JP4537156B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer having an LED head.

  2. Description of the Related Art Conventionally, a printer having an LED head is known as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-232449. In this type of printer, a linear LED head is disposed at a predetermined position of a cylindrical photosensitive drum so as to face the peripheral surface and parallel to the axis of the photosensitive drum. The LED head has a resolution of N [dpi (dot per inch)] and a printable size of L (inch). In the longitudinal direction, a dot corresponding to N × L light emitting elements made up of LEDs (Light Emitting Diodes). It has been arranged for several minutes.

  In this type of printer, each of the LED heads is rotated based on the dot pattern data of each line (a line parallel to the axis of the photosensitive drum; hereinafter referred to as a horizontal line as necessary) while rotating the photosensitive drum. By controlling the light emission of the LED, a negative image of the image is formed on the surface of the photosensitive drum in line units, and the negative image formed on the surface of the photosensitive drum on the downstream side in the rotation direction of the photosensitive drum. A toner image is formed by adhering toner to the developing device, and a toner image is formed on the downstream side of the toner image by a transfer device.

  In general, a printer is provided with a density setting switch on the operation panel, and the user can adjust the density of an image formed on a recording sheet in a plurality of stages by operating the density setting switch. Yes. The density of the image formed on the recording paper is determined by the density of the toner image formed on the surface of the photoconductive drum, that is, the density of the yellow image formed on the surface of the photoconductive drum. It is determined by the light emission time of each LED of the head.

  Accordingly, the printer has a plurality of light emission times set in advance corresponding to the respective stages of the image density of the plurality of stages that can be adjusted by the density setting switch, and the image set by the density setting switch at the time of image forming processing. The light emission time corresponding to the density setting value is set in the LED head, and the light emission of each LED of the LED head is controlled by this light emission time.

  Specifically, the exposure mechanism of the printer includes a control unit that controls the entire image forming process and an LED head unit that is connected to the control unit via a data bus and whose light emission operation is controlled by the control unit. For example, each time the bit pattern data of each horizontal line of the image is transferred from the control unit to the LED head unit, information on the light emission time is transmitted, and the LED to be emitted by the LED head unit is caused to emit light for this light emission time. Yes.

  Also, in recent years, the number of signal lines on the data bus between the control unit and the LED head unit has increased as the resolution of the printer has increased, so it has been replaced with a plurality of signal lines for transmitting light emission time information. One signal line is provided for transmitting a rectangular wave drive signal that is turned on only for a time corresponding to the light emission time (a rectangular wave signal that is high or low for the light emission time corresponding to the image density setting value). In addition, a method of transmitting a drive signal of an LED to be emitted from the control unit directly to the LED head unit using the signal line and controlling light emission of each LED of the LED head unit is also employed.

  FIG. 5 is a time chart showing an operation of light emission control in a method in which a driving signal for a light emitting element is directly transmitted from an existing control unit to an LED head.

  In the figure, “print data” is bit pattern data of each horizontal line, and “transfer clock” is a synchronization signal for receiving print data by the LED head unit, “transfer start signal” and “transfer end”. "Signal" is a signal indicating the start and end of bit pattern data for each horizontal line. The “driving signal” is a signal indicating the time for which the LED to emit light is emitted according to the print data, the “control clock” is a clock for measuring the ON period of the driving signal, and the “light emitting signal” emits light. This signal controls the light emission time of the power LED.

  As shown in the figure, when the bit pattern data of each horizontal line is transferred from the control unit to the LED head unit, a drive signal is transmitted from the control unit to the LED head unit. When the LED head unit receives the drive signal, it counts the control clock generated in the LED head unit from the rising timing to the falling timing of the driving signal, and this count value n is used as the bit pattern of the horizontal line. It is set as the light emission time when the light emitting element emits light based on data. After receiving the bit pattern data of each horizontal line, the LED head unit emits the LED to emit light based on the bit pattern data, and the time T (control clock of the control clock) is counted by the count value n. If the period is τ, a rectangular wave-like light emission signal that is turned on for n × τ light emission time) is output to the LED, and light is emitted for the light emission time T (= n × τ).

Japanese Unexamined Patent Publication No. 7-232449

  The conventional method of setting the light emission time T in the LED head unit based on the drive signal transmitted from the control unit is to synchronize the control clock generated in the LED head unit with the drive signal on the LED head unit side for each horizontal line. Thus, the light emission time T is generated by counting the time during which the drive signal is on. Therefore, when the control clock is out of synchronization with the drive signal, the count shift occurs between the horizontal lines (in the example of FIG. 5). The light emission time T for the print data of the nth line is 5τ, but the light emission time T for the print data of the (n + 1) th line is shifted to 4τ), as shown in FIG. There is a problem that density unevenness occurs between horizontal lines in the obtained image. In the example of FIG. 6, the density unevenness occurs when the density of the third and fifth lines becomes lighter than the density of the first and second lines when a black solid image is formed on the recording paper. It shows a state.

