JP4386365B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a laser printer, and a facsimile.

  Organic photoreceptors (OPC photoreceptors) and amorphous silicon photoreceptors (a-Si photoreceptors) are widely used as photoreceptor drums used in image forming apparatuses. Since the a-Si photoconductor has a high surface hardness and excellent wear resistance, it is widely used as a photoconductor drum of an image forming apparatus such as a high-speed copying machine or a network printer that requires durability.

  The a-Si photoconductor is manufactured by a method in which a gas is turned into a plasma by high frequency or microwave and solidified and deposited on an aluminum cylinder to form a film. Since it is difficult to place an aluminum cylinder, it is virtually impossible to make the film forming conditions uniform over the entire surface of the photoreceptor.

  For this reason, the sensitivity of the photosensitive drum varies depending on the position, and even if the photosensitive drum is exposed with a constant light amount, there is a problem that potential unevenness occurs such that the entire area of the photosensitive drum cannot be charged with a constant potential. is there.

  Therefore, various techniques for correcting such potential unevenness of the photosensitive drum have been disclosed. In Patent Document 1, the sensitivity information of the photosensitive drum stored in advance in the nonvolatile memory and the sensitivity information of the standard sensitivity drum stored in advance are compared by a comparison control unit, and a comparison signal is generated. A technique for setting a target light quantity reference signal of a laser light source so as to be zero is disclosed.

  Patent Document 2 discloses a technique for storing sensitivity information for each exposure position on the surface of the photosensitive drum in advance and correcting the light amount of the laser beam for each exposure position with reference to the sensitivity information. .

Patent Document 3 discloses a technique for detecting the surface potential, exposure potential, and residual potential of the photosensitive drum, and correcting the γ correction table by predicting the sensitivity characteristic of the photosensitive member based on the detection result. Yes.
JP-A-10-31332 JP 2004-61860 A JP-A-5-014729

  However, all of the techniques disclosed in Patent Documents 1 to 3 relate to an image forming apparatus in which a polygon mirror scans a laser beam to expose a photosensitive drum, and a light source such as a plurality of LEDs arranged in a line. It does not relate to an image forming apparatus that exposes a photosensitive drum using For this reason, the light amount is not corrected in consideration of the variation in the light amount of each light source.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of forming a good image without density unevenness in consideration of variation in the amount of light of each light source and variation in sensitivity of a photosensitive drum.

An image forming apparatus according to the present invention includes a photosensitive drum, a light source unit including a plurality of light sources arranged in a line in the longitudinal direction of the photosensitive drum so as to face the photosensitive drum, and the light source unit Light amount correction data storage means for storing light amount correction data calculated in advance for each light source in order to make the variation in the light amount of each light source uniform, and a plurality of positions set on the photosensitive drum facing each light source Based on the sensitivity correction data storage means for storing sensitivity correction data calculated in advance for each sample point in order to equalize the sensitivity variation at the sample points, and the light quantity correction data and the sensitivity correction data, Light source driving means for driving each light source by correcting the driving current of each light source determined accordingly, and the light amount correction data drives each light source with a constant driving current. Measure the amount of light output from each light source, calculate an average value of the measured light amount of each light source, and calculate the light amount correction data of the light source whose measured light amount is greater than the average value by the formula (C), The light amount correction data of the light source whose measured light amount is smaller than the average value is calculated by the equation (D).
P_LED (j) = 1− (y−Y) / Y (C)
P_LED (j) = 1 + (Y−y) / Y (D)
However, P_LED (j) indicates the light amount correction data of the jth light source, y indicates the measured light amount, and Y indicates the average value of the light amount.

  In the above configuration, the sample point is also set with respect to the rotation direction of the photosensitive drum, and the light source driving means is a sample point located in the vicinity of the exposure position of the photosensitive drum exposed by each light source. It is preferable to correct the drive current of each light source using the sensitivity correction data for.

In the above configuration, it is preferable that the sensitivity correction data is calculated using the following formulas (A) and (B).
When Vr ≧ Vk R (i) = 1− (Vr (i) −Vk) / Vk (A)
When Vr <Vk R (i) = 1 + (Vk−Vr (i)) / Vk (B)
However, Vk indicates a predetermined reference potential, and Vr (i) indicates the above-mentioned when the photosensitive drum is exposed with a predetermined amount of light so that the surface potential of the photosensitive drum becomes the reference potential Vk. Of the plurality of sample points set along the longitudinal direction of the photosensitive drum, the surface potential of the i-th sample point is indicated, and R (i) is the plurality of sample points set along the longitudinal direction of the photosensitive drum. The sensitivity correction data of the i-th sample point among the sample points is shown.

