CN1292878A - Optical sensor system for detecting position of object - Google Patents

Abstract

The present invention proposes a special light source that produces horizontal bands of light. This band of light is reflected by objects within the ambient range of the detector system and directed to the photoelectric converter through a special imaging device. This imaging setup is described in such a way that distant objects are displayed with a slight distance from each other so that, for objects that are farther from the detector system, an objective lens of conventional linear resolution can be used throughout the entire image. better positional resolution on the surface. Preferably, the light emitting diode is arranged on the optical axis of the lenticular lens as the light emitting unit. An analysis unit analyzes the position of the electrical signal sent by the photoelectric converter, and then determines the distance of the object that reflects the light by means of triangulation.

Description

Light detector system to detect target position

The invention relates to a light detector system for scouting a target and determining the position of the target. Such a detector system may preferably be provided on an autonomous mobile system in order to orient it in an unknown environment.

These autonomous mobility systems, which are in the development and planning stages, will also be encountered more and more in everyday life in the future. These systems perform their assigned tasks independently by means of an orientation system that enables them to ascertain the scene of their environment, thus fulfilling transport and sanitation tasks. In addition to carrying out different path design algorithms and evaluation algorithms, the detector system is also of great significance for the autonomous mobile unit to detect the obstacles it encounters in the environment. In order for autonomous mobility systems to be attractive to customers, it is particularly important that these systems be manufactured cheaply and technically in large quantities. Therefore, in the context of autonomous mobile systems, detector systems for detecting the location of objects must be robust and inexpensive to manufacture.

From the state of the art a number of photodetector systems are known which detect objects using triangulation. For example, a dedicated test method uses strip lighting to implement active optical triangulation. For example, the main units that make up this test system are: a light source for strip lighting in space, a light imaging system, a two-dimensional image receiver, and an electronic device that processes and analyzes signals received by the image receiver. device. For triangulation, such a system requires a light source that illuminates only the strip space. An important characteristic of this light source is the surface density of its radiated optical power. The requirement for this light source is that the optical power must be high enough to be able to identify dark targets. Another characteristic of the light source is the density of the illumination band, which not only affects the size of the detected spatial range, but also affects the resolution of the measured object during position measurement.

At present, it is known that the light source irradiated into a light band has the following possibilities in implementation: a cylindrical lens is placed in front of the objective lens of the collimator, and the objective lens of the collimator is aligned with the laser light source or an incandescent lamp, a halogen lamp or Light from an arc lamp; the light from an incandescent or halogen lamp is parallelized by a collimator objective and fanned by an axicon. Here, the imaging system used must above all meet two main requirements. First, the spatial range to be measured must be imaged on the surface of the two-dimensional image detector. Second, ensure the desired positional resolution of the target to be measured. For this purpose, the minimum distance between objects which can still be resolved after imaging on the photoelectric converter is understood to be the spatial resolution. This minimum distance is determined by the imaging system, as well as by the converter used. Here, the requirements of the two tasks are contradictory: wide-angle imaging of as large a spatial extent as possible in the form of the entire half-space and sufficient distance resolution with the same objective. One possible way to extend the measurement range with such an imaging system is to use a wide-angle objective that produces an undistorted image. However, such an objective with multiple lenses has the disadvantage that it cannot image the entire half-space surrounding the objective. On the other hand, other objectives which image the entire half-space are distorted in operation and are expensive to acquire. Distorted objectives also affect the positional resolution in triangulation. Here, the image plane distance between the scattered light images of two adjacent objects closer to the imaging system is larger than the image plane distance of two adjacent objects farther away from the imaging system. As a result, the positional resolution gets worse with distance from the objective lens or imaging system. By using standard or aspherical refractive surfaces - as is often the case with standard objectives - objects that are far away from the imaging system will not be able to be imaged together with each other. In order to image these objects it is necessary to use an optical imaging unit which is optimal for the particular purpose and which cannot be found in the literature.

European publication EP 0358628 A2 has disclosed a triangulation system used on transportation tools in the article entitled "Constituting Visual Navigation and Obstacle Avoidance Structured Lightsystem (Visual navigation and obstacle avoidance structured lightsystem)". The tool works with strip illumination and a standard objective of the imaging system. The disadvantage of this scheme is that, on the one hand, the means of transport can only detect objects located in front of the direction of travel, and on the other hand, by using standard objectives, with sufficient resolution, only limited range and close-range targets can be targeted ranging. Imaging of the environment by means of an axicon and an objective lens is published in the following document: by R. A． Jarvis, J． C． Article by Byrne: "An automated guided vehicle with map building and path finding capabilities"; edited by R. C． Bolles and B． Roth, ed., "The 4th International Symposium on Robotics Research," pp. 497-504, MIT Publishing, Cambridge, MA, 1988; and Y. Yagi, Y． Nishizawa, M. "Map based navigation of the mobile robot using omnidirectional image sensor COPIS" by Yachida, Proceedings of the 1992 IEEE International Conference on Robotics and Automation, May 1992, Nice, France . The axicon used does not change the resolution of the system when moving away from the target. Also, the resolution is determined by the camera's objective lens. In J． Hong, X． Tan, B． Pinette, R. Weiss, E． M． Riseman's paper "Image-based Homing" (Proceedings of the 1991 IEEE International Conference on Robotics and Automation, Sacramento, CA, April 1991) discloses the use of a spherical sphere to image an environment . But it doesn't use the strip lighting that helps with triangulation. A disadvantage of such passive systems is that position information is difficult to deduce since triangulation is not possible and the target is not illuminated with light from a known position altitude. For analysis, a real-time image processing system must be introduced, which requires high computer capacity, so its cost is also high. In addition, P. Article by Greguss "PAL-Optics-Based Instrumentation for Space Research and Robotics (PAL-Optik basierende Instrumente fuer Raumforschung und Robot-Technik)", Journal of Lasers and Optoelectronics 28(5)/1996, 43-49 page, discloses the use of a PAL objective for navigation tasks on autonomous mobile robots. Greguss' PAL objective is a wide-angle imaging unit that includes two mirrors and a refractive aspheric surface, and is capable of imaging the entire half-space. It also describes the application of the PAL optical system to the robot, and it is used as the imaging unit of the obstacle recognition system of active triangulation.

The object of the present invention is to provide a light detector system which can be mounted on a vehicle, for example an autonomous mobile robot, which is technically simple to implement and which can detect obstacles in all directions around the vehicle, Among them, the imaging system of the optical detector system can not only locate the target less than 50cm away from the system, but also has a sufficient position resolution of about 5-10cm and a < 1° angular resolution.

This task is achieved according to the features of claim 1 . Developments of the invention are given by the dependent claims.

Said detector system preferably consists of light sources which surround the unit in a band to illuminate the surroundings of the autonomous mobile unit, since this allows simultaneous detection of obstacles or objects around the unit. In this case, it is also preferable to provide a plurality of light sources arranged one above the other, which are switched on at different time intervals in order to detect or measure different heights in the space. In addition, by using a special wide-angle imaging unit (the unit has only a single arched, spherical or aspherical mirror for light guidance), combined with an objective lens, a filter, and a photoelectric converter, the illuminated target Scattered light can preferably pass through them, wherein the surroundings are projected onto the converter by the imaging system. With such a device, this task can be carried out with as little technical effort as possible.

According to an extension of the present invention, by using a spline function to represent the shape of the aspherical mirror surface of the wide-angle imaging unit, optimal spatial coverage and optimal resolution can preferably be obtained. The spline function describes the shape of the imaging unit in such a way that, depending on the type of objective lens used, the distance range is represented exaggeratedly by the spline function. In this case, the distance range and the subrange of the non-spherical imaging unit valid for the respective distance range is described with a spline function such that adjacent polynomial functions have the same value and the same value at the transition points of the individual detection ranges. derivatives, so the function used is continuous and uninterrupted. It can preferably be achieved by using such an imaging unit that a simple objective lens with a conventional viewing angle can be adapted to the wide-angle linear imaging properties required by the extension of the invention. By using the spline function, it is possible to produce the desired predistortion of light scattered back from distant regions before the light passes through the objective, so that distant regions can be displayed at a higher resolution than usual Higher when using objective lenses. Imaging systems provided in this manner are a simple and economical solution for producing wide-angle, linear optical systems.

Hereinafter, embodiments of the present invention will be further described with reference to the drawings.

Figure 1 shows an embodiment of a detector system.

Figure 2 shows a possible arrangement of the light source used in side view.

Figure 3 shows a possible arrangement for creating a band of light around the detector system.

Figure 4 shows another embodiment for generating a band of light around a detector system.

Figure 5 shows another embodiment for creating a band of light around an imaging device.

Figure 6 shows a possible configuration of a detector system mounted on a vehicle or robot in side view.

Figure 7 shows a top view of the detector system and vehicle.

Figure 8 shows a detector system using a one-dimensional photoelectric converter.

Figure 9 shows an embodiment using a two-dimensional optical position detector.

A possible embodiment of the detector system is shown in FIG. 1 , which is illuminated by four light sources 1 surrounding a band of light. For these light source devices that emit light strips, special attention should be paid to make these light strips lie on a plane that is substantially parallel to the base on which the autonomous mobile unit equipped with detectors can move. If the device cannot be parallel, it will make triangulation more difficult, because when analyzing the reflected beam, these beams should meet the reflected target at different angular positions, so as to produce different results. to determine the distance to the target while triangulating. In this case, the light source 1 generates a light strip 2 that illuminates the space. The imaging unit 4 used projects the light scattered back from the target 3 via the objective lens 6 onto a photoelectric converter 7 , which is configured as a two-dimensional CCD image detector of the camera 5 in this arrangement. The photoelectric converter 7 is connected to an evaluation electronics 8 , for example equipped with a computer, which is part of a detector system for determining the position of the object. Utilizing the principle of active optical triangulation, the evaluation electronics 8 can determine the position of the object 3 from the image projected onto the photoelectric converter 7, wherein, in particular, the height of the objective lens 6 and the imaging unit 4 are applied depending on the height of the plane illuminated by the light strips. Imaging properties. Such a detector system is preferably used on a mobile vehicle 12, such as a mobile robot. In this case, the current control information of the transport means 12 or of the robot is determined by the evaluation electronics 8 , on the basis of which other operating paths of the unit can be planned. For example, if this information provides the position of the objects 3 , then the vehicle 12 passes under the objects 3 or has to pass between the objects 3 .

According to the embodiment shown in FIG. 1 , the optical axis of the imaging unit 4 is preferably perpendicular to the light strip 2 emitted by the light source 1 . According to this embodiment, the imaging unit 4 is implemented as a light unit with a spherical or aspherical mirror 9 , wherein in the imaging system the outside of the mirror 9 is used to image the reflected light beam. The light band emitted by the light source and the light beam reflected by the target 3 pass through the target 3 and then pass through the imaging unit 4 and project onto the photodetector 7, as shown by the optical path marked with numbers in the figure. Here, according to the imaging properties of the objective lens and the imaging unit 4 , the distance of the light beam projected onto the photodetector 7 reflects the distance of the detection target 3 in the detector system. According to the embodiment of the detector system shown in FIG. 1, any desired two-dimensional pattern detector 7 can be used. For example, a photodiode matrix may be used instead of a two-dimensional CCD detector as the photoelectric converter 7 .

FIG. 2 shows a possible principle embodiment of the light source 1 used in a side view. Here, the light source 1 shown in FIG. 2 consists of a lenticular lens 11 with an aspherical cross-section according to the application, and a light emitter 10, such as a light-emitting diode. These light emitters are located on the focal line of the lenticular lens 11 . Here, the light emitters 10 are arranged adjacently in sequence on the focal line of the lenticular lens 11 , so that the light emitting surfaces of the light emitters 10 point in the direction of the aspheric lenticular lens 11 . Here, the light emitted by the light emitter 10 first reaches the aspheric cylindrical mirror 11 and then exits in the light strip 2 through the mirror. By using an aspheric mirror structure matched with the light emitter 10, a parallel light strip can be irradiated by the light source 1. In this regard, it should also be mentioned that light-emitting diodes (LEDs) are an inexpensive, simple and small light source, and since the selected LEDs are arranged on the axis of the lenticular lens, a cost-effective light source.

