JPH0626425B2 - Printer manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an optical printer or the like that reproduces a halftone image by a halftone image.

[Conventional technology]

Generally, an optical printer such as a laser printer is based on the mechanism of a conventional analog copying machine. In an analog copying machine, a document image from a document on a platen is directly irradiated onto a photoconductor through a lens system to expose the photoconductor. At this time, since the image of the original document exposes the photoconductor through the slit having a certain width, even if there is uneven rotation of the photoconductor drum, no influence is seen on the print. That is,
The effect of uneven rotation of the photosensitive drum is averaged by the width of the slit, and does not affect the original image.

On the other hand, in an optical printer, even when the same base machine is used, since exposure is performed by a thin line of a writing device (exposure device) such as a laser, an LED, and a liquid crystal shutter, uneven rotation itself appears as an exposure position error. Cheap. In particular, when a halftone image is reproduced using halftone dots, the effect of uneven rotation may appear as a striped pattern on the print. That is, if there is uneven rotation of the photoconductor drum, the density of the halftone dots changes, resulting in a striped pattern on the print.

However, in the optical printers currently on the market, since the dot density of the writing device is low and the degree of halftone expression is low, the effect of uneven rotation cannot be seen, so the problem has not surfaced.
Also, even if the striped pattern appears, it is still commercialized. That is, conventionally, the influence of the rotation unevenness on the image quality has not been clearly understood, and it is merely recognized that the smaller the rotation unevenness is, the better. That is, the relationship between the dot density or the number of halftone lines in the halftone image and the magnitude of the drum rotation fluctuation is not clearly understood.

[Problems to be solved by the invention]

However, at high density recording of, for example, 600 dots / inch or more, since the density of the image is reproduced faithfully, a striped pattern appears remarkably. In order to prevent this striped pattern from appearing, it is necessary to quantitatively grasp how much the rotation unevenness of the photosensitive drum needs to be suppressed. In addition, regarding the quality control of the printer, it is necessary to know the influence of rotation unevenness on the image quality.

The present invention clearly understands the influence of drum rotation unevenness on image quality when reproducing a halftone image with an optical printer having a high writing density, so that a high-density halftone image can be obtained without degrading the image quality. An object of the present invention is to provide a method of manufacturing a printer that can be reproduced.

[Means for solving problems]

In order to achieve the above-mentioned object, the present invention provides a method of manufacturing a printer including an image forming body and a driving source for driving the image forming body, which comprises an image forming body and a driving source for driving the image forming body. The driving source of the experimental system is forcibly given a plurality of disturbances having different amplitudes of a single frequency to cause uneven rotation in the image forming body of the experimental system, and the vibration of the image forming body of the experimental system at that time is generated. The image formation of the manufactured printer is higher than the allowable limit value expressed by the following formula, which is obtained by obtaining the relationship between the spatial frequency and the allowable limit of the size of rotation unevenness in which a striped pattern is recognized on the print. It is characterized in that the spatial frequency and the magnitude of the vibration of the drive source of the printer are adjusted so that the uneven rotation of the body is reduced.

^{y = (0.65x 2 -1.64x + a} ) ÷ (3.06 × 10 -1 -5.17 × 10 -2 x) ...... (3) formula where, x: the spatial frequency of the vibration of the image forming member [cycles / mm] y: Allowable limit value of the size of uneven rotation [% pk-pk] a = -0.0142 × b + 3.79 (80 ≦ b ≦ 180) a = 31.3 × b ^-0.61 (180 <b <300) b: Number of halftone lines [Operation] In the present invention, the spatial frequency of vibration of the image forming body is plotted on the abscissa, and the magnitude of vibration unevenness in which a striped pattern on the print is recognized is plotted on the ordinate, as shown in FIG. Get the tolerance curve. This allowable limit curve is obtained for each halftone number. Curves (a), (b), and (c) in FIG.
It is an allowable limit curve corresponding to images of 0 lines, 140 lines, and 175 lines.

When designing a printer, the size of the vibration
By changing the components or processes of the apparatus so that they are within the allowable limits shown in the figure, it is possible to obtain a printer that satisfies predetermined specifications.

The present invention is particularly useful when applied to a device having a resolution of 600 dots / inch or more and a number of halftone wires of 80 or more.

〔Example〕

Hereinafter, features of the present invention will be specifically described based on embodiments with reference to the drawings.

FIG. 2 is a block diagram of an experimental system for taking basic data of the present invention.

In the figure, reference numeral 1 denotes a photosensitive drum of a laser printer, and the photosensitive drum 1 is directly driven by a highly accurate servo motor 2. Therefore, normally, the photosensitive drum 1
The surface rolls very smoothly. The rotation speed of the servo motor 2 is controlled by the motor driver 3, and the noise superimposing unit 4 adds disturbance of a single frequency of the sine wave to the rotation control signal of the motor driver 3 to forcibly rotate the motor. Generate. The process speed of the printer
If it is 80 mm / sec, the frequency is 10 Hz to 160 Hz (0.125 cycles / mm to 2.0 cycles / mm in MTF),
Change at intervals of about Hz. The size of uneven rotation is pk-pk
(Peak-peak), 1% to 8% in 1% increments.

The characteristics of the servo motor 2 are that there is no specific noise component and that the rotation unevenness is sufficiently smaller than 1% in pk-pk. It must not resonate from 10Hz to just above 160Hz.

The laser optical system 7 uses a He-Ne gas laser and scans with a polygon mirror. A pattern generator 8 capable of forming an arbitrary image pattern is connected to the laser optical system 7.

In the experimental system shown in Fig. 2, the scanning width is 100 mm.
Although it is narrower than the scan width of an ordinary printer, it is wide enough to evaluate image quality. The characteristic of the laser optical system 7 is that the writing density can be changed to approximately 600,700,800,1000,1200,1400 dots / inch, and accordingly, the video clocks of the polygon motor (not shown) and the pattern generator 8 are also adjusted according to the density. It can be changed. The rotation unevenness of the photosensitive drum 1 and its frequency are detected by a rotation detector 5 connected to the photosensitive drum shaft by a flexible coupling, for example, an optical rotary encoder of 5400 pulses / rotation, and the rotation detector 5 It can be known by inputting the frequency signal of the output of 1 to the rotation unevenness measuring device 6 and performing arithmetic processing. As a result, it is possible to check whether the rotation unevenness has occurred according to the given noise.

Next, using this experimental system, a print sample of a halftone image with 90, 133, and 175 lines is output while forcibly generating uneven rotation. The halftone dots are n
The xn matrix method was used. When the frequency and size of the rotation unevenness are changed for each level, it is about 100 with one image quality.
A sample is obtained, and 13 engineers perform a subjective evaluation. Subjective evaluation is divided into 5 levels by a graded evaluation method, and each print sample is ranked. 13
The average of human evaluation values was taken, and the allowable limit of the striped pattern appearing in the print sample was obtained, and they were plotted as shown in FIG. However, the horizontal axis represents the spatial frequency MTF.
This tolerance limit indicates the boundary where the stripe pattern, which is the effect of uneven rotation on the image quality, can be clearly recognized when viewed from the distance to read or look at a text or book, that is, about 30 to 40 cm. is there.

In other words, it is shown that the upper limit of the permissible limit curve shown in FIG. 1 clearly shows a striped pattern on the image quality, and the lower side shows the striped pattern inconspicuous. Expressing this tolerance curve with a mathematical formula, y = (1.02 × 10 ⁻⁴ x ² −2.05 × 10 ⁻² x + a) ÷ (3.06 × 10 ⁻¹ −6.46 × 10 ⁻⁴ x) (1) a = − 0.0142 × b + 3.79 (2) However, x is the vibration frequency (Hz) y is the size of uneven rotation (% pk-pk) b is the number of halftone dots (80 ≦ b ≦ 180). First, the number of halftone lines b to be reproduced is input to the equation (2) to obtain the value of a, and the value is substituted into the equation (1). Then, in Expression (1), when the vibration frequency expected to occur is substituted for x, the magnitude y of the rotation unevenness at that time is calculated. Then, in an actual printer, by making the magnitude of the rotation unevenness smaller than the calculated value of y, it is possible to obtain a high-quality print sample with no noticeable stripe pattern. The smaller the rotation unevenness of the photosensitive drum 1 of the printer, the better. However, in order to realize it, an expensive and large precision motor and precision transmission device are required, and the cost becomes unnecessarily high depending on the type of image quality. . Here, in the present invention, the above formula
By (1) and (2), it is possible to clarify the magnitude of the rotation unevenness to be suppressed from the vibration frequency, and it is not necessary to use unnecessary expensive parts.

The above formula (1) is a formula that holds when the process speed is 80 mm / sec, and the MTF when the vibration frequency x is 80 Hz is
1.0 cycle / mm. It has been experimentally confirmed that Equation (1) holds even if the process speed is changed and the spatial frequencies are the same. Therefore, in order to have versatility, the vibration frequency x is replaced with the spatial frequency.

