Image forming apparatus capable of prompting for replacement of at least one of a charging roller and a cleaning blade

1. An image forming apparatus comprising:

an image forming portion which comprises

an image carrier including a photosensitive layer on a surface of the image carrier,

a charging device which causes the surface of the image carrier to be electrically charged,

an exposure device which exposes to light the surface of the image carrier electrically charged by the charging device, and forms an electrostatic latent image on the surface of the image carrier,

a developing device which develops the electrostatic latent image into a toner image by using a developer,

a transfer device which transfers the toner image from the surface of the image carrier to a transfer-receiving member, and

a cleaning device which cleans the surface of the image carrier; and

a control portion which controls an operation of the image forming portion, wherein:

the charging device includes a charging roller which is in contact with the surface of the image carrier;

the cleaning device includes

a cleaning blade which slidably contacts the surface of the image carrier, and

an adjustment portion which adjusts a linear pressure of the cleaning blade exerted on the surface of the image carrier; and

the control portion executes, when a rate of increase of an outer layer resistance value of the charging roller which is caused by a decrease in a function of the cleaning blade is greater than or equal to a first rate, linear pressure adjustment control of controlling the adjustment portion to increase the linear pressure of the cleaning blade exerted on the surface of the image carrier.

2. The image forming apparatus according to claim 1 , wherein the charging roller comprises:

a base layer including a conductive elastic body; and

an outer layer as a high-resistance coat layer.

3. The image forming apparatus according to claim 1 , wherein the cleaning blade is made of rubber.

4. The image forming apparatus according to claim 1 , wherein the control portion executes the linear pressure adjustment control on condition that the outer layer resistance value is smaller than a first threshold value.

5. The image forming apparatus according to claim 4 , wherein the control portion outputs a display prompting for replacement of the charging roller and the cleaning blade when the outer layer resistance value is not smaller than the first threshold value, and the linear pressure adjustment of the cleaning blade reaches a limit.

6. The image forming apparatus according to claim 1 , wherein the control portion calculates the outer layer resistance value based on a result of impedance measurement of the charging roller.

7. The image forming apparatus according to claim 6 , wherein the control portion executes the impedance measurement by bringing the charging roller to a halt at a time when image forming by the image forming portion is unexecuted.

8. The image forming apparatus according to claim 1 , wherein the control portion controls a voltage to be applied to the charging roller while an image is being formed by the image forming portion according to a total resistance value of the charging roller.

9. The image forming apparatus according to claim 8 , wherein the control portion executes the linear pressure adjustment control on condition that the total resistance value is smaller than a second threshold value.

10. The image forming apparatus according to claim 8 , wherein the control portion calculates the total resistance value based on a result of impedance measurement of the charging roller.