Optical Scanning Device, Image Forming Apparatus, Control Method, and Program

Abstract

To provide an optical scanner and the like, capable of properly controlling laser light-emitting amount according to laser characteristics or lens transmittance, when off-setting to an analog signal inputted to a laser driver on the basis of a target light amount of a laser light-emitting portion.SOLUTION: An optical scanner is equipped with a laser driver that controls a laser light-emitting portion so as to increase / decrease an excessive current from a bias current according to an inputted analog signal, an off-set value deciding portion that decides an off-set value of the analog signal to be inputted to the laser driver on the basis of a target light amount of the laser light-emitting portion, a bias current setting portion that controls a bias current of the laser driver to a setting value according to laser characteristics of the laser light-emitting portion or lens transmittance, and a laser driver control portion that controls the light-emitting amount of the laser light-emitting portion by inputting the off-set analog signal on the basis of a signal of the decided off-set value to the laser driver.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an optical scanning device and the like.

Background Art

[0002] In an image forming apparatus, in the process of forming an image based on an image signal on a recording paper (sheet-like image recording medium), a laser diode (light emitting element) emits laser light to scan a photosensitive drum as a scanned object for an exposure process of forming an electrostatic latent image on the surface of the photosensitive drum. An optical scanning device is mounted.

[0003] Generally, a laser diode has a characteristic that its optical output rises at a threshold current as the input current increases. From this characteristic, it has been common to always flow a bias current in order to shorten the delay in the rise time of laser oscillation.

[0004] In a laser driver that drives a laser diode, during standby, a predetermined bias current below the threshold is supplied, and during driving of the laser diode, a laser driver is known in which the current in excess of the bias current increases or decreases in proportion to an analog input signal. Also, an autobias control process for matching the bias current to the threshold during standby is known.

[0005] Patent Document 1 discloses an optical scanning device that relates to a laser driver with a fixed bias current that does not have an execution function for autobias control processing, and calculates the voltage value of an analog signal for controlling the laser driver according to a target light amount after storing the characteristics (PI characteristics) of the light amount and current of the laser diode for each temperature.

[0006] However, in Patent Document 1, since the PI characteristics of the laser are stored for each temperature and the voltage setting value of the analog signal corresponding to the target light amount is calculated, there are the following problems.

[0007] It took time for the process to calculate the voltage setting value again according to changes in the target light amount such as environment and life correction.

[0008] When shading was performed with a low target light amount, the resolution of the shading deteriorated. Also, when the PI characteristics of the laser and the fundamental light amount varied individually, there was a light deviation from the target light amount.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] In response to the above problems, it is conceivable to uniformly apply an offset to the analog signal according to the target light amount. However, simply setting a uniform offset value may cause problems in the laser emission amount due to variations in laser characteristics and lens transmittance.

[0011] In view of such circumstances, the present disclosure aims to provide an optical scanning device or the like that can appropriately control the laser emission amount according to laser characteristics and lens transmittance when offsetting the analog signal input to the laser driver based on the target light amount of the laser emission unit.

Means for Solving the Problems

[0012] The present disclosure relates to an optical scanning device, comprising: a laser driver that controls a laser light emitting unit such that an excessive current from a bias current increases or decreases according to an input analog signal; an offset value determination unit that determines an offset value of the analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a bias current setting unit that controls a bias current of the laser driver to a set value according to laser characteristics or lens transmittance of the laser light emitting unit; and a laser driver control unit that controls a light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver. Further, the present disclosure relates to an optical scanning device, comprising: a laser driver that controls a laser light emitting unit such that an excessive current from a bias current increases or decreases according to an input analog signal; an offset value determination unit that determines an offset value of the analog signal input to the laser driver based on a target light amount of the laser light emitting unit; and a laser driver control unit that controls a light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver, wherein the laser light emitting unit has a multi-beam laser light emitting unit having a plurality of laser light emitting elements that emit laser beams, and the laser driver control unit individually sets a shading correction signal for shading correction of the laser light scanned on an object for each of the laser light emitting elements of the multi-beam light emitting unit with respect to the laser driver, and commonly sets a signal of the offset value for the plurality of laser light emitting elements.

[0013] The present disclosure relates to an image forming apparatus, comprising: the above-described optical scanning device; an image carrier on which an electrostatic latent image is formed on a surface by scanning laser light emitted from the laser light emitting unit; and a developing unit that develops the electrostatic latent image formed on the surface of the image carrier.

[0014] The present disclosure is a control method for an optical scanning device including a laser driver that controls the laser light emitting unit such that the current exceeding the bias current increases or decreases according to an input analog signal, the method including: an offset value determination step of determining an offset value of an analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a bias current setting step of setting a bias current according to the laser characteristics or lens transmittance of the laser light emitting unit; and a laser driver control step of controlling the light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver while the bias current is set.

