48,933 research outputs found

    Dynamics of undeactuated cable-driven parallel robots

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    This thesis focuses on the dynamics of underactuated cable-driven parallel robots (UACDPRs), including various aspects of robotic theory and practice, such as workspace computation, parameter identification, and trajectory planning. After a brief introduction to CDPRs, UACDPR kinematic and dynamic models are analyzed, under the relevant assumption of inextensible cables. The free oscillatory motion of the end-effector (EE), which is a unique feature of underactuated mechanisms, is studied in detail, from both a kinematic and a dynamic perspective. The free (small) oscillations of the EE around equilibria are proved to be harmonic and the corresponding natural oscillation frequencies are analytically computed. UACDPR workspace computation and analysis are then performed. A new performance index is proposed for the analysis of the influence of actuator errors on cable tensions around equilibrium configurations, and a new type of workspace, called tension-error-insensitive, is defined as the set of poses that a UACDPR EE can statically attain even in presence of actuation errors, while preserving tensions between assigned (positive) bounds. EE free oscillations are then employed to conceive a novel procedure aimed at identifying the EE inertial parameters. This approach does not require the use of force or torque measurements. Moreover, a self-calibration procedure for the experimental determination of UACDPR initial cable lengths is developed, which consequently enables the robot to automatically infer the EE initial pose at machine start-up. Lastly, trajectory planning of UACDPRs is investigated. Two alternative methods are proposed, which aim at (i) reducing EE oscillations even when model parameters are uncertain or (ii) eliminate EE oscillations in case model parameters are perfectly known. EE oscillations are reduced in real-time by dynamically scaling a nominal trajectory and filtering it with an input shaper, whereas they can be eliminated if an off-line trajectory is computed that accounts for the system internal dynamics

    Molecular design of precise ionic polymer networks for fundamental structure-property-relationships and energy-related applications

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    Next generation applications such as wearable electronics, roll-up displays, tactile communications, and advanced energy storage require solid electrolytes that are flexible, highly conductive, and stable (mechanically, electrochemically, and environmentally) in their operating environments. However, the current challenge of the field is to achieve solid electrolytes with high stability and "liquid-like" ionic conductivity. In this dissertation, two model systems of network ionic polymers (nIPs) are carefully designed and investigated on how molecular structures affect their functional properties such as ionic conductivity, glass transition, and modulus. A highly conductive yet self-standing solid electrolyte was also designed to serve as the electrolyte material for dopant-free soft actuators and high temperature and voltage stable solid-state supercapacitors. The ammonium nIPs were synthesized by step-growth polymerization between trifunctional amine and dibromo species to form networks with ammonium cation fixed on the polymer backbone. The Br- anions were later exchanged to bis(trifluoromethanesulfonyl)imide (TFSI) and BF4 mobile anions. In this system, we have systematically demonstrated that the extent of ion exchange has a significant impact on the conductivity and thermal stability of the final material, with minimal changes in the glass transition temperature (Tg). In addition, when the linker of the ammonium nIPs is varied precisely, we observe an odd-even effect in the Tg; specifically, the Tgs follow a zig-zag trend as the linker switches between odd and even linker lengths. This effect causes the room temperature conductivity of these nIPs to vary by 1 to 2 orders of magnitude. The second model system consists of fixed TFSI like anion and Li+ mobile cation. Network structures such as crosslinking density, polymer backbone, and crosslinker length have a significant impact on the polymer dynamic (represented by Tg) and further affect the ionic conductivity of the Li+ conducting nIPs. At low crosslinking density (<8%), decoupling was observed where the modulus is increased by 8 times without affecting the ionic conductivity as the network Tgs stabilize at low crosslinking density. Other molecular parameters such as ion concentration and coordination environment are also shown to play a role in the ion conduction capability through more complex pathways. To improve the existing ionic polymer soft actuator and demonstrate the unique advantage of nIP electrolyte, an imidazolium-based nIP with TFSI mobile anion was designed and synthesized. This class of nIP electrolyte is self-standing with a modulus at the MPa range and conductivities comparable to linear low Tg ionic polymers (10-5 S/cm). When integrated with single-wall carbon nanotube (SWCNT) electrodes, a dopant-free soft actuator was fabricated with bending strain (0.9%) comparable to current state-of-the-art small molecule doped systems. Compared to the traditional salt solution doped ionic polymer-metal composite actuator, prolonged cyclability was observed due to the high electrochemical stability (3V) and no leakage of the electrolyte materials. Polar ethylene oxide polymer matrix and lower crosslinking density were shown to increase the conductivity and lower the modulus of the electrolyte, which ultimately contributed to the high performance of the device. When the flexible electrolyte was combined with flexible reduced graphene oxide (r-GO) polymer composite electrodes, a flexible, solid-state supercapacitor was fabricated. The high electrochemical and thermal stability of the nIP allowed the device to be charged to 3V at temperatures as high as 120 ňöC. These operating conditions are not possible with traditional salt solution electrolytes. The device shows an excellent specific capacitance of 300 F/g with respect to the mass of active materials. Furthermore, due to the mechanical flexibility of all the components, the device sustains performance when deformed to 180 degrees.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

    Towards Autonomous Selective Harvesting: A Review of Robot Perception, Robot Design, Motion Planning and Control

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    This paper provides an overview of the current state-of-the-art in selective harvesting robots (SHRs) and their potential for addressing the challenges of global food production. SHRs have the potential to increase productivity, reduce labour costs, and minimise food waste by selectively harvesting only ripe fruits and vegetables. The paper discusses the main components of SHRs, including perception, grasping, cutting, motion planning, and control. It also highlights the challenges in developing SHR technologies, particularly in the areas of robot design, motion planning and control. The paper also discusses the potential benefits of integrating AI and soft robots and data-driven methods to enhance the performance and robustness of SHR systems. Finally, the paper identifies several open research questions in the field and highlights the need for further research and development efforts to advance SHR technologies to meet the challenges of global food production. Overall, this paper provides a starting point for researchers and practitioners interested in developing SHRs and highlights the need for more research in this field.Comment: Preprint: to be appeared in Journal of Field Robotic

    Stable Real-Time Feedback Control of a Pneumatic Soft Robot

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    Soft actuators offer compliant and safe interaction with an unstructured environment compared to their rigid counterparts. However, control of these systems is often challenging because they are inherently under-actuated, have infinite degrees of freedom (DoF), and their mechanical properties can change by unknown external loads. Existing works mainly relied on discretization and reduction, suffering from either low accuracy or high computational cost for real-time control purposes. Recently, we presented an infinite-dimensional feedback controller for soft manipulators modeled by partial differential equations (PDEs) based on the Cosserat rod theory. In this study, we examine how to implement this controller in real-time using only a limited number of actuators. To do so, we formulate a convex quadratic programming problem that tunes the feedback gains of the controller in real time such that it becomes realizable by the actuators. We evaluated the controller's performance through experiments on a physical soft robot capable of planar motions and show that the actual controller implemented by the finite-dimensional actuators still preserves the stabilizing property of the desired infinite-dimensional controller. This research fills the gap between the infinite-dimensional control design and finite-dimensional actuation in practice and suggests a promising direction for exploring PDE-based control design for soft robots

    Filament extrusion-based additive manufacturing of NiTi shape memory alloys

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    Integrated additive manufacturing of actuators based on active materials could potentially replace conventional motors in numerous applications across disciplines like biomedical engineering, robotics, or aerospace. In this work, extrusion-based additive manufacturing of functional NiTi shape memory alloys is demonstrated via 3D printing of filaments consisting of thermoplastic binder and metal powder. Two alloys are fabricated, one showing superelastic, the other showing shape memory properties at room temperature. The microstructures of both alloys are characterized and set into perspective with the measured thermo-mechanical properties. The 3D-printed NiTi showed a shape memory strain of 1.9 %, respectively a superelastic strain of 1.3 % for an applied strain of 4 %. To enlarge the shape memory strain actuator geometries are designed, fabricated, and tested. The results of this study may find application in the field of additive manufacturing of active structures, also referred to as 4D printing. Commonly, polymeric materials are used in such structures, which often suffer from poor mechanical properties and durability. The use of metallic materials as it is investigated in this work could help to overcome these limitations.ISSN:0264-1275ISSN:1873-419

    Improved Surge Predictions for a Turbocharger Compression System

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    To address the growing concerns of greenhouse gas emissions, automotive manufacturers are improving the fuel conversion efficiency of their engines by downsizing and turbocharging them. However, the low flow instability phenomenon known as surge, exhibited by the compression system of a turbocharger, limits the fuel economy benefits of a turbocharged engine. A computational model of the unsteady surge behavior, characterized by self-excited oscillations of pressure and flow rate, has been developed for a one-dimensional engine simulation code to predict varying degrees of surge and help the design and development of engines. A compressor map preprocessor extrapolates and interpolates experimental bench measurements to facilitate the predictions of mild and deep surge. The model has been improved by adjusting the compressor map generation algorithm to account for nonuniformities in the flow field of the compressor inlet duct at low velocities. The level of improvement the new model provides is determined by comparing predictions of the stable operating limit and the transition from mild to deep surge with the earlier model and experimental data. The predicted amplitude and time-averaged values of flow rate and pressure in deep and especially mild surge are closer to the experimental observations using the new model. The flow rates at which mild surge oscillations begin, and where they are greatest, are distinctly lower in the new model, locating the operating points closer to the true surge line of the experimental compressor map. While the improvement to deep surge predictions is less pronounced, the time-averaged flow rate and pressure fluctuations still are closer to the experimental results. Hence, demonstrated by a comparison to an earlier model and experimental measurements, the improved predictions of surge from the new model captures better the underlying physics of the undesired and detrimental instability modes. The new model will be incorporated into engine simulation codes to improve their accuracy, thereby facilitating more efficient energy conversion devices to better suit the needs of society.No embargoAcademic Major: Mechanical Engineerin

    Variable optical elements for fast focus control

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    In this Review, we survey recent developments in the emerging field of high-speed variable-z-focus optical elements, which are driving important innovations in advanced imaging and materials processing applications. Three-dimensional biomedical imaging, high-throughput industrial inspection, advanced spectroscopies, and other optical characterization and materials modification methods have made great strides forward in recent years due to precise and rapid axial control of light. Three state-of-the-art key optical technologies that enable fast z-focus modulation are reviewed, along with a discussion of the implications of the new developments in variable optical elements and their impact on technologically relevant applications
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