JP2005144687A - Line head and image forming apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line head of the configuration without irregularities in an emitted quantity of light regardless of a lighting pattern of each light emitting element, and to provide an image forming apparatus using the same. <P>SOLUTION: A pseudo light emitting element Ex is connected in parallel to the light emitting element E1 connected to a connecting part Ja-Jb between a first power supply line 2 and a second power supply line 3. Moreover, a pseudo light emitting element Ey is connected in parallel to the light emitting element E2 connected to a connecting part Ka-Kb between the first power supply line 2 and the second power supply line 3. A dummy load is turned off by drive transistors Tr1 and Tr2 when the light emitting elements are on, and is turned on when the light emitting elements are off. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a line head configured to have no variation in the amount of emitted light regardless of the lighting pattern of each light emitting element when a plurality of light emitting elements are arranged in one line, and an image forming apparatus using the line head.

  An image forming apparatus using a line head provided with a large number of light emitting elements in one line as an exposure means has been developed. Patent Document 1 describes that one line of EL (Electroluminesence) element is arranged in an optical printer head, and gradation data corresponding to each EL element is held for each EL element. Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for eliminating variations in light emission characteristics in the main scanning direction in a printer head in which a plurality of LED chips are arranged in one line.

  FIG. 13 is an explanatory view schematically showing an example of a wiring configuration of a conventional organic EL element. In FIG. 13, in the line head 10, a large number of organic EL elements Ea are arranged in the main scanning direction to form one light emitting element line 1. Reference numerals 2 and 3 denote first and second power supply lines formed by thin film wirings, and reference numerals 6 and 7 denote feeding points. The feeding point 6 is provided on the power supply (VDD) side, and the feeding point 7 is provided on the ground (GND) side. A is an anode electrode of the organic EL element Ea, and K is its cathode electrode.

  Tr2 is a drive transistor, which is formed on the same substrate as the organic EL element Ea. D is connected to the power supply line 2 at the drain of the drive transistor Tr2. G is a gate, and a source S is connected to an anode electrode A of the organic EL element Ea. The gate G is connected to the source of the control transistor Tr1 (not shown) by the wiring Ga.

  FIG. 14 is a circuit diagram of FIG. 13, and the same components as those in FIG. As shown in FIG. 14, a gate signal line 4 and a drain signal line 5 are wired to the control transistor Tr1. Further, the drain of the drive transistor Tr2 is connected to the first power supply line 2 as described above, and the source of the control transistor Tr1 is connected to the gate thereof. Each organic EL element Ea arranged in the light emitting element line 1 is connected to the first power supply line 2 connected to the power supply point 6 on the power supply (VDD) side and the power supply point 7 on the ground (GND) side. It is connected between the second power supply line 3.

  A light emitting element using an organic EL element is a current driving element, and the power source line (VDD side) on the drain side of the drive transistor Tr2 and the power source line (GND) on the cathode (cathode electrode) side of the light emitting element depending on the light emission degree of the light emitting element. The current flowing to the side) increases or decreases. Here, these first and second power supply lines are made of thin film wiring, and resistances at both ends of these power supply lines differ depending on the size of the printer head, but on the order of several W to several tens W. Become.

  Further, the current of the light emitting elements is on the order of at least 10 mA when all the light emitting elements are on, and the voltage applied to the light emitting elements reaches several tens of mV to 100 mV. Here, when an organic EL element is used as the light emitting element, the current changes with respect to a slight difference in applied voltage, in other words, the amount of emitted light changes greatly. Therefore, the amount of emitted light may vary greatly depending on the distance between the light emitting element and the feeding point.

JP-A-6-64229 JP 11-198433 A

  FIG. 15 is a simplified circuit diagram of FIG. The left end side of the organic EL element Ea in the figure is E1, and the right end side is En. R and nR are both wiring resistances. R is the wiring resistance between the feeding points 6 and 7 and the organic EL element E1 on the left end side, and nR is the wiring resistance between the organic EL element E1 on the left end side and the organic EL element En on the right end side.

  The voltage between the feeding points 6 and 7 is V, the current is i, the applied voltage of the organic EL element E1 is Vp1, and the applied voltage of En is Vpn. In this case, Vp1 = V-4Ri and Vpn = V-4Ri-4nRi. In this way, when a plurality of light emitting elements are arranged in one line and each light emitting element is connected between the common first and second power supply lines, the applied voltage of each light emitting element depends on the distance from the feeding point. Is different.

  In addition, each light emitting element arranged in one line has a different current flowing depending on the lighting pattern. That is, current from the power supply line flows into the light emitting element that performs light emission, and current from the power supply line does not flow into the light emitting element that does not perform light emission. Therefore, the potential of the power supply line for applying a voltage to the light emitting element at the position where light emission is performed is different from the potential of the power supply line at the position of the light emitting element where light emission is not performed. In this way, depending on the shape of the lighting pattern, there are a mixture of those that emit light and those that do not emit light in one line of light emitting elements, so that potential fluctuations occur in the power supply line. For this reason, the light emission quantity of each light emitting element varies.

  Therefore, in the example of FIG. 15, the applied voltage difference between the light emitting elements increases depending on the position connected to the line, and the voltage applied to each light emitting element varies depending on the lighting pattern, causing unevenness in the amount of emitted light. End up. Since the lifetime of the light emitting element becomes shorter as the luminance increases, the life of the light emitting element varies. In addition, if the amount of emitted light is uneven, the print quality is degraded.

  In order to solve such a problem, the widths of the first and second power supply lines 2 and 3 may be increased. In this case, the width of the light emitting element is increased, and as a result, the printer size is increased. growing. Further, when the substrates have the same size, there arises a problem that the number of light emitting elements that can be manufactured is reduced. As another measure, the thickness of the power supply line can be increased. However, since the light emitting element is formed by a multilayer thin film process, the thickness of the power supply line cannot be increased more than necessary, and is about several hundred μm at most. It is a limit.

  Further, if only the power supply line is made extremely thick between the thin films, the level difference from the other layers becomes large, and the thin film layers are peeled off and defective. Further, the line head has a shape that is long in the main scanning direction and narrow in the sub-scanning direction. Thus, since the shape of the line head is extremely elongated, warping due to the difference in thermal expansion coefficient from the substrate (glass) occurs. In addition, when the thin film is thickened, the film forming time becomes long and the man-hour increases. That is, various unique problems due to the shape of the line head and the manufacture of the light emitting element occur.

  In the techniques described in Patent Document 1 and Patent Document 2, as shown in FIG. 10, the feeding points connected to the first and second power supply lines are provided on the same side of the line. In addition, the voltage applied to each light emitting element varies depending on the lighting pattern. For this reason, there existed a problem that the above-mentioned various subject was not solved.

  The present invention has been made in view of such problems of the prior art, and the object thereof is related to the lighting pattern of each light-emitting element when a plurality of light-emitting elements are arranged in one line to perform a light-emitting operation. It is another object of the present invention to provide a line head having a configuration in which the amount of emitted light does not vary and an image forming apparatus using the line head.

  The line head of the present invention that achieves the above object includes a plurality of light emitting elements arranged in one line, a first power supply line formed by thin film wiring connected to a power supply point on the power supply side, and a power supply point on the ground side. A line head for connecting each light emitting element between the first power supply line and the second power supply line, comprising: A control means is provided in which a pseudo load through which the same current flows is connected in parallel with each light emitting element, and the pseudo load is turned off when the light emitting element is on, and the pseudo load is turned on when the light emitting element is off. And With such a configuration, the total sum of currents flowing in the connection portions between the power supply lines to which the light emitting elements are connected is constant in any connection portion. Therefore, the potential of the power supply line between the connection portions to which the light emitting elements are connected does not vary regardless of the light emission pattern. For this reason, unevenness in the amount of emitted light according to the lighting state of the light emitting element does not occur, so that the printing quality is improved and the variation in life is suppressed.

  Furthermore, the present invention is characterized in that a light emitting element having the same characteristics as the light emitting element is used as the pseudo load. For this reason, since the current characteristic of the pseudo load is the same as that of the light emitting element, it is possible to effectively suppress the influence of the potential fluctuation of the power supply line. Moreover, since the pseudo load can be manufactured in the same process as the light emitting element, the manufacturing cost of the pseudo load can be reduced due to the mass production effect.

  Further, the present invention is characterized in that a resistor is used as the pseudo load. For this reason, there is an advantage that it is not necessary to shield light emitted from the pseudo load.

  Further, the present invention is characterized in that a thin film resistor stacked on the same substrate as the light emitting element is used as the resistor. In this case, the process of connecting the resistor to the connection portion of the light emitting element between the power supply lines is simplified. Moreover, the production of the pseudo load is simplified.

  Further, the present invention is characterized in that a pair of transistors respectively connected to the light emitting element and the pseudo load are provided as the control means, and the conductive layers of the transistors are configured with different polarities. This facilitates formation of control signals for the pair of transistors.

  Further, according to the present invention, as the control means, a pair of transistors respectively connected to the light emitting element and the pseudo load are provided, and the conductive layers of the transistors are configured with the same polarity. A signal is supplied. For this reason, there exists an advantage that a complicated process is not required for manufacture of a pair of transistor.

  The present invention is characterized in that the position of the one feeding point is provided at one end of the line, and the position of the other feeding point is provided at the other end of the line. In this way, since the positions of the feeding points are provided at both ends of the line, there is no difference in the voltage applied to each light emitting element, and the amount of emitted light can be made uniform.

  Further, the present invention is characterized in that the power supply side power supply point and the ground side power supply point are provided at both ends of the line, respectively. For this reason, the influence of the voltage drop of the power supply line is reduced and there is no difference in the voltage applied to each light emitting element, so that the amount of emitted light can be made uniform.

  Further, according to the present invention, a third power supply line on the power supply side and a fourth power supply line on the ground side are wired along the longitudinal direction of the line, and the third power supply line on the power supply side and the fourth power supply line on the ground side are provided. A second feeding point is provided for each of the power lines, and each of the second feeding points is connected to the first power line and the second power line. Thus, since the number of feeding points is increased, the influence of voltage fluctuations on the light emitting element can be suppressed.

  In addition, the present invention is characterized in that a plurality of second feeding points of each power line are provided. In this way, a large number of feeding points are provided, and feeding points are provided at both ends of the line. For this reason, the influence of the voltage drop of the power supply line is reduced and there is no difference in the voltage applied to each light emitting element, so that the amount of emitted light can be made uniform.

  Further, the invention is characterized in that a plurality of lines in which the plurality of light emitting elements are arranged are formed in the sub-scanning direction. For this reason, even if a failure of the light emitting element occurs in the light emitting element line that is lit, the printing process can be continuously performed without replacing the line head.

  Further, the invention is characterized in that the light emitting element of the line head is composed of an organic EL element or an LED. Since the organic EL element can be controlled statically, the control system can be simplified. Moreover, when it comprises with LED, manufacture of a light emitting element becomes easy.

  The image forming apparatus of the present invention includes at least two or more image forming stations in which each of the image forming units of the charging unit, the line head, the developing unit, and the transfer unit described above is arranged around the image carrier. And the image is formed in a tandem manner when the transfer medium passes through each station. For this reason, in the tandem type image forming apparatus, it is possible to equalize the applied light voltages of the respective light emitting elements provided in the line head to equalize the amount of emitted light.

  The image forming apparatus of the present invention includes an image carrier configured to carry an electrostatic latent image, a rotary developing unit, and the line head, and the rotary developing unit is housed in a plurality of toner cartridges. The toner is carried on the surface thereof, and the toners of different colors are sequentially conveyed to a position facing the image carrier by rotating in a predetermined rotation direction, and between the image carrier and the rotary developing unit. A developing bias is applied to the toner, and the toner is moved from the rotary developing unit to the image carrier, whereby the electrostatic latent image is visualized to form a toner image. For this reason, in the image forming apparatus provided with the rotary developing unit, it is possible to equalize the applied light voltages of the respective light emitting elements provided in the line head to make the amount of emitted light uniform.

  In addition, the image forming apparatus of the present invention includes an intermediate transfer member. For this reason, the applied voltage of each light emitting element provided in the line head can be made equal to equalize the amount of emitted light.

  According to the present invention, when a plurality of light emitting elements are arranged in one line and operated for light emission, a pseudo load is connected in parallel with the light emitting elements. The sum of the currents flowing through the connecting portions is the same in all connecting portions. For this reason, when a power supply line is formed by thin film wiring, a line head having a configuration in which there is no difference in the amount of emitted light of each light emitting element and an image forming apparatus using the line head can be obtained.

The present invention will be described below with reference to the drawings. FIG. 6 is a process diagram showing an example of a partial manufacturing process of a line head to which the present invention is applied. In FIG. 6A, an amorphous silicon layer (a-Si layer) 81 is formed on a substrate 80 such as glass. In (b), patterning 82 is performed on the a-Si layer 81 first. Next, a silicon dioxide (SiO ₂ ) insulating layer 83 is formed on the patterning 82 of the a-Si layer 81. Thereafter, the gate metal 82a is formed. Here, the gate G, the drain D, and the source S of the drive transistor Tr2 are formed at the illustrated positions by the gate metal 82a and the patterning 82 as shown in an enlarged manner.

In (c), the silicon dioxide (SiO ₂ ) insulating layer 84 is first formed on the silicon dioxide (SiO ₂ ) insulating layer 83 and the gate metal 82a. Next, two contact holes penetrating from the surface of the insulating layer 84 to the surface of the patterning 82 are formed. A source metal 85 and a drain metal 86 are formed in the contact hole.

In (d), a silicon dioxide (SiO ₂ ) insulating layer 87 is first formed on the silicon dioxide (SiO ₂ ) insulating layer 84, the source metal 85 and the drain metal 86. Next, a contact hole penetrating from the surface of the insulating layer 87 to the surface of the source metal 85 is formed. An anode-side transparent electrode ITO (Indium Tin Oxide) 88 having a contact portion with the source metal 85 extending partly in the contact hole is formed. That is, the anode electrode of the light emitting element and the source of the drive transistor are electrically connected. In (e), a partition wall 89 is formed on the insulating layer 87 and the ITO 88. Next, the light emitting layer 90 is formed in the space between the partition walls 89 and 89.

  FIG. 7 is an explanatory diagram showing a configuration around the light emitting element of the completed line head in association with a circuit diagram. In FIG. 7, a cathode electrode 90 of the light emitting element is further formed in FIG. 6 (e). The cathode electrode 90 is connected to a power supply line 91 on the ground side (GND side) formed of a thin film. Further, the other (VDD side) power supply line is connected to the drain line connected to the drain D of the drive transistor. Each of these power supply lines has a longitudinal direction in the direction orthogonal to the paper surface, and supplies power to a plurality of light emitting elements. Ga is a signal line connected to the source of the control transistor Tr1.

  FIG. 8 is an explanatory view partially showing the periphery of the light emitting portion in the line head of the present invention. The configuration of FIG. 8 omits the position of the feeding point, and the connection form of the first and second power supply lines to the organic EL element Ea is basically the same as the connection configuration to the organic EL element shown in FIG. No difference. In FIG. 13, the power supply points are formed on the same end side of the power lines 2 and 3. On the other hand, in the present invention, as will be described later, the positions of the one feeding point 6 and the other feeding point 7 in the first and second power supply lines 2 and 3 can be set in various positions with respect to the line. It can also be set as the structure provided in.

  FIG. 1 is a circuit diagram showing an embodiment of the present invention. The same parts as those in FIG. 14 are denoted by the same reference numerals. In FIG. 1, the line head 10 b forms the light emitting element line 1 by connecting the light emitting elements E <b> 1, E <b> 2... Between the first power supply line 2 and the second power supply line 3. The pseudo light emitting element Ex is connected in parallel to the light emitting element E1 connected to the connection portion Ja-Jb between the first power supply line 2 and the second power supply line 3. Further, the pseudo light emitting element Ey is connected in parallel to the light emitting element E2 connected to the connection portion Ka-Kb between the first power supply line 2 and the second power supply line 3.