[0015] The present disclosure is a program for a computer of an optical scanning device including a laser driver that controls the laser light emitting unit such that the current exceeding the bias current increases or decreases according to an input analog signal, the program realizing: an offset value determination function of determining an offset value of an analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a bias current setting function of setting a bias current according to the laser characteristics or lens transmittance of the laser light emitting unit; and a laser driver control function of controlling the light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver while the bias current is set.

Advantages of the Invention

[0016] According to the optical scanning device and the like of the present invention, by inputting an analog signal offset based on the offset value signal to the laser driver while setting the bias current according to the laser characteristics or lens transmittance of the laser light emitting unit, the light emission amount of the laser light emitting unit can be controlled, so that a necessary offset amount is ensured, the resolution when the target light amount is large is ensured, and an excellent effect that there is no deviation from the target light amount can be achieved.

Brief Description of the Drawings

[0017]

Figure 1

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Figure 10

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Figure 12

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Figure 14

Mode for Carrying Out the Invention

[0018] An embodiment of the present disclosure will be described below with reference to the drawings.

[0019] Note that the following embodiments are examples for explaining the present disclosure, and the technical scope of the invention described in the claims is not limited to the following description.

[0020] [1. Embodiment] First, the configuration of the image forming apparatus 10 according to the embodiment will be described. FIG. 1 is an external view of the image forming apparatus 10 equipped with the optical scanning device 200 according to the embodiment, and FIG. 2 is a control block diagram of the image forming apparatus 10 and the optical scanning device 200.

[0021] [1.1 Overall Configuration] As shown in FIG. 1, the image forming apparatus 10 is an information processing apparatus that includes a document reading unit 112 at the upper part of the image forming apparatus 10 to read an image of a document and output an image by an electrophotographic method. As an example of the image forming apparatus 10, a multifunction printer can be cited.

[0022] As shown in the control system diagram of FIG. 2, the image forming apparatus 10 mainly includes a control unit 100, an image input unit 110, a document reading unit 112, an image processing unit 120, an image forming unit 130, an operation unit 140, a display unit 150, a storage unit 160, a communication unit 170, and also has the functions of the optical scanning device 200.

[0023] [1.2 Image Forming Apparatus 10] The control unit 100 is a functional unit for controlling the entire image forming apparatus 10.

[0024] The control unit 100 realizes various functions by reading and executing various programs, and is configured by, for example, one or more arithmetic units (for example, a CPU (Central Processing Unit)).

[0025] The image input unit 110 is a functional unit for reading image data input to the image forming apparatus 10. The image input unit 110 is connected to the document reading unit 112, which is a functional unit for reading an image of a document, and inputs the image data output from the document reading unit 112.

[0026] Further, the image input unit 110 may input image data from a storage medium such as a USB memory or an SD card. Alternatively, the communication unit 170 that connects to another terminal device may input image data from another terminal device.

[0027] The document reading unit 112 has a function of optically reading a document placed on a contact glass (not shown) and passing the scanned data to the image processing unit 120.

[0028] The image forming unit 130 is a functional unit for forming output data based on image data on a recording medium (e.g., recording paper). For example, as shown in FIG. 1, recording paper is fed from the paper feed tray 122, an image is formed on the surface of the recording paper in the image forming unit 130, and then discharged from the discharge tray 124. The image forming unit 130 is configured by a laser printer using an electrophotographic process that utilizes an electrophotographic process.

[0029] In the electrophotographic process of the image forming unit 130, a laser beam (corresponding to laser light) corresponding to the image data is scanned on the surface of the photosensitive drum (image carrier) 130a (see FIG. 5) by the optical scanning device 200 described later to form an electrostatic latent image, the electrostatic latent image is developed with toner, and the developed toner image is transferred and fixed onto the recording medium to form an image.

[0030] The image processing unit 120 has a function of converting the image data read by the document reading unit 112 into a set file format (TIFF, GIF, JPEG, etc.). Then, an output image is formed based on the image data subjected to image processing.

[0031] The operation unit 140 is a functional unit for receiving operation instructions from the user, and is configured by various key switches, a device that detects input by contact, and the like. The user inputs the functions to be used and the output conditions via the operation unit 140.

[0032] The display unit 150 is a functional unit for displaying various information to the user, and is configured by, for example, an LCD (Liquid Crystal Display) or the like.

[0033] That is, the operation unit 140 provides a user interface for operating the image forming apparatus 10, and various setting menu screens and messages of the image forming apparatus are displayed on the display unit 150.

[0034] As shown in FIG. 1, the image forming apparatus 10 may include a touch panel in which the operation panel 141 and the display unit 150 are integrally formed as a configuration of the operation unit 140. In this case, the method of detecting the input of the touch panel may be a general detection method such as, for example, a resistive film method, an infrared method, an electromagnetic induction method, or a capacitance method.

[0035] The storage unit 160 is a functional unit in which various programs including control programs necessary for the operation of the image forming apparatus 10, various data including read data, and user information are stored. The storage unit 160 is configured by, for example, a non-volatile ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), or the like. Further, an SSD (Solid State Drive) which is a semiconductor memory may be provided.

