Development device and image forming apparatus including the same

An image forming apparatus, comprising:

• an image carrier having a surface on which an electrostatic latent image is formed;
• a development device supplying a one-component magnetic developer to the image carrier;
• a transferring device configured to transfer an image onto a sheet from the image carrier;
• and
• a developer container including a developer discharge port configured to store the developer supplied to the transferring device,
• wherein the a development device includes:
• a housing configured to contain a one-component the developer;
• a developer carrier arranged in the housing and configured to be rotationally driven and to have a circumferential face carrying the developer;
• a developer conveying path including, in the housing, one conveying path through which the developer is conveyed along the developer carrier in a first direction and other conveying path arranged along horizontally with the one conveying path through which the developer is conveyed in a second direction opposite to the first direction, wherein the developer is circulated and conveyed between the one conveying path and the other conveying path;
• one developer conveying member arranged in the one conveying path at a space from the circumferential face of the developer carrier, configured to have a rotation shaft and a screw blade formed around the rotation shaft and rotationally driven from a downward side to an upward side in a region facing to the developer carrier to convey the developer along the first direction and to supply the developer to the developer carrier;
• a layer thickness adjusting member arranged at a distance from the circumferential face of the developer carrier and configured to adjust a layer thickness of the developer supplied to the developer carrier;
• a facing magnet arranged at a distance from the circumferential face of the developer carrier on an upstream side of the layer thickness adjusting member in a rotation direction of the developer carrier;
• a replenishment port opened in the housing above the other conveying path and at a downstream side in the second direction of the other conveying path to receive the developer supplied from a storage section the developer discharge port of the developer container;
• other developer conveying member arranged in the other conveying path and configured to be rotationally driven to convey the developer supplied from the replenishment port in the second direction and to deliver the developer to the one conveying path;
• and
• a conveyance capacity suppressing part arranged at a downstream side from the replenishment port in the second direction in the other developer conveying member to partially suppress conveyance capacity of the developer of the other developer conveying member, and then, to form a retention part of the developer at a position in the developer conveying path to which the replenishment port faces,
• wherein, the rotation shaft of the one developer conveying member is located at a position below a lower end part of the circumferential face of the developer carrier and arranged at a distance from the lower end part in a horizontal direction,
• the one developer conveying member has an upper end part of its outer circumference edge arranged below the center of the rotation shaft of the developer carrier,
• the layer thickness adjusting member adjusts the thickness of the toner in a second position being located above a first position when the one developer conveying member supplies the developer to the first position on the circumferential face of the developer carrier,
• in a case where the amount of the developer in the developer conveying path is increased, the replenishment port is blocked by toner accumulating in the retention part,
• in another case where the amount of the developer in the developer conveying path is decreased, space is created to allow the developer to flow from the replenishment port to the developer conveying path, and
• the developer carrier has a circumferential speed Vd and the one developer conveying member has a circumferential speed Vs so that a circumferential speed ratio Vd/Vs satisfies a relationship represented by 1.3≦Vd/Vs≦5.0.