JP2009196170A - Optical scanner, image forming apparatus, controlling method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner which enables improvement of an illuminance correcting accuracy at the time of performing correction to make constant an image surface illuminance distribution on a photosensitive drum, and to provide an image forming apparatus. <P>SOLUTION: The image forming apparatus is equipped with the photosensitive drum 19, an optical scanning part 2, and an image surface illuminance measuring part 61. The optical scanning part 2 calculates a quartic approximate expression having measured values of illuminances on a plurality of image heights of the photosensitive drum 19 subjected to quartic approximation to a plurality of light amount set values at a laser. Next, an illuminance difference between the illuminance on an arbitrary image height of the photosensitive drum 19 and the illuminance on at least one or more other image heights is calculated for the plurality of light amount set values by using the quartic approximate expression. Then, an illuminance correction value is calculated on the basis of the illuminance difference, and a light amount of laser to be ejected from the semiconductor laser 12 is controlled on the basis of the illuminance correction value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that scans an image carrier with a laser beam, an image forming apparatus, a control method, and a program.

  Conventionally, a latent image is formed by scanning a photosensitive drum with a laser beam (hereinafter referred to as a laser) corresponding to image data read from an original, and a visible image obtained by developing the latent image is transferred to a sheet to form an image. There is an electrophotographic image forming apparatus. In an electrophotographic image forming apparatus, the amount of laser (image surface illuminance distribution) on the photosensitive drum in the main scanning direction orthogonal to the moving direction (or moving direction of the original) of the original reading unit may have different characteristics. In the case of an image forming apparatus having different image plane illuminance distributions, the image plane illuminance distribution on the photosensitive drum is made constant by correcting the amount of laser light in the main scanning direction.

As the related technique, the following technique has been proposed (for example, see Patent Document 1). In the technique described in Patent Document 1, the image surface illuminance of the photosensitive drum is measured in a state where the laser is set to a predetermined light emission intensity, and the image height at which the image surface illuminance becomes the minimum illuminance is obtained. The difference from the illuminance at an image height other than is the correction value. Further, except for the predetermined light emission intensity of the laser, the image plane illuminance distribution is calculated by multiplying the correction value by a ratio to the predetermined light emission intensity. The image height is a latent image formation position (laser irradiation position) in the longitudinal direction of the photosensitive drum.
JP 2005-262485 A

  However, the above-described conventional technique has the following problems. In the laser / optical characteristics when the photosensitive drum is scanned with a laser in the image forming apparatus, there are optical characteristic differences such as variations in FFP (far field pattern) with respect to the emission intensity of the laser and variations in the optical axis of the laser. For example, FIG. 10 shows the fluctuation of the FFP (horizontal) proportion with respect to the laser emission intensity. It can be seen that as the emission intensity of the laser decreases, the FFP proportion decreases without correlation to the amount of change in emission intensity.

  FIG. 22 is a diagram showing the measurement result of the image plane illuminance distribution when 100% light intensity is set. FIG. 23 is a diagram illustrating characteristics of a correction value using the correction value calculation method of the background art corresponding to the image height A in FIG. 22 and a correction value actually necessary.

  In FIG. 22, the horizontal axis indicates the image height, and the vertical axis indicates the illuminance. The line indicated by the horizontal arrow is the minimum illuminance when the 100% light quantity is set, and the range indicated by the vertical arrow is the correction amount. In FIG. 23, the horizontal axis represents the light amount setting value, and the vertical axis represents the correction value. The oblique solid line is a correction value characteristic (primary approximation correction value) calculated by multiplying the correction value for the 100% light quantity by the ratio, and the range indicated by the vertical arrow indicates the actually required correction value and the primary approximation. This is the difference from the correction value.

  When the correction is performed so that the image plane illuminance distribution on the photosensitive drum is constant, as shown in FIG. 23, there is a difference between the actually required correction value and the primary approximate correction value. For this reason, the correction residual (deviation from the target correction value) of the corrected image plane illuminance distribution may increase depending on the emission intensity of the laser. That is, the prior art has a problem that the illuminance correction accuracy is not sufficient when correction is performed so that the image plane illuminance distribution on the photosensitive drum is constant.

  An object of the present invention is to provide an optical scanning apparatus, an image forming apparatus, a control method, and a program capable of improving the illuminance correction accuracy when performing correction so that the image plane illuminance distribution on the photosensitive drum is constant. It is to provide.

  In order to achieve the above-mentioned object, the present invention provides an optical scanning apparatus for forming a latent image on the image carrier by irradiating the image carrier with a laser emitted by the laser light emitter, and the laser light emitter means Measuring means for measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier, and the illuminance at the plurality of laser irradiation positions measured by the measuring means for a plurality of light quantity setting values in the laser emitted from the laser emitting means The first calculating means for calculating the n-th order approximation formula (n ≧ 2) obtained by n-order approximation of the measured value of n and the n-th order approximation formula calculated by the first calculating means, The illuminance difference between the measured illuminance at an arbitrary laser irradiation position on the image carrier and the illuminance at at least one other laser irradiation position on the image carrier is calculated as follows. Second calculating means for calculating a number of light quantity setting values, third calculating means for calculating an illuminance correction value based on the illuminance difference calculated by the second calculating means, and the third calculating means. Control means for controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated by the above.

  In order to achieve the above-mentioned object, the present invention provides an optical scanning apparatus for forming a latent image on the image carrier by irradiating the image carrier with a laser emitted by the laser light emitter, and the laser light emitter means Measuring means for measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier, and the illuminance at the plurality of laser irradiation positions measured by the measuring means for a plurality of light quantity setting values in the laser emitted from the laser emitting means Calculated by an n-order approximation formula (n ≧ 2) obtained by n-order approximation of the measured value, and a first calculation means for calculating an expression obtained by differentiating the n-order approximation formula, and the first calculation means. The illuminance at an arbitrary laser irradiation position with respect to the image carrier measured by the measuring means using an expression obtained by differentiating the n-th order approximate expression, and at least one for the image carrier. An illuminance correction value based on the illuminance difference calculated by the second calculating means and the second calculating means for calculating the illuminance difference from the illuminance at the other laser irradiation position above with respect to the plurality of light amount setting values. And a control means for controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated by the third calculating means. To do.

  According to the present invention, it is possible to calculate an illuminance correction value suitable for the illuminance characteristics for each actual light amount setting value in the laser, and to control the laser light amount using the calculated illuminance correction value. This makes it possible to improve the illuminance correction accuracy when performing correction so that the image plane illuminance distribution of the image carrier is constant.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a main part of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of an optical scanning unit (optical scanning device) of the image forming apparatus.

  1 and 2, the image forming apparatus 1 includes an optical scanning unit 2, an engine control unit 3, an image control unit 5, a backup memory 6, a polygon mirror 15, a scanner motor unit 16, an f-θ lens 17, and a reflection mirror 18. A photosensitive drum 19 and a beam detection sensor 20.

