Position control and repeatability of a pneumatic rodless cylinder system for continuous positioning

Pneumatic cylinder systems have the potential to provide high output power to weight and size ratios at a relatively low cost. However, they are mainly employed in open-loop control applications where positioning repeatability is not of great importance. In this paper the repeatability of a pneumatic rodless cylinder system under closed-loop PD control is examined for its potential use in robotic applications. Our analysis shows that the linearized continuous time dynamics is dependent on the trimmed and operating conditions. This can cause positioning problems when a controller is designed based upon the transfer function obtained at a particular trimmed point. Furthermore, there are uncertainties associated with the dynamics which can lead to precision errors in both transient and steady-state responses. Due to these complexities, a pragmatic gain tuning methodology is proposed to achieve satisfactory nominal transient response characteristics over the range of loading requirements. With this scheme, it is suggested that the performance of the conventional controller be evaluated in terms of its repeatability. The repeatability of the system under different start–stop positions and loading conditions is experimentally found to be less than ±0.3 mm. This repeatability value is within typical industrial requirements.     

A novel microstrip square-loop dual-mode bandpass filter with simultaneous size reduction and spurious response suppression

In this paper, a new capacitively stepped-impedance resonator(CSIR) is proposed to develop the microstrip square-loop dual-mode bandpass filter. Using this new design, simultaneous size reduction and spurious response suppression for the dual-mode bandpass filter can be achieved. An analytical formulation of this novel resonator is given in order to elucidate the spurious frequencies relocation design. Together with this formulation, a generalized dual-mode bandpass filter model is developed so as to ease the analysis of transmission zero and insertion loss. A prototype filter is designed at 900MHz with 1.5% fractional bandwidth. Significant spurious suppressions up to 33 and 35 dB are measured at 1.8 and at 2.7 GHz, respectively. A circuitry size reduction of 54% is achieved when compared with that of the conventional structure. Moreover, the CSIR allows frequency tuning and, thus, a varactor-tuned filter is designed and a measured tunable center frequency between 1.5-1.62GHz is demonstrated. Utilizing the proposed structure, not only size reduction,as well as spurious response suppression, but also center frequency tuning can be achieved.     

An investigation by electron spectroscopy for chemical analysis of chemical treatments of the (100) surface of n-type InP epitaxial layers for Langmuir film deposition

The surface chemistry of InP substrates used for the fabrication of electronic devices (MIS structures) was examined by ESCA. Spectroscopic data on related materials such as indium metal, plasma-oxidized indium metal, In₂O₃, InPO₄(xH₂O), P₄O₁₀, AlPO₄, (C₆H₅O)₃PO and (C₆H₅)₃P were collected so as to aid the assignment of components in the spectra of as-received and etched InP surfaces on the basis of the chemical shifts and the intensity ratios. Surface features of InP substrates from several batches were examined in the as-received and the chemically etched forms. The effectiveness of several types of etchants and the features thus produced on the substrate surface were evaluated and are discussed.     

The design of school furniture for Hong Kong schoolchildren. An anthropometric case study

Anthropometric data of Hong Kong schoolchildren have been collected and analysed in order to develop recommendations for the design of chairs and tables for use in Hong Kong Government coeducational schools. The anthropometric data for Hong Kong have been compared with data from a Western population (United Kingdom) and another Asian population (Japan). Five sizes of chair and table combinations have been proposed to accommodate six primary and seven secondary forms (pupils aged from 6 to 18 years). The recommended design dimensions, based on the anthropometric characteristics of the Hong Kong target populations, are discussed in relation to recommendations from previous research in this area.     

MR imaging of the brain: comparison of gradient-echo and spin-echo pulse sequences

OBJECTIVE: Gradient-echo pulse sequences can reduce imaging time and decrease motion artifacts. If gradient-echo pulse sequences are shown to be comparable to spin-echo sequences in MR imaging of the brain, then gradient-echo imaging can be valuable for examining critically ill, anxious, or uncooperative patients and can increase patient throughput. The purpose of this study was to prospectively compare one fast multiplanar spoiled gradient-recalled acquisition in the steady state (GRASS) (FMPSPGR) sequence with one conventional T1-weighted spin-echo sequence to determine the reliability of the FMPSPGR sequence for detecting cerebral lesions. SUBJECTS AND METHODS: Fifty-one patients with 142 cranial lesions, including brain tumors, infarction, infection, and noninflammatory lesions, were examined. Forty-two unenhanced and 39 contrast-enhanced FMPSPGR (113-240/2.6-3.6/90 degrees/4 [TR/TE/flip angle/acquisitions]) and spin-echo T1-weighted (400-579/11-12/90 degrees/2) MR images of the head were obtained with a 1.5-T system. The visibility, margination, and extent of the lesions; image quality; contrast; and artifacts were qualitatively and quantitatively compared. RESULTS: Supratentorial lesions were more conspicuous on the unenhanced FMPSPGR images because of the higher signal-to-noise ratio of the normal brain resulting in higher lesion contrast. The higher contrast-to-noise ratio of neoplasms on the contrast-enhanced spin-echo images was not found to be significant in the independent qualitative analysis. The conspicuity and extent of other lesions evaluated with the two pulse sequences were not significantly different for either the unenhanced or the contrast-enhanced studies. Vascular pulsation artifacts were significantly reduced on the contrast-enhanced FMPSPGR images. Susceptibility and chemical-shift phase-cancellation artifacts were more pronounced on the FMPSPGR images. CONCLUSION: The FMPSPGR sequence provides high-quality images with fewer vascular pulsation artifacts three to four times faster than the spin-echo sequence. The FMPSPGR sequence can reliably show intracranial lesions and can substitute for the T1-weighted spin-echo sequence in routine brain imaging.     

