JP6991715B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine or a printer, which is provided with a fixing device for fixing an unfixed toner image.

With the recent increase in speed of image forming apparatus, the power consumed by the image forming apparatus is increasing. In particular, a high-speed color laser printer that needs to form images of a plurality of toner images at the same time consumes a large amount of current in a driving device such as a motor. Image forming devices are designed to supply the fuser with the power required for fixing under standard AC power supply voltage, ambient temperature, load, etc., but image forming devices with high power consumption are AC. It is becoming a design with a small margin for the maximum current that can be supplied by power. Therefore, factors such as a low input voltage of the AC power supply, a low room temperature, and a large load power consumption due to aging may overlap, and a state may occur in which the power required for the fixing process cannot be supplied to the fuser.

Therefore, environmental conditions such as room temperature, the temperature state of the fuser, and the load state of the printer are detected, and based on these detection results, whether or not the current required for printer operation exceeds the maximum current that can be supplied by the AC power supply. There is a proposal to predict (see, for example, Patent Document 1). When it is determined that the amount is exceeded, the throughput, which is the number of sheets to be printed per unit time, is reduced by widening the transport interval of the recording paper at the initial stage of printing. As a result, the current required for the operation of the printer is suppressed to the maximum current that can be supplied or less, and the situation in which the power required for ensuring good fixability cannot be supplied to the fuser is avoided.

Japanese Patent Application Laid-Open No. 2015-099180

A printing method that suppresses power consumption by widening the transport interval and keeps the required current below the maximum current is, for example, when the fuser warms up during continuous continuous printing and the required power of the fuser decreases. , It is easy to recover the throughput by narrowing the transport interval. However, in order to significantly reduce the electric power required for the fixing process, it is necessary to greatly widen the transport interval at the initial stage of printing. As a result, when the print job is about one or two sheets, the time required to complete the designated print job may become long.

The present invention has been made under such circumstances, and an object of the present invention is to provide an image forming apparatus having high productivity while suppressing the current required for printer operation to a maximum current that can be supplied.

In order to solve the above-mentioned problems, the present invention includes the following configurations.

(1) An image forming means for forming an unfixed toner image on a recording material, and a fixing means having a heater and fixing the unfixed toner image formed by the image forming means on the recording material by the heat of the heater. And the supplyable power acquisition means for acquiring the supplyable power that can be supplied to the heater, and the necessary power acquisition for acquiring the required power that is assumed to be required for the heater in order to fix the unfixed toner image on the recording material. Means, and based on the difference obtained by subtracting the required power from the available power, printing is started in the first mode, or a toner image that is less fixed than the first mode is printed on the heater. In an image forming apparatus that selects whether to start printing in a second mode that reduces the power supplied to the heater during the fixing process of fixing to the recording material by heat, the device is used before performing the fixing process. The first control for extending the period for heating the fixing means by generating heat of the heater, and the space between the papers between the rear end of the recording material previously conveyed and the tip of the recording material subsequently conveyed. It is possible to execute a second control for expanding the image and a third control for slowing down the image formation speed as compared with the case of the first mode, and the apparatus is the case where the second mode is selected. If the difference is smaller than the first threshold, the first control is selected, and if the difference is larger than the first threshold and smaller than the second threshold larger than the first threshold, the first control is selected. The image forming apparatus is characterized in that a combination of the control and the second control is selected, and when the difference is larger than the second threshold value, the third control is selected .

According to the present invention, it is possible to provide an image forming apparatus having high productivity while suppressing the current required for the operation of the printer to the maximum current that can be supplied or less.

Cross-sectional view of the image forming apparatus of Examples 1 and 2. Cross-sectional view of the fuser of Examples 1 and 2 The figure explaining the circuit applied to Examples 1 and 2. A block diagram showing a system configuration of the image forming apparatus of Examples 1 and 2. Flow chart showing the determination process of power supply availability in Examples 1 and 2. The figure explaining the range at the time of determining the printing rate of Example 1. A flowchart showing the selection process of the power saving mode of the first embodiment. A flowchart showing a process of determining whether or not to change the throughput after the start of printing in the first embodiment. The figure which shows the judgment process of the necessity change of the throughput after the start of printing of Example 1. A flowchart showing a change determination process of the printing speed after the start of printing in the first embodiment. The figure explaining the printing time required for each power saving mode of Example 2. A flowchart showing the selection process of the power saving mode of the second embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings by way of examples. The following examples are merely examples, and the present invention is not limited to these configurations.

[Image forming device]
FIG. 1 is a cross-sectional view of a tandem color image forming apparatus using an electrophotographic process. The configuration of the image forming apparatus 90 and the image forming operation will be described with reference to FIG. The tandem color image forming apparatus is configured to be able to output a full-color image by superimposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, the symbols Y, M, C, and K at the end of the code representing the color will be omitted unless necessary.

A laser scanner 11 and a cartridge 12 are provided for image formation of each color. The cartridge 12 includes a photosensitive drum 13 which is a photoconductor that rotates in the direction of the arrow in the figure, and a developer having a drum cleaner 14, a charging roller 15, and a developing roller 16 provided in contact with the photosensitive drum 13. Has been done. Further, an intermediate transfer belt 19 is in contact with the photosensitive drum 13 of each color, and a primary transfer roller 18 is installed so as to face the photosensitive drum 13 with the intermediate transfer belt 19 interposed therebetween.

On the downstream side (hereinafter referred to as the downstream side in the transport direction) of the cassette 22 for storing the paper 21 as a recording material in the transport direction, the paper feed roller 25, the separation rollers 26a and 26b, and the registration roller (hereinafter referred to as the registration roller) are located. A resist roller) 27 is provided. A transport sensor 28 is provided in the vicinity of the resist roller 27 on the downstream side in the transport direction. Further, a secondary transfer roller 29 is provided on the downstream side of the transport path in the transport direction so as to be in contact with the intermediate transfer belt 19, and a fixing device 30 as a fixing means is arranged on the downstream side of the secondary transfer roller 29 in the transport direction. It is set up. Further, the engine control unit 302 is a control unit of the laser printer. The engine control unit 302 includes a CPU (central processing unit) 32 equipped with a ROM 32a, a RAM 32b, a timer 32c, and the like, and various input / output control circuits (not shown). A member that forms an unfixed toner image on the paper 21 (on the recording material) functions as an image forming means.

Next, the electrophotographic process will be briefly described. The surface of the photosensitive drum 13 is uniformly charged by the charging roller 15 in a dark place in the cartridge 12. Next, the surface of the photosensitive drum 13 is irradiated with a laser beam modulated according to the image data (image information) by the laser scanner 11. As a result, the charged charge of the portion of the photosensitive drum 13 irradiated with the laser beam is removed, so that an electrostatic latent image is formed on the surface of the photosensitive drum 13. In the developing device, toner adheres to the electrostatic latent image on the photosensitive drum 13 due to the developing voltage from the developing roller 16 holding a certain amount of toner layer. As a result, toner images of each color are formed on the surface of each photosensitive drum 13.