  The optical scanning unit 2 includes a laser driving unit 11 (first calculation unit, second calculation unit, third calculation unit, correction unit, control unit), a semiconductor laser 12 (laser emission unit), and a collimator lens 13. A laser unit is provided. The laser drive unit 11 includes a laser drive circuit 21 and a nonvolatile memory 46. The engine control unit 3 includes a D / A converter 57. Note that illustrations and descriptions of the other components of the image forming apparatus 1 (document reading unit, developing unit, transfer unit, fixing unit, conveyance unit, etc.) are omitted.

  The optical scanning unit 2 forms a latent image on the photosensitive drum 19 by scanning the photosensitive drum 19 (image carrier) with a laser. The laser drive circuit 21 of the laser drive unit 11 drives the semiconductor laser 12 to emit a laser. The nonvolatile memory 46 stores an illuminance correction value to be described later. The engine control unit 3 controls the image forming engine including the optical scanning unit 2. The image control unit 5 outputs a non-inverted data signal 33 and an inverted data signal 34 described later to the optical scanning unit 2 based on the control of the engine control unit 3. The backup memory 6 stores backup data. Details of the laser driver 11 and the like will be described later with reference to FIG.

  First, the operation of the optical scanning unit 2 will be described for a non-image region (region where no laser is irradiated) of the photosensitive drum 19. The laser L1 emitted from the semiconductor laser 12 in the laser unit of the optical scanning unit 2 enters the cylindrical lens 14 and passes therethrough, and then reaches the polygon mirror 15. Further, the laser L1 is deflected by the polygon mirror 15 rotating at a constant angular speed by the scanner motor unit 16, and converted by the f-θ lens 17 to scan at a constant speed in a direction orthogonal to the rotation direction of the photosensitive drum 19. The Thereafter, the laser L1 is reflected by the reflection mirror 18 and received by the BD sensor 20.

  Next, the operation of the optical scanning unit 2 will be described with respect to the image region (region irradiated with laser) of the photosensitive drum 19. The laser L2 emitted from the semiconductor laser 12 in the laser unit of the optical scanning unit 2 passes through the f-θ lens 17 and is reflected by the reflection mirror 18 similarly to the laser L1, and then irradiates the photosensitive drum 19. As a result, a latent image is formed on the photosensitive drum 19, and the latent image is developed with toner by a developing unit (not shown). Thereafter, the toner image is transferred and fixed on the sheet, and image formation is performed.

  FIG. 3 is a block diagram illustrating a detailed configuration of the laser driving unit 11 of the optical scanning unit 2.

  In FIG. 3, the laser drive circuit 21 of the laser drive unit 11 controls the drive current of the semiconductor laser 12 to cause the semiconductor laser 12 to emit light with a predetermined amount of light (intensity). The semiconductor laser 12 includes a laser diode (hereinafter referred to as LD) 12a and a photodiode (hereinafter referred to as PD) 12b that monitors (detects) a laser output from the LD 12a. The PD 12b of the semiconductor laser 12 outputs a PD current 22 corresponding to the amount of laser light output from the LD 12a.

  The light amount adjusting variable resistor 23 is a resistor that adjusts so that the LD 12a of the semiconductor laser 12 emits light with a predetermined light amount. A PD current 22 corresponding to the amount of laser light output from the PD 12 b of the semiconductor laser 12 is voltage-converted by a light amount adjustment variable resistor 23 and output as a PD voltage signal 24. The PD voltage signal 24 is input to a sample / hold circuit (light quantity control circuit: APC CTL) 27 together with a reference voltage 26 generated by a reference voltage generation circuit (Vref) 25.

  The sample / hold circuit 27 compares the PD voltage signal 24 with the reference voltage 26 when the sample / hold (hereinafter referred to as S / H) control signal 29 input from the engine control unit 3 indicates a sample request. When the PD voltage signal 24 is lower than the reference voltage 26, the hold capacitor 51 is charged. When the PD voltage signal 24 is higher than the reference voltage 26, the hold capacitor 51 is discharged. In this manner, the LD 12a of the semiconductor laser 12 is set to a predetermined light amount by controlling the voltage value 28 according to the current. When the S / H control signal 29 indicates a hold request, the sample / hold circuit 27 holds a voltage value 28 corresponding to the current based on the result obtained when the sample is requested.

  The current mirror circuit 31 includes a transistor 31a and a transistor 31b. Here, for example, it is assumed that the mirror ratio of the current mirror circuit 31 is about 40 times. When a data output request for forming a latent image on the photosensitive drum 19 is requested, the voltage value 28 corresponding to the current output from the sample / hold circuit 27 is set to the operational amplifier 52 by the S / H control signal 29 input from the engine control unit 3. Is input to the positive input terminal. Therefore, the current output from the emitter of the transistor 53 flows through the resistor 54. The voltage value generated by the resistor 54 is output to the engine control unit 3 as a DAC reference signal 56 via the operational amplifier 55.

  Since the mirror ratio of the current mirror circuit 31 is about 40 times, the laser drive current 32 that is a current value output from the collector side of the transistor 31 a of the current mirror circuit 31 is about 40 times the current value flowing through the resistor 54. Become.

  The differential receiver (LVDS) 35 has a differential input, and receives a non-inverted data (hereinafter DATA) signal 33 and an inverted data (hereinafter / DATA) signal 34 input from the image control unit 5. The output selection circuit 38 outputs the switching signal a · 39 and the switching signal b · 40 determined by the S / H control signal 29 or the data output control signal 30.

  The current driver 41 has a differential amplification configuration in which the emitter terminals of the transistor 41a and the transistor 41b are connected. The transistor 41a of the current driver 41 performs switching driving of the LD 12a of the semiconductor laser 12 by the laser driving current 32 based on the switching signal a · 39. Similarly, the transistor 41b of the current driver 41 performs switching driving of the load resistor 42 by the laser driving current 32 based on the switching signal b · 40.

  The laser drive current 32 does not all flow through the LD 12 a of the semiconductor laser 12. Since the correction data voltage signal 43 output from the engine control unit 3 is input to the plus input terminal of the operational amplifier 44, the same voltage value as that of the correction data voltage signal 43 is output to the emitter of the transistor 45. Accordingly, the laser drive current 32 has a current value that is lower by the current calculated based on the voltage value output to the emitter of the transistor 45 and the resistor 50.

  Here, the correction data voltage signal 43 will be described. The laser drive circuit 21 outputs the voltage value generated in the resistor 54 to the engine control unit 3 as the DAC reference signal 56 via the operational amplifier 55. In the engine control unit 3, the DAC reference signal 56 is input to the D / A converter 57 and used as the reference voltage of the D / A converter 57, so that a voltage value from 0 to the DAC reference signal 56 can be output. The 8-bit data is output from the D / A control unit of the engine control unit 3 at a predetermined timing, and a voltage value corresponding to the 8-bit data is output to the laser drive circuit 21. This signal is the correction data voltage signal 43.

  The bias current determination unit 51 outputs a current to the LD 12a of the semiconductor laser 12 according to the value of the correction data voltage signal 43 so that the bias current value for the LD 12a of the semiconductor laser 12 does not change. Therefore, the range of the current value supplied to the LD 12a of the semiconductor laser 12 that can be changed by the correction data voltage signal 43 is the current variable range of the current-light quantity characteristic (laser IL characteristic) of the LD 12a of the semiconductor laser 12 shown in FIG. (Maximum current switching range). In FIG. 4, α × Ith is a lower limit value of the current variable range, Iop is an upper limit value of the current variable range, and (Iop−α × Ith) / 2 is an intermediate value of the current variable range.

  Next, the resistance value of the resistor 50 will be described. When the mirror ratio of the current mirror circuit 31 is 40 times, the resistance value of the resistor 50 is set to 1/40 of the resistance value of the resistor 54. The reason why the resistance value of the resistor 50 is set to 1/40 of the resistance value of the resistor 54 will be described using equations. The resistance value, current value, and voltage value of each part are set as follows.

  Resistance value of the resistor 50: R50. Current value flowing through the resistor 50: I50. Voltage value generated in the resistor 50: V50. Resistance value of the resistor 54: R54. Current value flowing through the resistor 54: I54. Voltage value generated in the resistor 54: V54. Current value flowing from the bias current determination unit 51: Ib. Mirror ratio of current mirror circuit 31: 40 times. The value of current flowing to the LD 12a of the semiconductor laser 12: Ild. The following formula is established between the resistance value, the current value, and the voltage value.

I54 = V54 / R54
Ild = 40 × V54 / R54 + Ib
When the correction data voltage signal 43 is input to the laser drive circuit 21 and it is desired to reduce the current flowing to the LD 12a of the semiconductor laser 12 to α × Ith in FIG. 4, the engine control unit 3 performs the D / A control from the D / A control unit. The 8-bit set value output to the A converter 57 is FFh. In this case, the correction data voltage signal 43 output from the D / A converter 57 is equal to V 54 that is a voltage value generated in the resistor 54. A current value I50 flowing through the resistor 50 is expressed by the following equation.

I50 = V50 / R50 = 40 × V54 / R54
Consider that the correction data voltage signal 43 when the 8-bit set value output from the D / A control unit to the D / A converter 57 in the engine control unit 3 is FFh and the voltage value V50 generated in the resistor 50 are equal. Then, the resistance value R50 of the resistor 50 is expressed by the following equation.

R50 = R54 / 40
This shows that the resistance value of the resistor 50 needs to be 1/40 of the resistance value of the resistor 54.

  Data for generating the correction data voltage signal 43 is stored in a nonvolatile memory (hereinafter referred to as EEPROM) 46 of the laser driving unit 11. The engine control unit 3 communicates with the EEPROM 46 of the laser driving unit 11 and reads data stored in the EEPROM 46 via a serial data output signal (DO) 49.

  FIG. 5 is a time chart showing the state transition of the laser drive circuit 21 of the laser drive unit 11 during image formation of the image forming apparatus.

  In FIG. 5, the operation of the laser drive circuit 21 is sequentially controlled in the following order based on the falling edge of the output signal of the BD sensor 20. Light amount control (APC) → Laser forced off (OFF) → Data output (DATA OUT) → Laser forced off (OFF) → Light amount control (APC). The output states of the output selection circuit 38 are data output, stop, forced output, stop, data output, stop, forced output, stop, data output, and so on.

  The operation state of the sample / hold circuit 27 is hold, sample, hold, sample, hold... The operating states of the laser drive circuit 21 are DATA OUT (data output), OFF (laser forced extinction), APC (light quantity control), OFF, DATA OUT, OFF, APC, OFF, DATA OUT. The data output from the image control unit 5 to the laser drive circuit 21 of the laser drive unit 11 corresponds to a latent image formed in the image area (laser irradiation area) of the photosensitive drum 19 that is the print range of the paper to be printed. .

  FIG. 6 is a diagram showing an operation function table of the laser drive circuit 21.

  In FIG. 6, when the S / H control signal 29 is L, the data output control signal 30 is H, the sample / hold circuit 27 is in the sample state, and the output selection circuit 38 is in the forced output state, the laser drive circuit 21 controls the light amount ( APC) state. When the S / H control signal 29 is H, the data output control signal 30 is H, the sample / hold circuit 27 is in the hold state, and the output selection circuit 38 is in the stop state, the laser drive circuit 21 is forcibly turned off (OFF). It becomes a state.

  When the S / H control signal 29 is H, the data output control signal 30 is L, the sample / hold circuit 27 is in the hold state, and the output selection circuit 38 is in the data output state, the laser drive circuit 21 outputs the data output (DATA OUT ) State. When the S / H control signal 29 is L, the data output control signal 30 is L, the sample / hold circuit 27 is 0 (initial value), and the output selection circuit 38 is in a stopped state, the laser drive circuit 21 is in a reset state. It becomes.

  Next, the operation of the laser drive circuit 21 of the laser drive unit 11 will be described in the order of light quantity control (APC), laser forced extinction (OFF), data output (DATA OUT), and reset state.

"Light control (APC)"
In the laser drive circuit 21, when the sample / hold circuit 27 is in the sample state, the output selection circuit 38 performs the following control. The output selection circuit 38 forcibly outputs ON data so that the LD 12a of the semiconductor laser 12 emits light regardless of the output of the receiver non-inverted output signal 36 and the receiver inverted output signal 37. The laser drive circuit 21 controls the light emission amount of the LD 12a of the semiconductor laser 12 to be a predetermined light amount based on a signal corresponding to the difference between the PD voltage signal 24 and the reference voltage 26. That is, control according to the magnitude relationship between the PD voltage signal 24 and the reference voltage 26 is performed as follows.

  When PD voltage signal 24> reference voltage 26: The laser driving circuit 21 determines that the light emission amount of the LD 12a of the semiconductor laser 12 is larger than the predetermined light amount, and discharges the hold capacitor 51. As a result, the voltage value 28 corresponding to the current is reduced and the laser drive current 32 is reduced, thereby reducing the amount of light emitted by the LD 12a of the semiconductor laser 12.

  When PD voltage signal 24 <reference voltage 26: The laser driving circuit 21 determines that the light emission amount of the LD 12a of the semiconductor laser 12 is smaller than the predetermined light amount, and charges the hold capacitor 51 with electric charge. As a result, the amount of light emitted from the LD 12a of the semiconductor laser 12 is increased by increasing the voltage value 28 corresponding to the current and increasing the laser drive current 32.

  When PD voltage signal 24 = reference voltage 26: The laser drive circuit 21 determines that the light emission amount of the LD 12a of the semiconductor laser 12 is the same as the predetermined light amount, and does not charge / discharge the charge of the hold capacitor 51. As a result, neither the voltage value 28 corresponding to the current nor the laser drive current 32 increases or decreases.

“Laser forced extinction (OFF)”
The sample / hold circuit 27 holds a voltage value 28 corresponding to the set current. The output selection circuit 38 forcibly outputs OFF data so that the LD 12a of the semiconductor laser 12 is turned off regardless of the output of the receiver non-inverted output signal 36 and the receiver inverted output signal 37.

"Data output (DATA OUT)"
Based on the voltage value 28 corresponding to the current set by the sample / hold circuit 27, the output selection circuit 38 outputs a signal corresponding to the receiver non-inverted output signal 36 and the receiver inverted output signal 37. Thereby, a current is passed through the LD 12a or the resistor 42 of the semiconductor laser 12.

"Reset state"
The laser driving circuit 21 is in a reset state, and the sample / hold circuit 27 initializes the set current value. The output selection circuit 38 forcibly outputs OFF data so that the LD 12a of the semiconductor laser 12 is turned off.

  Next, in the image forming apparatus of the present embodiment, (1) light amount adjustment, (2) image surface illuminance measurement, and (3) processing for generating illuminance correction values from image surface illuminance data for three types of laser light amounts. Description will be made in the order of calculation of the approximate expression before correction, (4) correction value calculation, and (5) correction value storage.

  FIG. 7 is a schematic diagram illustrating a configuration of the image plane illuminance measurement unit 61 of the image forming apparatus.

  In FIG. 7, the image plane illuminance measurement unit 61 (measurement means) includes an optical unit 62, a measurement photodiode (hereinafter referred to as APD) 63, and an optical drive unit 64. The APD 63 is configured as an avalanche photodiode (APD) and is fixed to the upper surface of the optical unit 62, and is disposed at a position corresponding to the laser irradiation position of the photosensitive drum 19. The optical drive unit 64 drives the optical unit 62 in the main scanning direction indicated by an arrow (a direction orthogonal to the rotation direction of the photosensitive drum 19). The laser L2 emitted from the LD 12a of the semiconductor laser 12 in the laser unit of the optical scanning unit 2 used for image plane illuminance measurement may be either scanning light or stationary light.

  The illuminance measurement control unit 66 includes an APD control unit 67, an A / D (analog / digital) converter 69, and a current control unit 71. The APD controller 67 is connected to the APD 63 via the measurement photodiode control signal line 65, supplies power to the APD 63, and converts the current output from the APD 63 into a voltage signal. The A / D converter 69 quantizes the APD voltage signal 68 output from the APD control unit 67 with a predetermined sampling rate and resolution.

  The current control unit 71 controls the laser drive circuit 21 of the laser drive 11 via the laser drive circuit control signal line 72 so that the LD 12a of the semiconductor laser 12 has a predetermined light amount. A signal that flows through the laser drive circuit control signal line 72 includes an S / H control signal 29, a data output (DATA OUT) control signal 30, and a correction data voltage signal 43. A set value for setting the LD 12 a of the semiconductor laser 12 to a predetermined light amount is transferred to the laser drive circuit 21 by the correction data voltage signal 43. The control method in the image plane illuminance measurement unit 61 is the same as the control method at the time of image formation using the photosensitive drum 19, and the description thereof is omitted.

(1) Light quantity adjustment First, the image height (± 150 mm) in the image area corresponding to the other end from the one end in the longitudinal direction in the image area (laser irradiation area) of the photosensitive drum 19 is equally spaced (25 mm). The image plane illuminance is measured by the image plane illuminance measurement unit 61 for the total of the divided 13 positions. In the present embodiment, an example is given in which the intervals between the positions of the image height are equal intervals. However, the intervals are not limited to equal intervals, and may be non-equal intervals.

  The illuminance at the image heights at the 13 positions is measured, the image height that is the minimum illuminance is detected, and the laser drive circuit 21 is set to the light amount adjustment mode so that the illuminance at the image height becomes a predetermined value. The light quantity is adjusted by 23. The amount of light obtained as described above is defined as 100% light amount, and the laser drive current 32 set at this time is defined as 100% light amount drive current. The 8-bit data output from the D / A control unit to the D / A converter 57 by the engine control unit 3 is 00h.

(2) Image surface illuminance measurement (3 types of light intensity)
Next, the image plane illuminance distribution (laser light amount on the photosensitive drum) with respect to a plurality of laser amounts (three kinds of light amounts) is measured. The light amount setting value (D / A value) is set to 75%, 50%, or 25% with respect to the maximum laser light amount 100% that can be output in the adjusted semiconductor laser 12, and the image plane illuminance measurement unit 61 Measure surface illuminance. In order to increase the 100% light intensity driving current to 3/4, 1/2, 1/4 (3/4, 1/2, 1/4) of the current variable range in FIG. Set up. The 8-bit data output from the D / A control unit to the D / A converter 57 by the engine control unit 3 is set to 40h, 80h, and C0h.

  In the state where the above setting is performed, the APD 63 of the optical unit 62 is moved by the optical driving unit 64 of the image plane illuminance measurement unit 61 to measure the image plane illuminance at the image heights at a plurality of locations (13 locations). The image plane illuminance measurement is performed with respect to three kinds of light amounts, and the measurement results are graphed as shown in FIG. 8 (horizontal axis: image height, vertical axis: light amount). FIG. 8 shows the illuminance distribution characteristics when 75% light intensity is set, 50% light intensity is set, and 25% light intensity is set.

  FIG. 9 is a graph showing the measurement results of the image height of −25 (correction block 10) with the horizontal axis representing the light amount setting value and the vertical axis representing the illuminance (horizontal axis: light amount setting value, vertical axis: illuminance). . FIG. 9 shows the illuminance characteristics of the correction block 10 when the 75% light intensity is set, when the 50% light intensity is set, and when the 25% light intensity is set, and the broken line indicates the actual illuminance characteristics.

  The reason why the non-linear characteristic is as shown in FIG. 9 even though the light amount setting value (D / A value) is linear with 40h, 80h, C0h (75% light amount setting, 50% light amount setting, 25% light amount setting). Is as follows. This is because the laser / optical characteristics have optical characteristic differences such as FFP variations and optical axis variations with respect to emission intensity.

  FIG. 10 shows the variation of the FFP (horizontal) proportion with respect to the laser emission intensity. FIG. 10 shows the FFP proportions at 100% emission, 75% emission, 50% emission, and 25% emission. As shown in FIG. 10, it can be seen that the FFP proportion decreases with no correlation to the amount of change in emission intensity as the emission intensity of the laser decreases. As a result, a phenomenon in which the light quantity does not change linearly even when the light quantity setting value is changed linearly, a phenomenon in which the profile of the image plane illuminance distribution fluctuates depending on the light quantity, or the like occurs.

(3) Calculation of approximate expression before correction Next, an approximate expression of image surface illuminance data before correction for each light quantity setting value is calculated. A set value of the D / A converter 57 of the engine control unit 3 is set to 40h, 80h, C0h, and a fourth-order approximation formula (nth-order approximation formula) from measured values of image plane illuminance at 13 image heights obtained by image plane illuminance measurement. (N ≧ 2)) is generated. FIG. 11 shows a graph in which the image plane illuminance measurement is performed with respect to the above three types of light quantity, and the measured values of the image plane illuminance with respect to each light quantity are fourth-order approximated (horizontal axis: image height, vertical axis: light quantity). FIG. 11 shows a quaternary approximation curve and a minimum illuminance approximated from respective illuminance distributions when 75% light intensity is set, 50% light intensity is set, and 25% light intensity is set.

(4) Correction Value Calculation Next, a correction value calculation (see FIG. 11) method will be described. It is assumed that the illuminance correction value (hereinafter referred to as correction value) is calculated with a total of 25 correction blocks at regular intervals of 12.5 mm for the image height in the image area (± 150 mm). As shown in FIG. 11, from the fourth-order approximation, the image plane illuminance differences (ΔP0H to ΔP23H, ΔP0M to ΔP23M, ΔP0L to ΔP23L) of the other 24 correction blocks with respect to the correction block having the lowest illuminance are set as the respective light amount setting values. (75%, 50%, 25%) are calculated.

  FIG. 12 shows image plane illuminance difference data of 25 correction blocks with respect to the respective light amount setting values (75%, 50%, 25%) in FIG. In FIG. 12, the image plane illuminance difference data of 75% light intensity setting value (D / A value 40h), 50% light intensity setting value (D / A value 80h), and 25% light intensity setting value (D / A value C0h). (Unit: μW). In FIG. 12, the image heights −150 to 150 associated with each of the correction blocks 0 to 24 are from one end in the longitudinal direction to the other end in the image area (laser irradiation area) of the photosensitive drum 19. Corresponding to

  Further, the image plane illuminance data of 25 correction blocks is calculated from the fourth-order approximation formula for each light quantity setting value in FIG. FIG. 13 shows image plane illuminance data calculated from the fourth-order approximation formula of 25 correction blocks for the respective light quantity setting values (75%, 50%, 25%) in FIG. In FIG. 13, image plane illuminance data (75% light intensity setting value (D / A value 40h), 50% light intensity setting value (D / A value 80h), and 25% light intensity setting value (D / A value C0h) ( (Unit: μW).

  A correction value calculation method will be described using the image plane illuminance differences (ΔP10H, ΔP10M, ΔP10L) and the image plane illuminance data (PH10, PM10, PL10) of the correction block 10 in FIG.

  First, a method of calculating the correction value C10H of the set value 40h (75% equivalent light amount set value) of the D / A converter 57 of the engine control unit 3 will be described. The image plane illuminance difference ΔP10H of the correction block 10 when the setting value 40h of the D / A converter 57 of the engine control unit 3 is 26.4 μW (image height -25 when the setting value is 40h) from FIG. (A value obtained by subtracting the light amount of 150). The image plane illuminance data PH10 is 176.8 μW from FIG.

  From the image plane illuminance data PH10 of the set value 40h (75% equivalent light amount set value) of the D / A converter 57 and the image plane illuminance data PM10 of the set value 80h (50% equivalent light amount set value) of the D / A converter 57, The light quantity change amount P1LSBH is calculated. The light quantity change amount P1LSBH is the slope of the first light quantity change when the D / A value changes by 1 h.

Since the difference between the light amount setting values of the image plane illuminance data PH10 and PM10 is 40h (decimal (hereinafter, dec) value is 64), the calculation formula is
P1LSBH = (PH10-PM10) / 64
= (176.8-117.5) / 64 = 0.927
It becomes.

The correction value C10H of the correction block 10 is calculated from the image plane illuminance difference ΔP10H and the light amount change amount P1LSBH when the D / A value changes by 1 h. The formula is
C10H = ΔP10H / P1LSBH
= 26.4 / 0.927 = 28.4 ≒ 28
It becomes. The actual correction value C10H of the correction block 10 is “1Ch”.

  Next, a method of calculating the correction value C10L of the set value C0h (25% equivalent light amount set value) of the D / A converter 57 of the engine control unit 3 will be described. The image plane illuminance difference ΔP10L of the correction block 10 at the setting value C0h of the D / A converter 57 is 7.2 μW from FIG. 12 (subtracting the light amount at the image height 150 from the light amount at the image height −25 at the setting value 40h). Value). The image plane illuminance data PL10 is 47.8 μW from FIG.

  From the image plane illuminance data PL10 of the set value C0h (25% equivalent light amount set value) of the D / A converter 57 and the image plane illuminance data PM10 of the set value 80h (50% equivalent light amount set value) of the D / A converter 57, A light amount change amount P1LSBL is calculated. The light quantity change amount P1LSBL is the slope of the second light quantity change when the D / A value changes by 1 h.

Since the difference between the light intensity setting values of the image plane illuminance data PL10 and PM10 is 40h (dec value is 64), the calculation formula is
P1LSBL = (PM10-PL10) / 64
= (117.5-47.8) / 64 = 1.089
It becomes.

The correction value C10L of the correction block 10 is calculated from the image plane illuminance difference ΔP10L and the light amount change amount P1LSBL when the D / A value changes by 1 h. The formula is
C10L = ΔP10L / P1LSBL
= 7.2 / 1.089 = 6.6 ≒ 7
It becomes. The actual correction value C10L of the correction block 10 is “07h”.

  Next, a method of calculating the correction value C10M of the set value 80h (50% equivalent light amount set value) of the D / A converter 57 of the engine control unit 3 will be described. The image plane illuminance difference ΔP10M of the correction block 10 when the setting value 80h of the D / A converter 57 is 17.7 μW from FIG. 12 (subtracting the light amount of the image height 150 from the light amount of the image height −25 when the setting value 40h. Value).

When the setting value 80h of the D / A converter 57 is set, the light amount change amount P1LSBM when the D / A value when the correction value C10M is calculated changes by 1h is calculated. The values used for the calculation are the light amount change amount P1LSBH and the light amount change amount P1LSBL. Using these values, the light quantity change amount P1LSBM when the D / A value at the setting value 80h of the D / A converter 57 changes by 1h is calculated. The formula is
P1LSBM = (P1LSBH + P1LSBL) / 2
= (0.927 + 1.089) / 2 = 1.008
And the average of the light quantity change amount P1LSBH and the light quantity change amount P1LSBL.

The correction value C10M of the correction block 10 is calculated from the image plane illuminance difference and the light amount change amount P1LSBL when the D / A value changes by 1 h. The formula is
C10L = ΔP10L / P1LSBL
= 17.7 / 1.008 = 17.5 ≒ 18
It becomes. The actual correction value C10L of the correction block 10 is “12h”.

By correcting the light quantity of one scanning of the laser in the main scanning direction using the three correction values calculated as described above, the image plane illuminance distribution on the photosensitive drum 19 is made constant. For example, the D / A value when the correction block 10 is set to 40h is
40h + 1Ch = 5Ch
It becomes. Similarly, when setting 80h and setting C0h,
80h + 12h = 92h
C0h + 07h = C7h
It becomes.

  The correction values other than those when 40h, 80h and C0h are set as the light intensity setting of the correction block 10 are graphs with the correction values when 40h, 80h and C0h are set, with the horizontal axis representing the D / A setting value and the vertical axis representing the correction value. Plot the values on the straight line connecting them. For example, the correction value at the time of setting 60h between 40h and 80h of the correction block 10 is considered as a straight line connecting the correction value at the time of setting 40h and the correction value at the time of setting 80h.

