JP2008290355A - Printing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing apparatus capable of improving printing quality. <P>SOLUTION: Characteristics of a laser unit is grasped by means of a laser output adjusted at the time of shipment from a factory and a monitor current of the laser output, which enables desired setting of a laser output to be continuously switched, thereby performing control with a desired laser output. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  According to the present invention, in a printing apparatus that creates a latent image on a photosensitive member by irradiating the photosensitive member with a laser, the control unit of the printing apparatus measures a laser characteristic at a preset value, and the measurement is performed. The present invention relates to a printing apparatus that performs laser power control using characteristics of a laser.

  FIG. 5 is a sectional view showing the structure of a semiconductor laser unit used in an electrophotographic apparatus such as a laser beam printer. In this figure, 16 is a semiconductor laser (laser diode), 17 is a base metal plate supporting the semiconductor laser 16, 18 is an electrical insulating material, and 19 is a divergent light beam from the semiconductor laser 16 that is converted into a parallel light beam. The collimator lens 20 includes an aperture for beam shaping, and 21 indicates a printer circuit board (PCB). These are assembled as an integral unit to constitute a semiconductor laser unit 22.

  FIG. 6 is a block diagram showing a state in which the semiconductor laser unit 22 is mounted on an image forming apparatus such as a laser printer to form a feedback control loop.

  In this figure, reference numeral 26 denotes a photodiode for monitoring the light emission output of the semiconductor laser 16, and the monitor current is input to the monitor output amplifier 23.

  The comparator 28 and the drive circuit 29 are provided on an external board other than the laser unit. The comparator 28 compares the output voltage Vm of the monitor output amplifier 23 with the internal reference voltage Vr output from the reference voltage generation circuit 25, A drive circuit 29 that emits light by supplying a drive current to the semiconductor laser 16 is controlled so that both voltages match.

  As shown in FIG. 7, the monitor output amplifier 23 includes an operational amplifier 31 and a gain adjusting variable resistor 32 forming a feedback circuit thereof.

  Further, as shown in FIG. 8, the reference voltage generating circuit 25 includes a resistor 33 and a Zener diode 34 connected in series between the power supply terminal to which the power supply voltage Vcc is supplied and the ground, and the Zener voltage of the Zener diode 34 is Is output as the internal reference voltage Vr.

  As described above, the semiconductor laser unit 22 is integrally provided with the output amplifier 23 and the reference voltage generation circuit 25 capable of gain adjustment, and the output voltage Vm of the monitor output amplifier 23 is previously determined for each semiconductor laser unit. When the output power of the semiconductor laser 16 reaches a predetermined value (standard setting power) on the photosensitive member, the gain is adjusted so as to coincide with the internal reference voltage Vr, and the reference voltage generation circuit 25 is set. deep. As a result, there is no need to make an on-site adjustment when replacing the semiconductor laser unit.

  In the manufacturing stage of the semiconductor laser unit 22, the following adjustment is performed for each semiconductor laser unit 22. In FIG. 6, part of the laser light emitted from the semiconductor laser 16 is also incident on the monitor photodiode 26, and the monitor current is input to the monitor output amplifier 23.

  Here, the laser beam emitted from the semiconductor laser 16 is also measured by the power meter 35 arranged so as to be received on the photosensitive member, and a predetermined standard setting power is obtained while checking the measured value. The variable resistor 32 for gain adjustment of the monitor output amplifier 23 is adjusted. The reference voltage generation circuit 25 is set so that a voltage (same voltage) corresponding to the output voltage Vm of the monitor output amplifier 23 when the standard set power is obtained is generated as the internal reference voltage Vr. For example, the Zener voltage of the Zener diode 34 shown in FIG. 8 is selected.

  As described above, even when the adjusted semiconductor laser unit 22 is used and the laser unit 22 is replaced in maintenance work after product shipment, the power meter 35 is not used and the laser printer main body side shown in FIG. By connecting the semiconductor laser unit 22 to the comparator 28 and the driving circuit 29, the output voltage Vm of the monitor output amplifier 23 is compared with the reference voltage Vr generated from the reference voltage generating circuit 25 by the comparator 28. The current selected to make the difference zero is supplied from the drive circuit 29 to the semiconductor laser 16 so that the output of the semiconductor laser 16 is controlled so that the output voltage Vm of the monitor output amplifier 23 matches the internal reference voltage Vr. The standard setting power is obtained.

  For example, the following patent documents can be cited regarding this type of technology.

Japanese Patent No. 2839889

  In the laser control method shown in the background art, the reference value for laser output control is a fixed value in which the laser output is set in advance using a laser output meter. Therefore, depending on the actual usage situation, for example, if you want to increase the laser intensity when you want to make the print density higher than the value adjusted at the time of shipment, install a laser output meter at the position where the laser light hits and adjust it to match the laser output Therefore, it is difficult to change the laser output to the operating state after product shipment.

