JPH0479523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) This invention relates to an error correction device for a tilt sensor, and more particularly, to an error correction device for a tilt sensor, and more particularly, to a tilt sensor that uses a change in the refractive index of a liquid in a tilt sensor that utilizes the angle of change of reflected light from a horizontal surface of the liquid. The present invention relates to an optical mechanism for correcting inclination angle detection errors caused by tilt angle detection.

(Prior Art) Conventionally, a tilt sensor has been put into practical use that detects the tilt of an inclinometer body having a container containing a liquid by utilizing the phenomenon that a liquid always forms a horizontal surface due to the action of gravity. This means that the path of reflected light from the horizontal surface of the liquid in the container fixed to the inclinometer body is
Since vibration occurs depending on the inclination of the main body, the inclination angle is determined by photoelectrically detecting this declination angle. At this time, the deflection angle of the reflected light changes according to the change in the refractive index of the liquid in the container, so in the above-mentioned tilt angle measurement, Measurement errors cannot be avoided.

To explain this in more detail, in the conventional tilt sensor system as shown in FIG. When the inclinometer body is tilted by θ as shown in the figure, the angle of the incident light to the container 1 does not change, so the light is deflected by 2θ as shown by the dashed arrow, and then is refracted when it passes through the liquid 2 and exits into the air. Then δ swings. However, for convenience's sake, before the angle θ tilts,
Although it is assumed that the light indicated by the solid arrow coming out of the liquid 2 is not refracted, this is not a necessary condition. Now, since there is a relationship of sin δ=n×sin 2 θ at this time, this is used to detect δ and obtain the inclination angle θ. Therefore, if n changes due to a change in temperature or the like, a corresponding measurement error will occur.

(Problems to be Solved by the Invention) The present invention provides an error correction device for improving measurement accuracy by correcting measurement errors caused by changes in the refractive index of liquid in the conventional tilt sensor as described above. The purpose is to

(Means for solving the problem) In FIG. 1, the reflected light from the horizontal surface 3 of the first liquid 2 passes through the second medium 8 having a thickness D after passing through the first liquid 2. This second medium 8 is set so as to satisfy the following relational expression.

k=t+D/N/D/N where, k: ratio of change rate of refractive index of second medium 8 and first liquid 2, t: air portion between imaging lens 6 and light receiving detector 7 thickness, t=t ₁ +t ₂ , D: thickness of second medium 8, N: refractive index of second medium 8.

(Function) The refractive index n of the first liquid 2 changes dn, and the first
Even if an error is introduced into the reflected light emitted from the liquid 2, if the second medium is set and arranged so as to satisfy the above relational expression, this error will be compensated for and the reflected light reaching the light receiving detector 7 will be does not introduce any error.

(Example) Next, an example of the present invention will be described with reference to FIGS. 1 and 2.

As shown in Figure 1, the inclinometer body (not shown)
In contrast, by fixing the container 1, light source 4, collimating lens 5, imaging lens 6, and light receiving detector 7 in the arrangement shown in the figure, parallel reflected light from the horizontal surface 3 of the liquid 2 contained in the container 1 is detected. In order to obtain a The image is formed on the container 7. In this way, a tilt sensor is constructed that detects the tilt angle by utilizing the displacement of the reflected light on the light receiving detector 7.

In the present invention, after the reflected light passes through the liquid 2, it passes through a second medium 8 having a uniform thickness, such as silicone oil, so that measurement errors due to a change in refractive index with the first liquid are caused. Correct. For this purpose, the refractive index and rate of change in the refractive index of the medium 8, or its thickness are set as described below.

FIG. 2 schematically shows the optical path of the tilt sensor shown in FIG. 1, and the principle of the present invention will be explained using FIG. 1 and FIG. 2 as follows.

n and N are the refractive indexes of the first liquid 2 and second medium 8, t=t ₁ + t ₂ is the thickness of the air portion, D is the thickness of the second medium 8, and θ is the inclination of the inclinometer body. , that is, the inclination angle to be detected, δ and γ, are the deflection angle of the light beam exiting from the first liquid 2 and the deflection angle of the light beam incident on the second medium 8, as shown in the figure, based on the case of θ=0. The position of the image of the light source obtained on the detector 7, that is, the displacement h of the reflected light, can be expressed as follows.

h=h ₁ + h ₂ ...(1) where h ₁ = t tan δ h ₂ = D tan γ where sin δ = n sin2θ, N sin γ = n×
Since there is a relationship of sin2θ, equation (1) becomes as follows.

If θ is very small, h≒2nθ(t+D/N)...(3). Therefore, the change in refractive index dn and the change in h due to dN, that is, the detection error dn, are as follows.

dh=2θ(t+D/N)dn+2nθD/N ² dN...(4) Therefore, in order to eliminate the error dh, it is sufficient that dh=0 holds, so let k be the rate of change in the refractive index of the liquid and medium. From equation (4), k=dN/Ndn/n=t+D/N/D/N...
(5). In other words, the refractive index N and the refractive index change rate dN/N of the second medium are selected so that equation (5) holds true, or D=N×t/(k
If the thickness D is set to satisfy -1),
The above objectives can be achieved.

(Effects of the Invention) As is clear from the above description, this invention makes it easy to measure inclination angles by detecting changes in light rays that pass through a liquid and are reflected on its horizontal surface. By simply adding an optical mechanism, it is possible to compensate for measurement errors caused by variations in the refractive index of the liquid based on changes in temperature, etc., making it possible to provide a highly accurate tilt sensor.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of the main part of an embodiment of a tilt sensor equipped with an error correction device according to the present invention, FIG. 2 is a schematic diagram showing the optical path of the tilt sensor of FIG. 1, and FIG.
The figure is a schematic diagram for explaining a conventional tilt sensor. DESCRIPTION OF SYMBOLS 1... Container, 2... First liquid, 3... Horizontal surface of first liquid, 4... Light source, 5... Collimating lens, 6... Imaging lens, 7... Light receiving detector,
8...Second medium.

Claims (1)

[Scope of Claims] 1. In a tilt sensor that detects a tilt angle based on the polarization angle of reflected light from a horizontal surface of a first liquid, after the reflected light passes through the first liquid, the first liquid has a uniform thickness. The second medium is configured to pass through the first medium.
An error correction device for a tilt sensor, characterized in that the refractive index and the rate of change in the refractive index of the second medium, or the thickness thereof, are set so as to correct a detection error due to a change in the refractive index of the liquid. 2. An error correction device for a tilt sensor according to claim 1, wherein the second medium is set to satisfy the following relational expression. k=t+D/N/D/N where, k: ratio of change rate of refractive index of the second medium and first liquid, t: thickness of the air portion between the imaging lens and the light receiving detector, D: Thickness of the second medium, N: Refractive index of the second medium.