Jun Shintake

Versatile Soft Grippers with Intrinsic Electroadhesion Based on Multifunctional Polymer Actuators

A highly versatile soft gripper that can handle an unprecedented range of object types is developed based on a new design of dielectric elastomer actuators employing an interdigitated electrode geometry, simultaneously maximizing both electroadhesion and electrostatic actuation while incorporating self-sensing. The multifunctionality of the actuator leads to a highly integrated, lightweight, fast, soft gripper with simplified structure and control.

Rollable Multisegment Dielectric Elastomer Minimum Energy Structures for a Deployable Microsatellite Gripper

Debris in space presents an ever-increasing problem for spacecraft in Earth orbit. As a step in the mitigation of this issue, the CleanSpace One (CSO) microsatellite has been proposed. Its mission is to perform active debris removal of a decommissioned nanosatellite (the CubeSat SwissCube). An important aspect of this project is the development of the gripper system that will entrap the capture target. We present the development of rollable dielectric elastomer minimum energy structures (DEMES) as the main component of CSOs deployable gripper. DEMES consist of a prestretched dielectric elastomer actuator membrane bonded to a flexible frame. The actuator finds equilibrium in bending when the prestretch is released and the bending angle can be changed by the application of a voltage bias. The inherent flexibility and lightweight nature of the DEMES enables the gripper to be stored in a rolled-up state prior to deployment. We fabricated proof-of-concept actuators of three different geometries using a robust and repeatable fabrication methodology. The resulting actuators were mechanically resilient to external deformation, and display conformability to objects of varying shapes and sizes. Actuator mass is less than 0.65 g and all the actuators presented survived the rolling-up and subsequent deployment process. Our devices demonstrate a maximum change of bending angle of more than 60° and a maximum gripping (reaction) force of 2.2 mN for a single actuator.

Variable stiffness actuator for soft robotics using dielectric elastomer and low-melting-point alloy

A novel variable stiffness actuator composed of a dielectric elastomer actuator (DEA) and a low-melting-point-alloy (LMPA) embedded silicone substrate is demonstrated. The device which we call variable stiffness dielectric elastomer actuator (VSDEA) enables functional soft robots with a simplified structure, where the DEA generates a bending actuation and the LMPA provides controllable stiffness between soft and rigid states by Joule heating. The entire structure of VSDEA is made of soft silicones with an elastic modulus of less than 1 MPa providing a high compliance when the LMPA is active. The device has the dimension of 40 mm length × 10 mm width × 1 mm thickness, with mass of ~1 g. We characterize VSDEA in terms of the actuation stroke angle, the blocked force, and the reaction force against a forced displacement. The results show the controllable actuation angle and the blocked force up to 23.7 ° and 2.4 mN in the soft state, and 0.6 ° and 2.1 mN in the rigid state. Compared to an actuator without the LMPA, VSDEA exhibits ~90× higher rigidity. We develop a VSDEA gripper where the mass of active parts is ~2 g, which is able to successfully hold an object mass of 11 g, exhibiting the high performance of the actuator.

Variable Stiffness Fiber with Self-Healing Capability

A variable stiffness fiber made of silicone and low melting point alloys quickly becomes >700 times softer and >400 times more deformable when heated above 62 °C. It shows remarkable self-healing properties and can be clamped, knitted, and bonded, as shown in a foldable multi-purpose drone, a wearable cast for bone injuries, and a soft multi-directional actuator.

A Foldable Antagonistic Actuator

We report on an actuator based on dielectric elastomers that is capable of antagonistic actuation and passive folding. This actuator enables foldability in robots with simple structures. Unlike other antagonistic dielectric elastomer devices, our concept uses elastic hinges to allow the folding of the structure, which also provides an additional design parameter. To validate the actuator concept through a specific application test, a foldable elevon actuator with outline size of 70 mm × 130 mm is developed with angular displacement range and torque specifications matched to a 400-mm wingspan micro-air vehicle (MAV) of mass 130 g. A closed-form analytical model of the actuator is constructed, which was used to guide the actuator design. The actuator consists of 125-μm-thick silicone membranes as the dielectric elastomers, 0.2mm-thick fiberglass plate as the frame structure, and 50-μm-thick polyimide as the elastic hinge. We measured voltage-controllable angular displacement up to ±26° and torque of 2720 mN · mm at 5 kV, with good agreement between the model and the measured data. Two elevon actuators are integrated into the MAV, which was successfully flown, with the foldable actuators providing stable and well-controlled flight. The controllability was quantitatively evaluated by calculating the correlation between the control signal and the MAV motion, with a correlation in roll axis of over 0.7 measured during the flights, illustrating the high performance of this foldable actuator.

