Sharif Digital Repository

The constitutive modeling of material is clearly a keystone of successful quantitative solution possibilities. No finite element code will provide results of better quality than that of the constitutive equation implemented in it. In this study, a nonassociated three-invariant cap plasticity model is presented for material under compressive stress. Generalized single-cap plasticity is developed which is based on the hardening-softening material functions. The hardening functions are consisted of isotropic and kinematic parts. Using the definition of yield surface, material functions and nonlinear elastic behavior, as function of hardening-softening parameters, the constitutive elasto-plastic... 

Exoskeleton is a newborn technology for disabled people. Personal exoskeleton is a type that is suitable for replacement of wheelchair. Exoped, the first Iranian exoskeleton made by Pedasys company, was a rehabilitation one. The purpose of this research was enhancing the design of its actuators to accomplish lighter, smaller and cheaper one. At first we identified the different loads that are applied to actuators of exoskeleton and we tried to decrease the number of actuators needed, as more as possible. Then we modeled the exoskeleton-user system to measure the required parameters. Using this model, we conducted an algorithm to design appropriate gait cycle for walking with the help of... 

Low back pain is the most prevalence musculoskeletal pain that people experience in their life. Some cases of low back pain are called non-specific. These are cases for which the reason of pain is not well defined. The aim of this study is to propose a simple approach to diagnose and cluster low back pain patients which helps clinicians to evaluate patients by an affordable and simple tool. In this study, data are collected in two steps using Inertial Sensors. Inertial Sensors consist of a 3-axis gyroscope and a 3-axis accelerometer which represent the kinematic parameters of lumbar movement. In the first step, we examine 24 healthy and 28 patients with low back pain and in the second, 84... 

Quantitative motion quality evaluation has been always of much significance for CVA patients, especially the HCP ones. The purpose of the present study is to introduce and analyze the efficiency of a novel index, namely “Consumed Energy Index”, for evaluating the quality of the motions performed by HCP patients. For this purpose, Firstly, a Musculo-Skeletal model of the human arm was provided on Matlab and OpenSim softwares, with four DoFs: three DoFs at shoulder and one DoF at elbow joint as well as eight muscles. The muscles are in pairs of flexor-extensor at each DoF. The model is capable of receiving Cartesian trajectories for joints and solving inverse kinematics and dynamics to obtain... 

Human body movements are achieved by activating a number of muscles. It has been shown that the central nervous system (CNS) plays the main role in controlling rhythmic activities (including walking, chewing, etc.). However, the way the central nervous system works in controlling different parts of the body has always been discussed due to the excess degrees of freedom to perform certain tasks. Controlling a group of muscles (under the name of muscle synergy analysis) instead of each one of them has been one of the most attractive and efficient recent ideas to better understand the CNS function. Also, a similar concept can be expressed for kinematic synergies (by the degrees of freedom of... 

Microrobots design and manufacturing has been one of interesting fields in robotics in recent decades. They have been designed in various types so far. In this paper a two-leg microrobot is simulated and controlled by using LuGre friction model.
The proposed microrobot is driven by a piezoelectric actuator mounted between centers of two legs. The piezoelectric is actuated by a frequency near the natural frequency of the robot. The nonlinear dynamical equations of the system are obtained considering LuGre friction model. To control the system, the equations of motion are linearized using feedback linearization method. Then a stabilizing control law is designed and the robot model is... 

In the present study, an adaptive sliding mode control method was employed to control a fish robotic system using the method of hardware in the loop. Following the introduction of the nonlinear model for the robot, elongated body theory, suggested by Lighthill, was used to analyze fish movements. Lighthill’s theory inspired from slender body theory in aerodynamics scope could be viable to exercise upon the carangiform mode of swimming. By simplifying Lighthill’s equations in planar motion of fish robot, the number of degrees of freedom exceeds the number of the control variables. In view of the fact that the presented model is an under-actuated model, there exist some parametric and... 

Spinal cord injury (SCI) is one of the most important causes of disability in the youth and costs enormous expenses for the government. Most SCI subjects use wheelchair as their main way of locomotion while standing and walking can benefit them in various aspects. The role of lower extremity muscles has been investigated in paraplegic gait with active orthoses or in partial weight support condition. However, due to the large expenses of active orthoses, their application have been limited to clinical trials and yet most SCI individuals use traditional AFO and KAFO for walking. The role and significance of trunk and upper extremity muscles (TUEM) has been investigated only in balance... 

One of the important challenges in gait analysis is to know the consequences and extent of the impact of an injury or failure and the outcome of any intervention. The purpose of this study was to identify and categorize three gait patterns of a healthy person, an individual with ruptured anterior cruciate ligament, and an individual with surgically reconstructed anterior cruciate ligament using knee joint kinematic information in normal walking. To do this, data from the knee joint curve during the gait cycle in sagittal, frontal and transverse planes were used as a neural network input. Four neural networks were designed to detect and isolate the three gait patterns from each other. The... 

The purpose of this study is to evaluate the performance of the optimized conditional source-term estimation approach. This model was first implemented in a computational fluid dynamics code, and then the Bernstein expansion was used to optimize it. For validation, two pre-mixed turbulent flames with different turbulence intensity and equivalence ratios were modeled with the optimized and RANS model. The results were obtained for mass fraction of the main and intermediate species, velocity and temperature examined in different sections. In the first flame, the turbulence intensity is low, and the flame is in the flamelet regimes; As a result, the results obtained with the optimized model are... 

During the past decade, micromachining technology has become available to fabricate micron-sized mechanical parts. The miniaturization of almost all types of devices and systems is arguably a greater opportunity for commercial profit and beneficial technological advances (e.g., micromechanical, microfluidic, microthermal, micromagnetic, microoptical and microchemical). However, instead of the traditional evolutionary engineering effort to reduce size and power while simultaneously increasing the performance of such a diverse set of systems, the field of microelectromechanical systems (MEMS) represents an effort to radically transform the scale, performance and cost of these systems by... 

The primary objective of this dissertation is to obtain a mechanism from the family of 5-dof parallel mechanisms of type 3T2R which gains the advantages of higher kinematic performance, low coupling of motion, and simple kinematics and control commands. Based on this aim, at first a method for structural synthesis of this type of mechanisms is introduced. The method is based on the theory of linear transformation and a geometrical analysis. By using this method, a set of novel 5-dof 3T2R parallel mechanism are introduced for the first time in the literature. In order to compare the designed mechanisms and to identify the promising ones, some important criteria which are a) low coupling... 

In the resent years, social robots has been emerged to improve the interactions between humans and robots. These intractions are intended more in human environment. So the reasonable performance of such robots is achieved if robots’ motion; become similar to humans. Hence, despite the complexities of manufacturing and controlling the bipedal and humanoid robots, the researches on this class of robots are still in continuing more and more. In 2013, the humanoid robot, R-50, made by Robokind Company, was purchased by the Mechanical Engineering Department of Sharif University of Technology. This robot was named Mina and to be used in the researches on the treatment of autism patients. Although... 

Typical Numerical Control Machines, mainly are made a mechanism with axes perpendicular to each other. Because of lower weight, the parallel mechanisms are focused by CNC manufacturers. the Hexaglide mechanism is popular in parallel mechanisms used in CNC.Today, software of Solid modelling, generate G-Codes but this Codes works for conventional Numerical Control machines. for use of this G-Code for Parallel Mechanism CNC, a new controller should be designed to convert the standard G-Code motion command for Hexaglide CNC.The End of this project, is design and manufacture a controller for Hexaglide CNC that convert conventional G-Code for that and initiate drivers.Finally, the controller is... 

User comfort in wearable robots and precise limb tracking of the robots' links can be considered as general and significant indicators of the robots' performance. On the other hand, due to the kinematic mismatches between the human body and conventional wearable robots, which often occur due to various reasons such as the kinematic differences between the body and robot joints (e.g. the knee joint), it seems unlikely to achieve a robot in which user's limbs comfortably follow its link without tracking error. In this study, in order to evaluate and improve the performance of the robot, two performance indices: limbs tracking error index (TEI) and user discomfort index (DI) were introduced,... 

In this study, we create an evolution function that assesses prosthetic hands in terms of their ability to grasp various objects like a human hand. It is required to evaluate the reachable workspace of prosthetic hands and grasp ability to assess it completely. The first one can be done by using forward kinematics. The Volume of the Grasp Wrench space, one of the grasp qualities indexes, is used to measure the second one. Randomization and grasp taxonomy are used to generalize the grasp quality to indicate the prosthetic hand functionality. Afterward, the created evaluation function is used to specify the importance of each finger and DOF. The results show that the most significant finger is... 

One of the main causes of low back pain is mechanical loads acting on it. These loads can be measured by in vivo measurement using force and pressure sensors. Although this method leads to accurate results, it is invasive and costly. Currently the only noninvasive way to estimate these loads is to utilize biomechanical models. Using these models requires body posture as an input. Imaging techniques are suitable for determining the posture accurately, but these equipments are expensive and often impractical. So today posture prediction models are used as an alternative cost effective with acceptable accuracy. These mechanisms predict body posture using body mass, height, position and the... 

The goal of fracture reduction in orthopedic surgery is to reposition the bone fragments in their anatomical orientation (alignment), and the fracture ends closed to each other (apposition). Reduction of long bone fractures is became an interesting subject in the field of robotic aided surgery in pervious decade. Nowadays reduction of femur is carried out by surgeons and medical staff in surgery. Due to the large holding forces necessary, exact positioning is difficult and time consuming. What is needed is an automated system whereby the fractured ends of the bone may be precisely positioned without the need for multiple docking attempts. The fragments need to be held in place as long as... 

In recent years, industrial robots have been greatly used as orienting devices in industry, especially in the automotive, shipbuilding and aerospace manufacturing industries. Industrial robots are gradually finding their niche in manufacturing, replacing less universal and more expensive CNC-machines. Application area of robots is constantly growing; they begin to be used for the assembly, pick-and-place operations, machining operations and etc. The use of robots for machining operations is growing because of their flexibility to perform a broad spectrum of tasks at a lower cost when compared with machine tools. Recently, parallel robots have attracted more and more researchers’ attention in... 

Hyper-redundant manipulators have large number Degrees of Freedom. Because of their redundancy, such manipulators have the advantage of obstacle avoidance, overcoming singularities and intrusion into highly constrained environments. The most challenging task in designing hyper-redundant manipulators is the synthesis of actuating mechanisms with appropriate kinematics and effective power supply. Most of previous techniques in implementing hyper-redundant robots have the disadvantages of: -Using large number of actuators, -Heavy weight due to large number of actuators, -Complexity of the control system due to need of synchronizing subsets of motors. In this thesis a novel hyper redundant...