Breathing produces chest motion 24 hours a day, hence it is ideal for continuous energy harvesting of up to milliwatt scale power levels. A soft band wrapped around the chest can extend by centimeters at relatively low force levels. A stiff band extends at higher force levels but with some discomfort to the user. Chest strain energy harvesters must balance power generation and the soft tissue compression associated with user discomfort. This paper explores the modeling and analysis of wearable chest strain energy harvesters that use electromagnetic generators and piezoelectric polymers including the effects of soft tissue compliance. Electromagnetic generators are shown to produce more power than piezoelectric polymers during deep breathing. During shallow breathing, however, the polymer harvester performs better because static friction and soft tissue compression limit power generation in the electromagnetic harvester.
This paper presents a novel approach for damping the vibration of a cantilever beam by bonding a fluidic flexible matrix composite (F2MC) tube to the beam and using the strain induced fluid pumping. The transverse beam vibration couples with the F2MC tube strain to generate flow into an external accumulator through an orifice that dissipates energy. The energy dissipation is especially significant at the resonances of the cantilever beam, where the beam vibrates with greatest amplitude and induces the most fluid flow from the F2MC tube. As a result, the resonant peaks can be greatly reduced due to the damping introduced by the flow through the orifice. An analytical model is developed based on Euler-Bernoulli beam theory and Lekhnitskii’s solution for anisotropic layered tubes. In order to maximize the vibration reduction, a parametric study of the F2MC tube is performed. The analysis results show that the resonant peaks can be provided with a damping ratio of up to 13.2% by tailoring the fiber angle of the F2MC tube, the bonding locations of the tube, and the orifice flow coefficient.
Refreshable Braille displays require many, small diameter actuators to move the pins. The electrostrictive P(VDF-TrFECFE)
terpolymer can provide the high strain and actuation force under modest electric fields that are required of this
application. In this paper, we develop core-free tubular actuators and integrate them into a 3 × 2 Braille cell. The films
are solution cast, stretched to 6 μm thick, electroded, laminated into a bilayer, rolled into a 2 mm diameter tube, bonded,
and provided with top and bottom contacts. Experimental testing of 17 actuators demonstrates significant strains (up to
4%). A novel Braille cell is designed and fabricated using six of these actuators.
Presented in this paper is the development of a novel honeycomb sandwich panel with variable transverse stiffness. In
this structure, the traditional sandwich face sheets are replaced by the fluidic flexible matrix composite (F2MC) tube
layers developed in recent studies. The F2MC layers, combined with the anisotropic honeycomb core material
properties, provide a new sandwich structure with variable stiffness properties for transverse loading. In this research,
an analytical model is derived based on Lekhitskii's anisotropic pressurized tube solution and Timoshenko beam theory.
Experimental investigations are also conducted to verify the analytical findings. A segmented multiple-F2MC-tube
configuration is synthesized to increase the variable stiffness range. The analysis shows that the new honeycomb
sandwich structure using F2MC tubes of 10 segments can provide a high/low transverse stiffness ratio of 60.
Segmentation and stiffness control can be realized by an embedded valve network, granting a fast response time.
