DIFFERENTIAL NON-LINEAR STRAIN MEASUREMENT USING BINARY CODE SYMBOL

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. provisional application No.

60/902,877, filed February 23, 2007, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a binary code symbol for use in differential non-linear strain measurement. More specifically, the invention relates to utilization of additional characteristics of binary code symbols for non-linear strain measurement where the strain in a region is non-uniform, in addition to being non-linear, and exhibits a differential in strain.

2. Related Art

There are numerous one-dimensional (ID) and two-dimensional (2D) symbols in use today, and most utilize a majority of the symbol's surface area to store the encoded information. These symbols are typically comprised of large, distinguishable blocks, dots, or bars called "cells" that enable data encoding. The spacing, relative size, state (i.e. black or white), or some combination of cell attributes is exploited to

encode and decode data. These types of symbols are designed for inexpensive, low- resolution reading devices (or sensors); therefore cell dimensions can be relatively large with respect to the overall symbol size.

While many applications require that a symbol's encoded information be "read," there are additional applications that warrant a detailed accounting of the symbol's spatial characteristics. Metrology is one such application, which involves making precise geometric measurements of the symbol's features. Symbols optimized for "reading" purposes are not necessarily, nor are they normally, optimized for "metrology" purposes. The UPC symbol, the Data Matrix symbol, and the MaxiCode symbol are examples of common symbols. Typical ID and 2D symbols utilize cell arrangements that result in a broken (or non-continuous) symbol perimeter. Additionally, each has cells that are distributed somewhat uniformly across the entire symbol area. These characteristics are an efficient use of the symbol's surface area as a data encoder/decoder, but can cause a reduction in accuracy for certain types of deformation analyses, e.g. strain measurement.

Sensor resolution for machine-enabled metrology is typically higher than the sensor resolution required to simply encode and decode symbol information. Therefore with high-resolution sensors, it is possible to relax some of the "reader" requirements placed on existing symbol design, and produce symbols specifically for deformation/strain measurement.

It is to the solution of these and other problems that the present invention is directed.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to use the components of a geometric-shaped binary symbol to obtain strain readings over regions encompassing less than the entire region of the binary symbol using a differential non-linear strain gage incorporating the binary symbol. It is another object of the present invention to determine plastic strain in materials as they undergo stress.

The invention relates to utilization of additional characteristics of the binary code symbols that are the subject of co-pending U.S. Patent Application Serial No. 11/167,558 (entitled "BINARY CODE SYMBOL FOR NON-LINEAR STRAIN MEASUREMENT AND APPARATUS AND METHOD FOR ANALYZING AND MEASURING STRAIN THEREWITH"), filed June 28, 2005, U.S. Patent Applications Serial Nos. 60/838,152 (entitled "MULTI-FORMAT, BINARY CODE SYMBOL FOR NON-LINEAR STRAIN MEASUREMENT"), 60/838,151 (entitled "HIGH DENSITY, RECTANGULAR BINARY CODE SYMBOL"), and 60/838,153 (entitled "AUGMENTED BINARY CODE SYMBOL"), all filed August 17, 2006, and U.S. Patent No. 6,934,013 B2 (entitled "COMPRESSED SYMBOLOGY STRAIN GAGE"), issued August 23, 2005, for non-linear

strain measurement where the strain in a region is non-uniform in addition to being non-linear and exhibits a differential in strain.

Other objects, features and advantages of the present invention will be apparent to those skilled in the art upon a reading of this specification including the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is better understood by reading the following Detailed Description of the Preferred Embodiments with reference to the accompanying drawing figures, in which like reference numerals refer to like elements throughout, and in which:

FIGURE IA illustrates a binary code symbol of the type disclosed in U.S. Patent Application Serial No. 11/167,558.

FIGURE IB illustrates a high density binary code symbol of the type disclosed in U.S. Patent Application Serial No. 60/838,151.

FIGURE 2A illustrates an element for which strain is to be measured, before deformation.

FIGURE 2B illustrates the element of FIGURE 2A, after uniform deformation. FIGURE 2C illustrates the element of FIGURE 2A, after non-uniform deformation.

FIGURE 3 illustrates the basic geometric form of a rectangular binary code symbol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. The following definitions are used herein:

Plastic strain ~ Strain has two components: (1) elastic and (2) plastic. Plastic strain is defined as the non-recoverable strain after removing the load from a specimen under a high strain; or a dimensional change that does not disappear when the initiating stress is removed. Plastic strain is accumulated damage, anomalies, crack initiation, and crack growth in materials as they undergo stress. It results in permanent changes in the material and eventually leads to failure.

Co-pending U.S. Patent Applications Serial Nos. 11/167,558, 60/838,152, 60/838,151, and 60/838,153, the disclosures of which are incorporated herein by reference in their entireties, disclose a binary code symbol for non-linear strain measurement comprising inner and outer perimeters, first and second data regions along adjacent sides of the perimeter, first and second utility regions along adjacent

sides of the perimeter opposite the first and second data regions, first and second finder cells at opposite corners of the rectangle, and inner and outer quiet regions distinguishing the first and second data regions, the first and second utility regions, and the first and second finder cells from their background. Each data region comprises a number of data cells, each data cell representing a single bit of binary data; and each utility region comprises a number of utility cells of alternating appearance.

U.S. Patent Applications Serial Nos. 11/167,558, 60/838,152, 60/838,151, and 60/838,153 disclose rectangular binary code symbols. Co-pending U.S. Patent Application Serial No. 60/838,152 further discloses a binary code symbol that can be constructed in any geometric shape having a perimeter constructed of intersecting line segments, wherein "line segment" designates a part of a line that is bounded by two end points, and that can be straight or curved and can be continuous or include discontinuities. FIGURES IA and IB illustrate the rectangular binary code symbol of U.S.

Patent Application Serial No. 1 1/167,558 and the high density binary code symbol of U.S. Patent Application Serial No. 60/838,151, respectively.

As shown in FIGURE IA, the rectangular binary code symbol 100 comprises inner and outer perimeters HOa and HOb, first and second data regions 120a and 120b along adjacent sides of the inner and outer perimeters 110a and 110b, first and second utility regions 130a and 130b along adjacent sides of the inner and outer

perimeters HOa and HOb opposite the first and second data regions 120a and 120b, first and second finder cells 140a and 140b at opposite corners of the rectangle, and inner and outer quiet regions 150a and 150b distinguishing the first and second data regions 120a and 120b, the first and second utility regions 130a and 130b, and the first and second finder cells 140a and 140b from their background. Each data region 120a and 120b comprises a number of data cells 122, each data cell representing a single bit of binary data; and each utility region 130a and 130b comprises a number of utility cells 132 of alternating appearance.

As shown in FIGURE IB, the rectangular binary code symbol 200 comprises inner and outer perimeters 210a and 210b, first and second data regions 220a and 220b along adjacent sides of the inner and outer perimeters 210a and 210b, first and second utility regions 230a and 230b along adjacent sides of the inner and outer perimeters 210a and 210b opposite the first and second data regions 220a and 220b, first and second finder cells 240a and 240b at opposite corners of the rectangle, and inner and outer quiet regions 250a and 250b distinguishing the first and second data regions 220a and 220b, the first and second utility regions 230a and 230b, and the first and second finder cells 240a and 240b from their background. Each data region 220a and 220b comprises a number of data cells 222, each data cell representing a single bit of binary data; and each utility region 230a and 230b comprises a number of utility cells 232 of alternating appearance.

The rectangular binary code symbols as described with respect to FIGURES

IA and IB and the geometric-shaped binary code symbols in U.S. Patent Application

Serial No. 60/838,152 (which include rectangular binary code symbols) can be used as described hereinafter to measure non-linear and non-uniform strain in a material with an anomaly such as a crack in the area of strain measurement.

FIGURE 2A illustrates an element for which strain is to be measured, having points M, N, O, and P before deformation, while FIGURE 2B illustrates the element of FIGURE 2A having points M*, N*, O*, and P* after uniform deformation and FIGURE 2C illustrates the element of FIGURE 2 A having points M**, N**, O**, and P** after non-uniform, or differential, deformation. As is seen in FIGURE 2B, in the element after uniform deformation, the lengths of sides O*N* and P*M* are the same. In contrast, as is seen in FIGURE 2C, in the element after non-uniform deformation, the lengths of sides O**N** and p**M** are different. This difference in length is attributable to an anomaly in the element, because even with non-linear strain, the deformation should be uniform in the absence of an anomaly. The rectangular binary code symbols disclosed in co-pending U.S. Patent Applications Serial Nos. 11/167,558, 60/838,152, 60/838,151, and 60/838,153, and the geometric- shaped binary code symbols also disclosed in U.S. Patent Application Serial No. 60/838,152, can be used to measure strain differentials, which indicate an anomaly in the material subjected to stress.

The rectangular binary code symbols 100 and 200 and the geometric-shaped binary code symbols in U.S. Patent Application Serial No. 60/838,152 can be represented by their basic geometric form, as shown in FIGURE 3. The basic geometric form of a rectangular binary code symbol as shown in FIGURE 3 has the characteristic that it includes (with reference to FIGURES IA and IB) the component elements of an inner perimeter HOa or 210a (defined by Ti, Li, Bi, Ri); an outer perimeter HOb or 210b (defined by Te, Le, Be, Re); four corners (defined by the intersections of the inner perimeters and the outer perimeters, a, h, a*, h*; b, c, b*, c*; d, e, d*, e*; and f, g, f*, g*); and four bands, defined by each pair of adjacent corners and their intervening inner and outer perimeters (Te, c, h, a*+Ti+b*; Le, a, f, g*+Li+h*;Be, d, g, e*+Bi+f*; and Re, b, e, c*+Ri+d*). The bands can be occupied by data regions and/or utility regions. The inner and outer perimeters can be solid and continuous, or they can be discontinuous (for example, dashed or broken).

In general, a geometric binary code symbol has a basic geometric form having the characteristic that it includes the component elements of an inner perimeter constructed of line segments; an outer perimeter constructed of line segments; at least three corners defined by the intersections of the inner perimeter line segments and the outer perimeter line segments, and a plurality of bands equal to the number of corners and defined by each pair of adjacent corners and their intervening inner and outer perimeter line segments. The inner and outer perimeters can be solid and continuous,

or they can be discontinuous (for example, dashed or broken); and the bands can be occupied by data regions and/or utility regions.

The present invention takes advantage of this characteristic of the geometric- shaped binary code symbol (that it can be broken into its component elements and analyzed using the same theory, algorithms, and computer programs as described in Application Serial No. 1 1/167,558) and using the encoded data to assign an identity to the binary code symbol.

In particular, when the geometric-shaped binary code symbol is incorporated into a differential, non-linear strain gage, the bands and corners of the geometric- shaped binary code symbol can be used to evaluate differential strains in the regions of the bands and corners; and the external and internal boundaries can be used to measure differentials in strain between the external boundaries and internal boundaries. That is, differentials can be calculated by a region defined by any parallel pair of inner and/or outer perimeter line segments, including opposing outer perimeter line segments, opposing inner perimeter line segments, and an opposing inner line segment and an opposing outer line segment.

If the inner and or outer perimeter is not solid and continuous, the same theory, algorithms, and computer program as described in Application Serial No. 11/167,558 will construct a solid, continuous line. Similarly, the same theory, algorithms, and computer programs can be used to identify the other components of

the geometric-shaped binary code symbol, and to obtain strain readings within areas defined by the components of the geometric-shaped binary code symbol.

A differential, non-linear strain gage employing the geometric-shaped binary code symbols as a target also uses the same theory, algorithms, and computer programs as described in the Application Serial No. 11/167,558, which (1) identify the geometric-shaped binary code symbols and the changes therein as a function of time and change in the load, (2) translate the changes in the binary code symbols into strain, and (3) display it in a suitable format.

Although the symbol shown in FIGURE 1 only has two distinct corners, the algorithms and computer program can identify, for any shape of the geometric-shaped binary code symbol, all of the geometrical components, including all of the corners.

That is, the computer program can identify components in any symbol and use the analysis technique to get strain readings within areas of the symbol used.

Modifications and variations of the above-described embodiments of the present invention are possible, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims and their equivalents, the invention may be practiced otherwise, than as specifically described.