JPH04186382A - Development method and device for electrophotography - Google Patents

Abstract

PURPOSE:To enable an electrophotographic image of uniform density to be obtained by measuring a fine gap between the external surfaces of a rotating sensitive drum and a development roller, and adjusting the magnitude of bias electric field applied across the gap, according to the size of the measured fine gap. CONSTITUTION:In a development process, a fine gap delta between the external surfaces of a sensitive drum 10 and a development roller 18 is measured by a distance measurement means 38. This distance measurement means 38 outputs a signal corresponding to the measured fine gap delta to a controller 42, and this controller 42 controls for a bias electric field generation device 44 to generate bias electric field of such magnitude as corresponding to the measured fine gap delta. Namely, when the gap delta becomes large, the bias electric field is increased to prevent the density of an image from being too light. On the contrary, when the gap delta is small, the bias electric field is reduced to prevent the density from being too deep. According to the aforesaid construction, an image can be developed without much influence by the machining precision of the sensitive drum 10 and development roller 18.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an electrophotographic developing method and apparatus.

(B) Conventional technology In the conventional electrophotographic development method, a uniform thin layer of developer is formed on the outer circumferential surface of a developing roll, and the surface layer of this thin layer of developer is prevented from coming into contact with the outer circumferential surface of the photoreceptor drum. The two are placed facing each other with a small gap between them, and a bias electric field is formed in this small gap.

There is a so-called "jump type". Generally, the developing roll and the photosensitive drum receive and transfer developer while rotating in opposite directions. Image information is exposed to light to form a latent image on the photosensitive surface of the outer periphery of the photosensitive drum. The developer on the developing roll is forcibly separated from the developing roll by the bias electric field, flies toward the latent image on the surface of the photoreceptor drum, and adheres to the latent image. An electronic photograph can be obtained by transferring this onto paper or the like and then performing 5 fixing processes.

(8) Problems to be solved by the invention However, according to the conventional developing method as described above,
For example, even if conditions such as the potential of the latent image portion on the surface of the photoreceptor drum are constant, the amount of developer flying from the developing roll surface toward the photoreceptor drum surface is
The larger the above minute gap becomes, the smaller it becomes. On the other hand, if the micro-gap is small, the amount of developer that will fly away will increase.In other words, even if other development conditions are constant, the developer density will change depending on the size of the micro-gap. Therefore, if the photoreceptor drum and the developing roll are eccentric, the above-mentioned minute gap changes according to the rotation of both, and the developed density changes along the rotation direction. Conventionally, the developed density is constant. Either the photoreceptor drum and the developing roll were processed with high precision so that when they were rotated, the variation in the outer circumferential surface was less than a predetermined value, or the size of the surface to be developed did not meet the Japanese Industrial Standards. When paper size is large like AO size (840mm x 1188mm), it becomes difficult to maintain a constant minute gap over the entire circumference of the developing surface. Larger diameter rolls and photoreceptor drums are required, and the concentricity and roundness of both members must be processed to within specified tolerances, i.e., fluctuations in the outer peripheral surface when both members are rotated. It is difficult to keep the value below a certain value using normal processing methods.Therefore, in order to obtain high-precision rolls and drums, special processing is required, leading to the problem that the cost of the equipment becomes high. was there.

The present invention aims to solve these problems.

(d) Means for Solving the Problems The present invention measures the distance between the outer circumferential surface of a rotating photoreceptor drum and the outer circumferential surface of a developing roll, and adjusts the bias electric field depending on the magnitude of this distance. The above problem is solved by changing the intensity. That is, in the electrophotographic developing method of the present invention, the minute gap (δ) between the outer peripheral surface of the rotating photoreceptor drum (10) and the outer peripheral surface of the developing roll (18) is measured, and the photoreceptor drum l ＼The outer peripheral surface of (10) and the developing roll (
The magnitude of the bias electric field applied between the outer circumferential surface of 18) is adjusted according to the magnitude of the measured minute gap (δ). Further, an apparatus for carrying out the above method includes a developing device (1) having a photosensitive drum (10) and a developing roll (18) disposed opposite to the outer peripheral surface of the photosensitive drum (10).
2), the outer peripheral surface of the photoreceptor drum (10) and the developing roll (
18) and a bias electric field generator (44) that applies a bias electric field between the outer circumferential surface of the photoreceptor drum (10) and the outer circumferential surface of the developing roll (18). a distance measuring means (38) capable of measuring a minute gap (δ) between the
2), and the bias electric field generator (44) can adjust the magnitude of the bias electric field according to the minute gap (δ) by a control signal from the controller (42). ing.

