Method of measuring the distance of a target and apparatus for its performance

• US 4,699,508 A
• Filed: 07/11/1986
• Issued: 10/13/1987
• Est. Priority Date: 06/09/1981
• Status: Expired due to Fees

• Current Assignee: Bayerische Motoren Werke AG
• Original Assignee: MTC Messtechnik und Optelektronik AG
• Inventors: Mehnert, Walter, Bolkow, Ludwig, Chaborski, Hoiko
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US06/885,335
• Time in Patent Office: 459 Days
• Field of Search: 356/5, 368/120, 343/13, 343/12, 342/135
• US Class Current: 356/5.07
• CPC Class Codes: G01S 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

The distance of a target object is determined from the time of travel of a measuring light pulse which is emitted by a transmitter toward the target object, reflected thereby and received by a receiver. In timed relation with the instant of generation of the measuring light pulse, a start signal for beginning a measuring signal transit time measurement is generated, and, on receipt of the reflected measuring light pulse, a stop signal is generated for terminating this time measurement. A completely independent reference light pulse is generated and forwarded along a reference light path establishing a predetermined time of travel from the transmitter to the receiver, and the respective reference signal transit time is measured which contains the same undesirable additional time spans contained in the measured transit time of the measuring signal. The reference signal transit time measurement value is subtracted from the measuring signal transit time value to eliminate the additional time spans and to obtain a high precision measurement value difference to which the predetermined time of travel of the reference light pulse is added to obtain the genuine time of travel of the measuring light pulse.

Claims

1. A method of measuring the distance of a target from a measuring appartus by determining the time of travel of individual unmodulated measuring light pulses of short duration to said target and therefrom, by reflection, back to the measuring apparatus, comprising the steps of:

(a) providing an electro-optical transmitter means for generating individual unmodulated light pulses in response to trigger signals provided from a trigger generator,

(b) generating for each individual unmodulated light pulse a start signal being related in time to the instant of generation of said light pulse,

(c) providing means for using said individual unmodulated light pulses either as individual measuring light pulses by forwardly them along a first light path inside the apparatus toward an optical transmitting means transmitting them toward said target, or using them as individual reference light pulses by forwarding them inside that apparatus along a reference light path establishing a predetermined time of travel for said individual reference light pulses,

(d) providing an electro-optical receiving means for receiving said individual measuring light pulses after reflection from said target as well as said individual reference light pulses, and for generating on receipt of each individual measuring light pulse and of each individual reference light pulse a respective stop signal,

(e) generating at least one individual measuring light pulse and measuring a measuring signal transit time, i.e. the time distance between a start signal and a stop signal both signals corresponding to said measuring light pulse, said measuring signal transit time comprising three components, a first of which is the time span between the instant at which the measuring light pulse is generated and the instant at which the time distance measurement is actually started, a second of which is the time of travel of the measuring light pulse beginning with the instant at which said measuring light pulse is actually generated by said electro-optical transmitter means and ending with the instant at which, after reflection from the target, said measuring light pulse is received by said electro-optical receiving means, and a third of which is the time span between the instant at which said measuring light pulse is received by said electro-optical receiving means and the instant at which said time distance measurement is actually stopped,

(f) generating at least one individual reference light pulse and measuring a reference signal transit time, i.e. the time distance between a start signal and a stop signal both signals corresponding to said reference light pulse, said reference signal transit time comprising three components, a first of which is the time span between the instant at which the reference light pulse is generated and the instant at which the time distance measurement is actually started, a second of which is the predetermined time of travel of the reference light pulse beginning with the instant at which said reference light pulse is actually generated by said electro-optical transmitter means and ending with the instant at which, after having travelled through said reference light path, said reference light pulse is received by said electro-optical receiving means, and a third of which is the time span between the instant at which said reference light pulse is received by said electro-optical receiving means and the instant at which said time distance measurement is actually stopped,

(g) determining a measurement value difference which comprises the difference between the time of travel of said at least one measuring light pulse and the predetermined time of travel of said at least one reference light pulse and from which said first and said third components of said signal transit time measurement values are eliminated, and

(h) adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

2. A method as claimed in claim 1,

wherein the step of providing an electro-optical transmitter means comprises providing one single transmitter for generating individual unmodulated light pulses in response to trigger signals from said trigger generator with a response time which, if at all, changes only slowly with respect to the repetition frequency of said trigger signals,

wherein the step of providing means for using said individual unmodulated light pulses either as individual measuring light pulses or as individual reference light pulses comprises providing a light path change-over switch being arranged in front of said single transmitter and being controllable to direct said individual unmodulated light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

wherein the step of generating for each individual unmodulated light pulse a start signal comprises using as start signal the respective trigger signal or any other signal electrically derived from said trigger signal and having a defined time relation thereto, and

wherein the step of providing an electro-optical receiving means comprises providing one single receiver which receives said reflected individual measuring light pulses as well as said individual reference light pulses and generates on each receipt of an individual light pulse a corresponding stop signal.

3. A method as claimed in claim 2,

wherein said step of generating for each individual unmodulated light pulse a start signal comprises

(a) using as start signal the corresponding trigger signal and

(b) delaying said trigger signal by a predetermined period of time before feeding it to said transmitter means.

4. A method as claimed in claim 1,

wherein the step of providing an electro-optical transmitter means comprises providing one single transmitter for generating individual unmodulated light pulses by responding to trigger signals from said trigger generator with a response time which may change from light pulse to light pulse,

wherein the step of providing means for using said individual unmodulated light pulses either as individual measuring light pulses or as individual reference light pulses comprises providing a light path change-over switch being arranged in front of said single transmitter and being controllable to direct said individual unmodulated light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

wherein the step of providing an electro-optical receiving means comprises providing a main receiver and an auxiliary receiver,

wherein the step of generating for each individual unmodulated light pulse a start signal comprises

(a) splitting each individual light pulse emitted by said transmitter into two parts, a first of which is directed toward said light path change-over switch for use either as individual measuring light pulse or as individual reference light pulse, and a second of which is directed via an auxiliary light patch inside said apparatus and establishing a predetermined time of travel, toward said auxiliary receiver, and

(b) using the output signal generated by said auxiliary receiver on receipt of each of said second parts of said individual unmodulated light pulses as start signal for the respective signal transit time measurement, each of the output signals generated by said main receiver on receipt of said first parts of said individual unmodulated light pulses being used as stop signal for the respective signal transit time measurement.

5. A method as claimed in claim 1,

wherein the step of providing an electro-optical transmitter means comprises providing a main transmitter and an auxiliary transmitter, each generating individual unmodulated light pulses in response to trigger signals provided from said trigger generator,

wherein the step of providing means for using individual unmodulated light pulses from said electro-optical transmitter means either as individual measuring light pulses or as individual reference light pulses comprises

(a) arranging said first light path to receive all individual light pulses from said main transmitter for use as measuring light pulses,

(b) arranging said reference light path to receive all individual light pulses from said auxiliary transmitter for use as reference light pulses, and

(c) alternately providing trigger signals for said main transmitter and said auxiliary transmitter,

wherein the step of providing an electro-optical receiving means comprises provided a main receiver and an auxiliary receiver, and

wherein the step of generating for each individual unmodulated light pulse a start signal comprises

(a) splitting each individual light pulse emitted by said main transmitter into two parts, a first of which is directed into said first light path for use as individual measuring light pulse, and a second of which is directed via a first auxiliary light path, inside said apparatus and establishing a predetermined time of travel, toward said auxiliary receiver, and

(b) splitting each individual light pulse emitted by said auxiliary transmitter into two parts, a first of which is directed into said reference light path for use as individual reference light pulse, and a second of which is directed via a second auxiliary light path inside said apparatus and establishing a predetermined time of travel toward said auxiliary receiver, the output signals generated by said auxiliary receiver on receipt of each of said second measuring and reference light pulse parts being used as start signal for the respective signal transit time measurement and each of the output signals generated by said main receiver on receipt of each of said first measuring and reference light pulse parts being used as stop signal for the respective signal transit time measurement.

6. A method as claimed in claim 1,

wherein the step of providing an electro-optical transmitter means comprises providing a main transmitter and an auxiliary transmitter each generating individual unmodulated light pulses in response to trigger signals from said trigger generator,

wherein the step of generating for each individual unmodulated light pulse a start signal comprises using as start signal the respective trigger signal or any other signal electrically derived from said trigger signal and having a defined time relation thereto,

wherein the step of providing an electro-optical receiving means comprises providing a main receiver and an auxiliary receiver,

wherein the step of providing means for using individual unmodulated light pulses from said electro-optical transmitter means either as individual measuring light pulses or as individual reference light pulses comprises

(a) providing means for using individual unmodulted light pulses from said main transmitter either as individual measuring light pulses by forwarding them via said first light path, and, after reflection from said target, via said second light path, to said main receiver, or as first auxiliary light pulses by forwarding them via a first auxiliary light path inside said apparatus and establishing a predetermined time of travel for said first auxiliary light pulses to said auxiliary receiver,

(b) providing means for using individual unmodulated light pulses from said auxiliary transmitter either as reference light pulses by forwarding them via said reference light path to said main receiver, or as second auxiliary light pulses by forwarding them via a second auxiliary light path inside said apparatus and establishing a predetermined time of travel for said second auxiliary light pulses to said auxiliary receiver,

wherein the step of generating at least one individual measuring light pulse comprises further generating at least one individual first auxiliary light pulse and measuring a first auxiliary signal transit time, i.e. the time distance between the respective start signal and the stop signal being generated by said auxiliary receiver on receipt of said at least one individual first auxiliary light pulse, said first auxiliary signal transit time comprising three components, a first of which is the time span between the instant at which said first auxiliary light pulse is generated and the instant at which said time distance measurement is actually started, a second of which is said predetermined time of travel of said first auxiliary light pulse beginning with the instant at which said first auxiliary light pulse is actually generated by said main transmitter and ending with the instant at which, after having travelled through said first auxiliary light path, said first auxiliary light pulse is received by said auxiliary receiver, and a third of which is the time span between the instant at which said first auxiliary light pulse is received by said auxiliary receiver and the instant at which said time distance measurement is actually stopped,

wherein the step of generating at least one individual reference light pulse comprises further generating at least one individual second auxiliary light pulse and measuring a second auxiliary signal transit time, i.e. the time distance between the respective start signal and the stop signal being generated by said auxiliary receiver on receipt of said at least one individual second auxiliary light pulse, said second auxiliary signal transit time comprising three components, a first of which is the time span between the instant at which said second auxiliary light pulse is generated and the instant at which said time distance measurement is actually started, a second of which is said predetermined time of travel of said second auxiliary light pulse beginning with the instant at which said second auxiliary light pulse is actually generated by said auxiliary transmitter and sending with the instant at which, after having travelled through said second auxiliary light path, said second auxiliary light pulse is received by said auxiliary receiver, and a third of which is the time span between the instant at which said second auxiliary light pulse is received by said auxiliary receiver and the instant at which said time distance measurement is actually stopped,

wherein the step of determining a measurement value difference comprises

(a) subtracting said at least one reference signal transit time measurement value from said at least one measuring signal transit time measurement value to obtain a first difference,

(b) subtracting said at least one second auxiliary transit time measurement value from said at least one first auxiliary transit time measurement value to obtain a second difference, and

(c) subtracting said second from said first difference.

7. A method as claimed in claim 6,

wherein the step of providing means for using individual unmodulated light pulses from said main transmitter either as individual measuring light pulses or as individual first auxiliary light pulses comprises

(a) splitting each individual light pulse emitted by said main transmitter into two parts, a first of which is directed into said first light path for use as individual measuring light pulse, and a second of which is directed into said first auxiliary light path for use as individual first auxiliary light pulse, and

(b) alternately suppressing said first part before reaching said main receiver or said second part before reaching said auxiliary receiver, and,

wherein the step of providing means for using individual unmodulated light pulses from said auxiliary transmitter either as individual reference light pulses or as individual second auxiliary light pulses comprises

(a) splitting each individual light pulse emitted by said auxiliary transmitter into two parts, a first of which is directed into said reference light path for use as individual reference light pulse, and a second of which is directed into said second auxiliary light path for use as individual second auxiliary light pulse, and

(b) alternately suppressing said first part before reaching said main receiver or said second part before reaching said auxiliary receiver.

8. A method as claimed in any of claims 2, 4, 5 or 6,

wherein the measurement of the time distance between a start signal and a stop signal corresponding to any of said individual unmodulated light pulses comprises

(a) permanently providing a time base signal consisting of a sequence of pulse signals having a predetermined constant repetition frequency, said trigger signals being generated independently of said time base signal,

(b) performing an analog measurement of the time distance between said start signal and a defined first subsequent pulse of said time base signal for obtaining a first precision time measurement value for each individual unmodulated light pulse,

(c) performing an analog measurement of the time distance between said stop signal and a defined second subsequent pulse of said time base signal for obtaining a second precision time measurement value for each individual unmodulated light pulse,

(d) counting the pulses of said time base signal occurring between said first and said second defined pulses and dividing the counted number by said predetermined repetition frequency for obtaining a coarse measurement value at least for each individual measuring light pulse, and

(e) computing said time distance between said start signal and said stop signal by subtracting said second precision time measurement value from said first precision time measurement value, and, at least in the case of a time distance measurement for an individual measuring light pulse, by adding said coarse measurement value to said difference in order to obtain one signal transit time measurement value.

9. A method as claimed in claim 8,

wherein the measurement of the time distance between a start signal and a stop signal comprises obtaining said coarse measurement value for each individual unmodulated light pulse.

10. A method as claimed in any of claims 2, 4, 5 or 6,

wherein the measurement of the time distance between a start signal and a stop signal corresponding to any of said individual light pulses comprises

(a) permanently providing a time base signal consisting of a sequence of pulse signals having a constant predetermined repetition frequency, each of said trigger signals being generated in synchronism with a pulse of said time base signal and being used as start signal,

(b) performing an analog measurement of the time distance between said stop signal and a defined subsequent pulse of said time base signal for obtaining a precision time measurement value for each individual unmodulated light pulse,

(c) counting the pulses of said time base signal occurring between said pulse, with which the respective trigger signal is in synchronism, and said defined subsequent pulse for obtaining a coarse time measurement value at least for each individual measuring light pulse, and

(d) computing said time distance between said trigger signal, being used as start signal, and said stop signal by subtracting said precision time measurement value, at least in the case of a time distance measurement for an individual measuring light pulse, from said coarse measurement value to obtain one signal transit time measurement value.

11. A method as claimed in claim 10,

wherein the measurement of the time distance between a start signal and a stop signal comprises obtaining said coarse measurement value for each individual unmodulated light pulse.

12. A method as claimed in claim 1,

wherein the step of providing an electro-optical transmitter means comprises providing a main transmitter and an auxiliary transmitter each generating individual unmodulated light pulses in response to trigger signals provided from said trigger generator,

wherein the step of providing an electro-optical receiving means comprises providing a main receiver and an auxiliary receiver,

wherein the step of providing means for using individual unmodulated light pulses from said electro-optical transmitter means either as individual measuring light pulses or as individual reference light pulses comprises arranging said first light path and said reference light path to receive individual light pulses from said main transmitter and alternately forwarding these light pulses either as measuring light pulses toward said main receiver or as reference light pulses toward said auxiliary receiver,

wherein the step of generating for each individual unmodulated light pulse a start signal comprises

(a) arranging a first and a second auxiliary light path, each inside said apparatus and establishing a predetermined time of travel, to receive individual light pulses from said auxiliary transmitter, and alternately forwarding these light pulses either via said first auxiliary light path toward said main receiver for use as first auxiliary light pulses, or via said second auxiliary light path toward said auxiliary receiver for use as second auxiliary light pulses,

(b) providing a first trigger signal for said auxiliary transmitter to generate an individual unmodulated light pulse and forwarding this light pulse as a first auxiliary light pulse via said first auxiliary light path toward said main receiver which, on receipt thereof, generates an output signal which is used as start signal for a measuring signal transit time measurement,

(c) providing a first trigger signal for said main transmitter having a predetermined time distance from said first trigger signal for said auxiliary transmitter, forwarding the individual unmodulated light pulse which is generated by said main transmitter in reaction on said first trigger signal as individual measuring light pulse via said first light path, and, after reflection from said target, via said second light path toward said main receiver which, on receipt thereof, generates an output signal which is used as stop signal for said measuring signal transit time measurement,

(d) providing a second trigger signal for said auxiliary transmitter to generate an individual unmodulated light pulse and forwarding this light pulse as a second auxiliary light pulse via said second auxiliary light path toward said auxiliary receiver which, on receipt thereof, generates an output signal which is used as start signal for a reference signal transit time measurement,

(e) providing a second trigger signal for said main transmitter having a predetermined time distance from said second trigger signal for said auxiliary transmitter, forwarding the individual unmodulated light pulse which is generated by said main transmitter in reaction on said second trigger signal as individual reference light pulse via said reference light path toward said auxiliary receiver which, on receipt thereof, generates an output signal which is used as stop signal for said reference signal transit time measurement.

13. A method as claimed in claim 12,

wherein providing said trigger signals for said main transmitter and said auxiliary transmitter comprises

(a) providing a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, and,

(b) generating said trigger signals in synchronism with said time base signal in order to establish said predetermined time distances between said first trigger signals and said second trigger signals.

14. A method as claimed in claim 12,

wherein the step of alternately forwaring said individual unmodulated light pulses which are generated by said main transmitter either as measuring light pulses toward said main receiver or as reference light pulses toward said auxiliary receiver comprises

(a) splitting each individual light pulse emitted by said main transmitter into two parts, a first of which is directed into said first light path for use as individual measuring light pulse, and a second of which is directed into said reference light path for use as individual reference light pulse, and

(b) alternately suppressing said first part before reaching said main receiver or said second part before reaching said auxiliary receiver, and

wherein the step of alternately forwarding said individual unmodulated light pulses, which are generated by said auxiliary transmitter either as first or as second auxiliary light pulses toward said main or said auxiliary receiver comprises

(a) splitting each individual light pulse emitted by said auxiliary transmitter into two parts, a first of which is directed into said first auxiliary light path for use as individual first auxiliary light pulse, and a second of which is directed into said second auxiliary light path for use as individual second auxiliary light pulse, and

(b) alternately suppressing said first part before reaching said main receiver or said second part before reaching said auxiliary receiver.

15. A method as claimed in claim 13,

wherein the step of measuring the time distance between a start signal and a stop signal, both corresponding to any of said individual measuring or reference light pulses comprises

(a) performing an analog measurement of the time distance between said start signal and a defined first subsequent pulse of said time base signal for obtaining a first precision time measurement value for each individual unmodulated light pulse,

(b) performing an analog measurement of the time distance between said stop signal and a defined second subsequent pulse of said time base signal for obtaining a second precision time measurement value for each individual unmodulated light pulse,

(c) counting the pulses of said time base signal occurring between said first and said second defined pulses and dividing the counted number by said predetermined repetition frequency for obtaining a coarse measurement value,

(d) computing said time distance between said start signal and said stop signal by subtracting said second precision time measurement value from said first precision time measurement value and by adding said coarse measurement value to said difference in order to obtain one signal transit time measurement value.

16. A method as claimed in claim 1,

wherein at least one pair of individual unmodulated light pulses, a first of which is used as measuring light pulse and a second of which is used as reference light pulse, is generated within a period of time being so short that said first and third components of each signal transit time measurement value cannot change and, therefore, are the same for the obtained measuring signal transit time measurement value and the obtained reference signal transit time measurement value, and

wherein the step of determining a measurement value difference comprises subtracting said obtained reference signal transit time measurement value from said obtained measuring signal transit time measurement value.

17. A method as claimed in claim 1,

wherein several pairs of individual unmodulated light pulses are generated, one light pulse of each pair being used as measuring light pulse and one being used as reference light pulse each pair being generated within a period of time being so short that said first and third components of each signal transit time measurement value cannot change, and

wherein the step of determining a measurement value difference comprises subtracting for each pair the respective reference signal transit time measurement value from the corresponding measuring signal transit time measurement value and of taking the average value of all such obtained differences.

18. A method as claimed in claim 1,

wherein at least three individual unmodulated light pulses, a first and a third of which are used as reference light pulses and a second of which is used as measuring light pulse, are generated within a period of time being so short that said first and third components of each signal transit time measurement value can change, if at all, only linearly, and

wherein the step of determining a measurement value difference comprises

(a) taking the average value of the reference signal transit time measurement values of said two reference light pulses, and

(b) subtracting said average value from said measuring signal transit time measurement value.

19. A method as claimed in claim 1,

wherein a series of individual unmodulated light pulses, which alternately are used as measuring light pulses and as reference light pulses, are generated within a period of time being so short that said first and third components of each signal transit time measurement value can change, if at all, only linearly, and

wherein the step of determining a measurement value difference comprises

(a) taking the average value of the reference signal transit time measurement values of all reference light pulses of said series,

(b) taking the average value of the measuring signal transit time measurement values of all measuring light pulses of said series, and

(c) subtracting said first, from said second average value.

20. A method as claimed in claim 19,

wherein said trigger generator is controlled to generate the trigger signals for the individual unmodulated light pulses of each of said series so that said individual light pulses periodically arrive at said electro-optical receiving means.

21. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having a main transmitter driven by trigger signals from a trigger generator for emitting individual unmodulated measuring light pulses of short duration, and an auxiliary transmitter driven by trigger signals from said trigger generator for emitting individual unmodulated reference light pulses,

a control means for controlling said trigger generator to alternately trigger said main transmitter and said auxiliary transmitter, for alternately generating measuring light pulses and reference light pulses,

an optical transmitting means for transmitting individual measuring light pulses toward said target,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

an electro-optical receiving means having a main receiver and an auxiliary receiver,

a first light beam splitter means which is arranged in front of said main transmitter for splitting each individual measuring light pulse from said main transmitter into two parts, a first of which is directed into a first light path and a second of which is directed into a first auxiliary light path, said first light path transmitting said first measuring light pulse parts to said optical transmitting means and said first auxiliary light path inside the apparatus establishing a predetermined time of travel for said second measuring light pulse parts and transmitting them to said auxiliary receiver,

a second light path from said optical receiving means to said electro-optical receiving means for supplying to said main receiver individual reflected first measuring light pulse parts,

a second light beam splitter means which is arranged in front of said auxiliary transmitter for splitting each individual reference light pulse from said auxiliary transmitter into two parts, a first of which is directed into a reference light path and a second of which is directed into a second auxiliary light path, said reference light path inside the apparatus establishing a predetermined time of travel for said first reference light pulse parts and transmitting them to said main receiver, and said second auxiliary light path inside the apparatus establishing a predetermined time of travel for said second reference light pulse parts and transmitting them to said auxiliary receiver,

a time measuring means for measuring signal transit times of individual measuring light pulses as well as of individual reference light pulses, the transit time of an individual measuring or reference light pulse being the time difference between a start signal generated by said auxiliary receiver on receipt of the respective second measuring light pulse part or of the respective second reference light pulse part, respectively, and a stop signal generated by said main receiver on receipt of the respective first reflected measuring light pulse part or of the respective first reference light pulse part, said time measuring means being operatively connected to said main and auxiliary receivers,

and a storage and computing means for storing obtained signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel of at least one measuring light pulse and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

22. A distance measuring apparatus as claimed in claim 21, wherein said time measuring means comprises a time base means permanently gnerating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, said trigger signals being generated independently of said time base signal, and further comprises an analog time measuring means for measuring the time distance between any start signal and a defined first subsequent pulse of said time base signal for obtaining for each signal transit time measurement a first precision time measurement value, and for measuring the time distance between the corresponding stop signal and a defined second subsequent pulse of said time base signal for obtaining for each siganl transit time measurement a second precision time measurement value, storage means for storing said first and said second precision time measurement values, and a counter means for counting the pulses of said time base signal occurring between said first and said second defined pulses for obtaining at least for each measuring signal transit time measurement a coarse time measurement value, each of said second precision time measurement values being subtracted from the corresponding first precision time measurement value and, at least in the case of measuring light pulses, the respective coarse measurement value being added to the resulting difference in order to obtain a signal transit time measurement value.

23. A distance measuring apparatus as claimed in claim 22, wherein said coarse time measurement value is obtained and added to the difference of the corresponding precision time measurement values for each signal transit time measurement.

24. A distance measuring apparatus as claimed in claim 21, wherein said time measuring means comprises a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, each of said trigger signals being generated in synchronism with a pulse of said time base signal, and further comprises an analog time measuring means for measuring the time distance between any stop signal and a defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a precision time measurement value, and a counter means for counting the pulses of said time base signal occurring between said pulse, with which the respective trigger signal is in synchronism, and said defined subsequent pulse for obtaining a coarse time measurement value at least for each measuring signal transit time measurement, said coarse time measurement value being added to said precision time measurement value in order to obtain a measuring signal transit time measurement value.

25. A distance measuring apparatus as claimed in claim 24, wherein said coarse time measurement value is obtained and added to the respective precision time measurement value for each signal transit time measurement.

26. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having a main transmitter and an auxiliary transmitter both being driven by trigger signals from a trigger generator for alternately emitting individual unmodulated light pulses of short duration,

a first light path and a first auxiliary light path extending inside said apparatus and being arranged to receive light pulses from said main transmitter, said first light path forwarding said received light pulses for use as measuring light pulses to an optical transmitting means transmitting them toward said target, and said first auxiliary light path forwarding said received light pulses for use as first auxiliary light pulses,

a reference light path and a second auxiliary light path extending inside said apparatus and being arranged to receive light pulses from said auxiliary transmitter, said reference light path establishing a predetermined time of travel for said received light pulses and forwarding them for use as reference light pulses, and said second auxiliary light path forwarding said received light pulses for use as second auxiliary light pulses,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

an electro-optical receiving means having a main receiver receiving via a second light path said individual reflected measuring light pulses from said optical receiving means and also receiving via said reference light path said individual reference light pulses, and having an auxiliary receiver receiving via said first and said second auxiliary light paths, both establishing predetermined times of travel, said first and second auxiliary light pulses,

a first controllable means for forwarding individual light pulses generated by said main transmitter either via said first light path, and, after reflection from said target, via said second light path to said main receiver or via said first auxiliary light path to said auxiliary receiver,

a second controllable means for forwarding individual light pulses generated by said auxiliary transmitter either via said reference light path to said main receiver or via said second auxiliary light path to said auxiliary receiver;

a control means for controlling said trigger generator to trigger said main and said auxiliary transmitters to alternately generate individual light pulses and for controlling said first and second controllable means to alternately provide the so generated light pulses for use as measuring light pulses, first auxiliary light pulses, reference light pulses or second auxiliary light pulses,

a time measuring means for alternately measuring signal transit times of individual measuring light pulses, of first auxiliary light pulses, of reference light pulses and of second auxiliary light pulses, the signal transit time of each of such light pulses being the time difference between a start signal, which is generated in response to the respective trigger signal from said trigger generator, and a stop signal which is generated either by said main receiver on receipt of the respective measuring light pulses or of the respective reference light pulse, or by said auxiliary receiver on receipt of the respective first auxiliary light pulse or of the respective second auxiliary light pulse,

and a storage and computing means for storing obtained signal transit time measurement values, for determining differences between signal transit time measurement values of measuring light pulses and signal transit time measurement values of reference light pulses, for correcting these differences by subtracting therefrom differences between signal transit time measurement values of first auxiliary light pulses and signal transit time measurement values of second auxiliary light pulses, and for adding to the such obtained corrected measurement value differences said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

