JP2003057583A - Optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly correct a focal position independently in main scanning and subscanning. SOLUTION: A light beam detection means for detecting a light beam emitted from a light source unit 1 includes a beam detector 8 movable in an optical axis direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device.

[0002]

2. Description of the Related Art In an optical scanning device used for an image recording device such as a digital copying device or a laser printer, or an image writing device in an image forming device, a light beam of Higher precision of beam spot diameter and beam pitch is required.

In this case, even if the beam is adjusted with high accuracy, the beam spot diameter and the beam pitch fluctuate due to disturbances such as temperature. Therefore, the image formation state of the light beam is detected, and when it deviates from the set value. It is necessary to correct it. Therefore, for example, in Japanese Unexamined Patent Application Publication No. 10-20225, a laser light source is caused to emit a pulsed light at a fixed point and the converging state of the pulse beam is detected to detect the converging state of the laser beam. There has been proposed a laser beam scanning optical device that drives an optical element based on a detection result of a state to adjust a focus position of a laser beam.

Further, in Japanese Patent No. 2761723, there is provided an adjusting means for adjusting the position of the collimator lens in the optical axis direction according to the output of the photoelectric conversion element which receives the laser beam after passing through the collimator lens. A scanning optical device has been proposed in which the means adjusts the position of the collimator lens according to the difference between the maximum output value and the minimum output value of the photoelectric conversion element when receiving the laser beam that blinks according to the image signal. There is.

[0005]

However, in the above-mentioned laser beam scanning optical device, pulse emission is premised on detection of the image formation state of the light beam.
Actually, there is a problem that the detection accuracy is lowered because the timing of pulse emission is shifted. In addition, although the knife-edge method is used in this laser beam scanning optical device, the imaging state of the light beam in the main scanning direction can be detected.
There is a problem that the imaging state of the light beam in the sub-scanning direction cannot be detected.

Further, in each of the conventional scanning optical devices described above, the adjusting mechanism for adjusting the focal position adjusts the collimator lens in the optical axis direction, but the positional relationship between the light source and the collimator lens is accurate. However, there is a problem that the adjustment is difficult in practice because the optical axis shift is required. There is also a problem that even if the collimator lens is adjusted in the optical axis direction, it is not always possible to correct the focus positions at the main and sub sides at the same time.

The present invention has been made in view of the above problems, and detects the image forming state independently of the main and sub parts by a simple mechanism.
It is an object of the present invention to provide an optical scanning device capable of quickly and rapidly correcting focal positions independently of each other.

[0008]

In order to solve the above problems, in the optical scanning device according to the present invention, the light beam detecting means for detecting the light beam emitted from the light source unit is a detector movable in the optical axis direction. Is included.

Here, it is preferable that the detector movable in the direction of the optical axis moves about a position that is optically equivalent to the surface of the photosensitive member as a center to detect the light beam.

Further, in the optical scanning device according to the present invention, the light beam detecting means for detecting the light beam emitted from the light source unit includes at least two detectors arranged at intervals in the optical axis direction.

Here, it is preferable that at least two detectors arranged at intervals in the optical axis direction are arranged with their positions substantially equivalent to the positions on the surface of the photoconductor as centers.

In each of the optical scanning devices according to the present invention, the beam spots on the surface to be scanned are so set that the beam spot diameters measured at at least two points are substantially the same or have a certain difference. It is preferable to control the diameter.

Further, when the light beam is detected at at least two points, the detector is moved or arranged so that the beam spot diameters are substantially the same, and at the time of correcting the focal position variation, the beam spot diameters at at least two points are corrected. It is preferable to control the beam spot diameter so that

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an optical scanning device to which the present invention is applied will be described with reference to FIG. A light beam (laser beam) emitted from a light source unit 1 equipped with an LD passes through a sub-cylindrical lens (sub-CYL) 2 and a main cylindrical lens (main CYL) 3 and is deflected and scanned by a polygon mirror 4. , Fθ lens 5 and toroidal lens 6 form an image on the photoconductor 7 to record an image.

Further, the scanning beam is reflected by the mirror 81 outside the recording area and scans on the light beam detector 8 of the light beam position detecting portion which is placed at a position optically equivalent to the image forming position of the photoconductor. The beam spot diameter (focus position) of the LD is initially set to a predetermined value, but the beam spot diameter (focus position) of the LD may change due to changes in the environment such as temperature.

Therefore, based on the light beam detection signal pulse of the LD from the light beam detector 8, the beam diameter measurement unit 9 measures the beam diameter, and the beam diameter control unit 10 determines the beam spot diameter in the main scanning direction. Main CYL3 that mainly controls and sub-CYL that controls the beam spot diameter in the sub-scanning direction
2 is moved in the optical axis direction by a pulse motor to control the beam spot diameter.

Next, the light beam detector 8 will be described with reference to FIG. The figure shows an example of a light beam detector constituting the light beam detector and its detection signal.
As shown in FIG. 3A, the beam detector 8 is masked so that the photodiode (PD) has a right triangular window 8a. The beam detector 8 is arranged so that one side of the right-angled triangular window 8a is perpendicular to the scanning direction of the LD beam.

At this time, the peak voltage values (Pm, Ps) of the two pulses of the signal shown in FIG. 7C obtained by time differentiating the beam detection signal shown in FIG. 7B correspond to the beam spot diameter. . The smaller the beam spot diameter and the narrower the beam, the larger the absolute value of the peak voltage value. The peak voltage value Pm corresponds to the beam spot diameter in the main scanning direction,
The peak voltage value Ps corresponds to the beam spot diameters in both the main scanning direction and the sub scanning direction, but in the present invention, it corresponds to the beam spot diameters in the sub scanning direction by the control method described later.

Therefore, in the first embodiment of the present invention, as shown in FIG. 3, a beam detector 8 is provided in the beam detector, and the beam detector 8 is equidistantly arranged on the optical axis with respect to the original focal position X0 of the detector. It is movably provided at a position X1 and a position X2 which are moved by a distance of (X).

Thus, if one beam detector is used and the detector is normally placed at a predetermined focal position X0,
Since it can also be used as a synchronization detector for detecting the writing start timing in the main scanning direction, the device can be simplified.

Further, in the second embodiment of the present invention,
As shown in FIG. 4, the beam detectors are provided with beam detectors 82 and 83 at positions X1 and X2, respectively, which are separated from the original focus position X0 by an equal distance (X) in the front-rear direction on the optical axis. is doing.

By using the two beam detectors in this way, the image forming state at the position X1 and the image forming state at the position X2 can be determined in one scan, so that the correction operation can be performed quickly. .

Next, an example of a circuit for measuring the above-mentioned peak voltage values Pm and Ps will be described with reference to FIG.
The light beam detection signal detected by the beam detector 8 is
It is amplified by the AMP 91 and differentiated by the differentiator 92 to output a differential waveform signal as shown in FIG.

The positive peak Pm of this differential waveform is held for a fixed time by the positive pulse peak hold 93-1.
The data is fetched by the ADC 95 via the changeover switch 97, converted into a digital value by the ADC 95, and then fetched by a CPU (not shown) or the like, and arithmetic processing is performed as data corresponding to the beam spot diameter in the main scanning direction.

Similarly, the negative peak Ps of the differential waveform is held for a certain time by the negative pulse peak hold 94, taken into the ADC 95 via the changeover switch 97, converted into a digital value by the ADC 95, and then shown in the figure. The data is fetched by a CPU or the like and processed as data corresponding to the beam spot diameter in the sub-scanning direction.

When the two beam detectors 82 and 83 are used as in the second embodiment, it is sufficient to have two circuits of the circuit shown in FIG.

Next, an example of a circuit for comparing the beam spot diameters when the two beam detectors 82 and 83 are used as in the second embodiment will be described with reference to FIG. The light beam detection signal detected by the beam detector 82 is
It is amplified by the AMP 91-1 and differentiated by the differentiator 92-1 to output a differential waveform signal as shown in FIG. The positive peak Pm1 of this differential waveform is held for a certain period of time by the positive pulse peak hold 93-1 and given to the comparator 96-1. Further, the negative peak Ps1 of the differential waveform is similarly processed by the negative pulse peak hold 94.
It is held for a fixed time by -1, and is given to the comparator 96-2.

On the other hand, the light beam detection signal detected by the beam detector 83 is amplified by the AMP 91-2 and differentiated by the differentiator 92-2 to output a differential waveform signal as shown in FIG. 2 (c). To do. The positive peak Pm2 of this differential waveform is held for a certain period of time by the positive pulse peak hold 93-2 and is given to the comparator 96-1. Similarly, the negative peak Ps1 of the differentiated waveform is held for a certain period of time by the negative pulse peak hold 94-2 and given to the comparator 96-2.

