WO2010020635A2

WO2010020635A2 - 3d-measuring system and 3d-measuring method

Info

Publication number: WO2010020635A2
Application number: PCT/EP2009/060664
Authority: WO
Inventors: Wolfgang Niem; Wolfgang Niehsen
Original assignee: Robert Bosch Gmbh
Priority date: 2008-08-19
Filing date: 2009-08-18
Publication date: 2010-02-25
Also published as: EP2326914A2; WO2010020635A3; DE102008041343A1

Abstract

Active 3D-measuring system (10) comprising a lens (12) for stripe light projection; a video camera (14) with analog video output; an analog operational amplifier circuit (16) which is designed so that it detects points (30) with high gray scale gradients in the analog video signal; and a microcontroller (18) which is designed such that it determines depths to the detected points (30).

Description

3D surveying system and 3D surveying method

The present invention relates to an active 3D surveying system for measuring objects and to a corresponding 3D surveying method.

Currently known 3D surveying systems are divided into active and passive systems. Active systems actively illuminate the system being measured with an artificial light source, while passive methods work alone with the ambient light. The actively illuminating methods include, for example, runtime-measuring laser scanners, range video sensors, active triangulation methods with a high-quality projector and digital video camera and ultrasound sensors. An example of a passive 3D surveying system is the stereo camera, for example.

Ultrasonic sensors today provide cost-effective 3D surveying systems, which are used in particular in the field of robotics. A disadvantage of ultrasonic sensors, however, is that you get only a small angular resolution and virtually only one 3D depth value per measurement.

With the other of the aforementioned active 3D surveying systems, many 3D depth values with good angular resolution can be determined per measurement. However, the costs for the systems are very high due to the very expensive individual components, such as digital camera or scanning mechanism, and due to the digital signal processing, which is why deliberately dispensed with the use of such systems in many technical applications.

Starting from this prior art, it is an object of the present invention to provide a low-cost 3D-surveying system with good angular resolution and high robustness. It is a further object of the present invention to provide a corresponding surveying method.

To achieve this object, the present invention provides an active SD surveying system with a striped light projection optics, a video camera with an analog video output; an analog operational amplifier circuit, which is designed such that it detects points with a high gray-scale gradient in the analog video signal, and a microphone rocontroller, which is designed such that it digitally determines the depth of the detected points.

In the active 3D-surveying system according to the invention, the detection of points with a high gray scale gradient and thus the detection of points projected onto the object to be measured strip light in the video signal is thus analogous using an analog operational amplifier circuit, for example, a video amplifier, differentiator, comparators and may have. Accordingly, on the one hand, an inexpensive video camera can be used and, on the other hand, expensive components that would be required for digital detection can be dispensed with. The subsequent further processing of the output signals of the analog operational amplifier circuit for determining depth values of the detected points can be carried out with the aid of an inexpensive microcontroller, preferably with the aid of a conventional 8-bit microcontroller, such as a PIC or the like.

The total cost of an active 3D surveying system with the structure described above is very small. Furthermore, many 3D depth values can be measured with good angular resolution per measurement with the SD measuring system according to the invention. This combination of positive properties opens up a broad spectrum of new application possibilities. For example, in the field of robotics, ultrasonic sensors that have low angular resolution and provide virtually only one 3D depth value per measurement can be replaced with no significant additional cost by 3D surveying systems according to the present invention, if a good angular resolution and a plurality of depth values are desirable per measurement. However, the surveying system according to the invention also has potential as a sensor for vehicle parking aids, measuring tools, monitoring systems, etc.

For synchronization between analog and digital signal processing, a sync separator between the analog operational amplifier circuit is provided according to a preferred embodiment of the present invention, which generates the required vertical and horizontal synchronization signals from the analog composite video signal.

The video camera is advantageously rigidly connected to an optical system, which improves the robustness of the active 3D surveying system according to the present invention. The optics preferably comprise an NIR light source, wherein an NIR filter is arranged in the beam path of the video camera, which at least partially filters out visible light. Accordingly, the points to be detected have a greater contrast or gray-scale gradient with respect to the environment, which is why the projected strip light is better detectable in the video image of the video camera.

Advantageously, the optics is further aligned such that the light stripes are emitted parallel to an axis of a coordinate system, which is based on the determination of depth values. In this way, the computational effort for determining the depth values or the scope of a look-up table (LUT), which is used to determine depth values, can be significantly reduced, as will be explained in more detail in the description of an embodiment of the present invention ,

In addition, the present invention provides a 3D surveying method, in particular using an active 3D surveying system of the kind described above, the method comprising the steps of: projecting strip light onto an object to be measured; Taking a video image of the object; Picking up an analog video signal; Searching for and detecting high gray scale gradient points on predefined search lines in the analog video signal; Associating the detected points with projected fringe lines; and determining depth values of the points. The depth values can be calculated or determined on the basis of a previously created LUT.

Preferably, the video image of the video camera is calibrated prior to carrying out the method according to the invention with respect to the projecting strip light.

The light stripes are advantageously emitted parallel to an axis of the coordinate system on which the determination of depth values is based in order to reduce the computational effort for determining the depth values.

Preferably, a further video image of the object is recorded as a reference image, wherein no light stripes are projected onto the object. In this way, a negative influence of the ambient light on the detection of points with a high gray-scale gradient can be minimized. Accordingly, incorrect measurements can be prevented.

Hereinafter, a preferred embodiment of the present invention will be described in more detail with reference to the accompanying drawings, wherein Figure 1 is a schematic view of a 3D surveying system according to the present invention;

Figure 2 is a schematic view of a camera image taken with the arrangement shown in Figure 1;

FIG. 3 is a diagram on the basis of which an exemplary sequence of the 3D surveying method according to the invention is explained using the arrangement illustrated in FIG. 1; and

Figure 4 is a view on which the calculation of the 3D depth values is explained.

Figure 1 shows a schematic view of one embodiment of an active SD surveying system according to the present invention, generally designated by reference numeral 10. The active 3D surveying system 10 comprises an optical system 12, a video camera 14 which is rigidly connected to the optical system 12, an analog operational amplifier circuit 16, a microcontroller 18 and an output device 20. The optical system 12 comprises an NIR light source which generates short-wave NIR radiation. Radiation in the form of light strips 22 in the direction of an object to be measured 24 radiates. In this case, the optics 12 is aligned such that the light strips 22 are emitted parallel to the y-axis of a coordinate system on which the calculation of the depth values is based. The light strips 22 are projected in the form of lines 26 onto the object 24 to be measured. These lines 26 are rectilinear and parallel to each other on a flat surface of the object 24, and are distorted accordingly when the surface topography of the object 24 is uneven. The video camera 14 takes a video image of the object 24 to be measured, wherein in the beam path of the video camera 14, an optical filter 28 is arranged, which filters out visible light at least partially, to detect the detectability of the projected using the NIR light source on the object to be measured 24 To improve light strip 26.

The video image recorded by the video camera 14 is supplied to the analog operational amplifier circuit 16 via an analog video output. The latter is designed such that it detects dots 30 with a high gray-scale gradient along predefined search lines 32 in the analog video signal and determines the intersection points of search lines 32 and light strips 26, as shown in FIG. The detected points 30 are then fed as an output signal of the analog operational amplifier circuit 16 to the microcontroller 18, which in the present case is an 8-bit microcontroller. The microcontroller 18 then digitally determines the depth values of the detected points 30, which can then be output via the output device 20. The output device 20 may be, for example, a display or the like.

To calculate the depth values, a preliminary calculation is first carried out in the microcontroller 18 in which the video camera 14 is calibrated with respect to the projected light strips 22. With the coordinate system defined in FIG. 4, each emitted light strip 22 can be described by a plane E: whose

Parameters to be determined during calibration. For each search line and each emitted light strip 22 then the corresponding 3D coordinates can be cut as a line of sight through a

Calculate pixel (x, y) and the respective light section plane E using the following equations, where f is the camera constant:

The computational effort can be significantly reduced if the design of the system ensures that the projected light slices are arranged parallel to the y-axis of the coordinate system. This is because the depth calculation is independent of y, i. The same calculation rule applies to each search line:

