JPH0382941A - Laser inspection apparatus - Google Patents

Abstract

PURPOSE:To make it possible to perform accurate inspection without the effects of disturbance light and temperature change by modulating a laser beam so as to decrease the power of the laser beam or to make the power to be zero during one scanning of the laser beam. CONSTITUTION:A laser driving circuit 11 modulates a semiconductor laser 12 constituting a laser light source at a constant period and drives the laser. The circuit 11 forms two clock signals and imparts the signals to a received- light-signal processing circuit 14. The circuit 14 detects the output signal when the power of the laser beam in the output signal of a means for detecting transmitted light or reflected light from a material to be inspected is decreased or becomes zero. The signal is made to be a reference signal. Namely, the circuit 14 receives the two clock signals of a correcting clock and a data clock and processes the electric signal from a photodetector 13 for receiving the reflected light from the material to be inspected. The signal is amplified and binary-coded. The binary-coded signal is imparted to an arithmetic circuit 15, and specified operation is performed. Thus, the presence or absence of the defects, the shapes of the defects and the like in the material to be inspected are judged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser inspection device and a laser inspection method for inspecting defects on the surface of a sheet-like object by irradiating the surface of a sheet-like object with a laser beam.

[Conventional technology]

2. Description of the Related Art There is a laser inspection device that uses a laser beam to inspect the surface of a sheet-like object such as a synthetic resin film for defects. Such a laser inspection device uses a sensor head made of bundled optical fibers or a transparent light guide, and FIG. 1 shows the vicinity of the sensor head of such a laser inspection device. A laser beam emitted from a laser light source 1 is made into a desired beam diameter by a lens system 2, reflected by a rotating polygon mirror 3 and a fixed reflecting mirror 4, and irradiated onto a sheet-like object 7, which is an object to be inspected. Here, the sheet-like object 7 is moving in its longitudinal direction, that is, in the direction of the arrow Y in the figure, and the laser beam is scanned in the direction of the arrow X in the figure, which is perpendicular to the Y direction, by the rotation of the rotating polygon mirror 3, and the sheet-like object is moved in the direction of the arrow X in the figure, which is perpendicular to the Y direction. 7 is irradiated. The reflected light (or transmitted light) of the laser light irradiated onto the sheet-like object 7 is received by the sensor head 5, and is applied to the photoelectric converter 6 via the optical fiber, where the optical signal is converted into an electrical signal.

[Problem to be solved by the invention]

In the conventional laser inspection apparatus described above, when disturbance light enters the light receiving section, the light reception signal is affected, and a non-defect may be determined to be a defect, or the area of a defect may be misidentified.

Furthermore, drift may occur in the circuit that amplifies the signal from the photoreceiver due to the influence of temperature, etc., and problems similar to disturbances may occur.

Therefore, an object of the present invention is to provide a laser inspection device that can perform accurate inspection without being affected by ambient light or temperature changes.

[Means to solve the problem]

In order to achieve the above object, in the present invention, one of the laser beams is
Reduce the laser beam power during the scans or zero
During this period, reflected light or transmitted light from the object to be inspected is detected and used as a reference signal, which is used as a reference for evaluating subsequent reflected light or transmitted light.

That is, according to the present invention, there is provided a means for irradiating an object to be inspected moving in the Y direction with a laser beam while scanning in the X direction, and a means for transmitting transmitted light or reflected light from the object to be inspected of the laser beam to one end face. a photoelectric conversion means for converting an optical signal emitted from the other end surface of the sensor head into an electrical signal; In a laser inspection device comprising an arithmetic circuit for determining a diffusion situation, means for modulating the laser beam at a constant cycle so as to reduce the power of the laser beam at least once per scan or to make it zero; Among the output signals of the means for detecting transmitted light or reflected light from the object to be inspected in response to the modulating means, an output signal when the power of the laser beam decreases or becomes 0 is detected and used as a reference signal. and the means to
There is provided a laser inspection apparatus further comprising means for processing an output signal of the detecting means using the reference signal as a reference.

[For production]

Since the laser inspection device of the present invention has the above configuration,
The level of normal reflected light or transmitted light can be measured based on the light reception signal when the laser beam power decreases or becomes 0. Therefore, accurate inspection can be performed without being affected by ambient light, temperature drift, etc.

〔Example〕

Embodiments of the laser inspection apparatus of the present invention will be described below with reference to the drawings. The appearance of the vicinity of the sensor head of the laser inspection apparatus of the present invention is the same as that shown in FIG. That is, the laser beam emitted from the laser light source 1 is directed toward the object to be inspected 7 moving in the Y direction through the lens system 2 and the rotating reflecting mirror 3.
The laser beam is irradiated by means of a fixed reflecting mirror 4 that scans and irradiates in the X direction.

The reflected light from the object to be inspected 7 is received by the sensor head 5A, guided to the photoelectric conversion element 6, and converted into an electrical signal. This electrical signal is processed in the signal processing circuit described below as follows.

FIG. 2 is a block diagram showing an electric circuit of the laser inspection apparatus of the present invention. As will be described later, the laser drive circuit 11 drives the semiconductor laser 12 constituting the laser beam 111X1 while modulating it at a constant cycle, and also generates two clock signals and supplies them to the light reception signal processing circuit 14. The light receiving signal processing circuit I4 receives the above two clock signals, that is, the correction clock and the data clock, and processes, amplifies, and binarizes the electrical signal from the light receiving element 13 that receives the reflected light from the object to be inspected 7. It is. The binarized signal is given to the arithmetic circuit 15, where a predetermined arithmetic operation is performed to determine the presence or absence of a defect in the inspection object 7, the shape of the defect, etc. This arithmetic circuit (
5 can be used as is, so further explanation will be omitted.

FIG. 3 is a block diagram showing details of a part of the laser drive circuit 11 and the received light signal processing circuit 14 shown in FIG. 2. A-1 in the figure is a signal of each part, and a waveform diagram is shown in FIG. 4. The phase synchronization circuit 21 outputs the clock signal from the oscillator 20 in synchronization with the line start signal A. Frequency divider 22
The pixel counter 24 generates a signal C obtained by dividing the signal B by (/2) and a signal obtained by dividing the frequency by 1/4. is loaded, the pulses of the signal are counted down, and when the value becomes O, a pulse E is generated.The D flip-flop 26 is responsive to the pulse E, and its D terminal is grounded, and the pulse E is generated. A signal A is applied to the S terminal, and a reset signal is applied to the R terminal.This line start signal responds to the one of the many optical fibers in the sensor head 5A that receives the first reflected light in the X direction scan. The reset signal is given by the control computer or is a signal generated after a predetermined period of time has passed after the power is turned on.The Q terminal output signal F of the D flip-flop 26 is given as the enable signal of the frequency divider 22. and is also given to the encoder 23.Encoder 23
The output signals C and D of the frequency divider 22 are also applied to the signal generator 22, and a correction clock G1 data clock H1 modulation signal I is generated from these three signals C, D and F.

The electrical signal converted by the light receiving element 13 in the photoelectric converter 6 shown in FIG. The output of the sample and hold circuit 28 is given to the other input of the differential amplifier 29. The output of the differential amplifier 29 is given to one input of a comparator 30, and the other large hole force is given a reference voltage set by a potentiometer 32. The output of the comparator 30 is given to the D terminal of the D flip-flop 31. A correction clock signal G is given as a clock signal to the sample-and-hold circuit 28, and the D flip-flop 3I
A data clock H is given as a clock signal. The Q output signal of the D flip-flop 31 is applied to the arithmetic circuit 15 in FIG.

Next, the operation of the circuit shown in FIG. 3 will be explained. When the line start signal is input manually, the pixel counter 24 loads a predetermined number stored in the pixel number register 25, then counts down the pulses of the signal, and when the count value reaches O, outputs the output pulse E. The clock terminal CK of the D flip-flop is generated.
is giving to The D flip-flop 26 outputs an H level as an output signal F in response to a line start signal A given before the pixel counter 24 starts counting, and the output signal F is set to an L level in response to the pulse E.

While the output signal F is at H level, the encoder 23 outputs a modulation signal I which is a pulse signal with a partial duty.
The semiconductor laser 12 shown in FIG. 2 is driven and modulated.

In this embodiment, the semiconductor laser 1 emits light when the modulation signal is at H level, and stops emitting light when it is at L level.

The correction clock G given from the encoder 23 to the sample-and-hold circuit 28 is at the H level only when the modulation signal (2) is at the L level. The output signal can be sampled. Next, when the modulation signal I becomes H level and the laser beam is irradiated, the output signal from the preamplifier 27 at that time and the immediately previous sample value held in the sample/hold circuit 28 are sent to the differential amplifier 29. The difference signal between the two is obtained.

This difference signal is compared with a reference value by a comparator 30,
If it is larger than the reference value, an H level output is given to the D terminal of the D flip-flop 31, and is outputted to the arithmetic circuit 15 at the timing of the data clock H and goes to 0.

What should be noted here is that the differential amplifier 28 is configured to output the difference between the received light signals when the laser beam is not irradiated and when the laser beam is irradiated. Even if the amount of received light changes due to incident light from a window, etc., the change can be offset.

In the above embodiment, the modulation signal is a pulse signal with a constant duty, and the laser beam is repeatedly irradiated and non-irradiated during - times of scanning, but the following modes of laser beam irradiation are also possible. It is possible.

FIG. 5 is a waveform diagram of the modulation signal I to show three laser beam irradiation modes different from those in the above embodiment. Fifth
In Figure (a), a period 1g='iT in which the laser beam is not irradiated is provided only once during - times of scanning, and continuous irradiation is performed during the other periods. FIG. 5(b) is an example in which modulation is performed at a period twice as many as the number of pixels (sampling number) required for one line. Here, the odd number lines represented by the n-th line, the n+2-th line, the n+4-th line, etc., and the even numbers represented by the n+1-th line, the n+3-th line, the n+5-th line, etc. On the line, the phase of the modulation signal is different by 180 degrees, and the pig sampling position is interpolated.

