1,720,956 research outputs found
EXPLORING TWISTED STRING ACTUATION FOR APPLICATION IN SOFT ROBOTICS
Get PDFTo make robots more ubiquitous, robotic structures that are compliant, lightweight, and low-cost are desired. Soft robots, which are fabricated using compliant materials and soft actuators, are ideal for such applications. However, producing high-performance soft robots is challenging due to the lack of systematic procedures and inherent limitations of the actuators which drive them. Despite many advances in the field of soft actuators and artificial muscles, the quest for an ideal soft actuator which exhibits sufficient contraction and force generation, while being compact is still an ongoing effort. In an attempt to explore novel actuation techniques for soft robotics, in this dissertation, the employment of twisted string actuation for soft robotic applications is investigated and potential limitations which arise as a consequence are addressed. Due to their tendon-based (muscle-like) linear actuation, high force generation, and high operational bandwidth, twisted string actuators (TSAs) are highly suitable to actuate soft robotic devices with advantages over other soft actuators. TSAs typically generate strains of 30--40% of their untwisted length, exhibit energy efficiency of 75--80%, and can exert more stress than skeletal muscles. Although TSAs have been widely adopted in multiple robotic applications, their inclusion in soft robots has been limited.In this dissertation, the application of TSAs in soft robotic manipulation is explored, in that a soft robotic manipulator is presented. The design of the robot is discussed. A physics-based model is developed to predict the manipulator's kinematic motion. An inverse model is derived to realize open-loop control. The proposed modeling and control approaches were experimentally verified to be effective. While the proposed soft robot exhibited promising performance, there were a few notable limitations due to the soft material and actuation mechanism: Firstly, the usage of soft material resulted in the nonlinear behavior called hysteresis. In addition, termed as lonely stroke, the first input-output cycle of the soft robots was inconsistent with subsequent cycles that were repeatable and exhibited hysteresis. The lonely stroke not only affected the behavior of the hysteretic system, but also presented coupling with the subsequent repeatable hysteresis cycles. As a part of this dissertation, a model to capture and compensate for the hysteresis with lonely stroke property is proposed. A modeling approach is developed through the expansion of the input range of the Preisach operator, a widely adopted hysteresis model, to physically infeasible region. The effectiveness of the proposed scheme was validated by simulation and experimental results.Secondly, most existing studies on control of TSAs assume that the external force applied to the TSA is measurable or predictable. Furthermore, existing studies also assume that all the TSA parameters such as the motor properties and string stiffnesses are accurately known. However, the system parameters could be difficult to measure, could change over time due to general wear and tear, and creep. The external forces applied to the TSA could be difficult to predict or measure. To address these issues, parameter estimation and control strategies were developed for TSAs, assuming {little or} no knowledge about the system parameters. A parameter estimation strategy which utilized the least squares algorithm and gradient algorithm is presented. An adaptive control strategy based on model reference control with feedback linearization is proposed. The developed estimation and control strategies were tested to be effective through simulation.Lastly, the limited strain exhibited by TSAs adversely affected the design and performance of the soft robot. Therefore, it is strongly desirable but challenging to enhance the TSAs' consistent strain generation while maintaining compliance. Existing studies predominantly considered coiling after the regular twisting stage to be undesirable�"non-uniform and unpredictable knots, entanglements, and coils formed to create an unstable and failure-prone structure. Coiling would work well for TSAs when uniform coils can be consistently formed. As a part of this dissertation, we realize uniform and consistent coil formation in coiled TSAs, which greatly increases their strain. Furthermore, we investigate methods for enabling uniform coil formation upon coiling the strings in a TSA and present a procedure to systematically “train” the strings. Coiling resulted in approximately 70% strain in stiff TSAs and approximately 60% strain in compliant TSAs. TSAs capable of operating in the coiling phase were termed as twisted and coiled string (TCS) actuators.To further establish the coiling mechanism as a reliable actuation mode for TCS actuators, the behavior of the TCS actuators in the coiling phase was experimentally characterized. The non-smooth behavior was investigated by using sequences of input motor turns with different frequencies. The hysteretic behavior and the properties of transitioning conditions were examined by applying input cycles with different bandwidths and under multiple loading conditions. Secondly, a physics-based kinematic modeling strategy which utilized the geometry of the coiled strings were developed to capture the behavior of the coiling-induced non-smooth behavior of the TCS actuators. Lastly, the kinematic model was inverted to realize open-loop control of TCS muscles through inverse compensation. The proposed modeling and control strategies were experimentally validated to be efficient
3d Global Acceleration Estimation Using inertial Measurement Unit For Biomechanical Research
Get PDFThe effects of mechanical vibrations on the body of a driver in off-road vehicles such as mining vehicles have become one of the intriguing research topics. To reduce the injuries of the operator of an off-road vehicle where vibrations of high magnitude occur, an indepth study of the nature of these vibrations must be done. The first step towards this objective is the correct estimation of acceleration of the vehicle by taking into consideration all the translational and rotational motion. The main goal of this study is the estimation of acceleration of an off-road vehicle in 3D space using an inertial measurement unit (IMU). In the past biomechanical studies, IMU along with a digital low-pass filter such as Butterworth filter has been used to estimate acceleration, but the estimation was only limited to vertical Z-direction. Also, the use of a low-pass filter requires deciding a threshold frequency by trial and error. In this study, to obtain the best estimate of three-dimensional acceleration, an algorithm is proposed using 3D transformations, Fourier analysis, and magnitude-based filtering methods. The use of magnitude-based filtering eliminates the trial-and-error process of selecting the threshold frequency for filtering and filters out the white noise and other sources of error present in the measurement signal. A preliminary experiment was first conducted in order to check the accuracy of the IMU used in this work. In the experiment, one-dimensional vibrations were produced in the vertical Z-direction using a heavy-duty excitor and the position was estimated using the IMU. The generated vibrations were sinusoidal with a frequency of 3Hz and a peak acceleration of 2.3 m/s2 . The estimated data using the IMU had a peak displacement of 2.38 m/s2 with 3Hz frequency. A final experiment was conducted to verify the proposed algorithm in which a three-dimensional motion including rotation about Z-axis was generated at three different frequencies using a 6-DOF robot (Adept 850s Viper). Based on a detailed error analysis, the final experiment results indicate that the proposed algorithm produces an acceptable degree of accuracy in estimation of 3D global accelerations
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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