JPH0692982B2 - Fiber Optic Gyro Accelerometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical fiber gyro accelerometer capable of measuring linear acceleration of a moving object in a state of being mounted on the object.

(Summary of the Invention) The optical fiber gyro accelerometer of the present invention uses an optical fiber loop of an optical fiber gyro as a pendulum for acceleration detection, and detects the rotational angular velocity of the pendulum by the Sagnac effect of the optical fiber gyro. The linear acceleration can be detected with high accuracy.

(Prior Art) Generally, an accelerometer produces a force when acceleration occurs in an object,
A physical quantity that changes in the accelerometer due to the force acting on the accelerometer is measured, and the acceleration of the object is measured.
There are various measuring methods, but the ones that are mainly used are those that electrically measure the expansion and contraction of a spring or elastic body due to acceleration, that that measures the deflection of a beam with a strain gauge, that that measures pressure with a piezoelectric element, and the level. There are those that electrically measure the movement of bubbles in the container, those that change the frequency of surface acoustic waves, and those that electrically measure the twist of the pendulum shaft. Further, as a method using light, a method using a phase change of propagating light by expansion and contraction due to elasticity of an optical fiber, a method utilizing a loss of propagating light due to an axis shift of a connecting point of the optical fiber, and the like are considered.

(Problems to be Solved by the Invention) By the way, an optical fiber gyro that has been receiving attention in recent years is
Since the light propagating in the optical fiber is not easily affected by the magnetic field or electric field, it does not have the problem of shielding and is highly sensitive and excellent in stability, but this optical fiber gyro can detect at the rotational angular velocity. Therefore, it cannot be applied as it is to the purpose of measuring linear acceleration acting linearly.

In view of the above points, an object of the present invention is to provide an optical fiber gyro accelerometer capable of detecting linear acceleration with high sensitivity by using an optical fiber gyro with high sensitivity and excellent stability.

(Means for Solving the Problems) In order to achieve the above object, the present invention can freely rotate an optical fiber loop of an optical fiber gyro within one plane about a point other than the center of gravity of the optical fiber loop. And a means for generating a restoring force for returning the optical fiber loop to a predetermined return position, and a rotational angular velocity of the optical fiber loop by a force acting in parallel to a plane in which the optical fiber loop is arranged. Is detected by the optical fiber gyro, detecting the acceleration due to the force acting in parallel to the plane by obtaining the time integration of the rotational angular velocity, or generating a restoring force that balances the rotational force of the optical fiber loop,
An acceleration due to a force acting in parallel with the plane is detected from the magnitude of the restoring force.

(Operation) In the optical fiber gyro accelerometer of the present invention, the optical fiber loop of the optical fiber gyro is used as a pendulum for acceleration detection, and the rotational angular velocity of the pendulum is detected by the Sagnac effect of the optical fiber gyro. The linear acceleration of an object equipped with an accelerometer can be detected with high accuracy.

(Example) An example of an optical fiber gyro accelerometer according to the present invention will be described below with reference to the drawings.

The present accelerometer measures the linear acceleration of a moving object by mounting it on the object, and is composed of a coefficient section 5 of an optical fiber gyro section (a) as shown in FIG. In the optical fiber gyro section (a), unlike the conventional optical fiber gyro, the optical fiber loop 4 can freely rotate about a point O in one plane, and this optical fiber loop is used for acceleration detection. It is used as an element (pendulum) (however, one point O is a point other than the center of gravity of the optical fiber loop 4). The optical fiber gyro (a) is provided with a light source 1 for generating laser light, a light distributor (or combiner) 2 and a light detection / signal processing unit 3. The light source 1 passes through the light distributor 2 and an optical fiber. The path to the loop 4 and the path from the optical fiber loop 4 to the light detection / signal processing unit 3 via the optical distributor 2 are connected by an optical fiber.

Here, the optical fiber gyro will be briefly described.
FIG. 2 is a basic configuration diagram of an optical fiber gyro. The light emitted from the light source 1 that generates laser light is split into two directions by the light splitter 2, and propagates in the optical fiber loop 4 clockwise and counterclockwise, respectively. The respective lights that have rotated the optical fiber loop 4 again pass through the light distributor 2 and enter the photodetector 3A.
At this time, if the optical fiber loop 4 is rotating with respect to the space (not only the optical fiber loop, this device, the entire optical fiber gyro may be rotating with respect to the space),
A phase difference occurs in the light propagating clockwise and counterclockwise in the optical fiber loop 4 (which is already known as the Sagnac effect). Due to this phase difference, the interference light in both directions reaches the photodetector 3A, and the phase difference of the light can be detected. Further, there is a relationship of Δθ = AΩ (A: a constant determined by the device) between the phase difference Δθ and the rotational angular velocity Ω of the optical fiber loop, and the rotational angular velocity can be calculated by executing a predetermined multiplication in the signal processing unit 3B. Ω can be detected. This is an optical fiber gyro.

