A soft crawling robot with a modular design based on electrohydraulic actuator.

The soft structure of creatures without a rigid internal skeleton can easily adapt to any atypical environment. In the same context, robots with soft structures can change their shape to adapt to complex and varied surroundings. In this study, we introduce a caterpillar-inspired soft crawling robot with a fully soft body. The proposed crawling robot consists of soft modules based on an electrohydraulic actuator, a body frame, and contact pads. The modular robotic design produces deformations similar to the peristaltic crawling behavior of caterpillars. In this approach, the deformable body replicates the mechanism of the anchor movement of a caterpillar by sequentially varying the friction between the robot contact pads and the ground. The robot carries out forward movement by repeating the operation pattern. The robot has also been demonstrated to traverse slopes and narrow crevices.

Solvation-Driven Electrochemical Actuation.

We demonstrate a novel principle of contactless actuation for ionic membranes in salt solution based on solvation. Actuation is driven by differential swelling of the sides of the membrane, due to comigrating water in the solvation shells of mobile ions. We validate our theory through a series of experiments, which unravel a strong dependence of membrane deflection on the hydration numbers of mobile ions in the external solution and membrane. Our study suggests a critical role of solvation in the chemoelectromechanics of natural and artificial selectively permeable membranes.

Multidirectional Cylindrical Piezoelectric Force Sensor: Design and Experimental Validation.

A common design concept of the piezoelectric force sensor, which is to assemble a bump structure from a flat or fine columnar piezoelectric structure or to use a specific type of electrode, is quite limited. In this paper, we propose a new design of cylindrical piezoelectric sensors that can detect multidirectional forces. The proposed sensor consists of four row and four column sensors. The design of the sensor was investigated by the finite element method. The response of the sensor to various force directions was observed, and it was demonstrated that the direction of the force applied to the sensor could be derived from the signals of one row sensor and three column sensors. As a result, this sensor proved to be able to detect forces in the area of 225° about the central axis of the sensor. In addition, a cylindrical sensor was fabricated to verify the proposed sensor and a series of experiments were performed. The simulation and experimental results were compared, and the actual sensor response tended to be similar to the simulation.

Thermal display glove for interacting with virtual reality.

Thermal perception is essential for the survival and daily activities of people. Thus, it is desirable to realize thermal feedback stimulation for improving the sense of realism in virtual reality (VR) for users. For thermal stimulus, conventional systems utilize liquid circulation with bulky external sources or thermoelectric devices (TEDs) on rigid structures. However, these systems are difficult to apply to compact wearable gear used for complex hand motions to interact with VR. Furthermore, generating a rapid temperature difference, especially cooling, in response to a thermal stimulus in real-time is challenging for the conventional systems. To overcome this challenge and enhance wearability, we developed an untethered real-time thermal display glove. This glove comprised piezoelectric sensors enabling hand motion sensing and flexible TEDs for bidirectional thermal stimulus on skin. The customized flexible TEDs can decrease the temperature by 10 °C at room temperature in less than 0.5 s. Moreover, they have sufficiently high durability to withstand over 5,000 bends and high flexibility under a bending radius of 20 mm. In a user test with 20 subjects, the correlation between thermal perception and the displayed object's color was verified, and a survey result showed that the thermal display glove provided realistic and immersive experiences to users when interacting with VR.

Soft Pneumatic Gripper With a Tendon-Driven Soft Origami Pump.

In this study, we propose a soft pneumatic gripper that uses a tendon-driven soft origami pump. The gripper consists of three pneumatic soft actuators that are controlled by a tendon-driven origami pump. An external air compressor that supplies air to the pneumatic actuator is replaced by an origami pump. The soft actuator is composed of silicone (Ecoflex 00-30) with a chamber-based structure, which is fabricated using a mold, and the origami pump is fabricated by folding a Kresling patterned polypropylene film. In addition, we conduct a series of experiments to evaluate the performance of the pneumatic actuator with a tendon-driven origami pump. Specifically, movement characteristics, frequency response, blocking force, and the relation between bending angle and pressure are analyzed from the results of the experiments. Furthermore, we understand the entire operation mechanism from the deformation of the origami pump to bending through pressure. Finally, we demonstrate the grasping of objects with diverse shapes and materials, and indicate the feasibility of the pneumatic gripper as an independent module without an external compressor.

