JPH08305215A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To provide an image forming apparatus, in which according to the quantity of a developer to be transferred and the kind of an image formation sheet or the like, a suitable quantity of heat can be applied thereto. CONSTITUTION: An image formation area on paper P is divided into a designated number of parts, the image density value of every divided area is found to estimate the quantity of a developer by an estimating circuit 20, the thickness of the paper P is detected by a paper thickness detecting sensor 50, the optimum fixing speed of every divided area is found from a table showing the relationship among the quantity of a developer, paper thickness and the fixing speed previously stored in a system controller 1, a motor driving part 61 is controlled for every divided area by the system controller 1 to change the fixing speed, and the optimum fixing heat quantity control is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine, which includes a control signal obtained by arithmetically processing an image signal and information such as the type of an image forming sheet such as copy paper. The present invention relates to an image forming apparatus that outputs a suitable image.

[0002]

2. Description of the Related Art In an image forming apparatus for forming an image by using a dry powder developer such as a copying machine, an image forming sheet on which an image is transferred is nipped by a pair of heated rollers and pressed. A method is adopted in which the image is fixed on the image forming sheet by being conveyed while being conveyed. FIG. 11 shows an outline of a fixing device that performs fixing by such a method.

In FIG. 11, the fixing device is provided between a fixing roller 31 installed so as to be rotatable by a drive motor (not shown) and a pressure roller 32 rotating while being pressed against the fixing roller 31. By sandwiching the image forming sheet P such as copy paper, the unfixed developer image t on the image forming sheet P is heated and pressed, and as a result, the developer image t is fixed to the image forming sheet P. It is something to do. Therefore, the fixing roller 31 and the pressure roller 3 are
Unfixed developer, paper dust, or the like may adhere to the surface of No. 2, so that the fixing roller 31 is provided with a release agent supplying / coating unit, which is a release agent supplying / coating unit, in order to prevent and remove the developer. The template applying device 33 and the cleaning device 34a are
Further, the pressure roller 32 is provided with a cleaning device 34b.

The heating operation in this fixing device is carried out by heating heaters 35a, 3a such as halogen lamps, which are heating means provided inside the fixing roller 31 and the pressure roller 32.
5b, the temperature of the fixing roller 3
The temperature is detected by a temperature measuring device 36 such as a thermistor arranged so as to come into contact with the surface of No. 1 and controlled so as to maintain a predetermined value.

That is, the temperature information detected by the temperature measuring device 36 is input to a system controller (not shown) that controls the operation of the entire image forming apparatus, and the surface temperature of the fixing roller 31 is the temperature required for fixing. ON / OFF of the heaters 35a and 35b so as to be maintained at Th
Control. In the conventional example device shown in FIG. 11, the temperature measuring device 36 is brought into contact with only the fixing roller 31, but it may be brought into contact with the pressure roller 32 side.

Such temperature control is carried out in order to secure the amount of heat required for fixing, but the amount of heat required for fixing is increased as the amount of developer to be fixed increases, and in particular, In a color image forming apparatus that performs multiple transfer of multicolored developers on one image forming sheet and fixes the same, heat is most difficult to transfer to the developer in the lowermost layer, so compared to a single color image forming apparatus. A fairly high amount of heat is needed,
The set amount of heat to be maintained must be set to a high value.

However, in the above-mentioned heat roller type fixing device, since the heat capacity of the roller is large, when the set temperature is set to a high value, problems such as a longer time required to raise the temperature may occur. is there.

Therefore, in particular, in a digital copying machine, a control method has been proposed in which the image is read as a digital amount, and the fixing value is made variable depending on the image by using the cumulative value of the image data as a control amount.

In recent years, instead of the above method,
A fixing method is also realized in which heat is fixed by transmitting heat through a film close to the heater. The outline is shown in FIG. The fixing device 70 shown in FIG. 12 includes a hollow heating roller 71 having a heater 72 built therein, a pressure rubber roller 73, and a belt-shaped film 78 conveyed by drive rollers 74, 75, and 76. 7
While detecting the surface temperature of 1 by a temperature measuring device 77 such as a thermistor, the image forming sheet conveyed in the conveying direction of the arrow is sandwiched between the heating roller 71 and the pressure roller 73 via a belt 78, The developer on the image forming sheet is melted and fixed by heating and pressing.

The heating roller 72 in this fixing device
Unlike the pressure rubber roller 73, since a hollow member is used, the heat conductivity can be significantly improved, and the responsiveness of temperature control can be improved.

Therefore, even in a color image forming apparatus that requires a high amount of heat, by using this fixing device, good fixing can be performed without problems such as temperature rise time, and good image formation can be performed.

Further, since the amount of heat required for the above-mentioned fixing depends not only on the amount of developer but also on the type of image forming sheet, for example, the light transmission system is used to discriminate between normal paper and OHP paper. For OHP paper having poor heat conduction, there is a method in which the conveyance speed of the fixing unit is decreased and a large amount of fixing heat is added to perform fixing.

[0013]

However, in particular,
In a full-color image forming apparatus, a large amount of multi-color developer such as a picture or photograph was transferred from an image such as a monochromatic (usually black) character original with a low suitable print ratio and a small amount of developer. The amount of the developer transferred to one image forming sheet up to the image has a large range, and the range of the necessary fixing heat amount having a positive correlation with such a developer amount is also wide. Therefore, the conventional control method may not be sufficient.

Further, in recent years, in a color image forming apparatus, thick paper or the like having a different thickness is used as an image forming sheet together with OHP paper in addition to normal paper. Therefore, in the control based on the discrimination of the paper in the paper feeding unit as described above. Sometimes it wasn't enough.

Therefore, a method of discriminating the type of the image forming sheet by an input instruction by the operator has been proposed, but it is necessary if the operator inputs the instruction of the type of the image forming sheet by mistake. Since the fixing is performed with a smaller amount of heat than the fixing heat amount, the fixing cannot be performed in the worst case, and the image forming sheet may be wound around the roller together with the half-melted developer.

On the other hand, it is conceivable to carry out the fixing with the maximum amount of fixing heat required, but in that case, even if the image can be fixed, the power consumption becomes maximum and
For a thin sheet that requires a relatively small amount of heat for fixing, the discharged sheet may be severely curved, and the stackability and the transportability during double-sided printing may be reduced.

Therefore, a first aspect of the present invention is to provide an image forming apparatus capable of applying an appropriate amount of heat according to the amount of developer to be transferred and the type of image forming sheet. There is.

In addition to the above object, the second invention of the present application aims to provide an image forming apparatus capable of applying an appropriate amount of heat according to the thickness of the image forming sheet.

Further, a third invention according to the present application aims at providing an image forming apparatus capable of appropriately achieving the above object, particularly when a heat roller heating system is adopted.

A fourth invention according to the present application aims to provide an image forming apparatus capable of appropriately achieving the above object, particularly when a film heating system is adopted.

Furthermore, in addition to the above object, the fifth invention of the present application provides an image forming apparatus capable of performing appropriate heat quantity control according to the developer quantity distribution in one image forming sheet. Is intended.

[0022]

According to the first invention of the present application, the above-mentioned object is to develop an image formed on the basis of image data with a developer in a developing device, and heat the image-forming sheet by heating. In an image forming apparatus for fixing and outputting, the estimation of the loading amount of the developer for each area based on the image data value of the area on the image forming sheet divided into predetermined ranges along the conveyance direction of the image forming sheet An estimating means for carrying out the above, a detecting means for detecting the type of the image forming sheet, and a controlling means for controlling the fixing heat quantity based on the estimated amount of developer loaded by the estimating means and the information based on the type of the image forming sheet by the detecting means. Achieved by being equipped.

