Electrophotography – Image formation – Exposure
Reexamination Certificate
2002-11-20
2004-06-22
Tran, Hoan (Department: 2852)
Electrophotography
Image formation
Exposure
C318S696000
Reexamination Certificate
active
06754463
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an image reading apparatus mounted on a copy machine, a printer, a facsimile machine, a scanner, etc., and a method of accelerating the drive of a reading portion of an image reading apparatus.
2. Description of the Related Art
With a conventional image reading apparatus for reading an image by scanning an optical unit (e.g. lamp, mirror) across an original document or the like, the optical unit accelerates while moving from a stop position (home position) to an image reading position to a predetermined speed, and then begins to read in a constant speed from the image reading position. However, in a case where a motor of the image reading apparatus is rapidly accelerated or decelerated, the optical unit cannot switch smoothly to the constant speed due to inertia caused by the rapid acceleration or deceleration thereof, thereby causing the optical unit to overshoot. Therefore, in a case where the optical unit reaches the image reading position before the overshot is recovered, the optical unit cannot move at a constant speed, thereby creating irregular images such as shaky images, or overlapped images. Particularly, in reading with a full color reading apparatus employing an RGB (Red-Green-Blue) tri-linear CCD (Charge Coupled Device) sensor, the optical unit lurches to cause the RGB tri-linear CCD sensor to deviate slightly from an RGB reading position, thereby resulting to problems such as inadvertently coloring both sides of a black line. An excessive rapid acceleration being uncontrollable for a torque of the motor causes the motor to lose synchronism, and result to stoppage of the image reading apparatus. However, attempting to solve the foregoing problem by reducing rapid acceleration requires a large runway space for acceleration, thereby requiring a large sized apparatus which results to an increase in manufacture cost. Therefore, in order to provide an image reading apparatus of high speed, small size, and low cost for enhancing productivity, the image reading apparatus is required to accelerate to high speed while restraining the shock or overshoot caused when the rate of acceleration is changed.
For example, in a conventional art shown in Japanese laid open publication No. Hei10-23215 for restraining overshoot, a motor is accelerated to a target rate from the exact point where the motor reaches peak speed in response to a rapid increase in the driving rate. Nevertheless, in a case where magnification for image reading is adjusted by changing the scanning speed of the optical unit, acceleration needs to achieve a suitable speed for any given magnification factor within the range of the magnification. Therefore, CPU for control would be burdened with a considerable load since an acceleration curve in achieving a required speed is to be calculated each time and since an acceleration rate is to be controlled for achieving smooth acceleration.
For solving such problem, another conventional art shown in Japanese patent laid open publication No. Hei8-186690 provides a memory apparatus storing therein curves for acceleration and deceleration beforehand, and controlling acceleration and deceleration by reading the curves from the memory apparatus.
Nevertheless, since the conventional art shown in Japanese patent laid open publication No. Hei10-23215 is not mainly aimed to restrain the problem of overshoot, the degree of overshoot and the timing of overshoot for the conventional art largely depend on factors such as the property of the driving components or the assembling method thereof. Accordingly, with the conventional art, the point at which peak speed is observed would be inconstant, and the motor may lose synchronism by failing to switch acceleration rate at the exact timing.
In a case of the conventional art shown in Japanese patent laid open publication No. Hei8-186690, an increase in acceleration rate is required for shortening runway length if a single table for acceleration is used to cover all ranges of reading speed. Such case causes problems such as irregular images and loss of synchronism of the motor. An attempt may be made to solve the foregoing problems by preparing a plurality of tables suitable for all reading speeds. For example, in a case of changing magnification from 25 percent to 400 percent, the fastest reading speed would be 16 times faster than the slowest reading speed. A considerably large memory capacity for storing the tables is thus required for covering such speed range.
It is therefore an object of this invention to provide an image reading apparatus, having high speed, small size and low cost, capable of reducing CPU load and capacity required for storing a table therein.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an image reading apparatus that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.
Features and advantages of the present invention will be set forth in the description which follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by an image reading apparatus particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an image forming apparatus, including a reading portion for reading an image by scanning an original document, driving means for driving the reading portion, and memory means for storing therein a plurality of driving frequencies for enabling the driving means to switch to a variety of speeds and drive in a step by step manner, and for storing therein a table indicative of a switching point for switching one driving frequency of the plurality of driving frequencies to another driving frequency of the plurality of driving frequencies, wherein one driving frequency of the plurality of driving frequencies is switched to another driving frequency of the plurality of driving frequencies at the switching point.
The reading portion of the image reading apparatus comprising a lamp, a mirror, and a carriage for supporting the lamp and the mirror, is formed as a single unit. The reading portion having a substantial amount of weight gains speed due to moment of inertia created when the reading portion is driven. The reading portion having gained speed will therefore overshoot when slowed down. The degree of overshoot increases in association with the increase in the difference between acceleration rate and deceleration rate, and also in association with the increase in the moment of inertia. A method of forming a reading portion as light as possible or a method of reducing the driving rate could be introduced for reducing overshoot. Nevertheless, there are limits in lightening the weight of the reading portion, and the reduction of driving rate would lower the performance of the image reading apparatus. In a conventional method, a reading portion before reaching an image reading area is moved to a prescribed point as fast as possible, and is then slowed down to a speed for preventing an overshoot upon reaching the proximity of the image reading area. The conventional method, however, has a drawback of requiring a considerable amount of memory capacity for storing therein various curves to cover all reading speeds corresponding to changes in magnification. In solving the foregoing problem, this invention uses a table indicative of a point for switching one driving frequency of a plurality of driving frequencies to another driving frequency of a plurality of driving frequencies, and determines driving frequency with reference
Nagao Yoshiaki
Nishikino Sachiko
Takahashi Takuji
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
Tran Hoan
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