JP5476858B2 - Ranging sensor - Google Patents

Description

  The present invention relates to an optical distance measuring sensor that measures the distance and displacement to an inspection object by a triangulation method.

  In recent years, optical distance measuring sensors have been opened for use as human sensors such as opening a toilet seat cover, energy saving of a mobile PC, and opening and closing of an automatic door, and miniaturization and cost reduction have been promoted.

  As an optical distance measuring sensor for measuring the distance and displacement to the object to be inspected by the triangulation method, an optical sensor that can detect the position of the spot-like light currently called PSD (Position Sensitive Detector) is used. Is commonly used. A distance measuring sensor using a PSD will be described with reference to Patent Document 1 (Japanese Patent Laid-Open No. 58-42007) as an example. The distance measuring sensor described in Patent Document 1 uses an LED as a light source. The light emitted from the LED is irradiated to the subject Ob (inspection object) through the projection lens L1. Among the light scattered by the subject Ob, the component of the light reflected in the oblique direction is detected by the PSD via the lens L2. When the distance l between the lens L1 and the subject Ob changes, the spot position on the PSD changes linearly, so that the displacement of the subject can be known from the PSD output signal.

  In order to increase the resolution of position information in such a conventional distance measuring sensor using PSD, it is necessary to increase the distance between the lenses L1 and L2 or to increase the focal length f of the lens L2. For this reason, there is a trade-off between high resolution and miniaturization, and both performances cannot be satisfied. In addition, the distance measuring sensor using the PSD moves the light spot position on the PSD widely when the object to be inspected is close to the lens L1 when measuring the displacement of the object to be inspected. I need.

  By the way, there is a tilt sensor using a volume hologram. This will be described by taking Patent Document 2 (Japanese Patent Laid-Open No. 2004-279191) as an example. The tilt sensor described in Patent Document 2 uses a light emitting diode 151 as a light source. The light emitted from the light emitting diode 151 is collimated by the collimator lens 152 and irradiated on the optical disk 15. The light reflected by the optical disk 15 enters the volume hologram 153, but the diffraction efficiency changes according to the incident angle of the incident light. Here, by taking the difference between the diffracted lights L + 1 and L−1, a linear signal (diffractive efficiency difference) can be obtained with respect to the incident angle of the light. Therefore, according to Patent Document 2, a linear signal can be acquired according to the inclination of the optical disk 15 that is the inspection object.

  The present invention has been made under such circumstances, and a first object thereof is to realize a distance measuring sensor capable of increasing or decreasing the sensitivity regardless of the size of the distance measuring sensor. A second object of the present invention is to realize a small distance measuring sensor without increasing the size of a detection portion even when an object to be inspected is nearby.

In order to solve the above problems, the distance measuring sensor according to the present invention specifically has the technical features described in the following (1) to (3) .
(1): It is arranged at a position different from a light source that irradiates substantially parallel light to the object to be inspected and a straight line connecting the object to be inspected and the light source, and diffracts the light scattered by the object to be inspected. From a volume hologram, a photodetector that individually receives + n-order light and -n-order light (where n is an integer) of the light diffracted by the volume hologram, and an output of the photodetector e Bei and a calculation circuit for outputting a displacement amount of the test substance, the volume hologram, wherein when the object to be inspected is in the center of the displacement measuring range, incident on light scattered in the object to be inspected The volume hologram has a groove shape that is arranged to have an angle of 0 degrees and is parallel to the light scattered by the object to be inspected and is rectangular, and the arithmetic circuit unit has the volume The diffraction efficiency of the + n-order light of the hologram is η (n), and the volume hologram When the diffraction efficiency of the −n-order light of the system is η (−n), the distance between the light source and the inspection object is L, and the distance between the light source and the volume hologram is A, the inspection object Is a distance measuring sensor characterized in that a distance ΔL displaced on a straight line connecting the object to be inspected and the light source is obtained by the following equation .
ΔL = − (L ² + A ² ) tan Δθ / (A + Ltan Δθ)
Δθ = (η (n) −η (−n)) / (η (n) + η (−n)) × 1 / C
However, C is a constant.

