36 research outputs found
Stiffness Enhancement and Motion Control of a 6-DOF Wire-driven Parallel Manipulator with Redundant Actuations for Wind Tunnels
Get PDFReal-time motion planning based vibration control of a macro-micro parallel manipulator system for super antenna
Get PDFA macro-micro manipulator (M3) system, composed of a rigid parallel manipulator serially mounted on a flexible cable suspended parallel manipulator, is used to precisely position the feed source of a super antenna. In order to reduce the impact of mechanical vibrations of the macro manipulator and achieve accurate positioning and orientating of the micro manipulator, a real-time motion planning based vibration control strategy is presented. This strategy comprises: (1)Â To determine the optimal position and orientation of the cable driven parallel manipulator, the real-time optimization is conducted according to the principle of uniform tension in the six driving cables; (2)Â Synchronized points and the âjudge and waitâ technique ensure the continuity and synchrony of the trajectory tracking of the two parallel manipulators; (3)Â The preadjustment of the micro parallel manipulator minimizes the drastic dynamical coupling as a result of its high-speed manipulation. Experimental results of the field model validate the high precision of the M3 system for super antenna when tracking a circular arc trajectory
Real-time motion planning based vibration control of a macro-micro parallel manipulator system for super antenna
Get PDFA macro-micro manipulator (M3) system, composed of a rigid parallel manipulator serially mounted on a flexible cable suspended parallel manipulator, is used to precisely position the feed source of a super antenna. In order to reduce the impact of mechanical vibrations of the macro manipulator and achieve accurate positioning and orientating of the micro manipulator, a real-time motion planning based vibration control strategy is presented. This strategy comprises: (1)Â To determine the optimal position and orientation of the cable driven parallel manipulator, the real-time optimization is conducted according to the principle of uniform tension in the six driving cables; (2)Â Synchronized points and the âjudge and waitâ technique ensure the continuity and synchrony of the trajectory tracking of the two parallel manipulators; (3)Â The preadjustment of the micro parallel manipulator minimizes the drastic dynamical coupling as a result of its high-speed manipulation. Experimental results of the field model validate the high precision of the M3 system for super antenna when tracking a circular arc trajectory
The Application Research of Inverse Finite Element Method for Frame Deformation Estimation
Get PDFA frame deformation estimation algorithm is investigated for the purpose of real-time control and health monitoring of flexible lightweight aerospace structures. The inverse finite element method (iFEM) for beam deformation estimation was recently proposed by Gherlone and his collaborators. The methodology uses a least squares principle involving section strains of Timoshenko theory for stretching, torsion, bending, and transverse shearing. The proposed methodology is based on stain-displacement relations only, without invoking force equilibrium. Thus, the displacement fields can be reconstructed without the knowledge of structural mode shapes, material properties, and applied loading. In this paper, the number of the locations where the section strains are evaluated in the iFEM is discussed firstly, and the algorithm is subsequently investigated through a simple supplied beam and an experimental aluminum wing-like frame model in the loading case of end-node force. The estimation results from the iFEM are compared with reference displacements from optical measurement and computational analysis, and the accuracy of the algorithm estimation is quantified by the root-mean-square error and percentage difference error
Short-Term Power Load Forecasting Method Based on Improved Exponential Smoothing Grey Model
Get PDFIn order to improve the prediction accuracy, this paper proposes a short-term power load forecasting method based on the improved exponential smoothing grey model. It firstly determines the main factor affecting the power load using the grey correlation analysis. It then conducts power load forecasting using the improved multivariable grey model. The improved prediction model firstly carries out the smoothing processing of the original power load data using the first exponential smoothing method. Secondly, the grey prediction model with an optimized background value is established using the smoothed sequence which agrees with the exponential trend. Finally, the inverse exponential smoothing method is employed to restore the predicted value. The first exponential smoothing model uses the 0.618 method to search for the optimal smooth coefficient. The prediction model can take the effects of the influencing factors on the power load into consideration. The simulated results show that the proposed prediction algorithm has a satisfactory prediction effect and meets the requirements of short-term power load forecasting. This research not only further improves the accuracy and reliability of short-term power load forecasting but also extends the application scope of the grey prediction model and shortens the search interval
