JP5094285B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine, a control method thereof, a control program, and a recording medium, and more particularly to a printing speed control technique of an image forming apparatus having an intermediate transfer member.

  When printing on transfer materials with large heat capacity, such as OHT film, cardboard, envelopes, etc., in full-color image forming devices, the transfer material does not degrade the fixing performance of the fixing device. The conveyance speed is reduced. By this operation, the time required for the transfer material to pass through the fixing device is lengthened, so that the amount of heat given from the fixing device to the transfer material is increased and the fixing temperature can be increased. As a result, even when printing on a transfer material having a large heat capacity, it is possible to ensure a stable fixability that can prevent a reduction in fixing performance of the fixing device.

  By the way, in a conventional one-drum type full-color image forming apparatus having an intermediate transfer member, a toner image is formed on a photosensitive member, and the formed toner image is transferred onto the intermediate transfer member (hereinafter referred to as primary transfer). The rotation speed of the photosensitive member and the intermediate transfer member is a normal printing speed. Then, after that, a method has been adopted in which the driving speed is switched in the subsequent steps of transferring the toner image on the intermediate transfer member to a transfer material (hereinafter referred to as secondary transfer). However, in a one-drum type image forming apparatus, a toner image developed by one photosensitive member and a plurality of developing devices is transferred on an intermediate transfer member for each color, so that much time is required for primary transfer. Cost.

  Therefore, in recent years, a four-drum type image forming apparatus capable of simultaneously forming toner images of respective colors on an intermediate transfer material by using four photoconductors and a developing device has come out. In this four-drum type image forming apparatus, first, a first toner image is formed on a first photosensitive member, and the formed first toner image is primarily transferred from the photosensitive member onto an intermediate transfer member. Then, a second toner image is formed on the second photoconductor, and the formed second toner image is transferred onto the first toner image transferred onto the intermediate transfer member. When this operation is continuously performed with four photoconductors (for example, four B, C, M, and Y), a color image that is an overlap of four toner images is formed on the intermediate transfer member. The color image formed on the intermediate transfer body is secondarily transferred from the intermediate transfer body to the transfer material at the secondary transfer position (for example, Patent Document 1).

In this four-drum type image forming apparatus, when image formation by a plurality of print jobs is continuously performed, a primary transfer process for a subsequent print job and an image secondary transfer process for a preceding print job are performed in parallel. To be implemented. Therefore, the primary transfer process and the secondary transfer process have the same speed. Therefore, when the print speed is switched by changing the print mode or the like, first, image forming processing such as primary transfer processing and secondary transfer processing is temporarily ended. Then, the image forming process has to be started by switching the primary transfer portion and the secondary transfer portion to the printing speed of the selected mode.
JP 2004-020616 A

  However, in the above-described four-drum type image forming apparatus having the intermediate transfer member, the distance from the position of the primary transfer unit that performs the primary transfer process to the position of the secondary transfer unit that performs the secondary transfer process is long. For this reason, when switching the print speed, the process during image formation must be temporarily ended and then switched to the next print speed, so that it takes a lot of time to perform the next primary transfer process. .

  As a result, if the image forming process is restarted from the primary transfer process after switching the speed of the primary transfer part and the secondary transfer part accompanying the switching of the print speed as in the past, the throughput is greatly reduced when the speed is switched. There was a disadvantage that it would be lowered.

The present invention has been made starting from solving the above-described problems of the prior art. Its purpose is to adjust an image forming equipment of as appropriate throughput is obtained and the sub-scanning direction of the image synchronization signal output timing and rate at which the primary transfer process with the printer engine at the time of continuous image formation Is to provide.

In order to achieve the above object, an image forming apparatus according to the present invention has the following arrangement. A primary transfer unit that primarily transferred to the intermediate transfer body images of the image bearing member, an image forming apparatus and a second transfer unit for transferring the secondary to the intermediate transfer body to a recording medium the primarily transferred images The rotational speed of the intermediate transfer member is changed from the first speed to the second speed in order to change the secondary transfer speed when the image is secondarily transferred to the recording medium by the secondary transfer unit. And a second speed change means for changing the rotation speed of the intermediate transfer body from the first speed to the second speed by the speed change means, while the rotation speed of the intermediate transfer body is at the first speed. A first image that is secondarily transferred by the second transfer portion, and a second image that is secondarily transferred by the second transfer portion following the first image with the rotation speed of the intermediate transfer body being the second speed. The rotational speed of the intermediate transfer member is in the first speed state Control means for controlling a primary transfer operation of the first image and the second image so as to be primarily transferred to the intermediate transfer body by the primary transfer section, and the control means An image interval between the rear end of the first image and the front end of the second image when the second image is primarily transferred following the first image and the first image with the rotation speed being the first speed. Is controlled so as to be equal to or greater than an interval corresponding to the moving distance of the intermediate transfer member necessary for changing the rotation speed of the intermediate transfer member from the first speed to the second speed .

  According to the present invention, an image forming apparatus capable of adjusting the image synchronization signal output timing in the sub-scanning direction and the speed for performing the primary transfer process so that an appropriate throughput of the printer engine can be obtained when continuously forming images. And a control method thereof. Therefore, for example, when a print job including print speed switching is received, it is possible to adjust so that an appropriate throughput of the printer engine can be obtained. Further, even when the designated print speed is not the fastest print speed of the image forming apparatus, the printer engine can be adjusted to obtain an appropriate throughput.

<First Embodiment>
[Feature]
The image forming apparatus according to the first embodiment reduces an increase in printing time that occurs when switching printing speed when printing is performed continuously using transfer materials having different heat capacities (fixing speeds) as compared with the conventional processing. It is characterized by. In the conventional print reservation process, when a print job at a print speed V1 and a print job at a print speed V2 are continuously performed, first, primary transfer and secondary transfer are performed at the print speed V1, and then the print speed is changed from V1 to V2. Had been switched to. Then, the primary transfer and the secondary transfer of the print job including the speed change at the print speed V2 are processed thereafter. However, in the print reservation process of the present embodiment, the primary transfer of a part of the print job including the speed change is performed using the primary transfer speed V1 before the speed change. Then, after the print speed is switched from V1 to V2, the secondary transfer of the image primarily transferred at the print speed V1 and the primary transfer and secondary transfer of the print job including the remaining speed change are performed at the print speed V2. Process. As a result, in the present embodiment, by executing the primary transfer of a part of the print job including the speed change that has been conventionally performed after the change of the print speed before the print speed is changed, the printed matter is provided to the user earlier than the conventional process. can do.

  Hereinafter, an image forming apparatus of the present invention will be described in detail with reference to the drawings.

[Image forming apparatus: FIG. 1A]
FIG. 1A is a cross-sectional view illustrating a schematic configuration of a color image forming apparatus which is an example of the image forming apparatus of the present embodiment.

  The color image forming apparatus according to the present embodiment includes four image carriers 3a, 3b, 3c, and 3d on which toner images of respective colors of yellow, magenta, cyan, and black whose normal charging polarity is negative are formed. Yes. In the present embodiment, the image carriers 3a, 3b, 3c, and 3d are photosensitive drums (drum-shaped electrophotographic photosensitive members), and are arranged in series. Around the photosensitive drums 3a, 3b, 3c, and 3d, primary chargers 4a, 4b, 4c, and 4d, developing units 8a, 8b, 8c, and 8d, and cleaning units 6a, 6b, and 6c corresponding to the photosensitive drums. , 6d are arranged. In addition, exposure units 5a, 5b, 5c, and 5d are disposed above the photosensitive drums 3a, 3b, 3c, and 3d.

  Each of the photosensitive drums 3a, 3b, 3c, and 3d is negatively charged by the charging rollers 4a, 4b, 4c, and 4d that are in contact with each other, and color-separated light images of yellow, magenta, cyan, and black are exposed to the exposure unit 5a, Exposure is performed using 5b, 5c, and 5d. Then, yellow, magenta, cyan, and black latent images are formed on the photosensitive drums 3a, 3b, 3c, and 3d. Thereafter, the latent images are developed by reversal development using the developing devices 8a, 8b, 8c, and 8d, and yellow, magenta, cyan, and black toner images are sequentially formed on the photosensitive drums 3a, 3b, 3c, and 3d.

  An intermediate transfer belt (hereinafter referred to as ITB) 2 serving as an intermediate transfer member (image carrier) is disposed below the photosensitive drums 3a, 3b, 3c, and 3d. The ITB 2 is stretched around the roller 21 that drives the intermediate transfer belt and the rollers 22, 23, and 24, and is rotated in the direction of the arrow at substantially the same speed as the photosensitive drum 3. The toner image formed and carried on the photosensitive drums 3a, 3b, 3c, and 3d is transferred to the ITB2 by the primary transfer bias (positive voltage) applied to the primary transfer rollers 22a, 22b, 22c, and 22d in the primary transfer portion. Is electrostatically primary-transferred onto the outer peripheral surface. As a result, toner images of a plurality of colors are formed on ITB2. The above-described components function as toner image forming means.

  Next, the paper 11 is fed from the paper storage cassette 13 by the pickup roller 12, reaches the registration sensor 15, and stops. After that, the sheet is fed again by the registration transport roller 14 at a predetermined timing. At the same time, a secondary transfer bias (positive voltage) is applied to the secondary transfer roller 7 as a secondary transfer device, and the toner image is electrostatically transferred from the ITB 2 to the paper 11. The sheet 11 is conveyed to the fixing unit 10 by the registration conveying roller 14 and the secondary transfer roller 7, and the transferred toner image is melted and fixed to obtain a color image.

  The transfer residual toner (secondary transfer residual toner) on the ITB 2 after the completion of the secondary transfer is charged to a polarity opposite to the normal charging polarity by the contact charger 1 which is an ITB cleaning unit (charging means). The transfer residual toner charged to the reverse polarity is transported to the primary transfer portion again by the movement of ITB2, and is applied to the primary transfer roller 22d. The positive primary transfer bias (voltage having a polarity opposite to the charged polarity of the toner) ) Is reversely transferred onto the photosensitive drum 3a which is the counter electrode. In this case, the cleaning unit 6d provided in association with the photosensitive drum 3d for the first color collects the secondary transfer residual toner. In the ITB cleaning unit 1, that is, the charging roller as the charging means is always in contact with the ITB 2.

[Control Configuration of Image Forming Apparatus: FIG. 1B]
FIG. 1B is a block diagram illustrating a control configuration of the image forming apparatus illustrated in FIG. 1A.

  101 is a CPU that controls the entire image forming apparatus, 102 is a ROM that stores various control programs and various data, 103 is a RAM, 104 is a print job receiving unit, and 105 is a display unit. And 106 is a printer engine unit. The printer engine unit 106 includes an exposure unit, a photosensitive drum, an intermediate transfer member, a paper feeding unit, a fixing unit, and a detection unit. The CPU 101 can perform various processes while controlling each unit using the RAM 103 as a work area based on an image formation control program stored in the ROM 102. For example, it is possible to perform adjustment processing that reduces an increase in image formation time that occurs at the time of switching the print speed when image formation is continuously performed using different types of recording media that require switching of the print speed. .

[ROM / RAM configuration: FIG. 1C]
Next, an example of the configuration of the ROM 102 and the RAM 103 described above will be described with reference to FIG. 1C. Note that FIG. 1C mainly describes what is necessary for the description of the present embodiment, and omits what is not necessary for the description of the present embodiment.

  The ROM 102 has a system program 110, an image formation control program 111, and a length 112 from the primary transfer position to the secondary transfer position of the fourth color photosensitive drum 3a (Lt12: see FIG. 3). Yes. Further, 113 stores the lengths of various image sizes in the sub-transport direction (Lp: see FIG. 3) and the distance between the images at the same primary transfer speed (Ld: see FIG. 3). That is, the distance Ld is the recording medium conveyance interval. Further, 114 stores a primary transfer speed before and after the change as shown in FIG. 4B and a distance Lc (movement time) necessary to change the primary transfer speed. The distance required to change the primary transfer speed is necessary to change the rotation speed of the intermediate transfer member from the position of the end of the last toner image on which image formation is performed at the primary transfer speed before the change. A long distance is memorized. Further, the distance used here means the length of the intermediate transfer member in the conveyance direction. Accordingly, a position at least a distance Lc away from the position of the end portion of the toner image described above is the image formation start position after the speed change. Further, 114 stores a fixing unit speed before and after the change, a sheet conveyance distance Ly (movement time) necessary for changing the fixing unit speed, an image interval Lx when changing the printing speed, and the like. Further, 115 stores an equation for calculating the number of images that can be subjected to primary transfer at the primary transfer speed before change among images subjected to secondary transfer at the changed secondary transfer speed.

  On the other hand, 116 of the RAM 103 stores image data and print job information (image size, type of recording medium to be used, and print speed) formed by each print job. Also, 117 stores various flags necessary for executing the program of FIG. 2 (comparison determination of the fixing speed of the print job, TOP signal / speed switching, completion of secondary transfer of the preceding image), and the like. Reference numeral 118 denotes a program load area.

