JP2005156992A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner and an image forming apparatus with which an excellent output picture with no beam pitch deviation due to temperature and vibration or the like is available by rapidly and accurately measuring the scanning position in the subscanning direction of a light beam and controlling a pitch. <P>SOLUTION: The optical scanner comprises a means 19, which is composed of a plurality of sensors so arranged that two or more sides facing each other are parallel and straight, and at least one of the parallel and straight sides has an angle, at which the side is not parallel to a subscanning direction, and outputs a beam position detection signal, by detecting a scanning position with a light beam on a plane to be scanned; means 26a, 26b and 26c which measure the temperature in the optical scanner; a means 21 which detects a scanning position with the light beam in the subscanning direction on the plane to be scanned, on the basis of the beam position detection signal and a measured temperature; means 23 which returns the scanning position with the light beam in the subscanning direction on the plane to be scanned to a defined scanning position, when the detected scanning position in the subscanning direction is deviated from a predetermined scanning position. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, and a laser facsimile machine, and an optical scanning device applicable to these image forming apparatuses.

In an optical scanning device used in an optical writing system of an image forming apparatus such as a laser printer, there is a method of increasing the rotational speed of a polygon mirror that is an optical deflecting means as means for improving the recording speed. However, this method has problems such as motor durability, noise, vibration, and laser modulation speed, and there is a limit to improving the recording speed. Thus, a so-called multi-beam scanning device has been proposed in which a plurality of lines are simultaneously scanned by simultaneously scanning a plurality of light beams.
As an example of the light source of this multi-beam scanning device, a plurality of semiconductor laser arrays (Laser Diode Array: LDA) having a plurality of light emitting points and a plurality of semiconductor lasers (Laser Diode: LD) having one light emitting point in the sub-scanning direction are used. There are light source units arranged. A plurality of light beams emitted from the light source unit are collectively deflected by a polygon mirror and scanned on the photosensitive member, whereby a plurality of lines can be recorded at a predetermined interval (sub scanning pitch) in the sub scanning direction. Therefore, the recording speed can be improved by increasing the number of light beams.

  Here, even if the light source unit is adjusted at the time of initial setting so as to obtain a predetermined sub-scanning pitch, a deviation from the predetermined sub-scanning pitch occurs over time due to external factors such as vibration and temperature. Therefore, in order to obtain a high-quality output image, it is necessary to detect and correct a sub-scanning pitch shift, and there have been proposals for detecting and correcting a sub-scanning pitch shift. (For example, see Patent Documents 1 and 2.) In Patent Document 1, two sensors whose scanning start end sides are not parallel to each other are used to detect the position of the light beam, and are output when the light beam passes through each sensor. It has been proposed to detect the scanning position of the light beam in the sub-scanning direction from the time difference between the light beam position detection signals. In Patent Document 2, a plurality of photosensors are arranged in the main scanning direction, and a pulse interval generated when crossing a sensor placed in parallel to the subscanning direction and a sensor having an angle in the subscanning direction are crossed. It has been proposed to convert the time difference from the interval of the generated pulses into the sub-scanning pitch between the beams.

However, since the detection position of this light beam position detection signal is shifted due to temperature in the optical scanning device or fluctuations in the amount of light of the light beam, an error in the detected scanning position of the sub-scanning and thus the detected sub-scanning beam pitch becomes large.
JP-A-7-72399 JP 9-325288 A

  The present invention is an optical scanning that can quickly and accurately measure the scanning position of the light beam in the sub-scanning direction and control the pitch to obtain a good output image free from beam pitch deviation due to temperature, vibration, etc. An object is to provide an apparatus and an image forming apparatus.

  The invention according to claim 1 is arranged such that two or more opposing edges are parallel and straight, and at least one of the parallel and straight edges has an angle non-parallel to the sub-scanning direction. A plurality of sensors, a light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal, and a temperature measuring means for measuring the temperature in the optical scanning device; A sub-scanning position detecting means for detecting a scanning position of the light beam on the scanned surface in the sub-scanning direction based on the beam position detection signal output by the light beam position detecting means and the temperature measured by the temperature measuring means; When the scanning position in the sub-scanning direction detected by the sub-scanning position detecting means is deviated from the specified scanning position, the scanning position in the sub-scanning direction of the light beam on the surface to be scanned is returned to the specified scanning position. Scanning position control means, and And wherein the Rukoto.