One possible principle device for generating the light band 2 consists of a part of a lenticular lens, as shown in FIG. 3 . Here, the lenticular lens 11 is in a so-called off-axis arrangement with respect to the light emitter 10, therefore, only a part of the aforementioned lenticular lens 11 shown in FIG. 2 is used. Here, the light emitters 10 may preferably be composed of LEDs, and are arranged in sequence on the focal line of the aspheric lenticular lens so that their light-emitting surfaces face in the direction of the aspheric lenticular lens 11 . The use of such a light source also produces a collimated beam effective for the detector system. This can be seen from the optical path indicated by the arrow.

As shown in Fig. 4, another possibility is to rotate a parallel light beam in order to generate the illumination light band 2 around the imaging device. In this case, the rotating light beam 2 is produced in such a way that not only the light transmitter 10 but also the collimator optics 14 are rotated about the axis t. For example, in another such embodiment, both the light emitter 10 and the collimator optics 14 are fixed, while the light beam 2 moves around using a rotating mirror.

FIG. 5 shows another possible embodiment of the circumferentially emitting light strip 2 . According to this embodiment, the light strip 2 is produced by the axicon 15 . In this case, the light emitted by the light emitter 10 first passes through the collimator optics 14 in parallel and then passes through the axicon 15 in a fan-shaped manner with the desired light strip 2 . In this embodiment, for example, the light emitter 10 can be configured as an incandescent lamp, a halogen lamp, an arc lamp or a laser, for example.

FIG. 6 shows a possible configuration of a detector system mounted on an autonomous mobile unit 12, such as a maintenance robot. Figure 6 shows a side view. On the mobile system, a plurality of superimposed light strips can preferably be formed, which are emitted by a plurality of superimposed light sources 1 . Preferably, when the light strips 2 are generated, they are offset in time from one another and illuminated in a pulsating manner. Through the stacked arrangement of multiple light sources, a better height distinction can be achieved for obstacles. In order to detect and measure as far as possible all obstacles surrounding the vehicle, preferably two imaging units 4 are provided, which are arranged with their associated cameras 5 at two opposite corners of the vehicle 12 . During the triangulation of obstacles, the evaluation electronics ensure that the corresponding height position of the currently connected light source is determined in order to evaluate the triangulation result.

FIG. 7 shows a vehicle 12 equipped with the detector system, such as a robot, and the receiving range of the detector system 13 in a top view. As further shown in FIG. 7 , a single imaging unit 4 is mounted on two opposite corners of the mobile system 12 . If two imaging units 4 are arranged as shown in FIG. 7 , the detection range 13 of the light detector system can be extended to the entire environment of the mobile system 12 or to the entire space surrounding the mobile system.

FIG. 8 shows a possible implementation of a photoelectric converter 7 in the form of a one-dimensional photoelectric converter 7 . Passing through the objective lens 6, the light is projected by the imaging unit 4 onto a one-dimensional photodetector that moves or preferably rotates within the image plane. For example, the photoelectric converter 7 can be implemented as a one-dimensional position-sensitive detector, such as a CCD or PSD. By moving or preferably turning in the image plane, the one-dimensional photodetector is able to detect the light intensity distribution in the entire image plane on which the imaging unit 4 and the objective lens 6 image the spatial extent around the vehicle 12 . The measurement results obtained in this way can preferably be temporarily stored or analyzed synchronously with the rotational speed of the photodetector.

FIG. 9 shows another possible embodiment of a photoelectric converter 7 , which is represented here as a two-dimensional position-sensitive detector. In this embodiment, the photoelectric converter 7 is implemented as a two-dimensional position-sensitive detector behind the objective 6 and in its image plane. According to this embodiment, a light-tight disk 16 with a gap 17 is arranged between the objective lens 6 and the photoelectric converter 7 . During rotation of the disk, the region of the position-sensitive detector currently scanned by the slit 17 is always light-transmissive. For example, the slit 17 installed on the opaque disk 16 can only pass through the light of a certain spatial range (eg, the opening angle is 1°). In this way, directional resolution capabilities with arbitrarily small angles can be achieved. The chosen slit width depends on how much light is scattered back, or how sensitively the detector is operating, and how intense the light band illuminated by the light source is. When using a rotating parallel beam of light as the light strip 2 - as shown in the exemplary embodiment of Fig. 4 - it is not necessary to use the disk 16, since the directional resolution is ensured by the rotating light source. Overall, the use of the described detector system has the advantage that its receiving range is greater than that of known embodiments and that its imaging is more uniform than other known triangulated detector systems. With wide-angle imaging, the position of targets at greater distances from the detector system can be measured. For this purpose, the special configuration of the imaging unit 4 ensures a uniform resolution of the distance measurement over the entire detection range of the detector system. The distant targets are separated from each other, so to a certain extent, the imaging unit can correct the insufficient resolving power of the objective lens 6 at a long distance of the detector system.

Claims (14)

1. A light detector system for detecting the position of a target, which has a light source to illuminate the environment, a photoelectric converter that converts the intensity distribution of the light scattered back from the target into an electrical signal and transmits the electrical signal to the detector signal analysis system , It is characterized in that, The detector system has a light source (1), whereby one or more horizontally oriented light bands are generated in a plurality of spatial directions, and The photodetector system has a light imaging unit (4) to reflect light scattered back from the target (3) and project it onto a photoelectric converter (7), wherein the light imaging unit (4) has only a single mirror (9). 2. The photodetector system of claim 1, An objective lens (6) is arranged in the optical path between the optical imaging unit (4) and the photoelectric converter (7). 3. A photodetector system according to claim 1 or 2, The optical axis of the optical imaging unit (4) is perpendicular to the irradiated light strip (2), and there are four light sources. 4. Photodetector system according to one of the preceding claims, It has a wide-angle imaging unit (4), and the wide-angle imaging unit (4) has only one spherical or non-spherical mirror surface (9). 5. Photodetector system according to one of the preceding claims, Wherein the optical imaging unit (4) has at least one aspheric mirror surface (9) described by two spline functions. 6. Photodetector system according to one of the preceding claims, There are at least two superimposed light sources (1) for generating two superimposed light strips (2). 7. Photodetector system according to one of the preceding claims, With a moving, one-dimensional position-sensitive photodetector as a photoelectric converter (7). 8. Photodetector system according to any one of the preceding claims 1-6, A two-dimensional position-sensitive detector is provided as a photoelectric converter (7), wherein a spatial light modulator is provided in the optical path between the photoimaging unit (4) and the photoelectric converter (7). 9. According to the photodetector system described in claim 8, A rotating, slotted disc (16) or a liquid crystal modulator is installed therein as a spatial light modulator. 10. Photodetector system according to any one of the preceding claims 1-6, Wherein the photoelectric converter (7) is formed as a two-dimensional pattern detection matrix. 11. Photodetector system according to any one of the preceding claims 1-5, The light source (1) is formed as a rotating light source. 12. A photodetector system according to any one of the preceding claims 1-10, Wherein, the light source (1) is constituted by a light emitting unit (10), and is composed of a cylindrical mirror surface (11) with an aspherical cross section, wherein the light emitting unit (10) is placed on the cylindrical mirror surface (11) in the form of a light emitting diode. ) on the focal line so that the light-emitting surface of the unit (10) faces the lenticular lens (11). 13. A photodetector system according to any one of the preceding claims 1-10, Wherein, the light source (1) that produces the light band (2) consists of a known light emitting unit such as an incandescent lamp, a halogen lamp, an arc lamp or a laser, a collimator optics (14) and an axicon (15 )constitute. 14. Autonomous mobile unit having a detector system according to claims 1-13.

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