Patent Grant
9213278
1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a printer or a copying machine.
2. Description of the Related Art
In recent years, there has been a demand for the image forming apparatus to shorten a first print out time (hereinafter, abbreviated as a FPOT), which indicates a time elapsing until the first sheet of a recording material is discharged after receiving a request to form an image. The FPOT largely depends on a time elapsing until a fixing device reaches a fixable temperature after receiving the request to form the image (hereinafter, referred to as a rising time).
Meanwhile, in order to cope with the colorization and speeding-up of an image forming apparatus, an inline-type color image forming apparatus has been developed. In the inline-type image forming apparatus, a plurality of photosensitive drums is mounted. Toner images with different colors are formed on the respective photosensitive drums, sequentially overlaid with each other on an intermediate transfer belt, and then collectively transferred onto a recording material. Alternatively, the toner images on the photosensitive drums are sequentially overlaid on the recording material which is disposed on a transfer belt.
In the case of an inline-type color image forming apparatus, a time elapsing until the recording material reaches the fixing device after starting the formation of the image on a first photosensitive drum is long. Japanese Patent No. 3265853 discusses the apparatus in which, when a time necessary for the fixing device to reach a fixing temperature calculated from a temperature rising rate of a heater is shorter than a time necessary for the recording material to reach the fixing device, the recording material starts to be fed immediately after the temperature rising rate is measured. In contrast, when the time necessary for the fixing device to reach the fixing temperature is longer than the time necessary for the recording material to reach the fixing device, the feeding of the recording material is to be delayed.
In order to shorten the FPOT, it is necessary to supply more power to the fixing device and determine, when the fixing device is at a lower temperature, whether “to start the formation of an image”. The apparatus discussed in Japanese Patent No. 3265853 is effective in setting the timing of sheet feeding. However, since the timing of sheet feeding is determined based on temperature change information of the fixing device, there is a limitation in shortening the FPOT.
The present invention is directed to an image forming apparatus capable of determining a timing of sheet feeding as early as possible.
According to an aspect of the present invention, an image forming apparatus includes an image forming unit configured to form an unfixed toner image on a recording material, a fixing unit configured to heat and fix the unfixed toner image formed onto the recording material, the fixing unit including a heater, a necessary integral power calculation unit configured to calculate a necessary integral power required for the fixing unit to reach a predetermined fixable temperature, a suppliable integral power calculation unit configured to calculate a suppliable integral power capable of being supplied to the heater in a time elapsing until the recording material reaches the fixing unit, a power source condition detection unit configured to detect a power source condition of a power source for supplying power to the heater, and a controller configured to control a timing to start conveyance of the recording material according to the necessary integral power and the suppliable integral power, wherein the suppliable integral power calculation unit calculates the suppliable integral power according to a resistance value of the heater and the power source condition.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
An image forming apparatus described below is a device which forms a color image using toners of four colors in total, i.e., yellow (Y), magenta (M), cyan (C), and black (Bk). Components which are common to the four-color toners will be described only using reference numerals, and redundant description will be avoided.
An electrostatic adsorption conveyance transfer belt (hereinafter, abbreviated as an ETB) 409 electrostatically adsorbs the recording material 32 to convey the recording material 32. A process cartridge 410 includes a photosensitive drum 305, a charging roller 303 which charges the photosensitive drum 305, a development roller 302 which develops an electrostatic latent image formed on the photosensitive drum 305 using a toner, a toner storage container 411, and a cleaner 306 which removes the toner from the photosensitive drum 305. The cartridge 410 is attachable/detachable to/from the printer main body 401.
A scanner unit 420 includes a laser unit 421 which emits laser light modulated based on an image signal for each color transmitted from a video controller 440, which will be described below. The scanner unit 420 further includes a polygon mirror 422 which scans the photosensitive drum 305 with the laser light emitted from the laser unit 421, a scanner motor 423, and an image forming lens group 424. A transfer roller 430 transfers a toner image from the photosensitive drum 305 onto the recording material on the ETB 409. Further, the process cartridges 410, the scanner units 420, and the transfer rollers 430 are each provided for four colors (yellow Y, magenta M, cyan C, and black Bk). The above-mentioned components constitute an image forming unit which forms an unfixed toner image onto the recording material.
A fixing device (a fixing unit) 431 heats the unfixed toner image, which is formed on the recording material, and fixes the unfixed toner image onto the recording material. The fixing device includes an endless belt (a heating sleeve) 433, a heater 432 which comes into contact with an inner surface of the endless belt 433, and a roller (a pressure roller) 434 which forms a nip portion (a fixing nip portion) which nips and conveys the recording material together with the heater 432 with the endless belt 433 therebetween. Further, a discharge roller pair 435 conveys the recording material 32 which has passed the fixing nip portion, and a storage unit (a memory) 323 stores a resistance value of the heater. The memory 323 is mounted on the fixing device 431 and a resistance value of a heat generator of the heater 432 measured at the time of manufacturing the fixing device 431 is stored in the memory 323. The heater 432 is a resistance heat generating heater in which the heat generator and a protective glass are printed on a ceramic substrate.
DC brushless motor 451 drives the process cartridge 410, the DC brushless motor 452 drives the ETB, and the DC brushless motor 453 drives the fixing device 431.
A printer controller 201 is a control unit of the laser printer 401 and includes a microcomputer 207 and various input/output control circuits (not illustrated).
A low voltage power source circuit 202 steps down a primary AC current after smoothing the primary AC current and supplies power to the DC brushless motors 451, 452, and 453 and the printer controller 201.
A video controller 440 expands, upon receiving image data transmitted from a host computer 441 such as a personal computer, the image data as bitmap data and generates an image signal for forming an image. A temperature detection sensor 324 detects an ambient temperature of the image forming apparatus.
Referring to
Referring to
Next, a temperature control operation and a heater current detecting operation of the fixing device 431 will be described with reference to
If the main switch 503 is turned on, a commercial current flows via the inlet 501 and the AC filter 502 to be full-wave rectified by the diode bridge 504 and the capacitor 581. The converter 505 is switched by the converter control circuit 506 and a ripple current is excited at a secondary side of the converter 505. The ripple current is rectified by the diode 507 and the capacitor 508.
A rectified voltage is detected by the constant voltage control circuit 509, and the converter control circuit 506 is controlled via the photo coupler 510 so that the rectified voltage becomes constant (24 V in the exemplary embodiment). The rectified voltage of 24 V is supplied to the DC brushless motor 451 and the DC/DC converter 511 to generate a voltage of 3 V. The generated voltage of 3 V is supplied to the printer controller 201 and used to control the image forming apparatus 401.
The printer controller 201 detects the divided voltage of the sub thermistor 530 and the resistor 531 via an A/D port 1. Further, The printer controller 201 detects the divided voltage of the main thermistor 532 and the resistor 533 via an A/D port 2. The thermistor has a characteristic that the resistance value is lowered as the temperature increases, and the printer controller 201 detects a temperature of the heater 432 by the divided voltages of the A/D ports 1 and 2. The commercial power source (power) is supplied to the heater 432 in the fixing device 431 via the relay 522, the triac 523, and the thermoswitch 529 (part (a) in
Next, an operation of detecting the heater current which flows in the heater will be described. Part (e) in
Next, an image forming operation will be described. First, the image data is transmitted from the host computer 441 to the video controller 440. The video controller 440 transmits, to the printer controller 201, a print signal which instructs the printer controller 201 to start the formation of an image and converts the received image data into bitmap data. Upon receiving the print signal, the printer controller 201 supplies power to the fixing device 431 and starts driving the scanner motor 423, the main motor 451, the ETB motor 452, and the motor 453 at a predetermined timing. Further, the printer controller 210 drives the pickup roller 404, the sheet feeding roller 405, and the retard roller 406 to pick out the recording material 32 from the sheet feeding cassette 402. The recording material 32 is conveyed to the registration roller pair 407 and then temporarily suspended. Thereafter, the recording material 32 is re-fed at a timing which will be described below, and conveyed to the ETB 409. In the meantime, the printer controller 201 transmits an image data transmission starting signal (hereinafter, referred to as a TOP signal) to the video controller 440 to match a timing of the re-fed recording material. Upon receiving the TOP signal, the video controller 440 transmits the bitmap data to the printer controller 201. Upon receiving the bitmap data, the printer controller 201 controls the laser unit 421 to be turned on/off according to the bitmap data and forms an electrostatic image on the photosensitive drum 305 charged at a predetermined potential by the charging roller 303 via the polygon mirror 422 and the image forming lens group 424. Thereafter, the electrostatic image is developed into a toner image by the development roller 302 and the toner image on the photosensitive drum 305 is transferred onto the recording material 32 by the transfer roller 430. Such an image forming operation is performed for yellow Y, magenta M, cyan C, and black Bk to form a color toner image on the recording material 32. The recording material 32, on which an unfixed color toner image has been formed, is conveyed to the fixing device 431 and the unfixed toner image is heated and fixed onto the recording material 32 between the heating sleeve 433 heated by the heater and the pressure roller 434. Thereafter, the recording material 32 is discharged by the discharge roller pair 435 to the outside of the image forming apparatus 401.
Next, an operation performed until the recording material 32, which has been temporarily suspended in the registration roller pair (sheet feeding unit) 407, is re-fed according to the instruction from the printer controller 201 will be described in detail with reference to
In
As illustrated in
Necessary integral power X(W·s)<R*I^2*T3 (1)
The right side of equation (1) is the suppliable integral power which can be supplied to the heater for a period from the time 0 to the time T3. In step S105, if the necessary integral power X(W·s) is smaller than the suppliable integral power (YES in step S104), the printer controller 201 re-feeds the recording material from the registration roller pair 407 at a timing of T2 (a predetermined timing) and starts forming an image onto the photosensitive drum 305. The time T2 (timing T2) is a shortest timing to re-feed the recording material 32. In the meantime, if the necessary integral power X(W·s) is larger than the suppliable integral power (NO in step S104), and if the recording material 32 is re-fed at the timing of T2, the toner image is insufficiently fixed since the fixing device 431 (heater) does not reach 200° C. when the recording material reaches the fixing device 431. Therefore, in step S106, equation (2) is calculated to delay the timing of re-feeding for B seconds from T2.
Re-feeding delay time B=X/(R*I^2)−T3 (2)
As a result of delaying the timing of re-feeding for B seconds, the heater temperature reaches 200° C. when the recording material 32 reaches the fixing device 431 (time T3′ in
As described above, in the exemplary embodiment, the recording material is fed from the sheet feeding unit at a timing corresponding to the necessary integral power required for the fixing unit to reach a predetermined fixable temperature and the suppliable integral power that can be supplied to the heater in a time necessary for the recording material to reach the fixing unit from the sheet feeding unit. If the suppliable integral power is smaller than the necessary integral power, the timing of sheet feeding is later than the timing of sheet feeding in a case when the suppliable integral power is larger than the necessary integral power.
Further, in the exemplary embodiment, as the necessary integral power X, power required for the heater to reach 200° C., which is the control target temperature at the time of fixing the toner image, is calculated. However, the necessary integral power X does not necessarily need to be power required to reach the control target temperature at the time of fixing, but may be power required to reach a predetermined temperature lower than the control target temperature. In other words, power required for the heater to reach a predetermined fixable temperature may be calculated.
As described above, according to the exemplary embodiment, the timing of sheet feeding is determined without using temperature information such as a temperature rising rate of the fixing device. Therefore, the determining timing can be earlier, and thus the FPOT can be shortened. Specifically, with a condition advantageous to the fixability (for example, when the power source voltage is high or a heater resistance value is low), a fastest FPOT (a time required until time T4) can be shorter. Further, a resistance value of a heat generator of the heater 432 has a large variation in the manufacturing process because it is difficult to adjust the resistance value after printing the heat generator on a heater substrate. In the exemplary embodiment, an actual resistance value, which is stored in the memory, measured when a fixing device is manufactured is used to calculate the delayed timing B of re-feeding so that an optimal timing of re-feeding can be accurately calculated.
In the first exemplary embodiment, an operation performed when the temperature of the fixing device 431 does not reach the predetermined fixable temperature by the time the recording material reaches the fixing device 431, has been described. In a second exemplary embodiment of the present invention, an operation performed when it is determined that the temperature of the fixing device 431 certainly reaches the fixable temperature by the time the recording material reaches the fixing device 431, will be described. Further, a configuration for determining an amount of power supplied to the fixing device 431 from a voltage applied to the fixing device 431 (heater 432) and a heater resistance value will be described.
An intermediate transfer belt 701 (hereinafter, abbreviated as an ITB) primarily transfers a toner image formed on a photosensitive drum 305 and includes a driving roller 702 which drives the ITB 701 and a tension roller 703 which maintains a tension of the ITB. A secondary transfer roller 704 transfers the toner image on the ITB onto a recording material, an ITB cleaning blade 705 removes remaining toner on the ITB, a used toner box 706 reserves the remaining toner which has been removed by the ITB cleaning blade 705, and an ITB driving motor 707 drives the ITB. A memory 708 is mounted on the printer controller 201 and a resistance value of a heat generator of the heater 432 measured when the fixing device 431 is manufactured is stored in the memory 708.
Next, an image forming operation will be described. First, the image data is transmitted from the host computer 441 to the video controller 440. The video controller 440 transmits, to the printer controller 201, a print signal which instructs the printer controller 201 to start the formation of an image and converts the received image data into bitmap data. Upon receiving the print signal, the printer controller 201 supplies power to the fixing device 431 and starts driving the scanner motor 423, the main motor 451, the ITB motor 707, and the motor 453 of the fixing device at a predetermined timing. Further, the printer controller 201 drives the pickup roller 404, the sheet feeding roller 405, and the retard roller 406 to pick out the recording material 32 from the sheet feeding cassette 402. The recording material 32 is conveyed to the registration roller pair 407 and then temporarily suspended. Thereafter, the printer controller 201 transmits an image data transmission starting signal (hereinafter, referred to as a TOP signal) to the video controller 440 at a predetermined timing.
Upon receiving the TOP signal, the video controller 440 transmits the bitmap data to the printer controller 201. Upon receiving the bitmap data, the printer controller 201 controls the laser unit 421 to be turned on/off according to the bitmap data and forms an electrostatic image on the photosensitive drum 305 charged at a predetermined potential by the charging roller 303 via the polygon mirror 422 and the image forming lens group 424. Thereafter, the electrostatic image is developed into a toner image by the development roller 302 and the toner image on the photosensitive drum 305 is transferred onto the ITB 701 by the transfer roller 430. Such an image forming operation is performed for yellow Y, magenta M, cyan C, and black Bk to form a color toner image on the ITB 701. Subsequently, the printer controller 201 re-feeds the recording material 32 from the registration roller pair 407 according to the color toner image formed on the ITB 701 and transfers the color toner image on the ITB 701 to the recording material 32 by the secondary transfer roller 704 to which a voltage having a predetermined potential has been applied. The color toner image formed on the recording material 32 is conveyed to the fixing device 431 and heated and pressed by the heating sleeve 433 heated at a predetermined temperature and the pressure roller 434, to be fixed on the recording material 32. Then, the recording material 32 is discharged by the fixing discharge roller pair 435 to the outside of the image forming apparatus 401.
Next, an operation performed until the printer controller 201 transmits the TOP signal to the video controller 440 after starting formation of the image will be described in detail with reference to
Referring to
As illustrated in
Necessary integral power X(W·s)<(V^2/R)*T13 (3)
The right side of equation (3) is the suppliable integral power that can be supplied to the heater for a period from the time 0 to the time T13. If the necessary integral power X(W·s) is smaller than the suppliable integral power (YES in step S204), then in step S205, the printer controller 201 calculates a period C(s) during which the power supply to the fixing device is suspended. The suspension period C satisfies the relationship indicated by equation (4) and is calculated from equation (5). Further, Y indicates a supplied power W per second which is additionally required according to the lowering of the temperature of the fixing device 431 during a power supply suspension period.
T13−(X+Y*suspension period C)/(V^2/R)=Suspension period C (4)
Suspension period C=((V^2/R)*T13)/((V^2/R)+Y)−X/((V^2/R)+Y) (5)
Next, in step S206, it is determined whether the suspension period C(s) has elapsed. If the suspension period C(s) has elapsed (YES in step S206), then in step S207, it is determined whether the power supply to the fixing device 431 has been resumed. If the power supply has not been resumed (NO in step S207), then in step S208, the power supply is resumed. If the suspension period C(s) has not elapsed (NO in step S206) or if the power supply to the fixing device 431 has been resumed (YES in step S207), the operation proceeds to step S209. In step S209, it is determined whether the TOP signal transmission timing T12 has been reached. If it is determined to reach T12 (YES in step S209), then in step S210, it is determined whether the TOP signal has been transmitted. If the TOP signal has not been transmitted (NO in step S210), then in step S211, the printer controller 201 transmits the TOP signal to the video controller 440. If it is not determined to reach T12 in step S209 (NO in step S209) or if the TOP signal has been transmitted in step S210 (YES in step S210), the operation proceeds to step S212. In step S212, it is determined whether the power supply to the fixing device 431 has been resumed and the TOP signal has been transmitted. If at least one of the operations has not been completed (NO in step S212), the operation returns to step S206 to repeat the above processes until both of the operations are completed. The time T12 (timing T12) is a shortest timing to transmit the TOP signal. By performing the above operations, the temperature of the fixing device 431 can reach the fixing temperature at a timing when the recording material enters the fixing device 431 (as illustrated by solid line in
In the meantime, in step S204, if the integral power X(W·s) is larger than the suppliable integral power (NO in step S204) and if the TOP signal is transmitted at the timing T12, the toner image is insufficiently fixed since the fixing temperature does not reach 200° C. when the recording material 32 reaches the fixing device 431. Therefore, in step S213, equation (6) is calculated to delay the timing of transmission of the TOP signal for D seconds from T12.
Re-feeding delay time D=X/(V^2/R)−T13 (6)
As a result, when the recording material 32 reaches the fixing device 431, the temperature of the fixing device has reached 200° C. (as illustrated by T13′ in
As described above, according to the exemplary embodiment, a similar effect to the first exemplary embodiment is obtained. Further, power can be reduced in a case where the fixing device reaches the fixing temperature before the recording material 32 reaches the fixing device 431, i.e., in a case where the fixing device 431 is heated in advance or the input voltage is high.
Further, in the exemplary embodiment, if the necessary integral power X(W·s) is smaller than the suppliable integral power, a period during which power supply to the fixing device 431 is suspended is provided to reduce the power. However, a method of reducing the power is not limited thereto. For example, control may be performed such that, by reducing the power supplied to the fixing device 431, the temperature is gradually increased, and the fixing device reaches the fixing temperature at a timing when the recording material reaches the fixing device 431.
In the first and second exemplary embodiments, the necessary integral power required for the thermistor to detect 200° C., which is the fixing temperature, is calculated using a constant relational expression. However, the necessary integral power changes according to an ambient environmental temperature of the image forming apparatus. In a third exemplary embodiment of the present invention, a control method for correcting the necessary integral power which is required to reach 200° C. depending on the ambient environmental temperature of the image forming apparatus will be described. Since the configuration of the image forming apparatus, the fixing device 431, and the circuit and the image forming operation are similar to those of the first exemplary embodiment, the description thereof will be omitted.
Next, an operation performed until the printer controller 201 re-feeds the recording material, which has been temporarily suspended on the registration roller pair 407, after starting formation of the image will be described in detail with reference to
In
Referring to
Next, in step S304, an integral supplied power Z to the time T22 is calculated from a resistance value R of the heater 432 and a heater current I using equation (7).
Integral supplied power z=∫0T22|(t)2*Rdt (7)
Next, in step S305, equation (8) is calculated to determine whether the heater reaches the fixing temperature of 200° C. by the time T23 when the recording material reaches the fixing device.
Integral supplied power Z>T22/T23*Xα (8)
When the integral supplied power Z is larger (YES in step S305), in step S306, the printer controller 201 re-feeds the recording material at the timing T22 and starts the formation of an image on the photosensitive drum 305. The time T22 (timing T22) is a shortest timing to re-feed the recording material 32. In the meantime, if the integral supplied power Z is smaller (NO in step S305) and if the recording material 32 is re-fed at the timing T22, the toner image is insufficiently fixed since the fixing temperature does not reach 200° C. when the recording material 32 reaches the fixing device 431. Therefore, in step S307, equation (9) is calculated to delay the timing of re-feeding for E seconds from T22.
Re-feeding delay time E=(T22*Xα)/X−T23 (9)
As a result, when the recording material 32 reaches the fixing device 431, the fixing temperature has reached 200° C. (as illustrated by T23′ in
As described above, according to the exemplary embodiment, even when the ambient environmental temperature of the image forming apparatus is changed, the FPOT can be shortened to the minimum.
The first to third exemplary embodiments have been described using a ceramic heater which has one resistance heat generator on the ceramic substrate. However, the number of resistance heat generators is not limited to one. In the case of a ceramic heater which includes a plurality of resistance heat generators, by storing a resistance value of each of the resistance heat generators for each fixing device, and using a combined resistance value of the resistance heat generators supplied with power at the time to start image formation, the similar effect may be obtained. Further, the exemplary embodiments may be applicable to an image forming apparatus in which a fixing device using a heater other than the ceramic heater as a heater is mounted.
Further, the first to third exemplary embodiments have been described using the inline-type color image forming apparatus. However, the similar effect may be obtained in a monochromic image forming apparatus or a four-path-type image forming apparatus.
According to the exemplary embodiments of the present invention, the timing of sheet feeding can be determined earlier and thus the FPOT can be shortened.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-124837 filed May 31, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-124837 | May 2012 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5656187 | Miyamoto et al. | Aug 1997 | A |
| 6185389 | Bartley et al. | Feb 2001 | B1 |
| 7224918 | Bartley et al. | May 2007 | B2 |
| 7787791 | Bartley et al. | Aug 2010 | B2 |
| 8725020 | Fukuzawa et al. | May 2014 | B2 |
| 20120148282 | Fukuzawa et al. | Jun 2012 | A1 |
| 20120269533 | Wakide et al. | Oct 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 3265853 | Mar 2002 | JP |
| 2009-175679 | Aug 2009 | JP |
| 2010-128465 | Jun 2010 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20130322907 A1 | Dec 2013 | US |
