JP2009137142A - Optical head, its control method, light emitting device, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a change in light emitting intensity of a light emitting element, which is caused due to the change of light emitting elements to be used. <P>SOLUTION: The optical head 100 has a plurality of unit circuits U (U<SB>1</SB>to U<SB>n</SB>). Each of the unit circuits U (U<SB>1</SB>to U<SB>n</SB>) includes: the plurality of light emitting elements 104 that emit light with luminance corresponding to a drive current Ids; a selecting part 120 that selects any one of the light emitting elements 104 to which the drive current Ids is supplied; a correction memory 108 that selectively stores correction data Cv corresponding to the light emitting element 104 selected from among the light emitting elements 104 by the selecting part 120; and a current generating part 400 that generates a drive current Ids corresponding to the correction data Cv stored by the correction memory 108. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical head using a light emitting element, a driving method thereof, a light emitting device, and an electronic apparatus.

For example, in an electrophotographic image forming apparatus, a light emitting device in which a plurality of light emitting elements are arranged on a substrate is used as an optical head for forming an electrostatic latent image on an image carrier such as a photosensitive drum. Patent Document 1 discloses a technique in which a plurality of light emission lines in which a plurality of light emitting elements are arranged along the main scanning direction are provided, and the light emission lines that are actually used for exposure of the image carrier are changed according to predetermined conditions. ing.
JP 2005-96259 A

By the way, since there is a manufacturing error between a light emitting element belonging to one light emitting line and a light emitting element belonging to another light emitting line, a driving current having the same current value is supplied to each light emitting element belonging to a different light emitting line. However, the light emission intensity of these light emitting elements varies. Accordingly, there has been a problem that the light emission intensity in the light emission line (the light emission intensity of the light emitting element to be used) also changes as the light emitting line (light emitting element) to be used is changed.
In view of such circumstances, an object of the present invention is to solve the problem of suppressing a change in light emission intensity of a light emitting element due to a change in a light emitting element to be used.

  In order to solve the above-described problems, an optical head according to the present invention is an optical head including a plurality of unit circuits, and each of the plurality of unit circuits emits a plurality of lights that emit light at a luminance corresponding to a drive current. And selecting correction means corresponding to the light emitting element selected by the selecting means from among the plurality of light emitting elements, and selecting means for selecting any one of the plurality of light emitting elements to which the driving current is supplied. First storage means for storing the current and current generation means for generating a drive current corresponding to the correction data stored in the first storage means.

  According to the present invention, when any one light emitting element is selected by the selecting means, correction data for correcting the current value of the drive current supplied to the selected light emitting element is stored in the first storage means. Writing is performed, and a drive current corresponding to the written correction data is generated. Accordingly, it is possible to suppress a change in the light emission intensity of the light emitting element due to a change in the light emitting element to be used. The first storage means alternatively stores correction data corresponding to the light emitting elements selected by the selection means, so that each unit circuit has a memory for storing correction data corresponding to all the light emitting elements. There is no need to provide it, and the configuration can be simplified.

  In the first aspect of the optical head according to the present invention, the selection means selects a light emitting element different from the previously selected light emitting element every time the power is turned on (for example, generates a random number and selects the light emitting element based on the generated random number). The selected light-emitting element is used until the power is cut off. According to this aspect, since a plurality of light emitting elements are used alternately, the life of the light emitting elements can be extended as compared with the case where one light emitting element is used continuously until the end of its lifetime. For example, in a mode in which one light-emitting element is used up and another light-emitting element is selected, a device that detects deterioration of the light emission intensity of the light-emitting element and a large-scale memory that can know a long-term use history are required. However, in the first aspect of the optical head according to the present invention, since a light emitting element different from the previously selected light emitting element is selected every time the power is turned on, such a configuration is unnecessary. Therefore, the life of the light emitting element can be extended with a simple configuration.

  In the second aspect of the optical head according to the present invention, the selection means selects the light emitting element each time the number of recording materials on which an image is formed reaches the reference number. Also in this embodiment, since a plurality of light emitting elements are used alternately, the life of the light emitting elements can be extended.

  Next, a light emitting device according to the present invention is a light emitting device including an optical head and a control circuit, and the optical head has a plurality of unit circuits, and each of the plurality of unit circuits corresponds to a drive current. A plurality of light emitting elements that emit light at a high luminance, a selection unit that selects any one of the plurality of light emitting elements to which a driving current is supplied, and a light emitting element selected by the selection unit among the plurality of light emitting elements The first storage means for selectively storing the correction data corresponding to, and the current generation means for generating the drive current according to the correction data stored in the first storage means, the control circuit, For each of the plurality of unit circuits, correction data corresponding to the light emitting element selected by the selection means among the correction data corresponding to each of the plurality of light emitting elements is supplied to the first storage means.

  According to the present invention, the control circuit can write the correction data corresponding to the light emitting element selected by the selection unit in the first storage unit included in the optical head. Accordingly, it is possible to suppress a change in the light emission intensity of the light emitting element due to a change in the light emitting element to be used.

  In a preferred embodiment of the light-emitting device according to the present invention, in each of the plurality of unit circuits, the plurality of light-emitting elements include a first light-emitting element and a second light-emitting element. Second storage means (second storage) for storing the corresponding first correction data and the difference between the first correction data and the second correction data corresponding to the second light emitting element for each unit circuit. When the second light emitting element is selected by the selection unit for each of the plurality of unit circuits, the control circuit includes the first memory 300 and the second memory 302) according to the embodiment. Second correction data is generated from the first correction data and the difference stored in the means and supplied to the first storage means. According to this aspect, since the amount of data stored in the second storage unit can be small, the capacity of the second storage unit can be reduced.

