JP2013052543A - Shading correction method, and shading correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shading correction method capable of promptly obtaining shading characteristics of a light scanning device using a light source means with a plurality of light emitting portions, easily obtaining shading correction data on the plurality of light emitting portions and scanning a scanned face by a plurality of light fluxes with uniform light intensity.SOLUTION: In the shading correction method, the shading characteristics within an effective scanning region of the scanned face of the light scanning device for forming image information are measured by a light amount measuring means, and by using the measured shading characteristics, the shading correction data for uniformizing the light intensity of incident light fluxes on the effective scanning range of the scanned face with respect to each light flux is determined with respect to each of the light emitting portions. By using the shading correction data determined with respect to each of the light emitting portions, the light intensity of the light fluxes emitted from the plurality of light emitting portions is adjusted. The shading correction data with respect to each of the plurality of light emitting portions is calculated based on the plurality of shading characteristics whose number is smaller than that of the light emitting portions included in the light source means.

Description

  The present invention relates to a shading correction method and a shading correction apparatus, and is suitable for an optical scanning apparatus such as a laser beam printer (LBP) having an electrophotographic process, a digital copying machine, or a multi-function printer (multi-function printer).

  Conventionally, in an optical scanning device used in a laser beam printer (LBP) or the like, a light beam modulated in accordance with an image signal is emitted from a light source means. Then, the light-modulated light beam is periodically deflected by an optical deflector composed of a polygon mirror, and an image is formed by optically scanning the photoconductor as a surface to be scanned through an imaging optical system having fθ characteristics. Yes. The light beam deflected by the optical deflector and transmitted through the imaging optical system is corrected so that the scanning speed is substantially constant on the surface to be scanned. However, the intensity of the light beam incident on the surface to be scanned varies depending on the image height (scanning position).

  This is because the transmittance and reflectance of an optical element such as an imaging lens or a mirror that passes or reflects before the light beam emitted from the light source means reaches the surface to be scanned varies depending on the incident angle of the light beam. Also, the thickness of the imaging optical system varies depending on the incident position of the light beam, and the constant velocity of the light beam on the scanned surface cannot be corrected by the imaging optical system, resulting in non-uniform speed, etc. It has become.

  Hereinafter, the intensity (difference) of the light intensity of the light beam when entering the image height on the surface to be scanned is referred to as shading (shading characteristics). This shading affects the image density in the main scanning direction during image formation. Conventionally, there has been known an optical scanning device provided with a correcting means for correcting shading at this time (Patent Document 1).

  The laser exposure apparatus disclosed in Patent Document 1 uses a light amount measurement unit that measures shading characteristics on the surface of a photoreceptor and a light intensity correction unit that corrects the light intensity of a light beam emitted from a light source unit, and is based on the measurement result of the shading characteristics. To correct shading. In Patent Document 1, the ratio of the light quantity of other image heights is obtained as shading correction data with reference to the image height at which the light intensity of the light beam incident on the scanned surface is the lowest.

  Also, in recent years, vertical cavity surface emitting lasers (VCSELs), which have much more light emitting parts than those of edge emitting lasers as light source means used in optical scanning devices, are two-dimensionally integrated in parallel, and the layout of the light emitting parts is easy. ) Is used. When this is used, the surface to be scanned can be scanned simultaneously with a plurality of light beams, and it becomes easier to form an image with the light beams.

JP 2003-5119 A

  When the number of light emitting portions of the light source means is increased, a plurality of scanning lines (images) can be formed by scanning the surface to be scanned once. A vertical cavity surface emitting laser having a plurality of light emitting portions as a light source means is difficult to align the polarization directions of the individual light emitting portions due to the construction. In addition, the shading characteristics tend to vary greatly depending on the light emitting portion. For example, if the polarization direction has an inclination of several degrees, the shading characteristics also change according to the amount of inclination of the polarization direction.

  As a result, in order to correct the shading characteristics on the surface to be scanned, the light quantity measurement of the light beam incident on the surface to be scanned is caused to emit light from each light emitting unit one by one, and the light amount (light intensity) of the incident light beam on the surface to be scanned each time. ) Is measured. For example, in an optical scanning device using light source means having eight light emitting units, the shading characteristics are measured eight times, and shading correction is performed based on the measurement data of the eight shading characteristics.

