Method for manufacturing optical fiber

Abstract

The method for manufacturing an optical fiber includes: a drawing step of drawing while heating and softening an optical fiber base material to manufacture an optical fiber as a part of a product; and a wiredrawing completion determination step for determining the wiredrawing completion of the optical fiber to be a product in the optical fiber base material on the basis of whether or not a predetermined condition is satisfied, in which the wire speed is controlled while the target value of the wiredrawing wire speed of the optical fiber is constant, and in which the wiredrawing completion determination step is performed while the target value of the wiredrawing wire speed of the optical fiber is controlled while the target value of the wiredrawing wire speed is constant. When the wire speed is reduced by a predetermined amount from the target value, it is determined that the drawing of the optical fiber is completed.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical fiber.

[0002] This application claims the benefit of priority based on Japanese Application No. 2022-058765 filed on March 31, 2022, and all the contents described in the above Japanese Application are incorporated herein by reference. Background Art

[0003] Conventionally, optical fibers are produced by heating and softening an optical fiber base material and drawing the base material. The optical fiber base material is composed of an effective portion that can be used as a product and an ineffective portion at the end of the effective portion. Patent document 1 below discloses a method in which, when heating and softening an optical fiber base material and drawing the optical fiber, it is determined that the optical fiber base material has reached the ineffective portion based on a sudden change in the line speed of drawing the optical fiber.

[0004] In Patent Document 1, when drawing an optical fiber while maintaining a constant line speed, the line speed decreases, and then increases sharply due to reaction. The sharp increase in line speed is detected, and it is determined that the optical fiber base material has reached the ineffective portion, and the drawing of the optical fiber is terminated.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-13328 Summary of the invention

[0006] The optical fiber manufacturing method of the present invention comprises: a drawing step, in which an optical fiber base material is heated to soften it and is simultaneously drawn to manufacture the optical fiber that becomes a product; and a drawing completion judgment step, in which the drawing completion of the optical fiber that becomes a product in the optical fiber base material is judged by whether specified conditions are met. In the drawing step, a target value of the drawing line speed of the optical fiber is set constant and the line speed is controlled. In the drawing completion judgment step, when the line speed decreases by a specified amount from the target value, it is judged that the drawing of the optical fiber is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic structural diagram of an optical fiber manufacturing apparatus capable of carrying out the optical fiber manufacturing method involved in one embodiment of the present invention.

[0008] Figure 2 yes Figure 1 A block diagram of a control device for an optical fiber manufacturing device.

[0009] Figure 3 This is a schematic diagram of the base material for optical fiber.

[0010] Figure 4 It is a graph of the line speed of optical fiber drawing. DETAILED DESCRIPTION

[0011] [Problems to be Solved by the Invention]

[0012] Sometimes, due to the difference in glass viscosity at the junction of the effective core glass and the ineffective core glass of the optical fiber base material, the melting state of the optical fiber base material changes, the glass melting progresses rapidly, and the optical fiber drawing speed increases rapidly. As described above, when the glass melting progresses rapidly, according to the method described in Patent Document 1, it is determined that the optical fiber base material has reached the ineffective part by the rapid increase in line speed, so that the line speed continues to increase rapidly at the end of the optical fiber drawing, which may become a problem.

[0013] An object of the present invention is to provide a method for manufacturing an optical fiber, which can quickly determine the switching from the effective part to the ineffective part of the optical fiber base material and prevent the line speed from increasing sharply and continuously when the optical fiber drawing is completed.

[0014] [Effects of the Invention]

[0015] According to the present invention, it is possible to quickly determine whether the effective portion of the optical fiber preform is switched to the ineffective portion, and it is possible to prevent the line speed from continuing to increase rapidly even when the drawing of the optical fiber is completed.

[0016] [Description of Embodiments of the Invention]

[0017] First, the contents of the embodiments of the present invention will be listed and described.

[0018] The present invention achieves the following effects by the configurations (1) to (5).

[0019] (1) A method for manufacturing an optical fiber, comprising: a drawing step, in which an optical fiber base material is heated to soften it and then drawn to manufacture a portion of the optical fiber that will become a product; and a drawing completion judgment step, in which the drawing of the optical fiber that will become a product in the optical fiber base material is judged to be completed by determining whether a specified condition is satisfied. In the drawing step, a target value of the drawing line speed of the optical fiber is set constant and the line speed is controlled. In the drawing completion judgment step, when the line speed decreases by a specified amount from the target value, it is determined that the drawing of the optical fiber has been completed.

[0020] According to the optical fiber manufacturing method configured as described above, it is possible to quickly determine the switching from the effective portion to the ineffective portion of the optical fiber preform, and prevent the line speed from continuing to increase sharply even when the optical fiber drawing is completed.

[0021] (2) In the above-mentioned method for manufacturing an optical fiber, the optical fiber base material includes an effective portion and an ineffective portion, wherein the effective portion is a central portion in the length direction and has a core, and the ineffective portion is an end portion in the length direction and does not have a core. In the drawing completion judgment step, the remaining length of the effective portion of the optical fiber base material is also considered to determine the drawing completion of the optical fiber.

[0022] As a result, the situation of switching from the effective part to the ineffective part of the optical fiber base material can be judged more reliably, so that the optical fiber can be drawn at a stable line speed at the end of drawing, and the timing of switching from the effective part to the ineffective part of the optical fiber base material can be grasped more accurately regardless of the influence of noise, etc., so the effective core glass of the optical fiber base material can be used up without waste.

[0023] (3) In the above-mentioned optical fiber manufacturing method, in the above-mentioned drawing completion judgment step, the conditions for judging the completion of optical fiber drawing are determined based on the linear speed reduction of the optical fiber base material drawn in the past and the inspection results of the optical fiber obtained from the optical fiber base material.

[0024] Thus, the conditions for judging the end of drawing can be set based on the inspection results of the optical fiber obtained through past drawing, so that accurate judgment on the end of drawing can be made corresponding to the specifications of the optical fiber manufacturing device used, the specifications of the optical fiber, various manufacturing conditions, etc.

[0025] (4) In the above-mentioned method for manufacturing optical fiber, in the drawing process, at least any one of the feed rate of the optical fiber base material, the output of the heating element of the heating furnace for heating the optical fiber base material, the speed of the capstan or the speed of the winding spool is controlled, thereby setting the target value of the optical fiber drawing line speed to be constant and controlling the line speed.

[0026] Thus, the line speed of the optical fiber drawn from the effective portion of the optical fiber preform follows a constant target value and becomes stable, so that a decrease in the line speed at the end of drawing can be reliably detected, and the end of drawing can be determined more accurately.

[0027] (5) In the above-mentioned optical fiber manufacturing method, the predetermined reduction amount of the line speed for determining the completion of optical fiber drawing in the drawing completion determination step is set to between 0.5% and 3% of the target value.

[0028] Thus, the range of setting the prescribed reduction amount of the line speed for determining the end of optical fiber drawing relative to the constant target value of the line speed of the optical fiber drawing at the effective part of the optical fiber base material can be determined, and the condition setting for determining the end of drawing can be appropriately performed. In addition, by setting the upper limit and lower limit of the prescribed reduction amount of the line speed for determining the end of optical fiber drawing relative to the constant target value of the line speed of the optical fiber drawing at the effective part of the optical fiber base material, it is possible to prevent erroneous setting when setting the condition for determining the end of drawing.

[0029] [Details of the embodiments of the present invention]

[0030] Next, a specific example of the method for producing an optical fiber according to the present invention will be described.

[0031] In the following description, structures denoted by the same reference numerals in different drawings are also assumed to be the same structures, and the description thereof may be omitted.

[0032] It should be noted that the present invention is not limited to these examples but is shown by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0033] [Implementation Method 1]

[0034] use Figures 1 to 4 The optical fiber manufacturing method according to the first embodiment of the present invention will be described. First, an optical fiber manufacturing device 10 capable of performing the optical fiber manufacturing method according to the present embodiment will be described. Figure 1 Provide explanation. Figure 1 It is a schematic structural diagram of an optical fiber manufacturing apparatus 10 capable of carrying out the optical fiber manufacturing method.

[0035] like Figure 1 As shown, the optical fiber manufacturing device 10 has: a longitudinal heating furnace 13, which heats the optical fiber base material G; a feeding device 11, which feeds the optical fiber base material G to the heating furnace 13; a base material feeding detector 12, which measures the feeding amount of the optical fiber base material G; a cooling device 19, which cools the glass fiber G1 after drawing; an outer diameter measuring device 20, which measures the outer diameter of the glass fiber G1; a female mold 21, which coats the periphery of the glass fiber G1 with an ultraviolet curing resin; an ultraviolet irradiation device 24, which cures the ultraviolet curing resin applied to the optical fiber G2 coated by the female mold 21; a tension meter 31, which measures the tension of the coated optical fiber G2; a capstan 40, which picks up the optical fiber G2 via a guide roller 30; a first winding bobbin 36 and a second winding bobbin 37, which wind the optical fiber G2 picked up by the capstan 40 via a tension adjustment roller 34; and a control device 50.

[0036] like Figure 2As shown in FIG. 1 , the control device 50 controls the control devices 52 and 53 of the optical fiber manufacturing device 10 based on the detection signals from the detectors 51 of each part, thereby adjusting each manufacturing process of the optical fiber manufacturing device 10 for manufacturing the optical fiber G2 of the target specification, and controlling so that the line speed of the optical fiber G2 becomes the target value. In addition, as described later, the control device 50 has a drawing end determination unit 71 for determining the prescribed drawing end condition of the optical fiber G2. In addition, the target specification of the optical fiber G2 to be manufactured is set by the target specification setting unit (not shown) of the control device 50.

[0037] The heating furnace 13 has: a cylindrical furnace core tube 16, into which the optical fiber base material G is supplied; and a heating element 15, which heats the furnace core tube 16. The furnace core tube 16 is heated by the heating element 15, and a heating space is formed in the space inside the furnace core tube 16. The heating space is a space where the glass of the optical fiber base material G is softened to a temperature that allows drawing. The heating space is not particularly limited, but the output of the heating element 15 is controlled in accordance with the control command from the control device 50, thereby adjusting it to a specified value of 1800°C or more, for example. In addition, a gas supply unit 14 is provided in the heating furnace 13, and the gas supply unit 14 controls the supply amount of a purge gas such as helium or nitrogen to the heating space in accordance with the control command from the control device 50.

[0038] The feeding device 11 feeds the upper portion of the optical fiber base material G, that is, Figure 3 The end portion of the Lc side of the optical fiber base material G is gripped, and the feeding amount of the optical fiber base material G into the heating furnace 13 is controlled in accordance with the control command from the control device 50 so that the lower end portion of the optical fiber base material G, i.e. Figure 3 The end side portion on the La side is located in the heating space inside the furnace core tube 16. The glass heated and melted in the heating space is pulled out from the lower end of the heating furnace 13 as a thin glass fiber G1. The feed device 11 is provided with a base material feed detector 12, which is used to measure the feed amount of the optical fiber base material G, the remaining amount of the optical fiber base material G, etc. In addition, the heating furnace 13 is provided with a temperature detector 17, which is used to measure the temperature of the heating area in the furnace core tube 16. The measured value of the feed amount of the optical fiber base material G obtained by the base material feed detector 12 and the measured value of the temperature of the heating area obtained by the temperature detector 17 are sent to the control device 50. Based on the effective portion length Lb of the optical fiber base material G and the measured value of the feed amount, the remaining amount of the optical fiber base material G is calculated in the control device 50.

[0039] A cooling device 19 is provided on the downstream side of the heating furnace 13, and the glass fiber G1 drawn out from the heating furnace 13 is cooled by the cooling device 19. The cooling device 19 is composed of a main body, and the main body is composed of a component divided into two parts in the circumferential direction of the glass fiber G1, and the components divided into two parts are separated in the radial direction, thereby enabling the main body to be opened. In general, the components divided into two parts are used in a state of being engaged and set as one. An insertion hole is provided in the main body of the cooling device 19, and the insertion hole is provided for the glass fiber G1 to be inserted and penetrated in the axial direction. The glass fiber G1 is cooled by sending cooling gas into the insertion hole. Inside the main body of the cooling device 19, a cooling flow path is formed along the axial direction, and a cooling fluid circulates inside the cooling flow path. The cooling gas in the insertion hole is cooled by the cooling fluid, and the glass fiber G1 is inserted and penetrated into the cooling gas atmosphere, thereby rapidly cooling the glass fiber G1 after drawing from a high temperature to near room temperature, thereby stabilizing the shape of the glass fiber G1. In addition, in the present embodiment, helium with high thermal conductivity is used as cooling gas. Helium has high thermal conductivity, so it is suitable for use as a purge gas in the heating furnace 13 and a cooling solvent for the cooling device 19. However, helium is more expensive than nitrogen, so nitrogen is sometimes used instead of helium when cost is important. For example, helium is used during normal operation, and after the wire drawing is completed, nitrogen can be supplied to the heating furnace 13 instead of helium.

[0040] In addition, an upper damper capable of opening and closing the entrance of the insertion hole is provided at the upper end of the cooling device 19, and a lower damper capable of opening and closing the exit of the insertion hole is provided at the lower end of the cooling device 19. The upper damper and the lower damper are closed during wire drawing to improve the cooling efficiency of the cooling device 6. In addition, the upper damper and the lower damper form a small diameter hole in the center thereof when they are closed. The small diameter hole has a diameter slightly larger than that of the glass fiber G1 drawn by wire drawing. The glass fiber G1 passes through the small diameter hole while maintaining a small gap with the upper damper and the lower damper, respectively. In addition, a plurality of cooling devices 19 can also be provided in series on the trajectory line.

[0041] Although not particularly limited, a laser-type outer diameter measuring device 20 is provided on the downstream side of the cooling device 19, for example. The outer diameter dimension of the glass fiber G1 sent out from the cooling device 19 is measured by the outer diameter measuring device 20. Although not particularly limited, the outer diameter of the glass fiber G1 is measured in the orthogonal axis directions on the plane in the direction orthogonal to the axis of the glass fiber G1, thereby improving the accuracy. In addition, the outer diameter measuring device 20 can also be provided at multiple locations of the trajectory line. The measured value of the outer diameter of the glass fiber G1 measured by the outer diameter measuring device 20 is sent to the control device 50.

[0042] On the downstream side of the outer diameter measuring device 20, there are provided: a female mold 21 for coating the glass fiber G1 with an ultraviolet curing resin; and an ultraviolet irradiation device 24 for curing the coated ultraviolet curing resin. Although not particularly limited, the ultraviolet irradiation device 24 irradiates ultraviolet light to the optical fiber G2 coated with the resin through a plurality of UV lamps to cure the ultraviolet curing resin. The ultraviolet curing resin is coated around the glass fiber G1 having a stable shape after being cooled by the cooling device 19 by the female mold 21, and the coated resin is cured by an ultraviolet curing reaction by the ultraviolet irradiation device 24 provided downstream of the female mold 21, thereby obtaining an optical fiber having an ultraviolet curing resin layer uniformly provided around it.

[0043] A tray 23 is provided on the downstream side of the female mold 21, and the tray 23 is usually arranged at a position separated from the trajectory line. The tray 23 moves to a position directly below the female mold 21 when the glass fiber G1 or the optical fiber G2 is broken, and can receive the ultraviolet curing resin when the ultraviolet curing resin overflows from the female mold 21. In addition, a cutter 22 is provided between the female mold 21 and the tray 23. The optical fiber G2 drawn and coated with resin can be cut by the cutter 22. The female mold 21, the cutter 22, and the tray 23 are controlled in accordance with the control command from the control device 50.

[0044] The optical fiber G2 formed with the ultraviolet curing resin coating layer is pulled into the capstan 40 via the guide roller 30. A predetermined tension is applied to the optical fiber G2 by the capstan 40. The capstan 40 includes a capstan belt 42 wound around a plurality of rollers 41, and a capstan roller 32 in close contact with the capstan belt 42. The capstan 40 sandwiches the optical fiber G2 between the capstan belt 42 and the capstan roller 32, thereby applying tension to the optical fiber G2, and the optical fiber G2 is continuously picked up on the downstream side.

[0045] A tension meter 31 for measuring the tension of the optical fiber G2 is provided between the guide roller 30 and the capstan 40. The measured value of the tension of the optical fiber G2 measured by the tension meter 31 is sent to the control device 50. The rotation speed of the capstan 40 is controlled in accordance with the control command from the control device 50 so that the measured value of the outer diameter measuring device 20 becomes a predetermined value.

[0046] The line speed detector 25 is incorporated in the capstan 40, and measures the line speed according to the rotation speed of the capstan 40. In addition, the line speed detector 25 can also be incorporated in the guide roller 30, the screening device 33, and the dancer roller 34. The measured value of the line speed of the optical fiber G2 measured by the line speed detector 25 is sent to the control device 50.

[0047] A screening device 33 for performing a strength test on the optical fiber G2 is provided on the downstream side of the capstan 40. In the screening device 33, a predetermined tension is applied to the optical fiber G2 to perform a strength test such as pulling and bending to test whether the optical fiber G2 meets the desired strength conditions relative to the target specification. If the optical fiber G2 is not cut during the test, it is a qualified product.

[0048] The qualified optical fiber G2 is conveyed to the first winding reel 36 and the second winding reel 37 via the tension adjustment roller 34. For example, the qualified optical fiber G2 is wound on one of the first winding reel 36 and the second winding reel 37, and the unqualified optical fiber G2 drawn out is wound on the other, for example, at the end of the drawing operation. Although not particularly limited, in the following description, it is assumed that the qualified product is wound by the first winding reel 36 and the unqualified product is wound by the second winding reel 37. The tension adjustment roller 34 is provided with a tension adjustment roller measuring unit 35 for detecting the displacement of the tension adjustment roller 34. The measured value of the displacement of the tension adjustment roller 34 detected by the tension adjustment roller measuring unit 35 is sent to the control device 50. In addition, the first winding reel 36 and the second winding reel 37 control the winding of the optical fiber G2 in accordance with the control command from the control device 50.

[0049] [Structure of the control device 50]

[0050] Next, regarding the structure of the control device 50, refer to Figure 2 Provide explanation. Figure 2 yes Figure 1 The control device 50 is a block diagram of the optical fiber manufacturing device 10. The control device 50 is composed of a detection unit 60, a line speed control unit 70, and a coating layer forming and cutting control unit 80. The detection unit 60 includes detection units such as a base material feeding detection unit 61, a furnace core temperature detection unit 62, an outer diameter measuring unit 63, a line speed detection unit 64, a tension detection unit 65, and a dancer roller displacement detection unit 67.

[0051] The measured values ​​measured by the detectors 51 of each part of the optical fiber manufacturing apparatus 10 are sent to the detection section 60. In each detection unit of the detection section 60, the measured values ​​measured by the detectors 51 of each part are totaled and calculated, and stored in a memory (not shown) so as to be used for the control calculation of the line speed control section 70 and the cladding layer forming and cutting control section 80. For example, the measured value from the base material feeding detector 12 is sent to the base material feeding detection section 61, the measured value from the temperature detector 17 is sent to the core temperature detection section 62, the measured value from the outer diameter measuring device 20 is sent to the outer diameter measuring section 63, the measured value from the line speed detector 25 is sent to the line speed detection section 64, the measured value from the tension meter 31 is sent to the tension detection section 65, and the measured value from the dancer roller measurement section 35 is sent to the dancer roller displacement detection section 67.

[0052] The line speed control unit 70 includes a drawing end judgment unit 71, a base material feeding control unit 72, a gas supply amount control unit 73, a heating element control unit 74, a capstan control unit 76, a winding control unit 77 and other control units. In the line speed control unit 70, a target value of the line speed for drawing the optical fiber G2 is determined, which is set according to the specifications and manufacturing conditions of the optical fiber G2. The target value is set to a constant value as described later. In addition, the line speed control unit 70 uses the total and calculated measured values ​​stored in the memory of the detection unit 60 to calculate the control command for controlling each control device 52 of the optical fiber manufacturing device 10 and sends the control command to each control device 52 so that the line speed for drawing the optical fiber G2 follows the target value.

[0053] The target specification of the optical fiber G2 to be manufactured is set by the target specification setting unit (not shown) of the control device 50. Each control device 52 is controlled in accordance with the control command sent from the line speed control unit 70, thereby manufacturing the optical fiber G2 through each manufacturing process of the optical fiber manufacturing device 10 so that the optical fiber G2 reaches the set target specification. For example, the base material feeding control unit 72 sends a control command to the feeding device 11, the gas supply amount control unit 73 sends a control command to the gas supply unit 14, the heating element control unit 74 sends a control command to the heating element 15, the capstan control unit 76 sends a control command to the capstan 40, and the winding control unit 77 sends a control command to the first winding bobbin 36 and the second winding bobbin 37. Thus, each control unit of the line speed control unit 70 sends a control command to each control device 52 of the optical fiber manufacturing device 10 based on the measured value of each detector 51 detected by the detection unit 60, and controls each control device, thereby controlling each process of the optical fiber manufacturing device 10 to manufacture the optical fiber G2.

[0054] More specifically, the measured value of the outer diameter of the optical fiber G1 measured by the outer diameter measuring device 20 is obtained in the outer diameter measuring unit 63, and the command value of the rotation speed of the capstan 40 is calculated in the capstan control unit 76 based on the measured value of the outer diameter of the optical fiber G1. The command value of the rotation speed of the capstan 40 is sent from the capstan control unit 76 to the capstan 40, and the rotation speed of the capstan 40 is controlled according to the command value.

[0055] The drawing end determination unit 71 determines whether the drawing of the optical fiber G2 is completed according to the drawing end condition described later. If it is determined that the drawing is completed, a control signal for completing the drawing of the optical fiber G2 is sent to each control unit of the base material feeding control unit 72, the gas supply amount control unit 73, the heating element control unit 74, the capstan control unit 76, the winding control unit 77, and the coating layer forming and cutting control unit 80. If the end control signal is received from the drawing end determination unit 71, each control unit calculates a control instruction for controlling each control device 52, 53 in order to complete the drawing of the optical fiber G2, and the control instruction is sent to each control device 52, 53, thereby each control device 52, 53 performs control for completing the drawing of the optical fiber G2.

[0056] The coating layer forming and cutting control unit 80 includes a female mold control unit 81, a cutter control unit 82, a tray control unit 83, etc., and uses the control signal from the line speed control unit 70 and the total and calculated measurement value stored in the memory of the detection unit 60 to calculate the command signal to the female mold, the cutter, and the tray 53. The female mold control unit 81, for example, sends a command to change the amount of ultraviolet curing resin applied to the outer periphery of the glass fiber G1, specifically, sends a command to change the temperature of the female mold 21 or the supply pressure of the resin supplied to the female mold 21 to the female mold 21. The cutter control unit 82 sends a control command to the cutter 22 to cut the optical fiber G2 when the drawing of the optical fiber G2 is completed. The tray control unit 83 sends a control command to the tray 23 when the optical fiber G2 is cut by the cutter 22, for example, and controls so that the tray 23 moves and is located on the lower side of the female mold 21 when the optical fiber G2 is cut.

[0057] [Structure of optical fiber base material]

[0058] For the structure of the optical fiber base material G, refer to Figure 3 Provide explanation. Figure 3: is a schematic diagram of the optical fiber base material G. When the optical fiber base material G is drawn, at the beginning of the drawing, the ineffective part La of the length La from the drawing start end of the optical fiber base material G, that is, the position a=0, to a1 is drawn. Then, the effective part Lb, which is the effective part having the core C and becoming a product, is drawn over the length Lb from the position a1 to a2. When the drawing of the effective part Lb having the core C is completed, the ineffective part Lc that does not become a product is continuously drawn for the length Lc from a2 to a3. Sometimes, the viscosity of the part Lb where the core C exists is high, while the viscosity of the part Lc where the core C does not exist is low, or conversely, the viscosity of the part Lb where the core C exists is low, while the viscosity of the part Lc where the core C does not exist is high, so that sometimes the difference in glass viscosity becomes large at the joint between the core glass of the effective part Lb and the core glass of the ineffective part Lc. When the difference in glass viscosity becomes large as described above, the drawing line speed may increase sharply.

[0059] [About line speed control]

[0060] For line speed control, refer to Figure 4 Provide explanation. Figure 4 It is a graph of the line speed of optical fiber drawing. Figure 4 The vertical axis is the line speed V [m / min] of the optical fiber G2, and the horizontal axis is the drawing distance L [km]. The drawing distance L is equivalent to the length of the optical fiber G2 wound by the capstan 40, and is, for example, a value calculated by the number of rotations of the capstan 40, or obtained by time integration of the measured value of the line speed detector 25. The solid line is a graph in the case where the drawing stop control implemented by the drawing end determination unit 71 of the present embodiment is performed, and the double-dotted line is a graph in the case of a comparative example in which the drawing stop control implemented by the drawing end determination unit 71 of the present embodiment is not performed.

[0061] When the optical fiber manufacturing device 10 of the present embodiment is used to draw the optical fiber base material G, the ineffective portion La at the drawing start end of the optical fiber base material G is drawn from L=0 to L1 at the drawing start time, and during this period, the drawing speed is gradually increased. Figure 4 Although the linear velocity V is shown to increase linearly, the characteristics of the velocity increase are not limited to linear increase, and for example, the acceleration may increase gradually at first, then be set constant, and then gradually decrease near L1.

[0062] From L1 to L2, the control is performed so that the target value Vc of the line speed V becomes constant. Until the state of drawing a1 of the optical fiber base material G is reached, the line speed V is stabilized and becomes constant at substantially the target value Vc. During the period from L1 to L2, the effective portion Lb of the core C having the optical fiber base material G is drawn. During the period from L1 to L2, at least one of the feed amount of the optical fiber base material G, the output of the heating element 15 of the heating furnace 13 for heating the optical fiber base material G, the speed of the capstan 40, and the speed of the first winding bobbin 36 or the second winding bobbin 37 is controlled by each control unit 72 to 77 of the line speed control unit 70 so that the line speed V coincides with the constant target value Vc. For example, the rotation speed of the capstan 40 is controlled in accordance with the control command from the control device 50 so that the measured value of the outer diameter measuring device 20 becomes a predetermined value, and each control device is stably controlled. In addition, the feed device 11 is controlled in such a manner that the feed amount is increased if the line speed V is low, and the feed amount is reduced if the line speed V is high. In addition, the heating element 15 of the heating furnace 13 is controlled in such a manner that the output is increased if the line speed V is low, and the output is reduced if the line speed V is high. However, the temperature of the heating furnace 13 is preferably controlled in such a manner that it becomes as constant as possible, so in order to keep the line speed V constant, control is performed so as to prioritize ensuring temperature stability. As described above, each control device 52 is stably controlled, thereby controlling so that the line speed V of the optical fiber G2 is kept constant at the target value Vc. Through the control of the line speed control unit 70, the variation of the line speed V of the optical fiber G2 is suppressed to a range of less than 0.5% of the target value Vc during the period from L1 to L2.

[0063] exist Figure 4 An example is shown in which the target value Vc of the line speed V is always constant during the period from L1 to L2, but the target value Vc of the line speed V can be changed when the manufacturing conditions of the manufacturing process of the optical fiber G2 are changed in the middle. When the target value Vc of the line speed V is changed to Vc', for example, after the change, the line speed V is controlled so as to follow the target value Vc', and the change of the line speed V relative to the target value Vc' is suppressed to be within a range of less than 0.5% of the target value Vc'.

[0064] During the period from L2 to L3, if the drawing position of the optical fiber base material G approaches the end portion of the effective portion Lb, i.e., the position of the length a2, the target value Vc of the line speed V remains constant, but the line speed V cannot follow the constant target value Vc, and the line speed V gradually decreases after L2. This is because if the remaining amount of the optical fiber base material G decreases, the amount of glass for drawing will relatively decrease, so after L2, the amount of glass cannot meet the amount of glass required for the line speed V to follow the target value Vc, and the line speed V continues to decrease. Figure 4The example shows a case where the line speed V decreases in a straight line from L2 to L3, but the present embodiment is not limited to this. The characteristics of the reduction of the line speed V vary accordingly with the manufacturing conditions, the specifications of the optical fiber G2 to be manufactured, etc. For example, sometimes the graph at L2 does not change in a bending shape, but the line speed V decreases gradually and continuously in a smoother curve.

[0065] At L3, the reference wire speed Vs, which is a condition for determining the end of wire drawing specified in the present embodiment, is reached. Figure 4 The graph of the double-dashed line of the comparative example shows that the line speed V continues to decrease from L2 to L5, and is lower than the reference line speed Vs. The line speed V rises and falls sharply at L5. The reason is that at the drawing position of the optical fiber base material G, which is the length a2 position where the effective part Lb of the core C is switched to the ineffective part Lc, a glass viscosity difference occurs at the joint between the core glass of the effective part Lb and the core glass of the ineffective part Lc. Moreover, after L6, the glass viscosity decreases, so the line speed V rises sharply.

[0066] In the optical fiber manufacturing method of the present embodiment, the rapid rise and fall of the line speed V at L5 and the rapid increase of the line speed V after L6 as in the comparative example are avoided, and stable line speed control is achieved even at the end of drawing.

[0067] In the method for manufacturing an optical fiber of this embodiment, Figure 4 As shown in the solid line graph, at L3, if the reference line speed Vs, which is a condition for determining the end of drawing specified in the present embodiment, is reached, the drawing end determination unit 71 determines that it is the end position of drawing, and sends a control instruction for the drawing stop process to each control unit 72 to 77. The reference line speed Vs is in a range of 0.5% to 3% relative to the normal target value Vc, for example, in a range of 0.8% to 1.5%, or is preferably set to a low line speed of 1%, for example. The reason is that the change of the line speed V of the optical fiber G2 is usually suppressed to a range of less than 0.5% relative to the target value Vc during the period from L1 to L2 by the control performed by the line speed control unit 70. Depending on the specifications of the optical fiber to be manufactured, the manufacturing conditions, or the manufacturing device, it is also conceivable that the variation range of the line speed V becomes slightly larger than 0.5%, for example, about 0.7%. On the other hand, when the drawing position is near the length a2 of the optical fiber base material G, the reduced line speed V sometimes rises sharply. Therefore, in order to achieve stable line speed control, the baseline line speed Vs is set low within a range not exceeding 3% relative to Vc compared to the target value Vc, for example, within a range not exceeding 1.5%.

[0068] At L3, if the wire speed V reaches the reference wire speed Vs, the wire drawing end determination unit 71 determines that it is the end position of wire drawing, and the wire drawing end determination unit 71 sends the control command for wire drawing end processing to each control unit 72 to 77 in a predetermined order. If each control unit 72 to 77 receives the control command for wire drawing end processing from the wire drawing end determination unit 71, it sends the control command for wire drawing end processing to each control device 52. The time from when the wire drawing end determination unit 71 determines that the wire drawing end position determination condition that the wire speed V reaches the reference wire speed Vs is satisfied to when the control command for wire drawing end processing is issued is appropriately determined according to the specifications of the optical fiber to be manufactured, the manufacturing conditions, the manufacturing device, etc., and may be simultaneously or after a certain time, for example, about 30 to 60 seconds, has passed since the determination condition for the wire drawing end position was satisfied.

[0069] In the wire drawing end process, first, according to the control command of the winding control unit 77, the winding is switched from the first winding bobbin 36 for winding of qualified products to the second winding bobbin 37 for winding of unqualified products. Next, according to the control command from the capstan control unit 76, the rotation speed of the capstan 40 is gradually reduced, and in addition, according to the control command from the female mold control unit 81, the thickness of the ultraviolet curing resin coated on the optical fiber G1 is gradually reduced. Next, according to the control command from the gas supply amount control unit 73, the gas supply unit 14 switches the purge gas from helium to nitrogen, and according to the control command from the heating element control unit 74, the output of the heating element 15 is gradually reduced, and the temperature in the furnace core tube 16 of the heating furnace 13 is gradually reduced. In response, according to the control command from the base material feeding control unit 72, the feed amount of the optical fiber base material G is adjusted so that the line speed V is gradually reduced.

[0070] According to the control command of the female mold control unit 81, the supply amount of the ultraviolet curing resin is sufficiently reduced so that the uncured ultraviolet curing resin does not spill from the female mold 21, and after the line speed V of the optical fiber G2 becomes less than the specified line speed, the cutter 22 cuts the optical fiber G2 according to the control command of the cutter control unit 82. Next, the tray control unit 83 moves the tray 23 to a position to receive the resin in the event that the uncured ultraviolet curing resin spills from the female mold 21 after the optical fiber G2 is cut. If the cut optical fiber G2 is wound by the second winding reel 37 for winding a defective product, the second winding reel 37 stops according to the control command from the winding control unit 77, and the wire drawing process is completed. As a result, the line speed V of the optical fiber G2 in the wire drawing process is gradually reduced from Vs to 0 in a stably controlled state during the period from L3 to L4. Figure 4In the figure, the slope of the line speed V from L3 to L4 is shown to be constant, but this is only an example. In practice, the line speed V does not need to decrease in a linear manner. The line speed V may be changed in a smooth curve at the time of L3, or the deceleration of the line speed V may be gradually reduced.

[0071] According to the optical fiber manufacturing method of the present embodiment, it is possible to quickly determine that the effective portion Lb of the optical fiber base material G is switched to the ineffective portion Lc, and it is also possible to prevent the line speed V from increasing sharply and continuously at the end of the optical fiber drawing. In addition, in the drawing process, at least one of the feed amount of the optical fiber base material G, the output of the heating element 15 of the heating furnace 13 that heats the optical fiber base material G, the speed of the capstan 40, or the speed of the winding bobbins 36 and 37 is controlled, thereby setting the target value Vc of the line speed V of the optical fiber drawn by the winding bobbin to be constant and controlling the line speed V, thereby stabilizing the line speed V of the optical fiber drawn from the effective portion Lb of the optical fiber base material G by following the constant target value Vc, and thus reliably detecting the decrease in the line speed V at the end of the drawing, and more accurately determining the end of the drawing. Furthermore, the prescribed amount of reduction in the line speed V for determining the end of drawing of the optical fiber in the drawing end determination step is set between 0.5% and 3% from the target value Vc, thereby determining the range in which the prescribed amount of reduction in the line speed V for determining the end of drawing of the optical fiber is set relative to the constant target value Vc of the line speed V of the optical fiber drawn from the effective portion Lb of the optical fiber base material G, and appropriately setting the conditions for determining the end of drawing. In addition, the upper limit and the lower limit of the prescribed amount of reduction in the line speed V for determining the end of drawing of the optical fiber relative to the constant target value Vc of the line speed V of the optical fiber drawn from the effective portion Lb of the optical fiber base material G are set, thereby preventing erroneous setting when setting the conditions for determining the end of drawing.

[0072] [Implementation Method 2]

[0073] A method for manufacturing an optical fiber according to a second embodiment of the present invention will be described. Figures 1 to 4 , and is referred to in common with Embodiment 1. In Embodiment 1, the judgment condition of the end position of the drawing involved in the drawing end judgment unit 71 is set to be until the line speed V of the optical fiber G2 is reduced to the reference line speed Vs, but in this embodiment, an embodiment in which the judgment condition of the end position of the drawing involved in the drawing end judgment unit 71 is further added is described.

[0074] In an actual manufacturing device, it is also conceivable that various noises are generated according to the specifications, manufacturing conditions, and manufacturing device of the optical fiber G2 to be manufactured. In order to prevent the drawing end determination unit 71 from erroneously determining that the drawing end position is reached even when the line speed V of the optical fiber G2 temporarily decreases to below the reference line speed Vs due to the noise as described above, in the present embodiment, a plurality of determination criteria are provided so that when all of the plurality of determination criteria are satisfied, the drawing end determination unit 71 correctly determines that the drawing end position is reached.

[0075] The first determination condition is the same as in the first embodiment, that is, the line speed V of the optical fiber G2 decreases to or below the reference line speed Vs.

[0076] The second determination condition is that the remaining amount of the optical fiber preform G is detected to be less than Ls by the preform feeding detector 12.

[0077] Ls=Lc+ΔL(ΔL≥0)···(Formula 1).

[0078] In Formula 1, ΔL corresponds to the surplus amount of the effective portion Lb from a2, which is a position between the effective portion Lb and the ineffective portion Lc where the core C exists, and is a positive real number.

[0079] In the present embodiment, when both the first determination condition and the second determination condition are satisfied, the wire drawing end determination unit 71 determines that it is the wire drawing end position. Therefore, in the present embodiment, even when the first determination condition that the line speed V of the optical fiber G2 temporarily decreases to below the reference line speed Vs due to noise or erroneous detection by the line speed detector 25 is satisfied, the wire drawing end determination unit 71 will not determine that it is the wire drawing end position when the second condition that the remaining amount of the optical fiber base material G decreases to below Ls is not satisfied, thereby preventing erroneous determination of the wire drawing end position caused by noise or the like.

[0080] In the present embodiment, a third determination condition can be further added. The third determination condition is that the winding length of the optical fiber G2 related to the capstan 40, that is, the drawing distance L reaches the reference length L. G .L G It is calculated based on the volume of glass of the optical fiber preform G from the front end a=0 of the optical fiber preform G to the end position a2 of the effective portion Lb having the core C, the outer diameter of the optical fiber G2, and a predetermined surplus preform glass amount.

[0081] In the case of using the first judgment condition, the second judgment condition, and the third judgment condition, when all of the first judgment condition, the second judgment condition, and the third judgment condition are satisfied, the wire drawing end judgment unit 71 judges that it is the end position of wire drawing. In order to detect early that the remaining amount of the optical fiber base material G is less than the specified amount, a margin is sometimes set in the detection signal of the base material feed detector 12. In the above-mentioned case, by adding the third judgment condition in the present embodiment, even if the first judgment condition that the line speed V of the optical fiber G2 is temporarily reduced to below the reference line speed Vs due to noise or erroneous detection by the line speed detector 25 is satisfied, in addition, a margin is set in the detection signal of the base material feed detector 12, so that even if the second judgment condition is satisfied early, the wire drawing distance L of the optical fiber G2 does not meet the reference length L. G Under the third condition, the wire drawing end determination unit 71 will not determine that it is the wire drawing end position, so it is possible to prevent the erroneous determination of the wire drawing end position caused by noise, detection margin, etc. Figure 4 As shown, the line speed V of the optical fiber G2 at the end of the drawing process is gradually and stably controlled from Vs to 0 during the period from L3 to L4. Therefore, according to the optical fiber manufacturing method of the present embodiment, the switching from the effective part Lb to the ineffective part Lc of the optical fiber base material G can be judged more reliably, so that the optical fiber can be drawn at a stable line speed V even when the drawing of the optical fiber is completed, and the switching period from the effective part Lb to the ineffective part Lc of the optical fiber base material G can be more accurately grasped regardless of the influence of noise, etc., so that the effective part core glass of the optical fiber base material G can be used up without waste.

[0082] [Implementation method 3]

[0083] A method for manufacturing an optical fiber according to a third embodiment of the present invention will be described. Figures 1 to 4 , which is referred to in common with Embodiments 1 and 2. In Embodiment 1, if the wire speed V reaches the reference wire speed Vs, the wire drawing end determination unit 71 determines that it is the end position of wire drawing, and the wire drawing end determination unit 71 sends the control command for wire drawing end processing to each control unit 72 to 77 in a prescribed order, but in this embodiment, the reference wire speed Vs is determined based on the historical data of wire drawing of the optical fiber base material G in the past.

[0084] When the optical fiber G2 is drawn from the optical fiber base material G, based on the specifications, manufacturing conditions and manufacturing apparatus of the optical fiber G2, the boundary portion between the effective portion Lb having the core C and the ineffective portion Lc having no core C of the optical fiber base material G is determined to have a value at which the drawing distance L becomes L3, which should be used as a judgment condition. In addition, the value at which the line speed V of the optical fiber G2, which is equivalent to the reference line speed Vs that serves as a judgment reference when the drawing distance L is L3, is measured, and the history thereof is stored in the memory of the line speed control unit 70 (not shown).

[0085] Regarding the optical fiber G2 wound on the winding bobbin, the transmission characteristics such as transmission loss, wavelength dispersion, cut-off wavelength, mode field diameter and polarization mode dispersion are measured in the subsequent inspection process to distinguish between qualified products that meet the required specifications and unqualified products that do not meet the required specifications. The qualified and unqualified product judgment data are stored in the memory of the detection unit 60 (not shown) together with the data of the drawing distance L.

[0086] Based on the data of the drawing distance L3 of the optical fiber G2 drawn from the optical fiber base material G in the past multiple times stored in the memory of the detection unit 60 and the reference line speed Vs which serves as the corresponding judgment criterion, the reference line speed Vs corresponding to the drawing completion judgment condition L3 for drawing the optical fiber G2 of the target specification from the optical fiber base material G this time is calculated through statistical processing.

[0087] In the statistical processing in this case, various conditions such as the specifications, manufacturing conditions, and manufacturing equipment of the optical fiber base material G and the optical fiber G2 are preferably considered. Although not particularly limited, for example, the specifications and manufacturing conditions of the optical fiber base material G and the optical fiber G2 are the same, or the average value of the past history information of the proximity condition within a specified range is obtained, and the reference line speed Vs corresponding to the drawing end judgment condition, i.e., L3, is calculated. For example, the reference line speed Vs is calculated based on the line speed reduction amount corresponding to the drawing distance of the boundary between the effective part Lb and the ineffective part Lc of the optical fiber base material G. Alternatively, the reference line speed Vs is calculated based on the line speed reduction amount corresponding to the drawing distance of the boundary between the qualified product and the unqualified product of the optical fiber G2.

[0088] Therefore, according to the optical fiber manufacturing method of the present embodiment, by performing calculations based on past records, using the reference line speed Vs that becomes the drawing end condition of the drawing end determination unit 71 when drawing the target specification, i.e., the optical fiber G2, from the optical fiber base material G this time, it is possible to perform accurate drawing end determination corresponding to the specification of the optical fiber manufacturing apparatus 10 used, the specification of the optical fiber, various manufacturing conditions, etc. As a result, it is possible to perform drawing end determination more reliably, more accurately, and more stably.

[0089] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. In addition, the various elements of the aforementioned embodiments can be combined as long as they are technically feasible, and the combination of these elements is also included in the scope of the present invention as long as it includes the features of the present invention.

[0090] Description of the label

[0091] 10···Optical fiber manufacturing device

[0092] 11···Feeding device

[0093] 12···Base material feed detector

[0094] 13···Heating furnace

[0095] 14···Gas supply unit

[0096] 15. Heat generating element

[0097] 16···Furnace tube

[0098] 17···Temperature detector

[0099] 19···Cooling device

[0100] 20···Outer diameter measuring device

[0101] 21···Negative mold

[0102] 22···Cutter

[0103] 23···Tray

[0104] 24···Ultraviolet irradiation device

[0105] 25···Line speed detector

[0106] 30···Guide roller

[0107] 31···Tensiometer

[0108] 32···Capstan Roller

[0109] 33···Screening device

[0110] 34···Density adjustment roller

[0111] 35···Dancer roller measuring unit

[0112] 36···1st winding spool

[0113] 37···Second winding spool

[0114] 40···Wind

[0115] 41···Roller

[0116] 42···Winch belt

[0117] 50···Control device

[0118] 51···Various detectors

[0119] 52···Various control devices

[0120] 53···Molds, cutters, trays

[0121] 60···Detection Department

[0122] 61···Base material feeding detection unit

[0123] 62···Furnace core temperature detection unit

[0124] 63···Outer diameter measuring unit

[0125] 64···Line speed detection unit

[0126] 65···Tension detection unit

[0127] 66···Fiber optic strength detection unit

[0128] 67···Dresser roller displacement detection unit

[0129] 70···Detection Department

[0130] 71···Wire drawing end judgment unit

[0131] 72···Base material feeding control unit

[0132] 73···Gas supply control unit

[0133] 74···Heating element control unit

[0134] 76···Winch control unit

[0135] 77···Winding control unit

[0136] 80···Cover formation·cutting control unit

[0137] 81···Female mold control unit

[0138] 82···Cutter control unit

[0139] 83···Tray control unit

[0140] C····Fiber Core

[0141] G····Optical fiber base material

[0142] G1···Fiberglass

[0143] G2···Fiber Optic

[0144] V····Line speed of optical fiber

[0145] Vc... Target value of line speed

[0146] Vs... Standard value of line speed

[0147] La... Non-effective part

[0148] Lb···Effective part

[0149] Lc···Invalid part

[0150] L····Drawing distance

Claims

1. A method for manufacturing an optical fiber, comprising: a drawing step of heating and softening the optical fiber base material and drawing the base material to produce an optical fiber that will become a product; and a drawing completion judging step of judging whether the drawing of the optical fiber to be a product in the optical fiber base material is completed by determining whether a predetermined condition is satisfied. In the drawing process, the target value of the optical fiber drawing line speed is set constant to control the line speed. In the drawing completion determination step, when the line speed decreases by a predetermined amount from the target value, it is determined that the drawing of the optical fiber is completed.

2. The method for manufacturing an optical fiber according to claim 1, wherein: The optical fiber base material includes an effective part and an ineffective part, wherein the effective part is a central part in the length direction and has a core, and the ineffective part is an end part in the length direction and has no core. In the drawing completion determination step, the completion of the optical fiber drawing is determined by further considering the remaining length of the effective portion of the optical fiber preform.

3. The method for manufacturing an optical fiber according to claim 1 or 2, wherein: In the drawing completion judgment step, conditions for judging the completion of optical fiber drawing are determined based on the amount of line speed reduction of the optical fiber preform drawn in the past and the inspection results of the optical fiber obtained from the optical fiber preform.

4. The method for producing an optical fiber according to any one of claims 1 to 3, wherein: In the drawing process, at least one of the feed rate of the optical fiber base material, the output of the heating element of the heating furnace that heats the optical fiber base material, the speed of the capstan or the speed of the winding bobbin is controlled, thereby setting the target value of the drawing speed of the optical fiber wound on the bobbin to be constant and controlling the speed.

5. The method for producing an optical fiber according to any one of claims 1 to 4, wherein: The predetermined reduction amount of the line speed for determining the completion of optical fiber drawing in the drawing completion determination step is set to be between 0.5% and 3% of the target value.

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