Scanning apparatus

The invention relates to a scanning device for an optical scanning system, consisting of a housing, with a device-fixed source for, esp. pulsed laser radiation, furthermore with beam deflection means in the form of a vibrating mirror to deflect the transmitted beams of the laser source and to scan an object space in a grid-like manner, furthermore with a device-fixed receiving device for beams reflected in the object space and an evaluation device that calculates distance values ​​from the transit time of the laser beams determined which are assigned to the respective deflection angles, further with first bearings for the rotatable mounting of the oscillating mirror about a first axis of rotation and with second bearings for the rotatable mounting of the oscillating mirror about a second axis of rotation, which is directed essentially normal to the first axis of rotation and defines an intersection with this, further with a window of a for the laser radiation transparent material, which closes the housing and through which the transmitted rays exit into the object space and rays reflected in the object space re-enter the device through said window.

Such a scanning device is known from US Pat. No. 4,025,193, which is part of a docking aid in an aircraft in-flight refueling system. The device has a laser source that emits laser beams that are emitted via an oscillating mirror that can be swiveled around 2 orthogonal axes. Rays reflected in the object space are directed to a sensor via the above-mentioned oscillating mirror. The transmitted rays and the reflected rays run parallel and at different heights.

In this device, the distance measurement is preferably carried out by means of a phase measurement, but according to the description of the cited US patent it is possible with a pulse transit time measurement . The task of this system is to first bring the tanker and the aircraft to be refueled into suitable relative flight positions via displays or by directly influencing the autopilots of both aircraft and then to direct the nozzle of the tanker pipe of the tanker into the filler neck of the recipient aircraft. For this second phase, retro reflectors are attached to the tank nozzle, to the nozzle of the tank pipe, which can be telescopically extended from a steerable tank nozzle, and to the end of the tank nozzle. These retro reflectors produce powerful reflected signals that stand out clearly from the background of the image. The pilots or the corresponding control devices of both aircraft must align the images of the reflectors on the tank nozzle and the tank pipe nozzle. The scanning device is arranged in the rear of the tanker, the transmitted beams exit through a flat window through which the reflected beams re-enter. With regard to this window, only a small field of view of the scanning device is possible. The transmitted rays and the reflected rays are offset differently through the window depending on the deflection angle, which results in corresponding distortions in the image. These restrictions are of no particular importance in this special application, since any imaging errors compensate each other, since the images of the two reflectors are made to coincide and the imaging errors affect both images equally. With this arrangement, it is not possible to scan a room with a large field of view and high image quality.

U.S. Patents 4,039,246 A and 4,024,392 A describe target acquisition and tracking systems for guided missiles. These are not imaging systems. If a target is detected in these systems, this is pursued further, the system being “blind” with regard to all other objects. In order to obtain the largest possible field of vision with these systems, the window was designed in the form of a spherical dome. In target acquisition systems, it is primarily important to know in which area (quadrant) of the field of view the target is located. Therefore, deviations and distortions in the optical image are of subordinate importance. According to the first-mentioned US-PS, a mirror telescope is provided, the primary and secondary mirrors of which are arranged to be rotatable about a common axis. Both mirrors are slightly tilted in relation to the axis of rotation and are driven at different speeds. The optical axes of the incoming rays thus describe loops, which in sum create a rosette-like pattern

AT 504 580 B1

Result in scanning patterns. The system works purely passively, i.e. only the radiation emitted by the targets is evaluated. A distance measurement is therefore not possible with this system. The rosette-like scanning pattern has a high resolution in the central area and a low one in the peripheral area. In order to compensate for this, the reflector telescope is mounted in a cardanic manner and is tracked to a target once it has been detected in such a way that it is always in the center of the field of view. The gimbal-mounted reflector telescope is covered by a transparent, spherical dome. The system is not able to scan an object field with constant resolution, image quality and high speed and moreover has very large masses and moments of inertia, so that it is sensitive to accelerations and vibrations.

