JPH01109387A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the power consumption and to extend the life of a pressure roll by detecting the humidity of a recording material to control the power supply to the pressure roll of a fixing device. CONSTITUTION:The humidity of a recording material P is detected by a humidity detecting sensor provided in a paper supply cassette. When this detected humidity exceeds a prescribed value, a thermistor 226 detects this state and a heat source 225 of a fixing device 22 is controlled to supply power to the heat source of a pressure roll 222. Since power is not always supplied but is supplied only on demand, the power consumption of the fixing device in an image forming device is reduced and the overrise of the temperature of the pressure roll is prevented to prolong the service life of the pressure roll.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an image fixing device having a fixing roller that heats and presses an unfixed image on a recording material t to fix it, and a pressure roller that comes into pressure contact with the fixing roller. The present invention relates to a forming apparatus, and particularly relates to an image forming apparatus having means for controlling the surface temperature of a pressure roller of a fixing device.

(Prior Art and Problems) A fixing device that fixes an unfixed toner image on a recording material by heating and applying pressure has two devices that come into pressure contact with each other in order to carry out fixing while conveying the recording material under pressure. Generally, a book fixing roller is provided, and a heat source such as a heater is provided inside only the roller on the side that contacts the unfixed image.

However, the recording material that has passed between the fixing rollers having the above configuration is heated on the toner image side and the humidity decreases, so that only the toner side shrinks. Therefore, the recording material tends to curl toward the toner image side, and this tendency becomes more pronounced especially in a high humidity environment.

If the recording material curls in this manner, it may cause jams or the like in the image forming apparatus after the fixing device. especially,
In the case of an image forming apparatus that has the function of double-sided image formation or multiple image formation, an intermediate tray is installed inside the apparatus! Recording materials for the fixing method are temporarily docked in It11, etc., and the recording materials are re-fed from this intermediate tray device to the developing section to perform image formation processing. This can cause many problems such as poor transfer in the developing section.

Conventionally, in order to minimize the curling of the recording material caused by heating in the fixing device and to improve the fixing performance, a fixing roller that comes into direct contact with the unfixed image, and a fixing roller that directly contacts the unfixed image and the recording material from the opposite side of the unfixed image have been used. An image forming apparatus has been proposed that has a fixing system *I in which a heat source such as a heater is provided inside both pressure rollers that apply pressure.

However, the heater in the conventional pressure roller is always heated regardless of the degree of moisture absorption of the recording material, so when the humidity in the recording material is low and there is no need to heat the recording material from the pressure roller side. This results in a lot of wasted electricity being consumed. Furthermore, in order to press the pressure roller against the fixing roller, in many cases the surface layer is a rubber layer, and the heat at the time when heating is not required is transmitted and accumulated in the rubber layer. New problems have arisen, such as deterioration and toner fusion to the photosensitive drum in the developing section due to excessive temperature rise inside the device.

(Means for Solving the Problems) As described above, the present invention solves the problems of the conventional devices that have heat sources inside both the fixing and pressure rollers, and reduces power consumption. It is an object of the present invention to provide an image forming apparatus in which the temperature is reduced, the useful life of the roller is extended, and excessive temperature rise within the apparatus is controlled.

In order to achieve the above object, the present invention provides a method in which both a fixing roller that contacts an unfixed image on a recording material and a pressure roller that rotates in pressure contact with the fixing roller have a heat source,
A fixing device that presses and heats a recording material carrying an unfixed toner image while conveying it under pressure.

a humidity detection sensor that detects the humidity of the recording material conveyed to the fixing device at a position in front of the fixing device; and a detection signal value received from the humidity detection sensor.

If the humidity is higher than a value corresponding to a set permissible humidity, a control means is provided for energizing a heat source inside the pressure roller to raise the surface temperature of the pressure roller to a predetermined temperature.

(Embodiment) A copying apparatus capable of double-sided copying or multiple copying will be described below as an embodiment of an image forming apparatus to which the present invention is applied, based on the accompanying drawings. As shown in FIG. 2, a copying apparatus M that performs double-sided copying and multi-copying on copy paper P as a recording material has a copying section 5 as an image forming section equipped with a photoreceptor 6 approximately in the center of the main body of the apparatus. Additionally, a document table 2 is provided at the top of the body. A scanning system 3 is provided below the document table 2, and a sheet feeding section 11 consisting of sheet cassettes 7. 15 is provided. Further, above the sheet cassette 7.9, a humidity sensor 80 is arranged to detect the humidity of the recording material stored in the cassette. A registration roller 19 is located near the photoreceptor 6. A transfer device 20 is provided, and a conveyor belt 21 and a fixing mold 2122 are also provided. A first flapper 23 is provided downstream from the fixing device 22 in the conveyance direction of the copy paper P, and the flapper 23 is connected to the discharge conveyance path P.
It can be switched to either the a side or the refeed conveyance path pb side leading to the intermediate stock device 30 for refeeding. The intermediate stock device 30 includes a first flapper 2
A second flapper 29, an intermediate tray 36 for refeeding the copy paper P, refeed rollers 45, 46, and the like are disposed downstream from the copy paper P in the conveying direction of the copy paper P.

FIG. 1 is an enlarged view of only the fixing section "JFn" of the apparatus of the present embodiment described above.The copying machine WIM of this embodiment, which is not shown, has a single-sided - To enter instructions for multiple copies, double-sided copies, or multiple copies,
In addition to each having an input capotan, a control means is provided at a predetermined portion inside thereof to control an increase in the surface temperature of the pressure roller 222 by intermittently energizing a heat source inside the pressure roller 222. It is being

In FIG. 1, reference numeral 2Z denotes a fixing device, which is located downstream of the conveyance system 21 and feeds the copy paper P onto which the unfixed toner image has been transferred via the conveyance system 21 to the fixing device 22. There is. The fixing device 22 includes a fixing roller 221 and a pressure roller 222 that is in pressure contact with the fixing roller 221 and rotates as a result of the fixing roller 221 .

The fixing roller 221 has a heat source 223 inside, and a thermistor 224 for controlling the surface temperature is pressed on the surface thereof. This thermistor 224 turns the heat source 223 to zero.
It is designed to be switched N-OFF.

The pressure roller 222 is also inside II4! It has a source 225 and a thermistor 226 is pressed on one surface. The pressure roller 222 is made up of a metal core 222a and an elastic member 222b made of silicone rubber or the like bonded thereon, and is biased by a biasing member such as a tension coil spring (not shown) to press the fixing roller. 221.

Note that the pressure roller 22 is set at the predetermined location described above.
A control means (not shown) for controlling energization to the internal heat source 225 of No. 2 receives signals from the humidity sensor 80 and thermistor 226, and maintains the surface of the pressure roller 222 at a predetermined temperature as described below. The recording material is set to be sufficiently heated from the side opposite to the toner image.

Control of the heat source 225 in the pressure roller 222 by the fixing device and control means in the image forming apparatus of the embodiment described above is performed as follows.

When power is turned on to the image forming device 21M and the device becomes ready, the humidity sensor 80, which has a predetermined reference value set,
It also detects the humidity of the copy paper in the cassette 7 or 9 and sends a signal to a control means (not shown). Upon receiving this signal, the control means determines that if the humidity of the copy paper is above the reference value,
At the same time, the heat source 225 inside the pressure roller 222 starts to be energized, and the thermistor 226 detects the surface temperature of the pressure roller 222 to a predetermined temperature (100 to 120 degrees Celsius in this embodiment).
). Further, the control means does not energize the heat source 27'5 if the humidity of the copy paper is less than the standard A1.

Note that the reference value of the humidity sensor 80 is preferably about 70% humidity in the case of commonly used copy paper with a weight of 60 to 80 g/m. Although various types of humidity sensors are available, electrical resistance humidity sensors that utilize the relationship between humidity characteristics and electrical resistance are best, and ceramic humidity sensors are particularly good.

Furthermore, a case will be described in which the copy sheet is passed through the fixing device multiple times in the image forming apparatus 2iM described above to perform double-sided copying or multiple copying. In this case, when double-sided copying or multi-copying is input using an input capo-button (not shown) set at a predetermined outside part of the image forming device 21M,
At the time of first copying, wA is controlled by the control means as described above.
When copying is performed for the second time or later, the control by the control means is stopped. The reason for this is that once the copy paper has passed through the fixing device, it is heated equally and moderately from both sides between the fixing roller 221 and the pressure roller 222, so the humidity that causes curling decreases equally on both sides, causing curling. Even if the heat source 225 in the pressure roller 222 is turned off, the pressure roller still has residual heat immediately after the heat source 225 in the pressure roller 222 is stopped.
This is because even if the copy paper absorbs moisture during the transportation process after passing through the fixing device twice, this residual heat will sufficiently prevent curling. In this way, by stopping the control by the control means from the second time onwards, it is possible to further reduce power consumption during double-sided copying or multiple copying.

The image form T&? of this embodiment has the fixing device as explained above. According to e'a, the power consumption of the heat source 225 in the pressurizing port 222 can be suppressed, curling of the copy paper can be prevented, and the image can be sufficiently fixed.

(Effects of the Invention) According to the image forming apparatus of the present invention configured as described above, when the humidity of the recording material is above a certain level, the heat source in the pressure roller is energized, and double-sided or multiple image formation is possible. In some cases, the control state is entered only during the first fixing, so power consumption is significantly reduced. As a result, an excessive temperature rise inside the pressure roller is prevented, resulting in an effect that the service life of the pressure roller is extended and troubles due to heating of peripheral equipment do not occur.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a fixing device of an embodiment of the present invention, and FIG. 2 is an overall schematic diagram of an image forming apparatus having the fixing device shown in FIG. 221--------- Fixed roller 223---
----------- Heat source 222 ----------- Pressure roller 225 --
−−−−−−−−−−Heat source

Claims (2)

[Claims] (1) Both the fixing roller that contacts the unfixed image on the recording material and the pressure roller that rotates in pressure contact with the fixing roller have heat sources, and while the recording material carrying the unfixed toner image is conveyed under pressure. , a fixing device that performs pressurized and heated fixing, a humidity detection sensor that detects the humidity of the recording material conveyed to the fixing device at a position in front of the fixing device, and a detection signal value received from the humidity detection sensor that is set. and control means for energizing a heat source inside the pressure roller to raise the surface temperature of the pressure roller to a predetermined temperature when the humidity is equal to or higher than a value corresponding to the permissible humidity. . (2) The image forming apparatus is capable of double-sided image formation or multiple image formation by performing fixing multiple times in the fixing device, and the control means is in a control state during the first fixing.
The image forming apparatus according to claim (1), wherein the image forming apparatus is set to a control stop state from the second time onwards.