JP6766543B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that forms an image with toner. More specifically, the present invention relates to an image forming apparatus that performs deflected scanning of a light beam onto an image-supporting photoconductor by rotating a rotating multifaceted mirror.

Conventionally, some image forming apparatus scans an optical beam (main scanning direction) for exposure of an image-supporting photoconductor by rotating a rotating polymorphic mirror. In such an image forming apparatus, even if the emission intensity of the light beam is constant, the phenomenon that the amount of irradiation light on the irradiated surface of the image-supporting photoconductor differs depending on the position within the scanning range tends to occur. .. Strictly speaking, this is because the irradiation path of the light beam differs depending on the position within the scanning range. This unevenness of the amount of irradiation light appears on the image as the shading of the density depending on the position in the main scanning direction, which causes deterioration of the image quality.

As a countermeasure, there is a method of coating optical components on the irradiation path in multiple layers, but in recent years, it has been proposed to adjust the emission intensity of the light beam according to the scanning position as a cheaper means. For example, in Patent Document 1, the light amount is adjusted according to the shading correction curve by controlling the increase / decrease cycle, which is a unit of the period for increasing / decreasing the light amount adjustment amount. As a result, it is possible to reduce density unevenness by performing smooth shading correction according to the optical characteristics without making the device configuration excessive.

JP-A-2010-241125

However, the above-mentioned conventional technique has the following problems. The amount of light cannot be adjusted well at the end of the scanning range. When deflection scanning is performed by rotating a rotating multi-sided mirror, the amount of irradiation light drops sharply toward the outside at the end of the scanning range. For this reason, it is not possible to take appropriate measures even near the edges by controlling the amount of light in the same way as in the central part of the scanning range. As a result, the scanning range that can be used for image formation is substantially limited.

The present invention has been made to solve the problems of the above-mentioned conventional techniques. That is, the problem is to provide an image forming apparatus capable of appropriately controlling the amount of light even near the end of the scanning range and using a wider scanning range for image formation.

The image forming apparatus according to one aspect of the present invention includes an image-bearing photoconductor, a light emitter that emits a light beam based on image data, and a rotating multi-faceted surface that reflects and deflects and scans the light beam emitted from the light beam while rotating. An image forming apparatus having a mirror and an optical member that guides a light beam deflected and scanned by a rotating multifaceted mirror to an irradiated surface of an image-bearing photoconductor, and is a subject when the light beam is emitted from a light emitter without correction. A pre-correction data acquisition unit that acquires the initial main scanning light amount, which is the irradiation light amount for each scanning position on the irradiation surface, a correction point setting unit that sets correction points at a plurality of locations within the scanning range, and an initial main scanning light amount. Based on the position of the correction point, the correction value determination unit that determines the correction value for correcting the irradiation light amount unevenness on the irradiated surface for each scanning position, and the amount of emitted light at the time of image formation by the light emitter according to the correction value. It has a light amount correction unit for correction, and the correction point setting unit uses the outermost correction point to be set (hereinafter referred to as "external correction point") to switch the reflecting surface by rotating the rotating polymorphic mirror. Along with this, it is configured to be arranged in the outer edge region where the initial main scanning light amount drops sharply toward the end of the scanning range, and the correction value determination unit is a correction point other than the external correction point (hereinafter referred to as the correction point). For the position (referred to as "internal correction point"), the correction value is determined so that the magnitude is opposite to the value of the initial main scanning light amount at that position, and for the position of the external correction point, from the outer edge region. The correction value is determined based on the approximation line based on the initial main scanning light amount at at least two inner locations, and the position between the correction points is based on the correction value at least on both sides of the correction point. It is configured to determine the correction value based on the approximation line.

In the image forming apparatus in the above aspect, the initial main scanning light amount is acquired at a time other than the time of image formation. That is, the data of the irradiation light amount for each scanning position on the irradiated surface when the light beam is emitted from the light emitter with a constant emission light amount is acquired. This data represents the light intensity unevenness that occurs when the light beam is scanned without correction. Then, the correction value for correcting the irradiation light amount unevenness on the irradiated surface is determined for each scanning position. The correction value is determined based on the initial main scanning light intensity and the position of the correction point. The scanning of the light beam at the time of image formation is performed with the amount of emitted light corrected according to this correction value. As a result, unevenness in the amount of irradiation light on the irradiated surface is suppressed.

Here, in this embodiment, when setting the correction points, the outermost external correction points are arranged in the outer edge region. There, the initial main scanning light intensity drops sharply toward the end of the scanning range. Then, the correction value is determined by three methods in relation to the correction point. First, for the position of the internal correction point, the correction value is determined so as to cancel the magnitude of the value of the initial main scanning light amount at the position. That is, a correction value having a large value is determined for a correction point in which the value of the initial main scanning light amount is smaller than that of the other correction points. On the contrary, a correction value having a smaller value is determined for a correction point in which the value of the initial main scanning light amount is larger than that of the other correction points. Secondly, for the external correction points, the correction values are determined based on the approximate lines based on the initial main scanning light amount at at least two points inward from the outer edge region. Thirdly, for the position between the correction points, the correction value is determined at least based on the approximate line based on the initial main scanning light amount of the positions of the correction points on both sides of the position. As a result, deflection scanning can be performed with a substantially constant amount of irradiation light over a wide scanning range up to just inside the outer edge region.

In the image forming apparatus of the above aspect, the correction point setting unit is configured to arrange all the internal correction points inward from the outer edge region, and the correction value determination unit is configured with respect to the position of the external correction point. It is preferable that the "two points" when determining the correction value are set to two points, the position of the outermost one of the internal correction points and the reference position outside the internal correction point. .. In this way, an approximate expression can be obtained based on the correction values of "two points" that are inside the outer edge region but as far as possible, and the correction value of the external correction point is determined by this approximate expression. Therefore, the correction is made based on the initial main scanning light amount at the position immediately inside the outer edge region. Therefore, a substantially constant amount of irradiation light can be obtained over a wide scanning range.

The image forming apparatus of the above aspect may be further configured such that the correction value determining unit sets the reference position to a position where the distance from the end of the scanning range is a predetermined fixed value. .. As a result, appropriate correction can be realized with relatively simple control.

The reference position may be a position where the initial main scanning light intensity is equal to or higher than a predetermined minimum light intensity. Alternatively, the reference position may be a position where the initial main scanning light intensity becomes the first maximum value from the end of the scanning range. As a result, the position inside the outer edge region where the initial main scanning light intensity is high is surely set as the reference position, so that the correction accuracy is high.

In the image forming apparatus of the above aspect, the correction value determining unit also determines the correction value for the position of the external correction point based on the approximate line based on the initial main scanning light amount of three or more points inside the outer edge region. It may be configured. By using a higher-order approximation formula, more accurate correction can be performed.

In the image forming apparatus of the above aspect, or in the correction point setting unit, a correction point candidate location that can be a correction point within the scanning range is specified in advance, and the correction point is set from the correction point candidate location for the initial main scanning light intensity. It is better that the image is densely arranged in the area where the rate of change is large with respect to the scanning position and is selected so as to be sparsely arranged in the area where the rate of change is small. As a result, the area where the initial main scanning light amount changes drastically is corrected with high accuracy, and the total calculation amount and storage amount are not excessive.

Alternatively, in the image forming apparatus of the above aspect, the rotating multifaceted mirror performs deflection scanning of the light beam at a plurality of levels of scanning speeds, and has a reference clock generating unit that generates a reference clock for each of the plurality of levels of scanning speeds. It is better that the maximum value of the ratio of each scanning speed to the frequency of each reference clock is within 1.01 times the minimum value, and the correction point setting unit sets the correction point according to the reference clock. As a result, it is possible to reduce the storage capacity and realize appropriate correction within a realistic range of the original oscillation frequency. Of course, it is even better if the ratio of the scanning speed to the frequency of the reference clock is constant for any scanning speed.

According to this configuration, there is provided an image forming apparatus capable of appropriately controlling the amount of light even near the end of the scanning range and using a wider scanning range for image formation.

It is sectional drawing which shows the schematic structure of the image forming apparatus which concerns on embodiment. It is a top view which shows the schematic structure of the print head part. It is sectional drawing which shows the schematic structure of the print head part. It is a block diagram which shows the structure of the control system of the image forming apparatus which concerns on embodiment. It is a graph which shows an example of the unevenness of the initial main scanning light amount. It is a graph explaining the setting of the correction value with respect to the uneven initial main scanning light amount. 6 is an enlarged graph showing the vicinity of the left shoulder of the graph of FIG. 6 is an enlarged graph showing the vicinity of the right shoulder of the graph of FIG. It is a graph (near the left shoulder) which shows the irradiation light amount on the irradiated surface by the correction in an embodiment. It is a graph (near the right shoulder) which shows the irradiation light amount on the irradiated surface by the correction in an embodiment. It is a flowchart which shows the determination procedure of the correction value in Embodiment. 6 is a graph (fixed position method) showing an enlarged view of the vicinity of the left shoulder of the graph of FIG. It is a graph (same as above) showing the vicinity of the right shoulder of the graph of FIG. 6 in an enlarged manner. It is a graph (minimum value method) showing the vicinity of the left shoulder of the graph of FIG. It is a graph (same as above) showing the vicinity of the right shoulder of the graph of FIG. 6 enlarged. 6 is a graph (peak position method) showing an enlarged view of the vicinity of the left shoulder of the graph of FIG. It is a graph (same as above) showing the vicinity of the right shoulder of the graph of FIG. 6 enlarged. It is a graph (quadratic approximation method) which shows the vicinity of the left shoulder of the graph of FIG. 6 enlarged. It is a graph (same as above) showing the vicinity of the right shoulder of the graph of FIG. 6 in an enlarged manner.

Hereinafter, embodiments embodying the present invention will be described in detail with reference to the accompanying drawings. This embodiment is an application of the present invention to the image forming apparatus 1 shown in FIG. The image forming apparatus 1 of FIG. 1 has a main body unit 2 and a reading unit 3. The main body 2 contains a paper feeding unit 4 and an image forming unit 5. The image forming unit 5 forms an image on the paper supplied from the paper feeding unit 4. The image forming unit 5 is provided with print head units 6 and 4 photoconductor drums 7, an intermediate transfer belt 8, and a fixing device 9. The scanning unit 3 is provided with an automatic document transporting unit 10 and a scanner unit 11. The image forming apparatus 1 is also provided with an operation display panel 12.

The feature of the image forming apparatus 1 of this embodiment is the exposure system by the print head unit 6. The print head portion 6 will be described with reference to FIGS. 2 and 3. As shown in FIG. 2, the print head unit 6 is provided with light emitters 13 for each of the four colors (Y, M, C, K). The light emitter 13 is a light source that emits a light beam for exposing the photoconductor drum 7 based on image data. By irradiating the surface of the photoconductor drum 7, that is, the surface to be irradiated with the light beam from the light emitter 13, an electrostatic latent image based on the image data is formed on the photophore drum 7. Based on this electrostatic latent image, the toner image is supported on the surface of the photoconductor drum 7 through a known development process. Then, this toner image is transferred onto the paper through a known transfer process, and is fixed by the fixing device 9.

The print head portion 6 is also provided with a collimator lens 14 and a reflector 15 for each of the four colors. The collimator lens 14 collects the light emitted from the light emitter 13 in the form of a beam. The print head unit 6 is further provided with a reflecting mirror 16, a polygon mirror (rotating multifaceted mirror) 17, and an Fθ lens 18 as common to the four colors. Light of four colors is collected by the reflecting mirror 15 in the reflecting mirror 16 and reflected toward the polygon mirror 17. Although it is drawn briefly in the figure, the four reflectors 15 are actually arranged with a step so as not to interfere with each other's optical paths. Alternatively, a half mirror may be used as the reflecting mirror 15. The polygon mirror 17 changes the reflection direction of the light beam by rotating, that is, deflects and scans the light beam. The Fθ lens 18 is an optical member that guides the light beam reflected by the polygon mirror 17 to the photoconductor drum 7.

Further, the print head portion 6 is provided with reflectors 19, 20 and an optical sensor 21. The reflector 19 reflects the light beam deflected and scanned by the polygon mirror 17 toward the photoconductor drum 7. The reflecting mirror 20 is arranged at a position where the light beam deflected and scanned by the polygon mirror 17 hits immediately before hitting the reflecting mirror 19. When the light beam is reflected by the reflector 20, the reflected light is guided to the light sensor 21. When the optical sensor 21 receives the reflected light, a scanning synchronization signal is emitted. That is, the timing at which the optical sensor 21 receives the reflected light is set as the reference timing for drawing.

Although omitted in FIG. 2, as shown in FIG. 3, the print head portion 6 is provided with reflectors 22 to 27 in addition to the above. Similar to the reflecting mirror 19, the reflecting mirrors 22 to 27 reflect the light beam deflected and scanned by the polygon mirror 17 toward the photoconductor drum 7. However, while one reflector 19 (for K color) fulfills that purpose, the reflectors 22, 23 (for Y color), the reflectors 24, 25 (for M color), and the reflectors 26, 27 (for M color) (For C color) consists of two sheets each. Although not shown in FIG. 3, the reflectors 22 and 24 and the reflector 26 are each provided with the same reflectors as the reflector 20, and all of them direct the light beam toward the optical sensor 21. It is designed to reflect. Further, as shown in FIG. 3, the polygon mirror 17 is provided with a drive motor 28.

