JPH06204565A - Inspection of lens array - Google Patents

Abstract

PURPOSE:To check a lens array of a LED head easily by measuring an amount of light which, being emitted from a source of light, passes through the lens array and forms an image and a beam diameter of the light and by determining that the lens array has a trouble when an amount of light is normal but the beam diameter is abnormal. CONSTITUTION:An amount of light from a LED of a LED head 2 is measured in dots, using a CCD element, a photo multiplier, and a photo transistor. Then, using a TV camera 10, a CCD camera, or other camera, a beam diameter of the image-forming light is measured. If a part of dots of light have abnormal beam diameters but there is no trouble in the emission output at their positions, a variation in the focusing performance which is caused by the ununiformity of a refractive index of a lens array 4 is adjusted. If most bits of light have expanded beam diameters, the lens array 4 is replaced with another one which has the correct focusing performance or a distance between the lens array 4 and a LED array 6 is readjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to inspection of lens arrays used in LED print heads, contact image sensors, liquid crystal shutter array heads and the like.

[0002]

2. Description of the Related Art A lens array is a main part of an LED head, a liquid crystal shutter array head, a PLZT optical head, a contact type image sensor, or the like. However, there have been almost no studies on abnormalities in the lens array. A related prior art is shown in Japanese Patent Application Laid-Open No. 62-282957.
The Japanese Patent Laid-Open Publication proposes that the intensity distribution of the light imaged through the lens array is obtained, and the intensity distribution of the light is obtained by integrating over the range above the slice level. The purpose here is
The purpose is to control the light emission time of light emitting elements such as LEDs so that the total amount of light that contributes to exposure is constant. Then, in order to determine the light emission time, the light intensities in the range above the slice level are integrated, and the light emission time is determined based on this. Further, Japanese Patent Laid-Open No. 2-52762 proposes to adjust the focus of the head while adjusting the focus of the LED head while observing an image formed by a CCD camera or the like. However, this publication does not relate to inspection of lens arrays. Similarly, Japanese Utility Model Laid-Open No. 4-81034 proposes to monitor the image from the LED head with a television camera and adjust the focus.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to propose a new lens array inspection method.

[0004]

According to the present invention, the amount of light and the beam diameter of the light imaged from the light source through the lens array is measured, and the abnormality in the lens array is detected because the light amount is normal and the beam diameter is abnormal. However, if there is an abnormality in the lens array only at some positions of the lens array, correct the optical system including the lens array at that position, and if there is an abnormality in the lens array at most positions of the lens array, Is characterized in that it is so modified as to be completely corrected.

Further, according to the present invention, at least one of the light source and the light receiving system is moved with respect to the lens array to be inspected, and when the beam diameter of the light to the light receiving system is increased by a predetermined ratio or more, the lens is moved. The feature is that an abnormality of the array is detected.

Further, the present invention is characterized in that the intensity distribution of the light imaged from the light source through the lens array is obtained, and the abnormality of the lens array is detected from the width of the tail portion of the intensity distribution. .

The lens array inspection method according to the present invention is
In addition to the inspection of the lens array of the LED head shown in the embodiment, it can be used for the inspection of the lens array such as the liquid crystal shutter array head and the contact type image sensor.

[0008]

There are basically the following four abnormalities in the lens array. (1) Abnormal mounting position of the lens array with respect to the light emitting element or light receiving element, (2) Variation in focus performance due to uneven refractive index of the lens array, (3) Light inside the lens array Spread of the hem of the beam due to the reflection of
(4) Deterioration of focusing performance due to tilting of the lenses used in the lens array.

Of these, the problem (1) is due to a defective mounting position of the lens array. The characteristic of this case is that the beam diameter of the light from the light source increases abnormally for most of the dots. Further, since the light source itself has no problem, the light amount does not have any problem. Therefore, if an abnormal beam diameter occurs on most of the dots and there is no abnormality in the emission intensity, it is determined that the position of the lens array is defective. In this case, the mounting position of the lens array is changed, or the positions of the light source and the image forming surface are changed so that a one-to-one image forming system can be obtained.

The problem (2) is due to the anomaly of the refractive index,
The feature is that the beam diameter of a specific dot increases abnormally. Also in this case, since the light source has no problem, the light amount itself does not have any abnormality. Therefore, in this case, the focus performance may be adjusted for the problem dot. For example, a transparent resin may be applied to the lens array to shorten or extend the focal length. Also, instead of adjusting the focusing performance by the lens array itself, for example, individual LEs of LED heads are used.
It is also possible to apply a transparent resin to D and make the LED apparently close to the lens array. Similarly in the case of the image sensor, it is also possible to apply a transparent resin or the like to the light receiving element and apparently bring the light receiving element closer to the lens array.

