Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item Determination of the Static Friction Present in Each Finger of a Three Fingered Modular Dextrous Hand(1989) Uber, J.A.; Loncaric, J.; ISRThe purpose of this experiment was to determine the static friction (stiction) present in each finger of a three fingered modular hand and determine the torque required to break away from a stuck position. The static friction is a function of both position and direction of movement of the mtor driving the finger. Upon completion of enough trial runs from each position in each direction the results obtained will be averaged together to produce a mapping of the static friction of each finger of the gripper as a function of position and direction. This stiction data base will then be incorporated as a torque look-up table into the open loop control systems architecture of the hand. This compensation has been used in other robotics control experiments to produce a significantly more accurate open loop movement, greatly easing the operational burden of the eventual closed loop control.Item Real-Time Control for a Zero Gravity Robotic End Effector(1989) Salter, C.A.; Baras, J.; ISRThere is no doubt that the task of gripping and handling objects in space is an important one. The ability to easily manipulate objects in a zero gravity environment will play a key role in future space activities. It is the aim of this research to develop control laws for the zero gravity robotic end effector designed by engineers at NASA Goddard. A hybrid force/position controller will be used. Sensory data available to the controller are obtained from an array of strain gauges and a linear potentiometer. Applying well known optimal control theoretic principles, the control which minimizes the transition time between positions is obtained. A robust force control scheme is developed which allows the desired holding force to be achieved smoothly without oscillation. In addition, an algorithm is found to determine contact force and contact location.Item Mobile Robot Navigation Using Potential Functions(1989) Shahidi, R.; Shayman, M.; Krishnaprasad, P.S.; ISRThis thesis presents a method to construct a smooth obstacle free path for a mobile robot on which to navigate. The first step is to assign potential functions to each obstacle and the goal. Then, the gradient system constructed by the gradient of the sum of the above functions generates the desired path. The construction is analytically proven to produce obstacle free paths to the goal for an environment whose obstacles can be approximated by disks. The procedure does not require complete information on the position of the obstacles beforehand, as long as they can be detected and approximated by disks. The algorithm presented shows a computationally simple way to construct paths and a systematic method to encode the geometric data about the environment into a smooth vector field, which is used for mobile robot navigation.Item Neural Networks for Low Level Processing of Tactile Sensory Data(1989) Pati, Y.C.; Krishnaprasad, P.S.; ISRAs the field of robotics continues to strive forward, the need for artificial tactile sensing becomes increasingly evident. Real-time, local processing of tactile sensory data also becomes a crucial issue in most applications of tactile sensing. In this thesis it is shown that analog neural networks provide an elegant solution to some of the problems of low level tactile data processing. We consider the particular problem of 'deblurring' strain data from an array of tactile sensors. It is shown that the inverse problem of deblurring strain measurements to recover the surface stress over a region of contact is ill-posed in the sense defined by Hadamard. This problem is further complicated by the corruption of sensor data by noise. We show that the techniques of 'regularization' may be used to introduce prior knowledge of the solution space into the solutions in order to transform the problem to one which is well-posed and less sensitive to noise. The particular regularizer chosen for the recovery of normal stress distributions is of the functional form of Shannon entropy. Formulation of the inverse problem so as to regularize the solutions result in a variational principles which must be solved in order to recover the surface stress. An analog neural network which provides the desired solutions to the variational principle as a course of natural time evolution of the circuit dynamics is proposed as a solution to the requirements for fast, local processing in tactile sensing. We discuss performance of the network in the presence of noise based upon computer simulations. We also demonstrate, by means of a breadboard prototype of the network, the speed of computation achievable by such a network. An integrated circuit implementation of the proposed network has been completed and the requirements of such implementations is discussed.Item Studies in Robust Stability(1989) Saydy, L.; Abed, E.; Tits, A.; ISRIn this thesis, questions in the analysis and synthesis of stability robustness properties for linear and nonlinear control systems are considered. The first part of this work is devoted to linear systems., where the emphasis is on obtaining necessary and sufficient conditions for stability of parametrized families of systems. This class of robustness problems has recently received significant attention in the literature [1]. In the second part of the thesis, questions of stabilization of nonlinear systems by feedback are considered. Part I of this work addresses the generalized stability, i.e. stability with respect to a given domain in the complex plane, of parametrized families of linear time-invariant systems. The main contribution is the introduction and application of the new concepts of "guarding map" and "semiguarding map" for a given domain. Basically, these concepts allow one to replace the original parametrized system stability problem with a finite number of stability tests. Moreover, the tool is very powerful in that it allows the treatment of a large class of domains in the complex plane. The parametrized stability problem is completely solved for the case stability of a one- parameter family with respect to guarded and semiguarded domains. The primary interest in semiguarded domains arises in a process of reduction of a given multiparameter problem to one involving fewer parameters. For the two-parameter case, we consider stability of families of matrices relative to domains with a polynomial guarding map. The first step replaces the two- parameter problem by a one-parameter stability problem relative to a new domain. The second step employs a polynomial semiguarding map for the new domain to obtain necessary and sufficient conditions for stability of the new problem. The case of three or more parameters, which involves technical questions not encountered in the one- or two-parameter case, is also considered. In Part II, a class of nonlinear control systems for which the linear part satisfies special stabilizability conditions is considered. These conditions naturally give rise to certain nonstandard algebraic issues in linear systems. Sufficient conditions for the existence of a linear feedback control which stabilizes a given