Image forming apparatus

Abstract

To provide an image forming apparatus that prevents a reduction in fixation quality caused by a variation in power supply voltage.SOLUTION: An image forming apparatus of the present invention has: a plurality of heaters that heat a medium to which a developer image is transferred, and operate with power supplied from an AC power supply; a pulse generation unit that generates pulses based on a change in AC voltage supplied from the AC power supply; and control means that controls the timing to turn on or off respective heaters on the basis of the pulses. The control means acquires a pulse width of the pulses in a first state where all of the heaters are turned off as a first pulse width, acquires a pulse width of the pulses in a second state where all of the heaters are turned on as a second pulse width, performs comparison processing of comparing the first pulse width with the second pulse width, and changes a heater control method of controlling the heaters according to a result of the comparison processing.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and can be applied to, for example, an electrophotographic printer including a fixing device.

Background Art

[0002] Conventionally, in an electrophotographic image forming apparatus, a fixing device that applies heat and pressure to a sheet on which a toner image has been transferred is provided. And in the fixing device of a conventional image forming apparatus, a heater such as a halogen heater is provided as a heating means.

[0003] Conventionally, as an image forming apparatus provided with a heater in a fixing device, for example, there is an image forming apparatus described in Patent Document 1. The heater included in the image forming apparatus described in Patent Document 1 generates heat when an AC voltage is applied. Therefore, the image forming apparatus described in Patent Document 1 is provided with a power supply unit that can apply an AC voltage to the heater. And the power supply unit of the image forming apparatus described in Patent Document 1 detects the timing at which the absolute value of the AC voltage becomes 0 (so-called "zero cross point", "zero cross point"), and uses a pulse (so-called "zero cross pulse") that switches at the zero cross point to control the heater.

[0004] In Patent Document 1, when the interval of the zero cross point (hereinafter referred to as "zero cross pulse width") is out of a predetermined range, it is detected as an abnormality of the power supply voltage supplied to the power supply unit, and when the zero cross pulse width is within the predetermined range, the power supply voltage is estimated from the zero cross pulse width, and parameters for controlling the fixing device are adjusted.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in conventional image forming apparatuses, when the zero-cross pulse width shifts due to fluctuations in the frequency of the power supply voltage, and furthermore, when a voltage drop (voltage droop) occurs due to the heater turning on and the load increasing, it is not possible to accurately estimate the power supply voltage (voltage estimation based on the zero-cross pulse width), and there is a risk that the parameters for controlling the fixing unit will shift and the fixing quality on the medium will deteriorate.

[0007] Therefore, an image forming apparatus capable of suppressing a decrease in fixing quality associated with fluctuations in the power supply voltage is desired.

Means for Solving the Problems

[0008] The image forming apparatus of the present invention heats a medium onto which a developer image has been transferred, and includes a plurality of heaters that operate with power supplied from an AC power supply, a pulse generation unit that generates pulses based on changes in the AC voltage supplied from the AC power supply, and control means for controlling the timing of turning on and off each of the heaters based on the pulses. The control means acquires the pulse width of the pulses in a first state in which all the heaters are off as a first pulse width, acquires the pulse width of the pulses in a second state in which all the heaters are on as a second pulse width, performs a comparison process of comparing the first pulse width and the second pulse width, and changes a heater control method for controlling the heaters according to the result of the comparison process.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an image forming apparatus that suppresses a decrease in fixing quality associated with fluctuations in the power supply voltage.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0011] (A) Main Embodiment Hereinafter, an embodiment of the image forming apparatus according to the present invention will be described in detail with reference to the drawings. In this embodiment, an example in which the image forming apparatus of the present invention is applied to a printer will be described.

[0012] (A-1) Configuration of the Embodiment First, the schematic configuration of the printer 1 will be described with reference to FIG. 2.

[0013] FIG. 2 is a diagram showing the schematic configuration (schematic cross-sectional view) of the printer 1.