Affordance-Driven Next-Best-View Planning for Robotic Grasping
Full text linkGrasping occluded objects in cluttered environments is an essential component
in complex robotic manipulation tasks. In this paper, we introduce an
AffordanCE-driven Next-Best-View planning policy (ACE-NBV) that tries to find a
feasible grasp for target object via continuously observing scenes from new
viewpoints. This policy is motivated by the observation that the grasp
affordances of an occluded object can be better-measured under the view when
the view-direction are the same as the grasp view. Specifically, our method
leverages the paradigm of novel view imagery to predict the grasps affordances
under previously unobserved view, and select next observation view based on the
highest imagined grasp quality of the target object. The experimental results
in simulation and on a real robot demonstrate the effectiveness of the proposed
affordance-driven next-best-view planning policy. Project page:
https://sszxc.net/ace-nbv/.Comment: Conference on Robot Learning (CoRL) 202
Vibration Isolation and Trajectory Following Control of a Cable Suspended Stewart Platform
No full textTo achieve high-quality vibration isolation and trajectory following control of a cable driven parallel robot based Stewart platform in the five hundred meter aperture spherical radio telescope (FAST) design, the integrated dynamic model of the Stewart platform including the electric cylinder is established in this paper, the globally feedback linearization of the dynamic model is implemented based on the control law partitioning approach. To overcome the disadvantages of the external disturbance on the base and unmodeled flexibility of the mechanism, a PID (Proportional-Derivative-Integral) controller with base acceleration feedforward is designed in the operational space of the Stewart platform. Experiments of the vibration isolation and trajectory following control of the cable suspended Stewart platform with presence of the base disturbance is carried out. The experimental results show that the presented control scheme has the advantage of stable dynamics, high accuracy and strong robustness
Modeling and Analysis of a 2-DOF Spherical Parallel Manipulator
No full textThe kinematics of a two rotational degrees-of-freedom (DOF) spherical parallel manipulator (SPM) is developed based on the coordinate transformation approach and the cosine rule of a trihedral angle. The angular displacement, angular velocity, and angular acceleration between the actuators and end-effector are thus determined. Moreover, the dynamic model of the 2-DOF SPM is established by using the virtual work principle and the first-order influence coefficient matrix of the manipulator. Eventually, a typical motion plan and simulations are carried out, and the actuating torque needed for these motions are worked out by employing the derived inverse dynamic equations. In addition, an analysis of the mechanical characteristics of the parallel manipulator is made. This study lays a solid base for the control of the 2-DOF SPM, and also provides the possibility of using this kind of spherical manipulator as a 2-DOF orientation, angular velocity, or even torque sensor
Workspace Classification and Quantification Calculations of Cable-Driven Parallel Robots
No full textLarge workspace is one of the promising advantages possessed by the cable-driven parallel robots (CDPR) over the conventional rigid-link robots. This paper focuses on the dynamic analysis and workspace classification based on the general motion equation of cable robot and the unilateral property of cables. The combinations of different types of two conditions lead to several different types of workspace, including static equilibrium workspace, wrench closure workspace, wrench feasible workspace, dynamic workspace, and collision-free workspace. A qualitative comparison of different types of workspaces is performed. The simulation results verify the relationship between the several types of workspaces
The second and third harmonic generation of GaAs/Ga
No full textThe objective of this study is to theoretically discuss the impact of additional tuning factors on the second and third harmonic generation (SHG and THG) of GaAs/GaAlAs quantum dots (QDs) with the inversely quadratic HellmannâKratzer (IQHK) potential by adjusting the depth of potential and radius of the QDs. Within the formula method, the energy levels and the corresponding wave-functions are calculated by solving the Schrödinger equation. Then, the SHG and THG coefficients are deduced using the density matrix formalism with an iterative procedure. Finally, the results indicate that the additional tuning factors and structural parameters have significant effects on the peak positions and magnitudes of the calculated SHG and THG coefficients
