JP2010099943A - Light exposure head, method for controlling light exposure head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of shortening the time required for detecting the light of the whole light emitting elements in a technique for detecting the light from the light emitting elements with which a light exposure head is equipped. <P>SOLUTION: The light exposure head includes: the light emitting elements E arranged in a first direction LGD; a first light detecting part LDS1 having first optical sensors SC1-(1) and SC1-(2) which receive lights from the light emitting elements E and output signals, and a first detecting circuit DC1 into which the signals of the first optical sensors SC1-(1) and SC1-(2) are inputted; and a second light detecting part LDS2 having second optical sensors SC2-(1) and SC2-(2) which receive lights from the light emitting elements E and output signals, and a second detecting circuit DC2 into which the signals of the second optical sensors SC2-(1) and SC2-(2) are inputted. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for detecting light from a light emitting element provided in an exposure head.

  As such an exposure head, one in which a plurality of light emitting elements are arranged in the main scanning direction and a surface to be exposed is exposed with light from each light emitting element is known. In order to execute such an exposure operation satisfactorily, it is desirable that the light amount of each light emitting element is within a predetermined range. However, since the light emitting element deteriorates due to repeated lighting, the light amount of the light emitting element may gradually decrease. Therefore, Patent Document 1 proposes a technique in which the light amount of each light emitting element is detected in advance at the timing when the exposure operation is not performed, and the lighting of the light emitting element in the exposure operation is controlled based on the detected value. Yes. Specifically, the light receiving sensor receives light from the light emitting element and outputs a signal corresponding to the amount of light received. This signal is input to the light quantity sensor input unit and then output to a CPU (Central Processing Unit). Then, the CPU controls lighting of the light emitting element in the exposure operation based on the received data.

JP 2002-1227489 A

  By the way, the exposure head described in Patent Document 1 includes a light detection system for receiving light from a light emitting element and outputting it to a control unit such as a CPU (in Patent Document 1, it is composed of a light receiving sensor and a light amount sensor input unit. There is only one system. Therefore, detection of light from each light emitting element has to be performed by turning on one light emitting element at a time, and it may take a long time to detect light from all the light emitting elements. In particular, when the number of light emitting elements is increased in order to cope with high resolution, there is a possibility that the increase in time required for light detection of all the light emitting elements becomes remarkable.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique capable of shortening the time required for light detection of all the light emitting elements.

  In order to achieve the above object, an exposure head according to the present invention includes: a light emitting element disposed in a first direction; a first optical sensor that receives light from the light emitting element and outputs a signal; A first light detection unit having a first detection circuit to which a signal of the light sensor is input, a second light sensor that receives light from the light emitting element and outputs a signal, and a signal of the second light sensor And a second light detection unit having a second detection circuit that is input.

  In order to achieve the above object, the exposure head control method according to the present invention receives a light from a light emitting element and outputs a signal, and a signal from the first optical sensor is input. A first light detection unit having a first detection circuit, a second light sensor that receives light from the light emitting element and outputs a signal, and a second detection that receives a signal from the second light sensor The exposure of an exposure head having a second light detection unit having a circuit is controlled based on detection results of the first light detection unit and the second light detection unit.

  In order to achieve the above object, the image forming apparatus according to the present invention receives the latent image carrier, the light emitting element disposed in the first direction, and the light from the light emitting element and outputs a signal. A first photodetecting unit having a first photosensor and a first detection circuit to which a signal from the first photosensor is input, and a second photosensor that receives light from the light emitting element and outputs a signal And a second detection circuit having a second detection circuit to which a signal of the second photosensor is input, and an exposure head for exposing the latent image carrier.

  In the invention configured as described above (exposure head, exposure head control method, image forming apparatus), an optical sensor that receives light from the light emitting element and outputs a signal, and a detection circuit to which the signal of the optical sensor is input are provided. There are two systems of light detection units (a first light detection unit and a second light detection unit). Therefore, these two systems of light detection units can execute light detection of the light emitting elements in parallel. Therefore, the present invention can shorten the time required for light detection of all the light emitting elements, as compared with the prior art in which only one light detection system is provided.

  A controller that controls the lighting of the light emitting element, the first light detection unit, and the second light detection unit, and performs light detection by the first light detection unit and the second light detection unit in parallel; You may comprise so that it may be provided. By providing the control unit in this way, the first light detection unit and the second light detection unit can appropriately perform light detection of the light emitting element in parallel.

