JPH055112B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to temperature control of a heat roll in a contact roller type fixing device of an electrophotographic copying machine.

Prior Art A contact roller type fixing device has a heat roll equipped with an internal heat source and a pressure roll, which are pivotally supported so that they come into contact with each other during fixing, and the copy paper on which the toner image has been transferred is By passing the toner image between the rolls, heat and pressure are applied to the toner image to fix the toner image on the copy paper.

At this time, so-called offset occurs in which minute amounts of toner adhere to the surface of the heat roll.

In order to prevent this offset, the heat roll is coated with a material with good mold releasability such as Teflon (trade name), but offset still occurs if the temperature of the heat roll is not appropriate.

In other words, if the temperature of the heat roll is too low,
Even if the toner image melts, cold offset occurs because the adhesion between the toner and the paper is not sufficient, and if the temperature of the heat roll is too high, the part where the toner touches the roll melts too much, causing the toner to become fragmented. This is a hot offset.

Note that the pressure between the rolls is not so strong as to mechanically press the toner onto the copy paper, but is just enough to bring the toner powder into close contact with each other, and the degree of fixation is mainly controlled by heat. It is something.

Therefore, during fixing, the heat roll must maintain a temperature between the maximum temperature at which cold offset occurs (cold offset temperature) T _C and the minimum temperature at which hot offset occurs (hot offset temperature) T _H.

Generally, as shown in Figure 1, the temperature distribution in the axial direction of a heat roll having an internal heat source is between the cold offset temperature T _C and the hot offset temperature T _H during standby, as shown by the solid line. .

During fixing, for example, if fixing is performed continuously on a plurality of copy sheets, the heat of the heat roll is gradually absorbed by the copy sheets, so it is necessary to apply more heat accordingly.

Therefore, the temperature of the heat roll is detected by a sensor at a predetermined location on the heat roll, and feedback control is performed to maintain the temperature at a predetermined temperature.

However, when small-sized copy paper is continuously fused under feedback control, the temperature decreases in the central part of the heat roll where the paper is fed, and the temperature rises at the other ends of the heat roll. The temperature distribution becomes as shown by the broken line in Figure 2,
There are cases where the hot offset temperature is exceeded at the end of the heat roll.

If a large size copy sheet is fixed in this state, the image will be destroyed by hot offset at the edges of the sheet.

Therefore, in the past, in addition to the main lamp in the center of the heat roll as a heat source, sub lamps were used at both ends of the heat roll. They were turned on only during standby to heat the ends of the heat roll, and turned off during fusing to keep the temperature above the hot offset temperature. There was something that prevented it from rising.

However, since a sub-lamp must be prepared in addition to the main lamp, it has the drawback of significantly increasing costs.

Problems to be Solved by the Invention The present invention solves these drawbacks. When a predetermined number of sheets or more are continuously copied, the heat roll end temperature is set by sequentially switching from the first set temperature to the second and third set temperatures. The purpose of this method is to prevent the temperature from rising beyond the hot offset of the sheet, so that subsequent fixing of large size sheets can be performed stably.

Means and actions for solving problems The configuration of the present invention will be explained based on FIG. 2.

In an image forming apparatus having a contact heat roll type fixing device that fixes unfixed images formed on sheets of different sizes, A is a roll drive detection means that detects the drive of the fixing heat roll, and B is a roll drive detection means that detects the drive of the fixing heat roll, and B is a roll drive detection means that detects the drive of the fixing heat roll. This is an image formation sheet number detection means for detecting the number of sheets of paper that has been formed.

C is a set temperature switching control means, which selects the set temperature of the heat roll from a normal first set temperature to n-stage second, third, . . .
When the nth set temperature is set and continuous image formation is performed on small size paper, the roll drive detection means A
Based on the information from the image forming sheet number detection means B,
Switching control is performed sequentially from the first set temperature to the second, third, . . . nth set temperature.

Since the present invention is configured as described above, when a small number of copies are to be made, the normal first set temperature is used, and when more than a certain number of copies are made, the temperature is lower than the first set temperature. Switching to the second and third set temperatures suppresses the temperature rise near both ends of the heat roll and always maintains it below the hot offset temperature to prevent mistakes from occurring even if large-sized copies are subsequently made. can.

Also, when the heat roll stops, the original
By returning the temperature to the set temperature, it is possible to prepare for the next copy.

Embodiment An embodiment of the present invention illustrated in FIGS. 3 to 6 will be described below.

FIG. 3 and FIG. 4 are a cross-sectional side view and a vertical cross-sectional front view of the heat roll and the pressure roll.

In both figures, 1 is a heat roll, 2 is a pressure roll, and the heat roll 1 has a lamp 3 as a heat source inside.

A temperature sensor 4 is disposed on the upper surface of the heat roll 1 at a position offset from the center to the edge, and detects the temperature at that position.

The toner image formed on the surface of the paper 5 by the toner 6 is transferred to the heated heat roll 1 when the paper passes between the heat roll 1 and the pressure roll 2.
As a result, the toner 6 is melted, welded and fixed to the paper.

As mentioned above, the surface temperature of heat roll 1 is the cold offset temperature T _C and the hot offset temperature.
Temperature detection is performed by a temperature sensor 4 to maintain a predetermined temperature between T _H and temperature control is performed by feeding back the detection signal.

The temperature distribution of the heat roll is as shown in Figure 5, and during standby, it shows the solid line (1), and the temperature at the temperature sensor position P is always at the first level.
The temperature is controlled to be the set temperature _T1 , and is kept between the hot offset temperature _TH and the cold offset temperature _TC throughout.

If we look at the temperature distribution when many copies of small size paper are made in succession, we will see a curve like the broken line (2), where the central part where the paper passes loses heat and decreases. The heat at both ends accumulates and rises, exceeding the hot offset temperature _TH .

If a large size sheet is fixed in this state, the images at both ends will be destroyed, resulting in a copy error.

Therefore, the number of copies is set before the temperature at both ends of the heat roll exceeds the hot offset temperature _TH , and when this number of copies is reached during continuous copying, the set temperature of the heat roll is set to the first setting. It is decided to switch from the temperature T ₁ to the second set temperature T ₂ which is lower.

When setting the second set temperature T ₂ in this way, the temperature distribution becomes a curve that is parallel to curve (2) downward.
(3), the temperature at both ends of the heat roll is below the hot offset temperature _TH , and even large size paper can be fixed in a sufficiently stable manner.

The temperature control of the heat roll is performed by a computer, and a schematic flowchart of the above set temperature switching program is shown in FIG. 6 and will be explained.

In this embodiment, two levels of temperature settings are used.

First, when the power is turned on (step), the lamp lights up (step) and the heat roll is turned on.
The temperature is controlled to be the set temperature _T1 .

Next, the number of copies M is set (step).
Wait until the temperature T of the heat roll reaches _T1 (step), then press the start button (step), the main motor of the copying machine is driven, and the drive of the heat roll is also started (step).

Here, the content of the symbol N for counting the number of copies is reset (step), copying work begins (step), and fixing is also performed (step).

After fixing, the contents of N are counted up (step), and it is determined whether or not N has reached the predetermined number of copies _N1 (step). If not, it is further determined in step whether the number of copies has reached the set number of copies. The above steps are repeated until the set number M of copies is reached.

During this period, the number of copies N exceeds the predetermined number _N1 because, as mentioned above, both ends of the heat roll are approaching the hot offset temperature _TH .
If fusing is continued under the set temperature _T1 any longer, the hot offset temperature will be exceeded, and when the next larger size paper is fusing, there is a risk that the image will be destroyed at both ends. When N reaches _N1 , the process proceeds to step and switches the set temperature of the lamp to a second set temperature _T2 lower than the first set temperature _T1 . Then, to indicate that the temperature is at the second set temperature, the content of the symbol S is set to 1 (step).

Thereafter, copying and fixing are performed under the second set temperature _T2 , and when the number of copies reaches the set number M, the process advances from step to step, the driving of the main motor and heat roll is stopped, and the set temperature is changed to the second set temperature. When it is at T ₂ , that is, when S=1 (step), proceed to step and set the first set temperature.
Return to T ₁ , set the contents of S to 0 (step), and return to step again.

If the value of S is 0 in the step, that is, the first set temperature
If it is at T ₁ , you will return to the step.

Although control is performed according to the operating procedure described above, maintaining the temperature of the heat roll itself at the set temperature is performed by another feedback control.

In this way, even if large size paper is copied after continuous copying of small size paper,
Stable copying is possible without image destruction.

In addition, when the small size paper is very small, it is expected that the temperature at both ends of the heat roll will rise quickly, so the set number of copies N ₁ when switching from the first set temperature to the second set temperature This can be dealt with by setting the value to an even smaller value.

In this case, it may be possible to input paper size information using a computer and automatically change the value of the set number of copies _N1 .

In addition, when continuously fixing very small paper for a long time, the temperature setting should be set at three or more levels instead of just two, and the number of copies to be set at the time of switching should also be set at N ₁ , N ₂ , N ₃ ... (N It is conceivable to change the set temperature one after another by setting the temperature in stages such as ₁ <N ₂ <N ₃ <...).

However, for paper sizes that are commonly used, two temperature settings are sufficient.

Effects of the Invention As described above, in the present invention, by using only one lamp as the heat source of the fixing heat roll, it is possible to suppress the temperature rise at the end of the heat roll due to continuous fixing of small size paper to below the hot offset temperature. Therefore, stable copying can be performed regardless of paper size, and costs can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the temperature distribution of the heat roll, Fig. 2 is a diagram corresponding to the claims of the present invention, Fig. 3 is a cross-sectional side view of the heat roll and pressure roll of the embodiment according to the present invention, and Fig. 4 is a diagram showing the temperature distribution of the heat roll. 5 is a diagram showing the temperature distribution of the heat roll in this embodiment, and FIG. 6 is a schematic flowchart of the set temperature switching program of this embodiment. 1...Heat roll, 2...Pressure roll, 3...
...Lamp, 4...Temperature sensor, 5...Copy paper, 6...Toner.

Claims (1)

[Claims] 1. In an image forming apparatus having a contact heat roll type fixing device that fixes unfixed images formed on sheets of different sizes, a drive detection means detects the drive of the fixing heat roll and detects the number of sheets of paper on which images have been formed. A means for detecting the number of images to be formed, and a set temperature of the heat roll including a normal first set temperature and n stages of second, third, ... nth set temperatures that are lower in stages than the normal first set temperature, and When continuous image formation is performed on paper, the temperature is sequentially changed from the first set temperature to the second, third, ... nth set temperature based on the information from the roll drive detection means and the image formation number detection means. A contact roller type fixing device characterized by having a set temperature switching control means for performing switching control.