In the present invention, only the optical fiber loop of this optical fiber gyro can freely rotate about one point in one plane. When linear acceleration parallel to the plane acts on the optical fiber loop, the optical fiber loop causes rotation corresponding to the linear acceleration direction, and the angular velocity of rotation is detected by the optical fiber gyro. Therefore, the relationship between the rotational angular velocity and the linear acceleration will be described with reference to FIG.

In FIG. 3, reference numeral 4 denotes an optical fiber loop, which is on the paper surface. O is the rotation center of the optical fiber loop 4, and the rotation axis is perpendicular to the paper surface. G is the center of gravity of the optical fiber loop,
O'is a fixing point for attaching the optical fiber loop to the accelerometer body, and AA 'is an elastic body. The optical fiber loop 4 is elastically attached to the accelerometer body by AA '. OGAA ′
Is on a straight line with no acceleration applied, and the elastic body AA 'is then in a state without expansion and contraction.

The elastic body AA 'functions as a means for generating a restoring force for returning the optical fiber loop 4 to a predetermined returning position.

Under the above conditions, the linear acceleration is X in the (X, Y) static coordinate system.
When acting in the direction, the acceleration α due to inertial force acts in the x direction in the (x, y) coordinate system attached to the accelerometer. For this reason, the optical fiber loop 4 rotates about the center of rotation O, but the optical fiber loop slightly rotates with respect to the (x, y) coordinate system due to the elastic force F due to the reaction force R and AA ′ at the point O, and the acceleration Despite that, it balances R and F and stands still.
When further force is applied to this, the optical fiber loop re-rotates and becomes stationary with respect to the (x, y) coordinate system as before.
When the force newly starts in this way, rotation is caused from the position of balance. When viewed from the (x, y) coordinate system, this can be considered to be stationary due to the force acting on the optical fiber loop, causing rotation, and the drag force acting on the optical fiber loop.

It is considered that the force f on the x-axis acts for a time δt and the rotational angular velocity of the optical fiber loop 4 becomes dφ / dt (= Ω) (where φ is the rotational angle).

The mass of the optical fiber loop 4 is M, and the moment of inertia about the rotation axis is I.

Is established, and from these two equations From this, and from equation (1), the acceleration is Becomes

If is regarded as the initial value when acceleration is applied, δt may be a small constant value, so if (dφ / dt) is the initial value when acceleration is applied, equation (2) becomes Becomes Let a be a constant having a dimension of [LT ^-1 ]. In the configuration of FIG. 1, the rotational angular velocity (d
φ / dt) is multiplied by the constant a in the equation (3) by the coefficient unit 5 to obtain an acceleration output. Since equation (3) detects only the amount of change in acceleration on the x-axis of the (x, y) coordinate system of the accelerometer, X of the (X, Y) stationary coordinate system is detected.
The acceleration on the axis is the sum of the accelerations on the x axis. For example, at times t ₁ , t ₂ , t ₃ , ..., tn, the accelerometers α ₁ , α ₂ , α ₃ ,
……, if αn and acceleration are detected, time tn of the moving object
The acceleration in the (X, Y) stationary coordinate system at is α ₁ + α ₂ + α ₃ + ... + αn (4).

That is, by providing the time integration means for calculating the above equation (4) at the subsequent stage of the coefficient unit 5 of the embodiment of FIG. 1 (X, Y)
The acceleration in the stationary coordinate system can be obtained.

As described above, the present accelerometer shown in the embodiment shows that the linear acceleration can be detected by using the optical fiber loop in the optical fiber gyro.

In the accelerometer of the above embodiment, the elastic force AA 'of FIG. 3 is used for the optical fiber loop (pendulum) to balance the rotational force and the drag force of the pendulum, but this need not be an elastic body. . It may be electric or magnetic.

When this electric or magnetic force is applied, this can be used as a restoring force for the rotational force of the pendulum, and a configuration can be adopted in which the position of the pendulum is maintained at the 0th position in terms of a signal. The structure is shown as another embodiment of the present invention in FIG. In this figure, a restoring force generating device 10 is installed in the optical fiber gyro portion. That is, a movable member 11 for generating a restoring force is attached to the optical fiber loop 4 of the optical fiber gyro unit, and the position of the pendulum between the movable member 11 and the main body of the accelerometer is set to the signal zero position. The fixed-side member 12 for generating an electrical or magnetic restoring force equivalent to the rotational angular velocity of the optical fiber loop from the optical detection / signal processing unit 3 is disposed. In this case, when the rotational angular velocity is generated, a negative signal proportional to the rotational angular velocity is given to the fixed-side member 12 during the minute displacement, and the optical fiber loop 4
Is restored to its original position, and the force that tries to rotate and the restoring force are balanced (even if the force that tries to rotate in a slightly displaced state and the restoring force are balanced even if the force is not restored to the original position). Good.). The optical fiber loop 4 is rotatably supported about one point in one plane, as in the embodiment shown in FIG.

Then, the optical detection / signal processing unit 3 of the optical fiber gyro unit
It is more desirable in terms of accuracy to apply feedback (a signal equivalent to the rotational angular velocity of the optical fiber loop 4) to the restoring force generating device 10 to control the restoring force and measure the acceleration rather than the restoring force. In this case, the acceleration on the X-axis of the stationary coordinate system is measured by using the restoring force, and therefore the (4) above is used.
The formula does not hold, and the value measured on the x-axis of the moving coordinate system is the acceleration acting on the object (accelerometer).

FIG. 5 is a specific example of how to obtain the rotation axis of the optical fiber loop 4 as the pendulum for acceleration detection used in the present invention. FIG. 5A shows the case where the rotation axis is located inside the optical fiber loop 4. In the figure (B), when the rotation axis is located outside the optical fiber loop 4, the figure (C) shows that the rotation axis is in the center of the optical fiber loop 4. This is the case when G is down. Thus, FIG. 5 shows that the rotary shaft can be placed at any position. However, it is assumed that the rotation axis is perpendicular to the loop surface and does not pass through the center of gravity of the loop.

Further, the optical fiber loop 4 does not necessarily have to be on the vertical plane of the gravitational field. The accelerometer of the embodiment of the present invention has a third
It is an accelerometer that detects the X-direction component of the acceleration in the figure (component perpendicular to OG in the loop plane). In order to detect an arbitrary acceleration, the accelerometer of the embodiment may be installed in each of the X, Y and Z directions of the Cartesian coordinate system. Further, in the uniform acceleration motion, the rotational angular velocity of the optical fiber gyro is zero in the accelerometer of the embodiment of the present invention, but at this time, the signal amount and the acceleration of the restoring force stored in the fixed side member 12 of FIG. Since they are balanced, the acceleration can be detected from this signal amount.

In each of the above embodiments, the optical fiber loop may have any shape as long as it is on one plane.

(Effect of the Invention) As described above, according to the optical fiber gyro accelerometer of the present invention, the optical fiber loop of the optical fiber gyro is used as a pendulum for acceleration detection, and the rotational angular velocity of this pendulum is used to measure the optical fiber gyro. By detecting by the Sagnac effect, the linear acceleration can be detected with high accuracy and a simple mechanism.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of an optical fiber gyro accelerometer according to the present invention, FIG. 2 is a basic configuration diagram of an optical fiber gyro, FIG. 3 is an operation explanatory diagram of the embodiment, and FIG. FIG. 5 is a constitutional view showing another embodiment of the present invention, and FIG. 5 is a perspective view showing a specific example of how to take the rotation axis of the optical fiber loop. 1 ... Light source, 2 ... Optical distributor, 3 ... Optical detection / signal processing unit, 4 ... Optical fiber loop, 5 ... Coefficient unit.

Claims (2)

[Claims] 1. An optical fiber gyro optical fiber loop is arranged in a plane such that the optical fiber loop can freely rotate about a point other than the center of gravity of the optical fiber loop, and the optical fiber loop is returned to a predetermined return position. A means for generating a restoring force in the direction is provided, the rotational angular velocity of the optical fiber loop due to the force acting in parallel to the plane in which the optical fiber loop is arranged is detected by the optical fiber gyro, and the time integration of the rotational angular velocity is calculated. An optical fiber gyro accelerometer characterized by detecting the acceleration due to a force acting parallel to the plane by obtaining the acceleration. 2. An optical fiber loop of an optical fiber gyro is arranged in a plane so as to be freely rotatable around a point other than the center of gravity of the optical fiber loop, and the optical fiber loop is returned to a predetermined return position. A rotational force of the optical fiber loop is detected by the optical fiber gyro by detecting a rotational angular velocity of the optical fiber loop due to a force acting in parallel with a plane in which the optical fiber loop is arranged. An optical fiber gyro-type accelerometer, which generates a restoring force that balances with, and detects an acceleration due to a force acting in parallel with the plane from the magnitude of the restoring force.