JPH0621775B2 - Surface inspection device - Google Patents

Description

The present invention relates to a surface for inspecting surface defects and image clarity of an object to be inspected such as an automobile body panel coating surface or a rolled strip steel sheet. Regarding inspection equipment.

[Conventional technology]

Scratches, protrusions, spots, etc. on the surface of the inspection object
The inspection of defects such as dirt tends to shift from visual inspection by an inefficient worker having individual differences to automatic inspection using, for example, a highly directional laser beam.

As a surface defect inspection apparatus utilizing such laser light, as shown in FIG. 2, a laser slit light LST is projected from a laser slit light generator 1 onto a surface 2 to be inspected, which is the surface of an object to be inspected, and its reflection is reflected. The light LST 'is projected on the screen 3 which is a diffuser, and the slit image on the screen is condensed by the condenser lens 4 of the camera section to form a CCD.
The applicant of the present invention has previously proposed a surface defect inspection apparatus which detects surface defects by detecting the surface defects by the line sensor 5 (Japanese Patent Application No. 59-83890).

According to this surface defect inspection apparatus, for example, as shown in FIG. 3, when there is a defect a such as a scratch or a spot at the laser slit light projection position on the surface to be inspected 2, the laser slit light LST is scattered there, so that Specular reflection light LST ′ from inspection surface 2
As shown in the figure, the slit image SL cut at the position corresponding to the defect a is projected on the screen 3 which receives the image.

Therefore, the video output signal of the line sensor 5 of FIG. 2 which constantly photographs the position where the slit image SL is projected on the screen 3 becomes as shown in FIG. 4 (a),
The envelope signal Vs shown in FIG. 7B is compared with a comparison signal Vr (threshold voltage level) obtained by averaging the envelope signal Vs,
As shown in FIG. 2C, the high level becomes “H” only when Vs <Vr, and the low level becomes “L” otherwise. 2
If the binarized signal is formed, the defect (a in FIG. 3) on the surface 2 to be inspected can be detected by the level of the binarized signal being "H".

In this case, the line sensor 5 shown in FIG. 2 uses the scattered light SC diffused by the screen 3 arranged at the focus position of the condenser lens 4.
Since the projection slit image SL on the screen 3 is captured by receiving the light, the focus of the condenser lens 4 can be fixed at all times, and the projection slit image SL is enlarged by diffusion. Therefore, the resolution of detecting surface defects is improved.

On the other hand, there is undulation due to slight irregularities on the surface of vehicle body pulses, etc., and conventionally, inspectors rely on visual inspection to measure the image clarity (hereinafter simply referred to as “image clarity”) that indicates the degree of undulation. However, at the same time as the above-mentioned inspection of surface defects, the present applicant has already applied for a patent for a surface inspection device that can measure the image clarity of the surface to be inspected by using laser slit light. Japanese Patent Application No. 60-251137).

Since this image clarity measuring means will be described in the description of the embodiment of the present invention, the description thereof will be omitted here.

[Problems to be solved by the invention]

However, in the surface inspection apparatus having the surface defect inspection means and the sharpness measuring means, which have been previously applied, the respective means individually detect the surface defects and measure the sharpness. Therefore, if you try to increase the detection sensitivity of the surface defect detection means to detect even small defects, if the surface to be inspected is poor in image clarity, it is difficult to distinguish it from defects due to surface waviness. Occurs,
There is a problem that it is easy to make an erroneous detection.

This problem will be described with reference to FIGS. 5 and 6.

As shown in FIG. 5, when the laser slit light LST is projected from the laser slit light generator 1 onto the surface to be inspected (hereinafter also referred to as "panel surface") 2, the reflected light LST 'causes a screen and a condenser lens not shown. If a slit image as shown by a thick line is formed on the light-receiving surface 5a of the line sensor 5 through the line sensor 2 and there are defects a and b (b is smaller than a) on the panel surface 2, the slit image corresponding to that portion. a ',
b ′ is chipped according to the size of the defect, but in addition, the undulation of the panel surface causes undulations in the slit image on the line sensor 5 as shown in the figure, and the amount of light hitting the light receiving surface 5a varies. Occurs. This waviness becomes larger as the image clarity of the panel surface 2 becomes worse.

Therefore, as shown in FIG. 6, the video output signal from the line sensor 5 has a waveform including a noise component having a dip other than the portions corresponding to the defects a and b, and is broken if the panel surface has a good image clarity. Although the drop is relatively small as shown by, the drop is increased as shown by the solid line when the image clarity is poor, and it is difficult to determine the drop due to a small defect.

Therefore, when inspecting the panel surface with poor image clarity, the defect b
When trying to detect such a small defect, noise due to undulation is erroneously detected.

On the contrary, if the detection sensitivity is lowered to prevent small defects from being detected in order to prevent erroneous detection, there arises an inconvenience that even if small defects are conspicuous on the panel surface with good image clarity, they cannot be detected.

The present invention aims to solve such problems.

[Means for solving problems]

Therefore, the surface defect inspection apparatus according to the present invention projects the first laser slit light on the surface to be inspected 2 and projects the reflected light on the screen as shown in the basic configuration of FIG. Surface defect inspection means A for detecting a surface defect of the surface 2 to be inspected from the slit image, and two parallel to each other adjacent to one end of the projection position of the first laser slit light and orthogonal to the extension line thereof. Second laser slit light
Is projected onto the surface to be inspected 2 as laser slit light of
On the surface 2 to be inspected by the surface defect inspection means A, the reflected light that changes due to the undulation due to slight irregularities on the surface 2 to be inspected is detected as a change in the interval between the two parallel laser slit lights. In a surface inspection device equipped with the image clarity measuring means B for measuring the image clarity near the inspection position, the defect inspection means A detects the image clarity measured by the image clarity measurement means B. A minimum detection size changing means C for changing the minimum defect size is provided.

[Work]

At the time of surface inspection, when the value of the image clarity measured by the image clarity measurement unit B is a value indicating that the image clarity is poor, the minimum detection size changing unit C detects the minimum defect size by the surface defect detection unit A. , And when the measured value of the sharpness is a value indicating that the sharpness is good, the minimum defect size detected by the surface defect detection means A is changed to be small, thereby When inspecting a panel surface or the like having poor performance, only relatively large defects can be detected without erroneous detection, and when inspecting a panel surface or the like having good image clarity, relatively small defects can be accurately detected.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 7 and subsequent drawings.

FIG. 7 is a front view of the detection head of the surface inspection apparatus according to the present invention, and FIG. 8 is a side view seen from the direction of arrow A in FIG.

10 is a detector, 11 is a laser slit light generator for surface defect inspection, and this laser slit light generator 11 is
A laser oscillation tube 11a, a lens system 11b including a cylindrical lens for converting a laser light beam generated by the laser oscillation tube into slit light, and a Fresnel lens for converting the slit light into parallel slit light that does not spread in the longitudinal direction are provided at the tip. And a hood portion 11c mounted on the inspection surface 2 for projecting the first laser slit light.

1 of the hood portion 11c of the laser slit light generator 11
A laser slit light generator 12 for measuring image clarity is attached to the side end portion by a bracket 16 with its optical axis parallel to the optical axis O ₁ of the laser slit light generator 11.

This laser slit light generator 12 includes two semiconductor laser generators 12a and 12b and two semiconductor laser generators 12a and 12b generated by the semiconductor laser generators 12a and 12b.
It is composed of a common cylindrical lens 12c for converting a laser beam of a book into slit light, is adjacent to one end of the projection position of the first laser slit light on the surface 2 to be inspected, and is parallel to each other in the direction orthogonal to its extension line. The two laser slit light beams are projected as a second laser slit light beam.

On the other hand, the detector 10 is equipped with a screen 13 made of a diffusion plate such as frosted glass at the tip, a detection cylinder 10a having two mirrors (flat mirrors) 17 and 18 attached to the inner surface thereof, and a condenser lens 14 and thereafter. And a camera section 10b having a line sensor 15 built therein.

As shown in FIG. 8, the portion of the tip surface of the detection cylinder 10a through which the second laser slit light from the laser slit light generator 12 is reflected by the surface 2 to be inspected is:
The screen 13 is cut out to form an opening 19.

The optical axes O ₁ and O _{2 of the} detector 10 and the laser slit light generator 11 have a predetermined angle δ (60 ° in this example).
It is held by the frame 21 so as to intersect with each other.

In this embodiment, in order to reduce the size of the detector 10 and increase the reduction ratio, the detection cylinder 10a is bent, and the reflected light of the first laser slit light is projected on the screen 13 to form a slit. The reflected light of the image and the second laser slit light on the surface 2 to be inspected is reflected by the two mirrors 17 and 18, and is focused by the condenser lens 14 on the detection line of one line sensor 15. I have to.