nonlinear control system within a prescribed ball of given radius (possibly infinite) are given. The feedback control is found to be robust in a certain sense against a class of modeling errors. A complete design methodology is obtained for planar systems and extended to a class of higher dimensional singularly perturbed nonlinear control systems. For these systems, nonlinear feedback laws achieving stabilization within prescribed cylindrical regions are presented.Item Visual Tracking Strategies(1988) Tsakiris, D.P.; Krishnaprasad, P.S.; ISRVisual tracking is one of the most important applications of Computer Vision and several tracking systems have been developed, which, either focus mainly on the tracking of targets moving on a plane or attempt to reduce the 3-dimensional tracking problem to the tracking of a set of characteristic points of the target. These approaches are seriously handicapped in complex visual situations from segmentation and point correspondence problems. A mathematical theory for visual tracking of a three-dimensional target moving rigidly in 3-D is presented here and it is shown how a monocular observer can track an initially foveated object and keep it stationary in the center of his visual field. Our attempt is to develop correspondence-free tracking schemes and take advantage of the dynamic segmentation capabilities inherent in the optical flow formalism. Moreover, a general tracking criterion, the Tracking Constraint is derived, which reduces tracking to an appropriate optimization problem. The connection of our tracking strategies with the Active Vision Paradigm is shown to provide a solution to the Egomotion problem. In the first part of this work, tracking strategies based on the assumption that we know the optical flow field are examined and tracking is formulated as a constrained optimization and a penalized least-squares problem. In the second part, tracking strategies based on the recovery of the 3-D motion of the target are devised under the assumption that we know the shape of the target. A correspondence-free scheme is derived, which depends on global information about the scene (provided from linear features of the image) in order to bypass the ill-posed problem of computing the spatial derivatives of the image intensity function and amounts to the solution of a linear system of equations in order to estimate the 3-D motion of the target. An important feature of these tracking strategies is that they do not require continuous segmentation of the image in order to locate the target. Supposing that the target is sufficiently textured, dynamic segmentation using temporal derivatives of the linear features provides sufficient information for the tracking phase. Therefore, this approach is expected to perform best when previous ones perform worst, namely in a complex visual environment. Experimental results of the algorithms presented here demonstrate their robustness in the presence of noise.Item Coupler-Point Curve Synthesis Using Homotopy Methods(1988) Lu, Jeong-Jang; Tsai, L.-W.; ISRA new numerical method called "Homotopy" method (Continuation method) is applied to the problem of four-bar coupler-point-curve synthesis. We have shown that, for five precision points, the link lengths of a four-bar linkage can be found by the "General Homotopy" method. For nine precision points, the "Cheater's Homotopy" can be applied to find some four-bar linkages that will guide a coupler point through the nine prescribed positions. The nine-coupler points synthesis problem is highly non-linear and highly singular. We have also shown that Newton-Raphson's method and Powell's method, in general, tend to converge to the singular condition or do not converge at all, while the cheater's homotopy always works. The powerfulness of Cheater's homotopy opens a new frontier for dimensional synthesis of mechanisms.Item Modeling and Control of Mixed and Flexible Structures(1988) Posbergh, T.A.; Krishanprasad, P.S.; ISRThe design of control systems for flexible spacecraft continues to be an important problem in current and future space missions. Crucial to successful controller design is accurate modeling of the underlying distributed parameter system. Current techniques frequently fail to capture the nonlinear feature of the dynamic behavior of flexible spacecraft. From a practical point of view a closely related issue is the fidelity of approximations in preserving the essential characteristics of the underlying distributed parameter system. This dissertation is concerned with distributed parameter models and rigorous approximations of the same as the basis for control system analysis and design. Specifically, we examine the generic case of a rigid spacecraft to which a flexible appendage is attached. The flexible appendage is modeled using geometrically exact rod theory. Equilibria for stationary and rotating configurations are computed and used as the basis of a subsequent linearization which preserves the Hamiltonian structure of the underlying system. These linearized models are the basis of the construction of the corresponding transfer functions. The associated transfer functions relate tip position and acceleration of the appendage to rigid body torques. In addition, stability of these equilibria is investigated using the Energy-Casimir method. Using the transfer functions of the linearized model, modern frequency domain methods can be employed to do compensator design. In addition, we show that a rigid n- body chain is a natural approximation to a limiting case of the geometrically exact beam. Such an approximation provides the basis for finite dimensional compensator design for our infinite dimensional system. The design, implementation, and actual performance of such a compensator for an existing laboratory test fixture is discussed.Item Tactile Perception for Multifingered Hands(1987) Yang, R.; Krishnaprasad, P.S.; ISRRecently, tactile sensors mounted on robot fingers have been identified as essential sensory devices for the control of multifingered robotic hands. A basic tactile sensing task is to determine the force distribution on the contact area between the fingers and grasped object. To increase the grasp stability and to protect the fragile sensors, a kind of elastic material is required to cover the tactile sensors. This thesis derives the relationship between the surface force profile and the stress or strain profile measured by tactile sensors beneath the contract surface for simplified situations. This relationship can be described by integral equations of convolution type, or more generally, integral equations of the first kind with two unknown functions. The algorithms for numerical inversion in real time, an analog network for solving the regularization problem is discussed. Finally, as an application of the tactile sensors, the equilibrium condition for stable grasping by a two-fingered robotic hand is derived.Item Object-Oriented Manipulator Design Exerciser(1987) Chen, Xin; Krishnaprasad, P.S.; ISRAbstract's technical formulas were not compatible with the database used to create this booklet. To obtain a copy, please contact Maggie Virkus at (301) 454-6167, maggie@ra.src.umd.edu or write at to the Center's address listed in the front of this booklet.