JP6696355B2 - Exposure control apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure control device and an image forming apparatus.

  In an electrophotographic printer, an electrostatic latent image is formed by exposing a charged photoconductor with an exposure device, and the image obtained by developing the electrostatic latent image with a color material such as toner is used as a printing paper or the like. The image is formed by transferring the image onto the recording medium and fixing it.

  As a light emitting device of this exposure apparatus, a method of scanning a laser beam to expose a photoconductor has been widely used. However, in recent years, an exposure apparatus of a method in which a plurality of light emitting elements such as LEDs are arranged (hereinafter, referred to as “LED PRINT HEAD method”) has been used instead of the laser light.

  When an exposure device is configured using such an LED PRINT HEAD method, a plurality of light emitting elements such as LEDs are arranged on one line, and exposure control is realized by sequentially performing lighting control of the plurality of light emitting elements. is doing.

  Here, the exposure amount of the light emitting element is determined by the product of the light emission intensity of each light emitting element and the light emission time. Therefore, in order to realize the required exposure amount, the required exposure amount is realized by changing the pulse width of the pulse signal for lighting each light emitting element and adjusting the lighting time of each light emitting element. ing.

  In Patent Document 1, the density control data is stored, and the exposure control signal is controlled so that the relationship between the exposure amount and the exposure time of the light source controlled by the exposure control signal for performing the lighting control of the LED PRINT HEAD system is linear. An image forming apparatus is disclosed which corrects at least one of current, voltage, and exposure time.

  In Patent Document 2, the surface potential of the photosensitive drum after the main scanning of the photosensitive drum with a constant amount of laser light is measured, and the frequency of potential unevenness of the surface potential is separated into a low frequency component and a high frequency component, and an image signal When an image is actually formed on the basis of the above, the potential unevenness related to the low frequency component is corrected by the laser drive current (bias current), and the potential unevenness related to the high frequency component is corrected by the PWM pulse width. An image forming apparatus is disclosed that reduces the above surface potential unevenness.

  Patent Document 3 discloses a light emitting device that drives a light emitting element by determining a pulse width and a current value of a drive signal based on a correction coefficient stored in advance.

JP, 2003-182143, A JP, 2005-234032, A JP, 2007-125705, A

  In the LED PRINT HEAD type exposure apparatus as described above, in order to realize the required exposure amount, the voltage and current of the pulse signal are switched to expand the adjustment range of the exposure amount.

  However, the exposure amount required for the exposure apparatus changes depending on the temperature and the like. For example, in a light emitting element including a semiconductor element such as an LED, the amount of light decreases as the temperature rises. Therefore, the required exposure amount may change even during continuous printing processing based on one print job (print instruction). In such a case, if the voltage or current of the pulse signal is switched during the printing process based on one print job, the quality of the printing process may not be maintained.

  This is because it takes a certain amount of time to switch the voltage and the current, so that the continuous printing process is temporarily stopped. Further, in reality, the waveform of the pulse signal is not an ideal rectangular shape due to the influence of parasitic capacitance and the like, so there is a possibility that a continuous change in the exposure amount cannot be realized when the voltage or current of the pulse signal is switched. .. Therefore, if the voltage or current of the pulse signal is switched during the continuous printing process, the printing density may suddenly change.

  An object of the present invention is to eliminate the need to switch the voltage or current for lighting the light emitting elements during the printing process based on one print instruction when sequentially controlling the lighting of the plurality of light emitting elements. An object of the present invention is to provide a possible exposure control device and image forming apparatus.

[Exposure control device]
The present invention according to claim 1 is a switching means for switching the voltage applied to the plurality of light emitting elements to either the first voltage or the second voltage,
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the voltage applied to the plurality of light emitting elements is set to the first voltage or the second voltage. And a control means for performing a control for adjusting the lighting time of the plurality of light emitting elements while selecting one of the voltages and switching by the switching means,
Adjustment range of the exposure amount that can be realized by changing the lighting time in a state where the first voltage is applied to the plurality of light emitting elements, and a state where the second voltage is applied to the plurality of light emitting elements The overlapping range of the adjustment range of the exposure amount that can be achieved by changing the lighting time is wider than the range of the required exposure amount that is expected to change during the printing process based on one print instruction. Exposure control device.

  According to a second aspect of the present invention, in the case where the control unit can realize the required exposure amount with either the first voltage or the second voltage, the first voltage and the second voltage can be obtained. The exposure control apparatus according to claim 1, wherein a high voltage is selected from among the selected voltages to switch the switching means.

According to a third aspect of the present invention, there is provided switching means for switching the voltage applied to the plurality of light emitting elements to either the first voltage or the second voltage,
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the voltage applied to the plurality of light emitting elements is set to the first voltage or the second voltage. And a control means for performing a control for adjusting the lighting time of the plurality of light emitting elements while selecting one of the voltages and switching by the switching means,
Adjustment range of the exposure amount that can be realized by changing the lighting time in a state where the first voltage is applied to the plurality of light emitting elements, and a state where the second voltage is applied to the plurality of light emitting elements The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time is less than the range of the required exposure amount that is expected to fluctuate during execution of the printing process based on one print instruction. The exposure control device is also characterized by being wide.

  According to a fourth aspect of the present invention, when the control unit includes the requested exposure amount in a range in which the exposure amount is larger than the center of the range where the two adjustment ranges overlap, the first and the first If a higher voltage is selected from the two voltages, and the two adjustment ranges are included in a range where the exposure amount is smaller than the center of the overlapping range, the lower voltage is selected from the first and second voltages. The exposure control device according to claim 3, wherein the switching means is switched.

