JP2517569B2 - Development device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Purpose of the invention [Industrial field of application] The present invention relates to a developing device for a latent image formed by an electrophotographic method or an electrostatic recording method, and in particular, a developer carrier and an image carrier. And a developing device for developing by applying an alternating electric field (bias) therebetween.

[Conventional technology]

Conventionally, as described in, for example, JP-B-58-32375 and JP-A-58-32377, the developer is held in a uniform thin layer on the developer carrier and transferred to a position close to the image carrier. Then
A developing device for developing a latent image on the image carrier by causing the developer on the developer carrier to fly to the carrier by an alternating electric field applied between the developer carrier and the image carrier is known. Has been.

FIG. 2 is a sectional view of the developing device described above applied to a copying machine using a drum type photoconductor. Although not shown in the drawing, a charging mechanism, an image exposure mechanism, a transfer mechanism, a cleaning mechanism, which are well-known electrophotographic processes, are provided around the photosensitive drum 6.
A charge removing mechanism and the like are provided.

In the figure, 1 is a hopper containing a developer 2 (one-component toner, two-component toner, or the like), and 3 is a hopper whose part of the peripheral surface is exposed to the outside from an opening 7 of the hopper 1 in the longitudinal direction. A non-magnetic cylinder (hereinafter referred to as a sleeve) as a developer supporting member rotatably attached between the side plates.

Reference numeral 4 denotes a magnet roller which is concentrically and fixedly provided in the sleeve, and has a plurality of magnetic poles N ₁ · N ₂ and S ₁ · S ₂ formed in parallel to the longitudinal direction of the circumferential surface.

5 is a hopper 1 with a gap g1 between it and the sleeve 3
A blade as a developer layer thickness regulating means attached to the photoconductor, and a photoconductor 6 as a latent image holding means rotatably supported by a copying machine body (not shown) as a latent image holding means. 3 are installed side by side. Reference numeral 7 is a developing section, and 8 is a developing bias power source for applying an alternating electric field between the sleeve 3 and the photoconductor 6.

When the sleeve 3 receives a driving force from a driving source (not shown) and rotates in the arrow direction, the developer 2 is restrained on the sleeve by a supporting force such as a magnetic force or an electrostatic force, and the rotation of the sleeve causes the developer 2 in the arrow a direction. It is conveyed and applied to a constant layer thickness t by the blade 5. On the surface facing the photoconductor 6, the applied developer electrostatically acts as a gap g2 corresponding to the latent image pattern on the photoconductor by the action of the alternating electric field by the above-mentioned alternating voltage.
Is subjected to jumping or extension movement and transferred to the latent image surface for development.

[Problems to be solved by the invention]

However, conventionally, as the above-mentioned alternating electric field, the rising speed in the development promoting direction and the falling speed in the development suppressing direction are symmetrical, and when a latent image formed by a document in which solid portions and line portions are mixed is developed. It was difficult to obtain good line development.

That is, in a developing device capable of favorably developing a latent image formed by an original composed of fine characters of a line portion and a solid portion, when a latent image formed by an original formed of bold characters of a line portion and a solid portion is developed, the line portion is It becomes difficult to read fat. On the contrary, in a developing device capable of favorably developing a latent image formed by a document composed of bold characters in a line portion and a solid portion, when a latent image formed by a document composed of thin characters in a line portion and a solid portion is developed, There is a problem that the part becomes thin and becomes a faint image, which is difficult to read.

Therefore, as a result of repeated experiments and studies, the present applicant changed the relationship between the rising speed of the alternating electric field in the development promoting direction and the falling speed in the development suppressing direction to form a solid image and a halftone latent image. On the other hand, it was found that the development has different image characteristics with respect to the latent image of the line portion while showing similar image characteristics.

This development seems to occur as follows.
FIG. 3 is an electric field diagram which acts on the solid portion 9A and the line portion 9B when the alternating electric field is in the development promoting direction and is large,
The electric flux lines 10A are open in both the solid portion 9A and the line portion 9B.

On the other hand, FIG. 4 is an electric field diagram that acts on the solid portion 9A and the rhombus portion 9B when the alternating electric field is in the development promoting direction and is small. The line of force 10B just wraps around the image background,
In the line portion B, the ratio of the electric flux lines 10B to the image background portion is larger than that of the opened electric flux lines.

It is considered that the image characteristics of the line portion with respect to the latent image are different due to the wraparound of the lines of electric force to the image background portion.

The present invention makes use of the above-mentioned development for a latent image formed by either a thin document or a bold document,
It is an object of the present invention to provide a developing device that can always perform good development to obtain a good quality image.

B, Configuration of the Invention [Means for Solving Problems] The present invention for solving the above problems forms an alternating electric field between a developer carrying member carrying a developer and an image carrying member carrying a latent image. In the developing device for performing the development by means of a control means capable of variably controlling both the rising speed and the falling speed from the peak on the development promoting side of the alternating electric field, the rising time and the standing time of the alternating electric field are increased. The feature is that the ratio of the fall time is variable.

[Work]

The alternating electric field in the present invention makes the rise in the development promotion direction gentle for the thin document and makes the fall in the development suppression direction abrupt, and makes the rise in the development promotion direction abruptly makes the fall for the thick document original. By controlling, the thin character is made a thick and solid image and the bold character is made a delicate image.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. First
The figure is a waveform diagram of the alternating electric field. In the figure, the horizontal axis is time, and the vertical axis is voltage.
The lower the position, the more the development is suppressed.

A solid line A is an alternating electric field having rising / falling waveforms symmetrical, and a broken line B is an asymmetrical electric field having an asymmetric waveform slowly rising in the development promoting direction and then slowly falling in the development suppressing direction. Is an alternating electric field having an asymmetrical waveform that slowly rises in the development promoting direction and then sharply falls in the development suppressing direction.

When the alternate electric field indicated by the alternate long and short dash line B is used, in the solid portion A, as shown in FIG. 4 (A), there is no difference in the direction of the electric force line 10A between the peak of development promotion and the middle thereof. , Shows the same development characteristics, but the development acceleration bias reaches a peak in a short time in the line portion, so the toner has not yet reached the latent image at the peak time, and then the development acceleration bias decreases, As shown in FIG. 4 (B), the lines of electric force 10B wrap around the background portion, so that the developer cannot reach the latent image, and the line portion becomes thin and a delicate image is obtained.

When the alternate electric field indicated by the alternate long and short dash line C is used, there is no difference in the direction of the lines of electric force between the peak of development promotion and the middle of development in the solid portion, and therefore the same development characteristics are exhibited. However, since the development acceleration bias rises gently in the line portion, when the developer starts moving toward the latent image, the lines of electric force wrap around as shown in FIG. 4 (B). In the latter half of the above, the lines of electric force are open as shown in FIG. 3 (B), and since the line end can be effectively developed, it is possible to obtain a thick and firm image even on a fine print original.

An experimental example in which the developing device of the present invention is applied to an electrophotographic copying machine will be described below. NP-150Z toner (-component magnetic toner) is used as a commercially available developer, a pulse generator is used as a power source, and an alternating electric field having a frequency f = 1800 Hz and a peak-to-peak voltage Vp-p = 1200 V is generated.・ Change to B and C waveforms. As the alternating electric field control means, the waveform A
The three alternating electric field sources B and C may be switched, or the alternating electric field sources may be switched steplessly by a volume control or the like. In this experimental example, the alternating electric field source was switched to waveforms B to A to C steplessly, and a DC voltage was superimposed on the alternating electric field for development. The results are shown in the table below. In the comparative example, the same alternating electric field as that of the waveform A of the experimental example is applied, and the change of the alternating electric field waveform cannot be controlled.

The values in the table are the image densities measured by Macbeth densitometer, D _0.3
(Φ5) and D _1.1 (φ5) are image densities of 0.3 and _1.1, respectively.
Means a circle of 5 mm. There was no fog in each of the examples and comparative examples.

As shown in the table, the image density of the solid portion is D _0.3 (φ
5) and D _1.1 (φ5) are not different between the waveforms A, B, and C, but there is a significant difference in the line portion, and the characters are thick in the order of waveform C> waveform A> waveform B.

In this way, by controlling the speed relationship between the rising in the development promoting direction and the falling in the development suppressing direction of the alternating electric field as the developing bias, and changing the ratio of the rising time and the falling time of the alternating electric field, the solid portion and the halftone It has become possible to make the image thicker or thinner only for the line portion without changing the image characteristics of the portion. Therefore, by controlling the alternating electric field source with, for example, one changeover switch so as to have the waveform B for the thin document and the waveform C for the bold document, it is possible to always obtain a good image even in the line portion. It has become possible.

As described above, according to the present invention, as described above, the alternating electric field applied between the developer carrying member and the image carrying member as the developing bias,
Since it is configured to control the speed relationship between the rising edge in the development promoting direction and the falling edge in the development suppressing direction, the characters can be thickened or thinned only in the line portion without changing the image characteristics of the solid portion. be able to. Therefore, by simply controlling the waveform of the alternating electric field as the developing bias, it is possible to obtain a good quality image of the line portion.

[Brief description of drawings]

FIG. 1 is a waveform diagram of an alternating electric field of a developing device according to an embodiment of the present invention, FIG. 2 is a sectional view of the developing device of the present invention applied to a copying machine, FIGS. 3 (A) and (B), and FIG. FIGS. 3A and 3B are explanatory views of lines of electric force acting on development. 2 ... Developer, 3 ... Developer carrier (sleeve), 6 ...
Image carrier (photoreceptor), means for applying an alternating electric field as a developing bias.

Claims (1)

(57) [Claims] 1. In a developing device for performing development by forming an alternating electric field between a developer carrying member carrying a developer and an image carrying member carrying a latent image, the rising of the alternating electric field toward a peak on the development promoting side. A developing device comprising control means capable of variably controlling both the speed and the falling speed from the peak, and changing the ratio of the rising time to the falling time of the alternating electric field.