JPH0312685A - Temperature controller for fixing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature control device for a fixing device used in an electrophotographic printer or the like.

[Conventional technology]

2. Description of the Related Art An electrophotographic printer such as a liquid crystal printer is provided with a heating roll and a pressure roll, and a fixing device that fixes a toner image transferred onto a sheet of paper using heat and pressure. In such a fuser, in order to maintain the heating roll at a predetermined temperature, a temperature sensing element such as a thermistor is provided on the surface of the heating roll, and energization of the heater provided within the heating roll is controlled according to the temperature detected by this temperature sensing element. A temperature control device is provided.

Conventional temperature control devices configure a bridge circuit using the above-mentioned temperature sensing element, a variable resistor, and a resistor, and connect the two connection points of the bridge circuit, which are not connected to the power supply or ground, to the inverting or non-inverting input of the comparator. Controls power supply to. That is, a temperature sensing element detects the temperature of the heating roll that changes due to the fixing operation, and a comparator detects the change in the detected temperature as a change in the resistance value of the temperature sensing element.
By comparing with the reference voltage, when the temperature of the heating roll is lower than the set temperature, the heater is energized, and when the temperature of the heating roll is higher than the set temperature, the temperature of the heating roll (fusing device) is determined by stopping the energization of the heater. is under control.

(Problems with the prior art) However, in the temperature control device of the fixing device described above, even if the heater is controlled to be energized or stopped, the surface temperature of the heating roll does not immediately rise or fall. Since the heater used in the heating roll is usually installed inside the heating roll, the surface temperature of the heating roll does not immediately follow when the heater is energized.This means that the temperature of the heating roll rises or falls extremely quickly, This causes large vertical temperature fluctuations in the heating roll when the initial heating of the heating roll is completed or during printing operations.

A diagram showing this state is the temperature characteristic diagram in FIG. 9.

In this figure, for example, the period shows the characteristics during idling when no paper is passing through, and the period [F] shows the characteristics during printing when paper is passing. In the case of the same figure, 180'C
is the set temperature of the heating roll, and it can be seen that with respect to this set temperature, the actual surface temperature of the heating roll fluctuates with a temperature difference E1 above and below during idling, as shown by the thick line in the figure. .

As shown in the figure, after the temperature sensing element detects that the surface temperature of the heating roll exceeds the set temperature, the surface temperature of the heating roll actually decreases only when a temperature of 180°C or higher is detected. 1 hour later, and conversely, it increases by 1
This is t2 hours after the temperature of 80°C or less was detected.

Further, the temperature fluctuation range during the printing operation, which is indicated by period B in the same figure, is even larger and is a temperature difference E2. This is because the heat on the surface of the heating roll is transferred to the paper by 2. This is because the temperature is being rapidly taken away, and the same temperature control as above is being performed. Note that the time t31t4 shown in the figure indicates the time from when the temperature sensing element detects the set temperature during the printing operation until the surface temperature of the heating roll actually decreases or increases.

From the above, in temperature control using conventional temperature control devices, the effective value of the predetermined temperature of the heating roll must be set high because the temperature fluctuation range of the heating roll is large as described above, and the heat from the heater is effectively used. This results in unnecessary power consumption.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide a temperature control device for a fixing device that effectively utilizes heat from a heater and does not waste power.

[Key points of the invention]

In order to achieve the above object, the present invention provides a temperature control device for a fixing device that turns on and off a heating heater according to the output of a temperature detection element to control the temperature to a preset temperature. an analog-to-digital converter for converting into a value, a measuring means for measuring a temperature gradient of increase or decrease in temperature based on the digital value converted by the analog-to-digital converter, and energization of the heating heater according to the temperature gradient. The present invention is characterized by comprising an energization rate setting means for setting the energization rate, and a control means for controlling on/off of the heating heater at the energization rate set by the energization rate setting means.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a circuit diagram of a temperature control device according to this embodiment, and it is assumed that the temperature control device according to this embodiment is installed in an electrophotographic printer (not shown).

In the figure, the circuit of this embodiment includes a heater 2 provided inside a heating roll 1, a thermistor 3 provided on the surface of the heating roll 1, and an analog-to-digital converter (hereinafter simply referred to as A).
/D) 4, a microprocessor unit (hereinafter simply referred to as MPU) 5, an energization/stopping circuit 6, an AC power source 7, and the like.

The thermistor 3 is a temperature sensing element that detects the surface temperature of the heating roll 1, and the resistance value of the thermistor 3 changes to a resistance value corresponding to the detected temperature, forming a DC circuit together with lines 8a, 8b and resistor Rf, Divides the power supply voltage at a predetermined ratio.

A/D4 converts the analog value of the divided voltage inputted through the input IQ into 8-bit digital data,
Output.

~Output from D7 to MPU5. In this example, the set value of the surface temperature of the heating roll l is 180°C, and the digital data (temperature data) at this time is expressed as a decimal number of 2.
It is 5゛.

The MPU 5 controls each part of the electrophotographic printer in addition to the temperature control in this embodiment, and controls each part according to a system program stored inside. The 8-bit temperature data input manually via inputs DO' to D and l is stored in the internal RAM. This RAM has a memory configuration shown in FIG. 2, and is composed of a flag area 11, a heater timer 12, a heater on time storage area 13, a heater off time storage area 14, a roll temperature buffer 15, and a gradient timer 16. . The flag area 11 is composed of 8 bits, and includes a temperature direction flag lla indicating whether the surface temperature of the heating roll l is rising or falling.
, a power flag flb for turning on the heater 2, a ready flag llc for indicating whether the electrophotographic printer is ready for printing, a heater on flag lid for indicating whether the heater 2 is being controlled to be on or off, etc. It is configured. The heater timer 12 is a timer that actually counts the on time and off time of the heater 2, the heater on time storage area 13 is a data area for presetting the time for energizing the heater 2, and the heater off time storage area 14 is a data area for presetting the time during which the heater 2 is not energized, and a roll temperature buffer 15
is a buffer that stores temperature data of the surface temperature of the heating roll l. The gradient timer 16 is a timer that counts the time until the temperature data (digital data) input to the MPU 5 changes by "1 degree."

Further, the MPU 5 compares the temperature data stored in the roll temperature buffer 15 with the newly input temperature data according to the control process described in detail later, and if the temperature data has changed, based on the timer time of the gradient timer 16, Calculate the heater on time or heater off time. Also,
According to this ON time, a low signal is outputted from the output Po to the light emitting element 9a of the photocoupler 9, and a current is caused to flow to the light emitting element 9a via the resistor R2, and the light emitting element 9a is turned on.

The energization/stopping circuit 6 is composed of the photocoupler 9, triac lO1 resistors R2 to R4, and a capacitor C.
When the light receiving element 9b in the photocoupler 9 receives the light from the light emitting element 9a, a current flows through the light receiving element 9b, and the triac 1
A trigger signal is supplied to the gate (G) terminal of 0, and the triac 10 is turned on. Further, when a high signal is output from the output Po, no trigger signal is supplied to the G terminal, and the triac IO is turned off. While the triac lO is on, the AC power source 7 is supplied to the heater 2 to heat the heater 2.

In the fuser temperature control device having the above circuit configuration,
The circuit operation will be explained below using the flowcharts shown in FIGS. 3 to 6. Note that the fixing control process shown in FIG. 3 and the heater output process shown in FIG. 4 are executed at predetermined intervals.

The MPU 5 performs initial setting processing for the electrophotographic printer by turning on a main power source (not shown). Thereafter, the fixing control process is executed, and first it is determined whether the ready flag llc in the RAM is set ("1" or not) (step (hereinafter referred to as S in the flowchart of FIG. 3) 1).

The ready flag 11C is set when the heating roll 1 is heated to a set temperature and becomes ready for operation. Therefore, since the ready flag llc is not set at first (
If Sl is N (No), the power flag llb should be set (S2), and it is determined whether the heating roll l has reached a temperature equal to or higher than the set temperature (S3). In this first judgment (S3), the heating roll l is not heated, so the judgment (S3) is N.

Next, the MPU 5 makes a judgment (step (hereinafter referred to as ST in the flowchart of FIG. 4) 1) according to the flowchart of FIG.
Execute. At this time, since the power flag llb is set by the above process (S2) (STI is Y), the judgment (ST2) is further executed, and the judgment (ST2) is N at this time as in the above process (S3). The heater 2 is energized (S73). The process of energizing the heater 2 is as described above, by outputting a low signal from the output PO of the MPU 5 to the light emitting element 9a, lighting the light emitting element 9a, causing the light emitting element 9b to receive this light, and turning on the triac 10. This is done by passing current from the AC power source 7 to the heater 2.

Thereafter, when the temperature of the heating roll l reaches or exceeds a predetermined temperature, the determination (S3) becomes Y (yes) and the process (S4) is executed. This process (S4) sets the ready flag 11, clears the power flag llb, stores the detected temperature of the heating roll 1 at this time in the roll temperature buffer 15, and starts the gradient timer 16. The stored data of the detected temperature in the roll temperature buffer 15 is temperature data that is manually input to the MPU 5 by converting an analog voltage value corresponding to the temperature detected by the thermistor 3 into digital data via the A/D 4. FIG. 7 shows the heating roll 1 after the heating roll 1 reaches the set temperature (180'c) for the first time.
FIG. 3 is a characteristic diagram showing temperature changes. As mentioned above, the point when the set temperature is reached for the first time after heating heater 2 is point a in the figure.
It is.

Next, the MPU 5 executes the judgment (STI) shown in FIG. At this time, the power flag llb is cleared by the above process (S4) (STI is N), and the temperature of the heating roll 1 is also higher than the set value (ST4 is Y). For this reason, M.P.
U5 outputs a high signal from output PO, and triac 1
0 is turned off to stop power supply to heater 2 (ST5)
.

Even if the power supply to the heater 2 is stopped by the above-described process, the surface temperature of the heating roll 1 does not immediately decrease but increases for a certain period of time. The temperature rise at this time is shown in FIG. 7b. During this time M
PU5 sends the temperature data detected by thermistor 3 to A/D4.
The temperature data in the roll temperature buffer 15 is compared with the previously stored (processing (S4)) temperature data in the roll temperature buffer 15. ″) (e.g. 18
When the temperature data "25" at 0°C changes to "24"), execute the judgment (S6), and if it is falling (35 is "〉roll buffer"), execute the judgment (S7) . 7th
As shown in b of the figure, the temperature increases in the first process (however, the temperature data becomes smaller), and the judgment (S6)
Execute.

This judgment (S6) is to judge whether or not the temperature direction flag lla is set, and is the same as the initial processing (S4).
), the temperature direction flag lla is set (however, if the temperature direction flag 11a is set, this indicates that the temperature is rising), the timer set B process (S8) is executed. This timer set B processing (S8
) is shown in FIG. 6. As shown in the figure, in the timer set B process, the MPtJ5 determines whether the temperature rise is rapid based on the time measured by the slope timer 16 started in the process (S4) (step (see FIG. 6)). In the flowchart, it is indicated by ■ below) 1). This judgment is made based on the length of time from when the gradient timer 16 is started (processing 34) until the next judgment (S5) is made, that is, the time until the temperature data changes from "25" to "24". do.

Here, if the MPU 5 determines that it is “sudden 1”, the process (■
Execute 2). As shown by b in FIG. 7, in the idling state, the heating roll 1 is rapidly heated to bring it into the ready state, and its rise is "+2.t+".This process is performed from the timer time of the gradient timer 16. The heater on time and heater off time are determined, and the determined time data is set in the heater on time storage area 13 and the heater off time storage area 14.

After storing the time data in the heater-on time storage area 13 and heater-off time storage area 14 as described above, when the process shown in FIG. 4 is executed, the power flag llb is cleared in process (■2). , the heater 2 is kept off. That is, when the temperature of the heating roll l is higher than the set temperature of 180°C, the above judgment (ST4) is Y, and the heater 2 remains in the off state (STI→
ST4→5T5). Therefore, the temperature of the heating roll changes from b to (-+d) in Fig. 7. When the state of d in Fig. 7 is reached, the temperature decreases, but the temperature data increases. ), the judgment (S7) is executed.This judgment is to judge whether or not the temperature direction flag 11a is set.At this time, the temperature direction flag l is set.
Since la has been set, clear the temperature direction flag (S7 → 511), and then reset the gradient timer 16.
The temperature data of the heating roll 1 is stored in the roll temperature buffer 15 (S9.510).
). Note that the temperature data stored during this time is cleared.

Then, when the MPU 5 makes the above determination (S7), since the temperature direction flag lla has been cleared, the timer set A process (S12) is executed. This process is specifically shown in the flowchart of FIG. 5, and similarly to FIG.
It is determined from the timer time of the gradient timer 16 whether the temperature drop of the heating roll 1 is sudden or slow (step (hereinafter indicated by U in FIG. 5) l), and if it is "sudden", it is processed (U2).
Execute. This process is similar to the above process (2), except that the power flag llb is set. Therefore, through the above processing, new heater-on time data is set in the heater-on time storage area 13, and new heater-off time data is set in the heater-off time storage area 14. After that, when the process shown in FIG.
1), it is determined whether the heater timer 12 is up (Sr6), the heater timer 12 is initially set to the up state (Sr6 is Y), and the MPU 5 then determines whether the heater on flag is set. (Sr.
1). Since the heater-on flag 14 is not initially set (Sr1 is N), the data set in the heater-off time storage area 14 is set in the heater timer 12 by processing (Sr8), and the heater-on flag li is set.
Set d. Then, according to the heater-off time data set in the heater timer 12, a high signal is output from the output PO, the triac IO is turned off, and the power supply to the heater 2 is stopped for the above-mentioned time. Then, the above process (S
When the heater timer 12 set in r8) times up (Sr6 is Y), the setting of the heater-on flag lid is determined (5T7), and the heater-on flag lid is set in the higher-order processing (S
Execute r9). This process sets the heater on time data stored in the heater on time storage area 13 in the heater timer 12, clears the heater on flag, and uses the output PO for the heater on time set in the heater timer 12. It outputs a low signal. Through this process, the heater 2 is supplied with power from the AC power source 7 during the set heater on time as shown in FIG. FIG. 8 shows the output voltage of the AC power supply 7 supplied to the heater 2 in accordance with the output of the low signal of the output PO. That is, when a low signal is output from the output PO once, one cycle of alternating current is supplied to the heater 2. When the power supply to the heater 2 is controlled as described above, the heater on time and heater off time are set by the gradient timer 16 as described above, and are determined according to the temperature gradient of the heating roll 1 detected by the gradient timer 16. It is possible to control the energization of the heater 2. Since the temperature of the heating roll 1 rises rapidly during idling as shown in FIG. 7, the ratio of the heater on time to the heater off time is set to 1:4, for example.

Thereafter, each time the temperature data output from the A/D 4 is updated, the timer set A process (S12) is executed, and the corresponding heater on time and heater off time are set from the timer time of the gradient timer 16, and the data is updated. (Sl-35→S7→312
→S9→310→S1→...), when the heater 2 is energized in this way, the temperature of the heating roll 1 reaches point e in FIG. 7, the above judgment (Sr2) becomes N, and from then on outputs a low signal from the output PO to turn on the heater 2. Thereafter, the temperature of the heating roll 1 starts to rise after reaching the lower peak point shown at point r in the figure (g in the figure).
When the temperature of the heating roll l starts to rise, it is determined that the newly detected temperature data input from the A/D 4 is smaller than the temperature data before being stored in the roll temperature buffer 15 (S5). Buffer”, M
The PU 5 determines whether the temperature direction flag lla is set (S6).

At this point, the temperature direction flag Ila is cleared as described above (S6 is N), so the temperature direction flag Ila is set (S13). Thereafter, the gradient timer 16 is reset and restarted as described above, and the temperature data of the heating roll 1 is set in the roll temperature buffer 15 (39.510). In the next process, the determination (S6) becomes Y, and the timer set B process is executed (513).

This process is specifically the process shown in FIG. 6, and has been described above. That is, from now on, the MPU 5 performs the above processing (S
1 →S 5 →S 6 →S 8 →S 9 →S
10-+Sl→...) is repeated. Therefore, if the temperature gradient at g in Fig. 7 is still steep, the process (■
2), clear the power flag llb, and control the energization of the heater 2 according to the data of the heater on time and heater off time set by the amount by which the temperature of the heating roll l is below the set temperature 5TI-) ST4 →S
T6→...→ST9→STI→), when the temperature of the heating roll 1 exceeds the set temperature, the power supply to the heater 2 is stopped (STI-3T4 →5T5-3TI), by controlling the power supply in this way. This prevents the temperature of the heating roll 1 whose temperature rises rapidly from rising above the set temperature (180°C). In addition, when the temperature rise of the heating roll 1 is "slow", the process (■2) is not executed, so the power flag llb remains set, and if the temperature of the heating roll 1 is below the set temperature, the heater 2 continues to be energized. (STI→ST2→ST3→5T
I) When the temperature exceeds the set temperature, the power supply to the heater 2 is controlled according to the set heater on time and heater off time data (STI-3T2→ST6→...
ST9→5TI). By controlling the energization in this manner, the temperature fluctuation of the heating roll 1, whose temperature rises slowly, is made extremely small.

Therefore, the temperature of the heating roll 1 can approach the set temperature of 180''C by repeating the above process during idling while reducing the temperature fluctuation range of the heating roll 1.

Next, when the electrophotographic printer starts printing, the printed paper is conveyed between a heating roll in the fixing device and a pressure roll (not shown), and the toner image on the paper is fixed to the paper by heat and pressure. At this time, the heat on the surface of the heating roll 1 is taken away by the paper, and the surface temperature of the heating roll 1 suddenly decreases. 7. h in FIG. 7 shows the state of the temperature drop of the heating roll I at this time.

Therefore, M, PU5 performs the above-mentioned process (31→S5→S7→
During the execution of S12→S9→S10→S1→...), it is determined that the temperature drop of the heating roll 1 is drastic (Ul is "sudden"). The previous temperature data stored in 15 is compared with the newly input temperature data, and the gradient timer 1 at this time is
From the timer time 6, it is determined that the temperature drop is extreme. Therefore, the MPU 5 executes the subsequent process (U2).

In this process, as described above, the heater on time data and heater off time data set by the MPU 5 are stored in the heater on time storage area 13 based on the timer time of the gradient timer 16.
Or set it in the heater off time storage area 14 and set the power flag llb. As the power flag flb is set by this process, the judgment (STI) becomes Y, and the judgment (Sr1) is executed. At this time, the temperature of the heating roll 1 is below the set temperature, so the heater 2 is energized (S
r3). As a result of this process, power continues to be applied to the heater 2, so that the temperature of the heating roll 1 starts to rise immediately after reaching the lower peak point i (i - * j in Fig. 7).
.

After that, the MPU 5 performs the same process as described above (Sl-35→S6
→ S8 → S9 → SIO → S1 →...) is repeated, and at this time, since the temperature rise is "slow", the set temperature (180°C) is set without performing the process (v2) (K in Fig. 7). ) Continue to energize heater 2 until (STI→ST2→5T3
), after the temperature of the heating roll 1 reaches a predetermined temperature or higher,
The set data in the heater on time storage area 13 and the heater off time storage area 14 are alternately set in the heater timer 12, and the energization of the heater 2 is controlled according to the on or off time set in the heater timer 12 (STI → ST2 → ST6 →・・・ST9→STI→
...). Note that the ratio of the heater on time and heater off time set during the printing operation is set to a ratio of 421 because the heat of the heating roll l is absorbed by the paper.

By controlling the heating of the heater 2 in this way, the fluctuation range of the surface temperature of the heating roll 1 gradually becomes smaller as shown in FIG. In this embodiment, the ratio of the heater on time to the heater off time during idling and printing operation is set to 1:4 or 4:1, but the ratio is not limited to this.

〔Effect of the invention〕

As described in detail above, according to the present invention, the range of temperature fluctuation of the heating roll is extremely small, thereby preventing waste of power and making effective use of the heat of the heater.

Further, since temperature fluctuations can be reduced, the life of the heating roll can be extended, and furthermore, since temperature fluctuations are small, curling of paper can be prevented.

Furthermore, since the temperature fluctuation is small, the set temperature of the heating roll can be lowered, and the temperature inside the apparatus is also lowered, which is advantageous in heat dissipation processing.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a temperature control device for a fixing device according to an embodiment, FIG. 2 is a configuration diagram of a RAM in an MPU, and FIGS. 3 to 6 are operation diagrams of a temperature control device for a fixing device according to an embodiment. FIG. 7 is a diagram showing the temperature characteristics of the heating roll. FIG. 8 is a diagram explaining the voltage supply waveform to the heater. FIG. 9 is a diagram showing the temperature characteristics of the conventional heating roll. l...Heating roll, 2...Heater 3...Thermistor, 4,0. A/D. 5... MPU, 6... Energization/stopping circuit, 7... AC power supply, 9... Photocoupler, 10... Triac, l 1 ・ ・ 11a ・ 11b ・ 11c ・ id 12 ・・ 13 ・ ・ 14 ・ ・ 15 ・ ・ 16 ・ ・ Flag area, ・Temperature direction flag, ・Power flag, ・Ready flag, ・Heater on flag, Heater timer, Heater on time storage area, Heater off time storage area, Roll Temperature buffer, slope timer

Claims (1)

[Scope of Claims] A temperature control device for a fixing device that turns on and off a heating heater according to the output of a temperature detection element to control the temperature to a preset temperature, comprising: an analog device that converts the output of the temperature detection element into a digital value; a digital converter, a measuring means for measuring a temperature gradient of temperature rise or fall based on the digital value converted by the analog-to-digital converter, and an energization device for setting the energization rate of the heating heater according to the temperature gradient. A temperature control device for a fixing device, comprising: a rate setting means; and a control means for controlling on/off of the heating heater at the energization rate set by the energization rate setting means.