JP2613390B2 - Scanning optical reader - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial Application Field) The present invention is to accurately scan information of a scanning target, in particular, bar code pattern information provided on the scanning target by scanning the scanning target. The present invention relates to a scanning optical reading device suitable for reading a document.

(Prior Art) Conventionally, a laser beam of a semiconductor laser emitted through a light projecting lens is deflected and projected on a scanning target, and the emitted laser beam reflected by the scanning target is received as a return beam. Then, there is a scanning optical reading device for reading information of the object to be scanned.

FIG. 9 shows a bar code reader 1 as an example of the scanning optical reading apparatus. The bar code reader 1 is a gun type, and a semiconductor laser 3 and a light projecting lens 4 are provided in a gun housing 2 thereof. And an optical system generally constituted by a polygon mirror 5, a condenser lens 6, and a photoelectric conversion element 7.

This conventional bar code reader 1 reads bar code pattern information in which black band codes 8 'and white band codes 8 "provided on a scanning surface of a scanning target 8 are alternately arranged in a strip shape. The laser beam P emitted from the semiconductor laser 3 is reflected and deflected by the polygon mirror 5 toward the object 8 to be scanned, and the direction crossing the extending direction of the band codes 8 ', 8 "is set as the scanning direction X. The object 8 is scanned, and the emission laser beam P reflected by each of the band codes 8 ', 8 "is focused as a return beam P' by the condensing lens 6 to form an image on the photoelectric conversion element 7, thereby forming a black band code. The bar code pattern information is read by detecting the light amount value of the return beam P 'caused by the width (thickness) of each of the white band code 8' and the white band code 8 "(see the waveform diagram in FIG. 4 described later). It has become.

(Problems to be Solved by the Invention) However, the emission laser beam P emitted from the light projecting lens 4 is not focused on one point in terms of wave optics, and is emitted as shown in FIG. The laser beam P has a beam waist 9. The beam diameter Φ at the beam waist 9 of the emitted laser beam P emitted from the light projecting lens 4 is obtained by dividing the distance 1 from the light projecting lens 4 to the beam waist 9 by the effective aperture D of the light projecting lens 4. When the proportional coefficients are α and λ, there is a relational expression of Φ = α · λ · 1 / D (1). Here, the proportional coefficient α is an amount related to the amplitude distribution of the emitted laser beam P on the pupil of the light projecting lens 4, and the proportional coefficient λ is an amount related to the wavelength of the emitted laser beam P.

The beam diameter 2ω of the emission laser beam P increases quadratically in proportion to the distance Z from the beam waist 9, and the beam diameter 2ω of the object 8 to be scanned is equal to the beam diameter Φ at the beam waist 9 and the beam waist 9. It is determined by the distance Z from 9.

The beam diameter 2ω is directly related to the reading accuracy of the scanning optical reading device, and as shown in FIG. 11, the beam diameter 2ω is smaller than the minimum interval t between adjacent band patterns 8 ′ and 8 ″. In some cases, the barcode pattern information can be read accurately, but the beam diameter 2ω is larger than the minimum interval t, and the emitted laser beam P is independent across a plurality of adjacent band patterns 8 ′, 8 ″. In the case where the irradiation is performed without any data, it is difficult to easily perform accurate reading.

That is, when the scanning surface of the scanning target 8 exists within the reading depth d defined by the beam diameter 2ω ′ corresponding to the minimum interval t, the optical system is configured to be able to read the barcode pattern information. As
Since the emission laser beam P spreads at the beam waist 9 as a boundary, when the scanning surface of the object 8 to be scanned is located farther than the reading depth d, the emission laser beam P emits a plurality of band patterns 8 ′, 8. ″ Straddling each band pattern 8 ′,
8 ″ cannot be read alone, and as a result, accurate reading of barcode pattern information cannot be easily performed.

