Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1994-12-09
2001-10-30
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462450
Reexamination Certificate
active
06308892
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to laser scanning systems for reading symbols such as bar code symbols and, more particularly, to a lightweight, multi-component, portable laser diode scanning head supportable by a user and aimable at each symbol to be read. Still more particularly, this invention relates to an aiming light arrangement for visually locating and, in some cases, tracking each symbol to be read when the head emits and/or receives light which is not readily visible and is, in effect, invisible to the user; to a trigger which controls the aiming light arrangement; to a laser diode optical assembly; to an optical element which reflects an aiming light beam but transmits non-readily-visible light; to a multi-purpose scanning/collecting/focusing mirror of one-piece construction; to an interchangeable component design, wherein one or more components, as desired, are receivable in a single handle of the head, or in interchangeable handles which are detachably mountable to the head; and to a light-blocking cover which overlies selected transparent portions of the head to prevent light from passing therethrough.
2. Description of the Prior Art
Various optical readers and optical scanning systems have been developed heretofore to optically read bar code symbols applied to objects in order to identify the object by optically reading the symbol thereon. The bar code symbol itself is a coded pattern comprised of a series of bars of various widths, and spaced apart from one another to bound spaces of various widths, said bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically decoded the coded pattern to a multiple alpha-numerical digit representation descriptive of the object. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798, 4,360,798; 4,369,361; 4,387,297; 4,409,470 and 4,460,120, all of which have been assigned to the same assignee as the instant application.
As disclosed in some of the above patents, a particularly advantageous embodiment of such a scanning system resided, inter alia, in emitting a laser light beam from a hand-held, portable laser scanning head which was supported by a user, aiming the head and, more particularly, the laser light beam, at a symbol to be red, repetitively scanning the laser beam in a series of scans across the symbol, detecting the scanned laser light which is reflected off the symbol, and decoding the detected reflected light. Inasmuch as the laser light beam was usually, but not always, generated by a helium-neon gas laser which emitted red laser light at a wavelength of about 6328 Angstrom units, the red laser light was visible to the user and, thus, the user, without difficulty, could properly aim the head and position and maintain the emitted red laser light on and across the symbol during the scanning.
However, in the event that the laser light beam was generated by a semiconductor laser diode, as by way of example, see U.S. Pat. Nos. 4,387,297; 4,409,480 and 4,460,120, then the aiming of the head relative to the symbol was rendered more difficult when the laser diode emitted laser light which was not readily visible to the user. For same laser diodes, the laser light was emitted at a wavelength of about 7800 Angstrom units, which was every close to infrared light and was on the borderline of being visible. This laser diode light was visible to the user in a darkened room, but not in a light environment where ambient light tended to mask out the laser diode light. Furthermore, if the laser diode light was moving, for example, by being swept across the symbol, and especially if the laser diode light was being swept at fast rates of speed on the order of a plurality of times per second, for example, at a rate of 40 scans per second, then the laser diode light was not visible to the user, even in a darkened room. Hence, due to one or more of such factors as the wavelength of the laser light, the intensity of the laser light, the intensity of the ambient light in the environment in which the laser light was operating, the scanning rate, as well as other factors, the laser diode light was rendered, in effect, “invisible”, or, as alternately defined herein and in the claims, as being “non-readily visible”.
This non-readily-visible laser diode light did not enable the user, however, to readily aim the laser diode light at the symbol, at least not without a great deal of difficulty and practiced effort because, simply put, the user could not see the laser diode light. The user, therefore, was required to hunt around by trial and error, hope that the scanning laser diode light was eventually properly positioned on and across the symbol, and wait until the scanning system advised him, typically by the lighting of an indicator lamp or by the sounding of an auditory beeper, that the symbol had indeed been successfully decoded and read. This hunting technique was a less-than-efficient and time-consuming procedure for reading symbols, particularly in those applications where is multitude of symbols had to be read every hour and every day.
Nevertheless, in the context of a laser scanning head which was desired to be made as lightweight, miniature, efficient, inexpensive and easy to use as possible, the laser diode was more advantageous than the helium-neon gas laser, despite the non-readily-visible laser diode light characteristic, because the laser diodes were smaller, were lighter in weight, had reduced power requirements (voltage supplies on the order of 12 v DC or less), were directly modulated for synchronous detection and for increased signal-to-noise ratios, etc., as compared to such gas lasers.
However, despite the above advantages, certain optical properties of the laser diode beam itself, aside from its invisibility, did not readily enable the laser diode beam to be focused to a desired spot size (e.g., a 6 to 12 mils circular spot) at a given reference plane exteriorly of the head, and to maintain said spot size within specified tolerances at either side of the reference plane within a predetermined depth of focus or field, i.e. the working distance in which a symbol located anywhere within the field can be successfully decoded and read. For example, the longer wavelength of the laser diode beam, as compared to that of the helium-neon gas laser, dictated a shorter working distance for the same spot size. The laser diode beam was also highly divergent, diverged differently in different planes, and was non-radially symmetrical. Thus, whereas the gas laser beam had the same small divergence angle of about one milliradian in all planes perpendicular to the longitudinal direction of beam propagation, the laser diode beam had a large divergence angle of about 200 milliradians in the plane parallel to the p-n junction planes of the diode, and a different larger divergence angle of about 600 milliradians in the lane perpendicular to the p-n junction. In the single transverse mode (TEM
00
), the gas laser beam had a radially symmetrical, generally circular cross-section, whereas the laser diode beam had a non-radially-symmetrical, generally oval cross-section.
By way of example, in a so-called geometrical approach to solve the aforementioned focusing problem, and ignoring the non-radially symmetrical nature of the laser diode beam, optical magnification factors in excess of 80 were obtained if one wished to focus the beam spot to have about a 9.5 mil spot diameter at a reference plane located about 3½″ from the head. However, such high magnification factors dictated that, if one optical focusing element were employed (e.g. see U.S. Pat. No. 4,409,470), it would have to be critically manufactured, positioned and adjusted. If one employed several optical focusing elements in a lens system designed with a large numerical aperture, i.e. on the order of 0.25, as suggested by U.S. Pat. No. 4,38,297 to accept a large divergent laser diode beam and to distribute the mag
Adelson Alexander M.
Barkan Edward
Barkan Eric F.
Krichever Mark J.
Metlitsky Boris
Frech Karl D.
Kirschstein et al.
Symbol Technologies Inc.
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