Heating apparatus, heating apparatus control method and noncontact thermal sensing device

A fixing apparatus according to one aspect of the present invention includes a non-contact temperature detecting element 81 allocated in non-contact with a heat roller, the sensing element detecting a temperature of the heat roller. The non-contact temperature sensing section 81 includes a thermopile P which detects a target temperature Pt of a heat roller 2, a temperature element CPU 100 which estimates an ambient temperature at the periphery of the thermopile P and computes an estimated ambient temperature SQt, and a thermister Q which detects an ambient temperature Qt at the periphery of the thermopile and outputs the ambient temperature Qt at an output voltage of a predetermined rate with respect to a total output voltage value corresponding to the estimated ambient temperature SQt.

FIELD OF THE INVENTION

The present invention relates to an image forming apparatus which forms an image on a transfer material by using an electronic photography process and a heating apparatus mounted on a copying machine, a printer or the like, the heating apparatus being incorporated in a fixing apparatus for fixing a developer onto the transfer material.

DESCRIPTION OF THE RELATED ART

In copying machine or a printer using an electronic process, it is known that a toner image formed on a photosensitive drum is transferred onto a transfer material, and then, the toner image molten by a fixing apparatus including a heat roller and a pressure roller is fixed onto the transfer material.

There is known a method of detecting a surface temperature by using a detecting element brought into contact with a surface of the heat roller and controlling a temperature of the heat roller. However, there is a possibility that such a contact temperature detecting element degrades the surface of the heat roller due to sliding, and there is a problem that a service line of the heat roller is reduced. In addition, due to surface degradation, responsiveness of the detecting element may be degraded and a temperature may be incorrectly detected.

Further, it is known to use a temperature detecting element which senses a red infrared ray radiated from a heat roller and detects a temperature of the heat roller in a non-contact manner.

However, at a radiation rate of a red infrared ray from the heat roller detected by the non-contact temperature detecting element, the surface of the heat roller is gradually degraded by contact with a transfer material which holds a toner, whereby a deviation occurs at the life beginning of using the heat roller and at the life end of the heat roller. Since the degradation of the surface of the heat roller is different depending on type of a transfer material passing through paper, or size of the transfer material, a deviation occurs also in a longitudinal direction of the roller at a red infrared radiation rate. That is, a time at which a temperature detected by the non-contact temperature detecting element reaches a set temperature is delayed due to a change of the red infrared radiation.

For example, as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-31390, there is known a technique using non-contact temperature detecting means which has self temperature detecting means to recognize a temperature T of the heat roller as a multiple order formula between a self temperature output T1and a sensor output T0of a non-contact temperature sensor sensed and outputted according to the self temperature and a heat roller temperature which is a non-sample, and controlling the temperature of the heat roller.

In addition, in Jpn. Pat. Appln. KOKAI Publication No. 9-281843, there is disclosed an electronic photography apparatus having a non-contact temperature sensor which senses a temperature of a heat roller in a non-contact manner and which controls the temperature of the heat roller by a sensor output of the non-contact temperature sensor. The electronic photography apparatus has means (fan) for supplying an air from a pair of image carriers to a fixing apparatus, and the non-contact sensor is allocated such that at least a part of the sensor is included in air between the fixing apparatus and the image carrier.

Further, Jpn. Pat. Appln. KOKAI Publication No. 9-212033 discloses a fixing apparatus having a self heat generation type heat roller and a temperature sensor which senses a temperature in a non-contact manner by a red infrared ray radiated by the heat roller, temperature control of the heat roller being made on the basis of an output of the temperature sensor. When a rise time from a room temperature of the heat roller to a fixing enable temperature is defined as Th, a diameter of the heat roller is defined as D cm, a maximum paper passage width of the heat roller is defined as W cm, and a response time of a fixing temperature sensor is defined as Ts, a relationship of 5 seconds≦Th≦0.23×DW seconds and 0.01 Th≦Ts<0.08 Th is established.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a heating apparatus comprising:

a heat roller which supplies a heat to sheet;

a heating device including a heating member which heats the heat roller and a first control section which controls power supplied to the heating member in order to heat the heat roller to a target temperature; and

at least one non-contact temperature sensing device provided in non-contact with a surface of the heating member, the at least one non-contact temperature sensing device comprising:a target temperature sensing section which detects a target temperature of the heat roller;a second control section which estimates an ambient temperature at the periphery of the target temperature sensing section and computes an estimated ambient temperature; anda self temperature detecting section which detects an ambient temperature at the periphery of the target temperature sensing section and outputs the ambient temperature at an output voltage of a predetermined rate with respect to a total output voltage value which corresponds to the estimated ambient temperature.

According to another aspect of the present invention, there is provided a heating apparatus control method comprising:

heating an outer periphery face of a heat roller by utilizing a plurality of inductive heating coils allocated outside of the heat roller;

detecting a target temperature from a target temperature detecting section provided in non-contact with the heat roller;

computing an estimated ambient temperature which is estimated as an ambient temperature at the periphery of the target temperature sensing section;

detecting an ambient temperature at the periphery of the target temperature sensing section which is outputted at an output voltage of a predetermined rate with respect to a total output voltage value which corresponds to the estimated ambient temperature;

computing a temperature of the heat roller on the basis of the target temperature and the ambient temperature; and

controlling power supplied to the inductive heating coil on the basis of the temperature of the heat roller.

According to further another aspect of the present invention, there is provided a non-contact temperature sensing device comprising:

a thermopile which detects a target temperature;

a control section which estimates an ambient temperature at the periphery of the thermopile and computes an estimated ambient temperature; and

a self temperature detecting section which detects an ambient temperature at the periphery of the thermopile and outputs the ambient temperature at an output voltage of a rate with respect to a total output voltage value which corresponds to the estimated ambient temperature.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an example of a fixing apparatus to which an embodiment of the present invention is applied will be described with reference to the accompanying drawings.

FIG. 1shows an example of the fixing apparatus to which the embodiment of the invention is applied.FIG. 2is a block diagram illustrating a control system of the fixing apparatus shown inFIG. 1.

As shown inFIG. 1, a fixing apparatus1has: a heating member (heat roller)2; a pressure roller member (press roller)3; a pressurizing spring4; a release claw5; a cleaning roller6; an induction heating device7; a temperature detecting mechanism8; and a thermostat9.

The heat roller2has: a shaft2acomposed of a material having rigidity (hardness) which is not deformed at a predetermined pressure; elastic layers2b(a foam rubber layer made by foaming a silicon rubber, a sponge layer, and a silicon rubber layer) allocated in order around the shaft2a; and an conductive layer (metal conductive layer)2c. Although not shown, a solid rubber layer and a mold release layer made of a thin film layer such as, for example, a heat resistance silicon rubber are further formed outside of the metal conductive layer2c.

It is preferable that the metal conductive layer2cis formed of an electrically conducting material (such as nickel, stainless steel, aluminum, copper, and composite material of stainless steel and aluminum). It is preferable that a length in a longitudinal direction of the heat roller2is 330 mm.

It is preferable that the foam rubber layer2bis formed to have thickness of 5 mm to 10 mm, that the metal conductive layer2cis formed to have thickness of 10 μm to 100 μm, and that the solid rubber layer is formed to have thickness of 100 μm to 200 μm, respectively. In the embodiment, the foam rubber layer2bis formed to have thickness of 5 mm, the metal conductive layer2cis formed to have thickness of 40 μm, the solid rubber layer is formed to have thickness of 200 μm, and the mold release layer is formed to have thickness of 30 μm, respectively. The heat roller2is formed to have a diameter of 40 mm.

The pressure roller3may be provided as an elastic roller coated with a silicon rubber having a predetermined thickness or a fluorine rubber at the periphery of a rotating shaft having a predetermined diameter. In addition, like the heat roller2, the pressure roller may be configured to have a metal conductive layer and an elastic layer.

The pressurizing spring4brings pressure contact with an axle of the heat roller2at a predetermined pressure, and the pressure roller3is maintained in approximately parallel to the axle of the heat roller2. A predetermined pressure is supplied from both ends of the pressure roller3via a pressurizing support bracket4awhich supports an axis of the pressure roller3, so that the pressurizing spring4can be in parallel to the heat roller2.

In this manner, a nip having a predetermined width is formed between the heat roller2and the pressure roller3.

By means of a fixing motor25shown inFIG. 2, the heat roller2is rotated in a clockwise CW direction indicated by the arrow at an approximately constant speed. The pressure roller3is brought into contact with the heat roller2at a predetermined pressure by means of the pressurizing spring4. Thus, the heat roller2is rotated, whereby the pressure roller3is rotated in an opposite direction to a direction in which the heat roller2is rotated at a position which comes into contact with the heat roller2.

The release claw5is positioned on the periphery of the heat roller2, on the downstream side in a direction in which the heat roller2is rotated by the nip at which the heat roller2and the pressure roller3come into contact with each other, and at a predetermined position in the vicinity of the nip. The release claw5releases paper P passed through the nip from the heat roller2. The present invention is not limited to the embodiment. For example, in the case where a large amount of developer is fixed onto paper, as is the case with forming a color image, the paper is hardly released from the heat roller. Thus, a plurality of release claws5may be provided. In addition, in the case where the paper is easily released from the heat roller, a release claw may not be provided.

The cleaning roller6removes dust such as toner or paper chips offset onto a surface of the heat roller1.

The induction heating device7has at least one heating coil (exciting coil) allocated outside of the heat roller, wherein predetermined power is supplied to supply a predetermined magnetic field to the heat roller2. In the embodiment, as shown inFIG. 2, the induction heating device includes: a coil71allocated to be opposed to a center portion in an axial direction of the heat roller2, the coil providing a magnetic field to the center portion of the heat roller2; and coils72,73allocated to be opposed to an end portion in the axial direction of the heat roller2, the coils each providing a magnetic field to the end portion of the heat roller2. As described later in detail, in the coils71to73, predetermined power is supplied from an exciting circuit22, thereby making it possible to generate a magnetic field according to this power and to inductively heat the metal conductive layer2cof the heat roller2.

The temperature detecting mechanism8includes at least one non-contact temperature detecting element provided in non-contact with the surface of the heat roller2, the non-contact temperature detecting element detecting a temperature on an outer periphery face of the heat roller2in a non-contact manner. The non-contact temperature detecting element is allocated on the downstream side in the rotation direction of the heat roller2more than a position at which the induction heating device7is allocated and on the upstream side more than the nip portion. The detecting element detects a surface temperature of the heat roller2heated by the induction heating device7.

In the embodiment, the temperature detecting mechanism8includes non-contact temperature detecting elements81,82,83,84,85allocated in order in the longitudinal direction of the heat roller2as shown inFIG. 2. The non-contact temperature detecting elements81,82,83each detect a surface temperature of the heat roller2opposed to the coils71,72,73. The non-contact temperature detecting element84detects a surface temperature of the heat roller2opposed to a joint of the coil71and the coil72. The non-contact temperature detecting element85detects a surface temperature of the heat roller2opposed to a joint of the coil71and the coil73.

The non-contact temperature detecting elements81,82,83,84,85are provided as non-contact temperature detecting elements capable of detecting temperatures of one or more sites by one element. These detecting elements each include: a thermopile (target temperature sensing section) P which detects a surface temperature of the heat roller2; a thermister (self temperature detecting section) Q which detects an ambient temperature in the vicinity of the thermopile; and a temperature element CPU100connected to the thermopile and the thermister.

The thermopile P detects a target temperature Pt which is a surface temperature of the heat roller2allocated oppositely, and the thermister Q detects an ambient temperature Qt in the vicinity of the thermopile P. The target temperature Pt and the ambient temperature Qt each are detected at a voltage value which corresponds to a sensing temperature.

The temperature element CPU100computes a roller temperature based on the output voltage values of the connected thermopile and thermister.

For example, the non-contact temperature detecting element81and the temperature element CPU100each estimate a temperature which will be detected by the ambient temperature Qt on the basis of a predetermined correlation table or the like with reference to the target temperature Pt detected from the thermopile P or a state of the past heating of the heat roller2. Hereinafter, the thus estimated ambient temperature is referred to as an estimated ambient temperature SQt. The estimated ambient temperature SQt is estimated depending on the state of the past heating of the heat roller, that is, a case in which power has been turned ON under a low temperature environment or a case in which resetting is carried out while long paper passage is in progress. In addition, the above predetermined correlation table corresponds to an inductive heating control method for heating a surface of the heat roller2in a short time, as in the present embodiment. That is, as in inductive heating, in the case where the surface of the heat roller2is heated in a short time, the target temperature Pt rapidly rises. However, the ambient temperature does not rise in response to a rise of the target temperature, and is different depending on the environment temperature or the past heating state of the heat roller. Therefore, the above predetermined correlation table is different depending on an equipment structure or performance of a non-contact temperature detecting element according to the target temperature Pt, the past heating state of the heat roller, and the like.

The temperature element CPU100selects a rate of an output voltage value of the ambient temperature Qt to a total output voltage on the basis of the estimated ambient temperature SQt, and detects the ambient temperature Qt. Then, the temperature element CPU100computes a surface temperature of the heat roller2based on the thus detected ambient temperature Qt and target temperature Pt, and outputs a roller surface temperature Rt1. In the embodiment, an error of about ±3° C. is allowed with respect to the estimated ambient temperature SQt.

In addition, the other non-contact temperature detecting elements82to85each have similar configuration, operation, and function and are capable of detecting roller temperatures Rt2, Rt3, Rt4, Rt5.

The thermostat9senses a heating abnormality indicating that a surface temperature of the heat roller2abnormally rises. If such a heating abnormality occurs, the thermostat is utilized in order to shut out the power supplied to a heating coil of the induction heating device7. It is preferable that at least one or more thermostats9are provided in the vicinity of the surface of the heat roller2.

Further, on the periphery of the pressure roller3, there may be provided: a release claw for releasing paper P from the pressure roller3or a cleaning roller which removes the toner adhered onto the peripheral face of the pressure roller3.

Thus, the paper P holding the toner T is passed through the nit portion formed between the heat roller2and the pressure roller3, whereby the molten toner T is brought into pressure contact with the paper P, and an image is fixed.

As shown inFIG. 2, a main CPU20is connected to a IH controller21, the exciting circuit22, a motor driver circuit24, the fixing motor25, a display section26, a RAM27, a ROM28, and a timer29.

The main CPU20integrally controls a fixing operation of the fixing apparatus1.

The IH controller21controls the exciting circuit22so that roller temperature information of the heat roller2detected by the non-contact temperature detecting elements81to85is inputted and predetermined power based on the temperature information or the like is supplied to the coils71to73of the induction heating device7. In more detail, the IH controller21controls the temperature of the heat roller2to be increased uniformly in an axial direction and to a fixing temperature required for fixing, on the basis of the roller temperature information of the heat roller2outputted from the non-contact temperature detecting elements81to85.

The exciting circuit22supplies predetermined power to the coils71to73in response to a control signal outputted from the IH controller21. In this manner, each of the coils71to73generates a magnetic flux which is a predetermined heating force. This heating force is determined by a size of a magnetic flux which forms a basis for causing the heat roller2to generate an eddy current and a size of the power supplied to each of the coils71to73. For example, in the case where paper passes through the center portion of the heat roller2, or alternatively, in the case where predetermined power for exciting the coil71is outputted, and then, the paper passes through the center portion and end part of the heat roller2, predetermined power (for example, 1300 W) for exciting the coils71to73is outputted.

The motor driver circuit24is connected to the fixing motor25which rotates the heat roller2. The motor driver circuit may be also connected to a main motor32which rotates the photosensitive drum33.

The display section26displays a device internal state message or a user message.

First Embodiment

Now, an example of temperature control of the IH controller21will be described with reference toFIGS. 3 and 4.FIG. 3is a flow chart showing an example of a temperature control method using the non-contact temperature detecting element81.FIG. 4is a view showing a relationship of an output voltage value of an estimated ambient temperature to all the output voltage values, the estimated ambient temperature being detected by the non-contact temperature detecting element according to the embodiment.

As shown inFIG. 4, for example, the non-contact temperature detecting element81outputs an output voltage which is 45% or higher of the total output voltage at an estimated ambient temperature of 50° C. (first temperature) or higher, and outputs an output voltage which is 70% or higher of the total output voltage at an estimated ambient temperature of 80° C. (second temperature). That is, when the target temperature Pt is a target temperature (160° C.), the non-contact temperature detecting element81can output a voltage obtained when an output voltage value outputted from the thermister Q is equal to or smaller than a maximum output value and is 50% or higher of the total output voltage.

In the case where the surface temperature of the heat roller2is the second temperature of 180° C., it is preferable that the thermister P of the non-contact temperature detecting element81outputs an output voltage which is at most 80% or less of the total output voltage. That is, in the case where the total output voltage of the thermister P is 1V, 0.8V is outputted.

As shown inFIG. 3, when the fixing apparatus is powered ON (S1), the IH controller21controls predetermined power to be supplied to the coils71to73via the exciting circuit22. When the fixing apparatus is powered ON, power is supplied to the non-contact temperature detecting elements81,82,83,84,85as well to detect a target temperature and an ambient temperature.

For example, the non-contact temperature detecting element81detects the target temperature Pt (S2) and estimates a temperature which will be detected by the ambient temperature Qt from the detected target temperature Pt. That is, the temperature element CPU100computes the estimated ambient temperature SQt with reference to the predetermined correlation table (S3).

The temperature element CPU100determines whether or not the computed estimated ambient temperature SQt is smaller than the first temperature of 50° C. (S4). In the case where the estimated ambient temperature SQt is smaller than the first temperature of 50° C. (S4—YES), the temperature element CPU100detects the ambient temperature Qt of the output voltage which is smaller than 45% of the total output voltage value (output limit) (S5), and computes the roller temperature Rt1on the basis of the target temperature Pt and ambient temperature Qt detected in step S2(S6).

On the other hand, in the case where the estimated ambient temperature SQt is equal to or higher than the first temperature of 50° C. in step S4(S4—NO), the temperature element CPU100further determines whether or not the estimated ambient temperature SQt is equal to or lower than the second temperature of 80° C. which is higher than the first temperature (S7). In the case where the estimated ambient temperature SQt is equal to or lower than the second temperature of 80° C. (S7—YES), the temperature element CPU100detects the ambient temperature Qt of the output voltage which is 45% or higher of the total output voltage value (output limit) (S8), and computes the roller temperature Rt on the basis of the target temperature Pt and ambient temperature Qt detected in step S2(S6).

On the other hand, in the case where the estimated ambient temperature SQt is higher than the second temperature of 80° C., (S7—NO), the temperature element CPU100detects the ambient temperature Qt of the output voltage which is 70% or higher of the total output voltage value (output limit) (S9), and computes the roller temperature Rt1on the basis of the target temperature Pt and ambient temperature Qt detected in step S2(S6).

The thus computed roller temperature Rt1is compared with a predetermined set value (for example, 160° C.) (S10). In the case where the roller temperature Rt1does not reach the set value (S10—NO), temperature control is executed by means of the IH controller21for heating the coil71to the set temperature (S11). On the other hand, when the roller temperature Rt1reaches the predetermined set value (S10—YES), the IH controller21determines whether or not a difference between the roller temperature Rt1and the roller temperature Rt2of another contact temperature detecting element82obtained as in the roller temperature Rt1is within a predetermined specified value (S12).

When the difference between the roller temperature Rt1and the roller temperature Rt2is within the specified value (S12—YES), it is determined that the heat roller2has been heated uniformly in the longitudinal direction up to a set temperature value, and warming up completes. In the case where a print reservation or instruction is made after warming up has terminated (S13—YES), a fixing operation of the fixing apparatus is started (S14), and temperature controls are executed by the IH controller21(S11). In the case where no print reservation is made (S13—NO), it is determined whether or not power has been turned OFF (S15). In the case where power has been turned OFF (S15—YES), these temperature controls are terminated.

If the power is kept to be turned ON (S15—NO), a ready state is established (S16), and the IH controller21makes control so as to maintain the surface temperature of the heat roller2(S11). In the case where this ready mode lasts for a predetermined time or longer, temperature control in an energy saving mode can be executed.

On the other hand, turning to step S12, if the difference between the roller temperature Rt1and the roller temperature Rt2is greater than the specified value, it is determined that the temperature of the heat roller2is not uniform in the longitudinal direction (S12—NO). In the case where the difference between the roller temperature Rt1and the roller temperature Tr2does not become equal to or lower than the specified value after the specified time has elapsed (S17—YES), the main CPU determines that a problem that precise temperature detection cannot be carried out occurs because the heat roller2fails or the not-contact temperature detecting element is dirty. Then, the display section26displays “service personnel inspection” as shown inFIG. 5, and requests roller replacement or cleaning of the non-contact temperature detecting element (S18). In step S17, in the case where the specified time has not elapsed (S17—NO), temperature control is executed by the IH controller21for making uniform the temperature in the axial direction of the heat roller2(S11).

In this way, temperature control is executed using the non-contact temperature detecting element81. The roller temperatures Rt2to Rt5are computed similarly in the other non-contact temperature detecting elements82to85. The IH controller21makes temperature control of the heat roller2on the basis of these roller temperatures Rt2to Rt5.

The temperature control by the IH controller21is provided as a control for increasing the surface temperature of the heat roller2uniformly in the axial direction up to the set temperature value and maintaining this set temperature value. The temperature control by the IH controller in step S11can be made in a mode different from another one according to determination of the previous step. For example, in the case where it is determined that the roller temperature Rt1does not read the set value in step S10, the IH controller21executes a control for making the temperature of the roller temperature Rt1to the set value as during warming up. In the case where the difference between the roller temperature Rt1and the roller temperature Rt2is greater than the specified value in step S12, the IH controller makes control so as to heat a region in which a temperature is lower in order to make uniform the temperature in the axial direction of the heat roller2. Further, in the case where it is determined that a ready state is established in step S16, an energy saving mode is established if a user does not supply a print instruction. Then, the set value of the surface temperature of the heat roller2is set at a temperature which is lower than a fixing temperature and which can be recovered in a short time, and the power supplied to the coils71to73is restricted.

Further, in the embodiment, the IH controller21makes control for supplying power to a coil in which the detected roller temperature is lower, thereby supplying power which is lower than power shared in the coil whose roller temperature is lower or stopping power supply. For example, in control of the coil71and the coil72, the roller temperature Rt1and the roller temperature Rt2are compared with each other, and when the roller temperature Rt1is lower, power is supplied to the coil71and power supply to the coil72is stopped.

The IH controller21can also control power supplied to the coils71,72so as not to lower a temperature between the coil71and the coil72with reference to the roller temperature Rt4.

Thus, the heat roller2can be increased to a temperature which is uniform in the axial direction and can be maintained by the IH controller21.

