Preparation process of optical fiber with temperature control system

Abstract

The invention relates to an optical fiber preparation process with a temperature control system, which is applied to the field of optical fiber production, and comprises the following specific steps of: 1, mounting a winding disc wound with an optical fiber on a pay-off device, and paying off the optical fiber by the pay-off device; 2, introducing the optical fiber paid off by the pay-off device into a preheating device for preheating; 3, introducing the preheated light into a stripping device, and stripping the outer plastic of the optical fiber by the stripping device; 4, introducing the stripped optical fiber into a plastic extrusion device, and wrapping the optical fiber by the plastic extrusion device; 5, introducing the wrapped optical fiber into a cold water group, gradually reducing the cold water temperature of each cold water tank, and adopting the cold water group to realize a step-by-step cooling mode, thereby preventing the rapid cooling of the optical fiber, reducing the reduction of the production quality of the optical fiber, accurately controlling the water temperature in the cold water tanks, and improving the quality of the optical fiber. The optical fiber production environment is stabilized, and the optical fiber production quality is improved.

Description

Technical Field

[0001] The present invention relates to optical fiber production, and in particular to an optical fiber preparation process with a temperature control system applied in the field of optical fiber production. Background Art

[0002] Optical fiber is the abbreviation of optical fiber, which is a fiber made of glass or plastic that can be used as a light transmission tool. The transmission principle is "total reflection of light". Optical cables using tight-buffered optical fibers can withstand multiple manual processing (such as moving, etc.) during use, and are easy to install and maintain; optical cables using tight-buffered optical fibers are mainly used in special applications such as indoor and field communications, ships, and aircraft.

[0003] The production process of optical fiber is as follows: Figure 1 As shown, almost all materials have the characteristics of thermal expansion and contraction (a few are the opposite), and the characteristics of polymers themselves determine that the material is more likely to shrink; molecules are randomly entangled chains, and the polymer chains are straightened in the direction of force. When the force disappears, they will return to the randomly entangled state, thus shrinking; when the polymer material is heated in the extruder, the polymer chain is activated, but the movement is restricted by pressure. When the polymer material comes out of the die mouth, the pressure is released and it expands, and it is stretched under traction. When passing through the water tank, the polymer chain is frozen; because the temperature of the water tank is low and the distance to the machine head is very close, it cools down as soon as it comes out, the polymer chain is frozen, the stress in the material cannot be relaxed, and it is more likely to shrink; if the shrinkage of the tight sleeve increases, the degree of squeezing of the light is too great, thereby damaging the optical fiber. Summary of the invention

[0004] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that the temperature of the water tank is low and the distance to the machine head is very close. As soon as it comes out, it cools down, the polymer chain is frozen, the stress inside the material cannot be relaxed, and it is more likely to shrink. If the shrinkage of the tight sleeve increases, the degree of squeezing of the light is too great, thereby damaging the optical fiber.

[0005] In order to solve the above problems, the present invention provides an optical fiber preparation process with a temperature control system, and the specific steps are as follows:

[0006] In the first step, a reel with the optical fiber wound on it is mounted on a pay-off device, and the pay-off device pays off the optical fiber;

[0007] In the second step, the optical fiber released by the pay-off device is introduced into the preheating device for preheating;

[0008] In the third step, the preheated light is introduced into a stripping device, and the stripping device strips the outer plastic layer of the optical fiber;

[0009] In the fourth step, the stripped optical fiber is introduced into a plastic extrusion device, and the plastic extrusion device wraps the optical fiber;

[0010] The fifth step is to introduce the wrapped optical fiber into a cold water group, wherein the cold water group includes a plurality of cold water tanks distributed linearly, and the cold water temperature of each cold water tank gradually decreases, and a temperature control module is arranged on the inner side of the cold water group, and the temperature control module includes a plurality of temperature controllers and a temperature detector, and the temperature controller includes an electric telescopic rod, one end of the electric telescopic rod is fixedly connected to the inner wall of the cold water tank, and the other end of the electric telescopic rod is rotatably connected to a rotating part, and a plurality of power grooves are cut on the rotating part, and the plurality of power grooves all penetrate the rotating part, and a plurality of movable grooves are cut on the side wall of the rotating part, and an electromagnet is fixedly connected to the bottom plate of the movable groove, and a stirring blade is inserted in the movable groove, and the stirring blade is made of heat-conducting material, and the stirring blade includes a heat-conducting blade, and the end of the heat-conducting blade close to the temperature controller is fixedly connected to the connecting part, and the end of the connecting part away from the heat-conducting blade extends into the movable groove, and is fixedly connected to a heat source part matching the size of the movable groove, and the heat source part is adsorbed with the energized electromagnet;

[0011] In the sixth step, the optical fiber separated from the cold water group passes through a blow dryer, and the blow dryer dries the optical fiber;

[0012] In the seventh step, the dried optical fiber is introduced into the take-up device through the traction device, and the take-up device reels the processed optical fiber.

[0013] In the above invention, the wrapped optical fiber is introduced into the cold water group. At this time, the wrapped optical fiber will not be cooled down immediately, thereby achieving step-by-step cooling. This effectively prevents the polymer chain from being frozen, and the stress in the material cannot be relaxed, which makes shrinkage more likely to occur. The shrinkage of the tight sleeve after production is reduced, and the degree of squeezing of the light is reduced, thereby protecting the optical fiber and improving production quality.

[0014] As a further supplement to the present application, in the first step, a tensioner is installed at the outlet of the wire-releasing device, and a traction force detector is installed at the outlet of the wire-releasing device.

[0015] As another improvement of the present application, in the second step, a speed measuring module is installed at the optical fiber outlet of the preheating device, and the speed measuring module is used to monitor the transmission speed of the optical fiber.

[0016] As another improved supplement of the present application, in the third step, a visual module is installed at the optical fiber outlet of the stripping device, and the visual module is composed of a plurality of high-speed cameras, and the high-speed cameras are used to capture the surface of the optical fiber.

[0017] As another improvement of the present application, in the fourth step, the plastic extrusion device includes an extruder and a mixing device, the discharge end of the mixing device is connected to the feed end of the extruder, and a dryness detector is installed inside the mixing device, and the stripped optical fiber is introduced into the mold head of the extruder.

[0018] As another improvement of the present application, a temperature measuring module is installed on the outside of the die head of the extruder, and the temperature measuring module is used to detect the temperature of the optical fiber after wrapping.

[0019] As another improvement of the present application, in the fifth step, each temperature detector is electrically connected to the temperature controller, and each temperature detector is installed in each cold water tank respectively.

[0020] As another improvement of the present application, support rollers are rotated inside both ends of the cold water tank, and multiple distribution rollers are fixed inside the cold water tank. In the fifth step, the wrapped optical fiber bypasses the support rollers and each distribution roller, and the wrapped optical fiber is distributed in a continuous S shape.

[0021] As another improvement of the present application, a plurality of stirring plates are fixed to the outer side of the distribution roller.

[0022] In summary, after adopting the above structure, the present invention has the following advantages compared with the prior art:

[0023] 1. The wrapped optical fiber is introduced into the cold water group. At this time, the wrapped optical fiber will not be cooled immediately, so that the temperature can be reduced step by step, which effectively prevents the polymer chain from being frozen, and the stress in the material cannot be relaxed, which makes it easier to shrink. The shrinkage of the tight sleeve after production is reduced, and the degree of squeezing of the light is reduced, thereby protecting the optical fiber and improving the production quality. Therefore, by cooling step by step, the optical fiber is prevented from cooling rapidly, and the occurrence of the reduction of the optical fiber production quality is reduced. At the same time, the water temperature in the cold water tank 12 can be accurately controlled, the production environment of the optical fiber is stabilized, and the production quality of the optical fiber is improved;

[0024] 2. In the entire process of preparing wrapped optical fiber, each process step has relevant detection elements. When a problem occurs in a process step, it can be reported in time, so that maintenance personnel can carry out timely repairs. It is also convenient to determine the problems in production and make timely improvements to ensure timely production in the future;

[0025] 3. The wrapped optical fiber bypasses the support roller and each distribution roller, and the wrapped optical fiber is distributed in a continuous S shape, thereby increasing the residence time of the optical fiber in each cold water tank, making the cooling of the optical fiber more sufficient, and there is no need to lengthen the production line, saving space;

[0026] 4. The two adjacent distribution rollers rotate in opposite directions. The stirring plates on the distribution rollers stir the water inside the cold water tank to increase the degree of heat exchange between water and optical fiber, thereby increasing the heat exchange rate and further improving the cooling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The figure is a schematic diagram of the existing process flow;

[0028] Figure 2 This is a schematic diagram of the process flow of the first embodiment of the present application;

[0029] Figure 3 This is a schematic diagram of the structure of the cold water group of the first embodiment of the present application;

[0030] Figure 4 This is a schematic structural diagram of a plastic extrusion device according to the first embodiment of the present application;

[0031] Figure 5 This is a schematic diagram of the overall structure of the first implementation method of the present application;

[0032] Figure 6 This is a schematic diagram of the internal structure of the first embodiment of the present application;

[0033] Figure 7 This is a schematic structural diagram of a temperature controller according to the first embodiment of the present application;

[0034] Figure 8 This is a front cross-sectional view of the temperature controller according to the first embodiment of the present application;

[0035] Fig. 9 This is a schematic structural diagram of the stirring blade of the first embodiment of the present application;

[0036] Fig.10 This is a schematic diagram of the working structure of the second implementation method of this application;

[0037] Fig.11 This is a schematic diagram of the three-dimensional structure of the third embodiment of the present application.

[0038] Description of the numbers in the figure:

[0039] 1. Speed ​​measurement module; 2. Temperature measurement module; 3. Cold water group; 4. Temperature control module; 5. Visual module; 6. Traction force detector; 7. Temperature detector; 8. Extruder; 9. Mixing device; 10. Dryness detector; 11. Tensioner; 12. Cold water tank; 13. Outlet pipe; 14. Water inlet pipe; 15. Drain pipe; 16. Support roller; 17. Distribution roller; 18. Stirring plate; 19. Temperature controller, 1901 electric telescopic rod, 1902 rotating part, 1903 power tank, 1904 movable tank, 20 stirring blade, 2001 heat transfer blade, 2002 connecting part, 2003 heat source part. DETAILED DESCRIPTION

[0040] The following is a detailed description of three implementation methods of the present application in conjunction with the accompanying drawings.

[0041] The first implementation method:

[0042] The present invention provides a process for preparing optical fiber with a temperature control system. Figure 1 - Figure 6 , the specific steps are as follows:

[0043] In the first step, a reel with the optical fiber wound on it is mounted on a pay-off device, and the pay-off device pays off the optical fiber;

[0044] In the second step, the optical fiber released by the pay-off device is introduced into the preheating device for preheating;

[0045] In the third step, the preheated light is introduced into a stripping device, and the stripping device strips the outer plastic layer of the optical fiber;

[0046] In the fourth step, the stripped optical fiber is introduced into a plastic extrusion device, and the plastic extrusion device wraps the optical fiber;

[0047] The fifth step is to introduce the wrapped optical fiber into the cold water group 3, wherein the cold water group 3 includes a plurality of cold water tanks 12 distributed linearly, and the cold water temperature of each cold water tank 12 gradually decreases, and an inlet pipe and an outlet pipe 13 are respectively fixed to the top of both ends of the cold water tank 12, and the wrapped optical fiber is introduced into the cold water tank 12 from the inlet pipe and led out of the cold water tank 12 from the outlet pipe 13, one end of the cold water tank 12 is fixed with a water inlet pipe 14 connected to the inside thereof, and one end of the cold water tank 12 is fixed with a drain pipe 15 connected to the inside thereof;

[0048] In the sixth step, the optical fiber separated from the cold water group 3 passes through a blow dryer, and the blow dryer dries the optical fiber;

[0049] In the seventh step, the dried optical fiber is introduced into the take-up device through the traction device, and the take-up device reels the processed optical fiber.

[0050] In the present invention, the wrapped optical fiber is introduced into the cold water group 3. At this time, the wrapped optical fiber will not be cooled down immediately, thereby achieving step-by-step cooling. This effectively prevents the polymer chain from being frozen, and the stress in the material cannot be relaxed, which makes it easier for shrinkage to occur. The shrinkage of the tight sleeve after production is reduced, and the degree of squeezing of the light is reduced, thereby protecting the optical fiber and improving the production quality.

[0051] Specifically, in the first step, a tensioner 11 is installed at the outlet of the wire-releasing device, and a traction force detector 6 is installed at the outlet of the wire-releasing device;

[0052] In the present invention, the tensioner 11 is a prior art, and its specific structure and working principle are not described in detail here. The tensioner 11 keeps the optical fiber tensioned at all times; the traction force detector 6 is a prior art, and its specific structure and working principle are not described in detail here. The tensioner 11 keeps the optical fiber tensioned at all times. If the traction force is too large, the wrapped optical fiber is stretched. After winding is completed, the wrapped tight sleeve is loosened, so that the tight sleeve cannot be put on the optical fiber, which reduces the production quality.

[0053] Specifically, in the second step, a speed measuring module 1 is installed at the optical fiber outlet of the preheating device, and the speed measuring module 1 is used to monitor the transmission speed of the optical fiber;

[0054] In the present invention, the above-mentioned speed measuring module 1 is supplemented with explanations. The speed measuring module 1 can use contact type and non-contact type. The contact type can use a wheel-type measuring instrument, and the speed measuring wheel of the wheel-type speed measuring instrument is in contact with the optical fiber. The non-contact type can use an infrared speed meter. The model of the speed measuring instrument is limited here, and the specific model is selected according to the actual production situation.

[0055] Specifically, a visual module 5 is installed at the optical fiber outlet of the stripping device, and the visual module 5 is composed of a plurality of high-speed cameras, and the high-speed cameras are used to capture the surface of the optical fiber;

[0056] In the present invention, the high-speed camera is a prior art, and its specific structure and working principle are not described in detail here. The high-speed camera is used to capture the surface of the optical fiber. If there is any residue on the surface of the optical fiber after stripping, the overall quality of the optical fiber will be reduced.

[0057] Specifically, in the fourth step, the plastic extrusion device includes an extruder 8 and a mixing device 9, the discharge end of the mixing device 9 is connected to the feed end of the extruder 8, and a dryness detector 10 is installed inside the mixing device 9, and the stripped optical fiber is introduced into the die head of the extruder 8;

[0058] In the present invention, the dryness detector 10 is a prior art, and its specific structure and working principle are not elaborated in detail here. The dryness detector 10 is used to detect the dryness of polymer materials. If the moisture content in the material is too high, bulges or particles will form on the surface. When the bulges or particles are too large, they cannot pass through the sizing die and are pulled apart, which will also cause material stripping, reduce the quality of the optical fiber, and even fail to meet qualified production requirements.

[0059] Specifically, a temperature measuring module 2 is installed outside the die head of the extruder 8, and the temperature measuring module 2 is used to detect the temperature of the optical fiber after wrapping;

[0060] In the present invention, the temperature measuring module 2 is non-contact, such as an infrared temperature measuring sensor. The infrared temperature measuring sensor is a prior art, and its specific structure and working principle are not elaborated in detail here. The temperature measuring module 2 is used to detect the temperature at all times. Because if the process temperature of the extruder is set unreasonably, the material cannot be fully plasticized or the flame retardant is decomposed, it will also cause bulging or uneven thickness on the surface of the optical fiber, resulting in uneven pressure or mismatched size of the molten material during plastic processing, excessive pressure, etc., which will cause the processed material to be unstable in molding, and even uneven thickness. If the above phenomenon occurs.

[0061] See also Figure 7 - Fig. 9 Specifically, in the fifth step, a temperature control module is provided inside the cold water group, and the temperature control module includes a temperature controller 19 and a plurality of temperature detectors, each temperature detector is electrically connected to the temperature controller 19, and each temperature detector is installed in each cold water tank;

[0062] The temperature controller 19 includes an electric telescopic rod 1901, one end of which is fixedly connected to the inner wall of the cold water tank 12, and the other end of the electric telescopic rod 1901 is rotatably connected to a rotating part 1902, and a plurality of power grooves 1903 are cut on the rotating part 1902, and the plurality of power grooves 1903 all penetrate the rotating part 1902, and a plurality of movable grooves 1904 are cut on the side wall of the rotating part 1902, and an electromagnet is fixedly connected to the bottom plate of the movable groove 1904, and the movable groove 1904 is fixedly connected to the bottom plate of the movable groove 1904. A stirring blade 20 is inserted into the movable groove 1904. The stirring blade 20 is made of heat-conducting material. The stirring blade 20 includes a heat-conducting blade 2001. The end of the heat-conducting blade 2001 close to the temperature controller 19 is fixedly connected with a connecting part 2002. The end of the connecting part 2002 away from the heat-conducting blade 2001 extends into the movable groove 1904 and is fixedly connected with a heat source part 2003 matching the size of the movable groove 1904, and the heat source part 2003 is adsorbed by the energized electromagnet.

[0063] Among them, the extension and retraction speed of the electric telescopic rod 1901 is controllable. When a slow temperature change is required, the extension and retraction speed of the electric telescopic rod 1901 can be reduced, thereby reducing the flow rate of liquid water in the power tank 1903 per unit time, thereby reducing the rotation speed of the rotating part 1902. At the same time, the centrifugal force on the stirring blades 20 is also reduced, and the stirring blades 20 are retracted in the direction close to the rotating part 1902, thereby reducing the heat exchange efficiency in terms of both stirring speed and stirring range.

[0064] When a rapid temperature change is required, contrary to the above process, the extension and retraction speed of the electric telescopic rod 1901 can be increased, thereby increasing the flow rate of liquid water in the power tank 1903 per unit time, thereby increasing the rotation speed of the rotating part 1902. At this time, the centrifugal force on the stirring blades 20 also increases, and the stirring blades 20 extend in a direction away from the rotating part 1902, thereby improving the heat exchange efficiency in terms of both stirring speed and stirring range.

[0065] In the present invention, the temperature detector 7 is a prior art, and its specific structure and working principle are not elaborated in detail here. It is used to detect the temperature at all times to prevent a cold water tank 12 from not reaching the specified temperature and continuing to work, causing quality problems in subsequent production. At the same time, it can achieve precise control of the water temperature in the cold water tank 12, stabilize the production environment of the optical fiber, and improve the production quality of the optical fiber.

[0066] In summary, in the entire process of preparing the wrapped optical fiber, each process step has relevant detection elements. When a problem occurs in a certain process step, it can be reported in time so that maintenance personnel can carry out timely repairs. It is also convenient to determine the problems in production and make timely improvements to ensure that subsequent production can be carried out in time. When the wrapped optical fiber is introduced into the cold water group 3, the wrapped optical fiber will not be cooled immediately at this time, thereby achieving step-by-step cooling, which effectively prevents the polymer chain from being frozen, the stress in the material cannot be relaxed, and shrinkage is more likely to occur. The shrinkage of the tight sleeve after production is reduced, and the degree of squeezing of the light is reduced, thereby protecting the optical fiber and improving the production quality.

[0067] Second implementation method:

[0068] See also Fig.10 This embodiment adds the following structure on the basis of embodiment 1, and the specific configuration is as follows: Figure 7 As shown, support rollers 16 are rotated inside both ends of the cold water tank 12, and multiple distribution rollers 17 are fixed inside the cold water tank 12. In the fifth step, the wrapped optical fiber bypasses the support rollers 16 and each distribution roller 17, and the wrapped optical fiber is distributed in a continuous S shape.

[0069] In summary, the wrapped optical fiber bypasses the support roller 16 and each distribution roller 17, and the wrapped optical fiber is distributed in a continuous S shape, thereby increasing the residence time of the optical fiber in each cold water tank 12, making the cooling of the optical fiber more sufficient, and there is no need to lengthen the production line, saving space.

[0070] The third implementation method:

[0071] See also Fig.11 Based on Implementation 1, this implementation adds the following structure, which is specifically configured as follows: Figure 8As shown, a plurality of stirring plates 18 are fixed to the outer side of the distribution roller 17 .

[0072] In summary, the two adjacent distribution rollers 17 rotate in opposite directions, and the stirring plate 18 on the distribution roller 17 stirs the water inside the cold water tank 12 to improve the heat exchange between water and optical fiber, thereby improving the heat exchange rate and further improving the cooling effect.

[0073] In view of current practical needs, the above-mentioned implementation mode adopted in this application is not limited to the scope of protection. Various changes made within the knowledge scope of technical personnel in this field without departing from the concept of this application still fall within the scope of protection of the present invention.

Claims

1. A process for preparing an optical fiber with a temperature control system, characterized in that: The specific steps are as follows: The first step is to install a reel with the optical fiber wound on it on a pay-off device, and the pay-off device pays off the optical fiber; In the second step, the optical fiber released by the pay-off device is introduced into the preheating device for preheating; In the third step, the preheated light is introduced into a stripping device, and the stripping device strips the outer plastic layer of the optical fiber; In the fourth step, the stripped optical fiber is introduced into a plastic extrusion device, and the plastic extrusion device wraps the optical fiber; In the fifth step, the wrapped optical fiber is introduced into a cold water group (3), wherein the cold water group (3) includes a plurality of cold water troughs (12) distributed in a linear manner, and the cold water temperature of each cold water trough (12) gradually decreases, and a temperature control module (4) is arranged on the inner side of the cold water group (3), and the temperature control module (4) includes a plurality of temperature controllers (19) and a temperature detector (7), and the temperature controller (19) includes an electric telescopic rod (1901), one end of the electric telescopic rod (1901) is fixedly connected to the inner wall of the cold water trough (12), and the other end of the electric telescopic rod (1901) is rotatably connected to a rotating part (1902), and a plurality of power grooves (1903) are excavated on the rotating part (1902), and the plurality of power grooves (1903) all penetrate the rotating part (1902), a plurality of movable grooves (1904) are formed on the side wall of the rotating part (1902), an electromagnet is fixedly connected to the groove bottom plate of the movable groove (1904), a stirring blade (20) is inserted into the movable groove (1904), the stirring blade (20) is made of a heat-conducting material, the stirring blade (20) comprises a heat-conducting blade (2001), an end of the heat-conducting blade (2001) close to the temperature controller (19) is fixedly connected to a connecting part (2002), an end of the connecting part (2002) away from the heat-conducting blade (2001) extends into the movable groove (1904), and is fixedly connected to a heat source part (2003) having a size matching that of the movable groove (1904), and the heat source part (2003) is attracted to the energized electromagnet; In the sixth step, the optical fiber separated from the cold water group (3) passes through a blow dryer, and the blow dryer performs a drying process on the optical fiber; In the seventh step, the dried optical fiber is introduced into the take-up device through the traction device, and the take-up device reels the processed optical fiber.

2. The optical fiber preparation process with a temperature control system according to claim 1, characterized in that: In the first step, a tensioner (11) is installed at the outlet of the wire-releasing device, and a traction force detector (6) is installed at the outlet of the wire-releasing device.

3. The optical fiber preparation process with a temperature control system according to claim 1, characterized in that: In the second step, a speed measuring module (1) is installed at the optical fiber outlet of the preheating device, and the speed measuring module (1) is used to monitor the transmission speed of the optical fiber.

4. The optical fiber preparation process with a temperature control system according to claim 1, characterized in that: In the third step, a visual module (5) is installed at the optical fiber outlet of the stripping device, and the visual module (5) is composed of a plurality of high-speed cameras, and the high-speed cameras are used to capture the surface of the optical fiber.

5. The optical fiber preparation process with a temperature control system according to claim 1, characterized in that: In the fourth step, the plastic extrusion device includes an extruder (8) and a mixing device (9), the discharge end of the mixing device (9) is connected to the feed end of the extruder (8), and a dryness detector (10) is installed inside the mixing device (9), and the stripped optical fiber is introduced into the die head of the extruder (8).

6. The optical fiber preparation process with a temperature control system according to claim 5, characterized in that: A temperature measurement module (2) is installed outside the die head of the extruder (8), and the temperature measurement module (2) is used to detect the temperature of the optical fiber after wrapping.

7. The optical fiber preparation process with a temperature control system according to claim 1, characterized in that: In the fifth step, each of the temperature detectors (7) is electrically connected to the temperature controller (19), and each of the temperature detectors (7) is installed in each of the cold water tanks (12).

8. The optical fiber preparation process with a temperature control system according to claim 7, characterized in that: Support rollers (16) are rotated inside both ends of the cold water tank (12), and a plurality of distribution rollers (17) are fixed inside the cold water tank (12). In the fifth step, the wrapped optical fiber bypasses the support rollers (16) and each distribution roller (17), and the wrapped optical fiber is distributed in a continuous S shape.

9. The optical fiber preparation process with a temperature control system according to claim 8, characterized in that: A plurality of stirring plates (18) are fixed to the outer side of the distribution roller (17).

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