JP2011133973A - Focus movement method and device in bar code reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an easy-to-manufacture stable bar code reader with simple configuration, while significantly reducing cost, and to provide a method thereof. <P>SOLUTION: The bar code reader includes: a first convex lens, a second concave lens, and a third convex lens receiving light emitted from a light source such as a laser, having the same optical axis, and sequentially provided in an exit direction; and a lens drive mechanism for moving the first lens, and moving a focus while keeping a beam diameter constant. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a barcode reader, and more particularly, to a variable focus barcode reader and a reading method for focusing on a barcode position.

  In the case of an optical pickup such as a CD, the focus variable (adjustment) range may be on the order of μm, and the position of the CD to be read is almost constant, so there is a problem in moving the objective lens that collects parallel light up and down. Never do. In this case, only the optical aberration affects the diameter of the focused spot, and the change in magnification due to the movement of the objective lens hardly affects.

  When the height of an object changes by several tens of centimeters at high speed, it is difficult to move the lens up and down at high speed while ensuring a working distance (WD) so as not to contact the object. is there. In addition, it is necessary to consider the change in optical magnification that affects the diameter of the focused spot.

  The barcode reader is a device that reads a barcode by scanning the barcode with a laser beam and detecting laser light that is modulated and scattered and reflected in accordance with the density of the barcode. The laser beam is converged so as to have the required spot diameter on the barcode, but the focal depth is proportional to the beam spot diameter. Therefore, if the spot diameter is reduced to increase the resolution, the focal depth becomes shallower. The readable range will be reduced.

  Therefore, in a device that requires a reading depth, such as a distribution barcode reader, a variable focus method is used in which the distance from the device to the barcode is measured in advance to focus on the barcode position.

  If an attempt is made to change the focal point by several tens of centimeters with two lenses, the magnification changes and the diameter of the focused spot changes. Against this background, an apparatus disclosed in Patent Document 1 (Japanese Patent No. 2998289) has been devised as a method of changing the focal point while keeping the beam diameter constant with three lenses.

  The apparatus disclosed in Patent Document 1 employs a so-called Kepler-type variable-focus optical system composed of three convex lenses that propagate laser light with a Gaussian beam.

Factors that determine the performance of a bar code reader include:
・ Minimum bar code line width that can be read ・ Reading depth in the focal direction (height of bar code label affixed to luggage)
・ Scanning width in the horizontal direction (position of bar code label affixed to luggage)
・ Bar code rotation direction (rotation relative to the direction of automatic conveyance)
・ Conveying speed and so on.

  A particularly difficult task is to achieve both the minimum line width and the reading depth. In the case of a bar code reading scanner device using optical scanning, in order to maintain the reading performance with the minimum line width, the converging spot diameter must be kept below a certain value to ensure the necessary reading depth. Thus, only a reading depth of several tens of centimeters can be obtained with a beam diameter of several hundred μm. In the case of physical distribution, a reading depth of about 1 m is often required, and various methods and devices have been devised, such as a device having a focus adjustment function and a plurality of fixed-focus devices shifted in the focus direction. Yes.

  Although a device for changing the focal spot diameter and changing the focal point has been devised, it has the following problems. However, a complicated zoom lens that moves a plurality of lenses is not considered here because it is limited to an inexpensive method with a simple configuration.

(1) Issues in terms of the method of converging and condensing laser light as a Gaussian beam Conventionally, gas lasers such as He-Ne lasers have been used, but semiconductor lasers are being used for miniaturization and ease of maintenance. Has come to be used. However, semiconductor lasers require the selection of a semiconductor laser element because of its beam quality (divergence angle) variation and vertical and horizontal divergence angles, and a complicated combination and difficult adjustment of the lens that converts it into the desired beam. There was a problem that required.

  That is, there is a problem in that the number of parts is high and a highly accurate one is required, and the yield is also low, so the cost is high.

(2) Problem in terms of method of changing focus by combining convex lenses In the method of changing focus by moving only one of the three lens groups, an optical system is constructed with a practical size of around 100 mm. In this case, the Kepler type using only a convex lens as disclosed in Patent Document 1 has a small focal length of the constituent lenses.

  When the focal length of the lens is small, high manufacturing (polishing) accuracy is required for the lens to be used, and also for the mechanism that holds the lens, vibration that occurs when the lens moves when the focus is variable. Therefore, there is a problem that the production cost is high in order to guarantee the quality.