In this research, the capability of utilizing fluidic flexible matrix composites (F2MC) for autonomous structural tailoring
is investigated. By taking advantages of the high anisotropy of flexible matrix composite (FMC) tubes and the high bulk
modulus of the pressurizing fluid, significant changes in the effective modulus of elasticity can be achieved by
controlling the inlet valve to the fluid filled F2MC structure. The variable modulus F2MC structure has the flexibility to
easily deform when desired (open valve), possesses the high modulus required during loading conditions when
deformation is not desired (closed valve - locked state), and has the adaptability to vary the modulus between the
flexible/stiff states through control of the valve. In the current study, a closed-form, 3-dimensional, analytical model is
developed to model the behavior of a single F2MC tube structure. Experiments are conducted to validate the proposed
model. The test results show good agreement with the model predictions. A closed/open modulus ratio as high as 56
times is achieved experimentally thus far. With the validated model, an F2MC design space study is performed. It is
found by tailoring the properties of the FMC tube and inner liner, a wide range of modulus and modulus ratios can be
This paper describes the development of the octopus biology inspired OctArm series of soft robot manipulators. Each OctArm is constructed using air muscle extensors with three control channels per section that provide two axis bending and extension. Within each section, mesh and plastic coupler constraints prevent extensor buckling. OctArm IV is comprised of four sections connected by endplates, providing twelve degrees of freedom. Performance of OctArm IV is characterized in a lab environment. Using only 4.13 bar of air pressure, the dexterous distal section provides 66% extension and 380° of rotation in less than .5 seconds. OctArm V has three sections and, using 8.27 bar of air pressure, the strong proximal section provides 890 N and 250 N of vertical and transverse load capacity, respectively. In addition to the in-lab testing, OctArm V underwent a series of field trials including open-air and in-water field tests. Outcomes of the trials, in which the manipulator demonstrated the ability for adaptive and novel manipulation in challenging environments, are described. OctArm VI is designed and constructed based on the in-lab performance, and the field testing of its predecessors. Implications for the deployment of soft robots in military environments are discussed.
In this paper, we describe our recent results in the development of a new class of soft, continuous backbone ("continuum") robot manipulators. Our work is strongly motivated by the dexterous appendages found in cephalopods, particularly the arms and suckers of octopus, and the arms and tentacles of squid. Our ongoing investigation of these animals reveals interesting and unexpected functional aspects of their structure and behavior. The arrangement and dynamic operation of muscles and connective tissue observed in the arms of a variety of octopus species motivate the underlying design approach for our soft manipulators. These artificial manipulators feature biomimetic actuators, including artificial muscles based on both electro-active polymers (EAP) and pneumatic (McKibben) muscles. They feature a "clean" continuous backbone design, redundant degrees of freedom, and exhibit significant compliance that provides novel operational capacities during environmental interaction and object manipulation. The unusual compliance and redundant degrees of freedom provide strong potential for application to delicate tasks in cluttered and/or unstructured environments. Our aim is to endow these compliant robotic mechanisms with the diverse and dexterous grasping behavior observed in octopuses. To this end, we are conducting fundamental research into the manipulation tactics, sensory biology, and neural control of octopuses. This work in turn leads to novel approaches to motion planning and operator interfaces for the robots. The paper describes the above efforts, along with the results of our development of a series of continuum tentacle-like robots, demonstrating the unique abilities of biologically-inspired design.
This paper presents a novel micro flextensional actuator design consisting of bulk PZT bonded to a silicon microbeam. The fabrication process includes boron doping, EDP etching, dicing, and bonding to produce actuators with large displacements (8.7 μm) and gain factors (32) at 100V. The theoretical model predicts that a thin beam with properly designed initial imperfection maximizes the actuator displacement and gain factor. For large PZT displacement, small imperfection maximizes gain factor but may not gaurantee, the desired (up or down) displacement direction. For small PZT displacement, large initial imperfection improves performance and guarantees displacement in the (desired) direction of the initial imperfection. The theoretical model, based on the measured initial beam shape, predicts the experimentally measured direction and magnitude of beam displacement for two devices.
Low temperature bonding techniques with high bond strengths and reliability are required for the fabrication and packaging of MEMS devices. Indium and indium-tin based bonding processes are explored for the fabrication of a flextensional MEMS actuator, which requires the integration of lead zirconate titanate (PZT) substrate with a silicon micromachined structure at low temperatures. The developed technique can be used either for wafer or chip level bonding. The lithographic steps used for the patterning and delineation of the seed layer limit the resolution of this technique. Using this technique, reliable bonds were achieved at a temperature of 200°C. The bonds yielded an average tensile strength of 5.41 MPa and 7.38 MPa for samples using indium and indium-tin alloy solders as the intermediate bonding layers respectively. The bonds (with line width of 100 microns) showed hermetic sealing capability of better than 10-11 mbar-l/s when tested using a commercial helium leak tester.