The toner image formed on the surface of the photosensitive drum 13 is transferred to the intermediate transfer belt 19 by the transfer voltage applied to the primary transfer roller 18 at the nip portion between the photosensitive drum 13 and the intermediate transfer belt 19. Further, the CPU 32 controls the timing of image formation in each cartridge 12 by the timing according to the transfer speed of the intermediate transfer belt 19. The CPU 32 sequentially transfers the toner images of each color formed on each photosensitive drum 13 onto the intermediate transfer belt 19. As a result, a full-color image is finally formed on the intermediate transfer belt 19.

On the other hand, the paper 21 in the cassette 22 is conveyed by the paper feed roller 25, only one sheet of paper 21 is separated by the separation rollers 26a and 26b, and the separated paper 21 passes through the resist roller 27 and the secondary transfer roller 29. Will be transported to. After that, the toner image on the intermediate transfer belt 19 is transferred to the paper 21 at the nip portion between the secondary transfer roller 29 and the intermediate transfer belt 19 on the downstream side in the transport direction of the resist roller 27. The paper 21 on which the unfixed toner image is transferred is conveyed to the fixing device 30, and the toner image on the paper 21 is fixed by the fixing device 30. The paper 21 that has been subjected to the fixing process is discharged to the outside of the image forming apparatus 90. The image forming apparatus 90 includes a temperature sensor 40 for measuring the temperature inside the apparatus, and the CPU 32 can set the image forming according to the temperature measured by the temperature sensor 40. The image forming apparatus 90 includes, as an optional device, a paper feeding unit 91 for increasing the amount of paper that can be fed, an ejection unit 92 for increasing the amount of paper that can be ejected, and an image scanner (image reader) that reads an image of a document. ) 93 is connected. The combination of options connected to the image forming apparatus 90 is not limited to the configuration shown in FIG.

[Fuser]
The configuration of the fuser 30 will be described with reference to FIG. FIG. 2 is a cross-sectional view of the fuser 30. The fuser 30 is a film heating type heating device using, for example, an endless film (cylindrical film), which drives a pressure roller to drive and rotate the film. The fuser 30 includes a heater 100, a heater holder 101, a heat-resistant film (hereinafter referred to as a fixing film) 102, a pressure roller 103, a protective element 104, and a thermistor 54 (see FIG. 3). The heater 100 is a ceramic heater in which a heating element 111 is printed on a ceramic substrate. The heater holder 101 holds the heater 100 so that the heating element 111 of the heater 100 is in contact with the printed surface. The material is PPS (Polyphenylene sulfide) and has excellent heat resistance and rigidity. The fixing film 102 is loosely fitted to the heater holder 101 to which the heater 100 is attached. The pressure roller 103 sandwiches the fixing film 102 and presses against the heater 100 to form a fixing nip portion N. The protective element 104 of this example is a thermo switch, and the heat-sensitive surface of the thermo switch comes into contact with the surface of the heater 100. The thermistor 54, which is a temperature detection element, is arranged side by side on the same straight line as the protection element 104 in the longitudinal direction of the heater 100 (the direction orthogonal to the paper surface of FIG. 2).

The pressure roller 103 is driven in the direction of the arrow by a motor (not shown). When the pressure roller 103 rotates, the fixing film 102 is driven by frictional force and rotates. The fixing film 102 rotates the outer loop of the heater holder 101 in the clockwise direction indicated by the arrow while the inner surface thereof slides in close contact with the heater 100.

The heater 100 is controlled to maintain a predetermined temperature during the fixing process. In a state where the heater 100 is controlled to a predetermined temperature, the paper 21 carrying the unfixed toner image T is conveyed to the fixing nip portion N. In the fixing nip portion N, the unfixed toner image T on the paper 21 is heated and pressurized to melt, and the toner image T is fixed on the paper 21.

The fuser 30 having a structure as shown in FIG. 2 has a feature that the heat capacity of the fixing film 102 is small and the temperature can be raised to a predetermined temperature in a short time. On the other hand, the structures other than the fixing film 102 have a larger heat capacity than the fixing film 102. Therefore, even if power is started to be supplied to the heater 100 at the same time as the printing instruction, when the first sheet (first) paper 21 in the printing job reaches the fixing nip portion N, the structures other than the fixing film 102 are present. Not warm enough. Therefore, the electric power required for the initial fuser 30 at which image formation is started is large because the electric power required for heating the structure inside the fuser 30 is also large, and is required as the fuser 30 gradually warms up. The power will be low. The fuser of this example does not supply any electric power to the heater 100 during standby waiting for a print instruction.

[Circuit configuration]
Subsequently, the main circuit configuration according to the first embodiment will be described with reference to the circuit diagram of FIG. The image forming apparatus 90 is connected to a commercial AC power source 50. The AC power supply 50 is connected to a switching power supply (hereinafter referred to as a power supply) 64 and a heater 100 of the fuser 30 via an AC filter 51. The CPU 32 is a control means for executing each control of the image forming apparatus 90 including the drive control of the heater 100, and is composed of each input / output port, a ROM 32a, a RAM 32b, and the like. Further, the AC power supply 50 is connected to a generation circuit 52 that generates a zero-cross signal via an AC filter 51. The generation circuit 52 is configured such that the zero cross signal, which is an output signal, is inverted when the voltage of the AC power supply 50 is less than or higher than the threshold voltage in the vicinity of 0V. The zero cross signal is used to control the drive timing of the heater 100. The output signal of the generation circuit 52 is input to the PA1 port of the CPU 32. The heater 100 is driven with reference to zero cross timing by a drive circuit 70 of the heater 100 configured around a bidirectional thyristor (hereinafter referred to as a triac) 71 and a triac coupler 72. The drive circuit 70 controls the electric power supplied to the heater 100.

The heater 100 generates heat when electric power is supplied. The temperature of the heater 100 is detected by a thermistor 54, which is a temperature detection element arranged on the back surface of the heater 100. The voltage divided by the thermistor 54 and the fixed resistor 55 is input to the analog input port AN0 (hereinafter referred to as AN0 port) of the CPU 32. The thermistor 54 has a characteristic that the resistance value decreases when the temperature becomes high, and the CPU 32 monitors the voltage input to the AN0 port and refers to a preset voltage-temperature conversion table to the heater 100. Detects the current temperature of. The CPU 32 outputs a Drive signal for driving the drive circuit 70 from the PA2 port to the drive circuit 70 based on the difference between the temperature detected by the voltage-temperature conversion table and the control target temperature. On the other hand, the power supply 64 has a diode bridge 61 for rectifying an AC voltage, a smoothing capacitor 62, and a DC-DC converter 63 which is a power supply unit for generating a DC voltage in the subsequent stage. The DC voltage generated by the power supply 64 is supplied to a load 65 on the secondary side such as a control unit and a drive unit of the image forming apparatus 90.

The line on the downstream side of the AC filter 51 is connected to the voltage detection circuit 66, which is the first detection means for detecting the AC voltage. The voltage detection circuit 66 outputs a voltage value corresponding to the effective value voltage of the AC power supply 50 to an output line isolated from the primary side by using, for example, a transformer. The voltage value from the voltage detection circuit 66 is input to the analog input port AN1 (hereinafter referred to as AN1 port). The CPU 32 detects the effective value voltage of the AC power supply 50 based on the input voltage value. The current detection circuit 67, which is the second detection means for detecting the alternating current, is provided on the side of the alternating current power supply 50 with respect to the branch portion to the power supply 64 and the drive circuit 70. The current detection circuit 67 outputs a voltage value corresponding to the effective value of the alternating current flowing through the output line isolated from the primary side by using a transformer. The voltage value from the current detection circuit 67 is input to the analog input port AN2 (hereinafter referred to as AN2 port). Based on the input voltage value, the CPU 32 can detect the total current value consumed by the power supply 64 as a load and the heater 100 of the fuser 30.

