Patent Grant
9280086
The present invention relates to an image forming apparatus of an electrophotographic type in general and particularly relates to the image forming apparatus including a developer amount detecting means for detecting an amount of a developer in a developing container for containing the developer.
In a conventional image forming apparatus of the electrophotographic type, a process cartridge type in which a process cartridge is detachably mountable to a main assembly of the image forming apparatus is widely employed. In the process cartridge type, e.g., a photosensitive drum and, as process means acting on the photosensitive drum, a charging roller, a cleaning device and a developing device are integrally assembled into a cartridge to provide the process cartridge. According to the process cartridge type, it is possible to perform maintenance of the image forming apparatus, such as replenishing of the developer or part exchange of the photosensitive drum or the like which reaches its end of a lifetime, by a user himself (herself) without relying on a service person.
In the image forming apparatus of the process cartridge type, in the case where the developer is used up, the user himself (herself) exchanges the process cartridge, so that the image forming apparatus is capable of forming an image again. Therefore, in the image forming apparatus of the process cartridge type, the developer amount detecting means for permitting detection of a level of a remaining developer amount in the developing container for containing the developer is provided in some cases. This is because by notifying the user that consumption of the developer is detected by using the developer amount detecting means, the user can know how much developer, which can be subjected to image formation, remains in the process cartridge in real time.
As a method of the developer amount detecting means in a developing device of a non-magnetic one-component developing type using a non-magnetic one-component developer, there is the following method in which electrostatic capacity between a supplying roller as a developer supplying member and a developing roller as a developer carrying member is detected (Japanese Laid-Open Patent Application (JP-A) 2009-9036). That is, in the developing container, the supplying roller including an electroconductive metal support and a foam layer provided around the metal support, and the developing roller including an electroconductive support and an elastic layer provided around the metal support are provided rotatably in contact with each other. The foam layer of the supplying roller is formed by a urethane sponge layer in which the developer can enter. Further, the developing device can retain a first attitude in which the developing roller contacts the photosensitive drum and a second attitude in which the developing roller is separated (spaced) from the photosensitive drum. Then, in the second attitude in which a developing operation is not performed, a voltage for detection is applied to the metal support of the supplying roller, so that the electrostatic capacity between the developing roller and the supplying roller is detected. This electrostatic capacity changes depending on an amount of an insulating developer present between the developing roller and the supplying roller and therefore it is possible to detect the developer amount by establishing association of a relationship between the electrostatic capacity and the developer amount in advance.
However, the developer amount detecting method as described above is accompanied with the following problem in terms of detection accuracy.
That is, in the case where an image with a high print ratio is formed, the amount of the developer contained in the supplying roller is temporarily decreased immediately after the image formation. For that reason, in that state, when the developer amount is detected, there is a possibility that the developer amount is erroneously detected so that it is less than an actual developer amount. Against this, an auxiliary driving operation performed for restoring a developer content in the supplying roller in a period from an end of the image formation to start of the developer amount detecting operation is effective. However, when this driving operation is excessively performed, there is a possibility of not only acceleration of abrasion (wearing) deterioration of respective members but also a lowering in productivity of the image formation.
Incidentally, in the above, the conventional problem was described by taking, as an example, the image forming apparatus of the process cartridge type for which the detection of the remaining developer amount level by the developer amount detecting means was particularly useful. However, in the case where the developer amount detecting method as described above is employed, there arises a similar problem also in image forming apparatuses in which the process cartridge type is not employed.
A principal object of the present invention is to provide an image forming apparatus capable of preventing a lowering in detection accuracy of a developer amount, which can occur depending on a difference in image formed before the detection, without shortening a lifetime of a developing device and without lowering productivity of image formation.
According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image bearing member for bearing an electrostatic latent image; a developing container for containing a developer; a developer carrying member, including a first electrode member, for carrying the developer contained in the developing container to develop the electrostatic latent image; a developer supplying member, including a second electrode member and a foam layer provided around the second electrode member, for supplying the developer contained in the developing container to the developer carrying member by rotation in contact with the developer carrying member; a measuring portion for measuring a print pixel number of an image to be formed; a supplying device for performing a supplying operation for supplying the developer to the developer supplying member on the basis of a measured print pixel number after image formation; and a detecting device for detecting an amount of the developer contained in the developing container by detecting electrostatic capacity between the first electrode member and the second electrode member after the supplying operation by the supplying device.
According to the present invention, it is possible to prevent the lowering in detection accuracy of the developer amount, which can occur depending on the difference in image formed before the detection, without shortening the lifetime of the developing device and without lowering the productivity of image formation.
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.
Parts (a) and (b) of
Part (a) of
Part (a) of
Part (a) of
Hereinbelow, the image forming apparatus according to the present invention will be described more specifically with reference to the drawings.
In a main assembly 1 of the image forming apparatus 100 (hereinafter referred to as an apparatus main assembly), the image forming portion 103 is provided. The image forming portion 103 includes a photosensitive drum 4 which is a drum type electrophotographic photosensitive member as an image bearing member. The photosensitive drum 4 is provided rotatably to a process cartridge described later and is rotationally driven in an arrow R1 direction (clockwise direction) indicated in
A peripheral surface of the rotating photosensitive drum 4 is uniformly charged to a predetermined polarity (negative in this embodiment) and potential by a charging roller 5 which is a contact type charging member as a charging means. The charging roller 5 includes a core metal and an electroconductive elastic (member) layer formed around and coaxially with the core metal. The charging roller 5 is disposed so that its rotational axis direction is substantially parallel to a rotational axis direction of the photosensitive drum 4. Further, the charging roller 5 contacts the photosensitive drum 4 with a predetermined pressure against elasticity of the electroconductive elastic layer. The core metal of the charging roller 5 is rotatably supported by the process cartridge 20 described later via bearing at its end portions with respect to the rotational axis direction of the charging roller 5. The charging roller 5 is rotated by the rotation of the photosensitive drum 4. To the charging roller 5, a charging power source E1 as a charging voltage application means is connected. Further, in this embodiment, during the image formation, to the core metal of the charging roller 5, a DC voltage of about −1000 V is applied as a charging voltage (charging bias). As a result, the surface of the photosensitive drum 4 is uniformly charged to a dark-portion potential VD of about −500 V.
The uniformly charged surface of the photosensitive drum 4 is exposed to light by an exposure device (laser scanner unit) 6 as an exposure means. As a result, an electrostatic latent image (electrostatic image) corresponding to image information is formed on the surface of the photosensitive drum 4. In this embodiment, the exposure device 6 employs an image exposure type in which an image portion is exposed to light. To the exposure device 6, a time-serial electric digital pixel signal of the image information which is image-processed after being inputted from the external host device 200 into the control circuit portion 101 via the interface 102. The exposure device 6 includes a laser outputting portion for outputting laser light L (exposure beam) modulated correspondingly to the inputted time-serial electric digital pixel signal, a rotatable polygonal mirror (polygon mirror), fθ lens, a reflecting mirror and the like. Then, the uniformly charged surface of the photosensitive drum 4 is exposed to the laser light L while being scanned with the laser light L in a main scan direction. By this exposure with the scanning in the main scan direction and movement of the photosensitive drum 4 surface in a sub-scan direction by the rotation of the photosensitive drum 4, the electrostatic latent image corresponding to an exposure pattern is formed on the surface of the rotating photosensitive drum 4. In this embodiment, a potential of an exposed portion on the surface of the photosensitive drum 4 is a light-portion potential VL of about −100 V, and by a potential contrast between the dark-portion potential VD and the light-portion potential VL, the electrostatic latent image corresponding to the exposure pattern is formed.
The electrostatic latent image formed on the surface of the photosensitive drum 4 is developed (visualized) as a toner image by a developing device 7 as a developing means. In this embodiment, the developing device 7 is of a non-magnetic one-component developing type using a toner T as a developer which is a non-magnetic one-component developer. Further, in this embodiment, the developing device 7 effects development by a reversal developing method. That is, the electrostatic latent image is developed into the toner image by depositing the toner, charged to the same polarity as a charge polarity of the photosensitive drum 4, on an exposure portion (light-portion potential portion) lowered in absolute value of electric charge amount by the exposure after the photosensitive drum 4 is uniformly charged. That is, in this embodiment, a normal charge polarity of the toner is negative.
The photosensitive drum 7 includes a developing container 7a for containing (accommodating) the toner. The developing container 7a is provided with a developing roller 2 as a developer carrying member so as to be partly exposed to the outside thereof from an opening provided at a position where the developing roller 2 opposes the photosensitive drum 4. Specifically, as described later, the developing roller 2 is contactable to the photosensitive drum 4. Further, the developing roller 2 is rotationally driven by a driving motor (not shown) as a driving means, provided to the apparatus main assembly 1, so that a surface of the developing roller 2 moves in the same direction as the surface movement direction of the photosensitive drum 4 at a contact portion where the developing roller 2 contacts the photosensitive drum 4. Further, in the developing container 7a, a supplying roller 3 as a developer supplying member for applying the toner T onto the developing roller 2 is provided. The supplying roller 3 is disposed in contact with the developing roller 2. As described later specifically, a surface layer of the supplying roller 3 is formed by a foam layer. Further, the supplying roller 3 is rotationally driven by a driving motor as a driving means, provided to the apparatus main assembly 1, so that a surface of the supplying roller 3 moves in an opposite direction (counter direction) to the surface movement direction of the developing roller 2 at a contact portion where the supplying roller 3 contacts the developing roller 2. Further, in the developing container 7a, a rotatable stirring member 7 for stirring the toner T in the developing container 7a is provided. Further, to the developing container 7a, a developing blade 7c as a developer layer thickness regulating member provided in contact with the developing roller 2 is provided.
The developing roller 2 includes a core metal and an electroconductive elastic layer formed around and coaxially with the core metal. The developing roller 2 is disposed so that its rotational axis direction is substantially parallel to the rotational axis direction of the photosensitive drum 4. Further, the developing roller 2 is contactable to and separable from the photosensitive drum 4 and as described later specifically, a contact and separation state thereof is controlled by a contact and separation cam as a contact and separation means provided to the apparatus main assembly 1. During the image formation, the developing roller 2 is rotationally driven in an arrow R2 direction (counterclockwise direction) indicated in
The toner T is fed toward the supplying roller 3 while being stirred by rotationally driving the stirring member 7b. This toner T is applied onto the surface of the developing roller 2 by the supplying roller 3 rotationally rotated in an arrow R3 direction (counterclockwise direction) indicated in
On the other hand, a sheet feeding roller 9 is rotationally driven with predetermined control timing, so that a sheet of the recording material S is separated and fed from a sheet feeding cassette 10. The fed recording material S is conveyed through a conveying path 11 to reach a registration roller pair 12, and a leading edge of the recording material S is received at a contact portion (nip) of the registration roller pair 12 which rotation is stopped at that time, thus being subjected to oblique movement correction. Then, the recording material S is fed again by the registration roller pair 12 which is rotationally driven with predetermined control timing to be introduced into a transfer portion (transfer nip) N which is a contact portion between the photosensitive drum 4 and a transfer roller 13 as a transfer means.
The transfer roller 13 includes a core metal and an electroconductive elastic (member) layer formed around and coaxially with the core metal. The transfer roller 13 is disposed so that its rotational axis direction is substantially parallel to a rotational axis direction of the photosensitive drum 4. Further, the transfer roller 13 contacts the photosensitive drum 4 with a predetermined pressure against elasticity of the electroconductive elastic layer to form the transfer portion N between itself and the photosensitive drum 4. The transfer roller 13 is rotated by the rotation of the photosensitive drum 4.
