Patent Application
20190033142
The present invention relates to a temperature detection circuit using a thermistor that can detect a temperature of, for example, a fuser roller or the like with high accuracy.
Conventionally, a thermistor is used as a temperature sensor for measuring a temperature of an object to be measured such as a fuser roller or the like used in a copying machine, printer, or the like by detecting infrared radiation radiated from the object in a non-contact manner. In order to measure a temperature of a fuser roller or the like using such a thermistor, an apparatus uses a temperature detection circuit for detecting a temperature of the fuser roller or the like based on an output of the thermistor. Especially, since the operation of the apparatus must be stopped when the fuser roller or the like is heated to an abnormal temperature, a high-accuracy temperature detection circuit has been demanded.
For example, Patent document 1 discloses a technology using a temperature detection circuit configured to detect the surface temperature of a fuser roller based on an output of a non-contact temperature sensor. Specifically, in this temperature detection circuit, an operational amplifier receives outputs each corresponding to the voltages VDET and VREF of a detection-side heat sensitive element and a compensation-side heat sensitive element respectively, and then performs an arithmetical operation of these outputs so as to provide a differential output VDIF (VDET−VREF). That is, this circuit detects the differential output VDIF as an output corresponding to the surface temperature of the fuser roller that is offset by the effect of an ambient temperature.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2008-111849 (see FIG. 6)
The following problems still remain in the conventional technologies described above.
In a conventional temperature setting circuit, when the change in a differential output VDIF relative to a compensation temperature is small, the influence by a conversion error of an AD converter configured to convert outputs into digital values is problematically increased, which causes a temperature calculation error of an object to be measured to become large. Specifically, if the differential output VDIF is similar at low and high temperatures and when the change in the differential output VDIF is small, an error caused depending on the resolution of an AD converter may have a great influence on the calculated temperature of an object to be measured.
The present invention has been made in view of the aforementioned circumstances, and an object of the present invention is to provide a temperature detection circuit that can detect a temperature of an object to be measured with high accuracy even when the change in a differential output VDIF relative to a compensation temperature is small.
The present invention adopts the following configuration in order to overcome the aforementioned problems. Specifically, a temperature detection circuit according to a first aspect of the present invention comprises: a differential output detection circuit portion having a thermistor for detection (hereafter referred to as “detection thermistor”) and a thermistor for compensation (hereafter referred to as “compensation thermistor”) configured to amplify a difference between an output of the detection thermistor and an output of the compensation thermistor and to detect it as a first differential output; a second differential amplifier portion configured to amplify a difference between the first differential output and the output of the compensation thermistor and to output it as a second differential output; and an AD converter portion configured to convert the output of the compensation thermistor and the second differential output into digital values.
Since the temperature detection circuit of the first aspect comprises the second differential amplifier portion configured to amplify a difference between the first differential output and the output of the compensation thermistor and to output it as a second differential output, the second differential output can be amplified by the second differential amplifier portion so that the change in the differential output relative to the compensation temperature becomes large even when the change is small, and thus the influence by an error caused during digital conversion by the AD converter portion can be reduced. Accordingly, a temperature of an object to be measured can be calculated with high accuracy from the output of the compensation thermistor and the second differential output both of which has been digitally converted.
A temperature detection circuit according to a second aspect of the present invention is characterized by the temperature detection circuit according to the first aspect, wherein the second differential amplifier portion can adjust the input level of the output of the compensation thermistor using a voltage divider circuit composed of two resistances.
Specifically, in this temperature detection circuit, the second differential amplifier portion can adjust the input level of the output of the compensation thermistor using a voltage divider circuit composed of two resistances, the input level of the output of the compensation thermistor can be readily changed based on the resistance ratio of the two resistances.
An temperature detection circuit according to a third aspect of the present invention is characterized by the temperature detection circuit according to the first or second aspect, wherein the detection thermistor is a temperature sensor for measuring a temperature of a fuser roller used in an image-forming apparatus.
Specifically, in this temperature detection circuit, since the detection thermistor is a temperature sensor for measuring a temperature of a fuser roller used in an image-forming apparatus, a temperature of the fuser roller can be detected with high accuracy, and thus the high-temperature anomaly of the fuser roller can be detected so as to stop the heating of the roller.
According to the present invention, the following effects may be provided.
Specifically, since the temperature detection circuit according to the present invention includes the second differential amplifier portion configured to amplify a difference between the first differential output and the output of the compensation thermistor and to output it as a second differential output, the influence by an error caused during digital conversion can be reduced even when the change in the differential output is small. Accordingly, a temperature of an object to be measured can be calculated with high accuracy.
In particular, when the detection thermistor is used as a temperature sensor for measuring a temperature of a fuser roller used in an image-forming apparatus, a temperature of a fuser roller can be detected with high accuracy, and thus the high-temperature anomaly of the fuser roller can be detected so as to stop the heating of the roller.
Hereinafter, a temperature detection circuit according to one embodiment of the present invention will be described with reference to
A temperature detection circuit 1 of the present embodiment is a circuit for detecting the high-temperature anomaly of, for example, a fuser roller used in an image-forming apparatus, which, as shown in
The second differential amplifier portion C2 can adjust the input level of the output of the compensation thermistor TH2 using a voltage divider circuit composed of two resistances R12 and R13. Specifically, the input level of the output of the compensation thermistor TH2 can be adjusted by dividing the voltage between a power source V1 and ground using two resistances R12 and R13.
The detection thermistor TH1, which is a non-contact temperature sensor that can receive infrared radiation so as to detect a temperature, is arranged opposed to a fuser roller that is an object to be measured so that it can receive infrared radiation radiated from the fuser roller so as to detect a temperature of the fuser roller.
The compensation thermistor TH2 has the same configuration as that of the detection thermistor TH1, but it can detect an ambient temperature (compensation temperature) by blocking the infrared radiation radiated from the fuser roller.
In addition, both of the detection thermistor TH1 and the compensation thermistor TH2 are NTC thermistor elements.
The differential output detection circuit portion C1 includes a bridge circuit portion B1 composed of the detection thermistor TH1, the compensation thermistor TH2, a resistance R1, a resistance R2, and a resistance R3; a buffer portion B2 configured to receive a compensation thermistor voltage VREF from the bridge circuit portion B1 and to output the compensation thermistor voltage VREF with a gain of 1; and a first differential amplifier portion B3 configured to receive the compensation thermistor voltage VREF through the buffer portion B2 and a detection thermistor voltage VDET directly from the detection thermistor so as to amplify the difference (VDET−VREF) and to output a first differential voltage VDIF as a differential output.
The buffer portion B2 is an impedance converting circuit for reducing the output resistance of the compensation thermistor voltage VREF.
The gain of the first differential voltage VDIF depends on the ratio of “resistance R8/resistance R7”.
In the second differential amplifier portion C2, a first differential voltage VDIF, which is an output from an operational amplifier U1 of a first differential amplifier portion B3, is input into the non-inverting input terminal of an operational amplifier U3, and the compensation thermistor voltage VREF is input into the inverting input terminal. Furthermore, a second differential voltage VDIF2 that has been amplified by the operational amplifier U3 is output from there.
The AD converter portion C3 converts the second differential voltage VDIF2 that has been output and the compensation thermistor voltage VREF into digital values VDIF2-D and VREF-D respectively and outputs them.
Note that, in order to prevent saturation of the second differential voltage VDIF2 due to the temperature condition of an object to be measured, the resistance constants of the resistances R9 to R14 are adjusted.
As described above, since the temperature detection circuit 1 of the present embodiment includes the second differential amplifier portion C2 configured to amplify a difference between the first differential output VDIF and the output of the compensation thermistor TH2 and to output it as a second differential output, the second differential output can be amplified by the second differential amplifier portion C2 so that the change in the differential output relative to the compensation temperature becomes large even when the change is small, and thus the influence by an error caused during digital conversion by the AD converter portion C3 can be reduced.
Accordingly, a temperature of an object to be measured can be calculated with high accuracy from the compensation thermistor voltage VREF-D and the second differential voltage VDIF2-D both of which have been digitally converted.
In particular, when the detection thermistor TH1 is used as a temperature sensor for measuring a temperature of a fuser roller used in an image-forming apparatus, a temperature of a fuser roller can be detected with high accuracy, and thus the high-temperature anomaly of the fuser roller can be detected so as to stop the heating of the roller.
Furthermore, since the second differential amplifier portion C2 can adjust the input level of the output of the compensation thermistor TH2 using a voltage divider circuit composed of two resistances R12 and R13, the input level of the output of the compensation thermistor TH2 can be readily changed based on the resistance ratio of two resistances R12 and R13.
The temperature detection circuit 1 of the present embodiment was examined for the change in a differential output voltage (second differential voltage VDIF2) relative to a compensation temperature (temperature detected by the compensation thermistor TH2). In addition, a reference circuit without the second differential amplifier portion C2 shown in
In the case of the reference circuit without the second differential amplifier portion C2, the change in the differential output voltage (differential voltage VDIF) relative to the compensation temperature can be small as shown in
In addition, the physical quantity to be detected with high accuracy in the detection circuit according to the Reference Example of the present embodiment and the detection circuit of the present embodiment is an analog output (VDIF) resulting from the thermistor voltage that is output from the differential output detection circuit. Therefore, in the present embodiment, when VDIF calculated from the differential output voltages after AD conversion (VDIF2-D and VREF-D) is defined as VDIF-CALC (the present embodiment), a temperature of an object calculated from an output signal of each detection circuit is influenced mainly by the difference between VDIF and VDIF-D in the Reference Example and the difference between VDIF and VDIF-CALC in the present embodiment, wherein ΔV1 and ΔV2 are defined as difference amounts expressed by the equations of “ΔV1=VDIF−VDIF-D” and “ΔV2=VDIF−VDIF-CALC”, respectively.
As compared with the detection circuit according to the Reference Example of the present embodiment (ΔV1), the detection circuit of the present embodiment (ΔV2) indicates smaller values over the entire range of the compensation temperature that was examined this time. This result shows that, VDIF-CALC calculated from the voltages after AD conversion (VREF-D and VDIF2-D) has a small error in the detection circuit of the present embodiment compared to the analog output (VDIF) resulting from the thermistor voltage that is output from the differential output detection circuit. Accordingly, a temperature of an object can be detected with high accuracy in the detection circuit of the present embodiment.
Furthermore, a temperature of an object to be measured calculated from the differential voltage VDIF-D and the compensation thermistor voltage VREF-D both of which have been digitally converted in the reference circuit described above and a temperature of an object to be measured calculated from the second differential voltage VDIF2-D and the compensation thermistor voltage VREF-D both of which have been digitally converted in the temperature detection circuit 1 of the present embodiment were analyzed when the temperature of an object to be measured was set to be 100° C. and 150° C. so as to examine the detection temperature errors relative to the compensation temperatures (25° C., 50° C., 75° C., and 100° C.). The results are shown in Table 1.
Note that the above examination was performed under the condition that the resolution of the AD converter portion C3 was 10-bit and the conversion error was ±3 LSB.
T
These results show that since the temperature detection circuit 1 of the present embodiment has a small detection temperature error compared with the reference circuit, the influence by a conversion error of the AD converter portion C3 is reduced, and therefore the temperature calculation error of an object is suppressed.
The technical scope of the present invention is not limited to the aforementioned embodiments, but the present invention may be modified in various ways without departing from the scope or teaching of the present invention.
1: temperature detection circuit, C1: differential output detection circuit portion, C2: second differential amplifier portion, C3: AD converter portion, TH1: detection thermistor, TH2: compensation thermistor
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-013277 | Jan 2016 | JP | national |
| 2016-149924 | Jul 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/002935 | 1/27/2017 | WO | 00 |
