JPH0527617A - Image forming device - Google Patents

Abstract

PURPOSE:To easily execute belt deviating control for correcting the deviating of a belt-like film by properly controlling the temp. distribution of a fixing heater. CONSTITUTION:The fixing heater 43 is formed on a ceramic substrate by printing an exhothermic resistor 43a, the resistor 43a branches on the way, and a branch resistor is gradually made thin to obtain the shape of a taper. In other words, the branch resistor is thinner than the basic resistor 43a, to increase a resistance value per unit length. Energizing of each branch is controlled according to the size of a recording form. In other words, electric power applied from a branching part to the top, which is a paper nonpassing part, is reduced to lower a temp., so that temp. of the paper nonpassing part is not risen compared with the temp. of a paper passing part on the heater 43. Thus, the temp. distribution of the heater 43 is easily brought close to tolerance, so that the deviation of the belt-like film can be surely controlled.

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 for fixing a toner image on a recording material using a fixing device.

More specifically, the present invention relates to a heating resistor having a plurality of branch resistors branched from a linear basic resistor,
An image including a thin plate that moves with the movement of the recording material and a fixing device that heats the toner image on the recording material through the thin plate by heat from the heating resistor controlled to a predetermined temperature More specifically, the present invention relates to an image forming apparatus suitable for fixing a toner image through a belt-shaped film using a ceramic heater.

[0003]

2. Description of the Related Art Conventionally, in this type of image forming apparatus, heat generated from a fixing ceramic heater is applied to a transfer paper via a belt-shaped film, and when the toner fixes an image, the resistance of the ceramic heater is increased. The pattern is shown in Figure 1.
It is formed as shown in FIG. That is, a pattern printed with a resistor is used on a ceramic substrate, and fixing is performed by energizing this resistor.

As shown in FIG. 11, the width and thickness of these patterns are all constant. With this branched pattern, power control is performed so that even when a small-sized transfer sheet passes over the heater, the sheet passing portion has the same power consumption per unit length. Specifically, the paper passing portion is heated by one resistance pattern, and the non-paper passing portion is heated by flowing a current in parallel to the two resistance patterns. As a result, the power consumption of the non-sheet passing portion is lower than that of the paper passing portion, so the so-called "belt deviation control" (that is, the control for correcting the deviation of the belt-like film on the roller) is compared. Easy to do.

[0005]

However, in the above-mentioned conventional example, when fixing a toner image on a transfer paper having a narrower width, the temperature difference between the paper-passing portion and the non-paper-passing portion becomes relatively large. There is a drawback in that the simple "belt deviation control" cannot be controlled. As a result, more complicated belt deviation control and heater sequence control have been required.

In other words, in the case of using transfer papers of various sizes, the belt-shaped film is deviated unless the ceramic heater having the branched resistance pattern is used, and the same width as in the conventional case is used. Even if a ceramic heater with a branched resistance pattern is used, the deviation cannot be completely eliminated, and other relatively high-cost motors, etc. can be used to adjust the feedback while applying the belt shape. There is a drawback in that the film shift must be controlled.

Therefore, in view of the above points, the object of the present invention is to facilitate the so-called "belt deviation control" for correcting the unevenness of the belt-shaped film by appropriately controlling the temperature distribution of the fixing heater. An object of the present invention is to provide an image forming apparatus configured so that it can perform.

[0008]

According to the present invention, a heating resistor having a plurality of branch resistors branched from a linear basic resistor, a thin plate that moves with the movement of a recording material, and a predetermined temperature are provided. In an image forming apparatus provided with a fixing device that heats the toner image on the recording material through the thin plate by the heat from the heating resistor controlled to, The resistance value is changed as compared with the resistance value per unit length of the basic resistor. Here, the resistance value per unit length is increased by gradually tapering the shape of the branch resistor, or the shape of the branch resistor is made thinner than the basic resistor. It is preferable to increase the resistance value per unit length by using a resistor.

[0009]

According to the present invention, by increasing the resistance value of the branching resistance pattern so that more power is consumed on the branching resistance pattern side, the temperature of the non-sheet passing portion is increased. It can be prevented from being lowered more than necessary. As a result, it is possible to perform appropriate belt deviation control even by relatively simple heater sequence control and belt deviation control.

[0010]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an image forming apparatus according to an embodiment of the present invention. In this figure, the drive system is divided into a main drive system that drives the paper feed unit, the transport unit, the photoconductor, and the fixing unit, and an optical drive system that drives the optical system that serves as a load. This main drive system has a synchronous motor 2
5 is an optical drive system (including a mechanism for reading an image)
The stepping motors 26 are used as drive sources.

CONT is a controller, and has a control circuit including a microcomputer (see FIG. 3) described later. Further, in the present embodiment, the stepping motor 26 is set to the two-phase excitation system according to the speed information set in the load.
Switching to two types of 1-2 phase excitation method.

As the paper feeding method, the paper feeding from the cassette 23 and the paper feeding from the multi-manual feeding section 24 can be selected. When paper is fed from the cassette 23, the state is managed by a switch for detecting the presence / absence of the cassette 23, a switch group 31 for detecting the size of the cassette 23, and a switch 37 for detecting the presence / absence of paper in the cassette 23. When an abnormality is detected by each of the above switches, it is displayed on the display unit described later.

When performing multi-manual feeding, the state is managed by a switch for detecting the state of the manual feeding portion 24, and when an abnormality is detected, it is displayed on a display portion described later.

The photosensitive member 12 rotates clockwise. The photoconductor 12 charged by the primary charger 13 is
An image is transferred onto a transfer sheet, which is exposed at a photosensitive position, which will be described in detail later, is developed by a developing unit 15, and is transferred by a transfer unit 14 from a paper feeding unit.

After the transfer, the cleaning unit 38 removes the residual toner from the photoconductor 12, and the pre-exposure lamp 16 removes the residual potential to repeat the process of forming an image again.

The transfer sheet on which the image has been transferred is the transport unit 2
It is sent to the fixing unit 21 on the 0 transport belt. The fixing unit 21 is composed of three rollers including a driving roller 35, a tension roller 45, and a pressure roller 44.

A heater (ceramic heater) 43 having a resistor printed on a ceramic substrate is used as a fixing heater, and the ceramic heater 43 is supported by a heat-resistant plastic supporter 42. Further, a metal stay (not shown) is attached to the plastic supporter 42 to make it strong.

The fixing unit 21 includes a driving roller 3
5, an endless film 47 is applied so as to surround the tension roller 45 and the ceramic heater 43.

A temperature detecting element (thermistor) 41 is attached to the metal stay attached to the plastic supporter, and the temperature detecting element 41 is in direct contact with the back surface of the ceramic heater 43. Another temperature detecting element (not shown) is also attached to the metal stay in the same manner as the temperature detecting element 41. In this way, the heater portion composed of the ceramic heater 43, the plastic supporter 42, and the metal stay and the endless film 47.
Are pressed by the pressure roller 44.

The transfer paper that has passed through the fixing unit 21 is discharged by the paper discharge rollers 22 and stored on the paper discharge tray 39.

The paper discharge sensor 34 is a sensor for detecting whether or not the transfer paper has normally passed through the fixing unit 21.

FIG. 7 is an external view of the ceramic heater 43 described above. As can be seen from this figure, the resistor forming this heater has a plurality of branches. The positions of the branches are A4 (A3) and B4 (B
5), A4R (A5), B5R, A5R. When the size is known by the cassette size detection switch 31, each branch on the heater resistor is switched according to each size.

The drive source of the optical drive system is the stepping motor 26 as described above. As will be described later in detail with reference to FIG. 4, this drive source is configured such that the stepping motor 26 drives a completely different load by operating the drive switching solenoid 27. That is, one load is the exposure lamp 4, the first mirror 5, the second mirror 6, and the third mirror 7.
And the other load is a unit that constitutes the zoom lens 8. These loads that do not need to be driven synchronously can be driven by the stepping motor 26, which is a common drive source.

