Comparative evaluation of the selective compliance in elastic joints for robotic structures

Large displacement compliant joints can substitute traditional kinematic pairs in robotic articulated structures for increasing ease-of-assembly, robustness, and safety. Nonetheless, besides their limited motion capabilities, compliant joints might be subjected to undesired spatial deformations which can deteriorate the system stability and performance whenever a low number of control inputs is available. In all these cases, it is convenient to select/design joint morphologies which enable a selectively compliant behavior, i.e., a low stiffness along a single desired direction. Within this context, this paper outlines an engineering method for quantifying the joint's selective compliance by means of local and global performance indices. The approach is validated by comparing two beam-like flexures whose analytic solution is known from the literature. Finally, two joint morphologies, previously employed in the fabrication of robotic/prosthetic hands, are critically compared on the basis of the proposed criteria.

The research subject of this paper is spherical 2-DOF Parallel manipulator with actuation redundancy, Mechanical dimension optimum design method of the manipulator has been presented, which considered both global performance index and local performance index, we can obtain relative synthetically optimization mechanical dimension by the method. We finished the optimum program by virtue of software VB and Matlab, and realized dimension optimum design of spherical 2-DOF parallel manipulator with actuation redundancy considered different performance index on different application occasion.

This paper presents a method for determining design parameters of parallel robots (PRs) in its optimal kinematic design. To produce a more compact and economical PR, the determination of an optimal workspace is important. This includes defining a workspace that encases the prescribed regular dexterous workspace (PRDW). Two requirements should be simultaneously satisfied: ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</i> ) the local or global performance index; ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</i> ) a regular shape. In this paper, the optimal problem is firstly discussed and translated into two linear problems. Then, an optimal design procedure which adopts the generalized pattern search algorithm in the genetic algorithm and direct search toolbox of Matlab is proposed to solve these problems. Taken as an example, a linear Delta robot is designed for the four different PRDWs, and its optimal result provides some useful information in measuring the distance between a PRDW and the maximal sized normalized robot. On the basis of the value of distance, some wrong solutions of PR are clarified. It is concluded that the optimal design method is useful for the design and comparison of a general PR.

This paper mainly presents a novel compliant universal joint with linear stiffness (CUJ-LS). This new type of architecture can maintain the linear stiffness while realizing two rotational DOFs. And the planar topology ensures that the rotation axis remains through the center of the moving platform, thus deducing the moment of inertia. According to the Freedom and Constrain Topology (FACT) theory, this paper firstly proposes a topological structure of the compliant universal joint. Then the stiffness model is established by the Beam Constraint Model (BCM) and the condition of achieving linear stiffness is derived: λ = 0.1273/0.8727. By introducing the intermediate platforms, the linear stiffness in two directions of rotation is realized. Finally, FEA method is implemented to verify and analyze the rotation performances of this compliant universal joint. Verified characteristics provide conditions for the applications of compliant universal joint in laser communication, antenna pointing, infrared tracking and aiming, laser processing, precision measurement and other fields which require high-speed, high-acceleration and high precision characteristics.

Diffuse solar radiation models play an extremely important role in solar photothermal utilization, resource assessment and energy consumption simulation, etc. The accuracy of these diffuse solar radiation models usually need to be evaluated by various statistical parameters. Among these statistical parameters, the Global Performance Index (GPI) has been extensively employed in recent years because of its comprehensiveness and wide applicability. This paper takes five cities in China as representatives of 5 typical climate regions, and 12 solar scattered radiation models are fitted with the meteorological data of 5 cities. Based on the comparative analysis of the existing GPI calculation methods, this paper points out that there are some defects in the existing GPI, and modifies the existing GPI based on the comprehensive consideration of statistical parameters, normalization preprocessing of statistical parameters, unified evaluation direction of parameters, weight redistribution of statistical parameters, and adjustment of extreme coefficient. 12 types of new GPI are established in this paper, and the performance of diffuse solar radiation models are compared based on these GPI. The rationality of GPI corrective measures is analyzed by means of the method reasonable index (MRI). The results show that the GPI calculation method (N10) which takes five corrective measures has the best performance, and the accuracy of the existing GPI can be improved by 13.33 to 65%.

New Three-Dimensional Speckle-Tracking Echocardiography Identifies Global Impairment of Left Ventricular Mechanics with a High Sensitivity in Childhood Cancer Survivors

The existing literature on Global Performance Indices (GPIs) is mostly dominated by unit-level analyses focused on specifying the relevant properties of the GPIs and the motivations of state actors in being influenced by GPIs. This article advances a systemic approach, which conceives of GPIs as collectively constituting a system of normative stratification in International Relations (IR). By bringing together the literature on GPIs with the relevant IR literatures on international hierarchies and status-seeking, we identify the structural attributes of the GPI-based system of stratification, how these structural attributes shape the distribution of normative status positions among states, and how this distribution is likely to condition the pursuit of status by states. In particular, we argue that the disaggregated structure and relative ranking of states, respectively, generate status ambiguity and immobility, which both dissuade states from seeking higher moral status through improving their scores in the existing indices. We illustrate the patterns of status ambiguity and immobility present in the GPI-based system of stratification through an empirical analysis of the scores and rank positions of the United States, European Union (EU) members, and “rising powers” in five different indices in the past decade.

Decision fusion for multi-route and multi-hop Wireless Sensor Networks over the Binary Symmetric Channel

Large components such as wing sections should be aligned and positioned in a desired position prior to the final manufacturing or assembly, so a digital alignment and position device based on six degree of freedom parallel manipulator with several prismatic-prismatic-prismatic-spherical branches was designed and fabricated to meet the needs. The digital alignment and position device is an alignment device based on the parallel manipulator, and it is also a positioning and holding fixture for large components manufacturing or assembly. In order to effectively and efficiently select the supporting points of large component where the digital alignment and position device branch is connected with, the performance of the parallel manipulator and the fixture should be comprehensively analyzed at the same time. The global performance indices such as the dexterity index, the bearing capacity index, and the stiffness index are calculated based on the mechanism Jacobean matrix of the parallel manipulator, and the positioning stability index is calculated based on the position Jacobean matrix of the fixture. The results show that the global performance indices are not related to the pose, but the positioning stability index is; in addition, all indices rely on the originally selected supporting points and provide the basis for the effective selection of the supporting points for large component aligned and positioned by the digital alignment and position device, which is based on parallel manipulator with prismatic- prismatic-prismatic-spherical pairs.

In this paper, we introduce a further optimization of morphology of compliant joint based on FEM analysis for a compliant-parallel mechanism with a wide working area and a high accuracy. Compliant-parallel mechanism is the mechanism that all joints are composed by compliant joints in a parallel structure. In the integration of compliant and parallel mechanism, the motion of compliant joints can be guided by mechanical constraints from the parallel structure; thus the mechanism can be precisely driven. However, since compliant joints generally have a limited working area due to limitation in their structural deformation, the working area is commonly limited in micrometer-scale. Designing the compliant joints within a wide range of working area presents us a new challenge: the joints should be elastic for the desired direction, but also rigid for non-desired direction to be deformed. From these requirements, the morphology of the compliant joint was optimized by FEM analysis, and newly serially layered-flat spring compliant joint was developed. The developed compliant joint was implemented on a parallel mechanism as a high precision micro-assembly system for optical components. The prototype enabled 50×50×5 mm of working area within 0.71 mm of repeatable accuracy. From these results, the effectiveness of the morphological optimization for compliant joint was shown.

This paper presents a novel method for identifying dynamic parameters of robot manipulators with elastic joints. A procedure based on the Lagrangianm formulation of the dynamic model is proposed. Each term is inspected to search for a linear relationship with the dynamic parameters, thus enabling the linearization of robot dynamic model. Hence, the torque vector is expressed as the product of a regressor matrix, suitably defined by the vector of dynamic parameters. A parametric identification based on a least-squares technique is applied to determine dynamic parameters of robots with elastic joints. The correctness of the proposed procedure has been tested in simulation on two robotic structures with elastic joints of different complexity, that is, a 2-degree-of-freedom (dof) and a 6-dof manipulator, controlled with a PD control in the joint space.

Knowledge of solar radiation and its components in a particular area is crucial in studying solar energy and constructing solar energy devices due to the many advantages solar radiation has over fossil fuels. In this two-year study, conducted at a tropical site in Ile-Ife, Nigeria, from January 2016 to December 2017, twenty-one empirical models were proposed to estimate diffuse solar radiation using continuous solar radiation data. The models were divided into five groups and developed using relative sunshine duration and/or clearness index as input variables. The performance of five models from the literature was also examined and compared to measured data. The models' performance was evaluated using the Akaike Information Criteria (AIC), the Global Performance Index (GPI), and various statistical errors. Model 11, a quadratic model with clearness index as an input variable, had the lowest AIC (1.8098), AICC (4.8099), &amp;#8710;AICC (0.0000), and GPI (-2.1796) values and was the most accurate model for estimating diffuse solar radiation at the study site and other locations with similar climatic conditions. None of the models selected from the literature was suitable for estimating diffuse solar radiation at the study site; hence, the proposed models performed better.

Large displacement elastic joints have been widely used in rehabilitation exoskeleton, in this paper, a brief reminder of the application of large displacement elastic joints in exoskeleton robotic structures has been given. A new concept of rigid-compliant exoskeleton joint has been presented using four-bar compliant linkage for exoskeleton robot applications. The paper describes the method of designing the rigid-compliant exoskeleton joint according to the motion of human knee.

Out-of-plane shear performance of a novel non-metallic CLT dovetail joint subjected to monotonic and cyclic loading

The main problems appearing in the compliant mechanism synthesis procedure are the realization of the accuracy of the pre-defined function as best as possible, as well as the realization of the motion range of the mechanism as large as possible. One of the most frequent compliant mechanism synthesis procedure is to develop the compliant mechanism on the basis of the rigid-body linkage being able to realize pre-defined function of the compliant mechanism. There are many advantages of using the compliant joints in the mechanism structure. On the other hand, the mechanisms with compliant joints can realize relatively small motion range, that is, their mobility is limited. Another limitation to their use is fatigue failure at the compliant joints. In each particular compliant joint the angular deflection of a flexure hinge is limited in depending of the contour and hinge dimensions as well as the type of the material being used for the production of the compliant mechanism. Therefore, if there are several rigid-body counterparts to be used in compliant mechanism synthesis procedure, it should be necessary to choose the particular rigid-body counterpart with the smallest values of the angular deflection of the compliant joints. This approach will be presented in the synthesis procedure of the compliant mechanism for rectilinear guiding.