Patent Grant
6891554
This application claims the priority benefit of Japanese applications serial no. 2002-060145, filed on Mar. 6, 2002 and serial no. 2002-149171, filed on May 23, 2002.
1. Field of the Invention
This invention relates in general to a writing control method, a writing control device and an image forming device. More particularly, the invention relates to an image forming device using an intermediate transcriber, such as a copy machine, a printer or a facsimile, etc.
2. Description of the Related Art
An image forming device, such as a copy machine, a printer or a facsimile, etc., is well known in the conventional art. The image forming device includes a scanning and writing device that is used to perform a scanning operation in a main scanning direction for image information according to a main scanning synchronizing signal that is detected after an image forming start signal in the sub-scanning direction is detected, and then to write an image to an image supporter moving in a sub-scanning direction.
Referring to
Next, operations related to the aforementioned image forming device is further described. As an image forming operation begins, the surface of the photosensor 102 is electrified to a prescribed potential by the electrifying device 106. The photosensor 102 is rotated in the arrow direction as shown in
Next, the electrostatic latent images corresponding to image information of each color on the photosensor are respectively developed by the developing devices 5K, 5C, 5M and 5Y. Each of the developing devices 5K, 5C, 5M and 5Y has a developer supporter for supporting developer that contains toner of black, cyan magenta and yellow respectively. By applying an immediate potential between a non-image potential and an image potential of the electrostatic latent image on the photosensor 102 from a power device (not shown) to the developer supporter, the selected color toner on the developer supporter is adhered onto the image portion of the photosensor 102. In the example, the developing devices 5K, 5C, 5M and 5Y are installed in a revolving manner. Thus, the four developing devices 5K, 5C, 5M, 5Y are rotated all together by a revolver mechanism (not shown), and in this way, the developing device opposite to the photosensor 102 is circularly altered. By the rotation of the developing devices, one developing device selected develops the electrostatic latent image on the photosensor 102 to form a toner image.
The first color toner image, formed on the photosensor 102 by one selected developing device, is transferred to the transfer drum 110 by a first transfer mechanism (not shown) at a first transfer section, i.e., a close region between the photosensor 102 and the transfer drum 110. As the revolver mechanism (not shown), which is to rotate the developing devices 5K, 5C, 5M, 5Y at one time, finishes the development of the electrostatic latent image corresponding to first color image information on the photosensor 102, the developing devices 5K, 5C, 5M, 5Y are then rotated all together to make one developing device, which is to develop an electrostatic latent image corresponding to second color image information on the photosensor 102, to be opposite to the photosensor 102.
The first color toner image on the transfer drum 110 is further transported to the first transfer section by rotating the transfer drum 110. At this time, each elements of the image forming device in this example is controlled by the controller 116 in such a manner that the second color toner image formed by the developing device on the photosensor 102 reaches the first transfer section, and the second color toner image on the photosensor 102 is transferred at the first transfer section by the first transfer mechanism (not shown) onto the transfer drum 110 so as to overlap with the first color toner image.
When the revolver mechanism (not shown) finishes the development of the electrostatic latent image corresponding to second color image information on the photosensor 102, the developing devices 5K, 5C, 5M, 5Y are then rotated all together to make one developing device, which is to develop an electrostatic latent image corresponding to third color image information on the photosensor 102, to be opposite to the photosensor 102. At this time, each elements of the image forming device in this example is controlled by the controller 116 in such a manner that the third color toner image formed by the developing device on the photosensor 102 reaches the first transfer section, and the third color toner image on the photosensor 102 is transferred at the first transfer section by the first transfer mechanism (not shown) onto the transfer drum 110 so as to overlap with the second color toner image.
When the revolver mechanism (not shown) finishes the development of the electrostatic latent image corresponding to third color image information on the photosensor 102, the developing devices 5K, 5C, 5M, 5Y are then rotated all together to make one developing device, which is to develop an electrostatic latent image corresponding to fourth color image information on the photosensor 102, to be opposite to the photosensor 102. At this time, each elements of the image forming device in this example is controlled by the controller 116 in such a manner that the fourth color toner image formed by the developing device on the photosensor 102 reaches the first transfer section, and the fourth color toner image on the photosensor 102 is transferred at the first transfer section by the first transfer mechanism (not shown) onto the transfer drum 110 so as to overlap with the third color toner image.
On the other hand, a transfer paper 114 is fed to resist rollers from a paper feeding device (10), and the resist rollers send out the transfer paper 114 accompanying with the full color image on the transfer drum 110. As a full color image is formed on the transfer drum 110, a receded or stopped secondary transfer mechanism (not shown) is activated, and then the full color image on the transfer drum 110 is entirely transferred to the transfer paper 114 (from the resist roller) by the secondary transfer mechanism. The full color image that has been transferred on the transfer paper 114 is fixed by the fixing device 112, and then the transfer paper 114 is ejected out of the image forming device.
The laser beam from the light source 120 is collimated by a collimator lens (15), and then deflected by a deflection reflection surface of a rotational polygon mirror 122 (as a scanning means). The rotational polygon mirror 122 is rotationally driven by a driving means (not shown) to scan repeatedly in the main scanning direction. The laser beam from the rotational polygon mirror 122 is converged by an imaging lens 124 and then is imaged on the photosensor 102 as a laser spot. By using that the rotational polygon mirror 122 is rotationally driven by the driving means (not shown), the laser spot scans the photosensor 102 repeatedly in the main scanning direction to form an electrostatic latent image on the photosensor 102.
An light receiving element 126 as a main scanning synchronizing signal generating means is arranged out of an image range that is within a laser beam scanning range. The light receiving element 126 receives a laser beam from a polygon mirror 122 and then detects it, so as to generate a main scanning synchronizing signal that determines a recording start position (lateral resist) in the main scanning direction.
On the other hand, an image forming start signal of the sub-scanning direction (i.e., an image forming start signal of the sub-scanning direction), which determines a recording start position (vertical resist) in the sub-scanning direction (i.e., an image forming start position in the sub-scanning direction), is detected and generated by such as a light receiving means to detect a reflection light or a transmission light that is obtained by irradiate a light beam to the mark formed on the transfer drum 110 and the mark formed on the photosensor 102, a rotation start timing of the resist roller, a detection signal from a paper detecting sensor that is used to detect the transfer paper 114 right after the resist roller, a rotary encoder built in a photosensor driving means, etc. There are many methods to generate the image forming start signal of the sub-scanning direction, but in this example, the image forming start signal of the sub-scanning direction is generated by that the detecting means (61) detects the mark M formed on the transfer drum 110.
The main scanning synchronizing signal from the light receiving element 126 and the recoding start signal of the sub-scanning direction that comes from the detecting means (61) are transmitted to the controller 116. Then, the controller 116 instructs the optical writing device 100 to perform an optical writing (exposure) operation onto the photosensor 102 according to the main scanning synchronizing signal from the light receiving element 126 and the recoding start signal of the sub-scanning direction from the detecting means (61).
As an initial main scanning synchronizing signal from the light receiving element 126 is detected after the image forming start signal of the sub-scanning direction from the detecting means (61) is detected, the controller 116 instructs an optical writing (exposure) operation to the optical writing device 100.
In the image forming device described above, because the main scanning synchronizing signal and the image forming start signal of the sub-scanning direction are not synchronized in general, when the image forming start signal of the sub-scanning direction from the detecting means (61) reaches the controller 116, angles of the rotational polygon mirror 122, which are respectively for when the optical writing corresponding to image information of the first color is started and for when the optical writing corresponding to image information of the second color is started, are different. Namely, when the image forming start signal of the sub-scanning direction from the detecting means (61) reaches the controller 116, the angles of the rotational polygon mirror 122 when the optical writing corresponding to image information of each color is started are not equal to each other.
Therefore, as shown in
In addition, in the specification, “line” means a pixel set that the positions in the sub-scanning direction are equal among the pixels forming image information. During the image formation, from the first scanned line to the subsequently scanned lines, these lines are represented by the first line, the second line, the third line, etc. Even though a scanning and writing device to form a plurality of lines by scanning once, each of lines is represented by the first line, the second line, the third line, etc. as shown in FIG. 21.
As a technology to avoid the aforementioned color deviation, there is a method to control the exposure by determining as to whether t1 to t4 are equal to or larger than a prescribed value. In this method, for example, when t1 is equal to or larger than T/2, the optical writing (the exposure) is started at time t1. When t1 is less than T/2, the optical writing (the exposure) is started at time t1+T. When the exposure is started at time t1+T, the optical writing device can be stopped at time t1, or the optical writing device can be still activated without emitting a laser beam.
