JPH02245778A - Image forming device - Google Patents

Abstract

PURPOSE:To attain cost reduction by permitting an electromagnetic clutch, which is on/off-controlled by a mode changeover switch, to transmit rotation to a developing roller shaft via a pair of gears in on-conditions. CONSTITUTION:When the electromagnetic clutches 46a-46d, all of which are on/off-controlled by the mode changeover switch 2, are turned on, rotation is transmitted to the shaft 44 of a developing roller via the pair of gears 92a-92d and 47a-47d in on-conditions. The gears 92a-92d of different number of teeth are attached to a rotation shaft 91, and are disposed so as to mesh with the gears 47a-47d to which the electromagnetic cluches 46a-46d disposed to the developing roller shaft 45 are connected. Thus, cost reduction and device miniaturization can be attained by means of a mechanically simple structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on a photoreceptor using a developer conveyed on a developing sleeve.

(Prior art and its problems) For example, an electrophotographic copying machine rotates a photoreceptor having a photosensitive layer on its surface, and as the photoreceptor rotates, an electrostatic latent image is formed on the photoreceptor. A copy image is obtained by developing the image with toner using a developing device. The developing device uses a cylindrical developing roller placed opposite the photoreceptor.
The developer is conveyed on the circumferential surface.

The developer (toner) conveyed on the circumferential surface is attached to the electrostatic latent image on the photoreceptor by electrostatic force at a position facing the photoreceptor, thereby developing the electrostatic latent image. Usually, by applying a bias potential to the developing roller, image fogging in the background area is prevented and a clear image is obtained.

On the other hand, in recent years, image forming devices such as copying machines have become smaller as the installation space has become smaller, and not only copying machines for office use but also copying machines for general home use have been developed. Further miniaturization and cost reduction are important issues.

In addition, not only for office or home use, the number of copies of originals is not limited to normal text, but also halftone documents such as photographs and pamphlets are increasingly being copied, and standard mode ( Image forming apparatuses have been proposed that have modes with different gradations, such as a text mode and a photo mode.

Generally, in an electrophotographic copying machine, the density of a developed image relative to the density of an original image is changed by changing the bias voltage applied to a developing roller. By changing the bias voltage of the developing roller, the toner holding power of the developing roller changes, and the amount of toner adhering to the electrostatic latent image changes.

That is, by changing the bias voltage, the amount of toner adhering to the electrostatic latent image is changed, and the image density is changed. However, with this method, the γ value, which represents the gradation of the developed density with respect to the original image density, does not substantially change. Although it is necessary to increase the bias potential, the current situation is that although raising the bias potential hardly causes gabbing, the overall density decreases, resulting in images that are more difficult to see, such as those of photographs.

Therefore, the present applicant first provided a rotational drive means for the developing roller, an image quality setting device for setting gradation, and a rotating body speed control means for controlling the speed of the rotating body of the rotational driving means in accordance with the support of the image quality setting device. proposed a developing device. (Unexamined Japanese Patent Publication No. 6
3-6582) In the developing device proposed above, when the image quality setting device is set to the soft side in order to obtain a soft image with excellent gradation, the rotating body speed of the variable motor is controlled by the rotating body speed control circuit. In order to reduce the rotational speed of the developing roller relative to the rotational speed of the photoconductor and, conversely, to reproduce strong contrast in the image, contrary to the case of obtaining a soft image as described above, set the image quality setting device to a high contrast. The rotating body speed of the variable motor is increased by the rotating body speed control circuit.

(Problems to be Solved by the Invention) Images developed by an image forming apparatus equipped with the above-mentioned developing device can be produced by increasing the rotational speed of the developing roller in areas where the electrostatic force of the electrostatic latent image is strong (high potential areas). ), resulting in a high-contrast image.Conversely, when the rotation speed of the developing roller is slowed down, the amount of adhesion in high-density areas of the original image decreases, but the amount of adhesion in low-density areas remains almost unchanged. ,the result,
This improves the reproducibility of halftones. however,
An image forming apparatus equipped with the above-mentioned developing device requires a variable motor and a control circuit to change the circumferential speed of the developing roller, resulting in an increase in cost and an increase in the size of the apparatus itself.

The present invention has been made in view of the above points, and an object of the present invention is to provide an image in which image modes with different gradations can be selected with a simple configuration without separately providing a control circuit or a drive motor for rotating the developing roller. An object of the present invention is to provide a forming device.

A further object of the present invention is to provide an image forming apparatus which can be switched between a standard (text) mode and a photographic mode and is miniaturized at a low cost.

(Means for Solving the Problems) According to the present invention, there is provided an image forming apparatus capable of switching between a high-contrast image mode and a soft-contrast image mode, which includes a mode changeover switch for changing over the image mode, and a developer disposed on the circumferential surface. a developing roller shaft that supports the developing roller being transported; a rotating shaft that transmits driving force from a drive source to the developing roller shaft;
An electromagnetic clutch interposed between the rotating shaft and the developing roller shaft includes a pair of gears having different tooth ratios, and the electromagnetic clutch is turned on by the mode changeover switch.
, an image forming apparatus is provided in which the rotational force from the rotating shaft is transmitted to the developing roller shaft by a gear pair in which the electromagnetic clutch is controlled to be OFF and the electromagnetic clutch is in the ON state.

