DE102017204665A1 - Time of flight camera system and method for determining system parameters of such a system - Google Patents

Abstract

A light transit time camera system with a time of flight camera and a modulatable illumination, wherein the time of flight camera has a light transit time sensor with a plurality of time of flight pixels, the time of flight pixels having charge transfer charge gates (Gam, Gbm) and charge integration integration nodes (Ga, Gb), wherein it is intended to determine an amplitude gain; that an amplitude and an intensity are recorded for different distances.

Description

The invention relates to a method for determining system parameters of a light transit time camera system with the aid of a calibration device according to the independent claim and to a light transit time camera system.

With the time of flight camera system, it is intended to encompass all the time of flight of light or 3D TOF camera systems which acquire 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 they are used, inter alia, in the DE 197 04 496 A1 described and for example by the company, ifm electronic gmbh 'or, pmdtechnologies ag' as a "frame grabber O3D" or as "CamBoard pico flexx" 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.

The object of the invention is to improve the accuracy of a distance measurement of a light transit time camera system.

The object is achieved in an advantageous manner by the method according to the invention.

• bei dem das Lichtlaufzeitkamerasystem eine Lichtlaufzeitkamera mit einem Lichtlaufzeitsensor mit wenigstens einem Lichtlaufzeitpixel aufweist, wobei das Lichtlaufzeitpixel ferner zur Ladungsintegration einen ersten und zweiten Integrationsknoten aufweist,
• wobei die Kalibriervorrichtung ein Lichtleitsystem mit Lichtwellenleiter unterschiedlicher Länge aufweist
• oder derart eingerichtet ist, dass das Lichtleitsystem aus einem Satz von Lichtwellenleitern unterschiedlicher Länge ein Lichtwellenleiter wahlweise integrativ aufnimmt,
• mit einer Einkoppelvorrichtung zur Erfassung eines von einer Beleuchtung des Lichtlaufzeitkamerasystems ausgesendeten Lichts und zur Einkopplung dieses Lichts in die Lichtwellenleiter oder den Lichtwellenleiter
• und mit einer Ausleuchtungsvorrichtung zur Beleuchtung des Lichtlaufzeitsensors der Lichtlaufzeitkamera über deren Kameraoptik mit dem Licht der Lichtwellenleiter oder des Lichtwellenleiters,
• wobei zur Durchführung des Verfahrens die Kalibriervorrichtung in einem vorgegebenen Abstand zur Lichtlaufzeitkamera angeordnet ist,
• mit den Schritten:
  • - Ermittlung von Entfernungswerten für verschiedene Längen von Lichtleitern, wobei für die Ermittlung wenigsten zwei unterschiedliche Phasenlagen eingestellt werden,
  • - Ermittlung einer Amplitude und einer Intensität für jeden ermittelten Entfernungswert, wobei die Amplitude ausgehend von Differenzsignalen der beiden Integrationsknoten ermittelt wird und die Intensität durch Bilden eines Summensignals der beiden Integrationsknoten oder durch eine weitere Messung ermittelt wird,
  • - Ermittlung der Systemparameter in Form von Amplituden-Wiggling-Werten für die verschiedenen Entfernungswerte unter Berücksichtigung der ermittelten Amplituden und Intensitäten.

Advantageously, a method is provided for determining system parameters of a light transit time camera system with the aid of a calibration device,

• wherein the light time-of-flight camera system comprises a light time-of-flight camera with a light transit time sensor having at least one light transit time pixel, the light transit time pixel further comprising a first and second integration node for charge integration,
• wherein the calibration device has a light guide system with optical fibers of different lengths
• or is set up such that the light guide system optionally integrally receives an optical waveguide from a set of optical waveguides of different lengths,
• with a coupling device for detecting a light emitted by an illumination of the time of flight camera system light and for coupling this light in the optical waveguide or the optical waveguide
• and with an illumination device for illuminating the light transit time sensor of the light transit time camera via its camera optics with the light of the optical waveguide or of the optical waveguide,
• wherein for carrying out the method, the calibration device is arranged at a predetermined distance from the time of flight camera,
• with the steps:
  • Determination of distance values for different lengths of optical fibers, at least two different phase positions being set for the determination,
  • Determination of an amplitude and an intensity for each determined distance value, wherein the amplitude is determined on the basis of difference signals of the two integration nodes and the intensity is determined by forming a sum signal of the two integration nodes or by a further measurement,
  • Determination of the system parameters in the form of amplitude-wiggling values for the different distance values taking into account the ascertained amplitudes and intensities.

This procedure has the advantage that the amplitude wiggling can be detected under defined conditions and made available for later use, for example, in the camera system or in later applications.

The amplitude-wiggling values are preferably determined for a plurality of light-propagation time pixels of the light transit time sensor, so that one pixel-individual evaluation is also possible.

In a further embodiment, it is advantageous if the intensity is determined from the differences of the integration nodes in a separate measurement in which the modulation gates of the pixels of the light transit time sensor are operated with a fixed voltage, so that the charge integration either at the first integration node or at the second Integration node takes place.

This means that the high potential is present at one of the two modulation gates and the low potential of the modulation voltage remains constant at the other modulation gate during the entire integration time.

In particular, it is useful if the determination of the amplitude-wiggling values takes place at different modulation frequencies.

Preferably, the amplitude-wiggling values can be made available in the form of a wiggling function and / or a wiggling data record.

It is equally advantageous to provide a light transit time camera system with a time of flight camera and a modulatable illumination,
wherein the time of flight camera has a light transit time sensor with a plurality of time of flight pixels, the time of flight pixels having charge transfer modulation gates and charge integration integration nodes,
wherein it is provided for the determination of an amplitude equinig,
that an amplitude and an intensity are recorded for different distances.

Preferably, the difference values used for determining the distance are used to determine the amplitude, wherein the intensity of the detected light is preferably determined in a separate measurement.

This approach has the advantage that, in addition to the distance values, the time of flight camera system can detect a wiggling of the amplitude, by means of which, for example, the quality of the measurement or other system properties can be assessed.

It is particularly advantageous if a time-of-flight camera system is designed for the use of amplitude-wiggling values which have been determined according to one of the aforementioned methods,

Preferably, the time of flight camera system is configured such that a determination of a distance value is considered erroneous,
if the amplitude wiggling values determined during operation of the system deviate more than a tolerated level from the amplitude wiggling values stored in the calibration method.

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

• 1 schematisch ein Lichtlaufzeitkamerasystem,
• 2 eine modulierte Integration erzeugter Ladungsträger,
• 3 eine erfindungsgemäße Kalibriervorrichtung mit mehreren Lichtwellenleitern gemäß einer ersten Ausführungsform der Erfindung,
• 4 eine Vorrichtung mit einer Einzelfaser im Nahfeld gemäß einer zweiten Ausführungsform der Erfindung,
• 5 eine Vorrichtung mit einer Einzelfaser und Diffusor im Nahfeld gemäß einer dritten Ausführungsform der Erfindung,
• 6 eine Vorrichtung mit Faserselektor und Diffusor im Nahfeld gemäß einer vierten Ausführungsform der Erfindung,
• 7 eine Vorrichtung mit Faserselektor und Linse gemäß einer fünften Ausführungsform der Erfindung.
• 8 eine Relation der Phasenverschiebung in einem IQ-Diagramm,
• 9 einen Modulationsverlauf über vier Phasenlagen,
• 10 einen Verlauf der Intensität und Amplitude über die Distanz,
• 11 eine Verlauf des Verhältnisses von Amplitude und Intensität über die Distanz,
• 12 eine Verlauf von Messwerte und ,gefitteter‘ Kurve über eine vollständigen Phasenverlauf.

Show it:

• 1 schematically a light transit time camera system,
• 2 a modulated integration of generated charge carriers,
• 3 a calibration device according to the invention with a plurality of optical waveguides according to a first embodiment of the invention,
• 4 a device with a single fiber in the near field according to a second embodiment of the invention,
• 5 a device with a single fiber and diffuser in the near field according to a third embodiment of the invention,
• 6 a device with fiber selector and diffuser in the near field according to a fourth embodiment of the invention,
• 7 a device with fiber selector and lens according to a fifth embodiment of the invention.
• 8th a relation of the phase shift in an IQ-diagram,
• 9 a modulation course over four phase positions,
• 10 a course of intensity and amplitude over the distance,
• 11 a plot of the ratio of amplitude and intensity over the distance,
• 12 a course of measured values and 'fitted' curve over a complete phase curve.

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 time camera system 1 as it for example from the DE 197 04 496 A1 is known.

The light transit time camera system 1 comprises a transmitting unit or a lighting module 10 with a lighting 12 and associated beam shaping optics 15 as well as a receiving unit or light runtime camera 20 with a camera optics (receiving optics) 25 and a light transit time sensor 22 ,

The light transit time sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is designed in particular as a PMD sensor. The camera optics 25 typically consists of improving the imaging characteristics of multiple optical elements. The beam shaping optics 15 the transmitting unit 10 may be formed for example as a reflector or lens optics. In a very simple embodiment, if necessary, optical elements can also be dispensed with both on the receiving side and on the transmitting side.

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 and thus the distance covered by the received light can be determined. For this purpose, the light source 12 and the light transit time sensor 22 via a modulator 30 together with a certain modulation signal M _o with a base phase position φ ₀ applied. In the example shown is also between the modulator 30 and the light source 12 a phase shifter 35 provided with which the base phase φ ₀ the modulation signal M ₀ the light source 12 around defined phase positions φ _var can be moved. For typical phase measurements, preferably phase angles of φ _var = 0 °, 90 °, 180 °, 270 ° used.

The light source transmits according to the set modulation signal 12 an intensity modulated signal S _p1 with the first phase position p1 respectively. p1 = φ ₀ + φ _var out. This signal S _p1 or the electromagnetic radiation is in the illustrated case of an object 40 reflected and hits due to the distance traveled accordingly phase-shifted Δφ (t _L ) with a second phase position p2 = φ ₀ + φ _var + Δφ (t _L ) as a received signal S _p2 to the Transit Time Sensor 22 , In the time of flight sensor 22 the modulation signal M _{o is} mixed with the received signal S _p2 , wherein from the resulting signal, the phase shift or the object distance d is determined.

As illumination source or light source 12 Preferably, infrared light emitting diodes or infrared lasers are suitable. Of course, other radiation sources in other frequency ranges are conceivable, in particular, light sources in the visible frequency range are also considered.

The basic principle of phase measurement is schematically in 2 shown. The upper curve shows the time course of the modulation signal Mo with the illumination 12 and the light transit time sensor 22 be controlled. The object 40 Reflected light strikes as a received signal S _p2 phase-shifted according to its light transit time t _L Δφ (t _L ) on the light transit time sensor 22 , The light transit time sensor 22 collects the photonically generated charges q over several modulation periods in the phase position of the modulation signal M ₀ in a first integration node ga and in a 180 ° shifted phase position Mo + 180 ° in a second integration node gb , The integration nodes ga . gb form so-called A and B channels. From the difference in the first and second nodes ga . gb or in the A and B channel collected charges qa, qb, to different phase angles φ _var were determined, can be in a known manner, the phase shift Δφ (t _L ) and thus a distance d of the object.

For a calibration of light-time camera systems 1 it is necessary to measure known light transit times. According to the invention, the different light propagation times or phase shifts are generated in particular by a fiber bundle with a plurality of fibers of different lengths. By cleverly arranging the fibers, all the required measurements can be made in a single, static setting.

For an offset measurement, each individual pixel must be illuminated with a known transit time. For distance or intensity-dependent effects, different transit times and / or light intensities must be measured. Standard calibration concepts require a lot of space for this. In this invention, all of these parameters are realized by means of optical waveguides which illuminate diffusely in the near or far field of a camera, the entire pixel matrix or sharply imaged individual pixel areas. This is a Kalibrationsappartur realized with the smallest dimensions.

Time-of-flight cameras designed according to the PMD principle 1 do not measure the light transit time directly but via the determination of the phase position of a modulated light signal. The determination of the phase position from the actual measurement data of the camera takes place approximately via known formulas of signal processing. These theoretical formulas are based on ideal signal forms (optical and electrical), which are not always realized, especially at modulation frequencies of several megahertz. For a more accurate determination of the phase position, it is therefore necessary to either directly measure the signals actually generated or to determine the deviations of the phase angles from the approximate calculation. To determine the deviations, it is customary to measure the time-of-flight camera in several, precisely adjustable distances to a reference object. From this, a correction function and / or a look-up table can be generated. This procedure is time consuming and requires a lot of space, as the required distances are usually several meters.

Similarly, offset values must be determined for all pixels of a matrix (FPPN). This is done either via large, precisely aligned reference surfaces, or by direct, diffuse illumination of the entire pixel matrix with a known phase angle of the optical signal.

In 3 is an arrangement of a light transit time camera system 1 and a calibration device 50 for calibrating such time of flight camera systems 1 shown. The light transit time camera system 1 is essentially the same as in 1 described system 1 with the lighting 12 having lighting module 10 and the light transit time sensor 22 having light time camera 20 , The calibration device 50 has three main assemblies 52 . 54 . 56 on, namely (i) a light guide system 52 comprising a plurality of optical fibers (in short: optical fibers) 58 of different lengths, (ii) a coupling device 54 to capture light, which is from the lighting 10 of the time of flight camera system 1 is emitted, and for coupling this light in the light guide system 52 and (iii) an illumination device 56 for the projection of the light of the light guide system 52 to a light transit time sensor 22 the light runtime camera 20 , wherein the illumination device 56 a positioning device 60 for positioning the decoupling areas 62 the optical fiber 58 having. This positioning device 60 is in the example shown as a holding plate 64 with openings for receiving the decoupling areas 62 the optical fiber 58 , In the arrangement according to 3 becomes the modulated light of illumination 12 of the time of flight camera system 1 such as a time-of-flight camera, into an optical fiber 58 integrated fiber bundle of the light guide system, which consists of fibers (optical fibers 58 ) of different lengths. The individual fibers / optical fibers 58 project the light onto an imaging screen 66 or alternatively to a diffusely scattering optical element 68 the illumination device 56 that of the light transit time sensor 22 (the light runtime camera 20 ) is displayed. Every single fiber (every single fiber 58 ) creates its own light spot. In a compact system, different light propagation times can be measured, which correspond to several meters of distance.

The in the 4 to 8th shown arrangements correspond substantially to the arrangement of 3 , so in the following mainly on the differences to the in 3 received arrangement is received.

4 shows a variant with only one optical fiber or a fiber 58 , The modulated light of the lighting 12 a time-of-flight camera gets into a light guide (single fiber 58 or fiber bundles with fibers 58 same length) coupled. The other end of the fiber optic cable 58 is in the near field N the receiver (the time of flight camera) 20 of the time of flight camera system 1 and is therefore out of focus on the receiver (sensor) 20 displayed. The calibration device 50 is set up, one optical fiber each 58 from a set of optical fibers 58 optionally of different length integratively. This allows any light transit times in a compact device 50 calibrate. Likewise, one can by different choice of optical fibers / fibers 58 or by adding added damping elements specifically set different light intensities.

5 shows a variant of in 4 shown arrangement with only one optical fiber or a fiber 58 , To calibrate an entire pixel matrix, especially the offset values, you can, as in 5 shown a diffuser element 68 between fiber and light runtime camera 20 position. The diffuser element is again a diffusely scattering optical element 68 ,

As an alternative to a single optical waveguide (single fiber or fiber bundle) 58 with a defined length, one can use a fiber bundle with optical waveguides / individual fibers 58 use different lengths. In the execution according to 6 is between camera sensor and the decoupling areas (ends) 62 the optical fiber (single fibers) 58 becomes a selector device 70 to selectively unlock or block the Light of the individual optical fiber (fiber selector), for example, an optical switch, inserted, which performs the function of a diaphragm, with which the individual optical fibers / fibers 58 can be selected specifically. The light of the selected fiber optic / fiber 58 is on the projection screen of the imaging screen 66 guided. The distance between the screen and the camera 20 is arbitrary to either a blurred figure in the near field N to reach, or to get a clean picture of the screen. Sequentially, all required light transit times can be measured.

Instead of a diffusely scattering optical element 66 or other diffuser can, according to 7 , as well as an additional lens or other optics 72 the calibration device 50 which leads to a blurred picture.

Usually, self-adhesive protective films are applied to lenses which lead to blurred images. Instead of a diffuser or other diffusely scattering optical element 68 in the calibration structure, it is also possible to use this protective film on a camera lens as a scattering object in order to allow calibration of the entire matrix. The protective film and its optical properties are specified exactly.

The illustrated calibration devices are not only suitable for range calibration, but also for the detection and calibration of a so-called amplitude wiggling

From the correlation measurement of a time-of-flight camera phase and amplitude can be determined. The value of the calculated amplitude here depends on the received light power, the real form of the optical and electrical signals and the demodulation contrast. The demodulation contrast is a constant quantity for a time-of-flight measurement, which indicates the ratio between the usable photo-mixed signal and the total received light quantity. The strength of the usable photo-mixed signal is referred to as amplitude. The measured variables phase and amplitude are measured in a time-of-flight camera from several independent measurements at different output phase angles φ _var , usually 4 measurements, calculated. The real form of the optical and electrical signals leads to amplitude values which are also dependent on the phase position.

This "amplitude wiggling" can be calibrated by isolating the wiggling component of the amplitude calculation for different phase angles. After a calibration, Wiggling-free amplitude values can be calculated, which are frequency-dependent for a given scene merely because of the demodulation contrast of a time-of-flight camera. If, after a calibration of the demodulation contrast, additional deviations in the amplitude in a scene are detected at different frequencies, these indicate a disturbed measurement and can be utilized for a plausibility check or for correction calculations.

One possible method for isolating the amplitude wiggling is to set the phase shift between the optical and electrical signal with an external frequency generator and precise deceleration in a targeted manner. For a camera system, however, a frequency generator usually can not be used between illumination and sensor modulation. If the phase is varied by changing real measuring distances, the amplitude does not change solely by the amplitude wiggling, but also by the change in the absolute light intensity which is received. In order to determine the amplitude equivalency, this distance-dependent proportion must be eliminated. This approach leads to the goal, but is error-prone and requires a precise measurement setup.

In contrast, it is proposed according to the invention to use the intensity pixel-accurately directly to measure and to determine the Amplitude Dowsing. The intensity can be calculated directly from the sensor data if, in addition to the difference channel (A-B), the sum (A + B) or the individual channels can also be read out separately (A, B). Alternatively, for normalization, the intensity can also be determined from the difference channel (A-B) by deactivating the modulation of the sensor and / or the modulation of the illumination in an additional measurement. The advantage of this method is that the exact phase position for determining amplitude amplitude does not need to be known, but is measured directly. As a result, the amplitude constant can be extracted from arbitrary scenes, for example with one of the aforementioned calibration devices.

According to this method, in addition to amplitude wiggling, the individual intermediate results of the ToF measurement can also be calibrated (real and imaginary parts of the correlation measurements). The evaluation of these values has an increased potential, in particular for a fault correction calculation.

The distance determination is mathematically a correlation of the received signal S _p2 with the modulating signal Mo. $$q\left(\tau \right)={\displaystyle \underset{0}{\overset{\tau }{\int }}{S}_{p2}\left(t-\tau \right)}{M}_0\left(t\right)dt$$

In a modulation with a square wave signal, the correlation function is a triangular function. For a modulation with, for example, a sine signal, the result would be a cosine function.

For complete detection of the phase shift, for example, the IQ (in-phase quadrature) method is known in which two measurements are performed with shifted by 90 ° phase angles, so for example with the phase angle φ _var = 0 ° and φ _var = 90 °.

The relationship between these two measurements can be determined in a known manner, for example for sinusoidal waveforms in an IQ diagram. 8th represent. In a first approximation, this is also readily applicable to rectangular modulation and the resulting triangular autocorrelation function.

The phase angle can then be determined in a known manner via an arctan function or arctan2 function: $$\phi =\mathrm{\Delta }\phi \left(t_L\right)=\text{arctan}\frac{\mathrm{\Delta }q\left(90°\right)}{\mathrm{\Delta }q\left(0°\right)}$$

Due to the linear relationship between charge and voltage, the phase angle can also be determined by the voltage differences: $$\phi =\mathrm{\Delta }\phi \left(t_L\right)=\text{arctan}\frac{\mathrm{\Delta }U\left(90°\right)}{\mathrm{\Delta }U\left(0°\right)}$$

In order to compensate, for example, asymmetries of the sensor, additional phase measurements shifted by 180 ° can be performed so that, as a result, the phase angle can be determined as follows. $$\phi =\mathrm{\Delta }\phi \left(t_L\right)=\text{arctan}\frac{\mathrm{\Delta }q\left(90°\right)\mathrm{-\Delta }q\left(270°\right)}{\mathrm{\Delta }q\left(0°\right)\mathrm{-\Delta }q\left(180°\right)}$$

Or shortened formulated: $$\phi =\text{arctan}\frac{a_2-a_4}{a_1-a_3}$$

Where the indices indicate the respective phase position of the differences ai, with a ₁ = Δq (0 °) etc.

An amplitude A as signal strength can be calculated from the same measured values a _i : $$A=\frac{1}{2}\sqrt{{\left(a_1-a_3\right)}^2+{\left(a_2-a_4\right)}^2}$$

From the phase shift φ respectively. Δφ (t _L ) can be used for object distances d which are smaller than half the wavelength λ of the modulation frequency d ≤ λ / 2, determine a distance in a known manner. $$d=\mathrm{\Delta }\phi \left(t_L\right)\frac{\lambda }{2\pi }\cdot \frac{1}{2}$$

In 9 an example of a course of a light modulation is shown, the four modulation periods 1 through 4 with four phase angles of 0 °, 90 °, 180 ° and 270 °. At the end of each modulation period, the difference a ₁ , a ₂ , a ₃ , a _{4 of} the accumulated charge carriers is read out and the integration nodes are reset by means of a reset. As already shown, a phase shift or a corresponding distance value can then be determined from the differences.

Typically, ToF systems use a 4-phase algorithm to determine the phase shift of the received light signal within a uniqueness range. In this algorithm, four interpolation points are determined equidistantly in the uniqueness range from 0 to 2π with the same modulation frequency, and then the phase angle of the fundamental wave passing through these interpolation points is calculated. The uniqueness range is converted by a transformation factor of radians in a distance / distance.

Objects at distances that lie in multiples of this uniqueness range (0 to 2π), lead to ambiguities of the phase position. These ambiguities can be converted into an unambiguous phase position by another phase measurement or by a renewed application of the 4-phase algorithm with other, typically a lower modulation frequency. This procedure therefore implies at least 8 measurements until a clear distance value / distance value can be calculated.

With the procedure according to the invention, it is possible to produce a system-dependent amplitude wiggling over the different phase shifts or light propagation times or

Determine distance values, compensate if necessary and / or detect disturbances of the distance measurement.

The basic behavior of amplitude A and intensity I over distance / distance is exemplified in FIG 10 shown. As the distance increases, both the intensity I and the amplitude A decrease. Due to the system, the course of the amplitude A deviates from the light intensity I, as already mentioned.

If the amplitude and intensity are set in proportion, an in 11 illustrated behavior. This type of presentation provides a way to describe the amplitude wiggling. In principle, other ways of looking at it are also conceivable. According to the invention, it is now provided to readjust the different distances or phase shifts by one of the aforementioned calibration devices.

The calibration devices have the advantage that different distances or phase shifts can be set by the length of the light guides or possibly also by phase shifters without the light intensity changing significantly. This procedure ensures that the effects triggering the amplitude wiggling can be measured more precisely.

