JPH08220869A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of accurately detecting the concentration of toner in a developing unit and outputting a stable image. CONSTITUTION: The image forming device is provided with a two-component magnetic brush developing system developing unit 40 having a toner concentration sensor for magnetically detecting the mixing ratio of toner and carrier, a variable speed main motor at least driving a photoreceptor, a motor used exclusively for developing 70 driving the developing unit 40 at a constant speed regardless of the rotational speed of the main motor and further, a sensor driving voltage control means for changing the driving voltage of the toner concentration sensor in accordance with the rotational speed of the main motor.

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 such as a copying machine, a facsimile and a printer.

[0002]

2. Description of the Related Art Conventionally, as an apparatus for forming an image by exposing a photosensitive member to an image with a light beam, there are some image forming apparatuses configured to be capable of recording images at a plurality of pixel densities by changing the pixel density. Has been proposed (Japanese Patent Laid-Open No. Hei 5)
"Image forming apparatus" described in Japanese Patent Laid-Open No. 197263, "Optical printing apparatus" described in Japanese Patent Application Laid-Open No. 2-79060, Japanese Patent Publication No.
"Laser beam recording device" described in JP-A-19551). The switching of the pixel density in these image forming apparatuses is basically performed by the frequency of the pixel clock and the rotation speed of the polygon mirror, that is, the exposure scanning speed of the image, as disclosed in Japanese Patent Laid-Open No. 5-197263. , By changing the combination with the rotation speed of the photoconductor.

Further, conventionally, as a developing device of an electrophotographic image forming apparatus, a two-component magnetic brush developing type developing device using a developer in which a toner and a carrier are mixed is widely used. It is also well known to control the mixing ratio of the toner and the carrier, that is, the toner concentration of the developer for stabilization. In order to control the toner density, a toner density sensor (hereinafter referred to as a T sensor) that magnetically detects the toner density in the developing device has been proposed (Japanese Patent Publication No. 3-71068 and Japanese Utility Model Publication No. 3-10768). "Magnetic detection device" described in Japanese Patent No. 55895).

[0004]

By the way, the T sensor in the developing device of the conventional image forming apparatus usually has a different detection value depending on the flow of the magnetic material (developer) on the sensor surface. Is stably driven, initial setting is performed to set the drive voltage of the T sensor so that the developer having a known toner concentration is detected at a certain specific value. However, in an image forming apparatus equipped with a drive system that drives both the photoconductor and the developing device by the main motor, if the rotational speed of the photoconductor is changed in order to switch the pixel density of the image formed on the photoconductor, Since the driving speed of the developing device also changes in accordance with the change of the rotation speed of the photoconductor, the flow of the developer in the developing device (flow velocity, flow rate, etc.) changes, so that the toner concentration is detected by the T sensor. If it is not correctly detected, the toner density in the developing device becomes improper, and a stable image cannot be output.

The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of accurately detecting the toner density in a developing device and outputting a stable image. To do.

[0006]

In order to solve the above-mentioned problems, the present invention provides a two-component magnetic brush developing device according to claim 1, which is equipped with a toner concentration sensor for magnetically detecting the mixing ratio of toner and carrier. In an electrophotographic image forming apparatus including a developing device of a system and a variable speed main motor for driving a photoconductor, a dedicated developing motor for driving the developing device at a constant speed regardless of the rotation speed of the main motor. Is provided.

According to a second aspect of the present invention, there is provided a two-component magnetic brush developing type developing device equipped with a toner concentration sensor for magnetically detecting the mixing ratio of toner and carrier, and a variable speed main motor for driving at least the photoconductor. The electrophotographic image forming apparatus has a configuration including sensor drive voltage control means for changing the drive voltage of the toner concentration sensor according to the rotation speed of the main motor.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 shows an example of the configuration around the photoconductor of the image forming apparatus in which the present invention is implemented. In FIG. 3, an image forming means for forming an image on the photoconductor 1 by a well-known electrophotographic method is arranged around the photoconductor 1. The image forming means includes a first charger 2, a first exposure device 3, a first developing device 4, a second charger 5, a second exposure device 6, a second developing device 7,
Transfer / separation device 8, P sensor 9, cleaning device 1
0, static eliminator 11, and the like.

