JP6130805B2 - Distance measuring apparatus and method - Google Patents

Description

  The present invention relates to a distance measurement technique, and more particularly to an optical distance measurement technique for irradiating and reflecting light on an object and measuring an objective distance to the object based on the reflected light.

  2. Description of the Related Art An optical measuring apparatus that can measure an objective distance to an object in a non-contact manner using light such as laser light is known. Such an optical measuring apparatus is not only for measuring an objective distance to an object, but is also considered to be applied to various uses such as measuring the surface shape of an object and measuring the thickness of a thin film.

  As such an optical measuring device, for example, laser light is irradiated obliquely to the surface of an object, and the distance to the surface is calculated based on the principle of triangulation based on the position where the reflected light has reached. It has been known. Such an optical measuring apparatus is widely used as an inexpensive measuring apparatus because the apparatus configuration is relatively simple. However, since the tilt of the reflecting surface directly affects the distance measurement value, the measurement error increases when the surface of the object to be measured is not flat.

  On the other hand, as a distance measuring device that can be applied even when the surface of an object is not flat, an optical measuring device that uses light interference has been proposed. For example, in the optical measuring apparatus described in Patent Document 1 below, light is irradiated to a measurement point of an object and reflected, and the reflected light reaches a CCD image sensor which is an interference fringe detection surface. It has a configuration.

  An optical lens system is disposed between the measurement point and the CCD image sensor, and the reflected light reaches the CCD image sensor through the optical lens system. The optical lens system is configured such that the reflected light from the point to be measured passes through a plurality of optical paths and is then irradiated on the CCD image sensor. Since the optical path lengths of the respective optical paths are different from each other, interference fringes are generated on the CCD image sensor due to the optical path difference.

  The fringe spacing of the interference fringes changes according to the objective distance between the measurement point and the CCD image sensor. Therefore, in this optical measuring device, the objective distance to the measurement point is calculated based on the fringe interval obtained from the output of the CCD image sensor.

JP 2004-28977 A

  However, in such a conventional technique, it is necessary to arrange an optical lens system in order to generate a plurality of optical paths having different optical path lengths. Such an optical lens system is a multifocal lens that requires precise polishing. Or a spherical lens. Accordingly, such optical lens systems are generally expensive and require precise assembly. For this reason, there existed a problem that the cost of a distance measuring device increased.

  An object of the present invention is to solve such a problem, and an object of the present invention is to provide a distance measuring device capable of accurately measuring an objective distance to an object with an optical lens system having a simple configuration.

  In order to achieve such an object, a distance measuring device according to the present invention is a distance measuring device that irradiates and reflects light on an object, and measures an objective distance to the object based on the reflected light. A diffraction grating that diffracts the reflected light from the object, a condensing lens that condenses the diffracted light from the diffraction grating on an imaging surface, and is disposed on the imaging surface, Among them, a spatial filter that allows only two different orders of diffracted light to pass through and blocks other orders of diffracted light, and two different orders of diffracted light that have passed through the spatial filter, are used for detecting the surface. A light detection element for detecting the generated interference fringe, and a detection result obtained by the light detection element are arithmetically processed to extract the pitch of the interference fringe, and based on this pitch, the light from the condenser lens to the object is extracted. Objective distance And a distance calculating unit for output.

Further, in one configuration example of the distance measuring device according to the present invention, the focal length of the condenser lens is f, the distance from the condenser lens to the detection surface is L, and the diffraction grating interval of the diffraction grating is When d is the order difference of the diffracted light passing through the spatial filter, m, the objective distance a from the condenser lens to the object is obtained by the following equation (12).

Another distance measuring device according to the present invention is a distance measuring device that irradiates and reflects light on an object, and measures an objective distance to the object based on the reflected light. A condensing lens for condensing the reflected light on the imaging surface, a diffraction grating for diffracting the reflected light collected by the condensing lens, and a diffraction grating disposed on the imaging surface and diffracted from the diffraction grating Detected by a spatial filter that allows only two different orders of diffracted light to pass through and blocks other orders of diffracted light, and two different orders of diffracted light that have passed through the spatial filter. A light detection element for detecting interference fringes generated on the surface; and a detection result obtained by the light detection element is processed to extract a pitch of the interference fringes, and the object is extracted from the condenser lens based on the pitch. Objective distance up to And a distance calculating unit for output.

  In addition, one configuration example of the distance measuring device according to the present invention further includes an objective lens that uses the reflected light from the object as parallel light, and the diffraction grating diffracts the parallel light from the objective lens. It is what I did.

The distance measuring method according to the present invention is a distance measuring method for irradiating and reflecting light on an object, and measuring an objective distance to the object based on the reflected light, wherein the reflection from the object is performed. A diffraction step for diffracting light by a diffraction grating , a condensing step for condensing the diffracted light from the diffraction grating onto an image forming surface by a condensing lens, and the diffracted light collected on the image forming surface. A diffracted light selection step that allows only two different orders of diffracted light to pass through and blocks other orders of diffracted light; and interference generated on the detection surface by the selected two different orders of diffracted light A light detection step for detecting fringes, and a calculation result of the detection result obtained by the light detection step to extract the pitch of the interference fringes, and based on this pitch, the objective distance from the condenser lens to the object is calculated. And a distance calculation step of leaving.

According to the present invention, an extremely simple optical element such as a diffraction grating and a spatial filter selects two different orders of diffracted light from reflected light from an object, and the interference fringe pitch changes according to the objective distance. Stripes are generated on the detection surface.
Therefore, it is not necessary to use a conventional multifocal lens or spherical lens that requires precise polishing, and an expensive optical lens and its precise assembly can be omitted. Therefore, it is possible to realize a distance measuring device that can accurately measure the distance to an object at a relatively low cost.

It is explanatory drawing which shows the structure of the distance measuring device concerning 1st Embodiment. It is a structural example of a spatial filter. It is explanatory drawing which shows the distance measurement principle concerning this invention. It is explanatory drawing which shows the diffraction in a diffraction grating. It is explanatory drawing which shows the relationship between the diffracted light of a different order, and a light spot space | interval. It is explanatory drawing which shows the relationship between a light spot space | interval and an optical path difference. It is an example of an image which shows the interference fringe which arose on the detection surface. It is an example of analysis of the detection result obtained with the photon detection element. It is explanatory drawing which shows the structure of the distance measuring device concerning 2nd Embodiment. It is a graph which shows the relationship between an objective distance and interference fringe pitch.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, with reference to FIG. 1, the distance measuring apparatus 10 concerning the 1st Embodiment of this invention is demonstrated. FIG. 1 is an explanatory diagram illustrating the configuration of the distance measuring apparatus according to the first embodiment.

This distance measuring device 10 has a function of irradiating and reflecting light on an object T to be measured for distance, and measuring an objective distance to the object T based on the reflected light.
As shown in FIG. 1, the distance measuring device 10 includes a light source 11, a light source lens 12, a beam splitter 13, a diffraction grating 14, a condensing lens 15, a spatial filter 16, a light detection element 17, and a main configuration. A distance calculation unit 18 is provided, and these are housed inside a casing (not shown).

The light source 11 is a device that emits light of a single wavelength (monochromatic light) used for distance measurement. As the light source 11, it is possible to use a monochromatic light such as a semiconductor laser device or a sodium lamp, or a device that emits light having a single wavelength by a white light source and a narrow band-pass filter.
The light source lens 12 has a function of condensing the light emitted from the light source 11 and outputting it to the beam splitter 13.

  The beam splitter 13 is disposed on the optical path O of the light collecting system, reflects the light from the light source 11 collected by the light source lens 12, and irradiates the light spot A of the object T along the optical path O. Among the reflected light diffusely reflected by the light spot A, the reflected light reflected in the direction of the optical path O is transmitted to the condenser lens 15.

The diffraction grating 14 is disposed on the optical path O and has a function of diffracting the reflected light from the object T transmitted through the beam splitter 13.
The condensing lens 15 is composed of, for example, a convex lens, and is disposed on the optical path O, and has a function of condensing the reflected light from the object T transmitted through the beam splitter 13 or the diffracted light from the diffraction grating 14 onto the imaging plane Q. Have.

  About the position of the condensing lens 15, as long as it is the range from the beam splitter 13 to the image plane Q, you may arrange | position in any position before and behind the condensing lens 15. FIG. For example, when the diffraction grating 14 is disposed between the beam splitter 13 and the condenser lens 15, the diffracted light from the diffraction grating 14 is imaged on the imaging plane Q via the condenser lens 15. When the diffraction grating 14 is disposed between the condenser lens 15 and the spatial filter 16, the reflected light collected by the condenser lens 15 is diffracted by the diffraction grating 14, and then the image plane Q Is imaged.

  The spatial filter 16 is disposed on the image plane Q, and selectively passes only two different orders of diffracted light among the diffracted lights from the diffraction grating 14, and diffracts of other orders. It has a function to block light.

  FIG. 2 is a configuration example of the spatial filter. The diffracted light from the diffraction grating 14 is focused on the light spot SP corresponding to the respective order on the image plane Q by the condenser lens 15. The spatial filter 16 is composed of a flat light shielding plate that shields light as a whole, and uses the light spot SP on the imaging plane Q to position the light spot SP according to two different orders set in advance. Are provided with translucent holes H1 and H2, respectively.

  These translucent holes H1 and H2 are formed at positions and sizes that allow only two different orders of diffracted light to pass through based on a measurement span indicating the range of measurable objective distance a. As a result, only two different orders of diffracted light set in advance pass through the light transmitting holes of the spatial filter 16, and other orders of diffracted light are blocked.

The light detection element 17 has a function of detecting an interference fringe generated on the detection surface I and formed of two orders of diffracted light passing through the spatial filter 16 and outputting a detection result. As the photodetecting element 17, for example, a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor) linear image sensor, or a light receiving element arranged in one dimension such as a photodiode array can be used.
The distance calculation unit 18 includes an arithmetic processing circuit using a CPU, extracts the period length of the interference fringes by performing arithmetic processing on the detection result obtained by the light detection element 17, and collects light based on the obtained period length. It has a function of calculating the objective distance from the lens 15 to the object T.

[Principle of distance measurement]
Next, the principle of distance measurement used in the distance measuring apparatus 10 according to the present invention will be described with reference to FIGS. FIG. 3 is an explanatory diagram showing the principle of distance measurement according to the present invention. FIG. 4 is an explanatory diagram showing diffraction by the diffraction grating. FIG. 5 is an explanatory diagram showing the relationship between the diffracted light of different orders and the light spot interval. FIG. 6 is an explanatory diagram showing the relationship between the light spot interval and the optical path difference.

In FIG. 3, only the light collection system of the distance measuring device 10 is shown as the main part, and the projection optical system is omitted. 3 to 6, the longitudinal direction of the diffraction grating 14 (the vertical direction on the paper surface) is the X direction, the periodic direction of the grating (the vertical direction on the paper surface) is the Y direction, and the direction perpendicular to the grating surface (the left and right sides of the paper surface) Direction) is the Z direction.
In addition, the lens originally has two principal points depending on the incident direction of light, and the positions thereof are different, but in the following, in order to avoid complication of the mathematical expression, the condenser lens 15 is composed of a thin single lens, Assuming that there is only one principal point at the lens center, each equation was derived.

As shown in FIG. 3, the objective distance from the object T to the principal point M, that is, the position of the condenser lens 15, is a, the distance from the principal point to the imaging plane Q, that is, the spatial filter 16, is b, and the condenser lens. When the focal length of 15 is f, these relationships are expressed by the following formula (1) by the imaging formula (lens formula).

As can be seen from this equation (1), the position of the imaging plane Q also changes according to the change in the objective distance a from the condenser lens 15 to the object T.
Further, as shown in FIG. 4, the diffraction grating interval of the diffraction grating 14 is d, the diffraction order is n (n = 0, ± 1, ± 2,...), The light source wavelength is λ, and the rotation of each diffracted light. When the folding angle θn is used, the optical path difference ΔL between adjacent diffracted lights is expressed by the following equation (2).

Further, as shown in FIG. 5, the diffracted light diffracted by the grating forms a plurality of light spots in the Y direction on the imaging plane Q by the condenser lens 15. Here, the diffraction angles of two different orders n and n ′ of the diffracted light are θn and θn ′, the light spots by the diffracted lights are An and An ′, and the light by the diffracted light of the order 0 on the imaging plane Q When the distances along the Y direction from the spot A0 to the light spots An and An ′ are W1 and W2, the deviation width W in the Y direction of the light spots An and An ′ is expressed by the following equation (3). The

Here, in equation (3), the actual diffraction grating interval d is sufficiently larger than nλ and n′λ, and nλ / d and n′λ / d are sufficiently small. (4) is approximated.

On the other hand, as shown in FIG. 6, the interval between the light spots An and An ′ on the imaging surface Q is W, and the diffracted light from the light spots An and An ′ is on the detection surface I of the light detection element 17. The arrival point reached is V, the point where the line extending in the Z direction from the intermediate point between the light spots An and An ′ and the detection surface I intersects is V0, and on the detection surface I from V0 to V along the Y direction. Is the distance from the imaging plane Q to the detection plane I, and the optical path length Ln of the diffracted light from the light spot An to the arrival point V can be obtained by the three-square theorem. Since the light spot interval W and the distance P are sufficiently small compared to the above, it can be approximated as the following equation (5).

Further, the optical path length Ln ′ of the diffracted light from the light spot An to the arrival point V can be approximated as in the following equation (6), similarly to the optical path length Ln.

Therefore, the optical path difference ΔL between these optical path lengths Ln and Ln ′ is obtained by the following equation (7). On the detection surface I, interference fringes are generated due to this optical path difference ΔL. Specifically, when the optical path difference ΔL is an integer m (m is an integer of 0 or more) times the wavelength λ of light, A bright line appears.

Here, among the bright lines generated on the detection surface I, the interval between adjacent bright lines is the interference fringe pitch p, which corresponds to the case of m = 1 in Expression (7). Therefore, the interference fringe pitch p of the interference fringes generated on the detection surface I is obtained by the following equation (8) by modifying the equation (7).

At this time, since the light spot interval W is obtained by Expression (4), if this is substituted into Expression (8), Expression (9) is obtained.

Further, the order difference between the diffraction orders n and n ′ is m, and the distance b from the principal point of the condenser lens 15 to the imaging plane Q and the distance c from the imaging plane Q to the detection plane I are defined as the condenser lens. When replacing with the distance L from the 15 principal points to the detection surface I, the equation (9) becomes the following equation (10).

Therefore, it can be seen that the interference fringe pitch p is obtained by a function depending on the distance L from the principal point of the condenser lens 15 to the detection surface I.
At this time, the distance b from the principal point of the condenser lens 15 to the imaging plane Q is the objective distance from the object T to the principal point M, that is, the position of the condenser lens 15 as shown in the above-described equation (1). It is represented by a and the focal length f of the condenser lens 15, and Equation (10) can be transformed into Equation (11).

Here, since the focal length f of the condenser lens 15, the distance L from the principal point of the condenser lens 15 to the detection surface I, and the order difference m of the diffraction orders n and n ′ are known values, As a result, it can be seen that the interference fringe pitch p is a function of the object distance a from the object T to the principal point M, that is, the position of the condenser lens 15. Therefore, by measuring the pitch p of the interference fringes generated on the detection surface I, the objective distance a to the object T can be obtained by the following equation (12).

  FIG. 7 is an image example showing interference fringes generated on the detection surface. The interference fringes are formed by repeating bright lines with high luminance and dark lines with low luminance in the form of stripes. Accordingly, the interval between adjacent bright lines (or dark lines) corresponds to the interference fringe pitch p.