  The invention according to claim 2 is arranged such that two or more opposing edges are parallel and form a straight line, and at least one of the parallel and straight edges has an angle non-parallel to the sub-scanning direction. A plurality of sensors, a light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal, and a temperature measuring means for measuring the temperature in the optical scanning device; The sub-scanning pitch detecting means detects the pitch of the plurality of light beams on the scanning surface in the sub-scanning direction based on the beam position detection signal output from the light beam position detecting means and the temperature measured by the temperature measuring means. And a pitch control means for returning the pitch in the sub-scanning direction of the plurality of light beams on the surface to be scanned to the prescribed pitch when the pitch detected by the sub-scanning pitch detecting means is deviated from the prescribed pitch. To have And butterflies.

  The invention according to claim 3 is arranged such that two or more opposing edges are parallel and straight, and at least one of the parallel and straight edges has an angle not parallel to the sub-scanning direction. A plurality of sensors, a light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal, and a temperature measuring means for measuring the temperature in the optical scanning device; The sub-scanning pitch detecting means detects the pitch of the plurality of light beams on the scanning surface in the sub-scanning direction based on the beam position detection signal output from the light beam position detecting means and the temperature measured by the temperature measuring means. And means for notifying the operator of the fact that the pitch detected by the sub-scanning pitch detecting means deviates from the specified pitch.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the temperature measuring means includes temperature sensors disposed at a plurality of locations.

  The invention according to claim 5 is the invention according to claim 4, characterized in that the temperature measuring means weights the measurement data from the temperature sensors arranged at a plurality of places according to the places where the temperature data is arranged to obtain a temperature measurement value. To do.

  The invention described in claim 6 is characterized in that, in the invention described in claim 4 or 5, the number of locations where the temperature sensor is provided is 2 or 3.

  According to a seventh aspect of the present invention, in the first or fourth to sixth aspects of the present invention, the sub-scanning position detection means has a sub-scanning position obtained from the beam position detection signal from the light beam position detection means. A sub-scanning position is obtained by multiplying a coefficient value for the temperature obtained from the temperature measuring means.

  According to an eighth aspect of the present invention, in the invention according to any one of the second to sixth aspects, the sub-scanning pitch detecting means measures the temperature at the sub-scanning pitch obtained from the beam position detection signal from the light beam position detecting means. The sub-scanning pitch is obtained by multiplying the coefficient value for the temperature obtained from the means.

  The invention described in claim 9 is characterized in that the optical scanning devices according to claim 1 or claims 4 to 7 are juxtaposed in the main scanning direction, and one scanning line is divided and scanned.

  According to a tenth aspect of the present invention, an optical writing device is the optical scanning device according to any one of the first to ninth aspects.

  The invention described in claim 11 is the invention described in claim 10, wherein a plurality of optical writing devices are provided corresponding to each color.

  According to the present invention, it is possible to obtain an optical scanning apparatus and an image forming apparatus capable of forming a good output image without deviation from a prescribed beam pitch due to a change with time such as the temperature in the apparatus.

  Embodiments of an optical scanning device and an image forming apparatus according to the present invention will be described below with reference to the drawings.

First, an embodiment of an optical scanning device according to the present invention will be described.
FIG. 1 is a perspective view showing an optical arrangement of an optical scanning device according to an embodiment of the present invention. The optical scanning device 20 is a device that scans a surface to be scanned with a light beam (light beam) emitted from a light source as a light spot, and includes semiconductor lasers (Laser Diodes) 11a and 11b and coupling lenses 12a and 12b. , A polygon mirror 14 which is a light deflecting means provided with a deflecting reflecting surface for deflecting a light beam (laser beam) from the light source unit 18, and the light beam deflected by the polygon mirror 14 is scanned. And a scanning optical system 15 guided to a surface (surface of the photosensitive drum) 16.
Here, the direction in which the light beam bundle scans the surface to be scanned 16 is the main scanning direction, and the direction orthogonal to the main scanning direction is the sub-scanning direction.

  In the example shown in FIG. 1, the light source unit 18 is configured by an LD and a coupling lens. However, the configuration of the light source unit of the optical scanning device according to the present invention is not limited to this. Further, although the scanning optical system 15 is shown as an example composed of two scanning lenses 15a and 15b and one folding mirror 15c, the number of optical elements constituting the scanning optical system is limited to this. is not. Furthermore, although the optical scanning device 20 is a two-beam optical scanning device that simultaneously scans two light beams, the optical scanning device according to the present invention is a multi-beam scanning device that scans a larger number of light beams. Applicable.

Hereinafter, a method of optical scanning by the optical scanning device 20 will be described.
The light sources 11a and 11b are modulated and driven based on the image signal and emit divergent light beams. The light beams emitted from the light sources 11a and 11b are coupled into beam forms suitable for the subsequent optical system by coupling lenses 12a and 12b, respectively. Each coupled light beam is a substantially parallel beam with the same beam form. The light beam that has passed through the coupling lens 12 is converged only in the sub-scanning direction on the deflecting / reflecting surface of the polygon mirror 14 by the action of the cylindrical lens 13, and forms a line image that is long in the main scanning direction.

  The polygon mirror 14 is rotated counterclockwise at a substantially constant speed by a motor (not shown), and deflects the incident light beam from the cylindrical lens 13 at an equal angular velocity. The light beam deflected by the polygon mirror 14 passes through the scanning lenses 15 a and 15 b, is then folded by the folding mirror 15 c, and is guided to the scanned surface 16. The light beam guided to the scanned surface 16 is converged on the scanned surface 16 by the operation of the scanning optical system 15 and is focused on the scanned surface 16 to form an image as a beam spot. Optical scanning is performed on the scanning surface 16 from the right side to the left side in FIG.

  The light beam deflected by the polygon mirror 14 is guided and detected by a synchronous detection sensor 19 which is a light beam position detecting means prior to entering the scanned surface 16. The synchronization detection sensor 19 generates an electrical signal when it detects a light beam, and this signal is processed by a synchronization detection circuit (not shown), and a writing start signal is transmitted after a certain timing. Here, the “certain timing” is the time from the detection position of the synchronization detection sensor 19 to the writing start position.

  FIG. 2B is a schematic diagram showing an array of beam spots formed on the surface to be scanned. Reference numerals PY and PZ denote intervals between the beam spots BS1 and BS2 in the main scanning direction and the sub-scanning direction, respectively. Is shown. Since the optical scanning device 20 is configured so that the two light beams incident on the polygon mirror 14 are not parallel to each other in the main scanning section, as shown in FIG. An interval PY in the main scanning direction between the spots BS1 and BS2 can be secured. Therefore, only one synchronization detection sensor 19 can independently detect the synchronization detection signal for setting the modulation start timing for the two light beams.

Here, the output of the beam position detection signal by the synchronization detection sensor 19 will be described.
As shown in FIG. 3A, the synchronization detection sensor 19 is configured by arranging two sensors (for example, photodiodes) PD1 and PD2 side by side in the main scanning direction. Sensors PD1 and PD2 have two opposite edges that are parallel and straight, and one of the two edges that are parallel and straight is an angle θ that is not parallel to the sub-scanning direction (0 ° <θ <90 °). The synchronization detection sensor 19 performs current-voltage conversion and voltage amplification on the output signals from the PD1 and PD2 by the amplifiers AMP1 and AMP2, respectively, and then compares the voltage by the comparator CMP. The output signal level of the AMP2 is the output of the AMP1. When it becomes lower than the signal level, a beam position detection signal is output.
The number of sensors constituting the light beam position detecting means may be two or more. Further, the number of opposing parallel straight lines may be two or more, and at least one of the edges may be arranged so as to have an angle that is not parallel to the sub-scanning direction.

FIG. 3B is a timing chart of signals output from the synchronization detection sensor 19 when two light beams pass through the sensors PD1 and PD2, and two pulses are output by the passage of one light beam. It has been shown. The interval between the two pulses to be output is proportional to the scanning position of the light beam in the sub-scanning direction. The beam pitch ΔP (= PZ) in the sub-scanning direction of BS1 and BS2 is calculated from the following equation, where T1 and T2 are the times when the beam spots BS1 and BS2 pass the sensors PD1 and PD2, and v is the velocity of the light beam. can do.
ΔP = v × (T2−T1) / tan θ = k × (T2−T1) (formula)

The speed v of the light beam is determined by the focal length of the scanning optical system 15 and the number of rotations of the polygon mirror 14, but varies depending on the temperature in the optical scanning device. For this reason, the beam pitch ΔP calculated from the above equation using the measured pulse intervals (time) T1, T2 causes an error from the actual pitch depending on the temperature in the optical scanning device. This error cannot be ignored when a high-quality output image is required, particularly when color reproducibility is improved in a color image.
Therefore, the optical scanning device 20 includes a temperature measuring unit that measures the temperature inside the device. In the example shown in FIG. 1, temperature sensors 26 a, 26 b, and 26 c that are temperature measuring means are provided in the vicinity of the light source unit 18, the scanning optical system 15, and the polygon mirror 14 that greatly affect the optical characteristics. The temperature sensor is a sensor IC or a thermocouple, but it is preferable to use a CMOS sensor IC that digitally outputs a measurement value.
Further, if there is only one temperature sensor in the optical scanning device, the pitch error increases due to temperature deviation, and therefore it is desirable to provide a plurality of locations, for example, two or three.
Furthermore, in order to perform more accurate temperature correction, the temperature measurement unit may weight the measurement data from the temperature sensors provided at a plurality of locations according to the locations provided to obtain temperature measurement values.

  FIG. 4 is a diagram showing another example of the light beam position detecting means. In FIG. 4, the light beam position detection means outputs one pulse for the passage of one light beam, and the pulse width is proportional to the scanning position of the light beam in the sub-scanning direction. Note that the pitch ΔP can be calculated from the above-described equation with the pulse widths T1 and T2.

On the surface 16 to be scanned, the beam spots BS1 and BS2 maintain a predetermined (regular) interval in the sub-scanning direction, that is, the beam pitch PZ shown in FIG. Is required. However, the beam pitch PZ may fluctuate due to environmental fluctuations such as temperature and humidity and the influence of time.
Therefore, the optical scanning device 20 calculates the beam pitch from the beam spot position detected by the synchronization detection sensor 19, and when the amount of deviation from the predetermined pitch is equal to or larger than a certain value, the light beam emitted from the light source unit 18 is calculated. The pitch is corrected (controlled) so that the amount of deviation is zero due to deflection.

As a means for controlling the scanning position in this way, the optical scanning device 20 is provided with a beam interval measuring circuit 21, a beam interval calculating circuit 22, and a beam deflection element driving circuit 23 as shown in FIG.
The beam interval measurement circuit 21 detects the scanning position of the light beam on the scanned surface 16 in the sub-scanning direction based on the beam position detection signal from the synchronization detection sensor 19 and the temperature measured by the temperature sensor 26, and the pitch Sub-scanning position detection means for calculating ΔP.
The beam interval calculation circuit 22 is a means for comparing the pitch ΔP calculated by the beam interval measurement circuit 21 with a predetermined pitch and calculating the deviation amount.
The beam deflection element drive circuit 23 controls the scanning position to return the scanning position of the light beam in the sub-scanning direction to the predetermined scanning position so that the shift amount becomes zero when the pitch ΔP is shifted from the predetermined pitch. Means.

A method by which the beam interval measurement circuit 21 detects the sub-scanning position will be described with reference to the flowchart shown in FIG.
First, the value (coefficient value) of the coefficient k with respect to the temperature in the optical scanning device 20 measured by the temperature sensor 26 is determined (S1, S2).
Next, BS1 is turned on, and two pulse intervals T1 are measured based on the beam position detection signal from the synchronization detection sensor 19 (S3).
Next, BS1 is turned off and BS2 is turned on, and two pulse intervals T2 are measured based on the beam position detection signal from the synchronization detection sensor 19 (S4).
Based on the coefficient value k thus determined and the measured pulse intervals T1 and T2, the pitch ΔP is calculated from the above-described calculation formula (S5).

Next, a method in which the beam deflection element driving circuit 23 returns the scanning position of the light beam in the sub-scanning direction to a predetermined scanning position will be described.
The beam deflection element drive circuit 23 generates a drive signal corresponding to the shift amount calculated by the beam interval calculation circuit 22 and outputs the drive signal to the light beam deflection element 29. As shown in FIG. 1, the light beam deflecting element 29 is disposed in the optical path of the coupling lens 12 and the cylindrical lens 13, and as shown in FIG. 2A, a wedge prism 30 having a vertex angle α and a ring. The ultrasonic motor 31 is attached to the holding member 29. However, the light beam deflecting element is not limited to the wedge-shaped prism, and for example, a liquid crystal element driven by an electric signal may be used. The ring ultrasonic motor 31 rotates the wedge prism 30 by γ based on the drive signal from the beam deflection element drive circuit 23. Therefore, the light beam traveling from the coupling lens 12 toward the cylindrical lens 13 changes by φ with respect to the optical axis depending on the rotation angle of the wedge-shaped prism 30.
As described above, the beam deflection element drive circuit 23 rotates the wedge-shaped prism 30 to deflect the light beam emitted from the light source unit 18 so that the deviation amount of the pitch ΔP from the predetermined pitch becomes zero. Generate a drive signal. Therefore, the optical scanning device 20 scans the scanned surface 16 of the light beam by deflecting the light beam emitted from the light source unit 18 so that the deviation amount of the pitch ΔP from the predetermined pitch becomes zero. The position can be returned to a predetermined scanning position.

  In the optical scanning device according to the present invention, instead of the beam deflection element driving circuit 23, when the deviation amount of the pitch ΔP from a predetermined pitch is more than a certain value, a notification to that effect is given to an operator such as a serviceman or a user. Means to do this may be provided. As a means for notifying, for example, a display or a notification lamp may be provided on an operation panel of an optical scanning apparatus or an image forming apparatus to which the apparatus is applied to display a message indicating the amount of deviation or to light the lamp. The operator can confirm the occurrence of the shift amount by such a simple means and method, and can take measures for correcting the shift amount, such as readjustment of the optical arrangement.

FIG. 5 is a functional block diagram of each means in the optical scanning device 20 related to pitch control when the sensor shown in FIG. 3 is used.
The synchronization detection sensor 19 outputs a beam position detection signal to the pulse interval measurement circuit 21 using the reference clock generated by the reference clock generator 24.
The pulse interval measurement circuit 21 receives the beam position detection signal from the synchronization detection sensor 19, and measures the pulse intervals T1 and T2 when the light beam passes through the interval between the two sensors PD1 and PD2, thereby calculating the pitch ΔP. To do.
The pulse interval calculation circuit 22 compares the pitch ΔP calculated by the pulse interval measurement circuit 21 with a predetermined pulse interval (pitch).
The beam deflection element drive circuit 23 generates a drive signal corresponding to the deviation amount and outputs it to the light beam deflection element 29 when the pitch ΔP is deviated by a predetermined distance or more with respect to a predetermined pitch.
The image clock generator 25 generates an image clock signal synchronized with the beam position detection signal from the synchronization detection sensor 19 and the reference clock generated by the reference clock generator 24 and outputs the image clock signal to the semiconductor laser control circuit 27.
The semiconductor laser control circuit 27 controls the image recording timing based on the image clock signal generated by the image clock generator 25, and modulates and drives the light sources LD1 and LD2 based on the image signal.

  FIG. 6 is a functional block diagram of each unit of the optical scanning device 20 related to pitch control when the sensor shown in FIG. 4 is used. Except that the measurement object by the beam interval measurement circuit 21 is the pulse width, the other is the same as the example shown in FIG.

In the embodiment described above, in the example shown in FIGS. 3 and 4, one edge of the sensor is arranged perpendicular to the main scanning direction. The beam position detection signal detected at the edge arranged perpendicular to the main scanning direction can also be used as a main scanning synchronization signal indicating the start position of image recording in the main scanning direction. Of course, both ends of the sensor can be arranged non-perpendicular to the main scanning direction. In this case, since the angle θ can be increased, the detection sensitivity of the sub-scanning position can be increased. In FIGS. 3 and 4, the distance between adjacent edges of the sensors PD1 and PD2 is made smaller than the beam spot diameter. For example, since the beam detection at PD2 starts before the beam detection at PD1 is completed, the output signals of AMP1 and AMP2 can be reliably crossed.
Further, in the example shown in FIGS. 3 and 4, the signal level when the light beam is not detected is set so that AMP2 is higher than AMP1. When there is a difference in signal level, even if noise is mixed in the signal, an erroneous signal is not output, so that noise resistance performance is improved.
Furthermore, the beam pitch in the sub-scanning direction is not limited to the beam pitch of a plurality of light beams, and can be applied as means for detecting the scanning position of one beam of sub-scanning.

Next, the image forming apparatus according to the present invention will be described.
FIG. 10 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention. This image forming apparatus is a laser printer.
In addition to the optical scanning device 117, the laser printer 100 is a photoconductive photosensitive member, electrostatic latent image formed in a cylindrical shape as a latent image carrier 111 that is exposed by the optical scanning device 117 to form an electrostatic latent image. The image forming apparatus includes means for performing an electrophotographic process, such as developing means for developing the toner image with toner and transfer means for transferring the visualized toner image onto a recording sheet.

Around the latent image carrier 111, process members according to an electrophotographic method (process) such as a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are sequentially arranged. A corona charger can also be used as the charging means.
The optical scanning device 117 is an optical writing device that performs optical writing on the image carrier, and performs an exposure process of an electrophotographic process. The optical scanning device 117 includes a latent image carrier 111 that is uniformly charged by the charging roller 112. The surface is scanned to form an electrostatic latent image. The formed electrostatic latent image is a so-called negative latent image, and the image portion is exposed. This electrostatic latent image is reversely developed by the developing device 113, and a toner image is formed on the image carrier 111.

The cassette 118 storing the transfer paper P is detachable from the main body of the laser printer 100, and when the transfer paper P is mounted as shown in the drawing, the uppermost sheet of the stored transfer paper P is fed by the paper feed roller 120. The leading edge of the fed transfer paper P is caught by the registration roller 119. The registration roller 119 sends the transfer paper P to the transfer unit in accordance with the timing at which the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114.
The transfer paper P to which the toner image has been transferred is sent to the fixing device 116, where the toner image is fixed by the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the paper discharge roller 122.
The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like.

  By using the above-described optical scanning device according to the present invention as the optical scanning device 117, it is possible to prevent the light spot array on the surface to be scanned from fluctuating from a predetermined array. An image can be formed.

The timing of detecting the light spot arrangement may be after the operator presses the start button of the image forming apparatus to print out, or several sheets (up to several tens) when outputting a large number of sheets. It doesn't matter if every.
In addition, when an electric signal is not input to the liquid crystal element during a period other than during printout (beam scanning), a memory function for storing the previous adjustment value may be added.
As described above, when the optical scanning device 20 of the present invention is used as an optical writing device of an image forming apparatus, an output image can be output by an operator operating from the operation panel of the main body. As a pattern (evaluation chart) of an output image, for example, a pattern described in JP-A-10-62705 may be prepared. By adopting a configuration in which the operator confirms the image quality based on the output image, not only the influence of the variation of the beam spot arrangement in the optical scanning device on the output image but also each process such as development / transfer / fixing is performed on the output image. It is possible to correct the degradation of the output image including the effect of the influence.
In addition, it is possible to omit one or both of the beam spot array detection means and the control means, and the cost of the optical scanning device can be reduced.

  The image forming process described above has been described assuming a single color image forming process, but the present invention is not limited to this, and is applied to a color image forming apparatus that forms a plurality of color images. It is also possible. In that case, the optical writing unit can be applied to an image forming apparatus sharing a plurality of colors. That is, it has one optical writing unit and an image carrier, performs optical writing with an image signal for each color, develops it with the corresponding color toner, transfers it to transfer paper, and then another color The image signal is written with light, developed with the toner of the corresponding color, and transferred to the transfer paper, and image formation is performed for each color and transferred onto one transfer paper. This is an image forming apparatus of the type.

  The optical writing unit can also be applied to a so-called tandem type image forming apparatus in which this is used as an exposure unit for each color. In other words, it has a plurality of optical writing units and image carriers corresponding to each color, and an image is written on the corresponding image carrier by the corresponding optical writing unit with the image signal of each color, and developed with the toner of the corresponding color The toner images of the respective colors are transferred so as to overlap each other on one transfer sheet. The tandem type image forming apparatus is advantageous for light beam writing of images and high-speed image formation.

FIG. 7 is a schematic diagram for explaining an example of the relationship between the optical scanning device and the image carrier constituting the image forming apparatus. Each of the image forming apparatuses shown in (a) to (d) is black (K). , Cyan (C), magenta (M), and yellow (Y), the image carriers 16K, 16C, 16M, and 16Y are provided. The relationship between the optical scanning device of each image forming apparatus shown in (a) to (d) and the image carrier is as follows.
(A) The optical scanning device is provided for each image carrier, and optical writing is performed on the corresponding image carriers 16K, 16C, 16M, and 16Y by the optical scanning devices 20K, 20C, 20M, and 20Y, respectively.
(B) The optical scanning device is shared by a plurality of image carriers, and optical writing corresponding to each color is performed on the image carriers 16K, 16C, 16M, and 16Y by the optical scanning device 20A.
(C) The optical scanning device is shared by a plurality of image carriers, and the optical scanning device 20A1 performs optical writing corresponding to each color on the image carriers 16K and 16C, and the optical scanning device 20A2 performs the image carrier 16M. , 16Y, optical writing corresponding to each color is performed.
(D) The optical scanning device is shared by a plurality of image carriers, and optical writing is performed on the image carrier 16K by the optical scanning device 20B1, and each color is applied to the image carriers 16C, 16M, and 16Y by the optical scanning device 20B2. Optical writing corresponding to is performed.

When the number of light beams emitted from all the optical scanning devices 20K, 20C, 20M, and 20Y is one, a full-color (four-color) image is obtained by an image output device to which the optical scanning device is applied. be able to.
Further, at least one of the four optical scanning devices (for example, the optical scanning device 20K corresponding to black) is a four-beam optical scanning device having the configuration of the present invention, and a full color image is obtained by performing optical scanning only with this optical scanning device. The density can be increased 4 times compared to the time.
Furthermore, if the conveyance speed (and process speed) of the recording medium is changed to 4 times, the number of image output sheets can be increased 4 times.
Furthermore, even in the case of a full-color image, since a character image is often written in black and high resolution is often required, it is added to the above four-beam light scanning device 20K (black) and other light. By simultaneously writing the scanning devices (20C, 20M, 20Y; 1 beam), it is possible to obtain a higher-quality output image even in an image in which characters / photos / line drawing images are mixed.

FIG. 8 is an optical layout developed in a plane parallel to the deflection rotation plane showing still another embodiment of the image forming apparatus according to the present invention.
In this image forming apparatus, the optical scanning device 20 according to the present invention described above is arranged in parallel in the main scanning direction, and the effective writing width is divided to scan the scanning surface 16. is there. That is, it comprises a plurality of optical scanning devices and one image carrier.
Thus, the effective writing width can be increased by juxtaposing a plurality of optical scanning devices. Further, if the effective writing width is the same, the optical element and the optical deflector can be reduced in size, the beam waist position fluctuation due to mechanical tolerance and temperature fluctuation can be reduced, and wavefront aberration can be reduced.

1 is an optical layout diagram (perspective view) showing an embodiment of an optical scanning device according to the present invention. (A) is a schematic diagram showing a light beam deflection method by a light beam deflecting element arranged in the optical scanning device, and (b) is a schematic diagram showing an array of beam spots formed on a surface to be scanned. (A) which shows the example of the light beam position detection means arrange | positioned at the said optical scanning apparatus is a subscanning sectional view, (b) is a timing chart of an output signal. (A) which shows another example of the light beam position detection means arrange | positioned at the said optical scanning apparatus is a subscanning sectional view, (b) is a timing chart of an output signal. It is a functional block diagram of the means in the said optical scanning device which controls a beam pitch using the light beam position detection means of FIG. FIG. 5 is a functional block diagram of means in the optical scanning device for controlling the beam pitch using the light beam position detecting means of FIG. 4. FIG. 3 is a schematic diagram for explaining an example of a relationship between an optical scanning device and an image forming apparatus constituting the image forming apparatus according to the present invention. FIG. 5 is an optical arrangement diagram developed in a plane parallel to a deflection rotation surface showing another embodiment of the image forming apparatus according to the present invention. It is a flowchart which shows the derivation example of a beam pitch. 1 is a central sectional view showing an embodiment of an image forming apparatus according to the present invention.

Explanation of symbols

11 Light source (semiconductor laser)
12 Coupling lens 13 Cylindrical lens 14 Light deflection means (polygon mirror)
15 Scanning optical system 16 Surface to be scanned (photosensitive drum)
18 Light source 19 Light beam position detection means (synchronous detection sensor)
20 Optical scanning device 21 Beam interval measurement circuit (pulse interval measurement circuit)
22 Beam interval calculation circuit (pulse interval calculation circuit, pulse width calculation circuit)
23 Beam deflection element drive circuit 26 Temperature sensor 29 Light beam deflection element

Claims (11)

A light source modulated and driven based on an image signal, a light deflector having a deflecting / reflecting surface for deflecting a light beam from the light source, and a light beam deflected by the light deflecting unit is condensed on a surface to be scanned. An optical scanning device comprising a scanning optical system for
Consists of a plurality of sensors arranged such that two or more opposing edges are parallel and form a straight line, and at least one of the parallel and straight edges has an angle non-parallel to the sub-scanning direction. A light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal;
Temperature measuring means for measuring the temperature in the optical scanning device;
Sub-scanning position detection for detecting the scanning position of the light beam on the surface to be scanned in the sub-scanning direction based on the beam position detection signal output from the light beam position detecting unit and the temperature measured by the temperature measuring unit. Means,
When the scanning position in the sub-scanning direction detected by the sub-scanning position detecting means is deviated from the specified scanning position, the scanning position in the sub-scanning direction of the light beam on the surface to be scanned is changed to the specified scanning position. And a scanning position control means for returning to the optical scanning device. A light source that is modulated and driven based on an image signal, a light deflecting unit that includes a deflecting reflecting surface that deflects a plurality of light beams from the light source, and a plurality of light beams deflected by the light deflecting unit on a surface to be scanned An optical scanning device comprising a scanning optical system for focusing light on
Consists of a plurality of sensors arranged such that two or more opposing edges are parallel and form a straight line, and at least one of the parallel and straight edges has an angle non-parallel to the sub-scanning direction. A light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal;
Temperature measuring means for measuring the temperature in the optical scanning device;
A sub-scanning pitch for detecting a pitch in the sub-scanning direction of the plurality of light beams on the surface to be scanned based on the beam position detection signal output from the light beam position detecting unit and the temperature measured by the temperature measuring unit. Detection means;
Pitch control means for returning the pitch of the plurality of light beams in the sub-scanning direction on the surface to be scanned to the specified pitch when the pitch detected by the sub-scanning pitch detecting means is deviated from the specified pitch; and An optical scanning device comprising: A light source that is modulated and driven based on an image signal, a light deflecting unit that includes a deflecting reflecting surface that deflects a plurality of light beams from the light source, and a plurality of light beams deflected by the light deflecting unit on a surface to be scanned An optical scanning device comprising a scanning optical system for focusing light on
Consists of a plurality of sensors arranged such that two or more opposing edges are parallel and form a straight line, and at least one of the parallel and straight edges has an angle non-parallel to the sub-scanning direction. A light beam position detecting means for detecting a scanning position of the light beam on the surface to be scanned and outputting a beam position detection signal;
Temperature measuring means for measuring the temperature in the optical scanning device;
A sub-scanning pitch for detecting a pitch in the sub-scanning direction of the plurality of light beams on the surface to be scanned based on the beam position detection signal output from the light beam position detecting unit and the temperature measured by the temperature measuring unit. Detection means;
An optical scanning apparatus comprising: means for notifying an operator when the pitch detected by the sub-scanning pitch detection means deviates from a specified pitch.   The optical scanning device according to any one of claims 1 to 3, wherein the temperature measuring means includes temperature sensors disposed at a plurality of locations.   5. The optical scanning device according to claim 4, wherein the temperature measurement means weights the measurement data from the temperature sensors provided at a plurality of locations according to the locations where the temperature data is provided to obtain a temperature measurement value.   6. The optical scanning device according to claim 4, wherein the temperature sensor is provided at 2 or 3.   2. The sub-scanning position detection unit obtains a sub-scanning position by multiplying the sub-scanning position obtained from the beam position detection signal from the light beam position detection unit by a coefficient value for the temperature obtained from the temperature measurement unit. Item 7. The optical scanning device according to any one of Items 4 to 6.   7. The sub-scanning pitch detecting means multiplies the sub-scanning pitch obtained from the beam position detection signal from the light beam position detecting means by the coefficient value for the temperature obtained from the temperature measuring means to obtain the sub-scanning pitch. The optical scanning device according to any one of the above.   An optical scanning device according to claim 1, wherein the optical scanning device according to claim 1 is juxtaposed in the main scanning direction, and each scanning line is divided and scanned. An apparatus that performs optical writing from an optical writing device to an image carrier and forms an electrostatic latent image on the image carrier by electrophotography,
The image forming apparatus according to claim 1, wherein the optical writing device is an optical scanning device according to claim 1.   The image forming apparatus according to claim 10, wherein a plurality of optical writing devices are provided corresponding to each color.

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