[0014] Printer 1 develops a toner image (developer image) and transfers it onto a sheet of paper M as a printing paper (a medium for image formation) for printing. Printer 1 includes four image forming units 2 (2-1 to 2-4), four LED heads 3 (3-1 to 3-4), four transfer rollers 10 (10-1 to 10-4), and a transfer belt 19 that is endless and conveys the paper M. The image forming units 2-1 to 2-4 each carry toner (developer) of the colors yellow, magenta, cyan, and black, and are means (developing means) for developing a toner image (developer image) using the carried toner. Also, Printer 1 includes a paper tray 25 on which a plurality of sheets of paper M can be placed, a paper feed roller 11 that separates and feeds out the sheets of paper M placed on the paper tray 25 one by one, and conveyance rollers 14, 15 that convey the paper M fed by the paper feed roller 11 to the downstream side (the image forming unit 2 / transfer belt 19 side). Further, Printer 1 includes a fixing unit 20 that applies heat and pressure to the medium M onto which the toner image has been transferred by the image forming unit 2 (2-1 to 2-4) for fixing, discharge rollers 26, 27 for discharging the paper M that has been subjected to the fixing process by the fixing unit 20 to the outside, and a stacker 28 for placing the discharged paper M. Furthermore, Printer 1 includes a paper feed sensor 12 for checking whether paper feeding has been performed by the paper feed roller 11, a writing sensor 16 that detects the leading edge of the paper M conveyed by the conveyance rollers 14, 15 and determines the writing start timing, and a discharge sensor 24 for monitoring conveyance errors or jams of the paper M that has been processed by the fixing unit 20. Also, Printer 1 includes a printer control unit 300 as control means for controlling each part within Printer 1 and a power supply unit 100. The power supply unit 100 is provided with a power connector 120 for connecting a power cable 500. In FIG. 2, the other end of the power cable 500 is connected to a commercial power supply 400. Note that the power cable 500 may be configured by connecting a plurality of cables (for example, an extension cable, etc.) in series.

[0015] In addition, the printer 1 is provided with rollers for paper feeding and the like (not shown) other than those described above. Also, the number (number of channels) of the image forming unit 2 and the LED head 3 mounted on the printer 1 is not limited to the above example. Further, in FIG. 2, the direction in which the paper M is conveyed (hereinafter referred to as the "paper conveyance direction") X is illustrated by an arrow (an arrow in the left direction in FIG. 2).

[0016] The transfer belt 19 operates in accordance with the rotation of a belt drive roller 18 that is rotationally driven by a motor and gears (not shown). Inside the transfer belt 19, a conveyance belt driven roller 17 is arranged that rotates in accordance with the rotation of the transfer belt 19 and is arranged to keep the tension of the transfer belt 19 constant. Further, the printer 1 has actuators and sensors (not shown) such as clutches and solenoids (not shown) other than those described above, and is integrally controlled by the printer control unit 300.

[0017] The fixing device 20 includes a fixing roller 21, a heating unit 210 as a heat source (heating means) for heating the fixing roller, and a fixing backup roller 22 for pressing the paper against the fixing roller 21. The fixing device 20 performs heating and pressurization on the paper M by sandwiching the paper M between the fixing roller 21 and the fixing backup roller 22 and conveying it downstream in the paper conveyance direction. The set temperatures at which the heaters 211 and 212 are to be heated are not limited, but here, it will be described as being about 170°C.

[0018] FIG. 3 is a diagram showing the arrangement configuration of the heating unit 210 in the fixing roller 21.

[0019] FIG. 3(a) is a side view of the fixing roller 21 (including the heating unit 210), and FIG. 3(b) is a cross-sectional view taken along the line A-A' in FIG. 3(a). In FIG. 3, the paper conveyance direction X and the direction orthogonal to the paper conveyance direction X (hereinafter referred to as the "width direction") are illustrated using arrows.

[0020] As shown in FIG. 3, the heating unit 210 is disposed inside the fixing roller 21. Further, as shown in FIG. 3, the heating unit 210 has two heaters 211 and 212, and two thermistors 213 and 214 as temperature detection units. The thermistor 213 detects the temperature of the heater 211, and the thermistor 214 detects the temperature of the heater 212.

