JPH0829711A - Optical scanner provided with light beam detecting mechanism - Google Patents

Abstract

PURPOSE:To obtain an optical scanner provided with a light beam detecting mechanism capable of highly accurately measuring deviation amount in a subscanning direction in the case of optically scanning a surface to be scanned. CONSTITUTION:When a light beam is guided on the surface 5 to be scanned through an image forming means 4 and optically scans the surface 5 after the light beam radiated from a light source means 1 is deflected and reflected by a deflecting means 3, the light beam from the means 1 passing through the means 3 is image-formed on a first light receiving means 6a arranged in the vicinity of the surface to be scanned and a second light receiving means 6b arranged in the vicinity of the means 6a by the means 4, and a signal from the means 6b is adjusted based on a signal from the means 6a, so that the deviation amount of a scanning line in the subscanning direction on the surface 5 to be scanned is measured.

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 having a light beam detecting mechanism, and more particularly to a manufacturing error of each deflecting surface of an optical deflector which constitutes the optical scanning device and driving of a motor for driving the optical deflector. For example, in a laser beam printer (LBP), which enables high-accuracy optical scanning by measuring the amount of deflection (pitch error) of the scanning position of the light beam in the sub-scanning direction when optically scanning the surface to be scanned due to an error or the like. The present invention relates to an optical scanning device having a suitable light beam detection mechanism.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device such as a copying machine or a laser beam printer (LBP), a light beam emitted from a laser light source (light source means) is optically modulated according to an image signal. Then, the light beam which has been subjected to the light modulation is periodically deflected by an optical deflector composed of, for example, a polygon mirror.
An image is recorded by focusing in a spot shape on a photosensitive recording medium by an image forming optical system having a −θ characteristic and performing optical scanning.

FIG. 9 is a schematic view of a main part of a conventional optical scanning device.

In the figure, a light beam optically modulated from a light source means 91 is deflected and reflected by a light deflector 93 composed of a polygon mirror through a collimator lens 92, and f
A θ lens (imaging lens) 94 focuses the light on a surface of a photosensitive recording medium (photosensitive drum) 95 via an optical path bending mirror 96 to perform optical scanning. Then, by rotating the optical deflector 93 in the direction of arrow A at a constant speed, the surface of the photosensitive drum 95 is in the direction of arrow B (main scanning direction).
Image scanning is performed two-dimensionally by performing optical scanning at a constant speed and rotating the photosensitive drum 95 in the direction of arrow C (sub-scanning direction) at a constant speed.

In such an optical scanning device, the accuracy of the incident position of the light beam on the photosensitive drum 95 has a great influence on the quality of the formed image, and therefore the accuracy of the incident position must be kept extremely high.

However, in general, due to uneven rotation (driving error) of the motor for driving the photosensitive drum, manufacturing error of each deflecting surface of the rotary polygon mirror, fθ lens, etc. There is a problem in that a position deviation (pitch error) in the sub-scanning direction occurs and a highly accurate image cannot be obtained. Therefore, in order to record characters, images, etc. with high precision in the conventional optical scanning device, it is inevitably necessary to measure this pitch error with high precision to reduce the pitch error.

Conventionally, various optical scanning devices having a light beam detection mechanism for measuring (detecting) the pitch error at this time have been proposed.

FIG. 6 is a schematic view of a main part of an optical scanning device having a conventional light beam detecting mechanism. In the figure, the same elements as those shown in FIG. 9 are designated by the same reference numerals.

In the figure, the bending mirror 96 shown in FIG. 9 is removed, and a light beam detecting mechanism (light receiving means) for detecting a pitch error of a scanning line on the surface to be scanned (photosensitive drum surface) 95 in the sub-scanning direction. 97 is arranged at a position optically conjugate with the surface to be scanned 95. And the light beam detection mechanism 9
The pitch error is measured using the signal obtained from No. 7.

