DE102011089636A1 - Light propagation time camera system, has evaluation unit connected with light propagation time sensor and photosensor and designed to start distance measurement depending on signals of photosensor - Google Patents

Abstract

The system (1) has an evaluation unit (130) connected with a light propagation time sensor i.e. photomix detector, for determining distances based on electrical signals of the sensor. The unit is connected with a photosensor (100) and designed to start distance measurement depending on signals of the photosensor. Light signals are detected in a listening phase over the photosensor. Integration time and/or illumination intensity of an illumination module and/or a phase number are adjusted depending on an interfering light signal.

Description

The invention relates to a light cycle camera and a method for operating such according to the species of the independent claims.

The time-of-flight camera system or the time-of-flight camera should not only include systems which determine distances directly from the time of light, but in particular all the time of flight or 3D TOF camera systems which obtain transit time information from the phase shift of an emitted and received radiation. In particular, PMD cameras with photonic mixer detectors (PMD) are suitable as the light transit time or 3D TOF cameras, as described, inter alia, in the applications EP 1 777 747 . US Pat. No. 6,587,186 and also DE 197 04 496 described and, for example, by the company, ifm electronic gmbh 'as frame grabber O3D relate. In particular, the PMD camera allows a flexible arrangement of the light source and the detector, which can be arranged both in a housing and separately. Of course, the term camera or camera system should also encompass cameras or devices with at least one receiving pixel, such as, for example, the distance measuring device O1D of the Applicant.

The object of the invention is to improve the reliability and accuracy of the distance measurements of a light runtime camera.

The object is achieved in an advantageous manner by the inventive time of flight camera and the method for operating such according to the independent claims.

Advantageously, a light cycle camera is provided, with a light transit time sensor, which is constructed in particular as a photonic mixer. In addition to the light transit time sensor is a photosensor, both sensors are connected to an evaluation unit. The evaluation unit is designed such that a distance measurement is started in dependence on signals of the photosensor.

This procedure makes it possible to adapt the measuring sequence of the light runtime camera to light events in the environment.

Likewise advantageously, a method is provided for operating a light-propagating time camera, in which light signals are detected in a listening phase via a photosensor, and a distance measurement is initiated as a function of the light signals detected in the listening phase.

Preferably, a distance measurement is initially not initiated when light signals of a foreign light transit time camera system are detected in the listening phase.

In response to the detected light signals, its own measurement and / or evaluation parameters can advantageously be determined and suitably adapted as a function of a detected interfering light signal.

In a further preferred refinement, a separate modulation frequency is determined deviating therefrom in the case of a detected foreign modulation frequency.

Furthermore, it is advantageously provided to adapt an integration time and / or a phase sequence and / or measurement pauses as a function of the detected interfering light signal.

The invention will be explained in more detail by means of embodiments with reference to the drawings.

They show schematically:

1 the basic principle of a time-of-flight camera based on the PMD principle,

2 a modulated integration of the generated charge carriers,

3 an inventive time of flight camera with photosensor and signal evaluation chain,

4 a process sequence which controls the time of flight measurement on the basis of a "listening phase",

5 a possible sequence according to the invention, in which the distance measurements of two time-of-flight cameras are coordinated one after the other with the aid of listening phases,

6 a possible sequence according to the invention, in which the distance measurements of two light transit time cameras interleave in time.

In the following description of the preferred embodiments, like reference characters designate like or similar components.

1 shows a measurement situation for an optical distance measurement with a light transit time camera, as for example from the DE 197 04 496 is known.

The light transit time camera system 1 comprises a transmitting unit or a lighting module 10 with an illumination light source 12 and associated beam shaping optics 15 as well as a receiving unit or TOF camera 20 with a receiving optics 25 and a light transit time sensor 22 , The light transit time sensor 22 has at least one pixel, but preferably a pixel array, and is designed in particular as a PMD sensor. The receiving optics 25 typically consists of improving the imaging characteristics of multiple optical elements. The beam shaping optics 15 the transmitting unit 10 is preferably formed as a reflector. However, it is also possible to use diffractive elements or combinations of reflective and diffractive elements.

The measurement principle of this arrangement is essentially based on the fact that, based on the phase shift of the emitted and received light, the transit time of the emitted and reflected light can be determined. For this purpose, the light source 12 and the light transit time sensor 22 via a modulator 30 acted upon together with a certain modulation frequency with a first phase position a. The light source sends according to the modulation frequency 12 an amplitude modulated signal with the phase a. This signal or the electromagnetic radiation is in the illustrated case of an object 40 reflects and hits due to the distance traveled correspondingly phase-shifted with a second phase position b on the light transit time sensor 22 , In the time of flight sensor 22 becomes the signal of the first phase a of the modulator 30 mixed with the received signal having the second time phase condition b, mixed, wherein the phase shift or the object distance d is determined from the resulting signal.

This basic principle is schematic in 2 shown. The upper curve shows the time course of the modulation frequency with the illumination 12 and the light transit time sensor 22 be controlled. The object 40 Reflected light b strikes the light transit time sensor out of phase in accordance with its light transit time t _L 22 , The light transit time sensor 22 collects the photonically generated charges q in a first accumulation gate Ga during the first half of the modulation period and in a second accumulation gate Gb in the second half of the period. The charges are typically collected or integrated over several modulation periods. From the ratio of the charges qa, qb collected in the first and second gate Ga, Gb, the phase shift and thus a distance of the object can be determined.

3 shows a construction according to the invention with a light time camera or camera system 1 and a spatially parallel photosensor 100 , The photosensor 100 has its own look 50 which is preferably configured such that the photosensor 100 essentially the same spatial area as the light transit time sensor 22 detected. The photosensor is in the example shown first with a signal conditioning 110 and subsequent with an AD converter 120 connected. The processed and digitized signal is thereafter in an evaluation unit 130 further processed.

The photosensor is preferred 100 constructed from at least one fast photodiode, which allows to detect light changes or modulation frequencies preferably in the range of 1 MHz to 100 MHz or possibly higher. Of course, the photosensor 100 also be constructed as a phototransistor or other photosensitive elements.

Advantageously, it is provided to detect interfering signals by means of a frequency analysis. In the simplest case, it may already be sufficient to carry out a frequency based on edge detection or, for example, a "peak / no peak" analysis. In such a case, the A / D converter does not necessarily need to sample twice the maximum modulation frequency. Optionally, a circuit is conceivable in which it is possible to dispense with the frequency analysis on an A / D converter.

Preferably, an FFT analysis is proposed, but also alternative frequency analysis methods are conceivable.

Based on the frequency analysis, it is provided according to the invention, this information the light transit time camera system 1 or the time of day camera 20 to provide.

A measurement according to the invention can be represented for example as follows: The photodiode or another suitable photosensitive component receives the light coming from the surroundings. Ideally, the photosensitive member observes the same aperture angle range as the objective 25 the light runtime camera 20 , The signal is then examined for modulation. If a modulation is detected, then the medium is "busy", otherwise "free". If you also check during your own measurement or modulation, your own signal must be taken into account accordingly (filtered out or detected and ignored). When the medium is busy it is waiting. When the medium is free, the camera can measure the time of flight. Preferably, all participating camera systems work cooperatively, ie they must all first check before they measure up. It should also be ensured that all systems involved have their turn.

It can, for. This can be done, for example, by introducing a pause or waiting time after each measurement before the next test in order to prioritize other systems that have been waiting for longer. The waiting time should preferably be random within reasonable limits, so that not several systems waiting to measure or send simultaneously. Thus, the probability of interference is reduced by simultaneous measurement.

One possible procedure is in 4 shown schematically. Before the actual distance measurement begins, a listening or test phase is connected upstream. If there is an interfering signal, the listening phase continues, otherwise the measurement is started. After successful measurement, the system may return to the listening phase after a break.

5 shows the procedure according to the invention with reference to a first and second time of day camera system L1, L2 or Lichtlaufzeitkamera. The first camera L1 begins with a first listening phase H1. Since there is no disturbing extraneous signal in this listening phase, camera L1 begins to measure the distance. In the illustrated case, the distance measurements become for different phase differences between illumination 10 and light transit time sensor 22 , namely 0 °, 90 °, 180 °, 270 ° performed. This is followed by a measurement break in which other cameras are given the opportunity to make their own measurements.

The second time-of-flight camera L2 has started a little later with the first listening phase H1 and in the first high-phase H1 receives a modulated light of the first time-of-flight camera system L1. This signal is also present in the second and third listening phases H2, H3. During the fourth listening phase H4, the distance measurement of the first camera L1 is ended, so that no disturbing signal is to be detected in this listening phase H4. According to the invention, the second camera L2 then initiates its own distance measurement.

In the illustrated case, the listening phases follow one another with an equidistant time interval. In a further embodiment of the invention, it is provided to set the time intervals within reasonable limits at random. This has the advantage that, in particular with the use of more than two cameras, a random temporal synchronicity of the listening phases can be avoided.

In a further embodiment, it can also be provided to allow the listening phases to begin immediately after the distance measurement or, if appropriate, also to carry out parallel listening during the distance measurement. This has the advantage that depending on the interferer further information about the extraneous light sources can be detected.

The listening phases preferably have the same time length in order to simplify, for example, an FFT evaluation. Of course, different lengths are conceivable and in particular a continuous Horchphase. Depending on the desired application, different evaluations can be carried out based on the signals detected by the photosensor. In particular, the measurement properties of a foreign light cycle camera can be determined, such as the length of the measurement intervals, breaks, etc.

6 shows an embodiment in which both cameras L1, L2 can perform distance measurements with larger pauses. The pauses between the distance measurements for the different measurements with different phases are so large that the second or possibly also a third camera can carry out its own distance measurements within these measurement pauses.

In the case shown, the second time-of-flight camera L2 permanently listens. After evaluating the received light signals, the exact measurement cycle of the first camera L1 can be determined and the measurement cycle of the second camera L2 can be adjusted accordingly. In the present case, it is provided to place the distance measurements for the individual phase positions in the measurement pauses of the phase measurement of the first camera L1.

In addition, other reaction options are possible. If, for example, the measuring camera detects that the foreign camera does not provide suitable measurement pauses, alternative measurement options may possibly be provided. For example, it could be provided to change its own modulation frequency and / or to change the sample length or possibly even if the receiver and transmitter are configured accordingly to change the wavelength of the illumination. In addition, in non-exhaustive enumeration, frame rates, integration rates, and evaluation algorithms can be changed and / or adjusted. It is also conceivable to change the number of phase measurements, for example to reduce the measurements to initially two phases.

Advantageously, the procedure according to the invention can be used in particular for cooperating time of flight cameras. As already shown above, it is quite possible in the listening phases to recognize basic characteristics of a foreign camera. According to the recognized Properties are adjusted by the listening light time camera according to their own measurement parameters.

Cooperating time of flight camera arrangements with more than two cameras are also conceivable in which the cameras use the detected light signals to recognize all the cameras operating in the overall arrangement and to adapt their measuring cycles accordingly.

If no cooperating cameras are detected, or if the light signals are caused by other interferers, appropriate remedial measures, as already described above, can be initiated depending on the detected disturbance property in order to minimize the influence of the interferer.

If, for example, a light signal has been detected whose modulation frequency disturbs its own modulation frequency, for example because it is essentially equal to or multiple from one another, then advantageously its own modulation frequency can be changed.

In the event that no suitable measures for reducing or avoiding impairments to one's own measurement performance can be taken by disturbing external light signal by the inventive time of day camera system, a subsequent processing system, an impaired measurement performance or data integrity or unavailability can be signaled. This is particularly advantageous in safety-relevant systems.

LIST OF REFERENCE NUMBERS

1

Time of flight camera system

10

Transmitting unit, lighting module

12

Illumination light source

15

Beam shaping optics

20

Receiving unit, TOF camera

22

Transit Time Sensor

25

receiving optics

30

modulator

40

object

50

optics

100

photosensor

110

signal conditioning

120

ADC

130

evaluation

q

charges

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1777747 [0002]
• US 6587186 [0002]
• DE 19704496 [0002, 0021]

Claims (9)

Photocell camera, with a light transit time sensor ( 22 ), which is constructed in particular as a photonic mixer, and with an evaluation unit ( 130 ), which with the light transit time sensor ( 22 ), and based on electrical signals of the light transit time sensor ( 22 ) Distances, characterized in that the evaluation unit ( 130 ) additionally with a photosensor ( 100 ), the evaluation unit ( 130 ) is designed such that a distance measurement in dependence on signals of the photosensor ( 100 ) is started. A time of flight camera according to claim 1, wherein the photosensor ( 100 ) separately from the light transit time sensor ( 22 ) is arranged. Photoflash camera according to one of the preceding claims, in which the photosensor ( 100 ) monitors the same solid angle as the light transit time sensor ( 22 ). Method for operating a light transit time camera, characterized in that in a Horchphase via the photosensor ( 100 ) Light signals are detected, and a distance measurement is initiated in dependence on the detected light signals in the Horchphase. Method according to one of the preceding method claims, in which a distance measurement is initially not initiated when light signals of a foreign light transit time camera system are detected in the listening phase. Method according to one of the preceding method claims, in which the own measuring and / or evaluation parameters are determined as a function of a detected disturbing light signal. Method according to one of the preceding method claims, wherein at a detected foreign modulation frequency a separate deviating modulation frequency is determined. Method according to one of the preceding method claims, in which, depending on the detected interfering light signal, an integration time and / or an illuminance of the illumination module ( 10 ) and / or a number of phases and / or a phase order and / or measurement pauses are adjusted. Method according to one of the preceding method claims, in which the light transit time camera system signals a fault and / or a reduced measurement performance or data integrity and / or unavailability as a function of the detected interfering light signal.

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