JPH07199721A - Image forming device - Google Patents

Abstract

PURPOSE:To fix a read-out image in a best fixing condition adapting to the original image density in an image forming device which fixs the read-out image on a prescribed paper by heating and pressurizing. CONSTITUTION:The image forming device is provided with a density detecting means 36 detecting an image density or an image area of the original D, a storage means 72 storing a control value corresponding to an output of the density detecting means 36, a pressure controlling means 72 adjusting a fixing pressure, a heating controlling means 76 adjusting a fixing temperature, a delay means 77 delaying heating starting time and a control means 70 controlling the pressure controlling means 74 and the heating controlling means 76 by judging the output of the density detecting means 36 and obtaining the control value stored in the storage means 72.

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 which heats and presses an image developed with toner to fix it on a transfer paper.

[0002]

2. Description of the Related Art In a conventional electronic image forming apparatus, particularly in a fixing device such as an electronic copying machine, a laser printer, a facsimile, etc., fixing conditions for fixing an image are set in advance. The surface temperature and pressure of the fixing roller are usually set as the fixing conditions.

For controlling the fixing condition, for example, regarding the surface temperature of the fixing roller, a temperature sensor is provided on the surface of the roller, and the output from the temperature sensor is compared with the set value of the fixing condition. The feedback control is performed by detecting the deviation from the above and adjusting and supplying the electric power of the heater lamp necessary for keeping the surface temperature of the fixing roller constant.

[0004]

In such a conventional technique, since the setting condition of the fixing roller is controlled to be constant for all images, a low density such as a character original having a lot of white background is obtained. Optimal conditions differ between an image and an image with many solid portions, that is, a high-density image, and under the condition set to be constant, one of the toner particles T shown in FIG. Under the conditions set to be optimal for a low density image in which one is dispersed and is sparsely adhered, a high density image in which the toner particles T shown in FIG. After fixing, the set temperature is too high and over-fixing proceeds, causing high-temperature offset and curl of the transfer paper P. On the contrary, if a low-density image in which the toner particles T are sparsely adhered is fixed under conditions set to be optimal for a high-density image in which the toner particles T are densely adhered, the set temperature is too low and unfixed. In this state, low-temperature offset and image loss due to unfixed images occur, and toner stains occur (see FIG. 13).

The following are possible causes for this. That is, assuming that the amount of heat Q given to one of the toner particles T from above the paper P is the same, in the case of a low-density image as shown in FIG. 12A, the heat loss to the atmosphere (in the figure, The arrow →) is 83%, and in the case of a high density image as shown in FIG. 12B, the heat loss to the atmosphere is 35%, and the higher the toner density for fixing, the better the thermal efficiency. However, the fixing rate is high even at low temperatures.

Particularly, in the fixing device having a small heat capacity, this tendency is strong, so that there is a problem that it is one of the causes for hindering the speeding up of image formation. The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that can fix the image under the optimum fixing conditions in accordance with the density of the original image.

[0007]

In order to solve the above problems, the image forming apparatus according to the first aspect of the present invention has a density detecting means for detecting the image density or image area of a document and an output of the density detecting means. A heating means for storing the control value, a heating control means for adjusting the fixing temperature of the fixing portion, and a heating start time of the fixing portion in association with the time for the image transfer medium to reach the fixing portion based on the output of the density detecting means. It comprises an adjusting means for adjusting, and a control means for determining the output of the concentration detecting means, obtaining a control value stored in the storage means, and controlling the heating control means.

In order to solve the above-mentioned problems, an image forming apparatus according to a second aspect of the present invention stores a density detecting means for detecting the image density or image area of a document and a control value corresponding to the output of the density detecting means. Means, a pressure control means for adjusting the fixing pressure of the heated fixing portion, and a pressing start time of the fixing portion in association with the time for the image transfer medium to reach the fixing portion based on the output of the density detecting means. And a control unit that determines the output of the concentration detection unit, obtains a control value stored in the storage unit, and controls the pressurization control unit.

In order to solve the above problems, an image forming apparatus according to a third aspect of the present invention is a density detecting means for detecting the image density or image area of a document, and a control value for each density rank corresponding to the output of the density detecting means. Storage means for storing, and pressure control means for adjusting the fixing pressure,

Heating control means for adjusting the fixing temperature, and delay means for delaying the pressurization start time and heating start time of the fixing portion in association with the time when the image transfer medium reaches the fixing portion based on the output of the density detecting means. And a control for determining the output level of the concentration detecting means, obtaining a ranked control value corresponding to the output level stored in the storage means, and controlling the pressurizing control means and the heating control means. And means.

In order to solve the above problems, an image forming apparatus according to a fourth aspect of the present invention stores in advance a density detecting means for detecting the image density or image area of a document and a control value for each density rank for the output of the density detecting means. The storage means, the pressure control means for adjusting the fixing pressure, the heating control means for adjusting the fixing temperature, and the pressing start time until the paper is conveyed to the fixing step based on the output of the density detecting means. The delay means for delaying and the time constant until the fixing roller surface temperature rises when power corresponding to the detected density based on the output of the density detecting means is supplied and the time until the sheet is conveyed to the fixing step are matched. The delaying means for delaying the heating start time and the output level of the density detecting means are discriminated, the control value stored in the storing means is obtained, and the unfixed image of the image optically detected Fixing temperature when it reaches the fixing step is configured and control means for controlling said pressure control means and the heating control means so that the maximum.

[0012]

With this configuration, in the image forming apparatus according to the present invention, the density detecting means detects the image density or image area of the document and outputs an output signal proportional to the density or set corresponding to the density. Then, the control means obtains a control value corresponding to the output of the density detection means stored in the storage means, and controls the heating control means for adjusting the fixing temperature based on the obtained control value to fix the unfixed image. The fixing temperature is set to the optimum condition when the sheet is conveyed to the process.

In the image forming apparatus, the density detecting means detects the image density or image area of the original and outputs an output signal proportional to the density or set corresponding to the density, and the control means is stored in the storage means. The control value corresponding to the output of the density detection means is obtained, and the pressure control means for adjusting the pressure is controlled based on the obtained control value to optimize the fixing pressure when the unfixed image is conveyed to the fixing process. Fix the condition.

In the image forming apparatus, the density detecting means detects the image density or the image area of the original, and the controlling means controls from the storing means which stores the control value for each density rank corresponding to the output of the density detecting means. The value is read, the pressurizing control means is controlled according to the read control value, the delaying means delays the pressurizing start time based on the output of the density detecting means, and the fixing pressure is adjusted. The heating control unit is controlled according to the value, and the delay unit delays the heating start time based on the output of the density detection unit to adjust the fixing temperature, and when the unfixed image is conveyed to the fixing process, Fixing is performed under the optimum fixing pressure.

In the image forming apparatus, the density detecting means and the image density or image area of the original are detected, and the control means corresponds to the output of the density detecting means from the storage means which stores the control value for each density rank. The control value is obtained, and the pressure control means for adjusting the fixing pressure and the heating control means for adjusting the fixing temperature are controlled based on the control value, and the unfixed image is fixed by the delay means based on the output of the density detecting means. In addition to delaying the pressurization start time until it is carried into the process, the delay unit supplies the power corresponding to the detected density based on the output of the density detection unit and the time constant until the fixing roller surface temperature rises and the unfixed image. The heating start time is delayed so as to match the time until it is carried into the fixing process, and the fixing conditions are controlled to be optimal when the unfixed image of the optically detected image reaches the fixing process. It is to fix.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case in which an embodiment of the image forming apparatus of the present invention is applied to a copying machine will be described in detail below with reference to the drawings.

[Structure of Copying Apparatus] As shown in FIGS. 1 and 2, the copying apparatus 2 serving as an image forming apparatus takes out an image of a document as image information of light and dark by the image reading section 4. The image forming unit 6 reproduces an image based on the light and shade information, and the control unit 8 that operates the image reading unit 4 and the image forming unit 6 according to a predetermined rule.

As shown in FIG. 1, the image reading section 4 is formed on a document table 10 on which an object to be read, that is, a document D is placed, and is formed so as to be openable and closable with respect to the document table 10 and placed on the document table 10. A document retainer 12 for closely attaching the placed document D to the document table 10.
have.

Below the document table 10, the exposure lamp 22 and the exposure lamp 2 for illuminating the document D placed on the document table 10.
Reflecting plate 2 for converging the illumination light generated from 2 on the document D
4 and a first mirror 26 that bends the reflected light from the document D are integrally formed, and the first carriage 20 that reflects the reflected light from the document D toward a second carriage 30 (described later) is arranged. ing.

The first carriage 20 is movably arranged in parallel with the document table 10 and is reciprocated along the document table 10 by a pulse motor (not shown). The exposure lamp 22 is connected to a lamp regulator (not shown),
It is turned on by a voltage adjusted so as to generate various light amounts corresponding to the exposure amount input from an operation panel (not shown).

On the second carriage 30, a second mirror 32 and a third mirror 34, which sequentially bend the reflected light from the first mirror 26 of the first carriage 20 in a predetermined direction, are arranged at right angles to each other. The second carriage 30 is driven by the first carriage 20 by a toothed belt or the like (not shown) that drives the first carriage 20, and is at a speed half that of the moving speed of the first carriage 20. Moved parallel to 10.

Below the first carriage 20, in a plane including the optical axis of the light reflected by the second carriage 30, it is movably formed by a driving mechanism (not shown). In addition to providing the converging property to the reflected light from 30, the imaging lens 36 forms an image of the reflected light at a predetermined magnification by moving itself, and the imaging lens 36 provides the converging property at the predetermined magnification. A folding mirror 38 for focusing the reflected light at a predetermined position on the photosensitive drum 42 described later is arranged. The folding mirror 38 can be moved along the optical axis of the lens 36 via a driving mechanism (not shown) in order to correct the variation of the focal length which is changed according to the copy magnification, like the imaging lens 36. Is formed in.

As shown in FIGS. 1 and 3, the light transmitted from the third mirror 34 to the folding mirror 38 passes through the same plane as that in which the lens unit (imaging lens 36) is arranged. An AES (automatic exposure sensor) 40 as a density detecting means for detecting the density of the image information of the document D is provided at a position where it does not block the light traveling toward the folding mirror 38 via a fixing member (not shown). Fixed.

Output voltage V output from the AES 40
Is a predetermined value proportional to the amount of light reflected from the document table, that is, the image density of the document D, as shown in FIG. Where A
The output voltage range of the ES40 is, for example, 0 volt to 5
If the whole surface is black (B) is set to a value close to 0 volt, and if the whole surface is white (W) is set to about 5 volts, white is determined according to the amount of light reflected from the document D. The voltage decreases from the side to the black side, and the voltage V1 represented by 4 volts, 3 volts, 2 volts, ... Is output. This AES4
Based on the output of 0, the image density of the original obtained by the copying operation is controlled to be maintained at a constant level.

As shown in FIG. 1, a photosensitive member which is a recording medium on which an image corresponding to the image of the original is formed by the light transmitted through the folding mirror 38 is formed substantially at the center of the image forming section 6. The drum 42 is arranged. The photoconductor drum 42 is moved at a predetermined speed by an arrow R by a main motor (not shown).
Is rotated in the direction of.

Around the photosensitive drum 42, the drum 42
A charging device 44 for charging a predetermined electric charge to the developing device, a developing device 46 for developing the electrostatic latent image formed on the drum 42 by supplying toner to the electrostatic latent image, and a transfer device for transferring the toner image formed on the drum 42 to the paper P. 48, and a cleaning static eliminator 50 that scrapes off the toner remaining on the surface of the drum 42 and removes the electric charges remaining on the surface of the drum 42 are sequentially arranged.

The charging device 44 includes a corona wire 44a which is connected to a charging transformer, which will be described later, and which provides the photosensitive drum 42 with a predetermined amount of electric charge, that is, a power failure potential. Developing device 46
Has a developing roller 46a that conveys a two-component developer (not shown) including a toner and a carrier and attaches only the toner to the electrostatic latent image formed on the photoconductor drum 42 while holding the developer. . The developing roller 46a includes
A developing bias voltage is applied via a developing bias transformer (not shown).

The transfer device 48 is connected to a transfer transformer (high-voltage transformer 80 in FIG. 2), and is used to transfer the toner image on the photosensitive drum 42 to the paper P and a transfer charger wire 48a and an AC voltage. The paper P that is connected to the supply circuit (AC voltage supply circuit 84 in FIG. 2) and is electrostatically attracted to the photosensitive drum 42 when the toner image is transferred.
Charger wire 4 for separating the photoconductor from the photoconductor
8b.

The cleaning static eliminator 50 is constituted by a blade 50a which is pressed against the photoconductor drum 42 and removes toner on the surface of the drum 42, a static erasing lamp 50b which removes the potential remaining on the surface of the photoconductor drum 42, and the like. .

The transfer device 4 on the right side from the center of the apparatus 2 of this embodiment, that is, in the direction in which the photosensitive drum 42 is rotated.
Slots 52a and 52b into / from which the first and second sheet cassettes 14a and 14b holding the sheet P for transferring the image formed on the photosensitive drum 42, that is, the toner image, are attached and detached at a position upstream of 8 Will be placed.

The paper cassette 1 is provided between the photosensitive drum 42 and the slot 52a (attachment / detachment port of the paper cassette 14a).
A sheet feeding roller 54a for pulling out the sheets P from the sheet 4a one by one, and a conveying roller 56a for feeding the sheet P pulled out through the sheet feeding rollers 54a and 54b to the photosensitive drum 42 are arranged. There is.

Similarly, the photosensitive drum 42 and the slot 52
The sheet feeding roller 5 that pulls out the sheets P one by one from the sheet cassette 14b is provided between the sheet feeding roller 5 and the sheet b (the attachment / detachment port of the sheet cassette 14b).
4b and a conveyance roller 56 for sending the paper P pulled out via the paper feed roller 54b to the photosensitive drum 42.
b is arranged.

Between the photosensitive drum 42 and the conveying rollers 56a and 56b, the inclination of the paper P taken out from the respective cassettes is corrected, and the tip of the toner image on the photosensitive drum 42 and the paper P are corrected. A timing roller 58 that aligns the leading end of the sheet P and feeds the sheet P at the same speed as the moving speed of the outer peripheral surface of the photosensitive drum 42 is arranged.

The left side position from the center of the device 2 of this embodiment,
That is, the toner image formed on the photoconductor drum 42 is transferred to the position downstream of the transfer device 48 in the direction in which the photoconductor drum 42 is rotated, and the toner is electrostatically attached. Conveying device 60 for conveying the paper P of
The toner transferred onto the paper is melted by heating and the paper P
It has a fixing device 62 for fixing the toner image to the outside and a pair of discharge rollers 64 for discharging the paper P on which the toner image is fixed to the outside of the device 2. Further to the left of the discharge roller 64,
A discharge tray 16 on which the paper P on which the toner image is fixed is stocked is arranged.

The fixing device 62 includes an upper heat roller 62a having a heater 62c inserted therein and an upper heat roller 62.
It has a lower heat roller 62b that is pressed against a through a spring 62g (see FIG. 5) described later and has an auxiliary heater (not shown) incorporated therein. The upper heat roller 62a is rotated at a predetermined speed by a motor via a transmission mechanism such as a gear. And the heater 62c
An auxiliary heater (not shown) is energized at a predetermined timing by a heater control circuit 76 (see FIG. 2) described later,
The toner held on the paper P is heated to melt the toner image, and the lower heat roller 62b presses the toner image and the paper P to fix the toner image on the paper P.

As shown in FIG. 5, the pressing mechanism utilizing the lower heat roller 62b of the fixing device 62 has a pressing arm 62 having one end pivotally supported and the other end vertically movable.
d is provided as a bearing support member for the lower heat roller 62b,
A lower heat roller 62b is provided at a substantially central portion of the pressing arm 62d.
Of the bearing 62e is slidably fitted into the groove 62f, and the bearing 6 is provided between the bottom surface of the groove 62f and the bearing 62e.
A spring 62g for urging 2e toward the upper heat roller 62a is interposed, a cam 62h is brought into contact with the lower side of the free end of the pressing arm 62d, and a pulse motor 62m is connected to the shaft of the cam 62h. A predetermined rotation angle is given to the document density, and the contact surface of the cam 62c has the free end of the pressing arm 62d depending on the rotation angle of the upper heat roller 62.
The outer shape is formed so as to be displaced to the a side. As shown in FIG. 5B, the maximum amount of displacement of the pressurizing arm 62d toward the upper heat roller 62a is the cam 62h.
Is given by the difference w between the maximum major axis and the minimum minor axis of.

As shown in FIG. 2, the control section 8 includes a ROM 70b (see FIG. 6) and an operation panel (not shown) in which data necessary for operation is previously written in a CPU 70 as a control means for controlling the entire apparatus. A memory 72 is connected as a storage unit including a RAM 72a (see FIG. 6) used for temporarily storing numerical data such as the number of copies or copy magnification input via the.

Further, the CPU 70 has a motor driver 74 for rotating the pulse motor 62m for driving the pressurizing cam 62h of the fixing device 62 by a predetermined angle, and the fixing device 62.
Heater 62c and an auxiliary heater (and illumination lamp 22) not shown in the figure are turned on at a predetermined timing, and an input circuit (A) for inputting an analog signal from the automatic exposure sensor (AES) 40 to the CPU 70.
/ D converter) 78 and the like are also connected. The input circuit 78 also receives an output from a temperature sensor (not shown) for detecting the temperature of the heater 62c.

The CPU 70 further includes a corona wire 44a of the charging device 44 and a transfer wire 48 of the transfer device 48.
a high voltage transformer 80 for supplying a predetermined high voltage to a, a bias voltage generating circuit 82 for supplying a predetermined bias voltage to the developing roller 46a of the developing device 46, and an AC voltage for supplying an alternating current to the separation charge wire 48b of the transfer device 48. A generation circuit 84, an input port 86 to which a paper detection signal output from many paper position detection switches (not shown) is input,
A mechanical controller 87 for activating many solenoids (not shown) or electromagnetic clutches, and data transmitted from an operation panel (not shown) are transmitted to the CPU 70 and an output corresponding to an instruction from the CPU 70 (for example, data display) is displayed on the operation panel. Supply (input / output)
The interface 88 and the like are also connected.

As shown in FIG. 6, the control system related to the fixing device 62 detects the image density from the reflected light of the image D1 of the document D irradiated with the light of the exposure lamp 22, and outputs the image density signal. AES40 as an optical detection element
And an input circuit 7 for converting an analog signal into a digital signal
From the A / D converter 78 incorporated in the CPU 8, the CPU 70 as a control device for managing the fixing condition, and the RAM 72a and the ROM 72b storing the program for setting the fixing condition and the data necessary for the setting. Memory 72, a D / A converter 76a for converting digital data of set fixing conditions into an analog signal, and heating control for energizing and heating the heater 62c of the fixing device 62 based on the control signal converted into an analog signal. A heater control circuit 76 as a means or a heater driver, a heater 62c that is electrically heated by the heater control circuit 76, and the lower heat roller 6 based on digital data of set fixing conditions.
A motor drive circuit 74 as a pressure control means or a motor driver for controlling the pressurizing operation of 2b, and a pulse motor 62m which is started by the motor drive circuit 74 and rotates the cam 62h by an angle corresponding to the set fixing condition. It has.

The motor drive circuit 74 incorporates a delay circuit 74a as a delay means for delaying the time until the unfixed image on the paper P arrives at the fixing device 62 after the density of the image is detected. And the timing of the motor drive is taken.

The heater control circuit 76 has a time constant until the surface temperature of the fixing rollers (upper and lower heat rollers 62a, 62b) rises to a predetermined temperature after the AES 40 detects the document density and then the heater 62c is energized. A delay circuit 77 as a delay means for delaying the energization of the heater 62c is incorporated so that the time until the unfixed image on the sheet P reaches the fixing device 62 is matched, and the delay time provided by the delay circuit 77 is The surface temperature of the fixing roller is set to be the highest when the unfixed image on the sheet P reaches the fixing device 62 and enters the fixing step.

As shown in FIG. 7, the delay circuit 74a or the delay circuit 77 has two NOs for inverting the ON / OFF signal.
T circuits 101 and 102, two resistors 103 and 104 that connect them in series, and resistors 103 and 104.
And grounded via a capacitor 105.

With such a circuit configuration, as shown in the timing chart of FIG.
When input to the circuit 101, it is output as a shaped on / off signal b from the NOT circuit 102 with a delay of time t0 determined by the time constant of the resistors 103 and 104 and the capacitor 105.

The capacity of the condenser 105 as a delay means for determining the delay time t0 is set to such a capacity that the unfixed image on the paper P can be activated before the transfer device 48 reaches the fixing device 62. . For this reason, the delay circuit 74a of the motor drive circuit 74 has a constant capacitance of the capacitor 1a.
05 is used to enable the pulse motor 62m to start operation when the unfixed image on the paper P reaches the fixing device 62. Further, the delay circuit 77 of the heater control circuit 76 is
In consideration of the heat capacity and heating temperature of the heater 62c, in the case of the white image (W), the delay time is the shortest, and the heater 62c is used at the minimum capacity to raise the heater temperature by conducting the electric heating earlier, and the black image (B In the case of), the maximum delay time is used to delay the energization heating to keep the heater temperature low, so that the optimum heater temperature can be given when the unfixed image on the paper P reaches the fixing device 62. The variable capacitance type capacitor 105 is used. This variable capacitance type capacitor 105 is
The capacity is controlled by a known method based on the output of S40.
The ROM 72b stores a conversion table (see FIG. 9A) between the output signal of the AES 40 and the document density, and the AES4.
It has a conversion table (see FIG. 9B) between the output signal of 0 and the rotation angle of the pulse motor 62m, and when the pressurizing operation is performed according to these setting conditions, the fixing roll pressure as shown in FIG. 10 is obtained. To be Then, by applying this pressurizing operation and heating and fixing, the fixing having the characteristics as shown in FIG. 11 is performed.