  Further, in the above configuration, the sensitivity correction data and the light amount correction data are calculated when the ambient temperature is a predetermined reference temperature, and a temperature measurement unit that measures the temperature around the photosensitive drum; A coefficient storage for preliminarily storing a temperature correction coefficient that cancels out both the change in the light amount of the light source unit caused by the difference between the temperature measured by the temperature measuring means and the reference temperature and the change in the sensitivity of the photosensitive drum. And the light source driving means further corrects the driving current calculated using the sensitivity correction data and the light amount correction data using a temperature correction coefficient for the temperature measured by the temperature measuring means. It is preferable.

  According to the first aspect of the present invention, the light source section includes a plurality of light sources arranged in a line in the longitudinal direction of the photosensitive drum. The light quantity correction data storage means stores light quantity correction data. This light amount correction data is data for correcting the drive current so as to equalize the variation in the amount of light output from each light source when each light source is driven with the same drive current, and is calculated in advance for each light source. It is. The sensitivity correction data storage means stores sensitivity correction data. This sensitivity correction data is the drive current of each light source so as to equalize the sensitivity variation at a plurality of sample points set on a line in the longitudinal direction of the surface of the photosensitive drum and facing each light source. It is data to be corrected, and is data calculated in advance for each sample point.

  The light source drive means corrects the drive current of each light source determined for each image data using the light amount correction data and the sensitivity correction data, and drives each light source. Accordingly, the electrostatic latent image from which the variation in sensitivity is removed and the variation in the amount of light from each light source is removed is formed on the photosensitive drum, and a good image without density unevenness can be formed.

  According to the second aspect of the present invention, the drive current is corrected in consideration of the variation in sensitivity in the rotational direction in addition to the variation in sensitivity in one line in the longitudinal direction of the photosensitive drum. Variation can be removed with higher accuracy, and density unevenness can be further reduced.

  According to the third aspect of the present invention, the surface potential Vr at each sample point when the photosensitive drum is exposed with a predetermined amount of light in order to set the surface potential of the photosensitive drum to the reference potential Vk is the reference potential Vk. Sensitivity correction data that corrects the drive current so as to approach can be calculated.

  According to the fourth aspect of the present invention, the temperature correction coefficient that cancels out the change in the light amount of the light source unit due to the temperature change with respect to the reference temperature and the change in the sensitivity of the photosensitive drum is calculated and stored in advance. Since the drive current is further corrected using the temperature correction coefficient, density unevenness due to sensitivity variations can be further reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an image forming apparatus 1 according to this embodiment. FIG. 2 is a drawing showing the configuration of the exposure apparatus 14. Hereinafter, the configuration of the image forming apparatus 1 will be described with reference to FIGS. 1 and 2. The image forming apparatus 1 includes a network printer and is connected to a terminal device 30 via a communication line such as a LAN, for example, and includes an arithmetic control unit 11, a storage unit 12, a control logic unit 13, an exposure device 14, a drum unit 15, a temperature. The detector 16, the high voltage unit 17, the charging device 18, and the developing unit 19 are provided. The terminal device 30 is composed of a known personal computer having a communication function, and prints various image data created using application software and various image data acquired via an internetwork from a user. In response to the command, the image is output to the image forming apparatus 1.

  The arithmetic control unit 11 rasterizes the image data represented by the vector format or the like transmitted from the terminal device 30 to convert it into bitmap format image data, and outputs the converted image data to the control logic unit 13. In this image forming apparatus, binary image data is handled as image data.

  Further, the calculation control unit 11 reads the surface potential distribution for the photosensitive drum 151 from the surface potential distribution storage unit 152, performs calculations of the following expressions (1) and (2) on the surface potential distribution, and will be described later. Sensitivity correction data R (i) for the sample points P1 to Pn to be generated is generated and stored in the storage unit 12. Here, R (i) indicates sensitivity correction data for the i-th sample point Pi.