FIG. 4 shows a block diagram of the control system of the image forming apparatus 1. The control system of the image forming apparatus 1 is mainly composed of the overall control unit 29. The overall control unit 29 controls the overall operation of the image forming apparatus 1. The print head unit 6 and the operation display panel 12 described above are also connected to the overall control unit 29. In addition to the above, the reading control unit 30 and the image processing unit 31 are also connected to the overall control unit 29. The reading control unit 30 has a function of controlling the reading unit 3 to acquire image data of a document. The image processing unit 31 is a unit that performs data processing for subjecting the image data acquired by the reading control unit 30 to image forming processing such as color space conversion and density correction. Image data for image formation is supplied from the image processing unit 31 to the print head unit 6.

The print head unit 6 is provided with a drawing control unit 32 and a storage unit 33 in addition to the above-mentioned light emitter 13 and drive motor 28, which are hard elements. The collimator lens 14, the reflecting mirror 15, 16, 19, 20, 22 to 27, the polygon mirror 17, the Fθ lens 18, and the optical sensor 21 described above are omitted in FIG. The drawing control unit 32 controls the light emission of the light emitter 13 and the rotation of the drive motor 28 for image formation. The storage unit 33 stores various data necessary for that purpose.

The light emission control of the light emitter 13 by the drawing control unit 32 includes blinking control based on image data and brightness control. Of these, the latter is the feature of the image forming apparatus 1 of this embodiment. The brightness control of the light emitter 13 in the present embodiment aims to make the amount of light emitted by the light beam on the irradiated surface of the photoconductor drum 7 uniform within a wide scanning range as much as possible. That is, when the amount of light emitted from the light emitter 13 is constant and the polygon mirror 17 performs the deflection scan, the amount of irradiation light (initial main scan light amount) on the irradiated surface is not constant, and is shown in FIG. 5, for example. As described above, the situation becomes uneven depending on the main scanning position. This uneven irradiation light amount is caused by the material of the reflecting surface of the polygon mirror 17 and the Fθ lens 18 not being completely uniform, but there is a limit to the improvement by improving the quality of these optical components. Therefore, in this embodiment, this uneven irradiation light amount is suppressed by controlling the brightness of the light emitter 13.

That is, as shown in FIG. 6, the correction value is set so as to cancel the intensity of the initial main scanning light amount. Then, the brightness of the light emitter 13 is controlled so that the amount of light emitted from the light emitter 13 becomes a value proportional to this correction value. As a result, the amount of irradiation light on the irradiated surface is made almost constant. Of course, the correction value shall be a small value for the scanning position where the initial main scanning light amount is large, and a large value for the scanning position where the initial main scanning light amount is small. This is to cancel the magnitude of the initial main scanning light amount. Here, the correction value is set so as to be proportional to the reciprocal of the initial main scanning light amount at that position. Instead of using the reciprocal, the correction value may be set so that the total of the initial main scanning light amount and the correction value becomes constant.

In the image forming apparatus 1 of the present embodiment, a correction point is further set within the scanning range. In the example of FIG. 6, the main scanning position where the shaded quadrangle of “correction point arrangement” is arranged is the position set as the correction point. The method of arranging the correction points within the scanning range will be described later. For the position of the correction point, the correction value is set in proportion to the reciprocal of the initial main scanning light amount as described above. For the position between the correction points, the correction value is basically set by the calculation from the approximate expression. The approximate expression is given as a polynomial determined by the correction values at the positions of a plurality of correction points (for example, correction points on both sides).

Looking closely at the initial main scanning light intensity in FIG. 6, the light intensity sharply decreases toward the outside of the scanning range in the outer edge region Z near the end of the scanning range. This is an unavoidable phenomenon that accompanies the switching of the reflecting surface due to the rotation of the polygon mirror 17. In this embodiment, in order to use the widest possible scanning range for image formation, correction points are intentionally arranged in this outer edge region. The correction points (hereinafter referred to as "external correction points") arranged in the outer edge region Z are, of course, the ones closest to the scanning range in the entire correction points. However, for this external correction point, the correction value is set by a special method described later, instead of setting the correction value proportional to the reciprocal of the initial main scanning light amount as described above.

The determination of the correction value for the external correction point will be described with reference to FIGS. 7 and 8. FIG. 7 is an enlarged view of the left shoulder portion (scanning start side end portion) of FIG. 6, and there is a region X in which the initial main scanning light amount is slightly raised. The outer edge region Z is a portion on the outside where the amount of light is sharply reduced.

