Alireza Doosthoseini

Coordinated path following for a multi-agent system of unicycles

We investigate a coordinated path following problem for a multi-agent system of N unicycles. Each unicycle is required to follow its own path while coordinating its motion along its path with the other unicycles. We assume that all the unicycles can communicate with each other. We view coordinated path following as a nested set stabilization problem. Stabilization of the first set corresponds to meeting the path following specification. Stabilization of the second, nested set, corresponds to meeting the coordination specification. The first set is characterized for the multi-agent system of N unicycles and feedback linearization is proposed to stabilize it. We provide sufficient conditions under which the second set is nonempty and stabilize it using feedback linearization.

Coordinated path following for unicycles

We formulate a coordinated path following problem for N unicycle mobile robots as an instance of a nested set stabilization problem. Stabilization of the first set corresponds to driving the unicycles to their assigned paths. Stabilization of the second set, a subset of the first, corresponds to meeting the coordination specification. The first set is stabilized, for initial conditions sufficiently close to the set, in a decentralized manner using feedback linearization. For general coordination tasks we utilize feedback linearization to stabilize the nested set in a centralized manner, again, for initial conditions sufficiently close to the second set. In the special case in which coordination entails making the unicycles maintain a formation along their paths, we employ a semi-distributed control law under less restrictive communication assumptions. Experimental results are provided.

Stability problems associated with the transverse feedback linearization normal form

Transverse feedback linearization (TFL) has previously been proposed as a method to solve set stabilization problems. TFL allows a designer to separately design a control law to stabilize the target set and a controller to achieve the desired motion on the set. However, care must be taken to ensure that the designed controllers work as expected when combined together. Two new results on the exponential stability of cascade connected systems are provided. Two examples are used to illustrate how these results can be applied to the stability analysis of set stabilization problems using TFL.

ANALYSIS OF WRINKLED MEMBRANES BOUNDED WITH MACRO-FIBER COMPOSITE (MFC) ACTUATORS

In this paper we focus on a study which involves quantifying the effects of Macro Fiber Composite (MFC) actuators on the pattern and magnitude of wrinkles in a membrane when exposed to various loadings. An ABAQUS finite element code is employed for this research. The membrane in this study has a rectangular shape which is clamped at one edge and is free to move in the horizontal direction at the other edge. MFC actuators are bounded to the membrane to make a bimorph configuration.Copyright

Force control of a shape memory alloy wire using fuzzy controller

An experimental setup is designed and fabricated to measure the force induced by voltage in an SMA wire. Using autoregressive model with exogenous input (ARX) method for system identification of the experimental data, two appropriate transfer functions of the force in SMA wire versus the applied voltage during each of heating and cooling processes were derived. Afterwards, a conventional PID controller and a self-tuning fuzzy PID controller were designed to control the force in SMA wire. The latter control algorithm is used by tuning the parameters of the PID controller thereby integrating fuzzy inference and producing a fuzzy adaptive PID controller, which is used to improve the force control performance. The responses of the system with the both designed controllers for different inputs are simulated and compared to each other. At the end, simulation results show that in force control of the SMA wire, self-tuning fuzzy PID controllers are more efficient than conventional PID controllers.

Local nested transverse feedback linearization

We study two local feedback equivalence problems for a nonlinear control-affine system with two nested, controlled-invariant, embedded submanifolds in its state space. The first, less restrictive, result gives necessary and sufficient conditions for the dynamics of the system restricted to the larger submanifold and transversal to the smaller submanifold to be linear and controllable. This normal form facilitates designing controllers that locally stabilize the smaller set relative to the larger set. The second, more restrictive, result additionally imposes that the transversal dynamics to the larger set be linear and controllable. This result can simplify designing controllers to locally stabilize the larger submanifold. This is illustrated by sufficient conditions under which these normal forms can be used to locally solve a nested set stabilization problem.

Fuzzy control of flexible structure using piezoelements

In this paper the vibration suppression of a flexible structure using fuzzy controller with bonded piezoelements is investigated. A flexible beam with PZT piezoceramics as sensor and actuators is fabricated at the Advanced Dynamic and Control Systems lab (ADCSL). A dynamic model of the smart structure is derived from an experimental system ID. On the other hand using finite element method (FEM), a theoretical model of the structure is obtained which is in good agreement with the experimental model. A fuzzy control system is then designed and implemented for vibration suppression of the smart beam subjected to the impulse excitation and resonance disturbances. Results show the effectiveness of the fuzzy controller and its advantage over conventional controllers.

Automotive coldstart emissions reduction using MIMO sliding mode control with actuator saturation

In this study, a modified version of multi-input multi-output (MIMO) sliding mode control technique is applied to reduce the total hydrocarbon emissions of an automotive engine during the coldstart period. This specific control design technique is suitable for MIMO systems with constraints on their input signals and it allows finding a set of upper limits for the gains of sliding mode controller (SMC) with regard to the given input constraints. In this context, an optimization problem is formulated to calculate the upper bounds of SMC gains to ensure the feasibility of the calculated control commands for the considered coldstart control problem. Through simulations, it is indicated that the devised SMC can properly track the given exhaust gas temperature (Texh) and engine-out hydrocarbon emission (HCraw-c) desired profiles in the presence of external disturbances without violating the existing engine system input constraints.

Local transverse feedback linearization for nested sets

We study a local feedback equivalence problem for a nonlinear control-affine system with two nested, controlled invariant, embedded submanifolds in its state space. The main result of this paper gives necessary and sufficient conditions for (i) the dynamics of the system transversal to the larger submanifold to be linear and controllable and (ii) the system dynamics, restricted to the larger submanifold, and transversal to the smaller submanifold to also be linear and controllable.

THERMAL ROBUSTNESS ASSESSMENT OF A RIGIDIZED SPACE INFLATABLE BOOM VIA EXPERIMENTAL MODAL ANALYSIS AND FINITE ELEMENT MODELING

The following paper presents the results of a thermal robustness assessment of a rigidized space inflatable boom. Modal testing is performed at three different environmental temperatures; spanning a range of 38°C, with the purpose of characterizing dynamic behavior and assessing changes in bending frequencies. Experimental results show that the natural frequencies of the boom shift only marginally within the tested bandwidth. A finite element model is developed in parallel with experiments to determine compatibility with beam theory. The resulting simulation shows that linear beam theory can be used to predict bending frequencies and frequency response function magnitudes with very good accuracy.Copyright