The detector 10 is fixed to the base end of the frame 21 in the shape of a hawk, but the laser slit light generator 11 is attached to the tip of the frame 21 by means of the pivot 22 as shown by the arrow θ in FIG.
It is rotatably supported in the y direction, and the intersection angle δ between the optical axis O _{2 of the} detector 10 and the optical axis O ₁ of the laser slit light generator 11 can be automatically adjusted by a mechanism (not shown). ing.

Further, the frame 21 is attached to a bracket 25 for attaching the detection head 20 to a scanning device such as a robot not shown or a fixed portion so as to be swingable in the direction of the arrow θx via an adjusting mechanism not shown. Optical axis O ₁ , O
_The surface formed by 2 is always adjusted to be perpendicular (90 °) to the surface 2 to be inspected.

Denoted at 23 in FIG. 7 is a defect marker (nozzle), and when a defect such as a spot or a scratch is present at the position of the surface 2 to be inspected irradiated with the first laser slit light, and its presence is detected,
It is a device for spraying a marking material such as a compound that can be wiped off in the vicinity of the defect that does not interfere with the laser slit light to mark the existence of the defect. The bracket 24 integrated with the detector 10 can be swung by a predetermined angle. It is attached to.

Then, the blowing direction of the defect marker 23 is switched according to the scanning direction, and is set to the illustrated direction when scanning in the arrow A direction.

Here, the operation of the detection head 20 will be described with reference to the principle diagram of FIG. In FIG. 9, the condenser lens 14 and the mirrors 17 and 18 shown in FIG. 7 are omitted for the sake of clarity, and the size of the line sensor 15 is extremely large. , Actually a condenser lens 1
The reduction ratio is significantly reduced, and the left and right image forming positional relationships are also reversed.

The first laser slit light LST ₁ is generated by the defect inspection laser slit light generator 11 and projected onto the surface 2 to be inspected, and the reflected light LST ₁ ′ is projected onto the screen 13 to form a slit image SL. The scattered light of the slit image SL is condensed by a condenser lens (not shown) and is formed as a slit image SL 'on the detection line 15a which is the light receiving surface of the line sensor 15.

On the other hand, by the laser slit light generator 12 for measuring the image clarity, two second laser slit lights LST ₂ , which are orthogonal to the extension plane of the _first laser slit light LST ₁ and are parallel to each other with a distance d, LST ₃ is generated and projected on the surface 2 to be inspected.

The reflected lights LST ₂ ′ and LST ₃ ′ are not projected onto the screen 13 but directly detected by a condenser lens (not shown) on the line sensor 15 to detect the detection line 15 a.
Two slit images SLa and SLb that intersect the detection line 15a are formed near the tip of the.

In the slit images SLa and SLb, the reflected lights LST ₂ and LST ₃ are slightly swung in the slit width direction due to fine unevenness of the surface 2 to be inspected, etc., so that random waviness occurs as illustrated.

By the way, in this embodiment, as the line sensor 15,
048-bit CCD, PDA, or PCD (Plasma C
oupled Device) line sensor, 1-25
6 bits are used as a clearness measurement area, and 257-2
048 bits are used as a defect inspection area.

Next, regarding the circuit in the control unit (not shown) for reading the video output signal from the line sensor 15 and obtaining the data indicating the surface defect detection and the image clarity,
This will be described with reference to FIG.

A clock pulse CP is generated by the clock generator 30.
Is generated, and the detection line 15a from the line sensor 15 is generated.
From 1 bit to 2048 bits, the video signal by the electric charge accumulated in each bit shown in FIG. 1 according to the amount of received light is sequentially read.

The envelope waveform of the video output signal amplified by the video amplifier 35 is, for example, as shown in FIG.

At this time, the image clarity window pulse generation circuit 31
A 56-bit window pulse is generated, and a window pulse generation circuit for defect detection 32 generates a 257-2048-bit window pulse to control the video switch circuits 33 and 34, respectively.

Then, the video switch circuit 33 allows only the video output signal from the image clarity measuring area of the line sensor 15 to pass therethrough, and reflects the second laser slit light reflected light LST ₂ ′, LS.
At the light receiving position of T ₃ ′, a signal whose level is increased like two pulses is extracted.