Note that the distance measuring means (38) is connected to the photoreceptor drum (1).
0) and the outer circumferential surface of the developing roll (18), and outputs a signal of a minute gap (δ) corresponding to the size of the capacitance. good.

The distance measuring means (38) also includes a photoreceptor drum (1).
The piezoelectric element is a piezoelectric element disposed between the outer circumferential surface of the photoreceptor drum (18) and the outer circumferential surface of the developing roll (18).
10] and the outer circumferential surface of the developing roll (18). Note that the symbols in parentheses indicate corresponding members in the embodiment.

(e) Function During the development process, a minute gap between the outer circumferential surface of the photoreceptor drum and the outer circumferential surface of the developing roll is measured by a distance measuring means. The distance measuring means outputs a signal having a magnitude corresponding to the measured minute gap to the controller, and the controller causes the bias electric field generating device to generate a bias electric field having a magnitude corresponding to the measured minute gap. , control this. That is, when the minute gap becomes large, the bias electric field is made thicker (so that the image density does not become too thin).

Furthermore, when the minute gap becomes small, the bias electric field is reduced to prevent the image density from being too high. In this way, even in the case of large size electrophotography, it is possible to develop the image with a uniform development density without being affected much by the processing accuracy of the photosensitive drum or the developing roll.

(F) Embodiment Figures 1 and 2 show an embodiment of the present invention. Photosensitive drum 1
A developing device 12 is disposed at a position facing the outer circumferential surface of 0. A photosensitive surface is formed on the outer peripheral surface of the photosensitive drum 10. The developing device 12 includes the photosensitive drum 1 in FIG.
A first side plate 14 disposed at the lower left of 0, a second side plate 16 disposed opposite thereto, a cylindrical developing roll 18 made of a non-magnetic material attached to both side plates 14 and 16, In order to generate a bias electric field of a size corresponding to the minute gap between the bearings attached to the plates 14 and 16, respectively,
Control this. That is, when the minute gap becomes large, the bias electric field is made thicker (so that the image density does not become too light).

Furthermore, when the minute gap becomes small, the bias electric field is reduced to prevent the image density from being too high. By doing this, even large-sized electronic photographs,
It is possible to perform development with a uniform development density without being greatly influenced by the processing accuracy of the photoreceptor drum or the developing roll.

(F) Embodiment Figures 1 and 2 show an embodiment of the present invention. Photosensitive drum 1
A developing device 12 is disposed at a position facing the outer circumferential surface of 0. A photosensitive surface is formed on the outer peripheral surface of the photosensitive drum 10. The developing device 12 includes the photosensitive drum 1 in FIG.
A first side plate 14 disposed at the lower left of 0, a second side plate 16 disposed opposite thereto, a cylindrical developing roll 18 made of a non-magnetic material attached to both side plates 14 and 16, Bearings 20 and 22 attached to plates 14 and 16, respectively
, a shaft member 24 whose both ends are supported by both bearings 20 and 22, and a cylindrical magnet 26 fixed to the shaft member 24.
and a case 28 (see Figure 1) that houses them. A developer 40 containing a magnetic material is stored in the case 28 . In FIG. 2, the first side plate 14 on the left side is formed with a shaft portion 14'a extending leftward. Further, a shaft portion 16a extending rightward is formed on the second side plate 16 on the right side in the figure. A ring-shaped first application roll 30 is arranged on the left side of the first side plate 14 in the drawing. The first application roll 30 has a bearing 35 in the center thereof, and is fitted onto the shaft portion 14a of the first side plate 14 so as to be rotatable. Further, a ring-shaped second application roll 32 is arranged on the right side of the second side plate 16 in the drawing. Second
The application roll 32 has a bearing 36 in the center thereof, and is fitted onto the shaft portion 16a of the second side plate 16 so as to be rotatable. The shaft portions 14a to 16a of the side plates 14 and 16 are rotatably supported by the case 28. That is, the first
Applying roll 30. The second application roll 32 and the developing roll 18 are rotatable independently of each other while being in contact with the outer circumferential surface of the photoreceptor 10 around the same axis. As shown in FIG. 1, the photoreceptor drum 1o rotates clockwise, and the developing roll 18 of the developing device 12 has side plates 14, 16. It is supported by both shaft portions 14a, 16a, etc., and rotates counterclockwise in FIG. An ear cutting blade 34 is fixed to the upper end of the case 28 in FIG. As the developing roll 18 rotates, the ear cutting blade 34 is attached to the developing roll 18 by the magnet 26.
Of the developer 40 adsorbed on the outer surface of the developing roller 18, only a predetermined thickness of the developer 40 is left on the developing roll 18, and the excess is returned to the inside of the case 28. The developing device 12 is pressed against the photoreceptor drum 10 by a pressing mechanism (not shown).That is, as shown in FIG.
The outer periphery of the rollers 30 and 32 are rotated while being in contact with the outer peripheries of both the application rolls 30 and 32. When a bias electric field is applied between the outer circumferential surface of the photoreceptor drum 10 and the outer circumferential surface of the developing roll 18 by the bias electric field generating device 44 described later, the outer circumferential surface of the photoreceptor drum 10 and the outer circumferential surface of the developing roll 18 are It is possible to measure the capacitance between and output a signal corresponding to the magnitude of the measured capacitance. The second signal corresponds to the minute gap δ. The developing device includes a controller 42 that receives the above signals and performs calculations, and a bias electric field that generates a bias electric field between the outer circumferential surface of the developing roll 18 and the outer circumferential surface of the photoreceptor drum 10 in accordance with the control signal. A generator 44;
is provided.

Next, the operation of this embodiment will be explained. The developing device 12 is pressed toward the photosensitive drum 10 by a pressing mechanism (not shown). As a result, when the photosensitive drum 10 rotates clockwise in FIG. 1, its outer circumferential portion and the outer circumferential portions of both the abutting rolls 30 and 32 rotate while contacting each other. That is, the developing roll 18 rotates counterclockwise in the figure at the same circumferential speed as the photosensitive drum 10. A latent image is formed on the photosensitive surface of the photosensitive drum 10 in a previous process. That is, the photosensitive surface of the photosensitive drum 10 is charged by a charging means (not shown), and then an image signal is exposed by an exposure device. As a result, the photosensitive surface of the photosensitive drum 1o remains at a high potential in the latent image area (image area).
This means that a low potential portion (background portion) that has lost potential due to exposure is formed. On the other hand, as the photoreceptor drum 10 rotates, the developing roll 18 is also rotated.

A magnetic developer 40 is attracted to the outer circumferential surface of the magnet 26 by the magnetic force of the magnet 26 . The thickness of the developer layer 400 is kept constant by being cut into ears by the ear cutting blade 34 as it rotates.

A developer is applied to the latent image portion of the photoreceptor drum 10 by a developing device 12 . That is, the photosensitive drum 10
A bias electric field is applied from a bias electric field generator 44 between the photosensitive surface of the developing roll 18 and the outer peripheral surface of the developing roll 18, and the developer 40 on the developing roll 18 is moved from the developing roll 18 by the magnetic force of the magnet 26 due to the bias electric field. It resists and is pulled away, flies toward the high-potential latent image portion of the photosensitive drum 10, and adheres to the latent image portion. At this time, if the minute gap δ between the outer peripheral surface of the photoreceptor drum 10 and the outer circumferential surface of the developing roll 18 is small, the image density will be higher even if the same magnitude of bias electric field is applied; δ
The thicker the image, the lighter the image density.

In the device of the present invention, as shown in FIG. 3, the minute gap δ is measured by the distance measuring means 38, and the measurement signal thereof is input to the controller 42, which
Bias electric field generator 4
The magnitude of the bias electric field generated from 4 is changed. That is, when the minute gap δ is small during the rotation of the photoreceptor drum 10 and the developing roll 18, the magnitude of the bias electric field generated from the bias electric field generator 44 in FIG. 3 is reduced to make the image density too high. If the minute gap δ is large, the magnitude of the bias electric field generated from the bias electric field generator 44 is increased to adjust the image density so that it does not become too dull. Therefore, in FIG. 1, the photosensitive drum 1o and the developing roll 1
During the rotation of 8, even if the minute gap δ changes, the image density can be kept constant. The developer 40 on the photoreceptor drum lo is transferred to a transfer material such as paper and fixed, thereby producing an electrophotographic image.

In the above description, the distance measuring means 38 for measuring the minute gap δ between the outer circumferential surface of the photosensitive drum 1o and the outer circumferential surface of the developing roll 18 measures the electrostatic capacitance generated between the two members 1o and 18. However, a piezoelectric element may be disposed between the outer circumferential surface of the photoreceptor drum 10 and the outer circumferential surface of the developing roll 18. In this case, the force generated from the piezoelectric element takes advantage of the fact that the magnitude of the force pushing the piezoelectric element while the photoreceptor drum 1o and the developing roll 18 are rotating changes in accordance with the size of the minute gap δ. What is necessary is to convert the magnitude of the voltage into the magnitude of the minute gap δ.

(g) As described in detail, according to the present invention, even if a developing device in which the minute gap between the outer circumferential surface of the photoreceptor drum and the outer circumferential surface of the developing roll fluctuates is used, the image density remains unchanged. It is possible to obtain an electronic photograph with a constant value. Therefore, even in a large format electrophotographic bag device where it is difficult to maintain a constant minute gap between the outer peripheral surface of the photoreceptor drum and the outer peripheral surface of the developing roll, a particularly high-precision developing device is used. The device can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a developing device according to an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view thereof, and FIG. 3 is a control block diagram of a bias electric field. 10... Photosensitive drum, 12... Developing device, 14...
...First side plate, 16... Second side plate, 18... Developing roll, 24... Shaft member, 26... Magnet, 28
...Case, 30...First application roll, 32.
...Second abutting roll, 38...Distance measuring means, 4
2... Controller, 44... Bias electric field generator, δ
...Minute gap. Patent applicant: Japan Steel Works Co., Ltd.
Person Patent Attorney Toshiyuki Miyauchi Figure 2

Claims (1)

[Claims] 1. Measure the minute gap (δ) between the outer peripheral surface of the rotating photoreceptor drum (10) and the outer peripheral surface of the developing roll (18), and determine the outer circumference of the photoreceptor drum (10). Surface and developing roll (18)
An electrophotographic developing method characterized in that the magnitude of a bias electric field applied between the outer circumferential surface of the image forming apparatus and the outer circumferential surface of the electrophotographic image forming apparatus is adjusted according to the magnitude of a measured minute gap (δ). 2. A developing device (12) having a photosensitive drum (10) and a developing roll (18) disposed opposite to the outer peripheral surface of the photosensitive drum (10).
), the outer peripheral surface of the photoreceptor drum (10) and the developing roll (1
8), a bias electric field generating device (44) that applies a bias electric field between the outer circumferential surface of the rotating photoreceptor drum (10) and the developing roll (18). Distance measuring means (3) capable of outputting a signal by measuring the minute gap (δ) between the
8) and a controller (42) that performs calculations by inputting signals from the distance measuring means (38), and the bias electric field generator (44) is controlled by the controller (42). Depending on the signal, the above minute gap (δ)
An electrophotographic developing device characterized in that the magnitude of the bias electric field can be adjusted according to the magnitude of the bias electric field. 3. The distance measuring means (38) is connected to the photosensitive drum (10
) and the developing roll (18), and outputs a signal corresponding to the size of the minute gap (δ). electrophotographic developing equipment. 4. The distance measuring means (38) is connected to the photosensitive drum (10
) and the outer circumferential surface of the developing roll (18).
3. The electrophotographic developing device according to claim 2, wherein the electrophotographic developing device generates a voltage corresponding to the size of a minute gap (δ) between the outer circumferential surface of the developing roller (18) and the outer circumferential surface of the developing roll (18).