G.C.T. Chow

Imperial College London, Londinium, England, United Kingdom

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Publications (10)4.37 Total impact

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    ABSTRACT: This paper presents a real-time control framework for a snake robot with hyper-kinematic redundancy under dynamic active constraints for minimally invasive surgery. A proximity query (PQ) formulation is proposed to compute the deviation of the robot motion from predefined anatomical constraints. The proposed method is generic and can be applied to any snake robot represented as a set of control vertices. The proposed PQ formulation is implemented on a graphic processing unit, allowing for fast updates over 1 kHz. We also demonstrate that the robot joint space can be characterized into lower dimensional space for smooth articulation. A novel motion parameterization scheme in polar coordinates is proposed to describe the transition of motion, thus allowing for direct manual control of the robot using standard interface devices with limited degrees of freedom. Under the proposed framework, the correct alignment between the visual and motor axes is ensured, and haptic guidance is provided to prevent excessive force applied to the tissue by the robot body. A resistance force is further incorporated to enhance smooth pursuit movement matched to the dynamic response and actuation limit of the robot. To demonstrate the practical value of the proposed platform with enhanced ergonomic control, detailed quantitative performance evaluation was conducted on a group of subjects performing simulated intraluminal and intracavity endoscopic tasks.
    IEEE Transactions on Robotics 01/2013; 29(1):15-31. · 2.57 Impact Factor
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    G.C.T. Chow, K.W. Kwok, W. Luk, P. Leong
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    ABSTRACT: Customisable data formats provide an opportunity for exploring trade-offs in accuracy and performance of reconfigurable systems. This paper introduces a novel methodology for mixed-precision comparison, which improves comparison performance by using reduced-precision data paths while maintaining accuracy by using high-precision data paths. Our methodology adopts reduced-precision data-paths for preliminary comparison, and high-precision data-paths when the accuracy for preliminary comparison is insufficient. We develop an analytical model for performance estimation of the proposed mixed-precision methodology. Optimisation based on integer linear programming is employed for determining the optimal precision and resource allocation for each of the data paths. The effectiveness of our approach is evaluated using a common collision detection problem. Performance gains of 4 to 7.3 times are obtained over baseline fixed-precision designs for the same FPGAs. With the help of the proposed mixed-precision methodology, our FPGA designs are 15.4 to 16.7 times faster than software running on multi-core CPUs with the same technology.
    Field-Programmable Custom Computing Machines (FCCM), 2011 IEEE 19th Annual International Symposium on; 06/2011
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    ABSTRACT: A constant-power control circuit has been built successfully for the digital operation of CNT-based alcohol vapor sensors. The sensors, which are based on bundles of chemically functionalized multi-walled carbon nanotubes (f-CNTs), have been proven to be sensitive towards alcohol molecules. The resistance of the sensors increases upon exposure to alcohol vapors. The constant-power configuration is developed to avoid the self-heating effect, which is a significant factor in affecting the sensor performance. On the other hand, we also utilized the self- heating effect to clean up the alcohol molecules on the f-CNTs between measurements. The comparison experiments between constant-power and constant-current configurations were conducted. The results demonstrated larger response under constant-power mode, especially when operating power was low or alcohol concentration was relatively high. The responsivity and the sensitivity of alcohol vapor sensors under different mode and operating powers are also discussed.
    Nano/Micro Engineered and Molecular Systems, 2008. NEMS 2008. 3rd IEEE International Conference on; 02/2008
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    ABSTRACT: Alcohol sensors, batch fabricated by forming bundles of chemically functionalized multiwalled carbon nanotubes (f-CNTs) across Au electrodes on SiO<sub>2</sub>/Si substrates using an AC electrophoretic technique, were developed for alcohol vapor detection using an ultralow input power of ~ 0.01 - 1 muW, which is lower than the power required for most commercially available alcohol sensors by more than four orders of magnitude. The multiwalled carbon nanotubes (MWCNTs) have been chemically functionalized with the COOH groups by oxidation. We found that the sensors are selective with respect to flow from air, water vapor, and alcohol vapor. The sensor response is linear for alcohol vapor concentrations from 1 to 21 ppm with a detection limit of 0.9 ppm. The transient response of these sensors is experimentally shown to be ~1 s and the variation of the responses at each concentration is within 10% for all of the tested sensors. The sensors could also easily be reset to their initial states by annealing the f-CNTs sensing elements at a current of 100-200 muA within ~ 100-200 s. We demonstrated that the response of the sensors can be increased by one order of magnitude after adding the functional group COOH onto the nanotubes, i.e., from ~0.9% of a bare MWCNTs sensor to ~9.6% of an f-CNTs sensor with a dose of 21 ppm alcohol vapor.
    IEEE Transactions on Nanotechnology 10/2007; · 1.80 Impact Factor
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    ABSTRACT: Sensing devices using electronic-grade carbon nanotubes (EG-CNTs) as resistive sensing element were fabricated by dielectrophoresis (DEP) manipulation. DEP-based fabrication of EG-CNTs is important as it allows some control of the nominal resistance of the fabricated sensors, which is essential to improve the SNR of CNT sensors. The devices were characterized and the potential of EG-CNTs to serve as a novel temperature and humidity sensing element has been demonstrated. Electrical characterization revealed that the EG-CNTs sensors, which exhibit large linear IiquestV range, have both positive and negative TCR at higher operational temperatures. In addition, its resistance-humidity linear dependency proves its humidity sensing capability. Moreover, the EG-CNTs device is capable of operating in nW range. On the foundation of these measurements, we aim to prove EG-CNTs as a promising material for future applications in nano-sensing.
    Nanotechnology, 2007. IEEE-NANO 2007. 7th IEEE Conference on; 09/2007
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    ABSTRACT: A micro inertial measurement unit (μlMU) which is based on Micro-Electro-Mechanical Systems (MEMS) accelerometers and gyroscope sensors is developed for real-time recognition of human hand motion. By using appropriate filtering, transformation and sensor fusion algorithms, a ubiquitous digital writing instrument is produced for recording handwriting on any surface. In this paper, we propose a method for deriving an error feedback to a Kalman filter based on the assumption that writing occurs only in two dimensions i.e. the writing surface is flat. By imposing this constraint, error feedback to the Kalman filter can be derived. Details of the feedback algorithm will be discussed and experimental results of its implementation are compared with the simple Kalman filter without feedback information.
    Robotics and Biomimetics, 2006. ROBIO '06. IEEE International Conference on; 01/2007
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    ABSTRACT: We have successfully chemically functionalized the multi-walled carbon nanotubes (MWCNTs) with COOH group by the method of oxidation and used AC electrophoresis to formed these bundles MWCNTs between Au electrodes on the Si substrate. We then demonstrated that these resistive elements are capable of detecting alcohol vapor using an ultra-low input power of only ∼0.01μW. The sensors exhibit fast, repeatable, highly sensitive, and reversible response. Our results show that the resistances of the sensors vary linearly with alcohol vapor concentration from 5ppth to 100ppth (ppth = part per thousand). We can also easily reverse the initial resistance of the sensors by annealing them in real time at 100-250μA current within 1-6 minutes. We have experimental proof that the functionalized MWCNTs have a much higher sensitivity towards the alcohol vapor than the bare MWCNTs. Based on our experimental results, we prove that MWCNTs sensors, especially for those with proper functionalized groups, are sensitive to a wide range of alcohol vapor and potentially other volatile organic compounds, and are very attractive for commercialization due to their extreme low-power requirements for activation.
    Nanotechnology, 2006. IEEE-NANO 2006. Sixth IEEE Conference on; 07/2006
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    ABSTRACT: This paper reports the characterization of a novel MEMS sensor using Carbon nanotubes (CNTs) as sensing elements. Using a MEMS-compatible process and the dielectrophoretic (DEP) nanoassembly of CNTs, we have successfully integrated bundled strands of CNT sensing elements on arrays of Polymethylmethacrylate (PMMA) diaphragms. With a thin film of Parylene-C to enhance the CNT to electrode contact, the CNT bundles show consistent and repeatable piezoresistivity from multiple electromechanical measurements. Using low noise data acquisition techniques and annealing treatments of the CNTs, the fluctuations of the sensor signal are greatly reduced. Based on these experimental evidences, we propose that embedded in Parylene-C thin film, CNT-bundles is a novel material for fabricating micro pressure sensors on polymer substrates-which may serve as ultra-low-power (μW) and low-noise sensors when bio-compatibility and low-cost applications are required.
    Nanotechnology, 2006. IEEE-NANO 2006. Sixth IEEE Conference on; 07/2006
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    ABSTRACT: Development and preliminary characterization on the performance of a micro-bubble generator using carbon nanotubes (CNTs) as heating elements are presented. Dielectrophoretic force was used to align CNTs between fabricated micro-electrodes. The contacts between the CNTs and electrodes were fixed by patterned SiO<sub>2</sub> thin film. Localized high temperature due to Joule-heating generated by an AC current of a few hundred muA (in general les100 Hz) in the carbon nanotubes vaporized surrounding water and generated micron sized bubbles (with diameter of 5 mum detectable under normal optical microscope). These experimental evidence indicate that exposed CNTs may function as a single nucleation site for bubble generation. The power required to generate these bubbles can be as small as 337 muW, which is with 1-2 order of magnitude smaller than that of typical metal or polysilicon based MEMS heaters. Precisely controlled micro bubble generation may find promising applications in ink-jet printing, micro-fluidic visualization, or micro-fluidic based bio-manipulation
    Nano/Micro Engineered and Molecular Systems, 2006. NEMS '06. 1st IEEE International Conference on; 02/2006
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    ABSTRACT: We have demonstrated multi-walled carbon nanotube (MWCNTs) based sensors, which are capable of detecting alcohol vapor with ultra-low power. We fabricated the Si-substrate sensors using an AC electrophoretic technique so as to form bundled MWCNTs sensing elements between Au microelectrodes. The I-V measurement illustrates that we can activate the sensors at the Ohmic region of the sensors (at 10 muA), which is without any overheat effect. The sensors only need an ultra-low power (~1 muW) to detect the alcohol vapor. They exhibit fast, reversible and repeatable response. We have tested the response of the sensors with alcohol concentrations from 10 ppth to 400 ppth (ppth = parts per thousand). Our result shows that there is a linear relation between the resistance of the sensors and alcohol concentration. Also, we can easily reverse the sensor to the initial reference resistance by annealing them at 100-250 muA current within 6 minutes. Moreover, the sensors are selective with respect to flow from air, water vapor, and alcohol vapor. Finally, we have also studied how the temperature of the sensors affects their response towards alcohol vapor. The result shows that the performance of the sensors will deteriorate as the temperature of the sensors increase. Also, the cooling effect of the vapor is not a dominating factor in determining the response of the sensor. Based on our experiments, we prove the feasibility of turning the MWCNTs sensors into a commercialized alcohol sensor with ultra-low power requirements
    Nano/Micro Engineered and Molecular Systems, 2006. NEMS '06. 1st IEEE International Conference on; 02/2006

Publication Stats

69 Citations
4.37 Total Impact Points

Institutions

  • 2011
    • Imperial College London
      • Department of Computing
      Londinium, England, United Kingdom
  • 2006
    • Huazhong University of Science and Technology
      • Department of Electronic Science and Technology
      Wuhan, Hubei, China