IMAGE FORMING APPARATUS HAVING HEAT-FIXING UNIT

Abstract

An image forming apparatus includes an image forming portion; a fixing portion having a fixing nip portion which heats and fixes the unfixed image and an discharge roller which discharges the recording material, wherein in the case where the recording material is the plain paper which is equal to or larger than the predetermined size, the discharge roller conveys the plain paper in a range from a front edge to a rear edge at a predetermined speed, in the case where the recording material is the plain paper smaller than the predetermined size, the discharge roller conveys the plain paper at a first speed until the rear edge passes through the fixing nip portion, and the discharge roller conveys the plain paper at a second speed higher than the first speed after the rear edge passed through the fixing nip portion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of an image forming apparatus in an embodiment 1 of the invention.

FIG. 2 is a diagram showing a method of increasing a speed in an embodiment 2 of the invention.

FIG. 3 is a schematic cross sectional view of a conventional image forming apparatus.

FIG. 4 is a schematic diagram of an discharge roller (divided roller).

FIG. 5 is a schematic diagram of an discharge roller (non-divided roller).

FIGS. 6A, 6B, 6C and 6D are diagrams illustrating speed control of the discharge roller in the case of printing onto plain paper of a size which is equal to or larger than a predetermined size (A4 size).

FIGS. 7A, 7B, 7C and 7D are diagrams illustrating speed control of the discharge roller in the case of printing onto a resin sheet.

FIGS. 8A, 8B, 8C and 8D are diagrams illustrating speed control of the discharge roller in the case of printing onto plain paper of a size smaller than the predetermined size (A4 size).

FIG. 9 is a diagram illustrating a relation of a driving transfer from a motor to a fixing portion and an discharge roller pair and a relation of a control signal transfer from a control unit to the motor.

FIG. 10 is a diagram illustrating a relation between an interval between projecting portions in both edge portions of the discharge roller and a size of plain paper.

Claims

1. An image forming apparatus for forming an image on a recording material, comprising: an image forming portion for forming an unfixed image on the recording material;a fixing portion having a fixing nip portion which heats and fixes the unfixed image onto the recording material,wherein if the recording material is plain paper in which a size in a direction which perpendicularly crosses a conveying direction is smaller than a predetermined size, the fixing portion conveys the plain paper at a speed lower than that in the case where the recording material is plain paper in which a size in the direction which perpendicularly crosses the conveying direction is equal to or larger than the predetermined size; anda discharge roller which discharges the recording material that has passed through the fixing nip portion toward a tray and which has a projection for kicking out the recording material in an area where the plain paper smaller than the predetermined size does not pass,wherein a length of conveying path between the fixing nip portion and the discharge roller is smaller than a length in the conveying direction of the plain paper smaller than the predetermined size, andwherein in the case where the recording material is the plain paper which is equal to or larger than the predetermined size, the discharge roller conveys the plain paper in a range from a front edge to a rear edge in the conveying direction of one sheet of the plain paper at a predetermined speed, in the case where the recording material is the plain paper smaller than the predetermined size, the discharge roller conveys the plain paper at a first speed until the rear edge in the conveying direction of the plain paper passes through the fixing nip portion, and the discharge roller conveys the plain paper at a second speed higher than the first speed after the rear edge in the conveying direction of the plain paper passed through the fixing nip portion.

2. An apparatus according to claim 1, wherein in the case where the recording material is a resin sheet, the discharge roller conveys the resin sheet at a third speed until the rear edge in the conveying direction of the resin sheet passes through the fixing nip portion, and the discharge roller conveys the resin sheet at a fourth speed higher than the third speed after the rear edge in the conveying direction passed through the fixing nip portion.

3. An apparatus according to claim 2, wherein the third speed is lower than the first speed.

4. An apparatus according to claim 3, wherein the fourth speed is the same as the second speed.

5. An apparatus according to claim 1, wherein the fixing portion and the discharge roller are driven by a same motor.