Abstract:
An improved laser light beam receiver rejects unwanted pulses of optical energy, such as strobe lights or other flashes of light, that can occur on a jobsite. The receiver analyzes a light beam reception by using a photosensitive light beam detector arrangement and a separate photoelectric detector serving as an interference signal detector. This additional detector is not easily able to detect the light beams needed in normal operation. On the other hand, the additional detector does detect mostly all interfering light flashes—caused by flash lamps and other similar devices—whose threshold limit is either at the same level or below that of the light beam detector arrangement. An evaluating circuit such as a microcontroller correlates the time of reception of the light beam detector arrangement and the interference signal detector in order to discard the result if the times of reception correspond to a major extent.

Description:
TECHNICAL FIELD 
     The present invention relates generally to laser receiver equipment and is particularly directed to a laser receiver of the type which detects position laser beams to determine physical elevation of the laser receiver. The invention is specifically disclosed as laser receiver that rejects unwanted pulses of optical energy, such as strobe lights or other flashes of light that can occur on a jobsite. 
     BACKGROUND OF THE INVENTION 
     Light beam receivers are required where light beams are used for surveying. They are typically applied with, e.g., rotation lasers that are used on construction sites and similar. In order to be able to use the different types of radiated laser light, special light beam receivers are required. Examples of different types of radiated laser light include a punctiform beam rotating or in motion, a stationary or moving fan beam, or a laser plane fanned out by means of conic mirrors. 
     For example, if a punctiform horizontal laser beam rotates around an exactly vertically aligned axis of rotation, such light beam detectors can be used to carry out precise measurements of elevation. For this purpose photo-electric detector components are provided as detectors which, when laser beams are received, allow the receivers to measure the elevation independently of their position considering the radiated level of reference. 
     The photodetectors provided are usually embodied as one of the following: a quasi-linear detector line (as disclosed in U.S. Pat. No. 5,471,049); or a light conductor based PSD (photosensitive detector), as disclosed in U.S. Pat. No. 7,110,092 of the applicant; or an arrangement of several individual detector elements which are identical but, due to the respective height, of different electronic weighting regarding their sensitivity (as disclosed in U.S. Pat. No. 6,873,413); or, in the simplest case, two photo-electric devices of the same size arranged on top of each other. 
     More or less all of the photo-electric detector arrangements described above are suitable for height-resolving or location-resolving laser reception if supported by suitable evaluation means. However, when the practical application of these light beam receivers is concerned, it must be considered that they are usually exposed to sources of interference signals which can falsify the measuring results. In the worst case there might be a display of measurement results even though no laser beams were received. 
     On construction sites typical sources of interference are, e.g., fluorescent lamps, flash lamps at construction machines and light flashes emitted by electric welding apparatus. Although it has already been possible to sufficiently suppress the interference emitted by fluorescent lamps for many years (e.g., by high-pass filtering of the electric detector signals), the light beam receivers available on the market so far have offered only insufficient suppression of light flashes, and then the only alternative for the user had been to wait until the interference had disappeared. 
     Such interfering light flashes also contain energy of a wavelength range of usually 530 to 790 nm at which common construction lasers operate. Therefore, it is not possible to use only one simple optical filter (like the commonly used red or green optical filters) as part of the detector arrangement in order to effectively suppress these interfering light flashes. 
     Instead, a possible technique to suppress these interfering influences is described in US 2006/0082790. This document describes the use of an additional photo detector—to be mounted either below or above the detector line—which is located behind a separated window inside the housing of the light beam receiver. The sensitivity of the detector lies in the same wavelength range as the one of the detector line, thus being especially suitable for the laser pulses. 
     Here two cases can be assumed: either, the laser beam, i.e., the “wanted” signal, does not hit both the additional detector and the detector line itself at the same moment of real time; or, the intensities measured at the detector line and at the additional detector can be used to decide whether the laser reception nevertheless is interference-free. If not, an interference signal, or an interfered wanted signal, is present but it is not shown on the display. 
