Print head device and image forming device equipped with the same

Abstract

To inexpensively detect a failure relating to emission / non-emission of a print head device equipped with an active light emission part in a fitted state.SOLUTION: This print head device comprises: an active light emission part having light emission sources which include driving elements and light emission elements that emit light at luminance based on driving current supplied from the driving elements and which are formed in at least one row; a control unit that controls each driving element to control light emission, light non-emission, and luminance at the time of light emission in each light emission source; and a current detection circuit that detects the size of the current. The current detection circuit detects total driving current targeting all or a plurality of light emission sources. The control unit determines, after setting a target light emission source in a light emission state, a failure of the target light emission source unless the driving current detected by the current detection circuit is equal to or larger than a predetermined first threshold value.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a print head device having a plurality of light-emitting sources arranged in at least one row, and an image forming apparatus including the same, wherein each light-emitting source includes a light-emitting element that emits light at a brightness corresponding to a current and a drive element that operates to pass a drive current corresponding to the data signal. [Background technology]

[0002] In addition to laser scanning devices, print head devices, which have multiple light-emitting sources corresponding to pixels arranged in one direction (main scanning direction), are known as devices that expose photosensitive bodies used in electrophotographic image forming devices. The basic print head device has multiple LED chips arranged in a row. Since the resolution in the main scanning direction is determined by the spacing between adjacent LEDs, and it is necessary to ensure spacing between adjacent LED chips during implementation, a configuration is also used in which multiple rows of LEDs are arranged at different positions in the sub-scanning direction, with the LEDs offset in the main scanning direction.

[0003] When using a laser scanning device, a certain distance must be secured between the photosensitive element (the irradiation surface) and the laser light source, and a scanning optical system must be placed there, whereas using a print head device shortens the distance between the photosensitive element and the light source, resulting in a compact image forming apparatus. On the other hand, while a laser scanning device usually requires only one laser light source, a print head device requires a high-density arrangement of tiny light sources, the number of which corresponds to the number of pixels in the main scanning direction.

[0004] In recent years, printhead devices that utilize the structure of OLED (organic light-emitting device, also known as organic electroluminescence) displays have been announced. These printhead devices (hereinafter referred to as OLED printhead devices) utilize OLED display technology to achieve the dense arrangement of numerous tiny light-emitting sources. The light-emitting portion of the OLED printhead device, which serves as the light-emitting source of the OLED printhead device, is formed as a TFT panel on a glass substrate. OLED printhead devices can be produced using OLED display manufacturing technology and manufacturing equipment. An OLED display configuration that compensates for variations and fluctuations in the characteristics of each light-emitting source within the pixel circuit is disclosed, for example, in Patent Document 1. The configuration of the display device is shown in FIG. 1, and the configuration of the pixel circuit in the display device is shown in FIG. 2, and their configurations are described in the specification. Figure 6 of this application corresponds to Figure 1 of Patent Document 1, and Figure 7 of this application corresponds to Figure 2 of Patent Document 1. Details of the configuration are described in Patent Document 1.

[0005] The following techniques are known as methods for detecting defects in light sources that use organic electroluminescence (EL) such as OLED displays. For example, in an OLED display panel inspection method, in order to detect each transistor that changes over time due to minute leakage current, a camera is used to detect bright spot defects after a predetermined time by controlling all the transistors to OFF, and this method detects defects in TFT transistors during manufacturing (see, for example, Patent Document 2). Furthermore, for example, a technology is known for a lighting control device for a single-circuit organic EL panel, such as a lighting device, that detects the voltage and current during operation, and if it falls outside a predetermined voltage-current range (safety area), determines that it is unsafe and stops operation (see, for example, Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 186765 [Patent Document 2] International Publication No. 2015 / 190043 [Patent Document 3] Patent No. 560187 Summary of the Invention [Problem to be solved by the invention]

[0007] OLED printhead devices are manufactured using manufacturing technologies and equipment for active-matrix OLED displays. Display devices incorporate circuits built into the TFT panel (hereinafter sometimes referred to as the active light-emitting unit) formed on a glass substrate along with each light-emitting source to suppress variations in brightness and aging of each light-emitting source and achieve brightness according to the drive current. However, they do not have circuits to detect defects related to the emission / non-emission of each light-emitting source. This is because defects related to the emission / non-emission of each light-emitting source in display devices can be easily detected visually or with an inspection device using a camera or other device (see Patent Document 2). Furthermore, since the TFT panel, driver, and display control circuit are typically mounted in a single housing and their relative positions do not change due to vibration, signal lines rarely break during use, eliminating the need for continuous monitoring for defects related to the emission / non-emission of each light-emitting source. In contrast, printhead devices can detect defects related to the emission / non-emission of each light-emitting source in the print result, but by that time, the development unit, photoconductor, and other components may already be damaged. Furthermore, the photoconductor is surrounded by a large number of moving parts, including the photoconductor itself and the development unit, which transmit vibrations. Furthermore, the display control circuit is often located away from the TFT panel, which should be located near the photosensitive element, and it is therefore highly desirable to detect any defects in the light-emitting source during use, including those caused by poor connections in the harness connecting the two, and to stop image formation if a defect is detected.

[0008] There is a need to inexpensively detect these light-emitting / non-light-emitting defects that are not built into the TFT panel of an OLED print head device, external to the TFT panel. The technology of Patent Document 2 is intended to be applied to inspection during manufacturing, and when applied to an OLED print head device, a means for optically detecting defects in each light source is required. However, if such an optical detection means is provided separately from the TFT panel, the configuration becomes complicated and the cost burden increases. Furthermore, if it is incorporated into the TFT panel, the configuration becomes significantly different from that of an OLED display, making it impossible to apply OLED display manufacturing techniques and manufacturing equipment as is. When applying the technology of Patent Document 3 to an OLED print head device, it is necessary to provide a current detection unit and a voltage detection unit corresponding to the light source. However, this invention aims to detect defects related to the light emission / non-emission of the light source, not to determine whether it is within the safe range. Providing a current detection unit and a voltage detection unit results in a complex configuration, which also increases the cost burden. The present invention has been made in consideration of the above circumstances, and provides a method for inexpensively detecting defects related to light emission / non-emission in a print head device equipped with an active light-emitting unit while the device is installed. [Means for solving the problem]

[0009] The present invention provides a print head device comprising: an active light-emitting section in which light-emitting sources are formed in at least one row, each including a driving element and a light-emitting element that emits light at a brightness corresponding to the driving current passed by the driving element; a control section that controls each driving element to control the emission, non-emission, and brightness of each light-emitting source when emitting light; and a current detection circuit that detects the magnitude of the current, wherein the current detection circuit detects the total driving current for all or a plurality of light-emitting sources, and the control section, after causing each of the target light-emitting sources to emit light, determines that the target light-emitting source is defective if the driving current detected by the current detection circuit is not equal to or greater than a predetermined first threshold value.

[0010] From another perspective, the present invention provides a method for determining defects in a print head device, the method comprising the steps of: a control unit controlling each drive element of an active light-emitting unit in which light-emitting sources are formed in at least one row, the control unit targeting all or a plurality of light-emitting sources and causing the target light-emitting sources to emit light; a current detection circuit being used to detect the total drive current of the target light-emitting sources; and determining that the target light-emitting source is defective if the drive current detected by the current detection circuit is not equal to or greater than a predetermined first threshold. [Effects of the Invention]

[0011] In the print head device of this invention, the control unit determines that the target light-emitting source is faulty if the drive current detected by the current detection circuit is not equal to or greater than a predetermined first threshold after the target light-emitting source is put into an emitting state, so that defects related to the light emission of a print head device equipped with an active light-emitting unit can be detected inexpensively while the device is installed. The method for determining defects in a print head device according to the present invention also provides the same advantageous effects. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an explanatory diagram showing an example of the configuration of a multifunction peripheral equipped with a print head device as one aspect of an image forming apparatus according to the present invention; [Figure 2] FIG. 2 is an explanatory diagram showing an image forming unit and a print head device of the multifunction peripheral shown in FIG. [Figure 3] FIG. 3 is a circuit diagram showing the configuration of each OLED element of the active light-emitting portion and the corresponding TFT circuit in the print head device shown in FIG. 2. [Figure 4] 4 is an explanatory diagram showing the configuration of a current detection circuit that detects the drive current of the active light-emitting unit shown in FIG. 3. FIG. [Figure 5] 10 is a flowchart showing the flow of processing executed by the control unit 300 to detect a defect in a light source in this embodiment. [Figure 6]FIG. 1 is a block diagram showing the overall configuration of a conventional organic EL display device disclosed in Patent Document 1. [Figure 7] FIG. 7 is a circuit diagram showing the configuration of a pixel circuit of the conventional organic EL display device shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below with reference to the accompanying drawings. Note that the following description is given by way of example only in all respects and should not be construed as limiting the present invention. (Embodiment 1) <Configuration of image forming apparatus> First, a configuration example of an image forming apparatus equipped with a print head device in this embodiment will be described. FIG. 1 is an explanatory diagram showing an example of the configuration of a multifunction peripheral equipped with a print head device as one embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the multifunction peripheral 10 includes a scanner unit 200 at its upper portion for scanning documents and an engine unit 100 at its lower portion for forming images. The multifunction peripheral 10 also includes a control unit 300 for controlling the scanner unit 200 and the engine unit 100. In the example shown in FIG. 1, the control unit 300 is implemented in a control circuit 18 located at the rear between the scanner unit 200 and the engine unit 100. The control unit 300 is primarily composed of a processor and memory. In addition to the processor, the control circuit 18 also includes hardware resources such as an input / output interface circuit, a timer circuit, an image processing circuit, and a communication circuit. The processor executes a control program pre-stored in memory, causing the control unit 300 to execute a series of processes related to image formation. The software and hardware resources work together to realize the functions of the control unit 300. It is also conceivable that the functions of the control unit 300 are not limited to the control circuit 18, but may be physically distributed across multiple circuits (circuit boards), with these circuits working together to function as the control unit 300. In this case, the control circuit 18 controls at least the print head device 13 and executes processes related to image formation in the multifunction peripheral 10 in cooperation with other circuits.

[0014] Scanner unit 200 includes image reading unit 201 and document feeder 202. Document feeder 202 is disposed above image reading unit 201. Document feeder 202 transports documents one by one. Image reading unit 201 reads documents transported one by one by document feeder 202 using image sensor 201S. Scanner unit 200 can also scan a document placed on a transparent document table 201P facing the bottom surface of document feeder 202 and read it using image sensor 201S. Scanner unit 200 generates image data of the scanned document.

[0015] The engine unit 100 includes a paper feed mechanism 101, an image forming unit 102, an intermediate transfer unit 103, a secondary transfer unit 104, a fixing unit 105, a duplex conveying path 106, and an output tray 107. The paper feed mechanism 101 stores print paper in a paper feed tray 101T and feeds the print paper used for a print job. The engine unit 100 shown in FIG. 1 forms color or monochrome images using yellow (Y), magenta (M), cyan (C), and black (K) toners. To this end, the engine unit 100 includes an image forming unit Py that forms a yellow toner image, an image forming unit Pm that forms a magenta toner image, an image forming unit Pc that forms a cyan toner image, and an image forming unit Pk that forms a black toner image. Each image forming unit includes a photosensitive drum 11 that is a photosensitive element for forming the toner image, a charging roller 12 that is a charging unit, a print head device 13, a developing unit 14, and a cleaning mechanism 15. The control unit 300 uses these components to form images.

[0016] The control unit 300 uses the charging roller 12 to uniformly charge the circumferential surface of the photosensitive drum 11 to a predetermined potential. The control unit 300 uses the print head device 13 to expose the circumferential surface of the photosensitive drum 11, which has been charged by the charging roller 12, to light to form an electrostatic latent image. The control unit 300 also irradiates the circumferential surface of the photosensitive drum 11 with light to discharge the charge. The control unit 300 also uses the developing unit 14 to develop the electrostatic latent image formed on the circumferential surface of the photosensitive drum 11 to form a toner image. Through the above-described series of operations, toner images of the respective colors Y, M, C, and K are formed on the circumferential surface of each photosensitive drum 11. The intermediate transfer unit 103 includes an intermediate transfer belt 16 and intermediate transfer rollers 17 corresponding to each of the image forming units Py to Pk. The control unit 300 transfers the toner images formed on the photosensitive drum 11 to the intermediate transfer belt 16 using the intermediate transfer rollers 17. The toner images transferred from the image forming units Py to Pk are then superimposed on the intermediate transfer belt 16 and conveyed to the secondary transfer section 104.

[0017] The control unit 300 causes the secondary transfer unit 104 to transfer the toner image on the intermediate transfer belt 16 onto the print paper fed from the paper feed tray 101T. Furthermore, the fixing unit 105 heats and fixes the toner image transferred in the secondary transfer unit 104 onto the print paper. In the case of single-sided printing, the control unit 300 causes the print paper to be discharged to the discharge tray 107. In the case of double-sided printing, after printing on the first side, the control unit 300 switches back the print paper just before the discharge tray 107 and guides it to the double-sided conveying path 106. The print paper is then guided again via the double-sided conveying path 106 to the secondary transfer unit 104, where the toner image is transferred to the second side, and the print paper is then discharged to the discharge tray 107.

[0018] <Configuration of print head device included in image forming unit> Next, the configuration of the image forming units in the multifunction peripheral 10 shown in FIG. 1 and the print head devices included in those image forming units will be described. FIG. 2 is an explanatory diagram showing the image forming units and print head devices of the multifunction peripheral shown in FIG. 1. The yellow image forming unit Py is shown in FIG. 2 as a representative of the image forming units of each color, but the other colors have similar configurations. The charging roller 12, developing unit 14, cleaning mechanism 15, and intermediate transfer belt are shown simply, but correspond to those in FIG. 1. Small gray circles highlight the toner TN particles. In reality, toner TN is smaller in diameter and more numerous.

