DE102016222334B4 - Method for determining system parameters of a time-of-flight camera system - Google Patents

Abstract

Method for determining system parameters of a time-of-flight camera system (1) with the aid of a calibration device (50), the time-of-flight camera system (1) having a time-of-flight camera (20) with a time-of-flight sensor (22), with at least one time-of-flight pixel, which has a first and second integration node for charge integration (Ga, Gb), wherein the calibration device (50) has a light-guiding system (52) with optical fibers (58) of different lengths or is set up in such a way that the light-guiding system (52) forms an optical fiber (58) from a set of optical fibers (58) of different lengths ) optionally records in an integrative manner, with a coupling device (54) for detecting a light emitted by an illumination (10) of the time-of-flight camera system (1) and for coupling this light into the optical waveguide (58) or the optical waveguide (58) and with an illumination device (56 ) for illuminating the time-of-flight sensor (22) of the time-of-flight camera (20) via its camera optics (25) with the light from the optical waveguide (58) or the optical waveguide (58), the calibration device (50) being at a predetermined distance from the time-of-flight camera to carry out the method (20) is arranged, with the steps: - Determination of distance values (d, Δφ (tL)) for different lengths of light guides, at least two different phase positions (φvar) being set for the determination, - Determination of an amplitude (A) and an intensity (I) for each determined distance value (d, Δφ(tL)), whereby the amplitude is determined based on difference signals from the two integration nodes (Ga, Gb) and the intensity by forming a sum signal from the two integration nodes (Ga, Gb) or by a further measurement is determined, - determination of system parameters in the form of amplitude wiggling values for the different distance values (d, Δφ (tL)) taking into account the determined amplitudes and intensities.

Description

The invention relates to a method for determining system parameters of a time-of-flight camera system using a calibration device according to the independent claim.

A time-of-flight camera system should include all time-of-flight or 3D-TOF camera systems that obtain travel time information from the phase shift of emitted and received radiation. PMD cameras with photomixing detectors (PMD), such as those in the DE 197 04 496 A1 described and can be obtained, for example, from the company “ifm electronic GmbH” or “pmdtechnologies ag” as “Frame Grabber O3D” or as “CamBoard pico flexx”. The PMD camera in particular allows a flexible arrangement of the light source and the detector, which can be arranged both in a housing or separately.

From the EP 1 705 497 A1 A laser distance measuring device is also known in which part of the optical energy is directed via optical delay lines that have different optical lengths for distance measurement.

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

The task is solved in an advantageous manner by the method according to the invention.

• - 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.

A method for determining system parameters of a time-of-flight camera system using a calibration device is advantageously provided,
in which the time-of-flight camera system has a time-of-flight camera with a time-of-flight sensor with at least one time-of-flight pixel, the time-of-flight pixel further having 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 in such a way that the light guide system optionally integrates an optical fiber from a set of optical fibers of different lengths,
with a coupling device for detecting a light emitted by an illumination of the time-of-flight camera system and for coupling this light into the optical waveguide or the optical waveguide
and with an illumination device for illuminating the time-of-flight sensor of the time-of-flight camera via its camera optics with the light of the optical fiber or the optical fiber,
in order to carry 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 light guides, with at least two different phase positions being set for the determination,
• - Determination of an amplitude and an intensity for each determined distance value, the amplitude being determined based on difference signals from the two integration nodes and the intensity being determined by forming a sum signal from the two integration nodes or by a further measurement,
• - Determination of the system parameters in the form of amplitude wiggling values for the various distance values, taking into account the determined amplitudes and intensities.

This procedure has the advantage that the amplitude wiggling can be recorded 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 several time-of-flight pixels of the light time-of-flight sensor, so that a pixel-specific evaluation is also possible.

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

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

It is particularly useful if the amplitude wiggling values are determined at different modulation frequencies.

The amplitude wiggling values can preferably be provided in the form of a wiggling function and/or a wiggling data set.

It is particularly advantageous if a time-of-flight camera system is designed for the use of amp litude wiggling values are formed, which were determined using one of the aforementioned methods,

The time-of-flight camera system is preferably designed in such a way that a determination of a distance value is considered incorrect if the amplitude wiggling values determined during operation of the system deviate from the amplitude wiggling values stored in the calibration process by more than a tolerated amount.

The invention is explained in more detail below using exemplary 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 time-of-flight camera system,
• 2 a modulated integration of generated charge carriers,
• 3 a calibration device according to the invention with several 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 a fiber selector and diffuser in the near field according to a fourth embodiment of the invention,
• 7 a device with a 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 progression over four phase positions,
• 10 a course of intensity and amplitude over distance,
• 11 a progression of the relationship between amplitude and intensity over distance,
• 12 a progression of measured values and a “fitted” curve over a complete phase progression.

In the following description of the preferred embodiments, the same reference numbers designate the same or comparable components.

1 shows a measurement situation for an optical distance measurement with a time-of-flight camera system 1, as shown, for example, in DE 197 04 496 A1 is known.

The time-of-flight camera system 1 includes a transmitting unit or an illumination module 10 with lighting 12 and associated beam shaping optics 15 as well as a receiving unit or time-of-flight camera 20 with camera optics (receiving optics) 25 and a time-of-flight sensor 22.

The time-of-flight sensor 22 has at least one time-of-flight pixel, preferably also a pixel array, and is in particular designed as a PMD sensor. The camera optics 25 typically consists of several optical elements to improve the imaging properties. The beam shaping optics 15 of the transmitting unit 10 can be designed, for example, as a reflector or lens optics. In a very simple embodiment, optical elements can also be dispensed with on both the receiving and transmitting sides.

The measuring principle of this arrangement is essentially based on the fact that the transit time and thus the distance traveled by the received light can be determined based on the phase shift of the emitted and received light. For this purpose, the light source 12 and the time-of-flight sensor 22 are supplied with a basic phase position φ ₀ via a modulator 30 together with a specific modulation signal M _o . In the example shown, a phase shifter 35 is also provided between the modulator 30 and the light source 12, with which the base phase φ ₀ of the modulation signal M ₀ of the light source 12 can be shifted by defined phase positions φ _var . For typical phase measurements, phase positions of φ _var = 0°, 90°, 180°, 270° are preferably used.

According to the set modulation signal, the light source 12 sends out an intensity-modulated signal S _p1 with the first phase position p1 or p1 = φ ₀ + φ _var . In the case shown, this signal S _p1 or the electromagnetic radiation is reflected by an object 40 and, due to the distance traveled, hits Δφ(t _L ) with a corresponding phase shift and a second phase position p2 = φ ₀ + (pvar + Δφ(t _L ) as a received signal S _p2 to the time-of-flight sensor 22. In the time-of-flight sensor 22, the modulation signal M _o is mixed with the received signal S _p2 , the phase shift or the object distance d being determined from the resulting signal.

Infrared light-emitting diodes or infrared lasers are preferably suitable as the illumination source or light source 12. Of course, there are also other radiation sources in other frequencies are conceivable; in particular, light sources in the visible frequency range can also be considered.

The basic principle of phase measurement is shown schematically in 2 shown. The upper curve shows the time profile of the modulation signal M ₀ with which the lighting 12 and the time-of-flight sensor 22 are controlled. The light reflected from the object 40 hits the light transit time sensor 22 as a received signal S _p2 in a phase-shifted manner Δφ(t _L ) in accordance with its light transit time t _L . 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 phase position M ₀ + 180° shifted by 180° in a second integration node Gb. The integration nodes Ga, Gb form so-called A and B channels. From the difference between the charges qa, qb collected in the first and second nodes Ga, Gb and in the A and B channels, which were determined at different phase positions φ _var , the phase shift Δφ( _t and thus determine a distance d of the object.

To calibrate time-of-flight camera systems 1, it is necessary to remeasure known time-of-flight times. According to the invention, the different light transit times or phase shifts are generated in particular by a fiber bundle with several fibers of different lengths. By cleverly arranging the fibers, all required measurements can be carried out 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 implemented using optical fibers that diffusely illuminate the entire pixel matrix or sharply image individual pixel areas in the near or far field of a camera. This makes it possible to create a calibration apparatus with the smallest dimensions.

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

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

In 3 an arrangement consisting of a time-of-flight camera system 1 and a calibration device 50 for calibrating such time-of-flight camera systems 1 is shown. The time-of-flight camera system 1 essentially corresponds to that in 1 described system 1 with the lighting module 10 having the lighting 12 and the time-of-flight camera 20 having the time-of-flight sensor 22. The calibration device 50 has three main assemblies 52, 54, 56, namely (i) a light guide system 52, which has a plurality of optical fibers (light guides for short) 58 of different lengths, (ii) a coupling device 54 for detecting light which is emitted by the lighting 10 of the time-of-flight camera system 1 and for coupling this light into the light guidance system 52 and (iii) an illumination device 56 for projecting the light of the light guidance system 52 onto one Time-of-flight sensor 22 of the time-of-flight camera 20, the illumination device 56 having a positioning device 60 for positioning the decoupling areas 62 of the optical waveguides 58. In the example shown, this positioning device 60 is a holding plate 64 with openings for receiving the coupling-out areas 62 of the optical waveguides 58. In the arrangement according to 3 the modulated light from the illumination 12 of the time-of-flight camera system 1, such as a time-of-flight camera, is coupled into a fiber bundle of the light guide system comprising the optical waveguides 58, which consists of fibers (light guides 58) of different lengths. The individual fibers/light guides 58 project the light onto an imaging screen 66 or alternatively onto a diffusely scattering optical element 68 of the illumination device 56, which is imaged by the time-of-flight sensor 22 (the time-of-flight camera 20). Each individual fiber (each individual light guide 58) produces its own light spot. Different light transit times can be achieved in a compact system be measured, which correspond to a distance of several meters.

The ones in the 4 until 8th Arrangements shown essentially correspond to the arrangement of 3 , so that the following mainly focuses on the differences to that in 3 shown arrangement is entered into.

4 shows a variant with only one optical waveguide or one fiber 58. The modulated light from the illumination 12 of a time-of-flight camera is coupled into an optical fiber (single fiber 58 or fiber bundle with fibers 58 of the same length). The other end of the optical waveguide 58 is located in the near field N of the receiver (the time-of-flight camera) 20 of the time-of-flight camera system 1 and is therefore imaged out of focus on the receiver (sensor) 20. The calibration device 50 is set up to selectively accommodate one optical waveguide 58 from a set of optical waveguides 58 of different lengths. This allows any light transit times to be calibrated in a compact device 50. You can also set different light intensities in a targeted manner by choosing different optical waveguides/fibers 58 or by adding damping elements.

5 shows a variant of the in 4 Arrangement shown with only one optical waveguide or one fiber 58. In order to calibrate an entire pixel matrix, in particular the offset values, can be done as in 5 shown, position a diffuser element 68 between the fiber and the time-of-flight camera 20. 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, you can use a fiber bundle with optical waveguides/individual fibers 58 of different lengths. In execution according to 6 is between the camera sensor and the decoupling areas (ends) 62 of the optical fibers (individual fibers) 58, a selector device 70 for selectively enabling or blocking the light of the individual optical fibers (fiber selector), for example an optical switch, is inserted, which has the function an aperture with which the individual optical waveguides/fibers 58 can be specifically selected. The light from the selected optical fiber/fiber 58 is guided onto the projection surface of the imaging screen 66. The distance between the projection surface and camera 20 can be selected as desired in order to either achieve a blurred image in the near field N or to obtain a clean image of the projection surface. All required light travel times can be measured sequentially.

Instead of a diffusely scattering optical element 66 or other diffuser, according to 7 , also an additional lens or other optics 72 of the calibration device 50 will be used, which leads to a blurred image.

Self-adhesive protective films are usually attached to lenses, which lead to blurry images. Instead of a diffuser or other diffusely scattering optical element 68 in the calibration setup, you can also use this protective film on a camera lens as a scattering object to enable calibration of the entire matrix. The protective film and its optical properties are precisely specified.

The calibration devices shown are suitable not only for distance calibration, but also for recording and calibrating a so-called amplitude wiggling

Phase and amplitude can be determined from the correlation measurement of a time-of-flight camera. The value of the calculated amplitude 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 that indicates the ratio between the usable photo-mixing signal and the total amount of light received. The strength of the usable photo-mixing signal is called the amplitude. In a time-of-flight camera, the measured variables phase and amplitude are calculated from several independent measurements at different initial phase positions φ _var , usually 4 measurements. The real form of the optical and electrical signals leads to amplitude values that also depend on the phase position.

This “amplitude wiggling” can be calibrated by isolating the wiggling portion of the amplitude calculation for different phase positions. After calibration, wiggling-free amplitude values can be calculated, which are frequency-dependent for a given scene only due to the demodulation contrast of a time-of-flight camera. If, after calibrating the demodulation contrast, additional deviations in the amplitude are found in a scene at different frequencies, these indicate a disturbed measurement and can be used for plausibility checks or for correction calculations.

A possible method for isolating amplitude wiggling is to specifically adjust the phase shift between the optical and electrical signals using an external frequency generator and precise delay. For a camera system, however, a frequency generator cannot usually be used between lighting and sensor modulation. If you vary the phase by changing the real measuring distances, the amplitude changes not only through the amplitude wiggling, but also through the change in the absolute light intensity that is received. To determine the amplitude wiggling, this distance-dependent component must be calculated out. This approach achieves the goal, but is prone to errors and requires a precise measurement setup.

In contrast, according to the invention, it is proposed to use the intensity directly to measure pixel accuracy and to determine the amplitude wiggling. 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 separately (A, B) can also be read out. 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 lighting in an additional measurement. The advantage of this method is that the exact phase position does not have to be known to determine the amplitude wiggling, but is measured directly. This allows the amplitude wiggling to be extracted from any scene, for example using one of the aforementioned calibration devices.

In addition to the amplitude wiggling, this method can also be used to calibrate the individual intermediate results of the ToF measurement (real and imaginary parts of the correlation measurements). The evaluation of these values has increased potential, especially for a disturbance correction calculation.

The distance determination is mathematically a correlation of the received signal S _p2 with the modulating signal M ₀ . $$q\left(\tau \right)={\displaystyle \underset{0}{\overset{\tau }{\int }}{S}_{p2}\left(t-\tau \right)M_0\left(t\right)dt}$$

When modulating with a square wave signal, the correlation function is a triangular function. If modulated with a sine signal, for example, the result would be a cosine function.

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

The relationship between these two measurements can be calculated in a known manner, for example for sinusoidal curves in an IQ diagram. 8th represent. As a first approximation, this can also be easily applied to rectangular modulation and the resulting triangular autocorrelation function.

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

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

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

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

The indices indicate the respective phase position of the differences a _i , 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 or Δφ(t _L ), a distance can be determined in a known manner for object distances d that are smaller than half the wavelength λ of the modulation frequency d ≤ λ/2. $$d=\Delta \phi \left(t_L\right)\frac{\lambda }{2\pi }\cdot \frac{1}{2}$$

In 9 An example of a course of light modulation is shown, which goes through four modulation periods 1 to 4 with four phase positions of 0°, 90°, 180° and 270°. At the end of each modulation period, the difference a ₁ , a ₂ , a ₃ , a ₄ accumulates The load carrier is read out and the integration nodes are reset using a reset. As already shown, a phase shift or a corresponding distance value can then be determined from the differences.

Typically, a 4-phase algorithm is used in ToF systems to determine the phase shift of the received light signal within a uniqueness range. In this algorithm, four support points, which are equidistant in the uniqueness range from 0 to 2π with the same modulation frequency, are determined and the phase position of the fundamental wave that runs through these support points is then calculated. The uniqueness range is converted from radians into a distance/distance using a transformation factor.

Objects at distances that are multiples of this uniqueness range (0 to 2π) lead to ambiguities in the phase position. These ambiguities can be converted into a clear phase position by further phase measurement or by re-application of the 4 phase algorithm with a different, typically 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 determine system-related amplitude wiggling via the various phase shifts or light transit times or distance values, to compensate if necessary and/or to detect disturbances in the distance measurement.

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

If amplitude and intensity are put in relation, the result is an in 11 behavior depicted. This type of representation provides one way to describe amplitude wiggling. In principle, other perspectives are also conceivable. According to the invention, it is now provided to adjust the various distances or phase shifts using 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 guide or possibly also by phase shifters without the light intensity changing significantly. This procedure ensures that the effects triggering amplitude wiggling can be measured more precisely.

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

In principle, this raw data could already be made available for further use. However, it is particularly advantageous if the raw data is prepared in a suitable form. In particular, it is advantageous to use a fit or adaptation function that physically and/or mathematically describes the amplitude wiggling. Sine functions or corresponding Fourier series are particularly suitable here, for example in the form: $$f\left(t\right)=\frac{a_0}{2}+{\displaystyle \sum _{k=1}^{\infty }{A}_k\text{cos}}\left(kt-{\phi }_k\right)$$

In the example shown, the raw data was “fitted” 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 set, in particular as a “look up table” for further use.