According to the second invention of the present application,
The above-mentioned object is achieved in the above-mentioned first invention by the means for detecting the type of the image forming sheet being a means for detecting the thickness of the image forming sheet.

Further, according to the third invention of the present application, the above object is achieved by controlling the fixing heat amount by adjusting the fixing speed in the first invention or the second invention. To be done.

According to the fourth invention of the present application,
The above object can be achieved by controlling the fixing heat amount in the first or second invention by adjusting the fixing temperature.

Further, according to the fifth invention of the present application, according to any one of the first to fourth inventions, the object of fixing is to control the fixing heat quantity as one image. This is accomplished by switching during formation.

[0027]

According to the first aspect of the present invention, the estimation means determines each of the image data based on the image data value of the area on the image forming sheet divided into a predetermined range along the conveying direction of the image forming sheet. Information on the basis of the estimated developer loading amount and the detected image forming sheet type is detected by the control unit by estimating the developer loading amount for each area and detecting the type of the image forming sheet by the detecting unit. Controls the amount of heat of fixing. Therefore, from an image with a relatively low suitable printing rate such as a monochromatic text original and a small amount of developer to an image with a large amount of multicolor developer transferred such as a picture or photograph, it is transferred to one image forming sheet. Even if the range of developer amount to be used is wide,
Since the amount of developer is estimated from each image data,
It recognizes the proper amount of heat for various images and, in addition, recognizes the appropriate amount of heat according to the type of image forming sheet, and as a result, for different types of images on various types of image forming sheets. Appropriate heat quantity control is performed.

According to the second invention of the present application,
In the first aspect of the present invention, since the means for detecting the thickness of the image forming sheet is used as the means for detecting the type of the image forming sheet, appropriate heat quantity control is performed in accordance with the thickness of the image forming sheet. .

Further, according to the third invention of the present application, in the first invention or the second invention, the fixing heat amount is controlled by adjusting the fixing speed, so that the heat capacity is relatively large. Even when a heat roller type fixing device is used, an appropriate amount of heat is controlled according to the types of the image and the image forming sheet.

According to the fourth invention of the present application,
In the above-mentioned first invention or second invention, since the control of the fixing heat amount is performed by adjusting the fixing temperature,
When using a film type fixing device having good temperature followability, appropriate heat control is performed according to the types of the image and the image forming sheet.

Further, according to the fifth invention of the present application, according to any one of the first invention to the fourth invention, the control of the fixing heat quantity is switched during one image formation. Therefore, even when the distribution of the developer amount in one image forming sheet is different, the appropriate heat amount control is performed.

[0032]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. The apparatus of this embodiment is a digital color image forming apparatus, and is composed of a reader unit A and a printer unit B as shown in FIG.

The reader unit A is composed of an image input unit 2 and an image processing unit 3. In the image input unit 2, the document placed between the document table 2a and the document pressure plate 2b is read by the lamp 2
When scanning is performed in the direction of arrow V while irradiating with c, the reflected light image from the document is RGB3
An image is formed on the CCD 2f with a color filter, and the CCD
2f photoelectrically converts into signals of RGB colors.

Then, the image signal which has become an electric signal is processed by the image processing section 3 as follows in the flow shown in FIG. The signal from the CCD 2f is the A / D & S / H section 3
At a, it is converted into digital data and corrected by the shading correction section 3b and the input masking section 3c. In the scaling operation, the scaling processing unit 3d performs scaling processing.
Next, in the LOG converter 3e, RGB data is converted into magenta (hereinafter, M), cyan (hereinafter, C), yellow (hereinafter, Y), and black (hereinafter, K) data. The converted image data is output to the companding unit 3f that compresses, stores, and expands the image data. The stored image data is read in synchronism with each color of the printer described later, masked by the masking / UCR unit 3g, and then output image data of CMYK by the γ correction unit 3h and the edge enhancement unit 3i. Printer part B
Sent to

In the printer section B, the laser driving circuit 4 synchronizes each color of M, C, Y and K, and the laser elements 5a to 5d are driven independently of MCYK according to the image data from the reader section A. , These laser beams are respectively 7M to 7K by the polygon scanner 6.
The photosensitive drums 8M to 8K in the image forming unit are scanned.

