DE102008025825A1 - Method for highly accurate distance measurement - Google Patents

Abstract

The present invention relates to a method for measuring a distance to an object with a radiation source, is provided with the individual pulses and which are directed to the object, wherein a recording means for detecting the reflected radiation from the object is provided and the measurement of the distance to the object on the Determination of the duration of the radiation between the radiation source and recording medium takes place. According to the invention, means are provided with which the individual pulses are provided as a wavelength- and time-coded pulse sequence and sent to the object, the radiation reflected by the object being detected by the recording means in a wavelength- and time-discrete manner.

Description

The The present invention relates to a method of measuring a distance to an object with a radiation source, with the individual pulses provided and which are directed to the object, with a Recording means for detecting the radiation reflected by the object is provided and the measurement of the distance to the object on the Determination of the duration of the radiation between the radiation source and Recording means takes place.

The Measurement of distances between a measuring arrangement and an object is based on the principle of transit time measurement of reflected on the measurement object Radiation. The radiation can be an electromagnetic wave with a wavelength which lies in the visible range. Also known are Radiation sources, which are designed as laser beam sources and wavelengths emit in the near or direct infrared range. applications find such transit time measurements in laser rangefinders, in LIDAR systems, Radar-related method for distance and speed measurement, being also laser pistols of the traffic police on the principle of Runtime measurement based. The resulting accuracy of such measuring systems becomes due to the limits of the technical feasibility of very short time measurements limited. In particular, the detection of the reflected radiation in the form of single pulses has a finite resolution, so that a pulse-to-pulse measurement can not be done in any short periods of time. To the accuracy about that It is well-known, besides the pure running time additional, to increase Gain information to determine the accuracy of the determination of the term and, as a result, to further increase the determination of the distance. This happens, for example, over the determination of interferences or the measurement of phase angles the emitted radiation. However, such a modulation is also The single pulse limits, so it is desirable to accuracy continue to increase the measurement of distances.

It is therefore the object of the present invention, a method to measure distances to an object that is another increase the measurement accuracy for determining the distance to an object allows.

These Task is based on a method for measuring a distance to an object according to the generic term of claim 1 in conjunction with the characterizing features. advantageous Further developments of the invention are specified in the dependent claims.

The Invention includes the technical teaching that means are provided with which the individual pulses as wavelength and time-coded pulse train and sent to the object be, with the reflected radiation from the object by the recording means wavelength- and discrete-time detected.

The Wavelength coding according to the invention is used instead of phase or interference information with the transmitted by the radiation source transmitted individual pulses. First single pulses are emitted by the radiation source, which is caused by the agents according to the invention be converted into a sequence of pulses, which are both in terms of their wavelength and in their time sequence differ from each other. The time coding of the individual pulses causes a split into several partial pulses, which together form a pulse sequence form. For example, the pulse train can consist of three pulses, each having different colors. The means of transfer of the Single pulses in a pulse sequence are designed such that the Distance of the pulse sequence forming color pulses is known. Further is the wavelength the color pulses known, so that the emission of the individual color pulses known in time and resumed by the receiving means, being the time resolution of the receiving means to differentiate the color pulses of different wavelengths can.

An advantageous embodiment of the pulse train includes a series of color pulses with a respective same time interval, wherein the individual pulse duration corresponds to the duration of the pulse train and is determined by the number of color pulses of the pulse train. The pulse duration .DELTA.T describes the sum of the respective time intervals .DELTA.t, which lie between the color pulses. The number of color pulses is marked with K, so that: ΔT = K · Δt.

A further embodiment of the method according to the invention has a recording means, which is formed from at least one camera, which specifies a sequence of exposure times. The exposure times can be described as T _N-1 , T _N , T _{N + 1} , etc., so that individual exposure time windows are formed. If the camera detects a pulse sequence, the color pulses of the pulse sequence can be classified into the individual exposure time windows T _N-1 , T _N and T _N-1 , etc., wherein the different color assignment of the color pulses is described in more detail below.

The increase in the measurement accuracy is based on the principle of assigning the pulse sequences to the exposure time windows, wherein the assignment is wavelength-dependent. Thus, individual color pulses can be allocated to respective exposure time windows be ordered. The shutter speed windows may also be referred to as time slots or so-called gates. The recording of the reflected light from the object is usually time-integrated in the gates, wherein the choice of the time length of such a gate affects the accuracy of the transit time measurement. Upon receipt of a reflected light pulse within a gate, the signal can be assigned only a single time T _LAUF . Any reduction of the exposure time to reduce the inaccuracy of the transit time measurement can not be done here, since at the same time the number of integrated photons is reduced, the number of photons integrated within the camera also limits the accuracy of the transit time measurement. If the time duration of an exposure time window was shorter, the number of photons integrated within the exposure time window is not large enough or the technical implementation of even shorter exposure time windows is not feasible. Thus, while shorter pulse train durations ΔT can be provided by the radiation source, the position of the trapped single pulse within the gate can not be determined. Consequently, the time constant of the transit time measurement is limited by the duration of the exposure time window. However, according to the invention, if the individual pulse is converted into wavelength- and time-coded color pulses and these are directed onto the object as a pulse sequence, the sequence of color pulses on the object reflects and can be recorded by the camera. If all the individual color pulses arrive within a gate, then the statement can be made that the single pulse lies centrally within the gate.

If a color is detected in an upstream gate T _N-1 and two remaining colors in the gate T _{N ,} it can be said that the single pulse within the gate N is adjacent to the gate T _N-1 . It is also possible that a color pulse in the gate T _{N + 1} is detected, and the remaining color in the gate pulses T _N. Consequently, the single pulse in the gate N is adjacent to the gate T _{N + 1} .

As a result, a correction term δ can be formed with which the position of the pulse train within the exposure time window is determined by first assigning the _travel time T _{LAUF of} the individual pulse to a transit time for an exposure time window T _N , and then performing the correction via the correction term δ. such that: T _RUN = T _N + δ.

Of the Correction term δ can assume the value -Δt, if one of the color pulses in an exposure time window upstream Exposure time window is detected. On the other hand, the correction term δ can be the value + Accept Δt, if one of the color pulses is downstream in the exposure time window Exposure time window is detected. Only if all color pulses are detected in the same exposure time window, the correction term δ takes the value 0 on.

advantageously, If the pulse sequence consists of three individual, consecutively Color pulses, the wavelengths the color pulses correspond to the colors blue, green and red. A further increase The accuracy of measuring the distance to an object can be with a pulse sequence allows which consists of more than three color pulses. In the result the correction term δ takes more as three different values if one, two or more color pulses be detected in an upstream or downstream gate.

The The invention also relates to a device for measuring the Distance to an object with a radiation source for deployment a sequence of individual pulses for irradiating the object. there are recording means for detecting the individual pulses reflected by the object provided, wherein the measurement of the distance to the object on the determination the duration of the individual pulses between the radiation source and recording means he follows. In this case, means are provided with which the individual pulses as wavelength and time-coded pulse sequence can be transferred and wherein the receiving means reflects the radiation reflected from the object wavelength- and discrete time detected.

The Means can be designed as a beam splitter, the individual pulses in several Divides individual beams that go through different path lengths. By the different path lengths can the individual pulses are converted into a pulse sequence, which by suitable Choice of extension the path lengths same distances to each other. The single pulses emitted by the radiation source can in Picosecond range or in the femtosecond range, so that the required difference of the path length of the individual pulses within the pulse sequence technically feasible in a limited space is.

Within the different path lengths are arranged optically non-linear materials through which the individual beams run through to a wavelength transformation to achieve the individual beams in different wavelengths and a pulse train provide color and time discrete color pulses. The optical nonlinear materials can a wavelength transformation in the colors blue, green or red, with one of the colors of the base color of the single pulse may correspond to the radiation source.

Further measures improving the invention will hereinafter be described together with the description of a preferred embodiment game of the invention shown in more detail with reference to FIGS.

It shows:

1 a schematic view of a transit time measurement using single pulses according to the prior art, wherein a sequence of multiple exposure time windows is shown on a timeline;

2 an embodiment of a transit time measurement using color-coded pulse series according to the present invention and

3 the schematic view of a transit time measurement using three individual pulses of a pulse series of different color, wherein three cases of detection of the color pulses are shown within adjacent gates.

In 1 a transit time measurement is shown using single pulses E, which corresponds to the prior art. At time T = 0, the single pulse E is emitted by the radiation source. The individual pulse formed as a light pulse reflects on the object or is backscattered on it. The backscattered light is captured with a camera. The recording of the backscattered light is time-integrated in exposure time windows, which are represented by T _N-1 , T _N and T _{N + 1} . As shown, the single pulse E is detected within the exposure time window T _N. It is not possible to give a statement about the position of the individual pulse within the duration of the exposure time window T _N. The following is in the 2 and 3 an embodiment of the present invention is given, with which the determination of the position of the individual pulse E within the exposure time window T _{N is} possible.

2 shows an example of a transit time measurement using color pulses, wherein three color pulses are provided, which represent a pulse train and are formed from the single pulse. The first color pulse corresponds to a red color and is marked with R, the central, central color pulse G having the color green and the third color pulse B having a wavelength corresponding to the color blue. The color pulses R, G and B are emitted at the time T = 0 from the radiation source. The exact time T = 0 corresponds to the green color pulse, so that the red color pulse is emitted at time T-Δt, and the blue color pulse is emitted at time T + Δt. Thus, the number K of color pulses corresponds to three color pulses. The transit time t is in turn divided into exposure time windows T _N-1 , T _N and T _{N + 1} , wherein the blue color pulse B and the green color pulse G in the exposure time window T _N and the red color pulse R in the exposure time window T _{N + 1 is} detected. Thus, a determination of the position of the average, green color pulse G within the exposure time window T _{N can be} determined, since the time interval .DELTA.t between the green color pulse G and the red color pulse R is known. Since the red color pulse R is detected in the exposure time window T _{N + 1} , the statement can be made that the green color pulse G must have a distance from the boundary to the subsequent exposure time window T _{N + 1} which corresponds at most to the time interval Δt. Consequently, the accuracy of the transit time measurement with the time interval .DELTA.t of the individual color pulses R, G and B can be specified.

3 again shows the transit time measurement using the color pulses R, G and B. Here, three cases are listed, which are described below.

Consider first the average exposure time window T _N. The duration of the exposure time window corresponds to the pulse duration .DELTA.T and is calculated to .DELTA.T = K · .DELTA.t, where .DELTA.t represents the time interval of the color pulses to each other.

In the first case I the blue color pulse is detected by the camera in the exposure time window T _N-1 . The second, central green color pulse G is shown in bold and is located in the exposure time window T _N , wherein the third, red color pulse R is also detected in the exposure time window T _N. Due to the known time interval .DELTA.t between the individual color pulses R, G and B, the green color pulse G is adjacent to the edge of the exposure time window T _N , which merges into the exposure time window T _N-1 .

In the second case II all three color pulses R, G and B are detected within the exposure time window T _N. In this case too, the temporal position of the mean, green color pulse G can be specified with the accuracy of the time interval Δt, since both the upstream, blue color pulse B and the downstream, red color pulse R within the middle exposure time window T _{N are} detected.

In the third case III Only the first, blue color pulse B and the central, green color pulse G within the exposure time window T _{N is} detected. The red color pulse R is detected in the exposure time window T _{N + 1} , so that the statement can be made that the central, green color pulse G is adjacent to the edge of the exposure time window T _N , which changes to the exposure time window T _{N + 1} .

As a result, the accuracy of the transit time measurement between the emission of a single pulse by the radiation source and the detection of the radiation by the camera after the reflection at Object with the time interval Δt possible. In the present example, the number K of the color pulses corresponds to three color pulses, with a further increase in the number of color pulses whose total time of the pulse duration .DELTA.T corresponds to the accuracies, further increased.

The present invention limited in their execution not to the preferred embodiment given above. Rather, a number of variants is conceivable, which of the illustrated solution also in principle different types Use.

B

blue color pulse

G

green color pulse

R

red color pulse

T _N-1

upstream first exposure time window

T _N

medium, second exposure time window

T _{N + 1}

downstream third exposure time window

e

Single pulse

t

running time

K

pulse number in the pulse sequence

.DELTA.T

Pulse repetition period

.delta.t

time distance

I

first case

II

second case

III

third case

Claims (10)

Method for measuring a distance to an object with a radiation source, with which individual pulses are provided and which are directed onto the object, wherein a recording means for detecting the radiation reflected by the object is provided and the measurement of the distance to the object via the determination of the propagation time of the radiation between radiation source and recording means, characterized in that means are provided with which the individual pulses are provided as wavelength and time-coded pulse sequence and sent to the object, wherein the reflected radiation from the object are detected by the recording medium wavelength and time discrete. Method according to Claim 1, characterized in that the wavelength- and time-coded pulse sequence has a series of color pulses with a respective time interval (Δt), the pulse duration duration (ΔT) corresponding to the duration of the pulse sequence and the number (K) of the color pulses Pulse train is determined to ΔT = K · Δt. A method according to claim 1 or 2, characterized in that the recording means is formed from at least one camera having a sequence of exposure time windows (T _N-1 , T _N , T _{N + 1} ), wherein the detected pulse sequences individual exposure time windows (T _{N -1} , T _N , T _{N + 1} ). A method according to claim 3, characterized in that the assignment of the pulse sequences to the exposure time windows (T _N-1 , T _N , T _{N + 1} ) is wavelength-dependent, so that individual color pulses respective exposure time windows (T _N-1 , T _N , T _{N + 1} ). Method according to one of claims 2 to 4, characterized that the pulse sequence is formed by three color pulses (B, G, R), where the wavelengths the color pulses correspond to the colors blue (B), green (G) and red (R). Method according to one of claims 3 to 5, characterized in that a correction term (δ) is provided which is determined from the position of the pulse train within the exposure time window (T _N-1 , T _N , T _{N + 1} ) by the transit time T _{LAUF of} the individual pulse is first assigned a running time for an exposure time window (T _N ), and following the correction is made via the correction term (δ), where: T _LAUF = T _N + δ. A method according to claim 6, characterized in that the correction term (δ) assumes the value -n · Δt when the number n of one of the color pulses is detected in an exposure time window (T _N-1 ) preceding the exposure time window (T _N ), wherein the correction term (δ) assumes the value + n · at, when the number n of the color pulses in a the exposure time window (T _N) downstream exposure time window (T _{N + 1)} is detected and wherein the correction term (δ) assumes the value 0 when all Color pulses are detected in the exposure time window (T _N ) itself. Device for measuring the distance to an object, with a radiation source to provide a train of single pulses for irradiating the object, wherein a recording means for detecting the is provided by the object reflected individual pulses and the measurement the distance to the object the determination of the transit time of the individual pulses between the radiation source and receiving means, characterized in that means are provided, with which the individual pulses as Wellenlangen- and time-coded pulse sequence can be transferred and wherein the recording means the radiation reflected by the object wavelength and time discrete detected. Device according to claim 8, characterized in that in that the means comprise beam splitters which divide the individual pulses into several Divides individual beams that go through different path lengths. Apparatus according to claim 8 or 9, characterized that optically non-linear materials are provided by the the individual beams pass through to a wavelength transformation to train the individual beams in different wavelengths and a pulse train provide color and time discrete color pulses.