Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-12-22
2001-07-17
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462260, C235S462160
Reexamination Certificate
active
06260764
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of detecting a bar code on a scan line, and to an apparatus for detecting and decoding a bar code.
A particular problem in plants for handling and sorting objects is that of quickly and univocally identifying the objects such that subsequent allotting operations can be speeded up and optimized.
In these plants, the objects to be identified are usually laid onto a feeding plane (e.g., a belt conveyor), and automatically identified by means of decoding bar codes carried on the objects themselves. The continuous movement of the feeding plane will take each object to a scan area, whereat a bar code scanner is provided which, once turned on, illuminates the code to be decoded along a read line (scan line); light scattered from spots on said line is picked up by a light-sensing element to generate an analog electric signal which is proportional to the intensity of the scattered light.
The analog signal thus generated is then processed in a digitalizer block, which will sample the signal to extract numerical features that are thoroughly representative of the signal, thereby to define a scan of the code on the object under examination.
This scan is processed through a bar code decoding program, to ultimately issue the sequence of the decoded characters of the bar code.
In conventional decoding processes, the laser beam continually sweeps across the scan area in a succession of linear scans. However, only a few of these scans are actually acquired and processed. In fact, scans “useful” to identify the object are only those effected along lines which cross the bar code. The acquisition and processing of all the code scans would slow down the decoding process and, therefore, be incompatible with the requirement for a high speed of response (a requirement due to that the objects only pass in the scan area for a short time).
In conventional decoding processes, the number of scans actually acquired and processed is far larger than that strictly necessary for reading the bar codes on the objects to be identified (the “useful” scans). In addition, once a scan is acquired, the scanner tries to decode the optical signal relating to all the samples of the scan line, regardless of whether they do or do not belong to bar code zones. All this is time consuming and cost intensive on account of the considerable storage and computing resources involved.
Thus, a need exists in this field for methods which be effective to detect the position of a likely bar code within a scan line. In this respect, the prior art method can be split into two basic categories:
methods based on analog circuits;
methods based on the digital processing of two-dimensional optical images.
While essentially achieving their objectives, either methods have, however, certain drawbacks.
The methods based on analog circuits do not lend themselves to use in a digital signal processing system like that employed for decoding bar codes. The methods based on two-dimensional image processing, on the other hand, require full acquisition of the entire two-dimensional image before processing can be initiated, and are thus very slow and expensive with regard to computing and storage resources.
SUMMARY OF THE INVENTION
The underlying technical problem of this invention is to enable a bar code to be detected on a scan line by a digital image processing method which is on the whole fast, reliable, and involves substantially less computing and storage resources (and hence, lower costs) than the aforementioned prior methods.
According to a first aspect, this invention provides a method of detecting a bar code on a scan line, comprising the following steps:
a) acquiring an analog electric signal representing variations in light intensity along a scan line;
b) sampling the analog signal for a predetermined number K of sampling intervals, so as to extract, for each interval, a sample x
k
identified by a pair of values (Px
k
, Lx
k
) representing the position and light intensity of a point of the sampling range in the scan line;
and being characterized in that it further comprises the following step:
c) each time comparing each of the samples x
k
extracted to the following samples x
k+h
, thereby to detect a plurality of zones of substantially constant brightness, said plurality of zones comprising, in succession, a broad initial zone, a plurality of narrow intermediate zones, and a broad final zone.
Throughout this description and the appended claims, the term “bar code” is used to indicate an optical code, also two-dimensional or colored, comprising, along at least one read direction (corresponding to the laser beam path during the scanning sweep), a succession of alternately black and white zones exhibiting sufficient relative light contrast (for simplicity, only traditional bar codes will be considered wherein these zones are defined as bar and space elements).
The terms “broad” and “narrow” should be intended in a relative sense. Broad is a zone which extends, along the read direction, with a width larger than four times the width of the smallest element in the code (module). Narrow is instead a zone which extends with a width smaller than four times the module width.
The above method allows the sampled signal to be processed in real time such that its portions can be detected which have features marking them as likely optical images of a bar code. Detecting these portions on the scan line allows then to identify a succession of zones having sufficiently sharp relative contrast (black and white areas), showing a certain uniformity in the ratio between their dimensions (succession of narrow zones), and being preceded and followed by relatively much broader zones of uniform brightness (also called quiet zones). Any zones which do not show the above features surely do not belong to a bar code, and are therefore rejected for the purpose of the subsequent decoding operations.
Unlike the prior art methods described above, in the method of this invention, the scan is processed as the samples are being made available from the previous operations; accordingly, this method is uniquely fast and simple to implement, since it does not require that the input signal be stored, nor the whole scan acquired, before it can proceed with the processing.
In addition, this being a digital method, it can be implemented using digital hardware or software in a microprocessor, thereby obviating the need for dedicated analog circuits.
Hardware implementation is also cost favorable on account of the required small storage capacity, while software implementation ensures uniquely fast processing because of the small number of operations to be carried out per sample.
The alternating black and white zones of the code produce alternating local maxima and minima of the analog signal, and the transitions between white and black zones of the code are represented by transitions of the signal between maxima and minima, and vice versa. Thus, the search for a potential bar code on the scan line can suitably be carried out as a search for such local maxima and minima. Preferably, therefore, step c) comprises the following steps:
c1) finding, among samples x
k
, those samples xm
i
which represent local maximum and minimum points, or local peaks, of the sampled signal;
c2) defining zones Dz
j
corresponding to the samples xm
i
found, and calculating the size of these zones;
c3) comparing the size of two successive zones Dz
j
and Dz
j+1
to find out the aforesaid plurality of zones.
In this way, the number of samples for a later decoding attempt can be drastically reduced. In fact, only scan portions as have been identified in the above operations will be indicated as potential codes to the decoding process to follow which will definitively establish whether or not they are code zones and will decode them. In this case, the decoding process, which is much more burdensome from the computational standpoint, can be applied to a smaller amount of data, thereby improving the overall process performance as regards spee
Calzolari Matteo
Zocca Rinaldo
Datalogic S.p.A.
Frech Karl D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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