Kinematic calibration of the 3-degree-of-freedom redundantly actuated spatial parallel module of a five-axis hybrid machine

As a new type of manufacturing equipment, redundant hybrid machines have the theoretical advantage over the traditional serial machines in efficiently processing large structural parts with high material removal ratio and complex parts with curved surfaces. In order to solve the accuracy problem of the redundantly actuated spatial parallel module of a five-axis hybrid machine, an improved kinematic calibration method is proposed in this article. First, different from error modeling for the corresponding non-redundant parallel module, the geometric error model of the redundantly actuated spatial parallel module considers the deformations at active joints caused by actuation redundancy as an error source. Then, the applicable error model is developed using projection technique to remove the need of active joints’ stiffness measurement or modeling. Later, the practical error model is derived from model reduction method to avoid using additional sensors or gratings. Finally, three forms of relative measurement and step identification are adopted for the calibration work, and the bilinear interpolation compensation function is introduced to ensure the calibration effect. On this basis, the kinematic calibration of the redundantly actuated spatial parallel module is conducted. The max position errors are reduced from original −0.192 to 0.075 mm after RM1 and SI1, and then further reduced to 0.014 mm after bilinear interpolation compensation, while the max orientation errors are reduced from −0.017° and 0.249° to −0.005° and −0.007° after RM2 and SI2, and RM3 and SI3, respectively. A contrasting experiment is also carried out with the previous method for the corresponding non-redundant parallel module. As a result, the proposed method shows better convergence value and speed in identifying error parameters, and therefore the effectiveness and efficiency of the proposed method for the redundantly actuated spatial parallel module are validated.

Reliability Analysis of Different Cell Configurations of Lithium ion battery Pack

To infer and predict the reliability of the remaining useful life of a lithium-ion (Li-ion) battery is very significant in the sectors associated with power source proficiency. As an energy source of electric vehicles (EV), Li-ion battery is getting attention due to its lighter weight and capability of storing higher energy. Problems with the reliability arises while li-ion batteries of higher voltages are required. As in this case several li-ion cells areconnected in series and failure of one cell may cause the failure of the whole battery pack. In this paper, Firstly, the capacity degradation of li-ion cells after each cycle is observed and secondly with the help of MATLAB 2016 a mathematical model is developed using Weibull Probability Distribution and Exponential Distribution to find the reliability of different types of cell configurations of a non-redundant li-ion battery pack. The mathematical model shows that the parallel-series configuration of cells is more reliable than the series configuration of cells. The mathematical model also shows that if the discharge rate (C-rate) remains constant; there could be an optimum number for increasing the cells in the parallel module of a parallel-series onfiguration of cells of a non-redundant li-ion battery pack; after which only increasing the number of cells in parallel module doesn’t increase the reliability of the whole battery pack significantly.

Design and Kinematic Analysis of a Novel Hybrid Kinematic Mechanism With Seven-Degrees-of-Freedom and Variable Topology for Operation in Space

We propose a novel hybrid robot with seven degrees-of-freedom (DOF) and variable topology for operation in space. Design specifications of the space robot are presented for the type synthesis of hybrid mechanisms. Based on GF set theory, three design rules are given, thus providing the design method of the 7DOF hybrid space robot mechanism. Twenty-four combinations of the hybrid robotic mechanisms are obtained. The final synthesized configuration for the design of the space robot has a 3DOF parallel module and a 4DOF serial module with four revolute (RRRR) joints. The parallel module consists of a limb with universal-prismatic (UP) joints and two limbs with universal-prismatic-spherical (UPS) joints. The topology of the hybrid robot can be changed, and it will become an RPRR four-bar mechanism when it is folded for launch. The closed-form solution for the inverse displacement model is developed, and then the forward displacement equations are also obtained. After that, the Jacobian matrix is derived from the displacement model; the Jacobian matrix will analyze the singularity and workspace. We find that there are four singularities of mechanisms. The dexterous workspace of the hybrid robot is a good match for the grapple operation in space. An experiment with the prototype shows the present hybrid robot can grapple to a satellite-rocket docking ring and therefore validates the kinematic equations.

Give Me Your Tired, Your Poor? Support for Social Citizenship Rights in the United States and Europe

This article investigates whether the commitment to social rights as integral to a well-functioning democracy exists among Americans in comparison with their European counterparts. In our comparison of data from the European Social Survey in 2012 with a special parallel module of the U.S. Cooperative Congressional Election Survey in 2014, the findings suggest that similar conceptions of ideal democracy are found on both sides of the Atlantic. Although Americans are less likely than Europeans to consider fighting poverty and reducing income inequality as important democratic ideals, the analysis shows that the United States is not exceptional in the existence of a social rights conception of democracy. A distinct feature of U.S. public opinion is that support for social rights is more strongly associated with a left-right divide than in Europe. The observed congruence between policy and public opinion in the United States highlights the importance of investigating the direction of causality between both phenomena.

Kinematics Analysis of a Snake Robot Module Using Screw Theory

A natural snake can navigate lots of diverse environments owing to their extreme agility and hyper-redundancy. However, earlier snake robot designs are inadequate to imitate the living snake locomotion comprehensively, since the deficiency of mobility in each single module. The application of parallel mechanism in snake robot can provide considerable dexterity and support-ability to overcome the aforementioned drawback. This paper presents a bionic parallel module for snake robot inspired by the anatomy of biological snake. To generate four distinct gaits of living snake, three motion screws of the mechanism are obtained via mobility analysis. Further, a kinematic model of this mechanism is investigated by reciprocal screw and Lie algebra aimed to evaluate the kinematic performance in an efficient and accurate scheme, which facilitates real-time motion control. Finally, a numerical result using this method is supplied, and its effectiveness is corroborated by kinematic simulation of ADAMS.