A similar system is described in US Pat. No. 4,024,392 A. Here, too, a reflector telescope is used, which is gimbal-mounted. The beams of a stationary laser are directed via a complex prism system through the bearings of the cardan frame into the center of the reflector telescope and are emitted in the optical axis of the system. The laser radiation is used to illuminate the field of view so that targets that do not emit radiation can also be detected. The reflected rays are directed by the telescope mirror onto a 4-quadrant sensor. The telescope is tracked to the detected target via a corresponding control device. A TV camera system can optionally be provided so that the target can also be observed. In this case, too, the reflector telescope is covered by a transparent dome.

Neither of the two systems has a laser rangefinder, so that they are not suitable for recording data from which distance images or 3-D models can be developed. With these target acquisition systems, the requirements for image quality and freedom from distortion are therefore comparatively low.

A similar system is described in DE 33 17 232 A1. This system also has two range or distance sensors which, however, are not part of an imaging system, but trigger the ignition of an explosive charge when it flies past a target.

In US patent application US 2003/0098387 A1, an all-round viewfinder for detecting approaching guided missiles is described. Here, too, the optical sensor is mounted in a cardan frame so that it can pivot about two orthogonal axes. When an infra-red source (engine of a guided missile) is detected, "countermeasures" are triggered. For this purpose, it is proposed in the application to emit high-energy laser beams by means of which the optical target tracking device of the guided missile is to be dazzled and the missile is thus to be switched off. There is no mapping system here either.

In EP 1 035 399 A1, a sensor for a guided weapon system is again described. The sensor is gimbaled. In the case of objects with low IR emissions, the target is illuminated with a laser, and distance measurement is also possible. Due to the large masses to be moved, only low sampling rates are possible.

US Pat. No. 6,422,508 B1 describes a camera system that includes TV cameras for different wavelength ranges and resolutions. The system is mounted on a stabilized platform and can be adjusted remotely about two axes. It is not possible with this system to generate distance images or 3-D models.

US Pat. No. 5,200,606 A describes a target search and tracking system which is similar to that known from EP 1 035 399 A1. It again has a reflector telescope, which is gimbaled. In addition, a fast scanning system consisting of an oscillating mirror that can be pivoted about an axis is provided. A second scanning direction results from a fan-like design of the transmission beams in conjunction with rows of diodes as receivers.

AT 504 580 B1

The US application US 2006/0152705 A1 describes a laser radar system which has a housing with flat windows for the transmitted beams and the reflected beams. The windows are kept free of adhering dirt and water droplets using compressed air.

DE 10 2005 013 817 A1 describes a distance detection system for vehicles which has a flat window each for the transmitted rays and the reflected rays. Additional transparent protective plates arranged in front of the windows are intended to protect them from damage.

It is an object of the invention to eliminate the drawbacks and limitations inherent in the prior art documented above and to provide a high quality 3-D imaging system that has high sampling rates and a large field of view, is robust and resistant to environmental and other factors external influences such as accelerations and vibrations on the one hand and rapid temperature and pressure fluctuations and high humidity on the other hand is insensitive.

The oa. Objectives are achieved according to the invention in that the window is spherical in a manner known per se, with the center of curvature essentially coinciding with the mentioned intersection of the axes of rotation (A1, A2) of the beam deflection means, as is also known, with the correction means preferably are provided in the beam path of the transmitted beams and / or the reflected beams, which compensate for the optical effect of the curved window, and that the transmitted beams and the reflected beams directed onto the receiving device run coaxially at least between the oscillating mirror and the spherical window, wherein in the beam path of the transmitted beams and in the beam path of the reflected beams, preferably between the oscillating mirror and the laser source or the receiving device a beam splitter for the transmitted beams and the reflected beams is provided, via which the reflected beams returned via the oscillating mirror are directed onto the device-fixed receiving device.

In the scanning device according to the invention, the beam splitter preferably consists of a mirror with a central opening through which the transmitted beams can pass while the reflected beams are reflected on the mirror surface.

Further advantages result if the optical axis of the transmission beams directed onto the oscillating mirror coincides with the first axis of rotation of the oscillating mirror.

A further improvement is obtained if an optical system is provided in the beam path of the transmitted rays and the rays reflected in the object space and, in the area in which the transmitted and reflected rays are guided coaxially, as a correction means to compensate for the negative refractive power of the spherical window a single, common correction lens is provided.

