Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-12-23
2001-12-04
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462230, C235S462220
Reexamination Certificate
active
06325289
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a laser beam focusing apparatus and process for reading optical codes on objects carried on a supporting plane.
Throughout this description and the appended claims, the term “optical code” will be used to indicate a code (such as a bar code, two-dimensional code, color code, or the like) adapted to univocally identify objects bearing that code. In particular, reference will be made to bar codes for convenience of illustration.
Especially in the material handling and sorting plants, there is the problem of enabling the identification and classification of objects, which may differ considerably in height from one another, by means of a single instrument (typically a laser scanner), so as to speed up and optimize the subsequent object sorting and storage operations. In such situations, a fixed optics type of laser scanner not always allows codes to be brought into focus on the objects to be identified.
Further problems are encountered where a fixed optics scanner is used for reading high-resolution bar codes. In this situation, the achievable depth of field sharply decreases with decreasing of the code bars width. For example, with code bars 0.3 mm wide, a depth of field of no more than 300 mm can be achieved, while with code bars 0.2 mm wide, the maximum depth of field achievable is virtually reduced to half.
In practical applications an increased depth of field is required.
Various arrangements have been proposed heretofore for increasing the depth of field of a laser scanner. Best known among these are arrangements based on the multi-laser technique and on the electro-mechanical driving of optical parts effective to focus the laser beam.
Among the known multi-laser systems, that described in U.S. Pat. No. 5,483,051 of the same Applicant is of special interest. This system utilizes a modulated light type of laser scanner associated with two or more laser sources, each adapted to generate scans focused on preset distances. Such a system allows to measure the distance from the scanner of an optical code to be read, and to utilize this information for selecting and activating the one of the laser sources which is focused on that distance.
While obviating the prior art drawbacks, due in particular to the need of providing outside the scanner an array of photocells for measuring the height of the object bearing the bar code, or alternatively, to the need of providing for continuous and sequential activation of all the laser sources until a given scan recognizes the presence of a code, the multi-laser system of the above type has a drawback in that it involves a complicated optical construction and, hence, high costs. Both factors are restrictive of the applicability of such a system to small-size and of limited capacity plants.
The systems based on the electro-mechanical driving of optical parts for focusing the laser beam onto the object are indeed more simple construction-wise and economical to manufacture.
Although substantially achieving their objective, the last-mentioned systems also exhibit a series of drawbacks that have been left without a remedy.
A first drawback is associated with the need of an external height or distance sensor (depending on the mounting position of the scanner relative to the conveyor belt) adapted to drive the movements of the optical parts for focusing the laser beam. The presence of this sensor complicates the system and makes difficult, and some time impossible, the reading of irregularly shaped objects. In fact, the external sensor can only detect the maximum height of the object being conveyed under the reading area. Since the scanner is to focus the optical system based on this information, the error involved is surely high because a significant portion of the working depth of field cannot be utilized as expected, while with objects having an irregular surface shape, focusing will never be optimized.
A further drawback of conventional electro-mechanical driving systems is associated with the high response time of such systems, which makes them unsuitable for high speed applications.
SUMMARY OF THE INVENTION
The underlying technical problem of this invention is to provide an apparatus of simple and economical construction which can focus the optical system correctly and automatically, such that optical codes can be read on objects of any shapes and different heights.
Thus, a first aspect of this invention relates to a laser beam focusing apparatus for reading optical codes on objects carried on a supporting plane which is provided with a means for moving the objects along a feeding direction, comprising:
a laser beam scanner, which scanner is positioned relative to the object supporting plane so as to illuminate the object surface bearing the optical code;
a data processing unit connected to the scanner;
a first scan means for generating at least a first scan in a first scan plane, so as to measure the instantaneous distance of each point on the surface of each of said objects from the scanner;
a second scan means for generating a plurality of second scans in a second scan plane, so as to read the optical code on the object;
a means for adjusting the laser beam focal setting according to the distance measured with the first scan.
This is, therefore, an apparatus with an electro-mechanically driven optics which, additionally to being economical and constructionally simple, is capable of calculating, with high periodicity, the distance to which the code to be read passes and thus of suitably focusing the laser beam for a correctly optimized reading from objects having any shapes and heights.
Preferably, the scanner of the apparatus of the invention is a scanner emitting modulated-light laser.
Compared to conventional apparatus, wherein the electro-mechanical driving is controlled by an external height sensor, the apparatus Of this invention has an electro-mechanical driving controlled by the distance measurement made by emitting the modulated light laser beam. The distance measuring procedure is described in detail in U.S. patent application Ser. No. 5,483,051 of the same Applicant.
With this measuring procedure, the distance from the scanner to the optical code is measured (not the maximum height of the surface bearing the code), and the driving of focusing optical system is controlled on the basis of this information. Thus, the prior art limitations and drawbacks connected with the difficulty and indefiniteness of the distance measurement on irregular surfaces are overcome.
This apparatus also allows, in successive steps corresponding to different focus settings, of achieving a great depth of field in the instance of high-resolution codes, and a continuous focusing onto irregular surfaces.
Advantageously, the second scan plane is different from the first scan plane. Even more advantageously, the first scan plane intercepts the object in advance of the second scan plane, relative to the object movement on the supporting plane along the feeding direction. In this way, the distance of the bar code can be known before the object enters the code reading area, thereby allowing this focusing system to be also used for high-speed applications.
A usual problem encountered in conventional scanners wherein all the beam rays act on the same plane is that the distance is measured simultaneously with the code reading, so that, the electro-mechanical driving system being typically slow, compared to the moving speed of the objects, in driving the optical parts dedicated to focusing the laser beam (typical values of the driving time for focusing the lens are in the 15 to 20 ms range to obtain full shifting in slower and less expensive systems, and may reduce to a few msec in more sophisticated systems), the driving system will bring the movable optical parts into correct position only after the object has entered the reading area, thereby wasting many useful reading scans and greatly restricting the application possibilities.
The apparatus of this invention obviates this drawback by performing the scans dedic
Cyr Daniel St.
Datalogic S.p.A.
Frech Karl D.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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