On the other hand, the current detection circuit 68, which is the third detection means, is arranged at a position where the current value flowing through the heater 100 without flowing through the power supply 64 can be detected. The current detection circuit 68 outputs a voltage value corresponding to the detected current value to the CPU 32. The voltage value from the current detection circuit 68 is input to the analog input port AN3 (hereinafter referred to as AN3 port). The CPU 32 detects the current flowing through the heater 100 based on the input voltage value. Further, the CPU 32 detects the electric power consumed by the heater 100 based on the detection result of the voltage detection circuit 66 and the detection result of the current detection circuit 68.

[Printer system configuration]
Next, the system configuration and interface of the printer will be described. FIG. 4 is a block diagram showing a system configuration around the printer shown in FIG. The operation of the engine control unit 302 is realized based on a program written in advance in the ROM 32a inside the CPU 32.

The engine control unit 302 includes a paper type detection unit 303 that detects information about the paper type of the paper 21, a paper type acquisition unit 304 that acquires information about the paper type of the paper 21 preset by a user or the like, and an image forming apparatus 90. Information is received from the temperature sensor 40 that detects the temperature of the paper. Further, the engine control unit 302 controls the power supply 64 and the drive circuit 70. Further, the engine control unit 302 includes a power measurement unit 308 that measures power consumption, a supplyable power calculation unit (supplyable power acquisition means) 309 that calculates the maximum power that can be supplied to the heater 100, and an image forming operation (image). It has a speed control unit 310 that controls the image formation speed (printing speed) of the formation process). Further, the engine control unit 302 includes a transport unit 311 that transports the paper 21, an execution unit 312 that is a member such as a photosensitive drum 13 that executes an image forming operation from the charging process to the transfer process, and a fixing device 30. To control. Further, the engine control unit 302 includes a temperature control unit 314 that controls the temperature of the heater 100, and a warm air state calculation unit 315 that calculates the degree of warmth (warm air state) of the fuser 30. Further, the engine control unit 302 is an average of the print rate acquisition unit 316 that acquires the print rate of the toner image printed on one side of the paper 21 based on the image information and the print rate acquisition unit 316. It has a print rate averaging unit 317, which is an averaging means for obtaining a print rate. Further, the engine control unit 302 has a number acquisition unit 318 for specifying the paper 21 having a printing rate higher than a predetermined printing rate from among the plurality of papers 21. Further, the engine control unit 302 has a required power calculation unit (required power acquisition means) 319 for calculating the power assumed to be required for the heater 100, and a power averaging unit 320 for obtaining the average power consumption. The controller unit 301 can communicate with the host computer 300 and the engine control unit 302. In the following description, the high print rate means a print rate higher than the predetermined print rate, and the low print rate means the print rate equal to or lower than the predetermined print rate.

[Print mode selection process]
Subsequently, the specific control of the first embodiment will be described with reference to the flowcharts of FIGS. 5, 7, and 8. The control process shown in the flowchart is executed by the CPU 32 of the engine control unit 302 according to the program stored in the ROM 32a in advance. The control of the first embodiment can be roughly divided into the following three.
(1) Judgment processing of whether power can be supplied to the heater (hereinafter referred to as power supply availability) (2) Power saving mode selection process (3) Whether it is necessary to change the throughput after the start of printing (hereinafter referred to as change) Each process will be described in detail after the determination process (referred to as necessity).

(1) Power supply availability determination process When a print job is transmitted, the CPU 32 calculates the power that can be supplied to the heater 100 of the fuser 30 by the supplyable power calculation unit 309, and prints by the required power calculation unit 319. Calculate the expected power required for the heater 100 at the beginning of the job. The CPU 32 compares the calculated electric power that can be supplied to the heater 100 with the electric power required by the heater 100. The CPU 32 determines whether or not it is possible to supply electric power to the heater 100 based on the comparison result. Then, the CPU 32 determines whether to execute normal image formation or to execute image formation in a power saving mode that reduces power consumption. The process of determining whether or not power can be supplied will be described with reference to the flowchart of FIG.

In step 101 (hereinafter referred to as S), the CPU 32 uses the power Ppusu, which is the power load power consumed by the load 65 on the secondary side, in order to calculate the power Limit that can be supplied to the heater 100 by the supplyable power calculation unit 309. Is calculated by the following equation (1).
Ppus = Pe + Pfeed + Pdeliv + Pis ... (1)
Here, the electric power Pe is the load power of the image forming apparatus 90 excluding the electric power consumed by the heater 100, and the electric power obtained from the results detected by the voltage detection circuit 66 and the current detection circuit 67 is used. The timing at which the electric power Pe is acquired is preferably the timing at which the electric power is not applied to the heater 100. For example, it is acquired at the timing after the power input to the heater 100 is completed at the end of the previous image formation. The electric power Pe acquired and calculated at such a timing is stored in, for example, the RAM 32b, and is used when calculating the electric power Ppus at the time of the next print job. The power Pfeed is the power consumed by the paper feed unit 91, the power Pdeliv is the power consumed by the discharge unit 92, and the power Pis is the power consumed by the image scanner 93.

The power Pfed uniformly adds Pfed = 60W when the paper feed unit 91 is mounted on the printer and the paper feed from the paper feed unit 91 is specified in the print job. Further, the electric power Pdeliv uniformly adds Pdeliv = 80W when the discharge unit 92 is mounted on the printer and the discharge to the discharge unit 92 is specified in the print job. The power values of the optional paper feed unit 91 and discharge unit 92 are obtained by examining the required power of each unit at the design stage, and are values stored in the ROM 32a in advance as fixed values. As another means, it is also possible to measure the electric power at the time of operation by operating each of them individually at a timing other than the image forming operation.

Further, the electric power Pis is the electric power consumed by the image scanner 93. The image scanner 93 has a function of attaching scanned data to an e-mail and sending it by fax, in addition to a copy function of printing a scanned (scanned) image, and the like, regardless of the print job. It is necessary to assume that it will be operated by. Therefore, when the image scanner 93 is attached to the printer, Pis = 80W is uniformly added. As in the case of the paper feed unit 91 and the discharge unit 92, the power Pis is not a fixed value, but a method of operating the power Pis individually and actually measuring the power during operation is also possible.

In S102, the CPU 32 calculates the power limit that can be supplied to the heater 100 by the supplyable power calculation unit 309 using the following equation (2).
Plimit = Illimit x Vin x Kpf-Ppusu ... (2)
Here, the voltage Vin is an input voltage value detected by the voltage detection circuit 66. Kpf is the power factor assumed for the entire device. For example, in Example 1, the power factor is a fixed value of 90 (%). This is generally determined by the current waveform of the power supply 64 and the current waveform supplied to the heater 100 by the phase control of the drive circuit 70, and is the worst value obtained at the time of design. Current Ilimit is an effective current value that must be limited to the source. For example, in a product for regions of 100V to 127V, 12Arms as a current Illimit is stored in ROM 32a in advance as an initial setting value. In the products for regions of 220V to 240V, 6Arms as the current Illimit is stored in the ROM 32a in advance as the initial setting value. Further, the current Illimit can be set by the user using an operation unit (not shown) included in the image forming apparatus 90. For example, it is possible to appropriately cope with a user who supports a 20A breaker and a user who has to limit the current to a low current due to individual circumstances. The CPU 32 calculates the power limit that can be supplied to the heater 100 by using the above-mentioned parameters and the like stored in the ROM 32a.

Subsequently, the CPU 32 calculates the power Pfsr assumed to be required for the heater 100 by the required power calculation unit 319. The power Pfsr is calculated based on the following three parameters and the information in the table of Table 1. Table 1 is a table containing information for determining the power Pfsr assumed to be required for the heater 100.
-Current environmental temperature Detected by the temperature sensor 40.
-Warm air level of the fuser 30 It is determined by the warm air state calculation unit 315 that calculates the degree of heat storage of the fuser 30.
-Average print rate information at the initial stage of printing The information is acquired by the print rate acquisition unit 316, and the average print rate is obtained by the print rate average unit 317.

The required power calculation unit 319 includes the temperature inside the device detected by the temperature sensor 40, the degree of heat storage of the fuser 30 calculated by the warm air state calculation unit 315, and the print rate acquired by the print rate acquisition unit 316. , The required power Pfsr is obtained. Here, the print rate of each of the predetermined number of sheets of paper 21 acquired by the print rate acquisition unit 316 is further obtained as an average print rate by the print rate average unit 317, and the power Pfsr is obtained based on the average print rate. Is required.

表１の値は、定着器３０の性能のばらつきを考慮して検討により得られた設計値であり、予めＣＰＵ３２のＲＯＭ３２ａに格納されるテーブルとなる。表１では、平均印字率情報、環境温度レベル及び暖気レベルＤｘに応じて、ヒータ１００に必要と想定される電力（Ｗ）が決定される。３つのパラメータの算出方法に関して次に説明する。なお、３つのパラメータはそれぞれ並行して算出されるものとし、図５に示すようにＳ１０２に続く処理を分岐させた流れとして記載する。

The values in Table 1 are design values obtained by consideration in consideration of variations in the performance of the fuser 30, and are tables stored in the ROM 32a of the CPU 32 in advance. In Table 1, the electric power (W) assumed to be required for the heater 100 is determined according to the average print rate information, the ambient temperature level, and the warm air level Dx. The calculation method of the three parameters will be described below. It is assumed that each of the three parameters is calculated in parallel, and as shown in FIG. 5, the process following S102 is described as a branched flow.

(Environmental temperature level)
The environmental temperature level (11 ° C to 15 ° C, etc.) on the horizontal axis of Table 1 is the temperature of the outside air. The temperature sensor 40 is arranged at a position in the image forming apparatus 90 so as to be able to detect a temperature substantially equal to the temperature of the outside air. In S103, the CPU 32 detects the temperature detected by the temperature sensor 40 as the ambient temperature level.

(Warm air level Dx)
The warm air level Dx of the fuser 30 on the vertical axis of Table 1 is detected by the warm air state calculation unit 315 by the predicted temperature (hereinafter referred to as the predicted temperature) D of the pressurizing roller 103 and the thermistor 54 at the start of printing. It is calculated from the temperature of the heater. First, the predicted temperature D of the pressurizing roller 103 is calculated by the following equation (3).
D = D0 + Preparation for image formation Number of rotations during operation x Δm-Number of continuously printed sheets x Δtp
-Print stop time x Δtw ... (3)
Here, D0 is the initial temperature of the pressure roller 103, and when the printing operation is started from the state where the pressure roller 103 is cold, the initial temperature of the pressure roller 103 is substantially room temperature. When the printing operation is started in a warm state of the pressure roller 103, the predicted temperature D of the pressure roller 103 calculated at the time when the printing operation is started is used. Δm is a temperature (hereinafter referred to as an increase temperature) in which the pressure roller 103 rises each time the pressure roller 103 rotates during the preparation operation for image formation. Δtp is a temperature at which the paper 21 is deprived of each time the pressure roller 103 prints one sheet. Δtw is the temperature at which the pressurizing roller 103 when printing is stopped is cooled per unit time (hereinafter referred to as the cooling temperature).

In S104, the CPU 32 calculates the predicted temperature D of the pressurizing roller 103 from the equation (3). The predicted temperature D of the pressurizing roller 103 is based on the number of times the pressurizing roller 103 rotates during the preparatory operation for image formation, the number of sheets of paper 21 printed continuously, and the time during which printing is stopped. Is calculated.

In the first embodiment, the temperature rise Δm of the pressure roller 103 for each rotation of the pressure roller 103 during the preparatory operation for image formation is, for example, 40 ° C. Further, the temperature Δtp at which the pressure roller 103 is deprived of the paper 21 each time one sheet is printed is set to, for example, 5 ° C. Further, the cooling temperature Δtw per unit time when printing is stopped is, for example, 1 ° C. Δm, Δtp, and Δtw are fixed values, respectively. For example, when the image forming apparatus 90 of the first embodiment described with reference to FIG. 1 repeats continuous printing of three sheets three times every 5 seconds at an initial temperature of 25 ° C., the predicted temperature of the pressurizing roller 103 after printing is completed. D uses equation (3) to
25 ° C + 3 times x 40 ° C- (3 sheets x 3 times) x 5 ° C- (5 seconds x 2 times) x 1 ° C = 90 ° C
Is calculated.
Δm, Δtp, and Δtw are not limited to fixed values. For example, when more accuracy is required, it may be variable depending on the environmental temperature, thermistor temperature, warm-up state, the number of sheets continuously conveyed (hereinafter referred to as the number of sheets to be passed), and the like.

Subsequently, in S105, the CPU 32 detects the temperature of the heater 100 by the thermistor 54. In S106, the CPU 32 obtains the warm air level Dx of the fuser 30 with reference to Table 2 based on the predicted temperature D of the pressurizing roller 103 calculated in S104 and the temperature of the heater 100 detected in S105.

表２は定着器３０の暖気レベルＤｘを求めるためのテーブルであり、加圧ローラ１０３の予測温度Ｄとヒータ１００の温度とから暖気レベルＤｘが求められる。例えば、加圧ローラ１０３の予測温度Ｄが１００℃、ヒータ１００の温度が９０℃である場合、定着器３０の暖気レベルＤｘは２と求められる。

Table 2 is a table for obtaining the warm air level Dx of the fuser 30, and the warm air level Dx can be obtained from the predicted temperature D of the pressurizing roller 103 and the temperature of the heater 100. For example, when the predicted temperature D of the pressurizing roller 103 is 100 ° C. and the temperature of the heater 100 is 90 ° C., the warm air level Dx of the fuser 30 is determined to be 2.

The higher the predicted temperature D of the pressurizing roller 103, the larger the amount of heat stored in the pressurizing roller 103, and the smaller the electric power can be used for fixing. Similarly, the higher the temperature of the heater 100, the larger the amount of heat stored in the fixing film 102, and the less power can be used for fixing. Therefore, the warm air level Dx in Table 2 becomes a higher value (higher level) as the values of the temperature of the heater 100 and the predicted temperature D of the pressurizing roller 103 are higher.