Here, the first charger 2 is (-) in the dark.
The corona discharge is controlled by the grid to charge the photoconductor 1 to a constant potential. The first exposure device 3 forms an electrostatic latent image of a black image on the photoconductor 1 by erasing the (−) charges on the photoconductor 1 by the laser diode emitting light corresponding to the black image. The first developing device 4 has (-) on the photoconductor 1.
A (-) charged black toner is attached to the part where the charge is erased (black image part) to form a visible image. Second charger 5
Represents the potential of the photoconductor 1 attenuated by the black image formation (-).
It is restored by the corona discharge of. The second exposure device 6 forms an electrostatic latent image of a red or blue image on the photoconductor 1 by causing the LED array to emit light for the red or blue image and erasing the (-) charge on the photoconductor 1. To do. Second developing device 7
Is a non-magnetic one-component non-contact developing method, which allows (-) charged red or blue toner to adhere to the electrostatic latent image portion of a red or blue image without disturbing the previously formed black image. Form a visual image. The transfer / separation device 8 applies a (+) bias to the transfer belt to transfer a black and red (or blue) visible image (toner image) charged to (−) onto the transfer paper 12 and conveys it. . Further, it has a separation claw for surely separating the transfer paper 12 from the photoconductor 1. P sensor 9
Reads the black image density of a fixed pattern developed on the photoconductor 1 with a photo sensor, and feeds back the detection signal to the toner replenishment control circuit of the toner replenishing device (for the first developing device 4) for black toner to feed the black image. Image control. The cleaning device 10 scrapes off the toner remaining on the photoconductor 1 after transfer with a cleaning blade, and collects the waste toner (residual toner) with a cleaning brush. Static eliminator 11
Prepares for the next copy by exposing (decharging) the entire surface of the photoconductor 1 with an LED to erase the (−) charge remaining on the photoconductor 1.

Although the above-mentioned image forming apparatus has a structure capable of performing two-color copying, since two-color copying is not directly related in the present invention, as an example thereof, the above-mentioned second charger 5, The second exposure device 6 and the second developing device 7 may be omitted.

FIG. 4 shows a general developing unit (first developing device 4 in FIG. 3) of an image forming apparatus in which the present invention is implemented.
A configuration example of is shown. The developing unit 40 is a dry two-component magnetic brush developing type developing device that uses a developer in which toner and carrier are mixed.

In FIG. 4, the developer is the paddle roller 4
1 is transferred to the upper developing sleeve 42 by being flipped up,
The doctor blade 43 regulates the thickness to a constant value, and the upper developing sleeve 42 and the lower developing sleeve 44 carry the photosensitive member 1 to a corresponding developing portion. And in this state,
First development P.I. By applying a developing bias to the upper developing sleeve 42 and the lower developing sleeve 44 by P,
The electrostatic latent image formed on the photoconductor 1 is developed (visualized).

The remaining developer regulated by the doctor blade 43 flows toward the separator, is agitated from the front to the back by an oblique guide (not shown) provided in the separator 46, and is circulated to the paddle roller 41. It
Here, a part of the developer on the back side of the separator 46 flows directly to the carrying screw 47 without passing through the separator 46, and is agitated from the back to the front by the carrying screw 47, and the paddle roller 41 and the agitating roller. It is cycled to 48.

The upper part of the developing unit 40 is
An air filter 49 for depressurizing the inside of the unit is provided. Further, above the stirring roller 48 of the developing unit 40, a toner replenishing unit 50 for replenishing new toner by an amount corresponding to the amount of toner consumed by the developing is disposed (see FIG. 4). (Dashed line display).
The toner replenishing unit 50 includes a toner hopper 51 for accommodating new toner, a toner agitating screw (agitator) 52 for agitating toner, and a toner replenishing roller 53 for quantitatively replenishing toner from inside the toner hopper 51. Has been done.

