JP2010060740A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents an image defect caused by deterioration of toner by forcibly discharging toner on a toner carrier, and suppresses the deterioration of the toner by suppressing the driving time of a developing device to absolute minimum. <P>SOLUTION: A developing device 16 is connected to a main motor 25 through a developing clutch 30. When performance of a refreshing stage is designated when turning on a power source or when restoring from a sleep mode, a main motor driving time X, a developing bias applying time Y and a developing clutch turn-on time Z are decided on the basis of absolute humidity. Thereafter, the toner is discharged to a photoreceptor drum 14 from a developing roller 16a in a state where the developing clutch 30 is kept off. After the predetermined time, the developing clutch 30 is turned on to drive the developing device 16 for the time Z. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a photosensitive drum and a developing device, and more particularly to an image forming device capable of executing a refresh process for refreshing toner on a developing roller during non-image formation.

  In the conventional image forming apparatus, when the image formation is repeated, particularly when the printing rate on the image (the ratio of the printed area to the area where the image can be formed (paper area); the same applies hereinafter) is low. Since there is little toner used for development by flying from the toner carrier (developing roller) to the electrostatic latent image carrier (photoreceptor drum), the replacement of toner particles in the developing device is reduced. As a result, the toner may be deteriorated due to peeling of the external additive or embedded in the toner, and the charging characteristics may be changed, and the toner may be excessively charged to cause a decrease in image density and fogging. In particular, an image forming apparatus having a plurality of developing devices such as a color machine can handle images with a high printing rate such as photographs and graphic images to images with a low printing rate such as only characters and logo marks. It is necessary to increase the variation in the printing rate for each developing device.

  In such a case, a large amount of toner is ejected from the developing roller to the photosensitive drum side by printing a pattern having a high original printing ratio such as solid, and the toner is transferred to a recording medium to consume the toner. However, if the solid pattern is left unprinted for a long period of time, the toner particles are fixed on the surface of the developing roller due to the influence of humidity and the like without being consumed. Sometimes it doesn't.

  Therefore, the toner surface has been improved so that the charge control ability of the toner is stabilized by optimizing the surface shape, material, or external additive of the toner. At present, it has not yet been surely prevented. In order to solve the above-described problems, various methods for forcibly discharging the toner on the developing roller have been proposed. For example, Patent Document 1 discloses that the photosensitive drum from the developing roller side when the printing rate is a predetermined value or less. A method has been proposed in which toner is forcibly discharged to the side and the toner discharge amount is corrected based on the number of prints or the development drive time until the start of toner supply.

  However, even if the method disclosed in Patent Document 1 is used, a user who prints only an image with a low printing rate has a longer driving time of the developing device with respect to the amount of toner consumption, and toner deterioration tends to proceed. Further, since the developing device is driven when the power is turned on or when returning from the power saving mode (sleep mode), the toner in the developing device is agitated and the toner deteriorates without being consumed. In particular, for users who use the device less frequently, since the device immediately enters the sleep mode, preliminary driving is required until the fixing temperature becomes stable. Generally, the fixing device and the developing device are driven in common. Since it is connected to the source, the preliminary driving time of the developing device is inevitably increased.

Patent Document 2 discloses a method of suppressing toner adhesion (fogging) to an image carrier by mounting a clutch on the developing device and turning the clutch on and off according to the rotation of the image carrier. ing.
JP 2003-270878 A Japanese Patent Application Laid-Open No. 7-5735

  By mounting the clutch in the developing device as in Patent Document 2, unnecessary driving time of the developing device can be reduced and toner deterioration can be suppressed. However, if the stirring of the toner in the developing device is limited only by using a clutch, the image density immediately after start-up may decrease or streaks may occur on the developing roller if the device is not used for a long time. The problem that it happens will occur. This is because the toner absorbs moisture in the air and easily aggregates, and is difficult to charge up, and is particularly noticeable in a high temperature and high humidity environment.

  In view of the above problems, the present invention forcibly discharges toner on a toner carrying member to prevent image defects due to toner deterioration, and can suppress toner deterioration by minimizing the drive time of a developing device. An object is to provide a forming apparatus.

  In order to achieve the above object, the present invention provides a housing for storing toner, an agitating / conveying member for agitating and conveying the toner in the casing, and carrying the toner conveyed by the agitating / conveying member to an image carrier. A developing device for developing an electrostatic latent image formed on the surface of the image carrier, a driving source for driving the developing device and an image forming unit including the image carrier, A bias applying means for applying a developing bias to the toner carrier, and a control means for controlling the drive of the bias applying means and the developing device. The toner is supplied from the toner carrier side to the image carrier side during non-image formation. In the image forming apparatus capable of executing a refreshing process for discharging, the control unit applies a developing bias in a state where driving of the stirring and conveying member is stopped at least when the refreshing process is performed. Rutotomoni is characterized in that the stirring carrying member after start of the application of the developing bias is driven for a predetermined time.

  According to the present invention, in the image forming apparatus configured as described above, the control unit stops and drives the toner carrier in synchronization with the stirring and conveying member.

  According to the present invention, in the image forming apparatus configured as described above, the control unit stops driving the developing device during non-image formation other than during the refresh process.

  According to the present invention, in the image forming apparatus having the above configuration, a temperature / humidity detection unit that detects a temperature and humidity inside or outside the apparatus is provided, and the control unit calculates an absolute humidity calculated from a detection result of the temperature / humidity detection unit. Based on the above, the drive time of the stirring and conveying member at the time of executing the refreshing step is determined.

  According to the present invention, in the image forming apparatus having the above-described configuration, a transfer unit that transfers a toner image formed on an image carrier onto a recording medium, and a toner image transferred onto the recording medium by the transfer unit A fixing device having a fixing member for pressurization; and a fixing temperature detecting means for detecting a temperature of the fixing member, wherein the control means is configured to detect the fixing temperature detecting means and the temperature when the power is turned on or when returning from the sleep mode. The refresh process is performed when the difference in detected temperature of the humidity detecting means is equal to or lower than a predetermined temperature.

  According to the present invention, in the image forming apparatus configured as described above, the developing device is connected to the drive source via a clutch.

  According to the first configuration of the present invention, the developing bias is applied at least when the driving of the agitating / conveying member is stopped during the refresh process, and the agitating / conveying member is driven for a predetermined time after the application of the developing bias is started. In addition, since toner is not supplied from the agitating / conveying member to the toner carrier during toner discharge, the deteriorated toner on the toner carrier is efficiently discharged to the image carrier without being mixed with the toner in the developing device. . Further, toner deterioration due to rotation of the stirring and conveying member can be suppressed.

  According to the second configuration of the present invention, in the image forming apparatus having the first configuration, the toner carrier is stopped and driven in synchronization with the stirring and conveying member, so that the toner carrier is stopped. Since the toner discharge is started, it is possible to preferentially discharge the toner adhering to the portion exposed from the housing of the toner carrier, which is particularly susceptible to moisture absorption and easily deteriorates.

  Further, according to the third configuration of the present invention, in the image forming apparatus having the above first or second configuration, the fixing temperature stabilization time when the power is turned on or when returning from the sleep mode, the sheet interval during continuous printing, etc. By stopping the driving of the developing device at the time of non-image formation, unnecessary driving of the developing device can be reduced, mechanical stress applied to the internal toner can be reduced, and toner deterioration can be minimized. . In addition, it is possible to suppress image density reduction and streaking on the developing roller when driving of the developing device is stopped for a long time by executing the refresh process.

  According to the fourth configuration of the present invention, in the image forming apparatus having any one of the first to third configurations, the refresh process is executed based on the absolute humidity calculated from the detection result of the temperature / humidity detection unit. By determining the driving time of the agitating / conveying member at the time, the driving time of the agitating / conveying member or the driving time of the agitating / conveying member and the toner carrier can be set to the minimum necessary time according to the environmental conditions. Deterioration can be further suppressed.

  According to the fifth configuration of the invention, in the image forming apparatus having the fourth configuration, the difference between the detected temperatures of the fixing temperature detecting means and the temperature / humidity detecting means is predetermined when the power is turned on or when returning from the sleep mode. By performing the refresh process when the temperature is equal to or lower than the temperature, the refresh process is performed only when a long time has elapsed since the power was turned off or the sleep mode was entered. Therefore, unnecessary execution of the refresh process is suppressed, so that the waiting time of the user can be shortened and the image forming efficiency can be improved.

  According to the sixth configuration of the present invention, in the image forming apparatus having any one of the first to fifth configurations, the developing device is connected to the drive source via the clutch, so that the developing device is Even in the case where the image forming units that are included are connected to a common drive source, the driving of the developing device can be controlled independently of the other parts of the image forming unit with a simple configuration.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall configuration of the image forming apparatus of the present invention. As shown in FIG. 1, an image forming apparatus (in this case, a monochrome printer) 100 includes a sheet feeding cassette 2 that accommodates stacked sheets at the bottom of the main body. Above this paper feed cassette 2 is formed a paper transport path 4 extending substantially horizontally from the front of the main body (right side in FIG. 1) to the rear of the main body and further upward to reach the paper discharge unit 3 formed on the upper surface of the main body. A pickup roller 5, a feed roller 6, an intermediate conveyance roller 7, a registration roller pair 8, an image forming unit 9, a fixing unit 10, and a discharge roller pair 11 are arranged in this order along the paper conveyance path 4 from the upstream side. Has been.

  The paper feed cassette 2 is provided with a paper stacking plate 12 that is rotatably supported with respect to the paper feed cassette 2 by a rotation fulcrum 12a provided at the rear end in the paper transport direction. The sheet thus formed is pressed against the pickup roller 5. A retard roller 13 is disposed in front of the paper feed cassette 2 so as to be in pressure contact with the feed roller 6, and when a plurality of sheets are simultaneously fed by the pickup roller 5, the feed roller 6 and the retard roller 13 are used to roll the paper, and only the topmost sheet is conveyed.

  Then, the sheet fed by the feed roller 6 and the retard roller 13 is conveyed to the registration roller pair 8 by changing the conveyance direction to the rear of the apparatus by the intermediate conveyance roller 7, and the timing is adjusted by the registration roller pair 8. And conveyed to the image forming unit 9.

  The image forming unit 9 forms a predetermined toner image on a sheet by an electrophotographic process. The image forming unit 9 is a photosensitive drum 14 that is an image carrier rotatably supported in the clockwise direction in FIG. Above the charging drum 15, the developing device 16, the cleaning device 17, the transfer roller 18 disposed so as to face the photosensitive drum 14 across the sheet conveyance path 4, and the photosensitive drum 14. A toner container 20 for supplying toner to the developing device 16 as necessary is disposed above the developing device 16.

  For example, the photosensitive drum 14 is formed by laminating a photosensitive layer on an aluminum drum. As the photosensitive material for forming the photosensitive layer, an amorphous silicon photoreceptor or an organic photoreceptor (OPC photoreceptor) is used. As the charging device 15, a scorotron charging device using a corona discharge charger is used, and a metal shield case having a U-shaped cross section disposed so that the opening faces the photosensitive drum 14 is disposed inside. Corona wires and grids, which are discharge members made of tungsten, stainless steel, etc., are provided, and a predetermined charging bias is applied to the corona wires and grids to generate corona discharge and control the amount of electrons. As a result, the surface of the photosensitive drum 14 is uniformly charged with a predetermined polarity and potential.

  Next, the photosensitive drum 14 is exposed to light by a laser beam from a laser scanning unit (LSU) 19 to attenuate charging, and an electrostatic latent image based on image data input to the surface of the photosensitive drum 14 is formed. . Then, the developing device 16 attaches toner to the electrostatic latent image to form a toner image on the surface of the photosensitive drum 14. The toner image formed on the photosensitive drum 14 is transferred onto a sheet supplied to the nip portion (transfer position) between the photosensitive drum 14 and the transfer roller 18 by the transfer roller 18.

  The sheet on which the toner image is transferred is separated from the photosensitive drum 14 and conveyed toward the fixing unit 10. The fixing unit 10 is disposed on the downstream side of the image forming unit 9 in the sheet conveyance direction, and includes a heating roller 21 and a pressure roller 22 that is pressed against the heating roller 21. The sheet on which the toner image is transferred in the image forming unit 9 is heated and pressed by passing through the nip portion between the heating roller 21 and the pressure roller 22, and the toner image transferred to the sheet is fixed. A fixing thermistor 23 that detects the surface temperature of the heating roller 21 is provided in the fixing unit 10.

  The paper that has passed through the fixing unit 10 is discharged to the paper discharge unit 3 by the discharge roller pair 11. On the other hand, the toner remaining on the surface of the photosensitive drum 14 is removed by the cleaning device 17. The photosensitive drum 14 is neutralized by a neutralizing device (not shown) and then charged again by the charging device 15, and image formation is performed in the same manner. Further, an external temperature / humidity sensor 24 is disposed above the toner container 20 for the purpose of measuring the apparatus installation environment (machine peripheral environment).

  When the image forming apparatus 100 is not transferred to a recording medium, for example, when the image forming apparatus is started from a power-off state or a sleep (power saving) mode to a copy start state, or a predetermined number of prints are performed. Sometimes, a refreshing process for discharging the toner on the developing roller 16a in the developing device 16 to the photosensitive drum 14 side can be executed.

  FIG. 2 is a side sectional view of the developing device. As shown in FIG. 2, the developing device 16 includes a casing 31a in which a one-component developer made of magnetic toner is stored, and a cover 31b that seals the developer stored in the casing 31a so as not to leak to the outside. A casing 31 is provided with a first spiral member 32, a second spiral member 33, a developing roller 16a, and a regulating blade 36.

  The inside of the casing 31a is partitioned into a first storage chamber 38 and a second storage chamber 39 by a partition plate 37 extending in the longitudinal direction. In the first storage chamber 38, a first spiral member 32 is provided in the second storage chamber 38. A second spiral member 33 is disposed in each storage chamber 39. Further, the partition plate 37 is not provided at both ends in the longitudinal direction (paper surface direction) of the casing 31 a, and this portion is a passage (toner) in which the toner moves between the first storage chamber 38 and the second storage chamber 39. It is a delivery section).

  The first spiral member 32 and the second spiral member 33 are respectively composed of rotating shafts 32a and 33a and spiral blades 32b and 33b integrally formed on the outer peripheral surface thereof, and rotate into the casing 31a so as to be substantially parallel to each other. The first spiral member 32 and the second spiral member 33 rotate in a predetermined direction so that the toner in the first storage chamber 38 and the second storage chamber 39 is circulated and conveyed. Yes.

  Further, a toner amount detection sensor (not shown) is arranged on the inner wall surface of the casing 31a, and the cover 31b has a cover 31b so that toner can be replenished in the casing 31a according to the detection result of the toner amount detection sensor 41. A toner supply port (not shown) through which toner is supplied from the toner container 20 (see FIG. 1) is provided.

  The developing roller 16 a is rotatably supported in the first storage chamber 38 so as to be substantially parallel to the first spiral member 32 and the second spiral member 33. The developing roller 16a uses a magnet roller having a magnetic field generating member (not shown) made of a permanent magnet fixed on the inner surface thereof, and toner adheres (carries) to the surface of the developing roller 16a by the magnetic force of the magnetic field generating member. ) To form a toner layer. Then, the toner adhering to the developing roller 16a in a predetermined developing area flies to the photosensitive drum 14 due to the potential difference between the surface potential of the photosensitive drum 14 and the developing bias applied to the developing roller 16a, and adheres to the photosensitive layer. As a result, a toner image is formed on the surface of the photosensitive drum 14.

  The regulating blade 36 regulates the amount of toner supplied to the photosensitive drum 14, that is, the amount of toner attached to the developing roller 16a. For example, a nonmagnetic SUS (stainless steel) such as SUS303 is used. The regulating blade 36 is disposed so that a predetermined gap is formed between the tip of the regulating blade 36 and the developing roller 16a, and the toner to the developing roller 16a is formed by the gap between the regulating blade 36 and the developing roller 16a. The amount of adhesion is regulated, and a thin toner layer of several hundred microns is formed on the surface of the developing roller 16a.

  FIG. 3 is a block diagram showing an example of a control path used in the image forming apparatus of the present invention. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit a control signal to each device in the temporary storage unit 94, the counter 95, and the image forming apparatus 100 for storing image data and the like, and receive an input signal from the operation unit 50. The I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. The counter 95 adds up the number of printed sheets and counts it. Note that the number of times may be stored in the RAM 93, for example, without providing the counter 95 separately.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. Examples of the parts and devices controlled by the control unit 90 include the fixing unit 10, the charging device 15, the developing device 16, the laser scanning unit 19, the toner container 20, the external temperature / humidity sensor 24, the main motor 25, and the developing clutch 30. , An image input unit 40, a bias control circuit 41, an operation unit 50, and the like.

