Soft manipulators and grippers: A review

Soft robotics is a growing area of research which utilizes the compliance and adaptability of soft structures to develop highly adaptive robotics for soft interactions. One area in which soft robotics has the ability to make significant impact is in the development of soft grippers and manipulators. With an increased requirement for automation, robotics systems are required to perform task in unstructured and not well defined environments; conditions which conventional rigid robotics are not best suited. This requires a paradigm shift in the methods and materials used to develop robots such that they can adapt to and work safely in human environments. One solution to this is soft robotics, which enables soft interactions with the surroundings while maintaining the ability to apply significant force. This review paper assesses the current materials and methods, actuation methods and sensors which are used in the development of soft manipulators. The achievements and shortcomings of recent technology in these key areas are evaluated, and this paper concludes with a discussion on the potential impacts of soft manipulators on industry and society

Design, fabrication and control of soft robots

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics.National Science Foundation (U.S.) (Grant IIS-1226883

Review of machine learning methods in soft robotics

Soft robots have been extensively researched due to their flexible, deformable, and adaptive characteristics. However, compared to rigid robots, soft robots have issues in modeling, calibration, and control in that the innate characteristics of the soft materials can cause complex behaviors due to non-linearity and hysteresis. To overcome these limitations, recent studies have applied various approaches based on machine learning. This paper presents existing machine learning techniques in the soft robotic fields and categorizes the implementation of machine learning approaches in different soft robotic applications, which include soft sensors, soft actuators, and applications such as soft wearable robots. An analysis of the trends of different machine learning approaches with respect to different types of soft robot applications is presented; in addition to the current limitations in the research field, followed by a summary of the existing machine learning methods for soft robots

Phase Change Materials for Controllable Stiffness of Robotic Joints

Snake-like manipulators are well suited for operation in restricted and confined environments where the manipulator body can bend around obstacles to place an end effector at a difficult to access location. They require high stiffness when self-supporting weight against gravity and undertake precision manipulation task, but also require soft properties when operating in complex and delicate environments. A controllable stiffness manipulator has the potential to meet the application demands as it can switch between rigid and soft state. This thesis experimentally investigates the properties of four materials, (low melting point solder, hot-melt adhesive, low melting point alloy and granular material) as candidates for mechanically altering the stiffness of the joints/modules in snake-like manipulators. These materials were evaluated for bonding strength, repeatability, and activation time. Modules for a snake-like manipulator were fabricated using 3D printing and silicone casting techniques including, for the first time, variable stiffness joints that use hot-melt adhesive and low melting point alloy. These modules were evaluated for stiffness properties and low melting point solder based module was found to achieve a stiffness change 150X greater than the state of the art granular material approach. In addition, the proposed modules were able to support 25X of their own weight

Electroosmotic Soft Actuators

This dissertation details the research involved in creating the first paper-based soft actuator driven by electroosmosis. To accomplish this, research breakthroughs were made in the fields of electrokinetic pumping and device manufacturing using soft materials. Electroosmosis is an electrically induced microfluidic flow phenomenon. When an electric field is applied to the fluid, across the microchannels, electroosmotic flow occurs in the direction of the applied electric field. In this work, liquid was electroosmotically displaced within a flexible microfluidic device to actuate an elastomeric membrane. The goal of this work was to create a fully sealed fluidic actuator. It was therefore necessary to encapsulate the pumping fluid within the device, and to maximize pressure it was necessary to eliminate compliance caused by trapped gases. Electrolytic gas formation is well known to disrupt pumping in DC electroosmotic systems that use water as the pumping liquid. In this work, electrolysis was eliminated by replacing water with propylene carbonate (PC): PC was determined to be electrochemically stable up to at least 10 kV, in the absence of moisture or salt contaminants. Bubble-free electroosmotic pumping with PC was achieved within sealed miniature actuators, which could be continuously operated for at least one hour. Benchtop fabrication techniques were developed to build encapsulated fluidic actuators composed entirely of soft, flexible materials. Stretchable electrochemically stable electrodes were made using a conductive paint made by mixing carbon nanoparticles into a silicone base. High-density microchannel networks were incorporated by using paper and other flexible porous materials, instead of conventional planar replica-molded microchannels. The device was filled with pumping fluid without the use of external tubing, and then encapsulated by casting a film of elastomer over the filled reservoir to form the actuating membrane. The resulting actuators were flexible and stretchable, demonstrating significant membrane deformations (hundreds of micrometers) within seconds of applying the electric field and ability to lift large loads (tens of grams). These polymeric electroosmotic actuators are unique among electroactive polymer actuators because they are able to simultaneously generate high force as well as large stroke. It is envisioned that this research will pave the way for the creation of artificial muscles and smart shape-changing materials that can be actuated by electroosmosis

Theoretical and Experimental Investigation on the Multiple Shape Memory Ionic Polymer-Metal Composite Actuator

