JPH04220679A - Correction method for temperature detection in fixing device - Google Patents

Abstract

PURPOSE:To ensure accurate correction of the surface temperature of a fixing roller, without giving damage to the surface of a fixing roller by a thermistor. CONSTITUTION:The switching of a thermistor 4 to a contact or noncontact position of a fixing roller 1 is performed by a switching means, and the ON/OFF control of a heater 3 is performed by the temperature measurement value of the noncontact position in a control mode, while the temperature measurement values at the contact and noncontact positions are compared with each other so as to correct the temperature measurement value obtained in the control mode, in a correction mode, and the timing of temperature measurement for comparison correction in the control mode is when the heater is turned off after the temperature of the fixing roller 1 becomes fixable.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature detection correction method for a fixing device in an electrophotographic copying machine, printer, or the like.

0002

2. Description of the Related Art Conventionally, in a fixing device equipped with a fixing roller having a heater and a thermistor that detects the surface temperature of the fixing roller, a control method for controlling the temperature of the heater based on a temperature signal detected by the thermistor is well known. It has become.

0003

[Problems to be Solved by the Invention] As a method for detecting the surface temperature of the fixing roller in the above case, (1)
(2) A method in which the thermistor does not contact the surface of the fixing roller (Japanese Patent Application Laid-Open No. 62-49174); (2) A method in which the thermistor does not contact the surface of the fixing roller (Japanese Patent Application Laid-Open No. 61-88170)
Publication No.). However, in the method (1) above, there is a problem that friction occurs between the fixing roller and the thermistor during rotation, causing scratches on the surface of the fixing roller. However, there is a problem in that it is not possible to measure the temperature of the paper passing portion of the fixing roller, where the temperature decreases as the transfer paper passes. Although the method (2) above does not cause any damage to the surface of the fixing roller, in order to ensure the accuracy of estimating the surface temperature of the fixing roller from the detected temperature value, it is necessary to The gap between the fixing rollers must be managed with high precision, and the measured values vary considerably depending on the ambient temperature, so the surface temperature of the controlled fusing roller may change immediately after the device warms up and after continuous operation. There is a problem with coming.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the conventional temperature detection correction method in a fixing device as described above, and to prevent damage to the surface of the fixing roller and to improve the temperature between the fixing roller and thermistor. An object of the present invention is to provide a temperature detection correction method that does not require highly accurate management of gaps.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fixing device as described above, in which the thermistor is placed at a contact position where it contacts the surface of the fixing roller and at a non-contact position spaced apart from the contact position. a control mode in which the heater of the fixing roller is controlled on and off based on the temperature measurement value at the non-contact position, and the temperature measurement value at the contact position and the non-contact position are compared; and a correction mode for correcting the temperature measurement value in the control mode, and the timing for performing temperature measurement for comparison correction in the correction mode is when the heater is turned off after the temperature of the fixing roller reaches a fixable temperature. It is characterized by:

[0006]

[Function] In this invention as described above, the switching means brings the thermistor into contact with the fixing roller during warm-up or standby, but makes it non-contact during copying, and controls the heater on and off based on the temperature measured during non-contact. This measured value is corrected by comparing the measured values during contact and non-contact, and the measurement timing for this correction is performed when the heater is turned off after the temperature of the fixing roller reaches a fixable temperature.

[0007]

[Embodiment] In the embodiment of the present invention shown in FIGS. 1 to 3, reference numeral 1 indicates a fixing roller provided with a heater 3 therein, and a pressure roller 2 is provided opposite to this fixing roller 1. is rotated in the direction of the arrow. A thermistor 4 is disposed above the fixing roller 1, and this thermistor 4 is provided at the tip of a lever 5 that is pivotally supported on the machine frame by a support shaft 6.
The base end of the lever 5 is connected to the operating rod of a solenoid 7 installed in the machine, and the lever 5 is pressed down by a spring 8 between the support shaft 6 and the thermistor 4, and the base end of the lever 5 is connected to the operating rod of a solenoid 7 installed in the machine. When the solenoid 7 is activated, the thermistor 4 is not brought into contact with the fixing roller 1 with a gap d, as shown in FIG. Sometimes, as shown in FIG. 2, the fixing roller 1 is brought into contact with the pressing force of a spring 8. In the non-contact state, the lever 5 comes into contact with the stopper 9, so that the gap d is kept constant.

FIG. 4 shows a control block diagram of the above-mentioned system, and 10 is a μCPU which executes a control program stored in a ROM 14. 11 is an interface with the operation unit 12 including a display unit, 13 is a RAM for reading and writing copy mode data and various flags, and 15 is an A/D that converts the analog voltage from the thermistor 4 into digital data and interfaces with the CPU 10. Converter 16 is for each load and sensor etc. in the copying machine and CPU 1
This is an I/O interface that interfaces with 0 on a one-to-one basis. The loads connected to the I/O interface 16 and related to the present invention include the solenoid 7 that connects and disconnects the thermistor 4, the main motor 19, and its constant speed control circuit 18 (in this embodiment, the I/O
It is triggered by the on/off signal from the interface 16, and uses a method that combines both the F/V control method and the PLL control method to achieve constant speed control), and is connected to the commercial power supply 29 and the driving SSR 20. Connected heater 3
is connected. In addition, each switch/sensor 24 and each load 22 from other units are connected to the I/O interface 16 through a signal line 25 and a drive element 23, respectively.

The thermistor 4 used in the present invention has a small thermal time constant τ in order to detect the temperature in the vicinity of the fixing roller 1 without contacting it when the fixing roller 1 is rotating, that is, when the main motor 19 is rotating. A thin film type is used. In this embodiment, a value of about 2.5 seconds is used as the thermal time constant τ in air, but the value is not limited to this. Furthermore, the temperature-resistance characteristic of this thermistor 4 has NTC, that is, a negative characteristic, as shown in FIG.
The detected analog voltage is A/
It is given to the D converter 15. A/D converter 15
converts the analog voltage input as described above into 8-bit data in this embodiment, and the 8-bit data is read by the CPU 10 and the thermistor detection temperature ts is determined by the corresponding data stored in the ROM 14. be done.

Heater 3 is turned on and off by turning on and off SSR20.
is driven, and the surface temperature tr of the fixing roller 1 is controlled to the control temperature tc (185°C in this embodiment). The relationship between the surface temperature tr of the fixing roller 1 and the detected temperature ts of the thermistor 4 is expressed by the following equation. It is assumed that 1, 2.

[Formula 1] tr=ts+to......When the thermistor is in contact (during warming up, during standby)

[Formula 2] tr=ts+to+Δt...When the thermistor is not in contact (during copying, etc., when the main motor is rotating), where to is the actual surface temperature tr of the fixing roller 1 when the thermistor 4 is in contact with the fixing roller 1. This is the temperature difference from the detected temperature ts of the thermistor 4, which varies depending on the structure and installation position of the thermistor 4, and is determined experimentally. Further, the temperature Δt is a correction term that is a key point of the present invention, and is determined based on the difference in temperature ts detected between the contact position and the non-contact position of the thermistor 4 with respect to the fixing roller 1. Details regarding the timing and method of measuring the temperature Δt will be described later.

According to equations 1 and 2 above, when the thermistor 4 is in contact with the fixing roller 1 during warming up or on standby, the temperature tr of equation 1 and the rotation of the main motor during copying etc. 4 cannot contact the surface of the fixing roller 1, the temperature tr in equation 2 is compared with the control temperature tc, and if the temperature tr is low, the fixing roller 1 is turned on, and if the temperature tr is high, the fixing roller is turned on. 1 is turned off, the surface temperature of the fixing roller 1 becomes temperature t.
It is controlled using c as a control value.

Fixing roller 1 for the thermistor 4 as described above
Contacting the surface of is carried out by the solenoid 7 according to the aforementioned mode. When the thermistor 4 is connected and separated by the solenoid 7 in this way, there is a temperature response time of the detected temperature ts of the thermistor 4 for a certain period of time, and from the contact state to the non-contact state, the temperature response time is several times the thermal time constant τ, The time required is 7.5 to 10 seconds, and the time from the non-contact state to the contact state is less than 1 second, but the heater control during this time is not controlled (heater off) in this embodiment.

FIG. 5 shows the execution sequence of the correction term Δt measurement mode during warm-up after turning on the main switch, after removing jam paper, and during warm-up after opening the door. In this Figure 5, 3
1 is the surface temperature tr of the fixing roller 1, 32 is the on/off state of the heater 3, 33 is the on/off state of the solenoid 7,
Reference numeral 34 indicates the state of contact and separation of the thermistor 4 with respect to the fixing roller 1, 35 indicates the detected temperature ts of the thermistor 4, and 36 indicates a copy enabled/disabled state indicating that warm-up is in progress or warm-up has ended.

During warm-up, the thermistor 4 is in contact with the fixing roller 1, so the heater 3 is controlled by equation 1 above. When the temperature tr becomes equal to the temperature tc, the heater 3 is turned off. When the heater 3 is turned off in this manner, the temperature tr naturally decreases after overshooting, but when this temperature becomes equal to the temperature tc again, measurement of the correction term Δt is started. Data is obtained from the temperature ts at this point as the temperature tsc, and then the solenoid 7
is turned on, and the thermistor 4 is separated from the fixing roller 1 by a certain distance. At this time, the heater 3 is forcibly turned off. When the time T1 (≒4τ), which is several times the thermal time constant τ, has elapsed, the temperature ts at that time is acquired as the temperature tsn, the solenoid 7 is turned off, and the thermistor 4
contacts the fixing roller 1 again. Control of the heater 3 is resumed after the temperature response time. When the temperature tr becomes equal to the temperature tc again and the heater 3 is turned off, the warm-up is considered to be complete and the state becomes ready for copying. In this case, the correction term Δt is determined by the following equation 3.

[Formula 3] Δt=tsc-tsn-t1 Here, t1 is the surface of the fixing roller 1 due to the heater 3 being turned off during the time T1 during which the thermistor 4 responds to the ambient temperature in a non-contact state, as shown in FIG. This is the decrease in temperature tr. In other words, the temperature tr when measuring the temperature tsn is the temperature t
This means that the temperature t1 is estimated to be sc-t1, and this temperature t1 is also obtained experimentally. When the correction term Δt is determined as described above, it is stored in the RAM 13 as valid data until the measurement timing of the next correction term Δt (usually carried out after copying is completed), and copying is started, and the thermistor 4 When there is no contact, the heater 3 is controlled according to Equation 2 above. Note that if the obtained correction term Δt2 is greater than or equal to a certain value or less than a certain value, it is determined to be abnormal, but the details of this point will be described later.

FIG. 6 shows the implementation sequence of the measurement mode of the correction term Δt after the copy operation is completed. 37 is the fixing roller 1
The surface temperature tr, 38 is the on/off state of the heater 3,
39 is the on/off state of the main motor 19 (copying/standby), 40 is the on/off state of the solenoid 7,
41 indicates the state of contact and separation of the thermistor 4 with respect to the fixing roller 1, and 42 indicates a change in the detected temperature tsc of the thermistor 4. During copying, the temperature tr is determined based on the previously measured value of the correction term Δt, and the heater 3 is controlled. Even if it remains on, the temperature tr shows a tendency to decrease. In this way, even if the main motor 19 is turned off after copying a predetermined number of sheets, the correction factor Δ
In order to carry out the measurement mode of t, the solenoid 7 is not turned off. After the surface temperature tr of the fixing roller 1 rises to the temperature tc and the heater 3 is turned off, measurement of the correction term Δt is started when the temperature tr becomes equal to the temperature tc again. At that point, data is first obtained from the temperature ts as the temperature tsn, and then the solenoid 7 is turned off and the thermistor 4 is brought into contact with the surface of the fixing roller 1. At this time, the heater 3 is forcibly turned off. Thermistor 4
Response time T2 (≒1 s) due to contact with the fixing roller 1
When , the temperature ts is measured as the temperature tsc, the forced off of the heater 3 is canceled, and the heater 3 is turned on again. Based on the newly obtained temperatures tsc and tsn, a new correction term Δt can be obtained from the following equation 4.

[Formula 4] Δ=tsc-tsn-t2 Here, temperature t2 is the temperature t during response time T2 as in equation 3.
This is the decrease in r and is determined experimentally. Next, as shown in FIG. 9, when the newly determined value of the correction term Δt is greater than or equal to a certain value (15°C in this example) or less than a certain value (1°C in this example), It is determined that the contact/separation mechanism of the thermistor 4 is abnormal, or the thermistor 4 is abnormal, an abnormality flag is set, and a machine stop and abnormality display is displayed on the operation unit 12. When the correction term Δt is within the range of the above values, a comparison is made with the previous correction term Δt, and if the difference is less than a certain value (1°C in this example), the inside of the fixing unit is heated. It is determined that an equilibrium state has been reached, and the correction term Δt is not updated, nor is the next measurement of the correction term Δt performed. If the difference exceeds a certain value, it is updated to a newly measured correction term Δt. The determination of abnormality in the correction term Δt value is also performed during measurement after warming up. Note that the correction term Δt may be measured every time, and if the difference is within a certain value, the data may not be updated.

It is shown that updating the correction term Δt by repeatedly measuring the correction term Δt in this way corresponds to the content shown in FIG. That is, when the ambient temperature tE1 inside the fixing unit is low, such as during warming up, the ambient temperature at the position of the thermistor 4 that is separated by the gap d from the fixing roller 1 becomes tsn1 as shown in characteristic 44, and the fixing roller 1 considerably lower than the surface temperature tr. As the copying operation is repeated, the ambient temperature tE increases, and the temperature tsn also increases to the saturation value ts.
Getting closer to n3. After this point, the measurement of the correction term Δt becomes meaningless, indicating that it is sufficient to control the temperature based on the temperature tsn3 unless there is a disturbance factor such as removing jam paper or opening the door.

FIG. 7 shows the execution sequence of the correction term Δt measurement mode after the copy operation, similar to FIG. 6, but the temperature tsn
The basic difference is that the measurement is performed by rotating the main motor 19, that is, the fixing roller 1. The temperature distribution near the fixing roller 1 shown in FIG. 8 is expected to be different when the fixing roller 1 is stopped and when it is rotating. As mentioned above, it is necessary to control the heater 3 with the thermistor 4 separated from the fixing roller 1.
9 rotation (basically in copy mode),
It can be considered that the temperature tsn at that time provides the correction term Δt value that is closest to the actual value. However, when this idea is applied to the post-warm-up correction term Δt measurement mode, some considerations must be made. Immediately after warm-up, the pressure roller 2 is paired with the fixing roller 1.
Since the temperature of the fixing roller 1 has hardly increased, the surface temperature of the fixing roller 1 rapidly decreases due to rotation, and the temperature t1
This is because it is difficult to estimate. Therefore, when executing the correction term Δt measurement mode in a rotating state, it is necessary to perform sufficient idle rotation to raise the surface temperature of the pressure roller 2 beforehand. The problem remains as to whether to use the correction term Δt, and the only possible methods are to provide a fixed correction term Δt or to allow idle rotation for a certain period of time, during which time the heater 3 is left on. After copying, the pressure roller 2 and the fixing roller 1
It is thought that the above-mentioned problems are resolved by the heating.

Now, in FIG. 7, when a predetermined number of copies have been completed, the main motor 19 and solenoid 7 are turned off, and the thermistor 4 is brought into contact with the fixing roller 1. When the temperature tr becomes equal to the temperature tc, the heater 3 is turned off, and the temperature tr=temperature tc again, measurement of the correction term Δt is started. In this case, the temperature ts is first measured with the thermistor 4 in contact, and the value is taken as the temperature tsc. Thereafter, the main motor 19 and solenoid 7 are turned on, and the heater 3 is forcibly turned off. When the response time T3 of the thermistor 4 has elapsed, the temperature ts is measured and the value becomes ts.
n, and the main motor 19 and solenoid 7 are turned off. The correction term Δt in this case is obtained by the following equation 5.

