JPH01299413A - Sensor for angular velocity of rotation - Google Patents

Abstract

PURPOSE:To obtain a sensor for an angular velocity of rotation which causes little noise in relation to a change in temperature and is stable, by a method wherein a sensing loop formed of an optical fiber is wound on bobbins by prescribed lengths from the center of the loop alternately so as to form symmetrical coils. CONSTITUTION:An optical fiber 7 to be manufactured is wound on bobbins 8a and 8b for rewind by the same length from the opposite end sides thereof to be divided in two. Beginning with the center of this optical fiber 7, the bobbin 8a side thereof is wound in one layer on a bobbin 9 for a sensing coil, and next the bobbin 8b side thereof is wound thereon in one layer as a second layer. This winding is repeated alternately and thereby a symmetrically-coiled sensing loop is obtained. By forming the loop in symmetrical coils in this way, a part of a change in temperature is made to exist symmetrically on the opposite sides of the center of the loop even when the change in temperature is given partially. Accordingly, the optical path lengths of a left-turn light and a right-turn light become the same, the lights undergo the same history, and thus noise is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotational angular velocity sensor, and particularly to the structure of its sensing loop or sensing coil.

[Prior Art] A rotational angular velocity sensor detects rotational angular velocity by applying the Sagnac effect, and basically, as shown in FIG. 5, a light source 1. Polarizer 32 Phase modulator 4. Sensing coil5. It is constructed using one detector 6 and two optical couplers 2. In this case, the sensing coil is wound sequentially from the bottom layer.

This rotational angular velocity sensor, another configuration example of which is shown in FIG.
It consists of a light source 21, an optical coupler 23, an optical fiber polarizer 24, an optical coupler 30, a sensing coil 25, a phase modulator 26, and a light receiver 27. The light emitted from the light source 21 is transmitted to an optical coupler 23. Passes through the optical fiber polarizer 24 and is split into a left-handed light and a right-handed light by an optical coupler 30, and sent to the sensing coil 2.
5. The left-handed light and right-handed light that have passed through the sensing coil 25 are combined by an optical coupler 30, and the interference light is sent back to the optical fiber IPA polarizer 24. Pass through the optical coupler 23,
It is detected by the light receiver 27. These optical components are fusion spliced, and their connecting portions 22a, 22b, 22c, 22d, 22
A heat-shrinkable tube containing copper wire is used for reinforcement.

[Problems to be Solved by the Invention] The above-mentioned negotiated rotational angular velocity detects the rotational angular velocity from a change in light intensity due to interference between left and right lights. Therefore, the light coupled to or emitted from the sensing coil must have the same polarization, and furthermore, the light in both left and right directions must propagate along the same optical path length.

The former restriction arises from the fact that if the polarizations are not the same, it appears as zero point drift or noise in the rotation angle sensor output. This point can be solved by using a birefringent (ASP) fiber with different attenuation amounts in orthogonal polarization modes, such as a polarization-maintaining optical fiber z<(SPF), for the polarizer and sensing coil.

On the other hand, no particular measures have been taken regarding the latter constraint that propagation must take the same optical path length, and conventionally,
The sensing coils were wound sequentially from the bottom layer. However, this winding method has a problem in that when a temperature change is applied to the sensing coil, noise increases due to expansion and contraction of the optical fiber.

This situation is shown in Figure 5. Since the zero winding direction is not symmetrical with respect to the temperature change point, there is a difference in the arrival time of the clockwise light, and the counterclockwise light has a high temperature (extension) and the clockwise light has a low temperature (shrinkage). Receive the history of. In Fig. 5, the clockwise light reaches 2 at the arrival time t1.
After receiving a history of 5°C, the counterclockwise light reaches 25°C at the arrival time t2.
The two lights, which show the case of receiving a history of 0°C, are combined by an optical coupler, but because they pass through different optical path lengths, the light intensity changes due to interference, resulting in noise. Therefore, conventional measures have been taken such as placing the sensing coil in a constant temperature bath.

On the other hand, rotational angular velocity sensors are required to be lighter and smaller. However, in the prior art shown in FIG.
A to 22e are all covered with heat-shrinkable tubes. This tube is long, approximately 70 mlI+ in size. Therefore, the entire rotational angular velocity sensor system can be miniaturized.
There was a problem with making it lighter.