  The main motor 25 drives the fixing unit 10, the photosensitive drum 14, the developing device 16, the cleaning device 17, the transfer roller 18 and the like according to a control signal from the control unit 90. The main motor 25 is connected to the developing device 16 via the developing clutch 30. By driving the developing clutch 30 in accordance with a control signal from the control unit 90, the driving of the developing device 16 is fixed to the fixing unit 10 and the photosensitive member. It can be controlled independently from the drum 14, the cleaning device 17, the transfer roller 18, and the like. As the developing clutch 30, an electromagnetic clutch that transmits and interrupts the driving force by turning ON / OFF the current is used.

  When the image forming apparatus 100 is a printer as shown in FIG. 1, the image input unit 40 is a receiving unit that receives image data transmitted from a personal computer or the like. When the image forming apparatus 100 is a copying machine, Scanning optical system equipped with a scanner lamp that illuminates the document during copying and a mirror that changes the optical path of the reflected light from the document, a condensing lens that focuses the reflected light from the document and forms an image It is an image reading unit composed of a CCD or the like that converts image light into an electrical signal. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, and the transfer bias power source 44, and operates each of these power sources according to an output signal from the control unit 90. These power sources are bias controlled. In accordance with a control signal from the circuit 41, a predetermined bias is applied to the charging device 15, the developing roller 16a, and the transfer roller 18.

  The operation unit 50 is provided with a liquid crystal display unit 51, LEDs 52 indicating various states, and a numeric keypad 53, and the user operates the operation unit 50 to input instructions, thereby making various settings of the image forming apparatus 100. And execute various functions such as image formation. The liquid crystal display unit 51 displays the state of the image forming apparatus 100, displays the image forming status and the number of copies, and can be used as a touch panel to perform various settings such as functions such as double-sided printing and black-and-white reversal, magnification setting, and density setting. It has become. The numeric keypad 53 is used for setting the number of copies to be printed and for inputting the other party's FAX number when the image forming apparatus 100 also has a FAX function.

  In addition, the operation unit 50 includes a start button for instructing the user to start image formation, a stop / clear button used when the image formation is stopped, and various settings of the image forming apparatus 100 in a default state. A reset button or the like is provided for use.

  In the image forming apparatus of the present invention, the developing clutch 30 is disengaged during non-image formation (when the power is turned on or when returning from the sleep mode, the interval between sheets during continuous printing, etc.) except during the refresh process. The driving of the developing device 16 is stopped. Thereby, unnecessary driving of the developing device 16 can be reduced as much as possible to reduce mechanical stress applied to the internal toner, and toner deterioration can be minimized.

  If the developing device 16 is left without being driven for a long time, the toner on the developing roller 16a deteriorates due to moisture absorption, the image density immediately after startup decreases, or the toner on the developing roller 16 becomes thin due to toner aggregation. Streaks may occur in the layer. Therefore, in the present invention, the above-mentioned problem is prevented by executing the refresh process when the power is turned on (when the apparatus is started up) or when returning from the sleep mode.

  FIG. 4 is an example of a timing chart showing ON / OFF timings of the main motor, the developing clutch, the developing bias, the charging bias, the laser exposure, and the transfer bias (cleaning bias) in the refresh process. The execution procedure of the refresh process of the present invention will be described using FIG. 4 with reference to FIGS. 1 to 3 as necessary. Here, a case where positively charged toner is used will be described.

  When the execution of the refresh process is instructed, as shown in FIG. 4, the main motor 25 is turned on, and the photosensitive drum 14, the cleaning device 17, and the transfer roller 18 start to rotate. At the same time, the charging bias applied to the charging device 15 is turned on, and the surface of the photosensitive drum 14 is uniformly positively charged. Next, laser exposure by the laser scanning unit 19 is turned on, and the charge on the surface of the photosensitive drum 14 is partially attenuated. The developing bias having the same polarity (positive) as the toner applied to the developing roller 16a is also turned on almost simultaneously.

  When this laser exposure area (charging attenuation area) comes to a position facing the developing roller 16a by the rotation of the photosensitive drum 14, the toner on the developing roller 16a repels the developing bias and adheres to the laser exposure area. As a result, a toner discharge pattern T as shown in FIG. 5 is formed on the photosensitive drum 14. The toner discharge pattern T has a rectangular shape having a width H of the developing region of the developing roller 16a (see FIG. 1) and a printing length (toner discharge length) L in the circumferential direction of the drum as two sides, and the toner discharge length L Is determined by the laser exposure time (= development bias ON time Y) in FIG. A method for determining the developing bias ON time Y will be described later.

  Since the developing clutch 30 is OFF when the developing bias is turned ON, the developing roller 16a, the first spiral member 32, and the second spiral member 33 in the developing device 16 are stopped. For this reason, the toner on the developing roller 16a that is exposed from the casing 31a having a particularly high degree of deterioration due to moisture absorption is discharged to the photosensitive drum 14 first. Further, since the first spiral member 32 and the second spiral member 33 are stopped, it is possible to suppress the problem that the toner in the casing 31a is sent to the vicinity of the developing roller 16a and discharged together with the deteriorated toner. Thereafter, after a predetermined time t1 (here, 500 msec) has passed and the deteriorated toner on the developing roller 16a has been sufficiently discharged, the developing clutch 30 is turned on, and stirring of the toner in the developing device 16 is started.

  Further, a configuration in which only the first spiral member 32 and the second spiral member 33 are stopped by turning off the developing clutch 30 is also possible. In this case, since the developing roller 16a rotates at the start of toner discharge, a part of the toner exposed from the toner casing 31a returns into the casing 31a. However, the spiral members 32 and 33 cause the toner to be applied to the developing roller 16a. Since the toner is not sent anew, mixing of the deteriorated toner on the developing roller 16a and the toner in the casing 31a is suppressed. That is, at least the first spiral member 32 and the second spiral member 33 stop rotating at the start of toner discharge, so that the chargeability and fluidity of the toner can be maintained well.

  The developing clutch ON time Z only needs to be ensured for a time during which the charging of the toner in the developing device 16 is stabilized. However, since the deteriorated toner on the developing roller 16a is not mixed into the developing device 16, the toner charge rises earlier. The stirring time can be shortened. Further, heat generation and toner aggregation due to agitation are suppressed, and toner deterioration can also be suppressed. Furthermore, by changing the developing clutch ON time Z according to environmental conditions, particularly humidity conditions, it is possible to maintain the density immediately after the start-up of the apparatus while suppressing toner deterioration. That is, the minimum required time for charging of the developing device 16 to be stable is achieved by increasing Z under high humidity conditions where the toner is difficult to charge up, and shortening Z under low humidity conditions where the toner is easily charged up. Can only be driven.

  On the other hand, when the drum surface is oxidized by repeatedly charging the surface of the photosensitive drum 14 by the charging device 15, the hydrophilicity of the drum surface increases and it becomes easy to adsorb moisture in the air. Then, adhesion of water-soluble ion products such as NOx and SOx generated by the discharge of the charging device 15 reduces the resistance of the surface of the photosensitive drum. As a result, a lateral flow of potential occurs at the edge portion of the electrostatic latent image formed on the surface of the photosensitive drum, and a so-called “image flow phenomenon” occurs.

  Therefore, drum refresh is performed to polish the photosensitive drum 14 using the toner discharged from the developing roller 16a. Specifically, when the cleaning device 17 collects toner including abrasives discharged onto the photosensitive drum 14, the cleaning roller (rubbing roller) is rotated with a speed difference with respect to the photosensitive drum 14. Then, the surface of the photosensitive drum 14 is polished, and moisture and contaminants on the drum surface are removed together with the toner.

  In order to prevent the toner discharge pattern T from adhering to the transfer roller 18, a transfer bias (transfer reverse bias) having the same polarity (positive) as that of the toner is applied almost simultaneously with the ON of the developing bias. The ON state of the transfer reverse bias is turned off after a predetermined time t2 (here, 1 sec) after the developing clutch 30 is turned off.

  Next, a cleaning bias (transfer positive bias) having a reverse polarity (negative) to the toner is applied to the transfer roller 18 for a predetermined time t3. As a result, the reversely charged toner adhering to the transfer roller 18 repels the cleaning bias and moves to the photosensitive drum 14 side. The application time t3 of the cleaning bias having the polarity opposite to that of the toner is preferably set to be longer than the time required for one rotation of the transfer roller 18 (here, 1 sec). Subsequently, when a cleaning bias (transfer reverse bias) having the same polarity (positive) as the toner is applied again, the positively charged toner attached to the transfer roller 18 is repelled by the cleaning bias and moves to the photosensitive drum 14 side.

  Then, after the predetermined time X has elapsed, the main motor 25 is turned off, and at the same time, the cleaning bias is turned off and the refreshing process is terminated. The main motor driving time X is determined in consideration of a time during which the fixing temperature of the fixing unit 10 is stabilized (hereinafter, referred to as a fixing stabilization time) and a time required for drum refreshing by the cleaning device 17. For example, under high-humidity conditions where image flow phenomenon is likely to occur, X should be sufficiently longer than the fixing stabilization time to sufficiently perform drum refresh, and under low humidity conditions where image flow phenomenon is unlikely to occur, X is set as fixing stability time. Just do it.

  Next, a method for determining the main motor drive time X (sec) and the development bias application time Y (msec) in the refresh process will be described. Table 1 shows a setting example of the driving time X of the main motor and the developing bias application time Y. Setting conditions are stored in the ROM 92 (or RAM 93).

  From Table 1, the main motor drive time X is set to a reference value of 150 sec when the absolute humidity (HUMID) is 150 to 249, and an appropriate drum refresh time is ensured at an absolute humidity of 250 or more at which image flow phenomenon is likely to occur. Therefore, it is set to 180 sec (reference value + 30 sec). Since the time required for temperature stabilization of the fixing unit 10 is longer than the time required for drum refreshing at an absolute humidity of 149 or less at which the image flow phenomenon is unlikely to occur, the fixing stabilization time is set.

  The developing bias application time Y is set in two stages depending on the linear velocity of the developing roller 16a. When the linear velocity is 230 mm / sec, the reference value is set to 540 msec when the absolute humidity (HUMID) is 150 to 249, and the toner discharge length L (see FIG. 5) is 230 (mm / sec) × 0.54 (sec). ) ≈124 mm. Since the toner discharge amount needs to be increased when the absolute humidity is 250 or more, where the toner is easy to absorb moisture, it is set to 810 msec (3/2 times the reference value). Further, when the absolute humidity is 149 or less where the toner hardly absorbs moisture, the amount of discharged toner can be reduced, so that it is set to 270 msec (1/2 times the reference value).

  When the linear velocity is 178 mm / sec, the reference value is set to 698 msec when the absolute humidity (HUMID) is 150 to 249, and the toner discharge length L is 178 (mm / sec) × 0.698 (sec) ≈124 mm. It becomes. That is, the toner discharge length L is set to be equal to that at the linear speed of 230 mm / sec. The absolute humidity of 250 or more and the absolute humidity of 149 or less are the same as in the case of the linear velocity of 230 mm / sec (3/2 times and 1/2 times the reference value).

  Next, a method for determining the developing clutch ON time Z (msec) will be described. FIG. 6 shows a reference image (solid patch) printed immediately after the image forming apparatus is left for 20 hours under H / H (high temperature and high humidity) conditions (32.5 ° C./80%) and the apparatus is started up (power ON). ) Is a graph showing the relationship between the image density (ID; image density) and the development drive time. As shown in FIG. 6, when the toner is left in the H / H condition for a long time, the toner on the developing roller 16a has deteriorated due to moisture absorption, so that the developing device 16 is not preliminarily driven immediately after the start-up of the device. When image formation is started, the ID of the reference image is reduced to 0.98. Further, when the developing device 16 is preliminarily driven, the ID of the reference image is gradually increased, and the image density is stable at around 1.25 by driving for about 40 sec. It can be seen that a development drive time of 30 sec is required to output an image having a reference density (ID = 1.2) immediately after the apparatus is started up.

  FIG. 7 shows the image density (ID) of a reference image (solid patch) printed immediately after starting the apparatus (power ON) after being left for 48 hours under N / N (normal temperature and normal humidity) conditions (23 ° C./50%). The image density) and the development drive time. In the case of FIG. 7, since the degree of deterioration of the toner on the developing roller 16a due to moisture absorption is lower than in FIG. 6, the ID of the reference image is 1.18 even when the developing device 16 is not preliminarily driven. In addition, the image density is stabilized at around 1.35 by driving for about 10 seconds, and a development driving time of about 1 second is sufficient to output an image having a reference density (ID = 1.2) immediately after the start-up of the apparatus. I understand.

  Here, since the H / H condition corresponds to the absolute humidity 300 and the N / N condition corresponds to the absolute humidity 100 to 150, if the relationship between the absolute humidity and the developing clutch ON time Z is determined based on FIGS. good. FIG. 8 is a graph showing a control example for determining the developing clutch ON time Z from the absolute humidity. In FIG. 8, when the absolute humidity (HUMID) does not exceed 150, the developing clutch ON time Z is set longer than the developing bias application time Y by 1 sec. The development clutch ON time Z is gradually increased in proportion to the increase in absolute humidity from 150 to 300, and is set to 35 sec (fixed value) when the absolute humidity exceeds 300. The setting conditions for the developing clutch ON time Z are stored in the ROM 92 (or RAM 93), as are the setting conditions for the main motor driving time X and the developing bias application time Y.

  FIG. 9 is a flowchart illustrating a control example for determining the execution condition of the refresh process based on the absolute humidity. The execution procedure of the refresh process of the present invention will be described according to the steps of FIG. 9 with reference to FIGS. 1 to 8 as necessary. In FIG. 9, it is assumed that the refresh process is executed immediately after the power is turned on or immediately after the return from the sleep mode and when the difference between the fixing temperature and the environmental temperature is within a predetermined temperature (50 ° C. in this case).

  First, when the power of the image forming apparatus is turned on, or when the image forming apparatus returns from the sleep mode by a copy, print command, FAX reception or the like (step S1), the control unit 90 detects the fixing temperature T1 detected by the fixing thermistor 23 and the outside of the apparatus. It is determined whether or not the difference T1-T2 between the outside temperature T2 detected by the temperature / humidity sensor 24 is 50 ° C. or less (step S2). When T1-T2 ≦ 50, the refresh process is started, and the controller 90 sets the setting conditions (see Table 1 and FIG. 8) stored in the ROM 92 (or RAM 93) and the temperature detected by the outside temperature / humidity sensor 24. Based on the absolute humidity calculated from the humidity, the main motor drive time X, the development bias ON time Y, and the development clutch ON time Z are determined (step S3).

  Next, the main motor 25 is turned on, and at the same time, the charging bias applied to the charging device 15 is turned on to uniformly charge the drum surface (step S4). Further, the exposure by the laser scanning unit 19 is turned on for a predetermined time (= development bias ON time Y), a laser exposure area is formed on the photosensitive drum 14, and the development bias applied to the developing roller 16a is turned on to develop. The toner on the roller 16a moves to the laser exposure area.

  At this time, since the developing clutch is OFF and the developing roller 16a and the spiral members 32 and 33 are stopped, only the deteriorated toner on the developing roller 16a is discharged onto the photosensitive drum 14. Then, the transfer bias applied to the transfer roller 18 is turned on (step S6). Here, in order to prevent the toner from adhering to the transfer roller 18, a reverse transfer bias (positive bias) having the same polarity as the toner is applied. Therefore, the toner discharged onto the photosensitive drum 14 is conveyed to the cleaning device 17 without adhering to the transfer roller 18 and is used for polishing the photosensitive drum 14 by the cleaning roller (sliding roller), and then the drum surface. Collected with dirt and moisture.

  Next, after a predetermined time has elapsed (after 500 msec in FIG. 4), the developing clutch 30 is turned on, the developing roller 16a and the spiral members 32 and 33 start to rotate, and stirring is performed until the charging of the toner in the developing device 16 is stabilized. (Step S7). Further, after a lapse of time Y from the development bias ON, the development bias is turned OFF (step S8). Subsequently, after the time Z has elapsed since the developing clutch 25 was turned on, the developing clutch 25 is turned off (step S9).

  Further, after the bias applied to the transfer roller 18 is switched from the transfer reverse bias to the transfer positive bias (negative bias) having a polarity opposite to that of the toner, the reversely charged toner attached to the transfer roller 18 is moved to the photosensitive drum 14 side. Switching to the reverse transfer bias again, the positively charged toner adhering to the transfer roller 18 is moved to the photosensitive drum 14 side (step S10). Thereafter, after time X has elapsed since the main motor 25 was turned on, the main motor 25 is turned off and at the same time the transfer bias is turned off, and the refreshing process is terminated (step S10). If T1-T2> 50 in step S2, only a short time has elapsed since the power was turned off or the sleep mode was entered, and the process ends without executing the refresh process.

  According to the above control, toner is discharged without driving the developing device 16 when the refresh process is executed, so that the deteriorated toner on the developing roller 16a can be preferentially removed. Further, after the developing device 16 is driven for a minimum time necessary to stabilize the charging of the toner in the developing device 16, the driving of the developing device 16 is stopped again. The image forming apparatus is highly convenient and can suppress the deterioration of the toner.

  Further, by changing the main motor drive time X, development bias application time Y, and development clutch ON time Z based on the absolute humidity, the refresh process execution time, the toner discharge amount during the refresh process, and the developer agitation time The minimum required time according to the absolute humidity. Therefore, the deterioration of the toner can be further suppressed according to the environmental conditions, and the waiting time of the user by the refresh process can be shortened.

  In addition, the average temperature and the average humidity per predetermined time (for example, the past 30 minutes) of the outside temperature and humidity detected by the outside temperature and humidity sensor 24 are calculated, and the absolute humidity is calculated based on the calculated average temperature and average humidity. May be set. According to this control, since the average value of the temperature and humidity is used to determine the refresh condition, it is possible to determine an appropriate refresh condition that reflects the use environment condition more accurately.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the refresh process shown in FIG. 4 and FIG. 9, the ON timing of the main motor 25 and the ON timing of the charging bias, and the ON timing of the developing bias and the ON timing of the laser exposure are almost the same. For example, after turning on the main motor, the charging bias may be turned on after a lapse of a predetermined time. Further, the ON timing of the developing bias is not particularly limited as long as the laser exposure region formed by laser exposure is not moved to a position facing the developing roller 16 a by the rotation of the photosensitive drum 14. Further, the ON timing of the transfer bias may be before the toner discharged onto the photosensitive drum 14 moves to a position facing the transfer roller 18, and the number of times of switching between the transfer reverse bias and the transfer forward bias is arbitrarily set. It can be set.

  In the above embodiment, the driving of the developing device 16 can be controlled independently by using the developing clutch 30. However, a sub motor for driving the developing device 16 may be provided separately from the main motor 25. The present invention is not limited to the monochrome printer as shown in FIG. 1, but various image forming apparatuses such as a digital multifunction peripheral, an analog monochrome copying machine, a tandem or rotary developing color copying machine, a printer, and a facsimile. Of course, it can be applied to.

  The relationship between the printing rate (toner consumption per unit time) and development streaks when the refresh mode was executed was investigated. As an evaluation method, a printing machine (KM-5035 manufactured by Kyocera Mita Co., Ltd.) was used, and the printing temperature was 1%, 2%, 3% under conditions where the environmental temperature (outside machine temperature) was 18 ° C, 23 ° C, and 28 ° C. The occurrence of streaks on the surface of the developing roller after the% and 6% test images were continuously printed for 24 hours in a non-sheet passing state was visually observed. The results are shown in Table 2. Note that the blade temperature in Table 2 indicates the temperature near the regulating blade 36 (see FIG. 2) of the developing device 16 during continuous printing (the temperature at which the head is cut off).

  As is apparent from Table 2, when the printing rate is 1%, one streak is formed on the developing roller at an environmental temperature of 23 ° C. (blade temperature of 36 ° C.), and four streaks are generated at an environmental temperature of 28 ° C. (blade temperature of 41 ° C.). Occurred. When the printing rate was 2%, one streak occurred at an environmental temperature of 28 ° C. (blade temperature of 41 ° C.). On the other hand, streaks did not occur even at an environmental temperature of 28 ° C. (blade temperature of 41 ° C.) at printing rates of 3% and 6%. From this result, it was confirmed that streaks are more likely to occur as the printing rate decreases and the environmental temperature (blade temperature) increases.

  Using the image forming apparatus of the present invention equipped with a developing clutch and the image forming apparatus not equipped with the developing clutch used in Example 1 (comparative example), the toner consumption per unit time and the effect of suppressing streaks on the developing roller Was evaluated. In the evaluation method, the image forming apparatuses of the present invention and the comparative example simulate the repetition of five continuous printings of test images (printing rate 5%) after returning from the sleep mode, and the toner consumption per unit time (5 printings) Toner consumption at the time / development drive time from the return to sleep mode until the end of printing). The results are shown in FIG. Similarly, the toner consumption per unit time under each condition of Example 1 was also calculated and plotted together in FIG.

  From the results of Example 1, streaks occurred at a blade temperature of 36 ° C. and 41 ° C. at a printing rate of 1% (indicated by ◇ in the figure), and at a blade temperature of 41 ° C. at a printing rate of 2% (indicated by Δ in the figure). As streaks occur, no streaks occur at a printing rate of 3% (indicated by a square in the figure) and a printing rate of 6% (indicated by a circle in the figure). The boundary line is as shown by the solid line A in the figure. That is, it is considered that the risk of streaking increases in the area below the solid line A.

  Then, the toner consumption amount per unit time in the present invention equipped with the developing clutch is as shown by a one-dot chain line B in the figure, and streaks do not occur regardless of the blade temperature. On the other hand, the toner consumption per unit time in the comparative example without the developing clutch is a broken line C, and it can be seen that the risk of streaking increases when the blade temperature exceeds 35 ° C. From this result, it was confirmed that by installing the developing clutch and reducing the driving time of the developing device, it is possible to suppress toner deterioration even under high temperature and high humidity conditions and to reduce the generation of streaks on the developing roller.

  INDUSTRIAL APPLICABILITY The present invention can be used for an image forming apparatus capable of executing a refresh process for discharging toner from the toner carrier to the image carrier during non-image formation, and at least the stirring and conveying member is stopped during the refresh process. The developing bias is applied, and the stirring and conveying member is driven for a predetermined time after the application of the developing bias is started.

  As a result, it is possible to provide an image forming apparatus that can efficiently discharge the deteriorated toner on the developing roller to the image carrier side and also suppress the deterioration of the toner due to the rotation of the stirring and conveying member. Furthermore, the deteriorated toner on the toner carrier can be discharged more efficiently by stopping and driving the toner carrier in synchronization with the stirring and conveying member.

  In addition, since the toner agitation time is further shortened by stopping the driving of the developing device during non-image formation other than during the refresh process, toner deterioration can be more effectively suppressed. At this time, if the developing device is stopped for a long time, the image density may decrease immediately after the start-up of the device or streaks may be generated on the toner carrying member. Therefore, it is possible to suppress the decrease in density and the generation of streaks. As a simple and low-cost method for independently controlling the developing device, there is a method of connecting the developing device and the drive source via a clutch.

  Further, by determining the drive time of the agitating / conveying member at the time of executing the refresh process based on the absolute humidity, the driving time of the agitating / conveying member or the driving time of the agitating / conveying member and the toner carrier is required according to the environmental conditions. The minimum time can be set, and toner deterioration can be further suppressed.

  In addition, if the temperature difference between the fixing temperature and the environmental temperature determines the elapsed time from the stop of the apparatus and the temperature difference is below a predetermined temperature after turning on the power or returning from the sleep mode, the refresh process is executed. Further, when only a short time has passed since the power is turned off or the sleep mode is entered, excessive refresh execution can be restricted, and an image forming apparatus capable of executing necessary and sufficient refresh according to the use state of the apparatus is obtained.

FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus of the present invention. FIG. 3 is a side sectional view showing an internal structure of the developing device. FIG. 3 is a block diagram showing a control path of the image forming apparatus of the present invention. These are timing charts showing examples of ON / OFF timings of the main motor, developing clutch, developing bias, transfer bias, charging bias, and laser exposure in the refresh process. FIG. 4 is a diagram illustrating an example of a toner discharge pattern used in the present invention. FIG. 4 is a graph showing the relationship between the image density of a reference image printed immediately after the start-up of the apparatus and the development drive time after the image forming apparatus is left under H / H conditions for 20 hours. 4 is a graph showing the relationship between the image density of a reference image printed immediately after the apparatus is started up and the development drive time after the image forming apparatus is left for 48 hours under N / N conditions. These are the graphs which show the example of control which determines the developing clutch ON time Z from absolute humidity. These are the flowcharts which show the execution example of the refresh process in the image forming apparatus of this invention. These are graphs comparing the toner consumption per unit time and the risk of streaks on the developing roller in the present invention and comparative examples.

Explanation of symbols

10 Fixing Unit 14 Photosensitive Drum (Image Carrier)
15 Charging device 16 Developing device 16a Developing roller (toner carrier)
17 Cleaning device 18 Transfer roller (transfer means)
20 Toner container 23 Fixing thermistor (fixing temperature detection means)
24 External temperature / humidity sensor (temperature / humidity detection means)
25 Main motor (drive source)
30 Developing clutch 32 First spiral member (stirring conveyance member)
33 Second spiral member (stirring conveying member)
41 Bias control circuit (bias applying means)
42 Charging Bias Power Supply 43 Development Bias Power Supply 44 Transfer Bias Power Supply 90 Control Unit (Control Unit)
91 CPU
92 ROM
93 RAM
100 Image forming apparatus

Claims (6)

A housing that contains toner, an agitation conveyance member that agitates and conveys the toner in the enclosure, and a toner carrier that carries the toner conveyed by the agitation conveyance member and supplies the toner to the image carrier. A developing device for developing the electrostatic latent image formed on the surface of the carrier;
A driving source for driving an image forming unit including the developing device and the image carrier;
Bias applying means for applying a developing bias to the toner carrier;
Control means for controlling the bias applying means and driving of the developing device,
In an image forming apparatus capable of executing a refresh process for discharging toner from the toner carrier side to the image carrier side during non-image formation,
The control means applies a developing bias in a state where driving of the agitating / conveying member is stopped at least during execution of the refreshing process, and drives the agitating / conveying member for a predetermined time after starting the application of the developing bias. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit stops and drives the toner carrier in synchronization with the stirring and conveying member.   The image forming apparatus according to claim 1, wherein the control unit stops driving of the developing device during non-image formation other than during the refresh process. Equipped with temperature and humidity detection means for detecting the temperature and humidity inside or outside the device,
The control unit determines a drive time of the stirring and conveying member during execution of the refreshing step based on an absolute humidity calculated from a detection result of the temperature and humidity detection unit. The image forming apparatus according to claim 3. Transfer means for transferring a toner image formed on the image carrier onto a recording medium;
A fixing device having a fixing member that heats and pressurizes the toner image transferred onto the recording medium by the transfer means;
Fixing temperature detecting means for detecting the temperature of the fixing member;
With
The control unit executes the refreshing step when a difference between detected temperatures of the fixing temperature detecting unit and the temperature / humidity detecting unit is equal to or lower than a predetermined temperature when the power is turned on or when returning from the sleep mode. Item 5. The image forming apparatus according to Item 4.   The image forming apparatus according to claim 1, wherein the developing device is connected to the drive source via a clutch.

Images