Method and device for optical distance measurement

Abstract

A method for optical distance measurement is proposed which comprises the emission of a plurality of measurement pulses, the reflection of emitted measurement pulses at at least one object and the receipt of reflected measurement pulses. A sequence of measurement pulses is emitted, wherein the sequence comprises temporal pulse spacings between temporally successive measurement pulses, and wherein each measurement pulse of the sequence has a temporal pulse width of T(Pulse). The pulse spacings form a first set, wherein the first set is defined by {T(delay)+i*T(Pulse): i is an element of the natural numbers between 0 and j}, wherein for all values of i it holds that: T(delay)+i*T(Pulse)<(2T(delay)+2T(Pulse)), wherein the first set only comprises one element for all values of i between 0 and j, respectively, and wherein T(delay) defines a pulse spacing base unit.

Claims

1. A method for optical distance measurement, wherein the method comprises the emission of a plurality of measurement pulses, the reflection of emitted measurement pulses at at least one object and the receipt of reflected measurement pulses, wherein a sequence of measurement pulses is emitted, wherein the sequence comprises temporal pulse spacings between temporally successive measurement pulses, wherein each measurement pulse of the sequence has a temporal pulse width of T(Pulse), wherein the pulse spacings form a first set, wherein the first set is defined by {T(delay)+i*T(Pulse): i is an element of the natural numbers between 0 and j}, wherein for all values of i it holds that: T(delay)+i*T(Pulse)<(2T(delay)+2T(Pulse)), wherein the first set only comprises one element for all values of i between 0 and j, respectively, and wherein T(delay) defines a pulse spacing base unit.

2. The method according to claim 1, wherein the method comprises the definition of T(delay) and/or T(Pulse).

3. The method according to claim 1, wherein T(delay)≥T(Pulse).

4. The method according to claim 1, wherein T(delay) corresponds to at least 2*T(Pulse), preferably at least 5*T(Pulse), further preferably at least 10*T(Pulse), most preferably at least 16*T(Pulse).

5. The method according to claim 1, wherein the method comprises determining the first set.

6. The method (100) according to claim 1, wherein the sequence is emitted in such a manner that each pulse spacing is greater than the previous pulse spacing.

7. The method according to claim 1, wherein the sequence is emitted in such a manner that each pulse spacing is smaller than the previous pulse spacing.

8. The method according to claim 1, wherein the method comprises the emission of a plurality of sequences.

9. The method according to claim 8, wherein temporal sequence spacings are arranged between temporally successive sequences, wherein each sequence has a temporal length of T(Sequence), wherein the sequence spacings form a second set, wherein the second set is defined by {T(delay2)+i*T(Sequence): i is an element of the natural numbers between 0 and k}, wherein for all values of i it holds that: T(delay2)+i*T(Sequence)<(2T(delay2)+2T(Sequence)), wherein the second set only comprises one element for all values of i between 0 and k, respectively, and wherein T(delay2) defines a sequence spacing base unit.

10. The method according to claim 1, wherein the method comprises the evaluation of the receiving measurement pulses, wherein the evaluation comprises the application of an optimal filter, and wherein the optimal filter comprises an adapted optimal filter.

11. The method according to claim 10, wherein the sequence comprises a pattern, wherein the optimal filter is adapted in such a manner that the optimal filter comprises the temporally reflected pattern.

12. A device for optical distance measurement, wherein the device is configured to carry out a method according to claim 1.

13. A computer program product which comprises a computer-readable storage medium on which a program is stored which, after it has been loaded into the memory of the computer, enables a computer to carry out a method according to claim 1.

14. A computer-readable storage medium on which a program is stored which, after it has been loaded into the memory of the computer, enables a computer to carry out a method according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In the figures, schematically:

(2) FIG. 1 shows a process diagram of a method according to the invention;

(3) FIG. 2 shows a sequence which can be emitted with a method according to the invention;

(4) FIG. 3 shows a further sequence which is defined by the same first set as the sequence from FIG. 2;

(5) FIG. 4 shows a further sequence which is defined by the same first set as the sequences from FIGS. 2 and 3;

(6) FIG. 5 shows a plurality of sequences which can be emitted according to the method according to the invention; and

(7) FIG. 6 shows the temporal course of a “matching” with an optimal filter.

PREFERRED EMBODIMENTS OF THE INVENTION

(8) FIG. 1 shows a process diagram of a method (100) according to the invention.

(9) The method (100) comprises the emission (101) of a plurality of measurement pulses (22), the reflection (102) of emitted measurement pulses at at least one object as well as the receiving (103) of reflected measurement pulses. According to the invention, a sequence (20) of measurement pulses (22) is emitted (105), wherein the pulse spacings (24) of the sequence (20) are defined by a first set.

(10) Before emitting (105) the sequence (20), the first set is determined (104) by pulse spacings (24). This comprises in particular the definition of the temporal pulse width (23) of the measurement pulses to be emitted, i.e. T(Pulse). Further preferably the pulse spacing base unit T(Delay) is defined.

(11) The first set is defined by {T(delay)+i*T(Pulse): i is an element of the natural numbers between 0 and j}, wherein for all values of i it holds that: T(delay)+i*T(Pulse)<(2T(delay)+2T(Pulse)), and wherein the first set only comprises one element for all values of i between 0 and j, respectively. Following definition of T(Delay) and T(Pulse), the first set can be finally be unambiguously determined.

(12) The sequence (20) is in particular emitted (105) in such a manner that firstly a first measurement pulse (22a) is emitted (105a). Then a pulse spacing (24) from the first set of pulse spacings is waited (105b). Thus, an element is selected from the first set of pulse spacings and the corresponding time interval of the pulse spacing (24) is waited. This corresponds to the first pulse spacing (24a) of the sequence (20).

(13) Then a further measurement pulse is emitted (105c), whereupon again another pulse spacing from the first set is waited (105d). To this end, an element is selected from the first set which had previously not yet been selected and its time interval waited. Then a further measurement pulse is emitted (105e), after which again another pulse spacing (24) not yet selected so far can be selected from the first set. This takes place until each element from the first set has been selected once. Then a last measurement pulse is emitted.

(14) Preferably a plurality of sequences (20) can be emitted (106). In this case, in particular sequence spacings (26) between the emission of sequences (20) can be waited which are defined by a second set described above. The emission (106) of a plurality of sequences (20) can therefore previously determine the second set. The emission of the sequences (20) and the awaiting for the sequence spacings (26) or the selection of a sequence spacing (26) from the second set takes place similarly to that described above for the first set.

(15) The received measurement pulses are preferably evaluated (107), wherein the evaluation preferably comprises the application (108) of an optimal filter (31). Within the framework of the evaluation the transit time of the sequence (20) is determined (109) and thus the distance from the object at which the sequence (20) was reflected is determined (110).

(16) FIG. 2 shows a sequence (200) which can be emitted with a method (100) according to the invention.

(17) The sequence (20) has a length (21). The sequence (20) is shown on a time scale (29). The termination condition is here achieved for j=2. The first set consists of and certainly conclusively of the following elements: a pulse spacing base unit, a pulse spacing base unit plus one pulse width, a pulse spacing base unit plus two pulse widths, wherein each aforesaid element is only contained once in the first set.

(18) The sequence (20) comprises four measurement pulses (22) and specifically a first measurement pulse (22a), a second measurement pulse (22b), a third measurement pulse (22c) and a fourth measurement pulse (22d). All the measurement pulses have T(Pulse) as pulse width (23). In other words, all the measurement pulses have the same pulse width (23).

(19) First, the first measurement pulse (22a) is emitted (104a). Then a pulse spacing (24) from the first set of pulse spacings (24) and specifically the first pulse spacing (24a) is waited until a second measurement pulse (22) is emitted. The first pulse spacing (24a) amounts to a pulse spacing base unit (25) (T(delay) plus two pulse widths (23) T(Pulse).

(20) After the emission of the second measurement pulse (22b), a pulse spacing (24), and specifically a second pulse spacing (24b) from the first set is awaited. The second pulse spacing (24b) amounts to a pulse spacing base unit (25) T(delay) plus a pulse width (23) T(Pulse). Then a third measurement pulse (22c) is emitted, after which a further pulse spacing (24) and specifically the third pulse spacing (24c) which amounts to a pulse spacing base unit (25) is waited. Finally a last measurement pulse (22) and specifically the fourth measurement pulse (22d) is emitted.

(21) The length of the signal (21) is therefore four pulse widths (23) and six pulse spacing base units (25).

(22) The measurement pulses (22) are emitted in such a manner that starting from the largest pulse spacing of the first set each pulse spacing is smaller than the previous one.

(23) FIG. 3 shows another sequence (20) which is defined by the same first set as the sequence from FIG. 2.

(24) The pulse spacings (24) and specifically the first pulse spacing (24a), the second pulse spacing (24b) and the third pulse spacing (24c) originate from the same set. In this case, however, in contrast to FIG. 2, the smallest pulse spacing (24) of the first set now follows as first pulse spacing (24), then the second smallest pulse spacing (24) of the first set as second pulse spacing (24b) and the longest pulse spacings the last third pulse spacing (24c). In other words, the pulse spacings (24) are arranged mirrored in time compared to the sequence (20) of FIG. 2. The pulse spacings (24) thus increase with advancing sequence until the maximum pulse spacing (24), here the third pulse spacing (24c) is reached.

(25) FIG. 4 shows a further sequence (20) which is defined by the first set like the sequences (20) of FIGS. 2 and 3.

(26) Compared to the sequences (20) of FIGS. 2 and 3, the first pulse spacing (24a) in time is the longest pulse spacing (24) of the first set, whereupon after emission of a second measurement pulse (22b) as second pulse spacing (24b), the smallest element of the first set follows. As the last, a pulse spacing (24) is waited as third pulse spacing (24c) which corresponds to one pulse spacing base unit (25) and one pulse width (23).

(27) FIG. 5 shows a plurality of sequences (20) which can be emitted according to the method (100) according to the invention. The plurality of sequences (20) are shown on a time scale (29) which is interrupted for space reasons.

(28) In this case, four sequences (20) are emitted, a first sequence (20a), a second sequence (20b), a third sequence (20c) and a fourth sequence (20d) which are all configured identically to one another. Each sequence (20) is configured as shown in FIG. 2.

(29) Sequence spacings (26) are arranged between the sequences (20), and specifically a first sequence spacing (26a) between the first sequence (20a) and the second sequence (20b), a second sequence spacing (26b) between the second sequence (20b) and the third sequence (20c) and a third sequence spacing (26c) between the third sequence (20c) and the fourth sequence (20d).

(30) In this case, the sequence spacings (26) form a second set which is given by the following elements: a sequence spacing base unit (27), a sequence spacing base unit (27) plus one sequence length (21), a sequence spacing base unit (27) plus two sequence lengths (21). Here the sequence length (21) preferably correspond to the sequence spacing base unit (27).

(31) FIG. 6 shows the time course of a “matching” of a received signal with an optimal filter (30).

(32) The sequence (20) which was emitted and which is contained in the received signal is configured similarly to the sequence of FIG. 2.

(33) Along a time scale (29) it is shown how an optimal filter (30), in other words a matching filter, runs over the received signal. In addition to the time scale (29), the time offset (31) of the optimal filter (30) is shown. The optimal filter (30) is configured in such a manner that it has a pattern which is time-mirrored with respect to the pattern of the sequence (20). This can be seen from the fact that the ones in the time behaviour direction shown in FIG. 6 firstly having a spacing from one another which corresponds to the third pulse spacing of the sequence, then a spacing which corresponds to the second pulse spacing and then a spacing which corresponds to the first pulse spacing. Zeroes not shown are arranged between the ones. The optimal filter (30) with time-mirrored pattern is successively, i.e. descendingly downwards along the time scale (29) correlated over the received signal comprising the sequence (20).

(34) As soon as the optimal filter (30) encounters a measurement pulse (22), a match (33) is registered. Otherwise no match (34) is the result. Matches (33) are shown in FIG. 6 in such a manner that the corresponding one is circled.

(35) The output (32) of the optimal filter (30) is shown in the right-hand column. The output (32) at a certain time is a sum of the matches (33) in the corresponding line. For example, in the first line (at T=9) only one match (33) has been established. The same applies to the third line and the fifth line. Only at the time T=0 does the output (32) have a result of 4, that is four matches (33) were identified for the same time. Apart from this principal maximum of 4 at time T=0, the output has no further maximum but only auxiliary maxima which are easy to distinguish from the principal maximum which are only 1.

(36) With the aid of the optimal filter (30), it can thus be unambiguously determined that the sequence (20) was received at time T=0. Since the receiving time and therefore the transit time of the sequence (2) can be ascertained, the distance from an object at which the sequence (20) was reflected can be unambiguously determined.