JPH0283789A - Light source unit for bar code reader - Google Patents

Abstract

PURPOSE:To decrease the number of parts, to miniaturize the title device, and to make the device efficient by making the major axis direction of an outgoing laser beam coincide with a bar direction and making the magnitude of a light spot into a fixed value or below. CONSTITUTION:Exit light from a laser diode 1 is made into the flux of parallel light rays in collimator lenses 2a and 2b, emitted through an aperture 4 while the flux still has anisotropy, and forms a light spot 8 on a bar code surface 6 by a condenser lens 5. The light spot 8 has an elliptic shape, a major axis W1 of the spot 8 is made to coincide with the bar direction, a minor axis W2 is made shorter than any of the interval between a bar and another bar and a bar minimum width d2, and the spot 8 reads bar code information. Further, the bar code information can be read even when a luminous flux converting prism is omitted by making the numerical aperture of the lens 5 into 0.00248 or below and making the minor axis W2 of the spot 8 into 0.2mm or shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light source unit for a barcode reader using a laser diode.

``Prior Art J'' There was a conventional device of this type that was not shown in Fig. 3. Fig. 3 is a sectional view schematically showing the configuration of a conventional light source unit for a barcode reader. ) is a laser beam source serving as a light source, (2a) and (2b) are collimator lenses that convert the laser beam emitted from the laser beam source 1) into a parallel beam, and (3a) and (3b) are beams with a cross section or ellipse. (4) is the aperture, (5) is the condensing lens, (6) is the barcode surface, and <7) is the barcode surface (6).
The bar drawn in (8) is a light spot on barcode surface F.

Next, the operation will be explained. Laser diode as a light source
The laser beam emitted from 1 to (1) uses a window structure to reduce light absorption at the end face in order to prevent the end face from being destroyed by optical energy, which is a factor that determines the output limit for high output. Countermeasures have been taken, such as increasing the beam diameter and lowering the optical energy density. As a result, in the high-power semiconductor laser, as shown in FIG. 3, the horizontal spread angle is smaller than the vertical spread angle, and the ellipticity of the laser beam is about 3=1. This property is referred to as anisotropy in this specification.

The laser beam emitted from the laser diode (1) is a diffused light with anisotropy, and this laser beam is converted into a parallel beam by the collimator lenses (2a>, (2b), and then converted into a beam for beam shaping. Conversion prism (3a), (3b
), the beam is shaped into a beam with a circular cross section (referred to as isotropic), and is then emitted through the aperture (4). The laser beam emitted from the aperture (4>) forms a light spot (8) on the barcode surface (6) by a condensing lens (5).

By scanning the bar (7) drawn on the barcode surface (6) with this light spot (8), barcode information is read from the difference in reflected light intensity.

[Problem to be solved by the invention] In the conventional light source unit for a barcode reader, beam shaping is performed using a light flux conversion prism as described above, which increases the number of parts and is disadvantageous in terms of manufacturing process and cost. becomes. In addition, there are problems such as light loss caused by the luminous flux conversion brism, resulting in poor efficiency.

The present invention has been made to solve this problem, and aims to provide a light source unit 1 for a barcode reader that is inexpensive, easy to manufacture, compact, and efficient.

[Means for Solving the Problems] The barcode reader lunar light source unit 1~ according to the present invention aligns the major axis direction of an elliptical laser beam emitted from a laser diode with a bar direction, so that the laser beam can read a barcode. The numerical aperture of the condenser lens was adjusted so that the short axis of the light spot formed on the surface was equal to or less than a predetermined value.

1 Effect] In the present invention, the major axis direction of the elliptical laser beam emitted from the laser diode is aligned with the bar direction, and the minor axis size of the light spot formed by the laser beam on the barcode surface is set to a predetermined value. Since the numerical aperture of the condenser lens is adjusted as follows, it becomes possible to omit the light flux conversion prism.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing the structure of a light source unit for a barcode reader according to the present invention, and the same reference numerals as in FIG. 3 indicate the same or corresponding parts.

Next, the operation will be explained. The laser beam emitted from the laser diode <1) is a diffused light with anisotropy as described above, and this laser beam is converted into a parallel beam bundle by the collimator lenses (2a) and (2b), and is anisotropic. The light is emitted through the aperture (4) while holding it, and the light spot (8) is focused on the barcode surface (6) by the condenser lens (5).
) to form.

FIG. 2 is a diagram for explaining the size and positional relationship between the light spot (8) and the bar (7) formed on the barcode surface (6), and the same reference numerals as in FIG. 1 are used in the figure. indicates the same part, (dl) is the interval between bars, (d2) is the minimum bar width, (wl) is the long axis of the light spot (8), (
w2) indicates the size of the short axis of the light spot (8).

As shown in FIG. 2, since the device according to the present invention does not have a light flux conversion prism, the light spot (8) is elliptical, and in order to read barcode information in such an elliptical light spot (8), The light spot (8
) is aligned with the direction of bar, and the short axis (w2)
It is necessary to make it shorter (0.2 mm or less) than both the distance between bars and the minimum width (d2) of the bars. The diameter of the light spot (8) is determined by the numerical aperture (NA) of the condensing lens 5), so NA = n sin θ <n; refractive index of the medium, which is air in this case, ≠ 1; θ; aperture angle) and w=2λ/πθ (w: diameter of the light spot, λ: wavelength of the light), if the short axis (w2) of the light spot (8) is set to 2 mm, the wavelength of the laser light is 780 mm. If nm, N
A=sin (2X 0.78X 10'/y
r
'/yr X O,0024,8"≠±40.4m
m.

Also, if the short axis (w2) of the optical spot 8) is set as a sail of 2 mm, its long axis (wl) will be approximately 0.56 mm, and the numerical aperture (NAI) at this time is determined as (NAI)-sin (2X 0.78X 10
'/πX sail56)≠0.000887, and the depth of focus (ΔZ) at this time is ΔZ;
'/πX0.0008872≠±316mm. That is, the short axis (w2) of the light spot (8) is 0.2
To be mm, the numerical aperture (NAI) is 0.0024
It must be 8 or less, and the short diameter (w2) must be 2 mm.
Since the major axis (Wl) is approximately 0.56 mm, the numerical aperture (NA2) in this case needs to be 0.000887 or more, so the numerical aperture of the condenser lens (5) is set to 0.0024.
If it is 8, both the short axis (W2) and the long axis (wl) can be sufficiently covered.

Further, the depth of focus is ±40.4 mm in the minor axis direction and ±316 mm in the major axis direction, so there is no problem.

With the above, the numerical aperture of the condenser lens (5) is set to 0.0024.
8 or less, and the short axis (w2) of the light spot (8) is set to 0.
If it is set to 2 mm or less, barcode information can be read in the same manner as in the past even if the light flux conversion prism is omitted.

[Effects of the Invention] As explained above, the present invention makes the long axis direction of the elliptical laser beam emitted from the laser diode coincide with the bar direction, and the short axis of the light spot formed by the laser beam on the barcode surface is adjusted. Since we decided to keep the size below a certain value determined by the numerical aperture of the condenser lens, we can omit the beam conversion prism and reduce the number of parts, making it possible to easily manufacture a compact and efficient device at low cost. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of the device according to the present invention, and FIG.
FIG. 3 is a diagram showing the operation of the present invention, and FIG. 3 is a sectional view showing the configuration of a conventional device. <1) is a laser diode, (2a) and (2b) are collimator lenses, (4) is an aperture, (5) is a condenser lens, (6> is a barcode surface, (7) is a bar, and (8) is a Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] A laser diode serving as a light source, a collimator lens that converts a laser beam emitted from the laser diode into a parallel beam, and a laser beam emitted from the collimator lens through an aperture to a barcode surface. In a light source unit for a barcode reader having a condensing lens for condensing light to form a light spot, the major axis direction of the elliptical laser beam emitted from the laser diode is aligned with the direction of the bar drawn on the barcode surface. means for making the diameter of the elliptical light spot formed by the laser beam on the barcode surface in the short axis direction shorter than the interval between bars drawn on the barcode surface and the minimum width of the bars; A light source unit for a barcode reader, comprising: means for adjusting the numerical aperture of the condensing lens.