The determination of the Z values can be realized via an LUT. For a system with N = 8 light stripes 22, TZ = 200 coordinates / line and a Q = 8-bit quantization of the depth values one needs for example N * TZ * Q = 12.8 kbit. If an object 24 is to be measured with the aid of the active 3D measuring system 10, as shown in FIG. 1, the method steps illustrated in FIG. 3 are carried out. First, in a first step S1, the above-described calibration of video camera 14 and projected fringe lines 22 is carried out in advance, and in a step S2 a precalculation of the depth values is carried out for each search line / for each projected fringe light line. Thus, in step S3, light strips 26 are projected onto the object 24 with the aid of the optics 12, whereupon the illuminated object 24 is recorded with the aid of the video camera 14 in step S4. Optionally, another shot of the object 24 can be made using the video camera 14, with no light strips 26 projected onto the object 24. This further image can then serve as a reference image in order to avoid negative influences of the ambient light on the measurement result. Subsequently, in step S5, the analog video signal of the video camera 14 is tapped. Then, in step S6, in the analog video signal on the predefined search lines 30, double gradients in the gray value profile are searched for. The video system used is based on a hybrid (analog / digital) signal processing concept. Here, image signal gradients are detected by the analog operational amplifier circuit 16, which includes, for example, a video amplifier, differentiator, comparators and the like, and further processed on the simple 8-bit microcontroller 18. Synchronization between analog and digital signal processing is achieved through the use of a sync separator, which generates the vertical and horizontal sync signals required from the composite analog video signal. However, this module can be omitted if necessary, if the required signals can be tapped directly in the video camera 14, which is why the sync separator is not shown in the figures. The signal processing provides for each search line 32 a plurality of measurement points 30 which mark the centers of the double gradients. At a clock frequency of the microcontroller 18 of 16 MHz and an 8-bit counter with 4 MHz counting frequency, a usable resolution in the line direction of about 200 pixels is achieved.

After the points 30 have been located with a high gray scale gradient, the points 30 are assigned to the light strips 26 in the step S7. In the simplest case, this is done on the assumption that the sequence of the imaged light strips 26 corresponds to the sequence in which the Light strips 22 were emitted from the optics 12.

After the assignment of the points 30, the corresponding 3D coordinates can then be calculated for these pixels in step S8 using the equations (1), (2), (3) or (4), or depth values can be read out from a previously calculated LUT. If one assumes that it is possible to detect about 200 measured values / line for the analogue line detection, a depth resolution on the average of 0.5% based on the measuring volume can be estimated.

In contrast to the prior art, the present invention thus provides an active 3D-surveying system, which allows in a simple manner and using very inexpensive individual components to detect a plurality of depth values per measurement with good angular resolution. As a result, the production costs can be reduced many times over with conventional active 3D surveying systems. Reductions in the production costs of more than 90% are possible.

Claims

claims

An active 3D surveying system (10) comprising

- An optics (12) for striped light projection;

- A video camera (14) with analog video output;

an analog operational amplifier circuit (16) arranged to detect high gray level gradient dots (30) in the analog video signal; and

- A microcontroller (18) which is designed such that it determines depths to the detected points (30).

2. Active 3D surveying system (10) according to claim 1, characterized in that the microcontroller (18) is an 8-bit microcontroller.

3. Active 3D surveying system (10) according to any one of the preceding claims, characterized in that a sync separator for synchronization between analog or digital signal processing is provided.

4. Active 3D surveying system (10) according to any one of the preceding claims, characterized in that the video camera (14) is rigidly connected to the optics (12).

5. Active 3D surveying system (10) according to one of the preceding claims, characterized in that the optics (12) has an NIR light source and an optical filter (28) in the beam path of the video camera (14) is arranged.

6. Active 3D-surveying system (10) according to any one of the preceding claims, characterized in that the optics (12) is oriented such that they are emitted light strips parallel to an axis of a coordinate system, which is based on the determination of depth values.

7. A 3D surveying method, in particular using an active SD surveying system (10) according to one of the preceding claims, the method comprising the steps:

a) projecting strip light onto an object (24) to be measured;

b) capturing a video image of the object (24);

c) picking up an analog video signal;

d) searching for and detecting high gray level gradients (30) on predefined search lines in the analog video signal;

e) associating the detected points (30) with projected fringe lines; and

f) determining depth values of the points (30).

8. 3D surveying method according to claim 7, characterized in that a calibration of video image and projected strip light before performing steps a) to f).

9. 3D surveying method according to claim 7 or 8, wherein the depth values are calculated or determined on the basis of a pre-established look-up table.

10. 3D surveying method according to one of claims 7 to 9, wherein the optics (12) is aligned such that the light strips are emitted parallel to an axis of a coordinate system, which is based on the determination of depth values.

11. 3D surveying method according to one of claims 1 to 10, characterized in that in addition to the video image of the object taken in section b), a further image of the object is taken as a reference image, without stripe light being projected onto the object.