JP4786314B2 - Light emitting device and image forming apparatus - Google Patents

Description

  The present invention relates to a light emitting device including a light emitting element array constituted by a plurality of light emitting elements, and an image forming apparatus including the light emitting device.

  As a light emitting device used as an optical printer head such as an electrophotographic printer, there is an LED array formed by arranging a large number of light emitting diodes (abbreviated as LEDs). This LED array has a large number of bonding pads in order to individually connect the light emitting diode and the driving circuit. For example, when an electrophotographic printer is configured with an A3 size, 600 dpi specification, the number of light emitting elements is required for the connection point between the bonding pad and the circuit wiring even when the anode or cathode of the LED is a common terminal with a conductive substrate. It reaches about 7300 places. For this reason, the operation | work which connects both by the conventionally well-known wire bonding method requires a very long time, and it is difficult to improve productivity. Further, in order to form the bonding pad, a larger area than that for forming the light emitting element is required, and as the image to be formed by the electrophotographic printer becomes higher definition, the light emitting element per unit length in the scanning direction. Therefore, the number of bonding pads also increases.

  In order to reduce the number of bonding pads, the anode and cathode of each LED are connected in a matrix of m × n (the symbols m and n are positive integers), and the drive signals are switched in a time-sharing manner. A dynamic drive type LED array that emits light has been proposed. In this dynamic drive type LED array, the number of bonding pads can be reduced to about ¼ compared to an LED array in which each LED and a drive circuit are individually connected. However, in this dynamic drive type LED array, m or n electrode wirings for connecting the anode or cathode every m or n and the entire array are required. This electrode wiring is connected to the anode or cathode, and a current proportional to the light emission intensity of the LED flows. Therefore, in order to reduce the resistance value, it is necessary to form a certain line width, that is, to increase the channel cross-sectional area. There is. For this reason, there is a problem that the area for forming the electrode wiring increases, and the surface area of the chip on which the LED array is formed increases.

  In view of such a problem, in the first conventional technique, a light-emitting thyristor having a PNPN structure is used as a light-emitting element, and either one of the anode and the cathode is used as a common terminal on the conductive substrate, and the other of the anode and the cathode, A light emitting device in which gates are connected in an mxn matrix and gates through which almost no current flows are connected by electrode wires throughout the array, thereby reducing the line width of the electrode wires and reducing the area for forming the electrode wires. Has been proposed (see, for example, Patent Documents 1 and 2).

  FIG. 8 is an equivalent circuit diagram showing a schematic circuit configuration of the basic structure of the light emitting device 1 of the first prior art. The cathodes of the light emitting elements T are connected in common, the anodes of the m light emitting elements T are connected in common as one block, and the n blocks A1, A2,..., An-1, An emit light. The light emitting device is configured by arranging the elements T in a line. In the light emitting device 1 shown in FIG. 8, m = 4 is selected. In the case where the blocks A1, A2,..., An-1, An are collectively referred to, and the block A1, A2,. In each of the blocks A, the light emitting elements T included in each block A are described as light emitting elements T1 to T4 from one to the other in the arrangement direction. In addition, m electrode wirings G1, G2,..., Gm−1, Gm equal to the number of light emitting elements T included in each block A extend along the light emitting elements T over the entire region in the arrangement direction of the light emitting element arrays. The gates of the m light emitting elements T formed in each block A are connected to different electrode wirings G1, G2,..., Gm−1, Gm, respectively. When the electrode wirings G1, G2,..., Gm-1, Gm are collectively referred to, and when the electrode wirings G1, G2,. There is. The m electrode wirings G include electrode wirings G1 to G4. As the order of connection of the gates of the light emitting elements T to the electrode wirings G, in the light emitting device 1, the blocks A1 to An are connected in the same order. That is, the light emitting element T1 of each block A is connected to the electrode wiring G1, the light emitting element T2 of each block A is connected to the electrode wiring G2, and the light emitting element T3 of each block A is connected to the electrode wiring G3. The light emitting element T4 of each block A is connected to the electrode wiring G4.

  In the light emitting device 1, a control signal is transmitted to the electrode wiring G1, the electrode wiring G2, the electrode wiring G3, and the electrode wiring G4 in this order in a time division manner, and a voltage is simultaneously applied to the anodes of the blocks A1 to An. Thus, the light emitting elements T1 to T4 in the blocks A1 to An can be made to emit light in order. That is, first, the light emitting elements T1 of the blocks A1 to An simultaneously emit light, then the light emitting elements T2 of the blocks A1 to An simultaneously emit light, and then the light emitting elements T3 of the blocks A1 to An simultaneously emit light. In addition, the light emitting elements T4 of the blocks A1 to An are caused to emit light simultaneously.

  In such a light emitting device 1, when the light emitting elements T1 to T4 of the blocks A1 to An are caused to emit light, the control signals are sequentially transmitted to the electrode wirings G1 to G4 in a time division manner, and the same timing is sent to the anodes of the blocks A. When the voltage is applied at, a large time lag occurs in the light emitting timing of the light emitting elements T adjacent to each other in the blocks A adjacent to each other. That is, among the blocks A adjacent to each other, the light emitting element T4 of the block A on the one side in the arrangement direction and the light emitting element T1 of the block A on the other side in the arrangement direction transmit the control signal to the electrode wiring G1 and control the electrode wiring G4. Until the signal is transmitted, the light emission timing is greatly shifted by the time during which the control signal is transmitted to the electrode wirings G2 and G3.

  When the light-emitting device 1 is used as an exposure device that exposes a photosensitive drum, the photosensitive drum is constantly rotating even during exposure, so that a large time is required for the timing at which the light-emitting elements T adjacent to each other emit light. If there is a misalignment, the photoconductive drum rotates by the time of the light emission timing, so that the exposure position by the light emitting elements T adjacent to each other on the photoconductive drum becomes discontinuous, and the print quality deteriorates. appear.

  In view of such a problem, in the light emitting device 2 of the second conventional technique, the light emitting element T adjacent to each other is changed by changing the connection between the light emitting element T and the electrode wiring G in the configuration of the light emitting device 1 described above. Is prevented from causing a large time lag.

  FIG. 9 is an equivalent circuit diagram showing a schematic circuit configuration of the basic structure of the light emitting device 2 of the second prior art. The light emitting device 2 has the same configuration as the light emitting device 1 shown in FIG. 8, and only the connection relationship between the light emitting element T and the electrode wiring G is different from the light emitting device 1. Therefore, the same components are denoted by the same reference numerals, and the description thereof is omitted.

  In the light emitting device 2, the order of connection between the gates of the respective light emitting elements T and the electrode wiring G is different in blocks adjacent to each other, and is connected in the opposite order. That is, each light emitting element T1 of the block Ai (the symbol i is a positive odd number and i ≦ n) and each light emitting element T4 of the block Aj (j is a positive even number and j ≦ n) Each light emitting element T2 of the block Ai connected to the electrode wiring G1, and each light emitting element T3 of the block Aj connected to the electrode wiring G2, each light emitting element T3 of the block Ai, and each light emitting element T2 of the block Aj Are connected to the electrode wiring G3, and each light emitting element T4 of the block Ai and each light emitting element T1 of the block Aj are connected to the electrode wiring G4.

Japanese Patent No. 2807910 JP 2003-69078 A

  In the light emitting device 2, the order of connection between the gate of each light emitting element T and the electrode wiring G is different in blocks adjacent to each other, and is connected in the opposite order, so that the blocks adjacent to each other are mutually connected. In the light emitting element T adjacent to the photosensitive drum, it is possible to eliminate the time lag of the light emission timing and to expose the photosensitive drum with continuous exposure positions of the light emitting elements T on the photosensitive drum.

  However, in the light emitting device 2, among the blocks adjacent to each other, the light emitting element T4 of one block A in the arrangement direction and the light emitting element T1 of the other block A in the arrangement direction are connected to the same electrode wiring G4. Among the blocks A adjacent to each other, the light emitting element T1 of one block A in the arrangement direction and the light emitting element T4 of the other block A in the arrangement direction are connected to the same electrode wiring G1. When the control signal is transmitted in order by division and a voltage is applied to the anode of each block A at the same timing, the light emitting elements T adjacent to each other in the block A adjacent to each other emit light at the same timing. For example, the light emitting element T4 of the block A1 and the light emitting element T1 of the block A2 emit light at the same timing, and the light emitting element T4 of the block A2 and the light emitting element T1 of the block A3 emit light at the same timing.

