Lars Nielsen

Controllability issues of robots in singular configurations

Examples are given that modify some oversimplified statements usually made about the motion of robots in singular configurations. A robot may be controlled in an arbitrary direction from a singular configuration if the velocity profiles are shaped in a proper way. The observations on possible motions open a number of questions, since a wider class of motions is possible that at first sight. Hence, the results are of relevance to path programming, to path following, and to controller design.<<ETX>>

A simple neuron servo

A simple servo controller built from components having neuronlike features is described. This VLSI servo controller uses pulses for control and is orders of magnitude smaller than a conventional system. The basic circuit elements are described. A key element is a component and neuronlike capability that takes voltages as inputs and generates a pulse train as the output. It is shown how the circuits are combined to a proportional and derivative controller. The advantages of using a pulsed output representation to improve slow-speed operation of a friction-limited system is demonstrated. The utility of exploiting parallelism, aggregation, and redundancy to improve system-level performance given imprecise low-level components is discussed. Experimental results illustrate the properties of the system compared with conventional controllers.

Projective area-invariants as an extension of the cross-ratio

Projective invariants provide a framework for computer vision where the image of an object is described by its intrinsic properties, independently of the particular view. It is advantageous if these intrinsic properties are defined in terms of computationally simple features. An area-measurement provides a good candidate that is easy to reliably compute from a particular image of the object. The main contributions of this paper are the definition and justification of area-invariants in projective geometry and the indication of its relevance in image analysis. A framework that covers one-dimensional intervals and two-dimensional figures has been developed. In the linear case, the invariants are linear only in two cases. The first case is the well known cross-ratio, and the second case is called the polar case. The generalization to the plane can be done in different directions. One can use either points (on the line or in the plane) or the geometric figures (intervals, triangles, circles) as the basic entities involved. The first view was adopted already by Mobius, who generalized the cross-ratio in various directions. The second view used here leads to another generalization of the cross-ratio, where the invariants are relations between the areas of a class of geometric figures, related to each other in a certain manner. Remarkably enough, these invariants turn out to be linear if the figures involved are related in a pole/ polar configuration

A neuron-based pulse servo for motion control

A design frame and a set of circuit elements with which generic motor controllers can be implemented are described. A simple proportional-derivative motor controller was embedded in the design frame. Its performance advantages over a more traditional controller are described. Also discussed are the merits of biologically inspired systems used in applications related to robotics.<<ETX>>

Optimal digitization of 2-d images

The problem of representing an image by M × N samples with b bits/sample, subject to the constraint of a fixed total number of bits, is discussed. Reasonable assumptions are made in such a way that the optimization problem has a closed form solution. The solution is tested experimentally and agrees well with human perception of visual quality. The analytical solution brings out the dependence of the optimal digitization on image characteristics very clearly. The results explain and agree with results of other subjective tests.

An architecture for application oriented robot programming

Application-oriented programming of industrial robots is considered. The authors formulate the problems and suggest one approach towards a solution. The problem is motivated by some typical examples that are outlined. These examples show some requirements from different applications. Even a very mature application like spot welding needs special care to obtain best possible performance in the short moves between spots. In more complicated sensor-based applications the need is even greater. An architecture called the open robot control (ORC) architecture is proposed for this type of application-oriented programming. Solutions to the examples using ORC are discussed. A brief discussion of related works is given. Some implementation aspects are presented.<<ETX>>

Discontinuity preserving visual reconstruction by means of potential theory

Discontinuity preserving interpolation methods are often desirable in image reconstruction from sparse visual data. Two such schemes are constructed by interpreting the image as the potentialcause by some distribution of charges, and then detecting certain patterns (notably dipole curves) among the charges. Experiments have been performed on an ink-jet plotter, showing good performance.