JP2012101435A - Exposure head and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately reflect light quantity of light emitting elements emitting light by leak current on detection values (offset values) by light detection parts (sensors).SOLUTION: This exposure head includes: a first light emitting element; a second light emitting element; a first drive element driving the first light emitting element; a second drive element driving the second light emitting element; first wiring electrically connected to the first drive element; second wiring electrically connected to the second drive element; a first power source supply part connected to the first wiring at a first position to supply a power source to the first wiring; a second power source supply part connected to the second wiring at a second position leaving a first clearance relative to the first position in a first direction of the first position to supply a power source to the second wiring; a first light detection part detecting light; and a second light detection part arranged on a substrate leaving a second clearance which is a half or less of the first clearance relative to the first light detection part in a first direction of the first light detection part to detect light.

Description

  The present invention relates to an exposure head that performs exposure using light emitted from a light emitting element to which a drive signal is applied, and more particularly to a technique for correcting the light amount of a light emitting element provided in the exposure head.

  Patent Document 1 describes an exposure head that emits light by driving each of a number of light emitting elements arranged in the longitudinal direction by a driving element. Further, in the exposure head, a plurality of sensors are provided at intervals in the longitudinal direction in order to correct the light amount of each light emitting element to an appropriate value. In other words, each of the plurality of sensors detects light from the light emitting element that it takes charge of, and the light quantity of each light emitting element is corrected to an appropriate value based on the detection result of each sensor.

  By the way, in order to drive the light emitting element, for example, a driving element such as a transistor described in Patent Document 2 can be used. Specifically, in Patent Document 2, the output terminal of the transistor is connected to the light emitting element. When the transistor is turned on, a drive signal (drive current) is applied to the light emitting element from the output terminal of the transistor, whereby the light emitting element emits light.

JP 2010-99945 A JP 2010-46858 A

  However, in the configuration in which the light emitting element emits light by such a driving element, there is a case where the light amount correction of the light emitting element cannot be performed with high accuracy. That is, in this light amount correction, one of the plurality of light emitting elements selectively emits light, and the detection value of the sensor at this time is obtained as the light amount of the light emitting element. At this time, the drive elements that drive the light emitting elements that are not selected are turned off and output of the drive signals is stopped. However, since a driving element such as a transistor outputs a constant leakage current even when it is off, a light emitting element that has not been selected emits light slightly due to the leakage current. Then, when the light due to this leakage current is added to the light from the light emitting element that is the light quantity detection target and detected by the sensor, the light quantity of the light emitting element that is the light quantity detection target is determined to be larger than the actual light, and as a result In some cases, the accuracy of light amount correction is reduced.

  In order to cope with such a problem, an operation for confirming the detection value of the sensor when all the drive elements are turned off as an offset value is sequentially executed by a plurality of sensors, and the sensor detects the light amount detection operation. By subtracting this offset value from the light amount value, it is conceivable to accurately detect the light amount of the light emitting element to be detected. Incidentally, it is desirable that the sensor offset value obtained at this time appropriately reflects the light amount of the light emitting element that emits light due to the leak current. However, the following problem may occur due to a change in the leakage current amount of the transistor.

  That is, power supply from the power supply to the transistor is performed via a power supply line that connects the power supply and the transistor to each other. At this time, since the power supply line has an electrical resistance, a voltage drop occurs in the power supply line. More specifically, while the power supply line maintains a high voltage level at the connection position with the power supply, the voltage of the power supply line decreases as the distance from the connection position increases, in other words, the voltage drop with respect to the power supply connection position. Occurs on the power line. Therefore, when a plurality of power supplies are provided side by side in the longitudinal direction and each power supply is connected to the power supply line, a plurality of power supply connection positions are arranged at intervals, and a voltage drop with the interval between these power supply connection positions as a cycle occurs. Arise. Then, by supplying power to the transistor from such a power line, the leakage current of the transistor fluctuates approximately periodically at the interval between the power connection positions, and as a result, the light amount of the light emitting element also varies at the interval between the power connection positions. Fluctuates approximately periodically. However, in some cases, the sensor could not catch the light amount fluctuation of the light emitting element, and as a result, the offset value of the sensor did not appropriately reflect the light amount of the light emitting element that emits light due to the leak current.

  The present invention has been made in view of the above problems, and is a technique that enables the amount of light of a light emitting element that emits light due to a leakage current to be appropriately reflected in the detection value (offset value) of a light detection unit (sensor). For the purpose of provision.