[0019] The print head device 13 is indicated by a dashed-line rounded rectangle in FIG. 2. The print head device 13 includes an active light-emitting unit 13E formed on a single substrate 13S. It also includes an imaging lens 13L that focuses the irradiated light IL emitted from each light-emitting source of the active light-emitting unit 13E onto the circumferential surface of the photosensitive drum 11. The direction into the plane of FIG. 2 is the main scanning direction, and the direction of arrow S, perpendicular to the main scanning direction and along which the circumferential surface of the photosensitive drum 11 irradiated with the irradiated light IL moves, is the sub-scanning direction. The active light-emitting unit 13E is disposed facing the circumferential surface of the photosensitive drum 11 across the imaging lens 13L. The print head device 13 also includes a connection unit 13C having a connector for connecting signals from a control circuit 18 that controls light emission to the active light-emitting unit 13E. A driver that supplies current to each light-emitting source of the active light-emitting unit 13E may be disposed on the substrate 13S or the connection unit 13C. The connection unit 13C of the print head device 13 and the control circuit 18 are connected via a signal harness 20.

[0020] FIG. 3 is a circuit diagram showing the configuration of each OLED element and corresponding TFT circuit of the active light-emitting unit 13E in the print head device 13 shown in FIG. 2. The OLED elements and circuit shown in FIG. 3 roughly correspond to the configuration of the pixel circuit shown in FIG. 2 of Patent Document 1. That is, the OLED element, transistors M1 to M7, and capacitor C1 shown in FIG. 3 correspond to the OLED element, transistors M1 to M7, and capacitor C1 in FIG. 7 (FIG. 4 of Patent Document 1). Signals in FIGS. 3 and 7, including signals with the same names and signals with different names, roughly correspond to each other. For example, SCAN1 in FIG. 3 corresponds to Gi in FIG. 7, EM1 in FIG. 3 corresponds to Ei in FIG. 7, and DIS0 in FIG. 3 corresponds to Gi-1 in FIG. 7. The print head device 13 has a configuration in which multiple light-emitting sources corresponding to the pixel circuits of Patent Document 1 are arranged in a row in one direction (the main scanning direction). FIG. 6 shows the overall configuration corresponding to FIG. 1 of Patent Document 1, which relates to a display device. The pixel circuits are arranged in a matrix, and the print head device 13 is substantially equivalent to a configuration in which light-emitting sources corresponding to at least one horizontal row of pixel circuits are arranged. However, there is a physical gap between adjacent OLED elements. Therefore, instead of a configuration in which a single horizontal row of OLED elements is arranged in the main scanning direction, multiple rows of OLED elements may be arranged at different positions in the sub-scanning direction. This configuration allows a predetermined resolution in the main scanning direction, i.e., a predetermined number of pixels in the main scanning direction, to be achieved even with gaps between adjacent OLED elements. Each row has fewer OLED elements arranged in the main scanning direction than the predetermined number of pixels in the main scanning direction. The positions of the OLED elements in each row in the main scanning direction are offset from the positions of the OLED elements in other rows. In one example, the number of OLED element rows is 2 to 16.

[0021] The drive transistor M1 operates in a saturation region where the drain current is almost constant regardless of the source-drain voltage. Before one cycle of light-emitting period, during a data write period (described later), a voltage corresponding to the magnitude of the data signal Dj is stored in the capacitor C1. At that time, the capacitor C1 is charged so as to compensate for variations in the threshold voltage of the drive transistor M1. During the subsequent light-emitting period, the drive transistor M1 passes a drive current of a magnitude corresponding to the voltage held in the capacitor C1 to an OLED element, which is a light-emitting element. The transistors M2 to M7 function as switches.

[0022] More specifically, at the beginning of each cycle, the control circuit 18 resets the voltage held in capacitor C1 (reset period). When the reset period begins, the control circuit 18 sets the EM1 signal to high level to turn off transistors M5 and M6. This puts the OLED element in a non-emitting state. This non-emitting state continues until the end of the subsequent data write period. During the reset period, the control circuit 18 sets DIS0 to low level to turn on transistor M4. This initializes the gate of the drive transistor M1 and one end of the capacitor C1 connected to it to the level of voltage VIN1. This voltage VIN1 is at a level that can maintain the drive transistor in an on state during the data write period, which will be described later.

[0023] During the subsequent data write period, the control circuit 18 sets the DIS0 signal to a high level to turn off transistor M4. It also maintains the data signal Dj at a voltage corresponding to the light emission intensity (brightness) of the next cycle. It also sets the SCAN1 signal to a low level to turn on transistors M2 and M3. This connects the gate and drain of the drive transistor M1, i.e., into a diode-connected state, and one end of the capacitor C1 connected to the drive transistor M1 is charged until it reaches a level lower than the data signal Dj by the threshold voltage of the drive transistor M1. By charging one end of the capacitor C1 in this manner, a voltage corresponding to the level of the data signal Dj is maintained in the capacitor C1, including compensation for variations and fluctuations in the threshold voltage of the drive transistor M1. Also during this data write period, the control circuit 18 sets the DIS1 signal to a low level to turn on transistor M7. This initializes the anode of the OLED element to the level of voltage VIN2, and discharges the charge accumulated in the parasitic capacitance of the OLED element.

[0024] Next, the control circuit 18 sets the DIS1 signal to high level to turn off transistor M7, and sets the EM1 signal to low level to turn on transistors M5 and M6. This marks the start of the light-emitting period. This causes the OLED element to emit light at a brightness corresponding to the level of the data signal Dj during the data write period until the reset period of the next cycle begins. For details on the function and circuit operation of each element, please refer to the explanation in Patent Document 1.

[0025] <Configuration of current detection circuit> This section describes a current detection circuit for detecting defects related to the emission / non-emission of light sources not incorporated in the active light-emitting unit 13E of the print head device 13 while the print head device 13 is attached to the image forming unit. Figure 4 is an explanatory diagram showing the configuration of a current detection circuit that detects the drive current of the active light-emitting unit shown in Figure 3 on the ELVSS side to which the cathodes of each OLED element are connected. Defects in the emission / non-emission of each light-emitting source of the print head device 13 are thought to be more likely to be caused by the connection between the active light-emitting unit 13E and the connection unit 13C, or the connection between the connection unit 13C and the control circuit 18, rather than by defects in the TFT panel.

[0026] For example, anisotropic conductive film (AFC) can be used for the signal connection between the active light-emitting unit 13E and the connection unit 13C. However, since many signal lines are connected at very small intervals, this does not provide high resistance to external forces. Furthermore, the print head device 13 and other components of the image forming unit are designed to be removable when a service engineer performs maintenance on the multifunction device 10. The photosensitive drum 11 and the developing unit 14 are replaced periodically, and it is conceivable that the print head device 13 will also be removed and cleaned at that time. In this respect, the usage environment differs from that of a display device, in which periodic replacement of the TFT panel is not anticipated.

[0027] Therefore, rather than detecting the light-emitting / non-emitting status of each light-emitting source individually, it is more reasonable to detect the light-emitting / non-emitting status of each light-emitting source by detecting the wiring unit of the drive current when the drive current is supplied to each light-emitting source collectively or in groups. That is, the light-emitting / non-emitting status of a light-emitting source can be determined by detecting the current in the ELVSS line or the ELVDD line common to all or each group of light-emitting sources. It is also possible to detect the light-emitting / non-emitting status of each light-emitting source by detecting the current in the unit of several anisotropic conductive films used to connect the active light-emitting unit 13E and the connection unit 13C. Alternatively, it is also possible to detect the light-emitting / non-emitting status of each signal harness 20 used to connect the connection unit 13C and the control circuit 18. In particular, the drive current can be detected with a relatively simple configuration using a current detection circuit. In this embodiment, a configuration for detecting the drive current is described.

[0028] As shown in FIG. 4, the current detection circuit 21 is provided outside the active light-emitting unit 13E. Specifically, an example in which the current detection circuit 21 is provided in the control circuit 18 is shown. However, this is not limiting, and a configuration in which the current detection circuit 21 is provided in the connection unit 13C is also possible. In this embodiment, the control circuit 18 performs a series of processes related to image formation. However, as described above, there is also an embodiment in which the control circuit 18 cooperates with other circuits to realize the functions of the control unit 300. For example, in such an embodiment, it is possible that the control circuit 18 can be provided in the connection unit 13C without providing a separate control circuit 18. In other words, it is also possible that the connection unit 13C also serves as the control circuit 18, and that the circuit connected via the signal harness 20 in FIG. 2 (the circuit indicated as the control circuit 18 in FIG. 2) cooperates with the other circuit. In this case, the current detection circuit 21 shown in FIG. 4 may be provided in the connection unit 13C.

[0029] As shown in FIG. 4, the current detection circuit 21 includes a current detection unit 21D and a threshold comparison unit 21C. The current detection unit 21D is composed of a current detection resistor 21S inserted in the ELVSS line and a differential amplifier that differentially amplifies the voltage drop across the resistor, which is proportional to the current. The differential amplifier is composed of an operational amplifier 21A and resistors R1 to R4. The threshold comparison unit 21C is a comparator that includes an operational amplifier 21B and resistors R5 to R8. Resistors R6 and R5 divide the voltage corresponding to the current output from the current detection circuit 21 and input it to amplifier 21B. Resistors R7 and R8 generate a threshold voltage. The threshold comparison unit 21C compares the voltage corresponding to the current with a threshold and outputs a binary high / low voltage as a determination signal. The control circuit 18 controls the light emission / non-emission of each light source and includes a determination unit 18J that determines whether the light source is faulty based on the signal output from the threshold comparison unit 21C. It is also possible to consider an embodiment in which the determination unit 18J includes an analog input circuit and incorporates the functions of the threshold comparison unit 21C. That is, the analog output from the current detection unit 21D is received by the analog input circuit of the determination unit 18J, the determination unit 18J performs A / D conversion of the input analog voltage, and compares it with the threshold value held inside the determination unit 18J to determine whether the light source is defective.

[0030] As shown in FIG. 4, the current detection resistor 21S is inserted into the ELVSS line common to the cathodes of the OLED elements to detect the total drive current of each OLED element. FIG. 4 illustrates an example in which all OLED elements in the active light-emitting unit 13E are commonly connected to the ELVSS line. In other words, the total drive current of each OLED element in the active light-emitting unit 13E is the target of detection. Alternatively, the cathodes of the OLED elements in several groups may be commonly connected, and the drive current of the ELVSS line for each group may be the target of detection. In this case, the total drive current of the OLED elements in each group is the target of detection. Furthermore, while FIG. 4 shows a configuration in which the current detection resistor 21S is inserted into the ELVSS line, a configuration in which the current detection resistor 21S is inserted into the ELVDD line instead is also conceivable.

[0031] <Processing of the Determination Unit> Next, an example of the process of determining a defect in a light-emitting source by the determination unit 18J of the control circuit 18 (control unit 300) shown in FIG. 4 will be described. FIG. 5 is a flowchart showing the flow of the process of detecting a defect in a light-emitting source executed by the control unit 300 as the determination unit 18J in this embodiment. The process of steps S11 to S19 shown in FIG. 5 is a process of detecting a defect (light-out defect) in which the target OLED element emits light even when set to a non-light-emitting state. The subsequent process of steps S21 to S33 is a process of detecting a defect (light-out defect) in which the target OLED element does not emit light even when set to a light-emitting state. The process of steps S11 to S19 related to the detection of a light-out defect is not essential and can be omitted. In FIG. 5, optional processes are indicated by dashed lines. In contrast, the process shown in steps S21 to S33 is essential. If steps S11 to S19 are omitted, the control unit 300 starts the process from step S21.

[0032] First, the process for a lighting failure will be described with reference to FIG. 5. The control unit 300 causes the OLED element to be determined to be in a non-emitting state (step S11). Typically, the control unit 300 controls the data signal Dj to cause the target OLED element to be in an emitting / non-emitting state. The target OLED element is an OLED element whose cathode is connected to the ELVSS line into which the current detection resistor 21S of interest is inserted. The control unit 300 acquires a determination signal output from the current detection circuit 21 when the target OLED element is in a non-emitting state (step S13). Then, the control unit 300 determines whether the drive current is equal to or less than a second threshold (step S15). The second threshold for detecting a lighting failure may be set to an absolute value greater than the first threshold for detecting a lighting failure.

[0033] If the determination result indicates that the drive current is greater than the second threshold (No in step S15), the control unit 300 determines that the non-light-emitting state of the target light source is abnormal (step S19). That is, it determines that the light source is in a light-emitting state in which the drive current flows even though each light source is in a non-light-emitting state. In this case, the control unit 300 proceeds to step S35, which will be described later. On the other hand, if the determination result in step S15 indicates that the drive current is equal to or less than the second threshold (Yes in step S15), it determines that the target light source is in a normal non-light-emitting state (step S17). If at least some of the light-emitting sources are emitting light even though the target light source is in a non-light-emitting state, toner TN will be developed on the photosensitive drum 11 corresponding to the unintended light-emitting portions during the image formation process. The processing shown in steps S11 to S19 is for determining whether this is a defect (light-off defect). According to the mode of executing steps S11 to S19, a fault where the target light source does not go into a non-light emitting state despite being set to a non-light emitting state (light-off fault) can be detected in addition to a fault where the target light source does not go into a light emitting state despite being set to a light emitting state (light-on fault).

[0034] Next, the processing of steps S21 to S33 related to lighting failure will be described. If it is determined in step S17 that the target light source is normally in a non-emitting state, the control unit 300 then causes the target OLED element to emit light (step S21). The control unit 300 acquires a determination signal output from the current detection circuit 21 when the target OLED element is in an emitting state (step S23). Then, it determines whether the drive current is equal to or greater than a first threshold (step S25). If the determination result indicates that the drive current is less than the first threshold (No in step S25), it determines that the light emission state of the target light source is abnormal (step S31). That is, even though each light source has been set to an emitting state, a drive current equal to or greater than the threshold does not flow, and it is determined that at least some of the light sources are in a non-emitting state. In this case, the control unit 300 causes the target OLED element to emit light (step S33) and executes processing for detecting an abnormality (step S35). Then, the processing ends.

[0035] On the other hand, if the determination result in step S25 is that the drive current is equal to or greater than the first threshold (Yes in step S25), the control unit 300 determines that the target light source is normally in a non-light-emitting state (step S27). In this case, the control unit 300 puts the target OLED element in a non-light-emitting state (step S29) and ends the process. If at least some of the light-emitting sources do not emit light even though the target light-emitting sources are in a light-emitting state, photo-neutralization is not performed properly, and unintended charges accumulate on the photosensitive drum 11. When an operation related to image formation is performed, the circumferential surface of the photosensitive drum 11 may reach an unintended potential, and developer that should be contained in the developing unit 14 may adhere to the circumferential surface of the photosensitive drum 11 or leak into the image forming unit. The processing shown in steps S21 to S33 is for determining whether the light source is lighting properly so as to prevent such a situation from occurring.

[0036] If it is determined that the target light source is abnormal, the control unit 300 executes, for example, the following process in step S35 described above. First, if the multifunction device 10 is performing an operation related to image formation, the operation is stopped. This is because continuing the operation related to image formation could damage the photosensitive drum 11, the developing unit 14, etc. Then, the control unit 300 executes a process to notify the user of the abnormality in the print head device 13. For example, a message notifying the user of the abnormality in the print head device 13 is displayed on an operation unit (not shown). The above is the flow of the process in which the control unit 300, functioning as the determination unit 18J, detects a defect in the light source.

[0037] <Timing for determining if the light source is defective> A preferable timing for the control unit 300 to execute the light source defect detection process shown in FIG. 5 will be described.

[0038] In a first preferred embodiment, the control unit 300 executes the light source defect detection process before rotating the photosensitive drum 11 in the sub-scanning direction, i.e., while the photosensitive drum 11 is stopped. The multifunction peripheral has a drive unit (not shown) for rotating the photosensitive drum 11. The drive unit has a drive motor and a transmission mechanism for transmitting the motor's rotation to the photosensitive drum 11. It also has a control circuit and a drive circuit for controlling the rotation of the motor. The control unit 300 controls the rotation and stopping of the drive unit. The control circuit and drive circuit may be arranged in the control circuit 18, or may be arranged on another circuit board. When forming an image, the control unit 300 rotates the photosensitive drum 11.

[0039] According to this aspect, with the print head device 13 installed, a defect in the light source can be detected while the photoconductor is stopped and before the photoconductor drum 11 is driven to form an image. Detecting a defect in the light source while the photoconductor is stopped can prevent a situation in which developer not normally attached to the photoconductor due to a defect in the light source, i.e., improper exposure or improper discharge of the photoconductor, occurs when the photoconductor is driven to form an image. This can prevent damage to the photoconductor or the developing unit and contamination of the interior of the machine.

[0040] In a second preferred embodiment, the control unit 300 executes the light source defect detection process before the photosensitive drum 11 is charged using the charging roller 12 to form an image, i.e., before the photosensitive drum 11 is charged, the photosensitive drum 11 is in an uncharged state. Even if the photosensitive drum 11 rotates, the toner TN or developer in the developing unit 14 will not adhere to the circumferential surface of the photosensitive drum 11 if the circumferential surface of the photosensitive drum 11 is in an uncharged state.

[0041] According to this aspect, with the print head device 13 installed, a defect in the light-emitting source can be detected before the photosensitive drum 11 is charged by the charging roller 12 and while the photosensitive drum 11 is in an uncharged state. Because a defect in the light-emitting source is detected while the photosensitive drum 11 is in an uncharged state, it is possible to prevent developer or carrier that is not normally attached to the charged circumferential surface of the photosensitive drum 11 due to a defect in the light-emitting source, i.e., due to an exposure defect or a discharge defect of the photosensitive drum 11. This in turn prevents damage to the photosensitive drum 11 or the developing unit 14 and contamination inside the image forming unit.

[0042] A third preferred aspect is as follows. The control unit 300 controls image formation by the image forming unit 102. In an aspect in which the control unit 300 is distributed, the control circuit 18, which includes the control unit 300 that controls the print head device 13, and a control circuit that controls other parts of the image forming unit 102 may cooperate to form images. When the power of the multifunction peripheral 10 is turned on by a user operation or when the control unit 300 detects an event in which the multifunction peripheral 10 returns from the power saving mode to the normal mode, power is supplied from the power supply circuit 22 to the image forming unit 102, which includes the print head device 13. According to this aspect, after power is supplied to the image forming unit 102, the control unit 300 performs a light-emitting source defect detection process before the image forming unit 102 starts image formation.

[0043] According to this aspect, with the print head device 13 attached, after power is supplied from the power supply circuit 22 to the image forming unit 102, a defect in the light source can be detected before the image forming unit 102 starts forming an image. Since the control unit 300 detects a defect in the light source after power is supplied to the image forming unit 102 and before the image forming unit 102 starts forming an image, it is possible to prevent the photosensitive drum 11 and the developing unit 14 from being damaged and the inside of the machine from being soiled.

[0044] It should be understood that the present invention also includes any combination of the above-described aspects. In addition to the above-described embodiment, various modifications of the present invention are possible. These modifications should not be interpreted as not falling within the scope of the present invention. The present invention should include all modifications that are equivalent to the scope of the claims and that fall within the scope of the present invention. [Explanation of symbols]

[0045] 10: Multifunction device, 11: Photosensitive drum, 12: Charging roller, 13: Print head device, 13C: Connection section, 13E: Active light emitting section, 13L: Imaging lens, 13S: Board, 14: Development section, 15: Cleaning mechanism, 16: Intermediate transfer belt, 17: Intermediate transfer roller, 18: Control circuit, 18J: Determination section, 20: Signal harness, 21: Current detection circuit, 21A, 21B: Amplifier, 21C: Threshold comparison section, 21D: Current detection section, 21S: Current detection resistor, 22: Power supply circuit 100: engine unit, 101: paper feed mechanism, 101T: paper feed tray, 102: image forming unit, 103: intermediate transfer unit, 104: secondary transfer unit, 105: fixing unit, 106: duplex transport path, 107: output tray, 200: scanner unit, 201: image reading unit, 201P: document table, 201S: image sensor, 202: document feeder, 300: control unit C1: capacitor, IL: irradiated light, M1: drive transistor, transistor, M2 to M7: transistor, TN: toner, Py, Pm, Pc, Pk: image forming unit, R1 to R8: resistor, VIN1, VIN2: voltage

Claims

1. an active light-emitting section in which light-emitting sources including drive elements and light-emitting elements that emit light at a luminance corresponding to a drive current passed by the drive elements are formed in at least one row; a control unit that controls each drive element to control the emission, non-emission, and luminance of each light source; a current detection circuit that detects the magnitude of the current; the current detection circuit detects a total driving current for all or a plurality of light-emitting sources; The control unit determines that the target light-emitting source is defective if the drive current detected by the current detection circuit is not equal to or greater than a predetermined first threshold value after causing the target light-emitting source to emit light.

2. 2. The print head device according to claim 1, wherein the control unit further performs a process of determining that the target light-emitting source is defective if the drive current detected by the current detection circuit is not equal to or less than a predetermined second threshold value after causing the target light-emitting source to be in a non-light-emitting state.

3. The print head device of claim 2 , wherein the first threshold has an absolute value less than or equal to the second threshold.

4. A print head device according to any one of claims 1 to 3; an imaging photoreceptor exposed by said printhead device; a drive unit that drives the photosensitive member, The control unit controls the drive unit or cooperates with a second control unit that controls the drive unit, and determines the defect when the photosensitive member is stopped before driving the photosensitive member to form an image.

5. A print head device according to any one of claims 1 to 3; an imaging photoreceptor exposed by said printhead device; a charging unit that charges the photosensitive member; The control unit controls the charging unit or cooperates with a second control unit that controls the charging unit, and determines the defect when the photosensitive member is in an uncharged state before using the charging unit to charge the photosensitive member and form an image.

6. A print head device according to any one of claims 1 to 3; an image forming unit including the print head device and performing image formation by an electrophotographic method; a power supply circuit for supplying power to the image forming unit; The control unit controls image formation by the image forming unit or cooperates with a second control unit that controls the image forming unit, and determines the defect after power is supplied from the power supply circuit to the image forming unit and before the image forming unit forms an image.

7. a control unit that controls each drive element of an active light-emitting unit in which light sources including drive elements and light-emitting elements that emit light at a luminance corresponding to a drive current passed by the drive elements are formed in at least one row, targeting all or a plurality of light-emitting sources to cause the target light-emitting sources to emit light; detecting a total drive current of the target light emitting source using a current detection circuit; and determining that the target light-emitting source is defective if the drive current detected by the current detection circuit is not equal to or greater than a predetermined first threshold.

Images