Abstract:A fractional order sliding controller and a fractional proportional differential controller are designed for attitude and position of 5-DOF air-bearing simulator, respectively. Firstly, a new fuzzy parameter self-tuning robust fractional sliding mode controller is designed for attitude platform model under considering gravity unbalance torque and actuator assembling error. The fractional differential operator is introduced in traditional sliding mode control because of its information memory and genetic characteristics, and then switching gain parameter is achieved self-tuning by fuzzy reasoning mechanism, so that the new controller has the multiple advantages of fuzzy control, fractional differential operator and sliding mode control. The stability of the whole system is proved by Fractional Lyapunov Theory. Secondly, a fractional proportional differential controller is proposed for translational platform considering coupling effects with attitude model. Finally, the actual operating characteristics of the actuator are considered in the process of the simulation. Numerical simulations are also included to reinforce the analytic results and to validate the excellent effect of the new robust fractional sliding mode controller.

Abstract:To study the impacts of centrifuge’s closing error on the calibration accuracy of gyro accelerometer, the centrifuge’s attitude errors, the angular rate errors of the main axis and the earth rotation rate are studied in detail respectively, and the corresponding expressions of input specific forces and input angular rates of gyro accelerometer are derived in consideration of the existent closing error. Furthermore, combining with the actual centrifuge test of gyro accelerometer, the input specific forces and the input angular rates affected by the closing error are calculated using the given tolerances towards centrifuge errors. The results show that the requirements for the calibration accuracy are satisfied by controlling the size of closing error and choosing the proper number of revolutions of the main axis.

Abstract:Based on the quasi equilibrium glide condition (QEGC), a numerical prediction method of three-dimensional reentry trajectory planning is presented for hypersonic vehicles with constraints. In this paper, both the angle of attack and the bank angle are seen as the control variables, so the QEGC can be fully used. Firstly, the range and the terminal velocity is predicted numerically according to the profiles of the angle of attack and the flight path angle respectively. Secondly, the bank angle is then calculated to keep the trajectory flying along with the QEGC, and the path constraints in flight are transformed into the bank angle constraints. Finally, the simulations for the CAV-H are constructed. The simulation results demonstrate that the proposed method can make the trajectory smooth enough, and has flexibility for different targets.

Abstract:A new modular rotary joint characterized with compact module structure, light weight and large output torque had been developed, in which the motor, encoder and brake were arranged parallel to the axis. The modular joints could be assembled into different manipulators based on the needs benefiting from their standard mechanical and electrical interface. To settle the non-commonality of modular manipulator kinematics, the spatial configuration was converted to coordinate relations in plane geometry on account of matching configuration plane, so that the modular kinematics solution of manipulator was realized. Besides, a manipulator kinematics simulation platform was designed to obtain kinematics of manipulators with different configurations. Finally, a distributed control system was built to control the manipulators with various configurations assembled with the developed joint module.

Abstract:Compared to the rigid actuator robot, the flexible actuator robot can absorb some external shock and lead to stable biped walking. A 10 D.O.Fs(Degrees of Freedom) humanoid biped walking robot with the type of FDUBR-I is designed and developed. The flexible drive unit FDU-II drives the pitch D.O.F of the hip joint for FDUBR-I. The FDUBR-I control system including hardware and software is built, which makes the host computer on-line control the joints of FDUBR-I. The switched Ethernet including PC and two motion control cards are set up for real-time communication. The control system includes two control subsystems of tension feedback and joint closed-loop control for FDU-II. The FDUBR-I walking experiment has been finished to verify the application of the FDU-II and the effect of the viscoelasticity dynamic model feedback based joint closed-loop controller and the tension feedback controller. The robot can reach the speed of 0.1 km/h during the steady biped walking.

Abstract:Aiming at the problem of nonlinear, non-stationary and multi-components of fault gear vibration signal, and with defining the intrinsic time-scale function(ITF) whose instantaneous frequency has real physical significance, a new time-frequency analysis method named adaptive time-scale decomposition(ATD) is proposed based on the construction method of baseline signal of the intrinsic time scale decomposition (ITD). By the ATD method, a complex multi-components signal can be adaptively decomposed into the summation of a number of ITFs whose instantaneous frequencies own physical sense. The simulation results verify the effectiveness of the ATD method and the feasibility of the definition of ITF. Combined with envelop demodulation analysis, the ATD, the empirical mode decomposition(EMD), the local mean decomposition(LMD) and the intrinsic time scale decomposition(ITD) are respectively applied to the gear fault diagnosis. The experimental results show that the ATD method has obvious advantage in computational efficiency with the guarantee of decomposition correctness, and the method can effectively extract gear fault features combining with the envelope demodulation analysis.

Abstract:To improve the speed and accuracy of path synthesis of planar hinge four-bar linkage, a path synthesis method based on B-spline curves was proposed. The method adopted cubic non-uniform B-spline curves to fit coupler curves and used angles between the two adjacent sides of the B-spline curve control polygon as characteristic parameters of coupler curves. Characteristic parameters with dimension parameters of the corresponding four-bar linkage were put into computer to establish an electronic atlas. When a certain number of ordered discrete points were given, a desired curve that passed through these points was constructed by B-spline curve fitting. Characteristic parameters of the desired curve were extracted. Then characteristic parameters of the desired curve with characteristic parameters of the electronic atlas were matched by neural networks to find the four-bar linkage which met the requirements. Ultimately the goal of path synthesis was achieved. Calculation examples show that it can quickly realize path synthesis of four-bar linkage and has high accuracy of path synthesis. And the extracted characteristic parameters have nothing to do with location and scale of coupler curve, reducing the atlas data redundancy.

Abstract:To solve the problem of coupling movements between degrees of freedom(DOF) of hyper-redundant shaking table while working with a load, a novel decoupling control strategy based on modal space is proposed. Linear model of hydraulic servo system is established and modal equation of hyper-redundant shaking table is given by considering hydraulic cylinder as a hydraulic spring. By standard modal matrix and its inverse matrix, the hyper-redundant shaking table is controlled in non-coupling modal space instead of DOF space. Three variables feedback control is employed in modal space to achieve decoupling control by pole placement. Simulation results show that the proposed decoupling control strategy can effectively improve tracking accuracy and reduce the dynamic coupling among DOF in both time and frequency domain.

Abstract:The 3D NS equation solver was coupled with the heat conduction solver based on unstructured meshes and Gama-Theta transition model, the direct-coupled method and LUSGS implicit method were adopted, and the conjugate heat transfer (CHT) simulation platform was established. The temperature was transmitted between interfaces by the area-weighted interpolation method to ensure the flux conservation and accuracy. The CHT numerical results were compared with experimental data of the 5411 experimental condition of MARKII blade. The thermal-elastic coupling solver based on second unit was developed, and was compared with analytic solutions of the hollow cylinder. The boundary temperature calculated by CHT simulation was transmitted into the finite element solver to calculate the displacement and thermal stress. It is indicated from the result of CHT simulation that the eddy viscosity calculated in the most of pressure surface and the area before transition of the suction surface is better agreement with the real flow. Because the eddy viscosity has a great influence on heat transfer simulations by influencing the temperature diffusion coefficient, the accuracy of heat transfer calculations is higher, and the result of static pressure simulations of Gama-Theta and SST is in good agreement with experimental results. The thermal-elastic coupling simulation results show that the distribution trend of the thermal stress and displacement of MARKII blade is reasonable. The Gama-Theta model affects the accuracy of the thermal-elastic coupling simulation indirectly by affecting the CHT simulation, and makes the calculated thermal stress more reasonable.

Abstract:To solve the problem of uniform temperature field distribution of the simulation system in the environment of underground extra-deep well, the system temperature field with large length-diameter ratio, large delay and many kinds of complex heat exchange mode were simulated numerically, and the effective uniform temperature distribution method was obtained. First, the components of simulation system and work principles are introduced. Then, heat transfer model of the system is given according to the heat transfer theory. At last, temperature field distribution status of the system is simulated, and compared with the actual heating curve, the effectiveness of simulation results is approved.

Abstract:Aiming at applying virtual time mechanism to data race detection, a model is proposed to uniformly describe different implementation forms of virtual time. We firstly establish an abstract model for a distributed execution. Based on this model, we give a unified description on virtual time’s three basic implementation forms: scalar time system, vector time system and matrix time system. Furthermore, we take vector time system and matrix time system for examples to illustrate four optimization techniques for virtual time. At last, we discuss the problems to be solved when applying virtual time to data races detection in shared-memory concurrent systems and four application examples. The model proposed in this paper unifies different implementation forms of virtual time and reduces the difficulty of applying virtual time to data race detection.

Abstract:The existing graph-construction methods for graph optimization-based SLAM are summarized. The SLAM methods can be divided into three main classes, Kalman filter-based, partical filter-based and graph optimization-based, and the advantages and disadvantages of each class are overviewed. Moreover, there are mainly three graph modeling methods for the graph optimization-based SLAM problem, namely dynamic Bayesian network (DBN)-based model, factor graph-based model and Markov random field-based model. The key techniques of the front-end stage in graph optimization-based SLAM method, which mainly include data association between consecutive frame and loop closure detection, are discussed. Some newest research achievements on feature extraction, matching method, motion estimation, loop closure detection are introduced.

Abstract:The range of the lightly damped resonant frequency in the flexible system is investigated based on D-decomposition approach. In the flexible system, the resonant frequency exists in the first-order and second-order terms, making its perturbation possess a nonlinear form. In this paper, two perturbation factors are introduced to reformulate the problem as a two-dimension parameter perturbation problem. Then, a geometric algorithm based on the D-decomposition approach is developed to determine the precise robust area of the two factors. The perturbation range of the resonant frequency can be obtained as the intersection points between the boundary of this area and a specific line. Numerical examples are provided to illustrate the effectiveness of the proposed method. Meanwhile, the relationship between the perturbation range and the H∞ norm is also revealed.

Abstract:An approach for low-thrust and gravity-assist trajectory optimization is presented in this paper based on automatic differentiation and pseudospectral method. The B-plane model is used to increase robustness of the trajectory optimization problem. A Gauss pseudospectral method is applied to the parameterization of the entire trajectory, which includes the search of launch date in the same calculation framework to avoid the slow convergence rate and poor precision caused by stochastic search algorithms. A sequential quadratic programming (SQP) method is adopted as the solver of the resulting large scale nonlinear programming (NLP) problem. Strategies of serial optimization and elastic constraints are proposed in order that the NLP problem converges rapidly. The derivatives required by the SQP method are obtained by automatic differentiation to ensure high accuracy and a rapid convergence rate. Taking the optimization of Earth-Venus-Mars low-thrust gravity-assist trajectory as an example, the results verify the correctness and validity of the proposed method.

Abstract:To achieve monitoring acceleration-sensitive drift coefficients DID_s of the skewed-installation liquid floated gyroscope in IMU(inertial measurement unit) on the condition of free disassemble, a system level separation algorithm using calibration parameters of inertial measurement unit is put forward. By the analysis of structure and skew installation principle of liquid floated gyroscope, the paper gives the liquid floated gyroscope and its system’s error models. Then based on error models and ever-obtained error parameters of skew inertial measurement unit,the system level separation algorithm of acceleration-sensitive drift coefficients is designed. It is unnecessary to design complex calibration tool when using this algorithm, and also without removing liquid floated gyroscopes from inertial measurement unit, these improvements can reduce error accumulations, so that the precision of parameters’s separation is high, and the residual error is small. The deviation between the single gyro separation algorithm and system level separation algorithm is smaller than 1.301×10-3(°)·(h·g₀)-1, which fully meets the requirements of high precision inertial measurement unit to acceleration-sensitive drift coefficients of liquid floated gyroscopes in engineering application.

Abstract:To provide accurate numerical basis for the forecast of lifetime and analysis of fretting wear of the spline couplings, the nonlinear dynamic characteristics of involute splines was studied. Four degrees of freedom nonlinear dynamic equations of the spline couplings using the lumped mass model was established, the number of actual meshing teeth and the time-varying mesh stiffness of the systems were calculated, and the nonlinear dynamic equations adopting the fourth order Runge-Kutta method was solved. The results show that: the time-varying mesh stiffness changes periodically with time and is a piecewise linear distribution with torque changing; when n=300 r／min, the system presents harmonic response; when n=348 r／min, the system presents double-cycle response; when n=360 r／min, the system presents 5-cycle response; and when n=1 080 r／min, the system gets into chaos response. The dynamic load coefficient of the spline couplings changes periodically and increases with torque and backlash. It is concluded that reducing the clearance of the spline couplings is beneficial to lowering the dynamic load and improving the stability of involute splines.

Abstract:A path planning method based on improved RRT (Rapidly-Exploring Random Tree) algorithm was proposed in application to local path planning of USV (Unmanned Surface Vehicle). Aiming at the high speed and real-time control of USV, the inhibitory factor, limited angle and distance heuristic information were introduced into classical RRT algorithm, thus the selection of exploration points and growing points were modified, and the speed of the algorithm was improved. The excess navigation points in planning path were processed and smoothed considering the gyration performance to make the navigation distance shorter and meet the special demands of maneuver performance of USV. The experiment of local path planning was completed based on the environment model constructed by the process results of typical radar images in the sea and lake experiments. The experimental results showed that the suggested algorithm could rapidly complete the path search, the efficient of algorithm was improved and the distance of path was reduced, the planning path after optimization treatment could satisfy the planning system need. The suggested method can apply to USV local path planning.

Abstract:The inertial sensor errors should be calibrated when strapdown inertial navigation system (SINS) restarts to maintain the high accuracy for a long time. In this paper, we use the global observability analysis method to build up the relationship between the motion status and the system observability. The rotating principle of SINS initial alignment and self-calibration is also proposed. An eight-position rotating method which rotates around the two horizontal axes is designed based on the principle. The simulation results show that the rotating method which rotates around the horizontal axis has a better performance than that rotates around the any other two axes. At last the experiment results show that the location accuracy is enhanced to 5 nm／10 h from 18 nm／10 h with the eight-position calibration method, which verifies the effectiveness of this new rotating method.

Abstract:For convenience of application, an analytic algorithm was proposed to design the pretensions of asymmetrical ring truss cable-net space-borne antennas. The projection equations of the main net in the plane perpendicular to the central line of the ring truss were given at first, and then the pretensions of the main net were obtained using the formula of the minimal norm method that is used to optimize the pretensions of a planar cable-net. The pretensions of the tension ties were calculated according to the vertical equilibrium equations of the points of the main net. A set of equilibrium pretensions of the auxiliary net were obtained by letting the tensions of the main net multiply the special coefficients respectively. The accuracy, validity and feasibility of the algorithm were proved by theoretical analysis, nonlinear finite element numerical simulations and comparisons with other pretension optimization algorithms. The algorithm can be used to design the pretensions of the asymmetrical or symmetrical ring truss cable-net space-borne antennas.