JP2006278403A - Light emitting element driving device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting element driving device capable of maintaining precision in light intensity control of a light emitting element even if there is a defective light emitting element. <P>SOLUTION: The light emitting element driving device comprises a plurality of light emitting elements LD, a light intensity monitor 400 for detecting light intensity of the light emitting element LD, an APC circuit 600 for sequentially generating control voltages for allowing the light intensity of the light emitting elements LD to agree with a target light intensity, and drivers 100<SB>1</SB>-100<SB>32</SB>for driving the light emitting elements LD based on the control voltage. The APC circuit 600 comprises an APC sequence control circuit 1005 for changing the order of generating control voltages for the light emitting elements LD, based on the light intensity of the light emitting elements detected by the light intensity monitor 400. By changing the order of generating control voltages about the light emitting elements LD based on the detected light intensity of the light emitting elements, the order of light emitting elements for which a control voltage is generated can be arbitrarily set. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light emitting element driving circuit and an image forming apparatus, and more particularly to a light emitting element driving apparatus suitable for driving a laser element used as a light source for laser xerography.

  In an image forming apparatus using a plurality of laser diodes, there have been proposed various methods for drawing on a photoreceptor using a remaining laser diode when a failure occurs in a part of the laser diodes.

  For example, Patent Document 1 proposes a method of drawing without increasing throughput by increasing the scanning speed in accordance with the number of laser diodes remaining without failure.

Japanese Patent Laid-Open No. 2000-180751

  However, Patent Document 1 does not disclose the light amount control when the laser diode fails. When APC (Auto Power Control) is executed for a faulty LD, the APC amplifier is shaken out, and the convergence of APC of the next LD deteriorates. Therefore, it is necessary not only to identify a fault LD and not to emit light, but also to prevent APC of a laser diode that has failed during APC execution.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light emitting element driving apparatus and an image forming apparatus capable of maintaining the light amount control accuracy of the light emitting element even when a failed light emitting element is present. To do.

  In order to achieve such an object, the light emitting element driving device of the present invention includes a plurality of light emitting elements, a light detecting means for detecting the light amount of the light emitting element, and a control for matching the light amount of the light emitting element with a target light amount. A controller that sequentially generates a voltage; and a driving unit that drives the light emitting element based on the control voltage. The control unit emits each light emission based on the light amount of each light emitting element detected by the light detecting unit. The device is configured to change the order in which the control voltage is generated for the element. As described above, according to the present invention, the control unit changes the order in which the control voltage is generated for each light-emitting element based on the light amount of each light-emitting element detected by the light detection unit. The order can be set arbitrarily. Therefore, the control voltage for only the necessary light emitting elements can be generated first, and the time for controlling the light amount can be shortened.

  In the light emitting element driving apparatus having the above configuration, it is preferable that the control unit sequentially generates the control voltage for the light emitting elements that can obtain a predetermined light emission amount. Since the control voltage of the light emitting element that can obtain a predetermined amount of emitted light is continuously generated, the control time for a failed light emitting element that cannot obtain the predetermined amount of emitted light can be shortened.

  In the light-emitting element driving device having the above-described configuration, the control unit may perform control so that the light amount control is not performed for the light-emitting elements that cannot obtain a predetermined light emission amount. It is possible to shorten the control time for a failed light emitting element that cannot obtain a predetermined amount of emitted light.

  In the light emitting element driving apparatus having the above configuration, the control unit may perform control so that the light amount control of the failed light emitting element is performed after the normally operating light emitting element. During the light amount control for the normal light emitting element, the light amount control for the failed light emitting element is performed, and the control voltage of the light amount control does not end with an abnormal value. For this reason, while shortening the time of light quantity control, the precision of light quantity control can be raised.

  In the light emitting element driving apparatus configured as described above, the control unit may use the control voltage of the light emitting element that has already been normally completed as the control voltage of the failed light emitting element when the light amount control is performed on the failed light emitting element. It is good to set. Since the control voltage of the normally completed light emitting element is the control voltage of the failed light emitting element, the time for controlling the light amount for the failed light emitting element is shortened, and the time for controlling the light intensity for the next light emitting element after the failed light emitting element is reduced. It can be shortened.

  In the light emitting element driving apparatus having the above configuration, a sample hold circuit that holds the control voltage generated by the control unit is provided corresponding to the plurality of light emitting elements, and the control unit performs light amount control of the light emitting element that does not perform light amount control. At the time of control, the sample hold circuit of the light emitting element immediately before the light emitting element may be selected, and the control voltage held in the sample hold circuit may be used as the control voltage of the light emitting element not performing the light amount control. Since the control voltage of the light emitting element that has completed normally is the control voltage of the light emitting element that does not perform light amount control, it is possible to shorten the time of light amount control for the light emitting element that does not perform light amount control.

