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Author(s):  
K.G. Erastova ◽  
P.A. Laryushkin

A delta robot with three degrees of freedom, having been well studied over the past 40 years, is one of the most popular parallel mechanisms. Nowadays, an urgent task is to study the properties of various modifications of this mechanism. The article considers a delta robot with four degrees of freedom, in which one of the kinematic chains with a parallelogram is divided into two, allowing the output link to have an additional rotational degree of freedom. To maximize the working area and minimize the cost of modification the optimization of the robot design was performed. The problem of maximizing a cubic workspace has been solved.


2021 ◽  
Vol 2021 (4) ◽  
pp. 56-65
Author(s):  
S.V. Khoroshylov ◽  
◽  
V.K. Shamakhanov ◽  
V.V. Vasyliev ◽  
◽  
...  

The aim of the article is to model the processes of centrifugal deployment of a three-section boom and preliminary analyze the feasibility of this deployment method for an Earth remote sensing (ERS) minisatellite (MS). During the research, methods of theoretical mechanics, multibody dynamics, control theory, and computer modeling were used. Centrifugal deployment of multi-section booms have been successfully used on spin stabilized satellites, but not on ERS satellites, which have other features of operation and require additional studies. The main part of the MS is a platform to which a transformable antenna is attached by means of a transformable boom. Before deployment, the stowed boom and antenna are attached to the MS platform. The boom sections are connected by joints with one rotational degree of freedom and deployed sequentially due to centrifugal forces when the MS rotates in the required direction. Each of the boom joints has a locking mechanism that latches when a predetermined deploy angle is reached. To model the processes of the boom deployment, the MS is presented as a system of connected bodies, where the platform and the stowed antenna are absolutely rigid bodies, and the boom consists of three flexible beams of a tubular cross-section. The differential equations of the MS dynamics during the deployment are obtained using the Lagrangian formalism, which are supplemented by algebraic equations describing the constraints from the joints. The scenarios of the boom deployment with a constant control torque and a constant angular velocity of the MS are considered. These scenarios are simulated, and estimates of the control actions needed to ensure full deployment of the boom and the stabilization of the MS after latching of the joints are calculated. Dependences of variations of the loads on the boom structure during deployment are obtained. The simulation results allow us to conclude that it is feasible to implement the method of the boom centrifugal deployment for the MS, which can perform fast rotations about the three axes of the body reference frame. Implementation of this method allows designers to reduce mass of the MS because it does not require any servo drives in the boom deployment system.


Author(s):  
Steven van Terwingen ◽  
Noah Nachtigall ◽  
Ulli Englert

Abstract The ligand 3-(4-(1,3,5-trimethyl-1H-pyrazol-4-yl)phenyl)acetylacetone (1) combines a Pearson hard O,O′ chelating acetylacetone donor with a softer pyrazole N donor bridged by a phenylene spacer. Deprotonation and coordination to CuII leads to a square planar bis-acetylacetonato complex; interpreting the close proximity of an adjacent complex’s pyrazole moiety as an η 2 ${{\eta}}^{2}$ coordination to the axial CuII position leads to a two dimensional extended structure. The N donor capabilities are proven by coordination to AgPF6 and AuCl; for AgI a cationic linear bis-pyrazole complex as a toluene solvate is obtained with toluene-pyrazole π-interactions and an essentially uncoordinated PF 6 - ${{\mathrm{PF}}_{6}}^{-}$ anion. In the case of AuCl a neutral linear coordination compound with one chlorido and one pyrazole ligand 1 is obtained. Comparing the dihedral angles with a closely related but shorter ligand reveals a larger rotational degree of freedom in 1, allowing for richer architectures in emerging coordination polymers.


Polymers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3653
Author(s):  
Franklin Langlang Lee ◽  
Jaehong Park ◽  
Sushmit Goyal ◽  
Yousef Qaroush ◽  
Shihu Wang ◽  
...  

Polyamides are often used for their superior thermal, mechanical, and chemical properties. They form a diverse set of materials that have a large variation in properties between linear to aromatic compounds, which renders the traditional quantitative structure–property relationship (QSPR) challenging. We use extended connectivity fingerprints (ECFP) and traditional QSPR fingerprints to develop machine learning models to perform high fidelity prediction of glass transition temperature (Tg), melting temperature (Tm), density (ρ), and tensile modulus (E). The non-linear model using random forest is in general found to be more accurate than linear regression; however, using feature selection or regularization, the accuracy of linear models is shown to be improved significantly to become comparable to the more complex nonlinear algorithm. We find that none of the models or fingerprints were able to accurately predict the tensile modulus E, which we hypothesize is due to heterogeneity in data and data sources, as well as inherent challenges in measuring it. Finally, QSPR models revealed that the fraction of rotatable bonds, and the rotational degree of freedom affects polyamide properties most profoundly and can be used for back of the envelope calculations for a quick estimate of the polymer attributes (glass transition temperature, melting temperature, and density). These QSPR models, although having slightly lower prediction accuracy, show the most promise for the polymer chemist seeking to develop an intuition of ways to modify the chemistry to enhance specific attributes.


2021 ◽  
Author(s):  
HUBERT COURTEAU-GODMAIRE ◽  
ANOUSH POURSARTIP ◽  
REZA VAZIRI

Forming simulation of uncured pre-preg can be made more efficient with the use of dedicated finite elements tailored for soft, layered media. These elements are based on the Cosserat continuum theory that introduces a rotational degree of freedom at each node within standard solid elements. In this study, a Cosserat element is developed within a 2D non-linear explicit finite element framework that uses the Carrera Unified Formulation for its spatial discretization. Two benchmark case studies involving bending deformations are presented as the verification of the developed model. It is demonstrated that similar accuracy of predictions can be achieved with much coarser meshes of Cosserat elements than the equivalent classical finite element models consisting of multi-layer stacks of solid elements.


2021 ◽  
Vol 11 (18) ◽  
pp. 8527
Author(s):  
Ji-wook Kim ◽  
Jae-wook Lee ◽  
Kun-woo Kim ◽  
Ji-heon Kang ◽  
Min-seok Yang ◽  
...  

One of the factors that influence the dynamic characteristics of machining systems is the cutting tool. Cutting tools are very diverse, and receptance coupling substructure analysis (RCSA) is essential for analyzing the dynamic characteristics of each tool. For RCSA, a full receptance matrix of the equipment and tools is essential. In this study, rotational degree-of-freedom receptance was estimated and analyzed using translational receptance. Displacement/moment receptance was analyzed according to the distance of the response point using the first-and second-order finite difference methods. The rotation/moment receptance was estimated according to the distance of the response point. Rotation/moment receptance was analyzed using Schmitz’s method and compensation strategies. The limitations of these strategies were analyzed, and the rotation/moment receptance for the beam under free-free boundary conditions was predicted using the second compensation strategy.


2021 ◽  
Vol 3 (8) ◽  
Author(s):  
Jiangxin Liu ◽  
Zhen-Yu Yin ◽  
Lijian Wu ◽  
Pierre-Yves Hicher

Abstract In traditional finite element failure analyses of geotechnical structures, the micro grain rotations cannot be modelled and numerical solutions are mesh dependent. In this study, a user element including rotational degree of freedom has been developed based on micropolar theory (Cosserat theory), then an enhanced non-associated sand model is calibrated with laboratory data and used to model the plane strain tests. The simulated results demonstrate the polarized model is able to model reasonably the sand behavior as well as the grain rotations in the localized region. What’s more, with this enhanced model, the mesh independent numerical solutions in terms of mechanical responses, shear bands thickness and orientations have been obtained. Article highlights In failure analysis of geostructures, significant rotations of soil grains have been observed to occur in the strain localized regions, but the current commercial Finite Element tools cannot model the micro rotations. Therefore, a user defined element must be developed to include the rotational degree of freedom. The micropolar approach is proven to be effective to model the grain rations in present paper. More suitable than other classical soil or sand constitutive models, the selected non-associated sand model in present paper is capable of describing well the contraction and shear dilatancy behaviors of sand. Then the model has been enhanced by means of micropolar technique, in this way, the reasonable strain localization phenomena in laboratory tests could be predicted well. There are always the mesh dependent problems for traditional simulations of the strain localization phenomena in finite element analysis. It can be found in present paper that the mesh independent numerical solutions are obtained by means of micropolar technique. Furthermore, the micropolar approach can obviously improve convergence difficulties in finite element analyses.


2021 ◽  
pp. 1-12
Author(s):  
Bingxing Chen ◽  
Hongzhou Jiang ◽  
Jingxuan Liu ◽  
Shuaibo Lu

Abstract We propose a method to design a tensegrity joint, making its elastic deformation an accurate joint-like motion, such as a rotation around the designed rotational center. The tensegrity joint can be a three rotational degree-of-freedom (DOF) joint through this method. Axis drift is presented as a design criterion to describe the rotational center's deviation degree concerning the compliance center since the rotational center is not fixed to one point for different positions of the tensegrity joint. The axis drift is designed to be in a prescribed range so that the tensegrity joint is approximately equivalent to a rigid joint. In other words, the tensegrity joint's elastic response under external torque and force becomes precise rigid-joint-like kinematics and can replace rigid joints to transfer motion, force, and energy. A large-size tensegrity joint is developed to verify the joint equivalence experimentally. The experimental results show that the tensegrity joint achieved maximum dimensionless axis drift less than 2%, and indicate an excellent joint equivalence. The tensegrity joints' ability to replace rigid joints as modular joints to construct a hyper redundant serial structure is demonstrated using a tensegrity robotic arm. The proposed tensegrity compliant joint has notable benefits of tensegrity structure such as high mechanical efficiency, modularity, and scalability, and can be extended to many robotic applications, such as large-size serial robotic arms and snake-like robots.


2021 ◽  
Vol 69 (2) ◽  
pp. 146-161
Author(s):  
Osman Taha Sen ◽  
Rajendra Singh

This article proposes a refined nonlinear mathematical model to conceptually investigate the brake pad kinematics and dynamics in order to reveal certain important aspects that have been ignored in prior studies. In particular, the proposed model is formulated as a three degree-of-freedom mass positioned on a rigid frictional surface moving at constant velocity. The mass is assumed to make planar motion in vertical plane, two translations and one rotation. The interfacial contact is first examined by a point contact model with linear translational springs at edges and then the line contact is defined over the entire interface. Furthermore, kinematic and clearance nonlinearities are included. The nonlinear governing equations with point contacts at edges are numerically solved at certain angular arrangements of normal force vectors. Then, the line contact interface is solved again for the same normal force vector arrangements. Comparison reveals that the line contact approach provides more meaningful results. Finally, a linearized system model and the existence of quasi-static sliding motion are examined over a range of the normal force vector arrangements. Overall, inclusion of the rotational degree of freedom in the source model is crucial and the importance of pad-disc separation is clearly explained by the proposed formulation. This leads to a better understanding of the hammering type brake squeal source mechanisms while overcoming the limitation of prior minimal order models


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