JPH04329566A - Image density controller - Google Patents

Abstract

PURPOSE:To keep image density and the toner concentration of developer constant. CONSTITUTION:In the case that the toner concentration is within a specified range based on the result of the detection of the toner concentration by a developer concentration sensor (F sensor) 118, a toner replenishment control circuit 122 controls toner replenishment based on the result of the detection of a reference toner image, which is formed by performing specified processing to a photosensitive body 101, by an optical sensor (P sensor) 106. Meanwhile, in the case that the toner concentration is out of the specified range the toner replenishment is controlled based on the result of detection by the F sensor 118, and further a magnetic roller revolving speed control circuit 120 controls the rotating speed of a magnetic roller 113 so that the image density may be kept appropriate.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an image density forming apparatus applied to an image forming apparatus using an electrophotographic method, and more specifically to an image density control that controls both developer density and image density. Regarding equipment.

0002

2. Description of the Related Art In an image forming apparatus applied to a copying machine or the like using an electrophotographic method, it is necessary to stabilize the image density in order to obtain good image quality. Generally, in order to stabilize the image density, toner supply control is performed to keep the toner density of the developer constant using the following method.

[0003] ■ A method of detecting the image density of a reference density pattern formed on a photoreceptor using an optical sensor and controlling toner replenishment so that the image density of the reference density pattern is constant (so-called P sensor method). . ■ Detecting the mixing ratio of a two-component developer composed of toner and carrier as changes in the magnetic permeability, dielectric constant, and fluidity of the developer;
A method of controlling toner supply so that these detected values are constant (so-called F sensor method). (2) A method of correcting toner density using the F sensor method based on the density level of the image density of a reference density pattern detected using the P sensor method (Japanese Patent Application Laid-open No. 136667/1983).

0004

[Problems to be Solved by the Invention] According to the conventional P sensor type toner replenishment control, when the developer and photoreceptor deteriorate due to changes over time, it is impossible to maintain a constant toner concentration in the developer. If the density is controlled high, scumming and toner scattering will occur, and if the toner density is controlled low, carriers may adhere to the photoconductor, damaging the photoconductor and putting a strain on cleaning. There was a problem.

Another problem with the F-sensor method is that, because the developer and photoreceptor deteriorate over time, variations in image density cannot be prevented even if the toner concentration in the developer is kept constant. was there.

Furthermore, according to the method disclosed in Japanese Unexamined Patent Publication No. 57-136667, toner density is controlled using a P sensor and an F sensor. Since this method corrects the toner density detected by the F sensor, there is a problem that the same problem as the P sensor method may occur.

The present invention has been made in view of the above, and an object of the present invention is to keep the image density and the toner density of the developer constant.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an image density sensor for detecting the image density of a reference toner image formed on a photoconductor, and a developing sleeve having a magnetic roller therein. An image applied to an electrophotographic image forming apparatus comprising a developing device, a developer concentration sensor for detecting toner concentration in the developing device, and toner replenishing means for supplying toner to the developing device. In the density control device, a toner replenishment control means for controlling the toner replenishment means based on the detection results of the image density sensor and the developer concentration sensor; and a toner replenishment control means for controlling the toner replenishment means based on the detection results of the image density sensor and the developer concentration sensor Accordingly, there is provided an image density control device comprising magnet roller rotation control means for controlling the rotation speed of the magnet roller.

Further, in the above-described configuration, the toner replenishment control means controls the toner replenishment means based on the detection result of the developer concentration sensor when the detection result of the developer concentration sensor is outside a predetermined range; When the detection result of the developer concentration sensor is within a predetermined range, it is desirable to control the toner replenishing means based on the detection result of the image density sensor.

Further, in the above-described configuration, when the detection result of the developer concentration sensor is outside a predetermined range, the magnet roller rotation control means, based on the detection result of the image density sensor,
It is desirable to vary the rotational speed of the magnetic roller.

[0011]

[Operation] In the image density control device according to the present invention, if the toner density is within a predetermined range based on the detection result of toner density by the developer density sensor (F sensor), the toner is formed on the photoreceptor by a predetermined process. A reference toner image is detected by an optical sensor (P sensor), and toner replenishment control is executed based on the detection result. If the toner density is outside the predetermined range, toner replenishment control is executed based on the detection result of the F sensor, and further, rotation speed control of the magnetic roller is executed so that the image density is maintained at an appropriate density.

0012

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic cross-sectional view of an image forming apparatus to which an image density control device of the present invention is applied, and shows reflected light (
A photoreceptor 101 that forms an electrostatic latent image upon exposure (light exposure); a charger 102 that applies charging to the surface of the photoreceptor 101 prior to exposure; and a charger 102 that removes the charged potential of non-image areas on the photoreceptor 101. An eraser 103, a developer 104 that attaches (develops) toner to the electrostatic latent image formed on the photoreceptor 101, and a developer 104 that transfers the toner image on the photoreceptor 101 onto a conveyed recording paper (not shown). It is composed of a transfer/separation charger 105 that separates the recording paper after the transfer process from the photoreceptor 101, and a phototransistor and an LED that detect the image density (toner amount) of a reference toner image formed by a predetermined process. reflective optical sensor (P sensor)
106, a cleaning unit 107 that removes residual toner on the photoreceptor 101 after the transfer process, a static elimination lamp 108 that erases the residual charge on the photoreceptor 101 after the cleaning process, and a toner image fixed on the recording paper. A fixing device 109 performs processing.

