In this paper, we propose a design of an underwater soft snake-like robot prototype that uses two actuators made of 3D-printed soft materials to build the robot body. Control signals with appropriate displacement phases and different voltages are used to control the water pump to drive the soft actuator to bend to generate a sine wave with increasing amplitude along the body axis. We test customized tail materials, phase shifts, and voltage growth rate signals to observe the effects of different parameters on the movement of the snake robot in water. Experiments show that the movement speed is positively correlated with the swing amplitude of the snake robot's motion module. In addition, measured data show that swimming efficiency and movement speed are also affected by tail flexibility and movement gait. When the phase offset is 2/3π, the tail is made of harder PLA material, and the voltage growth rate is 1.2, the maximum underwater movement speed achieved by the snake robot is 4.464 cm/s (0.076 BL/s). We also found that when the phase offset increases, the snake motion speed and motion efficiency first increase and then decrease. The results obtained in this study will aid in the advancement of soft, slender swimming robots and improve the understanding of the swimming capabilities of both robots and sea snakes.

Recent advancements in soft robotics have seen the rapid development of soft grippers for industrial pick-and-place applications. They are however ill-suited to bear heavy loads due to their compliant nature. Paradoxically, researchers have sought to increase the stiffness of soft grippers to improve loadbearing capabilities. Unfortunately, contemporary soft actuators with variable stiffness are fabricated using manual processes and their performance is subject to an individual's mastery. They are hence not reliable for long-term industrial use. In this paper, we present our work on a 3D-printed metalendoskeleton-reinforced actuator (MERA) for industrial pickand-place applications. We also highlight the fabrication processes needed to recreate it repetitively. Using stainless steel splints (SSS), we demonstrate that MERA is able to modulate its stiffness at selective junctures for stable and effective grasping. We also describe our design rationale with a qualitative mathematical model and validate its performance quantitatively using a finite element model, which is further investigated in the following fatigue test. In our experiments, the MERA equipped with SSS is able to output a peak tip force of 8N, which is a 291% increase compared to the one without metallic reinforcement. In addition, an increase of 76.5% in gripping load and a maximum holding force per actuator of 13.8N are realized through the stiffness tuning of a MERA-Gripper. Despite significantly improving loadbearing capabilities, the actuator manages to retain an overall low profile with a weight of 82g. Finally, we adapted the MERA into a reconfigurable gripper and tested its grasping capabilities on objects of various shapes, sizes, and weights.

THIS paper presents a bidirectional 3D-printed soft pneumatic actuator that is capable of inward and outward bending. A direct 3D-printing approach is adopted to fabricate the actuator, which reduces fabrication complexity and allows for easy customization of actuator dimensions for various applications. To illustrate the applicability of the bidirectional actuators, four of these actuators were incorporated into a gripper system. A suite of various functional grasping tasks, such as packaging, assembly, and alignment tasks, were successfully conducted. It was observed that the unique bidirectional bending characteristic of the actuator allows the gripper to grasp objects with sizes up to 245% larger than its default grasping width. To complement the gripper system, a graphite-based flex sensor that is able to sense bending in two directions is developed to control the bidirectional actuators. A preliminary test was conducted successfully where the user controlled the gripper system to grasp, hold, and release an object using a glove with the sensors.

The field of soft robotics has evolved as a domain for developing light, compliant and safe actuators. However, one of the challenges in the field is the lack of repeatable fabrication techniques as well as customizability that restricts the application of soft robots. We present a fabrication technique using sacrificial molding to fabricate pneumatic channels that are repeatable and less prone to variability. This technique enables the monolithic fabrication of actuators which eliminates conventional failure modes such as delamination. We then use embedded endostructures manufactured using Fused Deposition Modelling (FDM) 3D printers to customize the behavior of bending actuator by altering local mechanical characteristics. Finite element analysis (FEA) was used as a tool to tune the choice of materials and the geometry of the 3D printed layers based on the required application. We analyze the effect of the mechanical properties of the endostructures on actuator behavior and its utility in improving customizability. We analyzed the behavior of actuators with a variety of endostructures using visual markers. As predicted by the FEA and Euler-Bernoulli beam theory, the behavior of the actuators was seen to be influenced by the mechanical properties of the endostucture. Thus, we present a new methodology for tuning the mechanical properties of Soft Pneumatic Actuators (SPAs), which is simple and efficient to predict as well as easy to execute.

Loss of functional motor skills are common and often require patients to undergo rehabilitation so that they have a chance at motor recovery. Advancement in technology has seen to a rise in the use of robotic technology in conducting rehabilitative exercises that are traditionally carried out by physiotherapists. In recent years, soft robotic exoskeletons, using pneumatic-based actuation in particular, have gained much interest due to their compliant characteristics and safe operating conditions. In order to carry out complex task-based rehabilitative exercises, these soft pneumatic actuators must ideally be able to move with multiple degrees of freedom or minimally, in a bidirectional motion. Majority of the research covering soft actuators can only achieve finger flexion with some providing passive finger extension. Non-invasive intent detection in the control of these exoskeletons is also lacking in sensing both finger flexion and extension. In this paper we present our work on a fold-based bidirectional 3D printed intent-sensing soft pneumatic actuator (ISPA) that can achieve bidirectional motion and provide intent detection for finger flexion and extension for application in upper limb rehabilitative exoskeletons.

Soft robots are a burgeoning archetype in robotics due to their ability to perform intricate movements easily and seamlessly. They serve as an ideal concept for realistically emulating animal movements. However, the majority of soft robots today are unable to vary their motions due to the coupled interaction of the nature of their kinematics and structural composition. We therefore created Carpie, a robotic caterpillar adapted from a modular, pneumatic actuator. Carpie is designed to perform a variety of caterpillar movements by tuning its mechanical structure through physical reconfiguration. The robot has a completely soft body that enables a variety of movements and contortions into different shapes, making Carpie is perhaps the perfect example to showcase a soft robot's aptness for animal mimicry. We analyzed the robot's control aspect. Its capabilities were measured by performing gait velocity studies on three different configurations. Each configuration was executed by applying various modules on Carpie's structure without fully refabricating the entire assembly. We also analyzed the accompanying change in the robot's maximum height during gait. Finally, we demonstrate how physical reconfiguration was able to radically alter Carpie's movement, allowing it to perform a turning motion.

Rigid actuators that accompany traditional robotic systems allow them to perform tasks with unmatched precision and efficiency. However, such systems are inapt when flexibility and suppleness are required. Inversely, soft robotic actuators are constructed out of naturally compliant materials. This compliance allows them to execute complex motions while their inherent lack of hardness removes the dangers that commonly accompany traditional robots. One archetype of the soft robot is the pneumatic bending actuator. The actuators convert the flow of pressurized air into bending outputs; however, most bending actuators are only limited to one bending trajectory. A new bending actuator, capable of active reconfiguration, is realized through the combination of a non-inflating, flexible, plastic spine and multiple, inflatable, fabric modules. The spine acts as the primary conduit and is responsible for distributing the pressurized flow to the modules. Modules can be removed and replaced seamlessly. The combination of varying module geometries can produce a heterogenic bending trajectory. Blockages located along the spine can separate flow, allowing more customization of the trajectory. A physical model predicting the pressure-bending relationship was conceptualized and verified. When pressurized to 100kPa, the 5-module and 10-module actuators achieved bending angles of 48.76° and 137.65° respectively. The actuators behave as a first-order system when supplied with a step input.

This paper presents the design and preliminary investigation of a fully 3D printed soft robotic hand exoskeleton, Print-it-Yourself (PIY) Glove for stroke patients. The PIY Glove is fabricated with Fused Deposition Modeling (FDM) using consumer based 3D printing technology to lower fabrication costs and allow patients to 3D print a rehabilitative and assistive device at home. PIY Glove uses a novel, fold based design of 3D printed soft actuators to achieve bending motion in the fingers. Fabrication guidelines of the PIY Glove are laid out and characterization of the glove in terms of its range of motion and grip force are also presented. An EMG control system that achieves control of the PIY Glove is also described. This work paves the way for the implementation of printable pneumatics in real-world applications, particularly robot-assisted hand therapy.

This paper introduces a new concept of building soft pneumatic structures by assembling modular units of fabric-based rotary actuators (FRAs) and beams. Upon pressurization, the inner folds of FRA would expand, which causes the FRA module to unfold, generating angular displacement. Hence, FRAs would enable mobility function of the structure and its range of motion. The modular nature of the actuator units enables customized configuration of pneumatic structures, which can be modified and scaled by selecting the appropriate modules. FRAs are also designed to be bladder-less, that is, they are made without an additional layer of inner bladder. Thus, a simple fabrication process can be used to prepare the actuators. In this paper, we studied how the performance of the FRA modules changes with their dimensions and demonstrated how a soft gripper can be constructed using these modules. The kinematic response of the actuator segments of the gripper was analyzed and a pressure control algorithm was developed to regulate the pneumatic pressure of the actuator. The modular based soft robotic gripper alone weighs about 140g. Yet, based on the grip tests, it is able to lift heavier objects (up to 2.4kg), achieving a high payload-to-weight ratio of about 1714%, which is higher than the value reported by previously developed soft pneumatic grippers using elastomeric materials. Lastly, we also demonstrated that the gripper is capable of performing two essential grasping modes, which are power grasping and fingertip grasping, for objects of various shapes.