  In order to achieve the above object, an exposure head according to the present invention includes a substrate that transmits light, a first light emitting element that is disposed on the substrate and emits light that passes through the substrate, and a first light emitting element of the first light emitting element. A second light-emitting element that emits light that is disposed on the substrate in one direction and transmits the substrate, a first drive element that is disposed on the substrate and drives the first light-emitting element, and A second drive element disposed on the substrate in the first direction to drive the second light emitting element; and disposed on the substrate extending in the first direction and electrically connected to the first drive element. A first wiring, a second wiring extending in the first direction in the first direction of the first wiring and arranged on the substrate and electrically connected to the second drive element; A first power supply unit connected to the first wiring at a position to supply power to the first wiring; and a first power supply in a first direction of the first position. A second power supply unit that is connected to the second wiring and supplies power to the second wiring at a second position that is spaced apart from the first position, and a first that is disposed on the substrate and detects light. And a first interval between the first photodetection portion and the first photodetection portion with a second interval that is not more than half of the first interval in the first direction of the first photodetection portion. And 2 photodetection units.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a substrate that transmits light, a first light emitting element that is disposed on the substrate and emits light that passes through the substrate, and the first light emitting element. A second light emitting element disposed on the substrate in the first direction and emitting light transmitted through the substrate; a first driving element disposed on the substrate for driving the first light emitting element; A first driving element disposed on the substrate in the first direction and driving the second light emitting element; a first driving element extending in the first direction and disposed on the substrate and electrically connected to the first driving element; A second wiring that extends in the first direction in the first direction of the first wiring and is arranged on the substrate and electrically connected to the second driving element, and the first wiring at the first position. A first power supply unit that is connected to the first wiring and supplies power to the first wiring; a first position in a first direction of the first position; A second power supply unit that is connected to the second wiring at a second position with a first interval and supplies power to the second wiring, and a first light detection unit that is disposed on the substrate and detects light And a second light detection that is arranged on the substrate at a second interval that is not more than half of the first interval in the first direction of the first light detection unit and detects light. An exposure head having a portion, and a latent image carrier on which a latent image is formed by light emitted from the first light emitting element and transmitted through the substrate and light emitted from the second light emitting element and transmitted through the substrate, It is characterized by providing.

  In the invention configured as described above (exposure head, image forming apparatus), the first light emitting element is driven by the first driving element, and the second light emitting element is driven by the second driving element. The first driving element is connected to the first power supply unit via the first wiring, and the second driving element is connected to the second power supply unit via the second wiring, In other words, the first and second wirings function as power supply lines. In the present invention, the first and second power supply sections are connected at a second interval that is not more than half of the interval (first interval) between the connection positions where the first and second power supply units are connected to the power supply lines (first and second wirings). First and second light detection units for detecting light are arranged. Therefore, it is possible to appropriately reflect the light amounts of the first and second light emitting elements that emit light by the leak current in the detection values of the first and second detection units.

  At this time, the first wiring and the second wiring may be short-circuited. With this configuration, it is possible to supply power to the first wiring by the second power supply unit, and it is possible to suppress a voltage drop of the first wiring.

  At this time, the first driving element is disposed on the substrate on the opposite side of the first power supply unit in the first direction with respect to the first driving element, and is connected to the first wiring at the second position. You may comprise so that the 3rd power supply part which supplies power may be provided. With this configuration, power can be supplied to the first wiring also by the third power supply unit, and the voltage drop of the first wiring can be further reduced.

  A first drive control unit that controls driving of the first light emitting element by the first driving element; and a second drive control unit that controls driving of the second light emitting element by the second driving element; You may comprise so that it may be provided. At this time, the first drive control unit and the second drive control unit may be arranged in the first direction at the first interval.

  Incidentally, the first and second driving elements can be constituted by transistors.

1 is a diagram illustrating an embodiment of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 1. The fragmentary perspective view which shows the structure of a line head. The partial top view which shows typically a head substrate and the periphery structure. The figure which shows the electrical constitution of a sensor. FIG. 9 illustrates an electrical configuration for controlling light emission of a light-emitting element. The flowchart which shows the operation | movement performed by light quantity correction | amendment. The figure which shows the relationship between the period variation of dark light quantity, and the arrangement pitch of a sensor. The flowchart which shows the operation | movement performed by the light quantity correction | amendment in 2nd Embodiment. The figure which shows the electrical structure which controls light emission of the light emitting element in 3rd Embodiment. The figure which shows the electrical structure which controls light emission of the light emitting element in 4th Embodiment.

First Embodiment FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present embodiment. FIG. 2 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of yellow (Y), magenta (M), cyan (C) and black (K) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC, and based on this, an engine The controller EC controls each part of the device, such as the engine unit ENG and the head controller HC, and executes predetermined image forming operations, and responds to image formation commands on recording sheets such as copy paper, transfer paper, paper, and OHP transparent sheets. The image to be formed is formed.

  In the housing main body (not shown) included in the image forming apparatus according to this embodiment, an electrical component box (not shown) containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided. Yes. Further, the image forming unit 2, the transfer belt unit 8, and the secondary transfer unit 12 are also arranged in the housing body.