FIG. 6 is a block diagram showing the configuration of the encoder 23 that produces the modulated signal shown in FIG. 5(a). The D flip-flop 34 uses the line start signal A as a clock signal, and the reset signal shown in FIG. Also, 0 output is D
Since it is connected to the terminal, the Q output has an H level for each line.
L is reversed. A dd/even signal J is obtained. Here, the odd/even signal J indicates the above-mentioned odd lines and even lines. The selector 35 selects either the output signal of the frequency divider 22 shown in FIG. 3 or its inverted signal, and the selection is controlled by the odd/aven signal J. Since the output signal of the selector 35 is outputted as the modulation signal I via the AND gate 39, the modulation signal I given to the semiconductor laser 12 is one line per line.
806 phase will be different. 36 is a D flip-flop that controls AND gates 37-39. FIG. 7 shows the above-mentioned odd/even signal J in addition to the waveform diagram of FIG. 4.

FIG. 5(c) is an example in which the modulation is performed once every two pixels. Here again, the phase of the modulation signal is changed by 180° between the n line and the n+1 line, that is, the odd and even lines.

In each of the above embodiments, the laser beam is irradiated or not irradiated by 0N10FF driving of the laser.
It goes without saying that the same effect can be achieved by increasing or decreasing the output power of the laser.

If the scanning speed is 3000 times/see, the scanning time for one line in the X direction in FIG. 1 is 0.33 m5ec. In addition, the size of the defect on the surface of the inspected object 7 is as follows:
It is preferable to be able to find something that is close to 100. Therefore, it is preferable to reduce the power of the laser beam or set it to zero for a period of time equal to or shorter than the period for scanning a distance corresponding to such resolution. As mentioned above, the scanning time for one line is 0.88mf; the ecs scanning width is 5 (Jc
m, the time to scan this resolution of 1007J is 6
It becomes 6nsec. Therefore, it is possible to provide a maximum laser turn-off time of 86 nsec. However, considering the safety factor, in the above embodiment, one period of 0N10FF of the semiconductor laser 12 is set to 88 nsec (see FIG. 5(b)).

〔Effect of the invention〕

As is clear from the above detailed explanation, in the laser inspection apparatus of the present invention, the power of the laser beam is reduced or set to 0 at least once per scan of laser beam irradiation to the object to be inspected. The laser beam is modulated in such a way that the received light signal is used as a reference when the power of the laser beam decreases or becomes 0 when measuring the received light signal, so it is not affected by disturbance light, etc. This enables accurate inspection and judgment.

Furthermore, by shifting the phase of the laser beam modulation signal for each scanning line, the data sample positions are interpolated and the apparent resolution can be increased.

4

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the vicinity of the sensor head of the present invention and a conventional laser inspection device, FIG. 2 is a block diagram showing the electric circuit of the laser inspection device of the present invention, and FIG. 3 is a part of FIG. 2. FIG. 4 is a waveform diagram for explaining the operation of the circuit in FIG. 3, FIG. 5 is a waveform diagram showing the accumulation of modulated signals, and FIG. ) is a block diagram showing the configuration of an encoder that produces the modulated signal shown in FIG. DESCRIPTION OF SYMBOLS 1... Laser light source, 2... Lens system, 3... Rotating polygon mirror, 4... Fixed reflecting mirror, 5A... Sensor head, 6... Photoelectric converter, 7... Target Test object, 11...
- Laser drive circuit, 12... semiconductor laser, 13...
- Light receiving element, 14... Light receiving signal processing circuit, 15...
Arithmetic circuit, 20... Oscillator, 21... Phase locked circuit, 22... Frequency divider, 23... Encoder, 24...
・Pixel counter, 25... Pixel number register, 26.3
1°34, 36...D flip-flop, 27...
Preamplifier, 28...Sample/hold circuit, 29
...Differential amplifier, 30...Comparator, 32...
・Potentiometer, 35...5 Selector, 37-39...AND get. Inventor: Hiroaki Kimura, Masatoshita: Applicant: Mitsubishi Rayon Co., Ltd. Agent

Claims (3)

[Claims] (1) A means for irradiating an object to be inspected moving in the Y direction with a laser beam while scanning in the X direction, and a sensor head that receives transmitted light or reflected light of the laser beam from the object to be inspected at one end surface. and a photoelectric conversion means for converting an optical signal emitted from the other end surface of the sensor head into an electric signal, and determining a diffusion state of the transmitted light or reflected light in response to the electric signal from the photoelectric conversion means. In a laser inspection device consisting of an arithmetic circuit, the power of the laser beam is reduced at least once per scan, or
or 0, and a means for detecting transmitted light or reflected light from the object to be inspected in response to the modulating means. A laser inspection characterized by comprising means for detecting an output signal when the output signal decreases or becomes 0 and using it as a reference signal, and means for processing the output signal of the detecting means using the reference signal as a reference. Device. (2) reduce the power of the laser beam or
2. The laser inspection apparatus according to claim 1, wherein the period for scanning the object to be inspected is set to be equal to or shorter than a period for scanning a distance corresponding to a resolution required for inspecting the object to be inspected. (3) The laser inspection apparatus according to claim 1, further comprising means for shifting the phase of a signal for modulating the laser beam for each scanning line.