Hemispherical Cell-Inspired Soft Actuator.

As soft robots have been popular, interest in soft actuators is also increasing. In particular, new types of actuators have been proposed through biomimetics. An actuator that we proposed in this study was inspired by a motor cell that enables plants to move. This actuator is an electrostatic actuator utilizing electrostatic attraction and elastic force, and can be used repeatedly. In addition, this actuator, which can produce large and diverse movements by collecting individual movements like a cell, has a wide application field. As one of them, this actuator is stacked to construct a layer structure and propose an application example. In addition, a piezo sensor was built inside the actuator and real-time motion monitoring was attempted. As a result, the point laser sensor value and the piezo sensor value coincided with each other, which means that it is possible to detect motion in real-time with the built-in sensor.

Electrohydraulic Actuator for a Soft Gripper.

There is a considerable demand to develop robots that can perform sophisticated tasks such as grabbing delicate materials, passing through narrow pathways, and acting as mediators between humans and robots. Soft robots can provide a solution for such applications. In this study, we propose an electrohydraulic gripper, which is based on electrostatic and hydraulic forces. Interestingly, the gripper generates a hydraulic force without an external fluid supply source. In addition, it achieves good compliance, because the gripper is composed of soft materials such as polyethylene film and silicone. We experimentally investigate the characteristics of the actuator of the gripper. In addition, the electrohydraulic gripper demonstrates an ability to grasp delicate materials.

Soft mobile robot inspired by animal-like running motion.

There is a considerable demand for legged robots with exploring capabilities such as passing through narrow pathways. Soft robots can provide a solution for such applications. Here, we propose a soft legged mobile robot with bimorph piezoelectric main body and pre-curved piezoelectric legs. We experimentally demonstrate the performance of the soft mobile robot. The mobile robot can move 70% of the body length per second. In addition, we investigate physical mechanisms behind the locomotion of the mobile robot using a numerical simulation. Interestingly, the mobile robot generates an animal-like running motion. We find that the amplitude difference of the legs, depending on the leg activation condition, may affect the performance of the robot. We also confirm that the soft mobile robot can maintain the movement under impulsive shock owing to its flexibility.

Contactless actuation of perfluorinated ionomer membranes in salt solution: an experimental investigation.

A variety of modeling frameworks have been proposed for ionic polymer metal composites (IPMCs), but the physical underpinnings of their actuation remain elusive. A critical step toward the validation of existing theories and transition to engineering practice entails the design of new experimental paradigms that could support hypothesis-driven research. While several factors exacerbate the complexity of experimenting with IPMCs, the presence of the electrodes plays a major role by hindering the repeatability of the results and bringing a number of difficult-to-measure parameters into the picture. Here, we seek to address these experimental confounds by investigating contactless actuation of perfluorinated ionomer membranes in salt solution. In contrast to IPMCs that bend toward the anode in response to an applied voltage, ionomer membranes display a consistent deflection toward the cathode. Through hypothesis-driven experiments where the membrane width, solution concentration, and voltage applied across the electrodes are systematically varied, we elucidate electrochemistry and mechanics of contactless actuation. The applied voltage and solution concentration have a dominant role on the electrochemistry, while mechanics is mainly affected by the applied voltage and membrane width. Our results depict a complex scenario, which is expected to inform future theoretical inquiries about IPMC actuation.

Pneumatic actuator and flexible piezoelectric sensor for soft virtual reality glove system.