  The image forming unit 2 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan) and 2K (for black) that form a plurality of images of different colors. In FIG. 1, since the image forming stations of the image forming unit 2 have the same configuration, only some of the image forming stations are denoted by reference numerals for convenience of illustration, and the reference numerals are omitted for other image forming stations. To do.

  Each image forming station 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. Each photoconductor drum 21 is held by a dedicated photoconductor cartridge, and is configured to be detachable from the apparatus main body integrally with the photoconductor cartridge. Further, each photoconductor cartridge is provided with a non-volatile memory for storing information relating to the photoconductor cartridge. Then, wireless communication is performed between the engine controller EC and each photoconductor cartridge. In this way, information on each photosensitive member cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored as necessary. Based on these pieces of information, the usage history of each photoconductor cartridge and the lifetime of consumables are managed.

  Further, in a state where the photoconductor cartridge is mounted, each photoconductor drum 21 is arranged so that the rotation axis thereof is parallel or substantially parallel to the main scanning direction MD (direction perpendicular to the paper surface of FIG. 1). Yes. Further, the rotation shaft of each photosensitive drum 21 is connected to a dedicated drive motor DM and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD. As described above, in the present embodiment, a direct drive for directly driving the rotating shaft of the photosensitive drum 21 by the driving motor DM without providing a power transmission mechanism such as a gear between the rotating shaft of the photosensitive drum 21 and the driving motor DM. Drive system is adopted.

  A charging unit 23, a line head 29, a developing unit 25, squeeze rollers SQ1 and SQ2, and a photoconductor cleaner 27 are disposed around the photoconductor drum 21 along the rotation direction thereof. These functional units execute a charging operation, a latent image forming operation, a toner developing operation, and the like. When the color mode is executed, the toner images formed by all the image forming stations 2Y, 2M, 2C, and 2K are superimposed on the transfer belt 81 provided in the transfer belt unit 8 to form a color image. When the monochrome mode is executed, only the image forming station 2K is operated to form a black monochrome image.

  The charging unit 23 includes a so-called corona charger, and is a non-contact type charger that does not contact the surface of the photosensitive drum 21. The charging unit 23 is connected to a charging voltage generation unit (not shown), receives the power from the charging voltage generation unit, and the surface of the photosensitive drum 21 at a charging position where the charging unit 23 faces the photosensitive drum 21. Is charged to a predetermined surface potential.

  The line head 29 is arranged such that its longitudinal direction LGD is parallel or substantially parallel to the main scanning direction MD, and its width direction LTD is parallel or substantially parallel to the sub-scanning direction SD. The line head 29 includes a plurality of light emitting elements arranged in the longitudinal direction LGD, and is disposed to face the photosensitive drum 21. Then, light from the light emitting element is imaged on the surface of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image.

  FIG. 3 is a partial perspective view showing the structure of the line head. FIG. 4 is a plan view showing the configuration around the head substrate provided in the line head. The head substrate 294 is made of a light transmissive member such as glass, and a plurality of light emitting elements E are arranged on the back surface of the head substrate 294 in the longitudinal direction LGD at a pitch corresponding to the resolution. Each light emitting element E is a bottom emission type organic EL element formed on the back surface of the head substrate 294. Further, a drive circuit CT composed of a transistor Tr or the like is formed on the back surface of the head substrate 294.

  Further, a plurality of flexible printed boards BD linearly arranged at equal pitches in the longitudinal direction LGD are attached to one end of the head board 294 in the width direction LTD, and the head control module 400 and the head board are mounted by this flexible printed board BD. 294 is connected. In addition, a driver DV is mounted on each flexible printed circuit board BD. As a result, a plurality of drivers DV are linearly arranged in the longitudinal direction LGD with a driver pitch Pdv. The driver DV operates the drive circuit CT based on video data VD input from the head control module 400 via the flexible printed circuit board BD. Specifically, the driver DV writes a voltage value indicated by the video data VD to the drive circuit CT, and the drive circuit CT applies a drive current based on the written voltage value to the light emitting element E. Each light emitting element E receives a drive current from the drive circuit CT and emits light with the same or substantially the same emission spectrum. Thus, the light emitted from each light emitting element E passes through the head substrate 294 and is emitted from the surface of the head substrate 294.

  A plurality of sensors S (n) are linearly arranged on the back surface of the head substrate 294 at a predetermined sensor pitch Psc in the longitudinal direction LGD. Here, n is a natural number of 1 or more, and the sensor numbers are sequentially shown in the longitudinal direction LGD. Further, the sensor pitch Psc can be obtained, for example, as an interval in the longitudinal direction LGD of the geometric center of gravity of the light receiving surfaces of the adjacent sensors S (n) and S (n + 1). Each of these sensors S (n) is attached to the back surface of the head substrate 294 with its light receiving surface facing the back surface of the head substrate 294, and is emitted from the light emitting element E and travels inside the head substrate 294. Receives light.

  FIG. 5 is a diagram showing an electrical configuration of the sensor. As shown in the figure, the sensor S (n) includes a light receiving element PD and a detection circuit DC. The output of the light receiving element PD is connected to the input terminal Tin of the detection circuit DC. The detection circuit DC amplifies the input signal with an amplifier, converts it to a digital signal with an A / D converter, and outputs it from the output terminal Tout. Output. Thus, the sensor S (n) outputs a detection value at a level corresponding to the amount of received light.

  As described above, the sensor is disposed on the back surface of the head substrate 294, while the gradient index rod lens array 297 is opposed to the surface of the head substrate 294 with a predetermined interval. Therefore, the light beam emitted from the light emitting element E is transmitted from the back surface to the front surface of the head substrate 294, and then is imaged by the rod lens array 297 at an equal magnification. As a result, a spot SP is formed on the surface of the photosensitive drum 21 and a latent image is formed on the surface of the photosensitive drum 21.

  Such a latent image forming operation by the line head 29 is controlled by the main controller MC and the head controller HC. This control operation will be described with reference to FIG. When an image formation command is given from the external device to the main controller MC, the main controller MC transmits a control signal for starting the engine unit ENG to the engine controller EC. In addition, the image processing unit 100 provided in the main controller MC performs predetermined signal processing on the image data included in the image formation command, and generates video data VD for each toner color.

  On the other hand, the engine controller EC receiving the control signal starts initialization and warm-up of each part of the engine part ENG. When these are completed and the image forming operation can be executed, the engine controller EC outputs a synchronization signal Vsync that triggers the start of the image forming operation to the head controller HC that controls each line head 29.

  The head controller HC is provided with a head control module 400 that controls each line head 29 and a head-side communication module 300 that controls data communication with the main controller MC. On the other hand, a main-side communication module 200 is provided in the main controller MC. The main communication module 200 outputs video data VD for one line to the head communication module 300 for each request from the head communication module 300. The head side communication module 300 passes this video data VD to the head control module 400. Then, the head control module 400 operates the driver DV of each line head 29 based on the video data VD so that the light emitting element emits light appropriately, and the width of the image to be formed in the main scanning direction MD corresponds to one line. A line latent image is formed. This line latent image formation is sequentially executed in accordance with the movement of the surface of the photosensitive drum 21 in the sub-scanning direction SD. As a result, a two-dimensional latent image is formed on the surface of the photosensitive drum 21. The latent image formed in this way is developed as a toner image by the developing unit 25 (FIG. 1).

  The above is the outline of the line head 29 and the image forming apparatus to which the present invention can be applied. The line head 29 of the present embodiment corrects the light amount of each light emitting element E in order to cause each light emitting element E to emit light with the target light amount Po. Next, the configuration and operation related to this light amount correction will be described in detail.

  FIG. 6 is a diagram illustrating an electrical configuration for controlling light emission of the light emitting element. In the drive circuit CT, a transistor Tr for driving the light emitting element E is provided for each light emitting element E. More specifically, in FIG. 6, the drain (output terminal) of the transistor Tr is connected to the anode of the light-emitting element E indicated by a diode notation (by the way, the cathode of the light-emitting element E is short-circuited to the ground potential). . Accordingly, when the transistor Tr is turned on, the light emitting element E emits light upon receiving a driving current from the transistor Tr. On the other hand, when the transistor Tr is turned off, the application of the drive current from the transistor Tr to the light emitting element E is stopped, and the light emitting element E is turned off.

  Further, a plurality of power supply lines Lv1, Lv2,... Are provided side by side in the longitudinal direction LGD in order to supply power to each transistor Tr. Each of the power supply lines Lv1, Lv2,... Extends linearly in the longitudinal direction LGD, is connected to the power supply VEL via the switch SW, and is connected to the sources of a predetermined number of transistors Tr. Responsible for power supply to the previous transistor Tr. Specifically, the power supply line Lv1 is connected to the power supply VEL via the switch SW at the power supply connection position x1 at one end in the longitudinal direction LGD, and is longer than the power supply connection position x1 in the longitudinal direction LGD. Is connected to the transistor Tr on the other side. Similarly, the power supply VEL and the transistor Tr are connected to the other power supply line Lv2. Thus, the power supply lines Lv1, Lv2,... Are connected to the power supply VEL via the switch SW at the power connection positions x1, x2,... Arranged in the longitudinal direction LGD at the power supply pitch Pv. In this embodiment, the power supply lines Lv1, Lv2,... Are short-circuited with each other. In the first embodiment, the power supply pitch Pv is equal to the pitch Pdv of the driver DV (Pv = Pdv).

  Here, each switch SW switches the connection destination of the power supply lines Lv1, Lv2,... Between the power supply VEL and the ground. That is, by connecting the switch SW to the power source VEL, the transistor Tr can be turned on / off to cause the light emitting element E to emit light appropriately. On the other hand, by connecting the switch SW to the ground potential, the power source to the transistor Tr The supply can be cut off and the transistor Tr can be disabled. In the following description, it is assumed that the switch SW is connected to the power supply VEL side and the transistor Tr can be turned on / off unless otherwise specified.

  A capacitor C is inserted between the gate of each transistor Tr and the power supply lines Lv1, Lv2,..., And video data VD input from the correction data generation control unit 402 to the gate of each transistor Tr is written into the capacitor C. It is. The transistor Tr is turned on / off according to the video data VD written in the capacitor C, and causes the light emitting element E to emit light appropriately.

  The head control module 400 that controls the line head 29 includes a correction data generation control unit 402, a correction voltage storage unit 404, and an offset storage unit 406. The correction data generation control unit 402 performs light amount correction of the light emitting element E by adjusting the gate voltage Vg when the transistor Tr is on based on the light amount detection value of the sensor S (n). That is, the light amount detection value output from the sensor S (n) is output to the correction data generation control unit 402. Then, the correction data generation control unit 402 performs light amount correction based on the light amount detection value while using the correction voltage storage unit 404 and the offset storage unit 406.

  Next, details of the light amount correction executed by the correction data generation control unit 402 will be described. FIG. 7 is a flowchart showing an operation executed in light amount correction. In step S101, the offset values P2 of the plurality of sensors S (n) are confirmed in order. Specifically, in step S101, all the transistors Tr are turned off and all the light emitting elements E are turned off. However, since the transistor Tr outputs a leak current, each light-emitting element E emits light slightly (has a dark light amount) even when it is turned off. Therefore, the sensor S (n) receives light from the light emitting element E that emits light with a dark light amount, and outputs an offset value P2 corresponding to the light. Here, the light quantity of the light emitting element E that emits light by the leak current is referred to as dark light quantity. Then, the correction data generation control unit 402 sequentially checks the offset value P1 for each sensor S (n) one by one. This confirmation operation is executed for each sensor S (n), taking a sufficient time to complete the A / D conversion by the A / D converter. Thus, when the confirmation and storage of the offset value P1 of all the sensors S (n) are completed, step S102 is executed.

  In step S102, the difference (= | PL−P2 |) between the offset value P2 of the sensor S (n) and the stored value PL stored in the offset storage unit 406 is obtained. The stored value PL is an offset value of the sensor S (n) previously obtained in advance, and is stored in the offset storage unit 406 for each sensor S (n). If the change amount of the offset value P2 with respect to the stored value PL is abnormally large (for example, 10 times or more of the stored value PL), it is determined that the print image quality is affected, and the correction data generation control unit 402 is determined. Outputs an error signal (warning signal) to the engine controller EC (step S103). On the other hand, if the offset value P2 is not abnormal but changes by a predetermined level or more with respect to the stored value PL (for example, if it has changed by 1% or more), the correction data generation control unit 402 causes the offset value P2 to be changed. Is stored in the offset storage unit 406 as a new stored value PL (step S103), and the process proceeds to step S106. If the change amount of the offset value P2 with respect to the stored value PL is equal to or less than the predetermined level, the correction data generation control unit 402 does not update the stored value PL of the offset storage unit 406 (step S105). The process proceeds to S106.

  In step S106, one light emitting element E (i) of all the light emitting elements E is selectively turned on, and the light quantity PS (i) is detected ("i" is the number of the light emitting element E, and the longitudinal direction). It is assumed that the light emitting elements E are sequentially attached in the direction LGD). Specifically, while the light emitting element E (i) is lit, the light quantity detection value PS (i) of the sensor S (n) responsible for detecting the light quantity of the light emitting element E (i) is corrected data generation control. Read by the unit 402. Then, the correction data generation control unit 402 subtracts the offset value P2 of the sensor S (n) in charge of the light emitting element E (i) from the light amount detection value PS (i), and the actual light amount P (i) (= PS (i) -P1) is obtained (step S107).

  Subsequently, the correction data generation control unit 402 obtains a difference (= P (i) −Po) between the target light amount Po and the actual light amount P (i) given from the engine controller EC (FIG. 2) (step S108). Then, correction data for correcting the difference is calculated and stored in the correction voltage storage unit 404 (step S109). In this way, the light amount of the light emitting element E (i) is adjusted based on the correction data stored in the correction voltage storage unit 404, so that the light emitting element E (i) emits light with the target light amount Po. And the operation | movement of the said step S106 to step S109 is performed about all the light emitting elements E (step S110). The above is the operation executed by the light amount correction.

  Incidentally, in the configuration as described above with reference to FIG. 6, the power supply from the power supply VEL to the transistor Tr is performed via the power supply lines Lv1, Lv2,... Connecting the power supply VEL and the transistor Tr to each other. At this time, since the power supply lines Lv1, Lv2,... Have electric resistance, a voltage drop occurs in the power supply lines Lv1, Lv2,. Therefore, as shown in FIG. 6, when a plurality of power sources VEL are connected to the power lines Lv1, Lv2,..., A plurality of power connection positions x1, x2,. A voltage drop occurs with a period Pv (power supply pitch) of x2,... (refer to the “power supply line voltage” column in FIG. 6). Then, by supplying power to the transistor Tr from such power supply lines Lv1, Lv2,..., The leakage current of the transistor Tr fluctuates substantially periodically at the interval Pv between the power supply connection positions x1, x2,. The light amount (dark light amount) of the light emitting element E also varies substantially periodically at the interval Pv between the power connection positions x1, x2,.

In the present embodiment, in order to reliably capture such a change in the dark light amount of the light emitting element E by the sensor S (n), the interval Pv between the arrangement pitch Psc of the sensors S (n) and the power connection positions x1, x2,. Is the following formula: Psc = Pv × 1/2
Each sensor S (n) is arranged to satisfy the above. Therefore, the relationship between the dark light quantity fluctuation period Pv and the arrangement pitch of the sensors S (n) will be described in detail.

  FIG. 8 is a diagram showing the relationship between the periodic fluctuation of the dark light quantity and the arrangement pitch of the sensors. In the drawing, the dark light amount (solid line curve) of the light emitting element E in the initial stage and the dark light amount (broken line curve) of the light emitting element E after the change with time are shown together. It is fluctuating. In this embodiment, the sensor S (n) is arranged at the sensor pitch Psc (= Pv × 1/2) with respect to the periodic fluctuation of the dark light quantity. Therefore, not only the temporal change Δ1 of the dark light amount but also the periodic change Δ2 of the dark light amount can be captured by the sensor S (n). Thus, in the first embodiment, the light amount (dark light amount) of each light emitting element E that emits light due to the leak current can be appropriately reflected in the detection value of the sensor S (n).

Incidentally, in FIG. 8, the even-numbered sensors S (2), S (4),... Coincide with the positions of the power supply connection positions x1, x2,. 1), S (3),... Match the midpoints of the power connection positions x1, x2,... With the position in the longitudinal direction LGD. However, the arrangement of the sensors S (n) is not limited to this, and the interval Pv between the arrangement pitch Psc of the sensors S (n) and the power supply connection positions x1, x2,... Psc = Pv × 1/2
By arranging each sensor S (n) so as to satisfy the above, the above-described effect can be obtained.

  Further, the sensor pitch Psc is not limited to half of the interval Pv between the power connection positions x1, x2,... (Psc = Pv × 1/2), and the sensor pitch Psc is half of the interval Pv between the power connection positions x1, x2,. If the following (Psc ≦ Pv × 1/2), the above effect can be obtained.

  In the first embodiment, the power supply lines Lv1, Lv2,... Are short-circuited with each other. Therefore, the voltage drop of each power supply line Lv1, Lv2,. For example, the voltage drop of the power supply line Lv1 will be described as an example. The power supply line Lv1 is connected to the power supply VEL for the power supply line Lv1 provided on the left side in FIG. The provided power supply VEL for the power supply line Lv2 is connected to the other end. As a result, the power supply line Lv1 is connected to the power supply VEL at both ends thereof, and the voltage drop can be suppressed to be smaller than when the power supply line Lv1 is connected to the power supply VEL only at one end.

Second embodiment,
FIG. 9 is a flowchart showing an operation executed in light amount correction in the second embodiment. Since the difference between the first embodiment and the second embodiment is only the light amount correction operation, this difference will be mainly described below, and description of common parts will be omitted as appropriate. Needless to say, the same effects as those of the first embodiment can be obtained from this common portion.

  As described with reference to FIG. 6, the power supply lines Lv1, Lv2,... Are connected to the power supply VEL via the switch SW. Therefore, the power supply to the transistor Tr can be cut off by connecting the switch SW to the ground. Therefore, in step S201 in the flowchart of FIG. 9, the offset value P1 of each sensor S (n) is detected in a state where the power supply to each transistor Tr is cut off by connecting each switch SW to the ground. In step S202, the offset value P2 of each sensor S (n) is detected with each switch SW connected to the power source VEL. In step S203, a detection value PA (= P2-P1) of the sensor S (n) corresponding to the dark light quantity is calculated.

  The correction data generation control unit 402 executes steps S204 to S207 based on the result of executing the above steps S201 to S203. That is, in step S204, the difference (= | PAL−PA |) between the detected value PA corresponding to the dark light quantity and the stored value PAL stored in the offset storage unit 406 is obtained. The stored value PAL is a detected value PA corresponding to the amount of dark light previously obtained in advance, and is stored in the offset storage unit 406 for each sensor S (n). If the change amount of the detected value PA with respect to the stored value PAL is abnormally large, it is determined that the print image quality is affected, and the correction data generation control unit 402 sends an error signal (warning signal) to the engine controller EC. Is output (step S205). On the other hand, when the detected value PA is not abnormal but changes more than a predetermined level with respect to the stored value PAL, the correction data generation control unit 402 stores the offset value P2 in the offset storage unit 406 as a new stored value PL. (Step S206), the process proceeds to Step S208. On the other hand, when the amount of change of the detected value PA with respect to the stored value PAL is less than or equal to the predetermined level, the correction data generation control unit 402 does not update the stored value PL of the offset storage unit 406 (step S207), step Proceed to S208.

  In step S208, one light-emitting element E (i) of all the light-emitting elements E is selectively turned on to detect the light quantity PS (i) (“i” is the number of the light-emitting element E, It is assumed that the light emitting elements E are sequentially attached in the direction LGD). Specifically, while the light emitting element E (i) is lit, the light quantity detection value PS (i) of the sensor S (n) responsible for detecting the light quantity of the light emitting element E (i) is corrected data generation control. Read by the unit 402. Then, the correction data generation control unit 402 subtracts the offset value P2 of the sensor S (n) in charge of the light emitting element E (i) from the light amount detection value PS (i), and the actual light amount P (i) (= PS (i) -P1) is obtained (step S209).

  Subsequently, the correction data generation control unit 402 obtains a difference (= P (i) −Po) between the target light amount Po and the actual light amount P (i) given from the engine controller EC (FIG. 2) (step S210). Then, correction data for correcting this difference is calculated and stored in the correction voltage storage unit 404 (step S211). In this way, the light amount of the light emitting element E (i) is adjusted based on the correction data stored in the correction voltage storage unit 404, so that the light emitting element E (i) emits light with the target light amount Po. And the operation | movement of the said step S208 to step S211 is performed about all the light emitting elements E (step S212). The above is the operation executed by the light amount correction.

Third Embodiment FIG. 10 is a diagram illustrating an electrical configuration for controlling light emission of a light emitting element in a third embodiment. Unlike the first embodiment, in the third embodiment, the power supply lines Lv1, Lv2,... Are not short-circuited and are separated from each other. As a result, the voltage drop in each of the power supply lines Lv1, Lv2,... Is substantially parabolic in the first embodiment, but monotonously decreases in the right direction in the third embodiment. The other configurations are common to the first embodiment and the third embodiment, and the same effects as the first embodiment can be obtained from this common portion.

Fourth Embodiment FIG. 11 is a diagram showing an electrical configuration for controlling light emission of a light emitting element in a fourth embodiment. As in the first embodiment, in the fourth embodiment, power supplies VEL1, VEL2 are provided for the power supply lines Lv1, Lv2,. Here, the fourth embodiment differs from the first embodiment in that it is arranged on the opposite side of the power supply VEL1 with respect to the plurality of transistors Tr connected to the power supply line Lv1, and is connected to the power supply line Lv1 at the power supply connection position x2. The power source VEL3 is provided. Thus, two power supplies VEL1 and VEL3 are connected to the power supply line Lv1 with a plurality of transistors Tr sandwiched in the longitudinal direction LGD. Similarly, two power supplies are provided for the other power lines Lv2,. With this configuration, it is possible to supply power to each power supply line Lv1, Lv2,. It is possible to suppress the voltage drop of each power supply line Lv1, Lv2,. The other configurations are common to the first embodiment and the fourth embodiment, and the same effects as the first embodiment can be obtained from this common portion.

  The configuration shown in the fourth embodiment also has the following advantages. In other words, in the configuration shown in FIG. 6 in the first embodiment, the power supply line connected from the power supply VEL (via the switch SW) at the power supply position x2 flows into both the power supply lines Lv1 and Lv2. Since a current flows, a larger amount of current flows than the power supply line connected to the power supply position x1 from the power supply VEL (via the switch SW). Therefore, when considering the voltage drop of the power supply line itself, if the power supply line has the same thickness, the voltage drop of the power supply line connected to the power supply position x2 is larger, and the power supply line at the power supply position x1 is larger. The voltage at the power supply position x2 becomes lower than the voltage, and the voltage drop of the power supply line Lv1 becomes worse. Therefore, in the fourth embodiment, the power supply system at the power supply position x2 is divided into VEL3 and VEL2, and two independent power supplies VEL1 and VEL3 are connected to the power supply line Lv1, so that the voltage drop is further suppressed. It has been.

Others As described above, in the above embodiment, the head substrate 294 corresponds to the “substrate” of the present invention, the light emitting element E corresponds to the “first light emitting element” and the “second light emitting element” of the present invention, The transistor Tr corresponds to the “first driving element” and “second driving element” of the present invention, the power supply line Lv1 corresponds to the “first wiring” of the present invention, and the power supply line Lv2 corresponds to the “first driving element” of the present invention. 2 ”, and the sensor S (n) corresponds to the“ first light detection unit ”and the“ second light detection unit ”of the present invention. In the first to third embodiments, the power source VEL corresponds to the “first power supply unit” and “second power supply unit” of the present invention. In the fourth embodiment, the power source VEL1 corresponds to the present invention. , The power source VEL2 corresponds to the “second power supply unit” of the present invention, and the power source VEL3 corresponds to the “third power supply unit” of the present invention. The power supply pitch Pv corresponds to the “first interval” of the present invention, and the sensor pitch Psc corresponds to the “second interval” of the present invention. The longitudinal direction LGD corresponds to the “first direction” of the present invention, the line head 29 corresponds to the “exposure head” of the present invention, and the photosensitive drum 21 corresponds to the “latent image carrier” of the present invention. To do.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. Therefore, in the above embodiment, the sensor S (n) is disposed on the back surface of the head substrate 294. However, the position where the sensor S (n) is disposed is not limited to this. For example, the sensor S (n) is disposed on the surface of the head substrate 294. S (n) may be provided.

  Further, the position of the driver DV is not limited to the above. Therefore, the driver DV may be arranged on the head substrate 294.

  In the above-described embodiment, the case where the present invention is applied to the line head 29 that forms an image of light from the light-emitting element E at an equal magnification with the gradient index rod lens array 297 has been described. However, the application target of the present invention is not limited to this. For example, as in Japanese Patent Application Laid-Open No. 2008-36937, light from light emitting elements arranged two-dimensionally with reversal optical systems facing each reversal optical system. The present invention can also be applied to a line head 29 having another configuration, such as a line head 29 that forms an image.

  In addition to the organic EL element described above, a light source such as an LED (Light Emitting Diode) can also be used as the light emitting element E.

  29 ... Line head 402 ... Correction data generation control unit 404 ... Correction voltage storage unit 404, 406 ... Offset storage unit E ... Light emitting element, Tr ... Transistor, S (n) ... Sensor, PD ... Light receiving element, DC ... Detection circuit, Lv1, Lv2 ... Power line, x1, x2 ... Power connection position, DV ... Driver

Claims (7)

A substrate that transmits light;
A first light emitting element that emits light that is disposed on the substrate and passes through the substrate;
A second light emitting element disposed on the substrate in a first direction of the first light emitting element and emitting light transmitted through the substrate;
A first driving element disposed on the substrate and driving the first light emitting element;
A second driving element disposed on the substrate in the first direction of the first driving element to drive the second light emitting element;
A first wiring extending in the first direction and disposed on the substrate and electrically connected to the first driving element;
A second wiring that extends in the first direction in the first direction of the first wiring and is disposed on the substrate and electrically connected to the second driving element;
A first power supply unit connected to the first wiring at a first position and supplying power to the first wiring;
A second power source connected to the second wiring at a second position spaced apart from the first position in the first direction by the first position and supplying power to the second wiring; Power supply section of
A first light detector disposed on the substrate for detecting light;
A second light source disposed on the substrate to detect light at a second interval not more than half of the first interval in the first direction of the first light detection unit; A light detector of
An exposure head comprising:   The exposure head according to claim 1, wherein the first wiring and the second wiring are short-circuited.   The first driving element is disposed on the substrate on a side opposite to the first direction of the first power supply unit, and is connected to the first wiring at the second position. The exposure head according to claim 2, further comprising a third power supply unit that supplies power to the first wiring.   A first drive control unit that controls driving of the first light emitting element by the first driving element; and a second drive control unit that controls driving of the second light emitting element by the second driving element. An exposure head according to any one of claims 1 to 3, further comprising:   The exposure head according to claim 4, wherein the first drive control unit and the second drive control unit are arranged in the first direction at the first interval.   6. The exposure head according to claim 1, wherein the first driving element is a transistor and the second driving element is a transistor. A substrate that transmits light, a first light emitting element that is disposed on the substrate and emits light that is transmitted through the substrate, and is disposed on the substrate in a first direction of the first light emitting element and transmits the substrate. A second light emitting element that emits light, a first driving element that is disposed on the substrate and drives the first light emitting element, and is disposed on the substrate in the first direction of the first driving element. A second driving element for driving the second light emitting element; a first wiring which extends in the first direction and is arranged on the substrate and electrically connected to the first driving element; A second wiring that extends in the first direction in the first direction of the first wiring and is arranged on the substrate and electrically connected to the second driving element; A first power supply unit that is connected to one wiring and supplies power to the first wiring; and the first position A second power supply unit that is connected to the second wiring at a second position that is spaced apart from the first position in the first direction and supplies power to the second wiring; A first light detector disposed on the substrate for detecting light; and a second light detector that is not more than half of the first distance from the first light detector in the first direction of the first light detector. An exposure head having a second photodetection unit that is disposed on the substrate and detects light at an interval of
A latent image carrier in which a latent image is formed by light emitted from the first light emitting element and transmitted through the substrate and light emitted from the second light emitting element and transmitted through the substrate;
An image forming apparatus comprising:

Images