Mohammad Eghtesad

Vibration Control and Trajectory Tracking for General In-Plane Motion of an Euler-Bernoulli Beam Via Two-Time Scale and Boundary Control Methods

In this paper, general in-plane trajectory tracking problem of a flexible beam is studied. To obtain the dynamic equations of motion of the beam, Hamiltonian dynamics is used and then Lagrange’s equations of beam dynamics and corresponding expressions for boundary conditions are derived. Resulting equations show that the coupled beam dynamics including beam vibration and its rigid in-plane motion take place in two different time domains. By using two-time scale (TTS) control theory, a control scheme is elaborated that makes the orientation and position of the mass center of the beam track a desired trajectory while suppressing its vibration. TTS composite controller has two parts: one is a tracking controller designed for the slow (rigid) subsystem, and the other one is a stabilizing controller for the fast (flexible) subsystem. For the fast subsystem, the proposed boundary control (BC) method does not require any information about vibration along the beam except at the end points, nor requires discretizing the partial differential equation of beam vibration to a set of ordinary differential equations. So, the method avoids the need for instruments to measure data from vibration of any point along the beam or designing an observer for estimating this information. Also, the proposed method prevents control spillover due to discretization. Simulation results show that fast BC is able to remove undesirable vibration of the flexible beam and the slow controller provides very good trajectory tracking with acceptable actuating forces/moments.

Position control of a stewart-gough platform using inverse dynamics method with full dynamics

The Stewart-Gough platform is a six DOF parallel robot manipulator with a force-to-weight ratio and positioning accuracy far exceeding those of a conventional serial-link arm. In this article, application of an inverse dynamics control scheme Stewart-Gough platform is proposed. Control of the parallel manipulator is an open field and the works reported are not rigorous. Kinematic equations of the robot are presented; full dynamic equations of the Stewart-Gough platform are derived using Lagranges formulation approach. Simulation results illustrate the performance of the control algorithm

Workspace Analysis for Planar and Spatial Redundant Cable Robots

This paper presents workspace analysis of planar and spatial cable robots having one or more redundant cables. The proposed approach, which is based on a variant of Blands pivot rule, provides all poses (positions/orientations) reachable by the cable robot platform with any number of cable redundancies. By virtue of this method, there is no need to use successive determinants to compute the workspace; this results in less computation time. Additionally, another algorithm, which takes advantage of reduced row-echelon form of the system matrix, is proposed for the case of cable robots with only one redundant cable and also to include upper limit for tensions in cables as an important factor in workspace analysis of the cable robots. Simulation results are provided to show the merits of the proposed methods to compute the available static workspace of the redundant cable robots.

Neural network solution for forward kinematics problem of HEXA parallel robot

Forward kinematics problem of parallel robots is very difficult to solve in comparison to the serial manipulators. This problem is almost impossible to solve analytically. Numerical methods are one of the common solutions for this problem. But, convergency of these methods is the drawback of using them. In this paper, neural network approach is used to solve the forward kinematics problem of the HEXA parallel manipulator. This problem is solved in the typical workspace of this robot. The results show the advantages of this method in providing very small modeling errors.

Experimental study of the dynamic based feedback linearization of an autonomous wheeled ground vehicle

Abstract In this paper a combined open/closed-loop method for point stabilization of autonomous wheeled vehicles using feedback linearization technique is presented. For point stabilization of the vehicle in planar motion (the vehicle has 2 degrees of freedom), both position (in two directions) and orientation must be stabilized (approach their desired values). Here, we propose to apply feedback linearization and exponentially stabilize the position of the center of mass of the vehicle in curvilinear coordinates (closed-loop part) and the vehicle’s orientation along a path that connects the initial and final positions with the corresponding desired orientations (open-loop part with bounded error). The vehicle used for illustration in this paper has one front (steering and driving) and two rear (idle) wheels and also a computer, two dc motors, two batteries and two measurement systems is an example of an autonomous ground vehicle. The dynamic model of this vehicle is presented in the state-space form with steering and driving torques as inputs. The results of the simulation and the experimental study of the proposed controller on this three-wheel vehicle as a prototype show that when the arc length coordinate of the position of the center of mass of the vehicle reaches its desired value, the vehicle stops at the desired position with the desired orientation with small acceptable errors proving the validity of the proposed method.

Study of the internal dynamics of an autonomous mobile robot

Abstract The requirement of ideal rolling without sideways slipping for wheels imposes nonholonomic (non-integrable) constraints on the motion of the wheels and consequently on the motion of wheeled mobile robots. From the control point of view, the dynamics of nonholonomic systems can be divided in two parts: external and internal dynamics. The dimension of the external dynamics of nonholonomic systems depends on the number of inputs to the system and the dimension of the internal dynamics depends on the number of independent nonholonomic constraints. For different motion control problems of nonholonomic systems, a smooth (model based) state feedback control law only deals with the system external dynamics; therefore, the system internal dynamics must be examined separately and its stability has to be analyzed and proved. In this paper, the internal dynamics of a three-wheel mobile robot with front wheel steering and driving is investigated. In particular, its internal dynamics stability is analyzed for two different situations, when the mobile robot is moving and when it is stationary.

Vibration suppression of smart nonlinear flexible appendages of a rotating satellite by using hybrid adaptive sliding mode/Lyapunov control

In this paper, a hybrid adaptive sliding mode/Lyapunov controller is designed for both the rotational maneuver and the vibration control of smart flexible appendages of a satellite moving in a circular orbit. The satellite is considered as a rigid hub and two flexible appendages with attached piezoelectric layers as sensors and actuators. Each appendage is considered as a nonlinear beam undergoing large deflection. These governing equations of motion are obtained using a Lagrange–Rayleigh–Ritz technique and assumed mode method. The dynamic equations of motion are nonlinear and coupled due to the large angle trajectory and appendages large deflection. A through look at the resulting equations shows that the flexible satellite dynamics including the vibrations of the appendages and their rigid maneuver occur in two different time scales. Using the singular perturbation theory, the dynamics of the flexible satellite are divided into two slow and fast subsystems, the former associated with rigid-body maneuver, while the latter is a result of the vibrations of the appendages. Use of this hybrid controller allows us to cope with parameters uncertainty and disturbances of the system. The stability of the hybrid controller is studied by using the Lyapunov approach. Finally, the whole system is modeled and the simulation results show the efficient performance of the proposed hybrid controller.

Hybrid sliding mode control of semi-active suspension systems

In order to design a controller which can take both ride comfort and road holding into consideration, a hybrid model reference sliding mode controller (HMRSMC) is proposed. The controller includes two separate model reference sliding mode controllers (MRSMC). One of the controllers is designed so as to force the plant to follow the ideal Sky-hook model and the other is to force the plant to follow the ideal Ground-hook model; then the outputs of these two controllers are linearly combined and applied to the plant as the input. Also, since the designed controller requires a knowledge of the terrain input, this input is approximated by the unsprung mass displacement. Finally, in the simulation section of this study, the effect of the relative ratio between the two MRSMCs and the knowledge of the terrain on the performance of the controller is numerically investigated for both steady-state and transient cases.

A robust adaptive fuzzy sliding mode controller for trajectory tracking of ROVs

This study deals with dynamic modeling and tracking control of a remotely underwater vehicle (ROV) with six degrees of freedom (DOF). The sliding mode scheme for tracking control of an ROV is a powerful approach to compensate structured and unstructured uncertainties. In this study, performance of sliding mode approach modified by robust adaptive fuzzy control algorithm for an ROV is presented. Fuzzy algorithm is used for on-line estimation of external disturbances as well as unknown nonlinear terms of dynamic model of the ROV. A robust control rule is employed to compensate for estimation errors. The boundedness and asymptotic convergence properties of the control algorithm and its semi-global stability are analytically proven using Lyapunov stability theory and Barbalats lemma. Moreover, adaptation laws and robust control terms are derived from Lyapunov stability synthises. The adopted control scheme is implemented in numerical simulations, based on the dynamic parameters of Shiraz University Remotely Operated Vehicle (Ariana I ROV). Simulations show the effectiveness of the adopted controller for trajectory tracking.

Integrator backstepping control of a 5 DoF robot manipulator incorporating actuator dynamics

In this paper, dynamic equations of motion of a 5 DoF robot manipulator including mechanical arms with revolute joints and their electrical actuators are considered and the application of the integrator backstepping technique for trajectory tracking, in the presence of parameters uncertainty and disturbance is studied. The advantage of this control technique is that it imposes desired properties of stability by fixing the candidate Lyapunov functions initially, then by calculating the other functions in a recursive way. Simulation results are presented in order to evaluate the tracking performance and the global stability of the closed loop system. The results show the validity of the proposed technique for robot motion control when the system dynamics, including both mechanical arms and electrical actuators has become more complex.