When this conventional method is applied to a situation shown in
In addition, there is a disclosed image forming device in Japanese Laid Open No. 11-212009, in which the above method and a multi-beam technology are combined together. However, this image forming device is to reduce a position shift of image information of the first line, rather than to avoid toner image of each color from being shifted close to one line.
In the conventional image forming device, when the electrostatic latent image is formed by the writing device, a dot position shift occurs easily in the sub-scanning direction. As the dot position shift occurs, a color deviation occurs when overlapping each of the color images on the intermedium transfer body. Therefore, the image quality is degraded and the original image cannot be truly reproduced.
According to the foregoing description, an object of this invention is to provide a writing control method, a writing control device and an image forming device capable of avoiding a color deviation of a toner image, caused by that the main scanning synchronizing signal and the image forming start signal of the sub-scanning direction are not synchronized.
Another object of this invention is to provide an image forming device capable of suppressing a dot position shift in a sub-scanning direction to improve the image quality.
According to the objects mentioned above, the present invention provides an image forming device, comprising: a body to be scanned that moves in a sub-scanning direction; a writing means for scanning the body in a main scanning direction with a light beam according to image information to form a reference image on the body and repeating the scanning plural times to form plural images; and a second body on which the plural images are overlaid to form a color image. The writing means starts writing the reference image at a start time ty1 when a main scanning synchronizing signal is firstly generated by the writing means after a time tx1 when a predetermined time has lapsed from detection of an image forming start signal of the sub-scanning direction for the reference image. A start time for an image other than the reference image is changed depending on the start time of the reference image.
In the above image forming device, the predetermined time is T/2 where T is a period of the main scanning synchronizing signal of the writing means, and wherein the writing means delays starting writing the image other than the reference image by T when the following relationship is satisfied:
(t1−t2)>0
wherein t1=(ty1−tx1) and t2=(ty2−tx2) where tx2 represents a time when an image forming start signal of the sub-scanning direction for the image other than the reference image is detected, and ty2 represents a start time when the main scanning synchronizing signal is firstly generated by the writing means after the time tx2.
In the above image forming device, an assumptive image obtained by averaging start positions in the sub-scanning direction of a plurality of images that have been written is used as the reference image, and wherein the writing means delays starting writing a following image other than the reference image by T when the following relationship is satisfied:
(t3−t2)>0
wherein t3 represents a time from the time when the image forming start signal of the sub-scanning direction for the assumptive image is detected to the time when the writing means starts writing the assumptive image.
The image forming device further comprises a mark detecting means. The second body is an intermediate transfer body on which the plural images formed on the body are transferred and which has a mark thereon. The image forming start signal of the sub-scanning direction is generated when the mark is detected by the mark detecting means. The writing means comprises a first measuring means for measuring a first lapse time after the image forming start signal is detected; a storing means for storing the predetermined time T/2; a first determining means for comparing the first lapse time measured by the first measuring means with the predetermined time T/2 to determine whether the first lapse time is larger than the predetermined time T/2; a second measuring means for measuring and storing a second lapse time from a time when the lapse time measured by the first measuring means reaches the predetermined time T/2 to a time when the writing means generates a main scanning synchronizing signal; a calculating means for calculating a time difference between the first lapse time measured by the first measuring means and the second lapse time measured by the second measuring means, when forming the image other than the reference image; and a second determining means for determining as to whether the time difference is positive or negative. At a time point that the first lapse time is determined to be larger than the predetermined time T/2 by the first determining means, the writing means starts writing the reference image while synchronizing with the main scanning synchronizing signal, and the start time of the image other than the reference image is delayed depending on a result of the second determining means.
In the above image forming device, the writing means further comprises a counting means for counting a number of the main scanning synchronizing signal after the first lapse time reaches the predetermined time T/2 when forming the reference image, and for counting a number of the main scanning synchronizing signal after the image forming start signal is detected when forming the image other than the reference image. When the number of the main scanning synchronizing signal when forming the reference image is n, the writing means starts writing the reference image. When the second determining means determines that the time difference is negative, the writing means starts writing the image other than the reference image while synchronizing with the n-th synchronizing signal after the image forming start signal is detected, and when the second determining means determines that the time difference is positive, the writing means starts writing the image other than the reference image while synchronizing with the (n+1)-th synchronizing signal after the image forming start signal is detected.
In the above image forming device, if the image formation of the reference image is performed from m-th (m is a positive integer) line thereof, the image formation of the plural images other than the reference image is output from the m-th line thereof such that the m-th line is output as a first line of the plural images when the second determining means determines that the time difference is negative, and the image formation of the plural images other than the ‘reference image Is output from the m-th line thereof such that the m-th line is output as a second line while outputting empty data in the first line when the second determining means determines that the time difference is positive.
In the above image forming device, the reference image is changeable.
The present invention further provides a writing control device, comprising: a scanning and writing device for scanning in a main scanning direction a body that moves in a sub-scanning direction with light beams according to image information when a main scanning synchronizing signal generated by the scanning and writing device is detected after an image forming start signal of the sub-scanning direction is detected, to write an image on the body, and repeating the scanning plural times to form plural images including a reference image, which are overlaid on a second body to form a color image thereon, wherein the scanning and writing device performs n (n>0) line scanning per one scanning. In a case of t1<t2, in which t1 represents a time lapsing from the detection of the image forming start signal to the detection of the main scanning synchronizing signal when the scanning and writing device starts writing the reference image; and t2 represents a time lapsing from the detection of the image forming start signal to the detection of the main scanning synchronizing signal when the scanning and writing device starts writing an image other than the reference image, the scanning and writing device starts writing the image other than the reference image from a (i+1)-th line where i represents an integer so as to minimize |t1+T×(i/n)−t2| where T represents a time interval at which the main scanning synchronizing signal is generated.
In the above writing control device, in a case of t1>t2, the scanning and writing device starts writing the image other than the reference image while delaying the scanning by (−m) lines where m represents an integer so as to minimize |t1+T×(m/n)−t2|.
In the above writing control device, the scanning and writing device start writing the reference image from a (j+1)-th line where j represents a non-negative integer so as to minimize |t1−T×(j/n)| and the scanning and writing device starts writing the image other than the reference image from a (k+1)-th line where k represents an integer so as to minimize |t1−T×(j/n)+T×(k/n)−t2|.
In addition, a first image of the plural images can be used as the reference image. An assumptive image can also be used as the reference image, and wherein the assumptive image is obtained by averaging positions in the sub-scanning direction of images of the plural images that have been written.
Alternatively, when the plural images include at least two chromatic color images, one of the at least two chromatic color images is used as the reference image.
The plural images include at least three images, and wherein one of two images of the three images, which have a higher correlation with each other than any other combinations of the three images, is used as the reference image.
Furthermore, the reference image is changeable.
The present invention further provides a writing control device, comprising: a scanning and writing device for scanning in a main scanning direction a body that moves in a sub-scanning direction with light beams according to image information when a main scanning synchronizing signal generated by the scanning and writing device is detected after an image forming start signal of the sub-scanning direction is detected, to write an image on the body, and repeating the scanning plural times to form plural images including a reference image, which are overlaid on a second body to form a color image thereon. A time lapsing from the detection of the image forming start signal to the first detection of the main scanning synchronizing signal is t1 when the scanning and writing device writes the reference image, and a time lapsing from the detection of the image forming start signal to the first detection of the main scanning synchronizing signal is t2 when the scanning and writing device writes an image other than reference image. The scanning and writing device starts writing the reference image at a time when the time t1 has lapsed from the detection of the image forming start signal for the reference image. The scanning and writing device starts writing an image other than the reference image from a first line at a time when the time t2 has lapsed from the detection of the image forming start signal for the image when t1 is less than a first predetermined time and |t1−t2| is less than a second predetermined time; when t1 is less than the first predetermined time and |t1−t2| is not less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from a second line at the time when t2 has lapsed from the detection of the image forming start signal for the image; when t1 is not less than the first predetermined time and |t1−t2| is less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from the first line at the time when t2 has lapsed from the detection of the image forming start signal for the image; and when t1 is not less than the first predetermined time and |t1−t2| is not less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from the first line at a time when t2+T has lapsed from the detection of the image forming start signal for the image, where T represents a time interval at which the main scanning synchronizing signal is generated.
In the above writing control device, the time t1 is an average time from the detection of the image forming start signals to the write starting times of images of the plural images that have been written.
