JPH0242406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a visual inspection method and apparatus.

Conventional technology Inspecting the appearance or presence of flaws on processed metal surfaces, films, rolled iron plates, Si wafers for LSI, etc.
Various types of automatic inspection devices have been used in the past, including, for example, a system using an image pickup tube, a system using a semiconductor line sensor, and a system using a scanning laser beam. In addition, the method of detecting defects involves increasing the amount of light reflected from the surface to be inspected by 2.
There are simple methods that convert the defect into values and determine the presence or absence of flaws based on their size, methods that use spatial filtering, methods that examine the matching state of diffraction patterns, and methods that apply holographic technology, but most of these methods are There are few methods that simply determine the presence or absence of flaws on the surface to be inspected and detect even the unevenness of the flaws.

In addition, in recent years, due to the need for high-mix, small-lot production,
As FA is being strongly promoted, the automatic inspection equipment described above is increasingly being used in locations with poor environmental conditions, such as in the middle of the processing process.
In addition to the original machining defects that are concave, dirt, cutting chips, dust, etc. adhere to the surface to be inspected and create a convex shape, which causes false judgments and reduces the reliability of automatic inspection equipment. I will let you do it.

Figure 1 is a schematic diagram showing the laser scanning type visual inspection method, which is one of the conventional visual inspection methods. is projected. This laser beam is reflected by a total reflection mirror 2 and is incident on a vibrating mirror 3 that swings at a predetermined period in a direction indicated by an arrow mark R in the figure. The reflected light from the vibrating mirror 3 spreads into a fan-shaped beam for optical scanning, and passes through an objective lens 4 placed at a position where the distance from the reflection point on the vibrating mirror 3 is equal to its own focal length. As a result, the fan-shaped beam is converted into a parallel scanning beam, and then the surface S to be inspected is irradiated. The reflected light from the surface to be inspected S is scattered due to random roughness on the surface S to be inspected, mainly direct reflected light that satisfies the geometrical optical law of reflection (Snell's law). In addition to the diffusely reflected light, when the roughness of the surface S to be inspected has a certain degree of regularity due to the processing method, it includes the spread due to the diffracted light that occurs because the regularity acts as a diffraction grating. However, it is generally uniform (normal)
The reflected light from the inspected surface S falls within a fairly small solid angle centered on the direction of direct reflection. In addition, the proportions of the direct reflected light, diffuse reflected light, and diffracted light components vary depending on the processing method of the inspected surface S, but in general, the larger the surface roughness of the inspected surface S compared to the wavelength of the light, the more
It shows a tendency for the direct reflection component to decrease and the diffuse reflection component to increase.

On the other hand, in the case of reflection from a flaw on the inspected surface S, the direction of reflection according to Nestl's law of directly reflected light is:
The direction of reflection is different from the direction of reflection in the case of a normal surface S to be inspected.

This also adds to the spread of reflected light due to diffraction from flawed edges.

There are two characteristic phenomena. These 2
Due to two phenomena, the direction of reflection of the beam and the solid angle of its spread in the case of reflection from a flaw are significantly different from the direction of reflection and the solid angle of the beam in the case of reflection on a normal surface S to be inspected. Therefore, in this case, the amount of light entering the light receiving lens 6 generally tends to decrease compared to the amount of light incident during normal reflection (however, depending on the type of flaw, there may be a sharp directivity in the direction of normal reflection). ).

The reflected light containing such information regarding the surface to be inspected S is collected by a light receiving lens 6,
The light passes through a lens 8 and an interference filter 9 and is photoelectrically converted by a photomultiplier tube 10, and the amount of received light is detected as the magnitude of voltage. The iris diaphragm 7 appropriately limits the solid angle at which the light receiving section is viewed from the reflection point of the inspection surface S (flaw detection performance largely depends on this solid angle), and the lens 8 converges the light received by the lens 6. further strengthen. The interference filter 9 extracts a single wavelength light (6328 Å) from the light that has passed through the lens 8.
This is to remove noise caused by ambient light and obtain defect information with a good S/N ratio. The voltage signal taken out from the photomultiplier tube 10 changes correspondingly to the reflection state on the surface S to be inspected, so by observing the signal waveform amplified by the amplifier 11, it can be determined whether it is a normal reverse slope or an abnormal reflective surface. That is, the presence or absence of flaws on the surface S to be inspected is determined.

The above is a flying spot laser scanning method, which is one of the conventional flaw detection methods, but as is clear from the above explanation, this method does not discriminate even the unevenness of flaws.

Purpose This invention not only determines the presence or absence of a flaw on a surface to be inspected, but also simultaneously detects the unevenness of a location determined to be a flaw, thereby eliminating the problem of adhesion to the surface to be inspected, as seen in the conventional example described above. The purpose of the present invention is to provide a visual inspection method and device that can avoid erroneous judgments due to dust, cutting chips, grinding chips, dirt, etc., and improve inspection reliability, equipment maintenance, and scanning performance. do.

Overview The present invention distributes auxiliary optical systems on the left and right sides of a surface including a light projecting and receiving system, and determines the presence or absence of reflection on a surface to be inspected based on the amount of light received by the light receiving system. The uneven state on the surface to be inspected is determined from the difference in the time of change in the amount of received light between the optical systems.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 2 to 9.

In FIG. 2, 12 is a light projection system of a flying spot laser scanning type visual inspection mechanism, which includes a laser tube 1, a total reflection mirror 2, a vibrating mirror 3, an objective lens 4, etc., and 13 is a light projection system for the visual inspection mechanism. The light receiving system of the mechanism includes a light receiving lens 6, a photomultiplier tube 10, an amplifier 11, etc. This light emitting/receiving system has the same configuration as the conventional flying spot laser scanning system shown in FIG.
The reference numerals of each component are the same as those in FIG. In FIG. 2, since only a schematic configuration is shown, the iris diaphragm 7, lens 8, interference filter 9, etc. shown in FIG. 1 in the light receiving system 13 are omitted.
This light emitting/receiving system optically scans the surface S to be inspected in a direction perpendicular to the plane of the drawing in FIG.

In addition to the above-mentioned light emitting and receiving system, the present invention includes first and second auxiliary light receiving systems 14 and 15 on the left and right sides of the plane in which this light emitting and receiving system is included (the plane of the paper in FIG. 2).
The presence or absence of abnormal reflection on the surface S to be inspected is determined based on the amount of light received by the light receiving system 13, and the presence or absence of abnormal reflection on the surface S to be inspected is determined based on the difference in the time of change in the amount of received light occurring between the two auxiliary light receiving systems 14 and 15, which will be described later. This is to determine the uneven state of the inspection surface S.

In this embodiment, two auxiliary light receiving systems 14 and 15 are used.
is in a plane perpendicular to the plane containing the light emitting/receiving system (a plane parallel to the plane of the paper in Fig. 3), as shown in Fig. 3, which shows the state seen from the direction of the arrow mark - in Fig. 2. That is, when abnormal reflection occurs on the surface S to be inspected in a plane parallel to the optical scanning direction P, the abnormal reflection components are received by the auxiliary light receiving systems 14 and 15, respectively. The auxiliary light receiving system 14 includes a light receiving lens 16, a photomultiplier tube 17, and an amplifier 18.
The auxiliary light receiving system 15 includes a light receiving lens 19, a photomultiplier tube 20, and an amplifier 21.

The voltage signals taken out from each amplifier 11, 18, 21 of the light receiving system 13 and auxiliary light receiving systems 14, 15 are as follows.
It is processed by the signal processing system shown in FIG. 4, and based on the processing results, the presence or absence of flaws on the surface S to be inspected and the uneven state of the flaws are determined.

When the surface S to be inspected is a normal reflective surface without scratches or dirt, the light irradiated onto the surface S to be inspected from the light projection system 12 is almost reflected in the normal reflection direction, that is, toward the light receiving system 13, and is reflected in the auxiliary light receiving system. Almost no light is reflected in the directions 14 and 15.

