Optics: measuring and testing – Range or remote distance finding – With photodetection
Patent
1997-12-22
2000-03-21
Buczinski, Stephen C.
Optics: measuring and testing
Range or remote distance finding
With photodetection
342127, 342132, 356 515, G01C 308, G01S 1308
Patent
active
060408987
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an FMCW distance measurement method.
Many different types of distance measurement methods are known. The present invention relates to a contactless measurement method which is suitable for determining the distance to an object situated freely in space and, in particular, for measuring the contours of objects. Moreover, it can also be used to detect and measure imperfections in wave-guiding media and structures therein. The measurement principle consists in emitting and receiving intensity- or frequency-modulated acoustic, optical or other electromagnetic waves, in particular in the radio-frequency band. These are to be designated below in general as transmission wave and reception wave, respectively.
If the transmission wave is frequency modulated, the transmission signal can be represented by the expression ##EQU1## with the amplitude A, the carrier frequency f.sub.0 and the frequency modulation function f(t). In the case of intensity modulation, the transmission wave assumes the general form of transmission wave and an arbitrary phase .epsilon.. In the case of a sinusoidal amplitude modulation, it holds that ##EQU2## where f.sub.0 now represents the carrier frequency of the modulation and f(t) a frequency modulation function. In the following exposition, the frequency f.sub.0 is denoted as carrier frequency for all cases, and the frequency .nu. as transmission frequency. In the case of frequency modulation, the carrier frequency and transmission frequency are identical.
Known measurement methods are based, for example, on the pulse time delay method, in which the transmission wave is intensity-modulated using temporally limited pulses, and the distance information is derived from the measured time delay of the pulse. Such a method permits a unique measurement of a measuring point of interest or of a geometry of interest, as long as the time delay of the pulse to the object and back is shorter than the period of the pulse repetition of the system.
In the case of pulse repetition rates in the kHz region, such as occur in the case of typical systems, a very large uniqueness region results. Owing to the limited pulse energy of short pulses, which the wave-generating transmitter can output, and to the low statistical efficiency, the resolution of such systems is, however, low, or else the measuring time is long because of the summation of many measuring pulses.
In contrast thereto, the phase comparison method, which is likewise customary, is distinguished by a high statistical efficiency and thus by a high accuracy in conjunction with short measuring times. The periodicity employed in this case in the modulation of the continuously emitted and modulated waves produces, however, a limited uniqueness region determined by the modulation frequency. The requirements for higher resolution and a larger uniqueness region seem to contradict one another.
The measurement principle on which the pulse time delay method is based can be characterized in that use is made of the information in the so-called envelope of the reception signal. The envelope is given by the pulse shape of the transmission signal.
According to the results of estimation theory, the bandwidth of the modulation must be as high as possible for a high measurement resolution. This necessitates transmission pulses as short as possible. In real systems, the electrical bandwidth available is limited. In this case, the bandwidth is understood as the frequency band from the largest positive frequency to the largest negative frequency. This leads to the requirement to utilize the bandwidth of real systems with the aid of suitable modulation signals in an optimum way, and thus to configure the measuring arrangement in a statistically efficient fashion.
An optimum utilization of the electrical bandwidth results when in the case of frequency modulation the spectral energy of the signal s(t), or in the case of intensity modulation that of the signal A(t), is concentrated on the maximum frequency which can be tr
REFERENCES:
patent: 4812035 (1989-03-01), Freedman et al.
patent: 4833479 (1989-05-01), Carlson
patent: 5122803 (1992-06-01), Stann et al.
Woods et al; IEEE Transactions on Instr. & Meas., vol. 42, No. 4, Aug. 1993.
Wehr; Frequenz, 48(1994) 5-6; p. 123, May/Jun. 1994
Wehr; Frequenz, 48(1994) 3-4; p. 79, Mar./Apr. 1994.
Mrosik Jan Michael
Nagel Joerg
Stojanoff Christo G.
LandOfFree
FMCW distance measurement process does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with FMCW distance measurement process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and FMCW distance measurement process will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-734800