Sharif Digital Repository

Drill strings are subjected to complex coupled dynamics. Therefore, accurate dynamic modeling, which can represent the physical behavior of real drill strings, is of great importance for system analysis and control. The most widely used dynamic models for such systems are the lumped element models which neglect the system distributed feature. In this thesis, an infinite-dimensional model for the vibrational dynamics of the drill-string, called neutral-type time delay model, is modified to investigate the coupled axial-torsional vibrations in drill strings. This model is derived directly from the distributed parameter model by employing the d’Alembert method. Coupling of axial and torsional... 

Nowadays, due to the advancement of robotic technologies and development of industrial robots, the robot manipulators are widely used for automation of various manufacturing processes, such as finishing processes. In these applications, the contact has to be made between robot end-effector and environment. Therefore, control of interaction force in the constrained manipulators is an important demand. On the other hand, due to use of gear box and belts for energy transmission in robot joints, robot manipulators have flexible joints. The vibration, generated due to the interaction force and robot joint flexibility, can deteriorate surface roughness in automated finishing processes. In order to... 

Hybrid Exoskeletons refer to simultaneous use of wearable robots and functional electrical stimulation technology. Hybrid exoskeletons have many advantages compared to the separate application of each of these technologies, such as reducing the robot’s energy consumption and the need for lighter and cheaper actuators for the robot, using humans muscle power, and reducing muscle fatigue. As a result, these robots have recently attracted a lot of interest in rehabilitation applications for patients suffering from mobility impairment.Control in hybrid exoskeletons is more complicated than control in traditional exoskeletons. Because in addition to robot and functional electrical stimulation... 

The purpose of this study is to develop model predictive control approach to control a turbocompressor. The turbocompressor which is consisted of a gas turbine and a centrifugal compressor is manufactured for providing the necessary pressure for gas transport via the gas transmission network. The turbocompressor control system regulates the compressor outlet pressure by controlling the rotational speed of the gas turbine, while preventing the surge phenomenon in the compressor. Surge is a serious instability in the compressor that is associated with periodic fluctuations in system variables and can cause heavy damage to expensive machine parts.In this research, model predictive control has... 

The hand is an important part of the human body, the loss of all or part of it greatly reduces a person's ability to perform daily tasks. For people who have lost this significant organ, replacing it with an artificial limb that can meet some of their needs is essential. Today, all robotic prostheses use electromyographic (EMG) signals from the remaining muscles of the disabled limb as input signals. Classifying the EMG signal and converting it to a control signal faces serious challenges. Variation of signal properties over time, electrode slippage, muscle fatigue, changes in muscle contraction intensity, and changes in limb position and direction are some of these challenges. Therefore, a... 

In this thesis, an extended nonlinear model of peripheral milling process (2D) is presented. For the first time, cutting forces are described through a complete third order polynomial function of the axial depth of cut. Also, cubic nonlinearity is considered for the structural stiffness as a function of tool tip displacement. To complete the model, process damping and tool wear effects are also considered. A set of experiments including modal tests to determine natural frequencies and structural damping ratios; and also cutting force measurements at different feed rates to determine nonlinear cutting force coefficients, are carried out. Also, measurement of critical axial depth of cut at... 

Delivering high quality and clean air into occupied spaces is the main goal of Heating, Ventilation and Air Conditioning (HVAC) systems. HVAC systems draw supply air which usually contains fungi and moisture. Fungi and moisture plus organic materials create a good bed for mold growth. Studies prove that duct cleaning process can definitely reduce the amount of pollutants present in the ducts. Hence, it has positive impact on human lives both regarding psychological and physical points of view. Duct cleaning method’s application difficulties and ducts’ unreachable environments motivated duct cleaning firms to employ robots for duct cleaning tasks. Although there are considerable numbers of... 

Transparency is a measure of performance in haptic devices. In order to improve transparency and reduce the difference between the impedance transmitted to the user and the target impedance it is necessary to compensate for the dynamics of the haptic device. Due to stability reasons improvement of transparency is limited. Passivity as a stability criterion has been used widely in design and analysis of haptic devices. Since passivity is a conservative criterion, it acts as an obstacle in improving transparency of the haptic interfaces. In this project instead of passivity, robust stability of the interaction is studied in the presence of parametric uncertainties due to variations in user... 

Low back pain (LBP) problems are of concern to many researchers specially physiologists, biomedical engineers and... .biomechanical models can help us to furthering our knowledge of the mechanical characteristics of the spine and its neural control to know more about potential mechanisms of injury. This thesis involves computational model of lumbar spine to generate and control its flexion-extension movement.
Model has involved 7 links: 5 lumbar vertebrae, pelvis and trunk. Desired trajectory has been generated for rhythmic and discrete motion by the central pattern generators (CPGs). And then controller has produced torque of joints to track desired trajectory. CPGs have been... 

Providing energy for small but out-of-access devices has led industries to harvest energy from the environment, especially environmental vibrations. The problem of vibrational energy harvesters with linear behavior, is their small bandwidth and consequently, their high sensitivity to frequency content and excitation spectra. Particularly in random excitations with vibrational energy spreading over a frequency range, linear harvesters do not seem appropriate. Under these conditions, harvesters with nonlinear stiffness are possible substitutes for linear systems. However, prediction and estimation of the behavior of systems with nonlinear stiffness under random excitation has been complicated,... 

