JP2692889B2 - 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 for scanning a light beam from a light source on a scanning surface via a deflector and a lens system, and is particularly caused by environmental fluctuations such as temperature. The present invention relates to a scanning optical device provided with a mechanism for detecting and correcting a focal position shift of an imaging spot of a light beam on a scanning surface.

(Prior art)

In recent years, as a scanning optical device, a laser light source has been modulated in accordance with an image signal, and the laser light from the modulated laser light source has been periodically deflected by a deflector.
2. Description of the Related Art A laser beam printer apparatus that focuses on a photosensitive recording medium in a spot shape, performs exposure scanning, and records an image is widely and generally used.

By the way, in the conventional laser beam printer, each member constituting the lens system (optical system) is thermally deformed due to a change in environmental temperature, and the focus position of the laser beam on the photoconductor (scanning surface) is deviated, so that the image quality is deteriorated. There was a drawback that it decreased.

As means for solving the drawback, Japanese Patent Application Laid-Open No. 62-81873 discloses a scanning optical device having a mechanism for detecting and correcting a focal position shift of an image spot of a light beam on a scanning surface. .

In the above publication, as a method for detecting the focal position shift of the image spot of the light beam, a plurality of light receiving elements are provided in the scanning optical path and the focus is adjusted so that the number of the light receiving elements becomes a predetermined number. However, in this method, it is necessary to store a predetermined number of information in the device in advance, and if the storage of the predetermined number of information is lost due to some trouble, it is impossible to detect the focal position shift. .

[Summary of the Invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional device, to easily detect and correct the focal position shift with a simple configuration, and to detect the focal position shift in consideration of the field curvature with a simpler configuration. The purpose is to provide a method of correction.

An object of the present invention is to detect a light beam from a light source on a scanning surface via a deflector and a lens system, and to detect a focusing state of the light beam on the scanning surface and a detecting means on the scanning surface. In a scanning optical device provided with a focus position moving means for moving a light beam focusing position, as a detecting means for detecting a focused state of a light beam on the scanning surface, it is at a position optically equivalent to the scanning surface and in a scanning direction. A plurality of detectors having apertures are arranged at a predetermined interval in a direction parallel to, and a light beam from the light source is scanned a plurality of times on the plurality of detectors via a deflector and a lens system, and each scan is performed. By comparing or calculating the signals from the same detection unit for each, the light beam focusing position is moved by the focus position moving means for moving the light beam focusing position on the scanning surface to determine the light beam focusing position on the scanning surface. Key It is achieved by.

〔Example〕

1 is a view for explaining a first reference of a scanning optical device according to the present invention, in which 1 is a light source device composed of a semiconductor laser and a collimator lens, 2 is a lens system for moving a focus position, and 3 is a lens system. A rotary polygon mirror which is a deflector, 4 a rotary polygon mirror drive motor, 5 a scanning lens system, 6 a photosensitive recording drum which is a scanning surface, and 7 a part of a laser beam which is to scan the photosensitive recording drum. A beam splitter 8 that reflects the light and transmits the rest, and 8 is a mirror image of the scanning line (broken line) of the laser beam on the photosensitive recording drum and the split surface of the beam splitter, that is, optically equivalent to the scan surface. Is a spot detector for photoelectrically converting a laser beam spot which is arranged at a specific position and in a direction parallel to the scanning direction, and a plurality of detection units each consisting of a pair of a predetermined aperture and a photoelectric conversion surface are arranged at predetermined intervals. With something That. Further, 9 is a detection signal processing unit for processing an electric signal from the spot detector 8, and 10 is a drive signal for generating a driving signal for the lens system 2 for moving the focus position according to the signal output from the detection signal processing unit 9. This is a control unit.

FIG. 2 shows a cross-sectional view of the spot detector 8 in FIG. 1 in the spot scanning plane, in which a plurality of detecting portions each consisting of a pair of predetermined openings and photoelectric conversion surfaces are arranged at predetermined intervals. Reference numeral 11 is an aperture plate having a predetermined opening 13, 12 is a photoelectric conversion surface, and 14 is a support, which are generally electric signals output from the respective detectors when the laser spot is scanned in the direction A to B in the figure. 15 is represented as in FIG. Now the aperture plate
Reference numeral 11 denotes a position on the photosensitive surface 6 of FIG. 1 which is in a mirror image relationship with the laser beam scanning line (broken line), that is, at a position which is optically equivalent to the photosensitive surface with respect to the light source. When scanning is performed by changing the position of the laser beam waist by moving the system 2, the output pattern of the output signal I changes as S ₁ , S ₂ , and S ₃ with respect to time t. That is, as a result of scanning the spot detection unit 8 while changing the beam waist position for each detection unit, an output pattern having the largest central intensity or the output pattern having the smallest half-value width appears. The control unit 10 operates the lens system 2 for moving the focal position so that the beam waist position for the pattern is obtained. The control for detecting and correcting the focus position deviation may be performed before recording a certain unit of information, or during recording scanning (modulating the light source to form an image on the photoconductor surface). During the blanking period (while the image is not formed for a long period of time), the laser may be oscillated only in the vicinity of the spot detector to execute the control operation as described above. Of course, the control operation as described above is stopped during the recording scan. In addition, for example, during the blanking period of a predetermined number of images recorded on A4, A3, etc. sheets (until the image recording of one sheet ends and the image recording of the next sheet begins) May be executed. Of course, the control operation as described above is stopped while the image recording on the paper is being performed. Further, a timer is connected to the control unit 10 of the apparatus, the control unit is activated at predetermined time intervals, and the laser beam is scanned,
The focus position may be adjusted. In addition, the temperature
A sensor for detecting a change in environment such as humidity may be provided, and when the sensor detects a great change in environment, the above-described focus position adjustment operation may be performed.

 The signal processing system of the first reference example will be described below.

In the present invention, it is assumed that the field curvature is sufficiently corrected by the scanning lens system 5. Therefore, the focus position need only be adjusted correctly at any one point on the scanning line.

[Peak Value Detection Focus Adjustment] A method of performing focus adjustment according to the peak value of the amount of light passing through the opening will be described with reference to FIG.

In FIG. 1, the peak value of the amount of light passing through the spot detector 8 changes depending on the position in the optical axis direction. Since the peak value is maximum at the focus position, it can be found. The spot detector 8 is provided with a plurality of detection units 101 each having a predetermined opening and a light amount conversion surface. In the block diagram of (b), only three detectors 101 are shown as spot detectors 8 for convenience of drawing, but in reality, a plurality of detectors 101 are provided along the spot scanning direction. Two or four or more detectors may be used.

FIG. 4 (a) is a conceptual diagram thereof, and FIG. 4 (b) is a block diagram.

The focus adjustment signal processing system is mainly performed by the detection signal processing unit 9. Further, FIG. 5 is a flow chart.

The focus position is measured before recording the information signal.
The signal from the control unit 10 is sent to the detection unit position counter 107 which indicates the position of each detector on the spot detector, the detection unit position counter is set to the position 1, and the focus driving device is operated by the position command of the detection unit position counter 107. 110 moves the lens system 2 to the initial position 1 in the optical axis direction. As shown in FIG. 1, the scanning means scans the scanning beam in the direction orthogonal to the optical axis. The detector position counter 1 108 stores position information in the optical axis direction, which is always smaller than the detector position counter 107 by 1. After that, the detection unit position counter 107 is sequentially incremented by the output of the control unit 10 for each detection unit.

The output of the detector position counter 107 acts on the focus drive device 110 as a position command. The focus driving device 110 moves the position of the scanning beam in the optical axis direction to the positions 2, ..., K, ..., N by this command, and performs scanning on each detection unit. Here, it is assumed that the focus position is between them. If not, move the initial position.

The output of the detection unit 101 at this time is shown in FIG. As described above, the output of the detection unit 101 is an electrical output proportional to the amount of light passing through the slit, and its peak value changes in accordance with the change in the position in the optical axis direction.

The peak value of the output of the detection unit 101 is held by the peak value hold 102. This situation is shown in the output of the peak value hold circuit of FIG. It should be noted that the peak value obtained by the previous detection unit is reset by the output of the control unit 10 for each detection unit (= every position in the optical axis direction).

The held peak value is converted from an analog voltage to a digital amount by the A / D converter 103. This digital amount is held in the latest peak value register 104. The value held in the latest peak value register 104 before the scan of the next detection unit is transferred to the previous peak value register 105. The previous peak value register 105 is cleared before measurement.

The output of the latest peak value register 104 and the output of the immediately preceding peak value register 105 are discriminated by the magnitude discriminating circuit 106 as to whether their magnitude, that is, the peak value is increasing or decreasing. If the polarity of the output of the magnitude discriminating circuit 106 changes, it can be seen that it has passed the position along the optical axis where the peak value is maximum. Since the detection unit position counter 1108 stores position information immediately before the current position, if the polarity of the output of the magnitude discriminating circuit 106 changes, the position in the optical axis direction is stored. This position is the focus position. Then, the position information of the detection unit position counter 1 108 is transferred to the detection unit position counter 107, the lens system 2 is returned to the previous position by the focus driving device 110, and the detection unit position counter 107 issues a stop command to the control unit 10. The focus position adjustment is completed. Therefore, the optical axis direction of the scanning beam is fixed to the focus drive device 110 at the focus position at the focus. The focus position of the scanning beam is always fixed on the photoconductor recording drum 6 located at the same distance as the spot detector 8 in the optical axis direction.

In addition, in the example described above, the optimum position of the laser beam waist is set by one laser beam scanning. However, if the focus position cannot be detected by one laser beam scan, that is, if the polarity of the output of the peak value detection circuit does not change in the peak value detection method, the laser beam is scanned again on the detector to focus. Adjust the position.

Further, in the example shown above, a method of performing focus adjustment by the peak value of the amount of light passing through the aperture (slit) was used, but as in Japanese Patent Application No. 63-123624 filed by the present inventor earlier, A method of performing focus adjustment by the value of dispersion, a method of performing focus adjustment by measuring time, or the like may be used.

Further, in the above example, the auxiliary lens system is moved as a means for moving the focusing position of the light beam on the scanning surface, but other known techniques are used for the means for moving the focusing position of the light beam. You may use.

As means for moving the focusing position of the light beam, a means for moving a collimator lens as in JP-A-62-112123, or a laser light source or an imaging lens as in JP-A-59-116603. A method in which the optical distance between the scanning lens and the scanning medium is variable as in JP-A-112020, and a laser power is variable as in JP-A-61-275868 can be considered.

If the field curvature is sufficiently corrected by the scanning lens system 5, the laser beam waist of the laser beam waist is scanned by one laser beam on the spot detector having a plurality of spot detectors as in the above-described example. The optimum position can be set by operating the lens system 2 for moving the focus position by the control unit. However, when the curvature of field is not sufficiently corrected by the scanning lens system 5, a plurality of detection units having openings at positions optically equivalent to the scanning surface and parallel to the scanning direction are arranged at predetermined intervals. However, it is necessary to set the optimum position of the laser beam waist by scanning the plurality of detectors a plurality of times by operating the lens system for moving the focus position by the controller. An embodiment of the present invention for that purpose will be described below.

FIG. 6 is a view for explaining the signal processing system for focus adjustment of the first embodiment of the scanning optical device according to the present invention.
Is a block diagram of the focus adjustment method and its control. The basic configuration of the scanning optical device of the first embodiment is the same as that of the first reference example, but in the first embodiment, unlike the first reference example, the curvature of field is sufficient due to the scanning lens system. It has not been corrected to. Therefore, the focus position may be adjusted at any two or more points on the scanning line.

[Peak value detection focus adjustment] A case where the peak value is detected and focus adjustment is performed as in FIG. 4 will be described.

The spot detector is provided with a plurality of detecting portions each having a predetermined aperture and a photoelectric conversion surface along the spot scanning direction. Here, the number of detectors, that is, the position in the scanning direction is set to three.
Although it is described as points (A, B, C), any number of points may be used as long as it is two or more. The required measurement point may be determined depending on how much the field curvature is corrected.

The focus position is measured before recording the information signal.
The principle and operation of detecting the focus position based on the peak value of the output of each detector are the same as those in the first embodiment, and the description thereof will be omitted. Spot detectors 201A, 201B, 201C and focus position detector 20
By scanning the spot detector a plurality of times with 2A, 202B, and 202C, the position where the peak value of the output of the detector is maximum, that is, the focus position is obtained for each position in the scanning direction. In the focus position counters 203A, 203B, 203C, the focus positions of positions A, B, C in the scanning direction corresponding to the positions of the respective detectors are entered.

In response to a position command from an MPU (microprocessor unit) 204, the focus driving device 110 moves the scanning beam to position 1 in the optical axis direction, and scans the spot detector with a laser beam. Then, the peak value of the photoelectric output at the position 1 in the optical axis direction is measured for each of the scanning direction measurement points A, B, and C. MP
The output of U204 is the focus drive 110 as a position command.
Act on. Based on this command, the focus driving device 110 determines the position of the scanning beam in the optical axis direction as position 2, ..., Position k ,.
The position is moved to the position n, scanning is performed for each position, and the peak value is measured for each detection unit arranged in the scanning direction. Here, it is assumed that the focus position is between them. If not, move the initial position.

The outputs of the detection units 201A, 201B, 201C at this time are shown in FIG. In this way, the output of the detector is an electrical output proportional to the amount of light that has passed through the slit (opening), and its peak value changes for each position in the scanning direction corresponding to the change in position in the optical axis direction. The difference from the first reference example is that there is a field curvature, and therefore the position in the optical axis direction where the peak value is maximum differs for each detection unit. The degree of difference for each detector is determined by the field curvature. Then, the scanning direction measurement points A, B,
The focus position is determined for each C. The focus position counters 203A, 203B, 203C contain the focus positions of the respective scanning direction positions A, B, C. These numbers are sent to the MPU 204. Here, the MPU 204 obtains the focus position of the scanning direction position other than the measurement point by curve approximation. If the number of measurement points is n, it can be approximated by an (n-1) th order curve. Since many methods of curve approximation are known, the description thereof is omitted here. The obtained result is temporarily stored in RAM (random access memory) 205 in order for each position in the scanning direction.
Further, these calculation procedures, constants, etc. are stored in advance in a ROM (Read Only Memory) 206.

When the information signal is stored, the focus position obtained by measuring the focus position is sequentially entered in the RAM 205 for each position in the scanning direction. When recording the information signal, the value stored in RAM 205
Transfer to MPU204. Since the MPU 204 output is fixed for each position in the scanning direction, the position command is also fixed for each position in the scanning direction. The focus drive device 110 fixes the position of the scanning beam in the optical axis direction to the focal position for each position in the scanning direction.

According to the first embodiment as described above, even if the curvature of field by the scanning lens system is not sufficiently corrected, the photosensitive recording body having the same surface as the spot detector in the optical axis direction is obtained. The focus position of the scanning beam is always fixed on the drum.

FIG. 7 is a view for explaining the second embodiment of the scanning optical device according to the present invention. The same members as those in FIG. 1 are designated by the common reference numerals and the description thereof is omitted. Reference numeral 21 denotes a light source device composed of a semiconductor laser and a condensing image forming lens. A laser beam emitted from the light source device is passed through a lens system 22 for moving a focal position and a rotary polygon mirror 3 to a predetermined position on the photosensitive recording drum 6. It is imaged. Therefore, when the lens system 22 does not move, the laser beam emitted from the light source device 21 is deflected by the rotary polygon mirror 3, and as a result, a locus of the laser beam waist position that is almost an arc is drawn (one point in FIG. 7). Chain line). That is, unless the focus position control system is operated and the lens system 22 is operated, it may be impossible to keep the photosensitive recording drum surface, which is the scanning surface, within the depth of focus with respect to the locus of the scanning line. Also in this case, similarly to the above-described first embodiment, a plurality of detectors each having a predetermined opening and a photoelectric conversion surface are provided in the spot scanning direction on the detector 8 by a plurality of laser beam scanning operations.
The optimum position of the laser beam waist may be set by operating the lens system for moving the focus position by the control unit 10.

