JPH01203918A - Optical distance measurement between measuring apparatus and object - Google Patents

Abstract

PURPOSE: To obtain an accurate distance measuring apparatus by a constitution wherein the radiation diffused from an irradiated light spot is focused through a focus means and two photodetectors are arranged in the converged beam thereof. CONSTITUTION: A light spot 12 is projected onto an object 11 from a laser light source 62 through a hollow mirror 61 and a diffused radiation is produced as shown by a beam flux 33. A part of the beam flux 33 enters into a distance measuring apparatus 20 and focused 33' one-dimensionally through a mirror 61. The light source 62 is set in the optical axis 16 along with two photodetectors 28, 28' through arrangement of a split mirror 26 wherein the detector 28' is set in the focal line 63 of mirror 61. The detectors 28, 28' are dimensioned to detect all unfocused beams incident on the apparatus 20 one- dimensionally. Consequently, a desired distance can be calculated according to an expression specified by the functional link between each signal and the distance from the light spot 12 on the object 11.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the fields of geometric optics, electronics, and signal processing. This relates to a method and a device for measuring the distance between a point of illumination on an object reflecting light and a measuring device. The invention is based on the measurement of the intensity distribution of a focused diffusely reflected light beam at two different positions from the illuminated object, with a photodetector placed in the focal line of the optical system.

The photodetectors are arranged within a common optical axis but at different spacings. This is possible by splitting the diffusely scattered beam into two partial beams using a beam splitter.

Optical methods for distance measurement are well known. That is,
Distance measurements are made electrically by measuring the transit time of the light pulse reflected on the target. Device operation based on this principle is primarily used in land surveying. For short-range measurements in the cm and dm ranges, short transition times in the ns range require fast electro-optical and electrical switching elements, so the method is not suitable for labor-intensive measurements in the dm range. The triangulation method is more appropriate. This is based, first of all, on the creation of a light spot on the target by a sharp beam of light emanating from the measuring device. This light spot is imaged onto at least one photodetector arranged at an oblique angle to the primary beam.

From the angle between the primary beam and the optical spot-image spot connecting beam, the distance between the measuring device and the object is determined by triangulation.

To ensure accurate angle measurements in triangulation methods,
The light spot on the object surface must be clearly imaged by a lens onto a photodetector or diode array. In the case of fixed lenses, high measurement accuracy can be achieved over short distances simply by setting them, unless constant readjustment of the optical system is carried out in the iterative process, which requires considerable special effort and expense. It is possible to obtain.

A further optical distance measurement principle is based on the measurement of diffuse light scattered from a prespot created on an object by a precisely focused beam of light.

Assuming that this light spot emits pure diffusely scattered light, the radiation perpendicular to the object surface is approximately uniform (Lambertian radiation). Two photodetectors are placed at different distances within this beam, which is selectively focused using a collimating lens. Therefore, the divergence or convergence angle of the beam is determined from the measured illuminance. The desired distance of the object is therefore obtained based on the "inverse square law", ie the fact that the radiation intensity of a point light source is inversely proportional to the square of the distance.

As is clear from the patent specifications referred to below, methods of the above type are well known.

The method by which a light spot is created on an object by an optical system and then imaged was described by J. L.
Po i 11 eux) and J.
J, Tourret) in US Pat. No. 3,719,421. Two diaphragms arranged with a detector behind or in front of the image point enable distance measurements within a limited area by subtraction of the detector signal.

This method is suitable for accurately determining the distance 71P1 within a narrow area, but is not suitable for determining the distance 711I in general. Outside the aforementioned area, it is ambiguous to even consider the detector signal in relation to the distance between the object and the measuring device. Reference will be made below regarding the detailed construction of this device in connection with FIG.

A necessary criterion for the reliability of this method is the presence of diffuse backscattering, but if reflections occur in addition to diffuse scattering, measurement errors will occur. This US patent describes a method to increase the corresponding measurement accuracy.

A further method of distance measurement based on the "inverse square law" is described in East German Patent No. 65 320 by E. H. Mehnert. In this patent, distance from a point light source is determined by measuring the illumination of two surfaces placed at different distances from the light source.

There are three different devices for implementing this method. The first device is based on the measurement of a large-area illuminated surface using two photodetectors placed at different distances from the object after a long-range optical system. This long-range optical system allows clear imaging of only a small area of the object on the detector surface, and when the object is displaced, only the object spot is vaguely imaged on the detector, making the object extremely small. The illuminance of the image does not change unless it is a small light spot.

Therefore, the device according to claims 2 and 3 of the above-mentioned patent is not functional.

In the second device, an infrared diode as a light source;
A small light spot is therefore utilized on the object.

The radiation of this light source is measured by at least one receiver. Keeping the radiant intensity of the transmitter constant, the distance of the device from the infrared diode can be measured directly from the "inverse square law", and the distance within the optical axis, but also If there are two receivers arranged with different distances from the distance, the distance measurement is independent of the radiation intensity of the light source.

The relationship between the illuminance measured by the photodetector and the distance is rectangular and not linear. Using modern digital signal processing equipment, solving the "inverse square law" is not difficult. However, unlike the case where there is a linear action between the measured quantity and the distance, the measurement error is not constant, but is linearly dependent, as a first derivative, on the deviation from the desired value.

Furthermore, said second embodiment of the device has the disadvantage that the infrared diode must be placed precisely in the optical axis of the receiver. Otherwise, the photodetector signal can no longer be unambiguously related to the distance of the object.

Considering this latter fact, in the third embodiment,
The light source, in particular the laser, is arranged directly in the optical axis of the measuring device, the detailed description of the construction of which will be given below on the basis of FIG. However, it is pointed out here that even in this third embodiment, the link between the detector signal and the object distance is nonlinear, which has a considerable effect on the evaluation ability and measurement accuracy. .

A third method based on the "inverse square law" was introduced in December 1987.
German Patent Application Section P 37 43 194 filed on March 19th
．． This is the subject of issue 3. Here again, distance information is obtained from the illuminance of two photodetectors at different distances from the object. Diffuse radiation emanating from the illuminated light spot is focused by an optical system. However, focusing is done by J.L.Boal (J, L,
P.

111eux) and J. Tou
rret) is not done in two dimensions using an objective lens as described in US Pat. No. 3,719,421, but only in one dimension using a cylindrical mirror. A photodetector, one of which is placed within the focal line of the cylindrical optical system, measures in one dimension all the light rays entering the device. This construction example differs from East German Patent No. 65 320 by E. H. Mehnert, where no one-dimensional focusing is performed and the position of the detector is not specified. The new method provides a linear dependence of the measured distance on the quotient of the measured detector signal. The device on which this method is based will be described in detail in connection with FIG.

The object of the invention is to provide an accurate distance measuring device or rangefinder, in which an output signal is produced that is linearly dependent on the distance being measured, as described above, based on the well-known "inverse square law". The goal is to further develop this method. Furthermore, the measurement accuracy should be optimal for the predetermined measurement area.

This task is solved by the fact that, after the incidence of a closely focused parallel beam, the light flux reflected by the object is focused in an optical device and the measurement of the beam intensity of the partial beams is carried out in the focal plane of the optical system. resolved. The photodetector is equal to or larger than the beam diameter in one dimension.

The novel method and examples of corresponding devices are explained in more detail below in connection with the drawings.

Figure 1 illustrates the "inverse square law." This is based on the fact that the total amount of light emanating from a point source 12 in the center of said sphere, which passes through the sphere, is independent of the radius 14 of the sphere in the absence of any absorption. Due to the isotropic illumination of the light source 12, this means that the illumination E of the spherical section is inversely proportional to the square of the radius of the sphere.

Thus, in the case of known isotropic illumination, the distance of said detector from the light source is determined based on the illuminance on the detector. If the diffuse scattering object is point-illuminated, isotropy is almost guaranteed within a small observation angle 17. in this way,"
The distance measuring device is constructed based on the "inverse square law".

FIG. 2 shows a well-known embodiment of a method based on the "inverse square law".

No. 3,719,421, in which the object 11 is first illuminated point-wise by an optical system comprising a semi-reflector 22 and an objective lens 23, and this light spot is imaged by said objective lens 23 onto an image point 24. It was briefly mentioned at the beginning. The radiation emanating from the light spot 12 is divided into two partial beams 25.2 by a beam splitter mirror 26.
5', which in the first embodiment are subdivided into 2
pinhole diaphragms 27, 27'. One of these diaphragms 27' is in front of the image point 24', the other diaphragm 27 is in front of the image point 24'.
placed after. The radiation flux passing through the diaphragm 27.27' is measured by two photodetectors 28.28' and a corresponding electrical signal difference 29 is formed. If the holes in the diaphragm 27, 27' are of the same size and the distances of the opposite sides of the diaphragm from the point 24, 24' are equal, the magnitude of the luminous flux is equal and the signal difference 29 therefore disappears. If the distance 15 of the object 11 from the measuring device 20 is different, the position of the corresponding image point 24,24' will also be displaced. their distance to the diaphragm 27.27';
The amount of light reaching the detector 28, 28' therefore also changes.

As a result, the difference signal 29, which was originally O, changes. Within a narrow area, that is, the image point 24
．． If the distances between 24' and the diaphragms 27, 27' are approximately equal on the opposite side, the difference signal 29 is linearly dependent on the object-to-objective distance 15. However, the image point is 24.2
4' approaches one of the diaphragms 27, 27', the difference 29 approaches a maximum value and then decreases again.

Thus, although the method described in U.S. Pat. , not suitable for distance measurement in general. In fact, outside the narrow range mentioned above, it is ambiguous to even consider the difference signal in relation to the object-measuring device distance.

The radiation intensity of the scattered light spot 12 on the object surface 11 largely depends on its properties. Therefore, the signal difference 29 also depends on the object. In this way, the limited distance area 15
Within, quantity 29 provides information about the direction of the actual position, which differs from the desired value, but does not provide information about the effective magnitude of the horizontal displacement. Therefore, by this method it is not possible to create a measuring device that provides a valid output signal from which the actual distance to the object can be determined.

The distance measurement method described above is based on measuring the intensity of the light backscattered by the object 11. A necessary criterion for the reliability of this method is the presence of backscatter that is as diffuse as possible. Therefore, when reflection occurs in addition to diffuse scattering, the signal difference 29 is
It depends largely on the inclination of the measuring device 20 with respect to the optical axis 16. By replacing one of the two diaphragms 27' with a mirror with a central shield 27'' (another further embodiment of the invention), the measurement error due to non-diffuse backscattering is reduced to the simultaneous It can be reduced during tilting.

Figure 3 shows another example in which distance measurement is based on the inverse square law.
Two well-known methods are shown. This method is described in East German Patent No. 65 320 by E. H. Mehnert, two embodiments of which have already been described.

According to a third embodiment, a light source 21 in the form of a laser beam transmitter is arranged in the optical axis of the measuring device 20, which is also possible by using beam splitting mirrors 26, 26', 26'. . The laser light source 21 emits a dense beam 31, so that a point-like light spot 12 is formed on the object, which defines the optical axis 16 of the measuring device. Two receivers 28, 28' are also placed in this front shaft 16, but
They are arranged at different distances 32 within the light beam 33 emanating from the light spot. This is possible by inserting two beam splitting mirrors 26,26'. The laser power is controlled by decoupling 26' of the third partial beam and adding a photodetector 28'.

The relationship between the measured illuminance of the photodetector 28, 28' and the distance 15 is not linear, but quadratically dependent on the detector signal due to the "inverse square law". Digital signal processing means 34
ensures that the solution of the corresponding system of equations is easily obtained. However, unlike the case where there is a linear action between the δ-1 fixed quantity and the distance 15, the measurement error is not constant, but is linearly dependent on the deviation from the desired value, which is This is a serious drawback in the device.

FIG. 4 shows the principle of a newer distance measuring method, as also described in German Patent Application No. P 37 43 194.3, filed on December 19, 1987.

This distance measurement method is based on the "inverse square law." Its basic principle is to measure the light intensity of a diffused light scattering light spot 12 on the surface of an object 11. light spot 12
is formed by placing a laser light source 21 in the optical axis 16 (not shown in FIG. 4).

Diffuse radiation 33 from the illuminated light spot 12 is focused 33' by a focusing means, for example an objective lens 23. There are two photodetectors 28 in the focused beam.
．． 28' is placed. - one photodetector 28 is placed in the expanded beam, and the other photodetector 28' is placed at the focal point 41 of the optical system, ie at the point on which the parallel beam 42 will be focused. . It is assumed that the light intensity distribution in the parallel beam 33' is uniform. Based on this assumption, the convergence angle 44 of the beam 33' can be determined from the measured light intensity and, based on the lens equation, the determined object distance 45 can also be obtained.

Thus, the most important requirement for the operation of this method is that as little organization as possible on the object 11 be achieved.
The presence of constant diffuse light scattering.

In ideal Lambertian backscattering, uniformity of the radiation over a wide angle region is guaranteed, as shown in FIG. For example, a beam from a laser light source 21 is incident at an angle 51 and observed at a variable angle 52 . According to Lambert's law, the radiation measured at the observation angle 52 is
It is divided by the cosine of this angle 52 and provided as a constant value.

FIG. 6 shows an embodiment of the method according to FIG.

The essential difference is that a mirror is inserted to position the laser source and detector on-axis.

A light spot 12 created by a light source, in particular a laser light source 21, on the object 11 after passing through the hollow mirror 61 emits diffuse radiation. A portion of this, represented by the beam bundle 33, enters the distance measuring device 20 and is focused 33' by a hollow mirror 61.81. However, focusing is not performed two-dimensionally using the objective lens 23, but only one-dimensionally using the cylindrical parabolic mirror 61, for example. The laser light source 21 is 2
Together with the two photodetectors 28, 28', they are placed in the same optical axis 16, which is made possible by arranging the light splitting mirror 26. One of the detectors 28' is placed in the focal line 63 of a cylindrical parabolic mirror, which focal line is defined as the locus 63 of all points on which the parallel beam 42 entering the device is imaged. There is. The detectors 28, 28' are dimensioned so that they can detect in one dimension all the unfocused beams entering the device.

FIG. 7 shows a side view and a plan view of the cylindrical parabolic mirror 6.
1 and the corresponding optical distance 33 before reflection of mirror 61
and the optical distance 33' after reflection, and a reflection angle other than 90° has been chosen for ease of illustration.

According to this method, the measured distance will be linearly dependent on the quotient of the detector signal determined by 7Il11. Detector 2
signal E28' or E28 on 8' or 28;
The functional link between the distance from the light spot 12 on the object 11 is given by the relationship below.

Distance - (E2 a'/E2 a) *C, -c2
In the above, the two constants C, , C2 are device specific and depend mostly on the distance between the light spot 12 and the detector 28, 28', measured in the optical axis.

If the signal of the photodetector 28 is held at a predetermined fixed value, which is possible by adjusting the laser light source 21, the formula for this distance is further simplified, and it is no longer necessary to divide the signal. It disappears.

Another embodiment of the method according to the invention is shown in FIG.

The above-mentioned cylindrical parabolic mirror 61 is a bifocal parabolic mirror 81
will be replaced by

As shown in FIG. 7, a cylindrical parabolic mirror 61 would require a very wide detector 28,28'. In order to limit the width 33' of the reflected beam and thus also to reduce the width 71.71' of the photodetector 28.28', bifocal focusing means in the form of a bifocal parabolic mirror 81 are used. This proved advantageous.

The focal length relative to the plane of symmetry was adjusted to the geometrical situation.

On the other hand, in the direction perpendicular to the plane of symmetry, a focal length half the former was selected. As a result, the beam perpendicular to the plane of symmetry is focused at approximately half the distance between the mirror 81 and the focal line 63 of the hollow mirror 81 (perpendicular to the object plane), as shown in FIG. will be combined. In this way, the width 71. of the photodetector 28.28'.
A more desirable dimension of 71' is obtained.

FIG. 8 shows the configuration of a distance measuring device having a bifocal parabolic mirror 81. In the prototype embodiment, 9
A reflection angle of 0'' was chosen. The focal lengths of the bifocal parabolic mirror are 5 cm and 2.5 cm.

As long as the light spot 12 on the target 10 is an isotropic radiation source and therefore the irradiated light power is equal for each solid angle element, there is no problem with the distance measurement method described above based on the "inverse square law".

This is generally the case for self-illuminating light sources.

This condition is also largely fulfilled in the case of indirect illumination, if the object causes ideal diffuse scattering of the incident light beam and the standard surface in the light spot 12 coincides with the optical axis 16 of the measuring device 20. . Deviations from ideal Lambertian scattering (FIG. 5), such as light reflection, are detected by the photodetector 28.
．． 28' leads to local intensity fluctuations in the plane 45.45' and thus to distortions of the distance measurements. FIG. 9 shows the Bragg angle effect, ie the considerable deviation from Lambert's law. The illumination from the light spot is divided by the angle of incidence of the light, and as a function of the observation angle 52, 0°, 3
Plotted at four different angles of incidence 51: 0°, 45° and 60°. The sample is partially reflective, compressed BaSO4. It is clear that significant reflections with different angles of incidence can be distinguished from the diffuse component. It is clear that even if the forerunner angle 51 does not correspond to the observation angle 52, such reflections lead to a significant distortion of the intensity measurement and thus to a misinterpretation of the distance of the object. Therefore, a method must be sought to remove the effects of this interference from pure diffuse scattering. J, L, Pot
1 leux) and J, Tour
This problem was recognized, as can be deduced from US Pat. No. 3,719,421 by Ret. A countermeasure is described therein which is based on a modification of the geometry of the optical distances, ie replacement of the diaphragm 27' with the shield 27' in the center of the beam 25'.

Another way to remove fluctuations in distance measurements is to
It is based on the use of the polarization properties of the radiation emitted by the light source 12, as described in German patent application no.
37 43 See No. 194.3. Upon reflection, the polarization of the incident beam is preserved, while the diffuse scattering is assumed to be substantially unpolarized. However, complete depolarization of diffuse scattering is impossible, neither for parallel rays nor for light polarized at right angles to the plane of incidence (G. Corteum, "Reflection Spectroscopy," Schbringer Verlag 1969, 38. Page (G, Ko
r t iim “Reflexion speckt
Springer Verla
g 1969. p, 38)), but this effect is generally very small.

Efficient decoupling of reflected radiation components can be achieved by using an optical insulator 64 (FIG. 6) that includes linear and circular polarizers. According to this method, the primary beam is first circularly polarized in one direction, and the radiation component circularly polarized in the opposite direction is measured.

If the light source emits light that is already polarized, as is partly the case in the case of the laser light source 21, the separation of the unwanted reflected beam from the desired diffusely scattered beam is effected after the hollow mirror 61.81. By inserting a polarizer 65' (as shown in FIG. 14) - layering can be easily done.

Advantageously, the polarization directions of laser light source 21 and polarizer 65' are at right angles to each other. It is also advantageous to rotate the polarization direction of the laser by 45° relative to the object plane of the hollow mirror. In order to align the two polarization directions perpendicularly as described above, the polarization direction of the beam impinging on the beam splitter 26 is aligned with respect to the reflection plane of the beam splitter 26.
Can be rotated by °. In this way, as can be concluded from FIG. 10, the dependence of the beam splitting condition on the polarization intensity or depolarization of the incident beam 33' disappears.

Regarding the description of FIG. 6, it is advantageous for the evaluation to keep the signal on the photodetector 28 at a fixed, predetermined value, which is possible by adjusting the laser light source 21. stated.

This method naturally means that depending on the distance 15 and the properties of the object surface 11, the light source 21 has to be operated at quite different power levels, which leads to the problem explained below.

The degree of polarization of a polarized and activated semiconductor laser is power dependent. Thus, the radiation beam of a typical GaAs laser operating at 780 nm is 95% polarized at full power, but at reduced power the degree of polarization can drop to 70%. This means that at lower laser powers,
In other words, the distance 15 of the object is long, or the object surface 1
If the absorption of 1 is strong, it means that the reflected radiation component is no longer efficiently separated from the diffusely scattered radiation component. In some cases, this problem could be eliminated by replacing polarized laser 21 with an unpolarized laser light source having a polarizer 65 (FIG. 8).

When a semiconductor laser is electrically loaded, it not only changes its optical output, but also its emission wavelength can easily change due to the temperature dependence of the energy bandgap. Due to the weak dependence of the transmission or reflection power of the beam splitter 26 on the wavelength, the splitting of the input beam 33 into the two partial beams 25, 25' is easily dependent on the power of the laser light source 21. In this 1IIJ determination method, this change in intensity condition is interpreted as a change in the distance of the object with respect to the measuring device. By carefully selecting the beam splitter 26, this measurement error can be fully accounted for.

Further reflections in the light spot 12 due to power-induced changes in the degree of polarization of the semiconductor laser can result in further distance measurement errors. As shown in FIG. 10, the components of the incident beam 33 that are polarized parallel to and perpendicular to the plane of incidence are not reflected by the same amount at the beam splitter. . In particular, the so-called Brewster angle 1
00, the reflection of the beam polarized parallel to the plane of light incidence disappears, while the vertical component constantly increases with increasing light incidence angle. However, this source of error is easily removed since the polarization effect caused by reflection is only present to a limited extent for small angles of incidence, as shown in Figure 10. obtain. It is therefore clear that, unlike in FIG. 6, the beam splitter 26 is not arranged at 45°, but at a small angle. In particular, according to FIG. 10, the angle between the normal surface of the beam splitter 26 and the optical axis of the beam 33' is advantageously less than 20°, as shown in FIG.

Often, for example in robot optics, it is very important that the distance aP1 determination within a given area is very accurate. In this case, implementing a distance measuring method with a so-called neutral plane 121 is very suitable. For the desired value of the distance, the surface and position of the two detectors 28.28' are such that the boundary of the converging DJ constant beam received by the hollow mirror 61.81 It is a matter of fixing it exactly in line with the edges of the layers. This embodiment is shown in FIG. 12, with beam splitter 26 omitted for ease of understanding. When positioning the measuring surface 11 in the neutral plane 121, the light-sensitive layers of the photodetectors 28, 28' are both illuminated by the light spot 12 at exactly the same solid angle not only in terms of size but also in terms of shape.

The distance measurement in the neutral plane 121 region depends on the uniformity of the illumination on the detector surface, since the detector detects the radiant flux produced by backscatter and reflection, and therefore radiation inhomogeneities can have no effect. completely independent from.

Because of the neutral plane 121, instead of adapting the surface and shape of the photodetectors 28.28' exactly to the optical distance 33.33', the same detectors are used and their working surfaces 122
．． Advantageously, 122' is limited to a predetermined value by means of diaphragms 123, 123'. The use of the same detector is advantageous in order to ensure the same sensitivity, temperature dependence and aging.

The photosensitive layer or diaphragm 123.123' of the photodetector 28.28' is connected to the hollow mirror 61.81.
It should be pointed out that it does not have to be dimensioned to detect all radiation 33' reflected by. They also have only a portion of 33' connected to the photodetector 2.
8.28'. If the object 11 is placed in the neutral plane 121, it is only important that both photodetectors meet the light spot 12 at exactly the same solid angle.

Due to the high light intensity and excellent beam flux, the object 11
A laser light source 21 is optimal for creating a light spot 12 on the top. However, the high chromatic emission of these light sources leads to drawbacks. The laser's small bandwidth also means a large coherence length.

For semiconductor lasers, this is typically 0.1 mm to 0.5 mm. This large coherence length means that the reflected and scattered beams can interfere over a wider area of the light spot. This results in the typical intensity fluctuations in the laser beam, which appear as "grainy" structures with so-called speckles on the illuminated surface. This speckle is detected by the hollow mirror 61.81 in the photosensitive area 122, 1 of the photodetector 28.28'.
22'. When the beam is restricted by the edge of the detector or diaphragm, intensity fluctuations occur, manifesting in reduced accuracy of their measurements. To counteract this speckle, it is advantageous to use a light source with a small coherence length and therefore a wide bandwidth. For example, it is advantageous to use multimode lasers instead of single mode lasers.

As shown in FIG. 9, gloss effects on object surfaces can result in considerable inaccuracies in distance, as is evident for example from FIG. 13. Using a white, almost pure, diffuse scattering paper 131 provides extremely high precision for distance measurements as a function of the inclination angle 133 of the optical axis 16 relative to the standard surface 134. However, in the case of black, less glossy paper 132, a very significant dependence was observed as a function of tilt angle 134, even using the same al-determining apparatus.

As illustrated in FIG. 10, since reflection is highly polarization dependent, it is preferable to adapt the polarization direction of the laser light source 21 to the inclination of the object surface. For example, this may be achieved by minimizing the reflected portion of back-reflected radiation 33.

This objective can be achieved by rotating the polarizer or the polarized laser. By changing the polarization direction, it is possible to determine whether the surface of the target has polarizing properties, ie the light rays are partially reflected without being diffused. When the change in polarization direction disappears, there is no polarized radiation and therefore the distance M measurement can be trusted. If the signal does not disappear,
For example, an indication can be provided or a more preferred value can be determined regarding the position of the polarization direction.

It should be pointed out that, in addition to the plane of polarization of the laser light source 21, the plane of polarization of the reflected beam 33' must also be rotated so that the two polarization directions are also at right angles to each other. For example, the former rotation can be achieved by rotating the quarter-wave plate 1 by rotating the laser light source 21 itself.
41', by rotating the polarizer 65', or magnetically using the Faraday effect.

However, the Faraday effect is so small that it is problematic unless long Faraday cells or very high magnetic fields are used. In order to rotate the polarization of the beam 33', it is conceivable to selectively rotate the polarizer 65 or even the quarter wave plate 141. Quarter wave plate 141.141' or polarizer 65.6
5' can be driven, for example, by using a motor 142, 142'.

Quarter wave plate 141.141' or polarizer 65.
Instead of moving 65' continuously, they can also be made to vibrate. The disappearance of alternating signal components on the photodetector 28, 28' indicates the presence of pure diffuse light scattering and therefore that this distance measurement can be trusted.

[Brief explanation of the drawing]

FIG. 1 shows the "inverse square law". FIG. 2 shows a first known measuring device based on the "inverse square law". FIG. 3 shows a second, well-known measuring device based on the "inverse square law". FIG. 4 shows a device according to the invention. FIG. 5 shows Lambert's law for diffuse light scattering. FIG. 6 is a first embodiment of an apparatus constructed according to the method of the invention. FIG. 7 shows, in plan and side view, the optical distance of a device with a cylindrical concave mirror. FIG. 8 is a representation corresponding to an embodiment with a bifocal mirror. FIG. 9 is the intensity distribution as a function of observation angle for a point-illuminated, partially reflective surface. FIG. 10 is the light reflection on a mirror as a function of the inclination angle of a ray of light polarized parallel and perpendicular to the reflective surface. FIG. 11 shows a second embodiment of the device according to the invention, in which most of the polarization properties of the beam splitting mirror have been removed. FIG. 12 is a third embodiment illustrating the principle of the neutral point measuring method. FIG. 13 is a distance measurement of a strongly polarizing surface as a function of its tilt angle. FIG. 14 shows a fourth embodiment of the device according to the invention, in which the polarizer or quarter-wave plate is moved. In the figure, 11 is an object, 12 is a light spot, 16 is an optical axis, 20 is a measuring device, 21 is a light source, 28°28' is a photodetector, 61.81 is a hollow mirror, 64 is an optical insulator,
65.65' is a polarizing means, 121 is a neutral plane, 122.
122' is a photosensitive layer, 123 and 123' are diaphragms, and 141 is a quarter wavelength plate. Patent Applicant: Valamar Electric A.G.

Claims (34)

[Claims] (1) A tightly focused beam from a light source passes from the measurement device to the object, and the light reflected by the target is focused by the measurement device optical system;
upstream of the focal plane by a beam splitter into two partial beams whose radiation intensity is measured by two photodetectors located in a common optical axis but at different distances from the beam splitter; is an optical distance measurement method between a measuring device and an object in which the current is evaluated as a function of the distance to be measured, the light reflected by the target surface is reflected and focused into the measuring device, The measurement of the radiation intensity of one of the two partial beams is
in at least one focal plane defined as a standard plane relative to the optical axis, in the focal point or in the focal line of the back-reflecting means, and further light detection is carried out along one dimension and at least within the measuring device. A method characterized in that it is carried out for the same amount of beam as is incident on . 2. Method according to claim 1, characterized in that: (2) the light reflected back by the measurement surface is focused parabolically. 3. Method according to claim 1, characterized in that the light reflected back by the measurement surface is focused in one dimension. 4. Method according to claim 1, characterized in that the light reflected back by the measuring surface is focused bifocally. (5) The intensity of the light source, which depends on the distance of the measuring device from the object and on the surface properties of the latter, is continuously adjusted such that the output signal of one of the two photodetectors is constant. 5. A method according to any one of claims 1 to 4, characterized in that: (6) In particular, the photodetector closer to the beam splitter
6. Method according to claim 5, characterized in that it is kept at a constant value by adjusting the light intensity of the light source. (7) The beam impinging on the object is polarized, and upon detection of the two partial beams, the polarization state obtained during the direct reflection is removed, so that the direct reflection is suppressed. The method described in one or more of 1 to 6. 8. Method according to claim 7, characterized in that, in order to suppress direct reflections, the beam impinging on the object is polarized by 45° with respect to the plane of symmetry of the hollow mirror. (9) A method according to one or both of claims 7 and 8, characterized in that the light source of the measuring device emits polarized light. (10) direct reflection is suppressed by an optical insulator including a linear polarizer and a circular polarizer and placed within a common optical distance of the emitted narrow beam bundle and the incident beam bundle; 7. A method according to one or more of claims 1 to 6. (11) characterized in that the polarization of the partial beams caused by reflection on the beam splitter is prevented by the angle between the optical axis of the beam impinging on the beam splitter and the standard surface of the beam splitter being smaller than 20°; ,
A method according to one or more of claims 1 to 10. (12) If the measuring surface has a predetermined distance from the measuring device and is placed in the so-called neutral plane, the light-sensitive surface of the photodetector is located at exactly the same solid angle with respect to size and shape. dimensioned to encounter a light spot, which is achieved, for example, by the edge of the beam or its partial beam focused by the hollow mirror exactly coinciding with the edge of the light-sensitive surface of the photodetector; 12. Method according to one or more of claims 1 to 11, characterized in that: (13) If the measuring surface has a predetermined distance from the measuring device and is placed in the so-called neutral plane, a diaphragm that partially covers the light-sensitive surface of the photodetector has a size and shape. dimensioned to meet the light spots at exactly the same solid angle with respect to the diaphragm, which is achieved, for example, by the edges of the beam or its partial beams focused by the hollow mirror exactly coinciding with the edges of the diaphragm. Claim 1 characterized in that
The method according to one or more of 11 to 11. (14) If the measuring surface has a predetermined distance from the measuring device and is placed in the so-called neutral plane, the edge of the beam focused by the hollow mirror will move further away from the hollow mirror. 1-1, characterized in that there is a diaphragm coinciding with or corresponding to the edge of the light-sensitive surface of the photodetector positioned at the
3. The method described in one or more of 3. (15) The plane of polarization of the beam emerging from the measuring device and of the beam reflected by the focusing means can be rotated, so that the beam component directly reflected by the target can be reduced. The method according to one or more of paragraphs 1 to 9 and 11. (16) The plane of polarization of the beam emerging from the measuring device and of the beam reflected by the focusing means can be oscillated, so that the dependence of the detector signal on the polarization position of the polarizer can be measured. 16. The method according to claim 15, characterized in that: (17) a light source capable of emitting a tightly focused beam from the measurement device toward the object; an optical system that focuses the light reflected by the measurement surface; a beam splitter placed upstream of the focal plane of said optical system, splitting into two partial beams, and two beams placed in a common optical axis but at different distances, measuring the radiation intensity of the partial beams; 2. A device for carrying out the method according to claim 1, comprising a detector and further evaluation means for forming a quotient of the current of the detector, the focusing optics being a hollow mirror (61, 81). and one of the two photodetectors (28, 28') is located in the focal point or in the optical system (61, 28') with respect to the optical axis (16).
81) is defined as the standard surface within the focal line (63) of
The focal plane (45,
45'), furthermore a photodetector (28, 28') detects the beam (33, 45') incident on the measuring device (20) and deflected in the optical system (61, 81). 33'), which is larger in one dimension than, or at least as large as, in one dimension. (18) Device according to claim 17, characterized in that the hollow mirror (61, 81) is parabolic. (19) Claim 17 or 1, wherein the hollow mirror (61, 81) is a cylindrical parabolic mirror (61).
8. The device according to any one of 8. (20) Claim 17 or 1, wherein the hollow mirror (61, 81) is a bifocal hollow mirror (81).
8. The device according to any one of 8. (21) Polarizing means (65, 65') are provided after the hollow mirror (61, 81) in the beam impinging on the object and in the beam (33') reflected back by the object (11). 21. Apparatus according to one or more of paragraphs 17 to 20. (22) The beam hitting the object is caused by hollow mirrors (61, 8
22. Device according to claim 21, characterized in that the polarization means (65) are adjusted such that the polarization means (65) are polarized by 45[deg.] with respect to the plane of symmetry of 1). (23) Device according to claim 22, characterized in that the polarizing means (65) are polarizers. 24. Device according to claim 21, characterized in that the polarizing means (65) are quarter-wave plates placed in the already polarized beam. (25) The device according to any one of claims 21 to 24, characterized in that the light source of the measuring device includes a polarizer. (26) Claim characterized in that, upstream of the hollow mirror (61, 81) within the optical distance (33), an optical insulator (64) comprising a linear polarizer and a circular polarizer is arranged. Apparatus according to one or more of 17 to 20. (27) 2 from 17, characterized in that the beam splitter (26) is arranged approximately at right angles to the optical axis (16) in the focused beam (33).
5. The device according to one or more of 5. (28) The photoreactive surface (122, 1
22') is dimensioned such that it meets the light spot (12) at exactly the same solid angle with respect to size and shape, which is, for example, the edge of the beam (33') or its partial beam focused by a hollow mirror. is achieved by precisely coinciding with the edge of the photodetector (28, 28').
28. Apparatus according to one or more of 7 to 27. (29) If the measuring surface has a predetermined distance from the measuring device and is placed in the so-called neutral plane (121), the photosensitive layer (122, 12
The photodetector (2') encounters the light spot (12) at exactly the same solid angle with respect to size and shape.
8, 28') is provided with a diaphragm (123, 123'), which allows, for example, the edge of the beam (33') or its partial beam focused by the hollow mirror (61, 81) to be detected by the photodetector ( 28. Device according to one or more of claims 17 to 27, characterized in that this is achieved by precisely coinciding with the edge of the diaphragm (123, 123') of the diaphragm (123, 123'). (30) Device according to one or more of claims 21 to 25, characterized in that the polarizer (65, 65') or the quarter-wave plate (141') is provided with rotation means. 31. Device according to claim 30, characterized in that the rotation means of the polarizer (65, 65') or of the quarter-wave plate (141, 141') enable an oscillatory movement. (32) The device according to any one of claims 17 to 31, characterized in that the light source (21) is a laser light source. (33) Use of the method and the corresponding device according to claims 1 to 32, characterized in that distances in the range from 0 cm to 30 cm are measured. (34) Use of the method and the corresponding device according to claims 1 to 32, characterized in that the device is used in robotics.