JPS60150074A - Temperature sensor of fixing device - Google Patents

Abstract

PURPOSE:To perform accurate temperature detection and perform stable temperature control by providing a heat sensitive resistance element which has positive temperature characteristics to the cold junction part of a thermoelectric temperature sensor element, and holding the cold junction part at constant temperature. CONSTITUTION:The temperature sensor consists of a thermoelectric temperature sensor element 10 and a thermistor (PCT thermistor) 11 with positive temperature characteristics as the heat sensitive resistance element for holding the cold junction part of the sensor element 10 at constant temperature. Infrared radiant heat from the surface of a fixing roll enters a sense part 14 to measure the temperature from the thermoelectromotive force of a thermocouple 13, but the PCT thermistor 11 operates to perform temperature compensation automatically even if the ambient temperature varies, so the cold junction part of the sensor element 11 is held at invariably constant temperature. Consequently, the measured temperature is accurate and the fixing roll is brought under stable temperature control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a temperature sensor (1) used to detect temperature in a fixing device (1).

[Prior art]

Fixing devices of copying machines, etc. (Secondly, temperature control is performed to ensure good fixing, and a temperature sensor is used to detect the temperature. For example, copying machines use heating rolls and pressure rolls. Roll-type heat fixing devices are widely used, and when fixing a powder toner image onto a sheet by heating and applying pressure using a pair of rolls, the temperature of the high-temperature surface, especially the surface of the heating roll, is detected and the temperature is used in the fixing process. For example, the required temperature is 150~
Temperature control is performed to maintain a constant temperature within the range of 210'C. One type of temperature sensor used to detect temperature in such cases is a thermoelectric type that uses a thermocouple to measure the temperature difference between a hot junction and a cold junction as a thermoelectromotive force.

This temperature sensor can be a non-contact type that detects the temperature by detecting radiant energy emitted from the surface of the high-temperature object to be measured, so it can be used to detect the temperature of the heating roll surface of the fixing device as described above. However, compared to the contact type, it is advantageous in terms of heating roll wear, and also in terms of sensor wear and service life. Furthermore, if a heating roll with a particularly small heat capacity is used to shorten the rise time of a predetermined set temperature (secondly, the rate of temperature change is fast,
In such cases, it is difficult to keep the temperature of the heating hole constant using a contact type temperature sensor because the sensor has a large time constant and its response is poor. By using a non-contact type temperature sensor, more specifically, a non-contact infrared temperature sensor that uses infrared rays, the time constant can be made small and a predetermined temperature control performance can be obtained. Furthermore, thermoelectric infrared temperature sensors are superior to pyroelectric sensors.

In other words, in the case of a thermoelectric type, the temperature is measured by focusing the infrared light emitted by the object to be measured on the light receiving part and detecting the temperature gradient caused by heat absorption as a thermoelectromotive force using a thermocouple. , this is simpler in configuration than the pyroelectric type (= a method in which the electric charge generated when the temperature rises due to light reception is intermittently extracted as a signal using a chopper, and the heat capacity of the sensing part is also small. There are advantages such as better response than the pyroelectric type.

By the way, when the temperature sensor using a thermocouple as described above detects the temperature on the surface of the heating roll, the distance between the temperature sensor and the heating roll is usually set to about 5 to 30 meters, considering the viewing angle of the temperature sensor. On the other hand, as mentioned above, the temperature of the heating roll is generally around 2150 to 210°C, so if the heating roll is heated for a long time at the above setting distance, the temperature will rise due to radiation and convection from the heating roll. The entire sensor is heated, and the cold junction of the thermocouple is heated to 40~
70℃ (2 degrees). However, immediately after heating, the temperature sensor has not yet warmed up, so considering that the temperature of the cold junction of the thermocouple is equal to the ambient temperature, Max. 50-60℃ for cold junctions
This will result in a temperature change of . However, as mentioned above, thermocouples measure the temperature difference between the hot and cold junctions as a thermoelectromotive force, so if the temperature of the cold junction changes like that, the detected temperature will change. However, this has the disadvantage that when performing temperature control, stable temperature control that always maintains a predetermined temperature cannot be expected.

Therefore, as a measure to eliminate this inconvenience, a cold junction temperature compensation diode is provided near the cold junction to compensate for the temperature of the cold junction, so that even if the temperature of the cold junction changes as described above, A method has been proposed in which a constant output is always produced as long as the temperature of the hot junction does not change. According to this, when controlling the temperature of the fixing device, it is possible to always control the temperature to be constant.

Since the output from the ode is small, an amplifier circuit is required, and the correct control temperature cannot be set unless the output of the thermocouple is properly adjusted, which also requires time and effort. Moreover, not only this,
Since the output of the diode is not linear with respect to temperature, the control temperature can be changed from 180°C to 150°C, for example.
To change the control temperature to ℃ or 210℃, both the output amplification circuit of the temperature sensor and the output amplification circuit of the temperature compensation diode must be adjusted.
In this respect as well, there is a problem that the adjustment is complicated, and these problems in particular become a major obstacle during mass production.

Although the temperature sensor using the C1 thermocouple has various advantages as mentioned above, it also has the disadvantages mentioned above.As a countermeasure for this, it is easy to use a temperature compensation diode (the second is that it is difficult to adjust). This may cause problems such as not being able to do so.

[Purpose of the invention]

This invention was made in view of this point (1), and it is possible to detect temperature so as to enable stable temperature control when controlling the temperature of the fixing device without using the temperature compensation diode as described above. Furthermore, the purpose is to not make the adjustment or the like complicated, but to make it a very simple adjustment.

[Structure of the Invention] In order to achieve the above object, the present invention provides a thermosensitive resistance element having a positive temperature characteristic at the cold junction part of a thermoelectric temperature sensor element using a thermocouple. During temperature control, the temperature of the cold junction is always maintained at -C2 regardless of changes in ambient temperature.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows the structure of a fixing device to which the present invention can be applied. In the figure, the heating roll (1) has a diameter of, for example,
It was formed by covering a cylindrical metal core (2) with a length of 400 mm and a silicon RTV (injection rate 0.9) with a thickness of about 0.4wn on the surface of this metal core (2). It is composed of a silicone rubber layer (3) and
For example, a 900W halogen lamp (4) is provided inside the lamp. Further, the heating roll (1) is in contact with a pressure roller (5) made of a material having appropriate elasticity to form a fixing nip, and a toner image (6) is formed near the fixing nip. ) is provided with a peeling device (8) for peeling off the toner image supporting layer such as paper from the surface of the heating roll (1) after fixing.

The toner image supporting material (7) is fed into the fixing nip in such a direction that the toner image (6) side comes into contact with the surface of the heating roll (1) during fixing, and the toner image (6) The image support material (7) is attached to the heating roll (
The halogen lamp (4) described above is heated and pressurized by passing between the toner image supporting material (7) and the pressure roll (5). A heat source for heating the heating roll (1) to bring the surface temperature of the heating roll (1) to a required temperature required in the fixing process when the fixing process is performed. The surface temperature is maintained at 180° C. by being controlled by a temperature controller (not shown).

In order to perform such temperature control, a heat roller ( A temperature sensor (9) is installed to detect the temperature of the surface of 1).

FIG. 2 shows the structure of a temperature sensor according to an embodiment of the present invention used as such a temperature sensor (9).
This consists of a thermoelectric type temperature sensor element (10) and a positive temperature characteristic thermistor (10) as a thermosensitive resistance element having positive temperature characteristics.
(hereinafter referred to as a PCT thermistor). As shown in FIG. 54 pairs of thermocouples (131) made of , antimony, and tellurium are deposited around the sensing part (14),
The sensing portion (14) receives infrared radiation energy (151).Furthermore, in order to improve the responsiveness of the sensing portion (14), in the illustrated example, the sensing portion (14)
The silicon substrate (12) is made as thin as, for example, 3 to 4 μm by anisotropic etching, and the heat capacity is extremely reduced. With this structure, the response speed is reduced to approximately 3 μm.
0m5, and as mentioned above, the response is better than that of the general pyroelectric type.Also, the above PC
The T thermistor (11) is a semiconductor porcelain whose main material is barium titanate, and has a temperature characteristic such that its resistance value increases rapidly as the temperature rises once it reaches a certain temperature. As shown in Figure 4, for example, the − side is 8f.
Electrodes (lη) are provided on both sides of the square plate type barium titanate semiconductor (16) of i, and the electrode +17
) is coated with an insulating paint (181), and a constant voltage can be applied to the electrodes (171) from a DC power source via lead wires (19) connected to each electrode fl? There is.

These temperature sensor elements (1) and PCT thermistors (1)
1) has its temperature sensor element (1) as shown in FIG.
The silicon substrate (121) of the cold contact part of rjI and one side of the PCT thermistor (11) are bonded with a high thermal conductive thermal epoxy adhesive (4).
5. , cylindrical housing Q9 with a length of about 12 mm
is stored inside. At the top of the cylindrical housing Qη, a window (b) with a diameter of about 6 cm is provided for light entry, and this window is also provided with a filter (a) to cut wavelengths below visible light. , light energy (c)
is the window (a) opened at the tip of the cylindrical housing (c)
The filter (a) cuts out wavelengths of visible light and below, and the temperature sensor element (111
It is designed to be absorbed by the sensing part (14) of Il.

In addition, at the bottom of the cylindrical housing Qη, there is a thermocouple terminal (c) for taking out the output of the thermocouple (13) of the temperature sensor element (1o) and a terminal for applying voltage to the electrode +17) of the PCT thermistor (11). A PCT therminuta terminal (c) is provided.

In this way, the thermoelectric temperature sensor element (10) is used as a sensor for detecting temperature for temperature control in the fixing device, and the PCT thermistor +111 is provided at the cold junction of the sensor. 1
It is applied to detect the temperature on the surface of the heating roller (1) in the fixing device shown in the figure, and the infrared light emitted by the heating roller (1) is focused on the sensing circle, and the temperature gradient caused by the heat absorption is detected by the thermocouple. +
131 +2 When measuring temperature by detecting thermoelectromotive force, stable temperature control is possible even when the ambient temperature changes, and this can be achieved by using a temperature compensation diode as described above. It can be done without. That is, in the constant power region of the PCT thermistor (11), the ambient temperature changes from TI to T2 while a constant voltage vl is applied to the PCT thermistor terminal (c).
(TI < T2), if the ambient temperature changes to T1
If current □ flows when , the power consumption in that case is Wl = V,
2, the current decreases from 1 to 2 due to the increase in resistance value, and the power consumption W2 becomes W2=VIXI2, so Wl>W2 tonal.

In other words, the power consumption is large when the ambient temperature is low, and conversely becomes small when the ambient temperature is high, so the PCT thermistor (11) automatically operates to compensate for the temperature.
By utilizing the constant temperature heat generation characteristic of such PCT thermistor (11)! llEnvironmental temperature (-related PC)
The temperature of the T thermistor (11) will be kept constant. Therefore, the temperature of the cold junction part of the temperature sensor element (10) provided with the PCT therminutor (11) does not change even if the ambient environment temperature changes, so the detected temperature changes due to a change in the temperature of the cold junction part. There is no inconvenience that the above PC will change even if the ambient environment temperature changes.
Temperature sensor element (10) by T thermistor (11)
The temperature of the cold junction is always kept constant, allowing stable temperature control. Furthermore, since no temperature compensation diode is used, no amplifier circuit is required to amplify the output. Therefore, setting the control temperature does not take much time and effort as mentioned above, and when changing the control temperature, only the output of the thermocouple (13) needs to be changed, which is extremely This can be done with a simple adjustment.

In the case of the above example, when a 12V DC power supply was used as the DC power supply connected to the PCT thermistor terminal (c), if the ambient temperature was 10°C, the PCT thermistor terminal (c)
11), a current of about 60 mA flows through it, and its surface temperature becomes 70 mA.
℃, and when the ambient temperature is 60℃, a current of about 10mA flows and the surface temperature at that time becomes 70℃, which is the same as when the ambient temperature is 10℃, and the ambient temperature is 10℃.
Since the temperature of the PCT thermistor (11) was always maintained at 70°C even when the temperature changed from
The temperature was controlled at 0°C. In addition, even when the temperature of the heating roll (1) is changed from 180°C to 150°C to 210°C by a simple adjustment of changing the output of only the amplifier circuit of the thermocouple (13) to change the control temperature, Immediately after changing the temperature, it always showed a constant value, and no so-called temperature drift occurred.

〔Effect of the invention〕

As described above, the present invention enables stable temperature control in the fixing device even with a temperature sensor using a thermocouple without using a cold junction temperature compensation diode, and when changing the control temperature setting or the control temperature. It has the advantage that it can be easily adjusted, and that it does not pose a major hindrance even when mass-produced.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a roll-type heat fixing device using an infrared temperature sensor, Fig. 2 is a structural diagram showing a temperature sensor according to an embodiment of the present invention, and Fig. 8 is a thermoelectric type temperature sensor used in the sensor. The schematic structural diagram of the element, FIG. 4, is a structural diagram of the same PCT thermistor. Explanation of symbols (10)...Temperature sensor element (11)...
... PCT thermistor (131 ... Thermocouple patent applicant Fuji Xerox Co., Ltd. Agent Tomohiro Nakamura Patent Attorney Katsuo Naruse Figure 3 Figure 4

Claims (1)

[Claims] This sensor detects temperature for temperature control in a fixing device, and includes a thermoelectric temperature sensor element and a cold junction part C divided into two parts to keep the temperature of the cold junction part of this temperature sensor element constant. A temperature sensor for a fixing device, comprising a heat-sensitive resistance element having temperature characteristics.