As an alternative to the solution mentioned above, at least one of the mirrors arranged in the beam paths, for example the oscillating mirror, can be designed with a concave curve to compensate for the negative refractive power of the spherical window.

The oscillating mirror is preferably mounted in a U-shaped bearing block so that it can pivot about the second axis of rotation, which is arranged on a turntable which can be rotated around the first axis of rotation by means of an electric motor, preferably a stepping motor, with an angle decoder for determining the exact alignment of the Oscillating mirror is provided around the first axis.

According to a further feature of the invention, the oscillating mirror is provided by a torque motor arranged on the bearing block with a limited angle of rotation about the second axis

AT 504 580 B1 can be swiveled, with a further angle decoder being provided if necessary to measure the angle of rotation actually reached by the oscillating mirror.

In order to meet the requirement for particular insensitivity to environmental influences, the spherical window closes the housing tightly, preferably gas-tight, the housing being made tight and correspondingly tight bushings or bushing plugs for electrical lines and possibly also for light guides for the transmission beams and / or for the reflected rays. The housing is preferably filled with an inert gas and has a heater.

The housing is advantageously under excess pressure with respect to the surrounding atmosphere, a sensor for monitoring the pressure preferably being provided.

The spherical window preferably has a wall thickness of at most 4 mm, preferably 1 to 2.5 mm, and is advantageously made of plastic, in particular of polymethyl methacrylate.

In order to avoid the scattering of laser light into the receiving channel, the spherical window is coated on its inside with an anti-reflective coating that is matched to the wavelength of the radiation emitted by the laser source, with the spherical window especially on its outside with a hard one , scratch-resistant covering, for example made of silicon oxide, is coated.

In order to avoid the formation of a disturbing film of water or dirt or of drops, the spherical window is coated on its outside with an anti-rain coating.

The evaluation device preferably only releases those distance values ​​for further processing that are significantly larger than the radius of the spherical window.

The effect of disruptive reflections can also be suppressed in that the spherical window is coated on its outside with an anti-rain coating in order to avoid the formation of a water and possibly a dirt film or drops.

In order to avoid interference from contamination of the window surface, the evaluation device can continuously determine the amplitudes of the reflected rays, which correspond to a distance approximately equal to the radius of the spherical window and serve as a measure for any contamination of the same, with a signal when an amplitude threshold value is exceeded is triggered.

When the new scanning device is used in aircraft, such as in manned or unmanned fixed-wing aircraft or helicopters, the axis of the field of view of the scanning device is aligned essentially in accordance with the direction of flight. The data from the evaluation device are processed together with data from the aircraft, such as position, attitude, speed, course, climbing or Sinking speed is fed to a processing unit, which calculates the risk of a collision with a stationary or moving object determined in the field of view of the scanning device and, if such a risk is detected, triggers a warning signal or initiates a corresponding evasive maneuver.

Further features of the invention emerge from the following description of an exemplary embodiment and with reference to the accompanying schematic drawings.

Fig. 1 shows in section through a scanning device according to the invention.

2 illustrates a block diagram of the associated electronics.

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According to FIG. 1, the housing 1 has a spherical, dome-like window 2, behind which an oscillating mirror 3 is mounted. This oscillating mirror 3 serves as a beam deflection means, the

Emits transmission rays 4 through window 2.

The window 2 can consist of glass or polymethyl methacrylate. Windows made of this plastic are preferably coated with a scratch-resistant protective layer. Both when using glass and PMMA, it is advantageous to coat the surface of the window 2 with an anti-reflective and / or an anti-rain layer. The anti-rain layer is intended to prevent soiling of the surface or the formation of drops on it. The strength “th” of the window 2 should be as small as possible in order to reduce the optical effect of the same. The wall thickness of the window 2 should not be more than 4 mm. In order to meet the strength requirements, a wall thickness in the range of 1 mm to 2.5 mm could be selected depending on the window size and the maximum pressure difference between the interior of the housing and the surrounding atmosphere. The window 2 has a flange 34 on its edge. An O-ring seal 33 is inserted between the housing 1 and the flange 34. The O-ring seal 33 is tensioned down by means of a ring 35 and tensioning screws 36. The housing base 37 is sealed with seals which are known per se and are not shown in FIG. 1. The feed-through plug 20 (FIG. 2), which is inherently gas-tight and is installed tightly in the housing base 37, is not shown in FIG. 1. In order to cope with the extreme environmental conditions during use in an aircraft, such as strongly changing temperature, humidity and pressure values, without the formation of condensation or a misted window surface, the gas-tight encapsulated housing is filled with nitrogen, which removes any moisture has been. The housing is under increased internal pressure, which is monitored by a pressure sensor, not shown. If the pressure drops below a specified level, a warning signal is triggered. Optionally, a heater (not shown) can also be provided in the housing 1.

In order to make the oscillating mirror 3 pivotable about 2 axes, a substantially U-shaped bearing block 5 is provided, which is fastened on a turntable 6, which turntable is mounted in a bearing 7 and defines a substantially vertical axis A1. The two vertical legs of the U-shaped bearing block 5 have a bearing which defines a substantially horizontal axis A2 which runs normal to the vertical axis A1. The fig. 1 clearly shows that the two axes intersect in the reflective surface P of the mirror 3. In order to minimize distortions and other imaging errors, it should be taken into account that the transparent window 2 acts as a lens and can cause such distortions and imaging errors both in the transmission and in the reception channel. The point of intersection of the axes A1, A2 advantageously coincides as precisely as possible with the center of curvature of the window 2. As a result, the transmission beams 4 can sweep over the entire area of ​​the window 2 without the optical effect of the window changing.

In order to ensure the exact coincidence of the intersection of the axes A1 and A2 and the surface P of the oscillating mirror 3 and the center of curvature of the spherical window 2, appropriate adjustment devices are provided (not shown).

According to a further advantageous embodiment of the invention, one of the two axes A1 and A2, according to FIG. 2, is placed in the mirror plane P of the mirror 3 in the interest of minimizing the imaging errors and distortions. In principle, this could be both the axis A1 and the axis A2, but this is preferably the horizontal axis A2.

In order to pivot the oscillating mirror 3 about the axis A1, a first motor M1 is provided in order to drive the turntable 6. This motor M1 is preferably a stepping motor, so that a corresponding accuracy of the movement of the turntable 6 is guaranteed. The motor M1 can drive the turntable 6 directly; by engaging a gear, in particular a toothed belt 10, increased structural flexibility is achieved. The rotation of the turntable 6 is monitored by an angle encoder 11 which, for example, has an angle encoder disk 11a

AT 504 580 B1 and an optical reading head 11b. However, any angle encoder construction can also be used, such as other optical, inductive or capacitive systems.

Since the oscillating mirror 3 only has to be swiveled by a limited angle about the axis A2, it is advantageous to drive it about this axis with a Limited Angle Torque Motor (LAT) M2, i.e. with a torque motor with a limited angle of rotation. However, other types of motors can also be used. An angle encoder similar to the encoder 11 can be used to monitor the rotation about the axis A2. In Fig. 1 the angle encoder 11 'is only indicated schematically as an angle encoder disk. By moving the oscillating mirror 3 around the two axes A1 and A2, the field of view of the system is scanned through the window 2, the mirror oscillating around the axis A1 at 2 Hz, for example, and around the axis A2 at 20 Hz, for example The speeds of the movements of the mirror 3 are the masses or Moments of inertia of the moving elements with respect to the axis A2 are significantly lower than those with respect to the axis A1.

A laser transmitter or a laser source 12 is provided in the housing 1. The transmission beams 4 emitted by the laser transmitter 12 are directed onto the oscillating mirror 3 by a corresponding optical system 13, a deflecting mirror 18 and an (optional) correction lens 21. In the latter area, the optical axis is identical to the axis of rotation A1 of the oscillating mirror 3, which guides the transmission beams 4 over the entire height and width of the window 2.

The transmitted beams 4 are directed onto an object outside the window 2 and are reflected on this object. The reflected beams 4 'enter the device through the window 2 and hit the oscillating mirror 3 and are deflected by this onto a beam splitter 14 which separates the transmitted beams 4 from the reflected beams 4'.

The transmission beams 4 and the reflected beams 4 'can be separated in various ways, for example with a partially mirrored beam splitter. But since this is a damping or If both the transmitted and the reflected signal are attenuated, it is advantageous to design the beam splitter 14 with a central bore 15, which allows the thin bundle of the transmitted rays 4 to pass through the bore 15, while the reflector 14 does Directs relatively larger bundles of reflected rays 4 'through the receiver optics 16 onto the receiver 17. The transmitted and reflected beams run coaxially and are deflected together by the oscillating mirror 3. Since the bundle of the reflected rays 4 'has an essentially circular cross-section, it is advantageous to make the oscillating mirror 3 elliptical, the major axis of the ellipse resulting from the diameter of the bundle of the reflected rays 4' and the maximum deflection angle of the oscillating mirror 3 . The laser transmitter 12, the transmission optics 13, the deflecting mirror 18 and the beam splitter 14, 15 are fixedly arranged in the housing. The same applies to the receiver 17 together with the receiving optics 16 and the correction lens 21.

As indicated in FIG. 2, the connection between the laser transmitter 12 and the receiver 17, on the one hand, and the corresponding electronic circuits, on the other hand, takes place via a schematically shown, tight plug-in connection 20 explained in more detail.

It has already been mentioned above that the shape of the window 2 as a spherical dome has the effect of a lens. Although the effect of the measures according to the invention is small, it can be expedient to also eliminate the residual errors. This correction or compensation can either be carried out in such a way that it acts both on the transmitted beams 4 and on the reflected beams 4 'or also separately for the two beams. In the first case, this consists in introducing the correction lens 21 (FIG. 1) into the beam path. Alternatively, the surface of the oscillating mirror 3 can be used for compensation

AT 504 580 B1 can be designed with a slightly concave curve.

As can be seen in FIG. 2, a driver stage 22, 22 'is assigned to one of the motors M1 and M2. These driver stages 22, 22 ′ are controlled by a scanner controller 23 in such a way that a synchronous movement of the mirror 3 results. In order to achieve such a synchronous movement, on the other hand, the scanner controller 23 is supplied with the output signals of the two angle encoders 11, 11 '. The scanner controller is fed by a power supply stage 24 '. An output signal from the scanner controller 23 is fed to a first interface 25, which communicates with the laser controller 26 in order to control the transmitter stage 12 ′, which comprises the laser transmitter 12 (FIG. 1). In another embodiment of the invention, the laser transmitter 12 sends out pulses at any time, while the oscillating mirror 3, on the other hand, assumes any position.

This communication of the laser controller 26 in connection with the scanner controller 23 enables the first interface 25 to generate information signals based on laser synchronous signals (laser clock), which define the start of a countdown that is used to determine the running time (time of Flight) of a laser pulse. These information signals also include the scanning angle data and trigger a command to the second interface 27, which in turn sends the necessary signal information to a microprocessor 28 in order to determine the distance and, if necessary, other information. The microprocessor 28 receives signals from the receiving stage 17 ′ after they have been digitized in a digitizing stage 29. The reception level is different from Fig. 1 not arranged within the housing 1, but in a separate electronic unit 31. The connection to the receiving stage 17 'is made via a fiber optic cable 32 and a corresponding optical plug connection in the plug 20. Since the determined pulse transit time (time of flight) the distance in the direction of the transmission Rays 4 (FIG. 1) and the angle encoders 11, 11 'deliver 2-dimensional information via the second interface, with regard to which the distance value in the direction of the transmission beams 4 results in the third dimension, the microprocessor 28 has all the necessary data to use To generate a distance or a 3-D image. The microprocessor can generate such an image and feed it to a display or monitor (not shown) via a third interface 30. Suitable software in the microprocessor 28 or in a separate stage, which is similar to CAD software known per se and which is suitable for generating a three-dimensional image, can be used directly or in a modified version to display the 3-D image as desired on the screen to turn.