  In addition, the first photodetection unit includes N (N is an integer of 2 or more) first photosensors, and the second photodetection unit includes N second photosensors. May be. When configured in this manner, the amount of light reaching each photosensor from each light emitting element is larger than when each of the first photodetection unit and the second photodetection unit has only one photosensor. Thus, the signal output from the optical sensor can be stabilized. The reason is as follows. When there is only one light sensor, one light sensor is assigned to many light emitting elements arranged in the first direction, and thus the light emitting element whose distance from the light sensor is increased. There is. And since the distance is long, the light which reaches | attains an optical sensor from a light emitting element may become weak. On the other hand, when N photosensors are provided, the number of light emitting elements allocated to one photosensor can be reduced. Therefore, the distance between each light emitting element and the optical sensor can be shortened, and the amount of light reaching each optical element from the light emitting element can be increased to stabilize the signal output from the optical sensor.

  The first detection circuit includes an amplification circuit that amplifies the signal from the first photosensor, and the second detection circuit includes an amplification circuit that amplifies the signal from the second photosensor. If configured in this way, the level of the signal output from the optical sensor can be adjusted as appropriate to facilitate subsequent processing on the signal.

  By the way, in each of the first light detection unit and the second light detection unit, light detection of two or more light emitting elements cannot be performed in parallel. Therefore, in a configuration in which the light detection unit includes N light sensors, light detection of the light emitting element may be performed as follows in order to perform light detection of the light emitting element one by one in each of the light detection units. . That is, one first photosensor is selected from the N first photosensors of the first photodetection unit, the light emitting element corresponding to the one first photosensor is turned on, and the second It is also possible to select one second photosensor from the N second photosensors of the photodetection unit and turn on the light emitting element corresponding to the one second photosensor. .

  The first optical sensor and the second optical sensor are arranged in the first direction, and the control unit detects light by the first optical sensor adjacent to the first direction and detects light by the second optical sensor. The first optical sensor or the second optical sensor may be selected as a sensor for detecting light so that the two are not parallel. As a result, occurrence of crosstalk, which will be described later, is suppressed, and good light detection can be performed.

  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 and the like, the main controller MC gives a control signal to the engine controller EC, and based on this, the engine controller EC The controller EC controls each part of the device, such as the engine unit ENG and the head controller HC, to execute predetermined image forming operations, and responds to image forming commands on sheets that are recording materials such as copy paper, transfer paper, paper, and OHP transparent sheets. The image to be formed is formed.

  In the housing main body 3 of the image forming apparatus according to this embodiment, an electrical component box 5 is provided that incorporates a power circuit board, a main controller MC, an engine controller EC, and a head controller HC. An image forming unit 2, a transfer belt unit 8, and a paper feed unit 7 are also disposed in the housing body 3. In FIG. 1, a secondary transfer unit 12, a fixing unit 13 and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feed unit 7 is configured to be detachable from the housing body 3. The paper feeding unit 7 and the transfer belt unit 8 can be removed and repaired or exchanged.

  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 of the image forming stations 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 arranged such 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). Each photosensitive drum 21 is connected to a dedicated drive motor 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. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction thereof. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. 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 charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and is driven to rotate as the photosensitive drum 21 rotates. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at the charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 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.

  The developing unit 25 has a developing roller 251 that carries toner on the surface thereof. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Moves from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed on the surface thereof is visualized.

  The toner image made visible at the development position is transported in the rotational direction D21 of the photosensitive drum 21, and is then primarily transferred to the transfer belt 81 at the primary transfer position TR1 where the transfer belt 81 and each photosensitive drum 21 abut. .

  A photoreceptor cleaner 27 is provided in contact with the surface of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to remove the toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and an arrow D81 illustrated in FIG. And a transfer belt 81 that is circulated in the direction (conveyance direction). Further, four transfer belt units 8 are arranged on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations 2Y, 2M, 2C, and 2K when the cartridge is mounted. Primary transfer rollers 85Y, 85M, 85C and 85K. Each of these primary transfer rollers is electrically connected to a primary transfer bias generator (not shown).

  When the color mode is executed, as shown in FIGS. 1 and 2, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations 2Y, 2M, 2C, and 2K, so that the transfer belt 81 is imaged. A primary transfer position TR1 is formed between each photosensitive drum 21 and the transfer belt 81 by being pushed and brought into contact with the photosensitive drum 21 included in each of the forming stations 2Y, 2M, 2C, and 2K. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85Y or the like at an appropriate timing, the toner images formed on the surface of each photosensitive drum 21 are respectively transferred to the corresponding primary transfer positions. Transfer is performed on the surface of the transfer belt 81 in TR1. That is, in the color mode, the single color toner images of the respective colors are superimposed on the transfer belt 81 to form a color image.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the black primary transfer roller 85K and on the upstream side of the driving roller 82. The downstream guide roller 86 is common to the primary transfer roller 85K and the black photosensitive drum 21 (K) at the primary transfer position TR1 formed by the primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station 2K. It is configured to contact the transfer belt 81 on the tangent line.

  A patch sensor 89 is provided opposite to the surface of the transfer belt 81 wound around the downstream guide roller 86. The patch sensor 89 is composed of, for example, a reflection type photosensor, and optically detects a change in the reflectance of the surface of the transfer belt 81, so that the position and density of the patch image formed on the transfer belt 81 as necessary. Is detected.

  The sheet feeding unit 7 includes a sheet feeding unit having a sheet feeding cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds sheets one by one from the sheet feeding cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is adjusted in sheet feeding timing by the registration roller pair 80, and then the drive roller 82 and the secondary transfer roller 121 abut along the sheet guide member 15. Paper is fed to the secondary transfer position TR2.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. The sheet on which the image is secondarily transferred is guided to the nip formed by the heating roller 131 and the pressure belt 1323 of the pressure unit 132 by the sheet guide member 15, and in the nip, a predetermined value is formed. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 is formed by pressing the belt tension surface stretched by the two rollers 1321 and 1322 out of the surface of the pressure belt 1323 against the peripheral surface of the heating roller 131. Is configured to be widely taken. Further, the sheet thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface portion of the housing body 3.

  The drive roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 82, and secondary transfer is omitted by grounding through a metal shaft. A conductive path of a secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. Thus, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, image quality deterioration caused by transmission of the impact to the transfer belt 81 when the sheet enters the secondary transfer position TR2. Can be prevented.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt 81 after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83.

  The photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each of the image forming stations 2Y, 2M, 2C, and 2K are unitized as a unit. The cartridge is configured to be detachable from the apparatus main body. Each cartridge is provided with a nonvolatile memory for storing information related to the cartridge. Then, wireless communication is performed between the engine controller EC and each cartridge. Thus, information about each cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored. Based on these pieces of information, the usage history of each cartridge and the lifetime of consumables are managed.

  Further, the main controller MC, the head controller HC, and each line head 29 are configured as separate blocks, and these are connected to each other via a serial communication line. The data exchange operation between the blocks 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. Further, 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 and a head-side communication module 300 that controls data communication with the main controller MC. On the other hand, the main communication module 200 is also provided in the main controller MC. From the head-side communication module 300 to the main-side communication module 200, a vertical request signal VREQ indicating the head of an image for one page and a horizontal request for requesting video data for one line among the lines constituting the image. Signal HREQ is transmitted. On the other hand, the video data VD is transmitted from the main communication module 200 to the head communication module 300 in response to these request signals. More specifically, after receiving the vertical request signal VREQ indicating the head of the image, each time the horizontal request signal HREQ is received, the video data VD is sequentially output line by line from the head portion of the image. Each light emitting element emits light based on the video data VD.

  FIG. 3 is a partial perspective view showing the structure of the line head. FIG. 4 is a partial cross-sectional view showing a cross-section in the width direction of the line head. Since these are partial views, they do not represent all parts. A bottom emission type organic EL element is formed as the light emitting element E on the back surface 294-t of the head substrate 294 included in the line head 29. Further, a gradient index rod lens array 297 is disposed opposite to the surface 294-h of the head substrate 294. Therefore, the light beam emitted from the light emitting element E is transmitted from the back surface 294-t of the head substrate 294 to the front surface 294-h, and then imaged by the rod lens array 297 at an equal magnification. In this way, spots are formed on the surface of the photosensitive drum 21.

  FIG. 5 is a partial plan view showing the configuration of the back surface of the head substrate, and corresponds to a case where the head substrate back surface 294-t is viewed in plan from the head substrate front surface 294-h. As shown in the figure, a plurality of light emitting elements E are arranged in a straight line in the longitudinal direction LGD (main scanning direction MD) on the head substrate rear surface 294-t. Further, in the present embodiment, four photosensors SC1- (m), SC2- (m), two detection circuits DC1, DC2, a detection control circuit DCT, and a memory MMb are arranged on the head substrate back surface 294-t. Has been. Here, m is a variable for labeling the optical sensor and a light emitting element group described later, and takes a positive integer value. In this embodiment, m = 1 and 2. The arrangement relationship or functions of these light emitting elements and optical sensors are as follows.

  The light emitting elements E are grouped into a predetermined number to form light emitting element groups EG1- (m) and EG2- (m). Each light emitting element group EG1- (m), EG2- (m) has a width Weg in the longitudinal direction LGD. Here, the width Weg is the distance between the centers of the two light emitting elements E at both ends in the longitudinal direction LGD of the light emitting element group, and the center of the light emitting element E can be obtained as the geometric center of gravity of the light emitting surface of the light emitting element E. Further, four photosensors SC1- (m), SC2- (m) are provided in one-to-one correspondence with the four light emitting element groups EG1- (m), EG2- (m). The detailed relationship between the light emitting element group and the optical sensor will be described with reference to the light emitting element group EG1- (1) and the optical sensor SC1- (1). The optical sensor SC1- (1) is arranged so that the sensor center is located on the bisector of the width Weg of the light emitting element group EG1- (1). The light receiving surface of the sensor SC1- (1) faces the head substrate back surface 294-t. Therefore, of the light emitted from the light emitting element E of the light emitting element group EG1- (1), the light reflected by the surface 294-h of the head substrate 294 reaches the light receiving surface of the sensor SC1- (1), and the sensor SC1. -Detected at (1). The sensor center can be obtained as the geometric center of gravity of the light receiving surface of the sensor.

  In this way, the four photosensors SC1- (1), SC1- (2), SC2- (1), and SC2- (2) are arranged in a straight line in the longitudinal direction LGD. Two optical sensors SC1- (1) and SC1- (2) adjacent in the longitudinal direction LGD are connected in parallel to one detection circuit DC1, and two adjacent in the longitudinal direction LGD. Photosensors SC2- (1) and SC2- (2) are connected in parallel to one detection circuit DC2. Each of the detection circuits DC1 and DC2 has a sensor selection switch, an amplifier circuit, and an A / D converter which will be described later. These detection circuits DC1 and DC2 are connected to the detection control circuit DCT. Thus, in the present embodiment, the photosensors SC1- (1), SC1- (2) and the detection circuit DC1 constitute the first photodetection system LDS1 (photodetection unit) and the photosensor SC2- (1), SC2- (2) and the detection circuit DC2 constitute a second light detection system LDS2 (light detection unit), and two light detection systems LDS1 for detecting the light of the light emitting element E , LDS2 is provided. A memory MMb is connected to the detection control circuit DCT. Note that these circuits and the memory are connected via a wiring WL.

  Incidentally, the lighting of the light emitting element E is executed by the lighting control circuit ECT (FIG. 6). Specifically, the lighting control circuit ECT turns on the light emitting element E by a drive signal based on the video data VD from the head controller HC. The light emitting element E is lit with a light amount corresponding to the level of the drive signal. However, as described above, the light emitting element E deteriorates and the light amount gradually decreases. Therefore, in the present embodiment, the light amount of the light emitting element E is detected at a timing when the exposure operation is not performed, such as when the image forming apparatus is activated. And a drive signal is correct | amended based on the light quantity measured by light quantity detection. Accordingly, the light emitting element E can emit light with a desired light amount regardless of the deterioration of the light emitting element E. Below, this light quantity detection is demonstrated.

  FIG. 6 is a block diagram showing an electrical configuration of the line head. FIG. 7 is a flowchart showing the light amount detection of the light emitting element executed by the electrical configuration of FIG. The light quantity detection (light detection) of the light emitting element E will be described with reference to these drawings. First, in step S101, the CPU instructs the detection control circuit DCT to perform light amount detection. Thereby, the subsequent light quantity detection is executed under the control of the detection control circuit DCT. In step S102, a value 1 is set to the variable m. In step S103, the detection control circuit DCT notifies the lighting control circuit ECT that the light quantity detection of each light emitting element E of the light emitting element groups EG1- (m), EG2- (m) is started. In response to this, the lighting control circuit ECT turns off the light emitting element groups other than the light emitting element groups EG1- (m) and EG2- (m), which are the targets of the light amount detection (step S104). Thereby, erroneous light emission of the light emitting element group other than the light amount detection target during the light amount detection is prevented.

  Then, the detection control circuit DCT performs in parallel the light amount detection by the first light detection system LDS1 (steps S111 to S114) and the light amount detection by the second light detection system LDS2 (steps S121 to S124). To do. Since the first light detection system LDS1 and the second light detection system LDS2 perform similar light amount detection, only the light amount detection of the first light detection system LDS1 will be described here. In step S111, in response to an instruction from the detection control circuit DCT, the sensor selection switch SW-1 selects the optical sensor SC1- (m). The sensor selection switch SW-1 selects one of the optical sensors SC1- (1) and SC1- (2), and outputs only the output signal of the selected optical sensor to the subsequent circuit (amplifier circuit AMP1). ).

  In step S112, the lighting control circuit ECT turns on only one light emitting element E whose light amount is not detected among the light emitting elements E of the light emitting element group EG1- (m). The light emitting element E is turned on based on correction data stored in the memory MMa. That is, the correction data obtained before the currently executed light amount detection (for example, at the previous light amount detection) is stored in the memory MMa, and based on the drive signal corrected based on this correction data. The light emitting element E is turned on. Then, after the output signal of the optical sensor SC1- (m) when the light emitting element E is turned on is amplified by the amplifier circuit AMP1, it is converted into a digital signal by the A / D converter ADC1, and stored in the memory MMb (step S113). ). In step S114, it is determined whether or not the light amount detection of all the light emitting elements E in the light emitting element group EG1- (m) is completed. If it is not completed (“NO” in step S114), steps S111 to S114 are repeatedly executed until the light amount detection of all the light emitting elements E is completed. Specifically, in each of the light emitting element groups EG1- (m) and EG2- (m), the light amount detection of the light emitting element E is executed in order from the left end of FIG. On the other hand, if completed ("YES" in step S114), the process proceeds to step S105.

  In step S105, it is determined whether or not the variable m is a value 2. In step S105, the light quantity detection by the first light detection system LDS1 (steps S111 to S114) and the light quantity detection by the second light detection system LDS2 (steps S121 to S124) are completed. It is done at the time. If the variable m is not 2 (“NO” in step S105), m is incremented by 1 in step S106, and the process returns to step S103. On the other hand, when the variable m is 2 (“YES” in step S105), it is determined that the light quantity detection of the light emitting elements E of all the light emitting element groups is completed, and the process proceeds to step S107. In step S107, the detection control circuit DCT notifies the CPU of the completion of the light amount detection. In response to this, the CPU calculates correction data for correcting the drive signal from the light amount detection result stored in the memory MMb, and stores the calculation result in the memory MMa (step S108).

  As described above, in the present embodiment, the light detection system (light) includes the light sensor SC1- (1) that receives light from the light emitting element E and outputs a signal, and the detection circuit DC1 that receives the signal of the light sensor. Two detection systems LDS1 and LDS2 (two) are provided. Therefore, the two light detection systems LDS1 and LDS2 can execute light amount detection (light detection) of the light emitting element E in parallel. Therefore, it is possible to reduce the time required for detecting the light amount of all the light emitting elements E, as compared with the conventional technique in which only one light detection system is provided.

  In the present embodiment, a detection control circuit DCT (control unit) is provided in order to perform light amount detection in parallel by the two light detection systems LDS1 and LDS2. In this way, the light quantity detection performed in parallel in the two systems of the light quantity detection systems LDS1, LDS is controlled by the detection control circuit DCT, so that the two systems of light detection units LDS1, LDS2 perform the light quantity detection in parallel. Can be done appropriately.

  In the present embodiment, the number of photodetection systems LDS1 (or photodetection systems LDS2) is N (N is an integer equal to or greater than 2, N = 2 in the present embodiment), and photosensors SC1- (1), SC1- (2) (or optical sensor SC2- (1), SC2- (2)). When configured in this way, the amount of light reaching each light emitting element E from the light emitting element E to the light sensor is increased and the signal output from the light sensor is stabilized as compared with the case where the light detection system has only one light sensor. Can be made. The reason for this will be described by exemplifying the light detection system LDS1. When there is only one optical sensor, all the light emitting elements E arranged in the longitudinal direction LGD (first direction) (that is, all the light emitting elements E of the light emitting element groups EG1- (1), EG1- (2)). ), One light sensor is assigned to the light emitting element E, and there is a light emitting element E that is far from the light sensor. And since the distance is long, the light which reaches | attains an optical sensor from the light emitting element E may become weak. On the other hand, when two optical sensors SC1- (1) and SC1- (2) are provided as in this embodiment, the number of light-emitting elements E allocated to one optical sensor is reduced ( Can be halved). Therefore, the distance between each light emitting element E and the light sensor can be shortened, and the amount of light reaching each of the light sensors SC1- (1), SC1- (2) from each light emitting element E is increased, so that the light sensor SC1- (1) The signal output from SC1- (2) can be stabilized.

  In the present embodiment, the detection circuits DC1 and DC2 have amplification circuits AMP1 and AMP2 that amplify signals from the optical sensors. Therefore, it is possible to easily adjust the level of the signal output from the optical sensor to facilitate subsequent processing (A / D conversion) on the signal.

  By the way, in each of the light detection systems LDS1 and LDS2, the light quantity detection of two or more light emitting elements E cannot be performed in parallel. Therefore, in the present embodiment, in order to detect the light quantity of the light emitting element E one by one in each of the light detection systems LDS1 and LDS2, the light quantity detection of the light emitting element E is executed as follows. That is, in the light detection system LDS1 as an example, the detection control circuit DCT sequentially selects one light sensor from the two light sensors SC1- (1) and SC1- (2) of the light detection system LDS1, The light emitting elements E corresponding to the one optical sensor are sequentially turned on (turned on sequentially from the left end in FIG. 5). Then, the signal of the one photosensor selected by the detection control circuit DCT is input to the detection circuit DC1 of the light detection system LDS1. Thereby, the light quantity detection of the light emitting element E can be performed one by one in each of the light detection systems LDS1 and LDS2.

  By the way, in the configuration in which each photodetection system LDS1, LDS2 is provided with N photosensors, the distance between the photosensors arranged in the longitudinal direction LGD is shortened by increasing the number of photosensors. There is a risk of crosstalk. On the other hand, in the present embodiment, an optical sensor that performs light amount detection is selected so that the light amount detection by the optical sensors adjacent in the longitudinal direction LGD is not parallel. As a result, the occurrence of crosstalk is suppressed and good light quantity detection is possible. This will be described in detail below.

  FIG. 8 is an explanatory diagram of the effect of suppressing the problem of crosstalk. The upper graph in FIG. 8 shows the light quantity detection characteristics of the three optical sensors SC1- (1), SC1- (2), and SC2- (1). The horizontal axis of the graph shows the position of the light emitting element E in the longitudinal direction LGD, and the right side of the graph is positive. The vertical axis of the graph shows the magnitude of the output signal (voltage signal) of the optical sensor. That is, in the graph, the magnitude of the output signal of each of SC1- (1), SC1- (2), and SC2- (1) that detects light from the light emitting element E at the position indicated by the horizontal axis is the vertical axis. It is shown. As shown in the graph, each of the optical sensors SC1- (1), SC1- (2), and SC2- (1) has the largest amount of light from the light emitting element E at the same position as the sensor center in the longitudinal direction LGD. While detection is performed with a signal level (voltage), light from the light emitting element E farther from the sensor center is detected with a smaller signal level. Thus, the magnitude of the output signal of the photosensor depends on the distance between the photosensor and the light emitting element E.

  By the way, as described above, the two light detection systems LDS1 and LDS2 perform light quantity detection in parallel. At this time, light detection by the optical sensors SC1- (2) and SC2- (1) adjacent in the longitudinal direction LGD is performed. If they are performed in parallel, crosstalk may occur. That is, the light emitting element E1 at one end in the longitudinal direction LGD of the light emitting element group EG1- (2) and the light emitting element E2 at the other end in the longitudinal direction LGD of the light emitting element group EG2- (1) are the optical sensor SC1. -The distance to (2) is substantially equal to each other. Therefore, the optical sensor SC2- (1) detects the light LB1 from the light emitting element E1 and the light LB2 from the light emitting element E2 with signal levels of substantially the same magnitude. In this way, crosstalk occurs in which the light LB2 that is not the detection target is detected at the same signal level as the light LB1 that is the detection target. When this crosstalk occurs, the optical sensor SC2- (1) cannot accurately detect the amount of light LB1 from the light emitting element E1 that is the detection target.

  On the other hand, in the present embodiment, the optical sensors are selected so that the light quantity detection by the optical sensors SC1- (2) and SC2- (1) adjacent in the longitudinal direction LGD is not parallel. For example, the light sensor SC2- (2) performs light amount detection in parallel with the light sensor SC1- (2). And even if it is the light emitting element E3 closest to the optical sensor SC1- (2) among the light emitting elements E of the light emitting element group EG2- (2), the distance to the sensor SC1- (2) is much larger than that of the light emitting element E1. Far away. Therefore, the optical sensor SC1- (2) detects the light LB1 from the light emitting element E1 with a signal level much higher than the light LB3 from the light emitting element E3. Thus, in the present embodiment, the occurrence of crosstalk is suppressed, and the light amount of each light emitting element E can be obtained appropriately.

  As described above, in this embodiment, the line head 29 corresponds to the “exposure head” of the present invention, the light detection system LDS1 corresponds to the “first light detection unit” of the present invention, and the light detection system LDS2 The optical sensor SC1- (1), SC1- (2) corresponds to the “first optical sensor” of the present invention, and corresponds to the “second optical detector” of the present invention, and the optical sensor SC2- (1). SC2- (2) corresponds to the “second optical sensor” of the present invention, and the detection control circuit DCT corresponds to the “control unit” of the present invention.

  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. For example, in the above embodiment, a plurality of light emitting elements E corresponding to the respective light detection systems LDS1, LDS2 are grouped into two light emitting element groups (for example, light emitting element groups EG1- (1), EG1- (2)). It has become. However, the number of groups is not limited to two, and may be three as shown in another embodiment below.

  FIG. 9 is a block diagram showing an electrical configuration of a line head according to another embodiment. FIG. 10 is a flowchart showing the light quantity detection of the light emitting element executed by the electrical configuration of FIG. As shown in FIG. 9, a plurality of light emitting elements E corresponding to the light detection system LDS1 (LDS2) includes three light emitting element groups EG1- (1), EG1- (2), EG1- (3) (EG2- (1), EG2- (2), EG2- (3)). In addition, three light sensors SC1- (1), SC1- (2), one-to-one corresponding to the three light emitting element groups EG1- (1), EG1- (2), EG1- (3), SC1- (3) is provided. Since the configuration other than these is the same as the block diagram of FIG. 9 and the block diagram of FIG.

  The optical sensors SC1- (1), SC- (2), SC- (3) are respectively emitted from the light-emitting elements E of the corresponding light-emitting element groups EG1- (1), EG1- (2), EG1- (3). Detect the amount of light. This light quantity detection operation is executed according to the flowchart of FIG. Note that the flowchart of FIG. 10 differs from the flowchart of FIG. 7 only in step S205. That is, in another embodiment, since each of the light detection systems LDS1 and LDS2 detects the light amount of all the light emitting elements E of the three light emitting element groups, the light amount detection is repeatedly performed until the value of the variable m becomes 3. .

  Further, the number of groups can be expanded to N (N is an integer of 2 or more), which is a more general number, as shown in another embodiment below. FIG. 11 is a block diagram showing an electrical configuration of a line head according to still another embodiment. FIG. 12 is a flowchart showing the light quantity detection of the light emitting element executed by the electrical configuration of FIG. As shown in FIG. 11, a plurality of light-emitting elements E corresponding to the light detection system LDS1 (LDS2) include N light-emitting element groups EG1- (1), EG1- (2),... EG1- (N) ( EG2- (1), EG2- (2),... EG2- (N)). Further, the N light sensors SC1- (1), SC1- (2) correspond to the N light emitting element groups EG1- (1), EG1- (2),... EG1- (N) on a one-to-one basis. ,..., SC1- (N) are provided. Since the configuration other than these is the same as the block diagram of FIG. 11 and the block diagram of FIG.

  The optical sensors SC1- (1), SC- (2),..., SC- (N) emit light from the corresponding light emitting element groups EG1- (1), EG1- (2),. The amount of light from the element E is detected. This light quantity detection operation is executed according to the flowchart of FIG. Note that the flowchart of FIG. 12 differs from the flowchart of FIG. 7 only in step S305. That is, in yet another embodiment, since each of the light detection systems LDS1 and LDS2 detects the light amount of all the light emitting elements E of the N light emitting element groups, the light amount detection is repeated until the value of the variable m becomes N. Do.

  Moreover, in the said embodiment, in order to light up the light emitting element E of a light emitting element group sequentially, the light emitting element E was lighted in order from the left side of FIG. However, the lighting order of the light emitting element E is not limited to this.

  In the above embodiment, only two systems LDS1 and LDS2 are provided as the light detection system, but three systems may be provided as the light detection system. That is, the effect of the present invention can be achieved by providing at least two light detection systems and performing light detection in parallel in each light detection system.

  In the above-described embodiment, the plurality of light emitting elements E are arranged in a straight line in the longitudinal direction LGD. However, the plurality of light emitting elements E may be arranged in a zigzag of two rows or three or more rows in the longitudinal direction LGD.

  Moreover, in the said embodiment, although the organic EL element was used as the light emitting element E, you may use LED (Light-Emitting Diodes) as the light emitting element E. FIG.

  In the above embodiment, the optical sensor SC1- (1) and the like are arranged so that the sensor center is located on the bisector of the width Weg of the light emitting element group EG1- (1), etc. The arrangement position of sensor SC1- (1) etc. is not restricted to this.

  In the above embodiment, the optical sensor SC1- (1) and the like are arranged on the back surface 294-t of the head substrate. However, the arrangement position of the optical sensor SC1- (1) and the like is not limited to this. It may be 294-h. In this case, if the light receiving surface of the optical sensor SC1- (1) or the like is opposed to the head substrate surface 294-h, the optical sensor SC1- (1) or the like can receive light from the light emitting element E.

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 fragmentary sectional view which shows the width direction cross section of a line head. The partial top view which shows the structure of a head substrate back surface. The block diagram which shows the electric constitution with which a line head is provided. The flowchart which shows the light quantity detection of the light emitting element which the electrical structure of FIG. 6 performs. Explanatory drawing of the effect which suppresses the problem of crosstalk. The block diagram which shows the electric constitution with which the line head concerning another embodiment is provided. The flowchart which shows the light quantity detection of the light emitting element which the electrical structure of FIG. 9 performs. The block which shows the electric constitution of the line head concerning another embodiment. The flowchart which shows the light quantity detection of the light emitting element which the electrical structure of FIG. 11 performs.

Explanation of symbols

  29 ... line head, 297 ... rod lens array 297, DC1 ... detection circuit, DC2 ... detection circuit, DCT ... detection control circuit, LDS1, LDS2 ... light detection system, E1 ... light emitting element, E2 ... light emitting element, E3 ... light emitting element , E ... Light emitting element, ECT ... Lighting control circuit, EG1- (1), EG1- (2), EG2- (1), EG2- (2) ... Light emitting element group, HC ... Head controller, LGD ... Longitudinal direction, LTD ... Width direction, MD ... Main scanning direction, SD ... Sub scanning direction, SC1- (1), SC1- (2), SC2- (1), SC2- (2) ... Optical sensor, SW-1, SW- 2 ... Sensor selection switch, VD ... Video data

Claims (8)

A light emitting device disposed in a first direction;
A first photodetection unit having a first photosensor that receives light from the light emitting element and outputs a signal, and a first detection circuit to which the signal of the first photosensor is input;
A second photosensor having a second photosensor that receives light from the light emitting element and outputs a signal, and a second detection circuit to which the signal of the second photosensor is input;
An exposure head comprising:   Control that performs lighting detection by the first light detection unit and the second light detection unit in parallel by controlling lighting of the light emitting element, the first light detection unit, and the second light detection unit The exposure head according to claim 1, further comprising a portion.   The first photodetection unit includes N (N is an integer of 2 or more) first photosensors, and the second photodetection unit includes N second photosensors. 2. The exposure head according to 2.   The first detection circuit has an amplification circuit that amplifies a signal from the first photosensor, and the second detection circuit has an amplification circuit that amplifies a signal from the second photosensor. The exposure head according to claim 3.   The control unit selects one of the first photosensors from the N first photosensors of the first photodetection unit, and the light emitting element corresponding to the one first photosensor The light emitting element corresponding to the one second photosensor by selecting one second photosensor from the N second photosensors of the second photodetection unit The exposure head according to claim 3, wherein the exposure head is turned on. The first photosensor and the second photosensor are disposed in the first direction;
The control unit detects the first optical sensor or the second optical sensor as a sensor for detecting light so that light detection by the first light sensor adjacent in the first direction and light detection by the second light sensor are not parallel. The exposure head according to claim 5, wherein an optical sensor is selected.   A first photosensor that receives light from the light-emitting element and outputs a signal; a first photodetection unit that includes a first detection circuit to which the signal of the first photosensor is input; and the light-emitting element A second photosensor that receives light from the second photosensor and outputs a signal; and a second photodetection unit that has a second detection circuit to which the signal from the second photosensor is input. An exposure head control method, wherein exposure is controlled based on detection results of the first light detection unit and the second light detection unit. A latent image carrier;
A light emitting element disposed in a first direction; a first photosensor that receives light from the light emitting element and outputs a signal; and a first detection circuit that receives the signal from the first photosensor; A first photodetecting unit, a second photosensor that receives light from the light emitting element and outputs a signal, and a second detection circuit that receives the signal from the second photosensor. An exposure head that has a second light detection unit and that exposes the latent image carrier;
An image forming apparatus comprising:

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