Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent a deterioration in image quality by effectively discharging deteriorated toner in an image forming unit during double-sided printing.SOLUTION: An image forming apparatus of the present invention has: an image carrier that carries an electrostatic latent image; a developer carrier that develops the electrostatic latent image by using developer to form a developer image; a transfer unit that transfers the developer image to a conveyed medium; and a control unit that, in performing image formation on both sides of the medium, performs control of discarding the deteriorated developer on the image carrier, in a period after the developer image is transferred to a first surface of the medium until the developer image is transferred to a second surface of the medium.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus, and can be applied to, for example, an image forming apparatus such as a printer or a copier using an electrophotographic recording method.

Background Art

[0002] Conventionally, an image forming apparatus using an electrophotographic recording method for forming an image on a recording medium such as paper has been known. In such an image forming apparatus, toner as a developer that has been triboelectrically charged in the image forming unit is developed into an electrostatic latent image on a photosensitive drum as an image carrier to form a toner image, and the toner image is transferred onto a sheet-like recording medium in the transfer unit, and further, the toner image is fixed onto the recording medium in the fixing unit to form an image.

[0003] In addition, among image forming apparatuses, there are those that can perform double-sided printing for forming images on both sides of a recording medium. In such an image forming apparatus, when the transfer and fixing of an image onto one side of the recording medium are completed, the recording medium is reversed and conveyed, and image formation on the other side is performed as it is.

[0004] By the way, if the amount of toner used for image formation continues to be extremely small, the toner not used for image formation in the image forming unit will continue to be rubbed continuously, and the state will deteriorate. If a large amount of deteriorated toner accumulates in the image forming unit, defects will occur in the image quality of the formed image. Therefore, in a conventional image forming apparatus, when it is detected that the amount of toner used is small with respect to the operation amount of the image forming unit, it is determined that deteriorated toner has accumulated, and the deteriorated toner is developed on the photosensitive drum and discharged from the image forming unit by performing a toner disposal operation to suppress the deterioration of the image quality (Patent Document 1, etc.).

[0005] The toner disposal operation is performed during the intervals of the image forming operations, for example, immediately after the start of the operation of the image forming apparatus or immediately before the end of the operation.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in conventional devices, depending on the printing form, the waste of toner for maintaining image quality may not be sufficient, and in particular, the toner waste timing has not been sufficiently considered.

[0008] For example, there were cases where the deterioration of image quality when double-sided printing that forms an image on a recording medium once fixed by a fixing unit was continuous could not be sufficiently suppressed. That is, in double-sided printing, since an image is formed on a recording medium that has passed through the fixing unit once and been heated, the image forming unit becomes hot, and toner deterioration progresses more easily.

[0009] Therefore, in double-sided printing, an image forming apparatus that can suppress the deterioration of image quality by effectively discharging deteriorated toner in the image forming unit is desired.

Means for Solving the Problems

[0010] The image forming apparatus of the present disclosure includes: (1) an image carrier that carries an electrostatic latent image; (2) a developer carrier that develops the electrostatic latent image using a developer to form a developer image; (3) a transfer unit that transfers the developer image to a conveyed medium; and (4) a control unit that performs control to discard the deteriorated developer on the image carrier after transferring the developer image to the first surface of the medium and before transferring the developer image to the second surface of the medium when forming images on both surfaces of the medium.

Effects of the Invention

[0011] According to the present disclosure, in double-sided printing, the deterioration of image quality can be suppressed by effectively discharging deteriorated toner in the image forming unit.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0013] (A) Main Embodiment Hereinafter, embodiments of the image forming apparatus according to the present disclosure will be described in detail with reference to the drawings. In this embodiment, an example in which the image forming apparatus of the present disclosure is applied to a printer will be described.

[0014] (A-1) Configuration of the Embodiment FIG. 2 is a configuration diagram showing an outline of the overall configuration of the printer according to the embodiment.

[0015] In FIG. 2, the printer 1 includes an image forming unit 2 that forms a black (K) image, a transfer roller 20 as a transfer unit that conveys a sheet-like recording medium R and transfers the developer image formed by the image forming unit 2, a fixing unit 30 disposed on the conveyance path of the recording medium R, a paper feed tray 40 that houses the recording medium R, a paper feed roller 41 that feeds the recording medium R one by one from the paper feed tray 40, a registration roller 42 for conveying the recording medium R without skewing, a discharge roller 43 that discharges the recording medium R outside the apparatus, a paper discharge unit 44 that is the discharge destination of the recording medium R after image formation, and a medium inversion conveyance unit 50 for inverting the front and back of the recording medium to perform double-sided printing.

[0016] Note that the recording medium installation space of the paper feed tray 40 is, for example, about 297 mm in the left-right direction and about 220 mm in the depth direction. Therefore, the maximum size of the recording medium R that can be used in the printer 1 of this embodiment is A4 or letter size. Of course, the recording medium installation space of the paper feed tray 40 and the size of the recording medium R can be changed as appropriate and are not particularly limited.

[0017] In addition, in this embodiment, a monochrome printer that performs single-color image formation is taken as an example for description, but the present invention is similarly applicable to a color printer that performs image formation of a plurality of colors (for example, four colors of black (K), yellow (Y), magenta (M), and cyan (C)).

[0018] The image forming unit 2 includes a photosensitive drum 3 as an image carrier, a charging roller 6, an LED head 5 as an exposure device, a developing roller 7 as a developer carrier, a supply roller 8, a regulating blade 9, a cleaning unit 10 as a developer recovery unit, a charge elimination light irradiation unit 11, a toner cartridge 12 as a developer storage unit, a stirring member 15 for stirring the toner 4 inside the image forming unit 2, and the like.

[0019] The toner 4 used in this embodiment is a powder having a volume average particle diameter of about 6 μm per particle, which is composed of mother particles obtained by mixing and aggregating a colorant (carbon black), a binder resin, and wax, and external additives added to the mother particles.

[0020] The photoreceptor drum 3 is formed by applying a photosensitive layer to a conductor such as aluminum, has a gear at its axial end, and is rotatably arranged. It has a cylindrical shape with a diameter of 30 mm.

[0021] The charging roller 6 uniformly charges the surface of the photoreceptor drum 3. It is arranged around the photoreceptor drum 3 and is, for example, a metal such as stainless steel as the axis and is coated with a conductive elastic body. It rotates while being in contact with the photoreceptor drum 3 and being carried along.

[0022] The LED head 5 is an exposure device for selectively exposing the uniformly charged surface of the photoreceptor drum 3 in the main scanning direction to form a latent image pattern. The LED head 5 is composed of an LED element, an LED driving element, and a lens array, and is arranged at a position where the irradiation light from the LED element forms an image on the surface of the photoreceptor drum 3.

[0023] The developing roller 7 adheres toner 4 to the latent image pattern (electrostatic latent image) formed on the photoreceptor drum 3 to form a toner image as a developer image. The developing roller 7 is, for example, a metal such as stainless steel as the axis and is coated with a conductive elastic body such as urethane rubber or silicone rubber. It has a gear at the end of the axis and rotates by driving transmission from the photoreceptor drum 3.

[0024] The supply roller 8 supplies toner 4 to the developing roller 7. It is, for example, a metal such as stainless steel as the axis and is coated with a foaming elastic body such as silicon. It has a gear at the end of the axis and rotates by driving transmission from the developing roller 7.

[0025] The regulating blade 9 regulates the amount of toner adhesion on the developing roller 7. The regulating blade 9 is, for example, made of a thin stainless steel plate and is an elastic blade with one end fixed to a holder, and the other end is pressed against the developing roller 7. Also, the regulating blade 9 is electrically connected to the metal axis of the supply roller 8 through a contact point not shown in the figure.

[0026] The cleaning unit 10 scrapes off the external additives attached to the toner 4 on the photosensitive drum 3, the used toner that has not been transferred, and the like. The cleaning unit 10 has an elastic blade made of rubber or the like as one of its constituent members, and the elastic blade is in contact with the photosensitive drum 3.

[0027] At one end inside the cleaning unit 10, there is a waste toner conveying unit 13a, and inside the toner cartridge 12, there is a waste toner storage unit 14. Further, the waste toner storage unit 14 is provided with a waste toner conveying unit 13b. The waste toner conveying units 13a and 13b are connected by a conveying path (not shown). Inside the cleaning unit 10 and in the same conveying path, a conveying member (not shown), for example, a coil-shaped member that is rotationally driven by transmission of drive from the photosensitive drum 3, is passed through. The used toner recovered by the cleaning unit 10 is conveyed from the waste toner conveying unit 13a to 13b and stored in the waste toner storage unit 14.

[0028] The charge elimination light irradiation unit 11 is a device for removing variations in the surface potential of the photosensitive drum 3. A plurality of LED chips for uniformly exposing the surface of the photosensitive drum 3 are arranged on a substrate and are arranged so as to face the photosensitive drum 3.

[0029] The toner cartridge 12 is detachable from the main body of the image forming unit 2 and stores the toner 4.

[0030] The transfer roller 20 transfers the toner image formed on the photosensitive drum 3 to the conveyed recording medium R. The transfer roller 20 is formed with a semiconductive foamed elastic layer around a metal shaft, abuts against the photosensitive drum 3 with a certain amount of indentation, and at the same time has a gear at the end of the shaft and rotates by transmission of drive from the photosensitive drum 3.

[0031] The fixing unit 30 has a heat roller 31 and a pressure roller 32, and fixes the toner image transferred onto the recording medium R to the recording medium R by pressure and heating. The heat roller 31 includes, as a heat source, a fixing heater 33 (FIG. 1), such as a halogen lamp (not shown), inside the heat roller 31.

[0032] The medium reverse conveyance unit 50 includes a reverse conveyance path 51 formed of a plate-like member fixed inside the printer 1, a reverse roller 52 that conveys the recording medium R from in front of the paper discharge unit 44 to the reverse conveyance path 51, and a plurality (two are shown in FIG. 2, but the number is not limited) of conveyance rollers 53 around the reverse conveyance path 51.

[0033] The printer 1 is capable of duplex printing for forming images on both sides of the recording medium R. In duplex printing, a first image is printed on one side of the conveyed recording medium R through the image forming unit 2, and then the front and back of the recording medium R are reversed by the medium reverse conveyance unit 50 and then returned to a position in front of the image forming unit 2, and a second image is printed on the other side of the recording medium R.

[0034] The medium detection sensor 60 detects the passage of the recording medium R, includes a sensor lever 60a and a photoelectric coupler (not shown) that detects the rotation of the sensor lever 60a, and is attached near the outlet of the fixing unit 30. The sensor lever 60a is biased in the clockwise direction in FIG. 2 by a torsion spring (not shown), and rotates in the counterclockwise direction in FIG. 2 when the recording medium R comes into contact. Thus, when there is no recording medium R, a part of the sensor lever 60a partially shields the detection part of the photoelectric coupler.

[0035] Next, the configuration of the control system of the printer 1 will be described. FIG. 1 is a block diagram showing the configuration of the control system of the printer according to the embodiment.

[0036] In FIG. 1, the printer 1 includes an I / F control unit 100, a printing operation control unit 101, a drive system control unit 102, an image forming control unit 103, a charging voltage control unit 120, a developing voltage control unit 121, a supply voltage control unit 122, a transfer voltage control unit 123, a head control unit 104, a fixing control unit 105, a drum rotation amount detection unit 131, a light emitting dot detection unit 132, a count calculation unit 133, and a storage unit 134.

[0037] The printing operation control unit 101 is responsible for the main functions (such as printing operations) of the printer 1. The printing operation control unit 101 has, for example, a CPU, a flash ROM, a RAM, an EEPROM, a timer, an input / output interface unit, etc., which are not shown in the figure. The CPU executes a program stored in the flash ROM to realize the functions of the printer 1.

[0038] The I / F control unit 100 transmits various signals, image data, device settings, etc. obtained from an external host device (not shown) via a driver to the printing operation control unit 101.

[0039] The drive system control unit 102 transmits drive signals to the fixing drive motor 110, which is the power source of the heat roller 31, the drum drive motor 111, which is the power source of the photosensitive drum 3, the paper feed roller 41, the registration roller 42, and the transport roller 53, and the duplex printing motor 112, which is the power source of the discharge roller 43 and the reverse roller 52, according to the printing timing generated by the printing operation control unit 101, and drives them at a predetermined speed.

[0040] The fixing drive motor 110 rotates the heat roller 31 at a predetermined speed according to the signal from the drive system control unit 102.

[0041] The drum drive motor 111 rotates the photosensitive drum 3, etc. at a predetermined speed according to the signal from the drive system control unit 102.

[0042] The duplex printing motor 112 rotates the reverse roller 52, etc. at a predetermined speed according to the signal from the drive system control unit 102.

[0043] The image formation control unit 103 transmits signals regarding the magnitude and application timing of the applied voltage to the charging voltage control unit 120, the developing voltage control unit 121, the supply voltage control unit 122, and the transfer voltage control unit 123 according to the signal from the printing operation control unit 101.

[0044] The charging voltage control unit 120 generates and stops the charging voltage to the charging roller 6 according to the signal from the image formation control unit 103.

[0045] The developing voltage control unit 121 generates and stops the charging voltage applied to the developing roller 7 in accordance with a signal from the image formation control unit 103.

[0046] The supply voltage control unit 122 generates and stops the charging voltage applied to the supply roller 8 in accordance with a signal from the image formation control unit 103.

[0047] The transfer voltage control unit 123 generates and stops the charging voltage applied to the transfer roller 20 in accordance with a signal from the image formation control unit 103.

[0048] The head control unit 104 controls the light emission operations such as the light emission timing and light emission amount of each LED element of the LED head 5 based on the image data processed by the printing operation control unit 101 and the control conditions determined by the image formation control unit 103.

[0049] The fixing control unit 105 switches the on / off state of the fixing heater 33 according to a signal from the printing operation control unit 101 so that the temperature of the heating roller 31 detected by a fixing temperature sensor (not shown) falls within a predetermined range.

[0050] The drum rotation amount detection unit 131 calculates the rotational drive distance L of the photosensitive drum 3 from the drive signal of the drum drive motor 111.

[0051] The light-emitting dot detection unit 132 detects the number of light-emitting dots P of the LED head 5 from the head drive signal of the head control unit 104. Note that for the rotational drive distance L and the number of light-emitting dots P, the actual rotational drive distance of the photosensitive drum 3 and the actual number of light-emitting dots P of the LED head 5 itself may be used, or values obtained by performing some calculation processing and adding unit conversion or correction may also be used.

[0052] The count calculation unit 133 calculates the number of discarded dots W based on the rotational driving distance L of the photoreceptor drum 3 and the number of light-emitting dots P of the LED head 5. Next, the count calculation unit 133 calculates the latest cumulative number of discarded dots Ws using the calculated number of discarded dots W and the cumulative number of discarded dots Ws up to the previous calculation stored in the storage unit 134. Then, the count calculation unit 133 calculates the latest discard count C using the calculated cumulative number of discarded dots Ws and the discard count C up to the previous calculation stored in the storage unit 134. The discard count C is a unit of toner discard amount and is also a value used when determining whether to execute toner discard.

[0053] The count calculation unit 133 calculates the printing duty D per rotation distance using the rotational driving distance L of the photoreceptor drum 3 and the number of light-emitting dots P of the LED head 5. The printing duty is the ratio of the actual number of dots formed to the total number of dots that can be formed in a certain area, that is, the printing rate. In this embodiment, D100 indicating a printing duty of 100% is defined by the following formula (1) using the rotational driving distance L100 and the number of light-emitting dots P100 when dots are formed over the entire printing area when printing one sheet of the A4-sized recording medium R. D100 = P100 ÷ L100 = 100 [%] …(1)

[0054] Note that the definition of the printing duty may be any as long as it is related to the size of the recording medium R, the rotational driving distance L, and the number of light-emitting dots P, regardless of the above formula (1).

[0055] The storage unit 134 stores the cumulative number of discarded dots Ws, which is the cumulative value of the number of discarded dots W calculated by the count calculation unit 133, the discard count C, the count conversion value Cp for converting the cumulative number of discarded dots Ws into the discard count C, and the discard reference printing duty D0, which is the printing duty for determining the increase or decrease of deteriorated toner.

[0056] In this embodiment, the count conversion value Cp is set to the number of light-emitting dots corresponding to a printing duty of 5%, and the waste standard printing duty D0 is set to a printing duty of 2%. The values of the count conversion value Cp and the waste standard printing duty D0 may be changed as appropriate.

[0057] (A-2) Operations of the embodiment Next, the operations of the printer 1 according to the embodiment having the above configuration will be described. Hereinafter, before describing the characteristic operation of the printer 1 (toner waste is performed between printing on the first side and the second side during double-sided printing), first, the conventional operation of the printer 1 (toner waste at the end of printing) will be described.

[0058] (A-2-1) Conventional operation (toner waste processing at the end of printing) FIG. 3 is a flowchart showing the conventional operation (toner waste processing at the end of printing) in the printer according to the embodiment.

[0059] <Step S101> When the print operation control unit 101 receives a print command (print job) from an upper device (such as a personal computer) not shown via the I / F control unit 100, it transmits information regarding the driving timing and printing speed to the drive system control unit 102, and transmits information on the received image data to the image forming control unit 103 to prepare for print execution.

[0060] <Step S102> Based on the received timing and printing speed information, the drive system control unit 102 rotates the fixing drive motor 110, the drum drive motor 111, and the double-sided printing motor 112 at predetermined timings and speeds. At this time, the double-sided printing motor 112 rotates in the normal direction, that is, in the direction of conveying the recording medium R from the reversing roller 52 to the discharge roller 43. When the rotations of the fixing drive motor 110 and the drum drive motor 111 are transmitted, the respective rollers and the photosensitive drum 3 rotate, and the recording medium R is conveyed one by one from the paper feed tray 40 at a predetermined timing.

[0061] [Image forming process] At the same time, the image formation control unit 103 provides information on the applied voltage and voltage application timing to each of the charging voltage control unit 120, developing voltage control unit 121, supply voltage control unit 122, and transfer voltage control unit 123. Each of the voltage control units 120 to 123 applies a predetermined voltage to the charging roller 6, developing roller 7, supply roller 8, the regulating blade 9 electrically connected thereto, and the transfer roller 20 at a predetermined timing based on the received voltage control conditions.

[0062] In this embodiment, negatively charged toner 4 is used, and the charging voltage Vc applied to the charging roller 6 during image formation, the developing voltage Vd applied to the developing roller 7, the supply voltage Vs applied to the supply roller 8 and the regulating blade 9, and the transfer voltage Vtp applied to the transfer roller 20 are set to values such as Vc = -1000V, Vd = -150V, Vs = -300V, and Vtp = +2000V, respectively.

[0063] Also, the image data received by the printing operation control unit 101 is processed within the printing operation control unit 101 and the image formation control unit 103 and then transmitted to the head control unit 104. The head control unit 104 turns on the LED head 5 based on the received image data to selectively expose the surface of the photosensitive drum 3.

[0064] In the image forming unit 2, first, the surface of the photosensitive drum 3 is uniformly charged to -500V by the charging roller 6 to which the charging voltage Vc is applied. The charged surface of the photosensitive drum 3 is selectively exposed by the LED head 5 according to the image pattern, and an electrostatic latent image with a potential of -50V is formed at the exposed portions.

[0065] The electrostatic latent image faces the developing roller 7 to which the developing voltage Vd is applied at the contact portion between the photosensitive drum 3 and the developing roller 7, and the toner 4 carried on the developing roller 7 is developed onto the electrostatic latent image by the electric field formed between the two, forming a toner image on the surface of the photosensitive drum 3.

[0066] Before this developing process, the toner 4 is charged negatively by being rubbed at the contact portions of the developing roller 7 and the supply roller 8 and at the contact portion of the developing roller 7 and the regulating blade 9 by the rotational driving of the developing roller 7 and the supply roller 8. The toner 4 charged by friction is caused to move from the supply roller 8 to the developing roller 7 and from the regulating blade 9 to the developing roller 7 by an electric field formed by the potential differences (=Vd - Vs) between the developing roller 7 and the supply roller 8 and between the developing roller 7 and the regulating blade 9, respectively. The regulating blade 9 has a role of regulating the amount of toner adhering to the outer peripheral surface of the developing roller 7 and forming a uniform thin layer of toner on the surface of the developing roller 7 after passing through the regulating blade 9.

[0067] [Transfer process] The developed toner image is conveyed to the contact portion of the photosensitive drum 3 and the transfer roller 20. The toner image and the recording medium R reach the contact portion of the photosensitive drum 3 and the transfer roller 20 at the same timing. At this time, since a positive transfer voltage Vtp is applied to the transfer roller 20, the toner image on the photosensitive drum 3 is transferred onto the recording medium R by the electric field formed between the photosensitive drum 3 and the transfer roller 20.

[0068] Note that even after this transfer process, a small amount of toner remains on the photosensitive drum 3. This is removed as waste toner by the cleaning unit 10, conveyed from the waste toner conveying units 13a to 13b, and stored in the waste toner storage unit 14. After that, the entire surface of the photosensitive drum 3 is uniformly exposed by the charge eliminating irradiation unit 11, and the surface potential is reset.

[0069] [Fixing process] The toner image transferred onto the recording medium R is conveyed together with the recording medium R to the fixing unit 30 and fixed onto the recording medium R by heat and pressure at the contact portion of the heat roller 31 and the pressure roller 32. After the fixing of the toner image, in the case of single-sided printing, the recording medium R is conveyed (discharged) to the paper discharge unit 44 by the reversing roller 52 and the discharge roller 43.

[0070] [Processing during double-sided printing] On the other hand, when double-sided printing is performed on the recording medium R, the recording medium R on which the toner image has been fixed on the first side is not discharged to the paper discharge unit 44 but is conveyed to the medium reverse conveyance unit 50.

[0071] In this case, when the leading edge of the recording medium R that has passed through the fixing unit 30 contacts the sensor lever 60a and the sensor lever 60a rotates counterclockwise in FIG. 2, the light-shielding portion of the sensor lever 60a moves away from the front position of the sensor portion of the photocoupler, and the medium detection sensor 60 detects the presence (being in the process of passing) of the recording medium R. The recording medium R is conveyed as it is toward the paper discharge unit 44, and the trailing edge of the recording medium R passes through the sensor lever 60a. The sensor lever 60a rotates clockwise in FIG. 2 due to the reaction force of the torsion spring, and the medium detection sensor 60 detects that the light-shielding portion of the sensor lever 60a has blocked the sensor portion of the photocoupler, indicating that the recording medium R has finished passing through the sensor lever 60a, and notifies the print operation control unit 101 that the recording medium R has passed.

[0072] After the recording medium R has been conveyed a certain distance, the print operation control unit 101 rotates the duplex printing motor 112 in the reverse direction via the drive system control unit 102. As a result, the reverse roller 52 and the discharge roller 43 rotate in the reverse direction, so the recording medium R is conveyed in the direction from the discharge roller 43 toward the reverse roller 52, opposite to the previous direction, and is guided to the reverse conveyance path 51. The recording medium R guided to the reverse conveyance path 51 is conveyed to the registration roller 42 by the conveyance roller 53.

[0073] Thereafter, a toner image is transferred and fixed to the recording medium R in the same procedure as the first side. At this time, since the surface of the recording medium R facing the photosensitive drum 3 is the second side opposite to the first side, as a result, images are formed on both sides of the recording medium R. After the toner image has been fixed on the second side of the recording medium R, the print operation control unit 101 rotates the duplex printing motor 112 in the forward direction again via the drive system control unit 102, and discharges the recording medium R to the paper discharge unit 44 by the reverse roller 52 and the discharge roller 43.

[0074] [Calculation of Rotational Drive Distance L and Number of Emission Dots P] During the operation of step S102, the drum rotation amount detection unit 131 receives signals from the drum drive motor 111 respectively, and calculates the rotational drive distance L of the photoreceptor drum 3 in the current printing.

[0075] Similarly, the light-emitting dot detection unit 132 receives signals from the head control unit 104 and calculates the number P of light-emitting dots in the current printing.

[0076] <Step S103> The printing operation control unit 101 determines whether all received images have been printed. If there are still printing commands input to the printer 1, the printing operation control unit 101 executes the next printing operation in the same manner from the stage of step S101 described above. Note that the determination in step S103 may be executed as soon as the conditions for enabling the next printing are met without waiting for the preceding recording medium R to be discharged to the paper discharge unit 44 in step S102 described above. In the present embodiment, when performing continuous printing, the paper feeding timing of the recording medium is changed according to the printing surface and the conveyance direction length of the recording medium R (hereinafter referred to as the medium length).

[0077] FIG. 4 is an explanatory diagram showing a continuous printing operation for each printing condition of the printer according to the embodiment.

[0078] As shown in FIG. 4, when continuous single-sided printing is performed, the printer 1 feeds the subsequent recording medium with a 50 mm interval (paper gap) from the rear end of the preceding recording medium R regardless of the medium length.

[0079] Also, when continuous double-sided printing is performed and the medium length is 250 mm or more, the printer 1 performs one-page stack printing in which printing is performed on only one recording medium R at a time. When the medium length is long with respect to the conveyance route of the recording medium R, if the feeding of the subsequent recording medium R is started before the printing on the second side of the preceding recording medium R is performed, the subsequent recording medium R will catch up with the preceding recording medium R by one sheet, causing an obstacle to the medium conveyance. Therefore, the subsequent recording medium R is fed at the timing when the rear end of the second side of the preceding recording medium R passes through the registration roller 42.

[0080] Furthermore, when double-sided printing is continuous and the media length is less than 250 mm, the printer 1 performs two-page stack printing in which two or more recording media R are conveyed simultaneously. In two-page stack printing, the subsequent recording media R is fed at the timing when the preceding recording media R is guided to the media reverse conveyance unit 50. Therefore, for example, when four two-page stack prints are performed, image formation on the recording media R is performed in the order of the first side of the first sheet, the first side of the second sheet, the second side of the first sheet, the first side of the third sheet, the second side of the second sheet, the first side of the fourth sheet, the second side of the third sheet, and the second side of the fourth sheet. By performing such two-page stack printing, double-sided printing on a plurality of recording media R can be achieved in a shorter time.

[0081] When it is determined that the printing of all the images received in step S103 has been completed, the printer 1 executes the calculation of the waste count C and the toner waste operation in the operations after step S104. As described above, the toner 4 is charged by friction between the developing roller 7, the supply roller 8, the regulating blade 9, and the toner particles. However, due to the pressure and shear force of these frictions, the toner 4 is gradually damaged, resulting in the detachment and embedding of the external additives, making it impossible to be charged normally or causing aggregation with each other, thereby deteriorating the characteristics. When deteriorated toner accumulates inside the image forming unit 2, image quality deterioration such as changes in image density and a decrease in dot reproducibility, and image defects such as fogging, dirt, and blurring will occur. The deterioration of the toner 4 progresses, for example, when printing images with extremely low print duty, such as documents with only text, is repeated. This is because the toner 4 remaining in the image forming unit 2 without being used for image formation is repeatedly rubbed. In view of the above, the image forming unit 2 performs a toner waste operation according to the degree of accumulation of deteriorated toner to prevent image quality deterioration.

[0082] <Step S104> The count calculation unit 133 calculates the discard count C. The count calculation unit 133 obtains the rotation drive distance L in the current printing from the drum rotation amount detection unit 131 and the number of light-emitting dots P in the current printing from the light-emitting dot detection unit 132, and further reads the value of the discard reference print duty D0 stored in the storage unit 134, and calculates the current print duty D and the number of discarded dots W generated by the current printing.

[0083] The current print duty D is represented by the print duty per drive distance of the printing operation, and the current number of discarded dots W is represented by the number of light-emitting dots corresponding to the difference between the current print duty D and the discard reference print duty D0. The current print duty D and the current number of discarded dots W can be calculated by the following equations (2) and (3). D = P ÷ L ÷ P100 …(2) W = (D0 - D) × P100 …(3)

[0084] From the above equation (3), when D0 = D, W = 0; when D0 > D, W > 0; when D0 < D, W < 0. What this means is that when W > 0, the deteriorated toner increases, and when W < 0, the deteriorated toner decreases.

[0085] The count calculation unit 133 overwrites the value of Ws in the storage unit 134 with the sum of the number of discarded dots W calculated this time and the cumulative number of discarded dots Ws stored in the storage unit 134 as the new cumulative number of discarded dots Ws.

[0086] Furthermore, the count calculation unit 133 calculates the discard count C according to the following equation (4) based on the cumulative number of discarded dots Ws and the count conversion value Cp stored in the storage unit 134. C = Ws ÷ Cp …(4)

[0087] What the waste count C means is that when C > 0, it indicates that due to printing with a low printing duty, deteriorated toner has accumulated in the image forming unit 2 and toner waste is necessary. Conversely, when C ≤ 0, it indicates that due to printing with a high printing duty, there is no accumulation of deteriorated toner in the image forming unit 2 and toner waste is not required.

[0088] <Step S105> The printing operation control unit 101 receives the value of the waste count C calculated by the count calculation unit 133 and determines whether C > 0. When C > 0, the printing operation control unit 101 transitions to the next step S106. On the other hand, when C ≤ 0, toner waste is not performed and the printer 1 stops operating.

[0089] <Step S106> When it is determined in step S105 described above that C > 0, the printing operation control unit 101 develops and discards the toner 4 on the photosensitive drum 3 in the image forming unit 2. At this time, the waste execution dot number Wa, which is the number of dots for which the LED head 5 exposes the photosensitive drum 3 for toner waste, may be set as appropriate. However, in this embodiment, in order to quickly stop the apparatus after printing is completed, Wa is set to the dot number (= Cp) corresponding to C = 1.

[0090] Note that the toner image developed on the photosensitive drum 3 in step S105 described above is a pattern with a printing duty of 50% across the entire main scanning direction (toner waste pattern), but the printing duty and the toner developing location may be changed as appropriate. During toner waste, the transfer voltage control unit 123 applies a voltage of Vtn = -1000V, which is a negative voltage, to the transfer roller 20 so that the developed toner does not adhere to the transfer roller 20. The waste toner developed during the toner waste operation is collected by the cleaning unit 10 and then conveyed from the waste toner conveying unit 13a to 13b and finally stored in the waste toner storage unit 14.

[0091] <Step S107> Even while the toner is being discarded in step S106 above, the photoreceptor drum 3 rotates and the LED head 5 emits light, so the rotational drive distance L and the number of light-emitting dots P increase. The count calculation unit 133 adds or subtracts the count generated by toner discard in the same procedure as step S104 described above, updates the cumulative discarded dot count Ws and the discard count C, and stores them in the storage unit 134. Thus, the printing operation and the toner discard operation are completed.

[0092] <Problems of the conventional operation> In the conventional operation, since toner discard is executed after the printing operation has generally been completed as described above, when printing images with a low printing duty continuously on a large number of recording media R, there is no time to discard the deteriorated toner and image quality deterioration is likely to occur.

[0093] Particularly when double-sided printing is continuous, the printing duty per drive distance decreases due to performing inversion operations etc., and in the printing of the second side, the recording media R heated once by the fixing unit 30 in the printing of the first side comes into contact with the photoreceptor drum 3, leading to a temperature rise in the image forming unit 2 and making it easier to cause toner deterioration. Also, in double-sided printing, due to the need to print on both sides of the recording media R, the conveyance distance of the recording media R becomes longer, so the consumption of the toner 4 with respect to the operation amount of the image forming unit 2 decreases and toner deterioration progresses easily.

[0094] These days, the trend towards space saving and energy conservation of devices is accelerating, and due to the reduction in heat capacity due to the miniaturization of printers and the lowering of the melting point of toner, toner is in a situation where it is more easily damaged by heat. Particularly in single-sheet stack printing, during the period when the recording media R is being conveyed by the media inversion conveyance unit 50, unlike double-sheet stack printing where image formation of the subsequent recording media R is performed and toner is consumed, the image forming unit 2 is only idling for recording media conveyance. Therefore, in single-sheet stack printing, the drive distance per recording media becomes long, so toner deterioration with respect to the number of printed sheets progresses easily.

[0095] Regardless of whether it is single-page stack printing or not, in order to prevent image quality degradation caused by toner deterioration during continuous printing, there is a method of delaying the paper feeding timing of the subsequent recording medium R and performing toner disposal during the widened paper interval. However, this method not only reduces the number of printed sheets per unit time and productivity due to widening the paper interval, but also increases the driving distance of the photoreceptor drum 3 outside the printing operation by the amount of the widened paper interval, so the number of printable sheets until the service life of the image forming unit 2 is reduced, which is not preferable.

[0096] To solve the above conventional problems, the printer 1 of the present embodiment performs toner disposal during the idle period from the end of latent image formation on the first side of the recording medium R to the start of latent image formation on the second side in double-sided printing.

[0097] (A-2-2) Characteristic operation (toner disposal process performed between image formation on the first side and image formation on the second side of the recording medium R in double-sided printing) FIG. 5 is a flowchart showing the characteristic operation of the printer according to the embodiment (toner disposal process performed between image formation on the first side and image formation on the second side of the recording medium in double-sided printing). Hereinafter, the description will be made while comparing with the conventional operation of FIG. 3 described above.

[0098] <Step S201> When a print command (print job) is input, the print operation control unit 101 performs preparations for execution during printing in the same manner as in step S101 described above.

[0099] <Step S202> The print operation control unit 101 determines whether the current print satisfies predetermined conditions. In this embodiment, the print operation control unit 101 determines whether the current print is double-sided printing of a single-page stack. If the current print is double-sided printing of a single-page stack, the print operation control unit 101 transitions to step S203, while if the current print is not double-sided printing of a single-page stack, the print operation control unit 101 transitions to step S204.

[0100] In this embodiment, the condition where image quality degradation due to toner deterioration in double-sided printing is significant is single-sided stack printing, and it is also single-sided stack printing that can ensure an idle distance where toner disposal can be executed. Therefore, this is set as the condition for step S202. However, depending on the dimensions of the printer 1, the media length, and the method of recording media conveyance, if a sufficient idle distance can be obtained between the first-side printing and the second-side printing of each of the preceding and subsequent recording media R even in double-sided stack printing, the condition may be added to step S202.

[0101] <Step S203> When it is determined in step S202 described above that the current printing is single-sided stack printing, the printing operation control unit 101 performs toner disposal during the period from the end of electrostatic latent image formation of the first-side image to the start of electrostatic latent image formation of the second-side image.

[0102] FIG. 6 is an explanatory diagram showing, in chronological order, how the rotational drive distance and the number of light-emitting dots increase in single-sided stack printing according to the embodiment. In FIG. 6, the rotational drive distance L is shown by a solid line, and the number of light-emitting dots P is shown by a broken line.

[0103] In the operation of the image forming unit 2, since the photosensitive drum 3 is always rotationally driven, the rotational drive distance L increases linearly through the printing operation. Also, due to the formation of a latent image on the photosensitive drum 3, the number of light-emitting dots P increases, and it increases due to the formation of the printed image and the toner disposal operation.

[0104] FIG. 6 shows the case where toner disposal is executed at all timings when toner disposal is possible. However, if there are locations where toner disposal is not executed, the number of light-emitting dots P at those locations does not increase. Also, the way the number of light-emitting dots P at the latent image formation locations increases varies depending on the printing duty.

[0105] In the conventional operation of FIG. 3 described above, the printing operation control unit 101 only performed toner disposal (a) immediately before the end of printing. However, in the characteristic operation of the present embodiment shown in FIGS. 5 and 6, in addition to toner disposal (a), toner disposal (b) is performed between the latent image formation on the first side and the latent image formation on the second side of each recording media R.

[0106] In this embodiment, the number of dots Wb for waste execution in toner waste (b) is changed according to the value of the waste count C, and the larger the value of C, the more toner 4 is wasted. That is, when C = 1, Wb is the number of dots corresponding to C = 1 (= Cp), and when C ≥ 2, Wb is the number of dots corresponding to C = 2 (= 2Cp). The reason why Wb = 2Cp is the upper limit is that it is the maximum amount of toner that can be wasted once during the period when the recording medium R is conveyed by the medium inversion conveyance unit 50. If there is a margin during the period when the recording medium R is conveyed by the medium inversion conveyance unit 50, more toner 4 may be wasted. Conversely, a certain amount of toner may be wasted unconditionally without performing the determination as in step S303 described later.

[0107] Toner waste (b) is executed based on the waste count C calculated using the rotation drive distance L and the number of light emission dots P at the end of latent image formation on the first side of each recording medium R. That is, the count calculation unit 133 calculates the waste count C using the values of the rotation drive distance L1 and the number of light emission dots P1, and the rotation drive distance L2 and the number of light emission dots P2 at the timings of time t1 and time t2 in FIG. 6, respectively. The print operation control unit 101 determines whether toner waste (b) needs to be executed based on the calculation result.

[0108] Strictly speaking, since the photosensitive drum 3 is driven during the period from each of time t1 and time t2 to the start of toner waste, the rotation drive distance L increases. However, since this increase is included in the calculation of the next and subsequent print duties and is a very small fraction, it can be ignored here. Hereinafter, the procedure of toner waste (b) will be described with reference to FIG. 7.

[0109] FIG. 7 is a flowchart showing the toner waste process (toner waste (b)) performed between the printing of the first side and the second side during double-sided printing of the printer according to the embodiment.

[0110] (Step S301) The count calculation unit 133 calculates the waste count C in the same procedure as the above-described step S104 at a predetermined timing (for example, the period until the recording medium R is conveyed in the medium inversion conveyance unit 50 and reaches the resist roller 42).

[0111] (Step S302) The print operation control unit 101 receives the value of the waste count C calculated by the count calculation unit 133 and determines whether C>0. When C>0, the print operation control unit 101 transitions to the next step S303. On the other hand, when C≦0, toner waste is not performed, and the toner waste (b) flow ends.

[0112] (Step S303) When it is determined in step S302 above that C>0, the print operation control unit 101 further determines whether C≧2. When C≧2, the print operation control unit 101 transitions to the next step S304. On the other hand, when C<2, the print operation control unit 101 transitions to step S305.

[0113] (Step S304) When it is determined in step S302 above that C≧2, the print operation control unit 101 sets the waste execution dot number Wb = 2Cp.

[0114] (Step S305) On the other hand, when it is determined in step S302 above that C<2, the print operation control unit 101 sets the waste execution dot number Wb = Cp.

[0115] (Step S306) The print operation control unit 101 develops and discards the toner 4 on the photosensitive drum 3 in the image forming unit 2. At this time, the waste execution dot number Wb for the LED head 5 to expose the photosensitive drum 3 for toner waste is the dot number determined in step S304 or step S305 above.

[0116] The toner disposal in step S306 is performed between the end of the latent image formation on the first side shown in FIG. 6 and the start of the latent image formation on the second side. In this embodiment, for the convenience of switching the transfer voltage from Vtp to Vpn, the execution timing of the toner disposal is set to the period from the end of the toner image transfer to the first side until the recording medium R is conveyed within the medium inversion conveyance unit 50 and reaches the registration roller 42.

[0117] <Step S204> On the other hand, when it is determined in step S202 described above that the current printing is not one-page stack printing (in other words, in the case of single-sided printing or two-page stack printing), the printing operation control unit 101 executes normal printing (the process of step S102 described above) without toner disposal during the period from the end of the electrostatic latent image formation of the first-side image to the start of the electrostatic latent image formation of the second-side image.

[0118] <Step S205> The printing operation control unit 101 determines whether all the image data has been printed, in the same manner as in step S103 described above. When all the image data has been printed, the printing operation control unit 101 transitions to the next step S206. On the other hand, when there is still a printing command input to the printer 1, the printing operation control unit 101 transitions to step S201 described above.

[0119] The operations of steps S206 to S209 hereafter are the same as the operations of steps S104 to S107 described above, so the description is omitted. The operations of steps S206 to S209 are the operations from time tj to time te in FIG. 6. The count calculation unit 133 calculates the printing duty D and the waste count C using the rotational drive distance Lj and the number of light-emitting dots Pj at time tj, and the rotational drive distance Le and the number of light-emitting dots Pe at time te. When the count calculation unit 133 calculates the latest cumulative waste dot count Ws in step S209 and stores it in the storage unit 134, the printer 1 ends its operation.

[0120] As described above, in the case of double-sided printing (1-page stack), by discarding deteriorated toner between the image formation on the first side and the image formation on the second side of the recording medium R, it is possible to suppress image quality deterioration particularly when double-sided printing with a long idle running distance is continuous. The method of this embodiment is different from the method of widening the paper gap in order to execute toner discard during continuous printing, and does not impair productivity. Moreover, since the rotational driving distance of the photoreceptor drum 3 is not increased from the conventional printing operation for toner discard, it does not affect the number of printable sheets up to the service life of the image forming unit 2.

[0121] (A-3) Effects of the Embodiment According to this embodiment, the following effects are obtained.

[0122] The printer 1 performs toner discard during the period from when the electrostatic latent image on one side of the recording medium R is formed in double-sided printing until the electrostatic latent image on the other side starts to be formed. As a result, deteriorated toner in the image forming unit 2 can be effectively discharged in double-sided printing, so that the effect of suppressing the deterioration of image quality without impairing productivity can be obtained.

[0123] That is, when forming an image on the second side of the recording medium R, since the deteriorated toner is discarded, the possibility of image quality degradation is reduced.

[0124] (B) Other Embodiments The present invention is not limited to the above embodiment, and modified embodiments as exemplified below can also be cited.

[0125] (B-1) In the above-described embodiment, an electrophotographic printer is exemplified as the image forming apparatus. However, the present invention is also applicable to other apparatuses such as copiers, multifunction printers, and FAX machines.

[0126] (B-2) In the above embodiment, the method of stacking the recording medium R stacked on the paper feed tray 40 is shown as a method of stacking by so-called face-down printing in which the fixed image becomes the lower surface, but it is not limited to this embodiment. In addition to "face-down discharge" as in this embodiment, the discharge destination may be changed to use the "face-up discharge" route.

[0127] (B-3) In the above step S202, an example in which toner waste (b) is performed only in the case of double-sided printing and single-page stack printing is shown, but toner waste (b) may also be performed in the case of two-page stack printing. In this case, as described above, when two-page stack printing is performed four times, image formation on the recording medium R is performed in the order of the first side of the first sheet, the first side of the second sheet, the second side of the first sheet, the first side of the third sheet, the second side of the second sheet, the first side of the fourth sheet, the second side of the third sheet, and the second side of the fourth sheet.

[0128] Toner waste (b) (step S203 above) is executed, for example, between the first side of the second sheet and the second side of the first sheet, between the first side of the third sheet and the second side of the second sheet, and between the first side of the fourth sheet and the second side of the third sheet.

[0129] This is because in the printing of the second side in the above example, the recording medium R heated once by the fixing unit 30 in the printing of the first side comes into contact with the photosensitive drum 3, causing a temperature rise in the image forming unit 2 and making it easier to cause further toner deterioration. Therefore, there is an intention to discharge the toner that is already deteriorating to prevent further toner deterioration.

[0130] Of course, similar to toner waste between sheets, toner waste may be executed at all executable timings such as between the first side of the first sheet and the first side of the second sheet.

[0131] (B-4) In the flowchart of FIG. 5 above, toner waste (a) was performed at the timing immediately before the end of printing. As a modification, this toner waste (a) may be omitted and only toner waste (b) may be performed.

[0132] In the above example, toner disposal was performed during the period from the completion of latent image formation on the first side of the recording medium R to the start of latent image formation on the second side in double-sided printing. However, in addition to this, for example, toner disposal may be performed during the period from the transfer of the toner image to the first side of the recording medium R until the transfer of the toner image to the second side of the medium.

Explanation of Signs

[0133] 1…Printer, 2…Image forming unit, 3…Photoconductor drum, 4…Toner, 5…LED head, 6…Charging roller, 7…Developing roller, 8…Supply roller, 9…Restricting blade, 10…Cleaning unit, 11…Charge elimination light irradiation unit, 12…Toner cartridge, 13a, 13b…Waste toner conveyance unit, 14…Waste toner storage unit, 15…Stirring member, 20…Transfer roller, 30…Fixing unit, 31…Heat roller, 32…Pressing roller, 33…Fixing heater, 40…Paper feed tray, 41…Paper feed roller, 42…Registration roller, 43…Discharge roller, 44…Paper discharge unit, 50…Media inversion conveyance unit, 51…Inversion conveyance path, 52…Inversion roller, 53…Conveyance roller, 60…Media detection sensor, 60a…Sensor lever, 100…I / F control unit, 101…Printing operation control unit, 102…Drive system control unit, 103…Image formation control unit, 104…Head control unit, 105…Fixing control unit, 110…Fixing drive motor, 111…Drum drive motor, 112…Double-sided printing motor, 120…Charging voltage control unit, 121…Developing voltage control unit, 122…Supply voltage control unit, 123…Transfer voltage control unit, 131…Drum rotation amount detection unit, 132…Light emitting dot detection unit, 133…Count calculation unit, 134…Memory unit, C…Disposal count, Cp…Count conversion value, D0…Disposal reference printing duty, R…Recording medium.

Claims

1. An image carrier that carries an electrostatic latent image, A developer carrier that develops the electrostatic latent image using a developer to form a developer image, A transfer unit that transfers the developer image to a conveyed medium, When forming images on both sides of the medium, after transferring the developer image to the first side of the medium, until transferring the developer image to the second side of the medium, a control unit that performs control to discard the deteriorated developer on the image carrier An image forming apparatus, characterized by comprising the above components.

2. A developer recovery unit that recovers the developer on the image carrier, A developer storage unit that stores the developer to be supplied to the developer carrier, Further comprising a calculation unit that calculates the necessary discard amount of the developer stored in the developer storage unit, The control unit develops a component amount of the developer corresponding to the necessary discard amount calculated by the calculation unit from the developer carrier onto the image carrier to discard the developer The image forming apparatus according to claim 1, characterized by the above.

3. A fixing unit that fixes the developer image transferred to the medium onto the medium, Further comprising a reverse conveyance unit that reverses the surface of the medium fixed by the fixing unit and conveys it to the transfer unit, The control unit performs control to discard the developer while the medium is being conveyed by the reverse conveyance unit The image forming apparatus according to claim 1 or 2, characterized by the above.

4. When forming images on both sides of the medium, the control unit performs control to discard the deteriorated developer after forming the developer image to be transferred to the first side of the medium on the image carrier until forming the developer image to be transferred to the second side of the medium on the image carrier. The image forming apparatus according to claim 1 or 2, characterized by the above.

5. After transferring the developer image to the first side of the first medium, the control unit performs control to discard the deteriorated developer until transferring the developer image to the second side of the first medium. The image forming apparatus according to claim 1, characterized by the above.

6. After the developer image is transferred to the first side of the first medium and then to the first side of the second medium following the first medium, the control unit performs control to discard the deteriorated developer until transferring the developer image to the second side of the first medium. The image forming apparatus according to claim 1, characterized by the above.

Images