JP2013059906A - Laser light emission device, and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that if bias current supplied to respective plurality of light sources is determined based on a light receiving result of photodiode common to the plurality of light sources, the bias current having high accuracy cannot be set.SOLUTION: Light amount detected by a PD 13 using Pofs_a, or emission property based on a detection result of the PD 13 is corrected, and the actual emission property of each LD is calculated to determine the bias current of the each LD from the actual emission property.

Description

  The present invention relates to a laser light emitting device that emits laser light and an image forming apparatus including the laser light emitting device.

  FIG. 9A shows the relationship between the drive current and the amount of emitted light as one of the emission characteristics of the semiconductor laser. In FIG. 9A, the horizontal axis represents the drive current supplied to the semiconductor laser, and the vertical axis represents the light emission amount (intensity) of the laser beam with respect to the drive current supplied to the semiconductor laser. In general, it is known that a semiconductor laser exhibits light emission characteristics as shown in FIG. As shown in FIG. 9A, in the region where the value of the current supplied to the light emitting element is lower than the threshold current (Ith) (spontaneous emission region), the increase in the amount of emitted light is moderate with respect to the increase in current. On the other hand, in the region (laser oscillation region) higher than the threshold current, the amount of increase in the amount of emitted light with respect to the amount of increase in current increases relative to the spontaneous emission region.

  Incidentally, an electrophotographic image forming apparatus such as a laser beam printer forms an electrostatic latent image by scanning a photosensitive member with laser light emitted from a semiconductor laser, and develops the electrostatic latent image with toner. By doing so, an image is formed. In such an image forming apparatus, in recent years, it has become necessary to switch a semiconductor laser on and off at a high speed in order to achieve high resolution and high printing speed. Therefore, it is necessary to improve the light emission response of the semiconductor laser.

  As a method for improving the light emission response of a semiconductor laser, a method of supplying a bias current (Ib) to the semiconductor laser has been conventionally known. The bias current is a current set to a value near the threshold current. A semiconductor laser used in a laser beam printer or the like is supplied with a bias current, and when emitted from the semiconductor laser, a driving current in which a switching current is superimposed on the bias current is supplied to the semiconductor laser. By supplying a bias current to the semiconductor laser, it is possible to improve the light emission response of the semiconductor laser when the switching current is supplied, compared to the case where the bias current is not supplied.

  Patent Document 1 discloses a method for controlling a bias current. As shown in FIG. 9A, the laser diode driving device described in Patent Document 1 specifies the threshold current Ith based on the light emission characteristics of the laser diode in the laser oscillation region, and a predetermined coefficient α (α It is described that the bias current Ib is determined by multiplying ≦ 1).

JP-A-11-245444

  However, in the apparatus that exposes the photosensitive member with a plurality of laser beams emitted from a plurality of light emitting elements in order to increase the image forming speed, the bias current control method described in Patent Document 1 is used. There arises a problem that cannot be set with high accuracy.

  When determining the value of the bias current, a driving current for causing the light emitting element to be controlled to emit light with the first light amount P1 and the second light amount P2 is supplied. At this time, the drive current is controlled while detecting the light amount using a detection device such as a PD (photodiode), and the drive current when the first light amount is detected and the drive when the second light amount is detected. Each current is sampled. From these results, the light emission characteristics in the laser oscillation region of the light emitting element to be controlled are specified.

  At this time, a bias current is supplied to the light emitting elements other than the controlled object in order to ensure the light emission response. Since the PD is commonly used for a plurality of light emitting elements and is disposed in the vicinity of the plurality of light emitting elements, laser light spontaneously emitted from the light emitting elements when a bias current is supplied enters the PD. To do. Therefore, the PD detection result includes the amount of laser light from light emitting elements other than the control target. Then, as shown in FIG. 9B, the bias current of the light emitting element to be controlled is determined based on the light emission characteristic different from the actual light emission characteristic, and the value of the bias current cannot be accurately determined. Challenges arise.

  The present invention has been made in view of the above problems, and a laser beam emitting apparatus according to the present invention includes a first light emitting point that emits a first laser beam and a second light emitting point that emits a second laser beam. And a first drive current obtained by superimposing a switching current on the first bias current based on a first bias current or image data corresponding to the first light emission point. A second driving current obtained by superimposing a switching current on the second bias current based on the second bias current or image data corresponding to the second light emitting point is applied to the second light emitting point. A current supply means for supplying the light; a light receiving portion for receiving the first laser light and the second laser light; a detection means for generating received light amount data corresponding to the received light amount of the light receiving portion; The second bias current is Storage means for storing light quantity data corresponding to the light quantity of the second laser light emitted when supplied to the second light emitting point, and the current supply means at the first light emitting point. And the first drive based on the received light amount data and the light amount data generated by the detection means in a state where the second bias current is supplied to the second light emitting point. A light emission characteristic indicating a correspondence relationship between the value of the current and the amount of the first laser beam emitted from the first light emission point is determined based on the first drive current, and the first characteristic is determined based on the light emission characteristic. Determining means for determining a value of one bias current.

  In a laser emitting device that controls a bias current supplied to a light emitting point based on a result of receiving a plurality of laser beams emitted from a plurality of light emitting points by a common light receiving means, the value of the bias current is controlled with high accuracy. Can do.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus according to an embodiment. FIG. 2 is a schematic diagram schematically showing an optical scanning device and a photosensitive drum. The perspective view of a semiconductor laser. The block diagram of a laser diode drive device (laser beam emitting device). The figure which shows the operation mode of the current control part and current drive part in a laser diode drive device. The figure which shows the timing chart of APC. The figure for demonstrating the light emission characteristic of a laser diode. 7 is a control flow executed by the image forming apparatus according to the present embodiment. (A) The figure which shows the relationship between the drive current as one of the light emission characteristics of a semiconductor laser, and the amount of emitted light, (b) The figure which shows the relationship between an actual light emission characteristic and the light emission characteristic produced | generated.

Example 1
FIG. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus 100 according to the present embodiment, and illustrates a schematic configuration of an electrophotographic full-color printer. In the image forming apparatus 100 shown in FIG. 1, the photosensitive drums 101a to 101d, which are photosensitive members corresponding to the respective colors, are charged to a predetermined potential (charging potential) by the charging devices 102a to 102d. Each charged photosensitive drum is exposed to a laser beam (light beam) emitted from an optical scanning device 200a to 200d including a laser light source (semiconductor laser or the like), and an electrostatic latent image is formed on the surface. This electrostatic latent image is developed with toner by each of the developing units 103a to 103d. The toner images of the respective colors developed on the photosensitive drums 101a to 101d are transferred to the intermediate transfer belt 105 by a transfer bias applied to the transfer blades 104a to 104d. The four colors of the toner image transferred onto the intermediate transfer belt 105 are collectively transferred onto the recording paper S by the secondary transfer roller 106. Thereafter, the recording paper S carrying the toner image passes through the fixing device 107 and is subjected to fixing processing. After the fixing process, the paper is discharged out of the apparatus by a paper discharge roller 108 or the like.

The recording paper S is fed from the paper feed cassette 109 or the manual feed tray 110. The registration roller 111 is a roller for adjusting the timing at which the fed recording sheet S is conveyed to the secondary transfer roller 106. At the time of duplex printing, the recording sheet S that has passed through the fixing device 107 is guided in the direction of the duplex reversing path 112, reversed and conveyed in the reverse direction, and conveyed to the duplex path 113. The recording sheet S that has passed through the double-sided path 113 passes through the vertical path roller 114 again, and forms, transfers, and fixes the image on the second side in the same manner as the first side, and is discharged.
[Configuration of scanner (optical scanning device)]
Since the four optical scanning devices are the same, the optical scanning device 200a will be described as an example. FIG. 2 is a schematic view schematically showing the optical scanning device 200a and the photosensitive drum 101a. The optical scanning device 200a includes a semiconductor laser 201 (LD: laser diode) as a light source, a collimator lens 202, an aperture stop 203, a cylindrical lens 204, a polygon mirror 205, a polygon mirror driving unit 206, a toric lens 207, and a diffractive optical element. 208.