This apparatus (1) has a multi-step magnification selection function by controlling the position of the zoom lens 8 and the speed of the exposure lamp units 4 to 7 by the stepping motor 26 of the optical drive system, and (2) the original document. The function of automatically selecting the density by the optical sensor 40 that detects the reflected light of the document placed on the glass 3 surface, and (3) the copy magnification (having the communication means) by the connection with the external device (not shown). Automatic selection function, (4) Memory backup function to store various states when an abnormality such as paper jam occurs, for example, remaining number of sheets, magnification value, abnormality information, etc. (5) Position of exposure lamp 4 by stepping motor 26 The page continuous shooting function by controlling, and (6) since a plurality of color images can be formed by replacing the developing unit 15,
It has a function of switching a predetermined control state by a switch 36 for detecting the exchange state of the developing unit 15.

Next, the operation of this apparatus will be described. A power cord (not shown) of this device is connected to a predetermined power source.

FIG. 2 shows an operation panel of this apparatus, which is arranged on the upper surface of FIG. When one side of the power switch 51 is pressed, power is supplied to the device and at the same time, the power indicator lamp 52
Is lit up.

When the power is turned on, the display on the operation panel is set as the standard mode as follows. The number display 59 displays 1, the magnification display 67 displays equal magnification, and the automatic density adjustment display 76 A lights up.

The display portion of the start key 56 is displayed in red at the time of initial setting when the power is turned on (such as moving the lens to the same magnification position) and during copying, and normally the copying operation can be performed in green. Is shown.

The controlled temperature of the fixing unit 21 (see FIG. 1) differs depending on the type of the developing unit 15 installed, and is set by discriminating the type of the developing unit 15 by the switch 36 provided on the developing unit 15. Switch the temperature.

Next, the operation of the optical drive system after the power is turned on will be described.

The exposure lamp units 4 to 7 are the original glass 3
The upper original is scanned and moved from the left end in FIG. 1 to the right, and the original image is transferred to the first mirror 5, the second mirror 6, the third mirror 7, the zoom lens 8, the fourth mirror 9, the fifth mirror 10, and the sixth mirror. The document exposure on the photoconductor 12 is performed via the mirror 11. In this way, the starting point of movement is set at the left end. This position is called a home position (hereinafter abbreviated as HP).
This H. P. In order to detect H. P. A sensor 29 is provided.

When the power is turned on, the H. P. Sensor 29
If the position of the exposure lamp 4 is not detected, the control unit by the one-chip microcomputer shown in FIG. 3 controls the stepping motor 26 to rotate the exposure lamp unit. P. Move to the side.

Next, the start of the rotation control will be described below with reference to FIG. First, drive switching solenoid 27
Is off (there is no force in the b'direction), the switching gear moves in the A direction by the spring pressure. This allows
The output of the stepping motor 26 is connected to a lamp driving gear via a switching gear, and the exposure lamp units 4 to 7 are driven. At the time of connecting the gears, when the switching gear and the lamp driving gear are fitted, the rotation speed of the stepping motor 26 is controlled to be sufficiently lowered.

The exposure lamp units 4 to 7 are H.264. P. When it is located at, the stepping motor 26 moves the zoom lens 8. As described above, when the power is turned on, the equal magnification value is selected as the standard mode. Further, since the home position of the zoom lens 8 (hereinafter abbreviated as ZHP) is set to the same size position, the position of the zoom lens 8 is set to Z. H. P. It is unclear which side it is. Therefore, before the power is turned off, the position of the zoom lens 8 is set to Z. H. P. Which one is stored in the non-volatile memory.

In FIG. 4, the drive switching solenoid 2
Turning on 7 causes the plunger of the solenoid to move in direction b. Therefore, the force in the b'direction causes the switching gear to move in the b'direction against the spring force. By this movement, the fitting of the switching gear and the lamp driving gear is released. Further movement in the b'direction causes the switching gear to engage with the lens drive gear. The rotation control when the gears are fitted is the same as described above.

The zoom lens 8 is a Z. H. P. The lens position is Z. H. When it is at the position of the P sensor, it is 1 × and the Z. H. P. Optical system H.M. P. If it is on the side, it is enlarged, and if it is on the other side, it is reduced.
As a result, the position control is performed within the range of the enlargement ratio 200% to the reduction ratio 50%.

At the start of driving the zoom lens, the Z.
H. P. The operation is divided as follows depending on the state of.

1) Z. H. P. When the position of the zoom lens 8 is detected by the sensor 1) -1 Once the zoom lens 8 is moved to the optical system H.264. P. To the Z. side. H. P. The sensor stops in the range that the sensor does not detect.

1) -2 Move to the right and move to Z. H. P. It moves for a certain distance from the time when the sensor detects it and then stops.

2) Z. H. P. When the position of the zoom lens 8 is not detected by the sensor 2) -1 The moving direction of the zoom lens (ZH.P.
Sensor side) and move the zoom lens.

When moving to the right Z. H. P. It moves for a certain distance from the time when the sensor detects it and then stops.

When the zoom lens 8 is moved to the left side, the zoom lens 8 is once moved to the optical system H. P. To the Z. side.
H. P. The sensor stops in the range that the sensor does not detect.

Move to the right and move to Z. H. P. It moves for a certain distance from the time when the sensor detects it and then stops.

The above-described operation is the control necessary to prevent the setting position error due to the back crush of gears.

Thereafter, the drive switching solenoid 27 is turned off. As a result, as described above, the switching gear moves in the direction in which it engages with the lamp drive gear. However, in order to fit smoothly, it is necessary to rotate the switching gear as described above.

At this time, the exposure lamp units 4 to 7 are H.264. P. It is located on the sensor 29. Therefore, the stepping motor 26 rotates the exposure lamp units 4 to 7 in the direction to move them to the right. As a result, the exposure lamp units 4 to 7 are H.264. P. When it comes off from the sensor 29 (the fitting of the switching gear and the lamp drive gear is completed)
To stop the rotation and rotate it in the opposite direction again. P. After detecting the sensor 29, it stops at a predetermined position.

Upon completion of the initial operation of the optical drive system described above, the preparation for the copying operation of this apparatus is completed.

Next, the copying operation by feeding paper from the cassette 23 will be described.

When the copy start key 56 is pressed, the transfer paper size data by the input signal of the switch group 31 for detecting the cassette size, the number data set by the number key 54, the magnification selection keys 61, 62, 64, 65,
The copying operation is started based on the magnification data by 66 and the data by other various mode selection means.

When the copy start key 56 is received,
The display is changed from green to red, and the input of the mode switching keys such as the numeral key 54 and the magnification keys 61, 62, 64, 65, 66 is prohibited. And the main drive motor 2
5 starts to rotate, and the driving force is transmitted to the paper feed roller 18, the photoconductor 12, the transport unit 20, the fixing unit 21, and the like.

From the start of rotation of the main drive motor 25, 0.
After 5 seconds, a paper feeding solenoid (not shown) is operated, the paper feeding roller 17 is rotated accordingly, and the transfer paper in the cassette 23 is fed toward the paper feeding feed roller 18. The transfer paper feed amount of the paper feed roller 17 is controlled by the cassette size data. That is, when the transfer paper is larger than the predetermined value, the feed amount is increased. When the transfer sheet reaches the sheet feeding / feeding roller 18, the sheet is fed to the registration roller 19 by the sheet feeding / feeding roller 18, and is stopped when the sheet reaches the registration roller 19. Manual feed switch 3 installed near the paper feed roller 18
3 detects the transfer state of the transfer paper.