Considering a decimal value with B as a correction value and A as a D / A set value, the (A, B) coordinates when the D / A set value is 40h are (64, 28), and (A , B) The coordinates are (128, 18). Therefore, the formula is
B = −5 / 32A + 38
It becomes. The correction value at the time of setting 60h is 96 when A is substituted.
B = 23 = 17h
It becomes. Therefore, the D / A setting value at 60h setting is
60h + 17h = 77h
It becomes.

(5) Correction value storage Each light quantity setting value (00h, 20h, 40h, 60h, 80h, A0h, C0h, E0h) calculated in the above (1) to (4) and each correction block (correction blocks 0 to 24) A correction value is input to the D / A converter 57 from the D / A control unit in the engine control unit 3. Thereby, correction is executed. The correction data obtained by the above processing in the engine control unit 3 is stored in the EEPROM 46 of the laser driving unit 11 via the serial data input signal (DI) 48.

  As described above, the relationship between the light intensity setting value of the correction block 10 and the illuminance obtained when the illuminance distribution measurement is performed for the three kinds of light intensity is set to 75%, 50%, and 25% light intensity indicated by circles in FIG. However, the illuminance characteristic is actually indicated by a broken line.

  The correction values for the illuminance characteristics shown in FIG. 9 calculated in the conventional example are correction values at the time of setting 75%, 50%, and 25% light quantities in the characteristics indicating the relationship between the light quantity setting values and the correction values as shown in FIG. And the value on the straight line connecting them. However, if the correction value for the illuminance characteristic indicated by the broken line in FIG. 9 is not the correction value on the broken line in FIG. 14, the correction residual may increase depending on the light amount setting value of the laser.

  Next, in the image forming apparatus according to the present embodiment, the processing for generating an illuminance correction value from eight types of image plane illuminance data includes (1) light amount adjustment, (2) image plane illuminance measurement, and (3) approximation before correction. The calculation will be described in the order of calculating the equation, (4) calculating the correction value, and (5) storing the correction value. That is, a correction value calculation method using a quadratic approximate expression for improving the correction accuracy will be described below.

  The specifications for generating the correction data are as shown in the following table.

(1) Light quantity adjustment Adjustment is performed in the same manner as in the case of generating an illuminance correction value from the image plane illuminance data for the three types of light quantities described above.

(2) Image surface illuminance measurement (8 types of light intensity)
First, image plane illuminance measurement (75% equivalent light amount setting value) when the setting value of the D / A converter 57 of the engine control unit 3 is 40 h will be described. In order to make the 100% light amount driving current 3/4 (3/4 of the current variable range in FIG. 4), the 8-bit data output from the D / A control unit to the D / A converter 57 by the engine control unit 3 is 40h. Set. In this state, the optical driving unit 64 moves the APD 63 on the optical unit 62 in accordance with the above specifications, and measures the image plane illuminance at 13 image heights.

  Next, image plane illuminance measurement (50% equivalent light amount setting value) when the setting value of the D / A converter 57 of the engine control unit 3 is set to 80h will be described. In order to reduce the 100% light amount driving current to 1/2 (1/2 of the current variable range in FIG. 4), the engine control unit 3 outputs 8 bits of data to be output from the D / A control unit to the D / A converter 57 by 80h. The correction data voltage signal 43 when set to is input to the drive circuit 21. The correction data voltage signal 43 is ½ of the DAC reference signal 56. In this state, the image plane illuminance is measured in the same manner as the image plane illuminance measurement of 75% light quantity.

  Next, image plane illuminance measurement (25% equivalent light amount setting value) when the setting value of the D / A converter 57 of the engine control unit 3 is C0h will be described. In order to reduce the 100% light amount driving current to 1/4 (1/4 of the current variable range in FIG. 4), the 8-bit data output from the D / A control unit to the D / A converter 57 by the engine control unit 3 is C0h. The correction data voltage signal 43 when set to is input to the drive circuit 21. In this state, the image plane illuminance is measured in the same manner as the image plane illuminance measurement of 75% light quantity.

  Similarly, the image plane illuminance measurement for other set values of the D / A converter 57 of the engine control unit 3 is set to 00h, 20h, 60h, A0h, E0h, and the image plane illuminance is measured. The image surface illuminance measurement is performed for the above eight kinds of light amounts, and the measurement results are graphed as shown in FIG. 15 (horizontal axis: image height, vertical axis: light amount). FIG. 15 shows the illuminance distribution characteristics when the light amount is set to 100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%.

(3) Calculation of approximate expression before correction The set values of the D / A converter 57 of the engine control unit 3 are set to 00h, 20h, 40h, 60h, 80h, A0h, C0h, E0h, and FIG. A fourth-order approximate expression is generated from the measured values of the image plane illuminance at the image heights at the 13 positions shown. FIG. 16 shows a graph in which the image plane illuminance measurement is performed with respect to the above eight types of light quantity, and the measured values of the image plane illuminance with respect to each light quantity are fourth-order approximated (horizontal axis: image height, vertical axis: light quantity). In FIG. 16, a quaternary approximation curve approximated from the illuminance distribution at the time of setting 100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5% light intensity and Indicates the minimum illumination.

(4) Correction value calculation (see FIG. 16)
For example, an illuminance correction value (hereinafter referred to as a correction value) is calculated for a total of 25 correction blocks at an image area in-image height (± 150 mm) at equal intervals of 12.5 mm. The arrangement method of the correction block with respect to the image height may not coincide with the image height at the time of image plane illuminance measurement. As shown in FIG. 16, the image plane illuminance difference of the other 24 correction blocks with respect to the correction block having the lowest illuminance is calculated from the fourth-order approximation formula in the same manner as in FIG.

  Image plane illuminance difference data of 25 correction blocks for each light quantity setting value (100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%) Is shown in FIG. FIG. 17 shows image plane illuminance difference data (unit: μW) of each of the 100% light intensity setting value (D / A value 00h) to 12.5% light intensity setting value (D / A value E0h).

  Also, the image plane illuminance data of 25 correction blocks corresponding to the correction blocks are calculated from the fourth-order approximation formulas for the respective light intensity setting values in FIG. From the fourth-order approximation formula of 25 correction blocks for each light quantity setting value (100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%) The calculated image plane illuminance data is shown in FIG. 18 (unit: μW). FIG. 18 shows image plane illuminance data (unit: μW) of 100% light intensity setting value (D / A value 00h) to 12.5% light intensity setting value (D / A value E0h).

  Focusing on the correction block 10 (image height −25) in FIG. 17, a correction value calculation method will be described using the image plane illuminance difference and the image plane illuminance data of the correction block 10. FIG. 19 shows a graph of the correction block 10 of FIG. 18 when the horizontal axis is the D / A set value (dec) and the vertical axis is the illuminance. The graph of FIG. 19 can be subjected to quadratic approximation. FIG. 20 shows a graph obtained by secondarily approximating the data of the graph of FIG. 19 and calculating a quadratic approximate expression.

