Vision-assisted control for manipulation using virtual fixtures

We present the design and implementation of a vision-based system for cooperative manipulation at millimeter to micrometer scales. The system is based on an admittance control algorithm that implements a broad class of guidance modes called virtual fixtures. A virtual fixture, like a real fixture, limits the motion of a tool to a prescribed class or range of motions. We describe how both hard (unyielding) and soft (yielding) virtual fixtures can be implemented in this control framework. We then detail the construction of virtual fixtures for point positioning and curve following as well as extensions of these to tubes, cones, and sequences thereof. We also describe an implemented system using the JHU Steady Hand Robot. The system uses computer vision as a sensor for providing a reference trajectory, and the virtual fixture control algorithm then provides haptic feedback to implemented direct, shared manipulation. We provide extensive experimental results detailing both system performance and the effects of virtual fixtures on human speed and accuracy.     

Symbolic analysis and design of control systems using Mathematica

Contemporary computer tools can generate a tremendous amount of numerical data so the user might easily lose insight into the phenomenon being investigated. Those who use powerful computer algebra systems must thoroughly understand the assumptions that underlie the software. In this paper, the role and importance of symbolic computation in control engineering and signal processing is exemplified. Real-life application examples are presented in which systems are symbolically solved and simulated with Mathematica. We introduce an original approach to algorithm development, system design and symbolic processing that successfully overcomes some problems encountered in the traditional approach. Benefits of symbolic methods and the role of computer algebra systems are highlighted from the viewpoint of both academia and industry.     

Symbolic pattern manipulation of Karnaugh-Veitch maps for pneumatic circuits

Pneumatics continue to play a vital role in low-cost automation. The designing of pneumatic control circuits has to date been a slow manual process. This paper describes the computational symbolic manipulation of the Karnaugh-Veitch (KV) map which is the heart of the prototype expert system called PNEUMAES. The symbolic manipulation of a KV map is governed by two sets of generic rules for signal flow plotting and for logic equation minimisation applicable for complex pneumatic circuits. As the complexity of the circuit increases, the symbolic manipulation of a KV map leads to the combinatorial explosion problem. Because of this problem, PNEUMAES can only automatically generate pure pneumatic circuit design equations which will yield minimised circuit configuration for up to four cylinders with auxiliary control valves. A case study is included and issues and problems relating to the implementation of the KV map are discussed. Symbolic and sub-symbolic learning approaches are suggested as a means by which the search space of the symbolic patterns of the KV map can be pruned.     

Knowledge engineering and CAD

The technology of Computer Aided Design (CAD) has rapidly been changing the processes of machine design, especially in detail and production design. Conventional CAD systems are necessary in production design where precise geometrical data are indispensable, but we can point out some problems of those systems from a point of view of the total machine design process. Though the main aim of introducing CAD systems is to increase designers' creativities, it is doubtful whether designers are really supported by such CAD systems. We think that knowledge engineering is useful to improve such situations. In this paper, we discuss these problems and we study the feasibilities of future CAD systems that can really help designers very intelligently and efficiently. We also show some results of our experimental systems applying knowledge engineering.     

Symbolic approximate time-optimal control

There is an increasing demand for controller design techniques capable of addressing the complex requirements of today’s embedded applications. This demand has sparked the interest in symbolic control where lower complexity models of control systems are used to cater for complex specifications given by temporal logics, regular languages, or automata. These specification mechanisms can be regarded as qualitative since they divide the trajectories of the plant into bad trajectories (those that need to be avoided) and good trajectories. However, many applications require also the optimization of quantitative measures of the trajectories retained by the controller, as specified by a cost or utility function. As a first step towards the synthesis of controllers reconciling both qualitative and quantitative specifications, we investigate in this paper the use of symbolic models for time-optimal controller synthesis. We consider systems related by approximate (alternating) simulation relations and show how such relations enable the transfer of time-optimality information between the systems. We then use this insight to synthesize approximately time-optimal controllers for a control system by working with a lower complexity symbolic model. The resulting approximately time-optimal controllers are equipped with upper and lower bounds for the time to reach a target, describing the quality of the controller. The results described in this paper were implemented in the Matlab Toolbox Pessoa (Mazo et al., 2009 [12]) which we used to workout several illustrative examples reported in this paper.     

Symbolic manipulation techniques for low order LFT-based parametric uncertainty modelling

Symbolic techniques are very useful in obtaining low order LFT-representations of linear parametric models. The main role of symbolic manipulations is to find, via suitable pre-processing steps, equivalent representations of rationally dependent parametric matrices, which automatically lead to lower order LFT-representations. In this paper we give an overview of symbolic processing methods and we propose some new techniques and several enhancements of existing methods. All proposed methods are implemented in the latest version of the LFR-toolbox and served to illustrate the strengths of symbolic processing in obtaining low order LFT-representations of two challenging parametric model examples.     

Symbolic model checking composite Web services using operational and control behaviors

This paper addresses the issue of verifying if composite Web services design meets some desirable properties in terms of deadlock freedom, safety (something bad never happens), and reachability (something good will eventually happen). Composite Web services are modeled based on a separation of concerns between business and control aspects of Web services. This separation is achieved through the design of an operational behavior, which defines the composition functioning according to the Web services’ business logic, and a control behavior, which identifies the valid sequences of actions that the operational behavior should follow. These two behaviors are formally defined using automata-based techniques. The proposed approach is model checking-based where the operational behavior is the model to be checked against properties defined in the control behavior. The paper proves that the proposed technique allows checking the soundness and completeness of the design model with respect to the operational and control behaviors. Moreover, automatic translation procedures from the design models to the NuSMV model checker’s code and a verification tool are reported in the paper.     

CAD tools for aesthetic engineering

The role of computers and of computer-aided design tools for the creation of geometrical shapes that will be judged primarily by aesthetic considerations is reviewed. Examples are the procedural generation of abstract geometrical sculpture or the shape optimization of constrained curves and surfaces with some global ‘cost’ functional. Different possibilities for such ‘beauty functionals’ are discussed. Moreover, rapid prototyping tools based on layered manufacturing now add a new dimension to the visualization of emerging designs. Finally, true interactivity of the CAD tools allows a more effective exploration of larger parts of the design space and can thereby result in an actual amplification of the creative process.     

Cooperative object manipulation with contact impact using multiple impedance control

Impedance Control imposes a desired behavior on a single manipulator interacting with its environment. The Multiple Impedance Control (MIC) enforces a designated impedance on both a manipulated object, and all cooperating manipulators. Similar to the standard impedance control, one of the benefits of this algorithm is the ability to perform both free motions and contact tasks without switching control modes. At the same time, the potentially large object inertia and other forces are taken into account. In this paper, the general formulation for the MIC algorithm is developed for distinct cooperating manipulators, and important issues are detailed. Using a benchmark system, the response of the MIC algorithm is compared to that of the Object Impedance Control (OIC). It is shown that in the presence of flexibility, the MIC algorithm results in an improved performance. Next, a system of two cooperating two-link manipulators is simulated, in which a Remote Centre Compliance is attached to the second end-effector. As simulation results show, the response of the MIC algorithm is smooth, even in the presence of an impact due to collision with an obstacle. It is revealed by both error analysis and simulation that under the MIC law, all participating manipulators, and the manipulated object exhibit the same designated impedance behavior. This guarantees good tracking of manipulators and the object based on the chosen impedance laws which describe desired error dynamics, in performing a manipulation task.     

Symbolic models for control systems

In this paper we provide a bridge between the infinite state models used in control theory to describe the evolution of continuous physical processes and the finite state models used in computer science to describe software. We identify classes of control systems for which it is possible to construct equivalent (bisimilar) finite state models. These constructions are based on finite, but otherwise arbitrary, partitions of the set of inputs or outputs of a control system.     

An algebraic treatment of quantum vibrations using REDUCE

Many eigenvalue problems that arise in mathematical physics and chemistry can be solved using the algebra of non-commuting operators. REDUCE can readily be used to perform the many time consuming algebraic manipulations necessary to find the solutions to these problems. Applications of REDUCE are given to the quantum mechanical one and two dimensional nearly harmonic oscillator using an algebraic approach.     

Solving large systems of polynomial equations using REDUCE

Difficulties arising when numerically solving large systems of polynomial equations are discussed. Such systems determine the input data for the inverse task for the two-dimensional Schroedinger equation.     

Vibration damping in manipulation of deformable linear objects using sliding mode control

In this paper, we proposed a position-based control strategy for eliminating the vibration at the end of deformable linear objects (DLOs) during its manipulation. Using Schur decomposition of matrices and linear transform of variables, actuated and underactuated parts of the DLO dynamic model are separated. Based on the decoupled dynamic model of a DLO system, a sliding mode control with exponential approach law is designed to force the state variables to converge to an equilibrium and to allow vibration at the end of the DLO to be damped quickly. The DLO system, subjected to control input saturation, is further studied to solve the input saturation problem. An adaptive sliding mode control law is designed to suppress the damping at the end of the DLO. Proposed control strategies are verified by numerical simulations. The simulation results show that proposed methods can effectively damp the vibration at the end of the DLO.     

In-hand recognition and manipulation of elastic objects using a servo-tactile control strategy

Grasping and manipulating objects with robotic hands depend largely on the features of the object to be used. Especially, features such as softness and deformability are crucial to take into account during the manipulation tasks. Indeed, positions of the fingers and forces to be applied by the robot hand when manipulating an object must be adapted to the caused deformation. For unknown objects, a previous recognition stage is usually needed to get the features of the object, and the manipulation strategies must be adapted depending on that recognition stage. To obtain a precise control in the manipulation task, a complex object model is usually needed and performed, for example using the Finite Element Method. However, these models require a complete discretization of the object and they are time-consuming for the performance of the manipulation tasks. For that reason, in this paper a new control strategy, based on a minimal spring model of the objects, is presented and used for the control of the robot hand. This paper also presents an adaptable tactile-servo control scheme that can be used in in-hand manipulation tasks of deformable objects. Tactile control is based on achieving and maintaining a force value at the contact points which changes according to the object softness, a feature estimated in an initial recognition stage.     

Symbolic integration using homotopy methods

The homotopy algorithm is a powerful method for indefinite integration of total derivatives. By combining these ideas with straightforward Gaussian elimination, we construct an algorithm for the optimal symbolic integration that contain terms that are not total derivatives. The optimization consists of minimizing the number of terms that remain unintegrated. Further, the algorithm imposes an ordering of terms so that the differential order of these remaining terms is minimal. A different method for the summation of difference expressions is presented in Appendix B.     

Developments of CAD in civil engineering reviewed

Substantial progress has been made during the past decade in making the computer an effective analytical tool for the design engineer. However more recent development has concentrated on various features of a design offices final product. These areas comprise production of construction drawings, interactive graphics, colour graphics, pre-and post-processing of input and output data, linking analysis programs to modular design programs to provide a rapid transfer of design to the latest code requirement, use of microcomputers and personal computers. There is also significant software development for site management, cost analysis, general administration and documentation related to construction. This takes advantage of the availability of cheaper hardware which can communicate with other computers elsewhere in a network. User interaction facilities are being built into programs which allow the engineer to concentrate on design decisions. This paper reviews the developments during the last two-three years in CAD in Civil Engineering.