  When the light emitting elements T adjacent to each other emit light at the same timing, the light emitted from each other interferes, and there is a difference in energy for exposing the photosensitive drum between the case where both the light emitting elements T emit light and the case where light is emitted alone. Therefore, there arises a problem that the print quality is deteriorated. In addition, since the light emitting elements T adjacent to each other emit light at the same timing, the temperature change at the time of light emission is different from the light emitting elements T that emit light at other single timings. Therefore, carriers in the light emitting thyristor that is each light emitting element T. Even if the same voltage is applied to the anode, the light emission intensity varies among the light emitting elements T in the light emitting device, resulting in a problem that the print quality is deteriorated.

Furthermore, in order to print at high speed, the resolution of image quality is set to 600 dpi (Dots Per
Inch), when it is attempted to print at 300 dpi, it is necessary to emit only the odd or even numbered light emitting elements T in the arrangement direction. However, in the light emitting device 2, the gates of the odd-numbered or even-numbered light-emitting elements T in the blocks adjacent to each other can be achieved by switching the control signal applied to the electrode wiring G. Since the electrode wiring G connected to is different, even if only the odd-numbered or even-numbered light-emitting elements T are caused to emit light, the control signal is switched to the electrode wiring G connected to the gates of all the light-emitting elements T in a time division manner. There is a problem that it is impossible to increase the printing speed.

  SUMMARY OF THE INVENTION An object of the present invention is to prevent the light emission timing between adjacent light emitting elements from greatly deviating without complicating the structure of the apparatus, and to suppress light emission at the same timing, thereby exposing an exposure apparatus. The present invention is to provide a light emitting device that can obtain a recorded image with good image quality when used as an image forming apparatus and can easily cope with an increase in printing speed by reducing resolution, and an image forming apparatus including the light emitting device. .

The light emitting device of the present invention has a light emitting electrode to which a light emission signal is given and a control electrode to which a control signal is given, and when the light emission signal is given to the light emitting electrode in a state where the control signal is given to the control electrode, A plurality of light emitting elements that emit light when the voltage or current generated between the light emitting electrode and the control electrode is larger than the threshold voltage or threshold current, and the light emitting electrodes are connected to each other N (N is 2 A light emitting element array in which a plurality of light emitting element block portions composed of a group of the light emitting elements are formed, and the light emitting element block is formed by two light emitting element block portions adjacent to each other;
N + 1 control signal transmission lines for transmitting the control signal,
The control electrode of the nth (1 ≦ n ≦ 2 × N) th light emitting element from one side along the arrangement direction of the light emitting elements in the light emitting element block to the other, and the width extending along the arrangement direction of the light emitting elements Of the N + 1 control signal transmission lines arranged at intervals in the direction, the mth (1 ≦ m ≦ N + 1) th control signal transmission line from the side close to the light emitting element ,
When n is 1 ≦ n ≦ N, m satisfies m = n,
When n is N + 1 ≦ n ≦ 2 × N, m is connected so as to satisfy m = 2 × N + 2-n.

  In addition, the light emitting device of the present invention includes control signal transmission means for simultaneously transmitting control signals to the first and (N + 1) th control signal transmission paths among the control signal transmission paths.

The image forming apparatus of the present invention includes the light emitting device,
Driving means for driving the light emitting device based on image information;
Condensing means for condensing light from the light emitting element of the light emitting device on the photosensitive drum;
Developer supplying means for supplying the developer to the exposed photosensitive drum by which light from the light emitting device is condensed on the photosensitive drum by the condensing means;
Transfer means for transferring an image formed by a developer on the photosensitive drum to a recording sheet;
And fixing means for fixing the developer transferred to the recording sheet.

  According to the present invention, each light emitting element has a threshold voltage or current generated between the light emitting electrode and the control electrode when a light emitting signal is applied to the light emitting electrode while a control signal is applied to the control electrode. It emits light when it exceeds the voltage or threshold current. A light emitting element block portion is formed by a group of N (symbol N is an integer of 2 or more) light emitting elements to which light emitting electrodes are connected to each other, and a light emitting element block is formed by two light emitting element block portions adjacent to each other. Is done. Therefore, the light emitting element block includes 2 × N light emitting elements.

The control electrode of each light emitting element is connected to one of N + 1 control signal transmission paths for transmitting a control signal, and the nth (from the one along the arrangement direction of the light emitting elements in the light emitting element block toward the other) 1 and the control electrode of ≦ n ≦ 2 × n) th light emitting element, among the extending along the arrangement direction of the light emitting elements, n + 1 pieces of control signal transmission lines that are arranged at intervals in the width direction, the When the m-th (1 ≦ m ≦ N + 1) th control signal transmission line from the side close to the light emitting element is n = 1 ≦ n ≦ N, m satisfies m = n, and n is N + 1 ≦ N When n ≦ 2 × N, m is connected so as to satisfy m = 2 × N + 2-n. When the control electrode of each light emitting element and the control signal transmission line are connected in this way, among the N + 1 control signal transmission lines, the first control signal transmission line includes the light emitting element included in the light emitting element block. Only the first light emitting element is connected, and only the (N + 1) th light emitting element among the light emitting elements included in the light emitting element block is connected to the (N + 1) th control signal transmission path. In addition, among the light emitting elements included in the light emitting element block, in the light emitting element block portion on one side of the light emitting element block in one of the arrangement directions of the (N + 1) th light emitting elements, that is, one side of the light emitting element block in the arrangement direction of the light emitting elements. = M, each light emitting element is connected to the control signal transmission path, so that the control signal transmission path and the control signal transmission path of the light emitting element increase as the order of the light emitting elements increases. And are connected. Among the light emitting elements included in the light emitting element block, m is the other in the arrangement direction of the (N + 1) th light emitting element, that is, the light emitting element block portion on the other side in the arrangement direction of the light emitting elements among the adjacent light emitting element block portions. Since the light emitting elements are connected to the control signal transmission path so that m = 2 × N + 2-n, the control electrodes of the light emitting elements are arranged so that the order of the control signal transmission paths decreases as the order of the light emitting elements increases. A control signal transmission line is connected.

  Therefore, in the light emitting elements included in the light emitting element block and adjacent to each other, the respective control electrodes are individually connected to the kth and k + 1th (symbol k is an integer between 1 and N) control signal transmission lines. Therefore, even if the control signals are transmitted in order in a time-sharing manner to the first to (N + 1) th control signal transmission lines and the light emission signals are given to the light emitting electrodes of the respective light emitting element block portions at the same timing, It is possible to suppress the time shift of the light emission timing of the light emitting elements adjacent to each other from increasing, and further, since the adjacent light emitting elements are not connected to the same control signal transmission path, the light emitting elements adjacent to each other Can be prevented from emitting light simultaneously. Similarly, in the light emitting element blocks adjacent to each other, the control electrodes for the light emitting elements adjacent to each other are similarly controlled at the k-th and k + 1-th control signal transmission lines (symbol k is an integer of 1 to N). Therefore, it is possible to suppress the light emission timing between adjacent light emitting elements from being greatly shifted over the entire area of the light emitting element array, and to suppress light emission at the same timing. As a result, when the light emitting device of the present invention is used as an exposure device that exposes a photosensitive drum, exposure of the photosensitive drum to the photosensitive drum is suppressed by preventing the light emission timing between adjacent light emitting elements from greatly deviating. The light emitting elements adjacent to each other do not generate discontinuities, and the light emitting elements adjacent to each other are prevented from emitting light at the same time, thereby suppressing unevenness in heat generation when each light emitting element emits light. The light emission characteristics due to the temperature change of the element can be made uniform, and further, the light generated from the light emitting elements adjacent to each other can be prevented from interfering with each other, so that the photosensitive drum can be exposed with high accuracy. In the image forming apparatus, a recorded image with excellent image quality can be obtained.

  In addition, when printing is performed by reducing the resolution of the image quality in half for printing at high speed, for example, when printing is performed by dropping from 600 dpi to 300 dpi, from one of the light emitting elements included in the light emitting element array along the arrangement direction. Only the odd-numbered or even-numbered light-emitting elements need to emit light toward the other side. However, in the light-emitting device of the present invention, the control electrode of the odd-numbered light-emitting element has the odd-numbered control signal transmission path and the even-numbered light-emitting element. Since the control electrodes of the light emitting elements are respectively connected to the even-numbered control signal transmission lines, this is achieved by switching the control signal transmitted to the even-numbered or odd-numbered control signal transmission lines. Therefore, the printing speed can be easily increased only by switching the control signal transmitted to the even-numbered or odd-numbered control signal transmission line.

  Further, according to the present invention, among the control signal transmission lines, the first and (N + 1) th control signal transmission lines are each a control electrode of one light emitting element among the light emitting elements included in the light emitting element block. Since the control signal is supplied to the first and N + 1th control signal transmission lines at the same time, the number of times the control signal is switched can be reduced. The exposure speed can be increased.

  According to the invention, the photosensitive drum is driven by driving the light emitting device by a driving unit based on image information and condensing the light from the light emitting device on the charged photosensitive drum by the condensing unit. It is exposed to form an electrostatic latent image on its surface. When the developer is supplied to the photosensitive drum on which the electrostatic latent image is formed by the developer supplying means, the developer adheres to the photosensitive drum and an image is formed. An image formed with the developer on the photosensitive drum is transferred to the recording sheet by the transfer unit, and the developer transferred to the recording sheet is fixed by the fixing unit, whereby an image is formed on the recording sheet. Since the photosensitive drum can be accurately exposed by the light emitting device, a recorded image with excellent image quality can be obtained.

Embodiments of the light emitting device of the present invention will be described below with reference to the drawings.
FIG. 1 is an equivalent circuit diagram showing a schematic circuit configuration of a basic structure of a light emitting device 10 according to an embodiment of the present invention. FIG. 1 also shows driving means 17 for driving the light emitting device 10. The light emitting device 10 includes a light emitting element array 11, a light emission signal transmission unit 12, and a control signal transmission unit 13. The light emitting element array 11 includes a plurality of light emitting elements T. The plurality of light emitting elements T are arranged at intervals, and in the present embodiment, the light emitting elements T are arranged in a line. In the present embodiment, each light emitting element T is formed by a light emitting diode having a PN structure in which a P-type semiconductor layer and an N-type semiconductor layer are stacked. The light emitting element T includes a light emitting electrode 14 to which a light emission signal is given and a control electrode 16 to which a control signal is given.

  The light emitting element array 11 has a plurality of light emitting element block portions B1, B2,..., Bi-1, Bi (the symbol i is an integer of 2 or more). Hereinafter, when the light emitting element block portions B1, B2,..., Bi-1, Bi are collectively referred to, and when an unspecified one among the light emitting element block portions B1, B2,. The element block portion B is described.

  The light emitting element blocks C1, C2,..., Cj−1, Cj (the symbol j is a positive integer and j = i / 2) are formed by the light emitting element block portions B adjacent to each other. Hereinafter, when the light emitting element blocks C1, C2,..., Cj-1, Cj are collectively referred to, and when an unspecified one among the light emitting element blocks C1, C2,. C. In the present embodiment, the light emitting element block C1 is formed by the light emitting element block portions B1 and B2, the light emitting element block C2 is formed by the light emitting element block portions B3 and B4, and the light emitting element block Cj is the light emitting element block portion. It is formed of Bi-1 and Bi.

  Each light emitting element block portion B is composed of a group of N (symbol N is an integer of 2 or more) light emitting elements T to which the light emitting electrodes 14 are connected to each other. Since the light emitting element block C is formed by two light emitting element block portions B, the light emitting element block C is formed to include 2 × N light emitting elements T. In the present embodiment, a case where N is N = 4, that is, each light emitting element block portion B is composed of a group of four light emitting elements T, respectively.

  The light emission signal transmission unit 12 includes a plurality of light emission signal transmission paths E1, E2,..., Ei-1, Ei connected individually for each light emitting element block portion B. Hereinafter, when the light emission signal transmission paths E1, E2,..., Ei-1, Ei are collectively referred to, and when an unspecified one among the light emission signal transmission paths E1, E2,. It is described as a signal transmission path E. Specifically, the light emission signal transmission path E1 is a signal wiring and is connected to the light emitting electrode 14 of each light emitting element T of the light emitting element block portion B1, and the light emission signal transmission path E2 is each light emission of the light emitting element block portion B2. The light emitting signal transmission path Ei-1 is connected to the light emitting electrode 14 of each light emitting element T of the light emitting element block portion Bi-1, and the light emitting signal transmission path Ei is connected to the light emitting element block portion. It is connected to the light emitting electrode 14 of each Bi light emitting element T.

  The control signal transmission unit 13 includes N + 1 control signal transmission lines G1, G2,... GN, GN + 1. In the present embodiment, since N is selected as N = 4, the control signal transmission unit 13 includes five control signal transmission lines G1, G2, G3, G4, and G5. Hereinafter, when the control signal transmission lines G1, G2,..., GN, GN + 1 are collectively referred to, and when the control signal transmission lines G1, G2,. It describes. The control signal transmission line G is a signal wiring.

The control electrode 16 of the nth (1 ≦ n ≦ 2 × N) light emitting element Tn from one side along the arrangement direction of the light emitting elements T in the light emitting element block C to the other, and N + 1 control signal transmission lines G Of these, the m-th (1 ≦ m ≦ N + 1) th control signal transmission line Gm is connected so as to satisfy the following conditions (1) and (2).
Condition (1) When n is 1 ≦ n ≦ N, m is m = n
Condition (2) When n is N + 1 ≦ n ≦ 2 × N, m is m = 2 × N + 2-n

In the present embodiment, the connection between the control electrode 16 and the control signal transmission line G of the nth (1 ≦ n ≦ 8) light emitting element Tn included in the light emitting element block C and extending from one side to the other along the arrangement direction. When n is 1 ≦ n ≦ 4, that is, among the light emitting element block portions B included in the light emitting element block C, the light emitting elements T1 to T4 included in one light emitting element block portion B in the arrangement direction The control electrode 16 of the nth light emitting element Tn is connected to the nth control signal transmission line Gn, that is, the control electrode 16 of the light emitting element T1 is connected to the control signal transmission line G1 to control the light emitting element T2. The electrode 16 is connected to the control signal transmission line G2, the control electrode 16 of the light emitting element T3 is connected to the control signal transmission line G3, and the control electrode 16 of the light emitting element T4 is connected to the control signal transmission line G4. When n is 5 ≦ n ≦ 8, that is, among the light emitting element block portions B included in the light emitting element block C, the light emitting elements T5 to T8 included in the other light emitting element block portions B in the arrangement direction are The control electrode 16 of the nth light emitting element Tn and the 2 × N + 2-nth control signal transmission line _{G2N + 2-n} are connected, that is, the control electrode 16 of the light emitting element T5 is connected to the control signal transmission line G5, The control electrode 16 of the light emitting element T6 is connected to the control signal transmission path G4, the control electrode 16 of the light emitting element T7 is connected to the control signal transmission path G3, and the control electrode 16 of the light emitting element T8 is connected to the control signal transmission path G2. The

  The driving means 17 is connected to the light emission signal transmission path E and the control signal transmission path G, gives a light emission signal e to the light emission signal transmission path E, and gives a control signal g to the control signal transmission path G. The driving means 17 is realized by a driving driver IC (Integrated Circuit). The driving means 17 inputs image information and a reference clock pulse signal from the outside, and outputs the light emission signal e and the control signal g in synchronization with the clock pulse signal, and outputs the light emission signal transmission path E. To the control signal transmission line G. The image information and the clock pulse signal are supplied from the control means 96 of the image forming apparatus 87 described later. The clock cycle of the clock pulse signal is selected to be longer than the control cycle in the control means 96 of the image forming apparatus 87 described later.

  The drive unit 17 includes a control signal transmission unit 18. The control signal transmission means 18 simultaneously transmits the control signal g to the first and (N + 1) th control signal transmission paths G1 and GN + 1 of the control signal transmission path G. In this embodiment, N = 4. Therefore, the control signal g is transmitted simultaneously to the first and fifth control signal transmission lines G1 and G5.

  FIG. 2 is a partial plan view showing the basic configuration of the light-emitting device 10. The figure shows a plane of the light emitting device 10 arranged with the light emitting direction of each light emitting element T as a front side perpendicular to the paper surface. The light emitting signal transmission path E, the control signal transmission path G, and the control electrode of the light emitting element T The connecting portion 31 and the ohmic contact layer 27 are indicated by hatching for easy illustration. FIG. 2 shows the light emitting element blocks C <b> 1 and C <b> 2 of the light emitting device 10.

  The plurality of light emitting elements T included in the light emitting element array 11 are arranged at intervals. The light emitting element T is a light emitting element for exposure. In the present embodiment, the light emitting elements T are arranged at equal intervals and in a straight line. The arrangement direction X of the light emitting elements T is the left-right direction in FIG. Hereinafter, the arrangement direction X of the light emitting elements T may be simply referred to as the arrangement direction X. A direction along the light emission direction of each light emitting element T is defined as a thickness direction Z, and a direction perpendicular to the arrangement direction X and the thickness direction Z is defined as a width direction Y. The light emitting element T is formed so as to emit light having a wavelength of 600 nm to 800 nm.

  Since the light emitting element T is formed by a light emitting diode having a PN structure, the light emitting element T can be realized with a simple structure in which a P-type semiconductor and an N-type semiconductor are stacked, and the device can be easily manufactured. The light emitting element T has a voltage generated between the light emitting electrode 14 and the control electrode 16 when the light emitting signal is applied in a state where the control signal is applied to the control electrode connecting portion 31 to which the control electrode 16 is connected. The current becomes larger than the threshold voltage or threshold current and light is emitted.

  Each control signal transmission line G extends in the arrangement direction X along the light emitting element array 11 from one end to the other end in the arrangement direction X of the light emitting element array 11. Each control signal transmission line G is arranged at intervals in the width direction Y. In the present embodiment, the control signal transmission path G1, the control signal transmission path G2, the control signal transmission path G3, the control signal transmission path G4, and the control signal transmission path G5 are arranged in order from the side close to the light emitting element T. Is done. The interval between the control signal transmission lines G is selected as a distance that does not cause a short circuit between the control signal transmission lines G adjacent to each other, for example, 10 μm.

  The control signal transmission line G and the light emission signal transmission line E are formed of a conductive material such as a metal material and an alloy material. Specifically, gold (Au), an alloy of gold and germanium (AuGe), gold And zinc (AuZn), nickel (Ni), aluminum (Al), and the like.

Hereinafter, each configuration of the light emitting device 10 will be described more specifically.
3 is a partial cross-sectional view showing a basic configuration of the light-emitting device 10 as viewed from the section line III-III in FIG. 2, and FIG. 4 is a light-emitting device as viewed from the section line IV-IV in FIG. 10 is a partial cross-sectional view showing a basic configuration of No. 10. FIG. The light emitting element T includes one conductive semiconductor layer 24, the other conductive semiconductor layer 25, and an ohmic contact layer 27 formed on one surface 21 a in the thickness direction Z of the substrate 21.

In the present embodiment, the substrate 21 is a semiconductor substrate having electrical insulation.
In the light emitting element T, one conductive type semiconductor layer 24 is stacked on one surface 21 a in the thickness direction Z of the substrate 21, and the other conductive type semiconductor layer 25 is formed on one surface 24 a in the thickness direction Z of the one conductive type semiconductor layer 24. The ohmic contact layer 27 is laminated on the one surface 25a of the thickness direction Z of the other conductive type semiconductor layer 25.

More specifically, the substrate 21 is a semiconductor substrate capable of crystal growth such as III-V group compound semiconductor and II-VI group compound semiconductor, such as gallium arsenide (GaAs), indium phosphide (InP), gallium. It is formed of a semiconductor material such as phosphorus (GaP), silicon (Si), and germanium (Ge).

On the other hand, the conductive semiconductor layer 24 is formed of a semiconductor material such as aluminum gallium arsenide (AlGaAs) or gallium arsenide (GaAs). On the other hand, the carrier density of the conductive semiconductor layer 24 is desirably about 10 ¹⁸ cm ⁻³ . On the other hand, the conductive semiconductor layer 24 can be made of a semiconductor material such as aluminum gallium arsenide (AlGaAs) and gallium arsenide (GaAs), whereby high internal quantum efficiency can be obtained.

On the other hand, the conductive semiconductor layer 25 is formed of a semiconductor material such as aluminum gallium arsenide (AlGaAs) or gallium arsenide (GaAs). On the other hand, the carrier density of the conductive semiconductor layer 25 is preferably about 10 ¹⁸ cm ⁻³ .

The ohmic contact layer 27 is a semiconductor layer of the other conductivity type formed of a semiconductor material such as gallium arsenide (GaAs) or indium gallium phosphide (InGaP), and is used for performing an ohmic junction with the light emitting signal transmission line G. is there. The carrier density of the ohmic contact layer 27 is desirably 10 ¹⁹ cm ⁻³ or more.

  On the other hand, one end portion in the width direction Y of the conductive type semiconductor layer 24 protrudes to one side in the width direction Y from one end portion in the width direction Y between the other conductive type semiconductor layer 25 and the ohmic contact layer 27, and the control electrode connection portion 31 is constituted. On the other hand, in the other end portion in the width direction Y of the conductive semiconductor layer 24, the portion 24A where the other conductive semiconductor layer 25 is laminated is more than the portion 24B constituting the control electrode connecting portion 31 in the one conductive semiconductor layer 24. A large thickness is formed. Of the light emitting element T, the light emitting portion 32 is configured by a portion protruding in one of the thickness directions Z from the portion 24B constituting the control electrode connecting portion 31 of the one conductive type semiconductor layer 24 and the other conductive type semiconductor layer 25. Is done. The control electrode connection part 31 and the light emitting part 32 have a substantially rectangular parallelepiped shape. The dimension of the control electrode connecting portion 31 in the arrangement direction X is selected to be the same as the dimension of the light emitting section 32 in the arrangement direction X or larger than the dimension of the light emitting section 32 in the arrangement direction X.

  An interval W1 of the light emitting portions 32 of the light emitting elements T in the arrangement direction X and a dimension W2 of the light emitting portions 32 of the light emitting elements T in the arrangement direction X are images to be formed in an image forming apparatus 87 described later on which the light emitting device 10 is mounted. For example, when the image resolution is 600 dot per inch (dpi), the interval W1 is selected to be about 24 μm (micrometer), and the dimension W2 is selected to be about 18 μm.

  In the present embodiment, the dimension of the control electrode connection part 31 in the arrangement direction X is selected to be larger than the dimension of the light emitting part 32 in the arrangement direction X. When the dimension in the arrangement direction X of the control electrode connection part 31 is selected to be larger than the dimension in the arrangement direction X of the light emitting part 32, for example, if the resolution of the image is 600 dpi, the dimension in the arrangement direction X of the light emitting part 32 is as described above. W2 (= about 18 μm) is selected, and the dimension of the control electrode connection portion 31 in the arrangement direction X is selected to be about 30 μm. Thus, by selecting the dimension of the array direction X of the control electrode connection portion 31, the contact area between the one-conductivity-type semiconductor layer 24 and the control electrode 16 can be increased to facilitate the ohmic contact. The control electrode connection part 31 may be separated from the control electrode connection part 31 adjacent to each other in the manufacturing process, and the dimension of the control electrode connection part 31 in the arrangement direction X is the same as that of the control electrode connection part 31 adjacent to each other. You should choose it in the range where it does not touch.

  On the other hand, the conductive semiconductor layer 24, the other conductive semiconductor layer 25, and the ohmic contact layer 27 are covered with an insulating layer 28.

  The insulating layer 28 is formed of a resin material having electrical insulation, translucency, and flatness. The insulating layer 28 is formed of a resin material that transmits 95% or more of light having a wavelength emitted from the light emitting element T, and is formed of polyimide, benzocyclobutene (BCB), or the like.

  The light emitting electrode 14 is connected to one surface 27 a of the ohmic contact layer 27 in the thickness direction Z. A through hole 29 is formed in a portion of the insulating layer 28 formed on the one surface 27 a of the ohmic contact layer 27 in the thickness direction Z, and a part of the light emitting electrode 14 is formed in the through hole 29. , In contact with the ohmic contact layer 27. The through hole 29 is formed so that the center of the light emitting element T in the arrangement direction X and the center of the light emitting element T in the width direction Y are exposed from the insulating layer 28, and the current from the light emitting electrode 14 emits light. The light emitting element T can emit light by efficiently supplying the light to the central portion of the element T. In the light emitting element T, light is generated mainly in the vicinity of the interface between the one conductivity type semiconductor layer 24 and the other conductivity type semiconductor layer 25 and in the region near the one conductivity type semiconductor layer 24.

  The length W3 in the arrangement direction X of the light emitting electrodes 14 is formed to be 1/3 or less of the length W2 in the arrangement direction X of the light emitting portions 32 of the light emitting elements T. The light-emitting electrode 14 covers a part of the light emission direction of the light-emitting element T. However, by selecting the length W3 as described above, the light-emitting electrode 14 blocks the light emitted from the light-emitting element T and directed to one side Z1 in the thickness direction. Can be suppressed.

  Each light emitting electrode 14 extends to the other side in the width direction Y, and is connected to each other through the electrode connection portion 33 for each light emitting element block portion B on the other side in the width direction of the light emitting element array 11. The electrode connection portion 33 extends along the light emitting element array 11 from the light emitting element T at one end in the arrangement direction X included in the light emitting element block portion B in the arrangement direction X to the light emitting element T at the other end in the arrangement direction X. Each light emitting element block portion B extends and is connected to the light emitting electrode 14 of the light emitting element T.

  A light emission signal transmission path E is connected to the electrode connecting portion 33. The light emission signal transmission path E is connected to the center portion in the arrangement direction X of the electrode connection portions 33 and extends to the other side in the width direction Y. The light emitting electrode 14 and the electrode connecting portion 33 are formed of a conductive material such as a metal material and an alloy material similar to the light emitting signal transmission path E, and are integrally formed with the light emitting signal transmission path E.

  On the other hand, the control electrode 16 is connected to one surface 24Ba of the thickness direction Z of the portion 24B constituting the control electrode connection portion 31 of the conductive semiconductor layer 24. A through hole 30 is formed in one surface 24Ba of the thickness direction Z of the portion 24B constituting the control electrode connecting portion 31 of the one conductive type semiconductor layer 24 in the insulating layer 28, and the control electrode 16 is formed in the through hole 30. Formed and in contact with the conductive semiconductor layer 24. The control electrode 16 is connected to any one of the control signal transmission lines G based on the above-described conditions. The control electrode 16 is formed of a conductive material such as a metal material and an alloy material similar to the control signal transmission line G, and is integrally formed with the control signal transmission line G.

  The control electrode connection portion 31 of the light emitting element T extends to one of the width directions Y to a position where a control signal transmission path G to be connected to each other is formed. In the present embodiment, the control signal transmission path G1, the control signal transmission path G2, the control signal transmission path G3, the control signal transmission path G4, and the control signal transmission path G5 are arranged in this order from the side closer to the light emitting element array 11. Therefore, as the order of the light emitting elements T increases from the light emitting element T1 to the light emitting element T5, the dimension in the width direction Y of the control electrode connecting portion 31 increases, and from the light emitting element T5 to the light emitting element T8. As the order of the light emitting elements T increases, the control electrode connection portion 31 is formed so that the dimension of the control electrode connection portion 31 in the width direction Y decreases. Each of the light emitting element blocks C1 to Cj has a similar structure.

  Each light emitting element T is formed by epitaxial growth and chemical vapor deposition of a semiconductor material for forming one conductive type semiconductor layer 24, the other conductive type semiconductor layer 25, and an ohmic contact layer 27 on one surface 21a of the substrate 21, respectively. After sequentially stacking by a growth (CVD) method or the like, patterning and etching are performed by photolithography. Therefore, since the light emitting element T can be formed at the same time in a series of manufacturing processes, the manufacturing cost can be reduced.

  The insulating layer 28 is formed by forming each semiconductor layer, spin-coating the above-described resin material such as polyimide, and then curing the applied resin material to connect the light emitting electrode 14 and the control electrode 16 to the light emitting element T. The through holes 29 and 30 necessary for the above are formed by patterning and etching by photolithography.

  The control signal transmission path G, the light emission signal transmission path E, the light emitting electrode 14, the control electrode 16, and the electrode connecting portion 33 are formed by forming an insulating layer 28, and then applying a conductive material by an evaporation method or the like. After being laminated on the surface of the substrate, patterning and etching are performed by photolithography, and the layers are simultaneously formed. Therefore, the thicknesses of the control electrode transmission line G and the light emission signal transmission line E are formed approximately equal.

  In the present embodiment, one conductivity type is N-type, and the other conductivity type is P-type. In the light emitting element T, when one conductivity type is N type and the other conductivity type is P type, the light emitting electrode 14 functions as an anode, and the control electrode 16 functions as a cathode. The light emission signal transmission path E is configured to be connected to the anode of each light emitting element T. When the cathode potential is set to zero (0) volts (V), a positive power source is applied as a power source for applying voltage or current to each light emitting element T. Can be used. When the potential of the light emitting electrode 14 is higher than the potential of the control electrode 16 and the potential difference between the light emitting electrode 14 and the control electrode 16 becomes larger than the threshold voltage Vth, a current flows through the light emitting element T, and the light emitting element T Emits light. The threshold voltage Vth represents the forward diffusion potential of the diode. Conversely, the threshold current Ith represents the current that flows through the light emitting electrode 14 and the light emitting element T when a forward diffusion potential is applied between the light emitting electrode 14 and the control electrode 16.

  When the light emission signal e is at a high (H) level, the driving means 17 applies a potential V1 to the light emitting electrode 14, and when the light emission signal e is at a low (L) level, the driving means 17 applies a potential V2 to the light emitting electrode 14. When the control signal g is at a high (H) level, the driving means 17 applies a potential V3 to the control electrode 16, and when the control signal g is at a low (L) level, the driving means 17 applies a potential V4 to the control electrode 16. . The potential V2 of the light emitting electrode 14 when the light emission signal e is at the low (L) level and the potential V4 of the control electrode 16 when the control signal g is at the low (L) level are selected, for example, as 0V. When the light emission signal e is at the high (H) level, the potential V1 of the light emitting electrode 14 is equal to or higher than the value obtained by adding the threshold voltage Vth to the potential V4 (V4 + Vth) and less than the value obtained by adding the threshold voltage to the potential V3 (V3 + Vth). To be elected.

  When the control signal g is high (H) level and the light emission signal e is high (H) level, the voltage (V1−V3) of the light emitting electrode 14 with respect to the control electrode 16 does not exceed the threshold voltage Vth. The light emitting element T does not emit light. Further, when the control signal g is at the low (L) level and the light emission signal e is at the high (H) level, the voltage (V1-V4) of the light emitting electrode 14 with respect to the control electrode 16 exceeds the threshold voltage Vth. The light emitting element T emits light. When the control signal g is at the low (L) level and the light emission signal e is at the low (L) level, the voltage (V2-V4) of the light emitting electrode 14 with respect to the control electrode 16 does not exceed the threshold voltage Vth. Therefore, the light emitting element T does not emit light. When the control signal g is high (H) level and the light emission signal e is low (L) level, the voltage (V2-V3) of the light emitting electrode 14 with respect to the control electrode 16 does not exceed the threshold voltage Vth. Therefore, the light emitting element T does not emit light. Therefore, only when the control signal g is given, that is, when the control signal g is in the low (L) level, the emission signal e is given, and the emission signal e becomes the high (H) level, The light emitting element T emits light.

