Adjustment control and adjustment control method

Details Adjustment control and adjustment control method Adjustment control and adjustment control method

2001-03-07

2003-07-08

Follansbee, John (Department: 2121)

Data processing: generic control systems or specific application

Generic control system, apparatus or process

Optimization or adaptive control

C700S028000, C700S059000, C700S033000, C700S045000, C399S042000, C399S363000, C399S406000

Reexamination Certificate

active

06591147

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an adjustment control system such as an image quality maintaining adjustment means for an optical unit for reading an original image, a color laser printer, a color digital copying machine, etc., which is provided in an image forming apparatus such as an analog copying machine, a digital copying machine or a facsimile, as well as to an adjustment control method.
As an example of an image forming apparatus, an analog copying machine comprises an optical unit for reading an image of an original placed on an original table of glass, and a process unit for forming a developer image on the basis of the image read by the optical unit and transferring it onto a recording medium such as a paper sheet.
In the copying machine, a resolving power of a finally obtained copy image varies depending on a resolving power for exposure on a photosensitive drum and a fidelity reproducibility of an electrophotographic process for the exposure image.
The resolving power for exposure on the photosensitive drum varies depending on lens characteristics, a stop, mirror flatness, a position and an attitude of a lens and a mirror, relative positions of the original table and the photosensitive drum, etc. As regards the lens characteristics and stop, it is desired that a uniform, high resolving power (MTF characteristics) be obtained over the entire image region of an image surface, the exposure light amount be sufficient, and the total path length be as short as possible. In addition, it is required that the lens characteristics and stop provide a wide tolerable range of resolving power, i.e. focal depth, so as to cancel an error in a relative position among an object surface (original surface), a lens and an image-formation surface (photosensitive drum).
The above requirements are contradictory in physical aspects. In fact, the lens has aberration (e.g. curvature of field). Furthermore, if a demand for decrease in manufacturing cost is considered, it is difficult to meet all the requirements, and optimization needs to be achieved for a compromise.
Normally, a lens optimized as mentioned above is so designed that an ideal (design-value) image-formation surface may be included within a focal depth. However, the relative position among the position/attitude of the lens and mirror, the original table and the photosensitive drum will vary due to a sum of variances in tolerance of many parts and in tolerance of assembly.
Since the lens aberration gradually increases away from the optical axis at the center of the lens, the resolving power gradually decreases toward an end portion of the image-formation surface. In addition, since the photosensitive drum surface serving as the image-formation surface is cylindrical, the variation in the exposure position leads to a variation in optical path length. Degradation in resolving power occurs due to a deviation from the focal position. In addition, the magnification varies and the resolving power deteriorates because of displacement of the same image point due to scanning (since slit exposure is performed, a latent image will blur unless the position on the photosensitive drum is uniform in association with the image points of the original in the slit width in scanning). Thus, if the optical positional relationship between the object surface and the image-formation surface is not kept, the resolving power deteriorates more greatly at end portions of the image-formation surface.
Even if the original surface and the drum exposure position are set in a physically ideal positional relationship, the optical relationship between the object surface and the image surface or the relationship between the focal plane and the image-formation surface will differ from an ideal positional relationship due to the position and attitude of the mirror and lens. If optical parallelism between the focal plane and the image-formation surface is lost, there is only one contact point therebetween. Consequently, degradation in resolving power on the entire image region cannot be improved by the adjustment of the optical path length in the optical-axis direction.
The resolving power may degrade due to such factors as the lens characteristics, e.g. focal depth or MTF characteristics, and positioning of the original table, mirror, lens and photosensitive drum. If the degradation due to these factors are to be improved by enhancing precision in machining the respective parts and precision of parts of the support member, the cost will increase.
It is difficult to observe the degraded resolving power by the naked eye and to specify the factor of degradation, on the basis of the obtained copy image. In addition, to modify/correct the factor will considerably lower the productivity. The degradation in resolving power will occur not only due to optical factors but also due to factors in the image forming process. Moreover, distortion of images will occur due to optical factors, and similar phenomena will occur due to factors in a paper sheet conveying system, etc. Since the degree of distortion is on the order of 100 microns, it is very difficult to quantatively observe it by the naked eye.
Since the above-mentioned adjustment of the optical system is conducted in the production line of copying machines or in the maintenance work, if some element is adjusted, other elements may vary consequently. In most cases, it is difficult to satisfactorily adjust all elements.
Besides, in the case of another example of the image forming apparatus, many users may have felt that the density of copies varies despite the same original being copied by the same copying machine. The variation in image density in electrophotography occurs due to a change or degradation in image formation conditions resulting from a variation in environment or a variation over time. In multi-gradient printers or digital copying machines, as well as analog copying machines, it is important to suppress a variation in image density and to stabilize and maintain the image quality. In particular, in color modes, such a variation will affect not only the density reproducibility but also color reproducibility. Thus, the stabilization in image density is an imperative requirement.
Under the circumstances, a feedback control is performed in the prior art. Plural test patterns are formed on an image carrying body, and the image densities of these test patterns are detected and a variation in gradient characteristics is found. Thus, adjustment and good/bad judgment of the operating portions of the image forming section are repeated in this feedback control. In this case, the calculation of an operation amount corresponding to a control amount deviation is carried out on the basis of a look-up table prepared in advance. The content of such a look-up table is prepared in an off-line mode. In preparation, it is necessary to conduct various experiments and find the characteristics of the object to be adjusted (the operation amount corresponding to the control amount). Thus, a great deal of labor and time is required in the preparation work.
In a multi-input/multi-output system, in general cases, the input/output relationship is not independent. Thus, in order to describe the input/output relationship on the look-up table, the same number of look-up tables as the number of orders of inputs/outputs are required. In the case of the system with a large number of orders, a large memory capacity is required and the identification work is very large. In addition, the relationship does not always coincide with the object apparatus, because of non-linear characteristics, an inter-object variance, reproducibility and a variation over time, etc. The adopted feedback control is feasible for cases where the identification is somewhat incomplete, but the number of times of convergence and control time for good/bad determination become greater by a degree corresponding to a difference from the identified apparatus.
As has been described above, where there are plural adjustment points, such adjustment point

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