JP2016029425A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both a reduction of flicker and a reduction of harmonic current by dividing a plurality of fixing heaters into a plurality of groups and setting a different conduction angle in phase control for each of the groups.SOLUTION: Control means performs phase control in synchronization with a zero-cross timing detected by zero-cross timing detection means, and performs phase control at a first phase angle during a period from the start of power supply to a first heater group to the lapse of a predetermined time and performs phase control at a second phase angle different from the first phase angle during a period from the start of power supply to a second heater group to the lapse of a predetermined time.SELECTED DRAWING: Figure 8b

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  In an image forming apparatus using an electrophotographic system such as a copying machine or a printer, an electrostatic latent image formed on a photosensitive drum (rotating photosensitive member) can be formed by attaching a developer (hereinafter referred to as toner) with a developing device. It becomes a visual image (hereinafter referred to as a toner image). The toner image is transferred onto a recording sheet by a transfer device, and the toner image transferred onto the recording sheet is fixed on the recording sheet by a fixing device to form a fixed image.

  The fixing method of this fixing device is generally thermal fixing in which the toner on the recording paper is melted by the heat energy from the fixing roller heated using a heater as a heat source, and is melted into the fibers of the recording paper by the pressure of the fixing roller. It is.

  The heat source of the heat fixing device is a halogen heater supplied with power from a commercial AC power source, and an SSR (Solid State Relay) or an insulated switch circuit composed of a phototriac and triac is used as a heater. The power supply is controlled. Further, the switch circuit controls the power supply to the heater so that the fixing roller is in a predetermined temperature range according to the temperature detected by the temperature detection element disposed in the vicinity of the fixing roller in the heat fixing device.

  When the halogen heater is not energized, its resistance value is extremely small, and when the heater is heated to generate heat, the resistance value increases. Therefore, since a large inrush current flows immediately after the start of energization of the heater, the power supply voltage fluctuates and a so-called flicker phenomenon occurs.

  In order to avoid this, it is possible to use a so-called phase control that limits the conduction angle to the heater according to the phase of the commercial AC power supply, and to use a method of limiting the conduction angle for a predetermined time from the start of energization to the heater. It is general (refer patent document 1).

  FIG. 2 is a diagram showing a schematic configuration of a general heat fixing device 26. A heater 33 is disposed inside the heating roller 31 and heats the heating roller 31 from the inside. The temperature detection element 35 that detects the surface temperature of the heating roller 31 is disposed at a position facing the heating roller 31. Based on the output signal from the temperature detection element 35, the energization to the heater is controlled so that the surface temperature of the heating roller 31 is maintained at the fixing temperature or the standby temperature (standby temperature) at the time of non-fixing.

  Similarly, a heater 34 is disposed inside the pressure roller 32 to heat the pressure roller 32 from the inside. Similarly, a temperature detection element 36 for detecting the surface temperature is disposed at a position facing the pressure roller 32 in the pressure roller 32, and the surface temperature of the pressure roller 32 is determined based on an output signal of the temperature detection element 36. The energization of the heater is controlled so as to be maintained at the fixing temperature or the standby temperature during standby (standby temperature).

  FIG. 3 is a block diagram showing a configuration of a main circuit of a conventional image forming apparatus that controls energization of fixing heaters 33 and 34 used as a heat source in the heat fixing apparatus.

  In FIG. 3, reference numerals 111 and 112 denote input terminals connected to the commercial AC power supply 100, and AC power is input thereto. A series circuit composed of the fixing heater 33 and the switch element 133 and a series circuit composed of the heater 34 and the switch element 134 are connected in parallel between the input terminals 111 and 112, and power is supplied from a commercial AC power source.

  The fixing heaters 33 and 34 are incorporated so as to extend in the axial direction of a fixing roller (not shown), and a halogen lamp having a positive temperature coefficient and having a resistance value of about several hundred W to 1 kW is generally used. Yes. As the switch elements 133 and 134, an SSR (Solid State Relay), an insulating switch circuit composed of a photo triac and a triac, or the like is used.

  Reference numeral 101 denotes a zero-cross detection circuit connected to both ends of the above-described series circuit. The zero-cross detection circuit 101 detects the zero-cross of the commercial AC power supplied from the input terminals 111 and 112 to the series circuit. Reference numerals 35 and 36 denote temperature detection elements arranged in the immediate vicinity of the surfaces of the fixing roller 31 and the pressure roller 32, and a thermistor having a temperature coefficient with a known impedance is used. As a result, the surface temperature of the fixing roller can always be detected, and a temperature detection signal can be output to the temperature adjustment circuit 103 via the AD converter 102.

  The temperature control circuit 103 controls switching of the switch elements 133 and 134 based on the temperature detection signal to control the on / off timing of the heaters 33 and 34, thereby controlling the temperatures of the fixing roller 31 and the pressure roller 32. In order to control the temperature so as to keep within a predetermined temperature range, a heater on / off signal is output to the drive pulse generation circuits 233 and 234. That is, when the surface temperature of the fixing roller rises and reaches the upper limit value of the control range, an off signal is output. When the surface temperature of the fixing roller decreases after turning off and becomes the lower limit value of the temperature control range, an on signal is output.

  The drive pulse generation circuits 233 and 234 receive the heater on / off signal and the output from the zero cross detection circuit 101 as inputs, and switch elements 133 and 233 are controlled so that the surface temperature of the fixing roller is controlled within a certain temperature based on the respective values. A drive pulse for switching control of 134 is output.

  Next, the operation of the circuit of FIG. 3 will be described. FIG. 4 shows the current flowing through the heaters 33 and 34 when the phase control is not performed and the drive pulse to each heater. In FIG. 4a, power supply to the heater 33 is started at a timing t1, and then power supply to the heater 34 is started at a timing t2. As described above, since the halogen heater has a positive temperature coefficient, a large current flows immediately after the start of power supply (a period from about t1 to t4), and a flicker phenomenon occurs (FIG. 4b shows the vicinity of t1 and t2. It is an enlarged view).

  FIG. 5 shows an operation waveform when phase control is used to reduce this. In FIG. 5a, phase control is used to limit the power conduction angle to the heater from the time t1 and t2 of the start of power supply to the heaters 33 and 34 to the time t3 and t4, respectively (FIG. 5b shows the vicinity of t1 and t2. Is an enlarged view).

JP 2004-328869 A

  However, if phase control is used to reduce flicker, the harmonic current increases, so the conduction angle to the heater and the duration of phase control are optimal so that both flicker reduction and harmonic current reduction are compatible. It is necessary to make it.

  In recent years, the heater power required for the device to increase the printing speed has been increasing. Furthermore, with the diversification of corresponding print media, it is necessary to control a complicated amount of heat using a large number of heaters.

  For this reason, it has become difficult to achieve both the above-described flicker and reduction of harmonic current. In particular, when a plurality of heaters start energization almost simultaneously, phase control is applied at the same time, and instantaneous harmonic current peaks often overlap.

  In order to avoid this, it is possible to use a method such as limiting the energization start timing so that multiple heaters do not start energizing at the same time. However, energization cannot be started at the required timing, which reduces the temperature ripple of the fixing roller. It becomes a factor to let you.

The image forming apparatus of the present invention includes:
Image forming means for forming a toner image on recording paper;
A first rotator and a second rotator for fixing a toner image formed on the recording paper by the image forming unit therebetween;
A first heater group for heating the first rotating body;
A second heater group for heating the second rotating body;
A first temperature sensor for detecting a temperature of the first rotating body;
A second temperature sensor for detecting the temperature of the second rotating body;
Detection means for detecting the zero cross timing of the commercial power supply;
When power is supplied to the first heater group based on the output of the first temperature sensor, the power supply start timing to the first heater group is controlled according to the output of the detection means, and the second temperature Control means for controlling power supply start timing to the second heater group according to the output of the detection means when power is supplied to the second heater group based on the output of the sensor;
The control means performs phase control in synchronization with the zero cross timing detected by the zero cross timing detection means, and at a first phase angle during a predetermined time from the start of power feeding to the first heater group. The control is executed, and the phase control is executed at a second phase angle different from the first phase angle while a predetermined time elapses from the start of power supply to the second heater group.

  According to the present invention, a plurality of fixing heaters are divided into a plurality of groups, and a phase control conduction angle that is different for each group is set, thereby making it possible to reduce both flicker and harmonic current.

Schematic sectional view of the image forming apparatus Schematic configuration diagram of a conventional fixing device Conventional fixing heater drive circuit configuration diagram Conventional heater drive waveform without phase control Conventional heater drive waveform without phase control Conventional heater drive waveform using phase control Conventional heater drive waveform using phase control Schematic configuration diagram of a fuser with multiple heaters on one roller Heater drive circuit configuration diagram Heater drive waveform with different conduction angles Heater drive waveform with different conduction angles Heater drive waveform without shifting the conduction angle Heater drive waveform without shifting the conduction angle

[Example 1]
FIG. 1 is a schematic sectional view showing an image forming apparatus (printer 1). In FIG. 1, 1 is a printer main body, 2a to 2d are photosensitive drums of four colors, 3a to 3d are chargers, 4a to 4d are photosensitive drum cleaners, and 5a to 5d are laser scanning units. Further, 6a to 6d are primary transfer blades, 7a to 7d are developing units, 8 is an intermediate transfer belt, 10, 11 and 21 are rollers supporting the intermediate transfer belt 8, and 12 is an intermediate transfer belt cleaner.

  The paper feed cassette 17 stores the recording material S. Pickup rollers 18 and 19 are rollers for feeding the recording material S accommodated in the paper feed cassette 17. The vertical pass roller 20 is a roller that conveys the recording material S. The manual feed tray 13 is loaded with a recording material S such as paper. The pickup rollers 14 and 15 are rollers for feeding the recording material S loaded on the manual feed tray 13. The registration roller 16 is a roller for adjusting the delivery timing of the recording material S.

  In addition, the printer 1 includes a secondary transfer unit 22, a fixing unit 26, a paper discharge roller 24, and a paper discharge tray 25.

  In the printer 1, electrostatic latent images are formed on the photosensitive drums 2a to 2d by the laser scanning units 5a to 5d, and the electrostatic latent images are developed by the developing devices 7a to 7d. As a result, a toner image for each color component is formed on each of the photosensitive drums 2a to 2d. The toner images of the respective colors developed on the photosensitive drums 2a to 2d are transferred onto the intermediate transfer belt 8 so as to form a full color toner image.

  At this time, the recording material S is fed from the paper feed cassette 17 or the manual feed tray 13, the registration timing is adjusted by the registration roller 16, and conveyed to the secondary transfer unit 22. Note that paper transport units such as pickup rollers 18 and 19 for feeding from the paper feed cassette 17, vertical path roller 20, registration roller 16, pickup rollers 14 and 15 for feeding from the manual feed tray 13, It is driven by a stepping motor.

  The toner image on the intermediate transfer belt 8 and the recording material S pass through the secondary transfer unit 22, whereby the toner image on the intermediate transfer belt 8 is transferred to the recording material S. The recording material S to which the toner image has been transferred is conveyed to the fixing unit 26. The fixing unit 26 conveys the recording material S carrying the toner image T and applies heat and pressure to the recording material S to fix the toner image on the recording material S. Then, the recording material S on which the toner image is fixed is discharged from the printer 1.

  FIG. 2 is a schematic configuration diagram of the fixing unit 26. The heating roller 31 is a roller in which a layer of a heat-resistant elastic body such as silicone rubber or fluororubber is formed on a pipe material such as aluminum or iron and a release layer such as PFA or PTFE is coated on the surface.

  The fixing unit 26 includes a pressure roller 32 so as to press the heating roller 31. Similarly to the heating roller 31, the pressure roller 32 is a roller in which a layer of a heat-resistant elastic body such as silicone rubber or fluorine rubber is formed on a cored bar. When the pressure roller (pressing member) 32 presses the heating roller (fixing member) 31, a nip portion is formed. By passing the recording material S through the nip portion, the toner image T on the recording material S is heated and pressurized and fixed to the recording material S.

  FIG. 6 is a diagram showing a schematic configuration of a heat fixing device 26 in which a plurality of heaters are arranged on one roller.

  Inside the heating roller 31, two heaters 33a and 33b having different heat distributions in the longitudinal direction are disposed, and the heating roller 31 is heated from the inside. The temperature detection element 35 that detects the surface temperature of the heating roller 31 is disposed at a position facing the heating roller 31. Based on the output signal from the temperature detection element 35, the energization to the heater is controlled so that the surface temperature of the heating roller 31 is maintained at the fixing temperature or the standby temperature (standby temperature) at the time of non-fixing.

  Similarly, two heaters 34a and 34b having different heat distributions in the longitudinal direction are disposed inside the pressure roller 32, and the pressure roller 32 is heated from the inside. Similarly, a temperature detection element 36 for detecting the surface temperature is disposed at a position facing the pressure roller 32 in the pressure roller 32, and the surface temperature of the pressure roller 32 is determined based on an output signal of the temperature detection element 36. The energization of the heater is controlled so as to be maintained at the fixing temperature or the standby temperature during standby (standby temperature).

  FIG. 7 is a block diagram showing the configuration of a main circuit of a conventional image forming apparatus that controls energization of four fixing heaters used as heat sources in the thermal fixing apparatus.

  In FIG. 7, reference numerals 111 and 112 denote input terminals connected to the commercial AC power supply 100, and AC power is input thereto. Between the input terminals 111 and 112, a series circuit composed of the fixing heater 33a and the switching element 133a, a series circuit composed of the fixing heater 33b and the switching element 133b, a series circuit composed of the fixing heater 34a and the switching element 134a, and the fixing heater 34b and the switching element. A series circuit composed of 134b is connected in parallel, and power is supplied from a commercial AC power supply.

  The fixing heaters 33a, 33b, 34a, and 34b are built in such a manner as to extend in the axial direction of a fixing roller (not shown), and a halogen lamp having a positive temperature coefficient of several hundred W to 1 KW or the like. Commonly used. For the switch elements 133a, 133b, 134a, 134b, an SSR (Solid State Relay), an insulating switch circuit composed of a photo triac and a triac, or the like is used.

  Reference numeral 101 denotes a zero-cross detection circuit connected to both ends of the above-described series circuit. The zero-cross detection circuit 101 detects the zero-cross of the commercial AC power supplied from the input terminals 111 and 112 to the series circuit. Reference numerals 35 and 36 denote temperature detection elements arranged in the immediate vicinity of the surfaces of the fixing roller 31 and the pressure roller 32, and a thermistor having a temperature coefficient with a known impedance is used. As a result, the surface temperature of the fixing roller can always be detected, and a temperature detection signal can be output to the temperature adjustment circuit 103 via the AD converter 102.

  The temperature adjustment circuit 103 performs switching control of the switch elements 133a, 133b, 134a, and 134b based on the temperature detection signal to control the on / off timing of the heaters 33a, 33b, 34a, and 34b. In order to control the temperature of the pressure roller 32 so as to keep the temperature within a predetermined temperature range, a heater on / off signal is output to the drive pulse generation circuits 233, a233b, 234a, 234b. That is, when the surface temperature of the fixing roller rises and reaches the upper limit value of the control range, an off signal is output. When the surface temperature of the fixing roller decreases after turning off and becomes the lower limit value of the temperature control range, an on signal is output.

  The drive pulse generation circuits 233a, 233b, 234a, and 234b receive the heater on / off signal and the output from the zero cross detection circuit 101 as inputs, and the surface temperature of the fixing roller is controlled within a certain temperature based on the respective values. A drive pulse for switching control of the switch elements 133a, 133b, 134a, and 134b is output.

  Next, the operation of the circuit of FIG. 7 will be described. FIG. 8 shows currents flowing through the heaters 33a, 33b, 34a, and 34b and driving pulses to the heaters. Further, the sum of the currents flowing through the heaters 33a and 34a, the sum of the currents flowing through the heaters 33b and 34b, and the sum of the currents flowing through all the heaters 33a, 33b, 34a and 34b are shown.

  In FIG. 8a, power supply to the heater 33a is started at a timing t1, and then power supply to the heater 34b is started at a timing t2, power is supplied to the heater 33b at a timing t3, and power supply to the heater 34a is started at a timing t4. As described above, since the halogen heater has a positive temperature coefficient, a large current flows immediately after the start of power supply (a period from about t1 to t4) and a flicker phenomenon occurs. For the period of time, power is supplied using phase control that limits the conduction angle.

  FIG. 8b shows the phase control period expanded. In this phase control period, the drive pulse generation circuits 233a and 234a generate drive pulses at the same conduction angle, and the drive pulse generation circuits 233b and 234b drive pulses at a conduction angle different from that of the drive pulse generation circuits 233a and 234a. Is generated.

  For this reason, the current waveforms to the heaters 33a and 34a and the heaters 33b and 34b overlap with each other, but the current waveforms to these four heaters are shifted from each other.

  For reference, the waveform of each part when the conduction angles to these four heaters are all the same is shown in FIG. As can be seen by comparing FIG. 9b with the current waveform diagram 8b in the embodiment of the present invention, it can be seen that the current waveform peaks of the four heaters are reduced.

  Thus, even in a fixing device using a large number of heaters, it is possible to reduce harmonic current while suppressing flicker.

33 heater, 26 fixing device, 41 case, 43 infrared absorption filter,
44 Thermistor, 45 Thermistor, 57 CPU, 58 ROM

Claims (4)

Image forming means for forming a toner image on recording paper;
A first rotator and a second rotator for fixing a toner image formed on the recording paper by the image forming unit therebetween;
A first heater group for heating the first rotating body;
A second heater group for heating the second rotating body;
A first temperature sensor for detecting a temperature of the first rotating body;
A second temperature sensor for detecting the temperature of the second rotating body;
Detection means for detecting the zero cross timing of the commercial power supply;
When power is supplied to the first heater group based on the output of the first temperature sensor, the power supply start timing to the first heater group is controlled according to the output of the detection means, and the second temperature Control means for controlling power supply start timing to the second heater group according to the output of the detection means when power is supplied to the second heater group based on the output of the sensor;
The control means performs phase control in synchronization with the zero cross timing detected by the zero cross timing detection means, and at a first phase angle during a predetermined time from the start of power feeding to the first heater group. And performing phase control at a second phase angle different from the first phase angle while a predetermined time elapses from the start of power supply to the second heater group. apparatus. The first phase control duration for continuing phase control from the start of power supply to the first heater group and the second phase control duration for continuing phase control from the start of power supply to the second heater group The image forming apparatus according to claim 1, wherein time is set. Image forming means for forming a toner image on recording paper;
A thermal fixing device having a plurality of rotating bodies for fixing the toner image formed on the recording paper by the image forming means;
A plurality of temperature detecting means for detecting the temperature of each of the plurality of rotating bodies;
A plurality of heaters for heating the plurality of rotating bodies;
Detection means for detecting the zero cross timing of the commercial power supply;
In accordance with the output of the temperature detection means, the power supply to the heater for heating the corresponding rotating body is controlled so as to keep the temperature of the corresponding rotating body within a predetermined range. Control means for phase control in synchronization with the zero cross timing signal detected by the zero cross timing detection means,
2. The image forming apparatus according to claim 1, wherein each of the plurality of heaters includes a plurality of heater groups each including a plurality of heaters, and the phase control is executed at a different phase angle for each heater group. The image forming apparatus according to claim 3, wherein the phase control duration for continuing the phase control from the start of power supply to each heater group can be set to a different time for each heater group.