CN1303825A - Apparatus for tension of fibre-optical and method for controlling tension applying to optical fibre - Google Patents

Abstract

An optical fiber tensioning device receives an optical fiber (35) from a pulling device (37) at its input end and supplies the optical fiber to a storage device (40) at its output end. The tensioning device (1) comprises at least one fixed pulley (32), around which the optical fiber (35) is wound for at least a predetermined length; and at least one movable pulley (9), around which the optical fiber (35) is wound for at least a predetermined length. The means for measuring the tension applied to the fiber interacts with the motor means (24, 26, 5, 7) for moving the movable pulley (9) to control the axis (20, 33) of the pulley (9, 32) in the following manner The distance (Dp) between them is used to automatically keep the tension applied to the fiber substantially constant.

Description

Optical fiber tensioning device and method of controlling tension applied to an optical fiber

The present invention relates to an optical fiber tensioning device and a method of controlling the tension applied to an optical fiber, especially during winding of the optical fiber.

Typically, optical fibers are formed from preforms of glass material in a draw tower. A draw tower usually has a pulling device ("winch"), such as a motorized pulley, that pulls the fiber down and delivers it to a storage device; the latter usually consists of a motorized drum. Fiber optics are wrapped around it.

Under many operating conditions, the speed at which the pulling device draws the fiber (drawing speed) may not coincide with the speed at which the fiber is fed to the storage device, for example due to fluctuations in the speed of the motors driving the pulling device and the storage device. The difference between these two speeds causes the tension in the fiber to vary relative to the target tension; in particular, fiber tensions greater than the target tension can damage the fiber, while fiber tensions less than the target tension can lead to inefficient depositing processes.

In order to solve this problem, it is known practice to use a tensioning device which is inserted between the pulling device and the storage device and which is able to control the tension of the optical fiber. In particular, a drawing device is known comprising at least one fixed pulley and a movable pulley capable of guiding the optical fiber. The movement of the movable pulley can change the tension of the optical fiber. Here and in the rest of the specification, the term "fixed pulley" refers to a pulley that is free to rotate about its axis and the position of the axis is fixed, while the term "moving pulley" refers to a pulley that is free to rotate about its axis and the position of the axis can be changed. pulley.

US Pat. No. 4,712,866 describes a tensioning device arranged between the pulling device of the stretching tower and the storage device including the winding drum. The tensioner consists of a pair of fixed pulleys and a movable pulley on a swing arm, also called a "tensioner arm", with a weight. The tensioning arm performs conventional speed control to wind the fiber onto the reel at the tension determined by the aforementioned weight.

US Patent 5,790,292 relates to an optical fiber transmission line and describes a drawing tower in which a tensioning device with two pulleys is inserted between the drawing device and the take-up drum (Fig. 7).

US Patent No. 4,138,069 describes a winding apparatus for optical glass filaments in which a pulling device draws the filaments from molten glass and feeds them through a tensioning device to a set of winding drums. The tensioning device includes two fixed pulleys and a movable pulley installed at one end of the tensioning arm. The tensioning arm extends from a device in which a spring or other device applies a constant force to drive the movable pulley away from the fixed pulley.

Tensioners can also be used in devices other than stretch towers.

US Patent 5,076,104 describes a device for measuring the breaking load of an optical fiber having a tensioning device comprising a pair of fixed pulleys and a movable pulley. There is also a tensioning device comprising a fixed sheave and a movable sheave; the latter is located below the fixed sheave, is movable in a vertical direction and is connected to a predetermined weight. Fiber in the path is wound on fixed and movable sheaves so that constant tension is maintained.

US Patent 4,505,222 describes an optical fiber extrusion coating apparatus in which a tensioning device is provided immediately upstream of the take-up drum.

US Patent 4,127,370 describes an optical fiber extrusion coating apparatus in which first, second and third pulleys are located at the entrance of the apparatus, immediately downstream of the unwind drum. The first and second pulleys are separated from each other and from the unwind drum. The third pulley has no brackets and is supported on the fiber between the first and second pulleys such that the fiber follows a U-shaped path between the first and second pulleys due to the weight of the third pulley. A pair of photocells are used to detect the vertical position of the third pulley and control the vertical position of the third pulley in such a way as to control the rotational speed of the unwind drum, so that the tension of the fiber is kept substantially constant.

The inventors have found that known types of tensioning devices require the use of gravity and/or predetermined elastic action in order to control the position of the movable pulley, applying an uncontrollable predetermined force to the movable pulley. It is therefore not possible in any way to adjust the force applied to the fixed pulley in order to adjust the sensitivity of the tensioning device. Therefore, the tension control achieved with known devices is of the non-adjustable type and may not be sufficient under certain operating conditions.

The inventors have found that the above problems can be at least partially solved by using an optical fiber tensioning device having a movable pulley on which the optical fiber runs, a means for measuring the tension exerted on the optical fiber and a means for moving the movable pulley, The device is capable of controlling the position of the stop pulley based on the signal generated by the tension measuring device.

The tensioning device according to the present invention is capable of receiving, at its input end, an optical fiber from a fiber guide or a return element or from another type of device, such as a pulling device or an unwinding device, and is capable of, after automatically controlling the tension of the optical fiber, at its The output provides the fiber to a further rail or return element or to another device such as a fiber storage device (in particular a winding device).

In more detail, the tensioning device according to the present invention includes a fixed pulley supported by a bracket structure and a movable pulley supported by a slider capable of sliding along a linear guide rail supported by the bracket structure.

The optical fiber entering the tensioning device is wound for a certain length around the fixed pulley, and then transferred to the movable pulley, and the optical fiber is wound around the movable pulley for another certain length. The distance between the axes of the fixed and movable pulleys can be varied in order to vary the length of the portion of fiber extending between the two pulleys and thus the tension applied to the fiber. In order to vary the distance between the shafts of the fixed and movable pulleys, as described above, use fiber optic tension measuring devices such as load cells connected to the fixed pulleys, and means for moving sliders that can be provided according to the tension measuring device The signal controls the distance between the pulley shafts so that the tension in the fiber is kept almost constant automatically. The moving device may include an electric motor and a system for transferring motion from the electric motor to the slider, such as a screw and nut mating pair, wherein the screw extends parallel to a linear track and can rotate under the force of the motor, wherein the nut is connected to the slider On blocks or on conveyor belts, such as zigzag conveyor belts.

Because the fiber tensioning device described above automatically controls the tension in the fiber without using gravity or other predetermined forces, it can be used to adjust the tension applied to the fiber in a desired manner.

In this way, the movement of the movable pulley has nothing to do with gravity or predetermined elastic force, but can be realized with controllable force.

A tensioning device is thus provided which itself adapts automatically to changes in operating conditions.

According to a first aspect, the present invention relates to an optical fiber tensioning device for use in the forward path of an optical fiber, the device comprising at least one movable pulley around which the optical fiber is wound for at least a predetermined length, the position of said movable pulley being variable to vary the tension applied to tension on the fiber;

further comprising tension measuring means capable of measuring said applied tension and generating a signal indicative of said tension, and electric means for moving said movable pulley capable of receiving said signal indicative of tension and moving the movable pulley in accordance with said signal, In order to automatically keep the tension applied to the fiber substantially constant.

Preferably, the tensioning device further comprises a fixed pulley around which the optical fiber is wound for at least a certain length, the distance between the shafts of said fixed pulley and said movable pulley being variable in order to vary the tension applied to the optical fiber, said motorized movement means The distance can be controlled so as to automatically keep the tension applied to the fiber substantially constant.

The electric moving device may include a guide rail along which the slider supporting the movable pulley can slide, and a drag device for moving the slider along the guide rail.

The pulling means may comprise a screw capable of rotational movement by the force of an electric motor and a nut connected to the slider, or an electric motor and a drive belt type connecting the motor to the slider (for example, using a A zigzag belt) transmission system.

The tensioning device may comprise an electronic control device receiving at its input a reference signal and a measurement signal and capable of generating operating signals for closed-loop control of said motorized moving device in response to said input signals.

The electronic control device is preferably a device for closed-loop control of the tension applied to the optical fiber, including:

- a subtractor to which a tension reference signal proportional to a target tension of the fiber and a measurement signal consisting of said signal representative of the fiber tension are supplied; and

- a controller, preferably a proportional-integral-derivative controller, receiving at its input the tension error signal provided at the output of said subtractor and generating at its output a signal that can be used to operate said electric moving device and a drive signal that controls the distance.

This enables a closed-loop control of the tension in the fiber, by which the tension is continuously monitored, allowing immediate adjustment of the movement device when the measured tension deviates from the reference tension. This keeps the tension in the fiber always equal to the reference tension, enabling particularly precise control.

Preferably, said tension measuring means may comprise a load sensor connected to said fixed pulley and capable of generating said signal indicative of tension at its output.

Preferably, the electric moving device includes a guide rail and a drag device, the slider supporting the movable pulley can move along the rail, and the actuating device is used to move the slider along the guide rail; the electric control The device constitutes a system for closed-loop control of the position of said slider along said guide rail.

Preferably, for operation, the tensioning device is connected to means for storing optical fibers, said means for storing optical fibers is capable of receiving optical fibers from the tensioning device, and said means for closed loop controlling said slider along said guide rail The location system includes:

- another subtractor, to which a position reference signal related to the reference position of said slider along said guideway and a measurement signal proportional to the actual position of said slider along said guideway are supplied; and

- another controller, preferably a proportional-integral-derivative controller, receives at its input the position error signal provided at the output of said further subtractor and generates at its output a signal which can be used to operate said Another drive signal for the storage device.

Said storage device preferably comprises at least one motorized drum on which the optical fiber from said tensioning device is wound, which motorized drum rotates about its axis of rotation under the action of an electric motor, and said another A drive signal can be used to control the electric motor.

The electronic control device preferably includes an integrator which receives at its input a signal related to the velocity of the slider along the track and generates at its output a signal related to the velocity of the slider along the track. The measurement signal is proportional to the actual position of the track.

In this way, it is ensured that the movable pulley always remains near a reference position, from which it can always be moved in the usual way in order to compensate for tension variations; The movable pulley cannot be moved in one of the directions of motion.

According to another aspect, the present invention relates to a method of controlling the tension applied to an optical fiber along its advancing path, the method comprising the step of forming a portion of said path having a length which can be varied to vary the applied tension. tension to said optical fiber, and the steps of measuring the tension applied to said optical fiber and controlling said length in an automatic manner with a motor based on said measured tension so as to maintain the tension in the optical fiber substantially constant.

Preferably, the method comprises the step of closed-loop controlling the tension applied to said optical fiber based on at least one reference signal proportional to a target tension of the optical fiber and a measurement signal generated during the step of measuring tension and Proportional to the actual tension on the fiber.

The step of said closed-loop tension control preferably comprises the following steps:

- comparing said tension reference signal with said measurement signal to generate a tension error signal; and

- processing said tension error signal to produce a drive signal at an output which can be used to scale said length by a motor and keep the tension in the fiber substantially constant.

The method preferably comprises the step of closed-loop controlling the position of the movable element based on at least one position reference signal proportional to the target position of the movable element and a measurement signal proportional to the movable element. A change in the position of the movable element causes a change in the length in proportion to the instantaneous position of the movable element.

The method preferably further includes the step of depositing an optical fiber at a terminal end of the advancing path; the step of closed-loop controlling the position of the movable element includes the following steps:

- comparing said position reference signal with said position measurement signal to generate a position error signal; and

- processing said position error signal to generate a drive signal at the output, which drive signal can be used to vary the speed at which the fiber is deposited.

According to another aspect, the present invention relates to an optical fiber processing system, such as a draw tower, an extrusion line, or an apparatus for measuring the breaking strength of an optical fiber, having an optical fiber tensioning device capable of An input end of the optical fiber source, such as a fiber pulling device, receives the optical fiber, and can provide the optical fiber at its output end to a device for storing the optical fiber, such as a motorized reel, the tensioning device includes at least one movable pulley. The optical fiber surrounds the optical fiber said movable pulley is wound on at least a fixed length, the position of said movable pulley can be varied to vary the tension applied to said optical fiber, said tensioning device further comprising a tensioning device capable of measuring the applied tension and capable of generating a signal indicative of said tension measuring means, and a means for electrically moving said movable pulley capable of receiving said tension-indicative signal and capable of moving said movable pulley in response to said tension-indicative signal to automatically maintain a substantially constant tension in the optical fiber.

Preferably, the system includes an electronic control device capable of providing a closed-loop control system for tension applied to the optical fiber, and includes:

- a subtractor to which a tension reference signal proportional to a target tension of the fiber and a measurement signal consisting of said signal representative of the fiber tension are supplied; and

- a controller, preferably a proportional-integral-derivative controller, receiving at its input the tension error signal provided at the output of said subtractor and generating at its output a signal that can be used to operate said electric moving device drive signal.

Preferably, the electric moving device includes a guide rail and a drag device, the slider supporting the movable pulley can move along the guide rail, and the drag device is used to move the slider along the guide rail; An electronic control unit provides a closed loop control system of the position of the slider along the rail.

Preferably, for operation, the tensioning device is connected to the fiber storage device and said system for closed loop controlling the position of said slider along said guide rail comprises:

- a further subtractor to which a position reference signal related to a reference position of said slider along said track and a measurement signal proportional to the actual position of said slider along said track are supplied; and

- another controller, preferably a proportional-integral-derivative controller, receives at its input the position error signal provided at the output of said further subtractor and generates at its output a signal which can be used to operate said Another drive signal for the storage device.

The invention will now be described with particular reference to the accompanying drawings, which represent, without limitation, preferred embodiments of the invention, in which:

Figure 1 shows a plan view of an optical fiber tensioner made in accordance with the present invention; and

Figure 2 shows a block diagram of an electronic unit for controlling the device of Figure 1 made according to the invention.

In Fig. 1, numeral 1 denotes an optical fiber tensioning device as a whole.

The tensioning device 1 comprises a support plate 3 (for example made of metal), supported by a frame (not shown) which enables the support plate 3 to be positioned in a fixed manner, for example in a horizontal or vertical position.

The tensioning device 1 also comprises at least one linear guide 5, formed in this particular case by two cylindrical rods 12a, 12b, which are supported by the support plate 3, and a slide 7 which can It moves back and forth along the linear guide rail 5 and supports the first pulley 9, which will be called a movable pulley hereinafter. The direction of movement of the slider 7 is indicated by D in FIG. 1 .

The cylindrical rods 12a, 12b are arranged parallel to each other, and their respective end positions are supported by a pair of brackets 15a, 15b fixed to the support plate 3. The slide block 7 can be rectangular in plan view, and can have sliding elements 7a, 7b that cooperate with the rods 12a, 12b respectively; ring formation.

The movable pulley 9 is preferably supported by a pin 20 , and the pin 9 protrudes from the slider 7 and is perpendicular to the slider 7 . At this time, the rotation axis of the movable pulley 9 is perpendicular to the moving direction D of the slider 7 .

The slider 7 can be moved by the force of an electric motor 24, preferably the output shaft of which is connected to a screw 26 located between the rods 12a, 12b and extending parallel to them. The motor 24 may be mounted in a protruding manner on a support 28 fixed to the support plate 3 , and the ends of the screw 26 are preferably supported by corresponding brackets 30 a , 30 b also fixed on the support plate 3 . Preferably, the screw rod 26 is connected to a ball nut (circulating ballnut not shown) fixed on the side of the slider 7 opposite to the side where the movable pulley 9 is located.

Alternatively, the transmission from the motor 24 to the movable pulley 9 can be realized by a belt drive, for example a zigzag belt (not shown).

The tensioning device 1 also comprises a second pulley 32, hereafter referred to as a fixed pulley, supported by pins 33 which preferably extend perpendicularly to the support plate 3, for example on the part of the support plate 3 opposite to where the motor 24 is located superior.

The fixed pulley 32 preferably has the same diameter as the movable pulley 9, and the rotation axes of the pulleys 9 and 32 are preferably parallel to each other.

The angular displacement of the motor 24 produces a linear movement of the slider 7 along the guide rail 5 , thereby changing the distance Dp between the rotational axis of the movable pulley 9 and the fixed pulley 32 .

Specifically, the distance Dp can be continuously varied between a minimum value (DpMin) and a maximum value (DpMax), for which the slider 7 is located in a first extreme position (not shown), where it rests against On the brackets 15 a , 15 b remote from the motor 24 , the slider 7 is in a second extreme position (not shown) for said maximum value, in which it rests on the brackets 15 a , 15 b close to the motor 24 .

The tensioning device 1 can also comprise a transparent protective cover (housing - not shown) which can be connected to the support plate 3 and which can accommodate all the components supported by the support plate.

The tensioning device 1 may be mounted on the path of advancement of the optical fiber 35, for example in a fiber draw tower (not shown), and is capable of receiving the fiber from a fiber source 37 (schematically shown). In the non-limiting example considered here, the fiber source 37 is the pulling device ("capstan") of a fiber draw tower (not shown). Alternatively, the fiber source 37 may be any element or device that returns or guides a fiber or a fiber unwind drum.

The optical fiber 35 extends from the traction device 37 to the fixed pulley 32 to form a first straight portion 35a, is surrounded by the fixed pulley 32 (for example, goes around 180°), extends between the fixed pulley 32 and the movable pulley 9 to form a second straight portion 35b, and is formed by Wrapping around the movable pulley 9 (for example, by 180°), and finally extending between the movable pulley 9 and the other device 40, thus forming the third straight portion 35c. In the non-limiting example considered here, the device 40 (shown schematically) is a storage device comprising a motorized reel 42 on which the optical fiber 35 can be wound. The motorized reel 42 can rotate around the rotation shaft 43 under the action of the motor 45 . Alternatively, device 40 may be any element or device for returning or guiding an optical fiber.

Preferably, the straight portions 35a, 35b, 35c are parallel to each other, but not necessarily.

Between the device 37 and the tensioning device 1 and between the tensioning device 1 and the device 40 there are preferably return pulleys, not shown in FIG. 1 for the sake of simplicity.

The electronic control unit 50 is capable of controlling the electric motor 24 and the electric motor 45 via respective power drive circuits ("drivers") 24p, 45p.

Preferably, the tensioning device 1 comprises a tension measuring device 56 , such as a load cell, preferably connected to the pin 33 of the fixed pulley 32 . The tension measuring device 56 is capable of generating a signal Tmis proportional to the tension experienced by the optical fiber 35 and is connected to the electronic control unit 50 to provide the signal Tmis to the electronic control unit 50 .

With particular reference to Figure 2, the electronic control unit 50 is shown in detail. The electronic control unit 50 comprises a subtractor 60 to which a signal T ₀ proportional to the target tension of the fiber and a signal Tmis proportional to the tension actually experienced by the fiber 35 are supplied. The subtractor 60 generates at its output an error signal ε=ΔT=T ₀ −Tmis (tension error) and supplies this error signal to a controller 62, in particular a PID controller (proportional-integral-derivative) controller, The proportional-integral-derivative controller generates a signal ω (voltage signal, matched to the drive circuit 24p operated by voltage) at its output.

A PID controller is a controller that, upon receiving an input signal S _i, produces an output signal S _o , usually given by: $S_0\left(t\right)=K_p\&Center\; Dot;(S_i\left(t\right)+\frac{l}{T_i}{\∫}_0^t{S}_i\left(t\right)\&Center\; Dot;\mathrm{dt}+T_d\·\frac{d{S}_i\left(t\right)}{\mathrm{dt}})$

Therefore the PID controller can be represented by three constants K _p , K _i =K _p /T _i and K _d =K _p ·T _d .

The signal ω is used to operate the motor 24 after it has been converted and transformed into a power signal by a drive circuit 24p (of known type). The rotational speed of the motor 24 is therefore dependent on the signal ω. The signal ω is also supplied to a conversion unit 64 which generates at its output an output signal V which is related to the linear velocity of the movement of the slide 7 along the guide rail 5 .

In practice, if V _max is the maximum speed of the motor 24 (expressed in revolutions per second), ω _max is the (voltage) value of the signal ω related to the maximum speed V _max , p is the pitch of the screw 26, ω(t) is the general value of the signal ω at the instant t (provided by the output of the controller 62), at its output the conversion unit 64 produces a signal V whose value V(t) at the instant t is given by: $V\left(t\right)=\frac{{\mathrm{\ν}}_{\max }}{{\mathrm{\ω}}_{\max }}\·\mathrm{\ω}\left(t\right)\·p$

In practice, the conversion unit 64 completes the conversion function between the rotation angle of the screw 26 and the linear velocity of the slider 7 .

The signal V is supplied to a further conversion unit 66 which, by integrating the signal V, generates at its output a signal P _mis (voltage) related to the instantaneous position of the slider 7 along the guide rail 5 .

The position signal P _mis is supplied to a subtractor 70 , to which is also supplied a signal P0 corresponding to the target position of the slide 7 along the guide rail 5 . Preferably, the target position of the slider is an intermediate position between the first and second extreme positions.

Subtractor 70 produces an error signal ε=ΔP=P ₀ −P _mis at its output terminal, and provides this error signal to controller 72 (actually a PID (proportional-integral-derivative) controller), which controls The converter generates at its output a signal ωb, which is used to operate the motor 45 after conversion and conversion of this signal into a power signal by a drive circuit 45p (of known type). The signal ωb is related to the rotational speed of the spool 42 .

In operation, when the velocity imparted to the input fiber 35 by the storage means is greater than the velocity supplied to the fiber from the output end of the pulling means 37, the tension Tmis in the fiber increases and deviates from the target value _T0 .

Therefore, the absolute value of the tension error ΔT (a negative value in this case) increases, and the controller 62 rotates the motor 24 through the drive circuit 24p to move the slider 7 to the first limit position, so that the tension between the two pulleys The distance Dp between them and the length of the fiber portion 35b between them are reduced; such a reduction in the length of the portion 35b relatively increases the tension in the fiber, so that the tension in the fiber remains substantially unchanged.

Therefore, when the velocity imparted to the input fiber 35 by the storage device 40 is less than the velocity supplied to the fiber from the output end of the pulling device 37, the tension Tmis in the fiber decreases and deviates from the target value _T0 . Therefore, the tension error ΔT (a positive value at this time) increases, and the controller 62 rotates the motor 24 through the drive circuit 24p so as to move the slider 7 to the second extreme position, so the distance Dp between the two pulleys and part The length of 35b increases; such an increase in the length of portion 35b relatively reduces the tension in the fiber such that the tension in the fiber remains substantially constant.

This provides an electrical closed-loop tension control, thereby returning the tension in the fiber to the target value T ₀ .

Furthermore, the unit 66 determines the instantaneous position P _mis of the slider 7 along the guide rail 5 by integrating the signal V (related to the linear velocity of the slider 7 ). The instantaneous position is compared with the target position P ₀ , and the position error ΔP is processed by the conversion unit 72 to generate a rotational speed variable of the motor 45 . Specifically, when the slider 7 is closer to the first limit position than the reference position (the slider 7 moves to the left in FIG. 1 ), the control system causes the rotation speed of the motor 45 to decrease so as to reduce the tension in the optical fiber 35. small, and in order to compensate for the tension deviation, the tension control loop moves the slider 7 to the second extreme position (in other words, to the right in Fig. 1) (through the motor 24 and the screw 26), thereby compensating for the change in position

Furthermore, when the slider 7 is closer to the second extreme position than the reference position (the slider 7 moves to the right in FIG. 1 ), the control system causes the rotation speed of the motor 45 to increase so that the tension in the optical fiber 35 increases, In order to compensate for the tension deviation, the tension control loop moves the slide block 7 to the first limit position (in other words, to the left in FIG. 1 ) (by the motor 24 and the screw rod 26), thereby compensating for the position change.

This provides an electrical closed-loop position control to return the slider to the target value P ₀ .

If desired, the position controller can be omitted; in this case, the control unit does not include the elements indicated by reference numerals 64, 66, 70, 72 and 45p.

The above description clearly shows that the advantage of the present invention is that the movement of the movable pulley 9 depends only on the action of the motor 24, and is completely independent of gravity or other predetermined forces (such as known elastic types) exerted on the movable pulley 9. In this way, a force whose value can be automatically controlled according to the operating signal applied to the motor 24 is applied to the optical fiber 35 . The tensioning device 1 itself automatically adapts to any changes in operating requirements (such as changes in the drawing speed or changes in the position of the slider 7) and restores the tension value applied to the optical fiber to the target value

In addition, it is also ensured that the movable pulley 9 is always kept close to the reference position (specifically the middle position of the guide rail 5), so that it can always move from this position in an effective route (to the right or to the left) in order to compensate for tension changes . In other words, the slider 7 is prevented from being located close to the first or second limit position, where the slider cannot move in one of the two directions.

The tensioning device 1 can be used in different types of equipment, for example in draw towers, in extrusion lines or in testing equipment (also called "screening equipment") for measuring the breaking stress of optical fibers.

A draw tower typically includes a furnace for melting a preform of glass material, a pulling element (or "capstan," such as one of the single or double pulley types) for downwardly drawing the optical fiber resulting from the molten preform, A coating device for applying a protective surface coating (usually formed of acrylate) to the optical fiber, located between the furnace and the pulling element, and a fiber optic spool for receiving the optical fiber from the pulling element. As mentioned above, the tensioning device 1 can advantageously be positioned between the traction element and the winding drum.

Extruded lines are lines processed such that a plurality of optical fibers are advanced along the line along with a linear support element and along which a polymeric material is extruded onto the support element in such a way as to join the fibers and hold them In a fixed position around the support element, thereby forming the fiber core of the optical fiber. Extrusion lines typically include an unwind drum for the support element, a plurality of fiber unwind drums, an extruder capable of receiving the optical fiber and the support element at its inlet, for receiving from the extruder the Cooling chamber for optical fiber core, and terminal winding drum. A tensioning device 1 may eg be arranged downstream of each fiber unwinding drum in the extrusion line.

Screening equipment is often used to test whether an optical fiber can withstand a predetermined tension so that it is not affected by significant structural defects. Screening equipment typically includes an unwinding drum for the optical fiber, a take-up drum for the optical fiber and a plurality of guide and/or return elements capable of forming a fiber path between the unwinding and winding drums, Also, a predetermined tension can be imparted to the optical fiber during passage of the optical fiber. In the screening equipment, the tensioning device 1 can be arranged at any point of the above-mentioned path.

Finally, it is obvious that modifications and variants can be made to the tensioning device without departing from the scope of protection of the present invention.

In particular, the system for moving the slider 7 (screw 26 and nut connected to the slider 7) may differ from the system described, for example may include a Zigzag belt (not shown).

Finally, the position Pmis of the slider 7 along the guide rail 5 can be determined not by the indirect method shown in FIG. Photocells, or optical strips (in other words linear photosensitive elements, such as linear CCDs—not shown), are arranged along the guide rail 5 .

Claims (20)

1. An optical fiber tensioning device used on the advancing path of the optical fiber (35), comprising at least one movable pulley (9), the optical fiber (35) is wound at least a predetermined length around the movable pulley (9); the movable pulley (9) The position of can be varied in order to change the tension applied to the optical fiber (35), It is characterized in that it comprises a tension measuring device (56) capable of measuring the applied tension and generating a signal representing the tension (Tmis), and motorized moving means (24,26, 5, 7, 50), the device is capable of receiving said signal indicative of tension (Tmis) and moving the movable pulley according to said signal indicative of tension (Tmis) so as to automatically maintain the tension applied to the optical fiber (35) substantially constant. 2. The device according to claim 1, characterized in that it also comprises a fixed pulley (32) around which the optical fiber (35) is wound for at least a certain length; said fixed pulley (32) and said movable pulley The distance (Dp) between the axes (33,20) can be varied in order to change the tension applied to the fiber; The tension applied to the fiber is essentially constant. 3. The device according to claim 1 or 2, characterized in that said motorized moving device (24, 26, 5, 7) comprises a guide rail (5) and a drag device (26, 24) supporting said movable pulley The slider (7) of (9) can move along the guide rail (5), and the dragging device (26, 24) is used to move the slider (7) along the guide rail (5). 4. The device according to claim 3, characterized in that said dragging device comprises a screw (26) capable of rotational movement under the force of an electric motor (24) and connected to said slider (7) on a nut. 5. Apparatus according to claim 3, characterized in that said drive means comprise an electric motor (24) and a belt-type motion transmission system. 6. The device according to claim 2, characterized in that it comprises an electric control device (50) receiving at its input the reference signal (T ₀ , P ₀ ) and the measurement signal (Tmis, P _mis ) and capable of responding The input signal generates an operating signal (24p, 45p) for closed loop control of the electric moving device (24, 26, 5, 7). 7. The device according to claim 6, characterized in that said electronic control device (50) forms a system for closed-loop control of the tension applied to the optical fiber (35), comprising: - a subtractor (60) to which is supplied a tension reference signal (T ₀ ) proportional to the target tension of the fiber and a measurement signal (Tmis) consisting of said signal representative of the tension; and - a controller (62) receiving at its input the tension error signal (ε=ΔT=T ₀ -Tmis) provided from the output of said subtractor (60) and generating at its output a capable A drive signal (ω) for operating said electric moving means (24, 26, 5, 7) and controlling said distance (Dp). 8. Apparatus according to claim 7, characterized in that said controller (62) comprises a proportional-integral-derivative controller. 9. The device according to claim 7, characterized in that said tension measuring device (56) comprises a load cell (56) connected to said fixed pulley (32) and capable of generating at its output The signal indicative of tension (Tmis) is indicated. 10. Device according to claim 6 or 7, characterized in that said motorized moving device (24, 26, 5, 7) comprises a guide rail (5) and a drag device (26, 24) supporting said movable pulley The slider (7) of (9) can move along the guide rail, and the dragging device (26, 24) is used to move the slider (7) along the guide rail (5); the electric control device (50) constitutes a system for closed-loop control of the position of said slider (7) along said guide rail (5). 11. Device according to claim 10, characterized in that for operation it is connected to means (40) for storing optical fibers capable of receiving optical fibers from tensioning means, and in that said A system for closed-loop control of the position of said slider (7) along said guide rail (5) comprises: - another subtractor (70), the position reference signal (P ₀ ) related to the reference position of said slider (7) along said guide rail (5) and related to said slider (7) along said A measurement signal (Pmis) proportional to the actual position of the guide rail (5) is supplied to the subtractor (70); and - another controller (72) receiving at its input the position error signal (ε=Δp=P ₀ -Pmis) provided by the output of said further subtractor (70) and receiving at its output A further drive signal (ωb) is generated which can be used (45p) to operate said storage device (40). 12. Apparatus according to claim 11, characterized in that said further controller (72) comprises a proportional-integral-derivative controller. 13. Device according to claim 11, characterized in that said storage device (40) comprises at least one motorized reel (42) on which the optical fiber (35) from said tensioning device (1) is wound On the cylinder (42), the electric reel (42) can rotate around its rotation axis (43) under the action of the motor (45), and the other drive signal (ωb) can be used for (45p) The electric motor (45) is controlled. 14. The device according to claim 11, characterized in that said electronic control device (50) comprises an integrator (66) which receives at its input speed-dependent signal (V) moving along the guide rail (5) and generates at its output the measurement signal proportional to the actual position of the slider (7) along the guide rail (5) (Pmis). 15. A method of controlling tension applied to an optical fiber (35) along its advancing path, the method comprising the step of forming a portion (35b) of said path having a length (Dp), said length being variable so as to varying the tension applied to the fiber, characterized in that it further comprises the step of measuring (56) the tension applied to said optical fiber and the step of controlling said length (Dp) in an automatic manner by means of an electric motor according to said measured tension, so as to maintain the tension applied to said optical fiber The tension is essentially constant. 16. A method according to claim 15, characterized in that it further comprises the step of closed loop controlling the tension applied to said optical fiber based on at least one reference signal (T ₀ ) and a measurement signal (Tmis), said at least one reference signal (T ₀ ) is proportional to the target tension of the fiber, and the measurement signal (Tmis) is generated in the step of measuring the tension and is proportional to the tension actually experienced by the fiber. 17. The method according to claim 16, wherein said step of closed-loop tension control comprises the following steps: - comparing (60) said tension reference signal with said measurement signal (Tmis), generating a tension error signal (ε=ΔT=T ₀ -Tmis); and - processing (62) said tension error signal to produce at output a drive signal (ω) which can be used (24P) to vary said length (Dp) by means of an electric motor and to keep the tension in the fiber substantially constant . 18. A method according to claim 15, characterized in that it further comprises the step of closed-loop controlling the position of a movable element (7) based on at least one position reference signal (P ₀ ) and a measurement signal (Pmis), said at least one position The reference signal (P ₀ ) is proportional to the target position of the movable element, the measurement signal (Pmis) is proportional to the instantaneous position of the movable element, a change in position of the movable element (7) causes the The stated length (Dp) varies. 19. The method of claim 18, wherein optical fibers are deposited at the end of said forward path, and wherein said step of closed-loop controlling the position of said movable member comprises the steps of: - comparing (70) said position reference signal (P ₀ ) with said position measurement signal (Pmis), generating a position error signal (ε=ΔP=P ₀ -Pmis); and - processing (72) said position error signal to generate at output a drive signal (ωb) which can be used (45p) to vary the speed of the deposited fiber. 20. An optical fiber processing system comprising an optical fiber source (37), an optical fiber tensioner (1) capable of receiving an optical fiber (35) at its input end from the optical fiber source (37), and an optical fiber tensioner (1) capable of receiving an optical fiber (35) from the tensioner (1) an optical fiber storage device (40) for receiving an optical fiber, the tensioning device (1) includes at least one movable pulley (9), and the optical fiber (35) is wound at least a certain length around the movable pulley (9); the movable pulley The position of (9) can be varied in order to vary the tension applied to said fiber; said system is characterized in that said tensioning device (1) comprises a device capable of measuring the applied tension and producing a signal tension measuring device (56), and an electric moving device (7, 24, 26), which can receive said signal representing tension and can move movable pulley (9) according to said signal representing tension, so as to automatically maintain The tension in the fiber is essentially constant.

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