Tracking and force control for a class of robotic manipulators

The increasing utilization of robotic manipulators in industrial tasks, such as assembly, forming or shaping of surfaces, and handling hazardous materials, depends greatly on available hybrid force and position control schemes. Since the robot and its environment are often subject to parameter uncertainties that cannot be neglected, it is necessary to design controllers that are robust with respect to these uncertainties. In addition, the dynamics of the robot are nonlinear, requiring consideration of nonlinear control concepts. Another aspect to be taken into account is the relative stiffness of the robot, the force sensor, and the manipulated surface. That is, the behavior of the system normal to the surface is relatively stiff, while that tangential to the surface is relatively free. Separation of the controller for these two directions is therefore indicated. We propose a controller design that accounts for this point of view and demonstrate its efficacy with respect to robustness and accuracy of position and force tracking by means of numerical simulations. The design is based on the control concept of Corless and Leitmann [l]. The example considered is a Manutecr3 robot with three degrees of freedom. In addition, we account for the dynamics of the actuator, which also possesses three degrees of freedom. The considered parameter uncertainties are friction moments in the links and friction between the end effector and the manipulated object, as well as nonlinear dynamics, which are difficult to characterize.Recommended by J. Skowronski     

Continuous state feedback guaranteeing uniform ultimate boundedness for uncertain dynamic systems

We consider a dynamic system containing uncertain elements. Only the set of possible values of these uncertainties is known. Based on this information a class of state feedback controls is proposed in order to guarantee uniform ultimate boundedness of every system response within an arbitrarily small neighborhood of the zero state. These feedback controls are continuous functions of the state.     

A bounded harvest strategy for an ecological system in the presence of uncertain disturbances

We examine a bounded harvest strategy for an ecological system with uncertainty appearing in all system parameters. The instantaneous values of those system parameters are not known except for the bounds of their possible variations. The harvest strategy is required to stabilize the ecological system at a prescribed desired level.     

Reaching Turkey's spontaneous settlements: The institutional dimension of infrastructure provision

Spontaneous settlements, known as gecekondus, now constitute half or more of the housing stock in Turkey's major cities. They are often ill provided with infrastructure and urban services, to the detriment of their residents. A recent (1996) research project sought to understand this problem by using the analytical framework of new institutional economics. In theory, rules should create incentives that shape the behavior of infrastructure providers. In fact, the research discovered that formal rules are largely ineffective. Instead, in the absence of credible formal rules, pressures are exerted that shape informal operating procedures. This and other findings of the research work which are of relevance to both practitioners and theorists of urban development are elaborated upon.     

Semiactive control of a vibrating system by means of electrorheological fluids

A control scheme is designed for the purpose of suppression of vibratory motion of a dynamical system. The efficacy and robustness of the controller vis a vis unknown but bounded disturbances and state measurement errors is investigated analytically and numerically. As an example of a dynamical system we consider a single degree of freedom mass—spring—damper system that is excited by an unknown force. The control scheme presupposes that the spring and damping coefficients can be varied within prescribed bounds, albeit not independently. The construction of such a semiactive controller can be realized by using the properties of so calledelectrorheological fluids (see [1] for relevant experimental investigations). The called for changes in spring and damping properties can be effected in microseconds since the control does not involve the separate dynamics (inertia) of usual actuators. The design of the controller is based on Lyapunov stability theory which is also utilized to investigate the stabilizing properties of the controller. To accommodate state measurement errors the proposed control scheme is combined with afuzzy control concept. Simulations are carried out for examples of periodic, continuous nonperiodic, discontinuous periodic and random excitation forces.     

Adaptive control of aircraft in windshear

The control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value. An adaptive strategy is developed which uses only climb rate information. Robustness vis à vis windshear structure and intensity is illustrated via simulations employing four different windshear models.     

A composite controller ensuring ultimate boundedness for a class of singularly perturbed uncertain systems

We design a composite controller for a class of nonlinear singularly perturbed uncertain systems. The objective of the slow and the fast controllers is to ensure, for any realization of the uncertainties, uniform ultimate boundedness of the trajectories of approximate models of the slow and the fast system dynamics. The conditions under which the sum of these controllers leads to a composite controller guaranteeing uniform ultimate boundedness of the complete system are derived.     

A Differential Game Model of Oligopoly

Most of the literature on oligopoly deals with profit-maximizing firms engaging in “static” repetitive games. As the number of firms increases, the Nash-equilibrium strategy for each Cournot oligopolist converges to the competitive solution. In a two-person, zero-sum differential game model of duopoly [1] we introduced dynamic elements and explored alternative entrepreneurial goals. The duopolists endeavor to outsell each other subject to a no-loss constraint; the saturation of present markets by past sales and the impact on future goodwill by current advertisement are handled through “state variables.” The differential game formulation [1, 2] offers two advantages: (a) near perfect information leads to frequent existence of pure strategy equilibria and (b) the use of optimal control theory facilitates the characterization of the time structure of an equilibrium. However, the two-person, zero-sum framework is too restrictive while a general theory for solving n-person, non-zero sum differential games has still not been developed [3, 4].