JPH01206241A - Defect detecting method - Google Patents

Abstract

PURPOSE:To enable the detection of a defect in accordance with the kind of a sheet and the purpose of inspection, by judging the sheet as a defective article only when the defect is detected continuously substantially across scanning lines of a prescribed number or more. CONSTITUTION:A reflected light from the surface of a web 2 which is obtained from a light beam Q from a projecting means 3 is sensed by a light sensing means 4 and a light quantity signal, an electric signal of a level corresponding to the quantity of the sensed light is generated. This light quantity signal is amplified by an amplifier 5, the level of the amplified signal is compared with a reference level in a discriminator circuit 6, and when the level of the light quantity signal is lower, a defect signal is outputted. Then, it is detected in a counter-comparator circuit 8 whether or not the defect signal from the discriminator circuit 6 appears continuously across scanning lines of a prescribed number or more, and when it appears continuously, a decision signal is outputted to an alarm circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is applicable to, for example, in the manufacturing process of magnetic tapes such as video tapes and audio tapes, a support web before being coated with a magnetic substance, a magnetic tape after being coated with a magnetic substance, etc. This article relates to a method for automatically detecting surface defects on various sheet materials, and more specifically, it relates to a defect detection method that scans a light beam in the width direction of the sheet and detects surface defects on the sheet based on information on the amount of light from the sheet surface. be.

(Prior art) In the manufacturing process of magnetic tapes such as audio tapes and video tapes, it is necessary to detect surface defects caused by surface scratches, deformations, tubes with foreign objects, etc. in each process such as the support web manufacturing process and the final inspection process. Then, those with surface defects are sorted out.

As a method for detecting such surface defects, a light beam is scanned in the sheet width direction against a tape or a support web (hereinafter referred to as a sheet) running in the longitudinal direction, and the reflected light from the sheet surface is detected. A method is known in which sheet defects are detected based on a light amount signal of the detected reflected light.

Conventionally, in such a defect detection method, a point in the light amount signal where the level becomes extremely low is defined as a defect signal, and if even one defect signal is output in any scanning, that sheet is detected. were rejected as defective products.

(Problems to be Solved by the Invention) However, depending on the type of sheet and the purpose of the inspection, there are some sheets that do not need to be treated as defective even if one defect signal is output. For example, in a visual inspection, there is no need to judge a magnetic tape as defective just because there is a small scratch (medium in the scanning line) on the opposite side of the magnetic tape to the side coated with the magnetic material. Depending on the conventional method, if a defect signal is output without considering the type of sheet or the purpose of inspection, the sheet is treated as a defective product, resulting in excessive detection.

In view of these circumstances, the present invention is designed to remove the sheet only when a problematic level of defect is discovered, depending on the type of the sheet and the purpose of the inspection, even if it is determined that the sheet has a defect. The purpose is to provide a simple defect detection method that can determine that a product is defective.

(Means for Solving the Problems) The defect detection method of the present invention scans a light beam over a surface to be inspected of a sheet, and detects a change in the amount of light beam reflected from the surface to be scanned by a predetermined value or more. When a defect is detected, it is determined that a defect exists, and when this defect appears continuously or almost continuously over a predetermined number of scanning lines, it is determined that there is a defect of a problem level on the surface of the sheet, and the sheet is classified as a defective product. This feature is characterized in that it is determined as follows.

(Function) The defect detection method of the present invention determines that there is a defect when the amount of reflected light from the inspected surface of the sheet changes by more than a predetermined value, but when one defect is detected, it is immediately determined that the product is defective. Rather, when defects are detected substantially continuously over a predetermined number or more of subsequent scanning lines, the product is determined to be defective. In other words, for example, in visual inspection, if a defect is judged to be defective when it is seen by the human eye and has a length of A or more, then if the scanning line pitch of the inspection light beam is acceptable, five or more consecutive inspection light beams are detected. Since a defect is determined to be a defective product if a defect is detected over the scanning lines, defects on the sheet surface can be detected using the same criteria as the human eye. Note that such elongated defects are not necessarily detected at a uniform level, so depending on the detection based on the reflected light amount signal, some of the multiple scanning lines that cross such defects may be detected. Sometimes it is determined that there are no defects.

However, in such cases, most of the defects appear to the human eye as continuous defects, so the method of the present invention allows defects to appear not only continuously but also substantially continuously over a predetermined number of scanning lines or more. Even when the product is defective, it is determined that the product is defective, so that it is possible to perform defect detection that corresponds to visual inspection or the like and is more in line with the actual situation.

Additionally, when manufacturing magnetic recording tapes, etc., the long sheets are generally processed while running in the longitudinal direction during various manufacturing processes, so the surface of the long sheets has scratches and unevenness that extend in the running direction, that is, the longitudinal direction. Such defects are likely to occur. Therefore, when the long sheet is then cut in the longitudinal direction or in the middle direction and a surface inspection is performed on the cut sheet, most defects are found in a certain direction (the longitudinal direction).
It can be considered that whether or not the defect is visually conspicuous is determined by the length of the defect extending in this direction.

The defect detection method of the present invention is based on this empirical fact, and can easily detect defects by detecting the length of the defect in only one direction of the sheet (the direction corresponding to the traveling direction). It becomes possible.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a surface defect detection apparatus for carrying out a method according to an embodiment of the present invention. This device consists of a magnetic tape support web (hereinafter simply referred to as web) 2 that runs at a constant speed in the direction of arrow A between two take-up reels la and lb.
a light projecting means 3 for causing the light beam Q to perform a rask scan above;
A light receiving means 4 receives reflected light from the surface of the web 2 out of the light beam Q from the light projecting means 3, and generates a light amount signal, which is an electrical signal of a level corresponding to the amount of received light, and amplifies the light amount signal. an amplification section 5; a discrimination circuit 6 that compares the level of the light amount signal output from the amplification section 5 with a predetermined reference level and outputs a defect signal when the level of the light amount signal is lower; and a defect detection circuit 6; It consists of a counter/comparison circuit 8 that detects whether or not a signal appears continuously over a predetermined number of scanning lines or more, and outputs a judgment signal to an alarm circuit 7 if the signal appears continuously.

The light beam Q from the light projecting means 3 is scanned at a constant period in the width direction of the web, and since the web 2 runs at a constant speed as described above, the light beam Q is as shown in FIG. A rask scan is performed on the web surface as shown. The spot diameter of this light beam Q on the web 2 is 0.4 to 0.
．． It is about 5mm, and the web running speed is 15c.
m/SeC, and almost the entire surface of the web to be scanned is inspected. Incidentally, the incident angle α and reflection angle β of this light beam Q to the web 2 are, for example, 22
．． It is set at 5°. Light beam Q incident on light receiving means 4
contains light amount information of each part of the web 2 irradiated with the beam. That is, when the web surface is irradiated with the light beam Q, the amount of light received by the light receiving means 4 is maximum, and when the light beam Q deviates from the web surface, the amount of light received becomes approximately 0. If there is a surface defect 9, the amount of reflected light that enters the light receiving means 4 from that portion decreases. Thereby, by measuring the amount of light received by the light receiving means 4, it is possible to determine the presence or absence of surface defects such as scratches formed on the web 2. However, in reality, the light beam Q is photoelectrically converted into a light amount signal by the light receiving means 4, so the presence or absence of surface defects is determined by measuring the light amount information included in the light amount signal output from the light receiving means 4. become.

The discrimination circuit 6 extracts only the signal period corresponding to the reflected light from the web 2 from the light amount signal, and within this period,
If there is a level lower than a predetermined reference value, this is output as a "1" level defect signal, and specifically consists of a gate circuit and a comparator circuit. Note that the predetermined reference value can be set and changed from the outside using the cermet trimmer 6a.

In the counter/comparison circuit 8, the counter is incremented each time a defect signal is input, and when the value set by the external setting section 8a matches the value of the counter/comparison circuit 8, a judgment signal is output to the alarm circuit 7. be done. Also,
- When no defect signal appears during the scanning period, a reset pulse is output from the discrimination circuit 6 to the counter of the counter/comparison circuit 8, and the counter is reset to 0.
A determination signal is output only when defects exist continuously over the number of scanning lines set by the setting unit 8a. Note that since the probability that a defect will appear is extremely small, there is usually no need to consider the appearance of two defect signals during the -scanning period.

The alarm circuit 7 notifies the operator that there is a defective product by emitting a sound, but it also inputs a judgment signal into an LED to notify the operator visually, or inputs it into an automatic sorting machine to notify the operator that there is a defect. It is also possible to automatically sort items.

Next, a small defect 9a as shown in FIG. 3a is formed on the web 2.
In some cases, there is a slightly larger defect 9 as shown in Figure 3b.
The input signal and output signal to the discrimination circuit 6 in the case where there is b will be explained using FIGS. 4a and 4b.

If there is a small defect on the web 2 as shown in FIG. 3a, the defect 9a' is located only on one scan line (1) and not on scan lines (2) and (3). Therefore, the light amount signal Sa input to the discrimination circuit 6 includes the scanning line (1).
A signal portion smaller than the reference level P exists only in the section T1 corresponding to . A defect signal, which is a pulse signal of a predetermined width, is outputted from the discrimination circuit 6 in synchronization with the fall of this signal portion.

On the other hand, when a slightly elongated and large defect 9b is present on the web 2 as shown in FIG. 3b, the defect 9b is located on a plurality of scanning lines (1), (2), and (3). Therefore, the light amount signal sb input to the discrimination circuit 6 has sections TI corresponding to scanning lines (1), (2), and (3), respectively.

``2*There is a signal portion smaller than the reference level P for every T3.Therefore, in synchronization with the falling edge of each of these signal portions, the defective signal is detected by the discrimination circuit 6 at approximately one scanning period interval.
is output from. After this, this defect signal is output to the counter.
The signal is input to the comparator circuit 8, and the counter value is incremented to 3.

Therefore, if the setting value of the setting section 8a is, for example, 3, a determination signal will be output to the alarm circuit 7.

In the above embodiment, only when a predetermined number or more of defective signals are continuously input to the counter/comparison circuit 8,
In other words, a determination signal is output when a defect exists continuously over a predetermined number of scanning lines or more, but by changing the configuration of the counter/comparison circuit 8, It is also possible to output a determination signal when a defect exists in a predetermined number of eight or more scanning lines.

Further, the apparatus for carrying out the method of the present invention is not limited to the apparatus of the above embodiments, and it is possible to use apparatuses with various other configurations.

(Effects of the Invention) As explained above, according to the defect detection method of the present invention,
A sheet (web) is not immediately determined to be defective when one defect is detected, but a sheet is determined to be defective only when defects are detected substantially continuously across a predetermined number of scanning lines or more. In order to make a determination, it is possible to perform defect detection according to the type of sheet and the purpose of inspection. As a result,
For example, in appearance inspections, etc., only defects that are large enough to impress the human eye with defects can be determined as defective products, which corresponds to visual inspections, etc., and there is a risk of over-detection as in conventional methods. There is no.

Further, it is also possible to avoid a situation where the sheet is determined to be defective due to small dust or the like adhering to the sheet surface.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a surface defect detection apparatus for carrying out a method according to an embodiment of the present invention, FIG. 3a and 3b are schematic diagrams for explaining the relationship between defects formed on the web and scanning lines, and FIGS. 4a and 4b are schematic diagrams for explaining the relationship between defects formed on the web and scanning lines, and FIGS. 2 is a time chart showing the shape of a signal input to the discrimination circuit shown in FIG. 1 and a signal output from this circuit when there is a defect. 2...Support web (Giton)

Claims (1)

[Scope of Claims] A light beam is irradiated onto the surface to be inspected of the sheet, and the light beam is scanned in the width direction of the surface to be scanned and sub-scanned in the length direction, and the light beam from the surface to be scanned is In the defect detection method of detecting surface defects of the sheet based on the amount of reflected light of the light beam, the defects detected due to a change in the amount of reflected light of the light beam by a predetermined value or more are substantially continuous over a predetermined number or more of scanning lines. A defect detection method characterized in that when a defective sheet appears, the sheet is determined to be a defective product.