Hongjun Hu

Bio: Hongjun Hu is an academic researcher from Beijing Jiaotong University. The author has contributed to research in topics: Calibration & Visible spectrum. The author has an hindex of 1, co-authored 1 publications receiving 1 citations.

Modified Linear Active Disturbance Rejection Control for Uncertain Robot Manipulator Trajectory Tracking

Abstract: To solve the problems of model uncertainties, dynamic coupling, and external disturbances, a modified linear active disturbance rejection controller (MLADRC) is proposed for the trajectory tracking control of robot manipulators. In the computer simulation, MLADRC is compared to the proportional-derivative (PD) controller and the regular linear active disturbance rejection controller (LADRC) for performance tests. Multiple uncertain factors such as friction, parameter perturbation, and external disturbance are sequentially added to the system to simulate an actual robot manipulator system. Besides, a two-degree-of-freedom (2-DOF) manipulator is constructed to verify the control performance of the MLADRC. Compared with the regular LADRC, MLADRC is significantly characterized by the addition of feedforward control of reference angular acceleration, which helps robot manipulators keep up with target trajectories more accurately. The simulation and experimental results demonstrate the superiority of the MLADRC over the regular LADRC for the trajectory tracking control.

A novel AC flatness adjustment technique for wideband resistive voltage dividers.

Abstract: Resistive voltage dividers (RVDs) are commonly used as AC attenuation networks in measurement circuits; however, their high-frequency gain is always disturbed by nasty parasitic elements and deviates significantly from the desired design value. This paper proposes a closed-loop adjustment technique for adjusting the frequency response flatness of wideband RVDs (WRVDs). In the proposed adjustment scheme, the frequency response flatness of the WRVD is determined by a voltage-controlled compensation capacitor, whereas the corresponding control voltage is provided by a digital potentiometer. The settling time and the adjustment error of the loop are analyzed to evaluate the adjustment performance. To verify the concept, the adjustment loop is incorporated into a 100:1 WRVD for demonstration. Final experiments show that the proposed technique improves gain flatness by 81 times compared with uncompensated flatness, with 1.15% up to 2 MHz, and that the compensated voltage divider has an excellent linearity of 36 ppm up to 100 V.

Research on Beam Waveguide Focus Phase Calibration Method of Deep-space TT&C System

Abstract: The angle auto-tracking capability is needed in the deep space system, but in the sum-differential dual channels tracking model, the deep-space TT&C system must calibrate its phase before tracking a satellite. Because of the big aperture and high frequency of the deep-space TT&C system antenna, it is impossible to build a calibrating tower which satisfy the far-field condition, and the traditional phase calibration method relies on the tower is not suitable. The radio star calibration method selects a appropriate satellite as the calibrating signal source, but the signal of which is very weak and is affected easily. In this paper, the principle of phase calibration is analyzed, and the beam waveguide focus calibration method is studied, the processes of antenna tracking and angle error signal demodulation are given. The beam waveguide focus calibration method simulates the far field signal through controlling the position of horn antenna which is at the focus of the beam waveguide. The method can be realized easily in engineering, and the limit of the traditional calibration tower and the affections of the weather in using radio star calibration method are avoided.

Analysis of the Transmission Spectrum of Flat Glass from Near-infrared to the Ultraviolet

Abstract: Contemporarily, glass windows have a great impact on human beings’ daily life. It is crucial to design a glass with a reasonable thickness with a high transmission of visible light as well as a high reflection of near infrared light. In general, reflection from the glass surface and absorption of light waves by the glass material are important features for transmission. Therefore, for UV-visible near-infrared light waves, the greater the thickness of the glass, the greater the light absorption loss and the lower the transmission rate. However, it is believed that there are multiple reflections of light waves in flat glass and that the losses caused by reflections should also be related to the refractive index of the glass and the wavelength of the incident light. On this basis, this study has developed theoretical models of transmittance versus incident light wavelength and glass thickness, refractive index and absorption coefficient. According to the theoretical analysis, the thickness of the glass has a significant effect on the transmission spectrum of sunlight. To experimentally verify this theoretically predicted anomaly, this paper designed the experimental and measurement route and built the experimental test rig. A variety of glass samples in the thickness range of 1mm-10mm were designed and prepared for this project, and the UV-Vis-NIR transmission of the glass was scanned and measured, while the final measurement results observed anomalies in the variation of transmission with thickness. The experimental results, therefore, provide valid support for the theoretical model of this paper.

Dynamics Modeling with Realistic Constraints for Trajectory Tracking Control of Manipulator

Abstract: To meet the practical operation requirements of manipulators in industry, service and collaboration scenarios, trajectory tracking accuracy and system stability of manipulators are usually regarded as critical control objectives. This paper proposes a novel manipulator control method with three-level constraints, called the real deep Lagrangian network (Real-DeLaN). In this method, real data (also called physical data) are collected from the physical manipulator and utilized to train the Lagrangian dynamics network model to improve the migration ability from simulation to reality. The torque output of the dynamic model is corrected by the real-time calculation of friction in the network. The contact force on the end effector of the manipulator is compensated based on the principle of virtual displacement work. The experimental results show that Real-DeLaN can better control the joints to perform trajectory tracking, reduce the friction error of the manipulator, and show better anti-interference ability.

Trajectory Planning and Attitude Control of Manipulator

Abstract: In this paper, the stability and smoothness of trajectory planning and attitude control of the manipulator are studied. The DH motion model of Kinova Jaco Gen-2 manipulator was established to solve the forward and inverse kinematics equations. Firstly, the third-order Bezier curve is designed to plan the trajectory of manipulator, which has good continuity and smoothness, and can control the workspace. Secondly, an attitude interpolation method based on quaternion is proposed. And different attitude interpolation methods are compared and analyzed, and spherical linear interpolation method is used to solve the problem of uneven velocity of the linear interpolation method. Finally, MATLAB robot toolbox is used to simulate and verify that the angle of each joint changes smoothly, and the trajectory of manipulator has good smoothness and stability based on Bezier curve and quaternion interpolation. According to the experimental results, the path planning based on the third order Bezier curve and spherical linear interpolation has a continuous smooth joint trajectory curve and a continuous joint angular velocity curve. The manipulator can move smoothly to the target point under the constraint of the end posture. Therefore, the trajectory planning method can be used as an ideal planning method for manipulator.