JP2017069398A - Laser device and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to easily adjust the intensity of a laser beam even with the use of a variable resistance.SOLUTION: A laser device comprises: a laser beam emitting part; a monitor element that receives part of a laser beam and outputs a larger amount of current as a monitor current as the amount of reception of the laser beam becomes larger; a conversion part that converts the monitor current into a monitor voltage; and a driving circuit that controls a current to be caused to flow in the laser beam emitting part so that the monitor voltage becomes the same as a predetermined control voltage. The conversion part includes a parallel circuit including a variable resistance and a fixed resistance, and the variable resistance and fixed resistance are connected in parallel to the monitor element. The voltage between the monitor element and parallel circuit is input to the driving circuit as the monitor voltage.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a laser device and an image forming apparatus including an exposure device including the laser device.

  A laser emitting element such as a laser diode may be mounted on a device that scans an object with light. For example, a laser may be used in an apparatus that scans and reads an object. Some image forming apparatuses such as multifunction peripherals, copiers, printers, and facsimiles use a laser for exposure of a photosensitive drum. In order to accurately perform various types of scanning, it is preferable that the laser light amount (laser output) is stable. Patent Document 1 describes a method for controlling a semiconductor laser device for constantly stabilizing laser output.

  Specifically, in Patent Document 1, the amount of light of a semiconductor laser that can be controlled by current is monitored, and the amount of light of the semiconductor laser is feedback-controlled with a required time constant. A semiconductor laser control method is described in which the amount of light of the semiconductor laser is feedback-controlled with a first time constant, and when the amount is larger than a predetermined amount of light, the amount of light of the semiconductor laser (11) is feedback-controlled with a second time constant. Further, the second time constant is set to be longer than the first time constant. Thus, the laser output is corrected not at a rapid speed but at an appropriate change speed (Patent Document 1: Claims 1, 9, paragraphs [0083] to [0086]).

Japanese Patent Laid-Open No. 06-275896

  In order to adjust the light intensity (light quantity) of the laser light emitting element, a variable resistor may be provided. In principle, the amount of current flowing through the laser light emitting element is adjusted by changing the resistance value of the variable resistor to adjust the amount of light. The resistance value of the variable resistor is adjusted to a resistance value that provides a desired light amount.

  Due to reasons such as ease of use and low price, variable resistors of a type in which the resistance value is proportional to the amount of operation are widely distributed. For example, in a volume type variable resistor, a variable resistor whose amount of change in resistance value is constant (linear) with respect to a rotation angle change of 1 degree of the knob is widely used. In other words, variable resistors having a constant slope of change in resistance value with respect to the rotation angle are widely used.

  The amount of laser light corresponds to the amount of current flowing through the light emitting element. The greater the current, the greater the amount of light. The smaller the current, the smaller the amount of light. Here, when the voltage is constant, the magnitude of the current flowing through the variable resistor is basically determined by the voltage / resistance value. The parameter of the resistance value is located in the denominator of the basic equation of current change.

  Therefore, when a variable resistor having a proportional change in resistance value with respect to the manipulated variable is used, the current changes in inverse proportion to the change in resistance. For this reason, the change in the amount of laser light with respect to the operation amount (rotation angle) of the variable resistor may be inversely proportional. From such an inversely proportional relationship, there is a region in which the amount of light changes greatly only by slightly operating the variable resistor in the variable range of the resistance value of the variable resistor.

  For this reason, when the amount of light corresponding to the resistance value in the region where the amount of light changes greatly is the amount of light that is desired to be output, it is difficult to adjust the amount of laser light, and adjustment takes time.

  In the invention described in Patent Document 1, it is intended to output a constant amount of light stably. However, the voltage input to the operational amplifier 38 is adjusted by the variable resistor 37 (see Patent Document 1: FIG. 9). Therefore, the variable resistor 37 has a resistance value region in which the current changes greatly with a few operations. Therefore, the above problem cannot be solved.

  In view of the above problems, the present invention makes it possible to easily adjust the light amount of a laser light emitting element even when a variable resistor is used.