A parametric study on the fractal finite element method for two‐dimensional crack problems

The Fractal Finite Element Method for calculating 2D stress intensity factors is modified by making the similarity ratio in the construction of the fractal mesh a variable. A parametric study is then carried out to examine the effects of the similarity ratio, the number of transformation terms, reduced integration and the initial crack opening angle on the quality of the numerical solutions. It is concluded that a large similarity ratio should be used to create the fractal mesh, and that reduced integration and a small initial crack opening angle may be used without producing significant errors in the solutions. Copyright © 2003 John Wiley & Sons, Ltd.     

Experiments for first year engineering students using tin-bismuth alloys

Introductory courses, whether at the freshman or junior level, are frequently based on the paradigm that processing affects structure, which affects properties, which, in turn, determine performance, and is the basis for design. Once this is understood by the students, it is possible to have them make design decisions based on experimental data and have them identify alternative materials using the paradigm. This paper describes a series of experiments and demonstrations that can be incorporated into an introductory materials course to help students appreciate how processing changes structure, which leads to a change in properties.     

Opening Up the Future of Open Source: From Open Innovation to the Internet of Things for the Built Environment

The architecture, engineering and construction industry is increasingly operating within the merging of physical and digital that defines our era of connectivity. Meanwhile, new semi-open-source platforms such as WikiHouse and Resilient Modular Systems, together with the prospect of traditional supply chains being replaced by localised digital manufacturing, are challenging notions of design ownership. Guest-Editor Wendy W Fok considers what questions designers should be asking themselves in this climate     

Variable Temperature Blackbodies via Variable Conductance: Thermal Design,Modelling and Testing

This paper presents the overall design for large (\(\sim \)400 mm aperture) reference blackbody cavities currently under development at the Science and Technology Facilities Council Rutherford Appleton Laboratory Space Department (STFC RAL Space), in collaboration with the National Physical Laboratory (NPL). These blackbodies are designed to operate in vacuum over a temperature range from 160 K to 370 K, with an additional capability to operate at \(\sim \)100 K as a point of near-zero radiance. This is a challenging problem for a single blackbody. The novel thermal design presented in this paper enables one target that can physically achieve and operate successfully at both thermal extremes, whilst also meeting stringent temperature gradient requirements. The overall blackbody design is based upon a helium gas-gap heat switch and modified to allow for variable thermal conductance. The blackbody design consists of three main concentric cylinder components—an inner cavity (aluminium alloy), a radiation shield (aluminium) and an outer liquid nitrogen (\(\hbox {LN}_{2}\)) jacket (stainless steel). The internal surface of the cavity is the effective radiating surface. There is a helium gas interspace surrounding the radiation shield and enclosed by the \(\hbox {LN}_{2}\) jacket and the inner cavity. The blackbodies are now at a mature stage of development. In this paper, the overall design, focusing upon the thermal design solution, is detailed. This paper will also concern the full-scale prototype breadboard model, for which results on thermal stability, spatial gradients and other sensitivities will be presented.     

Tunable Optical Delay Using Four-Wave Mixing in a 35-cm Highly Nonlinear Bismuth-Oxide Fiber and Group Velocity Dispersion

In this paper, an optically controlled tunable delay scheme has been proposed using four-wave mixing (FWM) wavelength conversion in a 35-cm highly nonlinear bismuth-oxide fiber (Bi-NLF) together with group velocity dispersion (GVD) in a chirped fiber Bragg grating (CFBG). The Bi-NLF offers a very large nonlinearity and gives rise to significant FWM over a short fiber segment. With the use of a CFBG, a delay range over 185 ps has been experimentally demonstrated. To investigate the performance of the tunable delay, we have applied the scheme for variable delays of 10-Gb/s amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) data signals. The bit error rate (BER) measurements show a power penalty of less than 3.5 dB for both amplitude- and phase-modulated data formats. To further increase the delay time, the CFBG has been replaced by a dispersion compensated fiber (DCF) that provides a wider bandwidth of operation. A variable delay up to 840 ps has been obtained using dual-pump FWM that offers a conversion bandwidth of about 40 nm. The large conversion range helps to minimize GVD-induced pulse distortion as a shorter DCF can be used for a given delay. The Bi-NLF provides an enhanced stimulated Brillouin scattering (SBS) threshold, a reduced latency, and an increased compactness of the approach for practical applications.