JPS6281684A - Electrophotographic printing device - Google Patents

Abstract

PURPOSE:To prevent excessive deposition of tonr on a felt and soiling of print face due to the deposition by feeding back temperature information of paper to the controlling mechanism of a printing machine, changing feeding speed of felt automatically, and controlling using magnitude of heater current rate as criterion information of paper temperature. CONSTITUTION:When temperature of a heater 30 becomes lower than a specified value, resistance of a thermistor 32 increases, and a comparator 34, an inverter 35 and a driver 36 operate to apply current to the heater 30. At this time, a NAND gate 37 receives clock information and a counter counts current application period of the heater 30. A comparator 39 compares a peper width data reference circuit 40 and the count value 38, and outputs only when the count value is larger. On the other hand, a NAND gate 42 energized by a paper feed signal clocks the counter 43, and triggers a pulse generator 41 through a NAND gate 44 and an OR gate 45, and thereby, a step motor driving circuit 47 is made on. A motor 23 makes the rotation and indicates necessary felt feeding.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention prevents the printed surface of the paper from being smudged by the toner attached to the heat roller that completely fixes the toner i2 on the paper. For example, it relates to an electrophotographic printing device such as a laser beam printer.

[Background of the invention]

FIG. 2 shows a schematic diagram of a laser beam printer.

The surface of the photosensitive drum 1 is uniformly charged by the corer 2. The laser beam from the laser 3 is modulated into discontinuous laser beams corresponding to print data by an optical modulator 4, and is further scanned in the axial direction of the photosensitive drum 1 via a rotating polygon mirror 5gl and an F9I lens 6 for printing. Form an exposed image of the data.

The exposed image 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 the magnetic carrier 9 and electrostatically combined with the carrier 9 to be transported to the surface of the photosensitive drum 1 .

The toner image on the photosensitive drum 1 is transferred to a transfer device 13 to which a high voltage having a polarity opposite to the charged potential of the toner is applied from the back side of the paper 11.
The image is transferred onto the paper 11 by the following steps.

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. The tractors 12a and 12b transport the paper 11. The preheater 16 is provided to preheat the toner image on the paper 11. The toner image preheated by the preheater 16 is heated and pressed by a heat roller 17 and a pressure roller 18, and is fixed on the paper 11.

The suction 15 brings the paper 11 into close contact with the preheater 16 using air in order to ensure preheating in the preheater 16.

The suction 15 has a structure that eliminates air leakage due to the unevenness of the paper 11 by moving a suction shutter (not shown) according to the width of the fall.

The buffer 14 is provided to adjust the speed difference between the paper feed by the track rollers 12M and 12b and the paper feed by the heat roller 17 and the pressure roller 18. Felt 19
is provided for applying silicone oil, which is an anti-offset liquid, 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 paper 11 after fixing and help fold it. 22 is a splice table.

In such a printing apparatus, in order to obtain good fixing characteristics, the preheater 16 and the heat roller 17 are heated and controlled to maintain a constant temperature.

Paper used: 11u, speed: 55Kjl (paper thickness: approx. 8
0/jm) thin paper to speed 135 and 2 (paper thickness approximately 200 μm) thick paper l, and at the end of preheating, that is, on the exit side of the preheater 16, the paper 110 has the transferred toner image on it. Due to the difference in heat capacity of the paper 11, the temperature of the surface (the side with the toner image) (hereinafter referred to as paper temperature) is approximately 20 deg compared to the thicker paper and the thinner paper.
It gets lower. In such a case, the temperature of the heat roller 17 decreases, and a so-called cold offset occurs in which a portion of the toner of the toner 1 adheres to the surface of the heat roller 170 without being sufficiently melted.

With thick paper, since the operation is close to cold offset, a small amount of toner tends to adhere to the heat roller 17, and the felt 19Vc toner coated with silicone oil accumulates on the heat roller 17. Easy to do. The tendency for toner to accumulate on the felt 19 becomes more pronounced as the paper speed increases, and if the degree of cold offset is significant, the offset toner will accumulate excessively on the felt 19 7 and the toner pieces will be transferred to the heat roller 17 again. This causes a problem in that the printed surface of the paper 11 is smeared by adhesion to the paper 11.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the original technology, and to prevent excessive toner accumulation on the felt even when high-speed paper is used, thereby preventing printing by toner re-adhering to the heat roller. This is to prevent surface stains from occurring.

[Summary of the invention]

The present invention focuses on the fact that the higher the paper speed, the lower the paper temperature after preheating by the preheater, and the closer to the cold offset state, the stronger the tendency of toner to accumulate on the felt. Alternative information t-
Feedback is used to automatically switch the feeding speed of the felt to prevent excessive toner from accumulating on the same portion of the felt.

In addition, an infrared thermometer is available as a paper temperature detector, but it is expensive due to its high power of 111N.

Therefore, for thin paper with a low speed, the heat capacity of the paper is small, so the energization rate of the preheater is low.On the other hand, for paper with a large number of continuous lines, the heat capacity of the paper is large, so the energization rate of the preheater is high. With this in mind, we devised a way to use the energization rate of the heater as alternative information for the paper temperature.

The present invention will be described below with reference to the drawings.

[Embodiments of the invention]

FIG. 3 shows the paper feeding mechanism of the felt 19,
Both ends of the felt 19 are attached to a supply roller 25b and a take-up roller 25. The winding roller 25a is a reducer 24
It is driven by a felt drive motor 23 consisting of, for example, a step motor. Therefore, by driving the motor 23f, the felt 19 is wound up by a predetermined amount on the winding roller 25a.

As shown in FIG. 4, the preheater 16 is composed of four blocks, a first block to a fourth block 26 to 29, and each block is provided with two heaters and a thermistor. The temperature of each heater is detected by the resistance value of each thermistor, and the preheater 16 is controlled to a predetermined temperature by feeding back the detection results and turning the heaters on and off. An example of the schematic arrangement of the heater and thermistor is shown in the fourth block 29. The two heaters 30 and 31 share the heat generating part in the width direction of the paper 11, and when a narrow paper 11 is used,
This is to prevent the portion of the heater 1 that is not covered, for example, the right side heater 31, from becoming overheated. Therefore,
The left heater 30 is controlled to be de-energized when the left thermistor 32 detects a predetermined temperature. Also, the right side heater 3. IVi, when the right thermistor 33 detects a predetermined temperature, the current supply is controlled to be turned off.

FIG. 5 is a diagram showing the relationship between each position on the preheater 16 and the paper temperature. At the position x0 near the entrance, paper 11
The paper temperature is the same regardless of the speed, but the paper temperature is large for the position, X-shape, Differences arise. The reason for this is that thin paper with a speed of 55 is thin and easily warms up, while thick paper with a speed of 135 or 9 is
This is because it is difficult to warm up because it is thick.

Also, according to FIG. 5, thin paper with a speed of 55 to 9 is placed in the first block 26 (position xi) and the second block 27 (position XZ).
3rd block 28 (position XS) 4th
It can be seen that the temperature rise at block 29 (position Xa) tends to be small. This is considered to be because the paper temperature quickly approaches the control temperature of the preheater 16 because the heat capacity of the paper is small.

For thick paper with a speed of 135 to 9, the increase in paper temperature is small because the heat capacity of the paper is large, and the fourth block 29 must also heat the paper sufficiently.

As can be inferred from the relationship between the position on the preheater 16 and the paper temperature shown in FIG. The on-duty (current-carrying ratio) for paper No. 9 appears to be quite small, and the continuous f
The on-duty for f1135Kj+ paper appears to be quite high.

That is, the on-duty of the left heater 30 of the fourth block 29 significantly reflects the difference in speed of the paper 11 (indirectly, the difference in paper temperature). A feature of the present invention is that this feature can be used as alternative information for paper temperature. The heater targeted for on-duty detection is preferably the left heater 30 for the reasons described above. The right heater 31 is not covered when a narrow paper 11 is used, so it cannot be used for on-duty detection.

When the heater is turned on in FIG. 6, the energization status of the left side heater 30 (energized when the logical value is l) is 51 for money luck i55 and 135 for speed.
This is the result of research on 9. The on-duty of the left heater 30 is determined by providing a gate time (1.^7 blind) that is sufficiently longer than the on-off cycle of the heater 30 and counting the number of clocks (Fig. 6 (a)) during the heater on period. energization time ratio) can be detected.

In FIG. 1, the left side of the fourth block 29 (1i heater 3
When the temperature of 0 falls below a predetermined temperature, the resistance value of the left thermistor 32 increases, the output of the comparator 34 is inverted, and the output of the inverter 35 becomes a logical value of 1. As a result, the driver 36 composed of a solid state relay or the like is turned on, and the left heater 30 is energized. Nantes Gate 37
The clock in FIG. 6 (C
LOCK), and the counter 38 is
A counter that counts the on-duty of the left heater 30 and a comparator 39 are comparison circuits that determine whether to switch the feed speed of the felt 19. The data are compared and when the count value of the counter 38 is large, an output of logical value 1 is generated. The reference data circuit 40 is a circuit that provides comparison data for switching the felt feeding speed, that is, data indicating the reference on-duty.

The felt 19 is intermittently fed by the felt drive motor 23, which rotates by l steps in synchronization with felt feed pulses generated one by one from the felt feed pulse generation circuit 41 at fixed time intervals during the paper feed signal generation period.

When the paper feed signal reaches the logical value l, the Nantes gate 42 opens and the clock (FELT CLOCK) is output from the counter 4.
Sent to 3. When the output of the comparator 39 is a logical value, low-speed feeding of the felt is instructed and the Nantes gate 44 opens that gate.The counter 43 counts the clocks and when the output terminal Q, +1 becomes a logical value 1, the Nantes gate 44 and The signal passing through the invert OR gate 45 triggers the felt feed pulse generation circuit 41 and also triggers the integrator circuit 46.
The counter 43 is cleared via. The triggered felt feed pulse generation circuit 41 sends one pulse to the step motor 1 drive circuit 47, and the motor 23! Step rotation. As the motor rotates, a predetermined amount of the felt 19 is wound around the winding roller 25a as described above. Similarly, when the output of the comparator 39 becomes a logic value and high-speed feeding of the felt is instructed, the Nantes gate 48 opens the gate, and the output terminal Q1 of the counter 43 becomes a logic value 1.
The motor 23 rotates l steps each time the felt 19 is fed. Here, Qm < Qs +, and in the case of high-speed feeding, the felt 19 is fed at a shorter cycle than in the case of low-speed feeding.

Strictly speaking, the on-duty (energization ratio) of the left heater 30 shown in FIG. 6 is also affected by the width of the paper 11 covering the left heater 30. The narrower the paper width, the smaller the on-duty.

Therefore, a paper width sensor mechanism as shown in FIG. 7 is disposed in the paper feed mechanism shown in FIG. 2, and paper width data corresponding to the paper width is encoded.
By switching the comparison data of 0, the paper temperature becomes alternative 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. 7, the Hall element sensor 50 and the magnet 5
1 constitutes a sensor system. The structure is such that the paper width is detected depending on which of the Hall element sensors 50 arranged in the moving direction of the tractor 12a the magnet 51 attached to the tractor 12a faces.

The tractor drive shaft 52 is the @ of the tractor 12a.
It is an m-axis and is driven by a motor (not shown). The tractor guide shaft 53 is a guide shaft for moving the tractor 12a according to the paper width. The yoke side plate 54 is a plate that supports the paper feeding mechanism described above.

A sensor board 55 in FIG. 8 has Hall element sensors 50 arranged at a predetermined unit pitch (A inch or 1 inch) and encoded by an encoding circuit 56 to form paper width data, which is compared with the reference data circuit 40. This is the switching information.

In the above-described embodiment, the felt feeding speed is set to two values, but the felt feeding speed may be set to three or four values, and even in this case, it can be realized in substantially the same way.

〔Effect of the invention〕

According to the present invention, the temperature of the paper on the heater can be indirectly controlled by detecting the energization ratio to the heater of the preheater, so the felt feeding speed can be switched in accordance with the paper temperature, and the paper being transported can be used. Since it is possible to prevent excessive toner from being deposited on the felt during printing, it is possible to eliminate the problem of the deposited toner re-adhering to the heat roll and staining the print.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a plot diagram of essential parts showing an embodiment of the present invention, FIG. 2 is a side view schematically showing an example of a laser beam printer to which the present invention is applied, and FIG. Figure 3 is a front view showing the felt feeding mechanism section, Figure 4 is a plan view showing the preheater section, and Figure 5 is a front view showing the felt feeding mechanism section.
Figure 6 is a characteristic diagram showing the relationship between the position on the preheater and paper temperature, Figure 6 is a time chart showing how the energization ratio of the heater in the preheater changes depending on the paper speed, and Figure 7 is a characteristic diagram showing the relationship between the position on the preheater and paper temperature.
The figure is a plan view showing a paper feed mechanism section including a paper width detection e and a groove, and FIG. 8 is a plan view showing the configuration of the paper width detection mechanism section in FIG. 7. In the figure, l is a photoreceptor, 11 is paper, 16 is a preheater, 17 beat rollers, 19 is felt, 20\i oil application mechanism, 23 felt drive motor, 25a is a take-up roller, 30.31 is a heater, 32 and 33 are thermistors, 34 and 39 are comparators, 38 and 43 counters, 40 it reference data circuits, 41 are felt feed pulse generation circuits, and 47 are step motor drive circuits. Rut Applicant Name Hitachi Koki Co., Ltd. Ya20 Ru3Dushi4 (0C) Ashin - Yu no Istop 1
Figure 16 (Q) CtBcK ------------------------
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Claims (2)

[Claims] (1) It has a preheater and a heat roller that fixes the toner image attached to the paper, a felt that applies an anti-offset liquid to the heat roller, and a felt drive motor that winds up the felt via a winding roller. The electrophotographic printing apparatus includes means for turning on and off a heater in the preheater in response to a detection output of a detection means for detecting the temperature of the preheater, and measuring a time ratio during which the heater in the preheater is on. The present invention is characterized by comprising: means for comparing the measured time ratio with a reference value of the time ratio; and means for switching the driving speed of the felt drive motor in response to the output of the comparing means. Electrophotographic printing equipment. (2) The electrophotographic printing apparatus according to claim 1, wherein the reference value of the time ratio is changed in accordance with the width of paper used.