فهرست مطالب aghil yousefi-koma

Recent progress in robotic industry has increased efforts on robot ability enhancement to use them in factories and services instead of labors and human workers. One of the important ability which plays an important role to reach this aim, is tactile sensation which is not compensated by other ability including image processing. In this paper, a robot fingertip with tactile sensation is designed and fabricated which has a configuration very close to human fingertip for griping or other robotic applications. This fingertip consists of rigid body and elastic flexible cover which the area between these two parts is filled with a fluid which is connected to the pressure sensor. When the elastic cover which plays a skin role, touch the external body, regarding to the speed and amplitude of touch, the reaction of the cover is transferred to the fluid and also pressure sensor. Pressure sensor sense the pressure change and convert this to the output voltage which is detectable by designed electrical circuit. Outer layer of the elastic cover is corrugated to increase sensitivity of the sensor. The fabricated tactile sensor was tested to verify its performance in different experiments which was in good agreement with our expectation.

In this paper, hysteretic behavior modeling, system identification and control of a mechanism that is actuated by shape memory alloy (SMA) wires are presented. The mechanism consists of two airfoil plates and the rotation angle between these plates can be changed by SMA wire actuators. This mechanism is used to identify the unknown parameters of a hysteresis model. Prandtl–Ishlinskii method is employed to model the hysteresis behavior of SMA actuators, and then, a self-tuning fuzzy-PID controller is designed based on the obtained model and implemented experimentally on the mechanism. The process of designing the controller has been implemented based on the model which results in compensating time and price. Self-tuning fuzzy-PID controller is applied to the closed control loop in order to control the position of the morphing wing. The performance of the controller has been investigated under different input signals including square and sinusoidal waves, and the results show the proper effectiveness of the method.

In this paper, a new design approach for an admittance control method is presented to deal with the environmental disturbances for user-in-charge exoskeletons. Since the challenge of maintaining the stability of the robot and the human is met by the user, environmental disturbances as a set of external forces should be considered. However, the proposed control methods have already ignored the issue and focused on presenting a desired dynamic relation between the interaction forces and the robot motion. This paper aims to find a control solution to maintain the desired behavior of the classical controllers in response to the interaction forces as well as to deal with disturbances properly. For this purpose, a control structure is developed by substituting an impedance control method for the low-level layer of an admittance controller. A simulation on an exoskeleton leg is conducted to evaluate the performance of the proposed controller in comparison with the classical control methods for user-in-charge exoskeletons. In contrast to conventional control methods, the results shows that the proposed controller can deal with both the interaction forces and the disturbances properly as the consequence of establishing different dynamic mappings for each of them.

This paper proposes a two phase strategy for proportional myoelectric control of Surena 3 humanoid robot which benefits from strength of two common myoelectric control methods, Pattern recognition base and simultaneous proportional control, for improving joint angle estimation. The aim of this research is to present a human-robot interface to create a mapping between electrical activities of muscles known as electromyogram (EMG) signals and kinematics of corresponding motion. First phase concerns with motion classification using Quadratic Discriminant Analysis (QDA) and Majority Voting (MV). Several common motion classification algorithms and feature vectors including time domain and frequency domain futures were investigated which lead to QDA and a superior feature vector with more than 97% classification accuracy. The second phase concerns with continuous angle estimation of shoulder joint motion classes using Time Delayed Artificial Neural Network (TDANN) with overall accuracy of 90% R2. QDA serves as a high level controller which decides between four TDANN correspond to each shoulder motion classes. QDA and TDANN models trained with several sets of offline data and were tested with online dataset. Online and offline data estimation accuracy and model robustness against disturbances show a significant improvement compared to similar methods in this field.

In this paper, the forward kinematics of a parallel manipulator with three revolute-prismatic-spherical (3RPS), is analyzed using a combination of a numerical method with semi-analytical Homotopy Continuation Method (HCM) that due to its fast convergence, permits to solve forward kinematics of robots in real-time applications. The revolute joints of the proposed robot are actuated and direct kinematics equations of the manipulator leads to a system of three nonlinear equations with three unknowns that need to be solved. In this paper a fast and efficient Method, called the Ostrowski-HCM has been used to solve the direct kinematics equations of this parallel manipulator. This method has some advantages over conventional numerical iteration methods. Firstly, it is the independency in choosing the initial values and secondly, it can find all solutions of equations without divergence just by changing auxiliary Homotopy functions. Numerical example and simulation that has been done to solve the direct kinematic equations of the 3-RPS parallel manipulator leads to 7 real solutions. Results indicate that this method is more effective than other conventional Homotopy Continuation Methods such as Newton-HCM and reduces computation time by 77-97 % with more accuracy in solution in comparison with the Newton-HCM. Thus, it is appropriate for real-time applications.