Sign language is recognized by considering the combination of the hand gesture, orientation, location and patterns of hand and arm movement. These complex interactions make the character and word recognition very challenging. In this paper, with the aid of sensory gloves and multiple inertial measurement units (IMUs) we measure the shoulder and elbow joint trajectories and hand gesture to train the discriminant functions to recognize the words intended and represented by sign language. For recognition of hand gesture, the Naive Baysian classifier was used while for Eulerian angles a new time series similarity measures were computed. Different aggregation method was used to integrate temporal... 

Todays, the exoskeleton is known as a practical device for use in robotic rehabilitation and elderly assistance and has attracted the attention of many researchers. Impedance control is the most widely recognized control strategy in research on exoskeletons. Impedance control can properly handle soft interaction of robots with the environment. Optimal target impedance selection can increase the performance of the overall system and guarantee the stability. The main objective of this research was to introduce a variable impedance control system and verifying the presented control system on an exoskeleton. In this research, an exoskeleton with 4 active DoF and 8 semi-passive DoF is designed... 

The main purpose of this project is to propose a control method for medical robots (such as rehabilitation and surgical robots), such that they can be moved conveniently by the users’s hand while he senses a controllable resistance. For that purpose, a Model Reference Adaptive Impedance Control method is developed for controlling the robot end-effector impedance in Cartesian coordinates. The proposed nonlinear controller and the desired impedance model are presented in Cartesian coordinates of the robot end-effector which is sensible for the human user. The adaptation law is derived and a corresponding Lyapunov stability is provided to prove the asymptotic tracking of the impedance model. By... 

Sign language is the main medium of communication for mute and deaf people. Unfortunately most hearing people do not understand this language. This fact causes communication difficulties for hearing impaired people and negatively affects their social life. This problem motivates researchers to develop speaking aids and helps deaf people to communicate with hearing people. Sign language includes concurrent combination of hand shapes, orientation and movements of the hands, arms or body, and facial expressions which make the character and word recognition a challenging task. Generally there are two fields of study in sign language recognition based on measuring devices: 1- camera based 2-... 

Inspired by the behavior of creatures in nature, including fish, generating propulsive forces under water has attracted great interest in recent years. Various tools such as computer software and experimental laboratory observations can be used to study the movements for different types of fishes. In this research, two thin fins, the shape of which is inspired by fish tail, will be investigated as a simplified model under non-viscous and incompressible fluid conditions using the experimental results and Ansys CFX software. For this purpose, the fin is considered once as a unforked rigid cantilever and again as a rigid forked cantilever with a constant water inlet speed of 10 cm per second.... 

In this paper, a novel control approach for one-dimensional bilateral teleoperated nanomanipulation system is proposed. While manipulating objects with a nanomanipulator, real time visual feedback is not available. So, force feedback is used to compensate for the lack of visual information. Since nanometer scale forces are dominated by surface forces instead of inertial forces as in macro world, scaling of nanoforces is one of the major issues of teleoperation system. The Hertz elastic contact model is used to model the interactions between the slave robot and the environment. The proposed framework uses the simple proportional derivative control, i.e., the master and slave robots are... 

Underwater robots are broadly used in oceanography to explore ocean environments,inside inspection of pipes, and also to provide security at maritime boundaries. To design an underwater autonomous robot, it is compulsive to take advantage of a high efficient propulsion mechanism to lengthen the tour time span. Since fish-like propulsion mechanisms have presented higher efficiency comparing other mechanisms, they have been paid a lot of attention.In the present research, the hydrodynamic of a thunniform fish robot is analyzed under some reasonable simplifications. Based on the results achieved from this study, closed expressions are developed to predict the steady mean velocity and the... 

Over the years, The robots have entered the human community in addition to the factories and industrial centers, and a new branch in the field of robotics called social robots has been created. Such robots can become a personal companion for children and elderly people who accompany that person at home or outside. Social robots can even be used as a platform for health services or as a vendor in stores. The interaction of humans and robots in social robots and communicating with the audience is the main part of this series of robots. Human-robot interaction can be divided into three parts: visual, auditory and facial or body movements. Also, the behavior of a social robot must be as natural... 

Performing a safe and effective endoscopic sinus and skull based surgery (ESSS), requires special training programs to gain sufficient hand-eye coordination and instrument manipulation skills. In this regard, virtual-based haptic surgical training systems have been considered among the medical students and residents as an effective approach for training practices. Therefore, in this study, the development of a haptic training system for ESSS, based on an animal model has been addressed. By conducting various indentation and relaxation experiments, mechanical properties of the specific sino-nasal regions of sheep head, as a function of force, displacement and tool insertion rate, for three... 

With the continued improvement of sequencing technologies, the prospect of genome-based medicine is now at the forefront of scientific research. To realize this potential, however, a revolutionary sequencing method is needed for the cost-effective and rapid interrogation of individual genomes. Generally there are key factors in the definition and evalution of sequencing methods: 1-read length, 2-throughput, 3-read accuracy, 4-read depth, and 5-cost per base. The purpose of developing new sequencing methods is making better at least one of these factors. In order to reach the goal of rapid and low-cost sequencing method, one cannot rely only on current techniques. Improvements of current...