[Description of Operation of Copying Device 2]
When a power switch (not shown) is turned on, the power is warmed up, and a standby (copyable) state is set until a copy instruction is issued. During the warm-up, the motor for rotating the upper heat roller 62a and the lower heat roller 62b of the fixing device 62 is rotated at a lower speed than during the copying operation,
The heating time required for the surface temperatures of the upper and lower heat rollers 62a and 62b to reach a predetermined value (since most of the time required for warm-up is spent to heat the heat rollers of the fixing device, substantially, Warm-up time) is shortened.

The number of copies, via an operation panel (not shown),
Copying is started by inputting copy condition data such as copy magnification, enlargement / reduction, paper size selection, or mode selection, and turning on a copy start key (not shown).

When copying is started, a lamp regulator (not shown) is energized by an instruction from the CPU 70 to turn on the exposure lamp 22, and a scan motor (not shown) is started to activate the first carriage 20 and the second carriage. 30 is moved along the document table 10, and the reflected light (that is, image information) from the document D placed on the document table 10 is sequentially projected onto the photosensitive drum 42.

At this time, a part of the reflected light of the illumination light from the exposure lamp 22 reflected by the original D is incident on the AES 40, converted into a voltage corresponding to the intensity of the input light, and output. In this case, if the image density of the original D is low, that is, if the original has many white portions, a voltage close to 5 volts is output. If the image density of the original D is high, that is, if the original D has many black portions or a solid image. For a document containing many black images, a voltage close to O volt is output.

On the other hand, in the image forming section 6, when the reading of the image information of the document D is started, the main motor (not shown) is started, the photosensitive drum 42 is rotated at a predetermined speed,
At the same time, by applying a predetermined voltage to the corona wire 44a of the charging device 44, a predetermined amount of electric charge is supplied to the photosensitive drum by corona discharge, the fixing motor of the fixing device 62 is activated, and the upper and lower heat rollers 62a are activated. And 62b are rotated.

In this state, the light from the lamp 22 controlled to generate the light amount corresponding to the image density of the document D detected by the AES 40 is reflected on the image surface of the document D, and the first carriage 20 has the image light. The reflected light of the document D transmitted through the first mirror 26, the second mirror 32 and the third mirror 34 of the second carriage 30, the imaging lens 36, and the folding mirror 38 is formed on the surface of the photosensitive drum 42. Then, an electrostatic latent image corresponding to the image of the document D is formed on the surface of the photosensitive drum 42.

The electrostatic latent image formed in this manner is developed by the toner supplied from the developing roller 46a of the developing device 46 to which a predetermined developing bias voltage is applied, and transferred via the transfer device 48 to the transfer sheet. The toner image is transferred to P. The toner image transferred onto the sheet P is separated from the surface of the photoconductor drum 40 together with the sheet P, and then is conveyed to the fixing device 62 by the conveying device 60.

When the sheet P is carried into the fixing device 62, the voltage Di (i =
1 to n) are output, the CPU 70 determines the value, issues a command to the motor driver 74, and causes the pulse motor 62m to rotate at the rotation angle θi (i = 1 to n) corresponding to the output of the AES 40.
The lower heat roller 6 by rotating the pressurizing arm 62d by the amount of displacement set by the shape of the cam 62h.
2b is pressed against the upper heat roller 62a. At the same time, the command signal from the CPU 70 is converted into an analog signal by the D / A converter 76a and transmitted to the heater control circuit 76,
According to the signal, the heater 62c is energized and heated to melt the toner, and in combination with the pressing of the lower heat roller 62b to the upper heat roller 62a, a toner image (unfixed image) is obtained under a fixing condition suitable for the output from the AES 40. Paper P
Stick to.

At this time, in the heater control circuit 76, the time until the sheet P (that is, the unfixed image) on which the toner image has been transferred through the development and transfer after the image formation on the photosensitive drum 42 reaches the fixing device 62. In consideration of the above, by delaying the energization timing through the delay circuit 77, the heating temperature of the heater 62c is adjusted so that the heater temperature is heated high in the case of a white image and is kept low in the case of a black image. Thus, both the optimum heating temperature and the heating timing with fast response are realized.

The paper P to which the toner image is fixed (that is, the image is fixed) is sequentially ejected to the ejection tray 66 arranged outside the apparatus 2 via the ejection roller 64. Photoreceptor drum 42 with toner image transferred onto paper P
Is rotated as it is, and the residual toner is removed via the cleaning and static eliminator 50, and then the electric charge is eliminated to be used for the next image formation.

When the number of copies is two or more, or when the next original is present, the above series of copying operations are repeated. The above embodiments are specifically described in order to better understand the gist of the present invention, and the present invention is not limited to these embodiments. For example, as a means for detecting the ratio between the image portion and the background portion of a document, a CCD or the like is used in a printer or fax, and the ratio of black and white of the pixels of the image digital signal read by this CCD is integrated and the value is accumulated. R that stores the conditions predetermined by
The OM condition may be read and the control may be performed based on the read condition.

Further, in a surf fixing device known as a fixing device having a small heat capacity, an unfixed image is detected by detecting an image signal and timing the image forming portion so as to concentrate electric power on a portion where an image exists. It may be heated to the fixing temperature of the toner while being conveyed to the fixing area.

[0058]

As described above, in the image forming apparatus according to the present invention, the density detecting means detects the image density or image area of the original document and outputs an output signal proportional to the density or set corresponding to the density. The control unit obtains a control value corresponding to the output of the density detection unit stored in the storage unit, controls the heating control unit that adjusts the fixing temperature by changing the heating start time, and the unfixed image is fixed in the fixing step. By fixing the fixing temperature to the optimum condition when it is conveyed to the printer, it is possible to improve the image fixing property and the heating response, and shorten the warm-up time. Energy saving can be achieved. Therefore, it is possible to eliminate stains due to offset caused by improper fixing conditions, and prevent paper wrinkles and curls.

In the image forming apparatus, the density detecting means detects the image density or image area of the original and outputs an output signal set in proportion to or corresponding to the density, and the controlling means is stored in the storage means. The control value corresponding to the output of the density detection unit is obtained, and the pressure control unit that adjusts the fixing pressure by changing the pressure start time is controlled based on the obtained control value to control the unfixed image in the fixing process. By fixing the fixing pressure under the optimum condition when it is conveyed, the image fixing property can be improved, the warm-up time can be shortened, and energy saving can be achieved. . Therefore, it is possible to eliminate stains due to offset caused by improper fixing conditions, and prevent paper wrinkles and curls.

Further, in the image forming apparatus, the density detecting means detects the image density or image area of the original, and the controlling means controls from the storing means which stores the control value for each density rank corresponding to the output of the density detecting means. The value is read, the pressurizing control means is controlled according to the read control value, the delaying means delays the pressurizing start time based on the output of the density detecting means, and the fixing pressure is adjusted. The heating control unit is controlled according to the value, and the delay unit delays the heating start time based on the output of the density detection unit to adjust the fixing temperature, and when the unfixed image is conveyed to the fixing process, By making it possible to fix under the optimum fixing pressure, it is possible to improve the image fixability and heat responsiveness. Tree, it is possible to shorten the warm-up time, it is possible to achieve energy savings.
Therefore, it is possible to eliminate stains due to offset caused by improper fixing conditions, and prevent paper wrinkles and curls.

Further, the image forming apparatus detects the image density or the image area of the original and the density detecting means, and the control means corresponds to the output of the density detecting means from the storage means which stores the control value for each density rank. The control value is obtained, and the pressure control means for adjusting the fixing pressure and the heating control means for adjusting the fixing temperature are controlled based on the control value, and the unfixed image is fixed by the delay means based on the output of the density detecting means. In addition to delaying the pressurization start time until it is carried into the process, the delay unit supplies the power corresponding to the detected density based on the output of the density detection unit and the time constant until the fixing roller surface temperature rises and the unfixed image. The heating start time is delayed so as to match the time until it is carried into the fixing process, and the fixing conditions are controlled to be optimal when the unfixed image of the optically detected image reaches the fixing process. As a result, it is possible to improve the image fixability, improve the heat response, shorten the warm-up time, and achieve energy saving. it can. Therefore, it is possible to eliminate stains due to offset caused by improper fixing conditions, and prevent paper wrinkles and curls.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a copying apparatus according to an embodiment.

