JP2867840B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image device such as an LED head, a liquid crystal shutter array head, a plasma head, and an image sensor.

[0002]

2. Description of the Related Art An image apparatus combining a light receiving / emitting array and a monocular lens for image formation has been known for a long time (for example, US Pat. Nos. 4,532,526 and 4,532,527).
issue). However, an image device using a monocular lens has not been put to practical use yet. The inventor has studied the problems of an image device using a monocular lens and found the following. 1) The monocular lens which has been conventionally studied is a curved lens, and has a narrow allowable range with respect to temperature fluctuation of the image apparatus. That is, when the temperature fluctuates, the curvature of the lens surface changes, and in the case of a curved lens, the imaging position is determined by the curved shape of the lens surface.
The imaging position fluctuates significantly due to temperature fluctuations. In an image apparatus, heat is generated in the apparatus and heat is generated from surrounding photosensitive drums and the like, and the range of temperature change is wide. For this reason, even a monocular lens which is sufficiently used in a normal application can be used only in a narrow temperature range in an image device, which is impractical. 2) The performance of a curved lens is determined by the shape of the lens surface.
Generally expensive. 3) Image quality is likely to deteriorate at the transition point of the light receiving / emitting array. For example, in an image forming apparatus, white streaks and black streaks are easily generated in a printed image, and in an image reading apparatus, white streaks and black streaks are easily generated in a read image.

[0003]

SUMMARY OF THE INVENTION The object of the present invention is to 1) widen the permissible range of temperature fluctuation of a monocular lens, 2) obtain a homogeneous lens at low cost, and 3) change the light receiving / emitting array at a transition point. An object of the present invention is to prevent deterioration of image quality.

[0004]

According to the present invention, there is provided a light emitting / receiving array,
In an imaging apparatus having a monocular lens array, each lens of the monocular lens array is a distributed refractive index type rod-shaped lens, the refractive index of the lens is n, the refractive index at the central axis of the lens is n0, and the distance from the central axis of the lens is Let r be the radial distance of a and a be a positive constant, and let the refractive index distribution of the lens be: n = n0 (1−ar ² + f (r)), where f (r) is a positive value near the outer periphery of the lens. Has a value,
In almost 0. The correction function elsewhere, at an arbitrary position in the lens, | f (r) | <a ar ^2, characterized in that the the.

[0005]

In the image apparatus according to the present invention, a monocular lens array using a distributed refractive index type rod lens is used. The refractive index distribution of the lens, the refractive index at the center axis of the lens n0, the radial distance from the central axis of the lens r, the a is a positive ^{constant, n = n0 (1-ar} 2 + f (r)) (2) Here f (r) has a positive value in the vicinity of the outer periphery of the lens, almost 0. The correction function elsewhere, at an arbitrary position in the lens, | is <ar ² | f (r) . For comparison, Equation (1) shows the refractive index distribution for the self-focusing lens. n = n0 (1-ar 2 ) (1) without the use of arrays of compound lens such as self-focusing lens array in the present invention, using an array of monocular lens. And if you choose the length of the rod-shaped lens, it becomes an inverted reduced image or an inverted enlarged image, or an erect reduced image or an erect enlarged image,
The image can be changed.

[0006] Bar-shaped distributed index lenses have hardly been studied. For example, a known distributed index lens is a curved lens such as a hemisphere. On the other hand, the advantage of using a distributed refractive index type rod-shaped lens is that the deviation of the imaging position due to a temperature change is small. That is, even if the rod-shaped lens thermally expands due to a temperature change, the internal refractive index distribution itself hardly changes. For this reason, the imaging position is hardly affected by the temperature change. On the other hand, in the case of a curved lens, if the shape of the lens surface changes due to a change in temperature, the image forming position changes significantly. As the material of the rod-shaped distributed index lens, for example, glass or plastic is used. In the case of a plastic lens, when the surrounding humidity increases, the lens swells and the curved surface shape of the lens surface changes, so that the image forming position changes. On the other hand, water vapor hardly enters the inside of the rod-shaped lens, and therefore, even if a plastic lens is used, the influence of humidity is small.

