1. Field of the Invention
The present invention relates to temperature detection processing of a fixing member.
2. Description of the Related Art
In electro-photographic image forming apparatuses, a toner image transferred onto a recording material is fixed by a fixing device. The fixing device includes a fixing member having a heater, and a sensor for detecting a surface temperature of the fixing member. To keep the surface of the fixing member at a temperature (target temperature) at which the toner melts, based on the surface temperature of the fixing member detected by the sensor, a power supply of the heater is controlled.
As the sensor for detecting the temperature of the fixing member, a noncontact temperature detection element is used so as not to damage the surface of the fixing member. Japanese Patent Application Laid-Open No. 2003-57116 discusses a noncontact temperature detection device having a film for absorbing infrared rays emitted according to a surface temperature of a fixing member, and generating heat according to the amount of the absorbed infrared rays. The temperature detection device detects a surface temperature of the fixing member based on a value obtained by subtracting a temperature of an infrared absorbing film supporting member detected by one thermistor, from a temperature of the infrared absorbing film detected by another thermistor. More specifically, a surface temperature of the fixing member is determined based on a temperature difference between a detected temperature of the infrared absorbing film and a detected temperature of the supporting member, and the detected temperature of the infrared absorbing film, by referring to a data table. The temperature difference between the detected temperature of the infrared absorbing film and the detected temperature of the supporting member is calculated because an analog-to-direct (A/D) converter converts an output voltage of the thermistor element from an analog value to a digital value, and thereby the ability (resolution) to detect surface temperatures is restricted.
In this technique, the analog circuit is designed on the assumption that the temperature of the infrared absorbing film is higher than the temperature of the supporting member, and further, the data table is determined based on this assumption. Consequently, when the detected temperature of the thermistor provided on the infrared absorbing film is lower than the detected temperature of the thermistor provided on the supporting member, the device makes an incorrect decision that one of the thermistors is out of order. Consequently, when the temperature detected by the thermistor provided on the infrared absorbing film is lower than the temperature detected by the thermistor provided on the supporting member, the device may not detect the temperature of the fixing member.
For example, when the fixing member is replaced, the temperature of the infrared absorbing film rapidly decreases. On the other hand, the temperature of the holding member gradually decreases. That is, it is possible that, immediately after the replacement of the fixing member, the temperature detected by the thermistor provided on the infrared absorbing film may be lower than the temperature detected by the thermistor provided on the supporting member.
According to an aspect of the present invention, an image forming apparatus includes a fixing unit having a heater, and a fixing member configured to be heated by the heater. The fixing unit is configured to heat a recording material bearing an image using the fixing member so that the image is fixed on the recording material. Further, the image forming apparatus includes a film provided in non-contact with the fixing member. The film is configured to increase its temperature by absorbing infrared rays emitted from the fixing member. Further, the image forming apparatus includes a first sensor configured to measure a temperature of the film, a holding member configured to hold the film, a second sensor configured to measure a temperature of the holding member, a storage unit for storing a plurality of pieces of temperature determination information of different corresponding relations among information about measurement results of the first sensor and measurement results of the second sensor and the temperature of the fixing member, a selection unit configured to select temperature determination information for determining a temperature of the fixing member, based on the measurement results of the first sensor and the measurement results of the second sensor, from among the plurality of pieces of the temperature determination information stored in the storage unit, and a determination unit configured to determine a temperature of the fixing member using the temperature determination information selected by the selection unit, based on the measurement results of the first sensor and the measurement results of the second sensor.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
The first exemplary embodiment is described below.
A sheet cassette 17 stores a recording material S. Pickup rollers 18 and 19 are used to feed the recording material S stored in the sheet cassette 17. Vertical pass rollers 20 convey the recording material S. A manual feed tray 13 stores the recording material S such as paper. Pickup rollers 14 and 15 are used to feed the recording material S stored in the manual feed tray 13. Registration rollers 16 are used to adjust timing for sending the recording material S.
The printer 1 further includes a secondary transfer unit 22, a fixing unit 26, discharge rollers 24, and a discharge tray 25.
In the printer 1, on the photosensitive drums 2a to 2d, electrostatic latent images are formed by the laser scanning units 5a to 5d, and the electrostatic latent images are developed by the developing units 7a to 7d. The developing units 7a to 7d form toner images of the individual colors on the individual photosensitive drums 2a to 2d. The toner images of the individual colors developed on the photosensitive drums 2a to 2d are transferred onto the intermediate transfer belt 8, where the toner images of each color are superimposed to form a full-color toner image.
The recording material S is fed from the sheet cassette 17 or the manual feed tray 13, and its registration timing is adjusted by the registration rollers 16, and conveyed to the secondary transfer unit 22. A plurality of stepping motors drive a sheet conveyance unit including the pickup rollers 18 and 19 for feeding the paper from the sheet cassette 17, the vertical pass rollers 20, the registration rollers 16, and the pickup rollers 14 and 15 for feeding the paper from the manual feed tray 13.
The toner image on the intermediate transfer belt 8 and the recording material S pass through the secondary transfer unit 22 and thereby the toner image on the intermediate transfer belt 8 is transferred onto the recording material S. The recording material S on which the toner image is transferred is conveyed to the fixing unit 26. The fixing unit 26 conveys the recording material S carrying a toner image T while applying heat and pressure onto the recording material S to fix the toner image T on the recording material S. The recording material S on which the toner image T has been fixed is discharged from the printer 1.
The fixing unit 26 includes a pressure roller 32 for pressing the heating roller 31. The pressure roller 32 is formed, similarly to the heating roller 31, by forming a layer of a heat-resistant elastic member of silicone rubber, fluoro rubber, or the like on a core bar. The pressure roller (pressing member) 32 presses the heating roller (fixing member) 31 and thereby a nip portion is formed. The recording material S passes through the nip portion and the toner image T on the recording material S is heated and pressed, and thereby the toner image T is fixed onto the recording material S.
The heating roller 31 includes a heater 33 to heat the heating roller 31 from the inside. A temperature detection element 34 for detecting a surface temperature of the heating roller 31 is disposed in a noncontact manner at a position opposite to the heating roller 31. Based on an output signal from the temperature detection element 34, a power supply to the heater 33 is controlled such that a surface temperature of the heating roller 31 is maintained at a fixing temperature, or a standby temperature in a non-fixing state. On the heating roller 31, a thermoswitch 35 is provided in a noncontact manner to detect overheating. When overheating of the heating roller 31 is detected, power supply to the heater 33 is shut off.
With reference to
The infrared absorbing film 43 is a film member, and a temperature of the film increases according to an amount of the infrared rays absorbed by the film. A thermistor 44 is fixed on the infrared absorbing film 43 using an adhesive. Near the thermistor 44, a thermistor 45 for measuring an atmosphere temperature in the case 41 is provided. Lead wires 46 of the thermistor 44 and the thermistor 45 are respectively connected to sockets (not illustrated) provided in the case 41.
The thermistor 45 indicates a resistance value change according to temperatures (case temperatures) of the case 41 corresponding to ambient temperature of the temperature detection element 34. The thermistor 44 outputs a signal corresponding to a temperature (film temperature) of the infrared absorbing film 43 for absorbing infrared rays emitted from a measure target (heating roller 31). The temperature of thermistor 44 increases by the amount of the temperature increase due to the absorbed infrared rays, from the case temperature detected by the thermistor 45.
The thermistor 44 is connected with a resistance element R1 in series. The resistance element R1 is connected with a reference voltage Vref. With this configuration, a voltage at the contact point of the thermistor 44 and the resistance element R1 is output as a signal a (V_film) via an operational amplifier functioning serving as a voltage follower circuit 51.
Similarly, the thermistor 45 is connected with a resistance element R2 in series. The resistance element R2 is connected with the reference voltage Vref. With this configuration, a voltage at the contact point of the thermistor 45 and the resistance element R2 is output as a signal b (V_case) via an operational amplifier functioning as a voltage follower circuit 52. The resistance value of the thermistors 44 and 45 decreases as the detected temperature increases, and consequently, as the detected temperature increases, the output voltage (V_film, V_case) decreases.
A differential amplifier circuit 53 is an output circuit for outputting a signal c (V_def) generated by amplifying a difference value of an input V_case and an input V_film by 10 times. The difference between the output values of the thermistors 44 and 45 is amplified by the differential amplifier circuit 53 because the difference between the film temperature and the case temperature is very small.
The value of V_film is converted through analog to digital (A/D) conversion by an A/D conversion circuit 54, and the value of V_def is converted through A/D conversion by an A/D conversion circuit 55, respectively, and the values are input as digital signals to the CPU 57. The CPU 57 detects a temperature of the heating roller 31 when a film temperature is higher than a case temperature by referring to the data in
To components similar to those in the known temperature detection element 34 (
A difference between the temperature detection element 34 (
In this exemplary embodiment, the CPU 57 detects a surface temperature of the heating roller 31 based on a film temperature and a case temperature even if the case temperature is higher than the film temperature, that is, V_film is larger than V_case.
Hereinafter, a method of detecting a surface temperature of the heating roller 31 when V_film is larger than V_case is described.
In this exemplary embodiment, however, the CPU 57 detects a surface temperature of the heating roller 31 based on V_def and V_film when a film temperature is higher than a case temperature, that is, when V_film is smaller than V_case.
In other words, in a state of V_case≧V_film, that is, V_def<0, it is not possible to detect a roller temperature. Meanwhile, in the reversion table (
To solve the problem, in this exemplary embodiment, the CPU 57 selectively switches tables to be referred to depending on a difference (V_def) between V_film and V_case.
With reference to
In step S101, the CPU 57 starts the temperature detection, and in step S102, the CPU 57 determines whether V_def is larger than a threshold value Vth. The value of V_def is calculated by the following equation (1).
V_def=(V_case−V_film)×10 (1).
In step S102, if V_def>Vth (YES in step S102), the CPU 57 determines that V_film is sufficiently lower than V_case. That is, the CPU 57 determines that the film temperature is higher than the case temperature.
In step S103-1, the CPU 57 selects the data illustrated in
In step S102, if V_def≦Vth (NO in step S102), the CPU 57 determines that a difference between V_case and V_film is approximately zero, that is, there is substantially no difference between the case temperature and the film temperature, or determines that V_case is lower than V_film, that is, the case temperature is higher than the film temperature.
In this exemplary embodiment, in consideration of a detection error due to individual differences of the thermistors 44 and 45, and individual differences of the detecting circuit, the threshold value Vth is set to, for example, 0.5 [V]. Alternatively, the threshold value Vth can be set to zero.
In step S102, if V_def≦Vth, in step S103-2, the CPU 57 selects the data (reversion data) illustrated in
In the section A, the heating roller 31 was maintained at a fixing temperature (180° C.). In the section A, a film temperature of the temperature detection element 34 was about 140° C., a case temperature was about 100° C., and a differential amplification detected value V_def was (V_case−V_film)×10=V_def>Vth. In this case, the CPU 57 selected the normal data (
Next, a case where replacement operation of the heater 33 was started, and the operation was completed in a very short time is described. When the replacement operation of the heating roller 31 was completed in the section B from time T1 to time T2, a temperature of the new heating roller 31 was about a room temperature. However, the case temperature decreased to only around 80° C. At that time, differential amplification detected value V_def was (V_case−V_film)×10=Vth. In this case, the CPU 57 selected the reversion data (
Since the resolution of the temperature data table (
In the section C, as the roller temperature gradually increased, the film temperature increased, and at time T3, the temperature became (V_case−V_film)×10=V_def>Vth. Then, the CPU 57 selected the normal data (
In this exemplary embodiment, the heating roller 31 can be replaced as described above. Also in a structure where the heater 33 can be replaced, a similar problem may occur. That is, when the heater 33 is replaced and the CPU 57 detects that the case temperature is higher than the film temperature, according to the exemplary embodiment, the surface temperature of the heating roller 31 can be accurately detected.
In the temperature detection processing in
Alternatively, for example, a configuration which determines whether V_case is a predetermined value or more larger than V_film can be employed. In such a configuration, if V_case is the predetermined value or more larger than V_film, based on V_def and V_film, the CPU 57 detects a temperature of the heating roller 31. On the other hand, if V_case is not the predetermined value or more larger than V_film, based on V_film and V_case, the CPU 57 detects a temperature of the heating roller 31.
According to the present exemplary embodiment, even if the temperature of the film is lower than the temperature of the sensor itself, the temperature of the fixing member can be accurately detected. For example, when the fixing member is replaced, the temperature of the fixing member can be accurately detected.
Hereinafter, the second exemplary embodiment is described. In the first exemplary embodiment, after a difference (Vdef) between a case temperature and a film temperature becomes larger than the threshold value, when the temperature difference (Vdef) becomes smaller than the threshold value again, the CPU 57 determines a temperature of the heating roller 31 using the second table. In this exemplary embodiment, after a difference (Vdef) between a case temperature and a film temperature becomes larger than a threshold value, even if the temperature difference (Vdef) becomes smaller than the threshold value, the CPU 57 determines a temperature of the heating roller 31 using the first data table. For this purpose, the first data table includes data of V_def showing values under Vth. When the heating roller 31 is replaced, the CPU 57 determines whether a difference (Vdef) between a film temperature and a case temperature is larger than the threshold value. If the difference (Vdef) between the film temperature and the case temperature is larger than the threshold value, the CPU 57 determines a temperature of the heating roller 31 using the second data table again.
In the section E, the temperature of the heating roller 31 was maintained at a fixing temperature (180° C.). In the section E, a film temperature of the temperature detection element 34 was about 140° C., a case temperature was about 100° C., and a differential amplification detected value V_def was larger than a threshold value Vth. (V_case−V_film)×10=V_def>Vth.
In such a case, in the first exemplary embodiment, and in this exemplary embodiment, the CPU 57 selected the first data table (
At the timing T4, a printing operation was started. By this operation, the pressure roller 32 was pressed against the heating roller 31. At this time, the temperature of the pressure roller 32 was lower than the temperature of the heating roller 31. At the section F, the thick paper passed through the fixing unit 26, and the temperature of the heating roller 31 further decreased.
In section F, the film temperature decreased to about 90° C. Meanwhile, the case temperature decreased to only around 95° C. Consequently, the case temperature was higher than the film temperature. As a result, a differential amplification detected value V_def was (V_film−V_case)×10=V_def≦Vth. In the first exemplary embodiment, the CPU 57 selects the second data table (
The resolution of the second data table (
In the section H, the temperature of the heating roller 31 increased, and at time T6 the film temperature became higher than the case temperature, (V_case−V_film)×10=V_def>Vth. In the first exemplary embodiment, the CPU 57 selects the first data table (
In this exemplary embodiment, after a differential amplification detected value V_def becomes lower than the threshold value Vth, when once the differential amplification detected value V_def becomes higher than the threshold value Vth, based on the first data table (
By this operation, as illustrated in
In this exemplary embodiment, the heating roller 31 can be replaced. Also in a structure where the heater 33 can be replaced, a similar problem may occur. That is, when the heater 33 is replaced and the CPU 57 detects that the case temperature is higher than the film temperature, according to the exemplary embodiment, the surface temperature of the heating roller 31 can be accurately detected.
In the second exemplary embodiment, whether the differential amplification detected value V_def is larger than the threshold value Vth is determined. Alternatively, for example, whether V_case is larger than V_film can be determined. In such a case, if V_case is larger than V_film, the CPU 57 determines that the film temperature is higher than the case temperature, and based on V_def and V_film, the CPU 57 detects a temperature of the heating roller 31. On the other hand, if V_case is not larger than V_film, the CPU 57 determines that the film temperature is lower than the case temperature, and based on V_film and V_case, the CPU 57 detects a temperature of the heating roller 31.
Alternatively, for example, a configuration which determines whether V_case is a predetermined value or more larger than V_film can be employed. In such a configuration, if V_case is the predetermined value or more larger than V_film, based on V_def and V_film, the CPU 57 detects a temperature of the heating roller 31. On the other hand, if V_case is not the predetermined value or more larger than V_film, based on V_film and V_case, the CPU 57 detects a temperature of the heating roller 31.
According to the present exemplary embodiment, after a surface temperature of the heating roller 31 decreases, even in a transition period during which a difference (Vdef) between a case temperature and a film temperature becomes larger or smaller than the threshold value, it can be prevented that the surface temperature of the heating roller 31 changes stepwise.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-008935 filed Jan. 21, 2014, and No. 2014-255164 filed Dec. 17, 2014 which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2014-008935 | Jan 2014 | JP | national |
2014-255164 | Dec 2014 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
7062187 | Peng et al. | Jun 2006 | B2 |
7668473 | Nakajima et al. | Feb 2010 | B2 |
7778564 | Sone et al. | Aug 2010 | B2 |
8509666 | Kobayashi et al. | Aug 2013 | B2 |
8718502 | Yuasa et al. | May 2014 | B2 |
Number | Date | Country |
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2003-57116 | Feb 2003 | JP |
Number | Date | Country | |
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20150205236 A1 | Jul 2015 | US |