That is, when measuring the pitch error of the scanning line of the light beam in the sub-scanning direction in the figure, the light beam from the light source means 91 reflected and deflected by the deflecting surface of the light deflector 93 is passed through the fθ lens 94. It is made incident on the surface of a photodiode 97a as a light receiving means (light receiving element) having a wedge-shaped opening through, and a pitch error is measured by a shake amount measuring means (not shown) using a signal obtained by the photodiode 97a. .

FIGS. 7A and 7B are an explanatory view showing the shape of the photodiode having a wedge-shaped opening and an output signal from the photodiode at this time.

As shown in FIGS. 3A and 3B, the transit time (scanning time) is obtained using the output signal from the photodiode 97a when the photodiode 97a having a wedge-shaped aperture is scanned by the light beam. By comparing this passage time with a preset reference time (time when there is no pitch error), the pitch error of the scanning line in the sub-scanning direction is obtained.

For example, as shown in FIG. 2B, the output signal (scanning time) from the photodiode when the light beam is normal and the output from the photodiode when the output fluctuation or pitch error of the light beam occurs. By comparing each with the signal (scanning time), the pitch error (deviation amount) of the scanning line of the light beam in the sub-scanning direction is measured.

In addition, as a means (apparatus) for measuring the pitch error, for example, as shown in FIG. 8A, a line sensor in which a plurality of pixels are arranged in a direction perpendicular to the scanning line (sub-scanning direction) ( A light receiving means 87 composed of a CCD) is provided in the vicinity of the surface to be scanned, and a part of the light beam from the light source means reflected and deflected by the optical deflector is incident on the surface of the line sensor 87 via the fθ lens, By detecting the position of the light beam incident on 87, the pitch error of the scanning line in the sub-scanning direction is measured.

FIG. 8B shows the line sensor 8 at this time.
7 is an explanatory diagram showing an output signal from FIG. As shown in FIG. 7B, the output (peak position) from the line sensor 87 when the scanning line in the sub-scanning direction is normal and the output (peak position) from the line sensor 87 when a pitch error occurs.
The pitch error is measured by detecting and comparing and.

[0016]

Among the conventional optical scanning devices having a light beam detecting mechanism, a device for measuring a pitch error using a photodiode 97a having a wedge-shaped aperture is as follows.
As shown in FIG. 7B, the photodiode 97
Since the output of the light intensity from a is detected with a certain low level threshold value (threshold level), for example, the output fluctuation of the light beam emitted from the semiconductor laser 91 and the focus position of the imaging lens 94 There is a problem in that fluctuations due to changes are also detected as pitch errors at the same time.

On the other hand, a line sensor (C
In the case of a device for measuring the pitch error using the CD) 87, the detection pitch cannot be made fine due to the structure of the line sensor, so the detection accuracy becomes insufficient, and in order to improve the detection accuracy, a special calculation circuit or It requires a memory and the like, which causes a problem that a time and an economical loss are large.

According to the present invention, when measuring the deflection amount (pitch error) of the scanning line of the light beam in the sub-scanning direction, the first light receiving means for detecting the scanning state of the light beam and the sub-scanning provided in the vicinity thereof. By using the second light receiving means for detecting the shake amount of the scanning line in the direction, and adjusting the signal from the second light receiving means based on the signal obtained by the first light receiving means, By measuring the shake amount of the scanning line in the sub-scanning direction on the surface to be scanned, the shake amount can be measured with high accuracy regardless of the output fluctuation of the light beam and the change of the focal position of the imaging lens. An object of the present invention is to provide an optical scanning device having a light beam detection mechanism.

[0019]

An optical scanning device having a light beam detecting mechanism according to the present invention comprises: (1-1) After deflecting and reflecting the light beam emitted from the light source means by the deflecting means, When the light beam from the light source means via the deflecting means is guided near the scanned surface by guiding the light onto the scanned surface via the deflecting means, An image is formed on the first light receiving means and the second light receiving means arranged in the vicinity of the first light receiving means, and the signal from the second light receiving means is generated based on the signal obtained by the first light receiving means. It is characterized in that the amount of shake of the scanning line in the sub-scanning direction on the surface to be scanned is measured by the adjustment.