  The collimator lens 202 converts the light beam emitted from the semiconductor laser 201 into a parallel light beam. The aperture stop 203 restricts the luminous flux of the light beam that passes therethrough. The cylindrical lens 204 has a predetermined refractive power only in the sub-scanning direction, and forms a light beam that has passed through the aperture stop 203 as an elliptical image that is long in the main scanning direction on the reflection surface of the polygon mirror 205. The polygon mirror 205, which is a rotating polygon mirror, is rotated at a constant speed in the direction of arrow C in the figure by the polygon mirror driving unit 206, and deflects (reflects) the laser light imaged on the reflecting surface. The toric lens 207 is an optical element having fθ characteristics and has different refractive indexes in the main scanning direction and the sub-scanning direction. Both the front and back lens surfaces of the toric lens 207 in the main scanning direction have an aspherical shape. The diffractive optical element 208 is an optical element having fθ characteristics, and has different magnifications in the main scanning direction and the sub-scanning direction. A beam detector 209 (hereinafter referred to as BD209), which is a laser beam detecting means, is installed at a position corresponding to the outside of the image forming area of the photosensitive drum 101a included in the image forming apparatus 100, and is reflected by the reflecting mirror 210. By detecting this, a scanning timing signal (BD signal) is generated.

  On the photosensitive drum 101a, the spot of the laser beam deflected by the reflecting surface of the polygon mirror 205 that is driven to rotate moves (scans) linearly in parallel with the drum axis. The optical scanning device 200a in this embodiment includes a semiconductor laser 201 having a plurality of light emitting elements. The semiconductor laser 201 emits a plurality of beams, whereby a plurality of line-shaped electrostatic latent images can be formed by one scan. The photosensitive drum 101a is rotationally driven by the driving unit 211, and thereby the main scanning is turned back, whereby the image writing is performed in the sub-scanning direction (rotating direction of the photosensitive drum).

  FIG. 3 is a perspective view of the semiconductor laser according to the first embodiment. A base 11 is provided on one surface of the stem 10, and a light emitting point 12a (first light emitting point; hereinafter referred to as an LD 12a) for emitting a first laser beam as a laser light source on the base 11 and a second. A photodiode 13 (PD), which is a light receiving part for receiving the back light of the laser diode 12 (LD) having 12b (second light emitting point; hereinafter referred to as LD 12b), which emits the laser light of is fixed. The PD 13 generates received light amount data corresponding to the received light amount. A cap 14 is attached to the stem 10 so as to cover the base 11 on which these LD 12 and PD 13 are placed, and a window 15 that transmits laser beams La and Lb is provided on the tip surface of the cap 14. Further, on the opposite surface of the stem 10, an energization terminal 16 is provided for connecting the laser chip 12 and the PD 13 to a laser drive control system (not shown).

  FIG. 4 is a block diagram of a laser diode driving device (laser beam emitting device) according to the present embodiment. The laser diode driving device 11 is connected to the LD 12a, LD 12b, PD 13, the image signal generation unit 14, and the control unit 15.

  The image signal generation unit 14 outputs an image signal from a controller (not shown) to the laser diode driving device 11 as data signals (DATA_P, DATA_N) for LD driving at a predetermined timing. The control unit 15 outputs an external control signal for controlling the operation of the laser diode driving device 11 to the laser diode driving unit 11. Further, the control unit 15 performs data communication such as target voltage data to the laser diode driving device 11.

  The laser diode control unit 11 includes a laser control unit 16 and a mode control unit 17. The mode control unit 17 outputs a signal for controlling the operation mode of the laser control unit 16 and the gain of the current-voltage conversion circuit 18 in accordance with the external control signal from the control unit 15. The laser drive unit 16 functions as means for controlling the LD 12 to the target light amount. The PD 13 serving as a light amount detecting unit for detecting the light amount of the laser light output from the LD 12 outputs a current corresponding to the detected light amount of the laser light. The current output from the PD 13 is converted into a voltage with a predetermined gain by the current-voltage conversion circuit 18 and output as a PD output voltage. The gain of the current-voltage conversion circuit 18 is determined by a gain switching signal from the mode control unit 17.

  The PD output voltage-converted by the current-voltage conversion circuit 18 is input to the comparator 19 and compared with a target voltage (hereinafter referred to as Vref) set in the target voltage setting unit 20. The target voltage setting unit 20 includes a not-shown DAC (Digital-Analog-Converter), and outputs a voltage corresponding to the target voltage data set by the control unit 15.

