JP6379809B2 - Light emitting element head and image forming apparatus - Google Patents

Description

  The present invention relates to a light emitting element head and an image forming apparatus.

  In image forming apparatuses such as printers, copiers, and facsimiles that employ an electrophotographic method, after obtaining an electrostatic latent image by irradiating image information onto a uniformly charged photoreceptor by optical recording means The electrostatic latent image is visualized by adding toner, and the image is formed by transferring and fixing on the recording paper. As such an optical recording means, in addition to an optical scanning method in which a laser beam is scanned in a main scanning direction using a laser for exposure, in recent years, a large number of LED (Light Emitting Diode) array light sources are arranged in the main scanning direction. An optical recording means using an LED head is employed.

In Patent Document 1, in the LPH driving unit, the control unit sets the lighting time reference data in the total light amount instruction unit, thereby uniformly controlling the exposure amount of all LEDs (all dots) of the SLED. Further, an image forming apparatus that corrects the lighting time of each LED within the lighting possible time so as to eliminate the density unevenness by correcting the lighting time reference data based on the density unevenness correction data in the calculation unit is disclosed. Has been.
Patent Document 2 discloses the current and voltage of the exposure control signal so that the relationship between the exposure amount and the exposure time of the light source controlled by the exposure control signal for storing the density adjustment data and controlling the LPH lighting is linear. And an image forming apparatus that corrects at least one of the exposure time.

JP 2002-36628 A JP 2003-182143 A

  When a light source using a light emitting element such as an LED is employed in the image forming apparatus, variation in exposure amount for each light emitting element may increase when a change in lighting time is large. It is an object of the present invention to provide a light emitting element when the lighting time per light emitting element exceeds a predetermined first time as compared with a case where the light emitting element is not turned on using a plurality of times less than the first time. It is to reduce the variation of the exposure amount for each.

The invention according to claim 1 is a plurality of light emitting elements arranged along the main scanning direction and sequentially lit, an optical element for imaging an optical output of the plurality of light emitting elements, and the plurality of light emitting elements. of when the lighting time per each light emitting element exceeds a first predetermined time, and a control unit for lighting with several times less time the first time, the control When the lighting time per time of each light emitting element exceeds the predetermined first time, the unit lights up using a time equal to or longer than a predetermined second time, and the first The light emitting element head is characterized in that the time is set longer than the lighting time when the light quantity of each light emitting element is corrected, and the second time is set shorter than the lighting time when the light quantity of each light emitting element is corrected. It is.
According to a second aspect of the present invention, the control unit generates a lighting signal for controlling lighting and extinguishing of each light emitting element by dividing the light emitting element into a plurality of times less than the first time. The light emitting element head according to claim 1 , wherein the light emitting element head is turned on.
According to a third aspect of the present invention, there is provided an image carrier that holds an image, a charging unit that charges the surface of the image carrier, and light emitted from a plurality of light-emitting elements that are arranged in the main scanning direction and sequentially light up. An electrostatic latent image forming unit that exposes the image carrier to form an electrostatic latent image, a developing unit that develops the electrostatic latent image to form a toner image, and each of the light emitting elements. when more than a first time lighting time per element is predetermined, and a control unit for lighting with several times less time the first time, the control unit, respectively When the lighting time of each light emitting element exceeds the predetermined first time, the light emitting element is turned on using a time equal to or longer than a predetermined second time, and the first time is Lighting time with light amount correction of Ri large and the image forming apparatus characterized by setting smaller than the corrected lighting time of performing the light amount of the second time respectively of the light emitting element.

According to invention of Claim 1, when the lighting time per time of a light emitting element exceeds predetermined 1 time, compared with the case where it is not made to light by using time less than 1st time in multiple times. In addition, it is possible to provide a light emitting element head in which variation in exposure amount for each light emitting element is further reduced. Further, the variation in the exposure amount for each light emitting element is further reduced as compared with the case where the lighting is not performed using a time longer than the second time. Further, the first time is longer than the lighting time when the light amount of each light emitting element is corrected, and the second time is not set shorter than the lighting time when the light amount of each light emitting element is corrected. The variation in exposure amount for each element is further reduced.
According to the second aspect of the present invention, the lighting time can be controlled more easily than when the lighting signals are not generated separately.
According to invention of Claim 3 , when the lighting time per time of a light emitting element exceeds predetermined 1st time, compared with the case where it is not made to light by using time below 1st time in multiple times. It is possible to provide an image forming apparatus capable of suppressing the generation of streaks in the formed image.

1 is a diagram illustrating an outline of an image forming apparatus according to an embodiment. It is the figure which showed the structure of the light emitting element head to which this Embodiment is applied. It is a top view of the circuit board and the light emission part in a light emitting element head. (A)-(b) is the figure explaining the structure of the light emitting chip to which this Embodiment is applied. It is the figure which showed the structure of the signal generation circuit at the time of employ | adopting a self-scanning light emitting element array chip as a light emitting chip, and the wiring structure of a circuit board. It is a figure for demonstrating the circuit structure of a light emitting chip. It is a figure explaining the timing chart. (A)-(b) is the figure explaining the dispersion | variation in the exposure amount by each LED when changing lighting time uniformly. (A) is the figure which showed the lighting signal when lighting one LED once. (B) is a lighting profile of the LED when the lighting signal of (a) is input. (C) is the figure which showed the exposure amount when changing a pulse width. (A) is the figure which showed the lighting signal after correct | amending with respect to the lighting signal of Fig.9 (a). (B) is a lighting profile of the LED when the lighting signal of (a) is input. (C) is the figure which showed the exposure amount when changing a pulse width. It is a block diagram showing the functional structural example of the signal generation circuit in this embodiment. (A)-(d) is the figure which showed the method of dividing | segmenting a lighting signal into a some pulse. (A)-(b) compared the use range of lighting time in the case where the LED was lit without dividing the lighting signal and the case where the LED was lit by dividing the lighting signal multiple times. FIG.

