US-12619172-B2 - Image forming apparatus

US12619172B2US 12619172 B2US12619172 B2US 12619172B2US-12619172-B2

Abstract

In the first potential difference adjustment mode, the fogging toner amount is predicted from a toner charge amount and a fogging toner current sensed by a current sensing portion with a zero surface potential on the image carrying member. In the second potential difference adjustment mode, the carrier development amount is predicted from a toner concentration, a carrier charge amount calculated based on the toner charge amount, and a carrier development current sensed by the current sensing portion with a zero surface potential on the image carrying member.

Inventors

Tamotsu Shimizu
Masaki Kadota

Assignees

KYOCERA DOCUMENT SOLUTIONS INC.

Dates

Publication Date: 20260505
Application Date: 20250304
Priority Date: 20240314

Claims (7)

1 . An image forming apparatus comprising: an image carrying portion including: an image carrying member having a photosensitive layer formed on a surface thereof; a charging device that electrostatically charges the image carrying member; an exposure device that forms an electrostatic latent image by shining light to the image carrying member electrostatically charged by the charging device; and a developing device having a developer carrying member that is disposed opposite the image carrying member and that carries two-component developer containing magnetic carrier and toner, the developing device forming a toner image by attaching the toner to the electrostatic latent image formed on the image carrying member, a developing voltage power supply that applies to the developer carrying member a developing voltage having an alternating-current voltage overlaid on a direct-current voltage; a density sensing device that senses a density of the toner image formed by the developing device; a current sensing portion that senses a direct-current value of a direct current passing between the developer carrying member and the image carrying member; and a control portion that controls the image carrying portion and the developing voltage power supply, wherein the control portion can perform at least one of a first potential difference adjustment mode in which the control portion sets, based on a predicted fogging toner amount, a blank-part potential difference between an unexposed-part surface potential on the image carrying member and a direct-current component of the developing voltage during image formation and a second potential difference adjustment mode in which the control portion sets, based on a predicted carrier development amount, the blank-part potential difference during image formation, in the first potential difference adjustment mode, the fogging toner amount is predicted from a toner charge amount and a fogging toner current sensed by the current sensing portion with a zero surface potential on the image carrying member, and in the second potential difference adjustment mode, the carrier development amount is predicted based on a toner concentration, a carrier charge amount calculated based on the toner charge amount, and a carrier development current sensed by the current sensing portion with a zero surface potential on the image carrying member.
2 . The image forming apparatus according to claim 1 , wherein the control portion makes the developing device form a reference image on the image carrying member during non-image formation and calculates the toner charge amount based on a toner development amount observed wen the reference image is formed as calculated from a direct-current value sensed by the current sensing portion when the reference image is formed and a density of the reference image sensed by the density sensing device, and a direct-current value sensed by the current sensing portion when the reference image is formed.
3 . The image forming apparatus according to claim 1 , wherein in the first potential difference adjustment mode, the fogging toner current is a direct-current value sensed by the current sensing portion when a direct-current component of the developing voltage applied to the image carrying member with a zero surface potential on the image carrying member is zero, and the control portion sets the blank-part potential difference during image formation based on the predicted fogging toner amount and a previously stored relationship between the fogging toner amount and the blank-part potential difference.
4 . The image forming apparatus according to claim 1 , wherein in the second potential difference adjustment mode, the direct-current value of the carrier development current is a direct-current value sensed by the current sensing portion when a predetermined developing voltage is applied to the image carrying member with a zero surface potential on the image carrying member, and the control portion sets the blank-part potential difference during image formation based on the predicted carrier development amount and a previously stored relationship between the carrier development amount and the blank-part potential difference.
5 . The image forming apparatus according to claim 1 , wherein in the first potential difference adjustment mode, the control portion senses, with the current sensing portion, a plurality of the fogging toner currents as the blank-part potential difference applied to the image carrying member with a zero surface potential on the image carrying member is varied in a plurality of steps, and the control portion sets the blank-part potential difference during image formation based on the plurality of the fogging toner currents sensed and a plurality of the fogging toner amounts calculated from the toner charge amount.
6 . The image forming apparatus according to claim 1 , wherein in the second potential difference adjustment mode, the control portion senses, with the current sensing portion, a plurality of the carrier development currents as the blank-part potential difference applied to the image carrying member with a zero surface potential on the image carrying member is varied in a plurality of steps, and the control portion sets the blank-part potential difference during image formation based on the plurality of the carrier development currents sensed and a plurality of the carrier development amounts calculated from the toner charge amount.
7 . The image forming apparatus according to claim 1 , wherein the control portion performs image formation with the blank-part potential difference set in the first potential difference adjustment mode as a lower-limit value and the blank-part potential difference set in the second potential difference adjustment mode as an upper-limit value.

Description

INCORPORATION BY REFERENCE This application is based on and claims the benefit of priority from Japanese Patent Application No. 2024-040101 filed on Mar. 14, 2024, the contents of which are hereby incorporated by reference. BACKGROUND The present disclosure relates to image forming apparatuses incorporating an image carrying member, such as copiers, printers, and facsimile machines as well as multifunction peripherals having their functions integrated together, and relates particularly to image forming apparatuses that use two-component developer containing toner and carrier. A known image forming apparatus includes an image forming portion, a developing voltage power supply, a density sensing device, a current sensing portion, and a control portion. The image forming portion incudes an image carrying member, a charging device, an exposure device, and a developing device. The image carrying member has a photosensitive layer formed on its surface. The charging device electrostatically charges the image carrying member. The exposure device exposes to light the image carrying member electrostatically charged by the charging device to form an electrostatic latent image. The developing device is disposed opposite the image carrying member, includes a developer carrying member that carries two-component developer containing magnetic carrier and toner, and attaches toner to the electrostatic latent image formed on the image carrying member to form a toner image. The developing voltage power supply applies to the developer carrying member a developing voltage having an alternating-current voltage overlaid on a direct-current voltage. The density sensing device senses the density of the toner image formed by the developing device. The current sensing portion senses the value of the direct current that passes between the developer carrying member and the image carrying member. Based on the amount of electric charge with which the toner is charged (i.e., toner charge amount), the blank-part potential difference during image formation is adjusted. This helps suppress toner fogging during image formation. Among known image forming apparatuses, the relationship between toner charge amount and toner fogging is not always uniform, and this may lead to image defects. Also, carrier development may lead to image defects. In view of the above inconveniences, an object of the present disclosure is to provide an image forming apparatus that can suppress image defects. SUMMARY To achieve the above object, according to one configuration based on the present disclosure, an image forming apparatus includes an image forming portion, a developing voltage power supply, a density sensing device, a current sensing portion, and a control portion. The image forming portion includes an image carrying member, a charging device, an exposure device, and a developing device. The image carrying member has a photosensitive layer formed on its surface. The charging device electrostatically charges the image carrying member. The exposure device forms an electrostatic latent image by shining light to the image carrying member electrostatically charged by the charging device. The developing device has a developer carrying member that is disposed opposite the image carrying member and that carries two-component developer containing magnetic carrier and toner, and forms a toner image by attaching the toner to the electrostatic latent image formed on the image carrying member. The developing voltage power supply applies to the developer carrying member a developing voltage having an alternating-current voltage overlaid on a direct-current voltage. The density sensing device senses the density of the toner image formed by the developing device. The current sensing portion senses the direct-current value of a direct current passing between the developer carrying member and the image carrying member. The control portion controls the image forming portion and the developing voltage power supply. The control portion can perform at least one of a first potential difference adjustment mode and a second potential difference adjustment mode. In the first potential difference adjustment mode, the control portion sets, based on a predicted fogging toner amount, a blank-part potential difference between an unexposed-part surface potential on the image carrying member and a direct-current component of the developing voltage during image formation. In the second potential difference adjustment mode, the control portion sets, based on a predicted carrier development amount, the blank-part potential difference during image formation. In the first potential difference adjustment mode, the fogging toner amount is predicted from a toner charge amount and a fogging toner current sensed by the current sensing portion with a zero surface potential on the image carrying member. In the second potential difference adjustment mode, the carrier development amount is predicted bas