JP2706976B2 - Scanning optical device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical device such as an image forming apparatus that scans a recording medium such as a photoconductor with a flying spot from a laser or the like, and more particularly to stabilizing a spot diameter. Scanning optical device.

[Prior art] Conventionally, in a laser beam printer using an electrophotographic photoreceptor, a silver halide photographic photoreceptor, or the like, an image forming state of a beam spot formed on the photoreceptor is placed on a part of a laser beam scanning line. In general, the beam is observed by guiding the beam to the photoelectric conversion element through the reflecting mirror, and the imaging state of the beam spot on the photosensitive member is adjusted based on the result (for example, see Japanese Patent Application Laid-Open No. −275868).

In addition, there has been a device in which a reflection mirror is placed outside the photoreceptor on the scanning line of the laser beam and the image formation state of the beam spot is similarly observed (Japanese Patent Application Laid-Open No. 60-9243).

[Problems to be Solved by the Invention] However, in the above-described conventional example, the image formation state of the spot on the photoconductor is not observed by directly detecting the beam from the photoconductor, but is observed in a pseudo manner. Things.

On the other hand, with the rapid spread of desktop publishing in recent years, laser beam recording is required to have higher image quality. However, it is known that the resolution of the conventional method described above hits the limit in the range of 400 dpi (dot per inch) to about 600 dpi. Another observation method is needed.

Accordingly, the present invention provides a scanning optical device configured to directly detect a light-collecting state of a spot focused on an irradiation target such as a photoconductor in order to solve the above-described problem. It is an object.

[Means for Solving the Problems] In the present invention for achieving the above object, in the present invention, scanning light from a portion outside a use area (for example, an image forming area in an image forming apparatus) on an irradiation target such as a photoconductor is used. There are provided spot detection means for receiving the light and detecting the condensing state of the scanning light on the object to be irradiated, and control means for controlling the condensing state of the light beam in accordance with an output signal from the detecting means.

The reflectivity of the portion outside the use area is changed to an appropriate degree compared to the use area, whereby the scanning light is spotted by the spot detecting means between the use area and the portion outside the use area. You may comprise so that the time point which changes may be detected.

Further, the control means controls the collection of the luminous flux such that the change in the received light quantity of the luminous flux detected by the spot detecting means, which changes when the luminous flux moves between the use area and the portion outside the use area, becomes zero. It may be configured to control the light state.

[Operation] In the scanning optical device having the above-described configuration, since the spot detecting means for observing the spot of the scanning light formed on the object to be irradiated such as a photoconductor is provided, the collection of the spots on the object to be irradiated is provided. The light condition is directly and reliably detected, so that the light collection condition can be controlled very precisely.

FIG. 1 shows one embodiment of the present invention. In the figure, 1
Is a light source such as a semiconductor laser, 2 is a focal position control system including a collimator lens, 3 is a rotary polygon mirror, 4 is a drive motor for the polygon mirror 3, 5 is a scanning lens system, 6 is a drum supporting a photosensitive layer, and 7 is a drum. A sheet-like silver salt photosensitive layer, 7b is a reflection layer provided near the edge of the sheet-like photosensitive layer, 8 is a spot detector using a one-dimensional imaging device such as a CCD or MOS, and 9 is a reflection layer
An imaging lens 11 for imaging the scanning light 10 reflected by 7b on the spot detector; and 11, a control circuit for generating a control signal for the focal position control system 2 in accordance with an output signal from the spot detector 8 It is.

The signal processing of the embodiment of FIG. 1 will be described with reference to FIG. 2 and FIG.

As shown in FIG. 2, the output changes when the scanning light 10 is reflected by the reflection layer 7b and reaches the reflected light spot detector 8, but the photosensitive layer 7 of the drum 6 moves in the optical axis direction ( When the scanning light 10 moves in the optical axis direction due to a change in the vertical direction (FIG. 2) or some disturbance, the generation time of the output of the spot detector 8 changes. In the embodiment of FIG. 1, utilizing this fact, the light-collecting state of the scanning light 10 on the photosensitive layer 7 is directly detected, and the light-collecting state is optimized based on the detection signal. .

Now, it is assumed that the position of the photosensitive layer 7 has moved in the optical axis direction from A to B as shown in FIG. At this time, the reflective layer 7b integrally formed with the photosensitive layer 7 also changes its position in the same manner and moves from the position A (the focal position) to the position B.

The reflection layer 7b has a higher reflectance than the photosensitive layer 7 (the reflectance may be lower, and the larger the difference, the better the S / N ratio). Therefore, when the position of the reflective layer 7b changes from A to B, the output of the detector 8 also changes from A to B as shown in FIG. In this case, the output generation time is earlier. Thus, a change in the position of the photosensitive layer 7 is detected by directly receiving the scanning light from now on.

Next, as shown in the block diagram of FIG. 3A, the output of the detector 8 is input to the control circuit 11 and processed. That is, the output of the detector 8 is binarized at an appropriate level by the binarization circuit 110 of the control circuit 11 including the binarization circuit 110, the MPU 111, the ROM 112, and the RAM 113, and is input to the MPU 111.

Here, a scanning beam position sensor 20 (not shown in FIG. 1) (not shown in FIG. 1) is used to determine the timing of positioning the image on the photosensitive layer 7 in the raster direction.
At an appropriate position and the beam detector signal,
The output of the spot detector 8 is also input, and the scan beam position sensor 20 detects the scanning light 10 at a timing earlier than the detector 8. Is measured with reference to the output of the scan beam position sensor 20.

Now, as shown in the timing chart of FIG.
At the position B, the rise and fall times of the output of the binarization circuit 110, that is, the output of the detector 8 based on the output of the scan beam position sensor 20 are _defined as T _BR and T _BF . The time center of the output of the binarization circuit 110 is calculated as (T _BR + T _BF ) / 2 using the memory contents of the ROM 112, and the position A is also calculated as (T _AR + T _BF ) / 2 in the RAM 113. Is stored in.

At this time, the position change layer △ Z of the photosensitive layer 7 becomes ΔT =
(Z = K) as (( _TAR + _TAF ) / 2- ( _TBR + _TBF ) / 2)
Since this amount is represented by T (K: proportionality constant), this amount ΔZ is given to the focal position control system, and the focal position or the focusing state of the scanning light 10 on the photosensitive layer 7 is controlled so that ΔZ becomes zero. Is done.

The control system 2 moves, for example, a collimator lens in the optical axis direction, whereby the focal position of the scanning light 10 moves in proportion to the change amount of the photosensitive layer 7. Of course, the control system may be one that displaces a light source such as a laser with a piezoelectric element.

In this manner, by repeatedly detecting the state of focusing of the scanning light 10, calculating the same, and moving the focal position, the focusing state of the scanning light 10 on the photosensitive layer 7 can be optimized for each scan.

In the above-described embodiment, the silver salt photosensitive seal 7 is wound around the drum 6, but an electrophotographic photosensitive drum 6, an electrophotographic photosensitive member 7, and a mirror reflection part 7b may be used.

[Effects of the Invention] As described above, according to the present invention, scanning light on an object to be irradiated such as a photoreceptor is directly observed, and a beam spot on the object to be irradiated is collected using a detection signal thereof. Since the light state is controlled, a stable high-resolution image is always obtained in an image forming apparatus including such a scanning optical device.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a diagram for explaining the principle of this embodiment, FIG. 3 (a) is a block diagram of a control circuit, and FIG. 3 (b) is a timing chart. It is. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Focus position control system 3 ... Rotating polygon mirror 5 ... Scanning lens system 6 ... Drum 7 ... Photosensitive layer 7b ... Reflective layer 8 Spot detector , 9 ... imaging lens, 11 ... control circuit

Claims (5)

(57) [Claims] 1. A scanning optical apparatus for scanning a light beam from a light source onto an object to be irradiated via an optical system, wherein the light beam is received from a portion of the object to be illuminated outside a use area, and the light beam on the object to be irradiated is received. 1. A scanning optical apparatus, comprising: spot detecting means for detecting the light condensing state of the light beam; and control means for controlling the light condensing state of the light beam in accordance with an output signal from the detecting means. 2. The scanning optical apparatus according to claim 1, wherein the portion outside the use area is a reflection portion having a relatively high reflectance. 3. The scanning optical apparatus according to claim 1, wherein the use area is an image forming area on a photosensitive member in the image forming apparatus. 4. The scanning optical apparatus according to claim 1, wherein said spot detecting means detects a time when a light receiving amount of the light beam changes when the light beam moves between a use area and a portion outside the use area. 5. A scanning optical apparatus according to claim 4, wherein said control means controls the light-collecting state of the light beam so that the change at the time of the change becomes zero.