The developing device 104 is roughly divided into a developing section that performs a developing process on the electrostatic latent image on the photoreceptor 101, and a toner replenishing section that supplies toner to the developing section. The toner supply unit includes a toner hopper 110 filled with toner to be supplied.
and a toner supply roller 111 that discharges toner from a toner hopper 110. On the other hand, the developing section includes a paddle 112 that stirs the toner and carrier discharged from the toner hopper 110 and triboelectrically charges the toner and carrier, and a magnet roller 113 having a magnet disposed at a predetermined position inside, and a photoreceptor. Developing sleeve 114 that conveys toner to 101
, a doctor blade 115 for regulating the developer on the developing sleeve 114, and a separator 116 for returning the excess developer regulated by the doctor blade 115 to the accumulation section near the paddle 112, to mix the toner and carrier. It consists of a mixing roller 117. Note that 118 is a developer concentration sensor (F sensor) that detects magnetic permeability that changes depending on the toner concentration of the developer.

Furthermore, an image density detection circuit 119 for amplifying and outputting the detection signal of the P sensor 106 and a magnet roller rotation speed for controlling the rotation of the magnet roller 113 by inputting the output of the image density detection circuit 119 are provided. A control circuit 120;
A developer concentration detection circuit 121 for amplifying and outputting the detection signal of the F sensor 118, and a developer concentration detection circuit 121.
A toner replenishment control circuit 122 is connected as shown in the figure to input the output of the toner replenishment roller 111 and execute toner replenishment control to the developing section by rotating the toner replenishment roller 111.

With the above configuration, image density and developer toner density control by the image density control device of the present invention will be explained. FIG. 2 shows a characteristic diagram of F sensor output with respect to toner concentration. As shown in the figure, the image density control device of the present invention executes different toner replenishment control outside and within the range between the upper and lower limits of the predetermined specified value, and the toner replenishment control is performed separately in each case. explain. In addition,
The F sensor 118 always detects the magnetic permeability of the developer, and the P sensor 106 detects the density of the reference toner image formed outside the image forming area of the photoreceptor 101 every predetermined number of copies from the LED. The reflected light is incident on a phototransistor and detected as an electrical signal.

First, the case within the range will be explained. A detection signal corresponding to the density of the reference toner image output by the P sensor 106 is input to an image density detection circuit 119. The image density detection circuit 119 amplifies the input signal and inputs it to the toner replenishment control circuit 120 and the toner replenishment control circuit 122. The toner replenishment control circuit 122 controls the toner replenishment roller 1 when the input signal is smaller than a predetermined value.
By rotating the toner hopper 11, so-called toner replenishment control is executed to discharge the toner in the toner hopper 110 to the developing section. In addition, in this case, the magnetic roller 11
No. 3 rotation control is performed.

Next, toner replenishment control in the case of outside the range will be explained. A detection signal from the F sensor 118 is input to a developer concentration detection circuit 121, where the signal is amplified and input to a toner replenishment control circuit 122. The toner replenishment control circuit 122 executes toner replenishment control when the detection signal of the F sensor 118 (input signal of the toner replenishment control circuit 122) is smaller than a predetermined value.

Further, when this control is performed, it means that the toner concentration of the developer cannot be controlled within a predetermined range by the toner replenishment control by the P sensor 106. Therefore, for example, when the F sensor 118 detects that the toner concentration is low (at this time,
If the detection result of the P sensor 106 is good), the image density will be increased by executing toner replenishment control. Therefore, control is required to keep the image density constant based on the detection signal of the P sensor 106. The present invention
This control is performed by changing the rotation speed of the magnet roller 113, and the detection signal of the P sensor 106 (actually, the signal from the image density detection circuit 119) is input to the magnet roller rotation speed control circuit 120, and the rotation speed of the magnet roller 113 is changed. The roller rotation speed control circuit 120 executes rotation control of the magnet roller 113 based on the input signal.

The function of the magnet roller 113 will now be explained. Developing sleeve 11 by developing sleeve 114
The developer conveyed in the rotational direction No. 4 (see FIG. 1) adheres to the electrostatic latent image and becomes visible in the development area A (see FIG. 1). At this time, the amount of developer conveyed is regulated by the doctor blade 115 so that the space between the photoreceptor 101 and the developing sleeve 114 is filled in the developing area.

The developer filling between the photoreceptor 101 and the developing sleeve 114 is removed by the rotation of the magnet roller 113 (see FIG. 1).
This causes it to vibrate violently (randomly). That is, due to the influence of magnetic lines of force caused by different magnetic poles passing alternately, the toner vibrates violently (randomly), and the development drag force (for example, intermolecular force, etc.) acting between the toner and the carrier is weakened. As a result, the toner is easily separated from the carrier, and the developing ability is improved. In addition, since the developer in the developing area A moves (conveys) at the same speed as the developing sleeve 114, by controlling the linear speed of the photoreceptor 101 and the developing sleeve 114 to be equal, it is possible to prevent the developer from being affected by the reverse electric field in the background area. The developer is no longer in contact with the image area, and it is possible to prevent abnormalities at the trailing edge of the image area in solid cloth and the like.