Further, according to the present invention, there is provided an image forming apparatus capable of switching between a high-tone image mode and a soft-tone image mode, which includes a mode changeover switch for changing over the image mode, and a developing roller that supports a developing roller along which developer is conveyed on the circumferential surface. a roller shaft, a rotating shaft for transmitting a driving force from a drive source to the developing roller shaft, a gear pair interposed between the rotating shaft and the developing roller shaft and including a one-way clutch, and the rotating shaft and the developing roller shaft. A pair of gears having different tooth ratios are connected to an electromagnetic clutch interposed between the roller shaft, and the electromagnetic clutch is ON and OFF controlled by the mode changeover switch, and when in the ON state, the gears connected to the electromagnetic clutch are A pair of gears transmits the rotational force from the rotational shaft to the developing roller shaft, and when the gear pair is in an OFF state, a pair of gears incorporating a one-way clutch transmits the rotational force from the rotational shaft to the development roller shaft. provided.

The present invention will be explained below based on a first embodiment.

The image forming apparatus of the present invention uses an electrophotographic copying machine as shown in FIG. The electrophotographic copying machine includes a photoconductor 10 disposed in the center, a charging device 20, an exposure device 30, a developing device 40 of the present invention, a transfer/separation 50, and a cleaning device disposed around the photoconductor. 60 and a static eliminator 61. The photoreceptor 10 has a photosensitive layer 11 on its peripheral surface.
, and is rotatable in the direction shown by arrow B. The photoreceptor 10 is uniformly charged by the charging device 20 .

An exposure device 30 is arranged above the charging device 20. A document table 70 that is movable in the direction indicated by arrow A is provided on the top surface of the machine. The exposure device 30 exposes the image of the document placed on the document table 70, and forms an electrostatic latent image corresponding to the document image on the uniformly charged photoreceptor 10 by reflecting the light.

A developing device 40 according to the present invention is disposed downstream of the position of the photoreceptor 10 where the original image is exposed in the direction of rotation of the photoreceptor. The developer bag W40 includes a toner hopper 41 and a stirring chamber 42 disposed below the toner hopper 41. A stirring roller 43 and a developing roller 44 are disposed within the stirring device 42 . Stirring roller 43
The toner supplied from the toner hopper 41 is mixed with the carrier in the stirring chamber 42, and the toner and carrier are charged by friction.

The developing roller 44 is a magnetic roller, and faces the photoconductor 10 at a downstream position in the rotation direction of the photoconductor 10 from the exposure position of the photoconductor 10, and in the forward direction of the rotation direction of the photoconductor 10 (indicated by arrow C). It is possible to rotate. The developing roller 44 conveys developer onto its circumferential surface as it rotates, and the conveyed developer forms a magnetic brush on the circumferential surface of the developing roller 44 . Then, the formed magnetic brush ears come into contact with the electrostatic latent image on the photoreceptor 10, toner adheres to the electrostatic latent image, and the electrostatic latent image is developed with toner. In the present invention, the rotation speed of the developing roller 44 is determined as shown below. As shown in FIG. 1, the above-mentioned developing device 40 is driven by a main motor drive 90 that is a driving source for the entire image forming apparatus such as the photoreceptor, paper feeding section, conveying section, fixing section, etc.
The rotating shaft 91. transmits the drive from the rotating shaft 91. Then, the rotating shaft 91
are gears 92a, 92b, and 92C each having a different number of teeth.
192d) is attached, and the gears are connected to electromagnetic clutches 46a, 46b, 4 disposed on the developing roller shaft 45.
Gears 47a, 47b, 47c, which connect 6c, 46d,
47d.

First, start with the image quality mode switch 2 on the operation panel 1.
to select the desired image quality mode.

Then, when the print key 3 is turned on, a main motor (not shown) rotates and transmits drive to the rotating shaft 91 and each process of the entire apparatus.

At this time, an arbitrary mode is selected by the image quality mode changeover switch 2, and the electromagnetic clutch with a closed circuit (in this case, only 46d) is turned on by the switch, and the other circuits are opened. Electromagnetic clutch 46
a 146 bs 46 C remains OFF,
The rotational force from the main motor drive 90 is transmitted from the rotating body shaft 91 only to the gear 47d connected to the selected ON electromagnetic clutch 46d. Then, the rotational speed determined by the ratio of the number of teeth to the meshed gear 92d is transmitted to the developing roller shaft 45, and the rotational speed of the developing roller is determined. The rotary switch shown in the figure is preferably used as the switch.

In the above embodiment, the high-contrast mode is used in which characters and line drawings are reproduced with good contrast, and the gear combination (92d-47d) that rotates at the highest speed is selected.