In FIG. 7, three correction points P1, P2, and P3 are arranged. Of these, the outermost correction point P1 in the scanning range is an external correction point arranged in the outer edge region Z. Correction points P2 and P3 (hereinafter referred to as "internal correction points") other than the correction points P1 are arranged within the range inside the outer edge region Z even within the scanning range. Here, for the internal correction points P2 and P3, as described above, the correction values D2 and D3 are set so as to be proportional to the reciprocal of the initial main scanning light amounts E2 and E3 at that position. In the example of FIG. 7, since the initial main scanning light amounts E2 and E3 are both larger than 100%, the correction values D2 and D3 are both smaller than 100%.

However, the correction value for the external correction point P1 is determined by a method different from that for the internal correction points P2 and P3. If the correction value Da1 is determined for the external correction point P1 by the same method as the correction values D2 and D3, the correction value Da1 becomes a value considerably larger than 100%. This is because the value is small because the initial main scanning light amount E1 is in the outer edge region Z. In this case, the correction value Da1 is extraordinarily large with respect to the correction values D2 and D3, which does not meet the purpose of leveling the curve of the initial main scanning light amount.

Therefore, in this embodiment, Da1 is not adopted as the correction value for the external correction point P1, and the correction value D1 is determined by the following method. First, the position Pt (reference position) is set in the region X in FIG. 7. The position Pt is a position inside the outer edge region Z and outside the outermost internal correction point P2. Then, the correction value Dt is determined so as to be proportional to the reciprocal of the initial main scanning light amount Et at the position Pt. Then, the correction value D1 of the external correction point P1 is determined by the equation of Equation 1. P1 and P2 in Equation 1 represent the positions of the correction points P1 and P2 in the scanning direction.

That is, in the graph of FIG. 7, a straight line (first-order approximation formula) connecting the point Dt and the point D2 is drawn, and the straight line is extrapolated to the position of the correction point P1 to obtain the correction value D1. That is. Note that on FIG. 7, the correction value D1 seems to almost coincide with the initial main scanning light amount E1 at the correction point P1, but this is merely a coincidence. Further, the right shoulder (end of the scanning end side) in FIG. 8 may be determined in the same manner. Once the correction values have been determined for all the correction points in this way, the correction values for the section between the correction points are determined. This may be obtained by a linear approximation formula based on the correction values of the correction points on both sides.

The amount of irradiation light of the light beam on the irradiated surface at the time of actual image formation according to the correction value determined in this way will be described with reference to FIGS. 9 (left shoulder side) and 10 (right shoulder side). The “corrected main scanning light amount” shown in FIGS. 9 and 10 is obtained by multiplying the “initial main scanning light amount” by the “correction value”. Therefore, from the above-mentioned method of determining the correction value, the "main scanning light amount after correction" is almost 100% at the position between the internal correction points and the internal correction points, and the uniformity is high. Further, even in the region outside the outermost internal correction point P2, the uniformity is also high except for the outer edge region Z and the range in the immediate vicinity thereof. This is because the correction value D1 is appropriately determined as described above. Therefore, a wide scanning range R extending immediately before the outer edge region Z can be used for image formation.

If the above-mentioned Da1 is used as the correction value at the correction point P1, the corrected main scanning light amount outside the internal correction point P2 is as shown by the curve W of the alternate long and short dash line in FIGS. 9 and 10. That is, the amount of main scanning light after correction becomes considerably high in the vicinity corresponding to the point Et shown in FIG. 7. Therefore, the scanning range that can be used for image formation is almost limited to the range from the outermost internal correction point to the outermost internal correction point. On the other hand, in this embodiment, as described above, the entire wide scanning range R can be used for image formation.

The procedure for determining the correction value described above will be described with reference to FIG. In the flow of FIG. 11, first, the data of the initial main scanning light amount is acquired (S1). The data of the initial main scanning light amount acquired here is the data as shown in the graph of FIG. This data is acquired by forming a solid image and measuring the density distribution with respect to the main scanning direction in a state where the amount of light emitted from the light emitter 13 is constant.

Next, the arrangement of the correction points is determined (S2). In the image forming apparatus 1 of this embodiment, correction point candidate locations that can be set as correction points are predetermined. The correction point candidate locations are the shaded quadrangles of “correction point arrangement” and the white quadrangles of “correction point unarranged” in FIG. In the example of FIG. 6, these are 46 places in total. Correction point candidate locations also exist in the outer edge regions Z at both ends of the scanning range. The scanning direction position of the correction point candidate location is stored in the storage unit 33.

The process performed in S2 is to actually select some of these correction point candidate locations as correction points. In the example of FIG. 6, 30 correction point candidate points are selected as correction points, and the remaining 16 correction point candidate points are not selected. The selection of the correction points is performed so as to satisfy the following two guidelines.

