JPS6217725B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technique for detecting an inspection position in a method of optically scanning an object to be inspected using a flying spot method or a flying image method using a rotating mirror.

In processes where products are generally manufactured in continuous strips, such as glass plates, metal plates, and woven fabrics, optical scanning inspection methods are widely used as a method for continuously inspecting the entire width of the product, such as the thickness of the product and the presence or absence of defects on the product surface or inside. It is being done. Inspection methods using optical scanning can be roughly divided into flying spot methods, in which a light beam from a light source is reflected by a rotating mirror and then projected onto the object to be inspected, either directly or via a concave mirror, and the light spot is moved back and forth on the object to be inspected; 2. Flying image method in which the light reflected from the body is reflected by a rotating mirror, and the reflected image of the object to be inspected is moved back and forth to the optical inspection device.
There is a method.

All of these methods have in common that the object to be inspected is sequentially inspected with light, small parts at a time, and in these inspection methods, it is extremely important to accurately grasp the inspection position on the object throughout the entire scan. be.

The method of detecting the inspection position in such optical scanning is to generate electrical reference pulses at regular intervals, count these reference pulses at the same time as the start of scanning,
The most common method is to determine the inspection position from the relationship between the number of pulses known in advance and the distance in the scanning direction on the inspection object (section division and address assignment based on pulses).

As the reference pulse, a clock pulse at equal time intervals is used, or a disk called a rotary encoder, which has a large number of slits arranged at small intervals in the circumferential direction, is rotated in synchronization with a rotating mirror.
Conventionally, it has been most common to use pulses obtained by converting the intermittent light passing through the slit of the rotary encoder into an electrical signal.

However, when clock pulses are used as reference pulses for position detection, if the rotation speed of the rotating mirror is uneven, the position detection results (addresses based on the reference pulses) for the same inspection position will vary from scan to scan, and the reliability of the position data will be low. At the same time, in the case of defect detection, it can cause misunderstandings regarding the type or size of defects.

Also, in the method using a rotary encoder,
Due to manufacturing difficulties and strength issues, it is not possible to make the slit spacing of the rotating disk very close, so if the object to be inspected is relatively large, such as a glass plate, segmentation based on pulses along the scanning line is not possible. There is a problem that (unit address width) becomes coarse and sufficient position detection accuracy cannot be obtained.

A main object of the present invention is to provide a method that can detect an inspection position with high precision in optical scanning using a rotating mirror.

Another object of the present invention is to provide a position detection method in optical scanning that is not affected by uneven rotational speed of a rotating mirror.

Still another object of the present invention is to provide a position detection method in optical scanning that can subdivide divisions for positioning along a scanning line at an extremely high density.

In the method of the present invention, laser interference fringes are projected onto a rotating mirror, the interference fringes reflected by the rotating mirror are received by a light receiver, and the number of interference fringes passing through the light receiver as the rotating mirror rotates is counted. Then, the inspection position is determined based on this count value.

In the present invention, the term "rotating mirror" includes both a continuously rotating polygon mirror and a so-called oscillating mirror whose reflecting surface swings and rotates within a certain angle range.

The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIG. 1 shows an example in which the method of the present invention is applied to a flying spot type defect inspection apparatus. Reference numeral 1 denotes an object to be inspected, for example, a glass plate manufactured in a continuous band shape, which is transported in the direction of arrow 2.

The axis 3 tilted upward on the transport path of this glass plate 1
There is a polygonal rotating mirror 4 that continuously rotates around it, and a light beam 6 emitted from a main light source 5 is reflected by a reflective surface 4A of the rotating mirror 4 to form a light spot 7 on the glass plate 1.

The light spot 7 scans the glass plate 1 by reciprocating in the width direction on the glass plate 1 as the rotating mirror 4 rotates. Below the glass plate 1, there is a main light receiving device 9 configured by arranging a large number of photoelectric conversion elements along the reciprocating path of the light spot 7, that is, along the scanning line 8. Changes in the amount of transmitted light due to defects such as scratches, foreign matter, bubbles, etc. existing on the surface or inside are converted into electrical signals and transmitted to a defect determination device (not shown). On the other hand, the inspection position in the width direction of the glass plate 1 along the scanning line 8 is detected by the method described below and transmitted to the defect determination device.

A laser light source 12 and a light receiver 15 are fixedly installed, and the beam emitted from the laser light source 12 is converged by an optical lens system 13 and then an interference fringe generating device 14
The laser beam 20 containing the interference fringes is reflected by the reflecting surface 4A of the rotating mirror 4 and then received by the light receiving device 15.

More specifically, as shown in FIG. 2, the interference fringe generating device 14 is composed of a transparent plate having highly parallel planes, and a laser beam 21 is magnified by a lens 13A from an oblique direction onto the transparent plate 14, and then converged by a lens 13B. and project it. A semitransparent coating 16 is provided on one side of the transparent plate 14, and a reflective coating 17 is provided on the other side at a position that does not obstruct the optical path of the projection beam.
is provided. A part of the projected beam is covered with a semi-transparent coating 1
6 and the reflective coating 17 inside the transparent plate 14, and then emitted as a sub beam 23 in the same direction as the transmitted main beam 22. Both beams 22 and 23 interfere with each other while being diffused, and interference fringes with a very strong contrast between light and dark appear at the crossing portion 20 due to the optical path difference between the two beams. Although it is desirable to provide the semi-transparent coating 16 and the reflective coating 17, sufficiently clear interference fringes can be obtained even if they are not provided.

In addition, the converged laser beam is reflected on the surface of the transparent plate 14, and this reflected main beam and the transparent plate 14
Interference fringes may be generated by a main beam reflected internally and a sub beam emitted in the same direction.

The interference fringes are reflected by the reflecting surface 4A of the rotating mirror 4, and the reflected interference fringes 24 are received by the light receiver 15 through the slit 25.

Furthermore, a start pulse receiver 10 and an end pulse receiver 11 are provided at both ends of the main receiver 9 to detect the start and end of scanning for each scan.

As shown in FIG. 3, the interference fringe receiver 15 is connected to a counter 26, and the change in brightness of the interference fringe 24 passing through the receiver 15 as the rotating mirror 4 rotates causes the receiver 15 to receive an electrical signal. The signal is converted into a change, subjected to appropriate waveform shaping, and counted by a counter 26 in the form of pulses Pi corresponding to interference fringes.

A start pulse Ps is input from the photoreceiver 10 to this counter 26, and upon receiving this start pulse Ps, counting of interference fringe pulses Pi is started, and the photoreceiver 11
The counting ends upon receiving the end pulse Pe from.
The count data from the counter 26 is sent to the defect discrimination device 27.
On the other hand, a defect detection signal Pd is sent from the main light receiving device 9 to the defect discriminating device 27.

Based on the above results, the correspondence data between the addresses along the scanning line 8 based on the interference fringe counting start position and the inspection results (presence or absence of defects) within each address, for example, the third
A data table 29 indicating that a defect 30 exists from address r to address r+2 as shown in the figure.
is created in the defect discriminating device, and the edge position address of the glass plate 1 is detected in the same manner as the defect.

Then, the relative distance from the edge of the glass plate 1 to the defect is calculated based on the data regarding the unit address width along the scanning line 8 that has been given to the defect discriminating device in advance and the above address data. Note that the scanning position in the transport direction of the glass plate 1 is also measured at the same time as the position along the scanning line 8, but since this is not directly related to the present invention, a detailed explanation will be omitted. Based on this result, appropriate measures are taken in the cutting or forming process, such as removing glass plate portions containing defects or changing operating conditions.

Regarding interference fringes, the spatial density D of interference fringes (number per unit angle of beam divergence angle) is approximately as follows: D=tsin2θ/λo√ ² − ² 〓 t: Thickness of transparent plate 14 θ: Laser beam Incident angle λo: Laser beam wavelength n: Refractive index of the transparent plate 14. Therefore, in order to obtain interference fringes as closely spaced as possible, a thick transparent plate 14 is used. Furthermore, it is most effective to set the incident angle of the laser beam to around 49 degrees, assuming that the refractive index of the transparent plate 14 is 1.52.

According to experiments by the present inventors, when a commercially available float glass plate with a thickness of 19.0 mm is used as the transparent plate 14 having a highly parallel plane, the rotating mirror reflecting surface 4A
The number of interference fringes included within 1 degree of rotation angle is 172 when the laser beam incident angle θ is 34 degrees, 185 when the laser beam incident angle is 39 degrees,
It was confirmed that there were 197 lines at 49 degrees, 184 lines at 59 degrees, and 169 lines at 64 degrees. On the other hand, even with the most precise rotary encoder plate available at present, the number of slits per degree of rotation angle is less than 30, so the method of the present invention dramatically increases the division of the inspection object during optical scanning compared to the conventional method. Density subdivision is possible.
Furthermore, according to the method of the present invention, the inspection position address is counted in synchronization with changes in the rotation angle of the rotating mirror, so even if there is uneven rotation speed of the rotating mirror, the inspection position can be accurately detected without being affected by this. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the method of the present invention;
FIG. 2 is an enlarged plan view of the main part of FIG. 1, and FIG. 3 is a block diagram schematically showing the signal processing method in the same embodiment. 1... Test object, 4... Rotating mirror, 4A... Reflective surface, 8... Scanning line, 12... Laser light source, 14
...Interference fringe generator, 15...Interference fringe receiver, 2
4...Interference fringes, 26...Counter.

Claims (1)

[Scope of Claims] 1. In an optical scanning method in which the object to be inspected is sequentially inspected small parts while moving the light projected onto the object to be inspected or the light reflected from the object to be inspected using a rotating mirror, laser interference fringes are formed on the rotating mirror. The interference fringes projected and reflected by a rotating mirror are received by a light receiver, the number of interference fringes passing through the light receiver as the rotating mirror rotates is counted, and the inspection position is determined based on the counted value. A position detection method in optical scanning characterized by: 2 Laser interference fringes are created by focusing a converged laser beam obliquely on a transparent plate with highly parallel planes, and dividing the main beam through the transparent plate or reflecting it on the surface, and the main beam after being reflected inside the transparent plate. 2. The method according to claim 1, wherein the method is generated by mutual interference with a sub-beam emitted in a direction.