  In particular, when the print density on the recording paper is set to be light, the light emission time of the light emitting element is shortened, so the influence of the count value error on the drive signal is large, and the density unevenness of the image formed on the recording paper is large. Appears prominently.

  In this case, although the resolution of the LED head portion is increased, density unevenness occurs in characters, figures, and the like formed by dot printing for a plurality of horizontal lines, and the image quality is significantly lowered. .

  The present invention has been made in view of the above problems, and provides an image forming apparatus including a high-resolution LED head that does not cause density unevenness between horizontal lines.

In the present invention, density adjusting means operated by a user to adjust the density of an image formed on a recording paper and a plurality of light emitting elements are arranged in a row, and the arrangement direction thereof is parallel to the axis of the photosensitive drum. And a drive control means for controlling the light emission operation of the plurality of light emitting elements of the head, and causing the light emitting elements of the head to emit light to form a latent image of the image on the photosensitive drum in line units. A latent image forming means; and a latent image forming control means for controlling a latent image forming operation on the photosensitive drum by the latent image forming means, wherein the latent image forming control means A drive signal for controlling light emission or non-light emission of each light emitting element and a rectangular wave signal having a light emission time corresponding to the density adjusted by the density adjusting means as a pulse width are generated and transmitted to the drive control means, Drive control means The light emission time is calculated using the rectangular wave signal transmitted from the latent image formation control unit, and only the light emitting element that should emit light based on the drive signal transmitted from the latent image formation control unit is calculated. An image forming apparatus that controls to emit light only for a period of time , wherein the latent image formation control unit drives the drive with respect to a leading line of the image and a line immediately after the density of the image is changed by the density adjusting unit. A change notification signal transmitting means for transmitting a light emission time change notification signal for notifying a change in the light emission time to the latent image forming means when transmitting the signal and the rectangular wave signal, and the drive control means includes: A light emission time calculation control means for calculating the light emission time using the rectangular wave signal transmitted from the latent image formation control means only when a light emission time change notification signal is received; In the latent image formation for the line that has received the light time change notification signal and the line between the line and the line that has received the light emission time change notification signal, the light emission time calculated by the light emission time calculation control means is And a light emission time setting control means for setting the light emission time of the light emitting element of the head (claim 1).

Incidentally, the drive control unit includes a clock generating means for generating a high frequency clock than the rectangular wave signal, and a counting means for counting the number of previous chrysanthemums locks included in the pulse width of the square wave signal, The count value of the counting means may be calculated as the light emission time.

  Further, the drive control means includes light emission signal generation means for generating a light emission signal composed of a rectangular wave that is at a high level or a low level for a time obtained by counting the clock generated by the clock generation means by the number of counts by the counting means. It is preferable to control the light emission time of the light emitting element to emit light of the print head using the light emission signal generated by the light emission signal generating means.

According to the above configuration, when forming the latent image of the image on the photosensitive drum , the drive signal and density for controlling light emission or non-light emission of each light emitting element of the head from the latent image formation control unit to the latent image formation unit in units of lines. a square wave signal having a pulse width of the same period and light emission time corresponding to the adjusted adjustment means concentrations that are sent. Further, when the light emission time is initialized at the start of the apparatus and when the density is changed by the density adjusting unit, the latent image formation control unit applies the leading line and the line immediately after the density is changed by the density adjusting unit. A light emission time change notification signal is transmitted to the latent image forming means. Then, the drive control means calculates the light emission time from the rectangular wave signal only when the light emission time change notification signal is received, the line that has received the light emission time change notification signal, the line, and the light emission time change notification signal next. the latent image formation on a line between the incoming line, and controls the emission / non-emission of each light-emitting element of f head based on the driving signal, light emission is emission time calculated the light-emitting element to be emitted Thus, the latent image forming process of the image on the photosensitive drum is performed.

In the process of this, the process of calculating the light emission time from the rectangular wave signal is performed only when the head of the line and the immediately more concentration was changed to the concentration adjusting hand stage line, the latest in the line emission time not calculated The image forming process is performed using the calculated light emission time. Therefore, as long as the image density is not changed, i.e., as long as the light emission time is not changed, the latent image forming process of the image of each line to the same light emission time Dehe head photosensitive drum a light-emitting element to emit light of the image As a result, density unevenness due to light emission time calculation errors does not occur between lines.

According to the present invention, it is possible to prevent density unevenness between lines due to an error in light emission time of a light emitting element of a latent image forming unit when an image is formed in units of lines, and to achieve high resolution and high resolution. An image having a quality can be formed.

  FIG. 1 is an overview of an embodiment of an image forming apparatus according to the present invention.

  The image forming apparatus 1 according to the present embodiment is a page printer 1A that includes an LED head and forms an image on a cut sheet type sheet by a dry electrophotographic method in units of pages. The page printer 1A has a vertically long box shape, and is provided with a paper feeding unit 11 that stores paper for forming an image at the lower part of the apparatus, and paper (cut sheet) supplied from the paper feeding part 11 at the upper part of the apparatus. In addition, an image forming unit 12 for forming an image by a dry electrophotographic method is provided.

  The paper feed unit 11 has four stages of drawer-type paper feed trays 11a to 11d, and can accommodate, for example, A5, A4, A3 and B5, B4 sizes. A manual feed tray 11e for manually feeding paper is provided on the upper right side of the page printer 1A. This manual feed tray 11e can also be loaded with sheets of A5 to A3 size and B5 and B4 sizes. The paper stored or placed in the paper feed trays 11a to 11d and the manual feed tray 11e is fed to the image forming unit 12, and an image is formed while being conveyed through the image forming unit 12.

  The image forming unit 12 mainly includes a paper feeding device, a photosensitive drum, an exposure device, a developing device, a transfer device, a cleaning device, a fixing device, a paper transport device, and a paper discharge device as main components. A paper discharge tray 12A for discharging the formed paper is formed. The exposure device, the developing device, the transfer device, and the cleaning device are arranged in that order around the drum surface of the photosensitive drum along the rotation direction of the drum.

  The exposure apparatus mainly includes an LED head in which light emitting elements composed of a plurality of LEDs are linearly arranged in parallel to the axis of the photosensitive drum, and a dot pattern for each line so as to form a latent image on the surface of the photosensitive drum. 3 is composed of a drive control unit that controls light emission / non-light emission of each light emitting element of the LED head, and a light emission control unit that controls the light emission time of each light emitting element of the LED head (the LED in FIG. 3). Head unit 120). The details of the exposure mechanism according to the present invention will be described later.

  An operation panel 12B is provided on the front side of the upper right end of the image forming unit 12. The operation panel 12B includes an operation member for the user to input conditions necessary for various types of printing, such as a paper feed tray, a paper discharge tray, and print density, to the image forming apparatus 1, and operation contents of the operation member and a page printer. It functions as a display device that displays 1A status information. The operation panel 12B is provided with switches for inputting information such as a power switch, a numeric keypad, and image density, and a display device such as a liquid crystal display.

  As shown in FIG. 2, the density of the image formed on the recording paper can be adjusted in a plurality of levels (for example, 5 levels) in a dark direction and a light direction with respect to a preset standard density DS. The user can adjust the density to be darker or lighter than the standard density DS by one step by pressing the density adjustment keys KD provided in both the light and dark directions. An automatic density adjustment key KAD for automatically adjusting to the standard density is also provided, and the user resets the density shifted from the standard density DS to the standard density DS by pressing the automatic density adjustment key KAD. Can do.

  Specifically, the image density is adjusted by adjusting the light emission time of each light emitting element of the LED head, and the standard light emission time Tr with respect to the standard density DS is set in advance. Further, a change amount ΔT of the light emission time per stage that deviates from the standard density DS is also set in advance.

  When the page printer 1A is activated, the image density is initially set to the standard density DS. When the user presses the automatic density adjustment key KAD after starting the page printer 1A, the image density is automatically set to the standard density DS. That is, the light emission time of the light emitting element set in the exposure apparatus is the standard light emission time Tr. On the other hand, when the user presses the density adjustment key KD, the light emission time T is a time obtained by adding the light emission time change amount ΔT to the standard light emission time Tr (Tr + m · ΔT, where m is Each time the light is pressed in the light direction, the light emission time T is a time obtained by subtracting the light emission time change amount ΔT from the standard light emission time Tr (Tr−m · ΔT, where m is the number of times of the pressure operation).

  Returning to FIG. 1, a connection interface (not shown in FIG. 1) to which a computer is connected is provided on the back surface of the image forming unit 12. This connection interface is a 100BASE-TX or 10BASE-T connection interface standardized by, for example, Ethernet (registered trademark).

  From the computer, image data and data such as printing conditions of the image data on the paper are transmitted to the page printer 1A via the connection interface, and the image forming unit 12 performs an image forming operation on the paper based on these data. Done.

  That is, the image forming unit 12 rotates the photosensitive drum, and operates a predetermined light emitting element of the LED head of the exposure apparatus based on the image data when the predetermined latent image forming position on the drum surface reaches the predetermined exposure position. Light is emitted for a predetermined light emission time T based on the density setting value on the panel 12B to form a latent image for one page on the photosensitive drum, and when the latent image reaches a predetermined development position by rotation of the photosensitive drum. Then, the latent image is visualized by attaching toner. Further, the image forming unit 12 conveys the paper supplied from the paper feeding unit 11 or the manual feed tray 11e to the photosensitive drum by the paper feeding device at a predetermined timing, and the toner image visualized by the rotation of the photosensitive drum. When the toner reaches a predetermined transfer position, the transfer device transfers the toner image onto the paper to form an image, then transports the paper to the fixing device, and the fixing device fixes the image formed on the paper. After performing, it discharges to the paper discharge tray 12A.

  The photosensitive drum on which the toner image is transferred to the paper is cleaned of the toner remaining on the drum surface by the cleaning device, and when the latent image forming position reaches the predetermined exposure position again by the rotation of the photosensitive drum, the exposure device A latent image of the next page is formed based on the image data of the next page, and the series of image forming operations described above is performed by the developing device to the fixing device. Thereafter, the same image forming operation is performed on the image data of all pages.

  FIG. 3 is a block diagram of an electrical circuit related to the exposure mechanism of the page printer 1A according to the present invention.

  The page printer 1A includes a control unit 100, an operation unit 110 connected to the control unit 100, and an LED head unit 120 as an electrical circuit related to the exposure mechanism. The operation unit 110 corresponds to the operation panel 12B of the page printer 1A described above, and includes a power switch, a numeric keypad, other switches, and a control member for inputting the operation content of these operation members to the control unit 100. It is out.

  The control unit 100 executes processing of a print command transmitted from an externally connected computer (not shown). The control unit 100 controls the drive of the above-described unillustrated paper feeding device, photoconductor drum, exposure device, developing device, transfer device, cleaning device, fixing device, paper transport device, and paper discharge device from the computer. An image forming process is performed in response to the print command.

  The control unit 100 includes a storage device such as a ROM (Read Only Memory), a RAM (Random Access Memory), and an HD (Hard Disc). The ROM executes a processing program for performing an image forming process and the processing program. And processing data necessary for processing. The above-described data of the standard light emission time Tr and the light emission time change amount ΔT are also stored in advance in the ROM as processing data. When the page printer 1A is activated, the control unit 100 reads the processing program and processing data from the ROM into a predetermined work area of the RAM or HD, and executes the processing program. Accordingly, the page printer 1A enters a standby state, and when a print command is transmitted from the computer, an image forming process designated by the print command is executed.

  The LED head unit 120 exposes the surface of the photosensitive drum based on the bit pattern data transmitted from the control unit 100 in units of lines, thereby changing the latent image (the surface potential of the photosensitive drum in accordance with the bit patterns) in units of lines. A potential image), which is a substantial component of the exposure apparatus. The LED head unit 120 includes a bar-shaped LED head 121 parallel to the axis of the photosensitive drum, a drive control unit 122 that controls the driving of the LED head 121, and a light emission control unit 123 that controls the light emission time of the LED head 121. have.

  The LED head 121 has N [dpi (dot per inch)] resolution and L (inch) printable size, and the light emitting elements composed of LEDs are arranged in the longitudinal direction by the number of dots corresponding to N × L. It is a thing. In the present embodiment, light emitting elements for 10800 dots are arranged.

  Each LED of the LED head 121 is electrically connected to the drive control unit 122 and the light emission control unit 123 via the AND circuit 121a. That is, the drive control unit 122 outputs a drive signal Sp indicating whether or not each LED of the LED head 121 emits light based on bit pattern data (hereinafter referred to as print data D) of each horizontal line, and the light emission control. Since the unit 123 outputs a light emission signal Sq (a rectangular wave signal that is turned on only for the light emission time T) to each LED of the LED head 121, the AND circuit 121a emits a drive signal Sp and light emission to each LED of the LED head 121. A signal Sd that is a logical product of the signal Sq (hereinafter referred to as a light emission control signal Sd) is input.

  Among the print data, for example, a high level drive signal Sp is output from the drive control unit 122 to the LED corresponding to the dot to which the bit data of “1” is input, so the AND circuit 121a corresponding to this LED A light emission control signal Sd composed of the same rectangular wave signal as the light emission signal Sq is output and input to the LED. Therefore, this LED emits light only during the ON period of the light emission signal Sq. On the other hand, the low-level drive signal Sp is output from the drive control unit 122 to the LED corresponding to the dot to which the bit data of “0” is input. Therefore, the AND circuit 121a corresponding to this LED emits the light emission signal Sq. The same rectangular wave signal is not output (that is, the low-level light emission control signal Sd is output), and the LED does not emit light.

  The control unit 100 and the LED head unit 120 are electrically connected by six signal lines L1 to L6. More specifically, the signal lines L1 to L4 are connected to the drive control unit 122 in the LED head unit 120, and the signal lines L5 and L6 are connected to the light emission control unit 123 in the LED head unit 120.

  The signal line L1 is for transferring the print data D from the control unit 100 to the LED head unit 120. The signal line L2 is for transmitting the transfer clock CKT from the control unit 100 to the LED head unit 120. The transfer clock CKT is used as a synchronization signal for receiving each bit data of the print data D by the LED head unit 120.

  The signal line L3 is for transmitting a print data transfer start signal STS indicating the start of transfer of the print data D from the control unit 100 to the LED head unit 120. The signal line L4 is for transmitting a print data transfer end signal STE indicating the end of transfer of print data from the control unit 100 to the LED head unit 120. Accordingly, the drive control unit 122 in the LED head unit 120 recognizes that the transfer of the print data D from the control unit 100 is started by receiving the print data transfer start signal STS, and the print data transferred thereafter. Each bit data of D is received in synchronization with the transfer clock CKT.

  The drive control unit 122 has a built-in memory 122a for storing print data D for one line (bit data for 10800 dots in this embodiment), and sequentially stores the received bit data in the memory 122a. Since 10800 bits of print data D for each horizontal line is transferred from the control unit 100 in multiples of 32 bits, the drive control unit 122 receives the print data D in 32 bits and receives the memory 122a. Are stored in sequence. Then, after the reception of the print data D is completed, the drive control unit 122 reads 10800 bits of data from the memory 122a and forms each LED corresponding to each bit data when forming a latent image using the print data D. Output to the LED of the head 121 (more specifically, to the AND circuit 121a corresponding to the LED).

  The signal line L5 is for transmitting the LED drive signal SLD from the control unit 100 to the LED head unit 120. This LED drive signal SLD is a signal for calculating the light emission time T of the LED described above by the light emission control unit 123 in the LED head unit 120, and is specifically a rectangular wave signal that becomes high level only for the light emission time T. .

  The light emission control unit 123 converts a numerical value n (number) corresponding to the light emission time T from the LED drive signal SLD, and converts the numerical value n calculated by the counter 123a into an actual light emission time T (seconds). And a light emission signal generation circuit 123b that generates a light emission signal Sq composed of a rectangular wave signal that is at a high level for the light emission time T.

  The counter 123a receives a control clock CKC having a frequency higher than that of the LED drive signal SLD from the drive control unit 122. The counter 123a receives the control clock CKC at the rising timing of the LED drive signal SLD input from the control unit 100. Counting the number of clocks is started, and the counting operation is performed until the falling timing. When the counting is completed, the count value n is held in a memory (not shown) and input to the light emission signal generation circuit 123b.

  In the present embodiment, the high level period of the LED drive signal SLD is counted using the control clock CKC generated by the drive control unit 122. However, the clock generator is incorporated in the counter 123a, and the clock generator A high level period of the LED drive signal SLD may be counted using the generated clock.

  The light emission signal generation circuit 123b calculates the light emission time T by multiplying the count value n and the period τ of the control clock CKC, generates a rectangular wave signal (light emission signal Sq) that is at a high level only for this light emission time T, and an AND circuit. Input to 121a. The period τ of the control clock CKC is set in advance in the light emission signal generation circuit 123b.

  In the present embodiment, the drive signal Sp and the light emission signal Sq are high-level rectangular wave signals, but may be low-level rectangular wave signals. In this case, a NOR circuit is used instead of the AND circuit 121a.

  The signal line L6 is for transmitting a light emission time change notification signal SH for notifying the LED head unit 120 of a change in the light emission time from the control unit 100. Since the light emission time change notification signal SH is changed by the user by operating the density adjustment key KD of the operation panel 12B and changing the image density, the light emission time T of the LED also changes accordingly. This is a signal for notifying 120 that the light emission time T changes.

  In the present embodiment, an image density adjustment method that increases or decreases the density relative to the standard image density is employed. Therefore, whenever the user operates the density adjustment key KD on the operation panel 12B, the image density adjustment key KD is always operated. Since the density changes and the light emission time changes accordingly, the light emission time change notification signal SH is transmitted from the control unit 100 to the LED head unit 120 in accordance with the user's operation of the density adjustment key KD. That is, the light emission time change notification signal SH is substantially the operation information of the user's density adjustment key. However, in the image density adjustment method in which any one of the density values of a plurality of images is selected, the density value of the same image may be set even when the user operates the density adjustment key KD. In this case, the light emission time does not change. Therefore, when this image density adjustment method is adopted, the controller 100 controls the LED head unit only when the image density setting value changes, that is, when the light emission time changes. The light emission time change notification signal SH may be transmitted to 120.

  As will be described later, the page printer 1A according to the present embodiment transmits an LED drive signal SLD from the control unit 100 to the LED head unit 120 each time print data D is transferred in line units. When the light emission time T is first calculated from the LED drive signal SLD, the light emission time T is not calculated for the subsequent LED drive signal SLD, and the light emission time T calculated first is held. ing.

  Normally, unless the image density is changed by the user operating the density adjustment key KD of the operation panel 12B, an image should be formed uniformly at the set density. Even if the calculated light emission time T has an error with respect to the light emission time T transmitted from the control unit 100 to the LED head unit 120, the LED head unit 120 is not changed until the image density is changed by the user. As shown in FIG. 6, unevenness in image density occurs between the horizontal lines due to a calculation error caused by calculating the light emission signal T for each LED drive signal SLD. This is to prevent it.

  Therefore, when the counter 123a in the LED head unit 120 receives the light emission time change notification signal SH, immediately after that, the counter 123a calculates the light emission time T from the LED drive signal SLD transmitted from the control unit 100 and holds it first. The light emission time T is updated to the newly calculated light emission time T. As a result, the light emission signal Sq output from the light emission time generation circuit 123b is changed to the light emission signal Sq of the light emission time T newly calculated during the high level period.

  Next, the printing operation of the page printer 1A according to the present embodiment will be described with reference to the time chart of FIG.

  FIG. 4 shows print data D, transfer clock CKT, print data transfer start signal STS, print data transfer end signal STE, LED drive signal SLD, and light emission time change notification signal when two prints are printed. FIG. 7 is a time chart of SH, light emission signal Sq, and control clock CKC, and shows a time chart when the user sets an image density by operating a density adjustment key when printing each printed matter. In the following description, the timing at which each signal is transmitted or transferred from the control unit 100 to the LED head unit 120 will be described as the first rising timing or falling timing of each signal.

  As shown in the figure, when printing the first printed matter, first, the control unit 100 transmits the light emission time change notification signal SH to the LED head unit 120, and immediately after that, the LED drive signal SLD is transmitted. . The light emission time change notification signal SH is a rectangular wave signal having a high level period including a high level period of the LED drive signal SLD. When the counter 123a of the LED head unit 120 detects the rise of the light emission time change notification signal SH, the counter 123a starts counting the control clock CKC at the timing when the LED drive signal SLD rises thereafter, and at the fall timing of the LED drive signal SLD. The count ends. Then, the count value n is stored in the memory. In the example of FIG. 4, the count value n = 4 is stored in the memory.

  Further, after the light emission signal change notification signal SH and the LED drive signal SLD are transmitted from the control unit 100 to the LED head unit 120, the print data transfer start signal STS is transmitted, and immediately after that, the print data D of the first line The transfer clock CKT is transferred (see the portion corresponding to the print data D of the first line of the first printed product in FIG. 4). When the drive control unit 122 of the LED head unit 120 detects the rising edge of the print data transfer start signal STS, the drive control unit 122 receives each bit data of the print data D input thereafter in synchronization with the transfer clock CKT, and sequentially stores the memory 122a. To remember. The drive control unit 122 continues the reception operation of the print data D until the rising edge of the print data transfer end signal STE is detected.

  When the drive control unit 122 of the LED head unit 120 finishes receiving the print data D of the first line, the print control of the print data D is performed. That is, after receiving the print data transfer end signal STE, the drive control unit 122 outputs each bit data of the print data D of the first line from the memory 122a to the corresponding AND circuit 121a at a predetermined timing, and the light emission control. A command signal for causing the unit 123 to output the light emission time T is output. The light emission control unit 123 operates the light emission signal generation circuit 123b according to this command signal, and outputs the light emission signal Sq to all the AND circuits 121a. That is, the light emission signal generation circuit 123a generates a light emission signal Sq that is high for a period T = n × τ when the control clock CKC is counted by the count value n input from the counter 123a, and outputs the light emission signal Sq to all the AND circuits 121a. To do. In the example of FIG. 4, since n = 4, the light emission signal Sq that is at the high level for the time T = 4τ is input to all the AND circuits 121a.

  As a result, a light emission control signal Sd for controlling the light emission operation for the corresponding LED from each AND circuit 121a (a signal that is at a high level only for the light emission time T for an LED that should emit light, and for an LED that should not emit light) A low level signal) is output, and each LED is controlled to emit or not emit light based on this signal. That is, a latent image of the first line is formed on the surface of the photosensitive drum.

  During the printing operation of the first line of print data or after the end of the print operation, the print data of the second line is transmitted from the control unit 100 to the LED head unit 120 in the same manner as the print data of the first line. However, at this time, since the density change operation is not performed by the user, the light emission time change notification signal SH is not transmitted from the control unit 100 to the LED head unit 120. Accordingly, the LED drive signal SLD is first transmitted from the control unit 100 to the LED head unit 120, and immediately after that, the print data transfer start signal STS is transmitted. Immediately thereafter, the print data D and transfer clock of the second line are transmitted. CKT is transferred (see the portion corresponding to the print data D on the second line in FIG. 4).

  Since the LED head unit 120 does not receive the light emission time change notification signal SH, even if the LED drive signal SLD is received, the light emission time T is not counted, and the print data for the second line is processed in the same manner as the first line. Only receive. When reception of the print data for the second line is completed, the LED head unit 120 outputs each bit data of the print data D for the second line from the memory 122a to the corresponding AND circuit 121a at a predetermined timing, and emits light. A command signal for causing the control unit 123 to output the light emission time T is output. The light emission control unit 123 operates the light emission signal generation circuit 123b according to this command signal, and outputs the light emission signal Sq to all the AND circuits 121a. At this time, since the count value n calculated first is input to the light emission signal generation circuit 123b, the light emission signal generation circuit 123b generates a light emission signal Sq having the same light emission time T as in the first line, Output to all AND circuits 121a. That is, in the example of FIG. 4, since n = 4, the light emission signal Sq that becomes the high level for the time T = 4τ in the second line is input to all the AND circuits 121a.

  Accordingly, the print processing for the print data of the second line is performed with the same light emission time T as the print data of the first line. In this example, since it is assumed that the user does not change the density during the printing process of the first printed matter, the printing data from the third line to the last line is also referred to as the second line printing data. Similar print processing is performed. In other words, in the example of FIG. 4, the light emission signal Sq that is at the high level for the time T = 4τ from the second line to the last line is input to all the AND circuits 121a, and image forming processing is performed. As a result, the latent image forming process on the photosensitive drums of all the lines is performed with the same light emission time T, so that density unevenness due to the error of the light emission time T of the LED head unit 120 occurs in the first printed matter. There is nothing.

  Next, when proceeding to the printing process for the second printed material, the image density has been changed by the user at this time, so when performing the printing process for the first line of the second printed material, The light emission time change notification signal SH is transmitted from the control unit 100 to the LED head unit 120, and immediately after that, the LED drive signal SLD is transmitted. When the counter 123a of the LED head unit 120 detects the rising edge of the light emission time change notification signal SH, the counter 123a counts the high level period of the LED drive signal SLD received thereafter, and stores the memory content in the count value n ′. Update. That is, the count value n calculated during the printing process of the first printed matter is replaced with the newly calculated count value n ′. In the example of FIG. 4, since the count value n ′ = 5, the count value “4” in the memory is updated to the count value “5”.

  Subsequently, when the print data transfer start signal STS is transmitted from the control unit 100 to the LED head unit 120 and the print data D and the transfer clock CKT on the first line are transferred immediately thereafter, the LED head unit 120 is driven. The control unit 122 receives each bit data of the print data D in synchronization with the transfer clock CKT, and sequentially stores it in the memory 122a (corresponding to the print data D on the first line of the second printed matter in FIG. 4). See the part to do).

  When the drive control unit 122 of the LED head unit 120 receives the print data D for the first line, the drive control unit 122 uses the same method as the print process for the print data for the first line of the first printed matter described above. The print data D is printed. In this case, the light emission that becomes high for the period T ′ = n ′ × τ in which the control clock CKC is counted by the count value n ′ input from the counter 123a is sent from the light emission signal generation circuit 123b to all the AND circuits 121a. Signal Sq is output. In the example of FIG. 4, since n '= 5, the light emission signal Sq that is at the high level for the time T = 5τ is input to all the AND circuits 121a.

  As a result, the light emission control signal Sd from each AND circuit 121a to the corresponding LED (a signal that becomes high level only for the light emission time T ′ for the LED that should emit light, and a low level signal for the LED that should not emit light). ) Is output, and each LED is controlled to emit or not emit light based on this signal. That is, a latent image of the first line is formed on the surface of the photosensitive drum.

  Since the user does not change the image density for the second printed matter, the print processing of the print data D from the second line to the last line is performed on the first printed matter described above. This is performed in the same manner as the print processing of print data D for the second and subsequent lines. In other words, in the example of FIG. 4, the light emission signal Sq that is at the high level for the time T = 5τ from the second line to the last line is input to all the AND circuits 121a, and the image forming process is performed.

  As described above, in the second printed matter, the light emission time is calculated again based on the light emission time change notification signal SH by the LED head unit 120, and the previously calculated light emission time T is changed to the light emission time T ′ calculated later. Therefore, the second printed matter is printed at an image density that is totally different from that of the first printed matter. Since the latent image forming process on the photosensitive drums of all the lines is performed for the second printed matter in the same light emission time T ′, the density unevenness caused by the error in the light emission time T of the LED head unit 120 is also performed. Will not occur.

  As described above, in the page printer 1A according to this embodiment, the control unit 100 transmits the light emission time change notification signal SH for notifying the LED head unit 120 of the light emission time change based on the user density change operation. Since the light emission time T is calculated from the LED drive signal SLD transmitted from the controller 100 only when the light emission time change notification signal SH is received, the light emission time of the LED head 121 is controlled by the light emission time T. By calculating the light emission time T from the LED drive signal SLD for each line as in the prior art, it is possible to eliminate an error in the light emission time T between the lines. As a result, it is possible to reduce unevenness in the image density of the printed matter due to the error in the light emission time T of the LED head 121.

  In the above embodiment, a dry electrophotographic printer using an LED head has been described. However, the present invention can be applied to a multifunction machine such as a copying machine or a facsimile machine equipped with a printer using an LED head. it can. In the above embodiment, image formation using cut sheet type paper has been described. However, the present invention can be similarly applied to image formation using continuous sheet type paper.

1 is an overview of an embodiment of a page printer according to the present invention. It is a figure which shows the relationship between the adjustment amount of image density, and the light emission time. It is a block block diagram of the electrical circuit regarding the exposure mechanism of the page printer which concerns on this invention. Time chart of print data, transfer clock, print data transfer start signal, print data transfer end signal, LED drive signal, light emission time change notification signal, light emission signal, and control clock when printing operation is performed for two printed materials FIG. 5 is a diagram illustrating a time chart when the user sets the image density by operating the density adjustment key when printing each printed matter. It is a time chart which shows the operation | movement of the light emission control in the system which transmits the drive signal of a light emitting element directly to a LED head from the conventional control part. It is a figure which shows an example of the density nonuniformity of the image which arises due to the error of the light emission time calculated based on a drive signal in an LED head part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 1A Page printer 11 Paper feed part 11a-11d Paper feed tray 11e Manual feed tray 12 Image forming part 12A Paper discharge tray 12B Operation panel 100 Control part (Control means, Light emission time setting means, Print control means, Change notification means )
110 Operation section 120 LED head section (printing means)
121 LED head 122 drive control unit (calculation control means, light emission time control means)
122a memory 123 light emission control unit 123a counter (light emission time calculation means)
123b Light emission signal generation circuit (drive control means)
KD Density adjustment key (Density adjustment means)
KAD automatic density adjustment key (density adjustment means)

Claims (3)

A density adjusting means operated by a user to adjust the density of an image formed on a recording paper, and a head in which a plurality of light emitting elements are arranged in a row and arranged in parallel with the axis of the photosensitive drum And a drive control means for controlling the light emission operation of the plurality of light emitting elements of the head, and the latent image forming means for forming the latent image of the image on the photosensitive drum in units of lines by causing the light emitting elements of the head to emit light. And latent image formation control means for controlling a latent image formation operation on the photosensitive drum by the latent image formation means,
The latent image formation control unit is a rectangular wave having a pulse width as a drive signal for controlling light emission or non-light emission of each light emitting element of the head and a light emission time corresponding to the density adjusted by the density adjustment unit for each line. A signal is generated and transmitted to the drive control means,
The drive control unit calculates a light emission time using the rectangular wave signal transmitted from the latent image formation control unit, and emits light based on the drive signal transmitted from the latent image formation control unit An image forming apparatus that performs control to emit light only for the calculated light emission time ,
The latent image formation control means includes:
Light emission time change for notifying a change in light emission time when the drive signal and the rectangular wave signal are transmitted to the first line of the image and the line immediately after the density of the image is changed by the density adjusting means A change notification signal transmitting means for transmitting a notification signal together with the latent image forming means;
The drive control means includes
A light emission time calculation control means for calculating the light emission time using the rectangular wave signal transmitted from the latent image formation control means only when the light emission time change notification signal is received;
In the latent image formation with respect to a line that has received the light emission time change notification signal and a line between that line and the next line that has received the light emission time change notification signal, the light emission time calculated by the light emission time calculation control means is used. A light emission time setting control means for setting the light emission time of the light emitting element of the head;
An image forming apparatus comprising: Said drive control means includes a clock generating means for generating a high frequency clock than the rectangular wave signal, and a counting means for counting the number of previous chrysanthemums locks included in the pulse width of the rectangular wave signal, said counting 2. The image forming apparatus according to claim 1, wherein the count value of the means is calculated as the light emission time.   The drive control means includes a light emission signal generation means for generating a light emission signal composed of a rectangular wave that is at a high level or a low level for a time obtained by counting the clock generated by the clock generation means by the count number by the counting means, 3. The image forming apparatus according to claim 2, wherein a light emission time of a light emitting element to emit light of the print head is controlled using a light emission signal generated by the light emission signal generating means.

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