In the above writing control device, a first image of the plural images can be is used as the reference image.
Alternatively, an assumptive image is used as the reference image, and wherein the assumptive image is obtained by averaging positions in the sub-scanning direction of images of the plural images that have been written.
When the plural images include at least two chromatic color images, one of the at least two chromatic color images is used as the reference image. The plural images include at least three images, and wherein one of two images of the three images, which have a higher correlation with each other than any other combinations of the three images, is used as the reference image. The first predetermined time can be T/2.
The present invention further provides a writing control device, comprising: a scanning and writing device for scanning in a main scanning direction a body that moves in a sub-scanning direction with light beams according to image information when a main scanning synchronizing signal generated by the scanning and writing device is detected after an image forming start signal of the sub-scanning direction is detected, to write an image on the body, and repeating the scanning plural times to form plural images including a reference image, which are overlaid on a second body to form a color image thereon. A time lapsing from the detection of the image forming start signal to the first detection of the main scanning synchronizing signal is t1 when the scanning and writing device writes the reference image, and a time lapsing from the detection of the image forming start signal to the first detection of the main scanning synchronizing signal is t2 when the scanning and writing device writes an image other theft reference image. The scanning and writing device starts writing the reference image from a first line at a time when the time t1 has lapsed from the detection of the image forming start signal for the reference image when the time t1 is less than a first predetermined time, and the scanning and writing device starts writing the reference image from a second line at the time when the time t1 has lapsed from the detection of the image forming start signal for the reference image when t1 is not less than a first predetermined time. The scanning and writing device starts writing an image other than the reference image from a first line at a time when the time t2 has lapsed from the detection of the image forming start signal for the image when the time t1 is less than a first predetermined time and |t1−t2| is less than a second predetermined time; when the time t1 is less than the first predetermined time and |t1−t2| is not less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from a second line at the time when the time t2 has lapsed from the detection of the image forming start signal for the image. When t1 is not less than the first predetermined time and |t1−t2| is less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from the second line at the time when the time t2 has lapsed from the detection of the image forming start signal for the ‘image; and when t1 is not less than the first predetermined time and |t1−t2| is not less than the second predetermined time, the scanning and writing device starts writing the image other than the reference image from the first line at a time when the time t2 has lapsed from the detection of the image forming start signal for the image.
In the above writing control device, the time t1 is an average time from the detection of the image forming start signals to the write starting times of images of the plural images that have been written.
In the above writing control device, a first image of the plural images can be used as the reference image.
Alternatively, an assumptive image is used as the reference image, and wherein the assumptive image is obtained by averaging positions in the sub-scanning direction of images of the plural images that have been written. When the plural images include at least two chromatic color images, one of the at least two chromatic color images is used as the reference image. The plural images include at least three images, and wherein one of two images of the three images, which have a higher correlation with each other than any other combinations of the three images, is used as the reference image. In addition, the first predetermined time is T/2 where T represents a time interval at which the main scanning synchronizing signal is generated.
The present invention further provides an image forming device comprising: a body to be scanned by a scanning and writing device; any one of the writing control devices described above; and a second body on which the color image is formed.
The present invention further provides an image forming device comprising: any one of the writing control devices described above; a converting means for converting image information in a first color space into image information m a second color space; and a determining means for determining a correlation strength among color images in the second color space depending on an amount of the image information in the first color space. The color image is formed using the image information in the second color space.
While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:
According to the embodiment of the present invention, referring to
The exposure control unit 50 is connected to the storage device 54 to store data into the storage device 54 and to obtain data from the storage device 54 if necessary. A main scanning synchronizing signal (a main scanning synchronizing signal from the light receiving element 126) used when starting the optical writing operation for each color and an image forming start signal of the sub-scanning direction (an image forming start signal of the sub-scanning direction from the detecting means (61)) used when starting the optical writing operation for each color are input to the exposure control unit 116a. The exposure control unit 116a transmits an optical writing (exposure) start signal to the optical writing device 100 according to the main scanning synchronizing signal and image forming start signal of the sub-scanning direction.
As shown in
On the other hand, as shown in
If time t1<T/2, the exposure control unit 116a uses times t1 and t2, at which corresponding main scanning synchronizing signals are detected, to determines as to whether |t1−t2| is smaller than a prescribed time, for example, T/2 (Step 6). When |t1−t2|<T/2 is determined at Step 6, the optical writing device 100 is made to start the exposure operation from image information of the first line at time t=t2 (Step 8). When |t1−t2| is equal to or larger than T/2 at Step 6, the optical writing device 100 is made to start the exposure operation from image information of the second line at time t=t2 (Step 7). Namely, at Step 7, the image formation due to the exposure corresponding to image information of the first line is not processed. In addition, in the image forming device of the embodiment, image information sent from a scanner or a computer is stored with a bitmap format in a image information storage means (not shown) within the controller 116. A control of the exposure control unit 116a, which is to start the exposure from image information of the first line or to start the exposure from image information of the second line, is to read image information from the image information storage means and controlled by an image information reading start address in the image information storage means when transmitting information to the optical writing device 100.
On the other hand, if time t1≧T/2, the exposure control unit 116a determines as to whether |t1−t2| is smaller than a prescribed time, for example, T/2 (Step 9). When |t1−t2|<T/2 is determined at Step 9, the optical writing device 100 is made to start the exposure operation from image information of the first line at time t=t2 (Step 11). When |t1−t2| is equal to or larger than T/2 at Step 9, the optical writing device 100 is made to start the exposure operation from image information of the second line at time t=t2+T (Step 10). In the situation at Step 10, the optical writing device 100 delays image information by only one line to perform the scanning operation. As could be understood from the above description, at Steps 10 and 11, an exposure start time is selected in such a manner that dots formed by the exposure corresponding to image information of the second, the third and the forth colors at positions closer to dots formed by the exposure corresponding to image information of the first color.
In the present embodiment, by further arranging Steps 5, 8, 10 and 11, even though time t1 is equal to or greater than T/2, position shifts of image information of the second line and after the second line of the second, the third and the fourth colors can also be suppressed to half of a dot pitch with respect to image information of the first color. In this way, for all situation, position shifts of image information of the second line and after the second line of the second, the third and the fourth colors can also be suppressed to half of a dot pitch with respect to image information of the first color.
According to the above embodiment, position shifts of image information of other colors can be suppressed to half of a dot pitch with respect to image information of the first color or the second color that is used as a reference color. Additionally, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can also be avoided. At Steps 5, 6 and 9, the prescribed time used to compare with t1 and |t1−t2| is set T/2, but a value around T/2 can also be used to obtain substantially the same effect and result. Furthermore, at Steps 5, 6 and 9, even though the prescribed time used to compare with t1 and |t1−t2| is larger than 0 and smaller than T, position shifts of image information of other colors can be reduced to half of a dot pitch with respect to image information of the reference color.
Next, the second embodiment according to the present invention is described in detail. In the image forming device of the second embodiment, the exposure control unit 116a performs following processes.
As shown in
Next, the exposure control unit 116a determines as to whether time t1 is smaller than T/2 (Step 5). When time t1 is smaller than T/2, the optical writing device 100 starts an exposure operation corresponding to image information from image information of the first line. In addition, if time t1 is equal to or larger than T/2, the exposure control unit 116a controls the optical writing device 100 to start an exposure operation corresponding to image information from image information of the second line at time t1 (Step 7). Namely, at Step 7, the image formation due to the exposure corresponding to image information of the first line is not processed.
On the other hand, when an exposure control corresponding to image information of the second, the third or the fourth color is performed, the exposure control unit 116a obtains time t1, at which the main scanning synchronizing signal is detected when starting the exposure corresponding to image information of the first color, from the storage device 116b (Step 1). Then, the exposure control unit 116a checks regularly the image forming start signal of the sub-scanning direction that comes from the detecting means (61) and then determines as to whether the image forming start signal of the sub-scanning direction is detected (Step 2). If the image forming start signal of the sub-scanning direction is detected, time t is set t=0 (Step 3). Next, the exposure control unit 116a checks regularly the main scanning synchronizing signal that comes from the light receiving means 126 and then determines as to whether the main scanning synchronizing signal is detected (Step 4). If the main scanning synchronizing signal is detected, the exposure control unit 116a determines as to whether time t1 is smaller than a prescribed time, for example, T/2 (Step 5).
If time t1<T/2, the exposure control unit 116a uses times t1 and t2, at which corresponding main scanning synchronizing signals are detected respectively, to determines as to whether |t1−t2| is smaller than a prescribed time, for example, T/2 (Step 6). When |t1−t2|<T/2 is determined at Step 6, the optical writing device 100 is made to start the exposure operation from image information of the first line at time t=t2 (Step 8). When |t1−t2| is equal to or larger than T/2 at Step 6, the optical writing device 100 is made to start the exposure operation from image information of the second line at time t=t2 (Step 7). Namely, at Step 7, the image formation due to the exposure corresponding to image information of the first line is not processed.
Additionally, if time t1≧T/2, the exposure control unit 116a determines as to whether |t1−t2| is smaller than T/2 (Step 9). When |t1−t2|<T/2 is determined at Step 9, the optical writing device 100 is made to start the exposure operation from image information of the second line at time t=t2 (Step 11). When |t1−t2| is equal to or larger than T/2 at Step 9, the optical writing device 100 is made to start the exposure operation from image information of the first line at time t=t2 (Step 10). Namely, at Steps 10 and 11, according to whether dots formed by the exposure corresponding to the image formations of the second, the third and the forth colors are formed at positions closer to dots of the second line of the first color, the image formations of the second, the third and the forth colors are selected from the first line or the second line.
In the second embodiment, by further arranging Steps 6, 7 and 8 in
As shown in
According to the second embodiment, position shifts of image information of other colors can be suppressed to half of a dot pitch with respect to image information of the first color or the second color that is used as a reference color. Additionally, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can also be avoided. At Steps 5, 6 and 9, the prescribed time used to compare with t1 and |t1−t2| is set T/2, but a value around T/2 can also be used to obtain substantially the same effect and result. Furthermore, at Steps 5, 6 and 9, even though the prescribed time used to compare with t1 and |t1−t2| is larger than 0 and smaller than T, position shifts of image information of other colors can be reduced to half of a dot pitch with respect to image information of the reference color.
Next, the third embodiment according to the present invention is described in detail. The image forming device of the third embodiment is different from the first embodiment in a control method of the exposure control unit 116a for an optical writing (exposure) control corresponding to image information of the second color.
As shown in
Namely, according to the third embodiment, the exposure control unit 116a uses an average time as a reference, in which the average time is an average of exposure times corresponding to image information of the first line of colors whose corresponding image formation has been executed. Then, an exposure control corresponding to image information of the second, the third and the fourth colors is initiated. In the third embodiment, as compared with the first embodiment in which time t1 is used as the reference, position shifts of dots of the third and the fourth colors can be further reduced. In this embodiment, for a sake of a common circuit to calculate the average value ta1, a circuit same as the circuit for the exposure corresponding to image information of the second, the third and the fourth colors is used to calculate the average value ta1.
Proceeding to Step 12 from Steps 7, 8, 10 and 11, at Step 12 the exposure control unit 116a uses an exposure start time corresponding to image information of a new first line determined by Steps 7, 8, 10 and 11 to recalculate the average value ta1. When calculating the average value ta1, the exposure control unit 116a can execute imaginarily an exposure corresponding to image information of the first line to obtain an exposure start time, even though for a color that an exposure corresponding to image information of the first line is not actually performed. Therefore, a negative value can be obtained for the average value. Next, the exposure control unit 116a stores the newly calculated average value ta1 to the storage device 116b.
According to the third embodiment, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided. Furthermore, by using an assumptive image, which averages positions in the sub-scanning direction of the image where the scanning operation has been started by the optical writing device, as a reference image, position shifts of image where scan starts from the third one can be further reduced.
Next, the fourth embodiment according to the present invention is described in detail. In the image forming device of the fourth embodiment, only an exposure control corresponding to image information of the second, the third and the fourth colors, which is implemented by the exposure control unit 116a, is different from the second embodiment. In the fourth embodiment, the exposure control unit 116a executes substantially the flow chart shown in
In this way, the exposure control unit 116a uses a time, which averages the exposure start times corresponding to the first line of colors whose corresponding image formation is already finished, as a reference to perform an exposure control corresponding to image information of the second, the third and the fourth colors. Therefore, in the fourth embodiment, as compared with the first embodiment that time t1 is used as a reference, dot position shifts of dots formed by the exposure corresponding to image information of the third and the fourth colors can be further reduced. According to the fourth embodiment, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided.
Next, the fifth embodiment according to the present invention is described in detail. In the fifth embodiment, the light source 120 of the optical writing device 100 in the first embodiment uses a multi-beam light source. This single light source can generate n light beams (n>0). For convenience, n light beams that form the multi-beam are sequentially represented by the first beam, the second beam, . . . , and n-th beam, etc. along the sub-scanning direction, starting from a light beam that performs a scanning operation corresponding to image information whose line number is small.
In the optical writing device 100, the light source 120 is modulated according to image information by a modulating means (not shown). n lease beams, which are repeatedly modulated in sequence by image information of the same color, are emitted. Performing this operation sequentially according to image information of the black color, the magenta color, the cyan color and the yellow color, n laser beams, which are sequentially modulated by image information of the black color, the magenta color, the cyan color and the yellow color are emitted. As shown in
When performing the exposure control for the second, the third and the fourth colors, the exposure control unit 116a performs the optical writing (exposure) control flow corresponding to image information of second, the third and the fourth colors as shown in FIG. 17. First, the exposure control unit 116a obtains time t1 from the storage device 116b, wherein time t1 is a time where a main scanning synchronizing signal is detected when starting an exposure corresponding to image information of the first color (Step 1). The exposure control unit 116a checks regularly the image forming start signal of the sub-scanning direction that comes from the detecting means (61) and then determines as to whether the image forming start signal of the sub-scanning direction is detected (Step 2). If the image forming start signal of the sub-scanning direction is detected, time t is set t=0 (Step 3).
Next, the exposure control unit 116a checks regularly the main scanning synchronizing signal that comes from the light receiving means 126 and then determines as to whether the main scanning synchronizing signal is detected (Step 4). If the main scanning synchronizing signal is detected, a recursion calculation is executed in order to obtain an integer i such that |t1+T×(i/n)−t2| is a minimum (Step 5), wherein i is an integer from −n+1 to n−1.
Next, the exposure control unit 116a determines as to whether i is larger than 0 (Step 6). If i>0, because the exposure start time corresponding to image information of the second color is later than the exposure start time corresponding to image information of the first color, the image of the second color should be formed from a line where the position shift is least overlaid with the image of the first color. Therefore, if i>0, the exposure control unit 116a makes the optical writing device 100 to start at time t2 an exposure corresponding to image information of the (i+1)-th line (Step 7). In the multi-beam light source, in order that the laser beams modulated by image information are emitted to perform exposure processes from image information of the (i+1)-th line, the line can correspond to the light source suitable. For example, for i=0, the exposure control unit 116a is to write image information of the first line with he first laser beam, and for i=1, to write image information of the second line with the first laser beam.
On the other hand, if i≦0, the exposure start time corresponding to image information of the first color is later than the exposure start time corresponding to image information of the first color or substantially the same. Therefore, the exposure corresponding to image information of the second color is delayed according to a requirement and the exposure corresponding to image information of the second color must start at a time where the position shift is smallest. If i≦0, the exposure control unit 116a makes the optical writing device 100 to start the exposure corresponding to image information at time t2−T×(i/n) from image information of the first line (Step 8). In the case of Step 8, the optical writing device 100 delays image information by only one line to perform the scanning process.
On the other hand, for the exposure of the fourth color starting at time t4 earlier than time t1, by Step 8 the exposure is started from the second beam among the four beams (i=−1, image information is delayed by one line). In the sixth embodiment, according to the process of the exposure control unit 116a, position shifts of image information of the second, the third and the fourth colors can be suppressed below as half as the dot pitch with respect to image information of the first color.
In addition, in order to start the image recording with the exposure from the prescribed line as described above, the exposure control unit 116a selects an image formation start line by an address selection of the bitmap image stored in the image forming device. Furthermore, a proper beam is selected among the n beams forming the multi-beam as an actual exposure start beam. In addition, when determining a dot forming positions of the third and its subsequent colors, the fifth embodiment uses time t1 as a reference, but as described in the third embodiment, an average time ta1 of the first lines of colors formed till now can also be uses as a reference.
According to the fifth embodiment, even though a time lapse in detecting the image forming start signal of the sub-scanning direction for detecting the main scanning signal when performing the optical writing other than the reference image is longer than a time lapse in detecting the image forming start signal of the sub-scanning direction for detecting the main scanning signal when performing the optical writing of the first color image as the prescribed reference image, the position shift of image other than the reference image can be suppressed to below half of the dot diameter with respect to the reference image. Moreover, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided.
In addition, even though a time lapse for detecting the image forming start signal of the sub-scanning direction to detecting the main scanning signal when performing the optical writing other than the reference image is shorter than a time lapse for detecting the image forming start signal of the sub-scanning direction to detect the main scanning signal when performing the optical writing of the first color image as the prescribed reference image, the position shift of image other than the reference image can be suppressed to below half of the dot diameter with respect to the reference image. Moreover, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided.
Next, the sixth embodiment of the present invention is described in detail as follows. In the sixth embodiment, an optical writing device with a multi-beam light source is same as the fifth embodiment is used. n beams are emitted from one single light source.
As shown in
Next, the exposure control unit 116a checks regularly the main scanning synchronizing signal that comes from the light receiving means 126 and then determines as to whether the main scanning synchronizing signal is detected (Step 3). If the main scanning synchronizing signal is detected, a time t1 where the main scanning synchronizing signal is detected is stored into the storage device 116b. Next, the exposure control unit 116a performs a recursion calculation to obtain an integer j such that |t1−T×(j/n)−t2| is a minimum (Step 5), wherein j is from 0 to n−1. By using j obtained by above calculation, the optical writing device 100 starts the exposure corresponding to image information form image information of the (j+1)-th line at time t1.
As shown in
If the main scanning synchronizing signal is detected, the exposure control unit 116a performs a recursion calculation in order to obtain an integer i such that |t1−T×(j/n)+T×(i/n)−t2| is a minimum (Step 6), wherein i an integer from −n+1 to n−1.
Next, the exposure control unit 116a determines as to whether i is larger than 0 (Step 6). If i>0, because the exposure start time corresponding to image information of the second color is later than the time t1−T×(j/n) where the dot formation corresponding to the first line by using the exposure based on image information of the first color is started, the image of the second color should be formed from a line where the position shift is least overlaid with the image of the first color. Therefore, if i>0, the exposure control unit 116a makes the optical writing device 100 to start an exposure corresponding to image information from image information of the (i+1)-th line at time t2 (Step 8). In the multi-beam light source, in order that the laser beams modulated by image information are emitted to perform exposure processes from image information of the (i+1)-th line, the line can correspond to the light source suitably. For example, for i=0, image information of the first line is written with the first laser beam, and for i=1, to write image information of the second line is written with the first laser beam.
On the other hand, if i≦0, because the exposure start time corresponding to image information of the second color is earlier than or the same as the time t1−T×(j/n) where the dot formation corresponding to the first line by using the exposure based on image information of the first color is started. Therefore, if necessary, the exposure corresponding to image information of the second color is delayed according to a requirement and the exposure corresponding to image information of the second color should start at a time where the position shift is smallest. The exposure control unit 116a makes the optical writing device 100 to start the exposure corresponding to image information at time t2−T×(i/n) from image information of the first line (Step 9). In the case of Step 9, the optical writing device 100 delays image information by only one line to perform the scanning process.
On the other hand, the exposure of the fourth color starting at time t4 earlier than time t1 is started by executing Step 9 shown in
In addition, in order to start the image recording with the exposure from the prescribed line as described above, the exposure control unit 116a selects an image formation start line by an address selection of the bitmap image stored in the image forming device. Furthermore, a proper beam is selected among the n beams forming the multi-beam as an actual exposure start beam. In addition, when determining a dot forming positions of the third and its subsequent colors, the sixth embodiment uses time t1 as a reference, but as described in the fourth embodiment, an average time ta1 of the first lines of colors formed so far can also be used as a reference. In the fifth and the sixth embodiments, by using an assumptive image whose image (the optical writing device has started scanning) positions in the sub-scanning direction are averaged as the reference image, the position shift of the image where the scanning is started from the third one can be further reduced. In addition, in the fifth and the sixth embodiments, n is an integer equal to or larger than 1.
According to the sixth embodiment, the image position shifts of the second, the third and the fourth colors other than the reference can be suppressed below as half as the dot pitch of the image of the first color that is used as the reference image. In addition, the image forming position in the sub-scanning direction can become stable.
Next, the seventh embodiment according to the present invention is described in detail as follows. In the seventh embodiment, when the control objects for the optical writing (exposure) are exposures corresponding to image information of the cyan color, the magenta color and the yellow color, the method for selecting the reference image is different from the first embodiment. For example, during the exposures corresponding to image information of the cyan color, the magenta color and the yellow color, the reference image is selected in a manner that image information amounts of the red (R) color, the green (G) color and the black (B) color are used to minimize an influence of the position shift of image information.
Digital image information read from a network image input device or a scanner comprises an R (red) color signal, a g (green) color signal and a B (blue) signal, which are transmitted to the compression/expansion circuit 406. The compression/expansion circuit 406 compresses image information read from the image input device by using a compression format such as a JPEG2000 format or a JBIG format. Codes compressed by the compression/expansion circuit 406 are stored to the page memory 408. When making the second edition, the compression codes are read from the page memory 408, decoded by the compression/expansion circuit 406 with a process reverse to the compression, and transmitted to the next process. The logarithm conversion circuit 400 performs a table conversion to convert the characteristic of signals decoded by the compression/expansion circuit 406 from a reflection rate space (as a first color space) to a concentration space (as a second color space). In this way, image information of the R, the G and the B signals are converted into image information of the cyan color, the magenta color, the yellow color and the black color. The filter circuit 402 performs various filtering processes to image information from the logarithm conversion circuit 400. The gradation processing circuit 404 prepares a dither table and then perform an intermedium gradation process to image information from the logarithm conversion circuit 400. After image information is processed by the gradation processing circuit 404, processed image information is transmitted to the optical writing device 100.
With respect to that the exposure start timing is determined from a recording start signal of the present embodiment, a compression encoding amount of color species from the compression/expansion circuit 406 is further obtained to determine an exposure start timing (referring to FIG. 23). For example, the exposure control unit 116a obtains a compression encoding amount Fr of the red color, a compression encoding amount Fg of the green color and a compression encoding amount Fb of the blue color from the compression/expansion circuit 406. The compression encoding amount is a size in the page memory 408 for a compression code obtained by a compression process of the compression/expansion circuit 406. The larger the image information amount is, the larger the compression encoding amount is.
In the seventh embodiment, regarding the exposures corresponding to image information of all colors that have been started by the exposure control unit 116a, the storage device 116b stores times where the main scanning synchronizing signals are detected. For example, when the exposure corresponding to image information of the third color, the storage device 92 stores times t1, t2 where the main scanning synchronizing signals are detected when the exposures of the first and the second colors start. When the exposure corresponding to image information of the fourth color, the storage device 92 stores times t1, t2 and t3 where the main scanning synchronizing signals are detected when the exposures of the first, the second and the third colors start.
In the seventh embodiment, a control of an exposure start timing corresponding to image information of black color can use any one of the controls of the exposure start timing described in each of the aforementioned embodiments. Controls of exposure start timings corresponding to image information of the cyan (C) color, the magenta (M) color and the yellow (Y) color are executed according to a control flow shown in FIG. 24.
Referring to
When a result of the determination Step 3 is NO (both the exposures corresponding to image information of the M color and the Y color have not started), the exposure control unit 116a determines as to which one of the exposures corresponding to image information of the M color and the Y color have started (Step 4). When a result of the determination Step 4 is NO (both the exposures corresponding to image information of the M color and the Y color have not started), the exposure control unit 116a uses the image of the K color as a reference color and performs an exposure control, such as “the control flow for the exposure start timing corresponding to the second color as shown in
When a result of the determination Step 4 is YES (one of the exposures corresponding to image information of the M color and the Y color has started), the exposure control unit 116a uses one optical writing image, whose exposure corresponding image information of the M color or the Y color has started, as a reference image. Then, the exposure control unit 116a performs an exposure control, such as “the control flow for the exposure start timing corresponding to the second and its subsequent colors as shown in
Steps 4, 5 and 6 are one of the features of the present invention. For the exposure control unit 116a performs a control in such a manner that other color image is used as the reference image as if there are color images. Because one color image overlaps another color image to form an objective color image, the color deviation can not be so obvious by using the other color image as the reference image as possible.
On the other hand, when a result of the determination Step 3 is YES (both the exposures corresponding to image information of the M color and the Y color have started), the exposure control unit 116a obtains parameters Fg, Fb from the storage device 116b (Step 7), and then compares the two parameters Fg, Fb in order to determine as to whether Fg>Fb (Step 8). When a result of the determination Step 8 is Yes (Fg>Fb), the exposure control unit 116a uses the Y color image as the reference image, and then performs an exposure control, such as “the control flow for the exposure start timing corresponding to the second and its subsequent colors” as shown in
When a result of the determination Step 8 is NO (Fg≦Fb), the exposure control unit 116a uses the M color image as the reference image, and then performs an exposure control, such as “the control flow for the exposure start timing corresponding to the second and its subsequent colors” as shown in
Steps 8, 9 and 10 are the features of the embodiment, which is to perform a control for selecting a higher related color image as a reference image. In detail, Fg>Fb means that the image information amount of the G color is larger than the image information amount of the B color. In contrast, Fg<Fb means that the image information amount of the G color is smaller than the mage information amount of the B color. For example, when the image is made of only the G color, the amount of the G color in the image information is large, but the amount of the B color in the image information is 0 (for the compression code, in general, there exists information such as a header, and therefore, the image information amount is not 0). Therefore, when Fg is larger than Fb (Fg>Fb), prevention of a color deviation of image information of the G color rather than the image information of the B color can effectively reduce a degradation of an image quality.
The R color is formed from the M color and the Y color, the G color is formed from the C color and the Y color, and the B color is formed from the C color and the M color. Therefore, when the exposure corresponding to image information of the C color starts, the color deviation of the G color image is reduced if the Y color image is used as the reference image, and the color deviation of the B color image is reduced if the M color image is used as the reference image. Therefore, in the case that Fg is larger than Fb (Fg>Fb), when the exposure corresponding to image information of the C color starts, the method is effective in a view of a color deviation reduction while using the Y color image as the reference image. As a result, in the seventh embodiment, a higher related color image is selected as the reference image. In addition, as described above, when the exposure corresponding to image information of the M color is the control object, C can be taken for M and Fr can be taken for Fg. Similarly, when the exposure corresponding to image information of the Y color is the control object, C can be taken for Y and Fr can be taken for Fb.
According to the seventh embodiment, by using an image, where the optical writing device starts first to scan the image, as the reference image, the process becomes simpler and the image whose position shift is reduced can be easy to increase to the most. In addition, when the writing object other than the reference image is a color image, by selecting other color image priorly as the reference, the position shift of the color image is reduced and the image quality can be improved. Furthermore, by selecting an image highly related to an image of the writing object other than the reference image as the reference image, the position shift of the highly related image can be reduced and the image quality can be improved.
In the second to the sixth embodiment mentioned above, similar to the seventh embodiment, the method to select the reference image when the exposure timing control objects are exposures corresponding to image information of the cyan color, the magenta color, the yellow color can use image information of the R color, the G color and the B color during the exposures corresponding to image information of the cyan color, the magenta color, the yellow color to select the reference image, so that an influence of the position shifts of the image information can be reduced to the least.
Next, the eighth embodiment of the present invention is described in detail as follows. Basically, the eighth embodiment is the same as the third embodiment except for two features as follows.
First, the method to select the reference image is different. For example, a previous color image whose corresponding exposure has started is always selected as the reference image. In this case, if ta1 is not used as the average value, but is replaced by a ta1 relating to a color whose exposure has started right before the exposure is to be started, the exposure start control flow is the same as the exposure start control flow shown in FIG. 12. For example, at Step 12 of the exposure start control flow shown in
Second, the exposure start sequence is made by considering the color correlation. For example, if the exposure start sequence is the K color, the C color, the Y color and the M color, by the method for selecting the reference image described above, the color deviation of the C color with respect to the K color is reduced and the color deviation of the M color with respect to the Y color is reduced.
In the eighth embodiment, from a result of performing the above exposure start control, the color deviations of the C color and the Y color, which form the G color having great contribution to brightness information, is reduced, and furthermore, the color deviations of the G color and the K color is smaller since the color deviations of the C color and the K color. Therefore, a reproducibility of brightness information is good. As described above, each time the previous color image whose corresponding exposure has started is selected as the reference image and a color sequence is previously selected in such a manner that the color deviation is reduced, by which the color deviation of the image can be reduced by an algorithm simpler than the seventh embodiment. In addition, because the exposure control corresponding to image information of all colors can be done by the same process, the circuit can be simplified and the processing time can also be reduced.
In addition, in the eighth embodiment, the previous color image whose exposure has started is selected as the reference image. However, from an exposure to be started, the color image prior to the previous color image whose exposure has started is selected as the reference image, and a corresponding exposure start sequence can be set in advance.
According to the eighth embodiment, by selecting an image, which is highly related to an image as a writing object other than the reference image, as the reference image, a high related image could be effectively selected. In addition, in the first, the second, and fourth to seventh embodiments, the method used for selecting the reference image is the same as the eighth embodiment, and similar to the eighth embodiment, the exposure start sequence can be a sequence by considering the color correlation.
The present invention is applicable to image forming devices shown in
The image forming device shown in
In
As the marker on the intermedium transfer belt 206 is detected by the detection devices 261Y, 261M, 261C, 261K within the four image stations 200K, 200C, 200M and 200K, the controller 116 receives the main scanning synchronizing signals from optical receivers (the same optical receiver in the exposure device of the image forming device in
For the image stations 200K, 200C, 200M and 200K, the electrifying devices 204Y), 204M), 204C, 204K uniformly electrify the photosensors 202Y, 202M, 202C, 202K as the image supporters (i.e., the scanned bodies) respectively until the exposures start. The exposure devices 201Y, 201M, 201C, 201K perform the exposures respectively corresponding to image information of the K color, the C color, the M color and the Y color, and then electrostatic latent images corresponding to image information of colors are respectively formed onto the electrified photosensors 202Y, 202M, 202C, 202K. Then, the developing devices 205Y, 205M, 205C, 205K develop the electrostatic latent images corresponding to image information of each of colors, and then toner images of the K color, the C color, the M color and the Y color are respectively formed on the photosensors 202Y, 202M, 202C, 202K. The toner images of the K color, the C color, the M color and the Y color respectively formed on the photosensors 202Y, 202M, 202C, 202K are consistently overlapped on the intermedium transfer belt 206 by primary transfer rollers 262Y, 262M, 262C, 262K (as transfer means) in a primary transfer process so as to form a full color image. In addition, the photosensors 202Y, 202M, 202C, 202K and the intermedium transfer belt 206 are rotationally driven with the same rotational speed by a driving source (not shown).
On the other hand, a transfer paper 208 (as a recording medium) is fed to a resist roller (not shown) from the paper-feeding device 210. The resist roller sends out the transfer paper accompanying with the full color image on the intermedium transfer belt 206. The full color image formed on the intermedium transfer belt 206 is secondarily transferred on the transfer paper 208 by an electric field formed between the secondary transfer roller 264 (as a transfer means) and the opposite roller 263. The full color image is fixed by a fixing device 207, and then, the transfer paper 208 where the full color image is transferred thereon by the secondary transfer process is then ejected out of the image forming device. Afterwards, the photosensors 202Y, 202M, 202C, 202K are cleaned up by the cleaning devices 203Y, 203M, 203C, 203K after the primary transfer process for the toner image and the intermedium belt 206 is cleaned up by the cleaning device 267 after the secondary transfer process for the full color image.
In the image forming device, the exposure start times for the exposure devices 201Y, 201M, 201C, 201K are selected with timings that the toner images for all colors are overlapped. The image forming sequence is from an upstream side to a downstream side in a moving direction of the intermedium transfer belt 206; namely, a sequence of the Y color toner image, the M color toner image, the C color toner image and the K color toner image. Therefore, the Y color toner image is set as the first color toner image, the M color toner image is set as the second color toner image, the C color toner image is set as the third color toner image and the K color toner image is set as the fourth color toner image, and thus the exposure start control the same as the first to the fourth embodiments are performed by the exposure control unit 116a in the controller 116, so as to be able to avoid the color deviation.
In the image forming device shown in
Next, the operation of the image forming device is briefly described as follows. A detecting device 361MY among detecting device 361MY, 361CK (as means for generating an image forming start signal of the sub-scanning direction) generates the image forming start signal of the sub-scanning direction by detecting a pre-formed mark on the intermedium transfer belt 360 to transmit to the controller 116. Next, when the main scanning synchronizing signal from the optical receiver 314MY is transmitted to the controller 116, the exposure of the exposure device (1MY) is started in the same way as described in the aforementioned embodiments. In this case, first of all, the light beam modulated by image information of the Y color or the M color (here, the Y color is used as an example) from the light source for the image station 302 at the upstream, and then the exposure device (1MY) starts the exposure corresponding to image information of the Y color for the photosensor 320MY in the image station 302.
In the image station 302, when the exposure is started, the surface of the photosensor 320MY is electrified by the electrifying device 340MY with a prescribed potential to comply with the exposure. The electrified surface of the photosensor 320MY is exposed by the exposure device 380 to form an electrostatic latent image corresponding to image information of the Y color. The electrostatic latent image on the photosensor 320MY is developed by any one of the developing devices 350M, 350Y. The developing devices 350M, 350Y can be controlled to or not to execute the developing operation either by that one of the developing devices 350M, 350Y is receded from the photosensor 320MY or by that one of the developing devices 350M, 350Y is advanced to a developing position and then a developing bias is applied to thereon from a power source device (not shown). In this example, the electrostatic latent image on the photosensor 320MY is first developed by the developing device 350Y to form a Y color toner image. Then, the Y color toner image formed on the photosensor 320MY is transferred onto the intermedium transfer belt 360 in the primary transfer process by a transfer means (not shown).
Next, the detecting device 361CK generates an image forming start signal of the sub-scanning direction by detecting the pre-formed mark on the intermedium belt 360, and then transmits the image forming start signal of the sub-scanning direction to the controller 116. Then, when the main scanning synchronizing signal reaches the controller 116 from the optical receiver 314CK, the exposure device 380 deflects the light beam by the rotational polygonal mirror to start the exposure of the photosensor 320CK in the image station 304, wherein the light beam is modulated by image information of the K color from the light source for the image station 304.
In the image station 304, when the exposure is started, the surface of the photosensor 320CK is electrified by the electrifying device 340CK with a prescribed potential to comply with the exposure. The electrified surface of the photosensor 320CK is exposed by the exposure device 380 to form an electrostatic latent image corresponding to image information of the K color. The electrostatic latent image on the photosensor 320CK is developed by any one of the developing devices 350C, 350K. The developing devices 350C, 350K can be controlled to or not to execute the developing operation either by that one of the developing devices 350C, 350K is receded from the photosensor 320CK or by that one of the developing devices 350C, 350K is advanced to a developing position and then a developing bias is applied to thereon from a power source device (not shown). In this example, the electrostatic latent image on the photosensor 320CK is first developed by the developing device 350C to form a K color toner image. Then, the K color toner image formed on the photosensor 320CK is transferred to overlap the Y color toner image on the intermedium transfer belt 360 in the primary transfer process by a transfer means (not shown).
The overlapped image of the Y color toner image and the K color toner image on the intermedium transfer belt 206 moves to reach the image station 302 again by the rotation of the intermedium transfer belt 206. At this time, in the image station 302, the developing device at the developing position is switched to the developing device 350M. Then, the detecting device 361MY generates an image forming start signal of the sub-scanning direction by detecting the pre-formed mark on the intermedium belt 360, and then transmits the image forming start signal of the sub-scanning direction to the controller 116.
When the main scanning synchronizing signal reaches the controller 116 from the optical receiver 314MY, the exposure device 380 deflects the light beam by the rotational polygonal mirror to start the exposure of the photosensor 320MY in the image station 302, wherein the light beam is modulated by image information of the M color from the light source for the image station 302.
In the image station 302, when the exposure is started, the surface of the photosensor 320MY is electrified by the electrifying device 340MY with a prescribed potential to comply with the exposure. The electrified surface of the photosensor 320MY is exposed by the exposure device 380 to form an electrostatic latent image corresponding to image information of the M color. The electrostatic latent image on the photosensor 320MY is developed by the developing devices 350M. Then, the electrostatic latent image on the photosensor 320MY is developed by the developing device 350M to form a M color toner image. Then, the M color toner image formed on the photosensor 320MY is transferred to overlap with the Y and the K color toner images on the intermedium transfer belt 360 in the primary transfer process by a transfer means (not shown).
The overlapped image of the Y, K and M color toner images on the intermedium transfer belt 360 moves to reach the image station 304 again by the rotation of the intermedium transfer belt 206. At this time, in the image station 304, the developing device at the developing position is switched to the developing device 350C. Then, the detecting device 361CK generates an image forming start signal of the sub-scanning direction by detecting the pre-formed mark on the intermedium belt 360, and then transmits the image forming start signal of the sub-scanning direction to the controller 116.
When the main scanning synchronizing signal reaches the controller 116 from the optical receiver 314CK, the exposure device 380 deflects the light beam by the rotational polygonal mirror to start the exposure of the photosensor 320CK in the image station 304, wherein the light beam is modulated by image information of the M color from the light source for the image station 304.
In the image station 304, when the exposure is started, the surface of the photosensor 320CK is electrified by the electrifying device 340CK with a prescribed potential to comply with the exposure. The electrified surface of the photosensor 320CK is exposed by the exposure device 380 to form an electrostatic latent image corresponding to image information of the C color. The electrostatic latent image on the photosensor 320CK is developed by the developing devices 350C. Then, the electrostatic latent image on the photosensor 320CK is developed by the developing device 350C to form a C color toner image. Then, the M color toner image formed on the photosensor 320CK is transferred to overlap with the Y, K and M color toner images on the intermedium transfer belt 360 in the primary transfer process by a transfer means (not shown), so as to form a full color image.
On the other hand, a transfer paper 114 (as a recording medium) is fed to a resist roller (not shown) from the paper-feeding device 310. The resist roller sends out the transfer paper accompanying with the full color image on the intermedium transfer belt 360. The full color image formed on the intermedium transfer belt 360 is secondarily transferred on the transfer paper (8) by a transfer means (not shown). The full color image is fixed by a fixing device 370, and then, the transfer paper (8) where the full color image is transferred thereon by the secondary transfer process is then ejected out of the image forming device. Afterwards, the photosensors 320MY, 320CK are cleaned up by the cleaning devices 330MY, 330CK after the primary transfer process for the toner image. The intermedium belt 360 is cleaned up by the cleaning device (not shown) after the secondary transfer process for the full color image.
In the image forming device, the Y color image, the K color toner image, the M color toner image, and the C color toner image are sequentially formed, and these color toner images are overlapped on the intermedium transfer belt 360. Therefore, by setting the Y color as the first color, the K color as the second color, the M color as the third color, the C color as the fourth color, the exposures corresponding to those colors can be controlled according to the aforementioned embodiments. In addition, in the image forming device, considering a subtle eccentricity of the photosensors 320MY, 320CK, an image with a reserved developing color of the developing device can be used as a reference image.
Furthermore, the present invention is also applicable to either an image forming device to overlap toner images of different colors on the photosensor, or an image forming device to transfer a toner image to a recorded object directly without using an intermedium transfer body. Alternatively, the present invention is also applicable to an image forming device to perform an image formation by an image process other than the electrophotography; for example, toner (including ink) is blown form a rotating nozzle according to image information, and a toner image is formed onto a photosensor, an intermedium transfer belt or a recording paper moving in the sub-scanning direction by performing a scanning corresponding to image information in the main scanning direction. In short, the present invention can also suitable for an image forming device that overlaps a plurality of images, wherein the image is formed by using an optical scanning and writing device capable of forming a latent image or an image.
The ninth embodiments is described in detail accompanying with
Referring to
A brief operation of the image forming device is described as follows. Referring to
The developing device 506 has a structure to correspond developing units with a plurality of colors to developing regions. In a case of forming image with different colors (plural colors), the developing units are equally switched, and the above process for developing different colors are repeatedly performed, so as to overlap images of all colors onto the intermedium transfer belt 512.
The image overlapped onto the intermedium transfer belt 512 is transferred onto a recording medium, e.g., a transfer paper, by another transfer means (not shown). The transfer paper having the full color image is fixed by a fixing device (not shown) and then ejected out of the image forming device. In this example, the image formation for each color is started by referring to the mark on the intermedium transfer belt 512. However, when the writing means 504 is a scanning type using a laser scanning optical system, the detection of the mark on the intermedium transfer belt 512 and a main scanning synchronizing signal as a writing reference of the writing means 504 are not synchronized. Therefore, even though the image formation for each color is started by referring to the mark on the intermedium transfer belt 512, a deviation may occur on the image overlapped with the prime colors.
Next, a control configuration and an operation thereof according to the embodiment is described.
According to the first determining means 606, after T/2 is lapsed from the detection of the image forming start signal of the sub-scanning direction, the image forming start signal is synchronized with the synchronizing signal, and then the writing of the reference (the first color) image is started. At this time, there is a situation that the start timing of the reference image is like
After T/2 is lapsed from the detection of the image forming start signal, the second measuring means 608 measures and keeps a time t1min or a time t1max until the writing is started. In
The first measuring means 602 measures a time t11 or t12 from detecting the image forming start signal to generating the synchronizing signal of the writing means 504. The calculating means 610 calculates a time difference between a time t1min or t1max that is measured by the second measuring means 608 until the writing for the reference image is started, to a time t21 or t22 that is measured until the synchronizing signal of the writing means 504 for the image formation other than the reference image is generated. In the above case, t21 is t2min and t22 is t2max.
The second determining means 612 determines that the result of the calculating means 610 is positive or negative. When a determination result of the second determining means 612 is negative (t1−t2<0); namely, t11−t21=T/2+t1min−t2min<T/2, the dot shift is less than ½. Therefore, the image writing is started from the first synchronizing signal after the image forming start signal of the sub-scanning direction is detected. When the determination result is positive, i.e., T/2+t1min−t2min>T/2, the writing control unit 614 controls the writing means 504 to start the image writing from the second synchronizing signal after the image forming start signal of the sub-scanning direction is detected.
In a case that the reference image formation is started with a timing of the synchronizing signal shown in
Next, the tenth embodiment is described in detail according to FIG. 28. In addition, elements same as the previous embodiment are labeled with the same numbers. If not necessary, descriptions of their structures and functions are omitted and only the main parts are described (the following embodiments are the same).
If the synchronizing signal for forming the next image (the third one) other than the reference image is as shown in
Next, the eleventh embodiment of the present invention is described as follows by referring to FIG. 29. It should be noted first that the reference image formation is started with a synchronizing signal that is appeared immediately after a time T/2 is lapsed from the detection of the image forming start signal of the sub-scanning direction, but it is not a limitation for the present invention. In this embodiment, it features that a reference n is set in such a way that the synchronizing signal of the writing means 504 can be delayed by n periods to start the writing.
When forming the reference image, the number of the synchronizing signal of the writing means 504 is counted, starting from a time point that T/2 has lapsed after the image forming start signal of the sub-scanning direction is detected. A counting means 616 is disposed for counting the number of the synchronizing signal after the image forming start signal of the sub-scanning direction is detected when images other than the reference image are formed.
n is et to the counting means 616. When the counting value reaches n, start the image formation is indicated to the writing control unit 614. For example, when n=3 and if the synchronizing signal for the image formation of the reference image is a timing shown in
Next, the twelfth embodiment of the present invention is described as follows by referring to FIG. 30. In this embodiment, a storage/control means 618 and an indicating means 620 for indicating a start position of an image formation are set, and the reference n can be stored and kept. For example, the storage/control means 618 controls the indicating means 620 according to an environment temperature, a print-out number, and a use time. A preset reference value n can be set to the counting means 616. In this way, because the image forming position onto the intermedium transfer belt 512 can be changed according to an actual situation, and therefore a degradation of the intermedium transfer belt 512 (the intermedium transfer body) can be avoided.
Next, the thirteenth embodiment of the present invention is described as follows by referring to FIG. 31. In this embodiment, the second measuring means 608 in
Next, the fourteenth embodiment of the present invention is described as follows by referring to FIG. 32. For simplifying the description, a positive integer m is set to 1. The present embodiment is to control output image information according to a result of the second determining means 612. As a reference image formation is performed with a synchronizing signal shown in
When the synchronizing signals for forming images other than the reference image are as shown in
At this time, the result of the second determining means 612 is positive, and output data sequence is controlled. When the result of the second determining means 612 is positive, image information of the dot (equivalent to the dot J1) of the front line is output as an empty (not printed). Then, one line is delayed to output data in such a way that data of the front line is formed from the dot J1 that is equivalent to a dot position of the second line. When the image formation of the reference image is performed with the synchronizing signal in
Next, the fifteenth embodiment is described. This embodiment features that the printing speed is changed by directly reducing the dot shift by changing the frequency of the basic functional blocks that control operation of the whole image forming device. The reference value as a comparative object of the calculating means 610 and the first measuring means mentioned above is set as a counting value of the aforementioned basic functional blocks. By changing the printing speed with the above setting, even though the frequency of the synchronizing signal of the writing means 504 is changed, half of the frequency of the synchronizing signal can be usually set as the reference value. Therefore, even though the recording speed is changed, the position shift (the color deviation) of the overlapped images can be always reduced.
Next, the sixth embodiment is described as follows by referring to
Different features between FIG. 34 and
Because the formation of the reference image is started with a synchronizing signal that is lapsed a time T/2 after the image forming start signal of the sub-scanning direction is generated according to the first determining means 606, the start timing for the reference image is between a timing of
The second measuring means 608 measures and stores a time at which the writing is started by the synchronizing signal after the time T/2 has lapsed, for example, the time t101 or t102. The start timing of the image formation other than the reference image varies to the most between an interval shown in
In addition, when the determination result of the second determining means 612 is positive, the writing means 504 is controlled to start the image formation from one delayed synchronizing signal. Then, the absolute value of the calculated result is compared with T/4 by using the fourth determining means 624, and then output data is controlled according to the compared result as described above. In a case that the image formation of the reference image is started with the timing shown in
In a case that the results of fourth determining means 624 for both timings in
In addition, in a case that the formation of the reference image is started from the timing shown in
Next, the seventh embodiment is described by referring to FIG. 35. The present embodiment is an example wherein the aforementioned invention is suitable for an image forming device, a two-station type image forming device. The image forming device comprises a station 1 and a station 2 (as image forming means) under the intermedium transfer belt 512. The station 1 comprises an image supporter B1, a writing means D1, at least two developing means E11, E12 for developing an electrostatic latent image formed on the image supporter B1 by writing means D1, a development switching means (not shown) for selectively driving one of the developing means E11, E12. Similarly, the station 2 comprises an image supporter B2, a writing means D2, at least two developing means E21, E22 for developing an electrostatic latent image formed on the image supporter B2 by writing means D2, a development switching means (not shown) for selectively driving one of the developing means E21, E22.
Images can be formed by the plurality of image forming means according to an image formation start signal generated by the mark detecting means 518 as described above. In this way, an image with plural colors can be easily and accurately overlapped onto the intermedium transfer belt 512. Therefore, a high quality full color image forming device can be achieved.
In addition, according to one advantage of the present invention, even though a time lapsing from detecting the image forming start signal of the sub-scanning direction to detecting the main scanning signal when performing the optical writing other than the reference image is longer than a time lapsing from detecting the image forming start signal of the sub-scanning direction to detecting the main scanning signal when performing the optical writing of the prescribed reference image, the position shift of image other than the reference image can be suppressed below as half as the dot diameter with respect to the reference image. Moreover, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided.
In addition, according to one advantage of the present invention, even though a time lapse from detecting the image forming start signal of the sub-scanning direction to detecting the main scanning signal when performing the optical writing other than the reference image is shorter than a time lapse from detecting the image forming start signal of the sub-scanning direction to detecting the main scanning signal when performing the optical writing of the prescribed reference image, the position shift of image other than the reference image can be suppressed to below half as the dot diameter with respect to the reference image. Moreover, a color deviation of the toner image, which is caused by that the main scanning synchronizing signal and image forming start signal of the sub-scanning direction are not synchronized, can be avoided.
According to another advantage of the present invention, the image forming position in the sub-scanning direction can become stable, and the image whose position shift is reduced can be easy to increase to the most. Furthermore, the position shift of the image where the scanning is started from the third line can be further reduced. In addition, either the position shift of the color image is reduced or the position shift of the highly related image is reduced, so that the image quality is highly improved. Additionally, the image with a high correlation can be effectively selected.
According to other advantages of the present invention, the position shift (the color deviation) of the overlapped image can be reduced. In addition, even though the images are overlapped over three times, the position shift (the color deviation) can be reduced with a high accuracy. Furthermore, the position shift (the color deviation) of the overlapped image can be achieved by either using a simple device structure or a simple operation. Because the image forming position on the intermedium transfer body can be changed, a degradation of the intermedium body can be avoided.
While the present invention has been described with a preferred embodiment, this description is not intended to limit our invention. Various modifications of the embodiment will be apparent to those skilled in the art. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-060145 | Mar 2002 | JP | national |
| 2002-149171 | May 2002 | JP | national |
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| 20030169325 A1 | Sep 2003 | US |
