JPH01207665A - Accelerometer - Google Patents

Abstract

PURPOSE:To improve the accuracy of detection by providing light interference detection units which detect a shift in phase due to the interference between an irradiation beam and a reflected beam. CONSTITUTION:Reflecting plates 23 and 24 are fitted to a pendulum 22 and interference detection units 26 and 27 are provided oppositely to the reflecting plates 23 and 24. Then the light beam from a light source A is split into two by a beam splitter B and emitted to a reflecting mirror 23 and a fixed mirror C. The respective light beams are reflected by the reflecting mirror 23 and fixed mirror C to make incident on a photodetector D through the beam splitter B. Then the composite beam generated by the beam splitter B is made incident on the detector D while generating interference. When acceleration is applied, the pendulum 22 slants, so the light beams projected on the reflecting mirrors 23 and 24 vary in path length. Consequently, the composite beam shifts in phase, which appears as variation in the output level of the detector D. Namely, the units 26 and 27 generate output levels corresponding to the input acceleration. Thus, the acceleration is detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Application Field) The present invention relates to an accelerometer used in, for example, inertial navigation devices and robots.

(Prior Art) Generally, an accelerometer for detecting minute acceleration has a structure as shown in FIG. 4 or FIG. 5.

The accelerometer in Fig. 4 has a structure L' (that is, 7'2) that detects acceleration on the top surface of case 1, so that it can move freely in the direction of acceleration (a, b in the figure) within case 1. installation,
Metal plates 3.4 are attached to one side of the case 1 and the tip of the pendulum 2 so as to face each other in the direction of acceleration. That is, in this accelerometer, when acceleration is applied to the case 1, the pendulum 2 is displaced and the metal plate 3.4
The acceleration is detected by approximating the minute rotation speed of the pendulum 2 to the linear displacement of the capacitor by utilizing the change in the capacitance of the capacitor formed by the capacitor.

The accelerometer in Fig. 5 has a pendulum 12 attached to the top of the case 11 like the one in Fig. 4, but here the case 11 is attached in a direction perpendicular to the direction in which acceleration is applied (C1d in the figure) It has a structure in which a light source 13 is attached to one of the opposing sides, and a photodetector 14 is attached to the other side. In other words, this accelerometer uses the fact that the displacement of the pendulum 2 that occurs in response to the acceleration applied to the case 1 corresponds to the change in the amount of light reaching the photodetector 14 from the light source 13, thereby determining the minute rotational speed of the pendulum 2. Acceleration is detected by approximating linear displacement of the amount of light.

Although details are not shown in FIGS. 4 and 5, it is common to add a servo system so that the pendulum 2 always returns to its equilibrium point.

According to the above structure, the minimum detectable acceleration value is determined mainly by the dynamic characteristics of the pendulum, the displacement detection sensitivity, and the accuracy of the servo system. At present, even with typical accelerometers that have servo systems with high sensitivity and a wide dynamic range, the minimum detection acceleration is about 10"G. However, when used in inertial navigation systems or robots where accelerometers are the core, Even higher precision is required.

(Problems to be Solved by the Invention) As described above, conventional accelerometers have not been able to provide accuracy that can meet the specifications of future inertial navigation devices, robots, and the like.

The present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide an accelerometer with extremely high precision that can fully meet the specifications of future inertial navigation devices, robots, etc.

[Structure of the invention] (Means for solving the problem) In order to achieve the above object, the accelerometer according to the present invention has the following features:
In an accelerometer that is installed inside a case and detects input acceleration by replacing minute rotational displacement of a pendulum serving as a mass for detecting acceleration with linear displacement, a reflecting mirror formed on a side surface of the pendulum in at least the input direction of acceleration; , an optical interference detection unit installed inside the case to face the reflecting mirror and irradiating the reflecting mirror with a light beam, making the reflected beam incident thereon and detecting a phase change due to interference between the irradiated beam and the reflected beam; It is equipped with:

(Function) The accelerometer with the above configuration forms an optical interferometer using a reflecting mirror and an optical interference detection unit, and this optical interferometer converts the minute rotational displacement of the pendulum that occurs in proportion to the input acceleration into an interference phase displacement. This is used to detect the magnitude of input acceleration.

(Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 shows its configuration, where 21 is a case and 22 is a swing r. The pendulum 22 is designed to rotate in the direction in which the acceleration Ij is obtained (directions of arrows e and f in the figure), and a first,
A second reflecting plate 23, 24 is attached, and a magnetic body 25 is attached to the tip thereof. On the other hand, inside the case 21, first and second optical interference detection units 26.27 are installed facing the first and second reflection plates 23.24, respectively, and first and second optical interference detection units 26.27 are installed facing the magnetic body 25, respectively. Second torque controller 28
．． 29 is installed. The first and second torquer controllers 28 and 29 together with the magnetic body 25 constitute a servo system that generates a force to return the pendulum 22 to its original position.

The first and second optical interference detection units 26 and 27 have the same configuration, and together with the first and second reflecting plates 23 and 24 respectively constitute Tsl and a second optical interferometer. FIG. 2 shows a representative structure of the first optical interferometer. In the optical interference detection unit 26 shown in FIG. 2, A is a light source that emits a single wavelength light using a laser conductor, B is a beam splitter, C is a fixed mirror, and D is a photodetector. The emitted light beam passes through the beam splitter B and is illuminated by the reflecting plate 23, and a part of it is reflected by the beam splitter B and is irradiated onto the fixed mirror C.Then, the light beam is reflected by the reflecting mirror 23. The light beam is reflected by beam splitter B and is detected by photodetector 2'.
A light beam incident on AD and reflected by a fixed mirror C passes through a beam splitter B and is also incident on a light reflector. An optical interferometer with this structure is called a Michelson interferometer.

The operation of the above configuration will be explained below.

First, in the initial state (state where no acceleration is applied), the detection sensitivities of the first and second light 1-adjustment units 26 and 27 are adjusted to zero. First optical interference detection unit!・
26, a light beam emitted from a light source A is split into two by a beam splitter B, with one horn directed toward a reflecting mirror 23 and the other directed toward a fixed mirror C. Each light beam is reflected by the reflecting mirror 23 and the fixed r1C, returns to the beam splitter B, and enters the photodetector in a 1n-combined state.

Since the light beams reflected by the reflecting mirror 23 and the fixed mirror C follow paths with different distances, the combined beam combined by the beam splitter B causes interference and is incident on the photodetector. Since the output level of the photodetector changes depending on the phase of the combined beam, adjustment is made so that the output level becomes 0 level in the initial state as shown by the waveform αl in FIG.

When acceleration is applied, the pendulum 22 tilts, so the path length of the light beam irradiated onto the reflecting mirrors 23, 24 changes. For this reason, the position of the combined beam changes as shown, for example, by waveform a2 in FIG.

This phase shift appears as a change in the output level of the photodetector WD. That is, since the minute co-rotating displacement of the pendulum 22 is proportional to the input acceleration structure, and the phase of the composite beam is proportional to the minute co-rotating displacement of the pendulum 22, each optical interference detection unit 1-26, 27 receives the input An output level corresponding to acceleration will be obtained. If the first and second optical interference detection units 26 and 27 have exactly the same configuration, the output signs of the eight photodetectors in each unit will be opposite, and therefore the outputs of each photodetector will be mutually different. The phase is reversed.

Therefore, by inverting one output and combining it with the other output, the detection output can be increased.

By the way, since it is not possible to obtain a very large dynamic range in the usage method described in 1-, it is still necessary to add a servo system. In this embodiment, the configuration of the servo system includes a magnetic body 25, first and second torque coils 2.
8.2g is added.

Although details are not shown, the first and second torquer controls 2::28 and 29 include a control circuit that generates a control current according to the output of the first and second optical interference detection units 26 and 27, respectively, and It is composed of a torquer coil that generates magnetic force according to the control current from the control circuit, and when the displacement of the pendulum 22 is detected by optical detection 2:9D, the control circuit works to apply a current to the torquer coil and change the displacement of the pendulum 22. It generates a magnetic force that tries to return the object to its original state. Since the control current value corresponds to the force required to restore the original state, that is, λ·1 to the input acceleration, the input acceleration can also be detected based on the magnitude of this electric current i & l/1. By adding such a servo system, the pendulum 22 always returns to the center point (the position when no acceleration is applied), so the dynamic range of the optical interference detector can be widened.

Therefore, the acceleration 1 main meter with the above configuration uses optical interference, so it has very high sensitivity and high precision.If you use especially highly sensitive Michelson optical interference = 1, the sensitivity can be improved in terms of flight. It is possible to make someone move towards you.

For example, even if the light used by light source A is 0.028×10″'m, the detection sensitivity of lXlN7m or more will be reduced by 1″1.

In addition, in the example described above, the case where the four total outputs of the first and second lights are in reverse phase was explained, but when the input acceleration is O, each output position (11) may be shifted. It is also possible to detect the direction of acceleration lj. First and second reflecting mirrors 2
3.24 may be a part or the entire surface of the pendulum 22, and can be formed relatively easily by steaming or the like. The optical interference detection units 26 and 27 can be constructed by combining manual optical parts, but they can also be made into ultra-small parts in the form of optical ICs (integrated circuit devices).

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an accelerometer that has extremely high accuracy and can be used in future inertial navigation devices, robots, and the like.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of an accelerometer according to the present invention, Fig. 2 is a diagram showing the structure of an optical interferometer of the same embodiment, and Fig. 3 is a diagram showing the phase difference and output of the optical interferometer. The waveform diagrams illustrating the level relationship; FIGS. 4 and 5 are diagrams showing the configuration of a conventional accelerometer, respectively. 21... Case, 22... Pendulum, 23.24...
・Reflector, 25...Magnetic material, 26.27...Optical interference detection unit, 28, 2Q...Toruka controller, A...
・Light source, B...beam splitter, C...fixed mirror,
D... Photodetector. Applicant's agent Patent attorney Takeshi Suzue 6

Claims (3)

[Claims] (1) In an accelerometer that is installed inside a case and detects input acceleration by replacing minute rotational displacement of a pendulum, which serves as a mass for detecting acceleration, with linear displacement, an accelerometer is formed on the side surface of the pendulum at least in the input direction of acceleration. a reflecting mirror; and an optical interference device that is installed inside the case to face the reflecting mirror, irradiates the reflecting mirror with a light beam, makes the reflected beam incident thereon, and detects a phase change due to interference between the irradiated beam and the reflected beam. An accelerometer comprising a detection unit. (2) The optical interference detection unit includes a light source that emits a light beam toward the reflecting mirror, a beam splitter that splits the light beam from the light source into two, and a beam splitter that reflects the split light beam. a fixed mirror which is then returned to the beam splitter again; and a photodetector which receives a combined beam in which the reflected beam from the reflecting mirror and the reflected beam from the fixed mirror are combined at the beam splitter and detects the amount of light. The accelerometer according to claim (1), comprising: (3) A magnetic body provided at the tip of the pendulum and a magnetic field that causes a control current to flow through the torquer coil according to the output of the optical interference detection unit provided in the case to return the magnetic body to a position of zero acceleration. The accelerometer according to claim 1, further comprising a torquer controller that generates the torque.