Papers by Author: Li Ning Sun

Abstract: This paper presents a type of Ag/polydimethylsiloxane (Ag/PDMS) nanocomposite material for use in strain gauge element applications. In these elements, the Ag nanoparticles work as conductive elements by electron tunneling and the PDMS forms the tunneling dielectricstructure. In our experiments, the piezoresistance and piezocapacitance characteristics of these Ag/PDMS composites have been studiedunder applied rain/stress. From the results, the gauge factors for piezoresistance and piezocapacitance can reach up to 153 and 224, respectively. Also, when acting as strain elements, the Ag/PDMS composites show fine levels of repeatability and stability. The results given here prove that the material can be used to form anew type of high-sensitivity element for sensor applications. The detectionmethod used for the sensor signals also offersdiversity by including both piezoresistance and piezocapacitance.

Abstract: A novel micromachined tri-axis capacitive accelerometer based on the single mass is proposed in this paper. The presented accelerometer contains a single proof mass acting as the sensitive element which is suspended by two flexible beams above the substrate, and an array of movable and fixed electrodes is utilized. To match the sensitivity design requirement, the differential capacitive detection is utilized, and the cross-sensitivity problem of three orthogonal axes is avoided ideally. The accelerometer structure is based on the EPI-poly process to realize the 18 microns thickness. Thus the detection capacitance, sensitivity and reliability are improved, the mechanical noise is decreased. To reduce the thermomechanical stress’ effect on the offset, a special anchor-middle structure is designed. Simulation results show that the offset is insensitive to the thermomechanical stresses and the sensor has a good consistency in three axes which has been validated by the testing results.

Abstract: The working principle of a new kind of double-acting pneumatic-hydraulic pressure amplifier having two-step output pressure driven by the pneumatic cylinder with rodless piston is introduced. The output flux and the output pressure calculating formulae are also given out. Compared with the known single-acting pressure amplifier,the innovative pressure-amplifier is simple in structure and has much higher working efficiency. It can also output adaptive two-step liquid pressure, which is similar with the hydraulic differential connection, thus it is easy to realize move quickly in low pressure and move slowly at high pressure. This system also fits a trend of green manufacturing for using green air as transmission medium and with closed oil without leak to output pressure liquid.

Abstract: The gait phase determination is the basis of the control of intelligent prosthesis. The prosthetic usually determines the gait phase according to its own motion parameters, which will cause the asymmetry gait of the prosthesis wearer during level walking due to the lack of contralateral motion information. By using of a variety of sensors installed in the healthy leg and prosthesis, the gait phase determination method based on echo control can achieve good symmetry, but at the same time also made calculation difficult. Based on the existing echo method, a gait phase determination method by utilize of the contralateral motion parameters is proposed. According to gait test data collected from healthy subjects, motion parameters and their relation can be obtained. Then the proposed method can determine its gait phase and contralateral phase. Preliminary experiment is conducted and verified the effective of the method.

Abstract: Due to its simple structure, low consumption of energy but strong driving forces, Electrowetting on Dielectric (EWOD) is used most frequently in digital microfluidics for manipulation and control of droplets. In this paper, the internal mechanism of EWOD is explained though establishing the geometric model of unipolar board structure digital microfluidic chip. The digital simulation software COMSOL Multiphysics is applied to analyze the coupling fields. The results show that external flow velocity of micro-droplet is greater than the internal velocity. Based on the theoretic analysis, surface micromachining technologies are employed to fabricate the single-plate EWOD chip. Finally, an experiment platform is set up to test this chip. Experimental results show that 2μL droplet can be driven in velocity of 10cm/s and two droplets can be merged successfully. It will possibly provide an effective solution to the manipulation of droplets.

Abstract: Adhesion of solid surfaces plays a significant role in many technical fields especially at micro and nano scale. The effect of asperity shape on the adhesion hysteresis originated from surface roughness has been investigated theoretically in this paper. Based on the adhesive contact model of single asperities with axisymmetric power-law shapes, the roughness-induced adhesion hysteresis is modeled by assuming the asperity heights follow a Gaussian distribution on the rough surface. The analysis results show that the dissipation energy decreases dramatically when the surface becomes rougher for all the shape indices, and the shape index affects the adhesion hysteresis at different levels with the variance of surface roughness. A general parameter consisting of the shape index of asperities is proposed to characterize the adhesion hysteresis. These will be helpful to understand and control the adhesion hysteresis for solid-solid contact.

Abstract: Kinematic calibration is an effective method of improving robotic absolute position accuracy by means of measurement, identification and compensation etc. This paper investigates the technology of kinematic calibration and error compensation for the 2-DOF planar parallel robot. A multi-step calibration method is presented based on error itterative method and nonlinear optimum method. Experimental results indicate that the proposed method can effectively compensate position error of the robot in Oxy plane, and the absolute position error of the calibrated robot is less than 6μm.

Abstract: In this paper, aiming at solving the problems of dynamic coupling effects and flexibility of joints and links, a kind of control system specialized for high payload industrial robots is proposed . After the comparisons between the control systems in all kinds of robots and numerical machines, industrial PC with TwinCAT real-time system is chosen as the motion control unit, EtherCAT is used for command transmitting. The whole control system has a decoupled and centralized control structure. The proposed control system is applied in control of a kind of high payload material handling robots with complex compound control algorithms. The final results shows that the control commands can be easily calculated and transmitted in one sample unit. The proposed control scheme is meaningful to real engineering application.

Abstract: A hierarchical mobile robot simultaneous localization and mapping (SLAM) method that allows us to obtain accurate maps of large environments is proposed. The local map level is composed of a set of local metric feature maps that are guaranteed to be statistically independent. The global level is a topological graph whose arcs are labeled with the relative location between local maps. An estimation of these relative locations is maintained with local map alignment algorithm, and more accurate estimation is calculated through a global minimization procedure using the loop closure constraint. The local map is built with Rao-Blackwellised particle filter (RBPF). The particle filter is used to extend the path posterior by sampling new poses that integrate the current observation which drastically reduces the uncertainty about the robot pose. The landmark position estimation and update is also implemented through Kalman filter. Omnidirectional vision mounted on the robot tracks the 3D natural point landmarks, which are structured with matching Scale Invariant Feature Transform (SIFT) feature pairs. The matching for multi-dimension SIFT features is implemented with a KD-Tree. Experimental results on real robot in a medium size, real indoor environment show the practicality and efficiency of our proposed method.

Abstract: In response to the impossibility of directly using data of the actual road show experiment to the motion simulation of simulators, due to the limited work space of simulators, this paper begins with an attempt to extract the main frequency components of original signals by spectrum analysis and allow the input signal to meet performance requirements by adjusting the phase offset corresponding to the various frequency components. The paper proceeds with the regeneration of the signals capable of reflecting the motion characteristics of the original data and meeting the performance requirements of motion simulators by selecting these phase offsets as the design variables, selecting simulator’s displacement, velocity, and acceleration as the optimization objectives and applying Genetic Algorithm toolbox of Matlab to develop the optimization model. The paper ends with the efforts to check mechanism singularity by calculating the Jacobian matrix condition number of the regenerating signals and thus obtain the regenerating signals compatible with the work space, capable of fulfilling the performance requirements of motion simulators and free of continuous region singularity.