Patent Application
20140250679
1. Field of the Invention
The present invention relates to an optical inspection apparatus and an optical inspection system that are for inspecting an optical system of an optical scanning apparatus.
2. Description of the Related Art
Conventionally, various methods have been developed that inspect presence or absence of dust intruded in an optical system, stains on optical elements (hereinafter, simply referred to as dust) in an optical scanning apparatus used for a digital copier, a laser printer or the like. One of the methods has been known that perform inspection by condensing laser light emitted from an optical scanning apparatus onto a movable slit plate provided on an image plane. One slit is arranged such that the longitudinal direction of an aperture of the slit is perpendicular to the optical scanning direction (see Japanese Patent Application Laid-Open No. 2003-240675). This inspection method measures the state of a beam spot passing through the slit based on variation in light quantity of the beam spot, and performs inspection for presence or absence of dust on the optical system of the optical scanning apparatus based on the state.
This inspection method moves a photo detection unit including one slit and one detection sensor in a scanning direction to a position on an image plane where inspection is required, receives laser light at the position, thus performing inspection. The photo detection unit is then sequentially moved to many inspection positions across the entire image plane, receives laser light at each inspection position to perform inspection, thereby allowing inspection across the entire image plane.
However, in the method of inspecting an optical scanning apparatus described in Japanese Patent Application Laid-Open No. 2003-240675, a photo detection unit is required to be sequentially moved to many inspection positions across an entire scanning range. Accordingly, the inspection requires a long time.
It is an object of the present invention to provide an optical inspection apparatus and an optical inspection system that can reduce inspection time for inspecting an optical system of an optical scanning apparatus.
The present invention is an optical inspection apparatus inspecting an optical system of an optical scanning apparatus by measuring a light quantity of scanning light emitted from the optical scanning apparatus, including: a slit plate that has a plurality of slits; a diffuser that diffuses the scanning light having passed through the slit; a light guide that guides the scanning light diffused by the diffuser; an optical sensor that measures a light quantity of the scanning light guided by the light guide; and an inspection device that inspects a state of the optical system by comparing a measurement result acquired by the optical sensor with a preset reference value, in which the slits are arranged at intervals in a range including a scanning effective portion in a scanning range for the scanning light emitted from the optical scanning apparatus in a direction where scanning on the slit plate with the scanning light is performed.
An optical inspection system of the present invention includes: an optical scanning apparatus that includes a light source, and a rotary polygon mirror deflecting and reflecting light emitted from the light source as scanning light toward a slit plate; and the optical inspection apparatus.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
As illustrated in
In conformity with a range where scanning is performed with light emitted from the optical scanning apparatus, there are an effective portion and a non-effective portion of the optical scanning apparatus.
The non-effective portions are areas other than the effective portion. There is, however, a case of causing light to enter a sensor that generates a start signal for writing an image. In this case, the corresponding range may be an effective portion.
Subsequently, a range including the effective portion and the non-effective portions may be called a scanning range. The effective portion in this range may be called a scanning effective portion.
The optical inspection apparatus 1 includes: a photo detector 10 that receives scanning light emitted from the optical scanning apparatus 2 and converts the light into an electric signal; an AD converter 20 that AD converts the electric signal; and an inspection device 30 that inspect a state of the optical system of the optical scanning apparatus 2 based on the AD converted signal. The optical inspection apparatus 1 includes a trigger photo detector 40 for detecting timing of scanning with the scanning light.
The laser light emitted from the optical scanning apparatus 2 is condensed on a surface of an after-mentioned slit plate 11 provided in the photo detector 10, the surface serving as an image plane; the slit plate 11 is scanned with this light, a part of which is caused to pass slits 11s formed on the slit plate 11. Optical sensors 15 provided in the photo detector 10 measure the light quantity of the scanning light having transmitted through the slits 11s, and output the volume to the AD converter 20.
Meanwhile, the trigger photo detector 40 is arranged upstream of the photo detector 10 in the scanning direction, one electric signal (trigger pulse) is emitted on each scan every time the rotary polygon mirror 52 rotates, and the signal is transmitted to the AD converter 20. The AD converter 20 AD converts the electric signal acquired by the photo detector 10 and sequentially outputs the signal to the inspection device 30 in a time-series manner, according to the trigger pulse emitted from the trigger photo detector 40 as a reference for measurement timing, for each scan with the laser light emitted from the optical scanning apparatus 2.
The inspection device 30 includes, for instance, a computer, and calculates the light quantity having transmitted through the slits 11s based on the electric signal, which is a measurement result acquired by the photo detector 10. The computer configuring the inspection device 30 includes, for instance, a CPU, a ROM that stores a program for calculating the light quantity having transmitted through the slits 11s based on the electric signal from the photo detector 10, a RAM that temporarily stores various pieces of data, and an input and output interface circuit.
The inspection device 30 adds signals acquired from the multiple optical sensors 15 via the AD converter 20, and calculates the maximum value of the light quantity, having transmitted through the slits 11s, at this point in time. As described later, the inspection device 30 determines presence or absence of dust in the optical system of the optical scanning apparatus 2 using variation in the maximum value of the transmitted light quantity.
The photo detector 10, which characterizes this embodiment, is hereinafter described in detail.
As illustrated in
The pitch P of arrangement of the slits 11s, and the aperture width (slit width) W of the slit 11s will be described later.
Here, the slit plate 11 is made of a metal plate, and the slits 11s are light transmitting apertures formed on the slit plate 11. Alternatively, for instance, the incident surface of an after-mentioned diffuser 12 may be masked with coating, and slits may be formed on respective parts of the surface by patterning.
The scanning light having passed through the slit 11s enters the diffuser 12 provided in contact with the back of the slit plate 11, and is diffused while passing through the diffuser 12. The diffuser 12 has a shape substantially identical to the shape of the slit plate 11, and made of opal glass here.
The scanning light diffused by the diffuser 12 enters the light guide 13 provided on the back of the diffuser 12, and is guided by the light guide 13 to end faces 13c. In this embodiment, the light guide 13 is made of an acrylic rod, which is a colorless transparent light transmitting member, and is arranged at the rearward of the diffuser 12 such that the longitudinal direction coincides with the scanning direction. The front side face of the light guide 13 is formed as a planar incident surface 13a. The diffuser 12 is arranged in contact with the incident surface 13a. Accordingly, the scanning light, having been diffused by and passed through the diffuser 12, enters the light guide 13 from the incident surface 13a.
The rear face of the light guide 13, that is, the surface opposite to the incident surface 13a, is formed as a planer reflection surface 13b. The diffusion film 14 is provided on the reflection surface 13b. The reflection surface 13b is a rough surface. The reflection surface 13b is coated with a white reflective material, thereby forming the diffusion film 14. Here, the diffusion film 14 is thus formed by finishing the reflection surface 13b of the light guide 13 as a rough surface and coating the film with the reflective material. The configuration is not limited thereto. Alternatively, for instance, the reflection surface 13b may be formed as a flat surface and coated with a reflective material, or a diffusive reflection member may be provided so as to be in contact.
The scanning light entering the light guide 13 from the incident surface 13a is diffused and totally reflected by the diffuser 12 and the diffusion film 14, and reaches the end faces 13c of the light guide 13.
Optical sensors 15 that measure the light quantity of the scanning light guided by the light guide 13 are provided at the respective end faces 13c of the light guide 13. For instance, any of photosensors, such as photodiodes and photomultiplier tubes, and known or new appropriate sensors may be adopted as the optical sensors 15. Electric signals acquired by the two optical sensors are input into the inspection device 30 via the AD converter 20, added to each other by the inspection device 30, and the light quantity having passed through the slits 11s are calculated.
Next, setting of the pitch P of the arrangement of the slits 11s and the slit width W is described.
First, if dust is in the optical system of the optical scanning apparatus 2, abnormality occurs in reflection and refraction, and the shape of the beam spot S is changed. As a result, even if the beam total energy does not vary and the light quantity of the entire spot light does not change, variation in spot diameter D in turn changes the light quantity having transmitted through the slits 11s or the maximum value of the transmitted light quantity. To inspect variation in the light quantity having transmitted through the slits 11s or the maximum value of the transmitted light quantity, it is required to appropriately set resolution and sensitivity for variation in light quantity. It is thus desired to appropriately set the pitch P and the slit width W.
The resolution here is an indicator corresponding to an inspectable position interval in the scanning direction. If the resolution is high, the position of dust can be highly accurately detected. The sensitivity here is an indicator corresponding to variation (in the spot diameter and the maximum light quantity at a center portion) of the beam spot S generated at dust. If the sensitivity is high, variation in the spot diameter D is sensitively reflected, thereby allowing smaller dust to be detected.
As to the resolution, the smaller the pitch P of arrangement of the slits 11s is, the higher the resolution of the scanning direction is. To inspect variation in the light quantity having passed through the slits 11s to locate the position of dust, a high resolution in the scanning direction is preferred. However, if the resolution is too high above what is required, processes of fabricating the slit plate 11 and inspection are complicated. An appropriate pitch P is set in conformity with a required resolution. For instance, in the case where the spot diameter D of the beam spot S is set to about 0.1 mm for detecting dust of about 25 μm in the optical system of the optical scanning apparatus 2, the pitch P is preferred to be set to 0.1 mm equivalent to the spot diameter D.
In this embodiment, the slits 11s are arranged at intervals in the direction where the slit plate 11 is scanned with the scanning light, in each pitch (prescribed unit for inspection) P equivalent to the spot diameter D. This arrangement achieves a resolution supporting the size of dust detectable by the spot diameter D.
Next, setting of the sensitivity is described.
In the graphs of the spot light quantity in
In the examples illustrated in
In the graphs of transmitted light quantity in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
0.3<W/D<0.7
(P: pitch of slit; W: slit width; D: spot diameter)
In the case where
W/D=0.5,
the sensitivity becomes the maximum.
Next,
As illustrated in
As illustrated in
As illustrated in
Next,
Accordingly, as illustrated in
0.3<W/P<0.7
(P: pitch of slit; W: slit width; D: spot diameter),
the sensitivity is significantly high. In particular, when
W/P=0.5,
the sensitivity is the maximum.
Thus, as illustrated in
The spot diameter D of the beam spot S formed by the optical scanning apparatus 2 is not even across the entire range in the scanning direction on the slit plate 11 but is different on each scanning position. Accordingly, the slit width W of the slit 11s can be different in conformity with each scanning position. For instance, in the case where the spot diameter D around an end of the slit plate 11 is larger than the spot diameter D around the center portion, the slit width W around the end of the slit plate 11 is set wider than the slit width W. Instead, for instance, in the case where the spot diameter D around the end of the slit plate 11 is smaller than the spot diameter D around the center portion, the slit width W around the end of the slit plate 11 is set narrower than the slit width W around the center portion. Thus, setting of the slit width W for each position in conformity with the spot diameter D can maintain the sensitivity constant with respect to variation in the spot diameter D in each scanning position.
Operations of the forgoing optical inspection apparatus 1 inspecting the optical system of the optical scanning apparatus 2 are described.
In the optical scanning apparatus 2, the laser light source 50 emits laser light. The laser light passes through the lens 51 with the beam diameter being adjusted, is condensed on the reflection surface 52a of the rotary polygon mirror 52, deflected and reflected, enters the fθ lens 53, and is condensed on the slit plate 11, thus performing scanning.
In the optical inspection apparatus 1, the laser light emitted from the optical scanning apparatus 2 enters the trigger photo detector 40 one time for each scan. A trigger pulse generated by the trigger photo detector 40 is input into the inspection device 30 via the AD converter 20. Based on time from the trigger pulse and the scanning speed, the slit through which the light has passed among the slits can be identified. Accordingly, the position at which dust exists in the optical system of the scanning direction can be identified.
In the optical inspection apparatus 1, the laser light emitted from the optical scanning apparatus 2, which is the inspection target, is condensed on the surface of the slit plate 11 as the image plane, thereby performing scanning on the slit plate 11; a part of the laser light passes through the slit 11s. The scanning light having passed through the slit 11s enters the diffuser 12 provided in contact with the back of the slit plate 11, diffused while passing through the diffuser 12, and enters the light guide 13 provided on the back of the diffuser 12. The scanning light having entered the light guide 13 is guided to the end faces 13c of the light guide 13 while being diffused and totally reflected by the diffuser 12 and the diffusion film 14, and input into the two optical sensors 15.
Each optical sensor 15 generates an electric signal according to the input light quantity. The signal is input into the inspection device 30 via the AD converter 20. The inspection device 30 adds the signals from the optical sensors 15 to each other, calculates the maximum value of the light quantity, having passed through the slits 11s, at this point in time, and stores the value as temporal data corresponding to laser light scanning. The inspection device 30 compares the maximum value of the light quantity having passed through the slit 11s with a preset prescribed reference value, and determines presence and absence of variation. Based on the result, presence and absence of variation in the spot diameter D of the spot light is inspected. If it is determined that the spot diameter D varies, it is determined that dust is on the optical system of the optical scanning apparatus 2, which is the inspection target, and estimates the position where the dust exists based on the position of the varying beam spot S.
As described above, according to the optical inspection apparatus 1 of this embodiment, the slit 11s are arranged across the entire the slit plate 11 at each prescribed pitch P in a range including the effective portion (scanning effective portion). Accordingly, in one scan with the spot light, the light can be received at multiple positions where the slit 11s are formed. Furthermore, the photo detector 10 is provided in a fixed manner, which negates the need of moving components in the photo detector 10. Accordingly, time required for inspection can be reduced in comparison with the case of moving the photo detection unit with a single slit for each scan and receiving light.
The optical inspection apparatus 1 of this embodiment includes the diffuser 12 between the slit plate 11 and the light guide 13. Accordingly, even in the case where the light incident on any of the slits 11s obliquely enters the slit plate 11, the light beam can be diffused by the diffuser 12 and enter the light guide 13. Accordingly, the volume of the light can be reduced that obliquely enters the slit plate 11, is reflected by the surface of the light guide 13 and cannot enter the light guide 13. The light quantity received by the optical sensor 15 can be increased.
According to the optical inspection apparatus 1 of this embodiment, the diffusion film 14 is provided on the surface of the light guide 13 opposite to the incident surface 13a. The scanning light having entered the light guide 13 is diffused and totally reflected by the diffuser 12 and the diffusion film 14, and reaches the end faces 13c of the light guide 13. Accordingly, the scanning light having entered the light guide 13 can be efficiently guided to the optical sensors 15, and the inspection accuracy can be improved.
According to the optical inspection apparatus 1 of this embodiment, the optical sensors 15 are provided at both the end of the light guide 13. The configuration is not limited thereto. Alternatively, an optical sensor 15 may be provided at only one end of the light guide 13, and a total reflection mirror may be provided at the other end. In this case, the number of optical sensors 15 can be reduced, which facilitates reduction in cost.
In the optical inspection apparatus 1 of this embodiment, the light guide 13 has a rod shape. The configuration is not limited thereto. For instance, as illustrated in
In the optical inspection apparatus 1 of this embodiment, the light guide 13 has a rod shape. The configuration is not limited thereto. For instance, as illustrated in
In the optical inspection apparatus 1 of this embodiment, the light guide 13 is made of a single-piece member. The configuration is not limited thereto. For instance, as illustrated in
In the optical inspection apparatus 1 of this embodiment, the slit plate 81 is in contact with the diffuser 82. The configuration is not limited thereto. For instance, as illustrated in
Next, an optical inspection system 100 according to a second embodiment of the present invention is described with reference to
The optical inspection system 100 includes the optical inspection apparatus 1 of the first embodiment, and further includes the laser light source 50, the lens 51, and the rotary polygon mirror 52 included in the optical scanning apparatus 2. An inspection target is an optical component 101, such as an fθ lens, detachably attached between the rotary polygon mirror 52 and the photo detector 10. The optical component 101 can be attached and detached such that laser light from the laser light source 50 can be image-formed on a surface of the slit plate 11.
The optical inspection apparatus 1, the laser light source 50, the lens 51, and the rotary polygon mirror 52 have configurations equivalent to the configurations in the first embodiment. Accordingly, the same symbols are assigned to the equivalent components, and the detailed description thereof is omitted. The relationship between the pitch P of the slits 11s and the slit width W and the spot diameter D is equivalent to the relationship in the first embodiment.
The optical inspection system 100 of this embodiment can inspect the optical component 101, such as the fθ lens, only with this system as a single item. Accordingly, the optical component 101 including dust and stains can be preliminarily prevented from being incorporated into the optical scanning apparatus 2.
Thus, any one or a plurality of components among the laser light source 50, the lens 51, the rotary polygon mirror 52, and the optical component 101, such as the fθ lens, which are configurational elements of the scanning optical system 2, can be detachably provided in the first embodiment. Accordingly, each detachable configurational component as a single item can be inspected.
Furthermore, through use of the above-mentioned optical inspection apparatus, an optical scanning apparatus can be manufactured.
First, the above-mentioned optical inspection apparatus and the optical scanning apparatus as an inspection target are prepared. Subsequently, the optical inspection apparatus inspects the optical scanning apparatus, and then adjusts the optical scanning apparatus based on the inspection result, thereby allowing a high quality optical scanning apparatus to be manufactured.
According to the present invention, the multiple slits are provided on the slit plate at intervals in the direction where scanning with scanning light is performed. Therefore, one scan with spot light allows light reception at the multiple positions where slits are formed. Accordingly, time required for inspection can be reduced in comparison with the case where light is received while the photo detection unit having a single slit is moved for each scan with scanning light.
Furthermore, according to the present invention, the diffuser is provided between the slit plate and the light guide. Accordingly, even in the case where light incident on some slits among the slits obliquely enters the slit plate, the oblique incident light can be diffused by the diffuser and enter the light guide. Accordingly, the light quantity of the incident light that obliquely enters the slit plate and is reflected by the surface of the light guide not to enter the light guide can be reduced, and the light quantity received by the optical sensor can be increased. Thus, the inspection accuracy can be improved.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-046250, filed Mar. 8, 2013, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-046250 | Mar 2013 | JP | national |
