JPH02197971A - Optical system for laser reader - Google Patents

Abstract

PURPOSE:To attain the detection of the information on a reading subject despite a distance secured from the subject by shifting the optical axis of a condenser lens approximately in parallel to the optical axis of a light projecting part. CONSTITUTION:A condenser lens 20 is equal to a rotationally asymmeterical lens which is obtained by cutting a rotationally symmetrical lens L so as to have its center axis at a position deviated from an optical axis l1. At the same time, the axis l1 can be shifted from an optical axis l2 of a light projecting part. As a result, the information on a subject can be detected at a position distant from the subject. Furthermore no special space is required for the lens 20 since this lens 20 is set in the optical path of the luminous flux of the project ed light. Thus a compact optical system is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention emits a laser beam toward an object, receives the light reflected by the object, and detects a difference in reflectance of the object. This paper relates to improvements in the optical system of laser readers.

[Conventional technology]

An example of this type of reader is a so-called pen-shaped barcode reader.

The optical system of the conventional pen-type barcode reader 1, the sixth
The configuration is as schematically shown in the figure.

Reference numeral 1a in the figure is a casing of a barcode reader, and a light emitting diode (LED) 2 serving as a light source and a light receiving cable 3 are provided within this casing 1a.

The light emitted from Li1l12 illuminates a barcode pattern (not shown) to be read through the condensing element 4, and is reflected by this barcode pattern and passes through the condensing element 4 again into the casing 1a. A part of the incident reflected light is guided to the light receiving element 3 via the optical fiber 5.

When reading the barcode pattern, the reader is scanned with the light condenser 4 and the barcode pattern in contact with each other. Thereby, the light-receiving element 3 can detect information possessed by the barcode pattern in response to changes in reflectance of the barcode pattern due to scanning.

[Problems to be Solved by the Invention] However, the conventional barcode reader as described above has an extremely shallow reading depth, and cannot be read if the light condenser 4 and the barcode pattern are separated from each other. If the surface on which the barcode pattern is printed is not smooth, for example if it is printed on a flexible bag, the unevenness of the printed surface may cause the light condensing probe 4 and the barcode pattern to confuse during scanning. There was a risk that the discs would become separated and become unreadable.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and provides an optical system for a laser reader that can detect information on an object to be read even if there is a distance between the object and the object to be read. The purpose is to provide.

[Means for solving the problem] In order to achieve the above objective, it is necessary to increase the reading depth of the barcode reader. It is necessary to remove obstacles such as optical fibers so as not to deteriorate the focusing ability of the projected light flux, and to efficiently collect the reflected light onto the light receiving element.

In view of this point, the optical system of the laser reader according to the present invention includes a light projecting section that emits a focused laser beam toward an object, and a light projecting section that is provided in the optical path of the projected light flux emitted from the projecting section. A condenser lens having a transmitting part that transmits the projected light flux without changing its traveling direction in an overlapping part, and a light receiving element that detects the amount of the condensed reflected light, and the optical axis of the condenser lens is It is characterized by being shifted approximately parallel to the optical axis of the light projecting section.

[Function] Since the optical system of the laser reader according to the present invention has the above-described configuration, the laser focused light emitted from the light projecting section reaches the target object, and the zero reflected light reflected by the target object is focused. The light is focused through a lens toward a light receiving element located in a direction different from that of the light projecting section.

[Embodiment-Example] Hereinafter, an embodiment of the present invention will be described based on FIGS. 1 to 5.

A light projecting unit that projects laser focused light to the left side in the figure toward an object (not shown) is composed of a laser diode (hereinafter referred to as LD) 10 and a light projecting lens 11. This light projector is set to maintain a beam diameter that can be read with respect to the spatial frequency of information possessed by the object in the Q-H section before and after the beam waist.

The light beam reflected by the object is condensed toward the light receiving element 13 via the condenser lens 20 . At this time, the reflected light from the points Q and R on the object side is reflected by the condensing lens 20, respectively.
The light is focused at the positions Q' and R- through the .

The light receiving probe 13 is arranged to coincide with a point Q' that is conjugate to the far limit Q within the reading depth in order to read the reflected light from the object at both ends Q and H of the reading depth at a uniform level. There is.

