JP7175706B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a laser printer, a copying machine, and a facsimile, which is equipped with an optical scanning device for scanning a surface to be scanned with laser light emitted from a light source and deflected by a deflector.

A conventional optical scanning device used in an image forming apparatus such as a laser printer optically modulates a laser beam emitted from a light source according to an image signal, and deflects the optically modulated laser beam with a deflector composed of, for example, a rotating polygonal mirror. scanning. The deflected and scanned laser light forms an image on the surface of a photosensitive drum as a surface to be scanned by a scanning lens such as an fθ lens to form an electrostatic latent image. Next, the electrostatic latent image on the photosensitive drum is visualized into a toner image by a developing device, which is transferred to a recording material such as recording paper, sent to a fixing device, and printed by heating and fixing the toner on the recording material. (Printing) is performed (Patent Documents 1 to 4).

The reflecting surfaces of the rotating polygon mirror are processed with high precision in order to deflect and scan the laser light with high precision. However, due to the recent miniaturization of optical scanning devices and the like, variations in the precision of each reflecting surface of the rotating polygon mirror affect the quality of the printed image. Therefore, a technique has been proposed for detecting the reflecting surfaces of a rotating polygon mirror and electrically correcting the density unevenness of an image for each reflecting surface (Patent Document 1).

Further, a deviation occurs in the deflection scanning direction (main scanning direction) of the rotating polygon mirror due to mounting errors of the optical scanning device with respect to the image forming apparatus, fluctuations in the refractive index of the fθ lens, and the like. Since the deviation deteriorates the image quality and is not preferable, a technique for correcting the deviation in the main scanning direction by changing the image clock has been proposed (Patent Document 2).

In addition, although aluminum is generally used as a material for rotating polygon mirrors, it has been suggested that using plastic would allow the shape of the reflecting surface to be set freely, leading to greater freedom in design. (Patent Document 3).

Patent No. 5733897 Patent No. 5041583 Japanese Patent Application Laid-Open No. 2004-102006 JP 2013-242536

However, when the temperature of the installation space inside the device in which the rotating polygon mirror is installed changes, the reflecting surface of the rotating polygon mirror deforms due to thermal deformation. FIG. 13(b) shows the result of a numerical simulation of deformation of the reflecting surfaces when the rotating polygon mirror 51 composed of the four reflecting surfaces 51A to 51B shown in FIG. 13(a) is installed in a high-temperature environment. A plastic cycloolefin polymer (COP) was set as the material of the rotating polygon mirror, and a simulation was performed when the temperature was raised by Δ40K.

In FIG. 13A, the size l×h of each reflecting surface of the rotary polygon mirror 51 is approximately 14 mm×2 mm. The size l of the reflecting surface is the length from one longitudinal end to the other longitudinal end of the reflecting surface. The size h of the reflecting surface is the length from one end to the other end in the short direction orthogonal to the longitudinal direction, and is the length in the axial direction passing through the rotation center of the rotating polygon mirror.

The vertical axis of the graph shown in FIG. 13(b) indicates the amount of deformation in the normal direction of the reflecting surface shown in FIG. 13(a). The horizontal axis of the graph shown in FIG. 13(b) is the distance from the center of the reflecting surface to the end in the main scanning direction (longitudinal direction) of the reflecting surface shown in FIG. ). Therefore, FIG. 13B shows the amount of deformation in the normal direction of the reflecting surface from the center of the reflecting surface to the edge. Here, the normal direction of the reflecting surface refers to the outer side of the reflecting surface that is perpendicular to the tangent to the center of the reflecting surface (the line perpendicular to the line connecting the rotation center of the rotating polygon mirror and the center of the reflecting surface). It refers to the direction towards The aforementioned amount of deformation of the reflecting surface refers to the amount of deformation of the reflecting surface in this normal direction. In FIG. 13A, since the size l of the reflecting surface of the rotating polygon mirror is about 14 mm, the length l/2 from the center of the reflecting surface to the edge is about 7 mm.

As shown in FIG. 13B, according to the results of this simulation, the reflection surface is deformed by about 550 nm from the center of the reflection surface to the edge in the main scanning direction. Generally, the flatness of the reflecting surface is required to be λ/5 (λ is the wavelength of red light: λ=632.8 nm). Therefore, the thermal deformation of the rotating polygon mirror in this numerical simulation is a large amount of deformation from an optical point of view. Incidentally, the coefficient of linear expansion of aluminum, which is conventionally used as a material for rotating polygon mirrors, is about 1/3 that of COP, and even in the case of aluminum, thermal deformation has a considerable optical effect.

FIG. 14 is a diagram showing changes in scanning time for each reflecting surface of the rotating polygon mirror when the temperature of the space in which the rotating polygon mirror is installed is changed. FIG. 14 illustrates a rotating polygon mirror having four reflecting surfaces. In FIG. 14, the one-dot dashed line is for the temperature of 20°C, the dashed line is for the temperature of 60°C, which is higher than 20°C, and the solid line is for the temperature of 0°C, which is lower than 20°C. showing change. As can be seen from FIG. 14, the amount of change in scanning time with respect to temperature change differs for each reflecting surface. This is caused by the anisotropy of the material of the rotating polygon mirror and the method of support.

FIG. 15 shows the scanning time jitter within a certain section of the laser beam reflected by each reflecting surface and deflected and scanned when a rotating polygonal mirror made of plastic is actually used and rotated under each temperature environment shown in FIG. is the result of measuring The vertical axis shown in FIG. 15 is the scanning time jitter, which mainly represents the amount of jitter caused by the flatness of each reflecting surface. Here, the amount of jitter (scanning time jitter) is expressed as a percentage by dividing the value obtained by subtracting the minimum value from the maximum value of the scanning time of each reflecting surface (four surfaces) of the rotating polygon mirror by the average scanning time. The horizontal axis shown in FIG. 15 is the temperature of the space in which the rotating polygon mirror is installed. From FIG. 15, it can be seen that the amount of jitter caused by the flatness of each reflecting surface varies with temperature. This tendency is remarkable in plastic rotating polygon mirrors such as COP. The temperature of the rotating polygon mirror changes depending on the installation temperature environment of the image forming apparatus and the operating conditions of the image forming apparatus. When the amount of jitter of the rotating polygon mirror changes due to temperature, the imaging position in the main scanning direction on the photosensitive drum shifts. In the case where the rotating polygon mirror has four faces, if four scanning lines are periodically misaligned in the main scanning direction, moiré may occur in the image.

SUMMARY OF THE INVENTION It is an object of the present invention to realize an image forming apparatus that does not generate moire by correcting deviation in the main scanning direction according to the temperature change even if the temperature of the space in which the rotating polygon mirror is installed changes. be.

In order to achieve the above object, an image forming apparatus according to the present invention scans an image carrier with laser light emitted from a light source in a main scanning direction, which is the axial direction of the image carrier, by rotating a rotating polygonal mirror. an image forming apparatus comprising an optical scanning device, comprising: an output unit provided in the optical scanning device for receiving a laser beam reflected by a reflecting surface of the rotating polygonal mirror and outputting a signal; a surface identifying unit that identifies a specific reflecting surface among the plurality of reflecting surfaces of the rotating polygon mirror, based on the signal output from the rotating polygon mirror; deviation correction data for correcting deviation of the laser light in the main scanning direction of the image carrier, and predetermined correction parameters used for calculating temperature correction data for correcting the deviation correction data. a storage unit stored in advance; a temperature detection unit for detecting the temperature of the space in which the rotary polygon mirror is installed; and the temperature detected by the temperature detection unit and the correction parameter. calculating temperature correction data according to the temperature change of the space in which the rotating polygon mirror is installed; and using the calculated temperature correction data, correcting the deviation correction data to correction data according to the temperature change of the space in which the rotating polygon mirror is arranged. A correction data control section and a modulation section for generating a signal for modulating the laser light from the light source based on the correction data corrected by the correction data control section.

ADVANTAGE OF THE INVENTION According to this invention, the positional deviation of the laser beam reflected by the reflecting surface of the rotating polygon mirror caused by the temperature change in the main scanning direction can be reliably corrected. Therefore, even if the temperature of the space in which the rotating polygon mirror of the image forming apparatus is installed changes, image quality does not deteriorate, and high-quality images can be maintained.

1 is a perspective view of an optical scanning device according to an embodiment of the invention; FIG. FIG. 4 is a partial cross-sectional view of a deflector according to an embodiment of the invention; 4 is a block diagram showing a mechanism for correcting the amount of magnification deviation in the main scanning direction according to the embodiment of the present invention; FIG. FIG. 5 is a diagram showing an example of correspondence between surface IDs and BD periods β measured by a scanning period measuring unit in chronological order; (a) is a diagram showing a specific example of rotation speed, BD cycle, and correction data stored in a correction data storage unit according to the embodiment of the present invention. (b) is a schematic diagram showing a configuration for measuring the BD period of a rotating polygon mirror and correction data corresponding thereto. (a) is a diagram showing an example of a BD period α stored in a correction data storage unit. (b) is a diagram showing an example of a BD cycle β measured and stored in a scanning cycle storage unit. FIG. 11 is a conceptual diagram showing an example of the correspondence relationship between the surface ID and the BD period β and the BD period α in the correction data storage unit when pattern matching is successful; FIG. 10 is a diagram showing an example of correspondence between a surface ID, a BD period β measured by a scanning period measuring unit, and correction data stored in a correction data storage unit in chronological order; 8 is a flowchart of processing for identifying a reflecting surface and correcting main scanning magnification deviation according to the embodiment of the present invention. 1 is a schematic cross-sectional view showing an image forming apparatus according to an embodiment of the invention; FIG. FIG. 10 is a perspective view of an optical scanning device according to a modification of the embodiment of the invention; 10 is a flowchart of processing for identifying a reflecting surface and correcting main scanning magnification deviation according to a modification of the embodiment of the present invention; (a) is a perspective view of a rotating polygon mirror, and (b) is a diagram showing a numerical simulation result of the amount of thermal deformation of a reflecting surface of the rotating polygon mirror. FIG. 5 is a diagram showing changes in scanning time for each reflecting surface when temperature is changed. FIG. 4 is a diagram showing an example of scanning time jitter for each temperature of a rotating plastic polygon mirror;

An image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention will be described below with reference to the drawings. In the following description, first, an image forming apparatus including an optical scanning device according to an embodiment of the present invention will be described as an example, and then the optical scanning device in the image forming apparatus will be described. Next, a deflector to be assembled in the optical scanning device will be described.

[Image forming apparatus]
First, the image forming apparatus 110 will be described with reference to FIG. FIG. 10 is a schematic cross-sectional view of an image forming apparatus 110 including the optical scanning device 101 according to this embodiment.

The image forming apparatus 110 includes an optical scanning device 101, which scans a photosensitive drum as an image carrier, and forms an image on a recording material P such as recording paper based on the scanned image. Here, a laser beam printer will be described as an example of the image forming apparatus.

As shown in FIG. 10, an image forming apparatus (printer) 110 emits a laser beam based on image information from an optical scanning device 101 as exposure means, and a photosensitive drum, which is an image carrier built in a process cartridge 102 . 103 is irradiated. A latent image is formed on the photosensitive drum 103 by irradiating the photosensitive drum 103 with laser light and exposing the photosensitive drum 103 . A latent image formed on the photosensitive drum 103 is visualized as a toner image by toner as a developer. The process cartridge 102 integrally includes the photosensitive drum 103 and the charging means and developing means acting on the photosensitive drum 103, and is detachable from the image forming apparatus.

On the other hand, the recording material P accommodated in the recording material stacking plate 104 is fed while being separated one by one by the feeding roller 105, and further conveyed to the downstream side by the conveying roller . A toner image formed on the photosensitive drum 103 is transferred onto the transported recording material P by a transfer roller 107 . The recording material P on which the unfixed toner image is formed is further conveyed downstream, and the toner image is fixed on the recording material P by a fixing device 108 having a heater inside. After that, the recording material P is discharged out of the apparatus by the discharge roller 109 .

In the present embodiment, the charging means and the developing means acting on the photosensitive drum 103 are integrated with the photosensitive drum 103 in the process cartridge 102 . However, the present invention is not limited to this, and each process means may be constructed separately from the photosensitive drum 103 .

[Optical scanning device]
Next, the optical scanning device in the image forming apparatus will be described with reference to FIG. FIG. 1 is a perspective view of an optical scanning device according to this embodiment. An arrow Z shown in FIG. 1 indicates the axial direction (axial direction) of the rotating shaft 10 shown in FIG. Arrow X is a direction orthogonal to arrow Z, and arrow Y is a direction orthogonal to arrow Z and arrow X.

As shown in FIG. 1, the optical scanning device 101 has the following optical members. The optical scanning device 101 has a semiconductor laser unit 1 and a compound anamorphic collimator lens 2 . The semiconductor laser unit 1 is a light source that emits laser light L. As shown in FIG. The compound anamorphic collimator lens 2 is a lens in which an anamorphic collimator lens having both functions of a collimator lens and a cylindrical lens and a lens for detecting a synchronization signal (BD lens) are integrally molded. Further, the optical scanning device 101 has an aperture stop 3 , a deflector 5 for rotationally driving the rotary polygon mirror 4 , a synchronization signal detection sensor (BD sensor) 6 as an output section, and an fθ lens (scanning lens) 7 . The optical scanning device 101 accommodates the above optical members in an optical box 8 .

In the above configuration, the laser light L emitted from the semiconductor laser unit 1 is converted by the compound anamorphic collimator lens 2 into substantially parallel light or convergent light in the main scanning direction, and convergent light in the sub-scanning direction. Next, the laser beam L passes through the aperture stop 3, the width of which is restricted, and forms an image on the reflecting surface of the rotary polygon mirror 4 in the form of a focal line extending in the main scanning direction. The laser beam L is deflected and scanned by rotating the rotary polygon mirror 4 and enters the BD lens of the compound anamorphic collimator lens 2 . The laser beam L that has passed through the BD lens is incident on the synchronization signal detection sensor 6 . That is, the synchronization signal detection sensor 6 receives the laser light L reflected by each reflecting surface of the rotating polygon mirror 4 . At this time, the synchronization signal (BD signal) is detected by the synchronization signal detection sensor 6, and this timing is used as the synchronization detection timing of the writing position in the main scanning direction. A synchronizing signal (BD signal) is a signal for synchronizing the image writing position in the main scanning direction on each surface of the rotary polygon mirror 4 . Then, the synchronization signal detection sensor 6 outputs the signal (BD signal) to the surface identification signal generation section 300 (see FIG. 3), which will be described later. Next, the laser beam L enters the fθ lens 7 . The f.theta. lens 7 is designed to condense the laser light so as to form a spot on the photosensitive drum and to keep the scanning speed of the spot constant. In order to obtain such characteristics of the f.theta. lens 7, the f.theta. lens 7 is formed of an aspherical lens. The laser beam L that has passed through the fθ lens 7 is emitted from the exit port of the optical box 8 and is imaged and scanned on the photosensitive drum.

The rotation of the rotary polygon mirror 4 deflects and scans the laser beam, and main scanning is performed on the photosensitive drum by the laser beam in the axial direction of the photosensitive drum. is done. The direction of scanning along the axis of the photosensitive drum is defined as a main scanning direction, and the direction of scanning by rotating the photosensitive drum about its axis is defined as a sub-scanning direction perpendicular to the main scanning direction. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum.

[Deflector]
Next, the deflector in the optical scanning device will be described with reference to FIG. FIG. 2 is a partial cross-sectional view of the deflector according to this embodiment.

As shown in FIG. 2, the deflector 5 includes a rotor 20 including a rotating polygon mirror 4, a bearing 15, a stator core 16, a stator coil 17, a circuit board 18, and a hall element (magnetic sensor) 19 soldered on the circuit board. etc. In addition to the rotating polygon mirror 4 , the rotor 20 includes a rotating shaft 10 , a rotor boss 11 , a rotor frame 12 , a rotor magnet 13 , and a fixture 14 for the rotating polygon mirror 4 . The rotating polygon mirror 4 is made of plastic such as polycarbonate resin or cycloolefin resin.

In the above configuration, when a current is supplied to the stator coil 17 , electromagnetic force is generated between the stator coil 17 and the rotor magnet 13 , causing the rotor 20 to rotate about the rotating shaft 10 supported by the bearing 15 . The Hall element 19 is a magnetic sensor for determining the timing (commutation timing) of current flow through the stator coil 17, is arranged below the rotor magnet 13, and detects the magnetic poles (N, S) of the rotor magnet 13. there is

[Correction of Positional Deviation of Each Reflecting Surface in Main Scanning Direction According to Temperature Change of Rotating Polygon Mirror 4]
Next, a method of correcting the amount of jitter in the main scanning direction of each reflecting surface (positional displacement of the scanning line in the main scanning direction of each reflecting surface) according to the temperature change of the rotating polygon mirror 4 will be described with reference to the drawings. FIG. 3 is a block diagram showing a mechanism for correcting the amount of misregistration of scanning lines in the main scanning direction according to this embodiment. FIG. 4 is a diagram showing an example of correspondence between surface IDs and BD periods β measured by the scanning period measuring unit in chronological order. FIG. 5A is a diagram showing specific examples of the number of rotations, the BD period of each reflecting surface of the rotating polygon mirror, and the correction data stored in the correction data storage unit according to the present embodiment. FIG. 5B is a schematic diagram showing a configuration for measuring the BD period of the reflecting surface of the rotating polygon mirror and the correction data corresponding thereto. FIG. 6A is a diagram showing an example of the BD period α stored in the correction data storage unit, the reflecting surface corresponding thereto, and the correction data. FIG. 6B is a diagram showing an example of the BD period β measured and stored in the scanning period storage unit and the surface ID of the reflecting surface. FIG. 7 is a conceptual diagram showing an example of the correspondence relationship between the surface ID and the BD cycle β in the surface identification signal generation unit and the BD cycle α in the correction data storage unit when pattern matching is successful. FIG. 8 is a time-series diagram showing an example of correspondence between the surface ID, the BD period β measured by the scanning period measuring unit, and the correction data stored in the correction data storage unit.

As shown in FIG. 3, this mechanism includes a surface identification signal generator 300 , a main scanning position shift corrector 301 , an image signal generator 305 and a temperature detector 308 .

First, the temperature detection unit 308 in this embodiment will be described with reference to FIG. The image forming apparatus of this embodiment has a temperature detection unit 308 that is provided inside the image forming apparatus 110 and detects the temperature of the space inside the apparatus in which the rotating polygon mirror is installed. Conventionally, the temperature detection unit is installed for predicting the start-up time of the apparatus and controlling the fixing device 108 . The temperature detection unit 308 is generally installed near the apparatus housing away from the control board and the fixing device 108 . The detection result of the temperature detection unit 308 is used for positional deviation correction of scanning lines in the main scanning direction. The detection means of the temperature detection unit 308 is, for example, a temperature sensor.

As shown in FIG. 3, the main scanning magnification shift correction unit 301 has a correction data control unit and a surface identification unit (correction data control unit + surface identification unit 303) related to control. The surface identification unit 303a is a surface identification unit that receives information from the surface identification signal generation unit 300 and identifies a specific surface of the rotating polygon mirror. The correction data control unit 303b receives information from the surface identification signal generation unit 300, and based on the correction data of the identified specific surface, controls the laser driving unit 306 through the laser light modulation unit (image clock generation unit) 304. control the drive. Further, in this embodiment, the correction data control section and the surface identification section are performed by the CPU, which is a control section for controlling the operation of the apparatus. The image signal generator 305 generates an image signal and supplies it to the laser driver 306 . The laser drive unit 306 outputs laser light from the semiconductor laser unit 1 according to the supplied image signal and correction data (image clock generated by the main scanning position shift correction unit 301), which will be described later. A laser beam emitted from the semiconductor laser unit 1 is reflected by the reflecting surface of the rotating rotary polygon mirror 4 , and after the reflected laser beam is detected by the BD sensor 6 , the photosensitive drum 103 is scanned. Here, when the laser light is detected by the BD sensor 6, a BD signal is generated and output.

The correction data for the identified specific surface is main scanning positional deviation correction data for each reflecting surface at room temperature. As will be described later, the correction data control unit 303b corrects the correction data of the identified specific surface using the temperature correction data corresponding to the temperature change. Temperature correction data for correcting correction data according to temperature changes will be described later.

The surface identification signal generation unit 300 has a scanning cycle measurement unit, a scanning cycle storage unit, and a surface identification signal unit (not shown). The rotating polygon mirror 4 is stably rotated at a constant speed, and the process of assigning a surface ID is started. Then, the surface identification signal unit assigns a surface ID, which is a surface identification signal, to the current reflecting surface for the BD period, and updates the surface ID corresponding to the BD period each time a BD signal is input thereafter. Assign to the next reflective surface.

The “current reflective surface” is the reflective surface that supplied the reflected light that is the source of the BD signal that was output immediately before. Each time the rotary polygon mirror 4 rotates once, that is, each time the same number of BD signals as the number of reflecting surfaces (four) are output, the same reflecting surface becomes a source of reflected light. In this example, each BD signal output once every four times corresponds to one reflective surface. Therefore, the surface ID is information for specifying each reflecting surface and at the same time identifies each BD signal in one rotation of the rotating polygon mirror 4 .

In the scanning cycle measurement unit, an internal counter detects the “BD cycle”, which is the output interval of the BD signal, as the output interval for each reflecting surface. Therefore, the BD period is measured for the number of faces of the rotating polygon mirror 4 . Then, the BD period of each reflecting surface is stored in the scanning period storage unit in the order of measurement. The BD period of each reflecting surface stored in the scanning period storage unit is measurement data measured as an output interval for each reflecting surface by the scanning period measuring unit. The reflective surface corresponding to the BD signal on the start side of the BD period measured first is not fixed and may differ each time.

For example, as shown in FIG. 4, in the case where the rotating polygon mirror 4 has four reflecting surfaces, after starting the process of assigning the surface IDs, immediately after the first BD signal is output, Let the reflective surface which carries out the first surface. In this case, the surface identification signal section assigns the surface ID “ID1” to the first surface. When the next (second) BD signal is input, the interval from the first BD signal is measured by the scanning cycle measurement unit, and stored as the BD cycle (for example, β1) of the first surface in the scanning cycle storage unit. Store.

Furthermore, when the next (third) BD signal is input, the interval from the immediately preceding (second) BD signal is measured as the BD period of the next second plane, and the BD period (eg β2) is the scanning period. The second surface is stored in the storage unit, and "ID2" is assigned as the surface ID to the second surface. Such processing is performed for the number of faces of the rotating polygon mirror 4 . Then, the surface IDs (ID1 to ID4) are assigned at the same time that the BD periods β (β1 to β4) of the respective reflecting surfaces are stored in the scanning period storage unit. FIG. 6B shows the correspondence relationship between the BD cycle β stored in the scanning cycle storage unit and the surface ID generated by the surface identification signal unit. The BD cycle β is measurement data measured as an output interval for each reflecting surface by the scanning cycle measurement unit of the surface identification signal generation unit 300, and is cycle data associated with the output order assigned to the surface ID.

The main scanning positional deviation correction unit 301 includes a correction data storage unit 302 as a storage unit, a surface specifying unit 303a for specifying a specific reflecting surface, a correction data control unit 303b for reading data and performing correction control, and a laser beam. and a modulation unit (image clock generation unit) 304 . In this embodiment, the CPU serves as the correction data control section and the surface identification section, but the configuration of each section is not limited to this. Each unit that configures the main scanning misregistration correction unit 301 may be implemented by a dedicated circuit such as an ASIC, or may be implemented by a CPU, ROM, RAM, and computer program. Here, as described above, the CPU serving as the surface identification unit 303a and the correction data control unit 303b receives information from the surface identification signal generation unit 300, identifies the surfaces of the rotating polygon mirror, and uses the laser light modulation unit ( It controls driving of the laser driver 306 via an image clock generator 304 . As shown in FIG. 6A, the correction data storage unit 302 stores the BD period of each reflecting surface of the rotary polygon mirror 4, which is measured in advance in the assembly process, etc., in association with the corresponding deviation correction data. ing. Here, as a rotating polygon mirror having a plurality of reflecting surfaces, a rotating polygon mirror 4 having four reflecting surfaces AD as shown in FIG. 3 is exemplified.

As shown in FIG. 6A, the correction data storage unit 302 stores the BD period α corresponding to each of the reflecting surfaces A to D, and the deviation correction data corresponding to each of the reflecting surfaces A to D at room temperature. data and correction parameters are stored in advance. Here, the BD period α associated with each of the reflecting surfaces AD is the identification data.

Further, the identification data (BD cycle α) corresponding to each of the reflecting surfaces A to D, and the deviation correction data data and correction parameters corresponding to each of the reflecting surfaces A to D at room temperature are stored in the correction data storage unit 302 in advance. stored. That is, the correction data storage unit 302 stores the BD period α (α1 to α4) of each of the reflecting surfaces A to D of the rotary polygon mirror 4 and the main scanning positional deviation correction data (dataL1 to dataL4) and correction parameters x and z are stored in advance.

Further, since the main scanning positional deviation correction data is deviation correction data corresponding to each of the reflecting surfaces A to D at room temperature, it is necessary to perform correction according to temperature changes in the space in which the rotating polygon mirror is installed. In this example, in order to correct the deviation correction data stored in the correction data storage unit 302 in accordance with temperature changes, the temperature of the device installation space inside the device in which the rotary polygon mirror is installed and the operation rate of the deflector are I am using Correction parameters x (x1, x2, x3, x4) are parameters for using the apparatus installation space temperature as temperature correction data. Correction parameters z (z1, z2, z3, z4) are parameters for using the operation rate of the deflector as temperature correction data. Here, normal temperature is 25°C. Also, the temperature of the device installation space is the temperature difference from normal temperature. Therefore, since the deviation correction data corresponding to each reflecting surface and stored in advance in the correction data storage unit 302 are values obtained at room temperature (25°C), the temperature of the apparatus installation space is 0°C. Further, the operating rate of the deflector at the time of acquisition of deviation correction data corresponding to each reflecting surface stored in advance in the correction data storage unit 302 is assumed to be 0%. Using the correction parameters x and z, the temperature correction data for correcting the deviation correction data corresponding to each of the reflecting surfaces A to D is obtained by the following equation.

[Formula 1]
Temperature correction data = (x1, x2, x3, x4) x device installation space temperature + (z1, z2, z3, z4) x deflector operating rate

The temperature correction data shown in FIG. 5(a) is obtained by setting the temperature of the apparatus installation space to 30° C., which is a temperature difference from room temperature (here, 25° C.), and the operation rate of the deflector to 50%. It is a value obtained by the above equation 1 using the parameters x and z. For example, the temperature correction data for the reflecting surface A is 0.52×30+3.3×0.5≈17.3. The temperature correction data for the other reflecting surfaces B, C, and D can also be obtained in the same manner using the above equation (1).

Note that the temperature of the apparatus installation space inside the apparatus in which the rotating polygon mirror is installed is detected by a temperature detection unit 308 provided inside the image forming apparatus. The operating rate of the deflector counts the time for which the correction data control unit 303b receives the BD signal from the BD sensor, and detects the ratio of the operating time of the deflector in a predetermined time.

The BD period α of each reflecting surface shown in FIG. 6A and the corresponding main scanning position deviation correction data data are measured in advance using jigs and tools in the assembly process. Further, the correction parameters x and z are determined not in the assembly process, but after performing measurements at each temperature using the above-mentioned jigs and tools in advance by experiment or the like. Japanese Laid-Open Patent Publication No. 2002-100001 discloses a tool for measuring the partial magnification of an optical scanning device as an example of a tool for measuring the positional deviation of each reflecting surface of the rotating polygon mirror in the main scanning direction. Patent Document 2 discloses an example in which six scanning position detection sensors are provided, excluding BD sensors (synchronization signal detection sensors). On the other hand, in the present embodiment, three scanning position detection sensors other than the BD sensor are used to detect positional deviations at three locations in the main scanning direction of the photosensitive drum 103 (the image writing portion, the image center portion, and the image writing end portion). Correction data to be corrected is acquired. FIG. 5A shows a specific example of the measured BD period and the corresponding correction data and correction parameters.

6(a) and 5(a), the BD period means that the BD signal 1 is obtained when the BD signal 1 is obtained on one surface of the rotating polygon mirror, and the BD signal 2 is obtained on the next surface. is the time interval to signal 2; For example, the BD signal of the reflecting surface A of the rotating polygon mirror 4 shown in FIG. Next, the BD signal of the reflecting surface B, which is the next surface in the rotational direction adjacent to the reflecting surface A, is acquired as the BD signal 2 by the BD sensor 6 . The time interval from acquisition of the BD signal 1 to acquisition of the BD signal 2 is the BD period. That is, the output interval of the signal output by the BD sensor 6 is the BD period. BD periods (time intervals) between other reflecting surfaces are similarly acquired. In addition, the correspondence relationship between each reflecting surface and each BD period is such that the surface when BD signal 1, which is the previous signal, is acquired in one BD period is the time interval from BD signal 1 to BD signal 2 ( BD cycle). For example, the time interval (BD period) from the BD signal 1 on the reflecting surface A acquired by the BD sensor 6 to the BD signal 2 on the reflecting surface B is associated with the reflecting surface A of the BD signal 1, which is the previous signal. ing. The same applies to the correspondence between other reflecting surfaces and the BD period.

On the other hand, the deviation correction data corrects the deviation in the main scanning direction of the laser light L reflected by each reflecting surface of the rotating polygon mirror at room temperature (the amount of deviation in the main scanning direction from the ideal reference position). This data is for The positional deviation in the main scanning direction of the laser light L reflected by each reflecting surface means the distance from the scanning start position to the image area (the area from the position of the image writing portion to the position of the image writing end portion) in the main scanning direction. It is the difference in distance. Here, time may be used as conversion of distance. In this embodiment, as shown in FIG. 5B, in addition to the BD sensor 6, three scanning position detection sensors S1, S2, and S3 are used to scan the photosensitive drum 103 at three points in the main scanning direction (the image writing portion and the image center). and the image writing end portion) is acquired. As shown in FIG. 5B, the BD sensor 6 is arranged at the scanning start position. At the three positions in the main scanning direction of the photosensitive drum, the sensor S1 is arranged at the position of the image writing portion, the sensor S2 is arranged at the position of the central portion of the image, and the sensor S3 is arranged at the position of the end portion of the image writing. In the main scanning direction, symbol a is the distance from the scanning start position to the image writing position, symbol b is the distance from the scanning start position to the image center position, and symbol c is the position from the scanning start position to the image writing end part. is the distance to As deviation correction data, deviation amounts in the main scanning direction from the three ideal positions in the main scanning direction are stored. That is, the respective distances a, b, and c are measured, and the amount of deviation in the main scanning direction from the ideal distance serving as the reference for each of the measured distances a, b, and c is stored as deviation correction data in the correction data storage shown in FIG. 302 is stored in advance. In addition, in the measurement using the jigs and tools, the arrangement and number of the scanning position detection sensors other than the BD sensor are not limited to this, and should be appropriately set as necessary.

Here, the BD period α is measured in advance by specifying each of the reflecting surfaces A to D, and is a parameter corresponding to the BD period β. However, which reflecting surface each BD period β corresponds to can change in each surface identification. It is not determined unless processing for specifying the reflecting surface to be performed is performed.

The BD period α can be measured by the same method as for the BD period β, but the measurement method does not matter. That is, since it is assumed that the image forming apparatus will be measured before shipment, it is not essential to rotate the rotary polygon mirror 4 to actually perform scanning. The main scanning positional deviation correction data data (hereinafter also simply referred to as “correction data data”) is data for correcting the pre-measured deviation amount of scanning lines in the main scanning direction during image formation. It is assumed that this data is also measured before shipment of the device.

The correction parameters are determined not in the assembly process, but by experiments, etc. in advance using jigs and tools as described above, and are determined after performing measurements at each temperature, and are stored in the correction data storage unit 302 . The main scanning magnification deviation correction value corresponding to each reflecting surface for correcting the positional deviation in the main scanning direction of the laser beam reflected by each reflecting surface of the rotating polygon mirror caused by the temperature change is obtained by the following equation. .

[Formula 2]
Main scanning misalignment correction value = temperature correction data + main scanning misalignment correction data

The correction data control unit 303b outputs the read address adrs to the correction data storage unit 302 according to the surface ID generated by the surface identification signal generation unit 300. FIG. The deviation correction data data and the correction parameters x and z stored at the read address adrs are received from the correction data storage unit 302 . Temperature correction data is calculated using the correction parameters x and z, the apparatus installation space temperature, and the operating rate of the deflector. A main scanning position deviation correction value for each surface of the rotating polygon mirror 4 is calculated using the calculated temperature correction data and the deviation correction data data. That is, the main scanning positional deviation correction value is correction data obtained by correcting the deviation correction data using temperature correction data calculated in accordance with temperature changes. The main scanning positional deviation correction value, which is correction data corrected according to the temperature, is output to the laser light modulation section (image clock generation section) 304 .

It should be noted that the deviation correction data corresponding to each reflecting surface and stored in advance in the correction data storage unit 302 are values obtained at room temperature (25° C.) and a deflector operation rate of 0%. Therefore, when the room temperature is 0% and the operating rate of the deflector is 0%, the temperature correction data is zero. Under other conditions, a value obtained by adding temperature correction data according to temperature change to deviation correction data corresponding to each reflecting surface stored in advance in the correction data storage unit 302 is the corrected correction data. It becomes a scanning position deviation correction value.

Therefore, when the apparatus installation space temperature is 30° C., which is a temperature difference from room temperature (here, 25° C.), and the operating rate of the deflector is 50%, the main scanning position deviation correction value corresponding to each reflecting surface is obtained by the above formula 2, it can be obtained as follows. When the apparatus installation space temperature and the operating rate of the polarizer meet the above conditions, the temperature correction data of the reflecting surface A is 17.3 (see FIG. 5(a)). Therefore, the deviation correction data data on the reflecting surface A are corrected to 30.3 at the image writing portion, 79.3 at the center portion of the image, and 128.3 at the end portion of the image using the temperature correction data. That is, the main scanning positional deviation correction value, which is the corrected correction data, is 30.3 for the image writing portion, 79.3 for the image central portion, and 128.3 for the image writing end portion. Other reflecting surfaces B, C, and D can also be found in the same way.

Next, a method of associating the surface ID generated by the surface identification signal generation unit 300 with the read address adrs stored in the correction data storage unit 401 will be described.

The CPU reads the BD cycle β (β1 to β4) from the scanning cycle storage unit of the surface identification signal generation unit 300 and reads the BD cycle α (α1 to α4) from the correction data storage unit 302 . Then, the readout BD period β and BD period α are compared, and the read address adrs of the deviation correction data data in the correction data storage unit 302 is set for the surface ID of each reflecting surface of the rotary polygon mirror 4. .

For example, when the rotating polygon mirror 4 has a four-face structure, the sum of the squares of the differences between the BD period (β1 to β4) and the BD period (α1 to α4) is obtained for each of the four types of combination patterns as follows. First, when the BD signal is first output in the surface specifying process, the reflecting surface at the position where the laser light is reflected is arbitrarily determined. This arbitrarily determined reflecting surface is defined as the first surface (surface ID=ID1), and each reflecting surface is ordered in order of appearance along the rotation direction of the rotary polygon mirror 4, and each reflecting surface is ordered in advance from surface A. are combined in order to form a first combination pattern.

Each set in this first combination pattern (here, the set of the first surface and the A surface, the set of the second surface and the B surface, the set of the third surface and the C surface, and the set of the fourth surface and the D surface) , the process of calculating the square of the difference between the BD period β and the BD period α is executed. If the combination pattern is changed by shifting the pre-ordered reflecting surfaces one by one, there are four types of combination patterns (the number of reflecting surfaces of the rotating polygon mirror). For each set in all four combination patterns, the process of calculating the square of the difference is performed. For example, in the second combination pattern, calculations are made for the first surface and B surface pair, the second surface and C surface pair, the third surface and D surface pair, and the fourth surface and A surface pair. . In the third combination pattern, calculations are made for the first surface and C surface pair, the second surface and D surface pair, the third surface and A surface pair, and the fourth surface and B surface pair. In the fourth combination pattern, calculations are made for the set of the first surface and the D surface, the set of the second surface and the A surface, the set of the third surface and the B surface, and the set of the fourth surface and the C surface.

Then, for all the combination patterns, the sum of the squared differences of each pair (that is, the sum of the squared differences) is obtained and used as the difference value. Difference values 1 to 4 of combination patterns 1 to 4 are specifically calculated by the following formula.

Pattern 1: (β1-α1) ² + (β2-α2) ² + (β3-α3) ² + (β4-α4) ² = difference value 1
Pattern 2: (β1-α2) ² + (β2-α3) ² + (β3-α4) ² + (β4-α1) ² = difference value 2
Pattern 3: (β1-α3) ² + (β2-α4) ² + (β3-α1) ² + (β4-α2) ² = difference value 3
Pattern 4: (β1-α4) ² + (β2-α1) ² + (β3-α2) ² + (β4-α3) ² = difference value 4

When changing the combination pattern, the order of changing the combination of the BD period α and the BD period β does not matter. For example, in the above calculation formula, the BD cycle α is shifted one by one with respect to the BD cycle β, but the present invention is not limited to this, and the BD cycle β is shifted one by one with respect to the BD cycle α. You can

FIG. 6A is a diagram showing an example of BD cycles (α1 to α4) pre-stored in the correction data storage unit 302. FIG. FIG. 6B is a diagram showing an example of the BD cycles (β1 to β4) measured and stored in the scanning cycle storage unit of the surface identification signal generation unit 300. FIG.

Here, the correspondence between each BD cycle α in the correction data storage unit 302 and each BD cycle β in the scanning cycle storage unit of the surface identification signal generation unit 300 is determined by the combination pattern with the smallest difference value among the four combination patterns. is determined. At that time, a certain threshold is set, and it is determined whether or not the matching condition that "the minimum difference value is equal to or less than the threshold and all other difference values are greater than the threshold" is satisfied. Only when this matching condition is satisfied, it is determined that the matching (pattern matching) of each BD period α in the correction data storage unit 302 with each BD period β in the scanning period storage unit of the surface identification signal generation unit 300 has been successful. do.

Here, the surface ID and the BD period β are associated with each other in the surface identification signal generator 300 (see FIG. 6B). In the correction data storage unit 302, the read address adrs in which the deviation correction data data is stored is associated with the BD period α. In addition, the BD period α, the correction data data, and the correction parameters also have a corresponding relationship through the read address adrs (see FIG. 6A). Note that FIG. 7 exemplifies the correspondence relationship in the case of the combination pattern with the smallest difference value of 4 among the four combination patterns described above.

When the pattern matching is successful, based on the one-to-one correspondence between the BD period β and the BD period α in the combination pattern, among those stored in the correction data storage unit 302, corresponding to the surface ID of each reflective surface are used for main scanning misregistration correction. Here, what is stored in the correction data storage unit 302 is the deviation correction data data and the correction parameters, and among the correction data data and the correction parameters, those corresponding to the surface ID of each reflecting surface are used for the main scanning position deviation correction. . That is, the read address adrs corresponding to the face ID is obtained in the order of face ID→BD cycle β→BD cycle α→read address adrs (see FIG. 7). Then, the deviation correction data data and correction parameters stored in this read address adrs are read out as correction data used for main scanning position deviation correction.

Since the corresponding relationship between the BD period β and the BD period α is found, it is also possible to find out which reflecting surface is actually reflecting the laser beam at present. That is, at the stage before the completion of surface identification, only the surface ID is assigned to each reflecting surface of the rotating polygon mirror 4, and the absolute position of each reflecting surface is not actually known. However, after the surface identification is completed, each of the multiple reflecting surfaces of the rotary polygon mirror 4 is identified. Therefore, from the correspondence relationship with the BD signal, it is possible to identify whether each reflecting surface is a reflecting surface that reflects the laser beam, or the relative position of the reflecting surface with respect to the reflecting surface. can get. In this embodiment, this matching processing is performed by the surface identification unit, and it is possible to identify the four reflecting surfaces of the rotating polygon mirror by the processing in the surface identification unit. is not limited to If only one of the reflecting surfaces can be specified, it is possible to correct the shift in the main scanning direction with correction data for that specified surface.

If the pattern matching fails, the correction data in the correction data storage unit 302 is not set. Here, the process of not setting correction data when pattern matching fails has been exemplified, but the present invention is not limited to this. For example, even if pattern matching fails, the average value of the correction data stored in the correction data storage unit 302 may be set as common correction data for all reflecting surfaces. Here, the same correction data may be predetermined instead of the average value.

If pattern matching succeeds, the minimum difference value approaches 0 infinitely. Therefore, as a method of determining the threshold value T in the above matching condition, it is desirable to set the value of the error calculated from the rotational jitter of the rotating polygon mirror 4 when the pattern matching is successful.

For example, if the difference value 4, which is the minimum difference value, is equal to or less than the threshold T, and the difference values 1, 2, and 3 other than the minimum difference value 4 are all greater than the threshold T, pattern matching is successful. deemed to have been

On the other hand, if all the difference values are larger than the threshold T, it is assumed that pattern matching has failed. This can occur, for example, when the BD period of a certain reflecting surface cannot be accurately measured in the scanning period storage unit of the surface identification signal generation unit 300 due to noise in the BD signal.

For example, when the difference value takes the minimum value of 4 and pattern matching is successful, as shown in FIG. The BD cycle is the BD cycle α4. The pattern of the transition of the BD period β starting from the reflecting surface (the surface whose surface ID is ID1) corresponding to the BD period β1 in FIG. 6B, and the reflecting surface corresponding to the BD period α4 in FIG. 6A ( It can be seen that the transition pattern of the BD period α starting from the D plane) is most similar. After all, the pattern matching is also to specify the starting points of the BD cycles such that the pattern of transition of the BD cycle β and the pattern of transition of the BD cycle α match each other.

In this case, as shown in FIG. 7, "adrs4" is set as the read address adrs in the correction data storage unit 302 of the main scanning position shift correction unit 301 for ID1, which is the surface ID corresponding to the BD period β1. In the positional deviation correction, the deviation correction data dataL4 and the correction parameters x4 and z4 stored in the read address adrs4 are read out and used as correction data.

If the correspondence between the surface ID and the read address adrs in the correction data storage unit 302 is determined in this way, the deviation correction data data corresponding to the current reflecting surface of the rotating polygon mirror 4 and the parameters x, It is possible to retrieve and use z. FIG. 8 shows the correspondence between the BD signal, surface ID, and correction data when the difference value is 4. As shown in FIG. In the positional deviation correction, the laser drive unit 306 controls emission of laser light according to the read deviation correction data data and the correction parameters x and z. That is, the CPU controls the emission of laser light from the semiconductor laser unit 1, which is the light source, via the laser driving section 306 according to the read deviation correction data data and the correction parameters x and z corresponding to the temperature change. As a result, it is possible to reliably correct the displacement in the main scanning direction of the laser beam reflected by each reflecting surface caused by the temperature change of the rotating polygon mirror, and to suppress the deterioration of the image quality due to the displacement. .

Next, control processing for specifying a reflective surface and correcting positional deviation of the specified reflective surface in the main scanning direction by the CPU that serves as the surface specifying unit 303a and the correction data control unit 303b will be described. FIG. 9 is a flowchart of processing for specifying a reflecting surface and correcting main scanning positional deviation.

First, in step S101, the CPU determines whether or not image formation is started, and advances the process to step S102 when image formation is started. In step S102, the CPU causes the surface identification signal generator 300 to measure the BD period β (β1 to β4) of each reflecting surface of the rotating polygon mirror 4, and stores the measured BD period β in the scanning period storage unit. Control. Then, when the measurement of the BD period β1 for all reflecting surfaces of the rotating polygon mirror 4 is completed, the CPU advances the process to step S103. In step S<b>103 , the CPU reads the BD period β of each reflecting surface of the rotating polygon mirror 4 from the scanning period storage unit of the surface identification signal generation unit 300 .

Next, in step S104, the CPU reads the BD period α (α1 to α4) of each reflecting surface of the rotating polygon mirror 4 from the correction data storage unit 302. FIG. Next, in step S105, the CPU calculates a difference value in each combination pattern corresponding to the number of faces of the rotary polygon mirror 4 from the read BD period β and BD period α of each reflecting surface. For example, when the rotating polygon mirror 4 has four faces, there are four combinations of BD periods, so difference values 1 to 4 are calculated.

Next, in step S106, the CPU performs pattern matching between the BD period α and the BD period β according to the matching conditions described above, and determines whether or not the pattern matching is successful. As a result, when pattern matching is successful, the CPU advances the process to step S107.

In step S107, the CPU identifies the combination pattern that has the smallest difference value, and grasps the one-to-one correspondence between the BD period β and the BD period α in that combination pattern. That is, when the pattern matching is successful and the combination pattern with the minimum difference value is identified, the correspondence relationship between the BD period β associated with the surface ID and the BD period α previously associated with each reflecting surface is identified. , and each reflecting surface of the rotating polygon mirror 4 is specified. Then, as described above, the CPU traces the correspondence relationship and sets the read address adrs in the correction data storage unit 302 for each surface ID (see FIG. 7). Then, the CPU reads the deviation correction data data and the correction parameters x and z from the correction data storage unit 302 stored at the read address adrs set for each surface ID.

Then, in step S108, the correction data control unit 303b detects the temperature of the apparatus installation space inside the apparatus in which the rotating polygon mirror is installed from the temperature detection unit 308, and further determines the operation rate of the deflector based on the BD signal from the BD sensor 6. to get As mentioned above, the deflector utilization is the percentage of time that the deflector is in operation for a given period of time. The deflector operating rate is detected by counting the time for the correction data control unit 303b to receive the BD signal from the BD sensor. The operating rate of the deflector is acquired in order to correct the influence of the heat generated by the operation of the deflector on the temperature of the rotating polygon mirror. It is preferable that the timing for obtaining the device installation space temperature and the operating rate of the deflector be close to the timing for irradiating the photosensitive drum with the laser beam.

Then, in step S109, the CPU calculates the temperature correction data according to Equation 1 above, using the read correction parameters x and z and the apparatus installation space temperature and deflector operating rate obtained. Further, in step S110, the CPU uses the read deviation correction data of each reflecting surface and the calculated temperature correction data according to the temperature change of the reflecting surface to correct the main scanning positional deviation of each reflecting surface according to Equation 2 above. Calculate the value. The calculated main scanning positional deviation correction value is correction data for correcting the positional deviation of the laser beam in the main scanning direction with respect to the specific surface specified by the matching. Then, in step S111, the CPU sets a main scanning positional deviation value (correction data) for each surface ID.

Then, in subsequent step S112, the CPU controls the emission of laser light from the semiconductor laser unit 1, which is the light source, via the laser driving section 306 based on the main scanning positional deviation correction value set according to the temperature change. , to form an image. More specifically, the CPU controls to output the calculated main scanning positional deviation correction value to the laser light modulation unit (image clock generation unit) 304 .

A laser light modulator (image clock generator) 304 performs image clock modulation for each scanning line of each reflecting surface of the rotary polygon mirror 4 based on the main scanning positional deviation correction value to correct the main scanning positional deviation. The details of the means for performing image clock modulation from the main scanning positional deviation correction value can be achieved by using the technique disclosed in Japanese Patent Application Laid-Open No. 2002-200032, and the description thereof will be omitted.

A laser light modulation unit (image clock generation unit) 304 supplies an image clock modulated based on a main scanning positional deviation correction value set according to a temperature change to a laser driving unit 306 . The image signal generator 305 generates an image signal and supplies it to the laser driver 306 . The laser drive unit 306 outputs a laser beam from the semiconductor laser unit 1 according to the supplied image signal and the image clock generated by the main scanning position shift correction unit 301 to form an image. Then, in step S113, the CPU determines whether or not the image formation is finished, and when the image formation is finished, the control process is finished.

On the other hand, if pattern matching fails in step S106, the CPU advances the process to step S114. In step S114, the CPU does not set correction data. Here, the control process of not setting correction data when pattern matching fails has been exemplified, but the present invention is not limited to this. For example, even if pattern matching fails, the following control processing may be performed. That is, the average value of the correction data stored in the correction data storage unit 302 is set as common correction data for all reflecting surfaces. Then, the same correction is performed on the laser light for each reflecting surface of the rotating polygon mirror 4 . Control processing may be performed in this way.

By performing the main scanning positional deviation correction described above, it is possible to suppress deterioration of image quality caused by the positional deviation in the main scanning direction. In addition, by performing the positional deviation correction, the maximum amount of deviation from the ideal position in the image writing portion, the image center portion, and the image writing end portion is a predetermined value or less (here, about 5 μm or less) at each rotation speed. ). Also, the amount of relative displacement between the reflecting surfaces of the rotary polygon mirror 4 can be set to about 2 μm or less.

Also, although the rotating polygon mirror 4 is made of a resin material such as a polycarbonate resin or a cycloolefin resin, the present invention is not limited to this. Even if the rotating polygon mirror 4 is made of a metal material such as aluminum, the amount of deformation of the reflecting surface due to the rotation of the rotating polygon mirror 4 is not completely zero. Therefore, as described above, even if the rotating polygon mirror 4 is made of a metal material, a similar main scanning positional deviation correction value is obtained in accordance with temperature changes, and main scanning positional deviation correction is performed in accordance with temperature changes. good too.

By calculating the main scanning direction magnification deviation correction value based on the apparatus installation space temperature and the operating rate of the deflector in this way, the main scanning direction of the laser beam reflected by each reflecting surface caused by the temperature change of the rotary polygon mirror 4 can be calculated. Positional deviation in the scanning direction can be reliably corrected. Therefore, even if the temperature of the space in which the rotating polygon mirror of the image forming apparatus is installed changes, image quality does not deteriorate, and high-quality images can be maintained.

In the above-described embodiment, the temperature detection unit 308 is installed in the vicinity of the apparatus housing away from the control board and the fixing device 108 inside the image forming apparatus, but the installation position of the temperature detection unit is not limited to this. . As shown in FIG. 11, it may be provided inside the optical box of the optical scanning device. A modification of the above-described embodiment will be described with reference to FIGS. 11 and 12. FIG. FIG. 11 is a perspective view of an optical scanning device according to a modification of the above embodiment. FIG. 12 is a flowchart of processing for identifying a reflecting surface and correcting main scanning magnification deviation according to a modification of the above-described embodiment.

Since the schematic configuration of the image forming apparatus according to this example is the same as that of the above-described embodiment, the description thereof is omitted here. The configuration of the optical scanning device is also the same except for the arrangement of the temperature detection unit, so members having the same function are denoted by the same reference numerals, and description thereof is omitted.

In this example, as shown in FIG. 11, the deflector 5 has a temperature detection section 309 near the rotating polygon mirror 4 . More specifically, the temperature detector 309 is arranged near the rotating polygon mirror 4 on the circuit board 18 (see FIG. 2) that constitutes the deflector 5 . By arranging the temperature detection unit 390 inside the optical box 8 in this manner, the temperature of the rotating polygon mirror 4 can be detected more directly, and main scanning positional deviation correction can be performed more accurately.

As in the above-described embodiment, the main scanning positional deviation correction data stored in the correction data storage unit is deviation correction data corresponding to each of the reflecting surfaces A to D at room temperature. It is necessary to correct according to the temperature change of The correction parameters are parameters for correcting deviation correction data corresponding to each of the reflecting surfaces A to D at room temperature according to temperature changes in the space in which the rotating polygon mirror is installed. In this example, in order to correct the deviation correction data stored in the correction data storage unit 302 in accordance with the temperature change, the deflector temperature inside the optical scanning device in which the deflector is installed and the operation rate of the deflector are calculated. I am using A correction parameter y (y1, y2, y3, y4) is a parameter for using the deflector temperature as temperature correction data. Correction parameters z (z1, z2, z3, z4) are parameters for using the operation rate of the deflector as temperature correction data. Using these correction parameters y and z, the temperature correction data for correcting the deviation correction data corresponding to each of the reflecting surfaces A to D is obtained by the following equation.

[Formula 3]
Temperature correction data = (y1, y2, y3, y4) x deflector temperature + (z1, z2, z3, z4) x deflector operating rate

Note that the main scanning magnification deviation correction value corresponding to each reflecting surface for correcting the positional deviation in the main scanning direction of the laser beam reflected by each reflecting surface of the rotating polygon mirror caused by the temperature change is given by Equation 2 described above. is required.

Based on the deviation correction data stored in the correction data storage section and the correction parameters y and z corresponding to the temperature change, the semiconductor laser unit 1, which is the light source, controls the emission of laser light.

Here, control processing for specifying a reflective surface and correcting a positional deviation of the specified reflective surface in the main scanning direction by the CPU that serves as the surface specifying unit 303a and the correction data control unit 303b will be described. FIG. 12 is a flowchart of processing for identifying a reflecting surface and correcting main scanning positional deviation.

In FIG. 12, the operations of steps S201 to S206 and steps S212 to S214 are the same as the operations of steps S101 to S106 and steps S112 to S114 described with reference to FIG.

In step S207, the CPU identifies the combination pattern that has the smallest difference value, and grasps the one-to-one correspondence between the BD period β and the BD period α in that combination pattern. That is, when the pattern matching is successful and the combination pattern with the minimum difference value is identified, the correspondence relationship between the BD period β associated with the surface ID and the BD period α previously associated with each reflecting surface is identified. , and each reflecting surface of the rotating polygon mirror 4 is specified. Then, as described above, the CPU traces the correspondence relationship and sets the read address adrs in the correction data storage unit 302 for each surface ID. Then, the CPU reads the deviation correction data data and the correction parameters y and z from the correction data storage unit 302 stored at the read address adrs set for each surface ID.

Then, in step S208, the correction data control unit 303b detects the temperature of the deflector inside the optical scanning device in which the deflector is installed from the temperature detection unit 309, and the operation rate of the deflector based on the BD signal from the BD sensor 6. to get The timing for acquiring the deflector temperature and the operating rate of the deflector is preferably close to the timing for irradiating the photosensitive drum with the laser beam.

Then, in step S209, the CPU calculates the temperature correction data by Equation 3 above using the read correction parameters y and z and the acquired deflector temperature and deflector operation rate. Further, in step S210, the CPU uses the read deviation correction data of each reflecting surface and the calculated temperature correction data according to the temperature change of the reflecting surface to correct the main scanning positional deviation of each reflecting surface according to the above equation (2). Calculate the value. The calculated main scanning positional deviation correction value is correction data for correcting the positional deviation of the laser beam in the main scanning direction with respect to the specific surface specified by the matching. Then, in step S211, the CPU sets a main scanning positional deviation value (correction data) for each surface ID.

Based on the correction data set in this manner, the semiconductor laser unit 1, which is the light source, controls the emission of laser light.

In this example, the configuration in which the deflector 5 supports the temperature detection unit 309 was exemplified. If so, it may be supported by another member. For example, it may be supported from the optical box 8 .

In this way, by calculating the main scanning direction magnification deviation correction value according to the temperature detected by the temperature detection unit 309 in the vicinity of the rotating polygon mirror 4, the light reflected by each reflecting surface caused by the temperature change of the rotating polygon mirror 4 is Therefore, it is possible to reliably correct the positional deviation of the laser beam to be emitted in the main scanning direction. Therefore, even if the deflector temperature and the deflector operating rate change, it is possible to reduce deterioration in image quality due to the positional deviation and maintain a high-quality image.

In the above-described embodiments, a printer is used as an example of the image forming apparatus, but the present invention is not limited to this. For example, other image forming apparatuses such as a copying machine and a facsimile machine, or other image forming apparatuses such as a multi-function machine combining these functions may be used. Similar effects can be obtained by applying the present invention to these image forming apparatuses.

L: laser light 1: semiconductor laser unit 2: composite anamorphic collimator lens 3: aperture diaphragm 4: rotary polygon mirror 5: deflector 6: synchronization signal detection sensor (BD sensor)
7 ... fθ lens 101 ... optical scanning device 103 ... photosensitive drum 110 ... image forming apparatus 300 ... surface identification signal generation unit 301 ... main scanning position deviation correction unit 302 ... correction data storage unit 303 ... correction data control unit + specifying unit 303a ... Surface identification unit 303b ... correction data control unit 304 ... laser light modulation unit (image clock generation unit)
305 ... image signal generating section 306 ... laser driving section 308, 309 ... temperature detecting section

Claims (11)

An image forming apparatus comprising an optical scanning device that scans an image carrier with a laser beam emitted from a light source in a main scanning direction, which is an axial direction of the image carrier, by rotating a rotating polygon mirror,
an output unit provided in the optical scanning device for receiving a laser beam reflected by a reflecting surface of the rotating polygon mirror and outputting a signal;
a surface identifying unit that identifies a specific reflecting surface among a plurality of reflecting surfaces of the rotating polygon mirror based on the signal output from the output unit;
deviation correction data for correcting deviation in the main scanning direction of the image carrier of the laser beam reflected by the specific reflecting surface associated with the specific reflecting surface; and a temperature for correcting the deviation correction data. a storage unit pre-stored with predetermined correction parameters used for calculating correction data;
a temperature detection unit for detecting the temperature of the space in which the rotating polygon mirror is installed;
Based on the temperature detected by the temperature detection unit and the correction parameter, temperature correction data corresponding to the temperature change in the space in which the rotating polygon mirror is installed is calculated, and the deviation correction is performed using the calculated temperature correction data. a correction data control unit that corrects the data to correction data corresponding to temperature changes in the space in which the rotating polygon mirror is arranged;
a modulation unit that generates a signal for modulating the laser light from the light source based on the correction data corrected by the correction data control unit;
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the temperature detection unit is installed inside the image forming apparatus and detects the temperature inside the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the temperature detection unit is installed inside an optical scanning device having the rotating polygon mirror, and detects the temperature inside the optical scanning device. The optical scanning device has a deflector that rotates the rotating polygon mirror,
4. The image forming apparatus according to claim 3, wherein the deflector has the temperature detection section. 5. The deviation correction data stored in the storage unit is correction data for correcting deviation in the main scanning direction of the laser beam reflected by each reflecting surface of the rotating polygon mirror at room temperature. The image forming apparatus according to any one of . 6. The image forming apparatus according to claim 1, wherein said rotating polygon mirror is made of plastic. 7. The apparatus according to any one of claims 1 to 6, wherein the output unit outputs a signal for synchronizing image writing positions in the main scanning direction on each reflecting surface of the rotating polygon mirror. Image forming device. The deviation correction data stored in the storage unit is obtained by measuring the distance from the scanning start position where the output unit is arranged to a predetermined position in the image area of the image carrier in the main scanning direction. 8. The image forming apparatus according to claim 1, wherein the distance is an amount of deviation in the main scanning direction from an ideal distance that serves as a reference. The image area of the image carrier is an area from the position of the image writing part to the position of the image writing end part,
9. The image according to claim 8, wherein the predetermined positions of the image area of the image carrier are the position of the image writing portion, the position of the image center portion, and the position of the image writing end portion in the main scanning direction. forming device. The surface specifying unit stores in advance an output interval of the signals, which is measured based on the two signals output in order from the output unit, for the number of reflecting surfaces of the rotating polygon mirror, and an output interval of the signals. calculating a difference value of a combination pattern corresponding to the number of reflecting surfaces of the rotating polygon mirror using the output intervals of the signals,
The reflective surface is specified by a combination pattern that satisfies a matching condition that the minimum difference value among the calculated difference values for the number of surfaces, among the combination patterns for the number of surfaces, is smaller than a preset threshold value. 2. The image forming apparatus according to claim 1. If a matching condition is satisfied that the minimum difference value among the calculated difference values for the number of surfaces among the combination patterns for the number of surfaces is smaller than a preset threshold value, correction data for each reflecting surface is changed. 11. The image forming apparatus according to claim 10, wherein the correction data is not set if the matching condition is not satisfied.

Images