KR101329738B1 - An image forming apparatus and method for controlling the image forming apparatus - Google Patents

Abstract

An image forming apparatus and a method of controlling the image forming apparatus are disclosed. The image forming apparatus includes a developing roller, a toner supply roller, and a toner recovery roller, the image forming apparatus including a potential adjusting section for adjusting the potentials of the developing roller, the toner supply roller, and the toner recovery roller. The adjusting unit sets the potential of the developing roller to be higher than the potential of the toner supply roller at the time of image formation, and sets the potential of the toner supply roller to be higher than the potential of the developing roller when no image is formed. do. Therefore, according to the present invention, the toner is supplied only to the developing roller when the image is formed, and when the toner is not formed, the supply of the toner to the developing roller is interrupted, and the toner of the developing roller is recovered, so that the toner is applied to the developing roller only at the necessary timing. It can supply, and it can suppress that a toner scatters from a developing roller.

Description

An image forming apparatus and method for controlling the image forming apparatus

1 is a diagram showing the configuration of an image forming apparatus for explaining the present invention.

2 is a view showing in detail a toner supply roller and a toner recovery roller.

3 is a view showing a state in which the respective potentials of the developing roller, the toner supply roller, and the toner recovery roller are adjusted by the potential adjusting unit.

4 is a timing chart showing processing performed at image formation and at image non-formation, which is a timing chart showing one print mode in which one sheet of paper is printed.

Fig. 5 is a timing chart showing processing performed at image formation and at image non-formation, which is a timing chart showing two print modes in which two sheets of continuous printing are printed.

Fig. 6 is a diagram showing the magnitude relationship between the diameters of the toner supply roller and the toner recovery roller.

Fig. 7 is a diagram showing a relationship between gaps between a developing roller, a toner supply roller, and a toner recovery roller.

FIG. 8 is a diagram showing a configuration of an entry blocking member for preventing entry of a developer into a space between a toner supply roller and a toner recovery roller.

9 is a flowchart of a control method of an image forming apparatus for explaining the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus and a control method of the image forming apparatus, which can prevent unnecessarily scattering of toner from a developing roller.

In an electrophotographic image forming apparatus such as a laser printer, a laser fax machine or a digital copier, an electrostatic latent image in accordance with an image signal is formed by charging the photosensitive drum on the photosensitive drum and exposing the toner charged by the developer. After supplying and developing on the photosensitive drum, the developed image is transferred to a print medium such as transfer paper, and then fixed by a fixing unit to form an image.

In the image forming apparatus, a method of using a magnet roller as a method of supplying toner on a photosensitive drum is known. For example, in a device using a two-component developer consisting of a toner and a carrier, two magnetic rollers are used, one of the magnetic rollers is used to supply toner to the developing roller, and the other of the magnetic rollers is used from the developing roller. It is composed of a device for removing excess toner.

However, in the above conventional technique, since toner is always supplied to the developing roller, the toner adhered to the developing roller easily falls off, and the toner scatters in the apparatus and contaminates the apparatus.

In particular, the toner adheres to the surface of the photoconductor by being negatively charged. If a predetermined time elapses while the toner is attached to the developing roller, the toner is no longer charged. Therefore, when the operation of the image forming apparatus is stopped or the like, there is a problem that the toner easily falls off the developing roller with time. In addition, if the image forming apparatus is moved or the vibration is applied to the image forming apparatus while the toner is attached to the developing roller, a problem occurs that the toner falls from the developing roller. In addition, in the image forming apparatus using the two-component developer, when the carrier held by the magnetic roller falls from the magnetic roller, there is also a problem that the carrier is adhered on the photosensitive drum to deteriorate the image by performing the carrier development.

The technical problem to be solved by the present invention is that toner is supplied only to the developing roller when an image is formed, and when the toner is not formed, the supply of toner to the developing roller is interrupted and the toner of the developing roller is recovered, thereby toner is supplied to the developing roller only at a necessary timing. The present invention provides an image forming apparatus and a control method of the image forming apparatus, which can supply the ink and suppress the scattering of the toner from the developing roller.

In order to achieve the above object, the image forming apparatus according to the present invention comprises a developing roller, a toner supply roller, and a toner recovery roller, wherein the potentials of the developing roller, the toner supply roller, and the toner recovery roller are changed. And a potential adjusting portion for adjusting, wherein the potential adjusting portion sets the potential of the developing roller to be higher than the potential of the toner supply roller at the time of image formation, and sets the potential of the toner supply roller when the image is not formed. It is characterized by setting higher than the potential of the roller.

In order to achieve the above another object, the control method of the image forming apparatus according to the present invention comprises the steps of setting the potential of the developing roller higher than the potential of the toner supply roller at the time of image formation; And setting the potential of the toner supply roller higher than the potential of the developing roller when no image is formed, wherein the potential of the toner recovery roller is set when the image is formed and when no image is formed. It is characterized by setting higher than the potential of.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are assigned to components having substantially the same functional configuration.

First, a first embodiment of the present invention will be described.

1 is a diagram showing the configuration of an image forming apparatus 10 according to the present invention. The image forming apparatus 10 according to the present embodiment scan-exposes the laser beam 12 modulated according to the image signal to the photosensitive drum 14, and print media 15 such as paper or plastic sheet by an electrophotographic method. Will output The image forming apparatus 10 includes a laser printer, a laser fax machine, a digital copier, and the like.

The image forming apparatus 10 prints using a two-component developer consisting of a toner and a carrier, and is, for example, a high-speed printer capable of printing on A4 paper at a speed of about 60 [ppm] (pages / minute). To function.

The image forming apparatus 10 includes a laser exposure unit (not shown) that outputs a laser beam 12. The laser exposure unit scans the laser beam 12 formed in a very small spot on a straight line parallel to the axis of rotation of the photosensitive drum 14 at an exposure position A on the photosensitive drum 14 in a predetermined direction.

When the laser beam 12 is scanned on the surface of the photoconductor drum 14, an electrostatic potential is formed relative to the portion where the exposed portion of the photoconductor drum 14 is not exposed.

The developing roller 16 is disposed at the lower side of the exposure position A on the photosensitive drum 14. In addition, the developing unit 18 is disposed adjacent to the developing roller 16. In the developing unit 18, a two-component developer consisting of toner and a carrier is stored. The toner in the developing unit 18 is supplied to the surface of the developing roller 16 by the toner supply roller 24 in the developing unit 18, and is supplied to the surface of the photosensitive drum.

In the developing unit 18, a two-component developer T composed of a powder toner having a predetermined color and a metal powder carrier is stored. The toner contains a pigment, CCA, PMMA, or the like in polyester particles having a diameter of about 7 to 8 [탆]. The carrier is coated with a silicon coating on ferrite particles having a diameter of about 35 to 60 [nm]. The developing unit 18 is provided with a first stirrer 20 and a second stirrer 22 for stirring the toner and the carrier. In the developing unit 18, a toner supply roller 24 and a toner recovery roller 30 are provided at positions close to the developing roller 16.

2 is a view showing in detail the toner supply roller 24 and the toner recovery roller 30. As shown in FIG. The toner supply roller 24 and the toner recovery roller 30 are constituted by magnetic rollers. That is, the toner supply roller 24 is composed of a magnet body 26 fixed in a non-rotating state and a sleeve 28 installed around the magnet body 26 to rotate in the direction of the arrow. The toner recovery roller 30 is composed of a magnet body 32 fixed in a non-rotating state and a sleeve 34 provided around the magnet body 32 to rotate in the direction of the arrow.

As shown in FIG. 2, a plurality of magnetic poles S1, N1, N2 are formed in the rotational direction on the outer peripheral portion of the magnet body 26 of the toner supply roller 24. As shown in FIG. Further, a plurality of magnetic poles S1, N1, N2 are formed in the rotational direction on the outer circumferential portion of the magnet body 32 of the toner recovery roller 30.

When the two-component developer T is stirred in the developing unit 18, the toner is negatively charged and the carrier is positively charged. At this time, the charge amount of the toner is, for example, about -25 to -15 [μC / g]. The negatively charged toner thereby adheres to the surface of the positively charged carrier. At this time, if the weight of the toner stored in the developing unit 18 is about 6 to 10 [%], the toner is in a state of being attached to about 60 to 80 [%] of the surface area of the carrier.

The carrier to which toner is attached is sent to the vicinity of the toner supply roller 24 by the rotation of the stirrer 22. Then, the carrier to which toner is attached by the magnetic force of the magnet body 26 of the toner supply roller 24 is attached to the sleeve 28 of the toner supply roller 24. Thus, the carrier is attached in a layered manner on the sleeve 28 of the toner supply roller 24, and a so-called magnetic brush is formed by the layer of the carrier.

The sleeve 28 of the toner supply roller 24 and the sleeve 34 of the toner recovery roller 30 rotate in the direction of the arrows shown in FIGS. 1 and 2. The carrier attached on the sleeve 28 of the toner supply roller 24 is directed toward the developing roller 16 by the rotation of the sleeve 28.

As shown in FIG. 1, the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are connected to the potential adjusting unit 31. The electric potential adjusting part 31 adjusts the electric potential of each of the developing roller 16, the toner supply roller 24, and the toner recovery roller 30. As shown in FIG.

3 is a diagram showing a state in which the potentials of the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are adjusted by the potential adjusting unit 31. Here, Fig. 3A shows the potential of each roller at the time of image formation, and Fig. 3B shows the potential of each roller when no image is formed.

3 (A) and 3 (B), V0 and V1 represent potentials of the photosensitive drum, where V1 represents the potential of the exposed portion by the laser beam 12, and V0 represents the potential of the non-exposed portion. It is shown. Vsp denotes the potential of the sleeve 26 of the toner supply roller 24, Vmid denotes the potential of the developing roller 16, and Vwi denotes the potential of the sleeve 34 of the toner recovery roller 30.

In this embodiment, a predetermined gap is provided between the surface of the developing roller 16 and the surface of the photosensitive drum 14, and the toner of the developing roller 16 is applied to the photosensitive drum 14 by applying a high frequency voltage to the developing roller 16. Toner is adhered to the exposed portion of the photosensitive drum 14. Vmid shown in FIG. 3 has shown the direct current component of the electric potential of the developing roller 16. As shown in FIG.

In the examples of Figs. 3A and 3B, the values of V0, V1, Vmid, and Vwi are the same in both image formation and non-image formation. On the other hand, the value of Vsp is -500 [V] at the time of image formation, -200 [V] at the time of not forming an image, and is different from each other. As described above, in this embodiment, the toner supply to the developing roller 16 and the recovery of the toner from the developing roller 16 are properly performed by applying different potentials at the time of image formation and at non-image formation.

First, the case where the toner is supplied to the developing roller 16 at the time of image formation will be described. As shown in Fig. 3A, at the time of image formation, the potential of the developing roller 16 is set higher than the potential of the toner supply roller 24, so that Vsp = -500 [V], Vmid = -350 [V]. Becomes

As described above, the carrier attached to the sleeve 28 of the toner supply roller 24 together with the toner is directed toward the developing roller 16 by the rotation of the sleeve 28. When the toner and the carrier approach the developing roller 16, the potential of the developing roller 16 (-350 [V]) is higher than the potential of the sleeve 28 of the toner supply roller 24 (-500 [V]). The negatively charged toner is separated from the carrier and adhered to the surface of the developing roller 16. On the other hand, the carrier is still attached to the sleeve 28 by the magnetic force of the magnet body 26. Thus, the toner can be reliably supplied to the surface of the developing roller 16 by making the potential Vmid of the developing roller 16 higher than the potential Vsp of the toner supply roller 24.

1 and 2, the photosensitive drum 14 and the developing roller 16 rotate in the direction of the arrow. The toner attached to the developing roller 16 is supplied toward the photosensitive drum 14 in accordance with the rotation of the developing roller 16. In the photosensitive drum 14, the potential V1 of the exposed portion by the laser beam 12 becomes -50 [V], which is higher than the potential Vmid (= -350 [V]) of the developing roller 16. The toner corresponding to the exposed portion of the photosensitive drum 14 of the toner attached on the roller 16 is blown off and attached to the exposed portion on the photosensitive drum 14. Therefore, when the photosensitive drum 14 supplied with the toner to the exposed portion contacts the print medium 15, printing corresponding to the exposed portion can be performed.