In particular, the first light receiving means comprises a light receiving element having a rectangular opening which is divided into two in the sub scanning direction with respect to the main scanning line, and the second light receiving means in the sub scanning direction. On the other hand, it is characterized in that it is composed of a light receiving element having a wedge-shaped opening.

(1-2) When the light beam emitted from the light source means is deflected and reflected by the deflecting means and then guided onto the surface to be scanned through the image forming means to optically scan the surface to be scanned, The light beam from the light source means via the deflecting means is provided by the image forming means through a slit plate having at least two opening portions in the main scanning direction so as to correspond to the two opening portions. By guiding the light to the light receiving means and the second light receiving means and adjusting the signal from the second light receiving means based on the signal obtained by the first light receiving means, the sub-scanning direction of the surface to be scanned. The feature is that the shake amount of the scanning line is measured.

Particularly, one of the at least two openings provided on the slit plate is a rectangular opening divided in the sub-scanning direction with the main scanning line as a boundary, and the other opening. The part is characterized in that it comprises a wedge-shaped opening in the sub-scanning direction.

[0023]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention.

In the figure, reference numeral 1 denotes a light source means, which is composed of a semiconductor laser and emits a light beam optically modulated by image information. Reference numeral 2 denotes a collimator lens, which converts the light beam emitted from the light source means 1 into a substantially parallel light flux. Reference numeral 3 denotes an optical deflector as a deflecting means, which is composed of a rotary polygonal mirror having a plurality of deflecting surfaces and is rotated at a constant speed in the direction of arrow A by a driving means (not shown) such as a motor. Reference numeral 4 denotes an fθ lens (imaging lens) as an image forming means, which is composed of two lenses, a spherical lens 4a and a toric lens 4b, and is optically modulated based on image information deflected and reflected by the optical deflector 3. The formed light beam is imaged on the surface 5 to be scanned. The surface 5 to be scanned corresponds to the surface of the photoconductor drum in a copying machine or LBP, for example.

Reference numeral 6 denotes a light beam detecting mechanism, which is a surface to be scanned 5
2A, which is provided near the center of the first photodiode having a rectangular opening which is divided into two in order from the scanning start side with the main scanning line or the main scanning surface as a boundary (light receiving Element) P1 and second photodiode (light receiving element) P2
And a second light receiving means 6b formed of a third photodiode (light receiving element) P3 having a wedge-shaped opening in the sub-scanning direction and disposed in the vicinity of the first light receiving means 6a. .

In the present embodiment, as will be described later, the first and second photodiodes P1 and P1 obtained when the light beam scans the first and second photodiodes P1 and P2.
By using the output signal from P2, it is possible to detect (determine) the presence or absence of a pitch error (amount of shake) of the scanning line in the sub-scanning direction of the light beam, and to detect the state of the beam diameter of the light beam. There is. Then, the output signal from the third photodiode P3 obtained when the light beam scans the third photodiode P3 is adjusted based on the signal obtained by the first light receiving means 6a to adjust the output signal of the surface to be scanned. The pitch error (deflection amount) of the scanning line in the sub-scanning direction is measured.

In the present embodiment, the light beam emitted from the light source means 1 is made into a substantially parallel light flux by the collimator lens 2 and is incident on the deflecting surface of the optical deflector 3. Then, by rotating the optical deflector 3 in the direction of arrow A in the figure, the light beam reflected and deflected by the deflecting surface is imaged on the scan surface 5 by the fθ lens 4 and optically scanned. By rotating the optical deflector 3 in the direction of arrow A at a constant speed, the surface to be scanned 5 is optically scanned in the direction of arrow B (main scanning direction) at a constant speed to perform image recording.

At this time, in the present embodiment, the light beam from the light source means 1 which has been reflected and deflected by the deflecting surface of the optical deflector 3 in advance before optically scanning the surface to be scanned 5 passes through the f.theta. , The second photodiodes P1 and P2 and the third photodiode P3 are incident on the surface. At this time, from the photodiodes P1, P2 and P3, for example, as shown in FIG.
The output signal shown in (B) is obtained. Here, in the present embodiment, the detection signals obtained from the photodiodes P1, P2 and P3 are input to an arithmetic circuit that performs electrical processing via an amplifier.

In this arithmetic circuit, as will be described later, it is determined whether or not a pitch error has occurred by taking the difference between the output signals (output difference signal) using the signals from the first and second photodiodes P1 and P2. Signal (presence signal) is emitted. Further, by taking the sum of the output signals (output sum signal) using the signals from the first and second photodiodes P1 and P2, for example, the intensity of the light beam and the focal position of the imaging lens have changed. Since the output waveform sometimes changes, a signal (correction amount) for correcting the fluctuation is issued by detecting the change amount.

On the other hand, by measuring the output signal from the signal from the third photodiode P3, the pitch error (deviation amount) of the scanning line of the light beam in the sub-scanning direction is obtained. For example, if a pitch error in the sub-scanning direction occurs due to optical scanning, the scanning time of the light beam when optically scanning the wedge-shaped aperture deviates from the reference time (time when there is no pitch error). The time (scanning time) is compared with a reference time which is obtained in advance by correlating the output time of the light beam, and the pitch error (error amount) of the scanning line in the sub-scanning direction is measured from the compared time difference.

However, since this pitch error does not take into consideration variations in the intensity of the light beam and the focal position of the imaging lens, the variations generated from the first and second photodiodes P1 and P2 are corrected. An accurate pitch error signal is emitted by calculation with the signal (correction amount).

FIG. 3 is a principal block diagram showing the configuration of the arithmetic circuit of this embodiment.

In the figure, amplifiers are individually provided for the first, second and third photodiodes P1, P2 and P3 respectively, and the first, second and third photodiodes P1 and P2 are provided. , P3 output from each amplifier 31,3
After amplification by 2, 33, signal processing is performed. Here, the output signals from the first and second photodiodes P1 and P2 are amplified by the first and second amplifiers 31 and 32, respectively, and converted into predetermined outputs by the subtractor 34 and the adder 36, respectively. . Of these, the signal obtained by the subtractor 34 is input to a comparator 35 for comparing with a predetermined value (reference value), and an output signal is emitted according to the comparison result.

For example, if it is determined from this comparison result that no pitch error occurs, the displacement amount 0 (pitch error-free signal) is output as it is, and the switching circuit 40 is operated by an instruction from the signal generator 39 to perform a comparison correction calculation. The output from the circuit 38 is stopped.

If it is determined from the comparison result that a pitch error has occurred, the switching circuit 40 is opened by the instruction from the signal generator 39 so that the output from the comparison correction calculation circuit 38 is generated.

On the other hand, the signal obtained by the adder 36 can detect the variation of the output of the light beam and the variation of the focal position of the imaging lens from the output thereof.
The converter 37a converts the time displacement into a temporal displacement amount and outputs it to the comparison correction calculation circuit 38.

Next, the signal obtained by the third photodiode P3 is amplified by the third amplifier 33, converted into a temporal displacement amount by the second converter 37b, and compared and calculated by the comparison correction calculation circuit 38.
Is output to In the comparison correction calculation circuit 38, the first converter 3
The output from 7a is compared with a predetermined reference value to obtain the correction amount associated with the output fluctuation of the light beam and the change in the focal position of the imaging lens, and the output from the second converter 37b is compared. To perform correction. The signal corrected by the comparison correction calculation circuit 38 is output as the pitch error amount (pitch error signal) because the switching circuit 40 is open.

