JP2014010340A - Bias control device, developing device, process cartridge and image forming apparatus - Google Patents

Abstract

Provided is a developer replenishment control device that improves the uniformity of the developer in the developing device after replenishment and suppresses wasteful developer consumption and image quality degradation.
A bias is supplied to a developer carrier 35 and a supply member 36 provided in a developing device 5 that is supplied with a developer T1 for replenishment from a developer supply container 4, so that the developer carrier side is supplied from the supply member side. The bias control device 200 that moves the developer T to the developing device from the developer supply container until the predetermined period t elapses from the start of supply of the developer T1 for supply from the developer supply container to the developing device. Control means 100 for normally charging the reversely charged developer between the developer T1 and the developer T deteriorated in the developing device.
[Selection] Figure 2

Description

  The present invention relates to a bias control device for a developing device used in an image forming apparatus such as a printer, a facsimile machine, a copying machine, or a multi-function machine having a plurality of functions, and a process cartridge and an image forming apparatus including the developing device.

As market requirements for electrophotographic image forming apparatuses, downsizing of the apparatus main body and low running cost are high. As a recent trend, a process cartridge in which a developing portion and a photosensitive portion are integrated has been proposed. In order to reduce the running cost, the durability of the functional parts of the process cartridge has been improved and the frequency of replacement of the process cartridge by the user has been reduced. Is stored in the process cartridge, the process cartridge becomes large, and the size of the image forming apparatus main body increases.
Therefore, a toner cartridge system that is a developer storage container in which the amount of toner in the process cartridge is reduced and can be replaced independently from the image forming apparatus main body, and the user replaces only the toner has been proposed. It is already known as a technology for achieving both low running costs.
Patent Document 1 discloses a configuration in which the frequency and amplitude of the AC component of the developing bias are switched until a predetermined period has elapsed since the toner was replenished for the purpose of suppressing scumming and wasteful consumption of toner after toner replenishment. Has been.
A configuration is disclosed.

In the conventional process cartridge, the developer in the process cartridge has been used up, and the entire amount of the developer has been replaced with the replacement of the process cartridge. However, when the toner cartridge is replaced, the developer is subjected to physical and electrostatic stress remaining in the developing device. When the new developer in the toner cartridge is mixed with the developer, the charging characteristics of the developer fluctuate significantly, and the developer with reduced charging property adheres to the non-printing part, and wastes the developer. In addition, when the chargeability deteriorates, there is a problem that an abnormal image is formed by visually recognizing the developer in the non-printing area.
In Patent Document 1, the development bias is switched and controlled after toner replenishment. However, since the development bias affects the image density, there is a restriction that the development bias must be changed within a range where the image density does not change. There is a problem that the effect is small in that it suppresses background contamination and wasteful consumption of toner, and a sufficient effect cannot be obtained.

The present invention improves the uniformity of a developer on a developing device after replenishment, in particular, a developer carrying body without affecting the image density, and suppresses wasteful developer consumption and image quality degradation. It is an object of the present invention to provide a supply control device and an image forming device.
An object of the present invention is to avoid toner consumption and generation of a background image.

  The supply formed between the supply member and the developer carrier by supplying a bias to the developer carrier and the supply member provided in the developing device in which the developer is supplied from the developer supply container according to the present invention. The bias control device that moves the developer from the supply member side to the developer carrier side at the nip develops from the developer supply container until a predetermined period has elapsed since the developer supply from the developer supply container to the development device. And a control means for normally charging the reversely charged developer between the developer and the developer deteriorated in the developing device.

  According to the present invention, development that is reversely charged in the developer from the developer supply container and the developer deteriorated in the developing apparatus until a predetermined period has elapsed since the developer supply from the developer supply container to the developing device has elapsed. Since the developer is normally charged, the coulombic force between the reversely charged toner and the normally charged toner generated by mixing the replenished highly charged developer and the deteriorated and less charged developer existing in the developing device. The normally charged toner in the combined toner combined by the above is not attracted to the supply member and therefore hardly moves to the developer carrying member. In many cases, the reversely charged toner in the combined toner is normally charged by frictional charging with the developer carrier at the supply nip formed by the developer carrier and the supply member. When the reversely charged toner is charged to the polarity of the normal charge, the coulomb attractive force that has been acting between the normal charged toner and the reversely charged toner of the combined toner is separated as a repulsive force. Then, the toner that has become a normally charged toner adheres to the developer carrier and is carried. For this reason, even if developers with different deterioration states are mixed in the developing device after replenishment, sufficient uniformity of the developer can be maintained, and wasteful consumption of the developer and deterioration of image quality such as background stains are suppressed. Can do.

1 is a main part configuration diagram showing an embodiment of an image forming apparatus according to the present invention. The enlarged view which shows one form of the bias control apparatus which concerns on a process cartridge and this invention. The enlarged view which shows another form of a developing agent storage container. The characteristic view which shows 1st Embodiment of bias change control. The flowchart which shows the control content of 1st Embodiment. The characteristic view which shows 2nd Embodiment of bias change control. The flowchart which shows the control content of 2nd Embodiment. The figure which shows the experimental result by 1st, 2nd embodiment.

  A feature of the present invention is that, in an electrophotographic image forming apparatus having a developing device and a developer container, a bias supplied to a supply member for a predetermined period after supplying the developer to the developing device is applied to the developer carrier. Then, a bias having a polarity opposite to the normal charge polarity of the developer (for example, developer carrier -200 V, supply member -100 V) is applied. If the bias is changed at such a time, the normally charged toner of the combined toner is strongly attracted to the supply member in the supply nip formed at the opposed portion between the supply member and the developer support, and thus moves to the developer support. The reversely charged toner is more regularly charged due to frictional charging with the developer carrier at the supply nip. For this reason, when charged to the polarity of the normal charge, the Coulomb attractive force that has been acting between the normal charge toner and the reverse charge toner constituting the combined toner until then becomes a repulsive force, and is attached to the developer carrier and carried. It is a feature.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the overall configuration and operation of the image forming apparatus will be described, and then the bias control apparatus will be described.
FIG. 1 shows an embodiment of a tandem type image forming apparatus to which the present invention is applied. The image forming apparatus is of an electrophotographic system using a toner that is a non-magnetic, one-component developer of yellow, magenta, cyan, and black, and is capable of full color printing. The image forming apparatus includes process cartridges 10Y, 10M, 10C, and 10K corresponding to the respective colors in an image forming apparatus main body (not shown). Since the configuration corresponding to each color is basically the same configuration, in FIG. 1, the configuration corresponding to one color will be described with reference numerals, and the description and reference for other colors will be omitted. The members corresponding to yellow, magenta, cyan, and black are distinguished by being assigned (Y, M, C, K).

  The process cartridge 10K includes a photosensitive drum 1 that is an image carrier. Around the photosensitive drum 1, a charging means 2 for charging the drum surface, and a toner image as a charged developer is formed on a latent image formed on the photosensitive drum surface to form a toner image. The developing device 5, the first transfer means 7 for transferring the toner image formed on the photosensitive drum to the endless intermediate transfer belt 13 serving as an intermediate transfer member, and the residual toner on the photosensitive drum 1 is removed. A cleaning device 11 is arranged in order in the rotation direction of the photosensitive drum 1. On the photosensitive drum 1 between the charging means 2 and the developing device 5, exposure light 3 such as a laser beam for forming a latent image on a portion uniformly charged by the charging means 2 is not shown. Irradiated from. Above the developing device 5, a toner cartridge 4 serving as a developer storage container containing toner (hereinafter referred to as “replenishment toner” T <b> 1) that is a non-magnetic, one-component developer is contained in the developing device 5. It is detachable and replaceable. In this embodiment, the toner cartridge 4 is configured to directly supply the replenishment toner T1 into the developing device 5, but a replenishment path for connecting the toner cartridge 4 and the developing device 5 is provided in the main body of the image forming apparatus. The replenishment toner T1 in 4 may be replenished into the developing device 5 through this replenishment path, and the toner cartridge 4 and the developing device 5 are not limited to an integrated type.

  In the tandem type electrophotographic system, monochromatic toner images such as black, magenta, cyan, and yellow are mainly formed on the surface of each photosensitive drum 1. In such a configuration, when image formation is performed by a negative-positive method (lowering the exposure portion potential and attaching the toner), the photosensitive drum whose surface is uniformly negatively charged by the charging roller constituting the charging unit 2 In 1, an electrostatic latent image is formed on the surface of the photosensitive drum by the exposure light 3, and a toner T is attached to the surface of the photosensitive drum by the developing device 5 to visualize the latent image as a toner image. The toner image is composed of a roller member that constitutes a primary transfer unit, and a primary transfer bias is applied to the first transfer unit 7 so that the toner image is transferred to the intermediate transfer belt 13 that faces the respective photosensitive drums. Transferred from the drum 1 surface. Residual toner components that have not been transferred from each photosensitive drum 1 to the intermediate transfer belt 13 are removed from the surface of the photosensitive drum by the cleaning blade 12 of each cleaning device 11.

  The toner image transferred to the surface of the intermediate transfer belt 13 is applied with a secondary transfer bias to the second transfer means 8 constituted by a roller member constituting a secondary transfer portion, and is conveyed from a paper feed tray (not shown). The recording material P is transferred to a sheet P as a recording material. Residual toner components after transfer or toner remaining on the surface of the intermediate transfer belt 13 are removed by a cleaning unit 16 disposed in the vicinity of the intermediate transfer belt 13. The cleaning unit 16 includes a cleaning blade 14 that comes into contact with the moving direction of the intermediate transfer belt 13 as a counter, a metal cleaning counter roller 17 disposed so as to face the cleaning blade 14, and a conveying coil. 18 is provided. With the configuration of the cleaning unit 16, the toner removed by the cleaning blade 14 is transported by the transport coil 18 and stored in a waste toner storage unit (not shown). The toner image transferred to the paper P is fused and fixed on the paper P by heat and pressure by the fixing device 9, and is discharged from the paper discharge port (not shown) to the outside of the device.

  In the vicinity of the intermediate transfer belt 13, the amount of toner adhering from the developing device 5 transferred onto the intermediate transfer belt 13 and the position of each color toner image are detected and used for adjustment of image density and alignment. And a density detection sensor 15 serving as a surface state detection means combining the diffuse reflection method.

FIG. 2 shows the configuration around the process cartridge 10 </ b> K and the configuration of the bias control device 200.
In the developing device 5 provided in the process cartridge 10K, the toner cartridge 4 is connected to the upper part thereof. A stirring paddle 30 serving as a stirring member is disposed in the toner cartridge 4 in order to maintain the fluidity of the replenishment toner T1. The stirring paddle 30 is preferably constantly stirred when the power is turned on. In the toner cartridge 4, a conveying means 32 constituted by a screw or a conveying coil is disposed, and a toner replenishing port 31 corresponding to a connecting portion with the toner replenishing path of the developing device 5 or the image forming apparatus (development in the future). The replenishment toner T1 in the toner cartridge 4 is transported toward the container (described in the configuration in which the toner is directly replenished in the container). The conveying means 32 can be connected and disconnected by a known method such as a main body drive unit (not shown) and a clutch (not shown), and is configured to be able to control the toner supply operation.

  The amount of toner replenished from the toner cartridge 4 to the developing device 5 can be controlled by the driving time of the main body driving unit. For example, the main body driving is performed in response to the change in the fluidity of the replenishing toner T1 in a temperature and humidity environment. Control such as changing the drive time of the unit is also possible. That is, the predetermined time t for supplying the replenishment toner T1 in this embodiment can be obtained from this driving time.

  FIG. 3 shows another embodiment of a toner cartridge that becomes a developer container. The toner cartridge 40 shown in FIG. 3 is filled with toner T. The toner cartridge 40 includes an agitator 41 as a stirring member made of a flexible material made of, for example, a PET film fixed to a rotation shaft 43, and a conveying means 42. The toner cartridge 40 is rotated by rotating the agitator 41. The toner is supplied in the direction of the conveying means 42 while ensuring the fluidity of the replenishing toner T1. In order to use up the replenishment toner T1 in the toner cartridge 40, the shape of the lower portion 401a of the casing 401 of the toner cartridge 40 is formed in an arc shape so that the tip of the agitator 41 is in contact with the rotation trajectory. A toner replenishing port 31 for replenishing the replenishing toner T1 to the developing device 5 is formed in the lower portion 401a of the casing 401 located below the conveying means.

  The conveying means 42 sends the replenished toner T1 in the toner cartridge 40 in the axial direction by being rotated by a drive motor M1 serving as a drive source, which will be described later, installed on the image forming apparatus main body by a member formed by a screw or a coil. It is well known. The transport unit 42 can control the transport amount of the replenishment toner T1 by the pitch diameter, size, rotation speed, and the like.

  In FIG. 2, the developing device 5 includes a toner transport member 37 such as a screw for transporting the replenished toner T <b> 1 replenished from the toner cartridge 4 disposed on the upper portion thereof, and the toner T in the developing device 5. An agitator 34 serving as an agitating member for mainly agitating the toner, a developing roller 35 as a developer carrier for supplying the toner T to the surface 1a of the photosensitive drum 1, and a supply member for supplying the toner T to the developing roller 35 The supply roller 36 is provided. The supply roller 36 faces the developing roller 35 and is disposed so that the circumferential surfaces thereof are in contact with each other, and a supply nip N is formed between the supply roller 36 and the developing roller 35. The developing roller 35 has a rubber layer formed on the outer periphery of a metallic roller, and is rotatably supported by the casing of the developing device 5. The supply roller 36 is formed by winding a sponge material around the outer periphery of a metal core, and is rotatably supported by the casing of the developing device 5.

  The toner T moved from the supply roller 36 to the developing roller 35 via the supply nip N is subjected to a surface of the developing roller 35 by a doctor blade 38 serving as a regulating member disposed so that the vicinity of the tip contacts the developing roller 35. After the toner layer adhering to the surface of the photosensitive drum 1 is made uniform, an amount of toner T corresponding to the surface potential of the photosensitive drum 1 moves to the surface of the photosensitive drum 1 and is intermediated by the first transfer means 7 (see FIG. 1) The image is transferred to the transfer belt 13. The toner that has moved to the photosensitive drum 1 and remains on the surface of the photosensitive drum as a transfer residue is removed by the cleaning unit 11 and then transferred to a waste toner cartridge (not shown) disposed in the main body of the image forming apparatus. To be recovered.

  Next, the bias control apparatus 200 will be described. In this example, the control mode for the developing device 5 to which the replenishing toner T1 is supplied from the black toner cartridge 4 will be described. However, the developing devices of other colors are controlled by the bias control device 200 as in the case of black. Is done.

  The bias control device 200 is formed between the supply roller 36 and the development roller 35 by supplying a bias to the development roller 35 and the supply roller 36 provided in the development device 5 in which the supply toner T <b> 1 is supplied from the toner cartridge 4. The toner T is moved from the supply roller 36 side to the developing roller 35 side at the supplied nip N.

  The bias control device 200 rotates the conveying means 32 in the toner cartridge 4 for a predetermined time and starts the supply from the toner cartridge 4 to the developing device 5 at the start of replenishment of toner T1 from the toner cartridge 4 to the developing device 5. Control means 100 is provided for changing the bias to supply roller 36 (hereinafter referred to as “supply bias”) from the start of supply of supply toner T1 until a predetermined period t has elapsed.

  The control means 100 is constituted by a known computer, and controls the power supplies 60 and 61 connected to the developing roller 35 and the supply roller 36 to supply the developing roller 35 with bias (hereinafter referred to as “developing bias”). The supply bias supplied to the supply roller 36 is controlled. A drive motor (not shown) of the density detection sensor 15 and the transport means 32 is connected to the control means 100 via a signal line. In this embodiment, the control means 100 is configured to receive a detection signal from the concentration detection sensor 15. In the control means 100, the developing bias for the developing roller 35 is determined based on the detection result of the density detection sensor 15 in the back. The control unit 100 changes the supply bias to the supply roller 36 before and after the supply toner T1 is supplied from the toner cartridge 4 to the developing device 5. In this embodiment, the developing bias supplied to the developing roller 35 and the supplying bias supplied to the supplying roller 36 are DC voltages, and the control unit 100 determines that the toner T is changed after the bias change compared to before the bias change to the supply roller 36. The voltage is changed to the opposite side of the charge polarity. The supply bias supplied to the supply roller 36 has a polarity opposite to the charging polarity of the toner T with respect to the developing roller 35.

  In this embodiment, the control unit 100 applies a developing bias of −200 V to the developing roller 35 and applies a supplying bias of −100 V to the supply roller 36 before toner replenishment as shown in FIG. The power supplies 60 and 61 are controlled so as to apply a supply bias of +100 V within a predetermined period t after toner replenishment.

  The replenishment timing of the replenishment toner T1 from the toner cartridge 4 to the developing device 5 is the supply bias switching timing for the supply roller 36, and this switching timing information is input to the control means 100. In this embodiment, the number of printed sheets is used as the switching timing information. In a memory (not shown) of the control unit 100, print number information (A sheets) which is a supply bias switching timing is set in advance. This switching timing may be changed by a user or service staff using an operation panel (not shown). In the present embodiment, the end of the predetermined period t is set to print sheet number information (A sheet) +200 sheets. That is, the predetermined range t is A sheets ≦ predetermined range t ≦ (A sheets) +200 sheets.

One form of control contents of the bias control apparatus 200 having such a configuration will be described with reference to the flowchart of FIG.
In step S1 of FIG. 5, the control means 100 determines the toner replenishment timing from the integrated value of the number of dots in the print pattern, and proceeds to step S2.

  In step S2, the conveying means 32 is rotated to start replenishment of the replenishment toner T1 from the toner cartridge 4 into the developing device 5, and the process proceeds to step S3. In step S3, measurement of the rotation time of the conveying means 32 is started.

  In step S4, the supply bias already applied to the supply roller 36 is changed to the Δ supply bias, and the process proceeds to step S5. In this embodiment, the voltage is changed from -100V to + 100V. In step S5, it is determined from the rotation time of the conveying means 32 whether the replenishment period of the replenishment toner T1 has passed the predetermined time t. If the cumulative number of printed sheets has reached A + 200, the predetermined time t is set. It is determined that the time has elapsed, and the process proceeds to Step 6.

  In step S6, the rotation of the conveying means 32 is stopped to complete the supply of the supply toner T1, and the process proceeds to step S7 to return the supply bias to the supply roller 36. That is, the supply bias once set to + 100V is returned to -100V, and this control is finished. In this embodiment, the supply bias change time is set longer than the toner supply period. That is, the control is performed so that the supply bias is returned when the chargeability of the replenishment toner T1 is reduced after the toner replenishment.

  In this embodiment, if the supply bias after the change to the supply roller 36 is Δ supply bias, this is expressed by Equation 1.

Δ supply bias = supply bias−development bias
Further, it is preferable that the control means 100 performs density control using the output from the density detection sensor 15 of FIG. 1 at the timing when the Δ bias is changed from −100 V to +100 V.

  In the conventional configuration, a bias on the normal polarity side of the toner is applied to the supply roller 36 with respect to the development roller 35 (for example, −300 V is applied to the supply roller when −200 V is applied to the development roller). . For this reason, when the toner T in the developing device 5 is repeatedly subjected to image formation, the toner deteriorates and the chargeability decreases. When the toner amount in the developing device 5 decreases, the replenishing toner T1 is replenished from the toner cartridge 4 into the developing device 5. Since the replenishment toner T1 to be replenished is unused, the chargeability is high.

  When the toner T1 with high chargeability and the toner T with low chargeability are mixed in this manner, the toner (toner) T with low chargeability is deprived of the charge by the toner (supply toner) T1 with high chargeability. The charged polarity is opposite to that of the charged polarity (this is called reversely charged toner). The reversely charged toner is likely to be coupled to the normally charged toner by Coulomb force (this is called a coupled toner). The reversely charged toner has a Coulomb force acting on the side attracted to the supply roller 36 by the electric field of the supply nip N where the supply roller 36 and the developing roller 35 are in contact with each other. However, since the absolute value of the charge amount is not so high, the supply roller It is not held on the 36 side. Further, the reversely charged toner enters the supply nip N and rubs against the developing roller 35 to obtain a regular charge opportunity, so that the normally charged toner is attracted to the developing roller 35 by a strong Coulomb force at the entrance of the supply nip N. Simultaneously with this toner, the toner moves to the developing roller 35. That is, the reverse polarity toner moves to the developing roller 35 with the reverse polarity. After that, the combined toner is rubbed against the developing roller 35 by the doctor blade 38 and charged to the normal charge side, but the toner is still carried to the developing nip (the developing nip where the developing roller 35 and the photosensitive drum 1 are in contact) with the opposite polarity. Exists. In the developing nip, the reversely charged toner adheres to the photosensitive drum 1 on the background portion of the photosensitive drum 1 where the toner on the developing roller 36 is not developed, and wasteful toner is consumed. May appear in the image.

  However, as in the present embodiment, the supply bias for the supply roller 36 is changed before and after replenishment of the replenishment toner T1. Specifically, a bias having a polarity opposite to the normal charge polarity of the toner is applied to the developing roller 35 for a predetermined period t after the start of the toner supply operation. Then, in the supply nip N, of the combined toner obtained by combining the replenishment toner T1 and the toner T, the replenishment toner T1 that is a regular charged toner is strongly attracted to the supply roller 36, and thus hardly moves to the developing roller 35.

  However, among the combined toners, the toner T that is deteriorated and becomes a reversely charged toner is often regularly charged due to frictional charging with the developing roller 35 in the supply nip N. When charged to the normal charge polarity, the Coulomb attractive force that has been acting on the coupled toner until then becomes a repulsive force, and the originally charged toner and the toner that has become the normal charged toner from the reversely charged toner are transferred to the developing roller 35. Adhered and carried. That is, since the combined toner is attracted to the supply roller 36, the chance that the reversely charged toner comes into contact with the developing roller 35 is increased and the regular charged toner is easily charged, and the reversely charged toner is hardly supplied to the developing roller 35 with its charged polarity. Become.

  Then, it reaches the doctor blade 38 and is further charged normally by friction with the developing roller 35. Therefore, it does not move to the background portion of the photosensitive drum 1, and wasteful toner consumption and background smear images can be prevented.

  6 and 7 show a second embodiment of the bias control apparatus 200 according to this embodiment. In the first embodiment, the supply bias for the supply roller 36 is changed only once within a predetermined period t from the start of the replenishment toner T1, but in this embodiment, the supply bias is supplied to the supply roller 36 within the predetermined period t from the start of the replenishment toner T1. The supply bias is changed in a stepwise manner, and is finally controlled by the control means 100 so as to return to the bias before the change. In the first embodiment and the second embodiment, the configuration of the control unit 100 is the same except that the processing contents stored in the memory are different, and will be described using the configuration of FIG.

  In this embodiment, the control unit 100 applies a current bias of −200 V to the developing roller 35 and applies a supply bias of −100 V to the supply roller 36 before toner replenishment as shown in FIG. After toner replenishment (after the start of toner replenishment), the supply bias is first changed to +100 V within a predetermined period t, and thereafter, the step bias is changed to +40 V, −30 V, and −100 V and applied. Thus, the power supplies 60 and 61 are controlled. In FIG. 6, the predetermined range t is set to A sheets ≦ predetermined range t ≦ (A sheets) +300 sheets. Within this predetermined range t, when the number of printed sheets is A, that is, when supply of toner is started, the supply bias is changed from -100 V to +100 at a stretch, and the first predetermined period (A sheets) becomes +40 V when it reaches +100 sheets. The supply bias is changed, the supply bias is changed to −30 V when the second predetermined period (A sheet) +200 sheets is reached, and the third predetermined period (A sheet) +300 sheets is reached, that is, the predetermined period t. At the end, the supply bias applied to the supply roller 36 is controlled so as to change the supply bias to −100 V before the change.

  One form of the stepwise control contents of the bias control apparatus 200 having such a configuration will be described with reference to the flowchart of FIG.

  In step S11 of FIG. 7, the control means 100 determines the toner replenishment timing from the integrated value of the number of dots of the print pattern, and proceeds to step S12. In step S12, the conveying means 32 is rotated to start replenishment of the replenishment toner T1 from the toner cartridge 4 into the developing device 5, and the process proceeds to step S13. In step S13, measurement of the rotation time of the conveying means 32 is started.

  In step S14, the supply bias already applied to the supply roller 36 is changed, and the process proceeds to step S15. In this embodiment, the supply bias is changed from -100V to + 100V. In step S5, it is determined from the actual number of printed sheets whether or not a first predetermined period t1 has elapsed from the start of the replenishing toner T1, and if the actual number of printed sheets has reached A + 100, the first predetermined period is reached. It is determined that the period t1 has elapsed, and the process proceeds to step 16.

  In step S16, the supply bias applied to the supply roller 36 is changed so as to return by one step, and the process proceeds to step S17. Here, the supply bias is changed from + 100V to + 40V.

  In step S17, it is determined from the actual number of printed sheets whether or not a second predetermined period t2 has elapsed from the start of the replenishing toner T1, and if the actual number of printed sheets has reached A + 200, the second predetermined period is reached. It is determined that the period t2 has elapsed, and the process proceeds to step 18.

  In step S18, the supply bias applied to the supply roller 36 is further changed back to one step (two steps), and the process proceeds to step S19. Here, the supply bias is changed from + 40V to −30V.

  In step S19, it is determined from the actual number of printed sheets whether or not a third predetermined period t3 has elapsed since the start of the replenishing toner T1, and if the actual number of printed sheets has reached A + 300, the third predetermined period is reached. It is determined that the period t3 has elapsed, and the process proceeds to step 20.

  In step S20, the rotation of the conveying means 32 is stopped and the replenishment of the replenishment toner T1 is completed. That is, here, the supply bias is changed from -30 V to -100 V, and the supply bias is returned to the bias value before toner replenishment. Also in this embodiment, the supply bias change time is set longer than the toner replenishment period. That is, the control is performed so that the supply bias is returned when the chargeability of the replenishment toner T1 is reduced after the toner replenishment.

  Thus, the image density becomes more stable than changing the supply bias to the supply roller 36 after toner replenishment step by step, and returning to the supply bias before the change at once. Further, it is preferable that the control means 100 performs density control using the output from the density detection sensor 15 of FIG. 1 at the timing when the supply bias is changed from − + 30 V to +100 V.

FIG. 8 shows the conditions of the two embodiments and the comparative example (conventional example) and the measurement result of the background stain.
<Experiment method>
The developing device and the image forming apparatus were modified from Ricoh's IPSiO SP C310.

The toner used was charged negatively.
In this experiment, a 1% printing rate chart is output per JOB. The number of printed sheets when the toner in each developing device was reduced by 10% was defined as A sheet. After printing A sheet, 10% of replenishment toner was replenished to the developing device. Immediately thereafter, density control was performed, 10 sheets were printed, and background stains at that time were measured. The measurement method of background dirt is as follows.

The toner on the photosensitive drum during printing of the white paper was peeled off with a booker tape, and the L * value of the tape was measured by pasting the toner on the white paper, thereby evaluating the background stain. In this experiment, L *> 90 was set as an allowable level.
<Experimental result>
Looking at Example 1 and Comparative Example 1, here, the background stain is better evaluated when the supply bias for the supply roller 36 is changed to -100 V after printing A sheets, that is, after the start of the replenishment toner.

  Further, looking at Example 1 and Example 2, when the supply bias to the supply roller 36 is changed after the start of the replenishment toner, as shown in Example 2, it is more likely that the change is made in stages to evaluate the background contamination. Is good.

  As described above, if the supply bias to the supply roller 36 is changed after the supply toner T1 is supplied to the inside of the developing device 5, the background contamination is less than when the supply bias is not changed, and the supply bias to the supply roller 36 is started after the supply of the supply toner T1 is started. When changing, it can be said that the gradual change is less in the background.

  In the above embodiment, the predetermined period t is calculated from the number of printed sheets, which is one of the correlated parameters. However, the parameter is not limited to this, and the photosensitive drum serving as the image carrier traveling distance is used. The predetermined period t may be calculated from the number of rotations of 1, the number of rotations of the intermediate transfer belt 13 serving as an intermediate transfer member, and the number of rotations of the developing roller 35 serving as a developer carrier travel distance. That is, the number of rotations of the photosensitive drum 1, the number of rotations of the intermediate transfer belt 13, and the number of rotations of the developing roller 35 are used as switching timing information for supplying bias to the supply roller 36. The supply of the supply toner T1 may be started, and the supply bias for the supply roller 36 may be switched at the supply timing.

4 Developer supply container 5 Developing device 10 (Y, M, C, K) Process cartridge 13 Intermediate transfer body 35 Developer carrier 36 Supply member 100 Control means 200 Bias control device N Supply nip t Predetermined period T In the development device Developer T1 Developer to be replenished

Japanese Patent Application Laid-Open No. 2001-075341

Claims (10)

A supply nip formed between the supply member and the developer carrier by supplying a bias to the developer carrier and the supply member included in the developing device in which the developer is supplied from the developer supply container. A bias control device that moves a developer from a supply member side to a developer carrier side,
Until a predetermined period of time has elapsed since the developer supply from the developer supply container to the developing device, the developer charged in the developer from the developer supply container and the developer deteriorated in the developing device is charged in reverse. A bias control apparatus comprising control means for regular charging. The bias supplied to the supply member is a DC voltage,
The bias control apparatus according to claim 1, wherein the control unit changes the voltage to the opposite side to the charge polarity of the developer as compared to before the change.   3. The bias control apparatus according to claim 1, wherein the bias supplied to the supply member has a polarity opposite to a charge polarity of the developer with respect to the developer carrying member.   The control means determines a predetermined period for changing a bias supplied to the supply member based on at least one parameter of an image carrier travel distance, an intermediate transfer member travel distance, a developer carrier travel distance, or the number of printed sheets. 4. The bias control apparatus according to claim 1, 2, or 3.   The bias according to any one of claims 1 to 4, wherein the control means changes the bias so that the bias before the change is gradually returned after the change of the bias supplied to the supply member. Control device. The developer is replenished from the developer supply container, and further includes a developer carrier and a supply member that supplies the developer to the developer carrier, and a bias is supplied to the developer carrier and the supply member. Thus, in the developing device that moves the developer from the supply member side to the developer carrier side at a supply nip formed between the supply member and the developer carrier,
6. A developing device, wherein the bias to the supply member is controlled by the bias control device according to claim 1.   A process cartridge comprising the developing device according to claim 6. The developer is replenished from the developer supply container, and further includes a developer carrier and a supply member that supplies the developer to the developer carrier, and a bias is supplied to the developer carrier and the supply member. Thus, in a supply nip formed between the supply member and the developer carrying member, a developing device that moves the developer from the supply member side to the developer carrying member, and a developer from the developing device In the image forming apparatus that forms an image by developing the latent image formed on the image carrier by being supplied,
An image forming apparatus comprising the bias control device according to claim 1. The developer is replenished from the developer supply container, and further includes a developer carrier and a supply member that supplies the developer to the developer carrier, and a bias is supplied to the developer carrier and the supply member. Thus, in a supply nip formed between the supply member and the developer carrying member, a developing device that moves the developer from the supply member side to the developer carrying member, and a developer from the developing device In the image forming apparatus that forms an image by developing the latent image formed on the image carrier by being supplied,
An image forming apparatus comprising the developing device according to claim 6 as the developing device. In an image forming apparatus comprising at least an image carrier and a process cartridge comprising a developing device for developing a latent image formed on the image carrier with a developer.
An image forming apparatus comprising the process cartridge according to claim 7 as the process cartridge.

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