742 research outputs found
Compliant, Large-Strain, and Self-Sensing Twisted String Actuators with Applications to Soft Robots
The twisted string actuator (TSA) is a rotary-to-linear transmission system that has been implemented in robots for high force output and efficiency. The basic components of a TSA are a motor, strings, and a load (to keep the strings in tension). The twisting of the strings shortens their length to generate linear contraction. Due to their high force output, energy efficiency, and compact form factor, TSAs hold the potential to improve the performance of soft robots. Currently, it is challenging to realize high-performance soft robots because many existing soft or compliant actuators exhibit limitations such as fabrication complexity, high power consumption, slow actuation, or low force generation. The applications of TSAs in soft robots have hitherto been limited, mainly for two reasons. Firstly, the conventional strings of TSAs are stiff and strong, but not compliant. Secondly, precise control of TSAs predominantly relies on external position or force sensors. For these reasons, TSA-driven robots are often rigid or bulky.To make TSAs more suitable for actuating soft robots, compliant, large-strain, and self-sensing TSAs are developed and applied to various soft robots in this work. The design was realized by replacing conventional inelastic strings with compliant, thermally-activated, and conductive supercoiled polymer (SCP) strings. Self-sensing was realized by correlating the electrical resistance of the strings with their length. Large strains are realized by heating the strings in addition to twisting them. The quasi-static actuation and self-sensing properties are accurately captured by Preisach hysteresis operators. Next, a data-driven mathematical model was proposed and experimentally validated to capture the transient decay, creep, and hysteretic effects in the electrical resistance. This model was then used to predict the length of the TSA, given its resistance. Furthermore, three TSA-driven soft robots were designed and fabricated: a three-fingered gripper, a soft manipulator, and an anthropomorphic gripper. For the three-fingered gripper, its fingers were compliant and designed to exploit the Fin Ray Effect for improved grasping. The soft manipulator was driven by three TSAs that allowed it to bend with arbitrary magnitude and direction. A physics-based modeling strategy was developed to predict this multi-degree-of-freedom motion. The proposed modeling approaches were experimentally verified to be effective. For example, the proposed model predicted bending angle and bending velocity with mean errors of 1.58 degrees (2.63%) and 0.405 degrees/sec (4.31%), respectively. The anthropomorphic gripper contained 11 TSAs; two TSAs were embedded in each of the four fingers and three TSAs were embedded in the thumb. Furthermore, the anthropomorphic gripper achieved tunable stiffness and a wide range of grasps
Overtwisting and Coiling Highly Enhances Strain Generation of Twisted String Actuators
Twisted string actuators (TSAs) have exhibited great promise in robotic
applications by generating high translational force with low input torque. To
further facilitate their robotic applications, it is strongly desirable but
challenging to enhance their consistent strain generation while maintaining
compliance. Existing studies predominantly considered overtwisting and 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. Overtwisting would work well for TSAs when uniform
coils can be consistently formed. In this study, we realize uniform and
consistent coil formation in overtwisted TSAs, which greatly increases their
strain. Furthermore, we investigate methods for enabling uniform coil formation
upon overtwisting the strings in a TSA and present a procedure to
systematically "train" the strings. To the authors' best knowledge, this is the
first study to experimentally investigate overtwisting for TSAs with different
stiffnesses and realize consistent uniform coil formation. Ultra-high
molecular-weight polyethylene (UHMWPE) strings form the stiff TSAs whereas
compliant TSAs are realized with stretchable and conductive supercoiled polymer
(SCP) strings. The strain, force, velocity, and torque of each overtwisted TSA
was studied. Overtwisting and coiling resulted in approximately 70% strain in
stiff TSAs and approximately 60% strain in compliant TSAs. This is more than
twice the strain achieved through regular twisting. Lastly, the overtwisted TSA
was successfully demonstrated in a robotic bicep
Anthropomorphic Twisted String-Actuated Soft Robotic Gripper with Tendon-Based Stiffening
Realizing high-performance soft robotic grippers is challenging because of
the inherent limitations of the soft actuators and artificial muscles that
drive them, including low force output, small actuation range, and poor
compactness. Despite advances in this area, realizing compact soft grippers
with high dexterity and force output is still challenging. This paper explores
twisted string actuators (TSAs) to drive a soft robotic gripper. TSAs have been
used in numerous robotic applications, but their inclusion in soft robots has
been limited. The proposed design of the gripper was inspired by the human
hand. Tunable stiffness was implemented in the fingers with antagonistic TSAs.
The fingers' bending angles, actuation speed, blocked force output, and
stiffness tuning were experimentally characterized. The gripper achieved a
score of 6 on the Kapandji test and recreated 31 of the 33 grasps of the Feix
GRASP taxonomy. It exhibited a maximum grasping force of 72 N, which was almost
13 times its own weight. A comparison study revealed that the proposed gripper
exhibited equivalent or superior performance compared to other similar soft
grippers.Comment: 19 pages, 15 figure
Versatile spaceborne photonics with chalcogenide phase-change materials
Recent growth in space systems has seen increasing capabilities packed into
smaller and lighter Earth observation and deep space mission spacecraft.
Phase-change materials (PCMs) are nonvolatile, reconfigurable, fast-switching,
and have recently shown a high degree of space radiation tolerance, thereby
making them an attractive materials platform for spaceborne photonics
applications. They promise robust, lightweight, and energy-efficient
reconfigurable optical systems whose functions can be dynamically defined
on-demand and on orbit to deliver enhanced science or mission support in harsh
environments on lean power budgets. This comment aims to discuss the recent
advances in rapidly growing PCM research and its potential to transition from
conventional terrestrial optoelectronics materials platforms to versatile
spaceborne photonic materials platforms for current and next-generation space
and science missions. Materials International Space Station Experiment-14
(MISSE-14) mission-flown PCMs outside of the International Space Station (ISS)
and key results and NASA examples are highlighted to provide strong evidence of
the applicability of spaceborne photonics.Comment: 16 pages, 4 figure
ALICE Central Trigger System for LHC Run 3
A major upgrade of the ALICE experiment is in progress and will result in
high-rate data taking during LHC Run 3 (2022-2024). The LHC interaction rate at
Point 2 where the ALICE experiment is located will be increased to $50\
\mathrm{kHz}1\ \mathrm{MHz}$ in pp collisions. The
ALICE experiment will be able to read out data at these interaction rates
leading to an increase of the collected luminosity by a factor of up to about
100 with respect to LHC Runs 1 and 2. To satisfy these requirements, a new
readout system has been developed for most of the ALICE detectors, allowing the
full readout of the data at the required interaction rates without the need for
a hardware trigger selection. A novel trigger and timing distribution system
will be implemented, based on Passive Optical Network (PON) and GigaBit
Transceiver (GBT) technology. To assure backward compatibility a triggered mode
based on RD12 Trigger-Timing-Control (TTC) technology, as used in the previous
LHC runs, will be maintained and re-implemented under the new Central Trigger
System (CTS). A new universal ALICE Trigger Board (ATB) based on the Xilinx
Kintex Ultrascale FPGA has been designed to function as a Central Trigger
Processor (CTP), Local Trigger Unit (LTU), and monitoring interfaces.
In this paper, this new hybrid multilevel system with continuous readout will
be described, together with the triggering mechanism and algorithms. An
overview of the CTS, the design of the ATB and the different communication
protocols will be presented.Comment: 10 pages, 6 figures, submitted as a proceedings paper for 25th
International Conference on Computing in High-Energy and Nuclear Physics
(vCHEP 2021) to European Physical Journal (EPJ) Web of Conferences, May
17th-2th 2021, v2: corrected institution lis
Quinta-Gamelin Community Center: Architectural Design
The new facility will add meeting space for many of community organizations and sport leagues as well as people interested in renting the gymnasium and meeting rooms. Last year our community center gymnasium was given out 192 times on an average of two hours each, our meeting room was given out 68 times. Similar towns rent these facilities at approximately $15.00 an hour
Measurement of charm production at central rapidity in proton-proton collisions at TeV
The -differential production cross sections of the prompt (B
feed-down subtracted) charmed mesons D, D, and D in the rapidity
range , and for transverse momentum GeV/, were
measured in proton-proton collisions at TeV with the ALICE
detector at the Large Hadron Collider. The analysis exploited the hadronic
decays DK, DK, DD, and their charge conjugates, and was performed on a
nb event sample collected in 2011 with a
minimum-bias trigger. The total charm production cross section at TeV and at 7 TeV was evaluated by extrapolating to the full phase space
the -differential production cross sections at TeV
and our previous measurements at TeV. The results were compared
to existing measurements and to perturbative-QCD calculations. The fraction of
cdbar D mesons produced in a vector state was also determined.Comment: 20 pages, 5 captioned figures, 4 tables, authors from page 15,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/307
Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC
Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe
Azimuthal anisotropy of charged jet production in root s(NN)=2.76 TeV Pb-Pb collisions
We present measurements of the azimuthal dependence of charged jet production in central and semi-central root s(NN) = 2.76 TeV Pb-Pb collisions with respect to the second harmonic event plane, quantified as nu(ch)(2) (jet). Jet finding is performed employing the anti-k(T) algorithm with a resolution parameter R = 0.2 using charged tracks from the ALICE tracking system. The contribution of the azimuthal anisotropy of the underlying event is taken into account event-by-event. The remaining (statistical) region-to-region fluctuations are removed on an ensemble basis by unfolding the jet spectra for different event plane orientations independently. Significant non-zero nu(ch)(2) (jet) is observed in semi-central collisions (30-50% centrality) for 20 <p(T)(ch) (jet) <90 GeV/c. The azimuthal dependence of the charged jet production is similar to the dependence observed for jets comprising both charged and neutral fragments, and compatible with measurements of the nu(2) of single charged particles at high p(T). Good agreement between the data and predictions from JEWEL, an event generator simulating parton shower evolution in the presence of a dense QCD medium, is found in semi-central collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
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