Patent Grant
7535483
1. Technical Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and particularly to an image forming apparatus and an image forming method using an electrophotographic system.
2. Related Art
In recent years, various image forming apparatuses, such as digital copiers and laser printers, to perform image formation by scanning exposure using a laser light beam and an electrophotographic process have been developed.
The image forming apparatus includes a beam light scanning device to scan the laser light beam onto a photoconductive drum to form an electrostatic latent image on the photoconductive drum. The beam light scanning device includes, for example, a laser oscillator to generate the laser light beam, a polygon mirror to reflect the laser light beam outputted from the laser oscillator toward the photoconductive drum and to scan it onto the photoconductive drum, an f-θ lens and the like.
The electrostatic latent image formed on the photoconductive drum is toner-developed, and the toner-developed image is finally transferred as a recording image to a recording sheet. Accordingly, in order to form a uniform recording image without unevenness, it becomes necessary to form the electrostatic latent image of uniform intensity on the photoconductive drum, and it becomes important to stabilize the intensity of the laser light beam.
However, the intensity of the laser light beam irradiated onto the photoconductive body (photoconductive drum) is not necessarily constant in the beam scanning direction. The main cause is that the transmission loss of the f-θ lens varies according to the incident angle. In general, the incident angle of the laser light beam to the f-θ lens is almost vertical at the center of the f-θ lens, and is obliquely incident on a place close to the end of the f-θ lens. As a result, the transmission loss of the f-θ lens is least at the center, and becomes large toward the end.
This means that from the viewpoint of the intensity of the laser light beam irradiated onto the photoconductive drum, the intensity of the laser light beam is highest at the center of the f-θ lens, and it becomes weak toward the end, and the intensity of the laser light beam becomes uneven in the main scanning direction.
Besides, in a tandem system color image forming apparatus, in the case where a polygon mirror to scan a laser light is used commonly to four colors, a structure is such that the laser light is distributed to photoconductive bodies of respective colors by the mirror, and in addition to the irregularity of the mirror itself, since an incident angle to the mirror varies according to the lasers of the respective colors, even if the same laser light beam power is set, the laser light powers on the drum surfaces of the respective colors are different from each other.
JP-A 2003-320703 or the like discloses a method in which the laser light power of a laser light source is made low at the vicinity of the center of the lens according to the scanning position of the laser, and is made high at the end of the lens, so that the difference in power loss due to the transmissivity cancels out, the laser light power on the surface of the photoconductive drum is uniformed, and the exposure amount is made constant.
In the techniques disclosed in these, light amount correction values corresponding to the scan positions of the laser are prepared, and the adjustment of the laser light power is performed based on the light amount correction values.
Heretofore, with respect to the light amount correction values, the same memory capacity is secured for each of the colors, the absolute amount of the correction values is stored, and a correction circuit of correcting the light amount has a circuit structure of such a system that the value, the absolute amount of the correction value is directly used.
It is necessary that the correction circuit of the light amount processes a large amount of image data at real time, and high speed is required. Thus, it is necessary that the processing from the reading of the correction value to the D/A conversion is processed by the hardware, and a memory (RAM: Random Access Memory) to store these correction values is incorporated in an ASIC (Application Specific Integrated Circuit) or the like or a dedicated high speed RAM is used.
In the conventional system, when the light amount correction is performed, when the resolution of correction (the resolution here means two resolutions of 1) the resolution relating to the number of divided blocks in the main scanning direction, and 2) the resolution relating to the number of bits of a D/A converter used at the correction) is improved, the RAM capacity is increased in proportion thereto. Since picture quality required for an image forming apparatus becomes finer by a recent technical advance, these correction amounts tend to increase, and in the system in which the correction values are stored in all RAMs as they are, the increase of the correction information causes the increase of the RAM capacity, and causes the increase of cost.
The invention has been made in view of the above circumstances, and it is an object to provide an image forming apparatus in which in an image forming apparatus of an electrophotographic system, a light amount correction, in a main scanning direction, of laser light to expose a photoconductive body can be realized with a small memory capacity while keeping correction accuracy, and an image forming method.
In order to achieve the above object, the image forming apparatus according to an aspect of the invention includes plural photoconductive bodies for forming a color image, an exposure unit configured to scan a laser light in a main scanning directions of each of the photoconductive bodies and to perform exposure, and a light amount correction unit configured to create, for each of the plural photoconductive bodies, light amount correction data for correcting a light amount of the laser light outputted from the exposure unit so that a light receiving sensitivity of each of the plural photoconductive bodies in the main scanning direction becomes uniform, and the light amount correction unit includes a first storage unit configured to store reference correction data, a second storage unit configured to store relative correction data represented, when the reference correction data is made an absolute amount, by a relative amount correspondingly to each of the plural photoconductive bodies, and a combining unit configured to combine the reference correction data and the relative correction data to create the light amount correction data.
Besides, in order to achieve the above object, the image forming method according to another aspect of the invention is the image forming method of an image forming apparatus including plural photoconductive bodies for forming a color image, and an exposure unit configured to scan a laser light in a main scanning direction of each of the plural photoconductive bodies and to perform exposure, and includes a light amount correction step of creating, for each of the plural photoconductive bodies, light amount correction data for correcting a light amount of the laser light outputted from the exposure unit so that a light receiving sensitivity in the main scanning direction of each of the plural photoconductive bodies becomes uniform, and the light amount correction step includes storing reference correction data into a first storage unit, storing relative correction data represented, when the reference correction data is made an absolute amount, by a relative amount into a second storage unit correspondingly to each of the plural photoconductive bodies, and combining the reference correction data and the relative correction data to create the light amount correction data.
In the attached drawings:
Embodiments of an image forming apparatus and an image forming method of the invention will be described with reference to the accompanying drawings.
In the scanner unit 2, a document is read, and image data of, for example, three primary colors of R, G and B are created. In the image processing unit 3, color conversion processing from the three primary colors of R, G and B to four print colors of K (black), C (cyan), M (magenta) and Y (yellow) is performed on the respective image data, and further, various image processings are performed.
The image-processed K signal, C signal, M signal and Y signal are inputted to the exposure unit 4. The exposure unit 4 includes a laser oscillator (not shown) and generates laser lights corresponding to the intensities of the K signal, the C signal, the M signal and the Y signal.
The laser light generated by the exposure unit 4 is scanned by the polygon mirror 17 and the f-θ lens 18 in the main scanning direction, and is irradiated to photoconductive bodies 7a, 7b, 7c and 7d in the process cartridges 6a, 6b, 6c and 6d through the laser light path deflection unit 19.
The process cartridges 6a, 6b, 6c and 6d correspond to the four colors for color printing, including the four process cartridges for the K signal, the C signal, the M signal and the Y signal, and are structured to be attachable/detachable to/from the image forming apparatus 1. The basic structures of the respective process cartridges 6a, 6b, 6c and 6d are the same although the colors of toners included in developing units 8a, 8b, 8c and 8d are different. Then, in the following description concerning the process cartridge, the suffixes of a, b, c and d attached to reference numerals will be omitted and the description will be made.
The process cartridge 6 includes the photoconductive body 7, the developing unit 8, and a charging device 10. The surface of the photoconductive body 7 is charged to a specified potential by the charging device 10, and the electrostatic latent image is formed on the surface by the laser light irradiated from the exposure unit 4. The electrostatic latent image is developed with the toner supplied from the developing unit 8, and the developed image corresponding to each toner color is formed on the surface of the photoconductive body 7.
The developed image formed on the photoconductive body 7 is superimposed and transferred onto the intermediate transfer belt 11 in the order of Y, M, C and K, and at the time point when it passes through the photoconductive body 7a for K, full color toner images in which the four colors are combined are formed on the intermediate transfer belt 11.
The toner images on the intermediate transfer belt 11 are transferred in the recording sheet transfer unit 14 to the recording sheet supplied from the paper feed unit 13. The toner images transferred to the recording paper are fixed to the recording sheet in the fixing unit 15, and it is discharged to the outside from the paper discharge unit 16.
Although four laser lights generated in the exposure unit 4 reach the respective photoconductive bodies 7 through the polygon mirror 17, the f-θ lens 18, and the laser light path deflection unit 19, since paths of the respective colors are not necessarily completely identical to each other, attenuation amounts are slightly different in the respective colors. Besides, as described before, since the transmissivity of the f-θ lens 18 is high at the center and low at both ends, it does not become uniform in the main scanning direction of the photoconductive body.
Further, the output characteristic of the laser oscillator and the sensitivity characteristic of the photoconductive body 7 are influenced by aging and environmental change.
In order to correct the irregularity and the change of the characteristics, correction of the power of a laser light is generally adopted, and this correction is performed based on the light amount correction data generated by the light amount correction unit 5.
Before a light amount correction of the image forming apparatus 1 according to the first embodiment of the invention is described, a light amount correction generally performed will be roughly described.
The light amount correction in the main scanning direction is performed by a main scanning direction light amount correction unit 101 in
On the other hand, the light amount correction of aging or the like is performed by an aging etc. light amount correction unit 52. These two kinds of correction values are combined, and the combined correction data is outputted as light amount correction data from the light amount correction unit 100 to the exposure unit 4.
The exposure unit 4 determines the laser light powers of Y, M, C, K based on the light amount correction data and the image data outputted from the image processing unit 3, and supplies them to the photoconductive body 7.
Thus, the exposure amount (
To cope with this problem, as shown in
The correction data of the laser light power is previously stored in a storage unit 102 of the main scanning direction light amount correction unit 101, and the correction data is read from the storage unit 102 at a timing of the main scanning of the laser light.
A timing signal for reading, for example, a read control signal of the storage unit 102 or address data is generated by a timing signal generating unit 53 based on a detection signal (main scanning position detection signal) from a laser light sensor 20 (see
Since scanning in the main scanning direction is performed at high speed, the timing signal generation unit 53 is generally constructed of a hardware logic circuit, and is often constructed as an ASIC (Application Specific Integration Circuit) for miniaturization. Besides, since the storage unit 102 requires high speed reading, it is constructed of dedicated high speed REM. The high speed RAM may be incorporated in the ASIC.
In the example of
As shown in
Therefore, as shown in
Further, conventionally, each of the light amount correction data is stored as “absolute amount” for each of the colors as it is. That is, the light amount correction data stored in the storage unit 102 is directly D/A converted as it is, and is applied to the laser oscillator of the exposure unit 4.
However, when a demand for high picture quality is raised as in recent times, the need for more finely performing the light amount correction in the main scanning direction has been intensified. Thus, it is necessary to raise both the resolution of the correction in the main scanning direction (that is, the resolution in such a meaning that a division is made into how many blocks in the main scanning direction and the correction is performed) and the resolution of the correction data (that is, the resolution in such a meaning that as the magnitude of the correction data, the correction data of how many bits is formed).
The improvement of the resolution in the main scanning direction increases the RAM address in
Thus, it is an important problem that the RAM capacity is reduced while the accuracy (fineness) of the correction is made high, and the point of the invention is to solve this problem, Hereinafter, the light amount correction according to embodiments of the invention will be described.
The light amount correction unit 5 includes a main scanning direction light amount correction unit 51 to create light amount correction data in the main scanning direction, an aging etc correction unit 52 to create correction data to aging, environmental change or the like, and a second combining unit 57 to combine these correction data by addition/subtraction and the like.
The main scanning direction light amount correction unit 51 includes, as its inner structure, a timing signal generation unit 53, a first storage unit 54, a second storage unit 55, and a first combining unit 56.
The first embodiment is the embodiment in which specified areas of a RAM are allocated as the first storage unit 54 and the second storage unit 55. One light amount correction data selected as reference correction data among the light amount correction data for Y, M, C and K is stored in the first storage unit 54 of these. Besides, difference data relative to the reference correction data is stored as relative correction data in the second storage unit 55.
For example, as exemplified in
The respective light amount correction data for Y, M, C and K are the correction data relatively close to each other although the values are different. Thus, the values of the difference data ΔM, ΔC and ΔK are small values as compared with the absolute amount of the light amount correction data.
When the light amount correction data for Y as the reference correction data is represented by a size of 8 bits, the values of the difference data ΔM, ΔC and ΔK can be small values of, for example, about 2 to 4 bits.
Thus, as exemplified in
The reference correction data stored in the first storage unit 54 and the relative correction data stored in the second storage unit 55 are added and combined in the first combining unit 56, and as shown in
The main scanning direction light amount correction data is added to and combined with the aging etc. light amount correction data in the second combining unit 57, and is outputted as final light amount correction data to the exposure unit 4.
As kinds of the reference correction data and the relative correction data, various modes are conceivable in addition to this.
For example, as shown in
In this case, since the reference correction data becomes one value, it is unnecessary to store it in the RAM, and as shown in
In addition, for example, as shown in
In this case, although the reference correction data have four values, also in this case, it is not necessary to store them in the RAM, and as shown in
In the latter mode, although the number of registers is increased from 1 to 4, with respect to the relative correction data, since the basis of the difference data is the average value or the center value of each of the light amount correction data, the value of the difference data can be small as compared with the former mode, and accordingly, the saving effect of the RAM area becomes high.
According to contents of light amount correction curves, since correction start positions of respective colors are mutually shifted, there is a case where although the shapes themselves of the correction curves are very close to each other, different kinds of correction data must be eventually held for the respective colors.
In such a case, there is a case where only one light amount correction curve is stored in the RAM, and desired light amount correction data to the respective colors can be created by shifting the correction start positions of the respective colors with respect to the read output.
Besides, even if the shapes of the correction curves are not completely coincident with each other, the value of the relative correction data can be made small by adding the function (function of the correction start position adjustment unit 58) to shift the correction start position.
Among the difference data of the respective colors, since the difference (shift amount) in the main scanning direction is corrected by the correction start position adjustment unit 58, as the relative correction data to be stored in the second storage unit 55, only the difference in an amplitude direction may be stored, and as a result, the storage capacity can be further saved.
As described above, according to the image forming apparatus of the embodiment and the image forming method (light amount correction method), in the image forming apparatus of the electrophotographic system, the light amount correction in the main scanning direction of the laser light to expose the photoconductive body can be realized with a small memory capacity while the correction accuracy is maintained.
It should be understood that the present invention is by no means restricted to the above-described embodiments; rather, in carrying out the invention, various alterations and modifications may be made with regard to the components without departing from the spirit and scope of the present invention. Further, various arrangements may be made within the scope of the present invention by arranging the components in various ways, or by omitting one or more of the components. Moreover, arrangements obtained by suitably combining the components of the above-described embodiments with components of other embodiments according to the present invention are also encompassed by the present invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4794413 | Yamazaki et al. | Dec 1988 | A |
| 5099260 | Sato et al. | Mar 1992 | A |
| 5380610 | Haneda et al. | Jan 1995 | A |
| 5687002 | Itoh | Nov 1997 | A |
| Number | Date | Country |
|---|---|---|
| 59037570 | Mar 1984 | JP |
| H02-58019 | Feb 1990 | JP |
| 2000-71510 | Mar 2000 | JP |
| 2003-320703 | Nov 2003 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20080024588 A1 | Jan 2008 | US |
