JPS593943B2 - Temperature control method during glass production using MCVD method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 10 The present invention relates to a temperature control method during glass production by MCVD method.

Glass rods are the base material for these types of products, such as optical fibers as optical communication parts and rod lenses as optical system parts.
Manufacturing by the CVD method has already been carried out.

As shown in Figure 1, this MCVD method uses a quartz-based glass tube 1.
The glass tube 1 is rotated by the motor 3 while the glass tube 1 is supported at both ends by a pair of rotatable chucks 2A and 2B. Gas (glass component in gas phase,
dopant, carrier gas), and chemically reacts the raw material gas with the oxyhydrogen flame T from the burner 6 moving along the longitudinal direction of the glass tube 1 to oxidize it.
The powder is deposited on the inner peripheral surface of the glass tube 1, and at the same time, the powder is vitrified with high temperature heat.

Below, by repeating the above steps, a glass layer of a predetermined thickness is deposited on the inner peripheral surface of the glass tube 1, and then
The hollow portion left at the axial center of the glass tube 1 is removed by a high-temperature heat treatment process (collapse process), and the glass tube 1 is processed into a glass rod. Thus MCV
When carrying out method D, the burner 6 is reciprocated in the longitudinal direction 35 of the glass tube 1 via a traverse mechanism.

In other words, the traverse mechanism includes a guide shaft 8 having a screw thread, a motor 9 connected to one end of the feed shaft 8 and capable of rotating forward and backward, and a traverse unit 10 screwed onto the feed shaft 8. The burner 6 is attached to the traverse unit 10 together with a temperature detector 11 made of a phototube or the like, and as the traverse unit 10 reciprocates via the feed shaft 8 and motor 9, the burner 6 moves toward the outer circumference of the glass tube 1. It moves back and forth.

Normally, the movement range of the burner 6 via the traverse mechanism is determined by the position detector 12 located at point F and point B in FIG.
13, and during the forward motion when moving at a low speed from point F to point B, the burner 6 is set to high flame to heat the glass tube 1, but during the backward motion when moving from point B to point F at high speed, The burner 6 is set to a low flame, and during the formation of the glass layer described above, the burner 6 is moved back and forth between point F and point B about 100 times.

In the above MCVD method, when the burner 6 moves slowly from point F to point B, the thermal power of the burner 6 (the amount of oxyhydrogen On the other hand, when the burner 6 returns to a low flame state, the glass tube 1 is in a state where it is naturally cooled, and the temperature of the burner 6 is not controlled.

Further, during heating when the burner 6 moves from point F to point B, the heating temperature by the burner 6 is controlled by the PID method.

When performing the MCVD method as described above, the heat storage temperature of the glass tube 1 gradually rises due to repeated heating during forward movement of the burner, and this value becomes a bias, and the amount of overshoot during heating temperature control tends to increase. You will begin to take .

In other words, when L in Fig. 2 is a predetermined control temperature, L, ,
As heating is repeated like L2, L, L4, L5, etc., the overshoot amount increases, making it impossible to perform stable temperature control.

Of course, if such temperature control instability occurs, the refractive index distribution during glass production will vary, and the yield will deteriorate when manufacturing glass rods with a desired refractive index distribution.

In view of the above-mentioned problems, the present invention aims to provide a stable temperature control method in the MCVD method, and a specific method thereof will be explained below with reference to illustrated embodiments.

In the embodiment of the invention shown in FIG. 3, glass is deposited in the glass tube 1 in a manner similar to that described in FIG.

Therefore, the burner 6 becomes F-+B via the traverse mechanism.
The glass tube 1 is heated when moving forward in the high flame state, and is naturally cooled when moving back in the B-+F direction when the burner 6 is switched from the high flame state to the low flame state.

Further, a temperature detector 11 that moves together with the burner 6 by a traverse mechanism detects the surface temperature of the glass tube 1 and controls the burner 6, thereby performing predetermined temperature control.

To explain this temperature control below, first burner 6
The heating temperature of the glass tube 1 can be set to 1750 by adjusting the output of the PID regulator 14 via the temperature setting device 15.
℃ (accuracy: 5℃).

When the burner 6 is located at point F, the normally open limit switch FS on the F point side is closed, so the field coil C of the servo unit 16 is excited and the switch L is turned on.
OKl is closed by self-retention.

When the switch LOKl is closed in this manner, the normally closed switch LOK2 is opened and the normally open switch LOK3 is closed.

When the burner 6 moves from point F to point B for the first time under these conditions, the temperature detector 11 detects the surface temperature of the glass tube 1 and sends the detection signal (detection value) to the PID regulator 14. Let them input.

The PID regulator 14 compares and calculates the detected value with the set temperature, and inputs a signal based on the deviation output to the variable resistor (divided resistor) VRl of the servo unit port 6 as a gain adjustment input. The signal from the variable resistor VRl passes through the switch LOK3 and the amplifier (preamplifier) AMPL, and then enters the variable resistor VRO, and furthermore, the signal from the variable resistor VRO enters the flow rate regulators 19 and 19 of the oxygen supply system 17 and the hydrogen supply system 18, respectively. 20, thereby controlling the amount of oxyhydrogen supplied to both systems 17 and 18 to, for example, about 5 (oxygen):1 (hydrogen) and maintaining the burner thermal power, that is, the heating temperature of the glass tube 1 at the set temperature. Furthermore, when the burner 6 reaches the point B from the point F, the motor 9 rotates in the opposite direction due to the signal from the position detector 12, so the burner 6 moves back from the point B to the point F. The burner power is also switched to low heat as is known, but when the burner 6 reaches point B, the normally closed limit switch BS is opened.

When this limit switch BS is opened, switch L
When OK2 is closed, switch LOK3 is opened, and the detection signal from temperature sensor 11 is output to switch LO.
The signal is input to the amplifier AMP2 of the servo unit 16 through the K2 side.

When the burner 6 returns from point B to point F after the first heating, the heat storage temperature of the glass tube 1 is about 250°C, so the temperature detector 11 detects this temperature. This will be input to the amplifier AMP2.

On the other hand, upon receiving this detection signal, the amplifier AMP2 rotates the servo motor Ms by a predetermined value while changing the polyurethane VR2 based on the detection signal.
l is changed in proportion to the heat storage temperature.

In other words, when the burner 6 moves back from point B to point F, the temperature detector 11 detects the heat storage temperature of the glass tube 1 (approximately 250
℃), the servo unit 16 changes the variable resistor R to reduce the heat storage temperature based on this, so the first heating temperature (approximately the set temperature 1750℃) is set to T1 Assuming that the heat storage temperature for the second time is t1, the PID output is adjusted to maintain the set temperature in the state of (T-t1) during the second heating.

Furthermore, when the burner 6 moves back to point F and the variable resistor VRl is adjusted, the normally open memory switch LOK4 is closed and the power to the servo motor Ms etc. is turned off to stop the operation of the servo unit 16. It turns out. In the above, the PID regulator 14, the variable resistor V
R, Switch LOK3, Amplifier AMP, Variable resistor R
Oxygen supply system 17 and hydrogen supply system 18 by O system etc.
When the burner 6 reaches point B, the limit switch BS is closed, and when the burner 6 returns to point F, the limit switch is closed. FS will be opened, but the operations when these limit switches BS and FS are activated are the same as described above.

In this way, when the burner 6 finishes the second heating and returns to point F, the servo unit 16 operates as before,
The variable resistor VRl is adjusted based on temperature detection, but
Since the second glass tube heat storage temperature T2 is higher than the first heat storage temperature t1, during the second heating, P
ID output is adjusted.

Hereinafter, the fourth heating is the same as above, and during the fourth heating, the third heat storage temperature T3 is detected and the PID output is adjusted, and after the fifth heating, the heat storage temperature T3 is detected and the PID output is adjusted. Since the temperature reaches the saturation point (400° C.), the above temperature control is performed while keeping the PID output substantially constant in subsequent heating (6th to 100th times).

When heating the glass tube 1 repeatedly in the above, if the heat storage temperature of the glass tube 1 is ignored, the amount of overshoot during temperature control will increase due to the tendency of the heat storage temperature to increase. If the temperature during heating is controlled by reducing the heat storage temperature, the controlled temperature becomes stable as shown in FIG. 4, and the occurrence of defective products due to this can be prevented.

Next, a second embodiment of the present invention will be explained with reference to FIGS. 5 and 6. As mentioned above, the heat storage temperatures Tl, t2 . when the glass tube 1 is repeatedly heated. t3... is as shown in FIG.

In other words, the first time (T1 entered the second time (T2), the third time (T2),
T3) It increases as the number of times passes, and reaches the saturation point at the fifth time (T5).

In addition, the heat storage temperature for each time is determined by the dimensions of the glass tube 1, the heating temperature of the burner 6, the cooling status of the glass tube 1, etc., and if these setting conditions are constant, the heat storage temperature for each time is is also constant. Therefore, certain conditions are established,
By measuring the heat storage temperature each time, programming during automatic heating control can be realized based on the measured value. In the embodiment shown in FIG. 6, temperature control similar to that described above is performed based on this background.

To explain this point below, in the embodiment shown in FIG.
l, VR2, VR3...VR6 will be switched.

In other words, when the burner 6, which moves forward from point F and moves back at point B, is located at point F, the switch S of the stepping circuit 21
As a result, during the first burner heating, the switch S of the variable resistor VR is closed.
During the second burner heating, variable resistor R2 is closed,
Further, during the third burner heating, the switches S1S2S3...S6 of the variable resistor VR3 are closed in the same way as the switch S3...S6 of the variable resistor VR3.

During the first heating described above, the switch S1 of the variable resistor VRl is closed, but at the time of this heating, there is no heat storage temperature in the glass tube 1, and therefore the variable resistor is set corresponding to this situation. VRl includes a temperature detector 11 to maintain the glass tube 1 at a set temperature in a state where there is no heat storage temperature;
The signal from the PID regulator 14 is sent to the amplifier AMP and the variable resistance VROL flow regulators 19 and 20, thereby adjusting the thermal power of the burner 6. Next, during the second heating, the switch S2 of the variable resistor R2 is closed, but at this time the first heat storage temperature t1 is in the glass tube 1, so the first heat storage temperature t1 The variable resistor VR2, which is set corresponding to Make adjustments.

Thereafter, during the third, fourth, etc. heating, the burner adjustment is automatically performed according to the heat storage temperature T3, t4, etc. for each heating. The heat storage temperature T5 reaches a saturation point.

After the heat storage temperature reaches the saturation point, that is, after the fifth burner heating is completed, only the switch S6 of the variable resistor R6 is repeatedly closed by the switch S. Thereafter, during burner heating up to the final round (approximately the 100th round), burner control is performed to maintain the set temperature in a state in which the heat storage temperature that has reached the saturation point is subtracted.

Of course, in the embodiment shown in FIG. 6 as well, the glass tube 1 is heated while correcting the influence of the heat storage temperature, so that the same effects as in the previous embodiment can be obtained. As explained above, when using the method of the present invention, when depositing a glass layer inside a glass tube through the MCVD method, the temperature at which the glass tube is heated by the burner is controlled in correlation with the heat storage temperature generated in the glass tube. Therefore, the amount of overshoot during the heating temperature control will no longer increase due to the influence of the heat storage temperature, and therefore, when this type of glass is produced, variations in the refractive index distribution due to unstable temperature control will not occur. This improves the yield when producing glass rods with the desired refractive index distribution.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the MCVD method which is the premise of the present invention,
FIG. 2 is an explanatory diagram showing conventional heating temperature control characteristics, FIG. 3 is an explanatory diagram of main parts showing one embodiment of the method of the present invention, and FIG. 4 is an explanatory diagram showing heating temperature control characteristics of the present invention. FIG. 5 is an explanatory diagram showing the heat storage temperature of the glass tube, and FIG. 6 is an explanatory diagram showing another embodiment of the method of the present invention. 1... Glass tube, 4... Raw material supply system,
6... Burner, 10... Burner traverse unit, 11... Temperature detector, 14...
... PID regulator, 16 ... Servo unit for controlling the burner, 19, 20 ...
Burner flow regulator.

Claims (1)

[Scope of Claims] 1. A burner that reciprocates along the longitudinal direction of the outer periphery of the glass tube is set to heat the glass tube during reciprocation, and supplies raw material gas into the glass tube and heats the burner. In the MCVD method, in which a glass layer is repeatedly deposited on the inner periphery of a glass tube by reacting the raw material gas while performing the above steps, the heat storage temperature of the glass tube caused by the above heating is reduced by burner adjustment to maintain the glass tube at the set temperature. A method for controlling temperature during glass production using the MCVD method, which is characterized by heating to . 2 The heat storage temperature of the glass tube is detected during the backward movement of the burner, and when heating by the forward movement of the burner after the backward movement, the burner heating power is reduced according to the detected heat storage temperature, Claim 1 A temperature control method during glass production using the MCVD method described above. 3. A temperature control method during glass production using the MCVD method according to claim 1, wherein the heating power during heating by reciprocating burner is gradually reduced until the heat storage temperature of the glass tube reaches the saturation point.