According to the present invention, the refractive index distribution of the rod-shaped lens is slightly modified from the formula (1) for the self-focusing lens so that the refractive index near the outer periphery of the lens becomes slightly larger than the formula (1). . In this case, even if the position of the light emitting surface or the document surface fluctuates from the proper position, or the position of the image forming surface fluctuates from the proper position,
The effect on the imaging performance is reduced. This has the effect of preventing the occurrence of white streaks, black streaks, and the like at the transition between image arrays.

[0008] Light tends to travel through regions of high refractive index. As in the present invention, the refractive index distribution with respect to the self-focusing lens is slightly modified from Expression (1),
When the refractive index near the outer periphery of the lens is increased, light incident near the outer periphery of the lens is attracted to the outer periphery and tends to bend more. On the other hand, for light incident near the center of the lens, changing the refractive index near the outer periphery has almost no effect. The light passing near the outer periphery of the lens is mainly light near the transition between the light receiving and emitting array and the light receiving and emitting array. Such light is bent more in the lens than light from other parts,
As a result, the angle of incidence on the image plane becomes smaller. As the angle of incidence on the image plane decreases, the displacement when the position of the image plane fluctuates decreases. In this manner, the positional shift at the transition between the light receiving / emitting array and the light receiving / emitting array due to the change in the image plane position is reduced, and the generation of white streaks and black streaks is prevented. The same is true for misalignment of the light emitting surface and the original surface. If the refractive index near the outer periphery of the lens is set to be slightly larger than that of the equation (1), the position of the light emitting surface and the original surface may fluctuate. However, the influence on the imaging performance is reduced. This effect is particularly strong for light related to a transition between the light receiving and emitting array and the light receiving and emitting array.

As in the present invention, even if the refractive index distribution of the rod-shaped distributed index lens is slightly modified from the equation (1), if the value of the correction function f (r) is small, the imaging performance is hardly affected. It does not affect. Correction function f of refractive index distribution for equation (1)
(R) is preferably proportional to the cube of the radius r, the fourth power, or the like, or exponentially smaller as it enters the inside of the lens from the outer edge, and the correction function f ( r) has a large value. For any position in the lens,
The absolute value of the correction function f (r) is kept to be smaller than ar ² of the formula (1).

The rod-shaped lens of the present invention can be produced by a usual method of manufacturing a self-focusing lens, and it is not necessary to cut out the lens unlike a curved glass lens. For this reason, homogeneous lenses can be mass-produced at low cost.

[0011]

1 to 4 show an embodiment using an LED head as an example. FIG. 1 shows an optical system. In the figure, reference numeral 2 denotes an LED array, for example, an array 2 having a resolution of 508 DPI is arranged at intervals. Reference numeral 4 denotes a substrate of the LED array 2, for example, a glass substrate is used. Reference numeral 6 denotes an array of monocular lenses, in which a distributed refractive index type rod-shaped lens 8 is fitted in a black resin 10. The distributed refractive index type rod-shaped lens 8 is produced, for example, according to a method of manufacturing a self-focusing lens, and is formed by cutting and starting from a long lens. Unlike the self-focusing lens array, the rod-shaped lens 8 has a large diameter, so that the surface can be easily polished and smoothed. On the other hand, in the case of a self-focusing lens array, since a thin fiber lens is used, it is difficult to smooth the surface, and there is a problem of surface roughness. The rough surface of the lens causes scattering of light, and deteriorates imaging performance. Reference numeral 12 denotes an image forming surface, and the photosensitive drum becomes the image forming surface 12 in practical use.

The distance L between the LED array 2 and the image plane 12 can be as large as, for example, about 20 mm. As in the case of a self-focusing lens array, the distance between the LED array 2, the lens array and the photosensitive drum is extremely small. There is no need to assemble at small intervals. In the embodiment, the rod-shaped monocular lens 8 is a lens capable of obtaining a magnified inverted image with a magnification of 1.692 times, and the LED array 2 of 508 DPI provides an image with a resolution of 300 DPI on the image plane 12. Accordingly, the diameter of the monocular lens 8 becomes, for example, about 3 mm.