THIS paper presents the development of a bidirectional fabric-based soft pneumatic actuator requiring low fluid pressurization for actuation, which is incorporated into a soft robotic gripper to demonstrate its utility. The bidirectional soft fabric-based actuator is able to provide both flexion and extension. Fabrication of the fabric actuators is simple as compared to the steps involved in traditional silicone-based approach. In addition, the fabric actuators are able to generate comparably larger vertical grip resistive force at lower operating pressure than elastomeric actuators and 3D-printed actuators, being able to generate resistive grip force up to 20N at 120 kPa. Five of the bidirectional soft fabric-based actuators are deployed within a five-fingered soft robotic gripper, complete with five casings and a base. It is capable of grasping a variety of objects with maximum width or diameter closer to its bending curvature. A cutting task involved bimanual manipulation was demonstrated successfully with the gripper. To incorporate intelligent control for such a task, a soft force made completely of compliant material was attached to the gripper, which allows determination of whether the cutting task is completed. To the authors' knowledge, this work is the first study which incorporates two soft robotic grippers for bimanual manipulation with one of the grippers sensorized to provide closed loop control.

Silicone-based soft pneumatic actuator (SPA) is one of the key interests in soft robotic research. Currently, most of the SPAs bear a similar one-dimensional rod-like shape, regardless of their design and fabrication. There are few prototypes of SPAs with two-dimensional initial shapes, however, they are basically the linear combination of several one-dimensional SPAs. This paper presents a new class of silicone-based SPA named soft robotic pad (SRP). The SRP is shaped into a soft pad with a single flat air chamber and can generate different kinds of motions according to the internal constraint matrix within the SRP. In this paper, the design and fabrication of our SRPs are elaborated in detail, followed by the preliminary characterization of the different SRP prototypes. Although the current design is not optimized, our SRP prototypes prove the feasibility of the design and fabrication of a 2D shape-morphing SPA. With subsequent optimization, the SRP can work robustly in various real-world applications as strong flat artificial muscles for human joint rehabilitation, or as fins in marine robots.

This paper presents a soft robotic glove designed to assist individuals with functional grasp pathologies in performing activities of daily living. The glove utilizes soft fabric-regulated pneumatic actuators that are low-profile and require lower pressure than previously developed actuators. They are able to support fingers and thumb motions during hand closure. Upon pressurization, the actuators are able to generate sufficient force to assist in hand closing and grasping during different manipulation tasks. In this work, experiments were conducted to evaluate the performances of the actuators as well as the glove in terms of its kinetic and kinematic assistance on a healthy participant. Additionally, surface electromyography and radio-frequency identification techniques were adopted to detect user intent to activate or deactivate the glove. Lastly, we present preliminary results of a healthy participant performing different manipulation tasks with the soft robotic glove controlled by surface electromyography and radio-frequency identification techniques.

Soft robotics has garnered great research interest from robotics community due to their compliant control as compared to normal hard rigid robots. Particularly, these soft actuators only involve simple design of pneumatic channels to generate required actuation and are usually powered by pneumatics or hydraulics. These actuators are usually lightweight, inexpensive and easily fabricated with soft lithography technique. In this paper, we present a different application of soft robotics in shoe insole design that involves simple design and control. To our knowledge, this is the first study to design soft sensors and actuators which aim to redistribute the plantar pressure and eventually tackle foot problems such as ulcers and blisters. The abnormal, high repetitive stresses acting on the foot tissues can cause immediate breakdown of foot tissues, which will lead to ulcers and even a serious pathology that require foot amputation. A mold with a peripheral pneumatic ring channel feature was designed using computer-aided drawing and thereafter 3D-printed. Subsequently, elastomeric material was poured into the mold and cured to create a negative replica of the mold, which is then sealed using another 2mm layer of elastomeric material. Upon pressurization, the pneumatic channel embedded in the actuator will inflate in the regions that are most compliant and cushion the plantar soft tissues as well as reduce the peak plantar pressure.

In this paper, we present the design of a soft wearable exoskeleton that comprises of a glove embedded with pneumatic actuators of variable stiffness for hand assistive and rehabilitation application. The device is lightweight and easily wearable due to the usage of soft pneumatic actuators. A key feature of the device is the variable stiffness of the actuators at different localities that not only conform to the finger profile during actuation, but also provides customizability for different hand dimensions. The actuators can achieve different bending profiles with variable stiffness implemented at different localities. Therefore, the device is able to perform different hand therapy exercises such as full fist, straight fist, hook fist and table top. The device was characterized in terms of its range of motion and maximum force output. Experiments were conducted to examine the differences between active and passive actuation. The results showed that the device could achieve hand grasping and pinching with acceptable range of motion and force.