  For example, it is possible to switch the laser output by mounting and switching a plurality of reference voltages as reference values for laser output control, but only the setting corresponding to the reference voltage value mounted in advance, the type of paper and It was insufficient for the purpose of use. For this reason, the operator cannot change the laser output, and when adjusting the print density and contrast, the voltage of the developing bias and the charger voltage for exposing the photosensitive member are changed. When the developing bias voltage and the charger voltage are changed, the whole printing often becomes thin or fog occurs, and high quality printing is difficult.

  An object of the present invention is to eliminate such drawbacks of the prior art and provide a printing apparatus having excellent print quality.

  In order to achieve the above object, a first means of the present invention is a printing apparatus that creates a latent image on a photoconductor by irradiating the photoconductor with a semiconductor laser, and performs power control in consideration of the slope efficiency of the semiconductor laser. It is characterized by doing.

  According to a second means of the present invention, in the first means, the power control includes a characteristic of a photodiode or a phototransistor for detecting a laser emission intensity, and an individual difference in a transfer coefficient between the laser diode and the photodiode or the phototransistor. The laser output is controlled by correcting that the monitor current of the photodiode or phototransistor differs even when the laser emission intensity is the same.

  The laser output control of the present invention stores the relationship between the laser output adjusted at the time of factory shipment and the monitor current of the laser output, and calculates the monitor current output at the desired laser output by grasping the characteristics of the laser unit. By controlling with the laser output that outputs the calculated monitor current, it is possible to control with an arbitrary laser output and improve the print quality.

  In the present invention, it is possible to grasp the characteristics of the laser unit from the laser output adjusted at the time of shipment from the factory and the monitor current of the laser output, and to continuously switch the desired laser output setting. It becomes possible.

  The relationship between the laser output and the monitor current of the laser output is stored, the monitor current output at the desired laser output is calculated by grasping the characteristics of the laser unit, and the calculated monitor current is output by the laser output. Control was realized with a simple circuit.

  An embodiment of the present invention will be described with reference to FIGS. 1 is a schematic flowchart of laser output control in the present invention, FIG. 2 is a block diagram of laser output control, FIG. 3 is a characteristic diagram of laser current and laser output, and FIG. 4 is a characteristic diagram of laser output and monitor current.

  In the present invention, first, the monitor current at the time of a specific laser output of the laser unit is recorded in the control unit. FIG. 1 illustrates a power adjustment method using a monitor current at the time of outputting a specific laser. When the laser unit is activated, a transfer function is calculated from the monitor current at the time of specific laser output (Step 1). Next, the monitor current is calculated under the conditions of actual use from the calculated transfer function and the value of the laser output that is actually desired (Step 2). Next, laser output adjustment is performed so that the monitor current value calculated in the monitor current calculation matches the actual monitor current (Step 3).

  The fact that the monitor current matches the value calculated for the monitor current means that the laser output is actually desired to be used. In printers that use laser beams, the laser output power is periodically adjusted during printing. If you do not want to change the actual laser output settings, record the monitor current once calculated. The process of calculating the power transfer function and the monitor current can be omitted.

  FIG. 3 is a characteristic diagram showing the relationship between the current of the laser diode 14 and the laser output. As shown in this figure, when the laser exceeds the threshold current, the output increases. Above the threshold, the laser current and the laser output show a substantially linear relationship, but the slope efficiency indicating the relationship between the threshold current and the current and the laser output is the laser efficiency. There are individual differences and it is not constant.

  FIG. 4 is a characteristic diagram showing the relationship between laser output and monitor current. As shown in this figure, when the laser output is 30 mW, the monitor current is 6 mA at the maximum and 4 mA at the minimum. Depending on the characteristics of the individual laser, the relationship between the laser output and the monitor current is not constant but proportional.

  The switching of laser output according to the present invention will be described with reference to a typical block diagram of the present invention shown in FIG. The present invention comprises a laser output arbitrary setting value 9, a laser characteristic storage unit 10, a laser emission circuit 11, an arithmetic circuit 12, a laser intensity setting circuit 13, and a control unit 5, and a laser driver 7 and a laser 8. The laser 8 includes a laser diode 14 and a photodiode 15 that monitors the emission intensity of the laser. In FIG. 2, the laser 8 has a laser diode 14 and a photodiode 15, but the present invention can be implemented even if the laser diode 14 and the photodiode 15 are separately provided.

  As shown in FIG. 3, the laser diode 14 does not emit light until the current reaches a certain threshold current. However, when the current exceeds the threshold current, the laser output and the current have a substantially proportional relationship, and the ratio of the current to the laser output at this time is a slope. It becomes efficiency. However, since the laser diode 14 has different threshold efficiency and slope efficiency due to individual differences, even if the current value is constant, the laser output varies depending on the laser diode 14. Therefore, even if feedback is performed with current, the output of the laser diode 14 cannot be kept constant, and the laser light is converted into current by the photodiode 15 in order to accurately control the laser output. The photodiode 15 converts the laser output into a current. As shown in FIG. 4, the photodiode 15 has a linear relationship between the laser output and the monitor current, and is a unique value of the laser unit 6.

  Therefore, in the characteristics shown in FIG. 4, the value of the laser output of 30 mW has a maximum monitor current of 6 mA and a minimum of 4 mA. Therefore, the characteristics of each laser unit 6 (monitor current I / laser output P) are important parameters of the individual laser units 6.

  Next, the control unit 5 will be described. The laser output arbitrary setting value 9 in the control unit 5 is a value that can be set by an operator or the like actually used, and is set from an operator panel (not shown) of the printing apparatus, or the printing apparatus itself has environmental conditions such as temperature and humidity. Is a value to detect and set The laser characteristic storage unit 10 is a part for storing the parameters (monitor current I / laser output P) of the laser unit 6, and a storage element such as NV-SRAM is used. The arithmetic circuit 12 is a part for calculating the value set to the laser output arbitrary set value 9 and the value of the laser characteristic storage unit 10, and the laser diode is calculated from (monitor current I / laser output P) × (laser output arbitrary set value). The monitor current of the photodiode 15 at the laser output arbitrary setting value 9 of 14 is calculated. Since the calculation is performed with digital data, analog conversion is performed by the D / A conversion circuit 13, and the monitor current of the photodiode 15 when the laser 14 emits light at the laser output arbitrary setting value 9 is output to the laser driver 7.

  The laser driver 7 is a laser driver that drives the laser diode 14 so that the calculated monitor current of the photodiode 15 matches the actual output of the photodiode 15. The laser output of the laser diode 14 is determined by the D / A conversion circuit 13. The laser is turned on / off by a signal from the laser drive signal generation circuit 11.

  In the present invention, since the control unit 5 has the characteristics of the laser 7, the desired power can be set to the laser output arbitrary setting value 9 and adjustment can be performed without using a tool such as a laser output meter. Further, the laser output can be switched with a resolution determined by the resolution capability of the D / A conversion circuit 13. For example, if the D / A conversion circuit 13 is a 10-bit D / A converter, the laser output can be adjusted in 1024 stages.

  Therefore, fine adjustments such as adjusting the laser output weakly when the printing device wants to improve gradation such as printing an image such as a photo, and increasing the laser output when a clear contrast such as a barcode is required. It becomes possible. If the laser output arbitrary setting value 9 is displayed on the operator panel as an indicator bar or percentage number, it can be set according to the purpose of use by the operator himself, and high-quality printing can be achieved with multipurpose printing. realizable.

  High-quality printing can be realized by easily adjusting the laser intensity of an electrophotographic printing apparatus such as a laser beam printer or a copying machine.

It is a flowchart which shows the laser output adjustment in this invention. It is a typical block diagram of laser control of the present invention. It is a characteristic view which shows the relationship between the electric current of a laser diode, and a laser output. It is a characteristic view which shows the relationship between a laser output and a monitor current. It is sectional drawing of a semiconductor laser unit. It is a typical block diagram of the conventional laser control. It is a circuit diagram of a monitor output amplifier. It is a circuit diagram of a reference voltage generation circuit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 5 ... Control part, 6 ... Laser unit, 7 ... Laser driver, 8 ... Laser, 9 ... Laser output arbitrary setting value, 10 ... Laser characteristic memory | storage part, 11 ... Laser light emission circuit, 12 ... Arithmetic circuit, 13 ... D / A Conversion circuit, 14 ... laser diode, 15 ... photodiode, 16 ... semiconductor laser, 17 ... base metal plate, 18 ... electrical insulating material, 19 ... collimator lens, 20 ... aperture, 21 ... printer circuit board, 22 ... laser unit , 23 ... monitor output amplifier, 25 ... reference voltage generation circuit, 26 ... photodiode, 28 ... comparator, 29 ... drive circuit, 31 ... operational amplifier, 32 ... variable resistor for gain adjustment, 33 ... resistor, 34 ... zener diode 35 ... Power meter.

Claims (2)

  A printing apparatus for generating a latent image on a photosensitive member by irradiating the photosensitive member with a semiconductor laser, wherein the power control is performed in consideration of the slope efficiency of the semiconductor laser.   2. The printing apparatus according to claim 1, wherein the power control has the same laser emission intensity depending on characteristics of a photodiode or a phototransistor for detecting a laser emission intensity and an individual difference in a transfer coefficient between the laser diode and the photodiode or the phototransistor. However, the printing apparatus is characterized in that the laser output is controlled by correcting that the monitor current of the photodiode or the phototransistor is different.

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