Variable stiffness McKibben muscles with hydraulic and pneumatic operating modes

McKibben muscles have been shown to have improved stiffness characteristics when operating hydraulically. However, when operating pneumatically they are compliant and so have potential for safer physical Human Robot Interaction (pHRI). This paper presents a method for rapidly switching between pneumatic and hydraulic modes of operation without the need to remove all hydraulic fluid from the actuator. A compliant and potentially safe pneumatic mode is demonstrated and compared with a much stiffer hydraulic mode. The paper also explores a combined pneumatic/hydraulic mode of operation which allows both the position of the joint and the speed at which it reacts to a disturbance force to be controlled

RESEARCH TOWARDS THE DESIGN OF A NOVEL SMART FLUID DAMPER USING A MCKIBBEN ACTUATOR

Vibration reducing performance of many mechanical systems, decreasing the quality of manufactured products, producing noise, generating fatigue in mechanical components, and producing an uncomfortable environment for human bodies. Vibration control is categorized as: active, passive, or semi-active, based on the power consumption of the control system and feedback or feed forward based on whether sensing is used to control vibration. Semi-active vibration control is the most attractive method; one method of semi-active vibration control could be designed by using smart fluid. Smart fluids are able to modify their effective viscosity in response to an external stimulus such as a magnetic field. This unique characteristic can be utilised to build semi-active dampers for a wide variety of vibration control systems. Previous work has studied the application of smart fluids in semi-active dampers, where the kinetic energy of a vibrating structure can be dissipated in a controllable fashion. A McKibben actuator is a device that consists of a rubber tube surrounded by braided fibre material. It has different advantages over a piston/cylinder actuator such as: a high power to weight ratio, low weight and less cost. Recently McKibben actuator has appeared in some semi-active vibration control devise. This report investigates the possibility of designing a Magnetorheological MR damper that seeks to reduce the friction in the device by integrating it with a McKibben actuator. In this thesis the concept of both smart fluid and McKibben actuator have been reviewed in depth, and methods of modelling and previous applications of devices made using these materials are also presented. The experimental part of the research includes: designing and modelling a McKibben actuator (using water) under static loads, and validating the model experimentally. The research ends by presenting conclusions and future work

Development of a SMA-fishing-line-McKibben bending actuator

High power-to-weight ratio soft artificial muscles are of overarching importance to enable inherently safer solutions to human-robot interactions. Traditional air driven soft McKibben artificial muscles are linear actuators. It is impossible for them to realize bending motions through a single McKibben muscle. Over two McKibben muscles should normally be used to achieve bending or rotational motions, leading to heavier and larger systems. In addition, air driven McKibben muscles are highly nonlinear in nature, making them difficult to be controlled precisely. A SMA(shape memory alloy)–fishing–line–McKibben (SFLM) bending actuator has been developed. This novel artificial actuator, made of a SMA-fishing-line muscle and a McKibben muscle, was able to produce the maximum output force of 3.0 N and the maximum bending angle (the rotation of the end face) of 61°. This may promote the application of individual McKibben muscles or SMA-fishing-line muscles alone. An output force control method for SFLM is proposed, and based on MATLAB/Simulink software the experiment platform is set up, the effectiveness of control system is verified through output force experiments. A three-fingered SFLM gripper driven by three SFLMs has been designed for a case study, which the maximum carrying capacity is 650.4 ± 0.2 g

High Fidelity Dynamic Modeling and Nonlinear Control of Fluidic Artificial Muscles

A fluidic artificial muscle is a type of soft actuator. Soft actuators transmit power with elastic or hyper-elastic bladders that are deformed with a pressurized fluid. In a fluidic artificial muscle a rubber tube is encompassed by a helical fiber braid with caps on both ends. One of the end caps has an orifice, allowing the control of fluid flow in and out of the device. As the actuator is pressurized, the rubber tube expands radially and is constrained by the helical fiber braid. This constraint results in a contractile motion similar to that of biological muscles. Although artificial muscles have been extensively studied, physics-based models do not exist that predict theirmotion.This dissertation presents a new comprehensive lumped-parameter dynamic model for both pneumatic and hydraulic artificial muscles. It includes a tube stiffness model derived from the theory of large deformations, thin wall pressure vessel theory, and a classical artificial muscle force model. Furthermore, it incorporates models for the kinetic friction and braid deformation. The new comprehensive dynamic model is able to accurately predict the displacement of artificial muscles as a function of pressure. On average, the model can predict the quasi-static position of the artificial muscles within 5% error and the dynamic displacement within 10% error with respect to the maximum stroke. Results show the potential utility of the model in mechanical system design and control design. Applications include wearable robots, mobile robots, and systems requiring compact, powerful actuation.The new model was used to derive sliding mode position and impedance control laws. The accuracy of the controllers ranged from ± 6 µm to ± 50 µm, with respect to a 32 mm and 24 mm stroke artificial muscles, respectively. Tracking errors were reduced by 59% or more when using the high-fidelity model sliding mode controller compared to classical methods. The newmodel redefines the state-of-the-art in controller performance for fluidic artificial muscles

Fluidic Fabric Muscle Sheets for Wearable and Soft Robotics

Conformable robotic systems are attractive for applications in which they can be used to actuate structures with large surface areas, to provide forces through wearable garments, or to realize autonomous robotic systems. We present a new family of soft actuators that we refer to as Fluidic Fabric Muscle Sheets (FFMS). They are composite fabric structures that integrate fluidic transmissions based on arrays of elastic tubes. These sheet-like actuators can strain, squeeze, bend, and conform to hard or soft objects of arbitrary shapes or sizes, including the human body. We show how to design and fabricate FFMS actuators via facile apparel engineering methods, including computerized sewing techniques. Together, these determine the distributions of stresses and strains that can be generated by the FFMS. We present a simple mathematical model that proves effective for predicting their performance. FFMS can operate at frequencies of 5 Hertz or more, achieve engineering strains exceeding 100%, and exert forces greater than 115 times their own weight. They can be safely used in intimate contact with the human body even when delivering stresses exceeding 10$^\text{6}$ Pascals. We demonstrate their versatility for actuating a variety of bodies or structures, and in configurations that perform multi-axis actuation, including bending and shape change. As we also show, FFMS can be used to exert forces on body tissues for wearable and biomedical applications. We demonstrate several potential use cases, including a miniature steerable robot, a glove for grasp assistance, garments for applying compression to the extremities, and devices for actuating small body regions or tissues via localized skin stretch.Comment: 32 pages, 10 figure

Pneumatic Artificial Muscle Driven Trailing Edge Flaps For Active Rotors

This research focuses on the development of an active rotor system capable of primary control and vibration reduction for rotorcraft. The objective is to investigate the feasibility of a novel Trailing Edge Flap (TEF) actuation system driven by Pneumatic Artificial Muscles (PAMs). A significant design effort led to a series of experimental apparatuses which tested various aspects of the performance of the actuators themselves and of TEF systems driven by them. Analytical models were developed in parallel to predict the quasistatic and dynamic behavior of these systems. Initial testing of a prototype blade section with an integrated PAM driven TEF proved the viability of the concept through successful benchtop testing under simulated M = 0.3 loading and open jet wind tunnel tests under airspeeds up to M = 0.13. This prototype showed the ability of PAM actuators to generate significant flap deflections over the bandwidth of interest for primary control and vibration reduction on a rotorcraft. It also identified the importance of high pneumatic system mass flow rate for maintaining performance at higher operating frequencies. Research into the development and improvement of PAM actuators centered around a new manufacturing technique which was invented to directly address the weaknesses of previous designs. Detailed finite element model (FEM) analysis of the design allowed for the mitigation of stress concentrations, leading to increased strength. Tensile testing of the swaged actuators showed a factor of safety over 5, and burst pressure testing showed a factor of safety of 3. Over 120,000,000 load cycles were applied to the actuators without failure. Characterization testing before, during, and after the fatigue tests showed no reduction in PAM performance. Wind tunnel testing of a full scale Bell 407 blade retrofitted with a PAM TEF system showed excellent control authority. At the maximum wind tunnel test speed of M = 0.3 and a derated PAM operating pressure of 28 psi, 18.8° half-peak-to-peak flap deflections were achieved at 1/rev (7 Hz), and 17.1° of half-peak-to-peak flap deflection was still available at 5/rev (35 Hz). A quasistatic system model was developed which combined PAM forces, kinematics and flap aerodynamics to predict flap deflection amplitudes. This model agreed well with experimental data. Whirl testing of a sub-span whirl rig under full scale loading conditions showed the ability of PAM TEF systems to operate under full scale levels of centrifugal (CF), aerodynamic, and inertia loading. A commercial pneumatic rotary union was used to provide air in the rotating frame. Extrapolation of the results to 100% of CF acceleration predicts 15.4° of half-peak-to-peak flap deflection at 1/rev (7 Hz), and 7.7° of half-peak-to-peak flap deflection at 5/rev (35 Hz). A dynamic model was developed which successfully predicted the time domain behavior of the PAM actuators and PAM TEF system. This model includes control valve dynamics, frictional tubing losses, pressure dynamics, PAM forces, mechanism kinematics, aerodynamic hinge moments, system stiffness, damping, and inertia to solve for the rotational dynamics of the flap. Control system development led to a closed loop control system for PAM TEF systems capable of tracking complex, multi-sinusoid flap deflections representative of a combined primary control and vibration reduction flap actuation scheme. This research shows the promise that PAM actuators have as drivers for trailing edge flaps on active helicopter rotors. The robustness, ease of integration, control authority and tracking accuracy of these actuators have been established, thereby motivating further research

The design and mathematical model of a novel variable stiffness extensor-contractor pneumatic artificial muscle

This article presents the design of a novel Extensor-Contractor Pneumatic Artificial Muscle (ECPAM). This new actuator has numerous advantages over traditional pneumatic artificial muscles. These include the ability to both contract and extend relative to a nominal initial length, the ability to generate both contraction and extension forces and the ability to vary stiffness at any actuator length. A kinematic analysis of the ECPAM is presented in this article. A new output force mathematical model has been developed for the ECPAM based on its kinematic analysis and the theory of energy conservation. The correlation between experimental results and the new mathematical model has been investigated and show good correlation. Numerous stiffness experiments have been conducted to validate the variable stiffness ability of the actuator at a series of specific fixed lengths. This has proven that actuator stiffness can be adjusted independently of actuator length. Finally a stiffness-position controller has been developed to validate the effectiveness of the novel actuator

Design of a variable stiffness soft dexterous gripper

This article presents the design of a variable stiffness, soft, three fingered dexterous gripper. The gripper uses two designs of McKibben muscles. Extensor muscles which increase in length when pressurised are used to form the fingers of the gripper. Contractor muscles which decrease in length when pressurised are then used to apply forces to the fingers via tendons which cause flexion and extension of the fingers. The two types of muscles are arranged to act antagonistically and this means that by raising the pressure in all of the pneumatic muscles the stiffness of the system can be increased without a resulting change in finger position. The article presents the design of the gripper, some basic kinematics to describe its function and then experimental results demonstrating the ability to adjust the bending stiffness of the gripper’s fingers. It has been demonstrated that the finger’s bending stiffness can be increased by over 150%. The article concludes by demonstrating that the fingers can be closed loop position controlled and are able to track step and sinusoidal inputs

Volume 3 – Conference

We are pleased to present the conference proceedings for the 12th edition of the International Fluid Power Conference (IFK). The IFK is one of the world’s most significant scientific conferences on fluid power control technology and systems. It offers a common platform for the presentation and discussion of trends and innovations to manufacturers, users and scientists. The Chair of Fluid-Mechatronic Systems at the TU Dresden is organizing and hosting the IFK for the sixth time. Supporting hosts are the Fluid Power Association of the German Engineering Federation (VDMA), Dresdner Verein zur Förderung der Fluidtechnik e. V. (DVF) and GWT-TUD GmbH. The organization and the conference location alternates every two years between the Chair of Fluid-Mechatronic Systems in Dresden and the Institute for Fluid Power Drives and Systems in Aachen. The symposium on the first day is dedicated to presentations focused on methodology and fundamental research. The two following conference days offer a wide variety of application and technology orientated papers about the latest state of the art in fluid power. It is this combination that makes the IFK a unique and excellent forum for the exchange of academic research and industrial application experience. A simultaneously ongoing exhibition offers the possibility to get product information and to have individual talks with manufacturers. The theme of the 12th IFK is “Fluid Power – Future Technology”, covering topics that enable the development of 5G-ready, cost-efficient and demand-driven structures, as well as individual decentralized drives. Another topic is the real-time data exchange that allows the application of numerous predictive maintenance strategies, which will significantly increase the availability of fluid power systems and their elements and ensure their improved lifetime performance. We create an atmosphere for casual exchange by offering a vast frame and cultural program. This includes a get-together, a conference banquet, laboratory festivities and some physical activities such as jogging in Dresden’s old town.:Group 8: Pneumatics Group 9 | 11: Mobile applications Group 10: Special domains Group 12: Novel system architectures Group 13 | 15: Actuators & sensors Group 14: Safety & reliabilit