Patent Grant
8983318
The present invention relates to image forming apparatuses which form an image onto a medium such as paper, etc.
An image forming apparatus represented by a laser beam printer is known, wherein a light beam emitted from a light source is deflected and scanned in a main scanning direction by a deflecting and scanning unit, and is collected toward a drum (a photosensitive body) which has a face to be scanned, and a latent image is formed on a drum surface. In such an image forming apparatus, the latent image on the drum surface is transferred onto an intermediate transfer belt which is placed between the drum and a developing roller and an image which corresponds to the latent image is formed onto the intermediate transfer belt.
In the image which is formed onto the intermediate transfer belt, density fluctuations may occur in a main scanning direction and a sub-scanning direction, respectively. One possible cause of the density fluctuations is process gap (PG) fluctuations. First, the density fluctuations of the image in the main scanning direction are considered. As a factor for this, parallel characteristics of the drum (the photosensitive body) and the developing roller are possible. For example, when the mutual parallel characteristics of the drum and the developing roller are lost, variations occur in capabilities of developing onto the drum, possibly causing density fluctuations with respect to the main scanning direction. Here, the density fluctuations linearly change in the main scanning direction.
Next, the density fluctuations of the image in the sub-scanning direction are considered. One factor for this may be decentering of the drum. For example, when a slight movement of an axle of the drum occurs, positions at which a distance from a rotational axle of the drum to a surface differs occur, so that positions occur in which there is a difference in a gap between the drum and the developing roller. This difference in the gap becomes a developing variation, which would affect the image as the density fluctuations in the sub-scanning direction.
A different factor may be circularity of the drum. For example, assume that there is a second drum with low circularity relative to a first drum, which is circular. Then, with the second drum, at a time of rotation thereof, a difference occurs in a gap between the drum and the developing roller depending on a rotational angle, which may become a factor for fluctuations in developing. Due to the above-described factors, density fluctuations in the sub-scanning direction occur for an image formed on the drum surface. These density fluctuations become periodic, which occurs with a rotational period of the drum.
Factors for the density fluctuations include other factors such as potential variations of the drum, toner supply, toner removal, discharging, cleaning, etc., so that, combining them with density fluctuations due to process gap fluctuations, causes dynamic fluctuations to occur in both the main scanning direction and the sub-scanning direction.
In order to reduce such density fluctuations, for example, a light amount adjustment is performed in accordance with a transmitting characteristic of optics in the main scanning direction, for example. Moreover, for correcting in the sub-scanning direction, there is known a technique in which, for example, correction data are created in accordance with sensitivity variations of a photosensitive body to change a light amount in the sub-scanning direction, and a failure due to a phase offset of a rotational period of the photosensitive body and the correction data is avoided by an arithmetic calculation.
Patent document 1: JP2008-065270A
Patent document 2: JP2003-127454A
However, besides the transmitting characteristics of the optics, there are density fluctuation producing factors in the main scanning direction, so that density fluctuations may occur in the main scanning direction over time. Moreover, there are also multiple density fluctuation producing factors in the sub-scanning direction, so that complex density fluctuations may occur by a combination thereof. With the above-described technique, a dynamic range of the density correction is narrow, so that it is difficult to realize a highly accurate density correction.
In light of the problems described above, an object of the present invention is to provide an image forming apparatus which makes it possible to improve a dynamic range of density correction and realize a highly accurate density correction.
According to an embodiment of the present invention, an image forming apparatus is provided. The image forming apparatus includes a light source; a drum which is a photosensitive body; an optical scanning apparatus which deflects and scans, in a main scanning direction by a deflecting and scanning unit, a light beam emitted from the light source, and collects, by a scanning and image forming unit, the deflected and scanned light beam on the drum, which drum has a face to be scanned, to form a latent image onto a surface of the drum; and an endless belt which is arranged to be in contact with the drum and on which an image corresponding to the latent image is formed, the image forming apparatus further including a pattern forming unit which forms, on the endless belt along a conveying direction of the endless belt, a density fluctuation detecting pattern having a period; a density sensor which detects the density fluctuating detecting pattern and outputs a density signal including information on density fluctuations in the conveying direction of the endless belt; and a period detecting sensor which detects the period included in the density fluctuations.
The disclosed technique makes it possible to provide an image forming apparatus which improves a dynamic range of density correction and which can realize a highly accurate density correction.
Other objects, features, and advantages of the present invention will become more apparent from the following detailed descriptions when read in conjunction with the accompanying drawings, in which:
A description is given below with regard to embodiments of the present invention with reference to the drawings. In the respective drawings, the same numbers are applied to the same elements, so that duplicate explanations may be omitted.
In the image forming apparatus 10, the density sensor 18 reads a density of a toner pattern formed onto the intermediate transfer belt 17, and outputs, to the image processing unit 11, a density signal V, which is an output signal in which an affixed amount of toner is converted to a voltage. For example, the density sensor 18 may be arranged such that a light emitted by an LED is irradiated onto the intermediate transfer belt 17 and a specularly reflected light and a diffuse reflected light which are obtained in accordance with a toner density on the intermediate transfer belt 17 is detected by a light receiving element.
The HP sensor 19, which is a period detecting sensor which detects a rotational period of the drum 16, outputs a home position signal W (which may be called an HP signal W below) to the image processing unit 11. As described below, the image forming apparatus 10 may include multiple density sensors and multiple HP sensors.
The image processing unit 11 includes a CPU, a ROM, a RAM, a main memory, etc., for example, various functions of which image processing unit 11 may be realized by a program recorded in the ROM, etc., being read into the main memory to be executed by the CPU. A part or the whole of the image processing unit 11 may be realized by hardware only. Moreover, the image processing unit 11 may physically be configured with multiple apparatuses.
The image processing unit 11 detects density fluctuations based on an HP signal W and a density signal V input, calculates a light amount correction amount which corrects for the density fluctuations in the main scanning direction and the sub-scanning direction to generate and output, to the light source driving apparatus 12, a light amount control signal A. The light source driving unit 12 drives the light source 13 based on the light amount control signal A.
As the light source 13, a semiconductor laser, etc., may be used, for example. As a semiconductor laser, a VCSEL (Vertical Cavity Surface Emitting LASER), etc., may be used, for example.
A light beam emitted from the light source 13 is transmitted toward the drum 16, which is a photosensitive body by the optical scanning apparatus 15, and a latent image is formed onto a surface of the drum 16. The optical scanning apparatus 15 includes, for example, a deflecting and scanning unit (not shown) which deflects and scans, in a main scanning direction, a light beam emitted from the light source 13; a scanning and image forming unit (not shown) which collects the deflected and scanned light beam onto the drum 16, which is a face to be scanned, etc.
Then, after undergoing processes of developing and transferring, toner whose amount is based on a light emitting amount and a light emitting time of the light source 13 is affixed onto the intermediate transfer belt 17 and a predetermined image is formed. The intermediate transfer belt 17 is an endless belt which is arranged to be in contact with the drum 16 and onto which an image corresponding to the latent image is formed.
In this way, in the image forming apparatus 10, light emitting level control of the light source 13 is performed with a light amount based on a light amount control signal A which corrects for density fluctuations in the main scanning direction and the sub-scanning direction. In this way, the respective density fluctuations in the main scanning direction and the sub-scanning direction may be decreased by control of a light amount of the light source 13.
The light amount control signal A based on only density fluctuations in either one of the main scanning direction and the sub-scanning direction can also be generated to correct for only density fluctuations in the one of the main scanning direction and the sub-scanning direction. The main scanning direction is a direction which is orthogonal to a conveying direction of the intermediate transfer belt 17, while the sub-scanning direction is the conveying direction of the intermediate transfer belt 17.
Below main constituting elements of the image forming apparatus 10 are described in more detail.
With reference to
As shown in
When the toner 50 is affixed onto the intermediate transfer belt 17 as shown in
In this way, for a case in which the toner 50 is not affixed and for a case in which the toner 50 is affixed, detected signal levels of the respective specularly reflected light receiving element 182 and diffuse reflected light receiving element 183 differ. This makes it possible to detect a density of the toner 50 on the intermediate transfer belt 17. How the detected signal levels of the respective specularly reflected receiving element 182 and the diffuse reflected light receiving element 183 correspond to an actual image density cannot be discriminated only from the above-described configurations. This will be described below with reference to
Moreover, based on the density signal Va, as a correction signal Ha, a sinusoidal signal with a phase which is reverse that of the density signal Va and the same period as the period Td of the drum 16 may be generated. By controlling a light amount signal of the light source 13 using a correction signal Ha with a phase which is reverse that of the density signal Va, the density fluctuation detecting pattern can be formed to reduce density fluctuations of the formed density fluctuation detecting pattern in the sub-scanning direction, for example, see density signal Vx.
In other words, when the density fluctuation detecting pattern which is corrected for using the correction signal Ha is detected by the density sensor 18a, for example, a signal whose amplitude is smaller than that of the density signal Va is obtained. In lieu of the density signal Va, which is an output signal of the density sensor 18a, a correction signal may be generated based on an output signal of the density sensor 18b or 18c to reduce the density fluctuations in the sub-scanning direction. Moreover, a correction signal may be generated based on an average value of output signals of the density sensors 18a to 18c to reduce the density fluctuations in the sub-scanning direction.
In this way, a correction signal Ha which corrects for density fluctuations in the sub-scanning direction which is orthogonal to the main scanning direction may be generated based on an output signal of the HP sensor 19 and an output signal of at least one density sensor of multiple density sensors 18a, 18b, and 18c which are arranged in parallel in the main scanning direction. Then, light emitting level control of the light source 13 may be performed with a light amount based on the correction signal Ha to reduce density fluctuations in the sub-scanning direction. The correction signal Ha does not have to be a sinusoidal periodic pattern, and may be set to be a triangular periodic pattern, a trapezoidal periodic pattern, etc., for example, in accordance with conditions.
Based on the HP signal W, the density signals Va, Vb, and Vc may be sampled for one period or for multiple periods to detect density fluctuations in the main scanning direction as shown in
While the above explanations have been given by breaking down into the sub-scanning direction and the main scanning direction for convenience, in practice, the correction signal Ha in the sub-scanning direction and the correction signal Hb in the main scanning direction are independently generated, and a light amount control signal A (see
Then, between the respective patterns which make up the density calibrating pattern 25 and the light amount increased for changing the density, there is a generally linear relationship. Moreover, there is also a generally linear relationship between the density of the respective patterns which make up the density calibrating pattern 25 and the density signal V (including V1 to V11), a generally linear relational data between the light amount and the density signal V (including V1 to V11) may be obtained as shown in
Furthermore, an actual print may be performed to measure an image density with a colorimeter, a scanner, etc., and a correspondence thereof with the density signal V (including V1 to V11) may be made to take a correlation between an actual image density and the density signal V (including V1 to V11). Similarly, for the density sensors 18b and 18c, a correlation may be taken between the actual image density and the density signal.
While an example is shown in
In the present embodiment, the image area rates of the density fluctuation detecting pattern 20 shown in
On the other hand, when the image area rate is other than between 50% and 85%, in order to change the color difference in increments of 0.2, the light amount control resolution becomes approximately ±1%, so that a dynamic range of density correction becomes narrow when taking into account upper and lower limits of a light amount change. The image area rate is a numerical value which indicates how much of a basic matrix of a dot or a parallel line is occupied when outputting a certain density pattern, and may also be called a dot area rate. For example, for a checker-shaped density pattern, the image area rate becomes 50%. The image area rate on paper may be calculated by calculating backwards from a CCD or a spectroscope.
In this way, setting the image area rate of the density fluctuation detecting pattern 20 between 50% to 85% causes a dynamic range of density correction to be wide, so that accurate density fluctuation data for density correction can be obtained for density fluctuations caused by the drum 16, making it possible to realize an image forming apparatus 10 which can reduce density fluctuations in a simple configuration. The same applies also to the density calibrating pattern 25.
Here, density fluctuation correction is described in further detail below with reference to
With reference to
Next, in step S405, the calibrating unit 30a obtains correlation data between the respective density signal levels and light emitting power (light amount) of the light source 13 as shown in
Next, in step S407, the pattern forming unit 30b forms a density fluctuation detecting pattern 20 as shown in
Next, in step S409, the correction signal generating unit 30c obtains the respective density signals (density signals Va, Vb, and Vc, which are indicated in
Next, in step S413, the correction signal generating unit 30c generates a correction signal which is a sinusoidal signal with a phase which is reverse that of a periodic pattern corresponding to the density fluctuations in the sub-scanning direction. Next, in step S415, the correction signal generating unit 30c causes a correction signal pattern generated in step S413 to, for example, undergo an A/D conversion to save the converted pattern in the memory, etc. Only a periodic pattern of a correction signal that corresponds to one period may be saved as a basic pattern.
Next, in step S417, the correction signal generating unit 30c obtains an average value (see
Next, in step S419, the correction signal generating unit 30c generates an approximation formula (a formula which shows a pattern of an interpolation signal Sx shown in
Thereafter, based on the light emitting power correction formula saved in step S423 and the correction signal pattern saved in step S415, the correction signal generating unit 30c generates a light amount control signal A in which both are convolved, and performs light emitting level control of the light source 13 with a light amount based on the light amount control signal A. In this way, the respective density fluctuations in the main scanning direction and the sub-scanning direction may be reduced by control of a light amount of the light source 13. In other words, a density fluctuation correction is performed with a method in
In this way, setting an image area rate of the density fluctuation detecting pattern between 50% and 85% causes a wide dynamic range of density correction, so that accurate density fluctuation data for density fluctuation correction can be obtained for density fluctuations caused by the drum, making it possible to realize the correction with a simple configuration.
In a second embodiment, an example of a density fluctuation detecting pattern which is different from the first embodiment is shown.
The density fluctuation detecting patterns 20a, 20b, and 20c can be formed to suppress an amount of consumption of toner with an advantageous effect equivalent to that of the density fluctuation detecting pattern 20 shown in
According to a third embodiment is shown an example in which the present invention is applied to a tandem color machine which includes multiple photosensitive bodies.
The optical scanning apparatuses 45a, 45b, 45c, and 45d, which respectively include light sources (not shown), direct light beams emitted from the light sources to the respective drums 16a, 16b, 16c, and 16d via a deflector (not shown) and multiple optical components (not shown) and form a latent image on the respective drums 16a, 16b, 16c, and 16d.
In the vicinity of the drums 16a, 16b, 16c, and 16d are arranged HP sensors 19a, 19b, 19c, and 19d, respectively. Functions of the HP sensors 19a, 19b, 19c, and 19d are the same as those of the HP sensor 19 which were described in the first embodiment.
In the image forming apparatus 40, the rotational timing or period may differ somewhat for each of the drums 16a, 16b, 16c, and 16d. In other words, for the image forming apparatus 40, a drum differs for each of colors of cyan, magenta, yellow, and black, so that timings for generating an HP signal for each drum also differs. Thus, when density fluctuation detecting pattern of each color is generated onto the intermediate transfer belt 17, a density detecting pattern is generated in response to a timing of an HP signal which differs from color to color. In this way, from an aspect of image quality, an image with good color reproducibility in which density fluctuations for each of the drums 16a, 16b, 16c, and 16d are effectively reduced is obtained.
Moreover, in
In
The reason that the density fluctuation detecting pattern corresponding to two periods of the respective HP signals is generated is that there may a case in which an S/N ratio is small at a time of detecting by a density sensor with only a density fluctuation detecting pattern corresponding to one period of the respective HP signals. Therefore, in order to increase an S/N ratio when detecting by the density sensor, a density fluctuation detecting pattern corresponding to at least three periods of the respective HP signals may be formed.
A density fluctuation detecting pattern formed that corresponds to multiple periods of the respective HP signals may be detected by each density sensor and an average processing may be performed among signals at the same position to more accurately detect periodic density fluctuations which are caused by a drum shape, etc. Therefore, a correction signal may be generated based on the density signal and a light amount of a light source may be controlled to realize an apparatus which forms an image with a high image quality in which density fluctuations are reduced.
First, in describing an image forming apparatus according to a fourth embodiment, a related-art image forming apparatus as a comparative example is described.
In
A light beam emitted from the light source 14 is transmitted toward the drum 16, which is a photosensitive body, by the optical scanning apparatus 15, and a latent image is formed on a surface of the drum 16. The optical scanning apparatus 15 includes, for example, a deflecting and scanning unit (not shown) which deflects and scans, in the main scanning direction, the light beam emitted from the light source 14; a scanning and image forming unit (not shown) which collects the deflected and scanned light beam onto the drum 16, which is a face to be scanned, etc.
Then, after undergoing processes of developing and transferring, a toner whose amount is based on a light emitting amount and a light emitting time of the light source 14 is affixed onto the intermediate transfer belt 17 and a predetermined image is formed. The intermediate transfer belt 17 is an endless belt which is arranged to be in contact with the drum 16 and onto which an image corresponding to the latent image is formed.
The density sensor 18 reads a density of a toner pattern formed onto the intermediate transfer belt 17, and outputs, to the image processing ASIC 11, a density signal V, which is an output signal in which an affixed amount of toner is converted to a voltage. For example, the density sensor 18 may be arranged such that a light emitted by an LED is irradiated onto the intermediate transfer belt 17 and a specularly reflected light and a diffuse reflected light which are obtained in accordance with a toner density on the intermediate transfer belt 17 is detected by a light receiving element.
In the image forming apparatus 10, a light amount control signal A (main shading data) output from the image processing ASIC 11, a density signal V which is output from the density sensor 18, and a home position signal W (which may be called an HP signal W below) which is output from the HP sensor 19 are respectively input to the shading data converting unit 12. The HP sensor 19 is a period detecting sensor which detects a rotational period of the drum 16.
The shading data converting unit 12 includes a function of generating sub-shading data which corrects for shading in the sub-scanning direction as a signal which is synchronized to the HP signal W, etc. Moreover, it includes a function of multiplying the generated sub-shading data with the light amount control signal A (main shading data) to generate a light amount control signal B (main shading data+ sub-shading data).
The shading data converting unit 12 includes a CPU, a ROM, a main memory, etc., for example, various functions of which shading data converting unit 12 are realized by a program recorded in the ROM, etc., being read into the main memory to be executed by the CPU. A part or the whole of the shading data converting unit 12 may be realized by hardware only. Moreover, the shading data converting unit 12 may physically be configured with multiple apparatuses.
The light amount control signal B is input to the light source driving apparatus 13, which controls a light emitting level of the light source 14 with a light amount based on the light amount control signal B. In this way, the respective density fluctuations in the main scanning direction and the sub-scanning direction may be decreased by control of a light amount of the light source 14. It is also possible to control the light source 14 based on only sub-shading data, not combining the generated sub-shading data with the light amount control signal A (the main shading data), and correct for shading only in the sub-scanning direction. The main scanning direction is a direction which is orthogonal to a conveying direction of the intermediate transfer belt 17, while the sub-scanning direction is the conveying direction of the intermediate transfer belt 17.
Then, between the respective patterns which make up the density calibrating pattern 20 and the light amount increased for changing the density, there is a generally linear relationship. Moreover, there is also a generally linear relationship between the density in the respective patterns which make up the density calibrating pattern 20 and the density signal V (including V1 to V10), and generally linear relational data between the light amount and the density signal V (including V1 to V10) may be obtained as shown in
Here, a period T1 in a drum 16 is not necessarily equivalent to a print size, and a print starting position relative to the drum 16 is not constant. As density fluctuations of the drum 16 with a period T1 occur, with an HP signal W as a trigger, an HP sensor 19 may be provided to specify the period T1 of the drum 16.
A phase and the period T1 of the drum 16 are specified by the HP sensor 19 to obtain a density signal Va, which is close to a sinusoidal wave with the same period as the period T1 of the drum 16 from the density sensor 18. Based on density fluctuations of the density signal Va, as a correction signal Y, a sinusoidal signal with a phase which is reverse that of a density fluctuation Va and the same period as a period T1 of the drum 16 may be generated. Amplitude of the sinusoidal signal becomes a correction amount.
Forming the density fluctuation detecting pattern by inputting, into the light source driving apparatus 13, a correction signal Y with a phase which is reverse that of the density fluctuation Va to control a light amount of the light source 14 makes it possible to reduce density fluctuations of the formed density fluctuation detecting pattern in the sub-scanning direction. In other words, when the density fluctuation detecting pattern which is formed using the correction signal Y is detected by the density sensor 18, a signal whose amplitude is smaller than that of the density signal Va, such as a density signal Vb, is obtained. In the density signal Vb, a density fluctuating component with the period T1 of the drum 16 is reduced relative to the density signal Va.
While not shown in
Then, the HP sensor 19 includes an HP sensor 19a which detects a home position of the drum 16 and an HP sensor 19b which detects a home position of the developing roller 22. The HP sensor 19a is a first period detecting sensor which detects density fluctuations of a period T1 which corresponds to rotating of the drum 16, while the HP sensor 19b is a second period detecting sensor which detects density fluctuations of a period T2 which corresponds to rotating of the developing roller 22 which is different from a rotational period of the drum 16. The HP sensor 19a outputs an HP signal W1 to the shading data converting unit 12, while the HP sensor 19b outputs an HP signal W2 to the shading data converting unit 12. The period T1 is one representative example of the first period according to the present invention, while the period T2 is one representative example of the second period according to the present invention.
With reference to
In
The density fluctuation detecting pattern 23, which is a pattern formed in synchronicity with the HP signal W1 which is detected with rotating of the drum 16, has a first occurrence period. While the first occurrence period is set to six patterns within a period T1 of the HP signal W1 in an example in
Moreover, the density fluctuation detecting pattern 24, which is a pattern formed in synchronicity with the HP signal W2 which is detected with rotating of the developing roller 22, has a second occurrence period which is different from the first occurrence period. While the second occurrence period is set to five patterns within a period T2 of the HP signal W2 in an example in
The density fluctuation detecting pattern 23 is generated from a time which is delayed by Δt1, for example, relative to a rise of the HP signal W1 of period T1 (from tb0 to tb1) while the density fluctuation detecting pattern 24 can be generated from a time which is delayed by Δt2, for example, relative to a rise of the HP signal W2 of period T2.
Now, with reference to
A calibrating unit 30d, a first pattern forming unit 30e, a second pattern forming unit 30f, a first correction signal generating unit 30g, and a second correction signal generating unit 30h which are shown in
With reference to
Next, in step S103, the calibrating unit 30d obtains correlation data between the density signal and density calibrating pattern 20 of each column as shown in
Next, in step S104, the first pattern forming unit 30e forms the density fluctuation detecting pattern 23 (a first density fluctuation detecting pattern) as shown in
Next, in step S106, the first correction signal generating unit 30g generates a first correction signal Y11 (a signal with a period T1 and a frequency f1), which is a sinusoidal signal with a phase which is reverse that of density fluctuations as shown in
Next, in step S108, the second pattern forming unit 30f inputs the first correction signal Y11 in the light source driving apparatus 13 to control a light amount of the light source 14 to form a density fluctuation detecting pattern 24 (a second density fluctuation detecting pattern). Next, in step S109, the density sensor 18b detects the density fluctuation detecting pattern 24 and outputs a second density signal X12 as shown in
Next, in step S110, the second correction signal generating unit 30h generates a second correction signal Y12 (a signal with a period T2 and a frequency f2), which is a sinusoidal signal with a phase which is reverse that of density fluctuations as shown in
Thereafter, the second correction signal Y12, which is held in the memory (not shown), etc., may be input into the light source driving apparatus 13 to control a light amount signal of the light source 14 to form a density fluctuation detecting pattern in which density fluctuations with periods T1 and T2 are reduced. When the density fluctuation detecting pattern, which is corrected with the second correction signal Y12, is detected with a density sensor, a third density signal X13 is formed in which density fluctuations with periods T1 and T2 are reduced relative to the first density signal X11 and the second density signal X12 as shown in
While an example of performing a density correction only with sub-shading data (the second correction signal Y12) is shown, in practice, the sub-shading data (the second correction signal Y12) are multiplied with a light amount control signal A (main shading data) to generate a light amount control signal B (main shading data+ sub-shading data). Then, the light amount control signal B may be input to the light source driving apparatus 13 to control a light amount signal of the light source 14 to reduce the respective density fluctuations in the main scanning direction and the sub-scanning direction by a light control amount of the light source 14.
In this way, frequency components of both the frequency f1 which corresponds to the period T1, which is a rotational period of the drum 16, and the frequency f2 which corresponds to the period T2, which is a rotational period of the developing roller 22, may be corrected for dynamically to reduce density fluctuations which occur periodically. In other words, for density fluctuations which occur due to fluctuations in a physical position between the drum 16 and the developing roller 22, accurate density signals for density fluctuation correction can be obtained, so that an image forming apparatus which can reduce density fluctuations may be realized in a simple configuration.
Moreover, as the density fluctuation detecting patterns which detect two signals are generated simultaneously, a one time density detecting time becomes shorter in comparison to a case in which the density fluctuation detecting patterns for detecting two types of periodic signals that correspond to different home position signals are generated, so that a waiting time, etc. is reduced.
In a fifth embodiment, an example is shown of detecting the density fluctuation detecting patterns 23 and 24 by one density sensor.
In the density fluctuation correction according to the fifth embodiment, steps S101 to S107 in
In step S109, unlike in the fourth embodiment, one density sensor 18 simultaneously detects the density fluctuation detecting patterns 23 and 24 formed such that a part of each overlaps the other, so that a density signal X21 as shown in
Here, when the period T1 of the HP signal W1> the period T2 of the HP signal W2 (when the frequency f1 of the HP signal W1< the frequency f2 of the HP signal W2), as seen from the density signal X21, it is difficult to discriminate the density fluctuation with the period T2.
Then, the first correction signal generating unit 30d generates a correction signal Y21 (frequency f1) by causing data shown with a circle for the density signal X21 (data corresponding to the density fluctuation detecting pattern 23) to undergo an FFT (fast Fourier transform), etc. Then, the correction signal Y21 is multiplied by the density signal X21 to obtain a second density signal X22, in which density fluctuations with the period T1 are reduced. In the obtained second density signal X22, a density fluctuation component of a period T1 is reduced, so that a tendency of density fluctuations with the period T2 appears.
Next, in step S110, the second correction signal generating unit 30e generates a second correction signal Y22 (a signal with a period T2 and a frequency f2), which is a sinusoidal signal with a phase which is reverse that of density fluctuations as shown in
Thereafter, the second correction signal Y22, which is held in the memory (not shown), etc., may be input into the light source driving apparatus 13 to control a light amount signal of the light source 14 to form density fluctuation detecting patterns in which density fluctuations with periods T1 and T2 are reduced. When the density fluctuation detecting pattern which is corrected for with the second correction signal Y22 is detected by the density sensor, a third density signal X23 is obtained in which density fluctuations with periods T1 and T2 are reduced as shown in
In this way, in the fifth embodiment, the same advantages are yielded as in the fourth embodiment; as one density sensor 18 detects density fluctuation detecting patterns 23 and 24, which are formed such that a part of each pattern overlaps the other, a number of parts of the density sensor in the image forming apparatus may be reduced, contributing to a decreased cost.
In the sixth embodiment, an example is shown of detecting the density fluctuation detecting patterns 24 only by one density sensor.
In the density fluctuation correction according to the sixth embodiment, steps S101 to S103 in
Next, in step S105, the density sensor 18 detects a density fluctuation detecting pattern 24 and outputs a density signal X31, which is synchronized to the period T2 of the HP signal W2 as shown in
Next, in step S106, the first correction signal generating unit 30d generates a first correction signal Y31 (a signal with a period T1 and a frequency f1), which is a sinusoidal signal with a phase which is reverse that of density fluctuations as shown in
The HP signal W2 relative to the HP signal W1 is a non-synchronous signal, so that, a delay time of, for example, Δtd1, occurs for the density fluctuation detecting pattern 24 for which writing is started at a timing of the HP signal W2 relative to the HP signal W1. Then, the delay time of Δt12 between the HP signal W1 and the HP signal W2 may be detected to calculate a timing, relative to the HP signal W1, at which writing of the density fluctuation detecting pattern 24 is started. Thus, a phase difference of the density fluctuation signals may be detected, making it possible to accurately calculate density fluctuations with the period T1 of the HP signal W1.
In this way, even a method of forming only the density fluctuation detecting pattern 24 corresponding to a shorter period T2 twice may be used to reduce density fluctuations with periods T1 and T2.
Moreover, multiple density detections may be performed with one density fluctuation detecting pattern without a need to have multiple types of density fluctuation detecting patterns to realize a reduced size and cost of circuitry in the image forming apparatus.
In a seventh embodiment, an example is shown of forming a set of density fluctuation detecting patterns 23 and 24 in multiple numbers.
In this way, the sets of density fluctuation detecting patterns 23 and 24 are formed in multiple numbers at different positions in the vertical direction (the main scanning direction) relative to the conveying direction of the intermediate transfer belt 17 to obtain density signals by the corresponding density sensors, so that information on density fluctuations within a face in one round of the developing roller 22 and the drum 16 is obtained. As a result, an average value of density fluctuation detecting signals obtained at multiple positions in the main scanning direction on the intermediate transfer belt 17 may be taken, etc., to obtain information on average density fluctuations within the face and also to realize accurate density fluctuation detection and density fluctuation correction.
While preferred embodiments have been described in the above in detail, they are not limited to the above-described embodiments, so that various changes and modifications may be added to the above-described embodiments without departing from the scope recited in the claims.
For example, for an image forming apparatus having multiple developing rollers, an HP sensor corresponding to a drum and multiple HP sensors corresponding to each of the multiple developing rollers may be used to perform density correction. In other words, n HP sensors may be used to correct for density fluctuations with n periods.
Moreover, in lieu of a method of changing a light amount of a light source as a scheme of correcting for density fluctuations, a method of changing a developing bias of the developing roller, etc., may be used.
The present application is based on Japanese Priority Applications No. 2012-061245 and 2012-061246, which were filed on Mar. 16, 2012, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-061245 | Mar 2012 | JP | national |
| 2012-061246 | Mar 2012 | JP | national |
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