JPH0575325B2 - - Google Patents

Description

[Detailed description of the invention]

[Objective of the Invention] (Industrial Application Field) The present invention relates to a non-contact displacement measuring device, and in particular to a displacement measuring device that measures displacement with a target object with high precision using light seeping from a reflective surface. Regarding measurement methods. (Prior art) Conventionally, as shown in Fig. 5, a non-contact measurement method using light is such that a target object A is irradiated with a He-Ne laser beam B, and the spot of the light hitting the target object A is focused on a lens. For example, in system C, PSD ( Position S
An image is formed on the surface of a photoelectric element D (this element can output a voltage proportional to the position (x, y) of the light hitting the photoelectric element surface of, for example, 10 mm x 10 mm) such as sensing D iode). There is a method of calculating the variation in the distance ai between the sensor E and the object A from this output voltage. Such a displacement meter is commercially available. On the other hand, as another method, as shown in Fig. 6, the target object F and the sensor G surface are arranged as shown in the figure, and the reflected light R ₁ from the sensor G surface and the reflected light R ₂ from the target object interfere. Using , change (displacement) of distance d
There are methods for calculating. Although there are not many commercially available devices using this method, it is an extremely common measurement method. However, in the former method using PSD, the resolution of the displacement a is generally on the order of several μm to several tens of μm, which is on the order of several hundred times the wavelength of light. Also,
A working distance of several mm to several tens of mm is required. In the latter interference method, the resolution of the displacement d is on the order of a fraction of the wavelength of light. For example, if the optical path in the figure is set as l, then from the well-known interference condition, 2 ^l = nλ, n = 1, 2, 3, λ: For l that satisfies the wavelength of light, bright fringes will be detected. can. Furthermore, dark stripes can be detected for l that satisfies 2l=(m+1/2)λ, m=1, 2, 3. Therefore, in a displacement detection method using interference using this, the first thing that can be detected is a dark stripe with l = λ/4.
(when m=1), and the working distance (work
distance) is λ/4 or more, resolution λ/(1 to
32) (however, when using the interpolation method), it is common that the (Problems to be Solved by the Invention) The present invention was developed in consideration of the fact that the above-mentioned conventional displacement measurement method has a long working distance and has a limited measurement accuracy. Displacement measurement that measures the distance to the target object or the displacement of the object at a close working distance (specifically, within wavelength λ) and with extremely high resolution (1/10th to 1/100th of wavelength λ) The purpose is to provide a method. [Structure of the invention] (Means and effects for solving the problem) A light source that emits light, an incident surface that enters the light, and a device that totally reflects and non-transmits the light that enters the interior through the incident surface. an optical means having a total reflection surface provided opposite to the object to be measured, and a photoelectric conversion means for receiving light from the total reflection surface and photoelectrically converting the light from the total reflection surface, and at a position near the total reflection surface. A characteristic curve that determines the relationship between the amount of reflected light having a minimum value and the amount of displacement of the object to be measured is stored in advance, and the displacement is measured based on this characteristic curve. (Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the configuration of an apparatus used in the displacement measuring method of this embodiment. This device is He-
A laser light source 1 that emits Ne laser light, an optical component 2 that passes through and reflects the laser beam, a photoelectric sensor 3 such as a photodiode or phototransistor that measures the amount of laser beam, and an output (voltage or current) of the photoelectric sensor 3. ) and performs processing to be described later. A processing device 4 mainly composed of a microcomputer that inputs the following information and performs processing to be described later, and the distance x between the optical component 2 and the target object 5 or the distance x between the optical component 2 and the target object 5, which is the processing result in this processor 4.
and a display device 6 that displays the amount of displacement dx. Here, the target object 5 is assumed to be an object that reflects light, such as a metal mirror. Next, the displacement measuring method of this embodiment using the displacement measuring device having the above configuration will be described. First, the luminous flux L ₁ emitted from the laser light source 1 is
For example, the light is incident on a point A on the left side of the optical component 2 as shown in FIG. 1 at an incident angle θi ₁ . The transmitted light then enters the optical component at a refraction angle _θt1 . Now optical parts 2
The refractive index of nop is the refractive index of the medium outside optical component 2.
If nout, then sinθi ₁ /sinθt ₁ =nop/nout=nop−out from the well-known law of refraction or Snell's law. Generally, if the outside medium is air, nop
−out>1. The light beam L ₂ traveling inside the optical component 2 is incident on the point B on the bottom surface S of the optical component 2 at an incident angle θ ₂ . In this invention, the angle of incidence θ ₂ is θ ₂
> θ ₂ ^* . Free stock θ ₂ ^*
is a critical angle that satisfies sin θ ₂ ^* =nout−op=nout/nop=1. This is a state of so-called total reflection, where all of the light beam L ₂ is reflected at an angle θ ₂ to become a light beam L ₃ and directed toward the right side of the optical component. At the point C on the right side of the optical component 2, the light flux L ₄ at an angle θi 2 having the relationship sin θi ₂ /sin θt ₂ = nop−out according to the law of refraction, similar to what occurred at the left side point _A. emits the optical component. This luminous flux L ₄ is the photoelectric sensor 3 mentioned earlier.
and undergoes photoelectric conversion. The output obtained from the sensor 3 is input to the processing device 4 in the form of voltage or current. In conventional macroscopic optics, it is generally considered that the light totally reflected by the bottom surface S of the optical component 2 does not exist outside the optical component. but,
When viewed microscopically, it is recognized that light slightly leaks into the outside world at the boundary between the optical component 2 and the outside medium. Therefore, the bottom surface S of the optical component 2 is shown enlarged as shown in FIG. Assuming that the refractive index of this optical component 2 with respect to the external medium is nop-out=n, considering the virtual transmitted light LB' and the luminous flux _L2 , and without loss of generality from the previous law of refraction, sinθim/ _sinθ2 =n. Therefore, from now on, sinθ ₂ = sinθim/n

[ ] Then, the phase term of the luminous flux L ₂ ′ is

[C] becomes. That is, the amplitude is an exponential function of the distance Z from the boundary

〔Effect of the invention〕

The present invention has the following special effects. (a) As mentioned above, as a conventional method for measuring minute intervals, a method using optical interference is generally used. In this method, the working distance was several wavelengths, and the measurement resolution was on the order of λ/100. In contrast, the present invention can measure very close distances (within the wavelength distance) to the target object with very high accuracy (λ/10 to λ/1000). (b) In the conventional measurement method using light interference, it is necessary for the opposing surfaces of the optical component and the target object to cause interference, and therefore, generally, a plane large enough to observe interference fringes is required. be. However, according to the present invention, an ordinary He-Ne laser light source (beam diameter φ1 mm) can be used as the luminous flux _L2 , the required plane at point B is only about φ1 mm, and a non-contact displacement sensor with an extremely small tip can be used. can be configured. (c) Conventional optical interference methods have a wide measurement range of several wavelengths, but it is difficult to generate and analyze images to analyze fringes, and it is not necessary to perform such complicated processing. , complex processing circuits were required for fringe analysis, such as counting the number of fringe movements. However, according to the present invention, the distance can be measured very easily with high resolution and accuracy by simply detecting the amount of light. (d) Furthermore, in the specification of Japanese Patent Application No. 61-256817, which precedes the present invention, the output is minimized at the point where the total reflection surface and the target object come into contact. However, in this patent, the distance between the metal object and the total reflection surface is less than 1 μm, but the minimum value is generated at a slight distance, so it can be put into practical use as a displacement meter. has extremely high advantages.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a device used in a displacement measuring method according to an embodiment of the present invention, and FIGS.
FIG. 4 is an explanatory diagram of the measurement principle in FIG. 4, and FIG.
FIGS. 5 and 6 are explanatory diagrams of the prior art. 1... Light source, 2... Optical component (optical means), 3...
Photoelectric sensor (photoelectric conversion means), 4... Processing device (calculation means), 5... Target object (measured object).

Claims (1)

[Claims] 1. The steps of: 1. Opposing a non-transparent object to be measured against the total reflection surface of an optical means having an entrance surface and a total reflection surface; a step of reflecting the light that has entered the interior through the total reflection surface on the total reflection surface, a step of receiving the reflected light reflected on the total reflection surface and photoelectrically converting it, and the amount of the reflected light obtained by the photoelectric conversion. Find a characteristic curve that shows the relationship between the distance or displacement of the object to be measured with respect to the total reflection surface and the amount of reflected light, and where the amount of reflected light has a minimum value at a position near the total reflection surface. A displacement measuring method comprising the steps of: storing the characteristic curve; and calculating the distance or displacement of the object to be measured with respect to the total reflection surface based on the stored characteristic curve. 2. The displacement measuring method according to claim 1, wherein the object to be measured is made of metal.