The toner concentration of the developer in the developing unit 40 is T, which is disposed in the developer flow path below the stirring roller 48.
A sensor (toner concentration sensor) 60 magnetically detects the mixing ratio of the toner and the carrier, and the toner replenishing roller 53 is appropriately rotated according to the detection value of the T sensor 60 to cause the developing unit 40 of the developing unit 40 to rotate. By supplying new toner onto the stirring roller 48, it is controlled so as to always maintain the proper density.

By the way, the electrostatic latent image formation of the black image in the image forming apparatus of this embodiment is performed by the raster scan in which the laser light emitted from the laser diode is polarized by the polygon mirror. Further, in the image forming apparatus of the present embodiment, during normal copying as a copying machine, recording is performed with a pixel density of, for example, 400 dpi. 60
It is possible to record even with a pixel density such as 0 dpi.

As a method of switching such pixel densities according to the use, for example, when recording at a pixel density of 400 dpi or less, the speed of the photosensitive member 1 is not changed and the clock frequency is set in the main scanning direction and the sub-scanning direction. The pixel density is switched by making it proportional to the product of the pixel density in the scanning direction and making the rotation speed of the polygon mirror proportional to the pixel density in the sub-scanning direction. That is, when the pixel density is set to 300 dpi, for example, the clock frequency is set to 9/16 times as high as that when the pixel density is 400 dpi, and the rotation speed of the polygon mirror is set to 3/4.
Double it.

However, in this method, when the pixel density is set to, for example, 600 dpi and the pixel density is switched in the same manner as described above, the clock frequency and the rotation speed of the polygon mirror become extremely high values. I will end up.
Therefore, when switching to such a high pixel density, a method of reducing the rotation speed of the photoconductor 1 is adopted. In other words, this method does not change the speed of the polygon mirror,
The rotation speed of the photoconductor 1 is inversely proportional to the pixel density in the sub scanning direction, and the clock frequency is proportional to the pixel density in the main scanning direction. Specifically, the rotation speed of the photoconductor 1 is set to 2/3 times,
Increase the clock frequency by 3/2.

However, in an image forming apparatus provided with a drive system for driving both the photoconductor 1 and the developing unit 40 by the same main motor, in order to switch the pixel density of the image formed on the photoconductor 1. When the rotation speed of the photoconductor 1 is changed, the driving speed of the developing unit 40 is also changed with the change of the rotation speed of the photoconductor, and the flow of the developer (flow velocity, flow rate, etc.) in the developing unit 40 is changed. Resulting in. Therefore, in this type of image forming apparatus, although the toner concentration of the developer in the developing unit 40 is actually maintained at an appropriate value, the T sensor 60 operates at 400 dpi and 600 dpi. Since the toner concentration detection values are detected as different values, the toner concentration of the developer in the developing unit 40 cannot be detected correctly, the toner concentration in the developing unit 40 becomes incorrect, and a stable image can be output. There is a problem that disappears.

Therefore, in the image forming apparatus of the present invention, as shown in FIG.
As shown in, the developing unit 40 is driven at a constant speed by using the developing-dedicated motor 70 regardless of the rotation speed of the main motor. That is, in FIG. 1, the development-dedicated motor 70 is driven from the drive system of the photoconductor 1 via the first gear train 71, the timing belt 72, the second gear train 73, the developing drive clutch 74, and the toner replenishment clutch 75. The developing unit 40 is independently driven at appropriate times. Therefore, in the image forming apparatus of the present invention, even if the rotation speed of the photoconductor 1 changes due to the switching of the pixel density, the developing unit 40 is always driven by the developing motor 70 at a constant speed. The flow of the developer in the developer 40 (flow rate, flow rate, etc.) does not change, the toner concentration of the developer in the developing unit 40 is always accurately detected, and a stable image is output.

