JPS5918753B2 - optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device that uses laser beam scanning to read label information and expands the information reading depth area above the reading surface.

Recently, a method has been used in which a barcode on a label attached to the bottom or side of a product is read using a set of laser beam scanning line patterns of a laser beam scanning device.

For example, as shown in FIG. 1, a laser beam 5 is radiated obliquely upward from a scanning point 1 in an optical scanning device 10 via a reflecting mirror 2 and through a reading window 3. At this time, the distance from scanning point 1 to the beam convergence point is kept almost constant, so the effective reading area (A
+B), only the intersecting line area A above the reading surface is used.

Therefore, the shaded area B below the reading surface enters the interior of the optical scanning device 10 and cannot be used for reading the barcode of the product, thereby narrowing the reading area as a whole. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device that reads label information using laser light and expands the information reading depth region above the reading surface.

In order to achieve the above object, the optical scanning device of the present invention is an optical scanning device that projects a laser scanning light for reading information using a laser beam from inside the device, and uses a spherical wave on a photoconductor and a laser beam on the photoconductor. A hologram created by interfering with a plane wave incident at an angle other than perpendicular is used, a laser beam is incident on the hologram, and the imaging distance of the laser beam varies depending on the deflection angle of the laser beam deflected by the hologram. The lens system is characterized by having a lens system as shown in FIG.

The principle and embodiments of the present invention will be explained in detail below.

It has been proposed to use a hologram as a lens system for a laser beam scanning device that reads product barcodes. That is, in order to perform optical scanning, the same function as moving a convex lens can be obtained by using a Fresnel zone plate (FZP) made by interfering a coherent plane wave and a spherical wave. However, when actually creating an FZP, a spherical wave is used instead of a plane wave, so there is field curvature aberration, and when the FZP is moved, light does not converge uniformly on the reading surface. Therefore, in the case of FIG. 1, it is assumed that the distance from the scanning point 1 to the beam convergence point is approximately constant, but in reality, this field curvature aberration exists.

The present applicant is Japanese Patent Application No. 51-151618
No. 75950) proposed a method for creating a hologram that corrects this field curvature aberration. This method creates a hologram by making a plane wave and a spherical wave interfere with each other at a predetermined angle on a photoreceptor. Inject it at an angle. This is the so-called offset method. The proposed offset method will be explained below. As shown in FIG. 2a, in the past, a plane wave and a spherical wave were irradiated at a predetermined angle θ, and the plane wave was irradiated to the recording medium S at right angles. In this method, as shown in FIG. 2b, the angle θ between the plane wave and the spherical wave remains the same, but the recording medium S is tilted by an angle P, so that the plane wave is irradiated at the tilted angle. Here, the plane wave may be tilted. When the inclination angle is P when a plane wave is incident on the hologram surface when creating a hologram, the center deflection angle β(x) and the imaging distance Z when the incident angle P of the plane wave when creating the FZP is changed. The results of calculating the relationship by varying the deflection magnification are shown in FIGS. 3 and 4. In FIGS. 3 and 4, the horizontal axis is the central deflection angle (degrees), and the vertical axis is the imaging distance, which is a curve P.

, I). When the angle P between the plane wave and the spherical wave is 0, the curves PlO, PlO is 10, the curves Pl5, P'1,
shows the case of 15 flats. In FIG. 3, the deflection magnification M is 4, and in FIG. 4, M is 8. In Figures 3 and 4, when using the central deflection angle in the range of 200±5, P
When =0, the variation in the imaging distance is very large, and in particular, in FIG. 3, there is a difference of more than 10 times between the distance of 15 and the distance of 25. However, on P=10 and P=
In the case of 152, there is almost no change.

The following points have become clear from these Figures 2 and 3. (
1) Regardless of the value of the deflection magnification M, the predetermined central deflection angle β
There exists an inclination angle with respect to (x) at which the field curvature aberration is minimum.

(2) The amount of field curvature aberration under optimal tilt angle conditions increases as the deflection magnification M increases.

(3) As the optimal tilt angle increases, the value of the minimum imaging distance of 1 min decreases.

(4) The value of the beam diameter on the FZP surface of the optical scanning distance does not have a large effect on the value of the imaging distance l.

Regarding the first term above, when the deflection magnification M is constant, the ratio P/β(x
) remains unchanged, so the deflection magnification and P/
If you create a graph showing the relationship between β(x) and the deflection magnification M in the optical scanning device and the central deflection angle β(x), you can determine the optimal tilt angle when creating the FZP. P can be easily seen from this graph.

Regarding the third term, for each deflection magnification M, a graph showing the value of the imaging distance variation rate (1mi dry 1) with the imaging distance l as the standard when the central deflection angle β(x) = 0 deviation is shown. It is shown in FIG.

This result shows that the imaging distance variation rate increases as the central deflection angle and deflection magnification increase. Up to now, based on FIG. 2, we have described the field curvature aberration in the X-axis direction and a correction method for reducing the aberration.

On the other hand, in the Y-axis direction, a plane wave incident at an inclination angle P may be projected onto the YZ plane. In this case, the inclination angle P=0 throw. The central deflection angle β(x
)=0, β(y)=0 in the Y-axis direction can be obtained by using the FZP creation method as shown in FIG. On the other hand, also in the Y-axis direction, the central deflection angle β(y)〉0
If the condition of 0 is required, the above-mentioned correction method may be applied to this direction as well. In any case, the Y-axis direction, the field curvature aberration in the Y-axis direction, and the method of correcting the aberration can be handled independently. In the present invention, instead of correcting field curvature aberration, we actively emphasize the point that by using the above hologram, it is possible to construct a lens system in which the focal point of the laser beam can be freely changed depending on the polarization angle of the laser beam. The information reading area is expanded by providing field curvature aberration suitable for setting the label information reading area of the optical scanning device above the reading surface.

FIG. 6 is an explanatory diagram of main parts of an embodiment of the present invention.

Similar to FIG. 1, this figure shows a part of the optical scanning device 10, in which a laser beam 5 is irradiated obliquely upward from a scanning point 1 to a reading window 3 via a reflecting mirror 2. . The difference from FIG. 1 is that the locus of the light convergence point according to the deflection angle of the laser scanning light, that is, the above-mentioned field curvature aberration, is set to match the reading surface. Therefore, ideally, the area C formed by the crossing lines should be the label information reading area. This is achieved by applying the previously proposed hologram creation method.
It is easy to obtain the desired slope or curvature within the required range of deflection angles. FIG. 7 is a comparison in which the solid line D shows the change in the imaging distance of a hologram created by the method already proposed for the lens system of the present invention, and the dotted line E shows the change in the imaging distance of the hologram according to the conventional example. .

The optical deflection angle is selected within the range of 200±100, and the dotted line E in the conventional example is selected so that the imaging distance is almost constant.
The solid line D of the present invention is intentionally sloped so that the lower end of the information reading area in FIG. It is enlarged from the corresponding area A. Next, an example of the lens system used in the present invention will be explained with reference to FIG. 8. In the figure, 6 is a disk, 7
A and 7b are hologram plates, 8 is a scanning surface (reading surface), and 9 is a scanning pattern.

Hologram plates 7a and 7b are embedded in the disk 6, respectively. , the hologram plate 7a has a scanning line 9a
Draw hologram plates 7b1, 7b2, 7b3...
... draws scanning lines 9b1, 9b2, 9b3...

Here, the scanning plane 8 is curved as shown, and corresponds to area C shown in FIG.

To explain the operation, the disk 6 is rotated in the direction of arrow A by a motor (not shown).

In this case, the hologram plate 7a first crosses the light beam 5a laterally. As a result, the focal point of the hologram plate 7a moves in the lateral direction, so the light beam moves in the lateral direction and the scanning line 9
Draw a. When the disk 6 further rotates, the go hologram 7b1 crosses the light beam 5b in the vertical direction.

As a result, the focal point of the hologram plate 7b1 moves vertically, and the light beam also moves vertically to draw a scanning line 9b1. Next, since the hologram plates 7b2 and 7b3 successively cross the light beam 5b, scanning lines 9b2 and 9b3 are drawn in the same manner.

The scanning pattern 9 is drawn as described above.

Here, as mentioned above, the hologram plates 7a and 7b, 7b
The focal lengths of 2, 7b3, . . . are curved according to the scanning plane 8. Therefore, it is possible to draw a scanning line along the scanning plane.

As explained above, according to the present invention, a hologram can be created such that the distance from the scanning point to the beam convergence point (imaging point) forms a predetermined slope curve within the range of the deflection angle of the laser scanning light. Accordingly, it is possible to effectively form an information reading area on the reading surface, expand the area, and improve the utilization rate.

Although a hologram is used as the lens system in the above embodiment, the present invention can also be applied to a combination of lens systems having similar functions.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional example, Fig. 2 is a diagram showing the FZP creation system, Figs. 3 and 4 are diagrams showing changes in imaging distance with respect to the central deflection angle when P is changed, Fig. 5 is a graph showing the relationship between the central deflection angle and the imaging distance variation rate, Fig. 6 is an explanatory diagram of the main part of the embodiment of the present invention, Fig. 7 is an explanatory diagram of the characteristics of the lens system,
FIG. 8 shows an example of a lens system used in the present invention, and in the figure,
1 is a scanning point, 2 is a reflecting mirror, 3 is a reading window, 5 is a laser scanning beam, and 10 is an optical scanning device.

Claims (1)

[Claims] 1. In an optical scanning device that projects laser scanning light from inside the device to read information using a laser beam, a spherical wave on a photoconductor interferes with a plane wave that is incident on the photoconductor at an angle other than perpendicular to the photoconductor. It is characterized by comprising a lens system that uses the created hologram and makes the imaging distance of the laser beam vary depending on the deflection angle of the laser beam that is deflected by the hologram by making the laser beam incident on the hologram. optical scanning device.