  In order to achieve the above object, a laser apparatus according to claim 1 includes a laser light emitting section, a monitor element, a conversion section, and a drive circuit. The monitor element receives a part of the laser light emitted from the laser light emitting unit and outputs it as a monitor current, and the more the monitor current flows, the more the monitor current flows. The converter is connected to the monitor element and converts the monitor current as a monitor voltage. The drive circuit includes a drive circuit that receives a control voltage of a predetermined magnitude and controls a current that flows through the laser light emitting unit so that the control voltage and the monitor voltage are the same. The conversion unit includes a parallel circuit including a variable resistor and a fixed resistor, and the variable resistor and the fixed resistor are connected in parallel to the monitor element. A voltage between the monitor element and the parallel circuit is input to the drive circuit as the monitor voltage.

  According to the present invention, it is possible to easily adjust the basic light amount of the laser light emitting element even if a variable resistor is used.

1 is a diagram illustrating an example of a printer according to an embodiment. It is a figure which shows an example of the exposure apparatus which concerns on embodiment. It is a figure which shows a part of exposure apparatus which concerns on embodiment. It is a figure which shows an example of the laser apparatus which concerns on embodiment. It is a figure which shows an example of the variable resistance which concerns on embodiment. It is a figure which shows an example of the relationship between the change of the resistance value of a variable resistance, and the operation amount. It is the figure which removed the fixed resistance intentionally from the laser apparatus of FIG. It is a figure which shows an example of the light quantity change of the laser diode with respect to the change of the resistance value of a variable resistance when not providing a fixed resistance in a conversion part. It is a figure which shows an example of the light quantity change of the laser diode with respect to the change of the rotation angle of a knob when not providing a fixed resistance in a conversion part. It is a figure which shows an example of the change of the combined resistance value of the conversion part with respect to the change of the rotation angle of the knob of a variable resistance. It is a figure which shows an example of the light quantity change of a laser diode with respect to the change of the rotation angle of a knob in the case of providing a fixed resistance in a conversion part. It is a figure which shows an example of a modification.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. The present invention relates to a laser device 11. Further, the laser apparatus 1 relates to being included in the exposure apparatus 2. The exposure apparatus 2 is mounted on various image forming apparatuses such as a multifunction peripheral, a copier, and a FAX apparatus. In this description, a printer 100 including the exposure apparatus 2 (corresponding to an image forming apparatus) will be described as an example. However, the elements of the configuration and arrangement described in the present embodiment do not limit the scope of the invention and are merely illustrative examples.

(Schematic configuration of image forming apparatus)
First, the outline of the printer 100 according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating an example of a printer 100 according to the embodiment.

  As shown in FIG. 1, the printer 100 includes a storage unit 3 and a control unit 4. The control unit 4 controls each unit of the printer 100. The control unit 4 includes a CPU 41 that performs various calculations and an image processing unit 42 that generates image data used for printing. The CPU 41 performs control and calculation of each unit of the printer 100 based on a control program and control data stored in the storage unit 3. The storage unit 3 is a combination of a volatile storage device such as a RAM and a nonvolatile storage device such as a ROM or HDD.

  The control unit 4 controls the printing unit 5 (paper feeding unit 5a, conveyance unit 5b, image forming unit 5c, and fixing unit 5d) that performs printing by paper conveyance, toner image formation, transfer, and fixing. The control unit 4 performs control, calculation, and processing related to the portion included in the printing unit 5 based on the stored contents of the storage unit 3.

  The paper supply unit 5a stores a plurality of sheets, and sends out the sheets one by one at the time of printing. The transport unit 5b transports the paper supplied from the paper feed unit 5a. The image forming unit 5c includes a photosensitive drum 51 (see FIG. 3). The image forming unit 5c includes an exposure device 2 that scans the photosensitive drum 51 with a laser. The exposure apparatus 2 includes a laser apparatus 1. The exposure device 2 exposes the photosensitive drum 51 according to the image data. The image forming unit 5c transfers the toner image generated as a result of the exposure onto the conveyed paper. The fixing unit 5d heats and pressurizes the paper on which the toner image is transferred, and fixes the toner image on the paper. The paper that has passed through the fixing unit 5d is discharged to a discharge tray.

