm, a force of 0.47 N, at a bandwidth >10 Hz, and can render precise thermal stimuli in the range of 20 to 40 °C. The main performance of the EHA and Flex-TEA modules is characterized in extensive experiments and the effects of the key design and actuation parameters are investigated to optimise performance. Preliminary user tests verify the efficacy of our T-Touch design in immersive VR applications.

Pouch motors continue to attract research attention owing to their simple fabrication process, low cost, and excellent energy density. Existing pouch motors based on the liquid-gas phase transition (LGPT) principle exhibit significant stroke and force outputs but suffer from slow responses. Pouch motors that rely on the electrohydraulic actuation (EHA) demonstrate rapid responses and broad bandwidths, yet their stroke/force outputs remain limited. This paper presents a novel thermal-electrostatic dual-modal soft pouch motor (TES-SPM) that synergistically combines the advantages of LGPT and EHA. The output performance of the TES-SPM in both the LGPT and EHA modes is characterized by extensive experiments. The effects of key parameters including the liquid volumes and actuation voltage/current amplitudes are also investigated in experiments. In the EHA mode, the TES-SPM can exert a stroke of 2.5 mm within a rapid ~ 0.06 s, while in the LGPT mode, it is able to exhibit a maximum stroke of 22.8 mm and a blocking force of ~ 80 N. A novel folding fan-inspired actuator and accordion-inspired soft gripper based on the serially attached TES-SPM units are developed to demonstrate the potentials of soft robotic applications. The TES-SPM designed in this paper is envisioned to have promising applications in industrial soft grippers and wearable assistive devices.