  The image forming apparatus of the present invention has a configuration for driving a laser element using the light emitting element driving apparatus according to claim 1. An optimal image can be formed by optimal light quantity control.

  The present invention can maintain the light amount control accuracy of a light emitting element even when a failed light emitting element exists.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  First, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating an overall configuration of a light emitting element driving apparatus according to the present embodiment. In FIG. 1, a light emitting element driving apparatus 10 drives a plurality of light emitting elements. In the configuration of FIG. 1, the light emitting element driving device 10 drives 32 light emitting elements LD1 to LD32. In other words, the light emitting element driving device 10 has a 32 channel configuration. Each of the light emitting elements LD1 to LD32 is formed of a surface emitting diode (VCSEL: Vertical Cavity Surface Emitting Laser) and arranged in a matrix. The light emitting element driving device 10 is formed of, for example, an IC chip and includes a circuit described below.

The light emitting element driving apparatus 10 has drivers 100 _{1 to} 100 ₃₂ for each channel, that is, for each of the light emitting elements LD1 to LD32. Further, the light emitting element driving device 10 has a common control potential setting circuit 200, a current amplifier 300, a light amount monitor 400, a forced lighting circuit 500, an APC (Automatic Power Control) circuit 600 (control of the present invention) as a control unit common to each channel. Corresponds to the part).

The drivers 100 _{1 to} 100 ₃₂ receive signals from the control unit common to the respective channels via the bus 150, and perform control for driving and controlling the light emitting elements LD1 to LD32, respectively. Specifically, the drivers 100 _{1 to} 100 ₃₂ perform APC control for controlling the light amount of the light emitting elements LD ₁ to LD ₃₂ and modulation control after the APC control. As will be described later, in APC control, the drivers 100 _{1 to} 100 ₃₂ control both the voltage and the current applied to the light emitting elements LD ₁ to LD ₃₂ . During voltage driving, the drivers 100 _{1 to} 100 ₃₂ control the capacitors Cd _{1 to} Cd ₃₂ respectively connected to the cathodes of the light emitting elements LD1 to LD32 via the respective terminals COUT. At the time of current driving, the drivers 100 _{1 to} 100 ₃₂ control the amount of current flowing through the light emitting elements LD ₁ to LD ₃₂ via the terminals LDOUT.

A plurality of drivers 100 _{1 to} 100 ₃₂ are connected in common via a terminal LDCOM and connected to a load 105. In the configuration of FIG. 1, the LDCOM terminals of the drivers 100 _{1 to} 100 ₄ are connected in common, and one end is connected to the other end of the load 105 connected to the ground. Each driver 100 _{1 to} 100 ₃₂ outputs a current (complementary output) corresponding to the drive current when the corresponding light emitting element is not driven. By flowing this current through the load 105, the operation is stabilized by constantly flowing a constant current to the light emitting element driving device 10 without depending on the number of lighting of the light emitting elements.

The light quantity control device 10 performs modulation control after setting the laser light quantity of each of the light emitting elements LD1 to LD32 to an appropriate value by APC control. The outline of APC control is as follows. First, the laser light amount of the light emitting element LD1 is adjusted. The driver 100 ₁ drives the light emitting element LD1. A current corresponding to the laser light amount of the light emitting element LD1 flows through a light receiver PD (for example, a photodiode, which corresponds to the above-described light receiver 11) provided in common to each of the light emitting elements LD1 to LD32. The current amplifier 300 turns on the switch SWSa with respect to the current flowing through the light receiver PD, and amplifies the current obtained by adding the addition current from the current source 450 with low impedance. In this case, when the switch SWSb is turned on, the added current is canceled by the reference current supplied from the current source 460, the remaining current is supplied to the resistor connected to the reference voltage Vref2, and the current output from the current amplifier 300 is supplied. The voltage is converted into a voltage, and this voltage (referred to as a detection voltage) is output to the APC circuit 600 via the switch SW19. The APC circuit 600 includes a plurality of operational amplifiers 61, a series circuit of one switch (any one of SWfb1 to SWfb32) and a capacitor (any one of Cfb1 to Cfb32). Each series circuit is connected between the output terminal and the inverting input terminal of the operational amplifier 61. Each series circuit constitutes a sample and hold circuit. One sample and hold circuit corresponds to one light emitting element. For example, a sample and hold circuit including the switch SWfb1 and the capacitor Cfb1 corresponds to the light emitting element LD1. Similarly, a sample and hold circuit including the switch SWfb32 and the capacitor Cfb32 corresponds to the light emitting element LD32.

The operational amplifier 61 amplifies the difference voltage when the light emitting element LD1 is driven and outputs the amplified voltage to the corresponding signal line of the bus 150. Driver 100 ₁ changes the drive current applied to the light emitting element LD1 so that this differential voltage becomes zero. As a result, the amount of laser light from the light emitting element LD1 changes, and the amount of current flowing through the light receiver PD changes. A detection voltage corresponding to the current flowing through the light receiver PD is output from the current amplifier 300 to the APC circuit 600. By such feedback control, the added current applied to the input output of the current amplifier 300 is canceled and disappears, and the driving state of the light emitting element LD1 is set so that the laser light quantity corresponds to the reference current generated by the APC reference voltage Vref. Set. The setting of the driving state means that both the driving current and the driving current applied to the light emitting element LD1 are adjusted to a value corresponding to the APC reference voltage Vref.

  While controlling the light emitting element LD1 in this way, only the switch SWfb1 is turned on among the 32 sample hold circuits of the APC circuit 600, and the laser light quantity of the light emitting element LD1 corresponds to the APC reference voltage Vref. The voltage at the time of convergence to the value to be stored in the capacitor Cfb1. Similarly, the APC control is performed on the light emitting elements LD2 to LD32 one by one in order.

  As will be described later, the APC control is preferably performed twice. In the second APC control, the switch SWSa that was turned on in the first APC is turned off. Since the cancellation current supplied to the output side of the current amplifier 300 is the reference current + addition current, the received light current is controlled by a current corresponding to the reference current + addition current. The 32 sample and hold circuits in the APC circuit 600 can be commonly used in the first and second APC controls, but 32 sample and hold circuits may be newly provided for the second APC control.

  The light quantity monitor 400 outputs a light quantity monitor signal indicating the laser light quantity of each of the light emitting elements LD1 to LD32 from the current flowing through the current amplifier 300.

  The forced lighting circuit 500 is a circuit that generates a synchronization signal required before performing APC control. In image processing apparatuses such as copiers, printers, and facsimiles in which the light emitting element driving device 10 is incorporated, an optical sensor is provided slightly before the drawing start position in order to accurately determine the image drawing position, and the light emitting element outputs The drawing start position is determined based on the timing at which the light to be crossed the optical sensor.

  FIG. 3 shows a configuration example of a laser scanning system and output of each sensor in laser xerography, which is an aspect of an image forming apparatus including the light emitting element driving device of the present invention. The basic configuration of the laser beam scanning system in the laser xerography apparatus is as follows. The laser light emitted from the laser light source 10d is irradiated onto the photosensitive member surface 16 through the lens 15, the polygon mirror 12, and the lenses 13 and 14. As the polygon mirror 12 rotates, the laser beam repeatedly scans the photosensitive member surface 16. Further, part of the laser light emitted from the laser light source 10 d is input to the light receiver 11 via the semi-transmissive mirror 19. In FIG. 3, the output of the light receiver 11 at this time is shown as the light amount control sensor output, and the output of the optical sensor 17 provided slightly before the drawing start position is shown as the SOS (Start of Scan) sensor output. The area for APC is provided before and after the scanning area. Reference numeral 18 corresponds to the light emitting element driving apparatus 10 described above.

  As described above, since the individual laser light amounts of the light emitting elements LD1 to LD32 are smaller than those of the end face laser, a plurality of them are turned on simultaneously to scan the SOS sensor. In this case, it is particularly preferable to turn on only a plurality of light emitting elements located in the central portion among the light emitting elements arranged two-dimensionally. However, in APC control, the light emitting elements are turned on one by one and the conditions are set (gain of feedback loop). Therefore, if a predetermined number of light emitting elements are turned on at the same time, the feedback loop of APC control will oscillate. There is a possibility that. Therefore, in order to solve this problem, the forced lighting circuit 500 changes the load size of the current amplifier 300 according to the modulation signal (modulation data). That is, a load corresponding to the number of light emitting elements to be turned on is connected to the output of the current amplifier 300. In the configuration shown in the figure, a plurality of resistors are connected to the output of the current amplifier via a switch. Focusing on the operational amplifier 61, the forcible lighting circuit 500 reduces the current power conversion gain according to the number of light emitting elements to be turned on, so that the gain of negative feedback as a whole does not change. With such a configuration, a state equivalent to a state in which only one light emitting element is always turned on can be obtained. In other words, the gain of the feedback loop is a value in a state in which only one light emitting element is turned on. As a result, it is possible to prevent the feedback loop from oscillating.

The common control potential setting circuit 200 is a circuit that generates control potentials necessary for generating various currents required in the drivers 100 _{1 to} 100 ₃₂ . In the configuration of FIG. 1, the common control potential setting circuit 200 generates a common potential for setting a bias current flowing in each of the drivers 100 _{1 to} 100 _{32 and} a common potential for generating an offset current. Circuit. The bias current and the offset current are typical examples, and each driver 100 _{1 to} 100 ₃₂ can set a control potential necessary to generate other currents necessary for driving and control. The common control potential for setting the offset current is generated by a circuit including an operational amplifier (op-amp) 211, current sources 212 and 213, and loads 214 and 215. A common control potential for bias current setting and other current setting is also generated by the same circuit. In response to the offset current setting signal from the outside, the current source 212 supplies the supported current to the load 214. The terminal voltage of the load 214 is applied to the plus side terminal of the operational amplifier 211. A constant current source 213 connected to the constant voltage source 216 causes a current corresponding to the output of the operational amplifier 211 to flow through the load 215. The terminal voltage of the load 215 is given to the negative terminal of the operational amplifier 211. The operational amplifier 211 controls the current source 213 so that the current source 213 flows the same current as the offset current set by the offset current setting signal. At this time, the output signal of the operational amplifier 211 is output to the corresponding bus line of the bus 150. On the other hand, the positive voltage of the constant voltage source 216 is output to the corresponding bus line of the bus 150. This bus line is common to the respective common control potentials, and is common to the drivers 100 _{1 to} 100 ₃₂ . Thus, the offset current value set from the outside is supplied to each of the drivers 100 _{1 to} 100 ₃₂ via the bus 150 in the form of a differential voltage. Each driver 100 _{1 to} 100 ₃₂ generates an offset current from the received differential voltage as described later. As a result, even if the power supply voltage of the constant voltage source 216 fluctuates, the potential difference is constant, and the influence of fluctuations in the power supply voltage can be avoided. Note that the output voltage of the operational amplifier 211 and the voltage of the constant voltage source 216 are preferably transmitted by parallel two wires.

Next, the internal configuration of the drivers 100 _{1 to} 100 ₃₂ will be described with reference to FIG. Since each of the drivers 100 _{1 to} 100 ₃₂ has the same configuration, the subscripts ₁ to ₃₂ will be omitted below and will be described simply as the driver 100.

  The driver 100 has two multipliers 21 and 22. The multiplier 21 is provided for controlling the current source 30, and the multiplier 22 is provided for controlling a corresponding one of the capacitors Cd1 to Cd32 shown in FIG. Hereinafter, for convenience, one corresponding capacitor is denoted by Cd, and is shown by a broken line in FIG. The capacitor Cd functions as a voltage source for a short time when the drive voltage to the laser rises. The current source 30 generates a current that flows through the corresponding light emitting element LD, and the capacitor Cd that functions as a voltage source supplies a driving voltage to the corresponding light emitting element LD.

  Here, the relationship between the driving current and the driving voltage (terminal voltage) of the surface emitting laser (voltage-current characteristics) is proportional (linear relationship) in a practical range because the internal resistance of the surface emitting laser is high. Further, the relationship between the drive current and the laser light quantity is also proportional (linear relationship) within a practical range. Based on such characteristics, the current amount of the current source 30 in the first APC control is determined so that the laser light amount of the light emitting element LD becomes the reference light amount (first light amount). In the second APC control, the laser amount is determined. The amount of light is determined to be the second amount of light. Similarly, the driving voltage accumulated in the capacitor Cd in the first APC control is determined so that the laser light amount of the light emitting element LD becomes the reference light amount (first light amount), and the laser light amount is the second in the second APC control. The amount of light is determined. By the interpolation or extrapolation process using these two values, the laser light quantity can be corrected to an arbitrary light quantity.

  Multipliers 21 and 22 can use 4-quadrant analog multipliers, and capacitors can be used as voltage sources to be connected to the multipliers. The inputs of the multipliers 21 and 22 have a differential configuration. Assuming that two differential inputs represented by + and − of each multiplier 21 and 22 are V1a, V1b and V2a and V2b, respectively, each multiplier 21 and 22 having a differential configuration has Iout = α (V1a−V1b). The current described by (V2a-V2b) is output. Where α is a constant.

  In such a laser driving device, a correction signal is input to one input terminal (multiplier terminal) of each multiplier 21 and 22, and a control voltage is input to the other input terminal (multiplier terminal). When the + side output of the complementary output of a multiplier that is normally configured as a differential is used, there is an offset current, but even if there is an offset in each of the multipliers 21 and 22, the capacitors C1 and C2 connected to the output are used. The offset is canceled during APC. The correction signal takes into consideration the situation where the laser light quantity varies depending on the scanning position of the laser beam, and has a control voltage corresponding to the scanning position of the laser beam.

  First, by the first APC control, the first light amount (set as a reference value) is set as follows. Switch SWSa is on, SWSb is off, SW1 is off, SW2 is off, SW3 is off, SW5-1 is on, SW5-2 is off, SW5-3 is off, SW5-4 is on, SW6-1 is on SW6-2 is off, SW6-3 is off, SW6-4 is on, SW7 is off, SW8 is on, SW11 is on, SW11-1 is on, SW11-2 is off, SW12 is off, SW13 is on , SW15-1 is turned off, SW15-2 is turned on, SW16 is turned off, and the switch SWSa is turned on. Further, when setting the first light quantity, a 0 V correction signal is applied to the multiplier terminals of the multipliers 21 and 22. In this state, since the multiplier is 0, each multiplier 21 and 22 outputs an offset voltage regardless of what control voltage is input to the multiplicand terminal. Further, the first APC reference voltage Vref1 is supplied to the operational amplifier 61 of the APC circuit 600 shown in FIG. The operational amplifier 61 outputs a control voltage so that the laser light amount of the light emitting element LD becomes the first APC reference voltage Vref1. This control voltage is supplied to the current source 30 through the switch SW8, the operational amplifier 26, the inverter 28, and the switch SW11 of FIG. The current source 30 supplies a current corresponding to the received control voltage to the light emitting element LD. The control voltage output from the operational amplifier 26 is stored in the capacitor C3-1 of the sample and hold circuit. Since the correction signal is set to 0V, the multiplier 21 outputs an offset voltage. Therefore, the capacitor C1 is charged with a difference voltage between the control voltage and the offset voltage output from the multiplier 21. On the other hand, the control voltage output from the operational amplifier 61 of FIG. 1 is supplied to the capacitor C2 and stored in the capacitor C4-1 of the sample and hold circuit. Since the correction signal is set to 0V, the multiplier 22 outputs an offset voltage. Therefore, the capacitor C2 is charged with a difference voltage between the control voltage and the offset voltage of the multiplier 22.

  Then, the second light quantity (this is called a correction light quantity) is set as follows by the second APC control. Switch SWSa off, SWSb off, SW1 off, SW2 off, SW3 off, SW5-1 off, SW5-2 on, SW5-3 on, SW5-4 off, SW6-1 off SW6-2 is on, SW6-3 is on, SW6-4 is off, SW7 is off, SW8 is off, SW11 is off, SW11-1 is on, SW11-2 is off, SW12 is off, SW13 is on , SW15-1 is off, SW15-2 is off, SW16 is off, and SWSa is off. Further, when setting the second light quantity, a correction signal having a predetermined voltage is applied to the multiplier terminals of the multipliers 21 and 22. Further, since the switch SWSa is off, the operational amplifier 61 outputs a control voltage for the first APC control so that the amount of light from the light receiver PD increases by the amount of current added by the current source 450. This control voltage is supplied to the current source 30 through the switch SW8, the operational amplifier 26, the inverter 28, the switches SW5-2 and SW5-3, the multiplier 21, the resistor R11, and the capacitor C1 in FIG. The current source 30 changes the current from the light receiver PD from the reference current to a current obtained by adding the addition current to the reference current in accordance with the received control voltage. The control voltage output from the operational amplifier 26 is stored in the capacitor C3-2 of the sample and hold circuit. The capacitor C1 is charged with a voltage difference between the control voltage and the output of the multiplier 21. The current applied to the light emitting element LD in the first APC control can be described as I + ΔI. On the other hand, the control voltage output from the operational amplifier 61 in FIG. 1 is supplied to the capacitor C2 and stored in the capacitor C4-2 of the sample and hold circuit. The capacitor C2 is charged with a voltage difference between the control voltage and the output of the multiplier 22. If the voltage stored in the capacitor C2 in the first APC control is V, the voltage stored in the capacitor C2 in the second APC control can be described as V + ΔV.

  Here, the switches SW6-1 and SW6-4 are turned on, and SW6-2 and SW6-3 are turned off. However, in the second and subsequent APCs, SW6-3 and SW6-1 are turned on, and SW6-2 and SW6-4 are turned off. Since this is the same condition as during modulation, an improvement in accuracy can be expected.

  At the time of modulating the light emitting element LD, a correction voltage corresponding to the light amount correction amount corresponding to the scanning position of the laser light is input to the multiplier terminals of the multipliers 21 and 22. Thereby, both the drive voltage applied to the surface emitting laser from the voltage source constituted by the multiplier 22, the capacitor C2, and the operational amplifier 26 and the drive current supplied from the current source 30 to the light emitting element LD are simultaneously controlled. The light emitting element LD emits light with a light amount corrected according to the scanning position of the laser light.

  A resistor R11 is connected in series with the capacitor C1. That is, in this embodiment, the sample and hold circuit 110 including the capacitor C1 is configured with a low-pass filter. Thereby, the high frequency noise which generate | occur | produces when switching on / off of switch SW11 can be suppressed. In addition, a capacitor C11 is connected in parallel to this low-pass filter. Thereby, it is possible to prevent the phase of the negative feedback loop from being delayed by the time constant of the low-pass filter. Similarly, by connecting a resistor R21 in series with the capacitor C2, the sample and hold circuit 220 including the resistor R21 is configured by a low-pass filter. Thereby, the high frequency noise which generate | occur | produces when switching on / off of switch SW8 can be suppressed. Further, a capacitor C22 for preventing the phase delay of the negative feedback loop is connected in parallel to the low-pass filter composed of the capacitor C2 and the resistor R21 to prevent oscillation in the negative feedback loop.

  The voltage application time adjustment circuit 800 controls the switch SW2 to adjust the time for applying a voltage to the light emitting element LD. This voltage is a voltage accumulated in the capacitor Cd. As described above, in this embodiment, the light emitting element LD is driven by controlling both the voltage and current applied to the light emitting element LD. When the light emitting element LD is driven, it is first driven with a voltage and then with a current. By making the voltage application time for voltage drive adjustable, the voltage application time according to the mounting state of the light emitting element LD can be appropriately set as in the case where the wiring from the LDOUT end to the laser in FIG. Can be set.

  The voltage application time adjustment circuit 800 has two sets of delay circuits 81 and exclusive OR circuits 82. The two delay circuits 81 are connected by an inverter 83 as shown in the figure. The delay circuit 81 receives the voltage application time signal and the modulation signal, and delays the modulation signal according to the voltage application time signal. The exclusive OR of the output signal of one delay circuit 81 and the modulation signal is taken, and the switch SW2 is turned on by the output signal. As a result, the output signal has a first pulse rising at the rising edge of the modulation signal, a first pulse falling at the rising edge of the delayed modulation signal, and a second pulse falling at the falling edge of the delayed modulation signal. appear. That is, the voltage is applied at the rise and fall of the modulation signal with the same pulse width as the delay time of the delay circuit 81. In this way, it is possible to set an appropriate voltage application time. Similarly, the switch SW1 is controlled by the action of the other delay circuit 81 and the exclusive OR circuit 82 to supply an OFF bias, thereby controlling the operation of the light emitting element LD from on to off (speeding up).

  The current generation circuit 700 receives the differential voltage for each current output from the common control potential setting circuit 200 shown in FIG. 1 and outputs a current corresponding to the differential voltage. The operational amplifier 34 and the constant current source 32 of the current generation circuit 700 receive a differential voltage formed by the reference common potential and the reference offset potential, and generate an offset current corresponding to the differential voltage. The offset current flows to the load 24 via the switch SW16. The terminal potential of the capacitor C2 is determined in accordance with the offset current, whereby the driving voltage applied to the light emitting element LD by the capacitor C2 functioning as a voltage source can be adjusted. By adjusting the drive voltage, you can overshoot the drive pulse and follow the laser to a short pulse width to improve the reproducibility of highlights, and by setting the drive voltage slightly higher, the image outline can be It can also be used for image quality adjustment by appropriately setting these according to the image, such as emphasis. The operational amplifier 35 and the current source 31 receive the differential voltage formed by the reference common potential and the reference bias potential via the switch 750, and generate a bias current according to the differential voltage. Further, the current source 31 that has received the OFF bias voltage set by the voltage source in the drawing connected to the switch 750 generates a laser drive current according to the OFF bias voltage.

  In this embodiment having the above configuration, when a part of the light emitting elements LD fails or when only some of the light emitting elements LD are used, APC is performed on the failed or unused light emitting elements LD. The purpose is to ensure the APC accuracy that deteriorates to the same level as when all the light emitting elements are used.

  The deterioration of APC accuracy is due to the fact that when the light intensity control is performed on a faulty or unused light emitting element, the control voltage increases to match the reference light intensity even though it does not emit light, and the operational amplifier for monitoring the light intensity swings out. As a result, the start voltage at the time of controlling the light amount of the next light emitting element is high, resulting in deterioration of convergence.

  Therefore, in this embodiment, the APC circuit (control unit) 600 is provided with an APC order control circuit 1005 for setting the APC order of each light emitting element, and the APC order of unused (including faulty) light emitting elements is postponed.

  In addition, a control signal for controlling execution or non-execution of APC control can be set for each light emitting element by the APC order control circuit 1005. Based on this signal, the APC order of unused (including faulty) light emitting elements is set. When this happens, the level of the input voltage of the operational amplifier, which causes the APC accuracy deterioration, is held at the previous level.

  FIG. 4 shows the configuration of an APC sequence control circuit 1005 that sets the order of APC control by controlling the switches SWfb1 to SWfb32 connected to the operational amplifier 61 shown in FIG. Shift register 1000 provided corresponding to the plurality of light emitting elements, latch circuits 1001 (1) to 1001 (32), counter 1002, and comparators 1003 (1) to 1003 provided corresponding to the plurality of light emitting elements. (32) and an output control unit 1004 that controls ON and OFF of the switches SWfb1 to SWfb32.

  For example, APC execution order information of each light emitting element is input from a CPU (not shown) or the like. The APC execution order information is transferred as serial data as data for all light emitting elements and is input to the shift register 1000. The input data is sequentially transferred and output to the latch circuits 1001 (1) to 1001 (32) that accumulate information for each light emitting element. When an APC clock is input during execution of APC, the counter 1002 starts counting. Each comparator 1003 (1) to 1003 (32) outputs the output of the counter 1002 and latch circuits 1001 (1) to 1001. The value of (32) is compared, and the output of the matched comparator 1003 transitions (for example, high level), and APC of the corresponding light emitting element is executed.

  FIG. 5 shows a control signal output from the output control unit 1004 when a failure occurs in the third laser. The failure determination is made by a determination circuit (not shown) at the previous execution of APC, and information is transferred to the CPU as a failure laser. For example, even when the applied current value is set to the maximum, the failure is determined when the reference light amount is not reached or when the preset maximum applied current value is exceeded. Based on this information, the CPU sets APC execution order information and transfers it to the drive circuit. When the output control unit 1004 turns on the control signals LD1 to LD32 at a predetermined timing, the corresponding switches SWfb1 to SWfb32 are turned on. When the switches SWfb1 to SWfb32 are turned on, voltages when the laser light amounts of the corresponding light emitting elements LD1 to LD32 converge to a value corresponding to the APC reference voltage Vref are accumulated in the capacitors Cfb1 to Cfb32. FIG. 5A shows a control signal when all of the light emitting elements LD1 to LD32 are normal.

  FIG. 5B shows a control signal when a failure occurs in the light emitting element LD3. When the order of APC control is set last by a setting signal from a CPU (not shown), the switch SWfb3 is turned last without being turned on. As shown in FIG. 5B, the control signal LD4 is turned on next to the control signal LD2, and the switch SWfb4 is turned on. As a result, the start voltage at the time of APC control of each laser is not so large although there is a variation in the light emitting elements, and the convergence is not deteriorated. Note that for the next APC period, the switch SWfb32 of the LD32 is controlled to maintain the hold state.

  FIG. 5C shows an example in which only the switches SWfb1 to SWfb32 are controlled without changing the order. Since the light emitting element LD3 is out of order, the switch SWfb2 of the LD2 is held until the order of the LD4. That is, in the circuit of FIG. 2, setting information is input to the shift register 800 (2) corresponding to the switch Wfb2 so as to be turned on at the second and third positions. In the comparator 1003 (2), the count value of the counter 1002 is the same between the second and third counters, and therefore a signal for turning on the switch SWfb2 is output at this timing.

  The above can be applied to the case of using a different number of units, although it corresponds to a failure. If the number of light emission is changed according to the system (resolution, speed), it will be costly to manufacture the light source and circuit each time. By using the present invention, it becomes possible to cope with variable number.

  For example, when only the even-numbered 16 light-emitting elements among the 32 light-emitting elements are used, the register is rewritten so that the even-numbered light-emitting elements are assigned up to the first 16 and the odd-numbered light-emitting elements are assigned to the back 16. As a result, even if only 16 are used, they are not affected by the APC of the unused elements. Further, in this case, for example, if the APC period setting control signal (not shown) is controlled to stop at the end of 16 APC periods, the APC period can be halved.

  Further, the same APC accuracy can be secured only by not executing odd-numbered APCs. At this time, the APC period cannot be shortened, but it is not necessary to change other control signals only by rewriting the register value.

  The embodiment described above is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention. For example, in this embodiment, the APC order is described as being variable only in accordance with the faulty element. However, the order of the faulty element is further changed after making the order variable by correlating with other purposes, for example, the light quantity variation of the light emitting element. May be.

It is a circuit diagram which shows the whole structure of a light emitting element drive device. It is a circuit diagram which shows the structure of the driver 100 of a light emitting element drive device. It is a figure which shows the structural example of the laser scanning system in the laser xerography which is an aspect of an image forming apparatus provided with a light emitting element drive device. It is a figure which shows the structure of the circuit part which sets the order which performs APC. It is a figure showing the control signal output from the output control part 804. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 18 Light emitting element drive device 105 Load 10d Laser light source 11 Light receiver 12 Polygon mirror 13, 14, 15 Lens 16 Photoconductor surface 17 SOS sensor 21, 22 Multiplier 28 Inverter 23, 24, 214, 215 Load 81 Delay circuit 82 Exclusive OR circuit 150 Bus 100 _{1 to} 100 ₃₂ , 100 Driver PD Receiver 200 Common control potential setting circuit 216 Constant voltage source 230 Voltage source 250 Correction circuit 252 253 Current mirror circuit 212 213 Constant current source 300 Current amplifier 400 Light intensity monitor 500 Forced lighting circuit 600 APC circuit 700 Current generation circuit 800 Voltage application time adjustment circuit 26, 34, 35, 61, 211, 251 Operational amplifier (op amp)
30, 31, 32, 32 ′, 450, 460 Current source 110, 220 Sample hold circuit 1000 Shift register 1001 Latch circuit 1002 Counter 1003 Comparator 1004 Output control unit 1005 APC sequence control circuit LD1 to LD32 Light emitting element Vref, Vref1, Vref2 APC reference voltage COUT, LDOUT, LDCOM terminals R2, R3, R11, R21, R31, R32, R33, R34 Resistors C1, C2, C3-1, C4-1, C3-2, C4-2, C11, C22, Cd , Cd _{1 to} Cd ₃₂ , Cfb32 to Cfb32 Capacitors SW1, SW2, SW3, SW5-1, SW5-2, SW5-3, SW5-4, SW6-1, SW6-2, SW6-3, SW6-4, SW7 , SW8, SW11, SW11-1, SW11-2, SW12 SW13, SW15-1, SW15-2, SW16, SW19, SWfb1~SWfb32 switch Tr1, Tr3, Tr31, Tr33, Tr36 P-MOS transistor Tr32, Tr34, Tr35 N-MOS transistor

Claims (7)

A plurality of light emitting elements;
Light detection means for detecting the light amount of the light emitting element;
A controller that sequentially generates control voltages for causing the light amounts of the light emitting elements to match the target light amounts,
Driving means for driving the light emitting element based on the control voltage,
The said control part changes the order which produces | generates the said control voltage about each light emitting element based on the light quantity of each light emitting element detected by the said light detection means, The light emitting element drive device characterized by the above-mentioned.   The light-emitting element driving apparatus according to claim 1, wherein the control unit sequentially generates the control voltage for the light-emitting elements that can obtain a predetermined light emission amount.   The light-emitting element driving apparatus according to claim 1, wherein the control unit controls the light-emitting element that cannot obtain a predetermined light emission amount so that the light amount control is not performed.   4. The light emitting device according to claim 1, wherein the control unit controls the light amount control of the failed light emitting device after the light emitting device that operates normally. 5. Drive device.   The control unit is configured to set the control voltage of the light emitting element that has been normally completed to be used as the control voltage of the failed light emitting element during the light amount control for the failed light emitting element. The light emitting element drive device of any one of 1-3. A sample hold circuit that holds the control voltage generated by the control unit is provided corresponding to the plurality of light emitting elements,
The control unit selects the sample hold circuit of the light emitting element immediately before the light emitting element when controlling the light quantity of the light emitting element that does not perform the light quantity control, and controls the light intensity control using the control voltage held in the sample hold circuit. 6. The light emitting element driving device according to claim 5, wherein the control voltage of the light emitting element is not used.   An image forming apparatus for driving a laser element using the light emitting element driving apparatus according to claim 1.

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