Design and Analysis of a Cable-Driven Flexible Finger Based On Continuum Mechanism

We discuss a flexible robotic finger design and controller, which is used for a micro flexible robotic finger. In this study, we use piezoelectric bimorph cells for the micro flexible robotic finger's actuators. Another problem is controller design for more precise end point force control of the micro flexible finger. The controller adopted is the PD/PI mixed type fuzzy controller. The controller consists of two parts, one is a PD type fuzzy controller for increasing the rising time response, the other is a PI type fuzzy controller for decreasing the steady-state error.

Applied the artificial muscle based on oil hydraulic to design flexible manipulator finger joint. Builded mathematical model to express the relation among the structure parameters, workplace and dynamical features of the driving joints. According to the characteristic of flexible hydraulic components and the arrangement of the flexible components in driven band, proposed the driven principle to control the movement of flexible finger in different ways. Laid a theoretical foundation for practical application.

This personal reflection that celebrates the 50th anniversary of Circulation Research focuses on an area of integrative electrophysiology—the extension of continuous medium theory to the discontinuous nature of cardiac propagation produced by the cellular interconnections (gap junctions). It is appropriate to note that as a clinician who shifted to the laboratory, my collaboration with Drs Roger Barr, J. Francis Heidlage, and Paul Dolber has provided me long-term training and checks on ideas that involve conduction theory, computer modeling, and cardiac architecture. That process has been particularly influenced by advances in this field that involve the measurement and mathematical modeling of ionic channel currents, as well as the immunohistological targeting of cardiac gap junction connexins. Although journal references are not used here, I have felt compelled to mention a few scientists who advanced selected ideas about the spread of currents in cardiac muscle. It is noteworthy that the widespread use of optical mapping to measure spiral waves that represent the behavior of cardiac wavefronts at a macroscopic size scale illustrates the contemporary importance of continuous medium theory. Interestingly, van Cappele first described complex spiral wave activity for cardiac muscle in 1980 by generating a computer model of a continuous isotropic sheet. Nine years passed before this phenomenon was experimentally confirmed in cardiac muscle. With spiral waves, the nonuniformities necessary to initiate the conduction disturbances that lead to reentry are induced experimentally as repolarization inhomogeneities (primarily by introducing stimuli at two different sites). Spiral waves are mentioned at the outset because the concept of spiral waves at a macroscopic level and the concept of discontinuous conduction at a microscopic level have both gained acceptance during the past two decades as paradigms for mechanisms of cardiac arrhythmias. Thus, it may be of interest to the reader to consider how experiments done in the …

For general grasping, a strong lightweight and compact robot hand needs to be designed as a robot end effector. This paper describes the design of a 3D printed anthropomorphic robot hand that actuates flexible fingers using Twisted String Actuators (TSAs). A total of 6 of these actuators were fitted within a limited confined space, the palm of the hand. This gives the hand 6 Degrees of Freedom (DOFs) 2 in the thumb and 1 in each of the other fingers. A simple modular design was used which allows for rapid prototyping of different finger designs with respect to different requirements at low cost. In this paper, only power grasping is considered for simplicity. The hand is capable of performing both spherical and cylindrical grasps whereby the flexible nature of the fingers allows for forming around the geometry of a target object. The maximum holding load of the hand was found to be 10 kg in performance tests.

The efficiency index (Effindex) combines internal and external loads, and it has been considered a promising tool to evaluate physical fitness status. However, its real applicability and limitations have not been elucidated yet. To examine and discuss the findings from studies that used Effindex as a tool for the evaluation of physical fitness status in team sports. A systematic search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The databases conferred were PubMed, Scopus, Web of Science, SPORTDiscus, MEDLINE and CINAHL. The articles selected were published up to March 2021. Fourteen articles were included after meeting the inclusion criteria. A wide variety of combinations of external and internal loading parameters to calculate Effindex were found. The pooled sample included 349 male participants (23 ± 3 years). Fifty-nine percent of the sample were soccer players, 20% rugby players, 10% Australian football players, 7% hurling players, and 4% basketball players. Most Effindex calculations used total distance (TD) divided by heart rate derived parameters. However, recent studies have suggested the use of accelerations as the external load parameter. Effindex is a simple and powerful tool for the evaluation of physical fitness status in team sports athletes. The disparity of external and internal loading parameters used to calculate Effindex may affect its sensitivity to detect changes in fitness status in different team sport settings. More studies with indoor team sports and female athletes are warranted.