In the quadratic approximation, when Y is illuminance and X is D / A set value (dec),
Y = −9.172 × 10 ⁻⁴ X ² −7.773 × 10 ⁻¹ X + 231.2 Equation 1
It becomes. Equation 2 obtained by differentiating Equation 1 (second-order approximation equation) is
Y1 = −18.344 × 10 ⁻⁴ X−7.773 × 10 ⁻¹ Formula 2
It becomes.

  Y1 is the slope when the D / A set value (dec) for the quadratic expression is X (the amount of change in illuminance when the D / A value changes for 1 h). For example, if “32”, which is the D / A setting value (dec) of the 87.5% light intensity setting value (D / A value 20h) of the correction block 10, is substituted into the above equation 2, Y1 becomes the following value: .

Y1 (20h) = − 18.344 × 10 ⁻⁴ × 32−7.773 × 10 ⁻¹
≒ -0.836
It can be calculated that the amount of change in the amount of light when the D / A value changes for 1 h is 0.836 μW.

  The correction value can be calculated from Equation 2 above and the image plane illuminance difference data of FIG. For example, a method for calculating the correction value of the 87.5% light amount setting value (D / A value 20h) of the correction block 10 is as follows. Since the amount of change in the amount of light when the D / A value changes for 1 h is 0.836 μW and the image plane illuminance difference data is 30.9 μW from FIG. 18, the 87.5% light amount setting value (D / The correction value of A value 20h) is the following value.

30.9 / 0.836 = 36.9 ≒ 37 (dec) = 25h
Also for the light intensity setting values of the other correction blocks, a quadratic approximate expression of the relationship between the D / A value and the illuminance is calculated as described above, and the quadratic approximate expression (n-order approximate expression (n ≧ 2)) is calculated. The amount of change in illuminance when the D / A value changes for 1 h is calculated from the differentiated expression. Then, correction values are calculated from the image plane illuminance difference data of FIG. 17 and the amount of change in illuminance when the D / A value changes for 1 h.

  The correction values calculated by the above method are correction values when the light intensity setting values are 00h, 20h, 40h, 60h, 80h, A0h, C0h, and E0h. A method for calculating correction values other than the light amount setting values (00h, 20h, 40h, 60h, 80h, A0h, C0h, E0h) is as follows. The correction values of the respective light intensity setting values (00h, 20h, 40h, 60h, 80h, A0h, C0h, E0h) are plotted on a graph with the horizontal axis as the D / A setting value and the vertical axis as the correction value. The value on the connected straight line. The graph is shown in FIG. 21 (horizontal axis: D / A set value (dec), vertical axis: correction value).

  For example, when the light amount of the correction block 10 is set to 20h (87.5% light amount setting value) and between 40h (75% light amount setting value), 30h is set (81.25% light amount setting value). A method for calculating the correction value will be described. In order to calculate the correction value when the correction block 10 is set for 30h, an equation of a straight line connecting the correction value when the setting is 20h and the correction value when the setting is 40h shown in FIG. 21 is considered.

  Considering a decimal value with B as a correction value and A as a D / A set value, the coordinates (A, B) when the D / A set value is 20h are as follows. When 20h is expressed as a decimal number, it is 32. The correction value when the correction block 10 is set to 20h is 25h as calculated above, and is 25 when 25h is expressed in decimal. Accordingly, the (A, B) coordinates are (32, 37).

  Next, (A, B) coordinates when the correction block 10 is set to 40h are calculated. When 40h is expressed as a decimal number, it is 64. The correction value when the correction block 10 is set to 40h is calculated as follows from Expression 2 and the image plane illuminance difference data of FIG.

Y1 (40h) = − 18.344 × 10 ⁻⁴ × 64−7.773 × 10 ⁻¹
≒ -0.895
26.4 / 0.895 = 29.4 ≒ 29 (dec) = 1Dh
The correction value is 1Dh, and 1Dh is 29 in decimal. Accordingly, the (A, B) coordinates when the correction block 10 is set to 40h are (64, 29). Therefore, the straight line expression of the 20h and 40h correction values is
B = -1 / 4A + 45
It becomes. The correction value of the 30h set value of the correction block 10 is 48 when 30h is expressed in decimal, so when 48 is substituted for A,
B = −1 / 4 × 48 + 45 = 33 = 21h
It becomes. Therefore, the D / A set value when the correction block 10 is set to 30h is
30h + 21h = 51h
It becomes.

(5) Correction value storage The storage is performed in the same manner as the method for generating the illuminance correction value from the image plane illuminance data for the three types of light amounts described above.

  As described above, according to the present embodiment, in the process of generating the illuminance correction value from the image plane illuminance data for the three types of laser light amounts, the plurality of image heights of the photosensitive drum 19 with respect to the plurality of light amount setting values of the laser. A fourth-order approximation formula is obtained by fourth-order approximation of the measured illuminance value. Next, an illuminance difference between an illuminance of an arbitrary image height on the photosensitive drum 19 and an illuminance of at least one or more other image heights is calculated for a plurality of light amount setting values using a quaternary approximate expression. Next, an illuminance correction value is calculated based on the illuminance difference, and the amount of laser light emitted from the semiconductor laser 12 is controlled based on the illuminance correction value.

  Further, in the process of generating the illuminance correction value from the eight types of image plane illuminance data, a quadratic approximation formula that secondarily approximates the measured values of the illuminances at the plurality of image heights of the photosensitive drum 19 with respect to the plurality of laser light quantity setting values. And an equation obtained by differentiating the quadratic approximate equation is calculated. Next, an illuminance difference between an illuminance of an arbitrary image height on the photosensitive drum 19 and an illuminance of at least one other image height is calculated for a plurality of light amount setting values using an expression obtained by differentiating the quadratic approximate expression. To do. Next, an illuminance correction value is calculated based on the illuminance difference, and the amount of laser light emitted from the semiconductor laser 12 is controlled based on the illuminance correction value.

  With the above control, it is possible to calculate an illuminance correction value suitable for the illuminance characteristics for each actual light amount setting value (D / A value) in the laser, and it is possible to control the laser light amount using the calculated illuminance correction value. Become. This makes it possible to improve the illuminance correction accuracy when performing correction so that the image plane illuminance distribution on the photosensitive drum is constant.

[Other embodiments]
The object of the present invention is achieved by executing the following processing. That is, a storage medium that records a program code of software that realizes the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU, MPU, etc.) of the system or apparatus is stored in the storage medium. This is the process of reading the code.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

  Moreover, the following can be used as a storage medium for supplying the program code. For example, floppy (registered trademark) disk, hard disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM or the like. Alternatively, the program code may be downloaded via a network.

  Further, the present invention includes a case where the function of the above-described embodiment is realized by executing the program code read by the computer. In addition, an OS (operating system) running on the computer performs part or all of the actual processing based on an instruction of the program code, and the functions of the above-described embodiments are realized by the processing. Is also included.

  Furthermore, the present invention includes a case where the functions of the above-described embodiment are realized by the following processing. That is, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing.

1 is a block diagram illustrating a configuration of a main part of an image forming apparatus according to an embodiment of the present invention. 2 is a schematic diagram illustrating a configuration of an optical scanning unit of the image forming apparatus. FIG. It is a block diagram which shows the detailed structure of the laser drive part of an optical scanning part. It is a figure which shows the electric current-light quantity characteristic and current variable range of the laser diode of the semiconductor laser of an optical scanning part. 6 is a time chart showing state transition of a laser drive circuit of a laser drive unit during image formation of the image forming apparatus. It is a figure which shows the operation | movement function table | surface of a laser drive circuit. It is the schematic which shows the structure of the image surface illumination intensity measurement part of an image forming apparatus. It is a figure which shows the image surface illuminance distribution characteristic at the time of light quantity setting (75%, 50%, 25%). It is a figure which shows the characteristic of the light quantity setting value and illuminance of the correction block 10 at the time of light quantity setting (75%, 50%, 25%). It is a figure which shows the fluctuation | variation of FFP (horizontal) proportion with respect to the emitted light intensity of a laser. It is a figure which shows the characteristic which carried out the quadratic approximation of the measured value of the image surface illumination intensity with respect to each light quantity of FIG. It is a figure which shows the image surface illumination difference data of 25 correction blocks regarding each light quantity setting value. It is a figure which shows the image surface illumination intensity data calculated from the 4th approximation formula of 25 correction blocks regarding each light quantity setting value. It is a figure which shows the characteristic of the light quantity setting value regarding the image height-25 (correction block 10), and a correction value. It is a figure which shows the image surface illuminance distribution characteristic at the time of light quantity setting (100%, 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, 12.5%). It is a figure which shows the characteristic which carried out the quadratic approximation of the measured value of the image surface illumination intensity with respect to each light quantity of FIG. It is a figure which shows the image surface illumination intensity data of 25 correction blocks regarding each light quantity setting value. It is a figure which shows the illumination intensity data at the time of each D / A value setting of the correction block. It is a figure which shows the quadratic curve of the illumination intensity at the time of each D / A value of the correction | amendment block. It is a figure which shows the image surface illumination difference data of 25 correction blocks regarding each light quantity setting value. It is a figure which shows the characteristic of the D / A setting value and correction value regarding image height-25 (correction block 10). It is a figure which shows the image surface illuminance distribution measurement result at the time of 100% light quantity setting. It is a figure which shows the characteristic of the correction value using the correction value calculation method of the background art corresponding to the image height A of FIG. 22, and the correction value actually required.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Optical scanning part 3 Engine control part 5 Image control part 11 Laser drive part 21 Laser drive circuit 61 Image surface illumination intensity measurement part

Claims (9)

In an optical scanning device that forms a latent image on the image carrier by irradiating the image carrier with a laser emitted by a laser emitting unit,
Measuring means for measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier by the laser emitting means;
An nth-order approximation formula (n ≧ 2) is calculated by nth-order approximation of measured values of illuminance at a plurality of laser irradiation positions measured by the measurement unit with respect to a plurality of light amount setting values in a laser emitted from the laser emitting unit. First calculating means;
Using the nth-order approximation calculated by the first calculation means, the illuminance at an arbitrary laser irradiation position on the image carrier measured by the measurement means, and at least one or more of the image carrier A second calculating means for calculating an illuminance difference with the illuminance at another laser irradiation position for the plurality of light amount setting values;
Third calculation means for calculating an illuminance correction value based on the illuminance difference calculated by the second calculation means;
Control means for controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated by the third calculating means;
An optical scanning device comprising:   The optical scanning apparatus according to claim 1, wherein the n-th order approximate expression is a quaternary approximate expression. In an optical scanning device that forms a latent image on the image carrier by irradiating the image carrier with a laser emitted by a laser emitting unit,
Measuring means for measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier by the laser emitting means;
An nth-order approximation formula (n ≧ 2) is obtained by nth-order approximation of measured values of illuminance at a plurality of laser irradiation positions measured by the measuring unit with respect to a plurality of light amount setting values in a laser emitted from the laser emitting unit. First calculating means for calculating an expression obtained by differentiating the n-th order approximation expression;
Using an expression obtained by differentiating the n-th order approximate expression calculated by the first calculation means, the illuminance at an arbitrary laser irradiation position with respect to the image carrier measured by the measurement means, and at least the image carrier Second calculating means for calculating an illuminance difference with illuminance at one or more other laser irradiation positions for the plurality of light amount setting values;
Third calculation means for calculating an illuminance correction value based on the illuminance difference calculated by the second calculation means;
Control means for controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated by the third calculating means;
An optical scanning device comprising:   The optical scanning apparatus according to claim 3, wherein the n-th order approximate expression is a second-order approximate expression.   4. The optical scanning device according to claim 1, wherein the measuring unit is disposed at a position corresponding to a laser irradiation position of the image carrier.   An optical scanning device according to claim 1 is provided, and image formation is performed by transferring a visible image obtained by developing a latent image formed on an image carrier by the optical scanning device onto a sheet. An image forming apparatus. In a control method of an optical scanning device for forming a latent image on the image carrier by irradiating the image carrier with a laser emitted by a laser emitting unit,
A measurement step of measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier by the laser emitting means;
An nth-order approximation formula (n ≧ 2) is calculated by nth-order approximation of measured values of illuminance at a plurality of laser irradiation positions measured in the measurement step with respect to a plurality of light amount setting values in a laser emitted from the laser emitting unit. A first calculation step;
Using the n-th order approximate expression calculated in the first calculation step, the illuminance at an arbitrary laser irradiation position on the image carrier measured in the measurement step, and at least one or more on the image carrier A second calculation step of calculating an illuminance difference from the illuminance at another laser irradiation position for the plurality of light amount setting values;
A third calculation step for calculating an illuminance correction value based on the illuminance difference calculated in the second calculation step;
And a control step of controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated in the third calculation step. In a control method of an optical scanning device for forming a latent image on the image carrier by irradiating the image carrier with a laser emitted by a laser emitting unit,
A measurement step of measuring the illuminance of the laser at a plurality of laser irradiation positions on the image carrier by the laser emitting means;
An nth-order approximation formula (n ≧ 2) is obtained by nth-order approximation of measured values of illuminance at a plurality of laser irradiation positions measured in the measurement step with respect to a plurality of light amount setting values in a laser emitted from the laser emitting unit. A first calculation step for calculating an expression obtained by differentiating the n-th order approximation expression;
Using an expression obtained by differentiating the nth-order approximate expression calculated in the first calculation step, the illuminance at an arbitrary laser irradiation position on the image carrier measured in the measurement step, and at least the image carrier A second calculation step of calculating an illuminance difference with illuminance at one or more other laser irradiation positions for the plurality of light amount setting values;
A third calculation step for calculating an illuminance correction value based on the illuminance difference calculated in the second calculation step;
And a control step of controlling the amount of laser light emitted by the laser light emitting means based on the illuminance correction value calculated in the third calculation step.   A computer-readable program for causing a computer to execute the control method for an optical scanning device according to claim 7 or 8.

Images