  According to the configuration of (1), it is possible to increase or decrease the sensitivity regardless of the size of the distance measuring sensor by changing the groove depth and refractive index difference of the volume hologram. In addition, by using a photodetector that individually receives + n-order light (n is an integer) and -n-order light among the light diffracted by the volume hologram, even when the object to be inspected is detected The displacement amount of the inspection object can be measured without increasing the size of the portion.

Further , according to the configuration of (1) , the volume hologram is arranged so that the incident angle is 0 degree with respect to the light scattered by the object to be inspected, and the groove shape is a vertical rectangular shape. Thus, the output signal from the arithmetic circuit unit for starting the measurement of the displacement amount of the inspection object is set to 0, and it is possible to determine whether the inspection object is moving away or approaching according to the positive / negative of the output signal.

(2): It is arranged at a position different from a light source that irradiates the object to be inspected with substantially parallel light and a straight line connecting the object to be inspected and the light source, and diffracts light scattered by the object to be inspected From a volume hologram, a photodetector that individually receives + n-order light and -n-order light (where n is an integer) of the light diffracted by the volume hologram, and an output of the photodetector An arithmetic circuit unit that outputs a displacement amount of the inspection object, wherein the volume hologram is arranged perpendicular to the light from the light source toward the inspection object, and the groove shape of the volume hologram is: When the inspection object is at the center of the displacement measurement range, it is parallel to the light scattered by the inspection object, and the arithmetic circuit unit sets the diffraction efficiency of + n-order light of the volume hologram to η ( n) The diffraction efficiency of -n-order light of the volume hologram is expressed as η (-N) When the distance between the light source and the inspection object is L, and the distance between the light source and the volume hologram is A, the inspection object is the inspection object and the light source. The distance measuring sensor is characterized in that a distance ΔL displaced on a connecting straight line is obtained by the following equation.
    ΔL = − (L ² + A ² ) TanΔθ / (A + LtanΔθ)
    Δθ = (η (n) −η (−n)) / (η (n) + η (−n)) × 1 / C
  However, C is a constant.

According to the configuration of (2) above, it is possible to increase or decrease the sensitivity regardless of the size of the distance measuring sensor by changing the groove depth and refractive index difference of the volume hologram. In addition, by using a photodetector that individually receives + n-order light (n is an integer) and -n-order light among the light diffracted by the volume hologram, even when the object to be inspected is detected The displacement amount of the inspection object can be measured without increasing the size of the portion.
In the above-described configuration (2), a volume hologram is arranged perpendicularly to the light toward the object to be inspected from the light source, and the groove shape is parallel to the light scattered by the object to be inspected It is formed to become. As a result, as in the configuration of (1) above, the output signal from the arithmetic circuit unit for starting the measurement of the displacement of the inspection object is set to 0, and the inspection object moves away or approaches depending on whether the output signal is positive or negative Can be determined.

(3) : A plurality of volume holograms and a plurality of photodetectors are arranged in a plane perpendicular to the light from the light source toward the object to be inspected, centering on the light source. The distance measuring sensor according to (1) or (2) .

According to the configuration of the above (3) , by arranging a plurality of the volume holograms and photodetectors in a plane perpendicular to the light from the light source toward the object to be inspected around the light source, the volume hologram, By arranging a plurality of photodetectors, the measurement range can be increased to a plurality.

  According to the present invention, the sensitivity can be increased or decreased regardless of the size of the distance measuring sensor, and the small distance measuring sensor without increasing the size of the detection portion even when the object to be inspected is nearby. Can be provided.

It is the schematic which shows an example of embodiment of the ranging sensor which concerns on this invention. It is a figure for demonstrating the principle of the triangulation in this embodiment. It is the schematic which shows the structure of a volume hologram. It is a graph which shows the difference in the diffraction efficiency of a plane hologram and a volume hologram. It is the schematic which shows an example of other embodiment of the ranging sensor which concerns on this invention. It is a graph which shows the relationship between the diffraction efficiency of a volume hologram, and an angle variation. It is the schematic which shows the structure of the arithmetic circuit part of a ranging sensor. It is a graph which shows the output signal of an arithmetic circuit part. It is a graph which shows the output signal of a signal calculating part when the arrangement position of a volume hologram is used as a parameter. It is the schematic which shows the structure for implement | achieving the measurement in a some ranging range in the ranging sensor which concerns on this invention.

The distance measuring sensor according to the present invention is disposed at a position different from the light sources 1 and 2 that irradiate substantially parallel light to the inspection object 3 and a straight line connecting the inspection object 3 and the light sources 1 and 2. The volume hologram 4 that diffracts the light scattered by the object 3 to be inspected, and the + n-order light and the −n-order light (where n is an integer) of the light diffracted by the volume hologram 4 are individually provided. Photodetectors 6 and 7 that receive light, and an arithmetic circuit unit 8 that outputs a displacement amount of the inspection object 3 from outputs of the photodetectors 6 and 7.
Next, the distance measuring sensor according to the present invention will be described in more detail with reference to the drawings.
Although the embodiments described below are preferred embodiments of the present invention, various technically preferred limitations are given, but the scope of the present invention is intended to limit the present invention in the following description. As long as there is no description, it is not restricted to these aspects.

<Light sources 1, 2>
FIG. 1 is a schematic view showing an example of an embodiment of a distance measuring sensor according to the present invention.
An LD or LED is used for the point light source 1. The divergent light emitted from the point light source 1 is converted into a parallel light flux by the collimator lens 2.
The light source in the present invention may be in any form as long as it can irradiate substantially parallel light onto the object 3 to be inspected, but in this embodiment, the point light source 1 and the collimating lens 2 are used together as a light source. . As the collimating lens 2, a conventionally known lens can be applied as it is.

<Photodetectors 6, 7>
Next, the parallel light beam is irradiated onto the inspection object 3. The inspection object 3 is assumed to be a scatterer having a rough surface shape such as a human body or clothes. A part of the light scattered in the oblique direction by the inspection object 3 is diffracted by a volume hologram 4 to be described later and condensed by the detection lens 5. Of the light diffracted by the volume hologram (diffraction hologram) 4, diffracted light ± n-order light having a numerical value of the order n is received by the photodetector A 6 and the photodetector B 7, respectively. Here, n represents an integer.

The outputs of the photodetectors 6 and 7 are subjected to differential calculation by the arithmetic circuit unit 8 to obtain a displacement signal ΔL (displacement amount). If the axis connecting the point light source 1 and the inspection object 3 is the x axis, the displacement signal ΔL changes when the inspection object 3 moves on the x axis.
As the photodetectors 6 and 7, a conventionally known one can be applied as it is.

<Volume hologram 4>
The triangulation method in this embodiment will be described with reference to FIG. The inspection object 3 is located at a position L away from the collimating lens 2 in the x-axis direction. Further, the volume hologram 4 is installed at a position A away from the collimating lens 2 in the y-axis direction. Here, the angle formed by the collimating lens 2 -the inspection object 3 -the volume hologram 4 is defined as θ. At this time, the volume hologram 4 is arranged so that θ ≠ 0 deg, that is, at a position different from the straight line connecting the inspection object 3 and the light sources 1 and 2.
Now, it is assumed that the inspection object 3 is displaced by ΔL in the x-axis direction and moved to the position 3 ′ after the movement. At this time, if the angle formed by the collimating lens 2 -position 3 'after movement and the volume hologram 4 is θ + Δθ, the following two equations are established.

A / L = tan θ (1)
A / (L + ΔL) = tan (θ + Δθ) (2)

  When this is solved for ΔL, it can be seen that it is expressed as a function of the angle variation Δθ.

ΔL = − (L ² + A ² ) tan Δθ / (A + LtanΔθ) (3)

The volume hologram 4 used in the present invention will be described with reference to FIG. The volume hologram 4 is composed of glass materials (glass material 13 and glass material 14) having different refractive indexes with the uneven surface as a boundary.
The volume hologram will be described. For example, as described in “Lightwave Electro-Optics” (Corona), pages 117 to 132, by Oyama and Nishihara, holograms generally include planar holograms and volume holograms. Whether it is a planar hologram or a volume hologram is determined by the value (Q value) of the parameter Q calculated by the following equation (4). Here, λ is the wavelength of the incident light, T is the groove depth of the concavo-convex grating, n1 is the refractive index of the glass material 13, n2 is the refractive index of the glass material 14, and P is the groove spacing.

Q = 2πλT / P ² / (n1−n2) (4)

Usually, the case of Q ≦ 0.5 is called a planar hologram, and the case of Q ≧ 5 is called a volume hologram. One of the differences between the properties of a planar hologram and a volume hologram is whether or not the diffraction efficiency depends on the incident angle. For example, as shown in FIG. 4, the diffraction efficiency of a planar hologram is almost constant regardless of the incident angle of light. However, in the volume hologram, the diffraction efficiency changes greatly depending on the incident angle of light, and a specific incident angle θ _B ( The diffraction efficiency is maximized at the Bragg angle.

  Next, a technique for measuring an angle change amount Δθ using a volume hologram will be described. A volume hologram having a refractive index n1 = 1.71 of the glass material 13, a refractive index n2 = 1.5 of the glass material 14, a groove depth T = 6.5 μm, and a groove interval P = 5 μm will be described as an example. In this design example, Q = 6.46 when λ = 0.83 μm, which is defined as a volume hologram.

In the present embodiment, Δθ = 0 deg indicates a case where light incident on the volume hologram 4 is incident vertically. That is, in FIG. 1, the volume hologram 4 is arranged perpendicular to the light scattered by the inspection object 3.
That is, the volume hologram 4 is arranged so that the incident angle is 0 degree with respect to the light scattered by the inspection object 3 when Δθ = 0 deg, which is the center of the displacement measurement range. In addition, the groove shape is parallel to the light scattered by the inspection object 3. The groove shape is preferably a rectangular shape.

Alternatively, as shown in FIG. 5, only the groove of the volume hologram 4 may be configured to be parallel to the incident light.
That is, the volume hologram 4 is arranged perpendicularly to the light from the light sources 1 and 2 toward the inspection object 3 and the groove shape is such that the inspection object 3 is at the center of the displacement measurement range. It is parallel to the light scattered by the inspection object 3.

  FIG. 6 shows the calculation result of the diffraction efficiency when the incident angle (angle change amount) Δθ of the light incident on the volume hologram 4 is used as a parameter. At this time, the diffraction efficiency η1 of the + 1st order light and the diffraction efficiency η2 of the −1st order light exhibit line-symmetric characteristics with 0 deg as a boundary. Therefore, if the angle signal SΔθ is defined by the equation (5), a stable signal can be obtained regardless of the amount of light incident on the photodetector.

  SΔθ = (η1−η2) / (η1 + η2) (5)

  In particular, in the range of the angle variation ± 3 deg, SΔθ has a substantially linear characteristic. That is, the relationship of Formula (6) is established.

  SΔθ = C × Δθ (6)

<Operation circuit unit 8>
The arithmetic circuit unit (signal arithmetic unit) 8 of the distance measuring sensor of the present invention is configured by a circuit as shown in FIG. Outputs of the photodetectors A6 and B7 are subtracted by a subtracting circuit 9, and a signal A is obtained. Further, the outputs of the photodetectors A6 and B7 are added by the addition circuit 10, and a signal B is obtained. Then, by dividing the signal A by the signal B by the division circuit 11, the angle signal SΔθ in the equation (5) can be obtained. Furthermore, the amount of change in Δθ itself can be measured by amplifying the output signal to 1 / C. The displacement amount calculation circuit 12 calculates Expression (3). This makes it possible to measure the displacement ΔL (displacement amount) of the inspection object 3. Here, in the configuration shown in FIG. 1, when L = 100 mm and A = 20 mm, a displacement signal SΔL when the inspection object 3 is moved in the x-axis direction is shown in FIG. In the present embodiment, a linear signal is obtained at L = 100 mm ± 25 mm. Here, when the distance A between the collimating lens 2 and the volume hologram 4 is changed, as shown in Table 1, the measurement range of the inspection object can be changed.

  At this time, the signal shows a response as shown in FIG.

  Here, as shown in FIGS. 10 (A) and 10 (B), volume holograms 4, 54, 64, 74 are formed in a plane perpendicular to the light from the light sources 1, 2 toward the object 3 to be inspected. , Detection lenses 5, 55, 65, and 75, photodetectors A6, 56, 66, and 76, and photodetectors B7, 57, 67, and 77, respectively. By changing the installation position of the hologram to A1, A2, A3, A4, it becomes possible to detect a plurality of measurement ranges with one light source (point light source 1 + collimating lens 2). (The detection lenses 65 and 75, the photodetectors A66 and 76, and the photodetectors B67 and 77 are not shown.)

  According to the distance measuring sensor according to the embodiment described above, the sensitivity can be increased or decreased regardless of the size of the distance measuring sensor, and the size of the detection portion is increased even when the object to be inspected is nearby. Miniaturization could be realized without doing so.

1 Point light source (LD, LED)
2 Collimating lens 3 Non-inspection object 4 Volume hologram 5 Detection lens 6 Photodetector A
7 Photodetector B
8 arithmetic circuit unit 9 subtraction circuit 10 addition circuit 11 division circuit 12 displacement amount calculation circuit 13 glass material 1
14 Glass 2
54 Second volume hologram 55 Second detection lens 56 Second photodetector A
57 Second photodetector B
64 Third volume hologram 65 Third detection lens 66 Third photodetector A
67 Third photodetector B
74 Fourth volume hologram 75 Fourth detection lens 76 Fourth photodetector A
77 Fourth Photodetector B

JP-T-2006-503313 (FIG. 3) Japanese Patent Laying-Open No. 2003-202708 (FIGS. 7A, 7B, 8A)

Claims (3)

A light source that emits substantially parallel light to the object to be inspected;
A volume hologram that is arranged at a position different from the straight line connecting the inspection object and the light source, and diffracts light scattered by the inspection object;
A photodetector that individually receives + n-order light and -n-order light (where n is an integer) among the light diffracted by the volume hologram;
From the output of the photodetector, e Bei and a calculation circuit for outputting a displacement amount of the object to be inspected,
The volume hologram is arranged so that an incident angle becomes 0 degrees with respect to light scattered by the inspection object when the inspection object is at the center of a displacement measurement range, and the volume hologram The groove shape is parallel to the light scattered by the object to be inspected and is a rectangular shape,
The arithmetic circuit unit has a diffraction efficiency of + n order light of the volume hologram η (n), a diffraction efficiency of −n order light of the volume hologram η (−n), and a distance between the light source and the object to be inspected. Is the distance L between the light source and the volume hologram, and the distance ΔL by which the inspection object is displaced on the straight line connecting the inspection object and the light source is obtained by the following equation: Ranging sensor characterized by
ΔL = − (L ² + A ² ) tan Δθ / (A + Ltan Δθ)
Δθ = (η (n) −η (−n)) / (η (n) + η (−n)) × 1 / C
However, C is a constant.   A light source that emits substantially parallel light to the object to be inspected;
  A volume hologram that is arranged at a position different from the straight line connecting the inspection object and the light source, and diffracts light scattered by the inspection object;
  A photodetector that individually receives + n-order light and -n-order light (where n is an integer) among the light diffracted by the volume hologram;
  From the output of the photodetector, an arithmetic circuit unit that outputs the amount of displacement of the inspection object,
  The volume hologram is arranged perpendicular to the light from the light source toward the inspection object, and the groove shape of the volume hologram is such that the inspection object is at the center of the displacement measurement range. Parallel to the light scattered by the object under test,
  The arithmetic circuit unit has a diffraction efficiency of + n order light of the volume hologram η (n), a diffraction efficiency of −n order light of the volume hologram η (−n), and a distance between the light source and the object to be inspected. Is the distance L between the light source and the volume hologram, and the distance ΔL by which the inspection object is displaced on the straight line connecting the inspection object and the light source is obtained by the following equation: Ranging sensor characterized by
    ΔL = − (L ² + A ² ) TanΔθ / (A + LtanΔθ)
    Δθ = (η (n) −η (−n)) / (η (n) + η (−n)) × 1 / C
  However, C is a constant.   The volume hologram and a plurality of the photodetectors are respectively disposed in a plane perpendicular to the light from the light source toward the inspection object with the light source as a center. 2. The distance measuring sensor according to 2.

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