In this manner, the positive pulse peak Pm1 obtained by the beam detector 82 and the positive pulse peak Pm2 obtained by the beam detector 83 are compared with each other by the comparator 96.
-1 is compared and is output as a beam diameter comparison signal in the main scanning direction. Similarly, the negative pulse peak Ps1 obtained by the beam detector 82 and the negative pulse peak Ps2 obtained by the beam detector 83 are compared by the comparator 96-2 and output as a beam diameter comparison signal in the sub-scanning direction. .

The main scanning direction beam diameter comparison signal and the sub scanning direction beam diameter comparison signal, which are the comparison signals output from this circuit, are used as rotation instruction signals for the pulse motor for moving the main CYL3 and the sub CYL2. In addition, expensive components such as the ADC and the CPU are unnecessary for measuring the beam spot diameter and controlling the beam spot diameter, and the control circuit can be simplified.

Here, the beam spot diameter (focus position)
Changes with environmental changes such as temperature, as shown in FIG. It should be noted that the figure shows the case of the beam spot diameter in the main scanning direction, but the same applies to both the main and sub scanning directions.

In this case, the adjusted focus position X0 is set as the initial state, and the beam spot diameters at the positions X1 and X2 are set to R0. When the focus position deviates in the plus direction due to environmental changes such as temperature rise and the depth curve becomes indicated by the dotted line, the beam spot diameter at the position X1 becomes R.
1, the beam spot diameter at position X2 is R2,
R1 <R2. This is the main C so that R1 = R2
It can be adjusted by moving YL3 to the light source unit side.

Therefore, an example of beam spot diameter control and beam pitch control will be described with reference to FIG. First, the focus position in the main scanning direction is adjusted. This processing measures the positive pulse peak values Pm (X1) and Pm (X2). Then, Pm (X1) and Pm (X2) are compared.

At this time, when Pm (X1)> Pm (X2), since the beam diameter at the position X1 is small, it is considered that the focus position is displaced to the side opposite to the polygon mirror 4, so the focus is on the polygon mirror 4 side. In order to shift the position, the main CYL3 is moved to the light source unit 1 side.

On the other hand, Pm (X1) <Pm (X2)
In this case, it is considered that the focus position is shifted to the polygon mirror 4 side, so the main CYL 3 is moved to the polygon mirror 4 side for correction.

These operations are performed by Pm (X1) = Pm (X
It becomes 2) and it repeats until the beam diameters at the positions X1 and X2 become the same.

Next, after adjusting the focal position in the main scanning direction, the focal position in the sub scanning direction is adjusted. First, the negative pulse peak values Ps (X1) and Ps (X2) are measured, and Ps (X
1) and Ps (X2) are compared.

When Ps (X1)> Ps (X2), since the beam diameter at the position X1 is small, it is considered that the focus position is displaced to the side opposite to the polygon mirror 4, and therefore the focus position is on the polygon mirror 4 side. To shift
The sub CYL1 is moved to the polygon mirror 4 side.

When Ps (X1) <Ps (X2), the focus position is considered to be shifted to the polygon mirror 4 side, and therefore the sub CYL2 is moved to the light source unit 1 side for correction.

These operations are performed by Ps (X1) = Ps (X
2) is repeated until the beam diameters at the positions X1 and X2 become the same (or until there is a constant difference).

With this, the beam spot diameter can be controlled.

[0042]

As described above, according to the optical scanning device of the present invention, the light beam detecting means for detecting the light beam emitted from the light source unit includes the detector movable in the optical axis direction. It is possible to detect in which direction the focal position is deviated by a simple mechanism, independently of the main and sub directions, and quickly correct the focal position independently of the main and sub directions.

Here, the detector movable in the direction of the optical axis moves substantially centered on a position optically equivalent to the surface of the photoconductor to detect the light beam, thereby enabling more accurate detection. .

Further, in the optical scanning device according to the present invention, the light beam detecting means for detecting the light beam emitted from the light source unit includes at least two detectors arranged at intervals in the optical axis direction. It is possible to detect in which direction the positions are deviated by a simple mechanism independently of the main and sub directions, and to quickly correct the focal position independently of the main and sub directions.

Here, since at least two detectors which are arranged at intervals in the optical axis direction are arranged with their positions substantially optically equivalent to the positions on the surface of the photoconductor as the centers, more accurate detection can be performed. You can

In each of these optical scanning devices according to the present invention, the beam spots on the surface to be scanned are set so that the beam spot diameters measured at at least two points are substantially the same or have a certain difference. By controlling the diameter, highly accurate scanning can be performed.

Further, when the light beam is detected at at least two points, the detector is moved or arranged so that the beam spot diameters are substantially the same, and at the time of correcting the focal position variation, the beam spot diameter at at least two points is corrected. By controlling the beam spot diameter so that the values become substantially the same, highly accurate scanning can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating an example of an optical scanning device to which the present invention is applied.

FIG. 2 is an explanatory diagram illustrating a beam detector and its detection signal.

FIG. 3 is an explanatory diagram illustrating an arrangement of beam detectors according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating an arrangement of beam detectors according to a second embodiment of the present invention.

FIG. 5 is a block diagram illustrating an example of a circuit that measures a peak voltage value.

FIG. 6 is a block diagram illustrating an example of a circuit for comparing beam spot diameters according to the second embodiment.

FIG. 7 is an explanatory diagram for explaining a change in beam spot diameter.

FIG. 8 is a flowchart illustrating an example of beam spot diameter control and beam pitch control procedures.

[Explanation of symbols]

1 ... Light source unit, 2 ... Sub-cylindrical lens, 3 ...
Main cylindrical lens, 4 ... Polygon mirror, 5 ... f
θ lens, 6 ... Toroidal lens, 7 ... Photoconductor, 8 ... Beam detector, 9 ... Beam diameter measuring unit, 10 ... Beam diameter control unit 10.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C362 AA20 AA21 BA89 BB30                 2H045 CA88 CB01 CB22 DA41                 5C051 AA02 CA07 DB02 DB24 DB30                       DC02 DC04 DE22 DE26 FA01                 5C072 AA03 BA17 HA02 HA09 HA13                       HA20 HB10 XA01 XA05

Claims (7)

[Claims] 1. A light source unit for emitting a light beam, a scanning optical system for deflecting the light beam emitted from the light source unit and condensing it on a surface to be scanned, and a light beam detecting means for detecting the light beam. Optical scanning including beam spot diameter measuring means for measuring the beam spot diameter of the light beam based on the beam detection signal from the light beam detecting means, and beam diameter control means for controlling the beam spot diameter on the surface to be scanned. In the apparatus, the light beam detecting means includes a detector movable in the optical axis direction. 2. The optical scanning device according to claim 1,
An optical scanning device characterized in that a detector that is movable in the optical axis direction moves about a position that is optically equivalent to the photoconductor surface as a center to detect a light beam. 3. A light source unit for emitting a light beam, a scanning optical system for deflecting the light beam emitted from the light source unit and condensing it on a surface to be scanned, and a light beam detecting means for detecting the light beam. Optical scanning including beam spot diameter measuring means for measuring the beam spot diameter of the light beam based on the beam detection signal from the light beam detecting means, and beam diameter control means for controlling the beam spot diameter on the surface to be scanned. In the apparatus, the light beam detecting means includes at least two detectors arranged at intervals in the optical axis direction, the optical scanning apparatus. 4. The optical scanning device according to claim 3,
An optical scanning device characterized in that at least two detectors arranged at intervals in the optical axis direction are arranged with a position optically equivalent to that on the surface of the photoconductor being substantially the center. 5. The optical scanning device according to claim 2 or 4, wherein the beam spot diameters measured at at least two points are substantially the same or have a certain difference on the surface to be scanned. An optical scanning device characterized by controlling the beam spot diameter of the. 6. The optical scanning device according to claim 2,
When the light beam is detected at at least two points, the detector is moved so that the beam spot diameters are substantially the same, and at the time of correcting the focus position variation, the beam spot diameters are controlled so that the beam spot diameters are substantially the same at at least two points. An optical scanning device characterized by the above. 7. The optical scanning device according to claim 4,
The detectors are arranged so that the beam spot diameters will be approximately the same when detecting the light beam at at least two points, and the beam spot diameters will be controlled so that the beam spot diameters will be approximately the same at at least two points when the focus position fluctuation is corrected. An optical scanning device characterized by: