Low-resistance, high-force, and large-ROM fabric-based soft elbow exosuits with adaptive mechanism and composite bellows

Due to the lightweight and compliance, fabric-based pneumatic exosuits are promising in the assistance and rehabilitation of elbow impairments. However, existing elbow exosuits generally suffer from remarkable mechanical resistance on the flexion of the elbow, thus limiting the output force, range of motion(ROM), and comfortability. To address these challenges, we develop a fabric-based soft elbow exosuit with an adaptive mechanism and composite bellows in this work. With the elbow kinesiology considered, the adaptive mechanism is fabricated by sewing the interface of the exosuit into spring-like triangle pleats, following the profile of the elbow to elongate or contract when the elbow flexes or extends. The composite bellows are implemented by further sealing a single blade of bellows into two branches to enhance the output force. Based on these structural features, we characterize the mechanical performance of different soft elbow exosuits: exosuit with normal bellows-NB, exosuit with adaptive mechanism and normal bellows-AMNB, exosuit with adaptive mechanism and composite bellows-AMCB. Experimental results demonstrate that by comparing with NB, the mechanical resistance of AMNB and AMCB decreases by 80.6% and 78.6%, respectively;on the other hand, the output torque of AMNB and AMCB increases to 120.3% and 207.0%, respectively, at50 k Pa when the joint angle is 120°. By wearing these exosuits on a wooden arm model(1.25 kg), we further verify that AMCB can cover a full ROM of 0°–130° at the elbow with 500 g weight. Finally, the application on a health volunteer with AMCB shows that when the volunteer flexes the elbow to lift a weight of 500 g, the s EMG activity of the biceps and triceps is markedly reduced.

Confined spaces path following for cable-driven snake robots with prediction lookup and interpolation algorithms

While cable-driven snake robots are promising in exploring confined spaces, their hyper-redundancy makes the collision-free motion planning difficult. In this paper, by combining the prediction lookup and interpolation algorithms, we present a new path following method for cable-driven snake robots to high-efficiently slither into complex terrains along a desired path. In our method, we first discretize the desired path into points, and develop the prediction lookup algorithm to efficiently find the points matched with joints of the robot. According to geometric relations between the prediction lookup results and link length of the robot, we develop the interpolation algorithm to reduce the tracking errors caused by the discretization. Finally, simulations and experiments of inspections in two confined spaces including the obstacle array and pipe tank system are performed on our custom-built 25 degree of freedoms(DOFs) cable-driven snake robot. The results demonstrate that the presented method can successfully navigate our snake robot into confined spaces with high computational efficiency and good accuracy, which well verifies effectiveness of our development.

Synergistic control of soft robotic hands for human-like grasp postures

Although significant advances in the design of soft robotic hands have been made to mimic the structure of the human hands,there are great challenges to control them for coordinated and human-like postures.Based on the principle of postural synergies in the human hand,we present a synergistic approach for coordinated control of a soft robotic hand to replicate the human-like grasp postures.To this end,we firstly develop a kinematic model to describe the control variables and the various postures of the soft robotic hand.Based on the postural synergies,we use the developed model and Principal Component Analysis(PCA)method to describe the various postures of the soft robotic hand in a low-dimensional space formed by the synergies of actuator motions.Therefore,the coordinates of these synergies can be used as low-dimensional control inputs for the soft robotic hand with a higher-dimensional postural space.Finally,we establish an experimental platform on a customized soft robotic hand with6 pneumatical actuators to verify the effectiveness of the development.Experimental results demonstrate that with only a 2-dimensional control input,the soft robotic hand can reliably replicate 30 grasp postures in the Feix taxonomy of the human hand.

Performance characterization of ionic-hydrogel based strain sensors

Ionic hydrogels,owing to the advantages of stretchability,conductivity and transparency,have attracted more attention for developing new soft sensors and artificial skins.Existing works on ionic-hydrogel based sensors mostly focus on material synthesis,structure design and functional integration,while few studies investigate the characterization of their sensing performances.In this paper,we present a method to characterize the performance(e.g.,sensitivity,linearity and repeatability)of a kind of ionic-hydrogel based strain sensors by varying the testing frequencies and the sensors’geometry(e.g.,length-width(L/W)ratio).To this end,we first develop an experimental testing platform and fabricate a series of strain sensors made of the polyacrylamide(PAAm)hydrogel containing ionic conductive medium.We establish an equivalent electrical model to represent the ionic-hydrogel based strain sensors,indicating the influence of the testing frequencies and L/W ratio of the ionic hydrogels on their sensing performances.These theoretical predictions are in agreement with results obtained through experimental measurements.We further demonstrate that(1)the sensitivity of the strain sensors,characterized by the gauge factor(GF),increases with the rise of testing frequencies but tends to be stable over the frequency of 5 kHz;(2)the sensitivity GF has a nonlinear relation with the L/W ratio of the strain sensors,but with a certain maximum value under the same testing frequency when the L/W ratio equals to 4.80.We verify the above experimental observations with two commonly used electrolytes,including lithium chloride and sodium chloride.With the optimum testing frequency and L/W ratio,we finally conduct various experiments to demonstrate the low hysteresis and good repeatability of our ionic-hydrogel based strain sensors.This work provides an approach to characterize the performance of the ionic-hydrogel based strain sensors,which may be an important step forward in further applications of ionic hydrogels in soft robotics.

Soft ionic-hydrogel electrodes for electroencephalography signal recording

Wet gel electrodes have been widely used for electroencephalography(EEG) signal recording, which generally causes skin abrasion and longer preparation time. In this paper, we present soft ionic-hydrogel based electrodes to overcome such drawbacks.In order to conveniently measure the EEG signals, we design the claw-like and patch-like structures for robust connection between metal(Ag/Ag Cl) electrodes and skin scalps. Next, we experimentally show that the soft ionic-hydrogel based electrodes have similar performance with the conventional wet gel electrodes in terms of the short-circuit noise, electrical impedance, and skin-electrode contact impedance on unprepared human skin, significantly better than dry electrodes and water-based electrodes.We further perform the EEG measurements and steady-state visual evoked potentials(SSVEP) experiments with five subjects to verify the effectiveness of the soft ionic-hydrogel based electrodes. The experimental results demonstrate that our developed soft ionic-hydrogel electrodes can record high-quality EEG signals in a fast and clean way, being a compelling option for EEG-based brain-computer interfaces.

Operational-space wrench and acceleration capability analysis for multi-link cable-driven robots

Multi-link cable-driven robots(MCDRs)have potential advantages in confined spaces exploration because of their redundancy and flexibility.Operational space wrench and acceleration capability analysis of MCDRs is important for their design,manipulability optimization,and motion planning.However,existing works mainly focus on capability analysis in the joint space.In this paper,we present a zonotope-based iterative method and a simplified capability zonotope to analyze the operational-space wrench and acceleration capability of MCDRs.In the iterative method,the capability generated by some cables can be iteratively added to the initial capability zonotope based on the Minkowski sum.In the simplified zonotope capability representation,a threshold is put forward to reduce redundant vertices and faces with little volume loss.Finally,simulations on a 24 DOFs MCDR are performed to verify the effectiveness of the developed method.The results demonstrate that our iterative algorithm can easily generate the capability zonotope with a few MB ROM,while traditional operational wrench capability evaluation without our iterative algorithm needs 18432 GB ROM.Furthermore,our simplified representation reduces the vertices and faces from 1260 and 2516 to 88 and 172,respectively,but with only 3.3%volume loss,which decreases the constraints of the robot and is conducive to manipulability optimization and motion planning.