Image forming apparatus

An image forming apparatus comprising:

• an image read-out section for reading out an image;
• a photosensitive drum for forming an electrostatic latent image corresponding to said image based on image data supplied from the image read-out section;
• a vertical transfer passage for transferring a transfer material upward to the photosensitive drum;
• and
• a developing unit arranged below the photosensitive drum for depositing the toner on the electrostatic latent image formed on the photosensitive drum with the assistance of a small amount of magnetic carrier,
• wherein said developing unit comprises
• a housing;
• a toner hopper, which is a part of the housing, for containing a toner;
• a toner supply source for supplying the toner to the toner hopper;
• a magnetic roller positioned above the toner hopper for imparting a magnetic field to the magnetic carrier;
• a development sleeve, covering the outer periphery of the magnetic roller, holding the magnetic carrier, allowing the magnetic carrier to adsorb the toner, rotating in the opposite direction to the rotation direction of the magnetic roller, thereby allowing the toner to transfer and adhere onto the electrostatic latent image formed on the photosensitive drum;
• a doctor blade arranged a slight distance from the development sleeve for cutting and removing excessively supplied toner from the development sleeve;
• an agitator arranged within the toner hopper for agitating and mixing the toner contained in the toner hopper;
• a rotation arm arranged in the agitator and rotated about a rotation center lower than a rotation center of the development sleeve;
• a spoon having a substantially flat spoon surface (bowl) at a tip of the rotation arm for scooping up the toner from the toner hopper when the spoon surface (bowl of the spoon) comes close to the development sleeve and transferring the toner;
• a toner shelf, which is a part of the housing, arranged immediately under the development sleeve for holding the toner transferred by the spoon and for receiving the toner and the magnetic carrier cut and removed by the doctor blade;
• a developer returning member, arranged between the doctor blade and the toner hopper, for preventing the toner and magnetic carrier cut and removed by the doctor blade from transferring to the toner hopper, guiding and returning the toner and magnetic carrier to the toner shelf;
• and
• a weir, arranged between the toner shelf and the toner hopper, having a top portion which is equal to or higher than the spoon surface (bowl of the spoon) in height when the rotation arm is horizontal and which defines a space between the top portion and the developer returning member for passing the toner to be transferred by the spoon, and guiding and returning the toner and magnetic carrier cut and removed when the developer returning member returns the toner to the development sleeve.