Thumb Configuration and Performance Evaluation for Dexterous Robotic Hand Design

The force and/or motion transmissibility and the analyticity of inverse kinematics for a thumb mechanism depend on thumb configuration. This paper presents a general framework for the thumb configuration and performance evaluation in the design of dexterous robotic hand. The thumb configuration is described by the functional analysis of human thumb, and the thumb of robotic hand is generalized into 15 configurations. A performance evaluation method is proposed based on kinetostatic and dynamic dexterity as well as workspace. The kinetostatic dexterity is based on a Jacobian matrix condition number (JMCN). A dynamic dexterity measure is presented via acceleration analysis, which keeps a clear geometric meaning. The proposed method is applied to evaluate the performance of three examples, which cover thumb configurations of most existing dexterous hands. Performance evaluation results demonstrate the effectiveness of the proposed method. Using these results and the proposed performance evaluation method, meaningful design principles are presented to guide the design of the thumb configuration.

An Effective Independence-Improved Modal Strain Energy Method for Optimal Sensor Placement of Bridge Structures

In this study, an effective independence-improved modal strain energy (EI-IMSE) method is proposed for the optimal sensor placement (OSP) problem in the field of the structural health monitoring and moving force identification. The improved modal strain energy (IMSE) is used to modify optimal sensor placement results obtained by the effective independence (EI) method. The EI-IMSE OSP method is verified by some numerical simulations on a 2D planar truss bridge model. Based on the criteria of modal assurance criterion (MAC), trace of fisher matrix, matrix condition number, and the least mean square error, the EI-IMSE OSP method is assessed through comparing with those of EI, EI-driving point residue (EI-DPR), EI-average driving DOF velocity (EI-ADDOFV), and EI-average acceleration amplitude (EI-AAA). The illustrated results show that the proposed EI-IMSE OSP method is feasible with a higher accuracy.

Optimal Sensor Placement Based on Tabu Search Algorithms

In this study, the Tabu search (TS) algorithm is introduced into the optimal sensor placement (OSP) problem in the field of the structural health monitoring and moving force identification. A TS-based OSP procedure is proposed and further evaluated by some numerical simulations on a 2D planar truss model. The mean values of off-diagonal elements in a modal assurance criterion (MAC) matrix are used as the optimization objective function. Based on the criteria of MAC, determinant of fisher matrix, matrix condition number, and the least mean square error, the TS-based OSP procedure is evaluated through comparing with ones due to both of the energy coefficient-effective independence (ECEFI) and the effective independence (EFI) algorithms. The results show that the proposed TS-based OSP procedure is feasible with a higher accuracy.

Structural Parameters Optimization of Parallel Stable Platform Based on Physical Programming

Based on the parallel stable platform of 6-UPS, Jacobi matrix condition number and driving force of six rods are respectively identified as kinematics evaluation index and dynamics evaluation index of the parallel stable platform. By using physical programming preference functions the comprehensive preference function are constructed. Thus, a multi-objective optimization problem is formulated as a single objective optimization problem. Structural parameters with best working performance are computed by the genetic algorithm. Simulation results in Matlab show that the performance of optimization platform has been improved.

Workspace Analysis and Dimensional Synthesis on a Delta Parallel Mechanism with Branch Chain Offset

In this paper, we intend to design a force-feedback device that meets the requirements in workspace. First, based on the modified Delta mechanism, we introduced a chain offset angle that is defined as alpha. We established the positive and inverse kinematics model by the vector method. According to the inverse kinematics formula, envelope body equation of single-open-chain subspace was deduced. We drew the geometric shape of the subspace under three situations while L1 was more than or equal to or less than L2. Then the influence of alpha on the whole workspace and mechanism size is deeply discussed. The cross section view of the space was also plotted by MATLAB. Finally, we gave an example using the Jacobin matrix condition number as the mechanism performance index for dimensional synthesis. The results show that the workspace meets the requirements well.

The inverse problem of bimorph mirror tuning on a beamline

One of the challenges of tuning bimorph mirrors with many electrodes is that the calculated focusing voltages can be different by more than the safety limit (such as 500 V for the mirrors used at 17-ID at the Advanced Photon Source) between adjacent electrodes. A study of this problem at 17-ID revealed that the inverse problem of the tuningin situ, using X-rays, became ill-conditioned when the number of electrodes was large and the calculated focusing voltages were contaminated with measurement errors. Increasing the number of beamlets during the tuning could reduce the matrix condition number in the problem, but obtaining voltages with variation below the safety limit was still not always guaranteed and multiple iterations of tuning were often required. Applying Tikhonov regularization and using the L-curve criterion for the determination of the regularization parameter made it straightforward to obtain focusing voltages with well behaved variations. Some characteristics of the tuning results obtained using Tikhonov regularization are given in this paper.