     Practical experience has shown that this procedure is very useful when it comes to suppressing light flashes caused by flash lamps. However, where strongly expanded laser beams are concerned, which regularly occur at larger distances and at poorly collimated lasers, it has been observed that these types of laser beams cannot be measured at the edge of the elevation measuring range, since the receiver mistakes them for an interference signal. This is due to the fact that strong portions of the signal hit the additional detector as well as the opposite side of the detector line. A possible solution would be to mount the additional detector at a larger distance either above or below the detector line. However, this possible solution is not preferable, as the dimensions of the device would be overly enlarged, and the necessity to mount the detector either above or below the detector line arrangement of the light beam receiver in the first place can already be regarded as a needless and impractical enlargement. A further disadvantage is the fact that such an additional detector would require an amount of electronic processing comparable to that of the detector line intended for the laser reception, including, e.g., variable gain amplifiers, peak detectors and integrators, or the like. 
     SUMMARY OF THE INVENTION 
     Therefore it would be an advantage to provide an improved light beam receiver that does not feature any of the disadvantages mentioned above. 
     The present invention includes a light beam receiver for analyzing a light beam reception by using a photoelectric light beam detector arrangement and a separate photoelectric detector serving as an interference signal detector. Due to its construction or to a filter medium in place, this additional detector is not easily able to detect the light beams needed in normal operation. On the other hand, the additional detector is able to detect most of all interfering light flashes—caused by flash lamps and other similar devices, which have a rather wide optical emission spectrum and having a threshold limit that is either at the same level or below that of the light beam detector arrangement. 
     One mode of the present invention provides an optoelectronic detector that would be sufficiently insensitive to, e.g., the laser light of a rotation laser, and instead is specially designated for detecting interference signals. An evaluating circuit such as a microcontroller could be used to timely correlate the reception of the light beam detector arrangement and the interference signal detector in order to discard the measured result if the times of reception correspond to a major extent. 
     In an exemplary mode of the present invention, the release sensitivity of the interference signal detection is too low with regard to detecting the wanted signals, and therefore, the interference signal detector can be mounted anywhere on the enclosure, i.e., especially in areas that are usually hit by the normal laser beam. 
     The wavelength range of common construction lasers as well as those of the optical spectra of noble gas flash lamps or of light arc discharges caused by electric welding overlap to a certain extent, but these spectra expand into the infrared area in a quasi-continuous way. Therefore, a commonly available photodiode with an optical low-pass filter inserted—which is able to suppress wavelengths below 800 nm at a ratio of more than 1:100—would make an excellent interference signal detector. 
     The optical low-pass filter may be a filter window made of plastic colored with suitable coloring agents and mounted in front of the interference signal detector. Likewise, the plastic enclosure of the photodiode itself may be colored accordingly; even dielectric layers directly placed on the chip of the photodiode would be possible. A further option would be to use semiconductor materials for the photodiode to desensitize it in the frequency range in question, e.g., materials such as PbS, InGaAs, and the like. 
     Many flash lamps are colored in orange, red, green and blue using optical filters. However, it has been shown that optical filters which have a noteworthy share in the range of common laser wavelengths also have a share in the more remote infrared area at the same level or above. Therefore the inventive principles discussed above can also be used to suppress even such colored sources of light flashes. 
     A light beam receiver which serves as the basis of a preferred embodiment of the present invention, but is not equipped with any measures against pulsed interference signals, is disclosed in the patent specification of the applicant PCT/DE 2005/001989. The disclosure of this patent specification is incorporated by reference herein, in its entirety. 
     Additional advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. 
     Still other advantages of the present invention will become apparent to those skilled in this art from the following description and drawings wherein there is described and shown a preferred embodiment of this invention in one of the best modes contemplated for carrying out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description and claims serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a front view of a typical light beam receiver for manual operation, equipped with an additional detector for interference signal suppression, as known in the prior art. 
         FIG. 2  is a front view of a preferred embodiment of the present invention, of a light beam receiver  1  for manual operation, constructed according to the present invention and including the following components: a light beam detector arrangement  60 , an interference signal detector  20  mounted behind a window  10  (which could be an optical filter), and indicating display components. 
         FIG. 3  is a schematic diagram of the electronics for receiving interfering signals, for use with the light beam receiver of  FIG. 2 , comprising an interference signal detector  20  embodied as a photodiode, an amplifying and filtering circuit  30 , and a threshold limit detector  40 . 
         FIG. 4  is a block diagram of the major electronic components for constructing the light beam receiver of  FIG. 2 , including a light beam detector arrangement  60 , a signal processing unit  70 , an evaluating circuit  50 , an optical filter  10 , an optical interference signal detector  20 , a medium amplifying and filtering interference signals  30 , and a threshold limit detector  40 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings, wherein like numerals indicate the same elements throughout the views. 
     The prior art laser receiver  11  shown in  FIG. 1  represents the conventional approach described above, i.e., to use an additional photo detector  12 . It can be seen that this photo detector is located directly above the detector line  13 . Likewise the display components can be recognized. The device shown here is a handheld laser receiver to be used in conjunction with rotating laser light sources. 
     The handheld receiver shown in  FIG. 2 , designed according to the present invention, is constructed according to a preferred embodiment of the present invention, as described herein. It contains a considerably longer light detector arrangement  60  that stretches nearly across the whole length of the enclosure, behind a window. The use of a variant of such length and of a specifically ergonomic application can be possible if the interference signal detector  20  will be located next (or proximal) to the light detector arrangement, but not necessarily in line with the vertical axis of the light detector arrangement  60 . The interference signal detector  20  is mounted behind a window  10 , which could be an optical filter if desired. 
       FIG. 3  shows a detailed circuit diagram of the electronics used for receiving the interference signals which comprise the interference signal detector  20 , implemented as a photodiode, and a signal conditioning circuit which includes an amplifying and filtering circuit  30 , and a threshold detector  40 . This circuitry can be implemented at very low cost, especially if the microcontroller used within the evaluating (or signal processing) circuit is already equipped with an integrated analog comparator to determine the threshold value. Compared with prior art receivers, no additional integrators, peak value detectors, variable gain amplifiers, or A/D converting channels will be necessary. 
     In an exemplary embodiment of the present invention, the interference signal detector  20  is a silicon PIN photodiode, Part No. HPI6FGR4, sold by Kodenshi Corporation, and the window  10  is substantially clear. The HPI6FGR4 contains its own optical filter, which acts as a visible light cut-off filter, which provides the exemplary interference signal detector  20  with a spectral sensitivity of about 880-1050 nm. For the purposes of the present invention, a cut-off frequency could be as low as 850 nm, or even perhaps as low as 800 nm, which would still be substantially insensitive to standard laser transmitters that output laser beams at 630 nm, 670 nm, or even as high as 790 nm. 
     It will be understood that it is the combination of the actual photosensor element and any optical filter that is important. If the photosensor by itself has a wavelength sensitivity above 850 nm, for example, then no optical filters will be needed at all, either on the sensor itself, or for the window  10  of the housing of the laser receiver. In general, the wavelength sensitivity for the interference signal detector “system” (i.e., the combination of the sensor and any optical filter), should be above about 800 nm, or more preferably, above 850 nm. 
       FIG. 4  shows a block diagram for constructing a preferred embodiment of the light beam receiver shown in  FIG. 2 . This variant of  FIG. 4  comprises a light beam detector arrangement  60 , a signal processing unit  70 , an evaluating circuit  50 , the optical filter  10 , the interference signal detector  20 , the circuit for amplifying and filtering interference signals  30 , and the threshold limit detector  40 . This version of the light beam receiver  1  is designed according to the present invention, and works as follows: 
     If the light beam receiver is moved into a position where a moving laser beam  3 , emitted by a source of laser light  2 , falls onto a light-sensitive area of a light-detecting sensor (also referred to herein as a light “rod” sensor)  63  relating to the distances “l” and “m” of the light beam detector arrangement  60 , then two electrical signals  64  and  65  are generated by two optical sensors  61  and  62  that are placed proximal to the ends of the light rod  63 . The light rod sensor  63  is an exemplary photodetecting device such as that described in U.S. Pat. No. 7,110,092, titled “MEASURING DEVICE AND MEASURING METHOD FOR DETERMINING DISTANCE AND/OR POSITION,” by the same inventor(s), which is incorporated herein by reference in its entirety. 
     The light beam sensing arrangement  60  mainly comprises a longitudinal light conductor (or “rod”)  63  that has at least one photosensor element  61  or  62  positioned at (or near) each of its two distal ends. When a light beam strikes the rod conductor  63 , that light beam is radially coupled into the longitudinal light conductor  63 , and the beam then splits and travels toward both distal ends of the light conductor  63 . When the coupled light beams reach their respective distal ends, they exit the conductor  63  and each exiting beam impacts its proximal photosensor element  61  or  62 . The relation of magnitudes of the two light impacts on the two spaced-apart photosensors gives an indication of the dimensions l and m, and thus the position where the light beam struck the light conductor  63 . The photosensors  61 ,  62  can be virtually any type of optoelectronic sensor for most purposes, such as a standard photocell that generates current when receiving photons (e.g., a photodiode or phototransistor), or perhaps a photovoltaic cell. 
     The signal processing circuit  70  receives the output signals  64  and  65  from the photosensors  61  and  62 , respectively, of the light beam detector arrangement  60 . Signals  64  and  65  are directed to a pair of amplifying and filtering circuits  71  and  72 , respectively, and these circuits produce filtered signals  73  and  74 , respectively. Signals  73  and  74  are directed to a pair of integrator circuits  75  and  76 , respectively, which output voltage signals  8  and  9 , respectively. The voltage signals  8  and  9  are also directed to an integration timing and limiting circuit  77 , which provides a feedback/gate signal  78  for the integrators  75  and  76 , mainly to start/stop the integration simultaneously in both integrators and thus produce a quasi-automatic gain behavior. 
     Thus the two signals  64 ,  65  are converted into two voltage values  8  and  9  by the signal processing unit  70 ; then, in turn, these values are converted into digital values by the evaluating circuit  50 , e.g. a microcontroller which includes analog-to-digital (A/D) converters  51  and  52 . By inspecting these two digital values the evaluating circuit  50  is able to determine the position of the laser beam impact (at  3 ) by determining the distances l or m, and to display a corresponding numeric value, or to generate a similar corresponding external analog or digital signal or visual indication. 
     In an exemplary laser receiver according to the present invention, the photosensor elements  61  and  62  are silicon photodiodes, Part No. BPW46L, sold by Vishay. Such photodiodes have a “normal” silicon photo response curve, and will respond to laser light beams transmitted in the standard wavelengths of 630 nm, 670 nm, or 790 nm. The exemplary laser receiver may also have an optical filter that covers the light beam detector arrangement  60 , although this optical filter mainly is used to limit the effect of sunlight entering this portion of the laser receiver  1 . In other words, a “standard” silicon photodiode would be acceptable without optical filtering, with regard to the operating principles of the present invention. 
     If now a light flash is generated by a source of interfering light  4  (such as a strobe light, or other type of intermittent light pulse), of which a portion  5  falls onto the light beam detector arrangement  60  (at the photosensor  63 ), then this light flash or pulse may cause an incident in the subsequent parts of the analog processing circuitry which the evaluating circuit may not be able to distinguish from a “standard” laser beam reception. Thus, this incident would usually (using conventional devices) lead to the display of a false measuring value, that could be almost arbitrary. 
     However, in the illustrated embodiment 1 of the present invention, a certain portion  6  of the light pulse (or light flash) also falls through the optical filter  10  onto the interference signal detector  20 . The electrical output signal of this detector is further amplified and filtered by the interference signal amplifying and filtering circuit  30  before it reaches the threshold limit detector  40 , where the signal is compared to a predetermined threshold value. If this threshold value is exceeded (i.e., if a sufficiently strong interference signal is determined), then this result will be signaled via the comparator output signal  7 . 
     The evaluating circuit  50  recognizes the virtually simultaneous occurrence of the comparator signal  7  and the signals  8  and  9  output by the signal processing unit  70 , and the evaluating circuit  50  is thus able to suppress any false reading caused by the received interference signal. Therefore, the evaluating circuit  50  will be able to determine when the comparator signal  7  (that is output from the threshold detector  40 ) occurs substantially at the same real time instant as the “wanted” light beam signals  8  and  9  (that are output from the signal processing unit  70 ). If these signals do simultaneously occur (within a predetermined time tolerance), then the receiver&#39;s overall microcontroller will not display a position reading based on that particular sample of a light beam strike on the light beam detector arrangement  60 . 
     On the other hand, if a laser beam (the “wanted” signal) falls on the optical filter  10 , it is attenuated by the filter to such an extent that it will not trigger the comparator signal  7 . If this same laser beam also strikes the photosensor  63 , then its position of impact will be determined by the signal processing unit  70  and the evaluating circuit  50 , and this reading will be accepted and displayed on the laser receiver  1 . In other words, since the evaluating circuit  50  did not detect an “unwanted” pulse signal at  7 , then it was able to confidently evaluate and display the “wanted” signal that was received at  8  and  9 . 
     It will be understood that an external evaluation circuit could be used for determining whether or not a reading should be suppressed. A machine control box, for example, could make that decision, and then quickly output a signal to the laser receiver to prevent a new reading from being displayed or used (by the machine) during a particular instance of an optical noise signal (or strobe light) striking the receiver. 
     It should be noted that the signal conditioning circuit used for the optical interference signal detector  20  (i.e., the amplifier and filter  30 , and the threshold detector  40 ) do not include such complex components as a variable gain amplifier, an integrator stage, or a peak detector circuit. This not only makes the illustrated design of the present invention less expensive to produce, but also makes its operation more reliable, including less prone to calculation errors. In conventional designs for strobe light or pulsed light rejection circuits, such complex components are the norm. 
     It will be understood that other types of photosensors could instead be used with the remainder of the circuit depicted in  FIG. 4 , without departing from the principles of the present invention. In other words, conventional multiple photocell arrangements may be used to generate signals that will be evaluated and have the position of impact determined by their own types of special signal processor devices. If desired, the results of such conventional laser beam receivers could be used along with the combination of an interference signal detector  20 , amplifying and filtering circuit  30 , and threshold limit detector circuit  40 , that outputs the “unwanted” pulse signal  7  to the evaluating circuit  50 . 
     The particular receiver presented here is a handheld device used for simple elevation measuring and similar. In addition to this, however, it is also possible to apply the procedure of interference signal suppression presented herein to light beam receivers used for construction machine controls, camera systems, light barriers and other systems of optical sensing or positioning. Also it is not a mandatory requirement to use movable light beams; other options would include a static spatial radiation, e.g. of pulsed fanned out light beams, or some other similar arrangement. 
     As used herein, the term “proximal” can have a meaning of closely positioning one physical object with a second physical object, such that the two objects are perhaps adjacent to one another, although it is not necessarily required that there be no third object positioned therebetween. In the present invention, there may be instances in which a “male locating structure” is to be positioned “proximal” to a “female locating structure.” In general, this could mean that the two male and female structures are to be physically abutting one another, or this could mean that they are “mated” to one another by way of a particular size and shape that essentially keeps one structure oriented in a predetermined direction and at an X-Y (e.g., horizontal and vertical) position with respect to one another, regardless as to whether the two male and female structures actually touch one another along a continuous surface. Or, two structures of any size and shape (whether male, female, or otherwise in shape) may be located somewhat near one another, regardless if they physically abut one another or not; such a relationship could still be termed “proximal.” Moreover, the term “proximal” can also have a meaning that relates strictly to a single object, in which the single object may have two ends, and the “distal end” is the end that is positioned somewhat farther away from a subject point (or area) of reference, and the “proximal end” is the other end, which would be positioned somewhat closer to that same subject point (or area) of reference. 
     All documents cited in the Background of the Invention and in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. 
     The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Any examples described or illustrated herein are intended as non-limiting examples, and many modifications or variations of the examples, or of the preferred embodiment(s), are possible in light of the above teachings, without departing from the spirit and scope of the present invention. The embodiment(s) was chosen and described in order to illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to particular uses contemplated. It is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.