DE102013002399B4 - Device for generating light patterns with a one-dimensionally focused illumination device - Google Patents

Abstract

Apparatus for generating light patterns for multistep photogrammetric 3D surface reconstruction, comprising an illumination device which has a large number of light sources (1) arranged in a row, wherein the light means (1) can be switched on and off in such a way that different light patterns (6) can be generated, which are suitable for multi-step photogrammetric 3D surface reconstruction and juxtaposed in a row lenses (5), characterized in that the lenses (5) are cylindrical lenses and are arranged so that they from the light sources (1) emitted light (3, 3 ') in such a way that a light pattern (6, 11) of parallel light strips (6) is generated, and that a one-dimensional reflector (2) or a cylindrical lens for parallelizing or focusing the light beams of the illumination device in the direction transverse to Line is provided.

Description

The invention relates to a device for generating light patterns with a one-dimensionally focused illumination device.

So-called stripe patterns are needed in close-range photogrammetry in order to find unique correspondences with homogeneous surface texture. A high light intensity is a prerequisite for short integration and measurement times. For the application of multi-step measuring methods also different stripe patterns must be generated.

The switching times between different patterns must be correspondingly short in order to limit the measuring time accordingly over several steps. With large measuring fields, the generated light patterns should also cover a corresponding area without losing intensity. The prerequisite for this is that a scaling of the pattern intensity can also be used to scale the illuminance.

In general, close-range photogrammetry with active illumination uses slide or video projectors, so-called beamers. The results, which here in particular with multi-step method, z. Phase shift or time correlation, are sufficient for many practical applications. The procedural bases are z. As described in Wiora, G .: Optical 3D Metrology: Precise Shape Measurement with an Extended Fringe Projection Method, University of Heidelberg, Dissertation, 2001.

Currently, measuring systems with one or two cameras and one projector are commercially offered by many companies.

To solve metrological problems in industrial applications, projectors quickly reach their limits with regard to their maximum light intensity. The low light intensity results in relatively long integration times for image acquisition, resulting in long measurement times and lower measurement accuracy, eg. B. vibrations, leads. Because of the constant maximum output of a projector, the field of view can only be increased at the cost of a lower light intensity.

The simultaneous use of several projectors is generally not possible for metrological reasons, since the light patterns are superimposed between the projectors.

An apparatus for solving the above-mentioned technical problem with projectors is not known. One main reason for this is that the projected light is focused in a single lens and is also produced by only a single light source.

An alternative to using projectors is the use of laser light sources. However, laser light has the disadvantage that it causes speckle effects and at high intensity appropriate safety standards must be met.

In applications, laser light section methods are often used. The methods are also relatively robust in industrial use, but the measurement times are often even longer than when using projectors.

Laser light can also be used indirectly. In Schaffer M, Grosse M, Kowarschik R: High-speed pattern projection for three-dimensional shape measurement using laser speckles. Appl Opt. 2010 Jun 20; 49 (18): 3622-9. doi: 10.1364 / AO.49.003622 introduces a system that generates speckle patterns and then projects them through a lens to produce stochastic patterns.

The system achieves very fast switching times and high light intensities.

However, at higher intensities, a high laser protection class quickly becomes necessary, which is problematic for many applications. In addition, the patterns are always stochastically distributed in two dimensions. The generation of one-dimensional patterns, ie stripe patterns, is not possible with this technique.

Another possibility for generating patterns of light is the use of individual light spots. With light spots, the technical task can be solved with respect to light intensity, scalability and switching speed, but the generated light patterns are relatively coarse structured and not one-dimensional, d. H. not strip-shaped.

This allows a photogrammetric evaluation of the patterns only in a very limited area. The coarsely structured patterns can lead to systematic measurement errors on unsuitable surfaces.

From the US 2012/0293625 A1 goes out a 3D camera with at least one image sensor and at least one lighting unit. The lighting unit has a semiconductor array formed as a light source with a plurality of different light emitting elements. Each light element generates a separate light spot. The points of light are with a lens, a mirror or a Lens array shown on a surface to be scanned.

In the DE 10 2009 024 894 A1 a projection display is described in which a plurality of object structures to be imaged are each imaged with a field lens in such a way that an overall image results on a screen. As a rule, several identical object structures are imaged onto each other.

The US 2009/0185157 A1 discloses a light source for projecting predetermined patterns of light onto an object. In this case, the light source comprises a plurality of LEDs, which are arranged in a regular grid horizontally and vertically spaced from each other. The light from each individual LED passes through a predetermined mask associated with the LED. The mask shadows certain portions of the light beam while transmitting other portions of the light beam. The light passing through the predetermined mask is then focused by a lens, and in turn each lens mask or LED is associated with a lens.

The EP 2 280 239 A1 discloses a lighting device having a pattern generating element disposed in the beam path so that an illumination field is incident on the pattern generating element, thereby illuminating a monitoring area in a substantially rectangular portion having a patterned illumination pattern.

From the DE 10 2004 035 102 A1 is a method for fast, high-resolution, absolute and imaging 3D optical shape detection produced. A corresponding projector has at least three real or virtual light sources which have spectral intensity distributions separated from each other.

In the JP 2007-257857 A a lighting device is disclosed. The illumination device comprises a luminous means, a reflector and a lens arrangement of convex-shaped cylindrical lenses.

From the DE 11 2009 001 652 T5 show a multi-channel detection device and a corresponding method. Each channel of a multi-channel pattern projector may include a separate radiation source and a separate modulator spatially modulating a first radiation to produce a radiation pattern. In addition, a separate lens may be provided in the channel to align the first radiation substantially in parallel. It is provided that the many light sources each generate a pattern.

In the US 2010/0045894 A1 For example, a planar illumination device and a liquid crystal display having such a planar illumination device are disclosed.

From the DE 10 2011 014 779 A1 An apparatus and a method for measuring an object emerge. This device comprises a lighting unit, a projection optical system for shaping light onto an object arranged in a measuring field, a recording device for generating an image of the object and an evaluation unit for evaluating the generated image and for determining the distances. In particular, it is provided in this case that the optics has at least one free-form optical system in order to direct the light emitted by the illumination unit into the object plane by means of at least one freeform surface of the freeform optics to form a spatially structured light pattern.

In the DE 10 2007 004 122 B4 For example, there is disclosed an apparatus which, by means of a pattern projector, generates patterns on an object surface to measure a three-dimensional shape, moving a grating device n times by means of a grating mover and correspondingly emitting a grating pattern illumination onto a surface each time. A camera captures a picture of the surface after each movement of the grid to evaluate it.

From the US 2004/0130730 A1 shows a device having a grid, which is displaceable by means of a grating movement means to image different light patterns on a three-dimensional surface.

Similar devices go out of the US 2002/0018118 A1 , of the US 2003/0048939 A1 and the DE 10 2010 029 319 out.

In the US 2012/0293625 A1 or the EP 2 772 676 A1 a 3D camera with an image sensor and a lighting unit is described, which has a light source, which is designed for the generation of an irregular illumination pattern in a security area of the 3D camera. The light source is formed of a semiconductor array with many single emitter elements, which are arranged irregularly. In each case a single emitter element generates a pattern element of the irregular illumination pattern.

From the WO 2012/066501 A1 A camera emerges, which has a lighting device for illuminating a lighting field with stripe patterns. Different stripe patterns can be generated, with the individual patterns differing in the stripe width. The Stripe patterns can be generated by structured elements which are illuminated by a lighting device and imaged by means of an optical system on the area to be illuminated or scanned.

The US 5 572 368 A discloses a lighting device for generating a pattern of alternating light and dark stripes. The illumination device has an imaging system, which is formed exclusively by co-focusing lenses.

Alternative devices provide for modifying the imaging units with respect to their position to accommodate different patterns of light on an object surface. Such devices are for example from the DE 101 49 750 A1 and the DE 102 26 398 A1 known.

Against this background, the object of the present invention is to provide a device by means of which the aforementioned disadvantages can be overcome.

This object is achieved by a device according to claim 1 and the further advantageous embodiments according to the subclaims.

A device for generating light patterns is proposed, wherein the homogeneous light generated by a one-dimensionally focused illumination device is bundled over a field of juxtaposed lenses orthogonal to the illumination device such that parallel light strips can be imaged and specific one-dimensional light patterns can be generated.

• – in verschiedenen Höhen,
• – und bei Variation der räumliche Verteilung der Lichtquellen in der Beleuchtung deutlich voneinander.

The light patterns are different

• - at different heights,
• - And with variation of the spatial distribution of the light sources in the lighting clearly from each other.

In addition, the device allows the generation of light patterns with high intensity.

Although line illumination with very high light intensity is known from the field of line-based image acquisition systems. In many applications, line lighting is designed to bundle the light in one dimension in parallel.

The device comprises a field of parallel cylindrical lenses, which is brought into the beam path of a line illumination with LED's or fiber optics. The cylindrical lenses focus the homogeneous light from each individual illuminant, such as LED or optical fiber at the exit to small areas in the row direction. The light bundled in parallel by the reflector of the line illumination widens the areas focused by the cylindrical lenses into strips in the y direction.

The lens attachment produces exactly one light strip for each lamp in combination with each cylindrical lens of the lens attachment.

Depending on the focal length of the cylindrical lenses and the distance of the lens array from the line illumination, a light strip of different widths is imaged. The superimposition of the imaged light stripes results in a specific fringe pattern.

• 1. Verteilung der Leuchtmittel, d. h. von der Positionen in Zeilenrichtung,
• 2. Größe der Leuchtmittel, beispielsweise von der Breite in Zeilenrichtung,
• 3. Verteilung der Linsen, d. h. von der Positionen in Zeilenrichtung,
• 4. Größe der Linsen, von der Breite in Zeilenrichtung,
• 5. Brennweite der Linsen,
• 6. Abstand der Linsen zum Leuchtmittel,
• 7. Abstand der Linsen zur Messobjektoberfläche.

The stripe pattern corresponds to a one-dimensional brightness distribution, which essentially depends on the following variables:

• 1. Distribution of the lamps, ie from the positions in the row direction,
• 2. size of the lamps, for example, the width in the row direction,
• 3. distribution of the lenses, ie from the positions in the row direction,
• 4. Size of the lenses, from the width in the row direction,
• 5. focal length of the lenses,
• 6. distance of the lenses to the illuminant,
• 7. Distance of the lenses to the target surface.

• – Es wird eine sehr hohe Lichtintensität erreicht, da die Lichtmuster nicht durch Abschattung oder Ablenkung entstehen und kein zentrales Leuchtmittel existiert. Im Gegensatz zu Projektoren wird die maximale Lichtleistung aller eingesetzten Leuchtmittel prinzipiell nur durch den optischen Verlust an den Zylinderlinsen abgeschwächt.
• – Das System lässt sich in einer Dimension ohne Einschränkungen der Lichtintensität beliebig räumlich erweitern. Damit kann im Gegensatz zu Projektoren nach dem Stand der Technik die Messfläche vergrößert werden, ohne dass die Lichtintensität proportional abnimmt.

The generated stripe patterns are in principle suitable for stereoscopic evaluation with photogrammetric 3D measuring methods. Essentially, the device offers two distinct advantages over known measurement systems with projectors.

• - It is achieved a very high light intensity, since the light patterns are not caused by shading or distraction and no central bulb exists. In contrast to projectors, the maximum light output of all lamps used is only attenuated by the optical loss at the cylindrical lenses.
• - The system can be expanded in any dimension in any dimension without limiting the light intensity. Thus, in contrast to state-of-the-art projectors, the measurement area can be increased without the light intensity decreasing proportionally.

It is provided that the device is designed such that the resulting light patterns are suitable for photogrammetric 3D surface reconstruction by means of single or multiple camera systems in a predetermined measurement volume.

Photogrammetric surface reconstruction is the main field of application for the device. The improvements over other pattern projections can result in higher measurement speeds, higher measurement accuracy and robustness against vibration and other external influences when 3D surveying large surfaces. In particular, they allow the use of line scan cameras. Among other things, this will create new opportunities for quality assurance based on 3D surface reconstructions in the industrial environment.

A further embodiment of the invention provides that the light patterns differ significantly from one another at different heights and with variation of the spatial distribution of the light sources in the illumination.

The generation of different light patterns is a basic requirement for the application of multi-step 3D measuring methods. By choosing a suitable spatial distribution, it is also possible to generate suitable light patterns. In a limited height range, it is also possible to generate classical phase shift patterns.

Due to the dependence in the z-direction, the measurement volume can be decisively extended, since the pattern generation then does not depend on a limited depth of focus range. It also enables multi-step measurement with just one camera.

It is envisaged that the LEDs used in the illumination device can be switched on and off so that different light patterns can be generated for a given measurement volume, which are suitable for photogrammetric 3D surface reconstruction with multi-step methods in single or multiple camera systems.

Multi-step photogrammetric measuring methods have a higher lateral resolution compared to single-step measuring methods and are more robust in use against systematic measuring errors.

When using line scan cameras, however, different patterns are needed, which change their shape with each recorded line. Fast turnaround of patterns is therefore a prerequisite for time-efficient measuring procedures. The patterns can be changed very quickly when using LED's, since LED's as light sources are generally characterized by very short switching times.

Thus, the device has another decisive advantage over state-of-the-art projectors. The possibility that results from implementing multi-step 3D measuring methods with line scan cameras is an important prerequisite for many new areas of application of 3D measuring technology.

A further embodiment of the invention provides that optical fibers are used instead of the LEDs whose primary light sources can be quickly switched on and off.

In addition to LEDs, optical fiber is a commonly used tool to construct line lighting. Each individual fiber is a small light source at its output. If adjacent light guides fed by different primary light sources, then it is also possible when using optical fibers to produce different patterns equivalent to the embodiment with LED's.

Light guides have the advantage compared to LED's to have a much smaller emission area and be used as cold light. Therefore, there are applications in which the advantages of the device can only be used in conjunction with optical fibers

In a further embodiment of the invention, an assembly is provided which comprises a plurality or at least two devices of the aforementioned type, wherein the devices are arranged parallel to each other and a stripe pattern is extendable orthogonal to a row.

The device can be used not only in conjunction with line scan camera systems but also with matrix camera systems. Since matrix camera systems are characterized by a surface image acquisition, the extension of the stripe pattern orthogonal to line is necessary. By virtue of the already mentioned advantages of the device, it is thus also possible to decisively improve matrix camera systems for 3D surveying.

• – Zur Grundkonstruktion kann eine handelsübliche Zeilenbeleuchtung mit einem Reflektor oder einer Zylinderlinse verwendet werden.
• – Ein Array mit Zylinderlinsen kann im Spitzgussverfahren hergestellt werden. Handelsübliches Rillenglas kann auch verwendet werden.
• – Das Zylinderlinsenarray wird so montiert, dass es im Strahlengang der Zeilenbeleuchtung liegt und bei eingeschalteter Zeilenbeleuchtung ein Streifenmuster erzeugt.
• – Wenn zwischen verschiedenen Mustern umgeschaltet werden soll, muss eine elektronische Ansteuerung gebaut werden, die es erlaubt, alle verwendeten Leuchtmittel einzeln oder in Gruppen anzusteuern.
• – Wenn spezielle Muster und Musterabfolgen generiert werden sollen, dann ist die räumliche Anordnung von Leichtmittel und Zylinderlinsen entsprechend zu ändern bzw. zu optimieren.

The manufacture of such a device can take place, for example, in the following steps:

• - For the basic construction, a commercial line lighting with a reflector or a cylindrical lens can be used.
• - An array of cylindrical lenses can be made by injection molding. Commercially available grooved glass can also be used.
• - The cylindrical lens array is mounted so that it lies in the beam path of the line illumination and generates a striped pattern when the line illumination is switched on.
• - If you want to switch between different patterns, an electronic control must be built that allows all used bulbs individually or in groups to control.
• - If special patterns and pattern sequences are to be generated, then the spatial arrangement of light and cylindrical lenses must be changed accordingly or optimized.

By way of example, embodiments of the invention are illustrated in the following figures and described in more detail.

Show it:

1 : schematically the construction principle of a line illumination in the side view,

2 : the schematic structure of the device as line illumination with LED row in the front view,

3 schematically a line illumination with cylindrical lenses in the beam path and

4 schematically a system for generating one-dimensional brightness distributions

In 1 schematically shows the design principle of a row illumination in side view. From a light source 1 become light rays 3 over a one-dimensional reflector 2 in one direction, for example in the z-direction, to a line light 3 ' focused or parallelized.

Alternatively, the focusing or parallelization of the light beams 3 also via a cylindrical lens instead of the reflector 2 be made.

In 2 is schematically an LED line 1' comprising a plurality of bulbs 1 and a reflector 2 , shown in front view. The high light intensity of such line illumination is due to the fact that the light along a line over a large number of light sources 1 as light guides or LEDs is emitted.

Because the light rays 3 not focused or parallelized in the row direction, is the resulting line light 3 ' generally very homogeneous, which is needed for most applications. Due to the decentralized structure of the bulbs 1 is a scaling in the row direction x without loss of light intensity possible.

3 schematically shows an apparatus for generating light patterns in the form of stripes 6 , Here are bulbs 1 containing a row of illuminants, for example an LED row 1' form a reflector 2 and a cylindrical lens array 5 ' provided, wherein the cylindrical lens array 5 ' in the ray path of the line light 3 ' spaced from the bulb 1' is arranged at a distance B and a field of parallel cylindrical lenses 5 includes.

The cylindrical lenses 5 Focus on every single light source 1 emitted line light 3 ' , on small areas in the row direction x. By the reflector 2 the row illumination parallelized line light 3 ' become those of the cylindrical lenses 5 focused areas as stripes 6 in the y-direction on an imaginary and schematically represented measuring surface 4 displayed. The resulting stripes 6 are at a distance 0 from the cylindrical lens array 5 ' ,

In 4 schematically a system for generating one-dimensional brightness distributions 11 represents.

• 1. Verteilung der Leuchtmittel, d. h. von der Positionen in Zeilenrichtung,
• 2. Größe der Leuchtmittel, beispielsweise von der Breite in Zeilenrichtung,
• 3. Verteilung der Linsen, d. h. von der Positionen in Zeilenrichtung,
• 4. Größe der Linsen, von der Breite in Zeilenrichtung,
• 5. Brennweite der Linsen,
• 6. Abstand der Linsen zum Leuchtmittel,
• 7. Abstand der Linsen zur Messobjektoberfläche.

als Eingänge 9 eines Systems 10 interpretierbar, dessen Ausgang ein eindimensionales Lichtmuster bzw. die eindimensionale Helligkeitsverteilung 11 liefert. Nur die beiden letzten Größen, also der Abstand B der Linsen 5 zum Leuchtmittel 1 bzw. zur gedachten Messobjektoberfläche 4 sind skalar, die anderen Eingänge sind Vektoren, d. h., für jedes Leuchtmittel 1 der Zeilenbeleuchtung gibt es eine Position Lx1, Lx2, ..., Lxn sowie eine Breite Lb1, Lb2, ..., Lbn, und für jede Linse 5 gibt es eine Position Zx1, Zx2, ..., Zxn, eine Breite Zb1, Zb2, ..., Zbn und eine Brennweite Zf1, Zf2, ..., Zfn.Here are the seven sizes

• 1. Distribution of the lamps, ie from the positions in the row direction,
• 2. size of the lamps, for example, the width in the row direction,
• 3. distribution of the lenses, ie from the positions in the row direction,
• 4. Size of the lenses, from the width in the row direction,
• 5. focal length of the lenses,
• 6. distance of the lenses to the illuminant,
• 7. Distance of the lenses to the target surface.

as inputs 9 of a system 10 whose output can be interpreted as a one-dimensional light pattern or the one-dimensional brightness distribution 11 supplies. Only the last two sizes, so the distance B of the lenses 5 to the light source 1 or to the imaginary measuring object surface 4 are scalar, the other inputs are vectors, ie, for each light source 1 There is a position Lx1, Lx2, ..., Lxn and a width Lb1, Lb2, ..., Lbn, and for each lens 5 there is a position Zx1, Zx2, ..., Zxn, a width Zb1, Zb2, ..., Zbn and a focal length Zf1, Zf2, ..., Zfn.

The amount of input makes the system relatively complex. The inputs can be selected so that the resulting stripe patterns provide the best possible results for the photogrammetric method to be used. Because of the complexity of the system, multidimensional optimization methods are to be used. An important fixed edge size here is the measurement volume or the maximum height of the object surface to be measured.

Because the distance of the lenses 5 to the target surface 4 for example, in 3 in the xy plane, represents an input of the system, the fringe pattern changes 11 with the object height, or with the distance O.

For one-step measuring methods, the device is thus already complete, since time-invariant light patterns are generally used here.

The significant change in the pattern as a function of the height of a measured object gives better possibilities for photogrammetric evaluation than when using projectors.

Thanks to the principle of line illumination, the system can be easily scaled, at least in the line direction, without losing its light intensity. Orthogonal to the line, a plurality of identical lighting can be arranged and operated in parallel, whereby a scaling is possible here as well. With identical patterns, the strips then merge.

A maximum light intensity is achieved not least in the proposed device in that the light patterns are not caused by occlusion or shading, as in projection, but by bundling of light. A loss of power is recorded only on lenses and reflector. This power loss is relatively low.

For photogrammetric multi-step processes, time-variant patterns are needed. However, a time variance of the system can only be achieved by changing the input variables. If no mechanical effort is to be operated, only the distribution of the light source can be changed, which can be realized by switching on and off individual lamps.

When using LEDs, this can be implemented by appropriate electronics. When using optical fibers, correspondingly different primary light sources are to be used, which can be switched on and off independently of each other.

By using LEDs short switching times can be guaranteed. Thus, the best conditions are given to use the device for multi-step processes.

The illustrated figures show the applicability of the developed device and demonstrate possibilities for their production, the invention being not limited to the indicated uses and materials and combinations thereof.

Claims (5)

Apparatus for generating light patterns for multistep photogrammetric 3D surface reconstruction, comprising an illumination device comprising a large number of light sources arranged in a row ( 1 ), wherein the lighting means ( 1 ) are switched on and off in such a way that different light patterns ( 6 ), which are suitable for multistep photogrammetric 3D surface reconstruction, and lenses arranged side by side in a row (US Pat. 5 ), characterized in that the lenses ( 5 ) Are cylindrical lenses and are arranged so that they from the light sources ( 1 ) emitted light ( 3 . 3 ' ) in such a way that a light pattern ( 6 . 11 ) of parallel light strips ( 6 ) and that a one-dimensional reflector ( 2 ) or a cylindrical lens is provided for parallelizing or focusing the light beams of the illumination device in the direction transverse to the line. Device according to claim 1, characterized in that the lighting means ( 1 ) Are LEDs that form an LED line. A method for generating light patterns for multi-step photogrammetric 3D surface reconstruction, comprising the following steps - emitting light by means of a lighting device comprising a large number of light sources ( 1 ), - bundling the light emitted by the lighting means ( 3 . 3 ' ) by means of juxtaposed lenses ( 5 ), such that a light pattern ( 6 . 11 ) of parallel light strips ( 6 ) is generated, - switching on and off the lamps ( 1 ) such that different light patterns ( 6 ) suitable for multistep 3D photogrammetric surface reconstruction using an apparatus according to claim 1 or 2. A method according to claim 3, characterized in that a one-dimensional focusing of the light takes place. A method of scanning a surface, wherein light patterns are generated according to the method of claim 3 or 4 and the surface is scanned with a line scan camera.

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