27. A distance measuring apparatus as claimed in claim 26, wherein in front of said main transmitter a first light beam splitter means is arranged for splitting each individual light pulse provided therefrom into two parts, a first of which is directed into said first light path for use as measuring light pulse and a second of which is directed into said first auxiliary light path for use as first auxiliary light pulse, wherein in front of said auxiliary transmitter a second light beam splitter means is arranged for splitting each individual light pulse provided therefrom into two parts, a first of which is directed into said reference light path for use as reference light pulse and a second of which is directed into said second auxiliary light path for use as second auxiliary light pulse, and wherein said first controllable means comprises a first variable attenuation means arranged in said second light path, and a second variable attenuation means arranged in said reference light path, and said second controllable means comprises a third variable attentuation means arranged in front of said auxiliary receiver for attentuating said first as well as said second auxiliary light pulses, all three variable attentuation means being controllable to either not or totally attenuate the respective light pulses.

28. A distance measuring apparatus as claimed in claim 26, wherein said time measuring means comprises a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, said trigger signals being generated independently of said time base signal, and further comprises an analog time measuring means for measuring the time distance between any start signal and a defined first subsequent pulse of said time base signal for obtaining for each signal transit time measurement a first precision time measurement value, and for measuring the time distance between the corresponding stop signal and a defined second subsequent pulse of said time base signal for obtaining for each signal transit time measurement a second precision time measurement value, storage means for storing said first and said second precision time measurement values, and a counter means for counting the pulses of said time base signal occurring between said first and said second defined pulses for obtaining at least for each measuring signal transit time measurement a coarse time measurement value, each of said second precision time measurement values being subtracted from the corresponding first precision time measurement value and, at least in the case of measuring light pulses, the respective coarse measurement value being added to the resulting difference in order to obtain a signal transit time measurement value.

29. A distance measuring apparatus as claimed in claim 28, wherein said coarse time measurement value is obtained and added to the difference of the corresponding precision time measurement values for each signal transit time measurement.

30. A distance measuring apparatus as claimed in claim 26, wherein said time measuring means comprises a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, each of said trigger signals being generated in synchronism with a pulse of said time base signal, and further comprises an analog time measuring means for measuring the time distance between any stop signal and a defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a precision time measurement value, and a counter means for counting the pulses of said time base signal occurring between said pulse, with which the respective trigger signal is in synchronism, and said defined subsequent pulse for obtaining a coarse time measurement value at least for each measuring signal transit time measurement, said coarse time measurement value being added to said precision time measurement value in order to obtain a measuring signal transit time measurement value.

31. A distance measuring apparatus as claimed in claim 30, wherein said coarse time measurement value is obtained and added to the respective precision time measurement value for each signal transit time measurement.

32. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having a main transmitter and an auxiliary transmitter both being driven by trigger signals from a trigger generator for alternately emitting individual unmodulated light pulses of short duration,

a first light path and a reference light path extending inside said apparatus, and being arranged to receive light pulses from said main transmitter, said first light path forwarding said received light pulses for use as measuring light pulses to an optical transmitting means transmitting them toward said target, and said reference light path establishing a predetermined time of travel for said reveived light pulses and forwarding them for use as reference light pulses,

a first auxiliary light path and a second auxiliary light path both establishing predetermined times of travel and being arranged inside said apparatus to receive light pulses from said auxiliary transmitter for use as first auxiliary light pulses or as second auxiliary light pulses, respectively,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

an electro-optical receiving means having a main receiver receiving via a second light path said individual reflected measuring light pulses from said optical receiving means and also receiving via said first auxiliary light path said first auxiliary light pulses, and having an auxiliary receiver receiving via said reference light path said individual reference light pulses and also receiving via said second auxiliary light path said second auxiliary light pulses,

a first controllable means for forwarding individual light pulses generated by said main transmitter either via said first light path, and, after reflection from said target, via said second light path to said main receiver or via said reference light path to said auxiliary receiver,

a second controllable means for forwarding individual light pulses generated by said auxiliary transmitter either via said first auxiliary light path to said main receiver or via said second auxiliary light path to said auxiliary receiver,

a time measuring means comprises a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency,

a control means for controlling said trigger generator to trigger in synchronism with said time base signal said main and said auxiliary transmitters to alternately generate individual light pulses, and for controlling said first and second controllable means to provide a first light pulse generated by said auxiliary transmitter for use as first auxiliary light pulse, to provide the next subsequent light pulse generated by said main transmitter for use as measuring light pulse, to provide a further light pulse generated by said auxiliary transmitter for use as second auxiliary light pulse and to provide the next subsequent light pulse generated by said main transmitter for use as reference light pulse,

said main receiver being operatively connected to said time measuring means for forwarding to it, on receipt of any first auxiliary light pulse a start signal for beginning a measuring signal transit time measurement for a measuring light pulse the generation of which is triggered with a well defined delay with respect to the trigger signal for generating the corresponding first auxiliary light pulse, and for forwarding to it, on receipt of said measuring light pulse, a stop signal for terminating said measuring signal transit time measurement,

said auxiliary receiver being operatively connected to said time measuring means for forwarding to it, on receipt of any second auxiliary light pulse a start signal for beginning a reference signal transit time measurement for a reference light pulse the generation of which is triggered with a well defined delay with respect to the trigger signal for generating the corresponding second auxiliary light pulse, and for forwarding to it, on receipt of said reference light pulse, a stop signal for terminating said reference signal transit time measurement,

and a storage and computing means for storing obtained measuring and reference signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel or at least one measuring light pulse and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

33. A distance measuring apparatus as claimed in claim 32, wherein in front of said main transmitter a first light beam splitter means is arranged for splitting each individual light pulse provided therefrom into two parts, a first of which is directed into said first light path for use as measuring light pulse and a second of which is directed into said reference light path for use as reference light pulse, wherein in front of said auxiliary transmitter a second light beam splitter means is arranged for splitting each individual light pulse provided therefrom into two parts, a first of which is directed into said first auxiliary light path for use as first auxiliary light pulse, and a second of which is directed into said second auxiliary light path for use as second auxiliary light pulse, and wherein said first controllable means comprise a first variable attenuation means arranged in said second light path and a second variable attenuation means arranged in a part of said reference light path which said reference light path has in common with said second auxiliary light path, and said second controllable means comprise a third variable attenuation means arranged in said first auxiliary light path, all three variable attenuation means being controllable to either not or totally attenuate the respective light pulses.

34. A distance measuring apparatus as claimed in claim 32, wherein said time measuring means further comprises an analog time measuring means for measuring the time distance between any start signal and a first defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a first precision time measurement value, and for measuring the time distance between the corresponding stop signal and a second defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a second precision time measurement value, storage means for storing said first and second precision time measurement values, and a counter means for counting the pulses of said time base signal occurring between said first and said second defined pulses for obtaining for each signal transit time measurement a coarse time measurement value.

35. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having one single transmitter which is triggerable by trigger signals from a trigger generator for emitting individual unmodulated light pulses of short duration, and which responds to said trigger signals with a response time, which, if at all, changes only slowly with respect to the repetition frequency of said trigger signals,

a first light path from the transmitter means to an optical transmitting means for transmitting individual measuring light pulses toward said target,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

a second light path for supplying individual reflected measuring light pulses from said optical receiving means to an electro-optical receiving means comprising one single electro-optical receiver,

a reference light path for supplying individual unmodulated reference light pulses from said transmitter means to said single electro-optical receiver and establishing a predetermined time of travel for the reference light pulses,

a light path change-over switch being arranged in front of said single transmitter and being controllable by a control means to direct light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

a time measuring means for measuring signal transit times of individual measuring light pulses as well as of individual reference light pulses, the transit time of an individual measuring or reference light pulse being the time difference between a start signal related to the trigger signal for the respective individual measuring or reference light pulse and a stop signal which is generated on receipt of the respective individual measuring or reference light pulse by said electro-optical receiving means to which said time measuring means are operatively connected, said time measuring means having

a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, said trigger signals being generated independently of said time base signal,

an anaog time measuring means for measuring the time distance between any start signal and a defined first subsequent pulse of said time base signal for obtaining for each signal transit time measurement a first precision time measurement value, and for measuring the time distance between the corresponding stop signal and a defined second subsequent pulse of said time base signal for obtaining for each signal transit time measurement a second precision time measurement value,

storage means for storing said first and said second precision time measurement values, and a counter means for counting the pulses of said time base signal occuring between said first and said second defined pulses for obtaining at least for each measuring signal transit time measurement a coarse time measurement value, each of said second precision time measurement values being subtracted from the corresponding first precision time measurement value and, at least in the case of measuring light pulses, the respective coarse measurement value being added to the resulting difference in order to obtain a signal transit time measurement value,

and said distance measuring apparatus further comprising

a storage and computing means for storing obtained signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel of at least one measuring light pulse, and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

36. A distance measuring apparatus as claimed in claim 35, wherein said trigger signals from said trigger generator are directly fed to said time measuring means for use as start signals and wherein said trigger signals from said trigger generator are fed to said transmitter via a delay means providing a predetermined time delay.

37. A distance measuring apparatus as claimed in claim 35, wherein said coarse time measurement value is obtained and added to the difference of the corresponding precision time measurement values for each signal transit time measurement.

38. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having one single transmitter which is triggerable by trigger signals from a trigger generator for emitting individual unmodulated light pulses of short duration, and which responds to said trigger signals with a response time, which, if at all, changes only slowly with respect to the repetition frequency of said trigger signals,

a first light path from the transmitter means to an optical transmitting means for transmitting individual measuring light pulses toward said target,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

a second light path for supplying individual reflected measuring light pulses from said optical receiving means to an electro-optical receiving means comprising one single electro-optical receiver,

a reference light path for supplying individual unmodulated reference light pulses from said transmitter means to said single electro-optical receiver and establishing a predetermined time of travel for the reference light pulses,

a light path change-over switch being arranged in front of said single transmitter and being controllable by a control means to direct light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

a time measuring means for measuring signal transit times of individual measuring light pulses as well as of individual reference light pulses, the transit time of an individual measuring or reference light pulse being the time difference between a start signal related to the trigger signal for the respective individual measuring or reference light pulse and a stop signal which is generated on receipt of the respective individual measuring or reference light pulse by said electro-optical receiving means to which said time measuring means are operatively connected, said time measuring means having

a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, each of said trigger signals being generated in synchronism with a pulse of said time base signal, an analog time measuring means for measuring the time distance between any stop signal and a defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a precision time measurement value, and

a counter means for counting the pulses of said time base signal occurring between said pulse, with which the respective trigger signal is in synchronism, and said defined subsequent pulse for obtaining a coarse time measurement value at least for each measuring signal transit time measurement, said coarse time measurement value being added to said precision time measurement value in order to obtain a measuring signal transit time measurement value,

and said distance measuring apparatus further comprising

a storage and computing means for storing obtained signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel of at least one measuring light pulse and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

39. A distance measuring apparatus as claimed in claim 38, wherein said coarse time measurement value is obtained and added to the respective precision time measurement value for each signal transit time measurement.

40. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having one single transmitter which is triggerable by trigger signals from a trigger generator for emitting individual unmodulated light pulses of short duration, and which responds to said trigger signals with a response time which may change from light pulse to light pulse,

a first light path from the transmitter means to an optical transmitting means for transmitting individual measuring light pulses toward said target,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

a second light path for supplying individual reflected measuring light pulses from said optical receiving means to a main receiver of an electro-optical receiving means,

a reference light path for supplying individual unmodulated reference light pulses from said transmitter means to said main receiver of said electro-optical receiving means and establishing a predetermined time of travel for the reference light pulses,

a light path change-over switch being arranged in front of said single transmitter and being controllable by a control means to direct light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

a light beam splitter means which is arranged between said single transmitter and said light path change-over switch for splitting each individual light pulse from said single transmitter into two parts, a first of which is directed toward said light path change-over switch for use either as individual measuring light pulse or as individual reference light pulse and a second of which is directed into an auxiliary light path inside the apparatus, establishing a predetermined time of travel for said second light pulse parts and transmitting them to an auxiliary receiver of said electro-optical receiving means,

a time measuring means for measuring signal transit times of individual measuring light pulses as well as of individual reference light pulses, the transit time of an individual measuring or reference light pulse being the time difference between a start signal which is generated by said auxiliary receiver on receipt of the respective second measuring or reference light pulse part, and a stop signal which is generated by said main receiver on receipt of the respective first measuring or reference light pulse art, said time measuring means having

a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, said trigger signals being generated independently of said time base signal,

an analog time measuring means for measuring the time distance between any start signal and a defined first subsequent pulse of said time base signal for obtaining for each signal transit time measurement a first precision time measurement value, and for measuring the time distance between the corresponding stop signal and a defined second subsequent pulse of said time base signal for obtaining for each signal transit time measurement a second precision time measurement value,

a storage means for storing said first and said second precision time measurement values, and

a counter means for counting the pulses of said time base signal occurring between said first and said second defined pulses for obtaining at least for each measuring signal transit time measurement a coarse time measurement value, each of said second precision time measurement values being subtracted from the corresponding first precision time measurement value and, at least in the case of measuring light pulses, the respective coarse measurement value being added to the resulting difference in order to obtain a signal transit time measurement value,

and said distance measuring apparatus further comprising

a storage and computing means for storing obtained signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel of at least one measuring light pulse and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

41. A distance measuring apparatus as claimed in claim 40, wherein said coarse time measurement value is obtained and added to the difference of the corresponding precision time measurement values for each signal transit time measurement.

42. Distance measuring apparatus for determining the times of travel of individual unmodulated measuring light pulses to a target and therefrom, by reflection, back to the apparatus which for this purpose comprises:

a transmitter means having one single transmitter which is triggerable by trigger signals from a trigger generator for emitting individual unmodulated light pulses of short duration, and which responds to said trigger signals with a response time which may change from light pulse to light pulse,

a first light path from the transmitter means to an optical transmitting means for transmitting individual measuring light pulses towards said target,

an optical receiving means for receiving individual reflected unmodulated measuring light pulses from said target,

a second light path for supplying individual reflected measuring light pulses from said optical receiving means to a main receiver of an electro-optical receiving means,

a reference light path for supplying individual unmodulated reference light pulses from said transmitter means to said main receiver of said electro-optical receiving means and establishing a predetermined time of travel for the reference light pulses,

a light path change-over switch being arranged in front of said single transmitter and being controllable by a control means to direct light pulses from said single transmitter either into said first light path for use as measuring light pulses or into said reference light path for use as reference light pulses,

a light beam splitter means which is arranged between said single transmitter and said light path change-over switch for splitting each individual light pulse from said single transmitter into two parts, a first of which is directed toward said light path change-over switch for use either as individual measuring light pulse or as individual reference light pulse and a second of which is directed into an auxiliary light path inside the apparatus, establishing a predetermined time of travel for said second light pulse parts and transmitting them to an auxiliary receiver of said electro-optical receiving means,

a time measuring means for measuring signal transit time of individual measuring light pulses as well as of individual reference light pulses, the transit time of an individual measuring or reference light pulse being the time difference between a start signal which is generated by said auxiliary receiver on receipt of the respective second measuring or reference light pulse part, and a stop signal which is generated by said main receiver on receipt of the respective first measuring or reference light pulse part, said time measuring means having

a time base means permanently generating a time base signal consisting of a sequence of pulse signals having a constant repetition frequency, each of said trigger signals being generated in synchronism with a pulse of said time base signal,

an analog time measuring means for measuring the time distance between any stop signal and a defined subsequent pulse of said time base signal for obtaining for each signal transit time measurement a precision time measurement value,

and a counter means for counting the pulses of said time base signal occurring between said pulse, with which the respective trigger signal is in synchronism, and said defined subsequent pulse for obtaining a coarse time measurement value at least for each measuring signal transit time measurement, said coarse time measurement value being added to said precision time measurement value in order to obtain a measuring signal transit time measurement value,

and said distance measuring apparatus further comprising

a storage and computing means for storing obtained signal transit time measurement values, for determining a measurement value difference which comprises the difference between the time of travel of at least one measuring light pulse and the time of travel of at least one reference light pulse, and for adding to said measurement value difference said predetermined time of travel established by said reference light path and multiplying the result by the velocity of light in order to obtain one distance measurement value.

43. A distance measuring apparatus as claimed in claim 42, wherein said coarse time measurement value is obtained and added to the respective precision time measurement value for each signal transit time measurement.