Patent Document

BACKGROUND INFORMATION 
     A method for directly sampling a backscatter curve is typically used for the detection of surroundings. However, a disadvantage of this method is that it requires very high-speed analysis electronics for A/D conversion and for achieving high data transmission rates and/or high signal processing rates. 
     The so-called boxcar method, which is also used for the detection of surroundings, has the disadvantage that a complete backscatter curve is first provided after m*n pulses, where m is the number of resolution cells and n is the number of pulses which are averaged within a resolution cell. At low pulse-pause ratios of 1:1000, e.g., in the case of laser diodes, a measuring time is thus increased by approximately 30 μs per measured point or distance cell, so that, inter alia, an analysis system idles for a longer period of time. 
     SUMMARY OF THE INVENTION 
     The method according to the present invention for the detection of surroundings is performed using a source which emits pulse signals. Signals backscattered from an object are detected by a sensor. When performing the method, a presence of the object is detected during coarse sampling. To determine a variable related to the detected object, operating parameters of the source are set for fine sampling. 
     The present invention additionally relates to a device for the detection of surroundings, which is implemented in particular for performing the method according to the present invention. The device has a source which emits pulsed signals, and a circuit system, the circuit system having a reference pulse coil for generating a reference pulse in an input path on a primary side of an RF transmitter. 
     The present invention additionally relates to a computer program having program code means to perform all steps of the method according to the present invention when the computer program is executed on a computer or a corresponding arithmetic unit, in particular a control unit in the device according to the present invention. 
     Moreover, the present invention relates to a computer program product having program code means, which are stored on a computer-readable data carrier, to execute all steps of the method according to the present invention when the computer program is executed on a computer or a corresponding arithmetic unit, in particular a control unit in the device according to the present invention. 
     Using the present invention, a possibility is provided for the detection of surroundings using a boxcar method for pulsed sensor systems, e.g., lidar. Varying a pulse-pause ratio, a so-called duty cycle, is not known for boxcar methods. The pulse-pause ratio, also referred to as the sampling ratio, indicates a ratio of a length of an on state and thus a pulse duration to a period duration in a square-wave signal. 
     Using the method, cost-effective analysis is possible with coverage of a great distance range of, for example, 0.1 m to 80 m, in particular with the aid of laser diodes or infrared-emitting diodes (IRED) as the sources used. Typical delay components or their refinements thereof, e.g., “CC850” from Robert Bosch GmbH, having a maximum delay corresponding to a distance of 30 m, are to be used. Peripherals already existing around the delay component may be used for the analysis, measured data processing, end of tape check, and autocalibration. 
     The present invention may be used with known methods for measuring backscatter curves for propagation time determination in distance-measuring sensors using pulse operation, ultrasound, lidar, or radar. The variable related to the object may be a relative distance or a relative velocity of the object with respect to the device. 
     Using the method, finer location resolution of backscatter curves and thus less effort in processing of the signals result in comparison to direct sampling. The operating parameters of the source are preferably varied as a function of distance. 
     The provided implementation of the device has the advantage that an end of tape compensation only has to be performed for components or parts which are not located in a calibration chain of the circuit system. The end of tape compensation may be dispensed with if a scattering of the propagation times in the components which are not detected is so low that it is below the required measurement precision. The present invention thus only requires a minimal signal-technology engagement in high-sensitivity reception paths of known calibration circuits, which are now to be easily retrofitted with the reference pulse coil. Using the device, a method for autocalibration during direct sampling of backscatter signals may additionally be performed. The source may be connected to the circuit system; the operating parameters of the source are settable by the circuit system, for example. 
     By multiple uses of the RF transmitter, only one further primary winding and one additional switch are needed, and only a low component outlay is required. An additional switch in a transmission path is not necessary. A width of a reference peak which determines a number of sampling points is settable for adaptation to a light pulse incident in normal operation. 
     Typical application circuits are used for injecting analog signals into A/D converters via RF transformers with as little interference as possible. Using the present invention, the adapted RF transmitter for feeding the reference pulse is now provided for determining propagation times in calibration circuits. Using the present invention, autocalibration with direct sampling of backscattered signals for propagation time measurement in sensors for the detection of surroundings is possible using pulse operation, ultrasound, lidar, or radar. Generating or feeding the reference signal only slightly influences a function of typical application circuits. 
     Thermal drifts of propagation times in components of the device may be compensated by using temperature sensors. In a lidar system, components, e.g., laser diode drivers, have significantly temperature-dependent propagation times. Components of the device which have propagation times to be viewed as constant in regard to a desired measurement precision are, for example, laser diodes, receiver diodes, and amplifiers as possible components of the source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows two diagrams of a principle of a boxcar method. 
         FIG. 2  shows a diagram of a first example of a light output which may be emitted via a pulse-pause ratio for a laser diode. 
         FIG. 3  shows a diagram of a second example of a light output which may be emitted via a pulse-pause ratio for a laser diode. 
         FIG. 4  shows a diagram of a relationship of operating parameters. 
         FIG. 5  shows an example of a distance-dependent adaptation of operating parameters. 
         FIG. 6  shows a schematic illustration of a preferred specific embodiment of a circuit system of a device. 
         FIG. 7  shows a flow chart of a calibration. 
     
    
    
     DETAILED DESCRIPTION 
     A principle of the boxcar method is shown on the basis of two diagrams in  FIG. 1 . In diagram  1  shown on the left, a number of measurement pulses are plotted along an ordinate  2  over a number of distance cells along an abscissa  4 . According to this diagram  1 , signal averaging is performed over each ten pulses. A result follows on the basis of the signal averaging according to diagram  5  shown on the right, in which an intensity along an ordinate  6  is plotted against time along an abscissa  8 . This result provided here results after 50 measured pulses. In the boxcar method, slow motion measurement is performed. Sampling of a repeating signal is thus performed at different points in time, which may be implemented by a time delay circuit. A specific number of pulses are analyzed per set time delay; this is performed here by summation over each 10 pulses. 
     In the boxcar method, the local resolution is given by the dimension of a time delay and/or a delay step, for example, with 1000 delay steps at 30 m distance; this corresponds to a delay step of 200 ps. 
     Because individual data points arrive relatively slowly in the boxcar method, for example, one data point per pulse, the amount of data to be transmitted and/or calculated is comparatively low. The distance resolution is thus significantly better than with the method of direct sampling of the backscatter curve, in which the location resolution is given by a sampling rate of an A/D converter. In typical delay components, e.g., “CC8502” from Robert Bosch GmbH, a function for calibrating distance steps is additionally provided, which makes compensation of a sensor system at the end of tape significantly easier. 
     An advantage of the method of direct sampling of the backscatter curve is that all points of the backscatter curve are provided after one pulse, this corresponding to a period of time which the light needs to cover a maximum distance, e.g., 500 ns at a maximum distance of 75 m. These points may be processed further after transmission to analysis electronics. 
     For long-range lidar systems, laser diodes having high pulse powers are used, which are operated at a pulse-pause ratio (duty cycle) of 1:40 to 1:1000. By reducing a pulse power it is possible to operate laser diodes using an increased duty cycle. For this purpose, the pulse power is plotted along ordinate  11  against the duty cycle along abscissa  12  as an example in the diagram from  FIG. 2 . A bar  14  shows a number of delay steps. 
     In the present method, the boxcar method, which is more favorable in regard to analysis, resolution, and calibration, is used over a greater distance range, also with sources or light sources which may be operated using variable duty cycles, for example. 
     In the diagram from  FIG. 3 , it is illustrated in this regard that at a low pulse-pause ratio, which is plotted along an abscissa  16 , a number of the delay steps (bar  18 ) may be reduced to keep a total measuring time for a complete backscatter curve minimal. A resolution capability is thus reduced, which corresponds to a coarse scan at a higher pulse power. A number of delay steps (local resolution) and/or a number of sampling points per delay step is/are plotted along ordinate  20  here. At high pulse powers, the number of pulses over which averaging is performed may be reduced to shorten the measuring time for the backscatter curve. An optimal performance capability may be achieved for every operating state by suitable selection of the parameters duty cycle, number of distance cells, and number of averaging operations per distance cell. 
     An interaction of the operating parameters duty cycle  22 , resolution capability  24 , averaging operations per distance cell  26 , measuring time of a backscatter curve  28 , and pulse power  30  is shown in the diagram from  FIG. 4 . In the present method, to detect the presence of objects in principle, first a coarse scan is performed using the source at maximal pulse power and minimal duty cycle  22 , coarse distance resolution  24 , and minimal number of averaging operations per distance cell  26 . If objects are detected, the operating parameters are set, preferably as a function of distance. In a fine scan following the coarse scan, the light output is reduced and therefore duty cycle  22 , distance resolution  24 , and possibly the number of averaging operations per distance cell  26  are increased, so that a mode of operation or performance of the device is optimal; this includes an acceptable measurement time for the backscatter curve, eye safety, service life of the laser diode, and/or range. 
     In addition, a distance-dependent adaptation of the operating parameters may be performed within one measurement cycle of the backscatter curve to measure multiple targets in a detection area or environment optimally. For this purpose, an intensity  32  of a backscatter is plotted against the distance in the diagram from  FIG. 5 . The diagram shows a backscatter curve for a first set  36  on the left and a backscatter curve for a second set  38  on the right for distance-dependent operating parameters. 
     A block diagram of a circuit system  40  of an exemplary embodiment of the device according to the present invention is shown in  FIG. 6 . This circuit system  40  includes a receiver diode  42  having an amplifier, an RF transmitter  43 , a signal winding  44 , a pulse shaping unit  46 , a reference winding  48 , an analog/digital (A/D) converter  50 , an analysis unit  52 , which does not produce any propagation time effects here, a control unit  54 , a transmitter diode driver  56 , a switch  57 , and a transmitter diode  58  having intensity control as the source. Transmitter diode  58  having intensity control is provided for emitting light pulses  60  and receiver diode  42  having an amplifier is provided for receiving light pulses  62 . Operating parameters of the device and in particular of the source including transmitter diode  58  are settable depending on whether a coarse scan or fine scan is to be performed. 
     In normal operation of the device, a converter pulse  64  is sent to A/D converter  50  from the control unit  54  during measurement of the light propagation time. At a defined pulse flank of converter cycle  64 , a pulse  66  is generated by control unit  54 , which is emitted as a light pulse  60  by transmitter diode  58  after a specific propagation time through the electronics of the measuring device. Switch  57  is switched over by a release pulse  67  produced by control unit  54 . Emitted light pulse  60  is reflected from an object as light pulse  62 . This light pulse  62  reaches receiver diode  42  and is converted in a receiver circuit into an electrical pulse, which is converted in A/D converter  50  into a digital data word  68 , which finally reaches control unit  54  again. The backscatter curve is composed of data words  68  for a specific number of converter pulses. This backscatter curve is processed further in a signal processing unit, in which its peak position is determined. 
     To detect the analog signals here with as little interference as possible, a differential measurement of the signals with common-mode rejection is advantageously performed. Coupling capacitors are used for decoupling direct components. 
     In addition to signal winding  44  for the signal, the reference pulse winding for the reference pulse generated by the device is additionally applied to a primary side  70  of RF transmitter  43 . A service cycle for measuring the position of the reference pulse is executed essentially like the determination of the position of light pulse  62 . The difference is that electrical pulse  66  for resolving light pulse  60  is fed via a switch to primary side  70  of RF transmitter  43 . The emission of light pulse  60  is suppressed, an intensity being equal to zero, so that no signal which could interfere with the reference pulse arrives at signal winding  44 . The reference pulse, like light pulse  62  previously, is transmitted on a secondary side  74  of RF transmitter  43  and processed further to determine the peak position in the same way. A pulse shaping unit is also to be incorporated if needed to provide a constant propagation time behavior, in order to simulate light signal  62  arriving during normal operation, to which base signal processing is optimized as precisely as possible. A propagation time behavior may be determined by components  50 ,  54 ,  56 , which are enclosed by dashed lines, because of the design of circuit system  40 . 
     Interference in the normal operation is minimized by the injection provided here. In addition, no additional switch is required in the transmission path when the intensity of transmitter diode  58  is set to zero as described in the exemplary embodiment. In comparison to capacitive coupling of the signal, which is also possible, the advantages of coupling via RF transmitter  43  are maintained with common-mode rejection and electrical isolation. 
     The diagram shown in  FIG. 7  shows a sequence of a calibration of the device according to the present invention. In four steps  76 ,  78 ,  80 ,  82 , a service cycle  84  is performed to determine the propagation times of the components presented in  FIG. 6 . For this purpose, in first step  76 , an emission intensity of transmitter diode  58  ( FIG. 6 ) is minimized. In second step  78 , switch  72  ( FIG. 6 ) for the reference pulse is closed, in third step  80 , light pulse  60  ( FIG. 6 ) having settable length is emitted, and in fourth step  82 , the position of the reference pulse is ascertained for ascertaining the propagation times in components  50 ,  54 ,  56  ( FIG. 6 ) of the measuring device. In a last step  86 , the propagation time ascertained via the analysis of the reference pulse is subtracted from the propagation time of light.

Technology Category: 3