  The drive transistors Tr2 of the light emitting elements E1, E2,... Are composed of P channel transistors, and the drive transistors Tr3 of the pseudo light emitting elements Ex, Ey,. As described above, when the drive transistors of the light emitting elements E1, E2... And the drive transistors of the pseudo light emitting elements Ex, Ey... Are composed of complementary transistors, that is, transistors having different conductive layer polarities, When the same signal is supplied to the line Ga, the operations of the light emitting elements E1, E2... And the pseudo light emitting elements Ex, Ey.

  For example, when a signal for turning on the drive transistor Tr2 is supplied, the light emitting elements E1, E2,. In this case, the drive transistor Tr3 is turned off, and the pseudo light emitting elements Ex, Ey,... Do not emit light. In addition, when the pseudo light emitting elements Ex, Ey,... Emit light, the light emitting elements E1, E2,. As described above, the pair of drive transistors that control the lighting of the light emitting element and the pseudo light emitting element can be turned on and off with the same signal by setting the conductive polarities to be opposite to each other. This simplifies the formation of transistor control signals.

  In this manner, the pseudo light emitting element connected in parallel to the light emitting element that does not emit light due to the shape of the lighting pattern emits light, and the pseudo light emitting element connected in parallel to the light emitting element that emits light does not emit light. For this reason, the sum total of the electric current which flows into the connection part between the power supply lines 2 and 3 to which each light emitting element is connected becomes constant in any connection part. Therefore, the potential of the power supply line between the connection portions to which the light emitting elements are connected does not vary regardless of the light emission pattern. For this reason, unevenness in the amount of emitted light according to the lighting state of the light emitting element does not occur, so that the printing quality is improved and the variation in life is suppressed.

  As the pseudo light emitting elements Ex, Ey,..., Light emitting elements having the same characteristics as the light emitting elements E1, E2,. In this case, a masking process is performed so that light when the pseudo light emitting elements Ex, Ey,... Are turned on does not leak to the outside. In FIG. 1, the drive transistors Tr2 of the light emitting elements E1, E2,... Can be configured by N channel transistors, and the drive transistors Tr3 of the pseudo light emitting elements Ex, Ey,.

  Furthermore, the drive transistors Tr2 and Tr3 can be both N-channel transistors or P-channel transistors, that is, the conductive layers of the pair of control transistors can be configured to have the same polarity. In this case, the gate lines of the drive transistors Tr2 and Tr3 are separated, and when one is turned on, a signal of opposite polarity is supplied to the gates of the drive transistors Tr2 and Tr3 so that the other is turned off. .

  FIG. 2 is a circuit diagram partially showing another embodiment of the present invention. In the light emitting element line 1y of the line head 10c in FIG. 2A, the gate signal line 4 and the drain signal line 5 are wired to the control transistor Tr1, as described in FIG. Further, the drain of the drive transistor Tr2 is connected to the first power supply line 2 as described above, and the source of the control transistor Tr1 is connected to the gate thereof.

  The drain signal line 5 in the control transistor Tr1 on the light emitting element E1 side is branched to form a branch line 5a. An inverter 9 is connected to the branch line 5a. The output signal of the inverter 9 is supplied to the drain of the control transistor Tr1 on the pseudo light emitting element Ex side. Therefore, by using such an inverter 9, the light emitting element E1 and the pseudo light emitting element Ex can be complementarily operated. In this case, the same signal may be supplied to each drain of the control transistor Tr1 on the light emitting element E1 side and the pseudo light emitting element Ex side, so that the configuration of the control circuit is simplified.

  In the configuration of FIG. 1 and FIG. 2A, the pseudo light emitting element is turned on, and thus it is necessary to shield the light of the pseudo light emitting element. For this reason, there exists a problem that the structure of a line head becomes complicated. FIG. 2B is a circuit diagram showing an improved example for dealing with such a problem. The light emitting element line 1z of the line head 10d in FIG. 2B is connected to a resistor R instead of the pseudo light emitting element. Here, the resistance value of the resistor R is set so that the same current as that of the light emitting element E1 flows. The resistor R can be formed, for example, by stacking a conductive layer on the same substrate as the light emitting element E1. The configuration of FIG. 2B has an advantage that it is not necessary to shield light emitted from the pseudo load.

  As described above, in the embodiment of the present invention shown in FIGS. 1 and 2, a pseudo load such as a pseudo light emitting element or a resistor is connected between the power supply lines in parallel with the light emitting element. For this reason, the sum total of the electric current which flows between the power supply lines of the connection part to which each light emitting element is connected becomes the same in any connection part. For this reason, the influence of the voltage fluctuation of the power supply line is eliminated, and the amount of emitted light of each light emitting element can be made uniform.

  In the embodiment of the present invention, the positions of the feeding point 6 connected to the first power supply line 2 and the feeding point 7 connected to the second power supply line 3 are set to one of the lines as shown in FIG. It is not limited to the example provided on the end side. 3 to 5 are circuit diagrams showing examples in which the position of the feeding point is changed from that in FIG. In the circuit diagram of FIG. 3, the position of the feeding point 6 of the first power supply line 2 in the line head 10e and the position of the feeding point 7 in the second power supply line 3 are formed so as to be opposite to the lines, respectively. . In this case, the applied voltage Vp1 of the light emitting element E1 on the left end side in the figure is Vp1 = V−4Ri−nRi. Further, the applied voltage Vpn of the light emitting element En on the right end side in the drawing is Vpn = V−4Ri−nRi.

  That is, in the example of FIG. 3, the applied voltage Vp1 of the light emitting element E1 on the left end side is equal to the applied voltage Vpn of the light emitting element E1 on the right end side. For this reason, there is no difference in the amount of emitted light of the light emitting elements arranged in one line, and there is no variation in the lifetime of the light emitting elements. In addition, the print quality can be improved.

  In the circuit diagram of FIG. 4, the positions of the feeding points 6a and 6b of the first power supply line 2 of the line head 10f and the feeding points 7a and 7b of the second power supply line 3 are formed at both ends of the line, respectively. . That is, four feeding points are formed at both ends of the line. In this case, the applied voltage Vp1 of the light emitting element E1 on the left end side in the drawing is Vp1 = V−nRi. The applied voltage Vpn of the light emitting element En on the right end side in the figure is Vpn = V−nRi.

  That is, in the example of FIG. 4, the applied voltage Vp1 of the light emitting element E1 on the left end side is equal to the applied voltage Vpn of the light emitting element E1 on the right end side. Further, the voltage drop of the power supply line is ¼ of the example of FIG. 15, and the influence of the voltage drop of the power supply line on each light emitting element can be reduced. For this reason, there is no difference in the amount of emitted light of the light emitting elements arranged in one line, and there is no variation in the lifetime of the light emitting elements. In addition, the print quality can be improved.

  In the circuit diagram of FIG. 5, the positions of the feeding points 6a and 6b on the first power line 2a of the line head 10g and the feeding points 7a and 7b on the second power line 3a are formed at both ends of the line. . Further, the third power supply line 2b on the power supply side and the fourth power supply line 3b on the ground side are wired along the longitudinal direction of the line.

  The third power line 2b on the power source side and the fourth power line 3b on the ground side are each provided with a feeding point. Second power supply points 6c and 6d are provided on the third power supply line 2b on the power supply side. In addition, the second power supply points 7c and 7d are provided on the ground-side fourth power supply line 3b. The second power supply points 6c and 6d on the power supply side are connected to the first power supply line 2a. Furthermore, the second feeding points 7c and 7d on the ground side are connected to the second power supply line 2a. The first power supply line 2a on the power supply side and the third power supply line 2b on the power supply side may be the same power supply or different power supplies.

  As described above, since the number of feeding points is increased, it is possible to suppress the influence of the voltage fluctuation of the power supply line on each light emitting element. For this reason, there is no difference in the amount of emitted light of the light emitting elements arranged in one line, and there is no variation in the lifetime of the light emitting elements. In addition, the print quality can be improved. In FIG. 5, the first feeding point can be provided only at one end of the line.

  In FIG. 5, two second feeding points are provided on both the power supply side and the ground side, but the second feeding point may be one. Further, it is not necessary to set the same number of feeding points of the younger brother 2 on the power supply side and the grounding side, and it is also possible to arrange the feeding points in different positions with different numbers. In this way, the position and number of the second power feeding can be arbitrarily set.

  In each embodiment of the present invention, the light emitting element Ea may be, for example, an LED (Light Emitting Diode) other than the organic EL element. Since the organic EL element can be controlled statically, there is an advantage that the control system can be simplified. Moreover, when it comprises with LED, manufacture of a light emitting element becomes easy.

  FIG. 9 is an explanatory view showing a line head 10h according to another embodiment of the present invention. In FIG. 9, the line head 10h is provided with a light emitting element line 1a in which a large number of light emitting elements Ea are arranged in the main scanning direction (Y direction). The light emitting element lines are formed in a plurality of rows (lines) in the sub-scanning direction (X direction). In this example, four lines 1a, 1b, 1c, and 1d are provided.

  In the example of FIG. 9, the light emitting element line 1b is formed as a light emitting element line for preliminary operation and is not normally used. When one of the light emitting elements Ea of the light emitting element line 1a for normal operation used in the normal printing process fails, the light emitting element line 1b for preliminary operation is used by switching means described later in detail. The light emitting element lines 1c and 1d can be used, for example, when performing multiple exposure.

  In the line head of the present invention, the light emitting element line provided for the preliminary operation is not limited to one line. The light emitting element line 1c can be formed for preliminary operation of the light emitting element line 1d. In the example of FIG. 6, four light emitting element lines are formed in the sub-scanning direction. However, two light emitting element lines are formed, one of which is a light emitting element line for normal operation and the other is a line. It can also be set as the structure switched and used as the light emitting element line for preliminary | backup operation | movement. Note that in a multiple exposure line head, an arbitrary number of light emitting element lines for normal operation can be formed.

  As described above, in the present invention, a plurality of light emitting element lines of two or more lines can be provided in the sub-scanning direction of the line head, and at least one of them can be formed as a light emitting element line for preliminary operation. As described above, when the two light emitting element lines are divided into the light emitting element lines for normal operation and the light emitting element lines for preliminary operation as described above, the light emitting element lines are composed of three or more lines. A case where at least one line is formed and used as a light-emitting element line for preliminary operation is included. In the latter case, two or more light emitting element lines for preliminary operation can be formed.

  FIG. 10 is a circuit diagram showing another embodiment of the present invention. The line head 10i is provided with light emitting element lines 1a and 1b. In the light emitting element line 1a, for example, light emitting elements D00 to D23 using organic EL elements are arranged. In addition, light emitting elements D50 to D73 using organic EL elements are also arranged in the light emitting element line 1b. 2 is a first power supply line connected to power supply points 6a and 6b on the power supply (VDD) side, 3x and 3y are connected to power supply points 7a and 7b on the ground (GND) side (7b is not shown). The second power supply line.

  Reference numeral 8 denotes a changeover switch. When the contact 8c is turned on to the contact 8a side, a direct current voltage is applied between the power supply lines 2 and 3x, and the light emitting elements D00 to D23 of the light emitting element line 1a are turned on. . When the contact 8c of the changeover switch 8 is turned on to the contact 8b side, a direct current voltage is applied between the power supply lines 2 and 3y, and the light emitting elements D50 to D73 of the light emitting element line 1b are turned on. .

  The light emitting element line 1a is provided for normal operation, and the light emitting element line 1b is provided for preliminary operation. When a failure occurs in any of the light emitting elements D00 to D23 of the light emitting element line 1a, a voltage is applied to each of the light emitting elements D50 to D73 of the light emitting element line 1b by the changeover switch 8 to perform a light emitting operation. As described above, in the example of FIG. 10, the light emitting element lines are switched by switching the power supply lines 3 x and 3 y to which the cathode sides of the light emitting elements of the respective light emitting element lines are commonly connected by the changeover switch 8.

  At this time, the first power supply line 2 is commonly connected to the anode electrode of the light emitting element of each light emitting element line. In the example of FIG. 10, one power supply line 2 maintains a state in which two light emitting element lines are commonly connected, and only the other power supply lines 3x and 3y are switched. For this reason, compared with the case where both power supply lines are switched together, the structure of a switching means can be simplified. Further, the switching operation can be performed smoothly.

  The change-over switch 8 can be configured to use an electronic switch such as a transistor in addition to the mechanical switch as shown in FIG. Further, one of the light emitting element lines 1a and 1b is for normal operation and the other is for preliminary operation, and the light emitting element line 1b can be used for normal operation and the light emitting element line 1a can be used for preliminary operation. In addition, when the switching means is configured by a switching transistor, the light emitting element line can be switched quickly and accurately.

  The above description is directed to a line head used in an image forming apparatus such as a monochrome printer. However, in the present invention, the line head is naturally applied to a four-cycle color printer or a tandem color printer. In these color printers, by adopting the configuration of the present invention, it is possible to suppress variations in the amount of light emitted by the light emitting elements arranged in the line head.

  FIG. 11 is a longitudinal side view illustrating an example of an image forming apparatus using an organic EL as a light emitting element. This image forming apparatus includes four organic EL array exposure heads 101K, 101C, 101M, and 101Y having the same configuration and corresponding four photosensitive drums (image carriers) 41K, 41C, and 41M having the same configuration. , 41Y, respectively, and is configured as a tandem image forming apparatus. As shown in FIG. 11, this image forming apparatus is provided with a driving roller 51, a driven roller 52, and a tension roller 53. The tension roller 53 applies tension to the image forming apparatus and stretches it in the direction indicated by the arrow (counterclockwise). ) Is circulated and driven. Photosensitive members 41K, 41C, 41M, and 41Y having photosensitive layers are arranged on the outer peripheral surface as four image carriers arranged at predetermined intervals with respect to the intermediate transfer belt 50.

  K, C, M, and Y added after the reference sign mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are black, cyan, magenta, and yellow, respectively. The same applies to other members. The photoreceptors 41K, 41C, 41M, and 41Y are rotationally driven in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 50.

  Around each photoconductor 41 (K, C, M, Y), charging means (corona charger) 42 (K) for uniformly charging the outer peripheral surface of the photoconductor 41 (K, C, M, Y), respectively. , C, M, Y) and the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) are synchronized with the rotation of the photoconductor 41 (K, C, M, Y). In addition, the organic EL array exposure head (line head) 101 (K, C, M, Y) as described above of the present invention that sequentially scans the line is provided.

  Further, a developing device 44 (K) that applies toner as a developer to the electrostatic latent image formed by the organic EL array exposure head 101 (K, C, M, Y) to form a visible image (toner image). , C, M, Y) and a primary transfer roller 45 as transfer means for sequentially transferring the toner image developed by the developing device 44 (K, C, M, Y) to the intermediate transfer belt 50 as a primary transfer target. (K, C, M, Y) and a cleaning device 46 (K, C, Y) as a cleaning unit for removing the toner remaining on the surface of the photoreceptor 41 (K, C, M, Y) after being transferred. M, Y).

  Here, in each organic EL array exposure head 101 (K, C, M, Y), the array direction of the organic EL array exposure head 101 (K, C, M, Y) is the photosensitive drum 41 (K, C, M). , Y) along the bus. The emission energy peak wavelengths of the organic EL array exposure heads 1 (K, C, M, Y) and the sensitivity peak wavelengths of the photoconductors 41 (K, C, M, Y) are set so as to substantially match. ing.

  The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulating blade, and the developing roller is brought into contact with or increased in thickness by the photosensitive body 41 (K, C, M, Y), whereby the photosensitive body 41 (K, C, M, Y). The toner is developed as a toner image by attaching a developer according to the potential level.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). The toner image, which is sequentially primary transferred onto the transfer belt 50 and sequentially superposed on the intermediate transfer belt 50 to become a full color, is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66, and serves as a fixing unit. The toner is fixed on the recording medium P by passing through the fixing roller pair 61, and is discharged onto a paper discharge tray 68 formed in the upper part of the apparatus by a paper discharge roller pair 62.

  In FIG. 11, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P from the paper feed cassette 63 one by one, and 65 denotes a secondary transfer roller. A pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion 66, a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 50, 67 Is a cleaning blade as a cleaning means for removing the toner remaining on the surface of the intermediate transfer belt 50 after the secondary transfer.

  As described above, since the image forming apparatus of FIG. 11 uses the organic EL array as the writing means, the apparatus can be made smaller than when the laser scanning optical system is used.

  Next, another embodiment of the image forming apparatus according to the present invention will be described. FIG. 12 is a vertical side view of the image forming apparatus. In FIG. 12, the image forming apparatus 160 includes, as main constituent members, a rotary developing device 161, a photosensitive drum 165 functioning as an image carrier, and an image writing means (line head) 167 provided with an organic EL array. In addition, an intermediate transfer belt 169, a paper conveyance path 174, a fixing roller heating roller 172, and a paper feed tray 178 are provided.

  In the developing device 161, the developing rotary 161a rotates in the arrow A direction about the shaft 161b. The inside of the development rotary 161a is divided into four, and image forming units for four colors of yellow (Y), cyan (C), magenta (M), and black (K) are provided. Reference numerals 162a to 162d are arranged in the image forming units for the four colors. The developing rollers rotate in the arrow B direction, and the toner supply rollers 163a to 163d rotate in the arrow C direction. Reference numerals 164a to 164d are regulating blades that regulate the toner to a predetermined thickness.

  As described above, reference numeral 165 denotes a photosensitive drum that functions as an image carrier, 166 denotes a primary transfer member, 168 denotes a charger, and 167 denotes an image writing unit, which is provided with an organic EL array. The photosensitive drum 165 is driven in the direction of arrow D opposite to the developing roller 162a by a drive motor (not shown), for example, a step motor.

  The intermediate transfer belt 169 is stretched between the driven roller 170b and the drive roller 170a, and the drive roller 170a is connected to the drive motor of the photosensitive drum 165 to transmit power to the intermediate transfer belt. By driving the drive motor, the drive roller 170 a of the intermediate transfer belt 169 is rotated in the arrow E direction opposite to the photosensitive drum 165.

  The paper conveyance path 174 is provided with a plurality of conveyance rollers, a pair of paper discharge rollers 176, and the like, and conveys the paper. An image (toner image) on one side carried on the intermediate transfer belt 169 is transferred to one side of the paper at the position of the secondary transfer roller 171. The secondary transfer roller 171 is separated from and brought into contact with the intermediate transfer belt 169 by a clutch, and is brought into contact with the intermediate transfer belt 169 when the clutch is turned on, so that an image is transferred onto the sheet.

  The sheet on which the image has been transferred as described above is then subjected to a fixing process by a fixing device having a fixing heater H. The fixing device is provided with a heating roller 172 and a pressure roller 173. The sheet after the fixing process is drawn into the discharge roller pair 176 and proceeds in the arrow F direction. When the paper discharge roller pair 176 rotates in the opposite direction from this state, the paper reverses its direction and advances in the double-sided printing conveyance path 175 in the arrow G direction. 177 is an electrical component box, 178 is a paper feed tray for storing paper, and 179 is a pickup roller provided at the outlet of the paper feed tray 178.

  For example, a low-speed brushless motor is used as a drive motor for driving the transport roller in the paper transport path. The intermediate transfer belt 169 uses a step motor because it requires color misregistration correction. Each of these motors is controlled by a signal from a control means (not shown).

  In the state shown in the drawing, a yellow (Y) electrostatic latent image is formed on the photosensitive drum 165, and a high voltage is applied to the developing roller 62a, whereby a yellow image is formed on the photosensitive drum 165. When all of the yellow back side and front side images are carried on the intermediate transfer belt 169, the development rotary 161a rotates 90 degrees in the direction of arrow A.

  The intermediate transfer belt 169 rotates once and returns to the position of the photosensitive drum 165. Next, two images of cyan (C) are formed on the photosensitive drum 165, and this image is carried on the yellow image carried on the intermediate transfer belt 169. Thereafter, the 90-degree rotation of the development rotary 161 and the one-rotation process after the image is carried on the intermediate transfer belt 169 are repeated in the same manner.

  For carrying four color images, the intermediate transfer belt 169 rotates four times, and then the rotation position is further controlled to transfer the image onto the sheet at the position of the secondary transfer roller 171. The paper fed from the paper feed tray 178 is transported by the transport path 174, and the color image is transferred to one side of the paper at the position of the secondary transfer roller 171. The sheet on which the image is transferred on one side is reversed by the discharge roller pair 176 as described above, and stands by on the conveyance path. Thereafter, the sheet is conveyed to the position of the secondary transfer roller 171 at an appropriate timing, and the color image is transferred to the other side. The housing 180 is provided with an exhaust fan 181.

  The line head of the present invention and the image forming apparatus using the same have been described based on the embodiments. The present invention is not limited to these examples, and various modifications are possible.

  As described above, according to the present invention, when a plurality of light emitting elements are arranged in one line and operated for lighting, when a power supply line is formed by thin film wiring, each light emitting element is controlled regardless of the lighting pattern of each light emitting element. It is possible to provide a line head having a configuration in which there is no variation in the amount of light emitted from the light emitting elements, and an image forming apparatus using the line head.

It is a circuit diagram showing an embodiment of the present invention. It is a circuit diagram showing an embodiment of the present invention. It is a circuit diagram showing an embodiment of the present invention. It is a circuit diagram showing an embodiment of the present invention. It is a circuit diagram showing an embodiment of the present invention. It is process drawing which shows the manufacturing process of this invention. It is explanatory drawing which shows embodiment of this invention. It is explanatory drawing which shows embodiment of this invention. It is explanatory drawing which shows other embodiment of this invention. It is a circuit diagram which shows other embodiment of this invention. 1 is a longitudinal side view showing a schematic configuration of a tandem image forming apparatus according to the present invention. It is a vertical side view of an image forming apparatus showing another embodiment of the present invention. It is explanatory drawing which shows the structure of a prior art example. It is a circuit diagram which shows the structure of a prior art example. It is a circuit diagram which shows the structure of a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Light emitting element line, 2 ... 1st power supply line, 3 ... 2nd power supply line, 4, 5 ... Signal line, 6, 7 ... Feeding point, 8 ... Changeover switch, 9... Inverter, 10... Line head, 41 (K, C, M, Y)... Photosensitive drum (image carrier), 42 (K, C, M, Y).・ Charging means (corona charger), 44 (K, C, M, Y)... Developing device, 45 (K, C, M, Y)... Primary transfer roller, 46 (K, C, M, Y) Y) ... Cleaning device, 50 ... Intermediate transfer belt, 66 ... Secondary transfer roller, 101K, 101C, 101M, 101Y ... Organic EL array exposure head (line head), 161 ... Development Device, 165... Photosensitive drum, 167... Exposure head (line head), 169... Intermediate transfer belt 171: Secondary transfer roller, P: Recording medium, Ea: Organic EL element, E1, E2: Light emitting element, Ex, Ey: Pseudo light emitting element, R: Resistance, Tr1,. .Control transistor, Tr2,... Drive transistor,

Claims (15)

A plurality of light emitting elements arranged in one line, a first power supply line formed by a thin film wiring connected to a power supply point on the power supply side, and a second power supply formed by a thin film wiring connected to a power supply point on the ground side A line head for connecting each light emitting element between the first power supply line and the second power supply line, wherein a pseudo load through which the same current as each light emitting element flows is connected to each light emitting element. A line head which is connected in parallel and has a control means for turning off the pseudo load when the light emitting element is on and turning on the pseudo load when the light emitting element is off. The line head according to claim 1, wherein a light emitting element having the same characteristics as the light emitting element is used as the pseudo load. The line head according to claim 1, wherein a resistor is used as the pseudo load. The line head according to claim 3, wherein a thin film resistor laminated on the same substrate as the light emitting element is used as the resistor. The control means includes a pair of transistors respectively connected to the light emitting element and the pseudo load, and the conductive layers of the transistors are configured with different polarities, according to any one of claims 1 to 4. The line head described. As the control means, a pair of transistors respectively connected to the light emitting element and the pseudo load are provided, the conductive layers of the transistors are configured with the same polarity, and signals that are mutually inverted signals are supplied to the transistors. The line head according to any one of claims 1 to 4, wherein the line head is characterized. The position of the one feeding point is provided at one end portion of the line, and the position of the other feeding point is provided at the other end portion of the line. Line head. The line head according to any one of claims 1 to 6, wherein the power supply point and the grounding point are provided at both ends of the line. A third power supply line on the power supply side and a fourth power supply line on the grounding side are wired along the longitudinal direction of the line, and the third power supply line on the power supply side and the fourth power supply line on the grounding side are respectively connected to the third power supply line on the power supply side. The line according to claim 1, wherein two feeding points are provided, and each of the second feeding points is connected to the first power line and the second power line. head. The line head according to claim 9, wherein a plurality of second feeding points of each power line are provided. 11. The line head according to claim 1, wherein a plurality of lines in which the plurality of light emitting elements are arranged are formed in a sub-scanning direction. The line head according to any one of claims 1 to 11, wherein the light emitting element is configured by an organic EL element or an LED. At least two image forming stations in which image forming units including a charging unit, a line head according to any one of claims 1 to 12, a developing unit, and a transfer unit are arranged around an image carrier. An image forming apparatus provided as described above, wherein a transfer medium passes through each station and forms an image by a tandem method. An image carrier configured to carry an electrostatic latent image, a rotary developing unit, and the line head according to claim 1, wherein the rotary developing unit includes a plurality of toner cartridges. The toner stored in the toner is carried on the surface, and toners of different colors are sequentially conveyed to a position facing the image carrier by rotating in a predetermined rotation direction, and the image carrier, the rotary developing unit, An image forming method characterized in that a developing bias is applied between the toner and the toner is moved from the rotary developing unit to the image carrier to visualize the electrostatic latent image to form a toner image. apparatus. 15. The image forming apparatus according to claim 13, further comprising an intermediate transfer member.

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