The light intensity level of the reflected light is inversely proportional to the square of the distance from the light receiving element to the object. Therefore, by arranging the light receiving element 13 at a position where the amount of reflected light from the farthest part Q within the reading range is most effectively focused, and the reflected light from the nearer part R is dispersed, it reaches the light receiving element 13. The amount of light can be optically made uniform over the entire reading range.

The condensing lens 20 is a rotationally asymmetric lens L, whose outer diameter is shown by a two-dot chain line in FIG. It's a lens. The condensing lens 20 is arranged so that its optical axis g1 is shifted parallel to the optical axis g2 of the light projecting section.

The virtual lens L that is the base of the condensing lens 20 is an aspherical lens whose radius of curvature gradually increases from the center toward the periphery.

When the focal length of the condenser lens 20 is shorter, the distance between the condenser lens 20 and the light receiving element 13 can be shortened, and the barcode reader can be made more compact.

However, in order to shorten the focal length, it is necessary to reduce the radius of curvature of the lens surface, and in order to ensure the thickness of the lens periphery necessary for installation, the lens diameter becomes small. The condensing lens 20 according to the embodiment is
In order to maintain a sufficient thickness at the lens periphery while setting the focal length short, the lens is an aspherical lens whose radius of curvature gradually increases toward the periphery.

Note that due to such an aspherical shape, the refraction of light rays away from the optical axis is reduced, so as an additional effect, spherical aberration can be reduced, and the ability to collect light onto the light receiving element 13 can be improved. Contributing.

A transmitting section 21 is provided in the center of the condensing lens 20 to transmit the light beam emitted from the light projecting section without changing its traveling direction.

The transparent portion 21 is simply a through hole in this example.

However, the structure of the transmitting part 21 is not limited to a through hole, and planes having no power perpendicular to the optical axis 92 of the light projecting part may be formed on both sides of the condensing lens 20, or planes having a power different from the surroundings may be formed. It is also possible to form a surface having a function of converging the projected light beam.

According to the above configuration, the laser beam emitted from the LDIO becomes a focused light via the projection lens 11, passes through the transmission part 21 of the focusing lens 20, and is focused.

The projected light flux is reflected by an object placed between points Q and H. The reflected light takes the same optical path as the projected light flux until it reaches the condensing lens 2o, and is sent to the light projecting section by the condensing lens 20. The light deviates from the optical path of the light and is focused toward the light receiving element 13.

As long as the barcode pattern of a predetermined standard is located between points QR, information can be read even when the barcode pattern is separated from the opening of the casing 30.

It should be noted here that when reading a barcode pattern of a standard with a smaller spatial frequency (rougher pattern) than the above standard, the reading depth will be wider than point QR, and the barcode of a standard with a larger spatial frequency. When reading the pattern, the reading depth becomes narrower than the point QR. When the reading depth becomes narrow, it becomes impossible to read the barcode pattern with the barcode pattern in close contact with the opening. Therefore, when reading barcode patterns of several types of standards, the design is such that the limit point on the side closer to the reading depth for the barcode of the standard with the highest spatial frequency coincides with the exit port of the casing.

In Japanese Patent Application No. Sho 62-278943, the present applicant proposed that the Scheimpfl.
We have proposed a configuration in which reflected light from an object is effectively focused on a light receiving element over the entire reading range using the law of ug).

However, with this configuration, since the output level of the light receiving element changes depending on the distance to the object, it is necessary to have a wide allowable range of input to the electrical system.

If the light intensity level of the reflected light is made uniform by the arrangement of the light receiving elements 13 as shown in this embodiment, the reading output can be made uniform, and the allowable range of electrical system input can be narrowed to reduce the burden. Can be done.

Further, there is no need to tilt the condenser lens according to Scheimpfluf's law described above, and the condenser lens can be easily assembled.

Next, the structure of the casing 30 provided with the above-mentioned optical element will be explained based on FIG. 1 and FIG. 3.4.

The casing 30 includes a cylindrical central portion 30a, a cylindrical front end portion 30b that is threaded onto the distal end side of the central portion 30a,
Bottomed cylindrical rear end portion 3 screwed onto the rear end side of the central portion 30a
It is composed of three members: 0c and 0c.

The LDIO is placed against the cylindrical holding frame 31 from the left side in FIG. 1, and is fixed with a set screw 31b.

This holding frame 31 is fixed to a cylindrical light projector base 32 bolted to the casing central portion 30a.

The light projection lens 11 is housed in a lens frame 33 that is screwed onto the light projection base 32, and is fixed to the lens frame 33 by a lens holder 34 that is screwed into the lens frame 33 from the left side in the figure. Furthermore,
An aperture cap 35 is fitted into the lens holder 34 to limit the diameter of the projected light beam.

The light receiving cable 13 is attached to an element holding member 36 bolted to the casing central portion 31a. The element holding member 36 is integrally formed of a semi-cylindrical part 36a which is shaped along the inner wall of the casing and is screwed to the casing central part 30a, and a front wall 38b to which the light receiving cable 13 is attached. Note that an optical path hole 36c is formed in the front wall 38b to transmit the laser light from the LDIO.

The condensing lens 20 is assembled at the left end of the casing central portion 30a in FIG. Since the condensing lens 20 is rotationally asymmetric and has a certain direction when assembled, a protrusion 22 as an engaging part is formed on a part of the periphery of the condensing lens 20 as shown in FIG. By providing a hole 37 in the inner wall that engages with this protrusion 22, positioning during assembly can be easily performed. Protrusion 2
2 can be integrally formed during molding when the condenser lens 20 is a plastic lens.

A power cord for providing the drive current of the LDIO and a signal line for transmitting the output of the light receiving cable 13 (both not shown) are led to the outside on the rearmost bottom wall of the rear end portion 31c of the casing, which is the right end in the figure. A cord hole 38 is drilled for this purpose.

Although this embodiment has only described an example in which the optical system of the laser reader of the present invention is applied to a pen-shaped barcode reader, it is possible to detect optical information of an object without contact. It can also be used for inspection, inspection of dust attached to products, etc.

[Effects] As described above, according to the present invention, information on an object can be detected at a position separated from the object.

In addition, since the condenser lens is installed in the optical path of the projected light beam, there is no need to provide a special space for the condenser lens.
The optical system can be made compact.

Furthermore, if the light-receiving element is placed at a position that is almost conjugate with the far limit of the reading range, the amount of reflected light reaching the light-receiving element can be made uniform over the entire reading range, and the output of the light-receiving element can be The burden on the electrical system can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the optical system of a laser reader according to the present invention, FIG. 2 is a sectional view taken along the line II-II in FIG. 1, and FIG. 3 is a sectional view taken along the in-m line in FIG. 1. Cross-sectional view, Figure 4 is the first
17-IV line sectional view in the figure, FIG. 5 is a sectional view showing the engagement of the condensing lens and the casing, and FIG. 6 is an explanatory diagram showing the outline of the optical system of a conventional pen-type barcode reader. . 13... Light receiving element 20... Condensing lens 21... Transmitting section 1s... Optical axis of condensing lens 12... Optical axis of light projecting section.

Claims (6)

[Claims] (1) A light projecting unit that emits laser focused light toward a target object; and a part that is provided in the optical path of the projected light beam emitted from the light projecting unit and changes the traveling direction of the projected light beam to a part that overlaps the optical path. a condensing lens having a transmitting part that transmits the light without causing any damage, and a light receiving element that detects the amount of the condensed reflected light, and the optical axis of the condensing lens is substantially parallel to the optical axis of the light projecting part. The optical system of a laser reader is characterized by being shifted. (2) The light receiving element is provided at a position that is substantially conjugate to a far limit of the reading depth determined by the relationship between the spatial frequency of the object and the spot diameter of the laser beam. 1. The optical system of the laser reader according to 1. (3) The optical system of a laser reader according to claim 1, wherein the transmitting section is provided at a central portion of the condensing lens. (4) The optical system for a laser reader according to claim 1, wherein the condensing lens is an aspherical lens whose radius of curvature increases toward the periphery. (5) The condensing lens is a rotationally asymmetrical lens obtained by cutting out a part of a rotationally symmetrical plastic lens with an axis eccentric from the optical axis of the plastic lens as the central axis. 5. The optical system of a laser reader according to any one of 4 to 4. (6) The optical system of a laser reader according to claim 5, wherein the condensing lens has an integrally formed engaging portion used for positioning to the casing.