1. Field of the Invention
This invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function for correcting image density to maintain appropriate image density in accordance with variations of humidity in a simple and low cost structure.
This invention also relates to a method of performing the above-mentioned function.
2. Discussion of the Background
Generally, an image forming apparatus such as a copying machine, a printer, a facsimile machine, and the like includes a number of the following main functional units which are capable of cooperatively performing a series of processes for forming an image on a recording medium. An image forming unit performs an image forming process in which an electrostatic latent image is formed on a motor-driven image bearing member made of a photoconductor or the like. An image developing unit then performs an image developing process in which the electrostatic latent image formed on the image bearing member is visualized using toner. Subsequently, an image transfer unit performs an image transfer process in which the above-mentioned toner-forming image is transferred onto a recording sheet by an attractive force generated by electric charges. Then, an image fixing unit performs an image fixing process in which the toner-forming image is fixed on the recording sheet.
The image developing unit includes an image developing agent, for example, a two-component development compound composed of toner particles and carriers. During the above-mentioned series of the processes, the image developing unit performs the image processing process using the toner particles in the two-component development compound, and is filled with new toner particles by a toner supply unit which contains new toner. The image developing unit also performs a mixing operation to mix the development compound inside so as to generate and provide an electric charge to the development compound. By the electric charge provided onto toner particles, the electrostatic latent image formed on the image bearing member is developed into the visualized image through the operation of the electric charges which attract the toner particles to the electrostatic latent image.
Many background image forming apparatus include an image developing unit having various elements horizontally mounted therein. The various elements included in the image developing unit are, for example, a plurality of mixing and circulating members for mixing and circulating the two-component development compound and a transferring member for transferring the image development compound to the photoconductor from the development unit. Horizontally mounting the various elements provides an image developing unit relatively simple and, therefore, the developing unit can be manufactured in a relatively small size and at a relatively inexpensive cost.
Due to the above-mentioned size reduction of the image developing unit, many toner supply units have accordingly had a toner supply path required to be connected to the image developing unit around an end portion of the plurality of mixing and transfer members so as not to make the advantageously-reduced size of the image developing unit any larger.
In addition, during the above-mentioned series of the processes by such background image forming apparatus, the toner supply unit, particularly its supply amount, is controlled by the image forming unit which includes a toner density detecting unit and a toner density control unit. The image forming unit can recognize toner density in the image developing unit by detecting magnetic permeability of the two-component development compound with the toner density detecting unit. Then, the toner density control unit compares the value of the detected toner density with a predetermined value of reference toner density. Subsequently, the toner density control unit controls the toner supply unit in accordance with the resultant information of the comparison.
One problem with such image forming apparatus is that the electric charge on the toner particles varies when the ambient humidity varies. As a result, the image density will vary as the charge on the toner varies. More specifically, an amount of the electric charge on the toner is reduced when humidity increases so that the toner becomes less controllable and the quality of the resulting image is reduced. For example, so-called dirty-toner-spots may form on the background of the image.
Further, in a case of using a humidity sensor to overcome the above-mentioned problem, the humidity sensor may be affected by an air flow flowing in an interior of the image forming apparatus. As a result, the humidity sensor can not correctly detect humidity around the toner and, therefore, the above-mentioned problem remains unsolved.
Presently, there exists no image forming apparatus which is capable of stabilizing image density so as to avoid, for example, the dirty-toner-spot problem through correctly detecting variations of humidity while avoiding the effects of air flow flowing inside the image forming apparatus.