JPS5842421B2 - Method and device for detecting surface defects on objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting surface defects on objects, and more particularly, to converting defects such as surface scratches on metal workpieces into electrical signals using a photoelectric converter such as a photomultiplier tube. Conventional detection methods of this type regarding converting and detecting methods and devices are as follows:
As shown in FIG. 1, an illumination optical system consisting of a light source 1 and a condensing lens 2 uniformly illuminates the surface of, for example, a cylindrical object W to be inspected. A real image of the surface of the object W is formed in front of a photoelectric conversion means such as a photomultiplier tube 8 using an imaging optical system such as
The real image is scanned by a scanning mechanism consisting of a fixed slit 5, a rotating slit 6, etc. arranged in the imaging optical system, and the light is incident on the photomultiplier tube 8, where it is converted into an electrical signal and detected by the signal waveform. The presence or absence of is detected.

That is, the fixed slit 5 has a thin line-shaped opening as shown in FIG. As shown in Figure 2, a plurality of narrow openings are provided in the radial direction, and the two slits 5 and 6 are overlapped and arranged so that the openings cross each other, and the fixed slit 5 is used to remove excess light as shown in Figure 2C. The real image W' of the removed object is scanned by the rotation of the rotating slit 6, and the spot-shaped light that has passed through the fixed slit 5 and the rotating slit 6 is sent to the photomultiplier tube 8 via the condensing lens 7. It receives light and performs photoelectric conversion to obtain an electrical signal.

However, assuming that the test object is a polished cylindrical object, the condition of the surface of the test object W changes depending on its loft, or due to dressing or replacement of the grindstone, or even slight changes in the machining conditions. etc., and changes as shown in Figure 3 a, b, and c.

That is, in the same figure, Wa indicates a test object that is dark at both ends and bright at the center, and the electrical signal waveform at this time is like Wa' in figure a, and wb, contrary to the above, indicates that the center is bright. When the object to be inspected is dark and both ends are bright, the electric signal waveform is Wb' as shown in the figure. When the object Wc is dark at one end and becomes brighter toward the other end, the electric signal waveform Wc is as shown in C in the figure.
' appears.

This phenomenon is caused by the difference between the lofts, the dress of the grinding wheel,
In addition to variations in the surface roughness of the object to be inspected due to replacement, slight changes in machining conditions, etc., that is, changes in the surface condition, it also occurs due to subtle changes in the illumination system, imaging optical system, etc. Just because the signal waveform is not horizontal does not necessarily mean that there is a surface defect on the object to be inspected. If there is a surface defect, the waveform may suddenly change, as shown in the signal waveform Wa" in Figure 4a, for example. This causes a disturbance in the defect signal WL.
It is.

However, with a defect signal of this level, if the threshold level is set at Ll in the figure, it is impossible to detect the defect signal WI, and if the level is set at L2, as shown in the figure, it is impossible to detect the defect signal WI. A problem arises in that the signal waveform Wa' of the object to be inspected is also processed in the same way as a signal waveform with a defect.

Therefore, for example, each signal waveform is adjusted so that the electrical signal waveforms Wa', Wb', and Wc' of the defect-free test object as shown in FIGS. 5a, b, and c become approximately horizontal electrical signal waveforms (not shown). Prepare a light shielding plate S, a light amount adjustment filter F, a fixed slit 5, a light amount correction filter 5F, etc. corresponding to the
The waveform of the signal may be optically modified.

That is, when using the light shielding plate S, in the vicinity of the position A that satisfies 1-1 + (where f is the focal length bf of the condensing lens 2, and d is the multiplication factor), Light-shielding patterns Sa and Sb suitable for correcting each signal waveform by slightly shifting in the optical axis direction.

A light shielding plate S having Sc is selectively inserted to form a blurred image on the surface of the object to be inspected, and a light amount adjusting filter F has patterns Fa and Fb having a similar correction function.

By forming Fc and selectively inserting it in the A position instead of the light shielding plate S, the illuminance distribution of the illumination optical system can be changed in the axial direction when the object to be inspected is a cylinder. ,
Correcting the elements that make the electrical signal waveform non-horizontal, making the amount of light of the real image that has passed through the fixed slit of the defect-free object uniform in the length direction of the slit, and correcting the signal waveform to be horizontal. do.

On the other hand, instead of interposing a light shielding plate and a light amount adjustment filter in the illumination optical system, the opening width of the fixed slit 5 is changed in the length direction, and 5a and 5b are provided.

As shown in 5c, the signal waveforms Wa', Wb', Wc
', or by providing a light amount correction filter 5F on the fixed slit 5 itself or superimposed on it, whose light transmittance changes continuously or stepwise in the length direction of the slit, as shown in 5Fa, 5Fb, and 5Fc. Real image W formed on the front surface of the photomultiplier tube 8 of the test object W without defects
The brightness in the length direction is uniformly corrected, and the waveform is corrected so that the signal waveform becomes horizontal.

This type of waveform correction method can detect extremely small defect signals, such as extremely small scratches on the surface of the test object, with extremely high accuracy, making it possible to reliably prevent such malfunctions. However, to correct the waveform more correctly,
It is necessary to change the correction characteristics of the correction means such as the light shielding plate, that is, to replace it, in response to differences in the surface condition of the test object between lots, dressing of the grindstone, replacement, and other various conditions. ,Furthermore, even in the same lot, for example, for the first,nth specimen to be ground and then the Nth specimen,
Differences occur in the surface condition due to changes in the surface condition of the grinding wheel,
A situation may arise in which the custom correction of the correction means must be changed.

The manner in which the surface condition changes is discontinuous after dressing the grindstone, alternating current, etc., and changes continuously depending on the number of grinding pieces in the same lot.

Therefore, for example, the signal waveform shown in FIG. 5 also changes from Wa' to W.
There is a continuous change, such as a stepwise change to W a ', or a gradual change in the signal waveform of W a ' as the number of pieces to be ground increases, approaching W c'.

In order to cope with this, it is necessary for the operator to replace the correction means at an appropriate time while observing changes in the signal waveform, but in order to perform this replacement in a timely manner, it is necessary to observe the waveform frequently. In order to effectively correct the waveform, it is highly dependent on experience and requires the skill of the operator, so it has little effect on reducing the number of personnel, and it is not necessary to install it on the production line. There are still many problems left.

In detecting surface defects of an object as described above, the present invention automatically corrects the waveform in response to changes in the electrical signal waveform due to changes in the surface condition of the inspected part. The object of the present invention is to solve the above-mentioned problems that occur when installing this type of device on a production line.

Hereinafter, an embodiment in which the light amount correction filter 5F shown in FIGS. 5a, b, and c is used will be described.

FIG. 6a shows an example in which each pattern of the light amount correction filter 5F explained in FIG. 5 is arranged on one disc 5d, and the disc 5d is driven by a pulse motor 9. In the figure, the disc 5d is superimposed on the fixed slit 5 and its pattern is selectively matched to the opening position of the fixed slit 5, or each pattern of the disc 5d itself is overlapped with the fixed slit 5. 6 is a rotating slit that scans the real image passing through the fixed slit 5.

A large number of light amount correction filters 5FP formed on the disk 5d...
・>5Fq...>5FR is shown in Figure 6.

In Figures 6 and 6c, each pattern 5FP...5FQ.
...5FR... or 5FPl...
...5FQ'...5FR,' have a configuration in which the transmittance increases in the direction of the Y arrow in the figure, and in each filter, 5FP, 5FR, and 5FP', 5F
The arrangement is such that the change in transmittance of R,' is maximum, and the change in transmittance of one light amount correction filter becomes smaller toward the middle.

Further, the X direction corresponds to the length of the fixed slit, and in this case, the length of each pattern is equal to the fixed slit.

Figure T a shows a similar light intensity correction filter 5 F'; in this case, the transmittance distribution of one filter is continuously changed as shown in Figure C, and the correction characteristics are shown in Figure T. As shown, the change in transmittance corresponding to the fixed slit is maximum at the upper end p and lower end r of the filter 5F', and is minimum at the center q position.

Further, the length l in the figure corresponds to the fixed slit 5.

That is, l is the effective length of the filter with respect to the fixed slit, and by moving the filter 5F' in the X direction, two series of transmittance distributions in FIG. 6 can be obtained by one filter 5F'.

The filter 5F' is provided on a plate 10 movable in the XY directions, overlapped with a fixed slit (not shown), and driven by two pulse motors 9Xt9Y to a position where a predetermined change in transmittance can be obtained.

Further, the transmittance of the filter 5F' may be changed stepwise.

FIG. 8 is a block wiring diagram for driving the above-mentioned pulse motors 9, 9X, and 9Y to set a required light amount correction filter at a fixed slit position.

The electric signal photoelectrically converted by the photomultiplier tube 8 is amplified by the amplifier 11, and one of the output signals is sent to the defect detection circuit 12.

The other output signal is passed through the low-pass filter 13 to A
The signal is guided to a D converter 14.

The AD converter 14 performs AD conversion based on an instruction signal from the microprocessor 15, and inputs the signal to the microprocessor-15.

In response to the synchronization signal R8 of the rotating slit 6, the microprocessor 15 divides the output of the low-pass filter 13 as shown in FIG. 9 into n parts and stores each value. Measurements are taken at dozens of locations, and the average value is finally stored.

Further, this operation is performed for several or more test objects in response to the test object synchronization signal Ws, and all of these are averaged.

The resulting flatness (distortion and slope of the waveform) is then checked, and if it is within a certain range, it is necessary to correct the brightness of the object image that has passed through the fixed slit (and light intensity correction filter). It is determined that there is no microprocessor.
15 to the pulse motor drive circuit 16.

If the flatness of the average result exceeds a certain range, a signal is sent to the pulse motor drive circuit 16,
Either switch to a light amount correction filter suitable for the exceeded amount (in the case of FIG. 6), or select an appropriate position of the light amount correction filter.

(In the case of FIG. 8) As a result, the waveform will be within a certain range.

As can be seen from the above explanation, the pulse motor drive circuit 16' shown by the broken line in FIG. 8 is for driving one of the pulse motors when moving the light amount correction filter in the X and Y directions as shown in FIG. used for.

The data processing method of the microprocessor-15 is as follows:
As schematically shown in Figure 0, data equal to the number of objects to be averaged are always stored, and each time new data is measured, the oldest data at that time is canceled.

In other words, in the current situation where data of N test objects are stored, when data of a new test object N+1 is measured,
Cancel the first 1st data and N+ from the 2nd
The first N pieces of data are stored as the next situation.

Then, it is determined whether or not to drive the pulse motor 9 based on the N pieces of data at that time.

When the change in the detection signal waveform is continuous (mainly continuous change within the same lot), the purpose is achieved by performing the above processing, but the above-mentioned differences between lots, dressing of the grindstone, replacement, etc. Processing may not be possible if the signal waveform changes discontinuously due to changes in working conditions, replacement of light sources, etc.

In such a case, the microprocessor 15 receives a grindstone dressing instruction signal, a grindstone exchange signal Gs, and a workpiece number signal Ns from a machine tool such as a grinder, and starts another job according to the instructions.

When the first object to be inspected enters the predetermined position after replacing the grinding wheel or dressing, all previous data is canceled, and a light intensity correction filter suitable for correcting the signal waveform of the first object to be inspected must be selected. will be held.

After that, the same processing as the above method will be performed, but until the number of data reaches N, 2゜3...
...The determination is made based on the average of N-1 items.

When the number reaches N, the same process as above is performed.

Note that when a drive signal is sent to the pulse motor and the custom correction of the light intensity correction filter is changed, all previous data is canceled and N new data are added, just as when the signal waveform changes discontinuously. It operates in the same way as in the discontinuous change case until .

The method described above averages N data,
Although the method for making decisions has been described, N pieces of data may be weighted and averaged.

Further, a test object having a signal waveform that differs by more than a certain value from the information stored in the microprocessor may be judged as a defective product, excluded, and not added to the data.

The above description has been made regarding the case where the light amount correction filter 5F in FIG. is provided with a constant thin line aperture, and the illumination optical system includes a light shielding plate S whose pattern changes to the extent that it can be regarded as continuous or almost continuous.
It goes without saying that the same method can be implemented when using a light amount correction means such as a light amount adjusting filter F or the like.

As described above, the present invention includes a light amount correction means that can be considered to change continuously or almost continuously, and which is inserted into the illumination or imaging optical system of the object to be examined. The obtained information is averaged, and the light intensity correction characteristic can be set to the most suitable characteristic for waveform correction based on the command, and the operation can be performed accurately by a driving means such as a pulse motor or servo motor. It can be installed in the production line of the object to completely automatically detect defects such as surface scratches on the object, and also improves the detection accuracy to achieve rationalization of production, reduction of personnel, etc. It is something that can be done.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of an object surface defect detection device, Figure 2
Figures a, b, and c show a fixed slit and a rotating slit,
Figures 3a, b and c are diagrams illustrating the surface condition of the object to be inspected and custom-made waveforms of the detected electrical signals, respectively. Figures 4a and b are defect signals based on the waveforms. FIG. 5 atbtC is a diagram showing the signal waveform and a light amount correction means suitable for modifying the waveform. FIGS. 6 a, b, and c show the light amount correction means and its correction characteristics. Figures 7a, b, and c are diagrams showing other light amount correction means and their custom-made corrections, Figure 8 is a block diagram of the electric circuit according to the present invention, and Figure 9 shows the output signal of the low-pass filter. The figure shown in FIG. 10 is a diagram showing the data processing method of the present invention. 1...Light source, 2...Condensing lens, 3.
... Half mirror 14 ... Imaging lens,
5... Fixed slit, 6... Rotating slit, 7... Condensing lens, 8... Photomultiplier tube, 9 t 9x t 9y... ...Tsu smell smoke, 10...Movable plate, W...
・Test object, W'...Real image, W a', Wb
', Wc'... Electric signal waveform, S...
・・Light shielding plate, F・・・・Light intensity adjustment filter, 5F・
...Light level correction filter.

Claims (1)

[Claims] 1. Illuminating the object to be inspected through a condensing lens, scanning a real image of the object with a fixed slit and a rotating slit that intersects with the fixed slit, and converting it into an electrical signal by a photoelectric conversion means, In the method of detecting a surface defect based on the signal waveform, a light amount correction means for uniformly correcting the light amount of the real image over its length direction so as to make the electric signal waveform of the defect-free test object substantially horizontal. A custom-made correction change that can be considered to be continuous or almost continuous is applied to the signal, the electric signal waveform of each object is averaged, and the light amount correction means is driven to suit the situation of the next object. 1. A method for detecting surface defects on an object, the method comprising: setting the electric signal at a certain position, and correcting the waveform of the electric signal. 2. The detection method according to claim 1, wherein the light amount correction means is arranged at a predetermined position of an illumination optical system of the object. 3. The detection method according to claim 1, wherein the light amount correction means is arranged at a predetermined position of an imaging optical system of the object. 4 An illumination optical system that uniformly illuminates the surface of the object to be inspected, an imaging optical system that forms the real image on the front surface of the photoelectric conversion means, a mechanism that scans the real image, and a mechanism that converts the scanned real image into photoelectric converters. In a surface defect detection device for an object, which is equipped with a means for converting into an electric signal, the real image is provided to make the light amount of the real image uniform in its length direction, and can be regarded as continuous or almost continuous. A light amount correcting means having a custom-made correction that has changed as shown in FIG. A surface defect detection device for an object, comprising: a control circuit that provides a signal for setting a light amount correcting means; and a driving means that drives the light amount correcting means using a command signal from the circuit. 5. Claim 4, wherein the light amount correction means is provided with a large number of patterns whose correction characteristics change almost continuously, and is set by driving a desired pattern to a predetermined position by the driving means. The detection device described. 6. The light amount correction means is configured to be movable in one direction or two directions by continuously changing the custom-made correction, and is suitable for correcting the real image of the object to be almost uniform in brightness over its entire length. 5. The detection device according to claim 4, wherein the portion having the correcting characteristic is set at a predetermined position by being driven by the driving means. 7. The detection device according to any one of claims 4 to 6, wherein the light amount correction means is arranged at a predetermined position in an illumination optical system of the object. 8. The detection device according to any one of claims 4 to 6, wherein the light amount correction means is arranged at a predetermined position in an imaging optical system of the object.