Optics: measuring and testing – Range or remote distance finding – With photodetection
Patent
1998-11-18
2000-09-05
Buczinski, Stephen C.
Optics: measuring and testing
Range or remote distance finding
With photodetection
356 505, 356 503, B01C 308
Patent
active
061151122
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
For a long time there have been in general two types of distance measuring devices on the market, which work by transmitting and receiving through the atmosphere light pulses along the same path to a distant target and calculating the distance to the target based on the difference between external received light pulses transmitted to the target and reflected by it, and internal light pulses travelling over an internal path in the instrument. According to the first type the phase difference between the internal and external alternating signals with essentially the same pulse length as the pulse space is investigated. According to the other type the time between the transmission of a short light pulse and its reception is measured. The invention relates to the latter type of distance measuring device.
BACKGROUND OF THE INVENTION
Normally this type of distance meter has a comparator in the measuring channel which performs a propagation time measurement between the transmitted and received signal pulses as is described in for example EP-A-475 326. The trigger point and delay in a comparator are always partly dependent on the input amplitude of the received signal pulse because the pulse is not square shaped but has a non-negligible rise time. Such an error should be eliminated.
If a pulse received from the target is detected in a comparator, then the signal-noise ratio for each pulse must be sufficiently high in order to eliminate false triggering by pure noise. This condition determines the range of the instrument. If the light source used is a laser or light diode then it must not be too powerful or give a too powerful radiation per time unit in accordance with the safety classifications for laser based instruments.
Different techniques have been used in order to perform an accurate propagation time measurement. A common method is to make a coarse determination through counting clock pulses from a high frequency clock. The resolution, however, is not sufficient with reasonable clock frequencies, wherefore the determination is complemented with an interpolation method. Such a distance measuring device is described in U.S. Pat. No. 4,620,700. This type of distance measuring device is adversely affected by non-linearities in the position determination.
SUMMARY OF THE INVENTION
An object of the invention is to provide a distance measuring instrument of the propagation time measuring type, which measures the propagation time for a light pulse to and back from a target in an exact and reliable way.
Yet another object of the invention is to produce a distance measuring instrument which is adapted to the security regulations for laser based instruments concerning the radiation per time unit but which gives fast and, at the same time, accurate distance estimates and a long range.
Another object of the invention is to produce a distance measuring instrument of the propagation time measuring type without a comparator in the measuring channels.
Yet another object of the invention is to provide a distance measuring instrument of the propagation time measuring type without non-linearities in the position determination of the target.
Another object is to provide a distance measuring instrument of the propagation time measuring type with a good resolution which can work with a comparatively weak light source. Another object is to provide a distance measuring instrument which combines long range with high accuracy.
A further object is to provide a distance measuring device which can measure the direct reflection from a target without a prism or towards a prism and which is able to measure with visible lasers or IR lasers.
According to the invention a method and a device for measuring distances through the atmosphere by means of propagation time measuring is provided, where the measuring light signal is transmitted towards a target and the measuring light signal reflected by the target is received and wherein the distance measuring comprises a coarse measuring procedure and a fine measuring proce
REFERENCES:
patent: 3630616 (1971-12-01), Everest et al.
patent: 4259592 (1981-03-01), Frungel
Andersson Leif K-G
Ericsson Lars A.
Hertzman N. P. Mikael
Buczinski Stephen C.
Spectra Precision AB
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