Two window optical scanner

Details Two window optical scanner Two window optical scanner

2001-04-03

2003-10-14

Frech, Karl D. (Department: 2876)

Registers

Coded record sensors

Particular sensor structure

C235S462140, C235S462170, C235S462300, C235S462360, C235S462370, C235S462380, C235S462390

Reexamination Certificate

active

06631845

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical scanners and particularly to a scanner with at least two windows for scanning objects from different angles.
BACKGROUND OF THE INVENTION
Slot scanners are often used to read and decode bar codes which are disposed on various items. An example of a slot scanner is shown in U.S. Pat. No. 5,717,195, incorporated herein by reference. Two-window slot scanners essentially have a horizontal window and a vertical or generally vertical (referred to as “vertical” hereinafter) window on two surfaces of a generally L-shaped housing. Projecting generally upward out of the horizontal window is a light beam that creates a first set of scan lines while projecting generally horizontally out of the vertical window is a light beam that creates a second set of scan lines. When the scanner is in use, an operator (such as a person working at a supermarket checkout counter) moves an object with a bar code over the horizontal window and past the vertical window. If the bar code is located on the bottom of the object, the bar code reflects the light beam projecting out of the horizontal window. If the bar code is located on the side of the object facing the vertical window, the bar code reflects the light beam projecting out of the vertical window.
Attempts have been made to extend the reading ability of scanners beyond the bottom and one side of an object. One way to accomplish this, for example, is to have a light beam projecting out of the horizontal window at an angle, so that a bar code on some other sides of an object not facing the vertical window can be read. A light beam projecting out from near the top of the vertical window, but at a downward angle, may provide some ability to read a bar code located on the top of an object.
Heretofore, two-window scanners have used beam splitters to split a light beam from a single light source, such as a laser, into two beams. The two beams are directed at different sides of a spinning polygon mirror, which reflects the two beams toward arrays of stationary mirrors. A typical polygon mirror used in this fashion is mounted directly on a motor shaft and has three or four reflecting facets. The arrays of stationary mirrors provide paths for the two beams to form two scan patterns.
Use of a single light source with a beam splitter has several disadvantages. One disadvantage is that a single light source, such as a laser, must be powerful enough to provide two light beams of adequate intensity and therefore must operate at a higher power, which results in a shorter expected operating life. Another disadvantage is that use of a single light source with a beam splitter may be more costly to manufacture than use of two light sources with no beam splitter. This is because a system using beam splitters usually needs additional mirrors and alignment adjustments that actually are more expensive than having two light sources. Yet another disadvantage of using a single light source is that once that light source fails, the scanner becomes non-operational until the light source is replaced.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention relates to a two-window scanner having a plurality of light sources. The scanner has a housing with a horizontal window and a vertical window. Each window has associated with it a light source and a polygon mirror rotated by a motor. Preferably, each window also has a separate collection system for detecting the reflection of the light beam off a bar code. The collection systems send electrical signals to a decoder, which generates a digital signal that corresponds to the bar code. Preferably, the decoder is capable of reading a bar code even if part of the bar code is scanned by one of the windows and another part of the bar code is scanned by the other window.
It is an object of the present invention to provide a two-window optical scanner having two light sources.
It is another object of the present invention to provide a two-window optical scanner with a longer operational life expectancy than previously available.
It is another object of the present invention to provide a two-window optical scanner that is capable of reading bar codes when a light source or other component malfunctions.
It is another object of the present invention to provide a two-window optical scanner that distributes heat within its housing to avoid hot spots near heat-sensitive components.
It is another object of the present invention to provide a two-window optical scanner that utilizes fewer stationary mirrors.
Another object of the present invention is a slot scanner which uses two rotating polygons, each of which is operated by its own motor.
A further object is a slot scanner which uses two lasers, one laser directed at a polygon that scans out of the vertical window, and the other laser aimed at the other polygon and scanned out of the horizontal window.
The polygon that scans the horizontal window is preferably mounted on a motor with its axis of rotation oriented vertically. The axis of rotation of the motor and polygon that scan out of the vertical window is oriented horizontally. Both polygons have four reflective sides, and preferably the sides are tilted differently with respect to the axis of rotation on the two polygons.
The two lasers may be focused differently and/or may operate at different laser powers.
As mentioned above, the scan pattern that is projected out of the horizontal window is preferably generated by the polygon that rotates about a vertical axis. This polygon is located below the horizontal window at the end of the window that is closest to the vertical window.
The polygon scans a laser beam produced by one of the lasers across an array of mirrors located around the periphery of the horizontal window. Most of these mirrors direct the scanned beam downward, away from the window towards a large mirror on the bottom of the housing. The scanned laser lines reflected off this bottom mirror pass upwards through the horizontal window where they will strike a package passing over the window.
The mirrors in the array are preferably oriented such that they produce scan lines in all the orientations needed to read a symbol passed over the window, no matter how the symbol is oriented. The symbol doesn't have to be on the bottom of the package, because the scan lines don't shoot straight up. They emerge from the window at an angle, so they can also shine on the sides of a package moving across the window. There are lines that project on the front of a package (the side in the direction of travel), on the back of the package (opposite the front) and on the end of the package opposite the vertical window.
Some scan lines reflect off one mirror in the array to another mirror in the array and then out the window without reflecting off the large bottom mirror. This enables projection of some scan lines in different directions that can otherwise be obtained.
The use of second motor/polygon allows one to use a much simpler mirror array for the scan pattern projected from the vertical window than is possible with single polygon scanners. Preferably the design uses only four mirrors in this array. Unlike all other two-window scanners, the scan lines radiating from this second polygon (with a horizontal axis of rotation) are reflected off only a single mirror in the array passing out of the window. This makes the mirror array less expensive and also provides a stronger signal to the photodetector that senses the laser light reflected off symbols that are scanned by the vertical window. Eliminating a second mirror in the paths of the outgoing laser beams eliminates half of the losses that are due to the fact that the mirrors only reflect about 90 percent of the laser light.
Although the polygon can be mounted above the four mirrors in the array, it is understood that the scan pattern can also be generated by inverting the arrangement shown so that the polygon is below the mirror array. This inverted arrangement may enable one to separate the left and right pairs of mir

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