Since the toner attached to the position corresponding to the exposed portion on the developing roller 16 is supplied onto the photosensitive drum 14, the toner of a portion corresponding to the non-exposed portion of the photosensitive drum 14 is deposited on the developing roller 16. Remaining. The remaining toner is sent toward the toner recovery roller 30 as the developing roller 16 rotates.

On the other hand, after the toner is supplied from the toner supply roller 24 to the developing roller 16, the carrier remaining on the sleeve 28 of the toner supply roller 24 is subjected to the toner recovery roller ( Is sent to page 30). 1 and 2, in the outer circumferential direction of the developing roller 16, the S1 pole of the magnet body 32 is formed at a position facing the N1 pole of the magnet body 26, and the magnet body 26 is formed. The magnetic field is generated in a direction connecting the N1 pole of the pole and the S1 pole of the magnet body 32.

For this reason, the carrier remaining in the sleeve 28 of the toner supply roller 24 approaches the sleeve 34 as the sleeve 28 rotates, so that the N1 pole of the magnet body 26 and the S1 of the magnet body 32 are rotated. Flying over the magnetic field connecting the poles is sent over the sleeve (34).

On the other hand, in the magnet body 26 of the toner supply roller 24, the N2 pole is formed in the lower side of the rotation direction of the sleeve 28 with respect to the N1 pole. Further, the N1 pole of the magnet body 32 is formed at a position facing the N2 pole of the magnet body 26. For this reason, the magnetic field which repels between the N1 pole and N2 pole of the magnet body 26 generate | occur | produces, and the magnetic field which repels between the N2 pole of the magnet body 26 and the N1 pole of the magnet body 32 arises.

For this reason, it is suppressed that the carrier adhered to the sleeve 28 enters the area | region of these repulsive magnetic fields. Thus, the carrier attached to the sleeve 28 is reliably sent over the sleeve 34 without being sent to the stirrer 22 side.

After the toner is supplied to the photosensitive drum 14, the toner remaining on the developing roller 16 is directed toward the toner recovery roller 30 as the developing roller 16 rotates. As shown in Fig. 3A, the potential of the sleeve 34 is 0 [V], and the potential of the developing roller 16 is -350 [V]. Therefore, since the dislocation of the sleeve 34 is higher than the dislocation of the developing roller 16, the toner remaining in the developing roller 16 and negatively charged moves toward the sleeve 34 having a high dislocation so as to be placed on the sleeve 34. It is attached to a carrier that is positively charged. At this time, the toner on the developing roller 16 is surely attached to the carrier on the sleeve 34 because no toner is already attached to the carrier sent from the sleeve 28 to the sleeve 34.

The carrier with the toner sent from the developing roller 16 attached on the sleeve 34 moves in the rotational direction in accordance with the rotation of the sleeve 34. Then, the carrier on the sleeve 34 is released from the sleeve 34 together with the toner adhered to the developing unit 18 at the rotational position where the magnetic force of the magnet body 32 is weakened. The toner and the carrier returned into the developing unit 18 are stirred again and sent to the feed roller 24.

As described above, at the time of forming an image, Vsp> Vmid> Vwi supplies toner from the toner supply roller 24 to the developing roller 16, and reliably recovers the toner from the developing roller 16 to the toner recovery roller 30. You can do it.

In particular, when the recovery of the toner from the developing roller 16 becomes insufficient, the residual toner passes on the developing roller 16 toward the toner supply roller 24 through the position of the toner recovery roller 30. In this case, the toner remaining on the developing roller 16 and the toner newly supplied from the toner supply roller 24 are mixed on the developing roller 16 and the charging state of the toner becomes unstable, so that the exposed portion of the photosensitive drum 14 Deterioration of development easily occurs because the supply of toner to the resin is not made correctly. In this embodiment, since the potential of the toner recovery roller 30 is set higher than the potential of the developing roller 16, the toner remaining on the developing roller 16 can be reliably recovered, and the occurrence of development deterioration can be suppressed. have.

Next, an operation performed when no image is formed will be described. If toner remains on the developing roller 16 when the image is not formed, the toner on the developing roller 16 may be scattered by vibration or the like and adhered to or around the photosensitive drum 14. For example, when toner adheres on the photosensitive drum 14, image staining and the like easily occur at the next printing. For this reason, at the time of non-image formation, as shown in Fig. 3B, the toner supply roller 24 has a potential higher than that of the development roller 16 so that the toner from the toner supply roller 24 to the development roller 16 is increased. To cut off the supply of

That is, as shown in Fig. 3B, when the image is not formed, the potential Vsp of the sleeve 28 of the toner supply roller 24 becomes -200 [V] and the potential of the developing roller 16 (Vmid) becomes -350 [V]. For this reason, even if the toner adhered with the carrier on the sleeve 28 is sent near the surface of the developing roller 16 by the rotation of the sleeve 28, the negatively charged toner has a lower potential than the sleeve 28. The toner supply from the toner supply roller 24 to the development roller 16 is blocked because it does not move over the development roller 16.

On the other hand, the potential Vwi of the toner recovery roller 30 becomes 0 [V], and the potential of the developing roller 16 and the toner recovery roller 30 is maintained at the same setting as in Fig. 3A. Thus, the toner remaining on the developing roller 16 moves toward the toner recovery roller 30 having a higher potential and is recovered in the developing unit 18 together with the carrier.

Therefore, the toner on the developing roller 16 is fully developed by rotating the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 by a predetermined amount in the state where the potential shown in Fig. 3B is applied. It can be recovered in the unit 18.

As described above, when the image is not formed, Vmid > Vsp > Vwi blocks the toner supply from the toner supply roller 24 to the developing roller 16, and at the same time, the development roller 16 to the toner recovery roller 30. The toner can be recovered so that all of the toner on the developing roller 16 can be recovered. At this time, by setting Vsp ≧ Vwi, the movement of the toner from the toner supply roller 24 directly to the toner recovery roller 30 can be suppressed, thereby preventing the supply efficiency of the toner to the developing roller 16 from being lowered. When a predetermined time elapses while the toner is attached to the developing roller 16, it is expected that the charges charged in the toner are lost and the toner scatters on the developing roller 16 to contaminate the inside of the apparatus. In this embodiment, all the toner on the developing roller 16 can be recovered at the time of non-image formation, so that the occurrence of such contamination can be reliably suppressed.

Supplying the toner above the developing roller 16 is preferably performed in correspondence with the timing of printing on the printing medium 15. For example, in the case of continuously printing on a plurality of print media 15, a developing roller (not shown) may be supplied to the exposed portion of the photosensitive drum 14 at a timing at which the print media 15 and the photosensitive drum 14 are in contact with each other. 16) It is preferable to supply the toner above. Thus, for example, after the contact between the first sent print medium 15 and the photosensitive drum 14 is dropped, the next time the printed medium 15 is brought into contact with the photosensitive drum 14, There is no need to supply the toner, so it is not necessary to supply the toner on the developing roller 16.

According to the configuration of this embodiment, the supply and recovery timing of the toner can be freely controlled by controlling the potential of each roller, so that the toner on the developing roller 16 corresponds to the timing at which printing or the like is performed on the printing medium 15. Can be supplied. This makes it possible to minimize the supply of toner onto the developing roller 16 to a minimum and to reliably suppress contamination in the apparatus as toner scatters from the surface of the developing roller 16.

Next, processing performed at the time of image formation and at the time of image non-formation will be described based on the timing charts of FIGS. 4 and 5. 4 shows one print mode in which one sheet of paper is printed. 5 shows a two-print mode in which two sheets of paper are continuously printed.

First, one print mode will be described based on FIG. 4. First, the power supply of the main motor is turned on at time t1, and the driving parts of the photosensitive drum 14, the developing roller 16, the supply roller 24, the recovery roller 30, and the like are driven.

At time t2, the power supply of the charging device for uniformly charging the photosensitive drum 14 is turned on. This charging device includes a charging roller in contact with the photosensitive drum 14. At time t3, the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are set to a predetermined potential. Here, Vmid = -350 [V], Vsp = Vs2 = -200 [V], Vwi = Vw2 = O [V], and the potential of each roller is set at the time of image forming shown in Fig. 3B. Is set to state. In addition, before the time t3, the potentials to the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are turned off.

At time t4, exposure to the photosensitive drum 14 is performed by the laser beam 12. At time t5, Vsp = Vs1 = -500 [V] and Vwi = Vw1 [V]. Here, Vs2 becomes a potential of Vmid or less (Vs2 ≤ Vmid). As a result, the magnitude relationship between Vmid, Vsp, and Vwi is the same as in FIG. 3 (A). Toner is supplied from the toner supply roller 24 to the developing roller 16 and the toner remaining on the developing roller 16 is retained. It is recovered by 30. Thus, the toner supplied to the developing roll 16 is attached to the exposed portion of the photosensitive drum 14, and image formation to the print medium 15 is performed.

At time t6, the exposure to the photosensitive drum 14 is finished. At time t7, Vsp = Vs2 = -200 [V], Vwi = Vw2 = O [V], and the potential of each roller is set to the state at the time of non-image formation shown in Fig. 3B. .

At time t8, the power supply of the charging device is turned off. At time t9, the potentials of the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are turned off, and at time t10, the power of the main motor is turned off.

As described above, in the single print mode in which only one sheet of paper is printed, the potential of the magnitude relationship shown in FIG. 3 (A) is set only at the timing of image formation on the sheet, and shown in FIG. 3 (B) at the timing before and after that. One magnitude relation potential is set. Therefore, the toner supply onto the developing roller 16 can be performed only at the timing of forming the image.

Next, the two print modes will be described based on FIG. 5. First, at time t11, the power supply of the main motor is turned on to drive the driving parts of the photosensitive drum 14, the developing roller 16, the toner supply roller 24, the toner recovery roller 30, and the like.

At time t12, the power supply of the charging device for uniformly charging the photosensitive drum 14 is turned on. At time t13, the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are set to a predetermined potential. Here, Vmid = -350 [V], Vsp = Vs2 = -200 [V], Vwi = Vw2 = O [V], and the potential of each roller is at the time of non-image formation shown in Fig. 3B. Is set to the state of. In addition, before the time t13, the potentials to the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are turned off.

At time t14, exposure to the photosensitive drum 14 is performed by the laser beam 12. At time t15, Vsp = Vs1 = -500 [V] and Vwi = Vw1 [V]. Here, Vs2 is a potential of Vmid or less (Vs2? Vmid). As a result, the magnitude relationship between Vmid, Vsp, and Vwi is the same as in FIG. 3A, toner is supplied from the toner supply roller 24 to the developing roller 16, and the toner remaining on the developing roller 16 is recovered toner. It is collect | recovered by the roller 30. Thus, the toner supplied on the developing roller 16 is attached to the exposed portion of the photosensitive drum 14 so that image formation on the first sheet (print medium 15) is performed.

When the image formation on the first sheet is completed, the exposure to the photosensitive drum 14 is terminated at time t16. At time t17, Vsp = Vs2 = -200 [V], Vwi = Vw2 = 0 [V], and the potential of each roller is set to the state at the time of image non-formation shown in Fig. 3B.

At time t18, since the image is formed on the second sheet, exposure to the photosensitive drum 14 is performed by the laser beam 12. As shown in FIG. At time t19, Vsp = Vs1 = -50O [V] and Vwi = Vw1 [V]. As a result, the magnitude relationship between Vmid, Vsp, and Vwi is the same as in FIG. 3A so that toner is supplied from the toner supply roller 24 to the developing roller 16, and the toner remaining on the developing roller 16 is recovered. It is collect | recovered by the roller 30. Thus, the toner supplied on the developing roller 16 is attached to the exposed portion of the photosensitive drum 14, and image formation on the first sheet (print medium 15) is performed.

At time t20, the exposure to the photosensitive drum 14 corresponding to image formation on the second sheet is terminated. At time t21, Vsp = Vs2 = -200 [V] and Vwi = Vw2 = 0 [V], and the potential of each roller is set to the state at the time of non-image formation shown in Fig. 3B.

At time t22, the power supply of the charging device is turned off. At time t23, the potentials of the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 are turned off, and at time t24, the power supply of the main motor is turned off.

In this manner, even in the two-print mode in which only two sheets of paper are printed, each roller has the large and small potentials shown in FIG. 3 (B) until image formation of the second sheet is performed after image formation of the first sheet is performed. Is set. Therefore, the toner supply onto the developing roller 16 can be performed only at the timing of forming the image.

Next, the magnitude relationship between the diameter of the toner supply roller 24 and the toner recovery roller 30 will be described based on FIG. 6. As shown in FIG. 6, in this embodiment, a relationship of Ds ≧ Dw is established between the outer diameter Ds of the toner supply roller 24 and the outer diameter Dw of the toner recovery roller 30.

Thereby, the volume of the magnet body 26 can be increased compared with the magnet body 32, and the magnetic force of the magnet body 26 can be made stronger than the magnetic force of the magnet body 32. FIG. Thus, the carrier can be securely attached to the sleeve 28 of the toner supply roller 24. Therefore, the carrier can be prevented from adhering to the developing roller 16 from the sleeve, and the carrier can be supplied over the photosensitive drum 14 to reliably suppress the occurrence of so-called carrier development.

On the other hand, with regard to the toner recovery roller 30, the magnetic body 32 should be provided with a magnetic force such that a carrier is attached on the sleeve 34 and the magnetic brush is regulated, and the outer diameter Dw is the outer diameter Ds. It can be made smaller than). In the case where the magnetic force of the magnet body 32 is minimized, even if the carrier is detached from the sleeve 34, the outer diameter Ds is increased on the lower side in the rotational direction of the developing roller 16 to increase the magnetic force. Since the toner supply roller 24 having the magnet body 26 is disposed, the carrier detached from the sleeve 34 is adsorbed to the sleeve 26 of the toner supply roller 24, and the carrier is lower-side photosensitive drum 14 It is suppressed to send more toward). Therefore, the carrier can be sent to the photosensitive drum 14 to reliably suppress the occurrence of carrier phenomenon.

Therefore, by setting Ds ≧ Dw, it is possible to reliably suppress the carrier from being sent toward the lower side of the toner supply roller 24, and as a result, the deterioration of printing due to the adherence of the carrier to the photosensitive drum 14 can be suppressed. In addition, since the diameter of the toner recovery roller 30 can be suppressed to a minimum, the image forming apparatus 10 can be miniaturized. Moreover, since the magnetic force of the magnet body 26 and the magnet body 32 can be suppressed to the minimum, manufacturing cost can be reduced.

Next, the relationship between the gaps between the developing roller 16, the toner supply roller 24, and the toner recovery roller 30 will be described based on FIG. 7. As shown in FIG. 7, the gap between the developing roller 16 and the toner supply roller 24 is Gs-d, and the gap between the developing roller 16 and the toner recovery roller 30 is Gw-d and the toner supply roller ( If the gap between 24) and the toner recovery roller 30 is referred to as Gs-w, in this embodiment, the relationship of Gs-w≥Gs-d and Gs-w≥Gw-d is established.

That is, the gap Gs-w of the toner supply roller 24 and the toner recovery roller 30 is equal to or more than the gap Gs-d of the development roller 16 and the toner supply roller 24, and the development roller. It becomes more than the gap Gw-d of the 16 and the toner collection roller 30. The toner supply roller 24 and the toner recovery roller (when the potential shown in FIG. 3 is applied to each roller by making the gap Gs-w of the toner supply roller 24 and the toner recovery roller 30 more than the other gaps ( The voltage leaks out between 30), and it is possible to suppress the movement of the toner between the toner supply roller 24 and the toner recovery roller 30. Therefore, the toner can be moved only between the toner supply roller 24 and the developing roller 16 or between the developing roller 16 and the toner recovery roller 30, so that the toner moves to an unnecessary area and contamination occurs in the apparatus. Can be suppressed.

Next, based on FIG. 8, the structure which prevents a carrier and toner from moving to the space between the toner supply roller 24 and the toner collection roller 30 is demonstrated. In the space on the side of the agitator 22 between the toner supply roller 24 and the toner recovery roller 30, a magnetic field caused by the N 2 pole of the magnet body 26 and a magnetic field caused by the N 1 pole of the magnet body 32 are generated. . For this reason, when a carrier scatters toward this magnetic field from the stirrer 22 side, it is anticipated that a carrier will be sent to the vicinity of the developing roller 16. FIG. In this case, because the toner is attached to the carrier, the toner is supplied onto the developing roller 16 at the top of the toner supply roller 24. When toner is supplied from the toner supply roller 24 to the developing roller 16 in this state again, the charging state of the toner becomes unstable, which causes development deterioration.

In the structure shown in FIG. 8, the developer entry | blocking member 36 of the developer is provided in the space between the toner supply roller 24 and the toner collection roller 30. As shown in FIG. More specifically, the entry blocking member 36 is provided at a position corresponding to the repulsive magnetic field between the N 2 pole of the magnet body 26 and the N 1 pole of the magnet body 32. In this way, the movement of the toner and the carrier which intrudes toward the developing roller 16 through the space between the toner supply roller 24 and the toner recovery roller 30 on the stirrer 22 side is prevented by the entry blocking member 36. Therefore, it is possible to prevent the toner from flowing into the space between the toner supply roller 24 and the toner recovery roller 30, thereby causing deterioration of development.

9 is a flowchart of a control method of an image forming apparatus for explaining the present invention.

First, at the time of image formation, the potential of the developing roller is set higher than the potential of the toner supply roller (step 100). When no image is formed, the potential of the toner supply roller is set higher than the potential of the developing roller (step 102). On the other hand, when the image is formed and when no image is formed, the potential of the toner recovery roller is always set higher than the potential of the developing roller.

Such an image forming apparatus and a method of controlling the image forming apparatus of the present invention have been described with reference to the embodiments illustrated in the drawings for clarity of understanding, but these are merely exemplary, and those skilled in the art can make various modifications therefrom. And other equivalent embodiments are possible. Accordingly, the true scope of the present invention should be determined by the appended claims.

In the image forming apparatus and the control method of the image forming apparatus according to the present invention, since the potential of the developing roller is set higher than that of the toner supply roller at the time of image formation, the toner negatively charged from the toner supply roller can be easily supplied to the developing roller. When it is possible to supply and when no image is formed, the potential of the toner supply roller is set higher than the potential of the developing roller so that supply of the toner from the toner supply roller to the developing roller is blocked. In addition, since the potential of the toner recovery roller is set higher than that of the developing roller at the time of image formation and non-image formation, the excess toner on the developing roller is easily recovered by the toner recovery roller. Therefore, the toner is supplied to the developing roller only when the image is formed, and when the toner is not formed, the toner supply to the developing roller is blocked, and the toner of the developing roller is recovered, so that the toner can be supplied to the developing roller only at the necessary timing. It is possible to suppress the toner from scattering from the developing roller.

Claims (5)

An image forming apparatus comprising a developing roller, a toner supply roller, and a toner recovery roller, A potential adjusting unit for adjusting the potential of the developing roller, the toner supply roller, and the toner recovery roller; The potential adjusting section sets the potential of the developing roller to be higher than the potential of the toner supply roller when forming an image, and sets the potential of the toner supply roller to be higher than the potential of the developing roller when not forming an image. The potential of the toner recovery roller is set higher than that of the developing roller when the image is formed and when the image is not formed; And the magnetic force of the magnet body constituting the toner supply roller is greater than the magnetic force of the magnet body constituting the toner recovery roller. According to claim 1, wherein the potential adjusting unit And an electric potential of the toner recovery roller is set higher than that of the toner supply roller at the time of image formation and when no image is formed. The method of claim 1, wherein the toner supply roller, And an outer diameter of the toner supply roller is larger than an outer diameter of the toner recovery roller in the lower portion of the toner recovery roller with respect to the rotational direction of the developing roller. 4. The method according to any one of claims 1 to 3, And an entry preventing member for preventing entry of toner or carrier between the toner supply roller and the toner recovery roller, between the toner supply roller and the toner recovery roller. A control method of an image forming apparatus comprising a developing roller, a toner supply roller, and a toner recovery roller, During image formation, setting a potential of the developing roller higher than a potential of the toner supply roller; And When not forming an image, setting a potential of the toner supply roller higher than a potential of the developing roller, When the image is formed and when the image is not formed, the potential of the toner recovery roller is set higher than that of the developing roller, The magnetic force of the magnet body constituting the toner supply roller is larger than the magnetic force of the magnet body constituting the toner recovery roller.

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