Patent Grant
9658562
Field of the Invention
The present invention relates to an image forming apparatus and an optical scanning apparatus, such as a laser beam printer, a copy machine or a fax machine, that form an image by scanning light.
Description of the Related Art
There are image forming apparatuses that form an image by exposing a photosensitive member. Furthermore, some of these image forming apparatuses form a light spot on the surface of the photosensitive member by reflecting light with a rotating polygon mirror and focusing the reflected light using a scanning lens. By rotating the rotating polygon mirror, the light spot moves over the surface of the photosensitive member in a main scanning direction (direction orthogonal to a circumferential direction of the photosensitive member), and thereby forms a latent image on the photosensitive member.
Note that lenses having fθ characteristics are mainly used as the scanning lens. This is to ensure that the light spot moves at a uniform speed over the surface of the photosensitive member, when the rotating polygon mirror rotates at a uniform angular velocity. However, scanning lenses having fθ characteristics are comparatively large and costly. Thus, configurations that do not using a scanning lens or that use a scanning lens that does not have fθ characteristics are being considered with the aim of reducing the size and cost of image forming apparatuses. Japanese Patent Laid-Open No. 58-125064 discloses a configuration that changes the clock frequency during the scanning of one scan line, such that dots that are formed on the surface of the photosensitive member have a constant width, even when the light spot does not move over the surface of the photosensitive member at a uniform speed.
Image forming apparatuses are required to perform exposure that suppresses image distortion by making a LSF (Line Spread Function) profile of each pixel (dot) uniform in the main scanning direction. This still applies even when not using a scanning lens having fθ characteristics.
According to an aspect of the present invention, an image forming apparatus includes: a photosensitive member; a scanning unit configured to form a latent image on the photosensitive member, by forming a light spot on the photosensitive member with light emitted by a light source and scanning the light spot, wherein a scanning speed at which the photosensitive member is scanned with the light spot changes within a scan line; a control unit configured to perform correction control of a luminance and a light-emitting time of the light source, according to a pixel to be exposed; a holding unit configured to hold profile information indicating a change of the light spot due to an environment or due to a position of the pixel. The holding unit is further configured to hold scanning information indicating the light-emitting time of the light source or the luminance of the light source with respect to the pixel, for correcting a change in the scanning time of the pixel due to a change in the scanning speed, and the control unit is further configured to perform the correction control based on the scanning information and the profile information.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, illustrative embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are illustrative, and it is not intended to limit the present invention to the contents of the embodiments. Also, in the following diagrams, constituent elements that are not required in describing the embodiments are omitted from the diagrams.
First Embodiment
Light that has passed through the anamorphic lens 404 is reflected by the deflection surface or reflection surface 405a of the deflector (rotating polygon mirror) 405. The light 208 reflected by the deflection surface 405a passes through an imaging lens 406, and forms a light spot on a scan surface 407 of the photosensitive member 4. The imaging lens 406 is an imaging optical element. In the present embodiment, an imaging optical system is constituted by only a single imaging optical element (imaging lens 406). By rotating the deflector 405 at a constant angular velocity in the direction of arrow A using a drive unit that is not illustrated, the light spot moves in the main scanning direction over the scan surface 407, and thereby scans the photosensitive member 4. As shown in
A beam detector (BD) sensor 409 and a BD lens 408 constitute a synchronization optical system that determines the timing for writing the electrostatic latent image onto the scan surface 407. Light that has passed through the BD lens 408 is incident on the BD sensor 409, which includes a photodiode, and is detected. The write timing is controlled, based on the timing at which light is detected by the BD sensor 409.
The light source 401 is, for example, a semiconductor laser. The light source 401 of the present embodiment is provided with one light-emitting unit. However, it is possible to use a light source 401 provided with a plurality of light-emitting units whose light emission can be controlled independently. In the case where a plurality of light-emitting units are provided, the plurality of light beams that are generated each arrive at the scan surface 407 via the coupling lens 403, the anamorphic lens 404, the deflector 405, and the imaging lens 406. On the scan surface 407, light spots corresponding to the light beams are respectively formed at positions shifted in the sub-scanning direction. Note that the various optical members of the optical scanning apparatus 400 including the light source 401, the coupling lens 403, the anamorphic lens 404, the imaging lens 406 and the deflector 405 mentioned above are housed in the casing 400a shown in
As shown in
Also, although the imaging lens 406 according to the present embodiment is a plastic molded lens formed by injection molding, a glass molded lens may be employed as the imaging lens 406. Since the aspheric surface shape of molded lenses is easily formed and molded lenses are suited to mass production, an improvement in productivity and optical performance can be achieved by employing a molded lens as the imaging lens 406.
The imaging lens 406 according to the present embodiment is not a lens having so-called fθ characteristics. In other words, the light spot does not move at a uniform speed on the scan surface 407 when the deflector 405 is rotated at a uniform angular velocity. By using the imaging lens 406 that does not have fθ characteristics, it is thus possible to shorten a distance D1 in
The scan characteristic of the scan surface 407 due to the imaging lens 406 of the present embodiment is expressed with the following equation (1).
Y=K/B·tan(B·θ) (1)
Y in equation (1) is the position (image height) of the light spot on the scan surface 407 in the main scanning direction, and Y=0 in the case where the light spot is on the optical axis (hereinafter, simply “on-axis”), that is, in the case where the light spot is in the center of the scan line. Also, θ in equation (1) is the scanning angle (scanning field angle) of the deflector 405, and θ=0 corresponds to the case where the light spot is on the optical axis. Furthermore, K in equation (1) is the on-axis imaging coefficient, and B is the scan characteristic coefficient that determines the scan characteristic of the imaging lens 406. With the imaging lens 406, the light spot scans a range of Y=−Ymax to +Ymax. Also, in
When equation (1) is differentiated with the scanning angle θ, the following equation (2) showing the movement speed, that is, the scanning speed, of the light spot with respect to the position of the scan surface 407 in the main scanning direction is obtained.
dY/dθ=K/(cos2(B·θ)) (2)
From equation (2), the scanning speed of the light spot when θ=0. that is, at the on-axis image height, is K. When equation (2) is divided by K, the following equation (3) is obtained.
(dY/dθ)/K=1/(cos2(B·θ)) (3)
Equation (3) represents the ratio of the scanning speed of the light spot at each scanning angle to the scanning speed of the light spot at the on-axis image height. Note that since the image height and the scanning angle correspond, equation (3) shows the ratio of the scanning speed of the light spot at the on-axis image height and the scanning speed of the light spot at each image height. The following equation (4), which is obtained by subtracting 1 from equation (1), therefore shows the shift amount (hereinafter, partial magnification) of the scanning speed at each image height relative to the scanning speed of the light spot at the on-axis image height.
(dY/dθ)/K=(1/(cos2(B·θ))−1=tan2(B·θ) (4)
It is evident from equations (3) and (4) that with the imaging lens 406 according to the present embodiment, the scanning speed of the light spot changes depending on the image height of the deflector 405. In other words, with the optical scanning apparatus 400 according to the present embodiment, the scanning speed changes within the scan line.
The image signal generation unit 100 instructs the control unit 1 to start printing, using serial communication 113, when preparation for outputting an image signal for image formation is complete. The control unit 1 transmits a TOP signal 112, which is a synchronization signal in the sub-scanning direction, and a BD signal 111, which is a synchronization signal in the main scanning direction, to the image signal generation unit 100, when preparation for printing is complete. The image signal generation unit 100 outputs the VDO signal 110, which is the image signal, to the drive unit 300 at a predetermined timing when the synchronization signals are received. The configuration blocks within the image signal generation unit 100, the control unit 1 and the drive unit 300 shown in
The LSF profiles thus differing depending on image height is due to the profiles of the stationary spots respectively shown with the dashed lines in
With the configuration described in Japanese Patent Laid-Open No. 58-125064. the LSF profiles differing depending on image height is due to the shapes (profiles) of the stationary spots produced at each moment on the scan surface 407 by the imaging lens 406 differing depending on image height. Therefore, in the present embodiment, correction of the light-emitting time of the light source 401 (light-emitting time correction) is performed, in addition to partial magnification correction and luminance correction. The reproducibility of detailed images is thereby improved.