(Average print rate information)
FIG. 6 is a diagram illustrating a printing rate of paper. A region having a predetermined width in the width direction about the virtual position ps on the paper 21 corresponding to the position where the thermistor 54 is arranged, and having a length from the front end to the rear end of the paper 21 in the transport direction. Let be the area R. The width direction is a direction orthogonal to the transport direction. The information on the printing rate on the horizontal axis of Table 1 is the printing rate of the toner image transferred to the area R of the paper 21. Specifically, it is information on the average print rate in one image portion shown in FIG. The average printing rate here is the total value of the density percentages of each color. For example, when the region R shown in FIG. 6 is an image having 100% magenta color and 100% cyan color (hereinafter referred to as a secondary color solid image), the average print rate is 200% (= 100% + 100). %)It turns out that. For example, when the secondary color solid image is in half of the area R, the average print rate is 100% (= 200% ÷ 2). The information on the average print rate in the area R in one sheet (hereinafter, also referred to as the average print rate information) is calculated by acquiring the print rate information by the print rate acquisition unit 316 and averaging the print rates by the print rate average unit 317. Will be done.

The temperature of the heater 100 of the fuser 30 is controlled based on the detection result of the thermistor 54. If the printing rate at the position of the thermistor 54 is high, the temperature tends to decrease at the position of the thermistor 54. Therefore, the CPU 32 controls the temperature of the heater 100 so as not to lower the temperature at the position of the thermistor 54 by applying a large amount of electric power. On the other hand, if the printing rate at the position of the thermistor 54 is low, the feedback control is performed so that the power input is reduced, which is the opposite of the control described above.

First, in S107, the CPU 32 uses the print rate acquisition unit 316 and the print rate averaging unit 317 to determine the average print rate of a predetermined number of sheets from the first sheet in the print job, for example, the initial three sheets (predetermined number of sheets) of the print job. Get information respectively. In S108, the CPU 32 sets the average print rate information for three sheets as a high print rate when the average print rate information is 70% or more and a low print rate when the average print rate information is less than 70%. It is determined whether or not there is printing with a high printing rate even on a sheet. The number of 3 sheets is an example and is not limited to 3 sheets. In Example 1, the number is set to 3 for the following reasons. As will be described later, readjustment may be performed such as shortening or lengthening the transport interval of the paper 21 depending on the determination result of the electric power after the start of printing. In this case, the paper 21 that has already been conveyed exists in the image forming apparatus 90, or the toner image is already formed on the photosensitive drum 13 so as to be transferred to the paper 21. It is not possible to change the transport interval between these already transported papers. For example, in the image forming apparatus 90 of the first embodiment, when readjustment is performed, the number of sheets of paper 21 whose transport interval cannot be changed is set to three. This number is not limited to three, but is a number determined by each image forming apparatus. Since the transfer interval switching control is actually executed after the three sheets of paper that have already been conveyed in the device are ejected, the transfer interval switching control is actually executed from the third image or later after the transfer interval switching is decided at the earliest. Will be.

If the CPU 32 determines in S108 that even one of the three sheets has a high printing rate, the process proceeds to S109. In S109, the CPU 32 sets the print rate mode to the high print rate mode as a parameter for obtaining the power Pfsr assumed to be required for the heater 100. If the CPU 32 determines in S108 that none of the three sheets has a high printing rate, the process proceeds to S110. In S110, the CPU 32 sets the print rate mode as the low print rate mode as a parameter for obtaining the power Pfsr assumed to be required for the heater 100.
As described above, the three parameters necessary for obtaining the electric power Pfsr assumed to be required for the heater 100, that is, the environmental temperature level, the warm air level Dx, and the print rate information are obtained.

In S111, the CPU 32 is assumed to be necessary for the heater 100 by the required power calculation unit 319 based on the three parameters of the environmental temperature level, the warm air level Dx, and the print rate mode (average print rate information) and the table in Table 1. The electric power Pfsr to be generated is obtained. For example, when the environmental temperature level is 18 ° C., the warm air level Dx is 2, and the print rate mode is the low print rate mode, the CPU 32 determines from Table 1 that the power Pfsr assumed to be required for the heater 100 is 750 W. In S112, the CPU 32 uses the power Primit that can be supplied to the heater 100 calculated in S102 and the power Pfsr that is assumed to be required for the heater 100 obtained in S111, and sets the difference in power (hereinafter referred to as differential power) ΔPini as follows. It is calculated by the formula (4) of.
ΔPini = Plimit-Pfsr ... (4)

In S113, the CPU 32 determines whether or not the differential power ΔPini calculated in S112 is 0 W or more. If the CPU 32 determines in S113 that the differential power ΔPini is 0 W or more, the process proceeds to S114. In S114, the CPU 32 executes printing in the normal mode (first mode). The normal mode is a print mode in which an operation for power reduction such as a power saving mode (second mode) described later is not performed. If the CPU 32 determines in S113 that the differential power ΔPini is less than 0 W, the process proceeds to S115. In S115, the CPU 32 executes printing in the power saving mode.

(2) Power saving mode selection process Next, when it is determined in the determination process of FIG. 5 that printing is to be executed in the power saving mode, which power saving is performed based on the differential power ΔPini calculated in S112 of FIG. Confirm whether to start printing in the mode. The image forming apparatus 90 in the first embodiment has first to third controls for reducing the electric power required for the heater 100. The first control is a control that delays the start of image formation of the first image (extends the heat generation period of the heater before the start of printing) and warms the entire fuser before executing the fixing process. In the first embodiment, the start of the first image formation is delayed by extending the time of the image formation preparation operation. By storing a large amount of heat in advance in the pressurizing roller 103 having a large heat capacity, there is an effect of reducing the electric power required during the period when the paper passes through the fixing nip portion N. However, there is a problem that the first printout time (hereinafter referred to as FPOT) until the ejection of the first sheet 21 is completed becomes long. Hereinafter, the first control is also referred to as FPOT extension control.

The second control is a control for widening the transport interval of the paper 21. Increasing the transport interval of the paper 21 means widening the spacing (hereinafter, referred to as paper spacing) between the rear end of the paper 21 previously transported and the front end of the subsequently transported paper 21. By fixing one sheet of paper 21, both the fixing film 102 and the pressure roller 103 are deprived of heat by the paper 21. By compensating for the amount of heat lost to the paper 21 by the period between the spread papers, the average electric power is reduced. A print job started by widening the space between papers can easily reduce the space between papers. Therefore, it becomes easy to cope with the change of the throughput during printing described later. On the other hand, the amount of power reduction is smaller than that in the case of reducing the printing speed to reduce the power as in the third control described later. Therefore, if an attempt is made to increase the amount of power reduction, it becomes necessary to provide a certain amount of large paper space in the initial stage of printing.

The third control is a control in which the image forming speed (that is, the printing speed) is made slower than the image forming speed in the normal mode (the rotation speed of the photosensitive drum, the transport roller, or the like is slowed down). By slowing down the printing speed, the power required per unit time during the fixing process is reduced. The control that slows down the printing speed is the most effective as the control that reduces the required power. On the other hand, if excess power is generated after printing is started and an attempt is made to return the throughput to the same state as in normal mode by returning the printing speed to the speed in normal mode, the image formation operation is temporarily stopped. Therefore, it is necessary to change the operating speed of the entire device. Therefore, when returning the throughput, there is a control problem that a time loss of several seconds occurs.

