JP2967291B2 - Scratch inspection method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a method for inspecting a surface defect inspection apparatus for a drum such as a photosensitive drum of an electrophotographic copying machine or a metal plate.

(Prior Art) Devices for detecting defects such as scratches on the surface of a cylindrical drum or the like using optical means have been developed and widely used. This inspection apparatus emits slit light to an object to be inspected and receives the scattered light using a line sensor. Alternatively, the light beam is scanned by a rotary scanning mirror, and the scattered light is received by a photomultiplier tube. The detection signal received and photoelectrically converted is compared with a threshold value 51 preset by a signal processing circuit as shown in FIG.
It is binarized and the scratch is determined.

Since the light received by the line sensor uses a reduction optical system that condenses light by a lens, the distribution of the amount of received light differs between the central part and the peripheral part of the cylindrical drum by about twice as much as the amount of light reflected from the cylindrical drum. Unevenness occurs. Therefore, the pixels D ₀ , D ₁ , D ₂ ,.
On the other hand, instead of using a fixed threshold value 51 as shown in FIG. 5, a threshold value 61 corresponding to the amount of reflected light is used as shown in FIG.

In the installation environment for inspecting the photosensitive drum of this apparatus, 1) the temperature fluctuation of the installation place occurs about 10 ° C. in one year 2) The amount of slit light decreases due to the deterioration of the light source apparatus 3) The photosensitive drum to be inspected has manufacturing variations among manufacturing lots, and the signal output of the line sensor fluctuates due to a variable factor such as a difference in surface reflectance of about 10%.

That is, the signal output of the line sensor fluctuates with respect to the temperature fluctuation. Further, with respect to the fluctuation of the light amount of the slit light, the slit light is reflected by the inspection object, and the light amount received by the line sensor changes, and the signal output of the line sensor changes.

Also, with respect to variations in the reflectance of the inspected object, the amount of light received by the line sensor changes, and the signal output of the line sensor changes. In contrast to such a fluctuation 72 of the signal output of the line sensor as shown in FIG.
Since the object to be inspected was able to obtain a large N ratio (S: signal intensity due to flaws, N: signal intensity at unflawed parts),
It was possible to correctly determine the flaw even with a slight change in the threshold value, and the threshold value 71 of the signal processing circuit was often not changed after the initial setting.

(Problems to be Solved by the Invention) However, in the photosensitive drum, a difference in signal output level between a flaw signal causing a defect in image quality and a flaw signal not causing a problem in image quality is small. Also, image quality defects are:
It is mainly determined by the area. For this reason, a standard such as that there must be no spot-like black spots having a diameter of 0.01 inch or more in image quality as a standard for shipment. From this, the area value for performing the flaw determination is determined. In the conventional method of performing a flaw determination with a fixed threshold, the signal level caused by the flaw fluctuates due to the above-described variable element (FIG. 82 versus FIG. 92) and is cut out by the thresholds (81 and 91). Since the area of the flaw greatly varies (FIG. 9 vs. FIG. 93), the flaw determination cannot be performed accurately.

Therefore, in the present invention, high accuracy of a threshold such as a photosensitive drum is required regardless of a temperature change in a place where an inspection apparatus is installed, a change in a slit light amount, a change in the reflectance of an inspection object, and the like. It is an object of the present invention to provide a method for correctly determining a scratch on an object.

(Means for Solving the Problems) The present invention irradiates an object to be inspected with light, photoelectrically converts scattered light due to a defect present on the surface of the object to be inspected by a light receiving means to obtain a detection signal, a method of performing a surface flaw inspection by comparison, the output V ₁ when dark light receiving means measures the signal output V ₂ of the object to be inspected of a normal defect-free surface, Th = (V ₂ -V ₁ ) × p + V ₁ (p is a constant peculiar to the object to be inspected), and relates to a flaw inspection method for performing flaw determination using a threshold Th determined by:

The inspection method of the present invention provides a dark output representing a temperature drift component of a line sensor, that is, a signal output of a line sensor when the sensor is in a light-shielded state, and a line sensor signal based on reflected light of a reference inspection object having no defect. The output is subtracted from the value measured for each pixel D ₀ , D ₁ , D ₂ ,..., Dn of the line sensor, multiplied by a coefficient, and a threshold is calculated. is there.

Here, as the coefficient, among the proportional constants that differ depending on the type of defect, the lowest one among the scratches to be detected is used.

Further, the calculation of the threshold value is performed in response to a temperature change, a light amount change, a reflectance change of the inspected object, and the like. The threshold value may be changed. Alternatively, the threshold value may be changed every time the inspection target is measured.

(Operation) In the inspection method of the present invention, the dark output of the line sensor
Signal output V ₂ of the line sensor by the reflected light of the inspected object to be V ₁ and the reference, the signal output varies depending on the temperature of the location where the installation of both devices. Therefore, by subtracting V ₁ from V _2, to obtain a signal component V ₃ which it does not vary with temperature.

The signal output V ₄ of the line sensor of the light scattered by one defect a (not shown) is proportional to the signal output of the non-existing reference object to be inspected for defects, the signal component V ₃ which does not vary with temperature by multiplying the proportional constant n, the signal output value V ₄ is obtained by the defect (Figure 10). n is determined experimentally. If there are four types of defects a, b, c, and d that cause a problem with the object to be inspected, the proportional constants na, nb, and n respectively.
Find c and nd. In order to detect all of these four types of defects, by selecting the lowest proportional constant as p and calculating the threshold value, an appropriate threshold value is set according to the type of flaw to be inspected, and correct flaw determination is performed. It can be performed.

Example 1 Hereinafter, an example of the present invention will be described.

FIGS. 1A and 1B are configuration diagrams of a defect inspection apparatus used in the surface inspection method of the embodiment. This inspection apparatus is used for the purpose of detecting a defect existing on the surface of a cylindrical drum such as a photoconductor of a copying machine. A support section 1 for supporting the cylindrical drum, a rotating section 2 for rotating the cylindrical drum at a constant speed about the axis of the cylindrical drum, and a slit beam projected on the rotating cylindrical drum. Floodlight 3, linear sensor 4 for receiving scattered light due to defects existing on the cylindrical drum, for example, pixels D ₀ , D ₁ , D ₂ ,..., Dn, and scattered light condensed on the linear sensor It comprises a reduction optical system 5 and a signal processing circuit 6 which compares a linear sensor signal with a threshold value stored in a threshold value memory 7 to determine a flaw based on a binarized signal. The signal processing circuit 6 includes a dark output memory 8 and a reference light amount memory 9 in addition to the threshold memory 7 as memories.

Next, the operation of the inspection device having the above configuration will be described. First, the slit light emitted from the light projector 3 irradiates, for example, a slit light having a width of, for example, 1 mm onto the surface of the cylindrical drum that rotates once in 5 seconds, for example. In a cylindrical drum having a mirror-finished surface like a photoconductor of a copying machine, slit light is reflected in the regular reflection direction when no defect exists, and scattered light is generated when a defect exists. The linear sensor 4 is arranged at a position for receiving the scattered light while avoiding the regular reflection direction of the slit light.

FIG. 2 is a waveform diagram showing a linear sensor signal output. Since there is little scattered light on the surface of the cylindrical drum where no defects exist, the linear sensor signal output 21 is low, and the scattered light is strongly received on the surface of the defective cylindrical drum.
The linear sensor signal output 22 goes high. Since the light receiving device 4 uses the reduction optical system 5 to receive the axial length of the cylindrical drum, for example, 300 mm, the signal output is doubled at the linear sensor central portion 23 and the peripheral portion 24, for example. So-called unevenness in the amount of light occurs to some extent. For this reason, as the threshold value, each pixel D ₀ , D ₁ , D ₂ ,.
Corresponding to Dn, T ₁ , T ₂ , T ₃ , ... inside the signal processing circuit
... The light amount unevenness is corrected by setting a threshold value memory Tn. The linear sensor signal output is A
/ D converted, compared with the threshold value stored as a digital value,
A flaw determination is performed based on the obtained binary signal. A method of setting the threshold value of the inspection apparatus as described above will be described with reference to a flowchart shown in FIG.

Step 1 (Measurement of Dark Output) First, the linear sensor 4 is set in a light-shielded state by capping the reduction optical system 5 or the like. In this state, the linear sensor signal is A / D-converted and taken into the dark output memory 8 of K ₀ , K ₁ , K ₂ ,..., Kn.

Step 2 (Reading of Reference Light Amount) Next, the linear sensor is turned on, and measurement is performed by rotating a reference cylindrical drum (hereinafter abbreviated as a master drum). The measurement is performed for each pixel D ₀ , D ₁ , D ₂ ,
... By storing the Dn signal output in the reference light amount memory 9 of M ₀ , M ₁ , M ₂ ,. For example, in this embodiment,
By repeating the measurement 100 times and calculating the average of the signal output, the effects of abnormal values of the signal output due to dust and dirt attached to the master drum are reduced.

Step 3 (Calculation of Threshold) Next, the threshold is calculated by the equation (1). The contents V ₁ of the dark signal memory _{8 k 0, k 1, k} 2, and ...... kn, the contents V ₂ of the reference light quantity memory _{9 m 1, m 2, m} 3, when the ...... mn, determined The threshold value Th is defined as t ₀ , t ₁ , t ₂ ,..., Tn corresponding to the pixels D ₀ , D ₁ , D ₂ ,.

tq = (mq−kq) × p + kq (1) (0 ≦ q ≦ n, p is a constant that varies depending on the photosensitive material of the drum) Step 4 (determination of threshold) The value calculated by the equation (1) is used for the linear sensor. Each pixel D ₀ ,
The threshold values t ₀ , t ₁ , t ₂ ,... Tn corresponding to D ₁ , D ₂ ,..., Dn are set in the threshold value memory 7 of T ₁ , T ₂ , T ₃ ,.

Step 5 (rewriting of threshold value) A flaw inspection is performed by the device, and in accordance with the fluctuation of the linear sensor output of the master drum, for example, in the present embodiment, the threshold value calculation and setting of the above-described step 1 to step 4 are performed three times a day. Is carried out.

Next, it will be described that a flaw can be correctly determined by the threshold value set as described above.

According to the equation (1), the digital value of the dark output of the linear sensor is kq, the linear sensor signal output by the master drum is mq, and the signal output by the defect type a is rq.

First, for temperature fluctuations, the digital value kq of the dark output of the linear sensor and the digital value mq of the linear sensor signal output by the master drum fluctuate depending on the temperature, but as a result of the experiment, it was obtained by subtracting kq from mq. It has been found that the signal component Sq (hereinafter, abbreviated as an optical signal output) is a signal component that is not substantially affected by temperature. For example, in this embodiment, kq is 1 to 5 and mq is about 30. Next, as a result of the experiment,
The digital value rq of the linear sensor signal output due to the defect a is
It was found that it was proportional to the optical signal output value Sq of the scattered light by the master drum. For example, if the reflectivity of the master drum is
If the power is reduced by 10%, the optical signal output Sq is reduced by 10%. Then, the signal output rq due to a defect existing in the cylindrical drum having the same reflectance as that of the master drum is also reduced by 10%. Similarly, if the light amount of the slit light decreases by 10% due to deterioration of the light source or the like, the optical signal output Sq of the master drum decreases by 10%. Then, it was verified that the signal output rq due to the defect existing in the cylindrical drum was also reduced by 10%. As described above, since the signal output rq based on the defect type a is proportional to the optical signal output Sq from the master drum, the proportional constant n can be obtained. n is determined experimentally. For example, in this embodiment,
There are four types of flaws (dents, abrasions, adhesion, uneven coating), each of which is required to be na, nb, nc, nd, and the like.
Select the lowest value from na to nd, (1)
What is necessary is just to be p in a formula. The experimental results show that p is 2.0
To a value of 3.0. As described above, since the signal output due to the defect is proportional to the optical signal output from the master drum, the threshold may be set in proportion to the optical signal output from the master drum. As a result, it is possible to avoid the influence of a variable element that obtains a variable value on the signal output of the master drum, such as a temperature variation, a light quantity variation, and a reflectance variation.

In this embodiment, the temperature fluctuation, which is a fluctuation factor, occurs at a maximum of about 5 ° C. per day. If the temperature exceeds 5 ° C., the same threshold value makes it impossible to judge correct flaws. Further, as the light quantity fluctuation, every three months when the light source device is deteriorated, the reflectance fluctuation fluctuates about several times during the inspection work day. From this,
By changing the threshold several times a day using the master drum, a correct threshold can be obtained. Therefore, correct scratch determination can be performed, and the effect of correctly performing scratch determination is particularly effective for an inspected object that requires a high-precision threshold value in order to distinguish scratches that affect image quality, such as a photosensitive drum. large.

(Embodiment 2) In step 5 (rewriting of the threshold value) of the embodiment 1,
It is necessary to confirm that the variable element has changed as shown in FIG. 4 (A). On the other hand, according to the method of updating the threshold value for each drum before performing the inspection operation on the inspection object drum as shown in FIG. 4B, it is not necessary to manage the update of the threshold value. According to the above method, it is possible to cope with fluctuations of the line sensor signal output due to fluctuations in reflectance and light quantity for each drum manufacturing lot for each drum, so that it is not necessary to confirm fluctuations in the fluctuation factors.

Furthermore, in the reading of the reference light amount in step 3 of FIG. 4B, if a reference value is provided and the reference value of the threshold value is significantly different, a warning display of a difference in photosensitive material type and light source deterioration may be performed. This makes it possible to automate maintenance and inspection of the inspection device.

As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to the above-described embodiments. In the embodiments, for example, a combination using a slit light device as a light emitter and a line sensor as a light receiver is used. The present invention is also applicable to a method of scanning with an optical rotating mirror and receiving light with a photomultiplier tube. Also,
Although the embodiment of the photosensitive drum of the copying machine has been described, the present invention is not limited to this, and can be applied to, for example, a metal cylinder such as an aluminum pipe, a steel plate, an aluminum plate, and the like.

(Effects of the Invention) As described above, in the present invention, a detection signal is obtained by photoelectrically converting scattered light caused by a defect existing on the surface of an object to be inspected by a light receiving unit, and the detected signal is compared with a threshold value unique to the object to be inspected. By doing so, when performing a surface flaw inspection, thresholds are set according to temperature fluctuations, light quantity fluctuations, and the like, so that there is an effect that correct flaw determination can always be performed without being affected by these fluctuations.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a defect inspection apparatus used in the surface inspection method of the embodiment. FIG. 2 is a diagram showing an example of a signal output of a line sensor in the defect inspection apparatus in FIG. FIG. 3 is a flowchart illustrating a procedure for setting a threshold value in the inspection method according to the embodiment. FIG. 4 is a flowchart illustrating a threshold setting method according to the second embodiment. FIG. 5 is a diagram provided for explanation of a conventional technique, in which a threshold value is constant regardless of the position of a pixel. FIG. 6 is a diagram provided for explanation of a conventional technique, and shows a case where a threshold value is a value corresponding to uneven light amount depending on the position of a pixel. FIG. 7 is a diagram provided for explanation of the prior art, and shows that correct flaw determination cannot be performed because the threshold value is not different from that in FIG. 6 regardless of the fluctuation of the signal output of the line sensor. FIG. 8 and FIG. 9 are diagrams for explanation of the prior art. FIG. 10 is a diagram for explaining signal output of a line sensor in the inspection method according to the embodiment. DESCRIPTION OF SYMBOLS 1 ... Support part, 2 ... Rotating part, 3 ... Projector, 4 ... Linear sensor, 5 ... Reduction optical system, 6 ... Signal processing circuit,
7: threshold memory, 8: dark output memory, 9: reference light amount memory, 21, 22, 23, 24, 52, 62, 72, 82, 92 ...
Linear sensor output signal, 51, 61, 71, 81, 91 ... threshold.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 21/88 G01B 11/30 G03G 5/10 G03G 21/00 510

Claims (1)

(57) [Claims] An object to be inspected is irradiated with light, scattered light due to a defect present on the surface of the object to be inspected is photoelectrically converted by a light receiving means, a detection signal is obtained, and the detection signal is compared with a threshold value to perform a surface flaw inspection. in the method of performing an output V ₁ when dark light receiving means, a signal output V ₂ of the inspected object without defects normal surface _{measurement, Th = (V 2 -V 1} ) × p + V 1 (p is the A flaw inspection method in which flaw determination is performed based on a threshold value Th determined by a constant (inherent peculiar to the inspection object).