At a predetermined timing until the transfer paper is fed on the paper feed path and reaches the registration roller 19, the exposure lamp units 4 to 7 are permitted to start scanning the original document.
At this time, the exposure lamp 4 is H.264. P. It is in a position detected by the sensor 29. More specifically, when the H.S. P. It is stopped at a position which is moved backward by a distance corresponding to the selection magnification at that time from the position where the sensor 29 outputs the detection output.

When the document scanning is started, the stepping motor 26, which is the optical system driving source, moves in the direction in which the exposure units 4 to 7 move forward (to the right) until the driving pulse rate corresponding to the selected magnification value is reached. The applied pulse rate gradually increases (called slow-up control). That is, the moving speed is gradually accelerated to reach the target speed.

Although not shown in particular, the pulse motor drive circuit of this apparatus adopts a constant current control system and has a structure in which the drive current value can be switched among a plurality of steps (two steps in this embodiment) ( The stepping motor control signal for optical drive shown in FIG. 3 is selected by the PB4 output signal).

In general, the characteristic of the stepping motor is that the pull-in torque decreases as the pulse rate increases. Therefore, a means for switching the constant current set value is provided, and the current value is switched as necessary.

In this apparatus, the set current is lowered during the relatively low pulse rate from the start of movement, and the set current value is controlled to increase when the speed exceeds the predetermined value to reach the target speed. After that, the control for reducing the set current value is performed again after the elapse of a predetermined time. This is mainly intended to prevent noise, temperature rise and step-out phenomenon of the stepping motor 26.

Next, with reference to FIG. 5, a method for forming a margin at the leading edge of the image and a method for aligning the leading edge of the transfer paper will be described.

As a means for preventing toner adhesion in the non-image area, a charge eliminating means using a light source such as an LED lamp or a fuse lamp is generally used. In this apparatus, the voltage value of the grid 13a provided in the primary charging unit 13 is used. The same effect is realized by controlling. This is an important method in the present situation where it is difficult to arrange a plurality of members around the photoconductor due to the downsizing of the apparatus.

The distance (e) between the exposure point and the grid is
H. P. Since the distance between the sensor 29 and the document abutting position (B) cannot be sufficiently shortened, the distance from the start of the movement of the exposure lamp 4 is changed according to the magnification selection value in order to form a 2 mm margin at the leading end of the document. After a predetermined time, the grid is switched from the L level to a predetermined voltage. That is, when the grid voltage is at the L level, the toner image is not formed because the photoconductor is not charged with the electric potential, and the image is formed from the timing when the voltage is switched to the above-described predetermined voltage. A margin will be formed.

Next, the image leading edge alignment of the transfer paper will be described. The distance (c) between the exposure point and the transfer portion is shorter than the distance (d) between the registration roller 19 and the transfer portion. For this reason, before the image at the front end of the document is actually exposed on the photoconductor 12, it is necessary to re-feed the transfer paper waiting on the above-mentioned registration roller 19 and feed it toward the transfer unit.

At the time when the exposure lamp 4 starts moving and reaches the target speed, the H.V. P. It is detected by the sensor 29. H. P. The value obtained by dividing the value of the distance (b) +2 mm from the timing of passing the sensor 29 by the speed according to the selected magnification is H.264. P. It is the time required for the exposure lamp 4 to reach the edge of the white plate after passing the sensor 29, and this time is defined as x.

A value obtained by subtracting the time required for the image at the exposure point of the photoconductor 12 to reach the transfer portion from the time from the start of re-feeding by the registration rollers 19 until the transfer sheet reaches the transfer portion. Is y, and the time required to feed the transfer paper by 2 mm to this y (2 mm / 100 mm / s = 0.02 s
ec ... conveyance speed = 100 mm / s) is added. The above numerical values are calculated by the following formula.

[0064]

## EQU00001 ## x- (y + 0.02) = Z (sec) (1) That is, H.264. P. When the registration roller 19 is operated and re-feeding is performed at the timing when Z in the above formula has passed from the time when the sensor 29 was passed, a transfer paper image with a 2 mm margin is formed in accordance with the selected magnification.

The exposure units 4 to 7 move a predetermined distance according to the cassette size data, the magnification data, etc., gradually reduce the pulse rate at the time when the target position is reached (referred to as slowdown control), and after the stop, again. H. P. Slow-up control and low-speed control are performed toward the sensor 29 to move backward. And H. P. At the time when the sensor 29 is detected, slowdown control for stopping at a position corresponding to the selected magnification is performed, and the exposure units 4 to 7 are stopped.

The document scanning distance is also controlled by the trailing edge signal of the transfer sheet. The control operation described above is controlled by the one-chip microcomputer shown in FIG. Q ₁ shown in FIG. 3 is a one-chip microcomputer incorporating a ROM and a RAM. FIG. 6 shows a basic procedure of a program executed by this microcomputer. Since the contents of FIG. 6 are not directly related to the present invention, detailed description thereof will be omitted.

Next, the control of the exposure lamp 4 will be described. In this embodiment, a halogen lamp is used as the exposure lamp 4, and a lamp regulator (not shown) is used to control the AC power source so that the lighting voltage of the halogen lamp is constant. The lamp regulator, as the AC input voltage changes, also even if the power supply frequency changes, the lamp lighting voltage V _c is controlled to be constant. Therefore, the trigger signal of the exposure lamp for phase control is output from this lamp regulator and input to the controller CONT (see FIG. 1). The trigger signal of the exposure lamp is always output regardless of whether or not the lamp is turned on.

Further, a zero-cross generation circuit (not shown)
Input the zero-cross signal created in step 1 to the controller CONT and connect it to the microcomputer. By monitoring the time _Tc from the zero-cross signal to the trigger signal of the exposure lamp, it becomes possible to read the change in the input voltage.

[0069] The image forming apparatus according to this embodiment, the lamp lighting voltage V _c as the illuminance on the photosensitive drum surface for each device becomes constant is adjusted, and the lamp lighting voltage V _c is stored in non-volatile memory . From the stored lamp lighting voltage V _c and the time T _c from the zero-cross signal to the trigger signal of the exposure lamp, the AC input voltage E _max can be obtained from the following equation.

[0070]

[Equation 2]

[0071]

[Equation 3]

[0072]

[Equation 4] E _rms ² / V _c ² = 1 / {1-2 × T _c / T + sin (4πT _c / T) / 2π} (4) From the zero-cross signal to the exposure lamp trigger signal according to the equation (4) By inputting the time T _c of E _rms ² /
V _c ² can be obtained, and the AC input voltage E _rms can be obtained from the lamp lighting voltage V _c stored in the nonvolatile memory.

In this embodiment, E _rms ² / V _c ² is _calculated from T _c by the table stored in the ROM.

Next, the control of the ceramic heater 43 (see FIG. 1) in the fixing unit 21 will be described. As described above, the heater 43 is a heater in which a resistor is printed on the ceramic substrate, and has excellent thermal response. Therefore, in the normal ON / OFF control, the ripple (deviation from the set temperature: overshoot) becomes large with respect to the set temperature, or excessive electric power is excessively supplied to the heater itself, thereby damaging the heater. . Therefore, in this embodiment, power control is performed so that constant power is supplied. In addition, in order to reduce the ripple, control is performed to switch the electric power according to the temperature detected by the thermistor.

Regarding the electric power control of this heater, the phase control is performed in the same manner as the above-mentioned control of the exposure lamp.
The electric power W supplied to the resistor forming the ceramic heater 43 is

[0076]

## EQU5 ## W = V _H ² / R (5) V _H : voltage applied to the heater R: resistance value of the heater.

Since the resistance value R of the heater is stored in the non-volatile memory for each image forming apparatus and the electric power supplied to the heater is known in advance, the voltage V _H applied to the heater is set.
Is from the above formula

[0078]

[Equation 6] V _H ² = R × W (6) Further, from the equation of effective voltage, the voltage V _H given to the heater is

[0079]

[Equation 7]

[0080]

[Equation 8]

[0081]

E _rms ² / V _H ² = 1 / {1-2 × T _H / T + sin (4π T _H / T) / 2π} (9) V _H ² is calculated from the formula (6), and the formula (6) is calculated. By _obtaining E _rms ² from 4) and calculating E _rms ² / V _H ² , the time T _H from the zero cross signal to the trigger signal to the heater can be obtained from the equation (9).

In this embodiment, a table is used for E
T _H is _calculated from _rms ² / V _H ² .

The electric power of the heater 43 is controlled by the algorithm as described above. The power control of the heater 43 is always performed during the copy period so that the temperature of the heater 43 is constant.

FIG. 7 shows a resistance pattern of the heater 43 included in the fixing unit 21. 43a shown in this figure
Is a portion of the printed resistor, and at the same time it branches into five in the middle and becomes thinner toward the right side of the figure (the reason will be described in detail later).

Thus, according to the size of the recording paper,
Controls energization to each branch. The reason is that the temperature of the non-paper passing portion (the portion where the paper does not pass) is too high compared to the temperature of the paper passing portion (the portion where the paper passes) on the heater. The reason is that the total electric power applied to the end (non-sheet passing portion) from the branched portion is branched and the temperature is lowered. Of course, when branch energization,
It is necessary to control the total amount of electric power supplied so that the temperature of the paper passing portion becomes constant.

Then, the energization control of each branch according to the recording sheet size will be described with reference to FIG.

FIG. 8 is a diagram showing the electrical wiring of the fixing heater 43. Here, T1 to T6 are terminals of the resistor (see FIG. 7). These terminals T1 to T5 are connected to the relay RL1 according to a signal from the controller CONT (see FIG. 1).
~ RL5 is connected to the neutral end N of the AC power supply. The triac 50 also serves as a switch between the common terminal T6 of the resistor and the hot end H of the AC power source in response to a signal from the controller CONT.

Next, the actual operation will be described. For example, when B4 copy paper (transfer paper) is used, the controller CONT outputs a high level signal to the bases of the transistors Q3 and Q4, turns on the switches of the relays RL3 and RL4, and the branch end and AC- Connect N line. Then, by supplying a signal for turning on the triac 50, the resistors connected to the terminals T3 and T4 are energized.

The controller CONT turns on / off the triac 50 so that the voltage (effective value voltage) applied to the heater 43 becomes a predetermined constant voltage (phase control). Further, based on the output signal from the temperature detection element (thermistor) 41 attached to the heater 43, the energization is controlled so that the temperature of the heater portion becomes a predetermined temperature.

FIG. 9 shows each copy size (transfer paper size).
Shows the energized state to the branch end according to.

Next, a method for suppressing ripple (overshoot) when the temperature of the heater 43 is maintained at a predetermined temperature will be described.

Conventionally, the maximum electric power that can be applied is applied until the heater reaches a predetermined temperature, the power supply to the heater is turned off by detecting that the temperature becomes higher than the predetermined temperature, and when the temperature becomes lower than the predetermined temperature again. It was supplying maximum power. For this reason,
There was a large temperature variation due to overshoot.

Therefore, in this embodiment, the electric power P to be supplied is changed as follows according to the difference between the temperature detected by the temperature detecting element 41 attached to the heater 43 and the predetermined temperature.

[0094]

[Equation 10] P = K _P (T _G −T _R ) ... (10) K _P : Proportional constant [W / ° C.] T _G : Target temperature T _R : Detected temperature Various values can be obtained by changing this proportional constant K _P. Various controls can be performed. That is, if K _P is reduced, temperature control with less overshoot can be performed, but the response speed becomes slower. Conversely, if K _P is increased, the response speed is increased, but overshoot is increased.
Further, since the electric power P is changed according to the paper size (that is, the way of branching), an optimum K _P corresponding to each size is set.

As can be seen from FIG. 7, the branched resistor portion is gradually thinner toward the right side of the figure. As a result, the resistance value becomes higher, and the power consumption increases as you move to the right. Therefore, it is possible to prevent the temperature of this portion of the non-sheet passing portion from being lowered too much by increasing the temperature of the right portion, and the temperature difference of the heater becomes relatively small. This makes it possible to control the belt-shaped film appropriately by relatively simple heater control and belt deviation control.

Next, another embodiment will be described.

FIG. 10 shows the structure of a ceramic heater according to another embodiment of the present invention. The driving method of the heater shown in this figure is the same as that described in the above embodiment.

In the embodiment shown in FIG. 10, all the branched portions of the resistor have the same width, but they are thinner than the width of the resistor for A3. That is, in the previous example, by making the width of the resistor narrower toward the right, the temperature of the non-sheet passing portion is prevented from dropping beyond the allowable range as it goes to the right, but here it is Instead, they all have the same thickness.

The embodiment in which the width of the resistor is gradually narrowed as shown in FIG. 7 is relatively difficult to machine and may be disadvantageous in terms of cost. However, even in the embodiment shown in FIG. 10, this pattern is more useful if the temperature distribution of the heater is sufficiently within the allowable range and the deviation control of the belt-shaped film can be easily performed.

[0100]

As described above, according to the present invention, it is easy to bring the temperature distribution of the fixing heater close to the permissible range, and therefore it is possible to surely perform the deviation control of the belt-shaped film. Further, since the deviation control can be easily performed, it is possible to perform fixing at a higher speed, and as a result, it is possible to form an image at a higher speed.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation panel of the device shown in FIG.

FIG. 3 is a circuit diagram showing a one-chip microcomputer included in the controller of this embodiment.

FIG. 4 is an explanatory diagram showing a driving mode of a stepping motor 26.

FIG. 5 is an explanatory diagram showing a method for forming a margin at the leading edge of an image and a method for aligning the leading edge of a transfer sheet.

FIG. 6 is a flowchart showing an outline of a control procedure in this embodiment.

FIG. 7 is a ceramic heater 4 according to an embodiment of the present invention.
It is a figure which shows the resistance pattern of No. 3.

FIG. 8 is a diagram showing a drive circuit of a ceramic heater 43.

9 is a diagram showing a forward power control state of a heater 43 shown in FIG.

FIG. 10 is a diagram showing a resistance pattern of a ceramic heater 43 according to another embodiment of the present invention.

FIG. 11 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

3 Original Glass 4 Exposure Lamp 8 Zoom Lens 12 Photosensitive Member 14 Transfer Unit 15 Developing Unit 20 Conveying Unit 21 Fixing Unit 22 Paper Ejection Roller 23 Cassette 25 Main Drive Motor (Synchronous Motor) 26 Stepping Motor 35 Drive Roller 41 Temperature Detection Element (Thermistor) ) 42 plastic supporter 43 heater (ceramic heater) in which a resistor is printed on a ceramic substrate 45 tension roller 47 endless film

Claims (3)

[Claims] 1. A heating resistor having a plurality of branch resistors branched from a linear basic resistor, a thin plate that moves with the movement of a recording material, and the heating resistor controlled to a predetermined temperature. In the image forming apparatus including a fixing device that heats the toner image on the recording material by the heat from the thin plate, the resistance value per unit length of the plurality of branch resistors is set to the basic resistor. The image forming apparatus is characterized in that the resistance value is changed as compared with the resistance value per unit length. 2. The image forming apparatus according to claim 1, wherein the resistance value per unit length is increased by gradually tapering the shape of the branch resistor. 3. The resistance value per unit length is increased according to claim 1, wherein the branch resistor is a linear resistor having a shape smaller than that of the basic resistor. Image forming apparatus.