  For this reason, much time is required to perform the shading correction. In recent years, since further high definition of image formation has been demanded, when the number of light emitting units is further increased, an enormous measurement time corresponding to the number of light emitting units is required. In Patent Document 1, there is no description regarding a measurement method and the number of measurement of shading characteristics of an optical scanning device using a light source unit having a plurality of light emitting units. Further, it does not correspond to an optical scanning device using light source means having a plurality of light emitting portions.

  The present invention is suitable for an optical scanning device using light source means having a plurality of light emitting portions. The present invention provides a shading correction method and a shading correction apparatus capable of quickly obtaining shading characteristics, easily obtaining shading correction data for a plurality of light emitting units, and scanning a scanned surface with a plurality of light beams with uniform light intensity. For the purpose of provision.

According to the shading correction method of the present invention, a surface to be scanned is scanned with a plurality of light beams modulated by image signals from light source means having a plurality of light emitting units, and the surface to be scanned in an optical scanning device that forms image information is effective. The shading characteristic in the scanning range is measured by the light quantity measuring means, and the shading correction data for making the light intensity of the light beam incident in the effective scanning range of the scanned surface uniform for each light beam is measured using the measured shading characteristic. A shading correction method for adjusting the light intensity of a light beam emitted from the plurality of light emitting units using the shading correction data obtained for each of the plurality of light emitting units.
It is characterized in that shading correction data for each of the plurality of light emitting units is obtained by calculating from a shading characteristic having a number smaller than the number of the plurality of light emitting units included in the light source means.

In addition, the shading correction apparatus according to the present invention scans a surface to be scanned with a plurality of light beams modulated by image signals from light source means having a number of light emitting units, and forms an image information on the surface to be scanned. A light amount measuring means for measuring a shading characteristic within the effective scanning range of the light source, and a shading for making the light intensity of the light beam incident within the effective scanning range of the surface to be scanned uniform using the shading characteristics measured by the light amount measuring means A calculation means for calculating and obtaining characteristic data for each of the plurality of light emitting units;
And a control unit that controls the light intensity of the light beam emitted from the plurality of light emitting units using the shading characteristic data obtained by the calculation unit, wherein the calculation unit includes a plurality of light source units. It is characterized in that shading correction data for the plurality of light emitting units is obtained from a shading characteristic that is smaller than the number of light emitting units.

  According to the present invention, shading characteristics of an optical scanning device using a light source unit having a plurality of light emitting units can be quickly obtained, and shading correction data for a plurality of light emitting units can be easily obtained. As a result, a shading correction method and a shading correction device capable of scanning the surface to be scanned with a uniform light intensity with a plurality of light beams are obtained.

FIG. 3 is a main scanning sectional view of an optical scanning device using the shading correction method according to the first embodiment of the present invention. The enlarged view of the light source means of Example 1 using the shading correction method of this invention The figure which showed the light emission state of the light source means at the time of the shading characteristic measurement of Example 1 of this invention The figure which showed the light emission state of the light source means at the time of the conventional shading characteristic measurement Flowchart of the shading correction method according to the first embodiment of the present invention. Explanatory drawing which showed the relationship between the shading characteristic data of Example 1 of this invention, a laser emission amount (correction amount), and the light quantity distribution after shading correction | amendment. 1 is a perspective view of a main part of a color image forming apparatus according to a first embodiment using the shading correction method of the present invention. Explanatory drawing which showed the light emission state of the light source means at the time of the measurement of the shading characteristic based on Example 2 of this invention. Explanatory drawing which showed the light emission state of the light source means at the time of the measurement of the shading characteristic based on Example 3 of this invention. Explanatory drawing which showed the light emission state of the light source means at the time of the measurement of the shading characteristic based on Example 4 of this invention. Schematic diagram of essential parts of a color image forming apparatus of an embodiment using the shading correction method of the present invention.

  Embodiments of a shading correction method and a shading correction apparatus according to the present invention will be described below with reference to the drawings. The shading correction method of the present invention scans a surface to be scanned such as a photosensitive member with a plurality of light beams modulated by image signals from light source means having a plurality of light emitting units such as vertical cavity surface emitting lasers, and images Used in an optical scanning device for forming information. A shading characteristic, which is the intensity of a light beam incident within the effective scanning range of the surface to be scanned, is measured by a light amount measuring means provided at the position to be scanned or a conjugate position thereof.

  Then, using the shading characteristics measured by the computing means, a plurality of shading correction data for making the light intensity of the light beam incident within the effective scanning range of the scanned surface uniform for each light beam emitted from the plurality of light emitting units It calculates | requires for every light emission part. The shading correction data for each of the plurality of light emitting units at this time is obtained by calculating from a shading characteristic having a number smaller than the number of the plurality of light emitting units of the light source means. Specifically, the shading correction data of the plurality of light emitting units is obtained as follows.