On the other hand, when the inspected surface S is an abnormal reflection surface, the amount of reflected light in the normal reflection direction decreases, while the amount of reflected light in the direction of the surface including the auxiliary light receiving systems 14 and 15 increases, The reflection pattern is as shown in FIGS. 6 and 7. That is, FIGS. 6A and 6B show reflection patterns when there is a convex part on the surface S to be inspected due to adhesion of cutting waste, grinding waste, dirt, etc., and the reflected main beam initially changes as the optical scanning progresses. As shown in FIG. 6A, the light is reflected toward the start side of the light scanning direction P and is mainly received by the auxiliary light receiving system 14,
The reflection direction gradually shifts to the end side of the optical scanning direction P, and the light is mainly received by the auxiliary light receiving system 15 as shown in FIG. 6B. On the other hand, FIGS. 7A and 7B show reflection patterns when there is a concave part such as a processing flaw on the surface S to be inspected.Contrary to the case where there is a convex part, the reflected main beam starts at the beginning as the optical scanning progresses. 7 As shown in Fig. 7A, the light is reflected toward the end side of the light scanning direction
5, and the direction of reflection gradually changes to the optical scanning direction P.
Moving to the start side, the light is mainly received by the auxiliary light receiving system 14 as shown in FIG. 7B. This means that in the case of abnormal reflection, the peak of the amount of received light comes first in the auxiliary light receiving system 15 located on the final power side in the optical scanning direction P, and in the auxiliary light receiving system 15 on the starting side in the optical scanning direction P. If it is a little later than this, it is determined that there is a concave flaw on the surface S to be inspected, and conversely, if the peak of the amount of light received occurs first in the auxiliary light receiving system 14 on the starting side of the optical scanning direction P, the surface S to be inspected is judged to have a concave flaw. This means that it is determined that there is cutting waste or the like that has a convex shape attached to it.

In the signal processing system, the voltage signal a of the light receiving system 13 is
is received by an amplifier 22 to determine the presence or absence of abnormal reflection, and the voltage signal b of the auxiliary light receiving system 14 is received by the amplifier 23, and the voltage signal c of the auxiliary light receiving system 15 is
is received by the amplifier 24 and determines whether the abnormal reflection is due to the concave or convex shape of the surface S to be inspected. The output a' of the amplifier 22 is input to a comparator 25 for detecting the presence or absence of a flaw or abnormal reflection, and is compared with a predetermined reference level here. For example, when there is an abnormal reflection, the amount of light received by the light receiving system 13 decreases, the level of the input signal a' to the comparator 25 falls below the reference level, and the output d of the comparator 25 corresponds to the presence of an abnormal reflection. This results in an L signal. The setting level of the reference level differs depending on the minimum size of the flaw to be detected.

The output a' of the amplifier 22 is input in parallel to a measurement timing setting comparator 26 and an abnormal reflection section detection comparator 27, respectively. The reference level compared with the signal a' in the comparator 26 is:
It is set closer to the dark level side than the peak level of the signal a' at the time of abnormal reflection, so that the scanning section in which the laser beam from the projection system 12 netly irradiates the surface S to be inspected is detected as the measurement section. Ru. Reference level Vth compared with signal a′ in comparator 27
As shown in FIGS. 8A and 9A, is set near the bright level, that is, near the level corresponding to an increase in the amount of light received by the light receiving system 13, and when the amount of received light begins to decrease, that is, abnormal reflection occurs. Detection of the abnormal reflection section starts immediately.
The outputs d and e of the comparators 25 and 26 are input to the flaw presence/absence determining section 28 at the next stage, and the determination output f thereof is input to the comprehensive determining section 29 at the final stage. On the other hand, the output g of the abnormal reflection section detection comparator 27 is
Input to 0. Note that FIGS. 8A to 8H show output waveforms of each part of the signal processing system in the case of abnormal reflection caused by a concave flaw on the surface to be inspected S, and FIGS.
H indicates the output waveform of each part of the signal processing system in the case of abnormal reflection caused by a convex flaw (cutting chips, adhesion of dust, etc.).

On the other hand, the output b' of the amplifier 23 is differentiated by a differentiator 31, and the differentiated output h is input to the next stage zero-cross detector 32. The output c' of the amplifier 24 is similarly differentiated by a differentiator 33, and its partial output j
is input to the next stage zero cross detector 34.

When light scanning is performed from the side where the auxiliary light receiving system 14 is placed to the side where the auxiliary light receiving system 15 is placed as shown in FIG. Figure 8A shows the signal processing when
The explanation based on ~H is as follows.

When the comparator 27 starts detecting the abnormal reflection section as shown in FIG. 8B, a pulse waveform is first generated in the signal b' corresponding to the auxiliary light receiving system 14 as shown in FIG.
This is processed by the differentiator 31 into a differential signal h as shown in FIG. The zero cross detector 32 obtains an output k of a single pulse waveform as shown in _FIG . is input to. As shown in FIGS. 6A and 6B, the reception of the abnormally reflected light by the auxiliary light receiving system 15 is delayed from that of the auxiliary light receiving system 14, so that the signal c' corresponding to the auxiliary light receiving system 15 as shown in FIG. The pulse waveform is generated at a time a little later than time _tR in the abnormal reflection detection section. This signal c' is similarly processed by the differentiator 33 into a differential signal j as shown in G in the same figure, and in the next stage zero cross detector 34, the differential signal j crosses the zero level at the time t _L as shown in H in the same figure. An output m having such a single pulse waveform is obtained, and this output signal m is input to the comparator 30. In the comparison section, the auxiliary light receiving system 14
The output k corresponding to the auxiliary light receiving system 15 and the output m corresponding to the auxiliary light receiving system 15 are compared before and after the single pulse waveform generation time t _R , t _L , and the comparison result is sent to the unevenness determination circuit 35 in the next stage.
is input to.

Unlike the above case, in the signal processing when there is a concave flaw on the surface to be inspected S, FIG.
As shown in H, before and after the single pulse waveform generation times t _R and t _L of the outputs k and m, t _R >t _L , contrary to the previous case.

In the explanations with reference to FIGS. 8 and 9, the case where light scanning is performed from the side where the auxiliary light receiving system 14 is arranged to the side where the auxiliary light receiving system 15 is arranged is illustrated, so that convex defects on the surface S to be inspected can be t _L > t _R , for concave defects
Although a result of t _L <t _R was obtained, if the optical scanning direction is opposite to that described above, the relationship between the unevenness of the surface to be inspected S and t _R and t _L is completely reversed. Therefore, in the signal processing system shown in FIG. It is compared with a predetermined reference level, and the comparison result is input to the unevenness determination circuit 35 as a scanning direction determination signal q. for example,
In this embodiment, when scanning is performed from the side where the auxiliary light receiving system 14 is placed to the side where the auxiliary light receiving system 15 is placed as shown in FIGS. 6 and 7 (leftward direction), the scanning direction discrimination signal q becomes an H signal. On the contrary, when scanning is performed in the right direction, the scanning direction determination signal q is set to be an L signal.

In response to the determination output of the unevenness determination circuit 35 and the determination output f of the flaw presence/absence determination section 28, the comprehensive determination section 29 outputs a concave determination signal r that indicates the presence of concave defects such as machining defects on the surface S to be inspected, as well as cutting chips and dirt. A convexity determination signal u is output to notify of adhesion. If no abnormal reflection occurs, these determination signals r and u are not output.

On the other hand, in the signal processing system shown in FIG. 4, a signal a' corresponding to the light receiving system 13 and signals b' and c' corresponding to the auxiliary light receiving systems 14 and 15 are added by an analog adder 37, and the added output v is input to the comprehensive determination section 29. This addition output v is used to distinguish between light-absorbing stains on the inspected surface S and non-absorbing defects such as other flaws and dust. That is, when there is light-absorbing dirt on the surface S to be inspected, the amount of light received by the light receiving system 13 is significantly reduced.
While the output f of the flaw determination unit 28 shows an output waveform similar to that in the case of abnormal reflection, the abnormal reflection light is not received by the auxiliary light receiving systems 14 and 15, so the unevenness determination circuit 35 cannot obtain an unevenness determination result. do not have. In this case, since the level of the addition output v of the analog adder 37 is lower than that in the case of a non-absorbing defect, the overall judgment section 29 compares it with a predetermined reference level to obtain the dirt judgment signal w. . When the defect on the inspected surface S is non-absorbing, the reflectance is the same as when the inspected surface S is a normal surface, so the level of the added output v in this case is about the same as when the inspected surface S is a normal surface. .

An example of a specific circuit configuration of the comparator 30 that determines whether the outputs k, m of the zero-cross detectors 32 and 34 corresponding to the auxiliary light receiving systems 14 and 15, respectively, are ahead of or after the single pulse waveform generation time points t _R and t _L will be described below. It is shown in Figure 5. In the figure, P _R is a reset pulse output from a pulse generation circuit (not shown), and is obtained as a single waveform with a short pulse width (0.1 μsec or less) at the rising edge of the abnormal reflection section detection output g. In response to this reset pulse _PR , all flip-flops _F1 to _F6 in the figure
is reset and zero cross detectors 32 and 3
A standby state is entered in which outputs k and m of No. 4 can be accepted. After both outputs k and m are input, one of the flip-flops F ₃ and F ₆ is in the set state, and the other is in the reset state, depending on which of the two signals k and m is input earlier. keep it.
Based on this state, the magnitude relationship between t _R and t _L is determined. In the example shown in FIG. 6, if t _L <t _R , flip-flop F ₃ is set, and if t _L > t _R
If , flip-flop _F6 is set.

Effects According to the present invention, it is possible not only to determine the presence or absence of abnormal reflections caused by adhesion of cutting chips, dust, etc. to the surface to be inspected, or machining scratches, but also to determine whether the abnormal reflections are caused by the presence of concave portions on the surface to be inspected. It is also possible to determine whether the problem is due to the presence of a convex part or a convex part.
It is now possible to identify the presence of machining flaws (concave areas) and adhesion of cutting waste, dirt, etc. (convex areas), greatly improving the reliability of visual inspection.

In particular, as in the device of the embodiment, the detection outputs of the light receiving system 13 and the auxiliary light receiving systems 14 and 15 are added together by the analog adder 37, and the output is added to one piece of defect determination information. Abnormal reflection due to light-absorbing dirt or the like can also be identified from the level, further improving inspection accuracy.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a conventional visual inspection method, FIG. 2 is a schematic diagram showing an optical system according to an embodiment of the present invention, FIG. 3 is a view taken along the - line in FIG. 2, and FIG.
The figure is a block diagram of the signal processing system, Figure 5 is a circuit diagram showing an example of a specific configuration of the comparing section of the signal processing system, and Figures 6A and B and Figures 7A and B are respectively for cases of abnormal reflection. Explanatory diagram showing the reflection pattern, Fig. 8A
-H and FIGS. 9A-H are output waveform diagrams of each part of the signal processing system, respectively. 1... Laser tube, 2... Total reflection mirror, 3...
... Vibration mirror, 4 ... Objective lens, 6 ... Light receiving lens, 10 ... Photomultiplier tube, 11 ... Amplifier,
12... Light emitting system, 13... Light receiving system, 14, 15...
... Auxiliary light receiving system, 16 ... Light receiving lens, 17 ... Photomultiplier tube, 19 ... Light receiving lens, 20 ... Photomultiplier tube, 21 ... Amplifier, 25 ... Comparator (for abnormal reflection detection), 26... Comparator (for measurement timing/setting), 27... Comparator (for abnormal reflection section detection), 28... Flaw presence/absence discrimination section, 29... Comprehensive discrimination section, 30... Comparison section, 31, 33 ... Differentiator, 32, 34 ... Zero cross detector, 35 ...
Unevenness determination circuit.

Claims (1)

[Scope of Claims] 1. A visual inspection method in which a surface to be inspected is scanned with light in a predetermined direction intersecting with a direction in which the light projecting system and the light receiving system face each other, and the amount of reflected light is detected. Auxiliary light-receiving systems are distributed on the left and right sides of the included surface, and the presence or absence of abnormal reflection on the surface to be inspected is determined from the amount of light received by the light-receiving systems. An appearance inspection method characterized by determining an uneven state on a surface to be inspected. 2. A scanning optical system for optically scanning a surface to be inspected in a predetermined direction intersecting the opposing direction with a light projecting system and a light receiving system facing each other; an auxiliary light receiving system, an abnormal reflection detection means for photoelectrically converting the optical input in the first light receiving system and comparing it with a predetermined level to determine the presence or absence of abnormal reflection; and photoelectrically converting the optical input in the first auxiliary light receiving system. first light reception peak time detection means for detecting the peak time of input;
The second light reception peak time detection means photoelectrically converts the optical input in the second auxiliary light reception system and detects the peak time of the input, and the first and second light reception peak time detection means outputs are compared before and after the detection time. scanning direction detection means for detecting the scanning direction by the scanning optical system; and unevenness determining means for receiving the output of the scanning direction detection means and the output of the time comparison means and determining the unevenness state of the surface to be inspected. Appearance inspection equipment.