The most important issue is how to store the optical fiber polarizer 24. Conventionally, the polarizer 24 is wound on the sensing coil 25, and both ends of the polarizer 24 are exposed by about 50 cm and connected to the optical coupler 23.3.
0 and reinforced with heat shrink tubes 22b and 22c.

The optical fiber polarizer 24 is a polarization maintaining optical fiber S.
By setting the structural parameters of PF to certain conditions, S
The bending loss characteristics of the PF's eigenpolarization modes are different; the mode polarized in the direction of the short axis of the ellipse (Y polarization) has a high loss, and the mode polarized in the direction of the long axis (X polarization) has a high loss. Low loss. However, with current optical fiber polarizers, the bending loss characteristics of vermilion This often resulted in increased losses. Therefore, there was a problem in that the optical system could not be tightly housed in a small space.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a rotational angular velocity sensor with less noise in response to temperature changes.

Another object of the present invention is to provide a small and lightweight rotational angular velocity sensor that reduces the number of connection reinforcing parts using heat-shrinkable tubes and that does not cause increased loss due to small bends in the optical fiber polarizer during mounting. There is a particular thing.

[Means for Solving the Problems] The rotational angular velocity sensor of the present invention has a sensing loop made of an optical fiber that is alternately wound around a bobbin by a certain length from the center of the loop to achieve symmetrical winding. A branching/combining optical system is constructed in the loop, light is propagated in mutually opposite directions through the loop, and the rotational angular velocity is detected from the phase difference between them. Preferably, the length of this symmetrical winding corresponds to a single layer or one layer of winding of the pobbin.

Another example is a one-phase modulator-type rotational angular velocity sensor in which an optical fiber polarizer wound on a sensing coil is fusion-spliced to an optical coupler, and then wrapped around the sensing coil up to the connection point to complete the entire sensing coil. The structure is covered with resin such as silicone.

[Function] Since the sensing loop is symmetrically wound by winding alternately by a certain length from the center of the loop, even if a temperature change is applied to a part of the sensing loop, the temperature change part will be affected by the temperature change part of the loop. It will exist symmetrically from the center. Therefore, the optical path lengths of the counterclockwise light and the clockwise light become the same, and they receive the same history, so that noise due to temperature changes is not generated.

On the other hand, if the sensing coil is wound up to the connecting portion between the optical coupler and the optical fiber polarizer and the entire coil is covered with a resin such as silicone, the lead portion (terminal) of the optical fiber polarizer will not come out.

Therefore, during mounting, the end portion of the optical fiber polarizer is not bent or otherwise caused to increase loss. Also,
Since heat-shrinkable tubes with copper wire for reinforcement are not used in the connections, the overall structure is smaller and lighter.

Examples] The illustrated embodiment will be described below.

FIG. 1 shows an embodiment of a method for symmetrically winding a sensing loop of a rotational angular velocity sensor.

First, the manufactured optical fiber 7 (FIG. 1(d)) is wound into 52 equal lengths from both ends onto rewinding pobbins 8a and 8b (FIG. 1(b)).

Next, the first rewinding bobbin 8a side is wound one layer from the center of the optical fiber 7 around the sensing coil pobbin 9. Next, the rewinding bobbin 8b side is further wound as a second layer.
This process is repeated alternately to wind the third and subsequent layers to obtain a symmetrical winding sensing loop (FIG. 1(c)).

A sensing loop was prototyped using this method and its characteristics were measured. Figure 2 shows the configuration of the measurement system, where 1 is a light source, 2 is an optical coupler, 3 is a polarizer, 4 is a phase modulator, and 5
1 is a sensing coil, 6 is a detector, 10 is a lock-in amplifier, 11 is a recorder, and 12 is a synthesizer. It is configured as a rotational angular velocity sensor using a phase modulation method, and a synthesizer 12 drives a phase modulator, and a lock-in amplifier detects an output signal.

Figure 3 shows this optical system mounted on a turntable.

As can be seen from FIG. 5, which shows an example of the output when rotated left and right at 0.01 degrees/S for 1 hour, characteristics with less zero point fluctuation and noise can be obtained without using a constant temperature oven.

Figure 4 shows the temperature change (
In Figure 0, which shows the zero point fluctuation and noise characteristics when a temperature change (approximately 50°C) is applied, (0('■) indicates the time point when a temperature change (approximately 50°C) However, stable characteristics have been obtained.

Note that the sensing loop having the above configuration is effective not only for an interference type rotational angular velocity sensor but also for a ring resonance type rotational angular velocity sensor.

Next, a means for obtaining a small and inexpensive rotational angular velocity sensor in the form shown in FIG. 7 will be described.

Optical fiber polarizer 2 wound on sensing coil 25
Cut the terminal from step 4 into approximately 30cm long. Similarly, the terminal to which the optical coupler 23 is to be connected is cut to about 30 cm. This polarizer 24
After fusion-splicing one terminal of the optical coupler 23 and the terminal to be connected to the optical coupler 23 by aligning their inherent polarization axes, the entire terminal part of the polarizer 24 is wound around the sensing coil 25. At this time,
The connecting portion 22c between the other terminal of the polarizer 24 and the optical coupler 30, which also involves the connecting portion 22b, is processed in the same manner.

After performing the above-mentioned processing, the entire sensing coil 25 is covered with a resin such as silicone in order to improve the reliability of the connecting portions 22b and 22c.

In this way, by wrapping the terminal portion of the polarizer 24, including the connecting portions 22b and 22c, around the sensing coil 25, without using heat-shrinkable tubes containing copper wire for the connecting portions 22b and 22c, it is possible to avoid bending during mounting. The portion to which this is applied is up to the portion of the normal single polarization optical fiber SPF, and the optical fiber polarizer 24 is not subjected to bending or the like.

As a result of actually making a prototype, the entire optical system of the rotational angular velocity sensor could be tightly packed into a small space, and three problems of the conventional system could be solved.

Note that the other connecting parts 22d and 22e can also be wound around the sensing coil part in the same manner as in the above embodiment, without using the heat shrink tube containing copper wire.

[Effects of the Invention] In the rotational angular velocity sensor of the present invention, since the sensing loop is wound symmetrically, a stable rotational angular velocity sensor output can be obtained against temperature changes. Therefore, there is no need for a constant temperature bath to keep the temperature of the sensing loop constant.

In addition, since the lead part (terminal) of the optical fiber polarizer does not come out, there is no problem of increased loss due to bending etc. during mounting.
Therefore, it is possible to tightly house the entire optical system of the one-rotation angular velocity sensor in a small space. Furthermore, since a heat-shrink tube containing reinforcing copper wire is not used in the connection portion, the entire optical system of the rotational angular velocity sensor can be made smaller and lighter. Therefore, a small and lightweight rotational angular velocity sensor can be realized.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of a method for symmetrically winding a sensing loop, Figure 2 is a configuration diagram of the measurement system used to evaluate the sensing loop, and Figure 3 is a diagram showing the optical system shown in Figure 2 mounted on a turntable. Figure 4 shows the output when rotating left and right at 0.01 degrees/S for 1 hour. Figure 4 shows the output when temperature changes are applied to the sensing loop. Figure 5 shows the basic configuration of the rotational angular velocity sensor. FIG. 2 is a diagram showing a situation when a temperature change is applied to the sensing coil, and FIG. 7 is a diagram showing an optical system of a phase modulation type rotational angular velocity sensor. In the figure, 1 is a light source, 2 is an optical coupler, and 3 is a polarizer. 4 is a phase modulator, 5 is a sensing coil, 6 is a detector, 7 is a manufactured optical fiber, 21 is a light source, 22 is a connection reinforcement part, 23 is an optical coupler, 2 is an optical fiber / polarizer,
25 is a sensing coil, 26 is a detector, 27 is a light receiver, and 8a. 8b is a rewinding pobbin, 9 is a sensing coil bobbin,
10 is a lock-in amplifier, 11 is a recorder, 12 is a synthesizer, and 30 is an optical coupler.

Claims (3)

[Claims] 1. A sensing loop consisting of an optical fiber is wound symmetrically around a bobbin alternately by a certain length from the center of the loop, and a branching/coupling optical system is configured at both ends of this sensing loop, and windings are connected to the loop in opposite directions. A rotational angular velocity sensor characterized by propagating light and detecting rotational angular velocity from the phase difference between them. 2. 2. The rotational angular velocity sensor according to claim 1, wherein the fixed length of said symmetrical winding corresponds to a half-layer or one-layer winding of the bobbin. 3. In a phase modulation type rotational angular velocity sensor, an optical fiber polarizer wound on a sensing coil is fusion-spliced to an optical coupler, then wrapped around the sensing coil up to the connection point, and the entire sensing coil is covered with resin such as silicone. A rotational angular velocity sensor characterized by: