JPS6360464A - Electrostatic imaging machine - Google Patents

Abstract

PURPOSE:To improve the reproducibility of a half tone (photograph) original without deteriorating the reproducibility of a line drawing original, by providing an electrifying condition adjusting means for changing the initial electrification potential of a photosensitive body, an exposing condition adjusting means, and a developing condition adjusting means, so that the respective adjusting conditions can be set by the same switching device. CONSTITUTION:To an electrifier 1 of an electrostatic imaging machine for obtaining an imaged image in process, an electrification quantity adjusting device 15 being an electrifying condition adjusting means is connected, and to an exposing lamp 3, a lamp light quantity adjusting device 16 being an exposing condition adjusting means is connected, and the lamp light quantity adjusting device 16 is adjusted so that, for instance, with respect to the lamp potential, the light quantity of 10-40% drops under a low light quantity condition, comparing with a high light quantity condition, and set so that the exposure light quantity can be switched to two stages of a low light quantity and a high quantity. Also, to a developing device 10, a developing sleeve peripheral velocity adjusting device 17 being a developing condition adjusting means is connected. Each adjusting device is connected to a switching device 18, and the switching device 18 changes and sets simultaneously a copy condition by selecting and depressing a selection mode key of a selecting device 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a technique for improving the gradation reproducibility of a copy image of a halftone (photo) original in an electrostatic printing machine.

[Prior Art] Since the copy density relative to the original density in a conventional electrostatic printing machine (electrophotographic copying machine) is set corresponding to a line drawing original, the copy density reproduction characteristic relative to the original density has a steep slope. It had so-called high gamma characteristics. In addition, the brightness attenuation characteristics of the photoreceptor relative to the amount of exposure light rapidly reach saturation at low illuminances, so if you try to guarantee good reproduction of line drawings, the reproduction of halftones (photographs) will become hard-toned. Furthermore, gradations on the high density side are hardly reproduced.

Therefore, in order to improve the tone reproducibility of halftone originals, various processes have been reported that use screens, etc. and change the pixel area to achieve tone reproduction, but when using screens, etc., the quality of text documents is impaired Therefore, switching is required depending on the document, which has the disadvantage of making the device complicated.

[Objective] The present invention provides an electrostatic printing machine that can easily improve the gradation reproducibility of halftone (photographic) originals without requiring a complicated device.

[Structure] The present invention includes a charging condition adjusting means for changing the initial charging potential of the photoreceptor, an exposure condition adjusting means for changing the light amount of the exposure lamp, and a means for changing the peripheral speed of the developing sleeve or adjusting the developing bias. A developing condition adjusting means for changing the applied potential is provided, and several different conditions are set by combining different initial charging potentials of the photoreceptor, exposure light amount, peripheral speed of the developing sleeve, or applied potentials of the developing bias in advance. This is an electrostatic printing machine in which the conditions can be reset by one operation of a switch of a switching device.

Example An embodiment of the present invention will be described with reference to the drawings.

(Example 1) FIG. 1 is a schematic diagram of an electrostatic printing machine according to the present invention.

First, the printed image forming process will be explained with reference to FIG.

The photoreceptor 2 is installed so as to rotate in the direction of the arrow.
It is uniformly charged by the charger 1. On the other hand, exposure lamp 3
The reflected light 5 from the original 4 illuminated by the mirrors 6 .
The photoreceptor is exposed through steps 7 and 8 and 9 to form an electrostatic latent image on the photoreceptor 2. The electrostatic latent image on the photoreceptor is visualized by the developer held on the sleeve 11 of the developing device 10.

The developed toner image on the photoreceptor 2 is transferred to an object to be printed by a transfer device 12, and passes through a fixing device 13 to form a printed image.

A charge amount adjusting device 15 serving as a charging condition adjusting means is connected to a charger 1 of an electrostatic printing machine that obtains a printed image through the above process. This charge amount adjusting device 15 controls the amount of charge to the photoconductor 2 by adjusting the voltage applied to the charge wire in the case of a corotron charger, and by adjusting the grid voltage in the case of a scorotron charger. There is. The charge amount adjusting device 15 sets the initial charging potential of the photoreceptor to a high potential condition of at least 400V (absolute value) or more, and a condition where the same potential is 100V to 3V higher than the high potential condition.
It is designed to be set in two stages: a low potential condition of 00V and a low potential condition.

A lamp light amount adjustment device 16 is connected to the exposure lamp 3 as an exposure condition adjustment means. This lamp light amount adjustment device 16 adjusts the lamp potential so that the light amount is 10 to 40 times lower under low light amount conditions than under high light amount conditions, and the exposure light amount is set in two stages: low light amount and high light amount. It is set so that it can be switched to.

A developing sleeve circumferential speed adjusting device 17 is connected to the developing device 10 as a developing condition adjusting means. This sleeve circumferential speed adjusting device 17 adjusts the input to the sleeve drive motor to 1llll by using a variable resistor, for example, to adjust the photoconductor sleeve circumferential speed ratio from 0.5 to 2 under high circumferential speed conditions.
It is switched to two stages: a low speed condition and a low peripheral speed condition. In addition, the parts involved in stirring and transporting the developer in the developing device,
For example, the operating speed of the paddle 14 and the like is also adjusted at the same rate as the circumferential speed change of the developing sleeve.

Each adjusting device is connected to a switching device 18, and when the switching device 18 selects and presses a selection mode key of a selection device 19, copy conditions can be changed and set at the same time.

Next, when looking at the characteristics of the surface potential of the photoreceptor with respect to the original density when the initial charging potential of the photoreceptor and the exposure scene are changed, each curve in the graph of FIG. 2 is obtained. Further, the copy density characteristics (after fixing) with respect to the development potential (V) when the circumferential speed of the developing sleeve is changed are shown in the curves shown in FIG.

Tone reproduction in copying depends on the original density range in which the amount of change in photoreceptor surface potential is sufficiently large relative to the amount of change in original density shown in the graph shown in Figure 2, and the photoreceptor surface potential shown in the graph shown in Figure 3. It is determined by the copy density range in which copy density changes with respect to the amount of change in development potential, which is the difference in development bias. These ranges can be changed by adjusting the initial charging potential of the photoreceptor, the amount of exposure light, and the circumferential speed of the developing sleeve, as shown in FIGS. 2 and 3.

Therefore, the initial charging potential of the photoreceptor, the amount of exposure light, and the circumferential speed of the developing sleeve are set to four conditions as shown in Table 1 on the next page, so that they can be simultaneously switched by the switching device 18 via each adjustment device. This switching (selection) mode is the selection device 1
9 can be selected.

Table 1 The relationship between original density and copy density corresponding to Condition 1, Condition 2, Condition 3, and Condition 4 is curve 1, curve 2, curve 3, and curve 4 as shown in FIG. In other words, the gradation reproduction range for curve 1 (setting each adjustment device under condition 1) is between AB, that for curve 2 (setting each adjustment device under condition 2) is between CD, and that for curve 3 (setting each adjustment device under condition 3). For curve 4 (set), it is between ef and for curve 4 (each adjustment device is set for condition 4), it is between gh, and different gradation reproduction ranges can be obtained depending on each condition.

Therefore, the operator can make a copy with preferable reproducibility by selecting Condition 1 for line drawing originals and Condition 2 or Condition 3 for halftone (photograph) originals using the selection device 19 depending on the original. can get.

Furthermore, if condition 4 is selected for halftone (photographic) originals with relatively high density, a copy with high density and good gradation can be obtained.

(Embodiment 2) FIG. 5 is a schematic diagram showing an embodiment of the pond of an electrostatic printing machine according to the present invention. The image forming process of this printing machine is similar to the image forming process of the first embodiment.

The charger 1 of this electrostatic printing machine includes a charge amount adjusting device 20 as a means for stably adjusting the initial charging potential of the photoreceptor.
are connected.

The charger 1 has a grid 23 that is grounded via a constant voltage diode in order to uniformly charge the photoreceptor 2, but the charge amount adjustment device 20 has a constant voltage diode A and a constant voltage diode B. can be switched by a switching device 21 (see FIG. 6).

By switching the constant voltage diode A to a diode B having a different Zener voltage, the grid potential is adjusted, the amount of discharge is regulated, and the initial charging potential of the photoreceptor is switched in two stages. Here, the high potential condition is that the initial charging potential of the photoreceptor is at least 600 (absolute value) V or more, and the low potential condition is 100 to 300 (absolute value)
This is a condition where it becomes lower.

A lamp light amount adjustment device 22 is connected to the exposure lamp 3 as an exposure condition adjustment means. Lamp light amount adjustment device 22
The lamp light intensity is adjusted by adjusting the lamp voltage, and the low visibility condition is 10% lower than the high light intensity condition.
The light intensity is reduced by ~40%, and the exposure light intensity can be switched between two levels by a switching device 21 connected to a lamp light intensity adjustment device 22.

A developing bias adjusting device 24 serving as a developing condition adjusting means is connected to the developing device 10 . The potential applied as a developing bias is set to 50 to 200 (
The switching device 21 can switch between two stages: a low bias condition in which the applied voltage (absolute value) V is lowered.

In this embodiment, the lamp exposure light amount, development bias, and initial charging potential of the photoreceptor are determined by the charging amount adjusting device 20,
The four conditions shown in the table below can be set by the switching device 21 via the lamp light amount adjusting device 22 and the developing bias adjusting device 24.

Table 2 Copy density reproduction characteristics with respect to original density under these four conditions are shown in FIG.

That is, curve 5 is for condition 1 (high potential, high light amount, high developing bias), curve 6 is for condition 2 (low potential, high light amount, low developing bias), and curve 6 is for condition 3 (low potential, low light amount, high developing bias). In the case of condition 4 (low potential, high light amount, high development bias), curve 7 is obtained. The original gradation reproduction range for each curve is between a'b' for curve 5 (condition 1) and c'd' for curve 6 (condition 2).
For curve 7 (condition 3), e'f', curve 8
(Condition 4), the range is g″h°, and the original gradation reproduction range differs depending on each condition. By matching the characteristics of this original gradation reproduction range with the characteristics of the original, better printing can be achieved. An image is obtained.

From the above, when the original is a line drawing original, by selecting condition 1, even low-density characters can be reproduced satisfactorily.

By selecting condition 3 for half-tone (photographic) originals, it is possible to reproduce good gradation in high-density areas. By selecting condition 4 for a relatively high-density halftone (photograph) original, the gradation of the high-density portion can be further reproduced. Also,
By improving the gradation of the halftone (photograph) original without significantly lowering the maximum density under condition 2, it is possible to reproduce the image more favorably than the original with mixed light and shade 4.

[Effects] As described above, the present invention can produce halftone photographs without impairing the reproducibility of line drawing originals by selecting conditions according to the original.
The reproducibility of the original can be improved and a more preferable printed image can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an electrostatic printing machine according to the present invention, Fig. 2 is a graph of the photoreceptor surface potential with respect to the original density, when the initial charging potential of the photoreceptor and the amount of exposure light are changed, and Fig. 3 is a graph of the developing image. A graph showing the copy density characteristics with respect to the developing potential when the sleeve is set at a high peripheral speed and a low peripheral speed. Figure 4 is a graph showing the copy density with respect to the original density for each condition. Figure 5
The figure is a schematic diagram of an electrostatic printing machine showing another embodiment of the present invention, FIG. 6 is a schematic diagram of a charge amount adjusting device, and FIG. 7 is a copy density versus original density for each condition according to another embodiment. This is a graph representing. 1... Charger, 2... Photoreceptor, 3...
・Exposure lamp, 4...Original, 5...Reflected light,
1O...Developer, 11...Developer sleeve, 12...Transfer device, 13...Fixer, 1
5.20...Charging adjustment device, 16.22...Lamp light intensity adjustment device, 17...Sleeve peripheral speed adjustment device, 18.21...Switching device, 19...Selection Device,
24...Development bias adjustment device.

Claims (4)

[Claims] (1) A photoreceptor, which is a photoconductor, is uniformly exposed to light, an electrostatic latent image is formed on the photoreceptor by exposing the original, and the latent image is made visible in a developing section, and then transferred and fixed to make copies. In an electrostatic printing machine configured to obtain An electrostatic printing machine characterized in that settings are made on the device. (2) An electrostatic printing machine having a charging condition adjusting means, an exposure condition adjusting means, and a developing condition adjusting means, wherein the developing condition is adjusted by adjusting the circumferential speed of the developing sleeve. An electrostatic printing machine according to claim 1, characterized in that: (3) An electrostatic printing machine having a charging condition adjusting means, an exposure condition adjusting means, and a developing condition adjusting means, characterized in that the developing condition is adjusted by adjusting a developing bias. An electrostatic printing machine according to claim 1. (4) The switching device switches the initial charging potential of the photoreceptor, the amount of exposure light, the circumferential speed of the developing sleeve, or the developing bias to several different conditions set in advance.
An electrostatic printing machine according to claim 1, 2, or 3, in which the initial charging potential of the photoreceptor, the amount of exposure light, the circumferential speed of the developing sleeve, or the developing bias can be set simultaneously with a one-key operation. .