JPH03179382A - Controller - Google Patents

Abstract

PURPOSE:To improve the control characteristics of ON/OFF control by selecting either of comparison output signals of a main target value and a subordinate target value with a rectangular wave which is variable in duty ratio. CONSTITUTION:The subordinary target value Vref2 is provided in addition to the main target value Vref1 and comparators 102 and 103 compares the signal V from a sensor 101 with them and input their comparison outputs V1 and V2 to a selector 104. A comparator 108 compares a recurring sequence generated by an oscillator and a counter 107 with duty ratio data DA which is inputted from outside to generate a rectangular wave d(t, r) as the select signal of the selector 104, whose output is outputted as the ON/OFF signal of a controlled system 105. Consequently, the input/output characteristics of the ON/OFF control can be compensated and the controllability can be im proved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for controlling the heat roll temperature of a fixing device and the toner density of a developing device in an electrophotographic printer.

[Conventional technology]

FIG. 2 shows the configuration of a general fixing device. heat roller 2
The surface temperature of 01 is detected by the 2nd surface thermometer 204, converted to voltage 2, and sent to the temperature control device 205.

Therefore, hereinafter, the surface temperature will be expressed by the output voltage measured by the thermometer 204. The conventional control bag [205 is shown in FIG.
), it consists of a comparator 301 and a variable power supply 302. The voltage of the variable power supply 302 means the target surface temperature of the heat roller, and is herein referred to as voltage Vref.

On the other hand, the input/output characteristics of the comparator 301 are as shown in FIG. 3(b), and the output voltage from the thermometer 204 is V.
ref, that is, when the surface temperature of the heat roller 201 is higher than the target temperature, the switch 206 is turned off and the heat generation amount of the heater 203 becomes O; in the opposite case, the switch 2
06 is turned on and the amount of heat generated by the heater 203 becomes q.

When the heater 203 generates heat, the heat roller 201 warms up and the surface temperature (voltage V) increases. Conversely, if no heat is generated, the heat roller 201 radiates heat and the surface temperature (voltage V) decreases.

In the case of a simple control system as described above, if the heat roller 201 to be controlled has poor thermal conductivity, a limit cycle or overshoot will occur, and the stability of the surface temperature will deteriorate. In order to improve this problem, a dither signal may be mixed into the target value Vref or the thermometer output ■, as shown in FIG.

Regarding this method, see Institute of Instrument and Control Engineers: ``Automatic Control Handbook (Basic Edition)'', Ohmsha pp422-4.
24 (↓983).

[Problem to be solved by the invention]

In the prior art described above, a triangular wave or a sine wave is used as the applied dither signal d(t). The modified input/output characteristics then depend on their amplitude and period. However, it is difficult to create a triangular wave or sine wave with arbitrary amplitude or period using a simple device.

The present invention first uses a signal that can be generated by a simple device as a dither signal d(t), allows the input/output characteristics to be controlled arbitrarily to some extent, and uses this to realize optimal control characteristics for each condition. The purpose is to improve the control characteristics of on-off control.

[Means to solve the problem]

In order to achieve the above purpose, as shown in FIG.
2 are provided, and the magnitude is compared with the signal V from the sensor by comparators 102 and 103, and the comparison output Vl
, V2 and input them to the selector 104. On the other hand, the cyclic sequence created by the oscillator 106 and the counter 107 and the duty ratio data DA input from the outside
The rectangular wave d(t
, r) as the select signal S of the selector 104,
The output of the selector 104 is output as an on/off signal for the controlled object 105.

Furthermore, in order to achieve optimal control characteristics for each condition, the state within the controlled object 105 is estimated from the on/off timing of the power supply, recording start command, and comparison outputs Vl and V2, and the rectangular waveform is generated according to the state. The input/output characteristics are changed by changing the duty ratio r of d (t, r).

[Effect]

FIG. 4 is a block diagram equivalent to FIG. 1.

Therefore, the equivalent dither signal "D+r) is d'(t,
r)=(Vrefl-Vref2)·d(t, r), where, as shown in FIG. 5, the period is T and the duty ratio is r (O≦r≦1). At this time, the on-off characteristics shown in FIG. 3(b) can be linearized in a simulated manner as shown in FIG. However, since the duty ratio r is variable depending on the duty ratio data DA, the input/output characteristics can be controlled arbitrarily to some extent.

Control characteristics can generally be measured in terms of responsiveness and stability. However, it is difficult to achieve both in the case of a control target that has many delays and dam times. For example, in the heat roller 201 of the fixing device, a powerful heater 203 may be provided in order to shorten the preparation time from when the power is turned on until the temperature stabilizes at the target temperature, that is, to improve responsiveness. However, in the conventional on/off control, in the case of the heat roller 201 with poor thermal conductivity,
Even if the surface temperature reaches the target temperature and the heater 203 is turned off,
The temperature rises further (overshoot) and exceeds the heat resistance temperature of the equipment. In order to prevent this, in the case of the present invention, the overshoot can be reduced by setting Vref2 to an appropriate value lower than Vrefl and further setting the duty ratio r to a small value. However, once the target value is exceeded, unless the duty ratio r is appropriately increased, recovery will be delayed even by disturbances such as natural heat radiation.

In this way, it is desirable that the output of the heater 203 near the target value is changed depending on the state of the fixing device.

There is also a method of changing not only the vicinity of the target value but also the output of the heater 203 itself, but in that case, a sophisticated and accurate judgment function is required. This is because if a large disturbance occurs when the output is lowered, the response will be delayed. In the present invention,
In such a case, the output is immediately maximized so that fixing failures and the like do not occur.

Furthermore, in the case of the heat roller 201 having poor thermal conductivity, oscillations in the surface temperature called limit cycles are observed even after a sufficient period of time has elapsed after the power was turned on. Figure 7(a) shows
This shows the temperature distribution in the thickness direction of the heat roller 201 while the heater 203 is generating heat.

Temperature uniformity occurs within the roller, so that while the outer surface is 185°C, the inner surface reaches 225°C. When the heater 203 finishes generating heat, the heat is radiated both inside and outside, resulting in a flat temperature distribution as shown in FIG. 7(b).

Therefore, in the case of the heat roller 201 having poor thermal conductivity, there is a large difference in surface temperature between the roller immediately after heating and the roller immediately before heating, at least in the amount of heat possessed by the roller itself. In the fixing device, the heater 203 is turned on and off to keep the surface temperature of the heat roller 201 constant just before paper is delivered, that is, during standby. However, the on/off timing of this heater 203 and the timing when paper is fed have not conventionally been synchronized, so the heater 203 may be on or off when paper fixing starts. Since the heat roller 201 waits for a large amount of heat when it is on, the fixing power is strong. In order to design an efficient fixing device, it is desirable that the fixing force be uniform. By controlling the duty ratio during standby according to the present invention, the heater 203 can be kept in an on state at all times when paper fixing is started. When the duty ratio is increased, the amount of heat applied increases, so the heating time becomes shorter. Conversely, if the duty ratio is decreased, the heating time becomes longer.

Since there is a time of several seconds from the start of printing until the paper is sent to the fixing device, if the above control is performed during this time, fixing can be started when the fixing ability of the fixing device is at its maximum.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. FIG. 16(b) shows a generation circuit for the dither signal d(t). In this circuit, two types of rectangular waves d with different duty ratios are used.
Assume that a(t), d b(t) are generated. The duty ratio data are respectively DA and DB, and each is assumed to be a 4-bit signal here. Signal n (n=o, 1,
2.・15). They are each comparator 1
603.4. On the other hand, when the 8-bit binary counter 107 is counted by the vibrator 106,
The counter 107 is 0, 1, 2. ..., 255, then return to O and repeat this. The comparator 108-a compares the output Ca(t) of the upper 4 bits with the signal DA, and the comparator 108-b compares the output Cb(t) of the lower 4 bits with the signal DB. , when the signal DA or DB is smaller, it outputs rOJ, and when it is larger, it outputs "1". In other words, if you do this, the duty ratio r of each signal
a.

rb becomes DA+I DB+1. FIG. 16(,) shows an example of a temperature control device according to the present invention. The surface thermometer 204 is connected to the heat roller 20
A voltage V corresponding to the surface temperature of the work piece is generated. The dither signal da(t) is multiplied by ^ and added to this, and the comparator 1
Leads to 02,103. Comparators 102 and 103 are
It operates similarly to that shown in FIG. In other words, the input potential is compared with the reference potentials Vref 1 and Vref 2, and when the input potential is large, rOJ is set, and when it is small, rl
Output J.

These outputs are input to the selector 104. Selector 1
04 selects and outputs one of the input signals based on the selection signal S. The selection signal S is assumed to be a dither signal db(t). Depending on the output from the selector 104, the heater 203 is turned on (when it is "1") and off (when it is "O"), and the surface temperature of the heat roller 201 is controlled. If the above device is equivalently converted into the conventional device shown in FIG. 3, the result will be as shown in FIG. 8(a). However, V' = V+Ka-d a(+) Vref' = (1-d b (t)・Vref2+d
b (t)・Vrefl When the output voltage V of the thermometer 204 is under the following conditions, the input V' of the comparator 801 and Vr
The relationship with ef' and the amount of heat generated by the heater 203 are
As shown in the figure.

i) When V≦Vref2-Ka Figure 9 (,)
ii) Vref2-Ka (V≦Vrefl-Ka'
(b) iii) Vref 1- Ka <V≦Vr
ef2'(c)iv)Vref2 (V≦V
refl'(d)v)Vref 1
<V' (e) However, O≦V
ref 1 - Vref 2≦Ka. The same applies to other conditions, so the description will be omitted.

As a result, the input/output characteristics can be approximated to those shown in FIG. 8(b).

According to this embodiment, a plurality of dither signals da(t) and db(t) are generated from the same counter 104, so the circuit is simple. Since the duty ratio can be changed externally using the binary signals DA and DB, the duty ratio can be easily and accurately controlled.

ra, rb, Vrefl, Vref2. By manipulating each parameter of Ka, desired input/output characteristics can be realized and temperature controllability of the fixing device can be improved.

Next, an example of controlling the duty ratio of the dither signal d(t) will be described with reference to FIGS. 10 and 11. In this example, for simplicity, the dither signal db(t
) shall be used only. Therefore, the equivalent circuit is as shown in Figure 10(a), and its input/output characteristics are as shown in Figure 10(b).
It is approximated as follows.

rb in FIG. 10(b) is determined from the duty ratio data DB using equation (1). Data DB is output from microprocessor 1101 shown in FIG. The processor 1101 receives the output V1 from the comparator 102.
and a recording start signal PR are input. The fuser is powered on
When you press N, the warm-up mode (Mode) starts.
, and is heated by the heater 203 at the maximum output q.

The problem with conventional mode devices is that due to rapid heating (the heating time becomes the user's waiting time, so it is desirable to keep it as short as possible), a large temperature gradient occurs within the roller 201 as shown in Figure 7. Therefore, when the heater 203 is turned off at the set value of the thermometer output V (referred to as Vrefl), the temperature inside the roller 201 becomes too high, significantly shortening the life of the roller 201. Therefore, in the present invention, a new threshold value (V
= Vref 2 ), and during this period (Vref2≦
V<Vrefl), the output of the heater 203 is lowered. In this example, the duty ratio data DB=O and the output of the heater 203 is q/16. Then, roller 20 near the target temperature
The temperature gradient inside 1 becomes smaller and the 1 surface temperature reaches the set value (V=
Vref 1 ), the rise in the inner surface temperature of the roller 201 can be suppressed to a small level, and as shown in FIG. 12, the so-called overshoot, in which the temperature further increases after reaching the set value, can also be suppressed to a small level. When the surface temperature exceeds the set value and the output v2 of the comparator 106 becomes "O", the processor 11o1 determines that mode 1 has ended,
Next, it enters standby mode (mode 2). In mode 2, there are few disturbances to the temperature, so the surface temperature is set at the set value (V=
Vrefl), it rises and falls as the comparator L/-1l06 (7) output v1 turns on and off. This vertical vibration is
This is called a limit cycle due to system delay, and its amplitude can be reduced by appropriately selecting the output of the heater 203. In this example, the duty ratio data was set to DA=6 through experiment, and the output of the heater 203 was set to 7q/16.

Conventionally, as shown in FIG. I2, it was not possible to adjust the output of the heater 203 between modes 1 and 2, so it was not possible to simultaneously shorten the heating time in the mode and reduce overshoot and limit cycles. In the present invention, heating can be performed with the optimal heater 203 output for each. Further, if the surface temperature drops below Vref2 due to a large disturbance, stable fixing is possible because heating is immediately performed at full output regardless of the mode.

Next, when the user inputs the signal PR to start recording, the processor 1101 finishes WAM and then enters the rotation mode (mode 3). Since the heat roller 201 and the backup roller 202 start rotating, heat radiation from the heat roller 201 increases, and the surface temperature initially becomes V.
< V ref 1, and the heater 203 has full output q
generates a fever. When the surface temperature becomes V≧Vref2, in order to suppress the temperature gradient of the roller 201 as in mode 1, V
It is necessary to suppress the output of the heater 203 when ref2≦V<Vrefl. In mode 3, the backup roller 20
Since there is also heat radiation from 2, duty ratio data DB = 3
The output of the heater 203 is 4 (1/1 b.Same as mode 1, the output of the comparator 102 is rOJ
Then, the processor↓101 shifts from mode 3 to control mode (mode 4). In mode 4, the set temperature (
Controls the phase of the limit cycle that occurs near V = Vref 1 ). Mode 4 also has less disturbance to temperature, so duty ratio data DB=9 (heater 2
03 output 10q/lb), the period T of the limit cycle stabilizes at a constant value.

In Fig. 13, t is the time when the leading edge of the paper contacts the fixing device.
=tf, this time tf is predictable because it is a certain period of time after the signal PR. Therefore, at this time tf, the fuser has the highest amount of heat (Fig. 7(a)
) is desirable.This state is the state in which heater 2
03, the processor 1 sends a pace signal P such that the heating ends exactly at time tf.
The duty ratio is controlled so that this signal P and the output Vl of the comparator 102 match in phase. Letting To be the time from the fall of the signal P to the fall of the signal V1, control is performed as follows.

In Figure 13, the first T.

The measurement result is O≦To<-, so the signal DB is changed from 9 to 1.
Increased to 3. Then, the output of the heater increases, the heating time during the limit cycle becomes shorter, and the phase advances.

Conversely, when 1≦To<T, the heater The output is reduced and the phase is delayed.

As a result, the phases of the signal P and the signal v2 are aligned by the time tf, so that paper fixing starts when the fixing device meets the above conditions.

After time tz, the processor 1101 shifts from mode 4 to fixing mode (mode 5). During paper fixing,
Although it depends on the amount of heat generated by the heater 203, heating is normally performed at the maximum output. Therefore, duty ratio data DB=15 is set. Paper type information PI is input to the processor 1101, and in the case of particularly thin paper, mode 1 (discontinuous time) or return to mode 3 (continuous time). As mentioned above, there are several modes for controlling the temperature of the fixing device, and according to this method, heating can be performed with the output of the heater 203 that is optimal for each mode.

An embodiment of the present invention will be described below with reference to FIGS. 14 and 15. Figure I4 shows a general phenomenon machine 1 except for the control device.
It is 407. In the developing device 1407, carrier and toner are mixed at a constant ratio. Since only toner adheres to the electrostatic latent image formed on the photoreceptor 1409, if development is continued, the amount of toner in the developing device 1407 will decrease and the ratio of carrier will increase. Then, the toner density meter 14
03 detects the toner concentration from the change in reactance of the coil 1410 in the developing device 1407. Conventionally, the toner concentration is compared with a target value in a control device, and depending on the magnitude, the motor 1402 is turned on and off, and the supply roller 1405 is turned on and off.
Rotate. The toner stored in the toner hopper 1404 is supplied little by little into the developing device 1407 by a supply roller 1405, stirred by an agitation roller 1406, carried to a photoreceptor 1409 by a sleeve roller 1408, and adhered to the electrostatic latent image. do. Since toner is replenished through such a long path, it takes a long time from when the coil 1410 detects a decrease in density until the density is restored. Further, the amount of toner required for development also varies greatly depending on the type of image to be recorded. Therefore, in the conventional on/off control, the response is slow and the overshoot due to oversupply is large.

In particular, when developing a full-page image, the toner density drops rapidly and toner is replenished at full power, but if a nearly blank image continues after that, a large overshoot occurs, and after that the toner density does not come down easily, causing the toner density to drop. is too dark than specified, and images with lost details will be recorded for a while. Therefore, the control device 1401 is replaced with the device of the present invention (FIG. 15).

Vref2 is set to a value corresponding to the target toner density;
fl is set to a value suitably lower than Vrefl in consideration of system delay, and DB is set to a value for each mode for toner supply as follows.

When the power is turned on in mode 1), the gap roller 1406,
Sleeve roller 1408 rotates.

Assuming that the toner concentration is around the target value, it is set to an appropriate value that suppresses the limit cycle. In this example, DB=6.

Mode 2) In mode 1, the toner density is Vrefl
If the following condition continues for more than a certain period of time, the toner is stagnant near the stirring roller 1407, and if left as it is, it is expected that a large overshoot will occur.In this case, set DB=O, and if V≧Vref2 Return to mode 1.

According to this embodiment, even if toner is suddenly replenished, overshoot of the density is unlikely to occur, and the toner density is stably maintained even when the toner density is close to the target density. As a result, a recorded image with stable density can be obtained.

〔Effect of the invention〕

According to the present invention, input/output characteristics of on/off control can be compensated using two comparators and a rectangular wave with a variable duty ratio, so that sophisticated control can be realized with a simple circuit and controllability can be improved.

Separately, the same effect as described above can be obtained by simply superimposing a rectangular wave with variable amplitude and duty ratio on the signal from the sensor input to the control device. In this case, since the control device itself does not need to be improved, it can be combined with the above-mentioned devices, which allows input/output characteristics to be compensated for more freely, thereby improving controllability.

Further, since the present invention can be applied to control the surface temperature of a heat roller of a fixing device, it is possible to stably control the surface temperature even of a heat roller with poor thermal responsiveness. At this time, the input/output characteristics can be changed by changing the duty ratio according to the heating conditions of the heat roller, so the optimal control characteristics can be achieved under each condition. Further, at this time, the phase of the limit cycle of the surface temperature immediately before fixing can be controlled so that the amount of heat at the start of fixing, especially in the fixing device, is constant and maximum, thereby making stable fixing possible.

Furthermore, since the present invention can be applied to controlling the toner density within a developing machine, even a developing machine with poor density responsiveness can stably control the toner density. At this time, the input/output characteristics can be changed by changing the duty ratio according to the toner supply conditions of the developing machine, so the optimum control characteristics can be achieved under each condition.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the present invention, Fig. 2 is a conventional fuser configuration, Fig. 3 is a block diagram of the control device in Fig. 2, Fig. 4 is a block diagram equivalent to Fig. 1, and Fig. 5 is the dither signal d' in FIG.
(t, r), FIG. 6 is an input/output characteristic diagram of the control device shown in FIG. 4, FIG. 7 is a diagram showing the temperature gradient inside the heat roller, and FIG. 8 is a diagram showing the temperature gradient inside the heat roller. Input/output characteristic diagram of control device,
FIG. 9 is an explanatory diagram of the operation of the control device in FIG. 16, FIG. 10 is an input/output characteristic diagram of the control device according to an embodiment of the present invention, FIG. 11 is a configuration diagram of the microprocessor, and FIG. 12 is at startup. FIG. 13 is an explanatory diagram of phase control in mode 4, FIG. 14 is a configuration diagram of a conventional developing machine, FIG. 15 is a configuration diagram of a control device of the present invention, and FIG. 16 is a diagram of a control device of the present invention. FIG. 2 is a configuration diagram of a control device according to an embodiment. 101... Sensor, 102, 103... Comparator, 104... Selector, 1.05... Controlled object,
106・Fig. 2, Fig. 3, c) (b) Fig. 4, 5, Fig. 6, Fig. 7 (0-) (b) Fig. 8 (^ P Fig. 9) W・・・Plate-Ichishi---- (1-rku)rb) Fig. 10 Fig. 111 Fig. 12 Fig. 3 Fig. f4 (2) Fig. 5 Fig. 6

Claims (1)

[Claims] 1. In a control device that compares a signal from a sensor with a target value and turns on and off a controlled object depending on the magnitude of the signal, a secondary target value is provided in addition to the main target value, and each A control device characterized in that one of the comparison output signals is selected using a rectangular wave with a variable duty ratio, and a controlled object is turned on and off by the signal. 2. A control device that compares a signal from a sensor with a target value and turns on and off a controlled object depending on the magnitude of the comparison, characterized by superimposing a rectangular wave with variable amplitude and duty ratio on the signal from the sensor. control device. 3. A control device that compares a signal from a sensor with a target value and turns on and off a controlled object depending on the magnitude thereof, which has a selection function according to claim 1 for the signal from the sensor according to claim 2. A control device characterized by: 4. The control device according to claim 1, wherein the object to be controlled is a heat roller of a fixing device. 5. The control device according to claim 4, wherein several modes are defined according to the heating conditions of the heat roll, an optimal duty ratio is determined in advance for each mode, and control is performed using the duty ratio. . 6. The phase of the limit cycle of the surface temperature that occurs during standby immediately before fixing the paper is shifted so that the amount of heat that the fixing device waits for at the start of fixing the paper is constant and maximum. Control device. 7. The control device according to claim 1, wherein the object to be controlled is a toner supply device of a developing machine. 8. The control according to claim 7, wherein several modes are set according to the supply conditions of the toner supply device, an optimal duty ratio is determined in advance for each mode, and control is performed using the duty ratio. Device.