Research

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Monolithic systems lab creates synthesis, analysis and manufacturing tools for soft mechanical systems. Traditional machines with rigid links, joints and heavy actuators are designed using centuries-old knowledge often marked by a systems approach where kinematics, actuation and passive dynamics are decoupled. In contrast, bio-inspired soft mechanical systems have inherently coupled behavior, and extracting design methods pose a unique challenge. Read on understand past and current projects.

(1) Design of Soft wearable robots (in collaboration with Prof. Elizabeth Hsiao-Wecksler, MechSE). This project has two main goals: to develop novel high-force, energy storing, miniature soft pneumatic actuators, and to directly integrate them as the structure for soft robotic upper extremity orthoses for pediatric patients that use crutches for ambulation. While walking with crutches, peak loads observed in the wrist typically approach 50% of body weight and wrist postures experience extreme extension angles ~35°. These repetitive, high loads and poor wrist postures have been shown to lead to joint pain and injury, carpal tunnel syndrome, arthritis, or joint deformity. Currently, the natural progression finds pediatric crutch users often transitioning to using wheelchairs, as their arms cannot support their body weight as they grow and the effects of these secondary injuries become unsustainable. This transition reduces mobility, fitness, and quality of life. Creating an effective orthosis would be beneficial for these pediatric patients or any assistive mobility device users, whom are susceptible to overuse injury and pain (those with acute limb injury or surgery, elderly, adult pathology populations).

We seek to develop a light-weight (< 1 kg), pliable (tunable modulus of rigidity), powered (by <100 psi) wrist orthosis and integrated compact actuators to reduce these transient loads and associated wrist stresses by 50% and improve wrist posture to a more neutral position; therefore lowering the risk for joint injury such as carpal tunnel syndrome, while allowing for normal wrist and arm range of motion when not used for load bearing. We will expand the range and functionality of current contracting McKibben muscles, which are based on simple equal and opposite fibers, by developing a robust analysis framework to generalize the construction and operating principles for FREE actuators to yield different deformation patterns.

Personnel: Gaurav Singh

Sponsor: NSF ERC for Compact and Efficient Fluid Power

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(2) Analysis and Synthesis of Fiber Reinforced Elastomeric Enclosures: This project investigates the fundamental building blocks for soft mechanical systems known as the Fiber Reinforced Elastomeric Enclosure (FREEs). Fiber Reinforced Elastomeric Enclosures (FREEs) and are based in design and construction to the popular Pneumatic Artificial Muscles (PAM) or McKibben actuators. They constitute a hollow elastomeric core on which two families of helical fibers are reinforced. While in PAMs and their composite variants the two families of fibers are antisymmetric (see Figure below), FREEs permit arbitrary variation of fiber orientations. This not only broadens the design space, but also enables several spatial motion patterns that are otherwise unattainable with conventional actuators. This project deals with developing reduced order models that are amenable for quick synthesis of FREEs based on their kinematic and kinetostatic properties.

Personnel: Gaurav Singh

Sponsor: NSF ERC for Compact and Efficient Fluid Power and NSF CMMI-1454276

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(3) BR2 Soft Spatial Manipualtor: Soft pneumatic continuum manipulators are increasingly popular because of their ability to interact safely with humans, maneuver around obstacles and enable cost-effective operation. However, to increase their workspace, state-of-the-art soft manipulators are composed of independently controllable modular or serial segments that are complex to manufacture and integrate. Furthermore, they suffer from increased inertial effects and reduced load-bearing ability. This paper presents the design and forward analysis of a first-of-its-kind purely parallel manipulator BR2, (one bending mode and two rotation modes) which is capable of spatial motion. This manipulator uses a repertoire of deformation patterns that are obtainable from novel pneumatic actuators known as Fiber Reinforced Elastomeric Enclosures (FREEs). Experimental characterization of the manipulator reveals the importance of a “coupling effect”, where the deformation mode of one actuator is restricted by the other. The inclusion of this effect along with gravity and other external forces is used predict the workspace of manipulator with reasonable accuracy.

Personnel: Naveen Kumar Uppalapati, Hugo Friere and Xiaotian Zhang

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(4) Mobility analysis of Flexure systems and Soft Mechanical Systems using Load Flow Visualization: Mobility analysis is an important step in the conceptual design of flexure systems. It involves identifying directions with unrestricted motion (freedoms) and those that are constrained. This paper proposes a unique framework for mobility analysis of wire flexures by characterizing a kinetostatic vector field known as “load flow” through its geometry. The relationship between load flow and the flexure axis is used to determine if a flexure behaves as a constraint or a freedom. This knowledge is utilized to formulate a matrix-based reduction technique to determine flexure mobility in an automated fashion. Several examples with varying complexity are illustrated to validate the efficacy of this technique. This technique is particularly useful in analyzing complex hybrid flexure topologies, which may be non-intuitive or involved with traditional methods. This is illustrated through the automated mobility analysis of a bio-inspired fiber reinforced elastomer pressurized with fluids. The proposed framework combines both visual insight and analytical rigor, and will complement existing analysis and synthesis techniques.

Personnel: Sreeshankar Satheeshbabu

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(5) Design of Distributed Compliant Mechanisms using System-Level and Continuum-Level Design Maps : The objective of the project is to create a unifying framework for the synthesis of distributed compliant mechanisms by systematically channeling flow of information between the system-level and continuum-level phases in the design process. This flow of information is envisioned through two global design space maps that uniquely represent any compliant mechanism, namely (a) System Design Space (SDS) that characterizes the lumped system-level attributes, and a (b) Continuum Design Space (CDS) that characterizes topological, material and manufacturing attributes. The flow of information between the SDS and CDS will (i) enable objective comparison of several potential conceptual solutions based on inherent attributes that define the design space map, (ii) ascertain feasibility and existence of a solution by juxtaposing the problem specifications with these inherent attributes, (iii) enable synthesis of new designs at the system and continuum level by combining several sub-systems, (iv) set guidelines for systematic redesign of an existing solution to improve feasibility.

The theoretical underpinnings of the SDS and CDS will be enabled by three system and continuum level models namely, (a) Spring-Mass Lever model (SML) that characterizes the lumped behavior of any arbitrary compliant mechanism (b) a kinetostatic representation based on Load Flow Visualization that maps topological constituents of a compliant mechanism to its functionality and (c) a Distributed Compliance Metric that characterizes the state of stress distribution of the compliant mechanism.

Personnel: Sreekalyan Patiballa and John Shanley


(6) Nonlinear Spring Synthesis for Orthotic Brace (with Adicep Inc): Recent research indicates that utilization of nonlinear mechanical energy storage devices (i.e. springs) can fundamentally change rehabilitative/assistive device architectures in ways that result in benefits not previously possible. Currently, no unified theory or design methodology exists that can help researchers in assistive devices create nonlinear springs. Moreover, commercially available nonlinear springs limit rather than enable their research. This proposal seeks to develop a design framework for creating distributed-compliance energy storage devices by researchers in assistive devices that addresses this problem. The proposed innovation is to incorporate the constant-stress hypothesis in synthesizing springs made of compliant members that undergo large deformation compared to their overall size. These synthesized springs must meet specified force/displacement functions satisfying fatigue and manufacturing requirements (e.g. weight, size, maximum stress).

Four tasks involving basic and applied research are planned. The basic tasks are (1) quantify and evaluate distributed compliance from the fundamentals of continuum mechanics and (2) create a design framework for synthesizing energy storage devices given user specifications; the applied tasks include (3) create a real-world nonlinear torsion spring for use in an orthosis and (4) develop a practical scheme for field adjusting the weight handling capability of the spring element in a lower-limb orthosis

Personnel: Sreekalyan Patiballa and John Shanley

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