He Jingfeng

Analysis of Coupling Effects on Hydraulic Controlled 6 Degrees of Freedom Parallel Manipulator Using Joint Space Inverse Mass Matrix

This paper presents an analysis of the coupling effects between degrees of freedom of a hydraulic controlled six DOF parallel manipulator. Based on the singular value decomposition to the properties of its joint space inverse mass matrix, the method is put forward to analyze coupling effects between degrees of freedom using a transformation matrix, the product of transposed Jabobian matrix and an orthogonal unitary matrix, of which each element represents decoupled modal space coordinates with respect to physical task space frame. The simulation results in frequency domain prove the theoretical analysis right. The analysis will provide useful information to mechanism and controller designer, to asses from concept the coupling effects between DOF in respect of the requirement for a particular application and also for the study on decoupling control strategies.

A low-cost PC-based flight simulator development

Flight simulator is a large-scale simulation system. Because of the limitation by computer powers, only special computers ever were used to realize flight dynamics simulation and image generation in full flight simulator in the past. With the development of computer powers, high-performance computation and simulation can be realized applying by PC. While the need to reduce costs in every aspects of flight simulator become very important. A PC-based prototype system was implemented according to the architecture of flight simulator featuring a generic double engine airplane. Commercial-off-the-shelf (COTS) software components were use to reduce costs and improve developing efficiency. The detailed process was proposed. The integrated system shows that the feasibility of design based on PC.

Modal space decoupled optimal design for a class of symmetric spatial parallel mechanisms with consideration of passive joint damping

In this study, we analyze the influence of passive joint viscous friction (PJVF) on modal space decoupling for a class of symmetric spatial parallel mechanisms (SSPM). The Jacobian matrix relating the platform movements to each passive joint velocity is first gained by vector analysis and the passive joint damping matrix is then derived by applying the Kane method. Next, an analytic formula index measuring the degree of coupling effects between the damping terms in the modal coordinates is proposed using classical modal analysis of dynamic equations in task space. Based on the index, a new optimal design method is found which establishes the kinematics parameters for minimizing the coupling degree of damping and achieves optimal fault tolerance for modal space decoupling when all struts have identical damping and stiffness coefficients in their axial directions. To illustrate the effectiveness of the theory, the new method was used to redesign two configurations of a specific manipulator.

Variable-stiffness decoupling of redundant planar rotational parallel mechanisms with crossed legs:

For redundant planar rotational parallel mechanisms (RPRPM), stiffness consists of active stiffness resulting from internal forces and passive stiffness caused by compliances of flexible elements, and the active stiffness is coupled with the passive stiffness. The stiffness variations with stretching internal force and compressing internal force of flexible elements are analyzed. By combining the leg-crossed RPRPM and leg-uncrossed RPRPM of different leg arrangements, the active stiffness is decoupled from the passive stiffness. The stiffness is modulated by changing the internal force and hence the spring stretching length independently to avoid being influenced by the passive stiffness. The stiffness variation multiple with given spring stretching length is maximized by decoupling the active stiffness from the passive stiffness. The variation of natural frequency of RPRPM is maximized by maximizing the stiffness variation, and the RPRPM can employ vibration of resonance to improve the working performance in a large range of driving frequency.

Research on three-axis six-DOF shaking table based on rapid prototyping of DSP algorithms using SIMULINK

Three axes hydraulic shaking system as the means to recreate vibration environment can accurately reproduce reference power spectrum density and time history response. The vibration control is a key technique to meet the requirement. This paper introduces the principle of the three-axis six-DOF shaking table at first and then designs hardware system using TMS320C2812 to acquire the analog and digital variable and using TMS320C6713 to operate and communicate with S3C2410 via dual-RAM in order to improve real-time and rapidity of the system. In the end, this paper presents the implementation of a rapid prototyping control system, which involves the design of DSP algorithms using MATLAB Simulink blocksets, automated code generation in the CCS integrated development environment, and downloading of executable code to the Texas Instrumentspsila TMS320C2812 and TMS320C6713.