  The comparator 19 compares the PD output voltage with Vref and outputs a comparison result (voltage difference) to the current control unit 21. The current control unit 21 performs a current control operation according to a signal from the mode control unit 17. In accordance with the comparison result from the comparator 19, the drive current is controlled so that the LD 12 has a target light amount. The current value here is held as digital data. Detailed operation will be described later.

The current control unit 21 outputs the current value determined by the APC to the threshold current calculation unit 22.
The threshold current calculation unit 22 is determined by the current control unit 21 for two types of light amounts (hereinafter, the higher light amount is APC_H and the lower light amount is APC_L, which will be described in detail later). The threshold current (Ith) is calculated on the basis of the current that has been applied and the gain switching signal from the mode control unit 17. The threshold current calculation unit 22 calculates a first threshold current corresponding to the LD 12a, and calculates a second threshold current corresponding to the LD 12b.

  The bias current calculation unit 23 calculates a first bias current to be applied to the LD 12a from the first threshold current calculated by the threshold current calculation unit 22, and a second bias current to be applied to the LD 12b from the second threshold current. The first bias current value is set to be a value equal to or less than the first threshold current value, and the second bias current value is set to be a value equal to or less than the second threshold current value. In this embodiment, the bias current value is calculated by multiplying the threshold current value by a predetermined coefficient α (α ≦ 1). Further, the bias current calculation unit 23 sets a bias current value to be applied to each LD to the DAC (DAC_Ib_a24a, DAC_Ib_b24b) which is a bias current supply unit based on the beam selection signal from the mode control unit 17. The DAC_Ib_a24 applies a current corresponding to the set bias current value to the LD 12a as a first bias current. The DAC_Ib_b 24 applies a current corresponding to the set bias current value to the LD 12 as a first bias current.

  The switching current calculator 25 calculates a switching current to be applied to the LD 12 from the current value determined by the current controller 21 and the threshold current (Ith) calculated by the threshold current calculator 22. Further, the switching current calculation unit 25 sets to a predetermined switching current DAC (DAC_Isw_a 26a, DAC_Isw_b) by a beam selection signal from the mode control unit 17. The DAC_Isw 26 applies a current corresponding to the set current value to the current driver 27.

  The current driving unit 27 supplies a switching current to the LD 12a and the LD 12b at a timing based on the image data (DATA_P, DATA_N) from the image signal generation unit 14 in accordance with a signal from the mode control unit 17. That is, the first bias current is always supplied to the LD 12a during image formation, and the first bias current is superimposed on the first bias current in accordance with the image data (first switching current corresponding to the LD 12a). A drive current is applied. A second bias current is always supplied to the LD 12b during image formation, and a second drive current in which a switching current (second switching current corresponding to the LD 12b) is superimposed on the second bias current according to image data. Is applied. The sensitivity of the photosensitive drum is designed so that the surface potential is not displaced by the amount of laser light emitted from the LD 12a and LD 12b when only the bias current is supplied. The surface potential of the photosensitive drum is displaced by the laser beam emitted by supplying the driving current.

  Here, various control modes of the laser by the laser diode driving device 11 shown in FIG. 4 will be described in detail with reference to FIG. FIG. 5 is an operation mode chart of the current controller 21 and the current driver 27 in the laser diode driver 11.

(Automatic light control mode)
The automatic light amount control is hereinafter referred to as APC (Auto Power Control). While only the APC signal is input from the mode control unit 17, the current driving unit 27 forces the LD 12 to emit light based on the current set in the DAC_Isw 26 regardless of the output of the image signal generation unit 14. ON data is output to. At this time, the current driver 27 forcibly turns on only the beam data selected by the beam selection signal from the mode controller 17 and forcibly outputs OFF data to the other beams.
In the initial state, the current values of DAC_Ib24 and DAC_Isw26 are set to 0.

  The laser light emitted from the LD 12 is received by the monitoring PD 13. The PD 13 outputs a current corresponding to the amount of received laser light. The current-voltage conversion circuit 18 converts the output current from the PD 13 into a voltage with a gain corresponding to the gain switching signal from the mode control unit 17. The comparator 19 compares the output voltage from the current-voltage conversion circuit 18 with Vref, and outputs a voltage difference to the current control unit 21 as a comparison result. While only the APC signal is input from the mode control unit, the current control unit 21 performs control to set the light emission amount of the LD 12 as a predetermined light amount by a signal according to the voltage difference.

  When the PD output voltage> Vref, it is determined that the light emission amount of the LD 12 (LD to be controlled) is larger than the predetermined light amount, and the light emission amount of the LD 12 is reduced by reducing the current value set in the DAC_Isw26 (or DAC_Ib24).

  When the PD output voltage <Vref, it is determined that the light emission amount of the LD 12 is smaller than the predetermined light amount, and the light emission amount of the LD 12 is increased by increasing the current value set in the DAC_Isw26 (and the DAC_Ib24).

  When the PD output voltage = Vref, it is determined that the light emission amount of the LD 12 is the same as the predetermined light amount, and the current value set in the DAC_Isw26 (or DAC_Ib24) is not increased or decreased.

  The current control unit 21 does not increase or decrease the current values set in the DAC_Isw 26, DAC, and Ib 24 even while only the VIDEO mode signal is input from the mode control unit.

  FIG. 6 is an APC timing chart of the LD 12a and LD 12b. As shown in FIG. 6, the APC of each LD is performed once during one scanning cycle. First, a drive current is supplied to the LD 12a so that the amount of laser light emitted from the LD 12a is P1 (for example, FIG. 9A) (APCL1). Thereafter, a drive current is supplied to the LD 12a so that the amount of laser light emitted from the LD 12a becomes P2 (for example, FIG. 9A) (APCH1). Subsequently, APC of the LD 12b is performed. A drive current is supplied to the LD 12a so that the amount of laser light emitted from the LD 12b is P1 (APCL2). Thereafter, a drive current is supplied to the LD 12b so that the amount of laser light emitted from the LD 12b is P2 (APCH2). The bias current supplied to the LD 12a is determined from the light emission characteristics corresponding to the LD 12a obtained by performing the APCL1 and the APCH1. Further, the bias current supplied to the LD 12b is determined from the light emission characteristics corresponding to the LD 12b obtained by performing the APCL2 and the APCH2.

(OFF mode)
When the VIDEO mode signal and the APC signal are simultaneously input from the mode control unit 17, the current driving unit 27 determines that the current mode is the OFF mode and depends on the image data signal (DATA_P, DATA_N) from the image signal generation unit 14. First, OFF data is forcibly output so that the LD 12 is turned off. That is, in the OFF mode, only the bias current is applied to the LD 12.

  When the VIDEO mode signal and the APC signal are simultaneously input from the mode control unit 17, the current control unit 21 determines that the mode is OFF mode and holds (holds) the current value. Hereinafter, the laser diode driving device using the OFF mode will be described, but an OFF mode in which no bias current is applied may be used.

(Data output mode)
The current driving unit 27 performs the VIDEO mode operation while only the VIDEO signal is input from the mode control unit. In the VIDEO mode, a drive current is output to the LD 12 according to the image data signal from the image signal generation unit 14 by using the current from the DAC_Isw 26 and the DAC_Ib 24 determined by the APC operation.
The current control unit 21 holds the current value while only the VIDEO signal is input from the mode control unit.

(Discharge mode)
When neither the APC signal nor the VIDEO mode signal is input from the mode control unit 17, the current control unit 21 enters the discharge mode, initializes the current value, and initializes the current values set in the DAC_Isw26 and the DAC_Ib24. The current driver 27 forcibly outputs OFF data when neither the APC signal nor the VIDEO mode signal is input.

  Here, the characteristics of the laser diode driving apparatus of the present embodiment will be described. The laser diode driving apparatus of this embodiment executes APC of the light emitting point 12a in a state where a bias current is supplied to the light emitting point 12b. At this time, the amount of light received by the PD 13 includes the amount of laser light emitted from the light emitting point 12a and the amount of laser light spontaneously emitted from the light emitting point 12b when a drive current is supplied. Therefore, the light emission characteristic in the laser oscillation region of the light emission point 12a based on the amount of light received by the PD 13 is different from the light emission characteristic of the actual light emission point 12a. As shown in FIG. 9B, the threshold current determined from the light emission characteristics of the light emission point 12a based on the light received by the PD 13 is lower than the threshold current determined from the actual light emission characteristics. Therefore, the bias current obtained from the threshold current is set to a value greatly deviating from the threshold current of the actual light emission characteristics, leading to a decrease in light emission response.

  The image forming apparatus of this embodiment solves such a problem with the following configuration. FIG. 7 is a diagram for explaining the light emission characteristics, and FIG. 8 is a flowchart showing a control flow executed in the image forming apparatus in order to execute the control shown in FIG. FIG. 7 is a diagram showing the light emission characteristics indicating the correspondence between the drive current supplied to the LD 12a or the LD 12b and the amount of light.

  First, in step S801, the mode switching unit 17 outputs a gain switching signal such that the gain becomes x1, and the gain of the current / voltage conversion circuit 18 is set to x1. In step S802, an APC signal and a VIDEO mode signal are output, and the LD 12a and LD 12b are forcibly turned off. At this time, the bias current determined in the previous APC operation is applied to the LD 12a and LD 12b. At this time, the current calculation unit 21 calculates a comparison result between the PD output (Pofs_a + Pofs_b) voltage-converted by the current / voltage conversion circuit 18 with gain × 1 and Vref. Pofs_a is light amount data obtained by supplying a current equal to or smaller than the threshold current Ith to each LD at the time of factory shipment and detecting the light amount at that time. Pofs_a is stored in a memory serving as a storage unit in association with each of the LD 12a and the LD 12b. For this result, the value of Pofs_a determined in the previous APC operation of the LD 12b is subtracted and stored in the memory 28 as the light amount Pofs_b that affects the LD 12a due to bias emission of the LD 12b. At this time, Vref is 0 or a known numerical value is applied from the control unit 15.

  In step S803, an APC signal and a beam selection signal are output from the mode switching unit 17, and the LD 12a is forced to emit light. The APC operation is performed in accordance with the comparison result between the PD output obtained by the current / voltage conversion circuit 18 performing voltage conversion with a gain × 1 in the current calculation unit 21 and Vref, and the LD 12a is controlled to a predetermined light amount (Pa + Pofs_b). The predetermined light quantity at this time is a light quantity obtained by adding Pofs_b obtained in S802 to Pa.

  The current value (I_A1) at this time is stored in the memory 28. Thereafter, both the APC signal and the VIDEO mode signal are output from the mode switching unit 17 to forcibly turn off the LD 12a (off mode).

  In step S804, in order to cause the LD 12a to emit light with a ¼ light amount, a gain switching signal is output from the mode switching 17 so that the gain becomes x4, and the gain of the current / voltage conversion circuit 18 is set to x4. Thereafter, an APC signal and a beam selection signal are output from the mode switching unit 17 to force the LD 12a to emit light. The APC operation is performed in accordance with the comparison result between the PD output voltage-converted by multiplying the current / voltage conversion circuit 18 gain by the current calculation unit 21 and Vref, and the LD 12a is controlled to a predetermined light amount (Pa / 4 + Pofs_b). The predetermined light quantity at this time is the light quantity obtained by adding Pofs_b obtained in S802 to Pa / 4.

  The current value (I_A) at this time is stored in the memory 28. Thereafter, both the APC signal and the VIDEO mode signal are output from the mode switching unit 17 to forcibly turn off the LD 12b (off mode).

  In step S805, the threshold current calculation unit 22 calculates the threshold current Ith from Pa and Pa / 4 obtained by subtracting Pofs_b and the currents I_A1 and I_A2 corresponding to the amounts of light. In step S806, the bias current and the switching current are determined. .

  In step S807, the mode switching unit 17 outputs a gain switching signal that gives a gain of x1, and sets the gain of the current / voltage conversion circuit 18 to x1. In step S808, the APC signal and the VIDEO mode signal are output, and the LD 12a and LD 12b are forcibly turned off. At this time, the bias current determined in the previous APC operation is applied to the LD 12a and LD 12b. At this time, the current calculation unit 21 calculates a comparison result between the PD output (Pofs_a + Pofs_b) voltage-converted by the current / voltage conversion circuit 18 with gain × 1 and Vref. The value of Pofs_b determined in steps S801 to S806 is subtracted from this result and stored in the memory 28 as the light amount Pofs_a that affects the LD 12b due to the bias emission of the LD 12a. At this time, Vref is 0 or a known numerical value is applied from the control unit 15.

  In step S809, an APC signal and a beam selection signal are output from the mode switching unit 17, and the LD 12a and the light are forcedly emitted. The APC operation is performed in accordance with the comparison result between the PD output obtained by the current / voltage conversion circuit 18 performing voltage conversion with a gain × 1 in the current calculation unit 21 and Vref, and the LD 12b is controlled to a predetermined light amount (Pb + Pofs_a). The predetermined light quantity at this time is the light quantity obtained by adding Pofs_a obtained in S808 to Pb. The current value (I_B1) at this time is stored in the memory 28. Thereafter, both the APC signal and the VIDEO mode signal are output from the mode switching unit 17 to forcibly turn off the LD 12b (off mode).

  In step S810, in order to cause the LD 12b to emit light with a ¼ light amount, a gain switching signal is output from the mode switching 17 so that the gain becomes x4, and the gain of the current / voltage conversion circuit 18 is set to x4. Thereafter, an APC signal and a beam selection signal are output from the mode switching unit 17 to force the LD 12b to emit light. The APC operation is performed according to the comparison result between the PD output converted by the current / voltage conversion circuit 18 gain by the current calculation unit 21 and Vref, and the LD 12b is controlled to a predetermined light amount (Pb / 4 + Pofs_a). The predetermined light quantity at this time is the light quantity obtained by adding Pofs_a obtained in S808 to Pb / 4. The current value (I_B2) at this time is stored in the memory 28. Thereafter, both the APC signal and the VIDEO mode signal are output from the mode switching unit 17 to forcibly turn off the LD 12b (off mode).

  In step S811, the threshold current calculation unit 22 calculates the threshold current Ith from Pb and Pb / 4 obtained by subtracting Pofs_a and the currents I_B1 and I_B2 corresponding to the amounts of light. In step S812, the bias current and the switching current are determined. .

  As described above, the image forming apparatus according to the present exemplary embodiment corrects the light emission characteristic based on the light amount detected by the PD 13 or the detection result of the PD 13 using Pofs_a, and obtains the actual light emission characteristic of each LD. The bias current can be set with high accuracy.

Claims (4)

A laser light source comprising a first light emitting point for emitting the first laser light and a second light emitting point for emitting the second laser light;
Based on a first bias current corresponding to the first light emission point or image data, a first drive current obtained by superimposing a switching current on the first bias current is used as the second light emission point. Current supply means for supplying a second drive current obtained by superimposing a switching current on the second bias current to the second light emitting point based on the second bias current or image data corresponding to the light emitting point When,
A detector that receives the first laser beam and the second laser beam;
Storage means for storing light amount data corresponding to the light amount of the second laser beam emitted when the second bias current is supplied to the second light emitting point;
The received light amount generated by the detection means in a state where the current supply means supplies the first drive current to the first light emission point and supplies the second bias current to the second light emission point. Based on the data and the light amount data, a correspondence relationship between the value of the first drive current and the light amount of the first laser beam emitted from the first light emission point based on the first drive current is obtained. A laser light emitting apparatus comprising: determining means for determining a light emission characteristic to be displayed and determining a value of the first bias current based on the light emission characteristic.   The determining means determines a value obtained by subtracting a light amount based on the light amount data from the received light amount as a light amount of the first laser light emitted from the first light emission point based on the first drive current. The laser beam emitting apparatus according to claim 1.   The determination means determines a first threshold current value corresponding to the first light emission point from the light emission characteristics, and the value of the first bias current becomes a current value equal to or less than the first threshold current value. The laser beam emitting apparatus according to claim 1, wherein the value of the first bias current is controlled as described above. The laser beam emitting device according to any one of claims 1 to 3,
A photoconductor exposed by the first laser beam and the second laser beam;
An image forming apparatus comprising: a developing unit that develops an electrostatic latent image formed by exposure with the first laser light and the second laser light.

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