Pavel Krsek

The Trimmed Iterative Closest Point algorithm

The problem of geometric alignment of two roughly preregistered, partially overlapping, rigid, noisy 3D point sets is considered. A new natural and simple, robustified extension of the popular Iterative Closest Point (ICP) algorithm (Besl and McKay, 1992) is presented, called the Trimmed ICP (TrICP). The new algorithm is based on the consistent use of the least trimmed squares (LTS) approach in all phases of the operation. Convergence is proved and an efficient implementation is discussed. TrICP is fast, applicable to overlaps under 50%, robust to erroneous measurements and shape defects, and has easy-to-set parameters. ICP is a special case of TrICP when the overlap parameter is 100%. Results of testing the new algorithm are shown.

Robust Euclidean alignment of 3D point sets: The trimmed iterative closest point algorithm

Abstract The problem of geometric alignment of two roughly pre-registered, partially overlapping, rigid, noisy 3D point sets is considered. A new natural and simple, robustified extension of the popular Iterative Closest Point (ICP) algorithm [IEEE Trans. Pattern Anal. Machine Intell. 14 (1992) 239] is presented, called Trimmed ICP (TrICP). The new algorithm is based on the consistent use of the Least Trimmed Squares approach in all phases of the operation. Convergence is proved and an efficient implementation is discussed. TrICP is fast, applicable to overlaps under 50%, robust to erroneous and incomplete measurements, and has easy-to-set parameters. ICP is a special case of TrICP when the overlap parameter is 100%. Results of a performance evaluation study on the SQUID database of 1100 shapes are presented. The tests compare TrICP and the Iterative Closest Reciprocal Point algorithm [Fifth International Conference on Computer Vision, 1995].

Differential invariants as the base of triangulated surface registration

The paper addresses the problem of 3D model reconstruction from overlapping triangulated range images. A technique for automatic matching of curved freeform surfaces exploiting curvilinear differential structures of the surfaces is presented. We propose a hybrid registration algorithm that combines advantages of working with small amounts of interest points (to attain computational speed), estimates the Euclidean transform matching both surfaces, and uses all available points and the iterative closest reciprocal point algorithm to refine the estimate and finally match surfaces (to attain high precision, good initial estimation avoids local minima). The method works in a bottom-up manner using the hierarchy: points → differential structures (i.e., curvilinear line segments) → surface. The registration is automatic. The only parameter set by the user is the required level of mean curvature. The approach is demonstrated through examples.

Garment perception and its folding using a dual-arm robot

The work addresses the problem of clothing perception and manipulation by a two armed industrial robot aiming at a real-time automated folding of a piece of garment spread out on a flat surface. A complete solution combining vision sensing, garment segmentation and understanding, planning of the manipulation and its real execution on a robot is proposed. A new polygonal model of a garment is introduced. Fitting the model into a segmented garment contour is used to detect garment landmark points. It is shown how folded variants of the unfolded model can be derived automatically. Universality and usefulness of the model is demonstrated by its favorable performance within the whole folding procedure which is applicable to a variety of garments categories (towel, pants, shirt, etc.) and evaluated experimentally using the two armed robot. The principal novelty with respect to the state of the art is in the new garment polygonal model and its manipulation planning algorithm which leads to the speed up by two orders of magnitude.

Robotic Garment Folding: Precision Improvement and Workspace Enlargement

The trajectory performed by a dual-arm robot while folding a piece of garment was studied. The garment folding was improved by adopting here proposed novel circular folding trajectory, which takes the flexibility of the garment into account. The benefit lies in an increased folding precision. In addition, several relaxations of the folding trajectory were introduced, thus enlarging the working space of the dual-arm robot.

Physics-based model of a rectangular garment for robotic folding

The ability to perform an accurate robotic fold is essential to obtain the properly folded garment. Available solutions rely on a rough folding surface or on a comprehensive simulation, both preventing the garment from slipping on the table during folding. This paper proposes a new algorithm for a folding path design respecting the garment material properties and preventing the garment slipping. The folding path is derived based on the equilibrium of forces under the simplifying assumptions of a rectangular and homogeneous garment. This approach allows folding the rectangular garment on a low friction table surface as we demonstrated in the experiments performed by a dual-arm robotic testbed.

Accuracy of Robotic Elastic Object Manipulation as a Function of Material Properties

We deal with the problem of thin stringi¾?1D or platei¾?2D elastic material folding and its modeling. The examples could be metallic wire, metal, kevlar or rubber sheet, fabric, or as in our case, garment. The simplest scenario attempts to fold rectangular sheet in the middle. The quality of the fold is measured by relative displacement of the sheet edges. We use this scenario to analyse the effect of the inaccurate estimation of the material properties on the fold quality. The same method can be used for accurate placing of the elastic sheet in applications, e.g. the industrial production assembly. In our previous work, we designed a model simulating the behavior of homogeneous rectangular garment during a relatively slow folding by a dual-arm robot. The physics based model consists of a set of differential equations derived from the static forces equilibrium. Each folding phase is specified by a set of boundary conditions. The simulation of the garment behavior is computed by solving the boundary value problem. We have shown that the model depends on a single material parameter, which is a weight to stiffness ratio. For a known weight to stiffness ratio, the model is solved numerically to obtain the folding trajectory executed by the robotic arms later. The weight to stiffness ratio can be estimated in the course of folding or manually in advance. The goal of this contribution is to analyse the effect of the ratio inaccurate estimation on the resulting fold. The analysis is performed by simulation and in a real robotic garment folding using the CloPeMa dual-arm robotic testbed. In addition, we consider a situation, in which the weight to stiffness ratio cannot be measured exactly but the range of the ratio values is known. We demonstrate that the fixed value of the ratio produces acceptable fold quality for a reasonable range of the ratio values. We show that only four weight to stiffness ratio values can be used to fold all typical fabrics varying from a soft e.g. sateen to a stiff e.g. denim material with the reasonable accuracy. Experiments show that for a given range of the weight to stiffness ratio one has to choose the value on the pliable end of the range to achieve acceptable results.

Single arm robotic garment folding path generation

Abstract We address the accurate single arm robotic garment folding. The folding capability is influenced mostly by the folding path which is performed by the robotic arm. This paper presents a new method for the folding path generation based on the static equilibrium of forces. The existing approach based on a similar principle confirmed to be accurate for one-dimensional strips only. We generalize the method to two-dimensional shapes by modeling the garment as an elastic shell. The path generated by our method prevents the garment from slipping while folding on a low friction surface. We demonstrate the accuracy of this approach by comparing our paths (a) with the existing method when one-dimensional strips of different materials were modeled, and (b) experimentally with real robotic folding. Graphical Abstract The paper proposes a robotic garment folding path generation procedure. It uses the garment model represented by a thin shell. The path computation seeks states satisfying a static equilibrium condition.