<Description of Overall Configuration of Image Forming Apparatus>
Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an outline of an image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 is an image forming apparatus generally called a tandem type. The image forming apparatus 1 includes an image forming unit 10 that forms an image corresponding to image data of each color. The image forming apparatus 1 further includes an intermediate transfer belt 20 that sequentially transfers (primary transfer) and holds the color component toner images formed by the image forming units 11. The image forming apparatus 1 further includes a secondary transfer device 30 that collectively transfers (secondary transfer) the toner image transferred to the intermediate transfer belt 20 onto the paper P. Furthermore, the image forming apparatus 1 includes a fixing device 50 that fixes the second-transferred toner image on the paper P. Further, the image forming apparatus 1 includes an image output control unit 90 that controls each mechanism unit of the image forming apparatus 1 and performs predetermined image processing on the image data.

  The image forming unit 10 includes, for example, a plurality (four in the present embodiment) of image forming units 11 (specifically, 11Y (yellow), 11M (magenta)) on which each color component toner image is formed by electrophotography. 11C (cyan), 11K (black)).

  Each image forming unit 11 (11Y, 11M, 11C, 11K) has the same configuration except for the color of the toner used. Therefore, the yellow image forming unit 11Y will be described as an example. The yellow image forming unit 11Y includes a photosensitive drum 12 that has a photosensitive layer (not shown) and is rotatably arranged in the direction of arrow A. Around the photosensitive drum 12, a charging roll 13, a light emitting element head 14, a developing device 15, a primary transfer roll 16, and a drum cleaner 17 are disposed. Among these, the charging roll 13 is rotatably disposed in contact with the photosensitive drum 12, and charges the photosensitive drum 12 to a predetermined potential. The light emitting element head 14 irradiates the photosensitive drum 12 charged to a predetermined potential by the charging roll 13 with light, and writes an electrostatic latent image. The developing unit 15 stores corresponding color component toner (yellow toner in the yellow image forming unit 11Y), and develops the electrostatic latent image on the photosensitive drum 12 with this toner. The primary transfer roll 16 primarily transfers the toner image formed on the photosensitive drum 12 to the intermediate transfer belt 20. The drum cleaner 17 removes residues (toner and the like) on the photosensitive drum 12 after the primary transfer.

  The photosensitive drum 12 functions as an image holding body that holds an image. The charging roll 13 functions as a charging unit that charges the surface of the photosensitive drum 12, and the light emitting element head 14 functions as an electrostatic latent image forming unit that exposes the photosensitive drum 12 to form an electrostatic latent image. To do. Further, the developing device 15 functions as a developing unit that develops the electrostatic latent image to form a toner image.

The intermediate transfer belt 20 as an image transfer member is rotatably supported by a plurality of (five in the present embodiment) support rolls. Of these support rolls, the drive roll 21 stretches the intermediate transfer belt 20 and drives the intermediate transfer belt 20 to rotate. Further, the tension rolls 22 and 25 tension the intermediate transfer belt 20 and rotate according to the intermediate transfer belt 20 driven by the drive roll 21. The correction roll 23 is a steering roll that stretches the intermediate transfer belt 20 and restricts meandering in a direction substantially orthogonal to the conveyance direction of the intermediate transfer belt 20 (is disposed so as to be tiltable about one end in the axial direction). Function. Further, the backup roll 24 stretches the intermediate transfer belt 20 and functions as a constituent member of the secondary transfer device 30 described later.
Further, a belt cleaner 26 for removing residues (toner and the like) on the intermediate transfer belt 20 after the secondary transfer is disposed at a portion facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween.

  The secondary transfer device 30 includes a secondary transfer roll 31 disposed in pressure contact with the toner image holding surface side of the intermediate transfer belt 20 and a counter electrode of the secondary transfer roll 31 disposed on the back surface side of the intermediate transfer belt 20. And a backup roll 24. A power supply roll 32 that applies a secondary transfer bias having the same polarity as the charging polarity of the toner is disposed in contact with the backup roll 24. On the other hand, the secondary transfer roll 31 is grounded.

  The paper transport system includes a paper tray 40, a transport roll 41, a registration roll 42, a transport belt 43, and a discharge roll 44. In the paper transport system, the paper P stacked on the paper tray 40 is transported by the transport roll 41, and then temporarily stopped by the registration roll 42, and then the secondary transfer position of the secondary transfer device 30 at a predetermined timing. To send. Further, the sheet P after the secondary transfer is conveyed to the fixing device 50 via the conveying belt 43, and the sheet P discharged from the fixing device 50 is sent out to the outside by the discharge roll 44.

  Next, a basic image forming process of the image forming apparatus 1 will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, for example, when the image forming apparatus 1 is configured as a printer, the image output control unit 90 first receives image data input from the outside such as a PC (personal computer). The received image data is subjected to image processing by the image output control unit 90 and supplied to the image forming unit 11. The image forming unit 11 performs toner image formation for each color. That is, each image forming unit 11 (specifically, 11Y, 11M, 11C, and 11K) is driven according to the digital image signal of each color. Next, in each image forming unit 11, the photosensitive drum 12 charged by the charging roll 13 is irradiated with light corresponding to the digital image signal by the light emitting element head 14, thereby forming an electrostatic latent image. Then, the electrostatic latent image formed on the photosensitive drum 12 is developed by the developing device 15 to form toner images of each color. In the case where the image forming apparatus 1 is configured as a copying machine, a document set on a document table (not shown) is read by a scanner, and the obtained read signal is converted into a digital image signal by a processing circuit. Similarly, the toner images of the respective colors may be formed.

  Thereafter, the toner images formed on the respective photosensitive drums 12 are sequentially primary-transferred onto the surface of the intermediate transfer belt 20 by the primary transfer roll 16 at a primary transfer position where the photosensitive drum 12 and the intermediate transfer belt 20 are in contact with each other. . On the other hand, the toner remaining on the photosensitive drum 12 after the primary transfer is cleaned by the drum cleaner 17.

  The toner image primarily transferred onto the intermediate transfer belt 20 in this way is superimposed on the intermediate transfer belt 20 and conveyed to the secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the sheet P is conveyed to the secondary transfer position at a predetermined timing, and the secondary transfer roll 31 sandwiches the sheet P with respect to the backup roll 24.

  Then, at the secondary transfer position, the toner image carried on the intermediate transfer belt 20 is secondarily transferred to the paper P by the action of a transfer electric field formed between the secondary transfer roll 31 and the backup roll 24. . The sheet P on which the toner image is transferred is conveyed to the fixing device 50 by the conveyance belt 43. In the fixing device 50, the toner image on the paper P is heated and pressure-fixed, and then sent out to a paper discharge tray (not shown) provided outside the apparatus. On the other hand, the toner remaining on the intermediate transfer belt 20 after the secondary transfer is cleaned by the belt cleaner 26.

<Description of light emitting element head>
FIG. 2 is a diagram illustrating a configuration of the light emitting element head 14 to which the exemplary embodiment is applied. The light-emitting element head 14 includes a housing 61, a light-emitting unit 63 including a plurality of LEDs as light-emitting elements, a circuit board 62 on which the light-emitting unit 63, the signal generation circuit 100 (see FIG. 3 described later) and the like are mounted, And a rod lens (radial index distribution type lens) array 64 as an example of an optical element for forming an electrostatic latent image by forming an image of the light output emitted from the photosensitive member and exposing the photosensitive member.

  The housing 61 is made of, for example, metal, supports the circuit board 62 and the rod lens array 64, and is set so that the light emitting point of the light emitting unit 63 and the focal plane of the rod lens array 64 coincide. Further, the rod lens array 64 is arranged along the axial direction (main scanning direction) of the photosensitive drum 12.

<Description of light emitting unit>
FIG. 3 is a top view of the circuit board 62 and the light emitting unit 63 in the light emitting element head 14.
As shown in FIG. 3, the light emitting unit 63 has a light emitting chip C (C1 to C60) as an example of 60 light emitting element array chips on a circuit board 62 facing each other in two rows in the main scanning direction. Arranged in a shape. That is, in this case, the LEDs are mounted on the light emitting chips C for each predetermined number, and a plurality of light emitting chips C are arranged along the main scanning direction. In this case, the LEDs are arranged along the main scanning direction, and sequentially light up for each light emitting chip C in the main scanning direction or in the direction opposite to the main scanning direction. Further, the circuit board 62 includes a signal generation circuit 100 as an example of a control unit that controls light emission of a light emitting element array (see FIG. 4 described later) of the light emitting chip C.

<Description of Light Emitting Element Array Chip>
FIGS. 4A to 4B are diagrams illustrating the structure of a light-emitting chip C to which the present embodiment is applied.
FIG. 4A is a view of the light emitting chip C as seen from the direction in which the LED light is emitted. FIG. 4B is a cross-sectional view taken along line IVb-IVb in FIG.
In the light emitting chip C, as an example of the light emitting element array, a plurality of LEDs 71 arranged in a line in the main scanning direction are arranged in a straight line at equal intervals. Bonding pads 72 as an example of electrode portions for inputting and outputting signals for driving the light emitting element array are arranged on both sides of the substrate 70 so as to sandwich the light emitting element array. Each LED 71 is formed with a microlens 73 on the light emitting side. The light emitted from the LED 71 is collected by the micro lens 73, and the light can be efficiently incident on the photosensitive drum 12 (see FIG. 2).
The microlens 73 is made of a transparent resin such as a photocurable resin, and the surface thereof preferably has an aspherical shape in order to collect light more efficiently. The size, thickness, focal length, and the like of the microlens 73 are determined by the wavelength of the LED 71 used, the refractive index of the photocurable resin used, and the like.

<Description of Self-Scanning Light Emitting Element Array Chip>
In the present embodiment, it is preferable to use a self-scanning light emitting device (SLED) chip as the light emitting element array chip exemplified as the light emitting chip C. The self-scanning light-emitting element array chip uses a light-emitting thyristor having a pnpn structure as a constituent element of the light-emitting element array chip, and is configured to realize self-scanning of the light-emitting elements.

FIG. 5 is a diagram showing the configuration of the signal generation circuit 100 and the wiring configuration of the circuit board 62 when a self-scanning light emitting element array chip is adopted as the light emitting chip C.
The signal generation circuit 100 receives various control signals such as a line synchronization signal Lsync, image data Vdata, a clock signal clk, and a reset signal RST from an image output control unit 90 (see FIG. 1). . The signal generation circuit 100 performs, for example, rearrangement of image data Vdata, correction of output values, and the like based on various control signals input from the outside, and each of the light emitting chips C (C1 to C60). The lighting signal φI (φI1 to φI60) is output. In the present embodiment, lighting signals φI (φI1 to φI60) are supplied to each of the light emitting chips C (C1 to C60) one by one.

  The signal generation circuit 100 outputs a start transfer signal φS, a first transfer signal φ1, and a second transfer signal φ2 to each of the light emitting chips C1 to C60 based on various control signals input from the outside.

  The circuit board 62 is provided with a power supply line 101 for power supply Vcc = −5.0 V connected to the Vcc terminals of the light emitting chips C1 to C60 and a power supply line 102 for grounding connected to the GND terminal. Yes. The circuit board 62 has a start transfer signal line 103 for transmitting the start transfer signal φS, the first transfer signal φ1, and the second transfer signal φ2 of the signal generation circuit 100, the first transfer signal line 104, and the second transfer signal line. 105 is also provided. The circuit board 62 also has 60 lighting signal lines 106 (106_1 to 106_60) for outputting the lighting signals φI (φI1 to φI60) from the signal generation circuit 100 to the light emitting chips C (C1 to C60). Is provided. The circuit board 62 is provided with 60 light emission current limiting resistors RID for preventing an excessive current from flowing through the 60 lighting signal lines 106 (106_1 to 106_60). Further, the lighting signals φI1 to φI60 can take two states of high level (H) and low level (L), respectively, as will be described later. The low level has a potential of −5.0V, and the high level has a potential of ± 0.0V.

FIG. 6 is a diagram for explaining a circuit configuration of the light-emitting chips C (C1 to C60).
The light emitting chip C includes 60 transfer thyristors S1 to S60 and 60 light emitting thyristors L1 to L60. The light emitting thyristors L1 to L60 have the same pnpn connection as the transfer thyristors S1 to S60, and function as light emitting diodes (LEDs) by using the pn connection therein. The light emitting chip C includes 59 diodes D1 to D59 and 60 resistors R1 to R60. Further, the light-emitting chip C includes transfer current limiting resistors R1A and R2A for preventing an excessive current from flowing through the signal lines to which the first transfer signal φ1, the second transfer signal φ2, and the start transfer signal φS are supplied. , R3A. The light emitting thyristors L1 to L60 constituting the light emitting element array 81 are arranged in the order of L1, L2,..., L59, L60 from the left side in the drawing to form a light emitting element array, that is, the light emitting element array 81. The transfer thyristors S1 to S60 are also arranged in the order of S1, S2,..., S59, S60 from the left side in the drawing to form a switch element array, that is, a switch element array 82. Furthermore, the diodes D1 to D59 are also arranged in the order of D1, D2,..., D58, D59 from the left in the drawing. Furthermore, the resistors R1 to R60 are also arranged in the order of R1, R2,... R59, R60 from the left in the drawing.

Next, electrical connection of each element in the light emitting chip C will be described.
The anode terminal of each transfer thyristor S1 to S60 is connected to the GND terminal. A power supply line 102 (see FIG. 5) is connected to the GND terminal and grounded.

  Also, the cathode terminals of the odd-numbered transfer thyristors S1, S3,..., S59 are connected to the φ1 terminal via the transfer current limiting resistor R1A. The first transfer signal line 104 (see FIG. 5) is connected to the φ1 terminal, and the first transfer signal φ1 is supplied.

  On the other hand, the cathode terminals of the even-numbered transfer thyristors S2, S4,..., S60 are connected to the φ2 terminal via the transfer current limiting resistor R2A. The second transfer signal line 105 (see FIG. 5) is connected to the φ2 terminal, and the second transfer signal φ2 is supplied.

  The gate terminals G1 to G60 of the transfer thyristors S1 to S60 are connected to the Vcc terminal via resistors R1 to R60 provided corresponding to the transfer thyristors S1 to S60, respectively. A power supply line 101 (see FIG. 5) is connected to the Vcc terminal, and a power supply voltage Vcc (−5.0 V) is supplied.

  Further, the gate terminals G1 to G60 of the respective transfer thyristors S1 to S60 are connected to the gate terminals of the corresponding light emitting thyristors L1 to L60 in a one-to-one relationship.

  The anode terminals of the diodes D1 to D59 are connected to the gate terminals G1 to G59 of the transfer thyristors S1 to S59, and the cathode terminals of the diodes D1 to D59 are respectively adjacent to the transfer thyristors S2 in the next stage. Are connected to gate terminals G2 to G60 of .about.S60. That is, the diodes D1 to D59 are connected in series with the gate terminals G1 to G60 of the transfer thyristors S1 to S60 interposed therebetween.

  The anode terminal of the diode D1, that is, the gate terminal G1 of the transfer thyristor S1, is connected to the φS terminal via the transfer current limiting resistor R3A. The φS terminal is supplied with a start transfer signal φS via a start transfer signal line 103 (see FIG. 5).

  Next, the anode terminals of the light emitting thyristors L1 to L60 are connected to the GND terminal in the same manner as the anode terminals of the transfer thyristors S1 to S60.

  The cathode terminals of the light emitting thyristors L1 to L60 are connected to the φI terminal. A lighting signal line 106 (in the case of the light emitting chip C1, the lighting signal line 106_1: refer to FIG. 5) is connected to the φI terminal, and a lighting signal φI (in the case of the light emitting chip C1, the lighting signal φI1) is supplied. In addition, corresponding lighting signals φI2 to φI60 are supplied to the other light emitting chips C2 to C60, respectively.

  Next, the operation of the light-emitting chip C in the exposure operation will be described in detail with reference to the timing chart shown in FIG. In FIG. 7, for convenience of explanation, a case where the respective light emitting thyristors L are sequentially turned on in the main scanning direction will be described.

  In the initial state, the start transfer signal φS is at a low level (L), the first transfer signal φ1 is at a high level (H), the second transfer signal φ2 is at a low level, and the lighting signal φI is at a high level. , Each is set.

  As the operation starts, the start transfer signal φS input from the signal generation circuit 100 is changed from the low level to the high level. As a result, the high-level start transfer signal φS is supplied to the gate terminal G1 of the transfer thyristor S1 of the light emitting chip C. At this time, the start transfer signal φS is also supplied to the gate terminals G2 to G60 of the other transfer thyristors S2 to S60 via the diodes D1 to D59. However, since the voltage drop occurs in each of the diodes D1 to D59, the voltage applied to the gate terminal G1 of the transfer thyristor S1 is the highest.

  Then, in a state where the start transfer signal φS is at the high level, the first transfer signal φ1 input from the signal generation circuit 100 is changed from the high level to the low level. In addition, after the first period ta has elapsed since the first transfer signal φ1 is changed to the low level, the second transfer signal φ2 is changed from the low level to the high level.

  As described above, when the low-level first transfer signal φ1 is supplied in a state where the start transfer signal φS is at the high level, the light-emitting chip C is an odd number to which the low-level first transfer signal φ1 is supplied. Of the second transfer thyristors S1, S3,..., S59, the transfer thyristor S1 having the highest gate voltage and exceeding the threshold value is turned on. At this time, since the second transfer signal φ2 is at the high level, the cathode voltages of the even-numbered transfer thyristors S2, S4,..., S60 remain high and the turn-off state is maintained. At this time, in the light emitting chip C, only the odd-numbered transfer thyristor S1 is turned on. As a result, the odd-numbered transfer thyristor S1 and the light-emitting thyristor L1 whose gates are connected to each other are turned on and are allowed to emit light.

  In the state where the transfer thyristor S1 is turned on, the second transfer signal φ2 is changed from the high level to the low level after the second period tb has elapsed since the second transfer signal φ2 was changed to the high level. Then, among the even-numbered transfer thyristors S2, S4,..., S60 to which the low-level second transfer signal φ2 is supplied, the transfer thyristor S2 having the highest gate voltage and equal to or higher than the threshold value is turned on. At this time, in the light emitting chip C, the odd-numbered transfer thyristor S1 and the even-numbered transfer thyristor S2 adjacent thereto are both turned on. Accordingly, in addition to the light-emitting thyristor L1 that has already been turned on, the even-numbered transfer thyristor S2 and the light-emitting thyristor L2 whose gates are connected to each other are turned on and are ready to emit light.

  In a state where both the transfer thyristor S1 and the transfer thyristor S2 are turned on, after the third period tc has elapsed after the second transfer signal φ2 is changed to the low level, the first transfer signal φ1 is changed from the low level to the high level. Changed to Accordingly, the odd-numbered transfer thyristor S1 is turned off, and only the even-numbered transfer thyristor S2 is turned on. Accordingly, the odd-numbered light-emitting thyristor L1 is turned off and cannot emit light, and only the even-numbered light-emitting thyristor L2 is kept turned on and can emit light. In this example, the start transfer signal φS is changed from the high level to the low level as the first transfer signal φ1 is changed to the high level.

  In the state where the transfer thyristor S2 is turned on, the first transfer signal φ1 is changed from the high level to the low level after the fourth period td has elapsed since the first transfer signal φ1 was changed to the high level. Accordingly, among the odd-numbered transfer thyristors S1, S3,..., S59 to which the low-level first transfer signal φ1 is supplied, the transfer thyristor S3 having the highest gate voltage is turned on. At this time, in the light emitting chip C, the even-numbered transfer thyristor S2 and the odd-numbered transfer thyristor S3 adjacent thereto are both turned on. Accordingly, in addition to the light-emitting thyristor L2 that has already been turned on, the odd-numbered transfer thyristor S3 and the light-emitting thyristor L3 whose gates are connected to each other are turned on so that both can emit light.

  In a state where both the transfer thyristor S2 and the transfer thyristor S3 are turned on, the second transfer signal φ2 is changed from the low level to the high level after the fifth period te elapses after the first transfer signal φ1 is changed to the low level. Changed to Accordingly, the even-numbered transfer thyristor S2 is turned off, and only the odd-numbered transfer thyristor S3 is turned on. Accordingly, the even-numbered light-emitting thyristor L2 is turned off to be incapable of emitting light, and only the odd-numbered light-emitting thyristor L3 is kept in a turn-on state to be capable of emitting light.

  As described above, in the light-emitting chip C, the transfer thyristor S1 is switched by alternately switching between the high level and the low level while providing an overlap period in which both the first transfer signal φ1 and the second transfer signal φ2 are set to the low level. ˜S60 are sequentially turned on in numerical order. As a result, the light emitting thyristors L1 to L60 are also turned on sequentially in the order of numbers. At this time, only the odd-numbered transfer thyristor (for example, transfer thyristor S1) is turned on in the second period tb, and in the third period tc, the odd-numbered transfer thyristor and the even-numbered transfer thyristor provided in the next stage are turned on. (For example, the transfer thyristor S1 and the transfer thyristor S2) are turned on, and in the fourth period td, only the even-numbered transfer thyristor (for example, the transfer thyristor S2) is turned on, and in the fifth period te, the even-numbered transfer thyristor and The odd-numbered transfer thyristor (for example, transfer thyristor S2 and transfer thyristor S3) provided in the next stage is turned on, and then only the odd-numbered transfer thyristor (for example, transfer thyristor S3) is turned on again in the second period tb. This process is repeated.

  On the other hand, the lighting signal φI basically changes from the high level to the low level in the second period tb in which the odd-numbered transfer thyristor is turned on alone and in the fourth period td in which the even-numbered transfer thyristor is independently turned on. Change from low level to high level.

  Accordingly, for each light emitting chip C, the light emitting thyristors L1, L2, L3, L4,..., L59, L60 emit light one by one in order (turn on sequentially).

  In FIG. 7, the time for exposing one line on the photosensitive drum 12 is shown as one line period. Then, after one line is exposed on the photosensitive drum 12, the same drive signal is generated again, and the light emitting thyristors L1, L2, L3, L4,..., L59, L60 emit light one by one in order. The above line is exposed, and this is repeated thereafter. When one line is exposed, there is a rest period at the end, and no exposure is performed in the rest period. That is, one line cycle is the total of the period during which exposure is actually performed and the rest period.

<Explanation of exposure correction>
Here, a variation in the amount of light may occur for each LED 71 (see FIG. 4). The variation in the amount of light is usually not so large between the LEDs 71 arranged in each light emitting chip C, but tends to increase between the light emitting chips C. If the amount of light varies among the LEDs 71, the exposure amount of the photosensitive drum 12 varies, and therefore, the density of the toner image varies. In this case, since variation occurs in the main scanning direction, a line extending in the sub-scanning direction is generated in the formed image, and the image quality is likely to deteriorate.

  Therefore, it is necessary to correct variations in the amount of light of each LED 71. Therefore, for example, there is a method of correcting the lighting time according to the light amount of each LED 71. That is, the lighting time is lengthened for the LED 71 having a smaller light amount, and the lighting time is shortened for the LED 71 having a larger light amount. As a result, the amount of light with respect to the photosensitive drum 12 is corrected, and the variation in the amount of light is reduced, so that a streak is hardly generated in the formed image.

  However, this correction is performed when the LED 71 is turned on for a predetermined lighting time. This time is a lighting time when the LED 71 is turned on under normal use conditions. Then, the variation in the amount of light is corrected by slightly increasing or decreasing the lighting time of the LED 71 from the lighting time under the normal use conditions. For this reason, in the lighting time deviating from the lighting time, the light amount also varies, and the exposure amount may vary. For example, this occurs when the exposure amount of the entire LED 71 is uniformly increased or decreased to correct the sensitivity of the photosensitive drum 12 when the temperature condition of the photosensitive drum 12 changes. That is, the exposure amount may be uniformly doubled or halved, for example. At this time, the lighting time of the LEDs 71 changes uniformly, and the exposure amount varies at that time.

FIGS. 8A and 8B are diagrams for explaining the variation in the exposure amount by each LED 71 when the lighting time is uniformly changed.
Among these, Fig.8 (a) is the figure shown about the exposure amount of each LED71 when lighting time is changed uniformly. In FIG. 8A, the horizontal axis represents the position of each LED 71 in the main scanning direction, and the vertical axis represents the exposure amount. In this case, the line indicated by C represents the exposure amount of each LED 71 after correction in the lighting time under the normal use condition. Here, since the amount of light of each LED 71 is corrected, the variation in the exposure amount is also reduced, and the line C is relatively flat as shown in the figure.

  On the other hand, the line indicated by B is a case where the lighting time is further shortened than the case of C, and the line indicated by A is a case where the lighting time is further shortened compared to the case of B. Moreover, the line shown by D is a case where lighting time is made longer than the case of C. That is, the exposure amount increases in the order of A → B → C → D. In the case of A, B, and D, the variation in exposure amount is larger than in the case of C.

FIG. 8B is a diagram for explaining the difference in the exposure amount with respect to the lighting time when the lighting time is uniformly changed. In FIG. 8B, the horizontal axis represents the lighting time, and the vertical axis represents the exposure amount.
The three lines shown in the figure are plots of the average exposure amount of each LED 71 arranged on each light emitting chip Ca, Cb, Cc for the three light emitting chips Ca, Cb, Cc. Here, the case where the lighting time is A corresponds to the case of A in FIG. The lighting times B, C, and D correspond to the cases B, C, and D in FIG.

  As shown in the figure, when the lighting time is C, it is the lighting time during which the amount of light is corrected, so that the exposure amounts are almost the same for each light emitting chip Ca, Cb, Cc. However, when the lighting time deviates from the case of C, the exposure amount differs for each light emitting chip Ca, Cb, Cc, and the difference increases as the lighting time departs from the case of C.

As a prior art for further correcting this, there is the following method.
FIG. 9A shows a lighting signal when one LED 71 is turned on once. This corresponds to the lighting signal φI in the example of FIG. And the lighting signal shown to Fig.9 (a) is a pulse wave, and the lighting time of LED71 becomes this pulse width. That is, the lighting time of the LED 71 can be controlled by changing the pulse width.

  Ideally, the lighting profile of the LED 71 when this lighting signal is input is desirably as shown by the dotted line in FIG. In practice, however, the lighting profile of the LED 71 is as shown by the solid line in FIG. That is, the light quantity gradually increases from 0 after the lighting signal changes from H to L. That is, it takes time to rise. After this, the amount of light is saturated, and when the lighting signal changes from L to H, the amount of light decreases rapidly but does not immediately become zero. At this time, the exposure amount can be grasped as an area illustrated by hatching in FIG.

Therefore, the exposure amount when the pulse width is changed is as shown in FIG. In FIG. 9C, the horizontal axis represents the pulse width (lighting time) of the lighting signal, and the vertical axis represents the exposure amount.
At this time, the dotted line is the relationship between the pulse width and the exposure amount when the LED 71 is lit with an ideal lighting profile as indicated by the dotted line in FIG. In this case, the relationship between the pulse width and the exposure amount is linear. In practice, however, the lighting profile of the LED 71 is as shown by the solid line in FIG. In this case, particularly when the lighting time is short, it is easily affected by the time required for the rise of the light amount. For this reason, the relationship between the pulse width and the exposure amount is as shown by a solid line and lacks linearity.

Therefore, the following correction is performed to bring the solid line in FIG. 9C closer to the dotted line.
FIG. 10A is a diagram illustrating a lighting signal after the lighting signal of FIG. 9A is corrected. The part shown with the dotted line here respond | corresponds to the lighting signal of Fig.9 (a). Then, the lighting signal in FIG. 10A is corrected to increase the pulse width of the lighting signal by a portion indicated by offset. When this correction is performed, the lighting profile of the LED 71 becomes as shown by the solid line in FIG. 10B, and the exposure amount increases. As a result, the exposure amount when the pulse width is changed is as shown in FIG. That is, since the exposure amount is uniformly increased only in the portion indicated by offset, the solid line in FIG. 9C is moved upward in the drawing as indicated by the arrow. For this reason, the relationship between the pulse width and the exposure amount can be linear at a pulse width longer than the lighting time t.

  In this method, by adjusting the offset amount in FIG. 10A, the exposure amount can be adjusted in a region where the pulse width is small and the lighting time is short. That is, for example, when the lighting time in FIG. 8B is A, the exposure amounts of the light emitting chips Ca, Cb, and Cc are aligned. Then, if the exposure amount is the same at two points when the lighting time is A and the lighting time is C, the exposure amount is likely to be almost the same in the other regions, as shown in FIG. 8B. The lines almost overlap and the exposure variation is corrected.

  However, in this method, the amount of offset is on the order of ps (picosecond), and a highly accurate one is required by the driver that controls the pulse width. Moreover, it is necessary to measure the light quantity of each LED 71 at different lighting times, which requires a lot of labor and time.

  Therefore, in the present embodiment, the signal generation circuit 100 of the light emitting element head 14 has the following configuration, and the lighting signal is set as follows to suppress the above problem.

<Description of functional configuration of signal generation circuit>
FIG. 11 is a block diagram illustrating a functional configuration example of the signal generation circuit 100 according to the present embodiment. In FIG. 11, among the various functions of the signal generation circuit 100, those related to this embodiment are selected and shown.
As shown in the figure, the signal generation circuit 100 according to the present embodiment includes an image information acquisition unit 111, a step correction unit 112, a lighting order rearrangement unit 113, and a drive waveform generation unit 114.

  The image information acquisition unit 111 receives image data (image information) from the image output control unit 90. As described above, this image data can be used to form an image in the image forming unit 11 after image data input from the outside such as a PC is subjected to image processing in the image output control unit 90. Is. Specifically, the image processing includes, for example, rasterization processing, color conversion processing, pile height processing, screen processing, and the like.

  The level difference correcting unit 112 corrects the deviation of the electrostatic latent image caused by the level difference of the light emitting chip C. That is, since the light emitting chips C are arranged in a staggered manner as described above, if one line is output as it is, the lines of the electrostatic latent image are staggered. Therefore, it is necessary to correct this so that the line becomes a straight line. The level difference correction unit 112 considers the deviation of each light emitting chip C in the sub-scanning direction, and corrects the LED 71 of the light emitting chip C to light up corresponding to the time difference corresponding to this deviation.

  The lighting order rearrangement unit 113 determines the lighting order of the LEDs 71 of the light emitting chip C based on the result of correction by the step correction unit 112. The lighting order rearrangement unit 113 rearranges the lighting order of the LEDs 71.

  The drive waveform generation unit 114 generates a drive waveform for lighting the LED 71 and outputs it as a drive signal. Specifically, for example, the drive waveforms of the above-described lighting signal φI, start transfer signal φS, first transfer signal φ1, and second transfer signal φ2 are generated and output as drive signals. In this embodiment, the lighting signal φI is generated as follows.

<Description of lighting signal>
Next, the lighting signal φI generated by the drive waveform generation unit 114 will be described.
In the drive waveform generation unit 114, when the lighting time per time of each LED 71 exceeds a predetermined first time, a lighting signal is used so that the LED 71 is turned on by using a plurality of times less than the first time. φI is generated. That is, by generating the lighting signal φI for controlling the turning on and off of the LEDs 71 in a plurality of times less than or equal to the first time, each LED 71 is turned on in a plurality of times.
Conventionally, as described with reference to FIGS. 7, 9, and 10, the LED 71 is turned on for a predetermined lighting time by one light emission. That is, the lighting signal φI is one pulse as shown in FIGS. However, in the present embodiment, the lighting time is divided into a plurality of times and the divided number of times LEDs 71 are turned on. In this case, the lighting signal φI is composed of a plurality of pulses.

12A to 12D are diagrams showing a method of dividing the lighting signal φI into a plurality of pulses.
In this embodiment, the lighting time is managed by the number of clocks of the clock signal clk (see FIG. 5). That is, the lighting time is a multiple of one clock cycle time of the clock signal clk.
Here, the first time is set to 4 clock cycle times.
12A to 12D, the lighting signal φI generated for the set lighting time is compared between the conventional and the present embodiment (described as “this example” in the figure).

  Of these, FIG. 12A shows a case where the lighting time per LED 71 is 4 clock cycle times. In this case, since the lighting time does not exceed the first clock time of 4 clock cycles, the lighting signal φI is generated in one pulse for both the conventional and the present embodiment, and is the same.

  FIG. 12B shows a case where the lighting time per one time of the LED 71 is 5 clock cycle times. In this case, since the lighting time exceeds the four clock cycle time that is the first time, the lighting signal φI is divided. Here, the lighting signal φI is divided into two and generated by two pulses. Then, lighting times of 3 clock cycle times and 2 clock cycle times are set, respectively.

  Furthermore, FIG.12 (c) is a case where the lighting time per time of LED71 was 6 clock cycle time. Also in this case, since the lighting time exceeds the four clock cycle time which is the first time, the lighting signal φI is divided. The lighting signal φI is divided into two and generated by two pulses. Then, lighting times of 3 clock cycle times and 3 clock cycle times are set, respectively.

FIG. 12D shows a case where the lighting time per time of the LED 71 is 9 clock cycles. In this case, if the lighting signal φI is divided into two, one of them exceeds four clock cycle times, so that the lighting signal φI is divided into three and generated by three pulses. Then, lighting times of 3 clock cycle times, 3 clock cycle times, and 3 clock cycle times are set, respectively.
In addition, depending on the lighting time per time of LED71, it may become four or more divisions.

  FIGS. 13A to 13B show the use of lighting time when the LED 71 is turned on without dividing the lighting signal φI and when the LED 71 is turned on by dividing the lighting signal φI a plurality of times. It is the figure which compared the range. In addition, the part shown by C is the same as the case where the lighting time demonstrated in FIG.8 (b) is C. FIG.

  Among these, FIG. 13A shows a case where the LED 71 is lit with one pulse without dividing the lighting signal φI as in the prior art. FIG. 13B shows a case where the LED 71 is lit in a plurality of times equal to or less than the first time when the lighting time per time of the LED 71 exceeds a predetermined first time.

  As illustrated in FIG. 13B, the use range of the lighting time of the LED 71 does not exceed the time t1 which is the first time. On the other hand, in Fig.13 (a), the use range of lighting time is set over time t1 to time t3. In this case, as shown in the figure, when there are two light emitting chips C having different exposure amounts with respect to the lighting time, the difference in exposure amount is larger at time t3 than at time t1 in FIG. The upper limit of the usage range of the lighting time is preferably larger and smaller than the lighting time C without departing from the lighting time C in which the light amount of the LED 71 is corrected.

  The same applies to the lower limit of the lighting time usage range. That is, it is preferable to turn on each LED 71 when the lighting time per one time exceeds a predetermined first time, using a time equal to or longer than a predetermined second time. The lower limit of the use range of the lighting time is preferably not smaller than the lighting time C and larger than the lighting time C in which the light quantity of the LED 71 is corrected. In the present embodiment, as shown in FIG. 13 (b), the lower limit of the use range of the lighting time is larger than the time t4 shown in FIG. 13 (a), and is a predetermined second time t2. It is set as.

Eventually, in this embodiment, the usage range of the lighting time is narrower in the case of FIG. 13B than in FIG. As a result, even when there is a variation in the exposure amount by each LED 71 as shown in FIG. 8B, the difference in the actual exposure amount is not so large.
Compared with the conventional method described with reference to FIG. 10, a driver for controlling the pulse width in the order of ps (picoseconds) is not required, and a highly accurate driver is not required. Further, it is not necessary to measure the light quantity of each LED 71 at different lighting times, and labor and time required for measuring the light quantity of the LED 71 are reduced.

  In the above-described example, the case where the light emitting chip C is used and the self-scanning light emitting element array chip is used as the light emitting chip C has been described as an example. However, the present invention is not limited to this. Can be applied as long as they are arranged along the main scanning direction and light up sequentially in the main scanning direction or in the direction opposite to the main scanning direction.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 11 ... Image forming unit, 12 ... Photosensitive drum, 13 ... Charging roll, 14 ... Light emitting element head, 15 ... Developing device, 64 ... Rod lens array, 90 ... Image output control part, 100 ... Signal Generation circuit, 114... Drive waveform generation unit, C1 to C60... Light emitting chip, S1, S2, S3,..., S60 ... transfer thyristor, L1, L2, L3.

Claims (3)

A plurality of light emitting elements arranged along the main scanning direction and sequentially lit;
An optical element for imaging the light output of the plurality of light emitting elements;
A controller that turns on each of the plurality of light emitting elements by using a plurality of times equal to or less than the first time when a lighting time per one light emitting element exceeds a predetermined first time;
Equipped with a,
When the lighting time per time of each light emitting element exceeds the predetermined first time, the control unit causes the light to be turned on using a time that is equal to or longer than a predetermined second time, and The first time is set longer than the lighting time when the light amount of each light emitting element is corrected, and the second time is set shorter than the lighting time when the light amount of each light emitting element is corrected. Element head. The said control part lights up each light emitting element by producing | generating the lighting signal which controls lighting and light extinction of each light emitting element in multiple times below the said 1st time, It is characterized by the above-mentioned. 2. The light emitting device head according to 1. An image carrier for holding an image;
Charging means for charging the surface of the image carrier;
Electrostatic latent image forming means for exposing the image carrier with light emitted from a plurality of light emitting elements arranged along the main scanning direction and sequentially lit to form an electrostatic latent image;
Developing means for developing the electrostatic latent image to form a toner image;
A controller that turns on each of the plurality of light emitting elements by using a plurality of times equal to or less than the first time when a lighting time per one light emitting element exceeds a predetermined first time;
Equipped with a,
When the lighting time per time of each light emitting element exceeds the predetermined first time, the control unit causes the light to be turned on using a time that is equal to or longer than a predetermined second time, and An image characterized in that the first time is set longer than the lighting time when the light amount of each light emitting element is corrected, and the second time is set shorter than the lighting time when the light amount of each light emitting element is corrected. Forming equipment.

Images