As a result, in the obtained image, as shown in FIG. 4(a), the slope θ of the curve representing the copy image density relative to the original image density becomes large, and the T value expressed by r=tan θ becomes large.

Conversely, when the softest switch 2a is selected on the operation panel, the circuit of the electromagnetic clutch 46a is closed, the other circuits are open, and the rotation of the rotating body shaft 91 is controlled by the gear 92a.
This rotation is transmitted to the gear 47a and the developing roller 44 rotates at a low speed.

As shown in FIG. 4(B), the image characteristics of the image obtained at this time are such that the slope θ becomes small and becomes close to 1.

Generally, when changing the image quality from a high contrast image to a soft contrast image, when the developing roller rotates in the forward direction relative to the photoreceptor as in this example, the rotation speed of the developing roller is set to 1 to 4 times the rotation speed of the photoreceptor. When the developing roller rotates in the opposite direction to the rotational direction of the photoreceptor, the rotation speed of the developing roller is preferably 1 to 2 times that of the photoreceptor.

The toner image formed on the photoreceptor as described above is
The image is transferred onto the transfer paper by the transfer/separation device 50, and fixed onto the transfer paper by the fixing device 81.

Further, in the image forming apparatus of the above embodiment, the rotational force from the rotation shaft is transmitted to the developing roller shaft by selecting an arbitrary gear pair from among the gear pairs in which a plurality of electromagnetic clutches are connected. Considering miniaturization and cost reduction of the device, as shown in FIG. 2, a gear 4 equipped with a one-way clutch is attached to the developing roller shaft 45, and a gear 5 with a small number of teeth for the lowest speed on the rotating shaft side is installed. The gear connected and equipped with an electromagnetic clutch 6 is connected to a gear 7 with a large number of teeth for high speed, and when in high contrast mode, the electromagnetic clutch is turned on by the image quality mode changeover switch 2 on the operation panel 1. Rotation and light force from the rotating shaft is transmitted to the developing roller shaft, and in the soft contrast mode, the electromagnetic clutch is turned off, and the developing roller shaft is rotated by a pair of gears formed by a one-way clutch. In other words, the gear pair with the electromagnetic clutch in the ON state is used except at the lowest speed, and at that time the one-way clutch is in a slip state and does not transmit drive.

By adopting the above configuration, the cost and space of the negative layer can be reduced.

Also, needless to say, FIG. 2 shows one pair of gears connected to electromagnetic clutches, but if a plurality of pairs are used, the selection range of modes will be expanded.

(Effects of the Invention) According to the present invention, it is possible to provide an image forming apparatus that can switch between a high-tone image mode and a soft-tone image mode with a simple mechanical configuration without increasing the size of the apparatus. can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the rotational drive of the developing roller of the image forming apparatus of the present invention. FIG. 2 shows another embodiment of the invention. FIG. 3 is a diagram showing the image forming process of the image forming apparatus of the present invention. FIG. 4 is a diagram showing the gradation reproducibility of the developed image of the present invention. 2... Image quality mode selection switch, 46a, 46b, 4
6c, 46d...Electromagnetic clutch, 91...Rotating body shaft, 45...Developing roller shaft.

Claims (3)

[Claims] (1) An image forming apparatus capable of switching between a high-tone image mode and a soft-tone image mode, comprising: a mode changeover switch for changing the image mode; a developing roller shaft that supports a developing roller along which developer is conveyed; A rotary shaft for transmitting driving force from a drive source to the developing roller shaft; and a pair of gears with different tooth ratios connected to an electromagnetic clutch interposed between the rotary shaft and the developing roller shaft, The image forming apparatus is characterized in that the clutch is ON/OFF controlled by the mode changeover switch, and the electromagnetic clutch transmits rotational force from the rotating shaft to the developing roller shaft by a gear pair in the ON state. (2) An image forming apparatus capable of switching between a high-tone image mode and a soft-tone image mode, comprising: a mode changeover switch for switching between image modes; a developing roller shaft that supports a developing roller along which developer is conveyed; a rotating shaft for transmitting driving force from a drive source to the developing roller shaft; a gear pair equipped with a one-way clutch interposed between the rotating shaft and the developing roller shaft; and between the rotating shaft and the developing roller shaft. and a pair of gears having different tooth ratios connected to an electromagnetic clutch interposed therein, the electromagnetic clutch is ON/OFF controlled by the mode changeover switch, and when the electromagnetic clutch is in the ON state, the electromagnetic clutch in the ON state is The rotational force from the rotational shaft is transmitted to the developing roller shaft by a pair of gears connected to each other, and when the electromagnetic clutch is in the OFF state, the rotational force from the rotational shaft is transmitted to the development roller shaft by a pair of gears equipped with the one-way clutch. An image forming device characterized by transmitting information to a roller shaft. (3) The image forming apparatus according to claim 2, wherein the gear pair incorporating the one-way clutch is used when rotating the developing roller shaft at the slowest speed.