Device for obstacle detection for pilots of low flying aircrafts.

The invention relates, or the like to an arrangement for detecting obstacles such as power lines, ropes, poles., Low-flying for pilots aircraft, especially helicopters, pictorial with an existing transmitter and receiver pulse laser rangefinder for scanning a predetermined field of view and to representation of the progress of the perceived obstacle. Such an arrangement is known from DE-AS 24 02 537th

Low Flying aircraft such as helicopters flying low use, or the like are particularly at night or in poor visibility by the pilot barely perceptible obstacles such as power lines, wire ropes of cableways, masts., At risk. Warning devices have been proposed for detecting such obstacles already, which operate on the laser radar principle. In the arrangement known from DE-AS 24 02 537, the scanning of the area of ​​interest in concentric circles or spirally with the laser beam of an existing transmitter and receiver pulse laser rangefinder is done. The course of the perceived obstacle is displayed on a screen. However, scanning a predetermined field of view with a single laser beam requires a relatively long time. this addition are expensive components, such as required, a laser with a high pulse repetition rate and a complicated mechanism Scanner with high scanning mirror frequency in azimuth and elevation. This effort also affects the size and weight of the assembly unfavorable.

The invention is therefore based on the object to achieve in an arrangement of the type mentioned as simple as possible, compact structure and to keep the cost of the individual components as small as possible.

This object is achieved with an arrangement of the aforementioned type according to the invention that in each case an array of semiconductor laser diodes or of reception detectors is provided as a transmitter and as a receiver, and that the sampling of the visual field by the bundled laser pulses in a coarse grid made with a mesh-like pattern.

The invention is based, that the cost of scanning a predetermined field of view through the use of an array of semiconductor lasers and detectors of reception can be minimized knowledge. With such, after the laser radar principle with direct reception working arrangement a variety of operating in pulse mode semiconductor laser diode is used as a radiation source for the transmitter the laser rangefinder therefore used. Such semiconductor lasers have excellence to 100 W and high pulse repetition frequencies (some 10 kHz) and are prior art. They are well modulated, small, light and inexpensive, can be linked to a simple fiber optic components and integrated easily into an array. These advantages can be exploited to reduce the pulse repetition frequency of the laser diode and for reducing the scan mirror frequencies. Moreover, these benefits are both in on and build technical terms and in terms of size and weight of the assembly is important. A further advantage of using a semiconductor laser diode arrays for the transmitter of the laser rangefinder is that so that a multibeam laser radar is provided with a plurality of radiation sources for scanning. The inventive arrangement is thus no longer dependent on the function and reliability of a single radiation source, ie, the assembly is also in case of failure of individual radiation sources continue to work, which is not guaranteed in a scan of the visual field with the laser beam of a single laser transmitter and in case of failure. The scanning of a predetermined visual field with such a multi-beam laser radar also can be carried out also with a lower cost compared to a scan by the laser beam of a single laser transmitter.

For the recipient of the laser rangefinder, an array of reception detectors are provided. Preferably, these consist of photodiodes, eg Si diodes. This receiver technology can also adapt well with fiber optics to the task and is also state of the art.

Another basic idea of ​​the inventive arrangement can be seen in the net-mesh-like image scanning. Therein lies a further measure to reduce the expenditure, since such image scanning can be carried out as a result of low-held scanning mirror frequencies with a simple scanner assembly. Although a mesh-shaped scan pattern has gaps and produces fewer pixels but enables a lower sampling time and a saving of laser diodes. In addition, the mesh size of the scan and the number of laser diodes, taking into account the distance range of the arrangement can at any time choose optimally so that the tasks to be undertaken in accordance with the intended use of the assembly obstacles in a specific, user-defined distance are readily apparent. This means that certain obstacles at a certain distance, for example, wires of about 3 mm in diameter and at a distance of about 300 m, with a suitable choice of aperture size and number of laser diodes can be detected readily.

Advantageous embodiments of an arrangement according to claim 1 are specified in the dependent claims.

In case of using a working in the 10 micron range laser rangefinder to the cost of laser components and optics increased further. Therefore, the transmitter array of GaAs semiconductor laser diode is formed with the wavelength λ = 0.9 microns with an inventive arrangement in a preferred manner. A laser radar with semiconductor laser diodes of this wavelength may be at considerably lower cost and less expensive to realize as a working in the 10 micron range laser radar. For an inventive arrangement as well as semiconductor lasers used with a wavelength of 1.3 or 1.5 microns in consideration. Semiconductor lasers in the 1.5 micron range have the advantage of complete eye safety and are not detectable by night vision devices.

Advantageously, the semiconductor laser diode and the receiving detectors are coupled to fiber optic components. The advantage is that the semiconductor laser diode and its control as well as the receiving detectors in an optical of the components of the arrangement, that can be arranged by the scanner and optics, separate electronics.

Appropriately, the pulse width of the laser pulses of the semiconductor laser diode (about 5-100 nsec) limited to a few nanoseconds. By this measure the average power of the semiconductor laser diode can be kept low, and a sufficient depth resolution of eg less than 5 m can be achieved at 30 nsec pulse width.

In an arrangement according to the invention it is advantageous if the field of view of the receiver is adjusted by using a common lens to the front of the transmitter. The use of the same lens for transmitters and receivers is possible by a suitable choice of the dimensions of the semiconductor laser diode and the receiving detectors. By introducing a matching optics, however, it is also possible to use different semiconductor laser diodes and reception detectors in their dimensions.

In view of the expense in the optical components, it is advantageous if the transmitter and the receiver array are arranged in a coaxial system with a common front lens. The optical coupling of transmit and receive path in the coaxial system is advantageously carried out by means of a beam splitter.

In a first advantageous embodiment of an inventive arrangement, the semiconductor laser diodes or the reception detectors, Furthermore, the distance of the columns from each other, are each arranged in at least two parallel columns, wherein the spacing of the semiconductor laser diode or the reception detectors, a column from one another corresponds to the mesh width, equal to half a mesh opening, and the semiconductor laser diode or the reception detectors are offset from each second column against the semiconductor laser diode and the detectors receive the adjacent columns in elevation by half a mesh width. Here, the azimuth scan takes place via a scanning mirror, wherein, in each scan across the azimuth, an image is generated. In this case, the elevation angle is divided into a corresponding number of rows and each row is a semiconductor laser diode is provided which is guided by means of a micro-scanning mirror about a few milliradians in a zig-zag pattern in azimuth about the field of view. In such an arrangement, the mesh-shaped scan pattern corresponding configuration of the transmitter and the receiver array can be produced with a simple scanner in a scan.

In a second embodiment of an inventive arrangement, the semiconductor laser diodes or the reception detectors are respectively arranged in one or more parallel columns without gaps and without overlapping with each other. In this case, the net-mesh-shaped scan pattern is generated by a corresponding control of the release timing of the one below the other in a column semiconductor laser diode during the pivoting about the azimuth. This allows mesh and mesh angle, ie the angle of the grid strips of the scan against azimuth, by changing the delay time between the laser pulses, ie electronically change. In this embodiment, a micro-scanning mirror is not necessary.

In another embodiment, it is provided that in each case one or more missed rows in the array of semiconductor laser diodes or the receiving detectors and filled by one or more interlace movements of a scanning mirror is. This therefore involves the use of semiconductor laser diodes or receiving detectors is lower and therefore the transmitter or receiver array simple. However, it has the pulse repetition frequency of the semiconductor laser diode and the scan frequency of the azimuth scan mirror are proportional to the number of interlace movements increased in order to avoid a more time-consuming than with the two embodiments mentioned above. The generation of the mesh-shaped scan pattern, and thus the image formation carried out in this embodiment in two or more scans, either azimuth mirrors addition in elevation to a mesh size further or - in a preferred manner - the micro scanning mirror is also moved in the elevation. It may occur relative to the scene may arise due to angular movements as a low flying helicopter that the net meshes are not completely closed.

Embodiments of an inventive arrangement are described in more detail below with reference to the drawing. Show it<ul><li>FIG. 1 shows the structure of the arrangement</li><li>Figs. 2 and 3 shows the structure of an intended for the pulse-laser distance-measuring arrangement of the transmitter array and a receiver array,</li><li>Fig. 4 shows the scan pattern generated in the arrangement,</li><li>Fig. 5 is a low-flying helicopter, in its trajectory an overhead line is to be recognized as an obstacle, with a cut of the scan,</li><li>Fig. 6 another construction of a transmitter or receiver array,</li><li>Fig. 7, the scan pattern of these arrays and</li><li>Fig. 8 is an evaluation device.</li></ul>

The arrangement of FIG. 1 illustrates a laser radar is composed of a transmitter and receiver pulse-laser range finder and a scanner with an optical system. As a transmitter and as a receiver is an array in each case 1 (Fig.1,2) of semiconductor laser diodes 3 (Sender array) or an array 2 (Fig.1,3) of receiving detectors 4 (receiver array) provided. The transmitter array 1 is formed of GaAs semiconductor laser diodes 3 with the wavelength λ = 0.9 microns. The semiconductor laser diode 3 of the transmitter arrays 1 are coupled to optical fibers and configured to the indicated in Fig.2 Array. The receiving detectors 4 for the receiver array 2 consist of photodiodes, eg silicon diodes, and are also coupled to glass fibers.

Each a receiving detector 4 of the receiver array 2 of a semiconductor laser diode 3 of the transmitter array 1 is associated, wherein the angular placement of the receiver array 2 that of the transmitter arrays equals 1, that is, the semiconductor laser diode 3 and the receiving detectors 4 are - as shown in FIGS 2 and 3 show - in the same arranged to be explained in more detail later configuration.

The transmitter and the receiver array 1 and 2 are arranged in a coaxial system with a common front lens 5, which adjusts the field of view of the receiver to the radio station. For the optical coupling of the transmitting and receiving branch in the coaxial system, a beam splitter 6 is provided which couples the receiving branch in the transmit path and decouples from the coaxial system. The scanner consists here of a saw in the receive direction arranged in front of the front lens 5 scan mirror 7 for azimuth scan and a between the front lens 5 and the beam splitter 6 in the coaxial system inserted micro scanning mirror 8 for elevation scan.

The arrangement according to Figure 1 operates at a laser divergence of semiconductor laser diodes 3 to 1 mrad with a coarse grid sampling of the predetermined visual field (eg 30^O in elevation and 60^O in azimuth) as a nationwide sampling a very high pixel count, and therefore high laser pulse repetition frequencies (PRF) or scanning mirror frequencies would result. In order to reduce the pulse repetition frequency PRF, a plurality of semiconductor laser diodes 3 and a plurality of reception detectors 4 are used.

The field of view is, as in Figures 4 and 5, sampled with a mesh-like pattern, is the mesh width of the scanning function of the smallest size to be detected one at a certain distance still perceivable obstacle selected.

For an approximately 300 m still true growing obstruction of about 3 mm in diameter, the mesh size is, for example 12 mrad, which corresponds to a resolution of 6 m in 500 m distance. The width of the seamless, at an angle of 45^O set against azimuth about the visual field power strips 9 of the scan pattern corresponding to the laser divergence of example 1 mrad.

In order to produce the net-mesh-shaped scan pattern according to Figures 4 and 5, the semiconductor laser diode 3 and the receiving detectors 4 are configured in a corresponding manner in the transmitter array 1 and in the receiver array 2nd Accordingly, the semiconductor laser diodes are three in Fig.2 and the receiving detectors 4 disposed in Fig.3 respectively in at least two mutually parallel columns SP1 and SP2, the distance between the semiconductor laser diode 3 and the receiver 4 detectors within the column Sp1 or Sp2 equal to the mesh size, in the example, 12 mrad is. The spacing of the columns SP1 and SP2 from each other is equal to half a mesh opening, thus 6 mrad, wherein the semiconductor laser diode 3 and reception detectors 4 every other column, so the column Sp2 and optionally Sp4, Sp6, etc. or to the semiconductor laser diode 3 . the receiving detectors 4 of the adjacent columns, so the column Sp1 and optionally the columns Sp3, Sp5, etc. mrad by half a mesh opening, thus to 6 in elevation, are offset.

The scanning of the field of view in elevation and azimuth is now using the gem. Figure 2 configured in the transmitter array 1 The semiconductor laser diode 3, wherein the elevation angle is divided into a corresponding number of rows and each row is a semiconductor laser diode 3 is provided. Each semiconductor laser diode is driven by a micro scan over a small angle, that is reciprocated about a few milliradians, in the elevation. The micro scan is performed at a mesh width of eg 12 mrad over a row height of half a mesh width, ie about 6 mrad. In this manner, the semiconductor laser diodes 3 - as most clearly seen in Figure 5 is - out in a zig-zag pattern in azimuth about the field of view. To carry out the micro scans the aforementioned micro scanning mirror 8 is provided. Its scanning frequency is determined by the ratio of Sehfeldwinkels in azimuth to the width of the micro-scans (mesh). So its scanning frequency is at 60^O . Azimuth angle and 12 mrad micro scan width, for example 87 Hz, the azimuth scan is done - as already mentioned - by the scan mirror 7 located in front of the optical system, wherein, in each scan across the azimuth, an image is generated. The scanning frequency of the azimuth scan mirror 7 is the desired frame rate (for example, 5 Hz) and the number of semiconductor laser diodes 3 or the receiving detectors 4 determines if these cover the entire visual field in the elevation. At 30^O Elevation angles are approximately 44 semiconductor laser diode pairs, ie ca 88 diodes for two columns required. In this case, at each swing of the scene creates an image, the scanning frequency of the azimuth scan mirror 7 is then 2.5 Hz.

A section of the scanning semiconductor laser diodes 3 and its bundled laser pulses line by line zig-zag written, overall net-mesh-shaped scan pattern and the course of a wire fence is shown in Figure 5. Each zig-zag line with a semiconductor laser diode 3, namely, from that of FIG. 2 "1" marked semiconductor laser diode in column Sp1 bzw.der with "2" marked semiconductor laser diode of the column col2 bzw.der with "3" marked semiconductor laser diode in column Sp1 bzw.der with "4" marked semiconductor laser diode of the column col2 etc. written. This overlap - clearly seen in Figure 5 is - the individual amplified laser pulses slightly, as they cover to 20% (= overlap factor of 0.8). The pulse repetition frequency PRF of the semiconductor laser diode 3 is obtained from the desired frame rate, the scanned azimuth angle, the laser divergence, the angle of the micro scan, and the inclusion of a certain overlapping of the individual laser beams. At 5 Hz image sequence, an azimuth angle of 60^O, A micro-scan angle of 45^O and an overlap factor of 0.8 obtained for example 9.3 kHz pulse repetition frequency. This value is available today GaAs semiconductor laser diode of wavelength 0.9 micron realized. The pulse width of the laser pulses is limited to a few nanoseconds, eg nsec to 30 to keep the average power of the semiconductor laser and low to allow sufficient depth resolution &lt;5 m.

In another embodiment, after 6 shows the semiconductor laser diode 3a and the reception detectors 4a are respectively arranged in a column of Sp or in a plurality of mutually parallel columns, without gaps and without overlapping with each other. The net-mesh-shaped scan pattern (Figure 7) is generated here by the fact that the laser pulses are fired during the pans over the azimuth at the right time. This mesh size and angle can be by changing the delay time between the laser pulses, ie electronically, change. In this case, the micro-scanning mirror is not necessary.

In modifications of the above embodiments, each one or multiple rows can be omitted from the transmitter or the receiver array. These are then passed through one or more interlace movements of a scanning mirror, preferably of the micro-scanning mirror 8, replenished.

The signals obtained from the detectors 4 receiving the measured distance values ​​are amplified with matched to the laser pulse width amplifiers and then fed to an evaluation device, which attaches to the marked in Fig.1 interface of the assembly. The structure of the evaluation device is schematically shown in Figure 8 in a block diagram. For evaluation, the video signals are first digitized analog thresholds 20 and then transformed into a parallel / serial converter 21 in a continuous data stream. A subsequent counter 22 evaluates the distance. The methods known for rangefinders are used. The measured distance values, the position values ​​of the scan mirrors 7,8 and the values ​​for the time sequence is then processed in a signal processor 23 on. This saves the information depending on the distance, and puts them together into one image. From this image, the overall scene the image of the obstacle is then extracted and the pilot on a display 24th This image then representations, such as distance marks, sensor functions, enlarged image details, device functions or the insertion / inclusion carried over from the on-board computer flight data are possible. Furthermore, the pictorial representation can be further supported by intensity or color or acoustic or visual warning signals.