In this paper, the dynamic response of resonating nano-beams is investigated using a strain gradient elasticity theory. A nonlinear model is obtained based on the Galerkin decomposition method to find the dynamic response of the investigated beam around its statically deflected position. The mid-plane stretching, axial residual stress and nonlinear interaction due to the electrostatic force on the deflected beam are included in the proposed nonlinear beam model. Comparing the beam natural frequency using strain gradient theory with experimental data shows an excellent agreement among both approaches. The normalized natural frequency is shown to be increasing nonlinearly with the decrease of the applied DC voltage as well as beam thickness. The results also reveal that increasing the tension axial stress increases the natural frequency; however its influence decreases when decreasing the beam thickness. To investigate the effect of AC actuation voltage on the beam resonant frequency, a Lindstedt-Poincare based perturbation method is utilized and validated by comparison with experimental data. The results show that increasing the AC actuation voltage makes the beam stiffer by increasing its resonant frequency.

Rotor dynamics is known as the study of vibrational behavior in axially symmetric linear rotating structures. Devices such as engines, turbines, compressors and generators are located in this category. Study of vibrational behavior of these structures in different rotational velocities yields to recognition of critical points and preventing failures, especially high cycle fatigue. The case study of the present paper is a bladed disk used in the first stage of compressor of a gas turbine engine. The material of machined integrated bladed disk is aluminum alloy. The simulations have been done by ANSYS finite element software. By using the cyclic symmetry module of ANSYS the nodal diameter mode shapes of structure have been obtained. In the next step, experimental modal analysis test has been done by measuring 58 points on the bladed disk and the nodal diameters have been obtained experimentally. Finally, experimental and simulation results have been compared to each other. The novelty of this paper is the experimental procedure of obtaining nodal diameter of a bladed disk, which is so useful in verification of numerical simulation.

In this paper a push recovery controller for balancing humanoid robot under severe pushes for situation that contact surface is small is presented. Human response to progressively increasing disturbances can be categorized into three strategies: ankle strategy, hip strategy and stepping strategy. The reaction of human to external disturbances in the situations that contact surface is small or stepping is not possible is generating upper body angular momentum. In this way in this paper, a single model predictive controller scheme is employed to controlling the capture point by modulating zero moment point and centroidal moment pivot. The proposed algorithm is capable of recovering balance of humanoid robot under severe pushes without stepping in situation that contact surface is shrunked to a strip. The goal of the proposed controller is to control the capture point, employing the centroidal moment pivot when the capture point is out of the support polygon, and/or the zero moment point when the capture point is inside the support polygon. The merit of proposed algorithm is shown successfully in different simulation scenarios using characteristic of SURENA III humanoid robot.

Due to necessity of increasing performance in new generations of the humanoid robots, in this paper, a novel power transmission mechanism to actuate the ankle joint of a humanoid robot is presented in order to increase the motion speed of SURENAIII humanoid robot. Also, the energy consumption of the proposed and the previous mechanisms are studied. In the proposed mechanism, the actuators of the ankle joint are located in the shank link. Then, a combined timing belt-pulley and a harmonic drive module are exploited for power transmission for the pitch joint. Also, the roll joint drive has employed a roller screw. In order to validate the design procedure, the simulation results of the robot are compared with the experimental data. The results reveal that the dynamic model is fairly matched to the real behavior of the robot. Also, the revolutionary genetic algorithm is employed to optimize the effective path planning parameters with respect to the minimum knee joint torque. This optimization procedure which is employed in robot walking on flat terrains consist of straight motion, ensures the robot's stability. As a result, the optimal path planning parameters for proposed mechanism are obtained in such a way that has decreased the actuating torques of lower-body of SURENAIII. Also, the proposed mechanism can achieve using lighter motors and getting the robot faster by means of mass reduction of foot.