The present invention according to claim 5 further comprises storage means for storing values according to respective light emission characteristics of the plurality of light emitting elements,
5. The exposure control device according to claim 1, wherein the control unit performs control for adjusting the lighting time of each of the plurality of light emitting elements based on the value stored in the storage unit.

According to a sixth aspect of the present invention, there is provided switching means for switching the value of the current flowing through the plurality of light emitting elements to either the first current value or the second current value,
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the value of the current flowing through the plurality of light emitting elements is set to the first current value or the A control unit that selects any one of the second current values and switches by the switching unit, and that controls the lighting time of the plurality of light emitting elements.
The adjustment range of the exposure amount that can be realized by changing the lighting time with the value of the current flowing through the plurality of light emitting elements set to the first current value, and the value of the current flowing through the plurality of light emitting elements are described above. The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time in the state where the second current value is set is the required exposure amount that is expected to change during the execution of the printing process based on one print instruction. The exposure control device is characterized by being wider than the range.

[Image forming device]
According to a seventh aspect of the present invention, a plurality of light emitting elements, a switching means for switching a voltage applied to the plurality of light emitting elements to either a first voltage or a second voltage, and each of the input image data. When sequentially performing control to turn on or off the plurality of light emitting elements based on the pixel value, select either the first voltage or the second voltage as the voltage to be applied to the plurality of light emitting elements. And a control means for controlling the lighting time of the plurality of light emitting elements while switching by the switching means, and changing the lighting time while the first voltage is applied to the plurality of light emitting elements. The exposure amount adjustment range that can be realized by doing so and the exposure amount adjustment range that can be realized by changing the lighting time in the state where the second voltage is applied to the plurality of light emitting elements overlap. An exposure apparatus characterized by being wider than a required exposure amount range in which a variation is assumed during execution of a printing process based on one print instruction;
A developing device for developing the electrostatic latent image on the image carrier exposed by the exposing device;
The image forming apparatus includes a transfer unit that transfers the image on the image carrier developed by the developing device onto a recording medium.

  According to the first aspect of the present invention, when the lighting control of a plurality of light emitting elements is sequentially performed, it is not necessary to switch the voltage for lighting the light emitting elements during the printing process based on one print instruction. It is possible to provide an exposure control device capable of performing the above.

  According to the present invention of claim 2, when the lighting control of the plurality of light emitting elements is sequentially performed, the light emitting elements are turned on even when the required exposure amount increases during the printing process based on one print instruction. It is possible to provide an exposure control device capable of eliminating the need to switch the voltage for operating.

  According to the present invention of claim 3, when the lighting control of the plurality of light emitting elements is sequentially performed, it is not necessary to switch the voltage for lighting the light emitting elements during the printing process based on one print instruction. It is possible to provide an exposure control device capable of performing the above.

  According to the present invention of claim 4, when the lighting control of the plurality of light emitting elements is sequentially performed, the required exposure amount increases or decreases during the printing process based on one print instruction. In any of the above cases, it is possible to provide an exposure control device capable of avoiding switching the voltage for turning on the light emitting element.

  According to the fifth aspect of the present invention, even when the light emitting characteristics of the plurality of light emitting elements are different from each other, the variation in the exposure amount of each light emitting element is compared with the case of uniformly controlling the lighting time of the plurality of light emitting elements. It is possible to provide an exposure apparatus capable of suppressing the above.

  According to the present invention of claim 6, when the lighting control of the plurality of light emitting elements is sequentially performed, it is not necessary to switch the current for lighting the light emitting elements during the printing process based on one print instruction. It is possible to provide an exposure apparatus capable of performing the above.

  According to the present invention of claim 7, when the lighting control of the plurality of light emitting elements is sequentially performed, it is not necessary to switch the voltage for lighting the light emitting elements during the printing process based on one print instruction. It is possible to provide an image forming apparatus capable of performing the above.

It is a figure which shows the structure of the image forming apparatus 10 of the 1st Embodiment of this invention. FIG. 3 is a diagram showing a configuration of the print head 140 shown in FIG. 1. It is a figure for demonstrating the structure of the light-emitting device 50 shown in FIG. 3 is a diagram showing a circuit configuration of a light emitting chip 60. FIG. It is a figure which shows the equivalent circuit of a thyristor. FIG. 6 is a diagram for explaining the operation of the equivalent circuit of the thyristor shown in FIG. 5. FIG. 6 is a diagram for explaining a print image when a print process is performed on one print sheet. It is a figure for demonstrating the relationship between a line period and a transfer period. 30 light-emitting chips 60 _through 603 ₃₀ lighting control target of the light-emitting thyristor for each is a diagram showing how the (light emitting element) is gradually switched. 6 is a diagram showing a configuration of a lighting control circuit 80 for controlling lighting of the light emitting device 50. FIG. It is a figure which shows an example of the relationship of the light emission intensity of a light emitting thyristor, and time. It is a figure for demonstrating the case where each exposure amount adjustment range in the state which two voltages are applied does not overlap. It is a figure for demonstrating the case where each exposure amount adjustment range in the state which two voltages are applied does not overlap. It is a figure for demonstrating the case where each exposure amount adjustment range in the state which two voltages are applied does not overlap. It is a figure for demonstrating the case where each exposure amount adjustment range overlaps in the state where two voltages are applied. It is a figure for demonstrating the case where a low voltage is selected in order to implement | achieve required exposure amount Y1 in FIG. It is a figure for demonstrating the case where two voltages can be selected in order to implement | achieve required exposure amount Y2 in FIG. It is a figure for demonstrating the case where each exposure amount adjustment range in the state where two voltages were applied in the 2nd Embodiment of this invention overlap. FIG. 19 is a diagram for explaining a method of selecting a voltage in accordance with a position in the overlapping range of the required exposure amount in FIG. 18.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram showing the configuration of an image forming apparatus 10 according to the first embodiment of the present invention.

  As shown in FIG. 1, the image forming apparatus 10 includes an image reading device 12, an image forming unit 14, an intermediate transfer belt 16, a paper tray 17, a paper conveyance path 18, a fixing device 19, and a control unit 20. The image forming apparatus 10 has not only a printer function for printing image data received from a personal computer (not shown) or the like, but also a function as a full-color copying machine using the image reading device 12 and a function as a facsimile. It is a multifunctional machine.

  First, an outline of the image forming apparatus 10 will be described. Above the image forming apparatus 10, an image reading device 12 and a control unit 20 are arranged. The image reading device 12 reads the image displayed on the document and outputs the image to the control unit 20. The control unit 20 performs gradation correction, resolution correction, and the like on image data input from the image reading device 12 or image data input from a personal computer (not shown) or the like via a network line such as a LAN. Image processing is performed, the operation of the image forming unit 14 is controlled, and processing for generating an image based on image data is executed.

  Below the image reading device 12, four image forming units 14 are arranged corresponding to colors forming a color image. In the present embodiment, four image forming units 14K, 14Y, 14M, and 14C are arranged along the intermediate transfer belt 16 corresponding to each color of black (K), yellow (Y), magenta (M), and cyan (C). Are arranged horizontally at regular intervals. The intermediate transfer belt 16 rotates in the direction of arrow A in the figure as an intermediate transfer member, and these four image forming units 14K, 14Y, 14M, and 14C are of the respective colors based on the image data input from the control unit 20. Toner images are sequentially formed, and these toner images are transferred (primary transfer) to the intermediate transfer belt 16 at a timing when they are superimposed on each other. The order of the colors of the image forming units 14K, 14Y, 14M, and 14C is not limited to black (K), yellow (Y), magenta (M), and cyan (C), but yellow (Y). ), Magenta (M), cyan (C), black (K), and so on.

  The paper transport path 18 is arranged below the intermediate transfer belt 16. The recording paper 32 supplied from the paper tray 17 is conveyed on the paper conveyance path 18, and the toner images of the respective colors transferred onto the intermediate transfer belt 16 are transferred together (secondary transfer), The transferred toner image is fixed by the fixing device 19 and is discharged to the outside along the arrow B.

  Next, each configuration of the image forming apparatus 10 will be described in more detail.

  The image forming units 14K, 14Y, 14M and 14C (image forming means) are arranged in parallel in the horizontal direction at regular intervals, and have substantially the same configuration except that the colors of images to be formed are different. Therefore, the image forming unit 14K will be described below. The configuration of each image forming unit 14 is distinguished by adding K, Y, M, or C.

  The image forming unit 14K performs an exposure process according to the image data input from the control unit 20 to form an electrostatic latent image, and an image formation in which the electrostatic latent image is formed by the print head 140K. Device 150K.

  The print head 140K has a configuration in which a plurality of light emitting elements such as light emitting diodes (LEDs) and light emitting thyristors are arranged, and the light emitting elements corresponding to each pixel of the image data from the control unit 20 are turned on / off. Under the control, the photosensitive drum 152K is exposed.

  The image forming apparatus 150K includes a photosensitive drum 152K as an image carrier that rotates at a predetermined rotation speed in the direction of arrow A, a charging device 154K that uniformly charges the surface of the photosensitive drum 152K, and an exposure device. The cleaning device includes a developing device (developing device) 156K that develops the electrostatic latent image formed on the photosensitive drum 152K exposed by the device, and a cleaning device 158K. The photoconductor drum 152K is uniformly charged by the charging device 154K, and an electrostatic latent image is formed by the light emitted from the print head 140K that constitutes the exposure device. The electrostatic latent image formed on the photoconductor drum 152K is developed with black (K) toner by the developing device 156K and transferred to the intermediate transfer belt 16. Note that residual toner, paper dust, and the like that have adhered to the photoconductor drum 152K after the toner image transfer step are removed by the cleaning device 158K.

  Similarly to the above, the other image forming units 14Y, 14M and 14C also form yellow (Y), magenta (M) and cyan (C) toner images, and intermediately transfer the formed toner images. Transfer to the belt 16.

  On the intermediate transfer belt 16, primary transfer rolls 162K, 162Y, 162M, 162C are arranged at positions facing the image forming units 14K, 14Y, 14M, 14C, respectively, and the photosensitive drums 152K, 152Y, 152M, 152C are arranged. The toner images of the respective colors formed above are transferred in multiple layers onto the intermediate transfer belt 16 by these primary transfer rolls 162. The residual toner adhering to the intermediate transfer belt 16 is removed by a cleaning blade or a brush of a belt cleaning device 189 provided downstream of the secondary transfer position.

  A secondary transfer roll 186, which is in pressure contact with a backup roll 168, is disposed at a secondary transfer position on the sheet conveyance path 18, and the toner images of the respective colors transferred on the intermediate transfer belt 16 are Secondary transfer is performed on the recording paper 32 by the pressure contact force and electrostatic force of the next transfer roll 186. The recording paper 32 onto which the toner images of the respective colors have been transferred is conveyed to the fixing device 19 by the conveyor belts 187 and 188.

  The fixing device 19 heats and pressurizes the recording paper 32 onto which the toner images of the respective colors have been transferred, so that the toner is fused and fixed to the recording paper 32.

  Next, the configuration of the print heads 140K, 140Y, 140M, 140C (hereinafter simply referred to as 140) in the image forming apparatus 10 shown in FIG. 1 will be described.

  As shown in FIG. 2, the print head 140 includes a light emitting device 50 in which light emitting elements are arranged, and irradiates the rotating photosensitive drum 152 with light based on image data. Perform exposure processing.

Next, the configuration of the light emitting device 50 shown in FIG. 2 will be described with reference to FIG. As shown in FIG. 3, the light emitting device 50 includes 30 light emitting chips 60 _{1 to} 60 ₃₀ each having a plurality of light emitting elements, and drive control for outputting a drive signal to the light emitting chips 60 _{1 to} 60 ₃₀ . And a circuit 61.

In the light emitting device 50 of the present embodiment, each of the light emitting chips 60 _{1 to} 60 ₃₀ includes 512 light emitting elements, and a total of 15360 (512 × 30) light emitting elements are arranged on one line. It is composed.

The drive control circuit 61 receives the signal from the control unit 20, and receives the first transfer signal φ1, the second transfer signal φ2, the first lighting start signal φW1, the second lighting start signal φW2, the lighting end signal φR, and the reference potential. Vsub and ground potentials VI1 and VI2 are output to control lighting of each light emitting element in the light emitting chips 60 _{1 to} 60 ₃₀ .

Next, FIG. 4 shows a circuit configuration of each of the light emitting chips 60 _{1 to} 60 ₃₀ (hereinafter simply referred to as 60). As shown in FIG. 4, the light emitting chip 60 is composed of a shift circuit 71, a plurality of light emitting circuits 72, and a reset circuit 73.

  In the light emitting chip 60 of the present embodiment, the 512 light emitting thyristors (light emitting elements) L1 to L512 are turned on and irradiated with light to expose the photosensitive drum 152.

  Then, the light emitting chip 60 is configured to perform lighting control for sequentially turning on / off the two light emitting thyristors as one unit. For example, a circuit including the light emitting thyristors L1 and L2 constitutes one light emitting circuit 72, and in the shift circuit 71, either the first transfer signal φ1 or the second transfer signal φ2 is at a low level (hereinafter abbreviated as L). ), The light emitting circuit 72 including the two light emitting thyristors is controlled to be sequentially switched as the light emission control target.

  The light emitting circuit 72 is a circuit for controlling lighting of two even and odd light emitting thyristors. Then, in the light emitting circuit 72, when the light emission control is performed by the switching control of the shift circuit 71, the lighting control of the odd-numbered light emitting thyristors is performed by the first lighting start signal φW1 and the even lighting by the second lighting start signal φW2. The circuit controls the lighting of the second light emitting thyristor.

  The reset circuit 73 is a circuit for turning off the light-emitting thyristor that has been turned on when the light-emitting circuit 72 to be controlled for light emission is switched by the shift circuit 71.

  Here, the basic operation of the thyristor will be described before the operation of the light emitting chip 60 shown in FIG.

  The equivalent circuit of the thyristor is shown in FIG. The thyristor is provided with respective terminals of an anode, a cathode and a gate, and has a structure such that when a predetermined voltage or more is applied between the cathode and the gate, the thyristor is turned on and the anode and the cathode are electrically connected.

  The equivalent circuit of the thyristor is represented as a circuit in which a PNP type transistor Tr1 and an NPN type transistor Tr2 are connected, as shown in FIG.

  The operation of the equivalent circuit of this thyristor will be described with reference to FIG.

With respect to the equivalent circuit diagram of this thyristor, as shown in FIG. 6 (A), 3.3V is applied to the anode, the cathode is connected to the ground potential through an appropriate resistance value, and the cathode and the gate are connected. When 1.8 V is applied, the base current I _B2 flows through the transistor Tr2 and the Tr2 is turned on.

Then, the emitter of the transistor Tr2 - collector becomes conductive, base current I _B1 is flowed to the transistor Tr1, the Tr1 is turned on.

  Then, as shown in FIG. 6B, the emitter-collector of the transistor Tr1 also becomes conductive, a collector current flows through the transistor Tr1, and this collector current flows as a base current of the transistor Tr2.

  Therefore, even if the voltage of 1.8 V applied to the gate is lost, both Tr1 and Tr2 continue to be in the ON state, and the conduction state between the anode and cathode is maintained.

  In such a state, as shown in FIG. 6B, a voltage close to 3.3 V applied to the anode is output to the gate terminal. This is because the collector-emitter saturation voltage of the transistor Tr1 is a very small voltage. Then, a voltage of 1.8 V obtained by subtracting 1.5 V, which is the base-emitter voltage of the transistor Tr2, from 3.3 V is output to the cathode.

  The base-emitter voltage of 1.5V of the transistor Tr2 is a forward voltage of the PN junction, which will be expressed as Vf in the following description, and will be described as about 1.5V.

  Note that in the thyristor in the conducting state as shown in FIG. 6A, the conducting state is maintained until the voltage applied to the anode disappears or the connection between the cathode and the ground potential is cut off. ..

  Next, returning to FIG. 4, the circuit operation of the light emitting chip 60 will be described. In the circuit of the light emitting chip 60 shown in FIG. 4, 3.3V is applied as the reference potential Vsub and is applied to the anodes of the transfer thyristors T1 to T256, the switching thyristors S1 to S512, and the light emitting thyristors L1 to L512. The ground potentials VI1 and VI2 are both connected to the ground potential.

  The shift circuit 71 includes 256 transfer thyristors T1 to T256, 257 diodes Ds and D1 to D256, and a resistor Rt.

  In the shift circuit 71, the second transfer signal φ2 is 3.3V in the initial state. Therefore, 1.8 V, which is lower than 3.3 V by the forward voltage Vf (1.5 V), is output to the cathode of the diode Ds, and further lower by the forward voltage Vf (1.5 V) to the cathode of the diode D1. 0.3V is output, and no voltage is output to the cathode of the diode D2.

  When the first transfer signal φ1 becomes L (0V) in such a state, the transfer thyristor T1 is turned on. However, since the voltage required for turning on the gate of the transfer thyristor T3 is not applied, it remains in the off state.

  When the thyristor T1 is turned on, the gate of the thyristor T1 changes from 1.8V to 3.3V, and the cathode of the diode D1 also changes to 1.8V.

  When the second transfer signal φ2 becomes L (0V) in such a state, the transfer thyristor T2 is turned on. However, since the voltage required for turning on the gate of the transfer thyristor T4 is not applied, it remains in the off state. After that, the first transfer signal φ1 becomes 3.3 V, so that the thyristor T1 is turned off.

  As described above, each time the first transfer signal φ1 and the second transfer signal φ2 are alternately switched to L, the transfer thyristors T1 to T256 are sequentially turned on.

  Then, when the thyristor T1 is in the ON state, the light emitting circuit 72 including the light emitting thyristors L1 and L2 is an emission control target, and when the thyristor T2 is in the ON state, the light emitting circuit 72 including the light emitting thyristors L3 and L4. Is the emission control target.

  For example, when the thyristor T1 is in the ON state, the voltage of 3.3V output to the gate of the thyristor T1 is divided by the resistance elements Ru and Rb and applied to the gate of the switching thyristor S1. When the first lighting start signal φW1 becomes L in such a state, the switching thyristor S1 is turned on, 3.3V is applied to the gate of the switching thyristor S1, and the necessary voltage is also applied to the gate of the light emitting thyristor L1. As a result, the light emitting thyristor L1 is turned on and is turned on.

  Similarly, when the second lighting start signal φW2 becomes L in such a state, the switching thyristor S2 is turned on, 3.3V is applied to the gate of the switching thyristor S2, and the required voltage is also applied to the gate of the light emitting thyristor L2. As a result, the light emitting thyristor L2 is turned on and turned on.

  That is, by controlling the first lighting start signal φ1 and the second lighting start signal φ2 according to the value of the corresponding pixel of the image data at the time of performing exposure, whether to expose that pixel can be switched. It will be possible.

  Then, when the lighting end signal φR becomes L after the exposure is performed in such a state, the reset thyristors TR1 and TR2 connected to the cathode of the light emitting thyristor in the lighting state are turned on and the lighting state is changed. The voltage of the cathode of the light emitting thyristor is changed from 1.8V to 3.3V. Therefore, the light emitting thyristor that was in the light emitting state is turned off.

The lighting control for the 512 light emitting thyristors L1 to L512 is simultaneously performed in the _thirty light emitting chips 60 _{1 to} 60 ₃₀ , so that the printing process for one line as shown in FIG. 7 is executed.

  That is, as shown in FIG. 8, in one line period, two light emitting thyristors L1 to L512 of 512 are sequentially turned on in a lighting order controlled by the shift circuit 71 by 256 transfer periods, so that one line is controlled. The exposure processing is performed on the 15360 (512 × 30) pixels.

Next, FIG. 9 shows a state in which the light emitting thyristors (light emitting elements) to be controlled for lighting are switched for each of the ₃₀ light emitting chips 60 _{1 to} 60 ₃₀ in this way.

  In FIG. 9A, after the light emitting thyristors L3 and L4 having the second lighting order are controlled to be lighted, as shown in FIG. 9B, the light emitting thyristors L5 and L6 having the third lighting order are turned on. The manner in which the control is performed is shown.

  Next, the configuration of the lighting control circuit 80 (exposure control device) for performing the lighting control of the light emitting device 50 will be described with reference to FIG.

  The lighting control circuit 80 shown in FIG. 10 is configured in the control unit 20 shown in FIG.

  The lighting control circuit 80 and the light emitting device 50 realize an exposure device that exposes the photosensitive drum 152.

  As shown in FIG. 10, the lighting control circuit 80 includes a lighting time adjustment value storage unit 81, an exposure amount control unit 82, and a voltage switching unit 83.

  The lighting control circuit 80 sequentially performs control for lighting or extinguishing the light emitting thyristor based on the value of each pixel of the input image data for a lighting time corresponding to each light emitting characteristic of the plurality of light emitting thyristors. Further, the lighting control circuit 80 of the present embodiment performs control such that a plurality of light emitting thyristors are sequentially turned on in units of two light emitting thyristors.

  The lighting time adjustment value storage unit 81 stores the lighting time adjustment values according to the light emitting characteristics of the 15360 (512 × 30) light emitting thyristors. For example, when the emission intensity of the standard light emitting thyristor is 1.0, the value of the emission intensity ratio of each light emitting thyristor is stored as the lighting time adjustment value.

  Then, the exposure amount control unit 82 is based on the required exposure amount required for image formation, the image data corresponding to each pixel to be exposed, and the lighting time adjustment value stored in the lighting time adjustment value storage unit 83. Then, whether or not each light emitting thyristor is to be turned on (lighting / lighting off) and the lighting time for lighting are calculated, and lighting pulse width data is output.

  For example, for the light emitting thyristor with the lighting time adjustment value of 0.9 stored in the lighting time adjustment value storage unit 83, the exposure amount control unit 82 lights up 0.9 times the standard lighting time. It generates and outputs lighting pulse width data that is timed.

  Further, the exposure amount control unit 82 controls the voltage switching unit 83 to switch the voltage output as the reference potential Vsub. In the present embodiment, the voltage switching unit 83 sets the reference potential Vsub applied to the light emitting thyristors L1 to L512 to either 3.3V or 4.1V under the control of the exposure amount control unit 82. Switch to.

  Then, the exposure amount control unit 82 applies a voltage to the light emitting thyristors L1 to L512 when sequentially performing control to turn on or off the light emitting thyristors L1 to L512 based on the value of each pixel of the input image data. One of 3.3V and 4.1V is selected and switched by the voltage switching unit 83, and the lighting time of the light emitting thyristors L1 to L512 is adjusted to perform control so as to realize the required exposure amount.

  Here, when the lighting control of the light emitting thyristors L1 to L512 is performed based on the lighting pulse width data output from the lighting control circuit 80, an example of the relationship between the light emission intensity of a certain light emitting thyristor and time is shown in FIG. It will be described with reference to FIG.

  In the case of the circuit configuration as shown in FIG. 4, since many light emitting thyristors L1 to L512 are connected to the signal line, a parasitic capacitance is generated between the signal line and the power supply line. Therefore, the change in the light emission intensity of the light emitting thyristor does not have an ideal rectangular shape, and as shown in FIG. 11, the light emitting thyristor has such a shape that it has a large value immediately after lighting and then converges to a constant value. Since the exposure amount is determined by the product of the emission intensity and the lighting time, the exposure amount is the size of the area of the waveform as shown in FIG.

  Therefore, the exposure amount control unit 82 increases the exposure amount by lengthening the lighting pulse width for lighting the light emitting thyristor to lengthen the lighting time, and shortens the pulse width to shorten the lighting time to perform the exposure. Control is performed to reduce the amount.

  Here, before describing the operation of the exposure amount control unit 82 in the present embodiment, a case in which the respective exposure amount adjustment ranges in the state where two voltages switched by the voltage switching unit 83 are applied do not overlap with each other will be described with reference to FIGS. This will be described with reference to FIG.

  In the following description, in order to make the description easier to understand, a case where the maximum variable range of the pulse width is 20 ns to 80 ns will be described, but this value is an example and the present invention is limited to such a value. It is not something that will be done.

  In FIG. 12, for example, the two voltages that can be switched by the voltage switching unit 83 are V1 and V2 (> V1), and the exposure amount when the voltage V1 is applied to the light emitting thyristor to maximize the pulse width (810 ns). And the case where the exposure amount when the voltage V2 is applied to the light emitting thyristor to minimize the pulse width (20 ns) is set.

  That is, in the example shown in FIG. 12, the exposure amount adjustment range that can be realized by changing the lighting time while the voltage V1 is applied to the light emitting thyristors L1 to L512 and the voltage V2 are the light emitting thyristors L1 to L512. The setting is such that the exposure amount adjustment range that can be realized by changing the lighting time with the voltage applied to L512 does not overlap.

  In such a setting, for example, when the required exposure amount gradually increases with the temperature rise and exceeds the adjustment range of the voltage V1, the exposure amount control unit 82 applies the voltage to the light emitting thyristor. Is switched to V2 and the pulse width is adjusted to achieve the required exposure amount.

  For example, as shown in FIG. 13, when the required exposure amount is increased from X1 to X2, that is, from the point A where the required exposure amount is realized in the state of the voltage V1, the required exposure amount is actually stored at the voltage V2 B When it moves to the point, the exposure amount control unit 82 switches the voltage applied to the light emitting thyristor on the way from V1 to V2 to control the exposure amount.

  However, as described above, the shape of the graph showing the relationship between the light emission intensity of the light emitting thyristor and the lighting time is not an ideal rectangle. Therefore, as shown in FIG. 14, the voltage V1 is applied to the light emitting thyristor. The exposure amount when the pulse width is maximum (80 ns) and the exposure amount when the voltage V2 is applied to the light emitting thyristor to minimize the pulse width (20 ns) are not exactly the same value.

  Therefore, when the applied voltage of the light emitting thyristor is switched during the continuous printing process based on one print job, the exposure amount may change and the change in the print density may be noticeable.

  Further, since the voltage switching control takes a certain amount of time, for example, on the order of ms, a problem that the printing process needs to be temporarily stopped may occur.

  Therefore, in the image forming apparatus 10 of the present embodiment, as shown in FIG. 15, adjustment of the exposure amount that can be realized by changing the lighting time while the voltage of 3.3 V is applied to the light emitting thyristors L1 to L512. The range and the overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time while the voltage of 4.1V is applied to the light emitting thyristors L1 to L512 are included in one print job (print instruction). It is set to be wider than the maximum exposure amount variation range, which is the range of the required exposure amount that is expected to vary during the execution of the printing process based on the above.

  In other words, when two voltages of 3.3V and 4.1V can be selected as the applied voltage of the light emitting thyristor, when the pulse width of each voltage is changed from the minimum of the maximum variable range to the maximum, the two voltages are changed. The range of the exposure amount that can be realized with any of the voltages is set to be wider than the maximum exposure amount variation range.

  Then, as shown in FIG. 16, when the required exposure amount Y1 is lower than the overlapping range, the exposure amount control unit 82 in the present embodiment naturally selects the lower voltage 3.3V and selects the voltage switching unit 83. The pulse width for realizing the required exposure amount Y1 is calculated (point C).

  Further, in the present embodiment, the overlapping range of the two adjustment ranges is set to be wider than the maximum exposure amount variation range, so that even if the required exposure amount increases from Y1, one print job is performed. There is no need to switch the voltage value from 3.3V to 4.1V in the middle of the printing process based on the above.

  Then, as shown in FIG. 17, when the required exposure amount Y2 can be realized at 3.3V or 4.1V, the exposure amount control unit 82 selects 3.3V or 4.1V from among the 3.3V and 4.1V. The high voltage of 4.1 V is selected to switch the voltage switching unit 83. Specifically, as shown in FIG. 17, the exposure amount control unit 82 selects either point D when the voltage applied to the light emitting thyristor is 3.3V or point E when the voltage applied to the light emitting thyristor is 4.1V. If the exposure amount Y2 can be realized also in step 1, the higher voltage 4.1 is selected and the exposure amount Y2 is realized by the point E.

  Even in such a case, if the required exposure amount increases from Y2 with the progress of the printing process, it is necessary to switch the voltage value from 4.1V to 3.3V during the printing process based on one print job. do not do.

[Second Embodiment]
Next, an image forming apparatus according to the second embodiment of the present invention will be described.

  The image forming apparatus according to the present embodiment is different from the image forming apparatus 10 according to the first embodiment described above in that the output voltage of the voltage switching unit 83 is 3.3V and 3.7V. The operation of the overturn control in the exposure amount control unit 82 is different. Therefore, in this embodiment, the reference numerals in the above-described first embodiment will be used as they are for description.

  The image forming apparatus 10 according to the first exemplary embodiment described above is for dealing with the case where the required exposure amount increases during one continuous printing process. Considering in a short period as described above, the required exposure amount often increases during the printing process due to a temperature rise or the like. However, when considering for a long period of time, the required exposure amount may decrease due to abrasion of the photosensitive drum or the like. Therefore, the image forming apparatus according to the present exemplary embodiment is configured to handle both the case where the required exposure amount increases and the case where the required exposure amount decreases during one continuous printing process.

  In the image forming apparatus of the present embodiment, as shown in FIG. 18, an exposure amount adjustment range that can be realized by changing the lighting time while the voltage of 3.3 V is applied to the light emitting thyristors L1 to L512, and The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time while the voltage of 3.7 V is applied to the light emitting thyristors L1 to L512 is more than double the range of the required exposure amount. It is set wide.

  That is, as compared with the first embodiment, the voltage output from the voltage switching unit 83 is lowered from 4.1 V to 3.7 V, so that the adjustment ranges based on the two voltages are closer to each other and the overlapping range is increased. Is spreading. Therefore, the overlapping range, which is a range in which the required exposure amount can be realized with any of the two voltages that can be switched by the voltage switching unit 83, is widened and is wider than twice the maximum exposure amount variation range.

  Then, in the exposure amount control unit 82 in the present embodiment, as shown in FIG. 19, the requested exposure amount is included in a range in which the exposure amount is larger than the center (center) of the range where the two adjustment ranges overlap. In this case, a higher voltage of 3.7 V is selected from the two voltages, and if the two adjustment ranges are included in the range where the exposure amount is smaller than the center of the overlapping range, the lower voltage of the two voltages is set to 3 V. The voltage switching unit 83 is switched by selecting .3V.

  Specifically, as shown in FIG. 19, when the required exposure amount is Y3 and belongs to the lower side than the center of the overlapping range (point F), the lower exposure voltage 3. If 3V is selected and the required exposure amount is Y4 and belongs to the higher side than the center of the overlapping range (point G), the higher voltage of 3.7V is selected.

  By performing such voltage selection control, even if the required exposure amount fluctuates in either the increasing direction or the decreasing direction of the maximum exposure amount fluctuation range during the continuous printing process, the printing is performed. It is not necessary to switch the voltage applied to the light emitting thyristor during the process.

[Modification]
In the first and second embodiments, the present invention is applied to the configuration in which the voltage applied to the light emitting thyristor is switched to expand the adjustment range of the exposure amount, but the present invention is applied to this. The present invention can be similarly applied to a configuration in which the amount of current supplied to the light emitting thyristor is switched to expand the adjustment range of the exposure amount, without being limited thereto.

  In the case of such a configuration, when the exposure amount control unit sequentially performs control for turning on or off each of the plurality of light emitting elements based on the value of each pixel of the input image data, the required exposure amount Is realized by selecting either the first current value or the second current value of the current flowing through the plurality of light emitting elements and switching by the switching means, and adjusting the lighting time of the plurality of light emitting elements. Such control is performed.

  Then, the exposure amount adjustment range that can be realized by changing the lighting time in a state where the value of the current flowing through the plurality of light emitting elements is set to the first current value and the value of the current flowing through the plurality of light emitting elements are set to the second value. The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time with the current value of is the range of the required exposure amount that is expected to fluctuate during execution of the printing process based on one print instruction. It is set to be wider than.

10 image forming device 12 image reading device 14Y, 14M, 14C, 14K image forming unit 16 intermediate transfer belt 17 paper tray 18 paper conveying path 19 fixing device 20 control unit 32 recording paper 50 light emitting device 60 _{1 to} 60 ₃₀ light emitting chip 61 drive Control circuit 71 Shift circuit 72 Light emitting circuit 73 Reset circuit 80 Lighting control circuit 81 Lighting time adjustment value storage unit 82 Exposure amount control unit 83 Voltage switching unit 140K Print head 150K Image forming device 152K, 152Y, 152M, 152C Photoconductor drum 154K Charging Device 156K Developing device 158K Cleaning device 162K, 162Y, 162M, 162C Primary transfer roll 164 Drive roll 165, 166, 167 Idle roll 168 Backup roll 189 Cleaning device 168 Backup roll 181 Paper feed roller 186 Secondary transfer roll 187, 188 Conveying belt

Claims (7)

Switching means for switching the voltage applied to the plurality of light emitting elements to either the first voltage or the second voltage;
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the voltage applied to the plurality of light emitting elements is set to the first voltage or the second voltage. And a control means for performing a control for adjusting the lighting time of the plurality of light emitting elements while selecting one of the voltages and switching by the switching means,
Adjustment range of the exposure amount that can be realized by changing the lighting time in a state where the first voltage is applied to the plurality of light emitting elements, and a state where the second voltage is applied to the plurality of light emitting elements The overlapping range of the adjustment range of the exposure amount that can be achieved by changing the lighting time is wider than the range of the required exposure amount that is expected to change during the printing process based on one print instruction. Exposure control device.   When the required exposure amount can be realized by either the first voltage or the second voltage, the control unit selects the higher voltage from the first and second voltages and selects the higher voltage. The exposure control device according to claim 1, wherein the switching means is switched. Switching means for switching the voltage applied to the plurality of light emitting elements to either the first voltage or the second voltage;
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the voltage applied to the plurality of light emitting elements is set to the first voltage or the second voltage. And a control means for performing a control for adjusting the lighting time of the plurality of light emitting elements while selecting one of the voltages and switching by the switching means,
Adjustment range of the exposure amount that can be realized by changing the lighting time in a state where the first voltage is applied to the plurality of light emitting elements, and a state where the second voltage is applied to the plurality of light emitting elements The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time is less than the range of the required exposure amount that is expected to fluctuate during execution of the printing process based on one print instruction. The exposure control device is also characterized by being wide.   The control unit selects a higher voltage of the first and second voltages when the requested exposure amount is included in a range where the exposure amount is larger than the center of the range where the two adjustment ranges overlap. However, when the exposure amount is smaller than the center of the overlapping range of the two adjustment ranges, a lower voltage is selected from the first voltage and the second voltage to switch the switching means. Item 3. The exposure control device according to item 3. Further comprising storage means for storing values according to respective light emitting characteristics of the plurality of light emitting elements,
5. The exposure control apparatus according to claim 1, wherein the control unit performs control for adjusting the lighting time of each of the plurality of light emitting elements based on the value stored in the storage unit. Switching means for switching the value of the current flowing through the plurality of light emitting elements to either the first current value or the second current value;
When sequentially performing control to turn on or off the plurality of light emitting elements based on the value of each pixel of the input image data, the value of the current flowing through the plurality of light emitting elements is set to the first current value or the A control unit for selecting one of the second current values and switching it by the switching unit and for controlling the lighting time of the plurality of light emitting elements;
The adjustment range of the exposure amount that can be realized by changing the lighting time while the value of the current flowing through the plurality of light emitting elements is set to the first current value, and the value of the current flowing through the plurality of light emitting elements are described above. The overlapping range of the adjustment range of the exposure amount that can be realized by changing the lighting time in the state where the second current value is set is the required exposure amount that is expected to change during the execution of the printing process based on one print instruction. An exposure control device characterized in that it is wider than the range. A plurality of light emitting elements, a switching means for switching a voltage applied to the plurality of light emitting elements to either a first voltage or a second voltage, and the plurality of light emitting elements based on the value of each pixel of the input image data. When sequentially performing control for turning on or off the light emitting elements, the voltage applied to the plurality of light emitting elements is selected by the switching means by selecting either the first voltage or the second voltage, and A control unit for controlling the lighting time of the plurality of light emitting elements, and changing the lighting time in a state where the first voltage is applied to the plurality of light emitting elements, A print process based on one print instruction is an overlapping range of the adjustment range and the adjustment range of the exposure amount that can be realized by changing the lighting time while the second voltage is applied to the plurality of light emitting elements. An exposure apparatus characterized in that it is wider than the range of the required exposure amount that is expected to fluctuate during execution of
A developing device for developing the electrostatic latent image on the image carrier exposed by the exposing device;
Transfer means for transferring an image on the image carrier developed by the developing device onto a recording medium;
An image forming apparatus equipped with.

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