JP2754962B2 - Optical mark detector for printed matter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical mark detector for projecting light onto a mark printed on a running web or the like and detecting the reflected light.

[0002]

2. Description of the Related Art In the case of multi-color printing, a mark for each color is provided for each color, and a printing cylinder for printing the color is controlled on the basis of the mark for that color to control the occurrence of color misregistration. Is performed.

FIG. 7 is a diagram showing an optical system for detecting a mark printed on a non-transparent web. The light projecting axis 6 of the light source 1 is perpendicular to the web 2, and the light is condensed and projected by the light projecting lens 4. It is assumed that the web 2 is running in a direction perpendicular to the paper surface (the running direction in the following drawings is also the same). Light receiving axis 7
Is tilted at a predetermined angle with respect to the web 2, and the reflected light condensed by the light receiving lens 5 is received by the light receiving element 3 such as a photodiode or a phototransistor to detect a mark.

The reason why the light receiving shaft 7 is inclined at a predetermined angle with respect to the web 2 is to avoid the specular reflection light of the projection light and receive the diffuse reflection light. This is because in the case of paper or the like, the diffuse reflection light makes it easier to identify the mark. In FIG. 7, the light receiving axis 7 may be perpendicular to the web 2 and the light projecting axis 6 may be inclined with respect to the web 2.

FIG. 8 shows an apparatus embodying FIG. 7, which emits and receives light using an optical fiber.

FIG. 9 shows a mark detection optical system for a transparent web 2 such as a film. In the case of the transparent web 2, the light source 1 and the light receiving element 3 are opposed to each other, and the web 2 is disposed between the two to detect a change in the amount of transmitted light due to the mark.

FIG. 10 shows a mark detection optical system for the transparent web 2 using the reflection plate 8. The light from the light source 1 passes through the web 2, is specularly reflected by the reflection plate 8, and is received by the light receiving element 3.
The light projecting axis 6 and the light receiving axis 7 are line-symmetric.

FIG. 11 shows an apparatus embodying FIG. 10, which emits and receives light using an optical fiber.

[0009]

SUMMARY OF THE INVENTION In the case of multicolor printing,
Four colors of yellow, red, blue and black are often used. In this case, yellow or the like has a light color, and the light-colored mark has a small light absorption. Therefore, in the case of the non-transparent web 2, the light amount difference between the reflected light at the mark portion and the reflected light from the web surface is small, and Detection becomes difficult. In the case of the transparent web 2, the difference in the amount of light between the transmitted light of the mark portion and the transmitted light of the web portion is small, and it is difficult to detect the mark.

The surface reflected light includes a diffuse reflected light component and a specular reflected light component, and the glossy surface has a larger specular reflected light component. When the web 2 is non-transparent, for example, paper, the specular reflected light component has a large amount of light. For this reason, the light amount fluctuates greatly and is not suitable for detecting a mark. Therefore, as shown in FIGS. 7 and 8, when detecting a mark that has been marked on the web 2 by reflected light, the effect of specularly reflected light from the mark The light receiving shaft 7 is arranged to be inclined with respect to the web 2 so as to receive only the diffuse reflection light from the web surface without receiving the light.

However, when the distance from the mark detector to the web 2 fluctuates, that is, when the pass line fluctuates, or when the web 2 undulates, the angle of light incident on the light receiving element 3 changes. The output signal of the light receiving element 3 becomes unstable because it cannot receive the regular reflection light from the mark or cannot receive the diffuse reflection light from the web surface.

FIG. 12 shows a web 2 in the optical system shown in FIG.
Indicates that the light receiving element 3 has received specularly reflected light. At this time, the light intensity becomes strong, and the output fluctuation of the light receiving element 3 due to the waving of the web 2 is severe.

In order to increase the difference between the amount of light reflected from the web surface and the amount of light reflected from the mark portion, it is necessary to increase the field of view of the light receiving device composed of the light receiving lens 5, the light receiving element 3, and a light guide such as an optical fiber. It is necessary to increase the area occupied by the mark with respect to. That is, the visual field area is preferably smaller than the mark area.

By the way, when detecting a mark marked on the running web 2, the output signal of the light receiver starts to change when the mark reaches the field of view of the light receiver, and becomes maximum when the mark enters the entire field of view. . When this output signal becomes equal to or higher than a predetermined value (threshold voltage), it is detected as a mark position.

FIG. 5 is a diagram showing an output voltage with respect to time of the light receiving element 3 when a mark is detected. (A) shows the case where the field of view of the light receiver is wide, and (b) shows the case where the field of view is narrow. The maximum value of the output signal differs depending on the density of the mark. In other words, even if the running speed of the web 2 is constant, the mark with a high mark density reaches the threshold value earlier, and the mark with a lighter density reaches later.
Therefore, when the mark is light, the time for detecting the mark is delayed, and an error occurs in the mark position detection. If the field of view of the light receiver is narrowed as shown in (b), the difference in the detection time between the dark mark and the light mark is reduced, and the detection accuracy of the mark position is improved.

When the light receiving axis 7 is arranged to be inclined with respect to the light projecting axis 6, this intersection is the detection position. FIG. 13 shows a detection range of the optical system shown in FIG. 7 with respect to the fluctuation of the pass line of the web.
It is better not to narrow the luminous flux too much with 5. However, as described above, in order to increase the detection accuracy of the mark position, it is necessary to narrow the light beam and narrow the field of view. As described above, the conventional method has a trade-off characteristic in that the detection accuracy of the mark position deteriorates when the detection range is widened, and the detection range is narrowed when the detection accuracy of the mark position is raised.

When detecting a mark imprinted on the light-transmitting (or transparent) web 2, as shown in FIG. 9, a light projector including a light source 1, a light-projecting lens 4, and a light guide such as an optical fiber is used. And a photodetector are arranged to face each other, and a mark is detected from the amount of transmitted light. In such a system, it cannot be shared with the apparatus for detecting the non-permeable web 2 shown in FIGS.

In the method of receiving the specularly reflected light shown in FIGS. 10 and 11, the light receiving element receives the specularly reflected light by the fluctuation of the pass line or the waving of the web 2 or the diffusely reflected light. The output signal of No. 3 becomes unstable, and the position detection accuracy decreases due to the shading of the mark. Further, it is necessary to adjust the mounting angle of the reflection plate 8.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has low output fluctuation with respect to path line fluctuation and web waving, and has a small mark position detection error due to mark shading. The purpose is to provide a vessel.

[0020]

In order to achieve the above object, an optical mark detector for printed matter which emits light to a mark marked on a moving object to be measured and detects reflected light from the mark is provided. , the light projection axis and a light receiving axis with placing light receiving axis of the reflected light from the mark and the light projection axis of the light coaxially so as to angle inclined in a predetermined range with respect to the object to be measured, and further the light projecting axis Set a common objective lens on the light receiving axis.
It is a digit .

An optical mark detector for printed matter for projecting light on a mark marked on a transparent transparent object to be measured and detecting the mark from transmitted light transmitted through the object to be measured, A light projecting axis and a light receiving axis are arranged coaxially, and a retroreflective plate for transmitting reflected light along the light projecting axis is provided on a side opposite to the light source of the object to be measured. so as to angle inclined in a predetermined range with respect to the object to be measured, further projecting
A common objective lens is provided on the optical axis and the light receiving axis .

In addition, light is received and received using a coaxial optical fiber in which a light receiving optical fiber is disposed at the center and a light projecting optical fiber is disposed around the optical fiber.

[0023]

As shown in FIG. 1, the light projecting axis 6 and the light receiving axis 7 are coaxial, and are arranged so as to be inclined at a predetermined angle with respect to the moving object 2 to be measured. By being coaxial in this way, the light emitting and receiving lenses 9 are shared. In addition, the light receiving element 3 can receive only the diffuse reflection light by inclining it in the range of the predetermined angle in this manner. Further, as shown in FIG. 12, even if the device under test 2 undulates, specularly reflected light does not enter the light receiving element 3 unless the undulation is considerably large.

Further, since the light projecting axis 6 and the light receiving axis 7 are coaxial, even if the light beam is narrowed and the light receiving field is narrowed, the allowable range of the mounting distance from the object 2 to the mark detector is increased. Therefore, the influence of the density of the mark is small, and the mark position detection accuracy can be improved.

Also, when the object to be measured is transparent, the light projecting axis and the light receiving axis are coaxial, and are arranged at an angle within a predetermined range with respect to the object to be measured. Since a retroreflective plate that transmits reflected light almost along the axis is provided,
Specularly reflected light reflected from the surface of the object to be measured is not received, and the field of view of the light receiver can be narrowed by narrowing the light flux, so that the influence of the shading of the mark can be reduced and the mark position detection accuracy can be improved. . Further, even if the path line fluctuates or the object to be measured undulates, there is little possibility that the specularly reflected light is received.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram for explaining the configuration of the first embodiment of the present invention,
FIG. 3 is a diagram showing a specific configuration example. The first embodiment is directed to a non-transparent web.

In FIG. 2, a light projecting axis 6 of the light from the light source 1 is shown.
The coaxial optical fiber 10 is used to bring the light receiving axis 7 to the light receiving element 3 as close as possible. Coaxial optical fiber 10
As shown in the cross-sectional view of FIG.
Is placed at the center, and six light emitting fibers 12
Place. A light projecting / receiving lens 9 is arranged at the tip of the coaxial optical fiber 10 to collect light projected and received. The inclination angle θ between the web 2 and the coaxial optical fiber 10 is 50 to 80 degrees, and preferably about 50 to 70 degrees when the surface of the web is rough.

FIGS. 3A and 3B show a specific configuration of the coaxial optical fiber 10, wherein FIG. 3A shows the entire structure, and FIGS. 3B, 3C, and 3D.
Shows a sectional view of each part. Six light-emitting fibers 12 are provided around the light-receiving fiber 11 as shown in section A, and six light-emitting fibers 12 are provided around the light-emitting fiber 12 as shown in section B. The two are integrated at a terminal 13 and a coaxial optical fiber is formed as shown in section C. Make up 10.

Next, the operation will be described. Of the light emitted from the light projecting optical fiber 12 to the web 2, only the light reflected in the emission angle direction is received, so that only the diffuse reflected light is received without the regular reflected light, and the central light receiving optical fiber 11 is received. The light is received by the light receiving element 3 via.

FIG. 4 shows that the web 2 undulates greatly and the projection axis 6
Shows a state at right angles. Such large undulations are rare, and printing itself cannot be performed if such large undulations are used.Therefore, it is usually controlled to suppress such large undulations, and such a case does not occur. You can think.

FIG. 5 shows the relationship between the output voltage V of the light receiving element 3 and the light receiving time t, as described above. The output voltage is large for dark marks and small for light marks. Further, when the light beam is narrowed by the light projecting / receiving lens 9 and the field of view of the light receiving device is narrowed, the rise of the output voltage is accelerated.

(A) shows the case where the light beam of the light projecting / receiving lens 9 is not narrowed down so that the field of view of the light receiver is wide, and (b) shows the case where the light beam is narrowed down and the field of view is reduced. As shown in (a), when the field of view is wide, the time required to reach the threshold value of the output voltage of the light receiving element 3 for determining that the mark has been detected becomes longer, and the threshold voltage between the dark mark and the light mark is increased. , That is, the mark position detection error due to the density of the mark increases.

FIG. 3B shows the case where the light beam from the light projecting / receiving lens 9 is narrowed and the field of view is narrowed, and the rise of the output voltage of the light receiving element 3 is accelerated, so that the detection error of the mark position due to the density of the mark is reduced. . In this embodiment, since the light projecting axis 6 and the light receiving axis 7 are substantially on the same axis, it is possible to reduce the detection error of the mark position due to the shading of the mark by narrowing the light entering and exiting the lens 9. Since the depth of focus becomes deeper, the change in spot size is small even if the web pass line changes as shown in FIG. Further, since the projected light and the reflected light are on the same axis, the intersection does not deviate due to the fluctuation of the pass line.

Next, a second embodiment will be described. This embodiment is directed to a transparent web such as a film, and the configuration is shown in FIG. The specific configuration after the optical fiber is the same as in FIG.

In FIG. 6, the difference from FIG. 2 is that the web 2 is a transparent film, and a retroreflective plate 14 for emitting reflected light on the same optical axis as the incident light is provided on the opposite side of the web 2 from the light source. That is the provision. The range of the inclination angle θ of the coaxial optical fiber 10 with respect to the web 2 is about 50 to 80 degrees as in the case of the non-transparent web, but when the surface of the web 2 is smooth, the preferable angle is 70 degrees. ~ 80 degrees.

FIG. 6B is a diagram showing the principle of the retroreflective plate 14, in which small spheres are arranged on a sheet, and the reflected light is transmitted on the same optical axis as the incident light. This product is used for road signs, etc., and is commercially available.

Next, the operation will be described. Part of the light emitted along the light projecting axis 6 is specularly reflected on the surface of the web 2,
The rest passes through the web 2, is reflected by the retroreflective plate 14, is retransmitted through the web 2 along the light receiving axis 7 substantially on the same axis as the light projecting axis 6, is condensed by the projecting / receiving lens 9, and is received by the light receiving element. 3 and converted to an output voltage.

Also in this embodiment, since the light projecting axis 6 and the light receiving axis 7 are accommodated in the coaxial optical fiber 10, they are close to each other. Since the specular reflected light from the web 2 is not received and the light projecting axis 6 and the light receiving axis 7 are substantially coaxial, the range where both light beams intersect becomes longer on each optical axis. 9, the light beam can be narrowed and the light receiving field can be narrowed, and the influence of the density of the mark can be reduced, so that the mark position detection accuracy is improved.

Further, by using the retroreflective plate 14, the reflected light can be received without adjusting the coupling angle with the coaxial optical fiber 10.

The effects of this embodiment are summarized as follows. Since it is hard to be affected by the specular reflection light from the mark part marked on the DUT and the projection axis and the reception axis have the same inclination angle with respect to the web, against the waving of the DUT and the fluctuation of the pass line, Make the output stable. Even if the permissible range of the mounting distance from the mark detector to the object to be measured is widened, the luminous flux can be narrowed and the field of view can be easily narrowed, so that the mark position detection error due to the difference in density of the mark is small. As shown in FIG. 3, the same coaxial optical fiber 10 can be used for an object to be measured that transmits light and for an object that does not transmit light. The only difference between the two is that the retroreflector 14 is used. By using the coaxial optical fiber 10 and the retroreflector 14, the installation can be simplified and the installation place is not required. By using an optical fiber, a mark can be detected even in a narrow space. By using the optical fiber, the mark can be detected even in an atmosphere in which a flammable gas vapor such as a solvent exists.

[0041]

As is apparent from the above description, according to the present invention, the light emitting axis and the light receiving axis are made coaxial, and both axes have an inclination angle within a predetermined range with respect to the object to be measured. The influence is reduced, and the error of the mark detection position due to the density of the mark is reduced. When the object to be measured is transparent, the effect of specular reflection light is reduced by using a retroreflective plate, and errors in mark detection positions due to mark density are reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation of the present invention.

FIG. 2 is a diagram illustrating a configuration of a first embodiment.

FIG. 3 is a configuration diagram of a coaxial optical fiber according to a first embodiment.

FIG. 4 is a diagram for explaining an influence when a web is largely wavy.

FIG. 5 is a diagram for explaining the relationship between the density of a mark and the width of the field of view of a light receiving device.

FIG. 6 is a diagram illustrating a configuration of a second embodiment.

FIG. 7 is a view showing a conventional non-transparent web mark detection optical system.

8 is a diagram showing an example in which the optical system shown in FIG. 7 is realized using an optical fiber.

FIG. 9 is a diagram showing a conventional mark detection optical system for a transparent web.

FIG. 10 is a diagram showing a conventional optical system for performing mark detection on a transparent web using a reflector.

11 is a diagram illustrating an example in which the optical system illustrated in FIG. 10 is realized using an optical fiber.

FIG. 12 is a view for explaining an effect when a web is wavy in the optical system shown in FIG. 7;

FIG. 13 is a diagram showing a detection range when the web moves up and down.

[Explanation of symbols]

 Reference Signs List 1 light source 2 web 3 light receiving element 6 light emitting axis 7 light receiving axis 9 light emitting / receiving lens 10 coaxial optical fiber 11 light receiving fiber 12 light emitting fiber 13 terminal 14 retroreflector

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41F 33/14 G01B 11/00

Claims (3)

(57) [Claims] An optical mark detector for printed matter which projects light on a mark marked on a moving object to be measured and detects reflected light from the mark, comprises: The light receiving axis of the reflected light is arranged coaxially, the light projecting axis and the light receiving axis are inclined at a predetermined angle with respect to the object to be measured, and a common objective is provided on the light projecting axis and the light receiving axis.
Optical Mark detector printed matter characterized in that a lens. 2. A printed optical mark detector for projecting light onto a mark inscribed on a transparent transparent object to be measured and detecting the mark from transmitted light transmitted through the object to be measured, A light projecting axis and a light receiving axis are arranged coaxially, and a retroreflective plate for transmitting reflected light along the light projecting axis is provided on a side opposite to the light source of the object to be measured. so as to angle inclined in a predetermined range with respect to the object to be measured, further light projection axis
An optical mark detector for printed matter , wherein a common objective lens is provided on the light receiving axis . 3. An optical fiber according to claim 1, wherein a light receiving optical fiber is arranged at the center, and light is emitted and received by using a coaxial optical fiber around which a light emitting optical fiber is arranged. Optical mark detector for printed matter.