As described above, the first control to the third control have advantages and disadvantages, respectively, and which control is optimal depends on the state of the image forming apparatus 90 and the print job. In the first embodiment, in view of the characteristics of the three controls, the time for extending the heat generation period of the heater before the start of printing according to the table shown in Table 3 according to the differential power ΔPini (hereinafter referred to as the extension time (before the start of printing)). ) (S) and the extension time between the papers at the initial stage of printing (hereinafter referred to as extension time (paper spacing)) (s), and further, the speed of image formation (printing speed) is determined. The extension time (paper spacing) (s) is the time added to the paper spacing (s) in the normal mode.

例えば、図５のＳ１１２で算出された差分電力ΔＰｉｎｉが－５０Ｗだった場合、表３から、画像形成の準備動作の延長時間（印刷開始前）を３ｓ、延長時間（紙間）を０ｓ、印刷速度を通常速度、とする省電力モードで印刷が実行される。

For example, when the differential power ΔPini calculated in S112 of FIG. 5 is −50 W, from Table 3, the extension time (before the start of printing) of the image formation preparation operation is 3s, the extension time (between papers) is 0s, and printing is performed. Printing is executed in the power saving mode in which the speed is the normal speed.

(Power saving mode selection process)
The control when printing is executed in the power saving mode in S115 of FIG. 5 will be described with reference to the flowchart of FIG. As a result of the determination in S113 of FIG. 5, when printing in the power saving mode is selected in S115, the processing after S120 is executed. In S120, the CPU 32 determines whether or not the differential power ΔPini is −100 W or more. When the CPU 32 determines in S120 that the differential power Pini is -100 W or more, it determines that the FPOT is extended in S122, and then the normal printing operation (extension time (paper spacing) 0 s, printing speed is normal speed). ) Is executed. In S123, the CPU 32 determines the extension of the FPOT, that is, the extension time of the preparatory operation for image formation, based on the differential power Pini and Table 3, and starts printing in the power saving mode in S127.

If the CPU 32 determines in S120 that the differential power ΔPini is less than −100 W, the process proceeds to S121. In S121, the CPU 32 determines whether or not the differential power ΔPini is −200 W or more. When the CPU 32 determines in S121 that the differential power Pini is −200 W or more, the process proceeds to S124. In S124, the CPU 32 determines that the FPOT is extended and the paper spacing is extended, and printing is executed in the power saving mode. In S125, the CPU 32 determines the extension of the FPOT, that is, the extension time of the preparatory operation for image formation, based on the differential power ΔPini and Table 3. Further, the CPU 32 determines the paper-to-paper extension time at the start of printing based on the differential power Pini and Table 3, and starts printing in the power saving mode in S127.

When the CPU 32 determines in S121 that the differential power ΔPini is smaller than −200 W (that is, the power is significantly insufficient), the process proceeds to S126. In S126, as shown in Table 3, the CPU 32 executes an image forming operation at a low speed, which is a power saving mode with less power consumption. In this case, the CPU 32 sets the extension time of the image formation preparation operation to 0 seconds, the extension time between papers to 0 seconds, the printing speed to be slower than the normal speed by the speed control unit 310, and the power saving mode in S127. Start printing.

(3) Process for determining whether or not to change the throughput after the start of printing Next, the subsequent operation when printing is started in the power saving mode in which the space between papers is extended (S125 and S127 in FIG. 7) will be described. When printing is started with the inter-paper extension time (s) determined in the initial judgment based on the differential power ΔPini and Table 3, the control for continuously determining the next inter-paper extension time is performed even during printing. The control will be described with reference to the flowchart of FIG. When printing in the power saving mode for extending the space between papers is started, the process of S140 or less is executed. The variable N for counting the number of prints in S140 is set to 1. In S141, the CPU 32 determines whether or not the variable N of the number of printed sheets is less than 3. When the CPU 32 determines in S141 that the variable N of the number of printed sheets is less than 3, the process proceeds to the process of S142. In S142, the CPU 32 executes a printing operation, and the power actually consumed in the printing operation of the Nth sheet in S143 (hereinafter referred to as power consumption) is measured by the power measuring unit 308. The power measuring unit 308 actually prints the Nth sheet based on the input voltage of the AC power supply 50 detected by the voltage detection circuit 66 and the current flowing through the heater 100 detected by the current detection circuit 68. The electric power consumed by the heater 100 is measured. The CPU 32 stores the measured power consumption in, for example, the RAM 32b. The CPU 32 measures the actual power consumption consumed by the heater 100 in each printing operation while continuing the printing operation until the number of printed sheets N becomes three. In S141, three images are used as a criterion for determination, but as described above, this value is a value determined according to each image forming apparatus 90.

In S144, the CPU 32 determines whether or not printing is completed, and if it is determined that printing is completed, the process ends. For example, in the case of a print job that ends with one or two sheets, printing ends when printing of one or two sheets is completed. On the other hand, if the CPU 32 determines in S144 that printing has not been completed, it adds 1 to the variable N of the number of prints in S145 (N = N + 1), and returns to the process of S141. For example, when printing is continued for three or more sheets, the variable N of the number of printed sheets becomes 3, and in the determination of S141, the process of predicting the power assumed to be required for the heater 100 after S146 (S146 to S155). Transition.

When the CPU 32 determines in S141 that the number of printed sheets N is 3 or more, the process proceeds to S146. In S146, the CPU 32 calculates the average value of the actual power consumption of the past three heaters in order to perform the calculation for predicting the power expected to be required for the heater 100. Here, the power consumption of the Nth sheet measured in S143 is PN, the power consumption of the _N -1th sheet is _PN-1 , the power consumption of the N-2th sheet is _PN-2 , and the CPU 32 is a power source. The average value of the power consumption _PN , _PN-1 , and _PN-2 is calculated by the average unit 320. In S147, the CPU 32 uses the number acquisition unit 318 to determine the number of sheets having the highest printing rate among the three sheets based on the printing rate information of the past three sheets of the Nth sheet, the N-1st sheet, and the N-2 sheet. It is stored in RAM 32b as M. In S148, the CPU 32 acquires the average print rate information of the next (future) three sheets (N + 1st sheet, N + 2nd sheet, N + 3rd sheet) by the print rate acquisition unit 316 based on the image information. The average print rate information is described with reference to FIG.

In S149, the CPU 32 determines, by the number acquisition unit 318, whether or not even one sheet has a high print rate in the average print rate information of the N + 1st sheet, the N + 2nd sheet, and the N + 3rd sheet acquired in S148. do. If the CPU 32 determines in S149 that even one sheet has a high printing rate, the process proceeds to S150. In S150, the CPU 32 will set the printing mode for three sheets in the future as the high printing rate mode. Hereinafter, the electric power assumed to be required for the heater 100 in printing for three sheets in the future is referred to as the predicted required electric power _PNEXT . In S151, the CPU 32 obtains the predicted required power P _NEXT required in the high print rate mode by the following equation (5), and proceeds to S154 for processing.
P _NEXT = {(PN + P _{N -1} + P _N-2 ) + _PHL × (3-M)} / 3 ... (5)
Here, M is the number of sheets of paper having the highest printing rate among the above-mentioned three sheets in the past. Further, PHL is the power difference between the high print rate and the low print rate, and in Example 1, a fixed value obtained in advance by the study, for example, 80 _W is used. As described above, the CPU 32 determines the average value of the electric power for the predetermined number of sheets actually measured when the predetermined number of sheets of paper 21 in the past is fixed, the printing rate of the toner image for the predetermined number of sheets to be printed from now on, and the printing rate. Based on the above, the _PNEXT assumed to be required for the heater 100 is calculated from now on.

If the CPU 32 determines in S149 that there is no paper having a high printing rate, the process proceeds to S152. In S152, the CPU 32 sets the printing mode for three sheets in the future as the low printing rate mode. In S153, the CPU 32 obtains the predicted required power _PNEXT required in the low print rate mode by the following equation (6), and proceeds to S154 for processing.
P _NEXT = {(PN + P _{N -1} + P _N-2 ) -PH _-L x M} / 3 ... (6)
Here, M and _PHL are the same as those in the equation (5), and the description thereof will be omitted.

(Specific example of calculation of predicted required power _PNEXT )
A specific example of the calculation of the predicted required power _PNEXT will be described with reference to FIG. In FIG. 9, the time point of P is the present, and the N-2nd sheet represents the paper 21 three sheets before, the N-1st sheet represents the paper 21 two sheets before, and the Nth sheet represents the paper 21 one sheet before. There is. On each sheet 21, print rate information (average per sheet) (low print rate, high print rate, etc.) and power consumption measured by the power measuring unit 308 (average per sheet) are described. Further, in the N + 1th to N + 3rd sheets, the printing rate information of the three sheets to be printed in the future is described.

In the case of case A shown in FIG. 9A, high print rate information exists in the print rate information of three sheets in the future (N + 2nd sheet). Therefore, as the predicted required power P _NEXT in S151 of FIG. 8, the predicted required power P _NEXT in the high print rate mode is calculated using the equation (5). From the print rate information (M = 0) of the past three sheets and the measurement result of the power, the predicted required power _PNEXT required thereafter is calculated as follows.
P _NEXT = {(980 + 990 + 1000) +80 x (3-0)} / 3 = 1070 (W)

In the case B shown in FIG. 9B, there is no high print rate information among the three print rate information in the future. Therefore, as the predicted required power P _NEXT in S153 of FIG. 8, the predicted required power P _NEXT in the low print rate mode is calculated using the equation (6). From the print rate information (M = 2) of the past three sheets and the measurement result of the power, the predicted required power _PNEXT required thereafter is calculated as follows.
P _NEXT = {(960 + 1025 + 1040) -80 × 2} / 3 = 955 (W)

In the first embodiment, a configuration has been described in which the calculation formula of the predicted required power _PNEXT is used properly depending on whether or not the print rate information of the three sheets is high print rate in the future. However, the configuration may be such that the predicted required power _PNEXT is calculated based on the print rate information [%] of three sheets in the future. For example, it is required based on the past three print rate information IN, IN _{- 1} , _IN-2 and the power measurement result, and the future three print rate information _{IN + 1} , _{IN + 2} , _{IN + 3} . The predicted required power _PNEXT is calculated by the following equation (7).

P _NEXT = (PN + P _{N -1} + P _{N -2} ) / 3 + _PINK × {(IN + IN _-1 + _IN-2 )
-( _{IN + 1} + _{IN + 2} + _{IN + 3} )} / 3 ... (7)
Here, _PINK is the power difference when the print rate information changes by 1%.

Returning to the description of the flowchart of FIG. In S154, the CPU 32 calculates the differential power ΔPN _{+ 1} based on the power Limit that can be supplied to the heater 100 calculated in S102 of FIG. 5 and the predicted required power P _NEXT calculated in S151 or S153. The differential power ΔP _{N + 1} is obtained by the following equation (8).
ΔP _{N + 1} = Plimit-P _NEXT ... (8)

In S155, the CPU 32 determines the shortening or extension of the paper spacing (s) according to the value of the differential power ΔPN _{+ 1} . The table used for determining the shortening or extension between papers is the table shown in Table 4, and is stored in ROM 32a in the CPU 32 in advance.

例えば、Ｓ１５４で算出された差分電力ΔＰ_Ｎ＋１が、－１６０Ｗである場合、ＣＰＵ３２は、表４から紙間の延長を１．２５秒と決定する。

For example, when the differential power ΔPN _{+ 1} calculated in S154 is −160 W, the CPU 32 determines that the extension between papers is 1.25 seconds from Table 4.

[When printing starts at low speed]
In the above description, the subsequent operation when printing is started in the power saving mode in which the space between papers is extended has been described. Subsequently, the subsequent operation when printing is started in the low-speed power saving mode (S126, S127 in FIG. 7) will be described with reference to the flowchart of FIG. In FIG. 10, the same process as in FIG. 8 is assigned the same step number, and the description thereof will be omitted. The processing of S160 to S164 different from that of FIG. 8 will be described. The process of calculating the power is the same as in the power saving mode in which the space between papers is extended. In the low-speed power saving mode, when it is determined that the power is sufficient in the middle of printing, the driving of the image forming apparatus 90 is temporarily stopped between the papers of the print job, and the printing speed is faster than now again. Image formation will be restarted at. This takes some time, and frequent execution of this process results in reduced productivity. Therefore, when shifting from a low-speed power saving mode to a normal speed power saving mode or a normal mode, it is important to make a decision to switch to high-speed printing when it is judged that there is sufficient power. Become.

In S160, the CPU 32 assumes that the power required when the high print rate mode is set is required regardless of the subsequent three image information, and sets the print rate mode to the high print rate mode. The calculation of the predicted required power P _NEXT and the differential power ΔP _{N + 1} is the same as in S151 and S154. That is, the CPU 32 calculates the predicted required power _PNEXT by using the equation (5) in the high print rate mode. In S161, the CPU 32 determines whether or not the differential power ΔPN _{+ 1} calculated in S154 is 300 W or more, that is, whether or not there is sufficient power margin. When the CPU 32 determines in S161 that the differential power ΔPN _{+ 1} is 300 W or more, the process proceeds to S162. In S162, the CPU 32 determines that there is sufficient power margin, changes the image forming speed (printing speed) by the speed control unit 310, and switches to a high speed (speed up). Here, the value of 300 W used for the determination of S161 is merely an example, and is not limited to that value.

As shown in the table of Table 3, the image forming apparatus of the first embodiment has a configuration in which a low-speed power saving mode is set when the power is insufficient by 200 W. In view of this, 300 W, which is a power value obtained by adding a small margin to the numerical value of 200 W, is set as the threshold value at the time of determining the speed change. Further, in the case of a configuration in which the number of remaining print jobs is known, it is desirable to control not to switch the image formation speed when the number of remaining print jobs is small. That is, it may be configured to determine whether or not to switch the printing speed based on the predicted required power _PNEXT and the remaining number of prints in the print job.

In S163, the CPU 32 continues the printing operation after changing (increasing the speed) the image forming speed in S162. In S164, the CPU 32 shifts to the flowchart of FIG. In the process of S164 in FIG. 10, just in case, the power is confirmed after that, and the control is performed to shift to the flowchart of FIG. 8 so as to adjust the paper spacing as necessary. However, since the image formation speed has been switched with a sufficient margin secured for the electric power, the printing operation is continued as it is without shifting to the flowchart of FIG. 8 in S164 and not confirming the electric power thereafter. It may be configured to be used.

When the control described above is performed, the optimum power saving mode is selected according to the power shortage in the device that needs to start image formation with a throughput lower than the maximum throughput due to the power limitation of the AC power supply 50. Is done. This makes it possible to provide the user with the maximum productivity possible. As described above, according to the first embodiment, the optimum power saving mode can be selected according to the power condition and the printing condition, and the productivity can be improved to the extent possible.

In the first embodiment, the power saving mode is selected based only on the differential power ΔPini. In the second embodiment, an example in which the power saving mode is selected by using the differential power ΔPini and the parameters of the information regarding the total number of printed sheets of the print job will be described.

[Relationship between the number of prints and the time required for printing]
The graph shown in FIG. 11 is a graph showing the number of continuous prints (sheets) on the horizontal axis and the time required for printing (printing time) (s) on the vertical axis. The plot represented by the solid line A represents the printing time when printing is started at a low speed. On the other hand, the dotted line B shows, for example, the transition of the printing time when the FPOT is extended for 3 seconds when the differential power ΔPini is 60 W, the paper spacing is extended and printing is started, and then the paper spacing is shortened. Represents. With regard to the solid line A and the dotted line B, the case of the solid line A printed at a low speed while the number of printed sheets is small completes the printing job earlier than the dotted line B in which the paper spacing is gradually shortened after the paper spacing is extended. On the other hand, when the number of printed sheets is large, it can be seen that the printing job is completed earlier than the case of the solid line A when the printing operation as shown by the dotted line B is performed.

Similarly, the alternate long and short dash line C extends the FPOT for 5 seconds when the differential power ΔPini is 120 W, further extends the space between papers, and starts printing. It shows an example in which printing is started by extending the length of 5 seconds and further extending the space between papers. Although the point of intersection with the solid line A differs depending on the amount of the differential power ΔPini, when the number of printed sheets is small, it is better to start printing in the low-speed power saving mode so that the finished product after printing can be provided to the user earlier.

[Power saving mode selection process]
In the second embodiment, the configuration of the image forming apparatus 90, (1) power supply availability determination process, and (3) throughput change necessity determination process after the start of printing are the same as in the first embodiment, and the description thereof will be omitted. do. The second embodiment, which is different from the first embodiment, will be described with reference to FIG. 12 regarding (2) the selection process of the power saving mode. When the power saving mode is required in S115 in the power supply availability determination process of FIG. 5, the processes after S201 of FIG. 12 are executed.

In S201, the CPU 32 acquires information on the total number of prints of one print job. In S202, the CPU 32 acquires the value of the differential power ΔPini calculated in S112 of FIG. In S203, the CPU 32 determines the power saving mode using the table in Table 5 based on the differential power ΔPini acquired in S202.

表５は、差分電力ΔＰｉｎｉと印刷ジョブの総印刷枚数とに基づいて、省電力モードを決定するための表である。例えば、算出した差分電力ΔＰｉｎｉが－１２０Ｗで、印刷ジョブの総印刷枚数が２０枚であった場合、ＣＰＵ３２は、ＦＰＯＴを５秒延長し、かつ、紙間を延長する省電力モードを選択する。

Table 5 is a table for determining the power saving mode based on the differential power ΔPini and the total number of printed sheets of the print job. For example, when the calculated differential power ΔPini is −120 W and the total number of printed sheets of the print job is 20, the CPU 32 selects a power saving mode in which the FPOT is extended by 5 seconds and the space between papers is extended.

As a feature of Table 5, when the differential power ΔPini is small (0W> ΔPini ≧ -40W), the amount of heat can be replenished by extending the preparatory operation for image formation for a short time (for example, 2 seconds). Extend and print at normal speed. On the other hand, when the differential power ΔPini is large (−200 W> ΔPini), printing must be performed with a lower power, so printing is performed at a low speed (low-speed printing) in which the printing speed is lower than the normal speed. Further, when the differential power ΔPini is a certain amount of shortage (-40W> ΔPini ≧ −200W), the print job is set to be completed early according to the total number of prints of the print job. That is, as described with reference to FIG. 11, when the total number of printed sheets is small, printing is performed at a low speed, and when the total number of printed sheets is large, FPOT and the space between papers are extended for printing. In S204, the CPU 32 starts printing in the power saving mode determined in S203.

When the control described above is performed, due to the power limitation of the AC power supply 50, in the device that started image formation with a throughput lower than the maximum throughput, the optimum power saving according to the power shortage and the total number of prints of the print job. The power mode is selected. This makes it possible to provide the user with the maximum productivity possible. As described above, according to the second embodiment, the optimum power saving mode can be selected according to the power condition and the printing condition, and the productivity can be improved to the extent possible.

30 Fuser 32 CPU
100 Heater 309 Supplyable power calculation unit 319 Required power calculation unit

Claims (4)

An image forming means for forming an unfixed toner image on a recording material,
A fixing means having a heater and fixing an unfixed toner image formed by the image forming means to a recording material by the heat of the heater.
A supplyable power acquisition means for acquiring the supplyable power that can be supplied to the heater, and
Necessary power acquisition means for acquiring the required power assumed to be required for the heater in order to fix the unfixed toner image to the recording material, and
Have,
Printing is started in the first mode based on the difference obtained by subtracting the required power from the supplyable power, or a toner image unfixed from the first mode is fixed to the recording material by the heat of the heater. In an image forming apparatus that selects whether to start printing in a second mode that reduces the electric power supplied to the heater during the fixing process .
The device is
The first control for extending the period for heating the fixing means by generating heat before executing the fixing process, and
A second control that widens the space between the papers between the rear end of the recording material that is conveyed in advance and the tip of the recording material that is subsequently conveyed.
A third control that slows down the image formation speed compared to the first mode, and
Is feasible and
The device is the case where the second mode is selected.
If the difference is less than the first threshold, select the first control and select
When the difference is larger than the first threshold value and smaller than the second threshold value larger than the first threshold value, the combination of the first control and the second control is selected.
An image forming apparatus characterized in that when the difference is larger than the second threshold value, the third control is selected . The image forming apparatus according to claim 1, wherein the apparatus further selects one or a combination thereof from the first control to the third control based on the number of print jobs. The device further
The first detection means to detect the voltage of the AC power supply,
The second detection means for detecting the current of the AC power supply and
Equipped with
The supplyable power acquisition means is characterized in that the supplyable power is calculated based on the voltage detected by the first detection means and the current detected by the second detection means. The image forming apparatus according to claim 1 or 2 . The device further comprises a third detecting means for detecting the current flowing through the heater.
When the mode including the second control is selected from the plurality of the second modes, the apparatus performs a fixing process on a predetermined number of recording materials in the past by the fixing means. Based on the average value of the electric power for the predetermined number of sheets measured based on the detection result of the third detection means and the first printing rate of the toner image for the predetermined number of sheets to be printed from now on. The image forming apparatus according to claim 3 , further comprising calculating the required power assumed to be required for the heater and determining the extension time between the papers based on the calculated required power.

Images