[Formula 5] Δt=tsc-tsn-t3 Here, the temperature t3 is the decrease in the temperature Tr during the response time T3, as in equation 3, and is experimentally obtained, and the correction term Δt obtained is processed. is the same as that in FIG. 6, so the reference numerals in FIG. 6 will be cited and the explanation will be omitted. In FIG. 7, the main motor 19 is stopped once after the copying is completed and the thermistor 4 is brought into contact with the fixing roller 1, but the main motor 19 and the solenoid 7 are kept on until the timing of measuring the temperature tsc after the copying is completed. temperature ts
Next, the main motor 19 and solenoid 7 may be turned off and the temperature tsc may be measured.

FIGS. 10 to 12 show the program flow of the correction term Δt measurement sequence. 10 corresponds to FIG. 5, FIG. 11 corresponds to FIG. 6, and FIG. 12 corresponds to FIG. 7, and one subroutine is a combination of FIG. 10 and FIG. 11 or FIG. 10 and FIG. 12. Correction term Δt measurement flags FTH1, FTH2, determined in each flow
In the main routine, the explanation of which is omitted, the flag FTH3 is set at the heater-off timing during warming up, and the flag FTH3 or FTH3 is set at the first heater-off timing after copying is completed.

FIG. 10 will be explained according to the flow. First, it is determined whether the temperature tr has become equal to or lower than the temperature tc. When the temperature tr becomes lower than the temperature tc, it is determined whether the correction term Δt after warming up is being measured, that is, the flag FTH
It is determined whether 1 is set. Flag FTH1
If =1, it is determined whether or not timer T-1 is counting. This routine will be passed for the first time unless counting is in progress, so set the forced heater off flag FHO.
F is set, temperature ts is read out, and the value is set as tsc. Next, start timer T-1 and turn on solenoid 7.
Turn on. If timer T-1 is counting, it is determined whether it has been counted up, and if it has not been counted up, the process exits from this subroutine. If it is counting up, read the temperature ts, set the value as tsn, perform the calculation tsc-tsn-t1, and set the value as D.
far. It is determined whether this value D is normal or abnormal based on D≧15° C. and D≦1° C. If it is abnormal, the fixing abnormality flag FFER is set, the solenoid 7 is turned off, and the flag FTH1 is reset and RET is performed. On the other hand, if it is normal, the value D is Δt
, turn off solenoid 7, and set flag FFOR.
and reset FTH1 and perform RET.

The flow in FIG. 11 is based on the flag F in FIG.
It is executed when the result of the determination of TH1=1 is NO. First, if flag FTH2=1 is determined and it is YES, it is determined whether or not timer T-2 is counting, and if it is not counting, this routine will be passed for the first time, so the heater 3 forced off flag FHOF is set and the temperature ts is read out. Temperature ts is stored as tsn and timer T-2 is started. Subsequently, the solenoid 7 is turned off and RET is performed. If the timer T-2 is counting, it is determined whether the timer T-2 has been counted up, and if the timer T-2 has not been counted up, a RET is performed. While counting up, the temperature ts is read out and stored as tsc. Subsequently, tsc-tsn-t2 is calculated,
That value is set as D. Whether this value D is normal or abnormal is D≧
It is determined based on 15° C. and D≦1° C., and if it is abnormal, the fixing abnormality flag FFER is set, and the flag FTH2 is reset and RET is performed. On the other hand, if it is normal, the difference from the previous correction term Δt is calculated, and if the absolute value of the difference is 1°C or less, it is determined that a thermal equilibrium state has been reached, and subsequent correction term Δt measurements are performed. Set the flag FSTFTH, reset the flags FHOF and FTH2, and perform RET. ｜Δ
If t-D1|>1°C, it is determined that the equilibrium state is not yet reached, and the value D is substituted into the correction term Δt, and the flags FHOF and FTH2 are set.
Reset and RET. If the FSTFTH is not set when the thermal equilibrium state is determined, and the correction term Δt is not updated at the same time, the correction term Δt is measured every time after copying, and the data is updated only when there is a significant change. You can also do it like this.

The flow shown in FIG. 12 is another method of measuring the correction term Δt following FIG. 10, and is a method of measuring tsn by rotating the fixing roller 1 as described above. First, flag FTH3=1 is determined and if YES, timer T-
3 is being counted, and if it is not, this routine is passed for the first time, so the forced heater-off flag FHOF is set and the temperature tS is read and stored as tsc. Next, timer T-3
starts, the solenoid 7 and the main motor 19 are turned on, and RET is performed. If the timer T-3 is counting, it is determined whether or not it has counted, and if the timer T-3 has not counted up, a RET is returned. Conversely, when counting up, the read temperature ts is stored as tsn and tsc-tsn-t3 is calculated. The calculation result is placed as D, and whether this value D is normal or abnormal is determined by D≧15℃, D≦1℃
If there is an abnormality, the fixing abnormality flag FFER is set, the main motor 19 and the solenoid 7 are turned off, and the flag FTH3 is reset and RET is performed. If it is normal, the difference from the correction term Δt is taken, and the absolute value of the result is 1.
It is determined whether the temperature is below ℃. A flag FSTFTH that determines that a thermal equilibrium state has been reached when the temperature is 1°C or less and prohibits the setting of the correction term Δt measurement flag FTH3 thereafter.
is set, the flag FHOF is reset, the main motor 19 and the solenoid 7 are turned off, and the flag FTH3 is reset and RET is performed. If |Δt−D1|>1° C., the value D is set in the correction term Δt and the correction term Δt is updated, assuming that the equilibrium state is not yet reached. In this case, as in the case of FIG. 11, it is also possible to not set the flag FSTFTH when it is determined that the state is in thermal equilibrium.

[0023]

Effects of the Invention As described above, the present invention includes a switching means for switching the thermistor between a position in which it contacts the surface of the fixing roller and a non-contact position separated from the surface of the fixing roller. The correction mode includes a control mode for controlling on/off of the heater of the fixing roller, and a correction mode for correcting the temperature measurement value in the control mode by comparing temperature measurement values at a contact position and a non-contact position. Since the temperature measurement for comparison and correction is sometimes performed when the heater is turned off after the temperature of the fixing roller has reached the fixing temperature, the thermistor does not scratch the surface of the fixing roller, and the correction mode can be adjusted. Since the heater is turned off after the fixing roller temperature has reached the fixing temperature, the correction is performed when the surface temperature of the heater is much more stable than when the heater is turned on, making it possible to perform accurate correction. There is.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a state in which a thermistor of a fixing device used in carrying out the present invention is in contact with a fixing roller.

FIG. 2 is a front view showing the same non-contact state as above.

FIG. 3 is a cross-sectional view of FIG. 2 taken along line 3-3 and viewed in the direction of the arrow.

FIG. 4 is a control block diagram of the fixing device same as above.

FIG. 5 is a drawing showing a measurement sequence in a correction mode during warm-up.

FIG. 6 is a drawing showing a measurement sequence in a correction mode after the copy operation is completed.

FIG. 7 is a drawing showing an implementation sequence of a correction mode when a fixing roller is rotating after a copying operation is completed;

FIG. 8 is a temperature distribution diagram near the fixing roller.

FIG. 9 is a drawing showing a normal range and an abnormal range of correction terms.

FIG. 10 is a program flow diagram of the measurement sequence shown in FIG. 5;

FIG. 11 is a program flow diagram of the measurement sequence shown in FIG. 6;

FIG. 12 is a program flow diagram of the measurement sequence shown in FIG. 7;

[Explanation of symbols]

1 Fixing roller 2 Pressure roller 3 Heater 4 Thermistor 7 Solenoid 10 CPU 12 Operation section 13 RAM 14 ROM 18 Constant speed control circuit 19 Main motor 20　SSR

Claims (1)

[Claims] 1. A fixing device comprising a fixing roller having a heater and a thermistor for detecting the surface temperature of the fixing roller, the thermistor having a contact position where the thermistor contacts the surface of the fixing roller, and a non-contact position spaced apart from the contact position. a control mode in which the heater of the fixing roller is controlled on and off based on the temperature measurement value at the non-contact position, and the temperature measurement value at the contact position and the non-contact position are compared; and a correction mode for correcting the temperature measurement value in the control mode, and the timing for performing temperature measurement for comparison correction in the correction mode is when the heater is turned off after the temperature of the fixing roller reaches a fixable temperature. A temperature detection correction method for a fixing device characterized by: