JPH0495986A - Temperature detecting and correcting method - Google Patents

Abstract

PURPOSE:To accurately detect the surface temperature of a roller by making a temperature detecting element optionally take two positions, a position where it contacts with a fixing roller and a position where it does not contact therewith. CONSTITUTION:A thermistor 4 for controlling a temperature is set above the fixing roller 1 so that it may take two positions, the position where it contacts with the surface of the fixing roller 1 and the position with a specified gap (d) where it does not contact therewith. Namely, a solenoid 7 is turned off and a lever 5 moves down, so that the thermistor 4 comes in contact with the surface of the roller, and the solenoid 7 is turned on and the lever 5 moves up, so that the thermistor 4 is allowed to be in a non-contact state with the surface of the roller. Thus, the temperature of the surface of the roller is accurately detected without damaging the surface of the roller.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting and correcting the temperature of a fixing roller used in a fixing device such as a copying machine.

Marusen n support This type of temperature detection is divided into a contact type in which a thermistor (temperature sensing element) is brought into contact with the fixing roller, and a non-contact type in which the thermistor is separated or removed from the fixing roller with a predetermined gap. Broadly classified. Examples of the contact type include Japanese Patent Application Laid-open No. 61-285483 and Japanese Utility Model Application No. 62-4.
9174, and examples of non-contact type include Utility Model Application Publication No. 61-88170 and Japanese Patent Application Publication No. 62-20657.
There is No. 8.

However, in the contact type temperature detection described above, since the thermistor is in contact with the surface of the fixing roller, friction occurs between the roller and the thermistor during rotation, which inevitably causes scratches on the surface of the fixing roller. arrive. If the thermistor is installed in the non-paper passing section of the fixing roller, there will be no damage to the paper passing section, but the temperature of the paper passing section, which decreases depending on the paper, cannot be measured.

On the other hand, non-contact temperature detection does not damage the surface of the fixing roller, but in order to ensure the accuracy of estimating the roller surface temperature from the detected temperature value, the gap between the roller and thermistor must be tightened. need to be managed. Furthermore, since the measured value varies considerably depending on the ambient temperature state, there is a problem that the surface temperature of the controlled roller changes immediately after the machine warms up and after continuous copying.

Therefore, this invention solves the conventional problems as described above, can accurately detect the temperature of the roller surface without damaging the roller surface, and can keep the temperature of the roller surface constant based on this detected temperature. To provide a temperature detection correction method capable of controlling on/off of a heater to maintain the temperature at a certain value, and also capable of always obtaining accurate measured values by correction without changing the measured values even depending on the ambient temperature state. With the goal.

In order to achieve the above object, the present invention provides that the temperature sensing element can take any of two positions: a position in contact with the fixing roller, and a position in which it is not in contact with the fixing roller with a predetermined gap. When controlling the heater for heating the fixing roller on/off using the measured value of the temperature sensing element at the non-contact position, the measured value is combined with the measured value at the contact position and the non-contact position. The feature is that correction is performed using the measured value obtained by comparing the measured value with the measured value.

Figures 1 and 2 are a front view and a side sectional view of an embodiment of the present invention (implemented in a copying machine) with the thermistor in the non-contact position, and Figure 3 shows the thermistor in the contact position. It is a front view.

A fixing roller 1 is pressed by a pressure roller 2 and a pressure means (not shown) and rotated in the direction of the arrow. Reference numeral 3 denotes a heater built into the fixing roller 1, which is turned on/off by a control signal from a control section.

A thermistor 4 for temperature control is placed above the fixing roller 1 in contact with the surface of the fixing roller l (FIG. 3) or at a predetermined gap d.
It is installed so that it can take two positions: non-contact (Fig. 1). The thermistor 4 is integrally attached to a lever 5, and the lever 5 can swing around a fulcrum 6 by the operation of a solenoid 7. That is, when the solenoid 7 is turned off, the lever 5 moves down and the thermistor 4 comes into contact with the surface of the roller, and when the solenoid 7 is turned on, the lever 5 moves up and the thermistor 4 comes out of contact with the surface of the roller. ing. 8 is a spring that biases the lever 5 downward when the solenoid 7 is off, and 9 is a stopper that restricts the upward movement position of the lever 5 so that the thermistor 4 has the gap d.

FIG. 4 shows a control block diagram of the embodiment. 100 is μCPU (hereinafter referred to as CPU), and ROM10
The control program stored in 4 is executed. 101 is an interface with the operation unit (including a display unit) 102; 103 is a RAM for reading and writing copy mode data and various flags; and 105 is for converting analog voltage from the thermistor 4 for temperature detection of the fixing roller 1 into digital data. ,
An A/D converter 106 interfaces with the CPU 100, and a C
This is an I10 interface that interfaces with the PU 100 on a one-to-one basis. I10 interface 106
The loads connected to the F Constant speed control is achieved by adopting a method that combines both the C control method and the PLL control method.), the commercial power supply 139, and the fixing heater 3 connected to the driving 5SRI 10 are connected. . In addition, each switch/sensor 114 and each load 112 from other units are connected to the I10 interface 106 through a signal line 115 and a drive element 113, respectively.

The thermistor 4 employs a thin film type thermistor with a small thermal time constant τ in order to detect the temperature near the roller in a non-contact manner when the fixing roller 1 is rotating (when the main motor is rotating). The thermal time constant in this example is about 2 as the value in air.
．． I use one that lasts about 5 seconds. However, the thermistor 4 is not limited to a thin film thermistor. Furthermore, the temperature-resistance characteristic of the thermistor 4 used in this example is NT
Cl, that is, it has a negative characteristic, and a detected analog voltage is applied to the A/D converter 105 by a voltage dividing resistor 138 shown in FIG. The A/D converter 105 converts the input analog voltage into 8-bit data in this embodiment, and the 8-bit data is read by the CPU 100, and the thermistor detection temperature ts is determined based on the corresponding data stored in the ROM 104. Ru.

The heater 3 built into the fixing roller 1 is driven by turning on/off the 5SRIIO, and the surface temperature tr of the fixing roller 1 is controlled to the control temperature tC (185°C in this embodiment), or the surface temperature tr of the fixing roller 1 is The relationship between the temperature tr and the temperature ts detected by the thermistor 4 is assumed to be as shown in the following equation.

tr = ts + to --(1): Thermistor 4
- when in contact (during warming up, standby) tr = ts + to + t - (2): when thermistor 4 does not contact (during warming up, standby) 2, to is when thermistor 4 is connected to the fixing roller This is the temperature difference between the actual roller surface temperature when it is in contact with the roller 1 and the temperature detected by the thermistor 4, ts, which varies depending on the structure and installation position of the thermistor 4, and is determined experimentally. Also, Δ℃
is an important correction term, and is determined from the difference in ts detected between the contact position and the non-contact position of the thermistor 4 with respect to the roller 1. Details of the timing and method for measuring 8t will be described later.

According to the above relational expression, when the thermistor 4 is in contact with the fixing roller 1 during warming up or standby, (1)
The magnitude relationship between tr in equation (2) and control temperature tc is compared, and when thermistor 4 cannot contact the surface of fixing roller 1 due to rotation of main motor 109 during copying etc., tr in equation (2) and control temperature tC are compared. When tr is low, the heater 3 is turned on, and when tr is high, it is turned off, and the surface temperature of the fixing roller 1 becomes tC.
is controlled as the control value. The thermistor 4 is brought into contact with and separated from the fixing roller 1 by the thermistor contact and separation solenoid 7 according to the mode described above. Note that when the solenoid connects and disconnects the thermistor 4, there is a transient response time of the thermistor detected temperature ts for a certain period of time, and from the contact state to the non-contact state, it is several times the thermal time constant τ, specifically, The time is 7.5 seconds to 10 seconds, and the time from the non-contact state to the contact state is 1 second or less, but the heater control during this time is no control (heater 3 is turned off) in this embodiment.

Figure 5 shows the warm-up time after turning on the main switch,
This figure shows the execution sequence of the correction item △ measurement mode during warm-up after removing jammed paper or opening the door.

116 is the surface temperature tr of the fixing roller 1, 117 is the on/off state of the heater 3, 118 is the on/off state of the thermistor contact/separation solenoid 7, 119 is the contact/separation state of the thermistor 4 with respect to the fixing roller 1, 120 is the thermistor The detected temperature ts, 121 indicates a copy enabled/disabled state indicating that warm-up is in progress or that 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 the equation (1). When tr becomes equal to tC, the heater 3 is turned off.

When the heater 3 is turned off, the temperature of tr naturally decreases after overshooting, but when the temperature becomes equal to tC again, measurement is started. First, data is acquired as ts and tsc at that time, and then the thermistor contact/separation 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 a time T (z4τ) several times the thermal time constant τ has passed, the current ts becomes s
The data is acquired as n, the thermistor contact/separation solenoid 7 is turned off, and the thermistor 4 comes into contact with the fixing roller l again. Control of the heater 3 is resumed after the transient response time. t
When r becomes equal to tC again and the heater 3 is turned off, the warm-up is considered to be complete and the state becomes ready for copying.

ΔS is calculated from the following relational expression.

Δt = tsc −tsn −t, −−−−(3
) where t is the thermistor 4 as shown in FIG.
is the decrease in the roller surface temperature tr due to the heater 3 being turned off during the time T1 during which it responds to the ambient temperature in a non-contact state. That is, t and r at the time of tsn measurement are estimated as tsC-t. This 1 is also experimentally obtained.

When 8t is obtained in the above manner, the next △ is stored in the RAM 103 as valid data until the measurement timing (usually carried out after copying is completed), copying is started, and thermistor 4 is set to When it comes to contact, the above (2)
) The heater 3 is controlled according to the equation. Furthermore, the obtained △t
is determined to be abnormal if it is greater than or equal to a certain value or less than a certain value, but the details will be described later.

FIG. 6 shows the execution sequence of the correction term Δ and measurement mode after the copying operation is completed.

122 is the surface temperature tr of the fixing roller 1, 123 is the on/off state of the heater 3, and 124 is the main motor 109.
125 is the on/off state of the thermistor contact/disconnection solenoid 7, 126
is the state of contact and separation of the thermistor 4 with respect to the fixing roller 1, 1
27 indicates a change in the thermistor detection temperature tSC.

During copying, tr is determined based on the previously measured value of Δt, and the heater 3 is controlled. However, in this embodiment, the power required for fixing is greater than the heater power, so the heater 3 remains on. However, tr is showing a decreasing trend. Even if the main motor 109 is turned off after copying a predetermined number of sheets, △
However, in order to carry out the measurement mode, the thermistor contact/disconnection solenoid 7 is not turned off. The surface temperature tr of the fixing roller 1 is t
After the heater 3 is turned off, tr is raised to t again.
Measurement of Δ starts when it becomes equal to C. first,
At that point, data is acquired as ts and then the thermistor contact/separation solenoid 7 is turned off and the thermistor 4 is brought into contact with the surface of the fixing roller l. At this time, the heater 3 is forcibly turned off. When the transient response time T, (zls) due to the contact of the thermistor 4 with the roller 1 has elapsed, tS is measured as tSC, the forced OFF of the heater 3 is canceled, and the heater 3 is turned ON again. Using the newly obtained tsc and tSn, a new Δt can be obtained from the following equation.

Δt = tsc −tsn −t , --(4) Here, t2 is the decrease in tr between T2, as in equation (3), and is determined experimentally.

Next, as shown in FIG. 9, if the newly determined value of Δ℃ is above a certain value (15°C or more in this example) or below a certain value (1°C or less in this example), , it is determined that there is an abnormality in the thermistor contact/separation mechanism or the thermistor 4, an abnormality flag is set, and a machine stop and abnormality display is displayed on the operation unit 102. When Δt is within the range of the above values, a comparison is made with the previous Δt, and the difference is less than a certain value (in this example, 1
℃), it is determined that the inside of the fixing unit has reached a thermal equilibrium state, and Δ℃ is not updated and the next Δ is not measured. If the difference exceeds a certain value, it is updated to the newly measured Δt. The determination of abnormality in the value of Δ is also performed when measuring Δ°C after warming up. Note that the measurement of Δt may be performed every time, and when the difference is a constant value, the data may not be updated.

It is shown that repeating the measurement of ΔL and updating ΔL in this way corresponds to the content shown in FIG.

That is, when the ambient temperature te in the fixing unit is low, such as during warming up, the ambient temperature at the position of the thermistor 4, which is separated by the gap d from the fixing roller 1, becomes tsn, as shown in characteristic 134, and the roller surface considerably lower than the temperature tr. As the copying operation is repeated, the ambient temperature te increases and tsn approaches the saturation value tsn. After this point, the measurement at 6° C. becomes meaningless, and it is sufficient to control based on tsn unless there is a disturbance factor such as removing jammed paper or opening a door.

FIG. 7 shows the execution sequence of the measurement mode with the correction term Δ after the copying operation is completed in the same manner as in FIG.
The basic difference is that it is performed by rotating. 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.

Heater 3 with thermistor 4 separated from fixing roller 1
As mentioned above, it is necessary to control when the main motor 109 rotates (basically in copy mode)
Therefore, it can be considered that the tsn at that time provides the closest Δ correction value to the actual value. However, when applying this concept to the correction mode for Δ after warm-up, there are some things that must be considered. This is because the temperature of the pressure roller 2 paired with the fixing roller 1 has hardly increased immediately after warm-up, so the surface temperature of the fixing roller l rapidly decreases due to rotation, making it difficult to estimate the above-mentioned tl. . Therefore, when executing the 6°C measurement mode in a rotating state, it is necessary to perform sufficient idle rotation to raise the surface temperature of the pressure roller 2, but what is the control of the heater 3 during the idle rotation? The question remains as to whether to do so at all times, and the only possible options are to provide a fixed Δ or to allow idle rotation for a certain period of time and leave the heater 3 on during that time. After copying is performed, the pressure roller 2 is also heated by the fixing roller 1, and it is thought that the above-mentioned problem is resolved. Now, in FIG. 7, when a predetermined number of copies have been completed, the main motor 109 and thermistor contact/separation solenoid 7 are turned off, and the thermistor 4 is brought into contact with the fixing roller. tr
becomes equal to tC, heater 3 is turned off and tr is turned off again.
When = tc, the measurement is started. First, ts is measured with the thermistor 4 in contact, and the value is tSC
It is said that Thereafter, the main motor 109 and thermistor contact/separation solenoid 7 are turned on, and the heater 3 is forcibly turned off. When the response time T of the thermistor 4 has elapsed, ts
is measured and the value is set as tsn, and the main motor 10
9. Solenoid 7 is turned off. Δt in this case is obtained from the following equation.

Δt = tsc −tsn −t , --(5) Here, C3 is the decrease in tr between 13 and 13, as in equation (3), and is determined experimentally. The process of △ that was obtained is the 6th
Since this is the same as when explaining the figure, the explanation will be omitted. In FIG. 7, after copying is completed, the main motor 109 is stopped and the thermistor 4 is brought into contact with the fixing roller 1, but after copying is completed, the main motor 109 and solenoid 7 are turned off until the tSC measurement timing. May be measured.

FIG. 10 to FIG. 12 are program flows of the ∆ measurement sequence. Figure 10 is Figure 5, Figure 11 is Figure 6.
In the figure, Figure 12 corresponds to Figure 7, and one subroutine includes Figures 10 and 11, or Figure 1O and Figure 1.
This is a combination of the two figures.

Eight measurement flags F th, determined in each flow,
F th,, F th, in the main routine whose explanation is omitted, F th is the heater off timing during warming up, and F th or F th is set at the first heater off timing after copying is completed. Ru.

FIG. 10 will be explained according to the flow. First, it is determined whether tr has become less than or equal to tc. When tr becomes less than tC, it is determined whether the measurement is performed after warming up, that is, it is determined whether Fth is set. F
If th,=1, it is determined that the timer T1 is counting. Since this routine is passed for the first time unless counting is in progress, the forced heater-off flag Fhof is set, ts is read, and the value is set as tSC. Next, the timer T1 is started and the thermistor contact/disconnection solenoid 7 is turned on. If T1 is being counted, it is determined whether the count has increased, and if the count has not increased, exits from this subroutine.

When the count is up, read ts and set the value to t.
sn, perform the calculation tsc −tsn −t, and set the value as D. 0215 indicates whether the value of D is normal or abnormal.
℃ and 021℃, and if there is an abnormality, the fixing abnormality flag Ffer is set and the thermistor contact/separation solenoid 7 is activated.
is turned off, the flag F th is reset, and RET is performed.

If the value of D is normal, the value of D is stored as Δ, the solenoid 7 is turned off, Ffof and Fth are reset, and RET is performed.

The flow in FIG. 11 is executed when the result of the determination of Fth=1 in FIG. 10 is No. First, Fth,=
1 is determined, and if it is YES, it is determined whether or not timer T2 is counting, and if it is not counting, this routine will be passed for the first time, so the forced heater off flag F is set.
hof is set and ts is read. ts is ts
n, and a timer T is started. Subsequently, the thermistor contact/disconnection solenoid 7 is turned off and RET is performed. If T is counting, it is determined whether T has been counted up, and if it has not been counted up, RET is executed.
be done. When counting up, ts is read out and stored as tSC. followed by t, 5ctsn-t
, is calculated and placed as D. It is determined whether the value of D is normal or abnormal at 0215° C. and 021° C., and if it is abnormal, the fixing abnormality flag Ffer is set, the flag F th is reset, and RET is performed. If the value of D is normal, the difference from the previous 6℃ is calculated, and if the absolute value of the difference is 1℃ or less, it is determined that a state of thermal equilibrium has been reached, and the subsequent Δ is calculated. Measurement flag F th.

Set the flag Fsfth that prohibits the setting of F
Reset hof, F th, and perform RET. l△
If t-DI>1'C, it is determined that the equilibrium state is not yet reached, the value of D is substituted into 8t, Fhof and Fth are reset, and RET is performed. If we do not set Fsftth when it is determined that the thermal equilibrium state is reached, and at the same time do not update 6°C, we can measure Δt every time after copying and update the data only when there is a change. You can also do it.

The flow shown in FIG. 12 is another method of measuring tsn following FIG. 1O, and is a method of measuring tsn by rotating the fixing roller l as described above. First, Fth, = 1 is determined, and if YES, it is determined whether timer T3 is counting, and if it is not counting, this routine will be passed for the first time, so the forced heater off flag Fhof
is set and ts is read and stored as tSC. Subsequently, timer T3 is started, thermistor contact/disconnection solenoid 7 and main motor 109 are turned on, and R
It will be ET.

If T is in the process of counting, it is determined whether T has been counted up, and if T has not been counted up, RET is returned. While counting up, the read ts is
sn, and calculate tsc-tsn-t. The calculation result is placed as D, and whether the value of D is normal or abnormal is set to 0.
It is determined at 215°C and 051°C, and if it is abnormal, the fixing abnormality flag F fet is set, the main motor 109 and solenoid 7 are turned off, F th is reset, and RE
Do T. If the value of D is normal, the difference from eight is taken,
It is determined whether the absolute value of the result is 1° C. or less. 1
If it is below ℃, it is determined that a state of thermal equilibrium has been reached, and the flag F5tfth is set to prohibit the setting of the △ measurement flag Fth, and the Fhof is reset.
Main motor 109, solenoid 7 turned off, F th,
Reset and RET. If 1△ and -D1>1°C, it is determined that the equilibrium state has not yet been reached, and the value of D is set to △t, and △t is updated.

In this case, as in the case of FIG. 1I, it is also possible to not set F5tfth when it is determined that the state is in thermal equilibrium.

This invention is as described above, and the temperature sensing element can take any of two positions: a position in contact with the fixing roller, or a position in which it is not in contact with the fixing roller with a predetermined gap. Since it is equipped with a mechanism, it is possible to accurately detect the roller surface temperature without damaging the roller surface, and based on this detected temperature, the heater is controlled on/off to maintain the roller surface temperature at a constant value. I can do it. Also,
When controlling the heater for heating the fixing roller on/off using the measured value of the temperature sensing element at the non-contact position, the measured value is compared with the measured value at the contact position and the measured value at the non-contact position. Since the correction is made using the measured value obtained during the measurement, the temperature of the roller surface can be accurately estimated from the measured value at the non-contact position by making corrections that match the conditions such as the surrounding temperature state, and the roller surface temperature can be constantly checked. Can be controlled to a specified temperature. Therefore, it is possible to achieve effective fixing, to prevent dangers due to excessive temperature rise, and to prevent fixing failures that occur in machines whose temperature drops during continuous copying.

[Brief explanation of the drawing]

Fig. 1 is a front view showing an embodiment of the present invention with the thermistor in the non-contact position, Fig. 2 is a side sectional view of the same as above, Fig. 3 is a front view with the thermistor in the contact position, and Fig. 4 is a control The block diagram, Fig. 5, is the execution sequence of the above-mentioned correction item △ and measurement mode during warm-up after turning on the main switch, removing jammed paper, or opening the door, and Fig. 6 and 7 are copies. The correction item △ after the operation is completed is the execution sequence of the measurement mode. Figure 8 is a graph showing how the atmospheric temperature inside the fixing unit changes with the copying operation. Figure 9 is used to determine whether the value of △ is normal or abnormal. Graphs 0 to 12 show the program flow of the Δ measurement sequence. 1... Fixing roller 2... Pressure roller 3... Heater 4... Thermistor (temperature sensing element) 5... Lever 6... Fulcrum 7... Solenoid b Fig. 2 Fig. 5 r Fig. 4 Fig. 6 tr Fig. 7 Δ Fig. 8 Fig. 9

Claims (1)

[Scope of Claims] 1. In a fixing device such as a copying machine, the temperature sensing element can take any of two positions: a position in contact with the fixing roller or a non-contact position with a predetermined gap between the temperature sensing element and the fixing roller. When controlling the heater for heating the fixing roller on/off using the measured value of the temperature sensing element at the non-contact position, the measured value is combined with the measured value at the contact position and the non-contact position. A temperature detection correction method characterized by performing correction using a measured value obtained by comparing with a measured value.