In the image forming apparatus of the present invention, the drive voltage of the T sensor (toner density sensor) 60 is changed by the sensor drive voltage control means 80 (see FIG. 4) according to the rotation speed of the main motor. With this configuration, the same effect as that of the first embodiment can be obtained. That is, in this image forming apparatus, as shown in FIG. 2, the change amount of the output of the T sensor 60 of the developing unit 40 due to the switching of the pixel density is controlled and corrected by the sensor drive voltage control unit 80. Therefore, in the image forming apparatus of the present invention, the driving speed of the developing unit 40 changes in accordance with the change of the rotation speed of the photoconductor 1 due to the switching of the pixel density, and the flow of the developer in the developing unit 40 (flow rate and Even if the flow rate) changes, the change in the output of the T sensor 60 due to the change is corrected and controlled by the sensor drive voltage control means 80, so that the toner concentration of the developer in the developing unit 40 is always accurately detected, A stable image is output.

In the second embodiment, both the photosensitive member 1 and the developing unit 40 may be configured to be driven by the same main motor, or, similarly to the first embodiment, the photosensitive member 1 The body 1 and the developing unit 40 may be driven by separate motors. Here, when the photoconductor 1 and the developing unit 40 are configured to be driven by separate motors, there is an advantage that the driving speed of the developing unit 40 can be set to an optimum speed for development. When the developing unit 40 and the developing unit 40 are both driven by the same main motor,
The drive system of the developing unit 40 can be simplified to reduce the cost.

[0023]

As described above, according to the present invention, in claim 1, even if the rotation speed of the photoconductor changes due to the switching of the pixel density, the developing unit is always driven at a constant speed by the developing-dedicated motor. Therefore, the flow (velocity, flow rate, etc.) of the developer in the developing unit becomes constant, and the developing unit 40
The toner concentration of the developer inside can be accurately detected, and a stable image can be output.

In the second aspect, the driving speed of the developing unit 40 changes with the change of the rotation speed of the photosensitive member 1 by switching the pixel density, and the flow of the developer in the developing unit 40 (flow rate, flow rate, etc.). ) Changes, the change in the output of the T sensor 60 due to this is corrected and controlled by the sensor drive voltage control means, so that the toner concentration of the developer in the developing unit 40 can be accurately detected, and a stable image can be obtained. Can be output.

If the photoconductor and the developing unit are driven by separate motors, there is an advantage that the driving speed of the developing unit can be set to an optimum speed for developing. When the developing unit and the developing unit are both driven by the same main motor, the driving system of the developing unit can be simplified and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view of a drive system of a developing unit for explaining a first embodiment of an image forming apparatus of the present invention.

FIG. 2 is a graph showing the relationship between T sensor output and toner density for explaining the second embodiment of the image forming apparatus of the present invention.

FIG. 3 is a schematic diagram showing a configuration example around a photoconductor of an image forming apparatus in which the present invention is carried out.

FIG. 4 is a cross-sectional view showing a configuration example of a developing unit of the image forming apparatus in which the present invention is implemented.

[Explanation of symbols]

 1 Photoconductor 40 Development Unit 60 Toner Density Sensor (T Sensor) 70 Development Motor 80 Sensor Drive Voltage Control Unit

Claims (2)

[Claims] 1. An electrophotographic apparatus having a two-component magnetic brush developing type developing device equipped with a toner concentration sensor for magnetically detecting the mixing ratio of toner and carrier, and a variable speed main motor for driving at least a photoconductor. In the image forming apparatus of the system, an image forming apparatus is provided with a developing-dedicated motor that drives the developing device at a constant speed regardless of the rotation speed of the main motor. 2. An electrophotographic apparatus having a two-component magnetic brush developing type developing device equipped with a toner density sensor for magnetically detecting the mixture ratio of toner and carrier, and a variable speed main motor for driving at least a photoconductor. In the image forming apparatus of the type, an image forming apparatus is provided with a sensor drive voltage control means for changing the drive voltage of the toner concentration sensor according to the rotation speed of the main motor.