  Further, the arithmetic control unit 11 supplies the light amount correction data P_LED (j) calculated in advance for each of m light emitting diodes (hereinafter referred to as LEDs 1 to LEDm) constituting the LED array unit 142. The data is read from 143 and stored in the storage unit 12. Here, P_LED (j) indicates light amount correction data for the jth LEDj. Further, the arithmetic control unit 11 reads the sensitivity correction data R (i) and the light amount correction data P_LED (j) from the storage unit 12, calculates correction data CD (j) from both the correction data, and sends it to the control logic unit 13. Output.

  The arithmetic control unit 11 basically executes a process of reading the surface potential distribution from the surface potential distribution storage unit 152, calculating sensitivity correction data R (i), and writing it in the storage unit 12 when the power is turned on. However, when the sensitivity correction data R (i) calculated using the same surface potential distribution as the surface potential distribution stored in the surface potential distribution storage unit 152 is stored in the storage unit 12, this processing is omitted. do it. In this case, the arithmetic control unit 11 may determine whether the same data is stored with reference to the serial number of the drum unit stored in the surface potential distribution storage unit 152 when the power is turned on.

  The arithmetic control unit 11 basically reads out the light amount correction data from the light amount correction data storage unit 143 and writes it in the storage unit 12 when the power is turned on, but is stored in the light amount correction data storage unit 143. When the same light amount correction data as the light amount correction data being stored is stored in the storage unit 12, this processing may be omitted. In this case, the arithmetic control unit 11 determines whether or not the same light amount correction data is stored by referring to the serial number of the exposure apparatus 14 stored in the light amount correction data storage unit 143 when the power is turned on. Good.

  Further, when the calculation control unit 11 reads the surface potential distribution from the surface potential distribution storage unit 152, the calculation control unit 11 calculates the sensitivity correction data R (i) and writes the sensitivity correction data R (i) to the storage unit 12. However, instead of calculating the sensitivity correction data R (i), the surface potential distribution is written in the storage unit 12 as it is, and the surface potential distribution is read from the storage unit 12 every time a printing operation is performed. Sensitivity correction data R (i) may be calculated.

  Further, sensitivity correction data R (i) calculated by a device different from the image forming apparatus 1 is stored in the surface potential distribution storage unit 152, and the arithmetic control unit 11 stores this sensitivity correction data R when the power is turned on. (I) may be written in the storage unit 12.

  The storage unit 12 includes a rewritable nonvolatile memory such as a flash memory, and stores sensitivity correction data R (i) and light amount correction data P_LED (j) for the photosensitive drum 151.

  As will be described later, the image forming apparatus 1 can also measure the surface potential of the photosensitive drum 151. In this case, the arithmetic control unit 11 uses the surface potential distribution stored in the storage unit 12. Instead of this, the sensitivity correction data R (i) may be calculated using the surface potential distribution measured by the image forming apparatus 1.

  The control logic unit 13 is configured by an ASIC and controls the entire image forming apparatus 1. In particular, in the present embodiment, the control logic unit 13 outputs the image data output from the calculation control unit 11 to the LED drive unit 141 and performs calculation. The correction data CD (j) calculated by the control unit 11 is output to the LED drive unit 141.

  The exposure apparatus 14 includes an LED drive unit 141, an LED array unit 142, a light amount correction data storage unit 143, and a selfoc lens unit 144. As shown in FIG. 2, the LED array unit 142 has a flat printed circuit board having a length substantially equal to the longitudinal direction (main scanning direction) of the photosensitive drum 151, with the longitudinal direction of the photosensitive drum 151 being the longitudinal direction. A PWB (Printed Wiring Board) 145 and m LEDs 1 to LEDm arranged in a line so as to face the photosensitive drum 151 over almost the entire length of the PWB 145.

  In addition, the exposure apparatus 14 includes a prismatic casing 146, and an LED array 142 is attached inside the casing 146, and a SELFOC lens is exposed so that a part thereof is exposed toward the photosensitive drum 151 side. Part 144 is attached. The Selfoc lens unit 144 is composed of a plurality of Selfoc lenses arranged to face the LED array unit 142, and adjusts the beam diameter of light output from each LED. A reference pin P that protrudes toward the photosensitive drum 151 is attached to the left end of the lower portion of the housing 146.

  The LED drive unit 141 shown in FIG. 1 generates a drive signal for each of the LEDs 1 to LEDm based on the correction data output from the control logic unit 13 and the image data, and drives each LED. The light amount correction data storage unit 143 stores light amount correction data P_LED (i) calculated in advance for each of the LEDs 1 to LEDm and the serial number of the exposure device 14.

  The drum unit 15 includes a photosensitive drum 151 and a surface potential distribution storage unit 152. The photoconductor drum 151 includes a member made of a cylindrical aluminum tube whose longitudinal direction is the main scanning direction orthogonal to the recording paper conveyance direction, and an a-Si photoconductor is formed on the outer peripheral surface of the aluminum tube. It is formed in layers, and is driven to rotate at a predetermined process speed by a driving device such as a motor under the control of the control logic unit 13.

  The surface potential distribution storage unit 152 stores the surface potential distribution measured in advance for the photosensitive drum 151 and the serial number of the drum unit 15.

  The temperature detection unit 16 includes a temperature sensor, measures the temperature near the surface of the photosensitive drum 151, acquires temperature data, and outputs the temperature data to the calculation control unit 11. The high-voltage unit 17 is a voltage generation circuit that applies a high voltage (for example, 850 V) to the charging device 18 under the control of the control logic unit 13. The charging device 18 performs corona discharge with a high voltage from the high voltage unit 17 and charges the surface of the photosensitive drum 151 to a constant potential. The developing unit 19 supplies toner to the photosensitive drum 151 on which the electrostatic latent image is formed, and forms a toner image on the surface of the photosensitive drum 151.

  In the present embodiment, the arithmetic control unit 11, the control logic unit 13, and the LED driving unit 141 correspond to an example of a light source driving unit, and the storage unit 12 includes a light amount correction data storage unit, a sensitivity correction data storage unit, and This corresponds to an example of coefficient storage means.

  3A and 3B are diagrams for explaining the surface potential distribution of the photosensitive drum 151. FIG. 3A shows the arrangement relationship between the LEDs and the photosensitive drum 151, and FIG. 3B shows the surface potential distribution of the photosensitive drum 151. It is a graph. In the graph of (b), the y-axis indicates the surface potential, and the x-axis indicates the position on the line L1 in the main scanning direction of the photosensitive drum 151. Further, the graph of (b) shows the photosensitive drum 151 with a light amount (= 1/2 P) that is a potential of 1/2 Vs (corresponding to an example of the reference potential Vk) that is half of the predetermined product charging voltage Vs. The surface potential distribution of the photosensitive drum 151 when exposed is shown.

  An effective range W shown in (a) indicates a range in the main scanning direction in which the photosensitive drum 151 is irradiated with light from the LEDs 1 to LEDm. When an ideal photosensitive drum 151 having no sensitivity unevenness is exposed with a light amount of 1 / 2P, the graph shown in (b) is a straight line of y = 1/2 Vs. However, the photosensitive drum 151 has a sensitivity unevenness. Therefore, the surface potential of the photosensitive drum 151 varies greatly depending on the position as shown in FIG.

  This surface potential can be obtained as follows. First, light having a light amount of 1 / 2P is emitted from the LED array unit 142 while rotating the photosensitive drum 151 about the rotation shaft 151a. Next, the rotation of the photosensitive drum 151 is stopped, and the surface potential meter 153 slidably mounted in the main scanning direction is slid along the line L1, and the surface potentials of the sample points P1 to Pn on the line L1. Measure.

  Here, the sample points P1 to Pn are set at, for example, the midpoints of the regions facing the LEDs 1 to LEDm, respectively. Therefore, by measuring the surface potential of the photosensitive drum 151 with respect to the sample points P1 to Pn, the surface potential of the photosensitive drum 151 can be obtained in units of pixels. However, if the sample points P1 to Pn are based on the reference pin P, and there are d sample points P1 to Pd between the reference pin P and the left end L, the sample points P1 to Pd are connected to the reference pin P. The sample points Pd + 1 to Pd + m exist in the effective range W. Note that the reference start pixel number d indicating the number of sample points P1 to Pd between the reference pin P and the left end L is stored in the surface potential distribution storage unit 152. The number d of exposure start pixels is written in the storage unit 12.

The calculation of the expressions (1) and (2) is performed on the surface potential of each sampling point obtained in this way, and sensitivity correction data R (i) is calculated.
i) When Vr (i) ≧ 1/2 Vs R (i) = 1 − ((Vr (i) −0.5 Vs) /0.5 Vs) (1)
ii) When Vr (i) <1 / 2Vs R (i) = 1 + ((0.5 Vs−Vr (i)) / 0.5 Vs) (2)
However, Vr (i) represents the surface potential with respect to the sample point Pi, and is measured by the surface potential meter 153.

  For example, when the surface potential Vr (i) with respect to the sample point i is measured as Vr (i) = 0.8 Vs, since Vr is ½ Vs or more, Expression (1) is applied, and the sensitivity correction data R ( i) is calculated as R (i) = 0.4. Further, when the surface potential Vr (i) with respect to the sample point Pi is measured as Vr (i) = 0.4 Vs, since Vr (i) is less than 1/2 Vs, the equation (2) is applied, and sensitivity correction is performed. Data R (i) is calculated as R (i) = 1.2. If this sensitivity correction data R (i) is multiplied by the pixel data, a driving current having an opposite phase to the surface potential distribution shown in FIG. The sensitivity variation of 151 is made uniform.

  In the present embodiment, as shown in FIG. 4, the surface potential is applied to each of the lines L1 to L8 obtained by drawing, for example, eight straight lines in the longitudinal direction at equal intervals to the circumferential surface of the photosensitive drum 151. The surface potential Vr (i) for the sample points P1 to Pn is measured by the total 153, and the sensitivity correction data R (i) is calculated.

  FIG. 5 is a graph showing the surface potential distribution of the photosensitive drum 151 when the y-axis is the surface potential and the x-axis is the reciprocal of the amount of light to be exposed. In this graph, the graph Vr_L indicates the surface potential at the left end L of the effective range W, the graph Vr_C indicates the surface potential at the midpoint C of the effective range W, and the graph Vr_R indicates the right end R of the effective range W. The surface potential is shown. As shown in FIG. 5, it can be seen that the surface potential increases as the amount of light increases, and the surface potential decreases as the amount of light decreases. Further, when the exposure energy is constant, the surface potential increases in the order of the graphs Vr_L, Vr_C, and Vr_R, so that it can be seen that the sensitivity is higher in the order of the left end L, the middle point C, and the right end R.

  Next, processing during the printing operation performed by the arithmetic control unit 11 will be described with reference to the flowchart shown in FIG. Note that the processing shown in this flowchart is executed when image data is transmitted from the terminal device 30. First, the calculation control unit 11 reads the exposure start pixel number d from the storage unit 12 in step S1, reads the sensitivity correction data R (i) from the storage unit 12 in step S2, and the light amount correction data from the storage unit 12 in step S3. Read P_LED (j).

  In step S <b> 3, the arithmetic control unit 11 calculates correction data CD (j), which is correction data for each of the LEDs 1 to LEDm, using Expression (3).

CD (j) = P_LED (j) × R (id) (3)
Here, the control logic unit 13 controls the photosensitive drum 151 and the exposure device 14 so that the first line of one piece of image data is exposed on the line L1 shown in FIG. Accordingly, when the LED 1 exposes the region D1 surrounded by the lines L11 and L81, the arithmetic control unit 11 uses the sensitivity correction data R (d + 1) for the sample point Pd + 1 on the line L1 to correct the correction data CD (1). When the area D2 surrounded by the line L11 and the line L21 is exposed, the correction data CD (1) is calculated using the sensitivity correction data R (d + 1) for the sample point Pd + 1 on the line L2. Thus, the correction data CD is calculated using the sensitivity correction data for the sample points near the area where the LEDs 1 to LEDm expose the photosensitive drum 151.

  Here, the line L11 is a straight line passing through the midpoint of the width of the line L1 and the line L2 with respect to the rotation direction and parallel to the longitudinal direction. Lines L21 to L81 are also midpoints of the widths of the lines L2 to L3, lines L3 to L4, lines L4 to L5, lines L5 to L6, lines L6 to L7, lines L7 to L8, and lines L8 to L1 with respect to the rotation direction. And a straight line parallel to the longitudinal direction.

  Next, the light amount correction data P_LED (j) will be described. The LEDs 1 to LEDm cannot output the same amount of light even if the same drive current is input, and generally have variations. Therefore, conventionally, in the image forming apparatus, the light quantity correction of the LEDs 1 to LEDm is performed using the light quantity correction data P_LED (j) that makes the variation of the LEDs 1 to LEDm constant.

  Specifically, each of the LEDs 1 to LEDm is driven with a constant drive current, and the amount of light output from the LEDs 1 to LEDm is measured. FIG. 9 is a graph showing the amount of light output from the LEDs 1 to LEDm when the LEDs 1 to LEDm are driven with a constant drive current. The y axis represents the amount of light, and the x axis represents the LEDs 1 to LEDm. In this case, the light amount correction data is calculated as follows, for example. First, an average Y of the light amounts of the LEDs 1 to LEDm is calculated.

  For an LED having a measured light quantity y larger than the average Y, P_LED (j) = 1− (y−Y) / Y is calculated as light quantity correction data, and the measured light quantity y is smaller than the average Y. For the LED, P_LED (j) = 1 + (Y−y) / Y is calculated as the light amount correction data. Then, if this light quantity correction data P_LED (j) is multiplied by the pixel data, as shown by the dotted line in FIG. 9, a driving current having an opposite phase to the light quantity of LEDs 1 to LEDm is input to LEDs 1 to LEDm. , The variation of the LEDs 1 to LEDm is made uniform.

  In step S <b> 4, the arithmetic control unit 11 outputs the calculated correction data CD (j) to the control logic unit 13.

  In step S5, the control logic unit 13 sequentially sends correction data CD (j) and pixel data DAT (j) corresponding to the correction data CD (j) to the LED drive unit 141 in synchronization with a latch signal LAT described later. Output.

  FIG. 7 shows a circuit diagram of the LED drive unit 141. As shown in FIG. 7, the LED driving unit 141 includes a clock counter 201, m data latch units 211 to 21m corresponding to LEDs 1 to LEDm, m data latch units 221 to 22m corresponding to LED1 to LEDm, and LED1 to LEDm. M constant current blocks 231 to 23m corresponding to LEDm and m switches SW71 to SW7m corresponding to LED1 to LEDm are provided.

  The clock counter 201 counts the number of clocks of the latch signal LAT output from the control logic unit 13. When the clock counter 201 counts m clocks, the clock counter 201 outputs an STBRQ signal that instructs the data latch units 221 to 22m to latch.

  The data latch units 211 to 21m receive the latch signal LAT and the reset signal RST from the control logic unit 13, respectively. Here, the latch signal LAT is a clock signal having a predetermined cycle, and the data latch units 211 to 21m latch data in synchronization with the latch signal LAT, and latch when the reset signal RST is input. Reset the data that is stored.

  The data latch unit 211 receives 6-bit data CD0 (j) to CD5 (j) indicating the correction data CD (j) and pixel data DAT, and data CD0 (j) to CD5 in synchronization with the latch signal LAT. (J) and pixel data DAT are latched.

  Data latch units 212 to 21m receive data CD0 (j) to CD5 (j) and pixel data DAT latched by data latch units 211 to 21m−1, respectively.

  The data latch units 221 to 22m latch the data CD0 (j) to CD5 (j) and the pixel data DAT latched in the data latch units 211 to 21m, respectively, when the STBRQ signal is output from the clock counter 201. And output to the constant current blocks 231 to 23m.

  Each of the switches SW71 to SW7m is composed of a field effect transistor, the gate is connected to the data latch units 221 to 22m, and the LEDs 1 to LEDm and the constant current blocks 231 to 23m are electrically connected or disconnected. . Specifically, it is turned on when the pixel data DAT (j) is 1, and turned off when the pixel data DAT (j) is 0.

  The constant current blocks 231 to 23m are connected to the LEDs 1 to LEDm, respectively. Since the constant current blocks 231 and 23m have the same configuration, only the constant current block 231 will be described.

  The constant current block 231 includes six switches SW1 to SW6 and seven constant current sources A1 to A7. A reference voltage VDD is applied to the constant current sources A1 to A7. The constant current sources A1 to A7 generate direct currents of 5 mA, 3.2 mA, 1.6 mA, 0.8 mA, 0.4 mA, 0.2 mA, and 0.1 mA, respectively. The switches SW1 to SW6 are each composed of a field effect transistor, and the gate is connected to the output side of the data latch unit 221. The switches SW1 to SW6 are turned on according to the values of CD5 (j) to CD0 (j) and the pixel data DAT, respectively, to electrically connect the constant current sources A1 to A6 and the switch SW71.

  Taking SW1 as an example, when CD5 (j) is 1, the switch SW1 is turned on, and when CD5 (j) is 0, the switch SW1 is turned off. Therefore, the drive current shown by Formula (4) is input to LED1.

ΣIn [mA] = 5.00 + 0.05 × (CD0 (j) × 2 ⁰ + CD1 (j) × 2 ¹ + CD2 (j) × 2 ² + CD3 (j) × 2 ³ + CD4 (j) × 2 ⁴ + CD5 (j ) × 2 ⁵ ) ... (4)

  Next, the operation of the LED drive unit 141 shown in FIG. 7 will be described using the timing chart shown in FIG. Here, a process for m pieces of pixel data DAT (1) to DAT (m) in one line in the main scanning direction will be described. Here, it is assumed that the control logic unit 13 sequentially outputs the pixel data DAT (i) in the order of the pixel data DAT (m) to DAT (1) in synchronization with the latch signal LAT. At this time, the control logic unit 13 outputs correction data CD (m) to CD (1) corresponding to each of the pixel data DAT (m) to DAT (1) together with DAT (m) to DAT (1). To do.

  First, the data latch unit 211 receives the reset signal RST and latches the correction data CD (m) and the pixel data DAT (m) in synchronization with the first pulse PS1 of the latch signal LAT. Next, the data latch unit 212 latches the correction data CD (m) and the pixel data (m) latched in the data latch unit 211 in synchronization with the second pulse PS2 of the latch signal LAT. At this time, the data latch unit 211 latches the correction data CD (m−1) and the pixel data DAT (m−1).

  Thereafter, the correction data CD (m) and the pixel data DAT (m) are sequentially shifted to the data latch units 213 to 21m in synchronization with the latch signal LAT, and the correction data CD (m−1) and the pixel data (m -1) also sequentially shifts to the data latch units 212 to 21m-1. Then, when the latch signal LAT is input m clocks after the reset signal RST is input, the correction data CD (1) and the pixel data DAT (1) to the correction data CD ( m) and pixel data DAT (m) are latched.

  Next, the clock counter 201 outputs the STBRQ signal to the data latch units 221 to 22m. Thereby, the data latch units 221 to 22m respectively correct the correction data CD (1) and the pixel data DAT (1) to the correction data CD (m) and the pixel data DAT (m) latched in the data latch units 211 to 21m. Is output to the constant current blocks 231 to 23m. The constant current blocks 231 to 23m generate drive currents corresponding to the pixel data DAT (j) and the correction data CD (j), and drive the LEDs 1 to LEDm. The photosensitive drum 151 is exposed.

  As described above, according to the image forming apparatus 1, the correction data CD (j) is calculated using the sensitivity correction data R (i) and the light amount correction data P_LED (j), and the LEDs 1 to LEDm are driven. Therefore, the photosensitive drum 151 is free from variations in sensitivity of the photosensitive drum 151 and forms an electrostatic latent image from which variations in the amount of light from each light source are removed. A good image can be formed.

  In the above embodiment, the correction data CD (j) has not been calculated in consideration of the change in the sensitivity of the photosensitive drum 151 and the change in the light quantity of the LEDs 1 to LEDm due to the ambient temperature. In consideration, the correction data CD (j) may be calculated.

Specifically, the correction data CD (j) may be calculated using Expression (5).
CD (j) = P_LED (j) × η (t) × R (id) (5)
Here, η (t) is the reference temperature of the temperature detected by the temperature detector 16 when the sensitivity correction data R (i) and the light amount correction data P_LED (j) are calculated at a predetermined reference temperature. This is a coefficient that cancels out the change in the amount of light of the LEDs 1 to LEDm resulting from the fluctuation of the sensor and the change in the sensitivity of the photosensitive drum 151.

  For example, when the temperature is t degrees and the light quantity of the light emitting diode is 0.8 times that of the reference temperature and the sensitivity of the photosensitive drum 151 is 1.2 times, η (t) is expressed as (1 /0.8)×(1/1.2), it is possible to cancel the amount of change in light quantity and the amount of change in sensitivity with respect to temperature changes. Accordingly, the change in the sensitivity of the photosensitive drum 151 and the change in the light amount of the light emitting diode with respect to various temperatures are measured, and a temperature correction coefficient that cancels these changes is calculated in advance in the storage unit 12. If the temperature correction coefficient corresponding to the temperature measured by the temperature detection unit 16 is read from the storage unit 12 and the calculation of the equation (5) is performed, it is possible to calculate the drive current in consideration of the temperature change. Thereby, density unevenness can be corrected more accurately. It is known that the sensitivity of the photosensitive drum 151 increases as the temperature rises, and that the light emitting diode tends to decrease in light amount as the temperature rises.

In the above-described embodiment, a binary image has been described as an example. However, the present invention can also be applied to a multi-value image. In this case, the arithmetic control unit 11 may calculate the correction data CD (j) using Expression (6) when the pixel data is expressed by, for example, 256 gradations of 0 to 255.
CD (j) = P_LED (j) × R (id) × (gradation of pixel data) / 255 (6)

1 shows a block diagram of an image forming apparatus according to the present embodiment. It is drawing which shows the structure of exposure apparatus. 2A and 2B are diagrams illustrating a surface potential distribution of a photosensitive drum, in which FIG. 3A is a graph illustrating a positional relationship between a light source unit and the photosensitive drum, and FIG. 2B is a graph illustrating a surface potential distribution of the photosensitive drum. FIG. 6 is a diagram illustrating sample points set on a photosensitive drum. It is a graph which shows surface potential distribution of a photoreceptor drum. It is a flowchart which shows the process at the time of the printing operation of an arithmetic control part. The circuit diagram of a LED drive part is shown. It is a timing chart which shows operation | movement of a LED drive part. It is a graph explaining light quantity correction data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Computation control part 12 Memory | storage part 13 Control logic part 14 Exposure apparatus 15 Drum unit 16 Temperature detection part 17 High voltage | pressure unit 18 Charging device 19 Developing unit 30 Terminal device 141 LED drive part 142 LED array part 143 Light quantity correction data storage part 144 Selfoc Lens Unit 151 Photosensitive Drum 152 Surface Potential Distribution Storage Unit

Claims (4)

A photosensitive drum;
A light source unit including a plurality of light sources arranged in a line in the longitudinal direction of the photosensitive drum so as to face the photosensitive drum;
A light amount correction data storage means for storing light amount correction data calculated in advance for each light source in order to equalize variation in the amount of light of each light source constituting the light source unit;
Sensitivity correction data storage means for storing sensitivity correction data calculated in advance for each sample point in order to equalize variation in sensitivity at a plurality of sample points set at positions of the photosensitive drum facing each light source;
Based on the light quantity correction data and the sensitivity correction data, the light source driving means for driving each light source by correcting the drive current of each light source determined according to the image data,
The light amount correction data is obtained by driving each light source with a constant drive current, measuring the light amount output from each light source, calculating an average value of the measured light amount of each light source, and measuring the light amount as the average value. An image forming apparatus characterized in that light amount correction data of a larger light source is calculated by equation (C), and light amount correction data of a light source whose measured light amount is smaller than the average value is calculated by equation (D).
P_LED (j) = 1− (y−Y) / Y (C)
P_LED (j) = 1 + (Y−y) / Y (D)
However, P_LED (j) indicates the light amount correction data of the jth light source, y indicates the measured light amount, and Y indicates the average value of the light amount. The sample point is also set with respect to the rotation direction of the photosensitive drum,
2. The light source driving means corrects the driving current of each light source by using sensitivity correction data for a sample point located near the exposure position of the photosensitive drum exposed by each light source. The image forming apparatus described. 3. The image forming apparatus according to claim 1, wherein the sensitivity correction data R (i) is calculated by using the following formulas (A) and (B).
When Vr ≧ Vk R (i) = 1− (Vr (i) −Vk) / Vk (A)
When Vr <Vk R (i) = 1 + (Vk−Vr (i)) / Vk (B)
However, Vk indicates a predetermined reference potential, and Vr (i) indicates the above-mentioned when the photosensitive drum is exposed with a predetermined amount of light so that the surface potential of the photosensitive drum becomes the reference potential Vk. Of the plurality of sample points set along the longitudinal direction of the photosensitive drum, the surface potential of the i-th sample point is indicated, and R (i) is the plurality of sample points set along the longitudinal direction of the photosensitive drum. The sensitivity correction data of the i-th sample point among the sample points is shown. The sensitivity correction data and the light amount correction data are calculated when the ambient temperature is a predetermined reference temperature,
Temperature measuring means for measuring the temperature around the photosensitive drum;
Coefficient storage means for preliminarily storing a temperature correction coefficient that cancels out both the change in the light amount of the light source unit caused by the difference between the temperature measured by the temperature measurement means and the reference temperature, and the change in sensitivity of the photosensitive drum. And further comprising
The light source driving unit further corrects the driving current calculated using the sensitivity correction data and the light amount correction data by using a temperature correction coefficient with respect to the temperature measured by the temperature measuring unit. Item 4. The image forming apparatus according to any one of Items 1 to 3.

Images