JP2008026599A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of controlling the temperature of the surface of a heat roller to be appropriate temperature so as not to cause the deterioration of image quality even when a difference is made between the temperature detected by a non-contact thermistor and the actual surface temperature of the heat roller because of variance caused in space between the non-contact thermistor and the surface of the heat roller. <P>SOLUTION: The set temperature of the heat roller 8b is decided by judging a distance between the surface of the heat roller and the non-contact thermistor from a temperature gradient when starting up. Thus, even when the variance is caused in the space between the surface of the heat roller and the non-contact thermistor, the heat roller is controlled to be at the appropriate temperature in accordance with the distance, so that the deterioration of image quality such as offset is avoided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a fixing unit having a rotating body that fixes a developer on a medium by heat.

  Conventionally, a fixing unit of an image forming apparatus that outputs an image formed product by fixing an image formed with a developer such as toner on a recording medium by heat and pressure has a built-in heating source such as halogen. It comprises a heat roller and a pressure roller in pressure contact with the heat roller. In order to control the heat source of the fixing unit, a thermistor is used as a temperature detection unit that detects the surface temperature of the heat roller. Such a fixing unit performs on / off control of a heating source such as a halogen incorporated therein so that the heat roller is maintained at a predetermined set temperature based on the surface temperature detected by the thermistor.

  Since the thermistor as such a temperature detection unit is in contact with the surface of the heat roller, the friction between the thermistor and the heat roller may cause scratches on the surface of the heat roller, which is a rubber material, resulting in image quality degradation and the like. appear. For this reason, in order to prevent image quality deterioration, a non-contact type thermistor is used as a surface temperature detector of the heat roller. The distance between the non-contact thermistor and the surface of the heat roller is defined as a predetermined value when the image forming apparatus is assembled (see, for example, Patent Document 1).

JP 2005-156686 A

  However, the gap between the non-contact thermistor and the heat roller surface varies due to various factors. Due to this variation, there is a difference between the temperature detected by the non-contact thermistor and the actual surface temperature of the heat roller. As a result, there is a problem that image degradation such as offset occurs.

  Therefore, in view of the above situation, the present invention has a variation in the distance between the non-contact thermistor and the surface of the heat roller, and even if there is a difference between the temperature detected by the non-contact thermistor and the actual surface temperature of the heat roller. An object of the present invention is to provide an image forming apparatus capable of controlling the temperature of the surface of the heat roller to an appropriate temperature so as not to cause image quality deterioration.

  According to the image forming apparatus of the present invention, the image forming apparatus includes a fixing unit having a rotating body that rotates in the medium conveyance direction so as to fix the developer deposited on the medium by heat from a heating source. A temperature detector that faces the surface of the rotating body and is spaced apart from the rotating body by a predetermined distance, detects a temperature of the surface of the rotating body, and a temperature per unit time detected by the temperature detecting unit. A detection temperature control unit that calculates a temperature change amount, and a temperature control that determines a set temperature for controlling the temperature of the surface of the rotating body to a predetermined temperature based on the temperature change amount calculated by the detection temperature control unit Part.

  The image forming apparatus of the present invention determines the set temperature of the heat roller 8b by determining the distance between the surface of the heat roller and the non-contact thermistor from the temperature gradient at the time of activation. As a result, even if there is a variation in the distance between the surface of the heat roller and the non-contact thermistor, the heat roller can be controlled to an appropriate temperature according to the distance, so image quality degradation such as offset is avoided. can do.

  The present invention will be described below with reference to the drawings.

[Embodiment 1]
As shown in FIG. 1, the image forming apparatus 100 includes an image forming unit 21 having a photosensitive drum 3, a charging roller 4, a developing roller 6, a supply roller 22, a developing blade 23, and a cleaning blade 25 in a housing 21a, and a toner. It has a cartridge 24, a recording paper cassette 2, an LED (Light Emitting Diode) head 5, a transfer roller 7, a fixing device 8, a recording paper remaining amount sensor 9, a writing sensor 10, and a discharge sensor 11. The recording paper 12 is stored in the recording paper cassette 2.

  In addition, the image forming apparatus 100 includes a print control unit 1 connected to each of the above-described members as illustrated in FIG. The printing control unit 1 includes a temperature control unit 101 and a detection temperature control unit 15, and includes a charging roller 4, an LED head 5, a developing roller 6, a transfer roller 7, a recording paper remaining amount sensor 9, and a writing sensor. 10, a discharge sensor 11, an energization control unit 13, and a temperature detection circuit 14 are connected. The temperature detection circuit 14 includes a non-contact thermistor 8d.

  The recording paper cassette 2 is a box-shaped member having an opening on the upper surface so that recording paper 12 as a medium for forming an image is deposited and at least the recording paper 12 can be taken out. The recording paper cassette 2 is provided with a recording paper remaining amount sensor 9 for reading the remaining amount of the recording paper 12. The recording paper cassette 2 is provided with a paper feed roller so as to come into contact with the recording paper 12 in the recording paper cassette 2. The printing control unit 1 supplies the recording paper 12 from the recording paper cassette 11 to the transport path by operating the paper feed roller.

  The remaining recording paper sensor 9 is a sensor that detects whether or not the recording paper 12 is in the recording paper cassette 2. The recording paper remaining amount sensor 9 is connected to the printing control unit 1 and transmits the remaining amount of the recording paper 12 in the recording paper cassette 2 to the printing control unit 1. When it is detected that the recording paper 12 is present in the recording paper cassette 2, the recording paper 12 is supplied to the conveyance path by the paper feed roller. The print control unit 1 that has received the remaining amount of the recording paper 12 displays a signal indicating that the recording paper 12 of the recording paper cassette 2 has run out, for example, on a display unit (not shown) of the apparatus according to the remaining amount of recording paper. be able to.

  The writing sensor 10 is provided on the downstream side of the recording paper cassette 2 in the transport path, and detects whether or not the recording paper 12 has been transported to the transport path. The write sensor 10 is connected to the print control unit 1 and transmits a detected signal to the print control unit 1. Then, based on the signal transmitted by the writing sensor 10, the print control unit 1 controls each member described below so as to form an image on the recording paper 12.

  The photosensitive drum 3 is an electrostatic latent image carrier, and is configured to be able to store electric charges on the surface thereof by the charging roller 4. For example, the photosensitive drum 3 is fixed to a housing 21a of an image forming unit 21 including the photosensitive drum 3 so as to be rotatable about a fixed shaft. The charges stored on the surface are configured such that the charges on the surface can be removed by exposure with the LED head 5. The photosensitive drum 3 forms a toner image by adsorbing toner as a developer to the electrostatic latent image formed on the surface thereof.

  The charging roller 4 serving as a charger can store charges on the surface of the photosensitive drum 3 by applying a predetermined positive voltage or negative voltage to the photosensitive drum 3. The charging roller 4 is, for example, a semiconductive charging roller that is rotatably fixed to the housing 21a of the image forming unit 21 so as to contact the surface of the photosensitive drum 3 with a constant pressure. The charging roller 4 is controlled by the print control unit 1 in order to apply a predetermined voltage to the photosensitive drum 3.

  The LED head 5 is provided above the photosensitive drum 3 downstream of the charging roller 4 in the rotation direction of the photosensitive drum 3. The LED head 5 removes electric charges accumulated on the surface of the photosensitive drum 3 by the charging roller 4 by exposure, and forms an electrostatic latent image on the surface of the photosensitive drum 3. The LED head 5 is connected to the print control unit 1 and performs exposure via the print control unit 1 based on print data transmitted to the image forming apparatus.

  The developing roller 6 is a developer carrying member, and toner as a developer charged with the same charge as the charge charged on the surface of the photosensitive drum 3 by the charging roller 4 is electrically attracted to the surface of the photosensitive drum 3. To supply. As a result, the toner adheres to the portion where the charge has been removed by exposure of the surface of the photosensitive drum 3, and a toner image is formed on the surface of the photosensitive drum 3. The developing roller 6 is rotatable about the housing 21a of the image forming unit 21 so as to be in contact with the surface of the photosensitive drum 3 at a constant pressure, for example, on the downstream side of the rotation of the photosensitive drum 3 with respect to the LED head 5. It is fixed. In order to charge the toner with a predetermined charge, the developing roller 6 is controlled by the print control unit 1.

  The supply roller 22 supplies toner to the developing roller 6. The toner supplied from the supply roller 22 is carried on the developing roller 6, and the toner is charged with a predetermined charge. The supply roller 22 is rotatably fixed to the housing 21 a of the image forming unit 21 so that toner can be supplied to the developing roller 6 on the upstream side of the developing roller 6 relative to the photosensitive drum 3.

  The developing blade 23 scrapes off the toner supplied from the supply roller 22 on the surface of the developing roller 6 and regulates the toner carried on the developing roller 6 to have a uniform thickness. One end of the developing blade 23 is pressed against the surface of the developing roller 6 so that the developing blade 23 is at a predetermined angle on the downstream side of the developing roller 6 with respect to the downstream side of the developing roller 6 relative to the supply roller 22. It is fixed to the housing 21 a of the forming unit 21.

  The cleaning blade 25 cleans the photosensitive drum 3 by scraping off the toner remaining on the photosensitive drum 3 after transferring the toner image formed on the photosensitive drum 3 onto a recording sheet. The cleaning blade 25 is fixed to the casing 21 a of the image forming unit 21 so that one end of the cleaning blade 25 is in contact with the surface of the photosensitive drum 3 at a constant pressure on the upstream side of the photosensitive drum 3 with respect to the charging roller 4. .

  The toner cartridge 24 is a developer container having toner inside, and is detachably disposed on the upper portion of the casing 21 a of the image forming unit 21 so as to be above the supply roller 22. The toner cartridge 24 stores toner and supplies the stored toner into the housing 21 a of the image forming unit 21.

  The transfer roller 7 is applied with a predetermined positive voltage or negative voltage so that a charge opposite to the charge of the toner charged by the developing roller 6 is stored on the surface thereof. As a result, the transfer roller 7 transfers the toner image formed on the photosensitive drum 3 to the recording paper 12 conveyed through the conveyance path by an electric suction force. The transfer roller 7 is provided so as to face the photosensitive drum 3 of the image forming unit 21 with the conveyance path interposed therebetween, and is rotatably fixed to the shaft, for example. The transfer roller 7 is controlled by the print controller 1 to apply a predetermined voltage based on a signal from the writing sensor 10. The recording paper 12 having the toner image is conveyed to the fixing device 8 through the conveyance path.

  As shown in FIG. 3, the fixing device 8 includes a halogen 8a as a heating source, a heat roller 8b, a pressure roller 8c, and a non-contact thermistor 8d. The halogen 8a is stored in the heat roller 8b. The halogen 8 a is connected to the energization control unit 13 and is heated according to the voltage applied from the energization control unit 13. This heat is transmitted from the halogen 8a to the heat roller 8b. In the energization control unit 13, the voltage applied so that the heat roller 8b reaches a predetermined temperature is controlled by the print control unit 1. Instead of the halogen 8a, a ceramic heater may be housed in the heat roller 8b.

  The heat roller 8b is a rotating body whose axis is fixed so that the recording paper 12 can be rotated in the direction in which the recording paper 12 flows from the upstream side to the downstream side of the conveyance path so as to come into contact with the conveyed recording paper 12, and is rotated by a motor (not shown). To do. The heat roller 8b can be uniformly heated by the heat generated by the halogen 8a.

  The energization control unit 13 switches the energization state of the halogen 8 a connected to the energization control unit 13 according to a command from the print control unit 1. That is, the energization control unit 13 turns on / off the energization to the halogen 8a so that the surface temperature of the heat roller 8b detected by the non-contact thermistor 8d becomes a set temperature determined by the temperature control unit described later. For example, when the surface temperature of the heat roller 8b detected by the non-contact thermistor 8d is higher than the set temperature, the energization control unit 13 receives a command to turn off the energization to the halogen 8a from the print control unit 1 and transfers to the halogen 8a. Turn off the power. On the other hand, when the surface temperature of the heat roller 8b detected by the non-contact thermistor 8d is lower than the set temperature, the energization control unit 13 receives an instruction to turn on the energization of the halogen 8a from the print control unit 1 and transfers to the halogen 8a. Turn on the power.

  The pressure roller 8c is provided on the opposite side of the heat roller 8b via the conveyance path, and the recording paper 12 is provided downstream from the upstream side of the conveyance path so that a predetermined pressure is applied to the conveyed recording paper 12. The center of the shaft is fixed so as to be rotatable in the flowing direction, and is rotated by a motor (not shown). Thereby, a predetermined pressure can be applied to the recording paper 12 conveyed through the conveyance path. The toner image can be fixed to the recording paper 12 so that the toner on the recording paper 12 being conveyed is fused by the heat from the heat roller 8b and the pressure from the heat roller 8b and the pressure roller 8c.

  The non-contact thermistor 8 d is a temperature sensor for detecting the temperature of the surface of the heat roller 8 b, and the detected signal is sent to the print control unit 1 via the temperature detection circuit 14. As shown in FIG. 4, the temperature detection circuit 14 is composed of a thermistor element Rth and a detection resistor Rs. In the present invention, the thermistor element Rth is a non-contact thermistor 8d. In this temperature detection circuit, the thermistor element Rth and the detection resistor Rs are connected in series, one end of the thermistor element Rth is connected to the power supply part Vdd, and one end of the detection resistor Rs is grounded to the ground part GND. Then, a voltage value obtained by dividing the power supply unit Vdd by the thermistor element Rth and the detection resistor Rs is detected as the detection voltage Vout. The detection resistor Rs and the power supply unit Vdd are disposed on a substrate (not shown) and the power supply unit of the image forming apparatus 100.

  As shown in FIG. 5, the thermistor element Rth is an element whose resistance value changes as the temperature changes. There are types that change so that the resistance value decreases as the temperature increases, and conversely, those that change so that the resistance value decreases as the temperature decreases. In the present invention, the thermistor element that changes so that the resistance value decreases as the temperature increases is used. However, a thermistor element that changes so that the resistance value decreases as the temperature decreases may be used.

  In the thermistor element Rth having such characteristics, the resistance value of the thermistor element Rth changes and the voltage dividing ratio changes in accordance with the temperature change of the surface of the heat roller 8b as the part to be measured. Thereby, the detection voltage Vout also changes. For example, as shown in FIG. 6, the detection voltage Vout increases as the temperature increases. Therefore, the temperature detection circuit 14 can measure the temperature of the part to be measured by calculating the temperature from the detection voltage Vout.

  The discharge sensor 11 is provided downstream of the fixing device 8 in the conveyance path, and detects the recording paper 12 discharged from the fixing device 8. The discharge sensor 11 is connected to the print control unit 1 and transmits to the print control unit 1 as a signal whether or not the recording paper 12 is discharged.

  The print control unit 1 includes a microprocessor (not shown), a ROM (Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), a RAM (Random Access Memory) input / output port, a timer, an A / D converter, and the like. It has a function for controlling the operation of the image forming apparatus 100. Printed in response to a video signal consisting of control signals from a host controller or the like that is connected to an external information processing apparatus such as a personal computer and controls the operation of the image forming apparatus of the present invention, and data in which pit map data is centrally arranged. Processes such as operations are executed.

  The print control unit 1 includes a detected temperature control unit 15 and a temperature control unit 101. The detection temperature control unit 15 is connected to a temperature detection circuit 14 having a non-contact thermistor 8d, and causes the temperature detection circuit 14 to detect the temperature of the surface of the heat roller 8b via the non-contact thermistor 8d every unit time. Calculate the amount of temperature change per hour. Based on the temperature change amount per unit time calculated by the detected temperature control unit 15, the temperature control unit 101 connected to the detected temperature control unit 15 determines the set temperature, and the temperature detected by the non-contact thermistor 8d is The energization control unit 13 connected to the temperature control unit 101 is controlled so that the set temperature is reached.

  The image forming apparatus 100 having such a configuration is activated when the power is turned on. When the print controller 1 detects a print instruction from the host controller, the non-contact thermistor 8d detects whether or not the fixing device 8 is within a printable temperature range. If the fixing unit 8 is not within this temperature range, the printing control unit 1 controls the energization control unit 13 to energize the halogen 8a via the temperature control unit 101, so that the fixing unit 8 reaches the printable temperature range. Heat.

  Then, the print control unit 1 detects the presence or absence of the recording paper 12 in the recording paper cassette 2 by the recording paper remaining amount sensor 9, and if the recording paper 12 is present, the printing control unit 1 removes the recording paper 12 from the image forming apparatus 100. Feed the paper to the transport path. When the recording paper 12 is detected by the writing sensor 10, a voltage is applied to the charging roller 4 to charge the surface of the photosensitive drum 3. Then, according to the print data signal from the host controller, the LED head 5 exposes and an electrostatic latent image is formed on the surface of the photosensitive drum 3. Then, the negatively charged toner is sucked by the developing roller 6 by an electric suction force, and a toner image is formed on the surface of the photosensitive drum 3.

  When the photosensitive drum 3 is rotationally driven by a driving mechanism (not shown) and the recording paper 12 is conveyed between the photosensitive drum 3 and the transfer roller 7, the formed toner image is electrically attracted by the transfer roller 7. The image is transferred from the photosensitive drum 3 to the recording paper 12. Then, the recording paper 12 onto which the toner image has been transferred is conveyed to the fixing device 8 and heated and pressurized by the heat roller 8b and the pressure roller 8c that are driven to rotate, whereby the toner image on the recording paper 12 is fixed. The recording paper 12 on which the toner image is fixed passes through the fixing device 8 and is discharged. At this time, when the discharge sensor 11 detects the discharge of the recording paper 12, the print control unit 1 determines that the printing operation has ended normally.

  Hereinafter, temperature control of the fixing device 8 of the image forming apparatus 100 according to the first embodiment that operates in this manner will be described in detail.

  The non-contact thermistor 8d disposed at a predetermined distance from the heat roller 8b has a distance L between the surface of the heat roller 8b as shown in FIG. This distance L is designed to be optimized so that the surface temperature of the heat roller 8b can be correctly detected by the non-contact thermistor 8d and the temperature detection circuit 14. The set temperature for the distance L is Ts, the response time of the temperature detected by the non-contact thermistor 8d for the set temperature Ts is t, and the actual temperature of the surface of the heat roller 8b at the response time t is Tr. The set temperature Ts is a threshold for the energization control unit 13 to control energization in order to control the surface temperature Tr of the heat roller 8b to a predetermined temperature. The temperature detected by the non-contact thermistor 8d is compared with the set temperature Ts, and energization control of the energization control unit 13 is performed.

  However, it may be smaller or larger than the reference distance L0 due to various factors such as excessive pressure during assembly. When the distance L between the surface of the heat roller 8b and the non-contact thermistor 8d is different, the response time t of the temperature detected by the thermistor up to the set temperature Ts is different. When the response time t is different, the energization time of the halogen 8a by the energization control unit 13 up to a certain time is different, so that the actual temperature Tr on the surface of the heat roller 8b is different.

  Hereinafter, a detailed description will be given with reference to FIGS. 8 and 9. FIG. 8 is a detected temperature transition diagram of the non-contact thermistor 8d, and shows the difference in response time t to the set temperature Ts depending on the distance L. FIG. FIG. 9 is a diagram of the actual temperature of the surface of the heat roller 8b, and shows that the actual temperature Tr of the surface of the heat roller 8b at a certain time t varies depending on the distance L. FIG.

  First, the distance L between the non-contact thermistor 8d and the surface of the heat roller 8b is L0, which is the optimum distance (reference distance) set at the time of design, and the actual temperature of the surface of the heat roller 8b at the reference distance L0 is Let Tr0 be the response time t0.

  As shown in FIG. 8, when the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is L1 smaller than the reference distance L0, the response time t1 to the set temperature Ts is shorter than the response time t0. . That is, when L1 <L0, t1 <t0. As shown in FIG. 9, the detected temperature detected by the non-contact thermistor 8d is lower than the temperature detected by the non-contact thermistor 8d at the reference distance L0. On the other hand, when the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is L2 larger than the reference distance L0 as shown in FIG. 8, the response time t2 to the set temperature Ts is longer than the response time t0. become longer. That is, when L2> L0, t2> t0. As shown in FIG. 9, the detected temperature detected by the non-contact thermistor 8d is higher than the temperature detected by the non-contact thermistor 8d at the reference distance L0.

  The print control unit 1 controls the energization control unit 13 to turn on / off the energization of the halogen 8a in order to reach the set temperature Ts. However, if the response time is different in this way, the energization time of the halogen 8a Is different. Thereby, in the case of the distance L1, the energization time of the halogen 8a is shortened, and the actual surface temperature Tr1 of the heat roller 8b is lower than the surface temperature Tr0 (Tr1 <Tr0). On the other hand, in the case of the distance L2, the energization time of the halogen 8a becomes longer, and the actual surface temperature Tr2 of the heat roller 8b becomes higher than the surface temperature Tr0 (Tr2> Tr0). As described above, since the actual surface temperature Tr of the heat roller 8b varies depending on the difference in the distance L, image quality deterioration such as fixing failure and offset occurs in the printing result. Therefore, it is necessary to control the temperature of the surface of the heat roller 8b based on the detection temperature corresponding to the detection distance corresponding to the separation distance.

  Therefore, in the present invention, when the temperature change amount per unit time is calculated by the detected temperature control unit 15, and the separation distance between the surface of the heat roller 8b and the non-contact thermistor 8d is longer than the reference distance L0 based on the temperature change amount. When the set temperature is lowered and the separation distance is shorter than the reference distance, the temperature control unit 101 sets the set temperature so as to increase the set temperature and controls the temperature of the surface of the heat roller 8b. Specifically, as shown in FIG. 10, the detected temperature control unit 15 calculates the temperature gradient α (= ΔT / Δt) based on the temperature change ΔT in a unit time Δt at the time of activation detected by the non-contact thermistor 8d. calculate.

  Here, the temperature gradient at the reference distance L0 is α0, the set temperature is Ts0 (= 170 ° C.), the temperature gradient at the distance L1 smaller than the reference distance L0 is α1, and the set temperature is Ts1 (= 175 ° C.). A temperature gradient α2 and a set temperature Ts2 (= 165 ° C.) at a distance L2 larger than the distance L0 are set. At this time, the lower limit of the temperature gradient α is αmin, the upper limit is αmax, the lower limit of the temperature gradient α0 at the reference distance L0 is α0min, the upper limit is α0max, and the temperature gradient α is α ≦ αmin, αmin <α <α0min, α0min ≦ α. ≦ α0max, α0max <α <αmax, and αmax ≦ α.

  As described above, the temperature gradient α calculated by the detected temperature control unit 15 is compared, and if it is included in the region of αmin <α <α0 min, the detected temperature control unit 15 includes the non-contact thermistor 8d and the heat roller 8b. Is a distance L1 smaller than the reference distance L0, and the temperature gradient is determined as α1. From this determination, the temperature control unit 101 applies the set temperature Ts1 (= 175 ° C.) that is higher than the set temperature Ts0 (= 170 ° C.) of the reference distance L0.

  Further, the temperature gradient α calculated by the detected temperature control unit 15 is compared, and if it is included in the region of α0max <α <αmax, the detected temperature control unit 15 compares the surface of the non-contact thermistor 8d and the heat roller 8b. Is a distance L2 larger than the reference distance L0, and the temperature gradient is determined as α2. From this determination, the temperature control unit 101 applies the set temperature Ts2 (= 165 ° C.) that is lower than the set temperature Ts0 (= 170 ° C.) of the reference distance L0.

  Furthermore, the temperature gradient α calculated by the detected temperature control unit 15 is compared. If the temperature gradient α is included in the region of α0min ≦ α ≦ α0max, the detected temperature control unit 15 compares the surface of the non-contact thermistor 8d and the heat roller 8b. Is the reference distance L0, and the temperature gradient is determined as α0. From this determination, the temperature control unit 101 applies the set temperature Ts0 (= 170 ° C.) of the reference distance L0.

  Then, the temperature gradient α calculated by the detected temperature control unit 15 is compared. If α ≦ αmin and αmax ≦ α, the temperature gradient is determined as αmin and αmax, and it is determined that the non-contact thermistor 8d is abnormally attached. , Display an error.

FIG. 11 shows the relationship between the temperature gradient α and the applied set temperature and the temperature gradient area as a temperature setting table stored on the RAM. As shown in FIG. 11, the set temperature relationship is Ts2 <Ts0 <Ts1, and the relationship of the temperature gradient α is also α2 <α0 <α1. For example, when plain paper with a basis weight of 80 g / m ² is used, the set temperatures are 170 ° C. for Ts0, 175 ° C. for Ts1, and 165 ° C. for Ts2. This value is set by the thickness of the recording paper 12, and Ts1 and Ts2 are controlled by a value set to the set temperature Ts0 at the reference distance L0. In this manner, the temperature control unit 101 determines whether the distance L between the surface of the heat roller 8b and the thermistor 8d is larger or smaller than the reference distance L0 based on the temperature gradient α, sets the set temperature Ts, and energizes the halogen 8a. Control.

  The upper limit αmax and lower limit αmin of the temperature gradient used here, the temperature gradient α0 at the reference distance L0, the upper limit α0max, the lower limit αmin, and the set temperatures Ts0, Ts1, and Ts2 applied to the temperature gradient range are obtained through experiments. This value is stored on the RAM and is referred to by the set temperature control unit 15. Thus, the set temperature can be quickly determined by referring to the temperature setting table. Further, by controlling the set temperature according to the distance, an error due to heat transfer can be reduced, and image quality deterioration such as offset can be further prevented.

  The temperature control of the fixing device 8 of the image forming apparatus 100 will be described using the flowchart of FIG. First, the image forming apparatus 100 is turned on in step S101.

 When the input power is turned on, the print controller 1 starts ON / OFF control of the halogen 8a so that the temperature of the heat roller 8b is heated to a predetermined standby temperature by the energization controller 13 in step S102. Then, energization is started, and the process proceeds to step S103.

  When heating to the heat roller 8b is started, the detected temperature control unit 15 calculates a temperature gradient α (= ΔT / Δt) from the detected temperature result of the non-contact thermistor 8d in step S103.

  The detected temperature control unit 15 reads the upper limit αmax and the lower limit αmin of the temperature gradient stored in the RAM. In step S104, the detected temperature control unit 15 determines whether or not the temperature gradient α calculated in step S103 is αmin <α <αmax. If it is determined in step S104 that the temperature gradient α is not αmin <α <αmax, the process proceeds to step S105, an error is displayed on a display unit (not shown) of the image forming apparatus 100, and the operation of the image forming apparatus 100 is stopped. Terminate.

  On the other hand, when it is determined in step S104 that the temperature gradient α is αmin <α <αmax, the detected temperature control unit 15 reads the temperature gradient α0, the upper limit α0max, and the lower limit α0min at the reference distance L0 stored in the RAM. . In step S106, the detected temperature control unit 15 compares the calculated temperature gradient α with the read upper limit α0max and lower limit α0min.

  As a result, if the detected temperature control unit 15 determines in step S106 that the calculated temperature gradient α is α0max <α <αmax, the process proceeds to step S107. In step S106, when the detected temperature control unit 15 determines that the calculated temperature gradient α is α0min ≦ α ≦ α0max, the process proceeds to step S108. Furthermore, when the detected temperature control unit 15 determines in step S106 that the calculated temperature gradient α is αmin <α <α0 min, the process proceeds to step S109.

  When the calculated temperature gradient α is α0max <α <αmax, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is larger than the temperature gradient α0 stored in the RAM at the reference distance L0, the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is smaller than the reference distance L0. In response to the notification, the temperature control unit 101 determines the set temperature Ts as the set temperature Ts1 higher than the set temperature Ts0 at the reference distance L0 in step S107.

  When the calculated temperature gradient α is α0min ≦ α ≦ α0max, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is equivalent to the temperature gradient α0 stored in the RAM at the reference distance L0, the temperature control unit 101 receives the notification, and in step S108, sets the set temperature Ts to the reference distance L0. Is determined to be the set temperature Ts0.

  When the calculated temperature gradient α is αmin <α <α0 min, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is smaller than the temperature gradient α0 stored in the RAM at the reference distance L0, the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is larger than the reference distance L0. Therefore, upon receiving the notification, the temperature control unit 101 determines the set temperature Ts as the set temperature Ts2 lower than the set temperature Ts0 at the reference distance L0 in step S109.

  As described above, when the print data is received from the host controller after the set temperature Ts is determined by the temperature control unit 101, the print control unit 1 causes the energization control unit to set the determined set temperature Ts in step S110. 13 performs ON / OFF control of energization to the halogen 8a, starts printing control, and proceeds to step S111.

  In step S111, the detected temperature control unit 15 confirms whether or not the surface temperature of the heat roller 8b has reached the set temperature Ts determined as described above. When the temperature does not reach the set temperature Ts, the energization control unit 13 further performs ON / OFF control of energization to the halogen 8a to heat the heat roller 8b. On the other hand, when the set temperature Ts is reached, the process proceeds to step S112.

  In step S111, when the temperature of the surface of the heat roller 8b reaches the set temperature Ts determined as described above, the print control unit 1 performs the above-described processing based on the print data received from the host controller in step S112. Then, a predetermined image is formed on the recording paper 12.

  As described above, the image forming apparatus 100 described in the first embodiment determines the set temperature Ts of the heat roller 8b by determining the distance between the surface of the heat roller 8b and the non-contact thermistor 8d from the temperature gradient α at the time of activation. As a result, image quality degradation such as offset can be avoided.

  The image forming apparatus 100 described in the first embodiment obtains the temperature gradient α at the time of activation and determines the set temperature Ts, but the present invention is not limited to this. For example, when the fixing device 8 is detachable from the image forming apparatus 100, the temperature gradient α may be obtained even when the fixing device 8 is replaced while the power of the image forming apparatus 100 is ON. In this case, when it is detected that the fixing device 8 has been replaced by a fixing device replacement detecting unit (not shown), the temperature gradient α is calculated to determine the set temperature Ts.

[Embodiment 2]
As shown in FIG. 13, the image forming apparatus 100 described in the second embodiment includes the environment detection unit 16 in the print control unit 1 of the image forming apparatus 100 described in the first embodiment, and the image forming apparatus 100 is set. The fixing device 8 is controlled in consideration of the temperature of the surrounding environment. Since other than that is the same as Embodiment 1, it attaches | subjects the same number and abbreviate | omits description.

  The environment detection unit 16 is connected to the detection temperature control unit 15 and receives the temperature of the environment around the heat roller 8b detected by the temperature detection circuit 14 including the non-contact thermistor 8d, and this temperature and the temperature gradient described above. The temperature controller 101 controls the temperature of the heat roller 8b based on α.

  Even when the distance between the surface of the heat roller 8b and the non-contact thermistor 8d is equal and the actual temperature of the surface of the heat roller 8b is equal, the detected temperature of the non-contact thermistor 8d is different when the environmental temperature is different. come. FIG. 14 shows the difference in detected temperature of the non-contact thermistor 8d due to the difference in environmental temperature. In FIG. 14, the solid line a is a temperature detected by the non-contact thermistor 8d when the environmental temperature T0 is the reference temperature, and the solid line a converges to the dotted line a as time elapses. The solid line b is the temperature detected by the non-contact thermistor 8d in the case of the environmental temperature T1 higher than the reference environmental temperature T0, and the solid line b converges to the dotted line b over time. The solid line b is a temperature detected by the non-contact thermistor 8d in the case of the environmental temperature T2 lower than the reference environmental temperature T0, and the solid line c converges to the dotted line c as time elapses.

  Depending on the environment in which the image forming apparatus 100 is installed, a difference occurs in heat loss until the heat on the surface of the heat roller 8b is transmitted to the non-contact thermistor 8d. For example, when the temperature of the installation environment is a low temperature such as 5 ° C., the heat loss is larger than the reference temperature of 25 ° C. Therefore, even if the distance between the surface of the heat roller 8b and the non-contact thermistor 8d is the same and the actual temperature of the surface of the heat roller 8b is the same, the detected temperature of the non-contact thermistor 8d at the low temperature and the reference temperature. Will cause a difference. As a result, the detected temperature is lower at low temperatures than at the reference temperature, as shown by the relationship between a and c in FIG.

  On the other hand, when the temperature of the installation environment is 40 ° C., heat loss is smaller than the reference temperature. Therefore, even if the distance between the surface of the heat roller 8b and the non-contact thermistor 8d is the same and the actual temperature of the surface of the heat roller 8b is the same, the detected temperature of the non-contact thermistor 8d at the high temperature and the reference temperature. Will cause a difference. As a result, the detected temperature is higher at a high temperature than at the reference temperature, as in the relationship between a and b in FIG. Therefore, the image forming apparatus 100 described in the second embodiment determines the set temperature Ts based on the temperature of the surrounding environment measured by the environment detection unit 16.

  The image forming apparatus 100 including the environment detection unit 16 that detects such an environmental temperature is turned on, that is, turned on, and the temperature control of the heat roller 8b is started by the halogen 8a through the energization control unit 13. Before, the starting environmental temperature Te around the surface of the heat roller 8b is detected via the non-contact thermistor 8d under the control of the printing control unit 1. The starting environmental temperature around the surface of the heat roller 8b is the environmental temperature at which the image forming apparatus 100 is installed. The environment detection unit 16 receives the detected start environment temperature Te. Then, the environment detection unit 16 selects a table area from the received start environment temperature Te with reference to a set temperature table as shown in FIG. 15 stored in advance in the RAM.

  As shown in FIG. 15, when the detected start environment temperature Te is Te <Te1, the region 0 is selected, and when Te1 ≦ Te <Te2, the region 1 is selected, and Te2 ≦ Te <Te3. If the region 2 is selected, the region 3 is selected if Te3 ≦ Te. Te1, Te2, and Te3 are stored in advance in the RAM, and the table area is selected based on the relationship with the start environment temperature Te.

  After the table area is selected, the print controller 1 starts temperature control of the heat roller 8b. When the temperature control of the heat roller 8b is started, the temperature gradient α is calculated as in the first embodiment. When the temperature gradient α is calculated, the temperature control unit 101 determines a set temperature corresponding to the calculated temperature gradient α in the already selected table region.

  At this time, the temperature control unit 101 determines a preset temperature for each table region selected in advance based on the start environment temperature Te detected by the environment detection unit 16 based on the temperature gradient α. For example, as illustrated in FIG. 15, when the table area is the area 0 and the calculated temperature gradient α is α0min ≦ α ≦ α0max, the temperature control unit 101 determines the set temperature as Tes00.

  Based on the determined set temperature, the energization control unit 13 controls ON / OFF of energization to the halogen 8a via the temperature control unit 101, and the temperature of the surface of the heat roller 8b as in the first embodiment. Is controlled to reach this set temperature.

  The temperature control of the fixing device 8 of the image forming apparatus 100 will be described with reference to the flowcharts of FIGS. First, the image forming apparatus 100 is turned on in step S201.

  When the input power is turned on, the print controller 1 detects the ambient temperature around the surface of the heat roller 8b of the fixing device 8 with the non-contact thermistor 8d in step S202, and sends it to the environment detector 16 as the start ambient temperature Te. introduce.

  In step S203, the environment detection unit 16 refers to a set temperature table as shown in FIG. 15 stored in advance in the RAM and compares it with the detected start environment temperature Te.

  As a result, when the environment detection unit 16 determines in step S203 that the start environment temperature Te detected in step S202 is Te <Te1, the process proceeds to step S204. In step S203, when the environment detection unit 16 determines that the start environment temperature Te is Te1 ≦ Te <Te2, the process proceeds to step S205. Furthermore, when the environment detection unit 16 determines that the start environment temperature Te is Te2 ≦ Te <Te3 in step S203, the process proceeds to step S206. In step S203, when the environment detection unit 16 determines that the start environment temperature Te is Te3 ≦ Te, the process proceeds to step S207.

  When the detected start environment temperature Te is Te <Te1, the environment detection unit 16 selects the area 0 as the table area in step S204. When the detected start environment temperature Te is Te1 ≦ Te <Te2, the environment detection unit 16 selects the region 1 as the table region in step S205. When the detected start environment temperature Te is Te2 ≦ Te <Te3, the environment detection unit 16 selects the region 2 as the table region in step S206. When the detected start environment temperature Te is Te3 ≦ Te, the environment detection unit 16 selects the area 3 as the table area in step S207.

  After the table area is selected, in step S208, the printing control unit 1 starts ON / OFF control of the halogen 8a by the energization control unit 13 so that the temperature of the heat roller 8b is heated to a predetermined temperature. Then, energization is started, and the process proceeds to step S103.

  When heating of the heat roller 8b is started, the detected temperature control unit 15 calculates a temperature gradient α (= ΔT / Δt) from the detected temperature result of the non-contact thermistor 8d in step S209.

  The detected temperature control unit 15 reads the upper limit αmax and the lower limit αmin of the temperature gradient stored in the RAM. In step S210, the detected temperature control unit 15 determines whether or not the temperature gradient α calculated in step S209 is αmin <α <αmax. If it is determined in step S210 that the temperature gradient α is not αmin <α <αmax, the process proceeds to step S211, an error is displayed on a display unit (not shown) of the image forming apparatus 100, and the operation of the image forming apparatus 100 is stopped. Terminate.

  On the other hand, when it is determined in step S210 that the temperature gradient α is αmin <α <αmax, the detected temperature control unit 15 reads the temperature gradient α0, the upper limit α0max, and the lower limit α0min at the reference distance L0 stored in the RAM. . Then, the process proceeds to step S212, and the detected temperature control unit 15 compares the calculated temperature gradient α with the read upper limit α0max and lower limit α0min.

  As a result, when the detected temperature control unit 15 determines in step S212 that the calculated temperature gradient α is α0max <α <αmax, the process proceeds to step S213. If the detected temperature control unit 15 determines in step S212 that the calculated temperature gradient α is α0min ≦ α ≦ α0max, the process proceeds to step S214. Furthermore, when the detected temperature control unit 15 determines in step S212 that the calculated temperature gradient α is αmin <α <α0 min, the process proceeds to step S215.

  When the calculated temperature gradient α is α0max <α <αmax, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is larger than the temperature gradient α0 stored in the RAM at the reference distance L0, the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is smaller than the reference distance L0. Therefore, upon receiving the notification, the temperature control unit 101 determines the set temperature as the set temperature TesN1 higher than the set temperature at the reference distance L0 in step S213. The symbol N indicating the set temperature is 0, 1, 2, or 3, and is the number of regions selected by the above-described start environment temperature Te. For example, when region 0 is selected, the set temperature is Tes01.

  When the calculated temperature gradient α is α0min ≦ α ≦ α0max, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is equivalent to the temperature gradient α0 stored in the RAM at the reference distance L0, the temperature control unit 101 receives the notification, and in step S214, sets the set temperature at the reference distance L0. The set temperature TesN0 is determined.

  When the calculated temperature gradient α is αmin <α <α0 min, the detected temperature control unit 15 notifies the temperature control unit 101 to that effect. In this case, since the temperature gradient α is smaller than the temperature gradient α0 stored in the RAM at the reference distance L0, the distance between the non-contact thermistor 8d and the surface of the heat roller 8b is larger than the reference distance L0. Therefore, upon receiving the notification, the temperature control unit 101 determines the set temperature as the set temperature TesN2 lower than the set temperature at the reference distance L0 in step S215.

  In this way, when the print data is received from the host controller after the set temperature is determined by the temperature control unit 101, the print control unit 1 causes the energization control unit 13 to achieve the determined set temperature Ts in step S216. Then, ON / OFF control of energization to the halogen 8a is performed, printing control is started, and the process proceeds to step S217.

  Then, in step S217, the detected temperature control unit 15 confirms whether or not the temperature of the surface of the heat roller 8b has reached the set temperature determined above. When the set temperature has not been reached, the energization control unit 13 further performs ON / OFF control of energization to the halogen 8a to heat the heat roller 8b. On the other hand, when the set temperature is reached, the process proceeds to step S218.

  In step S217, when the temperature of the surface of the heat roller 8b reaches the set temperature determined as described above, the print controller 1 determines in step S218 based on the print data received from the host controller as described above. Then, a predetermined image is formed on the recording paper 12.

  As described above, the image forming apparatus 100 described in the second embodiment not only determines the distance between the surface of the heat roller 8b and the non-contact thermistor 8d from the temperature gradient α at the start-up, but also includes the image forming apparatus 100. The set temperature of the heat roller 8b is also determined from the temperature of the environment in which it is located. Thereby, image quality deterioration such as offset can be further avoided.

  The image forming apparatus 100 described in the second embodiment uses the temperature detected by the non-contact thermistor 8d as the environmental temperature before the power is turned on and the temperature control of the surface of the heat roller 8b is started. Is not limited to this. For example, as shown in FIG. 18, an environmental temperature sensor 31 that detects the environmental temperature in which the image forming apparatus 100 is installed may be provided, and the temperature detected by the environmental temperature sensor 31 may be used as the environmental temperature. In this case, the temperature control of the heat roller 8b can be performed even when the detected environmental temperature changes with the power supply of the image forming apparatus 100 turned on. Even when the image forming apparatus 100 is started immediately after the power of the image forming apparatus 100 is turned off, the accurate environmental temperature can be detected.

  The image forming apparatus 100 of the present invention can be used not only for a printer but also for a copying machine, a facsimile machine, a multifunction machine, and the like.

1 is a schematic diagram illustrating an outline of an image forming apparatus according to a first embodiment. 1 is a block diagram of an image forming apparatus according to a first embodiment. 2 is a diagram illustrating a fixing device of the image forming apparatus according to Embodiment 1. FIG. 3 is a diagram illustrating a temperature detection circuit of the image forming apparatus according to Embodiment 1. FIG. 3 is a diagram illustrating characteristics of a thermistor element used in the temperature detection circuit of the image forming apparatus according to Embodiment 1. FIG. 3 is a diagram illustrating a relationship between a voltage and a temperature detected by a thermistor element provided in a temperature detection circuit of the image forming apparatus according to Embodiment 1. FIG. 3 is a diagram illustrating a relationship between a heat roller and a non-contact thermistor of the image forming apparatus according to Embodiment 1. FIG. FIG. 3 is a diagram for explaining a detected temperature of a non-contact thermistor that varies depending on the distance between the surface of the heat roller and the non-contact thermistor of the image forming apparatus of the first embodiment. FIG. 4 is a diagram for explaining actual temperatures on the surface of the heat roller that vary depending on the distance between the surface of the heat roller and the non-contact thermistor of the image forming apparatus according to the first embodiment. FIG. 3 is a diagram for explaining a temperature gradient of the image forming apparatus according to the first embodiment. FIG. 3 is a diagram illustrating a set temperature table of the image forming apparatus according to the first embodiment. FIG. 3 is a flowchart illustrating temperature control of a heat roller in the image forming apparatus according to the first embodiment. 6 is a block diagram of an image forming apparatus according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a difference in detected temperature of a non-contact thermistor caused by a difference in environmental temperature of the image forming apparatus according to the second embodiment. FIG. 6 is a diagram illustrating a set temperature table of the image forming apparatus according to the second embodiment. FIG. 10 is a diagram illustrating a flowchart of temperature control of a heat roller in the image forming apparatus according to the second embodiment. FIG. 10 is a diagram illustrating a flowchart of temperature control of a heat roller in the image forming apparatus according to the second embodiment. FIG. 10 is a block diagram illustrating another example of the image forming apparatus according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Print control part 2 Recording paper cassette 3 Photosensitive drum 4 Charging roller 5 LED head 6 Developing roller 7 Transfer roller 8 Fixing device 8a Halogen 8b Heat roller 8c Pressure roller 8d Non-contact thermistor 9 Recording paper remaining amount sensor 10 Sensor 11 Discharge sensor 12 recording paper 13 energization control unit 14 temperature detection circuit 15 detection temperature control unit 15 set temperature control unit 16 environment detection unit 21 image forming unit 23 developing blade 25 cleaning blade 31 environmental temperature sensor

Claims (5)

An image forming apparatus including a fixing unit having a rotating body that rotates in a conveyance direction of a medium so as to fix a developer deposited on the medium by heat from a heating source,
A temperature detector that faces the surface of the rotating body and is disposed at a predetermined distance from the rotating body, and detects the temperature of the surface of the rotating body;
A detection temperature control unit for calculating a temperature change amount per unit time of the temperature detected by the temperature detection unit;
An image forming apparatus comprising: a temperature control unit that determines a set temperature for controlling the temperature of the surface of the rotating body to a predetermined temperature based on the temperature change amount calculated by the detected temperature control unit. .   The image forming apparatus according to claim 1, wherein the set temperature is determined with reference to a set temperature table corresponding to a temperature change amount.   The image forming apparatus according to claim 2, wherein the set temperature table includes a set temperature corresponding to a distance between the rotating body and the temperature detection unit. further,
An environmental temperature detector that detects the ambient temperature where the image forming apparatus is installed as an environmental temperature,
The image forming apparatus according to claim 3, wherein the set temperature table includes an area corresponding to an environmental temperature detected by the environmental temperature detection unit.   The image forming apparatus according to claim 4, wherein the environmental temperature detection unit detects the environmental temperature when the image forming apparatus is activated and before the control of the heating source is started.