JP2756028B2 - Laser scanner device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser scanner device such as a bar code reader.

2. Description of the Related Art In general, a barcode reader or the like requires reading with good resolving power.

For this reason, for example, according to Japanese Utility Model Laid-Open No. 53-16446,
By changing the focal length of each sector on the hologram disk, or by arranging convex lenses and changing the focal length of each convex lens, the focal point is substantially multifocal, and among the signals read multiple times, the resolution is good. The object is decoded as a bar code reading signal.

According to Japanese Patent Application Laid-Open No. 60-178587, a plurality of beams having different modulation beams are used to converge at different focal points (a convex lens is used for one beam, and a concave lens is used for the other beam). These additional beams are simultaneously scanned.

Furthermore, according to the “autofocus laser scanner” in the monthly “Barcode” (December 1988, Nikkan Kogyo Shuppan, pp. 54-57), the distance to the barcode is measured using a distance meter. It measures in advance and sends the result to a barcode reader, and the barcode reader controls the beam convergence system based on the result.

Problems to be Solved by the Invention However, it is difficult to manufacture a hologram disk having a plurality of different focal length sectors. That is, an optimum design including aberration correction is required for each sector, which complicates the optical system for exposing and producing a master disk.

In the case of the multiple beam system, since a plurality of beams are used, a laser light source and a converging optical system are required for each beam, and a modulation circuit for the laser beam is also required, resulting in high cost. .

Further, in the case of the distance measurement method, it is necessary to install a distance meter, which limits the use. In addition, the use of a distance meter increases costs. Further, the lens is mechanically moved based on the distance measurement result, but it is difficult to change the convergence position at a high speed. In addition, because it uses a mechanical system, it is also susceptible to vibration,
The equipment is also easy to increase in size.

Means for Solving the Problems According to the invention as set forth in claim 1, in a laser scanner device which converges a light beam from a laser light source by a converging optical system and deflects and scans by an optical deflector to optically read information. An electro-optic crystal in the converging optical system, and a size and a shape formed on both surfaces of the electro-optic crystal facing each other along the light beam transmission direction to provide a lens function of converging the light beam by applying a voltage. And an electro-optical lens comprising a power supply means for applying a voltage to the electrode pair.

According to the second aspect of the invention, the electrode pair of the electro-optic lens according to the first aspect is replaced with an electrode pair having a size and a shape giving a lens function of diverging the light beam by applying a voltage.

In the electro-optical lens, when a predetermined voltage is applied to the electrode pair by the power supply means, a refractive index distribution is generated in the electro-optical medium crystal due to the electro-optical effect. At this time, claim 1
In the described invention, the size and shape of the electrode pair give the crystal a lens function of converging a light beam, and the incident light beam is converged by the lens function. In this case, the convergence position can be changed continuously and arbitrarily by changing the applied voltage. According to the second aspect of the present invention, the size and shape of the electrode pair imparts a lens function to diverge the light beam to the crystal, and the incident light beam is diverged by the lens function. In this case, the divergence position can be changed continuously and arbitrarily by changing the applied voltage. The presence of such an electro-optical lens in the converging optical system enables reading with a wide reading depth. Also, since no mechanical movement is required, high-speed focus change is possible, and structurally, downsizing, vibration resistance, and long-term stability can be ensured.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. This embodiment is applied to a barcode reader. Its basic structure and operation are as follows. After a light beam emitted from a semiconductor laser 1 as a laser light source is collimated by a collimating lens 2 and converged by a converging lens 3 as a converging optical system, a polygon mirror 4 as an optical deflector is formed. The scanning is performed by deflection on one surface, and the bar code 6 at the convergence position A is scanned as the scanning beam 5. Bar code 6
The reflected beam from the surface is reflected again by the polygon mirror 4, passes through the converging lens 3 again, and passes through the center aperture mirror 7.
, And is separated from the incident beam, formed on the photodetector 9 by the lens 8 and read as barcode information.

In the present embodiment, an electro-optical lens 10 having a variable focal length function is provided on the optical path before the converging lens 3. The incident beam to the electro-optical lens 10 is assumed to be linearly polarized in the z-direction. This can be realized by disposing the semiconductor laser 1.

Here, the electro-optical lens 10 will be described with reference to FIGS. 3 and 4. FIG. The electro-optic lens 10 is formed based on a substantially rectangular electro-optic crystal 11, for example, a PLZT electro-optic crystal. The composition is suitably 9.0 / 65/35, but other compositions may be used. The input and output end faces are optically polished into a planar shape. Such an electro-optic crystal
A first electrode pair 12 and a second electrode pair 13 are formed on both surfaces in the z direction that are opposed to each other along the 11 optical path (light beam transmission y direction) in order from the incident side. The first electrode pair 12 includes an electrode film 12a,
Consists pairs 12b, these electrode films 12a, 12b is as shown, x-y plane within the linear strip-like shape formed in a length l ₁ at electrode portions d ₁ in the central portion of the medium width direction is of, these electrode films 12a, a first power supply means (power means) 14 made of voltages V ₁ is connected between 12b, a control system (not shown), the variable voltages V ₁ selectively by the switching means It is configured to be able to apply. The second electrode pair 13 comprises _two linear strip-shaped electrode films 13a ₁ , 13a ₂ , 13b ₁ , 13b ₂ each having a gap g in the x direction and a length l ₂ on both sides in the width direction. V ₂ is connected to a second power supply (power supply means) 15. The second power source 15 is also a control system (not shown), and is configured so as to selectively apply a variable voltage V ₂ by the switching means. For example, gold Au is used as these electrode materials, but other conductive materials may be used. The shape of the electrode film is formed by a screen printing method using a conductive paste or the like.

In such a configuration, the electro-optic lens 10 is such that a light beam in a linearly polarized state enters from the incident end face of the electro-optic crystal 11 and passes through the area affected by the electrode films 12a and 12b and the electrode films 13a and 13b. It is assumed that the light is emitted from the other emission end face as an emission light beam. Here, in a state where no voltage is applied to the first and second electrode pairs 12 and 13, the light beam proceeds to the emission end face side in the electro-optic crystal 11 without any change.

Thus, the first electrode pair 12 applies a voltage V _1, when the second electrode pair 13 applies a voltage V _2, a predetermined refractive index electrooptic crystal 11 in the region over which the effect of each of the electrode pairs Distribution occurs, and the first electrode pair 12 gives a lens effect of converging in the z direction, and the second electrode pair 13 gives a lens effect of converging in the x direction. Therefore, the linearly polarized light beam 1 incident on the electro-optic crystal 11 under such a voltage application state is emitted as an emission beam by receiving a predetermined lens action.

Here, the lens operation of the electro-optical lens 10 when applying a voltage will be described in more detail. First, the first electrode pair 12
When a voltage V ₁ is applied to the electro-optic crystal 11, an electric field distribution is generated in the electro-optic crystal 11 as shown by a broken line E ₁ in FIG. . The same applies to the second electrode pair 13. When a voltage V ₂ is applied to the second electrode pair 13, the electro-optical crystal 11 has a broken line in FIG. electric field distribution occurs as shown by E _2. As a result, due to the electro-optic effect of the PLZT electro-optic crystal, the refractive index distribution where the refractive index increases near x = 0 (with the origin at the center of the electro-optic crystal 11 shown in FIG. 4B) on the xz plane. Becomes In any case, based on such an electric field distribution, the electro-optic effect of PLZT electro-optic crystal (2
Next-order electro-optic effect) causes a refractive index distribution in the crystal.

Now, assuming that the direction of the electric field and the direction of linear polarization are the z direction, the direction of the incident light beam is the y-axis direction, and the z component of the refractive index in the electric field is n ₂ , Becomes Here, n ₀ is the refractive index of the PLZT electro-optic crystal at the electric field E = 0, and R ₃₃ is the matrix component of the secondary electro-optic constant.

(1) z-component of the refractive index change due to the electric field E _Z from equation Δnz
Is And is proportional to the square of the electric field strength. As a result, since the refractive index becomes small in the place where the electric field is strong, the refractive index distribution becomes low near the electrode part in the PLZT electro-optic crystal and high near the center in the crystal. Therefore, the lens action by the first electrode pair 12 occurs toward the center in one direction that is the z direction. The lens action by the second electrode pair 13 occurs toward the center in one direction, that is, the x direction. These lens effects become more significant as the electrode lengths l ₁ and l ₂ are longer.

Therefore, when a light beam linearly polarized in the z-direction is incident on the electro-optic crystal 11 during the application of electricity, the first electrode pair 12 receives a lens action in the z-direction.
Next f ₀ as shown in FIG, converges to a point P. When this light beam enters the region of the second electrode pair 13, it is then subjected to a lens action in the x direction by the second electrode 13, and converges to a point P with a focal length f ₀ ′. Therefore, at point P, a spot image subjected to lens action in both z and x directions is obtained. In order to converge the convergent light in both the z and x directions to the same point P, the length of the first and second electrode pairs 12 and 13 should be adjusted according to the convergence performance in each direction.
l ₁ and l ₂ or the applied voltages V ₁ and V ₂ may be set as appropriate.

Returning to the bar code reader shown in FIGS. 1 and 2, the operation will be described together with the operation of the electro-optical lens 10. First, when no voltage is applied to the first and second electrode pairs 12 and 13, the electro-optic lens 10 does not show any lens action, so that the incident light beam passes through the electro-optic crystal 11 as it is and converges. The light is converged (and further deflected) by the lens 3 and converged on the barcode 6 surface at the convergence position A.

On the other hand, when voltages V ₁ and V ₂ are applied to the _first and second electrode pairs 12 and 13,
As described above, in the area of the first electrode pair 12, a lens action is applied in the z direction, and in the area of the second electrode pair 13, the lens action is applied in the x direction. In this case, by appropriately setting the length of the electrode pair or the applied voltage, it is possible to form an image as a spot having the same convergent power in both the z and x directions. The light beam thus converged in the z and x directions by the electro-optical lens 10 is further deflected by the polygon mirror 4 while being converged by the converging lens 3, and scans the bar code 6 'at the convergence position B. . That is, scanning is performed at a focal position closer to the lens side than at the convergence position A. That is, the converging optical system is composed of a combined lens of the converging lens 3 and the electro-optical lens 10.

Now, let the focal length of the converging lens 3 be f ₀ and the electro-optical lens
Assuming that the focal length of 10 is fE _(V) , the combined focal length f
Is approximately expressed by the following equation (3).

Therefore, by appropriately varying the applied voltages V ₁ and V ₂ , the combined focal length f can be arbitrarily varied, and variable focal length scanning without mechanical movement becomes possible. The variable focal length control is performed for each scan or for a plurality of scans, and the reflected light from the barcodes 6 to 6 'is detected by the photodetector 9 to obtain barcode information, thereby obtaining information having the highest resolution. What is necessary is just to select and perform signal processing. In this case, the size of the light detector 9 is set so that the reflected beam does not deviate from the detection area of the light detector 9 due to a change in the distance of the reflection surface (bar code surface).

Next, a second embodiment of the present invention will be described with reference to FIGS.
This will be described with reference to the drawings. The same parts as those described in the above embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, the convergent lens effect is applied to the electro-optic lens 16 only in one direction, here, the x direction. That is,
On both surfaces of the electro-optic crystal 11 located in the z direction, only the electrode pair 17 similar to the second electrode pair 13 is formed.
Power supply means 18 having a voltage V is connected to a ₁ , 17a ₂ , 17b ₁ , and 17b ₂ .

In such a configuration, when no voltage is applied to the electrode pair 17, the electro-optic lens 16 does not exhibit any lens action and scans the bar code surface 6 at the convergence position A. FIG. 7 (a) is an example showing the state at this time, and the convergent beam 19 is spot-irradiated on the bar code 6 surface. When the voltage V is applied to the electrode pair 17, a converging lens function in the x direction is added, and the combined focal length is shortened.
Scanning is performed as a convergent beam 20 having an elongated beam shape as shown in FIG. 6B (a circular beam 20 'indicated by a virtual line indicates a case where no voltage is applied, and is blurred at a position B). Indicating that).

That is, according to the present embodiment, since the beam shape on the bar code 6 'surface is an elongated shape sharp in the direction perpendicular to the bar code line, there is local contamination on the bar code 6'. Can read barcode information,
N improves. Further, the electro-optic lens 16 itself is simpler than the electro-optic lens 10 of the above embodiment, and only one power source is required.

In this embodiment, the convergent beam shape is elongated when a voltage is applied. However, the beam shape is elongated when a voltage is not applied by adding a cylindrical lens. You may make it become.

Further, a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, an electro-optical lens 21 having a focal length variable function by a diverging action is provided on the optical path before the converging lens 3. The beam incident on the electro-optical lens 21 is linearly polarized in the z direction.

The electro-optic lens 21 has an x-direction lens 22 and a z-direction lens 23 arranged so that the diverging and diverging directions are orthogonal to each other with a half-wave plate 24 interposed therebetween. Here, the x-direction lens 22
The structure and operation will be described with reference to FIG.
The x-direction lens 22 is a substantially rectangular electro-optic crystal 25, for example,
It is formed based on a PLZT electro-optic crystal. PLZT
Changes the symmetry depending on the composition, for example, the composition is 9/65
Since the symmetry of / 35 belongs to cubic and has central symmetry, there is no primary electro-optic effect and only the secondary electro-optic effect. The lens action by the application of a voltage is due to the change in the refractive index caused by the electro-optic effect. Electrode pairs 26 for generating a lens function are formed on both sides of the electro-optic crystal 25 along the optical path in the z direction. The shapes of the electrode films 26a and 26b forming the electrode pair 26 are formed such that those on the same surface are semicircular and their arc sides face each other. Power supply means 27 with voltage V ₃ between electrode pairs 26 on both sides
There are connected, not shown control system, and is configured so as to selectively apply a variable voltage V ₃ by the switching means. Therefore, when a voltage is applied to V ₃ between the electrode pair 26, the lens action occurs in the sandwiched by the electrode pairs 26 region, the light beam causes diverging action in the direction orthogonal to the parallel optical axes to the electrode forming surface.

Now, assuming that a light beam linearly polarized in the z direction is incident in the y direction as shown in FIG. 10, the z component nz of the refractive index in the region sandwiched between the electrodes 26a and 26b is as described above (1).
It is similar to the case of That is, when the electric field Ez is applied to the electro-optic crystal 25, the change in the refractive index at that time becomes proportional to the two states of the electric field strength Ez. Here, when a voltage is applied to the regions of the electrode films 26a ₁ , 26a ₂ , 26b ₁ , 26b ₂ formed in a semicircular shape as shown in the drawing, the opposing electrode films 26a ₁ , 26b ₁ and 26a ₂ , 26b ₂ The refractive index of the semi-cylindrical region sandwiched by
Since nz <no, two cylinder lenses having a diverging effect are formed, and a lens effect of diverging in the x direction occurs. When the electric field strength Ez is increased, the focal length of the cylinder lens is shortened, and the diverging effect is increased.

The z-direction lens 23 of the present embodiment is basically the same,
Semicircular electrode films 29a ₁ and 29a on both sides of the electro-optic crystal 28 in the z direction.
_2, 29 b _1, 29 b ₂ of the electrode pair 29 is formed by, becomes configured so as to selectively apply a voltage V ₄ by the power supply means 30. Here, the polarization direction of the light beam incident on the x-direction lens 22 is in the z-direction. Is the x direction, the same as the direction of the electric field, and undergoes a divergent action in the z direction.

Therefore, the entire electro-optic lens 21 becomes a two-dimensional lens having a diverging action in the x and z directions as shown in FIG. 11, and the focal lengths are independently changed by appropriately changing the applied voltages V ₃ and V _4. Can be changed.

Also in this example, returning to the bar code reader shown in FIGS. 8 and 9, the operation of the electro-optical lens 21 will be described together. First, when no voltage is applied to the electrode pair 26, 29, the electro-optical lens 21 does not exhibit a lens function, so that the incident light beam passes through the electro-optical crystals 25, 28 as it is and is converged by the converging lens 3. The light is further deflected and converged on the surface of the barcode 6 at the convergence position A (the detection by the reflected light is the same as in the above-described embodiment).

On the other hand, when the voltages V ₃ and V ₄ are applied to the electrode pairs 26 and 29, as described above, the lens acts to diverge in the x direction at the x direction lens 22, and diverges in the z direction at the z direction lens 23. Subject to lens action. In this case, by appropriately setting the applied voltage, an image can be formed as a spot having the same convergence power in both the x and z directions. The light beam diverged in the x and z directions by the electro-optical lens 21 is converged by the converging lens 3 while the polygon mirror 4
And scans the bar code 6 'at the convergence position B. That is, scanning is performed at a focal position farther from the lens side than at the convergence position A. That is, the converging optical system is composed of a combined lens of the converging lens 3 and the electro-optical lens 21.

In the present embodiment, the electro-optic lens 21 having a function of diverging in both x and z directions is used.
It may have a lens function of diverging in one direction only by the directional lens 22 or the z-direction lens 23.

Further, in these embodiments, the polygon mirror 4 is used as the optical deflector, but a holo disk or the like having a hologram may be used.

Advantageous Effects of the Invention As described above, the present invention provides an electro-optic lens having a focal length variable function by converging or diverging according to an applied voltage in a converging optical system, so that mechanical The convergence position can be continuously and arbitrarily varied without any objective movement, so that a wide reading depth can be read. For example, a readable position range can be greatly expanded in bar code reading and the like. Since no specific movement is required, the focus of the constraint can be changed, and the structure can be reduced in size, vibration resistance, and long-term stability can be ensured.

[Brief description of the drawings]

1 is a plan view showing a first embodiment of the present invention, FIG. 2 is a side view thereof, FIG. 3 is a perspective view of an electro-optic lens, FIG. 4 (a) is a front view, and FIG. ) Is a longitudinal front view, FIG. 5 is a plan view showing a second embodiment of the present invention, FIG. 6 is a side view thereof, FIG. 7 is an explanatory view of a convergent beam shape on a bar code surface, FIG. Is a plan view showing a third embodiment of the present invention, and FIG.
The figures are side views, and FIGS. 10 and 11 are perspective views of an electro-optical lens showing a diverging function. DESCRIPTION OF SYMBOLS 1 ... Laser light source, 3 ... Converging optical system, 4 ... Optical deflector, 10 ... Electro-optical lens, 11 ... Electro-optical crystal, 12,1
3 ... Electrode pair, 14,15 ... Power supply means, 16 ... Electro-optic lens, 17 ... Electrode pair, 18 ... Power supply means, 21 ... Electro-optic lens, 25 ... Electro-optic crystal, 26 ... Electrode pair, 27: Power supply means, 28: Electro-optical crystal, 29: Electrode pair, 30: Power supply means

Claims (2)

(57) [Claims] 1. A laser scanner device in which a light beam from a laser light source is converged by a converging optical system and is deflected and scanned by an optical deflector to optically read information. A crystal, an electrode pair having a size and a shape formed on both surfaces of the electro-optic crystal facing each other along the light beam transmission direction and imparting a lens function of converging the light beam by applying a voltage, and a voltage applied to the electrode pair. A laser scanner device provided with an electro-optical lens comprising a power supply means for applying a voltage. 2. A laser scanner device wherein a light beam from a laser light source is converged by a converging optical system and information is read optically by deflection scanning by an optical deflector. A crystal, a pair of electrodes formed on both surfaces of the electro-optic crystal facing each other along the light beam transmission direction and having a size and a shape to provide a lens function of diverging the light beam by applying a voltage, and a voltage applied to the electrode body. A laser scanner device provided with an electro-optical lens comprising a power supply means for applying a voltage.