The problem of (3) the reflection of light inside the lens array cannot be dealt with by adjusting the focus performance, and the lens array must be replaced. The lens array is, for example, a rod-shaped lens solidified with black resin or the like. The light that reaches the interface between the lens and the resin should be absorbed by the resin, and no reflected light should be generated, but in reality, part of the light is reflected at the interface between the lens array and the black resin, and the bottom of the beam is reflected. spread.

As a problem similar to this, there is a problem of the tilt of the lens inside the array of (4). In the lens array, a large number of lenses should originally be arranged in parallel, but some of the lenses may tilt. In this case, since the lens array is a compound eye lens, the beam diameter spreads abnormally. Even such a problem cannot be corrected by adjusting the focus performance. Therefore, in order to solve the problems (3) and (4), the lens array is replaced with a lens array having no abnormality.

When light is reflected inside the lens array or when the lens is tilted, the bottom of the light beam is widened. For example, when light is reflected inside the lens array, flare light is generated and the skirt of the beam becomes extremely wide.
Further, when the lens is tilted, since the lens array is a compound eye lens, images are formed at different positions for each lens, and the skirt of the beam spreads. Therefore, if the beam diameter of the imaged light is measured at the skirt, it is possible to detect the abnormality of the lens array.

When light is reflected inside the lens array or the lens is tilted, the beam diameter is significantly increased by slightly shifting the positions of the light source and the light receiving surface. The inventor has confirmed this empirically. Therefore, by detecting the degree of change in the beam diameter when the positions of the light source and the light receiving surface are shifted, it is possible to detect the abnormality of the lens array.

[0015]

EXAMPLE An example will be described by taking a lens array inspection with an LED head as an example. FIG. 1 shows a flowchart of the inspection. In the embodiment, first, the mounting position of the LED array is inspected. LED arrays must be mounted along a straight line and at regular intervals. Observe the light emitters near both ends of the LED array with a TV camera, CCD camera, or the like. L
If the ED array is mounted correctly, the observed illuminants should be aligned and at regular intervals. Then, it is only at the transition of the LED array that the position of the light emitter becomes abnormal. Then, at the turn of the LED array, the distance between the light emitters is measured to detect whether the LED array is mounted at the correct distance. When the longitudinal direction of the array is the x direction, y at the turn of the array
Detect if the light emitters are not displaced along the direction. This inspection is also performed for all LED arrays. In this way, the mounting position of the LED array is first confirmed.

The amount of light emitted from the LED of the LED head is measured dot by dot using a CCD element, a photomultiplier, a phototransistor or the like. The light emission output is measured for each dot, and the light emission output is stored for each dot. When the emission output is measured for all dots, for example, a TV camera or CC
The beam diameter of the imaged light is measured using a D camera or the like. Here, the beam diameter is measured at the planned position of the image plane.

If the beam diameter is abnormal, for example, if the beam diameter fluctuates by ± 20% or more with respect to the planned beam diameter, the process goes to the abnormality inspection subroutine. In this subroutine, it is confirmed whether or not there is an abnormality in the light emission output at the position where an abnormal beam diameter is obtained. Both the beam diameter and the light emission output are abnormal because the LED is abnormal in most cases. When the lens array is abnormal, the light emission output does not change even if the beam diameter changes. The light emission output here means the light emission output detected by the light receiving element via the lens array. If the beam diameter abnormality and the emission output abnormality occur in the same dot, the LED
Replace the array, or apply a transparent resin to the surface of each LED to increase the light extraction efficiency, or conversely, apply a semi-transparent resin to the surface of the LED to cut part of the light. To

The reason why the light emission output is not abnormal and only the beam diameter is abnormal is that the lens array is abnormal.
There are two types of abnormalities in the lens array: defective mounting positions, and defects in the array itself such as reflection of light inside the array and inclination of the lens. When the beam diameter spreads over most of the dots, the mounting position of the lens array is defective. In this case, for example, the lens array is exchanged and replaced with one having a correct focus performance, or the distance between the lens array and the LED array is readjusted, and the distance between the lens array and the photosensitive drum is adjusted to the lens array and the LE.
The mounting position of the LED head is changed so as to match the interval with the D array and obtain a one-to-one imaging system. In this case, for example, the LED head is marked with an ink jet printer or the like at the mounting interval to the photosensitive drum, or
Finely adjust the adjusting screw for attaching the D head to the photosensitive drum so that it can be attached in the correct position.

If an abnormal beam diameter occurs only on some of the dots, and the light emission output is not abnormal at those positions, reflection of light inside the lens array and inclination of the lens,
Alternatively, the refractive index of the lens may be non-uniform. Among these, in the embodiment of FIG. 1, the variation in the focus performance due to the non-uniformity of the refractive index of the lens array is adjusted. When viewed through a material having a high refractive index, objects generally look close. What is important in the lens array is to match the distance between the lens array and the LED array and the distance between the lens array and the photosensitive drum. So L
LED of lens array if ED array is too far
Apply transparent resin or the like to the side. Conversely, when the photosensitive drum is too far, a transparent resin or the like is applied to the side of the lens array on the photosensitive drum. In this way, the deterioration of the focus performance due to the fluctuation of the refractive index is corrected.

In the embodiment shown in FIG. 1, it is difficult to deal with the reflection of light inside the lens array and the inclination of the lens.
For example, even if the beam diameter widens, it is not clear whether this is a problem that can be solved by adjusting the focus performance or a problem that requires replacement of the lens array. Therefore, it is preferable to inspect the lens array according to the flowchart of FIG. 2 before performing the inspection according to the flowchart of FIG.

In the embodiment shown in FIG. 2, the beam diameter is remarkably increased depending on the position of the camera when light is reflected inside the lens array or the lens is tilted. According to the experiments conducted by the inventor, in the case of an LED head, when the position of a normal lens array is changed by about 100 μm, the beam diameter generally increases by about 20%. On the other hand, if the light is reflected inside the lens array or the lens is tilted, the beam diameter increases by about 50 to 100% under the same conditions. Therefore, by monitoring the change of the beam diameter when the position of the camera is shifted from the image plane, it is possible to detect the abnormality of the lens array.

FIG. 3 shows a lens array inspection apparatus.
In the figure, 2 is an LED head, and 4 is its lens array, for example, a self-focusing lens array is used. Reference numeral 6 is an LED array, and 8 is a screw for finely adjusting a mounting position on the photosensitive drum or the like. 10 is a TV camera,
Other than this, a CCD camera, a photomultiplier, a photodiode, a phototransistor or the like can be used. Reference numeral 14 is a light emission output detection unit, and 16 is a beam diameter detection unit, which adjusts the LED output, the focus performance for each dot, or the mounting position of the LED head 2 based on the detection results. In the figure, the adjustment screws 8 and 8 are used to adjust the distance from the photosensitive drum so that a one-to-one imaging system can be obtained.

FIG. 4 shows the relationship between the position of the television camera 10 and the beam diameter. When the television camera 10 is on the image plane, the beam diameter becomes the minimum. If the television camera 10 is displaced from the image plane here, the beam diameter of the normal lens gradually increases. On the other hand, in the case of an abnormal lens, the beam diameter sharply increases. Therefore, whether or not the lens is abnormal is inspected based on the degree of increase in the beam diameter when the television camera 10 is displaced from the image plane. As parameters used for detection, the beam diameter on the image plane is X1, the beam diameter when displaced from the image plane is X2, X2 / X1, X2-X1, or the moving distance of the television camera 10 is δ, X2 / δ or the like is used. These parameters may be parameters that reflect the expansion of the beam diameter due to the displacement of the television camera 10 from the image plane.

FIG. 5 shows problems such as reflection of light inside the lens array 4 and inclination of the lens. Lens array 4
Is a rod-shaped lens 18 fixed with a black resin 20. The light reaching the interface of the rod-shaped lens 18 should be absorbed by the black resin 20 and should not be reflected inside the lens array. However, in reality, a part of the light is reflected at the interface of the rod-shaped lens 18 and is not absorbed, and the beam diameter is expanded. This situation is shown in the center of FIG. When the rod-shaped lens 18 is tilted, as shown on the right side of FIG.
The light from D forms an image at different positions. The lens array 4 is a compound eye lens, and the light from one light emitter is imaged by a large number of rod lenses 18. Therefore, if the lens 18 is tilted, the beam diameter will be abnormally expanded.

The characteristic of the case where the light is reflected inside the lens array 4 and the rod-shaped lens 18 is tilted is that flare occurs in the imaged beam and the skirt of the beam expands.
This situation is shown in FIG. If the lens array 4 has internal reflection of light, inclination of the rod-shaped lens 18, etc., the skirt of the beam of light from the LED spreads out and is detected. For example, as shown in FIG. 6, the detection line A is drawn on the line whose light intensity is ½ of the peak, and the line B is drawn on the line whose intensity is 1 / e ² (about 13.6%). If the beam diameter at which the intensity is ½ of the peak is a, the beam diameter at which the intensity is 1 / e ^{2 of the} peak is b, and b / a or (ba) is used, the lens array 4 becomes abnormal. Can be detected. A flowchart for this purpose is shown in FIG.