In addition, there is a problem that optical aberration is likely to occur, the aberration must be corrected using a plurality of lenses, and tolerance for environmental (temperature, vibration) changes is small.
Japanese Patent No. 2998289

  The optical system disclosed in Patent Document 1 is a Kepler type, and a lens with a short focal length must be used. For this reason, it is necessary to use a combination lens for aberration correction, but each lens requires high accuracy, and the cost is high.

  In addition, a complicated shaping optical system for converting an elliptical beam having different vertical and horizontal divergence angles into a perfect circle such as a semiconductor laser is required in the light source portion. Furthermore, the divergence angle of the semiconductor laser must be selected, which is also a factor that increases the cost.

  An object of the present invention is to realize a bar code reading apparatus and method that can be configured simply, can be easily manufactured, can realize a stable apparatus, and can greatly reduce costs.

The barcode reader of the present invention is
A first lens that is a convex lens, a second lens that is a concave lens, and a third lens that is a convex lens, which are incident on the light emitted from a light source such as a laser, have the same optical axis, and are sequentially provided in the emission direction;
It has a lens drive mechanism that moves the first lens to move the focal point while keeping the beam diameter constant.

The barcode reading method of the present invention includes:
A first lens that is a convex lens, a second lens that is a concave lens, and a third lens that is a convex lens, in which light emitted from a light source such as a laser is incident and have the same optical axis, are sequentially provided in the emission direction;
The focal point is moved while keeping the beam diameter constant by moving the first lens.

The effect of semiconductor laser beam quality variation can be eliminated by a method of condensing a laser beam with a uniform rectangular cross-section profile through a circular aperture without propagating the laser beam as a Gaussian beam.
-By using a Galilean zoom optical system including a concave lens, the lens focal length can be extended and the influence of manufacturing errors can be mitigated.
-Because of the galley type, the optical path length (unit size) can be shortened.
Similarly, since the focal length of each lens is long, the influence of the change in the focal length of the lens due to the environmental temperature or the like can be mitigated.
Similarly, since the focal length of each lens is long, the optical aberration can be reduced with a configuration of only a spherical single lens, not a lens combining a plurality of lenses.
・ The spot diameter can be easily adjusted by changing the aperture.
・ The focus position can be controlled without changing the focused spot diameter by moving only one lens.
(Condensation spot diameter can be kept constant even when the focus is changed over a long distance of about 1 m)
-For the above reasons, it is possible to achieve a simple configuration, easy manufacture, and a stable device can be realized. That is, the cost can be greatly reduced.

It is a block diagram which shows schematic structure of the optical system of the barcode reader by this invention. (1), (2) is a figure for demonstrating the structure of embodiment of this invention. (1), (2) is a figure for demonstrating the structure of embodiment of this invention. (1), (2) is a figure for demonstrating the structure of embodiment of this invention. It is a figure which shows the characteristic of the optical system in this invention. It is a figure which shows the characteristic of the optical system in this invention. It is a figure which shows the characteristic of the optical system in this invention. It is a figure which shows the characteristic of the optical system in this invention.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of an optical system of a barcode reader according to the present invention.

  This embodiment includes an auto power control (APC) circuit 1, a small laser light source (LD) 2, a collimating lens 3, a lens 5-7, and a lens driving mechanism 8 that moves the lens 5.

  For the small laser light source 2 such as a semiconductor laser, a red laser having a wavelength of about 635 nm is used. However, as long as an object such as a bar code can be read, a laser with another wavelength can be substituted.

  The laser light source 2 is maintained at a constant light output by the auto power control circuit 1. The output beam 10, which is a divergent laser beam emitted from the laser light source 2, is converted into a parallel beam 11 by the collimator lens 3, and the central portion of the beam is cut out by the aperture 4 disposed immediately thereafter.

  The collimating lens 3 may be a spherical plano-convex lens if there is no problem with spherical aberration, and it may be a combined lens of about two even when spherical aberration affects. The parallel light 11 exiting the aperture 4 is condensed by the first convex lens 5 held by the drive mechanism 8 and converted into divergent light by the second concave lens 6 thereafter.

  The first convex lens 5 may be a spherical plano-convex lens, and the second concave lens 6 may be a spherical biconcave lens. The lens driving mechanism 8 is composed of a mechanism unit capable of positioning such as a stepping motor. Then, the light is condensed again by the third convex lens 7 to form a condensed spot 12. The third convex lens may also be a spherical plano-convex lens.