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as biomimetic robotics, advanced medical devices and human affinity applications. Here, we report a Multiple Shape Memory Ionic Polymer-Metal Composite (MSM-IPMC) actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. Theoretical and experimental investigation on the MSM-IPMC actuator were performed. To date, the effect of the surface electrode properties change on the actuating of IPMC have not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC are presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. This study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators. In our study, we introduce a soft MSM-IPMC actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of our knowledge, this MSM-IPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability. The shape memory properties of MSM-IPMC were theoretically and experimentally studied. We presented the multiple shape memory properties of Nafion cylinder. A physics based model of the IPMC was proposed. The free energy density theory was utilized to analyze the shape properties of the IPMC. To verify the model, IPMC samples with the Nafion as the base membrane was prepared and experiments were conducted. Simulation of the model was performed and the results were compared with the experimental data. It was successfully demonstrated that the theoretical model can well explain the shape memory properties of the IPMC. The results showed that the reheat glass transition temperature of the IPMC is lower than the programming temperature. It was also found that the back-relaxation of the IPMC decreases as the programming temperature increases. This study may be useful for the better understanding of the shape memory effect of IPMC. Furthermore, we theoretically modeled and experimentally investigated the multiple shape memory effect of MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSM-IPMC was developed. Based on our previous study on the electro-mechanical actuation effect of IPMC, we proposed a comprehensive physics-based model of MSM-IPMC which couples the actuation effect and the multiple shape memory effect. It is the first model that includes these two actuation effects and multiple shape memory effect. Simulation of the model was performed using finite element method. To verify the model, an MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The multiple shape memory effect and reversibility of three different polymers, namely the Nafion, Aquivion and GEFC with three different ions, which are the hydrogen, lithium and sodium, were also quantitatively tested respectively. Based on the results, it is shown that all the polymers have good multiple shape memory effect and reversibility. The ions have an influence on the broad glass transition range of the polymers. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC. A biomimetic underwater robot, that was actuated by the MSM-IPMC, was developed. The design of the robot was inspired by the pectoral fish swimming modes, such as stingrays, knifefish and cuttefish. The robot was actuated by two soft fins which were consisted of multiple IPMC samples. Through actuating the IPMCs separately, traveling wave was generated on the soft fin. Experiments were performed for the test of the robot. The deformation and the blocking force of the IPMCs on the fin were measured. A force measurement system in a flow channel was implemented. The thrust force of the robot under different frequencies and traveling wave numbers were recorded. Multiple shape memory effect was performed on the robot. The robot was capable of changing its swimming modes from Gymnotiform to Mobuliform, which has high deformability, maneuverability and agility

Soft pneumatic actuators: a review of design, fabrication, modeling, sensing, control and applications

Soft robotics is a rapidly evolving field where robots are fabricated using highly deformable materials and usually follow a bioinspired design. Their high dexterity and safety make them ideal for applications such as gripping, locomotion, and biomedical devices, where the environment is highly dynamic and sensitive to physical interaction. Pneumatic actuation remains the dominant technology in soft robotics due to its low cost and mass, fast response time, and easy implementation. Given the significant number of publications in soft robotics over recent years, newcomers and even established researchers may have difficulty assessing the state of the art. To address this issue, this article summarizes the development of soft pneumatic actuators and robots up until the date of publication. The scope of this article includes the design, modeling, fabrication, actuation, characterization, sensing, control, and applications of soft robotic devices. In addition to a historical overview, there is a special emphasis on recent advances such as novel designs, differential simulators, analytical and numerical modeling methods, topology optimization, data-driven modeling and control methods, hardware control boards, and nonlinear estimation and control techniques. Finally, the capabilities and limitations of soft pneumatic actuators and robots are discussed and directions for future research are identified

Modular soft pneumatic actuator system design for compliance matching

The future of robotics is personal. Never before has technology been as pervasive as it is today, with advanced mobile electronics hardware and multi-level network connectivity pushing âsmartâ devices deeper into our daily lives through home automation systems, virtual assistants, and wearable activity monitoring. As the suite of personal technology around us continues to grow in this way, augmenting and offloading the burden of routine activities of daily living, the notion that this trend will extend to robotics seems inevitable. Transitioning robots from their current principal domain of industrial factory settings to domestic, workplace, or public environments is not simply a matter of relocation or reprogramming, however. The key differences between âtraditionalâ types of robots and those which would best serve personal, proximal, human interactive applications demand a new approach to their design. Chief among these are requirements for safety, adaptability, reliability, reconfigurability, and to a more practical extent, usability. These properties frame the context and objectives of my thesis work, which seeks to provide solutions and answers to not only how these features might be achieved in personal robotic systems, but as well what benefits they can afford. I approach the investigation of these questions from a perspective of compliance matching of hardware systems to their applications, by providing methods to achieve mechanical attributes complimentary to their environment and end-use. These features are fundamental to the burgeoning field of Soft Robotics, wherein flexible, compliant materials are used as the basis for the structure, actuation, sensing, and control of complete robotic systems. Combined with pressurized air as a power source, soft pneumatic actuator (SPA) based systems offers new and novel methods of exploiting the intrinsic compliance of soft material components in robotic systems. While this strategy seems to answer many of the needs for human-safe robotic applications, it also brings new questions and challenges: What are the needs and applications personal robots may best serve? Are soft pneumatic actuators capable of these tasks, or âusefulâ work output and performance? How can SPA based systems be applied to provide complex functionality needed for operation in diverse, real-world environments? What are the theoretical and practical challenges in implementing scalable, multiple degrees of freedom systems, and how can they be overcome? I present solutions to these problems in my thesis work, elucidated through scientific design, testing and evaluation of robotic prototypes which leverage and demonstrate three key features: 1) Intrinsic compliance: provided by passive elastic and flexible component material properties, 2) Extrinsic compliance: rendered through high number of independent, controllable degrees of freedom, and 3) Complementary design: exhibited by modular, plug and play architectures which combine both attributes to achieve compliant systems. Through these core projects and others listed below I have been engaged in soft robotic technology, its application, and solutions to the challenges which are critical to providing a path forward within the soft robotics field, as well as for the future of personal robotics as a whole toward creating a better society