Image forming apparatus and position control method

According to one embodiment, an image reading apparatus includes an exposure unit, a light sensor, and a controller. The exposure unit selectively emits light to positions along a first scan direction to write pixels in accordance with a main scan line of image data. The light sensor is at a position to receive light from the exposure unit and is configured to output a synchronization signal according to the detection of the light emitted for each main scan line of image data. The controller adjusts a starting pixel position along the first scan direction for a main scan line of image data based on a change in an output interval of the synchronization signal resulting from a change in an intensity of light emitted by the exposure unit.

FIELD

Embodiments described herein relate generally to an image forming apparatus and a position control method.

BACKGROUND

When forming an image on a sheet, the image forming apparatus scans the scanning area of a photoreceptor drum with a laser beam along the main scanning direction. The laser beam contains a signal in units of a pixel. Thus, the image forming apparatus forms a plurality of dots along the main scanning direction by scanning the laser beam through the scanning area from a dot start position to a dot end position. There may be cases where the positions of dots formed along the main scanning direction deviate from the reference or intended positions, thus there is a possibility that the position of the image on the sheet deviates from an expected or intended location. In order to prevent the position of the image from deviating, it is necessary to correct the positions of dots along the main scanning direction to be at appropriate positions.

In the related art, there is an image forming apparatus that detects a scanning laser beam with a sensor in order to prevent a deviation in the positions of dots along the main scanning direction. The image forming apparatus determines the timing for starting formation of the dots (dotting) along the main scanning direction based on a horizontal synchronization signal output from the sensor in response to the detection of the laser beam.

However, the reaction time of the sensor from the exposure by the laser beam to the actual output of the horizontal synchronization signal by the sensor may differ depending on the intensity of the laser beam. For example, different light intensities may be output according to the type of sheet being printed, the state of the photoreceptor drum deterioration, and the like. Thus, there may be a problem with deviation of the positions of dots along the main scanning direction from the reference positions if the laser beam output varies.

DETAILED DESCRIPTION

An image forming apparatus and a position control method are described. The apparatus and control method are capable of reducing deviations from intended dotting positions along a main scanning direction that might otherwise be caused by changes in the characteristics of a laser beam.

According to one embodiment, an image reading apparatus includes an exposure unit, a light sensor, and a controller. The exposure unit is configured to selectively emit light to positions along a first scan direction to write pixels in accordance with a main scan line of image data. The light sensor is at a position to receive light from the exposure unit and configured to output a synchronization signal according to the detection of the light emitted for each main scan line of image data. The controller is configured to adjust a starting pixel position along the first scan direction for a main scan line of image data based on a change in an output interval of the synchronization signal resulting from a change in an intensity of light emitted by the exposure unit.

An image forming apparatus and a position control method according to certain, non-limiting example embodiments will be described with reference to the drawings.

FIG. 1is a diagram illustrating an example of an internal configuration of an image forming apparatus1according to the embodiment. The image forming apparatus1is an electrophotographic image forming apparatus. For example, the image forming apparatus1is a multi-function peripheral (MFP). The image forming apparatus1may be referred to as a printer or a copier in some instances. In the present embodiment, the case where the image forming apparatus1is a double-tandem type image forming apparatus will be described as an example, but the present disclosure is not limited to this type of image forming apparatus.

The image forming apparatus1can generate image data. The image data is digital data generated by reading an image from recording medium such as sheet of paper or the like or the image data may be provided to the image forming apparatus1from an external device. The image forming apparatus1forms an image corresponding to the image data on a sheet by using toner. For example, the sheet is paper, film, or the like. In general, the sheet may be made of any material as long as the image forming apparatus1can form an image on the sheet.

The image forming apparatus1includes an operation display unit2, a scanner unit3, a printing unit4, a paper feeding unit5, a conveying unit6, and a paper ejecting unit7.

The operation display unit2includes a display unit11and an operation unit12.

The display unit11operates as an output interface and displays characters, text and images to a user. For example, the display unit11is a display device such as a liquid crystal display (LCD) or an organic Electro Luminescence (EL) display. The display unit11displays various information related to operations and functions of the image forming apparatus1.

The operation unit12operates as an input interface for a user and receives inputs reflecting the instructions from the user. For example, the operation unit12includes a plurality of buttons, keys, switches, or the like. The operation unit12receives user input operations via the buttons and the like.

The display unit11and the operation unit12may be integrated with each other as a touch panel display or the like. For example, the operation display unit2may be a touch panel type liquid crystal display. That is, the operation display unit2may operate as both an output device and an input device.

In a case where the operation mode of the image forming apparatus1is a scan (scanner) mode, the scanner unit3reads image information from an object to be scanned. The scanner unit3comprises, for example, a contact image sensor (CIS), a charge coupled device (CCD), or the like. The scanner unit3reads an image from a sheet, document, or other object by using a sensor to generate image data.

In a case where the operation mode of the image forming apparatus1is a copy (copier) mode, the printing unit4prints images on sheets based on the image data generated by the scanner unit3. In other operation modes, the printing unit4may print images based on image data acquired from another information processing apparatus (an external device) via a network or the like. The printing unit4forms an image on a sheet with toner. A sheet with an image formed thereon may be referred to as a hard copy, a printout, or the like.

As non-limiting examples of toner, a decolorable toner, a non-decolorable toner (“normal toner”), or a decorative toner (“specialty toner”) are described. The decolorable toner can be decolorized by an external stimulus, such as heat, light of a specific wavelength, or pressure. In this context “decolorized” or “decolorable” refers to an image or material that changes from an initial, printed color to either become a different color matching a base color of the paper on which the image was printed or otherwise substantially visually undetectable with an unaided eye. External stimuli which might be utilized for decolorizing decolorable images are temperature changes, exposure to light of a specific wavelength, and pressure changes, or combinations of such stimuli.

As a decolorable toner, any toner may be used as long as the toner has the above-described characteristics. For example, a colorant of the decolorable toner may be a leuco dye. The decolorable toner may be appropriately combined with a color developing agent, a decolorizing agent, a discoloration temperature adjusting agent, and the like.

The paper feeding unit5supplies the sheets to the printing unit4. The paper feeding unit5supplies sheets one by one to the printing unit4in accordance with a timing at which the printing unit4forms the toner image. The paper feeding unit5includes paper feeding cassettes15,16, and17. Each of the paper feeding cassettes15,16, and17stores sheets of a predetermined size and type. In this context, a sheet type may be based, for example, on sheet thickness, such that plain paper is one type and thick paper is another type.

The paper feeding cassettes15,16, and17include pickup rollers15-1,16-1, and17-1, respectively. The pickup rollers15-1,16-1, and17-1respectively take out a sheet from the paper feeding cassettes15,16, and17. The pickup rollers15-1,16-1, and17-1supply the taken-out sheets to the conveying unit6.

Sheets specifically for forming decolorable images may be stored in anyone of the plurality of paper feeding cassettes15,16, and17. In some examples, since an image of a sheet formed with the decolorable toner may be later decolorized, the sheet may be reused after the decolorization processing of the previously printed sheet in a decolorizing mode. Thus, it is possible to reuse such a sheet a plurality of times.

The conveying unit6transports the sheet between various portions of the image forming apparatus1. In the following description, since the sheets are conveyed from the paper feeding unit5to the paper ejecting unit7, points along the sheet conveyance path that are closer to the paper feeding unit5(may be referred to as “on the paper feeding unit5side” are referred to as being on an upstream side along a sheet conveyance direction Vs of the sheet conveyance path, and points along the sheet conveyance path that are closer to the paper ejecting unit7(may be referred to as “on the paper ejecting unit7side”) are referred to as being on a downstream side along the sheet conveyance direction Vs of the sheet conveyance path.

The conveying unit6includes a pair of conveying rollers20and a pair of registration rollers21.

The conveying roller20conveys the sheets supplied from the pickup rollers15-1,16-1, and17-1to the registration roller21. The conveying roller20abuts the downstream end of the sheet (“leading edge”) against the nip21-1of the registration rollers21. The conveying roller20thus adjusts the position of the downstream end of the sheet.

The registration roller21temporarily stops the sheet being conveyed by the conveying roller20. The registration roller21then sends the sheet toward a secondary transfer unit37in accordance with the timing at which the toner image is formed on an intermediate transfer body32. The toner image on the intermediate transfer body32is transferred to the sheet by the secondary transfer unit37. The registration rollers21face each other along a conveying path between the conveying roller20and the secondary transfer unit37. A nip21-1is formed between the pair of registration rollers21.

The registration roller21aligns the downstream ends of each sheet sent from the conveying roller20at the nip21-1, and after that the alignment, conveys the sheet along to the secondary transfer unit37side.

A reversing unit25reverses the sheets after fixing unit40by a switchback operation. The reversing unit25conveys the reversed sheet back to the front of the registration roller21again. The reversing unit25reverses the sheet so a toner image can be formed on the back surface of a sheet. Thus, double-sided printing can be performed on sheets.

The printing unit4is illustrated in more detail inFIG. 2.FIG. 2is a diagram illustrating one example of the schematic configuration of image forming apparatus1according to the embodiment.

The printing unit4includes a transfer unit30and a fixing unit40.

The transfer unit30includes an exposing unit31, the intermediate transfer body32, a cleaning blade33, image generating units34and35, primary transfer rollers36-1and36-2, a secondary transfer unit37, a temperature detection unit38, and a temperature adjustment unit39.

The temperature detection unit38detects the temperature around the secondary transfer unit37. For example, the temperature detection unit38is a temperature sensor.

The temperature adjustment unit39functions to adjust the temperature around the secondary transfer unit37based on the detection result of the temperature detection unit38. For example, the temperature adjustment unit39is a fan. The temperature adjustment unit39may have more functions and purpose beyond just adjusting the temperature around the secondary transfer unit37. For example, the temperature adjustment unit39may function for the purpose of ejecting or venting ozone from the image forming apparatus.

The image transfer process in the image forming apparatus1includes a first transfer step and a second transfer step.

In the first transfer step, the primary transfer rollers36-1and36-2can each transfer a toner image from respective photoreceptor drums34-1and35-1to the intermediate transfer body32.

In the second transfer step, the secondary transfer unit37transfers the toner images formed on the intermediate transfer body32to the sheet. In general, the toner images from each of the generating units34and35are stacked one upon the other on the intermediate transfer body32before being transferred together to the sheet at the secondary transfer unit37.

The scanner unit3reads an image from a sheet, document, or object to be scanned. For example, the scanner unit3reads a color image on a sheet and the generates image data corresponding to scanned color image. The scanner unit3outputs the generated image data to an image processing unit8.

The image processing unit8controls the exposing unit31based on a color signals corresponding to the image data from the scanner unit3.

The exposing unit31irradiates the photoreceptor drums34-1and35-1of the image generating units34and35with light (exposure) according to respective color signals.

The intermediate transfer body32rotates in the direction of an arrow A ofFIG. 2. The intermediate transfer body32may be a belt. A toner image is formed on the surface of the intermediate transfer body32.

The cleaning blade33removes the toner still attached to the intermediate transfer body32after the secondary transfer process. The cleaning blade33is, for example, a plate-shaped member. In some examples, cleaning blade33is made of a resin such as urethane resin. The tip of the cleaning blade33presses against the intermediate transfer body32to scrape off toner from the intermediate transfer body32. Instead of, or in addition to, a cleaning blade33, a charged brush may be brought into contact with the intermediate transfer body32.

The image generating units34and35form images using toner of different respective colors or types. The image generating units34and35are provided along the intermediate transfer body32in series. Image generating unit34is before the image generating unit35in the present example.

In the present example, image generating unit34utilizes a decolorable toner. The image generating unit34(referred to in this context as “decolorized image generating unit34”) contains the decolorable toner and thus transfers a decolorable toner image to the intermediate transfer body32. In the present example, the decolorable toner has a blue color when initially fixed to a sheet.

The image generating unit35is downstream of the decolorized image generating unit34along the rotation direction A of the intermediate transfer body32. The image generating unit35utilizes a non-decolorable toner32. In the embodiment, the image generating unit35(referred to in this context as “non-decolorized image generating unit35”) contains a non-decolorable black toner.

The image forming apparatus1of this example executes printing in the following two modes:Monochrome toner mode (An image is formed with non-decolorable toner)Decolorable toner mode (An image is formed with decolorable toner).

The mode can be selected by the user of the image forming apparatus1.

In the monochrome toner mode, an image is formed by operation of the non-decolorized image generating unit35using of black non-decolorable toner. The monochrome toner mode can be selected if the user desires to print a general monochrome image. For example, this mode is used if important materials are to be printed without reusing paper.

In the decolorable toner mode, an image is formed by operating just the decolorized image generating unit34using the decolorable toner. The decolorable toner mode can be selected if the paper is to be reused at a later time.

The decolorized image generating unit34and the non-decolorized image generating unit35have generally the same configuration although different toners are contained therein. Therefore, the decolorized image generating unit34will be particularly described as a representative example of both the image generating units34and35.

The decolorized image generating unit34includes a photoreceptor drum34-1, a developer34-2, a charger34-3, and a cleaning blade34-4.

The photoreceptor drum34-1is one type of image carrier. The photoreceptor drum34-1has a photoreceptor on the outer peripheral surface. For example, the photoreceptor is an organic photoconductor (OPC).

The developer34-2contains a developing agent. The developer includes toner. The developer34-2supplies toner to the photoreceptor drum34-1. For example, the toner is used as a one-component developing agent or as a two-component developing agent in combination with a carrier. For example, as a carrier, iron powder or polymer ferrite particles having a particle size of several tens of microns are used. In the present embodiment, a two-component developing agent containing a non-magnetic toner is used.

The charger34-3uniformly charges the surface of the photoreceptor drum34-1.

The cleaning blade34-4removes toner attached to the photoreceptor drum34-1.

The outline of the operation of the decolorized image generating unit34will be described.

The photoreceptor drum34-1is charged to a predetermined potential by the charger34-3. Next, the exposing unit31selectively irradiates the photoreceptor drum34-1with light (e.g., a laser beam). The electrostatic potential of the area irradiated with light in the photoreceptor drum34-1changes. An electrostatic latent image is formed on the surface of the photoreceptor drum34-1as a result of the selective irradiation. The electrostatic latent image on the surface of the photoreceptor drum34-1is then developed with the developing agent of the developer34-2. That is, a developed image formed toner is on the surface of the photoreceptor drum34-1.

The developed image formed on the surface of the photoreceptor drum34-1is then transferred to the intermediate transfer body32by the primary transfer roller36-1facing the photoreceptor drum34-1.

An image is formed by using only the decolorable toner in this example. That is, by the operation of the decolorized image generating unit34, a decolorable toner image is formed on the intermediate transfer body32.

If just the non-decolorized image generating unit35operates, a non-decolorable toner image is formed on the intermediate transfer body32.

The non-decolorized image generating unit35includes a photoreceptor drum35-1, a developer35-2, a charger35-3, and a cleaning blade35-4.

The respective one of the primary transfer rollers36-1or36-2is used for transferring the toner image formed by the image generating units34and35to the intermediate transfer body32.

The second transfer step will be described.

The secondary transfer unit37includes a secondary transfer roller37-1and a facing secondary transfer roller37-2. In the secondary transfer unit37, the intermediate transfer body32and the secondary transfer roller37-1are in contact with each other. For rectifying paper jams and the like, the intermediate transfer body32and the secondary transfer roller37-1may be configured to be separable from each other.

A bias voltage is applied to the secondary transfer roller37-2. Thus, an electric field is generated between the secondary transfer roller37-2and the secondary transfer roller37-1. With this electric field, the secondary transfer unit37transfers the toner image formed on the intermediate transfer body32to the sheet. The sheet is then guided to the fixing unit40.

The fixing unit40can be controlled to be in a fixing mode or a decolorizing mode. In the fixing mode, the toner image is fixed to the sheet. In the decolorizing mode, the toner image is decolorized. The fixing unit40fixes the toner image to the sheet by heat and pressure. For example, the fixing unit40includes a heated roller (heating unit) and a pressuring unit. After the fixing unit40the sheet can be ejected from the paper ejecting unit7to the outside of the image forming apparatus1.

The exposing unit31of the printing unit4will be described.FIG. 3is a plan view illustrating an example of a schematic configuration of the exposing unit31according to the present embodiment.

The exposing unit31includes a light source50, a light control circuit51, a light deflection unit52, a first imaging lens53, a second imaging lens54, an optical path changing unit55, an optical path changing unit56, a mirror57, and a sensor58.

The light source50in this example is a Laser Diode (LD) that emits a laser beam (light). In other examples, the light source50may be a Light Emitting Diode (LED).

The light control circuit51includes a laser driver that causes the light source50to emit light. The light source50outputs an optically-modulated laser beam based on an optical modulation signal by the control of the light control circuit51. For example, the optical modulation signal is generated based on an image data signal and a horizontal synchronization signal. The laser beam emitted from the light source50can be supplied to a collimator lens then be incident on the reflecting surfaces of the polygon mirror52-1.

The light deflection unit52in this example includes a regular polyhedral polygon mirror52-1having a reflecting surface formed on each side of the regular polyhedron. The polygon mirror52-1is rotated around the rotation axis52-2by the motor52-3. The polygon mirror52-1rotates in the direction of an arrow Ra at a steady angular velocity and deflects the laser beam at each reflecting surface generally increasing the direction of arrow Rb as the polygon mirror52-1rotates. It is generally preferable that the polygon mirror52-1rotates at constant angular velocity.

The polygon mirror52-1continuously reflects the laser beam output from the light source50at positions along the axial directions of the photoreceptor drums34-1and35-1. The polygon mirror52-1continuously reflects the laser beams from the light source50in a direction paralleling the scanning lines during reading the image by the scanner unit3. The laser beams reflected by the polygon mirror52-1pass through the first imaging lens53and the second imaging lens54, and at the exposure position on the photoreceptor drums34-1and35-1, the photoreceptor drums34-1and35-1are sequentially irradiated at positions along the axial directions.

The first imaging lens53and the second imaging lens54provide predetermined optical characteristics to the laser beam reflected by the polygon mirror52-1. The first imaging lens53and the second imaging lens54extend in the axial directions of the photoreceptor drums34-1and35-1. The first imaging lens53and the second imaging lens54help form an image on the photoreceptor drums34-1and35-1so that the relationship between the rotation angle of the polygon mirror52-1and the focal length satisfies an image height requirement. The first imaging lens53and the second imaging lens54cooperate with a cylindrical lens or the like to provide convergence to the laser beam reflected by the polygon mirror52-1.

The rotational axis of the photoreceptor drums34-1and35-1is parallel to the main scanning direction in the image formation process. The surfaces of the photoreceptor drums34-1and35-1are scanned along the main scanning direction with the laser beam reflected by the polygon mirror52-1. Reference numeral “Sc” inFIG. 3denotes the main scanning direction. The main scanning direction Sc is a direction parallel to the rotational axis. The sub-scanning direction is a direction perpendicular to the main scanning direction and thus corresponds to a circumferential direction of the photoreceptor drums34-1and35-1.

As depicted inFIG. 4, the optical path changing units55and56are arranged between the second imaging lens54and the photoreceptor drums34-1and35-1.

The optical path changing unit55directs a decolorizing image laser beam BD that passes through the second imaging lens54toward the photoreceptor drum34-1. The optical path changing unit55includes a plurality of mirrors55-1,55-2, and55-3. The laser beam BD that passes through the second imaging lens54is reflected by the mirrors55-1,55-2, and55-3in this order so as to be incident on the photoreceptor drum34-1.

The optical path changing unit56directs a non-decolorizing image laser beam BK that passes through the second imaging lens54toward the photoreceptor drum35-1. The optical path changing unit56includes a plurality of mirrors56-1,56-2, and56-3. The laser beam BK that passes through the second imaging lens54is reflected by the mirrors56-1,56-2, and56-3in this order so as to be incident on the photoreceptor drum35-1.

As depicted inFIG. 3, mirror57reflects light that passes through the first imaging lens53toward the sensor58.

The sensor58is arranged in an area away from the photoreceptor drums34-1and35-1. For example, the sensor58is positioned to receive light from near the starting edge side in the main scanning direction Sc. In other words, the sensor58receives light from a laser beam near the beginning of a scan in the main scanning direction Sc. The sensor58detects the laser beam with which scanning area J1will be scanned in order to synchronize the start timing of dot formation along the main scanning direction Sc.

In this context, the scanning area J1denotes the area on the surface of the photoreceptor drums34-1and35-1, which is scanned with the laser beam during the latent image formation process involving selective exposure of particular dot locations (image pixels) along the main scanning direction Sc according to the image data. The scanning start position in this context refers to the starting edge position of the scanning area J1along the main scanning direction Sc. The scanning start position is located at the starting edge of a scanning line. The scanning end position in this context refers to the ending edge position opposite to the scanning start position in the main scanning direction Sc. The scanning end position is located at the ending edge of a main scanning line formed in the scanning area J1.

The sensor58is a horizontal synchronization sensor in this example. The sensor58supplies a horizontal synchronization signal to the light control circuit51. The horizontal synchronization signal is used for a switching timing of each line formed in the scanning area J1. The horizontal synchronization signal can be used as a signal that indicates the end of a scanning of one line and the start of a scanning of another line (the next line).

The light control circuit51determines the time to start outputting the image data for each line based on the detection result of the sensor58. Specifically, the time is the dotting start time for dots along the main scanning direction Sc.

FIG. 5is a block diagram illustrating an example of the functional configuration of the image forming apparatus1according to an embodiment. Each functional unit of the image forming apparatus1is connected via a system bus100.

The control unit101controls the operation of each functional unit of the image forming apparatus1. The control unit101executes various processes by executing a software program or the like. The program can be recorded in advance in, for example, the storage device103. The program may be recorded in advance in the memory104or an external recording medium or the like. The control unit101acquires the instructions input by the user via the operation display unit2. The control unit101executes a control process based on the acquired instruction(s).

For example, the control unit101can control the rotation speed of the secondary transfer roller37-1.

The control unit101may increase the temperature of the fixing unit40to switch to decolorizing mode from the fixing mode. That is, the control unit101operates the fixing unit40to be at two or more target temperatures. Specifically, the memory104stores two target temperatures (set points) for the fixing unit40. The control unit101loads the target temperature from the memory104according to the selected mode and operates the fixing unit40according to the target temperature. A first temperature is a temperature target in the decolorizing mode. A second temperature is a temperature target in the fixing mode. The second temperature is lower than the first temperature.

FIG. 6is a block diagram illustrating an example of the functional configuration of the control unit101according to an embodiment.

The control unit101includes a time measuring unit110, a light amount switching unit111, a delay amount difference calculation unit112, a sheet information acquisition unit113, a deteriorated state acquisition unit114, and a timing correction unit115.

The time measuring unit110measures the interval at which the horizontal synchronization signal output from the sensor58is sent to the light control circuit51. The time measuring unit110measures the interval with a counter that counts, for example, the number of internal clock cycles.

The light amount switching unit111switches the power output of the laser beam from the light source50. In the present embodiment, the light amount switching unit111switches between a first light amount setting and a second light amount setting. The second light amount setting results in a laser beam that has less power (intensity) than the laser beam at the first light amount setting. The light supplied at first light amount setting is referred to as a “normal light amount,” and the light supplied at the second light amount setting is referred to as a “dimmed light amount”. In the present embodiment, the light amount switching unit111is configured to switch to between two different light amount settings, but in other examples the light amount switching unit111may be configured to switch between three or more light amount settings.

The delay amount difference calculation unit112calculates the difference (hereinafter, referred to as a “delay amount difference value”) between the delay amount when the laser beam is a normal light amount and the delay amount when the laser beam is a dimmed light amount. The delay amount referred to herein is the time from when the laser beam is first incident on the sensor58to when the sensor58subsequently outputs the horizontal synchronization signal to the light control circuit51. The delay amount difference calculation unit112records the calculated delay amount difference value in the storage device103.

The sheet information acquisition unit113acquires information (“sheet information”) indicating the type of sheet on which image formation will be performed. The type of sheet relevant in this context is, for example, whether the sheet is plain paper or thick paper. The sheet information can be generated, for example, when the user performs an operation with the operation unit12for selecting the type of sheet.

The deteriorated state acquisition unit114acquires information indicating the deteriorated state of the photoreceptor drums34-1and35-1. The deterioration referred to here is, for example, increased difficulty in changing the photoreceptor potential when exposed to the same light amount. The information indicating the deteriorated state of the photoreceptor drums34-1and35-1may be generated by any method. For example, the information may be a deterioration metric calculated or estimated based on the number of times the photoreceptor drums34-1and35-1have been used in an image formation process, the total exposure time to which each photoreceptor drum34-1and35-1has been subjected, and/or an age (e.g., the time since installation) of the photoreceptor drums34-1and35-1.

The light amount switching unit111acquires sheet information from the sheet information acquisition unit113. The light amount switching unit111also acquires the sheet type/light amount correspondence information recorded in advance in the storage device103. The sheet type/light amount correspondence information indicates a light amount to be used with different sheet types. For example, the normal light amount is to be used with plain paper, but the dimmed light amount is to be used with thick paper.

The light amount switching unit111specifies the light amount setting according to type of sheet based on the sheet type/light amount correspondence information. The light amount switching unit111switches the light amount setting for the laser beam output from the light source50to the specified light amount setting as necessary.

The light amount switching unit111may be configured to switch the light amount setting based on the information indicating the deteriorated state of the photoreceptor drums34-1and35-1as acquired from the deteriorated state acquisition unit114. In this case, the light amount switching unit111acquires the deteriorated state/light amount correspondence information from the storage device103. The deteriorated state/light amount correspondence information indicates the light amount to be used according to the deterioration state of the photoreceptor drums34-1or35-1. For example, the normal light amount is to be used with a more deteriorated photoreceptor drum, and the dimmed light amount is to be with a less deteriorated photoreceptor drum. The light amount switching unit111specifies the light amount setting according to the deteriorated state of the photoreceptor drums34-1and35-1based on the acquired deteriorated state/light amount correspondence information. The light amount switching unit111switches the light amount setting for the laser beam output from the light source50to the specified light amount as necessary.

The timing correction unit115acquires the delay amount difference value recorded in the storage device103by the delay amount difference calculation unit112. The timing correction unit115performs the control to correct the dotting start timing of dots in the main scanning direction Sc based on the acquired delay amount difference value.

For example, when the dimmed light amount is being used, the timing correction unit115corrects the delay in the dotting start timing of dots by the delay amount difference value. The delay amount difference value is, for example, a value such as a number of dots, a number of clock cycles, or a time. On the other hand, when the normal light amount is being used, the timing correction unit115may leave the dotting start timing of dots along the main scanning direction Sc unadjusted.

The network interface102transmits/receives data to/from another apparatus. The network interface102operates as an input interface and receives data transmitted from another apparatus. The network interface102also operates as an output interface and transmits data to another apparatus.

The storage device103stores various data. For example, the storage device103is a hard disk or a solid-state drive (SSD). For example, in this context various data may include digital data, screen data of a setting screen, setting information, a print job, a print job log, or the like. The various data may also include the above-described delay amount difference value, sheet type/light amount correspondence information, deteriorated state/light amount correspondence information, and the like.

The memory104temporarily stores the data being used by each functional unit. For example, the memory104is a random-access memory (RAM). For example, the memory104temporarily stores digital data, print jobs, print job logs, and the like.

The correction control of the deviation in the dotting positions of dots in the main scanning direction Sc caused by the change in the light amount of the laser beam will be described.

The image forming apparatus100according to the present embodiment changes the speed of scanning of the laser beam according to the type of sheet on which the image is being formed. For example, when a thick paper is to be used, the speed of scanning by the laser beam is controlled to be slower than that when plain paper is to be used.

In general, the faster the speed of scanning, the shorter the time that the laser beam dwells at the same nominal position, and therefore, it can be necessary to increase the intensity of the laser beam accordingly. Similarly, the slower the speed of scanning, the lower the intensity of the laser beam that can be used. However, delay times for output of the signal from the sensor58can also change with laser beam power. Generally, the higher the intensity of the laser beam, the shorter the delay time between when the laser beam enters the sensor58to when the sensor58outputs the horizontal synchronization signal to the light control circuit51. On the other hand, the lower the intensity of the laser beam, the longer the delay time between when the laser beam enters the sensor58to when the sensor58outputs the horizontal synchronization signal to the light control circuit51.

When delay time is long, the dotting start timing of dots in the main scanning direction Sc is delayed. Furthermore, since the light amount setting of the laser beam can be switched according to changes in the speed of scanning, the dotting positions of dots in the main scanning direction Sc can be further deviated from intended or expected position.

The image forming apparatus1according to the embodiment corrects the dotting start timing of dots in the main scanning direction Sc based on the delay amount difference value. The image forming apparatus1thus suppresses the occurrence of deviations in the dotting positions of dots in the main scanning direction Sc.

The image forming apparatus1according to the present embodiment calculates the delay amount difference value as in the following examples.

FIGS. 7, 8, and 9are diagrams illustrating examples of the delay amount difference value calculation process by the image forming apparatus1. InFIGS. 7 to 9, the horizontal axis represents the time axis.

InFIGS. 7 to 9, the upper horizontal axes indicate the timings at which the laser beam emitted from the light source50enters the sensor58, respectively. As illustrated in each figure, the interval at which the laser beam enters the sensor is an equal interval, which is an interval Ta. The horizontal axis in the lower portions ofFIGS. 7 to 9indicate the timing at which the sensor58outputs the horizontal synchronization signal to the light control circuit51according to the detection of the laser beam.

FIG. 7illustrates the case where the light amount of the laser beam is a normal light amount.FIG. 8illustrates the case where the light amount of the laser beam is a dimmed light amount. As illustrated inFIG. 7, the delay amount (delay interval) from the time when the laser beam enters the sensor to the time when the sensor58outputs a horizontal synchronization signal to the light control circuit51is a fixed interval Tb. As illustrated by the horizontal axis in the lower portion, since the same delay amount (interval Tb) occurs in each period, the interval at which the horizontal synchronization signal is output from the sensor58is still equal to the interval Ta. That is, the interval at which the laser beam enters the sensor58and the interval at which the horizontal synchronization signal is output from the sensor58are the same, though offset from each other in time.

As illustrated inFIG. 8, the delay amount (delay interval) from the time when the laser beam enters the sensor to the time when the sensor58outputs a horizontal synchronization signal to the light control circuit51is the fixed interval Tc. The interval Tc is longer than the interval Tb. As illustrated by the horizontal axis in the lower portion ofFIG. 8, since the same delay amount (interval Tc) occurs in each period, the timing at which the horizontal synchronization signal is output from the sensor58is still equal to the interval Ta, though offset in time.

The image forming apparatus1according to the present embodiment calculates the delay amount difference value by switching the light amount from the time when the laser beam enters the sensor58to the time when the laser beam enters the sensor58again in the next period (next main scanning). In the example illustrated inFIGS. 7 to 9, the delay amount difference value is the value of the interval (Tc−Tb).

FIG. 9illustrates the case where the normal light amount is switched to the dimmed light from one period to the next (the next main scanning). The interval at which the horizontal synchronization signal is output from the sensor58, which is illustrated on the horizontal axis in the lower portion, is the interval Ta in a normal light amount period.

However, as illustrated inFIG. 9, the interval at which the horizontal synchronization signal is output from the sensor58changes for the next period when the light amount is switched. In this example, the normal light amount is switched to the dimmed light amount after the second period, thus the interval at which the horizontal synchronization signal will be output from the sensor58becomes the interval (Ta+Tc−Tb).

The image forming apparatus1according to the embodiment can calculate the delay amount difference value (interval (Tc−Tb)) from an interval (for example, the interval Ta) of the output of the horizontal synchronization signal in the normal period and an interval (for example, the interval (Ta+Tc−Tb)) of the output of the horizontal synchronization signal in a period in which the light amount is switched.

As expressed by the Equation (1), when the interval Ta is 200 μsec (microseconds), the interval (Tc−Tb) is 10 nsec (nanoseconds), and the length of the scanning line is 250 mm, the deviation in the dotting positions of dots in the main scanning direction Sc between the case of normal light amount and the case of dimmed light amount is 12.5 μm (microns).
[(250×1000)/(200×1000)]×10=12.5  Equation (1):

In such a case, for example, when switching from the normal light amount to the dimmed light amount, the image forming apparatus1according to the embodiment corrects the dotting start position for dots along the main scanning direction Sc by 12.5 μm in the main scanning direction Sc.

Hereinafter, an example of the calculation process of the delay amount difference value by the image forming apparatus1will be described.

FIG. 10is a flowchart illustrating the calculation process of the delay amount difference value by the image forming apparatus1. The time at which the calculation process of the delay amount difference value is executed is, for example, an initial start-up time, each start-up time, or a time between printing jobs of the image forming apparatus1.

The control unit101starts the rotation of the light deflection unit52of the exposing unit31(ACT001). Next, the light control circuit51sets the light amount of the laser beam emitted from the light source50to the normal light amount based on the instruction from the control unit101(ACT002). Next, the light control circuit51controls the light source50and starts emitting the laser beam (ACT003).

Next, the control unit101detects whether or not the rotation of the light deflection unit52is stable (ACT004). In a case where the control unit101detects that the rotation of the light deflection unit52is not stable (NO in ACT004), the control unit101waits until the rotation becomes stable. When the control unit101detects that the rotation of the light deflection unit52is stable (YES in ACT004), the control unit101controls the light control circuit51and starts detection of the horizontal synchronization signal output from the sensor58. The light control circuit51waits for the arrival of the horizontal synchronization signal (ACT005).

When the light control circuit51detects the horizontal synchronization signal output from the sensor58(YES in ACT005), the control unit101resets the counter of the time measuring unit110(ACT006). As described above, the counter referred to herein is a counter for the time measuring unit110to measure the interval at which the horizontal synchronization signal is input to the light control circuit51. The light control circuit51again waits for the arrival of the horizontal synchronization signal (ACT007).

When light control circuit51detects the horizontal synchronization signal output from the sensor58(YES in ACT007), the control unit101acquires the count value of the counter of the time measuring unit110and resets the counter again (ACT006). The count value acquired herein is, for example, a value indicating the interval (interval Ta) of the first period on the horizontal axis in the lower portion ofFIG. 9. The time measuring unit110outputs the acquired count value to the delay amount difference calculation unit112.

Next, the light control circuit51switches the light amount of the laser beam emitted from the light source50to the dimmed light amount based on the instruction from the control unit101before the next horizontal synchronization signal is detected (ACT009). Again, the light control circuit51waits for the arrival of the horizontal synchronization signal (ACT010).

When the light control circuit51detects the horizontal synchronization signal output from the sensor58(YES in ACT010), the control unit101acquires the count value of the counter of the time measuring unit110(ACT011). The count value acquired herein is, for example, a value indicating the interval (interval (Ta+Tc−Tb)) of the second period on the horizontal axis in the lower portion ofFIG. 9. The time measuring unit110outputs the acquired count value to the delay amount difference calculation unit112.

Next, the delay amount difference calculation unit112calculates the delay amount difference value. For example, the interval (Tc−Tb)) is calculated from the interval in the first period (a period with a length of interval Ta in this example) and the interval in the second period (a period with a length of interval (Ta+Tc−Tb) in this example) (ACT012). Next, the delay amount difference calculation unit112records the calculated delay amount difference value in the storage device103(ACT013).

The calculation process of the delay amount difference value by the image forming apparatus1illustrated in the flowchart ofFIG. 10is thus completed.

In the process illustrated in the flowchart ofFIG. 10, the image forming apparatus1first sets the normal light amount and then calculates the delay amount difference value by switching to the dimmed light amount. However, the present disclosure is not limited thereto, and the image forming apparatus1may first set the dimmed light amount and then calculate the delay amount difference value by switching to the normal light amount.

By the above-described processes, the delay amount difference value is calculated in advance and recorded in the storage device103before the printing job (image formation on the sheet) by the image forming apparatus1. When each printing job is executed, the image forming apparatus1reads the delay amount difference value from the storage device103according to the light amount setting of the laser beam and corrects the dotting positions of dots in the main scanning direction Sc by the laser beam.

Hereinafter, an example of the correction process of the dotting timing of dots in the main scanning direction Sc by the image forming apparatus1will be described. The processes described below are processes performed, for example, when each printing job is executed.

FIG. 11is a flowchart illustrating the correction process of the dotting timing of dots in the main scanning direction Sc by the image forming apparatus1.

The sheet information acquisition unit113of the control unit101acquires the sheet information (ACT101). As described above, the sheet information is information indicating the type of sheet (such as plain paper or thick paper) to be used in the printing. The sheet information acquisition unit113acquires the sheet information generated by, for example, the user performing an operation of selecting the type of sheet by the operation unit12.

Next, the light amount switching unit111acquires sheet information from the sheet information acquisition unit113. The light amount switching unit111also acquires the sheet type/light amount correspondence information recorded in advance in the storage device103. As described above, the sheet type/light amount correspondence information is information in which the type of sheet and the light amount are stored in correspondence with each other.

The light amount switching unit111specifies the light amount setting for the type of sheet indicated by the acquired sheet information by referring to the sheet type/light amount correspondence information. The light amount switching unit111sets the light amount for the laser beam output from the light source50to the specified light amount setting (ACT102).

In this process, the light amount switching unit111is configured to determine the light amount to be used based on the sheet information acquired from the sheet information acquisition unit113, but the present disclosure is not limited thereto. For example, the light amount switching unit111may be configured to determine the light amount to be used based on the information indicating the present deterioration state of the photoreceptor drums34-1and35-1as acquired from the deteriorated state acquisition unit114.

In such a case, the light amount switching unit111identifies the light amount to be used based on the state of the photoreceptor drums34-1and35-1as indicated by the acquired information by referring to the deteriorated state/light amount correspondence information recorded in advance in the storage device103. Then, the light amount switching unit111switches the light amount setting to the specified light amount.

Next, the control unit101starts the rotation of the light deflection unit52of the exposing unit31(ACT103). Next, the light control circuit51controls the light source50and starts emitting the laser beam (ACT104). Next, the timing correction unit115of the control unit101acquires a delay amount correction value recorded in advance in the storage device103(ACT105). The delay amount correction value acquired herein is, for example, a value calculated by the process illustrated by the flowchart ofFIG. 10.

Next, the control unit101detects whether or not the rotation of the light deflection unit52is stable (ACT106). When the control unit101detects that the rotation of the light deflection unit52is not stable (NO in ACT106), the control unit101waits until the rotation becomes stable. When the control unit101detects that the rotation of the light deflection unit52is stable (YES in ACT106), the control unit101controls the light control circuit51and starts detection of the horizontal synchronization signal output from the sensor58. The light control circuit51waits for the arrival of the horizontal synchronization signal (ACT107).

When the light control circuit51detects the horizontal synchronization signal output from the sensor58(YES in ACT107), the timing correction unit115performs correction control of the dotting timing of dots in the main scanning direction Sc based on the light amount setting determined by the light amount switching unit111in the process of the ACT102.

When the light amount setting determined by the light amount switching unit111is the normal light amount (YES in ACT108), the timing correction unit115waits for a time corresponding to the delay amount difference value (ACT109), and after that, starts the dotting of dots in the main scanning direction Sc by the laser beam (ACT110). If the light amount setting determined by the light amount switching unit111is the dimmed light amount (NO in ACT108), the timing correction unit115starts the dotting of dots in the main scanning direction Sc by the laser beam without performing the above-described waiting (ACT110).

The control unit101repeatedly executes the processes of ACT107to ACT110until all the dotting of dots by the laser beam is completed (ACT111). By the above description, the correction process for the dotting timing along the main scanning direction Sc is completed.

As described above, the image forming apparatus100according to the present embodiment includes a light source50, a sensor58, and a control unit101. The light source50emits a laser beam (light) that is used to scan the scanning area J. The sensor58is arranged at a position which is also irradiated with the laser beam. The sensor58detects the laser beam emitted at each main scanning. The sensor58outputs a horizontal synchronization signal (synchronization signal) that synchronizes the writing positions of dots (pixels) in the main scanning direction Sc according to the detection of the laser beam. The control unit101controls the dotting positions (writing positions) of dots in the main scanning direction Sc based on the change in the output interval of the horizontal synchronization signal that can be caused by a change in the light output amount of the laser beam.

With such a configuration, the image forming apparatus1can correct the deviation in the writing positions of dots (pixels) in the main scanning direction Sc, which may otherwise be caused due to the change in the light amount setting of the laser beam, based on a delay amount difference value calculated in advance.

According to the image forming apparatus1of the present embodiment, even when the light amount of the laser beam is changed according to, for example, the type of sheet and/or the deteriorated state of the photoreceptor drum(s), it is possible to suppress the deviation in the dotting positions of dots in the main scanning direction that might otherwise be caused by the change. Accordingly, the image forming apparatus1can prevent the occurrence of deviation in the transfer position of the image on the sheet.