JP5780710B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus, and more particularly to an exposure apparatus used in an image forming apparatus.

  2. Description of the Related Art In recent years, attention has been paid to a print head including a light emitting element array in a copying machine, a printer, or the like (hereinafter referred to as an electrophotographic apparatus) employing an electrophotographic system (Patent Documents 1 and 2). The print head is sometimes referred to as a solid-state scanning optical system exposure device, and is characterized in that light is directly irradiated onto a photosensitive member without using a rotational scanning optical system such as a resonance mirror or a rotary polygon mirror. When high resolution (eg, 2400 dpi or more) and high-speed printability (eg, 100 ppm or more) are emphasized, the rotational scanning optical system is close to the limit, and the solid scanning optical system is advantageous.

  By the way, feedback control and feedforward control are necessary to suppress fluctuations in the amount of light of a plurality of light emitting elements constituting the light emitting element array. As a solution, for example, it is conceivable to arrange a plurality of light receiving elements corresponding to a plurality of laser elements in a one-to-one manner, and individually APC (automatic light quantity control) for the light quantity of each laser element. .

JP 2007-118495 A

  By the way, in order to realize 2400 dpi in the solid-state scanning optical system, the print head needs to include, for example, 20,000 light emitting elements. That is, high-precision light quantity control must be performed on all of a large number of light emitting elements, and an expensive control system is required. For example, if one light receiving element and a control circuit are provided for one light emitting element, the manufacturing cost becomes high.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to reduce the cost related to the light amount control of an exposure apparatus. Other issues can be understood throughout the specification.

The present invention is, for example,
A rotating photoreceptor,
A plurality of light emitting elements arranged in parallel with the rotation axis direction of the photosensitive member, first, second, and third light amount adjusting light emitting elements; and the first, second, and third light amount adjusting light emitting elements. First, second, and third light amount adjusting light-receiving elements that respectively receive light emitted from the first, second, and third light amount adjusting light-emitting elements. An exposure unit comprising: a control means for controlling currents for driving the plurality of light emitting elements based on outputs from the first, second, and third light quantity adjusting light receiving elements;
In the image forming apparatus for irradiating the photosensitive member with light from the plurality of light emitting elements,
The exposure unit includes: a first block that includes the first light amount adjustment light emitting element and a plurality of light emitting elements; a second block that includes the second light amount adjustment light emitting element and a plurality of light emitting elements; A third light amount adjusting light emitting element, and a third block including a plurality of light emitting elements,
The first, second, and third blocks are arranged at positions shifted from each other in a direction along the rotation axis direction, and the second block is different from the first block and the third block in the rotation axis direction. It is arranged at a position shifted in the direction orthogonal to
Regarding the direction along the rotation axis direction, away from said first light amount adjusting light-emitting element and the second light quantity adjusting light emitting element third light intensity adjustment light emitting element, and the first The plurality of light emitting elements of the first block are arranged between the light amount adjusting light emitting element and the second light amount adjusting light emitting element, and the second light amount adjusting light emitting element and the third light amount are arranged. The image forming apparatus is characterized in that the plurality of light emitting elements of the second block are arranged between the light emitting elements for adjustment.

  According to the present invention, it is possible to reduce the cost related to the light amount control of an exposure apparatus used for a print head or the like in a solid scanning optical system.

It is a circuit diagram explaining a light quantity control means. FIG. 2A is a photoelectric conversion characteristic diagram with respect to the amount of received light. FIG. 2B is a D / A conversion characteristic diagram for the D / A converter. It is a figure which shows the application example with respect to the exposure part of exposure apparatus and an electrophotographic apparatus. It is a timing chart explaining overall control. It is a timing chart which performs real-time APC. It is the figure which showed the structure in the exposure apparatus explaining a light-shielding structure. It is the figure which showed the structure for enabling the recyclability of exposure apparatus.

  In the following, a light source block that can be used in the exposure apparatus includes a light-emitting element array composed of n light-emitting elements, and m light-emitting elements (n>) having a value sufficiently smaller than n among the n light-emitting elements. An example constituted by m light receiving elements provided corresponding to m) will be described. Here, in order to simplify the description, the simplest case will be described assuming that m = 1. Of course, it goes without saying that m may be 2 or more.

In FIG. 1, the light amount detection circuit 11 includes a light emitting element LED M, a light receiving element PD, a transistor Tr M, a resistor RM, a detector resistor DR, and a switching transistor Sw M. That is, the light quantity detection circuit 11 is positioned as a feedback light quantity detection unit for APC. The light emitting element LED M is a light amount adjusting light emitting element that is not used for image formation. The light receiving element PD is a light amount adjusting light receiving element that receives light emitted from the light emitting element LED M. That is, the light emitting element LED M and the light receiving element PD are provided on a one-to-one basis. The light emitting element LED M is an example of m light emitting elements (n> m) among the n light emitting elements. The transistor Tr M operates according to the constant voltage value V _LED output from the digital A / D converter 21. The resistor RM determines a current value for driving the light emitting element LED M according to the constant voltage value V _LED . The light receiving element PD is an example of m light receiving elements provided corresponding to m light emitting elements (m is a value sufficiently smaller than n) among the n light emitting elements. The detector resistor DR is a resistor for converting the current value of the current received and photoelectrically converted by the light receiving element PD into a voltage value. The switching transistor Sw M functions as a switch for switching the blinking of the light emitting element LED M (whether or not the drive current flows to the light emitting element LED M). The switching transistor Sw M is controlled to be turned on / off based on the light amount control execution signal exe output from the control unit 40 such as a CPU.

  The light-emitting element array 12 for image formation includes light-emitting elements LED0 to LEDN (N is a natural number), transistors Tr0 to TrN, resistors R0 to RN, and switching transistors Sw0 to SwN. The light emitting elements LED 0 to LED N are (nm) light emitting elements among the n light emitting elements. The transistors Tr 0 to Tr N, the resistors R 0 to RN, and the switching transistors Sw 0 to Sw N form drive circuits for the corresponding light emitting elements LED 0 to LED N, respectively. That is, the drive circuit is provided for each light emitting element. The switching transistors Sw 0 to Sw N perform a switching operation according to the modulation signals from the corresponding PWM modulators PWM 0 to PWM N.

The voltage comparator 13 detects a light amount (voltage value) obtained by detecting light emitted from m light emitting elements with the corresponding m light receiving elements, and a target light amount (voltage) set by the setting unit. It is an example of a comparator that compares (value). The voltage comparator 13 compares the measured voltage value V _LPD output from the light amount detection circuit 11 with the reference voltage value V _ref output from the control unit 40. The control unit 40 is provided in common for a plurality of light source blocks, and functions as a setting unit that sets a target light amount in each light source block. The voltage comparator 13 compares the measured voltage value V _LPD corresponding to the measured light amount with the reference voltage value V _ref corresponding to the set light amount value, and the light amount of the light emitting element LED M is the target value (set light amount value). It is determined whether or not it has been reached. The voltage comparator 13 instructs Up (increase in the amount of light) if the amount of light does not reach the target value, and up / down multi-bit counter (multi-stage counter) if the amount of light exceeds the target value. 22). That is, the measurement light amount is fed back to the light emission amount (drive current).

The digital A / D converter 21 functions as a light amount control unit together with the control unit 40 and the voltage comparator 13. The light amount control unit increases the value of the drive current for driving the m light emitting elements if the detected light amount is less than the target light amount, and drives the m light emitting elements if the detected light amount is not less than the target light amount. It is a control part which controls to reduce the value of the drive current for doing. The digital A / D converter 21 includes a multistage counter 22, an R-2R ladder resistor 23 that converts an output value of the multistage counter 22 into an analog voltage value, and a buffer stage operational amplifier 24 that constitutes a voltage follower. The control unit 40 outputs to the multistage counter 22 a count clock Clk and an instruction signal CLR instructing to clear the output value of the multistage counter 22 in order to execute APC. The multistage counter 22 performs up-count / down-count according to the count clock Clk, the instruction signal CLR, and the comparison result of the voltage comparator 13. The multistage counter 22 initializes the output value to 0 when the CLR signal is input. The amount of received light is converted into a measured voltage value V _LPD according to the photoelectric conversion characteristic 201 shown in FIG. If the measured voltage value V _LPD is less than the reference voltage V _ref , the voltage comparator 13 outputs Low. If the measured voltage value V _LPD is equal to or higher than the reference voltage V _ref , the voltage comparator 13 outputs Hi. The multistage counter 22 performs up-counting when Low is input. The multistage counter 22 performs down-counting when Hi is input.

The output value (current count value) of the multistage counter 22 is converted into a voltage value V _LED proportional to the output value by the R-2R ladder resistor 23. That is, the output value of the multistage counter 22 is converted into an analog voltage value V _LED according to a proportional relationship as shown in FIG. The voltage value V _LED is maintained at a constant voltage value (V _LED ) by the operational amplifier 24 for voltage follower, and is applied to each of the plurality of transistors Tr 0 to Tr N and Tr M. This voltage value V _LED is a result of current control by the light emitting element LED M and the light receiving element PD for adjusting the light amount, and by reflecting this control result on the plurality of light emitting elements LED 0 to LED N (N is a natural number). The cost for controlling the light amount of the exposure apparatus can be reduced.

The voltage value V _LED is subtracted from the base-emitter voltage drop Vd of each transistor, and the remaining voltage is applied in parallel from the resistors R0 to RN and RM. Furthermore, it becomes possible to flow a constant drive current from the light emitting elements LED 0 connected in parallel to the LEDs N and M. Note that the switching transistors Sw 0 to Sw N and Sw M control the light emitting elements LED 0 to LED N and LED M so that they are forcibly turned on when APC is executed. Thus, if the voltage value V _LED of the operational amplifier 24 increases, the light quantity of each light emitting element can be increased.

Also in the light quantity detection circuit 11, the light quantity of the light emitting element LED M is increased as the voltage value V _LED is increased similarly to the plurality of light emitting elements LED 0 to LED N. The voltage value V _{LPD of the} inter-terminal voltage of the detector resistor DR rises due to the electromotive current generated by the light receiving element PD by receiving the light from the light emitting element LED M. Finally, as shown in FIG. 2A, when the voltage value V _LPD exceeds the reference voltage V _ref , the voltage comparator 13 inverts the output level from Lo to Hi. Therefore, the voltage value V _LPD converges to the reference voltage value V _ref , and the light emission amount of each light emitting element also converges to the target light amount.

A control unit 40 that controls the electrophotographic apparatus monitors the output level of the voltage comparator 13 and controls the count clock Clk of the multistage counter 22. After APC is completed, the process shifts to real time APC. That is, since the amount of emitted light decreases depending on the temperature rise of the light emitting element, the target amount of light is maintained by real-time APC. In the real-time APC, when the plurality of light emitting elements LED 0 to LED N and LED M are lit, the voltage value V _LED (that is, the drive current) is basically always (real time) so that the emitted light amount converges to the target light amount. It is corrected continuously.

  The image signal transmission circuit 31 is a circuit for controlling the blinking time of the plurality of light emitting elements LED 0 to LED N used for image formation. The blinking time corresponds to the image density. The image information distribution unit 32 shifts the input image signal (Video Data) according to the synchronization clock Shift Clk and outputs it as a PWM modulation signal. Each PWM modulation signal is output from the light emitting elements LED 0 to PWM modulators PWM 0 to PWM N corresponding to LED N. Signals from the PWM modulators PWM 0 to PWM N are output from the switching transistors Sw 0 to Sw N.

  The light amount control execution signal exe input from the control unit 40 to the switching transistor Sw M is a signal that is turned on when any of the light emitting elements LED 0 to LED N for image formation is lit. When all of the light emitting elements LED 0 to LED N for image formation are turned off, the light quantity control execution signal exe is turned off. As described above, when any one of the light emitting elements LED 0 to LED N for image formation is turned on, the light emitting element LED M for APC is also turned on. Thereby, the feedback information for APC is continuously updated in real time. As described above, the control unit 40 updates the value of the drive current by turning on the m light emitting elements when at least one of the (n−m) light emitting elements among the n light emitting elements is turned on. Keep doing.

  Thus, according to the embodiment, the light receiving elements are provided corresponding to only some of the light emitting elements, and the light amount control of the plurality of light emitting elements is performed according to the light amount of light received by the light receiving elements. Run. In the above example, the value of the drive current of the light emitting elements LED 0 to LED N is controlled in the same manner as the value of the drive current of the light emitting element LED M. Therefore, the total number of executions of APC for the number of light receiving elements and the number of all light emitting elements can be reduced. In addition, even if a slight fluctuation occurs in the amount of emitted light during image formation, the light quantity can be controlled so as to cancel the minute fluctuation by real-time APC.

Note that the control unit 40 may change the reference voltage V _ref input to the voltage comparator 13 in accordance with a predetermined condition (eg, print speed) of the electrophotographic apparatus.

  Next, application to an exposure apparatus in an electrophotographic apparatus will be described. Note that the number of light-emitting elements included in the light-emitting element array is not a limited number of light-emitting elements, as described above. In order to apply the light emitting element array to the exposure apparatus, the light emitting elements are taken out from the semiconductor wafer, and assembled and adjusted as the light emitting element array. Therefore, the number of light emitting elements included in the light emitting element array is a matter to be determined depending on the manufacturing yield. Of course, it is not possible to make a profit without using an inexpensive print head for exposure. For example, a light emitting element array of about 5000 bits is required at a resolution of 600 dpi, but a light emitting element array of 20,000 bits is actually required at a resolution of 2400 dpi. Therefore, depending on the resolution, the influence of the yield rate on the semiconductor wafer is significantly different. If one bad bit is found in the adjustment process, the printhead is discarded even if the remaining 19999 bits are normal. That is, the increase in the number of bits of the light emitting element array leads to a large risk and an increase in cost in exchange for higher resolution and higher throughput. Therefore, a light-emitting element array with a plurality of light-emitting elements in a uniform arbitrary number is configured without much reliance on the total number of bits of the head corresponding to the resolution required for the electrophotographic apparatus, and discovered in the inspection process. It is preferable to be able to replace the defective part. Thereby, the yield rate of the exposure apparatus can be improved and the cost increase can be suppressed. The light amount control circuit described in FIG. 1 is not necessarily limited to the case where the print head is configured by a plurality of blocks (light emitting element arrays) as described in FIG. As shown in FIG. 4A, the present invention may be applied to a print head including a single light emitting element array.

  As shown in FIG. 3A, the print head 301 of the solid scanning optical system is attached in parallel to the longitudinal direction (rotational axis direction) of the rotating photosensitive drum 302. That is, the rotation axis of the photosensitive drum 302 faces the print head 301 and is parallel to the longitudinal direction of the print head 301. A plurality of grooves called nano-in encoders 303 are provided on the surface of the photosensitive drum 302 so as to face the left end portion of the print head 301 in the drawing. The nano-in encoder 303 is disposed on the end side of the image forming region 306 on the surface of the photosensitive drum 302. In addition, the formation position of two adjacent grooves constituting the nano-in encoder 303 is offset. As described above, the nano-in encoder 303 is a position detection groove arranged on the end surface in the longitudinal direction of the photoreceptor among the surface of the photoreceptor.

  In order to increase the mounting accuracy of the print head 301, as shown in FIG. 4A, the print head 301 may be composed of one light emitting element array and a drive control circuit. However, if defective elements are mixed even in one bit, the print head 301 can no longer be used. For example, in a light emitting element array having a resolution of 2400 dpi and 20,000 bits, the yield rate is deteriorated. Therefore, as described with reference to FIG. 4B, a light-emitting element array including a predetermined number of light-emitting elements is used as one block, and a print head is configured by a plurality of blocks. The number of light emitting elements per block depends on, for example, the bit length taken out from the semiconductor wafer. Also, the number of blocks required per print head depends on the resolution. By the way, if a single light quantity control circuit and a single drive circuit are combined into one IC for all the blocks, the yield rate cannot be expected to improve much. In the configuration shown in FIG. 4B, the yield rate related to the light emitting element is improved as compared with the configuration shown in FIG. 4A, but a defective head is found in the final light amount adjustment process performed after the assembly process. The overall yield rate including IC cannot be expected.

  Therefore, in the present invention, the light quantity control circuit system shown in FIG. 1 is also provided for each block. That is, the light amount adjustment process is executed after the assembly process of each block, and the print head is assembled only with the normal blocks from which the defective blocks are omitted. This will significantly improve the yield rate of the print head. Furthermore, since the print head is an aggregate of blocks whose light quantity has been adjusted, it is easy to correct variations between adjacent blocks. Furthermore, the variation between the light emitting elements in the block is almost negligible. This is because the n plurality of light emitting elements in the block are light emitting elements manufactured by being taken out from the same wafer.

  In this embodiment, the target light amount can be adjusted independently for each block, but a reference voltage input to the voltage comparator 13 of each block can be applied in parallel. In other words, it may be advantageous that the input impedance matching need not be adjusted. However, since the light quantity control circuit is independent for each block, it is necessary to scan while instructing the timing for executing the light quantity control for each block.

  The timing related to the selection instruction for each block will be described with reference to FIG. Here, for simplification of explanation, it is assumed that there are 10 blocks per print head. The configuration of the print head here is a configuration in which a light amount control circuit is included in one block, as shown in FIG. The light quantity control circuit includes the APC circuit for independent light quantity setting and light quantity maintenance described with reference to FIG.

  In FIG. 1, an image signal transmission circuit 31 acquires and holds image information of a line to be exposed from the control unit 40 during exposure of the previous line. In the timing chart shown in FIG. 4C, a line synchronization signal is generated about every 70 μsec. When the line synchronization signal is generated, the control unit 40 outputs a light amount control execution signal exe and various operation control signals to the multistage counter 22 for each block according to the arrangement order of the blocks. The control unit 40 may perform sequential driving for each block in accordance with the operation conditions of the electrophotographic apparatus (for example, the rotational speed of the photosensitive drum). Only the block instructed to enter according to the execution timing adjusted by the control unit 40 of the aggregate of blocks (the prethead) operates.

  The above is the basic circuit configuration of the present invention. Hereinafter, real-time APC execution, life determination, and recyclability will be described based on the basic circuit configuration of the present invention.

A real-time APC for improving the stability of the light quantity by suppressing the fluctuation of the light quantity due to the thermal characteristics of each element of the light emitting element array will be described with reference to FIG. FIG. 5 shows details of light emission control in one block in FIG. The control unit 40 outputs a reference voltage V _ref . The value of the reference voltage V _ref is not particularly limited, and is a fixed voltage value determined based on the specification of the target light amount of the electrophotographic apparatus. The reference voltage V _ref is, for example, a value stored in a storage device (eg, non-volatile memory, dip switch) or a value calculated by the CPU according to the operating state of the electrophotographic apparatus.

  The specifications of the electrophotographic apparatus of this embodiment are, for example, a resolution of 2400 dpi (dot / inch), output of 40 sheets per minute (40 ppm), A4 horizontal feed, and a paper interval of 50 mm. Further, in order to realize power saving, each of the 10 divided blocks is driven by shifting the time sequentially. That is, since the amount of current used per unit time in one line matches the amount of current flowing through one block, power saving is realized. For example, if the resolution is 2400 dpi, the total number of light emitting elements is 20,000 bits, so one block includes 2000 bits of light emitting elements. If the value of the current applied to one bit is 0.01 mA, the total is 200 mA. When the output speed is more important than the power consumption as in a POD (print on demand) machine, 10 blocks are turned on simultaneously (parallel simultaneous lighting control). In this case, the value of the consumed current is 10 times 2A. In this manner, the output speed can be increased 10 times (400 ppm) by sequentially driving each unit block as parallel simultaneous driving of a plurality of blocks.

Let's calculate the device constants in the above specifications. The size per pixel is
25.4 mm / inch ÷ 2400 dots / inch = 10.58 μm / dot
It is. Therefore, it becomes 10.58 μm similarly per line.

Under the conditions of a paper interval of 50 mm and an A4 horizontal feed of 210 mm, the conveyance speed for outputting 40 sheets per minute is
10.58 μm ÷ {(50 + 210) mm / sheet × 40 sheets / min ÷ 60 seconds / min}
≈61 μsec / line. That is, an image is formed in 60 μsec per line. Since 10 blocks are used per line, the light emitting elements are simultaneously turned on in the unit block in 6 μsec per block. In 10 seconds, all 10 blocks are turned on sequentially. If a total of 10 scans are performed every 6 μs with the configuration shown in FIG. 4B, one line is completed. In practice, the light emission timing control of each block is performed so that the relative relationship between the image positions formed by each block is the original relative position with respect to the image forming position in the sub-scanning direction for each unit block. Has been made.

  In the image signal transmission circuit 31, the image information and the PWM data value for each of the n lines of elements that are execution lines for light emission of the elements are separated by, for example, a shift register circuit and a latch circuit included in the image information distribution unit 32. Image information of n lines is acquired when the shift register circuit is processing (n−1) lines, and is held by the latch circuit when n lines are executed. That is, when the execution line is n lines, the next n + 1 line image information is acquired by the shift register circuit. The latch circuit holds when executing n + 1 line. For example, Japanese Patent Application Laid-Open No. 11-286136 describes in detail the operation of a shift register circuit and a latch circuit in LED light emission.

  In FIG. 5, lighting control of a plurality of light emitting elements in one block is composed of two timing blocks. In one block, a plurality of light emitting elements are driven simultaneously. The formation time of one dot is 6 μs, the first half timing block is 2.56 μs, and the second half timing block is 3.44 μs. As shown in FIG. 5, the first half timing block is used for APC, and the second half is used for exposure for image formation and real-time APC.

  In the first half of the timing block, the multistage counter 22 is in a reset (CLR) state until it is selected by the light amount control execution signal exe described in FIG. Therefore, the drive current of the light emitting element array is zero (lights off). When the block is entered with the light quantity control execution signal exe, as shown in FIG. 5, the multistage counter 22 of that block immediately starts counting up and starts increasing the drive current to the light emitting element LED M. At this time, the other light emitting elements LED 0 to LED N maintain the extinguished state. This is because the image signal transmission circuit 31 keeps the PWM output reset. Therefore, only the switching transistor Sw M is turned on, and the switching transistors Sw 0 to Sw N are all turned off. That is, light irradiation for image information to the photosensitive drum 302 is not executed.

  The multistage counter 22 continues to count up until the output value of the voltage comparator 13 is inverted from Lo to Hi. When the output of the voltage comparator 13 becomes Hi, the multistage counter 22 shifts to the down-count state, but the multistage counter 22 is temporarily stopped by the control unit 40. This count-up time is assumed to be 256 bits in this embodiment. Therefore, the first half time is set to 2.56 microseconds in order to enable implementation up to 256 counts with a 100 MHz clock. The drive current value of the light-emitting element for image formation included in one block is variable from 0% to 100%, but the current value of 100% matches the drive current value of the light-emitting element LED M for APC. . The value of the driving current of the light emitting element for image formation is adjusted from 0% to 100% according to the width of the pulse output from the image signal transmission circuit 31. By setting the drive current value of the light emitting element LED M for APC to 100% of the drive current value of the light emitting element for image formation, the control accuracy of the target light amount of the light emitting element is improved.

Next, the second half timing block shown in FIG. 5 will be described. In the later timing block, exposure for image formation and real-time APC are executed. The image signal transmission circuit 31 performs PWM control of each light emitting element with a pulse width time determined for each light emitting element. That is, the switching transistors Sw 0 to Sw N are PWM driven, and the light emitting elements LED 0 to LED M execute lighting for image formation. On the other hand, in the second half timing block, which is 3.44 μs, real time APC is executed in accordance with the light amount control execution signal exe following the initial APC. That is, the multistage counter 22 counts down if the output of the voltage comparator 13 is Hi, and counts up if it is Lo. As a result, the 100% value of the drive current is corrected according to the change in the measured light quantity. That is, even if the relationship between the light amount and the drive current is shifted from the ideal curve in FIG. 5 to the substantial curve due to heat or the like, this shift is reduced by real-time APC, and the stability of the target light amount is improved. If the reference voltage V _ref issued by the control unit 40 is controlled, the absolute value of the target light amount can be easily changed at any timing.

  By the way, since the control unit 40 recognizes the number of clocks Clk generated by itself and the up / down count of the multistage counter 22, from the secular change of the value of the current driving the LED M (the above-mentioned 100% value), The lifetime of the light emitting element for image formation can be recognized. In other words, a drive current fluctuation allowable range for determining whether or not the lifetime has expired is determined in advance from 100% value data, and is stored in the storage device. The controller 40 determines whether or not the currently set fluctuation amount of the drive current deviates from a predetermined fluctuation allowable range. If the fluctuation amount deviates from the fluctuation allowable range, the control unit 40 determines that the light source block has expired. Thus, the control unit 40 functions as a life determination unit. Further, since the secular change and the life of each unit block can be determined, replacement and recycling for each block can be performed, and the cost of the electrophotographic apparatus can be reduced and the recyclability of the exposure apparatus can be improved.

  The configuration of the exposure apparatus will be described with reference to FIGS. FIG. 6 shows a mounting configuration of an execution sensing component for light amount detection that promotes improvement in accuracy of the real-time APC execution unit. The light emitting element array 600 shown in FIGS. 6A to 6C corresponds to one block described above.

  In FIG. 6A, it is intended to adjust the electromotive current characteristic of the light receiving element PD with respect to the heat generation of the light emitting element LED M for APC, and to suppress leakage light and stray light. In semiconductor manufacturing, the structure of the light receiving element PD is basically the inverse structure of the light emitting element. Therefore, the light amount of the light emitting element decreases as the temperature rises, but the detected light amount of the light receiving element increases as the temperature rises. As shown in FIG. 6A, each of the m (one in FIG. 6) light emitting elements is arranged to face the m light receiving elements. Thus, a pair of two semiconductor elements having contrasting characteristics with respect to heat is used. Even if the light emitting element LED M and the light receiving element PD are manufactured on different wafers, the influence of heat can be offset by adopting the close contact structure shown in FIG. In FIG. 6A, an electrode 601 serving as a common common terminal for the light emitting element LED M and the light receiving element PD is made of a metal such as gold, and the light receiving element is covered with the light emitting element LED M and the electrode 601. Close the PD. Thereby, heat is balanced through the electrode 601 and leakage light and stray light can be reduced.

  FIG. 6B shows a configuration in which the light emitting element LED M, the light receiving element PD, and the electrode 601 are covered with a cap-like cover 602 in order to tightly seal with the electrode 601 and to maintain strength rigidity. . It is possible to reduce stray light and light leakage by covering m pairs of m light emitting elements and m light receiving elements with m covers.

  FIG. 6C shows that each of m pairs of m light emitting elements and m light receiving elements is included with an adhesive having a light shielding property. As described above, the light emitting element LED M, the light receiving element PD, and the electrode 601 may be sealed with an adhesive (eg, epoxy resin-based cured adhesive) synthesized with a material that does not transmit light.

  Although not particularly illustrated, a pair of one light emitting element and one light receiving element may be integrally manufactured in a semiconductor manufacturing process or a manufacturing process on a wafer. In this embodiment, an example in which one light emitting element included in one block is paired with a light receiving element has been described, but a plurality of light emitting elements and the same number of light receiving elements may be paired. That is, a pair of a plurality of light emitting elements and light receiving elements is formed for APC, and the control result is reflected in the plurality of light emitting elements for image formation.

  With reference to FIG. 7, a mounting example of a light emitting element array for achieving recyclability and improving the yield of the exposure apparatus will be described. Here, the light emitting element array 600, the optical lens array 701, and the driving circuit 702 forming one block are integrated to form the IC chip 700.

  In general, an exposure apparatus of an electrophotographic apparatus requires an optical system that collects irradiation light from a light emitting element. In other words, the exposure apparatus of the electrophotographic apparatus has three components, ie, the light source, the condensing lens, and the photosensitive member, so that the accuracy required for these mounting positions is high. In particular, since the positional accuracy between the light source and the condenser lens is strict, it is inefficient to adjust and mount the exposure apparatus on the production line. Therefore, the semiconductor element level drive circuit 702 taken out from the wafer, the light emitting element array 600, and the optical lens array 701 such as a microlens are assembled using electrode wiring, bonding wiring, or the like. The optical lens array 701 includes sealing glass and the like and can transmit light. As described above, one light source block is used together with the optical lens array 701 having (nm) condenser lenses provided to face (nm) light emitting elements used for image formation. An IC chip 500 is configured. Further, the print head 301 for the image forming apparatus is configured by arranging a plurality of IC chips 700 in the length direction.

  By the way, in the conventional print head, the light source inspection and the light source adjustment cannot be executed unless the pret head is assembled. On the other hand, in the present embodiment, each IC chip 700 constituting one block includes a drive circuit that can be driven independently. Therefore, light source inspection and light source adjustment are performed when the IC chip 700 is completed. It becomes possible. Furthermore, if necessary, inspection and adjustment of items relating to yield, such as a light source irradiation position when mounted on an electrophotographic apparatus, can be performed at this stage. Therefore, if there is a defect, it is possible to eliminate the IC chip 700 as a unit. Conventionally, if even one of the light emitting elements included in the print head is defective, one print head composed of 20,000 elements has been discarded. However, in this embodiment, since it can be eliminated for each block (IC chip 700), the yield will be greatly improved. That is, there is a great difference in cost depending on whether the discard unit is one print head or one block. In addition, since the occurrence probability of defective light emitting elements is the same, it is natural that the yield rate is improved by 20 times if the total number of light emitting elements is 20,000 and 1,000.

  As described above, since the life detection of the light emitting element can be performed for each block, it is possible to replace in advance a block whose life is likely to end. Further, when the exposure apparatus is taken out from the discarded electrophotographic apparatus and recycled, it is possible to recycle in units of blocks or in units of print heads according to the life detection result for each block. Thus, it can be said that the structure of a present Example has high recycle performance compared with the conventional structure.

  The embodiment described above is a basic case in which one light receiving element PD is provided for a plurality of light emitting elements LED0 to LEDM. However, the same number of light receiving elements PD may be arranged corresponding to two or more light emitting elements among the plurality of light emitting elements LED0 to LEDM.

  According to FIG. 3B, deformed blocks 310 and 320 obtained by modifying the above-described block configuration are provided at the end of the print head 301. The deformation blocks 310 and 320 are position detection light source blocks including a light emitting element that emits light to the groove of the nano-in encoder 303 and a light receiving element that receives reflected light from the groove. The deformation blocks 310 and 320 are provided to face the nano-in encoder 303 on the image writing start side. Note that the nano-in encoder 303 is a groove dug in a size half the resolution of the electrophotographic apparatus (5.25 μm, which is half of 10.5 μm at 2400 dpi). That is, each time the photosensitive drum 302 moves half a line, one groove passes.

  The deformation block 310 has a pair of a light emitting element 304 and a light receiving element 305 for 6 bits from the writing side. These pairs are not used for APC. Furthermore, as shown in the enlarged view of FIG. 3A, the light receiving element 305 for 6 bits is located in the overlapping portion in the main scanning direction in the adjacent groove rows with respect to the groove row of the nano-in encoder 303. Two-bit pairs are arranged so as to face each other. That is, a total of 6-bit pairs are arranged with 2 bits dedicated to the n-line side column, 2 bits of the overlapping portion, and 2 bits dedicated to the n + 1 line-side column. When the 6-bit light emitting element 304 is always turned on and the reflected light from the groove is received by the corresponding 6-bit light receiving element 305, the control unit 40 monitors the unevenness of the moving speed of the photosensitive drum 302. That is, the control unit 40 can adjust the writing start timing in the sub-scanning direction according to the detected unevenness of the moving speed. In general, since the moving speed detection mechanism and the print head 301 are mounted at different positions, the accuracy is not obtained by the amount of mounting error. On the other hand, in this embodiment, since the moving speed detection mechanism is integrated with the print head 301, adjustment for the mounting error is unnecessary, and the moving speed detection accuracy can be improved.

  FIG. 3B illustrates a deformation block 320 that is different from the deformation block 310. As described above, a deformed block can be configured with a smaller number of light receiving elements than the number of light emitting elements for a plurality of light emitting elements. In the deformation block 320, a rectangular light receiving element 305 'is employed. In any of the deformation block 310 and the deformation block 320, the light receiving element may be arranged at a position of 180 ° with respect to the plurality of light emitting elements, and an angle of 0 ° to several tens of degrees with respect to the light emitting elements. You may arrange it. The position of the light receiving element may be any position as long as it can receive light from the light emitting element. For example, the light receiving element 305 may indirectly receive light from the light emitting element 304 via the mirror 307. However, it is necessary to devise a structural or control sequence so as not to receive light from the adjacent light emitting element adjacent to the target light emitting element. For example, a control sequence that avoids simultaneous light emission of the light emitting element of interest and the adjacent light emitting element may be designed.

  The specific circuit configuration described in the embodiments is not essential for the present invention, and any circuit configuration that reflects the technical idea of the present invention may be used. In addition, when the light amount detection is performed by m light receiving elements per block, m detection results are obtained. In this case, the data used for feedback may be an average value of m detection results, a weighted average value, or an average value excluding some of the m detection values. As described above, in this embodiment, the manufacturing cost of the exposure apparatus is reduced by reducing the number of light receiving elements, and the accuracy of light amount control is sufficiently ensured by executing APC in units of blocks.

Claims (7)

A rotating photoreceptor,
A plurality of light emitting elements arranged in parallel with the rotation axis direction of the photosensitive member, first, second, and third light amount adjusting light emitting elements; and the first, second, and third light amount adjusting light emitting elements. First, second, and third light amount adjusting light-receiving elements that respectively receive light emitted from the first, second, and third light amount adjusting light-emitting elements. An exposure unit comprising: a control means for controlling currents for driving the plurality of light emitting elements based on outputs from the first, second, and third light quantity adjusting light receiving elements;
In the image forming apparatus for irradiating the photosensitive member with light from the plurality of light emitting elements,
The exposure unit includes: a first block that includes the first light amount adjustment light emitting element and a plurality of light emitting elements; a second block that includes the second light amount adjustment light emitting element and a plurality of light emitting elements; A third light amount adjusting light emitting element, and a third block including a plurality of light emitting elements,
The first, second, and third blocks are arranged at positions shifted from each other in a direction along the rotation axis direction, and the second block is different from the first block and the third block in the rotation axis direction. It is arranged at a position shifted in the direction orthogonal to
Regarding the direction along the rotation axis direction, away from said the first light amount adjusting light-emitting element and the second light quantity adjusting light emitting element third light intensity adjustment light emitting element, and the first The plurality of light emitting elements of the first block are arranged between the light amount adjusting light emitting element and the second light amount adjusting light emitting element, and the second light amount adjusting light emitting element and the third light amount are arranged. The image forming apparatus , wherein the plurality of light emitting elements of the second block are arranged between the light emitting elements for adjustment. 2. The image forming apparatus according to claim 1 , wherein in the first block , when at least one of the plurality of light emitting elements of the first block is turned on, the first light amount adjusting light emitting element is also turned on.   The first light amount adjustment light emitting element is disposed to face the first light amount adjustment light receiving element, and the second light amount adjustment light emitting element is disposed to face the second light amount adjustment light receiving element. 3. The image forming apparatus according to claim 1, wherein the third light amount adjusting light emitting element is disposed to face the third light amount adjusting light receiving element. 4.   The image forming apparatus according to claim 3, further comprising a cover that covers the first light amount adjusting light emitting element and the first light amount adjusting light receiving element.   The image forming apparatus according to claim 3, wherein the first light amount adjusting light emitting element and the first light amount adjusting light receiving element are covered with an adhesive having a light shielding property.   The image forming apparatus according to claim 1, wherein the exposure unit includes a condenser lens provided to face each of the plurality of light emitting elements.   2. The exposure unit according to claim 1, further comprising: a light emitting element that irradiates light to a position detection unit disposed on a surface of the photoconductor; and a light receiving element that receives reflected light from the groove. The image forming apparatus according to claim 6.

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