Method and device for optical distance measurement

• US 20050030221A1
• Filed: 07/22/2004
• Published: 02/10/2005
• Est. Priority Date: 01/23/2002
• Status: Active Grant

• Current Assignee: Micro-Optronic-Messtechnik GmbH
• Original Assignee: Micro-Optronic-Messtechnik GmbH
• Inventors: Sperber, Peter
• Granted Patent: US 7,315,355 B2
• Time in Patent Office: Days
• US Class Current: 342/86
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal

Abstract

A method and a device for optically measuring a distance by emitting an amplitude modulated and bundled optical signal and by receiving the signal reflected from a target object. The modulation frequency is continuously regulated by means of a regulating loop in such a manner that between the emitted and the received signal a fixed phase difference prevails that is independent of the distance. For reducing the circuitry required for a distance evaluation circuit, while maintaining a high accuracy and for increasing the attainable regulation speed, the detection of the phase difference occurs with a phase comparator.

Claims

1. A method for optically measuring a distance comprising the steps of emitting an amplitude modulated and bundled optical signal, and receiving the signal reflected from the target object, wherein the modulation frequency is continuously regulated via a regulating loop in such a manner that between the emitted and the received signal a fixed phase difference prevails that is independent of the distance, and wherein the detection of the phase difference occurs via a phase comparator.

2. The method of claim 1, wherein the phase comparator has a high phase resolution at an interval around a desired phase difference, with the resolution being adjusted via a feedback amplification.

3. The method of claim 1, wherein the phase comparator compares whether the measured phase is greater or smaller than a desired phase difference.

4. The method of claim 1, wherein the phase difference is predetermined by a circuit.

5. The method of claim 1, wherein the phase comparator outputs digital information.

6. The method of claim 1, wherein the regulating loop comprises a two-position control, which changes only the sign of the variation rate of the modulation frequency.

7. The method of claim 6, wherein the time sequence of the regulating signals of the two-position control are shorter than the adjustment time of a modulation frequency generator that provides the modulation frequency.

8. The method of claim 1, wherein at the beginning of the measuring procedure the modulation frequency is varied from a predeterminable initial value until the phase comparator detects the reaching of a desired or the set-point phase difference.

9. The method of claim 1, wherein the modulation signal comprises a periodic or sinusoidal signal.

10. The method of claim 1, wherein a pulse train signal is used as a modulation signal.

11. The method of claim 10, wherein the pulse train signal is composed of short pulses.

12. The method of claim 10, wherein the amplitude fluctuations of the pulses are compensated with a delayed symmetry discriminator.

13. The method of claim 10, wherein the phase difference is constantly regulated between a received pulse and one of the subsequent pulses that are to be emitted.

14. The method of claim 10, wherein the phase difference is constantly regulated between a received pulse and the subsequent pulse that is to be emitted.

15. The method of claim 1, wherein the transit time of the optical signal to and from the target object is computed, except for an offset that is to be calibrated, as an integral multiple of the period duration of the emitted signal.

16. A device for optically measuring a distance comprising means for emitting an amplitude modulated and bundled optical signal and receiving the signal reflected from the target object, with the modulation frequency being continuously controllable via a regulating loop such that between the emitted and the received signal a fixed phase difference prevails that is independent of the distance, and wherein the phase difference is detectable with a phase comparator.

17. The device of claim 16, wherein the modulation frequency signal is generated by a VCO (voltage-controlled oscillator).

18. The device of claim 17, wherein the modulation frequency signal generated by the VCO is amplified by an amplifier that follows the VCO.

19. The device of claim 16, wherein the emitting means comprises a light source which is amplitude modulated with the modulation frequency signal.

20. The device of claim 19, wherein the light source includes an LED (light emitting diode) or a laser.

21. The device of claim 19, wherein the light of the light source is bundled with a focusing means which comprises a lens and/or a reflector mirror.

22. The device of claim 19, wherein the signal reflected from the target object is received by a light detector which comprises a photodiode, an avalanche diode, or a photomultiplier.

23. The device of claim 22, wherein the sign of the deviation of the actual phase position from the desired phase position between the modulation frequency signal and the detector output signal is determinable with the phase comparator.

24. The device of claim 16, wherein the output signal of the phase comparator is supplied to the regulating loop.

25. The device of claim 16, wherein a correction signal for the modulation frequency generator is generated with the regulating loop.

26. The device of claim 16, wherein the distance between the device and the target object is computed by measuring the modulation frequency.