Experimental Evaluation of A Cylinder Actuator Control Using McKibben Muscle

There has been an increased interest in applying pneumatic muscle actuator (PMA) in robotic systems because of its low weight and high compliant characteristics. On the other hand, pneumatic muscle actuator (PMA) is gaining attention in robotic applications because of its low weight and high compliant characteristics. It is known that the McKibben muscle is different from the fluidic cylinder actuator in that the cylinder was unstable in its position and in its velocity in an open-loop system unlike the McKibben that is stable in its position. The modeling and control of McKibben muscle as the actuator for the cylinder are crucial because it is known to have non-linear response, hysteresis and small stroke. In this project, a single acting cylinder model which would have uncontrolled extension to push direction by compressed air, is actuated and controlled using a PMA. The system is designed with two 1.3mm-diameter McKibben muscles attached to the cylinder. Open loop control was used and the result shows that the PMA is able to control the cylinder with good performance

Bidirection modeling and experimental analysis of underwater snake robot

Snakes have dedicate body and can maneuver in challenging environments. In this work, a soft snake-like robot is designed to locomote like a biological snake that can be used in search and rescue operation. The soft snake-like for underwater use has advantages of low inertia, high buoyancy, and more structural flexibility. Currently, the use of multi-redundant thin McKibben actuators for soft snake-like robot was not yet explored. Addressing this gap, a soft snake robot model using Finite Element (FE) will be developed. The FE model will be developed and used to investigate the snake bending motions in Matlab Simulink with Simscape Multibody Library (SML). Next, the actual fabrication of the robot will be validated with the simulated FE model using redundant mechanism of 10 McKibben actuators attached on a plastic plate. The structure of this robot uses 32 cm of a thin non-rigid plastic plate with five thin muscles at both sides of the body. Each thin muscle has 2.0 mm outer diameter with internal 1.3 mm silicone tube. The manipulator will be tested with different pressure and frequencies to perform various bending motions. Tracker application will capture every phase of the bending body and movements for analysis of the robot’s movement. It is expected that the snake-like robot can move and the errors of bending angle between simulation and experiment are less than 5%

Long-Legged Hexapod Giacometti Robot Using Thin Soft McKibben Actuator

This letter introduces a lightweight hexapod robot, Giacometti robot, made with long and narrow legs following the Alberto Giacometti's sculpture conception. The goal is achieved by, first, using multiple links with thin and soft McKibben actuators, and second, choosing a leg design which is narrow in comparison to its body's length and height, unlike conventional robot design. By such design characteristic, the leg will exhibit elastic deformations due to the low stiffness property of the thin link structure. Then, we model the leg structure and conduct the deflection analysis to confirm the capability of the leg to perform walking motion. The high force to weight ratio characteristics of the actuator provided the ability to drive the system, as shown by a static model and further validated experimentally. To compensate for the high elastic structural flexibility of the legs, two walking gaits namely customized Wave gait and Giacometti gait were introduced. The robot could walk successfully with both gaits at maximum speed of 0.005 and 0.05 m/s, respectively. It is envisaged that the lightweight Giacometti robot design can be very useful in legged robotic exploration

A Retrofit Sensing Strategy for Soft Fluidic Robots

Soft robots are intrinsically capable of adapting to different environments by changing their shape in response to interaction forces with the environment. However, sensing and feedback are still required for higher level decisions and autonomy. Most sensing technologies developed for soft robots involve the integration of separate sensing elements in soft actuators, which presents a considerable challenge for both the fabrication and robustness of soft robots due to the interface between hard and soft components and the complexity of the assembly. To circumvent this, here we present a versatile sensing strategy that can be retrofitted to existing soft fluidic devices without the need for design changes. We achieve this by measuring the fluidic input that is required to activate a soft actuator and relating this input to its deformed state during interaction with the environment. We demonstrate the versatility of our sensing strategy by tactile sensing of the size, shape, surface roughness and stiffness of objects. Moreover, we demonstrate our approach by retrofitting it to a range of existing pneumatic soft actuators and grippers powered by positive and negative pressure. Finally, we show the robustness of our fluidic sensing strategy in closed-loop control of a soft gripper for practical applications such as sorting and fruit picking. Based on these results, we conclude that as long as the interaction of the actuator with the environment results in a shape change of the interval volume, soft fluidic actuators require no embedded sensors and design modifications to implement sensing. We believe that the relative simplicity, versatility, broad applicability and robustness of our sensing strategy will catalyze new functionalities in soft interactive devices and systems, thereby accelerating the use of soft robotics in real world applications

Design of Generalized Fiber-reinforced Elasto-fluidic Systems.

From nature to engineered solutions, the metrics of mechanical systems are often strength, power density, resilience, adaptability, safety, scalability, and the ability to generate the necessary forces, motions, and forms. The use of fluidic structures with fiber reinforcement to realize these metrics is seen throughout nature; however, these structures are rarely used by engineers, in part due to the absence of a generalized understanding of their kinematics and forces. Fiber-reinforced elasto-fluidic systems use fluid pressure to actuate an envelope with tuned compliance to provide desired motion, forces, flexibility, and transmission of energy. These structures combine the high strain energy utilization and flexibility of fibers, the versatility and compressive load abilities of fluids, and the continuum nature of soft materials, exploiting the best features of each. This dissertation discovered a vast array of previously unknown fiber-reinforced elasto-fluidic systems, models their mechanical behavior, experimentally verifies the models, creates methods for easy design synthesis, and applies this knowledge to multiple practical applications. Only a small subset of elasto-fluidic systems, popularly known as McKibben actuators, has been thoroughly investigated. Therefore, a vast design space of possible structures with multiple sets of fibers and different orientations yielding a rich array of functionality were yet to be investigated and applied to a wealth of applications. This dissertation develops the mechanics of generalized fiber-reinforced elasto-fluidic systems by first modeling the relationship of volume change and fiber orientation to motion kinematics and force generation. The kinematics of motions including translation, rotation, screw, bending, and helical were all modeled. Fiber configurations spanning the design space were tested to experimentally verify the predicted forces and motion. The force and kinematics were combined to form a design synthesis tool that maps the desired motions, freedoms, and constraints to fiber configurations. Synthesis methods were created for parallel combination of fiber-reinforced structures using discretized force and freedom directions. Lastly, novel applications were created using these fiber-reinforced elasto-fluidic structures, including an orthosis device for arm rotation contractures, a soft hexapod robot with an actuated flexible spine, and a structure for anchoring within pipes.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/107202/1/joshbm_1.pd

Designing LMPA-Based Smart Materials for Soft Robotics Applications

This doctoral research, Designing LMPA (Low Melting Point Alloy) Based Smart Materials for Soft Robotics Applications, includes the following topics: (1) Introduction; (2) Robust Bicontinuous Metal-Elastomer Foam Composites with Highly Tunable Mechanical Stiffness; (3) Actively Morphing Drone Wing Design Enabled by Smart Materials for Green Unmanned Aerial Vehicles; (4) Dynamically Tunable Friction via Subsurface Stiffness Modulation; (5) LMPA Wool Sponge Based Smart Materials with Tunable Electrical Conductivity and Tunable Mechanical Stiffness for Soft Robotics; and (6) Contributions and Future Work.Soft robots are developed to interact safely with environments. Smart composites with tunable properties have found use in many soft robotics applications including robotic manipulators, locomotors, and haptics. The purpose of this work is to develop new smart materials with tunable properties (most importantly, mechanical stiffness) upon external stimuli, and integrate these novel smart materials in relevant soft robots. Stiffness tunable composites developed in previous studies have many drawbacks. For example, there is not enough stiffness change, or they are not robust enough. Here, we explore soft robotic mechanisms integrating stiffness tunable materials and innovate smart materials as needed to develop better versions of such soft robotic mechanisms. First, we develop a bicontinuous metal-elastomer foam composites with highly tunable mechanical stiffness. Second, we design and fabricate an actively morphing drone wing enabled by this smart composite, which is used as smart joints in the drone wing. Third, we explore composite pad-like structures with dynamically tunable friction achieved via subsurface stiffness modulation (SSM). We demonstrate that when these composite structures are properly integrated into soft crawling robots, the differences in friction of the two ends of these robots through SSM can be used to generate translational locomotion for untethered crawling robots. Also, we further develop a new class of smart composite based on LMPA wool sponge with tunable electrical conductivity and tunable stiffness for soft robotics applications. The implications of these studies on novel smart materials design are also discussed

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

Development and Optimisation of 3D Printed Compliant Joint Mechanisms for Hypermobile Robots

Hypermobile robots are an area of robotics that are often used as exploratory robots, but have facets that feature in other areas of the field. Hypermobile robots are robots that feature multiple body segments or modules, with joints between each. These robots are often used for exploratory purposes due to being able to maintain contact with the ground due to their flexible bodies. Wormbot was a hypermobile robot developed at the University of Leeds, which used a locomotion gait based on that of a Caenorhabditis elegans nematode worm, otherwise known as C.elegans. This movement pattern is reliant on compliance; a mechanism where the joints are slightly sprung and comply to the environment. The next iteration of Wormbot needs to be reduced in size, which would also require a new actuation and compliance system. This thesis describes the process of investigating a method of compliance to be used in the next version of Wormbot, while utilising the multi-material 3D printing capabilities available at the University. 3D printing provides quick manufacturing, allowing for fast changes to made to prototype components if required. During the process of this research, two 3D printed compliant actuation systems were produced; a pneumatic bellow and a Series Elastic Element (SEE) to be used in tandem with a servo motor. Both methods were tested to analyse their performance. The bellow was produced to utilise the capabilities of multi-material printing to strengthening suspected weak areas of the actuator. However, the performance of the bellow was unsatisfactory, failing twice in two actuation tests tests due to the device breaking. The SEE on the other hand, designed with two stiffer plates and a rubber-like spring element in the middle, initially proved to be reliable and repeatable in performance, with potential to behave linearly to a set spring constant. These results were acquired by performing rotational step response tests and fitting a spring-damper model to the results. However, issues with the plastic material were discovered when it was found to deform much more than anticipated, behaving in a similar manner to an additional spring element, complicating the model. Simulation work to explore the potential for using different spring constants of joint compliance in varying environments was also explored. This involved testing a virtual Wormbot in a range of environments while altering joint compliance. These simulations revealed that softer joints allow for favourable performance in constricting environments, while stiffer joints lend themselves more to quicker movement

Wearable exoskeleton systems based-on pneumatic soft actuators and controlled by parallel processing

Human assistance innovation is essential in an increasingly aging society and one technology that may be applicable is exoskeletons. However, traditional rigid exoskeletons have many drawbacks. This research includes the design and implementation of upper-limb power assist and rehabilitation exoskeletons based on pneumatic soft actuators. A novel extensor-contractor pneumatic muscle has been designed and constructed. This new actuator has bidirectional action, allowing it to both extend and contract, as well as create force in both directions. A mathematical model has been developed for the new novel actuator which depicts the output force of the actuator. Another new design has been used to create a novel bending pneumatic muscle, based on an extending McKibben muscle and modelled mathematically according to its geometric parameters. This novel bending muscle design has been used to create two versions of power augmentation gloves. These exoskeletons are controlled by adaptive controllers using human intention. For finger rehabilitation a glove has been developed to bend the fingers (full bending) by using our novel bending muscles. Inspired by the zero position (straight fingers) problem for post-stroke patients, a new controllable stiffness bending actuator has been developed with a novel prototype. To control this new rehabilitation exoskeleton, online and offline controller systems have been designed for the hand exoskeleton and the results have been assessed experimentally. Another new design of variable stiffness actuator, which controls the bending segment, has been developed to create a new version of hand exoskeletons in order to achieve more rehabilitation movements in the same single glove. For Forearm rehabilitation, a rehabilitation exoskeleton has been developed for pronation and supination movements by using the novel extensor-contractor pneumatic muscle. For the Elbow rehabilitation an elbow rehabilitation exoskeleton was designed which relies on novel two-directional bending actuators with online and offline feedback controllers. Lastly for upper-limb joint is the wrist, we designed a novel all-directional bending actuator by using the moulding bladder to develop the wrist rehabilitation exoskeleton by a single all-directional bending muscle. Finally, a totally portable, power assistive and rehabilitative prototype has been developed using a parallel processing intelligent control chip