JPH038691B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical distance sensor.

[Background technology]

Conventionally, a light spot on an object to be detected is imaged onto a one-dimensional light receiving element by a light receiving system arranged obliquely to the light emitting axis, and the displacement of the light spot image is detected to detect the object to be detected. A so-called light cutting type distance sensor that detects displacement along a light projection axis is known, for example, from Japanese Patent Laid-Open No. 57-67815.

For this type of distance sensor, the detection sensitivity of the one-dimensional light-receiving element such as one-dimensional image sensor or photodiode array has a significant effect on measurement accuracy, so it is extremely important to remove ambient light that enters from sources other than the light spot. is important. To this end, a conventional method has been to use light in a specific wavelength range as a light source and provide an optical filter in the light receiving system that transmits only the wavelength of the light source to remove ambient light. However, a high-performance optical filter has a complicated structure and is expensive, and has a problem in that it has a light transmittance of at most 50% and a large loss of light.

Furthermore, in order to improve detection accuracy, it is necessary to increase the magnification of the light receiving optical system, which causes the problem that the distance between the light receiving lens and the light receiving element increases, making the entire sensor larger.

[Purpose of the invention]

An object of the present invention is to reduce the loss of light for removing the above-mentioned disturbance light, and to make the overall size of the sensor as small as possible.

[Disclosure of the invention]

FIG. 1 is a schematic diagram of the distance sensor of the present invention. In the figure, a light projector is comprised of a light source 1 and a light projecting lens 2, and a light receiving optical system is comprised of a light receiving lens 3 and a dichroic mirror 4.
Reference numeral 5 denotes a one-dimensional light-receiving element, and its output, an electrical signal, is processed by a signal processing section 6. 7 is a light shielding plate.

In FIG. 1, if the dichroic mirror 4 were not present, a light spot P projected onto the object surface 8 to be detected by the beam projector would be imaged at a point _P1 .
The optical axis X ₂ of the receiving optical system is inclined with respect to the optical axis X ₁ of the projector, and both optical axes X ₁ X ₂ are approximately at the point P where object detection is planned.
are intersecting. When _the object _{8 moves} back and forth along _the optical _axis
It is known that the plane intersects with the plane including the light-receiving lens 3. Therefore, the imaging point _P2 of the light beam reflected by the dichroic mirror 4 moves on a straight line A2 that is symmetrical to the straight line _A1 with respect to the plane containing the dichroic mirror ₄ . One-dimensional light receiving element 5 is placed on this straight line _A2 .
A light-receiving surface is provided.

FIG. 2 shows a circuit diagram of the signal processing section 6 in FIG. 1, in which a PSD element manufactured by Hamamatsu Television Co., Ltd. is used as the one-dimensional light receiving element 5. Both current outputs of the PSD element 5 are converted into voltages V ₁ and V ₂ by amplifiers 11 and 12, respectively, and an adder circuit 13,
Processed by the subtraction circuit 14 and the division circuit 15,
The division result V _P =(V ₁ −V ₂ )/(V ₁ +V ₂ ) is obtained. This voltage V _P represents the position of the light spot image on the PSD element 5. Comparators 16, 17
constitutes a window type comparator, and an upper limit value and a lower limit value can be set by podensiometers 18 and 19, respectively.
The output of the window type comparator passes through the digital processing section 20 and the transistor output section 21, and is output to the far terminal (FAR), the near terminal (NEAR), and the appropriate terminal (GO).

〔Effect of the invention〕

As described above, the present invention inserts a dichroic mirror into the optical path of the light-receiving optical system and uses the wavelength range reflected by the dichroic mirror as the light source of the projector, making it possible to remove light other than the wavelength of the light source. Moreover, since the light beam used is reflected light rather than transmitted light, the loss of light can be suppressed to a few percent or less, and there is an advantage that the sensitivity can be significantly improved compared to the conventional method.

Also, when bending the optical path of the light-receiving optical system using a dichroic mirror, the light-receiving axis
By bending X ₂ in a direction that brings it closer to the projection axis X ₁ , the outer shape of the sensor body can be shortened in both length and width, thus increasing the magnification without increasing the size of the main body compared to conventional methods. It has the advantage of being possible.

Furthermore, in this type of distance sensor, there is an appropriate distance range in which the locus of the imaging point can be regarded as approximately a straight line, and if the distance is outside of this range, the error cannot be ignored. Therefore, as in the embodiment shown in FIG. 2, if the upper and lower limits of the appropriate range can be set in advance, there is an advantage that extremely high-speed determination can be made. Also, for the same reason, it is essential to fine-tune the optical path of the light-receiving optical system, and in the past, the position and direction of the light-receiving lens and one-dimensional light-receiving element had to be adjusted, making the mechanism and adjustment work complicated. However, according to the present invention, by allowing the position and angle of the dichroic mirror to be finely adjusted, the light-receiving lens and the one-dimensional light-receiving element can be fixed, which significantly simplifies the mechanism. It has the advantage of being able to

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG.
The figure is a circuit diagram of the main parts same as above. 1 is a light source, 2 is a light projecting lens, 3 is a light receiving lens, 4 is a dichroic mirror, 5 is a one-dimensional light receiving element, 6 is a signal processing section, 7 is a light shielding plate, 8 is a detected object surface, 11, 12 is an amplifier, 13 is an adder circuit,
14 is a subtraction circuit, 15 is a division circuit, 16 and 17 are comparators, 18 and 19 are potentiometers,
20 is a digital processing section, and 21 is a transistor output section.

Claims (1)

[Scope of Claims] 1. A beam projector that projects a light spot onto the surface of an object to be detected, a light-receiving optical system that forms an image of the light spot on a one-dimensional light-receiving element such as a photodiode array, and a one-dimensional light-receiving element. and a signal processing unit that processes the output signal of the light emitter and detects the distance from the light projector to the object surface to be detected, in which a dichroic mirror is provided in the optical path of the light receiving optical system, and the light reflected by the dichroic mirror is A distance sensor characterized by using a light source in a wavelength range as described above for the projector. 2. A window type comparator is provided in the signal processing section, the upper limit value and the lower limit value of which can be changed.
2. The distance sensor according to claim 1, wherein the distance sensor detects when the distance from the projector to the object to be detected falls within a set range.