Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/497—Means for monitoring or calibrating

Definitions

• the invention relates to a method and a device for determining a distance to a retroreflective object and, if appropriate, the degree of reflection of the object according to the terms of claim 1 and 10.
• a door opens when a measuring arrangement detects the approach of an object. Or a revolving door stops as soon as an obstacle is detected. Changes may occur due to the approach, presence or removal of an object and are detected by the measuring device.
• One way of distance measurement is to use the light transit time.
• a laser beam is directed at the object to be measured and the reflected light is measured.
• the delay until the reflected light arrives at the receiver is a value for the distance the light has traveled.
• the speed of light is around 300,000 km / s.
• a light pulse that covers a distance of 3 m takes about 10 nanoseconds.
• fast lasers or fast photodiodes and amplifiers are necessary.
• One solution makes use of the possibility of transforming the runtime information into an easily handled frequency range (cf., for example, DE 100 22 054 A1). This is for the purpose of determination the duration of the emitted light with a high frequency, z. B. modulated several hundred MHz.
• the received light is then mixed with a second frequency that is only slightly different than the transmitted frequency.
• a third, significantly lower frequency is formed, which can be processed in the wider circuit easier than the original high modulation frequency.
• this third frequency is in the phase, the information of the light transit time. Since the third frequency is usually downsampled in a frequency range of a few kHz, the determination of the phase information and thus the light transit time is very simple.
• the determined difference value is used to drive a phase shifter designed as a digital delay element, and the delay time is changed until the difference value becomes small.
• the disadvantage of this system is that only a certain distance range is covered, moreover, the phase information repeats periodically, so that indeterminacy occurs. In order to avoid these vagaries, extensive measures such as modulation with different frequencies are necessary. This system basically works with more than one light pulse, otherwise no mixing process can take place. In known systems, at least several thousand individual pulses are emitted to obtain several periods of the signal downconverted to the third frequency.
• a second method for determining the light transit time is the direct measurement of a single pulse.
• uncertainties are excluded, as they are disadvantageous in the method described above.
• the advantage of a single pulse is the possible higher power.
• much higher demands are placed on the detection of such a light pulse in the receiver.
• the receiver To measure distances below 15 cm, the receiver must have a response time under a nanosecond.
• a perfectly emitted light pulse with a rise time of theoretically zero, however, is "softened” by the inherently limited bandwidth in the receiver, ie when evaluated at a threshold of 50% of the maximum amplitude, this results in a "delay", which is generally dependent on the temperature but also depends on the received energy.
• the received signal is usually regulated to a fixed amplitude. This regulation of the amplitude can lead to an undesirable time shift. Also, determining the exact time to receive turns out to be difficult with very small signals and therefore high noise. By the way, should the received pulse with strong reflection the Do not overdrive the photodiode or the preamplifier, as the resulting non-linearities have a negative effect on the accuracy of the reception time.
• a fast photodiode usually an avalanche photodiode
• a fast preamplifier must also be provided here. Frequency ranges up to the gigahertz range are not uncommon.
• extraneous light which in extreme cases is several thousand times stronger than the reflected light of the emitted pulse. All these influences have a negative effect on the accuracy of the measurement.
• the method works exclusively with continuously successive pulses alternately from two different but electrically identical light sources and is therefore limited in its pulse power due to the temperature limit in the light-emitting diodes used.
• a disadvantage of this method however, a possibly occurring, not exactly ausregelbares to zero signal, created for example by an asymmetry of the light sources used or other electronic components.
• This residual signal can lead to a measurement error in strong ambient light radiation and at the same time strong reflection of the transmission signal.
• the said asymmetry arises, for example, when an LED has a different time Lich behavior when switching on or off or when different light sources, such as laser and LED are used mixed.
• the present invention has the object to provide a working with single pulses high energy density method.
• This object is achieved by a method and a device for determining a distance to a retroreflective object with the features of claim 1 or 10.
• the invention makes use of the fact that not a reflected pulse is measured and evaluated, but that a possible pulse in the receiver is made to disappear.
• the received pulse is preferably so "embedded" between two reference pulses also originating from a light path or electrically transmitted, so that it is no longer recognizable as a single pulse, but the comparison with a reference pulse is sufficient “Disappearance” brings, then corresponds to the duration of the light pulse from the transmitted light source to the reflecting object and back to the receiver and thus represents a value for the distance.
• the pulses can also be detected before and after the actual transmission signal and an average value can be formed from their amplitudes, which corresponds to the proportion of the reference signal and is compared with the amplitude value from the light signal.
• the clock change signals alone may under certain circumstances still contain an error potential in that rise and fall times of the light-emitting diodes are included.
• a clock change signal is used alone and compared to an amplitude value independent of the time of flight, these errors can be reduced, although a possible temperature drift can then have a slightly greater influence.
• the amplitude value adjusted by the amplitude control is used as the reference at the preamplifier.
• the light emitting diodes possibly occurring asymmetries or tolerances are corrected and have no effect on the measurement accuracy, not even under high external light influence.
• 5 is a schematic representation of a clock shift in the picosecond range
• 6 shows timing curves in an embodiment according to FIG. 5.
• a clock control 1.1 e.g. a correspondingly programmed microcontroller, delivers pulses to at least one transmitted light source 1.8 and a second, located in the immediate vicinity of the receiver second light source 1.9, which serves as a reference light source.
• the light sources may be light emitting diodes or laser diodes or alternatively both types mixed. At least one of the two light sources is adjustable in phase and amplitude by a determinable amount.
• the transmission light source 1.8 sends e.g. every 10 ms a pulse of 100 ns. This traverses the light path 1.24 and 1.25 to the object and from the object 1.26 to a receiver, such as e.g. the photodiode 1.10 and would appear without further action as a single pulse in the amplifier 1.11. To detect the time of arrival, the problems mentioned above would now occur in the prior art.
• a reference pulse 2.1 according to FIG. 2 is emitted. This is led from the second light source 1.9 directly over a short path in the photodiode 1.10.
• the actual transmission pulse 2.2 (FIG. 2) first of all includes the transmission light source 1.8.
• another reference pulse 2.3 emanates from the second light source 1.9.
• the transmission pulse 2.2 is embedded between two reference pulses.
• the method described also works with only one reference pulse.
• the reference pulses can also be transmitted directly as electrical reference signals to the preamplifier 1.10 or the subsequent controls.
• rapidly changing external light influences can then lead to short-term measured value errors.
• the light of the transmitted light source 1.8 and the light of the reference light source 1.9 initially arrive at the photodiode 1.10 with different intensity.
• the receiver converts the received signal, ie the received transmission signal 2.2 and possibly the at least one received reference signal 2.1, 2.3 into an electrical transmission signal 2.5 or an electrical reference signal 2.4, 2.6.
• the electrical reference signal can also be introduced directly into the circuit and subsequent regulation without the detour via a light path.
• the photodiode amplifier, the preamplifier 1.11 during the duration of all pulses by control line 1.30 is activated.
• the temporal range is considered, in which the light sources are active. Falsifications of the received signal by the increase in light at the first reference pulse 2.1 and light fall at the end of the second reference pulse 2.3 are thereby excluded.
• a decomposition of the received signal according to FIG. 2 into the clock sections A 1 B 1 C 1 D 1 E shows on the one hand two regions B, D with clock change signals between adjacent pulses 2.1, 2.2 or 2.2, 2.3 and on the other hand the regions A, C, E, in which the clock change signal has subsided and only pure amplitude information is pending.
• the signal path switch 1.17 switches the range A, E to a first input 1.19a of a comparator 1.19.
• the area C is inverted via inverting stage 1.12 to the areas A + E with signal path switch 1.18 to the same input 1.19a of the comparator 1.19.
• the second input 1.19b of the comparator 1.19 is located at a, formed by two equal resistances 1.13 averaging of the direct and the inverted signal of the preamplifier 1.11. Since both equally large signals cancel each other by alternating voltages, a pure DC voltage component is thus present at the summation point between the two resistors.
• the comparator 1.19 itself can be implemented as a high-gain operational amplifier with integration 1.31 of the input signal.
• This comparator 1.19 is to detect even the smallest difference of the input values and to provide them at the output 1.19c as control value 1.29.
• This control value can be evaluated for the detection of changes to or as a result of the object and thus serves e.g. for detecting the position, position and movement of the object 1.26.
• the circuits 1.31 of the comparators 1.16, 1.19 and 1.22 correspond to an integrating "sample and hold" function
• the amplitude values of the reference pulses 2.1 and 2.3 are compared with the amplitude values of the transmit pulse 2.2.
• a difference between the two values leads to a control voltage 1.29 at the output 1.19c of the comparator 1.19.
• this control voltage at least one of the two light sources 1.8 and 1.9 is readjusted in its amplitude until no difference of the input voltages at the comparator 1.19 is present or at least minimal.
• the reference light source 1.9 is controlled directly via the amplitude control 1.6, while the transmission light source 1.8 is controlled inversely via the amplitude control 1.7 and the inverter 1.12.
• the transmission step is e.g. regulated to high power, while the reference light source 1.9 is adjusted so far until the reference pulses 2.1, 2.3 appear the same as the transmission pulse 2.2 in the receiver 1.10. If we omit the time shift due to the light paths 1.24 and 1.25, the total transmit pulse in the receive signal consisting of the first reference signal 2.1, the transmit signal 2.2 and the second reference signal 2.3 is not visible as such. He has "disappeared", so to speak.
• the transmission pulse is embedded in a second signal environment so that it is no longer visible, but should be determined in the case of a light time measurement, the time that this pulse has traveled on the light paths 1.24 and 1.25.
• the 1.24 light range is 15 cm long, and thus 30 cm back and forth.
• the pulse arrives in the receiver as having a "delay" of one nanosecond. 2 shows the representation of the received signal 2.4 of the first reference pulse 2.1, of the received signal 2.5 of the transmission pulse 2.2 delayed by one nanosecond and of the received signal 2.6 of the second reference pulse 2.3.
• the delay is exaggerated; in practice, a delay of 1 nanosecond is barely visible in relation to the transmitted pulse length.
• a short gap of one nanosecond will arise between the received signal 2.4 of the first reference pulse 2.1 and the received signal 2.5 of the incoming transmit pulse 2.2, in which no light from one of the two light sources 1.8 and 1.9 hits the photodiode 1.10.
• a “slow” photodiode and a “slow” preamp can not resolve this short pulse. Since, in addition, the rise times for commercially available light-emitting diodes and driver stages in C-MOS technology are certainly longer than a nanosecond, in the best case a strongly attenuated and in its amplitude poorly determinable pulse would appear at the output of preamplifier 1.11.
• the transit time of the light signal is determined by the method described here, one is no longer dependent on an accurate measurement of the received light pulse. Rather, it is even advantageous if the received pulse is "smoothed" by a limitation of the photodiode or preamplifier bandwidth.
• the energy of the pulse is not lost when it is being polished, ie when passing through an amplifier with reduced bandwidth
• a pulse of one nanosecond and a pulse height of, for example, 10 mV will then have a pulse height of 10 microvolts, but with a length of 1000 nanoseconds.
• This "small", but long pulse can now be amplified without problems using C-MOS technology. With a gain of 8OdB then results in a pulse height of 100 mV.
• the photodiode amplifier 1.11 can also be designed as a high-gain limiter amplifier. The temporally precise assignment of the received pulse 2.5 is indeed lost, but is not needed in the method described here.
• the signal 2.9 in FIG. 2 shows the received signal at the output of the preamplifier 1.11 which is adjusted in amplitude but not yet in time. From the very short pulses at the Ü Transition between transmit and reference pulses has now become a long and easy to process pulse. In a further step, the received signal 2.9 is now examined for these pulses. For this purpose, the amplitude differences in the areas B and D are compared with the Signalwegschalter 1.14 and 1.15. The signal path switch 1.14 switches during the area B to a first input 1.16a of a comparator 1.16. The area D is given inverted to the area B with signal path switch 1.15 to the same input 1.16a of the comparator 1.16.
• the second input 1.16b of the comparator 1.16 is located at a mean value formation formed by two identical resistances 1.13 from the direct and the inverted signal of the preamplifier 1.11. Since both equally large signals cancel each other by alternating voltages, a pure DC voltage component is thus present at the summation point between the two resistors. Only a DC voltage drift in the output voltage of preamplifier 1.11 and inversion stage 1.12 is communicated to the summation point and thus to the second input 1.16b of the comparator 1.16. As a result of this measure, the influence of a temperature-induced DC drift of the amplifier 1.11 and of the inverter 1.12 in the comparator 1.16 is canceled out.
• the comparator can be identical to the comparator 1.19, ie as a high-gain operational amplifier with integration of the input signal.
• the execution of the comparators described here can also be different, it is only essential that they compare two signals with each other while having a high gain. A difference between the two input values of comparator 1.16 leads to a control voltage 1.27 at the output of comparator 1.16.
• the information from the sections B and D are compared directly with each other, as shown in Figure 1.
• properties of the LEDs can falsify the result.
• One way to reduce this influence is to trigger or minimize the amplitude of only one clock change signal compared to the amplitude of a reference value pending in the regulated state of the amplitude regulation at the output 1.11b of the preamplifier 1.19.
• the control voltage 1.27 is given to a control voltage processing 1.2. Depending on the control voltage 1.27, this stage shifts the phases of the reference pulses 2.1, 2.3 and the transmit pulse 2.2 relative to one another by means of the analog or digital phase controls 1.3, 1.4, 1.5 in such a way that the pulses applied to the preamplifier 1.11 in the periods B and D disappear. It is sufficient if only the transmission pulse 2.2 or only the reference pulses 2.1 and / or 2.3 are shifted in time, but of course also transmission and reference pulses can be shifted to each other. In the described example of a distance of the reflecting object 1.26 in 15 cm distance, the reference pulses and the transmission pulse must be shifted by exactly one nanosecond to each other.
• the clock change pulses of the received signal 2.9 are extinguished according to signal 2.10 and at the output 1.11b of the amplifier 1.11 is only the amplifier noise without any isochronous shares.
• the first and second reference pulses are combined and fed to the amplitude control 1.6.
• control voltage 1.27 is then the information of the light runtime.
• the value of the light runtime can also be obtained as a digital value.
• a determination of the light transit time according to the method described so far has the advantage of very high detection sensitivity with a very high dynamic range of the reflection. If necessary, the method described also works with only one reference pulse. However, rapidly changing extraneous light influences can then lead to short-term measured value errors.
• Fig. 4 shows the advantage of two reference pulses.
• the received signals 2.4, 2.6 of the reference pulses and the received signal 2.5 of the transmitted pulse are also influenced. Since the mean value 4.2 for the first reference pulse, the mean value 4.3 for the transmit pulse, and the mean value 4.4 for the second reference pulse are formed in the integration circuit 1.31, the resulting common mean value of the reference pulses 2.4 and 2.6 is equal to the mean value 4.3 of the transmit pulse. Fast ambient light changes thus have no influence on the measurement.
• FIG. 3 shows this state in the signals 3.1, 3.2 and 3.3.
• the output signal 3.4 of the preamplifier 1.11 shows an asymmetrical course without time correction of the reference or transmit pulse. After adjustment by means of comparator 1.16, the desired symmetry results, but a residual error remains in the clock ranges B and D.
• the clock sections A 1 C and E are compared with the clock sections B and D by means of a further comparator 1.22.
• the signal path switch 1.20 switches the clock sections A 1 C 1 E to an input 1.22a of the comparator 1.22, while the signal path switch 1.21 switches the clock sections B, D to the other input 1.22b.
• the output 1.22c of the comparator 1.22 is connected to the control voltage processing 1.2.
• the control voltage processing 1.2 acts on the phase control, for example, the transmission pulse is extended or shortened until the residual error 3.5 is completely extinguished and again only the amplifier noise is present without isochronous portions of the photodiode amplifier 1.11. It does not matter whether the transmit pulse or the reference pulses are influenced in the time length or the reference pulses are shifted in their position. All three regulations, ie amplitude, time shift and compensation of the reaction time can be active at the same time, without disturbing each other.
• a digital signal delay can be used for this purpose.
• a desired resolution of eg 1.5 mm then means a step size of 10 picoseconds.
• the clock rate of a possible microprocessor would theoretically be 100 gigahertz, a clock frequency z.Zt. not yet possible.
• a clock-shifting solution in the picosecond range is shown in FIG. 5.
• a clock 5.4 which can be extracted from the clock generator 1.1 with quartz precision, is sent through a specific number of gates 5.1 in an IC. Each of the swept gates delays the clock by a short time, eg 10 picoseconds. By means of the switches 5.8, any tap between the gates can be selected.
• An analog / digital converter 5.3 receives the control voltage from the comparator 1.16. This chooses according to the re- Voltage a corresponding switch off. At output 5.7, the binary value for the set delay can then be tapped, for example.
• the delay time of a gate depends on temperature and supply voltage.
• the clock 5.11 is compared after passing through all gates in a phase comparator 5.2 with the input clock 5.4. With a corresponding number of gates then the clock, which went through all the gates and the input clock 5.4 again have the same phase.
• phase comparator 5.2 a phase difference is detected and output as control voltage gate delay time 5.9. This controls the delay time of the gates.
• the supply voltage of the gates is influenced to control the signal delay. It is also possible to invert one of the two input signals of the phase comparator 5.2 (5.10), in which case only half of the gates are needed. This is illustrated in FIG. 6.
• the original input clock 6.2 is delayed by half a period and thus in phase again with the inverse input signal 5.10.
• a clock delay of quartz accuracy in the picosecond range is possible.
• phase control second reference source pulse 2.6 receive signal second pulse Refe ⁇
• Reference light source 2.9 Received signal with regulated
• Preamplifier 2.10 Receive signal with regulated output

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• Electromagnetism (AREA)
• Optical Radar Systems And Details Thereof (AREA)
• Measurement Of Optical Distance (AREA)

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• 2007
  • 2007-01-29 DE DE102007005187A patent/DE102007005187B4/de not_active Expired - Fee Related
• 2008
  • 2008-01-28 WO PCT/EP2008/000615 patent/WO2008092611A1/de not_active Ceased
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