JP2017142213A - Temperature detection device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously detect temperature in a non-image area of a recording material while conveying the recording material, even when the recording material has feed holes.SOLUTION: A temperature detection area of a temperature detection part 120 is arranged on a locus through which feed holes 122 provided in both ends in the width direction of a continuous form sheet P pass. This prevents the temperature detection part 120 from detecting the temperature of an image area of the continuous form sheet P. The minimum required number and a plurality of temperature detection parts 120 are arranged on the locus through which the feed holes 122 pass, and detection signals from a plurality of the temperature detection parts 120 are combined, to make it possible to constantly detect the temperature of the non-image area of the continuous form sheet P. The minimum required number and a plurality of temperature detectors 120 are specified on the basis of the specification of the continuous form sheet P and the specification of the temperature detector 120 (detection area).SELECTED DRAWING: Figure 4

Description

  The present invention relates to a temperature detection device and an image forming apparatus.

  For example, when an image is formed by an ink jet printer, the temperature of the recording paper may be measured for output control for a heater for drying droplets (ink).

  Patent Document 1 describes that ink temperature measurement is performed at a substantially central portion of a storage medium, and drying control is performed.

  Patent Document 2 describes that the temperature of the recording medium is made constant by measuring the temperature distribution of the recording medium and controlling a plurality of heaters based on the distribution.

  Patent Document 3 describes that the integrated value of the amount of heat applied to the recording medium is made constant by measuring the temperature distribution of the recording medium and controlling a plurality of heaters based on the distribution.

JP 2010-005996 A JP 2003-237034 A JP 2003-237036 A

  In order to avoid the influence of image density and color when measuring the temperature of the recording paper, it is preferable to measure the non-image area (blank area) of the recording paper, but in the case of the recording paper having a feed hole in the non-image area If the timing at which the feed hole passes through the temperature measurement position and the timing at which the temperature is measured overlap, temperature measurement becomes difficult.

  An object of the present invention is to provide a temperature detection apparatus and an image forming apparatus capable of continuously detecting a recording material temperature in a non-image area while conveying the recording material even if the recording material has a feed hole. And

  According to the first aspect of the present invention, the temperature detection unit that is provided in the recording material and is arranged so that the passage area of the feed hole for receiving the conveyance force becomes the detection area, and detects the temperature of the recording material; And a detection timing control means for controlling the detection timing so as to detect the temperature of the non-image area of the recording material while conveying the recording material.

  According to a second aspect of the present invention, in the first aspect of the present invention, at least one temperature detection unit is provided regardless of a relative positional relationship between the feed hole and the temperature detection unit during conveyance of the recording material. The required minimum number n of temperature detection portions in which the detection region is located at a position where the detection region does not interfere with the feed hole are arranged in the conveyance direction of the recording material.

  According to a third aspect of the present invention, there is provided the recording material according to the second aspect, wherein the diameter of the feed hole is φ1, the pitch of the feed hole is P, and the detection area diameter of the temperature detector is φ2. The number n of the temperature detection units arranged in the transport direction is an integer obtained by rounding up the decimal part of the calculation result of 1 / {(P−φ1−φ2) / P}.

  According to a fourth aspect of the invention, in the invention of the second or third aspect, the detection results of the non-image area are extracted from the detection results of the plurality of temperature detection units and synthesized.

  According to a fifth aspect of the present invention, there is provided a transport unit that transports the recording material along a specific transport direction by being connected to a feed hole provided in the recording material, and a droplet while transporting the recording material. The temperature detection means for detecting the temperature of the recording material, wherein the recording means for recording an image by landing and drying, and the passage area of the feed hole provided in the recording material are arranged as a detection area A detection timing control means for controlling the detection timing so as to detect the temperature of the non-image area of the recording material while conveying the recording material, and temperature information of the non-image area detected by the detection timing control means And a drying control means for controlling the drying capacity of the recording means.

  According to a sixth aspect of the present invention, in the invention of the fifth aspect, at least one temperature detection unit is provided regardless of a relative positional relationship between the feed hole and the temperature detection unit during conveyance of the recording material. The required minimum number n of temperature detection portions in which the detection region is located at a position where the detection region does not interfere with the feed hole are arranged in the conveyance direction of the recording material.

The invention according to claim 7 is the invention according to claim 6, wherein the diameter of the feed hole is φ1, the pitch is P, and the detection area diameter of the temperature detection unit is φ2.
The number n of the temperature detection units arranged in the conveyance direction of the recording material is an integer obtained by rounding up the decimal point of the calculation result of 1 / {(P−φ1−φ2) / P}.

  The invention according to claim 8 is the invention according to claim 6 or 7, wherein the detection result of the non-image region is extracted from the detection results of the plurality of temperature detection units and synthesized.

  According to the first aspect of the present invention, even if the recording material has a feed hole, it is possible to continuously detect the recording material temperature in the non-image area while conveying the recording material.

  According to the second aspect of the present invention, the temperature detection of the non-image area by the temperature detection unit can be continued.

  According to invention of Claim 3, the relative positional relationship of a temperature detection part and a feed hole can be specified.

  According to invention of Claim 4, the detection result of a some temperature detection part can be selected.

  According to the fifth aspect of the present invention, it is possible to continuously detect the recording material temperature in the non-image area while conveying the recording material.

  According to the sixth aspect of the present invention, the temperature detection of the non-image area by the temperature detection unit can be continued.

  According to invention of Claim 7, the relative positional relationship of a temperature detection part and a feed hole can be specified.

  According to invention of Claim 8, the detection result of a some temperature detection part can be selected.

It is a schematic block diagram which shows an example of the main components of the inkjet recording device which concerns on this Embodiment. It is a front view of a continuous form paper as a paper applied to the present embodiment. It is a temperature detection characteristic figure in a single temperature detection part in connection with this Embodiment. FIG. 5 is a front view for specifying the specifications of the continuous form sheet and the dimensions of the temperature detection region according to the present embodiment. It is the transition diagram and temperature characteristic figure which show the relative positional relationship with the feed hole in the time series of a temperature detection part. It is a front view which shows the arrangement | positioning state of the three temperature detection parts by the predetermined standard. It is a transition diagram which shows the relative positional relationship with the feed hole in the time series of the three temperature detection parts of FIG. FIG. 7 is a characteristic diagram in which detection results of three temperature detection units in FIG. 6 and detection temperatures of a non-image region are combined.

(Outline of equipment)
FIG. 1 is a schematic configuration diagram illustrating main components of an inkjet recording apparatus 12 as an image forming apparatus according to the present embodiment.

  The ink jet recording apparatus 12 includes, for example, two sets of image forming units 20A and 20B that are examples of a recording unit, a control unit 22 that is an example of a detection timing control unit, a storage unit 30, a paper feed roll 80, a discharge roll 90, and A conveyance roller 100 which is an example of a conveyance unit is provided.

  The image forming unit 20A includes, for example, a head drive unit 40A, a print head 50A, a heater drive unit 60A, a drying device 70A, and a paper speed detection sensor 110A.

  Similarly, the image forming unit 20B includes, for example, a head driving unit 40B, a print head 50B, a heater driving unit 60B, a drying device 70B, and a paper speed detection sensor 110B.

  Hereinafter, when it is not necessary to distinguish between the image forming unit 20A and the image forming unit 20B, and the common members included in the image forming unit 20A and the image forming unit 20B, the symbol “A” and the symbol at the end of the symbol are used. “B” is omitted.

  The controller 22 controls the rotation of the transport roller 100 connected to the paper transport motor via a mechanism such as a gear by driving a paper transport motor (not shown). A long paper P is wound around the paper feed roll 80 as a recording medium in the paper transport direction, and the paper P is transported in the paper transport direction as the transport roller 100 rotates.

  For example, the control unit 22 acquires image information stored in the storage unit 30 and controls the image forming unit 20A based on the color information for each pixel of the image included in the image information, so that one image of the paper P is obtained. An image corresponding to the image information is formed on the forming surface.

  Specifically, the control unit 22 controls the head drive unit 40A. Then, the head drive unit 40A drives the print head 50A connected to the head drive unit 40A in accordance with the ink droplet discharge timing instructed by the control unit 22 to discharge the ink droplets from the print head 50A and is conveyed. An image corresponding to the image information is formed on one image forming surface of the paper P to be printed.

  Note that the color information for each pixel of the image included in the image information includes information that uniquely indicates the color of the pixel. In this embodiment, as an example, the color information for each pixel of the image is represented by the respective densities of yellow (Y), magenta (M), cyan (C), and black (K). Other expression methods that uniquely indicate the color of the image may be used.

  The print head 50A includes four print heads 50AY, 50AM, 50AC, and 50AK corresponding to four colors of Y, M, C, and K, respectively, and droplets of the corresponding colors from the print head 50A. A certain ink droplet is ejected. The driving method for ejecting ink droplets in the print head 50A is not particularly limited, and a known method such as a so-called thermal method or piezoelectric method is applied.

  The heater driving unit 60A includes a switching element that controls the amount of heat by turning on and off a heater (not shown) included in the drying apparatus 70A, and drives the switching element based on an instruction from the control unit 22.

  Then, the control unit 22 controls the heater driving unit 60A to dry the ink droplets of the image formed on the paper P by the drying air including the radiant heat from the drying device 70A toward one image forming surface of the paper P. The image is fixed on the paper P. The controller 22 can improve the drying efficiency by performing the heater on / off control while maintaining the drive current based on the image information. In addition, you may make it control the strength of a drive current. In addition, you may use the dry form using a laser beam as a dry form.

  Thereafter, the sheet P is transported to a position facing the image forming unit 20 </ b> B as the transport roller 100 rotates. At this time, the paper P is conveyed so that the other image forming surface different from the image forming surface on which the image is formed by the image forming unit 20A faces the image forming unit 20B.

  The controller 22 forms an image corresponding to the image information on the other image forming surface of the paper P by executing the same control as the control for the image forming unit 20A on the image forming unit 20B. As described above, the inkjet recording apparatus 12 includes two sets of the image forming unit 20A and the image forming unit 20B in order to cope with double-sided printing on the paper P.

  Then, the paper P is transported to the discharge roll 90 as the transport roller 100 rotates, and is wound around the discharge roll 90.

  The paper speed detection sensor 110 is disposed, for example, at a position facing the image forming surface of the paper P, detects the transport speed of the paper P in the paper transport direction, and notifies the control unit 22 of it.

The control unit 22 uses the transport speed of the paper P acquired from the paper speed detection sensor 110 and the drying device 70 at a timing when the ink droplets ejected onto the paper P are transported to an area where the drying air of the drying device 70 is blown. The detection method for detecting the conveyance speed of the paper P in the paper speed detection sensor 110 is controlled without any particular limitation. Applies. The sheet speed detection sensor 110 is not an essential member for the inkjet recording apparatus 12 according to the present embodiment.

  In addition, there are water-based inks, oil-based inks that are inks whose solvent evaporates, ultraviolet curable inks, and the like. In this embodiment, water-based inks are used. In the present embodiment, the term “ink” or “ink droplet” simply means “water-based ink” or “water-based ink droplet”.

  Here, since the output control including the temperature and the air volume of the drying air generated by the drying device 70 in the heater driving unit 60 depends on the temperature of the paper P, the downstream side of the drying device 70 has a print process and a post-drying process. A temperature detector 120 (120A, 120B) for detecting the temperature of the paper P is disposed.

  In the temperature measurement for controlling the output of the drying device 70 by the heater driving unit 60, when the area printed by the print head 50 is measured, the detected temperature may be influenced by the density and color of the printed image. In other words, the temperature detection of the paper P by the temperature detection unit 120 is preferably performed on a non-image area of the paper P.

  In the present embodiment, the continuous form paper P wound around the paper supply roll 80 is applied as the paper P. Therefore, it is hereinafter referred to as continuous form paper P.

  As shown in FIG. 2, the continuous form paper P has a rear end portion and a front end portion of one unit area (one page) combined, and is subjected to, for example, cut line processing. In the printing process and the drying process, the long state is maintained and the sheet is wound around the discharge roll 90.

  Further, the continuous form paper P is provided with feed holes 122 at a uniform pitch along the transport direction at the end (one end or both ends) in the width direction intersecting the transport direction. This feed hole is accommodated in a sprocket pin (not shown) arranged at a uniform angle on the peripheral surface of the transport roller 100 (see FIG. 1) and is connected. When the transport roller 100 rotates, the continuous form paper P is transported by receiving a transport force due to the connection between the sprocket pin and the feed hole 122.

  In the continuous form paper P having the above structure, the non-image area where the temperature of the surface of the continuous form paper P can be detected continuously along the transport direction is at least deviated from the width dimension of the image area. The width is limited to both ends.

  On the other hand, the feed holes 122 are present at both ends in the width direction of the continuous form paper P as described above.

(Image area temperature detection avoidance structure)
Therefore, in the present embodiment, the temperature detection region of the temperature detection unit 120 is arranged on a trajectory through which the feed holes 122 provided at both ends in the width direction of the continuous form paper P pass.

  Thereby, the temperature detection unit 120 is prevented from detecting the temperature of the image area.

  In addition, the temperature detection unit 120 can detect the temperature of the non-image area of the continuous form paper P at a higher rate compared to avoiding an image area wider than the feed hole 122 although it is intermittent. Become.

  In the case where one temperature detection unit 120 is arranged on the trajectory passing through the feed hole 122, the ratio of the temperature detection area facing the non-image area while the continuous form paper P is transported between the feed holes of one pitch. (Equivalent to the above ratio) is {(pitch of feed hole−diameter of feed hole) / pitch of feed hole} × 100 (%).

(Temporal continuous temperature detection structure)
By the way, in the temperature detection region by one temperature detection unit 120, it is physically difficult to face the non-image region continuously without interruption on the time axis during the conveyance of the continuous form paper P. There is a case.

  In other words, in one temperature detection unit 120, the detection timing on the time axis of the imaged portion becomes intermittent (see FIG. 3).

  Therefore, in the present embodiment, by arranging the plurality of temperature detection units 120 on the trajectory through which the feed hole 122 passes, and by combining the detection signals from the plurality of temperature detection units 120, the minimum is necessary. The temperature of the non-image area of the continuous form paper P can always be detected.

  In the present embodiment, as shown in FIG. 4, the minimum required number of temperature detectors 120 are specified based on the specifications of the continuous form P and the specifications (detection areas) of the temperature detector 120. ing.

  That is, the values of the pitch P of the feed holes 122 of the continuous form paper P, the diameter φ1 of the feed holes 122, and the diameter φ2 of the detection region 120R of the temperature detection unit 120 on the paper surface of the continuous form paper P are acquired.

  The detection region 120R of the temperature detection unit 120 is circular, and the center of the detection region 120R moves on a line connecting the centers of the feed holes 122. When the detection area 120R is not circular, for convenience, a circumscribed circle of the non-circular detection area is set as the detection area 120R.

  As shown in FIG. 5, in a state where the continuous form paper P is being transported, the downstream side adjacent in the transport direction from the point when the upstream feed hole 122A adjacent in the transport direction and the detection region 120R are coaxial. Consider the position of the detection region 120R until the feed hole 122B and the detection region 120R are coaxial.

  In FIG. 5, in the pitch dimension of the feed hole 122A and the feed hole 122B, the detection region 120R interferes with the feed hole 122A or the feed hole 122B and does not interfere with the feed hole 122A or the feed hole 122B. being classified.

  The state of not interfering with the feed hole 122A or the feed hole 122B is a state in which only the temperature of the non-image area can be detected on the feed hole 122 (see the range of the entire non-image area in FIG. 5).

  An arithmetic expression for obtaining the dimension Pw that does not interfere with the feed hole 122A or the feed hole 122B with respect to the pitch dimension of the feed hole 122A and the feed hole 122B is expressed by the following formula (1).

Pw = P−φ1−φ2 (1)
Here, an arithmetic expression for obtaining a ratio R of the dimension Pw that does not interfere with the feed hole 122A or the feed hole 122B with respect to the pitch dimension P of the feed hole 122A and the feed hole 122B is expressed by the following formula (2). .

R = Pw / P = (P−φ1−φ2) / P (2)
The number n of the temperature detectors 120 is obtained from the Pw value calculated by the equation (2). The minimum necessary number n of the temperature detection units 120 is expressed by the following equation (3).

n = 1 / Pw = 1 / {(P−φ1−φ2) / P} = P / (P−φ1−φ2) (3)
However, in the equation (3), the decimal part of the calculation result is moved up.

  If the n temperature detection units 120 calculated by the equation (3) are arranged uniformly in the transport direction, that is, (P / n) + P × integer multiple pitch, any one of the temperature detection units 120 is It can be in a state where it does not interfere with the feed hole 122A or the feed hole 122B.

  Note that (P / n) + P × integer multiple pitch is a plurality (integer) when a plurality of temperature detection units 120 cannot be physically disposed between two feed holes 122 adjacent in the transport direction. It is assumed that they are shifted by the pitch.

  The operation of the present embodiment will be described below.

  By driving the paper transport motor, the paper P is transported from the paper feed roll 80 in the paper transport direction, the image information stored in the storage unit 30 is acquired, and the color information for each pixel of the image included in the image information is obtained. Based on this, the image forming unit 20A is controlled to form an image corresponding to the image information on one image forming surface of the paper P. Then, by controlling the heater driving unit 60A, the ink droplets of the image formed on the paper P are dried by the drying air including the radiant heat from the drying device 70A toward one image forming surface of the paper P, and the paper Fix the image on P.

  Thereafter, the sheet P is transported to a position facing the image forming unit 20 </ b> B as the transport roller 100 rotates. At this time, the paper P is transported so that the other image forming surface different from the image forming surface on which the image is formed by the image forming unit 20A faces the image forming unit 20B, and the other side of the paper P is transferred by the image forming unit 20B. An image corresponding to the image information is formed on the image forming surface, and dried by the drying device 70B to fix the image. Then, the paper P is transported to the discharge roll 90 as the transport roller 100 rotates, and is wound around the discharge roll 90.

  Here, drying in the drying apparatuses 70A and 70B takes into consideration the permeability of the ink and the like, and an appropriate amount of drying air is required. The basis is the temperature of the non-image area of the paper P. In the present embodiment, the temperature detection unit 120 detects the temperature of the non-image area of the paper P.

  The generally used continuous form paper P is ISO 2784, JISx6195, the pitch dimension P of the feed holes 122 is 12.7 mm, the diameter φ1 of the feed holes 122 is 4.0 mm, and the width of the continuous form paper P shown in FIG. The dimension W1 from the direction end to the feed hole 122 is defined as 4.34 mm, and the dimension W2 is defined as 6.35 mm, and this dimension is widely used as a standard dimension.

  Therefore, in the present embodiment, the minimum necessary number n of the temperature detection units 120 is obtained based on the specified dimensions.

  The diameter φ2 of the detection region 120R of the temperature detection unit 120 applied in the present embodiment is 4.3 mm.

  First, the dimension Pw which does not interfere with the feed hole 122A or the feed hole 122B with respect to the pitch dimension of the feed hole 122A and the feed hole 122B is obtained by the expression (1).

  Since P = 12.7 mm, φ1 = 4.0 mm, and φ2 = 4.3 mm, Pw = 12.7-4.0-4.3 = 4.4 mm.

  Next, the ratio R of the dimension Pw that does not interfere with the feed hole 122A or the feed hole 122B with respect to the pitch dimension P of the feed hole 122A and the feed hole 122B is obtained by the expression (2).

  Since Pw = 4.4 mm, R = 4.4 / 12.7≈0.35.

  The number n of the temperature detectors 120 is the reciprocal of the R value, and is obtained from the equation (3). The number after the decimal point is raised.

  That is, n = 1 / 0.35≈2.8573 (n = 3 by rounding up the decimal point).

  FIG. 6 is a plan view in the case where the three temperature detectors 120 are evenly arranged in the conveyance direction of the continuous form paper P. FIG. The temperature detection unit 120 applied to the present embodiment cannot be accommodated in the pitch P (12.7 mm) between the two feed holes 122, so that the temperature detection unit 120 between the two feed holes 122 is different. Each one was placed. That is, they are arranged at a pitch of 16.9 mm to 17.0 mm, which is a pitch of (P / n) + 1 × P.

  FIG. 7 is a transition diagram of the relative positional relationship between each temperature detection unit 120 and the feed hole 122 when the continuous form paper P is conveyed in the state where the three temperature detection units 120 of FIG. 6 are arranged. .

  From the left column to the right column in FIG. 7, the relative positional relationship between each temperature detection unit 120 and the feed hole 122 changes in time series.

  In FIG. 7, a solid circle indicates the feed hole 122, and a dotted circle indicates the detection region 120 </ b> R of the temperature detection unit 120.

  The detection area 120R indicated by the mesh line indicates the effective detection area, that is, the area that does not interfere with the feed hole 122, and the detection area 120R indicated by the white space interferes with the invalid detection area, that is, the feed hole 122. Indicates the area.

  In FIG. 7, if the sensor 1, sensor 2, and sensor 3 are identified in order from the bottom in order to identify the three temperature detectors 120, as shown in FIG. 8, the effective detection regions 120R are different on each time axis. However, when the effective detection regions 120R of the sensor 1, the sensor 2, and the sensor 3 are combined, the temperature of the non-image region of the continuous form paper P that does not interfere with the feed hole 122 can be detected continuously on the time axis. Recognize.

  In the present embodiment, the continuous form paper P conforming to the JIS standard or the like is used, so that the temperature detecting unit 120 is set to three pieces, continuously on the time axis, and does not interfere with the feed hole 122. Although it has been demonstrated that the temperature of the non-image area of the form paper P can be detected, the number of the temperature detection units 120 is not limited to three.

  Moreover, although the continuous form paper having the feed holes has been described, in the case of roll paper having no feed holes, the temperature may be measured at an arbitrary timing.

  Table 1 below is a list of the number n of the temperature detection units 120 set based on the calculation results of the expressions (1) to (3). In Table 1, theoretically, six or more temperature detectors 120 can be arranged, but up to five that can be applied in practice are shown.

Each ratio may overlap within a predetermined allowable range. For example, when the ratio R is 0.3 to 0.35 and the number n of the temperature detection units 120 is overlapped with three and four, and the calculation result ratio R is 0.32, the temperature detection unit 120 is uniform. The number may not be four, but three may be selected by relaxing the detection accuracy.

P paper (continuous form paper)
DESCRIPTION OF SYMBOLS 12 Inkjet recording device 20 Image formation part 22 Control part 30 Storage part 40 Head drive part 50 Print head 60 Heater drive part 70 Drying apparatus 80 Paper feed roll 90 Discharge roll 100 Conveyance roller 110 Paper speed detection sensor 120 Temperature detection part 120R Detection area 122 Feed hole

Claims (8)

A temperature detection unit that is provided in the recording material and is arranged so that a passage region of the feed hole for receiving the conveyance force becomes a detection region, and detects the temperature of the recording material;
A detection timing control means for controlling the detection timing so as to detect the temperature of the non-image area of the recording material while conveying the recording material;
A temperature detecting device.   Regardless of the relative positional relationship between the feed hole and the temperature detection unit during conveyance of the recording material, the minimum number necessary for the detection region of at least one temperature detection unit to be a position that does not interfere with the feed hole. The temperature detection device according to claim 1, wherein n temperature detection units are arranged in a conveyance direction of the recording material. When the diameter of the feed hole is φ1, the feed hole pitch is P, and the detection area diameter of the temperature detector is φ2,
The temperature detection device according to claim 2, wherein the number n of the temperature detection units arranged in the recording material conveyance direction is an integer obtained by rounding up the decimal point of the calculation result of 1 / {(P-φ1-φ2) / P}. .   The temperature detection device according to claim 2 or 3, wherein the detection results of the non-image region are extracted and synthesized from the detection results of the plurality of temperature detection units. Conveying means for conveying the recording material along a specific conveying direction by being connected to a feed hole provided in the recording material;
Recording means for recording an image by landing and drying droplets while conveying the recording material;
A temperature detection unit that is arranged so that a passage region of a feed hole provided in the recording material becomes a detection region, and detects the temperature of the recording material;
A detection timing control means for controlling the detection timing so as to detect the temperature of the non-image area of the recording material while conveying the recording material;
Based on the temperature information of the non-image area detected by the detection timing control means, a drying control means for controlling the drying capacity by the recording means,
An image forming apparatus.   Regardless of the relative positional relationship between the feed hole and the temperature detection unit during conveyance of the recording material, the minimum number necessary for the detection region of at least one temperature detection unit to be a position that does not interfere with the feed hole. The image forming apparatus according to claim 5, wherein n temperature detection units are arranged in a conveyance direction of the recording material. When the diameter of the feed hole is φ1, the pitch is P, and the detection area diameter of the temperature detection unit is φ2,
The image forming apparatus according to claim 6, wherein the number n of the temperature detection units arranged in the recording material conveyance direction is an integer obtained by rounding up a decimal point of a calculation result of 1 / {(P−φ1−φ2) / P}. .   8. The image forming apparatus according to claim 6, wherein the detection result of the non-image area is extracted from the detection results of the plurality of temperature detection units and synthesized.