The first guideline is that the correction point candidate points in the outer edge regions Z at both ends are also selected as correction points one by one. Otherwise, the correction process related to the above-mentioned correction point P1 cannot be performed. In order to execute this, it is necessary to automatically identify the range that should be the outer edge region Z in the distribution of the initial main scanning light amount acquired in S1 (for example, FIG. 6). Such an algorithm is used. It is already known. For example, the range to be the outer edge region Z is appropriately set based on the differential value of the initial main scanning light amount depending on the scanning position and the difference from the target light amount.

The second guideline is to place many correction points in the region where the curve is severely uneven and to place few correction points in the relatively flat region with respect to the distribution of the initial main scanning light amount acquired in S1. is there. This is because it is necessary to calculate the correction value by the approximate expression between the correction points described above with higher accuracy in the region where the unevenness of the curve is severe. As for the algorithm for extracting the region with severe unevenness from the entire scanning range in this way, a known algorithm can be appropriately used. That is, it is possible to appropriately distinguish between a region with severe irregularities and a region without irregularities by an index such as a differential value or a secondary differential value depending on the scanning position of the initial main scanning light amount.

After determining the arrangement of the correction points, the correction values of the set correction points are determined as described above for the internal correction points (S3). Further, for the external correction point, the correction value is also determined as described above (S4). Then, based on the corrected value of the determined correction points, the correction value is also determined for the position between the correction points as described above (S5). The determined correction value is stored in the storage unit 33. After that, when the image is formed, the correction value is read out from the storage unit 33, and the light emission amount of the light emitter 13 is corrected by the correction value. As a result, as described with reference to FIGS. 9 and 10, a uniform amount of main scanning light is obtained on the irradiated surface of the photoconductor drum 7 over a wide scanning range R.

The process of determining the correction value as described above is performed at least after the production of the image forming apparatus 1 and before the first image forming. However, not only that, it is desirable that the image be performed at an appropriate timing other than when the image is formed (immediately after the power is turned on, every predetermined number of images, etc.). In particular, it is desirable to redo the correction value determination process when the temperature inside the image forming apparatus 1 fluctuates beyond a certain limit or after some maintenance is performed on the scanning optical system.

Subsequently, a variation regarding the determination of the correction value with respect to the external correction point P1 will be described. The variations described here are mainly about how to determine the position Pt in FIG. 7.

The first variation is that the position Pt is set to a fixed position for each model of the image forming apparatus 1. As shown again in FIGS. 12 and 13, when the vicinity of both ends of the graph of FIG. 6 is enlarged and shown, it is possible to determine a shoulder-shaped point V in which the initial main scanning light amount sharply decreases outward. It is desirable that the position Pt is at the same position as the point V or at a position inside the point V and at a position as far as possible. On the other hand, the distribution of the initial main scanning light amount in the image forming apparatus 1 varies from one unit to another due to factors such as individual differences of each optical component. However, it is considered that the variation is not so large for the image forming apparatus 1 of the same model. Therefore, 20 image forming devices 1 of the same model were prepared, a graph of the initial main scanning light amount was created for each, and the positions of the points V on both the left and right sides were investigated. The results are shown in Table 1. Table 1 shows the number of units for each distance (indicated by "U" in FIGS. 12 and 13) in the main scanning direction between the position of the point V and the external correction points P1 and P30 for each of the left side and the right side. There is.

Looking at Table 1, the maximum value of the distance U is 1.7 mm on the left side and 2.3 mm on the right side. Therefore, for the image forming apparatus 1 of this model, the position Pt is fixed at a position 1.7 mm inside the external correction point P1 on the left side, and 2.3 mm inside the external correction point P30 on the right side. To be. As a result, it is possible to make an appropriate correction for the image forming apparatus 1 of the same model without determining the position Pt for each image forming apparatus 1. Therefore, the correction process can be simplified.

The second variation is that the position Pt is determined by setting the minimum value of the initial main scanning light intensity. That is, in this variation, as shown in FIGS. 14 and 15, the minimum line L required for the position Pt is set. In FIG. 14 (left side), 102.5% is set, and in FIG. 15 (right side), 105% is set as the minimum line L. Then, the position Pt is specified from within the range of the region T in which the initial main scanning light amount is the minimum line L or more. As a result, the position Pt can be specified so that the correction value D1 is appropriately set.