  FIG. 8 is an analysis example of the detection result obtained by the light detection element. Here, the horizontal axis indicates the pixel position [pic] of the image along the X direction perpendicular to the interference fringes, and the vertical axis indicates the light intensity (no unit) at each pixel position. The obtained detection result has a substantially sine wave shape, and its peak position corresponds to a bright line. Therefore, the actual distance indicating the interference fringe pitch p can be calculated from the number of pixels existing between the peak positions.

[Effect of the first embodiment]
As described above, in the present embodiment, after the reflected light from the object T is diffracted by the diffraction grating 14, the diffracted light is condensed on the imaging plane Q by the condenser lens 15, and is reflected on the imaging plane Q. Of the diffracted lights, only two different orders of diffracted light set in advance are allowed to pass through the arranged spatial filter 16, and the other two orders of diffracted light are blocked, and the different two orders passed through the spatial filter 16. The interference fringes generated on the detection surface I due to the superposition of the two orders of diffracted light are detected by the light detection element 17, the obtained detection results are arithmetically processed to extract the pitch of the interference fringes, and the distance calculation unit 18 The objective distance a from the condenser lens 15 to the object T is calculated based on the pitch.

Accordingly, two orders of diffracted light different from the reflected light from the object T are selected by extremely simple optical elements such as the diffraction grating 14 and the spatial filter 16, and the interference fringe pitch p changes according to the objective distance a. Interference fringes are generated on the detection surface I.
Therefore, it is not necessary to use a conventional multifocal lens or spherical lens that requires precise polishing, and an expensive optical lens and its precise assembly can be omitted. Therefore, it is possible to realize a distance measuring device that can accurately measure the objective distance a to the object T at a relatively low cost.

  At this time, since the spatial filter 16 is used to select two different orders of diffracted light, the interference fringe has a sinusoidal shape even if the transmittance distribution of the diffraction grating 14 is rectangular. It becomes easy and manufacture of the diffraction grating 14 also becomes easy. Further, since the interference fringe localization, that is, the phenomenon in which the interference fringe appears only in the vicinity of a specific periodic distance does not occur, the measurement span of the objective distance a can be widened. Furthermore, since the interference fringe pitch p is constant on the detection surface I, it is not necessary to correct the detection result of the light detection element 17, so that the arithmetic processing can be simplified and the measurement error of the interference fringe pitch p can be reduced.

[Second Embodiment]
Next, with reference to FIG. 9, the distance measuring device 10 concerning the 2nd Embodiment of this invention is demonstrated. FIG. 9 is an explanatory diagram illustrating the configuration of the distance measuring apparatus according to the second embodiment.
In the present embodiment, the objective lens 20 is provided in the condensing optical system in the first embodiment described above, and the reflected light from the object T is parallel in the section between the objective lens 20 and the condensing lens 15. The case of converting to light will be described.

In the present embodiment, the objective lens 20 has a function of converting reflected light from the object T into parallel light and outputting it to the condenser lens 15.
In the example of FIG. 9, the beam splitter 13 and the diffraction grating 14 are disposed between the objective lens 20 and the condenser lens 15. Thereby, the light emitted from the light source 11 is converted into parallel light by the light source lens 12, reflected by the beam splitter 13, and then condensed by the objective lens 20 and applied to the object T.

  Reflected light from the object T is converted into parallel light by the objective lens 20, then passes through the beam splitter 13 and is diffracted by the diffraction grating 14. As in the first embodiment, the diffracted light from the diffraction grating 14 is collected on the imaging plane Q by the condenser lens 15 and then set in advance by the spatial filter 16 on the imaging plane Q. Only two different orders of diffracted light are selected and applied to the detection surface I.

  As a result, as in the first embodiment, an interference fringe whose pitch changes according to the objective distance from the objective lens 20 to the object T is generated on the detection surface I. Therefore, the objective distance can be calculated from this pitch. it can.

FIG. 10 is a graph showing the relationship between the objective distance and the interference fringe pitch. Based on this Embodiment, the relationship between the objective distance a and the interference fringe pitch p was calculated | required by simulation. At this time, the focal length of the objective lens 20 is f ′ = 30 mm, the focal length of the condenser lens 15 is f = 9 mm, the distance from the condenser lens 15 to the light detection element 17 is L = 60 mm, and the diffraction grating 14 Was set to d = 0.02 mm.
From the graph of FIG. 10, it can be seen that the interference fringe pitch p monotonously increases as the object distance a increases.

[Effect of the second embodiment]
Thus, in the present embodiment, the objective lens 20 is provided in the condensing optical system, and the reflected light from the object T is converted into parallel light in the section between the objective lens 20 and the condensing lens 15. Therefore, even if the objective distance a to the object T changes, the optical path is changed in the section from the objective lens 20 to the detection surface I by replacing the objective lens 20 with a focal length corresponding to the objective distance a. It becomes constant.
For this reason, it is possible to deal with a wide range of objective distances a, and the measurement range can be greatly expanded.

[Extended embodiment]
The present invention has been described above with reference to the embodiments, but the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, each embodiment can be implemented in any combination within a consistent range.

  DESCRIPTION OF SYMBOLS 10 ... Distance measuring device, 11 ... Light source, 12 ... Light source lens, 13 ... Beam splitter, 14 ... Diffraction grating, 15 ... Condensing lens, 16 ... Spatial filter, 17 ... Photodetection element, 18 ... Distance calculation part, 20 ... objective lens, T ... object, Q ... imaging surface, I ... detection surface, a ... objective distance, p ... interference fringe pitch.

Claims (5)

A distance measuring device that irradiates and reflects light on an object, and measures an objective distance to the object based on the reflected light,
A diffraction grating that diffracts the reflected light from the object;
A condensing lens that condenses the diffracted light from the diffraction grating on the imaging surface;
A spatial filter that is disposed on the imaging plane and that allows only two different orders of diffracted light to pass through the diffracted light and blocks other orders of diffracted light;
A light detection element for detecting interference fringes generated on the detection surface by two different orders of diffracted light that have passed through the spatial filter;
A distance calculation unit that calculates a detection result obtained by the light detection element, extracts a pitch of the interference fringes, and calculates an objective distance from the condenser lens to the object based on the pitch; A distance measuring device characterized by. The distance measuring device according to claim 1,
The focal length of the condenser lens is f, the distance from the condenser lens to the detection surface is L, the diffraction grating interval of the diffraction grating is d, and the order difference of the diffracted light passing through the spatial filter is m and the pitch of the interference fringes is p, the objective distance a from the condenser lens to the object is expressed by the following equation:
A distance measuring device characterized in that it is obtained by: A distance measuring device that irradiates and reflects light on an object, and measures an objective distance to the object based on the reflected light,
A condensing lens for condensing the reflected light from the object on an imaging plane;
A diffraction grating that diffracts the reflected light collected by the condenser lens;
A spatial filter that is disposed on the imaging plane and allows only two different orders of diffracted light to pass through the diffracted light from the diffraction grating and blocks other orders of diffracted light;
A light detection element for detecting interference fringes generated on the detection surface by two different orders of diffracted light that have passed through the spatial filter;
A distance calculation unit for calculating the objective distance from the condenser lens to the object based on the pitch by extracting the pitch of the interference fringes by calculating the detection result obtained by the light detection element;
A distance measuring device comprising: In the distance measuring device according to any one of claims 1 to 3,
An objective lens that collimates the reflected light from the object;
The diffraction grating diffracts the parallel light from the objective lens. A distance measurement method for irradiating and reflecting light on an object, and measuring an objective distance to the object based on the reflected light,
A diffraction step of diffracting the reflected light from the object by a diffraction grating ;
A condensing step of condensing the diffracted light from the diffraction grating onto the imaging surface by a condensing lens ;
Of the diffracted light collected on the imaging surface, a diffracted light selection step for passing only two different orders of diffracted light set in advance and blocking other orders of diffracted light;
A light detection step of detecting interference fringes generated on the detection surface by the selected two different orders of diffracted light;
A distance calculation step of calculating a detection distance obtained by the light detection step to extract a pitch of the interference fringes and calculating an objective distance from the condenser lens to the object based on the pitch. A distance measuring method characterized by