JPH01163069A - Method and apparatus for detecting defects in liquid-crystal mask - Google Patents

Abstract

PURPOSE:To enable detection of defects in a liquid-crystal mask, by providing a polarizing filter between a laser oscillator and the liquid-crystal mask, provid ing a beam splitter between the mask and a projection lens to branch a laser beam, and picking up an image by a television camera. CONSTITUTION:A laser beam from a laser oscillator 1 is polarized directly by a polarizing plate 2, and is projected through a liquid-crystal mask 4. The mask 4 is provided with a required printing pattern by a liquid crystal controller 8, and the laser beam is transmitted, without changing the plane of polarization, through the area provided with the printing pattern. The laser beam transmitted through areas other than the printing pattern area of the mask 4 has the plane of polarization rotated by 90 deg. upon the transmission, and is then separated through reflection by a beam splitter 5. The rotated laser beam 16B reflected by the beam splitter 5 is attenuated by an attenuator 10, and is picked up as an inverted image by a television camera 13. The image is binary coded by an image recognition device 15, and is compared with an image obtained under a normal condition, whereby an abnormality in the mask 4 is detected.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention detects a failure by constantly monitoring whether or not a failure has occurred in a liquid crystal mask used in a laser marking device that prints using laser light. The present invention relates to a method and an apparatus for doing so.

[Conventional technology]

2. Description of the Related Art In a laser marking device that prints on an IC or the like using a laser beam, a method using a transmissive liquid crystal is known as a method of forming a print pattern.

A specific known example of this is JP-A-56-38888. This is shown in FIG. In FIG. 4, laser light emitted from a laser oscillator 1 is expanded by lenses 3a and 3b constituting a beam expander, and is incident on a liquid crystal mask 4. Print information is given to the liquid crystal mask 4 as a control signal by a controller 6'. This printing information is created by capturing an image of the original image 15 to be printed by the television camera 13 and sending it to the controller 9'.

Further, 14 is a monitor TV for monitoring this video.

The liquid crystal mask 4 allows the laser light to pass through only the portion to be printed, and the laser light is reduced and irradiated onto a print work 7 such as an IC through a projection lens 6 to print.

[Problem that the invention seeks to solve]

The conventional techniques described above have the following drawbacks. That is, since the liquid crystal mask 4 is thermally weak, 1. If excessive laser irradiation occurs or if the liquid crystal mask cooling device (not shown in Figure 4, means such as water cooling the mounting part of the mask 4 is provided) is damaged, a normal Character formation becomes impossible. Naturally, then, a problem arises in that correct printing cannot be performed.

As a countermeasure for this, as shown in Fig. 5, the printing work 7
One possible method is to import the characters printed on the image recognition device 14 into the image recognition device 14 to determine the abnormality. In FIG. 5, characters on a print work 7 are illuminated by an illumination light source 16, and the reflected light is taken into a TV camera 13 via an imaging lens 17 and a relay lens 18. The image captured by the TV camera 13 is binarized by the image recognition device 15' and compared with a normal image to determine whether there is a printing defect.

Such a method has the following drawbacks. This is because the character recognition accuracy depends on the surface condition of the printed work 7 (for example, dust adhesion) and the irradiation method. Furthermore, it is difficult to set the binarization level of the image recognition device. Filtering processing is performed inside the image recognition device to avoid error factors such as dust adhesion, but as a result, the time required for recognition increases, which is a bottleneck when incorporating such a detection device into an automatic line. There is.

The present invention has been made in view of the above-mentioned circumstances, and provides a detection method capable of detecting a failure of a liquid crystal mask with high precision and high reliability without performing filtering inside an image recognition device, and the above-mentioned invention. It is an object of the present invention to provide a failure detection device suitable for implementing the method. If filtering is no longer necessary by applying the present invention, the time required for recognition will be shortened, making it possible to incorporate this detection device into an automatic line.

[Means for solving problems]

In order to achieve the above objects, the present invention provides a polarizing filter on the optical path between the laser oscillator and the liquid crystal mask, and a beam splitter on the optical path between the liquid crystal mask and the projection lens to split the laser beam. The branched light is then imaged and monitored using a television camera.

[Effect]

According to the above configuration, the laser beam of the printing pattern formed by the liquid crystal mask passes through without changing the polarization direction and performs the printing operation.6 Furthermore, the laser beam of the negative pattern of the printing pattern has the polarization direction of 90°. ° rotated and split by a beam splitter.

Therefore, the health of the liquid crystal mask can be monitored by monitoring the negative video information included in the above-mentioned branched laser beam via the video camera. According to this method, since it is not affected by the surface condition of the printing object (presence of dirt, etc.), highly accurate and reliable monitoring and detection is possible.

Further, setting of the binarization level is easy, and filtering processing within the recognition device is not necessary. Therefore, the time required for recognition is short, and it is suitable for incorporating into an automated line.

〔Example〕

An example of implementing the method of the present invention using an example of the apparatus of the present invention will be described below with reference to FIGS. 1 to 3.

In FIG. 1, 1 is a laser oscillator. 2 is a polarizing plate for linearly polarizing the laser beam output from the laser oscillator 1. 3a and 3b are beam expanders for enlarging laser beams, and 4 is a liquid crystal mask for forming printed characters. 5 is a beam splitter that separates the polarized laser beam, and 6 is a projection lens that projects the laser beam onto a workpiece 7 that is a printing target. 8 is a liquid crystal controller that controls the liquid crystal mask 4. A main controller 9 receives signals from the laser oscillator 1 and the image recognition device 14 and controls the liquid crystal controller 8. 10 is an attenuator that attenuates the laser light separated by the beam splitter 5 to the required power. 11.12
is an imaging lens for capturing images into the camera 13,
It is a relay lens. 14 is a TV for monitoring the video signal of the camera.

The operation of the apparatus configured as described above will be explained below. Laser light from a laser oscillator 1 is linearly polarized by a polarizing plate 2, passes through beam expanders 3a and 3b, and is irradiated onto a liquid crystal mask 4.

At this time, the polarization plane of the laser beam is parallel to the plane of the paper, as shown by the reciprocating arrow a in FIG. A necessary print pattern is formed on the liquid crystal mask 4 by a liquid crystal controller 8. The laser beam passes through the area where the printed pattern is formed with the same polarization plane. This transmitted laser light is represented by 16A.

Other than the printed pattern, the polarization plane is 90' after passing through the liquid crystal mask.
It rotates and becomes perpendicular to the plane of the paper. (Indicated by a mark "・" in the figure. This rotating laser beam is represented by 16B.) In this way, the laser beam with two polarization planes is split by the beam splitter 5, and the transmitted laser beam 16 is parallel to the plane of the paper.
A is transmitted through the beam splitter 5, and a rotating laser beam 16B perpendicular to the plane of the paper is reflected by the beam splitter 5 and separated. The beam splitter transmitted laser beam 16A is transmitted through the projection lens 6.
As a result, the printing work 7 is irradiated in a reduced size and printed.

Also, the rotating laser beam 16 reflected by the beam printer 5
B is attenuated by an attenuator 10, and then transferred to an imaging lens 11. The image is captured by a television camera 13 through a relay lens 12.

In this way, characters are printed on the print work 7 as shown in FIG. 2, and the television camera 13 captures the inverted image of FIG. 2 as shown in FIG. This image is binarized by the image recognition device 15 and compared with a normal image to detect an abnormality in the liquid crystal mask 4.

Comparing the conventional method of recognizing characters printed on a printed work with the method according to the present invention, the present invention has the following advantages. That is, first, by capturing an inverted image of the printed portion of the liquid crystal mask into a camera, the surface condition of the printed object,
Not affected by irradiation dimensions, etc. Therefore, it is easy to set the binarization level, filtering processing in the recognition device 15 is not required, and high-speed image recognition is possible.

〔Effect of the invention〕

As detailed above, the method of the present invention has the excellent practical effect of being able to detect a failure of a liquid crystal mask with high precision and high reliability without performing filtering inside the image recognition device. 1. If filtering becomes unnecessary by applying the method of the present invention, the time required for recognition will be shortened, and this detection device can be incorporated into an automatic line.

Moreover, according to the apparatus of the present invention, the above-described method of the invention can be carried out easily and reliably, and its effects can be fully exhibited.

[Brief explanation of the drawing]

FIG. 1 is an optical path diagram showing one embodiment of the device of the present invention. FIGS. 2 and 3 are explanatory diagrams of the operation of the above embodiment. FIG. 4 and FIG. 5 are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1... Laser oscillator, 2... Polarizing plate, 3a, 3b.
... Beam expander, 4... Liquid crystal mask, 5...
・Bee. 6... Projection lens, 7... Work as a printing target, 11... Imaging lens, 12... Relay lens, 13... Television camera.

Claims (1)

[Scope of Claims] 1. A laser marking device in which a laser beam passes through a liquid crystal mask and an image of the passed laser beam is formed on the surface of an object to be printed by a projection lens, wherein: (a) the laser beam is incident on the liquid crystal mask; The laser beam is linearly polarized in advance by a polarizing plate, (b) the laser beam that has passed through the liquid crystal mask is split by a beam splitter, and (c) the laser beam that has passed through the beam splitter is used to perform laser marking. and (d) capturing an image of the laser beam reflected by the beam splitter using a television camera and monitoring the image. 2. In a device for detecting the occurrence of a failure in a liquid crystal mask used in a laser marking device that passes laser light through a liquid crystal mask and forms an image of the passed laser light on the surface of an object to be printed using a projection lens, (a) a polarizing plate disposed on the optical path of the laser beam incident on the liquid crystal mask; (b) a beam spiriter disposed on the optical path of the laser beam passing through the polarizing plate and the liquid crystal mask; and (c) the beam 1. A failure detection device for a liquid crystal mask, comprising: a television camera that captures an image contained in laser light that is reflected and branched by a spiritator;