As an example, the case where the light-emitting time at the maximum image height is set to 0.22T3, as shown in
16×(0.22/0.74)=4.75 [section]
Therefore, SRC1 need only be set such that the pixel pieces of a maximum of approximately five sections are lighted.
Next, luminance correction will be described. As a result of light-emitting time correction which has already been described, the light-emitting time of one pixel decreases as the absolute value of the image height Y increases. Accordingly, when luminance is fixed, the total light exposure amount (integrated light amount) of one pixel decreases as the absolute value of the image height Y increases. In the present embodiment, luminance correction for compensating for the decrease in this total light exposure is performed. In other words, the luminance of the light source 401 is corrected such that the total light exposure (integrated light amount) of one pixel is constant at each image height.
As shown in
The IC 3 of the control unit 1 adjusts a voltage 23 that is output from the regulator 22, on the basis of information on the correction current to the light-emitting unit 11 acquired from the memory 304 by serial communication 307, and outputs the adjusted voltage. The voltage 23 serves as a reference voltage of the DA converter 21. Next, the IC 3 sets input data 20 of the DA converter 21, and outputs a luminance correction analog voltage 312 that changes according to image height in one scan line, in synchronization with the BD signal 111. This luminance correction analog voltage 312 is converted into a current value by the VI conversion circuit 306, and output to the driver IC 9. Note that although, in the present embodiment, the IC 3 mounted in the control unit 1 outputs the luminance correction analog voltage 312, a DA converter may be mounted on the drive unit 300 and the luminance correction analog voltage 312 may be generated in proximity to the driver IC 9.
The driver IC 9 performs ON/OFF control of light emitted from the light source 401, by switching a current IL between flowing to the light-emitting unit 11 and flowing to a dummy resistor 10 with the switch 14, according to the VDO signal 110. The drive current value IL that is supplied to the light-emitting unit 11 is a current obtained by subtracting a current Id that is output from the VI conversion circuit 306 from a current Ia set by a constant current circuit 15. The current Ia that flows in the constant current circuit 15 is feedback controlled and automatically adjusted by a circuit inside the driver IC 9, such that luminance that is detected by a photodetector 12 provided in the light source 401 for monitoring the light amount of the light-emitting unit 11 is a predetermined value Papc1. This automatic adjustment is so-called APC (Automatic Power Control). Automatic adjustment of the luminance of the light-emitting unit 11 is implemented at the timing at which the light-emitting unit 11 is being caused to emit light in order to detect the BD signal 111. The method of setting the current value Id that is output by the VI conversion circuit 306 will be discussed later. A variable resistor 13 adjusts a value so as to be input to the driver IC 9 as a desired voltage, in the case where the light-emitting unit 11 is emitting light at a predetermined luminance at the time of assembly.
As described above, a configuration is adopted in which a current obtained by subtracting the current value Id that is output by the VI conversion circuit 306 from the current Ia required in order to perform light emission at a predetermined luminance is supplied to the light-emitting unit 11 as the drive current IL. This configuration ensures that the drive current IL is less than the current Ia. Note that the VI conversion circuit 306 constitutes a part of the luminance correction unit.
Luminance correction is performed by subtracting the current Id corresponding to the current ΔI(N) or ΔI(H) according to the image height from the automatically adjusted current Ia so as to perform light emission at a desired luminance. As mentioned above, the scanning speed increases as the absolute value of the image height Y increases. Also, the total light exposure amount (integrated light amount) of one pixel decreases as the absolute value of the image height Y increases. In the luminance correction, correction is performed such that the luminance increases as the absolute value of the image height Y increases. Specifically, the current IL is increased as the absolute value of the image height Y increases, by setting the current value Id to decrease as the absolute value of the image height Y increases. This enables the partial magnification to be appropriately corrected.
As described above, in the present embodiment, the scanning speed of the light spot that exposes the pixels of the photosensitive member 4 changes within a scan line. More specifically, the scanning speed of the light spot increases when the absolute value of the image height increases. As described using the exposure control configuration of
Note that when the light-emitting time of a pixel is defined, as described using
As described above, by controlling the light-emitting time and the luminance, accurate exposure in which distortion is suppressed can be performed without using a scanning lens having f-θ characteristics. Note that in the exposure control configuration shown in
Correction control of light-emitting time and luminance based on the characteristics of the optical scanning apparatus 400 alone was described above. However, the positional relationship between the optical scanning apparatus 400 and the photosensitive member 4, which is the scan surface, could possibly shift from an ideal relationship, due to variation in the attachment position when mounting the optical scanning apparatus 400 to the image forming apparatus. As a result, the scan characteristic at the surface of the photosensitive member 4 changes. Even when the above-mentioned correction is performed, it is not impossible to appropriately correct the profile of the light spot, based on the characteristics of the optical scanning apparatus 400 alone.
Also, in the present embodiment, the sensor 30C is disposed at the on-axis image height, and the sensors 30F and 30R are disposed near the maximum image height. This is to inhibit the profile of the light spot from shifting, even when the scanning speed at the on-axis image height is stable and the position of the optical scanning apparatus 400 shifts slightly. In other words, because a change in density does not readily occur at the on-axis image height, a change in density near the maximum image height where change readily occurs can be measured using the sensors 30F and 30R, on the basis of the measurement values of the sensor 30C.
Note that although the number of sensors 30 was given as three in the present embodiment, the present invention is not limited thereto. For example, if three or more sensors 30 are disposed, a change in density spanning the entire main scanning direction can be detected more accurately. Also, since the profile of the scanning speed basically has symmetry, it is also possible to reduce the sensors disposed near the maximum image height to one. For example, a configuration may be adopted in which two sensors 30C and 30F are provided. Also, although, in the present embodiment, a configuration is adopted in which a patch formed on the photosensitive member 4 is measured, a configuration may be adopted, in the case of an image forming apparatus equipped with an intermediate transfer body (not shown), in which a patch transferred from the photosensitive member 4 to the intermediate transfer body is measured. Patches 31F, 31C and 31R are formed so as to correspond to the respective sensors 30. Also, the patches 31 are assumed to be gradation patches that are contiguous from low density to high density, respectively.
Next, a method of correcting the profile of a light spot will be described. As shown in
Note that although, in the present embodiment, a plurality of gradation patches from low density to high density were formed as patches for density detection, the present invention is not limited thereto. Specifically, the pattern need only enable the change in density according to image height to be detected. For example, the slope may be derived from the detected density of two types of patches formed with the image data corresponding to a density of 30 percent and a density of 70 percent. Furthermore, although the change ratio of the light spot is derived using the ratio of the slope of the gradation density characteristic, the present invention is not limited to this configuration. In other words, any parameter that is correlated with the change in the light spot may be used, and a configuration may, for example, be adopted in which the detected densities of patches of specific image data are compared or in which a difference is used rather than a ratio.
As mentioned above, in the present embodiment, profile information indicating changes due to scanning position of the light spot, that is, the position of the pixel to be exposed is held. The profile information is, for example, the above-mentioned change ratio of the light spot according to the position of the pixel. Also, in determining the luminance and the light-emitting time of the light source with respect to a pixel, the image forming apparatus uses the above-mentioned scanning information and profile information. For example, either one or both of luminance and light-emitting time of the light source with respect to the pixel determined based on scanning information is corrected based on the profile information. Note that the control unit 1 forms the patches 31 for detecting density on the photosensitive member 4, and thereby detects changes in the density of each pixel in the main scanning direction and generates profile information. Specifically, the sensors 30F, 30C, and 30R are provided at a plurality of positions in the main scanning direction, and detect changes in the density of each pixel in the main scanning direction, based on the density detected by each sensor. Note that a configuration can, for example, be adopted in which sensors are provided at least in the middle and at an end part of a scan line. This configuration enables the profile of the light spot to be corrected, irrespective of any change in density due to a change in image height. As a result, it is possible to perform accurate exposure that suppressed distortion, without using a scanning lens having f-θ characteristics.
Second Embodiment
Next, a second embodiment will be described focusing on differences with the first embodiment. In the first embodiment, the change ratio of the light spot was derived from the density measurement result, with respect to a change in the light spot due to positional variation in the optical scanning apparatus 400, and light-emitting time and luminance were corrected. In the present embodiment, the light spot is directly measured after attaching the optical scanning apparatus 400 to an image forming apparatus. As the method of measuring the light spot, a spot measuring function of a common measuring device need only be used, for example. Even though there is an increase in costs compared with the configuration of the first embodiment since the task of measuring the spot arises with this method, measuring the spot directly enables the spot to be corrected more accurately. In the present embodiment, a measuring device 500 is used as a spot information detection unit.
Next, a method of correcting the profile of the light spot will be described. Profile information on the light spot measured by the measuring device 500 is written to the memory 304 of the drive unit 300. Also, a reference value of the light spot is held in the memory 304. The image signal generation unit 100 calculates the change ratio of the light spot to the image height, from the reference value of the profile of the light spot saved in the memory 304, and updates the correction value of light-emitting time and luminance, based on the calculated change ratio of the light spot. Note that the method of correcting light-emitting time and luminance is similar to the first embodiment, and description thereof has been omitted. Also, the measuring device 500 is detached after measuring the spot, and the photosensitive member 4 is mounted.
Note that if the image forming apparatus is not configured with a detachable photosensitive member 4, the profile of the light spot can also be measured by disposing the measuring device 500 between the optical scanning apparatus 400 and the photosensitive member 4, for example. Even though the light-receiving surface of the measuring device 500 does not coincide with the light-receiving surface of the photosensitive member 4 in the case of using this configuration, the light spot produced on the surface of the photosensitive member 4 can be derived from the measured light spot, based on the positional relationship therebetween and the optical characteristics of the lens.
According to the present embodiment, as described above, the profile of the light spot can be appropriately corrected even in the case where positional variation of the optical scanning apparatus 400 occurs, by directly measuring the profile of the light spot, after attaching the optical scanning apparatus 400 to the image forming apparatus. As a result, it is possible to perform accurate exposure in which distortion is suppressed, without using a scanning lens having f-θ characteristics.
Third Embodiment
Next, a third embodiment will be described focusing on differences with the first embodiment and the second embodiment. In the first embodiment and the second embodiment, the light spot was corrected for variation in the attachment position of the optical scanning apparatus 400. However, change in the light spot is also produced by factors other than variation in the attachment position. For example, the profile of the light spot may change as a result of the internal temperature of the image forming apparatus rising due to the influence of continuous printing or the like, causing thermal expansion of the imaging lens 406 and the like and changing the imaging characteristics. In the present embodiment, change in the profile of the light spot due to such changes in the environment of the image forming apparatus is also corrected. In the present embodiment, temperature is used as information indicating this environment, and, therefore, a temperature sensor 550 is provided as a temperature detection unit that measures the temperature inside the image forming apparatus.
The temperature sensor 550 is connected to the image signal generation unit 100, and transmits the measured temperature information to the image signal generation unit 100. The memory 304 of the drive unit 300 saves a table that is not illustrated showing the relationship between the temperature information measured by the temperature sensor 550 and the profile of the light spot on the photosensitive member 4. Because the thermal expansion and imaging characteristics of the imaging lens 406 are correlated, it is possible to create the table by taking the correlation between the ambient temperature of the optical scanning apparatus 400 and the profile of the light spot. Also, the memory 304 saves the reference value of the light spot.
Next, a method of correcting the profile of the light spot will be described. The image signal generation unit 100 derives the profile of the light spot based on the table, from the temperature information measured by the temperature sensor 550. Furthermore, the change ratio of the spot is calculated from the reference value saved in the memory 304. The profile of the spot can be appropriately corrected, by updating the correction values of light-emitting time and luminance, based on the calculated change ratio of the spot. The method of correcting light-emitting time and luminance is similar to the first embodiment, and the description thereof is omitted.
As described above, according to the present embodiment, it is possible to correct changes in the profile of the light spot due to mechanical influences that also include influences due to change of the environment in which the image forming apparatus is installed and change of operating state, in addition to positional variation of the optical scanning apparatus 400. As a result, it is possible to perform accurate exposure in which distortion is suppressed, without using a scanning lens having f-θ characteristics.
Fourth Embodiment
Next, the present embodiment will be description focusing on the differences with the first embodiment.
Next, exposure control in the image forming apparatus 50 will be described, with reference to
The CPU core 2 reads out partial magnification characteristic information from the memory 304 via the serial communication 307, and transmits the read partial magnification characteristic information to the CPU that is in the image signal generation unit 100 via the serial communication 113. The CPU core 2 generates partial magnification correction information, based on the acquired partial magnification characteristic information, and sends the generated partial magnification correction information to a pixel piece insertion/extraction control unit 128 discussed later that is provided in the image modulation unit 150 of
As mentioned above, the movement speed of light that is irradiated by the light source 401 differs according to the position in the main scanning direction. Accordingly, as shown in a toner image A of
Next, specific control of partial magnification correction for shortening the irradiation time of the light source 401 by an amount equivalent to the increase in partial magnification as the position shifts from the on-axis image height to the maximum image height will be described, with reference to
The density correction processing unit 121 stores a density correction table for printing an image signal received from the host computer at an appropriate density. The halftone processing unit 122 performs conversion processing for density representation in the image forming apparatus by performing screen (dither) processing on parallel multi-value 8-bit image signals that are input. The operations of the PS conversion unit 123, the FIFO 124, the PLL unit 127, and the pixel piece insertion/extraction control unit 128 will be discussed later.
The PS conversion unit 123 is a parallel-serial conversion unit, and converts a parallel 16-bit signal 129 input from the halftone processing unit 122 into a serial signal 130. The FIFO 124 receives the serial signal 130, stores the received serial signal in a line buffer, and, after a predetermined time has elapsed, outputs the buffered signal as the VDO signal 110 to the downstream laser drive unit 300, similarly as a serial signal. Control of writing to and reading from the FIFO 124 is performed by the pixel piece insertion/extraction control unit 128 controlling a write enable signal WE 131 and a read enable signal RE 132, in accordance with the partial magnification characteristic information that is received from the image signal generation unit 100 via the CPU bus 103. The PLL unit 127 supplies a clock (VCLK×16) 126 obtained by multiplying the frequency of the clock (VCLK) 125 equivalent to one pixel by 16 to PS conversion unit 123 and the FIFO 124.
Next, operations after halftone processing in the block diagram of
The FIFO 124 only imports the signal 130 from the PS conversion unit 123 in the case where the WE signal 131 from the pixel piece insertion/extraction control unit 128 is valid “HIGH”. In the case of shortening an image in the main scanning direction in order to perform correction of partial magnification, the pixel piece insertion/extraction control unit 128 is able to perform control so as to not allow the FIFO 124 to import the serial signal 130, by setting the WE signal partially to invalid “LOW”.
Also, the FIFO 124 only reads out stored data in the case where the RE signal 132 is valid “HIGH”, in synchronization with the clock 126 (VCLK×16), and outputs the VDO signal 110 to the laser drive unit 300. In the case of lengthening an image in the main scanning direction in order to perform correction of partial magnification, the pixel piece insertion/extraction control unit 128, by setting the RE signal 132 partially to invalid “LOW”, causes the FIFO 124 to continuously output data of the previous clock of the clock 126, without updating the readout data. In other words, pixel pieces of the same data as the data of pixel pieces that are adjacent on the upstream side in the main scanning direction processed immediately before will be inserted.
In the partial magnification correction, by thus changing the pixel width such that the length in the main scanning direction is less than one pixel, latent images of the dot shapes corresponding to the pixels of image data can be formed substantially equidistantly with regard to the main scanning direction. Note that “substantially equidistantly with regard to the main scanning direction” includes the case where pixels are not disposed perfectly equidistantly. In other words, some variation in the pixel intervals as a result of performing partial magnification correction is acceptable, and the pixel intervals in a predetermined image height range need only be equidistant on average. As described above, when comparing the number of pixel pieces constituting two adjacent pixels in the case of inserting or extracting pixel pieces at equidistant or substantially equidistant intervals, the difference in the number of pixel pieces constituting the pixels is desirably restricted to 0 or 1. Variation in image density in the main scanning direction when compared with the original image data is suppressed by thus restricting the difference in the number of pixel pieces, enabling favorable image quality to be obtained. Also, pixel pieces may be inserted or extracted at the same positions for every scan line (line) or the positions may be shifted, with regard to the main scanning direction.
As described above, the scanning speed increases as the absolute value of the image height Y increases. In the partial magnification correction, at least one of the abovementioned insertion and extraction of pixel pieces is thus performed, such that the image becomes shorter (the length of one pixel become shorter) as the absolute value of the image height Y increases. This enables latent images corresponding to the pixels to be formed substantially equidistantly with regard to the main scanning direction, and partial magnification to be appropriately corrected. Also, as another method of performing partial magnification correction, there is also a method that involves changing a clock frequency in the main scanning direction, for example.
Next, a configuration in which change information indicating partial magnification characteristics (amount of change in scanning speed) is acquired will be described. The present embodiment will be described using a sensor 200 as an example of an information acquisition unit. Due to factors such as error at the time of attaching the optical scanning apparatus 400 to the image forming apparatus 50, the distance between the deflection surface (reflective surface) 405a of the deflector (polygon mirror) 405 and the scan surface 407 and the scanning angle in the main scanning direction change from partial magnification characteristic information first acquired (hereinafter, first partial magnification characteristic information).
The solid line in
Since the characteristics may thus differ from the first partial magnification characteristic information due to factors such as aging or attachment error, it is necessary to acquire change information on the partial magnification characteristic information, in order to correct the partial magnification characteristics.
The photosensitive member 4 rotates upward in the diagrams. The sensors 200a and 200b are toner mark detection sensors that detect toner marks 201a and 201b on the photosensitive member 4, and are constituted by an LED and a phototransistor. The sensors 200a and 200b irradiate the photosensitive member 4 with light using the LED, and detect reflected light using the phototransistor. The intensity of the reflected light differs depending on the existence of toner, enabling toner to be detected, since the output of the phototransistor changes. In the present embodiment, a configuration for detecting the toner marks 201a and 201b on the photosensitive member 4 as a rotating body will be described. However, the present invention is not limited thereto, and a configuration may, for example, be adopted in which the toner marks 201a and 201b on the intermediate transfer belt are detected with the sensors 200a and 200b. The detected signals are sent to the CPU core 2 and processed.
The toner marks 201a and 201b are formed on a predetermined line parallel to the main scanning direction of the photosensitive member 4, at positions separated by a predetermined interval from the center of the line in different directions. Specifically, the toner marks 201a and 201b have a first contour and a second contour that is not parallel to the first contour. Furthermore, the first contour and the second contour of the toner marks 201a and 201b pass through detection positions of the sensors 200a and 200b due to the photosensitive member 4 rotating. In view of this, in the present embodiment, a time lag from a timing at which the first contour is detected to a timing at which the second contour is detected by the sensors 200a and 200b is acquired as the detection time of the marks.
Next, the case where the distance between the deflection surface 405a and the scan surface 407 is widens uniformly in the main scanning direction, as shown by the solid line in
X=Z %×(ΔT1−ΔT1′)/ΔT1 [%] (5)
assuming that the partial magnification first read by the sensor 200a was Z %. Regions other than those detected by the sensors 200a and 200b need only be interpolated as appropriate. For example, the partial magnification characteristics are known to exhibit quadratic function characteristics, and thus interpolation is performed to follow the quadratic function. The change in the detected partial magnification characteristics is calculated by the CPU core 2, and stored in the memory 304 as new partial magnification characteristics (hereinafter, corrected partial magnification characteristics). Thereafter, image modulation can be performed using the corrected partial magnification characteristics.
As another example, the case where the optical scanning apparatus 400 has shifted in the rotation direction of the deflector (polygon mirror) 405 as shown in
As described above, this image forming apparatus is provided with an imaging lens 406 that irradiates the photosensitive member 4 with light deflected by the deflector 405, and in which the scanning speed of laser light in the main scanning direction is not constant at different image heights on the surface of the photosensitive member 4. That is, a lens that does not have f-θ characteristics is provided. Also, this image forming apparatus detects, for each image height, the amount of change in scanning speed at the image height compared with the scanning speed at a reference image height on the surface of the photosensitive member 4, and controls the scanning speed of laser light in the main scanning direction to be constant at the respective image heights. Specifically, the image signal to be input to the light source is corrected, in accordance with the detected amount of change. The image forming apparatus according to the present embodiment is thereby able to acquire the amount of change in scanning speed (partial magnification) at each image height and correct the image signal in order to cancel the amount of change. That is, pixels can be disposed equidistantly using a lens that does not have f-θ characteristics, and shift due to factors such as aging and attachment error of the optical scanning apparatus can also be cancelled.
The present invention is not limited to the above embodiments, and various modifications can be made. For example, the toner marks 201a and 201b need only take a shape in which the slopes of the sides formed in the sub-scanning direction differ, such as a triangle or a trapezoid, for example. Also, although, in the present embodiment, a configuration was adopted in which there is also toner within the area of the triangles, similar effects are obtained even with toner marks 201a and 201b in which toner is only formed around the boundary of the triangles. Also, a configuration can be adopted in which toner marks 201a and 201b for color shift correction, which are second toner marks, are formed based on corrected partial magnification characteristics at the time of printing, and detected and corrected by sensors 200a and 200b or the like. Although, the present embodiment, an exemplary configuration for performing detection with two sensors 200a and 200b was shown, a configuration may be adopted in which three or more sensors or line sensors are disposed in order to correct partial magnification more accuracy.
Fifth Embodiment
Hereinafter, a fifth embodiment according to the present invention will be described. The present embodiment describes using the temperature sensor 220 as an example of an information acquisition unit. Configuration that is the same as the above fourth embodiment is given the same reference numerals and description thereof is omitted. In the case where the imaging lens 406 is fixed near the axis, the imaging lens 406 may expand from on the axis to off the axis due to the rise in temperature near the imaging lens 406. The temperature sensor 220 in
Other Embodiments
Embodiments of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiments. The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-031055. filed on Feb. 19, 2015. and Japanese Patent Application No. 2015-031056. filed on Feb. 19, 2015 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
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| 2015-031056 | Feb 2015 | JP | national |
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