The desire to directly touch and experience virtual objects led to the development of a tactile feedback device. In this paper, a novel soft pneumatic actuator for providing tactile feedback is proposed and demonstrated. The suggested pneumatic actuator does not use an external air compressor but it is operated by internal air pressure generated by an electrostatic force. By using the actuator, we designed a glove to interact with virtual reality. The finger motions are detected by attached flexible piezoelectric sensors and transmitted to a virtual space through Bluetooth for interconnecting with a virtual hand. When the virtual finger touches the virtual object, the actuators are activated and give the tactile feedback to the real fingertip. The glove is made of silicone rubber material and integrated with the sensors and actuators such that users can wear them conveniently with light weight. This device was tested in a virtual chess board program, wherein the user picked up virtual chess pieces successfully.

Fe3O4⁻Silicone Mixture as Flexible Actuator.

In this study, we introduce Fe3O4-silicone flexible composite actuators fabricated by combining silicone and iron oxide particles. The actuators exploit the flexibility of silicone and the electric conductivity of iron oxide particles. These actuators are activated by electrostatic force using the properties of the metal particles. Herein, we investigate the characteristic changes in actuation performance by increasing the concentration of iron oxide from 1% to 20%. The developed flexible actuators exhibit a resonant frequency near 3 Hz and their actuation amplitudes increase with increasing input voltage. We found that the actuator can move well at metal particle concentrations >2.5%. We also studied the changes in actuation behavior, depending on the portion of the Fe3O4-silicone in the length. Overall, we experimentally analyzed the characteristics of the newly proposed metal particle-silicone composite actuators.

Flexible Piezoelectric Sensor-Based Gait Recognition.

Most motion recognition research has required tight-fitting suits for precise sensing. However, tight-suit systems have difficulty adapting to real applications, because people normally wear loose clothes. In this paper, we propose a gait recognition system with flexible piezoelectric sensors in loose clothing. The gait recognition system does not directly sense lower-body angles. It does, however, detect the transition between standing and walking. Specifically, we use the signals from the flexible sensors attached to the knee and hip parts on loose pants. We detect the periodic motion component using the discrete time Fourier series from the signal during walking. We adapt the gait detection method to a real-time patient motion and posture monitoring system. In the monitoring system, the gait recognition operates well. Finally, we test the gait recognition system with 10 subjects, for which the proposed system successfully detects walking with a success rate over 93 %.

Patient Posture Monitoring System Based on Flexible Sensors.

Monitoring patients using vision cameras can cause privacy intrusion problems. In this paper, we propose a patient position monitoring system based on a patient cloth with unobtrusive sensors. We use flexible sensors based on polyvinylidene fluoride, which is a flexible piezoelectric material. Theflexiblesensorsareinsertedintopartsclosetothekneeandhipoftheloosepatientcloth. We measure electrical signals from the sensors caused by the piezoelectric effect when the knee and hip in the cloth are bent. The measured sensor outputs are transferred to a computer via Bluetooth. We use a custom-made program to detect the position of the patient through a rule-based algorithm and the sensor outputs. The detectable postures are based on six human motions in and around a bed. The proposed system can detect the patient positions with a success rate over 88 percent for three patients.

Flexible Piezoelectric Energy Harvesting from Mouse Click Motions.

In this paper, we study energy harvesting from the mouse click motions of a robot finger and a human index finger using a piezoelectric material. The feasibility of energy harvesting from mouse click motions is experimentally and theoretically assessed. The fingers wear a glove with a pocket for including the piezoelectric material. We model the energy harvesting system through the inverse kinematic framework of parallel joints in a finger and the electromechanical coupling equations of the piezoelectric material. The model is validated through energy harvesting experiments in the robot and human fingers with the systematically varying load resistance. We find that energy harvesting is maximized at the matched load resistance to the impedance of the piezoelectric material, and the harvested energy level is tens of nJ.

Energy harvesting from the tail beating of a carangiform swimmer using ionic polymer-metal composites.

In this paper, we study energy harvesting from the beating of a biomimetic fish tail using ionic polymer-metal composites. The design of the biomimetic tail is based on carangiform swimmers and is specifically inspired by the morphology of the heterocercal tail of thresher sharks. The tail is constituted of a soft silicone matrix molded in the form of the heterocercal tail and reinforced by a steel beam of rectangular cross section. We propose a modeling framework for the underwater vibration of the biomimetic tail, wherein the tail is assimilated to a cantilever beam with rectangular cross section and heterogeneous physical properties. We focus on base excitation in the form of a superimposed rotation about a fixed axis and we consider the regime of moderately large-amplitude vibrations. In this context, the effect of the encompassing fluid is described through a hydrodynamic function, which accounts for inertial, viscous and convective phenomena. The model is validated through experiments in which the base excitation is systematically varied and the motion of selected points on the biomimetic tail tracked in time. The feasibility of harvesting energy from an ionic polymer-metal composite attached to the vibrating structure is experimentally and theoretically assessed. The response of the transducer is described using a black-box model, where the voltage output is controlled by the rate of change of the mean curvature. Experiments are performed to elucidate the impact of the shunting resistance, the frequency of the base excitation and the placement of the ionic polymer-metal composite on energy harvesting from the considered biomimetic tail.

Bias-dependent model of the electrical impedance of ionic polymer-metal composites.

In this paper, we analyze the charge dynamics of ionic polymer-metal composites (IPMCs) in response to voltage inputs composed of a large dc bias and a small superimposed time-varying voltage. The IPMC chemoelectrical behavior is described through the modified Poisson-Nernst-Planck framework, in which steric effects are taken into consideration. The physics of charge build-up and mass transfer in the proximity of the high surface electrodes is modeled by schematizing the IPMC as the stacked sequence of five layers, in which the ionomeric membrane is separated from the metal electrodes by two composite layers. The method of matched asymptotic expansions is used to derive a semianalytical solution for the concentration of mobile counterions and the electric potential in the IPMC, which is, in turn, used to establish an equivalent circuit model for the IPMC electrical response. The circuit model consists of the series connection of a resistor and two complex elements, each constituted by the parallel connection of a capacitor and a Warburg impedance. The resistor is associated with ion transport in the ionomeric membrane and is independent of the dc bias. The capacitors and the Warburg impedance idealize charge build-up and mass transfer in the vicinity of the electrodes and their value is controlled by the dc bias. The proposed approach is validated against experimental results on in-house fabricated IPMCs and the accuracy of the equivalent circuit is assessed through comparison with finite element results.

Electrical impedance controls mechanical sensing in ionic polymer metal composites.

Ionic polymer metal composites (IPMCs) are a class of soft electroactive materials that are recently finding extensive application as mechanical sensors and energy harvesters in liquids. In their most fundamental form, IPMCs are composed of a hydrated ionomeric membrane that is sandwiched between two electrochemically deposited metal electrodes. Ionomer swelling, counterion diffusion, and the formation of electric double layers are some of the physical phenomena underpinning energy transduction in IPMCs; however, a thorough understanding of the relative influence of such phenomena is yet to be established. Here, we propose a physics-based modeling framework, based on the Poisson-Nernst-Planck system, to describe IPMC chemoelectrical response to an imposed time-varying flexural deformation. We utilize the method of matched asymptotic expansions to compute a closed-form solution for the electric potential and counterion concentration in the IPMC. The model predicts that IPMC sensing is independent of the time rate of deformation and linearly correlated to the mechanical curvature, with a coefficient of proportionality that is a function of the ionomer thickness and the temperature. Thus, our results demonstrate that the characterization of IPMC electrical impedance suffices to identify all the parameters that are relevant to sensing, in contrast with the current state of knowledge. Theoretical results are validated through experiments on patterned in-house fabricated IPMC samples that are subject to time-varying flexural deformations.