DETERMINATION OF SCREWS-GRADIENTS AND MUTUAL SCREWS THAT BRING L-COORDINATE MECHANISMS OF A PARALLEL STRUCTURE OUT OF SPECIAL POSITIONS AT VARIOUS POINTS OF FASTENING OF DRIVES

2021 ◽  
pp. 9-17
Author(s):  
E. S. Gebel ◽  
L. V. Gavrilina ◽  
V. A. Glazunov ◽  
A. B. Lastochkin ◽  
P. F. Shvets
Keyword(s):  
Parallel Structure ◽  
Output Link ◽  
Special Position

The article discusses the special configurations (singularities) of spatial l-coordinate mechanisms. At the beginning, the position is shown where all the l-coordinate axes intersect the OX axis. In this case, there is a twist, reciprocal to all unit screws of the axes of prismatic kinematic pairs, this reciprocal twist coincides with the OX axis. In addition, a twist-gradient was found, which brings the mechanism out of a special position (singularity). In this case, the centers of the spherical hinges of the base are located on the plane z = –1. The centers of the spherical hinges of the output link are located at different distances from the XOY plane. Then, all the centers of the spherical hinges of the output link are located on the plane z = 1. The twist-gradient changes in this case. When changing the positions of the planes on which the centers of the spherical hinges of the bases and the output link are located, the twist-gradient no longer changes.

Structural and Kinematic Analysis of the Isomorphic Mechanism of a Parallel Structure for Translational Movements of the Output Link

2021 ◽  
pp. 35-40
Author(s):  
T.V. Edakina ◽  
A.I. Edakin ◽  
V.V. Samoilova ◽  
V.S. Ramzhaev
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Kinematic Chain ◽  
Parallel Structure ◽  
Dimensional Model ◽  
Output Link ◽  
Three Dimensional Model ◽  
Industrial Enterprises ◽  
Three Degrees Of Freedom

The article considers the mechanism of a parallel structure with three degrees of freedom, having the property of isomorphism. The ratio between the movements in the drive and the movements of the output link is constant. This is due to the fact that all linear drivers are located parallel to the corresponding axes of the fixed coordinate system, and in each kinematic chain there are two rotational kinematic pairs, the which axes are parallel to the axes of the corresponding linear drivers. In addition, each kinematic chain has two dyads that provide linear motion of the linear driver rod. On the basis of the developed three-dimensional model, a structural analysis of the mechanism with determination of the number of degrees of freedom and solving the problem of its positions was carried out. The proposed mechanism can be applied in many areas of activity of industrial enterprises, including additive technologies due to the growth of automation, robotization and the development of artificial intelligence.

Designing Statically Determinable Mechanisms of Technological Mechatronic Machines with Parallel Kinematics

2019 ◽  
Vol 20 (7) ◽  
pp. 428-436
Author(s):  
A. K. Tolstosheev ◽  
V. A. Tatarintsev
Keyword(s):  
Structural Analysis ◽  
Hierarchical Structure ◽  
Degrees Of Freedom ◽  
Kinematic Chain ◽  
Parallel Structure ◽  
Parallel Kinematics ◽  
Output Link ◽  
Parallel Connection ◽  
Kinematic Chains ◽  
Chain Increase

The work is devoted to improving the reliability and manufacturability of mechatronic machine designs with parallel kinematics by replacing statically indeterminable manipulators with statically determinable mechanisms. A technique is proposed in which the design of statically determinable manipulators of technological mechatronic machines with parallel kinematics is performed by modifying the structure of prototypes and includes three steps: identifying and analyzing redundant links, eliminating redundant links, checking the correctness of eliminating redundant links. To determine the number of degrees of freedom of the mechanism, identify redundant links, and verify the solution, the authors use the proposed methodology for structural analysis of parallel structure mechanisms. In structural analysis, a manipulator is represented by a hierarchical structure and is considered as a parallel connection of elementary mechanisms with an open kinematic chain; as a kinematic chain consisting of leading and driven parts; as a set of links and kinematic pairs; as a kinematic connection of the output link and the rack. The article implements the following techniques for eliminating redundant links: mobility increase in kinematic pairs; introduction of unloading links and passive kinematic pairs to the kinematic chain; exclusion of extra links and pairs from the kinematic chain; increase in mobility in some kinematic pairs simultaneously with the exclusion of other kinematic pairs that have become superfluous. The authors developed several variants of structural schemes of self-aligning manipulators based on the Orthoglide mechanism, which retain the basic functional proper ties of the prototype. To increase the number of self-aligning mechanism diagrams, the redistribution of mobilities and links within the connecting kinematic chain and between connecting kinematic chains is used. The proposed methodics allow to determine the number of degrees of freedom of the mechanism, the number and type of redundant links, eliminate redundant links and, on an alternative basis, build structural diagrams of statically determinable mechanisms of technological mechatronic machines with parallel kinematics.

Evaluation and Optimum Design of Parallel Manipulators Having Defined Workspace

2000 ◽  
Author(s):  
Jürgen Schönherr
Keyword(s):  
Optimum Design ◽  
Degrees Of Freedom ◽  
Parallel Manipulators ◽  
Parallel Structure ◽  
Transmission Quality ◽  
6 Degrees Of Freedom ◽  
Kinematic Optimization ◽  
Method Of Design

Abstract The condition of the Jacobian characterizes the transmission quality of manipulators and is used in this paper for the determination of the dimensions of manipulators having best mobility for a defined workspace. Typical planar and spatial manipulators of parallel structure and having 3 or 6 degrees of freedom are used to demonstrate the method of design used. Manipulators having identical degrees of freedom and workspaces and different structures, including those having fixed or variable leg lengths, are compared with respect to their mobility. The computing program developed for the purpose of optimum design performs the kinematic optimization of machines and manipulators of any structure.

The Influence of Special Positions on the Rigidity of Parallel Structure Mechanisms

2020 ◽  
pp. 21-28
Author(s):  
K.G. Erastova
Keyword(s):  
Closed Loop ◽  
Jacobian Matrix ◽  
Parallel Structure ◽  
Geometrical Parameters ◽  
Chain Mechanism ◽  
Special Position ◽  
Working Zone ◽  
Kinematic Chains ◽  
New Methods ◽  
Promising Area

Due to a sharp increase in the accuracy of manufacturing and quality control of mechanical engineering products, robots based on mechanisms with closed-loop kinematic chains have become a promising area of engineering. One of the advantages of parallel structure mechanisms over serial mechanisms is their increased rigidity. The absence of patterns in the change of rigidity in the working zone and the influence of the so-called special positions necessitate the development of new methods of optimization synthesis of the mechanism. This paper presents an approach based on the Jacobian matrix using which it is possible to determine rigidity in the worst direction of the external force application in each point of the working zone. The same approach can also be used for determining the shape and size of the effective working zone. An example of a flat five-chain mechanism is used to demonstrate the application of the method and obtain a matrix of chain rigidity, construct the parallelogram of forces and determine rigidity distribution in the working zone. It is shown that when approaching a special position, the rigidity of the mechanism decreases ten-fold, and in the special position it equals a zero. The proposed method can be used for optimizing the geometrical parameters of the mechanism on the conditions of maximising the effective working zone.

Determination of Internal Forces of Complex Plane Truss

2014 ◽  
Vol 543-547 ◽  
pp. 3990-3993
Author(s):  
Ju Hua Huang
Keyword(s):  
Cross Section ◽  
Internal Force ◽  
Rigid Bodies ◽  
Special Position ◽  
Internal Forces ◽  
Comprehensive Judgment ◽  
Force Calculation ◽  
Cross Section Method ◽  
Made In

Further discussion of internal force calculation for the plane truss is made in this paper. The internal force of simple truss can be calculated with node method, according to the composition order of the truss. The internal force of joint truss can be calculated according to the composition rules of two or three rigid bodies. The internal force of complex truss requires the comprehensive judgment flexibly according to node method, cross section method and zero pole in special position and the symmetry of structure.

scholarly journals Punishment of the collaborationists in Vichy and other French regions (1944 – 1945)

2021 ◽  
pp. 86-93
Author(s):  
Aleksei Dmitrievich Medvedev
Keyword(s):  
Law Enforcement ◽  
The Other ◽  
Postwar Period ◽  
Special Position ◽  
French Government ◽  
Organized Violence ◽  
Other Hand

The goal of this article lies in examination of the process of preventing collaborationism in the former capital of the French state, as well as in determination of whether the process of suppressing cooperation with the German occupier has any peculiarities associated with the special position of Vichy in relation to other departments. The author examines such aspects of the topic as spontaneous and organized violence in Vichy and other French regions during the postwar period (1944 – 1945). Special attention is given to reprisal against the collaborationists in Vichy and the formation of representation on the unity of France during the occupation imbued by the Gaullist state. The main conclusions of this research consists in the two interpretations of the purges that took place in the postwar years in France. The situation in the agglomeration has several similarities with the situation in multiple departments: shaving of women; government branches responsible for repressions; urgent purges. However, the fact that namely Vichy was the seat of the French government has its own peculiarities:  weak first phase of the extrajudicial purge due to the presence of law enforcement forces during the occupation and opposition, and on the other hand, the cruelty of spontaneous violence in June of 1945,  numerous arrests in the first two weeks after the liberation, excessive city residents representation in the Court and  Civil Chamber, as well as severity of the sentences.

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