Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-01-22
2001-02-13
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S248000, C250S235000
Reexamination Certificate
active
06188424
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a light beam scanning apparatus for making laser light beams to scan and expose the surface of a single photosensitive drum simultaneously and thereby forming a single electro-static latent image on the photosensitive drum, an image forming apparatus, such as a digital copying machine or a laser printer, using the light beam scanning apparatus, and a method of adjusting the image forming apparatus.
In recent years, various digital copying machines have been developed which form images by, for example, scanning exposure by laser light beams (hereinafter, referred to as light beams) and electronic photographic processing.
To step up the image forming speed, the multi-beam digital copying machines have recently been developed. In this type of digital copying machine, more than one light beam is generated and they are made to scan in units of lines simultaneously.
The multi-beam digital copying machine is provided with an optical system unit acting as a light beam scanning apparatus. The optical system unit is composed primarily of semiconductor laser oscillators for generating laser beams, a polyhedral rotating mirror, such as a polygon mirror, and optical-path control means. The polyhedral rotating mirror reflects the laser beams emitted from the laser oscillators toward a photosensitive drum to make each laser beam to scan the surface of the photosensitive drum. The optical-path control means is composed of a collimator lens, an f-&thgr; lens, and a galvanomirror for shifting the passing position of each light beam over the photo-sensitive drum in the sub-scanning direction.
With the configuration of a conventional optical system unit, it is very difficult to control the positional relationship between light beams on the surface of a photosensitive drum (the scanning surface) or to bring the passing positions of light beams into an ideal positional relationship. To achieve this, not only very high-accuracy parts and assembly but also very high-accuracy light-beam passing position control are needed, which leads to a rise in the cost of the apparatus.
Even when the light beams have been controlled so as to have an ideal positional relationship, noise can interfere with the driving lines for a light beam actuator, such as a galvanomirror, after the control, which will possibly lead to an erroneous operation of the galvanomirror, permitting the passing positions of the light beams to deviate from the target position.
In addition, there is a possibility that the passing positions of the light beams will depart from the target position due to vibration made by the image forming apparatus or externally applied vibration.
Furthermore, noise can interfere with the output of a sensor for sensing the passing position of a light beam, which will possibly perform control on the basis of erroneous information on the light beam position.
Moreover, in a light beam actuator, such as a galvanomirror, the hysteresis or sensitivity generally varies. Such variations in the hysteresis or sensitivity have an adverse effect on control of the passing positions of the light beams. For example, there is a possibility that control will vibrate and the light beams will not converge in the control target area.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a light beam scanning apparatus and an image forming apparatus which are capable of eliminating the effect of noise and bringing the passing position of a light beam to the control target position accurately.
Another object of the present invention is to provide a light scanning apparatus and an image forming apparatus which enable control of the passing position of a light beam to converge in a short time reliably, taking into account variations in the hysteresis or sensitivity of a light beam actuator, such as a galvanomirror.
Still another object of the present invention is to provide a method of adjusting an image forming apparatus which enables servicemen to easily grasp the control state of a light beam through visual inspection and facilitates the investigation and determination of the cause of inadequate images and therefore maintenance service.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a light beam scanning apparatus comprising: light beam generating means for generating a light beam; scanning means for reflecting the light beam generated at the light beam generating means to a scanning surface and making the light beam to scan the scanning surface in the main scanning direction; shifting means for shifting the light beam in sub-scanning direction when the light beam is made to scan by the scanning means; light beam sensing means for sensing a passing position in the sub-scanning direction of the light beam made by the scanning means to scan the scanning surface; control means for controlling the shifting means on the basis of the result of sensing at the light beam sensing means so that the passing position of the light beam on the scanning surface may be within a target range; judging means for, after the control means has brought the passing position of the light beam on the scanning surface into the target range, measuring the passing position of the light beam scanning the scanning surface a specific number of times using the light beam sensing means and judging whether all of the passing positions lie in the target range; and re-executing means for making the control means to execute passing position control of the light beam again when the result of measuring the light beam passing position the specific number of times includes a value outside the target range.
To shift the optical path of the light beam in the sub-scanning direction, the passing position of the light beam is brought into a final target range in such a manner that the target range is forced to converge stepwise in a first range and then in a second range narrower than the first range.
According to another aspect of the present invention, there is provided an image forming apparatus which makes light beams to scan and expose an image retaining member and thereby forms an image on the image retaining member, the image forming apparatus comprising: a plurality of light beam generating means for generating light beams; scanning means for optically combining the light beams generated at the plurality of light beam generating means and then reflecting the resulting beams to a scanning surface and making the light beams to scan the scanning surface in the main scanning direction; a plurality shifting means for shifting the light beam in sub-scanning direction when the light beam is made to scan by the scanning means; a plurality of light beam sensing means for sensing passing positions in the sub-scanning direction of the light beams made by the scanning means to scan the scanning surface; control means for controlling the plurality of shifting means on the basis of the result of sensing at the light beam sensing means so that the passing position of each of the light beams on the scanning surface may be within a target range; judging means for, after the control means has brought the passing positions of the light beams on the scanning surface into the target range, measuring the passing position of each of the light beams scanning the scanning surface a specific number of times using the light beam sensing means and judging whether all of the passing positions of the light beams lie in the target range; re-executing means for making the control means to execute passing position control of the light beams again when the result of measuring the light beam passing position of each of the light beams the specific number of times includes a value outside the target range; and image forming means for, after the judging means has judged that all of the passing positions of the light beams are within the target range, driving the plurality of light beam generating means and scanning means on the basis of an inputted target data item a
Ide Naoaki
Komiya Kenichi
Sakakibara Jun
Tanimoto Koji
Foley & Lardner
Le N.
Nguyen Lamson D.
Toshiba Tec Corporation
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