  FIG. 5 is a waveform diagram showing clock pulses of the control signal g and the light emission signal e and the light emission intensities of the light emitting elements T1 to T8 when the light emitting device 10 is driven. The light emission intensity of the light emitting elements T1 to T8 indicates that light is emitted when the level is high (H), and that light is not emitted when the level is low (L). In FIG. 5, the horizontal axis represents time and represents the elapsed time from the reference time. Further, here, control signals g1 to g5 transmitted to the control signal transmission lines G1 to G5, and light emission signals e1 and e2 transmitted to the light emission signal transmission lines E1 and E2, respectively, are shown.

  For the control signal g and the light emission signal e, the vertical axis represents the signal level. The signal level represents the magnitude of the voltage. When the control signal g is high (H) level, a high voltage is supplied to the control signal transmission line G, and when the control signal g is low (L) level, the low voltage is It is supplied to the control signal transmission line G. When the light emission signal is at a high (H) level, a high voltage is supplied to the light emission signal transmission line E, and when the light emission signal e is at a low (L) level, a low voltage is supplied to the light emission signal transmission line E. In the case of voltage, the high level is 2-5 volts (V), for example, and the low level is 0 (zero) volts (V), for example.

  Hereinafter, the operation in this embodiment will be described. First, at time t1, the driving means 17 sets the control signal g1 applied to the first control signal transmission line G1 to a low level, and the control signals applied to the second to fifth control signal transmission lines G2 to G5, respectively. Set g2 to g5 to high level. At time t1, the driving unit 17 sets the light emission signals e1 and e2 applied to the light emission signal transmission lines E1 and E2 to low level. Since the light emitting element T emits light only when the control signal g is at a low level and the light emission signal e is at a high level, each of the light emitting elements T1 to T8 can be controlled by setting the light emission signals e1 and e2 to a low level. Does not emit light. When the signal level is changed from the low level to the high level for the control signals g1 to g5 and the light emission signals e1 and e2, the driving unit 17 changes the signal level to the high level until the signal level is changed from the high level to the low level next time. When the signal level is changed from the high level to the low level, the signal level is maintained at the low level until the signal level is changed from the low level to the high level next time.

  At time t2, the driving unit 17 changes the light emission signals e1 and e2 from the low level to the high level. As a result, among the light emitting elements T1 to T8 connected to the light emitting signal transmission lines E1 and E2, the light emitting element T1 in which the control signal g is at low level, the control signal g is at low level, and the light emitting signal e is at high level. The light emitting element T1 is turned on and emits light. The light emitting elements T2 to T8 whose control signal g is at the high level are turned off, that is, do not emit light.

  At time t3, the driving unit 17 changes the light emission signals e1 and e2 from the high level to the low level. As a result, the potential of the light emitting electrode 14 becomes 0 V, which is equal to the potential of the control electrode 16, so that the light emitting element T1 in the light emitting state is turned off and extinguished.

  At time t4, the driving unit 17 changes the control signal g1 from the high level to the low level at the same time as changing the control signal g1 from the low level to the high level. At time t4, the control signals g3 to g5 are at a high level, and the light emission signals e1 and e2 are at a low level. At time t4, all of the light emitting elements T1 to T8 are turned off.

  At time t5, the driving unit 17 changes the light emission signals e1 and e2 from the low level to the high level. As a result, among the light emitting elements T1 to T8 connected to the light emitting signal transmission lines E1 and E2, only the light emitting elements T2 and T8 whose control signal g is at the low level are turned on and emit light. The other light emitting elements T1, T3 to T7 are turned off and turned off because the control signals g1, g3 to g5 are at a high level.

  At time t6, the driving unit 17 changes the light emission signals e1 and e2 from the high level to the low level. As a result, the light emitting elements T2 and T8 in the light emitting state are turned off and turned off. At time t6, all of the light emitting elements T1 to T8 are turned off.

  At time t7, the driving unit 17 changes the control signal g2 from the low level to the high level, and simultaneously changes the control signal g3 from the high level to the low level. Similarly, from time t7 to time t16, the driving unit 17 sequentially switches the control signals g3 to g5 from the high level to the low level and outputs the light emission signals e1 and e2 when the light emission control signals g3 to g5 are at the low level. By changing from the high level to the low level, all of the light emitting elements T1 to T8 can emit light in order.

  In this embodiment, the control signal means 18 provided in the driving means 17 changes the control signals g1 and g5 from the high level to the low level at the same timing at time t13, and the control signals g1 and g5 are the same at time t16. Change from low level to high level at the timing. In the light emitting element block C, the driving means 17 turns on the light emitting element T1, then turns on the light emitting elements T2 and T8, then turns on the light emitting elements T3 and T7, and then turns on the light emitting elements T4 and T6. Next, the light emitting elements T1 and T5 are turned on. After time t13, the driving unit 17 lights the light emitting elements T1 and T5 simultaneously, lights the light emitting elements T2 and T8 simultaneously, lights the light emitting elements T3 and T7 simultaneously, and lights the light emitting elements T4 and T6 simultaneously. Can do.

  In the case of switching the control signals g1 to g5 in a time-sharing manner, the signal level of each control signal g1 to g5 is sequentially switched during the switching time of one cycle, so that the signal level of each control signal g is changed from a high level to a low level. Ts × 5 (times) switching time is required if Ts is the time from the transition to the transition to the high level again. In the light emitting device 10 of the present embodiment, the control signals g1 and g5 are By switching from the low level to the high level at the same timing and from the low level to the high level at the same timing, the switching time of one cycle can be set to Ts × 4 (times), so that the control signals g1 to g5 are The switching time of one cycle to be switched can be shortened, and the period for causing each of the light emitting elements T1 to T8 to emit light can be shortened. Compared with the technique, even if the control signal g is increased by 1, the period for causing the light emitting elements T1 to T8 to emit light does not become longer. Among the control signal transmission lines G1 to G5, the first and fifth control signal transmission lines G1 and G5 control one light emitting element T among the light emitting elements T1 to T8 included in the light emitting element block C, respectively. Since only the electrode 16 is connected, the control signals g1 and g5 are simultaneously supplied to the first and fifth control signal transmission lines G1 and G5, thereby reducing the number of times the control signal g is switched in this way. Therefore, it is possible to increase the exposure speed of the photosensitive drum 90 by the light emitting device 10.

  Further, the exposure amount to the photosensitive drum 90 to be described later is adjusted by the light emission time of the light emitting element T, with the light emission intensity of the light emitting element T being constant. That is, in the light emitting elements T1 to T8, the exposure amount is determined by determining the time during which the light emission signal e is at the high level. When the exposure amount is changed depending on the light emission intensity of the light emitting element T, it is difficult to finely control the voltage or current applied to the light emitting element T. However, by changing the exposure amount depending on the light emission time, the light emission signal e is changed. Since it is only necessary to adjust the high level time, it is easy to control the exposure amount, and a constant voltage or constant current is applied to the light emitting element T, so that the light emitting element T can emit light stably. The time for the light emitting element T to emit light, in other words, the time for the light emission signal e to be at a high level, is selected to be 80% or less of the time for the control signal g to be at a low level. The time during which the control signals g1 to g5 are at the low level is selected equally.

  FIG. 5 shows only the light emission signals e1 and e2 transmitted to the light emission signal transmission paths E1 and E2 for driving the light emitting elements T1 to T8 of the light emitting element block C1. The light emission signals e1 to ei transmitted to the light emission signal transmission paths E1 to Ei in order to drive the light emitting elements T1 to T8 of the element block C may have the same waveform as the light emission signals e1 and e2.

  FIG. 6 is a side view showing the basic configuration of the image forming apparatus 87 having the light emitting device 10. The image forming apparatus 87 is an electrophotographic image forming apparatus, and the light emitting device 10 is used as an exposure device for the photosensitive drum 90. The light emitting device 10 is mounted on a circuit board on which the driving unit 17 is provided.

