This paper mainly analyzes a hybrid position/force control strategy and experiment of a six-cable driven parallel manipulator for a forty-meter aperture radio telescope. Through the establishments of a kinematic model...This paper mainly analyzes a hybrid position/force control strategy and experiment of a six-cable driven parallel manipulator for a forty-meter aperture radio telescope. Through the establishments of a kinematic model, a catenary model and a cable-force characteristics model, a basic method is presented based on preventing the pseudo-drag problem of a flexible cable and realizing the hybrid position/force control for a six-cable driven parallel manipulator, and a hybrid position/force control system is developed. Some specific experiments in two typical velocities for astronomical observations are carried out. Experimental results show that the tracking accuracy is related to the speed of the movement. The desired tracking accuracy of the support system is achieved through an effective hybrid position/force control strategy, the cable forces are controlled effectively, and the pseudo-drag problem of flexible cable is solved. This study establishes the foundation of achieving the harmonious movement of the six-cable driven parallel manipulator, A-B rotating platform and the Stewart fine tuninz olatform.展开更多
Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A...Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O（prismatic-spherical-revolute） is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints＇ stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.展开更多
A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in en...A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii） stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it environment with complex characteristics. Finally, numerical robot manipulator. also shows robustness of the proposed controller to uncertain simulation verifies results via contact task of a two rigid-links展开更多
Clearances at joints cause an uncertainty in the actual posture of the end-effector of any mechanism. This uncertainty relays on the clearance dimension and the way these clearances are taken up by the mechanism under...Clearances at joints cause an uncertainty in the actual posture of the end-effector of any mechanism. This uncertainty relays on the clearance dimension and the way these clearances are taken up by the mechanism under the load and the inertial effects at every instant. As a matter of fact, the actual measure of the pose error is often replaced by an uncertainty measure. However, a side effect of the existence of clearances is that they can cause sudden changes in the posture of the mechanism as a motion is performed. Such discontinuities in the position produce task defects and impacts. In this work a tool to determine the pose error due to clearances is presented together with a discontinuity analysis. In addition, effects of mass distribution and inertial effects on such discontinuities are expounded, taking a 3-PRS robot as example.展开更多
A parallel imaginary EBE (element-by-element )method for solving positive definite linear systems is presented. The EBE strategy is originally used as a sequential method[1.2], and later it is converted to a parallel...A parallel imaginary EBE (element-by-element )method for solving positive definite linear systems is presented. The EBE strategy is originally used as a sequential method[1.2], and later it is converted to a parallelmethod for solving finite element problem in solid mechanics[3]. The main contribution of this paper is to forma general parallel EBE method for the solution of anyPOsitive definite linear system through a so-called imaginary finite element technique. It is then POssible to use.finite elemental without finite element.展开更多
现有的线性RankSVM已得到较有效的研究,但在训练大规模的线性Rank SVM时,过长的训练时间依然难以让人接受。通过对当前最先进算法Tree-TRON的分析可知,利用信任区域的牛顿迭代(trust region Newton method,TRON)去训练线性Rank SVM模型...现有的线性RankSVM已得到较有效的研究,但在训练大规模的线性Rank SVM时,过长的训练时间依然难以让人接受。通过对当前最先进算法Tree-TRON的分析可知,利用信任区域的牛顿迭代(trust region Newton method,TRON)去训练线性Rank SVM模型涉及大量的Hessian-vector内积(Hessian-vector product)计算,同时完成Hessian-vector内积计算又需计算大量的辅助变量和矩阵运算。为了有效地加速与Hessian-vector内积有关的计算,在多核系统下提出了一种高效的并行算法(命名为PRank SVM)用于提高大规模线性Rank SVM的训练速度。PRank SVM的特征主要体现为两个方面:训练数据按不同的查询划分为不同的子问题;在多核系统下,利用多核加速辅助变量和相关矩阵的计算。通过实验分析可知,相较于现有的算法(如Tree-TRON),PRank SVM不仅可以有效地提高训练速度,而且可以有效地确保预测的准确率。展开更多
基金Supported by the National Basic Research Program of China （ No. 2007CB714007） , the National Natural Science Foundation of China （ No. 50975149） , and the Important National Science ＆ Technology Specific Projects of China （No. 2009ZX04014-.035, 2009ZX04001-042-02）.
文摘This paper mainly analyzes a hybrid position/force control strategy and experiment of a six-cable driven parallel manipulator for a forty-meter aperture radio telescope. Through the establishments of a kinematic model, a catenary model and a cable-force characteristics model, a basic method is presented based on preventing the pseudo-drag problem of a flexible cable and realizing the hybrid position/force control for a six-cable driven parallel manipulator, and a hybrid position/force control system is developed. Some specific experiments in two typical velocities for astronomical observations are carried out. Experimental results show that the tracking accuracy is related to the speed of the movement. The desired tracking accuracy of the support system is achieved through an effective hybrid position/force control strategy, the cable forces are controlled effectively, and the pseudo-drag problem of flexible cable is solved. This study establishes the foundation of achieving the harmonious movement of the six-cable driven parallel manipulator, A-B rotating platform and the Stewart fine tuninz olatform.
基金Supported by National Natural Science Foundation of China(Grant No.51221004)National Hi-tech Research and Development Program of China(863 Program,Grant No.2012AA040605)
文摘Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O（prismatic-spherical-revolute） is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints＇ stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.
文摘A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii） stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it environment with complex characteristics. Finally, numerical robot manipulator. also shows robustness of the proposed controller to uncertain simulation verifies results via contact task of a two rigid-links
文摘Clearances at joints cause an uncertainty in the actual posture of the end-effector of any mechanism. This uncertainty relays on the clearance dimension and the way these clearances are taken up by the mechanism under the load and the inertial effects at every instant. As a matter of fact, the actual measure of the pose error is often replaced by an uncertainty measure. However, a side effect of the existence of clearances is that they can cause sudden changes in the posture of the mechanism as a motion is performed. Such discontinuities in the position produce task defects and impacts. In this work a tool to determine the pose error due to clearances is presented together with a discontinuity analysis. In addition, effects of mass distribution and inertial effects on such discontinuities are expounded, taking a 3-PRS robot as example.
文摘A parallel imaginary EBE (element-by-element )method for solving positive definite linear systems is presented. The EBE strategy is originally used as a sequential method[1.2], and later it is converted to a parallelmethod for solving finite element problem in solid mechanics[3]. The main contribution of this paper is to forma general parallel EBE method for the solution of anyPOsitive definite linear system through a so-called imaginary finite element technique. It is then POssible to use.finite elemental without finite element.
