Wedged-shape holographic collector

Details Wedged-shape holographic collector Wedged-shape holographic collector

1999-05-21

2001-01-02

Henry, Jon (Department: 2872)

Optical: systems and elements

Holographic system or element

Using a hologram as an optical element

C359S575000, C235S457000, C235S462490, C235S473000, C250S227110, C250S227320, C385S037000

Utility Patent

active

06169614

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a diffractive collector for a bar code scanner. In particular, the present invention relates to a wedged-shaped collector which includes a planar front surface and a holographic grating provided on a conical bottom surface.
2. Description of the Related Art
Bar codes are used in a wide variety of applications for retrieving information, such as price, from objects. In this respect, bar code scanners are of widespread use in grocery stores and department stores, for both inventory control and for point-of-sale (POS) transactions.
A bar code normally includes several bar code characters. A bar code character is a group of lines (bars) and spacings that represent a single number or letter. A bar code symbol is a collection of several bar code characters which represent an identification of a particular object. The lines of the bar code can vary, for example, in a range from about ⅛″ to 1 in height, and from about 1 to 50 mils in thickness. The spacings between the lines making up the bar code may be of various widths, with the variations in the spacing being one determination of the type of bar code characters making up the bar code.
Typically, bar codes are read by illuminating the bars and spacings in a sequential manner, with the bars absorbing light and the background spacings reflecting light. This results in a pattern of reflections and nonreflections that is sensed by a light detecting circuit resident in the bar code scanner. The light detecting circuit provides an input to a digital processor, which interprets the bar code into a digital word.
Various types of apparatuses are used for the light detecting circuits in bar code scanners. For example, a photodiode detector may be used to detect reflected light off of a bar code symbol. The photodiode detector generates an electrical signal indicative of the detected light intensity. The electrical signal is then output to signal processing circuitry, which processes the electrical signal and generates data descriptive of the symbol.
In general, light output by a light sensor within the bar code scanner impinges on a bar code symbol, causing some light to reflect off of the bar code symbol. Some of the reflected light is received by a mirror (typically a curved mirror) within the housing of the bar code scanner (but positioned behind a window that allows for light to pass therethrough). The mirror focuses the received light onto the photodiode detector. Such a system is described in U.S. Pat. No. 5,410,139, entitled “Peak Detecting Bar Code Reader”, issued to W. Barkan, which is incorporated herein by reference. In essence, the mirror acts as a “collector” for the reflected light, and outputs the collected light to the photodiode detector. A signal indicative of the amount of the received reflected light is thereby obtained.
Other detailed designs of bar code reading instruments are described in U.S. Pat. No. 5,258,604, which was issued to James Behrens et al. on Nov. 2, 1993, and is entitled “Bar Code Scanner”; U.S. Pat. No. 5,237,161, which was issued to Scott R. Grodevant on Aug. 17, 1993 and is entitled “System for Automatically Reading Symbols, Such as Bar Codes, on Objects Which are Placed in the Detection Zone of a Symbol Reading Unit, Such as a Bar Code Scanner”; U.S. Pat. No. 5,212,371, which was issued to John A. Boles et al. on May 18, 1993 and is entitled “Hand Held Bar Code Scanner with Improved Aiming Means”; U.S. Pat. No. 5,200,597, which was issued to Jay M. Eastman et al. on Apr. 6, 1993 and is entitled “Digitally Controlled System for Scanning and Reading Bar Codes”; and U.S. Pat. No. 5,019,698, which was issued to Jay M. Eastman et al. on May 28, 1991 and is entitled “Bar Code Reading System Having Electrical Power Conservation and Laser Radiation Power Limiting Means.” The entire contents of all of the patents and patent applications listed above are incorporated herein by reference. This application and the all of the above-identified patent applications and patents, except for the Barkan patent, are assigned to PSC Inc. (Webster, New York).
Holograms are currently being used for a variety of security-related purposes for smart cards. U.S. Pat. No. 5,101,184, entitled “Diffraction Element And Optical Machine-Reading Device”, issued to G. Antes, relates to the use of a hologram on a card, such as a credit card or bank note, so as to provide a measure of security for the card. The invention also relates to a device for reading the information on the card.
U.S. Pat. No. 4,400,616, entitled “Document Card Containing Information In Holographic Form”, issued to P. Chevillat et al., relates to a document card provided with secret data contained ill the form of a waveguide hologram, and a device for reading the secret data.
One conventional bar code scanner utilizes holograms for outputting light to a bar code symbol. U.S. Pat. No. 5,266,788, entitled “Laser Scanner For Bar Code Reader Having a Transparent Light Guide Plate”, issued to K. Yamazaki et al., which is incorporated herein by reference, describes such a conventional scanner.
FIG. 1
shows the use of a hologram for providing a output scan signal according to the Yamazaki invention. In
FIG. 1
, a transparent light guide plate
23
is integrally formed on a substrate
20
, and a scanning beam emission window
25
is formed as a hologram at an upper part of the light guide plate
23
. The substrate
20
incorporates a scanning optical system for the scanning beam P. Yamazaki's scanning optical system has a polygonal mirror
31
, which is rotated around a rotary shaft
33
by a motor
35
. In response to the rotation, the polygonal mirror
31
guides the beam P in a plane within the substrate
20
, so that the beam is reflected upward from a lower mirror
37
a
into the transparent light guide plate
23
. The scanning beam P undergoes repeated total reflections inside the transparent light guide plate
23
, and is diffracted by the hologram
27
in a predetermined direction and emitted from the emission window
25
. The emitting direction is optionally set according to the design of a desired pitch of interference fringes, etc., of the hologram
27
. In Yamazaki's invention, the light source of the scanning beam P is a semiconductor laser
41
, and the beam P is made incident on the polygonal mirror
31
from the inside of the substrate
20
.
FIG. 2
shows another embodiment of Yamazaki's invention, in which a hologram
38
is arranged at a lower end portion of the transparent light guide
23
. The hologram
38
diffracts the scanning beam P from the polygonal mirror
31
in a predetermined direction to guide the beam upwardly into the transparent light guide plate
23
.
Another conventional bar code scanner utilizes holograms for both outputting light to a bar code symbol, and for receiving light that is reflected off of the bar code symbol. U.S. Pat. No. 5,231,277, entitled “Optical Scanner Using Plannar Reflecting Holograms”, issued to H. Aritake et al., which is incorporated herein by reference, describes such a conventional scanner.
FIG. 3
shows a conventional bar code scanner according to Aritake, in which a rotary polygon mirror is employed as a laser beam scanning means and strip holograms of the transmission type are employed for a reading window. The reading window
10
is composed of three transparent substrates
11
,
12
and
13
having strip holograms
11
a
,
12
a
and
13
a
, respectively, of the transmission type formed in different directions from each other and adhered in layers to each other such that the strip holograms
1
a
,
12
a
and
13
a
extend in an intersecting relationship to each other. Located below the reading window
10
are a scanning pattern generating mirror means
14
which consists of three side mirrors
15
,
16
and
17
, a concave mirror
18
having a through-hole
18
a
formed therein, a bottom mirror
19
disposed in parallel to the reading window
10
, a photo-detector
20
, a mirror
21
, and a

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