[0021] As shown in FIG. 3, the thermistor 213 is arranged to mainly heat the central portion in the width direction, and the thermistor 214 is arranged to mainly heat both end portions in the width direction of the fixing roller 21 in the width direction. The thermistor 214 has heater portions 212a and 212b arranged separately at both end portions in the width direction, and a lead wire 212c connecting between the two heater portions 212a and 212b. The thermistor 213 is arranged around the heater 211. The thermistor 214 is arranged around either one of the heater portions 212a and 212b (in FIG. 3, around the heater portion 212a).

[0022] Note that in the fixing roller 21 (heating unit 210), the arrangement configuration of each heater and thermistor is not limited, and various combinations can be applied. Also, in the fixing roller 21 (heating unit 210), the number of sets of heaters and thermistors may be three or more.

[0023] Next, the configuration related to the control of the heating unit 210 in the printer 1 will be described with reference to FIG. 1.

[0024] FIG. 1 is a block diagram showing components related to the control of the heaters 211 and 212 in the printer 1.

[0025] As shown in FIG. 1, the printer control unit 300 includes a CPU 301 and a memory 302 in which a program to be executed by the CPU 301 is recorded. The memory 302 is assumed to be a non-volatile memory such as a FLASH (registered trademark) memory, for example. The CPU 301 is provided with a number of I / Os (input / output terminals) and integrally controls the on / off of each motor, clutch, etc. in the printer 1. In FIG. 1, only the I / Os related to the power supply unit 100 and the heating unit 210 are illustrated in the CPU 301. For example, in the 102 of the CPU, a paper feed sensor 12, a writing sensor 16, and a discharge sensor 24 are connected to detect the position of the paper M and determine the operation timing.

[0026] As shown in FIG. 1, the power supply unit 100 includes a bridge diode 101, a comparator 102, a current limiting unit 103, a photocoupler 104, and triacs 105 and 106 as components for controlling the heating unit 210. The power supply unit 100 also includes components for supplying power to other elements in the printer 1 in addition to the components shown in FIG. 1. For example, the power supply unit 100 generates a power supply for driving the CPU 301 and the like using a transformer and a regulator (not shown) based on the commercial power supply 400 and supplies it to the printer control unit 300 (including the CPU 301).

[0027] The power supply unit 100 processes the AC power supplied from the commercial power supply 400 via the power cable 500 (power connector 120). Hereinafter, in the power supply unit 100, the voltage input (observed) to the power connector 120 (the voltage input from the commercial power supply 400 via the power cable 500) shall also be simply referred to as the "power supply voltage". In the power supply unit 100, the power supply voltage is supplied (applied) to the bridge diode 101. Also, the power supply voltage is supplied to the heaters 211 and 212 via the triacs 105 and 106 which are switching elements. The triacs 105 and 106 control the thermistors 213 and 214 by switching (on / off) according to the control signals supplied to the gate terminals from the CPU 301 respectively. Here, the control signals (on / off signals) supplied from the CPU 301 to the triacs 105 and 106 shall be represented as "HT1" and "HT2" respectively. The CPU 301 grasps the temperatures of the heaters 211 and 212 (the temperatures detected by the thermistors 213 and 214) by receiving the supply of detection signals (voltage values corresponding to the temperature) from the thermistors 213 and 214. Here, the detection signals supplied from the heaters 211 and 212 to the CPU 301 shall be represented as "AD1" and "AD2" respectively. That is, while grasping the temperatures of the heaters 211 and 212 based on the detection signals AD1 and AD2, the CPU 301 controls the heaters 211 and 212 by turning the triacs 105 and 106 on / off at the timing based on the zero-cross pulse using the control signals HT1 and HT2, and maintains the optimum temperatures of the heaters 211 and 212.

[0028] The power supply unit 100 includes, as elements constituting a circuit (hereinafter referred to as the "pulse generation circuit") for generating a pulse (zero-cross pulse in the case of FIG. 1) based on the power supply voltage which serves as a trigger for suppressing the inrush current of the triacs 105 and 106 and reducing noise, a bridge diode 101, a comparator 102, and a current limiting unit 103 (sine wave current limiting unit).

[0029] In the pulse generation circuit, the sine wave of the power supply voltage is rectified (full-wave rectified) into pulsating current by the bridge diode 101 and supplied to the comparator 102 via the current limiting section 103. In the current limiting section 103, the pulsating current (current) supplied from the bridge diode 101 to the comparator 102 is limited (shunted) by the resistors R1 and R2. The resistance ratio of the resistors R1 and R2 is arbitrarily set by design, but here it is assumed that the resistance values of the resistors R1 and R2 are equal for explanation. The other end of the current limiting section 103 is grounded to GND108. A predetermined constant voltage (constant voltage for defining the slice voltage of the zero-cross pulse; hereinafter simply referred to as "slice voltage") is also input to the comparator 102 from the constant voltage section 107. The comparator 102 outputs the comparison result (H level or L level) between the voltage of the pulsating current supplied from the current limiting section 103 and the slice voltage as a zero-cross pulse. The zero-cross pulse output from the comparator 102 is supplied to the CPU 301 via the photocoupler 104. It is assumed that in the CPU 301, this zero-cross pulse is input as an interrupt input "INT_IN". In the pulse generation circuit of this embodiment, in the range where the power supply voltage is 0 to ±40V, a zero-cross pulse is generated (so that the level of the zero-cross pulse becomes H), and it is assumed that the above slice voltage and the configuration of the current limiting section 103 (the ratio of R1 and R2) are set. Note that the range of the zero-cross pulse is not limited to 0 to ±40V, and an arbitrary range may be set.

[0030] Next, the control process of the heaters 211 and 212 by the printer control unit 300 (CPU 301) (hereinafter referred to as "heater control process") will be described.

[0031] As described above, the printer control unit 300 (CPU 301) controls the heaters 211 and 212 via the power supply unit 100 to reach a predetermined set temperature during the fixing process. Specifically, the CPU 301 outputs control signals HT1 and HT2 for controlling the triacs 105 and 106 based on the zero-cross pulse INT_IN supplied from the pulse generation circuit of the power supply unit 100 and the detection signals AD1 and AD2 supplied from the thermistors 213 and 214. For example, at the start of printing, the printer control unit 300 (CPU 301) controls the heaters 211 and 212 (outputs the control signals HT1 and HT2) so that the thermistors 213 and 214 rise to a predetermined set temperature (target temperature) by a predetermined scheduled time (for example, the time when the paper M reaches the fixing unit 20).

[0032] Incidentally, the inventor of the present application discovered that the impedance in the transmission path from the commercial power supply 400 to the power supply unit 100 (that is, the configuration of the power cable 500) affects the zero-cross pulse (zero-cross pulse width). For example, when the total length of the power cable 500 forms a long path due to indoor wiring or the like (for example, when it becomes longer due to an extension cable or the like), the impedance of the power cable 500 may cause the supply voltage to the printer 1 (the power supply voltage in the power supply unit 100) to drop at the timing when the heaters 211 and 212 are turned on. In such a case, if the printer control unit 300 (CPU 301) performs the same heater control as in the prior art, the temperature rise of the heaters 211 and 212 will be slower than expected. As a result, the temperature rise of the heaters 211 and 212 may not be sufficient at the scheduled time, and sufficient heat may not be applied to the paper M, resulting in a fixing defect. For example, when the printer control unit 300 (CPU 301) raises the temperature of the heaters 211 and 212 to the paper feed startable temperature of 150°C and then starts paper feeding, and expects the temperature of the heaters 211 and 212 to reach the predetermined set temperature (170°C) by the time the paper M reaches the fixing unit 20 (heaters 211 and 212), if the heating of the heaters 211 and 212 cannot keep up with the scheduled time due to the voltage drop as described above, the heating of the paper M will be insufficient. Further, the printer control unit 300 (CPU 301) continuously determines the time for turning on the heaters 211 and 212 (hereinafter referred to as "heater on time") based on the difference between the set temperature (the set temperature of the heaters 211 and 212) and the real-time measurement result (the temperature detected based on the detection signals AD1 and AD2 by the thermistors 213 and 214), and performs predictive control of the heater's reaching temperature. However, since the temperature rise rate of the heaters 211 and 212 exceeds the temperature detection rate of the thermistors 213 and 214, when the voltage drop as described above occurs, it becomes difficult to control the temperature rise of the heaters 211 and 212 at the predicted speed, and there is a problem that the set temperature is not reached by the time the paper M reaches the fixing unit 20 (heaters 211 and 212). That is, when the voltage drop of the power supply voltage as described above occurs, there is a problem that it becomes difficult to predict the accurate temperature rise rate of the heaters 211 and 212 with the conventional heater control method.

[0033] Here, the inventor of the present application will explain the results of an experiment (hereinafter referred to as "this experiment") for measuring the zero-cross pulse width when a 30 m cord reel is applied to the power cable 500 in the printer 1.

[0034] FIG. 4 is a graph showing the results of this experiment (an experiment for confirming the characteristics of the zero-cross pulse width in the printer 1 of this embodiment).

[0035] In this experiment, when a 30 m cord reel is applied to the power cable 500, for each of the cases when both the heaters 211 and 212 are turned off (hereinafter referred to as "standby" or "heater off") and when both the heaters 211 and 212 are turned on (hereinafter referred to as "heater on"), the waveform of the power supply voltage input to the printer 1 (power supply unit 100) (the voltage input from the commercial power supply 400 to the power supply connector 120 via the power cable 500) and the waveform of the zero-cross pulse INT_IN were observed.

[0036] FIG. 4(a) shows the waveform of the power supply voltage, and FIG. 4(b) shows the waveform of the zero-cross pulse INT_IN. In this experiment, a 50 Hz 100 V AC power supply (AC100V / 50Hz power supply) was applied as the commercial power supply 400. Hereinafter, the zero-cross pulse width during standby (heater off) is represented by Ht, and the zero-cross pulse width during heater on is represented by Hp.

[0037] As shown in FIG. 4(a), the power supply voltage during standby is AC100V, and it drops to about AC72V when the heaters are on. Along with this voltage drop, the capabilities (temperature rise rates) of the heaters 211 and 212 also decrease.

[0038] Then, as shown in FIG. 4(b), with this voltage drop, in the power supply unit 100, the zero-cross pulse width also increases. In this experiment, when measuring the zero-cross pulse width Ht during standby (when the heater is off) and the zero-cross pulse width Hp when the heater is on, it was found that Ht = 2.12 mS and Hp = 2.56 mS. That is, in this experiment, it can be seen that when transitioning from standby to when the heater is on, the zero-cross pulse width increases by about 20%. Such an increase in the zero-cross pulse is caused by the voltage drop when the heater is on. That is, the greater the voltage drop when the heater is on, the greater the increase in the zero-cross pulse width.

[0039] Therefore, in the printer control unit 300 (CPU 301) of this embodiment, as described above, the amount of change in the zero-cross pulse width before and after the heater is turned on / off is measured. When the change is more than a predetermined amount, a process of changing the heater control method (the control method of heaters 211 and 212) (hereinafter referred to as the "heater control method determination process") is performed to control (limit) the power consumption (peak power) in the printer 1. Here, the printer control unit 300 (CPU 301) operates in either a heater control method of turning on heaters 211 and 212 simultaneously (hereinafter referred to as the "normal control mode") or a heater control method of controlling a plurality of heaters (heaters 211 and 212) to operate exclusively (controlling to limit the number of heaters turned on simultaneously; hereinafter also simply referred to as "exclusive control") (hereinafter referred to as the "peak power control mode").

[0040] When the printer control unit 300 (CPU 301) shifts to the peak power control mode, for a plurality of heaters, by performing exclusive control (control to limit the number of heaters to be turned on simultaneously), the load on the commercial power supply 400 (the impedance of the printer 1 as seen from the commercial power supply 400) can be reduced, and voltage drops such as those occurring in this experiment can be suppressed. For example, when the printer control unit 300 (CPU 301) shifts to the peak power control mode, for the two heaters 211 and 212, it controls them so that only one of them is turned on at a time instead of both being turned on simultaneously (for example, repeating an operation of alternately turning on / off between the heaters 211 and 212). By doing so, the load on the commercial power supply 400 can be reduced, and the voltage drop of the power supply voltage as described above can be suppressed. If the voltage drop of the power supply voltage as described above does not occur, since the capacity of the heaters 211 and 212 does not decrease, the printer control unit 300 (CPU 301) can accurately predict the temperature rise of the heaters 211 and 212, and fixing defects and the like can be suppressed.

[0041] (A-2) Operation of the First Embodiment Next, the operation of the printer 1 will be described.

[0042] First, the overall operation outline when printing is performed on the paper M by the printer 1 will be described.

[0043] The printer control unit 300 of the printer 1 is connected to a host (for example, an information processing terminal such as a PC) not shown through a cable or network (for example, a wireless LAN or a wired LAN) not shown. When the printer control unit 300 receives an instruction to transfer print data and print from this host, it starts driving the heaters 211 and 212 of the fixing unit 20 (heating unit 210). When the heaters 211 and 212 reach the paper feeding startable temperature (for example, about 150°C), the paper feeding roller 11 is rotated to feed the paper M on the paper tray 25 to the one-sheet conveying rollers 14 and 15. The printer control unit 300 starts rotating the rollers of the image forming units 2-1 to 2-4 almost simultaneously with the start of paper feeding, and along with this start of rotation, the belt driving roller 18 of the transfer belt 19 also starts rotating. When the fed paper M is further conveyed downstream by the conveying rollers 14 and 15 and the leading edge of the paper M reaches the writing sensor 16, the printer control unit 300 controls the image forming units 2-1 to 2-4, the LED heads 3-1 to 3-4, the transfer rollers 10-1 to 10-4, etc., to develop the toner images of each color and transfer them to the paper M. When the leading edge of the paper M reaches the writing sensor 16, the exposure of the LED head 3-1 starts after a certain time, and an electrostatic latent image is formed on the photosensitive drum 4-1. On the photosensitive drum 4-1, toner (developer) is supplied to the formed electrostatic latent image by the developing roller 6-1, and a toner image is formed. The toner image formed on the photosensitive drum 4-1 is attracted to the paper M side by the Coulomb force generated in the transfer roller 10-1 (the Coulomb force generated by applying a voltage of about +3000V) and transferred to the paper M. The printer control unit 300 performs the same control for the other color elements (image forming units (2-2 to 2-4), LED heads 3-2 to 3-6, transfer rollers 10-1 to 10-4, etc.) to transfer the toner images of each color to the paper M.

[0044] When the transfer of the toner images of each color to the paper M is completed, the printer control unit 300 controls the heaters 211 and 212 via the power supply unit 100 to heat the fixing roller 21 to a set temperature (about 170°C) suitable for the fixing process. Then, the printer control unit 300 conveys the paper M downstream while sandwiching the paper M between the fixing roller 21 and the fixing backup roller 22, heats and pressurizes the paper M to fix the toner image. After fixing, when the leading edge of the paper M reaches the discharge sensor 24, the printer control unit 300 drives the discharge rollers 26 and 27 to discharge the paper M to the stacker 28.

[0045] In the flow as described above, in the printer 1, printing processing (image forming processing including fixing processing) for the paper M is performed.

[0046] Next, the heater control processing (control processing of the heaters 211 and 212) by the printer control unit 300 (CPU 301) will be described.

[0047] FIG. 5 is a flowchart showing the processing in which the printer control unit 300 (CPU 301) controls the heaters 211 and 212 during printing.

[0048] In FIG. 5, only the processing related to the control of the heaters 211 and 212 among the controls performed by the CPU 301 during printing is shown.

[0049] First, it is assumed that the CPU 301 starts the printing process based on the supply of printing data from a host (not shown), etc. (S101).

[0050] Next, the CPU 301 reads and stores (records) the zero-cross pulse width Ht during standby before printing start (when the heater is off) (S102).

[0051] Next, the CPU 301 starts the control to turn on all the heaters (heaters 211 and 212) (starts heater control in the normal control mode) (S103).

[0052] Next, the CPU 301 reads and stores the zero-cross pulse width Hp when the heater is on (when both heaters 211 and 212 are on) (records it (S104).

[0053] Next, the CPU 301 calculates the pulse width ratio WR (WR = Hp / Ht) of the value in register Hp and the value in register Ht. When the pulse width ratio WR is a value equal to or greater than the threshold th (that is, when a voltage drop of a predetermined level or more occurs when the heater is on), it proceeds to step S106 described later. Otherwise, it proceeds to step S107 described later. The value of the threshold th can be set to any value greater than 1. Here, it will be described assuming that the threshold th = 1.1. That is, here, when the pulse width ratio WR is 1.1 or more (when Hp is 10% or more greater than Ht), the CPU 301 determines that a voltage drop (drop in the power supply voltage) of a predetermined level or more has occurred when the heater is on. Note that for the threshold th, it is preferable to design and set a suitable value in advance through experiments or the like.

[0054] In step S105, when the pulse width ratio WR is equal to or greater than the threshold th, the CPU 301 shifts the mode of the heater control method to the peak power control mode (S106) and operates from step S107 described later. When the CPU 301 shifts to the peak power control mode, it suppresses the maximum power consumption (load) of the printer 1 by performing exclusive control of the heater. When the CPU 301 shifts to the peak power control mode, the time for heaters 211 and 212 to reach a certain temperature will increase, but it is possible to suppress a voltage drop in the commercial power supply 400 due to an increase in the consumption current and the tripping of the safety breaker due to overuse of the current.

[0055] Thereafter, the CPU 301 performs printing processing on the paper M according to the print data while controlling the heaters 211 and 212 according to the latest set heater control method (normal control mode or peak power control mode) (S107, S108).

[0056] When the printing process is completed, the CPU 301 ends the control of the heaters 211 and 212 (S109) and ends the process and shifts to the standby state (S110).

[0057] (A-3) Effects of the Embodiment According to this embodiment, the following effects can be achieved.

[0058] In the printer control unit 300 (CPU 301) of this embodiment, the presence or absence of a voltage drop in the power supply is estimated from the change amount (pulse width ratio WR) between the zero-cross pulse width Ht when the heater is off and the zero-cross pulse width Hp when the heater is on. If a voltage drop is estimated, the voltage drop is suppressed by exclusive control of a plurality of heaters. As a result, in the printer 1 of this embodiment, problems such as fixing defects caused by low temperatures of the fixing heaters 211 and 212 can be suppressed, and good printing (image formation) can be realized.

[0059] Also, in the printer control unit 300 (CPU 301) of this embodiment, the presence or absence of a voltage drop in the power supply voltage is estimated based on the pulse width ratio WR. Therefore, regardless of changes in the frequency of the commercial power supply 400 (for example, 50 Hz, 60 Hz, etc.), the presence or absence of a voltage drop in the power supply voltage can be accurately estimated.

[0060] (B) Other Embodiments The present invention is not limited to the above-described embodiments, and modified embodiments as exemplified below can also be cited.

[0061] (B-1) In the above embodiment, an example of applying the image forming apparatus of the present invention to a color printer has been shown. However, the image forming apparatus of the present invention is not limited to a color printer and can be applied to all apparatuses that perform image formation by an electrophotographic method. For example, the image forming apparatus of the present invention may be applied to other image forming apparatuses such as a copying machine, an MFP (Multi Function Peripheral), and a facsimile apparatus.

[0062] (B-2) In the above embodiment, when the change amount of the zero-cross pulse width between when the heater is off and when the heater is on is equal to or greater than a predetermined value, the printer control unit 300 (CPU 301) changes the control method of the heater such as exclusive control. However, without performing exclusive control or the like, a coefficient for predicting the temperature reached by the heaters 211 and 212 (hereinafter referred to as "prediction parameter") or the printing speed (the speed at which the paper M is conveyed) may be changed (corrected). For example, due to a drop in the power supply voltage, the time required to heat the heaters 211 and 212 to the set temperature increases. However, the printer control unit 300 (CPU 301) may change to a prediction parameter corrected in consideration thereof (for example, a prediction parameter assuming that the heating time of the heaters 211 and 212 is extended by the amount of voltage drop) to control the heaters 211 and 212. Further, for example, due to a drop in the power supply voltage, the printing speed may be decreased by the amount by which the time required to heat the heaters 211 and 212 to the set temperature increases, so as to shift the time when the paper M reaches the fixing unit 20 and control so that the heating of the heaters 211 and 212 is in time.

[0063] (B-3) In the above embodiment, the ratio of the zero-cross pulse width Ht when the heater is off, the zero-cross pulse width Hp when the heater is on (pulse width ratio WR) is used to detect a drop in the power supply voltage. However, the drop in the power supply voltage may be detected by comparing the difference between Ht and Hp with a predetermined threshold value.

[0064] (B-4) In the above embodiment, the printer control unit 300 (CPU 301) controls the heaters 211 and 212 (the timing of turning on / off) based on the zero-cross pulse width of the power supply voltage. However, even for a circuit that generates a pulse based on a half-wave of the power supply voltage and detects a failure of the AC generation circuit, since the pulse width changes depending on the on / off of the heater, it can be used.

[0065] Further, instead of performing comparison based on the zero-cross pulse width, comparison may be performed based on a width that is not a zero-cross (for example, the time from the fall of a pulse including the Peak portion to the rise of the next pulse).

Explanation of Reference Numerals

[0066] 1... Printer, 2... Image forming unit, 2, 2-1 to 2-4... Image forming units, 3, 3-1 to 3-4... LED heads, 4, 4-1 to 4-4... Image forming units, 6, 6-1 to 6-4... Developing rollers, 10, 10-1 to 10-4... Transfer rollers, 11... Paper feed roller, 12... Paper feed sensor, 14... Conveyor roller, 15... Conveyor roller, 16... Writing sensor, 17... Conveyor belt driven roller, 18... Belt drive roller, 19... Transfer belt, 20... Fuser, 21... Fuser roller, 22... Fuser backup roller, 24... Discharge sensor, 25... Paper tray, 26... Discharge roller, 27... Discharge roller, 28... Stacker, 100... Power supply unit, 101... Bridge diode, 102... Comparator, 103... Current limiting section, 104... Optocoupler, 105... Triac, 106... Triac, 120... Power connector, 210... Heating section, 211... Heater, 212... Heater, 212a... Heater section, 212b... Heater section, 212c... Lead wire, 213... Thermistor, 214... Thermistor, 300... Printer control unit, 301... CPU, 302... Memory, 400... Commercial power supply, 500... Power cable

Claims

1. Image forming means for performing an image forming process of developing a developer image and transferring the developer image onto a medium; A device for heating the medium onto which the developer image has been transferred, the device including a plurality of heaters that operate with electric power supplied from an AC power source; A pulse generation unit that generates pulses based on changes in the AC voltage supplied from the AC power source; Control means for controlling the timing of turning on and off each of the heaters based on the pulses; The control means obtains the pulse width of the pulses in a first state in which all the heaters are off as a first pulse width, obtains the pulse width of the pulses in a second state in which all the heaters are on as a second pulse width, performs a comparison process of comparing the first pulse width and the second pulse width, and performs a heater control method determination process for determining a heater control method for controlling the heaters according to the result of the comparison process An image forming apparatus characterized by the above.

2. The image forming apparatus according to claim 1, wherein the control means performs the heater control method determination process before the image forming means starts the image forming process.

3. The image forming apparatus according to claim 1, wherein the control means corresponds to either a first heater control method of turning on all the heaters simultaneously or a second heater control method of limiting the number of heaters to be turned on simultaneously.

4. The image forming apparatus according to claim 3, wherein the control means applies the second heater control method when the amount of change between the first pulse width and the second pulse width is equal to or greater than a threshold value, and applies the first heater control method otherwise.

5. The image forming apparatus according to claim 4, wherein the amount of change is the ratio between the first pulse width and the second pulse width.

6. The image forming apparatus according to claim 4, wherein the amount of change is the difference between the first pulse width and the second pulse width.

Images