Image analysis – Image sensing
Reexamination Certificate
1997-12-18
2001-01-16
Grant, II, Jerome (Department: 2724)
Image analysis
Image sensing
C358S474000
Reexamination Certificate
active
06175666
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image scanning apparatus which can effect a sub-scanning operation by relatively and intermittently moving a main scanning unit and a recording medium stepwise, and can record or read an image by driving the main scanning unit each time the sub-scanning is stopped.
2. Description of the Prior Art
A number of image recording apparatuses for recording an image in an image scanning apparatus have been developed nowadays, which are each mounted with a digital exposure system. Generally, in the digital exposure system, an image is recorded on a recording medium in such a manner that a light beam outputted from a semiconductor laser is modulated with image data and the light beam is deflected by high-speed rotation of a polygon mirror (main scanning), and further the light beam reflected by the polygon mirror is subjected to sub-scanning with use of a galvano-mirror or the like, or the above main scanning is effected repeatedly while moving the recording medium (or moving the recording medium stepwise). In this case, as the recording medium, a photosensitive drum electrified by a corona discharge, a photosensitive material or the like may be used. Also, in place of the semiconductor laser, other light emitter such as an LED may be used as a light source.
In case of repeating the above main scanning while shifting the recording medium in a stepwise manner, it is general that a stepping motor is used for activating its stepwise movement. The stepping motor is suitable for performing a highly precise positioning because a stop position of the recording medium can be controlled according to pulse control.
A transmission system is usually interposed between a rotary shaft of the stepping motor and a conveying roller for carrying the recording medium, and a rotational speed of the stepping motor is transmitted to the conveying roller so as to be decelerated.
SUMMARY OF THE INVENTION
However, the aforesaid transmission system comprises a plurality of gears which mesh with each other. For this reason, even if the rotational speed of the stepping motor is controlled with high precision, there is a case where a step movement rate varies due to a meshing tolerance of these gears. If the step movement rate is not uniform, an interval between adjacent two main scanning operations (hereinafter referred to just as a main scanning interval) becomes irregular, whereby troublesome striped patterns occur in an image to cause a deterioration of an image quality thereof.
Taking such circumstances into consideration, it is an object of the present invention to provide an image scanning apparatus which can restrict unevenness in rotation of a transmission system, and can substantially make constant a main scanning interval so as to prevent a deterioration of an image quality.
To achieve the above object, the invention described in claim
1
provides an image scanning apparatus comprising: a drive motor; sub-scanning means for relatively and intermittently moving a main scanning unit and a recording medium stepwise when a driving force of the motor is transmitted; and main scanning means for effecting a main scanning operation by driving the main scanning unit each time a sub-scanning operation is stopped, wherein the image scanning apparatus further includes transmission means which is composed of a plurality of gears meshing with each other, and varies a rotational speed of the motor so that the driving force thereof is transmitted to the sub-scanning means, and is characterized in that one integer rotation of a selected one of the plurality of gears is adapted to be set as one step of a sub-scanning movement in the step movement.
In accordance with the present invention described in claim
1
, the gear is not strictly driven at an equal linear velocity within one rotation; for this reason, there is unevenness in the rotation due to a runout tolerance in a diameter direction. But an average linear velocity for one rotation is constant, and therefore, a feeding rate per one rotation is also constant. Based on this fact, one rotation is taken as a unit, and an integer rotation is set as one step of sub-scanning movement, whereby even if an error is caused in the moving rate of sub-scanning movement during its shifting movement, the sub-scanning operation is stopped at equal intervals when the main scanning operation is effected, preventing thereby an unevenness of the sub-scanning movement.
The number of teeth of gears is expressed by an integer. Therefore, if one gear is selected from the plurality of gears and an integer rotation of the selected gear (i.e., a rotation which usually makes constant a tooth position in the stopped state of the gear) is set as one step, an error which is normally caused when the same teeth are meshed with each other may be ignored.
For example, provided that the number of teeth of a gear (hereinafter, referred to as gear A) on a drive source side is 15 and the number of teeth of a gear (hereinafter, referred to as gear B) on an output side is 60, the relationship between the former (gear A) and the latter (gear B) is as shown in the following Table 1, and an error is converged at the number of rotation (a rotational speed) as shown in the Table 1.
TABLE 1
The number of integer
The number of
rotation of gear A
rotation of gear B
Convergence of error
1 (15 teeth)
¼
converged at 4 lines
2 (30 teeth)
½
converged at 2 lines
3 (45 teeth)
¾
converged at 4 lines
4 (60 teeth)
{fraction (1/1)}
converged at 1 line
As can be seen from the above Table 1, if four rotations of the gear A is set as one step, the gear B makes one rotation, and both gears A and B make an integer rotation, and an error is converged every one line. This is the most preferable selection of the gear.
The invention described in claim
2
provides the image recording apparatus according to claim
1
, in which the selected gear is a final step gear of the plurality of gears connected.
In accordance with the invention described in claim
2
, claim
1
has shown that an error may be converged at some few lines in number. Further, in the case where gears are connected to each other, there is the need of taking all the number of teeth of the gear connected in the downstream side of the selected gear into consideration. In the case where one gear is selected from the plurality of connected gears, if the final step gear thereof is selected, the only selected gear may be controlled so as to make an integer rotation; therefore, adjustment can be readily performed. In the above description, if the gear B is the final step gear, an error is constantly converged every one line, and a stable sub-scanning operation can be effected.
The invention described in claim
3
provides the image recording apparatus according to claim
1
or
2
, in which the plurality of gears have the number of teeth which is set in such a manner that two of those gears meshing with each other make an integer rotation.
In accordance with the invention described in claim
3
, the rotation of the gear is set so as to make an integer rotation. In this case, the sub-scanning moving rate is actually an extremely small value; for this reason, deceleration is a basic concept. If the gear on a drive side is set so as to make an integer rotation each time the gear on an output side makes one rotation, a duration until an error is converged can be shortened.
The invention described in claim
4
provides the image recording apparatus according to any one of claims
1
to
3
, in which an index indicative of the peak point of an error on a plus side is marked preliminarily onto one of the two gears meshing with each other and an index indicative of the peak point of an error on a minus side is preliminarily marked onto the other, and the two gears mesh with each other so that the two peak points meet each other.
In accordance with the invention described in claim
4
, it is preferable that an error is offset when gears mesh with each other. An index indic
Fuji Photo Film Co. , Ltd.
Grant II Jerome
Sughrue Mion Zinn Macpeak & Seas, PLLC
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