Of course, other curve adjustments are also conceivable.

If the light intensity I remains essentially constant for all detected phase shifts 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 wiggling.

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

As already described, the light intensity I can be determined, for example, by summing the A and B channels. The intensity I can also be determined from the difference between the A and B channels in an additional measurement in which the modu lation of the sensor is fixed. This has the advantage that the intensity I can be recorded on a pixel-by-pixel basis even during normal operation of the time-of-flight camera system.

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

Reference symbols

1

Time of flight camera system

10

Lighting module

12

lighting

15

Beam shaping optics

20

Receiver, time of flight camera

22

Time of flight sensor

25

Camera optics

30

modulator

35

Phase shifter, lighting phase shifter

40

object

50

Calibration device

52

Light guidance system

54

Coupling device

56

Illumination device

58

optical fiber

60

Positioning device

62

Coupling area (optical fiber)

64

Retaining plate

66

screen, illustration

68

optical element, diffusely scattering

70

Selector facility

72

optics

φ, Δφ(tL)

Transit time-related phase shift

φvar

Phase position

φ0

Basic phase

M0

modulation signal

p1, p2

first and second phase

Sp1

Transmit signal with first phase

Sp2

Receive signal with second phase

Ga, Gb

Integration node

d

Object distance

q

charge

N

Near field of the time of flight camera

Claims (7)

Method for determining system parameters of a time-of-flight camera system (1) with the aid of a calibration device (50), wherein the time-of-flight camera system (1) has a time-of-flight camera (20) with a time-of-flight sensor (22), with at least one time-of-flight pixel, which has a first and second integration node for charge integration (Ga, Gb), wherein the calibration device (50) has a light-guiding system (52) with optical fibers (58) of different lengths or is set up in such a way that the light-guiding system (52) consists of a set of optical fibers (58) of different lengths, an optical fiber ( 58) optionally records in an integrative manner, with a coupling device (54) for detecting a light emitted by an illumination (10) of the time-of-flight camera system (1) and for coupling this light into the optical waveguide (58) or the optical waveguide (58) and with an illumination device ( 56) for illuminating the time-of-flight sensor (22) of the time-of-flight camera (20) via its camera optics (25) with the light from the optical waveguide (58) or the optical waveguide (58), the calibration device (50) being at a predetermined distance from the camera to carry out the method Time-of-flight camera (20) is arranged, with the steps: - Determination of distance values (d, Δφ (t _L )) for different lengths of light guides, at least two different phase positions (φ _var ) being set for the determination, - Determination of an amplitude ( A) and an intensity (I) for each determined distance value (d, Δφ(t _L )), the amplitude being determined based on difference signals from the two integration nodes (Ga, Gb) and the intensity by forming a sum signal from the two integration nodes (Ga , Gb) or is determined by a further measurement, - determination of system parameters in the form of amplitude wiggling values for the various distance values (d, Δφ(t _L )) taking into account the determined amplitudes and intensities. Procedure according to Claim 1 , in which the amplitude wiggling values are determined for several time-of-flight pixels of the time-of-flight sensor (22). Procedure according to Claim 2 , in which the intensity is derived from the differences in the integration node th (Ga, Gb) is determined in a separate measurement, in which the modulation gates (yarn, Gbm) of the pixels of the time-of-flight sensor (22) are operated with a fixed voltage, so that the charge integration occurs either at the first integration node (Ga) or at the second Integration node (Gb) takes place. Procedure according to one of the Claims 2 - 3 , in which the amplitude wiggling values are determined at different modulation frequencies. Procedure according to one of the Claims 2 until 4 , in which the amplitude wiggling values are provided in the form of a wiggling function and/or a wiggling data set. Time-of-flight camera system designed for the use of amplitude wiggling values that were determined using one of the aforementioned methods. Time of flight camera system Claim 6 , which is designed in such a way that a determination of a distance value is considered incorrect if the amplitude wiggling values determined during operation of the system deviate from the amplitude wiggling values stored in the calibration process by more than a tolerated amount.

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