JPH07113549B2 - 3D optical distance sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-dimensional optical distance sensor that uses light to measure a step on an object surface in a non-contact manner.

2. Description of the Related Art The configuration of a conventional optical distance sensor will be described below with reference to the drawings. FIG. 5 is a block diagram of a conventional optical distance sensor. 1
Is a laser, 2 is a first deflection mirror for scanning a beam in the X direction in the figure, 3 is a second deflection mirror for scanning a beam in the Y direction in the figure, 4 is an object to be measured, 5 is an object to be measured A condenser lens for condensing the reflected light from 4 and a two-dimensional array photodetector 6 arranged behind the condenser lens.

Next, the principle of the conventional optical distance sensor will be described with reference to FIG. In FIG. 6, S is the center of the condenser lens 5, L is the center of the emitted beam from the laser 1, O is a point on the object to be measured 4, Θ and Φ are reflected beams from the point O, and laser from the laser 1 is shown. The angle between the outgoing beam and the base line LS is defined as P, the perpendicular line from the point O to the base line is defined as P, and the distance between SP is a, LP.
If the distance between them is b and (a + b) = D is the length of the base line LS, D = a + b = h (1 / tanΘ + 1 / tanΦ) holds from the relationship of a = h / tanΘ and b = h / tanΦ. The distance h to the point O is expressed by equation (1).

h = D tan Θ tan Φ / (tan Θ + tan Φ) Equation (1) where angle Θ is the direction of the optical axis of the condenser lens 5 and is given by Equation (2) tan Θ = f / d ··· Equation (2) f: Focal length of the condenser lens 5: Distance between the center of the condenser lens 5 and the beam detection point on the two-dimensional array photodetector Therefore, the first and second deflecting mirrors 2 and 3 are used to move in the X and Y directions. The laser beam is scanned and focused on the two-dimensional array photodetector 6, and the beam detection point S on the two-dimensional array photodetector, the center L of the outgoing beam and the point O on the measured object 4 are detected.
By expanding the equations (1) and (2) in three dimensions, the three-dimensional distance measurement with the measured object 4 becomes possible.

However, in the above configuration, the laser beam is
It is necessary to use a deflecting mirror to scan in the Y direction,
A rotary encoder is used as a detector that detects an angle for controlling the rotation of these deflection mirrors.
In such a rotary encoder, the resolution is only on the order of 0.01 degree, and the response frequency of the deflection mirror is several KH.
Only the order of z. Therefore, it is difficult to measure the surface of the object to be measured at high speed and in minute steps.

In view of such a problem, the present invention utilizes the wavelength dispersibility of an optical element and uses a means for changing the emission wavelength of a semiconductor laser, so that the surface of an object to be measured can be measured at high speed and in small steps. An object is to provide an optical distance sensor.

Means for Solving the Problems The present invention is directed to a semiconductor laser, a condensing means for condensing light from the semiconductor laser into parallel light, and a beam shape of the condensed laser light converted into a slit light beam. Beam shaping means, an optical element having a wavelength dispersive property that reflects or transmits light that has passed through the beam shaping means, and a two-dimensional photodetector arranged substantially in the same plane as the optical element having the wavelength dispersive property. A three-dimensional optical distance sensor, comprising: a semiconductor laser emitting wavelength varying means.

According to the present invention, the elliptic emission beam elongated slit shape of the semiconductor laser is first formed by the beam shaping means by the above-described configuration, and the emission wavelength of the semiconductor laser is tuned to change the wavelength of the incident light to the optical element having wavelength dispersion. By changing the emission angle of the slit-shaped emission light by wavelength dispersion, it becomes possible to scan the surface of the object to be measured as a surface, and it is possible to provide a high-speed scanning type three-dimensional optical distance sensor.

Embodiment 1 FIG. 1 is a plan view of a first embodiment of the present invention. 11 is a semiconductor laser, 12 is a collimator lens that collects the light emitted from the semiconductor laser into parallel light, and 13 is a shaping that reduces the short-axis direction of the elliptical beam emitted from the collimator lens to shape the light into elongated slit light. A prism, 14 is an object to be measured on which the light emitted from the shaping prism is projected, 15 is a condenser lens that collects the reflected light from the object to be measured 14, and 16 is arranged in substantially the same plane as the exit surface of the shaping prism. And a two-dimensional array photodetector that detects the beam condensed by the condenser lens 15, 17 is an emission power detector that detects the emission power of the semiconductor laser 11 from the back surface of the semiconductor laser 11, and 18 is emission power detection Output of the semiconductor laser 11, that is, the emission power of the semiconductor laser 11 is controlled by the variable reference voltage generating means 19 to be constant
(Automatic Power Control) circuit. The emission wavelength varying means 20 is composed of the emission power detector 17 and the APC circuit 1 described above.
8 and variable reference voltage generating means 19.

The operation of the first embodiment of the present invention configured as described above will be described below with reference to FIGS. 1 and 2. When the reference voltage of the APC circuit 18 is changed by the variable reference voltage generating means 19, the output of the APC circuit 18, that is, the injection current to the semiconductor laser 11, is maintained until the output voltage of the emission power detector 17 becomes equal to this reference voltage. As a result, the emission power of the semiconductor laser 11 changes. Since the emission wavelength of the semiconductor laser 11 has emission power dependency, the emission power also changes.

Next, the change in the emission angle of the light emitted from the shaping prism 13 due to the change in the emission wavelength will be described with reference to FIG. The apex angle of the shaping prism 13 is α, the incident angle to the prism entrance surface is β, the refraction angle there is γ, the exit angle from the prism is δ,
The refractive index of the prism glass material is n. Snell's law holds for each of the entrance and exit surfaces. Entrance surface: sinβ = nsinγ ・ ・ ・ Equation (3) Exit surface: nsin (γ + α) = sinδ ・ ・ ・ Equation (4) where the refractive index of the glass material is Considering wavelength dispersion, that is, dependency of refractive index n on wavelength of incident light, the following differential operation is performed. That is, when the apex angle α and the incident angle β, which do not depend on the wavelength, are taken as constants and the differentiation of the formulas (3) and (4) is taken, 0 = dnsinγ + ncosγdγ (Formula (5) Formula (4) From dnsin (γ + α) + ncos (γ + α) dγ = cosδdδ ...
-Equation (6) From equations (5) and (6), dδ = (dnsin (γ + α) -ncos (γ + α) dnsinγ / nco
sγ) / cosδ = dn (sin (γ + α) -cos (γ + α) tanγ) / cosδ
.. can be written as equation (7), so the change rate d? Of the emission angle due to the wavelength variation of the semiconductor laser 11 and the wavelength dispersion of the prism glass material can be expressed by equation (7).

On the other hand, the reduction ratio M of the shaping prism will be described with reference to FIG. Points a and c in the figure indicate points where an incident ray having a ray bundle diameter W1 represented by the distance ab is incident on the prism. Also, the ray bundle diameter W2 of the refracted rays at the incident surface
Is represented by cd.

From this figure, the relationship of distance ac = W1 / cosβ = W2 / cosγ is established, and therefore the reduction ratio on the incident surface is expressed by W2 / W1 = cosγ / cosβ. Similarly, the reduction rate at the exit surface is cosδ / cos (γ +
given in α).

Therefore, the reduction ratio M of the entire shaping prism is given by M = cosδcosγ / (cosβcos (γ + α)) (Equation (8)).

For example, if you select SF11 as the glass material for the shaping prism 13, Therefore, assuming that the apex angle α of the shaping prism 13 is 20 degrees and the incident angle β is 25 degrees, γ = 14.77 degrees M ≈ 0.4 times δ = 72.02 degrees Also, the change rate dδ of the exit angle δ with respect to the wavelength change is given by the formula (7). From the above values and dδ ≈ 0.002 (λ: 800 nm- → 830
nm).

Therefore, the actual change of the output angle is given by Δδ = dδ × δ = 0.002 × 72.02 ≈0.14 degrees.

Generally, the ellipticity of the far-field image of the semiconductor laser is about 2 to 3, so the ellipticity of the light emitted from the shaping prism is 5 to 7.5.
It becomes possible to form a slit-shaped light beam.

Further, when the emission wavelength of the semiconductor laser 11 is changed by 30 nm by the emission wavelength changing means 20, the change of the emission angle δ due to the wavelength dispersion of the prism glass material is Δδ≈0.14 degrees.

Therefore, for example, if the distance between the exit surface of the shaping prism 13 and the object surface to be measured is 1000 mm, then ΔY = 1000 × tan0.14 =
A slit-shaped light beam can be scanned in the Y direction within a range of 2.44 mm. That is, a change in the emission wavelength of the semiconductor laser 11 can be made in small step feeds of about 0.001 degree per 1 nm, and a few mm
A scan range of a degree can be easily obtained.

Therefore, if the light emission wavelength varying means 20 and the shaping prism 13 having the above-mentioned configurations are used, a deflection mirror for deflecting the light beam in two directions of X and Y and a rotary encoder for detecting the rotation angle thereof are used. Without this, it becomes possible to scan the slit-shaped light beam at a high speed in a minute step of about 0.001 degree.

Next, a second embodiment of the present invention will be described with reference to FIG.
The numbers 11 to 16 in the figure indicate the same as those in FIG. Reference numeral 21 denotes a Peltier element that cools or heats with an electric current and is fixed to the semiconductor laser 11. A temperature detector 22 detects the temperature of the semiconductor laser 11. 23 is
The Peltier device drive current is controlled so that the output of the temperature detector 22, that is, the temperature of the semiconductor laser 11 has a constant wavelength by the voltage supplied from the variable reference voltage generating means 24 which is an ATC (Automatic Tempreture Control) circuit. The light emission wavelength varying means 20 includes a temperature detector 22, a Peltier element 21, and an ATC circuit 2.
3 and variable variable reference voltage generating means 24.

Next, the operation of the second embodiment of the present invention will be described with reference to FIG. The emission wavelength of the semiconductor laser changes with temperature. Therefore, the ATC circuit 23 is controlled by the variable reference voltage generating means 24.
If the drive voltage of the Peltier device 21 is controlled by setting the reference voltage of, the temperature of the semiconductor laser 11 can be arbitrarily set and the emission wavelength can be made variable.

Therefore, similarly to the first embodiment of the present invention described above, by utilizing the wavelength dispersion of the shaping prism 13, the emission angle of the emitted light,
Scanning can be performed in minute steps, the same effect as that of the first embodiment of the present invention can be obtained, and unlike the first embodiment of the present invention, since the emission power of the semiconductor laser 11 can be made constant, the emission power There is also an advantage that a light amount change correction means associated with is not required.

Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram of an optical waveguide type laser called a distributed reflection laser (DBR laser) having a diffraction grating inside a semiconductor laser.

The reflectance r and the phase Φ1 in the DBR region are r = −jκsinhγL / (γcoshγL + (α + jΛB) sanh
γL) = | γ | exp (jΦ1) ・ ・ ・ Equation (10) where γ ² = κ ² + (α + jΔβ) ² Δβ = (2π / λ) n eq−π / Λ n eq: DBR region equivalent refractive index Λ: Period of diffraction grating κ: Coupling constant of light and diffraction grating α: Loss of DBR region β: Propagation constant On the other hand, phase Φ2 of emission region is Φ2 = βaLa ・ ・ ・ Equation (11) βa: Propagation constant La of emission region La : Length of light emitting region Such an optical waveguide type laser needs to satisfy the phase matching condition Φ1 = Φ2 + 2mπ of laser oscillation (12). That is, light is emitted at a wavelength that satisfies this condition.

However, when current is injected into the DBR region, electrons and carriers are stored in the optical waveguide layer. When the carriers are accumulated, the plasma effect reduces the equivalent refractive index n eq. Therefore,
In equation (10), Δβ = (2π / λ) n eq−π / Λ changes,
Φ1 also changes. Therefore, from the phase matching condition of equation (12),
The emission wavelength changes.

Therefore, if the emission wavelength varying means 20 is constituted by an optical waveguide type semiconductor laser having a diffraction grating inside thereof and an injection current control means for the internal diffraction grating region, the first and second aspects of the present invention described above can be obtained. The same effect as the embodiment can be obtained.

Further, according to the present embodiment, the emission power of the semiconductor laser can be integrated, and not only the Peltier device 21 and the temperature detector 22 are not required, but also the power for driving the Peltier device 21 is significantly reduced. It has an advantage that power consumption can be reduced.

In the above embodiments, the triangular prism is used as the means for converting into a slit-shaped beam, but it is not limited to this, for example, a slit-shaped aperture may be used, and a reflection is performed as an optical element having wavelength dispersion property. The same effect can be obtained by using a diffraction grating of a transmission type or a transmission type.

Advantageous Effects of Invention The three-dimensional optical distance sensor of the present invention includes a semiconductor laser, a beam shaping prism that reduces the beam width in the short axis direction of an elliptical far-field image of the semiconductor laser, and a plane substantially flush with the exit surface of the shaping prism. By providing a two-dimensional photodetector arranged in the inside and an emission wavelength changing means of the semiconductor laser, a slit-shaped light beam can be formed in minute steps without using a deflection mirror or the like.
It is possible to provide a three-dimensional optical distance sensor that scans the surface of an object to be measured at high speed.

[Brief description of drawings]

FIG. 1 is a plan view of the first embodiment of the present invention, FIG. 2 is an operation explanatory view of the first embodiment of the present invention, and FIG. 3 is a plan view of the second embodiment of the present invention. 4 is a configuration diagram of an optical waveguide type laser according to a third embodiment of the present invention, FIG. 5 is a configuration diagram of a conventional example, and FIG. 6 is an operation explanatory diagram of the conventional example. 11 …… Semiconductor laser, 12 …… Collimating lens, 13 ……
Shaping prism, 14 ... Object to be measured, 15 ... Condensing lens,
16 …… two-dimensional array photodetector, 20 …… semiconductor laser emission wavelength variable means.

Claims (2)

[Claims] 1. A semiconductor laser, a condensing means for condensing light from the semiconductor laser into parallel light, and a beam shaping means for converting the condensed laser light into a slit-shaped light beam. An optical element having a wavelength dispersive property that reflects or transmits light that has passed through the beam shaping means, an optical element having the wavelength dispersive property, a two-dimensional photodetector arranged in substantially the same plane, and the semiconductor laser A three-dimensional optical distance sensor, comprising: an emission wavelength varying means. 2. The beam shaping means and the optical element having a wavelength dispersion property are constituted by a beam shaping prism for reducing the beam width in the short axis direction of the elliptical far-field pattern of the laser light. Item 3. The three-dimensional optical distance sensor according to Item 1.