<Image Forming Processing Method including Switching of Fixing Speed of Embodiment>
Next, print reservation processing including switching of the fixing speed using the image forming apparatus of the present embodiment described above will be described. In the following description, the outline and details of the difference between this embodiment and the conventional print reservation processing method will be described first. Next, the number of primary transfer images and the transfer position of the primary transfer image performed before switching the fixing speed for a print job including switching the fixing speed will be described. Finally, the flow of print reservation processing including switching of the fixing speed will be described.

[1. Difference between this embodiment and conventional print reservation processing]
[Overview]
In the conventional print reservation process, when a print job at a print speed V1 and a print job at a print speed V2 are continuously performed, first, primary transfer and secondary transfer are performed at the print speed V1. Then, after the print speed is switched from V1 to V2, processing is performed such that primary transfer and secondary transfer of the print job including the speed change are performed at the print speed V2. However, in the print reservation process of the present embodiment, the primary transfer of a part of the print job including the speed change is performed using the primary transfer speed V1 before the speed change. Then, after the print speed is switched from V1 to V2, the secondary transfer of the image primarily transferred at the print speed V1 and the primary transfer and secondary transfer of the print job including the remaining speed change are performed at the print speed V2. Process as you do. For this reason, in the present embodiment, by executing the primary transfer of a part of the print job including the speed change that has been conventionally performed after the change of the print speed before the change of the print speed, it is possible to provide the user with a printed matter compared to the conventional case. Can be done faster. Next, the difference between the above-described conventional print reservation processing and this embodiment will be described in detail with reference to FIGS. 3 and 4A.

[Details of differences in print reservation processing: FIGS. 3 and 4A]
First, FIG. 3 will be described. FIG. 3 is a diagram illustrating a positional relationship between the primary transfer position, the intermediate transfer member, and the secondary transfer position (recording medium transfer position) related to the primary transfer to the secondary transfer of the image forming apparatus. In the example of FIG. 3, the N1 page (corresponding to the first toner image) is printed at the first print speed V1 for the images having the same image size on all the N1 to N3 pages, and the N2 and N3 pages. (Corresponding to a second toner image) is an example of processing when printing is performed at a second print speed V2 that is slower than the first print speed V1. In FIG. 3, the distance from the transfer roller T1a to the secondary transfer roller T2 at the final station (Black in this example) of the primary transfer unit is defined as Lt12, and the distance from the secondary transfer roller T2 to the fixing roller Fr is defined as Lf. Further, the length of the image size in the sub-scanning direction is Lp, and the movement distance of the intermediate transfer member corresponding to the image interval on the intermediate transfer member between the N1 page and the N2 page (images with different print speeds) is Lx, page N2. The space between the eyes and the N3th page is defined as Ld. The distance from the primary transfer position T1d of the first color photosensitive drum 3d to the primary transfer position T1a of the fourth color photosensitive drum 3a is defined as Lk. Further, the distance from the exposure position of the exposure unit 5d on the first color photosensitive drum 3d to the primary transfer position T1d of the photosensitive drum 3d is defined as Le. Lk + Le is set to Lm. That is, Lm represents the distance from the exposure position on the first color photosensitive drum 3d to the primary transfer position T1a of the fourth color photosensitive drum 3a. Further, the intermediate transfer member required for changing the rotational speed of the moving intermediate transfer body (that is, the same as the primary transfer speed and the secondary transfer speed or called the moving speed) from the first speed V1 to the second speed V2. Let Lc be the moving distance. Further, if the moving distance of the intermediate transfer member required for changing the speed of the fixing unit from the first speed V1 to the second speed V2 is Ly, Lx ≧ Lc and Lx ≧ Ly.

  Next, FIG. 4A will be described. FIG. 4A is an example of a schematic diagram comparing the time required until the end of image fixing in the print reservation process of the present embodiment and that of the present embodiment. In FIG. 4A, the N1 page of the image having the same image size shown in FIG. 3 is printed at the first print speed V1, and the N2 and N3 pages are printed at the second print speed V2 (slower than the first print speed V1). = V1 / 2) is compared.

  That is, (a) of FIG. 4A is a conventional print reservation process. After the primary transfer and secondary transfer of the image on page N1 at the print speed V1, the print speed is changed, and the print speed change target is changed. This shows a case where primary transfer and secondary transfer of images on pages N2 and N3 are started. Here, section A in FIG. 4A shows that primary transfer and secondary transfer of the N1 page are performed at the speed V1. Section B indicates that the rotation speeds of the primary transfer unit and the intermediate transfer member are changed from the speed V1 to the speed V2. Section C indicates that primary transfer and secondary transfer of the N2 and N3 pages are performed at V2. F1 is the first transfer start of the N1 page in the last station, F2 is the second transfer start of the N1 page, G1 is the first transfer start of the N2 page in the last station, G2 is the second transfer start of the N2 page, H indicates the end of secondary transfer on page N3. A section L indicates that image fixing of the N1 page is performed at the speed V1. A section M indicates that the speed of the fixing unit is changed from the speed V1 to the speed V2. A section N indicates that image fixing on the N2 and N3 pages is performed at V2. Further, O represents the image fixing start of the N1 page, P represents the image fixing start of the N2 page, Q represents the image fixing start of the N3 page, and R represents the image fixing end of the N3 page.

  Specifically, the primary transfer of the N1 page starts from X1s at the primary transfer position (T1a) at the primary transfer speed V1 and ends at X1e. The secondary transfer of the N1 page starts at Y1s at the secondary transfer position (T2) at the secondary transfer speed V1 and ends at Y1e. The image fixing of the N1 page starts from Z1s at the image fixing position (Fr) at the fixing speed V1 and ends at Z1e. The primary transfer of the N2th page starts from X2s at the primary transfer position (T1a) at the primary transfer speed V2 and ends at X2e. The secondary transfer of the N2 page starts at Y2s at the secondary transfer position (T2) at the secondary transfer speed V2, and ends at Y2e. The image fixing for the N2 page starts from Z2s at the image fixing position (Fr) at the fixing speed V2 and ends at Z2e. Similarly, the primary transfer of the N3th page starts from X3s at the primary transfer position (T1a) at the primary transfer speed V2 and ends at X3e. The secondary transfer on page N3 starts at Y2s at the secondary transfer position (T2) at the secondary transfer speed V2 and ends at Y2e. The image fixing of the N3 page starts from Z3s at the image fixing position (Fr) at the fixing speed V2 and ends at Z3e.

  On the other hand, FIG. 4A (b) shows the print reservation process of the present embodiment shown in FIG. The section A in FIG. 4A (b) indicates that the primary transfer from the N1 to the N3th page and the secondary transfer of the N1 page are performed at the speed V1. Section B indicates that the rotation speeds of the primary transfer portion and the intermediate transfer member are changed from the speed V1 to V2. Section C indicates that secondary transfer of pages N2 and N3 is performed at speed V2. F3 is the first transfer start of the N1 page in the final station, F4 is the secondary transfer start of the N1 page, G3 is the primary transfer start of the N2 page in the final station, G4 is the secondary transfer start of the N2 page, H indicates the end of secondary transfer on page N3. The sections L, M, and N indicate that the image fixing of the N1 page is performed at the speed V1 as in FIG. A section M indicates that the speed of the fixing unit is changed from the speed V1 to V2. A section N indicates that image fixing on the N2 and N3 pages is performed at V2. Also, O, P, and Q are the same as in FIG. 4A, O is the image fixing start of the N1 page, P is the image fixing start of the N2 page, Q is the image fixing start of the N3 page, and R is Indicates the end of image fixing on page N3.

  Specifically, the primary transfer of the N1 page starts from X1s at the primary transfer position (T1a) at the primary transfer speed V1 and ends at X1e. The secondary transfer of the N1 page starts at Y1s at the secondary transfer position (T2) at the secondary transfer speed V1 and ends at Y1e. The image fixing of the N1 page starts from Z1s at the image fixing position (Fr) at the fixing speed V1 and ends at Z1e. Further, the primary transfer of the N2 page starts at X2s at the primary transfer speed V1 at the position G3 that is separated from the primary transfer end position X1e of the N1 page by Lx (Lx ≧ Lc and Lx ≧ Ly) and ends at X2e. . In this example, Ly <Lc and Lx = Lc. Further, the secondary transfer of the N2 page starts from Y2s and ends at Y2e after changing the secondary transfer speed from V1 to V2. The image fixing for the N2 page is started from Z2s at the image fixing position (Fr) after the fixing speed is changed from V1 to V2 after the image fixing for the N1 page is completed, and is ended at Z2e. Similarly, the primary transfer of the N3th page starts at X3s at the primary transfer speed V1 and ends at X3e. Also, the secondary transfer of the N3 page starts at Y3s at the secondary transfer speed V2 and ends at Y3e. The image fixing of the N3 page starts from Z3s at the image fixing position (Fr) at the fixing speed V2 and ends at Z3e.

  Here, the time required from the start of the primary transfer of the N1 page to the completion of the image fixing of the N3 page will be compared between the conventional case and the print reservation process of the present embodiment.

  As can be seen from FIG. 4A, from the start of the primary transfer of the N1 page until the image fixing of the N1 page is completed, and after the N2 page reaches the image fixing position (Fr), the N3 page The time until the image fixing is completed is the same in the conventional and the present embodiment. The difference between the prior art and the present embodiment is the time required from the end of image fixing of the N1 page to the arrival of the N2 page at the image fixing position (Fr). This difference is related to the image interval on the intermediate transfer body of the N1 page and the N2 page.

  In the conventional print reservation process, the N1 page is subjected to primary transfer and secondary transfer at the print speed V1, and then the print speed is changed to V2, and then the primary transfer and secondary transfer of the N2 and N3 pages are performed. Therefore, the image interval on the intermediate transfer member of the N1 page and the N2 page is Lt12 + Lc + Lm (time conversion: [Lt12 / V2] + [movement time for Lc] + [movement time for Lm]).

  On the other hand, in the print reservation process of the present embodiment, primary transfer and secondary transfer are performed at the print speed V1 for the N1, N2, and N3 pages. Therefore, the image interval on the intermediate transfer body of the N1 page and the N2 page is Lx (time conversion: [movement time for Ly]).

  That is, the user is earlier by a time corresponding to the length of I shown in FIG. 4A (time conversion: Lt12 / V2 + [movement time for Lc] + [movement time for Lm] − [movement time for Ly]]). Can provide printed matter. In general, in the case of the present embodiment in which the transfer images for a plurality of pages are Lt12 of the printer engine on the intermediate transfer member, [movement time for Ly] is smaller than [Lt12 / V2].

  Here, the speed change of the fixing unit will be described. When the N1 page is printed at the first print speed V1 and the N2 and N3 pages are printed at the second print speed V2, the N1 page is fixed at the first print speed V1, and therefore the N1 page paper. The driving speed of the fixing unit is set to the first printing speed V1 until the leading end enters the fixing unit. Next, in order to perform image fixing on the N2 and N3 pages at the second printing speed V2, the driving speed of the fixing unit after the image formation on the N1 page is completed, that is, after the paper trailing edge of the N1 page passes through the fixing unit. Is changed to the second print speed V2. Further, before the start of image fixing of the N2 page, that is, until the leading edge of the N2 page enters the fixing unit, the driving speed of the fixing unit is changed to the second printing speed V2, and the N2 page, N3 The image is fixed at the second print speed V2 designated for the page.

  As described above, in order to fix each image at a designated printing speed, the transfer unit including the primary transfer unit and the secondary transfer unit and the fixing unit are driven at different speeds. Therefore, the transfer unit and the fixing unit 10 are driven by separate driving sources.

  By performing print reservation processing according to the present embodiment, when performing continuous printing with speed switching, it is possible to perform primary transfer processing that can reduce an increase in time required for speed switching of the intermediate transfer member as compared with the prior art, and printed matter. Can be provided to the user more quickly.

  FIG. 4B shows an example of the region 114 of FIG. 1C used in FIG. 4A. The area 114 stores the moving distance Lc (moving time) of the intermediate transfer member necessary for changing from the intermediate transfer member speed Va before the change to the intermediate transfer member speed Vb after the change. Further, in the area 114, when the intermediate transfer member moving distance Ly (moving time) and the intermediate transfer member speed required for changing from the fixing portion speed Va before the change to the fixing portion speed Vb after the change are changed. The image forming interval Lx (movement time) is stored. FIG. 4A (b) shows various operation timings for only pages N1 to N3. On page N4 following page N3, primary transfer, secondary transfer and fixing operations are performed at the second print speed. Is called.

  In the description of FIGS. 4A and 4B, for the sake of easy understanding, a comparison is made between the conventional example of primary transfer and secondary transfer of black (K) at the time of changing the speed of the intermediate transfer member and the present application. It was. However, in color image formation having a plurality of primary transfer portions, yellow (Y) is first transferred to the intermediate transfer member, so the actual primary transfer start position (start timing) is as shown in FIG. This is the start position of yellow (Y). In the case of FIG. 4C as well, the number N is determined based on the distance between the primary transfer position and the secondary transfer position of black.

[2. Number of primary transfer images and their placement before speed change]
Next, the image forming processing method including the switching of the fixing speed of the present embodiment described above will be specifically described. First, a calculation method of how many sheets of the primary transfer of the print job including the speed change that has been conventionally performed after the speed change can be performed before the print speed change will be described.

Expression 1 shown below is an expression for determining the number of sheets to be subjected to primary transfer of a part of the print job including the print speed change by using the print speed before the print speed change, and N satisfying Expression 2 is a print speed change. This is the number of sheets that can be primarily transferred using the previous print speed.
Lt12 ≧ Lx + Lp × N + Ld × (N−1) (Formula 1)
∴N ≦ (Lt12−Lx + Ld) / (Lp + Ld) (Expression 2)
Lt12: distance from the transfer roller T1a to the secondary transfer roller T2 at the final station of the primary transfer portion Lp: length of the image size in the sub-scanning direction Ld: image interval on the intermediate transfer member of the same print speed interval)
Lc: Movement distance of the intermediate transfer member for changing the speed of the primary transfer portion from the first speed to the second speed Ly: Movement of the intermediate transfer member for changing the speed of the fixing portion from the first speed to the second speed Distance Lx: Movement distance of the intermediate transfer member for changing the printing speed from the first speed to the second speed (where Lx ≧ Lc and the minimum Lx that satisfies Lx ≧ Ly)
N: Number of images First, the meaning of Equations 1 and 2 will be described.

  The left side of Equation 1 is the distance (Lt12) that the intermediate transfer body moves from the primary transfer of the toner image formed at the printing speed V1 to the secondary transfer at the final station until the secondary transfer. The right side of Equation 1 shows the distance (Lx) that the intermediate transfer member moves before the printing speed is changed from the first speed V1 to the second speed V2, the printing speed is the second speed V2, and N images are Ld images. This is the sum of the distance of the intermediate transfer member required for primary transfer onto the intermediate transfer member with an interval. Therefore, according to the equation 2 obtained from the equation 1, the print job to be printed at the second speed between the end of the primary transfer at the first speed and the end of the secondary transfer at the first speed. Of the images, the number of images that can be primarily transferred at the first speed V1 is obtained. The image primarily transferred at the first speed V1 is secondarily transferred immediately after the print speed is changed to the second speed V2. Therefore, by using Expressions 1 and 2, it is possible to determine the number of sheets to be subjected to the primary transfer of a part of the print job including the print speed change by using the print speed before the print speed change.

For example, if Lt12 = 1000, Lp = 250, Lx = 400, Ld = 50,
N ≦ (1000−400 + 50) / (250 + 50) = 650/250 = 2.6
Therefore, by forming N = 2 images satisfying Equation 2 at the primary transfer speed before changing the print speed, it is possible to reduce an increase in image formation time associated with the change in print speed compared to the conventional technique.

  Further, when the lengths in the transport direction of continuously fed recording media are different, the following formula is used. That is, even when the length in the transport direction is different for each image to be formed or when the image interval is different, the same accuracy as that of Equation 1 can be maintained by using the following Equation 3.

Lt12 ≧ Lx + (Lp1 + Lp2 + Lp3... + LpN) + (Ld1 + Ld2 + Ld3... + LdN-1) (Expression 3)
Here, Lp1, Lp2, Lp3,..., LpN indicate the length in the conveyance direction (sub-scanning direction) of the toner image transferred from the first sheet to the Nth sheet of the recording medium. Ld1, Ld2, Ld3, and LdN-1 indicate the interval between the first and second image intervals of the recording medium to the N-1 and Nth image intervals. In this way, by defining the length of the toner image in the transport direction and the image interval corresponding to each recording medium, the number of images to be formed can be determined in more detail using the speed before the change.

[3. Print reservation processing including switching of fixing speed: Fig. 2]
Next, a flow of print reservation processing including switching of the fixing speed according to the present embodiment described above will be described. FIG. 2 is a flowchart for explaining primary transfer processing for reducing an increase in image formation time in a print reservation schedule including switching of the fixing speed according to the present embodiment. In other words, in the present embodiment, the TOP signal is changed before the primary transfer speed is changed in order to change the part of the image that has been subjected to the primary transfer after the change of the secondary transfer speed to be performed at the primary transfer speed before the change. (Image print start signal) output switching processing is performed. As a result, it is possible to reduce an increase in image formation time associated with switching of the fixing speed as compared with the conventional method. FIG. 2 is executed by the CPU 101 using the RAM 103 as a work area while the CPU 101 controls each unit based on the image formation control program stored in the ROM 102 shown in FIG. 1B.

  First, when the printing operation is started in step S1, the process proceeds to step S2, where the CPU 101 starts rotation of the photosensitive drum, ITB, etc., and performs control so as to prepare for the printing operation.

  In step S3, the CPU 101 checks whether the current fixing speed is the same as the print speed of the print reservation for which primary transfer is to be started next. In step S3, processing is performed using a print job (image data) sent from the video controller to the printer engine via a video interface or the like and print job information (image size, type of recording medium used, print speed). . That is, if there is a print speed designation, the print speed is used, or a change in print speed is determined based on the type of recording medium. If it is determined in step S3 that the printing speed is not changed, the process proceeds to step S4.

  On the other hand, if it is determined in step S3 that the print speed is changed, the process proceeds to step S6. In step S6, when the CPU 101 resets the print speed, the CPU 101 calculates the number of images to be primarily transferred at the current fixing speed. Also, the TOP signal output timing of the image to be primarily transferred at the current fixing speed and the switching timing of the primary transfer speed are calculated. In step S7, the CPU 101 sets the number of images to be primarily transferred at the current fixing speed.

  Next, proceeding to step S8, the CPU 101 determines whether or not the set number of images is zero. If not, the CPU 101 proceeds to step S9 and controls to output the calculated TOP signal to the printer engine. In step S10, the CPU 101 performs control to perform primary transfer, and then proceeds to step S11 to set N = N-1 and then returns to step S8.

  On the other hand, if the set number of images is 0 in step S8, the CPU 101 proceeds to step S12 and waits until the secondary transfer of the preceding image is completed in order to cause the printer engine to switch the transfer speed. To do. Subsequently, when the secondary transfer is completed, the process proceeds to step S13, where the CPU 101 executes a process for switching the primary transfer speed of the printer engine, and then proceeds to step S4.

  In step S4, the CPU 101 performs control to output a TOP signal corresponding to the image data, and then proceeds to step S5, where the CPU 101 performs primary transfer of the toner image formed on the photosensitive drum to the intermediate transfer member. Control. Then, it progresses to step S14, it is discriminate | determined whether a process is complete | finished, and when continuing a process, it returns to step S3, and when complete | finishing a process, it progresses to step S15 and complete | finishes a series of work.

[Determination of the speed switching timing of the primary transfer portion: FIG. 3]
Next, the processing in steps S6 to S13 in FIG. 2 will be described using a specific example. Here, as a specific example, as shown in FIGS. 3 and 4A, the N1 page is printed at the first print speed V1 and the N2 and N3 pages are printed with respect to an image having the same image size of N1 to N3 pages. A description will be given by taking as an example a process of printing at the second print speed V2.

  In step S6, N is calculated using Equation 2. For example, if Lt12 = 1000, Lp = 250, Lx = 400, and Ld = 50, 2 is obtained as N that satisfies Equation 2. That is, two images can be primarily transferred before the speed is changed. Further, based on the calculated N (= 2), a TOP signal is calculated so that two images can be primarily transferred at a speed before the transfer speed is switched. Also, the transfer speed switching timing is set. Next, in step S7, N = 2 is set. Then, since N is not 0 in step S8, the process proceeds to step S9. In step S9, the TOP signal for the image on page N2 is output so that the image on page N2 can be primarily transferred at the position G1 in FIG. 4A. In step S10, the image on page N2 is primarily transferred. In step S11, N = 1 is set, and then the process returns to step S8. In step S8-11 described above, the image on page N3 is subjected to the primary transfer process, and after N = 0, the process returns to step S8. Next, in step S8, since N = 0, the process proceeds to step S12, waits until the secondary transfer of the preceding image (the N2 page image) is completed, and then proceeds to step S13 to perform a speed switching process.

  As described above, in the image forming apparatus of this embodiment, before the speed is switched, the speed is switched after the images of the N2 and N3 pages are transferred to the intermediate transfer member, and the speed reaches the speed after the switching. Later, the images on pages N2 and N3 can be secondarily transferred. Note that the speed change of the primary transfer portion and the intermediate transfer member in step S13 may be started from Lc before the secondary transfer roller T2 at the latest.

  By performing this embodiment, when performing continuous printing with speed switching, primary transfer can be performed without wasting time required for speed switching of the intermediate transfer body, and the printed matter is provided to the user more quickly. be able to.

<Second Embodiment>
Hereinafter, the second embodiment will be described. The image forming apparatus according to the second embodiment is similar to the image forming apparatus according to the first embodiment. Therefore, the description of the image forming apparatus of the second embodiment will be made only on the parts different from those of the image forming apparatus of the first embodiment, and the description of the common parts will be omitted because they overlap.

[Feature]
In the first embodiment, the processing for reducing an increase in print time when there is a change in print speed during continuous printing has been described. However, in the second embodiment, even when the print job received from the video controller does not include the switching of the print speed, the primary transfer speed and the secondary transfer speed are appropriately changed according to the print job information and the status of the printer engine. can do. That is, in the second embodiment, when the designated print speed is slower than the fastest print speed of the image forming apparatus, the primary transfer speed can be changed to a faster primary transfer speed than the designated print speed. Further, after the primary transfer at a fast primary transfer speed, the secondary transfer speed can be reduced to the designated print speed and then the secondary transfer can be performed. Therefore, in the second embodiment, when the designated print speed is lower than the fastest print speed of the image forming apparatus, the primary transfer image is changed to the secondary transfer speed by appropriately switching the primary transfer speed and the secondary transfer speed. It is possible to reduce the transport time before transfer. Further, since the secondary transfer and the image fixing process can be performed at a designated print speed, the printed material can be provided to the user more quickly without degrading the image quality of the printed material.

[Change to primary transfer speed faster than specified print speed]
When the print speed specified for a print job that does not include print speed switching is slower than the fastest print speed of the image forming apparatus, the secondary transfer speed is the specified print speed, and the primary transfer speed is faster. The speed change process will be described.

  FIG. 6 is a diagram illustrating a positional relationship between a primary transfer position, an intermediate transfer body, and a secondary transfer position (recording medium transfer position) related to primary transfer to secondary transfer of the image forming apparatus. Since FIG. 6 is similar to FIG. 3 described in the first embodiment, the same components as those in FIG. 3 are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  Lt2 in FIG. 6 is the distance from the leading toner image tip Ptop on the intermediate transfer member to the secondary transfer position T2, and Limg is the primary transfer from the transfer roller T1a of the final station of the primary transfer portion to the Nth page. It is the distance to Ptop at the time. Limg is expressed by (Formula 4).

Limg = Ld × N + Ld × (N−1) (Formula 4)
Here, when the primary transfer is performed at a speed VT1 faster than the print speed Vj designated at the time of printing reservation, and the time required to transport the primary transfer image to the secondary transfer position can be reduced, (Equation 5) This is the case.

(Lt12−Limg) ≧ Lc (Formula 5)
That is, this is the case where the distance Lt12 from the primary transfer final roller T1a to the secondary transfer roller T2 minus Limg (Lt2) is larger than the distance Lc required for speed switching of the primary transfer portion and the intermediate transfer body.

  When Equation 5 is satisfied, for example, when the printer engine is capable of primary transfer at a speed three times the speed Vj designated at the time of printing reservation, the time for forming the toner image on the intermediate transfer member is the intermediate transfer speed at the designated speed Vj. This can be reduced to one-third when image formation is performed on the body.

  Further, when Expression 4 is substituted into Expression 5, Expression 6 is obtained. Since the second embodiment does not include the speed switching of the fixing device, the one in which Lx in Expression 1 becomes Lx = Lc becomes Expression 6. That is, Equation 5 has the same meaning as in Equation 1 when Lx = Lc.

Lt12 ≧ Lc + Lp × N + Ld × (N−1) (Expression 6)
Therefore, as described in the first embodiment, the number N of sheets in which the primary transfer of a part of the print job including the print speed change is performed at the print speed before the print speed change can be obtained from the expression 1. However, the same processing as in the first embodiment can be performed.

  That is, even when the secondary transfer speed is set at a designated speed, the primary transfer speed is changed to a speed faster than the secondary transfer speed, and N images satisfying the expression 1 are quickly transferred to the primary as shown in FIG. Form at transfer speed. Thereafter, when the change of the rotation speed of the intermediate transfer member to the designated speed is started at the point Ptop in FIG. 6, the speed designated by the secondary transfer roller T2 is obtained, so that N images are designated by the designated two. Transfer can be performed at the next transfer speed.

[Print reservation processing not including fixing speed switching: FIG. 5]
Next, switching processing between the primary transfer speed and the secondary transfer speed in the print reservation process that does not include switching of the fixing speed according to the present embodiment described above will be described.

  FIG. 5 is a flowchart for the printing operation preparation in the printing reservation schedule not including the switching of the printing speed, the TOP signal output from the CPU, and the speed switching operation of the primary transfer unit and the intermediate transfer member of the image forming apparatus according to the present embodiment.

  The processing in FIG. 5 is executed by the CPU 101 that controls the printer engine unit based on the image formation control program stored in the ROM 102 shown in FIG. FIG. 5 shows the state where the primary transfer of all the images up to the Nth page to be printed is completed and the primary transfer unit and the intermediate transfer body are operating at the print speed specified in the print reservation (step S31).

  In step S21, when the print reservation of the printer engine is received from the video controller and the state changes from a state without a print reservation to a certain state, the CPU controls to start a print operation.

  In step S22, the CPU checks whether the print speed Vj designated at the time of print reservation is the fastest print speed Vh of the printer engine. If the designated print speed Vj is the same as the fastest print speed of the printer engine and Vh, the process proceeds to step S23, where the primary transfer unit and the intermediate transfer member are driven at the fastest print speed to prepare for the printing operation. Control to do.

  Next, in step S24, the CPU outputs a TOP signal at a desired timing (preset timing), and then proceeds to step S25, where toner images of respective colors are sequentially placed on the intermediate transfer member, and primary transfer is performed. Control to do.

  Then, returning to step S24, control is performed so as to end the primary transfer when the processes of steps S24 and S25 are repeated N times for the number of printed pages, and then a series of operations is ended.

  On the other hand, if it is determined in step S22 that Vj is not the fastest print speed, the process proceeds to step S26, where the CPU is at a speed VT1 different from the designated print speed Vj (however, VT1 is greater than Vj and less than Vh). It is determined whether or not to perform primary transfer.

  If the CPU determines in step S26 that the primary transfer is to be performed at VT1, the process proceeds to step S27, and processing such as preparation of a printing operation and setting of the number of images is performed at VT1. In step S27, processing corresponding to the processing shown in steps S6 to S7 in FIG. 2 described in the first embodiment is performed. That is, in step S27, the CPU 101 calculates the number N of images to be primarily fixed at the print speed VT1, and sets the calculated number of images (N = N). Further, the TOP signal output of the image to be primarily transferred at the printing speed VT1 and the switching timing of the primary transfer speed are calculated. That is, in step S27, the primary transfer speed VT1 higher than the designated print speed Vj is changed to prepare for primary transfer.

  Next, in step S28, the CPU outputs a TOP signal of an image to be primarily transferred at the printing speed VT1, and in step S29, the CPU performs control to perform primary transfer. Next, in step S30, the number N of images is checked. If N is not 0, the process proceeds to step S31. After N = N−1, the process returns to step S28, and the processes in steps S28 and S29 are performed N times. Proceed to step S32. In step S32, the print speed VT1 is returned to the designated print speed Vj.

  On the other hand, if it is determined in step S26 that the CPU performs primary transfer at the designated print speed, the process proceeds to step S23. In the processing after step S23, the same processing as in the case where the printing speed Vj designated in the check processing in step S22 is the fastest printing speed Vh is performed. Further, the speed at which the fixing unit performs the fixing preparation and the image fixing process follows the printing speed specified at the time of print reservation, regardless of the determination processing result in step S22 or step S26.

  By performing this embodiment, since the print processing operation is performed by appropriately switching the primary print speed according to the print job information and the status of the printer engine, it is necessary until the primary transferred image is secondarily transferred. Saving time. Further, since the image fixing process can be performed at a designated printing speed, the printed material can be provided to the user more quickly without degrading the image quality of the printed material.

<Third Embodiment>
Hereinafter, a third embodiment will be described. Note that the image forming apparatus of the third embodiment is similar to the image forming apparatus of the first embodiment. Therefore, the description of the image forming apparatus according to the third embodiment will be made only on the parts different from those of the image forming apparatus according to the first embodiment, and the description of the common parts will be omitted because they are duplicated.

[Feature]
The third embodiment relates to processing when there is a change in the print reservation schedule, such as when a new print reservation is added to the print reservation received from the video controller or the print reservation once received is canceled. is there. That is, the TOP signal output timing and the primary print speed can be changed from the status of the print reservation schedule after the print reservation of the image for which the TOP signal is output. Since the timing or the primary print speed can be changed according to the change status of the print reservation schedule, the optimum throughput according to the status can be exhibited.

  In this embodiment, the printer engine accepts print reservations up to the Nth page, and a new N + 1 page print reservation is added before the Nth page TOP signal output timing, or a print reservation before the Nth page. Is cancelled.

  FIG. 7 is a flowchart showing the TOP signal output timing, the primary transfer speed of the image, and the primary transfer speed switching timing when the print reservation list of this embodiment is changed.

  In step S41, when the printer engine changes from the state without printing reservation to the state with printing reservation, the printing operation is started. In step S42, the printer engine accepts the printing reservation for the Nth page during the printing process.

  Next, the process proceeds to step S42, and when a print reservation for the Nth page is received, a TOP signal output timing, a primary transfer speed, and a primary transfer speed switching timing for the Nth page print image are determined. The process in step S43 is a process corresponding to the fixing speed changing process shown in steps S6 to S7 in FIG. 2 described in the first embodiment. That is, in step S43, when the printer speed is changed, the CPU 101 calculates the number N of images to be primarily fixed at the print speed VT1, and sets the calculated number of images (N = N). Further, the TOP signal output of the image to be primarily transferred at the printing speed VT1 and the switching timing of the primary transfer speed are calculated. Next, the process proceeds to step S44, where the TOP signal output timing of the Nth page is monitored. If it is not the TOP signal output timing, the process proceeds to step S46 to check whether there is a change in the print reservation.

  If there is no change in the print reservation in step S46, the process returns to step S44 again, and the monitoring of the TOP signal output timing is continued. If there is a change in the print reservation in step S46, the process returns to step S43. In step S43, the TOP signal output timing, the primary transfer speed, and the primary transfer speed switching timing for the Nth page are determined again so that the throughput is improved in the entire currently accepted print reservation including the new print reservation.

  On the other hand, when the TOP signal output timing for the Nth page comes in step S44, the process proceeds to step S45. The process in step S45 is the image transfer speed changing process in steps S8 to 13 described in the first embodiment and subsequent steps S4 to S5.

  By performing this embodiment, the primary transfer speed is appropriately switched according to the status of the print reservation list even during the print operation, and the print processing operation is performed, so the primary transferred image is secondarily transferred. Can reduce the time required by Further, since the image fixing process is performed at a designated print speed, a printed matter can be provided to the user faster without degrading the image quality.

  As described above, in the image forming apparatus in which the primary transfer process and the secondary transfer process are performed in parallel as described in the first to third embodiments, the TOP signal output timing at which the maximum throughput of the printer engine can be achieved, the primary The print speed can be determined. Therefore, not only when there is speed switching, but also during normal printing without speed switching, it is possible to reduce the time required for printing, and it is possible to provide a printed matter to the user as soon as possible.

[Other Embodiments]
Further, an object of the present invention may be to supply a storage medium storing a program code of software executable by a computer that implements the functions of the embodiments to a system or apparatus. In that case, it is also achieved by the computer (or CPU, MPU, etc.) of the system or apparatus reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, and a CD-RW can be used. Further, a DVD-ROM, a DVD-RAM, a DVD-RW, a DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  Moreover, the function of the above-described embodiment is realized by executing the program code read by the computer. However, other than that, an OS (operating system) or the like running on the computer performs part or all of the actual processing based on the instruction of the program code, and the functions of the above-described embodiments are achieved by the processing. The case where it is realized is also included.

  Further, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. After that, based on the instruction of the program code, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing, and the processing of the above-described embodiment is realized by the processing. It is.

  Further, the functions of the respective embodiments described above are realized by executing the program code read by the computer. In addition to this, when the OS running on the computer performs part or all of the actual processing based on the instruction of the program code, the functions of the above-described embodiments are realized by the processing. However, it goes without saying that it is included in the present invention.

  In this case, the program is supplied by downloading directly from a storage medium storing the program or from another computer or database (not shown) connected to the Internet, a commercial network, a local area network, or the like.

  In the above embodiment, the case where the printing method of the image forming apparatus is an electrophotographic method has been described as an example, but the present invention is not limited to the electrophotographic method, and an inkjet method, a thermal transfer method, a thermal method, It can be applied to various printing methods such as an electrostatic method and a discharge destruction method.

  The form of the program may be in the form of object code, program code executed by an interpreter, script data supplied to an OS (operating system), and the like.

1 is a diagram illustrating an example of a schematic configuration of a color image forming apparatus according to an exemplary embodiment. It is a figure which shows an example of the control structure of the color image forming apparatus of this embodiment. It is a figure explaining an example of a structure of ROM and RAM. 3 is a flowchart illustrating primary transfer processing in the image forming apparatus according to the first embodiment. FIG. 4 is a diagram for explaining processing from primary transfer to secondary transfer in the image forming apparatus of the first embodiment. FIG. 10 is a diagram comparing the time required for the end of secondary transfer in the print reservation process of the prior art and this embodiment. Comparison of the moving distance (moving time) of the intermediate transfer member necessary for changing from the primary transfer speed before the change to the primary transfer speed after the change and the image formation interval (moving time) when changing the primary transfer speed. It is. FIG. 10 is a diagram illustrating an actual time required until the end of secondary transfer in the print reservation process of the present embodiment. 10 is a flowchart illustrating primary transfer processing in the image forming apparatus according to the second embodiment. FIG. 10 is a diagram for explaining processing from primary transfer to secondary transfer in the image forming apparatus according to the second embodiment. 10 is a flowchart illustrating primary transfer processing in an image forming apparatus according to a third embodiment.

Explanation of symbols

2: Intermediate transfer member (ITB)
3a, 3b, 3c, 3d: photosensitive drums 4a, 4b, 4c, 4d: charging rollers 5a, 5b, 5c, 5d: exposure units 6a, 6b, 6c, 6d: cleaning units 8a, 8b, 8c, 8d: developing units 7: Secondary transfer roller 10: Fixing unit 11: Paper 12: Pickup roller 13: Paper storage cassette 14: Registration roller 15: Registration sensor 21: ITB drive rollers 22a, 22b, 22c, 22d: Primary transfer rollers 23, 24: ITB roller

Claims (7)

An image forming apparatus comprising: a primary transfer unit that primarily transfers an image on an image bearing member to an intermediate transfer member; and a secondary transfer unit that secondarily transfers an image primarily transferred to the intermediate transfer member to a recording medium. And
Speed changing means for changing the rotational speed of the intermediate transfer member from the first speed to the second speed in order to change the secondary transfer speed when the image is secondarily transferred to the recording medium by the secondary transfer unit. When,
When the rotation speed of the intermediate transfer member is changed from the first speed to the second speed by the speed changing unit, the secondary transfer unit performs secondary rotation with the rotation speed of the intermediate transfer member at the first speed. The intermediate transfer includes a first image to be transferred and a second image that is secondarily transferred by the secondary transfer unit following the first image when the rotation speed of the intermediate transfer body is the second speed. Control means for controlling a primary transfer operation of the first image and the second image so that the primary transfer portion performs primary transfer to the intermediate transfer body with the rotation speed of the body at the first speed. And
The control means includes a rear end of the first image when the second image is primarily transferred following the first image and the first image in a state where the rotation speed of the intermediate transfer member is the first speed. And the image interval to the tip of the second image is equal to or greater than the interval corresponding to the moving distance of the intermediate transfer member necessary for changing the rotation speed of the intermediate transfer member from the first speed to the second speed. An image forming apparatus that is controlled as described above. Wherein, after said rotational speed of the intermediate transfer member is transferred all the secondary lines planted image secondary transfer by the secondary transfer portion in a state of the first speed, said intermediate by the speed change means The image forming apparatus according to claim 1, wherein the rotation speed of the transfer body is changed to the second speed. After the image transferred by the secondary transfer unit is transferred with the rotation speed of the intermediate transfer body being the first speed, the second transfer speed is the second speed while the rotation speed of the intermediate transfer body is the second speed. images of the next transfer unit Ru is secondarily transferred is claims, characterized in that it is secondarily transferred to the recording medium after the rotational speed of the intermediate transfer member is changed to the second speed by the speed changing means The image forming apparatus according to 2.   4. The image forming apparatus according to claim 2, wherein a rotation speed of the intermediate transfer member when performing the secondary transfer is changed according to a type of a recording medium. Receiving means for receiving image formation information for forming the image;
The image forming apparatus according to claim 1, wherein the control unit sets the image interval based on image forming information received by the receiving unit.   2. The control unit according to claim 1, wherein the first speed is changed to the fastest rotation speed of the intermediate transfer member when the first speed is slower than the fastest rotation speed of the intermediate transfer member. Image forming apparatus. The control means includes
The relationship of the following formula (1),
Lt12 ≧ Lx + (Lp1 + Lp2 + Lp3 ... + LpN) + (Ld1 + Ld2 + Ld3 ... + LdN-1) (1)
Here, N is the number of images, Lt12 is the moving distance of the intermediate transfer member from the primary transfer position to the secondary transfer position, Lp1, Lp2, Lp3,..., LpN are intermediate transfer members of the respective recording media. , Ld1, Ld2, Ld3,..., LdN-1 are the conveyance intervals of the recording media, and Lx is the first transfer of the first image that performs the secondary transfer at the first speed. The image interval from the start of the primary transfer of the second image that is secondarily transferred with the rotation speed of the intermediate transfer body at the second speed,
Holds,
The N images obtained by the expression (1) are primarily transferred to the intermediate transfer member at the first speed before the speed changing unit changes the intermediate transfer member to the second speed. Item 2. The image forming apparatus according to Item 1.

Images