US-20260126741-A1 - IMAGE FORMING APPARATUS

US20260126741A1US 20260126741 A1US20260126741 A1US 20260126741A1US-20260126741-A1

Abstract

An image forming apparatus includes an image carrying member, a charging device, an exposure device, a developing device, a toner container, a toner concentration sensor, a toner charge amount detection portion, and a control portion. The developing device includes a developer carrying member carrying a two-component developer and develops an electrostatic latent image into a toner image. The toner concentration sensor detects a toner concentration in the developing device. The toner charge amount detection portion detects a toner charge amount in the developing device. Based on a result of detection by the toner concentration sensor, the control portion controls replenishment of the developing device with the toner from the toner container. Based on the toner charge amount detected by the toner charge amount detection portion, the control portion executes first target value changing control of changing a target value of the toner concentration.

Inventors

Asami Sasaki
Hiroshi Yamazaki
Ryo Taniguchi

Assignees

KYOCERA DOCUMENT SOLUTIONS INC.

Dates

Publication Date: 20260507
Application Date: 20251103
Priority Date: 20241107

Claims (5)

1 . An image forming apparatus, comprising: an image carrying member that includes a photosensitive layer formed on a surface thereof; a charging device that charges the surface of the image carrying member to a prescribed surface potential; an exposure device that applies light to the image carrying member charged by the charging device so as to form thereon an electrostatic latent image with attenuated electrostatic charge; a developing device that includes a developer carrying member carrying a two-component developer containing a magnetic carrier and toner and develops, into a toner image, the electrostatic latent image formed on the surface of the image carrying member; a toner container that contains the toner with which the developing device is to be replenished; a toner concentration sensor that detects a toner concentration which is a ratio of the toner to the magnetic carrier in the developing device; a toner charge amount detection portion that detects a toner charge amount which is a charge amount per unit mass of the toner in the developing device; and a control portion that controls, based on a result of detection of the toner concentration by the toner concentration sensor, replenishment of the developing device with the toner from the toner container, wherein based on the toner charge amount detected by the toner charge amount detection portion, the control portion executes first target value changing control of changing a target value of the toner concentration.
2 . The image forming apparatus according to claim 1 , wherein the control portion executes, in conjunction with the first target value changing control, second target value changing control in which the target value is increased when an integrated consumption amount of the toner from an initial stage of use of the two-component developer has reached a prescribed value, and is set back to an original value after a lapse of a prescribed period of time.
3 . The image forming apparatus according to claim 2 , wherein when a change rate of the toner concentration during execution of the first target value changing control is referred to as a first change rate, and a change rate of the toner concentration at a time when the target value is set back to an original value during execution of the second target value changing control is referred to as a second change rate, the second change rate is equal to the first change rate.
4 . The image forming apparatus according to claim 2 , wherein the integrated consumption amount is calculated based on a dot count obtained when an electrostatic latent image is formed by the exposure device, an integrated printing rate of an image developed by the developing device, or an amount of the toner supplied from the toner container to the developing device.
5 . The image forming apparatus according to claim 1 , wherein based on a developing current that flows between the image carrying member and the developer carrying member when a reference image is developed on the image carrying member and a reflection density of the reference image, the toner charge amount detection portion estimates the toner charge amount.

Description

INCORPORATION BY REFERENCE This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2024-194954 (filed on Nov. 7, 2024), the entire contents of which are hereby incorporated by reference. BACKGROUND The present disclosure relates to an image forming apparatus provided with an image carrying member, such as a copy machine, a printer, a facsimile, or a multi-functional peripheral having functions thereof, and relates particularly to an image forming apparatus of an intermediate transfer type using a two-component developer containing toner and a carrier. In an image forming apparatus, an electrostatic latent image formed on an image carrying member formed of a photosensitive member or the like is developed by a developing device so as to be visualized as a toner image. An example of such a developing device adopts a two-component developing method that uses a two-component developer containing a magnetic carrier and toner. In the two-component developing method, under an influence of the number of sheets printed, environmental (temperature and humidity) fluctuations, a printing mode, a printing rate on an image (a ratio of a printing area to an area allowing image formation), or the like, the developer might deteriorate to change a charging characteristic of the toner in the developer. This makes it impossible for the toner to be sufficiently charged, leading to problems such as a decrease in image density, image fogging, toner scattering, and so on. SUMMARY An image forming apparatus according to one aspect of the present disclosure includes an image carrying member, a charging device, an exposure device, a developing device, a toner container, a toner concentration sensor, a toner charge amount detection portion, and a control portion. The image carrying member includes a photosensitive layer formed on a surface thereof. The charging device charges the surface of the image carrying member to a prescribed surface potential. The exposure device applies light to the image carrying member charged by the charging device so as to form thereon an electrostatic latent image with attenuated electrostatic charge. The developing device includes a developer carrying member carrying a two-component developer containing a magnetic carrier and toner and develops, into a toner image, the electrostatic latent image formed on the surface of the image carrying member. The toner container contains the toner with which the developing device is to be replenished. The toner concentration sensor detects a toner concentration that is a ratio of the toner to the magnetic carrier in the developing device. The toner charge amount detection portion detects a toner charge amount that is a charge amount per unit mass of the toner in the developing device. Based on a result of detection of the toner concentration by the toner concentration sensor, the control portion controls replenishment of the developing device with the toner from the toner container. Based on the toner charge amount detected by the toner charge amount detection portion, the control portion executes first target value changing control of changing a target value of the toner concentration. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view showing an internal configuration of an image forming apparatus according to one embodiment of the present disclosure. FIG. 2 is a sectional side view of a developing device incorporated in the image forming apparatus according to the embodiment. FIG. 3 is a partially enlarged view of and around an image forming portion, which includes control paths of the image forming portion. FIG. 4 is a graph showing a relationship between a toner concentration and a toner charge amount in a case where a cumulative number of sheets printed is made to vary. FIG. 5 is a graph showing a relationship between the cumulative number of sheets printed and the toner charge amount in a case where a target value of the toner concentration is changed. FIG. 6 is a graph showing a relationship between the cumulative number of sheets printed and an image density in a case where the target value of the toner concentration is changed. FIG. 7 is a graph showing a change amount of the toner concentration with respect to a dot count in second target value changing control. FIG. 8 is a graph showing the change amount of the toner concentration with respect to the dot count in a case where first target value changing control and the second target value changing control are executed in conjunction with each other. FIG. 9 is a flow chart showing a procedure for executing the first target value changing control and the second target value changing control in the image forming apparatus according to the embodiment. DETAILED DESCRIPTION [1. Overall Configuration of Image Forming Apparatus] With reference to the appended drawings, the following describes an embodiment of the present disclosure. FI