Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1990-02-14
1993-05-11
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250561, H01J 4014
Patent
active
052104028
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a detection system for a radiation profile line comprising a matrix containing M rows and N columns of photosensitive detection elements, means for shifting the output signals of the detection elements row by row in the column direction under the control of clock signals, and a read-out circuit, of which one input is always connected to an associated detection element in the Mth row of detection elements.
Systems for observing radiation profile lines are used, inter alia, in triangulation measurements in which a profile is illuminated with a fan-shaped light beam at a first angle while the illuminated profile is observed from a second angle, differing from the first, by means of a detection system. The profile line observed in this manner makes it possible to calculate absolute distances in the profile.
For observing the profile line, use may be made of a detection system consisting of a television camera or of a two-dimensional detector containing a matrix of rows and columns of photosensitive elements. A drawback of a television camera and of the existing two-dimensional detectors is that the picture elements or detection elements have to be read out serially line by line or row by row, which limits the number of profiles which can be observed per second to the normal raster speed. In this manner, M.times.N read-outs are necessary per read-out cycle with a matrix of M.times.N photosensitive elements.
The Dutch patent application 8500600 provides for a detection system in which this problem is recognized. According to said patent application, a solution for this problem is presented by not making use of columns of photosensitive detection elements but of a number of so-called "position sensitive devices" (PSD) placed parallel to each other in columns; such a PSD provides an output signal which is a measure of the position on the PSD where light radiation is incident upon the latter. Said output signal is determined by means of a sub-calculation. Although it is possible with said known detection system in the case of N PSDs, to obtain the complete information relating to the variation of the profile line by means of N consecutive read-outs, namely one per PSD, the use of PSDs also has a number of drawbacks. In the first place, the sub-calculations needed at higher frequencies are difficult to implement and/or can be implemented only at high costs due to the complex electronics required. In the second place, the output signal of a PSD contains a quantity of thermal noise due to the construction of such a PSD. In order to obtain a sufficiently high signal
oise ratio despite said thermal noise, it is necessary to employ high light levels in order that a sufficient quantity of light reaches the detection system containing the PSDs. Furthermore, the required electronics for processing the signals from a PSD cannot be implemented or can be implemented only at very high costs if a reasonably high resolution and a reasonably high dynamic range are required.
The European patent application no. 0,181,553 also describes a detection system for a radiation profile line which is intended to make it possible to read out the observed profile line at high speed. For this purpose an observation system for a profile line is provided in which it is not an entire profile line generated by means of a fan-shaped beam which is observed by the detection system, but a profile line which is built up from consecutive light points projected by means of a narrow light beam on the profile to be observed. The light points reflected by the profile to be observed are imaged as a line via a cylindrical lens on the detection system which consists of a number, for example eight, of oblong detector elements. Each of said detector elements is masked in a manner such that consecutive elements deliver a binary coded signal. If the quantity of light received by such a masked detector element exceeds a certain threshold value, which is determined by means of a level detector connected to each detector element, this means t
REFERENCES:
patent: 3894230 (1975-07-01), Rorden et al.
patent: 4093866 (1978-06-01), Kasdan et al.
patent: 4547676 (1985-10-01), Suzuki et al.
B.V. Optische Industies "De Oude Delft"
Marn Louis E.
Nelms David C.
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