Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
1999-09-20
2001-04-03
Grainger, Quana M. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S063000
Reexamination Certificate
active
06212341
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a developing apparatus adapted to a two-component developing method for use in an electrophotographic method employed in a copying machine, a printer, a facsimile machine or the like. More particularly, the present invention relate to an improvement in control of the density of toner by using a toner-density sensor for magnetically detecting the density of toner and a technique for detecting non-loading of a developer container and a failure of the toner-density sensor by improving the control of the density of the toner.
A conventional method of detecting the density of toner in an image forming apparatus which employs the two-component developing method using toner and a carrier has generally employed a method of magnetically detecting change in the magnetic permeability of the developer. In a case of monochrome images, magnetic toner and a magnetic carrier are employed, while non-magnetic toner and the magnetic carrier are employed in a case of color images. A fact that the mixture ratio of the toner and the carrier is changed and thus the magnetic permeability is changed is used such that the magnetic permeability of the developer is measured. Thus, the density of the toner is detected.
In the foregoing case, an output of, for example, a magnetic-permeability sensor denoting the detected density of the toner is compared with a predetermined reference value. To make the output denoting the detected density of the toner to be the same as the reference value, toner is supplied. Thus, control is performed in such a manner that the density of toner is constant.
However, the developer composed of toner and carrier cannot uniformly be stirred with facility. The developer remains in the vicinity of the detecting surface of the toner-density sensor or toner adheres to the detecting surface of the toner-density sensor after an elapse of long time. Thus, an error occurs in detecting the density of toner.
If an error in detecting the density of toner occurs, the control of the density of toner cannot correctly be performed. Thus, a required density of toner in the developer cannot be realized. Hence it follows that a problem arises in that the print density is lowered, toner is splattered and an undesirable state of the carrier is realized.
To overcome the foregoing problem, a method has been suggested in Japanese Patent Publication JP-2-64560. According to the suggestion, the toner which remains adjacent to the detecting surface is reliably raked out by a mechanical means to exert periodic vibrations on the developer. Moreover, the component of the vibration waveform is superimposed on the output of the toner-density sensor obtainable when no vibration is exerted. Thus, a comparison is made with a reference control level to form a pulse. Thus, the density of toner can be controlled for a long time without remaining of the developer adjacent to the detecting surface.
With the foregoing method, control is performed by using the formed pulse such that the output value, which has intentionally be superimposed, is binary-coded. Therefore, the dynamic range is narrowed excessively. If the dynamic range is widened, the inclination of the period of the vibrations must be moderated. Hence it follows that adjustment must be performed because of joining of the toner-density sensor and dispersion.
Hitherto, a color image forming apparatus has been known which forms a color image by using a plurality of different developer containers in which four different toner materials are enclosed. The four types of the developer containers have been structured such that each developer container is removable when inspection is performed in order to easily perform maintenance and the inspection.
Since the plural developer containers are provided, failure of resetting easily occurs when the container is loaded to perform the maintenance and inspection. To overcome the foregoing problem, a technique has been disclosed in Japanese Patent Publication JP-6-51625. That is, an apparatus is used which reshapes a detection signal supplied from the toner-density sensor into a pulse signal. In accordance with the number of generated pulse signals during a predetermined gate period, the apparatus detects the density. Thus, whether or not the developer container has been loaded is detected by making a determination that the developer container has not been loaded if no pulse signal is generated in the predetermined gate period.
However, the foregoing technique is arranged to simply detect whether or not the pulse signal has been generated in the gate period. If a stirring member of the developer container is broken down owing to stress of the developer or the like, the structure, in which the pulse signal is electrically reshaped, undesirably generates the pulse signal because the developer has been detected. Therefore, the stirring cannot sufficiently be performed. As an alternative to this, a determination is undesirably made that the developer container has not been loaded if the toner sensor is broken down. Hence it follows that accurate detection cannot be performed.
In recent years an image forming apparatus using an a-Si photosensitive material and exhibiting a long life has been developed. If the foregoing technique for detecting the density is employed, the developer remains adjacent to the detecting surface of the toner-density sensor or toner adheres to the detecting surface of the transmission after the apparatus has been used for a long time. Thus, an error occurs in detecting the density of toner. As a result, the density cannot stably be detected for a long time.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to permit use of a product for a long time, prevent remaining of a developer and adhesion of toner in the vicinity of a detecting surface of a toner-density sensor, stably measure and control the density of toner.
Another object of the present invention is to provide a low-cost and reliable product which is capable of detecting the density of toner with a wide dynamic range regardless of joining of a toner-density sensor and dispersion and which does not require an adjustment process.
Another object of the present invention is to provide a developing apparatus which has a simple structure and capable of precisely detecting a state of loading of a developer container and a problem in the developing apparatus which can be used for a long time and which is capable of stably controlling the density of toner.
To achieve the foregoing object, according to one aspect of the present invention, there is provided an apparatus for controlling the density of a developer, comprising a developer container in which a developer composed of a carrier and toner is enclosed; detecting means for magnetically detecting information about the density of the toner in the developer container; toner supply means for supplying the toner in accordance with an output value of information about the detected density of the toner; waveform forming means for forming a waveform obtained by reducing an output value from the detecting means by operating mechanical means for periodically raking out the developer existing on a detecting surface of the detecting means; and toner-density-detection delaying means for inhibiting detection of the density of the toner from a predetermined time at which the output value has been reduced by the waveform forming means to a time at which the output value of information about the density of the toner is restored, wherein the toner supply means can be operated in accordance with information about the density of the toner detected after the operation of the toner-density-detection delaying means has been suspended.
Since the foregoing structure is employed with which the developer on the detecting surface is periodically raked out by the mechanical means, remaining of the developer and adhesion of toner to the detecting surface can be prevented. As a result, the density of the developer can stably be
Miyamura Hiroaki
Toda Saeko
Fish & Richardson P.C.
Grainger Quana M.
Kyocera Corporation
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