JP2010071732A - Method for inspecting object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inspecting an object that can determine that only a resin lens capable of avoiding the occurrence of enlarging of a waist diameter due to surface undulation is good. <P>SOLUTION: This method for inspecting an object is adapted to inspect good or bad in quality of a scanning lens 6 made of a resin having a refraction index of 1.6 or more. In the method, it is determined that only the scanning lens 6 of which the PV value (a maximum height) of a undulation component having the wavelength same as an incident diameter of an optical beam in an optical system in terms of surface undulation by small irregularities on the surface of the scanning lens 6 to be a determination target of quality is equal to or less than "60/(the refraction index-1) [nm]", is made to be good. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inspection method for inspecting the quality of a resin lens made of a resin exhibiting a refractive index of 1.6 or more.

  Conventionally, the resin that has been generally used as the material of the resin lens has a low refractive index, so the thickness of the resin lens is increased or the thickness of the peripheral edge of the resin lens is extremely thin compared to the central portion. There was a problem of causing so-called uneven thickness. When a resin lens with uneven thickness is employed in an optical system of an image forming apparatus as described in Patent Document 1, the convergence position of the light beam to be converged on the image position on the scanning target surface is largely shifted from the image position, It will degrade the quality.

On the other hand, in recent years, development of a high refractive index episulfide resin or thiourethane resin as described in Patent Document 2 has been actively conducted. These high refractive index resins can significantly reduce the thickness of the lens compared to conventional resins, and avoid the occurrence of uneven thickness.
Japanese Patent Application Laid-Open No. 2004-219772 JP 2007-102096 A

  However, a resin lens using these resins (hereinafter referred to as a high refractive index resin lens) has a problem that it is easy to generate a waist diameter increase on the scanning target surface of the light beam. Waist diameter increase is a phenomenon in which the spot diameter of the light beam on the scanning target surface is not reduced and becomes larger than the original diameter.

  Therefore, the present inventors have conducted intensive research on the cause of the increase in waist diameter, and found the following. That is, in the high refractive index resin lens, the surface waviness formed by the minute unevenness on the surface causes the waist diameter to increase. Specifically, with respect to surface waviness, a high refractive index resin lens in which the PV value (maximum height) of the waviness component having the same wavelength as the incident diameter of the light beam falls within a certain range is almost entirely increased in waist diameter. I won't let you. On the other hand, when the PV value of the swell component exceeds a certain threshold value, the waist diameter is significantly increased. And it turned out that a favorable correlation is materialized between the threshold value and the refractive index of resin.

  The present invention has been made in view of the above background, and the object of the present invention is an inspection method that can determine that only a resin lens that can avoid the occurrence of waist diameter increase due to surface waviness is acceptable. Is to provide.

In order to achieve the above object, the invention of claim 1 is directed to an inspection method for inspecting the quality of a resin lens made of a resin exhibiting a refractive index of 1.6 or more. Predetermined threshold value by which the PV value (maximum height) of the swell component having the same wavelength as the incident diameter of the light beam in the optical system is obtained based on the refractive index of the resin. Only resin lenses having a PV value less than or equal to the threshold value are determined to be acceptable.
In the inspection method of claim 1, in the inspection method of claim 1, only a resin lens having the PV value equal to or less than “60 / (refractive index-1) [nm]” as the threshold is determined to be acceptable. It is characterized by doing.

  In these inventions, in the resin lens to be evaluated for quality, the PV value threshold that can distinguish whether or not the waist diameter is increased has a good correlation with the refractive index of the resin as described above. Show. For this reason, it is possible to obtain in advance a threshold value of the PV value that can distinguish whether or not the waist diameter is increased for the resin lens based on the refractive index of the resin of the resin lens. In the present invention, by setting only a resin lens having a PV value lower than the threshold value thus obtained or a resin lens having a PV value equal to or less than that of the threshold value, the waist diameter is increased due to surface waviness. Only resin lenses that can avoid the occurrence of the above can be determined as passing.

First, before describing an embodiment of a quality determination method to which the present invention is applied, an image forming apparatus equipped with a resin lens that is a quality determination target of the quality determination method to which the present invention is applied will be described.
FIG. 1 is a schematic configuration diagram showing an optical system in a first example of the image forming apparatus. The optical system of the image forming apparatus of the first example includes a light source 1, a coupling lens 2, an aperture 3, a cylindrical lens 4, a polygon mirror 5, a scanning lens 6, a bending mirror 7, and a belt-like photoconductor 8 as shown in the figure. , A mirror 9, a lens 10, a light receiving element 11, and the like. The illustrated optical system is of a single beam type that scans the photoreceptor 8 with one light beam. The light beam emitted from the light source 1 which is a semiconductor laser is composed of a divergent light beam, and is coupled to the subsequent optical system by the coupling lens 2. The coupled light beam may be a weak divergent light beam, a weak converging light beam, or a parallel light beam, depending on the optical characteristics of the subsequent optical system. When the light beam transmitted through the coupling lens 2 passes through the opening of the aperture 3, the peripheral portion of the light beam is blocked and shaped, and enters the cylindrical lens 4 which is a line image imaging optical system. The cylindrical lens 4 has a powerless direction in the main scanning direction and a positive power in the sub-scanning direction, and converges an incident light beam in the sub-scanning direction to form a polygon mirror as an optical deflector. 5 is condensed near the deflecting reflection surface.

  The light beam reflected by the deflecting reflecting surface passes through one scanning lens 6 while being deflected at a constant angular velocity as the regular hexahedral polygon mirror 5 rotates at a constant speed. Then, the light path is bent by the bending mirror 7 and is condensed as a light spot on the surface of the photoconductive photosensitive member 8. The light spot is sequentially generated in the main scanning direction with a very short period, whereby the surface of the photoconductor 8 is optically scanned. The light beam is incident on the mirror 9 prior to optical scanning, and is condensed on the light receiving element 11 by the lens 10. Based on the output of the light receiving element 11, the writing start timing of the optical scanning is determined. The optical system shown in the figure is an optical system that condenses a beam deflected by a rotating polygon mirror 5 as a light spot on a surface of a photoconductor 8 by a scanning lens 6. Although the number of scanning lenses 6 is one, it may be two or more.

  The scanning lens 6 is a high-refractive index resin lens made of a high-refractive index resin whose refractive index measured by sodium D line is 1.6 or more. The quality determination method according to the embodiment uses the scanning lens 6 as a determination target.

  FIG. 2 is a schematic configuration diagram illustrating an optical system in a second example of an image forming apparatus equipped with a resin lens that is a quality determination target of the quality determination method according to the embodiment. This optical system employs a multi-beam method in which the belt-shaped photosensitive member 8 is optically scanned with a plurality of light beams emitted simultaneously. The light beams emitted from the four light sources of the light source device 1 are coupled to the subsequent optical system by the common coupling lens 2. The plurality of coupled light beams are formed as a plurality of line images separated in the sub-scanning direction on the deflection reflection surface of the polygon mirror 5 by the common cylindrical lens 4. The four light beams after the deflection are respectively condensed as a plurality of light spots separated in the sub-scanning direction on the surface of the photoconductor 8 by the common scanning lens 6.

  The scanning lens 6 is a high-refractive index resin lens made of a high-refractive index resin whose refractive index measured by sodium D line is 1.6 or more. The quality determination method according to the embodiment uses the scanning lens 6 as a determination target.

  FIG. 3 is a schematic configuration diagram illustrating an optical system in a third example of an image forming apparatus equipped with a resin lens that is a quality determination target of the quality determination method according to the embodiment. This optical system uses a beam combining type light source. The light sources 1-1 and 1-2 are semiconductor lasers, each having a single light emitting source. The light beams emitted from the light sources 1-1 and 1-2 are coupled by the coupling lenses 2-1 and 2-2. The form of each coupled light beam can be a weak divergent light beam, a weak convergent light beam, or a parallel light beam, depending on the optical characteristics of the subsequent optical system. The light beams transmitted through the coupling lenses 2-1 and 2-2 are shaped by the apertures 3-1 and 3-2 and enter the beam combining prism 20. The beam combining prism 20 has a reflecting surface, a polarization separation film, and a half-wave plate. The light beam from the light source 1-2 is reflected by the reflecting surface of the beam combining prism 20 and the polarization separation film, and exits the beam combining prism 20. The beam from the light source 1-1 is rotated 90 degrees on the polarization plane by the half-wave plate, passes through the polarization separation film, and exits from the beam combining prism 20. In this way, the two beams are combined. By adjusting the positional relationship of the light emitting portions of the light sources 1-1 and 1-2 with respect to the optical axes of the coupling lenses 2-1 and 2-2, the two beams that are combined form a minute angle in the sub-scanning direction. .

