Sharif Digital Repository

Chatter suppression is of great importance in machining processes for achieving more material removal rate, high precision and surface quality. In this paper, an H∞ control algorithm is proposed for chatter suppression in the presence of tool wear and parameter uncertainties. Orthogonal turning process is modelled as a single degree of freedom model that includes the effect of tool flank wear. Control input of the system is the force provided by a piezo-actuator.The turning process model includes the uncertainties in cutting velocity, tool wear and dynamic model parameters. Using the μ-synthesis technique, an H∞ optimal controller is designed based on a DK-iteration algorithm. The... 

Chatter suppression is an important topic in any type of machining process. In this paper, orthogonal cutting process is modeled as a single degree of freedom dynamic system. A nonlinear delay differential equation is presented that models flank wear of the tool. Uncertainties in cutting velocity, tool wear size and parameters of the dynamic model are included in the model of cutting process. The force provided by a piezo-actuator is taken as the control input of the system. A sliding mode control scheme is used and an effective control law is derived which suppresses the chatter vibration. Results for two distinct cases of a sharp tool and a worn tool are presented and compared which shows... 

The main scope of this study is to analyse muscle-driven forward dynamics simulation of stair locomotion to understand the functional differences of individual muscles during the movement. A static optimization was employed to minimize a performance criterion based on the muscle energy consumption to resolve muscle redundancy during forward dynamics simulation. The proposed method was employed to simulate a musculoskeletal system with ten degrees of freedom in the sagittal plane and containing 18 Hill-type musculotendon actuators per leg. Simulation results illustrated that simulated joint kinematics closely tracked experimental quantities with root-mean-squared errors less than 1 degree. In... 

Chatter suppression is of great importance for achieving high precision and surface quality in machining processes. A single degree of freedom model of orthogonal turning process is used to set up the nonlinear delay differential equation of motion. Tool wear effect is considered as the contact force between the workpiece and tool flank surfaces. Uncertainties in parameters of dynamic model and machining conditions are included in the model. An adaptive control strategy is applied for chatter suppression in cutting process. The force provided by a piezoactuator is the control input of the system. Results of stability analysis and adaptive control for two distinct cases of sharp and worn... 

A new nonlinear model reference adaptive impedance controller is presented for the control of robot manipulators with uncertainties in model parameters such as friction coefficients. This method provides asymptotic tracking of a reference impedance model for the robot end-effector in operational space which is more sensible for the patient compared to the joint space impedance used in previous works. The model uncertainties such as friction coefficients are compensated using an adaptation law. The asymptotic tracking of the reference impedance model is shown using a Lyapunov function. The tracking performance and friction compensation are also demonstrated through simulation on a... 

In this paper, the occurrence of various types of bifurcation including symmetry breaking, period-doubling (flip) and secondary Hopf (Neimark) bifurcations in milling process with tool-wear and process damping effects are investigated. An extended dynamic model of the milling process with tool flank wear, process damping and nonlinearities in regenerative chatter terms is presented. Closed form expressions for the nonlinear cutting forces are derived through their Fourier series components. Non-autonomous parametrically excited equations of the system with time delay terms are developed. The multiple-scale approach is used to construct analytical approximate solutions under primary... 

In this paper, internal resonance and nonlinear dynamics of regenerative chatter in milling process is investigated. An extended dynamic model of the peripheral milling process including both structural and cutting force nonlinearities is presented. Closed form expressions for the nonlinear cutting forces are derived through their Fourier series components. In the presence of the large vibration amplitudes, the loss of contact effect is included in this model. Using the multiple-scales approach, analytical approximate response of the delayed nonlinear system is obtained. Considering the internal resonance dynamics (i.e. mode coupling), the energy transfer between the coupled x-y modes is... 

This paper deals with the problem of chatter suppression in milling process in order to achieve higher precision, better surface quality and larger material removal rate (MRR). The peripheral milling process is modeled as a two degrees of freedom system and the effects of tool wear and process damping are considered. It is shown that when regenerative chatter develops, both tool wear and process damping act as stabilizing factors. For larger values of depth of cut and consequently higher MRR, tunable vibration absorbers (TVA) (in x-y directions) are designed to improve stability. An optimal algorithm is developed which determines the optimum values for absorbers' parameters. The effects of... 

Peripheral milling is extensively used in manufacturing processes, especially in aerospace industry where end mills are used for milling of wing parts and engine components. Knowledge of the cutting forces is the first necessary stage in analysis of the milling process. In this paper, cutting forces are presented for both two and three dimensional models. Instead of the common linear dependency of cutting forces to the cut chip thickness, two nonlinear models are presented. In the first model, cutting forces are considered as a function of chip thickness with a complete third order polynomial. In the second one, the quadratic and constant terms of the third order polynomial are set to zero.... 

This paper presents a novel model-based algorithm which is able to detect and isolate major faults assigned to the gas exchange path of a gasoline engine both in the intake and exhaust sides. The diagnostics system is developed for detection and isolation of these faults: air leakage fault between the compressor and the air throttle, exhaust manifold pressure sensor fault, wastegate stuck-closed fault and wastegate stuck-open fault. Sliding mode observers (SMOs) are the core detection algorithms utilized in this work. A first order SMO is designed to estimate the turbocharger rotational dynamics. The wastegate displacement dynamics coupled to the exhaust manifold pressure dynamics is... 

This paper presents an analytical study of swarm motion in static environments, in which, motion of the swarm is modeled as a quasi static model. Motion of each member is being affected by interactive forces and environmental effects. Interactive effects on each member could be attractive or repulsive due to being far from or close to other members respectively. Environmental effects also could be attractive or repulsive or a combination of both. The method is based on Lyapunov analysis. Two objectives are investigated through the analysis; one is to preserve the unity of swarm i.e. not losing any member through motion, and the other is to move toward attractant areas and away from repellant... 

The innovative powertrain configuration of modern electric vehicles with four-wheel independent drive (4WID) provides the possibility of simple and exact yaw moment control by controlling the electric motor of every wheel independently. In this study, a genuine control strategy for optimum direct yaw moment control is proposed. Although this can be considered as a global control system for traction control of 4WID electric vehicles, the analysis is quite general and can be applied to other types of vehicle. The directional vehicle model is derived and, in accordance with the optimal control theory, an optimum yaw moment controller is designed. Two versions of the control law are developed... 

A comprehensive new dynamic model of a four-wheel independent drive electric vehicle has been developed and different types of the motor control laws were addressed. The first part of this study deals with the full description of the model scope in which the structure of the model including the sub-models has been fully developed. Subsequently, the sub-models including the tire sub-model, the body motion, and the motor dynamics were investigated, and the computer model of the vehicle has been simulated. Finally, the proposed motor control laws and the vehicle dynamic behavior of the vehicle were presented. Detailed analyses of the vehicle performance and comparison of the simulation results... 

A new control law for direct yaw moment control of an electric vehicle is developed. Although this study is considered as part of a global control system for the traction control of a four motorized wheel electric vehicle, but the results of this study is quite general and can be applied to other types of vehicles. The dynamic model of the system has been analyzed and, in accordance with the optimal control theory, an optimal controller is designed. Two different versions of the control law have been considered and the performance of each version has been separately studied and compared with each other. Finally, the numerical simulation of the vehicle-handling model with and without the use... 

A new optimal control law for direct yaw moment control, to improve the vehicle handling, is developed. Although, this can be considered as part of a multi-layer system, for the traction control of a motorized wheels electric vehicle, but the results of this study are quite general and can be applied to other types of vehicles. The dynamic model of the vehicle system is initially developed and, using the well-known optimal control theory, an optimal controller is designed. Two different versions of control laws are considered here and the performance of each version of the control law is compared with the other one. The numerical simulation of the vehicle handling with and without the use of... 

Purpose - Aims to describe design, prototyping and characteristics of a pole climbing/manipulating robot with ability of passing bends and branches of the pole. Design/methodology/approach - Introducing a hybrid (parallel/serial) four degree of freedom (DOF) mechanism as the main part of the robot and also introduces a unique gripper design for pole climbing robots. Findings - Finds that a robot, with the ability of climbing and manipulating on poles with bends and branches, needs at least 4 DOFs. Also an electrical cylinder is a good option for climbing robots and has some advantages over pneumatic or hydraulic cylinders. Research limitations/implications - The robot is semi-industrial... 

In this paper, we consider a control strategy of multi-robot systems, or simply, swarms, based on emotional control technique. First, we briefly discuss a "kinematic" swarm model in n-dimensional space introduced in an earlier paper. In that model, motion of every swarm member is governed by predefined inter-individual interactions. Limitations of every member's field of view are also considered in that model. After that, we consider a general model for vehicle dynamics of each swarm member, and use emotional control theory to force their motion to obey the dynamics of the kinematic model. Based on the kinematic model, stability (cohesion) analysis is performed and coordination controller.is... 

In this paper a magnetic levitation system is modeled and an eddy current based damping force is identified and used for position control of the levitated object in the system. In the magnetic levitation technology, contactless manipulation of a levitated object is done by use of magnetic fields. Also, the eddy-current based force is used to damp the motion of the levitated object. Eddy-current is generated in a plate which is placed underneath the levitated object due to the change of current in an electromagnet and the motion of the levitated object. First, using finite element method (FEM), the magnetic levitation system is modeled and the eddy-current based force acting on the levitated... 

Exoskeleton robots are developed for human rehabilitation and power augmentation. Human and robot interaction is an important issue involved with these robots. In this paper, the interaction force reduction is considered leading to the transparency of a lower limb exoskeleton during swing phase of walking. Achieving this goal, a robust Lyapunov based motion control method has been developed. The desired reference signals for motion control are generated using a direct force control approach. Robot accelerations are estimated by an observer to be employed in the control loop. An adaptation procedure has been proposed for the bound estimation of uncertainties. As part of assumptions, the... 

The objective of this study was to quantify individual muscle function differences between level walking and backpack load carriage at the same speed by using a muscle-actuated forward dynamics simulation. As experimental investigations have revealed that backpack loads of up to 64 per cent of an individual's body mass have little effect on the sagittal plane gait kinema-tics, further biomechanical analyses are necessary to investigate the contributions of individual muscle coordination strategies to achieve a given motor task by mechanical power generation, absorption, and transference to each body segment. A biomechanical framework consisting of a musculoskeletal model actuated by 18...