Rewrite the x of formula (1) and 80x and y = a ^{(0.65x 2 -1.64x + a) ÷} (3.06 × 10 -1 -5.17 × 10 -2 x) ...... (3). At this time, x indicates the spatial frequency of vibration (cycle / mm), and y indicates the magnitude of rotation unevenness (% pk-pk). The constant term a is a = −0.0142 × b + 3.79 (80 ≦ b ≦ 180) a = 31.3 × b ^−0.61 (180 <b <300), where b is the number of halftone ^dots .

Figure 1 shows this equation (3), which is 90 lines, 140 lines, 17 lines.
The curves corresponding to the image of 5 lines are (a), (b), (c),
It can be seen that the curve and the vertical position of the curve are determined by the spatial frequency x and the halftone frequency b.

As mentioned above, in the area below these curves, the striped pattern is inconspicuous. Therefore, in the case of a 90-line image, it is necessary to suppress the rotation unevenness to about 6% or less, and in the case of a 175-line image, It is understood that it should be suppressed to about 1% or less. The permissible range of these rotation irregularities is not fixed for each number of halftone lines, and the permissible range expands as the spatial frequency x deviates from 1 cycle / mm. Therefore, by changing the vibration frequency or the process speed, it is possible to make the striped pattern inconspicuous without changing other conditions.

In the present embodiment, a laser printer has been described as an example, but the present invention is not limited to this, and the present invention can be applied to a printer using another light source such as a laser, an LED, or a liquid crystal shutter. The image forming body can be applied to, for example, a belt-shaped photoconductor other than the drum type, and can also be applied to a printer having a writing device other than the optical printer.

As described above, using this experimental system, forcibly adding rotation unevenness from the outside to take print samples, subjectively evaluating them and graphing the results, the vibration frequency and rotation when reproducing a halftone image The relationship between the allowable level of unevenness and size was clarified.

An example of a procedure when the printer manufacturing method of the present invention is applied to actual product manufacturing will be described.

First, the permissible limit value of the vibration of the image forming body with respect to the image quality is obtained in advance from Expression (1) or Expression (3).

Next, the magnitude of the vibration for each frequency of the image forming body of the device to be adjusted is measured to detect the frequency of the maximum vibration.

Next, a vibration source having a natural frequency matching the detected frequency is identified. A motor, a gear or the like can be considered as the vibration source.

Finally, the frequency and / or the magnitude of the vibration of the vibration source is adjusted so that the vibration of the specified vibration source becomes equal to or less than the allowable limit value. Specifically, the vibration source itself is replaced, or vibration damping means is provided.

By the above-described work, it is possible to manufacture a printer that outputs a print in which a striped pattern is not noticeable.

(Experimental Example 1) A semiconductor laser printer was prototyped by modifying a dry copying machine (FX4700 manufactured by Fuji Xerox Co., Ltd.). Process speed is 80 mm / sec, 600 dots / second for both main and sub scanning
A laser optical system with an inch dot density and a beam diameter of 67 μm (1 / e ² ) was installed. The fluctuation in the rotation of the photoconductor due to the photoconductor drive system used in the copying machine of FX4700 is 20 in pk-pk.
The spatial frequency giving the maximum amplitude was 0.5 cycle / mm by Fourier analysis. This was obviously larger than the size of the rotation unevenness defined by the first equation.

When a halftone halftone dot image of 100 lines and 36 gradations was output by this laser printer, a striped pattern corresponding to the spatial frequency having the maximum amplitude appeared on the entire surface of the print, and the print quality was remarkably impaired. When the drive system of this laser printer was changed to direct drive with a DC servo motor (R720T made by Sanyo Denki Co., Ltd.), the rotation fluctuation of the photoconductor was 4 in pk-pk.
%, The spatial frequency giving the maximum amplitude was 0.15 cycles / mm. In addition, it was smaller than the size of the rotation unevenness defined by the equation (1) including other spatial frequencies. When a halftone dot image with 100 lines and 36 gradations was output by a laser printer with this drive system changed, a high quality image with no recognizable stripe pattern was obtained.

(Experimental Example 2) A semiconductor laser printer with 800 dots / inch for both main scanning and scanning was prototyped. The drive system for the photoconductor was the same as in Experiment Example 1, and a direct drive was used with a DC servo motor (R720T manufactured by Sanyo Denki). The dot-matrix method was used to output halftone images of 133 lines and 36 tones and 100 lines and 64 tones, and high-quality prints with no recognizable striped pattern were obtained.

(Experimental Example 3) A halftone image is output using each of the laser printers of Experimental Examples 1 and 2 by using a sub-matrix method for increasing the apparent gradation or the number of halftone lines, unlike the normal dot matrix method. .

In experiment example 1, 100 lines 72 gradations and 140 lines 36 gradations, in experiment example 2
I output a halftone image with 133 lines and 72 gradations, but the rotation fluctuation of the photoconductor that is directly driven by the DC servo motor (Sanyo Denki R720T) is smaller than the value defined by equation (1). A high quality image was obtained with no visible stripes on top.

(Experimental Example 4) A laser printer with 1400 dots / inch for both main scanning and sub-scanning was prototyped. The driving of the photoconductor was the same as in Experimental Example 1, and a dot matrix method was used to output a halftone dot image of 175 lines and 64 gradations. In this halftone image, the motor (Sanyo Denki R720
When the spatial frequency 0.15 cycles / mm of rotation unevenness of (T) is applied to the equation (1), the size of the rotation unevenness is 3.5% pk-pk, but the actual rotation unevenness of the motor is 4% pk-pk. As a result, some stripes were recognized on the entire print. Therefore, we changed the DC servo motor to the more accurate Sanyo Denki CN-400T.
At this time, the rotation unevenness of the photosensitive drum is 1% pk-pk, and the spatial frequency that gives the maximum amplitude is 0 when Fourier analysis is performed.
It is smaller than the size of the rotation unevenness defined by the formula (1) at 15 cycles / mm. This DC servo motor (CN-400 manufactured by Sanyo Denki)
A printer using T) output 64 gradations of 175 lines and 49 gradations of 200 lines, but both of them produced high-quality images with no visible stripe pattern.

〔The invention's effect〕

As described above, in the present invention, the influence of rotation unevenness on the image quality is grasped by the relationship between the spatial frequency of the vibration of the photoconductor and the rotation unevenness, and the allowable limit curve showing the limit at which the striped pattern is identified is defined by each mesh. For each number of lines, a subjective evaluation is made quantitatively in advance. Based on this allowable limit curve, by changing each component and process of the printer so that the uneven rotation is within the allowable range, it is possible to obtain a high-quality print with no visible stripes as the output of the printer. You can

That is, since it becomes possible to quantitatively grasp the relationship between the rotation unevenness and the image quality, which has been conventionally only empirically recognized, it is possible to stably maintain the quality of the product at a high level. In addition, quality control can be performed accurately, which is effective in production control. The present invention is particularly useful when applied to a device having a resolution of 600 dots / inch or more and a number of halftone wires of 80 or more.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the spatial frequency and the rotation unevenness level at which a striped pattern is recognized in each halftone image, and FIG. 2 is data showing the relationship between the frequency of the photosensitive member and the rotation unevenness. FIG. 3 is a schematic diagram of an experimental system used for manufacturing. 1: Photosensitive drum 2: Servo motor 3: Motor driver 4: Noise superimposing device 5: Rotation detector 6, Rotation unevenness measuring device 7: Laser optical system, 8: Pattern generator

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Koji Miyagi 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Business Office (72) Inventor Fumihiko Shibata 2274 Hongo, Ebina City, Kanagawa Fuji Xerox Co., Ltd.Ebina Business In-house

Claims (1)

[Claims] 1. A method of manufacturing a printer including an image forming body and a drive source for driving the image forming body, comprising: a driving source for an experimental system including the image forming body and the driving source for driving the image forming body. In addition, a plurality of disturbances having different amplitudes of a single frequency are forcibly applied to cause uneven rotation of the image forming body of the experimental system, and the spatial frequency of vibration of the image forming body of the experimental system at that time and the print are The rotation unevenness of the image forming body of the manufactured printer is smaller than the allowable limit value represented by the following formula, which is obtained by obtaining the relationship of the allowable limit of the size of the rotation unevenness where the stripe pattern is recognized. A method of manufacturing a printer, wherein the spatial frequency and magnitude of vibration of the drive source of the printer are adjusted so that ^{y = (0.65x 2 -1.64x + a} ) ÷ (3.06 × 10 -1 -5.17 × 10 -2 x) where, x: the spatial frequency of the vibration of the image forming member [cycles / mm] y: the rotational irregularity size of Allowable limit value [% pk-pk] a = -0.0142 x b + 3.79 (80 ≤ b ≤ 180) a = 31.3 x b ^-0.61 (180 <b <300) b: Number of ^screen lines