JP2007226078A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of efficiently cooling the inside of the apparatus without using a fan circulating air and then preventing trouble such as unintended toner fusion. <P>SOLUTION: A printer 1 includes a liquid cooling device 30 nearby a fixing device 20. The liquid cooling device 30 includes a liquid cooling jacket 31 as a heat absorber which comes into contact with the fixing device 20 to absorb heat and conducts the heat to cooling liquid, a radiator 32 as a heat radiator which radiates heat of the cooling liquid, a pump 33 which circulates the cooling liquid, and a pipe 34 which is connected to those components to one another to circulate the cooling liquid. Consequently, the fixing device 20 as a cooled body can efficiently be cooled without using a fan circulating air. A rise in temperature in the printer 1 can, therefore, be avoided to prevent various trouble due to a temperature rise such as fusion of toner etc., in the developing device and a cleaning device. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus represented by a copying machine or a printer.

  In an image forming apparatus represented by a copying machine or a printer, a heat roller fixing method is widely adopted as a method for fixing an unfixed toner image on a sheet. In the heat roller fixing method, a heat source is built in at least one roller of a roller pair forming a nip, and a toner carrying an unfixed toner image is inserted into the nip of the roller pair heated by the heat source, thereby supplying toner to the paper. To fix.

  However, heat tends to be trapped inside the image forming apparatus, and particularly in recent image forming apparatuses, speeding up has been promoted, and the temperature inside the image forming apparatus has increased remarkably. There is a concern that the temperature rise inside the apparatus may hinder the operation of the image forming apparatus. For example, a temperature rise around a developing device that supplies toner to the image carrier and a cleaning device that removes toner remaining on the surface of the image carrier after transferring the toner image is a serious problem.

  When the temperature around the developing device and the cleaning device rises, the toner in these devices melts and the fluidity is deteriorated, and there is a possibility that the toner adheres to a screw for conveying and stirring the toner. When the toner adheres to the screw and further accumulates, the toner conveyance performance is significantly reduced. In the developing device, the formation of a thin layer by the toner on the surface of the developing roller is disturbed, the toner image developed on the surface of the image carrier is adversely affected, and the image formed on the paper may be defective. There is. Further, in the cleaning device, there is a possibility that the waste toner overflows and contaminates the surroundings, or the waste toner adheres to the image carrier again, thereby deteriorating the cleaning performance. Moreover, there is a possibility that the screw may be damaged by braking the rotation of the screw.

In order to solve such a problem, various methods for avoiding a temperature rise inside the image forming apparatus have been proposed, and examples thereof can be seen in Patent Documents 1 to 3. In each of the image forming apparatuses described in Patent Documents 1 to 3, one or a plurality of fans are mounted therein, an air flow passage is secured, and air is forced to flow to cool the inside. Yes.
Japanese Patent Laid-Open No. 11-218987 (page 3-5, FIGS. 1 and 4) JP 2000-98858 A (page 3-4, FIG. 1) JP 2003-76253 A (page 4-5, FIG. 1-3)

  As in the image forming apparatuses described in Patent Documents 1 to 3, air is circulated inside the image forming apparatus by providing a cooling fan or an exhaust fan at an appropriate place, and the air heated inside is heated outside. Many methods of discharging are conventionally employed because they can be carried out relatively easily. However, when the inside of the image forming apparatus is cooled using a fan, there are concerns about wind noise and noise generated from the bearing portion. In particular, in an image forming apparatus characterized by high-speed printing, it is necessary to increase the size of the fan, increase the number of the fans, and rotate the fan at high speed. Furthermore, since it is necessary to secure a space for disposing the air flow passage in the apparatus, the image forming apparatus may be increased in size.

  In addition, when exhausting the heat-generated air inside the apparatus using a fan, it is necessary to take outside air from each part of the apparatus. As a result, dust may enter the apparatus, and the image forming operation may be adversely affected. When the optical system mirror and the charging device are contaminated, a cleaning operation by regular maintenance is required. In the image forming apparatus described in Patent Document 3, dust is prevented from entering the apparatus by moving the fan away from a place where outside air is taken in. However, as long as the fan is used, the dust can surely enter. It is difficult to prevent.

  On the other hand, the physical properties of paper used for printing are not always constant, but depend on the ambient temperature and humidity. When the amount of moisture contained in the paper increases, transfer and fixing of the toner image onto the paper and paper transport performance are adversely affected, and there is a concern that image quality will be greatly reduced, paper jams and wrinkles will occur. In an image forming apparatus for color printing, which is in high demand in recent years, there is a high possibility that problems such as being particularly susceptible to the moisture of the paper and of not being able to obtain a uniform gloss. In order to solve such problems, there has been proposed an image forming apparatus that removes moisture from a sheet using a heating device such as a heater. However, an increase in parts cost and running cost due to the installation of the heater is also a problem.

  The present invention has been made in view of the above points, and in order to prevent generation of noise and intrusion of dust into the apparatus, the inside of the apparatus can be efficiently cooled without using a fan that circulates air. An object of the present invention is to provide an image forming apparatus capable of performing a suitable image forming operation by preventing occurrence of problems such as unintended melting of toner. Furthermore, in addition to preventing such noise generation and dust intrusion, high-performance images that can maintain suitable image quality by removing moisture from the paper by exhaust heat that has been cooled and removed An object is to provide a forming apparatus.

  In order to solve the above problems, the present invention absorbs the heat of an object to be cooled or surroundings and transfers the heat to the coolant, a radiator that releases the heat of the coolant, and circulating the coolant. A liquid cooling type cooling device provided with a pump to be connected and a pipe through which a coolant flows through these components is provided.

  Further, in the image forming apparatus having the above configuration, the object to be cooled is a fixing device, and the liquid cooling type cooling device includes a liquid cooling jacket that is the heat absorber provided in a housing of the fixing device, and an image forming device. And a radiator that is the heat radiator provided near the exterior of the apparatus main body.

  In the image forming apparatus having the above-described configuration, the liquid cooling type cooling device includes the radiator in the vicinity of the sheet storage portion of the image forming apparatus, and the heat released from the radiator is circulated in the sheet storage portion. I decided to let them.

  In the image forming apparatus having the above-described configuration, the liquid cooling type cooling device includes a fan for forcibly circulating the heat released from the radiator into the sheet storage unit.

  According to the configuration of the present invention, the image forming apparatus absorbs the heat of the object to be cooled or the surroundings and transfers the heat to the cooling liquid, the radiator that releases the heat of the cooling liquid, and the cooling liquid. Since the liquid cooling type cooling device provided with the circulating pump and the pipe through which the coolant flows is connected between these components, the fixing device and the image can be used without using a fan for circulating air. It is possible to efficiently cool the object to be cooled such as the periphery of the forming unit. As a result, it is possible to prevent wind noise generated by using the fan, noise generated from the bearing portion, and enlargement of the image forming apparatus. It is also possible to prevent dust from entering the apparatus due to air circulation. In this way, an increase in the temperature inside the image forming apparatus can be avoided, and various problems caused by the temperature increase such as unintended melting of the toner in the developing device and the cleaning device can be prevented, and a suitable image forming operation can be performed. An image forming apparatus that can be performed can be provided.

  In addition, the object to be cooled is a fixing device, and the liquid cooling type cooling device includes a liquid cooling jacket that is a heat absorber provided in the housing of the fixing device, and a radiator provided in the vicinity of the exterior of the image forming apparatus main body. Therefore, the fixing device can be cooled by a liquid cooling type cooling device having a simple configuration such as a liquid cooling jacket or a radiator, and other components in the image forming apparatus are adversely affected by heat. Can be prevented from spreading. Therefore, it is possible to provide an image forming apparatus capable of efficiently cooling the fixing device while preventing noise and dust from entering, and capable of performing a suitable image forming operation.

  In addition, since the liquid cooling type cooling device includes a radiator in the vicinity of the sheet storage portion of the image forming apparatus and heat radiated from the radiator is circulated in the sheet storage portion, Exhaust heat generated from the cooling body can be easily carried to the paper storage unit and used to warm the paper stored in the paper storage unit. Further, while the image forming apparatus is activated, it is possible to continuously warm the sheet and remove moisture from the sheet. Accordingly, it is not necessary to provide a heating device such as a heater in the paper storage unit, and moisture of the paper can always be removed by heat released from the radiator while suppressing an increase in parts cost and running cost. Therefore, by using the liquid cooling type cooling device, in addition to preventing the generation of noise and the intrusion of dust, it prevents the occurrence of image defects, paper jams, wrinkles, etc. accompanying the increase in the amount of moisture contained in the paper, It is possible to maintain a suitable image quality.

  Further, since the liquid cooling type cooling device is provided with a fan for forcibly circulating the heat released from the radiator into the paper accommodating portion, the heated air is quickly and thoroughly supplied to every corner of the paper accommodating portion. Can be spread. Therefore, the dehumidifying efficiency of the paper can be further improved, and the action for maintaining the image quality of the paper can be further enhanced.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  First, an image output operation of an image forming apparatus according to an embodiment of the present invention will be described while explaining an outline of the structure with reference to FIG. FIG. 1 is a schematic vertical sectional front view showing a schematic structure of a tandem color printer which is an example of an image forming apparatus.

  As shown in FIG. 1, a paper cassette 3 that is a paper storage unit is disposed below the inside of the main body 2 of the printer 1. Inside the paper cassette 3, paper P such as cut paper before printing is stacked and accommodated. Then, the paper P is separated and sent one by one by the paper feeding device 4 toward the upper right of the paper cassette 3 in FIG. The paper cassette 3 can be pulled out horizontally from the front side of the main body 2.

  A paper feed path 5 and a registration roller 6 are disposed downstream of the paper cassette 3 in the paper transport direction. The paper P sent out from the paper cassette 3 is transported upward through the paper feed paper transport path 5 and reaches the position of the registration roller 6.

  A transfer conveyance belt 7 is disposed downstream of the registration roller 6. The transfer conveyance belt 7 is supported by being wound around a plurality of rollers, and is rotated counterclockwise in FIG. 1 by a driving device (not shown). The transfer / conveying belt 7 carries the paper P that has passed through the paper feeding paper conveying path 5 on the upper surface thereof and horizontally conveys the toner image from right to left in FIG. Used.

  Above the transfer / conveying belt 7, image forming units 8 are provided at four locations. As shown in FIG. 1, the four image forming units 8 are arranged in a line along the rotation direction of the transfer conveyance belt 7 from the upstream side to the downstream side in the rotation direction. The four image forming units 8 are, in order from the upstream side, a cyan image forming unit 8C, a magenta image forming unit 8M, a yellow image forming unit 8Y, and a black image forming unit 8B. To supplement the image forming unit 8 with toner, toner supply containers 9C, 9M, 9Y, and 9B corresponding to the image forming units 8C, 8M, 8Y, and 8B are provided above them. Replenished to each image forming unit 8.

  In the image forming unit 8, an electrostatic latent image is formed based on image data such as characters, figures, and patterns received from an external computer (not shown), and a toner image is developed from the electrostatic latent image. .

  Below each image forming unit 8, a transfer unit in which a transfer roller 10 is provided with a transfer conveyance belt 7 therebetween is formed. The transfer roller 10 is pressed against the image forming unit 8 via the transfer conveyance belt 7 to form a transfer nip portion. In the transfer nip portion, the toner image formed in the image forming unit 8 is synchronized by the registration roller 6 and transferred onto the paper P that is sent on the transfer conveyance belt 7. Then, the toner image of each image forming unit 8 is sequentially transferred onto the sheet P on the upper surface of the transfer conveyance belt 7 at a predetermined timing as the transfer conveyance belt 7 rotates, so that cyan, magenta, yellow, black on the surface of the sheet P A full color toner image is formed by superimposing the four color toner images.

  A fixing device 20 is provided downstream of the transfer conveyance belt 7 and each image forming unit 8 in the sheet conveyance direction. The paper P, which is placed on the upper surface of the transfer conveyance belt 7 and carries an unfixed toner image, is sent to the fixing device 20, and the toner image is heated and pressed by a heat roller and a pressure roller to be fixed.

  A discharge paper transport path 11 and a paper discharge unit 12 are disposed downstream of the fixing device 20. The paper discharge unit 12 is provided on the upper surface of the main body 2 at a position where the printed paper P can be taken out from the outside.

  Next, a detailed configuration around the fixing device 20 of the printer 1 will be described with reference to FIGS. 2 to 4 in addition to FIG. 2 is a partially enlarged front view of a vertical cross section showing a fixing device of the printer and its lower periphery, FIG. 3 is a front view of a vertical cross section of the fixing device, and FIG. 4 is a liquid cooling of a liquid cooling type cooling device provided for the fixing device. It is a right view which shows a jacket. In FIG. 2, the flow direction of the coolant is indicated by a broken line arrow, and the flow direction of the air is indicated by a white arrow. Moreover, in FIG. 4, the flow direction of the coolant is indicated by an arrow.

  As shown in FIG. 2, the fixing device 20 includes a heat roller 22 as a fixing member and a pressure roller 23 as a pressure member inside a housing 21.

  The heat roller 22 extends above the paper transport path in the paper width direction perpendicular to the paper transport direction, that is, in the depth direction of the paper surface of FIG. 2, and is arranged with its axis direction horizontal. The heat roller 22 has a diameter of 40 mm, and an elastic member layer made of silicon rubber or sponge is provided on the surface of a tubular core material made of metal such as aluminum or iron. On the surface of the elastic member layer, a release layer made of a fluorine-based resin is provided in close contact to improve smoothness and toner release properties.

  Inside the heat roller 22, a halogen heater 24 as a heat source is arranged. As shown in FIG. 2, the halogen heater 24 extends in the axial direction of the heat roller 22 and heats the heat roller 22 from the inside.

  The pressure roller 23 extends in the paper width direction below the paper conveyance path, that is, below the heat roller 22, similarly to the heat roller 22, and is disposed with its axial direction horizontal. The pressure roller 23 is provided with an elastic member layer made of silicon rubber or sponge on the outside of a cored bar made of metal such as aluminum or stainless steel.

  The fixing device 20 is provided with a biasing means (not shown) that biases the pressure roller 23 toward the heat roller 22. As a result, the heat roller 22 and the pressure roller 23 are brought into pressure contact with each other with a predetermined pressure, thereby forming a fixing nip having a predetermined length in the sheet conveying direction. A sheet P carrying an unfixed toner image passes through the fixing nip. The heat roller 22 is rotated by a driving means (not shown) so as to have the same peripheral speed as the paper transport speed. The pressure roller 23 rotates according to the rotation of the heat roller 22 by being in contact with the heat roller 22. In normal fixing operation, the heat roller 22 is added clockwise in order to fix the unfixed toner image on the surface of the paper P while conveying the paper P from right to left in FIGS. 1 and 2. The pressure roller 23 rotates counterclockwise.

  As shown in FIG. 2, a fixing unit discharge roller 25 is disposed on the downstream side of the portion where the heat roller 22 and the pressure roller 23 are provided. The fixing unit discharge roller 25 discharges the fixed paper P from the fixing device 20 and sends it to the downstream discharge paper transport path 11.

  As shown in FIGS. 1 and 2, a liquid cooling type cooling device 30 is disposed around the fixing device 20 having such a configuration. The liquid cooling type cooling device 30 includes a liquid cooling jacket 31 that is a heat absorber, a radiator 32 that is a heat radiator, a pump 33, and a plurality of pipes 34 that are connected between these components and through which the coolant flows.

  As shown in FIGS. 2 and 3, the liquid cooling jacket 31 is provided in contact with the housing 21 of the fixing device 20 that is the object to be cooled, and a part of the liquid cooling jacket 31 is configured as a part of the housing 21. Yes. One liquid cooling jacket 31 is provided at each of an upper part and a lower part of the fixing device 20. The liquid cooling jacket 31 at the top of the fixing device 20 is above the heat roller 22 and has a U-shape that protrudes upward to cover it. The lower liquid cooling jacket 31 is configured as an upstream side of the pressure roller 23 in the sheet conveying direction, that is, as a wall portion on the image forming unit 8 side with respect to the fixing device 20.

  Each of the two liquid cooling jackets 31 is provided with a water inlet 31a and a water outlet 31b shown in FIGS. The coolant is sent from the pipe 34 through the water inlet 31a into the liquid cooling jacket 31, and is sent out to another pipe 34 through the drain 31b. A plurality of partition walls 31 c are provided inside the liquid cooling jacket 31, and a cooling liquid flow path 31 d for effectively cooling the fixing device 20 is configured. The coolant in the liquid cooling jacket 31 smoothly flows through the coolant flow path 31d from the water injection port 31a to the drain port 31b. In this manner, the liquid cooling jacket 31 serves as a heat absorber that contacts the fixing device 20 to absorb heat and transfers the heat to the cooling liquid.

  In addition to water, an antifreeze such as an ethylene glycol solution or a propylene glycol solution can be used as the cooling liquid.

  As shown in FIG. 2, the radiator 32 is provided in the vicinity of the exterior of the main body 2 below the fixing device 20 and in the vicinity of the paper cassette 3 that is a paper storage unit. The coolant that has absorbed the heat of the fixing device 20 through the liquid cooling jacket 31 is then fed into the radiator 32. The radiator 32 plays a role of releasing the heat of the fixing device 20 absorbed by the liquid cooling jacket 31 as a heat absorber from the cooling liquid so that the cooling liquid functions effectively again.

  The radiator 32 is arranged such that the surface on the side from which more heat is released faces the paper cassette 3 shown in FIG. As a result, the heat released from the radiator 32 circulates in the paper cassette 3.

  The radiator 32 includes a liquid cooling fan 35 between the main body 2 and the exterior. The liquid cooling fan 35 introduces outside air into the main body 2 from an intake port 2a provided in the exterior of the main body 2 in the immediate vicinity thereof, and an exhaust port 2b provided in the main body 2 exterior on the opposite side across the paper cassette 3 (see FIG. 1)). As a result, the liquid cooling fan 35 quickly removes heat from the coolant flowing through the radiator 32 and forcibly distributes the heat released from the radiator 32 into the paper cassette 3. A partition 2c is provided between the upper part of the main body 2 provided with the fixing device 20 and the image forming unit 8 and the lower part of the main body 2 provided with the paper cassette 3, as shown in FIGS. Therefore, the air circulation provided by the liquid cooling fan 35 does not reach the upper part of the main body 2.

  The pump 33 is provided in the vicinity of the fixing device 20 and is connected via a pipe 34 to a liquid cooling jacket 31 that is a heat absorber and a radiator 32 that is a heat radiator. The pump 33 smoothly circulates the coolant through the pipe 34 between the liquid cooling jacket 31 and the radiator 32.

  In this way, the printer 1 as the image forming apparatus absorbs heat by contacting the object to be cooled, and releases the heat of the cooling liquid and the heat absorber (liquid cooling jacket 31) that transmits the heat to the cooling liquid. A liquid cooling type cooling device 30 provided with a radiator (radiator 32) that circulates, a pump 33 that circulates the coolant, and a pipe 34 that is connected between these components and through which the coolant flows. Without using a fan that circulates, the object to be cooled such as the fixing device 20 and the periphery of the image forming unit 8 can be efficiently cooled. Thereby, it is possible to prevent wind noise generated by using the fan, noise generated from the bearing portion, and further increase in size of the printer 1. It is also possible to prevent dust from entering the apparatus due to air circulation. In this way, an increase in the temperature inside the printer 1 can be avoided, and various problems caused by the temperature increase such as unintended melting of the toner in the developing device and the cleaning device can be prevented and a suitable image forming operation can be performed. It is possible to provide a printer 1 that can do this.

  In addition, the cooling target is the fixing device 20, and the liquid cooling type cooling device 30 uses a liquid cooling jacket 31 provided in the housing 21 of the fixing device 20 as a heat absorber, near the exterior of the main body 2 of the printer 1. Since the provided radiator 32 is provided as a radiator, the fixing device 20 can be cooled by the liquid cooling type cooling device 30 having a simple configuration such as the liquid cooling jacket 31 or the radiator 32, and other components in the printer 1. In addition, it is possible to prevent the adverse effects of heat from spreading. Therefore, it is possible to provide the printer 1 that can efficiently cool the fixing device 20 while preventing generation of noise and intrusion of dust, and capable of performing a suitable image forming operation.

  The liquid cooling type cooling device 30 includes a radiator 32 that is a radiator, in the vicinity of the paper cassette 3 that is a paper storage portion of the printer 1, and distributes heat released from the radiator 32 into the paper cassette 3. Therefore, the exhaust heat generated from the object to be cooled such as the fixing device 20 can be easily carried to the paper cassette 3 and used to warm the paper P stacked and accommodated in the paper cassette 3. Further, while the printer 1 is activated, it is possible to keep the paper P warm all the time and to remove moisture from the paper P. Accordingly, it is not necessary to provide a heating device such as a heater in the paper cassette 3, and moisture of the paper P can always be removed by heat released from the radiator 32 while suppressing an increase in parts cost and running cost. Therefore, by using the liquid cooling type cooling device 30, in addition to preventing the generation of noise and the intrusion of dust, the occurrence of image defects, paper jams, wrinkles, etc. due to an increase in the amount of moisture contained in the paper P is prevented. Thus, it is possible to maintain a suitable image quality.

  Furthermore, since the liquid cooling type cooling device 30 includes the liquid cooling fan 35 that forcibly distributes the heat released from the radiator 32 into the paper cassette 3, the heat is quickly supplied to every corner of the paper cassette 3. You can spread the air. Therefore, the dehumidifying efficiency of the paper P can be further improved, and the action for maintaining the image quality of the paper P can be further enhanced. The liquid cooling fan 35 is used as an aid for the release of heat by the radiator 32 and the circulation of the heated air into the paper cassette 3, so that it operates at a low speed to reduce noise as much as possible. can do.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the embodiment of the present invention, the tandem color printer using the transfer conveyance belt 7 is described as an example of the image forming apparatus, but the application target of the present invention is not limited to this. It may be an image forming apparatus for color printing having another configuration or an image forming apparatus for monochrome printing.

  Further, the fixing device 20 has been described as an example of the cooling target to be cooled by the liquid cooling type cooling device 30, but the cooling target is not limited to this, and the image forming unit 8 and other components are not limited thereto. May be used as the object to be cooled.

  Furthermore, the liquid cooling type cooling device 30 is not only attached to components such as the fixing device 20 and the image forming unit 8 and directly cooled, but also between these components, a heat absorber such as a liquid cooling jacket 31. Even if it is provided as a heat insulating wall so as to absorb the ambient heat, the temperature inside the printer 1 can be avoided, and the temperature rises due to unintended melting of the toner in the developing device and the cleaning device. It is possible to prevent the occurrence of various problems and perform a suitable image forming operation.

  The present invention can be used in general image forming apparatuses.

1 is a schematic vertical sectional front view of a printer according to an embodiment of the present invention. FIG. 2 is a partially enlarged front view of a vertical cross section showing a fixing device of the printer of FIG. 1 and its lower periphery. FIG. 3 is a vertical sectional front view of the fixing device of FIG. 2. FIG. 3 is a right side view showing a liquid cooling jacket of a liquid cooling type cooling device provided for the fixing device of FIG. 2.

Explanation of symbols

1 Printer (image forming device)
2 Body 3 Paper cassette (paper compartment)
DESCRIPTION OF SYMBOLS 8 Image formation part 20 Fixing device 21 Housing 22 Heat roller 23 Pressure roller 30 Liquid cooling type cooling device 31 Liquid cooling jacket (heat absorber)
32 Radiator
33 Pump 34 Pipe 35 Liquid cooling fan (fan)

Claims (4)

  A heat absorber that absorbs the heat of the object to be cooled or surroundings and transfers the heat to the coolant, a radiator that releases the heat of the coolant, a pump that circulates the coolant, and a connection between these components An image forming apparatus comprising a liquid cooling type cooling device provided with a pipe through which a cooling liquid flows.   The object to be cooled is a fixing device, and the liquid cooling type cooling device includes a liquid cooling jacket that is the heat absorber provided in a housing of the fixing device and the exterior provided near the exterior of the image forming apparatus main body. The image forming apparatus according to claim 1, further comprising a radiator that is a radiator.   The liquid cooling type cooling device includes the radiator in the vicinity of a sheet storage portion of the image forming apparatus, and distributes heat released from the radiator into the sheet storage portion. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 3, wherein the liquid cooling type cooling device includes a fan that forcibly distributes heat released from the radiator into the sheet storage unit.

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