  The two combined beams are combined with each other in the sub-scanning direction as long line images in the main scanning direction on the deflection reflecting surface of the polygon mirror 5 by the action of the cylindrical lens 4 which is a common line image forming optical system. Separated images are formed. The two beams deflected at a constant angular velocity by the deflecting reflecting surface are transmitted through one scanning lens 6 constituting a scanning optical system, and the optical path is bent by a bending mirror 7 to be on the photosensitive member 8 which is the actual surface to be scanned. Then, the light is condensed as two light spots separated in the sub-scanning direction, and the two scanning lines on the surface to be scanned are simultaneously optically scanned. One of the two beams is condensed on the light receiving element 11 prior to optical scanning. Based on the output of the light receiving element 11, the writing start timing of the two-beam optical scanning is determined. Alternatively, each of the two beams is focused on the light receiving element 11 prior to optical scanning. Based on the output of the light receiving element 11, the writing start timing of the two-beam optical scanning is individually determined.

  The scanning lens 6 is a high-refractive index resin lens made of a high-refractive index resin whose refractive index measured by sodium D line is 1.6 or more. The quality determination method according to the embodiment uses the scanning lens 6 as a determination target.

Next, an embodiment of a quality determination method to which the present invention is applied will be described.
FIG. 4 is a schematic diagram showing an example of an optical system in which a general resin lens made of a general resin whose refractive index measured by sodium D line is less than 1.6 is used as the scanning lens 6. The light source 1 in this optical system emits a light beam having a wavelength of 655 [nm]. The coupling lens 2 realizes coupling by convergence of light with a focal length of 15 [mm]. In the cylindrical lens 4, the focal length in the sub-scanning direction (direction orthogonal to the light beam deflection direction) is 71.9 [mm]. The polygon mirror 5 has a regular hexahedron structure having six reflecting surfaces, and its inscribed circle radius is adjusted to 16 [mm]. The angle formed between the beam incident angle from the light source 1 and the optical axis of the optical system is 60 [°].

The distance X in the optical axis direction at the light passing position of the optical surface (light reflecting surface, light incident surface or light emitting surface of the optical component) in such an optical system (the distance in the optical axis direction from the previous optical surface) ) Can be expressed by the following mathematical formula 1. In this equation, Y indicates the amount of deviation in the main scanning direction between the light passing position of the optical surface of interest and the previous optical surface. R _m represents the paraxial radius of curvature in the main scanning section at the light passage position of the optical surface of interest. A _n (n is a natural number) indicates an n-th order coefficient for Y. K _m represents a conic constant.

In this equation, when a numerical value other than zero is substituted for odd-order constants (A ₁ , A ₃ , A ₅ ...) For Y, the shape of the optical surface becomes asymmetric in the main scanning direction.

In the sub-scan section of the optical surface in the optical system, when the radius of curvature of the optical surface changes according to the position (Y) in the main scanning direction, the curvature radius C _S (Y) at the position (Y) is It is expressed by the mathematical formula of Formula 2. Taking the reciprocal of Cs (Y) calculated by this mathematical formula, the radius of curvature in the sub-scan section at an arbitrary position (Y) can be obtained. In this equation, R _S (0) represents the paraxial radius of curvature on the optical axis in the sub-scan section of the optical surface. B _n (n is a natural number) indicates an n-th order coefficient for Y.

In this equation, when a value other than zero is substituted for odd-order constants (B ₁ , B ₃ , B ₅ ...) For Y, the change in the radius of curvature in the sub-scan section is asymmetric in the main scanning direction. Become. In addition, the surface shape of the high refractive index resin lens that is symmetrical with the quality determination of the quality determination method according to the embodiment is not limited to the surface shape expressed by the mathematical formulas described so far.

The relationship between the optical surface of the optical system shown in FIG. 4 and the optical characteristics is shown in Table 1 below. In Table 1, a deflection reflection point means a light reflection point by the polygon mirror 5. A distance X at the deflection reflection point indicates a relative distance between the light reflection surface of the polygon mirror 5 and the light incident surface of the scanning lens 6 in the optical axis direction. The distance X on the light incident surface of the scanning lens 6 indicates the distance between the most protruding portion on the light incident surface of the scanning lens 6 and the most protruding portion on the light exit surface, which corresponds to the thickness of the scanning lens 6. To do. A distance X on the light exit surface of the scanning lens 6 indicates a relative distance between the light exit surface of the scanning lens 6 and the scanning surface optical axis direction. Further, n represents the refractive index (measured by sodium D line) of a resin material of a general resin lens functioning as the scanning lens 6. In this example, poly allephin resin is used as the resin material.

  5 shows the beam spot diameter in the main scanning direction on the scanning surface (photosensitive member surface) of the optical system shown in FIG. 4, the focal position deviation amount (Defocus), and the scanning direction of the photosensitive member 8 in the main scanning direction. It is a graph which shows the relationship with a beam arrival point. Legends (110, 30, 0, −30, −60, −110) of this graph indicate beam arrival points in the main scanning direction on the scanning surface of the photoconductor 8. This indicates that the beam arrival point “0” is due to the beam that has passed through the central position of the scanning lens 6 in the main scanning direction.

  6 shows the beam spot diameter in the sub-scanning direction on the scanning plane, the focal position deviation amount (Defocus) on the scanning plane in the optical system shown in FIG. It is a graph which shows the relationship. The legend of this graph is the same as in FIG.

  If the focal position shifts in the optical axis direction due to an attachment position error of the scanning lens 6 or a processing shape error of the cylindrical lens 4, the beam spot diameter on the scanning surface changes as shown in FIGS. Such a change in the beam spot diameter also occurs due to a change in the focal length of the lens accompanying a change in temperature. However, changes in the beam spot diameter due to defocus due to lens mounting position errors or machining shape errors can be corrected by adjusting the position of the lens or optical component. Further, the change in the focal length of the lens due to the temperature change can be suppressed by taking measures such as attaching a diffractive lens whose focal length change pattern is opposite to that of a normal refractive lens.

  The inventors of the present invention have found through experiments that the beam spot diameter on the scanning surface is changed as well as the “beam waist diameter increase” caused by the surface waviness of the scanning lens 6 in addition to the above-described factors. It was. When the PV value (maximum height) of the waviness component having the same wavelength as the incident diameter of the light beam on the scanning lens 6 among the surface waviness of the scanning lens 6 is increased to some extent, the diameter of the light beam on the scanning surface becomes remarkable. A thickening phenomenon occurs. In a high refractive index resin lens in which the PV value of the swell component having the same wavelength as the incident diameter of the light beam is less than a certain threshold value, the beam waist diameter is hardly increased. It has been found by experiments by the present inventors that the diameter increases significantly. This is probably because when the PV value of the undulation component having the same wavelength as the incident diameter of the light beam exceeds a certain threshold value, the undulation component acts like a microlens and increases the wavefront aberration. The beam waist diameter thickening caused by the surface waviness cannot be corrected by adjusting the position of the optical component, which is a big problem in realizing a small beam spot diameter.

  For the optical system of FIG. 4 employing a general resin lens as the scanning lens 6, the PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens 6 and the sub-scanning on the scanning surface (photoreceptor surface). The result of examining the relationship with the beam spot diameter in the direction is shown in FIG. As shown in the drawing, in a general resin lens, when the PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens 6 is 160 [nm] or less, the beam waist diameter is increased. Absent. On the other hand, if the PV value exceeds 160 [nm], a significant increase in beam waist diameter will occur. However, resin lenses are generally manufactured by injection molding, and the conventional injection molding technique produces a poor lens whose PV value exceeds 160 [nm]. It was rare. For this reason, the beam waist diameter increase resulting from the PV value was hardly generated.

