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S. W. E. Earles

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10 papers
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10

IROS Conference 1996 Conference Paper

General plane curve matching under affine transformations

  • Yonggen Zhu
  • Lakmal D. Seneviratne
  • S. W. E. Earles

It is common to use an affine transformation to approximate in dealing with the matching of plane curves under a projective transformation. The plane curve itself can be used as an identity to solve the parameters of an affine transformation. The objective of this paper is to obtain a closed form solution of the parameters using low order derivatives of the plane curve. A unique solution to the parameters of an affine transformation with up to second order derivatives is presented using differential invariants as well as the available global information. The computational time on verification has been significantly reduced. In computer vision, derivatives are obtained by numerical means. Achieving accurate numerical derivatives is an important application issue. Smoothing with a Gaussian filter modified by a linear combination of Hermite polynomials, can preserve the accuracy of continuous polynomials with powers up to the same order as the Hermite polynomials. In the discrete space however, the introduction of Hermite polynomials leads to a choice of a large smoothing scale /spl sigma/ in order to reduce computational errors at the expense of a reduction of local controllability and over-smoothing of the curve. It is shown that using a /spl sigma/ proportional to the order of the derivatives is more reliable in applications.

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ICRA Conference 1995 Conference Paper

A New Structure of Invariant for 3D Point Sets from a Single View

  • Yonggen Zhu
  • Lakmal D. Seneviratne
  • S. W. E. Earles

The invariant used as an index has shown many advantages over the pose dependent methods in model-based object recognition. Although perspective and even weak perspective invariants do not exist for general three dimensional point sets from a single view, invariants do exist for structured three dimensional point sets. However, such invariants are not easy to derive. A new special structure for calculating invariants of three dimensional objects is presented. The 3D invariant structure proposed by Rothwell (1993) requires seven points that lie on the vertices of a six-sided polyhedron and is applicable to position free objects. In comparison, the proposed algorithm requires only six points on adjacent (virtual) planes that provides two sets of four coplanar points and does not require the position free condition. Hence it is applicable to a wider class of objects. The algorithm is demonstrated on images of real scenes.

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IROS Conference 1995 Conference Paper

Three dimensional object recognition using invariants

  • Yonggen Zhu
  • Lakmal D. Seneviratne
  • S. W. E. Earles

The invariant used as an index has shown many advantages over the pose dependent methods in model-based object recognition. Although perspective and even weak perspective invariants do not exist for general three dimensional point sets from a single view invariants do exist for structured three dimensional point sets. However, such invariants are not easy to derive. The 3D invariant structure proposed by Rothwell (1993) requires seven points that lie on the vertices of a six-sided polyhedron and is applicable to position free objects. A new special structure for calculating invariants of three dimensional objects is developed by the authors (1995). In comparison, the proposed algorithm requires only six points on adjacent (virtual) planes that provides two sets of four coplanar points and does not require the position free condition. Hence it is applicable to a wider class of objects This paper is the extension of previous work to discuss how to use the projection to the base plane to obtain invariant conditions for the more general situation. The algorithm is demonstrated on images of real scenes.

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IROS Conference 1993 Conference Paper

Combined adaptive control of constrained robot manipulators

  • H. Yu
  • Lakmal D. Seneviratne
  • S. W. E. Earles

Two reduced, unconstrained robot models, in which the constraints are satisfied automatically, are introduced. The force tracking error is dependent on both the position tracking error and the estimated parameter error, so that in the constrained adaptive robot manipulator control, the convergence of the estimated parameter error becomes more important than in the unconstrained adaptive robot control. However, in the direct adaptive controller, the parameter adaptation is only driven by the tracking error in the joint motion, while in indirect adaptive controller, the parameter estimation is only driven by the prediction error in the filtered joint torque. Based on this observation, a combined adaptive controller for constrained robot manipulators, with uncertain dynamic model parameters, is proposed. The combined adaptive control law, which is driven by both the tracking error and the prediction error, gives much improved stability properties for parameter estimation and force tracking.

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IROS Conference 1993 Conference Paper

Finding the 3D shortest path with visibility graph and minimum potential energy

  • Kaichun Jiang
  • Lakmal D. Seneviratne
  • S. W. E. Earles

Finding a three dimensional shortest path is of importance in the development of automatic path planning for mobile robots and robot manipulators, and for practical implementation, the algorithms need to be efficient. Presented is a method for shortest path planning in three-dimensional space in the presence of convex polyhedra. It is based on the visibility graph approach, extended from two to three-dimensional space. A collineation is introduced for the identification of visible edges in the three-dimensional visibility graph. The principle of minimum potential energy is adopted for finding a set of sub-shortest paths via different edge sequences, and from them the global shortest path is selected. The three dimensional visibility graph is constructed in O(n/sup 3/v/sup k/) time, where n is the number of vertices of the polyhedra, k is the number of obstacles and v is the largest number of vertices on any one obstacle. The process to determine the shortest path runs recursively in polynomial time. Results of a computer simulation are given, showing the versatility and efficiency of the approach.

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IROS Conference 1993 Conference Paper

Forward kinematic analysis for the general 4-6 Stewart platform

  • Q. Liao
  • Lakmal D. Seneviratne
  • S. W. E. Earles

Presented is the forward kinematic solution for the most general case of the 4-6 Stewart platform mechanism, in particular, the spherical joints of both the top and the base platforms are not restricted to be in a single plane. The problem is reduced to a 32nd order polynomial equation in a single unknown. This new theoretical analysis is numerically verified.

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IROS Conference 1993 Conference Paper

Space representation and map building-A triangulation model to path planning with obstacle avoidance

  • W. S. Ko
  • Lakmal D. Seneviratne
  • S. W. E. Earles

Presents a triangulation modelling algorithm for representing the working environment of a mobile robot such that planning a collision-free path on the corresponding constructed road map (a graph) is simplified. Both the nodes and the edges of the graph can be exactly calculated by expressions F/sub n/(V, B) and F/sub B/(V, B), where V and B represent the total numbers of vertices and obstacles respectively, and both F/sub n/(V, B) and F/sub e/(V, B) are of complexity O(V). The solution path planned on the resulting graph keeps the robot at some clearance from the obstacles.

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