  Further, the control unit 4 recognizes the setting contents made on the operation panel 43 and recognizes the contents and settings of the job. The operation panel 43 displays the status of the printer 100, various messages, and setting screens, and includes a touch panel display panel (not shown). The operation panel 43 receives settings related to printing and the printer 100.

  A communication unit 44 is connected to the control unit 4. The communication unit 44 is an interface for communicating with the computer 200 such as a PC or a server. The communication unit 44 receives from the computer 200 print data including content data indicating print contents such as image data and text data and setting data indicating print setting contents. Then, the control unit 4 (image processing unit 42) generates image data used for printing based on the received printing data, and causes the printing unit 5 to perform printing based on the image data.

(Configuration of exposure apparatus 2)
Next, an example of the exposure apparatus 2 including the laser apparatus 1 according to the embodiment will be described with reference to FIGS. FIG. 2 is a view showing an example of the exposure apparatus 2 according to the embodiment. FIG. 3 is a view showing a part of the exposure apparatus 2 according to the embodiment.

  The exposure apparatus 2 is included in the printer 100. The exposure apparatus 2 is communicably connected to the control unit 4. The control unit 4 also operates as a part that controls the exposure apparatus 2. As shown in FIGS. 2 and 3, the exposure apparatus 2 is provided with a laser device 1, a polygon motor 21, a polygon mirror 22, an fθ lens 23 as an optical system member, and a beam detector 24.

  The laser device 1 emits a laser (beam) for scanning toward the photosensitive drum 51. As shown in FIG. 2, the laser device 1 includes a drive circuit 10 (laser diode 11 driver) and a laser diode 11 (corresponding to a laser light emitting unit). In accordance with the content of the image to be formed, the image processing unit 42 generates image data (light-on / off signal) instructing to turn on the laser in pixels on which toner is applied and instructing to turn off the laser in pixels on which toner is not applied . Then, the image data output unit 42 a of the image processing unit 42 transmits a turn-on / off signal to the drive circuit 10 of the laser apparatus 1. The drive circuit 10 turns on / off the laser diode 11 based on the image data (light on / off signal) received from the image processing unit 42.

  The polygon mirror 22 is a polygon mirror that reflects a laser. A collimating lens 25 for condensing the laser is provided between the laser diode 11 and the polygon mirror 22. The polygon mirror 22 is rotated at a high speed by the polygon motor 21. The laser diode 11 emits a laser toward the polygon mirror 22. The polygon mirror 22 reflects the laser from the laser diode 11 and moves it in the main scanning direction (see FIG. 3).

  An fθ lens 23 is provided on the optical path between the polygon mirror 22 and the photosensitive drum 51 to keep the scanning speed of the laser (moving speed of the laser irradiation position) on the photosensitive drum 51 constant (constant speed). (See FIG. 3). In addition to the fθ lens 23, another optical system member such as a mirror that changes the direction of the laser may be provided.

  Further, a beam detector 24 is provided within the laser irradiation range (scanning range) by the polygon mirror 22 and outside the irradiation range to the photosensitive drum 51. The beam detector 24 changes its output current (output voltage) when irradiated with a laser. The beam detector 24 is a light receiving element such as a photodiode or a phototransistor. The control unit 4 measures the predetermined time using the beam detection unit 24 as a trigger in order to make the positions of the leading dots coincide with each other. The control unit 4 starts scanning one line when a predetermined time has elapsed since the detection of the laser beam received by the beam detection unit 24.

(Laser device 1)
Next, the laser apparatus 1 will be described in the embodiment with reference to FIG. FIG. 4 is a diagram illustrating an example of the laser apparatus 1 according to the embodiment.

  The exposure apparatus 2 includes a laser apparatus 1. The laser device 1 includes, as a drive circuit 10 and a laser unit 13, a laser diode 11, a united photodiode 12 (corresponding to a monitor element), and a conversion unit 14.

  A power source is connected to the anode of the laser diode 11. The cathode of the laser diode 11 is connected to the drive circuit 10.

  The photodiode 12 receives a part of the laser light emitted from the laser diode 11. The photodiode 12 causes a larger amount of current to flow as the amount of received light increases. The photodiode 12 is an element for monitoring the light amount of the laser diode 11. The cathode of the photodiode 12 is connected to a power source. As shown in FIG. 4, the laser diode 11 and the photodiode 12 are connected in parallel to the power supply. On the other hand, the anode of the photodiode 12 is connected to the converter 14.

  The conversion unit 14 includes a parallel circuit 17 including a variable resistor 15 and a fixed resistor 16. The parallel circuit 17 (each of the variable resistor 15 and the fixed resistor 16) is connected to the photodiode 12 and the anode. The converter 14 is a circuit for converting the current (monitor current Io) flowing through the photodiode 12 into the monitor voltage V1. The generated monitor voltage V1 is input to the drive circuit 10.

  The drive circuit 10 receives a control voltage Vcont having a predetermined magnitude such as 1V. The control voltage Vcont is generated by the control voltage generator 18. The CPU 41 of the control unit 4 may generate the control voltage Vcont as the control voltage generation unit 18 and input it to the drive circuit 10. Further, a circuit for generating the control voltage Vcont such as a DA converter, a voltage dividing circuit, or a Zener diode circuit may be provided as the control voltage generating unit 18.

  Then, the drive circuit 10 controls the current flowing through the laser diode 11 so that the control voltage Vcont and the monitor voltage V1 are the same. The drive circuit 10 may include a current source 10 a such as one or a plurality of transistors that allows current to flow through the laser diode 11. Further, the drive circuit 10 may include a comparison circuit 10b that compares the control voltage Vcont and the monitor voltage V1. In addition, when the monitor voltage V1 is larger than the control voltage Vcont, the drive circuit 10 reduces the current that the current source 10a flows (current that flows through the laser diode 11), while the monitor voltage V1 is smaller than the control voltage Vcont. You may provide the current control circuit 10c which increases the electric current (current which flows into the laser diode 11) which the current source 10a flows. When the current control circuit 10c increases the current and light amount of the laser diode 11, the amount of light received by the photodiode 12 increases and the current of the photodiode 12 increases. When the current control circuit 10c decreases the current and the light amount of the laser diode 11, the amount of light received by the photodiode 12 decreases and the current of the photodiode 12 decreases.

  When one or a plurality of transistors are used as the current source 10a (voltage controlled current source 10a), the current control circuit 10c increases or decreases the voltage input to the base of the transistor, Control the size.

  The magnitude of the monitor voltage V1 is determined based on the current flowing through the photodiode 12. In a state where the combined resistance value R0 of the conversion unit 14 is fixed, the current flowing through the photodiode 12 increases as the light amount of the laser diode 11 increases, and decreases as the light amount of the laser diode 11 decreases. The current control circuit 10c increases or decreases the current of the laser diode 11 so that the monitor voltage V1 becomes a constant value (control voltage Vcont), and causes the laser diode 11 to emit light with a constant light amount. That is, the drive circuit 10 causes the laser diode 11 to emit light with a constant light amount.

  Even if the light emission efficiency of the laser diode 11 decreases due to aging, the drive circuit 10 increases the current flowing through the laser diode 11 more than before the efficiency decrease. As a result, the drive circuit 10 performs processing for keeping the light amount of the laser diode 11 constant.

(Outline of light amount adjustment of laser diode 11)
Next, an outline of light amount adjustment of the laser diode 11 according to the embodiment will be described with reference to FIGS. 4, 5, and 6. FIG. 5 is a diagram illustrating an example of the variable resistor 15 according to the embodiment. FIG. 6 is a diagram illustrating an example of a relationship between a change in the resistance value of the variable resistor 15 and the operation amount according to the embodiment.

  The laser is applied to the photosensitive drum 51. It is necessary to irradiate the photosensitive drum 51 with an appropriate amount of light. If the amount of light is too small, the photosensitive drum 51 is not properly exposed. As a result, the image quality is degraded. On the other hand, if the amount of light is too large, the life of the laser diode 11 tends to be shortened. Therefore, a target range (target light amount P1) of the light amount of the laser diode 11 is determined.

  Although the laser diode 11 emits a constant amount of light, the amount of light that is stably output itself is determined by the resistance value connected to the photodiode 12. When the resistance value of the conversion unit 14 cannot be varied at all, the magnitude of the monitor current Io when the monitor voltage V1 becomes equal to the control voltage Vcont is substantially fixed. On the other hand, the laser diode 11 has some variation in characteristics. If this variation cannot be accommodated and the resistance value of the conversion unit 14 cannot be varied, the light amount (intensity) of the laser irradiated on the photosensitive drum 51 may be outside the target range.

  Therefore, the conversion unit 14 of the laser device 1 includes a variable resistor 15 for adjusting the light amount of the laser diode 11. When the resistance value of the variable resistor 15 is increased, the combined resistance value R0 of the conversion unit 14 is increased. As a result, the monitor current Io becomes small. Therefore, the monitor voltage V1 and the control voltage Vcont have the same magnitude in a state where the light amount of the laser diode 11 is smaller than before the resistance value of the variable resistor 15 is changed. Therefore, when the target light amount P1 is adjusted so that the light amount of the laser diode 11 at the time of exposure is smaller than the current amount (when the light amount of the laser diode 11 is lowered), the resistance value of the variable resistor 15 is increased.

  On the other hand, when the resistance value of the variable resistor 15 is decreased, the combined resistance value R0 of the conversion unit 14 is decreased. As a result, the monitor current Io increases. Therefore, the monitor voltage V1 and the control voltage Vcont have the same magnitude in a state where the light amount of the laser diode 11 is larger than before the resistance value of the variable resistor 15 is changed. Therefore, when the target light amount P1 is adjusted so that the light amount of the laser diode 11 at the time of exposure is larger than the current amount (when the light amount of the laser diode 11 is increased), the resistance value of the variable resistor 15 is decreased.

  Actual adjustment is performed before shipment of the printer 100. A light amount measuring device (not shown) is prepared for adjusting the light amount of the laser diode 11. Using this measuring instrument, the variable resistor 15 is operated while checking the light quantity of the laser diode 11 by a predetermined measuring method. Then, the resistance value of the variable resistor 15 is set so that the light amount of the laser diode 11 becomes the target light amount P1 (so that it falls within the target range).

  In the printer 100 of the present embodiment, a volume type variable resistance whose resistance value changes when the knob 15 a is rotated is used as the variable resistor 15. This type of variable resistor 15 is sometimes referred to as a “variohm” or “potentiometer”.

  FIG. 5 shows an example of the variable resistor 15. The variable resistor 15 includes a circumferential resistor 15b inside. Further, it includes a movable terminal 15c that contacts the resistor 15b and slides on the upper surface of the resistor 15b in conjunction with the knob 15a. By moving the knob 15a, the position of the movable terminal 15c moves, and the length of the resistor 15b through which electricity flows changes. Thereby, the resistance value of the variable resistor 15 is changed by turning the knob 15a.

  As shown in FIG. 6, in the variable resistor 15 according to the embodiment, the rotation angle θ of the knob 15a and the resistance value are in a proportional relationship. The horizontal axis of FIG. 6 indicates the rotation angle θ of the knob 15a, and the vertical axis indicates the resistance value Rv of the variable resistor 15. As shown in FIG. 6, the gradient of the change amount of the resistance value Rv of the variable resistor 15 with respect to the change amount of the rotation angle θ of the knob 15a is constant. That is, the variable resistor 15 according to the embodiment has a B curve characteristic. The variable resistor 15 having the B curve characteristic can easily grasp how many ohms the knob 15a is positioned. Therefore, the variable resistor 15 having the B curve characteristic is widely used.

