DE102013019532A1 - Light beam receiver with improved noise suppression - Google Patents

Abstract

Light beam receiver for analyzing a light beam reception of a light beam transmitter with a light beam detector assembly, which consists of at least two light beam detector elements and an evaluation, characterized in that in the evaluation at least two heterogeneous parameters from the light beam reception are determined and this in a suitable combination for largely selective separation of interference events and Nutzereignissen the light beam reception are used.

Description

The present invention relates to the term claimed above and thus deals with a light beam receiver.

Light beam receivers are needed where light beams are used for the measurement. Typical applications include, for example, the rotary and line lasers used on construction sites and the like. In order to be able to use their radiated laser light, be it a rotating or moving point-shaped beam or a static or moving laser fan or a laser plane fanned out by conical mirrors, even at a great distance for the purpose of measurement, special light beam receivers are required.

Light beam receivers are as in 1 symbolically shown often as so-called hand receiver executed, sometimes as a machine receiver for attachment to the arms or shields of construction machinery for remote display or the automatic control of the position of editing tools.

If, for example, a point-shaped horizontal laser beam rotates about an exactly vertical axis of rotation in a rotating laser, then one can perform an exact height measurement with such light beam receivers, among other things. In this case, photoelectric sensor elements are provided as detectors, which allow these receivers in existing laser beam reception to measure a position largely independent of the position with respect to the radiated reference plane.

If, for example, laser fans or laser planes are used in line lasers, a modulation of the laser light sources with a carrier wave is necessary for the use of light beam receivers with them, since otherwise the signal intensity, which decreases sharply with the distance to the laser, no longer causes interference such as sunlight, Background noise and so on.

The detector elements of such light beam receivers used are usually referred to as quasi-linear detector lines (as in FIG US 5,471,049 disclosed) as a light guide based PSD (as in US 7,110,092 disclosed by the Applicant) or as a multiple array of many identical but electronically weighted single detector elements over the height ( US 6,873,413 ) or in the simplest case as two superposed equal sized photoelectric elements.

The photoelectric detectors described above are all suitable for height-resolving or spatially resolving laser reception with the aid of suitable evaluation circuits. The methods described in these documents relate primarily to undisturbed light beam reception.

Unfortunately, in real environments where such measurements are made with suitable laser light sources and light receivers, it is the case that reception of the useful signals also results in reception of optical interference signals.

• – Blitzereignisse aus Blitz- und Blinklampen, wie sie auf Baustellen üblich sind, bevorzugt erzeugt von Xenon-Entladungslampen oder LED-Quellen.
• – Blitzereignisse von starken breitbandigen Lichtquellen wie z. B. Schweissgeräten.
• – Reflektionen der Emission der Laserlichtquellen an mehr oder minder glatten Oberflächen.
• – Streulicht aus den Optiken der Laserlichtquellen, das sich besonders im Nahbereich negativ bemerkbar macht.
• – Gepulste Beleuchtungen (z. B. mit hochfrequenten Vorschaltgeräten, aber auch mit Netzfrequenz betrieben).

Such interference signals include the following phenomena:

• - Lightning events from flash and flashing lights, as they are common on construction sites, preferably generated by xenon discharge lamps or LED sources.
• - Lightning events of strong broadband light sources such. B. welding equipment.
• Reflections of the emission of laser light sources on more or less smooth surfaces.
• - Scattered light from the optics of the laser light sources, which is particularly noticeable at close range negative.
• - Pulsed lighting (eg operated with high-frequency ballasts, but also with mains frequency).

All these disturbing effects have in common that they can fall in terms of amplitude, as well as in terms of frequency, as well as their optical spectrum forth in the range of the useful signals. That's why it is z. B. to noise suppression not sufficient to use only optical or electronic filters in the individual electronic signal channels.

On the other hand, it is no longer acceptable under many operating conditions light beam receiver without over simple filtering out acting noise rejections equip, since it can easily come to erroneous measurements with these.

