Image forming apparatus and its control method

Abstract

The present invention provides an image forming apparatus, etc., that can suppress density unevenness in images. [Solution] In an image forming apparatus that performs color printing using a digital laser driver with an automatic bias current adjustment function, the apparatus comprises a laser light-emitting unit that emits laser light to expose a photoreceptor, an APC current control unit that controls the APC emission current of the laser light-emitting unit, and an APC control signal generation unit that generates a signal to cause the laser driver to calculate the bias current from the current values ​​of multiple APC emission from the laser light-emitting unit. The APC control signal generation unit generates a signal to cause the laser driver to calculate the bias current based on the current values ​​of multiple APC emission from the laser light-emitting unit at a timing outside the printing area in the sub-scanning direction when calculating the bias current of the laser light-emitting unit that exposes a predetermined color.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus that forms a color image by scanning a photoreceptor with a laser beam.

Background Art

[0002] Conventionally, in an image forming apparatus, a photoreceptor drum is exposed by a light beam emitted from a semiconductor laser of a light source to form an electrostatic latent image. Since the I-L (current-light amount) characteristic of the semiconductor laser has temperature dependence, the light amount of the emitted light beam varies according to the fluctuation of the temperature of the use environment.

[0003] Therefore, in a digital laser driver, an APC (Automatic Power Control) is adopted, which receives light with a light receiving element such as a photodiode so that a target light amount is stably emitted from the semiconductor laser, and controls the drive current of the semiconductor laser based on the received light amount, suppressing the fluctuation of the light amount.

[0004] Regarding a method for obtaining the threshold current Ith, which is the light emission start current of the semiconductor laser, in Patent Document 1, when calculating this threshold current Ith based on the I-L (current-light amount) characteristic of the semiconductor laser, the ratio of two light amounts Po_M and Po_L is uniformly set, and from two different current values of currents Iop_M and Iop_L flowing when emitting different light amounts Po_M and Po_L, the threshold current Ith is obtained by the following formula (1), and a method for setting the laser bias current Ib is disclosed.

[0005] Ith=(m×Iop_L - n×lop_M) / (m + n) ···(1)<T However, n < m ≦ 1

[0006] In Patent Document 2, as a technique for suppressing a decrease in the setting accuracy of the bias current value, an image forming apparatus using a dedicated circuit including a plurality of sw circuits in a laser drive for setting the threshold current value Ith is disclosed.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-16955 [Patent Document 2] Japanese Patent Publication No. 2015-217589 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the technology described in Patent Document 1, when adjusting the bias current of a digital laser driver, two emission modes are switched (to obtain two light intensities, Po_M and Po_L), the threshold current Ith is determined, and the bias current is set. As a result, variations occur in the internal adjustment values ​​for each mode, causing the bias current Ib to vary by approximately twice the total internal adjustment value with each adjustment.

[0009] When the variation in this bias current Ib is uneven, the response of the semiconductor laser changes, which can lead to problems such as streaky or band-like density unevenness occurring in halftone printing of black (K) color, where density differences are easily visible to the naked eye.

[0010] Patent Document 2 had the problem that it could not be applied to a general-purpose driver environment because it required the implementation of a dedicated circuit.

[0011] In view of these circumstances, this disclosure provides an image forming apparatus, etc., that can suppress density unevenness in images. [Means for solving the problem]

[0012] This disclosure relates to an image forming apparatus that performs color printing using a digital laser driver having an automatic bias current adjustment function, comprising: a laser light-emitting unit that emits laser light to expose a photoreceptor; an APC current control unit that controls the APC emission current of the laser light-emitting unit; and an APC control signal generation unit that generates a signal to cause the laser driver to calculate a bias current from the current values ​​of multiple APC emission from the laser light-emitting unit, wherein the APC control signal generation unit generates a signal to cause the laser driver to calculate a bias current based on the current values ​​of multiple APC emission from the laser light-emitting unit at a timing outside the printing area in the sub-scanning direction when calculating the bias current of the laser light-emitting unit that exposes a predetermined color.

[0013] This disclosure relates to a control method for an image forming apparatus that performs color printing using a digital laser driver having an automatic bias current adjustment function, comprising: a laser emission step of emitting laser light from a laser light-emitting unit to expose a photoreceptor; an APC current control step of controlling the APC emission current of the laser light-emitting unit; and an APC control signal generation step of generating a signal that causes the laser driver to calculate a bias current from the current values ​​of multiple APC emission from the laser light-emitting unit, wherein the APC control signal generation step generates a signal that causes the laser driver to calculate a bias current based on the current values ​​of multiple APC emission from the laser light-emitting unit at a timing outside the printing area in the sub-scanning direction when calculating the bias current of the laser light-emitting unit that exposes a predetermined color. [Effects of the Invention]

[0014] The image forming apparatus and the like of the present disclosure can achieve the excellent effect of suppressing density unevenness in images. [Brief explanation of the drawing]

[0015] [Figure 1] This is an external view of an image forming apparatus according to an embodiment. [Figure 2] This is a control block diagram of an image forming apparatus. [Figure 3]It is a circuit diagram of a signal transmission path of a laser light emitting unit and a laser driver of an image forming apparatus. [Figure 4] It is an explanatory diagram of a mechanical configuration of an optical scanning unit. [Figure 5] It is an explanatory diagram of adjustment of a bias current of an APC. [Figure 6] It is an explanatory diagram of variations in adjustment of a bias current of an APC. [Figure 7] It is an explanatory diagram of a response characteristic of a semiconductor laser, and is a diagram showing the relationship between (a) a change in a drive current Iop and (b) a photon number fluctuation. [Figure 8] It is an image diagram for explaining unevenness of a printed image, and is an explanatory diagram of (a) a case where APC is performed for each scan and (b) a case where APC is performed at a timing outside a printing area in a sub-scanning direction. [Figure 9] It was an explanatory diagram of a timing for performing APC. (a) is an explanatory diagram of a case where APC is performed for each color of K (black), C (cyan), M (magenta), and Y for each scan in a sub-scanning direction, and (b) is an explanatory diagram of a case where APC of K color is performed outside a printing area in a sub-scanning direction. [Figure 10] It is an explanatory diagram of a droop characteristic of a semiconductor laser. [Figure 11] It is an explanatory diagram of a setting example by a user interface of APC performed at a timing outside a printing area in a sub-scanning direction and APC performed for each scan. [Embodiments for Carrying Out the Invention]

[0016] An embodiment of the present disclosure will be described below with reference to the drawings. 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. [[ID= (35]]

[0017] [1. Embodiment] First, the configuration of an image forming apparatus 10 according to an embodiment will be described. FIG. 1 is an external view of the image forming apparatus 10 equipped with an optical scanning apparatus 200 according to the embodiment, and FIG. 2 is a control block diagram of the image forming apparatus 10 and the optical scanning apparatus 200.

[0018] [1.1 Overall Structure] As shown in Figure 1, the image forming apparatus 10 is an information processing device that reads an image from a document using a document reading unit 112 located on the upper part of the image forming apparatus 10 and outputs the image using an electrophotographic method. A multifunction printer can be given as an example of the image forming apparatus 10.

[0019] As shown in the control system diagram in Figure 2, the image forming apparatus 10 mainly comprises 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, and a communication unit 170, and also has the function of an optical scanning device 200.

[0020] [1.2 Image forming apparatus 10] The control unit 100 is a functional unit for controlling the entire image forming apparatus 10.

[0021] The control unit 100 implements various functions by reading and executing various programs, and is composed of, for example, one or more arithmetic units (e.g., a CPU (Central Processing Unit)).

[0022] 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 images of the original document, and receives image data output from the document reading unit 112.

[0023] Furthermore, the image input unit 110 may receive image data from a storage medium such as a USB memory stick or an SD card. Alternatively, the communication unit 170, which connects to other terminal devices, may receive image data from other terminal devices.

[0024] The document reading unit 112 has the function of optically reading a document placed on a contact glass (not shown) and passing the scanned data to the image processing unit 120.

[0025] The image forming unit 130 is a functional unit for forming output data based on image data onto a recording medium (e.g., recording paper). For example, as shown in Figure 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 the paper is ejected from the paper output tray 124. The image forming unit 130 is composed of a laser printer that utilizes an electrophotographic process using an electrophotographic method.

[0026] The electrophotographic process of the image forming unit 130 involves scanning the surface of the photoreceptor drum (image carrier) 130a (see Figure 4) with a laser beam (corresponding to laser light) corresponding to the image data using a light scanning device 200 (described later) to form an electrostatic latent image. This electrostatic latent image is then developed with toner, and the developed toner image is transferred and fixed onto a recording medium (such as recording paper) to form an image. In the image forming apparatus, the image forming unit 130 has photoreceptor drums 130a for each color K (black), C (cyan), M (magenta), and Y (yellow), and the images of each color formed on each photoreceptor drum 130a are transferred and fixed onto the same recording medium to form a color image.

