Method for manufacturing fiber optic cables

Abstract

To provide a method and an apparatus for manufacturing an optical fiber cable that enable detection of abnormality in an outer shape of an optical fiber cable.SOLUTION: A method for manufacturing an optical fiber cable is a method for manufacturing an optical fiber cable having a cable core, the method including: an application step of extruding resin onto a periphery of the cable core to apply the resin serving as a sheath thereto; a first measurement step of measuring an outer diameter of the optical fiber cable to which the resin is applied; and a sheath formation step of solidifying the resin to form the sheath after the first measurement step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing an optical fiber cable. In the law

Background Art

[0002] Patent Document 1 discloses a manufacturing apparatus and method for a loose tube type optical fiber cable, in which the outer diameter of the cable is measured by an outer diameter measuring instrument after cooling in a water tank. Further, Patent Document 2 describes a method for manufacturing an optical fiber tube in which the average ovality of a tube for housing an optical fiber is improved by a vacuum sizing method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The outer jacket of an optical fiber cable is formed by extruding a resin in a molten state at a high temperature from a crosshead, applying it onto the cable core, and then solidifying it with a cooling facility. Here, if there are air bubbles in the molten resin, the resin may not be uniformly applied to the cable core. Further, although an optical fiber cable is usually extruded from a crosshead at a constant speed, the extrusion speed may not be constant due to the viscosity of the resin, and the coating amount of the resin may vary. Due to such variations in air bubbles and coating amount, the outer shape of the optical fiber cable may not become the intended round shape and may be deformed.

[0005] ​To detect such deformation of the outer shape of optical fiber cables, there is an optical fiber cable manufacturing apparatus, as disclosed in Patent Document 1, which is installed downstream of the cooling equipment and has a measuring unit for measuring the outer diameter of the optical fiber cable. However, even if the outer diameter of the optical fiber cable is measured after passing through the cooling equipment and the resin has solidified, it is difficult to determine whether the cause of the deformation of the outer shape lies in the resin coating process or the resin solidification process. If the vacuum sizing method described above is used, the outer shape of the optical fiber cable will be round, and deformation of the outer shape can be suppressed. However, since there is no abnormality in the outer shape, even if the outer diameter is measured after passing through the cooling equipment, it may not be possible to detect that the thickness of the outer sheath is uneven due to the effects of air bubbles and variations in the amount of coating.

[0006] In optical fiber cables with distorted external shapes or uneven sheath thickness, radial stress is unevenly distributed in the circumferential direction, resulting in low break strength. Furthermore, within the cable, high density of optical fibers in certain areas can lead to stress concentration and high stress on the optical fibers, degrading transmission characteristics.

[0007] This disclosure relates to a method for manufacturing optical fiber cables that can detect abnormalities in the external shape of optical fiber cables. Law The purpose is to provide. [Means for solving the problem]

[0008] A method for manufacturing an optical fiber cable according to one aspect of this disclosure is: Cable core Furthermore, it may have a distorted outer shape or areas where the thickness of the outer covering is uneven. A method for manufacturing optical fiber cables, A coating step in which resin is extruded around the cable core to coat the outer sheath with the resin, , A first measurement step of measuring the outer diameter of the optical fiber cable to which the resin has been applied, The process includes, after the first measurement step, a covering formation step in which the resin is solidified to form the covering. fruit, The above-mentioned outer covering formation step is, The process of inserting the optical fiber cable into a sizing die, A sizing step comprising creating a negative pressure in at least a portion of the sizing die and passing the optical fiber cable through the said region, The process includes a cooling step of cooling the resin of the optical fiber cable that has passed through the region.

Advantages of the Invention

[0010] According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber cable capable of detecting an abnormal outer shape of the optical fiber cable. Law It can be provided.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a schematic configuration diagram showing a manufacturing apparatus for an optical fiber cable according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic configuration diagram showing a manufacturing apparatus for an optical fiber cable according to Modification 1 of the present disclosure. [Figure 3] FIG. 3 is a schematic configuration diagram showing a manufacturing apparatus for an optical fiber cable according to Modification 2 of the present disclosure.

Modes for Carrying Out the Invention

[0012] (Description of an Aspect of the Present Disclosure) First, embodiments of the present disclosure will be listed and described. (1) A method for manufacturing an optical fiber cable according to an aspect of the present disclosure is having a cable core Furthermore, it may have a distorted outer shape or areas where the thickness of the outer covering is uneven. a method for manufacturing an optical fiber cable, a coating step of extruding a resin around the cable core and applying the resin to be an outer sheath, a first measurement step of measuring an outer diameter of the optical fiber cable coated with the resin, after the first measurement step, an outer sheath forming step of solidifying the resin to form the outer sheath, and includes fruit, The above-mentioned outer covering formation step is, The process of inserting the optical fiber cable into a sizing die, A sizing step comprising creating a negative pressure in at least a portion of the sizing die and passing the optical fiber cable through the said region, The process includes a cooling step of cooling the resin of the optical fiber cable that has passed through the region.

[0013] According to this disclosure, the outer diameter of the optical fiber cable is measured after the resin is applied but before the resin hardens and the outer sheath is formed. Therefore, abnormalities in the outer shape of the optical fiber cable caused by air bubbles in the resin or variations in the amount of resin applied can be detected before the resin hardens. Furthermore, according to this disclosure, it becomes easier to identify the cause of deformation of the outer shape. This makes it possible to suppress damage to the optical fiber cable or a decrease in transmission loss caused by abnormalities in the outer shape or unevenness in the thickness of the outer sheath.

[0014] Furthermore, if an abnormality in the external shape is detected, depending on the location of the abnormal part on the cable, the optical fiber cable may be partially discarded, or the entire coating may be stripped off and re-coated, thereby enabling the manufacture of optical fiber cables with a non-distorted external shape and non-uneven coating thickness. When the cable core is angular or elliptical, the outer sheath formed on it will have a similar shape, and the outer shape of the optical fiber cable may not be the round shape originally intended. However, according to this disclosure, the outer sheath formation process includes a threading step of threading the optical fiber cable into a sizing die, a sizing step of creating negative pressure in at least a portion of the sizing die and passing the optical fiber cable through that area, and a cooling step of cooling the resin of the optical fiber cable that has passed through that area, so that the outer shape of the optical fiber cable can be made round. Furthermore, if the optical fiber cable passes through the sizing die with a distorted outer shape due to air bubbles in the resin or variations in the amount of resin applied, the outer shape of the optical fiber cable will become round, but the thickness of the outer sheath may be uneven. This unevenness in the thickness of the outer sheath can cause anisotropy in the bending direction of the optical fiber cable, and when the optical fiber cable is laid by air pressure or other means, the optical fiber cable may buckle. However, according to this disclosure, since the outer diameter of the optical fiber cable is measured before the insertion process in which the optical fiber cable is fed into the sizing die, even if there is no abnormality in the outer shape after the outer sheath is formed, abnormalities such as unevenness in the thickness of the outer sheath can be detected.

[0015] (2) In the above (1), the coating step is to apply the resin by the extrusion section, The first measurement step involves measuring the outer diameter using the first measuring unit. The first measuring unit may be located 200 mm to 400 mm downstream from the extrusion unit in the direction in which the optical fiber cable travels.

[0016] According to this disclosure, the first measuring section is located at least 200 mm downstream from the extrusion section in the direction of travel of the optical fiber cable. This prevents deterioration or damage to the first measuring section due to the high-temperature resin applied by the extrusion section. Alternatively, the first measuring section may be located at least 400 mm downstream from the extrusion section in the direction of travel of the optical fiber cable. If the first measuring section is located far from the extrusion section, the molten resin extruded from the extrusion section may deform downward due to gravity. However, according to this disclosure, the outer diameter can be measured before such deformation of the resin occurs.

[0017] (3) The manufacturing method according to (1) or (2) above may further include a second measurement step of measuring the thickness of the outer covering after the outer covering formation step. The resin coating the cable core shrinks when it solidifies. Furthermore, if the outer shape is distorted or contains air bubbles, the thickness of the sheath may fluctuate during the solidification process. Also, while the outer shape of an optical fiber cable is round, the thickness of the sheath may be uneven. In such cases, no abnormalities are visible on the surface. According to this disclosure, in addition to measuring the outer diameter before solidification, the thickness of the sheath is measured after solidification. Therefore, even if there are no visible abnormalities in the outer shape, abnormalities in the sheath thickness can be detected more accurately. A thinning of part of the sheath can cause localized concentration of lateral pressure on the optical fiber core, potentially degrading transmission characteristics. However, the manufacturing method of this disclosure measures the thickness of the solidified sheath, making it possible to detect abnormalities in the sheath thickness during the sheath formation process and avoid concentration of lateral pressure on the optical fiber.

[0023] (Details of one form of this disclosure) Hereinafter, examples of embodiments of the manufacturing method and manufacturing apparatus for optical fiber cables according to this disclosure will be described with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals or names even if they are in different drawings, and redundant explanations will be omitted as appropriate. In addition, the dimensions of each component shown in each drawing are for illustrative purposes only and may differ from the actual dimensions of each component.

[0024] (Equipment for manufacturing fiber optic cables) First, with reference to Figure 1, a manufacturing apparatus for optical fiber cables according to this embodiment will be described. Figure 1 is a schematic configuration diagram showing a manufacturing apparatus 1 for optical fiber cable 102 according to one embodiment of this disclosure. As shown in Figure 1, the manufacturing apparatus 1 comprises a supply drum 10, a feeder 20, an extruder 30, an optical sensor 80, a first water tank 40, a take-up machine 60, and a winding drum 70.

[0025] The supply drum 10 supplies the cable core 101, which is the internal material of the optical fiber cable 102. The cable core 101 contains multiple optical fiber cores inside. The cable core 101 may be a slot type in which multiple optical fiber cores are housed in a slot rod, or it may be a slotless type without a slot rod. The multiple optical fiber cores contained in the cable core 101 may be configured as multiple optical fiber ribbons. An optical fiber ribbon has a structure in which multiple optical fiber cores are arranged in parallel and covered with tape resin. An optical fiber ribbon may be an intermittently bonded type of optical fiber ribbon, in which adjacent optical fiber cores among the multiple parallel optical fiber cores are intermittently bonded with tape resin along the axial direction. The outer circumference of the cable core 101 is wrapped with, for example, a retaining tape.

[0026] The feeder 20 is equipped with a capstan belt. The feeder 20 controls the feed speed of the cable core 101 to the extruder 30 based on a control signal from, for example, a control device (not shown).

[0027] The extruder 30 is a device that extrudes molten resin around the cable core 101 to coat it with a molten resin outer covering. The molten resin can be any thermoplastic resin, such as polyethylene, without particular limitations. The molten resin may be, for example, low-density polyethylene (LDPE) or high-density polyethylene (HDPE). The extruder 30 is equipped with a crosshead 31. The extruder 30 heats the thermoplastic resin to molten resin and supplies the molten resin to the crosshead 31. The molten resin is applied around the cable core 101, which has been fed from the feeder 20, at the crosshead 31. The extruder 30 is an example of an extrusion unit.

[0028] In this embodiment, the crosshead 31 extrudes molten resin by pulling. The crosshead 31 includes a die located downstream and having a die hole in the center through which the cable core 101 passes, a point located upstream and having a point hole in the center through which the cable core 101 passes, and which is concentric with the die hole, and a flow path provided between the die and the point for supplying molten resin. As the cable core 101 passes through the die hole and the point hole, the molten resin supplied from the flow path is applied to the cable core 101. At this time, the molten resin extruded from the discharge port of the flow path does not immediately contact the cable core 101, but gradually becomes thinner and contacts and applies to the cable core 101 at a point away from the exit of the crosshead 31, forming the optical fiber cable 102. The optical fiber cable 102 coated with molten resin is sent to the optical sensor 80.

[0029] The optical sensor 80 is configured to measure the outer diameter of the optical fiber cable 102 coated with molten resin. The optical sensor 80 is, for example, a laser optical sensor. The optical sensor 80 has, for example, a U-shape and includes a light-emitting unit 81 at the first end that emits light, and a light-receiving unit 82 at the second end that receives the light emitted from the light-emitting unit 81. The optical sensor 80 emits light from the light-emitting unit 81 toward the optical fiber cable 102 running between the light-emitting unit 81 and the light-receiving unit 82. Since a portion of the emitted light is blocked by the optical fiber cable 102, the light emitted from the light-emitting unit 81 reaches the light-receiving unit 82 in a reduced state. The optical sensor 80 measures the outer diameter of the optical fiber cable 102 based on the range of light that is blocked and not received by the optical fiber cable 102 (the size of the shadow of the optical fiber cable 102). The optical sensor 80 is an example of a first measuring unit.

[0030] The optical sensor 80 is located 200 mm to 400 mm downstream of the extruder 30 in the direction of travel of the optical fiber cable 102. In other words, the distance d from the downstream end of the extruder 30 to the upstream end of the optical sensor 80 is 200 mm to 400 mm. In this specification, "upstream side" refers to the upstream side in the direction of travel of the optical fiber cable 102. Also, in this specification, "downstream side" refers to the downstream side in the direction of travel of the optical fiber cable 102. After the optical sensor 80 measures the outer diameter, the optical fiber cable 102 is sent to the first water tank 40.

[0031] The first water tank 40 solidifies the molten resin by cooling it, forming the outer sheath. The pressure inside the first water tank 40 is, for example, about the same as atmospheric pressure. The resin applied by the extruder 30 is in a molten state at a high temperature, but as the optical fiber cable 102 passes through the first water tank 40, the temperature of the resin decreases and the resin solidifies. This solidified resin becomes the outer sheath of the optical fiber cable 102. In other words, the first water tank 40 forms the outer sheath by cooling the resin of the optical fiber cable 102. In this embodiment, the first water tank 40 contains water as a medium, but it may contain a medium other than water. The first water tank 40 is an example of an outer sheath forming section.

[0032] The take-up machine 60 is equipped with a capstan belt. The take-up machine 60 controls the winding speed of the optical fiber cable 102 onto the winding drum 70 based on a control signal from, for example, a control device (not shown). The winding drum 70 is a drum on which the optical fiber cable 102 is wound.

[0033] (Manufacturing method for optical fiber cables) An example using the above-described manufacturing apparatus 1 will be described as a method for manufacturing an optical fiber cable according to one embodiment of the present disclosure. The method for manufacturing an optical fiber cable 102 according to this embodiment includes, for example, a coating step, a first measurement step, and a first passing step. In the method for manufacturing an optical fiber cable 102 according to this embodiment, the linear velocity of the optical fiber cable is not particularly limited, but is preferably, for example, 5 m / min or more and 40 m / min or less.

[0034] The coating process involves using an extruder 30 to extrude molten resin around the cable core 101, which is the internal material of the optical fiber cable 102, thereby coating it with the molten resin that will form the outer sheath. In the coating process, the extrusion temperature (resin temperature of the molten resin) is preferably, for example, 170°C or higher and 210°C or lower.

[0035] The first measurement step is to measure the outer diameter of the optical fiber cable 102 coated with molten resin using an optical sensor 80. For example, when the manufacturing apparatus 1 manufactures an optical fiber cable 102 having 864 optical fiber cores with an outer diameter of 250 μm and an outer diameter of 20 mm, if the measured value by the optical sensor 80 is 1.6 mm or more larger or smaller than the average of the measured values ​​by the optical sensor 80, the control device (not shown) may determine that there is an abnormality in the outer shape of the optical fiber cable 102. For example, when the manufacturing apparatus 1 manufactures an optical fiber cable 102 having 432 optical fiber cores with an outer diameter of 250 μm and an outer diameter of 10 mm, if the measured value by the optical sensor 80 is 0.8 mm or more larger or smaller than the average of the measured values ​​by the optical sensor 80, the control device (not shown) may determine that there is an abnormality in the outer shape of the optical fiber cable 102.

[0036] The first passing step is a step in which, after the first measurement step, the optical fiber cable 102 is passed through the first water tank 40 to solidify the resin and form the outer sheath. The pressure inside the first water tank 40 is set to approximately the same as atmospheric pressure. In the first passing step, the temperature inside the first water tank 40 is preferably, for example, 15°C to 50°C. The first passing step is an example of an outer sheath formation step.

[0037] As described above, in this embodiment, the outer diameter of the optical fiber cable 102 is measured by the optical sensor 80 after the molten resin has been applied but before the molten resin has solidified and the outer sheath has been formed. In the extruder 30, air bubbles may be generated in the molten resin or the amount of molten resin supplied may fluctuate, but according to this embodiment, abnormalities in the outer shape of the optical fiber cable 102 can be detected before the molten resin solidifies. Furthermore, according to this embodiment, since the outer diameter of the optical fiber cable 102 is measured before the molten resin solidifies, it becomes easier to identify the cause of the deformation in the outer shape as being in the application process. This makes it possible to suppress damage to the optical fiber cable or a decrease in transmission loss caused by abnormalities in the outer shape or unevenness in the thickness of the outer sheath that may occur during the application process.

[0038] In this embodiment, if an abnormality in the external shape of the optical fiber cable 102 is detected, the manufacturing method of the optical fiber cable may be changed depending on the location of the abnormal part on the cable. For example, if the abnormal part is located relatively close to the end, such as in the excess length portion of the total length of the optical fiber cable to be manufactured, the abnormal part may be partially discarded from the entire cable after the entire length has been manufactured. For example, if the abnormal part is located relatively close to the center of the total length of the optical fiber cable to be manufactured, the entire outer sheath may be peeled off from the cable core 101 after the entire length has been manufactured, and the outer sheath may be reformed. By this method, in this embodiment, it is possible to manufacture optical fiber cables that do not have a distorted external shape and optical fiber cables that do not have an uneven thickness of coating.

[0039] In this embodiment, the optical sensor 80 is located at least 200 mm downstream from the extruder 30 in the direction in which the optical fiber cable travels. If the optical sensor 80 were located close to the extruder 30, it could be degraded or damaged by the high-temperature molten resin applied in the extruder 30. However, in this embodiment, the optical sensor 80 is located at a position not too close to the extruder 30, thus preventing such degradation or damage to the optical sensor 80.

[0040] In this embodiment, the optical sensor 80 is located 400 mm or less downstream from the extruder 30 in the direction in which the optical fiber cable travels. If the optical sensor 80 were located far away from the extruder 30, the molten resin applied in the extruder 30 might deform downwards due to gravity. However, in this embodiment, since the optical sensor 80 is located not too far from the extruder 30, the outer diameter of the optical fiber cable 102 can be measured before deformation of the molten resin due to gravity occurs.

[0041] (Modified example 1 of optical fiber cable manufacturing equipment) The manufacturing apparatus 1 may also include a second water tank 50 and a thickness sensor 90 for measuring the thickness of the outer sheath of the optical fiber cable 102, in addition to the optical sensor 80. Figure 2 is a schematic diagram showing a manufacturing apparatus 1A for an optical fiber cable 102 according to Modification 1. Among the components shown in Figure 2, components that are the same as those shown in Figure 1 are denoted by the same reference numerals, and their descriptions are omitted.

[0042] As shown in Figure 2, the manufacturing apparatus 1A includes a supply drum 10, a feeder 20, an extruder 30, an optical sensor 80, a first water tank 40, a take-up machine 60, a winding drum 70, as well as a second water tank 50 and a wall thickness sensor 90.

[0043] The second water tank 50 is located downstream of the first water tank 40. The pressure inside the second water tank 50 is, for example, approximately the same as atmospheric pressure. The second water tank 50 is provided to further cool the outer sheath of the optical fiber cable 102. The second water tank 50 may be configured to contain a refrigerant other than water, rather than water.

[0044] The thickness sensor 90 is configured to measure the thickness of the sheath of the optical fiber cable 102. The thickness sensor 90 is, for example, an ultrasonic sensor. The thickness sensor 90 is located above the second water tank 50. The thickness sensor 90 emits ultrasonic waves toward the optical fiber cable 102 passing through the water in the second water tank 50. A portion of the emitted ultrasonic waves is reflected by the outer surface of the sheath of the optical fiber cable 102, and another portion of the emitted ultrasonic waves is reflected by the inner surface of the sheath of the optical fiber cable 102. By receiving these reflected ultrasonic waves, the thickness sensor 90 measures the thickness of the sheath of the optical fiber cable 102 based on the difference in the timing of reception of the two ultrasonic waves. The thickness sensor 90 is an example of a second measuring unit.

[0045] (Modified example 1 of the manufacturing method for optical fiber cables) The method for manufacturing an optical fiber cable 102 using the manufacturing apparatus 1A includes a second passing step and a second measurement step. The second passing step is a step in which the optical fiber cable 102 is passed through a second water tank 50 after the first passing step. The pressure inside the second water tank 50 is set to be approximately the same as atmospheric pressure. Furthermore, the temperature inside the second water tank 50 is preferably, for example, between 15°C and 50°C. The temperature inside the second water tank 50 may be the same as or different from the temperature inside the first water tank 40.

[0046] The second measurement step is a step in which, after the first passing step, when the optical fiber cable 102 passes through the second water tank 50, the thickness of the outer sheath is measured by the thickness sensor 90. For example, when the manufacturing apparatus 1A manufactures an optical fiber cable with an outer diameter of 20 mm and an outer sheath thickness of 1.5 mm, if the measured value by the thickness sensor 90 is 0.5 mm or more greater or less than the average of the measured values ​​measured by the thickness sensor 90, the control device (not shown) may determine that there is an abnormality in the thickness of the outer sheath of the optical fiber cable 102. For example, when the manufacturing apparatus 1A manufactures an optical fiber cable 102 with an outer diameter of 10 mm and an outer sheath thickness of 1.3 mm, if the measured value by the thickness sensor 90 is 0.5 mm or more greater or less than the average of the measured values ​​measured by the thickness sensor 90, the control device (not shown) may determine that there is an abnormality in the thickness of the outer sheath of the optical fiber cable 102.

[0047] Here, the molten resin applied to the cable core 101 solidifies and shrinks as it passes through the first water tank 40 and the second water tank 50. In this modified example, the first and second passing steps are examples of the sheath formation steps. If the molten resin contains air bubbles during the coating step, or if the outer shape of the optical fiber cable 102 is distorted during the coating step, the thickness of the sheath may fluctuate during the solidification process. In addition, even if the outer shape of the optical fiber cable 102 is round, the thickness of the sheath may be uneven. In such cases, no abnormality is visible on the surface. If a part of the sheath thickness becomes thinner, the lateral pressure applied to the optical fiber core may be concentrated in that area, which can degrade the transmission characteristics.

[0048] However, according to this disclosure, in addition to measuring the outer diameter before the molten resin solidifies, the thickness of the outer sheath of the optical fiber cable 102 is measured by the thickness sensor 90 after the molten resin solidifies. Therefore, even if there are no abnormalities in the outer shape on the surface, abnormalities in the thickness of the outer sheath can be detected more accurately. This makes it possible to avoid the concentration of lateral pressure on the optical fiber cores housed inside the optical fiber cable 102.

[0049] (Modified example 2 of optical fiber cable manufacturing equipment) Manufacturing apparatus 1 or manufacturing apparatus 1A may have a sizing die 43. Figure 3 is a schematic configuration diagram showing manufacturing apparatus 1B for optical fiber cable 102 according to modified example 2. Among the components shown in Figure 3, components that are the same as those shown in Figures 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0050] As shown in Figure 3, the first water tank 40 of the manufacturing apparatus 1B is a sizing tank provided for sizing the optical fiber cable 102. As shown in Figure 3, the first water tank 40 is equipped with a cooling section 41, a cable inlet 42, a sizing die 43, an exhaust pipe 44, and a vacuum pump 45.

[0051] In the example shown in Figure 3, the cooling unit 41 is located upstream of the cable entry port 42. The cooling unit 41 may also be located at the cable entry port 42, rather than upstream of it. The cooling unit 41 is equipped with, for example, shower holes (not shown) and a slow-cooling water tank (not shown). The shower holes spray water or the like towards the outer sheath covered by the crosshead 31 to pre-cool it before it is fed into the sizing die 43. The slow-cooling water tank has a relatively short length in the direction of travel of the optical fiber cable 102, and the optical fiber cable 102 is passed through the tank before it is fed into the sizing die 43. The viscous resistance of the outer sheath formed by the extruder 30 is relatively high before cooling. As a result, when the optical fiber cable 102 is fed into the entry port 42 or the sizing die 43, the shape of the outer sheath may become distorted, or the outer sheath may peel off from the outer circumference of the cable core 101, damaging the appearance of the cable. However, by pre-hardening the outer sheath to some extent with water from the shower holes or the slow-cooling water tank, such distortion of the outer sheath's shape can be reduced.

[0052] The exhaust pipe 44 is a pipe that guides the air inside the first water tank 40 to the outside. The vacuum pump 45 is installed on the exhaust pipe 44. The vacuum pump 45 discharges the gas inside the first water tank 40 to the outside of the first water tank 40 through the exhaust pipe 44, creating negative pressure inside the first water tank 40.

[0053] The entry port 42 is both the entrance to the first water tank 40 and the entrance to the sizing die 43. The optical fiber cable 102, with its sheath formed at the crosshead 31, enters through the entry port 42 into the sizing die 43 located inside the first water tank 40.

[0054] The sizing die 43 is a die for sizing the optical fiber cable 102 to a desired shape and size. In this embodiment, the sizing die 43 is cylindrical, and its inner circumference is circular. The inner diameter of the sizing die 43 is equal to the desired outer diameter of the optical fiber cable 102. In this specification, "equal" includes not only cases where they are exactly equal, but also cases where the difference between the two is sufficiently small and they are considered substantially equal.

[0055] The sizing die 43 is located in a first water tank 40 which is under negative pressure, so the area inside the sizing die 43 is under negative pressure. The sizing die 43 is provided with a plurality of holes (not shown). The plurality of holes are provided, for example, at predetermined intervals along the circumferential and axial directions of the sizing die 43. By providing a plurality of holes, it is easier to maintain the same pressure inside the sizing die 43 as inside the first water tank 40 even when the optical fiber cable 102 is passing through the sizing die 43. The second water tank 50 is provided downstream of the first water tank 40 and further cools the outer sheath of the optical fiber cable 102.

[0056] (Modified Method 2 of Manufacturing Optical Fiber Cables) The first step in the manufacturing method of the optical fiber cable 102 using the manufacturing apparatus 1B includes a pre-cooling step, a cable insertion step, a sizing step, and a cooling step.

[0057] The pre-cooling step is a step in which the outer sheath of the optical fiber cable 102 is pre-cooled by the cooling unit 41 before the optical fiber cable 102 is fed into the sizing die 43. In the pre-cooling step of this embodiment, the outer sheath of the optical fiber cable 102 is cooled, for example, by a slow-cooling water tank or by water from a shower hole. The feeding step is a step in which, after the pre-cooling step, the optical fiber cable 102 with the outer sheath applied is guided to the feeding opening 42 and fed into the sizing die 43.

[0058] The sizing process involves creating negative pressure in at least a portion of the sizing die 43 and passing the optical fiber cable 102 through that region. In this embodiment, the sizing die 43 is placed in a first water tank 40 that has been made negatively pressurized by a vacuum pump 45, so the entire area inside the sizing die 43 is under negative pressure. The pressure inside the sizing die 43 is preferably, for example, between -60 kPa and -5 kPa. Since the pressure inside the sizing die 43 is equal to the pressure inside the first water tank 40, the pressure inside the sizing die 43 can be controlled by controlling the pressure inside the first water tank 40.

[0059] The temperature inside the first water tank 40 is preferably, for example, between 15°C and 50°C. The temperature inside the sizing die 43 is equal to the temperature inside the first water tank 40. Furthermore, the time from when the molten resin is applied in the coating process until the optical fiber cable 102 enters the negative pressure region in the first passing process is preferably greater than 0 seconds and 10 seconds or less. This time can be controlled, for example, by adjusting the distance between the crosshead 31 and the first water tank 40, or by adjusting the linear velocity of the optical fiber cable 102.

[0060] Because the inside of the sizing die 43 is under negative pressure, the pressure inside the optical fiber cable 102 is higher than the pressure around the optical fiber cable 102. Therefore, as the optical fiber cable 102 passes through the sizing die 43, the air inside the optical fiber cable 102 expands, pushing the outer sheath outward radially, and the outer sheath 120 comes into contact with the inner wall of the sizing die 43. Thus, even if the shape of the optical fiber cable 102 is an irregular circle before entering the sizing die 43, after passing through the first passage process, it becomes a perfect circle defined by the inner circumference of the sizing die 43. In addition, the outer diameter of the optical fiber cable 102 becomes approximately equal to the inner diameter of the sizing die 43.

[0061] The cooling process is a process of cooling the resin of the optical fiber cable 102 that has passed through at least a portion of the negative pressure area within the sizing die 43. In this embodiment, the resin of the optical fiber cable 102 that has passed through the entire negative pressure area of ​​the sizing die 43 is cooled by passing through the first water tank 40. After the cooling process, the optical fiber cable 102 is sent to the second water tank 50 and proceeds to the second passing process. The second passing process is also an example of a cooling process.

[0062] In this case, if the cable core 101 is angular or elliptical, the outer sheath formed on it will have a similar shape, and the outer shape of the optical fiber cable 102 may not be round. However, according to this embodiment, the first passing step includes a feeding step in which the optical fiber cable 102 is fed into the sizing die 43, a sizing step in which at least a part of the area inside the sizing die 43 is made negatively pressurized and the optical fiber cable 102 is passed through that area, and a cooling step in which the resin of the optical fiber cable that has passed through that area is cooled, so that the outer shape of the optical fiber cable 102 can be made round.

[0063] Furthermore, if the optical fiber cable 102 passes through the sizing die 43 with a distorted outer shape due to air bubbles in the molten resin in the extruder 30 or fluctuations in the amount of resin applied, the outer shape of the optical fiber cable 102 will become round, but the thickness of the outer sheath may become uneven. This unevenness in the thickness of the outer sheath can cause anisotropy in the bending direction of the optical fiber cable, and when the optical fiber cable is laid by air pressure or other means, the optical fiber cable may buckle. However, according to this embodiment, since the outer diameter of the optical fiber cable 102 is measured by the optical sensor 80 before the cable entry process, it is possible to detect abnormalities such as unevenness in the thickness of the outer sheath, which can occur even if there is no abnormality in the outer shape.

[0064] Although this disclosure has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of this disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the embodiments described above and can be changed to a number, position, shape, etc. that is suitable for carrying out this disclosure.

[0065] For example, the crosshead 31 of the extruder 30 in this embodiment extrudes the molten resin by pulling it down, but the extrusion method is not limited to this. The molten resin may also be extruded by a solid extrusion method in which the molten resin is brought into contact with the cable core 101 within the crosshead 31 before being extruded. Furthermore, the manufacturing apparatuses 1, 1A, and 1B may be further equipped with other optical sensors downstream of the cooling equipment to measure the outer diameter of the optical fiber cable after cooling. [Explanation of symbols]

[0066] 1, 1A, 1B: Manufacturing equipment (for fiber optic cables) 10: Supply Drum 20: Feeding machine 30: Extruder 31: Crosshead 40: Tank 1 41: Cooling section 42: Entrance 43: Sizing Dice 44: Exhaust pipe 45: Vacuum pump 50: Second tank 60: Pickup machine 70: Reel Drum 80: Optical sensor 90: Thickness recovery 101: Cable core 102: Fiber optic cable d: distance

Claims

1. A method for manufacturing an optical fiber cable having a cable core, which includes parts where the outer shape is distorted or where the thickness of the outer sheath is uneven, A coating step in which resin is extruded around the cable core to coat the outer sheath with the resin, A first measurement step of measuring the outer diameter of the optical fiber cable to which the resin has been applied, The process includes, after the first measurement step, a covering formation step in which the resin is solidified to form the covering, The above-mentioned outer covering formation step is, The process of inserting the optical fiber cable into a sizing die, A sizing step comprising creating a negative pressure in at least a portion of the sizing die and passing the optical fiber cable through the said region, A method for manufacturing an optical fiber cable, comprising a cooling step of cooling the resin of the optical fiber cable that has passed through the region.

2. The coating step involves applying the resin using an extrusion unit. The first measurement step involves measuring the outer diameter using the first measuring unit. The method for manufacturing an optical fiber cable according to claim 1, wherein the first measuring unit is provided 200 mm to 400 mm downstream from the extrusion unit in the direction of travel of the optical fiber cable.

3. A method for manufacturing an optical fiber cable according to claim 1, further comprising a second measurement step of measuring the thickness of the outer sheath after the outer sheath forming step.

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