JPH0594091A - Image forming device - Google Patents

Abstract

PURPOSE:To stably and highly accurately detect image density in an image forming device such as a copying machine or printer. CONSTITUTION:First a photosensitive body 1 is controlled so that its potential becomes nearly zero and the bias voltage of the same polarity as toner is applied to a developing sleeve 11. Consequently, the toner from the developing sleeve 11 is stuck to the photosensitive body 1 and the prescribed reference image is formed. Changes on the photosensitive body 1 attending on the formation of the reference image are accumulated in a capacitor 6 and the quantity of the accumulated charges is measured by a controller 7, thereby detecting the image density based on the quantity of the charges.

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 or a printer, and more particularly to an image forming apparatus having a function of detecting image density.

[0002]

2. Description of the Related Art Generally, an image forming apparatus of this type is provided with a photoconductor, a developing device, etc., which is a toner replenishing device for replenishing toner from a hopper to a toner tank and a toner on the surface of the photoconductor. And a toner supply device for supplying toner to the developing sleeve. Then, when the photoconductor on which the electrostatic latent image is formed passes through a portion facing the developing device in the state where the bias voltage is applied, the toner from the developing sleeve is attached to the electrostatic latent image. , The electrostatic latent image is visualized. As a device having a function of performing such an image forming procedure and detecting the image density of a visible image on the photoconductor, for example, one disclosed in Japanese Patent Laid-Open No. 61-279876 is known. .. In the apparatus disclosed in the above publication (see FIG. 4), during a normal image forming operation, the developing device is connected to a stabilized developing bias power source to form an image. On the other hand, image density detection (toner adhesion amount detection)
At times, the developing bias power source is switched, and toner is attached to the basic latent image formed on the surface of the photoconductor by so-called self-bias development. At this time, the developing current flows through the resistance element, but the voltage generated with the flow of the developing current is measured, and the toner adhesion amount is calculated based on this voltage value. In this case, the basic latent image is obtained by scanning the black reference pattern attached to the lower surface side of the document table with the optical system.

[0003]

In the image density detection performed as described above, since the self-bias development is applied as described above, the development of the basic latent image is different from the case where the developing bias power source is used. The potential difference that sometimes occurs is not stable. That is, the amount of toner adhered to the surface of the photoconductor is not stable. Further, the potential difference due to the developing bias at the time of actual image formation performed using the developing bias power source is different from the potential difference caused by the adhesion of toner at the time of image density detection. That is, there is a gap in the correspondence relationship of the toner adhesion amount. Therefore, in the above conventional image forming apparatus,
The image density cannot be detected stably and highly accurately. Therefore, the present invention has been devised in view of the above circumstances, and provides an image forming apparatus capable of stably and highly accurately detecting an image density by utilizing a developing bias during normal image formation. It is intended.

[0004]

In order to achieve the above object, the main means adopted by the present invention is to form an electrostatic latent image on the surface of a photoconductor and to apply a bias voltage to a developing device. In the image forming apparatus for applying a toner to the electrostatic latent image to make the electrostatic latent image visible by applying toner to the electrostatic latent image. Means and the developing device, a bias voltage having the same polarity as that of the toner is applied, and the toner from the developing device is adhered to the photosensitive member which is brought to a state of substantially zero potential by the potential control means, so that a predetermined reference image is formed. Image forming means for forming a reference image, charge accumulating means for accumulating electric charges in the photoconductor associated with the formation of the reference image, and measuring means for measuring the amount of electric charge accumulated in the charge accumulating means. Image formation related to points It is the location.

[0005]

In the image forming apparatus according to the present invention, first,
The photoconductor is controlled to have a substantially zero potential, and a bias voltage having the same polarity as the toner is applied to the developing device. As a result, the toner from the developing device is attached to the photoconductor to form a predetermined reference image. The charge on the photoconductor due to the formation of the reference image is accumulated by the charge accumulating means, and the amount of charge accumulated in the charge accumulating means is measured. Then, the image density is detected based on this charge amount.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples of embodying the present invention and are not of the nature to limit the technical scope of the present invention. Here, FIG. 1 is a schematic diagram of a main part of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a flowchart showing a procedure for detecting an image density in the image forming apparatus, and FIG. 3 is a chart showing the correspondence relationship between the polarities of the photoconductor and the developing device at the time of image formation and at the time of image density detection. In the image forming apparatus according to this embodiment, for example, as shown in FIG. 1, a main charger 2, a developing device 3, a cleaning device 4 and the like are arranged around the photoconductor 1,
Are grounded via a grounding changeover switch 5 and a capacitor 6 arranged in parallel. The capacitor 6 is a control device 7 including a microcomputer and a memory.
And a control procedure at the time of image formation of the image forming apparatus, a control procedure at the time of image density detection, and the like are stored in advance in the memory. In the developing device 3, a toner hopper 9 is provided on the upper portion of the main body 8, and the toner hopper 9 is rotationally driven by a motor (not shown) to replenish the toner from the toner hopper 9 into the main body 8. A toner replenishing device 10 is provided. A motor (not shown) is provided in the main body 8.
A developing sleeve 11 that is rotatively driven by the motor 1 and supplies toner to the photoconductor 1, and a toner supply roller 12 that is rotatively driven by a motor (not shown) and supplies toner to the developing sleeve 11 are provided. The developing sleeve 11 and the toner supply roller 12 are connected to a bias power source 13.

When an image is formed in the above-mentioned image forming apparatus, for example, in the reversal development method (see FIG. 3), the main body 2 is charged with the main charger 2 when the grounding switch 5 is turned on and the grounded state is established. Are uniformly charged to the negative (-) side. Then, the uniformly charged surface of the photoconductor 1 is exposed to form an electrostatic latent image on the surface of the photoconductor 1. Subsequently, toner (charged to the negative side) from the developing sleeve 11 is attached to the electrostatic latent image to make the electrostatic latent image visible. In this case, the developing sleeve 11 is provided with the bias power source 1
At 3, a bias voltage of the same polarity is applied to the toner. Next, the procedure for detecting the image density in the image forming apparatus will be described with reference to FIG. In the figure, S1, S2, ... Show each processing step. In S1, the copy button provided on the operation panel (not shown) is turned on, and the image density detection processing is performed at an appropriate timing during the copying operation. That is,
At S2, control is performed to bring the potential of the photoconductor 1 to a substantially zero state. More specifically, first, the photosensitive member 1 is rotationally driven with the main charger 2 and the bias power source 13 turned off, and the entire surface of the photosensitive member 1 is exposed. At this time, the ground changeover switch 5 is turned on, and the photoconductor 1 is in the grounded state. As a result, the charges of the photoconductor 1 are released to the ground side. Subsequently, the ground changeover switch 5 is turned off, and the photoconductor 1 is in a state of being electrically connected only to the capacitor 6 (S3). Then, in S4, the photoconductor 1
The toner from the developing sleeve 11 is attached to the surface of the developing sleeve 11 to form a predetermined reference image. That is, the bias power supply 13 applies the same bias voltage (bias having the same polarity to the toner) to the developing sleeve 11 as in the normal image forming operation for a predetermined time (for example, 0.3 seconds), Toner is adhered (developed) on the photoconductor 1 in a known area (developing sleeve width (cm) × time (sec) × photoconductor peripheral speed (cm / sec)) to form the reference image. Therefore, the area of this reference image is small, and the amount of toner supplied to it is extremely small.

Then, the charges on the photoconductor 1 due to the formation of the reference image are accumulated in the capacitor 6, and the amount of charges accumulated in the capacitor 6 is measured by the controller 7 (S5). In this case, since the charge amount and the toner development amount are in a proportional relationship, the comparison circuit 14 compares and determines the charge amount in the capacitor 6 and the reference data corresponding to the preset toner development amount. As a result, the amount of development by the toner, that is, the image density is detected. After the image density is detected as described above,
The ground changeover switch 5 is turned on to return to a state where normal image formation can be performed (S6). In the image forming apparatus according to this embodiment, the image density is detected by the procedure as described above. That is, since the image density can be detected by utilizing the developing bias during the normal image formation, the image density can be detected more stably and with higher accuracy than in the case of the conventional apparatus. Further, since the reference pattern as in the case of the conventional device is unnecessary, it is possible to contribute to the simplification of the configuration. In the above embodiment, the case where the photoconductor 1 and the toner are both charged to the negative side in the reversal development method has been described as an example, but when the photoconductor 1 and the toner are charged to the plus (+) side. Further, even in the case of the positive development method, the image density can be detected by the same procedure as above. However, in the normal development method, it goes without saying that bias voltages of different polarities are applied to the toner during normal image formation (see FIG. 3).

[0009]

Since the image forming apparatus according to the present invention is configured as described above, it is possible to detect the image density by utilizing the developing bias during the normal image formation. Therefore, the image forming apparatus can detect the image density more stably and with higher accuracy than in the case of the conventional apparatus.

[Brief description of drawings]

FIG. 1 is a configuration diagram of main parts of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for detecting an image density in the image forming apparatus.

FIG. 3 is a chart showing a correspondence relationship between polarities of a photoconductor and a developing device at the time of image formation and image density detection in each developing method.

FIG. 4 is a schematic block diagram showing a main configuration of a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photosensitive member 2 ... Main charger 3 ... Developing device 5 ... Grounding switch 6 ... Capacitor 7 ... Control device 11 ... Developing sleeve 13 ... Bias power supply S1 to S6 ... Processing steps

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihisa Zamae 1-2-2 Tamazo, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Takeshi Watanabe 1-2-2 Tamazo, Chuo-ku, Osaka Mita Industry Co., Ltd.

Claims (1)

[Claims] 1. A latent electrostatic image is formed on the surface of a photoconductor and a bias voltage is applied to a developing device to adhere toner from the developing device to the electrostatic latent image so that the electrostatic latent image can be formed. In an image forming apparatus for visualizing, a potential control means for setting the potential of the photoconductor to a substantially zero state and a bias voltage of the same polarity as the toner are applied to the developing device, and the potential control means makes a substantially zero potential. Reference image forming means for forming a predetermined reference image by adhering the toner from the developing device to the photosensitive member in this state, and charge accumulating means for accumulating electric charges in the photosensitive member due to the formation of the reference image. An image forming apparatus comprising: and a measuring unit that measures the amount of electric charge accumulated in the electric charge accumulating unit.