  (A) All of the plurality of light emitting units emit light at the same time, and all light beams from the plurality of light emitting units are calculated from one shading characteristic obtained by measuring with a light amount measuring means.

  (B) It was obtained by measuring the luminous flux when the one light emitting unit closest to the midpoint of the line segment connecting the two light emitting units farthest apart among the plurality of light emitting units was measured by the light quantity measuring means. Calculated from one shading characteristic.

  (C) Two light-emitting parts that are the farthest apart among a plurality of light-emitting parts emit light at the same time, and all light fluxes from the two light-emitting parts are calculated from one shading characteristic obtained by measuring with a light quantity measuring means. What you are looking for.

  (D) Dividing the plurality of light emitting units into a group having a number smaller than the number of the light emitting units, and measuring all the luminous fluxes when the plurality of light emitting units of one group are all simultaneously illuminated by the light quantity measuring means. Calculated from one shading characteristic obtained in this way.

  Then, using the shading correction data obtained for each of the plurality of light emitting units, the light intensity of the light flux emitted from the plurality of light emitting units is adjusted by the control means. As a result, the light intensity when each of the light beams emitted from the plurality of light emitting portions is incident on each image height (within the effective scanning range) of the surface to be scanned is made uniform.

[Example 1]
FIG. 1 is a sectional view (main scanning sectional view) of a main part in the main scanning direction of the optical scanning apparatus according to the first embodiment of the optical scanning apparatus using the shading correction method of the present invention.

  In the following description, the sub-scanning direction (Z direction) is a direction parallel to the rotation axis of the deflecting means. The main scanning section is a section whose normal is the sub-scanning direction (direction parallel to the rotation axis of the deflecting means). The main scanning direction (Y direction) is the direction in which the light beam deflected and scanned by the deflecting means is projected onto the main scanning section. The sub-scanning cross section is a cross section whose normal is the main scanning direction.

  In the figure, reference numeral 1 denotes a light source means, which is composed of a vertical cavity surface emitting laser or the like, and has eight light emitting portions in this embodiment. FIG. 2 is a schematic view of the main part of the light source means 1. As shown in FIG. 2, the eight light emitting units 1a to 1h constituting the light source means 1 are aligned on a straight line, and the straight line is in a predetermined direction with respect to the main scanning direction (y direction) and the sub scanning direction (z direction). It is arrange | positioned to have the angle of.

  FIG. 1 shows only one light beam for simplification. Reference numeral 2 denotes an aperture stop, which shapes a divergent light beam emitted from the light source means 1 into a specific beam shape. Reference numeral 3 denotes a condensing lens (anamorphic lens) having different refractive power (power) in the main scanning direction (in the main scanning section) and in the sub scanning direction (in the sub scanning section). The condensing lens 3 converts the divergent light beam that has passed through the aperture stop 2 into a parallel light beam (or convergent light beam) in the main scanning direction and converts it into a convergent light beam in the sub-scanning direction. Each element of the light source means 1, the aperture stop 2 and the condenser lens 3 constitutes one element of the incident optical system LA.

  The incident optical system LA guides a plurality of light beams emitted from the light source means 1 to the same deflection surface 5a of the deflection means 5 described later. The condensing lens 3 may be composed of two optical elements (a collimator lens made of a spherical system and a cylinder lens having power in the sub-scanning direction). The condensing lens 3 may be configured by integrating a collimator lens and a cylindrical lens.

  An optical deflector 5 serves as a deflecting means for reflecting and deflecting an incident light beam, and is rotated at a constant speed (constant angular speed) in the direction of arrow A in the figure by a driving means (not shown) made of a motor or the like. Reference numeral 6 denotes an imaging optical system having a condensing function as an imaging means and an fθ characteristic.

  The imaging optical system 6 in the present embodiment is a first imaging optical element and a second imaging optical element that have different refractive powers in the main scanning direction (in the main scanning section) and in the sub scanning direction (in the sub scanning section). It has lenses (scanning lenses) 6a and 6b.

  The first and second imaging lenses 6a and 6b in the present embodiment are made of a plastic material (resin), and a plurality of light beams based on image information deflected by the same deflecting surface 5a of the optical deflector 5 are scanned surfaces. The image is formed on the photosensitive drum surface 7 (on the surface to be scanned). In addition, the first and second imaging lenses 6a and 6b are tilted of the deflection surface 5a by providing a conjugate relationship between the deflection surface 5a of the optical deflector 5 and the photosensitive drum surface 7 in the sub-scan section. Compensation is performed.

