JP2006193350A - Optical fiber drawing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber drawing method which can arrive at a target linear velocity stably in a short period of time. <P>SOLUTION: An optical fiber preform is fed into a heating furnace, and an optical fiber is drawn while controlling the feeding velocity Vf(t) of the optical fiber preform. A first subtracter 31 inputs a practical linear velocity v(t) and a practical linear velocity v(t-dt) before a certain time dt, and searches the difference between the velocities and the variation Δvdt in the practical linear velocity. A second subtracter 32 searches the difference between the variation Δvdt in the practical linear velocity and the target value Δvdta of the variation in the linear velocity. ΔVf1 is searched by inputting the difference (Δvdta-Δvdt) and the control gain G in a multiplier 33. The control gain G is set based on the absolute value of the difference between the target value Δvdta of the variation in the linear velocity and the variation Δvdt in the practical linear velocity. An adder 34 adds ΔVf1 to the set feeding velocity Vfset of the optical fiber preform 12, and outputs the result as the feeding velocity Vf(t)of the optical fiber preform 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber drawing method for producing an optical fiber by heating an optical fiber preform.

  In the process of manufacturing an optical fiber by drawing an optical fiber preform, the drawing speed of the optical fiber (hereinafter, “drawing speed” is also referred to as “drawing speed”) is gradually increased to the set drawing speed. And draw at a fixed line speed. In general, since the quality of the optical fiber is not ensured while the linear velocity is increasing, the portion of the optical fiber manufactured after the optical fiber reaches the set linear velocity and stabilizes is used as a non-defective product.

  In order to reduce the amount of defective parts generated, it is required to stabilize the optical fiber by reaching the set linear velocity as early as possible. Based on this requirement, an optical fiber drawing method is disclosed in which the drawing speed is stably increased to a desired setting drawing speed in a short time (see, for example, Patent Document 1).

According to Patent Document 1, the amount of change in the optical fiber linear velocity per set time is set, and the optical fiber mother drawn is based on the difference between the set change amount and the actual change in the linear velocity. The feed rate of the material to the furnace is controlled.
Specifically, ΔVf1 ′ is calculated as a value obtained by multiplying the difference between the set change amount Δvdtset ′ per linear time and the actual change amount Δvdt ′ by Vfg ′ (control gain). A calculation formula of ΔVf1 ′ is expressed by the following formula (A).
ΔVf1 ′ = Vfg ′ · {Δvdtset′−Δvdt ′} (A)
Based on this ΔVf1 ′, an optical fiber preform supply speed Vf (t) ′ is obtained, and the optical fiber preform supply speed is controlled. By controlling the supply speed of the base material in this way, it is possible to stably reach the set linear speed without causing a linear speed overshoot.
JP 2001-31441 A

  Incidentally, when the base material supply speed is controlled by the control method disclosed in Patent Document 1, in the low linear velocity region where the difference between the actual change amount Δvdt ′ and the set change amount Δvdtset ′ is large, the base material supply speed Vf. There is a problem that (t) 'is insufficient and the increase in linear velocity is delayed. If the increase in the linear velocity is delayed, as a result, it takes a long time to reach the set linear velocity.

  On the other hand, if the control gain Vfg ′ is set to a large value, the base material supply speed Vf (t) ′ in the low linear velocity region can be improved. However, if the control gain Vfg ′ is set to a large value, the actual change amount is increased. When the difference between Δvdt ′ and the set change amount Δvdtset ′ is small, the operation amount becomes large, and it becomes difficult to stabilize the actual change amount Δvdt ′ to the set change amount Δvdtset ′.

  As a countermeasure, it is possible to resolve the shortage of the base material supply speed in the low linear speed range by forcing the worker to increase the base material supply speed immediately after the start of the increase in the linear speed. The amount of increase in the line speed varies, making it difficult to stably reach the set line speed.

  An object of the present invention is to provide an optical fiber drawing method capable of stably reaching a target drawing speed in a short time.

In order to achieve the above-mentioned object, an optical fiber drawing method according to the present invention supplies an optical fiber preform to a heating furnace, and controls the optical fiber preform supply speed Vf (t) while controlling the optical fiber preform supply speed Vf (t). An optical fiber drawing method for drawing
A coefficient G set for control (hereinafter referred to as a control gain G) when the supply speed Vf (t) is calculated by the following formula from the start of drawing to the set linear speed vset in a steady state. Is expressed as | Δvdta− based on the absolute value | Δvdta−Δvdt | of the difference between the target value Δvdta of the drawing speed change of the optical fiber and the actual change Δvdt of the drawing speed of the optical fiber. It is characterized in that a large value is set in a region where Δvdt | is large and a small value is set in a region where | Δvdta−Δvdt | is small.
Vf (t) = Vfset + G · (Δvdta−Δvdt)
[Vfset represents the set supply speed of the optical fiber preform determined based on the set linear velocity vset, the outer diameter of the optical fiber preform, and the drawn outer diameter of the optical fiber. ]

  In the optical fiber drawing method configured as described above, when calculating the supply speed Vf (t) of the optical fiber preform, the control gain G is set to the target value Δvdta of the linear speed change amount and the actual linear speed change amount Δvdt. Since the control gain G is set to a large value in a region where the absolute value | Δvdta−Δvdt | of the difference between the two is large, and the control gain G is set to a small value in a region where | Δvdta−Δvdt | The linear velocity can be effectively increased in the low speed region where the difference between the value Δvdta and the actual linear velocity change amount Δvdt is large, and the arrival time to the set linear velocity can be shortened.

  The optical fiber drawing method according to the present invention is such that when the drawing speed v (t) of the optical fiber reaches a predetermined speed smaller than the set drawing speed vset in the steady state, the subsequent control gain G is kept constant. It is desirable to set it to a value.

  In the optical fiber drawing method configured as described above, the control gain G is set to a constant value when the drawing speed v (t) approaches the set drawing speed vset in the steady state, thereby preventing hunting due to disturbance. , Can reach the set linear speed stably.

  According to the drawing method of the present invention, when calculating the supply speed of the optical fiber preform, the control gain G for calculating the supply speed is obtained by setting the target value Δvdta of the linear speed change amount and the actual linear speed change amount Δvdt. Based on the absolute value of the difference | Δvdta−Δvdt |, the linear velocity can be quickly increased particularly in the low linear velocity region by setting the large value in the region where ΔΔvdta−Δvdt | is large and the small value in the small region. The target linear velocity can be stably reached in a short time. Therefore, it is possible to reduce the discarded portion of the optical fiber until the drawing speed reaches the set drawing speed, and it is possible to improve productivity.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram showing an example of an optical fiber drawing apparatus that can suitably implement the optical fiber drawing method according to the present embodiment. An optical fiber drawing apparatus 10 shown in FIG. 1 includes a heating furnace 13 that heats and melts an optical fiber preform 12 and a preform supply apparatus 11 that supplies the optical fiber preform 12 to the heating furnace 13. An outer diameter measuring device 15, a cooling device 17, a die 18, a curing furnace 19, and a capstan 16 are provided along the path through which the optical fiber 14 passes.

  The base material supply device 11 includes a motor 23 that can vary the supply speed of the optical fiber base material 12 to the heating furnace 13. The motor 23 is driven based on an electrical signal from the driver 22, and the driver 22 outputs an electrical signal to be sent to the motor 23 according to an instruction from the calculation unit 24. The calculation unit 24 can calculate the speed (supply speed Vf (t)) at which the optical fiber preform 12 should be supplied based on the outer diameter of the optical fiber 14, the actual linear speed, and the like. The arithmetic unit 24 may be a circuit including an adder, a subtracter, and a multiplier. The actual linear speed is obtained from the rotational speed of the capstan 16, for example.

  In order to draw an optical fiber by using this optical fiber drawing device 10, while supplying the optical fiber preform 12 to the heating furnace 13, the vicinity of the lower end of the optical fiber preform 12 is heated and melted to heat and melt the light. The optical fiber 14 is formed by reducing the diameter of the fiber preform 12 by pulling it with a capstan 16.

  After measuring the outer diameter of the optical fiber 14 melted by the heating furnace 13 with the outer diameter measuring device 15, the optical fiber 14 is cooled in the cooling device 17, and the coating resin liquid is poured around the optical fiber 14 by the die 18. Apply. The coating resin liquid is cured by a curing furnace 19 to form an optical fiber strand 20 having a coating resin layer, and the optical fiber strand 20 is wound up by a winder 21.

  The measured value of the outer diameter measured by the outer diameter measuring device 15 is fed back to the capstan 16 and the rotational speed of the capstan 16 is adjusted so that the outer diameter becomes constant. Further, the rotation speed of the capstan 16 is sent to the calculation unit 24, the actual linear velocity of the optical fiber 14 is calculated by the calculation unit 24, and the supply speed Vf (t) is calculated to heat the optical fiber preform 12. The supply speed when supplying to the furnace 13 is controlled.

  Hereinafter, a calculation process of the supply speed Vf (t) (particularly, the supply speed Vf (t) from the start of pulling until reaching the set linear speed vset in the steady state) and a method for controlling the supply speed of the optical fiber preform 12 will be described. explain. The supply speed Vf (t) of the optical fiber preform 12 described below is obtained by the calculation unit 24.

The supply speed Vf (t) is obtained by adding G · (Δvdta−Δvdt) (= ΔVft) to the set supply speed Vfset. That is, the supply speed Vf (t) is obtained by the following formula (1).
Vf (t) = Vfset + G · (Δvdta−Δvdt) (1)
[Δvdta represents the amount of change in the drawing speed of the optical fiber, and Δvdt represents the amount of change in the actual drawing speed of the optical fiber. ]

In equation (1), the set supply speed Vfset is a value determined based on the set linear velocity of the optical fiber 14 in a steady state, the outer diameter of the optical fiber preform 12, and the drawn outer diameter of the optical fiber 14. It can obtain | require by following formula (2).
Vfset = vset · d ² / D ² (2)
[Vset is the set linear velocity of the optical fiber 14 in a steady state, d is the outer diameter of the optical fiber 14, and D is the outer diameter of the optical fiber preform 12. ]

On the other hand, with respect to G · (Δvdta−Δvdt) in Expression (1), the actual linear velocity change amount Δvdt is defined as v (t) where the actual linear velocity of the optical fiber 14 at a certain time t is v (t). Assuming v (t-dt), it can be obtained from the following equation (3).
Δvdt = v (t) −v (t-dt) (3)
For example, when the current linear velocity is 300 m / min and the linear velocity 10 seconds before is 290 m / min, Δv10 is 10 m / min / 10 sec.

  Further, the target value Δvdta of the linear velocity change amount may be a constant value or a variable value, and can be arbitrarily set. However, the set linear velocity vset and the actual linear velocity v (t) in the steady state are It is preferable to change in proportion to the linear velocity difference. That is, as shown in FIG. 2, the target value Δvdta of the linear velocity change amount is taken on the vertical axis, and the linear velocity difference (vset−v (t)) between the set linear velocity vset and the actual linear velocity v (t) in the steady state. ) On the horizontal axis, the target value Δvdta of the linear velocity change amount is represented by a graph that passes through the origin and is proportional to the linear velocity difference. In this way, the fluctuation of the linear velocity can be prevented by changing the target value Δvdta of the linear velocity variation in proportion to the linear velocity difference.

  As shown in FIG. 2, when the absolute value of the linear velocity difference between the set linear velocity vset and the actual linear velocity v (t) is equal to or smaller than a predetermined value (for example, | vset−v (t) | ≦ 0.2vset) ) Change the linear velocity change target value Δvdta in proportion to the linear velocity difference, and in other ranges the linear velocity variation target value Δvdta is a constant value (for example, Δvset = 10 m / min / 10 sec). -10 m / min / 10 sec).

  Further, for the control gain G, | Δvdta−Δvdt | is based on the absolute value | Δvdta−Δvdt | (= Δa) of the difference between the target value Δvdta of the linear velocity change amount and the actual linear velocity change amount Δvdt. A large value is set in a large region, and a small value is set in a region where | Δvdta−Δvdt | is small. An example of the setting of the control gain G is shown in the graph of FIG. In the graph shown in FIG. 3, the vertical axis represents the control gain G, and the horizontal axis represents Δa.

  As shown in FIG. 3, the control gain G is represented by a function f (Δa) of Δa. The function f (Δa) is expressed by a straight line f (Δa) = p · Δa + q passing through the point (K1, A1) and the point (K2, A2) when Δa is K1 to K2 (provided that K1, K2 The minimum gain value A1 and the maximum gain value A2 are arbitrary constants, and K2> K1 and A2> A1.)

  The control gain G changes linearly in proportion to Δa when Δa is between K1 and K2. Then, when Δa is large, the control gain G is large and the multiplication (G · Δa) is also large, so that ΔVf1 can be increased. On the other hand, when Δa is small, the control gain G is small, so ΔVf1 is small. In this way, the control gain G is set to an appropriate value according to Δa.

When Δa is equal to or smaller than K1, the gain is kept at the minimum value A1, and when Δa is larger than K2, the gain is maintained at the maximum value A2. This is in consideration of the limit on the capability of the drawing apparatus 10.
As K1, K2, A1, and A2, for example, K1 = 5000, K2 = 10000, A1 = 30, and A2 = 50 can be set.

When the actual linear velocity v (t) of the optical fiber 14 gradually increases and approaches the set linear velocity vset, it is desirable to set the subsequent control gain G to a constant value G0. . By making the control gain G constant in this way, it is possible to prevent hunting when approaching the set linear velocity vset.
As the constant value G0, for example, A1 that is the minimum gain value of the function f (Δa) in FIG. 3 can be employed. Moreover, the predetermined speed which makes a control gain a fixed value can be set, for example in the range of 0.6vset-0.9vset.

  When the linear velocity change amount target value Δvdta and the control gain G are set as described above, ΔVf1 = G · (Δvdta−Δvdt) <0 in the region where Δvdta−Δvdt <0 (A region in FIG. 2). In the region where Δvdta−Δvdt> 0 (B region in FIG. 2), ΔVf1 = G · (Δvdta−Δvdt)> 0, and the optical fiber preform is pushed in. Will be controlled.

From the above formulas (1) to (3), the calculation unit 24 in FIG. 1 obtains the supply speed Vf (t) of the optical fiber preform 12, and the driver 22 determines the motor 23 based on the supply speed Vf (t). The optical fiber preform 12 is rotated and supplied at a supply speed Vf (t).
A circuit block when the arithmetic unit 24 is configured by a circuit will be described. FIG. 4 is a circuit block diagram illustrating an example of an arithmetic circuit that calculates the supply speed Vf (t) of the optical fiber preform 12.

  As shown in FIG. 4, the first subtracter 31 inputs the actual linear velocity v (t) at a certain time t of the optical fiber 14 and the actual linear velocity v (t−dt) before the predetermined time dt. Then, these differences are obtained, and the actual linear velocity change amount Δvdt expressed by the above equation (3) is obtained. The second subtracter 32 inputs the actual linear velocity change amount Δvdt obtained by the first subtractor 31 and the target value Δvdta of the linear velocity variation amount, and obtains a difference between these (Δvdta−Δvdt).

  The control gain G is set by substituting the absolute value Δa = | Δvdta−Δvdt | of (Δvdta−Δvdt) into the function f (Δa) shown in FIG. This control gain G and the difference (Δvdta−Δvdt) between the target value Δvdta of the linear velocity change amount and the actual linear velocity change amount Δvdt are input to the multiplier 33, and (Δvdta−Δvdt) is multiplied by the control gain G. Thus, ΔVf1 = G · (Δvdta−Δvdt) in the above equation (1) is output. Until the actual linear velocity v (t) becomes a predetermined velocity (for example, 0.8 vset), Δa is substituted into the function f (Δa), the control gain G is set according to Δa, and the actual linear velocity v (t) is When a predetermined speed (for example, 0.8 vset) is reached, the control gain G is set to a constant value A1.

  The adder 34 adds ΔVf1 to the set supply speed Vfset of the optical fiber preform 12 expressed by the above formula (2), and outputs the result as the supply speed Vf (t) of the optical fiber preform 12. .

  Changes in the linear speed and the base material supply speed when the linear speed is increased when the base material supply speed is controlled as described above will be described with reference to the graph shown in FIG. In FIG. 5A, the solid line graph shows changes in the linear velocity when the control gain G is set as shown in FIG. 3, and the dotted line graph is an ideal in which the linear velocity increases linearly. The linear speed (target linear speed) is shown. FIG. 5B shows a change in the base material supply speed.

As shown in FIGS. 5A and 5B, until the time t = T ₀ , the actual linear velocity of the optical fiber 14 is the low linear velocity v ₀ at the time of extraction, and the optical fiber preform 12 is supplied. The speed is the corresponding speed V _f0 . During this time, the calculation unit 24 does not perform the above calculation. After time t = T ₀ , in order to increase the drawing speed of the optical fiber 14 to the set drawing speed vset, the calculation unit 24 changes the control gain G according to Δa = | Δvdta−Δvdt | Calculate the speed.

Immediately after time t = T ₀ , Δa becomes very large. For this reason, the control gain G is set to a large value (see FIG. 3), the base material supply speed Vf (t) becomes a large value, and the linear speed temporarily rises. When the linear velocity increases, Δa decreases, the control gain G is set to a small value (see FIG. 3), and the base material supply speed Vf (t) decreases rapidly. When the base material supply speed Vf (t) decreases, the linear velocity decreases again, so that Δa and the control gain G become large again, and the linear velocity rapidly increases. By repeating such linear speed hunting several times, the target linear speed can be quickly approached. In addition, since the optical fiber manufactured at this low line speed is usually discarded, there is no problem even if the line speed is hunting.

In this way, hunting is repeated to gradually increase the linear velocity. When the linear velocity reaches, for example, 0.8 vset, the control gain G is thereafter set to a constant value A1 to control the supply velocity. By setting the control gain G in this way, it is possible to prevent hunting in the vicinity of the set linear velocity vset, and therefore it is possible to reach the set linear velocity vset more reliably in a short time.
Furthermore, when the drawing speed reaches the set drawing speed, the operator switches the control of the optical fiber preform supply speed to the PID control based on the following formula (4) and performs drawing.
Vft = Vfset + α (4)
[Α indicates the amount adjusted by PID control. ]

  As described above, in the optical fiber drawing method according to the embodiment of the present invention, the linear velocity is effectively increased in a low speed region where the difference between the target value Δvdta of the linear velocity change amount and the actual linear velocity change amount Δvdt is large. Therefore, the time required for the drawing speed of the optical fiber to reach the set drawing speed can be shortened. Therefore, the generation amount of defective portions of the optical fiber is reduced, and productivity can be improved.

The optical fiber drawing method of the present invention is not limited to the embodiment described above, and appropriate modifications and improvements can be made.
For example, in the above-described embodiment, the shape shown in FIG. 3 is used as a function of the control gain G, but the present invention is not limited to this. In addition, the linearly proportional portion in FIG. 3 can be changed stepwise, or can be changed to other curved shapes.

Next, the results of experiments using the optical fiber drawing method according to the above embodiment will be described.
The common conditions in these experiments are as follows. An optical fiber preform having an outer diameter of 90 mmφ was used, and an optical fiber having an outer diameter of 125 μmφ was drawn from the optical fiber preform. The drawing speed of the optical fiber is 30 m / min (the supply speed of the optical fiber preform is 0.0579 mm / min for the corresponding opening), and the setting speed of the optical fiber is 1000 m / min (corresponding optical fiber preform). The set supply speed of the material was 1.93 mm / min.

Example 1
In the first embodiment, the control gain G is set at f (Δa) shown in FIG. K1 = 5000, K2 = 10000, A1 = 30, and A2 = 50.
The sampling time was 10 seconds, and the target value Δvdta of the linear velocity change amount and the actual linear velocity change amount Δvdt were measured every 10 seconds.

  For the target value Δvdta of the linear velocity change amount, as shown in FIG. 2, when the absolute value of the linear velocity difference (vset−v (t)) between the set linear velocity and the actual linear velocity is equal to or smaller than a predetermined value, While the actual linear speed is between 80 and 120% of the set linear speed, the target value Δvdta of the linear speed change amount is changed in proportion to vset−v (t), and the actual linear speed is smaller than 80% of the set linear speed. In this case, and when the actual linear speed is greater than 120% of the set linear speed, the target value Δvdta of the linear speed change amount is set to a constant value of 60 m / min and −60 m / min, respectively. Using the above numerical values, the optical fiber preform was controlled from time 0 to draw the optical fiber.

(Comparative Example 1)
In Comparative Example 1, the control gain G ′ was set to a constant value (5000), and the others were drawn under the same conditions as in Example 1.
(Comparative Example 2)
In Comparative Example 1, until the time t = 3, the operator maximized the supply speed, and then the optical fiber was drawn under the same conditions as in Comparative Example 1.

The results of experiments conducted under the above conditions are shown in FIGS.
FIG. 6 shows a graph of the drawing speed and the base material supply speed when drawing is performed under the conditions of the first embodiment. As shown in FIG. 6, the linear velocity increased while repeating hunting, and the time required to reach the set linear velocity (1000 m / min) was 20 minutes.

  FIG. 7 shows a graph of the drawing speed and the base material supply speed when drawing is performed under the conditions of Comparative Example 1. As shown in FIG. 7, the linear velocity increased stably, but the linear velocity increase in the low linear velocity region (region a surrounded by a two-dot chain line) was slow, so it was necessary to reach the set linear velocity. The time took 25 minutes.

FIG. 8 shows a graph of the drawing speed and the base material supply speed when drawing is performed under the conditions of Comparative Example 2. As shown in FIG. 8, because the operator controlled the base material supply speed to maximize the linear velocity, the linear velocity was rapidly increased in the low linear velocity region (region b surrounded by a two-dot chain line). The time required to reach the speed was 20 minutes, the same as in Example 1. However, when the drawing of the optical fiber was repeated several times, the time required to reach the set linear velocity was varied.
From the above results, in Example 1 in which the drawing method according to the present invention was implemented, the time required for the drawing speed of the optical fiber to reach the set drawing speed was shortened compared to the drawing method according to the prior art. I understand that I can do it.

It is a block diagram which shows an example of the optical fiber drawing apparatus for practicing the optical fiber drawing method which concerns on embodiment of this invention. It is a graph which shows the target drawing acceleration of the optical fiber drawing method which concerns on embodiment of this invention. 4 is a graph showing an example of setting of a control gain G. It is a block diagram which shows the arithmetic circuit as a calculating part. (A) is a graph which shows an example of the actual drawing speed v (t) when the supply speed of the optical fiber preform is controlled using the control gain G shown in FIG. 3, and (B) is the preform supply. It is a graph which shows the change of speed Vft. (A) is a graph which shows the change of the linear velocity in Example 1, (B) is a graph which shows the change of a base material supply speed. (A) is a graph which shows the change of the linear velocity in the comparative example 1, (B) is a graph which shows the change of a base material supply speed. (A) is a graph which shows the change of the linear velocity in the comparative example 2, (B) is a graph which shows the change of a base material supply speed.

Explanation of symbols

12 Optical fiber preform 13 Heating furnace 14 Optical fiber D Optical fiber preform outer diameter d Optical fiber outer diameter G Control gain Vf (t) Optical fiber preform supply speed Vfset Optical fiber preform set supply speed vset Optical fiber preform Setting line drawing speed (setting line speed)
Δvdta Target value of linear speed change Δvdt Actual linear speed change

Claims (2)

An optical fiber drawing method for drawing an optical fiber while supplying an optical fiber preform to a heating furnace and controlling a supply speed Vf (t) of the optical fiber preform.
A coefficient G set for control (hereinafter referred to as a control gain G) when the supply speed Vf (t) is calculated by the following formula from the start of drawing to the set linear speed vset in a steady state. Is expressed as | Δvdta− based on the absolute value | Δvdta−Δvdt | of the difference between the target value Δvdta of the drawing speed change of the optical fiber and the actual change Δvdt of the drawing speed of the optical fiber. An optical fiber drawing method, wherein a large value is set in a region where Δvdt | is large and a small value is set in a region where | Δvdta−Δvdt | is small.
Vf (t) = Vfset + G · (Δvdta−Δvdt)
[Vfset represents the set supply speed of the optical fiber preform determined based on the set linear velocity vset, the outer diameter of the optical fiber preform, and the drawn outer diameter of the optical fiber. ] 2. The subsequent control gain G is set to a constant value when the drawing speed v (t) of the optical fiber reaches a predetermined speed smaller than a set linear speed vset in the steady state. The optical fiber drawing method described.

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