  Next, an electronic apparatus according to the present invention includes the light emitting device according to each aspect exemplified above. The light emitting device according to the present invention is used in various electronic devices. A typical example of the electronic apparatus according to the present invention is an electrophotographic image forming apparatus in which the light emitting device according to each of the above embodiments is used for exposure of an image carrier such as a photosensitive drum. The image forming apparatus includes an image carrier on which a latent image is formed by exposure, a light emitting device of the present invention that exposes the image carrier, and a developer (for example, toner) added to the latent image on the image carrier. A developing device to be formed.

  Furthermore, the above-described invention can also be understood as a method for controlling an optical head. That is, a plurality of unit circuits are provided, and each of the plurality of unit circuits emits light at a luminance corresponding to the drive current, and any one of the plurality of light emitting elements is supplied with a drive current. A method for driving an optical head, comprising: selection means for selecting the first storage means; first storage means for storing correction data; and current generation means for generating drive current according to the correction data stored in the first storage means. The correction data corresponding to the light emitting element selected by the selection means is supplied to the first storage means, and the first storage means selects the correction data corresponding to the light emitting element selected by the selection means. It memorize | stores automatically. The same effect as that of the optical head according to the present invention can be obtained by the above control method.

<A: First Embodiment>
FIG. 1 is a perspective view showing a partial configuration of an image forming apparatus using the light emitting device 10 according to the first embodiment of the present invention. As shown in FIG. 1, the image forming apparatus includes a light emitting device 10, a condensing lens array 11, and a photosensitive drum (image carrier) 12. The light emitting device 10 includes a large number of light emitting elements (not shown in FIG. 1) arranged linearly on the surface of the substrate 13. These light emitting elements selectively emit light according to the form of an image to be printed on a recording material such as paper. The photosensitive drum 12 is supported by a rotating shaft extending in the main scanning direction, and rotates in the sub-scanning direction in which the recording material is conveyed with the outer peripheral surface facing the light emitting device 10.

  The condensing lens array 11 is disposed in the gap between the light emitting device 10 and the photosensitive drum 12. The condensing lens array 11 includes a large number of gradient index lenses arranged in an array with each optical axis directed toward the light emitting device 10. As the condensing lens array 11, for example, there is SLA (Selfoc Lens Array) available from Nippon Sheet Glass Co., Ltd. (Selfoc / SELFOC is a registered trademark of Nippon Sheet Glass Co., Ltd.).

  Light emitted from each light emitting element of the light emitting device 10 passes through each gradient index lens of the condensing lens array 11 and reaches the surface of the photosensitive drum 12. By this exposure, a latent image (electrostatic latent image) corresponding to a desired image is formed on the surface of the photosensitive drum 12.

FIG. 2 is a diagram illustrating a schematic configuration of the light emitting device 10. The light emitting device 10 includes an optical head 100 and a control circuit 200. As shown in FIG. 2, the optical head 100 has a structure in which a shift register 102 and n unit circuits U (U _{1 to} U _n ) are arranged on the surface of the substrate 13. A start pulse SP and a clock signal CLK are supplied from the control circuit 200 to the shift register 102. The shift register 102 sequentially shifts the start pulse SP in accordance with the clock signal CLK and transfers it to each unit circuit U (U _{1 to} U _n ). At this time, a signal transferred from the shift register to each unit circuit U (U _{1 to} U _n ) is called a latch pulse signal LATi (i = 1 to n).

As shown in FIG. 2, each unit circuit U (U _{1 to} U _n ) includes a first light emitting element 104 a and a second light emitting element 104 b that emit light at a luminance corresponding to the driving current, a driving unit 106, and a correction unit. Memory 108. In each unit circuit U (U _{1 to} U _n ), one of the first light emitting element 104 a and the second light emitting element 104 b is selected, and a drive current is supplied to the selected light emitting element 104. Is supplied. To the drive unit 106 in each unit circuit U (U _{1 to} U _n ), gradation data D specifying the gradation of each light emitting element 104 is supplied from the control circuit 200 via the gradation data line 500. Further, the selection signals SEL1 and SEL2 for selecting the light emitting element 104 to be used are commonly supplied from the control circuit 200 to the driving unit 106 in each unit circuit U (U _{1 to} U _n ) via the signal line 600. The The correction memory 108 in each unit circuit _{U (U} 1 ~U _n), the correction data Cv via the correction data lines 700 corresponding to the light emitting element 104 selected in each unit circuit _{U (U} 1 ~U _n) Each is supplied from the control circuit 200.

In the first memory 300 shown in FIG. 2, n pieces of correction data Cva corresponding to the first light emitting elements 104a in the respective unit circuits U (U _{1 to} U _n ) are stored. The second memory 302 stores n correction data Cvb corresponding to the second light emitting elements 104b in the unit circuits U (U _{1 to} U _n ), respectively. In this embodiment, the first memory 300 and the second memory 302 are constituted by nonvolatile memories. The control circuit 200 reads the correction data Cv (Cva or Cvb) stored in the first memory 300 or the second memory 302, and uses the read correction data Cv as the correction memory 108 in the corresponding unit circuit U _i . To supply.

Figure 3 is a block diagram showing a detailed electrical configuration of the unit circuit U _1. Other unit circuit U ₂ ~U _n has the same configuration as the unit circuit U _1, here illustrating a unit circuit U ₁ as an example.
As shown in FIG. 3, the driving unit 106 includes a first selection circuit 110 and a second selection circuit 112, a latch circuit 114, a current generation unit 400, a switching transistor Tr, and a selection unit 120. Prepare. The current generator 400 generates a drive current Ids. When the switching transistor Tr is turned on, the drive current Ids generated by the current generator 400 is supplied to the selector 120. The selection unit 120 selects one of the first light emitting elements 104a and the second light emitting elements 104b to which the driving current Ids is supplied.

As shown in FIG. 3, the latch pulse signal LAT1 transferred from the shift register 102 in the unit circuit _{U 1} is supplied to the first selection circuit 110 and second selection circuit 112. A write enable signal WE1 is supplied from the control circuit 200 to the first selection circuit 110, and a write enable signal WE2 is supplied from the control circuit 20 to the second selection circuit 112. When the write enable signal WE1 becomes H level, the first selection circuit 110 takes in the correction data Cv (Cva or Cvb) from the correction data line 700 when the latch pulse signal LAT1 is supplied, and corrects the correction data Cv. This is supplied to the memory 108.