(Problem when the fixed resistor 16 is not provided in the conversion unit 14)
Next, problems when the fixed resistor 16 is not provided in the conversion unit 14 will be described with reference to FIGS. FIG. 7 is a diagram in which the fixed resistor 16 is intentionally removed from the laser device 1 of FIG. FIG. 8 is a diagram illustrating an example of a change in the light amount of the laser diode 11 with respect to a change in the resistance value of the variable resistor 15 when the fixed resistor 16 is not provided in the conversion unit 14. FIG. 9 is a diagram illustrating an example of a change in the light amount of the laser diode 11 with respect to a change in the rotation angle θ of the knob 15a when the conversion unit 14 is not provided with the fixed resistor 16.

First, each symbol shown in FIG. 7 is as follows.
I2: Monitor current at the target light quantity I3: Monitor current at the rated light quantity P1: Target light quantity P2: Rated light quantity Rv: Resistance value of the variable resistor 15 Here, the rated light quantity P2 is the rated current I3 in the specification of the laser diode 11 It is the amount of light on the specification when flowing.

First, from the relationship in which the amount of light changes according to the current, I2 can be determined as shown in (Equation 1) below.
(Formula 1) I2 = I3 × (P1 / P2)
Solving for P1 (Equation 2) P1 = I2 × P2 / I3
Further, from the relationship of control voltage Vcont = monitor voltage V1, Rv in the case where the fixed resistor 16 is not provided in the conversion unit 14 is expressed as (Equation 3) below.
(Formula 3) Rv = Vcont / I2
Solving for I2 (Equation 4) I2 = Vcont / Rv
Substituting (Equation 4) into (Equation 2) gives the following (Equation 5).
P1 = (Vcont × P2) / (Rv × I3)

  In (Expression 5), the resistance value Rv of the variable resistor 15 is in the denominator. If the conversion unit 14 is only the variable resistor 15, the target light amount P1 increases or decreases in an inversely proportional relationship with the resistance value Rv of the variable resistor 15, as shown in FIG.

  As shown in FIG. 6, the variable resistor 15 has a B curve characteristic (a characteristic in which the resistance value Rv changes linearly with respect to the rotation angle θ of the knob 15a). Therefore, as shown in FIG. 8, an angle in which the amount of change in the target light amount P1 is larger than the amount of change in the rotation angle θ in the rotation range of the knob 15a. That is, of the rotation range of the knob 15a, there is a range that is difficult to adjust because the light amount change is too steep when the knob 15a is operated.

  In FIG. 8, an example of the value of the target light amount P1 is indicated by a broken line. The target light amount P1 indicated by the broken line is in a range where the inclination is large in the rotation range of the knob 15a. Therefore, it is difficult to match the target light amount P1. Even if the adjustment can be made, if the resistance value Rv of the variable resistor 15 changes even a little due to factors such as vibration (if the knob 15a moves even a little), the light quantity may fall outside the target range. There is such a demerit when the fixed resistor 16 is not provided in the conversion unit 14 as in the laser apparatus 1 of the present embodiment.

(Conversion unit 14 of laser apparatus 1 according to the embodiment)
Next, the conversion unit 14 of the laser device 1 according to the embodiment will be described with reference to FIGS. 4, 10, and 11. FIG. 10 is a diagram illustrating an example of a change in the combined resistance value R0 of the conversion unit 14 with respect to a change in the rotation angle θ of the knob 15a of the variable resistor 15. FIG. 11 is a diagram illustrating an example of a change in the light amount of the laser diode 11 with respect to a change in the rotation angle θ of the knob 15a when the fixed resistor 16 is provided in the conversion unit 14.

  As shown in FIG. 4, in the laser device 1 according to the embodiment, the variable resistor 15 and the fixed resistor 16 of the conversion unit 14 are connected in parallel to the photodiode 12.

When the resistance value of the fixed resistor 16 is R1, the combined resistance value R0 of the conversion unit 14 is obtained as shown in the following (Equation 6) based on the product of the sum.
(Formula 6) R0 = (Rv × R1) / (Rv + R1)
When the denominator and numerator of (Expression 6) are multiplied by 1 / Rv, the following (Expression 7) is obtained.
(Formula 7) R0 = R1 / (1 + R1 / Rv)
The resistance value Rv of the variable resistor 15 is proportional to the resistance value with respect to the rotation angle θ. Therefore, R1 / Rv of the denominator of (Expression 7) decreases as the rotation angle θ of the knob 15a increases. As a result, as shown in (Equation 7), the amount of change in the resistance value of the combined resistance value R0 decreases as the rotation angle θ of the knob 15a increases.

  By providing the converting unit 14 with the fixed resistor 16 in parallel with the variable resistor 15, as shown in FIG. A characteristic in which the combined resistance value R0 changes logarithmically with respect to the rotation angle θ can be provided.

Here, the target light amount P1 in the case where the fixed resistor 16 is provided in parallel in the conversion unit 14 is obtained as the following (Expression 8) based on the same idea as in (Expression 5).
P1 = (Vcont × P2) / (R0 × I3)

  The combined resistance value R0 has a characteristic that the amount of change in resistance value decreases as the rotation angle θ of the knob 15a of the variable resistor 15 increases. Therefore, the amount of change in the target light amount P1 with respect to the amount of change in the rotation angle θ does not increase compared to the case where only the variable resistor 15 is provided in the conversion unit 14. That is, it is possible to eliminate a range in which the inclination of the change in the combined resistance value R0 with respect to the operation amount of the knob 15a is large in the rotation range of the knob 15a.

  Therefore, as shown in FIG. 11, the change amount of the rotation angle θ of the knob 15 a of the variable resistor 15 and the change amount of the light amount of the laser diode 11 can be brought close to a proportional relationship. Therefore, the light quantity of the laser diode 11 can be easily adjusted to the target light quantity P1 (so that it falls within the target range).

  Further, when the knob 15a of the variable resistor 15 is rotated by the same angle, the resistance value of the conversion unit 14 is greater when the fixed resistor 16 is provided in parallel with the variable resistor 15 in the conversion unit 14 than when the variable resistor 15 is not provided. Change will be gradual. Therefore, the light quantity of the laser diode 11 can be easily adjusted to the target light quantity P1.

(Modification)
Next, a modified example of the laser device 1 will be described with reference to FIG. FIG. 12 is a diagram illustrating an example of a modification.

  FIG. 12 shows a modification in which the fixed resistor 16a is further added to the converter 14 in the laser device 1 shown in FIG. In the modification, one variable resistor 15 and two fixed resistors 16 and 16a are provided as the conversion unit 14. The variable resistor 15 and the fixed resistors 16 and 16 a are connected in parallel to the photodiode 12. Thereby, even if the range (change width) of the variable resistor 15 is large, the change of the resistance value when the knob 15a is rotated can be made smooth.

  In this way, the laser device 1 according to the embodiment receives the laser light emitting part (laser diode 11) and part of the laser light emitted from the laser light emitting part and outputs it as the monitor current Io, and the amount of received light is large. A monitor element (photodiode 12) for passing a large amount of monitor current Io, a conversion unit 14 connected to the monitor element and converting the monitor current Io as the monitor voltage V1, and a control voltage Vcont having a predetermined magnitude are input. And a drive circuit 10 that controls the current flowing through the laser light emitting section so that the control voltage Vcont and the monitor voltage V1 are the same. The conversion unit 14 includes a parallel circuit 17 including a variable resistor 15 and a fixed resistor 16, and the variable resistor 15 and the fixed resistor 16 are connected in parallel to the monitor element. The voltage between the monitor element and the parallel circuit 17 is input to the drive circuit 10 as the monitor voltage V1.

  As a result, the monitor voltage V1 changes according to the combined resistance value R0 of the variable resistor 15 and the fixed resistor 16. Since the variable resistor 15 and the fixed resistor 16 are connected in parallel, the change in the combined resistance value R0 with respect to the amount of operation of the variable resistor 15 becomes more gradual than the change in the resistance value of the variable resistor 15. Therefore, compared with the case where only the variable resistor 15 is provided, the amount of change in the monitor current Io (monitor voltage V1) with respect to the operation amount of the variable resistor 15 becomes moderate. Therefore, the monitor current Io is hardly changed by a slight operation of the variable resistor 15. Therefore, it is possible to easily adjust the light amount of the laser light emitting unit (laser diode 11).

  Further, the change in the combined resistance value R0 with respect to the operation amount of the variable resistor 15 can have a C curve characteristic. When only the variable resistor 15 is used, the change in the amount of laser light with respect to the amount of operation of the variable resistor 15 has an inversely proportional relationship. However, the change in the amount of light with respect to the amount of operation of the variable resistor 15 can be made close to a proportional relationship by the C curve characteristic of the change in the combined resistance value R0. Therefore, the light amount adjustment of the laser light emitting section (laser diode 11) (laser diode 11) is further facilitated.

  The variable resistor 15 is a volume type whose resistance value changes when the knob 15a is rotated, and the rotation angle θ of the knob 15a and the resistance value are in a proportional relationship. As a result, the light quantity of the laser emitting part (laser diode 11) does not change greatly even if the knob 15a is slightly rotated. In addition, the relationship between the rotation amount (rotated angle) of the knob 15a and the change in the light amount of the laser light emitting unit can be brought close to a proportional relationship. Therefore, as compared with the case where only the variable resistor 15 is used as an element for converting the monitor current Io into a voltage, the light quantity of the laser light emitting unit can be easily adjusted by simply twisting the knob 15a.

  The parallel circuit 17 may include a plurality of fixed resistors 16. Thereby, the change of the monitor voltage V1 with respect to the operation amount of the variable resistor 15 (monitor current Io, the light quantity of the laser emission part) can be made smooth. Therefore, the light quantity of the laser emitting unit can be brought close to a desired value precisely.

  The image forming apparatus (printer 100) includes a photosensitive drum 51 and an exposure device 2 that exposes the photosensitive drum 51 with laser light. The exposure apparatus 2 includes a laser apparatus 1. The image forming apparatus can easily adjust the light amount of the laser light emitting unit (laser diode 11) of the laser device 1 to an appropriate value. Therefore, it is possible to provide an image forming apparatus with an appropriate amount of laser light. In addition, a high-quality image forming apparatus can be provided.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to a laser device or an image forming apparatus that exposes a photosensitive drum with a laser device.

DESCRIPTION OF SYMBOLS 100 Printer (image forming apparatus) 1 Laser apparatus 10 Drive circuit 11 Laser diode (laser light emission part)
DESCRIPTION OF SYMBOLS 12 Photodiode (monitor element) 14 Conversion part 15 Variable resistance 15a Knob 16 Fixed resistance 16a Fixed resistance 17 Parallel circuit 2 Exposure apparatus 51 Photosensitive drum Io Monitor current V1 Monitor voltage Vcont Control voltage

Claims (4)

A laser emitting unit;
A part of the laser light emitted from the laser light emitting unit is received and output as a monitor current, and a monitor element that causes a larger amount of the monitor current to flow as the amount of received light increases,
A conversion unit connected to the monitor element and converting the monitor current as a monitor voltage;
A control voltage of a predetermined magnitude is input, and includes a drive circuit that controls a current that flows to the laser light emitting unit so that the control voltage and the monitor voltage are the same.
The conversion unit includes a parallel circuit including a variable resistor and a fixed resistor, and the variable resistor and the fixed resistor are connected in parallel to the monitor element,
The laser device, wherein a voltage between the monitor element and the parallel circuit is input to the drive circuit as the monitor voltage.   2. The laser according to claim 1, wherein the variable resistor is of a volume type in which a resistance value changes when a knob is rotated, and a rotation angle of the knob and a resistance value are in a proportional relationship. apparatus.   The laser device according to claim 1, wherein the parallel circuit includes a plurality of fixed resistors. A photosensitive drum;
An exposure device for exposing the photosensitive drum with a laser beam;
The image forming apparatus, wherein the exposure apparatus includes the laser apparatus according to claim 1.

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