JP5094425B2 - Image forming apparatus - Google Patents

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 provided with 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 toner particles in the developing device are hardly replaced, and the toner is excessively charged. Image density reduction and image fogging may occur. 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 to the surface of the developing roller due to the effect of charge-up without consumption of the toner, It may not recover.

  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 problems, various methods for forcibly discharging the toner on the developing roller have been proposed. For example, Patent Document 1 discloses that an AC bias is applied to a DC bias when a non-image is formed on the developing roller. A one-component development type image forming apparatus that forcibly consumes toner on a developing roller by applying the superimposed toner is disclosed. Patent Document 2 proposes an image forming apparatus in which an image area ratio (average printing ratio) per unit driving time of the developing device is calculated and the forced consumption of toner is changed according to the image area ratio. Has been.

In Patent Document 3, the charge amount of the toner is calculated from the surface potential of the reference toner image, and compared with a plurality of reference values, the stirring time or stirring speed of the two-component developer is controlled to forcibly consume the toner. An image forming apparatus that performs the above is disclosed. Further, Patent Document 4 discloses an image forming apparatus in which the rotation speed of the developer carrying member is slower than that during normal image formation when the forced consumption operation is performed.
JP 2000-206770 A JP 2003-76079 A JP-A-6-186856 JP-A-2005-43799

  The above-mentioned patent document describes a method for performing the toner forcible discharge periodically according to the number of printed sheets or according to the printing rate. However, in a low-temperature and low-humidity environment, or in an extremely low printing rate, sufficient effects cannot be obtained only by periodic forced discharge, and image fogging may occur. Further, although it is possible to obtain the effect by changing the forced discharge amount according to the environmental conditions, there is a problem that increasing the toner discharge amount leads to an increase in the running cost of the apparatus, which is disadvantageous for the user.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of performing a refresh process at an appropriate timing according to environmental information in a printing rate measurement period.

  In order to achieve the above object, the present invention has a toner carrier that is disposed opposite to an image carrier, carries toner and supplies the image carrier, and a toner image corresponding to an electrostatic latent image on the surface of the image carrier. And a control unit that controls the amount of toner discharged from the toner carrier based on the printing rate of a printed image, and is configured to supply toner from the toner carrier side to the image carrier side during non-image formation. In the image forming apparatus capable of executing the refreshing process to be ejected, a first detection unit for detecting environmental information inside the apparatus is provided, and the control unit performs a refresh process based on a detection result of the first detection unit. It is characterized by determining execution timing.

  According to the present invention, in the image forming apparatus configured as described above, the first detection means is an in-machine temperature / humidity sensor that detects at least one of temperature and humidity inside the apparatus.

  According to the present invention, in the image forming apparatus configured as described above, the in-machine temperature / humidity sensor is disposed in the vicinity of the developing device.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, when the humidity at the printing start time detected by the in-machine temperature / humidity sensor is less than the first reference value H1, the control unit steps the execution timing of the refresh process. It is characterized by speeding up.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, the control unit performs a refresh process when the humidity at the printing start time detected by the in-machine temperature / humidity sensor exceeds a second reference value H2 (> H1). It is characterized by delaying the timing step by step.

  According to the present invention, in the image forming apparatus having the above-described configuration, the control unit finishes printing when the humidity at the printing start time detected by the in-machine temperature / humidity sensor is less than a third reference value H3 (<H1). It is characterized in that a refresh process is performed immediately afterwards.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, when the temperature at the printing start time detected by the in-machine temperature / humidity sensor is equal to or higher than the first reference value T1, the control unit steps the execution timing of the refresh step. It is characterized by speeding up.

  Further, according to the present invention, in the image forming apparatus having the above configuration, when the temperature at the printing start time detected by the temperature and humidity sensor in the apparatus exceeds the second reference value T2 (> T1), It is characterized by performing a refresh process immediately.

  Further, according to the present invention, in the image forming apparatus having the above-described configuration, the control unit compares the average value of the humidity or the average value of the temperature detected by the in-machine temperature and humidity sensor with the reference value to determine the execution timing of the refresh process. It is characterized by deciding.

  In the image forming apparatus having the above-described configuration, an external temperature / humidity sensor that detects at least one of temperature and humidity outside the apparatus is provided as a second detection unit that detects environmental information outside the apparatus. The control means is configured such that at least one of the temperature difference and the humidity difference between the inside of the apparatus and the outside of the apparatus at the start of printing detected by the internal temperature / humidity sensor and the external temperature / humidity sensor is equal to or greater than the first reference value ΔT1 or ΔH1. In this case, the execution timing of the refresh process is advanced in stages.

  According to the present invention, in the image forming apparatus having the above configuration, the control unit is configured to detect a temperature difference and a humidity difference between the inside of the apparatus and the outside of the apparatus detected by the in-machine temperature / humidity sensor and the outside temperature / humidity sensor. Among these, when at least one of the values is equal to or greater than the second reference value ΔT2 (> ΔT1) or ΔH2 (> ΔH1), the refresh process is executed immediately after the end of printing.

  According to the present invention, in the image forming apparatus having the above-described configuration, the control unit calculates a difference between an average value of humidity or an average value of temperature detected by the in-machine temperature / humidity sensor and the outside temperature / humidity sensor as the reference value. The execution timing of the refresh process is determined as compared with the above.

  According to the first configuration of the present invention, the optimum refresh process execution timing according to the environmental information inside the apparatus is determined, so that the refresh process is executed at a more appropriate timing without increasing the toner discharge amount. be able to.

  Further, according to the second configuration of the present invention, in the image forming apparatus having the first configuration, by using an in-machine temperature / humidity sensor as the first detection unit, the developer inside the developing device is used as environmental information inside the device. Temperature / humidity information having a great influence on the state change can be used.

  According to the third configuration of the present invention, in the image forming apparatus having the second configuration, the in-machine temperature / humidity sensor is arranged in the vicinity of the developing device, so that the state change of the developer inside the developing device is further improved. It can be accurately captured.

  According to the fourth configuration of the present invention, in the image forming apparatus having the second or third configuration, when the humidity at the start of printing is less than the first reference value H1, the execution timing of the refreshing process is stepped. As a result, it is possible to effectively suppress a decrease in image density and an image fog without increasing the toner discharge amount per refresh in a low temperature and low humidity environment where the toner is easily charged up by increasing the frequency of the refresh process. be able to.

  According to the fifth configuration of the present invention, in the image forming apparatus having the fourth configuration, when the humidity at the start of printing exceeds the second reference value H2 (> H1), the refresh process is executed in stages. Therefore, wasteful toner consumption can be suppressed by reducing the frequency of execution of the refresh process under high humidity conditions.

  According to the sixth configuration of the present invention, in the image forming apparatus having the fourth or fifth configuration, when the humidity at the printing start time is less than the third reference value H3 (<H1), the printing is finished. By performing the refreshing process immediately afterwards, it is possible to form a high-quality image that does not cause a decrease in image density or image fog even when the in-machine humidity is extremely low.

  According to the seventh configuration of the present invention, in the image forming apparatus having the second or third configuration, when the temperature at the start of printing is equal to or higher than the first reference value T1, the execution timing of the refresh process is stepwise. As a result, it is possible to effectively suppress a decrease in image density and an image fog without increasing the amount of toner discharged per refresh in a high temperature environment where the fluidity of the toner is lowered. Become.

  Further, according to the eighth configuration of the present invention, in the image forming apparatus having the seventh configuration, when the temperature at the start of printing exceeds the second reference value T2 (> T1), the refreshing process is performed immediately after the end of printing. By executing the above, it is possible to form a high-quality image that does not cause a decrease in image density or image fogging even when the in-machine temperature is extremely high.

  According to the ninth configuration of the present invention, in the image forming apparatus having any one of the fourth to eighth configurations, the humidity average value or the temperature average value detected by the in-machine temperature / humidity sensor is used as the reference value. By determining the execution timing of the refresh process as compared with the above, it is possible to determine an appropriate execution timing that reflects the state of the toner in the developing device more accurately.

  According to the tenth configuration of the present invention, in the image forming apparatus having the second or third configuration, an external temperature / humidity sensor that detects at least one of temperature and humidity outside the apparatus is provided, and the internal temperature / humidity is provided. When at least one of the temperature difference and the humidity difference between the inside of the apparatus and the outside of the apparatus at the start of printing detected by the sensor and the outside temperature / humidity sensor is equal to or greater than the first reference value ΔT1 or ΔH1, the execution timing of the refresh process is set. By accelerating in stages, it is possible to determine a more appropriate execution timing that reflects the environment surrounding the apparatus in addition to the environment information inside the apparatus.

  According to the eleventh configuration of the present invention, in the image forming apparatus of the tenth configuration, the temperatures inside and outside the apparatus at the start of printing detected by the in-machine temperature / humidity sensor and the outside temperature / humidity sensor. When at least one of the difference and the humidity difference is equal to or greater than the second reference value ΔT2 (> ΔT1) or ΔH2 (> ΔH1), the temperature and humidity in the machine and the machine are extremely low by executing the refresh process immediately after the printing is completed. Even if they are different from each other, it is possible to form a high-quality image without causing a decrease in image density or image fog.

  According to the twelfth configuration of the present invention, in the image forming apparatus having the tenth or eleventh configuration, the difference between the average values of the humidity or the temperature detected by the in-machine temperature / humidity sensor and the out-of-machine temperature / humidity sensor. By comparing the average value difference with the reference value and determining the execution timing of the refresh process, it is possible to determine an appropriate execution timing that reflects the state of the toner in the developing device more accurately.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus of the present invention. In the image forming apparatus (here, a color printer) 100, when performing a copying operation, the photosensitive drum 1 that rotates counterclockwise in the drawing is uniformly charged by the charging unit 2 in the apparatus main body. The exposure unit 3 irradiates the photosensitive drum 1 with a laser beam based on the original image data input to an image input unit (not shown) from a personal computer or the like, and the electrostatic latent image on the photosensitive drum 1. Is formed.

  The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the surface is charged by a charging unit 2. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received the laser beam from the exposure unit 3. As the photosensitive material for forming the photosensitive layer, an amorphous silicon photoreceptor or an organic photoreceptor (OPC photoreceptor) is used. When positive OPC is used as the photosensitive layer, the generation of ozone or the like is small and charging is stable. In particular, the positive OPC having a single-layer structure has little change in photosensitive characteristics even when the film thickness changes after long-term use. Since the image quality is stable, it is preferably used in a system having a long life.

  The rotary type developing unit 4 that supplies toner onto the photosensitive drum 1 includes cartridge type yellow, magenta, cyan, and black developing devices 4a, 4b, 4c, and 4d in which a developing device and a toner container are integrated. By sequentially rotating the developing devices 4a to 4d to positions facing the photosensitive drum 1, toner is attached to the electrostatic latent image on the photosensitive drum 1 to form toner images of the respective colors. The Toner supply (toner installation) to the developing cartridges 4a to 4d is performed from the toner cartridge 5 through the supply pipe 5a.

  The intermediate transfer belt 6 onto which the toner image is transferred is wound around the intermediate transfer rollers 7a and 7b, the belt driving roller 9 and the driven roller 10, and while being in contact with the photosensitive drum 1, the driving means (not shown) rotates clockwise in the drawing. Rotate to. A sheet made of dielectric resin is used for the intermediate transfer belt 6, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used.

  When the user inputs image formation start, a yellow toner image is formed on the photosensitive drum 1 at a predetermined timing. Then, the yellow toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by the intermediate transfer rollers 7a and 7b to which a negative transfer bias (when positively charged toner is used) is applied (primary transfer). . Thereafter, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning roller 8a and the cleaning blade 8b, and the developing unit 4 rotates by a predetermined amount (here, 90 °). Are formed on the photosensitive drum 1 and transferred onto the intermediate transfer belt 6.

  Thereafter, cyan and black toner images are transferred onto the intermediate transfer belt 6 from the photosensitive drum 1 by the same method as described above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. A transfer roller 14 is pressed against the intermediate transfer belt 6 at a position facing the belt driving roller 9, and a belt cleaning blade 15 for removing residual toner on the surface of the intermediate transfer belt 6 is disposed downstream of the transfer roller 14. ing.

  The sheet P is conveyed from the sheet feeding mechanism 11 via the sheet feeding roller 12 and the registration roller pair 13 toward the intermediate transfer belt 6 on which the toner image is formed as described above, and sequentially onto the surface of the intermediate transfer belt 6. The formed full-color toner image is transferred onto the paper P at once by the transfer roller 14 to which a negative transfer bias is applied (secondary transfer). Then, the sheet P on which the toner image is transferred is conveyed to the fixing device 16 and the toner image is fixed. The paper P that has passed through the fixing device 16 is discharged to a discharge tray 19 via a paper conveyance path 17 and a discharge roller pair 18.

  Further, an image density sensor 43 is disposed at a position facing the driven roller 10 with the intermediate transfer belt 6 interposed therebetween. As the image density sensor 43, an optical sensor provided with a light emitting element composed of an LED or the like and a light receiving element composed of a photodiode or the like is generally used. When measuring the toner adhesion amount on the intermediate transfer belt 6, when the reference light formed on the intermediate transfer belt 6 is irradiated with the measurement light from the light emitting element, the measurement light is reflected by the toner, and the belt surface Is incident on the light receiving element as light reflected by the light.

  When the toner adhesion amount is large, the reflected light from the belt surface is blocked by the toner, so that the light reception amount of the light receiving element is reduced. On the other hand, when the adhesion amount of toner is small, conversely, the amount of reflected light from the belt surface increases, resulting in an increase in the amount of light received by the light receiving element. Therefore, the density of each color is corrected by detecting the density of the reference image of each color based on the output value of the received light signal based on the amount of reflected light received and adjusting the characteristic value of the developing bias in comparison with the predetermined reference density. Is done.

  FIG. 2 is a side sectional view of the developing device mounted on the image forming apparatus of the present invention. In the following description, the configuration and operation of the developing device 4a opposite to the photosensitive drum 1 in FIG. 1 will be described. However, the configuration and operation of the developing devices 4b to 4d are basically the same, and the description is omitted. To do.

  As shown in FIG. 2, the developing device 4 a is provided with a toner stirring unit 21 in which toner is stored and a toner supply unit 22 to which toner is supplied from the toner stirring unit 21 in a resin-made developing container 20. The toner stirring unit 21 and the toner supply unit 22 are partitioned by a boundary wall 23. A first opening 28 and a second opening 29 are formed in the boundary wall 23, and the second opening 29 is positioned above the first opening 28 in the drawing.

  In the toner agitation unit 21, an agitation paddle 24 in which an agitation blade such as a PET film is attached to a rotation shaft is rotatably supported in a counterclockwise direction in FIG. In the toner supply unit 22, the photosensitive drum 1 (see FIG. 1) that carries a latent image faces the developing roller 25 for developing the latent image, and a supply roller for supplying toner to the developing roller 25. 26, a metal regulating member 27 for regulating the toner layer thickness on the developing roller 25 and charging the toner is provided.

  The toner layer on the developing roller 25 is regulated in layer thickness by a regulating member 27 (for example, a SUS foil having a thickness of 0.08 mm and regulated pressure = 25 N / m) and is triboelectrically charged. 1 is used for development of an electrostatic latent image on 1. A seal member 30 (for example, a conductive high molecular weight PE film is used as a gap between the developing roller 25 and the developing container 20 on the side opposite to the regulating member 27 and is backed up with a urethane sponge so as to uniformly contact the developing roller 25. The seal member 30 prevents toner leakage.

  Further, since the developing roller 25 and the supply roller 26 rotate clockwise in FIG. 2, the second opening 29 is formed downstream of the first opening 28 in the rotation direction of the supply roller 26, and the second opening 29 is positioned above the upper end of the supply roller 26. The first opening 28 is positioned below the rotation axis of the stirring paddle 24.

  The developing process by the developing device 4 a will be described. The toner in the toner stirring unit 21 is sent to the toner supply unit 22 through the first opening 28 by the rotation of the stirring paddle 24. The toner sent to the toner supply unit 22 side is conveyed to the development roller 25 by the supply roller 26, is regulated to a thin layer by the regulating member 27 and is conveyed to the development nip portion, and the electrostatic latent image on the photosensitive drum 1 is converted. develop. The toner that is not used for development and remains on the developing roller 25 passes through the seal member 30, and then is peeled off by the supply roller 26 and returned to the toner supply unit 22.

  Of the toner conveyed by the supply roller 26, excess toner regulated by the regulating member 27 stays in the toner supply unit 22 together with new toner supplied (filled) from the first opening 28. When the amount of toner in the supply unit 22 increases, excess toner passes through the second opening 29 and returns to the toner stirring unit 21 from the toner supply unit 22 side, and the internal pressure of the toner supply unit 22 is reduced.

  Next, the control path of the image forming apparatus of the present invention will be described. 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 temporarily stores necessary data generated during the control of the image forming apparatus 100, such as measurement data of the inside and outside temperature / humidity sensors 40 and 41 or the image density sensor 43 described later, and control of the image forming apparatus 100. Necessary data and the like are stored.

  In addition, the ROM 92 (or RAM 93) executes the refresh process as described later, in addition to the reference number of prints for determining whether or not the refresh process is necessary and the reference print rate used when determining whether or not the refresh process is necessary. In-machine temperature / humidity used to determine timing, or reference value of temperature / humidity difference between in-machine and outside machine, outer peripheral length of developing roller 25 and supply roller 26 for calculating printing length of toner discharge pattern, and photoconductor The linear speed ratio data for the drum 1 is also stored. 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.

  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. As each part and device controlled by the control unit 90, for example, the photosensitive drum 1, the exposure unit 3, the developing unit 4 (developing devices 4a to 4d), the paper feeding mechanism 10, the fixing device 16, the in-machine temperature and humidity sensor 40, Examples include an external temperature / humidity sensor 41, an image input unit 45, an operation unit 50, and the like.

  When the image forming apparatus 100 is a printer as shown in FIG. 1, the image input unit 45 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 45 is converted into a digital signal and then sent to the temporary storage unit 94.

  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.

  When the image forming apparatus of the present invention is not transferred to a recording medium, for example, when the image forming apparatus is started up 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 25 in the developing devices 4a to 4d to the photosensitive drum 1 side can be executed.

  An actual toner discharge pattern is shown in FIG. The toner discharge pattern T is a toner discharge length (printing length in the drum circumferential direction) obtained by multiplying the width H of the developing area of the developing roller 4a (see FIG. 2) and the toner discharge amount per image by the number of printed sheets. L is a rectangular shape with two sides. In addition, when separation claws (not shown) for preventing the paper from adhering to the drum surface are provided at a plurality of positions in the longitudinal direction of the photosensitive drum 1, a toner discharge pattern is provided so that the toner does not adhere to the separation claws. A white portion is provided in a portion facing the separation claw of T.

  A method for calculating the printing length L of the toner discharge pattern T will be described. Assuming that the number of printed sheets for executing the refresh process is A, the control unit 90 calculates a printing rate bn for each image based on the digital signal in the temporary storage unit 94, and further calculates an integrated printing rate Σbn obtained by integrating the printing rate bn. calculate.

  Then, the integrated printing rate Σbn is divided by the number of printed sheets A counted by the counter 95 to calculate an average printing rate B (%) per printed sheet A. Since the printing rate difference C−B between the average printing rate B and the reference printing rate (threshold of printing rate that requires refreshing) C (%) is a necessary discharge amount (shortage of consumption) per image, Multiplying this by the number of printed sheets A (C−B) × A (%) becomes the toner discharge amount when the refresh process is executed. Note that the number of printed sheets A and the reference print rate C (%) can be set as appropriate according to the usage status of the user, the characteristics of the toner of each color, and the like.

  The printing length L of the toner discharge pattern T is calculated by L = L0 × (C−B) × A / 100, where L0 is the circumferential length of the image size that is the reference (100%) for calculating the printing rate. The

  For example, assuming that the number of printed sheets A is 10 and the reference printing rate C is 5%, when the average printing rate B is 2%, the toner ejection pattern T for (5-2 = 3)% × 10 sheets is obtained. Print. This is because when an A4 size image (width 210 mm × circumferential length 297 mm) is used as a reference (100%) for calculating the printing rate, L = 297 (= L0) × (5-2) × 10/100 = 89. 1 mm, which corresponds to a toner ejection pattern T with L = 89.1 mm. Assuming that the rotational speed of the photosensitive drum 1 is 150 mm / second, it is sufficient to discharge the toner at 89.1 / 150 = 0.594 seconds. As described above, the printing length L of the toner discharge pattern T is calculated for each of the developing devices 4a to 4d, and the refresh process is executed.

  In the present invention, by switching the execution timing of the refresh process according to environmental information inside the apparatus, particularly temperature and humidity information, the amount of toner discharged per refresh is increased even under conditions where toner is easily charged, such as in a low humidity environment. It has been found that the reduction in image density and fog can be effectively suppressed without any problems.

  Here, the measurement of temperature and humidity in the present invention will be described. As shown in FIG. 1, an in-machine temperature / humidity sensor 40 is installed in the vicinity of the developing unit 4. This in-machine temperature / humidity sensor 40 is controlled by the control unit 90 and can measure the temperature / humidity unless the main power supply is turned off. For example, temperature / humidity information can be collected periodically every minute, and temperature / humidity information can also be collected by setting conditions such as at the start of printing.

  Further, an external temperature / humidity sensor 41 is installed above the paper feed mechanism 11 for the purpose of measuring the apparatus installation environment (machine peripheral environment). This is not limited to the developing unit 4 and is often installed for the purpose of controlling, for example, the influence of the paper moisture amount on the transfer condition. However, the temperature / humidity information of the external temperature / humidity sensor 41 can also be used. is there. Further, it is possible to substitute the information of the outside temperature / humidity sensor 41 without installing the inside temperature / humidity sensor 40 in the vicinity of the developing unit 4, and it is also possible to control using the temperature / humidity information from the two sensors. is there.

  In general, the charged state of a developer (toner) is easily affected by temperature and humidity, and often has a high charge amount when the humidity is less than 40%, particularly less than 20%. This value is not uniform and may vary depending on the developer, and it is likely to depend more on absolute humidity than relative humidity. On the other hand, in many cases, a decrease in charge amount is observed at a humidity of 70% or more, particularly 80% or more. Further, when the developer temperature rises to 45 ° C. or higher, particularly 50 ° C. or higher, the fluidity tends to decrease due to approaching the melting temperature of the toner.

  Therefore, based on the temperature and humidity information obtained by the in-machine temperature / humidity sensor 40 and the out-of-machine temperature / humidity sensor 41, the timing for performing the refresh process is optimized. For example, it is more frequent when the humidity is low, at intervals when the humidity is high, and frequently when the temperature is high.

  Next, a method for controlling the execution timing of the refresh process in the present invention will be described in detail. In each of the following control examples, a procedure in which the refresh process is executed for one of the developing devices 4a to 4d will be described, but the same procedure is executed for the other three developing devices. In addition, after the refresh process is executed, the number of printed sheets A is usually 40 (reference number A0) until the next refresh process is executed, and the average print rate B calculated for each 40 pages is the reference print rate C (for example, 3%). If the value is less than, the toner amount (= A × (C−B)) corresponding to the insufficient consumption from the reference printing rate C is controlled to be discharged.

  FIG. 5 is a flowchart showing the execution procedure of the refresh process using the first control. The refresh execution timing control method in the first control will be described along the flowchart of FIG. 5 with reference to FIGS. 1 to 4 as necessary. The first control shows a procedure for determining the refresh execution timing in a low humidity environment. First, when an image formation processing command is transmitted by the operation of the operation panel 50 or a personal computer by the user, development is performed by the in-machine temperature / humidity sensor 40. The in-machine humidity Hi around the unit 4 is measured (step S1). The measurement result is transmitted to the control unit 90. The controller 90 determines whether or not the transmitted in-machine humidity Hi is 45% (first reference value H1) or more (step S2). If it is 45% or more, the reference number A0 per printed sheet is determined. The subtraction from (hereinafter referred to as coefficient ka) is set to 0 (step S3).

  If Hi is less than 45% in step S2, it is next determined whether Hi is 35% or more (step S4), and if it is 35% or more, ka is set to 1 (step S5). . If Hi is less than 35% in step S4, it is next determined whether Hi is 25% (third reference value H3) or more (step S6), and if it is 25% or more, ka is determined. 2 (step S7).

  After the coefficient ka is determined as described above, printing is started, and the number of printed sheets n is counted by the counter 95 (step S8). The control unit 90 calculates a printing rate bn for each image based on the digital signal in the temporary storage unit 94, and further calculates an integrated printing rate Σbn obtained by integrating the printing rate bn. Next, it is determined whether or not the number n of printed sheets has reached A0−ka · n obtained by subtracting a value obtained by multiplying the number of printed sheets n by ka from the reference number A0 (step S9). Until n reaches A0-ka · n, the process returns to step S1, and the measurement of the in-machine humidity and the determination of the coefficient ka are repeated (steps S2 to S8).

  If n ≧ A0−ka · n in step S9, the control unit 90 calculates the average printing rate B (%) by Σbn / A, where n is the number of printed sheets A to be subjected to the refresh process. Next, the toner discharge amount (CB) × A (%) is calculated by multiplying the printing rate difference C−B between the average printing rate B and the reference printing rate C (%) by the number A of printed sheets, and further the printing rate. The printing length L of the toner ejection pattern T is calculated based on the circumferential length L0 of the image size serving as the calculation reference (100%), and the refresh process is executed (step S10).

  For example, assuming that the reference number A0 is 40, when 35 ≦ Hi ≦ 45, ka = 1, that is, the number is reduced by 1 for every printing, so 2n ≧ from n ≧ 40−1 × n. 40, and the refresh process is executed with n = 20 sheets. In addition, when 25 ≦ Hi <35, ka = 2, that is, two sheets are reduced for every print, so that 3n ≧ 40 and n ≧ 13.3 from n ≧ 40−2 × n, The refresh process is executed with n = 14 sheets.

  On the other hand, if Hi is less than 25% in step S6, the refresh process is executed immediately after the printing is completed (step S10). The toner discharge amount at this time is determined by calculating an average printing rate B for the number of printed sheets from the refresh process executed immediately before. For example, when Hi is less than 25% on the first printed sheet, the difference between the printing rate of the first sheet and the reference printing rate is discharged. Thereafter, the count number n of the counter 95 is reset to 0 (step S11), and the process returns to step S1 again.

  By performing this first control, in a low-humidity environment where the toner charge amount is high (there is a lot of charged fine powder toner), the refreshing step is performed frequently to remove the charged fine powder toner. Density reduction and image fog can be suppressed. In addition, when the humidity is extremely low (25% or less in this case), the refresh process is executed before the image formation, so that it is possible to reliably prevent a decrease in image density from the first printed sheet. Note that the first control and the second to sixth controls, which will be described later, only show the procedure for determining the execution timing of the refresh process, and are different from the determination of whether or not to actually execute the refresh process. Therefore, for example, when the average printing rate exceeds the reference printing rate in step S10, the refresh process is not executed.

  FIG. 6 is a flowchart showing the execution procedure of the refresh process using the second control. The second control shows a procedure for determining the refresh execution timing in a high humidity environment. When an image formation processing command is transmitted, the in-machine humidity Hi around the developing unit 4 is measured by the in-machine temperature / humidity sensor 40 ( Step S1). The measurement result is transmitted to the control unit 90. The controller 90 determines whether or not the transmitted in-machine humidity Hi is 70% (second reference value H2) or less (step S2). If it is 70% or less, the reference number A0 per printed sheet is determined. Is set to 0 (step S3).

  If Hi exceeds 70% in step S2, it is next determined whether Hi is 80% or less (step S4). If Hi is 80% or less, kb is set to 1 (step S5). If Hi exceeds 80% in step S4, kb is set to 2 (step S6). After the coefficient kb is determined as described above, printing is started, and the number of printed sheets n is counted by the counter 95 (step S7). The control unit 90 calculates a printing rate bn for each image based on the digital signal in the temporary storage unit 94, and further calculates an integrated printing rate Σbn obtained by integrating the printing rate bn.

  Next, it is determined whether the number of printed sheets n has reached A0 + kb · n obtained by adding a value obtained by multiplying the number of printed sheets n by kb from the reference number of sheets A0 (step S8). The process returns to step S1 until n reaches A0 + kb · n, and the measurement of the in-machine humidity and the determination of the coefficient kb are repeated (steps S2 to S7). When n ≧ A0−ka · n is satisfied in step S8, the refresh process is executed with n being the number of printed sheets A on which the refresh process is executed (step S9). However, the maximum number of printed sheets A is 60.

  By performing the second control, in a high humidity environment where the toner charge amount is reduced, it is possible to reduce the frequency of execution of the refresh process and suppress wasteful toner consumption. Further, by combining the first and second controls, the refresh process can be executed at an appropriate timing from the low humidity condition to the high humidity condition, and the toner consumption can be reduced while suppressing the decrease in the image density and the image fog. Can be minimized.

  It should be noted that if the refresh execution timing is extended in a high humidity environment as in the second control, the refresh process 1 may depend on the characteristics of the developer such as extremely reduced charging under high humidity conditions or the charge level of the developing device. In some cases, the amount of toner discharged per operation increases too much, causing problems such as image fogging. In such a case, control is performed to set the coefficient ka as in the first control instead of the coefficient kb. For example, when the internal humidity Hi is 70% to 80% (YES in step S4), ka = 1 is set. When the in-machine humidity H exceeds 80% (NO in step S4), the control may be performed such that ka = 2.

  FIG. 7 is a flowchart showing the execution procedure of the refresh process using the third control. The third control shows a procedure for determining the refresh execution timing in a high temperature environment. When an image formation processing command is transmitted, the in-machine temperature Ti around the developing unit 4 is measured by the in-machine temperature / humidity sensor 40 (step S1). The measurement result is transmitted to the control unit 90. The controller 90 determines whether or not the transmitted in-machine temperature Ti is lower than 40 ° C. (first reference value T1) (step S2), and if it is lower than 40 ° C., sets the coefficient ka to 0 (step S2). S3).

  If Ti is 40 ° C. or higher in step S2, it is then determined whether Ti is less than 45 ° C. (step S4). If it is less than 45 ° C., the coefficient ka is set to 1 (step S5). ). If Ti is 45 ° C. or higher in step S4, it is next determined whether Ti is less than 50 ° C. (step S6). If it is less than 50 ° C., coefficient ka is set to 2 (step S7). ). Since the procedure (steps S8 to S10) from when the number of printed sheets n is counted until the refresh process is executed is the same as the first control, the description thereof is omitted.

  On the other hand, if Ti is 50 ° C. (second reference value T2) or more in step S6, the refresh process is executed immediately after the printing is completed (step S8). Thereafter, the count number n of the counter 95 is reset to 0 (step S11), and the process returns to step S1 again.

  By performing this third control, in a high-temperature environment where the fluidity of the toner is lowered, the frequency of the refresh process is increased to promote the replacement of the toner on the developing roller 25, and the image density is lowered and the image fog is reduced. Can be suppressed. In addition, since the fluidity of the toner is not improved by the low temperature environment, the control for reducing the execution frequency of the refresh process is not performed as in the second control even in the low temperature environment.

  FIG. 8 is a flowchart showing the execution procedure of the refresh process using the fourth control. The fourth control shows a procedure for determining the refresh execution timing in a low humidity environment. When an image formation processing instruction is transmitted, the in-machine humidity Hi periodically measured by the in-machine temperature / humidity sensor 40 per predetermined time ( For example, the average humidity Ha for the past 30 minutes is calculated (step S1). The control unit 90 determines the number A of printed sheets until refresh execution based on the calculated average humidity Ha. The procedure for determining the number of printed sheets A and the execution procedure of the refresh process (steps S2 to S11) are the same as those in the first control, and thus description thereof is omitted.

  By performing this fourth control, as in the first control, in a low-humidity environment where the toner charge amount is high (there is a lot of finely charged toner), the refresh process is executed more frequently and charged up. By removing the fine toner, it is possible to suppress a decrease in image density and image fog. In the fourth control, since the average humidity Ha in the apparatus is used to determine the number of printed sheets until the refresh process is executed, it is possible to determine an appropriate execution timing that more accurately reflects the state of the toner in the developing device. It becomes.

  Although an example in which the average humidity Ha is used for determining the refresh execution timing in the low humidity environment is shown here, the refresh execution timing may be determined using the average humidity Ha in the second control in the high humidity environment. Also in the third control, if the refresh execution timing is determined by using the average temperature Ta per unit time of the in-machine temperature Ti periodically measured by the in-machine temperature / humidity sensor 40, the level corresponding to the state of the toner is further increased. Appropriate control can be performed.

  FIG. 9 is a flowchart showing the execution procedure of the refresh process using the fifth control. In the fifth control, the refresh execution timing in the low humidity environment is determined using the humidity difference ΔH between the in-machine humidity Hi and the out-of-machine humidity Ho instead of the in-machine humidity Hi of the first control. When the image forming process command is transmitted, the in-machine humidity Hi and the out-of-machine humidity Ho are measured by the in-machine temperature / humidity sensor 40 and the out-of-machine temperature sensor 41 (step S1). The measurement result is transmitted to the control unit 90. The control unit 90 calculates the humidity difference ΔH between the transmitted in-machine humidity Hi and the outside humidity Ho (becomes Hi-Ho because the in-machine humidity Hi is lower) (step S2), and the humidity difference ΔH is 3%. It is determined whether it is less than (first reference value ΔH1) (step S3). If ΔH is less than 3%, the coefficient ka is set to 0 (step S4).

  If ΔH is 3% or more in step S3, it is next determined whether ΔH is less than 7% (step S5). If it is less than 7%, coefficient ka is set to 0 (step S6). ). If ΔH is 7% or more in step S4, it is then determined whether ΔH is less than 10% (step S7). If it is less than 10%, the coefficient ka is set to 1 (step S8). ). Since the procedure (steps S9 to S11) until the number n of printed sheets is counted and the refresh process is executed is the same as the first control, the description thereof is omitted.

  Further, if ΔH is 10% (second reference value ΔH2) or more in step S7, a refresh process is executed immediately after the end of printing (step S11). Thereafter, the count number n of the counter 95 is reset to 0 (step S12), and the process returns to step S1 again.

  By performing the fifth control, as in the first and fourth controls, the refresh process is executed more frequently in a low humidity environment where the toner charge amount is high (the amount of finely charged toner is large). By removing the charged fine powder toner, it is possible to suppress a decrease in image density. Further, in the fifth control, since the humidity difference ΔH between the inside and outside of the apparatus is used for determining the number of printed sheets until the refresh process, the environment around the apparatus is reflected in addition to the environment information inside the apparatus, so that it is more appropriate. The execution timing can be determined. This is particularly effective in an image forming apparatus in which the fixing device needs to be preheated to a predetermined temperature even during standby.

  FIG. 10 is a flowchart showing the execution procedure of the refresh process using the sixth control. The sixth control shows a procedure for determining the refresh execution timing in a high temperature environment. When an image formation processing command is transmitted, the in-machine temperature Ti and the out-of-machine temperature To are detected by the in-machine temperature / humidity sensor 40 and the out-of-machine temperature sensor 41. Is measured (step S1). The measurement result is transmitted to the control unit 90. The controller 90 calculates a temperature difference ΔT between the transmitted in-machine temperature Ti and the out-of-machine temperature To (step S2), and determines whether the temperature difference ΔT is less than 3 ° C. (first reference value ΔT1). (Step S3). If ΔT is less than 3 ° C., the coefficient ka is set to 0 (step S4).

  If ΔT is 3 ° C. or more in step S3, it is next determined whether ΔT is less than 5 ° C. (step S5). If it is less than 5 ° C., the coefficient ka is set to 1 (step S6). ). If ΔT is 5 ° C. or more in step S4, it is next determined whether ΔT is less than 7 ° C. (step S7), and if it is less than 7 ° C., the coefficient ka is set to 2 (step S8). ). Since the procedure (steps S9 to S11) until the number n of printed sheets is counted and the refresh process is executed is the same as the first control, the description thereof is omitted.

  Further, when ΔT is 7 ° C. (second reference value ΔT2) or more in step S7, a refresh process is executed immediately after the end of printing (step S11). Thereafter, the count number n of the counter 95 is reset to 0 (step S12), and the process returns to step S1 again.

  By performing the sixth control, similar to the third control, in a high temperature environment where the fluidity of the toner is low, the frequency of the refresh process is increased and the replacement of the toner on the developing roller 25 is promoted. A decrease in image density and image fog can be suppressed. In the sixth control, the temperature difference ΔT between the inside and outside of the apparatus is used to determine the number of printed sheets until the refresh process, and therefore the environment around the apparatus is added to the environment information inside the apparatus as in the fifth control. It is possible to determine a more appropriate execution timing reflected. This is particularly effective in an image forming apparatus in which the fixing device needs to be preheated to a predetermined temperature even during standby.

  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, and the control which combined each said control example suitably is also included by this invention. For example, in the first and third controls, the execution timing of the refresh process is determined based on the in-machine humidity Hi or the in-machine temperature Ti, but the in-machine humidity Hi and the in-machine temperature are combined with the first and third controls. The execution timing of the refresh process can also be determined based on both Ti. Further, the execution timing of the refresh process may be determined based on both the humidity difference ΔH and the temperature difference ΔT by combining the fifth and sixth controls.

  In each of the above control examples, the toner discharge amount (printing length L) is obtained by calculation using the number A of printed sheets, the average printing rate B (or printing rate bn), and the reference printing rate C. The printing length L may be obtained by a method. For example, the print length L may be determined using a toner discharge amount setting table in which a plurality of toner discharge modes that define the toner discharge amount discharged from the developing roller 25 for each printing rate level during the refresh process are stored. it can. In each control example, the control unit 90 calculates the average printing rate. However, a calculation unit that calculates the average printing rate may be provided separately from the control unit 90.

  In the present invention, only a rotary development type color printer has been described as an example. However, an analog monochrome copying machine, a tandem color copying machine, an analog monochrome copying machine, a facsimile machine, a laser printer, etc. Of course, the present invention can be applied to various image forming apparatuses equipped with a developing device including a developing roller and a supply roller.

  When printing was performed using the image forming apparatus of the present invention shown in FIG. 1, the relationship between the execution timing of the refresh process and image defects was investigated. The test conditions were 14 mm and 13 mm in diameter of the developing roller 25 and the supply roller 26, 1.1 times the linear speed ratio S1 of the developing roller 25 to the photosensitive drum 1, and the linear speed ratio S2 of the supply roller 26 to the developing roller 25. Is 1.2 times, the rotational speed of the photosensitive drum 1 is 150 mm / second, and the execution timing of the refresh process is controlled according to the internal humidity Hi by the first control shown in FIG. 5 (Invention 1). In the case of no control (Comparative Example 1), when the test image was continuously printed at a rate of 1,000 sheets / day for 10 days at an in-machine humidity of 30% and 40%, a solid image density drop and image fogging The occurrence was investigated. It should be noted that the reference printing number A0, which is an interval for the refresh process, was 40 sheets, and the average printing rate B was 3%.

  In the evaluation method, the density of the printed image is measured by using a reflection densitometer (RD918) manufactured by Macbeth Co., Ltd., and the density reduction is evaluated by the reduction of the ID in the solid image. Image fogging was evaluated by the increase in ID at the part. The results are shown in FIGS.

  As is clear from FIG. 11, the number of printed sheets to be refreshed is 40 sheets when the in-machine humidity is 45% or more, 20 sheets when the in-machine humidity is 35% or more and less than 45%, and 25% or more and less than 35%. In the present invention 1 having 14 sheets, after the printing of 10,000 sheets (10 days after the start of the test), the humidity in the machine is 40% (indicated by x in the figure) and 30% (indicated by □ in the figure). The ID values of the eye) were 1.34 and 1.33, and hardly decreased from the initial values (1.41 to 1.42). On the other hand, in Comparative Example 1 in which the refresh process is always performed with 40 sheets regardless of the humidity in the machine, when the humidity in the machine is 40% (indicated by a triangle in the figure) and 30% (indicated by a black circle in the figure), 10, The ID values after printing 000 sheets decreased to 1.12 and 1.05, respectively.

  Further, as apparent from FIG. 12, in the first aspect of the present invention, after the printing of 10,000 sheets, the in-machine humidity is 40% (indicated by x in the figure) and 30% (indicated by □ in the figure). The ID values of the white portions of the images were 0.06 and 0.07, and the image fog was not noticeable by the naked eye. On the other hand, in Comparative Example 1, when the in-machine humidity is 40% (indicated by Δ in the figure) and 30% (indicated by black circle in the figure), the ID values are 0.12 and 0.14 after printing 10,000 sheets. And a remarkable image fogging was observed.

  When the execution timing of the refresh process is controlled according to the temperature difference ΔT between the in-machine temperature Ti and the out-of-machine temperature To by the sixth control shown in FIG. 10 (Invention 2), and not controlled (Comparative Example 2) ) And the occurrence of image fogging and image fogging when the test images were continuously printed. The test conditions and the evaluation method were the same as in Example 1. The temperature difference ΔT changed from 3 ° C. or less from the start of printing to the 100th sheet, from 5 ° C. or less from the 100th sheet to the 400th sheet, and from 7 ° C. or less from the 400th sheet. Further, when the exhaust duct was blocked, when the power was turned off immediately after printing after the 1,000th sheet, or when duplex printing was performed, the temperature difference ΔT was 7 ° C. or more. The results are shown in FIGS.

  As can be seen from FIG. 13, when the temperature difference ΔT is 3 ° C. or higher and lower than 5 ° C., the number of prints to be refreshed is 20 sheets, when 5 ° C. or higher and lower than 7 ° C., 14 sheets are printed. In the present invention 2 (indicated by □ in the figure) in which the refresh process is executed immediately afterwards, the ID value is 1.35 even after printing 10,000 sheets (10 days after the start of the test), and the initial value (1. 41) hardly decreased. On the other hand, in Comparative Example 2 (indicated by black circles in the figure) in which the refresh process is always performed with 40 sheets regardless of the temperature difference ΔT, the ID value decreased to 1.06 after printing 10,000 sheets.

  Further, as is apparent from FIG. 14, in the second aspect of the present invention (indicated by □ in the figure), the ID value of the white portion is 0.06 even after printing 10,000 sheets, and the image fog is visible with the naked eye. It was a grade that did not become. On the other hand, in Comparative Example 2 (indicated by black circles in the figure), the ID value increased to 0.13 after 10,000 sheets were printed, and noticeable image fogging was observed.

  From this result, it is confirmed that when the execution timing of the refresh process is controlled according to the in-machine humidity Hi or the temperature difference ΔT between the inside and outside of the machine, a high refresh effect can be obtained, and density reduction and image fog can be effectively suppressed. It was. Although not shown here, the same applies when the third to fifth controls for controlling the execution timing of the refresh process according to the internal temperature Ti, the average humidity Ha, the internal and external humidity difference ΔH, and the like are used. It has been confirmed that results are obtained.

  The present invention comprises a developing device that has a toner carrier that is disposed opposite to an image carrier and carries toner and supplies the toner to the image carrier, and forms a toner image corresponding to the electrostatic latent image on the surface of the image carrier. And a control means for controlling the amount of toner discharged from the toner carrier based on the printing rate of the printed image, and capable of executing a refresh process for discharging toner from the toner carrier to the image carrier during non-image formation. The apparatus is provided with first detection means for detecting environmental information inside the apparatus, and the control means determines the execution timing of the refresh step based on the detection result of the first detection means.

  As a result, it is possible to set the optimal refresh process execution timing according to the environmental information inside the apparatus, so that the refreshing effect of the toner carrier is enhanced regardless of the use environment and the characteristics of the toner on the toner carrier are stabilized. Therefore, it is possible to provide an image forming apparatus capable of forming a high-quality image without causing problems such as a decrease in image density and fogging.

  For the environmental information inside the apparatus, an in-machine temperature / humidity sensor can be provided as the first detection means, and the temperature / humidity inside the apparatus can be detected, or the detected temperature / humidity can be averaged. The execution timing of the refresh process can be set by adjusting the number of printed sheets between the refresh processes in accordance with the temperature / humidity detection result.

  In addition, if an external temperature / humidity sensor for detecting temperature / humidity outside the apparatus is provided as the second detection means, the execution timing of the refresh process can be determined based on the temperature difference and humidity difference between the inside and outside of the apparatus. This is effective for an image forming apparatus that requires preheating of a fixing device in which the inside of the apparatus is likely to be high temperature and low humidity.

FIG. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus of the present invention. These are sectional views of a developing device used in the image forming apparatus of the present invention. FIG. 3 is a block diagram showing a control path of the image forming apparatus of the present invention. FIG. 4 is a diagram illustrating an example of a toner discharge pattern used in the present invention. These are the flowcharts which show the execution procedure of the refresh process using 1st control. These are the flowcharts which show the execution procedure of the refresh process using 2nd control. These are the flowcharts which show the execution procedure of the refresh process using 3rd control. These are the flowcharts which show the execution procedure of the refresh process using 4th control. These are the flowcharts which show the execution procedure of the refresh process using 5th control. These are the flowcharts which show the execution procedure of the refresh process using 6th control. These are graphs showing the relationship between the number of printed sheets and the image density of a solid image in the case where the execution timing of the refresh process is controlled according to the humidity in the apparatus (invention 1) and in the case where it is not controlled (Comparative Example 1). . These are graphs showing the relationship between the number of printed sheets and image fogging when the execution timing of the refresh process is controlled according to the humidity in the machine (present invention 1) and when it is not controlled (Comparative Example 1). Shows the relationship between the number of printed sheets and the image density of the solid image when the execution timing of the refresh process is controlled according to the temperature difference between the inside and outside of the apparatus (present invention 2) and when not controlled (comparative example 2). It is a graph which shows. FIG. 6 is a graph showing the relationship between the number of printed sheets and image fogging when the refresh process execution timing is controlled according to the temperature difference between the inside and outside the machine (present invention 2) and when not controlled (comparative example 2). It is.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developing unit 4a to 4d Developing device 25 Developing roller (toner carrier)
26 Supply roller 40 In-machine temperature / humidity sensor (first detection means)
41 External temperature / humidity sensor (second detection means)
90 Control unit (control means)
91 CPU
92 ROM
93 RAM
94 Temporary storage unit 95 Counter 100 Image forming apparatus T Toner discharge pattern L (Toner discharge pattern) circumferential print length

Claims (4)

A developing device that has a toner carrier that is disposed opposite to the image carrier and carries toner and supplies the toner to the image carrier, and forms a toner image corresponding to the electrostatic latent image on the surface of the image carrier;
Control means for controlling the amount of toner discharged from the toner carrier based on the printing rate of the printed image,
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,
As first detection means for detecting environmental information inside the apparatus, there is provided an in-machine humidity sensor disposed in the vicinity of the developing device for detecting the humidity inside the apparatus , and the control means is detected by the in-machine humidity sensor. When the humidity at the start of printing is lower than the first reference value H1, the execution timing of the refresh process is advanced stepwise in accordance with the decrease in humidity . 2. The control unit according to claim 1, wherein when the humidity at the start of printing detected by the in-machine humidity sensor exceeds a second reference value H2 (> H1), the execution timing of the refresh process is delayed in stages. The image forming apparatus described in 1. The control means of claim humidity has been printing start time detected by the machine humidity sensor when less than a third reference value H3 (<H1), characterized by executing the printing completion immediately after the refresh process 1 or the image forming apparatus according to claim 2. The control means according to any one of claims 1 to 3, characterized in that determining the execution timing of the comparison to refresh step the average value of humidity detected by the machine humidity sensor and the reference value Image forming apparatus.