  The first imaging lens 6a has a positive refractive power in the main scanning section and the sub-scanning section on the optical axis of the first imaging lens 6a. The second imaging lens 6b has different positive refractive powers in the main scanning section and the sub-scanning section on the optical axis of the second imaging lens 6b. Reference numeral 7 denotes a photosensitive drum surface (photosensitive drum) as a surface to be scanned.

  In the present embodiment, the eight divergent light beams modulated and emitted from the light source means 1 according to the image information are regulated by the aperture stop 2 and incident on the condenser lens 3. Among the light beams incident on the condenser lens 3, the light beams are emitted as parallel light beams in the main scanning section. Further, in the sub-scan section, an image is formed on the same deflection surface 5a of the optical deflector 5 as a line image (line image elongated in the main scanning direction). The eight light beams deflected by the deflecting surface 5a of the optical deflector 5 are imaged in a spot shape on the photosensitive drum surface 7 via the first and second imaging lenses 6a and 6b.

  Then, by rotating the optical deflector 5 in the direction of arrow A, the photosensitive drum surface 7 is optically scanned in the direction of arrow B (main scanning direction). Thus, image recording (image formation) is performed on the photosensitive drum surface 7 as a recording medium.

  In the present embodiment, the material of the first and second imaging lenses 6a and 6b is formed of a plastic material (resin) as described above. However, the material is not limited to the plastic material, and may be a glass material. FIG. 2 is an enlarged view of the light source means 1 of FIG. FIG. 3 is an explanatory view showing the light emission state of the light source means 1 when measuring the shading characteristic indicating the intensity of light intensity on the scanned surface 7.

  In this embodiment, as shown in FIG. 2, the light source means 1 has eight light emitting portions 1a to 1h. When measuring the shading characteristics, as shown in FIG. 3, the polarizer 5 is rotated in a state where the eight light emitting units 1 a to 1 h emit light simultaneously, and eight light beams are scanned on the surface to be scanned 7. Then, the light quantity measuring unit (light quantity measuring means) 8 arranged at a considerable position on the surface to be scanned 7 is scanned in the main scanning direction to measure the light quantity at each image height at the same time and obtain the shading characteristics.

  In the present embodiment, the detection size in the sub-scanning direction of the sensor included in the light quantity measurement unit 8 is a size that allows all eight light beams to sufficiently enter. Since the amount of light incident on the light amount measuring unit 8 becomes large (close to eight times), the resolution of the sensor does not have to be very high. The light quantity measuring unit 8 is not limited to scanning in the main scanning direction, and a plurality of light quantity measuring units may be fixedly provided in the scanning region.

  In this embodiment, shading correction data for each of the eight luminous fluxes of the eight light emitting units is determined from one shading characteristic data obtained by one scan of the light quantity measuring unit 8. And the light emission amount of the light emission parts 1a-1h is adjusted in each image height. As a result, the light intensity of the light beam incident on each image height on the surface to be scanned is made uniform for each light beam.

  FIG. 4 is a diagram showing a light emission state of a plurality of light emitting units of the light source means 1 when measuring a conventional shading characteristic. Conventionally, as shown in FIG. 4, the eight light-emitting portions 8 a to 8 h emit light one by one, and the scan is performed eight times to measure the shading characteristics eight times. On the other hand, in this embodiment, since the shading characteristic can be obtained by one scan, the measurement tact is shortened to 1/8 compared with the conventional case.

  In this embodiment, individual (eight) shading characteristics are corrected using one shading correction data determined using one shading characteristic data obtained by causing all the light emitting portions of the light source means 1 to emit light. The variation in the correction residual at this time is slight and does not cause a problem of uneven image density.

  When it is desired to correct shading with higher accuracy, all the polarization angles of the eight light beams are measured in advance in order to grasp the polarization angle difference of a plurality of light beams emitted from the light source means 1 which is a main factor of variation in shading characteristics. . Then, a deflection angle table (information recording means) created from that is preferably used. From this polarization angle table, the inclination of the shading characteristic according to each polarization angle is predicted, and the shading characteristic predicted from each deflection angle is obtained in one shading characteristic data obtained by causing all the light emitting portions of the light source means 1 to emit light. Add the slope of.

  By using the eight determined shading correction data, the residual shading correction can be made substantially zero in all the scanning light beams of the eight light emitting units 1a to 1h. In this embodiment, a so-called underfilled optical system (UFS) is employed in which the width of the light beam incident on the deflecting surface 5a of the deflector 5 is smaller than the width of the deflecting surface in the main scanning direction. .

  Therefore, since the pupil of the imaging optical system 6 is conjugate with the position of the aperture stop 2, no significant illuminance unevenness occurs. For this reason, even if individual shading characteristics are corrected using the shading characteristics data obtained by causing the light source means 1a to emit all the light emitting sections 1a to 1h, the variation in the correction residual is slight and the problem of uneven image density is caused. Don't be.

  In the present embodiment, the light emission amount of the light source means 1 is changed and adjusted in accordance with the image height in order to perform shading correction. However, the present invention is not limited to this, and the light emission pulse width of the light beam is modulated in accordance with the image height. The shading correction may be performed accordingly.

  Next, the shading correction process in this embodiment will be described. FIG. 5 is a flowchart of the shading correction of this embodiment. FIG. 7 is a schematic diagram of a main part of a color image forming apparatus using the shading correction method of the present invention.

  First, a surface emitting laser (light source means) 1, a condensing lens 3, an optical deflector 5, and imaging lenses (optical elements) 6a and 6b are incorporated in the optical box (step S1). Next, all the light emitting parts of the light emitting parts 1a to 1h of the surface emitting laser (light source means) 1 incorporated in the optical scanning device are caused to emit light (step S2). Then, the shading characteristic is measured by the light quantity measuring means 8 of the optical scanning device incorporating the optical element (step S3).

  The shading characteristic data is written in a ROM as information storage means 101 mounted on the substrate of the surface emitting laser 1 (step S4). The information storage unit 101 is not limited to the ROM, and is not limited to this as long as it can hold information, such as a RAM or a two-dimensional barcode.

  A larger amount of data with this shading characteristic is sufficient in that high-accuracy shading correction can be performed, but since memory capacity is required, the accuracy of shading correction required for color image forming apparatuses is actually increased. Based on this, the number of data points is determined. The shading characteristic table of this embodiment is composed of a total of three data points of ± 153 mm and 0 mm with respect to the effective scanning width of 310 mm of the optical scanning device.

  Then, the shading characteristic is measured and the optical scanning apparatus having the shading characteristic data is incorporated into the image forming apparatus (step S5). Then, the light quantity measured at three points by the computing means 102 is approximated by a curve to a quadratic function in order to quantify it at each image height that has not been measured (step S6).

The approximate expression is
Z = AY ² + BY + C
Y: Image height in the main scanning direction Z: Measurement light quantity A, B, C: Coefficients are used.

  In order to perform curve approximation with such a quadratic function, values detected at least at three points in the main scanning direction are required. Increasing the number of light quantity measurements improves the accuracy of curve approximation, but also leads to an increase in memory capacity. Therefore, in practice, the number of light quantity measurements and the order of the polynomial for curve approximation are determined based on the accuracy of shading correction required for the image forming apparatus. Therefore, the number of light quantity measurements is not limited to three as in this embodiment, and may be three or more.

  Next, the calculation means 102 calculates the light emission amount (laser emission amount) of the light flux for each image height based on the light amount data approximated by a curve (steps S7 and S8). However, the order of the shading correction process is not limited to this. For example, before the optical scanning device is incorporated in the image forming apparatus, the shading characteristic data measured by the light amount measuring device is approximated by a curve in the light amount measuring device, These coefficients may be written in the information storage means 101. Then, the light emission amount of the surface emitting laser is controlled based on the light emission amount of the surface emitting laser calculated by the control means 103 (step S9).

  6A, 6B, and 6C are explanatory diagrams of the relationship between shading characteristic data, laser light emission amount (correction amount), and light amount distribution after shading correction. The light beam emitted from the light source means 1 is deflected and reflected by the deflector 5, and then passes through the first scanning lens 6a and the second scanning lens 6b in this order. Each time the light passes through the first scanning lens 6a and the second scanning lens 6b, the amount of light increases toward the end of the scanned surface 7 (FIG. 6A).

  Therefore, the shading correction is performed based on the shading characteristic measurement data so as to reduce the light emission amount (intensity) of the light source means at the end relative to the center of the surface to be scanned (FIG. 6B). By controlling the light emission amount in this way, a flat light amount distribution can be obtained with respect to each image height as shown in FIG. By controlling the laser emission amount in this way, the shading is corrected well in the entire image region, and a high-quality color image is obtained.

  In this embodiment, the light amount is measured by the light amount measuring device set in the optical scanning device, but the light amount may be measured in the image forming device after the optical scanning device is mounted on the image forming device. FIG. 7 is a perspective view of a main part of a color image forming apparatus equipped with an optical scanning device using the shading correction method of the present invention.

  In FIG. 7, reference numeral 11 denotes an optical scanning device, which includes the four optical scanning devices shown in FIG. 21, 22, 23 and 24 are photosensitive drums as image carriers, 51 is a conveyor belt, 10 a, 10 b and 10 c are density sensors as light quantity measuring means. A reference toner image pattern is formed on the conveying belt, and the amount of reflected light from the toner image is measured by density sensors (light amount measuring means) 10a, 10b, 10c arranged in the main scanning direction (y direction) above the conveying belt. To do.

  In this embodiment, of the three density sensors 10a, 10b, and 10c, one density sensor 10b is disposed at the center of the image area in the main scanning direction of the color image forming apparatus. The other two density sensors 10a and 10c are arranged at both ends of the image area in the main scanning direction of the color image forming apparatus.

  The arrangement position of the density sensor is not limited to the center of the image area, and the toner image density can be detected without any problem as long as it is near the center of the image area. Based on the detection value from the calculation sensor at this time, the shading correction value may be determined by the calculation means 102 and the shading correction may be performed. Further, the present invention is not limited to the detection of the density of the toner image before being transferred to the recording medium, and the density of the image after being transferred to the recording medium may be detected. Further, although the density sensor is provided as the three light quantity measuring means in the image forming apparatus, the present invention is not limited thereto, and a potential sensor or the like may be used.

  Thus, in this embodiment, the number of measurements is reduced in the measurement of the shading characteristics of the optical scanning device using the light source means having a plurality of light emitting portions. As a result, an optical scanning device with a shortened measurement tact and an image forming apparatus using the same are obtained. In this embodiment, a vertical cavity surface emitting laser having a plurality of light emitting portions on a single substrate is used as a light source means. However, a plurality of edge emitting lasers having a plurality of light emitting portions are provided with a small distance therebetween. Light source means may be used.

  As described above, the optical scanning device according to the present embodiment is manufactured using the shading correction data of the plurality of light emitting units corrected by the above-described shading correction method.

[Example 2]
Next, a second embodiment of the optical scanning device using the shading correction method of the present invention will be described. The difference between the present embodiment and the first embodiment is that the light amount of the light beam from the light emitting portion in a state where only one light emitting portion of the eight light emitting portions of the light source means is emitted in the light amount measurement for obtaining shading characteristic data. It is the point which measured. Other configurations and optical actions are the same as those in the first embodiment, and the same effects are obtained.

  FIG. 8 is an explanatory diagram showing the light emission state of the light source means when measuring the shading characteristics in this embodiment. The light source means 1 is composed of a vertical cavity surface emitting laser and has eight light emitting portions. As shown in FIG. 8, these eight light emitting sections are aligned on a straight line, and the straight lines are arranged to have a predetermined angle with respect to the main scanning direction and the sub-scanning direction.

  In the present embodiment, the shading characteristics are measured after only one light emitting unit 1d closest to the midpoint of the line segment connecting the two light emitting units 1a and 1h that are the farthest apart is emitted. Then, the shading correction data of the light beams from the eight light emitting units 1a to 1h is determined from the measured one shading characteristic data. Since it is the shading characteristic data obtained by the light emitting part 1d at the substantially center of the light source means 1, it can be the center value of the shading characteristics of the eight light emitting parts, so that the shading characteristic data of the eight light emitting parts can be obtained without any problems in one measurement. It is done.

  In addition, the light emitting unit at the time of measuring the shading characteristics is not limited to the light emitting unit 1d, and the other light emitting unit 1e that is closest to the midpoint of the line segment that connects the two lightest separated light emitting units 1a and 1h is emitted. Similar results can be obtained even when measured in a state. As described above, in this embodiment, the number of measurement of shading characteristics of the optical scanning device using the light source means having a plurality of light emitting portions is reduced. As a result, an optical scanning device with a shortened measurement tact or an image forming apparatus using the same is obtained.

[Example 3]
Next, a third embodiment of the optical scanning device using the shading correction method of the present invention will be described. In the present embodiment, the difference from the first embodiment described above is that the two light emitting sections 1a and 1h that are the farthest in the sub-scanning direction among the eight light emitting sections of the light source means in the light amount measurement for obtaining shading characteristic data. This is the point where shading characteristics were measured by simultaneous light emission. Other configurations and optical actions are the same as those in the first embodiment, and the same effects are obtained.

  FIG. 9 is an explanatory diagram showing the light emission state of the light emitting unit of the light source means 1 when measuring the shading characteristics in this embodiment. The light source means 1 is composed of a vertical cavity surface emitting laser and has eight light emitting portions. As shown in FIG. 9, these eight light emitting sections are aligned on a straight line, and the straight lines are arranged to have a predetermined angle with respect to the main scanning direction and the sub-scanning direction.

  In this embodiment, the shading characteristics are measured by simultaneously emitting light from the two light emitting portions 1a and 1h that are most separated in the sub-scanning direction. Then, the shading correction data for the eight luminous fluxes are determined from the measured one shading characteristic data.

  The light beams emitted from the two light emitting portions 1a and 1h that are most separated in the sub-scanning direction pass through the imaging lenses 6a and 6b, respectively, at positions that are the most separated in the sub-scanning direction. Since the imaging lenses 6a and 6b used in the optical scanning device of the present invention are made of plastic, birefringence distribution may occur in the imaging lenses 6a and 6b. It is well known that this birefringence affects the shading characteristics.

  Since this birefringence has a significant distribution in the sub-scanning direction, the shading characteristics vary depending on the light beam passage position in the sub-scanning direction. The shading characteristics are measured in a state where the two light emitting units 1a and 1h that emit a light beam having a large difference in the passing position of the light beam in the sub-scanning direction are simultaneously emitted. Thus, one shading characteristic data obtained by averaging both shading characteristic measurement values is obtained.

  From one shading characteristic data obtained by this measurement, shading characteristic correction data for eight light beams is determined. This shortens the measurement tact and corrects shading without unevenness among the eight light beams.

[Example 4]
Next, a fourth embodiment of the optical scanning device using the shading correction method of the present invention will be described. This embodiment differs from the first embodiment described above in that the arrangement of the light emitting portions of the light source means is two-dimensional as shown in FIG. Then, in the light quantity measurement for obtaining the shading characteristic data, the shading characteristics are measured by simultaneously emitting eight light emitting sections in one row among the 24 light emitting sections of the light source means. Other configurations and optical actions are the same as those in the first embodiment, and the same effects are obtained.

  FIG. 10 shows the light emission state of the light source means when measuring the shading characteristics in this embodiment. In FIG. 10, the light source means 1 'is composed of a vertical cavity surface emitting laser, and the light emitting portions are in a two-dimensional array of 8 × 3 rows. The straight lines composed of the eight light emitting units are arranged so as to have a predetermined angle with respect to the main scanning direction and the sub-scanning direction, respectively.

  In this embodiment, the shading characteristics are measured by simultaneously emitting light from the eight light emitting portions 1a to 1h included in the light emitting portion row arranged at the center in the sub-scanning direction. Then, the shading correction data of 32 light beams is determined from the measured one shading characteristic data.

  Since it is the shading characteristic data obtained by the light emitting section row at the center of the light source means, it can be the center value of the shading characteristics of the 32 light emitting sections. Therefore, the shading characteristic data of the 32 light emitting sections can be obtained without any problem in one measurement. can get.

  As described above, in this embodiment, the light-emitting unit of the light source means of the optical scanning device is two-dimensional, and even if the number of light-emitting units increases, the number of measurement of shading characteristics is reduced, and the optical scanning device with reduced measurement tact, or The used image forming apparatus is obtained.

[Color image forming apparatus]
FIG. 11 is a schematic view of a main part of a color image forming apparatus of an embodiment using the shading correction method of the present invention. This embodiment is a tandem type color image forming apparatus that scans four beams by an optical scanning device and records image information on a photoconductor as an image carrier in parallel. In FIG. 11, 60 is a color image forming apparatus, 11 is an optical scanning device having any of the configurations shown in the first to fourth embodiments, 21, 22, 23, and 24 are photosensitive drums as image carriers, Reference numerals 32, 33, and 34 denote developing units, and 51 denotes a conveyance belt.