As described above, in this embodiment, as described above, the difference between the output signals from the first and second photodiodes P1 and P2 (output difference signal) is obtained, so that the pitch error of the scanning line in the sub-scanning direction is obtained. The presence or absence of
By obtaining the sum (output sum signal) of the output signals from the second photodiodes P1 and P2, the interval between the rising and falling times of the light beam is detected, and the fluctuation of the output of the light beam and the imaging lens Changes in focus position are detected.

Then, the first and second photodiodes P
By reflecting the detection signals from P1, P2 (first light receiving means) in the output signal obtained by the third photodiode P3 (second light receiving means), it is possible to reduce the output fluctuation of the light beam and the fluctuation of the focal position. Nevertheless, the pitch error of the scanning line in the sub-scanning direction can be measured with high accuracy. This enables highly accurate optical scanning.

Although the first light receiving means 6a having a rectangular opening is provided on the scanning start side in this embodiment, the second light receiving means 6b having a wedge-shaped opening may be provided on the scanning start side.
In this case, the signal processing procedure is different from the above, but basically the same output signal is obtained.

That is, the output signal from the third photodiode P3 is amplified by the third amplifier 33, and the second converter 3
After being input to 7b and converted, and then input to a hold circuit (not shown), the signal from the first converter 37a is input,
The comparison correction calculation circuit 38 determines the correction value.

In this embodiment, the photodiode having the rectangular aperture and the photodiode having the wedge-shaped aperture are used. However, as described above, if the pitch error of the scanning line in the sub-scanning direction can be measured with high accuracy. The shape of the opening is not particularly limited.

FIG. 4 is a schematic view of the essential portions of Embodiment 2 of the present invention. FIG. 5 is an enlarged explanatory view of the vicinity of the slit plate shown in FIG. 4 and 5, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

4 and 5, a slit plate 46 has at least two openings 46a and 46b, and one opening 46 provided on the scanning start side of the surface 5 to be scanned.
Reference character a is composed of two rectangular openings divided in the sub-scanning direction with respect to the main scanning line, and the other opening 46b provided on the scanning end side is composed of a wedge-shaped opening in the sub-scanning direction. .

Reference numeral 47a denotes a first light receiving means, which is composed of two photodiodes corresponding to the two divided rectangular openings, and is arranged close to the slit plate 46. The first light receiving means 47 a is provided in the opening 4 of the slit plate 46.
The light beam that has passed through 6a is received to detect the presence or absence of a pitch error (amount of shake) of the scanning line in the sub-scanning direction, and to detect the state of the beam diameter of the light beam.

Reference numeral 47b is a second light receiving means, which is composed of a photodiode and is arranged in the vicinity of the slit plate 46 and in the vicinity of the first light receiving means 47a. The second light receiving means 47b uses the signal obtained by the first light receiving means 47a to receive the light beam that has passed through the opening 46b of the slit plate 46 and to detect the scanning line in the sub-scanning direction on the surface to be scanned. Pitch error (amount of shake) is detected. Reference numeral 47 is a light beam detection mechanism.

When measuring the pitch error in this embodiment, the slit plate 46 is optically scanned with the light beam from the light source means 1 which has passed through the fθ lens 4. And the slit plate 4
The light beams having passed through the two openings 46a and 46b of No. 6 are incident on the surfaces of the first light receiving means 47a and the second light receiving means 47b, respectively.

At this time, in this embodiment, as in the case of the above-described first embodiment, the presence or absence of the pitch error (deviation amount) of the scanning line of the light beam in the sub-scanning direction is determined by using the signal obtained by the first light receiving means 47a. And the state of the beam diameter of the light beam is detected. Then, the signal from the second light receiving means 47b is adjusted based on the signal obtained by the first light receiving means 47a to measure the pitch error (deviation amount) of the scanning line in the sub-scanning direction on the surface to be scanned. . As a result, the same effect as that of the above-described first embodiment is obtained.

Although a plurality of photodiodes are provided corresponding to the respective openings in this embodiment, they may be combined into a single light receiving element (for example, a photodiode). .

