Method for Automatically Generating Chain Stitches

This application is related to our copending contemporaneously filed United States patent application entitled "Method for Automatically Generating A Chenille Filled Embroidery Stitch Pattern" Ser. No. 08/323,157, the contents of which is specifically incorporated by reference herein in its entirety.

1. Field of the Invention

The present invention relates to methods for automatically generating filled embroidery patterns in a computer aided design system, and more particularly to an improved method for automatically generating chain stitches in a computer aided design system.

2. Description of the Prior Art

Computer aided design systems for controlling embroidery machines are well known in the art. Such systems allow the user to select embroidery patterns to be stitched either through a stored series of designs or creation of original designs, such as described in our copending United States patent application entitled "Method for Creating Self-Generating Embroidery Pattern" filed Oct. 4, 1993, and bearing U.S. Ser. No. 08/131142, U.S. Pat. No. 5,430,658 and our previously issued U.S. Pat. No. 5,343,401, entitled "Embroidery Design System". In such prior art systems, embroidery patterns may typically be generated in an outline form of a particular shape such as a letter or an animal, or may be filled in with stitches. It is also known in the art to be able to modify the embroidery design programs used in such computer aided design systems so that the user may independently vary and modify a large variety of characteristics of an existing embroidery design program including, such as described in our previously issued U.S. Pat. No. 5,270,939.

In addition, chenille type embroidery machines capable of providing chenille type stitching, which produces a towel like effect in the embroidery pattern, are also well known, such as disclosed, by way of example, in U.S. Pat. No. 5,056,444. A typical conventional chenille type embroidery machine is manufactured by Tajima Industries Ltd. of Japan. As noted in U.S. Pat. No. 5,056,444, which describes a prior art chenille type embroidery machine, chenille type embroidery machines provide a fuzzy appearance of a pattern, for example, such as on an athletic award or letter, with the fuzzy appearance being formed by the use of a hooked needle which, in combination with a looper, which wraps thread around the needle (as illustrated in FIGS. 1A-1E), pulls a thread through a piece of material. Such a stitch is known as a "moss" stitch and is performed by the looper looping thread over the hook of the needle below the material to be embroidered. The needle then pulls the looped thread through and above the material. Another device known as the X/Y drive then pulls the material away from the raised needle causing the looped thread to slip off the hook. The needle again penetrates the material and the process is repeated, resulting in a fuzzy patterned item.

By reversing the hook of the needle so that the looped thread remains on the hook after the X/Y movement of the material, a chain stitch can be formed. In such an instance, the X/Y drive pulls the material and the thread as in the above described prior art moss stitch procedure, but now the thread remains on the hook as the needle repenetrates the material and a linked chain stitch is formed, such as illustrated in FIGS. 2A-2E. Chain stitching is generally used to follow the perimeter of a shape. Chenille stitching may be used to create a cross hatch or lattice chenille, such as illustrated in FIG. 3, or a spiral type chenille. In a lattice chenille, the pattern that is created by the loop stitch in order to fill a shape, with the stitching starting at one point in the shape and moving in straight lines diagonally covering the area, whereas in a spiral type chenille, in order to fill the shape the stitching is performed in a spiral fashion causing the embroidery machine to place stitches at many varying angles to provide a random/hand-done appearance.

Chenille stitching in the past was generally performed by hand which is a very tedious, time consuming task, and did not utilize the advantages of a computer aided design system which could allow the operator to make decisions on how the coverage would take place. Prior to applicants' invention, spiral coverage for chenille stitches was not automatically generated, but, rather, was accomplished either by hand or manually entered in the computer. Moreover, where the pattern was a complex polygon, there were difficulties in the prior art in trying to place chain stitching around a complex polygon. Thus, applicants are not aware of any efficient prior art computer aided design systems for generating filled embroidery patterns which enable chenille filled embroidery patterns, or chain stitches, to be automatically generated and this is so despite the wide spread use of computer aided design systems for controlling embroidery machines.

In a method for automatically generating chain stitched stitch patterns in a computer aided design system capable of generating stitch patterns, the improvement comprises automatically generating a chain stitched stitch pattern by selecting an associated polygon type shape, determining a medial axis for that shape, constructing a plurality of concentric polygon shapes extending from the medial axis to the outer edge of the selected polygon shape, sorting the constructed concentric polygon shapes for proper sequencing and minimal jumping of the selected pattern from one part to another, and placing the chain stitches on the perimeter of the concentric polygons. Chain stitching is provided around the selected polygon shape for covering a filled embroidery pattern with chain stitches, with the chain stitches being placed on the perimeter of the constructed concentric polygon shapes at a predetermined length. The improved method of automatically generating chain stitches may be used to completely fill the selected polygon shape.

FIGS. 1A-1E are diagrammatic illustrations of a typical prior art method of providing a chenille stitch with a loop or moss stitch;

FIGS. 2A-2E are diagrammatic illustrations of a typical prior art method of providing a chain stitch;

FIG. 3 is a diagrammatic illustration of a typical cross hatch or lattice chenille;

FIGS. 4a and 4b are diagrammatic illustrations of a computer generated spiral type chenille;

FIG. 5 is a diagrammatic illustration of a design made entirely by placing chain stitches to cover the area in accordance with the preferred method of the present invention;

FIGS. 6A-6C are diagrammatic illustrations of a typical polygonal approximation procedure in accordance with the preferred method of the present invention;

FIG. 7 is a system flow diagram of the presently preferred method of automatically generating a spiral type chenille in accordance with the present invention; and

FIG. 8 is a system flow diagram, similar to FIG. 7, of the presently preferred method of automatically generating chain stitching in accordance with the present invention.

Referring to the drawings in detail, and initially to FIGS. 6A-6C, a typical framework for determining the medial axis of a polygon shape is illustrated. This framework is described in "Voronoi diagrams of Polygons: A Framework for Shape Representation", N. Mayya and V. T. Rajan, Proceedings of IEEE VVPR 1994, Seattle, Wash. In addition, the algorithm for analyzing the shape to be filled to determine its medial axis, sometimes referred to as its skeleton, is described in "A transformation for extracting new descriptors of shape", Models for the Perception of Speech and Visual Form (W. Wathen-Dunn, ed.), H. Blum, 1967, Cambridge Mass.: MIT Press. In accordance with the presently preferred method of the present invention, it is employed in a conventional computer aided design system for generating embroidery stitch patterns, such as described in our U.S. Pat. No. 5,343,401, the contents of which are incorporated by reference herein in their entirety, with the computer employed typically being an IBM PC compatible computer running Microsoft Windows, and programmed in the language known as "C" C++. Thus, as will be explained hereinafter, the method of the present invention adds the capability of automatically generating chenille as well as chain stitching to the embroidery designs which the computer aided design system can generate, and can be used in embroidery or any other concentric coverage of shapes.

As shown and preferred in FIG. 7, in accordance with the presently preferred method of the present invention, which may be used for automatically generating spiral type chenille to provide a chenille filled embroidery pattern, first the shape to be filled is analyzed to determine its medial axis, with the shape to be filled preferably comprising a complex polygon with or without holes. In accomplishing this analysis, the computer preferably creates rays emanating in towards the selected polygon shape from every corner of the shape that is less than 90 degrees by constructing a vector that bisects the angle of the corner. For corners of the selected complex polygon shape that have an interior angle that is greater than 90 degrees, preferably two rays are constructed by the computer, each pointing in a direction normal or perpendicular to one of the edges of the corner. The computer then preferably puts all of the rays in a circular list which is a list in which the last element points back to the first element. While these rays are in the circular list, preferably the computer calls the first element in the list the head and if the head points directly into another ray, the computer then removes the head and the other ray from the list, adds them to a list of final rays, and returns to calling the first element remaining in the list the head and repeats the procedure. The computer then finds an edge in the polygon that forces the head to stop and calls it the closest candidate and then uses the closest candidate and the head to compute all new rays that emanate from the head's endpoint. The new rays are then preferably added to the list, the head is removed and added to the list of final rays, and the entire procedure is repeated for rays remaining in the list, with the process being stopped when the list is empty and all rays have been added to the final list.

Having determined the medial axis, preferably the computer determines concentric polygons going from the outer edge of the selected shape to the medial axis. The distance between the concentric polygons is one of the determinants of the fill. In constructing the concentric polygons, the computer preferably, for each edge in the original selected polygon, constructs a new polygon made up of those edges of the medial axis that are closest to the edge being considered, sweeps a line through the polygon which has been generated and computes all the segments of all positions of the line that fall in the interior of the polygon and, once this has been done for all the segments in the whole shape, determines for each edge which edges are adjacent to it to construct the concentric polygons. The computer then outputs the list of polygons. Thereafter, the computer sorts these concentric polygons in order to allow for proper sequencing and minimal jumping from one part of the shape to another. In carrying out this sorting, preferably the polygons are sorted to determine which are inside which and, once all the polygons are sorted, they form a tree rooted at the outline of the selected shape. The outline preferably has one or more children which each, in turn, have one or more children inside them. Once the tree is constructed, preferably a standard depth first search is used to stitch the polygons in the correct order from the center emanating outwards to ensure that the stitches are in an order that will sew well and produce the desired design. Preferably, between each subtree of polygons, the location of the next subtree is run by following the edges of the previously constructed medial axis which ensures that connecting runs are in the interior of the selected shape. Up to this point in the presently preferred method of the present invention, it can be used to automatically generate chain stitches or chenille.

After this, assuming chenille is to be automatically generated, then, preferably, along these constructed polygons, spirals, like a spirograph, are placed, of varying size, in order to maintain a consistent filling of the area. Preferably the size of the spiral and the distance between the focal points from one to the next are the other determinant to the density of the fill. In placing the spirals, preferably prolate cycloids are generated. The stitches are then preferably placed along the spirals, at specified lengths, such as illustrated in FIG. 4.

Chain stitching is a necessary stitch around all chenille and, as shown and preferred in FIG. 8, the presently preferred method of the present invention also enables chain stitches to be automatically generated. In this instance, preferably the same procedure as for generating chenille stitches is employed up through the sorting of the concentric polygons. Thereafter, however, rather than placing spirals along the polygons, chain stitches are placed on the perimeter of the concentric polygons at a specified length. In this regard, if desired, an entire shape can be covered by chain stitches such as illustrated in FIG. 5. Thus, the chain stitching method of the present invention is not restricted to chenille and can be used in embroidery or any other concentric coverage of shapes.

It should be noted that the above described method of the present invention may be preferably carried out by conventionally programming the computer of the computer aided design system to cvarry out the above steps.