Showing papers by "Chongqing University of Technology published in 2004"

Lessons learned from the practice of mobile health application development

Abstract: This fast abstract briefly discusses lessons learned in terms of how to overcome limitations of PDA devices, effectively capture requirements for mobile health application development and effectively reengineer a desktop application on PDA. The limitation of PDA devices includes: (1) small screen size, which limits text-based data entry, reporting and browsing; (2) limited storage space and slow processing, which requires effective and efficient coding generation; (3) security limitations and inadequate third party application support, which poses challenge for application development. The corresponding strategies addressing the above challenges are: (1) providing check box, radio button, drop down list, text field, combo box based data entry and minimize text-based data entry, such as text area; (2) allocating as much as possible data storage, communication and computation tasks to the desktop system and minimize the function PDA component needs to handle, store data in file instead of database on PDA; (3) carefully selecting the device and implementation platform that supports development. To maximize the usability of PDA-based health application, the solution to be implemented on PDA ideally should be data management tasks with minimum text-based data entry and high frequency of recording. Challenges and solutions for software reengineering from desktop system to PDA-based application is outlined based on one application developed for World Health Organisation. In this example, the complex task of communication among PDA-based application, desktop system and the existent desktop application EpiData is effectively handled through the utilisation of XML files. A dynamic tool 'Questionnaire Designer' provides a completely dynamic user interface generation tool that could easily be handled by end user. The design idea for this application sets up a model for mobile health application with adequate flexibility of handling changing data management needs of end users.

Viscoplastic Flow of the MR Fluid in a Cylindrical Valve

Abstract: Bingham viscoplastic model is used to describe the constitutive behavior of Magnetorheological (MR) fluids subject to an applied magnetic field. Based on Navier-Stokes’ equation, a theoretical analysis of the effect of the applied magnetic field on the viscoplastic flow in a cylindrical valve is presented. The expressions for the velocity in viscoplastic flow are derived. The results indicate that the volumetric flow rate can be continuously adjusted by an external magnetic field. With the increase of the applied magnetic field the yield boundary gets closer to the two cylindrical surfaces, and the restriction of flow is increased. Introduction MR fluids are suspensions of micron-sized, magnetizable particles in a carrier fluid such as synthetic oil and silicone oil, which are regarded as the intelligent materials that respond to an applied magnetic field with a change in their rheological properties. Upon application of a magnetic field, the polarization between two induced dipoles causes the suspended particles in the MR fluids to form a chain-like microstructure aligned with the direction of the applied magnetic field. The magnetic chain structure restricts the movement of the MR fluids, thereby changing the rheological properties of the suspension. These fluids exhibit a viscoplastic behavior with yield strength. Thus the viscoplastic MR fluids have the properties of both viscosity and plasticity. Altering the strength of an applied magnetic field will precisely control the yield stress of the fluid. Based on the mechanical properties, these MR fluids can be used in brakes and clutches [1,2]. An MR valve is a device that uses the MR fluid flowing through a cylindrical orifice. In order to understand the flow behaviors and the yield characteristics of MR fluid in MR valve, in this paper, the viscoplastic flow of MR fluid in a cylindrical valve is investigated theoretically. Based on Navier-Stokes’ equation, the effect of the applied magnetic field on the viscoplastic flow of an MR fluid between two fixed cylinders is analyzed to locate the yield boundary that separates viscous flow and viscoplastic flow. The expressions for the velocity and the volumetric flow rate in viscoplastic flow are derived to provide a theoretical foundation for the design of MR valve. Rheological behavior of MR fluids In the absence of an applied magnetic field, MR fluids exhibit a Newtonian fluid behavior. Upon application of a magnetic field, the behavior of the controllable fluids is often represented by Bingham viscoplastic model. The flow is governed by Bingham’s equations [3]: Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 969-974 doi:10.4028/www.scientific.net/KEM.274-276.969 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,17:14:19) γ η τ σ & + = B rz for B rz τ σ ≥ (1) 0 = γ& for B rz τ σ < (2) where rz σ is the shear stress, η is the viscosity of MR fluid , and γ& is the fluid shear strain rate. rz σ is the absolute value of rz σ , and B τ is the yield stress developed in response to an applied magnetic field. Bingham model shows that without the applied magnetic field the yield stress of material equals zero, and MR fluid exhibits the characteristics of a conventional Newtonian fluid. When the magnetic field is applied, MR fluid exhibits the characteristics of Bingham viscoplasticity. For the flow field at B rz τ σ ≥ , MR fluid flows with a viscosity η . For the flow field at B rz τ σ < , the MR material behaves like a solid. Operating principle The operational principle is that the yield stress of MR fluids in the valve can be controlled by application of an external magnetic field. It can be classified as the constant flow valve in which the difference in pressure through the valve can be continuously controlled when the volumetric flow rate is constant, and the constant pressure valve in which the volumetric flow rate through the valve can be precisely controlled when the difference in pressure is constant. The characteristics of the MR valve are that the inner and outer cylinders don’t move in relation to each other, and the annular gap is constant. When the MR fluid flows through the gap, altering the strength of the magnetic field permits continuous control of the valve’s volumetric flow rate or the pressure drop. Flow analysis In order to derive the equation of the fluid flow between two cylinders, the following assumptions are given: the fluid is incompressible and experiences steady-state flow. There is no flow in circumferential and radial direction. The gradient of the pressure in radial direction is zero. Fig.1 shows the axial flow of an MR fluid in the annular gap between two fixed cylinders. In the cylindrical coordinate system ( z r , ,θ ), assume the distribution of the velocity of the flow is: Outer cylinder Inner cylinder MR fluid Coil-assembly Magnetic flux

A New Mechanical Model of MR Fluids

Abstract: Based on the Maxwell model, the visco-plastic behavior of magnetorheological fluids is discussed by a simple mechanical model. Then a new constitutive model is developed. The results of experiments show that the constitutive model can explain the mechanical properties of the magnetorheological fluids. Introduction Magnetorheological (MR) fluids are materials that respond to an applied magnetic field in their rheological behavior. In the absence of applied magnetic field, MR fluids exhibit Newtonian-like behavior. Upon application of a magnetic field, the behavior of the fluids is often represented as semi-solids having a controllable yield stress in milliseconds. The yield stress of MR fluids increases as the applied magnetic field increases. The feature provides reversible, quiet, rapid response interfaces between electronic controls and mechanical systems [1]. At present, the key question of the application of MR fluids is the mechanical model. Many models are used to describe the mechanical properties of MR fluids, but no one is very suitable for it. Properties and Operational Principle of MR Fluids MR fluids consist of stable suspensions of particles in a carrying fluid such as silicone oils. When an external magnetic field is applied, the polarization induced in suspended particles, resulting in the MR effect of the MR fluids. The MR effect is direct influences on the mechanical properties of the MR fluids. The suspended particles in the MR fluids become polarized and align themselves, like chains, with the direction of the magnetic field. The formulation of these particle chains restricts the movement of the MR fluids, thereby increasing the yield stress of the fluids. The behavior of the MR fluids is often represented as a Bingham fluid. In this model, the constitutive equation is derived by [2]. ηγ τ τ + = 0 (1) where τ is the stress, 0 τ is the dynamic yield stress, η is the viscosity, γ is the fluid shear rate. In fact, the true MR fluids behavior exhibits some significant differences from the Bingham plastic model. So other constitutive equations were presented by Shulman and Carlson [3,4]. But those equations are too complex to apply. Mechanical Model and Description of the Properties of MR Fluids Based on the true behavior of the MR fluids and Maxwell model [5], we give a mechanical model that describe the viscoFig.1 Mechanical model Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 965-968 doi:10.4028/www.scientific.net/KEM.274-276.965 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,17:14:18) plastic response of the MR fluids. the structure of the mechanical model is shown in Fig. 1. A i is the plastic damper (i=1.....n,the coefficient of plastic is i A δ ); B j is the viscosity damper(j=1......m,the coefficient of viscosity is j B δ ); elastic element C i and A i constitute the elastic-plastic system; elastic element C j and B j constitute the visco-elastic system; ε is the total strain; S is the total stress; i A is the strain of A i ; j B is the strain of B j ; the stress of the elasticplastic system is σ and the stress of the visco-elastic system isλ; the elastic deform of the C is C and that of C j is C 。From Fig. 1, we can get: ∑ ∑ = = + = + = m

Study on the Communication between Single Parameter Profilometer and PC

Abstract: With the rapid development of industrial technology, the requirements to surface feature of machinery parts are more and more high. It is far not enough to describe the machined surface feature with single roughness parameter Ra, but the instrument improvement for adding measurable roughness parameters is always companied with the cost increase. Therefore, how to acquire multi-parameter measurement of machined surface feature with existing single parameter profilometer is a significant and practical problem. It is a convenient and efficient way to acquire measurement data through the communication between measurement instrument and personal computer through parallel printer interface. This paper investigates the feasibility. A portable profilometer was taken as the displacement sensor, which was communicated with PC through parallel printer interface under the control of special software written by ourselves. The plentiful information of measured surface was entered the computer, through data processing the surface profile curve and various parameters were produced automatically. Consequently, the surface feature can be fully investigated. Introduction In the drastically international market competition, product quality is the strongest weapon by which enterprises win the competition. A lot of enterprises, especially small and medium-sized enterprises still acquire and process information manually in part manufacturing and quality controlling, which is time-consuming and easy to make mistakes, also difficult to set up effective information feedback system in time. The development of computer and measurement technologies make the automation of acquiring, transferring, analyzing and processing quality information possible. Machined surface roughness is an important consideration in the manufacture of parts; it has a significant effect on parts’ appliance capabilities such as wear resistance, corrosion resistance, fatigue strength, as well fitting between parts. It is necessary to design, measure and control machinery parts’ surface roughness so that the parts can meet a certain requirements. At present, there are several methods of measuring surface roughness, among them one applied widely is to use stylus instruments [1-2]. Though large or table-measuring instruments controlled by computer have already been applied in laboratories of research institutes and quality inspection departments of factories, on the working spot, particularly in the workshops of medium-sized or small factories, portable profilometer which can only measure single parameter of roughness is still used widely. Single parameter is clearly not enough to describe the features of measured surface. Therefore, it is quite practical to achieve multi-parameters which can indicate the feature of machined surface by means of single parameter profilometer. What this paper introduces is how to collect signals from the placement sensor of portable profilometer through computer parallel printer port, then analyze and calculate these signals in terms of computer data processing, finally print multi-parameters measurements This kind of method is also suitable for communicating between computer and those instruments measuring other analog quantities such as temperature, force, etc.. Output Signals of the Profilometer Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 687-691 doi:10.4028/www.scientific.net/KEM.259-260.687 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,19:03:50) 688 Advances in Grinding and Abrasive Processes Common surface profilometers are two-dimensional surface roughness surveying instruments. The operation principle of portable profilometer is as Fig.1 shows. When the sharp stylus is driven to slide directly on the measured surface, it will be up and down with the micro asperity of measured surface. The placement signal is transformed by sensor into faint voltage signal, through amplifying, filtrating and integrating circuit, then the parameter value of roughness is shown by an indicator [1]. Although this kind of instrument is quite small and convenient to use, its shortcomings are very obvious: single measurement parameter, low measurement precision, limited measurement range, inflexible measurement way (such as the choosing of assessing length, the selection of filter and so on), and can not record the measurement result and print the graph. Fig.1 Operating principle of portable profilometer From the operation principle of this kind of instrument, it is known that, when the stylus slides directly on the measured surface, in fact, as long as the stylus is sharp enough, the measured surface’s asperity information collected by the placement sensor ought to be quite abundant. However, the sequent treatment circuits only pick-up a part of the information, and depend on it to show the calculation result of the single parameter. That is to say, the sequent treatment circuits don’t make the best of the abundant collected information. So, in order to make good use of the traditional instrument for surface roughness measurement and overcome its shortcoming, computer’s strong function on information process can be use to improve this kind of instruments. As shown in Fig.2, the analog signal from the commuting circuit is amplified, then, through potential and analog/digital conversion, is entered into computer. After the datum is processed by software, the computer will print the calculation results and corresponding figures automatically on screen or printer. Parallel Port Communication of Computer With the rapid development of computer technology, conventional instruments for measuring various analogue quantities are being replaced gradually by digital instrument controlled by microcomputer or microprocessor. In process controlling and various measurements, personal computer also can control various sensors to acquire and process data quickly. The common method of connecting peripheral hardware to PC is using plug-in interface circuitry board. That is, making a data acquisition card which is connected to peripheral adapter by special cable, and plugging it in the PC’s bus. In this method the special plug-in card is rather expensive, and the host has to be opened for inserting the card in the bus expansion slot. What’s more, it needs skillful programmer to program the card. It is very obvious that the method not only increases the cost but also is inconvenient. Even, the host of portable PC or notebook computer has no built-in ISA extending slot. Besides the above way, PC can communicate with measurement instrument by own parallel or serial port. If by RS-232C, the speed of collecting data will be limited greatly (the max transmission speed is 20 kbit/s in its original criterion). However, the communication speed of parallel port is much faster than that of serial port. Parallel port, working as the host’s communication interface connected with peripheral equipments such as disk system, CD player, LAN adapter, printer and so on, is use widely in all PCs and its compatible computers. Utilizing parallel port LPT to collect information, what we have to do Sensor Driving box Amplifier commutating Filter Average Table Amplifier Integrator Integration Traverse Controller Zero Indicator Power Amplifier Recorder Ra 688 Advances in Grinding and Abrasive Processes