JP2003057116A - Temperature detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve safety by detecting break of wire by a simple means by using the same signal when detecting temperature by using a non-contact temperature sensor. SOLUTION: This temperature detection method utilizes a non-contact temperature detector means consisting of a film absorbing infrared from a heat element heated by a heat source, a thermal element for infrared detection for detecting the temperature of the film and a temperature compensation thermal element detecting the temperature of a support supporting the film. Among the first output voltage of a series circuit with the thermal element for infrared detection and a resistor element, the second output voltage of a series circuit with the temperature compensation thermal element and the resistor element, and the third output voltage of the difference between the first output voltage and the second output voltage, the first and the third output voltages are converted to digital values. Based on these digital values, the temperature of the heat element is detected, and based on the value of the first output voltage converted to a digital value, a break of wire of the thermal element for infrared detection is detected.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detecting method using non-contact temperature detecting means, and more particularly, to an electrophotographic apparatus,
The present invention relates to a fixing device used for an electrostatic recording device or the like, in which a temperature detecting element is arranged in a heating element in a non-contact manner. 2. Description of the Related Art A fixing device using a fixing roller heated by a heater is widely used in an image forming apparatus such as a copying machine and a laser printer. In such a fixing device, a thermistor for maintaining the surface temperature of the fixing roller at a predetermined temperature, a temperature fuse for shutting off a current supply path to a heater when the temperature of the fixing roller rises abnormally, and a thermoswitch are provided. The temperature detecting element is in contact with the surface of the fixing roller. [0004] For this reason, contact flaws may occur in the fixing roller, causing problems such as white streaks, black streaks, and poor fixing. Therefore, a method of contacting the temperature detecting means with the fixing roller outside the image area, which is the area where the recording material passes, can be considered. However, it is impossible to detect the temperature in the image area, and the fixing device is increased in size. For this purpose, a method has recently been considered in which the temperature detecting means is brought into non-contact with the fixing roller in the image area. [0006] The non-contact temperature detecting means includes a casing having an opening, and a casing provided inside the casing.
An infrared absorbing film made of a polymer material that absorbs infrared light that has passed through the opening, and a thermistor element for infrared detection arranged so as to be in close contact with the infrared absorbing film;
It has a thermistor element for temperature compensation for detecting the temperature of the casing. The non-contact temperature detecting means increases the temperature of the infrared absorbing film by absorbing the infrared light passing through the opening of the casing by the infrared absorbing film disposed immediately below the opening. The thermistor element disposed in close contact with the sensor detects the temperature change. Both the infrared detecting thermistor element 30 and the temperature compensating thermistor element 31 have the same temperature-resistance characteristics, and a fixed resistance R having the same resistance value as shown in FIG.
1 and R2 are each connected in series. When the infrared absorbing film absorbs infrared rays from the object, the temperature of the film rises, and the resistance value of the infrared detecting thermistor becomes smaller than that of the temperature compensating thermistor, so that a> b. As shown in FIG. 4, a bridge circuit detects a temperature difference from the temperature compensating thermistor element and an output voltage corresponding to a potential difference between A and B is detected as c. The output voltage c and the output voltage a of the temperature compensating thermistor element are converted into digital values by an A / D converter and taken into a microcomputer, and the microcomputer converts the digital values of these output voltages a and c into a data table or a function. The conversion is performed to detect the temperature of the fixing roller. However, in the temperature detecting method using the non-contact temperature detecting means described in the above-mentioned conventional example, a failure of the infrared detecting thermistor element or a transmission line during the temperature control of the fixing roller. Is disconnected and becomes an open state, the output voltage b becomes the same as the reference voltage V. Therefore, the relationship between a and b is reversed, a <b, and the output voltage c becomes zero. Then, when the microcomputer converts the digital values of the output voltages a and c into temperatures based on the digital values, the temperature of the fixing roller is detected as being lower than the actual temperature, and the fixing roller continues to be heated. There is a problem that the temperature of the fixing roller is excessively increased until the apparatus operates. The present invention provides a method for detecting a failure due to a disconnection of a thermal element for infrared detection when using the non-contact temperature detecting means as described above without increasing a circuit or cost. [0011] A film for absorbing infrared rays from a heating element heated by a heating source, a thermosensitive element for detecting the temperature of the film, and a temperature of a holder for holding the film. In a temperature detection method using a non-contact temperature detection means comprising a temperature compensation thermosensitive element for detecting a temperature, a first output voltage of a series circuit of the infrared sensing thermosensitive element and a resistance element, and the temperature compensation thermosensitive element The first and third output voltages of the second output voltage of the series circuit of the resistance elements and the third output voltage that outputs the difference between the first output voltage and the second output voltage are converted into digital values. Detecting the temperature of the heating element based on these two digital values, and detecting the disconnection of the infrared detecting thermosensitive element based on a value obtained by converting the first output voltage into a digital value. Characterized by Temperature detection method. Embodiments of the present invention will be described below with reference to the drawings. An image recording apparatus for fixing an unfixed image on a recording paper, which is not shown in the figure, has an image carrier for forming an electrostatic latent image on its surface and a charge on the surface of the image carrier. Pre-exposure means for removing static electricity, primary charging means for charging the surface of the image carrier to a desired potential, exposure means for exposing the charged image carrier to form an electrostatic latent image, electrostatic on the image carrier There are provided a developing device for developing the latent image with a developer to make it a visible image, a transfer device for transferring a toner image on the image carrier developed by the developing device to a recording material, and the like. A fixing unit 1 which is a roller fixing device for fusing and fixing the toner image transferred onto the recording material by a fixing roller heated and pressurized is arranged at a predetermined position of the image recording apparatus. A desired image can be obtained by appropriately executing the above processes. The recording material may be recording paper or OH
P paper or the like is used. Next, the configuration of the fixing unit 1 will be described. In FIG. 2, reference numeral 2 denotes a heating roller, which is a roller in which a layer of a heat-resistant elastic material such as silicone rubber or fluorine rubber is formed on a pipe material such as aluminum or iron and a release layer such as PFA or PTFE is coated on the surface. The pressure roller 3 disposed in pressure contact with the heating roller 2 is also a roller in which a layer of a heat-resistant elastic material such as silicone rubber or fluorine rubber is formed on a cored bar, similarly to the heating roller. A recording material S is passed through the heating roller (heating member) 2 and the pressure roller (backup member) 3, and the toner T on the recording material S is heated and heated between the heating roller and the pressure roller. It is pressed and fixed. A heater 4 is provided inside the heating roller 2 and heats the heating roller 2 from the inside. Further, a temperature detecting element 5 serving as a temperature detecting means for detecting the surface temperature of the heating roller 2 is arranged in a non-contact manner facing the heating roller, and detects the temperature of the heating roller 2. Based on data from the temperature detecting element 5, the surface temperature of the heating roller 2 is maintained at a predetermined set temperature (print temperature) or a non-fixing standby temperature (standby temperature). The heating roller is also provided with a thermoswitch 6 in a non-contact manner to detect an excessive temperature rise. When the excessive temperature rise is detected, the power supply to the heater is shut off. Next, the configuration of the temperature detecting element 5 will be described in detail with reference to FIG. Reference numeral 7 denotes a case made of a material having high thermal conductivity, such as aluminum, which is provided so that a heat-resistant film 9 that absorbs infrared light radiated from a heating roller is closed in an opening 8 provided on one surface of the case. On the inner surface side of the case of the heat-resistant film 9, a thermistor element 1 for infrared detection is provided.
0 is adhered and fixed with an adhesive or the like. In the vicinity of the infrared detecting thermistor element 10, a temperature compensating thermistor element 11 for measuring the ambient temperature in the case is provided. The lead wires 12 of the infrared detecting thermistor element 10 and the temperature compensating thermistor element 11 are respectively connected to sockets (not shown) provided in the case 7 to be taken out. Next, the operation of the temperature detecting element 5 will be briefly described. First, when infrared rays from the heating roller enter the resin film 9 attached to the opening 8 of the case 7,
The infrared rays are absorbed by the film 9, and the temperature of the film 9 increases according to the amount of the infrared rays. Then, the temperature of the resin film 9 is transmitted to the infrared detecting thermistor element 10 tightly fixed to the back surface of the film and detected as a resistance change of the thermistor element. The resistance of the infrared detecting thermistor element 10 is affected by the temperature of the case, and the temperature corresponding to the case temperature is detected using the temperature compensating thermistor element 11 to eliminate the influence. The reason why the casing is made of a material having high thermal conductivity such as aluminum is to improve the followability of the temperature compensating thermistor element 11 to a change in ambient temperature. Next, a temperature detecting circuit using the temperature detecting element 5 will be described with reference to FIG. Each of the infrared detecting thermistor element 10 and the temperature compensating thermistor element 11 is 3
It is connected in series with the 3 kΩ resistance elements R1 and R2, and is connected between the reference power supply V and the ground. The outputs of the temperature compensating thermistor element 11 and the infrared detecting thermistor element 10 are voltages a and b, respectively. The differential amplifier circuit 12 receives the voltages a and b as inputs, and the output amplified by a factor of 15 is the voltage c. The voltages b and c are input to the 8-bit A / D converters 13 and 14, and the microcomputer 15 reads a digital output j corresponding to the voltage b and a digital output k corresponding to the voltage c. The microcomputer 15 applies these digital outputs to the data table and detects the temperature of the heating roller 2. For the temperature detection, the output voltage b of the infrared detecting thermistor element is used instead of the output voltage a of the conventional temperature compensating thermistor element, but there is no influence on the detection accuracy and the like. The reason for this is that a small voltage difference between the output voltage a of the temperature compensating thermistor and the output voltage b of the infrared detecting thermistor is originally differentially amplified and used for temperature detection. However, the output voltage b changes, but the change is very small. Therefore, in a temperature control cycle of 1 second or less when actually used, the voltage change is 8
1 digit with A / D converter of about bit resolution
This is because: At the same time, the microcomputer 15 determines whether or not the value of the digital value j is FFH for detecting disconnection of the infrared detecting thermistor. The thermistor element for infrared detection is, for example, 0
Even at a temperature of 0 ° C., the resistance value of the resistor R1 is set to 33 kΩ. Therefore, even at a low temperature of 0 ° C., the digital output is F7.
H and does not become FFH except for disconnection. When the value of the digital value j is FFH, it is determined that the infrared detecting thermistor 10 or its transmission line is disconnected,
The power supply to the heater 4 is stopped and the operation of the apparatus is stopped, and the display device indicates that the temperature detecting element 5 has failed. The infrared detecting thermistor element 1
It is assumed that the 0 and the temperature compensating thermistor element 11 and the transmission line thereof are disconnected / short-circuited, respectively. Among them, it is most important to detect the disconnection of the infrared detecting thermistor element 10. Although the temperature detection circuit obtains the differential output c from the voltages a and b, when the voltage b becomes larger than the voltage a, the differential output c becomes 0, and when the temperature is converted, the temperature is lower than the actual temperature. Very low,
As a result of the microcomputer turning on the heater to increase the temperature of the heating roller, the temperature becomes excessively high, and the fixing device is damaged. The voltage b becomes higher than the voltage a because the voltage b
The maximum is the case where the infrared detecting thermistor 10 is disconnected and the case where the voltage a is minimum and the temperature compensating thermistor 11 is short-circuited. It is extremely possible that the temperature compensating thermistor 11 suddenly short-circuits during the temperature control. small. Because there is no possibility that the thermistor element itself will short-circuit,
Further, since the transmission line is not usually provided in the movable portion, there is no possibility that the coating or the like is damaged during the temperature control and short-circuited. Therefore, the short-circuit failure of the temperature compensating thermistor 11 can be considered only when the transmission line is pinched by the housing and short-circuited when disassembling / assembling the fixing unit or the electrophotographic apparatus main body for maintenance of the apparatus. In this case, since the temperature of the fixing roller has decreased to some extent, for example, the temperature of the fixing roller detected by the temperature detecting element 5 does not increase even though the heater is energized at the time of restart.
The failure of the temperature detection element 5 can be estimated. On the other hand, the disconnection of the infrared detecting thermistor element 10 is more likely than the short-circuit failure of the temperature compensating thermistor 11 in consideration of the deterioration of the material bonding the thermistor to the film and the deterioration of the solder on the transmission path. The disconnection during temperature control is not zero. As described above, the temperature of the fixing roller is detected using the two voltage values b and c input to the microcomputer for temperature detection, and the infrared detection thermistor is used using the voltage value b of the two. Ten disconnections can be detected, and safety can be improved without adding a circuit. According to the present invention, as described above, when the non-contact temperature detecting means is used, one of two voltage values taken into the microcomputer is used to detect a failure due to disconnection of the thermal element. Therefore, the safety of the apparatus can be improved without increasing the circuit and cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating a temperature detection circuit according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a fixing unit 1. FIG. 3 is a diagram illustrating a temperature detecting element 5. FIG. 4 is a diagram illustrating a conventional temperature detection circuit. [Description of Signs] 1 Fixing unit 2 Heating roller 3 Pressure roller 4 Heater 5 Temperature detecting element 6 Thermoswitch 7 Case 8 Opening 9 Infrared absorbing film 10 Infrared detecting thermistor element 11 Temperature compensating thermistor element 12 Lead wire 13A / D converter 14 A / D converter 15 Microcomputer

   ────────────────────────────────────────────────── ─── Continuation of front page    F term (reference) 2G066 AC11 AC16 BA09 BA51 BB11                       BC07 BC11 BC15 CA15 CB05                 2H027 DA12 DA32 DE04 DE07 DE09                       EA11 EC06 EC07 EC10 EC18                       ED25 EE01 EE07 EF04 EF06                       HA04 HA13 HA17 ZA07                 2H033 AA35 BA31 BA38 BB01 CA03                       CA06 CA07 CA23 CA24 CA28                       CA57

Claims (1)

Claims 1. A film for absorbing infrared rays from a heating element heated by a heating source, a thermosensitive element for detecting infrared rays for detecting a temperature of the film, and a temperature of a holder for holding the film. A temperature detecting method using non-contact temperature detecting means comprising a temperature-compensating thermosensitive element for detecting, wherein a first circuit of a series circuit of the infrared detecting thermosensitive element and a resistance element is provided.
And a second output voltage of a series circuit of the temperature-compensating thermosensitive element and the resistance element, and a third output of a difference between the first output voltage and the second output voltage.
Out of the output voltages, the first and third output voltages are converted into digital values, the temperature of the heating element is detected based on these two digital values, and the first output voltage is converted into digital values. Detecting a disconnection of the infrared detecting thermosensitive element based on the value converted into the temperature.