However, the photoreceptor 101 and the developing sleeve 11
If the linear speeds of No. 4 are the same, there is a problem that the developing ability decreases and uneven development may occur. Therefore, it is necessary to improve the developing ability by rotating the magnet roller 113. In other words, the rotation of the magnet roller 113 needs to satisfy the condition that the photoreceptor 101 encounters a plurality of magnetic poles while passing through the development area A.

The above-mentioned conditions will be explained in detail below. Here, the width of the developing area A is L, the linear velocity of the photoconductor 101 is VP, the rotation speed of the magnet roller 113 is N when the rotation direction of the photoconductor 101 is positive, and the diameter of the magnet roller is D.
The number of magnetic roller magnetic poles is P, and the linear velocity of the magnetic roller 113 is V.
Let it be M. Therefore, the time T1 required for one point of the photoreceptor 101 to move by the width L and the time T2 required for the photoreceptor 101 to meet from one magnetic pole to the next magnetic pole are as follows. T1 = L/VP T2 = πD/(P×|VP −VM |) Therefore, the number of magnetic poles M that the photoreceptor 101 encounters during time T1
is, M=T1/T2=(LP×|VP −VM
|)/πDVP. Here, VM = πDN/
60, so M=(LP×|VP −πDN/
60|)/πDVP. From the above, magnet roller 1
13 is controlled so that the number M of magnetic poles encountered by the photoreceptor 101 during time T1 is 2 or more.

[0023] As long as this condition is satisfied, the rotation of the magnet roller 113 contributes only to the developing ability. Also, Figure 3
As shown in the characteristic diagram of the amount of toner adhering to the photoconductor 101 (development amount) with respect to the development potential difference (potential of the photoconductor 101 - development bias potential), the amount of development can be easily controlled by controlling the rotation of the magnetic roller 113. Since it can be controlled, the reproduced image density (OD) can be adjusted to match the original image density (OD).
ID) can be accurately controlled.

As shown in FIG. 2, the toner replenishment control of the image density control device of the present invention is executed based on the detection signal of the P sensor 106 within the range of the upper and lower limits of the predetermined value. Out of range, F sensor 118
This is because there is some variation in the mixing ratio (magnetic permeability) of toner and carrier in the developing section.

[0025]

As is clear from the above, according to the present invention, there is provided an image density sensor for detecting the image density of a reference toner image formed on a photoreceptor, and a developing device having a developing sleeve having a magnetic roller therein. , an image density control device applied to an electrophotographic image forming apparatus, comprising a developer concentration sensor for detecting toner concentration in the developing device, and a toner replenishing means for supplying toner to the developing device. , a toner replenishment control means for controlling the toner replenishment means based on the detection results of the image density sensor and the developer concentration sensor; and a toner supply control means for controlling the toner replenishment means based on the detection results of the image density sensor and the developer concentration sensor; Since the magnetic roller rotation control means for controlling the rotation speed of the roller is provided, the image density and the toner density of the developer can be kept constant.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an image forming apparatus to which an image density control device according to the present invention is applied.

FIG. 2 is a characteristic diagram of F sensor output with respect to toner concentration.

FIG. 3 is a characteristic diagram showing the relationship between the development amount on the photoreceptor and the development potential difference.

[Explanation of symbols]

101 Photoreceptor
104 Developing device 106 P sensor
110 Toner hopper 111 Toner supply roller 11
3 Magnet roller 114 Developing sleeve
118 F sensor 119 Image density detection circuit
120 Magnet roller rotation speed control circuit 121 Developer concentration detection circuit 122
Toner supply control circuit

Claims (3)

[Claims] 1. An image density sensor that detects the image density of a reference toner image formed on a photoreceptor, a developing device that includes a developing sleeve that includes a magnetic roller, and a developing device that detects the toner density within the developing device. In an image density control device applied to an electrophotographic image forming apparatus including a developer concentration sensor and a toner replenishing means for supplying toner to the developing device, the image density sensor and the developer concentration sensor may toner replenishment control means that controls the toner replenishment means based on detection results; and magnet roller rotation that controls the rotational speed of the magnet roller based on the detection results of the image density sensor and the developer concentration sensor. An image density control device comprising a control means. 2. The toner replenishment control means controls the toner replenishment means based on the detection result of the developer concentration sensor when the detection result of the developer concentration sensor is outside a predetermined range; 2. The image density control device according to claim 1, wherein when the detection result of the developer density sensor is within a predetermined range, the toner replenishing means is controlled based on the detection result of the image density sensor. 3. The magnet roller rotation control means changes the rotation speed of the magnet roller based on the detection result of the image density sensor when the detection result of the developer concentration sensor is outside a predetermined range. The image density control device according to claim 1, characterized in that: