Patent Application
20210382436
The present invention concerns an image forming apparatus using electrophotographic technology, such as a printer, copier, FAX or multifunction device.
The image forming apparatus has a fixing device in the main assembly of the apparatus that fixes the toner image on the recording medium by applying heat and pressure to the recording medium on which the unfixed toner image is formed. The fixing device has a fixing belt and a pressure roller for applying pressure in contact with the fixing belt, and a fixing nip portion formed between the fixing belt and the pressure roller. The toner image is fixed to the recording medium by being nipped and fed while the recording medium is pressurized and heated.
By the way, since a large amount of toner adhering to the fixing belt can cause image defects, a toner containing wax (parting agent) is used to avoid this. In this case, when the toner is heated, the wax melts and covers the surface of the fixing belt, and the parting effect of the wax makes it difficult for the toner to adhere to the fixing belt afterwards. However, the wax adhered to the fixing belt starts to vaporize (gasify) when the surface temperature of the fixing belt becomes higher than a certain temperature. When the vaporized wax is cooled by the surrounding air, it forms particulate dust ranging from several nm to several hundred nm, which floats in the main assembly of the apparatus. This particulate dust is sticky, and when the ambient temperature becomes higher, some of them may gather together to form larger clumps of dust, which may adhere to various places in the main assembly of the apparatus. In the past, an image forming apparatus equipped with a filtration mechanism to collect these dusts has been proposed (Patent Document 1). The filtration mechanism has a suction fan for sucking the air inside the main assembly of the apparatus and a filter for filtering the dust contained in the sucked air.
In addition, the image forming apparatus has an exhaust mechanism that has an exhaust fan that exhausts air from the main assembly of the apparatus to the outside. In other words, since the recording medium is heated during the fixing of the toner image by the fixing device, the moisture contained in the recording medium may be vaporized in some cases. When the vaporized moisture is cooled, condensation occurs in the main assembly of the apparatus. In order to prevent such condensation, an exhaust mechanism is used to exhaust air from the main assembly of the apparatus to the outside.
However, the method of the image forming apparatus described in Japanese Laid-Open Patent Application No. 2017-120284 has room for improvement in terms of properly removing both dust and water vapor. The present invention was developed in consideration of the above-mentioned issue, and aims to provide an image forming apparatus that can properly remove both dust and water vapor.
According to an aspect of the present invention, there is provided an image forming apparatus comprising: an image forming portion for forming a toner image on a recording material by using toner containing a parting agent; a transfer portion for transfer the toner image formed by said image forming portion to a sheet at a transfer nip portion; a fixing potion for heat fixing the toner image transferred by said transfer portion on the sheet at a fixing nip portion; a duct provided with a suction opening opposite to a sheet feeding passage between said transfer nip portion and said fixing nip portion; a filter provided on said duct; a first fan for discharging an air taken into said duct from said suction opening to an outside; a second fan for discharging an air in a neighborhood of a sheet exit of said fixing portion; a control portion for controlling operations of said first fan and said second fan, wherein said control portion is capable of performing operations such that in a case in which a signal for forming the image on the sheet is inputted, an operation of said first fan is started in accordance with a heating operation of said fixing portion, and an operation of said second fan is started until a first sheet passes through said fixing nip portion after the operation of said first fan is started.
According to the present invention, both dust and water vapor can be properly removed.
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The following is an explanation of the present embodiment. First, the image forming apparatus of the present embodiment is explained using
A process of feeding the recording medium in the image forming apparatus 100 is described below. The recording medium P is stored in the cassette 72 in the form of a stack, and is fed one sheet at a time by the sheet feeding roller 73 to the feeding path 74 in accordance with the image forming timing. The recording medium P stacked in the manual feed tray or stacking device (not shown) may also be fed one sheet at a time into the feeding path 74. When the recording medium P is fed to the resist roller 75 located in the middle of the feeding path 74, the resist roller 75 corrects the skew and timing of the recording medium P, and then it is fed to the secondary transfer portion T2. The secondary transfer portion T2 is a transfer nip portion formed by the opposing secondary transfer inner roller 76 and secondary transfer outer roller 77. The secondary transfer inner roller 76 as the transferring roller presses the intermediate transferring belt 8 from the inside to form the transfer portion of the toner image against the recording medium P. In the secondary transfer portion T2, the secondary transfer voltage is applied to the secondary transfer outer roller 77 by the power supply 70, and the toner image is transferred from the intermediate transferring belt 8 to the recording medium P by the current flowing between the secondary transfer outer roller 77 and the secondary transfer inner roller 76.
In contrast to the above process of feeding the recording medium P to the secondary transfer portion T2, the process of forming an image that is fed to the secondary transfer portion T2 at the same timing is explained below. First, image forming portions PY to PK are described. However, the image forming portions PY to PK are configured almost identically, except that the toner colors used in developing devices 4Y, 4M, 4C, and 4K are different: yellow, magenta, cyan, and black. Therefore, in the following, the yellow image forming portion PY will be explained as an example, and the other image forming portions PM, PC, and PK will be omitted. For convenience of the figures, only the image forming portion PY is marked for a developing container 41Y and a developing roller 42Y described below.
The image forming portion PY mainly consists of a photosensitive drum 1Y, a charging device 2Y, a developing device 4Y, and a photosensitive drum cleaner 6Y. The surface of the photosensitive drum 1Y, which is driven by rotation, is uniformly charged in advance by the charger 2Y, and then an electrostatic latent image is formed by the exposure device 3, which is driven based on the image information signal. Next, the electrostatic latent image formed on the photosensitive drum 1Y is converted into a visible image through toner development by the developing unit 4Y. The developing device 4Y has a developing container 41Y containing the developer, a developing roller 42Y (also called a developing sleeve) that rotates carrying the developer, and by applying a developing voltage to the developing roller 42Y, the electrostatic latent image is developed into a toner image. After that, the image forming portion PY and the primary transferring roller 5Y, which is placed opposite to the intermediate transferring belt 8, apply a predetermined pressure and primary transfer voltage, and the toner image formed on the photosensitive drum 1Y is primarily transferred to the intermediate transferring belt 8. The toner image formed on the photosensitive drum 1Y is transferred onto the intermediate transferring belt 8. A small amount of residual toner remaining on the photosensitive drum 1Y after primary transfer is removed by the photosensitive drum cleaner 6Y to prepare for the next imaging process.
The intermediate transferring belt 8 is stretched by a tension roller 10, the secondary transfer inner roller 76, and idler rollers 7a and 7b as tensioning rollers, and is driven to move in a direction of a arrow R2 in the figure. In the case of the present embodiment, the secondary transfer inner roller 76 also serves as the drive roller that drives the intermediate transferring belt 8. The image forming process for each color processed by the image forming portions PY to PK described above is performed at a timing to sequentially superimpose on the toner image of the color upstream in the moving direction that has been primary transferred on the intermediate transferring belt 8. As a result, a full-color toner image is finally formed on the intermediate transferring belt 8, and is transferred to the secondary transfer portion T2. The toner remaining after the transfer passes through the secondary transfer portion T2 is removed from the intermediate transferring belt 8 by the transfer cleaner device 11.
With the feeding process and the imaging process described above, the timing of the recording medium P and the full-color toner image matches in the secondary transfer portion T2, and the toner image is transferred from the intermediate transferring belt 8 to the recording medium P. After that, the recording medium P is fed to a fixing device 103, and the toner image is melted and adhered to the recording medium P by being pressurized and heated by the fixing device 103. Thus, the recording medium P on which the toner image has been fixed is discharged onto a discharge tray 601 by the discharging roller 78.
As shown in
Next, the fixing device 103 of the present embodiment will be explained using part (a) of
As shown in part (a) of
The belt unit 101 is a unit that contacts the pressure roller 102 to form a fixing nip portion 101b between the belt 105 and the pressure roller 102, and fixes the toner image to the recording medium P in the fixing nip portion 101b. The belt unit 101 is an assembly consisting of multiple members as shown in parts (a) and (b) of
The heater 101a is a heating member that contacts the inner surface of the belt 105 and heats the belt 105. In the present embodiment, a ceramic heater that generates heat when energized is used as the heater 101a. The ceramic heater, which is not shown in the figure, is a low-heat-capacity heater that is equipped with a long, thin ceramic substrate and a resistance layer on the substrate surface, and the entire heater heats up quickly when the resistance layer is energized. The heater holder 104, which holds the heater 101a, has a semi-circular arc shape in the cross-sectional area and regulates the shape of the belt 105 in the circumferential direction. It is desirable to use a heat-resistant resin as the material of the heater holder 104.
The pressure stay 104a is a member that presses the heater 101a and heater holder 104 uniformly against the belt 105 in the longitudinal direction. The pressure stay 104a should be made of a material that does not flex easily even when high pressure is applied. In the present embodiment, stainless steel SUS304 is used as the material for the pressure stay 104a. A thermistor TH is installed on the pressure stay 104a. The thermistor TH outputs a signal to the control portion 500 according to the temperature of the belt 105.
The belt 105 is a rotating member that contacts the recording medium P and applies heat to the recording medium P. The belt 105 is a cylindrical (cylinder-shaped) belt (film) and has overall flexibility. The belt 105 is provided to cover the heater 101a, the heater holder 104, and the pressure stay 104a from the outside.
The flanges 106L and 106R are a pair of members that hold the widthwise end of the belt 105 in a rotatable manner. The flanges 106L and 106R have a flange portion 106a, a backup portion 106b, and a pressurized portion 106c, respectively, as shown in part (b) of
Next, the constitution of the belt 105 as the first rotating member, the pressure roller 102 as the second rotating member, and the fixing nip portion 101b will be explained using parts (a) of
As shown in part (a) of
As shown in
The belt unit 101 is supported by the side plates 107L and 107R so that it can slide in the direction of proximity to and separation from the pressure roller 102. In detail, the flanges 106L and 106R are provided so that they fit into the guide grooves (not shown) of the side plates 107L and 107R. The pressurized portions 106c of the flanges 106L and 106R are pressed with a predetermined pressing force in the direction toward the pressure roller 102 by the pressure springs 108L and 108R supported by the spring support portions 109L and 109R.
The above pressing force pushes the entire flanges 106L, 106R, pressure stay 104a, and heater holder 104 in the direction of the pressure roller 102. Here, the side of the belt unit 101 with the heater 101a faces the pressure roller 102. Therefore, the heater 101a presses the belt 105 toward the pressure roller 102. This constitution deforms the belt 105 and the pressure roller 102, and a fixing nip portion 101b (see part (a) of
When the pressure roller 102 rotates while the belt unit 101 and the pressure roller 102 are in close contact, the frictional force between the belt 105 and the pressure roller 102 at the fixing nip portion 101b exerts a rotational torque on the belt 105. The belt 105 rotates according to the pressure roller 102. The rotational speed of the belt at this time roughly corresponds to the rotational speed of the pressure roller 102. In other words, in the case of the present embodiment, the pressure roller 102 functions as a drive roller that rotates and drives the belt 105. Since the inner peripheral surface of the belt 105 and the heater 101a slide with each other, it is desirable to apply grease to the inner surface of the belt 105 to reduce the sliding resistance.
As shown in
The control portion 500 as the control means performs various controls of the image forming apparatus 100 such as image forming operations, and has, for example, a CPU 501 (Central Processing Unit) and a memory 502. The memory 502 is composed of ROM (Read Only Memory), RAM (Random Access Memory), and the like. The CPU 501 is capable of executing various programs stored in the memory 502, and can operate the image forming apparatus 100 by executing the various programs. In the case of the present embodiment, the CPU 501 is capable of executing the “image forming job processing (program)” (not shown) and the “fan control processing (program)” (see
An image forming job is a series of operations from the start of image forming to the completion of image forming operation based on the print signal to form images in recording medium P. In other words, it is a series of operations from the start of the preliminary operation (so-called front rotation) necessary for image formation, through the image formation process, to the completion of the preliminary operation (so-called back rotation) necessary for finishing image formation. Specifically, it refers to the period from the front rotation after receiving the print signal (preparative operation before image formation) to the back rotation (operation after image formation), including the image formation period and the paper interval.
An input device 310 is connected to the control portion 500 via an input/output interface. The input device 310 is, for example, an operation panel, an external terminal such as a personal computer, etc., which enables the user to give instructions for starting various programs such as an image forming job, input of various data, etc. When an instruction to start an image forming job is given from the input device 310, the CPU 501 executes the “image forming job processing” stored in the memory 502. The CPU 501 controls the operation of the image forming apparatus 100 based on the execution of the “image forming job processing”.
The control portion 500 is connected to the above thermistor TH, the inside temperature sensor 65, the outside temperature sensor 66, and the heater 101a via an input/output interface. The control portion 500 can adjust the temperature of the heater 101a based on the detection result of the thermistor TH. In addition, the sheet feeding portion 800, the first fan 63, the second fan 61, the third fan 62, and the fourth fan 64 (see part (a) of
Here, the control of the fixing device 103 (called the fixing process) and the fixing operation during an image forming job by the control portion 500 will be explained with reference to part (a) of
When the belt 105 is heated to the target temperature Tp and the fixing device 103 is ready to fix, and the control portion 500 determines that the image forming portion PY˜PK is ready to start image formation, the control portion 500 activates the image forming portion PY˜PK. In addition, the control portion 500 activates the image forming portions PY˜PK and feeds the recording medium P that was waiting in the secondary transfer portion T2 toward the fixing device 103. At this time, the control portion 500 emits a signal (referred to as ITOP in the present invention) that means the start of image formation, and the feeding of the recording medium P starts after the ITOP signal is generated. The time from when the signal ITOP is generated until the tip of the first recording medium reaches the fixing nip portion 101b is always constant (e.g., less than one second). This signal ITOP is used to control the operation of the fan as described below. The recording medium P to which the toner image has been transferred in the secondary transfer portion T2 is fed toward the fixing device 103 and is nipped and fed by the fixing nip portion 101b. In the process of being nipped and fed by the fixing nip portion 101b, the recording medium P is subjected to the heat of the heater 101a via the belt 105. The unfixed toner image on the recording medium P is melted by the heat of the heater 101a and is fixed to the recording medium P by the pressure applied to the fixing nip portion 101b. The recording medium P that has passed through the fixing nip portion 101b is guided by the guide 15 to the discharging roller 78 and is discharged onto the discharge tray 601 by the discharging roller 78 (see
In the fixing device 103, the toner image is fixed to the recording medium P by bringing the high-temperature belt 105 into contact with the recording medium P. In this case, some toner S may adhere to the belt 105 when the recording medium P passes through the fixing nip portion 101b during the fixing process described above (called offset phenomenon, etc.). Toner S adhering to the belt 105 causes image defects. Therefore, the present embodiment uses a toner S containing wax (parting agent) made of paraffin, for example, to prevent the toner S from adhering to the belt 105. When the toner S is heated, the wax dissolves and seeps out from the surface. When the toner S is heated and the wax dissolves during the fixing process, the surface of the belt 105 is covered with the dissolved wax. When the surface is covered with wax, the parting effect of the wax makes it difficult for the toner S to adhere to the belt 105.
In the present embodiment, the term “wax” is used to include not only pure waxes but also compounds containing the molecular structure of waxes. For example, a compound in which the resin molecule of the toner reacts with a wax molecular structure such as a hydrocarbon chain. In addition to waxes, substances with a parting action such as silicon oil may be used as the parting agent.
However, a portion of the wax adhered to the belt 105 will vaporize (gasify) when the surface temperature of the belt 105 rises above the predetermined temperature. When the vaporized wax components are cooled in the air, they solidify to form ultra fine particles (UFPs) with a particle diameter of several to several hundred nm. This phenomenon is called nucleation and it occurs when the wax vaporized by heat is exposed to a lower temperature environment and is supercooled. The degree of undercooling can be expressed by the degree of undercooling ΔT, which is the difference between the dust generation temperature Tws (see part (b) of
Supercooling temperature ΔT (° C.)=dust generation temperature Tws (° C.)−space temperature Ta (° C.) (Formula 1)
The larger the supercooling temperature ΔT, the more rapidly the vaporized wax is cooled and the more likely it is to nucleate. This means that nucleation occurs at more locations in a given volume of space. In other words, the larger the supercooling temperature ΔT is, the more dust (UFP) is generated. As the supercooling temperature ΔT decreases, the number of nucleation sites decreases. As the supercooling temperature ΔT decreases, the number of nucleation sites decreases, and the fine dust particles are agglomerated into the nuclei, resulting in larger clumps of dust. In other words, when the supercooling temperature ΔT is large, a large number of small particle size dusts (UFPs) are generated, and when the supercooling temperature ΔT is small, a small number of large particle size dusts are generated.
Since dust is an adhesive wax, it tends to adhere to various places in the main assembly of the apparatus 100a. For example, if the dust is carried to the vicinity of the guide 15 and discharging roller 78 by the updraft caused by the heat of the fixing device 103, the dust will adhere to the guide 15 and discharging roller 78 and be stuck to them. In order to remove it, the frequency of cleaning intervals needs to be increased, which increases the maintenance workload.
Parts (a) through (c) of
As shown in part (a) of
On the contrary, dust formation in the air is accelerated when the heating temperature is higher and the space temperature is lower, i.e., when the supercooling temperature moves to the upper left of the line L1 in the figure (supercooling temperature→large). This is because the higher the heating temperature, the higher the volatilization of the gas that is the seed of dust formation, and the lower the space temperature, the lower the saturated vapor pressure of the volatiles 21a, which promotes the atomization of the volatiles 21a (gas molecules). In other words, the larger the supercooling temperature ΔT is, the more dust generation is promoted and the more dust is generated. Furthermore, as the supercooling temperature ΔT increases and enters the region to the upper left of the line L2, the size of the dust becomes smaller and the number of dust particles increases. This is because as the supercooling temperature ΔT increases, the number of nucleation sites also increases.
Next, in part (b) of
Thus, fine dust particles (UFPs) have two properties: they coalesce and become larger in size at high temperatures, and they adhere more easily to surrounding objects due to their larger size. The ease of coalescence of dust depends on the constitution, temperature, and concentration of the dust. For example, if the component that tends to adhere becomes soft due to high temperature, and if the probability of dust colliding with each other increases due to high concentration, it will be easier to coalesce.
The dust generation temperature Tws, which is the temperature at which particulate dust (UFP) begins to be generated when volatile materials are gradually heated, is a physical property unique to toner that is used to calculate the supercooling temperature ΔT. The dust generation temperature Tws is explained using parts (a) and (b) of
The dust generation temperature Tws inherent to the toner is measured using a chamber with a content area of 0.5 m3. As the measurement conditions, the chamber is set at a temperature of 23±2° C., humidity of 50±5%, and ventilation rate of 4 times/h. The heater 101a installed inside is started at room temperature (23±2° C.) and the temperature is raised at a rate of 3° C./minute. A toner containing wax is placed on the heater 101a. The dust generated by the vaporization of the wax contained in the toner is measured by a nanoparticle particle size analyzer, “FMPS Model 3091 (manufactured by TSI)”, which is connected to the chamber.
From the relationship between the heater temperature and the dust concentration obtained as a result of the measurement of the nanoparticle particle size analyzer (see part (b) of
However, in the image forming apparatus 100, the actual dust generation temperature Tws is about 20° C. lower than the temperature measured using the dust generation temperature measurement device shown in part (a) of
As shown in part (c) of
Dust generation temperature Tws (° C.) of image forming apparatus=Dust generation temperature of experimental apparatus (° C.)−Z (° C.) (Formula 2)
Next, the location of dust generation will be explained using part (a) of
The present inventor and others have verified that the amount of particulate dust D (UFP) generated by the wax adhering to the belt 105 is larger upstream of the fixing nip portion 101b than downstream of the fixing nip portion 101b. The mechanism is explained below.
Immediately after passing through the fixing nip portion 101b, the surface of the belt 105 (the parting layer 105d) is deprived of heat by the recording medium P, so its temperature is lowered to about 100° C. On the other hand, the temperature of the inner surface (base layer 105a) of the belt 105 is maintained at a high temperature by contact with the heater 101a. Therefore, after the belt 105 passes through the fixing nip portion 101b, the heat of the base layer 105a, which is kept at a high temperature, is transferred to the parting layer 105d via the primer layer 105b and the elastic layer 105c. Therefore, the temperature of the surface of the belt 105 (parting layer 105d) rises after passing through the fixing nip portion 101b in the process of belt 105 rotation, and reaches the highest temperature near the entrance side of the fixing nip portion 101b.
On the other hand, the wax bleeding out from the toner S on the recording medium P intervenes at the interface between the belt 105 and the toner image when the fixing process takes place. A part of the wax then adheres to the belt 105. As shown in part (a) of
The dust D near the entrance of the fixing nip portion 101b is diffused in the direction of the arrow W by the airflow shown in
Note that the phenomenon that dust D is generated near the entrance of the fixing nip portion 101b and carried in the W direction in
Next, the amount of dust emission generated by the fixing device 103 is explained using parts (a) and (b) of
The analysis follows “RAL-UZ205” as well. First, the particle loss coefficient β (1/s) due to chamber ventilation, etc. is calculated. For the particle loss coefficient β, as shown in part (b) of
The instantaneous emission rate (instantaneous ER: PER(t) (1/s)) is obtained according to Formula (4) as dust concentration Cp(t), measurement time t, time difference between two consecutive data points Δt, particle loss coefficient β, and chamber volume Vk.
The instantaneous ER (PER(t)) described in formula (4) indicates the amount of dust emitted from the printer per unit time at time t, since disappeared particles are included in the calculation. It is possible to obtain the amount of dust emitted during printing by integrating formula (4) over entire printing time.
As shown in
When the dust emission amount is 80%, the elapsed time is 207 seconds (147 seconds after the start of printing), and the overcooling degree ΔT is 120.9° C. When the dust emission amount is 90%, the elapsed time is 256 seconds (196 seconds after the start of printing) and the overcooling degree ΔT is 116.4° C. When the dust emission amount is 100%, the elapsed time is 395 seconds (335 seconds after the start of printing) and the overcooling degree ΔT is 109.6° C. In the case of temperature A, the elapsed time and the degree of overcooling degree ΔT can be obtained in the same way when the dust emission reaches 80%, 90%, and 100%.
If the amount of dust emission is 80%, the first temperature is 120.9° C. If the amount of dust emission is 90%, the first temperature is 116.4° C. If the amount of dust emission is 100%, the first temperature is 109.6° C. These values are almost constant as long as the physical properties of the wax, such as a boiling point of a wax of toner and an easiness of aggregation of wax volatile substance, do not change significantly.
The physical properties of the wax should be kept within a certain range. In that case, the value of the first temperature (ΔT_stop) does not change significantly even if the configuration of the image forming apparatus or a toner is changed. Thus, if the overcooling degree ΔT is determined according to the measuring method and measuring condition as described above, it is possible to predict the ending time point of dust emission based on a value of the first temperature (ΔT_stop) even in the case that a different toner is used or the case that an image forming apparatus with a different configuration is used.
As shown in
The filter unit 50 will be described. The filter unit 50 is arranged between the belt unit 101 and the secondary transfer outer roller 77 in the feeding direction of the recording material P, as shown in
The filter unit 50 as a filtration mechanism collects dust D by sucking air containing dust D. As shown in part (a) of
The secondary fan 61 is an air sucking portion for sucking air near the sheet entrance 400 to the outside of the apparatus. As shown in part (a) of
The duct 52 is a guide portion for guiding air near the sheet entrance 400 toward the outside of the apparatus. The duct 52 is provided with an air suction port 52a near the sheet entrance 400 and an air discharge port 52e away from the sheet entrance 400. The air suction port 52a is an opening arranged between the fixing nip portion 101b and the secondary transfer portion T2, and is provided so as to face the fixing nip portion 101b side. With this configuration, the air suction port 52a receives dust D carried by the air flow F3 (see
As shown in part (b) of
Furthermore, the filter 51 is adhered along the curved portion 52d of the edge portion 52c. Thus, the filter 51 is supported by the duct 52 while being curved. In this embodiment, the center portion of the filter 51 in the short direction is protruding toward the inside of the duct 52. That is, the center portion of the filter 51 in the short direction is curved in a direction away from the fixing nip portion 101b. It is preferable that the filter 51 is supported while being curved, because it increases the surface area of the filter 51 in a limited space, thereby improving the efficiency of dust collection by the filter 51.
The filter 51 as described above is a filtration member which filters (collects and removes) dust from the air passing through the air suction port 52a. It is desirable that the filter 51 is an electrostatic nonwoven fabric filter, in the case of collecting dust resulting from wax attached to the belt 105. An electrostatic nonwoven fabric filter is a nonwoven fabric made of fibers which hold static electricity, and it is possible to filter dust with high efficiency. However, the higher the density of the fibers, the higher the filtration performance of the electrostatic nonwoven fabric filter, but on the other hand, the pressure loss tends to increase. This relationship also applies to the case that the thickness of the electrostatic nonwoven fabric is increased. If the charge strength (strength of the static electricity) of the fibers is increased, it is possible to improve the filtration performance while keeping the pressure loss constant. It is desirable that thickness and fiber density of the electrostatic nonwoven fabric and charging strength of the fibers is set appropriately according to the filtration performance required for the filter.
Fiber density, thickness, and charging strength of the electrostatic nonwoven fabric which is used for the filter 51 in this embodiment have been set so that the air communication resistance is approximately 40 Pa and the collection rate is approximately 95% at a passing air speed of “10 cm/s”. In the case of filtering toner in discharging air, the electrostatic nonwoven fabric is used with the air communication resistance of 10 Pa or less at passing air speed of 10 cm/s. Thus, in this embodiment, the filter 51, which is made of electrostatic nonwoven fabric with the relatively large air communication resistance, is used.
It is desirable that the air communication resistance of the electrostatic nonwoven fabric used for the filter 51 is greater than or equal to 30 Pa and less than or equal to 150 Pa at the passing air speed (in the case of this embodiment, greater than or equal to 5 cm/s and less than or equal to 70 cm/s) which it is expected to be used. If the air communication resistance of an electrostatic nonwoven fabric is greater than 150 Pa, it is difficult to obtain the necessary air speed with the air discharging fan which is able to be mounted in the printer 1. If the air communication resistance of an electrostatic nonwoven fabric is less than 30 Pa, it is easy to cause unevenness in the longitudinal direction with regards to the air speed of the air passing through the filter 51.
The faster the air speed of the air passing through the filter 51, the greater the amount of air per unit time which passes through the filter 51. However, the faster the air speed of the air passing through the filter 51, the easier it is to lower the temperature of the air in the vicinity of the sheet entrance 400. Thus, it is desirable that the air speed of the air passing through the filter 51 is adequate speed in the case of improving the dust collection efficiency. Specifically, it is desirable the air speed during passing through the filter 51 is greater than or equal to 5 cm/s and less than or equal to 70 cm/s. In this embodiment, the dust collection rate of the filter 51 is almost 100% at an air speed of 5 cm/s and approximately 70% at an air speed of 70 cm/s. Therefore, it is possible to collect dust with high efficiency at the air speed in this range. It is possible that the secondary fan 61 adjusts the air speed during passing through the filter 51 in the range from 5 cm/s to 70 cm/s.
The filter 51 is an elongated shape with the direction perpendicular to the feeding direction of the recording material P (along the longitudinal direction of the fixing nip portion 101b) as its longitudinal direction. Due to this shape, it is possible to collect the dust generated in the vicinity of the fixing nip portion 101b in a wide range in the longitudinal direction.
The shaded region on the recording material P in part (c) of
Since the fixing device 103 in this embodiment utilizes center(-line) basis feeding which feeds the recording material P on the basis of a center of the belt 105 with respect to the widthwise direction, it is likely to generate the dust in the region Wp-max on the minimum-width-size recording material P which is capable of being introduced into the fixing device, regardless of the width size of the recording material P. For that reason, in order to collect the dust efficiently, it is desirable that the dust is reliably collected at least in this region. Accordingly, a dimension Wf of the filter 51 may desirably be longer than the region Wp-max in the recording material P with a minimum-width size. Or, the dimension Wf of the filter 51 may desirably be longer than the recording material with the minimum-width size.
Further, the dust is capable of generating in the region Wp-max on the maximum-width-size recording material P capable of being introduced into the fixing device. For that reason, in order to reliably collect the dust, it is desirable to collect the dust in an entire region of this region. Accordingly, the dimension Wf of the filter 51 may desirably be longer than the region Wp-max in the maximum-width-size recording material P. Or, the dimension Wf of the filter 51 may desirably be longer than the maximum-width-size recording material P. In the case where the recording material P with a plurality of width sizes is available and in the case where the recording material P with a width size highest in frequency of use is known, in the region Wp-max of the recording material P thereof, it is desirable to satisfy Wf>Wp-max.
Incidentally, in this embodiment, a maximum size of the usable recording material P is an A3 size, and a minimum size of the usable recording material P is a post card size. The width of the recording material P perpendicular to the feeding direction is 297 mm for the A3 size and is 100 mm for the postcard size. Wp-max described above is a region excluding a blank region (non-image region) of 3 mm at each of end portions from the entire region of the recording material P with respect to the widthwise direction. For that reason, the width Wp max on the A3 size recording material P is 291 mm (=297−3−3), and the width Wp-max of the post card size sheet p is 94 mm (=100−3−3).
The filter 51 is disposed in the neighborhood of the belt 105 as shown in
As described above, when the filter 51 is mounted on the air suction port 52a of the duct 52, there is no need to employ a constitution of guiding the air toward the filter 51. For that reason, the filter unit 50 can be downsized. Further, as described above, when the filter 51 extending in the longitudinal direction is disposed in the neighborhood of the belt 105, the passing air speed of the air in the air suction port 52a of the duct becomes uniform with respect to the longitudinal direction. In other words, by disposing the filter 51 which is the air communication resistor on the air suction port 52a, an entire region of a rear surface region of the filter 51 can be maintained at a certain negative pressure. That is, the negative pressures at points 53a, 53b, 53c shown in part (b) of
When the air suction amount by the filter unit 50 is small, an amount of the air flowing into the neighborhood of the belt 105 also becomes small. For that reason, a lowering in temperature in the neighborhood of the belt 105 can be made small. As a result, generation of the dust can be suppressed, so that collection efficiency of the dust is also improved. Further, the temperature lowering of the belt 105 is suppressed, and therefore it is also advantageous for energy saving.
The cooling mechanism will be described as below. As shown in
A discharging mechanism 350 will be described as below. When the sheet P containing water content is heated by the fixing device 103, water vapor generates from the recording material P. By this water vapor, a space C on a side downstream of the fixing device 103 in the main assembly 100a is in a state in which humidity is high (see
Next, an air flow in the main assembly 100a will be described. In order to collect the dust efficiently, the air flow in the main assembly 100a, particularly the air flow at a peripheral portion of the fixing device 103 may desirably be controlled appropriately. In the following, a constitution relating to the air flow at the peripheral portion of the fixing device 103 will be specifically described.
In the filter unit 50 described above, if the air flow rate of the second fan 61 becomes larger, the air can be sucked in a large amount, while the temperature of the air in the neighborhood of the sheet entrance 400 is liable to be lowered. The lowering in temperature of the air increases the overcooling degree ΔT and promotes the dust generation. For that reason, the air flow rate of the second fan 61 is needed to be appropriately set. The air flow rate from 20 L/min to 100 L/min is a proper range, and in this embodiment it is set at 50 L/min.
Incidentally, the filter 51 is deteriorated by sucking not only the dust but also paper powder generating from the recording material P and scattered toner scattering in a very small amount from the unfixed image on the recording material P. This is because deposition of the dust, the paper powder and the scattered toner onto the filter 51 lowers the charging strength of the electrostatic nonwoven fabric which is the material of the filter 51. For that reason, the second fan 61 may desirably be at rest in the case where the dust does not generate.
The third fan 62 of exhaust mechanism 350 is a fan for preventing the occurrence of the dew condensation on the guide 15. The third fan 62 sucks the air from the outside of the printer 1 and blows the air against the guide 15, and thus lowers the humidity of the space C (see
The fourth fan 64 of the cooling mechanism 300 has action of discharging air in a space between the fixing device 103 and the secondary transfer portion T2 with respect to the feeding direction of the recording material P in order to prevent temperature rise in the neighborhood of the transfer portion T2 as described in
In this embodiment, by controlling the operation start timing of the first fan 63 and the second fan 61, the dust can be efficiently removed by the filter 51 and dew condensation of peripheral portion of the fixing device 103 can be prevented. That is, the second fan 61 is operated prior to the first fan 63 to collect the particulate dust by the filter 51 so that the particulate dust generated by the wax attached to the belt 105 is not discharged to the outside of the main assembly by the first fan 63. After that, the first fan 63 is operated and the air is exhausted. However, if the operation of the first fan 63 is started too late, it is likely to occur dew condensation in the main assembly 100a. Therefore, in this embodiment, the operation start timing of the first fan 63 and the second fan 61 is adjusted in order to achieve both suppressing the emission of particulate dust and preventing dew condensation. Particularly, in this embodiment, it is effective in such a case that the fixing device 103 is started up from a cold state (for example, at the time of startup associated with power-on) and an image forming job is performed.
The fan control process of the first embodiment will be described below using
As shown in
When the predetermined waiting time has not elapsed since the start instruction of the image forming job is received (“No” in S3), the control portion 500 waits for the progress of this fan control process until the predetermined waiting time elapses. When the predetermined waiting time has elapsed since the start instruction of the image forming job is received (“Yes” in S3), the control portion 500 starts the image forming job (S4). In this embodiment, the image forming job is started about 10 seconds after the start instruction of the image forming job is received (time t1). The time at this time is described as the print start time (which is the time at which the signal ITOP is sent as described above) “t2” (see part (a) of
In this embodiment, the time at which the operation of the first fan 63 starts is, from a predetermined time before the time at which the leading end of the first sheet of recording material P reaches the fixing nip portion 101b, to the rear end of the first sheet of recording material P passes through the fixing nip portion 101b. The predetermined time before the time when the leading end of the first recording material P reaches the fixing nip portion 101b is described as “t3”, and the time when the rear end of the first recording material P passes through the fixing nip portion 101b is described as “t5” (see part (a) and part (b) of
After the first fan 63 starts operating at time t4, the control portion 500 continues to judge whether to perform the adjustment operation or not (S6). If the adjustment operation is not performed (“No” in S6), the control portion 500 determines whether to terminate the image forming job or not (S11). If the image forming job is to be terminated (“Yes” in S11), the first fan 63 and the second fan 61 are stopped (S12). Next, the fan operation, in the case where the control portion 500 determines that the adjustment operation is to be performed after the start of image forming (“Yes” in S6), will be described using S7 through S10 of
As described above, in this embodiment, the operation of the second fan 61 is started before the operation the first fan 63 is started. Then, after the operation of the second fan 61 is started, the operation of the first fan 63 is started at a time between a predetermined time when the leading edge of the first recording material reaches the fixing nip portion and the time when the rear end of the first recording material passes through the fixing nip portion. In this way, by starting the operation of the second fan 61 before starting the operation of the first fan 63, since the particulate dust is collected in the filter 51, it is not likely that the particulate dust is discharged to the outside of the main assembly even if the first fan 63 is operated. In addition, since the operation of the first fan 63 is started at a timing that is neither too fast nor too slow, it is not likely to generate dew condensation inside the main assembly 100a even if the operation of the first fan 63 is started after the operation of the second fan 61 is started. In this way, by adjusting the operation start timing of the first fan 63 and the second fan 61, it is possible to achieve both suppression of discharging fine particulate dust and prevention of dew condensation. Furthermore, when the adjustment operation is performed after the image forming is started, by stopping the first fan 63 while the second fan 61 is operated, the effect of suppressing of discharging the dust and preventing dew condensation are enhanced.
Incidentally, the suppression effect of discharging the dust D in this embodiment is particularly effective when an adjustment operation, such as an image density adjustment operation, is performed before the image forming of the first recording material P starts. As described above, even before image forming of the first sheet of recording material P starts, if the temperature of the belt 105 rises, the dust D is generated from the residual wax on the belt 105. At this time, a part of the dust D does not move toward the direction where the filter 51 is disposed (W direction in
Next, the fan control process in the second embodiment will be described. In this embodiment, the second fan 61 is controlled depending on the overcooling degree ΔT. That is, in this embodiment, the generation of the dust is predicted by the overcooling degree ΔT, and the second fan 61 is operated if the generation of the dust is predicted. In the following, the fan control process of the second embodiment will be described by using
As shown in
Incidentally, the operation of the first fan 63 before the start of an image forming job may be performed when the detected value (Tin) of the inside temperature sensor 65 is lower than the detected value (Tout) of the outside temperature sensor 66. That is, in such cases, the warm outside air may flow into the cold main assembly 100a and increase the humidity inside the main assembly 100a. If an image forming job is started in such a state, the water vapor generated by the heating of the recording material P may further increase the humidity in the main assembly 100a and occur dew condensation inside the main assembly 100a. To prevent this, in this embodiment, the first fan 63 is operated before the start of an image forming job and the air inside the main assembly 100a is warmed by the outside air, so that it is not likely to occur dew condensation during the image forming job. In addition, by stopping the first fan 63 at the same time as heating the belt 105, it is possible to accelerate to raise the peripheral temperature of the belt 105. By accelerating the temperature rise, the supercooling degree ΔT can be lowered, thus it is possible to prevent the generation of the dust caused by wax attached to the belt 105.
Next, with the start of the image forming job, the control portion 500 discriminates whether or not both of the following formulas (5) and (6) are satisfied (S14).
(Surface temperature Tb (° C.) of belt 105)≥(Dust generation temperature Tws (° C.)) formula (5)
(Dust generation temperature Tws (° C.))−(Spatial temperature Ta (° C.) of measuring point To)>First temperature (° C.) formula (6)
The formula (5) described above is a formula for discriminating whether or not the surface temperature Tb of the belt 105 at which the dust is capable of being generated. In part (a) of
On the other hand, the formula (6) described above is a formula for discriminating whether or not the overcooling degree ΔT (=Tws−Ta) defined by the formula (1) satisfies an emission end condition of the particulate dust. When this formula (6) is not satisfied, discrimination that the emission of the dust is ended or there is no emission of the dust is made. In part (b) of
In the case where the formula (5) and the formula (6) described above are satisfied, a generation condition of the dust is satisfied. When the formula (5) and the formula (6) are satisfied (“Yes” in S14), the control portion 500 starts the operation of the second fan 61 (S15). The time at this point is defined as “t12” (see part (b) of
Here, a measuring point To in order to measure the spatial temperature Ta used for calculation of the overcooling degree ΔT (Tws−Ta) of the formula (6) will be described using
It is difficult to accurately measure a range of the space in which the nucleation occurs, but as a result that the present inventor measured a dust density of the peripheral portion of the belt 105, the nucleation occurred within a range of 20 mm or less from the belt 105 toward the direction of the secondary transfer portion T2. Further, in the case where the position of the measuring point To is excessively close to the belt 105, the measuring point To is strongly influenced by the heat of the belt 105, so that there is a possibility that the spatial temperature To cannot properly measured. For that reason, it would be considered that there is a need to space the measuring point To from the belt 105 by at least 1 mm. Therefore, the position of the measuring point To may pass through a cross-sectional plane center of the belt 105 and a central portion of the belt 105 with respect to a widthwise direction of the belt 105, and may fall within a range of 1 mm or more and 20 mm or less from the surface of the belt 105 toward the secondary transfer portion T2 along the straight line parallel to the feeding direction of the recording material P. In this embodiment, as described above, a distance from the belt 105 to the measuring point To is 6 mm.
As a manner of acquiring the temperature of the spatial temperature Ta of the measuring point To, a method of measuring the spatial temperature Ta by a temperature detector (not shown) or a method of predicting the spatial temperature Ta from temperature information of the outside temperature sensor 66 and operation information of each fan would be considered. In this embodiment, a latter method is used, and the control portion 500 predicts the spatial temperature Ta. In the following, an example of a predicting method of the spatial temperature Ta by the control portion 500 will be described.
An inside temperature of the image forming apparatus measured by the inside temperature sensor 65 of the image forming apparatus is Tin, an outside temperature measured by the outside temperature sensor 66 of the image forming apparatus is Tout, a surface temperature of the belt 105 based on a temperature of the thermistor TH is Tb. Duty of the first fan 63 during operation is “FAN 3_duty”, Duty of the second fan 61 during operation is “FAN 1_duty”, Duty of the third fan 62 during operation is “FAN 2_duty”, and Duty of the fourth fan 64 during operation is “FAN 4_duty”. In such a case, the control portion 500 predicts the spatial temperature Ta according to the formula (7). Duty in operation is the rotation ratio (%) with the maximum number of rotations as 100%.
The spatial temperature Ta (Prediction value)=Tin+(A×Tb)−(B×Tout×FAN 1_duty)−(C×R out×FAN 2_duty)−(D×Tout×FAN 3_duty)−(E×Tout×FAN4_duty) formula (7)
A first term of a right(-hand) side in the above-described formula (7) means that the spatial temperature Ta is predicted on the basis of the inside temperature Tin of the image forming apparatus. A second term means that the spatial temperature Ta of the measuring point To is increased by the heat of the surface temperature Tb of the belt 105. For that reason, a sign of the second term is plus. Further, a third term to sixth term mean that the spatial temperature Ta is influenced by operation of the fans having a function of sucking the outside air (the outside temperature Tout) to the measuring point To. The outside temperature Tout is lower than the inside temperature of the image forming apparatus Tin and the surface temperature Tb, and therefore, the spatial temperature Ta shifts in a lowering direction by the operation of the fans. For that reason, signs of the third to sixth terms are minus. Incidentally, in the formula (7), “A, B, C, D and E” are constants and are determined so that a spatial temperature obtained by actually measuring the temperature at the measuring point To through an experiment and a predicted value of the special temperature by the formula (7) coincide with each other.
Incidentally, the surface temperature Tb of the belt 105 may be a value obtained by subtracting 10° C. from a detection result of the thermistor TH. This is because, in this embodiment, the surface temperature Tb of the belt 105 which has resistance of heat conduction is about 10° C. lower than a detection result of the thermistor TH. In addition, as parameters used for predicting the spatial space Ta, in addition to the above parameters, a size, a feeding speed and the number of fed sheets for the recording material P, and Duty of the fans during operation, and further an operation frequency of each of the fans may also be included.
Returning to the description of
In this embodiment, the time when the operation of the first fan 63 starts is, from the predetermined time (for example, 0.1 second) before the time when the leading end of the first sheet of the recording material P reaches the fixing nip portion 101b, to the time when a plurality of sheets (for example, 3 sheets) of recording materials P pass through the fixing nip portion 101b. The reason why the first fan 63 is operated again at time “t15” (see part (c) of
Then, after the image forming job is started, the control portion 500 discriminates whether or not the following formula (8) is satisfied (S20).
Spatial temperature Ta (predicted value)≥second temperature formula (8)
The second temperature is set at, for example 90° C., as shown in part (c) of
When the above-described formula (8) is satisfied (“Yes” in S20), the control portion 500 operates the second fan 61 (S21). Although the second fan 61 is small in air flow rate compared with the first fan 63, the second fan 61 can suck the hot air in the entire widthwise region of the belt 105, and therefore the cooling efficiency is high. By the operation of the second fan 61, deterioration of the filter 51 may advance, but in this embodiment, image quality maintenance is prioritized and the second fan 61 is operated.
In the case where the formula (8) is not satisfied (“No” in S20), the control portion 500 discriminates whether or not both the formula (5) and the formula (6) is satisfied (S22). In the case where both of the formula (5) and the formula (6) are satisfied (“Yes” in S22), the control portion 500 regards that dust is generated and operates the second fan 61 (S23). On the other hand, in the case where at least one of the formula (5) and the formula (6) are not satisfied (“No” in S22), the control portion 500 stops the second fan 61 (S24) and the air of the peripheral portion of the secondary transfer portion T2 is discharged. As described above, in the case where at least one of the formula (5) and the formula (6) is no longer satisfied during an image forming job, for example, in the case where the elapsed time of 207 seconds shown in part (b) of
Then, the control portion 500 discriminates whether or not an image forming job should be ended (S25). In the case the image forming job is not ended (“No” in S25), the control portion 500 returns to the step S20 and repeats the above-described processes S20 to S25. On the other hand, in the case the image forming job is ended (“Yes” in S25), the control portion 500 stops the first fan 63 and the second fan 61, and ends this fan control process.
As described above, in this embodiment, the second fan 61 starts operating before the first fan 63 starts operating, and even if the first fan 63 is operated, the particulate dust is not readily discharged to the outside of the main assembly. In addition, even if the first fan 63 is started after the second fan 61 is started, dew condensation is hardly generated inside the main assembly 100a. Therefore, the effect of realizing both the suppression of the particulate dust emission and the prevention of dew condensation is obtained.
The third embodiment will be described in accordance with the flowchart shown in
As mentioned in the second embodiment, in the case the formula (5) and the formula (6) are satisfied, there is no need to operate the second fan 61 because dust is hardly generated. In addition, even if the first fan 63 continues to operate regardless of adjustment operation, there is no effect on the dust. By continuing to operate the first fan 63, the effect of securely suppressing the temperature rise of the peripheral portion of the image forming portion PY to PK is obtained. By suppressing the operation of the second fan 61, it is possible to suppress the wear and tear of the filter 51.
Incidentally, in each of the above-described embodiments, a color image forming apparatus of the intermediary transfer tandem method as the image forming apparatus 100 is described as an example, but is not limited to this. Each of the above-described embodiments can also be applied to an image forming apparatus of the direct transfer method in which a toner image is directly transferred from photosensitive drums 1Y to 1K onto a recording material born and fed by a feeding belt. Further, they can also be applied to an image forming apparatuses which forms toner images of a single color (for example, monochrome machines).
According to the present invention, there is provided the image forming apparatus of which removes both dust and water vaper properly.
The present invention is not limited to the above-described embodiments, but can be variously changed and modified without departing from the spirit and the scope of the present invention. Accordingly, the following claims are attached for making the scope of the present invention public.
The present application claims priority on the basis of Japanese Patent Application No. 2019-028862 filed on Feb. 20, 2019, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-028862 | Feb 2019 | JP | national |
This application is a continuation of International Application No. PCT/JP2020/007884 filed Feb. 19, 2020, currently pending; and claims priority under 35 U.S.C. § 119 to Japan Application JP 2019-028862 filed in Japan on Feb. 20, 2019; and the contents of all of which are incorporated herein by reference as if set forth in full.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2020/007884 | Feb 2020 | US |
| Child | 17403588 | US |
