JP2012093613A - Temperature controller for fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature controller for fixing devices that can provide calculated temperature values so that control of the whole printing apparatus is not affected even if its differential amplifier is caused to operate erroneously by noise or the like, to output abnormal values and to become temporarily incapable of temperature calculation.SOLUTION: A temperature controller comprising a first thermistor, a second thermistor, a circuit that obtains voltages based on the respective resistances of the two thermistors, and a differential amplifier that figures out the difference between the two voltages enables, even if the output of the differential amplifier is temporarily destabilized by the influence of noise or the like, temperature values to be calculated as an emergency measure on the basis of the resistances of the first and second thermistors inputted to the differential amplifier.

Description

  One embodiment of the present invention relates to a temperature control device for a fixing device used in a printing device or the like. In particular, the temperature of a heat source such as a heating roller is detected using a plurality of non-contact thermistors, and according to the detection result. The present invention relates to a temperature control device that controls a heat source to an appropriate temperature.

  2. Description of the Related Art Conventionally, in so-called electrophotographic image forming apparatuses, image formation is performed by forming a toner image on a photosensitive drum as an image carrier and transferring the toner image to a sheet material to form an image on the surface of the sheet material. And a fixing unit for heating and fixing the toner image formed on the sheet material on the downstream side thereof to weld and fix the toner on the surface of the sheet material.

  In the fixing unit, it is necessary to accurately control the temperature of a heating unit such as a pair of heating rollers that include a heating unit such as a heater and sandwich and convey the sheet material so that a certain amount of heat is transmitted to the sheet material. For example, in order to measure and manage the temperature of such a heating unit, a thermistor as a temperature detection sensor is disposed near the heating unit of the sheet material. The temperature of the heating unit is detected by detecting the temperature of the heating unit using the fact that the resistance value of the thermistor changes depending on the temperature of the heating unit.

  As a temperature sensor using such a thermistor, for example, Patent Document 1 discloses a non-contact temperature sensor. In addition, in order to prevent the surface of the heating roller from deteriorating due to friction between the thermistor and the surface of the heating roller, a fixing device is disclosed that detects the surface temperature of the heating roller in a non-contact manner using an infrared sensor.

JP 2006-098067 A JP 2008-0707039 A

However, for example, in the configuration shown in Patent Document 2, when a non-contact thermistor is controlled, a differential amplifier is generally used in a circuit to handle a minute voltage. Since it is amplified, it tends to malfunction due to noise and other factors.
For this reason, when an abnormal value of the differential amplifier is detected, the correct temperature cannot be calculated, which hinders the overall control, and it is necessary to provide an expensive noise removal circuit.

  In one embodiment of the present invention, even if the differential amplifier malfunctions due to noise or the like, the output becomes an abnormal value, and the temperature calculation is temporarily disabled, the temperature calculation is performed so as not to affect the control of the entire printing apparatus. The present invention provides a temperature control device for a fixing device that can provide a value.

  According to the first aspect of the present invention, the infrared absorbing member heated by radiant heat from the heating element, the first thermistor for measuring the temperature of the infrared absorbing member, and the temperature near the first thermistor are measured. A temperature sensor comprising a second thermistor; a ground circuit for connecting one terminal of the first thermistor and one terminal of the second thermistor to a ground potential; the first thermistor and the second thermistor; A power supply circuit for connecting the other terminal of the thermistor to a constant voltage power supply via a predetermined resistor, a first extraction circuit for extracting a first voltage based on the resistance value of the first thermistor, and the second A second extraction circuit for extracting a second voltage based on the resistance value of the thermistor, differential amplification means for amplifying a difference between the first voltage and the second voltage, and an output of the differential amplification means. Z Processing means for calculating the temperature of the heating element and controlling the driving of the heating element based on the calculation result, and the output of the differential amplifier is a value outside a preset range When identified, the processing means calculates a temperature of the heating element based on the first voltage and the second voltage, and controls driving of the heating element based on the calculation result. This can be achieved by providing a temperature control device for a fixing device.

  According to a second aspect of the present invention, in the temperature control device for a fixing device according to the first aspect, when a state where the output of the differential amplifier deviates from a numerical value within a preset range continues for a predetermined time, This can be achieved by providing notifying means for notifying the temperature abnormality of the heating element.

  According to a third aspect of the present invention, there is provided the temperature control device for a fixing device according to claim 1, wherein the processing means includes a temperature value calculated based on an output of the differential amplifier, and the first voltage. And when there exists a more than predetermined difference between the temperature value calculated based on the 2nd voltage, it can achieve by providing the alerting | reporting means which alert | reports the temperature abnormality of the said heat generating body.

  According to an embodiment of the present invention, even when a differential amplifier malfunctions due to noise or the like, an output becomes an abnormal value, and temperature calculation is temporarily disabled, control of the entire printing apparatus is not affected. Temperature calculated value can be provided.

1 is a cross-sectional view illustrating an internal configuration of a color printing apparatus including a temperature control device for a fixing device in an embodiment of the present invention. 2 shows an internal configuration of a fixing unit according to an embodiment of the present invention. The block diagram of the control apparatus which concerns on one Embodiment of this invention is shown. It is a figure which shows the structure of the non-contact temperature sensor which comprises the temperature control apparatus of the fixing device based on one Embodiment of this invention. FIG. 3 is a circuit diagram of a non-contact temperature sensor constituting a temperature control device of a fixing device according to an embodiment of the present invention. FIG. 6 is an operation flowchart of a CPU for realizing temperature control of the fixing device according to an embodiment of the present invention. FIG. 6 is an operation flowchart of a CPU for realizing abnormality notification processing performed in a temperature control operation of the fixing device according to an embodiment of the present invention.

  Hereinafter, a temperature control device for a fixing device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating an internal configuration of a color printing apparatus (hereinafter simply referred to as a printer apparatus) provided with a temperature control device for a fixing device according to an embodiment of the present invention.

  A printer apparatus 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color printer, and includes an image forming unit 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a duplex printing transport unit 5. It is configured.

  The image forming unit 2 has a configuration in which four image forming units 6 (6M, 6C, 6Y, 6K) are arranged in a multistage manner from right to left in FIG. The three image forming units 6M, 6C, and 6Y on the upstream side (the right side in the figure) of the four image forming units 6 are magenta (M) and cyan (C), which are subtractive three primary colors, respectively. A mono-color image is formed using yellow (Y) color toner, and the image forming unit 6K forms a monochrome image mainly using black (K) toner used for dark portions of characters and images.

  Each of the image forming units 6 has the same configuration except for the color of the toner stored in the toner container (toner cartridge). Accordingly, the configuration of the black (K) image forming unit 6K will be described below as an example.

  The image forming unit 6 includes a photosensitive drum 7 at the bottom. The peripheral surface of the photosensitive drum 7 is made of, for example, an organic photoconductive material. A cleaner 8, a charging roller 9, an optical writing head 11, and a developing roller 13 of the developing device 12 are arranged around the periphery of the photosensitive drum 7.

  The optical writing head 11 exposes an optical image corresponding to image information input from the outside via an interface (not shown) on the surface of the photosensitive drum 7 to form an electrostatic latent image. The optical writing heads 11 in the image forming units 6M, 6C, 6Y, and 6K are supplied with driving signals based on data corresponding to colors of magenta, cyan, yellow, and black among image information input from the outside, respectively. A light image corresponding to each color is exposed to form a latent image.

  The developing device 12 puts one of magenta (M), cyan (C), yellow (Y), and black (K) toners in the upper toner container as indicated by M, C, Y, and K in the drawing. An intermediate portion is provided with a toner replenishing mechanism for the lower portion.

  In addition, the developing roller 13 is provided in the lower portion of the developing device 12 at the side opening, and includes a toner stirring member, a toner supply roller for supplying toner to the developing roller 13, and a toner layer on the developing roller 13 as a fixed layer. It has a doctor blade that regulates the thickness.

  The toner layers of the respective colors formed on the surface of the developing roller 13 are close to the vicinity of the surface of the photosensitive drum 7 on which the latent image is formed, and the toner of each developing device according to the electric attractive force of the electrostatic latent image. A toner based on color is adhered to form a toner image on the surface of the photosensitive drum 7.

  The intermediate transfer belt unit 3 has an endless transfer belt 14 arranged in a flat loop shape from substantially the left and right sides of the drawing at the center of the main body device, and the transfer belt 14 is stretched over the transfer belt 14. A driving roller 15 and a driven roller 16 are provided to circulate and move the belt 14 counterclockwise in the drawing.

  The transfer belt 14 transfers Y, M, C, and K toner images formed on the surface of the photosensitive drum 7 in the image forming unit 6 provided for each toner color for each color image forming unit. The toner images of all the colors are transferred to the belt surface (primary transfer) while being aligned so that the positions of all the color toner images overlap each other, and the combined toner image is further transferred to the paper (secondary transfer). Since the intermediate toner image is conveyed to the transfer position while being held, the entire unit including the transfer belt 14 is referred to as an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 17 in the loop of the flat loop-shaped transfer belt 14. The belt position control mechanism 17 includes a primary transfer roller 18 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 7 via the transfer belt 14, and transfers a toner image formed on the surface of the photosensitive drum 7. In order to transfer to the belt 14 side, a high voltage is applied to the primary transfer roller 18.

  The belt position control mechanism 17 supports the three primary transfer rollers 18 corresponding to the three image forming units 6M, 6C, and 6Y of magenta (M), cyan (C), and yellow (Y) in a bowl shape. The color transfer mechanism can be switched between an active state and an inactive state by the structure in which the transfer belt 14 is separated from and contacted with the color photosensitive drum 7 by being configured to be rotationally movable at the same period around the axis.

  Then, the belt position control mechanism 17 rotates and moves one primary transfer roller 18 corresponding to the black (K) image forming unit 6K at a rotational movement cycle different from the cycle of the three primary transfer rollers 18. By providing a mechanism for separating the belt 14 from the photosensitive drum 7, only the K (black) color transfer mechanism can be switched to the active / inactive state independently.

  That is, the belt position control mechanism 17 sets the position of the transfer belt 14 of the intermediate transfer belt unit 3 in the full color mode (all four primary transfer rollers 18 are in contact with the transfer belt 14) and the monochrome mode (corresponding to the image forming unit 6K). Only the primary transfer roller 18 is in contact with the transfer belt 14) and all non-transfer modes (all four primary transfer rollers 18 are separated from the transfer belt 14), and the printer apparatus 1 performs the recording process. If not, the transfer belt 14 is disconnected from all the image forming units 6 in the all non-transfer mode state, and when the printer apparatus 1 is in the monochrome print processing state, the full belt mode is switched to the full color mode position. The relationship between the transfer belt 14 and the image forming units 6M, 6C, and 6Y for color printing is cut off. Has a configuration to prevent the exhaustion due to contact abrasion of the transfer belt 14 and the photosensitive drum 7.

  The intermediate transfer belt unit 3 is provided with a belt cleaner unit 35 for removing useless toner remaining on the surface of the transfer belt 14 further upstream of the uppermost image forming unit 6M on the upstream side in the belt movement direction. In order to store the waste toner removed by the belt cleaner unit, a flat and thin waste toner collection container 19 is detachably disposed so as to be substantially along the entire lower surface of the transfer belt 14.

  The paper feed unit 4 includes two paper feed cassettes 21 arranged in two upper and lower stages, and in the vicinity of the paper feed opening (right side in the figure) of the two paper feed cassettes 21, respectively, A feeding roller 23, a separating roller 24, and a standby conveying roller pair 25 are disposed.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 25, a secondary transfer roller 26 that is pressed against the driven roller 16 via the transfer belt 14 is disposed to form a secondary transfer portion to the paper. is doing.

  A fixing unit 27 is disposed on the downstream side (upward in the drawing) of the secondary transfer unit, and on the further downstream side of the fixing unit 27, a pair of carry-out rollers 28 for carrying out the sheet after fixing from the fixing unit 27, and its A pair of paper discharge rollers 31 is provided for discharging the discharged paper to a paper discharge tray 29 formed on the upper surface of the apparatus.

  The duplex printing conveyance unit 5 includes a start return path 32a that branches from the intermediate conveyance path between the carry-out roller pair 28 and the discharge roller pair 31 to the right lateral direction in the drawing, and then an intermediate return path 32b that bends downward. A terminal return path 32c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and four return roller pairs 33a, 33b, 33c, and 33d disposed in the middle of these return paths. ing.

  The exit of the end return path 32 c communicates with a conveyance path to the pair of standby conveyance rollers 25 corresponding to the sheet feeding cassette 21 below the sheet feeding unit 4. In this example, a belt cleaner unit 35 including a blade that slides on the surface of the transfer belt 14 and a take-in roller 36 is disposed on the upper surface of the intermediate transfer belt unit 3.

  The printer apparatus 1 of this example is a system in which a toner image is transferred via an intermediate transfer belt 14 to a sheet that is vertically conveyed to a secondary transfer portion by a standby conveyance roller pair 25. Therefore, it is possible to cope with the maintenance process for recovering from a problem such as a paper jam occurring in the paper transport path by simply opening the right side of FIG.

  FIG. 2 shows an internal configuration of the fixing unit 27 in the present embodiment. FIG. 2A is a diagram showing details of the fixing unit 27 which is the main part of the present example in the above-described configuration, and FIG. 2B shows only each of the related rollers. 2A and 2B, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

  FIG. 2A shows the paper transport unit 38, the intermediate transfer belt unit 3, the secondary transfer roller unit 39, and the fixing unit 27 that are provided along the paper transport direction (from bottom to top).

  The paper transport unit 38 includes the paper take-out roller 22, the feeding roller 23, the separating roller 24, and the standby transport roller pair 25 described with reference to FIG. 1, and other units (intermediate transfer belt unit) by the standby transport roller pair 25. 3) is formed in cooperation with (3).

  The intermediate transfer belt unit 3 forms a paper transport system that cooperates with the other units (the paper transport unit 38 and the fixing unit 27) in cooperation with the secondary transfer roller unit 39.

  The fixing unit 27 is a belt-type fixing unit. The fixing unit 27 is opposed to the fixing roller 41 through the fixing belt 42, the guide plates 30 a and 30 b, the heating roller 40, the fixing roller 41, an endless fixing belt 42 spanned between the heating roller 40 and the fixing roller 41. And a pressure roller 43 that presses the fixing roller 41 and the fixing belt 42, and the fixing roller 41 and the pressure roller 43 provide a paper conveyance system that cooperates with other units (intermediate transfer belt unit 3). Forming.

  The fixing unit 27 melts and fixes the toner image on the paper to the paper by applying heat and pressure. The fixing system is a system in which the heat of the heating roller 40 heated by the halogen heaters 44 and 45 is transferred to the fixing roller 41 by the fixing belt 42 and pressed by the fixing roller 41 and the pressure roller 43. Note that the pressing force on the pressure roller 43 side has a function to vary depending on the type of paper.

  FIG. 2B shows the rollers related to the sheet conveyance accuracy of the above components, that is, the standby conveyance roller pair 25 of the sheet conveyance unit 38, the driven roller 16 of the intermediate transfer belt unit 3, and the secondary transfer roller unit 39. Only the next transfer roller 26 and the fixing roller 41 and the pressure roller 43 of the fixing unit 27 are taken out.

  In order to monitor the surface temperature of the fixing belt 42 on the heating roller 40, a temperature sensor 53 is attached. The temperature sensor 53 may or may not be in contact with the fixing belt 42 depending on the type and design specifications of the sensor. However, in one embodiment of the present invention described below, the non-contact type The temperature sensor will be described as an example.

The non-contact type temperature sensor 53 used in the present invention detects the surface temperature of the fixing belt 42 by detecting infrared rays radiated from the surface of the fixing belt 42 heated by the heating roller 40. An infrared detection thermistor T1 and a temperature compensation thermistor T2 are provided inside. The infrared detecting thermistor T1 detects the temperature of the infrared absorbing film heated by the infrared rays radiated from the surface of the fixing belt 42, and the output voltage depends on the ambient temperature. In order to compensate for such temperature dependence, it is necessary to detect the temperature of the infrared detection thermistor T1 itself. For this reason, the temperature compensation thermistor T2 is disposed in the vicinity of the infrared detection thermistor T1 at a position not affected by the infrared rays radiated from the surface of the fixing belt 42, and heating is performed by detecting the potentials at both ends of these two thermistors. The temperature of the surface of the fixing belt 42 heated by the roller 40 can be grasped.
The average value of the potential difference between the two thermistors is converted into a digital value by an A / D converter built in the CPU 49, and the converted digital value is input by the CPU 49 executing a predetermined program. The surface temperature of the fixing belt 42 is obtained based on the digital value and a predetermined table, and energization control of the heater 1 and the heater 2 included in the heating roller 40 is performed so that the surface temperature is maintained constant. The specific control method will be described in detail below.

  FIG. 3 is a block diagram of the control device 47 of the printer apparatus 1 according to this embodiment.

  The control device 47 includes a CPU 49 that controls the entire printer apparatus 1 according to a control procedure stored in a read-only memory (ROM) 48, a read-only memory (ROM) 48 that stores a control procedure (control program) of the control device 47, and the like. A random access memory (RAM) 51 which is a main storage device used as a storage area for input data, a working storage area, etc., a control signal output from a CPU 49 for a load such as a main motor, and a sensor input signal are input. And an interface unit (I / O) 52 to be sent to the CPU 49.

  Then, signals of various devices provided in the printer device 1 or connected to the printer device 1 are transmitted to the CPU 49 via the I / O 52. Examples of various apparatus signals include sorter control, paper jam detection, sheet material conveyance control, and the like. Further, the RAM 51 may optionally record data of voltage values representing a normal range of an output (Vdef) of a differential amplifier 56 described later.

  FIG. 4 is a diagram illustrating a configuration of a temperature control device of the fixing device using the non-contact temperature sensor 53 according to an embodiment of the present invention. In FIG. 4, the non-contact temperature sensor 53 includes two thermistors, a detection thermistor T <b> 1 and a compensation thermistor T <b> 2. The thermistor for detection is in contact with the infrared absorbing film 54 and is used for detecting the temperature of the heating roller 40. The infrared ray absorbing film 54 absorbs the infrared ray 50 from the heating roller 40 and converts it into heat energy, and the heat is detected by the detection thermistor T1. On the other hand, the compensation thermistor T2 is used to detect the temperature of the non-contact temperature sensor 53 itself. The temperature of the heating roller 40 is calculated by using the resistance value changed by the detection temperature of the detection thermistor T1 and the resistance value changed by the detection temperature of the compensation thermistor T2.

FIG. 5 is a circuit diagram of a temperature control device for a fixing device using the non-contact temperature sensor 53 according to an embodiment of the present invention. Two thermistors T1 and T2 incorporated in the non-contact temperature sensor 53 are connected to a power source (5V) by resistors R2 and R1, respectively, and a common terminal is connected to GND.
R2 and R1 are resistance elements having substantially the same resistance value. For example, both have a resistance value of 33 KΩ here. The resistance values of the detection thermistor T1 and the compensation thermistor T2 shown in FIG. 5 vary in the range of several K to several MΩ depending on the temperature, for example, the resistance value increases as the temperature decreases (for example, It has a resistance value of about 1 MΩ at a low temperature around 0 ° C.). The compensation voltage V2 applied between the resistor R2 and the compensation thermistor T2 is input to the plus terminal 57 of the differential amplifier 56 and also to the V2 value terminal at the A / D converter port of the CPU 49. On the other hand, the detection voltage V1 applied between the resistor R1 and the detection thermistor T1 is input to the minus terminal 58 of the differential amplifier 56 and also to the V1 value terminal in the A / D converter port of the CPU 49. Further, an offset voltage (for example, 0.5 V here) is applied to the differential amplifier 56. The differential amplifier 56 amplifies a differential voltage between the input compensation voltage V1 and the detection voltage V2, adds an offset voltage to the amplified voltage, and outputs a voltage Vdef. Therefore, when V1 and V2 are equal voltages, the differential voltage is 0, and an offset voltage of 0.5 V is output as the output Vdef of the differential amplifier 56. The output Vdef of the differential amplifier 56 is input to the difference value terminal of the A / D converter port of the CPU 49. An A / D (analog / digital) converter built in the CPU 49 converts Vdef, V1, and V2 from voltage values to digital values. The CPU 49 performs various control processes, for example, the calculation of the temperature of the heating roller 40, using the data digitized by the A / D converter.

  The non-contact temperature sensor 53 according to an embodiment of the present invention includes a detection thermistor T1 and a compensation thermistor T2, and performs highly accurate temperature detection together with the following peripheral circuits. That is, a voltage, for example, 5V is applied by the constant voltage circuit 60, and the voltage V1 between the detection thermistor T1 and the resistor R1 and the voltage V2 between the compensation thermistor T2 and the resistor R2 are generated. Are input to the differential amplifier 56. When the difference voltage obtained by subtracting V1 from V2 is estimated from a general measurement temperature range in which the temperature sensor 53 is used, it is estimated that the difference voltage is about 200 mV at the maximum. Therefore, the differential amplifier 56 amplifies the differential voltage. As an example, in the present embodiment, the gain of the differential amplifier 56 is set to 20 times. The differential amplifier 56 amplifies a differential voltage obtained by subtracting V1 from V2, and further outputs a voltage Vdef obtained by adding an offset voltage. Therefore, for example, when the difference obtained by subtracting V1 from V2 is around the maximum 200 mV, (0.2V × 20) + 0.5V and 4.5V is output as the output Vdef of the differential amplifier 56. become. The output voltages Vdef and V2 are sent to the A / D converter port of the CPU 49, and the analog voltage is converted into a digital value by the A / D converter built in the CPU 49. In the CPU 49, a process of obtaining the temperature of the heating roller 40 by referring to a temperature table that is stored in the memory (RAM 51) using the digitized value and indicates the temperature relationship corresponding to the values of Vdef and V2. The amount of power supplied to the heaters 1 and 2 is controlled so that the obtained temperature is maintained at a desired fixing temperature in advance.

Further, the A / D converter of the CPU 49 used in the temperature control device of the present invention is a low-cost CPU and is a 10-bit type in which the number of operation digits is general, and therefore the resolution of the voltage value to be calculated is 5 mV. Yes.
However, in reality, the difference between V1 and V2 is about 200 mV at the maximum due to the characteristics of the non-contact temperature sensor 53, and the voltage change per 1 ° C. of temperature change is very small, about 1 mV.
Therefore, in the temperature control device of the present invention, the difference between the voltages V1 and V2 is amplified by the differential amplifier 56 (IC1), and the difference value (Vdef signal) together with V1 and V2 is the A / D converter port of the CPU 249. Is entered.
Since the differential amplifier 56 sets the offset voltage 0.5V as described above, the output is 0.5V when V1 and V2 are the same voltage.

In addition, because of the characteristic of the non-contact temperature sensor 53 of the present invention, the output of the differential amplifier 56 is 0.5 V or higher because V1 ≧ V2 is always satisfied.
The gain is set to 20 times, and the output Vdef of the differential amplifier 56 is set to 4.5 V when the maximum value of the difference between V1 and V2 is 200 mV.
Therefore, under normal conditions, the value of Vdef is in the range of 0.5V to 4.5V. When outside this voltage range, it is determined that the circuit is faulty (thermistor disconnection, short circuit, differential amplifier failure). Conventionally, the temperature calculation is stopped and the operation of the printing apparatus is stopped.

However, since the differential amplifier 56 amplifies a minute voltage, it is easily affected by noise and the like, and although the circuit is normal, the abnormal voltage (0.5 V or less or 4.. 5V or more), and there is a high possibility that a state in which it is erroneously determined to be abnormal will occur. In this case, an error state in which correct temperature calculation cannot be performed frequently occurs.
Thus, in the embodiment of the present invention, even when the output value of the differential amplifier 56 is a value outside the normal range, the printing operation is safely continued without simply determining as a failure and stopping the printing apparatus. This is a control system that can be used.

FIG. 6 is a flowchart showing a temperature control procedure performed by the CPU 49 included in the temperature control apparatus according to the embodiment of the present invention. Hereinafter, based on the flowchart of FIG. 6, the specific temperature control method which CPU49 processes is explained in full detail.
First, the CPU 49 measures the voltage values of the V1 and V2 input to the differential amplifier 56 based on the voltage values input to the V1 value terminal and the V2 value terminal of the A / D converter port (step). (Hereinafter referred to as S) S1). Since the temperature calculation is basically performed from the two thermistor voltages V1 and V2, as described above, first, the temperature calculation is performed from these V1 and V2 (S2).
However, as described above, since the difference between V1 and V2 is very small, the A / D converter with the 10-bit resolution as used in this embodiment has a low resolution, and if the V1 and V2 values are used as they are, Accurate temperature calculation is not possible. Therefore, here, the temperatures calculated by V1 and V2 are stored as temporary values (S3).

  Next, the output (Vdef) of the differential amplifier 56 is measured, and the temperature is calculated from V2 and Vdef as described above (S4). Since the difference value Vdef amplifies a minute difference between V1 and V2, even a 10-bit A / D converter (resolution of about 5 mV) used in this embodiment is not adversely affected by noise or the like. As long as the temperature can be accurately calculated, if normal (S5 is NO), temperature control is performed based on this calculated value (S6).

On the other hand, as described above, the output (Vdef) of the differential amplifier 56 may become an abnormal value (0.5V or less or 4.5V or more as described above) due to the influence of noise or the like. There is no guarantee that the temperature calculation can be performed.
Therefore, in this embodiment, when the output (Vdef) of the differential amplifier 56 shows an abnormal value in this way (S5 is YES), the temperature calculated from V1 and V2 previously set as the temporary value in step S3. Is used instead of the temperature value obtained from the Vdef value (S9).

Since V1 and V2 are not minute voltages, they do not malfunction as much as the differential amplifier output value, and are simple inputs. Therefore, countermeasures against noise are easy in terms of circuits using capacitors and the like. For this reason, the reliability with respect to malfunction is higher than the output obtained from the differential amplifier 56. Therefore, although the accuracy is not good as described above, it is possible to avoid the output of an abnormal temperature far away due to noise, and the differential amplifier 56 exhibits an abnormal value as described above for a short time due to the influence of noise or the like. Therefore, there is almost no influence on external temperature control (such as heater temperature management), and the printing apparatus is not stopped.
In addition, when the differential amplifier 56 is really out of order because it is not a short-term failure due to the influence of noise or the like, this abnormal value is always output instead of temporarily. It is determined that the abnormal value continues for a certain time or more (S7 is YES), and it is notified that the circuit is abnormal (S8).

  According to one embodiment of the present invention, for example, in the control of a non-contact temperature sensor that has two thermistors and measures the temperature of a heat source in a non-contact manner based on the difference between the measured values, By using a non-contact temperature sensor circuit having a differential amplifier that amplifies the difference in voltage generated by the thermistor and monitoring the output voltage of the differential amplifier, the temperature of the fixing device can be controlled with high accuracy. It is possible to provide a temperature calculation value so that it does not affect the control of the entire printing device even if the differential amplifier malfunctions due to noise etc., the output becomes an abnormal value, and the temperature calculation becomes impossible It has a function.

In the above-described embodiment, only when the output (Vdef) of the differential amplifier 56 is an abnormal value (0.5 V or less or 4.5 V or more), the value calculated by V1 and V2 is output. A malfunction may be considered in which the output (Vdef) of the amplifier 56 is not correct even if it is not an obvious abnormal value (the aforementioned 0.5 V or less or 4.5 V or more).
In view of such a case, another embodiment of the present invention compares the temperature calculated at the inputs V1 and V2 of the differential amplifier 56 with the value calculated at the output (Vdef) of the differential amplifier 56.
That is, since the values at the inputs V1 and V2 of the differential amplifier 56 depend on the accuracy as described above, although there is a slight difference from the value calculated by the temperature of the output (Vdef) of the differential amplifier 56, it is essentially the same element. So it should be the same value.
Accordingly, if there is a certain difference between the two values, the CPU 49 determines that a correct value is not calculated due to a malfunction of the differential amplifier 56. In this case, the inputs V1 and V2 of the differential amplifier 56 are determined. If the difference between the two values is within a certain range, the CPU 49 determines that the value is an accurate value and outputs the temperature calculated value at the output of the differential amplifier 56. You may adopt the method of judgment.

  In the above embodiment, 0.5V to 4.5V is used as the normal range of the output of the differential amplifier 56. However, it is needless to say that these ranges are not limiting and are shown as examples. For example, the voltage from the constant voltage circuit 59 that is the power supply voltage, the resistance value of the resistor used for R1 and R2, the temperature range to be detected by the thermistor, the offset voltage, and the gain value of the differential amplifier It will be understood by those skilled in the art that various ranges can be set by, for example.

Next, FIG. 7 is a flowchart showing the operation of the CPU 49 for realizing the abnormality notification process performed in the temperature control operation of the fixing device using the non-contact temperature sensor 53 according to the present embodiment. Since the basic configuration is the same as that of the above embodiment, the description is omitted.
The CPU 49 measures the output and Vdef value of the differential amplifier input to the differential value terminal of the A / D converter port (step (hereinafter referred to as ST) 1), and the magnitude is an abnormal value, as in the above embodiment. Judge whether or not. That is, it is determined whether or not the output Vdef of the differential amplifier 56 is in the range of 0.5V ≦ Vdef ≦ 4.5V (ST2).
In this determination, if the output Vdef of the differential amplifier 56 is in the normal value range (ST2 is NO), the value of the compensation voltage V2 input to the A / D converter port V2 value terminal is measured (ST3) and measured. Based on the Vdef value and the V2 value, an accurate temperature is calculated by referring to a table stored in the RAM 51 and temperature control is executed.

  On the other hand, in this embodiment, when the output (Vdef) of the differential amplifier 56 becomes an abnormal voltage (0.5 V or less or 4.5 V or more) (ST2 is NO), the Vdef value is not used and the differential amplifier 56 is used. The V1 and V2 values inputted to the A / D converter port are measured based on the voltage values inputted to the V1 value terminal and the V2 value terminal of the A / D converter port (ST5). Since the output (Vdef) of the differential amplifier 56 is generated from the difference between the inputs V1 and V2 of the differential amplifier, it is natural that the same value as the output Vdef of the differential amplifier can be calculated from the measured values of V1 and V2. However, as described above, since the differential voltage is very small, the A / D converter with 10-bit resolution as used in the present invention has a low resolution and does not have an accurate value. However, it is not only an accurate value for use in temperature calculation, and it can be sufficiently determined whether or not it is an abnormal voltage (0.5 V or less or 4.5 V or more at the differential amplification output).

For example, as described above, V1 is larger than V2, and this determination is sufficiently possible even with a low-cost CPU having a resolution of about 10 bits. That is, the same determination as that in which the output (Vdef) of the differential amplifier 56 is 0.5 V or less is possible.
On the other hand, if the differential amplifier 56 is 4.5V or higher, the offset voltage is 0.5V and the gain is 20 times. Therefore, the differential voltage between V1 and V2 is 0.2V or higher (YES in ST7). Even a bit A / D converter (resolution of about 5 mV) can be sufficiently judged.
Therefore, in the present embodiment, even if the differential amplifier 56 shows an abnormal value (0.5 V or less or 4.5 V or more), the abnormal amplifier is not immediately notified, and the differential amplifier 56 as described above. It is verified whether the difference is really an abnormal value from the inputs V1 and V2.
Since the inputs V1 and V2 of the differential amplifier 56 are not minute voltages, they are not easily affected by noise, and since they are single voltage inputs, it is easy to take noise countermeasures with a capacitor or the like.
Therefore, even if the output (Vdef) of the differential amplifier 56 is an abnormal voltage, the difference calculation by V1 and V2 is abnormal, that is, unless (V1 <V2) (ST6 is NO), it is regarded as the influence of noise, and the abnormality notification is performed. No (ST9).
Naturally, if the difference calculation ((V1−V2)> 0.2V) by the inputs V1 and V2 of the differential amplifier 56 is also an abnormal value (YES in ST7), it is regarded as a circuit abnormality and an abnormality notification is performed (ST8). .

From the operation control as described above, in the present embodiment, even if the output of the differential amplifier is an abnormal value, if the difference obtained from the two thermistor voltages is a normal value, the notification of a circuit abnormality is stopped. .
Therefore, even if the differential amplifier malfunctions due to noise or the like and outputs an abnormal value, a malfunction that erroneously reports an abnormality due to a circuit abnormality and stops the printing device system is avoided in advance. Will be able to.

  The fixing device temperature control device according to some embodiments of the present invention has been described in detail above. However, the present invention is not limited to these embodiments. Those skilled in the art will appreciate that these embodiments are provided as examples and that all modifications, additions, and alternatives may be made to the above-described embodiments without departing from the scope of the present invention. It will be. It is intended that the scope of the invention be determined only by the claims appended hereto and their equivalents.

DESCRIPTION OF SYMBOLS 1 ... Printer apparatus 2 ... Image formation part 3 ... Intermediate transfer belt unit 4 ... Paper feed part 5 ... Conveyance unit for double-sided printing 6 ... Image formation unit 7 ... Photoconductor Drum 8 ... Cleaner 9 ... Charging roller 11 ... Optical writing head 12 ... Developer 13 ... Developing roller 14 ... Intermediate transfer belt 15 ... Drive roller 16 ... Follower Roller 17 ... Belt position control mechanism 18 ... Primary transfer roller 19 ... Waste toner collection container 21 ... Paper feed cassette 22 ... Paper take-out roller 23 ... Feeding roller 24 ... Roller 25... Standby conveying roller pair 26... Secondary transfer roller 27 .. fixing unit 28... Carry-out roller pair 29 .. discharge tray 30 a... Guide plate 30 b. ..Eject roller 32a ... Start return path 32b ... Intermediate return path 32c ... End return path 33a ... Return roller pair 33b ... Return roller pair 33c ... Return roller pair 33d ... Return roller pair 35 ... Belt cleaner unit 36 ... Roller 38 ... Paper transport unit 39 ... Secondary transfer roller unit 40 ... Heating roller 41 ... Fixing roller 42 ... Fixing belt 43 ... Addition Pressure roller 44 ... Heater 1
45 ... Heater 2
47 ... Control device 48 ... Dedicated memory (ROM)
49 ... CPU
50 ... Infrared 51 ... Random access memory (RAM)
52 ... Interface part (I / O)
53 ... Temperature sensor 54 ... Infrared absorbing film 56 ... Differential amplifier 57 ... Positive terminal 58 ... Negative terminal 59 ... Constant voltage circuit 60 ... Temperature controller R1, R2, ..Resistance T1, T2 ... Thermistor

Claims (3)

An infrared absorbing member heated by radiant heat from the heating element;
A temperature sensor comprising a first thermistor for measuring the temperature of the infrared absorbing member and a second thermistor for measuring the temperature in the vicinity of the first thermistor;
A ground circuit that connects one terminal of the first thermistor and one terminal of the second thermistor to a ground potential;
A power supply circuit for connecting the other terminals of the first thermistor and the second thermistor to a constant voltage power supply via a predetermined resistor, respectively;
A first extraction circuit for extracting a first voltage based on a resistance value of the first thermistor;
A second extraction circuit for extracting a second voltage based on a resistance value of the second thermistor;
Differential amplification means for amplifying a difference between the first voltage and the second voltage;
Processing means for calculating the temperature of the heating element based on the output of the differential amplification means, and controlling the driving of the heating element based on the calculation result;
When the output of the differential amplifier is identified as a value outside the preset range,
The processing unit calculates a temperature of the heating element based on the first voltage and the second voltage, and controls driving of the heating element based on the calculation result. Temperature control device.   The fixing device according to claim 1, further comprising an informing unit for informing a temperature abnormality of the heating element when a state in which the output of the differential amplifier is out of a predetermined range is continued for a predetermined time. Equipment temperature control device.   The processing means has a predetermined difference or more between a temperature value calculated based on the output of the differential amplifier and a temperature value calculated based on the first voltage and the second voltage. The temperature control device for a fixing device according to claim 1, further comprising notification means for reporting a temperature abnormality of the heating element.

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