Least square approximate motion generation synthesis of spherical linkages by using Chebyshev and equal spacing

WOS: 000314011700008In this paper, approximate motion synthesis of spherical linkages is presented. Rigid body guidance of a spherical four-bar mechanism is performed by a spherical RR open chain. In the first step, position of a point on rigid body and orientation of a rigid body on a unit sphere are described. Synthesizing function of spherical dyad is derived by means of using unit vectors that describe location of two revolute joints and tip point. Being based on the theory of function approximation and besides the linearization of nonlinear synthesis equations by using superposition method, the design procedure for real solutions of fourth order polynomial equation is developed. In the second step, approximate motion generation synthesis of spherical dyad is presented by using least-square approximation. Chebyshev spacing and equal spacing are used in the determination of poses. In the final step, two numerical examples are given to show how error graph is varied in terms of selected poses. The spherical motion generation synthesis of spherical four-bar mechanism is obtained by the combination of the two real solutions of the synthesis of two spherical dyads. (C) 2012 Elsevier Ltd. All rights reserved

Geometric Design of Planar Scissor Linkages with Hybrid Loop Assemblies

Due to their expansion capabilities and the simplicity of their design, scissor linkages have been used in both architecture and engineering for various applications, such as expandable roofs and shelters, movable bridges, furniture, and as parts of mechanisms. The two main design methods used for scissor linkages are the unit-based method and the loop-based method. While the unit-based method is based on serial multiplication of the scissor units, the loop-based method is based on aligning predefined loop types onto the desired curve. When the input parameter is the desired curvature for the finally deployed configuration of the linkage, the loop-based method is easier and more convenient for defining the scissor units to create the whole linkage geometry. Most of the existing studies on the loop-based method deal with identical or arbitrary loops. Hybrid loop assemblies have not yet been studied, although they may offer different geometric alternatives. This work aimed to fill this gap in the literature and present a geometric design approach for scissor linkages composed of hybrid loop assemblies using frieze patterns. First, the basic terminology, such as loop types, loop assemblies, and frieze patterns, is introduced. Then, we discuss scissor linkages using hybrid loops, generated using a predefined rectilinear geometry in which frieze groups are used to provide diverse variations. The kinematic definitions of the represented linkages are then explained. To reveal the potential applications of the scissor linkages composed of hybrid loops, a case study was conducted in which the proposed linkages were used as a canopy structure. After discussing the potential for using hybrid loops, and their deployment, we present the concluding remarks and make suggestions for future research. (C) 2022 American Society of Civil Engineers

Spontaneous epidural and subdural hematoma in a child with afibrinogenemia and postoperative management

Congenital afibrinogenemia is a rare coagulation disorder that exhibits recessive inheritance. The prevalence of this disease is around 1 per 1 000 000, but it is increased in countries where consanguineous marriages are common. Umbilical cord bleeding during the neonatal period is generally the first manifestation of the disease, but a later age of onset is not uncommon. This disease may also be manifested by gastrointestinal, genitourinary, mucosal, muscular, articular, and intracranial bleeding during childhood. Intracranial hemorrhage is a rare condition, but it is the leading cause of death in patients with afibrinogenemia. In this report, we present the case of a 13-year-old female patient with afibrinogenemia who underwent an operation for spontaneous massive extradural and subdural hematoma