In order to accurately read the barcode pattern information on the scanning surface of the scanning target 8 regardless of whether the scanning target 8 is located at a distance or a distance, the distance from the light projecting lens 4 to the beam waist 9 is high. It is conceivable to configure an optical system so as to be able to change. For example, when reading barcode pattern information of a distant object 8 to be scanned,
The beam waist 9 of the emitted laser beam P is changed by some means so as to be formed at a distant place.
Then, as shown in FIG. 12, the beam diameter Φ at the beam waist 9 becomes larger than when the beam waist 9 is formed closer, the reading depth d becomes longer, and the spread angle θ of the emitted laser beam P becomes larger. Is small, it is easy to accurately read information on the distant object 8 to be scanned.

By the way, as is apparent from the equation (1), assuming that the effective aperture D of the light projecting lens 4 is constant, the beam diameter Φ at the beam waist 9 of the emitted laser beam P is from the light projecting lens 4 to the beam waist 9. Is proportional to the distance 1. Further, as the distance from the beam waist 9 increases, the beam diameter of the emission laser beam P increases quadratically. FIG. 13 shows how the beam diameter changes near the beam waist 9 when the position of the beam waist 9 is changed.
This will be described with reference to FIGS.

FIG. 13 shows the nose as the exit end of the gun housing 2 at 40 mm from the nose.
The beam diameter Φ at the beam waist 9 at the position
μm indicates a change in beam diameter near the beam waist 9 when the position of the beam waist 9 is changed.
The figure shows the change in beam diameter near the beam waist 9 when the beam diameter Φ at the beam waist 9 at a position 40 mm from the nose is changed by changing the beam waist 9 to 190 μm and the position of the beam waist 9. When the beam diameter Φ is large, the inclination of the straight line indicating the relationship between the beam diameter Φ and the change in the position of the beam waist 9 increases. The slope is
This corresponds to the proportional coefficient α in the above equation (1). If the proportional coefficient α is small, it becomes easy to accurately read the farther barcode pattern information.

By the way, as is well known, the semiconductor laser 3
The divergence angle K of the emitted laser beam P is different between the direction R1 parallel to 3a and the direction R2 perpendicular to the bonding surface 3a (see FIG. 15), and the direction R1 parallel to the bonding surface 3a and the bonding surface 3a are different. The amplitude distribution differs between the vertical direction R2 and the vertical direction R2 as shown in FIG.

The proportional coefficient α is an amount related to the amplitude distribution, and the semiconductor laser 3 is arranged so that the major axis direction in which the divergence angle K of the emission laser beam P is large is parallel to the scanning direction. Is preferable because it can be reduced.

That is, in the conventional barcode reader 1, in order to be able to read both barcode pattern information of a fine standard that exists near and barcode pattern information of a coarse standard that exists far, a beam waist is used. The beam depth is increased at the expense of the beam diameter of the beam to some extent, but if the position of the beam waist is changed, if the barcode pattern information is nearby, the beam waist is replaced by the barcode pattern. When the bar code pattern information is located far away, the beam waist can be formed far away in accordance with the bar code pattern information. It is preferable that the beam diameter of the beam waist be narrowed as much as possible without paying the following.

Further, when the semiconductor laser 3 is arranged so that the larger the spread angle θ is in the scanning direction X, even if the spread angle varies due to the individual difference of the semiconductor laser 3, the light projecting lens as shown in FIG. The change of the exit laser beam P incident on the scanning direction X is relatively small, and the beam diameter 2 in the scanning direction X is small.
When the semiconductor laser 3 is arranged such that the fluctuation of ω is small, but the short axis of the small divergence angle K is parallel to the scanning direction X, the variation of the divergence angle K based on the individual difference of the semiconductor laser 3 causes the variation shown in FIG. As shown, the change of the emission laser beam P incident on the light projecting lens 4 becomes relatively large, and the beam diameter in the scanning direction X fluctuates relatively largely. It is desirable to arrange the semiconductor lasers 3 such that

SUMMARY OF THE INVENTION (Means for Solving the Problems) In order to minimize the beam diameter at the beam waist and to suppress the fluctuation of the beam diameter in the scanning direction due to the variation of the spread angle, the present invention provides a semiconductor laser. Are arranged so that the direction in which the spread angle of the emitted laser beam is large is the scanning direction of the object to be scanned.

(Embodiment) An embodiment in which the scanning optical reading apparatus according to the present invention is applied to a gun-type scanning barcode reader will be described below with reference to the drawings.

1 to 5 are views showing a gun-type scanning barcode reader according to a first embodiment. FIG. 1 shows the arrangement of optical members used in the can-type scanning barcode reader. In FIG. 1, reference numeral 11 denotes a base, and the base 11 has the structure shown in the prior art (see FIG. 8).
A coreless motor 12 is provided at a position corresponding to the grip portion 2a of the gun housing 2. A buffer plate 14 is attached to the coreless motor 12 with screws 13, 13. The coreless motor 12 is attached to the base 11 together with the buffer plate 14 using a mounting plate 15 and screws 16. This core race motor
12 is driven when a trigger (not shown) is pulled.

A pulley 17 is attached to the output shaft 12a of the coreless motor 12. One side of a belt 18 is stretched over the pulley 17, and the other side of the belt 18 is stretched over a flywheel 19. The flywheel 19 is fixed to a lower part of a rotating shaft 20 rotatably held on the base 11, and a polygon mirror 5 is mounted on the upper part of the rotating shaft 20. The polygon mirror 5 is composed of a pulley gear body 17, a belt The rotation of the coreless motor 12 is transmitted via a flywheel 19 and rotates.

On the upper side of the base 11, a light receiving unit 21 and a light emitting unit 22 are provided. The light receiving unit 21 is a holding cylinder that holds the photoelectric conversion element 7
23 and a holding cylinder 24 for holding the condenser lens 6.
Reference numeral 20 denotes a holding tube 25 for holding the semiconductor laser 3 and a lens barrel 26 of the light projecting lens 4. The holding tubes 24 and 25 are mounting members
Mounted on 27. The holding cylinder 24 is provided with a coreless bearing 28, and the coreless bearing 28 includes
The rotation holding member 29 is fitted. The rotation holding member 29
2 is formed in a ring shape as shown in FIG.
A gear portion 31 meshing with a gear portion 17b formed on the outer periphery of the pulley 17 is formed on the outer peripheral portion. The rotation holding member 29 is rotated synchronously with the polygon mirror 5 by the rotation of the pulley 17.

The rotation holding member 29 has a connecting portion 29a for connecting the outer peripheral portion and the central portion, and has a pair of semicircular openings 29b. A semi-circular parallel flat plate 32 is attached to one of the pair of semi-circular openings 29b. Parallel plane plate
The glass plate 32 is made of, for example, a synthetic resin, and the plane-parallel plate 32 is located on the emission side of the light projecting lens 4 in this embodiment. The parallel plane plate 32 is rotated by the rotation of the rotation holding member 29 to emit the emitted laser beam P.
Is periodically advanced to the optical path M of this parallel flat plate.
When 32 enters the optical path M of the emission laser beam P, the third
As schematically shown in the figure, the refractive index n of the parallel flat plate 32
And its thickness k, the apparent optical distance on the exit side changes by k (1 / n-1).
The beam waist 9 'moves farther from the light projecting lens 4 than the position of the beam waist 9 when the beam 2 is retracted from the optical path M.

Therefore, the plane-parallel plate 32 functions as a beam waist position changing optical member for changing the position of the beam waist 9 with respect to the light projecting lens 4, and the rotation holding member 29 uses the beam waist position changing optical member as the emission laser beam P.
Functioning as a switching means for switching between a position at which the laser beam P enters the optical path M and a position at which the emitted laser beam P retracts from the optical path M. N is the number of reflection surfaces 5a of the polygon mirror 5.
Assuming that the rotation holding member 29 makes one rotation for one rotation of the polygon mirror 5, the scanning target 8 is moved N / 2 times each time the plane parallel plate 32 traverses the optical path M of the emission laser beam P once. Will be scanned.

That is, during the half rotation of the polygon mirror 5, the parallel plane plate 32 is at the retracted position from the optical path M. At this time, if the barcode reader 1 is pointed at the scanning target 8 located nearby, N / 2 As shown in FIG. 4, a scanning signal is obtained as a result of the scanning operation, and only the noise NS is obtained even when the scanning target 8 is located far away. During the half rotation, the parallel plane plate 32 is at the entrance position into the optical path M, and at this time, if the bar code reader 1 is pointed at the distant scanning target 8, scanning is performed N / 2 times. Thus, a read signal S is obtained, and only the noise NS can be obtained even when the read signal S is directed toward the scanning target 8 existing in the vicinity.

The semiconductor laser 3 is arranged such that the long axis direction where the divergence angle K of the emitted laser beam P is large is the same as the scanning direction X. Furthermore, the emission laser beam P
The beam diameter in the direction along the scanning direction X is greatly reduced by the light projecting lens 4. That is, the light projecting lens 4
5, the elliptical long axis L of the spot 10 of the emission laser beam P imaged on the scanning surface of the object 8 to be scanned, as shown in FIG.
Converges the emission laser beam P so as to have an elliptical shape intersecting the scanning direction X, whereby the black band code 8 ′ or 8 ′ even if the interval between the band codes 8 ′ and 8 ″ provided on the scanned object 8 is narrow. Bar code pattern information can be read without the disadvantage that the white band code 8 ″ cannot be read independently (it remains straddled). It is preferable that the rotation holding member 29 is arranged so that the direction in which the elliptical long axis L of the spot 10 extends extends through the rotation center O of the rotation holding member 29.

FIG. 6 is a view showing a first modification of the rotation holding member 29 according to the present invention. In this embodiment, the rotation holding member 29 itself has a semi-ring shape, and is parallel to the opening 29b.
2, and the gear 31 is provided on the outer periphery of the central portion.

FIG. 7 is a view showing a second modification of the rotation holding member 29 according to the present invention. In this embodiment, three fan-shaped openings 29b are formed in the rotation holding member 29, and two of them are formed. Opening 29b
And parallel flat plates 32 and 32 'having different refractive indices n are stuck to each other. According to this embodiment, the position of the beam waist 9 with respect to the light projecting lens 4 can be changed in three stages. In addition, instead of making the refractive index n different, the thickness k may be made different from each other, or both the refractive index n and the thickness k may be made different from each other. The number of parallel flat plates 32 to be attached to the holding member 29 is not limited to three, and may be more than three.

The rotation holding member 29 shown in FIGS.
In this case, as shown in FIG. 5, the optical power of the light projecting lens 4 is such that the elliptical long axis L of the spot 10 of the emission laser beam P imaged on the scanning surface of the scanning target 8 is in the scanning direction X.
Is set so as to converge the emission laser beam P so as to exhibit an elliptical shape intersecting with.

FIG. 8 shows a second example of the scanning optical reader according to the present invention.
In the embodiment, a cylindrical lens 44 as a beam waist position changing optical member is provided on the emission side of a laser beam P with respect to the light projecting lens 4 so as to be able to advance and retreat in an optical path M of the emitted laser beam P. When the cylindrical lens 44 enters the optical path M of the emitted laser beam P, the position of the beam waist 9 moves to a side closer to the light projecting lens 4. Here, if the cylindrical lens 44 is arranged so that the direction having the power of the cylindrical lens 44 is in the same direction as the scanning direction X in which the emitted laser beam P is deflected, the bar code of the scanning target 8 existing in the vicinity can be obtained. The reading of the pattern information can be performed more accurately.

In the second embodiment, the cylindrical lens 44 is used as the beam waist position changing optical member. However, a concave lens can be used as the beam waist position changing optical member. If the focal length f of the concave lens is appropriately selected, the position of the beam waist 9 can be moved farther from the light projecting lens 4. For example, if the focal length f of the light projecting lens 4 is set to 4.5 mm and the semiconductor laser 3 is placed at a position of 4.639 mm from the light projecting lens 4, the beam waist 9 from the light projecting lens 4 when the concave lens is in the retracted position. Is 1 = 150 mm, but using f = −375 mm, 1 = 250 mm. Also, a convex lens can be used. When this convex lens is used, when it enters the optical path M, the position of the distant beam waist 9 can be changed to the near side.

As described above, in the scanning optical reading apparatus according to the present invention, the semiconductor laser is arranged such that the direction in which the spread angle of the emitted laser beam is large is the scanning direction of the object to be scanned, and the polygon mirror is A rotation holding member that rotates around a rotation axis along the optical path of the light projecting system in synchronization with the rotation of the light projection system, and holds a beam waist position changing optical member in a predetermined circumferential angle region of the rotation holding member, thereby forming a beam. The waist position changing optical member is configured to be switched between the entry position into the optical path of the light projecting system and the retracted position from the optical path of the light projecting system by rotation of the rotation holding member, so that the beam diameter at the beam waist can be reduced. As small as possible, it is possible to suppress the fluctuation of the beam diameter in the scanning direction due to the variation of the spread angle, and it is possible to make the beam shape on the object to be scanned elliptical, The bar code pattern information can be read even more accurately.

[Brief description of the drawings]

FIGS. 1 to 5 are views showing a first embodiment of a gun-type scanning barcode reader according to the present invention. FIG. 1 is an optical member used in the gun-type scanning barcode reader. FIG. 2 is a plan view of the rotation holding member shown in FIG. 1, FIG. 3 is an optical path diagram schematically showing the action of the parallel flat plate shown in FIG. 1, and FIG. FIG. 5 is a view showing an output state of a read signal of the scanning bar code reader, FIG. 5 is a plan view showing a beam shape on a bar code pattern, and FIG. 6 is a view showing a state of the rotation holding member shown in FIG. FIG. 7 is a plan view showing a second modification of the rotation holding member shown in FIG. 2, and FIG. 8 is a view showing a second embodiment of the scanning bar code reader. FIG. 8 shows a cylindrical lens as an optical member for changing the beam waist position. FIG. 9 to FIG. 18 are views for explaining a conventional gun-type scanning barcode reader, and FIG. 9 is a view of the scanning barcode reader. FIG. 10 is a diagram showing a schematic configuration, FIG. 10 is an optical diagram for schematically explaining a beam waist based on a light projecting lens of the scanning bar code reader, and FIG. 11 is an explanatory diagram showing an illumination state of the scanning target. FIG. 12 is an optical diagram for schematically explaining a state in which the beam waist formed by the light projecting lens of the scanning bar code reader is farther away, and FIGS. 13 and 14 are light projecting diagrams. A graph showing how the beam diameter changes at the beam waist when the distance from the lens to the beam waist is changed.
FIG. 15 is a diagram for explaining the divergence angle of the emitted laser beam emitted from the semiconductor laser, and FIG. 16 is a graph for explaining the relationship between the divergence angle and the amplitude distribution.
FIG. 17 and FIG. 18 explain that it is desirable to arrange the semiconductor laser so that the long axis direction having a large divergence angle of the emission laser beam becomes the scanning direction in order to suppress the fluctuation of the beam diameter in the scanning direction. FIG. DESCRIPTION OF SYMBOLS 1 ... Bar code reader 3 ... Semiconductor laser 4 ... Projection lens 5 ... Polygon mirror 6 ... Condensing lens 7 ... Photoelectric conversion element 9 ... Beam waist 12 ... Coreless motor 17 ... Pulley gear body 29 …… Rotation holding member 32 …… Parallel flat plate K …… Spread angle

Claims (1)

(57) [Claims] A projection mirror for deflecting an emission laser beam of a semiconductor laser emitted through a projection lens by a polygon mirror and projecting the deflection laser beam to an object to be scanned; In a scanning optical reading device that receives a laser beam as a return beam and reads information on the object to be scanned, the direction in which the divergence angle of the emitted laser beam of the semiconductor laser is large is the scanning direction of the object to be scanned. A rotation holding member that rotates around a rotation axis along the optical path of the light projecting system in synchronization with the rotation of the polygon mirror, and changes a beam waist position in a predetermined circumferential angle area of the rotation holding member. The beam waist position changing optical member is rotated by the rotation of the rotation holding member so that the beam entering position enters the optical path of the light projecting system and the beam projection position is changed. System scanning optical reading apparatus characterized by switching between a retracted position from the optical path of the.