Precise modeling has great importance in systems which are designed to work in transonic regions. The scope of current investigation includes numerical simulation of static aeroelastic phenomena of deformable structures in transonic regimes. Transonic flow brings lots of instabilities for aerodynamic systems. These instabilities bring nonlinearity in flow and structure solvers. Due to improvements in numerical methods and also enhancement in computing technologies, computational costs reduced and high-fidelity simulations are more applicable. Simulations in this paper are done in transonic flow (M = 0.96) on the benchmark wing AGARD 445.6. The procedure includes modal analysis, steady flow simulation and investigation of structure’s elastic behavior. At the first phase, the geometry model is validated by modal analysis with regards to comparison of first four natural frequencies and corresponding mode shapes. Then, a loose or staggered coupling is used to analyze aeroelastic behavior of the wing. In each simulation step, imposed pressure on the surfaces of the wing caused by transonic flow regime, deforms the structure. In the results section, a comparison between imposed pressure coefficients in each step with the existing literature and experimental results are reported. Also, pressure coefficients in each steps are calculated and reported. In this investigation by using multiple steps in one-way fluid-structure analysis, deformations are reduced in each step and as a result, the structure reached its static stability point.

In this paper, designing optimal linear controller for non-holonomic wheeled mobile robots based on Linear Quadratic Gaussian (LQG) controller is considered. Parameters of the governing kinematics equation of motion are derived based on system identification techniques by using real experimental data. The autoregressive moving average-exogenous input (ARMAX) models are taken into account. The least square (LS) algorithm is utilized to estimate the parameters of the model. Thereafter, optimal model order and the performance of the model are determined using several statistical analyses. Also, the recursive LS (RLS) with forgetting factor is employed to demonstrate the convergence of the model parameters. Verification of discrete linear model implies the possibility of using the linear controllers. Therefore, the optimal LQG controller for wheeled mobile robots is designed to track the reference trajectory. The Kalman observer is used to estimate un-measurable states of the robot. Furthermore, the optimal linear control together with system identification techniques yields simpler controller than nonlinear controllers. Designed controller and verified model are simulated using the MATLAB-Simulink software. Results show the effectiveness of the controller in tracking the desired reference trajectory.

In this paper, the dynamic behavior of atomic force microscope (AFM) based on non-classical strain gradient theory was analyzed. For this aim atomic force microscope micro-beam with attached tip has been modeled as a lumped mass. Micro-beam has stimulated via a piezoelectric element attached to the end of clamped and non-linear partial differential equation of the system has extracted based on Euler-Bernoulli theory and to be converted into ordinary differential equation by using Galerkin and separation method. The classic continuum theory because of lack of consideration size effect that has been observed in many experimental studies, has little accuracy in predicting the mechanical behavior of Nano devices. In this study, the stability region of micro-beam are determined analytically and validated by comparison with numerical results. Difference between presented analysis in dynamic behavior of micro-beam by classic and non-classic theories has been shown with variety of diagrams. It is clear that consideration the size effect changes the dynamical behavior of the problem completely and it is possible while classical theory predicts stable behavior for microscope the size effect is caused bi-stability. The results in this paper are very useful for the design and analysis of atomic force microscope.

In this paper, to improve the accuracy of the one-mass and three-mass inverted pendulum models, which have been used for generating real-time walking patterns for biped robots, we propose a novel model based on the three-mass inverted pendulum. The proposed model employs an approximation of moment of inertia of the swing leg to improve the accuracy of the three-mass inverted pendulum in estimating dynamic behavior of the robot. In order to show significance of the proposed model, trajectories for the Center of Mass (CoM) are obtained using the three models, based on a desired ZMP trajectory. The task space trajectories, then, are mapped into the joint space, using inverse kinematics. Having the joint space variables, the actual ZMPs for the three obtained walking patterns are computed and compared. This comparison well shows merit of the proposed model in estimating dynamic behavior of the robot, especially for walking with relatively high speeds. The kinematic and dynamic properties of the models in this paper are based on the humanoid robot SURENA III, which has been designed and fabricated in the Center of Advanced System and Technologies (CAST), university of Tehran.

Research on wind turbine technologies have focused primarily on power cost reduction. Generally, this aim has been achieved by increasing power output while maintaining the structural load at a reasonable level. However, disturbances, such as wind speed, affect the performance of wind turbines, and as a result, the use of various types of controller becomes crucial.
This paper deals with two adaptive fuzzy controllers at full load operation. The first controller uses the generated power, and the second one uses the angular velocity as feedback signals. These feedback signals act to control the load torque on the generator and blade pitch angle. Adaptive rules, derived from the fuzzy controller, are defined based on the differences between state variables of the power and angular velocity of the generator and their nominal values.
The results, which are compared with verified results of reference controller, show that the proposed adaptive fuzzy controller in full load operation has a higher efficiency than that of reference ones, insensitive to fast wind speed variation that is considered as disturbance.

In this paper, the effects of the addition of an active toe joint on a 2D humanoid robot with heel-off and toe-off motions are studied. To this end, the trajectories of joints and links are designed firstly. After gait planning, the dynamic model of the humanoid robot in different phases of motion is derived using Kane and Lagrange methods. Then, the veracity of the derived dynamic model is demonstrated by two different methods. The under-study model, is in accordance with the features of SURENA III, which is a humanoid robot designed and fabricated at the Center of Advanced Systems and Technologies (CAST) located in University of Tehran. Afterward, the optimization procedure is done by selection of two different goal functions; one of them minimizes the energy consumption and the other maximizes the stability of the robot. At last, the obtained results are presented. According to the results, there is an optimum value for heel-off and toe-off angles in each velocity which minimizes the consumption of energy. The results also show that, the heel-off angle does not have any significant effects on the stability of the robot while increasing the toe-off angle improves the stability of motion. Finally, the effects of mass and length of the toe joint is inspected. These inspections suggest that heavier toe joints cause an increase in both energy consumption and stability of the robot while increasing the length of the toe joint does not have any effects on both goal functions.

Due to the importance of autopilot systems in Micro Aerial Vehicles (MAVs), in this paper first, parametric guidance and control systems are designed, and then they are implemented on a simulated nonlinear six-DOF MAV. The control system is fuzzy-supervisory which its gains are optimized using genetic algorithm. For designing the guidance system, first, two-dimensional (constant height) path following algorithms of vector field and carrot-chasing are developed to 3D algorithms. Then, an optimized 3D fuzzy carrot-chasing guidance system is presented using a combination of the carrot-chasing geometric algorithm, fuzzy logic, and genetic algorithm. Augmentation of the fuzzy logic to the carrot-chasing algorithm, improves its performance significantly. In any autonomous flight maneuver, guidance and control systems affect the performance of the aircraft, simultaneously. So, using a similar control system, the performance of the 3D carrot-chasing algorithm, 3D vector field method, and the proposed 3D fuzzy carrot chasing algorithms are compared with and without applying the wind external disturbance. Results have shown significant superiority of the proposed 3D fuzzy carrot-chasing approach in the horizontal plane of motion and the 3D vector field method in the vertical plane of motion.

The scope of the current investigation incorporates the entire process involved in design and development of a Shape Memory Alloy (SMA) actuated wing intended to fulfill morphing missions. At the design step, a two Degree-of-Freedom (DOF) mechanism is designed that is appropriate for morphing wing applications. The mechanism is developed in such a way that it can undergo different two DOF, i.e. gull and sweep, so that the wing can have maneuvers that are more efficient. Smart materials commonly are selected as the actuators due to their suitable thermo-mechanical characteristics. Shape Memory Alloy (SMA) actuators are capable of providing more efficient mechanisms in comparison to the conventional actuators due to their large force/stroke generation, smaller size with high capabilities in limited spaces, and lower weight. As SMA wires have nonlinear hysteresis behavior, their modeling should be implemented in a meticulous way. In this work, after proposing a two DOF morphing wing, an aerodynamic analysis of the whole wing for unmorphed and morphed wings is presented. The results show that the performance of the morphed wing in special flight regimes is improved.

The main objective of this article is to optimize the walking pattern of a 2D humanoid robot with heel-off and toe-off motions in order to minimize the energy consumption and maximize the stability margin. To this end, at first, a gait planning method is introduced based on the ankle and hip joint position trajectories. Then, using these trajectories and the inverse kinematics, the position trajectories of the knee joint and all joint angles are determined. Afterwards, the dynamic model of the 2D humanoid robot is derived using Lagrange and Kane methods. The dynamic model equations are obtained for different phases of motion and the unknowns, including ground reactions, and joint torques are also calculated. Next, the derived dynamic model is verified by comparing the position of the ZMP point based on the robot kinematics and the ground reactions. Then, the obtained trajectories have been optimized to determine the optimal heel-off and toe-off angles using a genetic algorithm (GA) by two different objective functions: minimum energy consumption and maximum stability margin. After optimization, a parametric analysis has been adopted to inspect the effects of heel-off and toe-off motions on the selected objective functions. Finally, it is concluded that to have more stable walking in high velocities, small angles of heel-off and toe-off motions are needed. Consequently, in low velocities, walking patterns with large angles of heel-off and toe-off motions are more stable. On the contrary, large heel-off and toe-off motions lead to less energy consumption in high velocities, while small heel-off and toe-off motions are suitable for low velocities. Another important point is that for the maximum stability optimization, compared to minimum energy consumption optimization, more heel-off and toe-off motions are needed.