JPS6348349B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copying machine equipped with a heat fixing device.

2. Description of the Related Art There is a copying machine equipped with a heat fixing device that melts toner with heat and fixes an image transferred to a transfer paper.

Conventionally, such fixing devices have been equipped with the following methods (a) to (c) in order to always control the heat generation temperature of the heat generating means (e.g. heating wire, heater lamp, etc.) to a set value to maintain constant copy quality. One of the following types of temperature control circuits is provided.

(b) On-off control method The power is turned on when the detected temperature is lower than the set temperature, and turned off when it is higher than the set temperature to adjust the temperature of the heat generating means.

(b) Phase control method with proportional control The conduction angle during the AC half cycle is changed according to the difference between the detected temperature and the set temperature to control the power supply to the heat generating means and adjust the temperature. (See Figure 1 A and B).

(c) Pulse width control method with proportional control The pulse width of the pulse based on the AC zero cross is changed according to the difference between the detected temperature and the set temperature, and the power is turned on for a period corresponding to the pulse width. The alternating current cycle is changed to control the electric power, thereby adjusting the temperature of the heating means (see Figure 2 A to C). For example, if the power is turned on and off every cycle, if the power supply is 50Hz, it will become 25Hz.

However, in the on/off control method (a) above, the overshoot of the heat generation temperature with respect to the set temperature is large, and in the phase control method (b), noise radiation occurs due to chopping. In addition, since the pulse width control type switches on and off in synchronization with the zero cross of the AC, there is no noise radiation, but if the amount of power is large (number of cycles: large), it may be necessary to use a lamp etc. connected to the same power line. Each of these has drawbacks, such as flickering and unsightly appearance.

By the way, since the power consumption capacity of the entire machine is specified (for example, 1.5 KVA) in a copying machine, the capacity distribution of each load of the machine including the fixing device is also determined.

For example, when converted to 100V, the total power consumption is 15A (1.5KVA) with a control/display section of 0.5A, a DC load section of 1.5A, an exposure lamp of 4A, a drive section of 1.5A, and a fixing device of 7.5A. case).

On the other hand, since it is better to have the shortest possible rise time until the heat generation temperature of the heat generation means of the fixing device reaches the set temperature, there is a demand for using a heat generation means with a large capacity. I can't make it too big because of the size.

However, among the above-mentioned loads, if they are not driven all the time like an exposure lamp, but are driven only during the exposure process, there is no need to provide that much power (400VA) at all times, and it is not necessary to provide that much power (400VA) at all times other than during exposure. This amount can be sent to the fixing device.

This invention was made in view of the above-mentioned background points, and aims to improve the efficiency of power distribution so that even if the capacity of the heat generating means of the heat fixing device is increased, the power consumption does not exceed a specified value. When the copying machine is on standby and the exposure lamp is off, noise radiation and deterioration of the heat generating means are suppressed, and when the exposure lamp is lit during copying operation, power is supplied to the heat generating means to prevent flickering. The purpose is to enable optimal control of

In order to achieve the above object, the present invention provides a copying machine equipped with a heat fixing device, which includes a pulse width control means for controlling the power supply to the heat generating means of the heat fixing device by pulse width control, and a pulse width control means for controlling the power supply to the heat generating means of the heat fixing device by pulse width control, and a pulse width control means for controlling the power supply to the heat generating means of the heat fixing device by pulse width control. A phase control means for controlling power supply to the heat generating means, and a pulse width control means for operating the pulse width control means when on standby or when the exposure lamp is off, and operating the phase control means when the exposure lamp is on. A switching means for switching is provided.

Hereinafter, embodiments of the present invention will be described with reference to FIG. 3 and subsequent figures of the drawings.

FIG. 3 is a block diagram of a control section of a copying machine to which the present invention is applied.

In the figure, a microcomputer (hereinafter referred to as
(abbreviated as "microcomputer") 1 is an 8-bit one-chip microcomputer, which includes program memory (ROM), data memory (RAM), CPU (central processing unit), and three 8-bit parallel I/O ports (ports P ₀ , port P ₁ , port P ₂ ), 2-channel multiplex analog input circuit (analog input terminals AN ₀ , AN ₁ ) and successive approximation A/D converter, zero-cross detection circuit and timer/counter circuit (T ₁ terminal), external It has an interrupt terminal _T0 , etc.

In addition to the control related to the present invention, which will be described later, this microcomputer 1 performs sequence control of each load as shown in the figure of the copying machine, etc. by controlling the lower (LSB) 4 of port _P2 .
This is done through ports _P4 to _P6 of the expansion input/output interface 2 connected to the bits. Note that the terminal PROG is where a strobe signal to the expansion input/output interface 2 is output. Further, 3 is a buffer group, 4 is a resistor group, and 5 is a driver group.

There is a connection between port P ₃ of expansion input/output interface 2 and port P ₁ of microcontroller 1 as shown in the figure.
28 matrix-shaped key switch circuits 6 are connected, each including a numeric key switch for inputting numerical values such as the number of copies and temperature settings, a BCD switch, a copy start switch, an interrupt copy switch, a clear/stop switch, a multi-copy switch, It includes a writer switch, darker switch, etc. for setting copy density. Note that the multi-copy switch is a switch that allows multiple copies to be made regardless of the input data, and the writer switch and darker switch change the copy density setting value sequentially from lighter to lighter while the switch is pressed.
It is starting to shift towards darker areas.

In addition, port P ₀ of microcontroller 1 has a 2-digit 7-segment LED 7 for count display, a 3-digit 7-segment LED 8 for temperature display, a 2-digit 7-segment LED 9 for time display, and a 2-digit 7-segment LED 9 for displaying various information. A group of LEDs 10 are connected to each other, and a dynamic scan display is performed by a scan pulse from each port _P1 . In addition, port P ₁ 8
The bit bus lines are time-divisionally controlled in order to be used for multiple purposes as described above. The LED group 10 for displaying various information is made up of 16 LEDs, each of which includes, for example, a green lamp indicating that copying is possible, a red lamp indicating that copying is not possible, a lamp indicating that the multi-copy switch is on, and a lamp that indicates that the interrupt copy switch is on. , 8 lamps indicating 8 levels of copy density, a lamp indicating toner shortage, a lamp indicating transfer paper out, a lamp indicating jam occurrence, and a lamp prompting replacement of the photoreceptor.

The AND/OR selector 11 alternately sends eight various sensor signals as shown in the figure to port _P2 of microcomputer 1, four at a time, in response to pulses input from port _P1 of microcomputer 1 to terminals A and B. Upper (MSB)
This is for inputting 4 bits. In addition, 1
2 is a pull-up resistor, 13 is an inverter,
It has a negative logic input type.

Timing pulses from the encoder 14 are input to the T ₀ terminal of the microcomputer 1 via the inverter I, and counting is performed for sequence control. The encoder 14 is configured to operate in synchronization with the rotation of the photosensitive drum, for example.

In addition, AC 3V obtained by stepping down AC 100V by transformer 15 is input to the _T1 terminal via capacitor C, and AC (for example, 50Hz) zero cross detection and time measurement from the point of time when zero cross is detected are performed. It's becoming like that. Note that the T ₀ and T ₁ terminals are called test terminals, and microcomputers having the above-mentioned functions are well known.

The AN ₁ terminal of the microcomputer 1 is input with a DC analog signal whose voltage is stepped down by a transformer 15 and then converted by a rectifier 16 and a smoothing circuit 17.
Voltage fluctuations in the power supply are detected.

A detection signal (voltage signal) from a thermistor 18 for temperature detection is input to the AN ₀ terminal of the microcomputer 1 via a linearizer 19, and temperature monitoring is performed.

A heater lamp 20 shown in FIG. 3 is a heat generating means of the fixing device, and constitutes a non-contact heating fixing type fixing device. The heater lamp 20 is controlled to be energized by turning on and off a solid state relay (hereinafter abbreviated as "SSR") 21 made of a triax or the like. In addition,
Trigger control of the SSR 21 is performed by a signal outputted from the microcomputer 1 via one bit of port _P6 of the expansion input/output interface 2 and inputted via a buffer, a resistor, and a driver. Also,
The SSR 21 should preferably be a combination of a photothyristor and a triax with very little time delay and a fast response when triggered by the microcomputer 1.

The above-mentioned thermistor 18 is provided near the heater lamp 20, and this thermistor 18
The temperature is measured by

The thermistor 18 is a temperature sensing element having negative characteristics as shown in FIG. 4, and its resistance value decreases as the temperature rises. Note that FIG. 4 shows the characteristics of four types of thermistors.

In this embodiment, a voltage is applied to the thermistor 18 to convert the resistance change into a voltage change. However, when a voltage is applied, nonlinearity appears in the resistance change due to the self-heating of the thermistor itself, so correction is required. is performed by the linearizer 19, and a voltage signal that changes linearly with temperature change is input to the AN ₀ terminal.

Note that as the temperature detection element, in addition to the thermistor, a posister, a thermocouple, an infrared sensor, etc. may be used.

Next, temperature detection accuracy by the microcomputer 1 will be explained. The A/D conversion function of the microcomputer 1 has 8 bits, that is, 256 resolutions.

In other words, the voltage (maximum V _cc ) applied between the V _AREF and AV _SS terminals of microcontroller 1 is equally divided by 256 series-connected resistors with equal resistance values in microcontroller 1, and the voltage is divided into equal voltages by the reference step. form a voltage. These 256 step voltages are used as reference voltages and are successively compared with the analog voltage input from the _AN0 terminal, thereby A/D converting the input analog voltage with a resolution of 256.

Therefore, for example, in the thermistor 18,
If a change in resistance corresponding to a temperature change from -20°C to 230°C is input as a voltage change from 0 to _Vcc to the AN ₀ terminal via the linearizer 19, the temperature can be measured with an accuracy of about 1°C.

If you want to improve the accuracy, change the range of voltage change from the thermistor 18 as it is [0~
V _cc ) and reduce the voltage applied between the V _AREF and AV _SS terminals. For example, if the applied voltage is reduced to 1/10, the accuracy is approximately 0.1℃ (accuracy 10 times)
It can be done.

In this way, since the control temperature of the heat generating means of the fixing device in the copying machine, the heater lamp 20 in this embodiment, is approximately 200°C, the heater lamp 20
The initial temperature and rising temperature can be measured accurately one after another, and these temperatures can be displayed in 7 segments for temperature display.
It can be displayed on LED8.

Furthermore, if the relationship between the temperature rise of the heater lamp 20 and time is determined in advance through experiments or the like, and that relationship is programmed, it is possible to calculate how many minutes and seconds after the heater lamp 20 reaches 200°C after being driven. The time until copying is possible can also be displayed on the 7-segment LED 9 for time display.

Next, the temperature control method according to the present invention will be explained, but before that, its outline will be explained with reference to FIG.

As mentioned above, the power capacity distribution of the fixing device is
In the case of 750VA, a 750W heater lamp must be used, but due to the requirement to shorten the rise time, a 1.2kW heater lamp is used in this example, and the power distribution is controlled to ensure that the total capacity is always 1.5KVA or more. I try not to become

That is, in FIG. 5, during period _T1 , the heater lamp 20 is turned on at full power (100%) because other loads of the copying machine are not driven at the start-up time.
However, if you continue to turn on the light at 100%,
Since overshoot occurs at a temperature of 200°C, on/off (intermittent) control is performed during period T ₂ to slow down the temperature rise gradient. Note that when this intermittent lighting is performed, the intermittent lighting is synchronized with the Xerox point by Xerox detection by the microcomputer 1 to prevent noise radiation.

Next, in period _T3 , pulse width control (hereinafter abbreviated as "PWM") is performed to perform even more fine control, and the temperature of the heater lamp 20 is brought to approximately the set temperature of 200° C. and maintained at that temperature. Note that when the temperature of the heater lamp 20 becomes 200° C. or higher, copying is enabled instead of copying disabled. Also, this period T ₂
During the waiting period from when copying becomes possible until the time T _x when copying starts, other loads on the copying machine are off, so even if the AC is PWMed, there is no adverse effect such as flickering. This PWM has the effect of lengthening the life of the heater lamp 20 because it not only generates almost no noise radiation but also triggers when the load current is close to zero.

However, when performing PWM, care must be taken that unless the AC waveform is symmetrical with respect to the zero point, a DC component will be generated and have an adverse effect on the load, but this can be prevented by programming.

Period T ₄ is the period when the exposure lamp is lit after the copy start, so the power supplied to the heater lamp 20 must be kept below 700W, and since this is the time when the load impedance is the largest, PWM is performed. Since this has a negative effect on the load, phase control should be performed.

During the period _T5 , the exposure lamp is turned off during the copy process, so the temperature is maintained at 200° C. again by PWM.

Since periods T ₆ and T ₇ are the second copy process, they are the same as periods T ₄ and T ₅ . And period
Since _T8 is on standby, the temperature is controlled by PWM.

The microcomputer 1 performs the above control while monitoring the temperature of the heater lamp 20 as the copying process progresses.

That is, this microcomputer 1 plays the roles of pulse width control means, phase control means, and switching means in this embodiment.

Next, details of temperature control of the heat fixing device by the microcomputer 1 will be explained with reference to flowcharts shown in FIGS. 6 to 10.

First, the control from period T ₁ to period T ₃ in FIG. 5 will be explained with reference to the flowcharts of FIGS. 6 to 9.

In Fig. 6, the temperature monitor as described above is performed in STEP 1, the diagnosis of a failure of a heater lamp, etc. is performed in STEP 2, and the processing to be performed when an abnormality is checked in STEP 2 in STEP 3, such as power cutoff, machine stop, etc. The contents are displayed (optical display or audio display), and the failure contents are stored (stored in a non-volatile memory, not shown).

Each of these routines in STEPs 1, 2, and 3 is tested as needed in subsequent STEPs.

Next, in STEP 4, a temperature test of 170°C is performed, and if that temperature has not been reached (initially always below 170°C), 100% lighting is performed in STEP 5. This 100% lighting means that the SSR21 in Figure 1 is triggered and turned on, and the heater lamp 20 (1.2kW) is turned on.
This means applying 100V AC for a full cycle.

In STEP 6, the heat generation temperature of the heater lamp 20 is
Test whether the temperature has exceeded 170℃. If not, 100% lighting will continue in STEP 5, and if it has exceeded 170℃, the lighting time will be reduced to 4/4 in STEP 7.
5. Lights off time 1/5 or 4/5 duty on/off
An off (intermittent) control program is selected to prevent overshoot.

That is, in STEP 8, Xerox detection is performed using AC3V input to the T1 terminal of microcomputer ₁ ,
Trigger SSR21 at the zero cross point (STEP 9).

Then, in STEP 10 and 11, the heater lamp 20
Measure the on time (4 seconds) of the , and when 4 seconds have passed,
Turn off the SSR 21, turn off the heater lamp 20 (STEP 12), and measure the extinguishing time (1 second) in STEP 13 and 14 of FIG.

Note that STEPs 10 and 13 and the subsequent "counter start" indicate the operation of the internal counter of the microcomputer 1. The counting operation of this internal counter is independent of the CPU of the microcomputer 1, and when the count value of the counter reaches a set value, an interrupt can be used to make other CPUs working on jobs aware of the count value.

Next, in STEP 15, it is tested whether the heat generation temperature of the heater lamp 20 has exceeded 180°C, and if it has not exceeded, the process branches to STEP 7 and is repeated again at 4/4.
5 duty on/off control is repeated. Also, if the temperature exceeds 180℃, STEP 16~
By each step in STEP 23 (see Figure 8), the duty is 7/10 (3.5 seconds on, 1.5 seconds off).
On/off control is performed.

Then, in STEP 24 of Fig. 8, a test is made to see if the heat generation temperature of the heater lamp 20 exceeds 190°C, and if it does not exceed 190°C, STEP 1
6, and the 7/10 duty on/off control is repeated again. If the temperature exceeds 190°C, on/off control of 1/2 duty (2.5 seconds on, 2.5 seconds off) is performed in each step of STEP 25 to STEP 32.

Next, test whether the temperature exceeds 195℃ in STEP 33, and if it does not exceed 195℃, then STEP 2
5, the 1/2 duty on/off control is repeated again, and if the temperature exceeds 195℃
In each step from STEP34 to STEP41 (see FIG. 9), the heat generation temperature T of the heater lamp 20 is controlled to 200°C<T<201°C by PWM at 1/3 duty.

Note that 1/3 duty PWM means that AC is turned on for one cycle and turned off for two cycles, as shown in FIG.

That is, first, a 1/3 duty PWM program is selected in STEP 34 of FIG. 8, and zero-cross detection is performed in STEP 35 of FIG. When the zero cross is detected, the SSR 21 is triggered and turned on in STEP 36, and the heater lamp 20 is turned on. Then, in STEP 37, zero cross is detected twice (one cycle), and when detected, SSR2
1 and the heater lamp 20 is turned off (STEP 38).

Next, in STEP 39, test whether the heat generation temperature T of the heater lamp 20 is 200℃<T<201℃.
If ℃＜T＜201℃, zero cross 4 in STEP 40
Detection is performed twice (2 cycles), and when detected,
The process branches to STEP 36, where one cycle of lighting is performed and a copy enable signal is output to enable copying.

If 200℃<T<201℃, STEP 4
Test whether T>201℃ in step 1, and if T>201℃
Branching to STEP 38, the heater lamp 20 is kept off, and the loop is repeated until 200°C<T<201°C is satisfied. Also, when T>201℃,
In other words, when T<200℃, branch to STEP 36,
Keep the heater lamp 20 lit.

The process explained above is the period T ₁ in Figure 5.
~ corresponds to T ₃ .

Next, with reference to the flowchart of FIG. 10, control during periods T ₄ to _{T 8} in FIG. 5 will be described.

First, until the copy start is recognized in STEP 1, the waiting routine (STEP 35 to STEP 41 in Figure 9) performs PWM at 1/3 duty of STEP 2.
(equivalent to) temperature control is performed.

When copy start is recognized in STEP 1,
In STEP 3, test whether the exposure lamp is turned on. If it is turned on, in STEP 4, check whether the number of continuous copies C is C > 10, and if C > 10.
If it is, proceed to STEP 5, otherwise proceed to STEP 6.

The reason why the above judgment is made in STEP 4 is that the transfer paper absorbs the heat of the fixing device, and for example, when 10 or more sheets are continuously copied, the temperature drops by 2 to 3 degrees Celsius. Therefore, if the number of continuous copies C is C > 10 sheets, use phase control (conduction angle 90°) in STEP 5 to maintain a temperature of 202℃ < T < 203℃, and if C≦10 sheets, use phase control (conduction angle angle 90°) to maintain a temperature of 200°C < T < 201°C.

As mentioned above, when the exposure lamp is on, the load capacity is large and the line impedance is large, so in order to reduce the influence on other loads, phase control is used instead of PWM.

The phase control method first detects zero crossings. And in the case of 50Hz alternating current, the half cycle is
Since it is 10msec, if you measure 5msec from the zero cross point using the internal counter of microcontroller 1 and trigger SSR21 at that point, the phase angle (conduction angle)
When the angle is 90°, the power is 50%.

If it is determined in STEP 3 that the exposure lamp is not turned on (such as when the optical system is returned), the process branches to STEP 7, where the number of continuous copies is checked in the same way as in STEP 4.

And if C > 10 pieces, 2/3 duty PWM
(STEP 8) to control the heat generation temperature T of the heater lamp 20 to 202℃<T<203℃, and if C≦10 sheets, control the heat generation temperature T of the heater lamp 20 to 202℃ by 2/3 duty PWM (STEP 9).
<T<201°C.

In addition, for high-speed machines with a fast return speed of the optical system or machines with no brim and the exposure lamp lights up during copying, STEPs 8 and 9 in Figure 10 can also be replaced with STEPs 5 and 6.
The phase control becomes as follows.

Also, in the flow diagram of Figure 10, STEP
Instead of branching depending on whether the number of continuous copies is 10 or more as in 4 and 7, the correlation between the number of continuous copies and the temperature drop (see Figure 12) is programmed in advance, and Therefore, the control temperature can also be made variable.

Further, in the above embodiment, a heater lamp is used as the heat generating means, but a heating wire may also be used.

As described above, according to the present invention, in a copying machine equipped with a heat fixing device, when the copying machine is on standby and when the exposure lamp is off, the power supply to the heat generating means of the heat fixing device is controlled by pulse width control. death,
When the exposure lamp is on, the power supply to the heat generating means can be controlled by phase control, so even if the capacity of the heat generating means is large, the power consumption is not exceeded, ensuring high efficiency in power distribution. It is possible to control the temperature with high precision and to control the temperature, suppress noise radiation and deterioration of the heat generating means when the copying machine is on standby and the exposure lamp is off, and prevent the exposure lamp from turning on during copying operations. It is possible to improve the copy image quality by preventing flickering when copying.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of phase control. FIG. 2 is an explanatory diagram of pulse width control. FIG. 3 is a block diagram of a control section of a copying machine to which the present invention is applied. FIG. 4 is a diagram showing the characteristics of the thermistor. FIG. 5 is a time chart for explaining the outline of the invention. Figures 6 to 10 are
FIG. 3 is a flow diagram of a program for a microcomputer to execute control according to the present invention. 11th
The figure is an explanatory diagram showing an example of pulse width control.
FIG. 12 is a diagram showing how heat is removed by transfer paper during continuous copying. 1...Microcomputer, 15...Transformer,
16... Rectifier, 17... Smoothing circuit, 18... Thermistor, 19... Linearizer, 20... Heater lamp,
21...Solid state relay.

Claims (1)

[Claims] 1. In a copying machine equipped with a heat fixing device, a pulse width control means controls the power supply to the heat generating means of the heat fixing device by pulse width control, and a pulse width control means controls the power supply to the heat generating means of the heat fixing device by phase control. A phase control means and a switching means are provided for operating the pulse width control means during standby and when the exposure lamp is off, and operating the phase control means when the exposure lamp is on. A copying machine featuring: