JPH0449638Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a roll-type fixing device for an image forming apparatus to which electrophotography technology is applied.

[Prior art and its problems]

Roll-type fixing devices of image forming apparatuses that apply electrophotographic technology generally store unfixed toner images between a pair of rolls: a heating roll, at least one of which is heated, and a pressure roll that is in pressure contact with the heating roll and rotates as a result of the heating roll. It is configured to clamp and convey a sheet of paper having a toner image thereon, thereby fixing a toner image thereon.

FIG. 6 is a diagram showing the cross section and surface temperature distribution of a conventional heating roll. In the same figure, heating roll 1
is formed to have a length capable of fixing paper of a predetermined size, and a rod-shaped heater 2 of approximately the same length is disposed inside it. This heating roll 1 is provided with a thermistor or the like (not shown) at approximately the center M in its longitudinal direction, and the thermistor detects the surface temperature and performs temperature control. Such heating roll 1
For example, when continuously fusing A4 size paper, set the maximum temperature that does not cause high temperature offset.
Temperature control is performed at a temperature t at the midpoint of the fixable temperature range T between T _H and the lowest temperature T _L that does not cause low-temperature offset, and the surface is flat as shown by A-B in the longitudinal direction. Set the heat distribution of the heater to match the temperature distribution.

However, when continuously fixing B5 size paper with such heating roll 1, A4 size and
There is no paper for the difference in width of B5 size, so
Heat escape is reduced, and the surface temperature distribution becomes as shown by A-D-E, where the temperature gradually increases from one end of the B5 size to the end of the heating roll 1. Therefore, if the maximum temperature T _H is exceeded,
The life of the separation claw, Teflon (registered trademark) layer, pressure roll, etc. may be extremely shortened, and if A4 size paper is passed through after continuous fixing of B5 size paper, the maximum There were drawbacks such as high temperature offset occurring in the region exceeding the temperature _TH .

In order to solve the above problems,
Japanese Patent No. 63570 discloses a technology related to a fixing device that has a plurality of heaters and temperature detection elements and performs temperature control independently in the longitudinal direction of a roller. However, in this conventional technique, the roller is heated with a plurality of heaters and temperature control is performed by detecting the temperature at different positions in the longitudinal direction of the roller, making the mechanism complicated and extremely expensive.

[Purpose of invention]

SUMMARY OF THE INVENTION In view of the above conventional problems, it is an object of the present invention to provide a fixing device that can uniformly control the surface temperature of a heating roll regardless of paper size without using a plurality of heaters.

[Key points of the idea]

In order to achieve the above object, the present invention fixes the unfixed toner image on the paper by sandwiching and conveying the paper having the unfixed toner image between a pair of rolls, at least one of which is a heating roll having an internal heat source. In the fixing device, the heat source is comprised of a heating element whose heat generation distribution in the length direction varies depending on the frequency of the applied power source.

[Example of idea]

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

FIG. 2 is a schematic side view showing the main parts of a recording apparatus equipped with a fixing device according to the present invention. In the figure, a photosensitive drum 11 is rotatably supported substantially in the center, and is driven and rotated at a predetermined speed in the direction of arrow a. A charger 12 that uniformly charges the circumferential surface of the photoconductor drum 11 to a predetermined polarity and a liquid crystal shutter are installed in the vicinity of the circumferential surface of the photoconductor drum 11 along the direction of rotation thereof, and a liquid crystal shutter is installed inside the photoconductor drum 11 to uniformly charge the circumferential surface of the photoconductor drum 11 to a predetermined polarity. An optical writing head 13 that irradiates the surface of the photoreceptor drum 11 with an optical signal corresponding to information to form an electrostatic latent image, a developer 14 that supplies toner to the formed electrostatic latent image to form a toner image, and a toner. A transfer device 15 that transfers the image onto the transfer paper T, a separation claw 16 that separates the transfer paper T onto which the toner image has been transferred from the photoreceptor drum 11, and a separation claw 16 that separates the toner remaining on the circumferential surface of the photoreceptor drum 11 without being transferred. The cleaners 17 for removal are sequentially arranged to form a one-cycle image forming process.

At the bottom of the machine, there is a paper feed cassette 18 loaded with transfer paper T, a paper feed roller 19, and a turn guide 20.
A pair of registration rolls 21 and a paper guide plate 22 are provided to adjust the timing for conveying the transfer paper T to the transfer position in order to align the toner image on the photosensitive drum 11 with each leading edge of the transfer paper T, and a paper guide plate 22 is provided. It is formed. On the other hand, on the opposite side of the transfer position, the above-mentioned separation claw 16 is arranged to separate the transfer paper T onto which the toner image has been transferred from the surface of the photoreceptor drum 11. A conveyance guide 23 formed in the shape of a square is installed, and a fixing device 24 for thermally fixing the transferred toner image onto the transfer paper T is installed on the leading end side of the conveyance guide 23, and a fixing device 24 that thermally fixes the transferred toner image onto the transfer paper T is arranged so that the transfer paper T with the toner image fixed thereon is moved upward. A conveyance guide 25 for discharging the transfer paper T to the paper ejection tray section 26 and a pair of discharge rolls 27 for discharging the transfer paper T to the paper discharge tray section 26.
is arranged, and a transfer paper ejection path is formed.

FIG. 3 is a perspective view of the paper feed cassette 18 of FIG. 2. In the figure, the paper feed cassette 18 is a cassette for feeding A4 size paper, and a label 28 for detecting the size is attached to the end surface on the transport side.
(28a for A4 size) is attached. Size detection sensors 29a and 29b are arranged at positions facing the label 28 when the paper feed cassette 18 is attached to the main body of the apparatus in the direction of arrow b. These size detection sensors 29a and 29b are each detected by the presence of the label 28.
This is a reflective sensor for detecting A4 size and B5 size.

FIG. 4 is a detailed configuration side view showing essential parts of the fixing device 24 shown in FIG. 2. FIG. In the figure, the heating roll 30 has a heating element 31 as a heat source such as a heater inside.
It is a roll whose peripheral surface is coated with a resin 30a such as Teflon (registered trademark) having heat resistance and toner releasability, and rotates in the direction shown in the figure. A pressure roll 32 whose peripheral surface is covered with heat-resistant and elastic silicone rubber or the like is pressed to the lower part of the heating roll 30 to form a nip portion 33. Follow. Then, the paper on which the toner image has been formed is caught and passed in the direction of arrow C, thereby pinching and pressing the paper. , the toner image is thermally fused onto the paper for fixing work. The tip of the peeling claw 34 is brought into contact with the paper discharge side of the circumferential surface of the heating roll 30, and the nip portion 33
The paper discharged from the heating roll 30 is peeled off from the heating roll 30, and then the paper is discharged from the machine by a discharge roll 35. Further, a thermistor 36 for detecting temperature is disposed near the heating roll 30 and comes into contact with the circumferential surface of the heating roll 30. This thermistor 36 is attached to an arm 37, and this arm 37 is rotatably provided on a shaft 37a.

FIG. 5 is a diagram showing a temperature control circuit of the fixing device. In the figure, the size detection sensor 29a is
The light emitting section is composed of a light emitting diode 38 and a phototransistor _Q1 . The light emitting diode 38 and the resistor R ₁ are connected in series between the power supply terminals 39 and 40, and the collector of the phototransistor Q ₁ is connected to the power supply terminal 3 by connecting the resistors R ₂ and R ₃ in series.
9, and the emitter is grounded. On the other hand, the size detection sensor 29b includes a light emitting diode 41 as a light emitting section and a phototransistor _Q2 . Light emitting diode 41 and resistor
R' ₄ is connected in series between power supply terminals 39 and 40, and the collector of phototransistor Q ₂ is connected to power supply terminal 39 with resistors R ₅ and R ₆ connected in series, and its emitter is grounded. Also, the resistance R ₂
and the connection point of resistor R ₃ is connected to the base of transistor Q ₃ . The emitter terminal of this transistor _Q3 is connected to the power supply terminal 39, and the collector terminal is connected to a frequency control circuit 44, which will be described later. Furthermore, the connection point between resistor _R5 and resistor _R6 is connected to the base of transistor _Q4 . The emitter terminal of this transistor _Q4 is connected to a power supply terminal 39, and the collector terminal is connected to a frequency control circuit 4, which will be described later.
Connected to 4. Further, the series circuit of resistors R ₇ and R ₈ and the series circuit of the thermistor 36 and resistor R ₉ are connected in parallel between the power supply terminals 39 and 40 to form a bridge circuit. The connection point between the resistor R ₇ and the resistance R ₈ is connected to the inverting input terminal of the comparator Q ₅ , and the connection point between the thermistor 36 and the resistor R ₉ is connected to the non-inverting input terminal of the comparator Q ₅ .
Further, the output terminal of comparator _Q5 is connected to the connection point between resistor _R10 and resistor _R11 . And resistance
A resistor _R12 is further connected to _R11 , and the above-mentioned resistor _R10 , _R11 , and _R12 form a series circuit.
Further, the base terminal of the transistor _Q6 is connected to the connection point between the resistor _R11 and the resistor _R12 . The emitter terminal of this transistor _Q6 is grounded, and the collector terminal is connected to a trigger circuit. Further, the trigger output of the trigger circuit 42 is connected to the gate terminal of a tri-up 43, and the tri-up 43, the heating element 31 (heater), and the frequency control circuit 44 constitute a closed circuit. This frequency control circuit 44 is connected to a power source 45, and is a circuit that switches and outputs a commercial frequency voltage and a high frequency voltage of 10 to 20 KHz based on the size detection signals of the transistors _Q3 and _Q4 .

Figure 1a is a diagram showing the longitudinal cross section of the heating roll and its surface temperature distribution, Figure 1b is a diagram showing the relative calorific value in the longitudinal direction of the heating element, and Figure 1c is a diagram showing the configuration of the heating element. It is. In the figure, heating roll 30
The heating element 31 disposed inside is made of a heating wire such as a nichrome wire, and is connected to a section 31b from one end to a length corresponding to a B5 size, and connected to the 31b section from one end to a length corresponding to an A4 size. It consists of a section 31a up to a length corresponding to the length. 31b part is
The heating wire has a diameter of about 0.5mm, and the 31a section is
A large number of heating wires with a diameter of about 0.05 to 0.1 mm are twisted together, and the total cross-sectional area is the same. Therefore, both the portions 31a and 31b are formed to have the same DC resistance per unit length. Although the heating element 31 is formed in a coil shape, it is shown as a straight line in the figure for ease of understanding.

Fixing device 2 of this embodiment configured as above
The operation No. 4 will be explained. First, to explain the circuit operation, turn on a switch (not shown),
Power is supplied between power terminals 39 and 40 to put the circuit into operation.

First, the size detection sensors 29a and 29b are
By detecting the label 28 attached to the paper feed cassette 18, the phototransistors _Q1 and
If Q ₂ is on and A4 size, the transistor
When Q ₃ is of B5 size, transistor Q ₄ is turned on and a size detection signal is input to frequency control circuit 44 . The frequency control circuit 44 outputs a commercial frequency voltage when the transistor Q ₃ is turned on, and outputs a high frequency voltage when the transistor Q ₄ is turned on. On the other hand, the heating roll 30
When the temperature of is low and the resistance of thermistor 36 is high, the voltage at the connection point of resistor _R9 and thermistor 36 is
V _N is higher than the voltage V ₁ at the connection point of resistors R ₇ and R ₈ (V _N > V ₁ ). Therefore, the output of the comparator _Q5 becomes an H (high) signal, which turns on the transistor _Q6 , turns on the trigger circuit 42, and turns on the triac 4.
An H signal is supplied to the gate of No.3. Through this series of operations, the triax 43 becomes conductive, and an alternating current with a frequency corresponding to the size detection signal flows through the closed circuit composed of the frequency control circuit 44, the heating element 31, and the triax. Therefore, the heating roll 30 is heated by the heating element 31, and the peripheral surface temperature increases. Next, when the thermistor 36 detects the fixing temperature, the magnitudes of the input voltages _VN and _V1 of the comparator _Q5 are reversed to those described above, and the output of the comparator _Q5 becomes an L (low) signal. Therefore, the transistor _Q6 is turned off, the trigger circuit 42 is also turned off, and the alternating current flowing through the closed circuit of the frequency control circuit 44, heating element 31, and triax 43 is cut off. Due to this circuit operation, the heating element 31 stops its heating operation. When the heating operation of the heating element 31 stops and the temperature detected by the thermistor 36 decreases, the output of the comparator _Q5 is reversed again.
The above-described operation is repeated to control the temperature of the heating roll 30 to a predetermined temperature.

In the circuit operation described above, when the transistor Q ₃ is turned on (when A4 size is detected), the frequency control circuit 44 outputs a commercial frequency voltage and the heating element 31 is energized. As a result, since the portion 31b of the heating element 31 has a low commercial frequency, the skin effect does not appear and heat is generated uniformly throughout the heating element 31 as shown by the solid line in FIG. 1b. On the other hand, when transistor Q ₄ is turned on (when B5 size is detected), frequency control circuit 44 operates at 10 to 20 KHz.
A high frequency voltage is output and the heating element 31 is energized. As a result, the 31a part of the heating element 31 has a thin heating wire, so the skin effect does not appear and the resistance is almost the same as the DC resistance, but the 31b part is thicker than the 31a part, so the skin effect appears and the high frequency resistance is higher than the DC resistance. It gets expensive. Therefore, as shown by the broken line in FIG. 1b, the relative calorific value of the portion 31a is lower than that of the portion 31b.

When passing A4 size paper with the above heat generation amount, the temperature distribution will be the same as when applying a commercial frequency AC voltage, and the heat supply and heat absorption by the paper will be balanced, resulting in A ₁ - B ₁ in Figure 1a. As shown, the temperature distribution is almost flat. In addition, when passing B5 size paper, the temperature distribution becomes the same as when a high-frequency AC voltage is applied, and heat supply and heat absorption are balanced as described above. That is, as shown in Figure 1a, D ₁ −B ₁ is A ₁ −
The heat generation (heat supply) is lower than D ₁ , but since the paper does not pass through it, only heat is radiated, resulting in A ₁ −D ₁ −B ₁
The temperature distribution is almost flat. In addition, in the case of high-frequency energization, the resistance value of the portion 31b increases, so the overall heat generation value also decreases, but since it is a closed loop in which temperature is detected by the thermistor 36, the control temperature t (for example, 180℃)
will never change. Therefore, the surface of the heating roll 30 is either A4 or B5 size.
without exceeding the maximum temperature T _H and the minimum temperature T _L
You can control the temperature without lowering the temperature. Further, since the heat generation distribution in the longitudinal direction can be varied by one heating element 31, the mechanism can be simplified and the cost can be reduced.

In addition, in this example, there are two sizes, A4 size and B5 size.
However, by changing the configuration of the heating element 31, the frequency of the frequency control circuit 44, etc., and varying the heat generation distribution in the longitudinal direction, the invention can be applied to a larger number of paper sizes.

Further, the shape of the heating element 31, the size of its heating wire, etc. are not limited to those of the embodiments, and can be arbitrary.

Further, in this embodiment, the size is detected by a size detection sensor composed of a light emitting diode and a phototransistor, but the present invention is not limited to this embodiment.

[Effect of idea]

As explained in detail above, according to the present invention, the temperature of the heating roll is controlled by the heating element whose heat distribution in the longitudinal direction varies depending on the frequency of the power supply, so the surface of the heating roll is Temperature can be controlled uniformly, extending the life of separation claws, Teflon layers, pressure rollers, etc. Furthermore, the surface temperature of the heating roller can be kept constant at all times, and image defects such as high and low temperature offsets do not occur.

[Brief explanation of drawings]

FIG. 1a is a diagram showing the longitudinal cross section of the heating roll of the present invention and its surface temperature distribution, FIG. 1b is a diagram showing the relative calorific value of the heating element of the present invention in the longitudinal direction,
Figure c is a diagram showing the configuration of the heating element of the present invention, Figure 2 is a schematic side view of the configuration showing the main parts of the recording device equipped with the fixing device according to the present invention, and Figure 3 is the paper feed cassette of Figure 2. 4 is a detailed configuration side view showing the main parts of the fixing device shown in FIG. 2, FIG. 5 is a temperature control circuit diagram of the fixing device, and FIG. 6 is a longitudinal section of a conventional heating roll and its It is a figure showing surface temperature distribution. 18... Paper feed cassette, 24... Fixing device, 2
8...Label, 29a, 29b...Size detection sensor, 30...Heating roll, 30a...Resin, 3
DESCRIPTION OF SYMBOLS 1... Heating element, 32... Pressure roll, 36... Thermistor, 42... Trigger circuit, 43... Triax, 44... Frequency control circuit, 45... Power supply, Q ₃ , Q ₄ , Q ₆ ... …Transistor, Q ₅ …Comparator.

Claims (1)

[Claims for Utility Model Registration] A fixing method for fixing an unfixed toner image on a sheet of paper by sandwiching and transporting the sheet of paper with the unfixed toner image between a pair of rolls, at least one of which is a heating roll having an internal heat source. The fixing device, wherein the heat source is comprised of a heating element whose heat generation distribution in the length direction varies depending on the frequency of the applied power source.