JPH09185276A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain optimum productivity in accordance with applied conditions, in consecutive feeding to the fixing device of an image forming device. SOLUTION: The surface temp. Tn of the heating roller of the fixing device is sampled at regular intervals, to obtain the difference value ΔTn between the detected temperatures at the time of consecutively sampling. It is judged whether CPM (the number of copies made per minute) is decreased or not by the relation of each value of a threshold temp. Ts1 at which the CPM is decreased, two temperatures Tn and Tn-1 at the time of consecutively sampling and the difference value ΔTn between these temperatures Tn and Tn-1. When the difference value ΔTn when the value of the temp. Tn-1 becomes a temp. Ts1+b sufficiently close to the temp. Ts1 or below is larger than a threshold (a) and the slope of a temperature change is steep, the CPM is decreased at the time when the detected temp. becomes the temp. Ts1. When the difference value ΔTn is smaller than the threshold (a), the CPM is not decreased even if the detected temp. becomes the temp. Ts1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of continuously feeding a transfer material, and more particularly to temperature control in a heat roller fixing device thereof.

[0002]

2. Description of the Related Art Regarding temperature control in a heat roller fixing device in an image forming apparatus capable of continuously feeding a transfer material, many proposals have been made to deal with problems such as nonuniform roller temperature. For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 3-65978, an example is shown in which the feeding interval of the transfer material is changed according to the heater lighting duty cycle in order to prevent the temperature of the pressure roller from decreasing and making it non-uniform. ing.
Further, in the technique disclosed in Japanese Patent Laid-Open No. 4-245280, an example is shown in which, in order to shorten the warm-up time, when the detected temperature is low, the number of rotations of the roller can be reduced to fix the roller. Further, the technique disclosed in Japanese Patent Application Laid-Open No. 5-6043 discloses an example in which the feeding interval of the transfer material is changed in order to correct the non-uniformity of the surface temperature in the roller longitudinal direction during continuous paper feeding. ing.

[0003]

In all of the above-mentioned conventional examples, the main object is to correct the nonuniformity of the roller temperature due to continuous sheet feeding, etc. However, in the image forming apparatus capable of continuously feeding the transfer material. Another major problem is a decrease in roller surface temperature during continuous paper feeding due to insufficient heat. That is,
The wattage of the heater, which is the heat source, is small, and even if the heater (for example, infrared halogen heater) is continuously turned on, the amount of heat absorbed by the paper and toner is larger when the paper is continuously fed, and as a result, it is necessary for fixing. It is conceivable that the lower limit of the roller surface temperature may be exceeded. In this case, there is no problem if a sufficient wattage of the heater is obtained in advance. However, especially when the number of continuously passed sheets is 50 CPM (copy per mi)
new: In high-speed machines that exceed the number of copies per minute (the same applies below), the required heater wattage exceeds 1 kW, and the normal commercial power supply (1.5 kW in Japan) moves the entire device. Can be difficult.

As a countermeasure, it is effective to lower the CPM according to the roller temperature as shown in the above conventional example, but it is necessary to considerably lower the CPM depending on the conditions, and in actual use it is used. People feel uncomfortable,
In some cases, productivity may decrease.

In this respect, for example, a device of 70 CPM is
This will be described with reference to FIGS. 3 and 4 showing the case of operating with a 0 W heater. The behavior of the fixing temperature decrease when the heat quantity is insufficient is shown in FIG.
As shown in, it becomes sharp in proportion to CPM. Where 70
When the CPM is reduced from CPM to 60 CPM, the line of temperature decrease becomes like the line A in FIG. At this time, the CPM down time t ′ varies widely depending on the usage situation of the user, so it is difficult to define the gradient. Although the CPM down is not a level of concern practically when it is reduced from 70 CPM to 60 CPM,
For example, when it is extremely lowered from 70 CPM to 45 CPM, it is considerably conspicuous.

Therefore, as shown in FIG. 4, 70 → 60 → 5
One possible idea is to gradually drop it from 0 to 45 CPM, but the area S of the shaded area in the figure is
Since productivity is reduced by the difference between the areas of 1 and S2, it is not preferable in consideration of this. In addition, if the user does the amount of work to finish the copying at the time t ′ in FIG. 3, even if it is possible to maintain 70 CPM,
If the mode is one in which the CPM is dropped step by step, productivity will decrease.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide an image forming apparatus capable of continuous sheet feeding to a fixing device, which can obtain optimum productivity according to the use situation.

[0008]

In order to achieve the above object, the image forming apparatus of the present invention according to claim 1 fixes an image by pressing and heating a transfer material between a pair of rollers. An image forming apparatus having a fixing device for causing the image forming device to continuously feed the image-unfixed transfer material to the fixing device, and means for detecting the surface temperature of at least one roller of the fixing device at a constant cycle. And a means for performing control for changing the continuous feeding interval of the transfer material according to a difference value between one detection value by the temperature detecting means and the next one detection value following the temperature detection means. Is characterized by.

In the image forming apparatus according to the second aspect, when the difference value between the continuous detection values is negative, the control means performs the feeding interval control according to the difference value, and the difference value is When it is positive, the feeding interval control is performed only by the detected value. That is, depending on the usage conditions, the roller temperature of the fixing device may drop or rise even during continuous heating. Therefore, there may be a case where the CPM increase at the time of temperature rise cannot be properly performed by only dealing with the above difference value. . Therefore, it is possible to handle the division when the temperature rises.

The image forming apparatus according to the third aspect of the invention is characterized in that the detection cycle of the surface temperature of the roller is set to a time period longer than the rotation cycle of the roller. That is, the surface temperature of the roller is not constant in the circumferential direction, there is a temperature difference, and if the temperature is detected in a short cycle and the difference is taken, the temperature is rising despite the overall temperature decrease. Considering that there is a possibility that false detection such as

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. First, as an example to which the present invention can be applied, FIG. 1 shows a configuration of a laser printer. In the figure, reference numeral 10 denotes a printer main body, and reference numerals 11 and 11 denote paper feed cassettes. In this printer, one paper feed cassette 11
A sheet 50 is fed in the direction of arrow A in the figure, and is conveyed to the drum-shaped photoconductor 13 by the registration roller pair 12 at a timing. The surface of the photoconductor 13 is uniformly charged by the charging charger 14 while rotating the photoconductor 13 in a clockwise direction, and a laser beam from the laser optical system 15 is irradiated to form an electrostatic latent image on the photoconductor 13. When this latent image passes through the developing device 16, it becomes a visible image with toner, and the visible image is transferred to the sheet 50 conveyed to the photoconductor 13 by the transfer charger 1.
Then, the transferred paper 50 is passed through the fixing device 18 to fix the visible image. Then, the paper 50 that has exited the fixing device 18 is conveyed in, for example, the arrow B direction in the figure, and the paper discharge unit 1
Discharge to either 9 or 19. On the other hand, after the transfer of the visible image, the cleaning device 20 removes the residual toner from the photoconductor 13.

A schematic diagram of the structure of the fixing device 18 is shown in FIG. The heat roller 21 constituting the fixing device 18 has a heater 23 inside.
The heat roller 21 is rotatably held in the frame via a heat roller bearing 28, and a gear (not shown) is arranged at the end of the heat roller 21 so that the apparatus main body can be rotationally driven through the gear. ing. On the other hand, a pressure roller 22 is provided on a pressure roller bearing 29 so as to face the heat roller 21, and the pressure roller 22 is urged toward the heat roller 21 side by a pressure spring 25 and a pressure lever 26 so as to be in pressure contact. The paper that is conveyed from the right side of the figure
The image is fixed by the action of heat and pressing force by passing between No. 1 and No. 22. In the figure, reference numeral 24 is a separation claw.

In the fixing device 18, the surface temperature of the heat roller 21 is detected by the thermistor 27, and the detected value is compared with a preset value to control the lighting of the heater 23 to determine the surface temperature of the heat roller 21. It is designed to be maintained within a certain range. When the wattage of the heater 23 is insufficient, the surface temperature of the heat roller 21 drops as described above, and the control according to the embodiment of the present invention at that time is performed as follows.

As shown in FIG. 5, the surface temperature Tn of the heat roller 21 is sampled at regular time intervals, and the difference value ΔTn of the detected temperatures during continuous sampling is taken. CPM
The threshold temperature at which the temperature is lowered is Ts1, and this Ts1 is
Two consecutive sampling temperatures Tn, Tn-1
And the difference value ΔTn between them, the CPM
It is determined whether or not to go down. That is, when the value of Tn-1 is sufficiently close to Ts1, if ΔTn at that time is large to some extent, in other words, if the gradient of the temperature change is steep, the CPM goes down at the time when the detected temperature Tx = Ts1. I do. On the contrary, if the difference value ΔTn is small to some extent, Tx
= Csm down is not performed at Ts1. It should be noted that the temperature Ts1 + b (° C.) in the figure is a judgment temperature for determining whether or not the CPM down is performed.

A flow chart of this control is shown in FIG. The i-th detection time ti corresponds to this sampling time tk
It is determined whether or not it matches xi (step 1), and YES
If so, it is determined whether or not the detection temperature Ti at the detection time ti is Csi down or lower than Tsi + b (step 2). If YES, the detection temperature Ti-1 and the detection temperature Ti-1 in the immediately preceding sampling are compared. It is determined whether the difference value ΔTn is larger than the threshold value a (° C.) (step 3). If the determination result is YES, the CPM is decreased (step 4), Tsi → Tsi + 1 is incremented (step 5), and the process proceeds to step 6 where i = i + 1.
And increments and returns to step 1. If NO in step 2, the process also proceeds to step 6, where i = i + 1 is incremented, the process returns to step 1, and ΔT is executed in step 3.
If n is less than or equal to the threshold value a, the process proceeds to step 5 and Tsi
→ increment by Tsi + 1 and i = i in step 6
Increment by +1 and return to step 1. By performing such control, as shown in FIG. 9, it is possible to set the optimum CPM according to the usage situation of the user, and it is possible to improve the productivity.

On the contrary, when the paper is not passed or the paper is intermittently fed after the CPM down, the heat roller 2
The temperature of No. 1 rises to reach the initial set temperature, but the temperature rise at this time is often not so rapid. In this case, the CPM is controlled by the same control as when the roller temperature drops.
When it is tried to increase, ΔTn is in a state of a or more, so CPM
Will not be changed, and CPM will not be restored. Therefore, when ΔTn is 0 or less, the CPM is recovered only by determining whether the temperature is Tn or Ts1 regardless of the difference in temperature gradient.

A flow chart of this control is shown in FIG. FIG.
If ΔTn is less than the threshold value a in the determination in step 3, the process proceeds to step 7 to increase CPM, and Tsi → T
Decrement with si-1 and proceed to step 6 in FIG.
If NO in the determination in step 7, the process proceeds to step 5 in FIG.

Further, the detection cycle of the surface temperature of the heat roller 21 is set equal to or larger than the roller rotation cycle in order to prevent the above-mentioned erroneous detection. This means that if the temperature is decreasing as a whole, the temperature is surely decreasing if the same point is measured, and if there is a time difference of more than one round, a temperature change larger than the temperature deviation for one round will occur. Because it can be expected.

The above description of all the embodiments has been made on the case where the surface temperature of the heat roller 21 is detected and controlled. However, as disclosed in Japanese Patent Application Laid-Open No. 3-65978, the fixability is improved. Pressure roller 2 to maintain
The contribution of the temperature of 2 is not negligible, and in some high-speed machines, the pressure roller 22 side has a heater 23 for heating inside, so the surface temperature on the pressure roller 22 side is detected and controlled. You may do it.

[0020]

In the image forming apparatus according to the first aspect of the present invention, the surface temperature of at least one of the rollers of the fixing device is detected in a constant cycle, and one detection value and the next detection value subsequent thereto are detected. Since the control is performed to change the continuous feeding interval of the transfer material according to the difference value of, it becomes possible to set the optimal feeding interval by the roller temperature and the temperature decrease gradient, and the temperature decrease of the roller It is possible to prevent the fixing failure due to the above, and to obtain the optimal productivity according to the usage situation of the user.

In the image forming apparatus according to the second aspect,
When the temperature rises, the control is divided, and if the difference between consecutive detection values is negative, the feeding interval control is performed according to the difference, and if the difference is positive, the feeding is performed only by the detection value. Since the interval control is performed, in addition to the common effects described above, there is an effect that appropriate CPM recovery can be performed.

In the image forming apparatus according to claim 3,
Since the detection cycle of the roller surface temperature is equal to or longer than the roller rotation cycle, in addition to the common effects described above, there is an effect that erroneous detection due to the circumferential deviation of the roller surface temperature can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a laser printer to which the present invention is applied.

FIG. 2 is a sectional view showing a fixing device of the apparatus of FIG.

FIG. 3 is a diagram showing a behavior of a fixing temperature decrease when a heat amount is insufficient in a fixing device of an image forming apparatus.

FIG. 4 is a diagram showing an example in which CPM is gradually reduced to cope with a case where the fixing temperature lowers when the amount of heat is insufficient as shown in FIG.

FIG. 5 is a diagram showing a case where the surface temperature of the heat roller of the fixing device is sampled at regular intervals and a differential value of the detected temperatures at successive samplings is obtained in the embodiment of the present invention.

FIG. 6 is a diagram showing a state in which CPM down is performed in the detection mode of FIG.

7 is a diagram showing a state in which CPM down is not performed in the detection mode of FIG.

FIG. 8 is a flowchart showing control contents in the state of FIG.

FIG. 9 is a diagram showing a state in which an optimum CPM can be set according to a usage situation of a user in the embodiment of the present invention.

FIG. 10 is a flow chart showing control when paper is not passed or intermittent feeding is performed after CPM down.

[Explanation of symbols]

 10 Printer Main Body 11 Paper Feed Cassette 12 Registration Roller Pair 13 Photosensitive Member 14 Charging Charger 15 Laser Optical System 16 Developing Machine 17 Transfer Charger 18 Fixing Device 19 Paper Ejection Section 20 Cleaning Machine 21 Heat Roller 22 Pressure Roller 23 Heater 24 Separation Claw 25 Pressure spring 26 Pressure lever 27 Thermistor 28 Heat roller bearing 29 Pressure roller bearing 50 Paper

Claims (3)

[Claims] 1. An image forming apparatus having a fixing device for pressing and heating a transfer material between a pair of rollers to fix an image, and a means for continuously feeding the transfer material on which the image has not been fixed to the fixing device. In the above fixing device, a means for detecting the surface temperature of at least one roller of the fixing device at a constant cycle is provided, and the difference between one detection value by the temperature detection means and the next one detection value consecutive thereto. An image forming apparatus comprising means for controlling to change the continuous feeding interval of the transfer material according to a value. 2. When the difference value between the consecutive detection values is negative, the control means performs the feeding interval control according to the difference value, and when the difference value is positive, only the detection value is detected. The image forming apparatus according to claim 1, wherein the feeding interval control is performed by the following. 3. The image forming apparatus according to claim 1, wherein a detection cycle of the surface temperature of the roller is set to a time longer than a rotation cycle of the roller.