  The image forming apparatus 87 is an apparatus that employs a tandem system that forms four color images of Y (yellow), M (magenta), C (cyan), and K (black), and is roughly divided into four light emitting elements. Devices 10Y, 10M, 10C, 10K, lens arrays 88Y, 88M, 88C, 88K as condensing means, a circuit board on which the light emitting device 10 and the driving means 17 are mounted, and a first holder 89Y for holding the lens array 88, 89M, 89C, 89K, four photosensitive drums 90Y, 90M, 90C, 90K, four developer supply means 91Y, 91M, 91C, 91K, a transfer belt 92 as transfer means, four cleaners 93Y, 93M, 93C, 93K, four chargers 94Y, 94M, 94C, 94K, a fixing unit 95 and a control unit 96.

  Each light emitting device 10 is driven by the driving means 17 based on the color image information of each color. For example, the length of the four light emitting devices 10 in the arrangement direction X is selected from 200 mm to 400 mm, for example.

  Light from the light emitting element T of each light emitting device 10 is condensed and applied to each of the photosensitive drums 90Y, 90M, 90C, and 90K via the lens array 88. The lens array 88 includes, for example, a plurality of lenses disposed on the optical axis of the light emitting element, and is configured by integrally forming these lenses.

  The circuit board on which the light emitting device 10 is mounted and the lens array 88 are held by the first holder 89. By the first holder 89, alignment is performed so that the light irradiation direction of the light emitting element T and the optical axis direction of the lenses of the lens array 88 substantially coincide.

  Each of the photoconductive drums 90Y, 90M, 90C, and 90K is formed, for example, by adhering a photoconductive layer on the surface of a cylindrical substrate, and the outer peripheral surface receives light from the light emitting devices 10Y, 10M, 10C, and 10K. Then, an electrostatic latent image forming position where the electrostatic latent image is formed is set.

  The exposed photosensitive drums 90Y, 90M, 90C, and 90K are sequentially exposed at the periphery of the photosensitive drums 90Y, 90M, 90C, and 90K toward the downstream side in the rotational direction with respect to the electrostatic latent image forming positions. Developer supplying means 91Y, 91M, 91C, 91K for supplying developer to the transfer belt 92, cleaners 93Y, 93M, 93C, 93K, and chargers 94Y, 94M, 94C, 94K are arranged, respectively. A transfer belt 92 that transfers an image formed on the photosensitive drum 90 with a developer onto a recording sheet is provided in common to the four photosensitive drums 90Y, 90M, 90C, and 90K.

  The photosensitive drums 90Y, 90M, 90C, and 90K are held by a second holder, and the second holder and the first holder 89 are relatively fixed. The photoconductor drums 90Y, 90M, 90C, and 90K are aligned so that the rotation axis directions of the respective light emitting devices 10 and the arrangement direction X of the light emitting devices 10 substantially coincide with each other.

  The recording sheet is conveyed by the transfer belt 92, and the recording sheet on which an image is formed by the developer is conveyed to the fixing unit 95. The fixing unit 95 fixes the developer transferred to the recording sheet. The photosensitive drums 90Y, 90M, 90C, and 90K are rotated by a rotation driving unit.

  The control unit 96 supplies a clock signal and image information to the driving unit 17 described above, and also rotates and drives the photosensitive drums 90Y, 90M, 90C, and 90K, developer supply units 91Y, 91M, 91C, and 91K, Each part of the transfer means 92, the charging means 94Y, 94M, 94C, 94K and the fixing means 95 is controlled.

  As described above, in the light emitting device 10, in the light emitting elements T included in the light emitting element block C and adjacent to each other, the respective control electrodes 16 are kth and k + 1th (the symbol k is an integer of 1 to N). ) Are individually connected to the control signal transmission line G, so that the control signals g are sequentially transmitted to the first to (N + 1) th control signal transmission lines G in a time-sharing manner, and each light emitting element block portion B is transmitted. Even if the light emission signal e is given to the light emitting electrodes 14 at the same timing, it is possible to suppress a time lag of the light emission timings of the light emitting elements T adjacent to each other from increasing. Since T is not connected to the same control signal transmission line G, the light emitting elements T adjacent to each other do not emit light at the same time. In the light emitting elements T adjacent to each other, the light emitting element T2 emits light from the time from the time when one light emitting element T emits light to the time when the other light emitting element T emits light, for example, from the time t2 when the light emitting element T1 emits light. The time up to the time t5 is selected to be equal to the time when the control signals g1 to g5 are at a low level, for example, 1 μsec (μs). Therefore, the time lag of the light emission timing of the light emitting elements T adjacent to each other can be set to about 1 μsec.

  Similarly, for the light emitting elements T adjacent to each other in the light emitting element blocks C, the respective control electrodes 16 are similarly controlled at the k-th and k + 1-th (symbol k is an integer from 1 to N). Since the light transmission elements G are individually connected to the signal transmission line G, it is possible to prevent the light emission timing between the light emitting elements T adjacent to each other from being greatly shifted over the entire area of the light emitting element array 11, and at the same timing. Light emission is prevented. Accordingly, when the light emitting device 10 of the present invention is used as an exposure device that exposes the photosensitive drum 90, the light emitting timing between the light emitting elements T adjacent to each other is suppressed from being greatly shifted, and thus the photosensitive member. Discontinuity does not occur at the exposure position where the drum 90 is exposed, and the light emitting elements T adjacent to each other are prevented from emitting light at the same time. The light-emitting characteristics due to the temperature change of each light-emitting element T can be suppressed and light generated from the light-emitting elements T adjacent to each other can be prevented from interfering with each other. The image forming apparatus 87 can obtain a recorded image with an excellent image quality.

  In the control device 10, the driving unit 17 can drive the light emitting device 10 in the high-speed printing mode based on a control command from the control unit 96. When a mode selection button provided on the image forming apparatus 87 is operated and the high-speed printing mode is selected, the control unit 96 gives a control command for driving the light emitting device 10 to the driving unit 17.

  FIG. 7 is a waveform diagram showing the control signal g and the clock pulse of the light emission signal e and the light emission intensity of the light emitting elements T1 to T8 when the driving unit 17 drives the light emitting device 10 in the high speed printing mode. The light emitting elements T1 to T8 emit light intensity when high (H) level, and indicate that light is not emitted when low (L) level. In FIG. 7, the horizontal axis represents time and represents the elapsed time from the reference time. Further, here, control signals g1 to g5 transmitted to the control signal transmission lines G1 to G5, and light emission signals e1 and e2 transmitted to the light emission signal transmission lines E1 and E2, respectively, are shown.

  For the control signal g and the light emission signal e, the vertical axis represents the signal level. The signal level represents the magnitude of the voltage. When the control signal g is high (H) level, a high voltage is supplied to the control signal transmission line G, and when the control signal g is low (L) level, the low voltage is It is supplied to the control signal transmission line G. When the light emission signal is at a high (H) level, a high voltage is supplied to the light emission signal transmission line E, and when the light emission signal e is at a low (L) level, a low voltage is supplied to the light emission signal transmission line E. In the case of voltage, the high level is 2-5 volts (V), for example, and the low level is 0 (zero) volts (V), for example.

  In the high-speed printing mode, in order to print at high speed, printing is performed with the resolution of the image quality reduced to half, for example, from 600 dpi to 300 dpi. For this purpose, the driving means 17 causes only the odd-numbered or even-numbered light-emitting elements T to emit light from one side along the arrangement direction X to the other among the light-emitting elements T included in the light-emitting element array 11. Here, the case where only the odd-numbered light emitting elements T of the light emitting elements T included in the light emitting element array 11 emit light from one side along the arrangement direction X to the other will be described. The same applies to the case where only even-numbered light-emitting elements T emit light from one side along the arrangement direction X to the other side among the light-emitting elements T.

  First, at time t1, the driving means 17 sets the control signal g1 applied to the first control signal transmission line G1 to a low level, and the control signals applied to the second to fifth control signal transmission lines G2 to G5, respectively. Set g2 to g5 to high level. At time t1, the driving unit 17 sets the light emission signals e1 and e2 applied to the light emission signal transmission lines E1 and E2 to low level. Since the light emitting element T emits light only when the control signal g is at a low level and the light emission signal e is at a high level, each of the light emitting elements T1 to T8 can be controlled by setting the light emission signals e1 and e2 to a low level. Does not emit light. When the signal level is changed from the low level to the high level for the control signals g1 to g5 and the light emission signals e1 and e2, the driving unit 17 changes the signal level to the high level until the signal level is changed from the high level to the low level next time. When the signal level is changed from the high level to the low level, the signal level is maintained at the low level until the signal level is changed from the low level to the high level next time. Here, since only the odd-numbered light emitting elements T are caused to emit light, the driving means 17 always keeps the control signals g2 and g4 given to the even-numbered light emitting elements T at a high level.