For comparison, the optical path when the refractive index distribution for the self-focusing lens is determined according to the equation (1) is shown by a broken line in FIG. On the other hand, in the example, the optical path in the case where the refractive index distribution is n−n0 (1−ar ² + f (r)) (2) is shown by the solid line in FIG. f (r) is a correction function for Expression (1), and may be any function as long as the refractive index near the outer periphery of the rod-shaped lens 8 is slightly larger than that of Expression (1). Further, the correction function f (r) is determined to be substantially zero near the center axis of the rod-shaped lens 8, and the correction function value f
The absolute value of (r) is made smaller than ar ^{2 at} an arbitrary point of the lens 8. In the embodiment, the correction function f
Br ² was used as (r). Where b is a constant, br
² is always smaller than ar ^2. The used refractive index distribution is as shown in Expression (3). n = n0 (1−ar ² + br ³ ) (3)

Light generally tends to select a portion having a high refractive index and try to travel. For this reason, if a distribution in which the refractive index is slightly large near the outer peripheral portion of the monocular lens 8 is used as in Expression (2), light in the lens 8 tries to travel along the outer peripheral portion of the lens, and as a result, the optical path Changes from a broken line in the figure to a solid line. For this reason, the incident angle with respect to the image plane becomes smaller than the case of the broken line in the figure. Further, the emission angle of light with respect to the same image forming position is smaller than that in the case of the broken line in FIG. This means that the LED array 2 and the LE
It has an effect of preventing the generation of white streaks and black streaks at the transition of the D array 2.

FIG. 2 shows a refractive index distribution and an optical path of the rod-shaped monocular lens 8. The broken line in FIG. 2 shows the characteristics of the comparative example according to the expression (1) of the refractive index distribution for the self-focusing lens. The solid line in FIG. 2 shows the characteristics of the embodiment in which the refractive index is slightly increased at the outer peripheral portion of the lens 8 according to the equation (3).
In the case of Expression (1), the refractive index distribution of the lens 8 is a parabolic distribution shown on the left side of FIG. On the other hand, in equation (3), br ³ is used as the correction function f (r).
As shown by the solid line in the figure, the refractive index slightly increases near the outer periphery of the lens 8.

In the case of the refractive index distribution of the equation (1), the optical path in the lens 8 is as shown by a broken line in the figure, and the light travels meandering. Here, for example, when the lens 8 is cut along the cutting plane A in FIG. 2, an inverted image is obtained. Further, when cut at the cutting plane B, an erect image is obtained. When the position of the cutting plane A or the cutting plane B is shifted, an enlarged image or a reduced image is obtained, and the magnification changes.
Here, if correction is made so that the refractive index becomes slightly large near the outer peripheral portion of the lens 8 as in the equations (2) and (3), the light travels as shown by the solid line in the figure. This indicates that light tries to travel by selecting a portion having a high refractive index. And the larger the light bends in the lens, the more the lens 8
The incident angle and the outgoing angle of light in portions other than the above become small, and as a result, the incident angle and the outgoing angle decrease as shown by the solid line in FIG. The above discussion relates to light from both ends of the LED array 2. Light from near the center of the LED array 2 has a small incident angle to the monocular lens 8, and light travels near the central axis of the monocular lens 8. And a correction function f to the refractive index near the outer periphery.
Not affected by (r). Therefore, the correction to the refractive index distribution by the equation (2) acts only on light from near both ends of the LED array 2. In equation (2), if the correction function f (r) is small, that is, | f (r) |
If it is sufficiently smaller than ² , the resolution of the lens 8 is hardly affected.

FIG. 3 shows the influence of the refractive index distribution of the rod-shaped lens 8 on the displacement of the image plane 12. One of the causes of the occurrence of white streaks and black streaks when using a monocular lens is the displacement of the image plane 12. That is, light from the light emitters near both ends of the LED array 2 enters the image plane 12 at a large incident angle. Here, if the position of the imaging plane 12 is shifted by δ,
Suppose that it has shifted to position 12 '. Then, in the comparative example of the refractive index distribution of Expression (1), the position of the dot on the image forming plane is as shown in FIG.
As shown by the broken line in FIG. Equation (2)
In the embodiment of the refractive index distribution, the change in the position of the dot on the image plane 12 'is smaller than the comparative example of the equation (1), as indicated by the solid line in FIG. Assuming that the incident angle on the imaging surface 12 is θ, the change in the dot position due to the displacement of the imaging surface 12 is proportional to tan θ. Therefore, the smaller the incident angle θ is,
Has a small effect when the position is shifted.

The cause of the occurrence of white streaks or black streaks due to the displacement of the image plane 12 will be described. When the position of the image forming plane 12 is shifted, the image forming position from the light emitter near both ends of the LED array 2 changes as shown in FIG. If you use an inverted image here,
Light from left LED array 2 and right LED array 2
The image position is shifted in the opposite direction at the transition between the arrays. Then, when these image forming positions approach each other, black streaks occur. Further, when these image forming positions are separated, white streaks are generated. On the other hand, when the refractive index distribution of the equation (2) is used, the incident angle on the imaging surface 12 is reduced, the change in the dot position due to the displacement of the imaging surface 12 is suppressed, and the white streak and the black streak are reduced. Generation can be prevented.

The second cause of the occurrence of white and black streaks is LED
The position of the array 2 varies with respect to the lens array 6. This mechanism is shown in FIG. Reference numeral 14 in the figure indicates that the position of the LED array 2 has shifted and shifted to the position 2 '. When the angle of incidence on the monocular lens 8 is large,
The incident position of light on the lens 8 greatly changes as shown on the right side of FIG. On the other hand, when the angle of incidence on the monocular lens 8 is small, the position of incidence on the lens 8 changes as shown on the left side of FIG. And here also, the shift of the incident position from the light emitting body 14 to the lens 8 is proportional to tan θ. For this reason, if the incident angle θ to the lens 8 is reduced using the refractive index distribution of the equation (2), the influence on the imaging position can be reduced even if the position of the LED array 2 is shifted. The imaging position of light from the light emitter in the same LED array 2 is
Does not change relatively even if the position is shifted. On the other hand, since the inverted image is used, the image forming position of the light from the adjacent LED array 2 is a transition point between the array 2 and the array 2.
It changes significantly due to misalignment. Therefore, by using the refractive index distribution of Expression (2), the incident angle to the lens 8 is reduced, and the LED
The effect of the displacement of the array 2 is reduced. In this way, the occurrence of white streaks and black streaks due to the displacement of the LED array 2 and the displacement of the image plane is suppressed.

[0020]

According to the first aspect of the present invention, the following effects can be obtained. 1) The allowable range for the temperature fluctuation of the monocular lens is widened, and the fluctuation of the image forming position can be prevented even in an image apparatus having a wide temperature range. 2) A homogeneous lens can be obtained at low cost. 3) It is possible to prevent a decrease in image quality at a transition between light receiving and emitting arrays.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system in an image apparatus according to an embodiment.

FIG. 2 is a characteristic diagram showing a refractive index distribution of a monocular lens and an optical path in the lens in the image apparatus of the embodiment.

FIG. 3 is a characteristic diagram showing an influence of a shift of an imaging plane in the image apparatus according to the embodiment.

FIG. 4 is a characteristic diagram showing an influence of a shift of a light emitting surface in the image device according to the embodiment.

[Explanation of symbols]

 2 LED array 4 Substrate 6 Monocular lens array 8 Bar-shaped monocular lens 10 Black resin 12 Image plane 14 Light emitting body

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G03G 15/04 111 H04N 1/028 Z H01L 33/00 1/036 A H04N 1/028 1/036 (56) References JP JP-A-59-51445 (JP, A) JP-A-4-234701 (JP, A) JP-A-60-140307 (JP, A) JP-A-2-284107 (JP, A) JP-A-1-217476 (JP) JP-A-4-141601 (JP, A) JP-A-4-141602 (JP, A) JP-A-4-251805 (JP, A) JP-A-5-238060 (JP, A) 5-238062 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41J 2/44 B41J 2/45 B41J 2/455 G02B 3/00 G03G 15/04 111 H01L 33/00 H04N 1/028 H04N 1/036

Claims (1)

(57) [Claims] 1. An image apparatus in which a monocular lens array is arranged opposite to a light receiving / emitting array, wherein each lens of the monocular lens array is a distributed refractive index type rod-shaped lens, the refractive index of the lens is n, and the refractive index of the lens is n. the refractive index at the center axis n0, the radial distance from the central axis of the lens r, the a is a positive constant, the refractive index distribution of the ^{lens, n = n0 (1-ar} 2 + f (r)), where the f (r) is almost 0. the correction function elsewhere have a positive value in the vicinity of the outer periphery of the lens, at an arbitrary position in the lens, | f (r) | a <ar ^2, and the An imaging device, characterized in that: