Belt driver, image forming apparatus, and method that can reduce the time until speed control of a belt is performed Number:7,133,627 from the United States Patent and Trademark Office (PTO) owispatent A belt driver includes a belt having a constant number of regions dividing the belt in the perimeter direction thereof. A plurality of marks have different widths in the perimeter direction and are formed in the respective regions of the belt. A sensor detects the marks on the belt. A storage part stores in advance the relationship between position information of the belt and speed variation of the belt for one rotation of the belt. Speed variation of the belt is reduced by correcting the drive speed of the belt based on the relationship. The position of the belt is detected from a time required for one of the marks to pass the sensor, and speed correction control of the belt is performed in accordance with the detected position.<H performed, apparatus, Belt, driver, ima, 7133627.html, Patent, pto, 7133627

Title: Belt driver, image forming apparatus, and method that can reduce the time until speed control of a belt is performed

Abstract: A belt driver includes a belt having a constant number of regions dividing the belt in the perimeter direction thereof. A plurality of marks have different widths in the perimeter direction and are formed in the respective regions of the belt. A sensor detects the marks on the belt. A storage part stores in advance the relationship between position information of the belt and speed variation of the belt for one rotation of the belt. Speed variation of the belt is reduced by correcting the drive speed of the belt based on the relationship. The position of the belt is detected from a time required for one of the marks to pass the sensor, and speed correction control of the belt is performed in accordance with the detected position.

Patent Number: 7,133,627 Issued on 11/07/2006 to Nishizaki

Inventors: Nishizaki; Shingo (Kanagawa, JP)
Assignee: Ricoh Company, Ltd. (Tokyo, JP)

Appl. No.: 10/742,059

Filed: December 18, 2003

Foreign Application Priority Data


Dec 20, 2002 [JP]			2002-370124
Feb 26, 2003 [JP]			2003-049674
Nov 10, 2003 [JP]			2003-380385

Current U.S. Class: 399/167 ; 399/297

Current International Class: G03G 15/00 (20060101); G03G 15/16 (20060101)

Field of Search: 399/162,165,167,297,301 347/116 198/810.03

References Cited [Referenced By]

U.S. Patent Documents


5452073	September 1995	Kataoka
5523823	June 1996	Ashikaga
5854958	December 1998	Tanimoto et al.
5995717	November 1999	Tanaka
6222566	April 2001	Takeyama et al.
6282396	August 2001	Iwata et al.
6317147	November 2001	Tanaka
6336019	January 2002	Castelli et al.
2001/0004425	June 2001	Shinohara et al.
2002/0136570	September 2002	Yamanaka et al.

Foreign Patent Documents


10141446	Mar., 2002	DE
0575162	Dec., 1993	EP
0919882	Jun., 1999	EP
57120970	Jul., 1982	JP
61278871	Dec., 1986	JP
03260664	Nov., 1991	JP
04016969	Jan., 1992	JP
8-328443	Dec., 1996	JP
11-249380	Sep., 1999	JP
2001-51479	Feb., 2001	JP

Primary Examiner: Gray; David M.
Assistant Examiner: Gleitz; Ryan
Attorney, Agent or Firm: Cooper & Dunham LLP

Claims

What is claimed is:

1. A belt driver, comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of marks having different widths in the perimeter direction and formed in said respective regions of said belt; a sensor detecting said marks on said belt; and a storage part storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected from a time required for one of said marks to pass said sensor, and speed correction control of said belt is performed in accordance with the detected position.

2. The belt driver of claim 1, wherein said marks are formed prior to a time that image formation is requested.

3. The belt driver of claim 1, the information stored in said storage part indicates for each position a corresponding speed variation of said belt.

4. A belt driver, comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of linear marks having different widths in a main scan direction and formed in said respective regions of said belt; a sensor detecting said marks on said belt; and a storage part storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by comparing a predetermined value with a detected value of said sensor, and speed correction control of said belt is performed in accordance with the detected position.

5. A belt driver, comprising: a belt; one or more marks on said belt; a plurality of sensors that detects said marks on said belt; and a storage part storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by detecting one of said marks by one of said sensors, and speed correction control of said belt is performed in accordance with the detected position.

6. An image forming apparatus, comprising: a belt driver comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of linear marks having different width in a main scan direction and formed in said respective regions of said belt; a sensor detecting said marks on said belt; and a storage part storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by comparing a predetermined value with a detected value of said sensor, and speed correction control of said belt is performed in accordance with the detected position.

7. An image forming apparatus, comprising: a belt driver comprising: a belt; one or more marks on said belt; a plurality of sensors that detects said marks on said belt; and a storage part storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by detecting one of said marks by one of said sensors, and speed correction control of said belt is performed in accordance with the detected position.

8. A belt driver, comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of marks having different widths in the perimeter direction and formed in said respective regions of said belt; sensing means for detecting said marks on said belt; and storage means for storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected from a time required for one of said marks to pass said sensing means, and speed correction control of said belt is performed in accordance with the detected position.

9. A belt driver, comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of linear marks having different widths in a main scan direction and formed in said respective regions of said belt; sensing means for detecting said marks on said belt; and a storing means for storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by comparing a predetermined value with a detected value of said sensing means, and speed correction control of said belt is performed in accordance with the detected position.

10. A belt driver, comprising: a belt; one or more marks on said belt; a plurality of sensing means for detecting said marks on said belt; and storage means for storing in advance a prior to an image formation request relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by detecting one of said marks by one of said sensing means, and speed correction control of said belt is performed in accordance with the detected position.

11. An image forming apparatus, comprising: a belt driver comprising: a belt having a constant number of regions dividing said belt in a perimeter direction thereof; a plurality of linear marks having different width in a main scan direction and formed in said respective regions of said belt; sensing means for detecting said marks on said belt; and storage means for storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by comparing a predetermined value with a detected value of said sensing means, and speed correction control of said belt is performed in accordance with the detected position.

12. An image forming apparatus, comprising: a belt driver comprising: a belt; one or more marks on said belt; a plurality of sensing means for detecting said marks on said belt; and storage means for storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, wherein speed variation of said belt is reduced by correcting drive speed of said belt based on the relationship, and wherein a position of said belt is detected by detecting one of said marks by one of said sensing means, and speed correction control of said belt is performed in accordance with the detected position.

13. A method of driving a belt, comprising the steps of: forming a constant number of regions on said belt, said regions dividing said belt in a perimeter direction thereof; forming a plurality of marks having different widths in the perimeter direction in said respective regions of said belt; detecting said marks on said belt by a sensor; storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, reducing speed variation of said belt by correcting drive speed of said belt based on the relationship, and detecting a position of said belt from a time required for one of said marks to pass said sensor, and performing speed correction control of said belt in accordance with the detected position.

14. A method of driving a belt, comprising the steps of: forming a constant number of regions on said belt, said regions dividing said belt in a perimeter direction thereof; forming a plurality of linear marks having different widths in a main scan direction in said respective regions of said belt; detecting said marks on said belt by a sensor; and storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, reducing speed variation of said belt by correcting drive speed of said belt based on the relationship, and detecting a position of said belt by comparing a predetermined value with a detected value of said sensor, and performing speed correction control of said belt in accordance with the detected position.

15. A method of driving a belt, comprising the steps of: forming one or more marks on said belt; detecting said marks on said belt by a plurality of sensors; and storing in advance prior to an image formation request a relationship between position information of said belt and speed variation of said belt for one rotation of said belt, reducing speed variation of said belt by correcting drive speed of said belt based on the relationship, and detecting a position of said belt by detecting one of said marks by one of said sensors, and performing speed correction control of said belt in accordance with the detected position.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to image forming apparatuses and to belt drivers that perform speed correction control of belts, such as carrying belts and transfer belts.

2. Description of the Related Art

In these days, based on the requirements of the marketplace, there are many electrophotographic apparatuses that output color images, such as color copying apparatuses and color printers. Especially nowadays, it is expected for electrophotographic apparatuses forming full-color images to achieve the speed as fast as that of electrophotographic apparatuses forming black-and-white images. Thus, mainstream printers are printers that are provided with a developing apparatus for each of a plurality of photo conductors, form a monochrome toner image on each of the photo conductors, sequentially superimpose the monochrome toner images, and transfer the images to paper so as to record a color image thereon.

Tandem printers include direct transfer printers and indirect transfer printers. As shown in FIG. 1, in a direct transfer printer, images of respective colors formed on photo conductors 2K, 2M, 2C and 2Y by image forming means 1K, 1M, 1C and 1Y are sequentially superimposed on paper that is carried by a transfer belt 4 by transfer apparatuses 3K, 3M, 3C and 3Y, respectively. As shown in FIG. 2, in an indirect transfer printer, images of respective colors formed on photo conductors 5K, 5M, 5C and 5Y are sequentially superimposed on a transfer belt 7 by transfer apparatuses 6K, 6M, 6C and 6Y, respectively. Then, the images on the transfer belt 7 are simultaneously transferred to paper by a secondary transfer apparatus 8.

In each of the direct transfer printer and the indirect transfer printer, the images of the respective colors are transferred to the transfer belt 4(7) at different positions thereon. Thus, image data of the respective colors are output to the image forming means 1K, 1M, 1C and 1Y with respective delays corresponding to the intervals among the photo conductors. For this reason, when the moving speed of the transfer belt 4(7) is not constant, a shift occurs to the transfer positions to which the images of the respective colors are to be transferred. As a result, color shift occurs with the formed image. Therefore, it is necessary for tandem electrophotographic apparatuses to control with a high accuracy the speed of the transfer belt such that it is constant at all times.

However, it is structurally difficult for the transfer belt 4(7), which is used here, to realize a uniform thickness. Especially, the thickness variation tends to be generated in the longitudinal direction (direction of movement). In a case where the thickness of the transfer belt 4(7) is not uniform, even if the rotating speed of a drive shaft driving the transfer belt 4(7) is controlled to be constant, periodic speed variation occurs in the surface speed of the transfer belt 4(7). For this reason, tandem printers have a problem in that shifts occur in the transfer positions to which images of respective colors are to be transferred, which tends to result in out of color registration of a formed image.

In order to correct the speed variation that is synchronized with the rotation period of the transfer belt, a method is conceived which measures in advance the thickness variation or the speed variation for one rotation of the transfer belt, and corrects the rotating speed of the drive shaft of the transfer belt or the write timings of respective colors based on the information, so as to reduce the speed variation of the transfer belt. However, it is impossible to correct the speed of the transfer belt unless it is determined which position of the transfer belt is being driven. Hence, a method is conceived that marks a home position mark 11 representing a reference point on the transfer belt 4(7) as shown in FIG. 3, and detects the home position mark 11 by a sensor 12 as shown in FIG. 4, so as to detect a home position (hereinafter referred to as a "HP") of the transfer belt 4(7).

When forming an image, it is possible to control the speed of the transfer belt 4(7) by starting the running of the transfer belt 4(7), thereafter starting a detecting process of the home position mark 11 by the sensor 12, and, when the home position mark 11 on the transfer belt 4(7) is detected by the sensor 12, starting a speed correction control of the transfer belt 4 (7) based on speed correction data that are prepared in advance (refer to Japanese Laid-Open Patent Application No. 8-328443, for example).

Japanese Laid-Open Patent Application No. 2001-51479 describes an image forming apparatus that includes: a plurality of image forming means; an endless movable body that places and conveys a recording medium such that respective images formed by the plurality of image forming means are transferred to the recording medium at the transfer positions; a position detecting means for detecting a placing position at which the recording medium is placed on the endless movable body; and correcting means for correcting the image formation timings of the plurality of image forming means based on a detection output of the position detecting means.

Japanese Laid-Open Patent Application No. 11-249380 describes a color image forming apparatus that forms a color image on a recording medium by sequentially superimposing and transferring, to the recording medium carried by the carrying belt, images formed by a plurality of electronic process parts, including image carriers, arranged along a carrying belt. The color image forming apparatus includes: a light emitting element illuminating the carrying belt; a slit through which the light transmitted through or reflected by the carrying belt passes; a light receiving element receiving the light that passes through the slit; a shift amount detector for detecting a position shift amount of a detection pattern, the shift amount detector having means for processing a signal from the light receiving element; pattern forming means for activating each of the electronic process parts such that the same electronic process part forms a plurality of pairs of toner marks as the position shift amount detection pattern for each color with the shape corresponding to the slit, each pair including two toner marks of the same color and the same shapes, one toner mark of the pair is distant from the other toner mark for the half peripheral length of the image carrier, and adjacent toner marks among the plurality of pairs of toner marks are formed with a predetermined distance (hereinafter referred to as a "mark pitch") therebetween. The toner marks formed by the pattern forming means are detected by the shift amount detector. The shift amounts among respective images formed by the electronic process parts are detected. Among the plurality of pairs of toner marks, when focusing attention to the first formed toner mark (hereinafter referred to as a "reference mark") of two toner marks constituting a pair of toner marks formed by a predetermined reference color, a toner mark for correction (hereinafter referred to as a "correction mark") is formed while setting the target to the position that is distant for one peripheral length of the image carrier that forms the reference mark. The correction mark is also the target to be detected by the shift amount detector.

In tandem printers, the peripheral length of the transfer belt 4 (7) becomes structurally long. Thus, depending on the stop position of the transfer belt 4(7), there is a problem in that it takes a long time for the sensor 12 to detect the home position mark 11 on the transfer belt 4(7) after the rotation of the transfer belt 4(7) is resumed when an image forming process is started, which results in a long time until an image is formed.

In order to make the time shorter in which the sensor 12 detects the home position mark 11 on the transfer belt 4(7) after the rotation of the transfer belt 4(7) is resumed when the image forming process is started, a method is conceived in which the home position mark 11 on the transfer belt 4(7) is detected by the sensor 12 at the time the transfer belt 4(7) is stopped, and the transfer belt 4(7) is stopped such that the home position mark 11 always comes immediately before the sensor 12 based on a detected signal. However, this method has a problem in that the life of the transfer belt is shortened since the transfer belt is rotated more than necessary. Additionally, the method has another problem in that, when the apparatus is stopped since, for example, the cover is opened or a jam occurs while forming an image, it is impossible to set the stop position of the transfer belt to a predetermined position.

Therefore, it is desired to perform speed control of the transfer belt by detecting the current relative position of the transfer belt as quickly as possible after an image forming process is started, irrespective of the stop position of the transfer belt.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improved and useful belt driver and an image forming apparatus in which one or more of the above-mentioned problems are eliminated.

A more specific object of the present invention is to provide a belt driver capable of reducing the time required until speed control of a belt is performed.

A further object of the present invention is to provide an image forming apparatus capable of reducing the time required until speed control of a belt is performed and reducing the time required to form a first image.

In order to achieve the above-mentioned objects, according to one aspect of the present invention, there is provided a belt driver including:

a belt having a constant number of regions dividing the belt in a perimeter direction thereof;

a plurality of marks having different widths in the perimeter direction and formed in the respective regions of the belt;

a sensor detecting the marks on the belt; and

a storage part storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

wherein speed variation of the belt is reduced by correcting drive speed of the belt based on the relationship, and

wherein a position of the belt is detected from a time required for one of the marks to pass the sensor, and speed correction control of the belt is performed in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided an image forming apparatus including the above-mentioned belt driver.

Additionally, according to anther aspect of the present invention, there is provided a belt driver including:

a belt having a constant number of regions dividing the belt in a perimeter direction thereof;

a plurality of marks formed in the respective regions of the belt, the marks each being constituted by one or more lines of a number indicating a corresponding one of the regions,;

a sensor detecting the marks on the belt; and

a storage part storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

wherein speed variation of the belt is reduced by correcting drive speed of the belt based on the relationship, and

wherein a position of the belt is detected by counting the number of lines of one of the marks in a corresponding one of the regions from a detected signal of the sensor, and speed correction control of the belt is performed in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided an image forming apparatus including the above-mentioned belt driver.

Additionally, according to another aspect of the present invention, there is provided a belt driver including:

a belt having a constant number of regions dividing the belt in a perimeter direction thereof;

a plurality of linear marks having different width in a main scan direction and formed in the respective regions of the belt;

a sensor detecting the marks on the belt; and

a storage part storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

wherein speed variation of the belt is reduced by correcting drive speed of the belt based on the relationship, and

wherein a position of the belt is detected by comparing a predetermined value with a detected value of the sensor, and speed correction control of the belt is performed in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided an image forming apparatus including the above-mentioned belt driver.

Additionally, according to another aspect of the present invention, there is provided a belt driver including:

a belt;

one or more marks on the belt;

a plurality of sensors that detects the marks on the belt; and

a storage part storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

wherein speed variation of the belt is reduced by correcting drive speed of the belt based on the relationship, and

wherein a position of the belt is detected by detecting one of the marks by one of the sensors, and speed correction control of the belt is performed in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided an image forming apparatus including the above-mentioned belt driver.

Additionally, according to another aspect of the present invention, there is provided a belt driver including:

a belt;

a home position mark provided on the belt;

a detecting part that detects the home position mark;

a measuring part that measures a variation relating to a moving amount of the belt;

a temporary storage memory that stores position information of a stop position of the belt; and

a storage part storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

wherein speed variation of the belt is reduced by correcting drive speed of the belt based on the relationship, and

wherein the stop position of the belt is calculated by measuring, by the measuring means, the variation until the belt is stopped since the home position mark is detected by the detecting part, the position information in the temporary storage memory is updated by the calculated position information, and, at the time of next activation, speed control of the belt is performed in accordance with the updated position information.

Additionally, according to another aspect of the present invention, there is provided an image forming apparatus including the above-mentioned belt driver.

Additionally, according to another aspect of the present invention, there is provided a method of driving a belt that includes the steps of:

forming a constant number of regions on the belt, the regions dividing the belt in a perimeter direction thereof;

forming a plurality of marks having different widths in the perimeter direction in the respective regions of the belt;

detecting the marks on the belt by a sensor;

storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

reducing speed variation of the belt by correcting drive speed of the belt based on the relationship, and

detecting a position of the belt from a time required for one of the marks to pass the sensor, and performing speed correction control of the belt in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided a method of driving a belt that includes the steps of:

forming a constant number of regions on the belt, the regions dividing the belt in a perimeter direction thereof;

forming a plurality of marks in the respective regions of the belt, the marks each being constituted by one or more lines of a number indicating a corresponding one of the regions;

detecting the marks on the belt by a sensor; and

storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

reducing speed variation of the belt by correcting drive speed of the belt based on the relationship, and

detecting a position of the belt by counting the number of lines of one of the marks in a corresponding one of the regions from a detected signal of the sensor, and performing speed correction control of the belt in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided a method of driving a belt that includes the steps of:

forming a constant number of regions on the belt, the regions dividing the belt in a perimeter direction thereof;

forming a plurality of linear marks having different widths in a main scan direction in the respective regions of the belt;

detecting the marks on the belt by a sensor; and

storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

reducing speed variation of the belt by correcting drive speed of the belt based on the relationship, and

detecting a position of the belt by comparing a predetermined value with a detected value of the sensor, and performing speed correction control of the belt in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided a method of driving a belt that includes the steps of:

forming one or more marks on the belt;

detecting the marks on the belt by a plurality of sensors; and

storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

reducing speed variation of the belt by correcting drive speed of the belt based on the relationship, and

detecting a position of the belt by detecting one of the marks by one of the sensors, and performing speed correction control of the belt in accordance with the detected position.

Additionally, according to another aspect of the present invention, there is provided a method of driving a belt that includes the steps of:

forming a home position mark on the belt;

detecting the home position mark;

measuring a variation relating to a moving amount of the belt;

storing position information of a stop position of the belt; and

storing in advance a relationship between position information of the belt and speed variation of the belt for one rotation of the belt,

reducing speed variation of the belt by correcting drive speed of the belt based on the relationship, and

calculating the stop position of the belt by measuring the variation until the belt is stopped since the home position mark is detected, updating the position information by the calculated position information, and, at the time of next activation, performing speed control of the belt in accordance with the updated position information.

According to the present invention, it is possible to reduce the time required until speed control of a belt is performed.

Also, it is possible to provide an image forming apparatus capable of reducing the time required for speed control of a belt and reducing the time required to form a first image.

Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a tandem direct transfer printer;

FIG. 2 is a cross-sectional view showing a tandem indirect transfer printer;

FIG. 3 is a perspective view of a transfer belt of a conventional tandem printer;

FIG. 4 is a schematic diagram showing a sensor and the transfer belt shown in FIG. 3 before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 5 is a cross-sectional view of Embodiment 1 of the present invention;

FIG. 6 is a plan view of a transfer belt in Embodiment 1 before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 7 is a flow chart showing an operation flow in Embodiment 1;

FIG. 8 is a schematic diagram showing the transfer belt and a sensor in Embodiment 1;

FIG. 9 is a schematic diagram showing the transfer belt and another sensor;

FIG. 10 is a schematic diagram showing the transfer belt and still another sensor;

FIG. 11 is a plan view of a transfer belt in Embodiment 2 of the present invention before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 12 is a schematic diagram showing marks on the transfer belt;

FIG. 13 is a flow chart showing an operation flow in Embodiment 2;

FIG. 14 is a plan view of a transfer belt in Embodiment 3 of the present invention before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 15 is a flow chart showing an operation flow in Embodiment 3;

FIG. 16 is a plan view of the transfer belt in Embodiment 4 of the present invention before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 17 is a schematic diagrams showing marks on the transfer belt;

FIG. 18 is a flow chart showing an operation flow in Embodiment 4;

FIG. 19 is a perspective view of a sensor and a transfer belt in Embodiment 5;

FIG. 20 is a perspective view of a sensor and a transfer belt in Embodiment 6;

FIG. 21 is a plan view of the transfer belt in Embodiment 6 of the present invention before a state where the transfer belt is formed into an endless shape by interposing both ends thereof;

FIG. 22 is a block diagram showing a motor control apparatus in Embodiment 7 of the present invention;

FIG. 23 is a flow chart showing an operation flow in Embodiment 7;

FIG. 24 is a timing chart for explaining an operation of a counter in Embodiment 7;

FIG. 25 is a flow chart showing an operation of Embodiment 8 of the present invention;

FIG. 26 is a flow chart showing an operation of Embodiment 9 of the present invention; and

FIG. 27 is a flow chart showing an operation of Embodiment 10 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 shows Embodiment 1 of the present invention. Embodiment 1 is a printer serving as an image forming apparatus. The printer is a tandem color printer, which is an electrophotographic apparatus. The color printer employs a direct color system which forms a color image on paper serving as a transfer medium that is carried by a carrying apparatus 14 by sequentially transferring and superimposing images of respective colors formed by image forming units 13K, 13M, 13C and 13Y, which serve as a plurality of image forming means.

The image forming units 13K, 13M, 13C and 13Y are constituted by arranging charging apparatuses (not shown), write units 16K, 16M, 16C and 16Y serving as exposing means, developing units 17K, 17M, 17C and 17Y, and cleaning apparatuses (not shown) around drum photo conductors (photosensitive drums) 15K, 15M, 15C and 15Y serving as image carriers, respectively. The carrying apparatus 14 is constituted by an endless transfer belt 18, and a drive roller 19 and a driven roller 20 that support the transfer belt 18. The transfer belt 18 is rotated such that the drive roller 19 is driven by a transfer belt driving motor (hereinafter referred to as a "motor"), which motor is coupled to the shaft of the drive roller 19. The motor is controlled by a control part 21 such that the transfer belt 18 is rotated at a constant speed. A transfer unit is constituted by the transfer belt 18, and transfer rollers 22K, 22M, 22C and 22Y that face the photosensitive drums 15K, 15M, 15C and 15Y, respectively, via the transfer belt 18. The transfer rollers 22K, 22M, 22C and 22Y are applied with transfer bias by a power source (not shown).

Referring to FIG. 5, a description is given below of a procedure for forming a color image on paper in Embodiment 1.

First, image data are broken down into image data of respective colors, i.e., cyan (C), magenta (M), yellow (Y) and black (K), converted to write data of respective colors, and sent to the write unit 16K, 16M, 16C and 16Y serving as the exposing means by the control part 21. The write units 16K, 16M, 16C and 16Y convert the image data of respective colors, i.e., K, M, C and Y, from the control part 21 to optical signals such as laser beams, and expose the photosensitive drums 15K, 15M, 15C and 15Y, respectively, with the optical signals.

The photosensitive drums 15K, 15M, 15C and 15Y are rotated by respective drive parts (not shown) and uniformly charged by the charging apparatuses. The photosensitive drums 15K, 15M, 15C and 15Y are exposed by the optical signals such as laser beams from the write units 16K, 16M, 16C and 16Y. Thereby, electrostatic latent images corresponding to the image data of respective colors, i.e., C, M, Y and K are formed. The electrostatic latent images on the photosensitive drums 15K, 15M, 15C and 15Y are developed by the developing units 17K, 17M, 17C and 17Y with toners of K, M, C and Y, and toner images K, M, C and Y are formed, respectively.

Paper serving as a transfer medium is supplied from a paper feeder (not shown) to the transfer belt 18 via resist rollers 23. The paper is carried by the transfer belt 18, and the toner images of respective colors on the photosensitive drums 15K, 15M, 15C and 15Y are sequentially transferred and superimposed on the paper to form a color image by applying transfer bias from the power source (not shown) to the transfer belt 18 via the transfer rollers 22K, 22M, 22C and 22Y. Then, the color image is fixed to the paper by a fixing part 24, and the paper is delivered to the outside. Residual toners on the photosensitive drums 15K, 15M, 15C and 15Y are removed by the cleaning apparatuses (not shown) after the toner images are transferred, thereby preparing for the next image forming process.

The drive roller 19 is driven by the motor and thus the transfer belt 18 is rotated. The motor is controlled by the control part 21 such that the transfer belt 18 is rotated at a constant speed. When the thickness of the transfer belt 18 is not uniform, however, periodical speed variation occurs in the surface speed of the transfer belt 18. Therefore, in Embodiment 1, the relationship between position information of the transfer belt 18 and speed variation of the transfer belt 18 for one rotation is stored in storage means (storage part) in advance. The amount of speed variation of the transfer belt 18 is reduced or cancelled by correcting the drive speed of the transfer belt 18 based on the relationship. Also, marks are provided which have different widths in the peripheral length direction (moving direction) on respective regions of a predetermined number dividing the transfer belt 18, i.e., "divided regions", in the perimeter direction, and a sensor for detecting the marks on the transfer belt 18. The position of the transfer belt 18 is detected from the time required for one of the marks to pass the sensor. Speed correction control of the transfer belt corresponding to the detected position is performed.

FIG. 6 shows a state before both ends of the transfer belt 18 are overlapped to form the transfer belt 18 into an endless shape. The transfer belt 18 is divided into a plurality of regions, i.e., "divided regions", in the longitudinal direction (perimeter direction, i.e., moving direction), for example, eight regions a1 through a8. Marks M1 through M8, having different widths in the perimeter direction, are formed on the surfaces of the regions a1 through a8, respectively. In the illustrated exemplary embodiment, the marks M1 through M8 are formed outside the image forming region (the region corresponding to the image forming region of paper to be carried to which region a toner image is transferred) on the surface of the transfer belt 18. The marks M1 through M8 are formed in the respective regions a1 through a8 such that each mark extends in the moving direction of the transfer belt with the length of the corresponding region.

FIG. 7 shows an operation flow of Embodiment 1.

When an image forming (printing) start request is issued in step A1, the control part 21 drives the motor to rotate the transfer belt 18 at a constant speed for the length of one of the divided regions in step A2, then stops driving in step A4. Concurrently with the rotation of the transfer belt 18, in step A3, a HP sensor (not shown), which serves as a mark detecting sensor, detects the pattern (line pattern) of one of the marks M1 through M8 on the transfer belt 18.

The HP sensor, at a fixed position, is arranged to be able to detect the marks M1 through M8 on the transfer belt 18. As shown in FIG. 6, the patterns of the marks M1 through M8 on the transfer belt 18 are formed with different widths in the perimeter direction (moving direction) of the transfer belt 18 in the respective regions a1 through a8. The control part 21 determines the region of the transfer belt 18 that passes the HP sensor by detecting from an output signal of the HP sensor the width of the pattern of one of the marks M1 through M8 that passes the HP sensor during the rotation of the transfer belt 18.

In practice, when detecting the patterns of the marks M1 through M8 in step A3, the control part 21 performs a process for obtaining the width (line width) of one of the marks M1 through M8 (step A5) by binarizing the output signal of the HP sensor with a comparator, and measuring the time interval between the edges of the binarized signals with a timer. Based on the obtained line width, the control part 21 determines at which of the eight regions (i.e., a determined regions) of the transfer belt 18 the current position of the HP sensor is. Then, in step A6, the control part 21 reads the speed correction control data from a memory, serving as storage means, for one rotation of the transfer belt 18 with the speed correction data of the determined region as the starting point.

The memory stores in advance the relationship between position information of the transfer belt 18 and speed variation (speed correction data) of the transfer belt 18 for one rotation of the transfer belt 18. In step A7, the control part 21 starts speed control of the transfer belt 18 by controlling the speed of the motor based on the speed correction data that are read from the memory. In step A8, the control part 21 controls each part of the printer according to Embodiment 1 so that image output (image forming) is performed as mentioned above.

The correction control of speed variation that synchronizes with the period of one rotation of the transfer belt 18 is performed as follows.

The thickness variation or speed variation of the transfer belt 18 for one rotation from the reference position is measured in advance. The measured information is saved in the memory, serving as storage means, in the apparatus. The thickness variation or speed variation of the transfer belt 18 is measured by using a high-precision measuring device when assembling the apparatus. The results of the measurement are saved in the memory in the apparatus as the speed correction data.

The speed correction data are related to the positions of the regions a1 through a8 dividing the transfer belt 18. It is possible to read from the memory the speed correction data of an arbitrary region of the regions a1 through a8.

When driving the transfer belt 18, the control part 21 performs a process for reducing speed variation of the transfer belt 18 by controlling the rotation speed of the drive shaft of the transfer belt 18 (or the write timing of image data of respective colors by the write units 16K, 16M, 16C and 16Y) such that the speed variation of the transfer belt 18 is reduced or canceled based on the speed correction data.

The description is given above that the marks M1 through M8 are formed outside the image forming region of the transfer belt 18, and the HP sensor for mark detection detects the marks M1 through M8 by a reflective sensor 25 at a fixed position facing the front or outer surface of the transfer belt 18 as shown in FIG. 8. However, as shown in FIG. 9, the marks M1 through M8 may be formed in the respective regions a1 through a8 on the back surface of the transfer belt 18, and the marks M1 through M8 may be detected by the reflective sensor 25 at a fixed position facing the back or inner surface of the transfer belt 18. The reflective sensor 25 includes a light-emitting part 25a and a light-receiving part 25b. The reflective sensor 25 illuminates end parts of the transfer belt 18 where the marks M1 through M8 are provided by means of the light-emitting part 25a, and receives the reflected light by means of the light-receiving part 25b.

Additionally, in a case where the transfer belt 18 is made of a transparent material, as shown in FIG. 10, the light-emitting part 25a and the light-receiving part 25b, constituting the HP sensor for mark detection, may be arranged to interpose the transfer belt 18 therebetween. The marks M1 through M8 may be detected by receiving, by means of the light-receiving part 25b, light that is emitted from the light emitting part 25a and is transmitted through the parts of the transfer belt 18 where the marks M1 through M8 are provided.

According to Embodiment 1, the marks M1 through M8, having different widths in the perimeter direction, are formed in the respective regions a1 through a8 of the constant number, which regions divide the transfer belt 18 in the perimeter direction. Additionally, the sensor 25 is provided that detects the marks M1 through M8 on the transfer belt 18. The position of the transfer belt 18 is detected based on the time during which one of the marks M1 through M8 passes the sensor 25, and speed correction control of the transfer belt 18 corresponding to the detected position is performed. Thus, it is possible to detect the relative position of the detected position with respect to the entire transfer belt 18 by starting running of the transfer belt 18 and detecting the mark on the surface of the transfer belt 18 only in a partial region. Hence, irrespective of the stop position of the transfer belt 18, by detecting the current relative position of the transfer belt 18 in a short time and starting the speed correction control of the transfer belt 18, it is possible to reduce the time required until speed control of the transfer belt 18 is started. Also, it is possible to realize an image forming apparatus that reduces the time to form a first image.

FIG. 11 shows the structure of the transfer belt 18 in Embodiment 2 of the present invention. In Embodiment 2, as shown in FIG. 12, marks M9 through M16 are formed in the regions a1 through a8, respectively, dividing the transfer belt 18 in Embodiment 1. The marks M9 through M16 are each constituted by one or more lines (vertical lines with respect to the moving direction of the transfer belt 18) of a number indicating the corresponding region. The marks M9 through M16 are formed outside the image forming region of the surface of the transfer belt 18. In the illustrated exemplary embodiment, the marks M9 through M16 are formed in the respective regions a1 through a8 such that each extends in the moving direction of the transfer belt 18 with the length of the corresponding region.

FIG. 13 shows an operation flow of Embodiment 2.

When an image forming (printing) start request is issued in step B1, the control part 21 first drives the motor to rotate the transfer belt 18 at a constant speed for one of the regions dividing the transfer belt 18 in step B2, and then stops driving in step B4. Concurrently with rotation of the transfer belt 18, in step B3, the HP sensor 25 detects the patterns (line patterns) of the marks M9 through M16, which are constituted by lines, on the transfer belt 18, and the control part 21 detects a mark by counting the number of lines that pass the HP sensor 25 during the rotation of the transfer belt 18 based on an output signal of the HP sensor 25.

When counting the number of lines, the control part 21 obtains the number of lines by binarizing the output signal of the HP sensor 25 with the comparator and counting the number of edges of the binarized signal. Based on the obtained number of lines, the control part 21 determines at which region (i.e., a determined region) the HP sensor 25 is among the regions a1 through a8 dividing the transfer belt 18 into 8 regions. Then, in step B5, the control part 21 reads from the memory the speed correction data for one rotation of the transfer belt 18 with the speed correction data of the determined region as the starting point. In step B6, based on the speed correction data that are read from the memory, the control part 21 starts speed control of the transfer belt 18 by speed control of the motor. In step B7, the control part 21 controls each part of the printer according to the manner set forth above with respect to Embodiment 1, for example, so that image output (image forming) is performed.

According to Embodiment 2, the marks M9 through M16, each of which is constituted by one or more lines of a number indicating the corresponding region, are formed in the respective regions a1 through a8 of a constant number dividing the transfer belt 18 in the perimeter direction. Additionally, the HP sensor 25 is provided that detects the marks M9 through M16 on the transfer belt 18. The position of the transfer belt 18 is detected by counting the number of lines of one of the marks M9 through M16 in the respective regions a1 through a8 based on a detected signal of the HP sensor 25. The speed correction of the transfer belt 18 is performed in accordance with the detected position. Thus, it is possible to detect the relative position of the detected position with respect to the entire transfer belt 18 by starting running of the transfer belt 18 and detecting the mark on the surface of the transfer belt 18 by the HP sensor 25 only in a partial region of the transfer belt 18. Hence, irrespective of the stop position of the transfer belt 18, by starting the speed correction control of the transfer belt 18 by detecting the current relative position of the transfer belt 18 in a short time, it is possible to reduce the time required until the speed control of the transfer belt 18 is started. Also, it is possible to realize an image forming apparatus that reduces the time to form a first image.

FIG. 14 shows the structure of the transfer belt 18 in Embodiment 3 of the present invention. In Embodiment 3, as shown in FIG. 14, linear marks M17 through M24, having different widths in the main scan direction that is perpendicular to the moving direction of the transfer belt 18, are formed as patterns in the respective regions a1 through a8 dividing the transfer belt 18 into eight regions in the above-mentioned Embodiment 1. In the illustrated exemplary embodiment, the marks M17 through M24 are formed outside the image forming region of the surface of the transfer belt 18. The marks M17 through M24 are formed in the respective regions a1 through a8 such that each mark extends in the moving direction of the transfer belt with the length of the corresponding region.

FIG. 15 shows an operation flow of Embodiment 3.

When an image forming start request is issued in step C1, the control part 21 causes the HP sensor 25 to measure the marks M17 through M24 on the transfer belt 18 and reads a value of the HP sensor 25 in step C2. In step C3, the control part 21 digitizes the output value of the HP sensor 25 by converting the output value into a digital value by an A/D converter (not shown). The control part 21 compares the digital value with threshold values that are set in advance, and determines at which of the regions a1 through a8, dividing the transfer belt 18 into eight regions, the current position of the HP sensor 25 is. The control part 21 reads from the memory the speed correction data for one rotation of the transfer belt 18 with the speed correction data of the determined region as the starting point. In step C4, based on the speed correction data that are read from the memory, the control part 21 starts speed control of the transfer belt 18 through speed control of the motor. In step C5, the control part 21 controls each part of the printer according to the manner set forth above with respect to Embodiment 1, for example, so that image output (image forming) is performed.

According to Embodiment 3, the linear marks M17 through M24, having the different widths in the main scan direction, are formed in the respective regions a1 through a8 of the constant number dividing the transfer belt 18 in the perimeter direction. Additionally, the HP sensor 25 is provided that detects the marks M17 through M24 on the transfer belt 18. The position of the transfer belt 18 is detected by comparing the detected value from the HP sensor 25 with a preset value. The speed correction control of the transfer belt 18 is performed in accordance with the detected position. Thus, without driving the transfer belt 18, it is possible to detect the relative position of the detected position of the transfer belt 18, which position is detected by the HP sensor 25, with respect to the entire transfer belt 18. Hence, it is possible to reduce the time required until the speed control of the transfer belt 18 is started. Also, it is possible to realize an image forming apparatus that reduces the time to form a first image.

FIG. 16 shows the structure of the transfer belt 18 in Embodiment 4 of the present invention. In Embodiment 4, as shown in FIG. 17, marks M26 through M33 are formed as patterns on the surfaces of the respective regions a1 through a8 dividing the transfer belt 18 into eight regions in Embodiment 1. The marks M26 through M33 are each formed by arranging a plurality of thin lines in parallel in the main scan direction, which is perpendicular to the moving direction of the transfer belt 18. The marks M26 through M33 each has a different number of lines in the respective regions a1 through a8. In the illustrated exemplary embodiment, the marks M26 through M33 are formed outside the image forming region of the surface of the transfer belt 18. The marks M26 through M33 are formed in the respective regions a1 through a8 such that each mark extends in the moving direction of the transfer belt 18 with the length of the corresponding region.

FIG. 18 shows an operation flow of Embodiment 4.

When an image forming start request is issued in step D1, the control part 21 causes the HP sensor 25 to measure the marks M26 through M33 on the transfer belt 18 and reads a value of the HP sensor 25 in step D2. In step D3, the control part 21 digitizes the output value of the HP sensor 25 by converting the output value into a digital value by the A/D converter. The control part 21 compares the digital value with a threshold value that is set in advance and determines at which of the regions a1 through a8, dividing the transfer belt 18 into eight regions, the current position of the HP sensor is. The control part 21 reads from the memory the speed correction data with the speed correction data of the determined region as the starting point. In step D4, based on the speed correction data that are read from the memory, the control part 21 starts speed control of the transfer belt 18 by speed control of the motor. In step D5, the control part 21 controls each part of the printer according to the manner set forth above with respect to Embodiment 1, for example so that image output (image forming) is performed.

According to Embodiment 4, the patterns of the marks M26 through M33 formed in the respective regions a1 through a8 on the transfer belt 18 are constituted by combining thin lines along the direction perpendicular to the moving direction of the transfer belt 18. Thus, without moving the transfer belt 18, it is possible to detect the relative position of the detected position of the transfer belt 18, which position is detected by the HP sensor 25, with respect to the entire transfer belt 18. Hence, it is possible to reduce the time required until the speed control of the transfer belt 18 is started. Also, it is possible to realize an image forming apparatus that reduces the time to form a first image. Further, even if the position of the transfer belt 18 is varied in the main scan direction since, for example, the transfer belt 18 is shifted, variation in the detected value of the HP sensor 25 is small. Accordingly, the possibility of erroneous detection is decreased, and thus it is possible to detect the marks more stably.

FIGS. 19 and 20 show a part of Embodiments 5 and 6 of the present invention, respectively. In Embodiments 5 and 6, a plurality of, for example, two HP sensors 34 and 35 are arranged with respect to the transfer belt