JP2003240675A - Method of examining defect of lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of examining the defect of a lens capable of easily examining the defects which causes the deterioration of intrinsic performance as the lens. <P>SOLUTION: This method of examining the defect of lens used in a scanning optical system, applies a light scanning means for making the scanning light irradiate an examined lens, a scanning light receiving means for receiving the scanning light having passed through the examined lens while partially shielding and limiting the scanning light, a moving means for moving the scanning light receiving part in the scanning direction, and a defect detecting means for extracting and detecting the defect on the basis of the waveform of a light receiving signal from the scanning light receiving means, and the defects of the examined lens is detected in a state of moving the scanning light receiving means by the moving means. The scanning light receiving means is provided with a defect detection light receiving means for detecting the defect, and two scanning light detecting means mounted at both sides in the light scanning direction of the defect detection light receiving means, and they are integrally moved by the moving means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a lens defect of a scanning optical system such as a laser printer.

[0002]

2. Description of the Related Art Conventionally, in the evaluation of a scanning optical system including a defect inspection of a lens or the like, one slit forming plate is disclosed in Japanese Patent Laid-Open No. 05-346317 in order to detect the scanning light over the entire scanning range. By arranging a slit for scanning position detection in addition to a pinhole for scanning light detection,
The intensity waveform of the scanning light and the scanning position detection pulse are simultaneously obtained from the transmitted light signal from the slit.

Further, in Japanese Patent Laid-Open No. 11-72383,
Depending on the image height position where the light receiving element for scanning light detection that performs measurement based on the signal detection by the sensor for synchronization signals is arranged,
A method of obtaining scanning light for one dot after a time calculated in advance from the scanning speed is known. Further, as an evaluation method of a scanning optical system including an fθ lens, Japanese Patent Laid-Open No. 2000-3105
As disclosed in Japanese Patent No. 60, a method is known in which the intensity distribution of the scanning light obtained over the entire width of the scanning region is obtained from the obtained intensity of the scanning light.

Further, conventionally, a defect inspection of a lens or the like is carried out by a worker in a factory or the like by direct visual inspection, or mechanically, a lens to be inspected is irradiated with a scanning light, and the light passing therethrough is received by a light receiving means to be waveformd. In order to sample the signal as accurately as possible, the input was made with a sufficiently narrow aperture compared to the beam, and the waveform itself was input and processed to identify defects.

[0005]

However, in order to detect the scanning light over the entire width of the scanning range, Japanese Patent Application Laid-Open No. 05-
In the case of Japanese Patent No. 3463, the transmitted light signal from the slit forming plate includes a scanning light intensity waveform and a scanning position detection pulse at the same time, and when the two waveforms have similar shapes, the scanning light intensity waveform and scanning position are similar. It is difficult to separate the detection pulse, and according to Japanese Patent Laid-Open No. 11-72383, the light receiving element is scanned due to the deviation of the position where the light receiving element is located from the lighting position of the scanning light in the scanning range due to fluctuations in the scanning speed and the like. There was a case where light did not enter, and stable scanning light could not be detected.

Further, in Japanese Unexamined Patent Publication No. 2000-310560, the output fluctuation of the laser light source and the AD
Since noise components due to the quantization error of the converter are included,
There was a problem in the reliability of the evaluation result.

Furthermore, in the conventional visual inspection, it is difficult to associate the inspection result with the performance itself of the lens to be inspected for defects, and there are problems such as oversight due to variations among operators and fatigue. . Further, in the conventional beam input processing by high resolution sampling, an extremely high sensor sensitivity is required, resulting in an expensive device and a lot of data for processing the input waveform, which makes the processing complicated. In the device that realized this, it becomes an expensive device,
For example, it is difficult to introduce it in 100% inspection at the production site.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a lens defect inspection method capable of easily inspecting a defect that originally deteriorates the performance of a lens. is there.

[0009]

In order to achieve the above object, the present invention provides an optical scanning means for irradiating a lens to be inspected with scanning light in defect inspection of a lens used in a scanning optical system, and an inspected lens. Scanning light receiving means for blocking and limiting a part of the scanning light passing through the light receiving means, moving means for moving the scanning light receiving portion in the scanning direction, and a defect extracted and detected from the waveform of the light receiving signal from the scanning light receiving means. And a detection means,
A defect of the lens to be inspected is detected while moving the scanning light receiving unit by the moving unit.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing an example of an apparatus for inspecting a defect of a lens 100 to be inspected. Here, 101 is a light source of a scanning optical system, for which a laser light source or the like is used.

Reference numeral 102 denotes a rotating mirror for deflecting and scanning,
By rotating in the 105 direction, the lens 100 to be inspected is deflected and scanned in the 106 direction. At this time, the position in the 106 direction is also called the image height. 104 is the lens 100 to be inspected
The light receiving unit receives the deflected beam that has passed through and the synchronization signal is output from the synchronization signal detection sensor for each scanning.

A stage 103 for moving the light receiving unit 104 in the scanning direction is provided in order to receive the beam at each deflected light changing position, and generally, the stage 103 is provided.
Is set to a speed sufficiently slower than the beam deflection scanning.

The light receiving unit 104 is shown in FIG.
A beam detection light-receiving element 204, a measurement start trigger detection light-receiving element 301, and a measurement end trigger detection light-receiving element 302 are arranged in parallel in the beam scanning direction in the beam scanning direction. At this time, the beam A is incident on the light receiving element 301 for measurement start trigger detection, the light receiving element 204 for beam detection, and the light receiving element 302 for measurement end trigger detection in this order, and the AD conversion unit 109 causes the light receiving element 301 for measurement start trigger detection. Beam injection into the measurement start trigger PS and measurement end trigger detection beam reception into the light receiving element 302 for measurement end trigger P
As E, the output signal from the beam detecting light-receiving element 204 is AD-converted and taken into the buffer memory 110, so that the beam detection signal B as shown in FIG. 3 can be obtained. The timing of the synchronization signal and the measurement start trigger PS and the measurement end trigger PE at this time are as shown in state X of FIG.

At this time, the capacity P [Byte] of the buffer memory 110 required to obtain the detection signal at an arbitrary image height position is the time ΔT [sec] from the measurement start trigger PS detection to the measurement end trigger PE detection. And the AD conversion unit 109
Can be obtained from P = R · ΔT · Q / 8 from the sampling cycle R [Sample / sec] and the sampling resolution Q [bit]. Since the time ΔT is sufficiently shorter than the cycle TH of the synchronization signal, the beam detection can always be performed at a stable timing without being affected by the cycle TH of the synchronization signal that fluctuates due to fluctuations in the rotation speed of the polygon mirror. it can.

However, at both ends of the effective range of the fθ lens 100 to be measured, the measurement start trigger detecting light receiving element 301 or the measurement end trigger detecting light receiving element 302.
The beam is not incident on either one of them, and the trigger signal required for measurement cannot be obtained. Therefore, both ends of the effective range of the fθ lens 100 can be measured,
A method for quasi-obtaining one trigger signal that cannot be obtained will be described with reference to FIG.

State Y in FIG. 4 shows a state in which the measurement start trigger PS cannot be obtained at one end of the fθ lens 100. At this time, in the trigger generation unit 112, after a lapse of the pseudo measurement start timer value TS from the measurement end trigger PE obtained from the measurement end trigger detection light receiving element 302,
A pseudo measurement start trigger DS is generated in a pseudo manner. The AD conversion unit 109 performs AD conversion of the detection signal from the beam detection light receiving element 204 by the pseudo measurement start trigger DS and the measurement end trigger PE immediately after the pseudo measurement start trigger DS. This pseudo measurement start timer value TS is equal to the period TH of the horizontal synchronizing signal and the measurement start trigger PS in the state X of FIG.
Is a value obtained from TS = TH-ΔT using the time ΔT from the measurement end trigger PE to the measurement end trigger PE, and a numerical value measured in advance is set as an inspection parameter in the trigger generation unit 112, the controller 113, or the like.

In the state Z of FIG. 4, the fθ lens 100
At the other end of, the measurement end trigger PE is not obtained. At this time, the trigger generation unit 112
Then, a pseudo measurement end trigger DE is pseudo-generated after a lapse of the pseudo measurement end timer value TE from the measurement start trigger PS obtained from the measurement start trigger detection light receiving element 301.

In the AD converter 109, the measurement start trigger PS
And a detection signal from the beam detection light receiving element 204 is AD-converted by the pseudo measurement end trigger DE. This pseudo measurement end timer value TE is equal to the time ΔT from the measurement start trigger PS to the measurement end trigger PE in the state X of FIG. 5, and a previously measured numerical value is set in the trigger generation unit 112 or the controller 113 as an inspection parameter. .

The detection signal B AD-converted by the AD converter 109 is passed through the buffer memory 110 to the signal processor 11
Sent to 1.

The signal processing section 111 performs beam measurement according to the flow chart shown in FIG. First, step S
In 1, the detection signal B is averaged. This step S1 is performed to correct the fluctuation of the detection signal caused by the difference in the reflectance of each surface of the polygon mirror 102, and the state of this processing is shown in FIG.

FIG. 8 shows a case where the polygon mirror has four surfaces, for example, and it is assumed that four continuous output signals BA, BB, BC and BD are obtained corresponding to each surface of the polygon mirror. At this time, the positions CEA, CEB, CEC, C of the respective peak values of the output signals BA, BB, BC, BD
The averaged waveform G can be obtained by aligning the phases so that the EDs match and averaging the phases. In FIG. 8, the output waveform for four times, that is, the output waveform for one round of the polygon mirror is averaged, but the output waveform for two or more rounds of the polygon mirror can be averaged. At this time, the number of detected waveforms B to be averaged is determined by the number of polygon mirrors 10.
It is an integral multiple of the number of faces.

Next, the peak value P and the beam width W are detected from the averaged waveform G averaged at each image height position by peak detection (step S2) and beam width measurement (step S3). At this time, in step S2, in the averaged waveform G averaged as shown in FIG. 9, the average value of the range ΔP of 0.5% with respect to the maximum value MAX is detected as the peak value P. .

The detection results obtained in steps S2 and S3 are as shown in FIG. 6 for the peak and the beam width is shown in FIG. 6, and the detection results corresponding to each image height can be obtained. From these detection results, the defect variation (step S4) is followed by the local variation C of the peak value P according to the standard of the fθ lens, for example, as shown in FIG.
And a variation D over a wide range of image heights, or a local variation temporary E of the beam width W and a variation F over a wide range of image heights as shown in FIG. To do.

Next, a method of setting the slit opening width will be described.

FIG. 10 is a view of the light receiving sensor 104 of FIG. 1 viewed from the beam incident side. Since the description of the timing of the entire apparatus is as described above, the sensor for timing detection is omitted here.

Here, 201 is a beam which is scanned by deflection, and scans and moves in the 202 direction. Reference numeral 203 denotes a slit opening for blocking a part of the beam, and 204 denotes a light receiving sensor arranged behind the slit opening 203 with respect to the beam direction, which is converted into an electric signal by photoelectric conversion. 205
Is a signal waveform in response to the beam that is deflected and scanned by the beam, passes through the slit opening 203, and is projected onto the light receiving sensor 203.

Generally, the position of the light receiving sensor in the optical axis direction is arranged at a position corresponding to a photosensitive drum in a laser printer or the like used as a scanning optical system. At this time, the laser beam diameter is set to be the smallest beam waist,
The laser beam has a Gaussian distribution. Further, in the present embodiment, the beam diameter and the beam width refer to a width equal to or larger than a level light amount of about 13.5% which is 1 / e ² (e is the base of natural logarithm) of the beam profile peak value at rest. I will.

In the lens defect inspection, the light from the laser light source 101 is deflected and scanned on the lens 100 to be inspected by rotating the polygon mirror 102 in the direction of 105. At this time, the light is scanned in the 106 direction, and the light receiving unit 1
Pass 04 at high speed. The light receiving unit 104 on the stage 103 is moved at a predetermined speed in the scanning direction 106 of the lens 100 to be inspected over an area to be inspected. When the deflection scanning light passes through the light receiving unit during movement, the waveform of the deflection beam is sequentially processed.

FIG. 12 is a waveform when the beam passes the light receiving sensor while moving in the image height direction, and is a diagram schematically showing the influence of scanning light due to a defect of the lens, etc. (a)
Is a diagram showing that the diameter of the original laser beam expands due to the refractive index abnormality of the lens 100 to be inspected, etc., (b).
FIG. 4 is a diagram showing that the transmittance has changed due to a defect in the lens 100 to be inspected.

In the processing of the waveform, the defect is discriminated from the maximum value of the waveform at the time of receiving each light and the like by the change of the value detected at a predetermined interval in the image height direction of the lens 100 to be inspected. FIG. 6 is a diagram schematically showing how the peak value changes in the image height direction of the lens 100 to be inspected. For example, when there is a defect, the peak value sharply changes as in the part (c). Change and determine that there is a defect.

FIG. 11 illustrates how the input in the light receiving unit 104 changes when the slit width provided in the light receiving unit 104 is changed. Here, in the above graph, the horizontal axis represents the position in the scanning direction and the image height direction (time in the scanning state), and the vertical axis represents the ratio of the beam having the Gaussian distribution that has passed through the slit to the total light amount. The following figures (a) to (c) are diagrams schematically showing the state when the slit width for the beam is changed,
(A) shows a case where the width of the slit 203 is wider than the beam 201, and (b) shows 50% of the beam 201.
When the slit width is set to (c) and the slit width is set to be sufficiently narrower than the beam 201, the light receiving waveform of the light receiving unit 204 in FIG. .

In the case of (a) where the slit width is sufficiently wide with respect to the beam 201, the graph is 1203, and the peak value of the waveform is a value obtained by integrating almost the entire beam amount.
(C) is the case where the slit width is sufficiently narrow, and the graph shows 120
Although the peak value of the amount of received light is low, the beam profile is close to the original shape of the beam. When the slit width is 50% with respect to the beam, the waveform of (b) becomes a graph like 1202, and the peak value of the waveform receives about 70% of the light amount of the entire beam.

FIG. 12 shows how the slit width changes when the width of the beam that passes through the lens 100 to be inspected and is received by the light receiving unit 104 changes due to the influence of a defect or the like. In the graph, the horizontal axis 400 indicates the slit width, and the vertical axis 401 indicates the ratio of the peak value change to the beam diameter change, which is 402. The slit width on the horizontal axis is a relative value indicating the slit width when the beam width is 1. From this, it can be seen that the optimum slit width is 50% of the beam width in order to most sensitively respond to the change in the beam width of beam width 1.

Further, as shown in FIG. 13, the slit portion 501 in FIG. 13A has an opening with a beam width of 50%, but FIG.
As shown in FIG.
Since the same sensitivity can be obtained by setting the ratio to%, the slit portion may be an opening or a light shield.

Although an example of changing the width of the constraint has been given above, it is easily presumed that a waveform having a peak value according to the transmittance can be obtained as a matter of course when the light amount itself changes due to lens transmission.

Thus, when inspecting a defect of the lens 100 to be inspected, a slit having an opening of 50 um is arranged in the light receiving unit 104 in a system having a beam width of 100 um, and the lens to be inspected at a predetermined pitch. The peak value of the waveform obtained from the beam at each point over the entire image height of
Alternatively, by processing and determining the amount of change and the like, it is possible to detect a change in beam width due to a local anomaly in the refractive index and a change in beam light amount due to a foreign substance or the like.

As another embodiment, the fθ lens 10
Not only the defect inspection of 0 but also the defect inspection of the polygon mirror 102 and the characteristic evaluation of the laser scanning optical device can be applied by the same method.

[0039]

As is apparent from the above description, according to the present invention, in the defect inspection of the lens used in the scanning optical system, the optical scanning means for irradiating the inspected lens with the scanning light,
Scanning light receiving means for blocking and limiting a part of the scanning light that has passed through the lens to be inspected and receiving light, moving means for moving the scanning light receiving portion in the scanning direction, and extraction from the waveform of the received light signal from the scanning light receiving means Since it has a defect detecting means for detecting and detects the defect of the lens to be inspected while moving the scanning light receiving means by the moving means, it is possible to easily inspect the defect that deteriorates the performance as the original lens. The effect of being able to do is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of a laser scanning optical system inspection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a light receiving unit.

FIG. 3 is a diagram showing an output signal obtained from a light receiving element for beam detection.

FIG. 4 is a diagram showing a method of interpolating a measurement start and measurement end trigger.

FIG. 5 is a diagram showing a change in beam intensity with respect to an image height position.

FIG. 6 is a diagram showing a change in beam width with respect to an image height position.

FIG. 7 is a diagram showing a flowchart for detecting a defect from an averaged waveform G.

FIG. 8 is a diagram for explaining a process for obtaining an averaged waveform G from a detected waveform B.

FIG. 9 is a diagram showing a process for obtaining a peak value P from an averaged waveform G.

FIG. 10 is a diagram illustrating a partial configuration of a light receiving unit.

FIG. 11 is a diagram illustrating the amount of received light when the slit width is changed.

FIG. 12 is a diagram showing a change in beam width and a change in beam light amount.

FIG. 13 is a diagram illustrating slit openings and light blocking.

[Explanation of symbols]

100 fθ lens 101 laser light source 102 polygon mirror 103 stage 104 Light receiving unit 107 Horizontal sync signal detection sensor 108 Stage control unit 109 AD converter 110 buffer memory 111 Signal processing unit 112 Trigger generator 113 controller 199 Laser scanning unit 204 Photodetector for beam detection 301 Photodetector for detecting measurement start trigger

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F065 AA49 BB05 CC22 FF02 GG04                       HH15 JJ02 JJ05 LL13 LL28                       LL62 MM16 MM28 PP02 QQ03                       QQ23 QQ29 QQ42                 2G051 AA90 AB02 BA10 BB07 BC06                       CB02 CC07 CD04 CD06 EA02                       EA11 EC03                 2G086 FF05                 2H045 CA63 CA97 DA00

Claims (5)

[Claims] 1. In a defect inspection of a lens used in a scanning optical system, an optical scanning means for irradiating a lens to be inspected with scanning light, and a scanning for limiting a part of the scanning light passing through the lens to be inspected and receiving light. A light receiving unit, a moving unit for moving the scanning light receiving unit in the scanning direction, and a defect detecting unit for extracting and detecting from the waveform of the light receiving signal from the scanning light receiving unit,
A method of inspecting a lens defect, wherein a defect of a lens to be inspected is detected while moving the scanning light receiving unit by the moving unit. 2. The scanning light receiving means is provided with a defect detecting light receiving means for detecting a defect and two scanning light detecting means on both sides of the defect detecting light receiving means in the optical scanning direction, and is integrated by the moving means. The lens defect inspection method according to claim 1, wherein the lens defect inspection method comprises moving the lens defect. 3. The scanning light detecting means generates a pseudo timing signal corresponding to an optical scanning time interval when the scanning light is detected by only one of the two detecting means. Lens defect inspection method. 4. The lens defect inspection method according to claim 1, wherein an average value of sampling points in a range of 0.5% from the obtained peak value of the sampling signal is used as the peak value of the intensity shape. 5. In the scanning light receiving means, the defect detection light receiving means receives the light of a portion which passes the beam by limiting the beam with a slit-shaped opening having an opening width of about 50% of the scanning beam width in the scanning direction. The lens defect inspection method according to claim 1, wherein