Regarding the level setting of the minimum line L, it is necessary to satisfy two points: 100%, that is, higher than the target light amount itself and lower than the peak value of the initial main scanning light amount near the end of the scanning range. is there. In general, a portion exceeding 100% of the peak value of the initial main scanning light amount (about 104% in FIG. 14 and about 105.5% in FIG. 15) is multiplied by a predetermined coefficient less than 1. Alternatively, it may be determined by subtracting a predetermined value (about 0.5 to 1.5%) from the peak value. Further, it may be arbitrary as to which part of the region T is set as the position Pt, but a rule such as setting the position as far as possible may be set.

The third variation is that the position Pt is the peak position of the initial main scanning light amount near the end of the scanning range. The setting of the position Pt according to this variation will be described with reference to FIGS. 16 (left side) and 17 (right side). That is, in this variation, the position Pt is the first position from the end side of the scanning range where the slope (position derivative) of the initial main scanning light amount becomes zero. As a result, the peak position of the initial main scanning light amount becomes the position Pt. Therefore, an appropriate correction can be made.

The fourth variation is not a variation on how to determine the position Pt, but a variation on how to determine the correction value D1. In this variation, the correction value D1 is determined by using the second-order approximation formula instead of using the first-order approximation formula as described above. That is, as shown in FIG. 18 (left side), as an approximate expression for calculating the correction value D1, a quadratic expression connecting the three points of the point Dt, the point D2, and the point D3 is used. The correction value D1 is determined by this quadratic approximation formula. The same applies to FIG. 19 (right side). As a result, the correction value D1 can be determined with higher accuracy, and more appropriate light intensity correction can be performed. A higher-order equation using more internal correction points may be used as an approximate equation. Any of the above may be used for determining the position Pt.

The fifth variation is a variation regarding the frequency of the reference clock. In this variation, there are three types of image formation in the image forming unit 5 shown in the leftmost column of Table 2. The scanning speed on the photoconductor drum 7 differs depending on the mode of image formation. The frequency of the reference clock is also different for each mode. In this variation, the frequency of the reference clock in each mode is defined so that the ratio of the scanning speed to the frequency of the reference clock is constant in all modes. By making the ratio of the scanning speed to the frequency of the reference clock constant regardless of the mode in this way, the position of the above-mentioned correction point candidate location becomes constant in all modes. That is, the position of the correction point is constant regardless of the mode. Therefore, it is not necessary to store the position of the correction point and the correction value of each correction point separately for each mode. Therefore, the capacity of the storage unit 33 can be reduced. Note that "us" in the main scanning speed column in Table 2 means microseconds (the same applies to Table 3).

The sixth variation is also a variation regarding the reference clock frequency. In this variation as well, there are three types of image formation modes as in the case of the fifth variation. However, unlike the case of the fifth variation, the ratio of the scanning speed to the reference clock frequency is slightly different depending on the mode (Table 3). What this means is that the original oscillation frequency for achieving a different reference clock frequency for each mode is kept as low as possible.

In this variation, the original oscillation frequency of about 75 MHz can correspond to three reference clock frequencies. This is a much lower frequency than in the case of the fifth variation, which requires about 750 MHz. The sixth variation is that the reference clock frequency is selected so that the decrease in the position accuracy of the correction point is within the permissible range within the range of the constraint. That is, in Table 3, the maximum value of the ratio of the scanning speed to the reference clock frequency is only about 1.006 times the minimum value, and is within 1.01 times. Therefore, in the sixth variation, the correction accuracy is slightly disadvantageous as compared with the fifth variation, but the capacity of the storage unit 33 is still small, and the original oscillation frequency is also low.

As described in detail above, according to the present embodiment, the amount of light emitted from the light emitter 13 is corrected by a correction value according to the scanning position, so that the amount of light emitted from the photoconductor drum 7 is uneven on the irradiated surface. I am trying to reduce. Therefore, a plurality of correction points are set within the scanning range. Here, correction points (external correction points) are also set in the outer edge region Z where the amount of light sharply drops near both ends of the scanning range. Then, for the external correction point, the correction value is determined by a special method different from the internal correction point. As a result, an almost uniform amount of irradiation light can be obtained on the irradiated surface with as wide a scanning range as possible. In this way, the image forming apparatus 1 capable of using the widest possible scanning range for image forming is realized.

It should be noted that the present embodiment is merely an example and does not limit the present invention in any way. Therefore, as a matter of course, the present invention can be improved and modified in various ways without departing from the gist thereof. For example, the target image forming apparatus 1 is not limited to the copier type shown in FIG. 1, and may be a printer type having no reading unit 3. Alternatively, it may have a function of sending and receiving print jobs via a public line. Further, the image forming unit 5 may be of a type (multicycle type or monochrome type) that does not have the intermediate transfer belt 8. It should be noted that the use of optical components (polygon mirror 17, Fθ lens 18, each reflecting mirror) having a coating on the surface is not excluded.

1 Image forming device 2 Main body part 5 Image forming part 6 Print head part 7 Photoreceptor drum 13 Light emitter 17 Polygon mirror (rotating multifaceted mirror)
18 Fθ lens 19 Reflector 22 Reflector 23 Reflector 24 Reflector 25 Reflector 26 Reflector 27 Reflector 29 Overall control unit 32 Drawing control unit (data acquisition unit before correction, correction point setting unit, correction value determination unit, light intensity Correction unit, reference clock generator)
33 Storage unit Dn Correction value Pn Correction point Z Outer edge area

Claims (7)

An image-bearing photoconductor, a light emitter that emits a light beam based on image data, a rotating multi-sided mirror that reflects and deflects the light beam emitted from the light-emitting device while rotating, and a polarized scanning with the rotating multi-sided mirror. An image forming apparatus including an optical member that guides the light beam to the irradiated surface of the image-bearing photoconductor.
An uncorrected data acquisition unit that acquires the initial main scanning light amount, which is the irradiation light amount for each scanning position on the irradiated surface when the light beam is emitted from the light emitter without correction, and
A correction point setting unit that sets correction points at multiple points within the scanning range,
A correction value determining unit that determines a correction value for correcting unevenness of the irradiation light amount on the irradiated surface for each scanning position based on the initial main scanning light amount and the position of the correction point.
It has a light amount correction unit that corrects the amount of emitted light at the time of image formation by the light emitter according to the correction value.
The correction point setting unit directs the outermost correction point (hereinafter referred to as “external correction point”) toward the end of the scanning range as the reflecting surface is switched by the rotation of the rotating polymorphic mirror. It is configured to be arranged in the outer edge region where the initial main scanning light amount is steeply dropped.
The correction value determination unit
For the positions of the correction points (hereinafter referred to as "internal correction points") other than the external correction points, the correction values are determined so that the magnitude is opposite to the value of the initial main scanning light amount at the position.
For the position of the external correction point, a correction value is determined based on at least two approximate lines based on the initial main scanning light amount inside the outer edge region.
The position between the correction points is characterized in that the correction value is determined at least based on an approximate line based on the correction value of the positions of the correction points on both sides of the position. Image forming device. The image forming apparatus according to claim 1.
The correction point setting unit is configured to arrange all the internal correction points inward from the outer edge region.
The correction value determining unit sets the "two points" when determining the correction value with respect to the position of the external correction point to the position of the outermost one of the internal correction points and the scanning range outside the position . An image forming apparatus characterized in that the distance from the end portion is configured to be two locations with a predetermined fixed value position. The image forming apparatus according to claim 1.
The correction point setting unit is configured to arrange all the internal correction points inward from the outer edge region.
The correction value determining unit sets the "two points" when determining the correction value with respect to the position of the external correction point to the position of the outermost one of the internal correction points and the initial main outside the position. An image forming apparatus characterized in that it is configured to have two locations where the scanning light amount is equal to or higher than a predetermined minimum light amount . The image forming apparatus according to claim 1.
The correction point setting unit is configured to arrange all the internal correction points inward from the outer edge region.
The correction value determining unit sets the "two points" when determining the correction value with respect to the position of the external correction point to the position of the outermost one of the internal correction points and the scanning range outside the position . An image forming apparatus characterized in that the image forming apparatus is configured so as to have two positions from an end portion to a position where the initial main scanning light amount becomes the first maximum value . The image forming apparatus according to any one of claims 1 to 4 , wherein the correction value determining unit is used.
The image is characterized in that the correction value for the position of the external correction point is determined based on the approximate lines based on the initial main scanning light amount at three or more points inside the outer edge region. Forming device. The image forming apparatus according to any one of claims 1 to 5 , wherein the correction point setting unit is used.
Correction point candidate points that can be the correction points within the scanning range are specified in advance, and
From the correction point candidate locations, the correction points are selected so as to be densely arranged in a region where the rate of change of the initial main scanning light amount with respect to the scanning position is large and sparsely arranged in a region where the rate of change is small. An image forming apparatus characterized by being a The image forming apparatus according to any one of claims 1 to 6 .
The rotating multi-sided mirror performs deflection scanning of an optical beam at multiple scanning speeds.
It has a reference clock generator that generates a reference clock for each of the multiple levels of scanning speed.
The maximum value of the ratio of each reference clock to the frequency of each of the scanning speeds is within 1.01 times the minimum value.
The image forming apparatus is characterized in that the correction point setting unit sets a correction point according to the reference clock.

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