JPS5949537B2 - Defect detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a light beam in a defect detection device using a conical mirror.

In a defect detection device that uses a rotating polygon mirror to scan a light beam, it is desirable that the scanning locus on a flat plate be the same for any of the reflective surfaces of the polygon mirror.

However, in reality, the angles formed between the reflecting surface of the polygon mirror and the rotating axis are slightly different for each surface, so conventionally, the trajectories were not the same.

Due to these causes, the scanning line fluctuates, so when inspecting the surface of a traveling sheet material to be inspected, even if the entire surface is scanned without repeating, there will be areas that are not scanned and defects will be overlooked. become. As a way to correct this inconvenience, attempts have been made to minimize the fluctuation of the scanning line by improving the manufacturing precision of the polygon mirror or by reducing the vibrations associated with rotation, but these efforts are quite difficult. When small fluctuations become a problem, we run into a barrier due to the limitations of manufacturing technology, and overcoming this requires dramatic innovation in technology or an enormous economic burden.

The present invention is intended to provide an apparatus for optically correcting variations in a scanning light beam, while recognizing such limitations in manufacturing accuracy.

In other words, in a defect detection device using a conical mirror, the present invention uses an imaging optical system using a lens or the like to detect light emitted from a single object point, regardless of its direction. By applying the characteristic of light converging at one point, the scanning method and light receiving method have been devised to enable detection of surface defects on the object to be inspected with high accuracy and sensitivity.

Now, the configuration and operation of the present invention will be explained with reference to the drawings.

FIG. 1 shows a program diagram of a conventional defect detection device, in which the light beam emitted from a device 1 that emits a light beam is arranged so that a light spot is connected on the surface of the material to be inspected (traveling sheet material) 7. It passes through the arranged lens system (consisting of the first lens 2, second lens 4, and slit 3) to the rotating polygon mirror 5, and is scanned by the rotating polygon mirror 5, which is rotated by a drive source (not shown). The light beam passes through a semi-transparent mirror 9 (second plane reflecting mirror), has an optical path bent at right angles by a conical mirror 6, and travels in one direction in an arc shape from point A to point B and point C. Scan to.

The light reflected by the traveling sheet material (in the case of a transparent sheet, the light reflected by the first plane reflecting mirror 8) passes through the conical mirror 6 again, is reflected by the half mirror 9 of the second reflecting mirror, and is received. Gather in vessel 10.

The signal photoelectrically converted by the light receiver 10 is used to determine the size, length, grade, coordinates, etc. of the flaw in a known signal processing system (not shown).

In such an apparatus, fluctuations in the scanning line often occur due to fluctuations in the angles formed by the respective reflecting surfaces of the rotating polygon mirror 5 with respect to the rotation axis.

Figures 2, 3, and 4 show a plan view, a side view, and a schematic diagram of the arrangement of one embodiment of the present invention, and the arrangement of each component is shown for ease of explanation. are shown on the same plane. The cylindrical lens 21 is for making a light beam such as a laser beam as small as possible in the side view (FIG. 3) at the reflecting surface position of the rotating polygon mirror 5. This light beam is scanned in a plan view (FIG. 2). The scanned light beam is
The first lens 2 is arranged so that its reflective surface is at the focal length position, and its optical axis is made parallel to the optical axis of the lens 2. Inject under the same conditions.

The light beam that has passed through the second cylindrical lens 41 is scanned by the lens 2 with point 0 as the scanning center, and is passed onto the traveling sheet material 7 via the conical mirror 6 having its rotation center axis at point 0. is scanned.

When the running sheet material T is transparent, it is reflected by the first plane reflecting mirror 8, and then reflected again by the conical mirror 6,
They are separated by a semi-transparent second plane reflecting mirror 9.

The optical position is at point 0 with the second plane reflecting mirror 9 as the plane of symmetry.
A light receiver 10 having a light entrance window at a position such that
Reflected light is incident on the

The optical axes of the scanning light and the reflected light may coincide or may be slightly shifted.

When the incident optical axis is slightly shifted, the second reflecting plane mirror 9 does not necessarily need to be a half mirror, and may be a total reflection mirror that reflects almost all of the reflected light to the light receiver 10. Regarding Figure 2 (top view), rotating polygon mirror 5
The light beam on the reflecting surface is a very small point in Fig. 3 (side view), and this point is considered to be the object point of the lens diameter, and the light emitted from this object point is transmitted to the traveling sheet material 7 or the 1
Since the image is formed on the plane reflecting mirror 8 of the rotating polygon mirror 5, even if the angles of the reflecting surfaces of the rotating polygon mirror 5 with respect to the rotation axis vary, the object point does not change.
Since only the direction of the light emitted from the object point changes at the image point, there is no variation in the scanning locus even if there is variation in the angle of the reflecting surface with respect to the rotation axis at the image point.

The optical axis of the light reflected by the traveling sheet material 7 or the first plane reflecting mirror 8 becomes the same as the incident optical axis.

Therefore, by using the semi-transparent second flat reflecting mirror, the light can be received in the form of points by the light receiver 10. Thus, according to the present invention, an optical system that corrects variations in the scanning trajectory is combined with a scanning optical system using a conical mirror, so that it is possible to avoid overlooking defects due to overlapping scanning or interlaced scanning, or to avoid overlapping the same defective part. This eliminates the inconvenience of having to manually detect the device, allowing for stable testing.

Furthermore, the deflection of the reflected optical axis at the photoreceiver window position is reduced, and a mask with minute holes can be provided on the photoreceiver window, making it possible to perform very highly sensitive inspections.

[Brief explanation of the drawing]

Figure 1 is a program diagram of a conventional defect inspection device.
FIGS. 2, 3, and 4 show a plan view, a side view, and a process diagram of an embodiment of the present invention. 1... Device that emits a light beam, 2, 4...
...first and second lenses, 3...slits,
5... Rotating polygon mirror, 6... Conical mirror,
7... Material to be inspected (running sheet material), 8, 9...
...First and second reflective plane mirrors, 10... Light receiver, 21, 41... First and second cylindrical lenses.

Claims (1)

[Claims] 1. A device that emits a light beam, a first cylindrical lens that minimizes the size of the light beam in the direction of the rotation axis of the polygon mirror on the reflecting surface of a rotating polygon mirror, and a device that scans the light beam by rotation. A rotating polygon mirror, a first lens arranged so that its focal point is at the position of the reflecting surface of the rotating polygon mirror, a second cylindrical lens whose optical axis is the same as that of the first lens, and a second lens.
a conical mirror having a central axis of rotation at the focal position of the second lens; a first flat reflecting mirror that reflects the light reflected by the conical mirror back to the conical mirror; It is characterized by comprising a second plane reflection mirror for separating the reflected light from the plane reflection mirror via a conical mirror, and a light receiver configured to receive and detect the separated light. defect detection equipment.