Poo Aun Neow
Email Address
mpepooan@nus.edu.sg
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98 results
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Now showing 1 - 10 of 98
Publication Measurements of surface coordinates and slopes by shearography(1992-08) Tay, C.J.; Shang, H.M.; Poo, A.N.; Luo, M.; MECHANICAL & PRODUCTION ENGINEERINGThis paper represents an optical method which is based on speckle-shearing interferometry for the measurement of surface coordinates and slopes. The technique enables generation of carrier fringes which measure surface coordinates, or displacement derivative fringes which measure surface slope. The theory of the method as well as some experimental results are presented. © 1992.Publication A DDA parabolic interpolator for computer numerical control of machine tools(1994-10) Chai, O.H.; Wong, Y.S.; Poo, A.N.; MECHANICAL & PRODUCTION ENGINEERINGThis paper is primarily concerned with the development of a parabolic interpolation algorithm for implementation in a computer numerical control (CNC) system to perform tool path control with constant tangential velocity (feedrate). Less segments of parabolic curves are required than of line or circular arcs for piece-wise approximation of higher-order curves. Hence, there is a need to develop an efficient algorithm for real-time control of a tool to follow a specified parabolic curve. A software approach based on the digital differential analyzer (DDA) method is presented. This integer computation method simplifies real-time implementation using assembly language or digital hardware. The developed parabolic interpolator has been implemented on a multiprocessor CNC system. Results of tests of the implemented algorithm are compared with those obtained from a hardware interpolator with parabolic interpolation capability. Results of fitting techniques using linear, circular and parabolic segments are also presented and plotted. Considerations in the parabolic interpolation include the accuracy in following the theoretical parabolic curve and the ability to maintain a constant tangential velocity. Word address codes for NC programming to generate the parabolic curves are also proposed. © 1994.Publication The implementation of adaptive isoplanar tool path generation for the machining of free-form surfaces(2005-10) Ding, S.; Mannan, M.A.; Poo, A.N.; Yang, D.C.H.; Han, Z.; MECHANICAL ENGINEERINGMachining of steep regions is an important research topic in the machining of free-form surfaces. A new tool path generation algorithm to adaptively machine free-form surfaces has been recently developed. However, similarly to many newly emerged methods, so far it has not been used in industry because no commercial platform is currently available and the user-developed system is not robust enough for industrial applications. To solve this problem, this paper presents a new implementation method by integrating it in a commercial CAD/CAM system (Pro/Engineer). With this strategy, other than conducts detailed computations for parameters, such as scallop heights and forward steps, or designing the non-cutting functions such as engaging and retracting methods, which are routines in every tool path generation process, the implementation utilizes existing tool path generation templates in Pro/E to generate the required tool paths. This makes the tool path generation process easier and the tool paths generated more practicable because the integration is relieved of the time-consuming routine calculation and the entire cutting and non-cutting functions in the commercial system are transparent to users. Based on the API of Pro/E, the new tool path generation method was successfully implemented and cutting tests were conducted. Not losing generality, the implementation could also be conducted in other commercial systems as similar templates are available in these systems as well. © Springer-Verlag London Limited 2005.Publication Design and implementation of a parallel multivariable adaptive controller for a free gyro stabilized mirror(1991) Lee, T.H.; Poo, A.N.; Koh, E.K.; Loh, M.K.; Tay, S.L.; ELECTRICAL ENGINEERING; MECHANICAL & PRODUCTION ENGINEERINGFast close loop response requires sampling intervals in the milli-second range, which is difficult to achieve with uniprocessor computers. Parallel computers are able to achieve faster computation through load sharing. In this paper, we present our results in controlling the gyro stabilized mirror using transputers.Publication Application of a modified strain transient dip test in the determination of the internal stresses of PVC under tension(1987-04) Teoh, S.H.; Chuan, C.L.; Poo, A.N.; MECHANICAL & PRODUCTION ENGINEERINGA modified strain transient dip test which involves the design of a load reduction apparatus to perform rapid step unloading and extrapolating to zero extension rate has been developed to measure the internal stresses (recovery and effective stress) of PVC under uniaxial tension. This simple technique appears to be consistent with other internal stress measurement techniques. It was found that the effective stress approaches a limiting value with applied strain and an extrapolated yield point could be defined. The limiting value is a function of the strain rate during the initial load application. The general increase in applied stress (at fixed applied strain) with crosshead speed was attributed to the increase in magnitude of the effective stress. The maximum peak ratio of effective over recovery stress, at each crosshead speed, could indicate that it was the energy-dissipating part of the material that played a dominant role in the early stages of the deformation while the energy-storage part dominated the latter stages. © 1987 Chapman and Hall Ltd.Publication Thermal error measurement and modelling in machine tools. Part II. Hybrid Bayesian Network - Support vector machine model(2003-03) Ramesh, R.; Mannan, M.A.; Poo, A.N.; Keerthi, S.S.; MECHANICAL ENGINEERINGPrediction accuracy of machine tool thermal error significantly depends on the structure of the error model. Machine tool thermal error varies considerably depending upon the specific operating parameters adopted. Most error models developed thus far generally employ neural networks to map temperature data against thermal error. However, it is very important to account for the specific conditions as well within the model. This paper presents a hybrid Support Vector Machines (SVM)-Bayesian Network (BN) model that seeks to address this issue. The experimental data is first classified using a BN model with a rule-based system. Once the classification has been effected, the error is predicted using a SVM model. The hybrid thermal error model thus predicts the thermal error according to the specific operating conditions. This concept leads to a more generalised prediction model than the conventional method of directly mapping error and temperature irrespective of conditions. Such a model is especially useful in a production environment wherein the machine tools are subject to a variety of operating conditions. © 2002 Elsevier Science Ltd. All Rights Reserved.Publication Application oriented test procedure for designing microstepping step motor controllers(1988-11) Rahman, Muhammed F.; Poo, Aun-Neow; MECHANICAL & PRODUCTION ENGINEERINGThe authors describe an application-oriented setup for determining current references for a microstepping motor controller. This eliminates the need for calculating these references from motor characteristics. The method is based on a procedure that calculates microstepping current references from motor torque-displacement data and retains the attributes of the motor found under conventional stepping. Motor nonlinearities and asymmetries are taken into consideration and references for controllers can be obtained by an unattended test for any microsteop size desired.Publication Shape memory alloy microgripper for robotic microassembly of tissue engineering scaffolds(2004) Zhang, H.; Bellouard, Y.; Burdet, E.; Clavel, R.; Poo, A.-N.; Hutmacher, D.W.; BIOENGINEERING; MECHANICAL ENGINEERINGThis paper presents a monolithic Shape Memory Alloy (SMA) microgripper, which was developed to assemble microscopic building blocks of width 60μm into tissue engineering scaffolds. It consists of two small fingers for grasping, an actuator which changes its shape upon heating by Joule effect and a parallel elastic structure to provide a pullback force on cooling as well as to guide the finger movement. All the elements are laser-cut from the same Ni-Ti-Cu sheet but have different mechanical properties and are used for different functions. Using local laser annealing, a local shape memory effect is introduced on the actuator while leaving other areas in a cold-worked state, i.e. no shape memory effect occurs. The material has nonlinear mechanics and the actuator undergoes large deflections. A numerical method is introduced to compute the nonlinear dynamics of the coupled system formed by the actuator and pull-back spring. The predicted deflection and force are in good agreement with the measured ones, and this model can be used to optimize the design.Publication Motion control of robotic manipulators with disturbance decoupling(1993) Zhu, H.A.; Teo, C.L.; Hong, G.S.; Poo, A.N.; MECHANICAL & PRODUCTION ENGINEERINGA scheme for the decoupling control of robotic manipulators, based on a dynamic model that includes both the mechanical dynamics of the links and the electrical dynamics of the joint motors, is proposed in this paper. The highly nonlinear and strongly cross-coupled electromechanical system is firstly decoupled and linearized into a set of decoupled linear subsystems. Disturbance decoupling is then conducted for disturbance and uncertainty attenuation. And what is more encouraging, the resulting algorithm is so simple that both modelling difficulty and control complexity of the manipulator systems can be reduced significantly.Publication Decoupling control and disturbance rejection of mechanical manipulators with partially known dynamics(1995) Zhu, H.A.; Teo, C.L.; Hong, G.S.; Poo, A.N.; MECHANICAL & PRODUCTION ENGINEERINGIt is known now that the dynamics of the motor drives of mechanical manipulators is of utmost importance and it is necessary to take this into account in achieving high control performance. At the same time, it is also known that the cross-coupled motor-manipulator dynamics is more complex and hence more difficult to be controlled than when only the manipulator dynamics is considered. In this paper, the dynamics of both the actuator and mechanical manipulator are considered together and a control strategy is developed for achieving ease of controller design and high control performance. By using the algorithm developed in this paper, not only can the highly complicated motor-manipulator dynamics be effectively controlled, but the motors are also made sensitive for sensing and compensating for the uncertain dynamics acting at manipulator joints. Furthermore, as a significant result, the modelling difficulty and control complexity of the manipulator dynamics can be significantly reduced.