Further, the shapes of the two openings provided in the slit plate are not limited to the rectangular and wedge-shaped openings, and for example, the shake amount of the scanning line in the sub-scanning direction on the surface to be scanned can be detected with high accuracy as described above. The shape is not particularly limited as long as it can be formed.

[0051]

According to the present invention, as described above, the first light receiving means for detecting the scanning state and the like of the light beam on the surface to be scanned and the scanning surface of the surface to be scanned provided in the vicinity thereof in the sub-scanning direction. A second light receiving means for detecting the amount of deflection of the scanning line is provided, and the signal from the second light receiving means is adjusted based on the signal obtained by the first light receiving means to adjust the signal in the sub-scanning direction. It has a light beam detection mechanism that can measure the shake amount (pitch error) with high accuracy by measuring the shake amount of the scanning line, regardless of the output fluctuation of the light beam and the change of the focus position of the imaging lens. The optical scanning device can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the shape of each light receiving means and an output signal from the light receiving means according to the first embodiment of the present invention.

FIG. 3 is a principal block diagram showing the configuration of an arithmetic circuit according to the first embodiment of the present invention.

FIG. 4 is a schematic view of the essential portions of Embodiment 2 of the present invention.

5 is a schematic view of a main part near the slit plate shown in FIG.

FIG. 6 is a schematic view of a main part of an optical scanning device having a conventional light beam detection mechanism.

FIG. 7 is an explanatory view showing a shape of a light receiving means of an optical scanning device having a conventional light beam detecting mechanism and an explanatory view showing an output signal from the light receiving means.

FIG. 8 is an explanatory view showing a shape of a light receiving means of an optical scanning device having a conventional light beam detection mechanism and an explanatory view showing an output signal from the light receiving means.

FIG. 9 is a schematic view of a main part of an optical scanning device having a conventional light beam detection mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source means 2 collimator lens 3 deflecting means 4 image forming means 5 surface to be scanned 6,47 light beam detecting mechanism 6a, 47a first light receiving means 6b, 47b second light receiving means P1 first photodiode P2 second Photodiode P3 Third Photodiode 46 Slit plate

Claims (4)

[Claims] 1. A deflecting means for deflecting and reflecting a light beam emitted from a light source means by a deflecting means, and then guiding the light beam onto a surface to be scanned through an image forming means to optically scan the surface to be scanned. The light beam from the light source means via the image forming means forms an image on the first light receiving means arranged near the surface to be scanned and the second light receiving means arranged near the first light receiving means by the image forming means. By adjusting the signal from the second light receiving means based on the signal obtained by the first light receiving means, the shake amount of the scanning line in the sub-scanning direction on the surface to be scanned is measured. An optical scanning device having a light beam detection mechanism characterized by the above. 2. The first light receiving means comprises a light receiving element having a rectangular opening which is divided into two in the sub scanning direction with respect to the main scanning line, and the second light receiving means is in the sub scanning direction. 2. An optical scanning device having a light beam detecting mechanism according to claim 1, wherein said optical scanning device comprises a light receiving element having a wedge-shaped opening. 3. The deflecting means when the light beam emitted from the light source means is deflected and reflected by the deflecting means and then guided to the surface to be scanned through the image forming means to optically scan the surface to be scanned. A light beam from the light source means via the first image receiving means and a first light receiving means provided corresponding to the two openings through a slit plate having at least two openings in the main scanning direction by the image forming means; The first light is guided to the second light receiving means,
By adjusting the signal from the second light receiving means based on the signal obtained by the second light receiving means, the deflection amount of the scanning line in the sub-scanning direction on the surface to be scanned is measured. An optical scanning device having a light beam detection mechanism. 4. At least two provided on the slit plate
One of the two openings is a rectangular opening divided in the sub-scanning direction with respect to the main scanning line.
4. The optical scanning device having a light beam detecting mechanism according to claim 3, wherein the other opening is a wedge-shaped opening in the sub scanning direction.