WO2001090778A1

WO2001090778A1 - Method for determining the distance between a reference object and at least one target object

Info

Publication number: WO2001090778A1
Application number: PCT/EP2001/005322
Authority: WO
Inventors: Holger Schanz
Original assignee: Automotive Distance Control Systems Gmbh
Priority date: 2000-05-25
Filing date: 2001-05-10
Publication date: 2001-11-29
Also published as: EP1295151A1; JP2003534556A; DE10025844A1

Abstract

The invention relates to a method for determining the distance between a reference object and at least one target object by means of timing the interval between transmission and return of the reflected signal. The aim of the invention is to provide a simple, economical means of determining the distance between a reference object and at least one target object located in the range of observation and/or the speed and/or the acceleration of at least one target object located in the range of observation with a high degree of accuracy. The transmitting unit that is used to emit a pulse-type transmission signal is controlled in a clocked manner with a first control signal and the receiving unit used for detecting the resulting reflective signal is controlled in a clocked manner by a second control signal in order to sample the reflected signal at specific sampling points. The second control signal is phase-shifted in relation to the first control signal in such a way that the distance deviation between the distance to the target object determined based on the interval between the transmission and return of the reflected signal and the actual distance to the target object is minimized. The invention also relates to a method for supporting driver assistance systems for automobiles.

Description

Method for determining the distance between a reference object and at least one target object

For many applications, the distance of a reference object to moving or stationary objects (target objects) and / or the speed and / or the acceleration of moving or stationary objects (target objects) must be determined for different areas of observation (distance ranges). Often, in particular, observation areas with a short distance between the pulling object and the target objects are of interest ("close range", for example depending on the application up to 20 m or 250 m distance), e.g. to detect the traffic area surrounding a motor vehicle, i.e. to determine the distance (the distance) of a motor vehicle as a reference object to preceding, following or oncoming vehicles or other reflection objects and / or the relative speed of the motor vehicle with respect to preceding, following or oncoming vehicles or other reflection objects and / or the relative acceleration of the motor vehicle with respect to preceding, following ones or oncoming vehicles or other reflection objects. The measuring systems used for this purpose in particular have a measuring unit with a transmitting unit and a receiving unit, as well as a

Control unit (evaluation unit) on: the transmission signal emitted by the transmission unit - this can e.g. emitted as an optical transmission signal in the infrared (IR) spectral range or in the visible spectral range or as a radar signal in the HF spectral range or as an ultrasound signal - is detected by the receiving unit of the measuring unit after reflection on the target objects located in the observation range and this reflection signal as a measuring signal by the control unit (Auswer ^¬ teeinheit) after signal processing (finishing) with respect to evaluation of the runtime; in particular, the desired distance Informa ^¬ tion and / or speed information and / or acceleration information thereof can then be recovered. In the case of measuring systems operated in a clocked manner, the transmission signal is cyclically interrupted in accordance with a clock specified by a clock generator, ie it is triggered by controlling the transmission unit with a specific one

P303I98.DOC Control signal emitted as a transmission signal transmission pulses with a certain pulse duration; in the pulse pauses between two transmission pulses, the reflection signals of the preceding transmission pulses are detected as reception signals, ie the reflection signal of a transmission pulse is recorded at fixed time intervals and the signal transit time is measured over the elapsed time in the form of clock units, and the distance to the target objects is determined therefrom.

This distance to the target objects should be determined with sufficient accuracy in the entire observation area; this is particularly important if (as is the case with clocked measurement systems) further information is derived from the distance to the target objects, e.g. by

Differentiation of successive distance measurements the relative speed or relative acceleration. Therefore, sampling methods are often used in which the received signal is sampled at a sampling frequency (sampling period) predetermined by a clock, i.e. measured values are generated on the basis of the received signal at specific sampling times; The accuracy of the distance determination (the distance resolution) can be increased by an interpolation or center of gravity of the measured values. In the case of measuring systems operated in a clocked manner, the greater the ratio of the pulse length of the transmit pulses to the sampling period, the better: when the pulse length of the transmit pulses is increased, however, the possibility of separating different target objects is adversely affected; with a reduction in the sampling period, the demands on the clock generator, the receiving unit and the control unit (evaluation unit) become very high (in particular with regard to the speed and quality of the components, and with regard to the stability with regard to parameter scattering and temperature changes), which in turn entails high costs.

The invention has for its object to provide a method for determining the distance between a reference object and at least one target object according to the preamble of claim 1, with which the distance to simple

Can be determined with high accuracy and at low cost.

This object is achieved according to the invention by the features in the characterizing part of patent claim 1. Advantageous developments of the method are part of the further claims.

The invention is based on the knowledge that with scanning methods (in particular when evaluating their measured values by means of interpolation or center of gravity formation) the achievable distance accuracy, i.e. the functional dependency of the distance (the measured distance) between the reference object and the target object determined by the scanning method on the actual distance between the reference object and the target object has a periodic behavior with the periodicity of the sampling frequency (sampling period), since the distance determined by the scanning method (the measured Distance) differs from the actual distance depending on the location of the sampling time; E.g. the achievable distance accuracy (and thus the actual distance) has a sinusoidal shape with respect to the measured distance. In particular, the minima of the achievable distance accuracy are always in a fixed phase relationship

Sampling period, the phase ratio depending on the interpolation method and the pulse shape used.

According to the invention, therefore, for triggering the transmission pulse and thus for the time of emission of the transmission signal (i.e. for controlling the transmission unit) and for the scanning process and therefore for the time of detection of the

Received signal (ie for controlling the receiving unit) uses different, mutually detuned control signals (clock signals); the phase shift between these two control signals (clock signals) is chosen so that the achievable range accuracy has a minimum given the resulting phase position of the transmitted signal and the received signal, ie that the deviation between the distance determined by the scanning method (the measured distance) and the actual distance becomes minimal. The phase shift between the two control signals (clock signals) is preferably controlled in small steps or linearly by means of suitable circuit means, and is preferably regulated by means of a control loop. In particular, the same clock generator is used to control the transmission unit and to control the reception unit, whose clock signal is the first control signal either for the transmission unit or for the reception unit. is left unchanged and its clock signal is phase-shifted as a second control signal for the receiving unit or for the transmitting unit by means of suitable phase shifters; Preferably, due to the more complex detection of the received signal than the emission of the transmitted signal, the receiving unit is supplied with the unchanged clock signal) as the second control signal and the transmitting unit with the phase-shifted clock signal as the first control signal.

The phase shift between the two control signals (clock signals) must be taken into account as an offset when determining the distance, i.e. the distance resulting from the phase shift must be added to the measured distance. With a fixed value, the phase shift can be measured in a simple manner; with a value specified by means of a control or regulation, the phase shift is known as a control variable or controlled variable or reference variable. The method according to the invention can only be used for certain (selected) of the target objects located in the field of observation and thus the

Determination of their distance are carried out with high accuracy, while the distance to the other target objects located in the observation area is determined with the "normal" measurement accuracy resulting from the scanning method; in particular, the method according to the invention is used for target objects with high relevance, for example target objects , in which further measured variables are derived from the distance (e.g. the speed or the acceleration) or for target objects which are used for control functions and / or regulating functions. In particular, depending on the application or target object, the sampling frequency of the sampling method can be reduced (simple re handling of the measuring system) and the resulting reduction in the range accuracy via the phase shift between the two control signals (clock signals) can be compensated or overcompensated again If the control loop is implemented, the specified phases of the two control signals or their phase shifts only have to be stable during the duration of the measurement and the phase control; E.g. this period of time is clocked at RF measurement systems (radar measurement systems) or clocked optical measuring systems (laser measurement systems) between 10- ⁵ and 10 ^"s. Advantageously, the method can be implemented in a simple manner with a small number of inexpensive and commercially available components, so that the distance resolution and thus the accuracy of the distance determination for a given (arbitrary) number of target objects is increased significantly by simple means and consequently with only a small additional cost can be.

A method for determining the distance between a motor vehicle and target objects by means of optical IR pulses is explained in more detail below in connection with the drawing as an exemplary embodiment.

Here shows

1 shows a schematic representation of the distance determination by means of

Principle based on transit time measurement, FIG. 2 shows the functional dependency of the distance deviation on the measured distance,

Figure 3 is a schematic block diagram with the for the phase shift

Control signals required components.

In the vicinity of a motor vehicle, the distance and / or the speed and / or the acceleration of those located in the observation area can be

Target objects, ie the distance between your own motor vehicle and vehicles ahead, oncoming or following vehicles, people and other reflection objects and / or the speed of your own motor vehicle with regard to vehicles traveling ahead, oncoming or following vehicles, people and other reflection objects and / or the acceleration of your own Motor vehicle with regard to preceding, oncoming or following vehicles, people and other reflection objects can be used as the basis for driver assistance systems. The distance and / or speed and / or acceleration must be determined clearly and with high resolution: e.g. the desired range uniqueness range is 10 m Desired distance resolution 0.5 m, the desired speed resolution 1 m / s and the desired acceleration resolution 0.1 m / s ² .

According to Figure 1, the example. Implemented as an optical measuring system measuring system 10 from measuring unit 3 (transmitting unit 4, receiving unit 5) and control unit 7 (evaluation unit) implemented at a predetermined position in the motor vehicle 1 depending on the application.

In several successive measuring processes, the transmitter unit 4 of the measuring unit 3 generates a pulse-shaped transmit signal 13 in the infrared (IR) spectral range with the wavelength of e.g. 850 nm emitted; that is due to reflection at the distance range and angle range (horizontal opening angle α, for example α = 50 °; vertical opening angle β, for example β = 1 2 °) located in the opening field 22, that is to say in the range of distance and angle detected by the pulse-shaped transmission signal 13 Target objects 2 (for example the vehicles or obstacles in front) received reflection signal 14 is detected by the receiving unit 5 of the measuring unit 3 at certain times during the pulse pause of the transmission signal 13 as an analog reception signal. From the control unit 7, e.g. a CPU ("central process unit"), which also functions as an evaluation unit, scans the received signal at certain times ("sampling") and thereby increases the accuracy of the distance measurement; The scanned measured values are evaluated with regard to the transit time, from which the distance information and / or the speed information and / or the acceleration information is obtained by processing the distance information, i.e. the distance dz between the motor vehicle as reference object 1 and the reflection object as target object 2 and / or the speed of the reflection object as target object 2 and / or the acceleration of the reflection object as target object 2. The opening field 22 or the detected angular range (opening angle α, β) is subdivided into several target sectors 21 (for example in 1 ό target sectors 21), each of which is assigned to detecting reflection object is assigned as target object 2 and by means of the information of which an object matrix of target objects 2 is created. FIG. 2 shows the functional dependence of the distance deviation Δd = dz-d "as the difference between the measured distance dz and the actual distance d" from the measured distance dz. Depending on the sampling time of the received signal and thus the position of the various (e.g. 3) sampled measured values with respect to the received signal, in particular with regard to their deviation (asymmetry) with respect to the symmetry of the received signal, this "distance accuracy function" results in a more or less large distance deviation Δd or a more or less large difference between the measured distance dz and the actual distance d _s ; the distance deviation Δd can thus have a value between Δd _™ (minimum distance deviation Δd with a symmetrical position of the sampling times with respect to the received signal) and Δd, _™ ( maximum distance deviation Δd with an asymmetrical position of the sampling times with respect to the received signal), in particular this distance deviation Δd and thus the distance accuracy function due to the statistical distribution of the sampling times with respect to the received signal as a periodicity with the period T _{* of} the scanning process, e.g. the sinusoidal curve shown in Figure 2. By influencing the control signal (the clock signal) for the control of either the transmitting unit 4 or the receiving unit 5 of the measuring unit 3 and thus by shifting their phase position, the distances which can be determined with a distance deviation Δd between Δd _min and Δd »become in the range of the distance accuracy function shifted with a minimal distance deviation of Δd = Δd _™ », whereby the measured distance to the target object 2 is determined with the maximum possible accuracy of the measuring system 10. For example, with a sampling frequency of fT = 100 MHz or a period T _{* of} the sampling operation of TA = 10 ns and a focus-forming method based on a Gaussian method, the minimum distance deviation Δd _{™ is} 1 cm and the maximum distance deviation Δd _m »10 cm. The phase shift Δφ between the first control signal AS1 and the second control signal AS2 can assume any values within a period of the control period, ie the phase shift Δφ can be between 0 ° and 3ό0 °. FIG. 3 shows the components of the measuring system 10 which are relevant for the specification of the control signals AS1, AS2 and their relative phase shift.

The transmitter unit 4 of the measuring unit 3 has, for example. a transmission element designed as a pulsed IR semiconductor laser, which emits a pulse-shaped transmission signal 1 3

Performance of ex. 10 W and a wavelength of e.g. 850 nm emitted. To specify the first control signal AS1 (clock signal) for the transmission unit 4 and the second control signal AS2 (clock signal) for the reception unit 5, the clock generator ό is provided (for example a quartz oscillator), the clock frequency fT of which, for example. Is 100 MHz. The receiving unit 5 is driven directly by the clock generator 6, that is to say it is operated in clocked fashion with the second control signal AS2, which is unchanged in the phase position, with the clock frequency fT for specifying the sampling times of the received signal 14. The transmitter unit 4 is driven by the clock generator 6 via a phase shifter 8, that is to say it is operated in a clocked manner with the first drive signal AS1, which has been changed in the phase position, for specifying the pulse-shaped transmission signal 13 at the clock frequency fT. As a phase shifter 8 for specifying the phase difference or phase shift Δφ between the first control signal AS1 and the second control signal AS2, for example, an easy to implement, analog controllable delay element is provided. The results (data) of the distance measurements are transmitted to the control unit 7 (evaluation unit) connected downstream of the measuring unit 3 and evaluated by the latter; From the results of the distance measurements, ie the measured distances dz to the target objects 2 in the observation area, speed values and / or acceleration values can be derived and the temporal processes of the measuring process can be controlled, in particular the coordination of transmission mode and reception mode, ie the coordination of the transmitter unit 4 for specifying the pulse-shaped transmission signal 13 and receiving unit 5 for specifying the sampling times of the received signal 14. The output signal of the phase shifter 8 is fed to a (easy to implement) phase detector 9 (at the same time, the phase shifter 9 is also included with the second drive signal AS2 generated by the clock generator ό the clock frequency fT), the output signal of which is in turn processed by the control unit 7 and used to control the phase shifter 8; this means that a simple control realized by the resulting phase shift Δφ between the second control signal AS2 for controlling the receiving unit 5 and the first control signal AS1 for controlling the transmitting unit 4 depending on the position of the sampling times with respect to the received signal.

Claims

claims

1 . Method for determining the distance (dz) between a reference object (1) and at least one target object (2) by means of a transit time measurement of the pulse-shaped transmission signal (1 3) emitted by a transmission unit (4) of a measuring unit (3), whereby the 5) the measuring unit (3) detected reflection signal (1) is sampled at certain sampling times, characterized in that the transmitter unit (4) with a first control signal (AS1) for controlling the transmission signal (13) is driven clocked that the receiving unit ( 5) with a second control signal (AS2) for the scanning process, and that the second control signal (AS2) is shifted in phase with respect to the first control signal (AS1) such that the distance deviation (Δd) between the distance determined on the basis of the transit time measurement (dz ) to the target object (2) and the actual distance (d _R ) to the target object (2) becomes minimal.

2. The method according to claim 1, characterized in that the first control signal (AS1) for controlling the transmitter unit (4) and the second control signal (AS2) for controlling the receiving unit (5) are generated by the same clock generator (6).

3. The method according to claim 1 or 2, characterized in that the phase shift (Δφ) wipe the first control signal (AS1) for controlling the transmitter unit (4) and the second control signal (AS2) for controlling the receiving unit (5) by means of a phase shifter ( 8) is generated. Method according to one of claims 1 to 3, characterized in that the phase shift (Δφ) between the first control signal (AS1) for controlling the transmitter unit (4) and the second control signal (AS2) for controlling the receiver unit (5) is controlled by means of a control loop becomes.

Method according to Claim 4, characterized in that the phase shift (Δφ) between the first control signal (AS1) for controlling the transmitter unit (4) and the second control signal (AS2) for controlling the receiver unit (5) is determined by means of a phase detector (9) that the control unit (7) is supplied with the output signal of the phase detector (9) which is dependent on the phase shift (Δφ), and that the phase shifter (8) is dependent on the output signal of the phase detector (9) evaluated in the control unit (7) by the control unit (7) is controlled.

Method according to one of claims 1 to 5, characterized in that the

The speed of a target object (2) is determined by differentiating the distances (dz) to the target object (2) determined in successive runtime measurements.