Patent Grant
9829845
The present invention relates to an image forming apparatus, such as an electrophotographic copying machine or a laser beam printer, including a developing device for developing an electrostatic latent image formed no an image bearing member into a toner image.
Generally, in the image forming apparatus when a proportion in which image forming processing of an original having a low print ratio is large, a proportion of toner transferred from a developing sleeve in the developing device onto a photosensitive drum becomes small. In such a state, when the developing sleeve is continuously rotated for a long time, the toner is stirred and fed in the developing device. Further, the toner is sheared by stirring and rubbing with a stirring screw for supplying the toner to the developing sleeve or by rubbing with a regulating member for uniformizing a toner layer on the developing sleeve. As a result, an additive contained in the toner for controlling electric charges or flowability comes off or is buried in the toner surface, so that a charging property or the flowability is deteriorated.
As a result, when the image forming processing of the original having the low print ratio is continued, the toner deteriorated in charging property or flowability is increased in a developing container and on the developing sleeve. For that reason, degree of toner scattering, fog, graininess, and the like are deteriorated.
In order to solve such problems, the following operation was conventionally performed so that the toner did not remain in the developing container for a long time. That is, even in a state in which the image forming processing on a recording material (recording paper or the like) was not effected, the developing sleeve for carrying the toner was driven and rotated while being supplied with a predetermined voltage. As a result, the toner was transferred from the developing sleeve onto the photosensitive drum, so that the toner on the developing sleeve was removed. Then, a toner discharging operation (also referred to as toner forced consumption or toner refreshing processing) for removing the toner transferred on the photosensitive drum was performed.
For example, in Japanese Laid-Open Patent Application (JP-A) 2003-263027, when a drive rotation time of the developing sleeve reaches a predetermined time, an average amount of toner consumption with the predetermined time is estimated. Then, when the estimated value is lower than a threshold, the toner is judged that toner deterioration has gone and then a toner image is formed in a non-image area on the photosensitive drum in a predetermined pattern for toner discharging and is collected by a cleaner without being transferred onto the recording paper. In this way, a technique for forcedly discharging the deteriorated toner from the photosensitive drum in an amount corresponding to the toner image formed in the predetermined pattern has been proposed.
As a result, into the developing container, the toner which has not been deteriorated is supplied in an amount corresponding to the discharged amount of the deteriorated toner.
However, a method in which the average of the drive rotation time of the developing sleeve is taken as described in JP-A 2003-263027 is accompanied with a problem such that the ongoing deterioration cannot be accurately perceived and therefore good development cannot be effected in some cases.
That is, in the averaging method, the forced toner discharging operation cannot be performed until the image formation on the print ratio number of sheets effected for taking the average is completed. In the case where the image formation is continuously effected at the low print ratio, the toner deterioration goes abruptly, so that the good development cannot be carried out.
Further, it would be considered that a method of ensuring the good development by shorten an averaging interval (every one sheet in the extreme) is employed but there has arisen a problem such that downtime by the toner discharging operation in the non-image area and thus productivity is lowered.
Therefore, e.g., in JP-A 2006-023327, a control method in which the lowering in productivity is minimized while preventing deterioration in image quality has been proposed. Specifically, in the case where a value which indicates the amount of the toner used every image formation (e.g., a video count value every image formation) is smaller than a preset threshold, a difference therebetween is calculated. The control method in which the forced toner discharging is executed when an integrated value obtained by integrating the calculated difference reaches a predetermined value has been proposed.
As a result, setting of the threshold for the amount of toner consumption by the image formation and setting of the threshold for the integrated value of the difference for judging whether or not the forced toner discharging should be executed are made properly. Thus, the forced toner discharging operation is not performed until moment before the lowering in image quality due to the toner deterioration occurs but can be performed immediately after the image quality deterioration is liable to occur. That is, the control which minimizes the lowering in productivity while preventing the image quality deterioration can be effected.
Here, the image forming apparatus capable of effecting the above-described control of the forced toner discharging operation (forced toner consumption) will be considered more specifically.
In the prior art, as described in JP-A 2003-263027 and JP-A 2006-023327, the toner discharging has been properly performed while paying attention to such a point that the toner deterioration in the developer depends on the rotation time of the developing sleeve and depends the toner consumption amount in the rotation time or while paying attention to such a point that the toner deterioration in the developer depends on the print ratio of the original to be subjected to the image formation. Thus, the methods for minimizing the lowering in productivity while retaining the image quality have been proposed.
However, in recent years, with speed-up of a copying machine, a lowering in melting point of the toner has been advanced in order to improve fixability. As a result, the above-described toner deterioration by the image formation not only depends on the print ratio of the original but also largely depends on a temperature in the image forming apparatus (or in the developing device or the developer in the developing device). Specifically, with a higher temperature, the toner deterioration tends to go earlier.
As a result, in the prior art which does not pay attention to the temperature in the image forming apparatus (or in the developing device or the developer in the developing device), the toner discharging operation is not sufficient when the temperature of the developer is increased by long-time continuous output of the image forming apparatus, a change in ambient environment, and the like. As a result, image quality deteriorations due to the toner deterioration such as an increase of toner scattering, fog deterioration, and deterioration of graininess are caused to occur. On the other hand, even the case where an execution frequency of the toner discharging operation is increased or an execution threshold of the toner discharging operation is lowered, when the temperature of the developer after long-time standing or the like is sufficiently low, the toner is discharged excessively. As a result, an increase in waste toner, a lowering in productivity, and an increase in running cost are caused.
Therefore, a principal object of the present invention is to provide an image forming apparatus, including a developing device and a toner discharging means for preventing the toner deterioration described above, capable of alleviating a lowering in productivity while preventing the toner deterioration by changing a toner discharging operation depending on a temperature in the developing device.
According to an aspect of the present invention, there is provided an image forming apparatus comprising:
a developing device for developing a latent image formed on an image bearing member into a developer image;
a transferring device for transferring the developer image from the image bearing member onto a transfer material;
temperature detecting means, disposed in a main assembly of the image forming apparatus, for detecting a temperature; and
a controller for controlling a forced consumption operation in which toner is forcedly consumed by the developing device without transferring the developer image from the image bearing member onto the transfer material,
wherein the controller is capable of controlling the forced consumption operation so that a frequency of the forced consumption operation or an amount of toner consumption per one forced consumption operation when the temperature detected by the temperature detecting means is higher than a predetermined temperature is more than that when the temperature detected by the temperature detecting means is lower than the predetermined temperature.
According to another aspect of the present invention, there is provided an image forming apparatus comprising:
a developing device for developing a latent image formed on an image bearing member into a developer image;
a transferring device for transferring the developer image from the image bearing member onto a transfer material;
temperature detecting means, disposed in a main assembly of the image forming apparatus, for detecting a temperature; and
a controller for controlling a forced consumption operation in which toner is forcedly consumed by the developing device without transferring the developer image from the image bearing member onto the transfer material,
wherein the controller is capable of controlling the forced consumption operation so that the forced consumption operation is performed when the temperature detected by the temperature detecting means is higher than a predetermined temperature and so that the forced consumption operation is not performed when the temperature detected by the temperature detecting means is lower than the predetermined temperature.
According to a further aspect of the present invention, there is provided an image forming apparatus comprising:
a developing device for developing a latent image formed on an image bearing member into a developer image;
a transferring device for transferring the developer image from the image bearing member onto a transfer material;
temperature detecting means, disposed in a main assembly of the image forming apparatus, for detecting a temperature; and
a controller for controlling a forced consumption operation in which toner is forcedly consumed by the developing device without transferring the developer image from the image bearing member onto the transfer material,
wherein the controller is capable of controlling the forced consumption operation so that an amount of toner consumption per unit drive time of the developing device when the temperature detected by the temperature detecting means is higher than a predetermined temperature is more than that when the temperature detected by the temperature detecting means is lower than the predetermined temperature.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
Hereinbelow, an image forming apparatus as a first embodiment of the present invention will be described in detail.
As shown in
In this embodiment, the surface of the photosensitive drum 101 electrically charged by a primary charging device 102 (102Y, 102M, 102C and 102K) of a corona charging type in which non-contact charging is effected is exposed to light by a laser 103 (103Y, 103M, 103C and 103K) driven by an unshown laser driver. As a result, an electrostatic latent image is formed on the photosensitive drum 101. The latent image is developed by each of developing devices 103 (104Y, 104M, 104C and 104K), so that toner images (developer images) of yellow, magenta, cyan and black are formed.
The toner images formed at the respective image forming stations are transferred and superposed on the intermediary transfer belt 121 of polyimide resin by a transfer bias with transfer blades 105 (105Y, 105M, 105C and 105K) as a primary transfer means. The four-color toner images transferred on the intermediary transfer belt 121 are transferred onto recording paper P as a transfer material by a secondary transfer roller 125 as a secondary transfer means disposed opposite to the roller 124. The toner remaining on the intermediary transfer belt 121 without being transferred onto the recording paper P is removed by an intermediary transfer belt cleaner 114b. The recording paper P on which the toner images are transferred is pressed and heated by a fixing device 130 including fixing rollers 131 and 132, so that a permanent image is obtained. Further, primary transfer residual toners remaining on the photosensitive drums 101 after the primary transfer are removed by cleaners 109 (109Y, 109M, 109C and 109K), so that the image forming apparatus prepares for subsequent image formation.
Further, with reference to
Referring to
In a block diagram of
Referring to
A video signal count portion 207 adds up a level for each pixel (0 to 255 level) for a screenful of the image with respect to 600 dpi of the image data input into the LUT portion 203. The integrated value of the image data is referred to as a video count value. A maximum of this video count value is 1023 in the case where all the pixels for the output image are at the 255 level. Incidentally, there is a restriction on the constitution of the circuit, by using a laser signal count portion 208 in place of the video signal count portion 207, the image signal from the laser drive 205 is similarly calculated, so that it is possible to obtain the video count value.
The developing device 4 will be further described more specifically with reference to
In this embodiment, the inside of the developing container 20 is horizontally divided by a partition wall 23 into a developing chamber 21a and a stirring chamber 21b. The partition wall 23 extends in the direction perpendicular to the drawings of
In the developing chamber 21a and the stirring chamber 21b, first and second feeding screws 22a and 22b which are feeding members as developer stirring and feeding means are disposed, respectively. The first feeding screw 22a is disposed, at the bottom portion of the developing chamber 21a, roughly in parallel to the axial direction of the developing sleeve 24. It conveys the developer in the developing chamber 21a in one direction parallel to the axial line of the developing sleeve 24 by being rotated. The second feeding screw 22b is disposed, at the bottom portion of the stirring chamber 21b, roughly in parallel to the first feeding screw 22a. It conveys the developer in the stirring chamber 21b in the direction opposite to that of the first feeding screw 22a.
Thus, by the feeding of the developer through the rotation of the first and second feeding screws 22a and 22b, the developer is circulated between the developing chamber 21a and the stirring member 21b through openings 26 and 27 (that is, communicating portions) present at both ends of the partition wall 23 (
In this embodiment, the developing chamber 21a and the stirring chamber 21b are horizontally disposed. However, the present invention is also applicable to a developing device in which the developing chamber 21a and the stirring chamber 21b are vertically disposed and developing devices of other types.
In this embodiment, the developing container 20 is provided with an opening at a position corresponding to a developing area A wherein the developing container 20 opposes the photosensitive drum 1. At this opening, the developing sleeve 24 is rotatably disposed so as to be partially exposed toward the photosensitive drum 1.
In this embodiment, the diameters of the developing sleeve 24 and the photosensitive drum 1 are 20 mm and 80 mm, respectively, and a distance in the closest area between the developing sleeve 24 and the photosensitive drum 1 is about 400 μm. By this constitution, development can be effected in a state in which the developer fed to the developing area A is brought into contact with the photosensitive drum 1.
Incidentally, the developing sleeve 24 is formed of nonmagnetic material such as aluminum and stainless steel and inside thereof a magnetic roller 24m as a magnetic field generating means is non-rotationally disposed.
In the constitution described above, the developing sleeve 24 is rotated in the direction indicated by an arrow (counterclockwise direction) to carry the two component developer regulated in its layer thickness by cutting of the chain of the magnetic brush with the trimming member 25. Then, the developing sleeve 24 conveys the layer thickness-regulated developer to the developing area A in which the developing sleeve 24 opposes the photosensitive drum 1, and supplies the developer to the electrostatic latent image formed on the photosensitive drum 1, thus developing the latent image. At this time, in order to improve development efficiency, i.e., a rate of the toner imparted to the latent image, a developing bias voltage in the form of a DC voltage biased or superposed with an AC voltage is applied to the developing sleeve 24 from a power source. In this embodiment, the developing bias is a combination of a DC voltage of −500 V, and an AC voltage which is 1,800 V in peak-to-peak voltage Vpp and 12 kHz in frequency f. However, the DC voltage value and the AC voltage waveform are not limited to those described above.
In the two component magnetic brush developing method, generally, the application of AC voltage increases the development efficiency and therefore the image has a high quality but on the other hand, fog is liable to occur. For this reason, by providing a potential difference between the DC voltage applied to the developing sleeve 24 and the charge potential of the photosensitive drum 1 (i.e., a white background portion potential), the fog is prevented.
The regulating blade 25 as the trimming member is constituted by a nonmagnetic member is formed with an aluminum plate or the like extending in the longitudinal axial direction of the developing sleeve 24. The regulating blade 29 is disposed upstream of the photosensitive drum 1 with respect to the developing sleeve rotational direction. Both the toner and the carrier of the developer pass through the gap between an end of the trimming member 25 and the developing sleeve 24 and are sent into the developing area A. Incidentally, by adjusting the gap between the regulating blade 25 and the developing sleeve 24, the trimming amount of the magnetic brush chain of the developer carried on the developing sleeve 24 is regulated, so that the amount of the developer sent into the developing area A is adjusted. In this embodiment, a coating amount per unit area of the developer on the developing sleeve 24 is regulated at 30 mg/cm2 by the regulating blade 25.
The gap between the regulating blade 25 and the developing sleeve 24 is set at a value in the range of 200-1,000 μm, preferably, 300-700 μm. In this embodiment, the gap is set at 500 μm.
Further, in the developing area A, the developing sleeve 24 of the developing device 4 moves in the same direction as the movement direction of the photosensitive drum 1 at a peripheral speed ratio of 1.75 by which the developing sleeve 24 moves at the peripheral speed which is 1.75 times that of the photosensitive drum 1. With respect to the peripheral speed ratio, any value may be set as long as the set value is in the range of 0-3.0, preferably, 0.5-2.0. The greater the peripheral (moving) speed ratio, the higher the development efficiency. However, when the ratio is excessively large, problems such as toner scattering and developer deterioration occur. Therefore, the ratio is desired to be set in the above-mentioned range.
Further, at the opening (communicating portion) 26 in the developing container 20, as a temperature detecting means for detecting information relating to the temperature in the developing device, the band gap temperature sensor 4T is disposed. The band gap temperature sensor 4T is disposed in the developing device so as to be buried in the developer and directly detects the temperature of the developer. The disposition place of the temperature sensor in the developing container 20 may desirably be a position in which a sensor surface is buried in the developer in order to improve detection accuracy but is not limited thereto. Although the accuracy is somewhat lowered, it is also possible to employ a constitution in which the temperature in the developing device is detected by using the temperature sensor provided in the image forming apparatus main assembly.
Here, the temperature sensor 4T will be described more specifically. In this embodiment, as the temperature sensor 4T, a temperature/humidity sensor (“SHT1X series”, mfd. by Sensiron Co., Ltd.) was used. As shown in
The temperature sensor 4T used in this embodiment can detect both of the temperature and the humidity. However, actually, only a detection result of the temperature is utilized, so that the use of other sensors capable of detecting only the temperature may also be sufficient.
Here, the two component developer used in this embodiment, which comprises the toner and the carrier, stored in the developing container 20 of the developing device 4 will be described more specifically.
The toner contains primarily binder resin, and coloring agent. If necessary, particles of coloring resin, inclusive of other additives, and coloring particles having external additive such as fine particles of colloidal silica, are externally added to the toner. The toner is negatively chargeable polyester-based resin and is desired to be not less than 4 μm and not more than 10 μm, preferably not more than 8 μm, in volume-average particle size.
