JPH0615972B2 - Distance measuring method and device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a distance measuring method and a device for measuring a distance to an object point in a non-contact manner.

[Conventional technology]

In order to measure the distance to an object point using an optical system in a non-contact manner, a triangulation method as shown in FIG. 15 has been conventionally used.

To briefly explain this, the first lens 1 and the second lens 2
Are arranged at a distance of the baseline length B, the laser light emitted from the laser diode 3 is applied to the object point P on the object to be distance-measured by the first lens 1, and the reflected light from the object point P is emitted to the second point.
The lens 2 forms an image on an image sensor 4 such as a CCD to detect the distance x of the image point P ′ from the optical axis O ₂ .

Here, when the focal length of the second lens 2 is f, the distance S from the first lens 1 to the object point P is calculated by the following equation.

Now, assuming that the detection accuracy of the sensor 4 (which indicates the pitch of the light receiving element of the image sensor 4) is ε, the distance measurement accuracy | Δ
S | Then, assuming that the detection accuracy ε of the image sensor 4 is constant. The accuracy of the distance measurement is improved in proportion to the baseline length B between the first and second lenses 1 and 2 and the focal length f of the second lens 2,
It becomes worse in proportion to the square of the distance S to the object point.

[Problems to be solved by the invention]

However, in such a conventional distance measuring method, in order to improve the distance accuracy, the focal length f of the second lens 2 and the baseline length B between the first and second lenses 1 and 2 must be increased. Since the distance measuring device becomes large and the distance S to the object point P becomes long, the distance measuring accuracy deteriorates rapidly in proportion to the square of the distance S.

An object of the present invention is to provide a distance measuring method and an apparatus therefor capable of solving such a conventional problem.

[Means for solving problems]

Therefore, the distance measuring method and apparatus according to the present invention are, in the first invention, the first optical system having the first optical axis and the second optical system which is parallel to the first optical system with a predetermined distance from the first optical system.
A second telecentric optical system having an optical axis of
The rear focal plane of the first optical system is arranged so as to coincide with the front focal plane of the second optical system, and the object point to be measured is located on the first optical axis. , The distance from the second optical axis of the image point by the second optical system is detected, the distance from the second optical axis, the focal lengths of the first and second optical systems, and the first and second optical systems.
The distance from the optical axis to the object point is calculated.

A second invention is an apparatus for carrying out the first invention, which comprises a first optical system having a first optical axis and the first optical system.
Has a second optical axis parallel to the optical axis of
A second optical system whose front focal plane coincides with the rear focal plane of the first optical system, and a second optical system which is provided around the front focal point of the second optical system. Aperture, irradiation means for irradiating an object point along the first optical axis, a photoelectric conversion sensor provided in the vicinity of the rear focal point of the second optical system, and an output from this photoelectric conversion sensor. An arithmetic means for arithmetically processing the signal is provided.

Here, the focal plane means a plane including a focal point and orthogonal to the optical axis.

[Work]

The distance measuring device configured as described above is faced to the object point to be measured so that the object point is located on the first optical axis.

In this state, the distance from the second optical axis of the image point on the photoelectric conversion sensor by the first and second optical systems of the object point is detected by the output signal from this sensor, and this value and the first and second By inputting each focal length of the optical system and the distance between the first and second optical axes into a predetermined calculation formula and processing by the calculation means, the distance to the object point can be known.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 14 of the accompanying drawings. However, in order to simplify the description, the following optical system has an extremely small thickness as compared with the radius of curvature. It is assumed that the lens system is such that both the front principal point and the rear principal point thereof coincide with the center of the lens, that is, the optical center, and the front focal length is equal to the rear focal length.

FIG. 1 shows an optical system of a distance measuring device according to the present invention.

1 denotes a first lens constituting the first optical system having a first optical axis O _1, 2 will have a first optical axis O ₂ of parallel spaced a predetermined distance from the first optical axis O ₁ And is a second lens that constitutes a second optical system.

Then, the rear focal plane of the first lens 1 and the front focal plane of the second lens are arranged so as to coincide with each other, and the diaphragm 5 having a small aperture diameter is provided around the front focal point F ₂ of the second lens 2. The lens 2 is a telecentric optical system.

A CCD (Charge Coupled Device) or a PSD (Position Sensitive Device) is provided in the vicinity of the rear focal point F ₂ ′ of the second lens 2 perpendicular to the first and second optical axes O ₁ and O _2. The image sensor 4 which is a photoelectric conversion sensor such as the above is provided.

Here, the focal length of the first lens 1 is f ₁ , and its radius is h
₁ , the focal length of the second lens 2 is f ₂ , its radius is h ₂ ,
The distance between the _first and second optical axes O ₁ and O ₂ is R, the length of the image sensor 4 from the second optical axis O ₂ is the lower side h ₄ ′ in the figure,
Upper side h ₄ ″, total length h ₄ , resolution ε, aperture 5 diameter 2
r and the principal points of the first and second lenses are H ₁ and H ₂ .

Now, the reflected light of the object point P irradiated with the laser light at the distance S (distance s from the front focus F ₁ ) from the first lens ₁ on the _first optical axis O ₁ is the first and second lenses 1. , 2 to reach the point P ′ on the image sensor 4 will be considered.

At this time, since the second lens 2 is a telecentric lens,
As shown in FIG. 2, a light flux Ψ passing from the object point P through the first lens 1 and the diaphragm 5 advances symmetrically with respect to its principal ray Pr by the second lens 2, and its image plane is the principal ray Pr. The image sensor 4 is symmetrical with respect to the intersection P '.

Therefore, when a CCD is used as the image sensor 4, the output I of each pixel reaches its maximum at the center distance Δ as shown in FIG. ₀ can be obtained by Δ ₀ = Δ ₁ + (Δ ₁ + Δ ₂ ) / 2.

Note that when PSD is used, an output corresponding to the center Δ _{0 of the} light amount distribution is obtained, so the value of Δ ₀ can be used as it is.

FIG. 4 shows that in the optical system shown in FIG. 1, the ray ρ emitted from the object point P is refracted by the first lens 1 and the second lens 2
It passes through the rear focal point F ₂ , further refracted by the second lens 2, travels in parallel to the _second optical axis O ₂ , reaches the point P ′ on the image sensor 4, and from the object point P to the first lens. Point C of 1
Ray ρ that reaches the first focal point F ₁ of the first lens 1
Ray ρ ₀ refracted by the lens and traveling on the second optical axis O _2.
Shows the case of being parallel to. ΔPCH ₁ and ΔF ₁
From the similarity of DH ₁ Also, from the similar relationship between ΔF ₂ CD and ΔF ₂ EH ₂ , From both formulas (a) and (b) Since S = f ₁ + S here, However, Δ is positive when facing upward in the figure.

When the detection accuracy (resolution) of the image sensor 4 is ε, its measurement accuracy | δS | FIG. 5 is an enlarged view of a part of the optical system shown in FIG. 1, in which an image P of an object point P (see FIG. 1) by the first lens 1 is shown.
'When, ss from the official Newtonian' distance from the 'side focal point _{F 1} after' ^₁ s _{= f 1} ² 'and [Delta] P _1' (a) The [Delta] P _{1 'F} 1' A and _H 1 'C' From the similarity of However, C'is the incident height at which the light ray from the object point P passing through the upper limit A'of the diaphragm 5 enters the first lens 1.

When s is obtained from the equations (a) and (b), This distance s shows the maximum value for the second lens 2 to be telecentric, and the work area S that can be measured by the optical system shown in FIG. Becomes

In order to increase the work area from the equation (c), the distance R between the first optical axis O ₁ and the second optical axis O ₂ and the radius r of the diaphragm 5 are set.
And the focal length f ₁ of the first lens ₁ and its radius h
It turns out that ₁ should be increased.

Here, if the distance s'is obtained from the equation (b), Next, in FIG. 6 showing the latter half of the optical system shown in FIG. ₁ , let s ″ be the distance from the rear focal point F ₂ ′ of the image P ₁ ′ to the image P ₂ ′ by the second lens 2. , S ′s ″ = f ₂ ² (e) Substituting equation (d) into this, Further, the magnification β of the image point P ₂ ′ by the second lens 2 with respect to the point P ₁ ′ is Therefore, the distance R ′ from the image point P ₂ ′ to the second optical axis O ₂ is By the way, from the similar relationship between ΔF ₂ H ₂ E and ΔP ₁ ′ JF ₂ , That is, Therefore, the value of R ′ in the expression (g) is such that the chief ray is the second lens 2
Equal become incident height incident on, P 2 _'E second optical axis O
Parallel to ₂ .

Now, next, the incident heights h ₂ ′ of the light rays that have passed through the upper limit A ′ of the diaphragm 5 to the second lens 2 and the incident heights h ₄ ′ and h ₄ ″ of the image sensor 4 are obtained.

From the similar relationship between ΔP ₁ ′ F ₂ A ′ and ΔP ₁ ′ EC From the similar relationship between ΔP ₂ ′ E and ΔP′KM Substituting equation (h) into this From equations (k), (l) and (e) Substituting equations (m) and (n) into equations (k) and (l),
Using equation (b) Further, the image point P 'maximum diameter of the diameter of the image point in the work area maximum position, i.e. 2 (h _4' is -Q). In this formula
Using the expressions (d), (h) and (p), Further, considering that the object point P is inside the front focus F ₁ of the first lens 1, in this case, the telecentric condition of the second lens can be satisfied at all positions as shown in FIG. It is possible, and its extreme position is as shown in FIG.
This is a state in which the object point P coincides with the principal point H ₁ of the first lens 1.

In FIG. 8, the light beam emitted from the object point P passes through the upper limit A ′ of the diaphragm 5 and enters the second lens 2 at a point G ′ at an incident height h ₂ ′ and then is refracted to be a point on the image sensor 4. P ′ is reached, and the distance from the second optical axis O ₂ to the point P ′ is h
₄ ″, from the similarity relationship between ΔPG′K and ΔF ₂ K′H _2. Therefore, the total length h ₄ of the image sensor ₄ is expressed by the formula (l) and
From equation (r), Radius _{h 2} of the second lens 2, _{h 2} 'and _{"larger, h 2 = max {h 2} h 2', h 2" is a} (6).

Further, in FIG. 8, since ss '= f ₂ ² and s = f ₂ , s' = f ₂ (t).

To summarize the above results, the distance S of the object point P from the principal point H ₁ of the first lens 1 is However, Δ is positive when it is above the second optical axis O _{2 in} FIG.

When the resolution of the image sensor 4 is ε, the distance measurement accuracy | δS | Therefore, the distance measurement accuracy is constant regardless of the distance S to the object point.

The distance measuring range S of the object point S is The maximum diameter δφ of the image point P ′ is Higher accuracy can be obtained if the value of δφ is smaller.

The total length h ₄ of the image sensor 4 is Radius _{h 2} of the second lens _{2, h 2 = max {h 2} ', h 2 "} (6) where, Here, the effective length and the number of divisions of the image sensor 4 will be further considered.

In FIG. 8, the length l ₄ from the _second optical axis O ₂ of the image sensor 4 by the chief ray when the object point P is at the closest distance.
Is the similarity between ΔF ₂ H ₂ K ″ and ΔF ₂ MH _1. Further, the length Q from the optical axis O _{2 in} FIG. 2 when the object point P is at the farthest distance from FIG. 6 is given by the equations (d) and (f). Therefore, the effective length l of the image sensor 4 is Since the resolution of the image sensor 4 is ε, the number of divisions N
Is Becomes

If the above equation (3) is divided by this number of divisions N, Then, we can obtain equation (2).

Now, assume that an optical system is designed to have an image diameter of 1 mm using an image sensor 4 having a resolution of 0.3 μm and a total length of 12 mm, and if the margins at both ends of the image sensor 4 are 0.2 mm, The effective length l of the sensor 4 is l = 12−0.7 × 2 = 10.6. Therefore, the number of divisions N is N = 10.6 / 0.0003 = 35333. The measurable range S for various measurement accuracy δS The result is shown in Table 1.

Next, a specific example of the distance measuring device to which the present invention is applied will be described with reference to FIG.

What is shown in FIG. 10 includes a first lens 1 having a _first optical axis O ₁ and a second lens 2 having a _second optical axis O ₂ parallel to the _first optical axis O _1. The optical axes O ₁ and O _{2 of} are separated by a distance R, and the front focal plane of the second lens 2 is aligned with the rear focal plane of the first lens 1.

Further, a diaphragm 5 having a sufficiently small aperture diameter is provided around the front focal point of the second lens 2 to make the second lens 2 a telecentric optical system, and the first lens 1 is provided near the rear focal point of the second lens 2. The CCD or P is orthogonal to the second optical axes O ₁ and O _2.
An image sensor 4 such as SD is provided.

Further, the condenser lens 6 for irradiating the light beam of the laser diode 3 onto the object to be measured and the reflecting mirrors 7 and 8 are provided, and the laser light reflected by the reflecting mirror 8 passes through the center of the first lens 1 and the first light beam O _The object point irradiating means is configured to be capable of irradiating the object point located above ₁ .

FIG. 11 shows that the laser light reflected by the reflecting mirror 9 can illuminate an object point on the first optical axis by the half mirror 10 in front of the first lens and from the object point. It has the same configuration as that of FIG. 10 except that the reflected light of (1) can enter the first lens through the half mirror 10.

In both of the above embodiments, the output signal from the image sensor 4 is displayed on the display unit after being processed according to the above-described formulas in the calculating unit which is a calculating unit for performing a predetermined calculation. Although it is possible to know the distance to and other necessary numerical values, since these methods are publicly known, description thereof will be omitted.

By accommodating such an optical system, a calculation unit, and a display unit in the housing 11, a non-contact micrometer as shown in FIG. 12 can be configured, and the thickness of an object can be measured in contact. .

As an application example of the distance measuring method according to the present invention, a device as shown in FIG. 13 that always keeps the object point P at a constant distance is conceivable. This device uses an image sensor 4 consisting of two-divided cells and forms an image point P'of an object point on the first and second cells 4a and 4b as shown in FIG. The sum V ₁ + V _{2 of the} outputs V ₁ and V ₂ and the difference | V ₁ −V ₂ | are obtained respectively.

This sum V ₁ + V ₂ is compared with a predetermined output value Vr by a comparator, and is subjected to logic control together with the difference | V ₁ −V ₂ |, and when V ₁ + V ₂ <Vr, it is indefinite, that is, uncontrollable V ₁ + V ₂ When Vr is | V ₁ −V ₂ | ≦ ε, it may be left as it is, and when | V ₁ −V ₂ |> ε, when V ₁ + V ₂ , the object point P is moved in the + direction, and V ₁ <V _{When 2} , the object point P is moved in the-direction.

However, ε is a quantity determined by the positioning accuracy.

〔The invention's effect〕

As described above, the distance measuring method and apparatus according to the present invention includes the first optical system having the first optical axis and the telecentric lens having the second optical axis parallel to the first optical axis at a predetermined distance. The second optical system is arranged such that the rear focal plane of the first optical system coincides with the entire focal planes of the second optical system, and the first and second object points to be distance-measured. The distance of the image point from the second optical axis by the optical system is detected, and this distance and the focal lengths of the first and second optical systems and the distance between the first and second optical axes to the object point are detected. Since the distance is calculated, the accuracy of the measurement is constant regardless of the distance to the object point, and the distance measurement system does not deteriorate due to the attack if the distance becomes long as in the conventional triangulation method.

Therefore, it is possible to measure a wide range of distance from micron order to metric order depending on the setting of the optical system to be used, and there is no fear that the device becomes extremely large unlike the conventional case even if the accuracy is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical system of an embodiment of the present invention, FIG. 2 is an optical path diagram showing the action of a diaphragm which makes the second optical system a telecentric, and FIG. 3 is a CCD used as an image sensor. 4 is an optical path diagram showing a representative optical path of the optical system shown in FIG. 1, and FIG. 5 is an optical path diagram showing an enlarged part of the optical system shown in FIG. 6 is an optical path diagram of the latter half of the optical system shown in FIG. 1, FIG. 7 is an optical path diagram when the object point is inside the front focus of the first lens, and FIG. FIG. 9 is a front view showing an example of an image sensor, and FIG. 10 is an explanatory view showing an arrangement example of a concrete optical system of the present invention. Similarly, an explanatory view showing another arrangement example, FIG. 12 is a perspective view showing a non-contact micrometer to which the present invention is applied, 13 is an explanatory view showing an optical system of an application example of the present invention, FIG. 14 is a block diagram showing an example of the detection circuit of the same, and FIG. 15 is an explanatory view showing an optical system of a conventional distance measuring device and its optical path. Is. 1 ... First lens (first optical system) 2 ... Second lens (second optical system) 3 ... Laser diode 4 ... Image sensor (photoelectric conversion sensor) 5 ... Aperture, 6 ... light lens 7,8,9 ...... reflector 10 ...... half mirror f ₁ ...... front focal point F ₁ of the end point distance F ₁ ...... first lens having a focal length f ₂ ...... second lens of the first lens' ...... Rear focus of the first lens F ₂ ...... Front focus of the second lens F ₂ ′ ... Rear focus of the second lens O ₁ …… First optical axis, O ₂ …… Second optical axis R: Distance between first and second optical axes P: Object point, P '... Image point on image sensor Δ: Distance between image point P'and second optical axis

Claims (2)

[Claims] 1. A first optical system having a first optical axis, and a telecentric second optical system having a second optical axis parallel with a predetermined distance from the first optical axis. The rear focal plane of the first optical system is arranged so as to coincide with the front focal plane of the second optical system, and the object point for distance measurement is located on the first optical axis. The distance from the second optical axis of the image point by the first and second optical systems is detected, and the distance from the second optical axis and the focal lengths of the first and second optical systems are detected. And a distance measuring method which calculates a distance to an object point from the distance between the first and second optical axes. 2. A rear side of the first optical system having a first optical system having a first optical axis and a second optical axis parallel with a predetermined distance from the first optical system. A second optical system whose front focal plane coincides with the focal plane position; and an aperture provided around the front focal point of the second optical system for making the second optical system a telecentric, Irradiation means for irradiating an object point along the optical axis of, a photoelectric conversion sensor provided in the vicinity of the rear focal point of the second optical system, and calculation means for calculating the output signal from the photoelectric conversion sensor. A distance measuring device comprising: