Keywords: Computer Vision for Other Robotic Applications, Compliant Joint/Mechanism, Biologically-Inspired Robots
Abstract: The ability to sense compliant interactions through internal state measurements improves adaptability and robustness of robotic grasping and manipulation, without interfering with any carefully designed passive dynamics. This work presents a collocated sensing and actuation system using a compliant tendon driven hand and its accompanying model. Using a simple vision-based measurement device the approach is able to estimate its internal state and applied external forces. The camera-based sensor uses off-the-shelf components and has the ability to measure many more than 15 tendons simultaneously, giving a low-cost, scale-able, high-bandwidth sensing solution. The collocated configuration provides a framework for developing stable feedback controllers. Our results show that the system can estimate change in posture with <10% error with the potential to estimate contact forces using the same scheme.

Keywords: Biologically-Inspired Robots, Biomimetics, Soft Robot Materials and Design
Abstract: Exploration robots are challenged by a continuous adaptation to the terrain induced by ever changing environments. These adaptations can be subtle (e.g. when moving from a smooth to a rough terrain), however drastic changes in environment require robots to address different locomotion modes (e.g. crawling vs swimming). While each locomotion mode can be driven by a dedicated set of actuators, nature shows that multimodal locomotion is also possible by activating the same set of actuators in different sequences (e.g. swimming snakes). In this paper, we present EELWORM, a 40 cm long soft-bodied robot consisting out of an arrangement of five inflatable bending and elongating actuator modules that can be addressed individually. EELWORM is capable of both crawling and swimming by varying the actuation sequences within the same embodiment. We show multimodal locomotion at speeds of 2 body lengths per minute (crawling) and 3 body lengths per minute (swimming).

Keywords: Biologically-Inspired Robots, Compliant Joint/Mechanism, Tendon/Wire Mechanism
Abstract: Biological fish differ widely in anatomical structure (body stiffness, fin, body length, etc.) and swimming gait, and it is known that their physical characteristics have a close correlation to their locomotion capabilities. By systematically studying these correlations between the soft body structures of a fish-vertebrate-mimicking swimming robot and its swimming efficiency, we can elucidate the relationships between form and function and provide guidance on the design of novel non-biomorphic swimming robots capable of performing complex underwater maneuvers. In this work, we design a soft modular swimming robot platform to systematically explore the relationship between body structure, swimming gaits, and locomotion performance. The proposed one degree of freedom (DOF) swimming robot platform includes an underactuated, cable-driven design that mimics the cascaded skeletal structure of soft spine tissue and hard spine bone seen in many fish species. The cable-driven actuation mechanism is oriented laterally for forward or backward motion and steering in a 2D plane. The modular platform design allows for easy modification of morphological parameters such as fin configuration, soft joint stiffness distribution, and body length, to vary the robot's swimming mode. During experiments, we varied the swimming robot design and actuation parameters over multiple trials and observed the emergent locomotion behaviors in a controlled, underwater testbed. Results showed that the swimming robot is able to achieve biomorphic swimming modes which change from oscillatory (2.3 cm/s) to undulatory (11.0 cm/s) by simply tuning motor oscillation frequency. In addition, unnatural, non-biomorphic swimming behaviors, such as the ability to change the swimming direction from forward to backward at different actuation frequencies, were also observed for certain joint stiffness and fin configurations.

Keywords: Soft Sensors and Actuators, Grasping, Soft Robot Materials and Design
Abstract: Soft and adaptable grippers are desired for their ability to operate effectively in unstructured or dynamically changing environments, especially when interacting with delicate or deformable targets. However, utilizing soft bodies often comes at the expense of reduced carrying payload and limited performance in high-force applications. Hence, methods for achieving variable stiffness soft actuators are being investigated to broaden the applications of soft grippers. This paper investigates the structural optimization of adaptive soft fingers based on the Fin Ray® effect (Soft Fin Ray), featuring a passive stiffening mechanism that is enabled via layer jamming between deforming flexible ribs. A finite element model of the proposed Soft Fin Ray structure is developed and experimentally validated, with the aim of enhancing the layer jamming behavior for better grasping performance. The results showed that through structural optimization, initial contact forces before jamming can be minimized and final contact forces after jamming can be significantly enhanced, without downgrading the desired passive adaptation to objects. Thus, applications for Soft Fin Ray fingers can range from adaptive delicate grasping to high-force manipulation tasks.

Keywords: Soft Robot Applications, Wearable Robots, Tendon/Wire Mechanism
Abstract: The scope of this work is to show the applicability of the Twisted String Actuators (TSAs) for lightweight, wear- able and assistive robotic applications. To this aim, we have developed a novel surface electromyography (sEMG)-driven soft ExoSuit using the TSAs to perform both single and dual- arm elbow assistive applications. The proposed ExoSuit, with an overall weight of 1650g, uses a pair of TSAs mounted in the back of the user, connected via tendons to the user’s forearms to actuate each arm independently for supporting external loads. We confirm this new light-weight and customizable wearable solution via multiple user studies based on the biceps and tricep’ sEMG measurements. We demonstrate that user muscles can automatically activate and regulate the TSAs and compensate for the user’s effort: by using our controller based on a Double Threshold Strategy (DTS) with a standard PID regulator, we report that the system was able to limit the biceps’ sEMG activity under an arbitrary target threshold, compensating a muscular activity equal to 220% (related to a single arm 3kg load) and 110% (related to a dual arm 4kg load) of the threshold value itself. Moreover, the triceps’ sEMG signal detects the external load and, depending on the threshold, returns the system to the initial state where it requires no assistance from the ExoSuit. The experimental results show the proposed ExoSuit’s capabilities in both single and dual- arm load compensation tasks. Therefore, the applicability of the TSAs is experimentally demonstrated for a real-case assistive device, fostering future studies and developments of this kind of actuation strategy for wearable robotic systems.

Keywords: Soft Robot Applications, Rehabilitation Robotics, Wearable Robots
Abstract: Intense therapy is a key factor to improve rehabilitation outcomes. However, when performing rehabilitative stretching with the upper limb of stroke survivors, therapist fatigue is often the limiting factor for the number of repetitions per session. In this paper we present an inflatable soft wearable robot aimed at improving severe stroke rehabilitation by reducing therapist fatigue during upper extremity stretching. The device consists of a textile-based inflatable actuator anchored to the torso and arm via functional apparel. Upon inflation, the device created a moment of force about the glenohumeral joint to counteract effects of gravity and assist in elevating the arm. During a device-assisted (i.e. inflated) standard stretching protocol with a therapist, we showed increased range of motion across five stroke survivors, and reduced muscular activity and cardiac effort by the therapist, when comparing to a vented device condition. Our results demonstrate the potential for this technology to assist a therapist during upper extremity rehabilitation exercises and future studies will explore its impact on increasing dose and intensity of therapy delivered in a given session, with the goal of improving rehabilitation outcomes.

Keywords: Wearable Robots, Rehabilitation Robotics, Soft Robot Applications
Abstract: This paper presents the design of a soft robotic ankle-foot orthosis (SR-AFO) exosuit to aid in plantarflexion for gait rehabilitation in individuals who suffer from irregular gaits due to stroke or other injuries. The SR-AFO exosuit is a sock-like garment fabricated from compliant fabrics. The SR-AFO exosuit aids in late stance of the walking gait in plantarflexion by contracting the actuator to pull the posterior end of the foot upward. This helps to reduce the muscle effort of the user during plantarflexion. The addition of a second actuator shows a 45.3% increase to 13.51+/-0.31 kg payload capacity. The actuators are oriented at an optimal angle of 5degrees to produce the highest pulling force. Three healthy participants are evaluated during walking trials with and without SR-AFO exosuit assistance while ankle angle and muscle activity are monitored. The gastrocnemius (GA) and soleus (SOL) muscle activity during late stance is reduced by 13.4% and 16.6% respectively. Tibialis anterior (TA) increases slightly during swing most likely due to the hysteresis in the system deflating during that window. The ankle range of motion remains within natural walking limitations and plantarflexion angle increases when the SR-AFO exosuit is active.

Keywords: Soft Sensors and Actuators, Soft Robot Materials and Design, Wearable Robots
Abstract: The application of pneumatic soft robots is limited by factors such as operational pressure and air flow rates. Pneumatic soft robots are typically tethered in nature due to the high energy costs for actuation as well as the lack of portable pneumatic sources capable of providing high pressures and air flow rates. This work presents a low-volume inflatable actuator composite (IAC) designed to reduce energy costs of actuation and a portable pneumatic source to overcome the aforementioned issues towards untethered applications. The pressure-deflection characteristics of the fabricated IAC are compared with those of a completely fabric-based beam using experimental results and finite element analysis. FEM models of IACs with varying volumes are generated and actuation speeds are measured using a pressure step response test. The force output and hysteresis of the actuator are studied. The developed portable pneumatic source is capable of generating a pressure and flow rates of 0.131 MPa and 21.45 standard litres per minute (SLPM), respectively. The IACs and portable pneumatic source are integrated with a soft exosuit to assist knee extension, and the integrated system is evaluated with three healthy participants for incline walking. A reduction of muscle activities in the Vastus Lateralis muscle group is observed for all the three participants when the exosuit is active.

Keywords: Modeling, Control, and Learning for Soft Robots, Soft Sensors and Actuators, Soft Robot Applications
Abstract: Exploring complex, unstructured environments requires a large set of information acquired by several sensors. Besides, a high level control is necessary to transfer and elaborate the whole data. Taking inspiration from plants, we aim at developing a system that is able to explore its surrounding environment paying a very low cost in terms of computation and data processing. Here, we demonstrate how a soft manipulator can identify the presence of an obstacle, or of a supporting structure, by means of a single sensor used together with a simplified mathematical model. The model can compute the configuration of the system only if no other forces other than the actuation are applied to it, while the sensor readings alone are not sufficient to infer the configuration. Exploiting the limitation of the model, an occurring mismatch between the expected position (computed by the model) and the measured one (by the sensor) provide sufficient information to identify the contact with a possible supporting structure. We validated the proposed methods in different scenarios in which we considered free motion without any obstacles, and in the presence of possible supports and impassable structures. To avoid false detection, we also considered the frequency of the discrepancy. In all the test cases the result is promising and this can pave the way toward a simplified approach for plant-inspired, non-vision-based navigation for soft devices.

Keywords: Soft Sensors and Actuators, Haptics and Haptic Interfaces, Soft Robot Materials and Design
Abstract: We present a lightweight, low power, and compliant miniature dielectric fluid transducer intended for haptic surface display. The actuator has large strain and fast response without an external compressor. It consists of a thin oil-filled pouch with a 1.5 mm diameter opening covered with a silicone membrane. The application of voltage causes the pouch to squeeze the oil and form a bump by stretching the silicone membrane. The actuator produces 1.45 mm bump height at 3 kV and 13 mN at 3.5 kV using ≈10 μl of oil. The power consumption is <3 mW. Though the largest bump height has a bandwidth near 5 Hz, the device achieves perceivable vibration at 200 Hz with a bump height of 200 μm. The actuators can be packed closely and controlled individually to create dynamic texture displays, suitable for active surface exploration with the fingertips. The simulation results show the width of the actuator can be reduced without affecting the performance. Tests with human subjects show that users differentiated simple bump patterns with a 98.8% success rate.

Keywords: Soft Robot Applications, Grippers and Other End-Effectors, Soft Robot Materials and Design
Abstract: Anchoring is an important capability for mobile robots to conserve power, survey an area, or deploy a payload. However, the careful placement of an anchor in unstructured environments requires a great deal of dexterity, perception, and planning. Furthermore, many of the reversible adhesives that may be used for anchoring are surface-dependent. We introduce inflatable pouch anchors as a versatile, low-power, and easy-to-position technology for anchoring in natural surfaces. By using negative space such as gaps and cracks with a flexible pouch, the challenge of placing an anchor is greatly simplified. We used a compressed CO-2 canister to supply pressure, and a three-way normally-closed valve to allow for multiple uses. We tested the anchor with high friction interfaces such as microspines and gecko-inspired adhesives. We validated the performance with tests on smooth acrylic, sandpaper, manufactured rock, and natural rock. The 425 g anchor actuated at an internal pressure of 105 kPa held over 700 N when anchored in natural rock with a microspine interface.

Keywords: Soft Robot Applications, Soft Sensors and Actuators, Soft Robot Materials and Design
Abstract: One of the key challenges in soft robotics is the development of actuators which are truly soft and compliant, and can be adapted and tailored for different applications. In particular, the development of untethered soft actuators could enable robots to autonomously explore the world in an unrestricted manner, exploiting their compliant behaviour. In this paper we present a method for creating fully soft, degradable actuators where the actuation of the system is controlled by setting physical parameters which `mechanically program' the actuator determining the characteristics of the actuator. The actuation process is driven by the release of gas from a reaction between a bio-compatible acid and base. This approach allows for the creation of fully untethered actuators which could be deployed for use in agriculture, to make ingestible robots or to allow untethered exploration. This paper provides the `recipes' for the development of the actuators used, and the methods for mechanically programming of the actuators.

Keywords: Soft Robot Materials and Design, Soft Sensors and Actuators, Soft Robot Applications
Abstract: Soft robots require strong, yet flexible actuators for locomotion and manipulation tasks in unstructured environments. Dielectric elastomer actuators (DEAs) are well suited for these challenges in soft robotics because they operate as compliant capacitors and directly convert electrical energy into mechanical work, thereby allowing for simple design integration at a minimal footprint. In most demonstrations, DEA-based robots are limited to a single mode of locomotion, for example crawling, swimming, or jumping. In this work, we explored a range of actuation patterns in combination with a novel actuator design to enable multi-modal locomotion, whereby an actuation pattern is defined by an actuation voltage (proportional to the applied electric field) and frequency (the actuation rate). We present a DEA robot capable of three different gaits including crawling, hopping, and jumping. In addition, our robot can set itself upright by performing a roll, for example to prepare for the next jump after landing on its side. These results demonstrate that DEAs can be used as versatile experimental devices to validate locomotion models, in both natural and engineered systems.

Keywords: Soft Robot Materials and Design, Soft Robot Applications
Abstract: Soft robots employ flexible and compliant materials to perform adaptive tasks and navigate uncertain environments. However, soft robots are often unable to achieve forces and precision on the order of rigid-bodied robots. In this paper, we propose a new class of mobile soft robots that can reversibly transition between compliant and stiff states without reconfiguration. The robot can passively conform or actively control its shape, stiffen in its current configuration to function as a rigid-bodied robot, then return to its flexible form. The robotic structure consists of passive granular material surrounded by an active membrane. The membrane is composed of interconnected robotic sub-units that can control the packing density of the granular material and exploit jamming behaviors by varying the length of the interconnecting cables. Each robotic sub-unit uses a differential drive system to achieve locomotion and self-reconfigurability. We present the robot design and perform a set of locomotion and object manipulation experiments to characterize the robot's performance in soft and rigid states. We also introduce a simulation framework in which we model the jamming soft robot design and study the scalability of this class of robots. The proposed concept demonstrates the properties of both soft and rigid robots, and has the potential to bridge the gap between the two.

Keywords: Soft Robot Applications, Micro/Nano Robots, Compliant Joint/Mechanism
Abstract: In many cases, soft and continuum robots represent an interesting alternative to articulated robots because they have the advantages of miniaturization capability, safer interactions with humans and often simpler fabricating and integration. However, these benefits are usually considered to arise at the expense of accuracy and precision because of the soft or flexible limbs. This paper demonstrates that, with a proper design, a planar parallel continuum robot is capable of great precision. Indeed, the proposed 3-Degrees-of-Freedom planar parallel continuum robot exhibits a precision of 9.13 nm in position and 1.2 µrad in orientation. In addition, the novel robotic design leverages the effect of the actuators' defects, making the robot more precise than its own actuators. Finally, the workspace of the proposed robot (62.3 mm², 36.97 deg) is significantly larger than most compliant mechanisms, which is particularly interesting when both very high precision and relatively large displacements are required.

Keywords: Soft Sensors and Actuators, Hydraulic/Pneumatic Actuators
Abstract: Soft robotics require unique and novel actuators for various applications. Therefore, a novel soft electrohydraulic actuator is proposed and its ability to manipulate a spherical object on an active plate is demonstrated. The proposed actuator has two actuation parts with asymmetric electrodes. Two types of deformations are created by applying voltages to the asymmetric electrodes of the actuator. By using various deformations from four electro-hydraulic actuators, an active plate is realized. The active plate can exhibit eight different inclinations that, allow a ball to be rotated to the desired target point. The results demonstrate that the ball moves well in an orbit without stopping. Further, the ball can stop at the desired target points.

Keywords: Soft Sensors and Actuators, Modeling, Control, and Learning for Soft Robots, Soft Robot Materials and Design
Abstract: Modern robotics has been greatly facilitated by the standardized tool sets surrounding actuation and sensing for human-scale systems, with the design and control techniques for electromechanical motors serving as a prime example. No such tool sets have become standard at the millimeter- and micrometer-scale however, often leaving actuation and sensing as bottlenecks when developing small-scale robotic systems. In this paper, we develop manufacturing and algorithmic tools for a promising class of small-scale rotary actuator -- rotary pouch motors. We present a design approach that allows for integration of both actuation and sensing into low-profile, laminate linkages of almost arbitrary length and complexity and demonstrate this approach with the design of a three degree-of-freedom (DOF) spatial manipulator. We also present dynamic models of rotary pouch motors and integrate these models into estimation and control laws that we use for real-time control of a 1-DOF joint. The presented state-estimation algorithm exhibits a root-mean-square (RMS) error of approximately 0.87-degrees and the presented control law demonstrates RMS tracking error of approximately 6.70-degrees when tracking sinusoids up to 3 Hz. By developing rotary pouch motors as controllable dynamic systems, they can used in myriad small-scale robotic systems, including insect-scale legged robots and millimeter-scale manipulators.

Keywords: Soft Robot Materials and Design, Modeling, Control, and Learning for Soft Robots, Soft Robot Applications
Abstract: Jamming is a phenomenon in which a collection of compliant elements is encased in an airtight envelope, and a vacuum-induced pressure enhances frictional and kinematic coupling, resulting in dramatic changes in stiffness. This paper introduces the jamming of square cross-sectioned fibers, which allow for tunable and programmable anisotropic stiffness. A theoretical model captures the effect of major geometric design parameters on the direction-variant bending stiffness of these long and slender jamming elements. The model is experimentally validated, and a 13-fold stiffening in one direction and a 22-fold stiffening in the orthogonal direction is achieved with a single jamming element. The performance of a square-fiber-jamming continuum robot structure is demonstrated in a steering task, with an average reduction of 74% in the measured insertion force when unjammed, and a direction-variant 53% or 100% increase in the measured tip stiffness when jammed.