Sharif Digital Repository

The robots that can move on rough terrains are very important especially in Rescue operation, exploration, etc. In this research, a mechanism is introduced for a ring-like robot with a flexible body. This robot is moved by arms which are placed radially and have Reciprocating motion in this direction. By controlling the contraction and the extension of the arms which contact lhe ground, the robot will be forced to move which is called rolling-creeping motion. The robot is stable in stationary state.; also the maximum angle which it can be stable is determined. Considering the speed of contracted arm is the input parameter, the speed of the extended arm for locomotion of the robot has been... 

Background: An effective master robot for haptic tele-surgery applications needs to provide a solution for the inversed movements of the surgical tool, in addition to sufficient workspace and manipulability, with minimal moving inertia. Method: A novel 4+1-DOF mechanism was proposed, based on a triple parallelogram linkage, which provided a Remote Center of Motion (RCM) at the back of the user's hand. The kinematics of the robot was analyzed and a prototype was fabricated and evaluated by experimental tests. Results: With a RCM at the back of the user's hand the actuators far from the end effector, the robot could produce the sensation of hand-inside surgery with minimal moving inertia. The... 

Kinematic boundary condition is usually used when dealing with transient free-surface flow problems in isotropic media. When dealing with anisotropic problems, a transformation can transform the anisotropic media to an equivalent isotropic media for seepage analysis, but the kinematic boundary condition cannot be used directly in the transformed media. A generalization of the kinematic boundary condition along any arbitrary direction is derived for use in the transformed domain for general three-dimensional anisotropic problems. A boundary element method for solving transient free-surface seepage problems is developed and the treatment of the proposed kinematic boundary condition in the... 

Recent research indicates that accurate material behavior modeling plays an important role in the estimation of residual stresses in the bore of autofrettaged tubes. In this paper, the material behavior under plastic deformation is considered to be a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. The yield surface is assumed to depend on the first stress invariant and the Lode angle parameter which is defined as a function of the second and the third invariants of the deviatoric stress tensor. Furthermore for estimating the unloading behavior, the Chaboche's hardening evolution equation is modified. These... 

This paper presents inverse dynamics equations for a 3-UPS mechanism using virtual work principle. This mechanism has three UPS legs connecting the base to a triangular platform. By changing the orientation of leg's actuators a non-symmetric mechanism with a suitable workspace near the origin without any singularity is obtained. Direct and inverse kinematics Jacobian matrices of the mechanism are obtained by the Newton-Euler approach. Then the inverse dynamics problem is solved using the principle of virtual work, so that the force and torque of active actuators have been obtained by having external forces (force and torque) acted on the platform. Force analysis of the 3-UPS mechanism has... 

In this paper, we propose a leader following control for autonomous air robots. The separated design strategy with kinematic acceleration commands is used. The location of the robot with respect to the leader is specified by a range and two angles. We obtain the kinematic model of the system represented by the state-space equations. The controller is designed based on the sliding mode control which asymptotically stabilizes the tracking errors in presence of uncertainties and disturbances. In order to implement the leader following controller in the air robots, a control system is introduced which converts the acceleration commands to the actuator commands. Simulations are provided to show... 

In General, there are two methods to analyse the inverse kinematic of manipulators, one of which can be selected with respect to the conditions and the type of the manipulator. One of the methods is the closed solution which is based on the analytical expressions or forth degree or less polynomial solution in which the calculations are non-repetitive. The other method is the numerical solution. In the numerical solutions, the numbers are repeated and generally it is much slower than the closed solutions. The slowness of this method is so noticeable in such a way that principally there is no interest to use the numerical solutions to solve kinematic equations. The purpose of the present paper... 

Presented is a novel approach for online trajectory modification of joint motions to transfer a free open kinematic chain, undergoing flight phase, from a specified initial configuration to a specified final configuration. Formally, it is assumed that a nominal trajectory, computed offline, can reorient the kinematic chain (reconfiguration problem) for a given angular momentum on a time interval. A modification algorithm of body joints, based on optimal control, is developed such that for different angular momentums and time intervals, the same reconfiguration problem can be solved online. This approach can be utilised for space robotics applications and online computation of planar running... 

The logarithmic or Hencky strain measure is a favored measure of strain due to its remarkable properties in large deformation problems. Compared with other strain measures, e.g.; the commonly used Green-Lagrange measure, logarithmic strain is a more physical measure of strain. In this paper, we present a Hencky-based phenomenological finite strain kinematic hardening, non-associated constitutive model, developed within the framework of irreversible thermodynamics with internal variables. The derivation is based on the multiplicative decomposition of the deformation gradient into elastic and inelastic parts, and on the use of the isotropic property of the Helmholtz strain energy function. We... 

Positioning for kinematic applications is of great importance in terms of accuracy and computational complexity. In this paper, we present an algorithm based on correlation between error components in three directions, i.e. Δx, Δy, Δz to decrease positioning error of a GPS receiver for kinematic applications. The main feature of proposed algorithm is that it modifies data at each instant and in each direction using data of two other directions at the same instant (i.e. some sort of online modification). This feature was acquired using an approach introduced to model state transition matrix using AR coefficients of two other directions. The algorithm was implemented on the output raw position... 

A generalized equation based on modified Eyring's theory for predicting kinematic viscosity of petroleum fractions is proposed in this work. The equation uses two reference fluids including a pair of (C6 and C10), (C10 and C14), or (C14 and C20) for petroleum fractions of molecular weight higher than 70 and lower than 300. Validity and accuracy of this equation have been confirmed by comparing the obtained results of this equation with experimental data. In contrast to other correlations that require so many specific parameters for oil viscosity prediction, this type of equation requires only molecular weight and true boiling point. The results obtained in this work are in agreement with... 

Workspace of a mechanism is generally defined as the region of space which end-effector of that mechanism can reach. Determination of workspace is an important task in the design of a mechanism. However, for parallel mechanisms, due to the complexity of solving the forward kinematic equations, determination of workspace is much more complicated than for serial mechanisms. In the literature, time-consuming numerical methods, such as point-by-point searching, are usually employed for this purpose. In this paper, an optimization-based algorithm is introduced for the boundary determination of inclusive and constant orientation workspaces of parallel mechanisms. In the proposed algorithm, thanks... 

A variable kinematic 1D finite element (FE) method is presented for 3D thermoelastic analysis of rotating disks with variable thickness. The principle of minimum potential energy is used to derive general governing equations of the disks subjected to body forces, surface forces, concentrated forces, and thermal loads. To solve the equations, the 1D Carrera unified formulation (CUF), which enables to go beyond the kinematic assumptions of classical beam theories, is employed. Based on the 1D CUF, the disk is considered as a beam, which can be discretized into a finite number of 1D elements along its axis. The displacement field over the beam’s cross section is approximated by Lagrange... 

One of the major issues related to parallel kinematic machine tools (PKMs) is their structural dependency on their configuration. In this paper, the machine configuration effect on its stability is investigated for the case of a Hexaglide machine tool. An FEM model of the Hexaglide machine tool is developed. The frequency response function (FRF) at the tool tip is obtained by a modal analysis. The numerical results are validated through comparison with those of an experimental modal test. The pose dependency of the PKM stability over its workspace is investigated. It is shown that the machine stability over the workspace is dependent on the spindle/tool/holder system characteristic. For... 

Aims. EROS (Expérience de Recherche d'Objets Sombres) has searched for microlensing toward four directions in the Galactic plane away from the Galactic center. The interpretation of the catalog optical depth is complicated by the spread of the source distance distribution. We compare the EROS microlensing observations with Galactic models (including the Besançon model), tuned to fit the EROS source catalogs, and take into account all observational data such as the microlensing optical depth, the Einstein crossing durations, and the color and magnitude distributions of the catalogued stars. Methods. We simulated EROS-like source catalogs using the HIgh-Precision PARallax COllecting Satellite... 

In the past few years, parallel manipulators have become increasingly popular in industry, especially, in the field of machine tools. Hexaglide is a 6 DOF parallel manipulator that can be used as a high speed milling machine. In this paper, the kinematics and singularity of Hexaglide parallel manipulator are studied systematically. At first, this robot has been modeled and its inverse and forward kinematic problems have been solved. Then, formulas for solving inverse velocity are derived and Jacobian matrix is obtained. After that, three different types of singularity for this type of robot have been investigated. Finally a numerical example is presented. Copyright © 2008 by ASME  

Motion capture systems are used to gauge the kinematic features of the motion in numerous fields of research. Despite superb accuracy performance, the commercial systems are costly and difficult to use. To solve these issues, Kinect has been proposed as a low-priced markerless motion capture sensor, and its accuracy has been assessed using previous motion capture systems. However, in many of these studies, the anatomical joint angles captured using the Kinect are compared to the 3D rotation angles reported by the gold standard motion capture systems. These incompatibilities in the determination of the human joint angles can lead to higher error estimation. To accomplish a valid accuracy... 

In this paper, a method for modeling of elastic-plastic hardening materials under large deformations is proposed. In this model the generalized strain rate tensor is used. Such a tensor is obtained on the basis of the method which was introduced by the authors. Based on the generalized strain rate tensor, a flow rule, a Prager-type kinematic hardening equation and a kinematic decomposition is proposed and the governing equations for such materials are obtained. As an application, the governing equations for the simple shear problem are solved and some results are compared with those in the literature. Copyright © 2008 by ASME