For this reason, in the past, various methods have been devised, especially for lightning events, in order to master them as completely as possible. Amongst these methods, the prior art includes, inter alia, a method of the inventor ( US 7,838,813 ) for distinguishing between monochrome (laser) and optically broadband (due to plasma discharge) events. With this method, lightning events of discharge lamps or welding equipment can be almost completely suppressed. In this method is additionally evaluated by an additional detector element, which is largely insensitive in the wavelength range of the useful signals. As a result, broadband flash events can be very reliable, narrow band (monochrome), however, can not be suppressed.

Unfortunately, in the recent past, however, it has increasingly come to the conclusion that many lightning and direction indicators on construction sites can no longer be safely suppressed because they are just equipped with narrow-band, monochrome LED light sources. This otherwise highly reliable method of noise suppression after ( US 7,838,813 Unfortunately, in the future it will increasingly lose its effectiveness.

Another method also with an additional cell, but in contrast to the aforementioned method with largely identical sensitivity profile in the range of the useful signals in series and preferably at one end of the detector line is in ( US 7,224,473 ). The main problem of this method is that especially for relatively short detector lines of the light beam receiver whose length corresponds approximately to the beam diameter at long distances, the useful signals are often accidentally detected as spurious signals, or too high set threshold for the additional detector element spurious signals are insufficiently suppressed , It can therefore not reliably and sharply distinguished between a diffuse, omnidirectional lightning event and a wide light spot of the useful signal with short detector lines. It is probably due to this circumstance that this method is no longer used by laser handheld receivers.

A similar procedure was also used in ( US 5,742,069 ). In this case, the attempt is made to use a specific pattern of illumination (for example reception on at least three detector elements) for distinguishing between diffuse interference signal and sharp beam in the case of a detector line having at least four elements for useful signal reception. Newer derived implementations of this method use two additional small detector elements at the two ends of the detector line to detect their simultaneous illumination by an optical event, this as a disturbance event and to suppress in the further processing and measured value display. Unfortunately, this approach is limited to quite long and thus costly detector lines, as with smaller detector lines again no sharp distinction between interfering and useful signal are possible.

In a fourth method of the prior art ( US 7,372,011 ), it is proposed that in an arrangement of a plurality of weighted detector rows in a largely vertical overall arrangement, the ratio of the signal amplitudes of the weakest signal to the strongest signal of the detector lines are used to distinguish between interference signal and useful signal safely. Such an arrangement thus consists of at least two colinearly arranged linearly height-sensitive detector arrays or PSDs or, as mentioned above, of at least four individual detector elements. Such an arrangement also works reliably only if the total length of the detector lines is significantly greater than the maximum expected beam diameter over long distances.

None of the four methods described above exploit the fact that lightning events differ greatly in their time course (eg, always quasi-simultaneous incidence of light on all possible detector elements and strongly asymmetric course of the peak event) from the course of useful signal reception , since in this stetes a higher symmetry and in horizontally offset detector elements of the detector arrangement, a temporal offset of the light beam reception is to be expected. These time courses are still very meaningful especially when the reception of some or all of the detector elements is changed except for a single one by shading the stray light. This is also a disadvantage of all previously described methods.

• – Es werden nur Ereignisse von breitbandigen, nicht monochromen Lichtquellen sicher als Störereignisse erkannt.
• – Es werden mindestens vier einzeln ausgewertete Detektorelemente benötigt.
• – Bei kurzen Detektorzeilen wird entweder die erzielbare Reichweite oder die Störsicherheit eingeschränkt.
• – Es werden lediglich die Amplituden untereinander oder gegenüber bestimmten Schwellen unterschieden, nicht aber das Zeitverhalten des Lichtstrahlempfangs eines einzelnen Ereignisses auf den unterschiedlichen Detektorelementen.
• – Reflektierte Nutzstrahlen und Streulicht der Nutzstrahlen können überhaupt nicht von direkt empfangenen Nutzstrahlen unterschieden werden.
• – Der Empfang von Störereignissen nach Abschattung einzelner Detektorelemente wird nicht korrekt erkannt.
• – Es wird immer jeweils nur ein Kriterium oder eine Klasse gleichwertiger Kriterien für den Ausschluss von Störereignissen verwendet.

Thus, the above-mentioned prior art methods each have at least one of the following disadvantages:

• - Only events from broadband, non-monochrome light sources are reliably detected as disturbing events.
• - At least four individually evaluated detector elements are required.
• - For short detector lines, either the achievable range or interference immunity is limited.
• - Only the amplitudes with each other or against certain thresholds are distinguished, but not the timing of the light beam reception of a single event on the different detector elements.
• Reflected useful beams and scattered light of the useful beams can not be distinguished at all from directly received useful beams.
• - The reception of interference events after shading of individual detector elements is not recognized correctly.
• - Only one criterion or class of equivalent criteria is always used to exclude disruptive events.

• – Es werden monochrome Lichtblitze ebenso sicher unterdrückt wie breitbandige
• – Große erzielbare Reichweiten, bei möglichst guter Störsignalunterdrückung, auch bei kleiner Detektorzeile
• – Möglichst geringe Zahl an Detektorelementen und eine etwaige größere Anzahl um durch Redundanz eine bessere Störsicherheit zu erreichen
• – Er erreicht eine höhere Sicherheit in der Erkennung eines Störlichtempfanges durch Auswertung des zeitlichen Verlaufes des Lichtempfangsereignisses auf den Detektorelementen bzw. in den einzelnen elektronischen Signalkanälen.
• – Er verwendet gleichzeitig zwei oder mehrere, möglichst heterogene Parameter/Kriterien in passender Kombination, um eine trennschärfere Unterscheidung zwischen Stör- und Nutzereignissen möglich zu machen.

It would be desirable to provide a light beam receiver which, if possible, does not possess all of the above-mentioned disadvantages of the prior art, but in particular has one or more of the following desired properties:

• - Monochrome flashes of light are as surely suppressed as broadband
• - Large achievable ranges, with the best possible noise suppression, even with small detector line
• - As small as possible number of detector elements and a possible larger number to achieve by redundancy better interference immunity
• - It achieves greater security in the detection of Störlichtempfanges by evaluating the time course of the light-receiving event on the detector elements or in the individual electronic signal channels.
• - He uses two or more, heterogeneous as possible parameters / criteria in an appropriate combination to make a separation sharper distinction between interference and Nutzereignissen possible.

A light beam receiver having one or more of the o. G. Possesses properties is described according to the invention in the main claim. Further concretizations and refinements can be found in the subclaims.

In US 7,394,527 In particular, the Applicant proposes a light beam receiver equipped with at least one photoelectric element intended to receive light rays and outputting at least one electrical signal which, after signal conditioning and amplification, is directed to an A / D converter generating a data stream from which the signal amplitude can be derived in proportion to the light beam reception in order to determine a certain property of the beam reception, such. B. to close its position on the detector element and its time course.

The disclosure of the US 7,394,527 is incorporated herein by reference in its entirety and is intended to serve as a basis for a particularly preferred variant of the invention disclosed herein.

Early implementations of this approach used a digital trigger based on the values of the digital data stream to control its reading into a sample buffer. The disadvantage of this approach, however, is that it must always be scanned while waiting for a beam reception, which z. T. requires considerable power consumption, especially if you could switch to a power-saving mode in long breaks, but then have no criterion for waking up with light beam reception.

For this reason, recent implementations use a trigger pulse generated by an analogue comparator fed with an analogue threshold, as well as a further amplified and filtered sum of the electrical signals for the A / D converters. This means that the A / D converters and the amplifier stages with programmable amplification can be switched off in long pauses, but the evaluation circuit can be woken up again at any time by a light beam reception. The evaluation circuit (in this case a microcontroller) contains mostly analog comparators anyway, so that it is to be expected only minimal additional costs.

Such a particularly preferred light beam receiver for rotating light beams, as it is already known in the art, is described in 3 shown.

Such a light beam receiver 1 consists of an arrangement 24 of two light-sensitive detector elements which receive electrical output signals when light beam is received 4 generate, each of two gain and signal conditioning levels 5 be further processed. The output signals 6 the gain and signal conditioning stages become the evaluation unit 18 fed.

To these signals 6 to be further strengthened in the evaluation unit 18 two programmable amplifiers 9 before the A / D converters 11 provided, whose gain is adjustable by software. These are only shown here because the evaluation unit is preferably a microcontroller and its A / D converter sections are usually equipped with adjustable gain amplification stages and these play a role in the expansion according to the most preferred variant of the invention disclosed herein. For rotary laser reception, however, it is sufficient to program this to a gain of 1 or to switch it off, in this case the signals arrive 9 directly to the A / D converter inputs.

In order to detect an incoming light pulse of the rotating laser beam, the signals 6 in a summing amplifier and signal conditioner 7 further processed and the analog trigger signal 8th in the evaluation unit 18 supplied signal comparator supplied. The signal comparator compares the analog trigger signal 8th with fixed or software programmable threshold voltage 14 , The digital result of this comparison, the digital trigger signal 13 , is now to control the scanning process and storage in the internal memory 23 ready.

While the evaluation unit is waiting for a light beam event, the data of the data stream generated by the A / D converters is stored in a ring buffer that is located in the internal memory 23 is stored, and older values are successively overwritten. The sampling rate 20 The A / D converter is chosen to be at least twice faster than the maximum bandwidth of the signals 6 is. The length of the ring buffer is designed in such a way that even very slow events (when receiving at a short distance) are largely stored completely in the ring buffer.

The trigger signal 13 stops writing the ring buffer after a predefined time which is slightly shorter than the time it takes to write the ring buffer once. Thus, transient events just before the occurrence of the trigger signal can barely be detected, as well as the complete course of the signals 6 during a light pulse. From the course of the stored data, the evaluation unit can now calculate separate digital values whose ratio largely corresponds to the ratio of the signal amplitudes of the light beam reception on the detector elements 3 equivalent. From this, the evaluation unit can then look for the point of impact of the beam on the arrangement 24 the detector elements close and the user height information about the display 15 or the speaker 17 give.

To the according to the 3 To expand the prior art described according to the invention disclosed here, it is necessary to expand the evaluation unit 18 in that it can derive at least two linearly independent heterogeneous parameters from the light beam reception.

Examples of such parameters are z. B. Time parameters such as the peak width 21 , the location of the peak maximum 22 of the laser reception event and a time offset 23 between signal channels 6 and 19 due to the spatially shifted arrangement of a detector element 10 opposite to the other detector elements 3 , Regarding the peak width of disturbance events from sources of interference 20 is known to coincide with the step response of the gain and signal conditioning stages 5 , result in relatively narrow value ranges of the peak width. The position of the peak maximum within the time defined by the peak width is always asymmetric, ie significantly shifted towards the beginning of the peak time, by xenon and LED flash lamps as well as pulsed LED illuminations ( 5 ) during regular use events of the laser light source 2 rather centered or slightly shifted towards the end ( 6 ).

A parameter for symmetry (eg position of the peak maximum / peak width) would therefore be a very strong indicator for the distinction between interference events and useful events.

Another of the heterogeneous parameters may be a numerical value that represents a measure of the beam diameter when hitting the detector array and is independent of the absolute amplitude of the light beam reception. Such a parameter may, for example, according to three detector elements 3 according to 2 be determined from the ratio of the sum of the signal amplitudes of the two outer elements and the signal amplitude on the middle element. However, many other calculation methods are conceivable in order to calculate a numerical value from the ratios of the signal amplitudes of three or more detector elements and to determine a rather accurate conclusion about the beam diameter of the expected useful signal.

Another heterogeneous parameter represents the measured height of the impact point according to Lichstrahlempfang on the arrangement of the detector elements 24 This value is used regularly to display the altitude measurement on the display 15 used. This parameter alone would not allow useable noise suppression criteria, but works well in combination with other parameters discussed here.

At the in 2 shown classical arrangement with three cells is z. As the beam diameter parameter is particularly accurate when the detector array is hit in the middle. However, this is precisely the case when omnidirectional flashes strike the detector arrangement and the supposedly detected useful signal has a very large supposed beam diameter with the position on the center of the detector arrangement.

From this fact it can be concluded that the combination of the parameters beam diameter and measured height (impact point on the detector array) always very likely to suggest an interfering lightning event when the determined beam diameter is very large and the light beam reception is calculated at the center of the detector array to come to rest.

If one were to use the beam diameter parameter alone (as has been so similarly realized in the cited prior art), many useful events would be erroneously eliminated as disturbing events at the same threshold. Only the addition of the condition of the position near the central position on the detector arrangement brings a clean distinction.

The addition of further time-related heterogeneous parameters then leads to even more precise differentiation.

It can be conclusively concluded from the above statements that it is the combination of two or more heterogeneous parameters that makes it possible to distinguish between the disruption events of useful events that are necessary for operation on today's construction sites.

A particularly preferred variant of the invention disclosed here is in 4 to see.

Here contains the light beam receiver in addition to the three in the classic triple arrangement of the detector elements 3 and associated signal channels 6 also another, to the three detector elements not in a substantially vertical line so that is laterally displaced from the line of the arrangement additional detector element 10 including the associated signal channel 19 ,

In this lateral offset it comes z. B. when sweeping a rotating laser beam (useful signal) to the fact that the electrical signals 6 and 19 appear mutually delayed. The signal evaluation unit can determine this time offset from the digital data streams of the individual A / D converters by means of temporal center of gravity calculation with high subsample precision and, as mentioned above, use these as heterogeneous parameters for interference signal suppression. But this is only possible reliably if at the same time the signal 19 is strong enough to make a precise determination of the time focus possible. So here too, at least two heterogeneous parameters are needed for robust interference suppression.

The concept of heterogeneous parameters stands out from the state of the art u. a. in that it is possible to span mathematically multi-dimensional value spaces with several linearly independent parameters, in which the distinction between different useful and interfering light sources is much simpler than with single one-dimensional comparisons.

It can even be implemented an artificial intelligence, in which z. B. a neural network with these parameters for real useful and interference signals is learned to make the detection even more robust.

The light beam receiver concept described here is not limited to rotary laser and line laser with modulation. It can also slow moving modulated light fan, as z. B. occur in motorized tachymeters or slowly moving or stationary modulated target beams of point lasers to tachymeters, tunneling lasers or sewer construction lasers are received, and many applications outside the construction sector, such. As light grids, photocells and electronic cameras and much more are covered.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5471049 [0006]
• US 7110092 [0006]
• US 6873413 [0006]
• US 7838813 [0012, 0013]
• US 7224473 [0014]
• US 5742069 [0015]
• US 7372011 [0016]
• US 7394527 [0021, 0022]

Claims (11)

Light beam receiver for analyzing a light beam reception of a light beam transmitter with a light beam detector assembly, which consists of at least two light beam detector elements and an evaluation, characterized in that in the evaluation at least two heterogeneous parameters from the light beam reception are determined and this in a suitable combination for largely selective separation of interference events and Nutzereignissen the light beam reception are used. Light beam receiver according to the first claim, characterized in that one of the parameters is the incident height of the light beam detector on the light beam detector arrangement. Light beam receiver according to one of the preceding claims, characterized in that one of the parameters is a measure of the beam diameter for an assumed Nutzereignis. Light beam receiver according to one of the preceding claims, characterized in that at least one of the light beam detector elements is spatially offset so that a time offset parameter for the temporal offset of the light beam reception of the differently offset detector elements can be determined. Light beam receiver according to one of the preceding claims, that the time offset parameter is one of the two heterogeneous parameters of the light beam reception. Light beam receiver according to one of the preceding claims, characterized in that one of the parameters from the time course of a light beam receiving event can be determined. Light beam receiver according to one of the preceding claims, characterized in that the parameter from the time course is largely dependent on the temporal symmetry of the light beam receiving event. Light beam receiver according to one of the preceding claims, that one of the parameters is dependent on the absolute amplitude of the laser reception. Light beam receiver according to one of the preceding claims, characterized in that it is designed to receive a non-modulated, rotating light beam of the light beam transmitter. Light beam receiver according to one of the preceding claims, characterized in that it is designed to receive a modulated non-rotationally moving light beam of the light beam transmitter. Light beam receiver according to one of the preceding claims, characterized in that a trained neural network for distinguishing useful and interference signals from the heterogeneous parameters is used.

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