As described above, the temperature element CPU100can estimate a temperature which will be detected by the ambient temperature Qt on the basis of the target temperature Pt detected by the thermopile P and can select a rate of an output voltage of the ambient temperature Qt in response to the estimated ambient temperature SQt. In this manner, the thermister Q can output sufficient output power. Therefore, in the thermister Q, the non-contact temperature detecting elements81to85can detect a temperature more precisely because a difference in output voltage broadens in response to a temperature change.

In addition, in the embodiment, when the heat roller2has been heated up to a target temperature (160° C.), i.e., when the estimated ambient temperature is 80° C., an output voltage of the thermister Q is 70% (i.e., 50% or higher) of the total output voltage. Thus, this thermister is effective in particular in the case where the ambient temperature rapidly changes as during warming up.

Further, the power supplied to the coils71to73is also selected according to the temperature detected by the non-contact temperature detecting elements81to85, thus making it possible to utilize power with no wastefulness without excessive power being supplied to the coils71to73and to contribute to energy saving.

Namely, in the case where the ambient temperature rapidly changes as during warming up, the output voltage value detected by the thermister greatly changes concurrently. In this case, if a difference between an output voltage value of the ambient temperature of the thermister and an output voltage value of the target temperature of the thermopile is small, there has been a problem that the roller temperature of the heat roller2cannot be precisely measured.

However, the non-contact temperature detecting elements81to85as described above can output a sufficient output voltage as the ambient temperature Qt outputted from the thermister Q, in particular, until a fixing temperature of the heat roller2has reached about 180° C. Thus, even in the case where the difference in output voltage of the ambient temperature outputted from the thermister Q broadens, and then, the ambient temperature Qt rapidly changes as during warming up, the non-contact temperature detecting elements81to85can detect the surface temperature of the heat roller2precisely.

FIG. 6shows a relationship between a time (horizontal axis) and a temperature (vertical axis) when the heat roller2has been heated by means of such temperature control. This temperature is provided as a temperature detected from the non-contact temperature detecting element when temperature control has been made such that the heat roller is heated to a predetermined temperature (160° C.). A result utilizing the temperature control according to the present invention is designated by L1, and a result of the temperature control according to a conventional method is designated by L2. The conventional temperature control method is provided as a temperature control method for computing a surface temperature of the heat roller2by utilizing the output voltage itself detected from the thermister and the thermopile.

As shown inFIG. 6, with respect to the result L1of the temperature control according to the invention, when a temperature is increased to the set temperature of 160° C., the surface temperature of the heat roller2controlled to be turned ON/OFF in the vicinity of the temperature of 160° C. is detected as is controlled. On the other hand, with respect to the result L2of the conventional temperature control, although the heat roller2has been increased to the set temperature of 160° C., the surface temperature of the heat roller2controlled to be turned ON/OFF in the vicinity of 140° C. which is lower than the set temperature by about 20° C. is detected. Therefore, in the conventional method, a large detection error occurs.

The invention can solve such a conventional problem and is effective in a fixing apparatus which executes feedback control based on temperature information. In addition, according to the embodiment, in the fixing apparatus utilizing IH control, a temperature rise within a short time can be achieved. Thus, according to the embodiment, an abnormal temperature rise of the heat roller2can be prevented by precisely detecting a temperature. Therefore, damage imparted to the heat roller is reduced, and the service life is extended.

Second Embodiment

Now, another example of temperature control of the IH controller21will be described with reference toFIGS. 7 and 8.FIG. 7is a flow chart showing an example of a temperature control method using the non-contact temperature detecting element81.FIG. 8is a view showing a relationship between an output voltage value and a total output voltage value of an estimated ambient temperature detected by a non-contact temperature detecting element according to the embodiment.

As shown inFIG. 8, for example, the non-contact temperature detecting element81outputs an output voltage which is 30% or higher of the total output voltage when an estimated ambient temperature is equal to or higher than 20° C. (third temperature) which is a minimum temperature when warming up completes. The detecting element also outputs an output voltage which is 90% or higher of the total output voltage at an estimated ambient temperature of 80° C. (second temperature).

That is, when a target temperature Pt is a target temperature (100° C.), the non-contact temperature detecting element81can output a voltage in the case where an output voltage value outputted from the thermister Q is equal to or smaller than the maximum output value and is 30% or higher of the total output voltage.

As shown inFIG. 7, when the fixing apparatus is powered ON (S21), the IH controller21makes control so that predetermined power is supplied to the coils71to73via the exciting circuit22. In addition, when the fixing apparatus is powered ON, power is supplied to the non-contact temperature detecting elements81,82,83,84,85as well to detect a target temperature and an ambient temperature.

For example, the non-contact temperature detecting element81detects the target temperature Pt (S22), and estimates a temperature which will be detected by the ambient temperature Qt from the detected target temperature Pt. That is, the temperature element CPU100computes the estimated ambient temperature SQt with reference to the predetermined correlation table (S23).

The temperature element CPU100determines whether or not the computed estimated ambient temperature SQt is smaller than the third temperature of 20° C. (S24). In the case where the estimated ambient temperature SQt is smaller than the third temperature of 20° C. (S24—YES), the temperature element CPPU100detects the ambient temperature Qt of an output voltage which is smaller than 30% of the total output voltage value (output limit) (S25), and computes a roller temperature Rt1based on the target temperature Pt and ambient temperature Qt detected in step S22(S26).

On the other hand, in the case where the estimated ambient temperature SQt is equal to or higher than the third temperature of 20° C. in step S24(S24—NO), the temperature element CPU100further determines whether or not the estimated ambient temperature SQt is equal to or lower than the second temperature of 80° C. which is higher than the third temperature (S27). In the case where the estimated ambient temperature SQt is equal to or lower than the second temperature of 80° C. (S27—YES), the temperature element CPU100detects the ambient temperature Qt of an output voltage which is equal to or higher than 30% of the total output voltage value (output limit) (S28), and computes the roller temperature Rt on the basis of the target temperature Pt and ambient temperature Qt detected in step S22(S26).

On the other hand, in the case where the estimated ambient temperature SQt is higher than the second temperature of 80° C. (S27—NO), the temperature element CPU100detects the ambient temperature Qt of an output voltage which is 90% or higher of the total output voltage value (output limit) (S29), and computes the roller temperature Rt1on the basis of the target temperature Pt and ambient temperature Qt detected in step S22(S26).

The thus detected roller temperature Rt1is compared with a predetermined set value (for example, 160° C.) (S30). In the case where the roller temperature Rt1does not reach the set value (S30—NO), temperature control is executed by the IH controller21for heating the coil71to the set temperature (S31). On the other hand, if the roller temperature Rt1reaches the predetermined set value (S30—YES), the IH controller21determines whether or not a difference between the roller temperature Rt1and a roller temperature Rt2of another non-contact temperature detecting element obtained in the same manner as when the roller temperature Rt1is obtained is within a predetermined specified value (S32).

When the difference between the roller temperature Rt1and the roller temperature Rt2is within the specified value (S32—YES), it is determined that the heat roller2has been heated uniformly in the longitudinal direction up to the set temperature value, and warming up completes. In the case where a print reservation or instruction is made after warming up has terminated (S33—YES), a fixing operation of the fixing apparatus is started (S34), and temperature controls are executed by the IH controller21(S31). In the case where no print reservation is made (S33—NO), it is determined whether or not power has been turned OFF (S35). In the case where power has been turned OFF (S35—YES), these temperature controls are terminated.

If power is kept to be turned ON (S35—NO), a ready state is established (S36), and the IH controller21makes control so as to maintain a surface temperature of the heat roller2(S31). In the case where this ready state lasts for a predetermined time or longer, temperature control can be executed in an energy saving mode.

On the other hand, turning to step S12, if the difference between the roller temperature Rt1and the roller temperature Rt2is greater than the specified value, it is determined that the temperature of the heat roller2is not uniform in the longitudinal direction (S3—NO). In the case where the difference between the roller temperature Rt1and the roller temperature Rt2is not equal to or smaller than the specified value after a specified time has elapsed (S37—YES), the main CPU determines that there occurs a problem that precise temperature detection cannot be carried out because the heat roller2fails or a non-contact temperature detecting element is dirty. Then, the display section26displays “service personnel inspection” as shown inFIG. 5, and requests roller replacement or cleaning of the non-contact temperature detecting element (S38). In the case where the specified time has not elapsed in step S37(S37—NO), temperature control is executed by the IH controller21for making uniform the temperature in the axial direction of the heat roller2(S31).

The above-described third temperature is provided as a minimum temperature required when warming up completes, and the third temperature has been set to 20° C. in the embodiment. Thus is because, as shown inFIG. 9, 20° C. has been set when warming up completes as a result of measuring the ambient temperature during warming up in a low tone and low humidity environment. Therefore, the ambient temperature when warming up completes reaches at least 20° C. or higher under a normal temperature environment or under a high temperature environment.

As described above, the non-contact temperature detecting elements81to85can output an ambient temperature of a sufficient output voltage value from an ambient temperature in a state in which the ambient temperature has reached the minimum temperature required when warming up completes to an ambient temperature at which the surface temperature of the heat roller2is heated and maintained to the fixing temperature. Consequently, the non-contact temperature detecting elements81to85can detect a temperature more precisely. Therefore, the power supplied to the coils71to73is also selected according to the temperatures detected by the non-contact temperature detecting elements81to85, thus making it possible to utilize power with no wastefulness without excessive power being supplied to the coils71to73and contribute to energy saving.

Third Embodiment

Now, a still another example of the heating apparatus control method according to the invention will be described with reference toFIGS. 10 to 16.

FIG. 10is a block diagram illustrating a control system of a non-contact temperature detecting element.FIG. 11is a view showing a relationship between temperature detection of an ambient temperature detecting section and program change.FIG. 12is a view showing a relationship between an output voltage value and a total output voltage value of an estimated ambient temperature in a first thermister according to the embodiment.FIG. 13is a view showing a relationship of an output voltage value and a total output voltage value of an estimated ambient temperature in a second thermister according to the embodiment.FIG. 14is a view showing a relationship between an output voltage value and a total output voltage value of an estimated ambient temperature of a third thermister according to the embodiment.FIGS. 15 and 16are flow charts each showing an example of a temperature control method using the non-contact temperature detecting element81.

As shown inFIG. 10, the non-contact temperature detecting element81comprises a thermopile P, a first thermister QA, a second thermister QB, a third thermister QC, a temperature element CPU100, and a thermister selector circuit200.

The temperature element CPU100is connected to the thermopile P, the thermister selector circuit200, and the IH controller21to input a target temperature Pt detected by the thermopile P and ambient temperatures QtA, QtB, QtC detected by the first to third thermisters QA, QB, QC selected via the thermister selector circuit200. The temperature element CPU100computes a roller temperature Rt based on these items of inputted information, and outputs the computed temperature to the IH controller21.

Specifically, when the thermister selector circuit200selects the first thermister QA, a program A described later is used to output the ambient temperature QtA which is a voltage value of a rate set with respect to the total output voltage according to the ambient temperature, as described in the first and second embodiments. Similarly, when the second thermister QB is selected, a program B is used to output the ambient temperature QtB which is a voltage value of a rate set with respect to the total output value according to the ambient temperature. When the third thermister is selected, a program C is used to output the ambient temperature QtC which is a voltage value of a rate set with respect to the total output value according to the ambient temperature.

As described above, the temperature element CPU100can compute the estimated ambient temperature SQt with reference to the target temperature Pt detected by the thermopile P on the basis of the predetermined correlation table.

The thermister selector circuit200selects a self temperature detecting section for detecting an ambient temperature according to the above estimated ambient temperature SQt. In the embodiment, in the case of (A) −5° C.≦the estimated ambient temperature SQt<28° C. (first temperature range), the thermister selector circuit200selects the first thermister QA. In the case of (B) 28° C.≦the estimated ambient temperature SQt<57° C. (second temperature range), the selector circuit selects the second thermister QB. In the case of (C) 57° C.≦the estimated ambient temperature SQt<80° C. (third temperature range), the selector circuit selects the third thermister QC.

When the program A is used, the first thermister QA is controlled to output an output voltage which is equal to or higher than −5° C. in estimated ambient temperature SQt and which is 20% or higher of the total output voltage, as shown inFIG. 12and to output an output voltage which is 28° C. in estimated ambient temperature SQt and which is 90% or higher of the total output voltage, by means of the temperature element CPU100.

When the program B is used, the second thermister QB is controlled to output an output voltage which is equal to or higher than 28° C. in estimated ambient temperature SQt and which is 20% or higher of the total output voltage, as shown inFIG. 13and to output an output voltage which is 57° C. in estimated ambient temperature SQt and which is 90% or higher of the total output voltage, by means of the temperature element CPU100.

When the program C is used, the third thermister QC is controlled to output an output voltage which is equal to or higher than 57° C. in estimated ambient temperature SQt and which is 20% or higher of the total output voltage, as shown inFIG. 14and to output an output voltage which is 80° C. in estimated ambient temperature SQt and which is 90% or higher of the total output voltage, by means of the temperature element CPU100.

That is, the first to third thermisters QA, QB, QC, as described in the first and second embodiments, are controlled based on the programs A to C such that a rate of an output voltage to a total output voltage is selected according to the threshold value of the respective estimated ambient temperature SQt.

Therefore, as in the non-contact temperature detecting element according to the embodiment, a plurality of thermisters capable of outputting a sufficient output voltage are provided in association with an ambient temperature range delimited by an arbitrary threshold value, whereby a difference in output voltage according to a temperature change broadens, thus making it possible to carry out more precious temperature detection.

As shown inFIG. 15, when the fixing apparatus is powered ON (S61), the IH controller21makes control so as to supply predetermined power to the coils71to73via the exciting circuit22. In addition, when the fixing apparatus is powered ON, power is supplied to non-contact temperature detecting elements81,82,83,84,85as well to detect a target temperature and an ambient temperature.

For example, when the thermopile P of the non-contact temperature detecting element81detects the target temperature Pt (S62), the temperature element CPU100computes the estimated ambient temperature SQt with reference to the predetermined correlation table (S63).

The temperature element CPU100determines whether or not the computed estimated ambient temperature SQt is within the range between −5° C. or higher and lower than 28° C. (S64). In the case where the estimated ambient temperature SQt is within the range of −5° C.≦the estimated ambient temperature SQt<28° C. (S64—YES), the thermister selector circuit200selects the thermister QA. The temperature element CPU100detects the ambient temperature QtA from the thermister QA at an output voltage of 20% or higher and lower than 90% of the total output voltage by using the program A (S65).

On the other hand, in step S64, in the case where the estimated ambient temperature SQt is not within the range of −5° C.≦the estimated ambient temperature SQt<28° C. (S65—YES), the temperature element CPU100determines whether or not the inputted estimated ambient temperature SQt is within the range between 28° C. or higher and lower than 57° C. (S66). In the case where the estimated ambient temperature SQt is within the range of 28° C.≦the estimated ambient temperature SQt<57° C. (S66—YES), the thermister selector circuit200selects the thermister QB. The temperature element CPU100detects the ambient temperature QtB from the thermister QB at an output voltage in the range between 20% or higher and lower than 90% of the total output voltage by using the program B (S67).

On the other hand, in the case where the estimated ambient temperature SQt is not within the range of −28° C.≦the estimated ambient temperature SQt<57° C. (S66—YES), the temperature element CPU100determines whether or not the inputted estimated ambient temperature SQt is within the range between 57° C. or higher and lower than 80° C. (S68). In the case where the estimated ambient temperature SQt is within the range of 57° C.≦the estimated ambient temperature SQt<80° C. (S68—YES), the thermister selector circuit200selects the thermister QC. The temperature element CPU100detects the ambient temperature QtC from the thermister QC at an output voltage in the range between 20% or higher and lower than 90% of the total output voltage by using the program C (S69).

On the other hand, in step S66, in the case where the estimated ambient temperature SQt is not within the range of −28° C.≦the estimated ambient temperature SQt<57° C. (S66—YES), the thermister selector circuit200selects any one of the thermister QA to QC. In the embodiment, the thermister QC is selected. The temperature element CPU100detects the ambient temperature QtC from the thermister QC at an output voltage which is 90% or higher of the total output voltage by using the program C (S70).

The temperature element CPU100computes a roller temperature Rt1on the basis of any one of the ambient temperatures QtA to QtC detected as described above and the target temperature Pt detected in step S2(S71).

The computed roller temperature Rt1is compared with a predetermined set value (for example, 160° C.) (S72). In the case where the roller temperature Rt1does not reach the set value (S72—NO), temperature control is executed by the IH controller2for heating the coil71to the set temperature (S73). On the other hand, when the roller temperature Rt1reaches the predetermined set value (S72—YES), the IH controller21determines whether or not a difference between the roller temperature Rt1and a roller temperature Rt2of another non-contact temperature detecting element82obtained in the same manner as when the roller temperature Rt1is obtained is within the predetermined specified value (S74).

When the difference between the roller temperature Rt1and the roller temperature Rt2is within the specified value (S74—YES), it is determined that the heat roller2has been heated uniformly in the longitudinal direction up to the set temperature value, and warming up completes. In the case where a print reservation or instruction is made after warming up has terminated (S75—YES), a fixing operation of the fixing apparatus is started (S76), and temperature controls are executed by the IH controller21(S73). In the case where no print reservation is made (S75—NO), it is determined whether or not power is turned OFF (S77). In the case where power has been turned OFF (S77—YES), these temperature controls are terminated.

If power is kept to be turned ON (S77—NO), a ready state is established (S78), and the IH controller21makes control so as to maintain a surface temperature of the heat roller2(S73). In the case where this ready state lasts for a predetermined time or longer, temperature control can be executed in an energy saving mode.

On the other hand, turning to step S74, if the difference between the roller temperature Rt1and the roller temperature Rt2is greater than the specified value, it is determined that the temperature of the heat roller2is not uniform in the longitudinal direction S74—NO). In the case where the difference between the roller temperature Rt1and the roller temperature Rt2is not equal to or smaller than the specified value after a specified time has elapsed (S79—YES), the main CPU determines that there occurs a problem that precise temperature detection cannot be carried out because the heat roller2fails or because the non-contact temperature detecting element is dirty. Then, the display section26displays “service personnel inspection” as shown inFIG. 5, and requests roller replacement or cleaning of the non-contact temperature detecting element (S80). In step S79, in the case where the specified time has not elapsed (S79—NO), temperature control is executed by the IH controller21for making uniform the temperature in the axial direction of the heat roller2(S73).

In this manner, temperature control is executed using the non-contact temperature detecting element81. With respect to the other non-contact temperature detecting elements82to85as well, the roller temperatures Rt2to Rt5are computed similarly. The IH controller21makes temperature control of the heat roller2on the basis of these roller temperatures Rt2to Rt5.

As described above, the non-contact temperature detecting elements81to85according to the embodiment each has the first to third thermisters capable of, in a predetermined estimated ambient temperature range (first to third temperature ranges), detecting an ambient temperature of an output voltage which is in the range between 20% or higher and lower than 90% of the total output voltage in this temperature range. In addition, the first to third temperature ranges are provided as continuous temperature ranges. A thermister selected by the thermister selector circuit200is switched according to the computed estimated ambient temperature, whereby the ambient temperature of an output voltage in the range between 20% or higher and lower than 90% of the total output voltage can be detected in the first to third temperature ranges. Thus, a difference in output voltage of the ambient temperature output from the thermister Q broadens, and the thermister can carry out precise temperature detection.

In step S70shown inFIG. 15, although the thermister QC has been utilized, the present invention is not limited to this thermister. For example, a fourth thermister is further provided to output an output voltage which is equal to or higher than 80° C. in estimated ambient temperature and which is equal to or higher than 20% of a total output voltage, so that an ambient temperature may be detected by the fourth thermister.

In addition, the invention utilizing a non-contact temperature detecting mechanism can prevent an occurrence of a slide contact trace which may be formed on the surface of the heat roller2by the temperature detecting mechanism of contact type, and thus, the service life of the heat roller2can be executed.

The present invention is not limited to the above-described embodiments themselves. The invention can be embodied by modifying the constituent elements without departing from the spirit of the invention at the stage of carrying out the invention. In addition, a variety of inventions can be formed by using a proper combination of a plurality of constituent elements disclosed in the above-described embodiments. For example, some of all the constituent elements shown in the embodiments may be erased. Further, the constituent elements over the different embodiments may be properly combined with each other.

For example, the non-contact temperature detecting elements81to85may sense the surface temperature of the heat roller2on the downstream side in the rotation direction of the heat roller2more than a position at which the induction heating device7is allocated and on the upstream side more than the nip portion. For example, these non-contact temperature detecting elements may be configured to sense the surface temperature of the heat roller2between the coil and the heat roller2, immediately after the coil, and immediately before the nip.

In addition, as described above, while the non-contact temperature detecting elements81to85have been described as constituent elements capable of detecting a temperature of one site by one element, the present invention is not limited to these detecting elements. For example, there may be used a non-contact temperature detecting element which detects temperatures of two or more sites by one element.

Further, as described above, while the non-contact temperature detecting elements81to85have been described to be allocated in a region opposed to the coil joint or the center of the coils71to73, the present invention is not limited to these detecting elements. For example, these detecting elements may be allocated at both ends in the longitudinal direction of the heat roller2, i.e., in a region opposed to the ends of the coils72,73. In addition, the detecting elements may be configured so as not to be allocated at the joint and so as to be allocated in a region opposed to at least the center coil71and in a region opposed to the end coil72.

Furthermore, in temperature control as shown inFIG. 3, the heat roller2may be configured to be rotated at the same time as when power is turned ON or may be configured to be rotated after a predetermined time has elapsed.

Moreover, while the embodiment has described that a fixing temperature of the heat roller2is set to 180° C., the present invention is not limited to this fixing temperature. The setting can be changed according to an equipment structure, a melting point of a developer to be utilized or the like. In addition, this set value depends depending on the size, type or thickness of a recording medium. For example, when the recording medium is thick, the set value is set to be higher than usual.

In addition, while the embodiment has described a method for setting an amount of power, thereby generating a magnetic flux which is an arbitrary heating force from the coils71to73, the present invention is not limited to this method. This method may be provided as a method for selecting a frequency of a flow current for the coils71to73, thereby changing the heating force.

While the embodiment has described a configuration of applying a pressure from the pressure roller to the heat roller, the present invention is not limited to this configuration. This configuration may be provided as a configuration of applying a pressure from the heat roller to the pressure roller.

In addition, this configuration may be provided as a configuration of detecting the temperature of the heat roller2by using a sensor of contact type. Further, in the non-contact temperature detecting element81, at least the thermopile P and the thermister Q may be allocated in the fixing apparatus. The temperature element CPU100or the like may be allocated outside of the fixing apparatus.