Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-09-30
2002-12-31
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S216100, C250S236000
Reexamination Certificate
active
06501585
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a multi-beam exposure apparatus scanning a plurality of light beams and usable for a plural drum type color printer apparatus, a plural drum type color copier, a multicolor printer, a multicolor copier, a monochromatic high speed laser printer, a monochromatic high speed digital copier and the like.
BACKGROUND ART
For example, in an image forming apparatus such as a color printer apparatus, a color copying apparatus which employs an image forming unit including a plurality of photosensitive drums, there is employed an exposure apparatus which supplies a plurality of light beams having the number the same as the number of plural image data corresponding to separated color components, that is, at least the number of image forming units.
This kind of exposure apparatus has a plurality of semiconductor laser elements emitting a predetermined number of light beams corresponding to the image data at each of the separated color components, a first lens group stopping down a cross sectional beam diameter of the light beam after each of the semiconductor laser elements is emitted to a predetermined size and shape, an optical deflecting apparatus operated in accordance that a recording medium holding the image formed by each of the light beams continuously reflects in a direction perpendicular to a transferred direction, a second lens group image forming the light beam deflected by the optical deflecting apparatus on a predetermined position of the recording medium, and the like. Here, in many cases, a direction in which the laser beam is deflected by the optical deflecting apparatus is indicated to be a main scanning direction, and a direction in which the recording medium is transferred, that is, a direction perpendicular to the main scanning direction is indicated to be a sub scanning direction.
The exposure apparatus mentioned above is classified into an embodiment which employs a plurality of exposure apparatuses corresponding to each of the image forming units according to the applied image forming apparatus and an embodiment which employs a multi-beam exposure apparatus capable of supplying a plurality of light beams by means of one exposure apparatus. In this case, in recent days, in order to increase an image forming speed and improve a resolution, there has been also proposed a high speed printer apparatus capable of forming an image having a high resolution and forming an image at a high speed by exposing image data having the same color in a parallel manner.
However, in the exposure apparatus mentioned above, when a rotational speed of the reflection surface of the optical deflecting apparatus is increased in order to increase the speed of the image forming apparatus and improve the resolution, it is necessary to employ an expensive bearing such as an air bearing which can stand against the high speed rotation on the reflection surface. On the other hand, as well as the rotational speed of the motor has an upper limit, the motor capable of rotating at a high speed is expensive and a drive circuit for rotating the motor is also expensive, so that there is a problem that an increase of the rotational speed of the reflection surface corresponding to an increase of the cost can not expected. In this case, when the rotational speed of the reflection surface is increased, as a result, there is generated problems that the wind sound is increased as well as the wind damage on the reflection surface is accelerated.
On the other hand, it is possible to restrict an increase of the rotational speed of the motor when increasing the number of the reflection surfaces, however, since an image frequency is increased, there is a problem that a noise component superimposed on the image signal (image data) at a high possibility is increased. Further, when the image frequency is increased, there is a problem that various kinds of limitations are generated in designing or mounting the control circuit.
Accordingly, there has been proposed a multi-beam exposure which can reduce each of the rotational speed of the reflection surface and the image frequency by allocating a plurality of light beams to each of the separated color components and deflecting (scanning) them at one time, however, even in the case of employing the multi-beam exposure, there are various kinds of problems as mentioned below.
That is, in the multi-beam exposure, there is employed a method of using a plurality of light sources for each of the separated color components and combining the light beams emitted from each of the light sources at a color component unit so as to deflect (scan) as one light beam, and a semiconductor laser element is employed for the light source.
However, it has been known that a wavelength of the light beam (the laser beam) irradiated from the semiconductor laser element is varied in a luminescent wavelength according to a temperature of an environment in which the laser element is placed. Further, each of the semiconductor laser elements is different in a changing amount of the luminescent wavelength with respect to the temperature change. In this case, when the temperature is varied in the periphery of each of the semiconductor laser elements and levels of a change with age are different from each other in each of the laser elements, the wavelengths of the light beams emitted from the respective light sources are varied.
Further, since the characteristic of the semiconductor laser element includes a mode hopping phenomenon that the luminescent wavelength is about 1.5 nm changed with respect to the temperature change about 0.1° C., it is hard to uniformly align the luminescent wavelength of all the laser elements at a wide environmental temperature range even when aligning the luminescent wavelength under a certain condition.
As mentioned above, in the case that the luminescent wavelength of the light beam irradiated from each of the semiconductor laser elements is changed due to the temperature change, in detection of a horizontal synchronism and definition of a writing position structured such as to arrange a beam detecting sensor for detecting the horizontal synchronism, for example, at a position equivalent to a mirror surface, to detect the fact that the light beam enters into the sensor by emitting the light beam prior to a timing at which the beam passes through the sensor, and to write the image by setting that the light beam is at the same position at the detecting timing and enters into the image area after a fixed time thereafter, an oscillating angle when the light beam is guided to each of the reflection surfaces of the deflecting apparatus becomes a different angle even when the timing at which the light beam enters into the sensor is the same.
That is, since the position of the beam detecting sensor is fixed, the writing position of the image is substantially maintained to a fixed value when writing the image a fixed time after detecting the fact that the light beam enters the sensor in the case that the luminescent wavelength is changed due to the temperature change, however, at a position opposite to the writing position, at which the exposure of the image is finished, there is a problem that a twice times of change (2×&Dgr;&thgr;) is generated when setting the change amount of the oscillating angle on each of the reflection surfaces in the deflecting apparatus when the light beam scanned to the same place by the change component of the wavelength changing due to the change of the temperature reaches, to &Dgr;&thgr;.
This generates a phenomenon that a color is shifted, a predetermined color can not reproduced and the like, in a color printer apparatus, and there is a problem of reduction of the resolution and generation of jitter caused by changing an outer diameter and a shape of a dot (an assembly of the light beam on the photosensitive body) constituting the image, in a high speed printer apparatus.
DISCLOSURE OF INVENTION
An object of the present invention is to provide an exposure apparatus for scanning a plurality of beams,
Fukutome Yasuyuki
Shiraishi Takashi
Yamaguchi Masao
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