[0036] The communication unit 170 performs communication connection with an external device. A communication interface (communication I / F) used for data transmission and reception is provided as the communication unit 170. By the communication I / F, data stored in the storage unit of the image forming apparatus 10 can be transmitted and received to and from other computer devices connected via a network according to an operation by the user on the image forming apparatus 10.

[0037] [1.3 Optical Scanning Device 200] As shown in FIG. 2, an optical scanning device 200 is mounted on the image forming apparatus 10. FIG. 3 shows a specific circuit diagram of a signal transmission path around the laser driver in the optical scanning device 200.

[0038] As shown in FIGS. 2 and 3, the optical scanning device 200 includes a laser light emitting unit 200a composed of a laser light emitting element (semiconductor laser element), a laser driver 210 that controls the laser light emitting unit (LD: Laser Device) 200a so as to increase or decrease in proportion to an analog signal into which an excessive current from a bias current is input, an optical scanning unit 220 that scans a laser beam (laser light) emitted from the laser light emitting unit 200a onto a photosensitive drum 130a of an object, a shading correction signal unit 230 that outputs a signal (Vshade) of a shading correction value for shading correction of the light scanned onto the object, an offset value determination unit 240 that determines an offset value of an analog signal input to the laser driver 210 based on a target light amount (Vref) of the laser light emitting unit 200a, a bias current setting unit 250 that sets a bias current for the laser driver 210 according to the laser characteristics or lens transmittance of the laser light emitting unit 200a, an overlay unit (overlay circuit) 260 that overlays and offsets a signal (Voffset) of the determined offset value on an analog signal (a signal of an offset value of a shading correction value signal (Voffset)), and a laser driver control unit 270 that controls the light emission amount of the laser light emitting unit (LD) 200a by inputting a shading correction signal (Vsw) of the analog signal offset by the overlay to the laser driver (LD Driver) 210 in a state where the bias current is set. In FIG. 3, Vcc is a power supply voltage.

[0039] The laser light emitting unit 200a is composed of one or more laser light emitting elements (semiconductor laser elements such as laser diodes), and the output light amount is detected by a light amount detection unit 280 composed of a photodiode (PD).

[0040] The bias current setting unit 250 outputs a set value of the bias current of the laser light emitting unit 200a. The set value is input as a control signal corresponding to the bias current control value to the bias current control circuit 290 through the laser scanning unit 220a, and the bias current control circuit 290 controls the bias current of the laser driver 210 to be according to the set value.

[0041] The shading correction value (Vshade) output by the shading correction signal unit 230 is calculated in the adjustment process of the optical scanning device 200 and stored in the ROM or the like of the storage unit 160. The shading correction value is sequentially read from the storage unit 160 according to the irradiation position of the laser beam on the surface of the photosensitive drum 130a in the main scanning direction.

[0042] As shown in FIG. 3, in the optical scanning device 200, the optical scanning unit 220 has a laser scanning unit (LSU) 220a as a control system. The laser scanning unit inputs signals output from the shading correction signal unit 230, the offset value determination unit 240, and the bias current setting unit 250 to the laser driver 210 according to the control signal of the control unit 100, and is composed of an application specific integrated circuit (LSUASIC). A reference clock signal 200m and a detection signal of the BD sensor 200k are input to the integrated circuit (LSUASIC) of the laser scanning unit 220a.

[0043] The signal (Vshade) of the shading correction value output by the shading correction signal unit 230 is obtained in advance by experiments or the like and stored in the ROM or the like of the storage unit 160. The signal (Vshade) of the shading correction value is an analog voltage signal. The laser driver 210 controls so that the current exceeding the bias current of the laser light emitting unit 200a is proportional to the input of the signal of the shading correction value. The reading is sequentially read from the storage unit 160 according to the irradiation position of the laser beam on the surface of the photosensitive drum 130a in the main scanning direction based on the detection signal of the BD sensor 200k.

[0044] The offset value signal (Voffset) output by the offset value determination unit 240 is an analog voltage signal. It is a voltage signal for correcting the shading ratio and adds a current from the bias current of the laser light emitting unit 200a to the threshold value.

[0045] In addition, based on the light emission amount of the laser light emitting unit 200a detected by the light amount detection unit 280, the laser driver control unit 270 and the laser scanning unit 220a control the light emission amount of the laser light emitting unit 200a to be the target light amount (APC (Automatic Power Control) described later).

[0046] Specifically, the signal of the target light amount is controlled according to the reference voltage (Vref) in the sub-scanning direction. This reference voltage signal (Vref) becomes the reference voltage of APC and is input to the laser driver 210. The laser driver 210 controls the current of the laser light emitting unit 200a so that the light emission amount is proportional to this reference voltage signal (Vref).

[0047] The light amount detection unit 280 includes, for example, a photodiode (PD: Photo Diode) of a light amount detection element arranged near the laser light emitting element of the laser light emitting unit 200a. In addition, the laser driver control unit 270 monitors the light output (optical power) P of the laser light emitting unit 200a detected by this light amount detection unit 280, and automatically controls the drive current of the laser light emitting unit 200a so that it becomes a constant value according to the level of the reference voltage signal (Vref) so that the light output becomes the target light amount. It adopts the control method of APC.

[0048] Note that APC is roughly divided into initial APC and steady-state APC. The initial APC refers to the lighting mode performed at the time of initialization of the laser light emitting element, and is called initialization or 1st APC. In addition, the steady-state APC refers to the APC performed for each line scan, and is called line APC or simply APC.

[0049] In FIG. 3, a signal XSH output from the control system of the optical scanning unit 220 (laser scanning unit 220a) is a signal for APC, and APC is executed when this XSH signal is valid (Low). Also, image data is output toward the laser driver 210, and thereby, an electrostatic latent image corresponding to the image data is formed on the photoreceptor drum 130a.

[0050] Also, the detection signal of the BD sensor 200k is generally used so that monitoring and synchronous detection in normal APC are performed simultaneously. The shading correction value signal (Vshade) and the offset value signal (Voffset) are superimposed in the superimposing circuit 260, and an analog signal (Vsw) in a state where the shading correction signal is offset is input to the laser driver 210.

[0051] Also, the optical scanning device 200 has a light quantity detection unit 280 that detects the light emission quantity of the laser light emission unit 200a, and the laser driver control unit 270 adopts a control method of APC that controls the drive current of the laser diode by a reference voltage signal (Vref) so that the light emission quantity of the laser light emission unit 200a detected by the light quantity detection unit 280 becomes the target light quantity.

[0052] The offset value determination unit 240 determines an offset value (signal Voffset) based on the target light quantity signal (reference voltage signal (Vref)) of the laser driver control unit 270 during APC control. The storage unit 160 stores an offset adjustment table 240a in which the relationship between the target light quantity and the offset value is set, and the offset value determination unit 240 determines the offset value based on the target light quantity with reference to the stored offset adjustment table 240a.

[0053] In the embodiment, an offset adjustment table 240a as shown in FIG. 4 as an example is stored in the ROM (Read Only Memory) of the storage unit 160. The offset adjustment table 240a is set with the relationship between the target light quantity signal (reference voltage signal (Vref)) and the offset value (signal Voffset).

[0054] By temporarily storing the offset adjustment table 240a in the memory unit 160, it is not necessary to recalculate the set value of the analog signal to the laser driver 210 according to changes in the target light amount such as environment or life correction, and the process does not require time.

[0055] Also, in order to cope with the change of the offset value (signal Voffset) according to the temperature, it is preferable to store a plurality of offset adjustment tables 240a corresponding to the temperature in the memory unit 160.

[0056] FIG. 5 shows the mechanical configuration of the optical scanning unit 220 of the optical scanning device 200.

[0057] As shown in FIG. 5, the optical scanning unit 220 scans the laser beam on the photosensitive drum 130a to form an electrostatic latent image on the photosensitive drum 130a.

[0058] As shown in FIG. 5, the optical scanning device 200 includes a laser light emitting unit 200a composed of a laser light emitting element that generates a laser beam (laser light), and in the emission direction of the laser beam emitted from the laser light emitting unit 200a, there is a collimator lens 200b that converts the incident laser beam into a parallel beam, an aperture 200c composed of a plate-like member having an opening 200c1 formed in a substantially central portion, a concave lens 200e that expands the incident laser beam by a combination with an fθ lens 200d that expands the laser beam in the scanning direction described later, a cylindrical lens 200f, and an incident beam folding mirror 200g arranged in sequence.

[0059] Also, in the reflection direction of the laser beam by the incident beam folding mirror 200g, an fθ lens 200d and a polygon mirror 200h having a plurality of reflection surfaces on its outer peripheral surface are arranged in sequence, and in the reflection direction of the laser beam by the reflection surface of the polygon mirror 200h, an fθ lens 200d, a reflection mirror 200i, an emission beam folding mirror 200j that corrects the tilting of the polygon mirror 200h, and a photosensitive drum 130a are arranged.

[0060] The reflected light reflected by the reflection mirror 200i is detected by a beam detection sensor (BD sensor) 200k. The BD sensor 200k is an optical sensor that outputs a detection signal according to the amount of received laser beam. The BD sensor 200k has a function of detecting the reflected light from the start end side of the main scanning area of the laser beam (the scanning area along the axial direction of the photosensitive drum 130a), and is used for controlling the timing of writing an electrostatic latent image on the photosensitive drum 130a. As shown in FIG. 6, the detection signal of the BD sensor 200k becomes trigger-like.

[0061] In addition, the laser light emitting unit 200a is provided with a light amount detection unit 280 having a PD (photodiode) for detecting the laser emission amount in the vicinity.

[0062] [1.4 Control Signal Examples] An example of the control signal of the optical scanning unit 220 shown in FIG. 3 will be described with reference to FIG. 6. FIG. 6 shows examples of voltage signals such as a shading correction value signal (Vshade), an offset value signal (Voffset), and an offset shading correction signal (laser driver input signal: Vsw).

[0063] In this case, the shading correction value signal (Vshade) is an analog voltage for shading correction. An excessive current from the bias current is proportional to this voltage.

[0064] The offset value signal (Voffset) is a voltage for correcting the shading ratio, and a current from the bias current to the threshold current is added.

[0065] The sub-scanning reference voltage signal (Vref) becomes the reference voltage of the APC, and the light amount is proportional to this voltage.

[0066] The APC signal (XSH) causes the APC to be executed when this signal is valid (Low).

[0067] The laser driver input signal (Vsw) indicates an offset shading correction signal.

[0068] Any of the signals is an analog voltage signal. The BD signal is a detection signal from the start side of the main scanning area detected by the beam detect sensor (BD sensor) 200k.

[0069] As shown in FIG. 6, the shading correction value signal (Vshade) has a portion close to the 0 level, but is lifted by overlapping with the offset value signal (Voffset), and the offset shading correction signal (Vsw) is away from the 0 level. The analog signal of this offset state shading correction signal (Vsw) is input to the laser driver 210.

[0070] As shown in FIG. 3, in the optical scanning unit 220, the bias current setting unit 250 controls the bias current of the laser driver 210 to a set value. Therefore, according to the set value signal, a bias current control signal is input to the bias current control circuit 290 via the laser scanning unit 220a.

[0071] FIG. 7 is a circuit diagram for explaining Example 1 of the bias current control circuit 290. As shown in FIG. 7, the bias current control circuit 290 according to Example 1 is provided with a plurality of resistors for setting the bias current of the laser driver 210, and the resistance value is changed by turning them on and off to control the bias current to a set value.

[0072] Specifically, a setting resistor R1 and R2 are connected in parallel to the connection terminal Rbi of the resistor R0 that defines the bias current of the laser driver 210 via switches SW1 and 2. The resistors R1 and R2 are switched on and off by the switches SW1 and 2 to change the resistor (resistance value) connected to the connection terminal Rbi and control the bias current to a set value.

[0073] In this case, according to the magnitude of the offset (Voffset), the resistance value connected to the connection terminal Rbi is switched by turning on and off the switches SW1 and SW2 as follows, so that both the required offset amount and the resolution when the target light amount is large can be ensured.

[0074] OFF of SW1 and SW2: Resistance value is R0 SW1 ON and SW2 OFF: Resistance value is R0×R1 / (R0 + R1) SW1 OFF and SW2 ON: Resistance value is R0×R2 / (R0 + R2) SW1 ON and SW2 ON: Resistance value is R0×R1×R2 / (R1×R2 + R0×R2 + R0×R1)

[0075] Note that the resistors are not limited to two, R1 and R2, and can be one or three or more. Also, although the resistance value can be accurately set because the resistors are switched by switches, it is not limited thereto, and it is also conceivable to install variable resistors.

[0076] FIG. 8 is a circuit diagram for explaining Example 2 of the bias current control circuit 290. As shown in FIG. 8, in the bias current control circuit 290 according to Example 2, when the connection terminal Rbi for connecting the bias current setting resistor R0 of the laser driver is of a constant voltage source, a variable voltage source Vbias is connected in parallel to the connection terminal Rbi to change the voltage applied to the connection terminal Rbi and control the bias current to a set value. Note that R1 is an adjustment resistor.

[0077] In this case, by changing the overvoltage applied to the connection terminal Rbi by the variable voltage source Vbias, the bias current is changed to vary the assist amount of the bias current. Since it is not a stepwise switching by turning on and off the switches as in Example 1, the voltage can be smoothly switched to select an appropriate voltage. Also, when the bias current setting unit is a constant voltage source, the bias current can be controllable.

[0078] Next, an explanation will be given regarding the determination of the set value of the bias current of the laser driver according to the laser characteristics or lens characteristics.

[0079] FIG. 9 is a graph for explaining the characteristics of a semiconductor laser element used for the laser emitting element of the laser emitting unit 200a.

[0080] For the semiconductor laser element, the relationship between the flowing current (forward current) I and the optical output P is as shown in FIG. 9.

[0081] As shown in FIG. 9, when the current I is gradually increased, the semiconductor laser element gradually emits light. At first, it emits LED (light emitting diode) light instead of laser light. However, at a certain point, the optical output suddenly increases and laser oscillation starts. The current at which this laser oscillation starts is called the threshold current Ith. Also, the change in the optical output P with respect to the current I after exceeding this threshold current Ith is extremely rapid, and the rate of change of the optical output P with respect to this current I is called the differential efficiency.

[0082] Even if the semiconductor laser elements have the same design, their characteristics such as the threshold current and differential efficiency are different due to variations in materials and various conditions during the manufacturing process.

[0083] FIG. 10 is an explanatory diagram of the variation in the lens transmittance in the laser emitting unit 200a. A main factor for the variation in the lens transmittance is the variation in the emission angle (horizontal / vertical) of the semiconductor laser element.

[0084] As shown in FIG. 10, the laser light (200a1) output from the laser emitting unit 200a composed of a semiconductor laser element is converted into parallel light by the collimator lens 200b of the incident unit 205 and is restricted to a predetermined light amount by the aperture 200c.

[0085] Generally, since the emission angle (horizontal / vertical) of the semiconductor laser element itself varies, the amount of laser light that can be extracted after the aperture 200c of the incident unit performs the aperture adjustment also varies. Other factors include the deviation of the central axis between the semiconductor laser element and the incident unit 205 and the variation in the reflectivity of the mirrors in the optical scanning device.

[0086] FIG. 11 is an explanatory diagram of the operation image of the semiconductor laser element. (a) is a case where the offset amount increases, (b) is a case where the offset amount decreases, and (c) and (d) are explanatory diagrams of the correction image.

[0087] When the characteristics of the semiconductor laser element are such that the threshold current Ith is large, the differential efficiency is large, and the laser light amount is small as shown in FIG. 11(a), the offset amount (Voffset) to be ensured becomes large.

[0088] Also, when the characteristics of the semiconductor laser element are such that the threshold current Ith is small, the differential efficiency is small, and the laser light amount is large as shown in FIG. 11(b), the offset amount (Voffset) becomes small and the resolution becomes a problem.

[0089] Therefore, in the bias current setting unit 250 of the embodiment, when the offset amount becomes large as shown in FIG. 11(a), the set value of the bias current is increased as shown in FIG. 11(c). Also, when the offset amount becomes small as shown in FIG. 11(b), the set value of the bias current is decreased as shown in FIG. 11(d).

[0090] FIG. 12 is a flowchart for determining the set value of the bias current according to the embodiment. Note that FIG. 4 is an explanatory diagram of an example of the offset value table. Each step 100~ is abbreviated as S100.

[0091] First, as shown in FIG. 12, the offset amount is set (S100). The offset amount (Voffset) is determined (set) corresponding to the signal (Vref) of the sub-scanning reference voltage as in the table shown in FIG. 4.

[0092] Next, it is determined whether the offset amount (Voffset) is smaller than a predetermined amount, for example, 255 (dec) (S110). If the offset amount is smaller than the predetermined amount (S110: Yes), the bias current is determined to be the current one (S120), and the process ends.

[0093] On the other hand, when the offset amount is equal to or greater than a predetermined amount (S110: No), a bias current is increased by ΔI and a set value is obtained (S130). It is determined whether the obtained set value of the bias current is greater than the specified value of the semiconductor laser element (S140). When the bias current is greater than the specified value (S140: Yes), the set value of the bias current is inappropriate (NG) and the adjustment is set to NG. When the bias current is equal to or less than the specified value (S140: No), the process returns to the process after S100 and is executed.

[0094] The case of the multi-beam laser light emitting unit 200a having a plurality of laser light emitting elements that emit laser beams will be described.

[0095] FIGS. 13(a) and (b) are explanatory diagrams of the bias current with respect to the offset amount of the multi-beam laser. FIG. 14 is an explanatory diagram of the setting of the offset amount of the multi-beam laser.

[0096] In a multi-beam laser, a common bias current is set for a plurality of laser elements. Bringing the bias current closer to the threshold current makes it possible to reduce the required offset amount. However, since there is a variation in the threshold current between the beams in a plurality of semiconductor laser elements, the set value of the bias current cannot be arbitrarily close to the threshold current.

[0097] As shown in FIG. 13(a), in the light emitting unit of the multi-beam laser, for example, when having two semiconductor laser elements (laser light emitting elements) LD1 and LD2 with different characteristics, when the bias current is made larger than that of the semiconductor laser element LD1 with a smaller threshold value, there is a possibility that the bias current exceeds the threshold value of the semiconductor laser element LD1. In this way, in a state where the bias current exceeds the threshold value, the light amounts between the beams are likely to be different at the time of a low light amount command. Also, laser oscillation may occur due to individual variations and temperature variations in the threshold current.

[0098] On the other hand, as shown in Fig. 13(b), if the bias current is set smaller than that of LD1, which has the lowest threshold value among the multi-beam semiconductor laser elements LD1 and LD2, both the semiconductor laser elements LD1 and LD2 operate normally.

[0099] Therefore, in a multi-beam laser, it is preferable to commonly set the bias current for a plurality of laser light-emitting elements and set the bias current to be smaller than the threshold current of the laser light-emitting element having the lowest threshold current among the respective laser light-emitting elements.

[0100] Note that it is preferable that the setting of the bias current ensures a margin for individual variations and temperature variations of the laser light-emitting elements.

[0101] Fig. 14 is an explanatory diagram of the setting of the offset amount of the multi-beam laser.

[0102] When the laser light-emitting unit 200a includes a multi-beam laser light-emitting unit, when the laser driver control unit 270 individually sets a shading correction signal (Vshade) for shading correction of the laser light scanned on the object for each laser light-emitting element of the multi-beam light-emitting unit 200a, it is preferable to commonly set a signal of an offset value for a plurality of laser light-emitting elements.

[0103] However, the bias current and the signal (Voffset) of the offset value are commonly set, but the signal (Vshade) of the shading correction value is different for each laser light-emitting element. In Fig. 14, by setting different signals (Vshade) of the shading correction values for the respective laser light-emitting elements LD1 and LD2, it is possible to adjust to a target light amount.

[0104] Note that when the signal (Voffset) of the offset value is made common, there are advantages that the circuit scale and the capacity of the ROM can be reduced, and the jig adjustment time of the laser light-emitting element does not increase.

[0105] [1.5 Effects] The optical scanning device and the image forming device according to the embodiment assume that a signal (reference voltage signal (Vref)) of a target light amount of the laser driver control unit 270 during APC control and a signal (Voffset) of an offset value linked thereto are combined into a shading correction value signal (Vshade).

[0106] Since it is configured to apply an offset according to the target light amount, it is necessary to secure the necessary offset amount in consideration of variations in laser characteristics (threshold current, differential efficiency) and lens transmittance. However, if the secured offset amount is large, the resolution of the offset may be insufficient when the target light amount is large, and there is a possibility that the target light amount deviates. Also, when the bias current is brought close to the threshold current in order to reduce the necessary offset amount, the following problems occurred.

[0107] · Due to variations in the individual laser emitting elements and temperature variations, the bias current may exceed the threshold current and may emit light constantly.

[0108] · When the bias current of the multi-beam laser is set commonly for all beams, there is a possibility that a beam that oscillates the laser may occur due to variations in the threshold current.

[0109] Also, when adjusting the offset for each beam in a multi-beam laser configuration, the circuit scale and the ROM capacity increase, and the jig adjustment time also increases.

[0110] 〔Feature 1〕 On the other hand, in the embodiment, as shown in FIGS. 3 to 12, in the optical scanning device and the image forming device using a laser driver in which the current exceeding the bias current increases and decreases in proportion to the analog input signal, according to the laser characteristics (threshold current, differential efficiency) and the lens transmittance, it has the feature of setting the bias current. Thereby, the following effects are obtained. · The necessary offset amount is secured. · The resolution when the target light amount is large is secured, and there is no deviation in the target light amount. · There is no need to reduce the necessary offset amount, and due to the individual variations and temperature variations of the threshold current, the bias current does not exceed the threshold current, and continuous laser oscillation does not occur.

[0111] 〔Feature 2〕 In the configuration of Feature 1, as shown in FIG. 13, there is a Feature 2 in which the bias current setting of the multi-beam laser is set commonly for all beams and is set smaller than the beam with the smallest threshold current. Thereby, the following effects are achieved. · Laser oscillation does not occur due to the bias current setting. · The jig adjustment time does not increase.

[0112] 〔Feature 3〕 In the configuration of Feature 2 based on FIG. 13, it is preferable to make a setting to secure a margin for the individual variations and temperature variations of the laser light emitting element. This is defined as Feature 3. · Setting example When the minimum value of the threshold current at room temperature of 25°C is 3 (mA), when the temperature changes to low temperature (5°C), the minimum value decreases by -0.5 (mA). Based on the above, considering the margin for individual variations and temperature variations, it is set to 2.0 (mA). By making a setting considering this margin, the following effects are achieved. · Due to individual variations, the threshold current is not exceeded, and continuous laser oscillation does not occur. · Due to temperature variations, the threshold current is not exceeded, and laser oscillation does not occur.

[0113] 〔Feature 4〕 In an optical scanning device and an image forming device using a laser driver in which the current exceeding the bias current increases and decreases in proportion to an analog input signal, as shown in FIG. 14, there is a Feature 4 in which the offset amount of the multi-beam laser is set commonly for all beams. Thereby, the following effects are achieved. · The circuit scale and the ROM capacity can be reduced. · The jig adjustment time does not increase.

[0114] Although the embodiments have been described above, the specific configuration is not limited to the embodiments, and designs and the like within the scope not departing from the gist of the present invention are also included in the claims.

[0115] Also, in the embodiments, the programs operating on each device are programs (programs that enable a computer to function) that control a CPU or the like so as to realize the functions of the above-described embodiments. And the information handled by these devices is temporarily stored in a temporary storage device (for example, RAM) during its processing, and then stored in storage devices such as various ROMs and HDDs, and read out by the CPU as necessary for correction and writing.

[0116] Here, as the recording medium for storing the program, any non-transitory recording medium such as a semiconductor medium (for example, ROM or non-volatile memory card, etc.), an optical recording medium or magneto-optical recording medium (for example, DVD (Digital Versataile Disc), MO (magneto Optical Disc), (MD (Mini Disc), CD (Compact Disc), BD, etc.), a magnetic recording medium (for example, magnetic tape, flexible disk, etc.) may be used.

[0117] Also, by executing the loaded program, not only the functions of the above-described embodiments are realized, but in some cases, the functions of the present disclosure are realized by processing in cooperation with an operating system or other application programs or the like based on the instructions of the program.

[0118] Also, when distributing the program on the market, the program can be stored in a portable storage device for distribution, or transferred to a server computer connected via a network such as the Internet. In this case, it goes without saying that the storage device of the server computer is also included in the present invention.

[0119] Furthermore, part or all of each device in the above-described embodiments may typically be realized as an LSI (Large Scale Integration), which is an integrated circuit. Each functional block of each device may be individually chip-sized, or part or all may be integrated and chip-sized. Also, the method of integrating into a circuit is not limited to LSI and may be realized by a dedicated circuit or a general-purpose processor. Also, when a circuit integration technology that replaces LSI appears due to the progress of semiconductor technology, it goes without saying that it is also possible to use an integrated circuit based on such technology.

Explanation of Signs

[0120] 10 Image forming apparatus 100 Control unit 130 Image forming unit 130a Photoconductor drum 160 Storage unit 200 Optical scanning device 200a Laser light emitting unit 210 Laser driver 220 Optical scanning unit 230 Shading correction signal unit 240 Offset value determination unit 240a Offset adjustment table 250 Bias current setting unit 270 Laser driver control unit 280 Light quantity detection unit 290 Bias current control circuit

Claims

1. a laser driver that controls a laser light emitting unit so that the current exceeding the bias current increases or decreases according to the input analog signal; an offset value determination unit that determines an offset value of an analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a laser driver control unit that controls the light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver, and the laser light emitting unit has a multi-beam laser light emitting unit having a plurality of laser light emitting elements that emit laser beams, the laser driver control unit individually sets a shading correction signal for shading correction of the laser light scanned on the object for each laser light emitting element of the multi-beam light emitting unit with respect to the laser driver, and commonly sets a signal of an offset value for a plurality of laser light emitting elements. The optical scanning device is characterized by the above.

2. The optical scanning device according to claim 1, further comprising a bias current setting unit that controls the bias current of the laser driver to a set value according to a set value corresponding to the laser characteristics or lens transmittance of the laser light emitting unit.

3. The optical scanning device according to claim 2, wherein the bias current setting unit controls the bias current to a set value by changing the resistance value of a bias current setting resistor of the laser driver.

4. The optical scanning device according to claim 2, wherein when the terminal to which the bias current setting resistor of the laser driver is connected is a constant voltage source, a variable voltage source is connected in parallel to the terminal, and the voltage applied to the terminal is changed to control the bias current to a set value.

5. The set value of the bias current is set in common for the plurality of laser light emitting elements, and is set to be smaller than the threshold current of the laser light emitting element having the smallest threshold current among the respective laser light emitting elements. The optical scanning device according to any one of claims 2 to 4.

6. The setting of the bias current is characterized in that it secures a margin for individual variations and temperature variations of the laser light emitting elements. The optical scanning device according to any one of claims 2 to 5.

7. The optical scanning device according to any one of claims 1 to 6, and An image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed on a surface by scanning laser light emitted from the laser light emitting unit; a developing unit that develops the electrostatic latent image formed on the surface of the image carrier. **Claim 8** A control method for an optical scanning device, the laser light emitting unit having a multi-beam laser light emitting unit having a plurality of laser light emitting elements that emit laser beams, and a laser driver that controls the laser light emitting unit such that the current exceeding the bias current increases or decreases according to the input analog signal, the method comprising: an offset value determination step of determining an offset value of an analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a laser driver control step of controlling the light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal to the laser driver, and individually setting a shading correction signal for shading correction of the laser light scanned on an object for each laser light emitting element of the multi-beam light emitting unit and commonly setting an offset value signal for a plurality of laser light emitting elements. **Claim 9** A computer for an optical scanning device, the laser light emitting unit having a multi-beam laser light emitting unit having a plurality of laser light emitting elements that emit laser beams, and a laser driver that controls the laser light emitting unit such that the current exceeding the bias current increases or decreases according to the input analog signal, the computer realizing: an offset value determination function of determining an offset value of an analog signal input to the laser driver based on a target light amount of the laser light emitting unit; a bias current setting function of setting a bias current according to laser characteristics or lens transmittance of the laser light emitting unit; a program that controls the light emission amount of the laser light emitting unit by inputting an analog signal offset based on the determined offset value signal with the bias current set, and individually sets a shading correction signal for shading correction of the laser light scanned on an object for each laser light emitting element of the multi-beam light emitting unit and commonly sets an offset value signal for a plurality of laser light emitting elements, thereby realizing a laser driver control function.

Images