  The beam incident diameter with respect to the scanning lens 6 in the optical system shown in FIG. 4 is 2 [mm]. The PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens 6 is measured as follows. That is, the surface shape within the range of the beam incident diameter is measured with a stylus type three-dimensional shape measuring machine, and the measurement data is approximated by an arc so as to be the smallest in RMS (square sum of squares), and approximated from the measurement data. The difference between the maximum value and the minimum value obtained by fitting a component obtained by subtracting the arc component with a sixth-order polynomial is obtained.

  FIG. 8 is a schematic diagram showing an example of an optical system that employs a high-refractive resin lens made of a high-refractive resin whose refractive index measured by sodium D-line is 1.6 or more as the scanning lens 6. The light source 1 in this optical system emits a light beam having a wavelength of 655 [nm]. The coupling lens 2 realizes coupling by light divergence at a focal length of 15 [mm]. In the cylindrical lens 4, the focal length in the sub-scanning direction (direction orthogonal to the light beam deflection direction) is 71.9 [mm]. The polygon mirror 5 has a regular hexahedron structure having six reflecting surfaces, and its inscribed circle radius is adjusted to 16 [mm]. The angle formed between the beam incident angle from the light source 1 and the optical axis of the optical system is 60 [°].

The relationship between the optical surface of the optical system shown in FIG. 8 and the optical characteristics is shown in Table 2 below. As shown in Table 2, in the optical system of FIG. 8, a high refractive resin lens made of a high refractive index resin that exhibits a high refractive index of 2.0 is employed as the scanning lens 6. As the high refractive index resin, a hybrid polymer in which high refractive particles such as titanium oxide are homogeneously dispersed in a polyolefin resin and subjected to a crosslinking reaction is employed.

  FIG. 9 shows the beam spot diameter in the main scanning direction on the scanning plane of the optical system shown in FIG. 8, the focal position shift amount (Defocus), and the beam arrival point in the main scanning direction on the scanning plane of the photoconductor 8. It is a graph which shows a relationship. FIG. 10 shows the beam spot diameter in the main scanning direction on the scanning plane of the optical system shown in FIG. 8, the focal position shift amount (Defocus), and the beam arrival point in the sub-scanning direction on the scanning plane of the photoconductor 8. It is a graph which shows the relationship. As shown in these figures, when a high refractive index resin lens is used as the scanning lens 6, as in the case of using a general resin lens, the lens assembly position error, the machining shape error, the temperature The beam spot diameter changes due to a change or the like. However, the change can be eliminated by adjusting the position of the optical component or attaching a diffraction lens.

  For the optical system of FIG. 8 employing a high refractive index resin lens as the scanning lens 6, the PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens 6 and the sub-scanning on the scanning surface (photoconductor surface). The result of investigating the relationship with the beam spot diameter in the direction is shown in FIG. As shown in the figure, even in the case of a high refractive index resin lens, as in the case of a general resin lens, when the PV value is below a certain threshold value, the beam waist diameter does not increase. Fatness will occur remarkably. The threshold is found to be 60 [nm] from the graph shown. Since the beam incident diameter with respect to the scanning lens 6 is 2 [mm] as in the optical system of FIG. 4, is a general resin having a normal refractive index of less than 1.6 used as the resin material? Depending on whether a high refractive index resin exhibiting a high refractive index of 6 or more is used, the threshold value is different by a factor of two or more.

  The numerical value of 60 [nm], which is the threshold value of the PV value in the high refractive resin lens used in the optical system of FIG. 8, is a value that is relatively difficult to realize by the injection molding method. In particular, the PV value easily exceeds 60 [nm] unless the injection pressure at the time of injection molding is kept constant. Therefore, it is important to manage the PV value in the high refractive resin lens.

Hereinafter, the refractive index of the resin constituting the scanning lens 6 used in the optical system shown in FIG. 4 is indicated by n ′, while the high refractive index resin constituting the scanning lens 6 used in the optical system shown in FIG. Is represented by n. Moreover, while the PV value threshold (160 nm) in the optical system shown in FIG. 4 is indicated by p ′, the PV value threshold (60 nm) in the optical system shown in FIG. 8 is indicated by p. Then, the relationship represented by the following formula 3 is established between the refractive index n and the refractive index n ′.

Further, the relationship represented by the following equation 4 is established between the threshold value p and the threshold value p ′.

From the mathematical formulas 3 and 4, the following formula can be obtained.

When this is expanded for p, the following equation can be obtained.

Substituting n ′ = 1.527 and p ′ = 160 [nm] into this formula yields the following formula.

As for the threshold value p, the safety factor increases as the value is estimated to be smaller (it is less likely that a rejected product is erroneously determined to be acceptable). For safety reasons, the following decimal point of the numerator in Equation 7 is rounded down. A mathematical formula is obtained.

  Therefore, a high refractive index resin lens whose PV value of the surface waviness component having the same wavelength as the beam incident diameter is equal to or less than the threshold value p indicated by this mathematical formula does not cause an increase in beam waist diameter. Therefore, in the quality determination method according to the embodiment, a high refractive index resin lens in which the PV value of the swell component having the same wavelength as the incident diameter of the light beam in the optical system is equal to or less than the threshold value p indicated by this formula is used. While determining with the pass, the high refractive index resin lens exceeding a threshold value is determined with a failure. Thereby, only the resin lens which can avoid generation | occurrence | production of the waist diameter thickening resulting from surface waviness can be determined as a pass.

1 is a schematic configuration diagram illustrating an optical system in a first example of an image forming apparatus equipped with a resin lens that is a quality determination target of a quality determination method according to an embodiment. FIG. 3 is a schematic configuration diagram showing an optical system in a second example of the image forming apparatus. FIG. 5 is a schematic configuration diagram showing an optical system in a third example of the image forming apparatus. The schematic diagram which shows an example of the optical system which employ | adopted the general resin lens which consists of general resin whose measured value of the refractive index by sodium D line is less than 1.6 as a scanning lens. 5 is a graph showing the relationship between the beam spot diameter in the main scanning direction on the scanning plane of the optical system shown in FIG. 4, the focal position shift amount (Defocus), and the beam arrival point in the main scanning direction on the scanning plane of the photosensitive member. 6 is a graph showing the relationship between the beam spot diameter in the sub-scanning direction on the same scanning plane, the focal position shift amount, and the beam arrival point in the main scanning direction on the scanning plane of the photoconductor. For the optical system of FIG. 4 employing a general resin lens, the relationship between the PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens 6 and the beam spot diameter in the sub-scanning direction on the scanning plane is shown. Graph showing. The schematic diagram which shows an example of the optical system which employ | adopted the high refractive resin lens which consists of a high refractive resin whose measured value of the refractive index by a sodium D ray is 1.6 or more as a scanning lens. 9 is a graph showing the relationship between the beam spot diameter in the main scanning direction on the scanning surface of the optical system shown in FIG. 8, the focal position shift amount, and the beam arrival point in the main scanning direction on the scanning surface of the photoconductor. 6 is a graph showing the relationship between the beam spot diameter in the sub-scanning direction on the same scanning plane, the focal position shift amount, and the beam arrival point in the main scanning direction on the scanning plane of the photoconductor. For the optical system of FIG. 8 employing a high refractive index resin lens as the scanning lens, the PV value of the surface waviness component having the same frequency as the beam incident diameter in the scanning lens and the beam spot diameter in the sub-scanning direction on the scanning surface. A graph showing the relationship.

Explanation of symbols

1: Light source 2: Coupling lens 3: Aperture 4: Cylindrical lens 5: Polygon mirror 6: Scanning lens (resin lens)
7: Bending mirror 8: Photoconductor (scanned body)

Claims (2)

In an inspection method for inspecting the pass / fail of the quality of a resin lens made of a resin exhibiting a refractive index of 1.6 or more,
The PV value (maximum height) of the waviness component having the same wavelength as the incident diameter of the light beam in the optical system in the surface waviness due to minute irregularities on the surface of the resin lens subject to quality judgment is the refraction of the resin. An inspection method characterized in that only a resin lens that falls below a predetermined threshold obtained based on a rate, or a resin lens whose PV value is equal to or less than the threshold is determined to be acceptable. The inspection method according to claim 1,
An inspection method, wherein only a resin lens having a PV value equal to or less than “60 / (refractive index-1) [nm]” as the threshold is determined to be acceptable.

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