  On the other hand, when the write enable signal WE2 becomes H level, the latch pulse signal LAT1 is supplied from the second selection circuit 112 to the latch circuit 114. The latch circuit 114 fetches and holds the gradation data D from the gradation data line 500 when the latch pulse signal LAT1 is supplied. In a period in which the latch circuit 114 holds the gradation data D, the gradation data D is supplied from the latch circuit 114 to the gate of the switching transistor Tr. The gradation data D in this embodiment is data that designates either lighting (high gradation) or extinguishing (low gradation) for the light emitting element 104 selected by the selection unit 120.

  The current generator 400 includes a reference current generator 116 and a correction circuit 118. The drive current Ids is generated by combining the reference current Iref generated by the reference current generator 116 and the correction current Ic generated by the correction circuit 118. More specifically, the reference current generator 116 includes a P-channel type current source transistor Tg. A power supply potential VEL is supplied to the source of the current source transistor Tg, and a reference potential VREF is supplied to its gate. Thus, the current source transistor Tg functions as a constant current source that generates the reference current Iref.

  The correction circuit 118 generates a correction current Ic based on the correction data Cv stored in the correction memory 108. The correction data Cv is 3-bit data (x, y, z) indicating the correction current Ic generated by the correction circuit 118. As shown in FIG. 3, the correction memory 108 includes memories M1, M2, and M3. The 3-bit correction data Cv supplied to the correction memory 108 is stored one bit at a time in each of the memories M1, M2, and M3. As shown in FIG. 3, the correction circuit 118 includes P-channel type correction current source transistors Tc1, Tc2, and Tc3. The transistors Tc1, Tc2, and Tc3 are connected in parallel, the power supply potential VEL is supplied to the source, and the reference potential VREF is supplied to the gate. The sizes (for example, channel width and channel length) of the transistors Tc1, Tc2, and Tc3 are different. In this embodiment, each channel width is expressed as a relative ratio of powers of 2 (Tc1: Tc2: Tc3 = 1: 2: 4). Further, as shown in FIG. 3, transistors Tm1, Tm2, and Tm3 are connected to the drain sides of the correction current source transistors Tc1, Tc2, and Tc3, respectively. These transistors Tm1, Tm2, and Tm3 are switching elements that are turned on or off based on a signal (H or L) supplied to the gate according to the bits stored in the memories M1, M2, and M3.

  For example, when each bit (x, y, z) of the correction data Cv written in the correction memory 108 is (1, 1, 1), the transistors Tm1, Tm2, and Tm3 are all turned on, and each correction current All of the currents Ic1, Ic2, and Ic3 generated by the source drive transistors Tc1, Tc2, and Tc3 flow through the transistors Tm1, Tm2, and Tm3, and the correction current Ic = Ic1 + Ic2 + Ic3 is generated. In this embodiment, since the relative ratio of the channel widths of the correction current source transistors Tc1, Tc2, and Tc3 is 1: 2: 4, the relative ratio of the currents generated by the correction current source transistors Tc1, Tc2, and Tc3 is also 1 : 2: 4. Accordingly, the correction current Ic at this time is expressed as 7 × Ic1. In this way, multi-step correction currents Ic are generated according to the correction data Cv stored in the correction memory 108 (Ic1 to 7 × Ic1).

  As shown in FIG. 3, a node Nc connected to the correction circuit 118 is provided on the path from the drain of the current source transistor Tg to the switching transistor Tr. At the node Nc, the reference current Iref generated by the current source transistor Tg and the correction current Ic generated by the correction circuit 118 are combined to generate the drive current Ids. The drive current Ids is supplied to the selection unit 120 while the switch transistor Tr is on.

The selection unit 120 is a unit that selects any one of the first light emitting element 104a and the second light emitting element 104b to which the driving current Ids is supplied. More specifically, the selection unit 120 includes selection transistors Tsw1 and Tsw2. The transistor Tsw1 is provided on the current path from the node Nc to the first light emitting element 104a, and the transistor Tsw2 is provided on the current path from the node Nc to the second light emitting element 104b. The selection signal SEL1 is supplied from the control circuit 200 to the gate of the selection transistor Tsw1, and the selection signal SEL2 is supplied from the control circuit 200 to the gate of the selection transistor Tsw2. When the selection signal SEL1 becomes H level (active state), the selection transistor Tsw1 is turned on, and the driving current Ids is supplied to the first light emitting element 104a. At this time, the selection signal SEL2 becomes L level, and the selection transistor Tsw2 is turned off. On the other hand, when the selection signal SEL2 becomes H level (active state), the selection transistor Tsw2 is turned on, and the drive current Ids is supplied to the second light emitting element 104b. At this time, the selection signal SEL1 becomes L level, and the selection transistor Tsw1 is turned off. Since the selection signals SEL1 and SEL2 are commonly supplied to the unit circuits U (U _{1 to} U _n ), when the selection signal SEL1 is at the H level, the n firsts of the unit circuits U _{1 to} U _n . is selected of the light emitting element 104a is collectively, when the selection signal SEL2 is at the H level, n-number of the second light emitting element 104b of the unit circuit _U 1 ~U _n are collectively selected.

The selection unit 120 selects a light emitting element 104 different from the previously selected light emitting element 104 every time the light emitting device 10 is turned on, and uses the selected light emitting element 104 until the power is turned off. For example, when the power is turned on last time, the first light emitting element 104a is selected in each unit circuit U (U _{1 to} U _n ), and the first light emitting element 104a is used until the power is turned off. In this case, when the power is turned on next time, the second light emitting element 104b is selected in each unit circuit U (U _{1 to} U _n ), and the second light emitting element 104b is used until the power is cut off.

Incidentally, the first light emitting element 104a and the second light emitting element 104b have variations in characteristics (for example, light emission efficiency) due to manufacturing errors and the like, and thus the first light emitting element 104a and the second light emitting element 104b. Even when the same drive current Ids is supplied to 104b, the light emission intensity of the first light-emitting element 104a and the light emission intensity of the second light-emitting element 104b are different. Therefore, when the light emitting element 104 to be used is changed, there is a problem that the light emission intensity of the light emitting element 104 before the change and the light emission intensity of the light emitting element 104 after the change are different.
Also, each of the unit circuits U (U 1 _{~U n)} in various transistors (for example, a current source transistor Tg, etc.), since the variation in characteristics due like manufacturing errors (eg, channel width and channel length) is present The drive current Ids generated in each unit circuit U (U _{1 to} U _n ) also varies. As a result, there is a problem in that the light emission intensity of the light emitting element 104 in each unit circuit U (U _{1 to} U _n ) varies.

In this embodiment, it is selected any of the light emitting element 104 in each unit circuit _{U (U} 1 ~U _n), emission intensity of the light emitting element 104 in each unit circuit _{U (U} 1 ~U _n) is equalized As described above, separate correction data Cv (Cva and Cvb) are prepared for a set of n first light emitting elements 104a and a set of n second light emitting elements 104b, and each unit circuit U is selected. Correction data Cv (Cva or Cvb) corresponding to the light emitting element 104 selected by the unit 120 is written in the correction memory 108. That is, in each unit circuit U (U _{1 to} U _n ), the correction data Cv corresponding to the light emitting element 104 selected by the selection unit 120 among the first light emitting element 104a and the second light emitting element 104b is stored in the correction memory 108. The current generator 400 generates the drive current Ids according to the correction data Cv stored in the correction memory 108.

Here, the correction data Cv is not only the variation of the first light emitting element 104a and the second light emitting element 104b in each unit circuit U (U _{1 to} U _n ), but also the variation of various transistors in each unit circuit U. Is set to be compensated. That is, the n pieces of correction data Cva stored in the first memory 300 and the n pieces of correction data Cvb stored in the second memory 302 shown in FIG. 2 are represented by the unit circuits U (U _{1 to} U _n ). The n light emitting intensities of the n first light emitting elements 104a are made uniform and the light emitting intensities of the n second light emitting elements 104b are made uniform, and each of the first light emitting elements 104a and each of the second light emitting elements 104b is made uniform. The light emission intensity with the light emitting element 104b is individually set so as to be uniform.

In this embodiment, the period during which the light emitting device 10 operates is divided into a selection period and a driving period. The selection period is a period from when the light emitting device 10 is turned on until a predetermined period elapses. In this selection period, one of the light emitting element 104 of the first light emitting element 104a and the second light-emitting element 104b is selected, the light emitting element is selected in each unit circuit _{U (U} 1 ~U _n) 104 N correction data Cv corresponding to are supplied to the correction memory 108 in each unit circuit U (U _{1 to} U _n ).

When the selection period is started, the control circuit 200 sets the write enable signal WE1 to H level and then sets one of the selection signals SEL1 and SEL2 to H level. Accordingly, one of the first light emitting element 104a and the second light emitting element 104b is selected. Then, the control circuit 200 supplies n correction data Cv (Cva or Cvb) corresponding to the light emitting element 104 selected in each unit circuit U (U _{1 to} U _n ) to the first memory 300 or the second memory. The data is read from 302 and output serially to the correction data line 700. The first selection circuit 110 activated by the H level write enable signal WE1 takes in the correction data Cv (Cva or Cvb) supplied to the correction data line 700 when the latch pulse signal LATi is supplied. To the correction memory 108. Accordingly, correction data Cv corresponding to the selected light emitting element 104 is alternatively stored in the correction memory 108. Since the write enable signal WE2 is set to the L level in the selection period, the second selection circuit 112 does not operate regardless of whether the latch pulse signal LATi is supplied or not, and the switching transistor Tr is turned off, so that the light emitting element 104 The drive current Ids is not supplied.

When the supply of correction data Cv for each unit circuit _{U (U} 1 ~U _n) is completed, the control circuit 200 sets the write enable signal WE1 L level, the write enable signal WE2 to the H level. As a result, the selection period is switched to the driving period. In the driving period, the control circuit 200 serially outputs the gradation data D of each of the _n unit circuits U (U _{1 to} U _n ) to the gradation data line 500. The second selection circuit 112 activated by the H level write enable signal WE 2 supplies the latch circuit 114 with the latch pulse signal LATi supplied from the shift register 102. The latch circuit 114 takes in the gradation data D supplied to the gradation data line 500 when the latch pulse signal LATi is supplied and supplies it to the gate of the switching transistor Tr. A drive current Ids corresponding to the correction data Cv written in the correction memory 108 in the selection period is supplied to the light emitting element 104 selected by the selection unit 120 while the switch transistor Tr is in the ON state.

According to the configuration of the present embodiment, the control circuit 200 uses the first memory 300 or the second correction data Cv corresponding to the light emitting element 104 selected in each unit circuit U (U _{1 to} U _n ). The data is read from the memory 302 and written to the correction memory 108 in each unit circuit U (U _{1 to} U _n ). As a result, in each unit circuit U (U _{1 to} U _n ), a drive current Ids corresponding to each correction data Cv is generated and supplied to the selected light emitting element 104. Therefore, even if the selected one of the light emitting element 104 in each unit circuit _{U (U} 1 ~U _n), can be made uniform emission intensity of each light-emitting element 104 in each unit circuit _{U (U} 1 ~U _n). In addition, the correction memory 108 in each unit circuit U (U _{1 to} U _n ) has correction data Cv (Cva or Cvb) corresponding to the light emitting element 104 selected from the first light emitting element 104a and the second light emitting element 104b. ) Is alternatively stored, a memory for storing correction data Cv (Cva and Cvb) of both the first light emitting element 104a and the second light emitting element 104b is stored in each unit circuit U (U _{1 to} U _n ). There is no need to provide it. Therefore, it is possible to simplify the configuration of each unit circuit _{U (U} 1 ~U _n).

  Further, in this embodiment, the first light emitting element 104a and the second light emitting element 104b are alternately used, so that any one of the light emitting elements 104 is used continuously until the end of its lifetime. Thus, the life of the light emitting element 104 can be extended. For example, in a mode in which one light-emitting element 104 is used up and another light-emitting element 104 is selected, a large-scale device that can detect deterioration of light emission intensity of the light-emitting element 104 and a long-term use history can be understood. Where a memory is required, in this embodiment, a light emitting element 104 different from the previously selected light emitting element 104 is selected every time the light emitting device 10 is turned on, and thus such a configuration is unnecessary. Therefore, the life of the light emitting element 104 can be extended with a simple configuration.

<B: Second Embodiment>
In the first embodiment, the first memory 300 stores correction data Cva corresponding to the first light emitting element 104 a in each unit circuit U (U _{1 to} U _n ), and is stored in the second memory 302. Stores the correction data Cvb corresponding to the second light emitting element 104b in each unit circuit U (U _{1 to} U _n ). In this embodiment, in the second memory 302, the difference ΔCv between the correction data Cva corresponding to the first light emitting element 104a and the correction data Cvb corresponding to the second light emitting element 104b is stored in each unit circuit U (U ₁ ~ U _n ). Since other configurations are the same as those of the first embodiment, description of overlapping portions is omitted.

In the selection period, when the control circuit 200 selects the first light emitting element 104a, the n correction data Cva is read from the first memory 300 and the read correction data Cva is read from each unit circuit as in the first embodiment. respectively supply the U _(U 1 ~U _n). On the other hand, when the second light emitting element 104b is selected, the control circuit 200 reads n pieces of correction data Cva from the first memory 300 and also reads n pieces of difference ΔCv data from the second memory 302. It generates data obtained by adding these data supplied to each unit circuit U (U 1 _{~U n).} The data added at this time corresponds to correction data Cvb corresponding to the second light emitting element 104b in each unit circuit U (U _{1 to} U _n ).

For example, in the unit circuit U1, the correction data Cva corresponding to the first light emitting element 104a is ( ₁ , 0, 1) (that is, the correction current Ic = 5 × Ic1), and the correction data Cvb corresponding to the second light emitting element 104b. Is (1, 1, 0) (that is, correction current Ic = 6 × Ic1). In this case, the data representing the difference ΔCv between the correction data Cva corresponding to the first light emitting element 104a and the correction data Cvb corresponding to the second light emitting element 104b is (0, 0, 1) (in the correction current Ic1). 1 bit of data is sufficient for the data of the difference ΔCv stored in the second memory 302. The smaller the manufacturing error between the first light emitting element 104a and the second light emitting element 104b, the smaller the correction data Cva corresponding to the first light emitting element 104a and the correction data Cvb corresponding to the second light emitting element 104b. The difference ΔCv is small and the amount of data stored in the second memory 302 can be small. Therefore, according to the configuration of this embodiment, the capacity of the second memory 302 can be saved. In the present embodiment, the first memory 300 and the second memory 302 are provided separately. However, the present invention is not limited to this. For example, the content stored in the first memory 300 and the second memory 302 are stored. It is also possible to store the contents to be stored in a single memory.

<C: Third Embodiment>
In each of the above-described embodiments, the reference current Iref generated by the reference current generator 116 and the correction current Ic generated by the correction circuit 118 are combined to generate the drive current Ids. In this embodiment, the correction circuit 118 generates the drive current Ids according to the correction data Cv without providing the reference current generation unit 116. Since other configurations are the same as those of the above-described embodiments, description of overlapping portions will be omitted.

Figure 4 is a block diagram showing an electrical configuration of the unit circuit U ₁ according to this embodiment. As shown in FIG. 4, in the current generator 400, the reference current generator 116 of the first embodiment is omitted, and only the correction circuit 118 is provided. As in the above-described embodiments, the correction memory 108 selects the correction data Cv corresponding to any one of the light emitting elements 104 selected by the selection unit 120 from the first light emitting element 104a and the second light emitting element 104b. Remember me. The correction circuit 118 generates a correction current Ic corresponding to the correction data Cv stored in the correction memory 108. In this embodiment, the correction current Ic is the drive current Ids supplied to the selected light emitting element 104.

  In the configuration of the present embodiment, the reference current generator 116 is omitted, so that the same effect can be obtained with a simpler configuration as compared to the above-described embodiments.

<D: Modification>
The present invention is not limited to the above-described embodiments, and for example, the following modifications are possible. Also, two or more of the modifications shown below can be combined.

(1) Modification 1
In each of the embodiments described above, the selection unit 120 selects the light emitting element 104 that is different from the previously selected light emitting element 104 every time the light emitting device 10 is turned on. The conditions for changing the light emitting element 104 to be changed are arbitrary. Specific embodiments will be exemplified below.

[Example 1]
For example, it is possible to generate a random number every time the power is turned on, and change the light emitting element 104 to be used based on the random number. In this case, the light emitting element 104 selected at the previous power-on may be selected again, but this is not always the case, and a light-emitting element 104 different from the light-emitting element 104 selected at the previous power-on is selected. Of course, this also occurs. Therefore, the life of the light emitting element 104 can be extended as compared with the case where any one of the light emitting elements 104 is continuously used until the end of its lifetime. In short, it is sufficient to use a mode in which a plurality of light emitting elements 104 are used instead of continuously using one light emitting element 104 until the end of its lifetime.

[Example 2]
For example, in an image forming apparatus (for example, a printer) using the light emitting device 10 according to the present invention, the selection unit 120 has a predetermined number of recording materials (for example, paper) on which an image is formed (hereinafter referred to as “image forming number”). It is also possible to change the light emitting element 104 to be used every time the reference number is reached. For example, in each of the embodiments described above, it is assumed that a memory for storing the number of image formations is provided separately, and the predetermined reference number is set to 10,000. Each time an image is formed on one recording material, the data of the number of formed images is incremented and written to the memory. When the number of image formations written in the memory reaches 10,000, which is the reference number, the selection unit 120 selects the second light emitting element 104b as the light emitting element 104 to be used. At this time, the number of image formations stored in the memory is initialized to zero, and the number of image formations with the second light emitting element 104b selected is sequentially incremented and written to the memory. Similarly, when the number of formed images reaches 10,000 when the second light emitting element 104b is selected, the selection unit 120 selects the first light emitting element 104b again as the light emitting element 104 to be used.

  Even in this embodiment, the first light emitting element 104a and the second light emitting element 104b are alternately used, so that any one of the light emitting elements 104 is used continuously until the end of its lifetime. Thus, the life of the light emitting element 104 can be extended. Further, by configuring the memory for storing the number of image formations with a non-volatile memory, it is possible to ensure the number of image formations with the selected light emitting element 104 even when the power supply is suddenly shut down during use. Can be held in memory. Note that the means for measuring the number of formed images is not limited to the memory, and for example, a mode in which a register and a counter are provided separately may be employed. In addition, the selection unit 120 may change the light emitting element 104 to be used every time the usage time of the selected light emitting element 104 reaches a predetermined reference time.

[Example 3]
For example, in an image forming apparatus (for example, a printer) using the light emitting device 10 according to the present invention, a time during which an image is not formed on a recording material (for example, paper) has elapsed for a certain period of time, and the image forming apparatus enters an idle state (standby mode). Each time, the selection unit 120 can change the light emitting element 104 to be used. In this case, a light emitting element 104 that is different from the light emitting element 104 selected before the image forming apparatus enters the idle state may be selected, or a random number may be generated as in [Example 1] above, based on this. The light emitting element 104 may be selected. According to this aspect, the memory for storing the number of formed images as in [Example 2] is not necessary, and the life of the light emitting element 104 can be extended with a simpler configuration.

(2) Modification 2
In the embodiments described above, each of the unit circuits U ₁ ~U _n is provided with a switching transistor Tr for switching whether to supply the driving current Ids generated by the current generator 400 to the light emitting element 104, for example, As shown in FIG. 5, it is possible to adopt an aspect in which the switching transistor Tr is not provided. In the configuration of FIG. 5, AND gates 122a and 122b are provided corresponding to selection transistors Tsw1 and Tsw2 in selection unit 120, respectively. The AND gate 122a is supplied with the gradation data D supplied from the latch circuit 114 and the selection signal SEL1 during the driving period of the light emitting device 10. The AND gate 122b is supplied with gradation data D and a selection signal SEL2.

  When the selection signal SEL1 is at the H level and the selection signal SEL2 is at the L level during the driving period of the light emitting device 10, the output signal from the AND gate 122a is supplied to the gate of the selection transistor Tsw1, and the selection transistor Tsw1 is turned on. . Accordingly, the driving current Ids is supplied to the first light emitting element 104a. On the other hand, when the selection signal SEL2 is at the H level and the selection signal SEL1 is at the L level, the output signal from the AND gate 122b is supplied to the gate of the selection transistor Tsw2, and the selection transistor Tsw2 is turned on. Accordingly, the driving current Ids is supplied to the second light emitting element 104b.

(3) Modification 3
In each of the embodiments described above, the number of the correction current source transistors Tc in the correction circuit 118 is three. However, in order to set the correction current Ic generated by the correction circuit 118 in more stages, the correction currents having different sizes are used. An embodiment in which four or more source transistors Tc are provided may be employed. Moreover, it can also be set as the structure that each size of several correction current source transistor Tc is the same. That is, the number of correction current source transistors Tc in the correction circuit 118 and their sizes (for example, channel width or channel length) can be changed as appropriate.

(4) Modification 4
In the embodiments described above, each of the unit circuits _U 1 ~U _n is provided with a first light emitting element 104a and a second light emitting element 104b, the light emitting element of each unit circuit _U 1 ~U _n 104 The number of is arbitrary. For example, each of the unit circuits _U 1 ~U _n may also be an embodiment that includes a light emitting element 104 triplicate.

(5) Modification 5
The light emitting element 104 may be an OLED element, an inorganic light emitting diode, or an LED (Light Emitting Diode). In short, all elements that emit light in response to supply of electric energy (application of electric field or supply of current) can be used as the light-emitting element 104 of the present invention.

<E: Electronic equipment>
Next, with reference to FIG. 6, an image forming apparatus which is one aspect of the electronic apparatus according to the invention will be described. This image forming apparatus is a tandem type full color image forming apparatus using a belt intermediate transfer body system.

  In this image forming apparatus, four light emitting devices 10K, 10C, 10M, and 10Y each having the same configuration are provided with four photosensitive drums (image carriers) 110K, 110C, and 110M having the same configuration. , 110Y are arranged at positions facing the image forming surface 110. The light emitting devices 10K, 10C, 10M, and 10Y have the same configuration as the light emitting device 10 according to each of the above embodiments.

  As shown in FIG. 6, this image forming apparatus is provided with a driving roller 121 and a driven roller 122. An endless intermediate transfer belt 120 is wound around these rollers 121 and 122, and an arrow indicates. As shown, the periphery of the rollers 121 and 122 is rotated. Although not shown, tension applying means such as a tension roller that applies tension to the intermediate transfer belt 120 may be provided.

  Around the intermediate transfer belt 120, four photosensitive drums 110K, 110C, 110M, and 110Y each having a photosensitive layer on the outer peripheral surface are arranged at a predetermined interval. The subscripts “K”, “C”, “M”, and “Y” mean that they are used to form black, cyan, magenta, and yellow visible images, respectively. The same applies to other members. The photosensitive drums 110K, 110C, 110M, and 110Y are rotationally driven in synchronization with the driving of the intermediate transfer belt 120.

  Around each photosensitive drum 110 (K, C, M, Y), there is a corona charger 111 (K, C, M, Y), a light emitting device 10 (K, C, M, Y), and a developing unit. 114 (K, C, M, Y) are arranged. The corona charger 111 (K, C, M, Y) uniformly charges the image forming surface 110A (outer peripheral surface) of the corresponding photosensitive drum 110 (K, C, M, Y). The light emitting device 10 (K, C, M, Y) writes an electrostatic latent image on the charged image forming surface 110A of each photosensitive drum. In each light emitting device 10 (K, C, M, Y), a plurality of light emitting elements 20 are arranged along the bus (main scanning direction) of the photosensitive drum 110 (K, C, M, Y). The electrostatic latent image is written by irradiating the photosensitive drum 110 (K, C, M, Y) with light by the plurality of light emitting elements 20. The developing device 114 (K, C, M, Y) has a visible image (that is, a visible image) on the photosensitive drum 110 (K, C, M, Y) by attaching toner as a developer to the electrostatic latent image. ).

  The black, cyan, magenta, and yellow developed images formed by the four-color single-color image forming stations are superimposed on the intermediate transfer belt 120 by being sequentially primary-transferred onto the intermediate transfer belt 120. As a result, a full-color visible image is formed. Four primary transfer corotrons (transfer devices) 112 (K, C, M, Y) are arranged inside the intermediate transfer belt 120. The primary transfer corotron 112 (K, C, M, Y) is disposed in the vicinity of the photosensitive drum 110 (K, C, M, Y), and the photosensitive drum 110 (K, C, M, Y). The electrostatic image is electrostatically attracted from the toner image to transfer the visible image to the intermediate transfer belt 120 passing between the photosensitive drum and the primary transfer corotron.

  A sheet 102 as an object (recording material) on which an image is to be finally formed is fed one by one from the sheet feeding cassette 101 by the pickup roller 103 and is subjected to secondary transfer with the intermediate transfer belt 120 in contact with the driving roller 121. Sent to the nip between the rollers 126. The full-color visible image on the intermediate transfer belt 120 is secondarily transferred to one side of the sheet 102 by the secondary transfer roller 126 and fixed on the sheet 102 through the fixing roller pair 127 as a fixing unit. . Thereafter, the sheet 102 is discharged onto a paper discharge cassette formed in the upper part of the apparatus by a paper discharge roller pair 128.

  Next, another embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. This image forming apparatus is a rotary developing type full-color image forming apparatus using a belt intermediate transfer body system. As shown in FIG. 11, a corona charger 168, a rotary development unit 161, the light emitting device 10 according to the above-described embodiment, and an intermediate transfer belt 169 are provided around the photosensitive drum 110. Yes.

  The corona charger 168 uniformly charges the outer peripheral surface of the photosensitive drum 110. The light emitting device 10 writes an electrostatic latent image on the charged image forming surface (outer peripheral surface) of the photosensitive drum 110. In the light emitting device 10, a plurality of light emitting elements 32 are arranged along the bus line (main scanning direction) of the photosensitive drum 110. The electrostatic latent image is written by irradiating the photosensitive drum 110 with light from these light emitting elements 32.

  The developing unit 161 is a drum in which four developing units 163Y, 163C, 163M, and 163K are arranged at an angular interval of 90 °, and can rotate counterclockwise about the shaft 161a. The developing units 163Y, 163C, 163M, and 163K supply yellow, cyan, magenta, and black toner to the photosensitive drum 110, respectively, and attach the toner as a developer to the electrostatic latent image, thereby the photosensitive drum 110. A visible image (ie, a visible image) is formed.

  The endless intermediate transfer belt 169 is wound around a driving roller 170a, a driven roller 170b, a primary transfer roller 166, and a tension roller, and is rotated around these rollers in a direction indicated by an arrow. The primary transfer roller 166 transfers the visible image to the intermediate transfer belt 169 that passes between the photosensitive drum 110 and the primary transfer roller 166 by electrostatically attracting the visible image from the photosensitive drum 110.

  Specifically, in the first rotation of the photosensitive drum 110, an electrostatic latent image for a yellow (Y) image is written by the light emitting device 10, and a developed image of the same color is formed by the developing device 163Y. The image is transferred to the transfer belt 169. Further, in the next rotation, the electrostatic latent image for the cyan (C) image is written by the light emitting device 10A, and a developed image of the same color is formed by the developing device 163C, and the intermediate transfer is performed so as to overlap the yellow developed image. Transferred to the belt 169. Then, while the photosensitive drum 110 rotates four times in this way, the yellow, cyan, magenta, and black visible images are sequentially superimposed on the intermediate transfer belt 169, and as a result, a full-color visible image becomes a transfer belt 169. Formed on top. When images are finally formed on both sides of a sheet as an object on which an image is to be formed, the same color images of the front and back surfaces are transferred to the intermediate transfer belt 169, and then the front and back surfaces are transferred to the intermediate transfer belt 169. A full-color visible image is formed on the intermediate transfer belt 169 in such a manner that the visible image of the next color is transferred.

  The image forming apparatus is provided with a sheet conveyance path 174 through which a sheet passes. The sheets are picked up one by one from the paper feed cassette 178 by the pick-up roller 179, advanced through the sheet transport path 174 by the transport roller, and between the intermediate transfer belt 169 and the secondary transfer roller 171 in contact with the drive roller 170a. Pass through the nip. The secondary transfer roller 171 transfers the developed image to one side of the sheet by electrostatically attracting a full-color developed image from the intermediate transfer belt 169 collectively. The secondary transfer roller 171 can be moved closer to and away from the intermediate transfer belt 169 by a clutch (not shown). The secondary transfer roller 171 is brought into contact with the intermediate transfer belt 169 when a full-color visible image is transferred onto the sheet, and is separated from the secondary transfer roller 171 while the visible image is superimposed on the intermediate transfer belt 169.

  The sheet on which the image has been transferred as described above is conveyed to the fixing device 172 and is passed between the heating roller 172a and the pressure roller 172b of the fixing device 172, whereby the visible image on the sheet is fixed. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the direction of arrow F. In the case of double-sided printing, after most of the sheet passes through the paper discharge roller pair 176, the paper discharge roller pair 176 is rotated in the reverse direction and introduced into the double-sided printing conveyance path 175 as indicated by an arrow G. The Then, the visible image is transferred to the other surface of the sheet by the secondary transfer roller 171, the fixing process is performed again by the fixing device 172, and then the sheet is discharged by the discharge roller pair 176.

  Since the image forming apparatus illustrated in FIGS. 6 and 7 uses a light source (exposure means) that employs an OLED element as the light emitting element 20, the apparatus is made smaller than when a laser scanning optical system is used. . Note that the light-emitting device 10 of the present invention can also be employed in electrophotographic image forming apparatuses other than those exemplified above. For example, the light emitting device according to the present invention is also applied to an image forming apparatus that directly transfers a visible image from a photosensitive drum to a sheet without using an intermediate transfer belt, and an image forming apparatus that forms a monochrome image. 10 can be applied.

  The use of the light emitting device according to the present invention is not limited to exposure of a photoreceptor. For example, the light emitting device of the present invention is employed in an image reading device such as a scanner as a line type optical head (illumination device) that irradiates a reading target such as an original with light. As this type of image reading apparatus, there is a scanner, a copying machine or a reading part of a facsimile, a barcode reader, or a two-dimensional image code reader for reading a two-dimensional image code such as a QR code (registered trademark). In addition, a light-emitting device in which a plurality of light-emitting elements (particularly light-emitting elements) are arranged in a planar shape is also employed as a backlight unit disposed on the back side of a liquid crystal panel. A light-emitting device in which a plurality of light-emitting elements are arranged in a matrix is employed as a display device for various electronic devices.

1 is a perspective view showing a partial configuration of an image forming apparatus according to a first embodiment. It is a figure which shows schematic structure of the light-emitting device which concerns on the same embodiment. 2 is a block diagram showing an electrical configuration of a unit circuit U ₁ according to the same embodiment. FIG. Is a block diagram showing an electrical configuration of the unit circuit U ₁ according to the third embodiment. FIG. 10 is a block diagram illustrating an electrical configuration of a unit circuit U ₁ according to Modification 5. It is a perspective view which shows the specific example (image forming apparatus) of the electronic device which concerns on this invention. It is a perspective view which shows the specific example (image forming apparatus) of the electronic device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Light-emitting device, 100 ... Optical head, 104 ... Light-emitting element, 106 ... Drive part, 108 ... Correction memory, 116 ... Reference current generation part, 118 ... Correction circuit, 120 ... Selection part, 200 ...... control circuit, 300 ...... first memory, 302 ...... second memory, 400 ...... current _generator, U 1 ~U _n ...... unit circuit, Tg ...... current source transistor, TC1 to TC3 ... ... correction current source transistor, Tr ... switch transistor, Tsw1, Tsw2 ... select transistor, Iref ... reference current, Ic ... correction current, Ids ... drive current.

Claims (7)

An optical head having a plurality of unit circuits,
Each of the plurality of unit circuits is
A plurality of light emitting elements that emit light at a luminance corresponding to the driving current;
Selection means for selecting any one of the plurality of light emitting elements to which the driving current is supplied;
First storage means for selectively storing correction data corresponding to the light emitting element selected by the selection means among the plurality of light emitting elements;
An optical head comprising: a current generation unit that generates a drive current according to the correction data stored in the first storage unit. 2. The optical head according to claim 1, wherein the selection unit selects the light emitting element different from the previously selected light emitting element every time the power is turned on, and uses the selected light emitting element until the power is turned off. An optical head for exposing an image carrier that carries an image formed on a recording material,
The optical head according to claim 1, wherein the selection unit selects the light emitting element every time the number of recording materials on which an image is formed reaches a reference number. A light emitting device including an optical head and a control circuit,
The optical head has a plurality of unit circuits,
Each of the plurality of unit circuits is
A plurality of light emitting elements that emit light at a luminance corresponding to the driving current;
Selection means for selecting any one of the plurality of light emitting elements to which the driving current is supplied;
First storage means for selectively storing correction data corresponding to the light emitting element selected by the selection means among the plurality of light emitting elements;
Current generating means for generating a drive current according to the correction data stored in the first storage means,
The control circuit includes:
For each of the plurality of unit circuits,
A light-emitting device that supplies the correction data corresponding to the light-emitting element selected by the selection unit among the correction data corresponding to each of the plurality of light-emitting elements to the first storage unit. In each of the plurality of unit circuits,
The plurality of light emitting elements include a first light emitting element and a second light emitting element,
The first correction data corresponding to the first light emitting element and the difference between the first correction data and the second correction data corresponding to the second light emitting element are stored for each unit circuit. Comprising a second storage means;
When the second light emitting element is selected by the selection unit for each of the plurality of unit circuits, the control circuit uses the first correction data and the difference stored in the second storage unit. The light emitting device according to claim 4, wherein the second correction data is generated and supplied to the first storage unit.   An electronic apparatus comprising the light emitting device according to claim 4. With multiple unit circuits,
Each of the plurality of unit circuits is
A plurality of light emitting elements that emit light at a luminance corresponding to the driving current;
Selection means for selecting any one of the plurality of light emitting elements to which the driving current is supplied;
First storage means for storing correction data;
Current generation means for generating a drive current according to the correction data stored in the first storage means;
An optical head driving method comprising:
The correction data corresponding to the light emitting element selected by the selection means is supplied to the first storage means, and the first storage means corresponds to the correction corresponding to the light emitting element selected by the selection means. An optical head control method that selectively stores data.

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