JP3740257B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly to energization control of a heater of a heat fixing apparatus.
[0002]
[Prior art]
Conventionally, a fixing device used in an image forming apparatus that transfers a toner image onto a transfer material and heat-fixes the toner image to obtain a permanent image has a structure as shown in FIG.
[0003]
In FIG. 8, reference numeral 1 denotes a fixing roller. As an example, a releasable resin layer 12 such as PFA or PTFE is provided on a core metal 11 such as aluminum or iron, and the inside is heated by a heater 4. It has become. The temperature of the fixing roller 1 is detected as a surface temperature of the fixing roller 1 by a temperature detecting element 3 (hereinafter referred to as a thermistor) that is in contact with the fixing roller 1, and the heater 4 is controlled by a temperature control circuit shown in FIG. By operating intermittently, the surface temperature is controlled to a predetermined temperature.
[0004]
The fixing device having the cleaning means can be installed in the paper area with the temperature detecting element. However, in the fixing apparatus having no cleaning means, it should be installed in the non-image area in order to avoid image smearing. Is common.
[0005]
Reference numeral 2 denotes a pressure roller that rotates in contact with the fixing roller 1. As an example, an elastic layer 14 such as silicone rubber or silicone sponge having heat resistance and low hardness is provided on a metal core 13 such as aluminum or iron. And has a structure having a coating layer 15 made of a resin having high releasability such as PFA or PTFE on the surface thereof.
[0006]
Further, the transfer material P carrying the toner image T is guided to the nip portion between the fixing roller 1 and the pressure roller 2 by the inlet guide 6 and fixed by being heated and pressed. The entrance guide 6 is generally made of a resistance control material such as PBT (10E8 to 10E10Ω), or a guide surface is made of a metal such as stainless steel, and the resistance control material is used as a contact point with the fixing frame. .
[0007]
This is because, when the entrance guide is formed of an insulator or the like, the guide surface is charged by sliding with the transfer material, and adverse effects such as toner scattering occur. In addition, an appropriate reverse crown shape is provided in the longitudinal direction of the fixing roller 1 and the pressure roller 2 so that wrinkles do not occur when the transfer material P passes through the nip portion. Generally, the intrusion position is optimized. The transfer material P that has been heated and pressed in the fixing nip to fix the toner image is separated from any of the rollers by the fixing roller separation claw 5 or the pressure roller separation claw 9 and discharged by the paper discharge guide 8. To the outside and discharged from the device.
[0008]
In the temperature control circuit shown in FIG. 9, a commercial power source (AC power source) 51 is connected to the heater 4 in the fixing device via a triac 53a of an SSR 53 described later. One end of the triac 53a in the SSR 53 is connected to T1 of the triac 62 through the resistor 63, and the other end is connected to T2 of the triac 62 through the gate of the triac 62 and the resistor 64.
[0009]
The SSR 53 is a solit state relay, and includes a triac 53a, an LED 53b, a zero cross detection circuit (not shown), and the like. When the LED 53b emits light, the triac 53a is turned on and the heater 4 is turned on. The LED 53b has an anode connected to a DC power supply via a resistor 60, and a cathode connected to the collector of an NPN transistor 57 whose emitter is grounded. The base of the transistor 57 is connected to the output port of the CPU 24.
[0010]
Therefore, when the CPU 24 sets the output port to L (OFF), the LED 53b is not lit, so the main heater 4 is not lit, and when the output port is set to H (ON), the LED 53b is lit and the main heater 4 is turned on. 4 lights up.
[0011]
On the other hand, the thermistor 3 in the fixing unit has one end connected to a DC power source and the other end connected to a resistor 55. An analog voltage determined by the value of the resistor of the thermistor 3 is input to the A / D conversion input port of the CPU 24, and the CPU 24 detects the temperature of the fixing device.
[0012]
In such temperature control of the fixing device, the output voltage of the thermistor is monitored and it is determined whether or not the CPU 24 has reached a predetermined temperature, and the energization to the heater is switched by the triac 53a by the control circuit shown in FIG. By doing.
[0013]
The actual heater control can be broadly divided into
1: At first launch in the morning,
2: At the front multi-turn,
3: During forward rotation,
4: When printing
5: During standby
FIG. 10 shows the lighting states of the respective heaters.
[0014]
1: When starting up in the morning, the heater is turned on continuously.
2: At the time of multiple front rotation, the heater is driven in a blinking state to prevent overshoot.
[0015]
3: At the time of pre-rotation, the heater is continuously lit or blinked until a predetermined temperature is reached. This lighting state varies depending on the strength of the heater and the heat capacity of the fixing roller.
[0016]
4: At the time of printing, 5: At the time of standby, if the predetermined temperature is reached, the energization to the heater is turned off, and if it is lower than the predetermined temperature, the energization to the heater is turned on. At the time of printing, the heater is controlled to a predetermined temperature by being turned on / off every 2 to 3 seconds.
[0017]
In order to reduce the heat capacity of the fixing roller for the purpose of shortening the warm-up time, the thickness of the fixing roller 1 may be set to 1.0 mm or less. In such a case, in the configuration using one heater, an excessive temperature rise in the non-sheet passing area becomes a problem when printing small size paper.
[0018]
Particularly in a high-speed machine, the printing speed is remarkably lowered when printing small-size paper.
[0019]
Therefore, as a means for solving this problem, two heaters having different light distributions are used. FIG. 11 shows the cross-sectional configuration, and FIG. 12 shows the light distribution and segment arrangement of the heaters.
[0020]
Here, the heater light distribution in the case where paper conveyance is used as a central reference is shown. The heater (main heater) 4a is used when printing small size paper, and distributes the light distribution largely to the portion where the paper takes heat. The heater (sub-heater) 4b is used in combination with the heater 4a to print large size paper.
[0021]
FIG. 13 shows the lighting ratio of the heater with respect to the paper size. In this case, when the heater 4a is turned on for 500 msec, the heater 4b is turned on at a rate of 500 msec for A3 printing, 300 msec for B4 printing, and 100 msec for A4 vertical printing.
[0022]
These lighting ratios are generally set so that the temperature distribution of the fixing roller becomes substantially flat when the most frequently used paper of 65 g / mE2 to 80 g / mE2 is printed. Thus, the power supply circuit of the fixing device using a plurality of heaters is provided with two systems that are the same as those in FIG.
[0023]
[Problems to be solved by the invention]
When the fixing device configured as described above is actually used, the temperature distribution of the fixing roller may not fall within a predetermined range due to variations in heater output.
[0024]
For example, in a fixing device in which a temperature detection element is mounted at the end, when the output of the main heater 4a is the maximum manufacturing tolerance and the output of the sub heater 4b is the lower limit of the manufacturing tolerance, the temperature of the fixing roller As shown in FIG. 14A, the distribution has a higher central portion with respect to the roller end portion. As a result, problems such as a large overshoot during warm-up and curling during paper feeding occur.
[0025]
On the other hand, when the output of the sub-heater 4b is larger than that of the main heater 4a, both ends have a high temperature distribution as shown in FIG. 14B, and the fixing property at the center cannot be satisfied.
[0026]
Further, in a fixing device having a temperature detection element at the center, when the temperature distribution is as shown in FIG. 14A, the fixing property at the end becomes unsatisfactory, and the temperature distribution as shown in B of FIG. In such a case, an excessive temperature rise in the non-sheet passing area at the time of printing a small size paper becomes a problem.
[0027]
An object of the invention according to the present application is to provide a fixing device capable of adjusting the temperature of a fixing roller with high accuracy and improving print quality such as good fixability and paper shape.
[0028]
[Means for Solving the Problems]
The configuration for realizing the object of the invention according to the present application is a constant voltage circuit that can supply a constant voltage to the heater regardless of the voltage of the commercial power supply as a heater driving circuit, and a driving circuit that can arbitrarily change the voltage applied to the heater. Use.
[0029]
Thereby, it becomes possible to obtain | require the temperature rise rate with respect to the applied voltage of each heater.
[0030]
Here, the variation in the temperature rise rate when a constant voltage is applied to the heater can be obtained as shown in FIG.
[0031]
The upper limit of the heater output is as shown in U of FIG. 1, and the lower limit of the heater output is as shown in L of FIG. 1. Therefore, with respect to the temperature increase rate deviation with respect to C in FIG. 1 indicating the reference temperature increase rate (heater output). By changing the voltage applied to the heater, the temperature rise rate, that is, the output of the heater is corrected. In this way, by correcting the deviation of the heater output, it becomes possible to keep the temperature distribution of the fixing roller constant even when a plurality of heaters are used in combination. Good print quality can be maintained.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
( Prerequisite technology )
2, 3 and 4 show the prerequisite technology of the present invention.
[0033]
The configuration of the fixing device of the base technology is basically the same as that of FIG. 11 shown as a conventional example, and uses two heaters (main heater and sub heater) having different light distributions. The light and the segment arrangement are the same as those in FIG.
[0034]
The fixing device of the base technology is a central reference that conveys a transfer material having an A3 (297 mm) width as a maximum sheet passing size with respect to the sheet passing center of the apparatus, and the heater light distribution is also based on the sheet passing reference. It has a symmetric distribution.
[0035]
Further, the main heater 4a and the sub heater 4b have a rated power of 500 W, use a DC 90 V rated voltage, and are a step-down type corresponding to an input voltage of 90 V to 260 V in the control circuit shown in FIG. By using a constant voltage power supply (FIG. 9), it is possible to apply a rated voltage to the heater for all power supply voltages in the world.
[0036]
The fixing roller 1 is a roller having a diameter of 40 mm and a thickness of 1.0 mm using aluminum as a metal core 11, and a PFA release layer 12 is coated on the surface layer. The pressure roller 2 has a silicone sponge elastic layer 14 on a stainless steel core 13 and a PFA release layer 15 on the surface, and has a diameter of 30 mm and a product hardness of 50 °, and applies a pressure of 200 N. Thus, a nip width of 5.0 mm can be formed between the fixing roller and the fixing roller. Since the temperature detection element is installed outside the image area, there is no toner adhesion to the temperature detection element, and no cleaning means is required. In this configuration, printing at 30 sheets / minute is possible with A4 horizontal feed.
[0037]
In the fixing device control circuit using the constant voltage circuit shown in the figure, the AC power supply voltage from the commercial AC power supply 51 is rectified and smoothed by the rectification circuit 62 and the smoothing capacitor C1 of the AC / DC conversion circuit 61 to obtain a DC voltage. This is given to the output control device 71.
[0038]
The output control device 71 controls the DC voltage from the AC / DC conversion circuit 61 by pulse width modulation (PWM) and supplies it to the heater 4. The output control device 71 has a positive input terminal connected to the positive output terminal via the drain D / source S path of the FET 72 and a negative input terminal connected to the negative output terminal. The output control device 71 has a positive output terminal connected to one input terminal of the heater 4 and a negative output terminal connected to the other input terminal of the heater 4.
[0039]
The constant voltage circuit 73 of the output control device 71 detects the average voltage of the voltage applied to the heater 4 by the voltage detection terminals 73a and 73b of the main heater and the sub heater, respectively. In the constant voltage circuit 73, the source voltage detection terminal 73c is connected to the source S of the FET 72. By detecting the voltage of the source S of the FET 72, the frequency of the current I1 flowing in the drain D / source S path of the FET 72 is detected. Is detected.
[0040]
The constant voltage circuit 73 starts when a start control voltage is supplied from switch means (not shown), controls the pulse width based on the detection result of the voltage urged by the heater, and determines the frequency detection result of the current I1. A pulse voltage with corrected frequency deviation is supplied from the output terminal 73d to the gate G of the FET 72.
[0041]
The negative output terminal of the output control device 71 is connected to the positive output terminal via the anode / cathode path of the diode D1. The diode D1 is for absorbing the counter electromotive force of the heater 4 generated when the FET 72 is turned off. When two halogen heaters are used as in the base technology , the fixing device control circuit using the constant voltage circuit includes two systems shown in FIG.
[0042]
Next, heater output correction will be described. As for the output of the heater, first, a constant reference voltage is applied to the heater by the constant voltage circuit shown in FIG. 2, and the temperature rise rate at that time is obtained from the output of the temperature detection element 3. This reference voltage is a voltage applied when obtaining the reference temperature rise rate, and the heater is measured using the constant voltage circuit shown in FIG. Correction is performed by increasing or decreasing the applied voltage.
[0043]
In the base technology , this correction is performed immediately after the power is turned on, and the subsequent heater control is performed at the corrected voltage. In an image forming apparatus equipped with a non-volatile memory, it is possible to always obtain an optimal fixing roller temperature distribution simply by obtaining the heater correction voltage when the fixing device is replaced or removed, and storing the value in the memory unit. It becomes possible.
[0044]
FIG. 3 is a timing chart for correcting the energization of the heater based on the lighting state of the heater and the output of the temperature detection element 3, and FIG. 4 is a flowchart showing the operation.
[0045]
In the base technology , energization of both heaters in the operation for obtaining the correction value of the input voltage for the main heater 4a and the operation for obtaining the correction value of the input voltage for the sub heater 4b are performed separately.
[0046]
In FIG. 4, immediately after the power is turned on, the reference voltage Vref is applied to the main heater 4a (S1), the temperature rise rate Xa at that time is obtained from the output of the temperature detecting element 3, and compared with the reference temperature rise rate Xrefa ( S3).
[0047]
If the detected temperature increase rate Xa is larger than the reference temperature increase rate Xrefa, the applied voltage is lowered (S4). If the detected temperature increase rate Xa is smaller than the reference temperature increase rate Xrefa, the applied voltage is increased. (S5) The applied voltage correction operation for the main heater 4a is continued until the applied voltage becomes equal to the reference voltage.
[0048]
After the correction of the applied voltage Va of the heater 4a is completed, the reference voltage Vref is applied to the sub heater 4b, and the temperature rise rate Xb (heater output) of the sub heater 4b is predetermined as in the case of the main heater 4a described above. The applied voltage of the heater 4b is changed so that the value Xrefb becomes (S6 to S10).
[0049]
Then, after the setting of the applied voltages of the heaters 4a and 4b is completed, all the heaters are turned on to perform normal startup control (S11), and the subsequent control drives the heaters with the corrected applied voltage.
[0050]
When the fixing device or the image forming apparatus has a non-volatile memory, the applied voltage of the main heater 4a and the sub heater 4b is corrected when the initial power is turned on or when the fixing device is attached / detached, and the correction value is set in a non-volatile manner. By recording in the memory, the subsequent control refers to the correction value and drives the heater. Thereby, the influence on the warm-up time due to the correction of the heater applied voltage can be eliminated, and the control can be performed in the same manner as in a normal fixing device.
[0051]
( Embodiment )
FIG. 5 shows an embodiment of the present invention.
[0052]
In this embodiment, the warm-up time is shortened with respect to the base technology .
[0053]
In the base technology described above, an example in which the correction of the main heater 4a and the sub heater 4b is performed independently has been shown. However, since only one heater is lit during the applied voltage correction, Is at a disadvantage. As shown in FIG. 12, the light distribution of the two sub-main heaters is different, and therefore, when the same voltage is applied to each heater, the temperature rise rate is different as shown in FIG.
[0054]
Therefore, in this embodiment, as shown in FIG. 5, after correcting the applied voltage of the sub-heater 4b having a high temperature rise rate, the applied voltage of the main heater 4a is corrected while the sub-heater 4b is lit.
[0055]
That is, since the sub heater 4b is corrected so as to have a predetermined temperature rise rate (heater output), the main heater with respect to the reference temperature rise rate when both the main heater 4a and the sub heater 4b are lit. The applied voltage 4a is corrected.
[0056]
Here, by correcting the sub heater 4b first, the temperature distribution of the fixing roller can be brought close to a predetermined temperature distribution. If the main heater 4a having the main light emission area at the center as shown in FIG. 12 is lit first, the warm-up time is increased and the temperature at the center of the fixing roller is significantly higher than the end. Thus, there are problems such as an excessive temperature rise at the center or poor fixing due to insufficient temperature at the edges.
[0057]
Conversely, when the sub-heater 4b having the main light emitting area at the end is turned on first as in the present embodiment, the temperature difference between the center and the end of the fixing roller can be reduced, and the print state can be smoothly achieved. You can migrate.
[0058]
Also in this embodiment, the corrected heater applied voltage is stored in a nonvolatile memory, so that the normal fixing can be performed by correcting the heater applied voltage only once when the initial power is turned on or when the fixing device is detached. It can be controlled in the same way as the apparatus, and at the same time, adverse effects caused by variations in heaters can be prevented.
[0059]
( Reference example )
6 and 7 show a reference example of the present invention.
[0060]
The above-described base technology and embodiments have described a fixing device having two heaters in a fixing roller. These are fixing devices mainly used for black-and-white printing, and the fixing device used for color printing has heaters 4 ′ and 4 ″, one each for fixing roller 1 ′ and pressure roller 2 ′, as shown in FIG. It is common to take a configuration.
[0061]
In FIG. 6, the fixing roller 1 ′ is aluminum having a diameter of 40 mm, the core metal 11 is aluminum having an inner thickness of 2 mm, and has a 3 mm silicone rubber layer 16 on the surface layer. Further, the pressure roller 2 ′ is 40 mm in diameter, the core metal 13 is aluminum having a thickness of 2 mm, and the surface layer has a 2 mm silicone rubber layer 17. By making the thickness of the elastic layer of the fixing roller surface layer larger than that of the pressure roller surface layer, the transfer material can be separated without having a separation claw.
[0062]
One heater 4 ′, 4 ″ is disposed in each of the fixing roller 1 ′ and the pressure roller 2 ″. The temperature detecting element 3 is brought into contact with the pressure roller 2 'side so that a scratch caused by the roller does not appear on the image surface.
[0063]
Reference numeral 18 denotes a cleaning device for the fixing roller 1 ′, and reference numeral 19 denotes a cleaning blade for the pressure roller 2 ′. Even in such a fixing device, the temperature balance between the upper and lower rollers can always be optimally corrected by correcting the heater output as described above.
[0064]
As shown in FIG. 13, since the temperature detecting element 3 is in contact with the pressure roller 2 ′ side, the correction of the heater output on the fixing roller 1 ′ side is performed on the surface of the pressure roller 2 ′ while the roller is rotating. Judging from the heating speed.
[0065]
FIG. 7 shows the output of the temperature detecting element 3 and the temperature change of the pressure roller 2 ′ at this time. Here, only the heater of the fixing roller 1 ′ is turned on while rotating the pressure roller 2 ′, the output of the main heater 4 ′ is corrected from the temperature change of the pressure roller 2 ′, and then the pressure roller 2 ′. The output correction of the sub-heater 4 ″ of the pressure roller 2 ′ is performed in a state where the rotation of is stopped.
[0066]
In this case, even if the main heater 4 ′ of the fixing roller 1 ′ is lit, when the rotation of the pressure roller 2 ′ is stopped, there is little influence on the correction of the sub-heater 4 ″ of the pressure roller 2 ′. It is possible to make corrections.
[0067]
In this reference example , the heater output is corrected immediately after the power is turned on. However, the timing is not particularly limited to this, and it is possible to select a timing that is convenient in designing the heater control sequence in a non-printing state. .
[0068]
【The invention's effect】
According to the present invention, in the fixing device in which the voltage applied to the heater as the heating source can be made constant regardless of the power supply voltage by the constant voltage circuit , the temperature rise of the heat fixing means during continuous lighting of the heater with respect to the reference voltage The speed is measured, and the deviation from the reference temperature rise speed is corrected by changing the voltage applied to the heater. As a result, in the fixing device having a plurality of heaters, it becomes possible to always distribute the fixing roller at a predetermined temperature, prevent deviation from the design value of the temperature distribution due to manufacturing variation of the heater output, and good fixability, Print quality such as paper shape can be maintained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a change in temperature of a fixing roller due to a variation in heater output and showing a correction concept of a heater voltage according to the present invention.
FIG. 2 is a circuit diagram of a control circuit showing a prerequisite technology of the present invention.
FIG. 3 is a diagram showing a change in temperature and a lighting state of a heater when output correction is performed on two heaters in the base technology of the present invention .
FIG. 4 is a control flow in the case of using a constant voltage control circuit in the base technology of the present invention .
FIG. 5 is a diagram illustrating a change in temperature and a lighting state of the heater when output correction is performed on two heaters according to the embodiment of the present invention .
FIG. 6 is a cross-sectional view of a fixing device according to a reference example of the present invention .
FIG. 7 is a diagram illustrating a change in temperature and a lighting state of a heater when output correction is performed on two heaters in a reference example of the present invention .
FIG. 8 is a cross-sectional view of a conventional fixing device.
9 is a circuit diagram of a control circuit of the fixing device in FIG. 8. FIG.
FIG. 10 is a diagram illustrating a heater control state and a fixing roller temperature transition using a conventional fixing device control circuit.
FIG. 11 is a cross-sectional view of a conventional fixing device having a two-heater configuration.
FIG. 12 is a diagram showing long arrangement light distribution and segment arrangement of a two-heater configuration.
FIG. 13 is a diagram showing a heater lighting ratio with respect to a paper size of a two heater configuration.
FIG. 14 is a diagram showing a change in the fixing roller temperature distribution when the output of the heater varies.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 3 Temperature detection element 4 Heater 5 Fixing roller separation claw 6 Fixing entrance guide 7 Paper discharge roller 8 Paper discharge guide 9 Pressure roller separation claw P Transfer material T Toner 51 Commercial power supply 53 Triac 61 AC / DC Conversion circuit 62 Rectifier circuit 71 Output controller 72 FET

Claims (2)

Thermal fixing means comprising a fixing roller for fixing the toner image on a transfer material carrying the toner image on the surface ;
A pressure unit that includes a pressure roller that presses the fixing roller to form a nip portion, and carries a transfer material at the nip portion ;
A heating means for heating the thermal fixing means by energization from a power supply means;
Temperature detecting means for detecting the surface temperature of the heat fixing means;
In the fixing device having a control means for controlling the power supply means based on the detection information of the temperature detecting means,
The control means includes a temperature rise speed measurement unit that measures the temperature rise speed of the thermal fixing means by the temperature detection means, and the measurement value measured by the temperature rise speed measurement section is a reference temperature rise speed. changing the voltage output from the power supply means have a correction unit,
The heating means includes a first heating source having a heat generation distribution for preferentially heating a central portion in the axial direction of the fixing roller of the thermal fixing means, and an end portion in the axial direction of the fixing roller of the thermal fixing means. And a second heating source having a heat generation distribution for heating mainly, and each of the heating sources is provided with power supply means,
The control means independently changes a voltage applied to each of the heating sources, performs correction energization control on the second heating source, sets the second heating source to an energized state, and then sets the first heating source. A fixing device that performs correction energization control . The fixing device according to claim 1 , wherein the control unit stores the value in a nonvolatile memory after correcting the applied voltage of the heating source.

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