Arrangement Of Limbs Research Articles

A novel hybrid machine tool integrating a symmetrical redundantly actuated parallel mechanism: Design, kinematics, prototype and experiment

Hybrid machine tools are suitable for machining structural components with complex geometries due to their merits of flexible posture adjustment and quick dynamic response. This paper proposes a novel hybrid machine tool with 5-axis machining capability by integrating a newly invented redundantly actuated parallel mechanism (RAPM). For this purpose, a screw theory based type synthesis methodology is proposed to synthesize a RAPM with a topology of 2PRU-(2PRU)R. The synthesized RAPM is conceptually designed as a spindle head, which is characterized by symmetrical limb arrangement and usage of only PRU-type kinematic chains. The spindle head is further integrated with a two-sliding gantry to construct a novel 5-axis hybrid machine tool. The kinematic performances of position and singularity of the proposed hybrid machine tool are analyzed. After then, a laboratory prototype of the hybrid machine tool is engineered and an open-architecture numerical control system is developed to perform 5-axis machining tasks. The large orientation capacity and 5-axis machining capability of the hybrid machine tool are verified by some motion experiments and machining tests.

A constraint embedding approach for dynamics modeling of parallel kinematic manipulators with hybrid limbs

Parallel kinematic manipulators (PKM) are characterized by closed kinematic loops, due to the parallel arrangement of limbs but also due to the existence of kinematic loops within the limbs. Moreover, many PKM are built with limbs constructed by serially combining kinematic loops. Such limbs are called hybrid, which form a particular class of complex limbs. Design and model-based control requires accurate dynamic PKM models desirably without model simplifications. Dynamics modeling then necessitates kinematic relations of all members of the PKM, in contrast to the standard kinematics modeling of PKM, where only the forward and inverse kinematics solution for the manipulator (relating input and output motions) are computed. This becomes more involved for PKM with hybrid limbs. In this paper a modular modeling approach is employed, where limbs are treated separately, and the individual dynamic equations of motions (EOM) are subsequently assembled to the overall model. Key to the kinematic modeling is the constraint resolution for the individual loops within the limbs. This local constraint resolution is a special case of the general constraint embedding technique. The proposed method finally allows for a systematic modeling of general PKM. The method is demonstrated for the IRSBot-2, where each limb comprises two independent loops.

Multi-stability of a planar three-limb flexible mechanism

In general, the classical multi-stable mechanisms are made of single-loop bi-stable mechanism elements, but this paper proposes a novel structure of a planar three-limb flexible mechanism whose multi-stability is dependent on the structure parameters. The structure of this flexible mechanism is ingeniously designed to have a large selection range of the original limb length, resulting in the variation of the multi-stability distribution and the possible switching paths. To analyze the variation of this flexible mechanism, the paper introduces a method avoiding computational singularity to determine the stability by contour map and a method to draw the multi-stability topology to seek for the possible switching paths. Using these methods, the paper presents the variation of the multi-stability topology of an axisymmetric and two mirror-symmetric planar three-limb flexible mechanisms as the original length of the limbs increases. The results shows the mulita-stability of this flexible mechanism can be determined by the original length of the limbs and limb arrangement. The whole statements provide a theoretical basis for designing and applying such type of flexible multi-stable mechanism.

Design and analysis of a class of two-limb non-parasitic 2T1R parallel mechanism with decoupled motion and symbolic forward position solution - influence of optimal arrangement of limbs onto the kinematics, dynamics and stiffness

The two-limb11Throughout this paper, the two-limb parallel mechanism means that the base and moving platforms of a parallel mechanism are directly connected with two independent limbs, despite the existence of closed sub-loop in one limb (i.e., in this work, it is named as hybrid-single-ordered-chain, and HSOC for short). parallel mechanisms (PMs) can have the advantages, in terms of avoidance of mechanical collision, simple architecture, rapid configuration transformation and large workspace volume. This paper consists of two major contents. The first aspect pertains to the design of a class of two-limb PMs with two translations and one rotation (2T1R), where a family of PMs featuring two translations actuated by sliding units are proposed, with decoupled position and orientation as well as symbolic forward position solution, without parasitic motions. The second aspect is to analyze the influence of the arrangement of limbs onto the kinematic, dynamic and stiffness performance of the PMs. Using the kinematic modeling method based on topological characteristics, the unified symbolic forward and inverse position solutions of the PMs are derived, together with the workspace, rotational capacity and singularity. Finally, a comparative study regarding the kinematics, dynamics and stiffness of the two PMs is carried out to find the optimal PM configuration. This paper presents a systematic analysis for the synthesis, optimal design and performance evaluation of two-limb parallel mechanisms.

Finite displacement screw-based group analysis of 3PRS parallel mechanisms

When limbs of a parallel mechanism have been selected, the geometric relation among limbs determines the mechanism's motion. The limb arrangement which affects the mechanism's motion raises a fundamental and significant issue. If a mechanism only owns limbs with Lie group motions, it is convenient to predict how a limb arrangement determines the mechanism's motion. However, if a mechanism is mainly or purely constituted by limbs with motions of general differential manifolds, it is difficult to find the influence of a limb arrangement. On this regard, this paper provides an in-depth investigation by focusing on motion analysis of parallel mechanisms consisting of three PRS limbs with planar-spherical manifolds. By formulating and comparing the motion characteristics of these mechanisms which though could be modeled difficultly by a mathematical tool without using the finite displacement screw, a finite displacement screw-based group method is proposed in this paper to resolve the raised issue. The novel approach presents results in expressions of new types of manifold motions, providing a foundation for design and application of parallel mechanisms having the various three-planar-spherical manifolds’ intersection motions.

Description of the standard operating procedure «Implementation of therapy with biofeedback for the elbow joint using ArmTutor»

The article presents description and results of rehabilitation measures for children carried out using ArmTutor innovative system (MediTouch) with biofeedback developed by Israeli specialists. This therapy is aimed at improving sensory support for movements, increasing amplitude and accuracy of movement, activating concentration of attention on sensations such as degree of muscle contraction and spatial arrangement of limbs of small patients.

Evaluation of the impact of sagittal spinal curvatures on musculoskeletal disorders in young people

In Poland, about 85% of the population report low back pain (LBP) symptoms overall. Moreover, 70-80% of people aged below 20 have already experienced back pain. The primary cause of LBP is the loss of spinal lordosis, which initiates changes in geometry of the spine and has impact on limb arrangement. The aim of the study was to attempt to verify the relationship between the 2 main curvatures of the spine and its relation to symptoms in different parts of the musculoskeletal system, in a group of adults. It was assumed that hyperlordosis of the lumbar spine and misbalance of the thoraco-lumbar junction are risk factors for LBP. The study coverd 231 first-year students, (aged 19-21) of the University of Economics in Katowice. There were 103 men aged 19.5±0.8 years and 128 women aged 19.6±0.8 years. The students completed the Nordic Musculoskeletal Questionnaire (NMQ): 7 days (NMQ7) and 6 months (NMQ6). A Rippstein's plurimeter, was used to measure the angles of thoracic kyphosis (KTH) and lumbar lordosis (KLL). Cut of points was set at 30±5. The results indicate strong and very strong correlation (r = 0.6 and r = 0.8, p < 0.05) between the concave of the back and LBP, which may suggest the relationship between these symptoms and the increased lordosis. Postural defects in the sagittal plane may predict the occurrence of pain. The results of the study indicate a higher frequency of pain in people with a higher angle of lumbar lordosis. Med Pr 2018;69(1):29-36.

Unified Singularity Modeling and Reconfiguration of 3rTPS Metamorphic Parallel Mechanisms with Parallel Constraint Screws

This paper presents a unified singularity modeling and reconfiguration analysis of variable topologies of a class of metamorphic parallel mechanisms with parallel constraint screws. The new parallel mechanisms consist of three reconfigurable rT PS limbs that have two working phases stemming from the reconfigurable Hooke (rT) joint. While one phase has full mobility, the other supplies a constraint force to the platform. Based on these, the platform constraint screw systems show that the new metamorphic parallel mechanisms have four topologies by altering the limb phases with mobility change among 1R2T (one rotation with two translations), 2R2T, and 3R2T and mobility 6. Geometric conditions of the mechanism design are investigated with some special topologies illustrated considering the limb arrangement. Following this and the actuation scheme analysis, a unified Jacobian matrix is formed using screw theory to include the change between geometric constraints and actuation constraints in the topology reconfiguration. Various singular configurations are identified by analyzing screw dependency in the Jacobian matrix. The work in this paper provides basis for singularity-free workspace analysis and optimal design of the class of metamorphic parallel mechanisms with parallel constraint screws which shows simple geometric constraints with potential simple kinematics and dynamics properties.

Kinematics Performance Comparison of a Family of 3-RPS Parallel Mechanisms Affected by Limb Arrangement

The kinematics performance comparison of a family of 3-RPS parallel mechanisms affected by limb arrangement has been studied in this paper. Firstly, arrangement parameters of single RPS limb are identified. Based on these parameters, variant configurations of 3-RPS parallel mechanisms are enumerated. Then, the inverse kinematic problems of these different mechanisms are solved, and the kinematic performance comparison of these mechanisms is carried out. Simulation results illustrate that limb arrangement has a great influence upon kinematic performance for the 3-RPS parallel mechanisms.

Cinemática de variáveis de técnica-chave nos flic flacs de ginastas de elite

INTRODUÇÃO: A ginástica é o esporte de habilidades fechadas mais antigo e espetacular. Contudo, parâmetros técnicos de execução geralmente são somente ensinados por treinadores experientes. Desta maneira, existe uma lacuna de informações objetivas sobre o desempenho de ginastas (referências cinemáticas). OBJETIVO: No presente estudo, tentamos quantificar movimentos de inversão linear e de hiperextensão durante a execução de flic flacs. MÉTODOS: Foi efetuada uma detecção não invasiva de flic flacs com o auxílio de um instrumento óptico eletrônico 3D. Treze marcadores esféricos retrorreflexivos (1 cm de diâmetro) foram posicionados no corpo de 9 ginastas experientes: maléolos laterais direito e esquerdo, cabeça da fíbula, trocanter maior, acrômio, olecrano, processo estiloide da ulna e vértex. Na mesma sessão e após um período de aquecimento, cada participante executou 15 repetições de flic flacs. Dez repetições forma analisadas, e os trajetos 3D das 13 manobras medidos. RESULTADOS: Em média, os homens obtiveram altura vertical maior (mulheres, 62% da altura; homens, 58%). O alinhamento dos membros inferiores foi homogêneo entre os ginastas: ângulos posteriores de joelho variaram entre 80° e 118°. Nenhuma abdução de membro inferior foi observada: a largura de joelho foi 7 cm menor do que a largura intertrocanter; a largura de tornozelo foi 8 cm menor do que a largura de joelho. Na saída do movimento, o ângulo tronco-coxa apresentou excelente alinhamento corporal, com valores bem próximos de 180°. As mulheres executaram a fase de apoio das mãos com pulsos mais próximos do que os homens (homens, 134% de largura de ombro; mulheres, 121%). CONCLUSÃO: Os resultados podem fornecer informações para melhor conhecimento, definindo assim, a execução de padrão-ouro obtida de ginastas de elite com poucas lesões.

Silurian horseshoe crab illuminates the evolution of arthropod limbs.

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

A New Method for Recording Complex Positional Behaviours and Habitat Interactions in Primates

In an arboreal habitat, primates have to cope with a complex meshwork of flexible supports in order to obtain food, find mates and avoid predators. To understand how animals interact with such complex environments we can study their positional behaviour. However, due to the intricate variation in locomotion and posture it can be difficult to capture details such as limb use (i.e. weight and balance), limb flexion and substrate use. This paper presents a suitable method replicable for any primate species, based on the movement notation technique, Sutton Movement Writing (SMW), aiming to record the spatial arrangement of limbs during positional behaviours on multiple, compliant supports. This method was piloted during a year-long field study of wild orangutans (Pongo abelii) and validated and tested for inter- and intraobserver reliability using videos from the field. Overall, SMW shows considerable promise for increasing the resolution with which positional behaviours can be recorded under field conditions and provides a way to extract numerical data for use in statistical analyses. This will facilitate our understanding of how behaviours vary in response to the environment, and the capabilities of primates to perform key tasks in their distinct niches.

Parasitic motion comparison of 3-PRS parallel mechanism with different limb arrangements

The 3-PRS parallel mechanism (PM) is an important category of lower-mobility parallel mechanisms. Because it can undergo one translational degree of freedom (DOF) and two rotational DOFs, the 3-PRS PM has great potential in practical application and has received extensive attention. Parasitic motion occurring in the constrained DOFs of a 3-PRS PM is a key issue affecting its application. First, the 3-PRS PM is classified into seven subcategories based on the geometrical arrangements of limbs. Then, parasitic motion of each subcategory is discussed in detail and case studies are presented. It is illustrated that the complexity of parasitic motion of the 3-PRS PM is determined by the limb arrangement. The architecture of the 3-PRS PM without parasitic motion is also identified.

Embryology of Congenital Differences

Embryogenesis of the upper limb occurs between 4 and 8 weeks after fertilization. Limb development is controlled by signaling centers that guide spatial axes formation and genes that encode limb arrangement. This article will discuss the signaling centers, genes, and molecular events that yield limb formation.

Functional morphology of the prosoma of Baltoeurypterus tetragonophthalmus (Fischer) (Chelicerata: Eurypterida)

AbstractThe prosomal morphology ofBaltoeurypterus tetragonophthalmus(Fischer) from the Baltic Silurian is redescribed and reconstructed. The first eurypterid labrum and new secondary sexual characters ofBaltoeurypterusare described. The radially-arranged coxae ofBaltoeurypteruswere capable of adduction and abduction for food mastication, but not promotor-remotor movements for locomotion. Joint diagrams are presented for the first time for an extinct arthropod. Promotion and remotion of the limbs occurred about subvertical trochanteral pivots, as in all other chelicerates except xiphosurans.Baltoeurypterusprobably walked in a &amp;ldquo;slow&amp;rdquo; gait; a method of choosing possible gaits for extinct arthropods is outlined. Swimming inBaltoeurypteruswas effected by means of a rowing action of the posterior limb pair, which is provided with complex joints for collapsing the paddle during the recovery stroke. The limb arrangement and joint mechanisms ofBaltoeurypterusare intermediate between those of the xiphosurans and the arachnids. It is possible that a sister relationship exists between the eurypterids and some arachnid groups, which would render Merostomata and Arachnida unnatural assemblages.

Terminal fetal postures observed in a bovine caesarean survey

The posture of 1255 bovine fetuses was determined using a direct surgical examination. This caesarean survey examined the incidence of variable features, including fetal presentation, head posture and the arrangement of limbs. The fetuses had incidences of 86.8% with anterior presentation, 90.2% with head extension, 96.1% with extended forelimbs and 56.5% with extended hind limbs in posterior presentation. Pronation, with extension of the digits and carpal joints of the forelimbs, was predominant. Reduced responsiveness was recognized in varying degrees from the minor one of one flexed forelimb, to the major one of deflected head with both forelimbs flexed. Polarization of the fetus in the anterior presentation was usual. This occurred with highest incidence in the first pregnancy and with heavy, male fetuses. In the posterior presentation, female fetuses under 27 kg predominated and a high proportion of these were in “breech presentation”. The influence of the “trapping fold” of the uterine lesser curvature in assisting the fetus to secure polarity was considered to be evident in these data. Recognition has been given to the consequences of fetal kinesis, warranting its further study.