The recording material S is nipped and conveyed at the transfer portion N by the photosensitive drum 4 and the transfer roller 13. To the transfer roller 13, a transfer power source E3 as a transfer voltage application means is connected. During the conveyance of the recording material S through the transfer portion N, to the transfer roller 13, as a transfer voltage (transfer bias), a DC voltage having a predetermined potential and an opposite polarity (positive in this embodiment) to the normal charge polarity of the toner is applied. By applying to the transfer roller 13 the transfer voltage of the opposite polarity to the normal charge polarity of the toner T, at the transfer portion N, electric charges of the opposite polarity to the normal charge polarity of the toner T are provided to the back surface of the recording material S (a surface of the recording material S opposite from the surface facing the photosensitive drum 4). As a result, the toner image on the photosensitive drum 4 is electrostatically transferred onto the surface of the recording material S.
The recording material S coming out of the recording material S is separated from the surface of the photosensitive drum 4 and passes through a conveying path 14 to be introduced into a fixing device 15 as a fixing means. In the fixing device 15, an unfixed toner image on the recording material S is fixed on the recording material S. In this embodiment, the fixing device 15 is a heating roller type and includes a heating roller 15a which surface is heated and temperature-controlled to a predetermined fixing temperature and a pressing roller 15b for forming a fixing portion (fixing nip) in press-contact with the heating roller 15a. The heating roller 15a and the pressing roller 15b are disposed so that their rotational axis directions are substantially parallel to each other. Each of the heating roller 15a and the pressing roller 15b is rotationally driven in an arrow direction indicated in
The recording material S coming out of the fixing device 15 is, as an image-formed product, conveyed upward in the apparatus main assembly 1 through a conveying path 16 and then is discharged onto a sheet discharge tray 19 as an upper surface of the apparatus main assembly 1.
Further, the photosensitive drum 4 after the separation of the recording material S therefrom is subjected to removal of a deposited matter, such as the toner (transfer residual toner) deposited on the surface thereof without being transferred onto the recording material S, by the cleaning device 8 as a cleaning means, thus being cleaned. As a result, the photosensitive drum 4 is repetitively subjected to the image formation. In this embodiment, the cleaning device 8 includes a cleaning blade 8a as a cleaning member. The cleaning blade 8a is contacted to the rotating photosensitive drum 4 so that its free end is directed toward an upstream side (in a counter direction) with respect to the surface movement direction of the photosensitive drum 4 with a predetermined penetration depth (amount). The deposited matter, such as the transfer residual toner, on the photosensitive drum 4 is scraped off from the surface of the rotating photosensitive drum 4 at a contact portion between the edge of the cleaning blade 8a and the photosensitive drum 4 and is collected in a residual toner container 8b.
In this embodiment, four process devices consisting of the photosensitive drum 4, the charging roller 5, the developing device 7 and the cleaning device 8 are collectively assembled into a cartridge and an image forming unit which is detachably mountable to the apparatus main assembly 1, thus constituting a process cartridge 20. The process cartridge 20 is detachably mounted to a mounting portion in the apparatus main assembly 1.
As shown in (a) of
The process cartridge 20 is positioned and fixed to a predetermined mounting portion in the apparatus main assembly 1, in a state in which it is mounted to the apparatus main assembly 1, by a positioning and fixing means 28. In that state, from a driving means (not shown) of the apparatus main assembly 1, a driving force to the photosensitive drum 4, a driving force to the developing roller, a driving force to the supplying roller 3 and a driving force to the stirring member are transmittable. Further, in that state, from the power sources E1, E2, E3 and E4 of the apparatus main assembly 1, the voltages are applicable to the charging roller 5, the developing roller 2, the transfer roller 13 and the supplying roller 3, respectively. Incidentally, at an upper surface of the process cartridge 20, an exposure window 20a is provided.
Further, the process cartridge 20 is provided with a memory 21 as a storing means and a cartridge-side information transmitting portion 22. In a state in which the process cartridge 20 is mounted in the apparatus main assembly 1, the cartridge side information transmitting portion 22 opposes a main assembly-side information transmitting portion 23 provided at the apparatus main assembly 1 side. As a result, between the memory 21 and the control circuit portion 101, information transfer (information reading and writing) is enabled via the cartridge-side information transmitting portion 22 and the main assembly-side information transmitting portion 23 which constitute a communicating means.
In this embodiment, in the memory 21, lifetime information intrinsic to the process cartridge 20 including information on at least a remaining lifetime amount of the photosensitive drum 4 and a remaining developer amount is stored. This lifetime information can be communicated between the control circuit portion 101 and the memory 21 via the cartridge-side information transmitting portion 22 and the main assembly-side information transmitting portion 23. Then the control circuit portion 101 displays the lifetime information at an operating panel portion (not shown) provided to the apparatus main assembly 1 in real time, so that it is possible to notify a user of the remaining lifetime amount of the process cartridge 20.
In this embodiment, as the developer, the toner T which is a negatively chargeable non-magnetic one-component developer is used. During the development, the toner T is triboelectrically charged negatively, so that cohesion (agglomeration degree) of the toner is 15%. The toner cohesion was measured in the following manner.
As a measuring device, a powder tester (mfd. by Hosokawa Micron Group) including a digital vibration meter (“Model 1332”, mfd. by Showa Sokki Corp.) was used. As a measuring method, the following method was used. A 390-mesh sieve, a 200-mesh sieve, and a 100-mesh sieve were superposed and set in the order of narrow aperture, i.e., in the order of the 390-mesh sieve, the 200-mesh sieve, and the 100-mesh sieve from the bottom so that the 100-mesh sieve is located at an uppermost position. On the thus set 100-mesh sieve, 5 g of a sample (toner) which had been accurately weighed was added and then a value of displacement of the digital vibration meter was adjusted at 0.60 mm (peak-to-peak), followed by vibration application for 15 seconds. Thereafter, the weight of the sample remaining on each of the sieves was measured and the cohesion was obtained on the basis of an equation shown below. The measurement sample was left standing for 24 hours before the measurement in an environment of 23° C. and 60% RH and was then subjected to the measurement in the environment of 23° C. and 60% RH.
Cohesion (%)=((remaining sample weight on 100-mesh sieve)/5 g)×100+((remaining sample weight on 200-mesh sieve/5 g)×60+((remaining sample weight on 390-mesh sieve)/5 g)×20
As shown in (a) of
In this embodiment, the supplying roller 3 is the developer supplying member and is also a detecting member constituting the remaining developer amount detecting means. As shown in (a) of
Further, the supplying roller 3 had a surface air flow amount of 1.8 liters/minute or more.
Here, the “surface air flow amount” of the supplying roller 3 will be described. Part (a) of
First, the supplying roller 3 is inserted into a measuring jig 43 as shown in (b) of
On left and right sides of the hollow cylindrical member 44a of the ventilation holder 44, as shown in (a) of
At intermediate portions of the ventilation pipe 45, a flow meter 47 (“KZ Type Air Permeability Tester”, mfd. by Daiei Kagaku Seiki Mfg. Co., Ltd.) and a different pressure control valve 46 are provided. Connecting portions of the measuring jig 43, the ventilation holder 44, the ventilation pipe 45 and the acrylic pipes 42a and 42b are sealed with a tape or grease. This is because when the inside air of the ventilation pipe 45 is evacuated by a pressure reducing pump 48, the ambient air is prevented from entering the inside of the ventilation pipe 45 through a portion except the through hole of the exposed measuring jig 43.
The “surface air flow amount” is measured in the following manner. First, referring to (a) of
The developing roller 2 is rotationally driven in the direction indicated by the arrow R2 in
As shown in (a) and (b) of
From the state shown in (a) of
Here, the developing roller 2 and the photosensitive drum 4 are connected so that their bearing members (not shown) are connected with each other by a spring member 32 as an urging means. When the developing roller 2 and the photosensitive drum 4 are contacted to each other, these members are held in a contacted state by an urging force of this spring member 32. For that reason, in the case where the developing device 7 is a direction in which the developing roller 2 is separated (spaced) from the photosensitive drum 4, the developing device 7 is moved against a tension of the spring member 32. At this time, a force for moving upward the cleaning device 8 which holds the photosensitive drum 4 is exerted but a fixing means (mounting/demounting guide member) 28 (
On the other hand, in the case where the contact and separation cam 30 is rotated from a position where it raises the developing device 7 to a position where it does not contact the developing device 7, the developing device 7 is rotationally moved downward with the supporting point 33 as the center. As a result, as shown in (a) of
In this embodiment, the contact and separation cam 30 is controlled by the driving motor and the solenoid, which are provided at the apparatus main assembly 1 side, so as to be rotated by a half-turn every operation. Every half-turn of the contact and separation cam 30, a switching between an image forming state (contact position) and a stand-by state (separated position) is repeated. Further, at the apparatus main assembly 1 side, a phase detecting sensor (not shown) for detecting a phase of the contact and separation cam 30 is provided. The control circuit portion 101 controls the phase of the contact and separation cam 30 by controlling the driving motor and the solenoid depending on a detection result of the phase detecting sensor.
Here, the state where the developing roller 2 and the photosensitive drum 4 are contacted to each other is taken as a first position ((a) of
Next, a toner amount detecting method utilizing a change in electrostatic capacity in this embodiment will be described.
As shown in
The supply voltage output portion 80b may also be a power source capable of applying both of positive and negative DC voltages to the supplying roller 3. In the state in which the developing device 7 is mounted at a predetermined position in the apparatus main assembly 1, the contact electrodes 85 and 86 are electrically connected to each other and the contact electrodes 83 and 84 are electrically connected to each other even when the developing device 7 is located at either of the first position and the second position. That is, even when the developing device 7 is swung between the first position and the second position, the first developing device contact electrodes 85 and the first main assembly contact electrode 86 still contact each other and the second developing device contact electrodes 83 and the second main assembly contact electrode 86 still contact each other.
During a normal developing operation, the developing device 7 is located at the first position and the DC voltage of about −300 V is applied, as the developing voltage, from the developing power source E2 to the developing roller 2 through the first main assembly contact electrode 86 and the first developing device contact electrode 85. At this time, the voltage is not supplied from the detecting voltage output portion 80a but is supplied from only the supply voltage output portion 80b, so that the DC voltage of about −300 V which is substantially equal to the developing voltage is applied to the supplying roller 3. That is, during the developing operation, the detector 82 and the detecting voltage output portion 80a are switched to the developing power source E2 and the supply voltage output portion 80b of the supplying member power source E4.
During a non-image forming operation, the developing device 7 is located at the second position and in this embodiment, to the core electrode 3b of the supplying roller 3, a detecting voltage is applied from the detecting voltage output portion 80a of the supplying member power source E4, so that the detection of the amount of the toner in the developing container 7a is made.
As the detecting voltage, an AC voltage of 50 kHz in frequency f and 200 V in peak-to-peak voltage (Vpp) is used. At this time, the supply voltage output portion 80b of the supplying member power source E4 and the developing power source E2 do not supply the voltage. As a result, in the core electrode 2a of the developing roller 2, a voltage is induced by the detecting voltage and is detected by the detector 82.
As described above, during the non-image formation, more specifically, when the developing operation is not performed, the developing device 7 is located at the second position, i.e., is placed in the state in which the photosensitive drum 4 and the developing roller 2 are spaced from each other. More specifically, the toner amount detection can be realizing, e.g., in the following periods as during the non-image formation. First, the period is a period (sheet interval) corresponding to an area, on the photosensitive drum 4, between sheets of the recording material S during continuous image formation on a plurality of sheets of the recording material S. Further, the period is during a preparatory operation (pre-rotation operation) before start of the image forming step. Further, the period is a period of an apparatus operation (post-rotation operation) from completion of the image forming operation to discharge of the recording material S from the image forming apparatus to the outside of the image forming apparatus. In the case where the developing device 7 is located at the second position, the photosensitive drum 4 and the developing roller 2 are spaced from each other and therefore even when the AC voltage is applied to the supplying roller 3 as detecting voltage, there is no occurrence of white background contamination which is called fog. Further, there is also no occurrence of impact noise generated, in the case where the developing roller 2 and the photosensitive drum 4 contact each other, by vibration such that they impact each other. Further, the developing roller 2 is used as an antenna for electrostatic capacity detection by applying an AC voltage, for the purpose of detecting the toner amount, to the core electrode 3b of the supplying roller 3, so that it is possible to prevent toner conveyance inhibition which can occur in a constitution in which a separate antenna is provided in the developing device. Incidentally, as shown in (a) and (b) of
However, the amount of the toner contained in the supplying roller 3 is not changed. That is, the amount of the toner present between the developing roller 2 and the supplying roller 3 is not changed, so that output of the voltage induced in the developing roller 2 is not changed. Specifically, the supplying roller 3 includes the foam layer which permits entry of the toner into the inside of the foam layer and thus the toner in the foam layer is less liable to move even when the attitude of the developing device 7 is changed, so that the output of the voltage is not changed. In addition, in this embodiment, when the remaining toner amount detection utilizing the electrostatic capacity is performed in the state in which the developing roller 2 and the photosensitive drum 4 are spaced from each other, the drive of the developing roller 2 and the supplying roller 3 is stopped. By stopping the drive of the developing roller 2 and the supplying roller 3, the toner supply to the developing roller 2 and the removing operation of the development residual toner interrupted. For that reason, the amount of the toner contained in the supplying roller 3 is constant during the toner amount detection, so that accuracy of the toner amount detection can be enhanced.
According to the toner amount detecting method as described above, the influence of the electrostatic capacity generated between the photosensitive drum 4 and the developing roller 2 is eliminated, so that the toner amount detection accuracy can be improved. Further, as described above, the detecting voltage is applied only during the attitude in which the developing roller 2 and the photosensitive drum 4 are spaced from each other and therefore it is also possible to prevent the occurrence of fog image and the occurrence of the impact noise due to the vibration between the photosensitive drum 4 and the developing roller 2.
Next, the toner amount detection accuracy by the above-described toner amount detecting method will be described in detail.
Part (a) of
Here, with an increasing surface air flow amount in the supplying roller 3, there is a tendency that an absolute value of the electrostatic capacity detection output value is increased. When the supplying roller 3 has the surface air flow amount of 1.8 liters/min. or more, a correlation between the electrostatic capacity output value and the toner amount in the developing container 7a is good, so that the detection accuracy of the toner amount is further enhanced. Further, when the surface air flow amount of the state 3 is large, a pore portion of the foam layer of the supplying roller 3 is increased and a strength of the supplying roller 3 is decreased, so that the foam layer of the supplying roller 3 is liable to broken. In order to prevent the breaking of the foam layer, the surface air flow amount of the supplying roller 3 may preferably be 5.0 liters/min. or less. That is, the range of the surface air flow amount of the supplying roller 3 may preferably be from 1.8 liters/min. to 5.0 liters/min. (i.e., 1.8≦L≦5.0 where L is the surface air flow amount (liters/min.)).
Incidentally, the toner T in the supplying roller 3 is partly discharged when the supplying roller 3 is started to be deformed at the time of start of the contact of the rotating supplying roller 3 with the developing roller 2. Further, the toner T in the supplying roller 3 is partly inhaled when the deformation of the supplying roller 3 is eliminated (i.e., the deformed shape of the supplying roller 3 is returned to the original shape) at the time of end of the contact of the supplying roller 3 with the developing roller 2. Thus, the toner T enters and comes out of the supplying roller 3 but the amount of the toner in the supplying roller is generally kept in the equilibrium state unless the toner amount in the developer container 7a is changed. Experimental data shown in (a) and (b) of
Here, the correlation shown in (a) of
As described above, the amount of the toner contained in the supplying roller 3 is detected as the electrostatic capacity and is associated with the toner amount in the developing container 7a in advance, it is possible to detect the toner amount in the developing container 7a.
However, in the case where an image with a high print ratio such as a solid (image of a maximum density level) is continuously formed, a balance of the above-described entry and exit of the toner T with respect to the supplying roller 3 is destroyed from the equilibrium state, so that the amount of the toner contained in the supplying roller 3 is temporarily decreased. Correspondingly, the electrostatic capacity between the supplying roller 3 and the developing roller 2 is also temporarily decreased and therefore the detection result of the toner amount can be derived from an actual toner amount in the developing container 7a.
Actually, as shown in (a) of
However, in the case where the image with the print ratio of 100% (“100%”) is similarly formed continuously and then the image formation is switched to the image formation with the print ratio of 0% (“0%) at the time indicated by an arrow X in (a) of
Therefore, in this embodiment, the toner amount detection accuracy is intended to be improved by performing a toner supplying operation described below specifically.
Incidentally, the average print ratio P can be calculated from a proportion of an integrated value of density information at each pixel in an associated page to an integrated value (total), taken as 100%, of the density information at each pixel for one page in the case where the image segments at all of the pixels in an image formable area corresponding to one page are the solid image. The image density information is information indicating that the density level at each pixel is which level of, e.g., 256 gradation levels from 0 to 255. The image density information and the toner amount per unit area are associated with each other in advance and therefore the integrated value of the density information at each pixel for one page corresponds to a toner consumption (amount) for the associated one page.
Next, a computing means 105 of the control circuit portion 101 computes a toner content Wm in the supplying roller 3, which is an index of the amount of the toner contained in the supplying roller 3 immediately after the job, from the calculated average print ratio P for each page.
Here, the toner content Wm is defined as 100% in the state in which the balance of the entry and exit of the toner T with respect to the supplying roller 3. The computing means 105 calculates, on the basis of the information on the average print ratio P, the toner content Wm as a deviation amount from that in the equilibrium state with respect to the amount of the toner contained in the supplying roller 3.
Specifically, the computing means 105 performs the following computation with respect to the toner content Wm immediately after job in which the images for m pages are continuously formed.
Wm=W(m−1)×(1+Km×10−3)
In the above, a coefficient Km is a fluctuation (increase and decrease) coefficient determined depending on a toner content W(m−1) immediately after image formation on (m−1)-th page and an average print ratio Pm on m-th page, and can be associated in advance as shown in Table 1.
Specifically, the relationship shown in Table 1 is based on experimental data obtained by checking the increase and decrease of the toner content depending on the print ratio of the image to be continuously formed. For example, as shown in (c) of
In the case where the toner content Wm is detected that it is smaller than 100%, the control circuit portion 101 restores the state of the amount of the toner contained in the supplying roller 3 to the equilibrium state by a toner supplying means 106 (supplying device) and thereafter executes the toner amount detection be operating a toner amount detecting means 107. This is because in this case, the state of the amount of the toner contained in the supplying roller 3 is predicted as being a temporarily exhausted state. The toner detecting operation to the supplying roller 3 by the toner supplying means 106 can be realized by controlling the rotation number (the number of turns) of the supplying roller 3 during the so-called post-rotation operation after the image formation. That is, in this embodiment, the toner amount detecting means 107 as the developer amount detecting means is constituted by the developing roller 2, the supplying roller 3, the detector 82, the supplying member power source E4 (the detecting voltage output portion 80a) and the like.
Specifically, the control circuit portion 101 obtains the number of rotations (turns) of the supplying roller 3, as the toner supplying operation, required until the toner content reaches that (100%) in the equilibrium state. In this embodiment, e.g., as shown in Table 2, information on a relationship between the toner content Wm and the rotation number of the supplying roller 3 is set in advance in the control circuit portion 101. The control circuit portion 101 obtains, by using the information on the relationship as shown in Table 2, the rotation number of the supplying roller 3 necessary for the toner detecting operation depending on the toner content Wm calculated by the computing means 105, thus controlling the rotation drive operation of the supplying roller 3 performed before the toner amount detecting operation.
Here, the relationship shown in Table 2 is based on experimental data obtained, as shown in (b) of
When the image forming apparatus 100 is in a print stand-by state, a print signal is inputted from the external host device 200 into the control circuit portion 101 (S101). Thereafter, the control circuit portion 101 starts the image forming operation (S102). Thereafter, the pixel number measuring means 104 of the control circuit portion 101 measures the pixel number of the image to be formed on the basis of image data sent from the external host device 200, so that the average print ratio P for each page in the job is calculated (S103). Then, the computing means 105 of the control circuit portion 101 calculates, on the basis of the average print ratio P for each page calculated from the measurement result of the pixel number, the toner content Wm immediately after the job in which the images for m pages are continuously formed (S104). When the image formation is ended (S105), the control circuit portion 101 moves the developing device 7 from the first position to the second position by the spacing means 30 (S106). Next, the control circuit portion 101 judges whether or not the toner content Wm calculated in S104 reaches that in the equilibrium state (whether or not Wm<100(%)) (S107).
In S107, in the case where the amount of the toner contained in the supplying roller 3 is judged as being in the equilibrium state (Wm=100(%)), the control circuit portion 101 stops the developing roller 2 and the supplying roller 3 (S109) and then executes the toner amount detecting operation (S110). On the other hand, in S107, the amount of the toner contained in the supplying roller 3 is judged as being in the exhaust state (Wm<100(%)), the control circuit portion 101 executes the toner supplying operation (S108). That is, the control circuit portion 101 obtains, from the toner content Wm calculated in S104, the necessary rotation number of the supplying roller 3 on the basis of the table as shown in Table 2 and then rotationally drives the developing roller 2 and the supplying roller 3 on the basis of the result. Thereafter, the control circuit portion 101 stops the developing roller 2 and the supplying roller 3 (S109) and then executes the toner amount detecting operation (S110).
Thus, the image forming apparatus 100 in this embodiment includes the developer amount detecting means 107 for detecting the developer amount in the developing container by detecting the electrostatic capacity between the developer carrying member 2 and the developer supplying member 3 during the non-image formation. Further, the image forming apparatus 100 includes the computing means 105 for predicting (estimating) the amount of the developer contained in the developer supplying member 3 after the image formation, and the supplying means 106 for supplying the developer into the developer supplying member 3 until the detection by the developer amount detecting means 107 is executed after the image formation. Further, the supplying means 106 increases the amount of the developer to be supplied into the developer supplying member 3 with a smaller amount of the developer contained in the developer supplying member 3 estimated by the computing means 105. In this embodiment, the computing means 105 estimates the amount of the developer, contained in the developer supplying member 3 after the image formation, from information of the amount of the developer used for the formed image (from the average print ratio in this embodiment). Further, in this embodiment, the supplying means 106 increases the rotation number of the developer supplying member 3, in a period from after the image formation until the detection by the developer amount detecting means 107 is executed, with a smaller amount of the developer contained in the developer supplying member 3 estimated by the computing means 105. As a result, the amount of the developer supplied into the developer supplying member 3 is increased.
As described above, according to this embodiment, the pixel number of the image to be formed is measured and the temporary toner content of the supplying roller 3 immediately after the image formation is estimated by the computation. Then, depending on the estimated toner content, an optimum toner supplying operation is performed and then the toner amount detecting operation is performed. For that reason, it is possible to detect the toner amount in the developing container 7a with high accuracy. Further, the toner content is estimated on the basis of the pixel number of the image to be formed and therefore it is possible to obtain a good toner amount detection accuracy by performing a necessary minimum toner supplying operation depending on the image to be formed. For that reason, the toner amount detection accuracy can be improved without shortening the lifetime of the developing device 7 and lowering productivity of image formation which are caused due to abrasion or the like of the toner T or parts such as the developing roller 2 and the supplying roller 3.
Incidentally, in this embodiment, the toner content Wm and the rotation number of the supplying roller 3 during the post-rotation operation necessary before the execution of the toner amount detecting operation were stepwisely associated as shown in Table 2. However, the rotation number of the supplying roller 3 may also be computed more specifically by using a mathematical expression in the computing means 105 and typically may be computed so that it can be substantially changed continuously. Further, in order to execute in a shorter time the toner supplying operation necessary until the amount of the toner contained in the supplying roller 3 reaches that in the equilibrium state, it is also possible to increase the rotational speed of the supplying roller 3 during the toner supplying operation. In this case, the time of the post-rotation operation can be shortened without impairing the toner amount detection accuracy, so that the operation can be quickly transferred to a subsequent image forming operation and therefore the increase of the rotational speed is advantageous also from the viewpoint of the productivity of image formation. Further, the good toner amount detection accuracy can be obtained by the necessary minimum drive of the developing device 7 during the post-rotation operation and therefore the increase of the rotational speed is advantageous also from the viewpoint of the lifetime of the developing device affected by the abrasion or the like of the toner T or the parts such as the developing roller 2 and the supplying roller 3.
Next, another embodiment of the present invention will be described. A basic constitution and operation of an image forming apparatus in this embodiment are the same as those in Embodiment 1. Therefore, elements (means) identical or corresponding to those in Embodiment 1 are represented by the same reference numerals or symbols and will be omitted from detailed description.
In this embodiment, the pixel number measuring means 104 of the control circuit portion 101 more specifically measures the print ratio of each of areas obtained by dividing the image area of the image to be formed for the associated page into a plurality of the areas. Further, on the basis of a measurement result of the print ratio, the computing means 105 of the control circuit portion 101 calculates the toner content immediately after the image formation for each of the divided areas. Thus, on the basis of the thus obtained toner content, the rotation number of the supplying roller 3 during the post-rotation operation necessary before the execution of the toner amount detection operation is controlled. This will be described below more specifically.
In this embodiment, the pixel number measuring means 104 of the control circuit portion 101 divides, as shown in
The pixel number measuring means 104 of the control circuit portion 101 individually measures, as shown in
Incidentally, the average print ratio (P01 to Pij) can be calculated from a proportion of an integrated value of density information at each pixel in an associated area to an integrated value (total), taken as 100%, of the density information at each pixel in each area in the case where the image segments at all of the pixels in each area are the solid image. The image density information and the toner amount per unit area are associated with each other in advance and therefore the integrated value of the density information at each pixel in each area corresponds to a toner consumption (amount) in the associated area.
Next, the computing means 105 of the control circuit portion 101 performs the following computation on the basis of a calculation result of the average print ratio in each area. That is, for each page, the following computation is performed every range divided with respect to the main scan direction and then the toner contents (W0j to Wij) immediately after the end of the image formation every area divided with respect to the sub-scan direction are successively calculated individually every range divided with respect to the main scan direction.
In the above, a coefficient Kij is a fluctuation (increase and decrease) coefficient determined depending on a toner content Wi(j−1) immediately after image formation in area Ai(j−1) and an average print ratio Pij in area Aij, and can be associated in advance as shown in Table 3.
Specifically, the relationship shown in Table 3 is based on experimental data obtained by checking the increase and decrease of the toner content depending on the print ratio of the image to be formed. That is, similarly as in Embodiment 1, for example, as shown in (c) of
Next, the control circuit portion 101 selects the range, in which the toner content is lowest, from the ranges of the toner contents (W0j to Wij) which are calculated by the computing means 105 and are divided with respect to the main scan direction immediately after the image formation. Then, the control circuit portion 101 defines a minimum (MIN(W0j:Wij)) of the toner contents in the range as Wm. That is, the control circuit portion 101 controls the toner supplying operation, performed from after the image formation until the toner amount detecting operation is started, depending on a computation result of the toner content Wm at a position where the toner content in the supplying roller 3 with respect to the main scan direction is most exhausted at the time immediately after the image formation.
Specifically, in the control circuit portion 101, similarly as in Embodiment 1, the table as shown in Table 2 is set in advance. As described above, in this embodiment, the toner content Wm in Table 2 corresponds to the minimum (MIN(W0j:Wij)) of the toner contents. The control circuit portion 101 obtains, by using the information on the relationship as shown in Table 2, the rotation number of the supplying roller 3 during the toner supplying operation corresponding to the toner content Wm in the range in which the toner content in the supplying roller 3 with respect to the main scan direction is lowest.
When the image forming apparatus 100 is in a print stand-by state, a print signal is inputted from the external host device 200 into the control circuit portion 101 (S201). Thereafter, the control circuit portion 101 starts the image forming operation (S202). Thereafter, the pixel number measuring means 104 of the control circuit portion 101 measures, every divided area, the pixel number of the image to be formed on the basis of image data sent from the external host device 200, so that the average print ratios P01 to Pij in the respective areas is detected (S203). Then, the computing means 105 of the control circuit portion 101 calculates, on the basis of the average print ratios P01 to Pij in the respective areas calculated from the measurement result of the pixel number, the toner content W0j to Wij immediately after the image formation in the respective ranges divided with respect to the main scan direction (S204). When the image formation is ended (S205), the control circuit portion 101 moves the developing device 7 from the first position to the second position by the spacing means 30 (S206). Next, the control circuit portion 101 judges whether or not the minimum Wm of the toner contents W0j to Wij, in the respective ranges divided with respect to the main scan direction, calculated in S204 reaches that in the equilibrium state (whether or not MIN(W0j:Wij)<100(%)) (S207).
In S207, in either of the ranges, in the case where the amount of the toner contained in the supplying roller 3 is judged as being in the equilibrium state (MIN(W0j:Wij)=100(%)), the control circuit portion 101 stops the developing roller 2 and the supplying roller 3 (S209). Then, the control circuit portion 110 executes the toner amount detecting operation (S210). On the other hand, in S207, the amount of the toner contained in the supplying roller 3 is judged as being in the exhaust state (MIN(W0j:Wij)<100(%)), the control circuit portion 101 executes the toner supplying operation (S208). That is, the control circuit portion 101 sets the minimum (MIN(W0j:Wij)) of the toner content calculated in S204 at Wm and then obtains the necessary rotation number of the supplying roller 3 on the basis of the table as shown in Table 2. Then, the control circuit portion 110 rotationally drives the developing roller 2 and the supplying roller 3 on the basis of the result. Thereafter, the control circuit portion 101 stops the developing roller 2 and the supplying roller 3 (S209) and then executes the toner amount detecting operation (S210).
As described above, according to this embodiment, the computation of the toner content necessary to determine the rotation number of the supplying roller 3 in the toner supplying operation is performed in further detail. As a result, with respect to every image pattern, it becomes possible to effect the control for restoring the state of the amount of the toner contained in the supplying roller 3 to the equilibrium state in further detail. As a result, the better toner amount detection accuracy can be obtained.
Incidentally, similarly as in Embodiment 1, the rotation number of the supplying roller 3 may also be computed more specifically by using a mathematical expression in the computing means 105 and typically may be computed so that it can be substantially changed continuously.
Further, similarly as described in Embodiment 1, the rotational speed of the supplying roller 3 during the toner supplying operation may also be increased.
Further, the number of division of the image area for the page subjected to individual pixel number measurement is merely an example and does not limit the present invention. For example, the range of each area with respect to the sub-scan direction may also be a length of not less than one-full circumference of the supplying roller 3 and, e.g., one page may be divided into (two) halves. Further, with respect to one of the sub-scan direction and the main scan direction, it is also possible that the division is not made. For example in the case where the division is not made with respect to the sub-scan direction, it is possible to obtain the rotation number of the supplying roller 3 in the toner supplying operation depending on the minimum of the toner contents, successively calculated every page, immediately after the image formation in the respective ranges divided with respect to the main scan direction. Further, in the case where the division is not made with respect to the main scan direction, the toner contents immediately after the image formation are successively calculated for the respective ranges divided with respect to the sub-scan direction to finally calculate the toner content immediately after the image formation, so that it is possible to obtain the rotation number of the supplying roller 3 necessary for the toner supplying operation. In this case, the processing for obtaining the minimum of the toner contents in this embodiment can be omitted. That is, the information on the amount of the developer used for the formed image may be consisting of information on the developer amount in each of the areas of the formed image with respect to a direction corresponding to at least one of the rotational axis direction of the developer supplying member 3 and a direction perpendicular to the rotational axis direction.
Next, another embodiment of the present invention will be described. A basic constitution and operation of an image forming apparatus in this embodiment are the same as those in Embodiment 1. Therefore, elements (means) identical or corresponding to those in Embodiment 1 are represented by the same reference numerals or symbols and will be omitted from detailed description.
In this embodiment, during the toner supplying operation, a predetermined DC voltage of the opposite polarity to the charge polarity of the toner is applied to the supplying roller 3 from the supply voltage output portion 80b of the supplying member power source E4, so that the developing roller 2 and the supplying roller 3 are rotated.
Specifically, after the end of the image formation, the developing device 7 is moved from the first position to the second portion and thereafter in the case where the amount of the toner contained in the supplying roller 3 is detected as being temporarily exhausted, the following operation is performed. That is, the rotational drive of the developing roller 2 and the supplying roller 3 is effected while applying 0 V from the developing power source E2 to the developing roller 2 and applying +500 V from the supply voltage output portion 80b of the supplying member power source E4 (the supplying device as the supplying means) to the supplying roller 3. As a result, the toner supplying operation into the supplying roller 3 is executed.
Thus, during the toner supplying operation, by applying the DC voltage of the opposite polarity to the toner charge polarity, the supplying roller 3 is rotated while causing the electrostatic attraction force to act on the toner T. That is, in this embodiment, the supplying means applies the DC voltage of the opposite polarity to the normal charge polarity of the developer to the developer supplying member 3 when the developer is supplied into the developer supplying member 3 in a period from after the image formation until the detection by the developer amount detecting means 107 is executed. As a result, it is possible to reduce the rotation number of the supplying roller 3 in the toner supplying operation necessary until the amount of the toner contained in the supplying roller 3 reaches that in the equilibrium state.
Incidentally, in this embodiment, methods of the pixel number measurement and the print ratio calculation by the pixel number measuring means 104 and a computation method of the toner content immediately after the end of the job by the computing means 105 are similar to those in Embodiment 1 or 2. Further, the flow of the series of image forming operations is also similar to that in Embodiment 1 or 2. However, in this embodiment, the rotation number of the supplying roller 3 corresponding to the same toner content can be set so as to be smaller than that in Embodiment 1 or 2.
Further, also in this embodiment, similarly as described in Embodiment 1, the combination of the control of the rotation number with the method in which the rotational speed of the supplying roller 3 during the toner supplying operation is effective in that the toner T can be more efficiently supplyed into the supplying roller 3.
Further, the DC voltage potential of the opposite polarity to the toner charge polarity applied to the supplying roller 3 during the toner supplying operation may also be changed depending on an operational environment (temperature and/or humidity) in which the image forming apparatus 100 is placed.
In the above, the present invention is described based on the specific embodiments but is not limited to the above-described embodiments.
For example, in the above-described embodiments, the image forming apparatus employs the contact developing system but the present invention is not limited to the contact developing system. For example, the present invention is effective also in an image forming apparatus using a non-magnetic jumping developing system or the like in which the supplying roller is used.
Further, in the above-described embodiments, the image forming is described as the image forming apparatus for a single color but the present invention is not limited thereto. For example, the present invention is effective also in an image forming apparatus capable of obtaining a full-color member by arranging a plurality of process cartridges similar to the process cartridge in the above-described embodiments.
Further, in the above-described embodiments, the image forming apparatus is described as that employing the process cartridge type but the present invention is not limited thereto. For example in the present invention, the developing device is singly formed in the cartridge so as to be detachably mountable to the main assembly of the image forming apparatus but the present invention is also effective in a constitution in which the developing device itself is fixed to the main assembly of the image forming apparatus so as to permit the replenishing of the developer.
Further, in the above-described embodiments, the toner supplying operation is performed at the second position where the developing roller of the developing device and the photosensitive drum are spaced but as desired may also be performed at the first portion where the developing roller and the photosensitive drum contact each other. In this case, there is a need to perform the toner supplying operation with timing other than during the image formation.
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. 004403/2011 filed Jan. 12, 2011, which is hereby incorporated by reference.
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