Patent ID: 8311422

Claim:
An image forming apparatus comprising: a latent image carrier configured to carry an electrostatic latent image; a latent-image forming unit configured to form an electrostatic latent image on the latent image carrier; a developing unit configured to develop the electrostatic latent image formed on the latent image carrier into a toner image by applying toner to the electrostatic latent image; a first toner container configured to contain therein toner to be supplied to the developing unit; a second toner container that is located along a toner conveying path for conveying toner from the first toner container to the developing unit, wherein the second toner container temporarily holds toner conveyed from the first toner container and feeds the toner to the developing unit; a toner-filling control unit configured to control a toner filling operation for supplying toner from the first toner container to the second toner container so that the second toner container contains toner equal to or more than a predetermined amount of toner; a toner-supply control unit configured to control a toner supply operation for supplying toner from the second toner container to the developing unit depending on requirements of the developing unit; a reference toner-image detecting unit configured to detect a reference toner image that is a toner image with a predetermined shape formed on any one of the latent image carrier and an image carrier to which the toner image is transferred from the latent image carrier; an image-density control unit configured to control image density by adjusting an image forming condition in accordance with a detection result obtained from the reference toner-image detecting unit; a problem-occurrence determining unit configured to determine whether a problem occurs at some stage of an image forming process in accordance with the detection result; a toner-consumption calculating unit configured to calculate accumulated toner consumption by accumulating toner consumption after a previous toner filling operation is stopped; a problem-occurrence area determining unit configured to, if the problem-occurrence determining unit determines that the problem has occurred, determine that the problem is caused by the toner filling operation if the accumulated toner consumption calculated by the toner-consumption calculating unit is larger than an amount of toner contained in the second toner container when the previous toner filling operation is stopped; and a notifying unit configured to notify a determination obtained by the problem-occurrence area determining unit as to whether the problem is caused by the toner filling operation.