DE102010043615B4 - Optical distance sensor - Google Patents

Abstract

Optical distance sensor comprising a light source (1), a single projection grating (2; 12; 22) with a defined grating period (T1), a periodic detector arrangement (3; 13; 23) and an evaluation unit (4)
- The light source (1) the projection grid (2; 12; 22) divergently irradiated and
in the plane of the detector arrangement (3; 13; 23) results in a periodic fringe pattern with a defined fringe pattern period (VP) without the interposition of an imaging optics, and
- The evaluation unit (4) is adapted to determine the distance (u) between the light source (1) and the projection grating (2, 12, 22, 22) from the determined fringe pattern period (VP) and further known geometry parameters (v, T1) of the measuring arrangement ).

Description

The present invention relates to an optical distance sensor.

For optical distance detection distance sensors are known which determine distances to DUTs on the principle of triangulation. Here, the radiation of a light source is emitted in the direction of a measurement object and scattered there on a reflective surface. An imaging lens is used to image the new light source emerging in the reflective surface onto a suitable spatially resolving detector. The position of the light spot imaged on the detector is in a defined relationship to the distance of interest between the light source and the reflecting surface. From the determination of this position, the measuring distance can be determined via a suitable evaluation unit. With regard to such systems, for example, see DE 10 2007 058 505 A1 directed. A disadvantage of these systems is that well focusable light sources are required, for example laser diodes. Such light sources are usually relatively expensive. In the case of the use of laser diodes also result interference effects on the reflective surface, which adversely affect the distance measurement.

In addition, to achieve a high accuracy in the distance measurement, the imaged light spot may not exceed a certain size. At constant resolution, therefore, the measuring range of such distance sensors is relatively limited.

Furthermore, from the US 5 075 562 A a device for optical distance measurement is known in which a light source illuminates a first grid, which is arranged on the reflective measurement object. By means of a suitable optical system, this first grating is imaged onto a second grating. In a detection plane in which a detector arrangement is placed, a (moiré) stripe pattern results, from which the distance between the light source and the object to be measured can be determined via an evaluation unit. A disadvantage of this system is that a grid must be arranged or projected on the measurement object. This in turn has certain restrictive requirements for the object to be measured. So this must be sufficiently large for the grid and have a suitable surface finish to support the grid and to avoid lattice distortions.

The object of the present invention is to provide an optical distance sensor in which, in particular, low-cost light sources can be used and in which the o.g. Disadvantages are avoided.

This object is achieved by an optical distance sensor with the features of claim 1.

Advantageous embodiments of the optical distance sensor according to the invention result from the measures in the dependent claims.

The optical distance sensor according to the invention consists of a light source, a single projection grating with a defined grating period, a periodic detector arrangement and an evaluation unit. In this case, the light source irradiates the projection grating divergently, so that a periodic fringe pattern with a defined fringe pattern period results in the plane of the detector arrangement without the interposition of imaging optics. The evaluation unit is designed to determine the distance between the light source and the projection grating from the determined fringe pattern period and further known geometry parameters of the measuring arrangement.

Advantageously, the light source is formed here as a point light source.

In one possible embodiment, the periodic detector arrangement comprises a detector chip, which consists of individually readable detector elements in a row and before the periodically opaque covers are arranged with the grating period of the projection grating.

Furthermore, it is possible for the periodic detector arrangement to be designed as a periodic arrangement of individual detector elements in the grating extension direction with half the grating period.

It can be provided in each case that the projection grid is arranged on a glass carrier on the side facing the light source and the periodic detector arrangement is arranged on the opposite side.

ermitteln, mit

• u := Abstand zwischen der Lichtquelle und dem Projektionsgitter
• v := Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung
• VP := Streifenmusterperiode
• T1 := Gitterperiode

The evaluation unit can measure the distance u between the light source and the projection grid according to the relationship $$\text{u}=\text{v}·\left(\text{VP / T1}-\text{1}\right)$$

determine with

• u: = distance between the light source and the projection grid
• v: = distance between the projection grid and the plane of the detector array
• VP: = stripe pattern period
• T1: = grating period

mit:

• u := Abstand zwischen der Lichtquelle und dem Projektionsgitter
• v := Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung
• T1 := Gitterperiode

Preferably, the extent of the light source in the grating extension direction applies $$\text{b}<\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}1·\left(1+\text{u / v}\right)\text{/}\mathrm{2,}$$

With:

• u: = distance between the light source and the projection grid
• v: = distance between the projection grid and the plane of the detector array
• T1: = grating period

mit

• d := Länge der Detektoranordnung in der Gitter-Erstreckungsrichtung
• VP := Streifenmusterperiode

The same applies to the extent of the detector arrangement in the grating extension direction $$\text{d}>1.5·\text{VP}.$$

With

• d: = length of the detector arrangement in the grating extension direction
• VP: = stripe pattern period

It can further be provided that on the opposite side of the glass carrier to the projection grid, the opaque covers are arranged periodically with the grating period of the projection grating.