FIG. 8 shows the principle of MTF, which is conventionally known as an inspection method for the lens array 4. In this inspection method, the original image shown in the lower part of FIG. 8 is imaged via the lens array 4, and the maximum value of the intensity of the imaged light is Pmax and the minimum value is Pmin. The MTF is defined by the equation (1). MTF = (Pmax−Pmin) / (Pmax + Pmin) × 100 (%) (1) However, the MTF is not very effective for evaluation of a lens array used for an LED head, an image sensor or the like. For example, as shown in FIG. 5, when light is reflected inside the lens array 4 and the rod-shaped lens 18 is tilted, what characteristically indicates this is the spread of the hem of the light beam. . Even if this is evaluated by MTF, the skirt of the beam overlaps the beam of light from the adjacent LED, and MT
Not much is reflected in F.

9 and 10 show the inspection procedure and device for the mounting position of the LED array 6. The LED array 6 must be mounted in a straight line with a constant spacing between the arrays. What is shown in the upper part of FIG. 9 is a normal mounting position, and the interval D between the light emitting bodies 22 at the transition between the arrays is, for example, resolution 3
In the case of 00 DPI, it becomes 84.6 μm. The one shown in the middle of FIG. 6 has a defect in the mounting interval between the arrays,
In this example, D is increasing. Also, the one shown in the lower row is
In this example, the mounting position of the LED array 6 is displaced in the y direction.

Therefore, before mounting the lens array 4, FIG.
It is confirmed whether the mounting position of the LED array 6 is correct by using the above device. In the figure, reference numeral 24 denotes an image processing device, 2
6 is a monitor. The turn of the LED arrays 6 and 6 is observed by the television camera 10 and displayed on the monitor 26 via the image processing device 24. On the monitor 26, for example, a total of 6 dots for each 3 dots are displayed on the upper part of the monitor so that the entire situation can be observed. Further, in the lower part of the monitor, the light-emitting bodies 22 at the turn of the array are displayed dot by dot, and the dots are displayed so as to overlap with the reference pattern indicating the position of the light-emitting body 22 which should be. The actual position of the light emitter 22 is the measurement pattern in FIG. If the mounting of the LED array 6 is correct, the reference pattern and the measurement pattern overlap, and if there is an error, the measurement pattern deviates from the reference pattern. Therefore, due to the deviation from the reference pattern, L
It is checked whether the ED array 6 is mounted correctly.

[0029]

According to the present invention, it is possible to inspect a lens array and provide a high quality image device. Particularly, in the invention of claim 1, when the mounting position of the lens array is defective,
Poor focus performance for each individual lens can be easily detected. According to the second and third aspects of the invention, it is possible to detect a defect in the lens array due to reflection of light inside the lens array, inclination of the rod-shaped lens, or the like.

[Brief description of drawings]

FIG. 1 is a flowchart showing a lens array inspection method according to a first embodiment.

FIG. 2 is a flowchart showing a method of inspecting a lens array according to a second embodiment.

FIG. 3 is a diagram showing a lens array inspection device used in each example.

FIG. 4 is a characteristic diagram showing the principle of abnormality detection of a lens array in the second embodiment.

FIG. 5 is a diagram showing a mechanism of abnormality occurrence in the lens array.

FIG. 6 is a characteristic diagram showing the principle of abnormality detection of the lens array in the third embodiment.

FIG. 7 is a flowchart showing a method for inspecting a lens array according to a third embodiment.

FIG. 8 is a characteristic diagram showing a method for measuring MTF in a conventional example.

FIG. 9 is a diagram showing an arrangement error of an LED array.

FIG. 10 is a diagram showing an LED array placement error detection device used in Examples.

[Explanation of symbols]

 2 LED head 4 Lens array 6 LED array 8 Mounting position adjusting screw 10 TV camera 12 Lead screw 14 Light emission output detection unit 16 Beam diameter detection unit 18 Rod lens 20 Black resin 22 Light emitter 24 Image processing device 26 Monitor

Claims (3)

[Claims] 1. A lens array is detected by measuring a light quantity and a beam diameter of light imaged from a light source through the lens array and detecting the abnormality of the lens array because the light quantity is normal and the beam diameter is abnormal. If there is an abnormality in the lens array at only some positions of the lens array, correct the optical system including the lens array at that position, and if there is an abnormality in the lens array at most positions of the lens array, make the optical system completely. A method for inspecting a lens array, characterized by being modified. 2. Abnormality of the lens array when at least one of the light source and the light receiving system is moved with respect to the lens array to be inspected and the beam diameter of the light to the light receiving system is increased by a predetermined ratio or more due to this movement. A method for inspecting a lens array, which is adapted to detect the. 3. A method of inspecting a lens array, wherein an intensity distribution of light that has passed through a lens array and is imaged from a light source is obtained, and an abnormality of the lens array is detected from a width of a skirt portion of the intensity distribution.