2015)Design and control methodology of a 3-DOF flexure-based mechanism for micro/nanopositioning. Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way.
A stick-slip based linear actuator was proposed in this paper, which applied the axial motion of the micropositioner to adjust the preload, and the lateral motion to drive the slider. The bi-directional motion of the micropositioner was realized through the asymmetric structure of a flexure-based mechanism, which includes two right circular flexure hinges and four leaf-spring flexure hinges. The static analysis, kinematic analysis and optimization design were successively implemented on the flexure-based mechanism. The Finite Element Analysis (FEA) proved the flexure-based mechanism could generate the bi-directional motion as designed. A prototype of the linear actuator was developed and the measuring system was constructed. A modified sawtooth wave with a cycloid fall curve was designed to improve the output property. The experimental results showed the modified sawtooth wave generated larger velocity than the traditional sawtooth wave in same driving voltages, fall times, driving frequencies and loads. The amplification coefficient and resolution of the proposed linear actuator in single step were 3.16 and 60 nm, respectively. The maximal velocity was 26.2 mm/s with the modified sawtooth wave in driving frequency of 500 Hz.
Based on the self-developed three dimensional micro/nano machining system, the effects of machining parameters and sample material on micro/nano machining are investigated. The micro/nano machining system is mainly composed of the probe system and micro/nano positioning stage. The former is applied to control the normal load and the latter is utilized to realize high precision motion in the xy plane. A sample examination method is firstly introduced to estimate whether the sample is placed horizontally. The machining parameters include scratching direction, speed, cycles, normal load and feed. According to the experimental results, the scratching depth is significantly affected by the normal load in all four defined scratching directions but is rarely influenced by the scratching speed. The increase of scratching cycle number can increase the scratching depth as well as smooth the groove wall. In addition, the scratching tests of silicon and copper attest that the harder material is easier to be removed. In the scratching with different feed amount, the machining results indicate that the machined depth increases as the feed reduces. Further, a cubic polynomial is used to fit the experimental results to predict the scratching depth. With the selected machining parameters of scratching direction d3/d4, scratching speed 5μm/s and feed 0.06μm, some more micro structures including stair, sinusoidal groove, Chinese character "田", "TJU" and Chinese panda have been fabricated on the silicon substrate.
The day-to-day dynamics of commuter decisions on urban traffic networks induced by route-choice dynamics is investigated. More specifically, this investigation analyzes the stability and reliability of system performance due to route-choice dynamics under real-time information, relaxing key restrictions associated with user equilibrium models. A simulation-based framework is developed to analyze day-to-day dynamics by integrating an empirically calibrated model of route-choice decisions with a dynamic network assignment model. Computational experiments are used to investigate the effect of certain experimental factors—recurrent network congestion level, market penetration, nature of information, and frequency of information updates—on network performance stability and reliability. The findings provide evidence of considerable day-to-day variations and stochasticity in network flows and performance, even when departure-time decisions and the origin-destination matrix are assumed to be fixed. The results indicate that (a) network performance may deviate significantly from equilibrium because of route-choice decisions under information; (b) within-day route choices have a significant effect on day-to-day network flow evolution; (c) user equilibrium path flows may not be reached or may not be stable when uncoordinated route-choice decisions are made under real-time information; (d) route-choice decisions do not exhibit convergence to an equilibrium, although the switching rate may be near steady-state conditions; (e) advanced traveler information systems (ATIS) information strategies can affect both within-day and day-to-day dynamics; and (f) some information strategies can lead to improved reliability and stability but at the expense of longer trip times. The results indicate that the trade-off between trip time performance and stability must be considered in network analysis and design. These results have important implications for the design of traffic control strategies, more-effective ATIS implementation guidelines, and incident management strategies.
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