FIG. 2 is a block diagram showing a control system of the copying apparatus of the embodiment.

FIG. 3 is a perspective view showing an arrangement relationship between an imaging lens and AES of an example.

FIG. 4 is a graph showing output voltage with respect to image density in AES of an example.

FIG. 5 is a side view showing the pressure mechanism of the embodiment,
(A) is a general view, (b) is an enlarged explanatory diagram of the cam.

FIG. 6 is a block diagram illustrating a fixing control system according to an exemplary embodiment.

FIG. 7 is a circuit diagram showing a delay circuit of the embodiment.

FIG. 8 is a time chart in the delay circuit of the embodiment.

FIG. 9 is a graph showing conversion table data for AES output stored in the ROM of the embodiment, (a)
Is a density conversion table, and (b) is a rotation angle table.

FIG. 10 is a graph showing the surface pressure of the fixing roll with respect to the rotation angle in the pulse motor of the embodiment.

FIG. 11 is a fixing characteristic graph showing the relationship between the image density on the paper and the fixing roll nip surface pressure in the fixing device.

FIG. 12 is an explanatory diagram schematically showing heating conditions of an unfixed image in the fixing device.

FIG. 13 is a graph showing the fixing conditions in the fixing device by the surface temperature of the fixing roll with respect to the image density on the paper.

[Explanation of symbols]

 40 ... AES (concentration detection means), 62c ... Heater, 62m ... Pulse motor, 70 ... CPU (control means), 72 ... Memory (storage means), 72a ... RAM, 72b ... ROM, 74 ... Motor drive circuit (pressurization) Control circuit), 74a ... Delay circuit (delay means), 76 ... Heater control circuit (heating control means), 76a ... D / A conversion circuit, 77 ... Delay circuit (delay means), 78 ... Input circuit, 78a ... A / D conversion circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G05D 23/19 J 7740-3H

Claims (4)

[Claims] 1. A density detecting means for detecting an image density or an image area of a document, a storage means for storing a control value corresponding to an output of the density detecting means, and a heating control means for adjusting a fixing temperature of a fixing section. Adjusting means for adjusting the heating start time of the fixing part in association with the time when the image transfer medium arrives at the fixing part based on the output of the density detecting part; An image forming apparatus comprising: a control unit that obtains a stored control value and controls the heating control unit. 2. A density detecting means for detecting an image density or an image area of an original, a storage means for storing a control value corresponding to an output of the density detecting means, and a fixing pressure of a heated fixing portion. Pressure control means, adjusting means for adjusting the pressurization start time of the fixing section in association with the time for the image transfer medium to reach the fixing section based on the output of the density detecting section, and determining the output of the density detecting section. An image forming apparatus, comprising: a control unit for controlling the pressure control unit by obtaining a control value stored in the storage unit. 3. A density detecting means for detecting an image density or an image area of a document, a storing means for storing a control value for each density rank corresponding to an output of the density detecting means, and a fixing pressure adjusting member. Pressure control means, heating control means for adjusting the fixing temperature, and delaying the pressurization start time and heating start time of the fixing part in association with the time for the image transfer medium to reach the fixing part based on the output of the density detecting part. The output levels of the delay unit and the concentration detection unit are discriminated, the control values ranked corresponding to the output levels stored in the storage unit are obtained, and the pressurization control unit and the heating control unit are controlled. An image forming apparatus, comprising: 4. A density detecting means for detecting an image density or an image area of a document, a storage means for storing a control value for each density rank with respect to an output of the density detecting means in advance, and a pressurizing for adjusting a fixing pressure. Control means, heating control means for adjusting the fixing temperature, delay means for delaying the pressurization start time until the paper is conveyed to the fixing step based on the output of the density detecting means, and output of the density detecting means Delaying means for delaying the heating start time so as to match the time constant until the fixing roller surface temperature rises with the supply of power corresponding to the detected density and the time until the sheet is conveyed to the fixing step; The output level of the density detection means is determined, the control value stored in the storage means is obtained, and the fixing temperature becomes maximum when the unfixed image of the optically detected image reaches the fixing step. An image forming apparatus comprising said that equipped with control means for controlling the pressure control means and the heating control means to.