12 schematically shows a measurement course, in which, for example, with the aid of 30 individual fibers of different lengths a phase shift Δφ (t _L ) from 0 to 2π in one step. For each phase shift, an amplitude and an intensity are determined, wherein in the case shown, the quotient of amplitude and intensity for each distance value is plotted as measured value. Each measuring point thus corresponds to a measured amplitude-wiggling value for the respective phase shift.

In principle, these raw data could already be made available for further use. However, it is particularly advantageous if the raw data are processed in a suitable form. In particular, it is advantageous to use a fitting or adaptation function which physically and / or mathematically describes the amplitude wiggling.

In particular, sine functions or corresponding Fourier series are suitable here, for example in the form: $$f\left(t\right)=\frac{a_0}{2}+{\displaystyle \underset{k=1}{\overset{\infty }{\Sigma }}{A}_k\text{cos}\left(kt-{\phi }_k\right)}$$

In the example shown, the raw data was 'fit' using a sine function. The adapted or fitted function can preferably be made available directly as a wiggling function and / or as a wiggling data record, in particular as a look-up table, for further use.

Of course, other curve adjustments are conceivable.

If the light intensity I for all detected phase shifts or phase positions remains substantially constant with the aforementioned calibration devices, the amplitude A determined from the difference signals of the A and B channels directly reflects the behavior of the amplitude wiggle. For example, I ₀ = I ₉₀ = I ₁₈₀ = I ₂₇₀ where the amplitude of the different phase positions typically differ A ₀ ≠ A ₉₀ ≠ A ₁₈₀ ≠ A ₂₇₀ and Aφ _i ≠ Aφ _j with i ≠ j.

If necessary, the amplitude wiggling can additionally be detected for different light intensities, which can be carried out, for example, by weakening the light source and / or an actual distance change of the calibration device.

It is likewise advantageous to determine the amplitude wiggling not only for different light intensities and / or phase positions but also for different modulation frequencies, the intensity being kept constant for a comparison measurement, with I _f1 = I _f2 and typically A _f1 ≠ A _f2 . Likewise, the intensities can be varied. Thus, for different intensities I1, I2, without interference, the same amplitude pairings or ratios always result (A _f1 (I ₁ ) | A _f2 (I ₁ )) or (A _f1 (I ₂ ) | A _f2 (I ₂ )) ,

In real measuring operation, a malfunction of the measurement can then be detected, for example, if the ratio or a difference of the amplitudes exceeds a limit value. If necessary, such a limit value can also be determined depending on the frequencies used. $$\left|{\text{A}}_{\text{f1}}\left({\text{I}}_{\text{1}}\right)-{\text{A}}_{\text{f2}}\left({\text{I}}_{\text{1}}\right)\right|>\text{GW}$$

Since the amplitude A to be expected for an applied intensity I is known in a calibrated system, it is also possible, conversely, to deduce the applied intensity on the basis of the amplitude A.

As can be determined from the amplitude of the first frequency _f1 A (I ₁₎ close to the intensity I _1, as well as the amplitude for the second frequency _f2 A (I ₁₎ should also pass the same result I ₁ pass. However, if this reversal does not lead to the same result, it is also possible in this case to assume that the system has malfunctioned. For example, if the difference between the two results exceeds a threshold: $$\left|\text{I}\left({\text{A}}_{\text{f1}}\right)-\text{I}\left({\text{A}}_{\text{f2}}\right)\right|>\text{GW}$$

As already described, the light intensity I can be determined, for example, by summing the A and B channels. Likewise, the intensity I can be determined from the difference of the A and B channels in an additional measurement in which the modulation of the sensor is fixed. This has the advantage that even during normal operation of the light transit time camera system, the intensity I can be detected pixel-individually.

The operation of a light transit time pixel is described in detail, for example, in the already mentioned DE 197 04 496 A1 described in full here.

LIST OF REFERENCE NUMBERS

1

Time of flight camera system

10

lighting module

12

lighting

15

Beam shaping optics

20

Receiver, light time camera

22

Transit Time Sensor

25

camera optics

30

modulator

35

Phase shifter, lighting phase shifter

40

object

50

calibration

52

fiber optic system

54

coupling device

56

lighting device

58

optical fiber

60

positioning device

62

Decoupling area (optical fiber)

64

Retaining plate

66

Screen, imaging

68

optical element, diffusely scattering

70

Selector means

72

optics

φ, Δφ (t _L )

term-related phase shift

φ _var

phasing

φ ₀

base phase

M ₀

modulation signal

p1, p2

first and second phase

Sp1

Transmission signal with first phase

sp2

Received signal with second phase

Ga, Gb

integration node

d

subject Distance

q

charge

N

Near field of the light runtime camera

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

• DE 19704496 A1 [0002, 0020, 0075]

Claims (11)

Method for determining system parameters of a light transit time camera system (1) with the aid of a calibration device (50), wherein the time of flight camera system (1) comprises a light transit time camera (20) with a light transit time sensor (22) having at least one light transit time pixel which for charge integration comprises a first and second integration node (Ga, Gb), wherein the calibration device (50) has a light guide system (52) with light waveguides (58) of different lengths or is arranged such that the light guide system (52) consists of a set of light waveguides (58) of different lengths an optical waveguide ( 58) optionally integratively receives, with a coupling device (54) for detecting a light emitted by a lighting (10) of the time of flight camera system (1) light and for coupling this light in the optical waveguide (58) or the optical waveguide (58) and with an illumination device ( 56) for illuminating the light transit time sensor (22) of the light transit time camera (20) via the camera optics (25) with the light of the optical waveguide (58) or the optical waveguide (58), wherein for performing the method, the calibration device (50) is arranged at a predetermined distance to the light time camera (20) , comprising the steps of: - determining distance values (d, Δφ (t _L )) for different lengths of optical waveguides, wherein at least two different phase positions (φ _var ) are set for the determination, - determination of an amplitude (A) and an intensity ( I) for each determined distance value (d, Aφ (t _L )), wherein the amplitude is determined from difference signals of the two integration nodes (Ga, Gb) and the intensity by forming a sum signal of the two integration nodes (Ga, Gb) or by a determination of system parameters in the form of amplitude-wiggling values for the different distance values (d, Aφ (t _L )) under consideration tion of the determined amplitudes and intensities. Method according to Claim 1 in which the amplitude-wiggling values are determined for a plurality of light-propagation time pixels of the light transit time sensor (22). Method according to one of the preceding claims, in which the intensity is determined from the differences of the integration nodes (Ga, Gb) in a separate measurement in which the modulation gates (Gam, Gbm) of the pixels of the light transit time sensor (22) are operated with a fixed voltage such that the charge integration takes place either at the first integration node (Ga) or at the second integration node (Gb). Method according to one of the preceding claims, in which the determination of the amplitude-wiggling values takes place at different modulation frequencies. Method according to one of the preceding claims, in which the amplitude-wiggling values are provided in the form of a wiggling function and / or a wiggling data record. Time-of-flight camera system with a light-time camera and a modulable illumination, wherein the time of flight camera has a light transit time sensor with a plurality of time of flight pixels, the time of flight pixels comprising charge-steering modulation gates (Gam, Gbm) and charge integration integration nodes (Ga, Gb), wherein it is provided for the determination of an amplitude equinig, that an amplitude and an intensity are recorded for different distances. Light time camera system according to Claim 6 in which the difference values used for determining the distance are used to determine the amplitude. Light time camera system according to Claim 6 or 7 , in which the intensity of the detected light is determined in a separate measurement. Light time camera system according to one of Claims 6 to 8th in which the time of flight camera system is adapted to use amplitude wiggling values determined by one of the methods according to Claim 1 to 5 were determined. Light time camera system according to Claim 9 , which is designed such that a determination of a distance value is considered to be erroneous if the amplitude-wiggling values determined during operation of the system deviate more than a tolerated level from the amplitude-wiggling values stored in the calibration method. Light time camera system according to one of Claims 6 to 10 in which amplitudes and / or intensities for different phase shifts and frequencies are determined in a calibration method, wherein the time of flight camera system is designed such that a disturbance of the measurement is detected in a distance measuring operation, if deviations of the amplitudes and / or intensities are greater than a tolerated Limit.

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