JPH09146361A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a copy whose image quality is always stable irrespective of a copy mode. SOLUTION: The device is equipped with a toner recycling mechanism which returns recovered toner to a developing device 100 by scraping the toner off an image carrier 1 by means of the cleaning blade 201 of a cleaner 200. On the bottom of the toner hopper 130 is a replenishment roller 131 which replenishes the developing container 101 of the developing device 100 with toner from the toner hopper 130 according to whether a patch image density has reached the specific density or not. In special-size copy mode, the specific density is controlled so that toner is added more than in ordinary copy modes, by rotating the replenishment roller 131, provided on the bottom of the toner hopper 130, more than in the other copy modes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for visualizing an electrostatic latent image or the like formed on the surface of an image carrier as a toner image, and particularly to suppress the reduction of copy image density as much as possible. The present invention relates to the image forming apparatus.

[0002]

2. Description of the Related Art During execution of an image forming process, a developing device is replenished with both toner from a toner hopper and toner collected from an image carrier, and a stable image quality is obtained in either an intermittent copy mode or a continuous copy mode. An image forming apparatus to be obtained has been proposed (see Japanese Patent Publication No. 14794/1992).

[0003]

However, both the intermittent copy mode and the continuous copy mode, which can be supported by the conventional image forming apparatus (see Japanese Patent Publication No. 4-14794), detect the size of the transfer material and perform the image forming process. However, it does not correspond to the special size mode in which the image forming process is executed at the maximum size without detecting the size of the transfer material.

The special size mode is, for example, A4.
When copying a small size such as B5, the ratio of the non-image area to the image area transferred to the transfer material becomes large. As a result, the special size mode has a large non-image area as compared with the intermittent copy mode, and thus a large amount of collected toner is generated. Further, in the special size mode, since the developing device is driven for a long time, the charge amount of the developer is reduced and it becomes difficult to supply the toner from the toner hopper. For this reason, in the special size mode, the ratio of the collected toner in the developing device becomes large, the developing property and the transfer property are deteriorated, and the image deteriorates. Further, since the collected toner is inferior in cleaning property, poor cleaning of the image carrier causes deterioration of the image. For the above-mentioned reason, the conventional image forming apparatus (see Japanese Patent Publication No. 4-14794) cannot support the special size mode.

In view of the above problems, an object of the present invention is to provide an image recording apparatus capable of always obtaining stable image quality regardless of the copy mode.

[0006]

The above object is achieved by the following constitution.

(1) A recycling mechanism for returning the collected toner cleaned from the image carrier to the developing device and a toner replenishing mechanism for replenishing the toner from the toner hopper to the developing device depending on whether the patch image density has reached a predetermined density. An image forming apparatus comprising: a control unit that replenishes a predetermined amount of toner from a toner hopper in a special size copy mode more than in other copy modes.

(2) The control means changes the threshold value for judging whether or not to replenish toner from the toner hopper with the image density detected from the patch image in the special size mode and other copy modes ( The image forming apparatus of 1).

(3) The other copy mode is a mode for detecting the size of the transfer material (1)
Alternatively, the image forming apparatus of (2).

According to the above configurations (1) to (3), the ratio of the recovered toner in the developing device can be suppressed by controlling the toner supplied from the toner hopper to be increased in the special size copy mode. It is possible to suppress deterioration of developability and transferability, suppress occurrence of cleaning failure, and stably obtain a good image.

[0011]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a vertical sectional view showing the image forming apparatus of this embodiment, and FIG. 2 is a horizontal sectional view showing the structure of the image forming apparatus of this embodiment.

The image forming apparatus of this embodiment is shown in FIGS.
As shown in FIG. 3, a toner recycling mechanism for returning the collected toner to the developing device 100 by scraping it off from the image carrier 1 with the cleaning blade 201 of the cleaning device 200 is provided, and depending on whether or not the patch image density has reached a predetermined density. Toner is developed from the toner hopper 130 to the developing device 10.
Replenishing roller 131 for replenishing 0 developing container 101
Is provided at the bottom of the toner hopper 130, and a predetermined density is provided at the bottom of the toner hopper 130 in the special size copy mode compared to other copy modes.
Is provided with a CPU 10 for controlling so as to replenish a larger amount of toner than in the normal copy mode by rotating a large number of.

The image forming apparatus of the present embodiment, which executes an electrophotographic process, includes a charger, an image exposure device, a transfer device, a separator, and a fixing device, which are not shown.

The image forming apparatus of this embodiment is provided with a manual feed mechanism for use in the special size mode in addition to a universal cassette or a mechanism for feeding a transfer material from a normal cassette as a paper feed mechanism.

The special size mode is a mode in which the electrophotographic image forming process is executed with the maximum image size without detecting the size of the transfer material, for example, the manual feed mode. The other copy mode is a mode in which the size of the transfer material is detected and the electrophotographic process is executed in that size.

The respective structures of the toner recycling mechanism and the toner replenishing mechanism, which are the main components of the image forming apparatus of this embodiment, will be described below with reference to FIGS. 1 and 2.

The image carrier 1 is a photosensitive drum, which irradiates the surface of a photosensitive drum with light to form an electrostatic latent image, and rotates in the direction of arrow a shown in FIG.

In the developing device 100, as shown in FIGS. 1 and 2, a developing roll 112 is arranged facing the image carrier 1 and a paddle for supplying the developing roll 112 with a developer D composed of toner and a magnetic carrier. Agitating / mixing member 121, 1 that conveys the wheel 113 and the developer while mixing and agitating the developer.
22 are arranged. The mixing / stirring member 121 and the mixing / stirring member 122 are arranged in parallel with each other along the longitudinal direction, and are separated by a partition plate 115 except both ends thereof. A developer layer regulating member 114 is arranged above the developing roll 112, and regulates the layer thickness of the developer D conveyed onto the developing roll 112 to a predetermined thickness. The mixing and stirring member 121 and the mixing and stirring member 122 have the same shape as each other, and the mixing and stirring members 121b and 122b are attached to the outer peripheral portion of the rotating shaft 121a. The mixing and stirring members 121 and 122 are conveyed in different directions and circulated around the partition plate 115. The developing roller 112 is formed of a non-magnetic material in a cylindrical shape, and includes a developing sleeve 112a rotatable by a motor (not shown) and a magnet roller 111 fixedly arranged inside the developing sleeve 112a. The magnetic force of the magnet roller 111 forms a magnetic brush of the two-component developer D composed of a magnetic carrier and toner on the surface, and the bias voltage applied to the developing roll 112 and the rotation of the developing sleeve 112a cause the image carrier 1 to rotate. By rubbing the electrostatic latent image formed on the surface of the toner, the toner image is visualized.

The toner hopper 130 is for loading toner, and a new toner is provided on the upper surface of the developing container 101 so as to face the end of the mixing and stirring member 122 by rotating the supply roller 131 with the motor M. Toner supply port 1
It is supplied from 01a. The toner hopper 130 is a toner replenishing mechanism. The replenishment control circuit from the toner hopper 130 will be described later with reference to FIG.

As is well known, the cleaning device 200 has the image carrier 1 even after the toner image is transferred from the image carrier 1.
The image carrier 1 is cleaned by scraping off the toner remaining on the surface with the cleaning plate 201. The cleaning device 200 is provided with a mixing and stirring member 202 by tilting the bottom of the device in order to return the collected toner to the developing container 101 of the developing device 100. The cleaning device 200 has an opening 200a at the bottom. The collected toner is sent out through the opening 200a.
The conveying pipe 210 connects the opening 200a at the bottom of the cleaning device 200 and the toner supply port 101b of the developing device 100, and as shown in FIG.
11 and the collected toner is rotated by rotating such a mixing and stirring member 211.
It is to be transported to 01b.

As described above, the toner recycling mechanism is a mechanism for returning the collected toner from the cleaning device 200 to the toner replenishing port 101b of the developing container 101 by the conveying pipe 210.

The mixing / stirring members 202 and 211 have substantially the same structure as the above-mentioned stirring / mixing members 121 and 122, and a description thereof will be omitted. The above is the schematic mechanical configuration of the image forming apparatus of this embodiment.

FIG. 3 is a block diagram showing a toner density control circuit adopted in the image forming apparatus of this embodiment, and FIG. 5 is a graph showing the relationship between the image density sensor output and each threshold value.

The toner concentration control circuit of this embodiment is a CPU
10, the image density sensor 20, the operation panel 30, the motor driver 40, and the motor M, the reflection density of the patch image is detected as a voltage, and the detection value is compared with a threshold value. The toner is supplied to the developing container 101 by rotating the
Its main purpose is to control the toner density in 1 to a predetermined value, and it further has a function of changing the control state between the special size mode and other copy modes. The configuration of each part will be described below.

The CPU 10 detects the optical reflection density of the patch image to control the toner density in the developing container 101 of the developing device 100 to a predetermined value, and also distinguishes between the special size mode and other copy modes to obtain the patch image. It has a function of changing the threshold value for determining whether or not to replenish the toner from the toner hopper 130 based on the optical reflection density detected from.

The relationship between the threshold value set by the CPU 10 and the image density sensor output will be described with reference to FIG.

In this embodiment, the output voltage from the image density sensor 20 is amplified to less than 5 (V) at maximum, and if the toner density decreases, the optical reflection density also decreases. In the graph shown, the output is high, and as the toner concentration increases, the optical reflection density also increases, so the output in the graph shown in FIG. 5 becomes low. Therefore, the threshold value used in the special size copy mode is set lower than the threshold value a used in the other copy modes as indicated by the dotted line b. Therefore, the CPU 10 selectively uses either the threshold value a or the threshold value b based on the mode signal.

The image density sensor 20 is, for example, the image carrier 1.
The optical reflection density from the patch image formed in the non-image area of the
D21 and a phototransistor 22 which receives the reflected light from the patch image and photoelectrically converts it. The LED 21 is connected to a drive power source 23 and a variable resistor 24 for controlling the voltage applied to the LED 21 in order to control the amount of light emission. The phototransistor 22 includes voltage dividing resistors 25 and 26 for converting an emitter current into a voltage and an amplifier circuit 2 for boosting a terminal voltage of the voltage dividing resistor 26 to a drive voltage 5V of the CPU 10.
7 is connected. The output voltage from the amplifier circuit 27 is CP
It is input to U10.

The operation panel 30 is used for instructing an operation method, and in particular, a CPU sends a mode signal indicating whether the special size mode or another copy mode is selected.
It is to be sent to 10.

The motor driver 40 drives the motor M with a control signal from the CPU 10, and
The motor M is rotationally driven for the driving time and the number of rotations set from the above.

The motor M is a motor for driving the supply roller 131.

In the image forming apparatus of this embodiment, the image carrier 1 and the developing sleeve 112 of the developing device 100, the mixing and agitating member 121, and the mixing and stirring member 121, are provided by a single main motor (not shown) in order to reduce the cost. 122, the mixing and stirring member 202 of the cleaning device 200, and the paper feeding system are collectively driven.

The above is the electrical schematic configuration of the image forming apparatus of this embodiment.

Next, the toner density control operation of the image forming apparatus of this embodiment will be described with reference to FIG.

FIG. 4 is a flow chart showing the toner density control operation of this embodiment.

The operator inputs the paper feed tray from the operation panel 30 (step 1). As a result, the operation panel 30 sends a mode signal to the CPU 10.

The CPU 10 determines whether or not the state of the mode signal is manual copy in the special size mode (step 2). If the CPU 10 determines in step 2 that the manual feed mode is set, the CPU 10 sets the paper feed stage flag to "0" (step S3). It is set to 1 "(step S4). The CPU 10 proceeds to step S5.

The CPU 10 operates the operation panel 3 in step 5.
When the pressing of the copy button provided at 0 is detected, the state of the paper feed stage flag is confirmed (step 6).

Here, in the developing device 100, the developing container 1
The developer D filled in 01 is the paddle wheel 113.
Is conveyed to the developing roll 112 side. Developing roll 1
In 12, the peripheral developing sleeve 112a rotates counterclockwise as shown in FIG. 3, whereby the developer D is conveyed to the developing area facing the image carrier 1. The developer D on the developing sleeve 112a is regulated to an appropriate thickness by the developer layer regulating member 114, and then exerts a developing action on the electrostatic latent image formed on the surface of the image carrier 1 in the developing region. As a result, the toner in the developer D is consumed. At this time, the patch image is simultaneously developed on the non-image portion, and the image density sensor 20 detects the reflection density of the patch image.

If the paper feed stage flag is "0" in the judgment at step 6, the CPU 10 outputs the output voltage from the image density sensor 20 to 2 (V) by the threshold value b shown by the solid line in FIG.
Whether or not the above is confirmed (step 7). CPU1
If 0 is judged to be 2 (V) or more in step 7,
A predetermined drive signal is sent to the motor driver 40 (step S8). The CPU 10 activates a built-in replenishment timer at the same time when the drive signal is transmitted.

Here, toner is replenished from the toner replenishing port 101b into the developing container 101. The toner and the developer D that have entered the developing container 101 are mixed by the spiral blade members 121b and 122b of the mixing and stirring member 122 and are conveyed while being stirred.

Thereafter, the developer D is mixed and stirred by the mixing member 121.
Thus, the paddle wheel 113 is moved to the right while being partially exchanged. As a result, the density of the toner conveyed to the high toner side of the developer D is increased as a whole.

The CPU 10 refers to the count value of the replenishment timer and confirms whether the counting is completed for a predetermined time (step 9). When the CPU 10 detects the count-up of the replenishment timer, it outputs a drive stop signal to the motor driver 40.
To stop the rotation of the motor M (step 10).

The CPU 10 confirms the counter value of the built-in copy counter, and if the predetermined number has not been reached (step 11), returns to step 6.

In the developing device 100, the developer D filled in the developing container 101 in step 6 is conveyed to the developing roll 112 side by the paddle wheel 113. In the developing roll 112, the surrounding developing sleeve 112a is shown in FIG.
By rotating in the counterclockwise direction, the developer D is conveyed to the developing area facing the image carrier 1. The developer D on the developing sleeve 112a is the developer layer regulating member 1
After being regulated to have an appropriate thickness by 14, the developing action is exerted on the electrostatic latent image formed on the surface of the image carrier 1 in the developing area, whereby the toner in the developer D is consumed.

On the other hand, when the CPU 10 sets the paper feed stage flag to "1" in step 6, whether the output voltage from the image density sensor 20 is 3 (V) or more by the threshold value a shown by the dotted line in FIG. It is confirmed whether or not (step 12). CPU1
When 0 is determined to be 3 (V) or more in step 12, a predetermined drive signal is sent to the motor driver 40 (step S8). The CPU 10 activates a built-in replenishment timer at the same time when the drive signal is transmitted. CPU10
Refers to the count value of the replenishment timer, and confirms whether the counting is completed for a predetermined time (step 9). CPU1
When 0 counts up the replenishment timer, the drive stop signal is sent to the motor driver 40 to stop the rotation of the motor M (step 10). If the CPU 10 determines in step 10 that the predetermined number has been reached, the operation is ended.

Since the toner recycling mechanism is driven while the main motor (not shown) is rotating, the collected toner is always supplied to the developing device 100.

As described above, the image forming apparatus of this embodiment is
Toner hopper 1 for special size copy mode
By controlling the amount of toner supplied from 30 to be large, the ratio of the collected toner in the developing container 101 can be suppressed, so that the deterioration of the developing property and the transfer property can be suppressed, and the occurrence of cleaning failure can be suppressed to obtain a good image. It can be stably obtained.

[0050]

As described above, the present invention can provide an image recording apparatus having the above-mentioned configuration, which can always obtain a stable image quality regardless of the copy mode.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing an image forming apparatus of this embodiment.

FIG. 2 is a cross-sectional view showing the configuration of the image forming apparatus according to this embodiment.

FIG. 3 is a block diagram showing a toner density control circuit adopted in the image forming apparatus of this embodiment.

FIG. 4 is a flowchart showing a toner density control operation of this embodiment.

FIG. 5 is a graph showing a relationship between an image density sensor output and each threshold value.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 10 CPU (equivalent to control means) 20 Image density sensor 100 Developing device 111 Magnet roll 112 Developing roll 112a Developing sleeve 113 Paddle wheel 130 Toner hopper 200 Cleaning device 210 Conveying pipe

Claims (3)

[Claims] 1. A recycling mechanism for returning collected toner cleaned from an image carrier to a developing device and a toner replenishing mechanism for replenishing toner from the toner hopper to the developing device depending on whether or not a patch image density has reached a predetermined density. An image forming apparatus comprising: an image forming apparatus including control means for supplying a larger amount of toner from a toner hopper in a special size copy mode with the predetermined density than in other copy modes. 2. The control means changes a threshold value for determining whether to replenish toner from a toner hopper with an image density detected from a patch image in a special size mode and another copy mode. 1. The image forming apparatus according to 1. 3. The image forming apparatus according to claim 1, wherein the other copy mode is a mode for detecting a size of a transfer material.