JPS59208446A - Laser type surface inspecting device - Google Patents

Abstract

PURPOSE:To make it possible to stabilize defect detecting accuracy, to facilitate the determination of an effective defect detecting range, and to facilitate the judgment of the causes of abnormality of devices and the like, by arranging a photoelectric converter element so that a laser beam is received at the scanning end of the laser beam, and detecting the level of the received light signal. CONSTITUTION:A photodiode 10 is arranged so that one end of beam scanning is received immediately before a plate to be inspected 5 is scanned by a laser beam. A signal is outputted only when one side is passed by an electromagnetic vibrating mirror 3 among the back and forth scanning of the mirror 3. The signal becomes a pulse signal, which is repeated at the vibrating frequency of the electromagnetic vibrating mirror 3. The height of the wave of the signal is proportional to the intensity of the laser beam. The output of the photodiode 10 is amplified by a preamplifier 11 and amplified by a main amplifier 30 in a signal processing circuit 9b. Then the height of the wave is detected by a peak-value detecting circuit 31. Based on this value, the gain of the main amplifier 21 is adjusted by a gain adjusting circuit 32. Then the wave height signal, which is constant with respect to the change in intensity of the laser beam 1, can be outputted from the amplifier 21. Thus the defect detecting sensitivity can be kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser surface inspection device that uses a laser to detect surface defects on metal plates and the like.

Conventionally, there have been devices of this type as shown in FIGS. 1 and 2. Referring to Figure 1, (1) is a laser beam emitted from an oscillator (not shown), (2) is a lens system for narrowing the laser beam to a required beam diameter, and (8) is a device that scans the laser beam. (4) is a plane mirror for changing the direction of the beam, (5) is the board to be inspected, (6)
is an optical fiber molded product for receiving and focusing the laser beam reflected light from the inspection plate (5), (γ) is a photomultiplier tube for photoelectric conversion, (8) is a preamplifier, (
9a) is a signal processing circuit, and as shown in FIG. An example of a comparator to extract, an example of a gate circuit that fully recovers the effective range of defect signal detection, and various processes for extracted defect signals?
In addition, it has a built-in determination circuit μs for determining defects.

The laser type surface inspection system that includes all of the above components operates as follows. A -n* laser beam (1) emitted from a laser oscillator (not shown) is passed through a lens system (2) to a plate to be inspected (5).
), the beam is focused to a predetermined beam shape, is swung by an electromagnetic oscillating mirror (8), and is scanned in the board width direction onto a board to be inspected (5) by a plane mirror (4) for changing the optical path. The reflected light of the scanned laser beam (1) is received and focused by the object fiber molded product (6), and the photoelectron multiplier tube (
γ) and converted into an electrical signal. The reflected light of the laser beam from the inspected plate (5) forms a special pattern due to the diffraction phenomenon, and if a defect exists on the inspected plate surface, this diffraction pattern changes and the amount of light received by the optical fiber molded product (6) changes. The defect signal will eventually appear as a change in the electrical signal.

This signal is amplified by a single-place amplifier (8), and the signal processing circuit (
9a), the signal processing circuit (9a) further amplifies it in the main amplifier (211) and outputs it to the waveform shaping circuit (211).
2) After converting the waveform into a waveform that is easy to detect defective signals, a certain set threshold level '-Mtft-ratio M a 1I81 CH constant v HEL or less signal is extracted, and then the defect signal is extracted. In an example of a gate circuit that determines the effective range of signal extraction, only defective signals are extracted. This signal is passed through a judgment circuit (support) that detects and calculates the degree of defect according to the threshold level, the continuity of the defect signal, the width of the defect signal, etc., and classifies the rank of the defect, etc., and the judgment result is output. It's starting to look like this.

Conventional equipment is configured as described above, so if there is a change in the laser beam gi due to a change in laser power or contamination of the optical system, the signal level will drop even though there are no defects. Misjudgments were sometimes made, and accurate judgments could not be made. Further, there is a drawback that when an abnormality occurs in the optical equipment, such as an abnormal amplitude change in the electromagnetic vibrating mirror (8) or a laser stops oscillating, the abnormal operation cannot be easily confirmed.

Therefore, the present invention was created in order to eliminate the above-mentioned drawbacks of the conventional ones, and is equipped with a small, high-speed response photoelectric conversion element that detects the laser beam scanning the inspection target plate, and adjusts the laser power. By inducing an electric signal according to the intensity of the detection signal and monitoring the entire laser power, the amplification gain of the input signal to the signal processing circuit that performs defect judgment is adjusted according to the level of the detected signal. The overall purpose of the present invention is to provide a laser type surface inspection device that can perform defect determination and also detect abnormalities in the optical system, such as detection in the scanning direction and abnormality detection in the electromagnetic vibrating mirror.

Hereinafter, one embodiment of the present invention will be explained based on FIGS. 3 and 4, in which the same parts as in FIGS. 1 and 2 are denoted by the same reference numerals. In FIG. is the board to be inspected (
5) A photodiode, which is a photoelectric conversion element, is installed so that a portion of the laser beam (1) is received at a position in front of the surface that is scanned upward, and the detection signal is sent to the preamplifier. α1) is amplified and sent to the signal processing circuit (9b) of this embodiment. However, the signal processing circuit (9
b), as shown in the detailed configuration in FIG. 4, includes an example of a main amplifier that fully amplifies the detection signal via the preamplifier 01), and a peak amplifier that detects the peak level of the pulse signal via this preamplifier 01). Value detection circuit (811, main amplifier according to the peak level of the pulse (211 gain adjustment circuit L'11.1B+31 is an example of a comparator that detects the presence or absence of the pulse signal) which controls the amplification level of the pulse signal. An example of a comparator that detects that the pulse signal is above a certain value, and an abnormality detection circuit that detects that a pulse signal is continuously generated at a certain period and outputs an abnormality detection signal when there is an interruption (n) is provided to accurately determine defects in the inspection target board (5) as will be described later.

That is, in FIG. 6, the photodiode is arranged to receive one end of the beam scanning in front of the surface on which the laser beam is scanned on the inspection target board (6), and the photodiode is arranged to receive one end of the beam scanning in front of the surface where the laser beam is scanned on the inspection target board (6), A signal is output only when one side of the scan passes. This signal becomes a pulse signal that repeats at the vibration frequency of the electromagnetic vibrating mirror (8) 6-, and its peak value is proportional to the intensity of the laser beam. Therefore, after the output of the photodiode 00) is amplified by the preamplifier ◇1), the main amplifier (80) of the signal processing circuit (9b)
), the peak value is detected by the peak value detection circuit (81), and this value is used to connect the main amplifier (
If the gain of 211 is adjusted by the amplifier (n), a constant peak value signal will be generated by the amplifier (
21), the defect detection sensitivity is constant.

On the other hand, the output signal of the main amplifier (1) is completely shaped into a pulse signal by a comparator 183) having a threshold level sufficiently lower than its peak value, and the entire gate circuit example is controlled using the phase of this shaped pulse signal as a reference. Sunba, 1! Sharp vibrating mirror (8
) given scanning direction? You can select and determine the effective defect detection range.

Furthermore, the output signal of the main amplifier (211) is compared with a comparator (open) that waits for a certain threshold, and the abnormality detection circuit (kari) monitors whether or not this signal occurs at a predetermined period. If so, it is sent to the judgment circuit (E) as an abnormal signal.
For example, it is possible to determine abnormalities such as when the laser power falls below a specified value, when the laser malfunctions, or when the amplitude of electromagnetic vibration (81) falls below a specified value.

In the above embodiment, all the detection elements are photodiodes, but other photoelectric conversion elements may be used if the detection conditions are met. Also, when all rotating mirrors are used instead of the electromagnetic vibrating mirror (8), the same effect can be obtained except for the selection of the scanning direction.

As described above, according to the present invention, the photoelectric conversion element is rearranged to receive the beam at the scanning end of the laser beam, and the level of the received light signal is detected, thereby stabilizing defect detection accuracy. This makes it easier to determine the effective range of defect detection and to determine the cause of device abnormality.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional laser type surface inspection device, Fig. 2 is a block diagram showing a conventional signal processing circuit, and Fig. 3 is a block diagram of a laser type surface inspection device according to an embodiment of the present invention. 4 are block diagrams of the signal processing circuit. (8): Electromagnetic vibrating mirror (5): Board to be inspected (9a),
(9b): Signal processing circuit: Photodiode Ql): Preamplifier (211: Main amplifier example: Boot circuit (To): Signal processing circuit): Main amplifier
+81): Peak value detection circuit t, '121 Nigain adjustment circuit 1831: Comparator (341: Comparator
(2): Abnormality Detection Circuit In the figures, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa 9- Figure 1 Figure 2 Procedural amendment (voluntary) Mr. Commissioner of the Japan Patent Office], Indication of case Japanese Patent Application Sho II 8-84321 No. 2, Name of invention Laser type surface inspection device 3, Make amendment Contents of the amendment (1) “(1)” on page 2, lines 13 to 14 of the specification
1(1) is a laser oscillator that emits a laser beam" is corrected to "1 (1) is a laser oscillator that emits a laser beam." (“The laser beam (1) emitted from a laser oscillator (not shown) is” in 21 Specification No. 300, lines 9 and 10.)
The statement "The laser beam emitted from the laser oscillator (1) is" is corrected. (3) The statement ``Laser beam (1) is 1'' on page 5, line 16 to line 17 of the specification is corrected to ``Laser beam is''. (4) In the drawings, Figures 1 and 3 will be corrected as shown in the attached sheet. 7. Catalog drawing of attached documents 1st ring top 2-

Claims (1)

[Scope of Claims] (1) A laser beam scanning means for scanning a laser beam on an object to be inspected; In a laser surface inspection apparatus equipped with a signal processing circuit for determining all defects on the surface, a photoelectric conversion element for detecting the entire intensity of the laser beam scanning the object to be inspected is provided, and the signal processing circuit is provided with a photoelectric conversion element for detecting the entire intensity of the laser beam scanning the inspection object. A laser type surface inspection device characterized by having a gain adjustment circuit that adjusts the amplification gain of an input signal according to the level of a detection signal by an element. (2) The signal processing circuit includes a first comparator that controls the gate phase of a gate circuit that detects the presence or absence of a detection signal from the photoelectric conversion element and determines an effective defect detection range. The laser type surface inspection device described in Section 1. (8) confirming that the output pulse of the second comparator, which is sent out when the detection signal from the photoelectric conversion element is equal to or higher than a predetermined level, is generated at a predetermined period in the processing circuit;
Claim 1 and Fi 2 include an abnormality detection circuit that sends out an abnormality detection signal when the output pulse is interrupted.
The laser type surface inspection device described in Section 1.