JP2014142445A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents the occurrence of scumming and unnecessary consumption of toner during stirring, even when the apparatus is started up from a state where the apparatus has been left unused for a long period and the Q/M is reduced.SOLUTION: An image forming apparatus includes a developing device, developer stirring means for stirring a developer in the developing device, and a photoreceptor arranged to face the developing device. The image forming apparatus further includes control means for controlling to make a setting value of a background potential larger than that during image formation, during stirring of developer performed before image formation at the start-up of the apparatus after being left unused for a time period beyond a reference value.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having both functions.

  2. Description of the Related Art Image forming apparatuses that develop an electrostatic image formed on a photoreceptor using a two-component developer containing toner and a carrier are widely used. In the two-component development, development is performed as follows. That is, the developer is transported to the surface of a non-magnetic sleeve with a built-in magnet as a developing roller, the developer is held in a brush shape and brought into contact with or close to the photoreceptor, and the photoreceptor and sleeve on which the electrostatic latent image is formed, The toner is selectively attached to the latent image surface by an electric field between the two and development is performed. The charge amount per unit mass of toner in the developing device: Q / M [-μC / g] has a certain width due to variations in the surface characteristics and mass of the toner and carrier (somewhat Range). Further, since the toner is frictionally charged by coming into contact with the carrier, Q / M varies greatly depending on the developer leaving time and the stirring time. For this reason, if the charge amount of the toner is too high, the adhesion with the carrier is too great and the image density is lowered, and if it is too low or the reverse polarity, it adheres to the background portion of the non-image portion on the photoreceptor. There was a bug. Therefore, conventionally, the standing time, temperature / humidity, and the like are monitored, and when a certain threshold value is exceeded, concentration adjustment and stirring are performed to control Q / M.

  However, it is generally difficult to control the charge amount of toner in the developing device. In the left developer, the developer reaches the developing sleeve before the toner rises and comes into contact with the photosensitive member, or a lot of background stains are generated by the developer or the like originally on the sleeve. For example, when it is used less frequently and left for a long time, the charge of the toner and carrier in the developing device may spontaneously discharge and the charge amount may decrease. Further, due to a decrease in the charge amount of the toner, there is a problem in that toner scattering and background contamination occur when image formation is performed after being left for a long time. In particular, when left in a high temperature and high humidity environment, the charge amount tends to decrease. Normally, in order to raise the charge amount of the developer, the developer is stirred for a certain period of time after the power is turned on, and then an image is output. However, if the stirring time is simply increased before printing from the state where Q / M has decreased, this stirring is performed. Sometimes the toner adheres to the photoreceptor due to soiling and is wasted. Due to this phenomenon, there have been problems such as a decrease in toner yield, a shortening of the life of a toner recovery mechanism such as a waste toner tank, and a defective cleaning. Incidentally, the start-up of the developer (toner) means that the charge amount of the toner on the developing sleeve apparently reaches an equilibrium state.

  In Patent Document 1, in order to obtain a high-quality image with no background stain regardless of the standing time, and to eliminate wasteful toner consumption during stirring, the developer is allowed to stand for a predetermined time without stirring during image formation. It has been proposed to make a determination as to whether or not it was. If it is determined that the image carrier is left as it is, the developer carrier is driven while the image carrier is charged and then left stationary for a certain period of time, and then image formation is performed. If NO is determined, the image bearing member is charged and then the developer bearing member is driven without being stopped to form an image.

  However, in Patent Document 1, the driving structure of the unit also involves costs such as separate driving of the development and the photosensitive member, and scumming is generated although only a part of the photosensitive member, and the original purpose can be sufficiently achieved. Not.

  Japanese Patent Application Laid-Open No. 2004-228561 proposes to suppress image defects due to carrier adhesion even when the toner charge amount is higher than a normal level due to control for setting an upper limit on the toner density. That is, when the detected value of the density of the patch image formed on the photoreceptor exceeds the upper limit value, the toner replenishment control is changed to prevent further increase of the toner density. At the same time, the fog removal voltage is lowered below the specified value. However, Patent Document 2 does not relate to the toner problem that is consumed due to scumming due to the standing time or the environment.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that prevents the occurrence of scumming and does not waste toner during agitation even when the apparatus is started from a state in which the Q / M is lowered by being left for a long time. There is.

  In the image forming apparatus having the developing device, the developer agitating means for agitating the developer in the developing device, and the photosensitive member arranged to face the developing device, at the time of starting after the standing time exceeding the reference value This is solved by providing a control means for controlling the background potential to be larger than the set value at the time of image formation when the developer is stirred before the image formation.

  According to the present invention, when the leaving time in which the developer is not stirred exceeds a reference value, the developer is stirred before image formation at startup with a background potential larger than the set value at the time of image formation. Therefore, even when the apparatus is started from a state where Q / M is lowered, the repulsive force between the photosensitive member and the toner increases, and the toner (soil stain) adhering to the photosensitive member during stirring can be reduced. It is possible to eliminate wasted toner that is consumed. With regard to carrier adhesion, which is concerned by increasing the background potential, no image is formed when the developer is stirred, so there is no solid portion or edge portion, and there is no problem because the margin increases with respect to the background potential.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a graph which shows the relationship between background potential and background dirt, carrier adhesion, and the relationship between background potential and edge part carrier adhesion / non-image part carrier adhesion. It is a figure for demonstrating the margin of background potential between edge part carrier adhesion and non-image part carrier adhesion. It is a flowchart regarding control. It is a graph which shows the effect comparison by the control which concerns on conventional control and embodiment of this invention.

Embodiments of the present invention will be described below.
As shown in FIG. 1, a process unit 30 that is a printer engine, light that emits a light beam and irradiates a photoconductor 60 with a scanning line by the light beam is provided at a substantially central portion inside the main body case 20 of the image forming apparatus 10. A writing device 40, an intermediate transfer belt 50, and the like are disposed. The printer engine includes four process units 30Y, 30C, 30M, and 30K that form toner images for each color. Each process unit 30Y, 30C, 30M, 30K is formed with the same structure. In each of the process units 30Y, 30C, 30M, and 30K, different color toners supplied from the toner bottles 32Y, 32C, 32M, and 32K disposed above are used, and toner images of different colors are formed. . The toner bottles 32Y, 32C, 32M, and 32K are detachably attached so that they can be replaced with new ones when the toner runs out. Note that the subscripts Y, C, M, and K in the process unit and its components indicate yellow, cyan, magenta, and black colors, respectively, and these subscripts are omitted as necessary.

  Each of the process units 30Y, 30C, 30M, and 30K includes a photoreceptor unit 70Y, 70C, 70M, and 70K having a photoreceptor 60 that is driven to rotate in the direction of an arrow, and developing devices 80Y, 80C, 80M, 80K. The photoconductor unit 70 has at least a cleaning device 90 for removing the transfer residual toner and a charging device 92 for charging the photoconductor around the photoconductor 60. A photosensitive layer is provided on the cylindrical outer peripheral surface of the photoreceptor 60. A well-known developer stirring means is provided in the developing device 80.

  The optical writing device 40 irradiates each of the photoconductors 60Y, 60C, 60M, and 60K through a plurality of lens mirrors while polarizing the laser light L with the polygon mirror 41 based on the image information. As the optical writing device 40, an LED (light emitting diode) array method can be used in addition to the polygon scanning method for driving the polygon mirror 41.

  At the time of printing, the photosensitive member 60 is rotationally driven by a drive motor (not shown), and the outer peripheral surface of the photosensitive member 60 is irradiated with the light beam emitted from the optical writing device 40. An electrostatic latent image corresponding to the image data is written.

  The developing device 80 supplies toner to the photoreceptor 60. The supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photoconductor 60, whereby the electrostatic latent image on the photoconductor 60 is visualized as a toner image.

  The intermediate transfer belt 50 is a loop belt formed with a resin film or rubber as a base, and a toner image formed on the photoreceptor 60 is transferred to the intermediate transfer belt 50. The intermediate transfer belt 50 is supported by rollers 100, 110, and 120 and is driven to rotate in the direction of the arrow. Four primary transfer rollers 130 </ b> Y, 130 </ b> C, 130 </ b> M, and 130 </ b> K for transferring the toner image on each photoconductor 60 onto the intermediate transfer belt 50 are disposed on the inner peripheral surface side (inside the loop) of the intermediate transfer belt 50. Has been. When the intermediate transfer belt 50 is sandwiched between the primary transfer roller 130 and the photoreceptor 60, a primary transfer nip is formed. The primary transfer roller 130 is in contact with the inner side of the intermediate transfer belt 50, is applied with a primary transfer bias, and a toner image on the photoconductor 60 is transferred to the surface of the intermediate transfer belt 50 due to a potential difference with the photoconductor 60. . As described above, the toner images formed on the photoconductors 60Y, 60C, 60M, and 60K are sequentially transferred onto the intermediate transfer belt 50, whereby a color toner image is formed on the intermediate transfer belt 50. A cleaning unit 140 that cleans residual toner, paper dust, and the like attached to the outer peripheral surface of the intermediate transfer belt 50 is disposed on the outer peripheral surface side of the intermediate transfer belt 50 (outside the loop).

