A reliable optical time-of-flight method for determining distance values.

Abstract

The distance value (d, d i In a method and optical time-of-flight sensor for determining a distance (d), an illumination light (40) is emitted that is modulated with a modulation frequency (f) and a modulation phase (φ). A reflected light (42) is acquired as an output signal (Rx) and evaluated by acquiring a phase shift (δ) between the illumination light (40) and the reflected light (42), resulting in an output signal (d, d i ) is generated. i ) is determined for a series of consecutive frames, where in each frame multiple acquisitions are made in the form of microframes (μF1-μF8) with different modulation phases (φ). 1 -φ 4 ) is assigned for each frame. To achieve a particularly high reliability of the data delivered, the modulation phase (φ 1 -φ 4 ) is varied. In an initialization step (60) self-calibration and self-validation take place. Subsequent data acquisition takes place in a frame acquisition step 62 with acquisition of the signal and calculation and output of distance values ​​for each pixel for further processing (68). Each frame acquisition step (62) is divided into a setup step (64) and the subsequent acquisition of the signal in microframes (μF1-μF8). In the setup step (64), the central processing unit MCU calculates (pseudo)random numbers and uses these to determine the sequence of the microframes (μF1-μF8), i.e. their respective modulation frequencies (f) and phase angles (φ). The optical time-of-flight method, in which acquisition and signal evaluation are performed with a variable sequence of modulation phases, is particularly suitable for safety-related applications, such as optical range monitoring systems for industrial production facilities.

Description

[Technical Field]

[0001] The present invention relates to a method for determining distance values ​​using the time-of-flight method and to an optical time-of-flight sensor for determining distance values. [Background technology]

[0002] The optical time-of-flight method for determining distance values ​​involves emitting an incident light beam, acquiring a reflected light beam, and evaluating the delay between the incident light and the reflected light caused by the time of flight. These cameras are based on the known ToF (Time of Flight) measurement principle, whereby not only an image containing the reflection intensity and / or color of a large number of pixels is obtained, but also distance values ​​are determined using the Time of Flight method.

[0003] DE 10 2019 13 1988 A1 describes a 3D time-of-flight camera and a method for acquiring three-dimensional image data. An illumination unit emits a transmitted light modulated at a first modulation frequency. An image sensor with a plurality of receiving elements generates a received signal from which sample values ​​are obtained by demodulation at the first modulation frequency. A control and evaluation unit controls the illumination unit and / or the demodulation unit for a plurality of measurement repetitions with different phase offsets between the first modulation frequency of the transmitted light and the first modulation frequency of the demodulation. A distance value is determined from the sample values ​​obtained from the measurement repetitions of each receiving element. The control and evaluation unit is designed to vary the number of measurement repetitions.

[0004] DE 10 2013 207 654 A1 discloses a method for operating a time-of-flight camera system that determines a distance value based on a phase shift between a transmitted signal and a received signal, where the phase shift is determined in two successive phase measurement cycles, where each phase measurement cycle is performed with at least two phase positions, and where at least two of the phase positions used have different modulation frequencies.

[0005] DE102013207649A1 discloses a time-of-flight camera system and a method for operating such a system. In a distance measurement, a first distance-related variable is determined using a phase shift between a transmitted signal and a received signal at a first modulation frequency. In a control measurement, a second distance-related quantity is determined, the control measurement being performed at a second modulation frequency different from the first modulation frequency. The control measurement is performed at a smaller number of phase positions than the distance measurement.

[0006] The use of optical time-of-flight sensors, such as ToF cameras, in safety-critical applications requires a high level of reliability in the data they provide. In safety applications where optical time-of-flight sensors are used to detect objects or people in danger zones (e.g. to protect the operation of machines or vehicles, such as industrial robots), it is important that the acquisition and evaluation of distance values ​​by the time-of-flight sensor works properly. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] DE102019131988A1 [Patent Document 2] DE102013207654A1 [Patent Document 3] DE102013207649A1 Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to provide an optical time-of-flight method and an optical time-of-flight sensor for determining distance values ​​which allows achieving a particularly high reliability of the data provided by the operating mode. [Means for solving the problem]

[0009] This object is solved by a method according to claim 1 and an optical time-of-flight sensor according to claim 13. The dependent claims relate to advantageous embodiments of the invention.

[0010] In the method according to the invention or the optical time-of-flight sensor according to the invention, an illumination light modulated with a modulation frequency and a modulation phase is emitted. The reflected light is acquired as a received signal, which is evaluated by determining the phase shift between the illumination light and the reflected light, and an output signal including at least one distance value is generated. Preferably, the distance values ​​of a plurality of pixels are acquired separately from each other, for example by an image sensor with a matrix arrangement of pixels.

[0011] The distance values ​​are determined successively in a series of successive determination steps called frames, in each of which a distance value (or, in the preferred case where there are multiple pixels, a distance value for each of these pixels) is determined.

[0012] According to the invention, multiple acquisitions are made in the form of microframes, i.e., for each microframe, modulated illumination light is emitted and the reflected light is evaluated by determining the phase shift, the multiple microframes differing in terms of shifted modulation phase and possibly also in terms of shifted modulation frequency.

[0013] For each frame, a sequence of modulation phases (and possibly modulation frequencies) of the microframes is specified. The method according to the invention and the device according to the invention are characterized in that the temporal order of the modulation phases (and possibly modulation frequencies) used successively for the individual acquisitions in the microframes of a frame is variable.

[0014] This means changing the order of modulation phases (and possibly modulation frequencies) for each new frame, meaning that the sequence of microframes for successive frames is always different from each other. However, it is also possible that a specified modulation phase (and possibly modulation frequency) sequence of microframes is maintained for successive groups of two or more successive frames, and then the sequence is changed for successive groups of frames.

[0015] The size of the group, i.e., the number of consecutive frames with the same sequence, can be appropriately selected depending on the frame rate and the desired response time, i.e., the acceptable delay until a fault is detected, as explained below. To detect faults quickly, the group size should be limited as much as possible. Based on these considerations, the group size can be increased, for example, to 100, or even larger if the requirements are very low. However, small groups of up to 10, especially groups with a maximum of 5 frames or only 1-3 frames per group, are recommended, especially for shorter response times. For example, if the frame rate is in the range of approximately 100 FPS, a group size of 5 can achieve a good response time of 50 ms.

[0016] The inventors discovered, in analyzing the acquisition and evaluation of a series of microframes with different modulation phases, that unexpected variations in modulation phase have a significant and characteristic effect on the determined phase shift between the illuminated and reflected light, and thus on the determined distance values. As explained in more detail below, unexpected deviations in modulation phase can affect the distance values ​​of all pixels as an additive term, while deviations in modulation frequency can affect the distance values ​​of all pixels as a multiplicative effect, i.e., a factor.

[0017] Deviations between the modulation frequencies and / or modulation phases used for various microframes result in characteristic and easily detectable signal deviations, especially when processing multiple pixels that are all affected in the same way. For this reason, time-of-flight methods and time-of-flight sensors in which the order of modulation phases of the microframes is variable according to the present invention are highly sensitive and can quickly detect faults. Therefore, correct functioning can be easily verified by monitoring the signal provided by the time-of-flight sensor. However, the value provided by the time-of-flight sensor can still be used, i.e., verification can be performed using a valid signal provided by the time-of-flight sensor.

[0018] Optical time-of-flight methods and optical time-of-flight sensors in which acquisition and signal evaluation are performed according to the principles of the invention with variable order modulation phases are therefore particularly suitable for safety-related applications.

[0019] According to a further development of the invention, the verification is carried out by comparing values, e.g., distance values, calculated from the phase shifts of at least two consecutive frames, in which the modulation phases (and possibly modulation frequencies) of the microframes are ordered differently. As already explained, unexpected deviations in the modulation will lead to characteristic deviations in the resulting distance values. Deviations in the values, e.g., distance values, calculated from the phase shifts will occur if different sequences of microframes are not applied correctly when the modulated illumination light is emitted or when the received signal is evaluated. By comparing the values ​​of consecutive frames with different sequences of microframes, characteristic deviations can be recognized and corresponding faults can be recognized, thereby detecting such faults. The frames whose values ​​are compared may follow one another, but the frames used as references for the comparison may also be spaced apart in time, and other frames may be acquired in the meantime.

[0020] Preferably, the order of modulation phase (and possibly modulation frequency) of the microframes is changed for each frame or group of successive frames compared to the immediately preceding frame or group of immediately preceding successive frames, allowing for continuous verification of control and signal evaluation.

[0021] Values ​​calculated from the phase shift, e.g., distance values, can be compared using various calculation methods, in particular by forming the difference and / or ratio of consecutive values. Values ​​calculated from the phase shift can be compared directly with each other, or a characteristic value can first be calculated from the values ​​and then compared. The calculation of the characteristic value can be performed, for example, in the preferred case of acquiring multiple pixels, as the sum or average of several or all values ​​calculated from the phase shift acquired in a frame. While it is possible to use the values ​​of all pixels acquired in a frame, in many cases meaningful statements can also be made by evaluating the values ​​of only a portion of the pixels, e.g., less than half of the pixels, simplifying the process. If only the values ​​of some pixels are used, it is preferred that these pixels are spaced apart, e.g., evenly distributed across the entire sensor surface. According to a preferred further development, the comparison can consider only pixels for which a valid distance value or a distance value less than or equal to a maximum distance value exists in at least one, preferably both, of the frames under consideration. If no object is present in certain image regions within the sensor's measurement range, a comparison of the pixels in these image regions may result in no meaningful statements or only limited meaningful statements. Therefore, it may be preferable to limit the formation of feature values ​​for both frames to be compared to pixels for which measurements are available (or pixels for which measurements are within a maximum range and less than or equal to a maximum threshold).

[0022] According to a further development of the invention, the modulation phases of two microframes within a frame are preferably opposite each other, i.e., have a phase difference of 180° from each other. If, during signal evaluation, at least two signal contributions from microframes of opposite phase relative to the frame are processed, these can preferably be subtracted from each other. By this subtraction, interference can be eliminated or at least reduced.

[0023] Since the determination of the distance value is based on a phase comparison between the modulated incident light and the reflected light, ambiguity occurs if the transit time causes a phase difference of more than 360°. To resolve such ambiguity, modulation frequencies offset from each other can be used. Therefore, when determining the distance value of a frame, it is desirable to process at least two signal contributions from microframes with different modulation frequencies. When using two different modulation frequencies, the ambiguous distance corresponds to the least common multiple of the two modulation frequencies.

[0024] The sequence of microframes, i.e. the sequence of modulation phases (and possibly modulation frequencies) of the respective microframes, can be suitably selected for each frame or each group of consecutive frames according to a specific sequence determined, for example, by a calculation rule or by pre-stored values, for example in the form of a table. Particularly preferably, for each frame or each group of consecutive frames, the order of modulation phases (and possibly modulation frequencies) of the microframes can be selected by a (pseudo)random generator. The use of a random sequence eliminates certain repetitions and patterns, allowing for a particularly reliable verification.

[0025] Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. [Brief explanation of the drawings]

[0026] [Figure 1]FIG. 1 is a schematic diagram of a first example system for monitoring the operation of an industrial plant using time-of-flight sensors. [Figure 2] FIG. 2 is a schematic diagram of the operation of the time-of-flight sensor in FIG. 1. [Figure 3] FIG. 3 is a schematic diagram of the elements of the time-of-flight sensor in FIGS. 1 and 2. [Figure 4a] FIG. 2 is a time response diagram of a reference signal, a transmitted signal, and a received signal with different modulation phases. [Figure 4b] FIG. 2 is a time response diagram of a reference signal, a transmitted signal, and a received signal with different modulation phases. [Figure 5] 1 is a diagram of curves of useful and interference signals over time to illustrate the combination of opposite signals; [Figure 6] FIG. 1 illustrates the geometric relationships between signal processing variables. [Figure 7] 1 is a flowchart of signal acquisition. [Figure 8] FIG. 1 is a schematic diagram of a second example system for monitoring danger areas of a vehicle using time-of-flight sensors. DETAILED DESCRIPTION OF THE INVENTION

[0027] In various fields, such as industrial production facilities, protective devices are used to protect people and others from hazards in the production process or to protect the production process from disruptions (disturbances). In addition to or instead of guards, non-contact, especially optical, area monitoring systems are also used, which have proven to be particularly advantageous in fields where cooperation between people and machines is required.

[0028] 1 shows, as a first application example, a system 10 for monitoring the operation of an industrial plant, which includes, for example, an industrial robot 14 and an autonomous industrial truck 16. A safety zone 12 is defined around the industrial robot 14. A controller 22 controls the industrial robot 14 and also the industrial truck 16 via a wireless connection (not shown).

[0029] To allow the industrial robot 14 to operate safely, in this example, no people 24 are permitted within the safety area 12. The industrial truck 16 is allowed to traverse the safety area 12, and therefore the movable cutout area 18 of the safety area 12 is defined to move with the industrial truck 16.

[0030] To implement these safety requirements, an optical monitoring device 20 with a risk assessment unit 26 is fixedly mounted and optically acquires the industrial robot 14 and its surroundings, ie at least the safety area 12 .

[0031] The control device 22 is connected to the risk assessment unit 26 of the optical monitoring device 20 and receives therefrom an evaluation signal A, for example via OSSD outputs. As will be explained in more detail below, the evaluation signal A indicates whether or not a person or unauthorized object is currently detected in the security area 12. The optical monitoring device 20 and the risk assessment unit 26 are designed with safety in mind, i.e., redundancy and self-verification ensure that the evaluation signal A only indicates that the security area 12 is free if not only are no people 24 or objects detected there, but also that the monitoring device 20 is functioning properly.

[0032] As long as the evaluation signal A in the form of an enable signal indicates that the safety area 12 is free and that the proper functioning of the optical monitoring device 20 is also ensured, the control device 22 controls the operation of the machines 14, 16 in accordance with the respective work process.

[0033] As long as the person 24 remains or moves outside the safety area 12, he is not put at risk by the first machine 14. If the risk assessment unit 26 detects the presence of a person or object within the safety area 12 from the signals of the optical monitoring device 20 and transmits this to the control device 22 in the form of an alarm or warning signal by means of a corresponding evaluation signal A, as will be explained below, the control device 22 stops further operation of the machines 14, 16 or puts them into a safe state so that the person is protected and a collision with the object is avoided. The same applies if internal verification of the optical monitoring device 20 indicates that it is not functioning properly and the evaluation signal A is output as an alarm or warning signal.

[0034] The optical monitoring device 20 is a time-of-flight sensor, i.e., a signal d i and a ToF (Time of Flight) camera with a control unit 30 that provides a signal S to the risk assessment unit 26. As will be explained in more detail below, the signal d i is the value of the distance d between the optical monitoring device 20 and the object captured by it. i contains distance values ​​for multiple pixels. Signal S is a safety signal that indicates that optical monitoring device 20 is functioning properly.

[0035] The risk assessment unit 26 uses the distance values ​​d provided by the optical surveillance device 20 to detect the presence of a person 24 or object within the safety area 12. i Furthermore, the optical monitoring device 20 also provides conventional 2D camera images, which are also processed by the risk assessment unit 26. Furthermore, the risk assessment unit 26 processes the safety signal S provided by the optical monitoring device 20. The distance value d i Only if after evaluation of the data (and possibly 2D image data) no object or person is detected within the safety area 12 and at the same time the safety signal indicates that the optical monitoring device 20 is functioning normally is an enable signal output as evaluation signal A, otherwise an alarm or warning signal is output.

[0036] Distance value d from optical monitoring device 20 iThe structure and functioning principle of the acquisition are explained with reference to Figure 2, which shows a schematic representation of the arrangement of objects 38 within the area acquired by the optical monitoring device 20, also called the field of view (FoV). By means of the optical system 36 and the pixel sensor 32, a conventional 2D pixel image of the objects 38 is recorded. Furthermore, the distance d between the optical monitoring device 20 and each object 38 is determined for each pixel of the sensor 32, and a 3D image is acquired as a whole.

[0037] 2, the optical monitoring device 20 comprises an optical system 36 and a pixel sensor 32, as well as a controlled light source 34 and a control and evaluation unit 30. The control and evaluation unit 30 controls the pixel sensor 32, which in turn controls the light source 34, which emits modulated, i.e., pulsed, illumination light 40 according to certain specified parameters. Reflected light 42 from an object 38 is received by the pixel sensor 32 and transmitted to the control unit 30 for processing.

[0038] Depth measurements, i.e., signal processing and evaluation to determine distance values, are based on the time of flight of photons. Due to the short distances and therefore very short flight times at the speed of light C, special processing is required to obtain accurate measurements of the distance d.

[0039] The basic principle is as follows: instead of emitting and timing based on a single light pulse, a rapid sequence of light pulses is emitted by a light source 34 as illumination light 40. The light source 34 is preferably formed as a VSCEL (Vertical Cavity Surface Emitting Laser) laser diode. The illumination light 40 corresponds to a pulse signal Tx with a specific modulation frequency f.

[0040] In an advantageous embodiment, the modulation frequency f is specified by the sensor 32. A typical modulation frequency f is, for example, 100 MHz. A corresponding control signal is suitably transmitted from the sensor 32 to the laser diode driver 44 (see FIG. 3), for example, via a low-voltage differential signal.

[0041] 4a shows exemplary time curves of the reference signal Ref, the transmitted signal Tx of the light source 34, and the received signal Rx of the pixel. In ideal representation, these are each rectangular signals. The reference signal Ref with modulation frequency f and resulting period duration T=1 / f is specified, for example, by the sensor 32.

[0042] In the example of FIG. 4a, the transmission signal Tx, ie the modulation of the illuminating light 40 of the light source 34, has the same frequency and is in phase with the reference signal Ref.

[0043] The reflected light 42 is converted into a voltage signal in the sensor 32 in a known manner for each pixel, and in each case acquired during an integration time, and the voltage value of each pixel is preferably converted into a digital value to generate a digital received signal Rx.

[0044] The received signal Rx received at each pixel of the sensor 32 is also modulated at the modulation frequency f, but is phase shifted by a phase difference δ compared to the reference signal Ref and the transmitted signal Tx due to the time of flight.

[0045] The corresponding delay time t δ teeth, t δ =δ / (2πf) is equivalent to

[0046] Then the distance d is d(δ)=1 / 2vt=1 / 2δc / (2πf) is equivalent to Here, the factor 1 / 2 is included because the light traverses the distance d twice.

[0047] Due to the periodicity of the modulation signals Tx and Rx, the phase angle δ repeats after one period and is therefore limited to the interval [0,2π]. Thus, for example, it is not possible to distinguish between δ=π / 4 and θ=2π+π / 4 → δ=θ(mod2ππ)=π / 4. To achieve uniqueness of acquisition beyond the uniqueness distance d(2π), successive acquisitions at different modulation frequencies can be performed in a known manner and evaluated in combination as described below.

[0048] To improve the quality of the acquired data, the acquisition is advantageously performed multiple times in successive microframes, whereby a set of distance values, i.e., one distance value for each pixel, is determined for each successive time period (frame) from the received signals Rx acquired in combination within the microframes.

[0049] As an example, four microframes can be acquired for each modulation frequency. For each microframe i in the interval [1..4], the initial phase angle φ is set in the interval [0,2π] as shown in Figure 4b. i is specified, that is, the transmitted signal Tx is compared with the reference signal Ref at each microframe i by a phase angle φ i During signal evaluation, the phase angle φ i is also taken into account, i.e., the distance value d is calculated based on the phase angle φ i It is calculated as a function of d(δ-φ i )=1 / 2(δ-φ i )c / (2πf)

[0050] During frame acquisition, different phase angles φ i microframes with phase angles φ are acquired one after the other. i represents the shift of the measurement, i.e., the phase angle φ between 0 and 360° i can cause a shift across the entire measurement range, the crucial factor here being that this affects all pixels in the same way.

[0051] The inventors have determined that the expected value φ i The effect of a phase angle that deviates from the initial phase angle was determined. If there is a shift in the initial phase angle that was not considered in the evaluation, i.e., φ i '=φ i +Δφ i This results in a shift of Δd in the distance value d' determined according to the above formula compared to the correct distance value d. d'=1 / 2(δ-φ i ')c / (2πf)=d-1 / 2Δφ i c / (2πf)=:d-Δd

[0052] This shift Δd is global, i.e. all pixels are affected in the same way. All distance values ​​d of individual pixels i The average value of the characteristic value <d>If we consider this, the result is <D’> = <d>+Δd becomes.

[0053] As mentioned before, the distance value d of each pixel in each frame i The acquisition of is usually done in microframes, where on the one hand, different phase angles φ i On the other hand, a different modulation frequency f is specified, so that the ambiguity can be resolved and the measurement range can be extended.

[0054] We have also investigated the effect of the modulation frequency f on the possibility that the actually used modulation frequency f' may have unexpected deviations from the expected modulation frequency f. For example, it is assumed that: f'=αf Using the expected frequency f, we calculate the distance d" according to the formula above, giving us: d”=1 / 2(δ-φ i ')c / (2παf)=d / α That is, the deviation from the correct value d by a deviation factor 1 / α, which is again global, i.e. the distance values ​​of all pixels are affected equally.

[0055] Typically, microframes are recorded in pairs of opposite phase angles, i.e., in the above four microframe example, the phase angles are φ1=0°, φ2=90°, φ3=180°, and φ4=270°. Since the signals from the opposite phase angle pairs (0° and 180°, and 90° and 270°) are opposite to each other, the additive interference can be eliminated by subtracting the opposite signals from each other. This can be seen in the example of Figure 5, where the opposite signal I P° and I P°+180° and an additive superimposed interference signal N, which is assumed to be identical in both microframes. Here, the subtraction I P° -I P°+180° The interference signal N is rejected by

[0056] For signal evaluation, the intensities determined in each microframe are combined pixel by pixel. In the four microframe example above, these are the signals I 0° , I 90° , I 180° , I 270° The inverse signal is subtracted and the following auxiliary variables are defined: I n =I 0° -I 180° I d =I 90° -I 270° A=(I n / I n )

[0057] Next, as shown in Figure 6, the phase angle φ Tx,Rx The following formula applies to φ Tx,Rx =tan -1 (A) therefore, tan(φ Tx,Rx )=A This becomes:

[0058] The inventors have also taken into account the effect of unexpected changes in the phase angle in the above evaluation by combining two inverse signals. For example, if a change of magnitude x is expected at a phase angle of 180°, this is equivalent to the undisturbed signal I n A signal I that is changed by a factor β compared to n ' leads to. I n =I 0° -I 180° ≒2I 0° =>I n '=I o° -I 180°+x ≒I 0° -βI 180° =I n (1-β) where β is a proportional value that does not depend on the signal intensity, i.e., it is the same for each pixel. Phase deviation within a microframe - here, for example, I 180° - will result in a value A' that is deviated from the actual value A. A' = γA = γtan(φ Tx,Rx )=tan(φ' Tx,Rx )

[0059] Thus, in the evaluation, the deviation phase value comes into play in the form of a multiplicative deviation of the argument A, and the deviation distance value d is also determined here.

[0060] The effect of the deviation of the modulation frequency and / or modulation phase is in any case global, i.e., the distance values ​​d i Since the deviation affects the distance values ​​d of all pixels (or a representative subset of them) in the same way, i characteristic value, e.g., sum or arithmetic mean <d>The distance value d can be determined by determining a series of values ​​obtained within a microframe or by combining them for a frame. i In the method, successive values ​​are compared to determine, for example, the ratio or difference of the respective characteristic values, e.g., the arithmetic mean. <d>By forming the deviation, it is possible to detect the deviation.

[0061] The distance value d for each frame i To obtain this, a series of microframes with specific modulation phases and modulation frequencies are specified. For example, as shown in the following table, two modulation frequencies f1 and f2 and four modulation phase angles φ1=0°, φ2=90°, φ3=180°, and φ4=270° are specified.

[0062] Frame 1 Microframe number Modulation frequency Modulation phase angle μF1f1φ1 μF2f1φ2 μF3f1φ3 μF4f1φ4 μF5f2φ1 μF6f2φ2 μF7f2φ3 μF8f2φ4

[0063] To dynamize both signal generation and signal evaluation, the sequence of microframes, i.e., the time order of a series of modulation frequencies and modulation phase angles, is constantly changed. In each frame, the same microframes, i.e., combinations of modulation frequencies and modulation phase angles, are used, only the time order is changed as follows:

[0064] Frame 2 Microframe number Modulation frequency Modulation phase angle μF1f2φ2 μF2f1φ4 μF3f1φ3 μF4f1φ2 μF5f2φ4 μF6f1φ1 μF7f2φ3 μF8f2φ1

[0065] FIG. 3 shows diagrammatically the components of a control and evaluation unit 30 of the optical monitoring device 20 which operates according to the functional principle explained above.

[0066] The central unit MCU 50 is designed with safety in mind, i.e. with a lockstep processor for synchronizing the results of redundant components, or as two redundant MCU central units. The MCU 50 central unit controls the entire optical monitoring device 20 and outputs a safety signal S. The MCU 50 central unit is coupled to the DSP 46 for signal processing.

[0067] The FPGA or ASIC 48 includes, as functional units, an internal high-speed communication unit 52, such as a DSI interface specified according to MIPI, an image processing unit 54, and a distance signal d i and an input / output unit 56 such as a safety bus to which the signals are output.

[0068] The operating mode is explained using the flow chart of Figure 6. After starting, self-calibration and self-validation are carried out in an initialization step 60. Subsequent data acquisition is carried out in each case in a (summarized) frame acquisition step 62, which results in signal acquisition and the distance value d for each pixel for subsequent processing (step 68), as explained in more detail below. i The frame acquisition 62 and calculation / output of distance values ​​68 are constantly repeated.

[0069] Each step 62 in the frame acquisition is divided into a setup step 64 followed by acquisition of the signals of microframes μF1-μF8. In the setup step 64, the central processing unit MCU 50 calculates a (pseudo)random number and uses it to determine the order of microframes μF1-μF8, i.e., their respective modulation frequencies f and phase angles φ. The central processing unit MCU 50 sets register values ​​in the sensor 32 according to the randomly determined microframe order. Furthermore, in the setup step 64, the sensor 32 performs power calibration of the driver 44 by operating the light source (VCSEL) 34 at an initial operating current and optimizing the operating current based on a feedback signal received from the light source 34.

[0070] After the setup step 64, the acquisition of microframes μF1-μF8 is performed in the previously defined (determined) order. In each case, the sensor 32 controls the driver 44 with a timing signal Tx based on the data, i.e., frequency and phase, specified in each microframe. The light source 34 is thereby activated and emits pulsed light 40 according to the specified frequency and phase.

[0071] The reflected light 42 is received by the sensor 32 as described above and converted into a digital signal Rx that varies by pixel, frequency and phase.

[0072] The received signal Rx of each pixel is transmitted to the control and evaluation unit 30, in particular to an internal high-speed communication unit 52, and from there to an image processing unit 54, which generates a distance value d for each pixel according to the aforementioned operating mode. i The distance value d is determined. i is output by input / output unit 56 to risk assessment unit 26 for further processing.

[0073] During image processing, the DSP 46 calculates distance values ​​d i Calculate the characteristic value A in parallel as the arithmetic mean of a subset of A, for example, 5% or 10% of A. t It is calculated as:

[0074] DSP46 is a continuous characteristic value A t The ratio of F t =A t / A t-1 The deviation of successive frames is continuously determined by forming

[0075] If the image is unchanged and the data is acquired correctly, F t is always (exactly or approximately) 1. Due to noise and other influences, particularly the movement of the target 38 relative to the optical monitoring device 20, F t may deviate slightly from 1. On the other hand, deviations exceeding the maximum deviation value ±ΔF indicate an error, for example an incorrectly applied microframe sequence during signal acquisition or evaluation.

[0076] ratio F t If is within the range [1-ΔF, 1+ΔF], the MCU 50 central unit detects the correct functioning of the signal detection and evaluation and issues a corresponding confirmation as a safety signal S. Otherwise, it issues an alarm or warning signal.

[0077] As an example of the second embodiment, Figure 8 shows a system 110 for monitoring the operation of two mobile machines 114, 116, each equipped with an optical monitoring device 20 to monitor a safety area 112. A cutout area 118 is excluded from this area. The optical monitoring devices 20 of the vehicles 114, 116 are designed for safety, as described above for the optical monitoring devices 20 of the system 10 of the first example embodiment.

[0078] In summary, the described embodiments enable an apparatus and a method for determining distance values ​​by optical time-of-flight, whereby dynamization occurs in both signal generation and signal evaluation by changing the order of microframes. By monitoring possible deviations, verification can be performed and a high level of reliability can be achieved.

[0079] It should be understood that the above-described devices and methods are merely illustrative and not limiting, and it is possible to deviate from the above examples within the scope of protection of the claims.

[0080] For example, instead of changing the order of the microframes after each frame, it is also possible to acquire a group of several frames, e.g., up to 100 frames, with microframes in the same order before changing the order. The number of modulation frequencies and phases used can deviate from the above example. Instead of changing the order randomly, the change can follow a fixed change scheme.

[0081] The evaluation of distance values ​​to determine whether the provided 3D image indicates the intrusion of a person 24 or object into the safety area 12 is preferably performed internally, as explained, not by a separate risk assessment unit 26, but by a central processing unit, for example, the MCU 50, designed for safety technology and supported by the DSP 46. In this case, a separate risk assessment unit 26 is not required, but the control and evaluation unit 30 can further take over this task using existing hardware. In any case, it should be pointed out that the naming and representation of separate components and function blocks in the example embodiments and in the claims should be understood primarily functionally and not as necessarily requiring them to be separate hardware components. Indeed, various functions can be performed using appropriate software on hardware components such as the central processing unit MCU 50 or the DSP 46.< / d> < / d> < / d> < / d>

Claims

1. The distance value (d, d ｉ ) , comprising the steps of: Illuminating light (40) is modulated with a modulation frequency (f) and a modulation phase (φ) and emitted; The reflected light (42) is acquired as a received signal (Rx), The received signal (Rx) is evaluated by determining the phase shift (δ) between the illuminated light (40) and the reflected light (42) to produce an output signal (d, d ｉ ) is generated, The distance value (d, d ｉ ) is determined for a series of consecutive frames, where each frame contains a microframe (μF) with a different modulation phase (φ). １ -μF ８ ) multiple acquisitions are made in the form The microflame (μF １ -μF ８ ) of a series of modulation phases (φ １ -φ ４ ) is specified for each frame, The modulation phase (φ １ -φ ４ ) order is changed, A method comprising:

2. The microflame (μF １ -μF ８ ) is a series of modulation phases (φ １ -φ ４ ) and modulation frequency (f １ , f ２ ), The modulation frequency (f １ , f ２ ) order is changed, 2. The method of claim 1 .

3. The microflame (μF １ -μF ８ ) modulation phase (φ １ -φ ４ The verification is carried out by comparing the values ​​(A, d) calculated from the phase shifts (δ) of at least two consecutive frames having different orders of A, d, 3. The method according to claim 1 or 2.

4. the values ​​(A, d) of successive frames calculated from said phase shift (δ) are compared by determining at least one characteristic value (<D>) for each of the two frames, comparing the two characteristic values ​​(<D>) and recognizing a fault condition in case of a deviation exceeding a defined threshold value (ΔF) or a correct functional condition in case of a deviation below a defined threshold value (ΔF); 4. The method according to claim 3 .

5. The values ​​(A, d) or characteristic values ​​calculated from the phase shifts (δ) are compared by forming differences and / or ratios, 5. The method according to claim 3 or 4.

6. The reflected light (42) is acquired as a received signal (Rx) for a number of pixels; An output signal (Rx) is generated for each pixel by determining the phase shift (δ) between the illuminated light (40) and the reflected light (42).

6. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

7. The characteristic value (<D>) is an average value over multiple pixels of two frames.

6. A method according to claim 4 or 5.

8. Not all pixels are used in calculating the average value.

8. The method of claim 7.

9. In determining the distance value (d) of said frame, at least two signal contributions (I ０° , I ９０° , I １８０° , I ２７０° ) are subtracted from each other, 9. The method according to claim 1, wherein the first and second electrodes are connected to a first electrode.

10. The microflame (μF １ -μF ８ ) modulation phase (φ １ -φ ４ ) is changed for each frame or group of frames compared to the immediately preceding frame or group of frames; 10. The method according to claim 1 , wherein the first and second electrodes are connected to a first electrode.

11. For each frame or group of frames, the microframes (μF １ -μF ８ ) modulation phase (φ １ -φ ４ ) is chosen by a random generator, 11. The method according to any one of claims 1 to 10.

12. In determining the distance value (d) of a frame, different modulation frequencies (f １ , f ２ At least two signal contributions from a microframe having a first signal contribution and a second signal contribution from a microframe having a second signal contribution are processed to resolve ambiguities; 12. The method according to claim 1 ,

13. The distance value (d, d ｉ 1. An optical time-of-flight sensor for determining a controllable illumination device (34) designed to emit illumination light (40) modulated with a modulation frequency (f) and a modulation phase (φ); a receiver (32) designed to receive the reflected light (42) and provide a received signal (Rx); The received signal (Rx) is evaluated by determining the phase shift (δ) between the illuminated light (40) and the reflected light (42), and an output signal (d, d ｉ ), and further, a sequence of successive frame distance values ​​(d, d ｉ ), and in each frame, microframes (μF) with mutually different modulation phases (φ) are determined. １ -μF ８ an evaluation device (30) in which a plurality of acquisitions are made in the form of The irradiation device (34) microflame (μF １ -μF ８ ) of a series of modulation phases (φ １ -φ ４ ) and the modulation phase (φ １ -φ ４ A verification device (50) designed to vary the order of A time-of-flight optical sensor.

14. The verification device (50) further includes a microframe (μF １ -μF ８ ) modulation phase (φ １ -φ ４ ) of at least two temporally consecutive frames having different orders of phase shifts (δ) (A, d) calculated from the phase shifts (δ) of the frames, 14. The optical time-of-flight sensor of claim 13.

Images