  At time t2, the driving unit 17 changes the light emission signals e1 and e2 from the low level to the high level. As a result, among the light emitting elements T1 to T8 connected to the light emitting signal transmission lines E1 and E2, the light emitting element T1 in which the control signal g is at low level, the control signal g is at low level, and the light emitting signal e is at high level. The light emitting element T1 is turned on and emits light. The light emitting elements T2 to T8 whose control signal g is at the high level are turned off, that is, do not emit light.

  At time t3, the driving unit 17 changes the light emission signals e1 and e2 from the high level to the low level. As a result, the potential of the light emitting electrode 14 becomes 0 V, which is equal to the potential of the control electrode 16, so that the light emitting element T1 in the light emitting state is turned off and extinguished.

  At time t4, the driving unit 17 changes the control signal g1 from the high level to the low level at the same time as changing the control signal g1 from the low level to the high level. At time t4, the control signals g2, g4, and g5 are at a high level, and the light emission signals e1 and e2 are at a low level. At time t4, all of the light emitting elements T1 to T8 are turned off.

  At time t5, the driving unit 17 changes the light emission signals e1 and e2 from the low level to the high level. As a result, among the light emitting elements T1 to T8 connected to the light emitting signal transmission lines E1 and E2, only the light emitting elements T3 and T7 whose control signal g is at the low level are turned on and emit light. The other light emitting elements T1, T2, T4 to T6, and T8 are turned off and turned off because the control signals g1, g2, g4, and g5 are at a high level.

  At time t6, the driving unit 17 changes the light emission signals e1 and e2 from the high level to the low level. As a result, the light emitting elements T3 and T7 in the light emitting state are turned off and turned off. At time t6, all of the light emitting elements T1 to T8 are turned off.

  At time t7, the driving unit 17 changes the control signals g3 and g5 from the high level to the low level at the same time as changing the control signal g3 from the low level to the high level. At time t7, the control signals g2 and g4 are at a high level, and the light emission signals e1 and e2 are at a low level. At time t7, all of the light emitting elements T1 to T8 are turned off.

  At time t8, the driving unit 17 changes the light emission signals e1 and e2 from the low level to the high level. As a result, among the light emitting elements T1 to T8 connected to the light emitting signal transmission lines E1 and E2, only the light emitting elements T1 and T5 whose control signal g is at the low level are turned on and emit light. The other light emitting elements T2 to T4 and T6 to T8 are turned off and turned off because the control signals g2 to g4 are at a high level.

  At time t9, the driving unit 17 changes the light emission signals e1 and e2 from the high level to the low level. As a result, the light emitting elements T1 and T5 in the light emitting state are turned off and turned off. At time t9, all of the light emitting elements T1 to T8 are turned off.

  At time t10, the driving unit 17 changes the control signals g1 and g5 from the low level to the high level and simultaneously changes the control signal g3 from the high level to the low level. At time t10, the control signals g2 and g4 are at a high level, and the light emission signals e1 and e2 are at a low level. At time t10, all of the light emitting elements T1 to T8 are turned off.

  As described above, in the light emitting device 10, the control electrodes 16 of the odd-numbered light emitting elements T are connected to the odd-numbered control signal transmission path G, and the control electrodes 16 of the even-numbered light emitting elements T transmit the even-numbered control signal. Since it is connected to the path G, by switching the control signal g transmitted to the even-numbered or odd-numbered control signal transmission path G, the resolution of the image quality can be reduced to half and the printing speed can be easily increased. is there.

  In still another embodiment of the present invention, each semiconductor layer may be formed in multiple layers in the light emitting device of the above-described embodiment. For example, the one-conductivity-type semiconductor layer may be configured by stacking a plurality of one-conductivity-type semiconductor layers, and the other-conductivity-type semiconductor layer may be configured by stacking a plurality of other-conductivity-type semiconductor layers. Good.

  In still another embodiment of the present invention, the light emitting element block portion B may be composed of four or more light emitting elements T. As the number of light emitting elements T constituting the light emitting element block portion B increases, the number of light emitting signal transmission paths E can be reduced, the apparatus can be downsized, and the light emitting device 10 and the driving means 17 are connected. Therefore, the number of bonding wires can be reduced.

  The light emitting device 10 includes a plurality of light emitting element blocks C. However, the number of the light emitting element blocks C may be one. In the light emitting device 10, one conductivity type is an N type and the other conductivity type is a P type. However, the one conductivity type may be a P type and the other conductivity type may be an N type.

  In addition, this invention is not limited to the above-mentioned form, A various change, improvement, etc. are possible in the range which does not deviate from the summary of this invention.

It is an equivalent circuit diagram which shows the schematic circuit structure of the basic structure of the light-emitting device 10 of one Embodiment of this invention. It is a partial top view which shows the basic composition of the light-emitting device 10 of one Embodiment of this invention. It is sectional drawing seen from the cut surface line III-III of FIG. It is sectional drawing seen from the cut surface line IV-IV of FIG. It is a wave form diagram which shows the clock pulse of the control signal g and the light emission signal e when driving the light-emitting device 10, and the light emission intensity of the light emitting elements T1-T8. 2 is a side view showing a basic configuration of an image forming apparatus 87 having a light emitting device 10. FIG. It is a wave form diagram which shows the control signal g when the drive means 17 drives the light-emitting device 10 in a high-speed printing mode, the clock pulse of the light emission signal e, and the light emission intensity of light emitting element T1-T8. It is an equivalent circuit diagram which shows the schematic circuit structure of the basic structure of the light-emitting device 1 of a prior art. It is an equivalent circuit diagram which shows the schematic circuit structure of the basic structure of the light-emitting device 2 of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light-emitting device 11 Light-emitting element array 12 Control electrode transmission part 13 Light emission signal transmission part 17 Drive means 18 Control signal transmission means 87 Image forming apparatus T Light-emitting element G Control signal transmission path E Light emission signal transmission path

Claims (3)

A light emitting electrode to which a light emission signal is applied and a control electrode to which a control signal is applied; when the light emission signal is applied to the light emitting electrode in a state where the control signal is applied to the control electrode, the light emitting electrode and the control electrode A plurality of light emitting elements that emit light when a voltage or current generated therebetween is larger than a threshold voltage or threshold current, and the light emitting electrodes are connected to each other (N is an integer of 2 or more). A light emitting element array in which a plurality of light emitting element block portions each composed of a group of light emitting elements are formed, and a light emitting element block is formed by two light emitting element block portions adjacent to each other;
N + 1 control signal transmission lines for transmitting the control signal,
The control electrode of the nth (1 ≦ n ≦ 2 × N) th light emitting element from one side along the arrangement direction of the light emitting elements in the light emitting element block to the other, and the width extending along the arrangement direction of the light emitting elements Of the N + 1 control signal transmission lines arranged at intervals in the direction, the mth (1 ≦ m ≦ N + 1) th control signal transmission line from the side close to the light emitting element ,
When n is 1 ≦ n ≦ N, m satisfies m = n,
When n is N + 1 ≦ n ≦ 2 × N, m is connected so as to satisfy m = 2 × N + 2-n.   2. The light emitting device according to claim 1, further comprising control signal transmission means for simultaneously transmitting control signals to the first and (N + 1) th control signal transmission paths among the control signal transmission paths. The light-emitting device according to claim 1 or 2,
Driving means for driving the light emitting device based on image information;
Condensing means for condensing light from the light emitting element of the light emitting device on the photosensitive drum;
Developer supplying means for supplying the developer to the exposed photosensitive drum by which light from the light emitting device is condensed on the photosensitive drum by the condensing means;
Transfer means for transferring an image formed by a developer on the photosensitive drum to a recording sheet;
An image forming apparatus comprising: fixing means for fixing the developer transferred to the recording sheet.

Images