On the other hand, the video switch circuit 34 allows only the video signal of the defect detection area of the line sensor 15 to pass therethrough, and
When there is a defect in the projection position of the first laser slit light LST ₁ above, the video signal Vsa whose level sharply drops at the position corresponding to the defect is extracted.

This video signal Vsa is input to the binarization circuit 36 and binarized to obtain the defect detection signal Sa.

The binarization circuit 36 is an offset voltage variable type binarization circuit including an integration circuit 37, an offset circuit 38, and an analog comparison circuit 39. The integration circuit 37 integrates the video signal Vsa from the video switch circuit 34. , A signal having a waveform as shown by a broken line in FIG. 12 is created, and this signal is offset by the offset circuit 38 according to the measured value of the image clarity to obtain the comparison signal Vr.

That is, when the measured value of the sharpness described later is converted into an analog signal by the D / A conversion circuit 47 and input to the offset circuit 38 which is the minimum detection size changing means, and the sharpness is very good. The signal indicated by the broken line in FIG. 12 is used as it is as the comparison signal Vr, and when the image clarity is poor, the signal averaged by the integration circuit 37 as shown in FIG. The comparison signal Vr is offset so as to lower the level.

Then, the analog comparison circuit 39 compares the comparison signal Vr with the video signal Vsa, and outputs the pulse-like defect detection signal Sa which becomes the high level “H” only when Vsa <Vr.

Therefore, if the surface 2 to be inspected has a good image clarity, the 12th
As shown in the figure, even small size defects can be accurately detected, and when the image clarity is poor, only relatively large size defects are detected as shown in FIG. 13 to prevent erroneous detection due to noise waveforms. be able to.

This defect detection signal Sa is input to the defect display circuit 40,
The defect display unit 41 displays the defect position on the display, for example.

In addition, the defect marker driving circuit 42 allows the defect marker 23
Is operated to apply a marking material in the vicinity of the detected defective portion to make a mark.

In this embodiment, the comparison voltage Vr is offset according to the sharpness, but the comparison voltage Vr may be fixed and the video signal Vsa may be offset according to the sharpness. .

Here, scanning is performed so that the relative position between the detection head 20 and the surface 2 to be inspected is moved in the direction of arrow B in FIG. 9 (direction orthogonal to the _first laser slit light LST ₁ ).
After the completion of the second scanning, the position of the first slit light LST ₁ is shifted in the slit length direction and the same scanning is repeated, so that the surface defects on the entire surface to be inspected can be detected and displayed.

On the other hand, the video signal Vsb extracted by the video switch circuit 33 is binarized by the binarizing circuit 43, and the image clarity arithmetic processing circuit 44 causes the image plane to be inspected by the binarizing signal Dv. Data indicating the sharpness of 2 is calculated and input to the freshness display circuit 45 to display the freshness on the freshness display unit 46.

The sharpness calculation processing circuit 44, for example, as shown in FIG. 14, has a position counter 47 for counting the pulse intervals of the binarized signals of the respective bits sequentially input from the binarization circuit 43 by a clock pulse, and a count result thereof. And a microcomputer 48 having a RAM, a ROM, and an I / O port for arithmetically processing the output data from the microcomputer 48.
Input the data in 5 and display the data showing the sharpness.
Digitally displayed on.

The microcomputer 48 also controls the scanning operation by the scanning device 50 such as a robot to which the above-described detection head 20 is attached.

Next, regarding the image clarity measuring function by these circuits,
It will be described with reference to FIGS. 5 to 18.

The video signal Vsb as shown in FIG. 15 (a) extracted by the video switch circuit 33 of FIG. 10 is input to the binarization circuit 43 and compared with the comparison signal Vrb of a predetermined level,
Binarization is performed so that the high level becomes “H” only when Vsb> Vrb, and the low level becomes “L” in other cases.
A binarized signal Dv as shown in FIG. 5 (b) is obtained.

The position counter 47 shown in FIG. 14 counts the binarized signal Dv for each bit, count value T ₁ from when it first becomes “H” to when it returns to “L”, and then again “H”.
It outputs the count value T ₂ until it becomes, and the count value T ₃ until it returns to "L" (see FIG. 15 (b)).

The microcomputer 48 receiving this operates according to the flow chart of FIG.

First, the count values T ₁ , T ₂ , T ₃ by the position counter 47 are read in step, and P = T ₂ + in step.
The data corresponding to the interval between the two peak points of the video signal Vsb shown in FIG. 15 (a), that is, the second laser slit light LST ₂ by the line sensor 15 is calculated by calculating (T ₁ + T ₃ ) / 2. , LST ₃ reflected light LST ₂ ′, L
Data P indicating the light receiving position interval of ST ₃ ′ is obtained and stored.

Next, it is judged whether or not the required number P of data P stored in the step has reached N, and if not, the start signal is output to the scanning device 50 in step and the detection head 20 is moved in the scan direction (first step). Move one pitch in the direction of arrow B in FIG. 9).

Then, in step again, a new count value T ₁ ,
T ₂ and T ₃ are read, and the data P is obtained and stored in step. The operations from step to are repeated until the number of stored data P reaches N, and when the number of stored data P reaches N, the operation proceeds to step.

Reflected light of the second laser slit light LST ₂ ′, LS
T ₃ ′ is slightly deflected by the unevenness of the surface to be measured 2 and the like, and as shown in FIG. 9, each has an irregular “waviness”.
Cause Further, when the relative position between the detection head 20 and the surface 2 to be measured changes, the reflection position of each slit light of the portion received by the line sensor 15 changes.

Therefore, the two peak positions of the video signal Vsb detected by the line sensor 15 are irregularly deviated, and the data P indicating the peak position interval for each time calculated in step.
The values of are also slightly different as shown in FIG.

Therefore, in step, if the data P of a certain number of times is Pi, M / 2 pieces of data before and after that (total of M pieces) are averaged to calculate an average value ▲ ▼. However, for the M / 2 data from the beginning and the M / 2 data from the end (total M data) of the stored N data, the average value calculation data for each M / 2 data before and after cannot be obtained. An average value ▲ ▼ is calculated for the NM data Pi.

Next, at a step, as shown in FIG. 17 (b), a variation amount (deviation) ΔP with respect to the average value of each of the N−M data pieces Pi.
i is obtained by performing a calculation of ΔPi = ▲ ▼ −Pi. And at the step Is calculated to obtain the root mean square value σ.

Since the value of σ corresponds very well to the value of the sharpness that has been conventionally used as shown in FIG. 18, the value of σ may be displayed as it is. Indicates that the smaller the display value, the better the sharpness, and the larger the display value, the worse the sharpness.

In this embodiment, a freshness conversion table as shown in FIG. 18 is stored in the memory in advance, and the value obtained by converting σ to the freshness by the table is displayed on the display unit 46 in step. ing.

According to this embodiment, as described above, the data indicating the sharpness is obtained by the variation of the detection position interval of the pair of reflected slit light by the line sensor, and the variation of each data Pi ( The deviation .DELTA.Pi is determined by the difference between the average value of a predetermined number of data before and after each data. Therefore, the reflection slit is determined by the relative inclination between the detection head 20 and the surface 2 to be inspected. Even when the detection position of light changes as a whole, it is not affected by the change, and accurate image clarity can be measured at all times.

The value .sigma. Thus calculated by the sharpness calculation processing circuit 44 is converted into an analog signal by the D / A conversion circuit 47 in FIG. 10 to control the offset voltage of the offset circuit 38.

FIG. 19 is a block diagram similar to FIG. 10 showing another embodiment of the present invention.

This embodiment is different from FIG. 10 in that the offset voltage variable type binarizing circuit 36 is replaced with a binarizing circuit 51 similar to the conventional one, a defect size counting circuit 52 and a digital comparing circuit 53. The comparison value setting circuit 54 is provided in place of the / A conversion circuit 47.

The binarization circuit 51 is a circuit in which the offset circuit 38 in the binarization circuit 36 in FIG. 10 is omitted, and the video signal Vsa and the comparison signal obtained by integrating and averaging the video signal Vsa are irrespective of the sharpness. In comparison, the defect detection signal Sa as shown in FIG. 12 is output.

The defect size counting circuit 52 uses the defect detection signal Sa.
Is high level "H", for example, the clock pulse CP generated by the clock generator 30 is counted and the pulse width W thereof is measured to output the digital value Da corresponding to the defect size.

The digital comparison circuit 53 compares the digital value Da with the digital value Dr set by the comparison value setting circuit 54, and outputs the detection signal Sp only when Dr ≦ Da. The defect position is displayed by the defect display unit 41 when the signal Sp is output, and the defect marker 23 is activated, as in the above-described embodiment.

Here, the comparison value setting circuit 54 uses the sharpness calculation processing circuit 4
According to the data σ showing the sharpness calculated by 4,
The smaller σ is, the smaller the comparison value Dr is set, and the larger σ is, the larger the comparison value Dr is set.

Even in this case, even if the image clarity of the surface to be inspected is good (small σ), even small defects can be accurately detected, and when the image clarity is poor (large σ), only defects of relatively large size are detected. Can be detected without false detection.

In these embodiments, the laser slit light generator 12 for measuring the sharpness produces two laser slit lights which are parallel to each other and projects them as second laser slit light on the surface to be inspected. Even with one laser slit light, it is possible to calculate the data showing the sharpness.

Also, an example in which one line sensor is divided into areas for surface defect detection and image clarity measurement has been described.
You may make it separate and use two line sensors.

〔The invention's effect〕

As described above, by scanning the surface of the object to be inspected by using the surface inspection apparatus according to the present invention, the defect existing on the surface can be surely detected, and at the same time, the image clarity of the surface can be visualized. Image quality can also be measured automatically and accurately, and the minimum defect size to be detected is changed according to the measured value of image clarity, so even when inspecting a panel surface etc. with poor image clarity Detection can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic structure of a surface inspection apparatus according to the present invention, FIG. 2 is a principle explanatory view of the surface defect inspection apparatus previously filed, FIG. 3 is the same operation explanatory drawing, and FIG. 4 is the same. Waveform diagrams for explaining the binarization processing of the video output signal by the line sensor, FIGS. 5 and 6 are explanatory diagrams for explaining the problems to be solved by the present invention, and the video from the line sensor. FIG. 7 is a waveform diagram of the output signal, FIG. 7 is a front view showing a structural example of the detection head in one embodiment of the present invention, FIG. 8 is a side view seen from the direction of arrow A in FIG. 7, and FIG. FIG. 10 is a block diagram showing the configuration of the signal processing circuit according to the present invention in the control unit, and FIG. 11 is an envelope waveform and a clear image of the video output signal output from the line sensor 15. Sex measurement And waveform diagram showing a defect detection area, Fig. 12 and Fig. 13 binarizing circuit 3 in FIG. 10
6 is a waveform diagram for explaining the operation of FIG. 6, FIG. 14 is a block diagram showing the configuration of the image clarity arithmetic processing circuit 44 in FIG. 10 and its related circuits, and FIG. 15 is a video switch circuit 33 of FIG. FIG. 16 is a waveform diagram showing the waveforms of the output video signal and the binarized signal output from the binarization circuit 43. FIG. 16 is a flow chart of the processing operation executed by the microcomputer 48 of FIG. FIG. 18 is an explanatory diagram showing a calculation method and a calculation result of the average value P and the variation amount ΔP of the data P by the micro computer 48, and FIG. FIG. 19 is a block diagram similar to FIG. 10 showing another embodiment of the present invention. 2 ... Inspected surface (panel surface), 10 ... Detector 11 ... Laser slit light generator for surface defect inspection 12 ... Laser slit light generator for image clarity measurement 13 ... Screen, 14 ... Optical lens 15 ... Line sensor, 17, 18 Mirror 20 ... Detection head, 21 ... Frame 33, 34 ... Video switch circuit 36, 43, 51 ... Binarization circuit 38 ... Offset circuit (minimum) Detecting size changing means 40 ... Defect display unit 44 ... Freshness display unit 53 ... Digital comparison circuit (minimum detection size changing means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 61-93934 (JP, A) JP 62-112003 (JP, A) JP 62-233712 (JP, A)

Claims (1)

[Claims] 1. A surface defect inspection means for projecting a first laser slit light on a surface to be inspected, projecting the reflected light on a screen, and detecting a surface defect on the surface to be inspected from the slit image, Adjacent to one end of the projection position of the first laser slit light, two laser slit lights parallel to each other in a direction orthogonal to the extension line are projected as second laser slit light on the surface to be inspected, Near the inspection position on the surface to be inspected by the surface defect inspection means by detecting the reflected light that changes due to the undulation due to slight unevenness of the surface to be inspected as a change in the interval between the two parallel laser slit lights. In the surface inspecting device, which includes a sharpness measuring unit for measuring the sharpness of the image, the minimum defect size detected by the defect inspecting unit according to the value of the sharpness measured by the sharpness measuring unit. Surface inspection apparatus characterized in that a minimum detection size changing means for changing the's.