Further, in the example shown above, a method of performing focus adjustment by the peak value of the amount of light passing through the aperture (slit) was used, but as in Japanese Patent Application No. 63-123624 filed by the present inventor earlier, A method of performing focus adjustment by the value of dispersion, a method of performing focus adjustment by measuring time, or the like may be used.

Further, in the above example, the auxiliary lens system is moved as a means for moving the focusing position of the light beam on the scanning surface, but other known techniques are used for the means for moving the focusing position of the light beam. You may use.

As means for moving the focusing position of the light beam, a means for moving a collimator lens as in JP-A-62-112123, or a laser light source or an imaging lens as in JP-A-59-116603. A method in which the optical distance between the scanning lens and the scanning medium is variable as in JP-A-112020, and a laser power is variable as in JP-A-61-275868 can be considered.

〔The invention's effect〕

As described above, according to the present invention, the conventional detecting means for scanning the light beam from the light source on the scanning surface via the deflector and the lens system and detecting the focused state of the light beam on the scanning surface. And a scanning optical device including a focus position moving means for moving a light beam focusing position on the scanning surface,
As a detecting means for detecting the focused state of the light beam on the scanning surface, a plurality of detecting portions having openings are arranged at predetermined intervals in a direction optically equivalent to the scanning surface and in a direction parallel to the scanning direction, The light beam from the light source is scanned a plurality of times on the plurality of detection units via a deflector and a lens system, and signals from the same detection unit for each scan are compared or calculated to obtain the scanning surface. By moving the light beam focusing position by the focus position moving means for moving the upper light beam focusing position and adjusting the light beam focusing position on the scanning surface, it is possible to easily defocus with consideration of the field curvature with a simple configuration. It is possible to detect and correct.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a first reference example of a scanning optical device according to the present invention, FIG. 2 is a schematic sectional view of a detector, and FIG. 3 corresponds to spots in various states output from the detector. FIGS. 4 (a) and 4 (b) are conceptual diagrams of the focus adjustment method and a block diagram of its control, and FIG. 5 shows the focus adjustment method shown in FIGS. 4 (a) and 4 (b). Flow chart,
6 (a) and 6 (b) are schematic diagrams of the focus adjusting method according to the present invention and a block diagram of the control thereof, and FIG. 7 is a diagram for explaining another embodiment of the scanning optical device according to the present invention. . 1 ... Light source device, 2 ... Lens system 3 ... Rotating polygon mirror, 5 ... Scanning lens system 6 ... Photosensitive recording drum, 7 ... Beam splitter 8 ... Spot detector, 9 ... Signal processing Section 10 ... Control section

Claims (1)

(57) [Claims] 1. A detecting means for scanning a light beam from a light source on a scanning surface through a deflector and a lens system, and detecting a focused state of the light beam on the scanning surface, and light on the scanning surface. In a scanning optical device provided with a focus position moving means for moving a beam focusing position, as a detecting means for detecting a focused state of a light beam on the scanning surface, a position optically equivalent to the scanning surface and a scanning direction A plurality of detectors having openings are arranged at predetermined intervals in a parallel direction, and a light beam from the light source is scanned a plurality of times on the plurality of detectors via a deflector and a lens system, and each scan is performed. By comparing or calculating the signals from the same detection unit, the light beam focusing position is moved by the end point position moving means for moving the light beam focusing position on the scanning surface, and the light beam focusing position on the scanning surface is adjusted. You A scanning optical device characterized in that.