[0027] The image processing unit 120 has the function of converting the image data read by the document reading unit 112 into a set file format (TIFF, GIF, JPEG, etc.). Then, it forms an output image based on the image data that has undergone image processing.

[0028] The control unit 140 is a functional unit for receiving operation instructions from the user and is composed of various key switches and devices for detecting input by contact. The user inputs the functions to be used and output conditions via the control unit 140.

[0029] The display unit 150 is a functional unit for displaying various information to the user, and is composed of, for example, an LCD (Liquid Crystal Display).

[0030] In other words, the operation unit 140 provides a user interface for operating the image forming apparatus 10, and the display unit 150 displays various setting menu screens and messages for the image forming apparatus.

[0031] Furthermore, as shown in Figure 1, the image forming apparatus 10 may include a touch panel in which an operation panel 141 and a display unit 150 are integrally formed, as part of the configuration of the operation unit 140. In this case, the method for detecting input from the touch panel can be any common detection method, such as a resistive touch method, an infrared touch method, an electromagnetic induction method, or a capacitive touch method.

[0032] The memory unit 160 is a functional unit that stores various programs, including control programs necessary for the operation of the image forming apparatus 10, as well as various data, including read data, and user information. The memory unit 160 is composed of, for example, non-volatile ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), etc. It may also be equipped with a semiconductor memory such as an SSD (Solid State Drive).

[0033] The communication unit 170 establishes communication connections with external devices. The communication unit 170 is equipped with a communication interface (communication I / F) used for sending and receiving data. Through the communication I / F, the user can operate the image forming apparatus 10 to send and receive data stored in the storage unit of the image forming apparatus 10 to other computer devices connected via a network.

[0034] [1.3 Optical scanning device 200] As shown in Figure 2, the image forming apparatus 10 is equipped with an optical scanning device 200. Figure 3 shows a specific circuit diagram of the signal transmission path around the laser driver 210 in the optical scanning device 200.

[0035] As shown in Figures 2 and 3, the optical scanning device 200 includes a photosensitive drum 130a that forms an image using an electrophotographic method, a laser light-emitting unit 200a having a semiconductor laser (LD: Laser Device, also called a laser diode) that emits laser light to form an electrostatic latent image on the photosensitive drum, and a digital type laser driver (laser diode driver (LDD): Laser Diode) that controls the amount of light emitted from the laser light-emitting unit 200a so that the amount of light emitted increases or decreases in proportion to the input analog signal, which is the excess current from the bias current. It also refers to the laser driver 210. The laser driver 210 comprises a laser light emitter 200a, an optical scanning unit 220 that scans the laser light emitted from the laser light emitter 200a onto the photosensitive drum 130a of the object, an optical light intensity detection unit 250 that detects the amount of laser light emitted from the laser light emitter 200a, a laser driver setting unit 240 that sets the APC light intensity of the laser light emitter 200a, and an APC control signal generation unit 230 that generates a signal that causes the laser driver 210 to calculate a bias current from the current values ​​due to multiple APC emission from the laser light emitter 200a.

[0036] The APC control signal generation unit 230 generates a signal that causes the laser driver 210 to calculate the bias current of the laser light-emitting unit 200a, which performs exposure of a predetermined color (in this embodiment, K (black)), based on the current values ​​from multiple APC emission from the laser light-emitting unit 200a at a timing outside the printing area in the sub-scanning direction.

[0037] The laser driver setting unit 240 is used to set the APC light intensity and bias current of the laser light emission unit 200a.

[0038] The image forming unit 130 forms a color image, and the photoreceptor drum 130a, optical scanning unit 220, laser light emitting unit 200a, and light intensity detection unit 250, etc., have components for K (black), C (cyan), M (magenta), and Y (yellow). As shown in Figures 2 and 3, the laser light emitting unit 200a that emits laser light toward the photoreceptor drum 130a for each of the K, C, M, and Y colors is denoted by the symbols 200ak, 200ac, 200am, and 200ay, and the light intensity detection unit 250 is denoted by the symbols 250k, 250c, 250m, and 250y.

[0039] As shown in Figures 2 and 3, in the optical scanning device 200, the optical scanning unit 220 has a laser scanning control unit 220a as a control system. The laser scanning control unit 220a is used to input image data output from the image processing unit 120 and the storage unit 160 to the laser driver 210 based on the control signal from the control unit 100, and is composed of an application-specific integrated circuit (LSUASIC). The reference clock signal 200m and the detection signal from the BD sensor 200k are input to this laser scanning control unit 220a's integrated circuit (LSUASIC).

[0040] Image data is read out sequentially from the storage unit 160 based on the detection signal from the BD sensor 200k, according to the irradiation position of the laser beam on the surface of the photoreceptor drum 130a in the main scanning direction.

[0041] Furthermore, the APC current control unit 260 controls the amount of light emitted from the laser light emitter 200a detected by the light intensity detection unit 250, based on the control signal generated from the APC control signal generation unit 230 and the APC light intensity set in the laser driver setting unit 240, thereby controlling the amount of light emitted from the laser light emitter 200a to reach the target light intensity (APC (Automatic Power Control)).

[0042] The light intensity detection unit 250 is equipped with, for example, a photodiode (PD) light intensity detection element located near the laser light-emitting element of the laser light-emitting unit 200a. The APC current control unit 260 monitors the optical output (optical power) P of the laser light-emitting unit 200a detected by the light intensity detection unit 250 and employs a method of automatically controlling the drive current of the laser light-emitting unit 200a so that the optical output reaches the target light intensity.

[0043] Figure 4 shows the mechanical configuration of the optical scanning unit 220 in the optical scanning device 200. As shown in Figure 4, the optical scanning unit 220 scans the photoreceptor drum 130a with laser light to form an electrostatic latent image on the photoreceptor drum 130a. As described above, the image forming unit 130 includes the photoreceptor drum 130a, the optical scanning unit 220, the laser light emitting unit 200a, and the light intensity detection unit 250, etc., each provided for K (black), C (cyan), M (magenta), and Y (yellow).

[0044] The optical scanning device 200 is configured such that a laser light-emitting unit 200a, which consists of a semiconductor laser light-emitting element that generates a laser beam (laser light), is sequentially arranged in the direction of emission of the laser beam from the laser light-emitting unit 200a. This includes a collimator lens 200b that converts the incident laser beam into a parallel beam, an aperture 200c made of a plate-shaped member with an opening 200c1 formed in approximately the center, a concave lens 200e that magnifies the incident laser beam in combination with an fθ lens 200d (described later) that magnifies the laser beam in the scanning direction, a cylindrical lens 200f, and an incident beam reflection mirror 200g.

[0045] Furthermore, in the direction of reflection of the laser beam by the incident beam reflection mirror 200g, an fθ lens 200d and a polygon mirror 200h having multiple reflective surfaces on its outer surface are arranged in sequence. In the direction of reflection of the laser beam by the reflective surface of the polygon mirror 200h, an exit beam reflection mirror 200j that corrects the misalignment of the fθ lens 200d, the reflection mirror 200i, and the polygon mirror 200h, and a photoreceptor drum 130a are arranged.

[0046] The reflected light from the reflective mirror 200i is detected by the beam detect sensor (BD sensor) 200k. The BD sensor 200k is an optical sensor that outputs a detection signal corresponding to the magnitude of the amount of light received by the laser beam. The BD sensor 200k has the function of detecting reflected light from the starting end of the main scanning area of ​​the laser beam (the scanning area along the axial direction of the photoreceptor drum 130a) and is used to control the timing of writing the electrostatic latent image to the photoreceptor drum 130a. Generally, the detection signal from the BD sensor 200k is trigger-like.

[0047] Furthermore, the laser light-emitting unit 200a is equipped nearby with a light intensity detection unit 250 that has a photodiode (PD) for detecting the amount of laser light emitted.

[0048] [1.4 Control Principles of Semiconductor Lasers] <Adjusting the bias current> In the laser light-emitting section 200a of the semiconductor laser, the relationship between light intensity and current is as shown in Figure 5, and a current value greater than or equal to the bias current Ib is supplied to the semiconductor laser to drive light emission.

[0049] In the APC of the laser light-emitting unit (semiconductor laser) 200a, as shown in Figure 5, the threshold current Ith is determined based on the detection current values ​​of the semiconductor laser at low light intensity APC-L and high light intensity APC-H (examples of the light intensity of multiple APC emission) within the light intensity range used for printing (specifically, the threshold current Ith is determined based on the change characteristics of the detection current values ​​of APC-H and APC-L (optical output-forward current characteristics)). The current value obtained by subtracting the register setting value Icoef from the threshold current Ith is the bias current Ib (Ith - Icoef = Ib). Here, the register setting value Icoef is a setting value that is pre-set in the laser driver 210 (or laser driver setting unit 240).

[0050] <Variations in bias current adjustment> In digital laser drivers, as shown in Figure 6, the optical output-forward current characteristics of the semiconductor laser are affected by temperature changes, causing the current value to fluctuate with respect to the amount of light. Therefore, at high and low temperatures (APC-H and APC-L), a decrease in temperature results in a current change of -LSB, and an increase in temperature results in a current change of +LSB, resulting in an overall current value adjustment error of ±1LSB. Therefore, since the threshold current Ith changes by a total of ±2LSB with each adjustment, the bias current Ib will fluctuate.

[0051] Note that the light output of a semiconductor laser (laser diode) decreases as the temperature rises. This is because when the semiconductor laser is energized for a long time, heat is generated in the junction part, the device temperature rises, and if the heat dissipation is insufficient, the case temperature rises and the light output decreases. Therefore, in order to maintain a constant light output, more current needs to be passed through the semiconductor laser.

[0052] <Response Characteristics of Semiconductor Laser> Variations in the bias current Ib also have an adverse effect on the response characteristics of the semiconductor laser. That is, as shown in Fig. 7, in the photon number fluctuation S (output light amount change) shown in (b) with respect to the change in the drive current Iop shown in (a), from the rate equation of the following formula (2), the oscillation delay time t d is derived as follows.

[0053] t d =τ s 1og e {(Iop―Ib) / (Iop―Ith)} ···(2) However, τ s : Carrier lifetime

[0054] Therefore, the closer the bias current Ib is to the threshold current Ith (since t d approaches 0), the faster the response of the semiconductor laser. Therefore, it is necessary to accurately set the bias current from the aspect of response characteristics.

[0055] In the image forming apparatus, during printing, the laser light emitting unit 200a repeatedly generates and dissipates heat, causing repeated temperature changes. Due to this temperature change, as shown in Fig. 6, the bias current set by the APC becomes inappropriate, and an appropriate current is not supplied to the laser light emitting unit, resulting in uneven density.

[0056] <Uneven Density of K (Black) Color> Fig. 8 is an explanatory diagram of printing a halftone image. (a) shows the case where APC is performed for each color of K (black), C (cyan), M (magenta), and Y during each scan, and (b) shows the case where APC for the K color is performed outside the printing area in the sub-scanning direction.

[0057] As shown in Figure 8(a), when using a digital laser driver for halftone printing, density unevenness sometimes occurred within the K color page when APC was performed after each scan. On the other hand, for C, M, and Y colors, density differences are inherently difficult to perceive visually, so even if they occur, they are difficult to notice.

[0058] Therefore, when performing APC for each semiconductor laser for K, C, M, and Y colors, as shown in Figure 8(b), if the semiconductor laser for K is driven in a constant ON state without performing K-color APC within the printing area in the sub-scanning direction, while APC for C, M, and Y colors, including K, is performed outside the printing area in the sub-scanning direction, it can be seen that no noticeable density unevenness occurs in the printed image.

[0059] Based on the above, in this embodiment, the APC control signal generation unit 230 generates a signal that causes the laser driver to calculate the bias current of the laser light-emitting unit 200a, which performs exposure of a predetermined color (in this embodiment, K (black)), based on the current values ​​from multiple APC emission from the laser light-emitting unit 200a at a timing outside the printing area in the sub-scanning direction.

[0060] [1.5 Control details of the embodiment] Figure 9 shows a specific timing diagram of the signals generated by the APC control signal generation unit 230 to cause the laser driver to calculate the bias current. (a) illustrates the timing outside the print area, and (b) illustrates the timing inside the print area for K (black) APC control. Note that the Nth scan of each sub-scan direction is shown as an example.

[0061] As shown in Figure 9(a) for the APC at the out-of-print area timing during the Nth scan, all APCs (black, cyan, magenta, and yellow) are performed.

[0062] On the other hand, Figure 9(b) shows the APC timing within the print area in the sub-scan direction during the Nth scan. Within the print area, APC is performed for C (cyan), M (magenta), and Y (yellow), but K (black) is in a mode where it is forced to emit light without APC (indicated by the symbol "ON" in Figure 9). Note that the portion where K (black) is forced to emit light (ON) is used for BD signal generation, and the N+1th scan begins from the timing when the BD signal is received during the Nth scan.

[0063] [1.6 Effects of the Embodiment] Therefore, in this embodiment, it is possible to suppress density unevenness of the easily recognizable K (black) color. Furthermore, for C (cyan), M (magenta), and Y (yellow) colors, it is possible to suppress color unevenness in the sub-scanning direction, as in the conventional method.

[0064] Therefore, according to this embodiment, the bias current for the K (black) color does not change during printing, and the response of the semiconductor laser does not change, thus eliminating streaky or band-like density unevenness caused by bias current adjustment. Furthermore, for the C (cyan), M (magenta), and Y (yellow) colors, APC is performed even during printing, making them less susceptible to the effects of the laser's droop characteristics and suppressing color unevenness in the sub-scanning direction.

[0065] [2. Variation 1] Modification 1, which takes into account the droop characteristics of a semiconductor laser, will be explained.

[0066] Semiconductor lasers have a property (droop characteristic) where the amount of light decreases as the temperature rises or as the operating time elapses when driven with a constant current, resulting in a decrease in light intensity over time. Here, the rate of decrease in light intensity due to time (droop rate) can be expressed by the following equation (3), referring to the graph of light intensity as a function of current for a semiconductor laser shown in Figure 10.

[0067] ΔP=(P1-P2) / P2×100[%] ···(3)

[0068] Furthermore, P1 is defined as the maximum output from the rise time of the optical output until the fall time, starting from 1 μs (microseconds), and P2 is defined as the optical output at the fall time. The conditions are temperature Tc = 25°C, rated maximum output P0 = 3 mW, f = 1 kHz, and duty cycle = 50%, resulting in ΔP being 10%.

[0069] If APC (Automatic Printing Control) is performed using a K-color semiconductor laser outside the printing area in the sub-scanning direction, and APC is not performed within the printing area, continuous light emission will occur within the printing area, such as in the case of solid printing (where the printing surface is covered with a single color without gradation), resulting in smaller line widths and dot diameters in the latter half of the page.

[0070] Therefore, in the case of printing only characters such as those on a facsimile (character printing mode), the APC control signal generation unit 230 generates a signal that causes the laser driver 210 to calculate the bias current for each scan, even within the printing area timing, which improves print quality and is preferable.

[0071] In other words, in text printing modes such as those used for facsimile, there is no halftone area, so it is not necessary to address streaky or band-like density variations caused by bias current adjustments. On the other hand, if APC is not performed during printing, lines may become thinner due to the effects of droop characteristics. Therefore, in text printing mode, performing APC after each scan can suppress the effects of droop characteristics and improve print quality.

[0072] Therefore, as shown in Modification Example 1, the influence of droop characteristics can be suppressed by performing APC in the case of high-density printing of characters, etc.

[0073] [3. Variation 2] Modification 2 allows the user interface to arbitrarily switch between generating a signal for the laser driver 210 to calculate the bias current using the APC control signal generation unit 230 at the timing outside the printing area in the sub-scanning direction and per scan.

[0074] Modification 2, as shown in the setting example in Figure 11, allows switching between enabling or disabling APC within the K-color printing area (within the printing area in the sub-scanning direction) for job combinations of print mode (print, facsimile (FAX), copy) and document type (text, text / printed photo, text / photographic paper photo, printed photo, photographic paper photo, map, faint document) via input from the operation unit 140 (user interface) or operation panel 141.

[0075] In modes primarily used for printing text, it is preferable to perform APC (Advanced Printing Control) to suppress the effects of droop characteristics. Therefore, in Modification 2, the operation unit 140 or operation panel 141 allows the user to enable or disable APC for each mode, thus allowing them to customize the process to their preference.

[0076] In the example settings shown in Figure 11, when printing characters in facsimile mode, APC is enabled within the K-colored printing area (within the printing area in the sub-scanning direction), while in other cases, APC in the K-colored printing area is disabled. Figure 11 is just one example, and other settings can be customized to the user's preferences.

[0077] While embodiments have been described above, the specific configuration is not limited to these embodiments, and designs and the like that do not depart from the spirit of the present invention are also included in the scope of the claims.

[0078] Furthermore, in the embodiments, the programs that run in each device are programs that control the CPU and the like (programs that make the computer function) in order to realize the functions of the embodiments described above. The information handled by these devices is temporarily stored in a temporary storage device (e.g., RAM) during processing, and then stored in various ROMs or HDDs, and read, modified, and written by the CPU as needed.

[0079] Here, the recording medium for storing the program can be any non-temporary recording medium, such as semiconductor media (e.g., ROM or non-volatile memory cards), optical recording media / magneto-optical recording media (e.g., DVD (Digital Versatile Disc), MO (magneto Optical Disc), MD (Mini Disc), CD (Compact Disc), BD, etc.), or magnetic recording media (e.g., magnetic tape, flexible disk, etc.).

[0080] Furthermore, in addition to realizing the functions of the above-described embodiment by executing the loaded program, the functions of this disclosure may also be realized by processing in cooperation with the operating system or other application programs, etc., based on the instructions of that program.

[0081] Furthermore, when distributing a program to the market, it can be stored in a portable storage device and distributed, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is, of course, also included in the present invention.

[0082] Furthermore, some or all of the devices in the embodiments described above may be implemented as LSIs (Large Scale Integrations), which are typically integrated circuits. Each functional block of each device may be individually chipped, or some or all of them may be integrated into a single chip. Moreover, the method of implementing the integrated circuit is not limited to LSIs; it may also be implemented using dedicated circuits or general-purpose processors. Furthermore, if advances in semiconductor technology lead to the emergence of integrated circuit technologies that can replace LSIs, it is of course possible to use integrated circuits based on those technologies. [Explanation of Symbols]

[0083] 10 Image forming apparatus 100 Control Unit 130 Image forming unit 130a Photoconductor Drum 140 Operation section 141 Control Panel 200 Optical scanning device 200a Laser light-emitting section 210 Laser Driver 220 Optical scanning unit 220a Laser scanning control unit 230 APC Control Signal Generation Unit 240 Laser Driver Setting Section 250 Light intensity detection unit 260 APC Current Control Unit

Claims

1. In an image forming apparatus that performs color printing using a digital laser driver with an automatic bias current adjustment function, A laser light emitter that emits laser light to expose the photosensitive material, The APC current control unit controls the APC emission current of the laser light-emitting unit, The system includes an APC control signal generation unit that generates a signal to cause the laser driver to calculate a bias current from the current values ​​generated by multiple APC emissions from the laser light-emitting unit, The APC control signal generation unit is An image forming apparatus characterized by generating a signal that causes a laser driver to calculate the bias current of a laser light-emitting unit that performs exposure of a predetermined color, based on the current values ​​from multiple APC emission from the laser light-emitting unit at a timing outside the printing area in the sub-scanning direction.

2. The image forming apparatus according to claim 1, wherein the predetermined color is black, and for the laser light-emitting unit that performs exposure of a color other than the predetermined color, the APC control signal generation unit generates a signal that causes the laser driver to calculate the bias current for each scan, even at the timing within the printing area in the sub-scanning direction.

3. The image forming apparatus according to claim 1, characterized in that the APC control signal generation unit generates a signal that causes the laser driver to calculate a bias current for each scan, including the predetermined black color, even at the timing within the printing area in the sub-scanning direction in the character printing mode.

4. The image forming apparatus according to claim 1, characterized in that the APC control signal generation unit allows switching between APC performed at timings outside the printing area in the sub-scanning direction and APC performed with each scan via a user interface.

5. In a control method for an image forming apparatus that performs color printing using a digital laser driver with an automatic bias current adjustment function, A laser emission process in which a laser beam is emitted from a laser emission unit to expose a photosensitive material, APC current control step for controlling the APC emission current of the laser emission unit, The system includes an APC control signal generation step that generates a signal that causes the laser driver to calculate a bias current from the current values ​​generated by multiple APC emission units of the laser light-emitting section, The APC control signal generation process is as follows: A control method for an image forming apparatus, characterized in that, in calculating the bias current of a laser light-emitting unit that performs exposure of a predetermined color, a signal is generated that causes the laser driver to calculate the bias current based on the current values ​​from multiple APC emission from the laser light-emitting unit at a timing outside the printing area in the sub-scanning direction.

Images