Model and design of dielectric elastomer minimum energy structures

Fixing a prestretched dielectric elastomer actuator (DEA) on a flexible frame allows transformation of the intrinsic in-plane area expansion of DEAs into complex three-dimensional (3D) structures whose shape is determined by a configuration that minimizes the elastic energy of the actuator and the bending energy of the frame. These stuctures can then unfold upon the application of a voltage. This article presents an analytical modelling of the dielectric elastomer minimal energy structure in the case of a simple rectangular geometry and studies the influence of the main design parameters on the actuatorʼs behaviour. The initial shape of DEMES, as well as the actuation range, depends on the elastic strain energy stored in the elastomeric membrane. This energy depends on two independent parameters: the volume of the membrane and its initial deformation. There exist therefore different combinations of membrane volume and prestretch, which lead to the same initial shape, such as a highly prestretched thin membrane, or a slightly prestretched thick membrane. Although they have the same initial shape, these different membrane states lead to different behaviour once the actuation voltage is applied. Our model allows one to predict which choice of parameters leads to the largest actuation range, while specifying the impact of the different membrane conditions on the spring constant of the device. We also explore the effects of non-ideal material behaviour, such as stress relaxation, on device performance.

Soft Robotic Grippers

Advances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research.

Towards a deployable satellite gripper based on multisegment dielectric elastomer minimum energy structures

Dielectric Elastomer Actuators (DEAs) are an emerging actuation technology which are inherent lightweight and compliant in nature, enabling the development of unique and versatile devices, such as the Dielectric Elastomer Minimum Energy Structure (DEMES). We present the development of a multisegment DEMES actuator for use in a deployable microsatellite gripper. The satellite, called CleanSpace One, will demonstrate active debris removal (ADR) in space using a small cost effective system. The inherent flexibility and lightweight nature of the DEMES actuator enables space efficient storage (e.g. in a rolled configuration) of the gripper prior to deployment. Multisegment DEMES have multiple open sections and are an effective way of amplifying bending deformation. We present the evolution of our DEMES actuator design from initial concepts up until the final design, describing briefly the trade-offs associated with each method. We describe the optimization of our chosen design concept and characterize this design in terms on bending angle as a function of input voltage and gripping force. Prior to the characterization the actuator was stored and subsequently deployed from a rolled state, a capability made possible thanks to the fabrication methodology and materials used. A tip angle change of approximately 60° and a gripping force of 0.8 mN (for small deflections from the actuator tip) were achieved. The prototype actuators (approximately 10 cm in length) weigh a maximum of 0.65 g and are robust and mechanically resilient, demonstrating over 80,000 activation cycles.

Effect of mechanical parameters on dielectric elastomer minimum energy structures

Soft robotics may provide many advantages compared to traditional robotics approaches based on rigid materials, such as intrinsically safe physical human-robot interaction, efficient/stable locomotion, adaptive morphology, etc. The objective of this study is to develop a compliant structural actuator for soft a soft robot using dielectric elastomer minimum energy structures (DEMES). DEMES consist of a pre-stretched dielectric elastomer actuator (DEA) bonded to an initially planar flexible frame, which deforms into an out-of-plane shape which allows for large actuation stroke. Our initial goal is a one-dimensional bending actuator with 90 degree stroke. Along with frame shape, the actuation performance of DEMES depends on mechanical parameters such as thickness of the materials and pre-stretch of the elastomer membrane. We report here the characterization results on the effect of mechanical parameters on the actuator performance. The tested devices use a cm-size flexible-PCB (polyimide, 50 μm thickness) as the frame-material. For the DEA, PDMS (approximately 50 μm thickness) and carbon black mixed with silicone were used as membrane and electrode, respectively. The actuators were characterized by measuring the tip angle and the blocking force as functions of applied voltage. Different pre-stretch methods (uniaxial, biaxial and their ratio), and frame geometries (rectangular with different width, triangular and circular) were used. In order to compare actuators with different geometries, the same electrode area was used in all the devices. The results showed that the initial tip angle scales inversely with the frame width, the actuation stroke and the blocking force are inversely related (leading to an interesting design trade-off), using anisotropic pre-stretch increased the actuation stroke and the initial bending angle, and the circular frame shape exhibited the highest actuation performance.

Biomimetic underwater robots based on dielectric elastomer actuators

Dielectric elastomer actuators (DEAs), a soft actuator technology, hold great promise for biomimetic underwater robots. The high-voltages required to drive DEAs can however make them challenging to use in water. This paper demonstrates a method to create DEA-based biomimetic swimming robots that operate reliably even in conductive liquids. We ensure the insulation of the high-voltage DEA electrodes without degrading actuation performance by laminating silicone layers. A fish and a jellyfish were fabricated and tested in water. The fish robot has a length of 120 mm and a mass of 3.8 g. The jellyfish robot has a 61 mm diameter for a mass of 2.6 g. The measured swimming speeds for a periodic 3 kV drive voltage were ~8 mm/s for the fish robot, and ~1.5 mm/s for the jellyfish robot.