In the image forming section 7M, since the photosensitive drum 8M which is exposed to the laser beam is charged to a desired potential by the primary charger 9M, an electrostatic latent image is formed on the photosensitive drum 8M by the exposure. The formed electrostatic latent image is developed as a toner image by the developing sleeve 11M in the developing device 10M to which a developing bias is applied, and is conveyed to a transfer portion facing the transfer charger 12M.

Similarly, the toner images of the respective colors are formed in the respective image forming sections 7C to 7K and are conveyed to the respective transfer sections.

Further, in the above apparatus, the developing sleeve 10M
-10K toner is the developer concentration sensor 13M-1
3K detects the developer density based on the amount of reflected light,
The amount of reflected light of the toner images formed on the photosensitive drums 8M to 8K is detected by the development density sensors 14M to 14K.

On the other hand, the paper P as the image forming sheet is
Paper is fed from the paper feeding devices 40 a and 40 b, the paper refeeding device 41, or the manual paper feeding device 42, and is fed onto the transfer belt 43. Here, the paper feeding devices 40a, 40
Paper size detectors 47a and 47b including a size detection switch for outputting a code signal corresponding to the size of the paper P being used are attached to b, and the size of the paper P used can be recognized. There is. Further, when the paper is fed from the manual paper feeding device 42, the paper is recognized by inputting the paper used by the user from an operation unit (not shown) in order to enable image formation on various papers. .

Then, the toner images formed on the photosensitive drums 8M are sequentially transferred onto the paper P conveyed by the transfer belt 43 by the transfer chargers 12M, so that the image of M is transferred onto the paper P. Is formed. This electrophotographic process is performed by each image forming unit 7 corresponding to each color of C, Y and K.
By performing the same in C to 7K, a color image corresponding to the original is formed.

The surfaces of the photosensitive drums 8M to 8K after the transfer are cleaned by the cleaners 16M to 16K,
Further, a primary charger 9 is provided by an auxiliary charger (not shown).
After the auxiliary charging is performed at M to 9K so as to obtain good charging, the residual charges are erased by the pre-exposure lamps 17M to 17K.

Then, the paper P on which the above-mentioned color image has been transferred passes through the pre-fixing conveyance guide 44 and is conveyed to the fixing device 30, where the toner image is heated and fixed on the paper P by the fixing device 30. , Is output as an image on the paper P.

In the case of performing the back surface paper ejection for reversing and ejecting the image surface, the paper P is conveyed to the reversal conveyance path 45, is reversed in the reversal conveyance path 45, and is then ejected. In the double-sided image forming mode, the fixed sheet P is conveyed from the reverse conveying path 45 to the re-feeding conveying path 46 and is sent to the re-feeding device 41 to form the second side image. It is arranged as a paper for.

Further, in the apparatus of this embodiment as described above, the paper thickness detecting sensor 50 as the type detecting means of the image forming sheet for detecting the thickness of the paper P before the image formation,
The paper P is more than the image forming units 7M to 7K and the transfer belt 43.
Is disposed in the vicinity of the registration roller 48 that is upstream in the conveyance direction of, and that determines the timing of conveying the paper P to the image forming units 7M to 7K by temporarily stopping the paper P.

Next, the fixing control system in this apparatus will be described with reference to the block diagram of FIG.

In FIG. 1, reference numeral 1 denotes a system controller which is a control means for controlling various controls of the apparatus. The system controller 1 controls the image processing section 3 which processes the signal from the image input section 2 described above. It has become. The image data processed by the image processing unit 3 is input to the laser drive circuit 4 described above, and the semiconductor lasers 5a to 5d are driven by the laser drive circuit,
As described above, the latent image is recorded on the photosensitive drums 8M to 8K, and the latent image is developed by the developing devices 10M to 10K.

The image data output from the image processing unit 3 is also input to the estimation circuit 20 for estimating the image density distribution, and the above-described paper thickness detection for detecting the thickness of the paper P is performed. A signal from the sensor 50 is also input to the system controller 1, and the system controller 1 performs a fixing heat amount control as described later based on the image density distribution data and the paper P thickness data.

In this fixing heat quantity control, generally, the temperature of the fixing roller 31 heated by the heater 35 is detected by the thermistor 36, and the heater driving unit 60 is controlled based on the output thereof to turn on the heater 35. / OFF
Although the time and the like are adjusted, in the present embodiment, further, based on the image density distribution data and the paper thickness data,
The fixing heat amount control is performed by sending a speed switching signal to the motor drive unit 61, driving the motor 62 at a predetermined speed, and conveying the paper P at a predetermined speed.

Hereinafter, the fixing heat amount control in this embodiment will be described in detail. First, the estimation circuit 20 as an estimation means will be described in detail with reference to FIG.

The estimation circuit 20 is intended to estimate the amount of developer consumed. Since the amount of developer consumed is considered to be roughly proportional to the integrated value of the image data, the density distribution estimation circuit 20. As a result, one image is divided into a plurality of areas in the paper feeding direction, and the image data value in each area is integrated to estimate the developer consumption amount. In this embodiment, the image forming area is divided into four as shown in FIG. 7, and the image density values C _{0 to} C ₃ of each area are obtained. Therefore, the estimation circuit is required for each color independently, but since the configuration is the same, only the description for a single color will be given below.

In FIG. 2, Data is image data output from the above-mentioned image processing unit 3, and is an 8-bit signal in this embodiment. Vclk is a synchronization clock signal of image data, Vsync is a sub-scanning synchronization signal indicating the start of one image section, Hsync is a main scanning synchronization signal indicating one main scanning section, Henable is a main scanning image effective section signal, V
enable is a sub-scanning image effective section signal.

First, the above-mentioned paper size detecting section 47a,
Based on the paper size detected by 47b, the system controller 1 determines the number of sub-scanning pixels m for forming an image.
Is calculated, and m / 4 corresponding to one region of the density distribution is calculated. Then, the number of pixels m / 4 in the sub-scanning area is input to Vsync via the OR gate 202 before image formation.
The counter 201 is loaded with, the Hsync is used as a coefficient for down-counting, and when counting from m / 4 to 0, m / 4 is reloaded and the up-counter 2
By outputting a carry as a clock to 03, and incrementing the counter value of the up counter 203, that is, the numerical value indicating the sub-scanning area, the sub-scanning area is counted every m / 4 pixels.

On the other hand, the image data is detected by the AND gate 205 in a section in which both Henable and Venable are enabled, and is stored in the flip-flop 204 in synchronization with Vclk in this section. The output of the flip-flop 204 is input to one input of the adder 206. Then, to the other input of the adder 206, the data output of a predetermined area from the buffers 216 to 219 whose output is controlled by the encode signal of the encoder 207 indicating each area is input. The two data are added, and the output of the flip-flop 208 is enable-controlled so as to correspond to a predetermined area.
To 211, the integrated values C _{0 to} C ₃ of the output of the encoder 207 based on the output of the up counter 203 and the image data corresponding to the area designated by the AND gates 212 to 215 are stored in the flip-flops 20.
8-211 and read by the system controller 1 to estimate the concentration distribution.

Incidentally, FIG. 5 shows each signal Vsyn of the video system.
c, Venable, Hsync, Henable, D
The approximate timings of ata and count value C are shown. The count value C is determined when one image is completed.

Next, FIG. 6 shows an example of a generally known paper thickness detecting sensor 50. Light emitted from the light emitting diode 51 is reflected by the reflection surface 53, which is a measurement surface, and enters the light receiving position sensor 52. Here, in the present apparatus, the reflection surface corresponds to the paper surface. When the distance from the light receiving position sensor 52 to the reflecting surface changes as shown by the solid line and the dotted line in the figure, the incident position on the light receiving position sensor 52 changes, and the analog signal 54 corresponding to the light receiving position is output. . The analog signal 54 is transferred to the AD converter 5
The data is converted into a digital signal by 5 and made into data that can be recognized by the system controller 1.

The resolution of such a sensor at present is about 10 μm, and it is possible to detect a difference in sheet thickness (10 μm) to the extent that the fixing heat amount needs to be changed.

The system controller 1 switches the fixing speed based on the paper thickness information D and the developer loading amount Cn thus obtained. As an example of the control, speed S,
Table 1 shows the relationship between the speed switching signal SS, the paper thickness information D, and the developer loading amount Cn.

[0059]

[Table 1]

[0060]

In this table, the developer loading amount Cn is 0 to a relative value when the entire solid image in the area is 100.
25% range "0", 26-50% range "1", 51-25% range "2", 76-100%
It is expressed as "3" in the range. Further, as the paper thickness information D, "0" of about 64 to 100 g paper, which is called normal paper, "1" of about 100 to 150 g paper, 15 of thick paper.
The following shows what is discriminated in three stages of "2" of 0 g paper or more.
The speed value S and the speed switching value SS are the paper thickness D
And the concentration value Cn can be expressed as a matrix.
Here, the speed value is expressed as a relative value to the normal speed 1. In this example, the speed value S is 1, 2
There are four stages of / 3, 1/2, and ⅓, and the speed change signal SS from the system controller 1 to the motor drive unit 61 for that purpose can be a 2-bit signal. Therefore, the speed switching signal SS is as shown in Table 1.

Therefore, the system controller 1 determines the speed control value SS based on the paper thickness information D and the developer loading amount Cn.
Can be determined. In addition to this, it is also possible to implement a configuration in which a synchronous clock is given from the system controller 1 side to the motor drive unit 61 and the motor 62 is driven so that the rotation speed corresponds to the clock.

FIG. 8 shows a flowchart in the copy sequence of the fixing speed control. When a signal to start the copy sequence is input (step S1), the feeding of the paper P is started, and the paper P is temporarily moved by the registration roller 48 that determines the timing of the conveyance of the paper P to the image forming units 7M to 7K. After stopping, the thickness of the paper P is detected by the paper thickness detection sensor 50, and D = 0, 1, 2 is determined (step S
2). Next, the registration roller 48 is turned on, the conveyance of the paper P is restarted, and the timer Ti in the system controller 1 for timing is started from 0 (step S3). Then, at the same time when the image is formed on the paper P, the density is estimated from the image data by the estimation circuit 20 for each area as described above, and Cn is determined (step S4). The speed S (D, Cn) and the speed switching value SS (D, Cn) are determined from the paper thickness D and the density Cn thus obtained based on the relationship in Table 1 (step S5), and n = the initial value. Set 0 (Step S
6), the timing value Tn is determined by the following equation (step S7).

[0064]

[Equation 1]

Here, L is the distance from the registration roller 48 to the fixing device 30, PS is the conveying speed of the paper P from the registration roller 48 to the fixing device 30, and m is the length of the paper P in the sub-scanning direction. When the value Ti of the timer becomes equal to Tn, that is, when the sheet P reaches the fixing device 30 (step S8), the speed switching value SS (D, C).
n) is sent to the motor drive unit 61 to switch the fixing speed (step S9). Then, n corresponding to the area is incremented (step S10), the speed switching is repeated at the timing when the paper P reaches the area, and the control is ended when the entire area is ended (step S11). By this control, the fixing speed control based on the paper P and the image density becomes possible.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIGS. 9 and 10. The first
The same parts as those of the above embodiment are designated by the same reference numerals and the description thereof will be omitted.

The present embodiment is a system for controlling the fixing temperature within one image section based on the paper thickness information D and the developer loading amount C. In this case, as a suitable fixing device, there is a fixing device of a type in which heating is performed through a belt-shaped film having a good temperature following property as shown in FIG. This method is remarkably better than the heat transfer roller method to the fixing surface, and thus enables quick temperature control. FIG. 10 shows a schematic view of an apparatus system using this type of fixing device 70. The configuration is the same as that of FIG. 1 of the first embodiment except for the fixing device 70 and the heater driving unit 62.

Then, the sheet thickness is detected and the developer loading amount is estimated from the image density data. The system controller switches the fixing speed based on the paper thickness information D and the developer loading amount Cn obtained in the same manner as in the first embodiment. As an example of the control, Table 2 shows the relationship between the fixing temperature T, the paper thickness information D, and the developer loading amount Cn.

[0069]

[Table 2]

[0070]

In this table, the developer loading amount Cn is 0 to a relative value when the entire solid image in the area is 100.
"0" in the range of 25%, "1" in the range of 26 to 50%,
It is expressed as "2" in the range of 51 to 75 and "3" in the range of 76 to 100%. Further, as the paper thickness information D, "0" of 1 to 64 g paper which is called normal paper and 1
It shows what is discriminate | determined in three steps, "1" of about 100-150 g paper, and "2" of 150 g or more of thick paper. The temperature value T can be expressed as a matrix of the paper thickness D and the density value Cn.

FIG. 9 shows a flowchart in the copy sequence of the fixing speed control. When a signal for starting the copy sequence is input (step S21), the feeding of the paper P is started, and the registration roller 48 determines the timing of the conveyance of the paper P to the image forming units 7M to 7K.
Is temporarily stopped, the thickness of the paper P is detected by the paper thickness detection sensor 50, and D = 0, 1, 2 is determined (step S22). Next, the registration roller 48 is turned on, the conveyance of the paper P is restarted, and the timer Ti in the system controller 1 for timing is started from 0 (step S23). Then, at the same time when the image is formed on the sheet P, the density is estimated for each area from the image data to determine Cn (step S24), and the temperature control value (D, Cn) is determined based on the relationship in Table 2 (step S25).

Then, n = 0 is set as the initial value (step S26), the temperature control value T (D, Cn) is sent out (step S27), and the temperature control is started (step S).
28, 29). Then, the timing value Tn is determined by the following equation (step 30).

[0074]

[Equation 2]

Here, L is the distance from the resist roller to the fixing device, and PS is the resist roller to the fixing device 3.
The conveyance speed of the paper P up to 0, m is the length of the paper P in the sub-scanning direction. When the value Ti of the timer is equal to or lower than Tn, the temperature control is continued (steps S28 and 29), and when the value Ti of the timer becomes equal to Tn, that is, when the paper P reaches the switching point of the area (step S28). S31), n indicating the area is incremented (step S32), the temperature control value T (D, Cn) is changed (step S33), and the temperature is sent to the heater driving unit 62 to switch the fixing temperature (step S27). Hereinafter, the temperature switching is repeated at the timing when the paper P reaches the area, and the control is ended when the entire area is completed (step S33). By this control,
It is possible to control the fixing temperature based on the paper and the image density.

[0076]

According to the first invention of the present application, based on the image data value of the area on the image forming sheet divided into predetermined ranges along the conveying direction of the image forming sheet,
An estimation unit that estimates the amount of developer loaded for each area, a detection unit that detects the type of image forming sheet, and an amount of heat of fixing based on the estimated amount of developer loaded and information based on the detected type of image forming sheet. Since it has a control means for controlling, from images with a low comparative suitable printing rate such as monochromatic text originals and a small amount of developer, to images in which many multicolor developers have been transferred such as pictures and photographs, Even when the range of the amount of developer transferred to one sheet is wide, and when various types of image forming sheets are used, it is possible to always perform appropriate heat quantity control, sheet winding, and power consumption. It is possible to prevent the stacking property and the transporting property from being deteriorated due to the increase of the number of sheets and the bending of the sheet.

According to the second invention of the present application,
In the first aspect of the present invention, since the means for detecting the thickness of the image forming sheet is used as the means for detecting the type of the image forming sheet, it is necessary to appropriately control the amount of heat according to the thickness of the image forming sheet. Therefore, it is possible to prevent the winding of sheets, the increase of power consumption, and the deterioration of stackability and transportability due to the bending of sheets.

Further, according to the third invention of the present application, in the above-mentioned first invention or second invention, the fixing heat amount is controlled by adjusting the fixing speed, so that the heat having a relatively large heat capacity is used. When using a roller-type fixing device, it is possible to perform appropriate heat control according to the type of image and sheet, and prevent winding of the sheet, increase in power consumption, and deterioration of stackability and transportability due to bending of the sheet. be able to.

According to the fourth invention of the present application,
In the first invention or the second invention, the amount of heat of fixing is controlled by adjusting the fixing temperature. Therefore, when a film type fixing device having good temperature followability is used,
Appropriate heat quantity control can be performed according to the type of image and sheet, and it is possible to prevent the winding of the sheet, the increase in power consumption, and the deterioration in stackability and transportability due to bending of the sheet.

Further, according to the fifth invention of the present application, according to any one of the first invention to the fourth invention, the control of the fixing heat amount is switched during one image formation. Since it is carried out by the above, even if the developer amount distribution in one sheet is different, it is possible to perform appropriate heat amount control, winding of the sheet, increase of power consumption, deterioration of stackability and transportability due to bending of the sheet. Can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram of a control circuit according to a first embodiment of the present invention.

FIG. 2 is a detailed block diagram of an estimation circuit in the circuit of FIG.

FIG. 3 is a configuration diagram of a digital copying machine according to the first embodiment of the present invention.

FIG. 4 is a block diagram of image data processing according to the first embodiment of the present invention.

FIG. 5 is a timing schematic diagram of image data control signals in the first embodiment of the present invention.

FIG. 6 is an explanatory diagram of a paper thickness detection sensor according to the first embodiment of this invention.

FIG. 7 is an explanatory diagram of an image density region in the first embodiment of the present invention.

FIG. 8 is a flowchart of fixing heat amount control according to the first embodiment of the present invention.

FIG. 9 is a flowchart of fixing heat amount control according to the second embodiment of the present invention.

FIG. 10 is a block diagram of a digital copying machine according to a second embodiment of the present invention.

FIG. 11 is a configuration diagram of a conventional pressure-heating type fixing device.

FIG. 12 is a configuration diagram of a conventional film type fixing device.

[Explanation of symbols]

1 system controller (control means) 10M to 10K developing device 20 estimation circuit 50 paper thickness detection sensor (means for detecting the type of image forming sheet) P paper (image forming sheet)

Claims (5)

[Claims] 1. An image forming apparatus for developing an image formed on the basis of image data with a developer in a developing apparatus, fixing the image on a sheet by heating, and outputting the image, in a predetermined direction along the conveying direction of the image forming sheet. Estimating means for estimating the loading amount of the developer for each area based on the image data value of the area on the image forming sheet divided for each range, detecting means for detecting the type of the image forming sheet, and the estimation. An image forming apparatus comprising: a control unit that controls a fixing heat amount based on an estimated amount of developer loaded by the unit and information based on the type of the image forming sheet by the detecting unit. 2. The image forming apparatus according to claim 1, wherein the means for detecting the type of the image forming sheet is means for detecting the thickness of the image forming sheet. 3. The image forming apparatus according to claim 1, wherein the control of the fixing heat amount is performed by adjusting the fixing speed. 4. The fixing heat amount is controlled by adjusting a fixing temperature.
The image forming apparatus according to item 1. 5. The image forming apparatus according to claim 1, wherein the control of the fixing heat amount is performed by switching the control fixing heat amount during one image formation.