It is furthermore possible that the evaluation unit is designed to determine a lateral offset of the light source relative to the projection grid from the phase change of the fringe pattern in relation to the periodic detector arrangement, further known geometry parameters of the measuring arrangement and the specific distance between the light source and the projection grating.

As an advantage of the optical distance sensor according to the invention is to be stated that this can be realized with little effort. For example, relatively simple light sources such as LEDs can be used. Furthermore, the optical distance sensor according to the invention allows the immediate determination of the absolute distance between the measurement object and the light source.

A particularly simple construction also results in comparison to known systems of the prior art since any imaging optics in the beam path can be dispensed with according to the invention; Optics components for imaging optics are not required.

Furthermore, the present invention allows a simple adjustment of the various components to each other, for example in stacked construction. This makes it possible to automate the production of corresponding distance sensors.

In addition, there are no restrictions on the size and / or nature of a measurement object in the optical distance sensor according to the invention.

Furthermore, the optical distance sensor according to the invention has a larger measuring range and a greater accuracy than the triangulation sensors mentioned above.

Further advantages and details of the present invention will become apparent from the following description of embodiments with reference to the accompanying figures.

• 1 eine schematisierte Prinzipdarstellung zur Erläuterung des grundsätzlichen Aufbaus des erfindungsgemäßen optischen Abstandssensors;
• 2 eine schematische Darstellung zur Erläuterung bestimmter Geometrieparameter im erfindungsgemäßen optischen Abstandssensor;
• 3 eine erste mögliche Detektoranordnung für den erfindungsgemäßen optischen Abstandssensor;
• 4 eine zweite mögliche Detektoranordnung für den erfindungsgemäßen optischen Abstandssensor;

It shows here

• 1 a schematic diagram for explaining the basic structure of the optical distance sensor according to the invention;
• 2 a schematic representation for explaining certain geometry parameters in the optical distance sensor according to the invention;
• 3 a first possible detector arrangement for the optical distance sensor according to the invention;
• 4 a second possible detector arrangement for the optical distance sensor according to the invention;

Based on the schematic representation in 1 Let us explain below the basic principle of the optical distance sensor according to the invention. Provided here is a light source 1 that a single projection grid 2 divergently lit, in the distance u from the light source 1 is arranged. As a light source 1 In this case, a point light source, for example a VCSEL light source (vertical cavity surface emitting laser) or an LED with a sufficiently small spatial extent in the grating direction is preferably provided. The projection grid 2 is as a transmission grating with the grating period T1 educated. At a distance v behind the projection grid 2 is a periodic detector arrangement 3 over which a periodic fringe pattern resulting in a detection plane is scanned. The periodic detector arrangement 3 includes in the present example a detector chip 3.1 from individually readable detector elements in a row, in front of the periodically opaque covers 3.2 with the grating period T1 of the projection grid 2 are arranged. About the interaction of the projection grid 2 generated light pattern with the periodic detector array 3 results in the plane of the detector array 3 without the interposition of an imaging optics, a periodic stripe pattern or a Verniermuster with a defined stripe pattern period VP , The detector arrangement 3 is an evaluation unit 4 downstream; this is designed to be from the determined fringe pattern period VP and other known geometry parameters of the measuring arrangement the distance u between the light source 1 and the projection grid 2 to determine.

mit:

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

VP :=

Streifenmusterperiode

T1 :=

Gitterperiode des Projektionsgitters

In the present embodiment, the evaluation unit uses 4 for determining the distance u the following relationship: $$\text{u}=\text{v}·\left(\text{VP / T1}-\text{1}\right)$$

With:

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

VP: =

Fringe pattern period

T1: =

Grating period of the projection grating

With the metrological determination of the fringe pattern period VP, it is thus possible to know the geometry parameters v (Distance between the light source and the projection grid) and T1 (Grating period of the projection grating) the distance u between light source 1 and projection grids 2 determine. It does not matter if it is the light source used 1 is a real light source or possibly a virtual light source.

In the case of using a virtual light source, the light source would be arranged together with the detector arrangement in a measuring head and emit in the direction of a reflective measuring object. The radiation reflected back from the reflecting measurement object is then detected in the detector arrangement. In such a measuring arrangement, the above-mentioned magnitude u would then result from the distance between the light source and the reflecting measuring object plus the distance between the reflecting measuring object and the projection grid.

mit:

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

VP :=

Streifenmusterperiode

T1 :=

Gitterperiode des Projektionsgitters

T2 :=

Periodizität der Detektoranordnung

In principle, it is not absolutely necessary in the context of the present invention that the periodicity on the part of the detector arrangement 3 with the periodicity T1 of the projection grid 2 matches. In the case of a deviating periodicity T2 the detector assembly 3 the required distance u would result according to the following relationship: $$\text{u}=\text{v}·1\text{/}\left[\left(\text{<figure-callout id="2" label="T" filenames="DE102010043615B4\_0016.png,DE102010043615B4\_0017.png" state="{{state}}">T</figure-callout>}2·\text{VP}\right)\text{/}\left(\text{VP}·\text{T1}-\text{T2}·\text{T}1\right)-1\right]$$

With:

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

VP: =

Fringe pattern period

T1: =

Grating period of the projection grating

T2: =

Periodicity of the detector arrangement

The intended evaluation unit would then divide the distance u or a distance derived therefrom via Eq. 2 determine. In the following explanations, it should be assumed in principle that the evaluation unit determines the distance u in question from Eq. 1 determined.

Important for the precise determination of the distance u is the most accurate metrological determination of the stripe pattern period VP via the detector arrangement 3 , This is grds. possible if a high-contrast fringe pattern or pattern is generated in the detection plane.

mit $$\text{d}=\text{n}·\text{T}{1}^2\text{/}\mathrm{\lambda }$$

wobei

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

T1 :=

Gitterperiode des Projektionsgitters

n :=

1, 2, 3, ....

Ä :=

Lichtwellenlänge

To produce a well-contrasted stripe pattern in the detection plane, the following relationships should be fulfilled in the optical distance sensor according to the invention: $$1\text{/ u}+1\text{/ v}=1\text{/ d}$$

With $$\text{d}=\text{n}·\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}{1}^2\text{/}\mathrm{\lambda }$$

in which

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

T1: =

Grating period of the projection grating

n: =

1, 2, 3, ....

Ä: =

Light wavelength

As further advantageous for the generation of a well-contrasted stripe pattern proves to be when the light source used 1 is chosen as small as possible in terms of their spatial extent. For this purpose, further conditions are explained below, the adherence of which has an advantageous effect on a well-contrasted stripe pattern.

mit

b :=

reale Ausdehnung der verwendeten Lichtquelle 1 in der Ausdehnungsrichtung des Projektionsgitters

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

T1 :=

Gitterperiode des Projektionsgitters

Describes the size b - as in 2 illustrates - the real extent of the light source used 1 in the extension direction of the projection grating 2 Thus, a grid edge is projected onto the detector array 3 imaged with a blur dk. As long as dk is less than half the grating period T1 of the projection grid shown 2 is, the generated resulting fringe pattern is sufficiently contrasted imaged. As a condition for a high-contrast fringe pattern, the extension b of the light source results in: $$\text{b}<\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}1·\left(1+\text{u / v}\right)\text{/}2$$

With

b: =

real extent of the light source used 1 in the extension direction of the projection grating

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

T1: =

Grating period of the projection grating

mit

u_min :=

zulässiger Minimalabstand u_min zwischen Lichtquelle und Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

T1 :=

Gitterperiode des Projektionsgitters

b_max :=

maximale Ausdehnung der verwendeten Lichtquelle

From Eq. 4 again allows a permissible minimum distance u _min between the light source 1 and projection grids 2 determine if the maximum expansion bmax of the light source used 1 known is: $${\text{u}}_{\text{min}}=\text{v}·\left(\left(2·{\text{b}}_{\text{Max}}\text{/ T}1\right)-1\right)$$

With

u _min : =

permissible minimum distance u _min between light source and projection grille

v: =

Distance between the projection grid and the plane of the detector array

T1: =

Grating period of the projection grating

b _max : =

maximum extension of the light source used

Smaller distances between the light source 1 and the projection grid 2 as u _min can not be determined with the optical distance sensor according to the invention.

mit

Ω :=

Abstrahlwinkelbereich der Lichtquelle in der Messebene

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

T1 :=

Gitterperiode des Projektionsgitters

Furthermore, go into the picture of the projection grid 2 the emission characteristic of the light source 1 ie that of the light source 1 achievable radiation angle range Ω of the light source in the detection plane. So, in principle, it should be ensured that at least two periods of the vernier pattern on the light source 1 be illuminated so that at least one period of Verniermusters reliably present in the detector area and their length can be determined. This is in principle the more difficult the smaller the distance u is. However, in the case of small pitches u, the resulting fringe pattern period VP also becomes smaller, but this is not so significant. It can be estimated that the quantity tan Ω / 2 must be greater than the ratio of VP to u + v. In conjunction with Eq. 1 thus results: $$\text{tan}\mathrm{\Omega }\text{/}2>\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}1\text{/ v}$$

With

Ω: =

Beam angle range of the light source in the measurement plane

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

T1: =

Grating period of the projection grating

Following the basic design considerations for the optical distance sensor according to the invention, options for the specific design of the periodic detector arrangement are explained below.

A first variant of a suitable detector arrangement 13 for the optical distance sensor according to the invention is in 3 partially shown schematically.

In this embodiment, a detector chip is provided on the detector side, on the individually readable detectors 13.2 are arranged periodically in a row. The individual detectors 13.2 are running in the same direction as the projection grid 12 arranged, the periodicity of the arrangement of the detectors 13.2 corresponds to the grating period T1 of the projection grid 12 , Immediately in front of the photosensitive surfaces of the detectors 13.2 are latticed opaque covers 13.1 arranged periodically. their Periodicity is also according to the grating period T1 of the projection grid 12 selected. The opaque covers 13.1 For example, they may be formed as planar metal structures; This makes it possible to minimize the distance between the detection plane and the covers 13.1 to ensure.

In the illustrated embodiment, the covers 13.1 on the underside of a glass slide 15 arranged the thickness v having. On which, the - not shown - light source facing top is the projection grid 12 with the grating period T1 placed. About such an arrangement is in a simple manner a defined and immutable size of the distance v guaranteed, the according to Eq. 1 goes directly into the distance determination.

In the case of the divergent illumination of the projection grating 12 via the light source is the projection grid 12 in central projection on the periodically or grid-like arranged covers 13.1 projected so that in the plane of the covers a central projection image of the projection grid 12 or a light pattern with the period T1 * (1 + v / u) results.

In the case of a presumed constant emission intensity over a certain solid angle range of the light source, adjacent detectors detect 13.2 due to the different periodicity of the light pattern and the periodicity of the cover assembly different light intensities. Therefore, a periodic fringe pattern or Vernier fringe pattern is formed in the detection plane, which is the periodicity VP which can be determined from the detector signals.

A second variant of a suitable detector arrangement 23 for the optical distance sensor according to the invention is in 4 partially shown schematically. In contrast to the previous example, it is now provided that the periodic detector arrangement 23 from a periodically arranged in the grating extension direction arrangement of individual detectors 23.2 consists. Their periodicity is as in 4 indicated T1 / 2. There are therefore no separate covers provided, the extent and periodicity of the detectors 23.2 is chosen as specified.

Consistent with the previous example, it is again provided on top of a glass slide 25 the projection grid 22 to arrange and on the bottom desselbigen the individual detectors 23.2 ,

Both variants of the periodic detector arrangement allow the determination of the periodicity VP the generated Vernier stripe pattern. Together with the known geometry parameters T1 and v determines the evaluation unit according to Eq. 1 the desired distance u and provides this size for further processing.

Finally, a further embodiment of the optical distance sensor according to the invention is explained, in which in addition to the determination of the distance u between the light source and the projection grid additionally information with respect. A lateral displacement movement of the light source relative to the projection grid can be generated.

Basically changes in a measuring arrangement according to 1 in the case of a lateral displacement movement of the light source 1 by the shift amount s opposite the projection grid 2 not the distance u and thus not the periodicity VP of the generated stripe pattern in the detection plane. In this case, however, the phase position of the fringe pattern generated in the detection plane changes relative to the individual detectors of the periodic detector arrangement. However, the phase position of the stripe pattern relative to the detectors is dependent on the amount of shift s , In case of a shift of the light source 1 by the lateral shift amount s1 this results in a change in the phase position of the fringe pattern or a phase change φ result: $$\mathrm{\phi }=\text{s}1\text{/}\left[\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}1·\left(1+\text{u / v}\right)\right]$$

mit

s1 :=

lateraler Verschiebebetrag der Lichtquelle

φ :=

Phasenänderung

u :=

Abstand zwischen der Lichtquelle und dem Projektionsgitter

v :=

Abstand zwischen dem Projektionsgitter und der Ebene der Detektoranordnung

T1 :=

Gitterperiode des Projektionsgitters

The lateral shift amount s1 can thus be determined from the phase change φ according to $$\text{<figure-callout id="1" label="s" filenames="DE102010043615B4\_0016.png" state="{{state}}">s</figure-callout>}1=\mathrm{\phi }·\left[\text{<figure-callout id="1" label="T" filenames="DE102010043615B4\_0016.png" state="{{state}}">T</figure-callout>}1·\left(1+\text{u / v}\right)\right]$$

With

s1: =

lateral shift amount of the light source

φ: =

phase change

u: =

Distance between the light source and the projection grid

v: =

Distance between the projection grid and the plane of the detector array

T1: =

Grating period of the projection grating

An absolute information about the shift amount s1 Of course you only get this, as long as the shift amount s1 is less than T1 · (1 + u / v); in the case of a larger shift, counting the zero crossings of the phase change φ is necessary to determine the shift amount.

In order to detect a lateral displacement movement of the light source relative to the projection grating, the detection of the phase change φ is accordingly required by measurement in the optical distance sensor according to the invention. On the 7.2 Gl, then the shift amount s1 be determined.

In the context of the present invention, of course, there are a number of other possible embodiments in addition to the illustrated variants.

Claims (10)

Optical distance sensor, comprising a light source (1), a single projection grating (2; 12; 22) with a defined grating period (T1), a periodic detector arrangement (3; 13; 23) and an evaluation unit (4) - The light source (1) the projection grid (2; 12; 22) divergently irradiated and in the plane of the detector arrangement (3; 13; 23) results in a periodic fringe pattern with a defined fringe pattern period (VP) without the interposition of an imaging optics, and - The evaluation unit (4) is adapted to determine the distance (u) between the light source (1) and the projection grating (2, 12, 22, 22) from the determined fringe pattern period (VP) and further known geometry parameters (v, T1) of the measuring arrangement ). Optical distance sensor after Claim 1 , wherein the light source (1) is designed as a point light source. Optical distance sensor after Claim 1 , wherein the periodic detector arrangement (13) comprises a detector chip which consists of individually readable detector elements (13.2) in a row and before the periodically opaque covers (13.1) with the grating period of the projection grating (12) are arranged. Optical distance sensor after Claim 1 , wherein the periodic detector arrangement (23) is designed as a periodically arranged in the grating extension direction arrangement of individual detector elements (23.2) with half the grating period. Optical distance sensor after Claim 3 or 4 , wherein on a glass carrier (15; 25) on the side facing the light source, the projection grating (12; 22) is arranged and on the opposite side of the periodic detector array (13; 23) is arranged. Optical distance sensor after Claim 1 wherein the evaluation unit (4) determines the distance (u) between the light source (1) and the projection grating (2; 12; 22) according to the relationship $$\text{u}=\text{v}·\left(\text{VP / T}1-1\right)$$

determined, with u: = distance between the light source and the projection grating v: = distance between the projection grating and the plane of the detector array VP: = fringe pattern period T1: = grating period Optical distance sensor after Claim 1 , wherein for the extension of the light source (1) in the grating extension direction $$\text{b}<\text{T}1·\left(1+\text{u / v}\right)\text{/}2$$

is valid, with: u: = distance between the light source and the projection grating v: = distance between the projection grating and the plane of the detector array T1: = grating period Optical distance sensor after Claim 1 , wherein for the extension of the detector arrangement (3; 13; 23) in the grating extension direction $$\text{d}>1.5·\text{VP}$$

with d: = length of the detector arrangement in the grating extension direction VP: = fringe pattern period Optical distance sensor after Claim 3 and 5 , wherein on the projection grid (12) opposite side of the glass carrier (13), the opaque covers (13.1) are arranged periodically with the grating period (T1) of the projection grating (12). Optical distance sensor after Claim 1 , wherein the evaluation unit (4) is adapted to determine the phase change (φ) of the fringe pattern in relation to the periodic detector arrangement (3; 13; 23), further known geometry parameters (v, T1) of the measuring arrangement and the determined distance (u). between the light source (1) and the projection grating (2; 12; 22) to determine a lateral offset of the light source (1) relative to the projection grating (2; 12; 22).

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