JPH04190131A - Method for measuring mtf - Google Patents

Abstract

PURPOSE:To certainly detect the inferiority of a refractive index distribution type rod-shape lens array (SLA) by measuring the quantity of detected light with respect to predetermined width and operating an MTF value on the basis of the max. and min. quantities of light. CONSTITUTION:At first, a moving mechanism is driven to move an SLA 3 to the position where the lights emitted from rod shape lenses 3a-3d are detected by a CCD sensor 6. Next, a light source 5 is allowed to light to emit light to a slitted test chart 4 and the incident light becomes longitudinal slit like light to be allowed to be incident to the SLA 3. Next, the sensor 6 is moved from the initial position P1 to a position P2 and light is emitted to the sensor 6 from the light source 5 and the quantity of light is detected by the sensor 6. The sensor 6 is moved in the same way and the detection processing of light is repeated up to the final position Pn. By this method, the detection processing of the lights emitted from the lenses 3a-3d over predetermined with L is completed. The detection processing of light is executed with respect to all of the lenses 3a-3c... arranged in the SLA 3 and an MTF value is operated using a predetermined formula.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a gradient index rod-shaped lens array that images light emitted from minute light-emitting elements onto, for example, a photoreceptor. This invention relates to an MTF measurement method.

[Conventional technology]

A gradient index rod lens array (hereinafter referred to as 5LA) is used as a lens to image light emitted from minute light emitting elements such as LED elements or light from a light source via a liquid crystal shutter onto a photoreceptor.
SELFOC lens array (made by Nippon Sheet Glass)) is widely used in printers using array-shaped bends such as LED printers and LCS printers.

This SLA is constructed by arranging a plurality of rod-shaped lenses in an array, and each rod-shaped lens is a minute lens such as a minute light emitting element or the like that can image one or more light beams on a photoreceptor. For this reason, flare occurs on the imaging surface due to improper placement of each rod-shaped lens that makes up this SLA, partial loss of each rod-shaped lens, etc., and it is not possible to form an image with sufficient resolution on the photoreceptor. There is.

Therefore, as a conventional method for measuring the resolving power of the SLA and discovering defects in the SLA, light is irradiated onto the slit-shaped test chart 8 as shown in FIG. By irradiating 5LA9, 5L
The light emitted from A9 is detected by a line sensor 10 such as a CCD, and the resolving power of 5LA9 is measured. Figure 5 (b
The hatched areas 11a, llb, llc, . . . shown in FIG.
A light image when viewed from the direction of arrow C in a) is shown. Therefore, arrow A is the main scanning direction, and arrow opening is the sub-scanning direction. The light amount detection position 10' of the linear sensor 10 is set approximately at the center of the shaded areas (light images) lla, llb, llc, . . . . Therefore, the shaded area (light image) lla, ll
The received light amount characteristics when the linear sensor 10 detects the signals b, llc, . . . are shown in FIG.

Then, from the maximum value 1 mmK and the minimum value 1st of the amount of received light measured by the conventional line sensor IO, the resolving power of the 5LA9 is measured using the calculation formula %, and the quality of the 5LA9 is determined. . The method for measuring the resolution of 5LA9 in this way is MTF (m.

duration transfer function
n) Widely adopted as a measurement method.

[Problems with the Prior Art] However, in the conventional MTF measuring method, the light emitted from the 5LA 9 is detected by the line sensor 10, and therefore only one line of the emitted light is measured and inspected. Therefore, if some of the rod lenses in 5LAQ are defective as shown in FIG. Cannot be detected.

That is, if the light amount detection position 10' of the linear sensor 10 is not set at the position where flares llb' and IIC' occur, the received light amount characteristic will be as shown in FIG.
Unable to detect defects.

Therefore, when printing is performed using a printer using such a defective SLA, printing defects shown in FIGS. 6(a) and 6(b) occur. In other words, in (a) of the same figure, a portion with a light intensity lower than the threshold level S is not detected.
An image printed using LA is shown, and it is shown that a black band image B is generated in the case of reversal development. Furthermore, FIGS. 3A and 3B show that a white band image W is generated when printing is performed using SLA in which a portion with a light amount higher than the threshold level S is not detected. In addition, the above-mentioned black belt image B or white belt image W
is reversed in the case of normal development. Furthermore, the threshold level S is not constant depending on the bias voltage to the developing device, the amount of light from the light source, etc.

[Object of the Invention] In view of the above conventional problems, the present invention makes it possible to reliably detect 5LAO defects by measuring the emitted light of the SLA over a predetermined width and calculating the MTF value. The purpose of this invention is to provide a method for measuring MTF.

[Key points of the invention]

In order to achieve the above object, the present invention arranges a light source, a slit-shaped test chart, a refractive index distribution rod-shaped lens array, and a light amount detection element in this order, and directs the emitted light from the light source to the slit-shaped test chart, refractive index distribution In the MTF measurement method, the MTF of the gradient index bar lens array is measured by irradiating light onto the light quantity detection element through the gradient index bar lens array. The amount of received light is measured for a predetermined width in a direction perpendicular to the optical axis of the emitted light and perpendicular to the arrangement direction of the rod lenses in the gradient index rod lens array, and the maximum amount of light within the predetermined width is determined. The method is characterized in that the MTF value is calculated based on the minimum amount of light.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a perspective view of an apparatus that measures the light amount of SLA by applying the MTF measurement method of one embodiment. In the same figure, 5
LA3 is used, for example, in an LCS printer, and is used to form an image of light emitted from a liquid crystal shank onto a photoreceptor. This 5LA3 has a plurality of rod-shaped lenses 3a arranged in two stages.
, 3b, 3C1..., each rod-shaped lens 3a, 3b
, 3C1 . . . can image light emitted through one or more microshades (not shown) in the liquid crystal shunter onto a photoreceptor. Further, 5LA3 in the figure is configured to be movable in the direction of arrow A by a moving mechanism (not shown).

The slit-shaped test chart 4 uses 5LA3 as slit-shaped light emitted from a light source 5 composed of a halogen lamp or the like.
The slit-shaped test chart 4 has slits 4' formed at predetermined intervals in the vertical direction. The spacing of the slits 4' is approximately 4 to 8 per 1 mm, for example, 5 per 1 mm (
When using a slit-shaped test chart (5 pair lines), 5LA3 will be irradiated with a slit-shaped light having a width of 0.1 m+. However, this is the case where the width ratio of the slits 4' of the slit-shaped test chart 4 to the light-shielding grating 4'' is 1:1.

Although not shown, a filter, a diffuser plate, etc., for example, are provided between the light source 5 and the slit-shaped test chart 4 to eliminate unnecessary wavelengths of light.

On the other hand, the CCD sensor 6 is a line-type light amount detection element, and is configured to be movable in the direction of arrow B by a moving mechanism (not shown). Furthermore, the CCD sensor 6 is provided with a
The CD elements are arranged at a much finer pitch than the slit pitch (for example, 0.2 mm) of the slit-shaped test chart 4 described above, for example, about 10 μm.

A method for measuring the MTF of light emitted through the 5LA3 using the apparatus having the above configuration will be described.

First, the moving mechanism (not shown) is driven to move 5LA3 in the direction of arrow A, and the light emitted from the rod lenses 3a to 3d located at the ends of the rod lenses disposed within 5LAa is transmitted to the CCD sensor. 6 to move to a position where it can receive light.

Next, the position of the CCD sensor 6 is moved in the direction of arrow B by a moving mechanism (not shown) and set to the initial position. For example, this initial position is P shown in FIG. 1(a), and corresponds to the position of the first line of light irradiated onto the CCD sensor 6 via 5LA3. Note that L shown in the same figure indicates a predetermined width in which the amount of light is measured by the MTF measuring method of this embodiment, and L shown in the same figure (a
) is the same as the width L' in FIG. Here, the width L' shown in FIG.
5LA3, which is measured and inspected using the F measurement method, is the maximum width of the liquid crystal shutter of the LCS printer used.

In other words, in the dotted line direction (main scanning direction) shown in (1) in the same figure.
The maximum arrangement width in the sub-scanning direction of the micro shunters a and 7b arranged in two rows is L'. Incidentally, this opening/closing drive of the liquid crystal shutter is performed every line in the main scanning direction shown in the figure.

Next, the light source 5 is turned on and the light emitted from the light source 5 is emitted onto the slit-like test chart 4. Since the slits 4' are formed at predetermined intervals in the slit test chart 4 as described above, the light incident on the slit test chart 4 becomes vertical slit light and enters 5LA3.

Here, when there is a defect in the rod-shaped lens and the emitted light through 5LA3 is in the state indicated by diagonal lines I to ■ shown in FIG. , m'
), and the amount of light received by the CCD sensor 6 is shown in Figure 3 (a
) is the data shown. However, diagonal lines I to ■ shown in FIG. 1(a) are optical images when the output light of 5LA3 is observed from the direction of arrow C' shown in FIG. 2, and arrow A and the opening are the same as in FIG. It is the direction.

Next, the position of the CCD sensor 6 is changed to the above-mentioned initial position P1 (
It moves from the position of the first line) to the position of Pl (the second line) shown in FIG. 1(a). For example, the distance from the Pl position to the Pl position is 10 μm. Then l
Similar to the line, the light emitted from the light source 5 is emitted to the CCD sensor 6 via the slit-shaped test chart 4.5LA3, and
The CD sensor 6 detects the amount of incident light. The measurement data at this time is shown in Fig. 3, etc.).

Similarly, move the CCD sensor 6 in the direction of arrow B by 10 am.
The light reception detection process is repeated in the same manner up to the last position Pn of the n-th line (the detection data shown in FIG. 3(C) is for the n-th line).

In this way, when the light reception detection processing for the predetermined width of the emitted light from the rod lenses 3a to 3d is completed, next 5LA3
is moved in the direction of arrow A to a position where the light passing through the rod lenses 3e to 3h is received by the CCD sensor 6.

At this time, the position of the CCD sensor 6 in the direction of arrow B is also returned to the above-mentioned initial position P+.

Thereafter, the detection processing of the light emitted through the 5LA3 from the 1st line to the nth line is performed in the same manner as described above, and the amount of light detected by the CCD sensor 6 for each line is measured. Thereafter, in the same manner, the above-mentioned light amount detection process is performed on all the rod lenses 3a, 3b, 3c, .
) is used to calculate the measured MTF value, and thereafter processing is performed according to the flowchart shown in FIG. That is, as described above, the calculation process of the MTF value is performed based on the above-mentioned formula (1).
7, the MTF value is calculated as 70%, and the maximum value j eamx is 80 and the minimum value 1 mi+++ is 34.
If so, the MTF value is calculated to be approximately 40 (%) (step 1).

Thereafter, the MTF value calculated as described above is compared with a preset constant value X% (step 2). If the minimum value of the MTF value is equal to or greater than the above-mentioned constant value X%, the measured 5LA3 is determined to be a good product, and if it is equal to or less than X%, it is determined to be a defective product. For example, the constant value X% mentioned above is 45
%, 5LA3 in the above example containing the MTF value of 40% is determined to be a defective product.

As described above, according to this embodiment, it is possible to measure and inspect the light emitted from the rod-shaped lens over the entire predetermined width, which is the same as the maximum width L' of the liquid crystal shutter in which 5LA3 is used, and to determine the reliable MTF value for the practical range of 5LA3. Measurements can be taken.

Although a line type CCD sensor is used as the CCD sensor 6 in the MTF measurement method of this embodiment, a so-called two-dimensional type CCD sensor that covers the entire predetermined area described above may also be used. And this two-dimensional CCD
If the sensor is used, there is no need to move the CCD sensor as in the above embodiment.

Further, in this example, the configuration is such that the 5LA3 is moved in the direction of the arrow A, but a configuration may be adopted in which the light source 5, the slit-shaped test chart 4, and the CCD sensor 6 are movable in the direction of the arrow A while the 5LA3 is fixed.

〔Effect of the invention〕

As described above in detail, according to the present invention, the MTF value can be measured over a predetermined width of the emitted light of a gradient index rod lens array such as SLA, and it is possible to reliably measure the MTF value of the light emitted from a gradient index rod lens array such as SLA. It is possible to detect defects in lens arrays.

[Brief explanation of the drawing]

FIG. 1(a) is a diagram explaining the MTF measurement method of one embodiment, and FIG. 1(b) is a diagram explaining the relationship between the predetermined width of MTF measurement of one embodiment and the maximum width L' of the liquid crystal shutter. Figure 2 is a perspective view of a measuring device for an MTF measuring method according to an embodiment, Figures 3 (a) to (C) are light intensity characteristic diagrams measured by an MTF measuring method according to an embodiment, and Figure 4 is a perspective view of a measuring device for an MTF measuring method according to an embodiment. A flowchart explaining a part of the MTF measurement method of one embodiment, FIGS. 5(a) to (C) are diagrams explaining the conventional MTF measurement method, and FIGS. 6(a) and (b) show the conventional MTF measurement method. FIG. 4 is an explanatory diagram of printing defects when printing is performed using SLA tested by a measurement method. 3...SLA, 4...Sliding test chart, 5...Light source, 6...CCD sensor. Patent applicant Casio Electronics Industries Co., Ltd. Same as above
Casio Computer Co., Ltd. Figure 2 Figure 4 Figure 5 (a) (b)

Claims (3)

[Claims] (1) A light source, a slit-shaped test chart, a gradient-index rod-shaped lens array, and a light amount detection element are arranged in this order, and the light emitted from the light source is passed through the slit-shaped test chart and the gradient-index rod-shaped lens array. In the MTF measurement method of measuring the MTF of the gradient index rod-shaped lens array by irradiating light to a light intensity detection element, the light intensity detection element is aligned with the optical axis of the light emitted through the gradient index rod lens array. The amount of received light is measured for a predetermined width in a direction perpendicular to the arrangement direction of the rod lenses in the gradient index rod lens array, and the MTF value is determined based on the maximum and minimum light amounts within the predetermined width. An MTF measurement method characterized by calculating. (2) The light amount detection element is a line type light amount detection element, and the line type light amount detection element is perpendicular to the optical axis of the light emitted through the refractive index distribution type rod-shaped lens array and is of the refractive index distribution type. The rod-shaped lenses in the rod-shaped lens array are moved by the predetermined width in a direction perpendicular to the arrangement direction, and the light amount is measured each time the rod-shaped lenses are moved by the predetermined amount, and based on the maximum light amount and minimum light amount within the predetermined width. 2. The MTF measuring method according to claim 1, further comprising calculating an MTF value. (3) The M according to claim 1, wherein the predetermined width corresponds to a maximum light output width in the sub-scanning direction of an optical writing head in an apparatus in which the gradient index rod-shaped lens array is used.
TF measurement method.