JPH024909B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a temperature control device for a powder image fixing device in an electronic copying machine or the like. Conventionally, temperature control in copying machines and the like has been performed using phase control or simple ON-OFF control. However, although phase control has good temperature stability, it has the disadvantage of generating large noise every half cycle of the power supply.
Furthermore, although ON-OFF control suppresses the generation of noise, it has drawbacks in terms of temperature stability and fine control. The present invention was made based on the above circumstances, and
It is an object of the present invention to provide a temperature control device for a powder image fixing device in an electronic copying machine, etc., which has excellent temperature stability and fine control, and generates little noise. Hereinafter, the present invention will be explained with reference to an illustrated embodiment. FIG. 1 is a diagram showing the configuration of the temperature control device of this embodiment, in which 1 is a terminal to which a stabilized positive voltage is applied, and 2 and 3 are sine waves in phase with an AC power source, which will be described later. terminals to which voltage is applied,
4 and 5 are terminals connected to an AC power source.
TH is a thermistor which is also a temperature detector of the powder image fixing device, R1, R2 and R3 are resistors, and the resistor R1 is connected in series with the thermistor TH and forms a bridge with the resistors R2 and R3. .
A is a differential input amplifier that amplifies the output of a bridge consisting of resistors R1, R2, and R3 and a thermistor TH, and ADC is an AD (analog-digital) converter that digitizes the output of amplifier A into 6 bits. PG is a pattern generator and converter
Generates an 8-bit signal from the 6-bit output of the ADC.
The AD converter ADC and the address decoder of the pattern generator PG function as a temperature level discriminator. ZCD is a zero cross detector and also a synchronization signal generation circuit that detects the point in time when the power supply voltage passes zero voltage and outputs a synchronization signal with the power supply voltage. C
is a 3-bit counter that outputs one pulse for every eight outputs of the target detector ZCD, and DL is a delay circuit that delays the output of the detector ZCD by 1/4 cycle or less of the AC power supply. SR is an 8-bit parallel-in/serial-out shift register that operates as a time-series pulse converter, which inputs the output pulse of the counter C as a set input, the output signal of the pattern generator PG, and the output of the detector ZCD. Outputs serially as a clock. L is a latch that holds the output of the shift register SR at the time when the output of the delay circuit DL is received. AG is an AND circuit that applies the output of latch L at the time when the power supply voltage detected by detector ZCD becomes zero to driver circuit DR. LED is a light emitting diode driven by the driver circuit DR, and PT is a bidirectional optical thyristor as a switching means triggered by the light of the diode LED to control the energization of the heater H. Figure 2 a is the power supply voltage applied to terminals 4 and 5 in Figure 1, b is the output CP of the detector ZCD, c is the output SE of the counter C, and d is the output of the delay circuit DL.
DLO, e is the output DRO of the driver circuit, and f is a waveform corresponding to four cycles of the power supply voltage, which is one cycle of controlling the load current LC flowing through the heater. In the figure, the V axis indicates voltage, and the arrow t indicates the time axis. Here, one cycle of the power supply voltage from the time when the power supply voltage reaches 0V to the next 0V is counted as one wave, and each of the four waves included in one control cycle is assigned a sign in order, and the first half wave is W ₀ , the second half wave is W ₁ , and so on, and similarly W ₂ , W ₃ , W ₄ , W ₅ ,
It was set as W ₆ and W ₇ . FIG. 3 shows an indirect electrophotographic copying machine in which the temperature of the fixing device is controlled by the temperature control device of this embodiment. P is a copy paper, 11 is a paper feed roller, and 12 is a restart roller which stops the copy paper that has been fed once and restarts it at the same timing. 13 is a transfer device, 14 is a copy paper transport roller, 15 is an oven-type powder image fixing device, 16 is a paper discharge roller, and 17 is a paper transport receiver. 20 is a photoreceptor drum which rotates in the direction of the arrow; 21 is a movable document table; 22 is an exposure optical system; and 23 is a charger for charging the entire surface of the photoreceptor. 24 is a magnetic brush developing device, 25 is a charger for static elimination, and 26 is a cleaning device. This fixing device 15 has a heater H as a heat source, and a thermistor TH is closely attached to the upper part for temperature detection. Next, the operation of the temperature control device of this embodiment will be explained. The temperature of the fixing device 15 is detected by a thermistor TH. As the temperature near the thermistor TH increases, the resistance of the thermistor TH decreases, and the voltage at point A1 divided by resistor R1 decreases, and as the temperature decreases, the voltage at point A1 increases. Point A2
The stabilized voltage is divided by resistors R2 and R3, and a stable voltage appears, and this voltage is applied to the amplifier A.
is input to the non-inverting input of Further, the voltage at point A1 is input to the inverting input of amplifier A, and therefore, when the temperature of fixing device 15 increases, the output voltage of amplifier A also increases. The output of amplifier A is AD converter ADC
It is input into the , converted into a 6-bit digital value, and output to 6 output lines. The output of the converter ADC is applied to the pattern generator PG. The pattern generator PG can be formed using a ROM or PROM semiconductor memory. In this embodiment, a PROM having a capacity of 64 words was used, with 8 bits as one word. The six outputs of the converter ADC are connected to the six address inputs of the PROM, and the chip selection input of the PROM is always in a selected state. The contents of one word in the PROM selected by the converter ADC are output from the pattern generator PG in parallel through eight output lines and applied to the shift register SR. The shift register SR uses the signal SE from the counter C as a set signal, and uses the pattern generator PG as a set signal.
Input the 8-bit output in parallel and set it in the register. The set bit pattern is sent to the shift register SR from the output CP0 of the zero cross detector ZCD,
Each time a pulse of CP1,...CP7 is applied, it is shifted one digit lower, and the lowest digit of the contents of the register is output as the output SRO of the shift register SR. This shift register output SRO is the output of the delay circuit DL
When the voltage of DLO falls, it can be held at 1 bit latch L. The timing of signals around these shift registers SR is as follows. pattern generator
The output of the PG is constantly output and changes as the temperature of the fixing device changes, that is, the output of the converter ADC. The output SE of the counter C is pulsed once every eight times the pulse of the output CP of the zero cross detector ZCD is output. Similarly, the output CP of zero cross detector ZCD
It rises when the eighth pulse CP0 falls, and falls after the output of the pattern generator PG is set in the shift register SR. As shown in FIG. 2d, the output DLO of the delay circuit DL falls after the fall of the pulse of the output SE, so that the fixed contents of the register SR are held in the latch L. The information held in the latch L is ANDed by the output CP of the detector ZCD and the AND circuit AG, and a signal is given to the driver circuit DR when the power supply voltage is close to zero. Since the driver circuit DR receives signals in this way, the light emitting diode LED is driven only near the zero cross point, and the thyristor PT performs zero cross switching. That is, the thyristor PT is controlled by the bit pattern shown in the following table contained in the pattern generator PG. It is more desirable that this bit pattern be determined so that the wave numbers of the positive half-wave and the negative half-wave of the current during one cycle of control are as close as possible and zero-cross switching is not biased.

【table】

[Table] In the above table, P ₀ , P ₁ , P ₂ , P ₃ , P ₄ , P ₅ ,
_P6 and _P7 are the 1st bit, 2nd bit, 3rd bit, 4th bit from the bottom of the bit pattern, respectively.
The 5th bit, 6th bit, 7th bit, and 8th bit are shown, and the bit pattern is output from the shift register SR starting from the 1st bit, and after the 8th bit is output, a new bit pattern is started again. is set. Further, in the table, the temperature levels are divided into nine levels, which are the maximum possible with the number of bits of the bit pattern being 8, with level 0 being the lowest temperature, and the higher the number, the higher the temperature. In Figure 2, the bit pattern for temperature level 2 is used and the driver is placed in column e.
The output of DR is shown, and the column f shows the load current LC. The timing relationship of this control will be explained below. Count the pulses of the output CP of the zero cross detector ZCD from the beginning of the 1/2 period of the power supply voltage in which the pulse of the output SE of the counter C is first output, and calculate the pulses of the output CP of the counter C, CP0, CP1, CP2, CP3, CP4, respectively. CP5,
CP6 and CP7. Then, the pattern (11011110) is set in the register SR, and the content " ₀ " of bit P0 appears as the output of the driver at the time of the pulse CP1 of the output CP.
This is because the pulse CP0 falls and the output SE rises, creating a pattern (11011110) in the shift register SR.
is set, the output SE falls, the contents of the shift register SR are fixed, and the output becomes stable.
This is because the output DLO of the delay circuit DL falls, the content of bit PO is latched to the latch circuit L as "0", and after this, it is logically ANDed with the pulse CP1 in the AND circuit AG and then added to the driver circuit DR. be. (However, since PO is "0" at temperature level 2, no pulse is actually output from the driver circuit DR.)Next, when the content "1" of bit P1 is latched in the latch circuit L, the AND circuit is
Since it is first added to the driver circuit DR after performing an AND with pulse CP2 in AG, the content of bit P1 "1" appears as the driver output at the time of pulse CP1 of output CP, as described above. Become. (In this case, since the content of P1 is "1", a pulse is actually output from the driver circuit DR.) The same relationship holds true for the other bits. (For example, pulse CP1 and pulse P1 of output DLO) The temporal relationship between the power supply voltage and the drive pulse for the light emitting diode LED of the driver circuit DR is as follows. Since the input to the driver circuit DR is the logical product of the output CP of the detector ZCD and the output of the latch circuit L, the rising and falling timings of the output CP are almost equal. The driver circuit DR causes the output DRO to rise with a slight delay from the rise of the input due to the above-mentioned AND, and without delaying the passing of the power supply voltage to zero.
The output DRO falls after a sufficient time for the light from the light emitting diode LED to turn on the optical thyristor PT. As a result, the heater H, which is the load, has a bit pattern f corresponding to the temperature level 2 bit pattern (11011110).
The load current LC shown in the column flows. These are also numbered in the same way as the power supply voltage, and the numbers P ₁ , P ₂ , P ₃ , P ₄ , P ₆ and P correspond to the bit numbers of the bit pattern of the pulse of the output DRO of the driver circuit DR. ₇ , LC1, LC2, LC3, LC4, LC6 and
A number is assigned to each wave as LC7. In this way, the load current LC is adjusted to 1 according to the bit pattern corresponding to the nine temperature levels 0 to 8.
It can flow in waves. By the way, in this embodiment, the power of the heater H has been controlled by using four waves of the power supply voltage as one cycle of control, and increasing and decreasing the power in half waves. But the temperature level is 0 to 8.
Instead of using all nine levels, only five levels 0, 2, 4, 6, and 8 may be used. In this case, the power control pattern is reduced from nine stages to five stages, but the second diagram f of the current during one control cycle
It has the advantage that the wave number of the half wave in the upward (positive) direction and the wave number of the half wave in the downward (negative) direction shown in the column are always equal. As detailed above, according to the present invention, the pulse generator outputs an output pattern according to the temperature of the heater.
Since the switching means is triggered by this output pattern and the zero-cross signal, it is possible to provide a temperature control device with low switching noise and fine precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of one embodiment of the temperature control device of the present invention, FIG. 2 is a graph showing the waveform of voltage or current at each part during one control period in the same embodiment, and FIG. The figure shows an indirect electrophotographic copying machine to which the present invention is applied. TH……Thermistor (temperature detector), ADC……
AD converter, PG...pattern generator, C...
...Counter, SR...Shift register, PT...Bidirectional optical thyristor (switch means), 2, 3,
4, 5...Power connection terminal.

Claims (1)

[Scope of Claims] 1. A heater as a heat source of the fixing device, a temperature detector that detects the temperature of the fixing device, a converter that converts the output of the temperature detector into digital data, and detection of the fixing device. generating a pattern for storing a plurality of output patterns of trigger pulses for energizing the heater in correspondence with temperature, and selectively outputting one of the output patterns in response to the digital data output by the converter; a shift register for converting the output pattern output from the pattern generator into time-series pulses; and a shift register for converting the output pattern output from the pattern generator into time-series pulses; A synchronization signal generation circuit outputs a synchronization signal generated at a passing point, and the time series pulses from the shift register sequentially outputted by the synchronization signal from the synchronization signal generation circuit are switched as trigger pulses. A temperature control device for a powder image fixing device, comprising: a switch connected in series to the heater and the power source.