JPH0695176B2 - Scanning optics - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical system, and more particularly to miniaturization used in an apparatus for irradiating light on a medium to be scanned to record or detect information. The present invention relates to a suitable scanning optical system.

[Conventional technology]

First, a conventional technique will be described by taking a laser beam printer as an example of a recording apparatus to which a scanning optical system is applied.

FIG. 7 is a perspective view showing a schematic configuration of a conventional laser beam printer. In FIG. 7, a laser diode 1 generates a laser beam whose pulse modulation is controlled by a laser driving circuit 2. The laser beam generated by the laser diode 1 is condensed by the coupling lens 3 to become a light beam, which is deflected and scanned by the rotary polygon mirror 4, narrowed down by the Fθ lens 5 and focused on the irradiated surface of the photoconductive photosensitive drum 6. Image
A minute beam spot is formed. In the electrophotographic laser beam printer, a charging device 7, a developing device 8 and a transfer device 9 which are indispensable for the electrophotographic process are provided around the photosensitive drum 6.
Etc. are arranged. That is, the surface of the photosensitive drum 6 which is rotated in the direction of the arrow A in the drawing by a drive source (not shown) is uniformly charged by the charger 7, and then is exposed by scanning with the laser beam by the above-described scanning optical system to form an electrostatic latent image. An image is formed. The developing unit 8 develops an electrostatic latent image by rubbing the photosensitive drum 6 with a magnetic brush having a magnetic roll that adsorbs a one-component phenomenon agent with magnetic fine powder toner or a two-component phenomenon agent with magnetic carrier and differential toner. , A toner image is formed on the photosensitive drum 6. On the other hand, the recording paper 10 conveyed by a paper feed mechanism (not shown) comes into contact with the photosensitive drum 6, and the toner image on the surface of the photosensitive drum 6 is transferred by the electrostatic transfer device 9. Through the above process, the laser printer can record predetermined information. Further, as a control of these functions, a small reflecting mirror 11 for synchronizing the modulation signal, a photodetector 12, a synchronization signal generation circuit 1
3, the print signal control circuit 14 and the like are arranged.

FIG. 8 is a sectional view showing the main structure of a conventional general laser beam printer. 8, in the electrophotographic process described above, the components described in FIG. 7 are arranged around the photosensitive drum 6 in the order of the process as shown in the figure. Cleaning means for removing the toner remaining on the surface of 1
5. An erase lamp 16 for removing the electric charge remaining on the surface of the photosensitive drum 6 is arranged. On the other hand, the recording paper 10 stored in the paper feed cassette 17 is fed from the paper feed cassette 17 by the paper feed roller 18 and is paired with the upper and lower registration roller pairs 19, 1.
After the timing is adjusted at 9 ', the toner image is transferred to the transfer portion and transferred. After that, the recording paper 10 is fixed to the fixing device 20.
Then, the toner image is fixed and discharged onto the paper tray 22 by the upper and lower discharge roller pairs 21, 21 '.

In the laser beam printer described above, each element of the electrophotographic process emphasizes the stability of transfer, and
It is customary to arrange the 10 so that it can travel stably in the direction of gravity. That is, if the transfer device 9 is arranged below the vertical line passing through the center of the photosensitive drum 6 and the other elements are arranged in this order in the order of the process, the structure shown in FIG. 8 is naturally completed. become.

Further, since the photoconductive photosensitive drum 6 requires time for so-called light decay, in which the potential of the exposed portion decreases after exposure, the potential difference between the exposed portion and the non-exposed portion, that is, the potential contrast of the latent image is sufficient. In order to ensure the above, it is desirable to make the interval from exposure to development as large as possible. Therefore, as is apparent from FIG. 8, the exposed portion must be positioned above the photosensitive drum 6 (position facing the transfer device 9).

On the other hand, since the laser diode 1 (see FIG. 7) has a larger lifespan and temperature dependence of emission output characteristics than other semiconductor elements, it is usually arranged at a position where the change in ambient temperature is as small as possible. Therefore, in a laser beam printer of the electrophotographic system whose mainstream is the heat fixing system, it is inevitably located on the opposite side of the fixing device 20. Further, the developing device 8 usually occupies a large space as compared with other process components for the purpose of increasing the toner supply capacity, and the laser scanning optical system 23 has its optical path in the developing device 8. After passing through the upper side, it is inevitable to be bent by the reflecting mirror 24 to reach the information on the photosensitive drum 6.

The laser beam printer having the conventional general structure described above has a long shape in the conveying direction of the recording paper when the recording paper feeding device is included, and as a result, the installation floor area, that is, the laser beam printer Occupied floor area tends to increase. In this respect, recording devices other than the electrophotographic system,
For example, thermal transfer type printers, daisy-hole type printers, wire dot type printers, etc. have the feature that they occupy an overwhelmingly small floor area. At present, it is widely used for general-purpose OA equipment.

However, in recent years, the high speed of the laser beam printer,
The advantages of low noise and high resolution have been recognized, and the demand for printers for personal use is increasing. Along with this, there has been a strong demand for downsizing to the same extent as conventional lightweight printers.

[Problems to be solved by the invention]

As mentioned above, miniaturization of the laser beam printer,
In particular, it is desired to reduce the occupied floor area, and as a method for realizing it, the electrophotographic process is downsized, and the paper feeding / discharging device configuration method is devised, while the scanning optical unit is downsized. As a method, it has been considered to increase the deflection angle of the rotary polygon mirror to shorten the optical path length, but this method has a certain limit for the following reason.

(1) The angle of view of the Fθ lens increases and aberration increases, which deteriorates the imaging performance.

(2) The amount of deflection reflection points of the rotary polygon mirror that come in and out with rotation increases, and the imaging performance of the Fθ lens deteriorates.

(3) The number of rotations of the rotary polygon mirror increases, noise, rotation accuracy,
It causes a decrease in life.

(4) The change of the refraction entering and refracting the optical element becomes large, and the optical path efficiency changes in the scanning direction.

(5) As the angle of view increases, the diameter of the Fθ lens increases, resulting in higher cost, and the number of lenses increases due to aberration correction, which also increases cost.

Therefore, in the conventional scanning optical system, the number of images of the rotary polygon mirror is a minimum of 6, the practical deflection angle is 100 degrees, and the optical path length is 200 mm between the rotary polygon mirror and the photosensitive drum. That is,
It is difficult to downsize the scanning optical system with respect to the other components, which hinders the downsizing of the laser beam printer.

On the other hand, in recent years, an exposure means using an LED array or a liquid crystal shutter has been put into practical use, and downsizing of the apparatus can be realized by using these, but the light source becomes an enormous number of aggregates. Therefore, there is a problem in its reliability and a modulation method, and it has not been widely spread yet.

In short, conventionally, the Fθ lens used in the scanning optical system is a relatively large optical element because it is configured by housing three or more spherical single lenses in the lens barrel. In a scanning optical system using a rotary polygon mirror, a method of providing a long convex cylindrical lens in the vicinity of the photosensitive drum is known for the purpose of correcting the surface tilt of the rotary polygon mirror. This is one of the factors that make it difficult to miniaturize the system.

On the other hand, in the scanning optical system having the tilt correction function proposed in Japanese Patent Laid-Open No. 57-144516, a very simple scanning optical system in which the Fθ lens is composed of two single lenses can be realized. There is, but according to this,
The Fθ lens is composed of a spherical single lens and two single lenses having a toric surface in order from the deflection point of the rotary polygonal mirror, and the single lenses are separated by a gap, which is not so great for downsizing the scanning optical system. It doesn't seem to have much effect.

An object of the present invention is to provide a scanning optical system capable of ensuring a space capable of increasing the hopper capacity of the developer of the developing device and shortening the optical path to the minimum.

[Means for solving problems]

The object is to provide a light source, a deflection scanning means for deflecting and scanning the light from the light source onto a medium to be scanned, and a deflection scanning means which is located in an optical path between the deflection scanning means and the medium to be scanned. Image forming optical means for forming an image on the surface to be scanned of the medium to be scanned by receiving the emitted light, and driving means for rotating or rotating the deflection scanning means about the reference axis is the reference axis. This is achieved by a configuration in which the deflection scanning means on the center is arranged above the deflection scanning means.

[Work]

Since the driving means for turning or rotating the deflection scanning means around the reference axis is arranged above the deflection scanning means on the center of the reference axis, a space for increasing the hopper capacity can be secured, and the imaging optics can be secured. Since the Fθ lens of the means is composed of a plurality of single lenses and the optical path passes through the gap between the single lenses at least twice, the optical path can be shortened to the minimum.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in FIGS.

FIG. 1 is a sectional view showing an embodiment of the scanning optical system of the present invention, showing an example applied to the laser beam printer shown in FIG. 8, and the constituent elements corresponding to FIG. Is attached.

In FIG. 1, the paper feed cassette 17 is arranged above the laser beam printer, and the paper discharge tray 22 is also arranged above the laser beam printer. By doing so, it is possible to incorporate most of the paper feeding / discharging mechanism that has conventionally been projected outward from the laser beam printer, and it is possible to greatly reduce the occupied floor area.

In response to this, the scanning optical system 23 is configured as described below. That is, the laser beam deflected and scanned by the rotary polygon mirror 4 has an Fθ lens 5 composed of two single lenses.
After passing through the first single lens 5a and the second single lens 5b, the light is reflected by the first reflecting mirror 25 and the second reflecting mirror 26 as shown in FIG. An image is formed on the surface to be scanned of the photosensitive drum 6 through the gap between the lenses 5b. Comparing this with FIG. 8, since the optical path of the scanning optical system is folded back twice and further passes through the gap between the two single lenses 5a and 5b, the scanning optical system 23 is shortened to the minimum size. It is clear that

A further noteworthy feature is that the second single lens 5b can be moved to a position overhanging the rotary polygonal mirror 4 on the vertical line passing through the center of the photosensitive drum 6. Conventionally, attempts have been made to miniaturize the scanning optical system by folding the optical path of the laser beam so as to intersect in space.
In the present invention, by adopting the above-mentioned optical path configuration, at least the size of the second single lens 5b can be made smaller than the conventional method.

Still another feature is that the distance between the rotary polygon mirror 4 and the photosensitive drum 6 becomes very short. That is, the photosensitive drum 6
The space on the right side of FIG. As a result, the dimensions of the laser beam printer housing are not restricted by the scanning optical system 23 as in the conventional example, and can be greatly reduced.

By the way, due to the downsizing of the scanning optical system, the rotary polygon mirror 4 is located almost directly above the developing device 8, but the developing device 8 is provided with a hopper for replenishing the developer, and its capacity is It is desired to be as large as possible to reduce the supply cycle. However, since the rotary polygon mirror 4 is located above, the capacity thereof is limited. In order to avoid this problem, the present invention further improves the following points.

FIG. 2 is a sectional view corresponding to FIG. 1 showing another embodiment of the present invention. In FIG. 2, the drive motor 27 of the rotary polygon mirror 4 is rotated with respect to FIG. It is moved to the upper side of the rotary polygon mirror 4 on the central axis. By doing so, a wide space can be secured above the developing device 8 and the hopper capacity of the developer can be secured as in the conventional case.

3 to 6 are sectional views showing other embodiments of the scanning optical system of the present invention. In FIG. 3, the Fθ lens is composed of three monospherical lenses, and the scanning beam passes through the gap between the first single lens 5a and the second single lens 5b twice. In addition, the same effect can be obtained by separately passing the gap between the second single lens 5b and the third single lens 5c twice.

In FIG. 4, the second reflecting mirror 26 in FIG. 2 is replaced with a cylindrical mirror 28. By making the reflecting mirror non-planar, the degree of freedom in designing the optical system is increased and the performance is improved. is there.

In FIG. 5, the third reflecting mirror 29 is used in addition to the first reflecting mirror 25 and the second reflecting mirror 26, and all the gaps between the three single lenses 5a, 5b, 5c of the Fθ lens are used. The scanning beam passes through twice.

In FIG. 6, in FIG. 5, a long cylindrical lens 30 is provided side by side with respect to the photosensitive drum 6 to form a compact surface tilt correction scanning optical system.

〔The invention's effect〕

As described above, according to the present invention, since the gap between the plurality of single lenses forming the Fθ lens is the scanning optical system having the optical path configuration that allows the scanning beam to pass through at least twice, the optical path can be shortened to the minimum. Moreover, since the driving motor for the rotary polygon mirror is arranged above the rotary polygon mirror, it is possible to increase the hopper capacity of the developer of the developing device, and moreover, in the apparatus using the scanning optical system. There is an effect that the occupied floor area can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an example applied to a laser beam printer showing an embodiment of a scanning optical system of the present invention, and FIG. 2 is a sectional view corresponding to FIG. 1 showing another embodiment of the present invention. 3 to 6
FIG. 7 is a sectional view showing another embodiment of the scanning optical system of the present invention, FIG. 7 is a perspective view showing a schematic configuration of a conventional laser beam printer, and FIG. 8 is a main view of a conventional general laser beam printer. It is sectional drawing which shows a structure. 1 ... Laser diode, 2 ... Laser driving circuit, 3 ... Coupling lens, 4 ... Rotating polygon mirror, 5 ... F.theta. Lens, 5a ... First single lens, 5b ... Second single lens, 5c ... third single lens, 6 ... photoconductive photosensitive drum, 8 ... developing device, 25 ... first reflecting mirror, 26 ... second reflecting mirror, 27 ... drive motor, 28
...... Cylindrical mirror, 29 …… Third reflecting mirror, 30 …… Long cylindrical lens.

Claims (9)

[Claims] 1. A light source, a deflection scanning means for deflecting light from the light source onto a medium to be scanned, and a deflection scanning means positioned in an optical path between the deflection scanning means and the medium to be scanned. Image forming optical means for receiving light to form an image on the surface to be scanned of the medium to be scanned, and driving means for rotating or rotating the deflection scanning means around the reference axis. A scanning optical system characterized in that it is arranged above the deflection scanning means on the center. 2. The image forming optical means includes an Fθ lens composed of a plurality of single lenses, and an optical path of light to be scanned passes through a gap between the single lenses at least twice and the scanned medium. The scanning optical system according to claim 1, wherein the scanning optical system is configured to change so as to reach. 3. The scanning optical system according to claim 1, wherein the light source comprises a laser beam generating means. 4. The scanning optical system according to claim 1, 2 or 3, wherein said deflection scanning means is a rotary polygon mirror. 5. The scanning optical system according to claim 2, wherein the Fθ lens is composed of three or less single lenses. 6. The scanning optical system according to claim 2, wherein said Fθ lens is composed of two single lenses, and the single lens on the side of the medium to be scanned includes a toric surface. 7. The scanning optical system according to claim 2, wherein the means for changing the optical path of the scanned light comprises a plurality of reflecting mirrors. 8. The scanning optical system according to claim 7, wherein the reflecting mirror includes a plane mirror. 9. The medium to be scanned is a photoconductive photoconductor of an electrophotographic recording apparatus, claim 1 or 2 or 3 or 4 or 5 or 7. Alternatively, the scanning optical system according to item 8.