Given two ascending lists xs and ys of combined length greater than n, consider the computation of

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The standard function merge merges two ascending sequences and (!!) denotes list indexing. With a lazy evaluator the computation takes O(n) steps; with an eager one it takes O(p+q) steps, where p=length xs and q=length ys. Now in functional programming it is more efficient to index a tree than a list, so the question arises: can we find a faster solution if xs and ys are each represented by a tree? Somewhat surprisingly the answer is yes: if xs and ys are each represented by balanced binary search trees, then the computation can be reduced to O(log p+log q) steps. This is despite the fact that there is no known method for merging two binary search trees in better than linear time. The details, presented below, depend on a subtle relationship between merging and indexing.

This paper addresses the tracking control problem of roboticmanipulators with unknown and changing dynamics. In this study, nonlineardynamics of the robotic manipulator is assumed to be unknown and a controlscheme is developed to adaptively estimate the unknown manipulator dynamicsutilizing generic artificial neural network models to approximate the underlyingdynamics. Based on the error dynamics of the controller, a parameter updateequation is derived for the adaptive ANN models and local stability propertiesof the controller are discussed. The proposed scheme is simulated andsuccessfully tested for trajectory following tasks. The controller alsodemonstrates remarkable performance in adaptation to changes in manipulatordynamics.

This paper presents a novel approach for seam tracking usingultrasonics. An ultrasonic seam tracking system has been developed for roboticwelding which tracks a seam that curves freely on a two-dimensional surface. Theseam is detected by scanning the area ahead of the torch and monitoring theamplitude of the waves received after reflection from the workpiece surface.Scanning is accomplished by using two ultrasonic sensors (a transmitter and areceiver) mounted on a stepper motor such that the transmitter angle is the sameas the receiver angle. The motor is mounted on the end-effector just ahead ofthe welding torch and covers a ninety degree arc in front of the torch. If thereis no seam then the receiver receives most of the transmitted waves afterreflection, but if there is a seam then most of the transmitted waves aredispersed in directions other than that of the receiver. The system has beentested and is very robust in the harsh environments generated by the arc weldingprocess. The robustness of the system stems from using various schemes such astime windowing, a waveguide, air and metal shields, and an intelligent sensormanager. This ultrasonic system offers some distinct advantages over traditionalsystems using vision and other sensing techniques. It can be used to weld veryshiny surfaces, and is a very economical method in terms of cost as well ascomputational intensity. The system can be used to detect seams less than 0.5 mmwide and 0.5 mm deep.

A link position tracking controller is formulated for an n-link, rigid,revolute, serially-connected robot. The controller generates torque commands tothe individual robot links based on adaptive estimates of the system parametersand measurements of only link positions. A filtering technique, based on thelink position signal, is used to alleviate the need for velocity measurements. Acomplete development of the controller is presented along with a proof ofsemiglobal asymptotic link position-velocity tracking performance. Experimentalvalidation of the proposed controller on the Integrated Motion Inc. (IMI)two-link direct drive robot is also presented. Several extensions to the basiccontroller are described that consider the use of fixed parameterestimates.

We derive a simple abstract machine for lazy evaluation of the lambda calculus, starting from Launchbury's natural semantics. Lazy evaluation here means non-strict evaluation with sharing of argument evaluation, i.e. call-by-need. The machine we derive is a lazy version of Krivine's abstract machine, which was originally designed for call-by-name evaluation. We extend it with datatype constructors and base values, so the final machine implements all dynamic aspects of a lazy functional language.

This paper identifies the need for a new range of end effectors suitablefor non-rigid products and introduces a novel non-contact gripping device. Theend effector operates on the principle of generating a high-speed flow betweenthe end effector and product surface thereby creating a vacuum which levitatesthe product. The lifting forces and conditions are theoretically discussed. Theexperimental results are presented using the end effector that has been operatedto lift non-rigid food materials such as jelly blocks.

In this paper we develop a sound and complete type and behaviour inference algorithm for a fragment of CML (Standard ML with primitives for concurrency). Behaviours resemble terms of a process algebra and yield a concise representation of the communications taking place during execution; types are mostly as usual except that function ypes and ‘delayed communication types’ are labelled by behaviours expressing the communications that will take place if the function is applied or the delayed action is activated. The development of the present paper improves a previously published algorithm in achieving completeness as well as soundness; this is due to an alternative strategy for generalising over types and behaviours.

The UK Magnetics Society's one-day seminar Advances inInstrumentation for Magnetics Measurements was held at the University ofWales Cardiff on 10 July 1996. Ten presentations were made during the eventwhich was attended by over 65 participants.

A special issue of the Journal of Functional Programming will be devoted to functional programming and computational complexity. The submission deadline is 1st November 1997.

A path planning method is presented based on non-autonomous dynamicmodeling of open-loops in articulated systems. It is assumed that one part ofthe mechanical system is submitted to specified motions laws, while movements ofthe complementary part are free. Thus, motion optimization is related to freejoint movements but it is achieved on the basis of the dynamic model of thewhole mechanical system. This approach introduces a non-autonomous stateequation of a special type in the sense that it can not only depend on therunning time but also on the unknown travelling time. The cost function to beminimized involves the travelling time and the actuating inputs. Optimization isachieved by applying the Pontryagin Maximum Principle which yields a newoptimality condition concerning the travelling time dependency of the statedproblem. Two simulation examples are presented. The first one shows how thedeveloped technique makes possible both the reducing and mastering the dynamiccomplexity of a four degrees of freedom-vertical manipulator. Set at fourdegrees of freedom, the second one deals with a redundant planar manipulatorcharacterized by a mobile base that is submitted to a specified drivingmotion.

1. Robodogs

The American public has greeted the arrival of the Robodog with a great deal of enthusiasm, but not the animal rights lobby. The Robodog is, in fact, an ordinary police dog that has been equipped with the latest high tech systems, and is still under control of a human handler.

New methods have been developed to control a mechanism's realtimeCartesian motion along spatially complex curves such as Non-Uniform RationalB-splines (NURBS). The methods dynamically map the critical trajectoryparameters between parameter space, Cartesian space, and joint space. Trajectorymodels that relate Cartesian tool speeds and accelerations to joint speeds andaccelerations have been generalized so that they can be applied to most classesof robots and CNC mechanisms.

A simple and efficient predictor-correctormethod uses finite difference theory to predict the parametric changes requiredto generate the desired curvilinear distances along the trajectory, and thencorrect the erorrs arising from this prediction. Polynomial approximationmethods successfully approximate joint speeds and accelerations rather thanrequire a closed-form inverse Jacobian solution.

The numericalalgorithms prove to be time bounded (fixed number of computational steps), andthe generated trajectories are smooth and continuous. Both simulation andphysical experiments using an Open-Architecture Controller demonstrate thefeasibility and usefulness of the developed trajectory generation algorithms andmethods. The methods can be conducted at trajectory rates greater than 100 Hz,depending on mechanism complexity.

This paper presents the design and development of a laboratory facilityconstituting a constrained planar flexible manipulator system. The system isdesigned for experimental investigations within research programmes involvingflexible manipulator systems. An outline of a generic design procedure forflexible manipulator systems is given. The design criteria developed throughthis procedure account for the strength and stiffness of the manipulator and therequired transducers and instrumentation. These are considered in detail and thesystem designed accordingly. Finally, practical problems encountered arehighlighted and methods of dealing with such problems are presented anddiscussed.

Variable structure control is applied to an underactuated two andthree-link robot. Control laws are developed to invert the robot from itsstable, downward equilibrium position to an inverted position. This maneuver isaccomplished by pumping energy into the system with the variable structurecontroller. A linear balancing controller is activated once the robot nears theinverted position. Numerical simulations are presented for both the two andthree-link robot.

1. The International Federation of Robotics expects to have a presence on the World Wide Web by the time this issue of Robotica is published. The URL will be http://www.ifr.org. The IFR Web pages will include information about the Federation's activities as well as links to its member associations in Europe, Asia, North America and Australia.

Thirty-five years ago, thunks were used to simulate call-by-name under call-by-value in Algol 60. Twenty years ago, Plotkin presented continuation-based simulations of call-by-name under call-by-value and vice versa in the λ-calculus. We connect all three of these classical simulations by factorizing the continuation-based call-by-name simulation [Cscr]n with a thunk-based call-by-name simulation [Tscr] followed by the continuation-based call-by-value simulation [Cscr]v, extended to thunks.

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We show that [Tscr] actually satisfies all of Plotkin's correctness criteria for [Cscr]n (i.e. his Indifference, Simulation and Translation theorems). Furthermore, most of the correctness theorems for [Cscr]n can now be seen as simple corollaries of the corresponding theorems for [Cscr]v and [Tscr].

The conceptual basis of the UPIC system is described and discussed, in particular its relation to the work of its orginator, Iannis Xenakis, to the science of acoustics and to the development of an intuitive graphic imagery. A possible pedagogical approach to musical creation using the resources of the UPIC is developed, and the particular pedagogical ethos of the system is emphasised. There follows a detailed description of the practical arrangements for a number of different workshop situations using the UPIC system in which the author has participated, and an evaluation of the outcomes of using the system in this way.

Intersection types and bounded quantification are complementary extensions of a first-order programming language with subtyping. We define a typed λ-calculus combining these extensions, illustrate its unusual properties, and develop basic proof-theoretic and semantic results leading to algorithms for subtyping and typechecking.