JPH0132922B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a knife mark detection circuit of a knife mark detection device for detecting linear scratches (knife marks) formed on the surface of a sheet-like object to be inspected.

FIG. 1 shows a schematic configuration diagram of a knife mark detection device A, in which light from a lamp 1 is transmitted through a cylindrical lens 2.
This strip-shaped light 3 is projected onto a sheet-shaped object 4 to be inspected from diagonally above in the width direction of the object 4 to be inspected. As shown in FIG. 2, a cylindrical lens 7 is disposed vertically above the light emitting area through a slit plate 6 in which a slit 5 is opened in the width direction of the object 4 to be inspected. Furthermore, a ground glass 8, this slit plate 9, and a photomultiplier 10 are arranged in this order, and are used to remove linear scratches (knife marks) caused by scraping of the slicer blade or clogging with foreign objects on the surface of the inspected object 4. (hereinafter referred to as ) 11 reaches the light projection site, an image of the knife mark 11 is formed on the ground glass 8 via the slit 5 and the cylindrical lens 7. This knife mark image is passed through the slit 12 of the slit plate 9 to the photo multiplier 10.
It receives light. The object to be inspected 4 moving in this way
The knife mark 11 on the surface is converted into an electrical signal, and the conventional knife mark detection circuit amplifies the output signal of the photo multiplier 10 with an appropriate amplifier to generate the amplifier shown in FIG. 3a. When the voltage exceeds the threshold level L, knife mark detection is performed by generating the judgment signal shown in Figure 3b, but as shown in Figure 3a, the output voltage of the amplifier is There was a problem that the S/N ratio of the knife mark signal A was not very good due to fluctuations due to the undulations (undulations, etc.) of the knife mark signal A. In addition, the noise level fluctuates due to the difference in the background color of the inspected object 4 for each product type.
It was necessary to set a threshold level L for each product type.

The present invention has been made in view of the above-mentioned problems, and its purpose is to remove linear scratches (knife marks) on a sheet-like object to be inspected from undulations, power supply noise, and An object of the present invention is to provide a detection circuit for a knife mark detection device capable of reliably detecting by eliminating the influence of differences in brightness depending on the type of an object to be inspected.

The present invention will be explained below using examples. FIG. 4 shows a circuit block diagram of one embodiment, in which the outputs of ten photomultipliers are amplified by an amplifier 13. The output of this amplifier 13 is passed through a low-pass filter 14 of about 20 Hz and inputted to a subtracter 15, and subtraction is performed with the output of the amplifier 13 that does not pass through the low-pass filter 14 to remove the influence of the waviness of the object to be inspected 4. That's what I do. 16 is a high pass filter of about 200 Hz, and this high pass filter 16 is for removing power supply noise (for example, 120 Hz). 1
7 is a divider, and this divider 17 divides the signal after passing through the high-pass filter 16 by the output of the amplifier 13 after passing through the low-pass filter 14, thereby removing the influence of brightness difference due to the type of the object to be inspected 4. (Normalization)
This is to improve the S/N ratio. 18 is a comparator, which compares the output of the divider 17 with a preset threshold level L, and when the output of the divider 17 exceeds the threshold level L as shown in FIG. 5a, that is, the knife mark signal is detected. When A exists, a determination signal is generated as shown in FIG. 5b.

FIG. 6 is a circuit diagram of another embodiment of the present invention,
In this embodiment circuit, the output of the amplifier 13 is passed through a low-pass filter 14 and a high-pass filter 16, respectively, and divided by a divider 17.
Subtraction in the illustrated embodiment is omitted.

The present invention is configured as described above to pass amplified signals obtained by amplifying the output of the photo multiplier to 20 Hz.
a divider that has a low-pass filter of about 100 kHz and a high-pass filter for removing power supply noise, and divides the output signal of the high-pass filter by the output signal of the low-pass filter, and compares the output of the divider with a preset threshold level. Since it is equipped with a comparator that outputs a judgment signal when the output of the divider exceeds a threshold level, it is possible to eliminate the influence of fluctuation components in the level of the amplified signal due to undulations of the object to be inspected. Power supply noise can be removed. Moreover, since it is equipped with a divider that divides the output signal of the high-pass filter by the output signal of the low-pass filter, it is possible to calculate the fluctuation component of the knife mark part of the object to be inspected from other parts by ratio (normalize it). Therefore, it is possible to cancel out the difference in brightness between the knife mark part and other parts, which varies proportionally depending on the type of object to be inspected. If it's a knife mark,
The same variation component can be extracted, and the influence of the difference in brightness of the type of object to be inspected can be removed.
As a result, the S/N ratio of the knife mark signal improves. Since a knife mark is detected by comparing the output of this divider with a threshold level in a comparator, there is an advantage that there is no need to change the threshold level of the comparator for each type of object to be inspected.

[Brief explanation of drawings]

Fig. 1 is a partially omitted schematic configuration diagram of the knife mark inspection device, Fig. 2 is an enlarged side sectional view of the same as above, and Fig. 3 is a partially omitted schematic diagram of the knife mark inspection device.
Figures a and b are time charts for explaining the operation of the conventional example, Figure 4 is a circuit block diagram of an embodiment of the present invention, Figures 5 a and b are time charts for explaining the operation of the same, and Figure 6 is 2 is a circuit block diagram of another embodiment of the present invention, in which 4 is an object to be inspected, 10 is a photomultiplier, 14 is a low-pass filter, 16 is a high-pass filter, 17 is a divider, 18 is a comparator, and A is a knife mark signal. , L is the threshold level.

Claims (1)

[Scope of Claims] 1. A light projecting means that projects a band-shaped light onto the surface of a sheet-like object to be inspected, and a photo multiplier that receives light of an image formed by reflected light from the light projecting portion. The knife mark detection device includes a low-pass filter of about 20 Hz that passes amplified signals obtained by amplifying the output of the photo multiplier, and a high-pass filter for removing power supply noise. It comprises a divider that divides the output signal of the filter, and a comparator that compares the output of the divider with a preset threshold level and outputs a measurement signal when the output of the divider exceeds the threshold level. A knife mark detection circuit of a knife mark detection device characterized by: 2. The knife mark of the knife mark detection device according to claim 1, wherein the knife mark is passed through a high pass filter after subtracting the output signal of the low pass filter and the amplified signal obtained by amplifying the output of the photo multiplier. detection circuit.