  In accordance with height information from an external height sensor (not shown), the driving mechanism 8 shown in FIG. 1 moves the first convex lens 5 in the light traveling direction, and the synthetic lens system with the second concave lens 6 Change focal length and principal point. Due to this change, the position of the focused spot 12 changes, and the focused spot diameter is kept constant.

  As an advantage of the configuration of the present embodiment, the size of the focused spot 12 can be adjusted by simply changing the hole diameter of the aperture 4 without requiring adjustment with a complicated lens.

  Hereinafter, a configuration of the present embodiment for solving the above-described problems (1) and (2) will be described in detail.

(1) Concerning the problem of the method of condensing laser light as a Gaussian beam In this embodiment, the laser light does not propagate as a Gaussian beam. The influence of variation in the beam quality of the semiconductor laser is eliminated by a method in which the central portion of the Gaussian beam is cut out by a circular aperture aperture and condensed as a rectangular beam having a uniform cross section. As described above, in the present embodiment, the focused spot does not depend on the beam quality of the light source, and is determined by the aperture diameter, so that stable quality can be ensured without element selection.

  In addition, since it is not necessary to use a cylindrical lens that corrects the difference between the vertical and horizontal divergence angles of the semiconductor laser, it can be configured with a single lens, and adjustment is easy. These effects can reduce the manufacturing cost.

(2) Concerning the problem of the method of changing the focal point by combining the convex lenses When considering the same size as the convex lens configuration, the focal length of the lens can be increased by using a galley type optical system including a concave lens. . As a result, the optical aberration is alleviated, and it is possible to reduce the accuracy by using only a spherical single lens to reduce the accuracy. In addition, it is possible to secure tolerance for environmental (temperature, vibration) changes.

  In addition, Patent Document 1 also describes a concave lens configuration. The first and second lenses are concave lenses, the third lens is a convex lens, and the second lens is moved. However, a solution with a constant beam diameter cannot be found. There is no detailed description.

  In the present invention, the first lens is composed of a convex lens, the second lens is composed of a concave lens, the third lens is composed of a convex lens, and the method of moving the first lens allows the beam diameter to be constant. is there.

  First, consider the third lens. As shown in FIG. 2, the focal length of the third lens 7 is f3, the object distance in the case of the short distance (hereinafter referred to as the near point) in FIG. 2A is a1, and the image distance is b1. In addition, the object distance in the case of a far distance (hereinafter referred to as a far point) in FIG. 2B is a2, and the image distance is b2.

From the imaging formula,
(Near) 1 / f3 = 1 / a1 + 1 / b1
(Far point) 1 / f3 = 1 / a2 + 1 / b2
The imaging magnification m is
(Near) m1 = b1 / a1
(Far point) m2 = b2 / a2
If the distances b1 and b2 for which the focal point is desired to be changed and the focal length f3 of the third lens 7 are set, the distances a1 and a2 of the object plane 20 and the imaging magnification can be obtained.

If the diameter of the focused spot 12 on the image plane 21 is set, the spot radii w1 and w2 on the object plane 20 can be obtained from the imaging magnification. When the condensing spot radius of the image plane 21 is ω,
(Nearest point) w1 = ω / m1
(Far point) w2 = ω / m2
That is, the spot diameters w1 and w2 may be formed at the distances a1 and a2 from the third lens 7 by the first and second lenses. If the spots w1 and w2 formed here are real images, they become Kepler type, and if they are virtual images, they become Galilean type.

  The embodiment shown in FIG. 1 is a galley type of the first lens movement described above.

  Next, the first lens 5 and the second lens 6 will be considered. It is assumed that the parallel beam 11 enters the first lens from the aperture 4 in FIG. If the parallel beam 11 is ideal light with uniform intensity (amplitude) and the same phase, the spot collected by the aberration lens having the focal length F becomes an Airy disk, and the radius r is given by the following equation.

r = 0.41 × λF / r0
λ is the optical wavelength and r0 is the incident beam radius. Now, if the light wavelength λ and the incident beam radius r0 are set, the condensing spot radius r may be set to the aforementioned w1 and w2, so that the combined focal lengths F1 (near point) and F2 (far point) of the first lens and the second lens are set. Point).

As shown in FIGS. 3 and 4, the combined focal lengths F1 and F2 are set such that the focal length of the first lens 5 is f1, the focal length of the second lens 6 is f2, and the first lens 5 and the second lens 6 are combined. When the distance of d1 (near point) and d2 (far point) is given, the formula of the synthetic focus (near point) F1 = f1 × f2 / (f1 + f2-d1)
(Far point) F2 = f1 * f2 / (f1 + f2-d2)
The distance α from the second principal point H2 ′ of the second lens to the focal point of the composite lens system is
(Near) α1 = f2 (f1−d1) / (f1 + f2−d1)
(Far point) α2 = f2 (f1-d2) / (f1 + f2-d2)
Given in. Here, it can be selected which of the first lens 5 and the second lens 6 is moved. FIG. 3 shows a case where the first lens is moved, and FIG. 4 shows a case where the second lens is moved.

Assuming the lens movement amount z, when moving the first lens, FIG.
z = d1-d2
Δ = α2−α1
When the second lens is moved from FIG.
z = d1-d2
Δ = (d2 + α2) − (d1 + α1)
The relationship holds. Since the shift amount Δ of the position to be imaged is already obtained by the third lens, when the lens movement amount z is set, f1, f2, d1, and d2 are obtained from the above relationship.

Next, specific calculation results are shown.
Wavelength λ = 635 nm, image distance b1 = 1000 mm, b2 = 2000 mm,
Condensing spot radius ω = 100 μm, third lens focal length f3 = 60 mm,
It is assumed that the lens moving distance z = 10 mm and the incident beam radius (aperture radius) r0 = 1.0 mm.

  However, this time, it is assumed that the principal point exists inside the lens without considering a complicated lens in which the principal point of the lens comes out of the lens. That is, the distances d1 and d2 between the principal points of the first lens and the second lens are positive values. When calculating under such conditions, there are three types of solutions as shown in FIG.

  That is, there are a Kepler type and a Galilean type as moving the first lens, and a Kepler type as moving the second lens (negative focal length indicates a concave lens).

  However, when the lens interval is changed, the first lens moving Kepler type is as shown in FIG. 6, the first lens Galilean type is as shown in FIG. 7, and the second lens Kepler type is as shown in FIG. It can be seen that the second lens movement type is established only at the nearest point and the farthest point and does not satisfy the performance in the middle.

  Therefore, as the three-beam fixed focal length variable optical system, only the Kepler type or the Galilean type of the first lens movement is a solution. Comparing the two in FIG. 5, it can be seen that the minimum focal length is the same, but the total distance is small for the galley type. Therefore, when an optical system of the same size is configured, the focal length of the galley type is longer.

Other Embodiments If the aperture 4 is a mechanism that can automatically change the hole diameter, not only the focal position adjustment but also the beam diameter can be controlled.

DESCRIPTION OF SYMBOLS 1 Auto power control circuit 2 Small laser light source 3 Collimate lens 5-7 Lens 8 Lens drive mechanism

Claims (6)

In the barcode reader,
A first lens that is a convex lens, a second lens that is a concave lens, and a third lens that is a convex lens, which are incident on the light emitted from a light source such as a laser, have the same optical axis, and are sequentially provided in the emission direction;
A bar code reader having a lens driving mechanism that moves the first lens to move the focal point while keeping the beam diameter constant. The barcode reader according to claim 1, wherein
A barcode having a circular aperture provided between the light source and the first lens and having a circular aperture corresponding to a portion of the light emitted from the light source that can be regarded as having a uniform light intensity. Reader. The barcode reader according to claim 1 or 2,
A barcode reader having a spherical single lens for suppressing aberration. A barcode reading method with variable focus performed by a barcode reader,
A first lens that is a convex lens, a second lens that is a concave lens, and a third lens that is a convex lens, in which light emitted from a light source such as a laser is incident and have the same optical axis, are sequentially provided in the emission direction;
A bar code reading method, wherein the focal point is moved while keeping the beam diameter constant by moving the first lens. The barcode reading method according to claim 4, wherein
Provided between the light source and the first lens is a circular aperture aperture having a circular aperture corresponding to a portion of the light emitted from the light source that can be regarded as having a uniform light intensity, and the light emitted from the third lens. The bar code reading method is characterized in that the diameter of the condensing spot is determined by the size of the circular aperture without the beam divergence angle being affected by manufacturing variations. The barcode reading method according to claim 4 or 5,
A bar code reading method comprising a spherical single lens for suppressing aberration.

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