219,674 research outputs found
Three Roller Curvature Scotch Straightening Mechanism Study and System Design
AbstractDuring the process of straightening, hot rolled deformed bars rotate around autologous axis, which cause out of the vertical of straightening surface and the straightening precision is deduced. To solve the problem of the bars's rotation , parallel roller collocation scheme of hot rolled deformed bars with high speed and no scratches is presented. Based on the theory of elastoplasticity large deformation, elastic recovery torque variety during the setting out of coiled bars is analyzed in accordance with the triple-roller equal curvature rotation blocking straightening system. The mechanical model of bars in triple-roller is established and rotation blocking mechanism of the triple-roller equal curvature rotation blocking straightening system is researched. The results indicate that the system has the effect of consistent original curvature and rotation blocking toguarantee straightening precision and supply the demand of operation
Error modelling and validation of a high-precision five degree of freedom hybrid mechanism for high-power high-repetition rate laser operations
The accuracy, repeatability and speed requirements of high-power laser operations demand the employment of five degree of freedom motion control solutions that are capable of positioning and orientating the target with respect to the laser(s)-target interaction point with high accuracy and precision. The combined serial and parallel kinematic (hybrid) mechanism reported in this paper is a suitable candidate for this purpose; however, a number of error sources can affect its performance. A kinematic model to analyse the errors causing the positional and orientational deviations of the target is described considering two rotational degrees of freedom of the hybrid mechanism. Strategies are outlined to simplify the error analysis and to determine the error parameters of the mechanism using the error model and an experimental technique
A novel monolithic piezoelectric actuated flexure-mechanism based wire clamp for microelectronic device packaging
A novel monolithic piezoelectric actuated wire clamp is presented in this paper to achieve fast, accurate, and robust microelectronic device packaging. The wire clamp has compact, flexure-based mechanical structure and light weight. To obtain large and robust jaw displacements and ensure parallel jaw grasping, a two-stage amplification composed of a homothetic bridge type mechanism and a parallelogram leverage mechanism was designed. Pseudo-rigid-body model and Lagrange approaches were employed to conduct the kinematic, static, and dynamic modeling of the wire clamp and optimization design was carried out. The displacement amplification ratio, maximum allowable stress, and natural frequency were calculated. Finite element analysis (FEA) was conducted to evaluate the characteristics of the wire clamp and wire electro discharge machining technique was utilized to fabricate the monolithic structure. Experimental tests were carried out to investigate the performance and the experimental results match well with the theoretical calculation and FEA. The amplification ratio of the clamp is 20.96 and the working mode frequency is 895 Hz. Step response test shows that the wire clamp has fast response and high accuracy and the motion resolution is 0.2 ÎĽm. High speed precision grasping operations of gold and copper wires were realized using the wire clamper
Miniaturized modular manipulator design for high precision assembly and manipulation tasks
In this paper, design and control issues for the development of miniaturized manipulators which are aimed to be used in high precision assembly and manipulation tasks are presented. The developed manipulators are size adapted devices, miniaturized versions of conventional robots based on well-known kinematic structures. 3 degrees of freedom (DOF) delta robot and a 2 DOF pantograph mechanism enhanced with a rotational axis at the tip and a Z axis actuating the whole mechanism are given as examples of study. These parallel mechanisms are designed and developed to be used in modular assembly systems for the realization of high precision assembly and manipulation tasks. In that sense, modularity is addressed as an important design consideration. The design procedures are given in details in order to provide solutions for miniaturization and experimental results are given to show the achieved performances
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Enhancing recall and precision of web search using genetic algorithm
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Due to rapid growth of the number of Web pages, web users encounter two main problems, namely: many of the retrieved documents are not related to the user query which is called low precision, and many of relevant documents have not been retrieved yet which is called low recall. Information Retrieval (IR) is an essential and useful technique for Web search; thus, different approaches and techniques are developed. Because of its parallel mechanism with high-dimensional space, Genetic Algorithm (GA)
has been adopted to solve many of optimization problems where IR is one of them. This thesis proposes searching model which is based on GA to retrieve HTML
documents. This model is called IR Using GA or IRUGA. It is composed of two main units. The first unit is the document indexing unit to index the HTML documents. The second unit is the GA mechanism which applies selection, crossover, and mutation operators to produce the final result, while specially designed fitness function is applied to evaluate the documents. The performance of IRUGA is investigated using the speed of convergence of the retrieval process, precision at rank N, recall at rank N, and precision at recall N. In addition, the proposed fitness function is compared experimentally with Okapi-BM25 function and Bayesian inference network model function. Moreover, IRUGA is compared with traditional IR using the same fitness function to examine the performance in terms of time required by each technique to retrieve the documents. The new techniques
developed for document representation, the GA operators and the fitness function managed to achieves an improvement over 90% for the recall and precision measures. And the relevance of the retrieved document is much higher than that retrieved by the other models. Moreover, a massive comparison of techniques applied to GA operators is performed by highlighting the strengths and weaknesses of each existing technique of GA operators. Overall, IRUGA is a promising technique in Web search domain that provides a high quality search results in terms of recall and precision
Performance improvement of the LM device and its application to precise measurement of motion trajectories within a small range with a machining centre
In order to apply the LM device previously developed to precisely measuring small motion trajectories located on the different motion planes, three major improvements are successfully performed under the condition of completely maintaining the advantages of the device. These improvements include 1) development of a novel connection mechanism to smoothly attach the device to the spindle of a machining centre; 2) employment of a new data sampling method to achieve a high sampling frequency independent of the operating system of the control computer; and 3) proposal of a set-up method to conveniently install the device on the test machining centre with respect to different motion planes. Practical measurement experiment results with the improved device on a machining centre sufficiently demonstrate the effectiveness of the improvements and confirm several features including a very good response to small displacement close to the resolution of the device, high precision, repeatability and reliance. Moreover, based on the measurement results for a number of trajectories for a wide range of motion conditions, the error characteristics of small size motions are systematically discussed and the effect of the movement size and feed rate on the motion accuracy is verified for the machining centre tested
Design and implementation of an electro-optical backplane with pluggable in-plane connectors
The design, implementation and characterisation of an electro-optical
backplane and an active pluggable in-plane optical connector technology
is presented. The connection architecture adopted allows line cards to
be mated to and unmated from a passive electro-optical backplane with
embedded polymeric waveguides. The active connectors incorporate a
photonics interface operating at 850 nm and a mechanism to passively
align the interface to the optical waveguides embedded in the backplane.
A demonstration platform has been constructed to assess the viability of
embedded electro-optical backplane technology in dense data storage
systems. The demonstration platform includes four switch cards, which
connect both optically and electronically to the electro-optical backplane
in a chassis. These switch cards are controlled by a single board
computer across a Compact PCI bus on the backplane. The electrooptical
backplane is comprised of copper layers for power and low speed
bus communication and one polymeric optical layer, wherein waveguides
have been patterned by a direct laser writing scheme. The optical
waveguide design includes densely arrayed multimode waveguides with
a centre to centre pitch of 250ÎĽm between adjacent channels, multiple
cascaded waveguide bends, non-orthogonal crossovers and in-plane
connector interfaces. In addition, a novel passive alignment method
has been employed to simplify high precision assembly of the optical
receptacles on the backplane. The in-plane connector interface is based
on a two lens free space coupling solution, which reduces susceptibility
to contamination. Successful transfer of 10.3 Gb/s data along multiple
waveguides in the electro-optical backplane has been demonstrated and
characterised
Polycyclic aromatic hydrocarbons (PAHs) in air and vegetation: case study at three selected toll stations along North South Expressway in Johor, Malaysia
Polycyclic aromatic hydrocarbons (PAHs) from vehicular emission are products of
the incomplete combustion of organic fuel, and are usually attached to the particulate
matter from the emission and can caused pollution and hazard to human health due to
its carcinogenic, mutagenic and teratogenic characteristics. The objective of this
study is i) to determine the concentration PAHs in the air of sampling area, ii) to
determine the concentration PAHs in vegetation, iii) to determine the relationship of
concentration of PAHs in plants and air of sampling area and iv) to study the
different composition of PAHs in different species of plants to determine the
potential biomonitoring agent. The study is carried out at three toll stations along
PLUS’ North-South Expressway in Johor. Air sample and plant leaves sample
collected were extracted with ultrasonic agitation in dichloromethane and
fractionated according to polarity before submitted to gas chromatography – mass
spectrometry analysis to determine the concentration of the PAHs compounds.
Spearman’s rank correlation test was carried out using SPSS to determine the
correlation between concentration of PAHs in air and plant leaves sample. Seven
PAHs were identified and quantified in the atmospheric sample and plant leaves
sample. Those PAHs were acenaphtylene (ACN), phenanthrene (PHE), fluorene
(FL), pyrene (PY), chrysene (CHR), benzo[a]anthracene (BaA), and benzo[a]pyrene
(BaP). Significant correlation at 0.05 level (2-tailed) was observed in samples
of Ficus microcarpa, Cordyline fruticosa, Hibiscus spp., and Ixora coccinea with the
value 0.622, 0.643, 0.680 and 0.608 respectively. The positive correlation shows that
the plants have capabilities to absorb organic pollutants from the environment. Based
from this research, the most suitable species to be introduced into the environment as
a biomonitoring agent and to be further studied as a medium for low and medium
level pollution bioremediation is Ficus microcarpa, Cordyline fruticosa, and Ixora
coccine
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