  Below the four process units 30Y, 30C, 30M, and 30K and the optical writing device 40 in the main body case 20, a first paper feed tray 151 for stacking and holding paper P as a print medium, a second feed A paper tray 152 is arranged. The paper P held in the first paper feed tray 151 and the second paper feed tray 152 is fed in order from the top one by the paper feed rollers 161 and 162. Further, the manual paper feed tray 222 on the side surface of the main body case 20 is used for supplying paper P having a size different from that of the first paper feed tray 151 and the second paper feed tray 152, for example.

  In the main body case 20, a transport path 170 is formed through which the paper P separated and fed from the first paper feed tray 151 and the second paper feed tray 152 is transported. On this conveyance path 170, a registration roller 180, a transfer roller 190, a fixing device 200, a paper discharge roller 210, and the like having a timing matching and skew correction function are arranged. When the paper feed roller 160 or 224 is driven to rotate, the paper P stored in any of the paper feed trays 151 and 152 and the manual paper feed tray 222 is taken out one by one from the uppermost paper and conveyed. It is conveyed to the path 170. A secondary transfer nip is formed by the roller (transfer facing roller) 120 and the transfer roller 190 that stretch the intermediate transfer belt 50. The color toner image transferred and formed on the intermediate transfer belt 50 is transferred to the paper P while the paper P conveyed from the paper feed trays 151 and 152 or the manual paper feed tray 222 passes through the secondary transfer nip. .

  The registration roller 180 is a roller that is intermittently rotated at a predetermined timing. When the registration roller 180 is intermittently driven to rotate, the sheet P that has been transported to the position of the registration roller 180 and stopped is skew-corrected, and the timing is adjusted to 2 with the toner image on the intermediate transfer belt 50. It is fed to the next transfer nip. Then, the toner image on the intermediate transfer belt 50 is transferred to the paper P in the process in which the paper P passes through this transfer position.

  The fixing device 200 is a unit that applies heat and pressure to the paper P on which the toner image is transferred to melt the toner, and fixes the toner image on the paper P. The fixing device 200 includes a pressure roller 201 containing a heater 201a (heat generation source) such as a halogen lamp, and a fixing belt unit 202. The fixing belt unit 202 includes a fixing belt 204, a heating roller 203 including a fixing heater 203a (heat generation source) such as a halogen lamp, a driving roller 206, and the like. The fixing belt 204 is rotated counterclockwise in the drawing by the driving roller 206 and is heated by the heating roller 203 to be maintained at a constant temperature. The pressure roller 201 also rotates clockwise, is heated by the internal heater 201a, and is maintained at a constant temperature. The fixing belt 204 and the pressure roller 201 are in contact with each other to form a fixing nip.

  The paper P onto which the toner image on the intermediate transfer belt has been transferred passes through the fixing device 200 to fix the toner image, and the paper discharge tray 220 formed on the upper surface of the main body case 20 by the paper discharge roller 210. Paper is discharged to the top.

Next, the relationship between the background potential, background contamination, and carrier adhesion will be described.
FIG. 2 is a graph showing the relationship between the background potential and background contamination and carrier adhesion, and the relationship between the background potential and edge portion carrier adhesion / non-image portion carrier adhesion.

The background potential [V] is the potential difference between the photosensitive member surface potential [Vd] and the developing bias potential [Vb] at the portion (non-image portion) where the toner is not adhered.
The background dirt tends to be worse as the background potential is smaller, and the carrier adhesion tends to be worse as the background potential is larger. Conventionally, the background potential V0 that can maintain the balance between soil contamination and carrier adhesion as shown in FIG. 2 is determined by the system employed, and control is performed at a constant value. When determining the background potential, the tendency of edge carrier adhesion is taken into account. At the time of image formation, the background potential is determined in consideration of the tendency of the carrier adhesion on the edge portion, not the carrier adhesion on the non-image portion since the edge portion of the image exists as long as it is not blank paper.

  As shown in FIG. 2, it can be seen that the edge potential carrier adhesion and the non-image part carrier adhesion have a larger margin of background potential than the carrier adhesion. The reason will be described with reference to FIG. Since the electric field concentrates at the edge portion, Vd partially increases, so that the background potential increases only at the edge portion. This phenomenon tends to cause carrier adhesion. Since such a phenomenon does not occur in the non-image area, the value of Vd−Vb is simply the background potential. Due to this difference, as shown in FIG. 2, the background potential V0 when the edge portion carrier adhesion at the time of normal image formation is considered and the background potential V1 when the non-image portion carrier attachment is considered are in a relationship of V0 <V1. . That is, the margin for V1 is greater with respect to background dirt.

  Further, it is known that when the Q / M of the actual developer is low, both the background stain curve and the carrier adhesion curve in FIG. 2 shift to the right side. This is because when the Q / M is low, soiling is deteriorated and carrier adhesion is improved. In the case of high Q / M, the reverse phenomenon occurs.

  In the present embodiment, when the developer is agitated (when the developer is started up) that is performed in a state where the Q / M is lowered when the machine is left for a long time, at high temperature and high humidity, or when the initial unit is started, the background potential is increased. Is increased to V1 when non-image part carrier adhesion is taken into consideration. By doing so, even if the Q / M of the toner is lowered, the repulsive force between the photoconductor and the toner is larger than that at the time of image formation, and the toner (soil stain) that adheres to the photoconductor during stirring is reduced. Can do. As a result, there is an effect of eliminating useless toner that has been conventionally consumed as background dirt during stirring. Further, since no image is formed during agitation, the edge carrier adhesion can be ignored, and even if the background potential value is increased to V1, the possibility of carrier adhesion is reduced. By doing so, even when Q / M is lowered and the background becomes easy to be stained, the background potential is increased to avoid the background stain.

The control in this embodiment is demonstrated below based on FIG.
The machine (image forming apparatus) is activated (S401). This indicates a case where the image formation is started from a state where it is temporarily stopped, such as power-on or energy-saving recovery. Next, the temperature and humidity in the machine are detected by detection means (not shown). Then, the combination condition of the threshold temperature and the threshold humidity in the machine is set to Th1, and it is determined whether or not the detected combination value (detection result) Th is larger than Th1 (S402). For example, in the case where the temperature is 27 ° C. and the humidity is 60% in Th 1, if Th exceeds both the temperature and the humidity, the process proceeds to step S 403. This temperature / humidity threshold value is divided into temperature and humidity, and one of them is determined. If either one is exceeded, the process may proceed to step S403. In particular, since the influence of humidity is large on Q / M, it is also possible to focus on humidity.

  In step S403, the elapsed time from the end of the previous developer stirring, that is, the time T during which the machine has been left is detected by a timer (measuring means) (not shown). When the reference value of the leaving time is T1, if the detected time (actually measured leaving time) exceeds the reference value (T> T1), the process proceeds to step S405, and if T ≦ T1, the process proceeds to step S407. The reference value T1 is set to a time during which the reference value T1 is lowered to Q / M, which can be disadvantageous to soiling. Since the reference value T1 varies depending on the toner and the image forming system, the set value is changed depending on the system conditions. Even when the condition is not satisfied in step S402, the leaving time is confirmed (S404). If it is considered that the standing time at this time is longer than T1 and the Q / M of the developer is decreasing, it is necessary to execute this control. On the other hand, if it is shorter than T1, it is considered that neither the standing time nor the temperature / humidity satisfies the conditions, and the soiling due to the decrease in the charge amount does not occur, so proceed to step S409 and start up the machine with the conventional control method. Do.

  When both the temperature / humidity inside the machine and the threshold of the standing time are satisfied, the background potential is raised to V2 (S405). Then, the stirring time is set to M2 and stirring is performed (S406). V2 and M2 are set according to the conditions of the adopted system.

  If the temperature / humidity is satisfied in step S402 but the step leaving time is not satisfied in step S403, and if the temperature / humidity is not satisfied in step S402 but the leaving time is satisfied in step S404, the background potential is V1. (S407). Then, stirring is performed with the stirring time set to M1 (S408). V1 and M1 are set to values that meet the conditions of the adopted system.

After the stirring before the image formation is completed, the image is formed by lowering the background potential determined by the image forming conditions (S410).
The background potentials V1 and V2 are set so that the relationship V1 <V2 is established. Since the temperature / humidity and the standing time both exceed the threshold, it is considered that the degree of Q / M reduction of the developer is large. For this reason, since the Q / M is low, the tendency of carrier adhesion also shifts to the right in FIG. 2, so that the background potential can be increased. The values of V1 and V2 need to be changed depending on the image forming system (material of the system, toner, carrier, etc.) employed.

  The stirring times M1 and M2 are also set so that the relationship of M1 <M2 is established. M2 having a longer stirring time is set to a condition that is considered to have a large Q / M drop. The values of M1 and M2 also need to be changed and set by the image forming system in order to eliminate insufficient start-up of the developer and waste due to excessive stirring.

As a result, it is possible to minimize the amount of toner developed as background stains during stirring.
In addition, if there are multiple reference values (threshold values) for the temperature / humidity and leaving time in the machine, make detailed judgments, give multiple control potentials such as background potential and agitation time, and finely control them. It is believed that more efficient and wasteful stirring can be achieved for the imaging system.

Finally, the effect comparison between the conventional control and the main control will be described.
Two machines with the same imaging system were prepared and left in a room with high temperature and high humidity for a long time. The standing time at this time was set to a sufficiently long time to reduce the Q / M of the developer to such an extent that the smudge occurs.

  After the machine was started up, one unit performed the stirring operation for starting up the developer with the background potential at the time of image formation as before, and the other unit performed control according to the flow of FIG. Even in the conventional control, it is known that a developer start-up operation is performed after the machine is started when the leaving time is long.

  Comparison was made between TC (toner concentration in developer) immediately after being left in these two machines and TC immediately after stirring. As a result, as shown in FIG. 5, it was found that the TC change amount before and after stirring is significantly smaller in this control than in the conventional control. This TC change amount indicates the difference between the TC immediately after being left to stand and the TC after stirring. That is, when a large amount of scumming is generated on the photosensitive member during stirring, the toner in the developer is consumed, so that the TC after stirring decreases and the TC change amount increases. As shown in FIG. 5, in the conventional control, since the developer Q / M is lowered after being left and the background potential at the time of image formation is stirred, the background is soiled on the photosensitive member. It is considered that the toner was consumed and the TC change amount became large. When this control is used, considering the standing time and temperature / humidity, since the optimum ground potential is set during stirring, the occurrence of background contamination is suppressed and the TC change amount is also a low value. . As a result, compared to the conventional control, by controlling the optimal background potential and stirring time during stirring, it is possible to minimize the toner that is developed due to background contamination during stirring, and to suppress wasteful toner consumption. I was able to confirm. In addition, even when an image is formed after stirring, the occurrence of abnormal images such as background stains can be prevented by sufficiently raising Q / M.

  The process cartridge according to the present embodiment is divided into each color as process units 30Y, 30C, 30M, and 30K, and is configured to be detachable from the main body of the image forming apparatus. In addition, when the initial unit is activated, for example, when the process cartridge is replaced due to a life or failure, this control is always executed for the replaced unit. Since the Q / M of the developer is extremely low in the initial unit, this control is always executed for the replaced unit regardless of the leaving time, temperature and humidity.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Main body case 30 Process unit 60 Photoconductor 70 Photoconductor unit 80 Developing device

JP 2009-216974 A JP 2011-118146 A

Claims (5)

  In an image forming apparatus having a developing device, a developer agitating means for agitating a developer in the developing device, and a photoconductor disposed opposite to the developing device, image formation at start-up after a standing time exceeding a reference value An image forming apparatus comprising: control means for controlling the background potential to be larger than a set value at the time of image formation during the previous stirring of the developer.   The image forming apparatus according to claim 1, further comprising: a measurement unit that measures a time after the developer agitation is completed; and a determination unit that determines whether the measured time exceeds a reference value.   The detection means for detecting temperature and humidity is provided, and the background potential that is larger than the set value at the time of image formation is made different depending on whether or not the detection result exceeds a threshold value related to temperature and humidity. The image forming apparatus according to 2.   4. The time for stirring the developer at a background potential larger than a set value at the time of image formation is changed according to the relationship between the measured time and the detected temperature and humidity. The image forming apparatus described in 1.   A process cartridge having at least a developing device and a photoconductor is configured to be detachable from the main body case. When replacing the process cartridge, the background potential is set larger than the set value at the time of image formation when the initial unit is started. The image forming apparatus according to claim 1, wherein the developer is stirred.

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