Method and apparatus for measuring the distance and/or relative elevation between two points in an opto-electronic manner

• US 3,900,260 A
• Filed: 01/23/1974
• Issued: 08/19/1975
• Est. Priority Date: 07/19/1972
• Status: Expired due to Term

• Current Assignee: MTC Messtechnik und Optelektronik AG
• Original Assignee: Gerhard Wendt
• Inventors: Wendt, Gerhard
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Buczinski, S. C.
• Application Number:
  US05/435,936
• Time in Patent Office: 573 Days
• Field of Search: 356/1,5,141,152 343/15
• US Class Current: 356/5.12
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated

Abstract

The distance between a target and a measuring point is measured by optical and electronic elements, forming an opto-electronic circuit arrangement, wherein a light beam modulated by a first frequency signal is divided to produce a measuring beam and a reference beam. The measuring beam reflected from the target and the reference beam are supplied through switching means to a light sensitive detector in accordance with a predetermined switching function. The output signal of the detector is supplied together with a second frequency signal to a first mixing stage to form a first intermediate frequency signal. A further mixing stage mixes a third frequency signal with the first modulating frequency signal to form a second intermediate frequency signal. Both intermediate frequency signals are supplied to signal evaluating and indicating circuit means. By measuring the distance to the same target twice with regard to two definitely spaced retro-reflectors and by employing a computer in the signal evaluating it is possible to also ascertain and digitally indicate the relative elevation and the base distance between the measuring point and the target without any angular measurement.

Claims

1. An opto-electronic apparatus for the measuring of the distance (x or y) between a measuring point (M) and a target (T), comprising:

light source means (10) located at said measuring point (M), first signal generating means (11,

     12) for producing a first frequency signal (f1) operatively connected to said light source (10) for modulating a light beam produced by said light source (D), optical means (50, . . . ) operatively arranged to divide said modulated light beam (MB) into a measuring beam (2) and into a reference beam (1), said target (T) including retroreflecting means (14) located to receive said measuring beam (2) and to return a reflected beam (2'"'"''"'"'), light switching means (15a, 15b) located to receive said reference beam (1) and said reflected beam (2'"'"''"'"'), switch control means (15c) operatively connected to said light switching means (15a, 15b) for alternating actuation of said light switching means (15a, 15b), a first signal channel (I) comprising a first signal mixing stage (19) and second signal generating means (18) for producing a second frequency signal (f2), said first mixing stage being connected to receive a signal from said detector means (16) and said second frequency signal to produce a first intermediate frequency signal, a second signal channel (II) comprising a second signal mixing stage (21), and a third signal generating means (20) for producing a third frequency signal (f3), said second signal mixing stage (21) being connected to receive said first frequency signal (f1) and said third frequency signal (f3) to produce a second intermediate frequency signal, and signal evaluating means (22,

     23) having inputs connected to said first and second signal channels (I, II) respectively, logic circuit means (24,

     26), said signal evaluating means having outputs connected to said logic circuit means (24,

     26) and computing means (25a) connected to said logic circuit means (25,

     26) for computing said distance.

2. The apparatus according to claim 1, wherein said logic circuit means comprise a pulse counter (26) connected to one of said signal channels, and signal combining means (24) connected to both signal channels and to said pulse counter for starting the counter in response to a pulse flank derived from one signal channel and for stopping the pulse counter in response to a pulse flank derived from the other signal channel, wherein said two pulse flanks are spaced from each other by a defined time interval.

3. The apparatus according to claim 2, wherein said pulse counter (26) comprises digital indicator means for displaying the pulses counted during said time interval as a function of the measured distance.

4. The apparatus according to claim 1, for ascertaining a base spacing and relative elevation, wherein said signal evaluating means comprise pulse forming means (22, 23) one of which is connected to each of said first and second mixing stages respectively in said first and second signal channels, first logic signal combining means (24) connected to both pulse forming means for producing pulse pairs each of which includes a pulse flank from one signal channel and a pulse flank from the other signal channel, said pulse flanks of a pair being spaced from each other by a defined time interval correlating said first and second signal channels to each other, signal counter means (26) connected to one or the other of said pulse forming means, further logic signal combining means (25) connected to said first logic signal combining means (24) and to said signal counter means (26), computer means (25a) including fixed program storage means (30) having a fixed program stored therein, and connected through said further logic signal combining means to said signal counter means (26) and to said first signal combining means (24), whereby signals counted by said signal counter means are processed by said computer means in response to the counting during said time interval and in response to said fixed program storage means to calculate said base spacing and said relative elevation between said measuring point and said target from two distance measurements and said fixed program.

5. The apparatus according to claim 4, wherein said first signal combining means (24) comprise a signal difference computing circuit or logic signal combining circuit means.

6. The apparatus according to claim 4, wherein said computer means (25a) comprise digital value indicator means (31) for digitally displaying the calculated base spacing and said relative elevation.

7. The apparatus according to claim 4, wherein said retro-reflecting means comprise two retro-reflectors arranged at said target vertically one above the other and with a given spacing between said two retro-reflectors.

8. The apparatus according to claim 7, wherein said measuring point is located above ground at a given height, and wherein the lower of said two retro-reflectors at said target is arranged at a height above ground which corresponds to said given height.

9. The apparatus according to claim 7, wherein each of said two retro-reflectors has its given fixed spacing above ground level.

10. The apparatus according to claim 1, wherein said light switching means comprise minor galvanometer means (15a, 15b).

11. The apparatus according to claim 1, wherein said light switching means comprise optical intensity control means (32) including crystal means, electric field means for exciting said crystal means, and polarization filter means operatively associated with said crystal means.

12. The apparatus according to claim 1, wherein said rectro-reflecting means comprise a single retro-reflector having a diameter corresponding to a given proportion of the distance to be measured.

13. The apparatus according to claim 1, wherein said optical means comprise a single lens (54) constituting an optical output as well as an optical input, whereby the light of the measuring beam is allocated to one region of said lens and the light of the reflected beam is allocated to another region of said lens.

14. The apparatus according to claim 12, wherein said single lens has a central region and a circumferential region, and wherein the light of the measuring beam is allocated to one of these regions whereas the light of the reflected beam is allocated to the other of these regions.

15. The apparatus according to claim 1, wherein said optical means comprise a single eyepiece.

16. The apparatus according to claim 1, further comprising signal level control means (17) operatively connected between said light sensitive detector means (16) and said first signal mixing stage (19).

17. A method for opto-electronically measuring the distance between a measuring point and a target, comprising the following steps:

a. producing first, second and third frequency signals with predetermined frequency differences between said three frequency signals;

b. modulating the light of a light source with said first frequency signal to produce a modulated light beam;

c. dividing the modulated light beam into a measuring beam and into a reference beam, and directing the measuring beam onto a retro-reflecting target to provide a reflected beam;

d. alternately directing the reference beam and the reflected beam onto light sensitive detector means through light switching means;

e. producing on a first signal channel a first intermediate frequency signal by mixing the output signal of said light sensitive detector means with said second frequency signal;

f. producing on a second signal channel a second intermediate frequency signal by mixing the first frequency signal with said third frequency signal, said first intermediate frequency signal and said second intermediate frequency signal differing from each other by a beat frequency fs;

g. combining said first and second intermediate frequency signals to produce pairs of pulse flanks whereby one pulse flank of a pair is derived from one of said two signal channels and the other pulse flank of the same pair is derived from the other signal channel, said pulse flanks being spaced from each other by a definite time interval representing the distance to be measured, and h. electronically calculating said distance from said definite time interval.

18. The method according to claim 17, wherein said first and second intermediate frequency signals are combined by calculating a difference signal.

19. The method according to claim 17, wherein said first and second intermediate frequency signals are combined by logic circuit means.

20. The method according to claim 19, comprising producing the first and second intermediate frequency signals as standard square wave pulses, and relating said standard square wave pulses on said first and second intermediate frequency signal channels to each other at a given time, ascertaining the polarity condition of the flanks of said square wave pulses, and counting the pulses until the same polarity condition is again established after the cycle duration of one of said first and second intermediate frequency signals, whereby the resolution of said cycle duration of said intermediate frequency signal may be determined by respectively selecting the intermediate frequency.

21. The method according to claim 17, further comprising maintaining said reflected beam and said reference beam substantially at the same intensity.

22. The method according to claim 17, for ascertaining, in addition to the distance between said measuring point and said target, the relative elevation between said measuring point and said target, further comprising locating two retro-reflectors at said target one vertically above the other and with a given spacing between said retro-reflectors, measuring the distances between said measuring point and each of said retro-reflectors, and calculating from said two distances and said given spacing, the relative elevation.

23. The method according to claim 22, further comprising digitally indicating said relative elevation and/or a distance.

24. The method according to claim 22, further comprising calculating from said two distances and said given spacing, a base distance between the measuring point and said target.

25. The method according to claim 24, further comprising digitally indicating said base distance and elevation.

26. The method according to claim 17, comprising counting during said defined time interval, pulses containing the intermediate frequency on one of said signal channels and digitally displaying the resulting count directly as a function of the distance to be measured.