Abstract: An image forming apparatus provides a photosensitive body, a main charger, an exposing unit, developing unit and a contact-transfer charger. The main charger charges the photosensitive body with a predetermined electric potential. The exposing unit applies a laser beam on the surface of the photosensitive body to form an electric latent image. The developing unit develops the electrostatic latent image to form a toner image. The contact-transfer charger transfers the toner image on an image transfer paper. The image forming apparatus further provides controller for power supplies. The controller controls the power supplies after an image forming operation in a manner to enhance the electric potential of the photosensitive body to a high level by the main charger, drop the surface potential of the photosensitive body to a low level by the contact-transfer charger and then to cut off a bias voltage of the developing unit.

Abstract: An image forming apparatus includes a charging roller for charging a surface of a photoconductive layer in a photoreceptor so as to have a prescribed polarity, a first exposing unit which is arranged on a downstream side of the charging roller on the basis of a direction in which the photoreceptor moves, a developer unit which is placed on a downstream side of the first exposing unit and which keeps toner, to which a charge with a polarity opposite to the prescribed polarity is applied, in contact with a photoconductive layer, and a second exposing unit for directing light generated according to an image signal to a back of the photoconductive layer at a contact position of the toner and the photoconductive layer. The first exposing unit directing light reflected from a document to which a light is applied to the surface of photoconductive layer so as to form a first electrostatic latent image.

Abstract: An image forming apparatus provides a photosensitive body, a main charger, an exposing unit, developing unit and a contact-transfer charger. The main charger charges the photosensitive body with a predetermined electric potential. The exposing unit applies a laser beam on the surface of the photosensitive body to form an electric latent image. The developing unit develops the electrostatic latent image to form a toner image. The contact-transfer charger transfers the toner image on an image transfer paper. The image forming apparatus further provides controller for power supplies. The controller controls the power supplies after an image forming operation in a manner to enhance the electric potential of the photosensitive body to a high level by the main charger, drop the surface potential of the photosensitive body to a low level by the contact-transfer charger and then to cut off a bias voltage of the developing unit.

Abstract: A contact charger includes a photoreceptor having a photosensitive layer formed on a surface of an electrically conductive drum base and a fixed coil connected to the drum base and ground. The contact charger charges the photosensitive layer by making a charge roller in contact with the photosensitive layer while being applied thereto DC voltage from a power supply. With this arrangement, in the case where a pin hole exists on the photosensitive layer, there may have a continuity between the charge roller and the drum base which may results in a sudden increase in current flowing between the drum base and ground. When this happens, however, since self-induced electromotive force, having a direction opposite to the electromotive force of the power supply, is generated by the fixed coil in response to a sudden increase in current, excessive current will not flow between the drum base and ground, thereby eliminating the possibility of a large drop in voltage of the power supply.

Abstract: An image forming apparatus has a charging roller disposed in contact with a photoconductor having a photoconducting layer for charging the surface of the photoconductor, and a photoconductor life judging device including an element for detecting the change of the value of the current flowing through the charging roller and an element for judging the photoconductor life on the basis of the change of the current value.

Abstract: A laser printer comprising a photoreceptive means, a laser beam emitting device, a detecting means for detecting a factor of degradation of the image quality, the factor originating in the photoreceptive means, and a control means which controls the output level of said laser beam emitting device in accordance with the detected level of said factor.

Abstract: An expiration valve for an automatic respirator comprises a main body which is separable into a valve body and a diaphragm and a container which engages to a tube for supplying control pressure to one side of the diaphragm. A means for controlling such an expiration valve comprises a means for generating pressure for opening and closing the valve, a means for controlling this pressure, a pressure detector means, an exhaust means and a control means so that the valve can be electronically controlled for both the valve opening/closing functions and for the positive end expiratory pressure function.