Method for data matrix print quality verification

Details Method for data matrix print quality verification Method for data matrix print quality verification

2000-01-21

2001-06-12

Hilten, John S. (Department: 2854)

Typewriting machines

Code-printing typewriter

C400S104000, C400S074000

Reexamination Certificate

active

06244764

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for verifying data matrix print quality. More particularly, the present invention relates to a method of verifying the quality of two dimensional part marks on all types of direct part marking applications and label marking applications. The overall symbol grade, symbol contrast, print growth, axial non-uniformity, unused error correction, and other parameters relating to direct part marking are identified.
2. Description of the Prior Art
One and two dimensional part marks have achieved wide spread acceptance throughout a wide variety of industries. At most, systems and devices for reading such one and two dimensional symbols begin by determining the orientation of the markings before trying to read the symbol. Usually this is done by locating an outer reference bar(s) or a central symbol. Once the orientation of the marking is determined, the marking is read.
The term data matrix has been certified by AIM-USA and AIM-International as a fully public-domain symbology. AIM stands for Automatic Identification Manufacturers International, Inc. The data matrix is a unique machine readable symbol capable of storing a large amount of information within a small physical size. The data matrix symbol allows for two-dimensional encoding and decoding. Users are not constrained by the limitations of a printed symbol. Data matrix symbols are capable of carrying 25 to 100 times more information than the typical barcode. This range is directly related to the image quality the printer is capable of producing.
Data matrix codes have the following characteristics: both height and width are used to encode data, works with contrast as low as 20%, readable through 360° of rotation, designed to survive harsh industrial environments, codes can be marked on the surface of a part, without using a paper label, and several error correction schemes are available to ensure damage recovery.
No method or system has been developed for determining the quality of the part markings.
SUMMARY OF THE INVENTION
These and other deficiencies of the prior art are addressed by the present invention which is directed to a method for verifying data matrix print quality that can provide a high level of validation of two dimensional barcodes, and verify that the marks or labels have been properly applied and are readable.
The method is designed to run on a Windows based personal computer, and is compliant with the AIM Uniform Symbology Specification for Data Matrix Symbology. A camera
10
, shown in
FIGS. 1
a
and
1
b,
is employed to verify the data matrix symbol. The camera
10
is mounted on a camera mount
20
, as shown in
FIG. 2
to control the position of the camera
10
.
The method measures symbol contrast, print growth, axial non-uniformity, unused error correction, and overall grade. In addition to these parameters, the cell placement accuracy, cell size uniformity, and overall symbol quality are also measured. The method may also provide other relevant information about the data matrix, such as polarity, symbol size, error correction level, image style, and encoded data string.
An object of the present invention is to provide a method of precisely measuring the quality of data matrix marks.
Another object of the present invention is to provide a method of determining the quality of dot peen or ink jet marks.
Yet another object of the present invention is to provide a method of determining the quality of laser etched or printed marks.
Still another object of the present invention is to provide a method of measuring the quality of data matrix marks utilizing center offset and size offset measurements.


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