The article presents the results of theoretical studies of a multi-purpose machine when assembling an HSK spindle-mandrel connection for accuracy, contact stiffness and strength. Studies were based on the developed original mathematical program complex for assessing the quality parameters of machine connections. They have been carried out with respect to HSK spindle-mandrel connections under conditions of multiple tool changes. Simulation of the coupling of connection parts for different values of the fastening (assembly) forces showed that HSK-type connections have a static uncertainty of basing under external loading conditions. Analysis of the stress-strain state of the connection joints was based on the finite element method when using software in the FEMAP 11.1 with NX NASTRAN. It showed that an unorganized change of bases occurs under the influence of external conditional load. It has been established that for tool mandrels of the HSK-63 type with a fixing force of 900 to 23000 N, the elastic displacements at the end of the mandrel vary from 1.5 to 0.6 μm under the condition of an external conditional load of 1732 N and, accordingly, from 8.0 to 2.5 μm with an external load of 6070 N. It was established that with a limiting value of the mandrel clamping force equal to 23000 N under conditions of external loading an unorganized change of bases occurs, namely: the end faces of the contact of the tool mandrel and the spindle are pressed, which reduces the geometric accuracy of a multi-purpose machine with a CNC.

Continuum manipulators can operate in complex environments where traditional rigid manipulators fail. However, the modeling of inverse kinematics remains challenging because of its inherent nonlinearities and various external conditions. This work proposes an online learning control framework with a data cache pool utilizing a constant‐curvature model inspired neural network (CCMINN) model to obtain the inverse kinematics model of tendon‐actuated continuum manipulators. The CCMINN model is a kind of geometric relationships‐inspired neural network, which is inspired by the geometric relationships within the constant‐curvature model. This model improves the ability of traditional fully connected neural network models on high convergence speed and precision through its constant‐curvature inspiration layers. These layers embed geometry insights into the neural network structure rather than loss functions like physics‐informed neural networks. The online learning framework enables CCMINN to maintain high control accuracy in a variety of external load scenarios. Experiments show average tracking errors of 1.4 mm, 1.38 mm, and 1.48 mm (0.7%, 0.64%, and 0.74% of the continuum manipulator length) in the free space, under constant and variable loading conditions, respectively. The results show that combining the fast‐converging CCMINN with an online learning control framework enables high‐precision and robust positioning control of continuum manipulators under various external payloads.

In order to enhance currently used beam theories in $$\mathbb {R}^2$$ and $$\mathbb {R}^3$$ to include mechanisms of dissipation and memory, it is necessary to establish if the mathematical models for these theories can be derived using the conservation and the balance laws of continuum mechanics in conjunction with the corresponding kinematic assumptions. This is referred to as thermodynamic consistency of the beam mathematical models. Thermodynamic consistency of the currently used beam models will permit use of entropy inequality to establish constitutive theories in the presence of dissipation and memory mechanism in the currently used beam theories. This is the main motivation for the work presented in this paper. The currently used beam theories are derived based on kinematic assumptions related to the axial and transverse displacement fields. These are then used to derive strain measures followed by constitutive relations. For linear beam theories, strain measures are linear functions of displacement gradients and stresses are linear functions of strain measures. Using these stress and strain measures, energy functional is constructed over the volume of the beam consisting of kinetic energy, strain energy and potential energy of loads. The Euler’s equation(s) extracted from the first variation of this energy functional set to zero yields the differential equations describing the evolution of the deforming beam. Alternatively, principle of virtual work can also be used to derive mathematical models for beams. For linear elastic behavior with small deformation and small strain, the two approaches yield same mathematical models. In this paper we examine whether the currently used beam mathematical models with the corresponding kinematic assumption (i) can be derived using the conservation and balance laws of classical continuum mechanics or (ii) are the conservation and balance laws of non-classical continuum mechanics necessary in their derivation. In order to ensure that the mathematical models for various beam theories result in deformation that is in thermodynamic equilibrium we must establish the consistency of the beam theories with regard to the conservation and the balance laws of continuum mechanics, classical or non-classical in conjunction with their corresponding kinematic assumptions. Currently used Euler–Bernoulli and Timoshenko beam mathematical models that are representative of most beam mathematical models are investigated. This is followed by details of general and higher-order thermodynamically consistent beam theory that is free of kinematic assumptions and other approximations and remains valid for slender as well as deep beams. Model problem studies are presented for slender as well as deep beams. The new formulation presented in this paper ensures thermodynamic equilibrium as it is derived using the conservation and the balance laws of continuum mechanics and remains valid for slender as well as non-slender beams.

This paper presents an analysis on the mechanics of grasping general solid objects under frictional point contact model. Any disturbing force/moment pair at the mass center of an object can be balanced (or force-closured) if there exist a particular set of internal forces falling inside the friction cone of the contact points. Based on this principle, sufficient conditions for the geometrical properties of the contact points guaranteeing the existence of such internal contact forces are investigated.

Purpose Slim and dexterous manipulators with long reaches can perform various exploration and inspection tasks in confined spaces. This paper aims to present the development of such a dexterous continuum manipulator for potential applications in the aviation industry. Design/methodology/approach Benefiting from a newly conceived dual continuum mechanism and the improved actuation scheme, this paper proposes a design of a slim and dexterous continuum manipulator. Kinematics modeling, simulation-based dimension synthesis, structural constructions and system descriptions are elaborated. Findings Experimental validations show that the constructed prototype possesses the desired dexterity to navigate through confined spaces with its kinematics calibrated and actuation compensation implemented. The continuum manipulator with different deployed tools (e.g. graspers and welding guns) would be able to perform inspections and other tasks at remote locations in constrained environments. Research limitations/implications The current construction of the continuum manipulator possesses quite some friction inside its structure. The bending discrepancy caused by friction could accumulate to an obvious level. It is desired to further reduce the friction, even though the actuation compensation had been implemented. Practical implications The constructed continuum manipulator could perform inspection and other tasks in confined spaces, acting as an active multi-functional endoscopic platform. Such a device could greatly facilitate routine tasks in the aviation industry, such as guided assembling, inspection and maintenance. Originality/value The originality and values of this paper mainly lay on the design, modeling, construction and experimental validations of the slim and dexterous continuum manipulator for the desired mobility and functionality in confined spaces.

Uniformly strained anisotropic elastoplastic rods: Determination of elastoplastic constitutive relations and yield surface in terms of rod’s variables

The physical composition and stress state of soil-rock mixture (SRM) materials have a crucial influence on their mechanical properties, and play a vital role in improving the performance of subgrade. To reveal the resilient behavior and mesostructure evolution of SRM materials, triaxial tests and discrete element method (DEM) numerical analysis have been carried out. In the triaxial test section, the mechanical response of SRM materials was investigated by preparing samples under different stress states and physical states and conducting triaxial tests on samples. Simultaneously, a new irregular particle modeling method was developed and applied to the discrete element modeling process to analyze the mesostructure evolution of SRM materials under cycling loading. First, a cyclic triaxial test of SRM material is performed on the SRM material, and the effects of bulk stress, octahedral shear stress and rock content on the resilient modulus of the SRM material are analyzed. It is revealed that the resilient modulus increases with increasing bulk stress and rock content, and decreases with increasing octahedral shear stress. Based on a new resilient modulus prediction model, the relationships among the rock content, stress state and resilient modulus are established. Then, based on an improved DEM modeling method, a discrete element model of the SRM is established, and the influence of rock content on coordination number and mesostructure evolution of the SRM is analyzed. The results show that in SRM materials, the increase of crushed rock changes the mesostructure of the SRM material. With the increase of rock content, the internal contact force changes from “between soil and rock” to “between rocks”, and the skeleton formed in the rocks gradually develops overall stiffness. Under the condition of low stress, the anisotropy of the SRM material is mainly caused by the shape and grade distribution of crushed rock. The induced anisotropy caused by the change of stress state has little effect on its mechanical behavior, which may lead to the greater dispersion of multiple SRM test results.

The classical definition and analysis of force closure in robotic grasping focuses only on the fingertip bodies and their contacts with the grasped object. However, the kinematic properties of the hand mechanism can have a non-trivial effect on the actual type of force closure which can be realized at a given grasp. This paper takes a new look at this classical problem, and introduces technical results on force closure, or wrench resistance, which incorporate the hand mechanism's kinematics in this important grasp security measure. Based on a decomposition of the finger contact forces into canonical subspaces, the paper introduces a division of the finger contact forces into active and passive forces, as well as a dual division into resistant and internal contact forces. The paper develops new formal definitions of these concepts, and describes their mutual orthogonality relationships. Based on these definitions, the paper introduces new theorems of wrench resistant grasps which factor the hand mechanism's structure into the analysis of a given grasp. Examples illustrate how the hand mechanism's structure affects its ability to maintain secure wrench resistant grasps.

Influence of cohesive stresses on shear capacity of reinforced SFRC beams without stirrups: A discrete crack approach

Purpose of research is to develop high-precision mathematical models for the read channel of TLC flash memory to conduct a comparative analysis of the effectiveness of error-correcting coding for flash memory from different manufacturers. Methods. This article presents static and dynamic models of the read channel of TLC flash memory. The static channel model is a set of Gaussian distributions defined by their mean and variance. A new feature of the static model is the proposed function for calculating the variances of the TLC flash memory read channel distributions in accordance with the specified RBER (Raw Bit Error Rate) parameter. Dynamic models of the read channel are used to estimate temporal changes in the distribution parameters over the life of the flash memory. In this article, a vector autoregressive model is proposed as a dynamic model of the flash memory read channel. Results. The result of this research is the development of mathematical models of flash memory. The static model simplifies the analysis of flash memory from different vendors without the need for specific IBIS (Input/Output Buffer Information Specification) models for each variant. This model can be used to analyze the effectiveness of various error-correcting coding schemes. The proposed dynamic model improves the accuracy of expectation estimation, taking into account flash memory operating time and the number of rewrites. On average, the estimation error of the proposed autoregressive model is 25 % lower. The autoregressive model of TLC flash memory improves the effectiveness of dynamic thresholds to reduce the RBER estimation bias. Conclusion. Static and autoregressive models of flash memory, along with methods for calculating/optimizing their parameters, are obtained. Using these models improves the cost-effectiveness of flash memory hardware development and its reliability by reducing dependence on lengthy low-level modeling and the adaptability of the models to different memory types.