JP2024137628A - Developing device, process cartridge and image forming apparatus - Google Patents

Abstract

To prevent shortage of a developer on a developing roller and prevent occurrence of anomalous images by carrying out operation to stabilize developer balance against switching of paper-feeding speeds in a developing device.SOLUTION: Provided is a developing device 39 for developing with a developer an electrostatic latent image formed on an image carrier (photoreceptor drum 11). The developing device comprises: a screw member for stirring and conveying a developer; a developing roller for supplying the developer stirred and conveyed by the screw member onto the image carrier; and drive means capable of driving the rotation of the developing roller and the screw member at a plurality of prescribed revolution speeds. Before the electrostatic latent image is developed with a developer, the developing roller and the screw member (first conveyance screw 43, second conveyance screw 44) are driven for a prescribed duration by drive means (drive motor 38), with a length of the prescribed duration being incremented or decremented on the basis of a difference between a prescribed revolution speed in the previous development and a prescribed revolution speed in the current development.SELECTED DRAWING: Figure 5B

Description

The present invention relates to a developing device, process cartridge, and image forming device that uses electrophotography to transfer an image formed on a latent image carrier such as a photoreceptor and record it on a recording medium such as paper or an OHP sheet, such as a laser-based copier, printer, facsimile, or a combination machine of these.

Conventionally, image forming apparatuses equipped with developing devices using dry developers have been well known, including copiers, facsimiles, and printers. Developing devices using dry developers use dry developers when visualizing electrostatic latent images formed on image carriers by electrostatic recording or electrophotography. As dry developers, one-component developers using toner containing magnetic material and two-component developers consisting of toner and carrier are commonly used.

The rotation speed (process speed) of the image carrier should be optimized according to the type of recording material being used to avoid image defects. For this reason, image forming devices that can be switched between multiple stages according to the type of recording material have been put into practical use.

On the other hand, in recent years, developing devices that allow the developer to overflow through a discharge port, such as trickle development, have become smaller, and the amount of developer filled has fallen to, for example, around 300 g. Also, to accommodate high process speeds that increase productivity, the circulation speed of the developer inside the developing device has increased.

As a result, the change in developer level (one-axis developer surface height) when the process speed is switched is greater than in the past. If the change in developer level is large, the density of the toner image tends to decrease or increase in parts during image formation after the process speed is switched, which can lead to image defects.

To deal with such image defects, in Patent Document 1 (JP 2013-054106 A), when paper is passed at normal speed after a slow paper passing speed (process speed), the developer stirring and transporting screw is rotated at a faster speed. However, with the technology in Patent Document 1, changing the paper passing speed (process speed) changes the developer balance in the developing device, which causes an issue of an insufficient amount of developer being pumped up to the developing roller, resulting in abnormal images.

The object of the present invention is to prevent a shortage of developer on the developing roller and the occurrence of abnormal images by performing an operation in the developing device that stabilizes the developer balance when the paper passing speed is changed.

In order to solve the above problem, the developing device of the present invention is a developing device that develops an electrostatic latent image formed on an image carrier with a developer, and has a screw member that stirs and transports the developer, a developing roller that supplies the developer stirred and transported by the screw member onto the image carrier, and a driving means that can rotate and drive the developing roller and the screw member at a plurality of predetermined rotation speeds, and is characterized in that before developing the electrostatic latent image with the developer, the developing roller and the screw member are driven by the driving means for a predetermined time, and the length of the predetermined time is increased or decreased based on the difference between the predetermined rotation speed in the previous development and the predetermined rotation speed in the current development.

This invention makes it possible to prevent a shortage of developer on the developing roller and prevent the occurrence of abnormal images.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of a hardware block configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a developing device used in the image forming apparatus. FIG. FIG. 11 is a diagram showing a change in developer surface height with a change in process speed. 2 is a block diagram of a drive motor that drives the developing device and a control unit. 4 is a control flowchart of a drive motor of the developing device.

Below, the best mode for carrying out the present invention will be explained with reference to the drawings. Note that a person skilled in the art can easily change or modify the present invention within the scope of the claims to create other embodiments, and these changes and modifications are included in the scope of the claims. The following explanation is an example of the best mode for the present invention, and does not limit the scope of the claims.

Image forming apparatus An embodiment in which the present invention is applied to an electrophotographic direct transfer type color laser printer (hereinafter referred to as a "laser printer"), which is an image forming apparatus, will be described with reference to Figures 1A to 3. Figure 1A is a schematic diagram of the laser printer, which is an image forming apparatus 110 according to this embodiment. Figure 1B is a diagram showing an example of the hardware block configuration of the image forming apparatus 110.

The direction in which belt 60 runs along arrow A in Figure 1A is the direction in which transfer paper 100 moves. Four sets of toner image forming units 1Y, 1M, 1C, and 1K are arranged in this order from the upstream side in the direction in which transfer paper 100 moves. Y, M, C, and K represent the colors yellow (Y), magenta (M), cyan (C), and black (K).

The toner image forming units 1Y, 1M, 1C, and 1K each include a photoconductor drum 11Y, 11M, 11C, and 11K as an image carrier, and a developing unit. The toner image forming units 1Y, 1M, 1C, and 1K are arranged so that the rotation axes of the photoconductor drums are parallel to each other and at a predetermined pitch in the transfer paper movement direction.

In addition to the toner image forming units 1Y, 1M, 1C, and 1K, this laser printer also includes an optical writing unit 2, paper feed cassettes 3 and 4, a pair of registration rollers 5, a transfer unit 6 as a belt drive device having a transfer transport belt 60 as a transfer transport member that carries transfer paper 100 and transports it through the transfer positions of each toner image forming unit, a fixing unit 7 using a belt fixing method, and a paper discharge tray 8. It also includes a manual feed tray MF and a toner supply container TC, and also includes a waste toner bottle, a duplex/reversal unit, a power supply unit, and the like, all of which are not shown, in the space S indicated by the two-dot chain line.

The optical writing unit 2 constitutes a latent image forming means, and includes a light source, a polygon mirror, an f-θ lens, a reflecting mirror, etc., and is configured to perform a writing operation on each of the photoconductor drums 11Y, 11M based on image data.
, 11C, and 11K are irradiated with a laser beam while scanning the surfaces of the substrates.

The dashed line in FIG. 1A indicates the transport path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3, 4 or manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown) and sent to a temporary stop position where a pair of registration rollers 5 is provided. The transfer paper 100 sent out at a predetermined timing by the pair of registration rollers 5 is supported by the transfer transport belt 60 and transported toward each of the toner image forming units 1Y, 1M, 1C, and 1K, passing through each transfer nip.

Each toner image developed on the photoconductor drum 11Y, 11M, 11C, 11K of each toner image forming unit 1Y, 1M, 1C, 1K is superimposed on the transfer paper 100 at each transfer nip, and is transferred onto the transfer paper 100 under the action of the transfer electric field and nip pressure. This superimposed transfer forms a full-color toner image on the transfer paper 100. After the toner image transfer, the surfaces of the photoconductor drums 11Y, 11M, 11C, 11K are cleaned by a cleaning device and further discharged in preparation for the formation of the next electrostatic latent image.

Meanwhile, after the full-color toner image is fixed by the fixing unit 7, the transfer paper 100 moves in the first paper discharge direction B or the second paper discharge direction C according to the rotational position of the switching guide G. When it is discharged onto the paper discharge tray 8 from the first paper discharge direction B, it is stacked with the image side facing down, that is, face-down. On the other hand, when it is discharged in the second paper discharge direction C, it is transported to another post-processing device (such as a sorter or binding device) not shown, or is transported again to the registration roller pair 5 via the switchback section for double-sided printing.

1B, the image forming apparatus 110 includes a control unit 37 including a CPU 78. The control unit 37 includes a ROM 70, a RAM 71, a printer control unit 72, an image reading control unit 73, a storage control unit 74, an input control unit 75, and an output control unit 76. The components constituting the control unit 37 are connected to each other via a bus 77 and are also connected to the CPU 78.

The image forming device 110 also includes hardware such as a storage (storage unit) 80, an input unit 81, an output unit 82, a printer unit 90, a scanner unit 91, and a document transport unit 92. The printer unit 90 is connected to a drive motor 38 and a developing device 39, as well as to an operation time recording device 93, a print area recording device 94, and a detection unit 95. The detection unit 95 is connected to a temperature sensor 96 and a humidity sensor 97. The printer control unit 72, image reading control unit 73, storage control unit 74, input control unit 75, and output control unit 76 of the control unit 37 function as interfaces that allow the CPU 78 to control each piece of hardware.

The control unit 37, which includes the CPU 78, controls the entire image forming device 110. The CPU 78 starts the OS using a boot program stored in the ROM 70. The CPU 78 then executes control programs stored in the storage 80 and the ROM 70 on the OS.

RAM 71 is used as a temporary storage area such as the main memory or work area of CPU 78. Storage 80 is a readable/writable non-volatile storage device such as an HDD. This storage stores various data such as programs for controlling the entire image forming device 110, various application programs, data for managing consumable parts, and videos showing a series of tasks required to resolve a maintenance event.

The CPU 78 accesses the storage via the storage control unit. The CPU 78 reads out control programs and application programs from the storage 80 and ROM 70, and controls the image forming device 110 by executing the programs deployed in the RAM 71. In this way, the hardware constituting the control unit 37, such as the CPU 78, ROM 70, RAM 71, and storage 80, constitutes the so-called computer of the present invention.

In the image forming device 110 of this embodiment, one CPU 78 executes each process shown in the flowchart (FIG. 5B) described below using a program deployed in one memory (RAM 71), but other configurations are also possible. For example, multiple processors, RAM, ROM, and storage may work together to execute each process shown in the flowchart described below. Also, some of the processes may be executed using hardware circuits such as ASICs and FPGAs.

The CPU 78 controls the scanner unit 91 via the image reading control unit 73 to read the image on the document and generate image data. The CPU 78 cooperates with the printer control unit 72 and the printer unit 90 to form an image on a sheet (recording medium) such as paper.

The input control unit 75 connects the input unit 81 to the control unit 37, and accepts user operation instructions from the input unit 81, such as a touch panel or hard keys. The output control unit 76 connects the output unit 82 to the control unit 37, and controls the output unit 82, which has a display unit such as an LCD or CRT, to display operation screens and videos to the user.

In this embodiment, the output unit 82 is described as a display unit that performs display output, but the output unit 82 may also include a speaker that performs audio output in addition to display output. Furthermore, the input unit 81 may also include a microphone that performs audio input in addition to input from a touch panel or hard keys, etc.

2 and 3 are diagrams showing the developing device 39. The developing device 39 has a developing roller 42 arranged so as to be partially exposed from an opening in its casing. It also has a first transport screw 43, a second transport screw 44, a regulating blade 45, a toner concentration sensor (hereinafter referred to as a T sensor) 46, etc. Hereinafter, the first transport screw 43 may be simply referred to as the "first shaft" and the second transport screw 44 may be simply referred to as the "second shaft".

The casing contains a two-component developer 49 that contains a magnetic carrier and a negatively charged toner. This two-component developer 49 is triboelectrically charged while being stirred and transported by the first transport screw 43 and the second transport screw 44, and then is supported on the surface of the developing roller 42.

Then, the layer thickness is regulated by the regulating blade 45, and the toner is transported to the development area facing the photoconductor 11, where the toner adheres to the electrostatic latent image on the photoconductor 11. This adhesion forms a toner image on the photoconductor 11. The two-component developer, from which the toner has been consumed by development, is returned to the casing as the developing roller 42 rotates.

A partition wall 47 is provided between the first transport screw 43 and the second transport screw 44. This partition wall 47 separates the first supply section 40, which houses the developing roller 42, the first transport screw 43, etc., from the second supply section 41, which houses the second transport screw 44, within the casing.

The developing roller 42, the first transport screw 43, and the second transport screw 44 are connected by a gear train and driven by a drive motor as a driving means. The developing roller 42, the first transport screw 43, and the second transport screw 44 each rotate at a constant ratio and in a constant direction at a rotational speed determined by the gear ratio of the gear train. The ON/OFF and rotational speed of the drive motor are controlled by the control unit 37.

The first transport screw 43 is rotated by a drive motor, and transports the two-component developer in the first supply section 40 from the rear side to the front side in FIG. 2 while supplying it to the developing roller 42. The two-component developer transported to the end of the first supply section 40 by the first transport screw 43 enters the second supply section 41 through an opening (not shown) provided in the partition wall 47.

In the second supply section 41, the second transport screw 44 is rotated by a drive motor and transports the two-component developer sent from the first supply section 40 in the opposite direction to the first transport screw 43. The two-component developer transported to the vicinity of the end of the second supply section 41 by the second transport screw 44 returns to the first supply section 40 through the other opening (not shown) provided in the partition wall 47.

The T sensor 46, which is a magnetic permeability sensor, is provided on the bottom wall near the center of the second supply section 41 and outputs a voltage value corresponding to the magnetic permeability of the two-component developer passing above it. Since the magnetic permeability of the two-component developer shows a certain degree of correlation with the toner concentration, the T sensor 46 outputs a voltage value corresponding to the toner concentration.

This output voltage value is sent to the control unit 37 in FIG. 5A, which will be described later. This control unit 37 has a RAM 71, which stores Vtref, which is the target value of the output voltage from the T sensor 46.

The controller also stores data on Vtref, which is the target value of the output voltage from a T sensor (not shown) mounted on another developing device. Vtref is used to control the drive of a toner transport device (not shown). Specifically, the controller controls the drive of a toner transport device (not shown) to replenish toner into the second supply unit 41 so that the value of the output voltage from the T sensor 46 approaches Vtref.

This replenishment maintains the toner concentration of the two-component developer in the developing device 39 within a specified range. Similar toner replenishment control is also performed for the developing devices of the other process cartridges.

● Fluctuation state of developer surface height on first shaft Figure 4 is a diagram showing the fluctuation state of the developer surface height (developer surface height on first shaft) in the first supply section 40 that houses the first transport screw 43 and the like, accompanying a change in process speed (standard speed ⇒ low speed). Three types of fluctuation states are shown, from the top of Figure 4, as dashed lines, solid lines, and dashed lines. The left end of Figure 4 (time 0) is the developer surface height (mm) at the moment (instant) when the process speed (paper passing speed) is changed from standard speed to low speed.

In all three graphs, the agent surface height temporarily drops after the process speed (paper feed speed) is changed (after about 10 seconds). The top two graphs (dash line, solid line) show a drop of about 1 mm, while the bottom graph (dashed line) shows a drop of about 1.5 mm.

When the developer surface height on one axis becomes low, a sufficient amount of developer is not drawn up to the developing roller, which can result in white spots in the image or uneven density on the pitch, resulting in abnormal images. Therefore, in this embodiment, when the paper passing speed is switched, a smoothing operation is performed until the developer surface height stabilizes before the image is output.

The developer replenishment operation is not performed during this leveling operation. This maintains the appropriate developer balance, eliminates the shortage of developer pumped up to the developing roller, and prevents the occurrence of abnormal images.

The leveling operation can be performed either before or after printing. This embodiment makes it possible to maintain an appropriate developer balance in developing devices that do not perform trickle development or that are capable of two or more paper passing speeds, and to eliminate a shortage of the amount of developer pumped up to the developing roller, thereby preventing the occurrence of abnormal images.

If the next rotation speed is undecided when performing the smoothing operation immediately after printing, the smoothing operation can be performed by provisionally setting the next rotation speed to the standard speed. Alternatively, it is also possible to refer to the records of past usage conditions accumulated in the controller of the image forming device 110, set the most likely (most frequently used) rotation speed as the next rotation speed, and perform the smoothing operation immediately after printing.

The following Table 1 shows the rotation time (smoothing time) depending on the linear speed difference in the first embodiment.

The time it takes for the one-axis developer surface height to stabilize is approximately 50 seconds in the three graphs in Figure 4, but it was found that this stabilization time differs depending on the previous print speed and the current print speed. Therefore, in this embodiment, we decided to change the mixing time (smoothing time) as shown in Table 1 depending on the difference between the previous and current rotation speeds. By changing the mixing time (smoothing time) in this way, it is possible to minimize the print wait time and also minimize the load on the developer caused by mixing.

As a result of experiments conducted by the inventor, it was found that the 1-axis developer surface height is affected not only by differences in rotation speed (process speed), but also by the installation environment of the developing device 39 or image forming device 110 and the number of pages printed (operating time, printing area), etc. In other words, the fluidity of the developer differs depending on the installation environment (temperature, humidity) and the number of pages printed, and this also affects the 1-axis developer surface height.

Specifically, when the toner concentration of the developer is low, when the charge amount of the toner T decreases in a high temperature and high humidity environment, or when the process linear speed is set fast and the rotation speeds of the developing roller 42, the first transport screw 43, and the second transport screw 44 are high, the bulk density of the developer becomes high and the developer surface height on one axis becomes low overall.

In contrast, when the toner concentration of the developer is high, when the toner charge is high in a low temperature and low humidity environment, or when the process linear speed is set slow and the rotation speeds of the developing roller 42, the first transport screw 43, and the second transport screw 44 are low, the developer becomes sparse with a low bulk density, and the single-axis developer surface height becomes high overall.

Therefore, a temperature sensor 96 and a humidity sensor 97 in FIG. 1B are provided to detect the temperature and humidity of the environment in which the developing device 39 is placed, an operating time recorder 93, a print area recorder 94, etc., and the driving time of the drive motor 38 of the developing device 39 is increased or decreased based on the detection results of the temperature sensor 96 and the humidity sensor 97 and the records of the recorders 93 and 94. By further correcting the mixing time (leveling time) in Table 1 based on the installation environment (temperature, humidity) and the number of printed sheets, etc., it is possible to further optimize the single-axis agent surface height.

Figure 5A is a block diagram of the developing device 39, the drive motor 38 that drives the developing device 39, and the control unit 37 that controls the drive motor 38. Figure 5B is a flow chart showing the control contents by the control unit 37 for executing the smoothing time of Table 1 described above.

As shown in FIG. 5B, in this embodiment, the mixing time (smoothing time), i.e., the drive motor drive time, is varied depending on the previous rotation speed (standard speed, medium speed, low speed) and the current rotation speed (standard speed, medium speed, low speed). In this way, the first and second shafts (first conveying screw 43 and second conveying screw 44) in FIG. 3 are rotated and driven with mixing times (smoothing times) that differ depending on the previous and current rotation speeds.

In this way, by rotating the first and second axes before printing (image creation) begins, the first axis agent surface height can be stabilized. This prevents the density of the toner image from decreasing or increasing in parts, resulting in poor image quality.

The present invention has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments, and it goes without saying that various modifications can be made within the scope of the technical ideas described in the claims. For example, in Table 1 and FIG. 5B, the rotation speed (process speed) is determined in three stages (standard speed, medium speed, low speed) to select the optimal smoothing time, but the rotation speed (process speed) may be determined in at least two stages (standard speed, low speed), or it may be determined in four or more stages to make it possible to select an even more optimal smoothing time.

<Additional Notes>
Preferred aspects of the present invention will be described below.
<Aspect 1>
A developing device which develops an electrostatic latent image formed on an image carrier with a developer, the developing device comprising: a screw member which stirs and transports the developer; a developing roller which supplies the developer stirred and transported by the screw member onto the image carrier; and a driving means which can rotate and drive the developing roller and the screw member at a plurality of predetermined rotation speeds, characterized in that before the electrostatic latent image is developed with the developer, the developing roller and the screw member are driven by the driving means for a predetermined time, and the length of the predetermined time is increased or decreased based on the difference between the predetermined rotation speed in a previous development and the predetermined rotation speed in a current development.
<Aspect 2>
A developing device which develops an electrostatic latent image formed on an image carrier with a developer, the developing device comprising: a screw member which stirs and transports the developer; a developing roller which supplies the developer stirred and transported by the screw member onto the image carrier; and a driving means which can rotate and drive the developing roller and the screw member at a plurality of predetermined rotation speeds, wherein after the electrostatic latent image is developed with the developer, the developing roller and the screw member are driven by the driving means for a predetermined time, and the length of the predetermined time is increased or decreased based on the difference between the predetermined rotation speed in the current development and the predetermined rotation speed in the next development.
<Aspect 3>
The developing device according to aspect 1 or 2, further comprising a thermo-hygrometer for detecting the temperature and humidity of an environment in which the developing device is installed, and the driving time of the driving means is corrected based on the detection result of the thermo-hygrometer.
<Aspect 4>
3. The developing device according to aspect 1 or 2, further comprising an operation time recording device for recording an operation time of the developing device, and the drive time of the drive means is corrected based on the record of the recorder.
<Aspect 5>
3. The developing device according to aspect 1 or 2, further comprising a printing area recorder for recording a printing area of the developing device, and the driving time of the driving means is corrected based on the record of the printing area recorder.
<Aspect 6>
A process cartridge or an image forming apparatus comprising: a latent image carrier; a latent image forming means for forming a latent image on the latent image carrier; and a developing device for developing the latent image on the latent image carrier with a developer containing a toner and a carrier, the toner image formed on the latent image carrier by the developing device being transferred to a recording material to form an image on the recording material, the process cartridge or the image forming apparatus being characterized in that the developing device of aspect 1 or 2 is used as the developing device.

1Y, 1M, 1C, 1K: toner image forming section 2: optical writing unit 3, 4: paper feed cassette 5: pair of registration rollers 6: transfer unit 7: fixing unit 8: paper discharge tray 11Y, 11M, 11C, 11K: photoconductor drum 37: control section 38: drive motor 39: developing device 40: first supply section 41: second supply section 42: developing roller 43: first transport screw (single shaft) 44: second transport screw (two shafts)
45: Regulating blade 46: T sensor 47: Partition wall 49: Two-component developer 60: Transfer transport belt 70: ROM
71: RAM 72: Printer control unit 73: Image reading control unit 74: Storage control unit 75: Input control unit 76: Output control unit 77: Bus 78: CPU
80: Storage (memory unit) 81: Input unit 82: Output unit 90: Printer unit 91: Scanner unit 92: Document transport unit 93: Operation time recording device 94: Print area recording device 95: Detection unit 96: Temperature sensor 97: Humidity sensor 100: Transfer paper 110: Image forming device A: Belt running direction B: First paper ejection direction C: Second paper ejection direction G: Switching guide MF: Manual feed tray S: Space T: Toner TC: Toner supply container

JP 2013-054106 A

Claims (6)

A developing device that develops an electrostatic latent image formed on an image carrier with a developer, comprising:
A screw member that agitates and transports the developer;
a developing roller that supplies the developer agitated and transported by the screw member onto the image carrier;
a driving means capable of rotating the developing roller and the screw member at a plurality of predetermined rotational speeds;
a developing device characterized in that, before developing the electrostatic latent image with a developer, the developing roller and the screw member are driven by the driving means for a predetermined time, and the length of the predetermined time is increased or decreased based on the difference between the predetermined number of rotations in the previous development and the predetermined number of rotations in the current development. A developing device that develops an electrostatic latent image formed on an image carrier with a developer, comprising:
A screw member that agitates and transports the developer;
a developing roller that supplies the developer agitated and transported by the screw member onto the image carrier;
a driving means capable of rotating the developing roller and the screw member at a plurality of predetermined rotational speeds;
a developing device characterized in that, after the electrostatic latent image is developed with a developer, the developing roller and the screw member are driven by the driving means for a predetermined time, and the length of the predetermined time is increased or decreased based on the difference between the predetermined number of rotations in the current development and the predetermined number of rotations in the next development. The developing device according to claim 1 or 2, further comprising a thermo-hygrometer for detecting the temperature and humidity of the environment in which the developing device is installed, and the driving time of the driving means is corrected based on the detection result of the thermo-hygrometer. The developing device according to claim 1 or 2, further comprising an operating time recording device for recording the operating time of the developing device, and the operating time of the driving means is corrected based on the records of the recording device. The developing device according to claim 1 or 2, further comprising a printing area recording device for recording the printing area of the developing device, and the driving time of the driving means is corrected based on the records of the printing area recording device. A process cartridge or an image forming apparatus comprising: a latent image carrier; a latent image forming means for forming a latent image on the latent image carrier; and a developing device for developing the latent image on the latent image carrier with a developer containing a toner and a carrier, the toner image formed on the latent image carrier by the developing device being transferred to a recording material, thereby forming an image on the recording material,
3. A process cartridge or an image forming apparatus, comprising the developing device according to claim 1 or 2 as said developing device.

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