JPH07215725A - Apparatus for producing porous preform for optical fiber - Google Patents

Abstract

PURPOSE:To improve the accuracy of weight measurement in real time of a porous preform by supporting a revolving shaft of this porous preform vertically movably relative to a perpendicular moving body, installing a sensor between the moving part of a supporting mechanism thereof and this perpendicular moving body and providing the moving part with a vibration absorbing mechanism. CONSTITUTION:This apparatus has the perpendicular revolving shaft 11 which rotates while supporting the porous preform 17 for an optical fiber during production at its bottom end and the perpendicular moving body 27 which moves this revolving shaft 11 upward according to the growth of the porous preform 17. The apparatus is provided with a vertical movement permitting mechanism which vertically movably supports the revolving shaft 11 to the perpendicular moving body 27. The weight sensor 41 for detecting the weight of the porous preform 17 is disposed between the moving part of this vertical movement permitting mechanism and the perpendicular moving body 27. Further, a passive type vibration absorbing mechanism 45 and/or active type vibration absorbing mechanism 47 for absorbing the vibrations in a vertical direction is disposed in a part of the moving part of the vertical movement permitting mechanism and the revolving shaft.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing a porous preform for optical fibers by the VAD method, and more particularly to an apparatus for measuring the weight of the porous preform during production in real time.

[0002]

2. Description of the Related Art An apparatus for producing a porous preform for optical fibers by the VAD method is provided with a vertical rotary shaft for supporting and rotating the porous preform for optical fiber being manufactured at the lower end, and this rotary shaft. And a vertical moving body that is raised according to the growth of the.

The stability of soot density in the longitudinal direction is important for the porous preform for optical fibers manufactured by the VAD method. For that purpose, it is necessary to accurately measure the pulling distance and weight of the porous base material during manufacturing in real time, and to accurately control the feed amount of the raw material gas to the burner, the pulling distance, etc. based on that. The pulling distance can be measured relatively easily and accurately by attaching an encoder or the like to the ball screw that moves the vertical moving body. However, it is extremely difficult to measure the weight of the growing porous base material in real time and with high accuracy.

Conventionally, as a device capable of measuring the weight of the porous base material in real time, a weight sensor is attached to a part of the rotary shaft, and the weight applied to the rotary shaft is detected by the weight sensor to detect the weight of the porous base material. It has been proposed to measure the weight of.

[0005]

However, the conventional device has the following problems. That is, since a part of the rotary shaft is made into a sensor, the rigidity of the rotary shaft is lowered, and whirling tends to occur. Further, when trying to improve the accuracy of weight measurement, the weight sensor becomes vulnerable to overload, and the weight sensor often breaks when the porous base material is replaced. When replacing the porous base material, it is very laborious to replace the rotary shaft together. Therefore, the conventional device is difficult to apply to an actual production facility.

[0006]

[Means for Solving the Problems] As a means for measuring the weight of a porous base material while maintaining the rigidity of a rotating shaft, the rotating shaft is not directly supported by a vertical moving body, but the rotating shaft is moved by the vertical moving body. It is conceivable that the structure is supported so that it can move up and down, and a weight sensor is installed between the movable part of the support mechanism and the vertical moving body so that the weight sensor receives the weight of the porous base material.

However, in this structure, since the rotating shaft is supported so as to be vertically movable with respect to the vertical moving body, vertical vibration is generated in the rotating shaft when the vertical moving body is gradually raised by the on / off control. Cheap. When vertical vibration occurs on the rotating shaft, there is a problem that not only cracks are likely to occur in the porous base material, but also the weight measurement accuracy decreases.

In view of the above, the present invention provides a vertical axis of rotation at the lower end for supporting and rotating the porous preform for optical fiber being manufactured,
In an apparatus for producing a porous preform for optical fibers, which is provided with a vertical moving body that raises the rotating shaft according to the growth of the porous preform, an upper and lower unit that supports the rotating shaft so as to be vertically movable with respect to the vertical moving body. A motion permitting mechanism is provided, and a weight sensor for detecting the weight of the porous base material is provided between the movable part of the vertical motion permitting mechanism and the vertical moving body, and further, the movable part of the vertical motion permitting mechanism or a part of the rotary shaft. It is characterized in that a vibration absorbing mechanism for absorbing vertical vibration is provided in the.

As the vertical movement allowance mechanism, a shaft support member that rotatably supports a rotary shaft and a vertical portion of a vertical moving body are connected by parallel links so that the shaft supporting member moves up and down with respect to the vertical moving body. It is desirable to use a parallel link mechanism that is possible, but it is also possible to use a linear guide or a spline shaft. As the vibration absorbing mechanism, either one or both of a passive type vibration absorbing mechanism and an active type vibration absorbing mechanism can be used. Further, the apparatus of the present invention may be provided with an acceleration sensor that detects acceleration when the vertical moving body rises, and a correction unit that corrects the weight value detected by the weight sensor according to the output of the acceleration sensor. desirable.

[0010]

The rotating shaft supporting the porous base material is supported by the vertical movement allowing mechanism so as to be vertically movable with respect to the vertical moving body. On the other hand, a weight sensor is installed between the vertical moving body and the movable portion of the vertical movement allowance mechanism. This weight sensor receives the weight applied to the rotating shaft. That is, since the output of the weight sensor changes in accordance with the increase in the weight of the porous base material, the weight of the porous base material can be measured in real time. Moreover, the rigidity of the rotating shaft is not reduced.

Further, since the rotary shaft is supported so as to be vertically movable, there is a concern that the rotary shaft may vibrate in the vertical direction. This vibration is absorbed by the movable portion of the vertical motion allowance mechanism or a part of the rotary shaft. It is absorbed by the mechanism.

The weight value measured by the weight sensor includes a variation in the weight measurement value due to a change in acceleration when the vertical moving body rises. The measurement error of the weight sensor due to the change in the acceleration can be reduced by separately providing an acceleration sensor and correcting the weight measurement value of the weight sensor according to the output thereof.

The acceleration sensor may be provided if necessary. When the acceleration sensor is not provided, for example, the weight measurement accuracy can be improved by not performing the weight measurement only when the vertical moving body's rising acceleration changes.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. This apparatus is an apparatus for producing a porous preform for optical fibers by the VAD method. In the figure, reference numeral 11 is a vertical rotary shaft, 13 is a chuck provided at the lower end of the rotary shaft 11, 15 is a starting member held by the chuck 13, and 17 is an optical fiber which is attached to the starting member 15 and is growing. Porous matrix, 19 is porous matrix
It is a burner that blows soot (fine particles of glass raw material) on the lower end of 17.

This apparatus is provided with a shaft support member 23 that rotatably supports the upper portion of the rotary shaft 11 via a bearing 21. The rotary shaft 11 is a motor fixed to the upper end of the shaft support member 23.
Rotated by 25.

Reference numeral 27 is a vertical moving body that rises in accordance with the growth of the porous base material 17, 29 is a ball screw that meshes with a female screw portion of the vertical moving body 27, 31 is a motor for rotating the ball screw 29, and 32 is on / off. Rotation of ball screw 29 by control
A clutch for switching the stop, 33 is a guide rod for guiding the vertical moving body 27 to move vertically. Vertical moving object 27
Is vertically raised or lowered by the rotation of the ball screw 29.

The vertical moving body 27 has a vertical portion 27a,
The vertical portion 27a and the shaft support member 23 are connected by two parallel links 35A and 35B. Links 35A, 35B
And connecting portions 37A and 37B between the vertical portion 27a of the vertical moving body and connecting portions 39A and 39B between the links 35A and 35B and the shaft support member 23.
Each is composed of a shaft and a bearing, and it is made with high precision so that it rotates but does not move at all in other directions. The distance between the connecting portions 37A and 37B and the distance between the connecting portions 39A and 39B are the same, and the distance between the connecting portions 37A and 39A and the connecting portion 37B,
The distance between 39B is also the same.

That is, the vertical portion 27a of the vertical moving body, the shaft support member 23, and the two links 35A and 35B constitute a parallel link mechanism. As a result, the shaft support member 23 can freely move up and down with respect to the vertical moving body 27 in a vertical state. Particularly when the parallel links 35A and 35B are in a substantially horizontal state, the shaft support member 23 and the rotary shaft 11 supported by the shaft support member 23 can move up and down substantially vertically.

A weight sensor 41 such as a load cell is installed between the tip of the lower link 35B and the vertical moving body 27 located therebelow. The weight sensor 41 is fixed to the vertical moving body 27 and supports the tip end of the link 35B at its upper end so as not to descend. The link 35B is substantially horizontal with its tip end supported by the weight sensor 41. Link 35B to adjust the load on the weight sensor 41.
A balance weight 43 is attached to the rear end side. In addition, a stopper is installed as necessary to prevent the weight sensor 41 from being overloaded (not shown).
The stopper does not contact the link 35B under normal conditions.

With the above construction, the weight increase due to the growth of the porous base material 17 acts on the weight sensor 41 as a force to lower the shaft support member 23. The weight of the base material 17 can be measured. The weight Q applied to the weight sensor 41 and the weight R applied to the shaft support member 23 (= weight of the porous base material 17) are given by the equation 1 from the balance of moments (see FIG. 1 for a and b). ).

[0021]

[Formula 1] R = Q · (a + b) / a

Further, in the above structure, since it is not necessary to attach a weight sensor to the rotary shaft 11, it is not necessary to reduce the rigidity of the rotary shaft 11. In addition, the vertical movement allowance mechanism that uses the parallel link mechanism has less frictional resistance during vertical movement, higher rigidity in directions other than vertical movement, and assembly adjustment compared to the vertical movement allowance mechanism that uses a linear guide or spline shaft. Is easy. Further, due to the weight of the porous base material 17, even if the shaft support member 23 is displaced slightly downward, the horizontal displacement amount of the lower end position of the porous base material 17 is negligible,
It has no effect on the production of the porous matrix.

This device also includes a passive vibration absorbing mechanism 45 and an active vibration absorbing mechanism 47 in order to absorb the vibration of the movable portion of the parallel link mechanism. The passive vibration absorbing mechanism 45 and the active vibration absorbing mechanism 47 may be attached to any of the movable parts of the parallel link mechanism, but in the example shown in the figure, the passive vibration absorbing mechanism 45 is used for the balance weight 43 and the active vibration absorbing mechanism. The mechanism 47 is attached to the shaft support member 23.

The passive vibration absorbing mechanism 45 comprises a balance weight 43, a vibration absorbing material 49 made of gel-like soft rubber, and a damper weight 51. The passive vibration absorbing mechanism 45 absorbs the vertical vibration of the movable portion of the parallel link mechanism by the inertia of the damper weight 51 and the elastic deformation resistance of the vibration absorbing material 49.

On the other hand, the active vibration absorbing mechanism 47 includes a cylinder 53 fixed vertically to the shaft supporting member 23, an auxiliary weight 57 supported in the cylinder 53 by a coil spring 55 so as to be movable up and down, and a cylinder 53. It is composed of a communication pipe 59 that connects the upper end and the lower end, a regulating valve 61 provided in the middle of the communication pipe 59, a cylinder 53, and oil 63 filled in the communication pipe 59.

The active vibration absorbing mechanism 47 absorbs vertical vibration by the inertia of the auxiliary weight 57 and the flow resistance of the oil 63. Particularly, since the vibration absorbing mechanism 47 can adjust the flow resistance of the oil 63 by the opening degree of the adjusting valve 61, the vibration absorbing characteristic can be changed. Rotating shaft 11
Since the vibration characteristics of the movable portion including the change with the growth of the porous base material 17, if the vibration absorption characteristics can be changed, it is possible to obtain the optimum vibration absorption effect according to the growth of the porous base material 17. it can. For example, when the porous base material 17 is small, the vibration absorbing action can be weakened, and as the porous base material 17 is large, the vibration absorbing action can be strengthened.

By providing the vibration absorbing mechanism as described above, the vertical vibration can be quickly attenuated even when the vertical moving body 27 is impacted by the switching of the clutch 32 or the like, and the vertical movement of the porous base material 17 is prevented. Vibration can be suppressed.
Also, because vibration noise that enters the weight measurement value can be reduced,
The weight measurement accuracy can be improved.

The device also includes an acceleration sensor 65. The acceleration sensor 65 is attached to the shaft support member 23 and detects acceleration when the vertical moving body 27 rises.
The weight sensor 41 tends to detect the weight larger than the actual weight when a positive acceleration occurs in the rising speed of the vertical moving body 27 and to detect the weight smaller than the actual weight when the negative acceleration occurs. is there. Therefore, this device uses a correction circuit for the output of the weight sensor 41 and the output of the acceleration sensor 65.
The input value is input to 67, and the weight measurement value of the weight sensor 41 is corrected according to the magnitude of acceleration. Correction circuit
In 67, the relationship between the acceleration and the weight measurement value is previously checked and stored.

The weight value measured in this way is used to control the motor 31 for raising the vertical moving body 27 and the burner 19
It is used to control the raw material gas supplied to. The acceleration sensor 65 may be attached to the vertical moving body 27 instead of the shaft support member 23. Further, the acceleration sensor 65 is provided as necessary and can be omitted.

Next, the method of correcting the weight measurement value will be described more specifically. Since the acceleration does not act on the weight sensor 41 when the vertical moving body 27 is stationary or is rising at a constant speed, it is not necessary to correct the weight value measured by the weight sensor 41. Acceleration acts on the weight sensor 41 when the vertical moving body 27 switches from stationary to rising and when it switches from rising to stationary. The acceleration acts on the weight sensor 41 as a force proportional to the mass supported by the weight sensor 41, that is, an inertial force. That is, the porous matrix
When the mass of 17 is small, the inertial force is small and the porous matrix 17
When the mass of is large, the inertial force becomes large. The inertial force also varies depending on the mass of the weight measuring mechanism (including the movable part of the parallel link mechanism, the vibration absorbing mechanism, the rotating shaft 11, etc.). The relationship is expressed by the equation (2).

[0031]

[Equation 2] R = P · G + (P + K) · α

However, P: true mass of the porous matrix (kg) R: measured weight of the porous matrix (kgf) α: measured acceleration (m / s ² ) K: equivalent of the weight measurement mechanism Mass (kg) G: Gravitational acceleration (m / s ² )

Therefore, the measured weight value R of the porous base material is corrected by the formula 3 which is a modification of the formula 2.

[0034]

[Formula 3] P = (R−K · α) / (G + α)

By doing so, it becomes possible to measure the weight of the porous base material in real time with extremely high accuracy.

Next, the results of trial production of the porous base material by the apparatus shown in FIG. 1 will be described. First, when the porous base material was manufactured without attaching the vibration absorbing mechanisms 45 and 47, cracks were generated in the porous base material 17 3 hours after the start of synthesis. With this device,
The time from the impact being applied until the vibration subsided (vibration damping time) was 20 seconds. Weight measurement accuracy is 0.2%
(The error was ± 2 g for 1 kg of the porous base material).
The weight sensor 41 used was a load cell, and the rating was 50.
N, the rigidity of the detection part was 250 kN / m.

Next, as shown in FIG. 1, a passive vibration absorbing mechanism
45 and an active vibration absorbing mechanism 47 were attached and a manufacturing experiment of a porous base material was conducted. The vibration absorbing material 49 of the passive vibration absorbing mechanism 45 has a stress of 0.1 MPa at 10% compression, a thickness of 5 mm, and an area.
It is 100 cm ² of soft rubber, and the weight of the damper weight 51 is 1 kg. In addition, the active vibration absorbing mechanism 47 includes a cylinder 53
Has an inner diameter of 30 mm, auxiliary weight 53 has a weight of 0.5 kg, coil spring 55 has a spring constant of 2 kN / m, and oil 63 has a viscosity of 100 ×.
10 ^-3 Pa · s, the opening adjustment range of the adjusting valve 61 is 1 to 10 mm ² . The opening degree of the adjusting valve 61 was adjusted to be large while the porous base material 17 was small and to be small as the porous base material 17 was large.

The vibration damping time of this device was within 1 second over the entire time from the start to the end of the synthesis. In addition, no cracks were generated in the porous base material 17 for 16 hours until the completion of the synthesis. The accuracy of weight measurement is 0.1% (10kg ± 10
g). The weight sensor 41 used was a load cell, the rating was 200 N, and the rigidity of the detection part was 1000 kN / m.

Next, FIG. 2 shows another embodiment of the present invention. This device is different from the device of FIG. 1 in that only a passive vibration absorbing mechanism 45 is provided as a vibration absorbing mechanism and an active vibration absorbing mechanism is omitted. Since the other configurations are the same as those of the apparatus of FIG. 1, the same parts are designated by the same reference numerals.

When a porous base material was prototyped with this apparatus,
No cracks were generated in the porous base material 17 until 10 hours passed after the synthesis was started, but cracks were often generated when the amount was more than 10 hours. The vibration damping time of this device was within 1 second from the start of synthesis up to 10 hours. The accuracy of the weight measurement was 0.1% (1 kg ± 1 g). The weight sensor 41 used was a load cell, the rating was 50 N, and the rigidity of the detecting portion was 250 kN / m. According to this result, when the finished weight of the porous base material 17 is about 1 kg (synthesis time is within 10 hours), the passive vibration absorbing mechanism 45 alone is sufficient as the vibration absorbing mechanism.

Next, FIG. 3 shows still another embodiment of the present invention. This device is different from the device of FIG. 2 in that the passive vibration absorbing mechanism 45 is attached to the rotating shaft 11 instead of the balance weight 43. This passive vibration absorption mechanism 45
Is a structure in which a cylindrical vibration absorbing material 49 and a cylindrical damper weight 51 are coaxially attached around the rotating shaft 11.
The lower end of the vibration absorbing material 49 is received by the flange portion 69 formed on the rotating shaft 11, and the vibration absorbing material 49 is also interposed between the flange portion 69 and the lower end of the damper weight 51. Since the other configuration is the same as that of the apparatus of FIG. 2, the same reference numerals are given to the same portions. With such a device, the same vibration absorption effect and weight measurement accuracy as those of the device of FIG. 2 can be obtained.

[0042]

As described above, according to the present invention, the weight of the porous base material can be measured in real time without lowering the rigidity of the rotating shaft. Further, by providing the vibration absorbing mechanism, it is possible to prevent the generation of cracks in the porous base material and improve the accuracy of weight measurement.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of an optical fiber porous base material manufacturing apparatus according to the present invention.

FIG. 2 is an overall configuration diagram showing another embodiment of the present invention.

FIG. 3 is an overall configuration diagram showing still another embodiment of the present invention.

[Explanation of symbols]

11: Rotating shaft 17: Porous base material 19: Burner 21: Bearing 23: Shaft support member 25: Motor 27: Vertical moving body 29: Ball screw 31: Motor 33: Guide rod 35A, 35B: Link 37A, 37B,
39A, 39B: Connection part 41: Weight sensor 43: Balance weight 45: Passive vibration absorption mechanism 47: Active vibration absorption mechanism 49: Vibration absorption material 51: Damper weight 53: Cylinder 55: Coil spring 57: Auxiliary weight 59: Communication pipe 61: Regulator valve 63: Oil 65: Acceleration sensor 67: Correction circuit

Claims (4)

[Claims] 1. A vertical rotating shaft for supporting and rotating a porous base material for an optical fiber being manufactured at its lower end, and a vertical moving body for raising this rotating shaft according to the growth of the porous base material. In an apparatus for manufacturing a porous preform for optical fibers, a vertical movement allowing mechanism that supports the rotating shaft so as to be vertically movable with respect to a vertical moving body is provided, and between the movable part of the vertical movement allowing mechanism and the vertical moving body. A weight sensor for detecting the weight of the porous base material is provided, and further, a vibration absorbing mechanism for absorbing vertical vibration is provided at the movable part of the vertical movement allowance mechanism or a part of the rotating shaft. Quality base material manufacturing equipment. 2. The manufacturing apparatus according to claim 1, wherein the vertical movement allowance mechanism connects a shaft support member for rotatably supporting the rotary shaft and a vertical portion of the vertical moving body with parallel links, A parallel link mechanism in which a shaft support member is vertically movable with respect to a vertical moving body. 3. The manufacturing apparatus according to claim 1, wherein the vibration absorbing mechanism includes one or both of a passive vibration absorbing mechanism and an active vibration absorbing mechanism. . 4. The manufacturing apparatus according to claim 1, 2 or 3, further comprising: an acceleration sensor for detecting acceleration when the vertical moving body rises, and a weight sensor for detecting an output of the acceleration sensor. A correction means for correcting the weight value is provided.