Patent Grant
8482720
1. Technical Field
The invention relates to a method for the detection of objects in a detection region in which at least one transmitted light bundle is transmitted into the detection region and transmitted light reflected back or remitted back by an object is detected, when present, by a receiver unit, with the distance of the object being determined by triangulation from the position of the at least one light patch generated by the light reflected or remitted at the receiver unit. The invention furthermore relates to an optical sensor for the carrying out of the method in accordance with the invention.
2. Description of Related Art
It is known to determine the distance of real objects in a detection region, for example, in optical sensors using the so-called triangulation principle. For this purpose, the sensor comprises a transmission unit, for example, a light emitting diode or a laser unit having a corresponding optical transmission system, said sensor transmitting a light beam into the detection region to an object to be detected, when present there. The light reflected or remitted by such an object is detected by a receiver which comprises a receiver unit and an optical receiver system which directs the reflected or remitted light to the receiver unit. The receiver unit comprises an array of photosensitive elements in known solutions. Both the transmitter and the receiver as a rule include a corresponding optical transmission or reception system which are arranged next to one another (so called “double-eye system”). The position of the detected light on the detector changes in dependence on the distance between the sensor and the reflecting object. There is a clear geometrical relationship between the point of incidence on the detector and the distance of the detected object. An evaluation of the light distribution on the receiver array, as a rule by evaluation of the location of the center of intensity of the light patch, can therefore be used for the distance determination. Such a triangulation sensor is described, for example, in DE 197 21 105 A1.
DE 102 38 075 B4 describes a triangulation sensor having two parallel measurement channels which are formed in that two lasers transmit light in parallel into the detection region, said light being detected by two correspondingly arranged arrays of light-sensitive elements.
The above-described known triangulation process can be error-prone or bring along an imprecise scanning distance estimate under certain circumstances, in particular if the object is shiny, that is it is not of a “Lambertian” remission characteristic, or if the transmitted light bundle simultaneously detects a plurality of objects at different distances in the detection range. In addition, it can be problematic if the transmitted light bundle is defected by shiny metallic surfaces on the way to or from the object to be detected or if reflective surfaces are present in the background. Objects moving in the detection region can also be problematic, in particular if the object moves from the deep in the direction of the transmitter/receiver arrangement. Finally, it can be problematic if an object has different remission or reflection properties at different surface regions. This namely has the result that the energetic center of intensity of the reflected light deviates from the geometrical center of intensity so that the center of intensity evaluation becomes imprecise at the array of light-sensitive elements.
It is known for light barriers to transmit light through a monitored zone onto a stationary two-dimensional reflector or retroreflector. The reflected light is reflected back to a receiver again through the monitored zone. An object which is located in the monitored zone blocks the light path so that a corresponding signal can be generated. It is known from DE 10 2005 060 399 A1 for light barriers to use two-dimensional receiver arrays to be able to detect deviations from a light patch geometry which is expected when there is no object in the monitored zone.
Other systems work in accordance with the camera principle in which an image of a scene is taken and is supplied completely to an evaluation unit. Specific features, for example object shape, object location or object movement, are then analyzed and evaluated with the help of corresponding image processing algorithms to obtain information on the object located in the detection region.
DE 10 2005 062 258 A1 describes a triangulation sensor in which a distance determination in accordance with the triangulation principle is carried out. For this purpose, a multi-reception element is used on whose operation the breadth of the signal curves of the reception light patches on the multi-reception element is determined. Differently shiny objects can thus be detected reliably and optionally a printing or structuring of the object surface can be evaluated.
DE 10 2004 053 219 B3 describes an optical sensor in which the energy distribution of a light patch is evaluated at a receiver unit by column-wise or row-wise summation of the output signals.
A method for the detection of objects in a detection region having the features of the preamble of claim 1 is known from DE 10 2007 003 024 A1.
It is the object of the present invention to provide a method for the detection of objects and an optical sensor which provide a measurement of the distance and an evaluation of additional information to increase the precision and to convey additional object information.
This object is satisfied by a method for the detection of objects having the features of claim 1 and an optical sensor having the features of claim 11. Dependent claims are each directed to preferred embodiments or embodiment types.
It is in particular provided in accordance with the invention that an M×N matrix of reception elements is used as the receiver unit, where M and N are larger than one. In addition to the position of the reflected or remitted light, from which, for example, the distance the of the object can be determined with the help of triangulation by evaluation of the center of intensity, in accordance with the invention the two-dimensional energy distribution of the at least one received light patch within the light incident on the receiver unit is evaluated to be able to determine further information on the object in addition to the distance of the object determined by the triangulation. The use of a two-dimensional matrix of reception elements in this respect makes it possible that the light distribution or energy distribution is measured and evaluated in two dimensions. In this way, further information is available, in addition to the distance of the object determined by triangulation, which can be used to increase the precision of the distance measurement and/or, for example, to determine movement parameters or the surface property of the object located in the detection region. A measured value derived from the energy distribution of the light patch or a correspondingly derived measured curve can then be made available to an evaluation unit, for example, for further processing. Complex image processing algorithms are not necessary.
A particular embodiment of the method in accordance with the invention evaluates the movement of the light patch at the receiver unit to draw a conclusion on the movement status of the object in the detection region, in particular its direction of movement. It is possible in this respect by the two-dimensional matrix arrangement of reception elements not only to determined the movement of the object when its distance from the transmitter/receiver unit changes, but also in the lateral direction.
In an embodiment of the method in accordance with the invention, the contour of the light patch is evaluated to draw a conclusion on the location of the object with respect to the transmitted light bundle. It can in particular be determined by evaluation of the contour whether the transmitted light bundle is completely incident on the object.
On the other hand, a conclusion on the number of objects in the monitored zone can also be drawn from the contour of the at least one light patch.
Another advantageous embodiment of the method in accordance with the invention evaluates the light patch size at the receiver unit to draw a conclusion on the distance of the detected object from it. It is possible in this manner to obtain, in addition to the measured distance value determined by triangulation, a further estimate of the distance so that the precision of the measurement method is considerably increased. For this purpose, in particular the determined light patch size can be compared with a light patch size such as was measured with an object at a known distance and the distance can be estimated by application of physical imaging laws to the optical receiver system.
The energy distribution or the contour of the light patch received at the receiver unit is utilized in another preferred embodiment of the method in accordance with the invention to obtain information on the surface property of an object in the detection region. Inhomogeneities of the surface of the object are thus reflected in the two-dimensional energy distribution of the reflected or remitted light patch in a manner still to be described.
If, on the other hand, for example, the distance of the object is known from the triangulation evaluation, it is possible to conclude from the size of the light patch whether the object is a reflective or matte (Lambertian) target. On the other hand, with a known reflectance property of the object to be detected, when present, the light patch size can be used as described for the additional securing of the distance determination.
To obtain information on the homogeneity of the object surface, the homogeneity of the light reflected or remitted at the object is evaluated, for which purpose a light patch quality value can be determined in accordance with the invention. In this respect, it can be a case, for example, of the standard deviation of the spatial energy distribution or of the mean contrast. Such a value provides a value on the surface property without any great evaluation algorithms which can be used, for example, to be able to distinguish individual objects which, for example, have different portions of reflective regions.
It is generally possible to evaluate any individual reception element of the matrix-like receiver unit individually. It is, however, particularly economic, fast and cost-effective if the energy distribution of the light patch at the receiver unit is only determined for subsets which have more than one reception element. Such a process management is in particular suitable if objects to be detected, when present, whose distance should be determined are known, at least largely, with respect to their reflectance properties or remission properties and/or with respect to their sizes so that not the total receiver unit is of interest, but rather only a subset in which the object to be detected will be located as a rule.
An alternative embodiment provides that the energy distribution of the light patch at the receiver unit is evaluated by column-wise or row-wise summation of the output signals of the reception elements of the receiver unit. In this manner, only a very small number of individual values arises which corresponds to the number of rows or columns and which—at least with selected applications—nevertheless provides sufficient information for the identification of objects to be detected.
The method in accordance with the invention can also use structured transmitted light which is reflected or remitted, for example, at a plurality of different points of an object to be detected or which illuminates different regions of the detection region. Such an embodiment delivers additional spatial information on the location of the object or objects in the detection region or on the location of different surface regions at one or more objects.
An optical sensor in accordance with the invention has at least one light transmitter for the transmission of at least one transmitted light bundle and has at least one receiver unit which is arranged such that the transmitted light bundles reflected or remitted back from an object arranged in the detection region are incident onto the receiver unit. An evaluation unit is designed such that, in accordance with the triangulation principle, it can draw a conclusion on the distance of the object from the position, preferably from the center of intensity position, of the transmitted light reflected back or remitted back from an object in the detection region and incident on the receiver unit. In accordance with the invention, the receiver unit has a plurality of reception elements arranged in the form of an M×N matrix, with M and N each being larger than one. The at least one transmitter is made in accordance with the invention such that it generates at least one laterally extended light bundle which forms at least one light patch after reflection at an object in the detection region, said light patch being incident on a plurality of reception elements in the two lateral dimensions. The lateral dimensions in this respect designate the spatial directions which are substantially perpendicular to the transmitted light bundle.
The optical sensor in accordance with the invention has an evaluation unit which is made such that it can evaluate the two-dimensional energy distribution of the at least one light patch in addition to the position of the at least one reflected or remitted light patch to be able to determine further information on the object in addition to the distance of the object determined by triangulation.
Light sources which generate an extended light patch are possible as the light transmitters. The use of a light emitting diode is particularly economic and simple.
A CCD array or a CMOS array is particularly suitable for the receiver unit which has a matrix-like arrangement of reception elements.
The invention will be explained in detail with reference to the enclosed Figures which represent arrangements or process managements in accordance with the invention only in a schematic representation not necessarily true to scale. There are shown
a the light patch on a receiver unit with a representation of the column-wise or row-wise summation of the energy values or intensity values;
a an example of a light patch at the receiver unit after reflection of the transmitted light at an object which has only partially entered into the transmitted light bundle;
b an arrangement which produces a light patch in accordance with
a and 8b examples of light patches at the receiver unit which are generated at different times by reflection or remission of the transmitted light of an object moving in the X direction;
a an example of a light patch geometry at the receiver unit after reflection of the transmitted light at a plurality of objects in the detection region;
b a representation of an arrangement which produces a light patch geometry in accordance with
a to 10c the time curve of the light patch geometry which is produced at the receiver unit by a moving object when light is also reflected to the receiver unit without any object in the detection region;
The receiver unit 26 comprises individual reception elements 28 which are arranged in the form of a two-dimensional matrix.
The geometry shown is a so-called double-eye geometry since the transmitter and the receiver each have a separate optical system and are arranged next to one another in a system 10. The distance of the object 12 can be determined in accordance with the triangulation principle from the distance between the transmission unit 16 and the light patch 30 formed by the reflected light on the receiver unit 26. A plurality of reception elements in the Y direction enable the determination of the center of intensity of the light patch in this direction. Objects 12 at different distances 14 in this respect generate light patches 30 with different positions in the Y direction of the indicated coordinate system.
The individual light reception elements 28 are formed, for example, by photodiodes. The total reception element can in particular be made as a CCD chip or as a CMOS chip.
As is indicated in
The reception elements 28 are of different sizes in the Y direction of the indicated coordinate system in order to compensate the resolution of the system dependent on the distance of the object 12 in a manner known per se.
A plurality of rows of reception elements 28 are arranged next to one another in the X direction of the indicated coordinate system. There are three rows in the example of
An evaluation unit 32, to which the reception unit 26 is connected for the evaluation, is likewise only shown schematically. The evaluation unit can, for example, additionally have a display or similar to display the parameters determined during operation, in particular the distance 14 of the object 12.
The number of reception elements 28 shown in
As is shown in
a shows a receiver unit 26 having reception elements 28. 64 reception elements 28 are shown here; as a rule, however, for example, CMOS chips with 64×64 reception elements 28 are used. A light patch 30 is shown such as arises on the receiver unit 26 when a matte object 12 is located in the detection region and is completely struck by the transmission light bundle 18. The corresponding geometry is shown schematically in
The columns or rows can in this respect be evaluated in a preset order or in an algorithm taking account of the previous sensor state. For example, an algorithm can thus be preset which only evaluates the column S2 when the value from column 1 has exceeded a specific threshold.
The energy distribution of the light patch 30 of an ideally homogeneous object 12 is shown in dashed lines in the energy distributions to the side of and beneath
In a similar manner, not shown here, it can also be recognized whether there is an edge in the object which separates different reflection regions from one another.
a and 8 shows similar images at a time T0 and a time T0+dT. An object is shown here which moves laterally into the detection light beam 18 in the X direction. The light patch 30 is shown on the reception element 26 such as arises when an object 12 moves laterally into the detection light beam in the X direction. A movement of the object in the direction of the triangulation sensor 10 or away from this would effect a movement of the light patch 30 in the Y direction so that such a movement can be easily distinguished form a lateral movement. In a simple manner, the speed or the direction of movement can additionally be determined when a check is made of which column or of which reception element 28 is first struck by reflected light.
a shows the receiver unit 26 having the reception elements 28 on which a light patch 30 is shown which comprises two parts here. This received image can arise when two objects 12a and 12b are located in the detection region 20, as is shown in
a to 10c show corresponding images which arise when a closure is located at the end of the detection region 20 remote from the detector. A light patch from this closure will also arise at the receiver unit 26 without an object in the detection region 20, as is shown schematically in
It is finally possible that the different assessment criteria shown, for example, in
The triangulation sensor 10 in accordance with the schematic drawing of
For this purpose, the position of the light patch 30 on the receiver unit is evaluated in its location in the Y direction of the indicated coordinate system of
The object distance can additionally also be determined from the size of the light patch via the imaging laws of the optical receiver system to obtain a redundant measurement of the distance 14 of the object 12 from the triangulation sensor 10.
in addition, the system in accordance with the invention still provides useful information on the lateral energy distribution of the light patch 30 on the receiver unit 26, in particular in the X direction, which can be evaluated as follows, for example:
A light patch 30 in accordance with
If the object, for example, has some reflective regions, a light patch arises at the receiver unit 26 such as is shown in
As described,
Finally, the time curve of the light patch 30 at the receiver unit 26 can be observed so that information on the direction of movement, on the speed of movement and on other movement parameters can be extracted, as is shown in
As described, the direction of movement, the speed of movement, etc. of an object 12 which produces a light patch 30 on the receiver unit 26 can be read off from a time sequence in accordance with
An energy distribution in the X direction and Y direction, such as is shown, for example, in
The evaluation of the individual signals is shown by way of example in
In accordance with the invention, the homogeneity of the light patch can also be evaluated, for which purpose, for example, the standard deviation or a mean contrast is determined over the area of the two-dimensional receiver unit. It is sufficient in a number of cases to compare this measured value with a previously taught measured value to enable a reliable object identification. In addition, a conclusion can be drawn from such a light patch quality value whether a signal is based on a defective evaluation.
The determined and evaluated evaluation criteria can be compared with fixed or settable/taught thresholds to derive measured signals or switch signals for the control or regulation of systems.
In another embodiment a plurality of portion of a structured light beam are used which results in a pattern such as is shown in
The arrangement in accordance with the invention can be used in a very versatile manner, increases the robustness of the detection and serves for the independence of in particular specific object properties, object geometries or object entry directions. Information on the movement of the object, on the entry direction, on the entry speed, on the presence of reflective backgrounds (“passive interferers”) or on light source background (“active interferers”) is possible in addition to the determination of the distance.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 061 035 | Dec 2008 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 7460250 | Keightley et al. | Dec 2008 | B2 |
| 7724353 | Iizuka | May 2010 | B2 |
| 20050111009 | Keightley et al. | May 2005 | A1 |
| 20080137103 | Torii et al. | Jun 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 197 21 105 | Nov 1998 | DE |
| 102 38 075 | Mar 2004 | DE |
| 10 2004 003 386 | Sep 2004 | DE |
| 10 2004 005 460 | Sep 2004 | DE |
| 10 2004 053 219 | Apr 2006 | DE |
| 10 2005 037 490 | Feb 2007 | DE |
| 102005041466 | Mar 2007 | DE |
| 10 2005 060 399 | Jun 2007 | DE |
| 10 2005 062 258 | Jul 2007 | DE |
| 10 2006 057 878 | Apr 2008 | DE |
| 20 2007 002 260 | Jun 2008 | DE |
| 10 2007 003 024 | Jul 2008 | DE |
| 1 496 335 | Jan 2005 | EP |
| 1 988 389 | Nov 2008 | EP |
| Entry |
|---|
| Burns, R.D., et al., “Object Location and Centroiding Techniques with CMOS Active Pixel Sensors”, IEEE: Transactions on Electron Devices, vol. 50, No. 12, pp. 2369-2377, (Dec. 2003). |
| Hong, C.S., et al.,“Single-chip Camera Modules for Mosaic Image Sensor”, Proceedings Paper, vol. 4306, SPIE, pp. 1-13, (May, 15 2001). |
| Number | Date | Country | |
|---|---|---|---|
| 20100157278 A1 | Jun 2010 | US |
