JPH03171108A - Optical scanner - Google Patents

Abstract

PURPOSE:To improve the SN of signals by setting the focusing position where the signal light scanned and scattered on a reading surface is condensed by a condenser lens and the focusing position where the disturbing light entering from the same direction as the incident direction of the signal light is condensed by the condenser lens at the positions different from each other. CONSTITUTION:The focusing position P where the signal light A scanned and scattered on a bar code surface 9 is condensed and formed by the condenser lens 10 and the focusing position Q where the disturbing light B entering from the same direction as the incident direction of the signal light A is condensed and formed by the condenser lens 10 are set at the positions different from each other. The disposition position of the condenser lens 10 is so set that the relation of equation I is obtd. when the distance from the bar code surface 9 to the condenser lens 10 is designated as (a) and the distance from the condenser lens 10 to a photodetector 11 as (b). The beam diameter of the disturbing light B detected by the photodetector 11 is expanded to a large size in this way, by which the intensity of the disturbing light B with respect to the intensity of the signal light A per unit area is weakened. The SN of the detected signal is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical scanning device such as a laser barcode reader using a hologram.

2. Description of the Related Art An example of a conventional optical scanning device will be described with reference to FIG. The beam emitted from the laser light source 1 is shaped into a beam by a beam shaping prism 2, and then passes through a hole 3a formed in a perforated mirror 3, and is sent to a hologram scanner 4.
incident on . In this hologram scanner 4, a rotating body 5
A plurality of scanning lines 8 are drawn in a plurality of directions on the upper part by being reflected by a polygon mirror 6 provided on the upper part of the polygon mirror 6 and reflected by a plurality of mirrors 7 disposed below the polygon mirror 6 . By scanning the barcode surface 9 as a reading surface placed on the scanning line, information on that surface is read. The scattered light is again sequentially reflected by the mirror 7 and the polygon mirror 6, and this time is reflected by the reflective surface 3b of the perforated mirror 3, and is reflected by the condenser lens 10.
The light is collected by the photodetector 11 and detected by the photodetector 11. This allows the information recorded on the barcode surface 9 to be read.

Problems to be Solved by the Invention FIG. 9 schematically shows the optical positional relationship between the barcode surface 9, the condensing lens 10, and the optical detector 11. That is, the light emitted from the laser light source 1 passes through the beam shaping prism 2 and the mirror 12, and then enters the condenser lens 10.
As a result, a beam waist of the scanning light A (hereinafter referred to as signal light 8) is formed on the barcode surface 9, and reading scanning on that surface is thereby performed. The signal light A scattered by the barcode surface 9 is
The light is collected by the condensing lens 10 and the photodetector 1
1 is detected, and the information is thereby read.

Generally, in order to secure a certain amount of scanning width, the light focused on the barcode surface 9 is focused through a gently long path. In addition, in order to make the overall configuration of the device more compact, from the condenser lens l○ to the photodetector 1.
1 is designed to be as short as possible.

Now, in FIG. 9, the focal length of the condensing lens 10 is r, the distance from the position of the beam waist formed on the barcode surface 9 of the signal light A to the condensing lens 10 is a, and the condensing lens If the distance from the lens 10 to the photodetector l{ is b, the following relationship generally holds true.

In this equation (1), if a>>b, then b#f
... (2) becomes.

On the other hand, at this time, assuming that in addition to the signal light A, disturbance light B, which is a parallel light beam, is incident on the photodetector 11, a=(
1), so the equation (1) is b=f
...(3) It can be set as follows.

Therefore, from the relationship of equations (2) and (3), in addition to the signal light A, the disturbance light B is also focused almost in the vicinity of the photodetector 11, and both lights are detected. Generally, light from sunlight or indoor lighting exists at a far position compared to the path length of the photodetector l1, and that light can be considered as disturbance light B, and the disturbance light B happens to be the signal light A. When the disturbance light B enters the photodetector 11 from the same direction as the optical path of the condensing optical system or from the same direction as the optical path of the condensing optical system, the disturbance light B is much stronger than the original signal light A, so the S/N ratio of the detected signal is almost reduced to 0. Therefore, there is a problem that normal detection cannot be performed.

Means for Solving the Problems Therefore, in order to solve such problems, the present invention shapes the light emitted from the laser light source using a beam shaping prism, and inputs the shaped light into an optical scanner. In an optical scanning device that reads information by scanning the light on the reading surface and then condensing the reflected light from the reading surface with a condensing lens and guiding it to a photodetector, the light is scanned on the reading surface. A convergence position is formed by condensing the signal light scanned and scattered by the condenser lens, and a convergence position is formed by condensing the disturbance light incident from the same direction as the signal light by the condenser lens. The positions were set to different positions.

In addition, the light emitted from the laser light source is shaped by a beam shaping prism, the shaped light is input to an optical scanner, the light is scanned on the reading surface, and the reflected light from the reading surface is collected. In an optical scanning device that reads information by condensing light with an optical lens and guiding it to a photodetector, the distance from the beam waist position of the scanning light scanned on the reading surface to the condensing lens is a. The arrangement position of the condenser lens was set so that the relational expression a can be obtained, where b is the distance from the condenser lens to the photodetector.

Effect: Therefore, the disturbance light that enters the photodetector via the condensing lens is not condensed on the detection surface, but is guided as a spread beam, so the detected light intensity increases. The light intensity becomes weaker than that of the signal light, thereby improving the signal-to-noise ratio of the signal.

Embodiment First, a first embodiment of the present invention will be described based on FIGS. 1 to 3. Note that the same reference numerals are used for the same parts as in the prior art (see FIG. 9).

In this embodiment, the signal light A scanned and scattered on the barcode surface 9 (see FIG. 8) is focused by the condenser lens 10, and the focusing position P is formed in the same direction as the signal light A. A focusing position Q formed by condensing the disturbance light B incident from the condensing lens 10 is set at a mutually different position.

In this case, in order to make the focusing position P of the signal light A and the focusing position Q of the disturbance light B different, as shown in FIG. There is a need. That is, when the distance from the beam waist position of the signal light A scanned on the barcode surface 9 to the condenser lens 10 is a, and the distance from the condenser lens 10 to the photodetector l1 is b, Make b and f different.

Specifically, by modifying the relationship in equation (1), the relationship a f = Taking into account the reduction of , the position of the condenser lens 10 is set so that the following relational expression is obtained.

By setting as shown in equation (5), the signal light A
FIG. 1 shows how the focusing position P of the parallel light beam differs from the focusing position Q of the disturbance light B, which is a parallel light beam. As a result, for example, the optical path for scanning the signal light A and the signal light A as shown in FIG.
A relationship such as equation (5) can be established in a reflexive optical system in which the optical path for detecting the signal is the same as that in the optical path, or in an optical system in which the optical path for scanning and the optical path for detecting the signal are separated, as shown in Figure 3. Can be done.

Therefore, by making the focusing position P of the signal light A and the focusing position Q of the disturbance light B different in this way, the photodetector 1
As a result, the beam diameter of the disturbance light B detected in l is greatly expanded, and as a result, the light intensity of the disturbance light B relative to the light intensity of the signal light A per unit area can be weakened, so that the S/N ratio of the detected signal is reduced. can be improved.

Next, a second embodiment of the present invention will be described based on FIGS. 4 to 7. In the case of the first embodiment described above, by making the focusing position P of the signal light A and the focusing position Q of the disturbance light B different, a difference in intensity is created between the two lights guided to the photodetector 11. This allows only the signal to be detected, but in addition, as shown in Fig. 4, a reflecting mirror 13 is newly placed as a light shielding plate at the east concentration position Q of the disturbance light B. be. Below are some specific examples of such light shielding plates.

In FIG. 5, a mirror l4 with a hole 1}J serving as a light shielding plate is disposed at a focal position Q of the disturbance light B.

Moreover, in FIG. 6, a partial reflection mirror l5 as a light shielding plate is arranged at the convergence position Q of the disturbance light B.6 In this case, in the partial reflection mirror l5, the east convergence position of the disturbance light B is disposed. A reflective portion 15a is formed in a portion corresponding to Q. Furthermore, FIG. 7 shows that at the focal position Q of the disturbance light B,
A partial diffraction mirror 16 is provided as a light shielding plate. In this partial diffraction mirror l6, a diffraction grating 16a is formed at a focal position Q of the disturbance light B. In this case, some of the disturbance light B diffracted by the diffraction grating 16a heads toward the photodetector II, but its intensity is very small and is difficult to detect. has almost no effect.

As mentioned above, by arranging various light shielding plates at the focal position Q of the disturbance light B, the SN in the detection of the signal light A can be reduced.
This makes it possible to further improve the ratio compared to the first embodiment.

Effect of 1 vJ The present invention shapes the light emitted from a laser light source using a beam shaping prism, enters the shaped light into an optical scanner, scans the light on a reading surface, and then scans the light on the reading surface. In an optical scanning device that reads information by condensing reflected light from a surface using a condensing lens and guiding it to a photodetector, the signal light that has been scanned and scattered on the reading surface is condensed by the condensing lens. The formed focused position and the focused position formed by the disturbance light incident from the same direction as the signal light being focused by a condensing lens are set to different positions, or the scanning is performed by scanning on the reading surface. When the distance from the light beam waist position to the condenser lens is a, and the distance from the condenser lens to the photodetector is b, the condenser lens should be arranged so that the following relational expression can be obtained. By setting , the disturbance light that enters the photodetector via the condensing lens is not condensed on the detection surface, but is guided as a spread beam, so that it can be detected. The light intensity becomes weaker than that of the signal light, thereby making it possible to further improve the signal-to-noise ratio than in the past.

[Brief explanation of the drawing]

FIG. 1 is an optical path diagram showing a first embodiment of the invention, FIGS. 2 and 3 are optical path diagrams showing a modified example of the structure of the optical system, and FIG. 4 is an optical path diagram showing a second embodiment of the invention. An optical path diagram showing an example, FIGS. 5 to 7 are optical path diagrams showing modified examples of the light shielding plate, FIG. 8 is a configuration diagram showing the overall configuration of the optical scanning device, and FIG. FIG. 3 is an optical path diagram showing how the image is influenced by the above. ■... Laser light source, 2... Beam shaping prism, 9
...Reading surface, 10... Condensing lens, 11... Photodetector, A... Signal light, B... Disturbance light, P, Q...
Focusing position applicant Ricoh Co., Ltd. 3 4 3 5 Mother

Claims (1)

[Claims] 1. The light emitted from the laser light source is shaped by a beam shaping prism, the shaped light is incident on an optical scanner, the light is scanned on the reading surface, and then the reading surface is In an optical scanning device that reads information by condensing reflected light from a surface using a condensing lens and guiding it to a photodetector, the signal light scanned and scattered on the reading surface is condensed by the condensing lens. and a focusing position formed when the disturbance light incident from the same direction as the signal light is focused by the focusing lens are set to different positions from each other. . 2. Shape the light emitted from the laser light source using a beam shaping prism, enter the shaped light into an optical scanner, scan the light on the reading surface, and then collect the reflected light from the reading surface. In an optical scanning device that reads information by condensing light with an optical lens and guiding it to a photodetector, the distance from the beam waist position of the scanning light scanned on the reading surface to the condensing lens is a. , the arrangement position of the condenser lens is set so that the relational expression a/(a+b)≦0.9 is obtained, where b is the distance from the condenser lens to the photodetector. optical scanning device.