  In FIG. 11, the color image forming apparatus 60 receives R (red), G (green), and B (blue) color signals from an external device 52 such as a personal computer. These color signals are converted into image data (dot data) of Y (yellow), M (magenta), C (cyan), and K (black) by a printer controller 53 in the apparatus. These image data are input to the optical scanning device 11. The optical scanning device 11 emits light beams 41, 42, 43, and 44 that are modulated in accordance with each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are mainly formed by these light beams. Scanned in the scanning direction.

  The color image forming apparatus in this embodiment scans four beams by the optical scanning device 11, and each corresponds to each color of Y (yellow), M (magenta), C (cyan), and K (black). In parallel, image signals (image information) are recorded on the surfaces of the photosensitive drums 21, 22, 23, and 24, and color images are printed at high speed.

  In the color image forming apparatus according to the present embodiment, as described above, the optical scanning device 11 forms the latent images of the respective colors on the corresponding photosensitive drums 21, 22, 23, and 24 using the light beams based on the respective image data. doing. Thereafter, a single full color image is formed by multiple transfer onto a recording material.

  As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 60 constitute a color digital copying machine.

  As described above, according to each embodiment, it is possible to obtain an optical scanning device in which the number of measurement of shading characteristics of an optical scanning device having a plurality of light emitting units is reduced and the measurement tact time is shortened, and an image forming apparatus using the optical scanning device. .

DESCRIPTION OF SYMBOLS 1 Light source means, 2 Aperture stop, 3 Condensing lens, 5 Deflection means, 6a 1st imaging lens, 6b 2nd imaging lens, 7 Scanning surface, LA incident optical system, 6 Imaging optical system, 8 Light amount detection means, 102 calculation means, 103 control means

Claims (7)

A scanning surface is scanned with a plurality of light beams modulated by image signals from a light source unit having a plurality of light emitting units, and a shading characteristic within an effective scanning range of the scanning surface in an optical scanning device that forms image information Using the measured shading characteristics, the shading correction data for making the light intensity of the light beam incident within the effective scanning range of the scanned surface uniform for each light beam is obtained for each of the plurality of light emitting units. A shading correction method for adjusting light intensity of a light beam emitted from the plurality of light emitting units using shading correction data obtained for each of the plurality of light emitting units,
A shading correction method characterized in that the shading correction data for each of the plurality of light emitting units is calculated and calculated from a shading characteristic having a number smaller than the number of light emitting units included in the light source means.   The shading correction data for each of the plurality of light emitting units is based on one shading characteristic obtained by causing all of the plurality of light emitting units to emit light at the same time and measuring all the light beams from the plurality of light emitting units by the light amount measuring unit. 2. The shading correction method according to claim 1, wherein the shading correction method is calculated.   The shading correction data of the plurality of light emitting units includes a luminous flux obtained by causing one light emitting unit closest to a midpoint of a line segment connecting two lightest spaced apart light emitting units among the plurality of light emitting units to emit light. 2. The shading correction method according to claim 1, wherein the shading correction method is calculated and obtained from one shading characteristic obtained by measurement with a light amount measuring means.   The shading correction data of the plurality of light emitting units is obtained by simultaneously emitting light from two light emitting units that are farthest among the plurality of light emitting units, and measuring all light beams from the two light emitting units by the light amount measuring unit. 2. The shading correction method according to claim 1, wherein the shading correction method is obtained by calculating from one obtained shading characteristic.   The shading correction data of the plurality of light emitting units is divided into a plurality of light emitting units divided into a number of groups smaller than the number of light emitting units, and all of the plurality of light emitting units of one group emit light simultaneously. The shading correction method according to claim 1, wherein the light flux is calculated from one shading characteristic obtained by measuring the light quantity by the light quantity measuring means. A surface to be scanned is scanned with a plurality of light beams modulated by image signals from a light source means having a plurality of light emitting sections, and shading characteristics within an effective scanning range of the surface to be scanned are measured in an optical scanning device that forms image information. Using the light quantity measuring means and the shading characteristics measured by the light quantity measuring means, the shading characteristic data for making the light intensity of the light beam incident within the effective scanning range of the scanned surface uniform is calculated for each of the plurality of light emitting units. Computing means to be calculated;
And a control unit that controls the light intensity of the light beam emitted from the plurality of light emitting units using the shading characteristic data obtained by the calculation unit, wherein the calculation unit includes a plurality of light source units. A shading correction apparatus characterized in that shading correction data of the plurality of light emitting units is obtained from a shading characteristic of a number smaller than the number of light emitting units.   An optical scanning device manufactured using the shading correction data of the plurality of light emitting units corrected by the shading correction method according to claim 1.