JP3490792B2 - Surface inspection equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection device for detecting defects by scanning spot light on an object to be inspected.

[0002]

2. Description of the Related Art A flying spot type surface inspection apparatus is generally used to detect a defect existing on the surface of a continuously running sheet. This surface inspection device utilizes the fact that the reflectance and the transmittance of light differ between the normal portion and the defective portion, and the surface of the object to be inspected is scanned with a spot light by a laser, and the reflected light or the transmitted light is detected. The presence or absence of various defects is evaluated from the change in the intensity of the reflected light or the transmitted light that is detected photoelectrically by a light receiver.
In such a surface inspection apparatus, the inspection is performed with sufficient overlap between the scans so that the inspection leak does not occur on the inspection object.

In order to maintain high defect detection accuracy,
It is important that the light emitted to the object to be inspected has a uniform light amount on the inspection part. However, the intensity distribution of the spot-shaped light follows a Gaussian distribution, and the light intensity is highest at the optical axis portion, and the light intensity decreases as the distance to the outer ring portion increases.
Therefore, in the above-described surface inspection apparatus, as shown in FIG. 9, the diameter R ₈₀ of the range in which the light intensity of the spot light 2 is 80% or more of the maximum intensity is set as the beam diameter of the spot light 2, and scanning is performed. Spot light 2 adjoining each other in the direction intersecting with the direction
Are designed to overlap each other at the end positions of the beam diameter R ₈₀ . Then, the inspected body 3 travels by the inspection length L _T having the same length as the beam diameter R ₈₀ of the spot light 2 each time one scanning is performed. As a result, within the inspection length L _T of the inspection object 3, the light intensity difference is 20% or less of the maximum intensity.

By the way, as shown in FIG. 10, in the case of spot light having the same amount of energy, the smaller the diameter R _S is, the more the light is concentrated in a narrow range, so that the light intensity at the central portion is extremely high. Become. Then, as the diameter R _S increases, the difference in light intensity between the central portion and the outer ring portion decreases, and the intensity distribution becomes gentle. Therefore, the diameter R _S
When a spot light having a smaller size is scanned, the amount of light whose transmission rate or reflectance is affected by the presence of a defect increases, so that the defect detection accuracy increases.

[0005]

However, when the diameter R _{S of the} spot light becomes smaller, the beam diameter R ₈₀ also becomes smaller, so that the inspection length L _T becomes shorter and the inspection speed is reduced. Therefore, a method of increasing the scanning speed of the spot light in order to increase the inspection speed is conceivable, but there is a limit in increasing the scanning speed. Further, since the signal detected by the light receiver must be processed at high speed, on the contrary, there is a possibility that the defect detection accuracy may be lowered.

As described above, the maximum strength is 8
Although light having a 0% or more of the intensity is the set the beam diameter R ₈₀ so as to irradiate the object to be inspected, the light receiver also all the light of the outer ring portion deviated from the scope of the beam diameter R ₈₀ Enter the light.
However, the light from the outer ring part is the inspection length L _T
The incident light enters the light receiver without any relation to the defect existing in the range of., And only the detected light amount of the light receiver is increased, so that the change in the light amount due to the existence of the defect is obscured and the defect This causes a decrease in detection accuracy.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a surface inspection apparatus capable of improving the defect detection accuracy without reducing the inspection speed.

[0008]

In order to achieve the above object, the present invention provides a flying spot method using a laser.
Type surface inspection apparatus, a light-shielding plate having a slit opening linearly extending in the scanning direction of the inspection light is arranged between the projector and the inspection object, and the inspection light is passed through the slit opening. The configuration is such that the body is scanned, and the opening width of the slit opening in the traveling direction of the inspection object is made narrower than the beam diameter of the inspection light from the light projector. The width of the slit opening is preferably set within the range of (1/10) to (2/3) of the beam diameter of the inspection light from the light projector. Further, it is preferable that the light shielding plate is arranged within a distance of 100 mm from the surface of the inspection object.

FIG. 2 schematically shows the basic structure of the surface inspection apparatus of the present invention. The surface inspection apparatus 10 includes a light projector 11, a light receiver 12, a pair of light shielding plates 13a and 13b,
It is composed of an optical sensor 14 and a signal processing circuit 15. The sheet-shaped film 17 which is the inspection object is run between the light projector 11 and the light receiver 12 in the direction of the arrow in the figure at a constant speed.

The projector 11 is composed of a laser oscillator 20, a lens group 21, a rotary polygon mirror 22, and two mirrors 23 and 24 for bending the optical path. The laser light 20a emitted from the laser oscillator 20 is reflected by the mirror 2
It is incident on the lens group 21 via 3, and after its spot diameter is adjusted, it is incident on the rotating polygon mirror 22 rotating at high speed via the mirror 24. And this laser light 20a
Is the inspection light 25 that is scanned at a high speed in the width direction on the film 17 substantially orthogonal to the traveling direction of the film 17 by the rotation of the rotary polygon mirror 22. This inspection light 25 is supplied to the film 17
Of the light receiver 12 which is emitted from the light projector 11 toward the inspection unit 17a, passes through the inspection unit 17a, and then extends in the scanning direction.
Incident on. The light receiver 12 is an inspection unit 17 of the film 17.
The inspection light 25 transmitted through a is photoelectrically detected, and a photoelectric conversion signal proportional to its intensity is sent to the signal processing circuit 15.

As shown in FIG. 1, the spot diameter of the inspection light 25 emitted from the projector 11 is greatly adjusted. The pair of shading plates 13a and 13b are arranged between the light projector 11 and the film 17, and each of the inspection light 2
A slit opening 13c penetrating from the vertical direction into the optical path 5 and extending linearly along the scanning direction of the inspection light 25 is formed. As a result, the inspection portion 17a of the film 17 is scanned by the light near the optical axis 25a that has passed through the slit opening 13c.

Inspection light 2 immediately after being emitted from the projector 11.
Reference numeral 5 denotes Gaussian light whose intensity distribution is a Gaussian distribution. As shown in FIG. 3A, the light intensity is highest at the optical axis 25a, and the light intensity decreases as it approaches the outer ring portion.
As shown in (B) of the figure, the inspection light 25 has its intensity distribution almost equal when it reaches the inspection portion 17a by blocking the upper and lower portions of the light flux by the light shielding plates 13a and 13b. It is a uniform rectangular light.

Further, the film 17 has a length (inspection length) L _{T that} is traveled during one scan so that the adjacent inspection lights 25 are overlapped with each other during each scan. Is set to be shorter than the diameter R _E of the inspection light 25 that has reached. Therefore, the opening width W of the slit opening 13c formed by the pair of light-shielding plates 13a and 13b is determined by the inspection length L _T of the film 17 and the inspection light 25 between each scan.
It may be determined according to the overlapping length L _{o of} If the overlapping length L _O of the inspection light 25 is too long, the overlapping length L _O is likely to be influenced by the adjacent inspection lengths. Further, when the diameter in the direction intersecting the scanning direction in the range where the light intensity of the inspection light 25 emitted from the light projector 11 is 80% or more of the maximum intensity is the beam diameter R ₈₀ , the opening width of the slit opening 13c W is
The beam diameter R ₈₀ is preferably set within the range of (1/10) to (2/3). If the aperture width W is larger than 2/3 times the beam diameter R ₈₀ , the slit aperture 13
The intensity distribution of the inspection light 25 passing through c cannot be approximated to a uniform distribution. Also, the aperture width W is the beam diameter R
_If it is smaller than 1/10 times ₈₀ , the ratio of the energy used effectively to the total energy amount of the inspection light 25 becomes low, so that the laser output of the inspection light 25 is equivalent when emitted from the projector 11. It needs to be large and impractical.

Further, referring to FIG. 1, a pair of shading plates 13 are provided.
The distance L between the a and 13b and the inspection unit 17a is preferably 100 mm or less. When the distance L is longer than 100 mm, the inspection light 25 reaching the inspection portion 17a becomes unstable in light intensity at the end due to the influence of the diffracted light from the edge of the slit opening 13c, and is approximated to a rectangular light. Can't do it.

In FIG. 2, the optical sensor 14 is the inspection light 2
It is provided at a position deviated from the scanning region X on the film 17 on the upstream side of the scanning by 5 and generates a pulsed light receiving signal at the moment when the inspection light 25 is received and sends it to the signal processing circuit 15.

FIG. 4 schematically shows the configuration of the signal processing circuit 15. The signal processing circuit 15 includes an inspection width setting circuit 31, a filter circuit 32, a binarization circuit 33, and an AND circuit 34. The light reception signal S1 of the optical sensor 14 is input to the inspection width setting circuit 31. Inspection width setting circuit 31, the light receiving signal S1 becomes from low level to high level when the time T _a from the input has elapsed, time T _b and a test width signal S2 returns to the low level when the elapsed circuit 34 Output to. The time T
_a and T _b are set in advance according to the scanning speed and the width dimension of the film 17, and the time T _a is from the time when the inspection light 25 passes through the optical sensor 14 until the inspection start position on the inspection unit 17a is reached. The time T _b is set to the time from when the light passes through the optical sensor 14 until the inspection end position on the inspection unit 17a is reached.

The photoelectric conversion signal S3 from the light receiver 12 is input to the filter circuit 32. Filter circuit 32
Removes low-frequency and high-frequency noise components contained in the photoelectric conversion signal S3, and sends the output signal S4 to the binarization circuit 33. The binarization circuit 33 includes the filter circuit 3
When the signal level of the output signal S4 from _{No. 2 becomes} equal to or lower than the preset threshold value L _THLD , the light amount reduction signal S5 which becomes high level is generated and sent to the AND circuit 34. The AND circuit 34 operates the binarization circuit 3 while the inspection width signal S2 from the inspection width setting circuit 31 is at the high level.
When the light amount reduction signal S5 is input from 3, the defect signal S6 is sent at this timing.

FIG. 5 shows a schematic waveform of each output signal of the surface inspection apparatus 10 configured as described above. The film 17 runs at a constant speed, and at the same time, irradiation of the inspection light 25 from the light projector 11 is started. When the inspection light 25 passes through the optical sensor 14, the sensor 14 generates a pulsed light receiving signal S1 and sends it to the inspection width setting circuit 31. The inspection width setting circuit 31 changes the signal level from the low level to the high level when the inspection light 25 reaches the inspection start position of the film 17 after the time T _a has elapsed since the light receiving signal S1 was input. Further, when the time _Tb has passed and the inspection light 25 reaches the inspection end position of the film 17, the inspection width setting circuit 31 returns the signal level to the low level again. Therefore, the inspection width signal S2 output from the inspection width setting circuit 31 is at the high level only while the inspection light 25 scans the inspection portion 17a of the film 17.

The inspection light 25 is a pair of light-shielding plates 13a, 13a.
After the upper and lower parts of the light flux are blocked by b, the film 1
The light passes through the inspection unit 17 a of No. 7 and enters the light receiver 12. Immediately after being emitted from the projector 11, the inspection light 25 is Gaussian light whose intensity distribution follows a Gaussian distribution, but after passing through the slit opening 13c formed by the light shielding plates 13a and 13b, it intersects with the scanning direction. The diameter R _{E in} this direction is equal to the opening width W of the slit opening 13c, and the intensity distribution is substantially uniform rectangular light. Therefore, the inspection unit 17a
The inspection light 25 having a uniform light amount in the traveling direction of the film 17 is irradiated on the upper side.

The light receiver 12 photoelectrically detects the inspection light 25 and outputs a photoelectric conversion signal S3 proportional to its intensity. At this time, when there is no defect on the inspection unit 17a, the entire luminous flux of the inspection light 25 transmitted through the inspection unit 17a enters the photodetector 12, so that the photoelectric conversion signal S3 of the photodetector 12 remains at the high level. . On the other hand, when there is a defect on the inspection unit 17a, the inspection light 25 is scattered and transmitted from the inspection unit 17a at various angles. As a result, the amount of light incident on the photodetector 12 is reduced, and the photoelectric conversion signal S3 of the photodetector 12 has an abnormal signal S _E with a lowered signal level at a position corresponding to the defect.
Occurs.

The photoelectric conversion signal S3 of the light receiver 12 is sent to the binarization circuit 33 after the low frequency and high frequency noise components are removed by the filter circuit 32. Binarization circuit 33
_Generates a light amount decrease signal S5 and sends it to the AND circuit 34 when the signal level of the output signal S4 from the filter circuit 32 _becomes equal to or lower than a preset threshold value L _THLD . At this time, the output signal S from the filter circuit 32
The signal level of 4 is the position where the abnormal signal S _E is generated and the light receiver 1
Since it decreases at the end position of the second light receiving window 12a, the binarizing circuit 33 outputs the abnormal signal S _E and the light receiving window 12a.
The light amount reduction signal S5 is generated at the end position of a. The AND circuit 34 sends out the defect signal S6 when the light amount reduction signal S5 is inputted from the binarization circuit 33 while the inspection width signal S2 is at the high level. Therefore, the defect signal S6 is generated only at the position corresponding to the abnormal signal S _E.
Then, when the defect signal S6 is sent to the CPU (not shown), the CPU displays, for example, "defective" on the display panel (not shown).

During one scan, the film 17 runs for the inspection length L _T. Thereby, the inspection unit 17a
The next inspection length L _T portion is located above, and the scan within this new inspection length L _T is subsequently performed. At this time, the inspection light 25
Since the light intensity of is always constant within the inspection length L _T , the inspection can be stably performed. Moreover, since the overlapping length L _O of the inspection light 25 between the scans is short,
Defects can be detected with high accuracy without being affected by the state in the adjacent inspection lengths.

[0023]

EXAMPLE Next, in the apparatus A of the present invention that uses rectangular light as the inspection light and the conventional apparatuses B and C that use Gaussian light as they are, a comparative evaluation of the defect detection power in the traveling direction of the object to be inspected. I went. The defect detection power is
Evaluated by the ratio of the amount of energy acted on by the defect to the total amount of energy of the inspection light, and when the defect is located in the center of the inspection length and across the boundary between adjacent inspection lengths. The theoretical value was calculated for each case. In addition, the size of the defect in the running direction of the inspection object was set to 1.0 mm for evaluation.

In the apparatus A, the inspection length L _T is 1.5 mm, and the inspection light overlap amount L _O between the scans is 0.2 at both ends.
5 mm at a time, slit opening opening width W is 2.0 mm
And In the conventional devices B and C, the inspection length L _T , that is, the beam diameter R ₈₀ of the inspection light is 1.0
mm and 1.5 mm. The calculation results of the defect detection power in each of the devices A, B, and C are shown below.

First, in the device A, as shown in FIG. 6, the energy amount I _A of the inspection light reaching the inspection portion is uniform over the entire area of the diameter R _E = 2.0 mm. Therefore, as shown in FIG.
When the defect 40 is located at the center of the inspection length L _T , the ratio P _C of the amount of energy applied to the defect 40 to the whole is P _C = 1/2 = 0.5 . On the other hand, as shown in FIG.
Is located at the end of the inspection length L _T , the ratio P _{E of the} energy amount acting on the defect 40 to the whole is
Becomes P _E = 0.75 / 2 = 0.375.

Next, the defect detection power of the conventional devices B and C is calculated. First, the energy amount I of Gaussian light can be calculated by the formula I = exp (−2 · r ² / w ² ). In the above equation, r represents the distance from the optical axis, and w represents the beam width at which "I = 1 / e ² ".

In the conventional apparatus B, since the beam diameter R ₈₀ of the inspection light is 1.0 mm, substituting r = R _80/2 = 0.5 I = 0.8 into the above equation gives 0.8. = Exp [-2 · (0.5) ² / w ² ], and w ² ≈2.24 can be obtained. Therefore, the amount of energy I _B of the inspection light in the conventional device _{B, I B = exp (-2 ·} r 2 /2.24) = a exp (-r ² /1.12). Further, the total energy amount E of the inspection light of the conventional device B is
_T is _calculated by the following equation.

[0028]

[Equation 1]

Here, as shown in FIG. 7A, when the defect 40 is at the center of the inspection length L _T , this defect 4 is detected.
The energy amount E _C exerted by 0 is calculated by the following equation.

[0030]

[Equation 2]

Therefore, the ratio P _C of the energy amount E _{C to} the whole is P _C = E _C / E _T ≈0.4985.

On the other hand, as shown in FIG.
When 0 is at the end of the inspection length L _T, the energy amount E _E acting on this defect 40 is obtained by the following equation.

[0033]

[Equation 3]

Therefore, the ratio P _E of the energy amount E _{E to} the whole is P _E = E _E / E _T ≈0.4113.

[0035] In the conventional apparatus C, the beam diameter R ₈₀ of the inspection light is 1.5 mm, as in the conventional apparatus B, and _{wherein, r = R 80/2 =} 0.75 I = 0.8 By substituting for, w ² ≈5.0416 can be obtained. Therefore, the amount of energy I _C of the inspection light in the conventional apparatus _{C, I C = exp (-2 ·} r 2 /5.0416) = a exp (-r ² /2.5208). Also, the total energy E of the inspection light of the conventional device C is
_T is _calculated by the following equation.

[0036]

[Equation 4]

As shown in FIG. 8A, when the defect 40 is at the center of the inspection length L _T , the energy amount E _C acting on this defect 40 is obtained by the following equation.

[0038]

[Equation 5]

Therefore, the ratio P _C of the energy amount E _{C to} the whole is P _C = E _C / E _T ≈0.344.

In addition, as shown in FIG.
When 0 is at the end of the inspection length L _T, the energy amount E _E acting on this defect 40 is obtained by the following equation.

[0041]

[Equation 6]

Therefore, the ratio P _E of the energy amount E _{E to} the whole is P _E = E _E / E _T ≈0.279.

Table 1 shown below summarizes the calculation results of the above theoretical values, and also shows the inspection speed of each device. The inspection speed is 3000sc for the scanning speed of the inspection light.
It was calculated as an / sec.

[0044]

[Table 1]

In Table 1, looking at the values of the conventional devices B and C, the defect detection power decreases when the inspection length L _T is increased and the inspection speed is increased, and conversely, the detection power is improved. Then, it can be seen that the inspection speed decreases. In this respect, in the device A of the present invention, the inspection speed is set to the conventional device C.
The defect detection power is the same as that of the conventional device
Holds the same high level as. From this, according to the present invention, it was confirmed that the defects can be detected with high accuracy without lowering the inspection speed.

In the above embodiment, an example in which a pair of light-shielding plates are arranged with the optical axis sandwiched in order to block a part of the inspection light has been described. However, only the light flux near the optical axis of the inspection light is transmitted to the inspection unit. Since it is sufficient that the light-shielding member can pass through toward the scanning direction, a single light-shielding member having an opening extending in the scanning direction may be arranged between the light projector and the inspection unit.

Further, in the above-mentioned embodiment, an example in which the present invention is applied to the transmission type surface inspection device for photoelectrically detecting the light transmitted through the inspection part is explained. However, the present invention detects the light reflected by the inspection part. Of course, it can be applied to a reflection type surface inspection device.

[0048]

As described above, according to the surface inspection apparatus of the present invention, the light shielding plate having the slit opening linearly extending in the scanning direction of the inspection light is arranged between the light projector and the object to be inspected. In addition, since the opening width of the slit opening in the traveling direction of the inspected object is configured to be narrower than the beam diameter of the inspection light from the projector, the inspection light emitted from the projector has only the light beam near the optical axis in the inspection section. You will reach the top. As a result, the inspection light reaching the inspection unit becomes rectangular light with a substantially uniform light intensity distribution in the direction intersecting the scanning direction, so the inspection length for performing inspection by one scan of the inspection object is increased. It becomes possible to set a long time, and the inspection speed can be increased. Moreover, since the overlapping length of the inspection light between the scans may be such that there is no gap between the inspection lights, it is not affected by the state within the adjacent inspection lengths, and the defect detection accuracy can be improved.

Further, the opening width of the slit opening is (1/10) to (2/3) with respect to the beam diameter of the inspection light from the projector.
By setting it within the range, it becomes possible to approximate the intensity distribution of the inspection light passing through the slit opening to a more uniform distribution. Further, by disposing the light shielding plate within a distance of 100 mm from the surface of the object to be inspected, the influence of the diffracted light from the edge of the slit opening is suppressed, and the intensity of the inspection light reaching the inspection part is extended to the end part. It can be kept constant and stable inspection can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a positional relationship between inspection light and a light shielding plate.

FIG. 2 is a schematic diagram showing a configuration of a surface inspection device of the present invention.

FIG. 3 is an explanatory diagram showing a change in intensity distribution of inspection light,
(A) shows the intensity distribution immediately after being emitted from the projector.
(B) represents the intensity distribution when it reaches the inspection portion.

FIG. 4 is a block diagram showing a configuration of a signal processing circuit.

5 is a chart showing an outline of a signal waveform in each part of the signal processing circuit shown in FIG.

6A and 6B are explanatory views showing the acting force of the inspection light with a defect in the surface inspection apparatus of the present invention, where FIG. 6A shows the case where the defect is located in the center of the inspection length, and FIG. Each case is located across the inspection length.

FIG. 7 is an explanatory diagram showing the acting force of the inspection light on the defect in the conventional apparatus in which the beam diameter of the inspection light is reduced, FIG.
Represents the case where the defect is located in the center of the inspection length, and (B) represents the case where the defect is located across the adjacent inspection lengths.

FIG. 8 is an explanatory diagram showing the acting force of the inspection light on the defect in the conventional apparatus in which the beam diameter of the inspection light is increased;
Represents the case where the defect is located in the center of the inspection length, and (B) represents the case where the defect is located across the adjacent inspection lengths.

FIG. 9 is an explanatory diagram showing the relationship between the scanning of the inspection light and the inspection length of the inspection object in the conventional surface inspection apparatus.

FIG. 10 is an explanatory diagram showing the relationship between the diameter of spot light and the intensity distribution.

[Explanation of symbols]

10 surface inspection device 11 light projector 12 light receivers 13a, 13b light shielding plate 13c slit opening 15 signal processing circuit 17 film 17a inspection unit 25 inspection light 25a optical axis 40 defect R ₈₀ beam diameter W opening width

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 21/84-21/958 G01B 11/00-11/30

Claims (2)

(57) [Claims] 1. A laser against continuous traveling object to be inspected
A spot-shaped inspection light is emitted from the projector and the scanning mechanism
The inspection light is moved in the width direction of the object to be inspected,
While scanning the body in its width direction and running direction, the inspection light reflected or transmitted through the object to be inspected is received by the light receiver, and in the surface inspection device for inspecting for the presence or absence of a defect based on the output from the light receiver, It is arranged between the light projector and the object to be inspected and is irradiated with the light.
Width within the range of 1/10 to 2/3 of the beam diameter of inspection light
The narrow slit opening is straight along the width direction of the DUT.
Equipped with a line-shaped shading plate, the inspection light is used as a shading plate.
Irradiate and scan the inspected object with the light passing through the light shield
A surface inspection device characterized by: 2. The surface inspection apparatus according to claim 1, wherein the light shielding plate is arranged within a distance of 100 mm from the surface of the object to be inspected.