As for the material for the carrier, particles of iron, the surface of which has been oxidized or has not been oxidized, nickel, cobalt, manganese, chrome, rare-earth metals, alloys of these metals, and oxide ferrite are preferably usable. The method of producing these magnetic particles is not particularly limited. A weight-average particle size of the carrier may be in the range of 20-60 μm, preferably, 30-50 μm. The carrier may be not less than 107 ohm·cm, preferably, not less than 108 ohm·cm, in resistivity. In this embodiment, the carrier with a resistivity of 108 ohm·cm was used.
Incidentally, the volume-average particle size of the toner used in this embodiment was measured by using the following apparatus and method. As the measuring apparatus, a Coulter Counter T-II (mfd. by Coulter Co. Ltd.), an interface (mfd. by Nikkaki Bios Co., Ltd.) for outputting number-average distribution and volume-average distribution, and a personal computer (Model “CX-1”, available from Canon K.K.) were used. As the electrolytic solution, a 1%-aqueous solution of reagent-grade sodium chloride was used.
The measuring method was as follows. To 100-150 ml of the electrolytic solution, 0.1 ml of a surfactant as a dispersant, preferably, alkylbenzenesulfonic acid salt, was added, and to this mixture, 0.5-50 mg of a measurement sample was added.
Then, the electrolytic solution in which the sample was suspended was placed in an ultrasonic dispersing device for roughly 1-3 minutes to disperse the sample. Then, the particle size distribution of the sample, the size of which is in the range of 2-40 μm was measured with the use of the above-mentioned Coulter Counter TA-II fitted with a 100 μm aperture, and the volume-average distribution was obtained. Then, a volume-average particle size was obtained from the thus-obtained volume-average distribution.
Further, the resistivity of the carrier used in this embodiment was measured by using a sandwich type cell with a measurement electrode area of 4 cm2 and a gap between two electrodes of 0.4 cm. A voltage E (V/cm) was applied between the two electrodes while applying 1 kg of weight (load) to one of the electrodes, to obtain the resistivity of the carrier from the amount of the current which flowed through the circuit.
Next, referring to
The developing device 4 is provided, at its upper portion, with a hopper 31 which accommodates a two-component developer for supply comprising a mixture of the toner and the carrier. In
The developer container 20 is supplied with toner in an amount equal to the amount of the toner consumed for image formation, from the hopper 31 through the developer supply opening 30 by a rotational force of the supply screw 32 and the weight of the developer itself. In this manner, the developer for supply is supplied from the hopper 31 into the developing device 4.
The supply amount of the developer for supply can be roughly determined by the number of revolutions of the supply screw 32, and the number of revolutions is determined by an unshown toner supply amount controlling means on the basis of the above-described video count value of the image data and a detection result of a patch detection sensor 11, shown in
Hereinafter, a control method of a toner forced consumption (toner discharging) operation which is a characteristic feature of the present invention will be described in detail.
First, in the case where the image formation at the low print ratio is continued in the image forming apparatus having the above-described constitution, the proportion of the toner transferred from the developing container 20 onto the photosensitive drum 1 is small. For this reason, the toner in the developing container 20 is subjected to stirring of the first and second feeding screws 22a and 22b and rubbing at the time of passing through the trimming member 25, for a long time. As a result, the above-described external additive for the toner comes off the toner or is buried in the toner surface, so that the flowability or charging property of the toner in deteriorated and thus the image quality is deteriorated.
Therefore, a method in which downtime is provided and the deteriorated toner in the developing device 4 is used for the development in a non-image area and thus is forcedly discharged (consumed) has been conventionally proposed. In the conventional method, by paying attention to a difference in degree of toner deterioration progression depending on the print ratio (i.e., a larger proportion of the deteriorated toner with a lower print ratio), a length of the downtime by the toner discharging operation or a toner discharging frequency is changed depending on the print ratio. Incidentally, the print ratio means an area of the toner image formed in a maximum image forming area, and is 100% for a solid black image and is 0% for a solid white image. In this embodiment, attention is also paid to the difference in degree of toner deterioration progression depending on the developer temperature or an ambient temperature in an environment in which the image forming apparatus is placed. That is, depending on not only the print ratio but also the detection result of the developer temperature detecting means 4T, a discharge amount of the developer unit time is changed. Specifically, depending on the detection result of the developer temperature detecting means 4T, the length of the downtime by the toner discharging operation (i.e., an execution time of the toner discharging operation) or the toner discharging frequency.
In the following, in this embodiment, the difference in degree of the toner deterioration progression depending on the developer temperature will be described first and then how to determine an operation condition of the toner forced consumption depending on the temperature and how to execute toner discharging operation will be described.
As described above, in the case where the proportion of the toner transferred onto the photosensitive drum is small and the amount of the toner supply into the developing container 20 is small, i.e., in the case where the print ratio is low, the toner deterioration has gone. Further, a speed of the toner deterioration progression varies depending on an environment in which the developing device is placed. The present inventor conducted the following experiment. That is, the developing device 4 is placed in various constant environments and in each of the constant environments, continuous one-side-image formation on 10,000 A4-sized sheets was effected while changing the print ratio (from 0% to 5%) for each of the colors, so that a change in image quality before and after the continuous image formation. A result of this experiment is shown only for black in the table of
From
In other words, in the image forming apparatus in this embodiment, unless the image formation is effected at a certain print ratio or more (i.e., at a certain value or more of the video count), the image quality deterioration due to the toner deterioration, such as the deterioration of the degree of the fog, the toner scattering or the graininess. Further, the print ratio which is the threshold at which the image quality deterioration occurs (i.e., the video count which is the threshold) varies depending on the temperature of the developer in the developing device.
In this embodiment, in order that the image quality deterioration due to the toner deterioration is not caused to occur, the video count corresponding to a minimum necessary amount of toner consumption is defined as a “toner deterioration threshold video count Vt”. The toner deterioration threshold video count Vt is the value varying depending on the developer temperature as described above and is also a value which can be calculated by the above-described experiment or the like. Here, in
Next, the control method and operation condition of the toner forced consumption operation (forced toner consumption operation) will be described. First, as a precondition, a concept of the toner forced consumption and the control method for each of the colors is the same. Therefore, the colors are omitted from description along the following flow charts is some cases but in which common control is effected for each of the colors. In this embodiment, as an easy-to-understand example, the case where such an image that the print ratios per (one) sheet for the colors of Y, M, C and K are 5% for Y, 5% for M, 5% for C and 3% for K (hereinafter, this image is referred to as a “black low duty image chart”) is continuously formed on A4-sized sheets is considered. The toner discharging control in this case is described along the flow chart shown in
When the image formation is started, as described above with reference to
Then, the toner deterioration threshold video count Vt at the current temperature is calculated from the detection result of the temperature detecting means 4T and the table (
Here, progression of the detection result of the temperature detecting means 4T(K) provided in the developing device for black in the case where the above-described “black low duty image chart” is continuously formed on the A4-sized sheets is shown in
Referring again to the flow chart of
Further, with respect to the toner deterioration integrated value X calculated and updated every image formation in the above steps, a difference (A−X) of the toner deterioration integrated value X from a discharge execution threshold is calculated (step S6). Here, the discharge execution threshold A is a print ratio value which is arbitrarily settable. The smaller the discharge execution threshold A, the higher the frequency of execution of the toner discharging operation even in the continuous image formation at the same print ratio. The discharge execution threshold A is set at 512 in this embodiment. When the set value of the discharge execution threshold A is excessively large, a time in which the toner deterioration goes until the toner discharging operation is performed is long, so that it is desirable that the set value is approximately equal to the video count value of the whole surface solid image (the image with the print ratio of 100%) on one surface of A4-sized sheet to A3-sized sheet. Further, e.g., with a larger volume of the developer which can be retained in the developing container 20, there is a tendency that the toner discharge execution threshold
A can be set at a larger value.
Finally, the sign (positive or negative) of the difference (A−X), between the toner deterioration integrated value X and the discharge execution threshold A, calculated in the preceding step is judged (step S7). Here, in the case where (A−X) is positive, the toner is judged that the toner deterioration does not go to the extension that the toner discharging is required to be performed immediately, so that the image formation is continued (step S8). On the other hand, in the case where (A−X) is negative, the toner is judged that the toner deterioration goes considerably and therefore there is a need to execute the toner discharging immediately, so that the image formation is interrupted and then the toner discharging operation is performed (step S9).
Here, the toner discharging operation will be described with reference to
Here, in the above-described toner discharge control method, the case where the above-described “black low duty image chart” is subjected to the continuous image formation on 10,000 sheets will be considered specifically.
First, in the case where the “black low duty image chart” is formed on one sheet, how to calculate the toner deterioration integrated value X for each color in the toner discharge control in this embodiment is shown in
On the other hand, with respect to K (black), in the first half of the continuous image formation, the toner deterioration integrated value X per one sheet is zero but as described above, the developer temperature is increased with a later stage in the latter half of the continuous image formation (
More specifically, from
The controller 1007 controls the operation condition so that the execution frequency in the case where the temperature in the developing device is higher than a print ratio temperature is higher than that in the case where the temperature in the developing device is lower than the print ratio temperature, on the basis of the detection result of the temperature detecting means 4T. That is, the controller 1007 controls the operation condition so that the amount of the toner discharged per unit image formation satisfies the following relationship in the case where the image is continuously formed at the same print ratio. That is, the controller 1007 controls the operation condition so that the amount of the toner discharged per unit image formation in the case where the temperature in the developing device is higher than the print ratio temperature is larger than that in the case where the temperature in the developing device is lower than the print ratio temperature. Here, the continuous image forming operation means a series of image forming operations for continuously forming the image on a plurality of sheets of the recording material.
Further, a simple control block diagram is shown in
In the above-described manner, in this embodiment according to the present invention, in the continuous image formation of the “black low duty image chart” on the 10,000 A4-sized sheets, the toner discharging is executed while interrupting the image formation about 115 times. Further, by one toner discharging operation, the toner in the amount corresponding to the video count of 512 is consumed. Here, in the conventional toner discharge control, the change in toner deterioration threshold value by temperature is not factored, so that the toner deterioration integrated value X per one sheet during the continuous image formation on, e.g., 10,000 sheets is always t11 and thus the toner discharging is required to be executed about 214 times. Therefore, by employing this embodiment according to the present invention, the frequency of the toner discharging operation can be reduced by half and in addition, the toner consumption amount can also be reduced by half.
According to the constitution in this embodiment, during the continuous image formation for continuously forming the image on the plurality of sheets of the recording material, the operation condition is controllable so that the frequency of the discharging operation executed per unit number of sheets subjected to the image formation is higher with a higher temperature in the developing device. Thus, the suppression of the downtime can be realized while realizing the suppression of the toner deterioration.
Incidentally, in this embodiment, the execution frequency of the discharging operation is changed on the basis of the temperature in the developing device but the discharge amount (execution time) in one discharging operation may also be changed.
In Embodiment 1 described above, the control method of performing the efficient toner discharging operation was proposed by paying attention to the fact that the toner deterioration goes in the case where the print ratio per one sheet is low (i.e., in the case where the video count is small) and that the degree of the toner deterioration progression varies depending on the temperature. In this embodiment, a method in which attention is paid to dependency of the deterioration of the toner in the developer on (1) a driving time of the developing sleeve, (2) the toner consumption amount per unit time, and (3) the temperature of the developer at that time and then the toner discharging operation is controlled will be described.
First, as a precondition, a concept of the toner forced consumption and the control method for each of the colors is the same. Therefore, the colors are omitted from description along the following flow charts is some cases but in which common control is effected for each of the colors. Also in this embodiment (Embodiment 2), for the purpose of easy-to-understand description, the case where the “black low duty image chart” with the print ratios per (one) sheet for the colors of Y, M, C and K are 5% for Y, 5% for M, 5% for C and 3% for K is continuously formed on A4-sized sheets is considered. The toner discharging control in this case is described along the flow chart shown in
First, every print ratio number (A) of sheets, a total sleeve rotation time integrated value St and a total toner consumption amount video count Vall are calculated (step S201). Here, the print ratio number (A) of sheets is an arbitrarily determined value in the image forming apparatus in this embodiment and may desirably be about 100 sheets. Further, the total sleeve rotation time integrated value St is a total integrated value of a sleeve rotation time from start of the image formation to completion of the image formation on the print ratio number (A) of sheets and contains the sleeve rotation time during sheet intervals, pre-rotation, and the like. Further, the total toner consumption amount video count Vall is a value which indicates a total toner consumption amount from the start of the image formation to the completion of the image formation on the print ratio number (A) of sheets. This value also contains the amount of the toner consumed by patches for density control, toner supply control, misregistration correction, and the like, in addition to the video count calculated by the above-described video signal count portion 207 shown in
Next, a toner consumption amount per unit driving time (Vall/St) is calculated from the total sleeve rotation time integrated value St and the total toner consumption amount video count Vall which are (Vall/St) is a value which indicates a degree of the toner deterioration.
Further, a threshold T (which depends on the temperature) of the toner consumption amount per unit drive time in which the toner deterioration goes will be considered. The threshold T can be calculated by investigating a change in image quality before and after the experiment described above with reference to
In a subsequent step (step S204), the sign (positive or negative) of a difference between the above-described toner consumption amount per unit drive time (Vall/St) and the threshold T of the toner consumption amount calculated in step S203, i.e., T−(Vall/St) is judged. That is, the controller controls the forced consumption operation on the basis of the average of the result of the detection by the temperature detecting sensor 4T before and after the image formation on the print ratio number of sheets.
First, in the case where T−(Vall/St) is negative, the toner consumption amount per unit drive time is sufficiently large, so that the toner deterioration has not gone. Therefore, the toner discharging operation is not performed in the case where T−(Vall/St) is negative and both of the total sleeve rotation time integrated value St and the total toner consumption amount video count Vall are reset to zero (step S206) and then the image formation is continued.
On the other hand, in the case where T−(Vall/St) is positive, the toner consumption amount per unit drive time is small and therefore the toner deterioration has gone. For this reason, in the case where T−(Vall/St) is positive, the toner discharging operation is performed so that the toner in the amount corresponding to the video count calculated by Vall−(T×St) is consumed (step S205). That is, the controller judges whether or not the toner discharging operation (the forced consumption operation) should be performed, every print ratio number of sheets subjected to the image formation. Here, the operation flow chart of the toner discharging operation itself is similar to that of
Incidentally, in this embodiment, the case where the rotational speed of the developing sleeve is constant is described but in the case where a plurality of rotational speeds is employed, these rotational speeds may also be taken into consideration. Specifically, in step S202, a toner consumption amount per unit drive amount Vall/(St×Vsl) is calculated by using a developing sleeve speed Vsl in addition to the total sleeve rotation time integrated value St and the total toner consumption amount video count Vall. In this case, a unit of the threshold T is [video count/(sec.rotation speed)] and a similar flow is executed. For example, based on the sign (positive or negative) of T−(Vall/(St×Vsl)], judgment as to whether or not the discharging operation should be performed may be made. In the case where T−(Vall−(St×Vsl) is positive, the toner in the amount corresponding to the video count calculated by Vall−(T×St×Vsl) may be consumed.
Along the flow chart of
Here, the calculated toner consumption amount per unit drive time (Vall/St) of 22 during the image formation on the print ratio number (A) of 100 sheets and the threshold T of the toner consumption amount per unit drive time in which the toner deterioration goes shown in the table of
On the other hand, as a conventional embodiment, in the case where the toner discharging is executed every print ratio number of sheets, the toner discharging is executed 20 times (=2000/100) during the image formation on 2,000 sheets in the first half of the image formation, so that the deterioration of the image quality cannot be prevented unless the toner discharging is executed 100 times in total. Further, the toner forced consumption (discharge) controlling in Embodiment 2 is also effected in accordance with the control block diagram of
According to the present invention, it is possible to provide an image forming apparatus, including a developing device and a toner discharging means for preventing the toner deterioration described above, capable of alleviating the lowering in productivity while preventing the toner deterioration by changing the toner discharging operation depending on the temperature in the developing device.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 195702/2009 filed Aug. 26, 2009, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-195702 | Aug 2009 | JP | national |
This application is a divisional of application Ser. No. 13/755,298, filed Jan. 31, 2013, which is a divisional of application Ser. No. 12/859,371, filed Aug. 19, 2010, now U.S. Pat. No. 8,401,406, issued Mar. 19, 2013.
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| Number | Date | Country | |
|---|---|---|---|
| 20160170360 A1 | Jun 2016 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13755298 | Jan 2013 | US |
| Child | 15008828 | US | |
| Parent | 12859371 | Aug 2010 | US |
| Child | 13755298 | US |
