JP6459617B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses that the length of a toner image for density measurement is an integral multiple of the circumferential length of a support roll that rotates while supporting an intermediate transfer belt.

JP 2007-322909 A

  An object of the present invention is to improve the productivity of a measurement toner image while maintaining the density measurement accuracy at the same level as compared with the case where the length of a measurement toner image is an integral multiple of the circumference of a support roll. And

Claim 1 is an image forming apparatus for forming an image on a sheet by forming a toner image and transferring and fixing the toner image on the sheet.
A toner image forming section for forming a toner image for measurement;
A measuring unit for measuring a reflected light amount from the measurement toner image formed by the toner image forming unit and calculating a density value of the measuring toner image from the reflected light amount obtained by the measuring device;
A holding body that holds and moves the measurement toner image formed by the toner image forming unit, and a support roll that rotates while supporting a measurement region facing the measuring device,
The measuring device measures the amount of light reflected from the bare surface of the holder on which the toner image is not formed over one turn of the support roll, and the measuring unit measures the one round measured by the measuring device. The center point is the point where the measured value that matches the average value of the reflected light amount of the minute is obtained,
The toner image forming section, the two regions from the central point in the moving direction on both sides of the front Symbol holder equidistant, to form a measuring toner image pairs for calculating one concentration value,
The measurement unit divides the average value of the reflected light amount from the pair of measurement toner images measured by the measuring device by the average value of the reflected light amount over the circumference measured from the bare surface measured by the measuring device. Thus, the density value of the pair of toner images for measurement is calculated.

A second aspect of the present invention is an intermediate transfer belt in which the holding body receives a primary transfer of a toner image while circulating and holding the toner image, and secondarily transfers the toner image onto a sheet, and the support roll includes: The image forming apparatus according to claim 1, wherein the image forming apparatus is a roll that is disposed at a position facing the measuring device with the intermediate transfer belt interposed therebetween and is in contact with a back surface of the intermediate transfer belt.

According to the image forming apparatus of the present invention , compared to the case where the length of the measurement toner image is an integral multiple of the circumference of the support roll, the density measurement accuracy is maintained at the same level and the measurement toner image Productivity is improved.

Further , according to the image forming apparatus of the present invention , the center point can be easily calculated.

1 is a schematic configuration diagram of a printer as an embodiment of an image forming apparatus of the present invention. It is a figure which shows the internal structure of a control part. FIG. 6 is a diagram illustrating an arrangement pattern of toner patches and a measurement sequence. FIG. 6 is a diagram illustrating a change over time in the amount of reflected light from an intermediate transfer belt base surface. FIG. 3 is a diagram illustrating a first example of a toner patch in the present embodiment. FIG. 6 is a diagram illustrating a second example of a toner patch in the present embodiment. FIG. 6 is a diagram illustrating a third example of a toner patch in the present embodiment. It is the figure which showed the sequence of adjustment in this embodiment.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic configuration diagram of a printer as an embodiment of the image forming apparatus of the present invention.

  A plurality (two in this case) of paper trays 150 are provided in the lower part of the printer 100, and the paper P before use, which is used for image printing, is stacked in each paper tray 150. Contained. When printing an image, the paper P is picked up one by one from the designated paper tray among the plurality of paper trays 150 by the paper take-out roll 151, and moved on the paper transport path 153 by the paper transport roll 152 or the like in the direction of arrow D. It is conveyed to.

  The printer 100 is equipped with four image forming engines 130. In each image forming engine 130, a single-color toner image is formed with a single-color toner having a different color for each of the image forming engines 130Y, 130M, 130C, and 130K.

  Here, regarding the image forming engine 130, when representing the toner color, “Y” (yellow), “M” (magenta), which are codes representing the toner color in addition to the code “130” representing the image forming engine. , “C” (cyan), “K” (black). For the description irrelevant to the color, the reference numeral representing the color is omitted and the image forming engine 130 is referred to. The same applies to other elements other than the image forming engine.

  In the present embodiment, all four image forming engines 130 have the same configuration. Each image forming engine 130 includes a photoconductor 131 that rotates in the direction of arrow A, and a charger 132, an exposure device 133, a developing device 134, and a cleaner 135 disposed around the photoconductor 131.

  The charger 132 is in contact with the photosensitive member 131 and uniformly charges the surface of the photosensitive member 131.

  The exposure device 133 irradiates the photosensitive member 131 with exposure light 133a modulated based on the image signal, thereby forming an electrostatic latent image on the photosensitive member 131.

  Each exposure unit 133 is input with an image signal representing a single-color image formed from the color toner shared by the image forming engine 130 from the control unit 200. The exposure device 133 emits exposure light 133a modulated with an image signal representing the monochrome image, and an electrostatic latent image corresponding to the image signal representing the monochrome image is formed on the photoreceptor 131. Is done.

  The developing device 134 includes a developing roll 134 a that conveys toner to a region facing the photoreceptor 131. A developing bias is applied to the developing roller 134a, and the electrostatic latent image formed on the photoreceptor 131 is developed with toner by the action of the developing bias, and the electrostatic latent image is formed on the photoreceptor 131. A single color toner image having a toner distribution corresponding to the potential distribution is formed.

  Each toner cartridge 139 is provided above each image forming engine 130. Each toner cartridge 139 contains a single color toner for each corresponding image forming engine 130. The toner in the toner cartridge 139 is supplied into the developing device 134 and used for forming a toner image. The toner cartridge 139 is replaceable, and is replaced with a new toner cartridge 139 when empty.

  An intermediate transfer unit 160 is disposed below the image forming engine 130. The intermediate transfer unit 160 includes an endless intermediate transfer belt 161, a driving roll 162 that rotationally drives the intermediate transfer belt 161, a tension applying roll 163 that applies tension to the intermediate transfer belt 161, and an intermediate transfer belt 161. A pressing roll 164 that presses against the secondary transfer roll 170 is provided. The intermediate transfer belt 161 is supported by the driving roll 162, the tension applying roll 163, and the pressing roll 164, and receives a rotational driving force from the driving roll 162 to move along the four image forming engines 130. Circulates and moves in the direction of arrow B. Further, the intermediate transfer unit 160 is provided with four primary transfer rolls 165, a cleaner 166, and a sensor 167.

  The four primary transfer rolls 165 are disposed at positions facing the photoconductor 131 of each image forming engine 130 with the intermediate transfer belt 161 interposed therebetween, and the toner image formed on the photoconductor 131 is intermediated. It plays a role of transferring onto the transfer belt 161.

  The toner images formed on the respective photoreceptors 131 of the four image forming engines 130 are sequentially overlapped on the intermediate transfer belt 161 moving in the arrow B direction by the action of each primary transfer roll 163. Transcribed.

  After the toner image is transferred to the photoreceptor 131, the toner remaining on the surface is removed by the cleaner 135.

  The toner images transferred so as to sequentially overlap the intermediate transfer belt 161 are transferred onto the paper P that has been transported in time by the action of the secondary transfer roll 170. The sheet P to which the toner image has been transferred is further conveyed on the sheet conveying path 153 and is heated and pressurized by the fixing device 180, whereby an image composed of the fixed toner image is printed on the sheet P. The paper is discharged from the printer 100 onto a paper discharge tray (not shown).

  On the other hand, the toner remaining on the surface of the intermediate transfer belt 161 is removed by the cleaner 166 after the toner image is transferred.

  In the four image forming engines 130, not only a toner image representing an image instructed by the user to form an image but also a toner patch for density measurement is formed. This toner patch is an example of the measurement toner image referred to in the present invention.

  The toner patch formed by the image forming engine 130 is transferred onto the intermediate transfer belt 161. The sensor 167 is a sensor that irradiates the toner patch with light, receives the reflected light, and measures the amount of reflected light. The toner patch after the reflected light amount measurement is removed from the intermediate transfer belt 161 by the cleaner 166. A measurement result obtained by the sensor 167 is input to a control unit 190 described later and converted into a toner patch density. Then, the density of the toner patch is adjusted by adjusting the potential of the developing bias applied to the developing roll 134a and gradation correction LUT (look-up table) so that the printer 100 can always form a high-quality image. (Refer to FIG. 2).

  The printer 100 shown in FIG. 1 further includes a control unit 190 and a UI (user interface) 200. The control unit 190 is responsible for controlling the cooperative operation of the above-described units of the printer 100. Further, the control unit includes the above-described LUT (look-up table), and also plays a role in adjusting the image quality of the printer 100 such as correcting the gradation of the input image signal. The image signal after the gradation correction is sent to the exposure device 133, and the exposure device 133 outputs the exposure light 133 a modulated based on the corrected image signal and irradiates the photosensitive member 131. An electrostatic latent image is formed thereon.

  The UI 200 includes a touch-panel display screen 210 and plays a role of receiving various user operation screens and receiving user operations. In the printer 100, processing corresponding to the operation by the user on the operation screen is executed.

  FIG. 2 is a diagram illustrating an internal configuration of the control unit.

  The control unit 190 is responsible for controlling each unit of the printer 100 shown in FIG. 1 and controlling communication with external devices. The control unit 190 includes a timing generator 191, a memory 192, a pattern generator 193, an LUT storage unit 194, and a control unit 195.

  The timing generator 191 generates a timing signal that determines the operation timing of each unit constituting the printer 100.

  The memory 192 stores various programs and data for operating the printer 100.

  The pattern generator 193 forms various patterns such as a halftone dot pattern and a toner patch pattern during image formation.

  The LUT storage unit 194 is a storage unit that stores a gradation correction LUT.

  The control unit 195 communicates with the inside and outside of the control unit 190 to control the operation and the like of each unit of the printer 100.

    FIG. 3 is a diagram illustrating a toner patch arrangement pattern and a measurement sequence.

  Here, the intermediate transfer belt 161 developed in the circulating movement direction (arrow B direction) is shown over three rounds. Here, a sensor 167 is shown at the head position in the direction of arrow B.

  When the toner patch is measured by the sensor 167, the toner patch is formed on the intermediate transfer belt. No toner patch is formed during the first circumference T1 of the intermediate transfer belt 161. A toner patch 10A for adjusting the potential of the developing bias is formed between the second circumference T2 of the intermediate transfer belt 161. In the example shown here, a total of four toner patches 10A for potential adjustment are formed, one for each color of CMYK. Further, a toner patch 10 </ b> B for adjusting the LUT for gradation correction is formed between the third circumference T <b> 3 of the intermediate transfer belt 161. In the example shown here, a total of 16 LUT adjustment toner patches 10B are formed, four for each color of CMYK. The four toner patches 10B in one color have different image densities (halftone dot area ratios).

  The present embodiment is characterized by the arrangement position and arrangement pattern of the toner patch, which will be described later. Here, in order to show the concept of measurement of the toner patches 10A and 10B in an easy-to-understand manner, the toner patch 10A. , 10B are shown as one toner patch for each color of CMYK and for each image density (halftone dot area ratio).

  The intermediate transfer belt 161 circulates in the direction of arrow B, and the amount of reflected light from the surface of the intermediate transfer belt 161 on which the toner is not placed is measured by the sensor 167 first in the first circumference T1.

  The sensor 167 measures the amount of reflected light from the toner patch 10A for potential adjustment in the second round T2, and measures the amount of reflected light from the toner patch 10B for LUT adjustment in the third round T3. The

  These measured values are transmitted to the control unit 190 (see FIG. 1), and the control unit 190 calculates the densities of the toner patches 10A and 10B. Then, the potential of the developing bias is adjusted based on the density of the toner patch 10A for potential adjustment, and the LUT for gradation correction is adjusted based on the density of the toner patch 10B for LUT adjustment.

  FIG. 4 is a diagram showing a change over time in the amount of light reflected from the intermediate transfer belt surface.

  The horizontal axis is the elapsed time (msec), and the vertical axis is the sensor output (V) representing the amount of light received by the sensor 167.

  The amount of reflected light from the surface of the intermediate transfer belt 161 is essentially constant except for dirt on the surface. Nevertheless, the amount of reflected light measured by the sensor 167 fluctuates periodically as shown in FIG. This is because the sensor 167 and the intermediate transfer belt are rotated with the rotation of the tension applying roll 163 due to the eccentricity of the tension applying roll 163 (see FIG. 1) disposed at a position facing the sensor 167 with the intermediate transfer belt 161 interposed therebetween. This is due to the periodic change in the distance to 161. The tension applying roll 163 corresponds to an example of a support roll referred to in the present invention.

  Since the amount of light reflected from the bare surface measured by the sensor 167 periodically varies as shown in FIG. 4, when a toner patch having a length less than one period is formed and measured, the density is affected by the variation. The calculation accuracy of the image quality decreases, and the adjustment accuracy of the development bias and the LUT may decrease accordingly.

  In the above-mentioned patent document 1, in order to avoid the influence of this variation, it is proposed to form a toner patch having a length that is an integral multiple of the rotation period of the roll. According to this proposal, the influence of the fluctuation can be avoided. However, in this case, the length of each toner patch is long, leading to an increase in toner consumption. Further, since each toner patch is long, it is necessary to form and measure the toner patch while circulating the intermediate transfer belt 161 many more times to form the toner patch as shown in FIG. Cause the problem of long time required.

  Therefore, in the present embodiment, in order to perform highly accurate measurement without causing these problems, the following devices are adopted.

  FIG. 5 is a diagram illustrating a first example of a toner patch in the present embodiment.

  In FIG. 5, the waveform W of the waveform indicates a measured value (a sensor output (V) shown in FIG. 4) of the amount of light reflected from the raw surface of the intermediate transfer belt 161 over one turn of the tension applying roll 163 by the sensor 167. Yes. Here, the length of one round is referred to as a roll circumferential length L. Moreover, the straight line S is a line which shows the average value of the sensor output (V) over one round. An arrow B indicates the circulating movement direction of the intermediate transfer belt 161 (see arrow B shown in FIG. 1).

  Here, the center point C on the intermediate transfer belt 161 corresponding to the intersection of the waveform W of the sensor output and the average value S is calculated. This center point C indicates one point in the circulating movement direction on the intermediate transfer belt 161.

  In FIG. 5, the hatched area represents the area on the intermediate transfer belt 161 where the toner patches T1, T2 are formed. That is, in the case of the first example shown in FIG. 5, the length of a quarter of a circle (L / 4) forward from the center point C, which is one point on the intermediate transfer belt 161, in the circulating movement direction (arrow B direction). Toner patch T1 is formed, and a toner patch T2 having a length corresponding to one-fourth of a round (L / 4) is formed backward from the same center point C. These toner patches T1 and T2 are toner patches having the same toner color and image density (halftone dot area ratio). The toner patch T1 and the toner patch T2 are one continuous toner patch, but here, the toner patches T1 and T2 are conceptualized as being divided by a central point C.

  The sensor 167 measures the amount of reflected light for both of these two toner patches T1, T2. Then, the control unit 190 calculates a density value corresponding to the average value of the average values of the reflected light amount measurement values from both of the two toner patches T1 and T2. The calculated density value is a highly accurate density value in which the periodic fluctuation of the sensor output due to the eccentricity of the tension applying roll 163 is canceled.

  FIG. 6 is a diagram illustrating a second example of the toner patch in the present embodiment. The meanings of the waveform W, the straight line S, the arrow B, and the center point C are the same as those in FIG.

  Also in the second example, as in the first example shown in FIG. 5, the toner patch is formed over a half of the roll circumferential length L.

  In the case of the second example shown in FIG. 6, a toner patch T11 having a length D1 is formed forward from the center point C, which is one point on the intermediate transfer belt 161, in the circulating movement direction (arrow B direction), and at the same center. A toner patch T12 having a length D1 is also formed behind the point C in the circulation movement direction (arrow B direction). These two toner patches T12 and T22 are toner patches formed of the same color toner and having the same image density (halftone dot area ratio).

  Further, in the second example shown in FIG. 6, the toner patch T21 having the length D2 is formed from the position separated from the center point C by the distance D1 in the circulating movement direction (arrow B direction), and the same center point C is formed. A toner patch T22 having a length D2 is formed from a position separated by a distance D1 rearward in the circulation movement direction (in the direction of arrow B). These two toner patches T21 and T22 are compared with the two toner patches T11 and T12. At least one of the toner color and the image density (dot area ratio) is different. However, the two toner patches T21 and T22 are toner patches formed of the same color toner and having the same image density (halftone dot area ratio).

  In the second example, these four toner patches T11, T12, T21, and T22 are formed over the length L / 2 of the roll circumferential length when the sum of L / 4 before and after the center point C is added.

  The sensor 167 measures the amount of reflected light from each of the four toner patches T11, T12, T21, and T22. Then, the density value corresponding to the average value of the measured values for the two toner patches T11 and T12 that are equidistant from the center point C and the measurement for the two toner patches T21 and T22 that are also equidistant from the center point C. A density value corresponding to the average value is calculated. Both of the two calculated density values are highly accurate density values in which the periodic fluctuation of the sensor output due to the eccentricity of the tension applying roll 163 is canceled.

  FIG. 7 is a diagram illustrating a third example of the toner patch in the present embodiment. The meanings of the waveform W, the straight line S, and the center point C are the same as in the case of FIG.

  Also in the third example, as in the first and second examples shown in FIGS. 5 and 6, the toner patch is formed over a half region of the roll circumferential length L.

  In the case of the third example shown in FIG. 7, a toner patch T11 having a length D1 is formed forward from the center point C, which is one point on the intermediate transfer belt 161, in the circulating movement direction (arrow B direction), and at the same center. A toner patch T12 having a length D1 is also formed behind the point C in the circulation movement direction (arrow B direction). These two toner patches T12 and T22 are toner patches formed of the same color toner and having the same image density (halftone dot area ratio).

  Further, in the third example shown in FIG. 7, the toner patch T21 having the length D2 is formed from the position separated from the center point C by the distance D1 in the circulation movement direction (arrow B direction), and the same center point C is formed. A toner patch T22 having a length D2 is formed from a position separated by a distance D1 rearward in the circulation movement direction (in the direction of arrow B). These two toner patches T21 and T22 are compared with the two toner patches T11 and T12. At least one of the toner color and the image density (dot area ratio) is different. However, the two toner patches T21 and T22 are toner patches formed of the same color toner and having the same image density (halftone dot area ratio).

  Further, in the third example shown in FIG. 7, a toner patch T31 having a length D3 is formed from a position separated by a distance D1 + D2 forward from the center point C in the circulating movement direction (arrow B direction), and the same center point C is formed. A toner patch T32 having a length D3 is formed at a distance D1 + D2 from the rear in the direction of circulation movement (in the direction of arrow B). These two toner patches T31 and T32 are different from the four toner patches T11, T12, T21, and T22 in at least one of toner color and image density (halftone dot area ratio). However, the two toner patches T31 and T32 are toner patches formed of the same color toner and having the same image density (halftone dot area ratio).

  In this third example, these six toner patches T11, T12, T21, T22, T31, and T32 are formed over the length L / 2 of the roll circumferential length in total, L / 4 before and after the center point C. Has been.

  The sensor 167 measures the amount of reflected light of each of the six toner patches T11, T12, T21, T22, T31, and T32. Then, the density value corresponding to the average value of the measured values for the two toner patches T11 and T12 that are equidistant from the center point C and the measurement for the two toner patches T21 and T22 that are also equidistant from the center point C. A density value corresponding to the average value of the values and a density value corresponding to the average value of the measured values for the two toner patches T31 and T32 that are also equidistant from the center point C are calculated. All of the three calculated density values are highly accurate density values in which periodic fluctuations of the sensor output due to the eccentricity of the tension applying roll 163 are canceled.

  That is, as illustrated in FIG. 5 to FIG. 7, in this embodiment, a measurement object having a uniform density (here, the raw surface of the intermediate transfer belt 161) is measured over the entire circumference of the tension applying roll 163 by the sensor 167. In this case, a point that coincides with the average value of the measured values over the entire circumference is set as a center point C, and 2 at the same distance from the center point C on both sides of the intermediate transfer belt 161 in the circulating movement direction (arrow B direction). A pair of toner patches for density value calculation is formed in one area. Then, the control unit 190 calculates a density value corresponding to the average amount of reflected light from the pair of toner patches measured by the sensor 167. In this embodiment, in this way, a highly accurate density value is calculated in which fluctuations in sensor output due to the eccentricity of the tension applying roll 163 are canceled. Further, it is not necessary to form a toner patch having a length as long as an integral multiple of the roll circumference as proposed in the above-mentioned Patent Document 1, and the toner consumption can be reduced and adjusted (adjustment of development bias and gradation). This contributes to shortening the time required for adjustment of the correction LUT.

  FIG. 8 is a diagram showing an adjustment sequence in the present embodiment.

  When there is a print instruction, the processing of FIG. 8 is started.

  Here, first, an image is printed on one sheet (step S11), and a print counter for counting the number of prints is counted up (step S12). Then, it is determined whether or not the count value of the print counter has reached a count threshold value (for example, 1000) indicating the patch formation timing (step S13).

  If the count value of the print counter has not yet reached the count threshold value, the process proceeds to step S22. In step S22, it is determined whether or not all the prints to be output this time have been completed.

  If there are still prints to be output, the process returns to step S11, and a print output operation is performed for the next sheet.

  If it is determined in step S13 that the count value of the print counter has reached the count threshold, the process proceeds to an adjustment sequence.

  Here, first, the process of the first circumference T1 shown in FIG. 3 is performed. Here, the sensor 167 measures the amount of reflected light on the surface of the intermediate transfer belt 161 (step S14), and the control unit 190 calculates the average value (step S15). Next, the center point C on the intermediate transfer belt 161 is calculated from the measured value (for example, the waveform W in FIG. 5) and the average value (straight line S in FIG. 5) of the bare surface (step S16).

  Next, the processing of the second turn T2 and the third turn T3 of FIG. 3 is performed.

  Here, toner patches for density measurement (including both the toner patch 10A for developing bias potential adjustment and the toner patch 10B for adjusting the gradation correction LUT shown in FIG. 3) are formed (step S17). ). Here, for each density value calculation, a paired toner patch is formed before and after the center point C as illustrated in FIGS.

  Then, the amount of reflected light from the paired toner patch is measured by the sensor 167 (step S18), and the control unit 190 calculates the density value Dpatch (step S19).

This density value Dpatch is obtained from the average value Vpatch of the reflected light amount of the two toner patches that form a pair, and the average value Vclean of the measured value over the roll circumference of the reflected light amount from the raw surface of the intermediate transfer belt 161.
Dpatch = Vpatch / Vclean x1023
Is calculated by Here, “1023” is a value for normalizing the density value Dpatch to a numerical value (9 bits) from 0 to 1023.

  After calculating the density value Dpatch, the control unit 190 adjusts the developing bias potential and the tone correction LUT based on the calculated density value Dpatch (step S20).

  Thereafter, the print counter is cleared to zero (step S21). When there are still prints to be output (step S22), the process returns to step S11. When all the prints are completed (step S22), the print process is terminated.

  In the present embodiment, as described above, the paired toner patches are formed before and after the center point C. Therefore, the error in the measured value by the sensor due to the eccentricity of the roll is canceled, and a highly accurate density value is calculated. . In addition, toner consumption is reduced, and the time for adjustment is shortened.

DESCRIPTION OF SYMBOLS 100 Printer 130 Image formation engine 131 Photoconductor 134 Developing device 150 Paper tray 161 Intermediate transfer belt 167 Sensor 190 Controller 200 UI (user interface)
210 Display screen

Claims (2)

An image forming apparatus for forming an image on a paper by forming a toner image and transferring and fixing the toner image on the paper,
A toner image forming section for forming a toner image for measurement;
A measuring unit for measuring a reflected light amount from the measurement toner image formed by the toner image forming unit and calculating a density value of the measuring toner image from the reflected light amount obtained by the measuring device;
A holding body that holds and moves the measurement toner image formed by the toner image forming unit, and a support roll that rotates while supporting a measurement region facing the measuring device,
The measuring device measures the amount of light reflected from the bare surface of the holder on which the toner image is not formed over one turn of the support roll, and the measuring unit measures the one round measured by the measuring device. The center point is the point where the measured value that matches the average value of the reflected light amount of the minute is obtained,
The toner image forming section, the two regions from the central point in the moving direction on both sides of the front Symbol holder equidistant, to form a measuring toner image pairs for calculating one concentration value,
The measurement unit divides the average value of the reflected light amount from the pair of measurement toner images measured by the measuring device by the average value of the reflected light amount over the circumference measured from the bare surface measured by the measuring device. And calculating the density value of the pair of measurement toner images . The holding body is an intermediate transfer belt that receives a primary transfer of a toner image while circulating and holding the toner image, and secondary-transfers the toner image onto a sheet,
The image forming apparatus according to claim 1, wherein the support roll is a roll that is disposed at a position facing the measuring device with the intermediate transfer belt interposed therebetween and is in contact with the back surface of the intermediate transfer belt .