JPS6135472A - Fixing device - Google Patents

Abstract

PURPOSE:To eliminate the trouble of print staining caused by offset toner by putting the operation area of the fixing device as far away from a hot offset area or cold offset area as possible. CONSTITUTION:A preheater 16 equipped with a preheater and a heat roller consists of the 1st block PH1, the 2nd block, the 3rd block PH3, and the 4th block PH4; two heaters and two thermistors are arranged in every block to detect temperature variation from variations in the resistance values of the thermistors of each block and temperature information on that is fed back to turn on and off a heater, controlling the preheater to specific temperature. Two heaters prevent a preheater at the part which is not covered with a form from overheating when a narrow form is mounted while a heat generation part is divided in the form width direction. An RF heater 31 is powered off when a THF thermistor 33 detects the specific temperature and an RR heater 32 is powered off when a THR thermistor 34 detects the specific temperature. A form width sensor mechanism is provided to a form feeding mechanism to code form width data corresponding to the form width, and comparison data of a reference data circuit are switched to obtain alternate information on form temperature in which the influence of the form width is reflected.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the performance of a fixing device having a preheater and a heat roller, such as a laser beam printer.

FIG. 1 shows a schematic diagram of a laser beam printer.

The surface of the photosensitive drum 1 is uniformly charged by a charger 2. The laser beam (continuous beam) from the laser 3 is modulated into discontinuous laser beams corresponding to print data by a modulator 4, and scanned in the axial direction of the photosensitive drum 1 by a rotating polygon mirror 5 to convert the print data. Form an exposed image. The Fθ lens 6 is provided to correct the difference in scanning speed between the axial center and side edges of the photoreceptor 1 when the rotating polygon mirror 5 scans.

The exposed image of print data on the photoreceptor 1 is developed with toner 8 in a developing device 7 . The toner 8 in the developing device 7 is triboelectrically charged with a carrier 9 made of iron oxide balls, electrostatically bonded to the carrier 9, and transported to the surface of the photosensitive drum 1.

The toner image (print data developed with toner) on the photosensitive drum 1 is transferred to the printing paper 1 by applying a high voltage having a polarity opposite to the charged potential of the toner from the back side of the printing paper 11 in the transfer device 13.
Transfer the toner image to 1.

The cleaner 10 is provided to clean the toner remaining on the surface of the photosensitive drum 1 during transfer in preparation for the next charging process (charging process by the charger 2).

The tractors 12a and 12b are transport vehicles with claws that transport the printing paper 11. A preheater (preheating plate) 16 is provided to preheat the toner image on the printing paper 11. The toner image preheated by the preheater 16 is fixed to the printing paper 11 by being heated and pressed by a heat roller 17 and a pressure roller 18 .

In order to ensure preheating in the preheater 16, the suction 15 sucks air and heats the printing paper 11.
This is a mechanism for bringing the preheater 16 into close contact with the preheater 16.

The suction 15 has a structure that moves a suction shutter according to the width of the printing paper 11 to eliminate air leakage from outside the width of the printing paper 110. The buffer 14 is
It is provided to adjust the speed difference between paper feeding by the tractors 12a and 12b (feeding by a conveyor with claws) and paper feeding by the heat roller 17 and the pressure roller 18. The felt 19 is provided for applying silicone oil to the heat roller 17. The oil application mechanism 20 is provided to supply silicone oil to the felt 19. The puller roller 21 is provided to pull in the printing paper 11 after fixing to help fold it. The splice table 22 is provided as a splicing table when the printing paper 1 comes to the end and is spliced with the next printing paper 11.

The fixing area of the fixing device including the preheater, heat roller, and suppression roller is as shown in FIG.

The horizontal axis represents the printing paper 11 on which the transferred toner image is placed.
Temperature of the surface (side with toner image) (hereinafter referred to as "paper temperature")
).

The printing paper 11 has a speed of 55 Kf (paper thickness of approximately 80μ
m) thin paper, the speed is 135Kt (paper thickness approx.
There are thick papers up to 0μm'), and thin paper with a speed of 55Kg will have a paper temperature of about 85-90℃, but
For 5KF thick paper, the paper temperature is approximately 60 to 65°C. For medium-thick paper (paper thickness of about 140 pvn), the paper temperature should be about 75°C.
It is around ~80°C.

The vertical axis in FIG. 2 is plotted by varying the surface temperature of the heat roller (hereinafter referred to as "heat roller temperature") by adjusting the temperature control of the heat roller.

The hot offset area shown in Figure 2 is an area that cannot be selected as the operation area of the fuser because the heat roller temperature is too high and some of the melted toner is transferred (offset) to the surface of the heat roller. .

The cold offset region shown in FIG. 2 cannot be selected as the operation region of the fixing device because the heat roller temperature is too low and some toner of the toner image remains unmelted and adheres to the surface of the heat roller.

The temperature of the heat roller is 180°C (TH180°C) in order to enter the fixing area shown in Figure 2 as the operating area of the fixing device.
) is set.

This fixing device is capable of handling thin paper (paper temperature: 85 Kf) at a speed of 55 Kf.
~90°C), the operating region is close to the hot offset region, and for thick paper with a speed of 135 Kf,
Since the operating area is close to the cold offset area, there is a drawback that malfunction may occur if the paper is dry and the paper temperature becomes too high, or if the paper absorbs moisture and the paper temperature does not rise sufficiently.

If the degree of hot or cold offset is significant, the offset toner may
9, the toner particles are deposited on the heat roller 1 again.
7 and may stain the print.

Furthermore, since the operation is performed in an operating region close to the hot offset region or the cold offset region, a small amount of toner tends to adhere to the heat roller 17.
9 Hetner is j[L easy. Therefore, the feeding speed of the felt 19 must be increased, which results in frequent replacement of the felt, resulting in high running costs.

It is an object of the present invention to eliminate printing smear problems caused by gold-offset toner by moving the operating area of the fuser as far as possible from the hot or cold offset areas.

Another object of the present invention is to reduce the amount of toner adhering to the other felts, thereby extending the period for replacing the felts.

The present invention adjusts the heat roller temperature to 190°C (Tutqo) and 170°C (TH17) according to the paper temperature as shown in
0), the heat roller braking temperature is automatically switched by feeding back the paper temperature or alternative information of the paper temperature by being placed away from the hot offset area or the cold offset area. It was devised.

Infrared thermometers are available as paper temperature detectors, but they are expensive and would be expensive to incorporate into the device. Therefore, for thin paper with a low speed, the paper temperature on the preheater will be high, but because the heat capacity of the paper is small,
The energization rate of the preheater is small. On the other hand, for paper with a high speed, the paper temperature on the preheater is low, but the paper has a large heat capacity, so the preheater's energization rate is high. By using this information as a substitute for temperature, the control temperature of the heat roller can be switched depending on the paper temperature.

In Fig. 4, there are 6 preheaters, 1st block (PH
1), a second block (PH3), and a fourth block (PH4). Each block has 2
A main heater and two thermistors are installed, and the temperature change is detected by the resistance value change of the thermistor of each block.The temperature information is fed back and the heater is turned on/off to keep the preheater at a predetermined temperature. Control. The approximate arrangement of the heater and thermistor is shown for the fourth block (PH4). The two heaters are configured to share the heat generating portion in the paper width direction to prevent the preheater in the portion not covered by the paper from overheating when narrow paper is loaded. When the RF upper heater 1 Fi, THp thermistor 33 detects a predetermined temperature, it is controlled to turn off the electricity. The upper RR heater 2 is controlled to turn off the current when the IR sustainer 34 detects a predetermined temperature.

In the case of narrow paper, the paper does not pass through the RR upper heater 2, so as long as the THR thermistor 34 indicates a predetermined temperature, the RR upper heater 2 is not energized.
Do not overheat the preheater in areas not covered by paper.

The suction/15 is a mechanism that sucks air through the printing paper 11 to bring the printing paper 11 into close contact with the preheater 16. The structure is such that the position of the suction shutter is controlled according to the paper width to prevent air leakage from outside the paper width.

In FIG. 5, near the entrance x of the preheater 16.

At the position , the paper temperature is almost the same regardless of the speed 55 and 135b, but at the preheater position X1 + xt
As I xs I x4, there is a large difference in paper temperature between thin paper with a speed of 55 Kf and thick paper with a speed of 135 kf. The reason for this is that thin paper with a speed of 55 Kf is thin and easily warms up, whereas thick paper with a speed of 135 Kg is difficult to warm up due to its thickness.

Furthermore, as shown in FIG. 5, for thin paper with a speed of 55 Kf, the rise in the first block PH1 (position x1) and the second block PH2 (position) h) is large, and the rise in the third block PH3 and fourth block PH4 is large. It can be seen that the temperature tends to be warmer and smaller. This is considered to be because the heat capacity of the paper is small, so that the paper temperature quickly approaches the control temperature of the preheater.

For thick paper with a speed of 135 kg, the heat capacity of the paper is large, so the increase in paper temperature is small, and the 4th block (PH
Even the preheater (4) must be used to heat the product sufficiently.

As can be inferred from the relationship between the preheater position and paper temperature shown in FIG. The ON duty (current carrying ratio) for paper with a continuous speed of 155 Kf appears to be quite small, and the ON duty (on duty) for paper with a speed of 135 t appears quite small.
on) date appears quite high. In other words, the fourth
The ON duty (energization ratio) of block R and heater 31 is determined by the difference in paper speed (indirectly, the difference in "paper temperature")
is clearly reflected. The key point of the present invention is to utilize this feature to provide alternative information for paper temperature. ON
The heater to be subjected to duty detection is preferably the RF heater 1 for the reasons described above. The RR upper heater 2 cannot be used for ON duty detection because it is not covered when paper having a narrow paper width is used.

Fig. 6(b) RF-ON indicates the energization status of the RF upper heater 1 (0N10FF status) at a speed of 55Kf and a ream rate of 135K.
This is the result of investigating y. Heater ON10F
By setting a gate time (tGATE') that is sufficiently longer than the F cycle and counting all the clocks (Fig. 6 (a)) during the heater ON period, the ON duty (current-carrying time ratio) of the RF heater 1 can be calculated. can be detected.

In FIG. 7, when the temperature of the preheater of the fourth block (PH4) falls below a predetermined temperature, the resistance value of the THF thermistor 33 increases, the output of the THF comparator 44 is inverted, and the output of the inverter 42 becomes logic "'1". . A heater driver 43 composed of a solid state relay (SSR) or the like is turned on, and the heater 31 is energized.

The AND gate 44 is a circuit that allows the clock (CLOCK) to pass only when the RF heater 1 is ON, the counter 45 is a counter that counts the ON duty of the R and heater 31, and the comparator 46 is This is a comparison circuit for determining whether to switch the control temperature of the heat roller to 190°C.

The reference data circuit 47 sets the control temperature of the heat roller to 19
This is a circuit that provides comparison data for switching to 0°C. When the output of the comparator 46 is set, the heat roller 1
7, the control temperature of 190°C is specified.

The 190° C. thermoferrite 51 and the 170° C. thermoferrite 52 are temperature sensors that utilize the fact that the magnetic permeability of ferrite changes significantly near the Curie temperature. The differential transformer 53 has a primary coil wound around the center pole of an E-shaped core, and a carrier wave voltage of 10 to 100 KHz is applied thereto. A secondary coil is wound around the poles on both sides, and an electromotive voltage is generated due to changes in magnetic flux caused by the primary coil.

The thermoferrite is mounted on one side of the open end of the E-shaped core, and the differential transformer 53 is mounted on the other side so as not to face it. 190℃ thermoferrite 51
When the 170° C. thermoferrite 52 does not reach the specified temperature, the magnetic permeability of the thermoferrite is large and a large electromotive voltage is generated on one side of the differential transformer 53, so that an output appears in the differential transformer 53.

On the contrary, when the specified temperature is reached, the magnetic permeability of the thermoferrite becomes significantly smaller, so the above-mentioned electromotive voltage becomes smaller, and the differential output of the differential transformer 53 becomes smaller.

As shown in FIG. 8, the temperature of the heat roller 17 is 170°C.
When the temperature is below 19°C, the rotation of the heat roller 17
There is an output when the 0°C thermoferrite 51 and the 170°C thermoferrite 52 face each other, and when the temperature exceeds 170°C, there is an output only when the thermoferrite 51 faces the 190°C. Since the 170°C thermoferrite 52 exceeds the Curie temperature, its magnetic permeability decreases and the differential transformer 5
8 (
a) TaM! At 5IGL, the peak due to 170°C disappears.

When the heat roller temperature exceeds 190°C, the 190°C thermoferrite 51 also exceeds the Curie temperature, so TH
All MSIGL output disappears.

Figure 8 (a) Starting from the first output of THM S IGL, a window ((b) THM GATF, ) is provided to check the presence or absence of the second output (detection of 170°C), and the THM S IGL is installed within that window. If there is, it means that the temperature of the heat roller is 170℃ or less, and (C) LOW
170 is output. Temperature 170℃ or higher (TEMP1
70) is performed by a sample-and-hold circuit having a sample-and-hold time tJ (with the LOW170 signal as input. The sample-and-hold time tsl is selected to be longer than the cycle of one rotation (tHR) of the heat roller.

Detection of temperature 190℃ or higher (TEMP 190)
Sample hold time t with HMSIGL signal as input
This is done using a sample and hold circuit with sH.

The temperature detection circuit 54 in FIG. 7 includes a circuit for applying a carrier voltage to the primary coil of the differential transformer 53, a circuit for modulating the output from the secondary coil, and a sensor signal processing circuit as shown in FIG. This is a circuit that is equipped with a circuit that performs the following steps.

The inverter 55, AND gate 56, AND gate 57, and NOR gate 58 in FIG. 7 are circuits for switching the control temperature of the heat roller.

:ff 7 HaL/l 46 (7) THIII
When the O output is not set, the AND gate 56
When the temperature is satisfied (when the temperature reaches 170° C.), the heater lamp driver 59 composed of a solid state relay (SSR) or the like is turned off, and the heater lamp 60 is controlled to be de-energized.

When the TI (190 output) of the comparator 46 is set, until the AND gate 57 is established (190°C),
The heater lamp 60 is energized without turning off the heater lamp driver 59, and when the TEMP 190 is set (FIG. 8(e)), the heater lamp 60 is controlled to be energized.

Strictly speaking, the ON duty (energization ratio) of the RF upper heater 1 shown in FIG. 6 is also affected by the width of the paper covering the RF upper heater 1. The narrower the paper width, the smaller the ON duty.

Therefore, a paper width sensor mechanism as shown in FIG. 10 is arranged in the paper feed mechanism shown in FIG. If this is the case, the paper temperature will be replaced by information that also reflects the influence of the paper width, so that the gist of the present invention can be carried out more faithfully.

In FIG. 9, a Hall element sensor 71 and a magnet 7
2 constitutes a sensor system. The structure is such that the paper width is detected depending on which of the Hall element sensors 71 arranged in the moving direction of the tractor 12a the magnet 72 attached to the tractor 12H faces.

The tractor drive shaft 75 is a drive shaft of the tractor 12a. The drive motor is not shown. The tractor guide shaft 74 is a guide shaft for moving the tractor 12m according to the paper width.

The yoke side plate 73 is a plate that supports the paper feeding mechanism described above.

The sensor board 81 shown in FIG. 10 has Hall element sensors 71 arranged at a predetermined unit pitch (1/2 inch or 1 inch), encoded by an encoding circuit 82 as paper width data, and the above-mentioned reference data circuit 47 comparison data switching information.

In FIG. 3, the control temperature of the heat roller is changed to two values, and the embodiments shown in FIGS. 4 to 8 have been explained based on binary values. The switching of the control temperature between three values and four values can be realized in exactly the same manner.

In addition, although Fig. 7 describes a case in which the heat roller temperature sensor is configured by a combination of a thermoferrite and a differential transformer, there is a method in which a thermistor is used to switch the control temperature at the comparator section (explanation is omitted). But it can be achieved.

According to the present invention, the temperature of the paper on the preheater can be indirectly detected by detecting the energization ratio of the heater of the preheater, so the control temperature of the heat roller can be changed according to the paper temperature, and the control temperature of the heat roller can be changed according to the paper temperature. Since the operating point can be moved away from the hot offset region or the cold offset region, it is possible to eliminate the problem of offset toner staining the print. 1. Applying silicone oil to the heat roller can reduce the accumulation of toner on the felt, so the felt replacement cycle can be extended.

Furthermore, since the temperature of the heat roller is automatically switched to be higher for thick paper, the problem of weak fixing strength for thick paper can be solved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a laser beam printer, FIG. 2 is a graph showing the operating points of the fixing device according to the prior art, FIG. 3 is a graph showing the operating points of the fixing device according to the present invention, and FIG. FIG. 5 is a plan view showing the configuration, FIG. 5 is a diagram showing the relationship between the position of the preheater and the paper temperature on the preheater, and FIG. 6 is a diagram showing the relationship between the preheater's heater energization ratio (O
Figure 7 is a block diagram showing the concept of detecting the duty of the preheater and switching the control temperature of the heat roller. A time chart showing the concept of identification, Fig. 9 is a plan view of the paper feed mechanism equipped with a paper width detection mechanism, Fig. 10 is a schematic diagram showing the configuration of the paper width detection sensor, and Fig. 11 is a control of the heat roller. 7 is a graph showing the operating points of the fixing device in a modified application in which the temperature is changed to three or four values. In the figure, 1... photosensitive drum, 2... charger, 3
...Laser, 4...Modulator, 5...Rotating polygon mirror,
6...F19 lens, 7...Developer, 8...Toner, 9...Carrier, 10...Cleaner, 11...
...Printing paper, 12...Tractor, 13...Transfer machine, 14...Buffer plate, 15...Suction, 16...Preheater, 17...Heat roller, 1
8... Press roller, 19... Felt, 20...
Oil application mechanism, 21... Puller roller, 22...
Splice table, 16a...first block (p
H1), 16b...Second block (pH2), 16
C...Third block (1) H3), 16d...Fourth
Block (1) H4), 31...RFF2O 3ta, 32...RR upper heater 33...THF thermistor, 34...THR thermistor, 41...TH,
Comparator, 42... Inverter, 43... Heater driver, 44... ANII'-), 45...
Counter, 46... Comparator, 47... Reference data circuit, 51... 190°C thermoferrite, 52
...170°C thermoferrite, 53... Differential transformer, 54... Temperature detection circuit, 55... Inverter, 56-AND gate, 57 - AND gate, 5 B
-NORK), 59... Heater lamp driver, 6
o... Heater lamp, 71... Hall element sensor,
72... Magnet, 73...-Yoke side plate, 74... Tractor guide shaft, 75... Tractor drive shaft, 81... Sensor board, 8
2... Engineering/coder circuit. Name of patent applicant Hitachi Koki Co., Ltd. g, g 3 4 2 N to -1 N N ゝ--''-50-FatC? C) OC+ OC1() +NC) To glossy size N N N -1 ---1 ÷ J3-
-Z-C1-仝9髫饖 and C [＾ and +3 M 9 B ,,E.

Claims (1)

[Claims] 1. In a fixing machine equipped with a preheater and a heat roller, there is provided a means for detecting the temperature of the preheater, and a means for feeding back the output of the temperature detecting means to turn on/off the heater in the preheater. a means for measuring the time ratio during which the heater is on; a means for comparing the time ratio with a prescribed time ratio; and a means for switching the control temperature of the heat roller in response to the output of the comparison means. and a means for detecting the temperature of the heat roller, and a means for comparing the temperature of the heat roller with the above-mentioned switchable control temperature instruction and turning on/off the energization of the heater lamp in the heat roller. A fusing machine featuring the following. 2. means for detecting the temperature of the preheater; means for feeding back the output of the temperature detection means to turn on/off the heater in the preheater; and means for measuring the ratio of time during which the heater in the preheater is turned on; means for comparing the time ratio with a prescribed time ratio; means for detecting the paper width; means for changing the prescribed time ratio according to the paper width data; and a heat roller in response to the output of the comparison means. A means for switching the control temperature of the heat roller, a means for detecting the temperature of the heat roller, and a means for comparing the temperature of the heat roller with the above-mentioned switchable control temperature instruction to turn on/off the energization of the heater lamp in the heat roller. 2. The fixing device according to claim 1, further comprising means for causing the fixing device to perform the fixing operation.