A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Control of a Heavy-Lift Robotic Manipulator with Pneumatic Artificial Muscles(MDPI, 2014-04-24) Robinson, Ryan M.; Kothera, Curt S.; Wereley, Norman M.Lightweight, compliant actuators are particularly desirable in robotic systems intended for interaction with humans. Pneumatic artificial muscles (PAMs) exhibit these characteristics and are capable of higher specific work than comparably-sized hydraulic actuators and electric motors. The objective of this work is to develop a control algorithm that can smoothly and accurately track the desired motions of a manipulator actuated by pneumatic artificial muscles. The manipulator is intended for lifting humans in nursing assistance or casualty extraction scenarios; hence, the control strategy must be capable of responding to large variations in payload over a large range of motion. The present work first investigates the feasibility of two output feedback controllers (proportional-integral-derivative and fuzzy logic), but due to the limitations of pure output feedback control, a model-based feedforward controller is developed and combined with output feedback to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the physical parameters of the pneumatic muscles and the manipulator dynamics. Simulations were performed in order to validate the control algorithms, guide controller design and predict optimal gains. Using real-time interface software and hardware, the controllers were implemented and experimentally tested on the manipulator, demonstrating the improved capability.Item Extensile Fluidic Artificial Muscles in Payload-Carrying Continuum Soft Robots(2023) Garbulinski, Jacek; Wereley, Norman M.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intrinsically actuated continuum soft robots merge the features of hyper-redundant and soft robots. The soft structure and redundancy allow the robots to conduct tasks in confined or unstructured environments. Extensile fluidic artificial muscles (EFAMs) can be used to construct soft actuated structures that feature large deformation and enable the robots to access large reachable workspaces. However, the soft robots’ low structural stiffness limits their ability to exert force or carry payloads. This dissertation aims to improve the continuum soft robot's spatial and payload-carrying performance. The work seeks to accomplish the following: 1. Compare multi-segment continuum robots to understand how the number of segments and robot geometry affect their spatial performance.2. Experimentally characterize and model EFAMs to close existing knowledge gaps in their axial and bending behaviors. 3. Investigate the impact of radial reinforcement on the payload-carrying ability of an EFAM robot. 4. Propose a modeling approach that captures the deformation of the robot under payloads.Item Pneumatic Artificial Muscle Actuators for Compliant Robotic Manipulators(2014) Robinson, Ryan Michael; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Robotic systems are increasingly being utilized in applications that require interaction with humans. In order to enable safe physical human-robot interaction, light weight and compliant manipulation are desirable. These requirements are problematic for many conventional actuation systems, which are often heavy, and typically use high stiffness to achieve high performance, leading to large impact forces upon collision. However, pneumatic artificial muscles (PAMs) are actuators that can satisfy these safety requirements while offering power-to-weight ratios comparable to those of conventional actuators. PAMs are extremely lightweight actuators that produce force in response to pressurization. These muscles demonstrate natural compliance, but have a nonlinear force-contraction profile that complicates modeling and control. This body of research presents solutions to the challenges associated with the implementation of PAMs as actuators in robotic manipulators, particularly with regard to modeling, design, and control. An existing PAM force balance model was modified to incorporate elliptic end geometry and a hyper-elastic constitutive relationship, dramatically improving predictions of PAM behavior at high contraction. Utilizing this improved model, two proof-of-concept PAM-driven manipulators were designed and constructed; design features included parallel placement of actuators and a tendon-link joint design. Genetic algorithm search heuristics were employed to determine an optimal joint geometry; allowing a manipulator to achieve a desired torque profile while minimizing the required PAM pressure. Performance of the manipulators was evaluated in both simulation and experiment employing various linear and nonlinear control strategies. These included output feedback techniques, such as proportional-integral-derivative (PID) and fuzzy logic, a model-based control for computed torque, and more advanced controllers, such as sliding mode, adaptive sliding mode, and adaptive neural network control. Results demonstrated the benefits of an accurate model in model-based control, and the advantages of adaptive neural network control when a model is unavailable or variations in payload are expected. Lastly, a variable recruitment strategy was applied to a group of parallel muscles actuating a common joint. Increased manipulator efficiency was observed when fewer PAMs were activated, justifying the use of variable recruitment strategies. Overall, this research demonstrates the benefits of pneumatic artificial muscles as actuators in robotics applications. It demonstrates that PAM-based manipulators can be well-modeled and can achieve high tracking accuracy over a wide range of payloads and inputs while maintaining natural compliance.Item Analysis of Nonlinear Behavior in Novel Pneumatic Artificial Muscles(2012) Hocking, Erica Grace; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Motivated by the excellent actuator characteristics of pneumatic artificial muscles (PAMs), two novel actuators based on this technology were developed for applications where traditional PAMs are not suitable. The first of these actuators is a miniature PAM that possesses the same operating principle as a full-scale contractile PAM, but with a diameter an order of magnitude smaller. The second actuator, a push-PAM, harnesses the operational characteristics of a contractile PAM, but changes the direction of motion and force with a simple conversion package. Testing on these actuators revealed each PAM's evolution of force with displacement for a range of operating pressures. To address the analysis of the nonlinear response of these PAMs, a nonlinear stress vs. strain model, a hysteresis model, and a pressure deadband were introduced into a previously developed force balance analysis. The refined nonlinear model was shown to reconstruct PAM response with higher accuracy than previously possible.Item HIGHLY EXTENSIBLE SKIN FOR A VARIABLE WING-SPAN MORPHING AIRCRAFT UTILIZING PNEUMATIC ARTIFICIAL MUSCLE ACTUATION.(2009) Bubert, Edward Adams; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Two different technologies are demonstrated for a span-morphing wingtip: a linear controller for a pneumatic artificial muscle (PAM) actuator, and a passive 1-D morphing skin. A generic PAM system incorporating a single PAM working against a nonlinear spring is described in a Simulink model, which is validated using experimental data. A linear PID controller is then incorporated into the model. Frequency responses are obtained by both simulation and experiment, and the ability to track relatively high frequency control inputs is demonstrated. The morphing skin system includes an elastomer-fiber-composite surface layer that is supported by a flexible honeycomb structure, each of which exhibit a near-zero in-plane Poisson's ratio. Composite skin and substructure configurations are designed using analytical methods and downselected after experimental evaluation. A complete prototype morphing skin, mated to a PAM driven extension mechanism, demonstrates 100% uniaxial extension accompanied by a 100% increase in surface area. Out-of-plane deflections under surface pressures up to 200 psf (9.58 kPa) are reported at varying levels of area change.