METHOD AND OPTICAL SENSOR FOR MEASURING THE DISTANCE OF AN OBJECT

Description

[0001] The present invention relates, in a first aspect, to a method for measuring the distance of an object according to the preamble of claim 1. In a second aspect, the invention relates to an optical sensor for measuring the distance of an object according to the preamble of claim 13.

[0002] In a generic method for measuring the distance of an object according to the time-of-flight principle, in which light pulses are emitted into a monitoring area, light pulses reflected back from an object in the monitoring area are detected by a receiving unit, and a distance to the object is determined based on the time of flight of the light pulses, wherein a basic correction of a reception time of the respective light pulse is carried out, wherein an intensity of ambient light arriving at the receiving unit or a photodetector in the vicinity of the receiving unit is determined, and wherein, depending on the determined intensity of the ambient light, an ambient light correction of the reception times of the detected light pulses is carried out, characterized in that .that the basic correction of the reception time of a detected light pulse is carried out depending on a pulse width determined for the detected light pulse, and that the extraneous light correction of the reception time of a detected light pulse is carried out depending on the pulse width determined for the light pulse in question.

[0003] An optical sensor of the generic type for measuring the distance of an object according to the time-of-flight principle, for carrying out the methods disclosed above, comprising a transmitter unit for emitting light pulses into a monitoring area, a receiver unit for detecting light pulses reflected back from an object in the monitoring area, and a control and evaluation unit for controlling the transmitter unit and the receiver unit and for evaluating light pulses detected by the receiver unit, wherein the control and evaluation unit is configured to determine the effective reception times of the detected light pulses, depending on a pulse width determined for a detected light pulse, and to determine a distance to the object based on the time of flight of the light pulses, wherein the control and evaluation unit is configured toto evaluate the intensity of ambient light arriving at the receiving unit or a photodetector in the vicinity of the receiving unit and to perform an ambient light correction of the reception times of the detected light pulses depending on the detected intensity of the ambient light, characterized in that the control and evaluation unit is further configured to perform the basic correction of a reception time (t1, t2) of a detected light pulse depending on a pulse width determined for the detected light pulse and to perform the ambient light correction of the reception time of a detected light pulse depending on the pulse width determined for the light pulse in question.

[0004] A generic method and a generic optical sensor are known, for example, from DE 103 56 797 A1, JP 2021 076589 A and US 2019 / 250257 A1. An object of the invention can be considered to be to create a method and an optical sensor of the type described above, with which good measurement accuracy is achieved even when ambient light is present.

[0005] This problem is solved by the method with the features of claim 1 and by the optical sensor with the features of claim 13.

[0006] The method of the type described above is further developed according to the invention in that an intensity of extraneous light arriving at the receiving unit or a photodetector in the vicinity of the receiving unit is determined and that, depending on the determined intensity of the extraneous light, an extraneous light correction of the reception times of the detected light pulses is carried out.

[0007] The optical sensor of the type described above is further developed according to the invention in that the control and evaluation unit is configured to evaluate the intensity of ambient light arriving at the receiving unit or a photodetector in the vicinity of the receiving unit and, depending on the detected intensity of the ambient light, to perform an ambient light correction of the reception times of the detected light pulses.

[0008] Advantageous embodiments of the method according to the invention and preferred embodiments of the optical sensor according to the invention are explained below, in particular in connection with the dependent claims and the figures.

[0009] In principle, any known component capable of emitting light pulses with the desired intensity, spectral range, and temporal structure can be used as the transmitter. Typically, light-emitting diodes (LEDs) or lasers, especially semiconductor lasers, are used, emitting in the infrared or visible spectrum.

[0010] The measurement of a distance to a reflecting object using the time-of-flight principle is known. Using the speed of light c in the relevant medium, typically air, and the difference between a transmission time ts and a reception time tr, the distance d of the reflecting object is determined as follows: d = tr − ts / 2 c . Typically, many distance measurements are added together to improve measurement statistics.

[0011] The term "monitoring area" refers to the area of ​​space in which objects to be detected may be located and which can be optically captured by the sensor. The transmitting unit is therefore positioned so that light pulses can be emitted into the monitoring area, and the receiving unit is positioned so that light pulses can be received from within the monitoring area.

[0012] To detect light pulses arriving at the receiving unit from the monitoring area, the receiving unit includes at least one light detector. In principle, known components can be used for this purpose. Semiconductor detectors, for example CMOS, CCD, SPAD, or MPPC detectors (SPAD = Single-Photon Avalanche Diode, MPPC = Multi-Pixel Photon Counter), are preferred. In certain embodiments of the optical sensor according to the invention, a plurality of such detectors can also be present, for example in a line arrangement or in a two-dimensional matrix arrangement.

[0013] The transmitting unit can include optical components, such as lenses, mirrors, and / or optical fibers, of a generally known type for guiding and / or directing the light pulses into the monitored area. Likewise, the receiving unit can include optical components, such as lenses, mirrors, and / or optical fibers, of a generally known type for guiding and / or directing the light pulses arriving from the monitored area onto a light detector located in the receiving unit.

[0014] Known components, such as microcontrollers or other programmable components, can be used as the control and evaluation unit for controlling the transmitting unit and the receiving unit and for evaluating the light pulses detected by the receiving unit.

[0015] The control and evaluation unit can be set up to carry out the method according to the invention.

[0016] Backscattering means that at least some of the energy from the light pulses striking an object is reflected back to the receiving unit. Typically, the receiving and transmitting units are housed in the same casing. However, it is also possible to design the receiving and transmitting units in separate casings and possibly in different locations.

[0017] In transit-time measurements, the measured transit time depends significantly on the amplitude of a detected light pulse, also known as an echo signal. Typically, the echo signal is only detected above a certain intensity or amplitude threshold. Therefore, weak echo signals exceed this intensity threshold later than stronger echo signals, resulting in a longer transit time measured from the start signal. Measurement errors caused by the amplitude can be determined, for example, by performing measurements with targets of different reflectivities but the same distance from the measurement system.

[0018] The corrections, i.e., the basic correction and the ambient light correction, of the reception times can be performed using a determined amplitude of a detected light pulse. According to the invention, the pulse widths of the detected light pulses are determined, and the basic correction is applied depending on the determined pulse width. The control and evaluation unit is preferably configured to determine the pulse width of the detected light pulses. Determining the pulse widths of the detected light pulses means that the control and evaluation unit calculates a quantitative value from the intensity profiles of the detected light pulses, which characterizes the pulse width of the detected light pulses. Depending on the pulse width for a specific detected light pulse, a basic correction of the reception time is performed for this light pulse in this variant.

[0019] Ambient light refers to any type of light that triggers detection signals in the receiving unit and that does not originate from light pulses reflected back from the monitored area. Key and typical sources of ambient light are daylight and artificial light at the location of the receiving unit, for example, in a factory hall.

[0020] The purpose of correcting the reception times, both the basic correction and the ambient light correction, is to determine an effective reception time, which, together with the transmission time of the relevant light pulse, is then used to calculate the transit time and thus the distance. The effective reception time is therefore a corrected reception time that should lead to a measurement result with lower measurement uncertainty.

[0021] In general, correcting the time of reception is equivalent to correcting the measured distance.

[0022] The exposure to extraneous light naturally leads to changes in the detection signals of the receiving unit.

[0023] A first important insight of the invention can be considered to be that the corrections to the reception times are sensitive to the intensity of the ambient light. Because the amplitudes and pulse widths of the detected light pulses change depending on the ambient light, the intensity of the ambient light plays a particularly important role when the corrections to the reception times are made depending on the pulse width determined for the respective light pulses.

[0024] Another important finding of the invention is that the accuracy of the distance determination can be significantly increased if the effects of ambient light are taken into account.

[0025] In this context, the fundamental idea of ​​the invention can be considered to be to determine the intensity of ambient light reaching the receiving unit and then, depending on the determined intensity of the ambient light, to perform a further correction of the reception times of the detected light pulses. This further correction is referred to as ambient light correction.

[0026] The correction of a reception time, which is known per se and uses a pulse shape of the detected reflected light pulse, is thus extended in the present invention by a compensation for the influence of ambient light. For this purpose, the intensity of the ambient light is determined according to the invention.

[0027] To determine the intensity of the ambient light, a measurement signal from the receiving unit itself can be evaluated. Alternatively, a separate photodetector can be used, located near the receiving unit, to measure the intensity of the ambient light.

[0028] A significant advantage of the present invention is that by taking ambient light into account, the measurement accuracy provided by the method and the optical sensor is increased, and additional application possibilities for the method and the optical sensor are created.

[0029] The optical sensor according to the invention is particularly suitable and configured for carrying out the method according to the invention.

[0030] The optical sensor according to the invention can be a single optical sensor for measuring the distance of an object in a fixed direction in space. The direction in which a distance is measured can also be varied. For example, the optical sensor according to the invention can be a 2D or 3D scanner.

[0031] Using an assumption about the pulse shape of the reflected light pulses, the pulse width of a light pulse can be deduced from its measured amplitude. Alternatively or additionally, in a preferred embodiment of the method according to the invention, the pulse width of a detected light pulse is determined by comparing the received signal, particularly a digitized one, with an intensity threshold.

[0032] In other words, the pulse widths of the detected light pulses are measured between the rising and falling edges of the detected light pulse. Weak reflected light pulses, i.e., weak echo signals, then have a smaller pulse width than stronger echo signals. The pulse width and the amplitude of a pulse are thus related by a monotonic function. The pulse width of the echo signal, defined in this way, is therefore a measure of the amplitude and can be used for time-of-flight correction.

[0033] According to the invention, the ambient light correction of the reception time of a detected light pulse is performed as a function of the pulse width determined for the respective light pulse. Additionally, the ambient light correction of the reception times can be performed based on the amplitudes of the detected light pulses.

[0034] For the basic correction of the reception time, any mathematical operation can be applied to the reception time. In a preferred embodiment of the method according to the invention, a correction value, which depends on the pulse width determined for the light pulse in question, is subtracted from the reception time during the basic correction of the reception time of a detected light pulse.

[0035] Any mathematical operation can also be applied to the reception time for the correction of ambient light. In a further preferred embodiment of the method according to the invention, when correcting the reception time of a detected light pulse, a correction value is subtracted from the reception time, which depends on the pulse width determined for the light pulse in question and on a determined intensity of the ambient light.

[0036] The basic correction and the ambient light correction can be performed sequentially. For example, a first correction value, which performs the basic correction, is subtracted from the received time, and then a second correction value, which performs the ambient light correction, is subtracted from the already basic-corrected received time. The order in which the basic correction and the ambient light correction are performed is essentially arbitrary.

[0037] In principle, it is also possible for the basic correction and the extraneous light correction to be carried out as a single correction of the reception time.

[0038] For example, in the uniform correction of the reception time of a detected light pulse, a correction value dependent on the pulse width determined for the light pulse in question is subtracted from the reception time, which depends on the pulse width and on the determined intensity of the ambient light.

[0039] Determining the ambient light intensity means measuring at least one quantity that is monotonically related to the intensity of the ambient light at the location of the receiving unit. In principle, it is possible to use a separate photodetector within or near the receiving unit for measuring the ambient light intensity. In a particularly preferred embodiment of the invention, the same detector used to detect the reflected light pulses is also used to determine the ambient light intensity. The intensity of the ambient light can be determined, for example, by measuring the photocurrent of a detector. For instance, the photocurrent can be measured by measuring the voltage drop across a voltage divider.

[0040] In the manufacture of optical sensors of this type, the correction values ​​are typically determined by a so-called shutter cycle. A target with known reflectivity is positioned at a fixed distance in front of the optical sensor. The light pulses reflected from this target are attenuated in several stages by a grayscale wedge, and the attenuated light pulses are measured. This yields different pulse shapes—namely, amplitudes and pulse widths—of the reflected light pulses at a constant target distance. From the amplitudes and / or pulse widths, the necessary correction values ​​for correcting the reception time can then be determined. This shutter cycle can also be performed at multiple distances.

[0041] Other methods are also possible for determining the correction values ​​as a function of the pulse width of the echo signal. For example, the correction values ​​can be determined using a target of known reflectivity at different, known distances. It is also possible to measure against targets of different reflectivities at a fixed distance.

[0042] Preferably, before the actual measurement operation, correction values ​​for different pulse widths of the detected light pulses are determined and stored for a plurality of ambient light intensities, particularly those specifically set or simulated, and / or for different reflectivities and / or distances of a test object. These correction values ​​can be stored in tables. The control and evaluation unit expediently includes a storage device for this purpose.

[0043] In principle, it is possible to perform these learning processes, also known as shutter cycles, for different, specifically set intensities or levels of ambient light.

[0044] In a particularly preferred embodiment of the invention, instead, when setting up the optical sensor to simulate different intensities of the ambient light, a parameter or control parameter of the receiving unit, for example a bias voltage of the receiving unit, is varied.

[0045] The defined variation of, for example, a bias voltage is easier and less complex to implement than the defined variation of ambient light levels. A prerequisite for this design is that the variation of the relevant control parameter or parameter, for example, the variation of the bias voltage, has essentially the same effect on the measurement result of the receiving unit as an ambient light input, at least within the parameter's value range.

[0046] To at least partially compensate for the effects of ambient light, the control of a detector in the receiving unit can be adjusted depending on the detected intensity of the ambient light. However, in a preferred embodiment of the method according to the invention, the control is not changed; rather, the control of the receiving unit, in particular the control of a photodetector, is not modified depending on the intensity of the ambient light. It has been shown that corrections to the reception time can be achieved more reliably in this way.

[0047] Further features and advantages of the invention are explained below in connection with the accompanying figures. These show: Figure 1: A schematic representation of an optical sensor according to the invention; Figure 2: A diagram illustrating the concepts of detected light pulse, pulse width, and intensity threshold. Figure 3: A diagram plotting the change in the measured apparent distance against the width of the reflected pulse; Figure 4: A schematic representation of the circuitry of a detector in the receiver unit of an optical sensor; Figure 5: A diagram plotting the change in voltage at Vm against the intensity / level of the ambient light; Figure 6: A diagram plotting the width of the reflected pulse against the intensity / level of the ambient light; Figure 7: A diagram plotting correction values ​​for different undervoltage values ​​at Vm corresponding to different intensities / levels of the ambient light against the width of the reflected pulse.

[0048] An embodiment of an optical sensor 100 according to the invention and a variant of the method according to the invention are described with reference to the Figures 1 to 7 explained.

[0049] The in Figure 1 The schematically represented optical sensor 100 according to the invention for measuring a distance d of an object 40 according to the time-of-flight principle includes as essential components a transmitter unit 10, a receiver unit 20 and a control and evaluation unit 80.

[0050] The transmitting unit 10 is used to emit light pulses 12 into a monitoring area 50 and has at least one light source, typically at least one LED or at least one laser diode. The receiving unit 20 primarily serves to detect light pulses 14 reflected back from an object 40 in the monitoring area 50 and has at least one photodetector, for example, at least one MMPC detector. In this embodiment, the receiving unit 20 also serves to detect the intensity of ambient light, for example, daylight or artificial light, at the location of the optical sensor 100.

[0051] The control and evaluation unit 80 can, for example, be a microcontroller and, according to the invention, serves to control the transmitter unit 10 and the receiver unit 20 and to evaluate light pulses detected by the receiver unit 20. 14. In the exemplary embodiment, the control and evaluation unit 80 has a Figure 1 not shown separately, in which correction tables for correcting the reception times are stored depending on a determined intensity of the ambient light and depending on parameters of the pulse shape of the detected light pulses, for example amplitude and / or pulse width.

[0052] According to the invention, the control and evaluation unit 80 is configured to perform a basic correction of the reception times of the light pulses in order to determine effective reception times of the detected light pulses and to determine a distance d to the object 40 based on the transit time of the light pulses.

[0053] Using the speed of light c in the medium in question, typically air, and the difference between a transmission time ts and a reception time tr, the distance d of the reflecting object is determined: d = tr − ts / 2 c .

[0054] Furthermore, the control and evaluation unit 80 is designed to evaluate the intensity of ambient light arriving at the receiving unit 20 and, depending on the detected intensity of the ambient light, to perform an ambient light correction of the reception times of the detected light pulses.

[0055] To determine the transit time and thus the distance, the corrected reception time is used, which is also referred to as the effective reception time te.

[0056] The optical sensor 100 of the exemplary embodiment and in particular the control and evaluation unit 80 are suitable and equipped for carrying out the method according to the invention.

[0057] Some key terms for correcting the reception time are explained using the diagram in Figure 2 explained. In Figure 2The diagram schematically depicts a first received light pulse p1 and a second received light pulse p2, each as a curve of intensity Int versus time t. The intensity is the intensity detected and, if necessary, amplified by a photodetector. The amplitude of light pulse p1 is greater than that of light pulse p2. For example, the light pulses p1 and p2 can originate from two test objects with different reflectivities, positioned at the same distance d in front of the optical sensor 100. The test object with the lower reflectivity causes light pulse p2, and the one with the higher reflectivity causes light pulse p1. The time of reception of a light pulse can be defined as the time at which the intensity curve of the light pulse crosses an intensity threshold. For light pulses p1 and p2, these are times t1 and t2, respectively.As can be seen, the lower amplitude of the light pulse p2 causes it to reach the threshold S at a later time t2 compared to t1. Despite the nominally identical distances between the two test objects, different reception times of the reflected light pulses would therefore be obtained, resulting in different travel times and different distances.

[0058] Figure 3The diagram shows measurement results for a test object at a constant distance from the optical sensor, each with a different attenuation of the reflected pulse represented by a gray wedge. The graph plots the change Δd of the measured apparent distance in cm on the vertical axis against the pulse width PW of the detected reflected light pulse in m on the horizontal axis. The change Δd of the measured distance is only apparent because the distance to the test object does not actually change. The pulse width in time units is obtained by dividing the pulse width PW in meters by the speed of light in the relevant medium, typically air.

[0059] The change Δd of the measured apparent distance is relative to the light pulses of maximum intensity. In the example of the Figure 3These light pulses have a pulse width of 3 m. The change Δd of the measured apparent distance at a pulse width of 3 m is therefore 0. As the light pulses are attenuated by the gray wedge, the amplitude decreases, and consequently, so does the pulse width PW of the detected light pulse. The point of penetration through the intensity threshold S (see Figure 2 ) shifts at later times, and the measured apparent distance increases accordingly. The diagram in Figure 3 This shows that with decreasing pulse width, the measured change in apparent distance increases from 0 cm at a pulse width of 3 m to about 6 cm at a pulse width of 1 m, and to about 50 cm at a pulse width of almost 0.

[0060] A basic correction for this systematic measurement error is possible using the pulse width of the detected light pulses p1 and p2. The pulse width is defined as the time difference between the points in time at which the intensity profile of a detected pulse is equal to that of the threshold value S. For the first detected light pulse p1, the pulse width pw1 is obtained, and for the second detected light pulse p2 with a lower amplitude, the smaller pulse width pw2 is obtained. With essentially the same pulse shape, the pulse width defined in this way increases monotonically with the amplitude.A correction for the systematic measurement error caused by the different amplitudes or, equivalently, the different pulse widths of the detected light pulses is possible by, for example, subtracting the difference between t2 and t1 from the reception time t2. Accordingly, for the second detected light pulse, p2, te = t1 is obtained as the effective reception time. The correction for the first detected light pulse, p1, would be 0 in this definition; that is, for the first detected light pulse, te = t1 would also apply.

[0061] Preferably, the basic correction of a reception time t1, t2 of a light pulse p1, p2 is carried out as a function of a pulse width pw1, pw2 determined for the relevant light pulse p1, p2.

[0062] An example of stray light correction is given with reference to the Figures 4 to 7 explained.

[0063] Figure 4Figure 28 shows an example of the circuitry of a photodetector 22, for example, an MPPC detector. It also describes how the intensity of the ambient light can be determined. The photodetector 22 is reverse-biased by applying a constant positive voltage to V1 and becomes conductive when irradiated with light. In this embodiment, a detection signal is coupled out via a capacitor 24 and fed to an amplifier 26. An amplified signal is available at the output of the amplifier 26 for further processing by the control and evaluation unit 80.

[0064] A photocurrent generated by irradiating the photodetector 22 with light causes a voltage drop in the voltage divider R1 / R2 that is proportional to the photocurrent and thus to the intensity of the incident light. Typically, R2 is much larger than R1. This voltage is tapped between R1 and R2 and fed to the further voltage divider R4 / R3. A suitably scaled voltage is available at tap Vm, which can be measured by an analog-to-digital converter of the control and evaluation unit 80. Capacitors C1 and C2 short-circuit higher-frequency components, and the voltage measured at Vm can thus be used as a measure of the ambient light reaching the photodetector 22. The greater the ambient light input to the photodetector 22, the greater the drop in the voltage measured at Vm.In comparison to a situation without any extraneous light, where a partial voltage of V1 corresponding to the division ratio of the voltage divider R4 / R3 is measured at Vm, a non-vanishing extraneous light result in an undervoltage at Vm.

[0065] Figure 5 The diagram shows the change in voltage at Vm in volts, i.e., the undervoltage, plotted on the vertical axis against the intensity / level of ambient light in kLux on the horizontal axis. The change in voltage refers to the change compared to the situation without any ambient light. Figure 5 shows that with increasing intensity of the ambient light, the voltage at Vm (see Figure 4 ) by up to approximately 4.3V at an ambient light intensity of 100 kLux compared to the situation without ambient light.

[0066] These changed conditions for the photodetector 22 are reflected in the pulse widths of the back-emitted detected light pulses measured for one and the same target at one and the same distance. Figure 6 This effect is illustrated in a diagram where the width of the reflected pulse in meters is plotted on the vertical axis against the intensity / level of the ambient light in kilolux on the horizontal axis, all for the same target and object distance. As can be seen, the pulse width of the detected reflected light pulses decreases with increasing ambient light intensity, specifically from approximately 2.3 meters without ambient light to only about 0.2 meters at an ambient light intensity of 100 kilolux.

[0067] Because of the issues related to Figure 2As explained, the effects of pulse width on the reception time of a light pulse make it clear that ambient light represents a significant source of error. The invention recognizes that this source of error can also be largely compensated for.

[0068] In addition to the basic correction, in this embodiment of the present invention the drop in voltage at the receiver due to extraneous light is used to correct the reception time or, equivalently, to correct the measured distance.

[0069] An example of this will be given in connection with Figure 7 explained. Figure 7The diagram shows correction values ​​in cm for different intensities / levels of ambient light plotted on the vertical axis against the width of the reflected pulse in m on the horizontal axis. The correction values ​​are given here in cm and can thus be directly subtracted from a measured distance. The corresponding correction values ​​for the time of reception would be obtained by dividing the correction values ​​in cm by the speed of light in the relevant medium, for example, air. Figure 7 This shows correction values ​​for a situation where the ambient light correction and the basic correction are performed sequentially. For example, the ambient light correction can be performed after the basic correction.

[0070] Figure 7 shows five different correction curves k0, k1, k2, k3 and k4, which correspond to different undervoltages at Vm (see description of Figure 4The correction curve k0 corresponds to the undervoltage of 0, i.e., to zero ambient light ingress. The correction curves k1, k2, k3, and k4 correspond to undervoltage values ​​of -1V, -2V, 3V, and -4V, respectively, at Vm. As can be seen, all correction values ​​are zero for correction curve k0; therefore, no further correction is made beyond the basic correction. With increasing ambient light ingress from correction curve k1 to correction curve k4, the values ​​increase as shown in the diagram. Figure 7 The correction values ​​for the distance, which must be subtracted for different pulse widths, are also evident.

[0071] The correction curves k0, k1, k2, k3 and k4 can each be obtained by selectively adjusting certain intensities of the ambient light.

[0072] In an advantageous embodiment of the invention, which is easier and less expensive to implement in comparison, a parameter of the receiving unit 20, in particular the bias voltage of the receiving unit 20 at V1, is used instead. Figure 1 ) is specifically varied so that, at Vm, when no light pulses are measured, the undervoltage values ​​specified above for the correction curves k0, k1, k2, k3 and k4 are established.

[0073] The present invention introduces a novel method and a novel optical sensor for determining the distance of an object according to the time-of-flight principle, which enable reliable distance measurements even in the presence of ambient light. Reference symbol list

[0074] 10 Transmitter unit 12 Light pulses emitted into the monitoring area 50 14 Light pulses reflected back by an object 40 20 Receiver unit 22 Photodiode, receiver 24 Output capacitance 26 Amplifier 28 Output 40 Object 50 Monitoring area 80 Control and evaluation unit 100 Optical sensor c Speed ​​of light, especially in air C1 Capacitance C2 Capacitance d Distance of the object 40 to the optical sensor 100 Int Intensity in arbitrary units k0 Correction values ​​as a function of the pulse width at ambient light level 0V k1 Correction values ​​as a function of the pulse width at ambient light level -1V k2 Correction values ​​as a function of the pulse width at ambient light level -2V k3 Correction values ​​as a function of the pulse width at ambient light level -3V k4 Correction values ​​as a function of the pulse width at ambient light level -4V p1 Intensity profile of a first detected light pulse p2 Intensity profile of a second detected light pulse PW Pulse width of a detected light pulsepw1 Pulse width of the light pulse p1 pw2 Pulse width of the light pulse p2 R1 Ohmic resistance R2 Ohmic resistance R3 Ohmic resistance R4 Ohmic resistance S Intensity threshold t Time in arbitrary units ts Transmission time tr Receipt time te Effective reception time tc Propagation time t1 Reception time of the first received pulse (=time at which p1=S is on the rising edge of the pulse) t2 Reception time of the second received pulse (=time at which p2=S is on the rising edge of the pulse) V1 Blocking voltage Vm Measuring voltage Δd Change Δd of the measured apparent distance

Claims

1. Method for measuring a distance of an object according to the transit time principle, in which light pulses (12) are emitted into a monitoring area (50), light pulses (14) reflected back from an object (40) in the monitoring area (50) are detected by a receiving unit (20) and a distance (d) to the object (40) is determined on the basis of a transit time (tc) of the light pulses (12), wherein a basic correction of a reception time (t1, t2) of the respective light pulse (p1, p2) is carried out, wherein an intensity of extraneous light arriving at the receiving unit (20) or at a photodetector in the vicinity of the receiving unit (20) is ascertained and wherein an extraneous light correction of the reception times of the detected light pulses (p1, p2) is carried out as a function of the ascertained intensity of the extraneous light, characterized in that the basic correction of a reception time (t1, t2) of a detected light pulse (p1, p2) is carried out as a function of a pulse width (pw1, pw2) ascertained in each case for the detected light pulse (p1, p2) and in that the extraneous light correction of the reception time of a detected light pulse (p1, p2) is carried out as a function of the pulse width (pw1, pw2) ascertained for the light pulse in question.

2. Method according to claim 1, characterized in that a pulse width (pw1, pw2) of a detected light pulse (p1, p2) is determined by comparing the, in particular digitized, received signal with an intensity threshold (S).

3. Method according to any one of claims 1 or 2, characterized in that, in the basic correction of the reception time of a detected light pulse (p1, p2), a correction value dependent on the pulse width (pw1, pw2) ascertained for the light pulse (p1, p2) in question is subtracted from the reception time (t1, t2).

4. Method according to any one of claims 1 to 3, characterized in that, in the extraneous light correction of the reception time of a detected light pulse (p1, p2), a correction value dependent on the pulse width (pw1, pw2) ascertained for the light pulse (p1, p2) in question is subtracted from the reception time (t1, t2).

5. Method according to any one of claims 1 to 4, characterized in that the basic correction and the extraneous light correction are carried out sequentially.

6. Method according to any one of claims 1 to 4, characterized in that the basic correction and the extraneous light correction are carried out as a unitary correction of the reception time.

7. Method according to claim 6, characterized in that, in the unitary pulse width correction of the reception time of a detected light pulse (p1, p2), a correction value dependent on the pulse width (pw1, pw2) ascertained for the light pulse (p1, p2) in question is subtracted from the reception time (t1, t2).

8. Method according to any one of claims 1 to 7, characterized in that an intensity of the extraneous light is ascertained by measuring a photocurrent of the receiving unit (20).

9. Method according to claim 8, characterized in that the photocurrent is measured by measuring a voltage drop (Vm) across a voltage divider (R3, R4).

10. Method according to any one of claims 1 to 9, characterized in that, prior to the actual measuring operation, correction values for different pulse widths (pw1, pw2) of the detected light pulses (p1, p2) are determined and stored for a plurality of, in particular specifically set or simulated, intensities of the extraneous light and / or for different reflectivities and / or distances of a test object.

11. Method according to claim 10, characterized in that, in order to simulate different intensities of the extraneous light, a parameter of the receiving unit (20), in particular a bias of the receiving unit (20), is varied.

12. Method according to any one of claims 1 to 11, characterized in that an actuation of the receiving unit (20), in particular an actuation of a photodetector (22), is not changed as a function of an intensity of the extraneous light.

13. Optical sensor for measuring a distance of an object according to the transit time principle, for carrying out the method according to any one of claims 1 to 12, comprising a transmitting unit (10) for emitting light pulses (12) into a monitoring area (50), comprising a receiving unit (20) for detecting light pulses (14) reflected back from an object (40) in the monitoring area (50) and comprising a control and evaluation unit (80) for actuating the transmitting unit (10) and the receiving unit (20) and for evaluating light pulses (p1, p2) detected by the receiving unit (20), wherein the control and evaluation unit (80) is designed to carry out a basic correction of a reception time (t1, t2) of a light pulse (p1, p2) as a function of a pulse width (pw1, pw2) ascertained for the detected light pulse (p1, p2) in order to determine effective reception times (te) of the detected light pulses (p1, p2) and to determine a distance (d) to the object (40) on the basis of the transit time (tc) of the light pulses, wherein the control and evaluation unit (80) is designed to evaluate an intensity of extraneous light arriving at the receiving unit (20) or at a photodetector in the vicinity of the receiving unit (20) and to carry out an extraneous light correction of the reception times of the detected light pulses (p1, p2) as a function of the ascertained intensity of the extraneous light, characterized in that the control and evaluation unit (80) is further designed to carry out the basic correction of a reception time (t1, t2) of a detected light pulse (p1, p2) as a function of a pulse width (pw1, pw2) ascertained in each case for the detected light pulse (p1, p2) and to carry out the extraneous light correction of the reception time of a detected light pulse (p1, p2) as a function of the pulse width (pw1, pw2) ascertained for the light pulse in question.

14. Optical sensor according to claim 13, characterized in that the receiving unit (20) comprises at least one of the following photodetectors: MMPC detector, SPAD detector, CMOS detector, CCD detector.

15. Optical sensor according to claim 13 or 14, characterized in that the control and evaluation unit (80) comprises a memory device, in which correction values for different pulse widths (pw1, pw2) of the detected light pulses (p1, p2) are stored as a function of an ascertained intensity of the extraneous light.

16. Optical sensor according to any one of claims 13 to 15, characterized in that the control and evaluation unit (80) is designed to carry out the method according to any one of claims 1 to 12.