Scanning apparatus

Summary.

Scanning device for an optical scanning system consisting of a

Housing (1) which comprises a laser source (12) fixed to the device, an oscillating mirror (3) for deflecting the laser beams (4) and a receiving device (17) for reflected laser radiation (4 '), further comprising a

Evaluation device (31) obtained from the transit time of the laser radiation

Distance values ​​are determined which are assigned to the respective deflection angles, furthermore with a window (2) made of a material transparent to the laser radiation, which closes the housing (1) and through which the transmitted laser beams (4) exit into the object space and are reflected in the object space Rays (4 *) preferably through the said

Window (2) can re-enter the device, the window (2) being spherical and the center of curvature coinciding with the intersection of the two axes of rotation (A1, A2) of the oscillating mirror (3) and correction means (21) in the beam path of the laser Rays (4,4 ') are provided, which the optical effect of the curved

Compensate window (2).

(Fig. 1)

Horn, on November 21, 2007 RIEGL

Laser Measurement Systems GmbH ···· ·· • · «

Pat. 32Θ ·· ···· ···

RIEGL

Laser Measurement Systems GmbH. HORN

Scan facility.

The invention relates to a scanning device for optical scanning

System consisting of a housing that encloses a device-fixed source for, esp. Pulse-shaped, laser radiation, further beam deflection means, esp. in the form of an oscillating mirror to deflect beams from the laser source and scan an object space like a grid, furthermore with a receiving device for laser radiation reflected in the object space and an evaluation device that determines distance values ​​from the transit time of the laser radiation that are assigned to the respective deflection angles.

Laser scanners, also called lidar or laser radar systems, have been developed for a wide range of applications and are used, for example, as systems for generating distance or 3 D images or 3 D models. In terrestrial use, such as when recording structures or terrain formations, a high spatial resolution and image quality are generally required, while the measurement duration, the maintenance-free system and also the resistance of the same to environmental influences are viewed as less important.

When using such systems on moving platforms, for example in

Aircraft, such as those in helicopters or fixed-wing aircraft, are completely different

Criteria in the foreground: The system must be insensitive to

Pat 320 ···· ·· ···· ·· • · ·· · · · · • · · · · ··· ··· ··· ·· ··· ·· · · · · ·· · ·· ·· ♦ ·· ···· ··· ·· extreme environmental influences, such as accelerations and vibrations, high or low temperatures and / or humidity, as well as rapid changes in these parameters. The measuring speed must be as high as possible in fast moving systems, but still a high one

Resolution and quality of the measurement or the image is required.

After all, a large field of view is of decisive importance in many application cases.

To achieve the highest possible scanning speed and

Insensitivity to accelerations, it is essential that the

Beam deflection means have the lowest possible masses or moments of inertia. This goal can be achieved by an appropriate arrangement or mounting of the beam deflection means, in particular the oscillating mirror. This storage includes first bearings for the rotatable mounting of the aforementioned

Beam scanning means about a first axis of rotation and second bearings for rotatable

Mounting of said beam deflection means about a second axis of rotation which is directed essentially normal to the first axis of rotation and defines an intersection point with the latter. To protect the system, a window made of a material transparent to the laser radiation is provided, which closes the housing and through which the transmitted laser beams exit into the object space and rays reflected in the object space can re-enter the device, preferably through said window.

The oa. According to the invention, objectives are achieved in that the window is designed spherically in a manner known per se, the

The center of curvature of the window essentially coincides with the mentioned intersection of the axes of rotation and correction means are provided in the beam path of the laser beams, which compensate for the optical effect of the curved window.

Pat. 320 • 4444 44 ···· ·· • · 4 4 4 4 · • 4 · 444 444 • 4 4 4 4 * •• 4 4 4 4 * ··· 44 444 · 444 44

In known systems it has been proposed to design the window in the form of a dome in order to obtain the largest possible field of view. This is particularly important with target acquisition systems such as those described in US Patent Nos. 4,039,246 and 4,024,392. 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 patent, 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 beam describe loops that result in a rosette-like scanning pattern. 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 on a gimbal and is tracked to a target once it has been captured so 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 and image quality 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 U.S. Patent 4,039,246. Here, too, a reflector telescope is used, which is gimbal-mounted. The beams of a stationary laser are directed through the bearings of the cardan frame into the center of the reflector telescope via a complex prism system and are emitted in the optical axis of the system. The laser radiation is used to illuminate the field of vision so that targets are also captured ·· ···· ··· ··

Pat. 320 ·· ·· · that do not emit radiation. The reflected laser beams 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. Also in this case it is

Reflecting telescope covered by a transparent dome.

Neither of the two systems has a laser distance meter, so that they are not suitable for recording data from which distance images or even

3-D models can be developed. With these target acquisition systems, the requirements for image quality and freedom from distortion are therefore comparatively low.

The housing of the scanning device according to the invention advantageously contains a device-fixed receiving device which emits laser beams from the laser source, deflects them by the beam deflection means, emits them through the window, reflects them from an object in the field of view and re-enters the housing through the spherically curved window receives, the reflected rays, preferably from the beam deflection means of the

Transmission beam, deflected and directed to the device-fixed receiving device.

Further advantages result if the transmission beams and the reflected laser beams directed onto the receiving device run coaxially, with between the beam deflection means and the laser source or the

Receiving device a known beam splitter is provided for the two beams.

The beam splitter preferably consists of a mirror with a central one

Opening through which one of the two rays, preferably the ···· ··· ··

Pat. 320

Transmit beam, while the other beam at the

Mirror surface is reflected.

In the case of a scanning device with an oscillating mirror as the beam deflection means, there are further advantages if the optical axis of the

Oscillating mirror directed transmission laser beam 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 transmission beam and the radiation reflected in the object space, through which, on the one hand, the laser radiation is focused on a medium distance of the object space and, on the other hand, the reflected radiation is concentrated on the receiving device, at least in one of these systems an optical element with positive refractive power, for example a

Corrective lens to compensate for the negative refractive power of the spherical

Window is provided and, if necessary, in the case of a coaxial transmit and receive beam, the compensation is carried out by a single, common correction lens, or at least one of the two optical systems is adjusted accordingly to compensate for the refractive power of the window.

As an alternative to the solution mentioned above, at least one of the mirrors arranged in the beam path, 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 as to be pivotable 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

Determination of the exact alignment of the oscillating mirror around the first axis is provided.

Pat. 320

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According to a further feature of the invention, the oscillating mirror is limited by a torque motor arranged on the bearing block

Rotation angle pivotable about the second axis, where appropriate for

Measurement of the angle of rotation actually reached by the oscillating mirror

Angle decoder is provided.

To meet the requirement for special insensitivity to

To correspond to environmental influences, the housing together with the spherical window encloses the scanning device tightly, preferably gas-tight, with correspondingly tight bushings or bushing plugs for the electrical lines and optionally also for light guides for the laser beams, the gas-tight housing optionally being filled with an inert gas, is preferably filled with nitrogen and preferably equipped with a heater.

Advantageously, the housing is under excess pressure in a manner known per se with respect to the surrounding atmosphere, a sensor for monitoring the pressure preferably being provided.

The spherical window preferably has a wall thickness of a maximum of 4 mm, preferably 1 to 2.5 mm, and is advantageously made of plastic, in particular of polymethyl methacrylate (PMMA or Plexiglas).

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.

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Pat. 320 ·· • · · • · • · • ·

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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 effect of disruptive reflections can also be suppressed in that the evaluation device only processes distance values ​​that are significantly larger than the radius of the spherical window.

In order to avoid disturbance due to soiling of the window surface, the evaluation device continuously determines the amplitudes of the radiation reflected on the spherical window as a measure of any contamination of the same and, if necessary, triggers a warning signal.

When using the new scanning device in aircraft, such as in manned or unmanned fixed-wing aircraft or helicopters, the axis of the

Field of view of the scanning device aligned essentially according to the direction of flight. The data from the evaluation device, together with data from the aircraft, such as position, attitude, speed, course, rate of climb or descent, are fed to a computer, which uses them to calculate the risk of a collision with a stationary or moving object determined in the field of view of the scanning device if such a risk is detected, a warning signal is triggered 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 a laser scanner according to the invention.

2 illustrates a block diagram of the associated electronics.

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Pat. 320

According to FIG. 1, the housing 1 has a spherical, dome-like window 2 behind which an oscillating mirror 3 is mounted. This mirror 3 serves as a beam scanner which emits a transmission beam 4 through the window 2. Instead of the oscillating mirror 3, other known beam deflection devices, such as rotating prisms or rotating mirrors, etc., can be used.

The window 2 can be made of glass, of polymethyl methacrylate (PMMA or Plexiglas). Windows made of this plastic are preferably coated with a scratch-resistant protective layer. Both when using glass and PMMA, it is advantageous to cover the surface of the window 2 with a

To coat 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. To the

To meet strength requirements, a 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 atmosphere. The window 2 has a flange 34 on its edge. Between the housing 1 and the flange

34 an O-ring seal 33 is inserted. By means of a ring 35 and

The O-ring seal 33 is tensioned down by clamping screws 36. The housing base 37 is sealed with seals which are known per se and are not shown in FIG. 1. In Fig. 1, the bushing plug 20 (Fig. 2), which is gas-tight in itself and tight in the

Housing bottom 37 is installed. 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 each

Moisture has been removed. The housing is under increased

Internal pressure that is monitored by a pressure sensor, not shown.

Pat. 320 ·· ···· ·· ···· ·· • · ·· ···· · • · · · · ··· ··· • · · ·· · · · ·· ··· · · · Φ ·· * ·· ·· ···· ··· ··

When the pressure drops below a specified level, a

Warning signal triggered. Optionally, a heater (not shown) can also be provided in the housing 1

In order to make the mirror 3 pivotable about 2 axes, an im

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 that is one in

Defines a substantially horizontal axis A2 that is normal to the vertical axis

Al runs. 1 clearly shows that the two axes intersect in the reflective surface P of the mirror 3. Slight deviations from an exact point of intersection are permissible as long as the resulting errors are acceptable for the specific application.

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 Al, A2 coincide as exactly as possible with the center of curvature of the window. As a result, the beam 4 can sweep over the entire surface of the window 2 without changing the optical effect of the window.

In order to ensure the exact coincidence of the intersection of the axes A1 and A2 as well as 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, in

Interest in minimizing the aberrations and distortions of one of the two axes A1 and A2, according to FIG. 2, in the mirror plane P of the φ φ φφφ φφφ • φφ φφφφ φφφ φφ

Pat. 320

Mirror 3 laid 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 mirror 3 about the axis A1, a first motor M1 is provided in order to drive the rotary control 6. This motor Ml is preferably a stepping motor, so that a corresponding accuracy of the movement of the turntable is guaranteed. The motor Ml 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 comprises, for example, an angle encoder disk 11a and an optical read head 11b. However, any angle encoder construction can also be used, such as other optical, inductive or capacitive systems.

Since the 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 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 Al

A laser transmitter 12 is provided in the housing 1. The laser light is through a corresponding optical system 13, a deflection mirror 18 and

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Pat. 320

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9 ·· 9 an (optional) correction lens 21 is directed onto the oscillating mirror 3. In the latter area, the optical axis is identical to the axis of rotation A1

Oscillating mirror 3, the laser beam 4 over the entire height and width of the

Window 2 leads.

The laser beam 4 is directed onto an object outside the window 2 and is reflected on this object, as is known per se. 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 which separates the transmitted beam 4 from the incident beam 4'.

The transmission beam and the incident beam can be separated in various ways, for example with a partially mirrored reflector 14

Transmission as well as the incoming signal, it is advantageous to use the

To design a reflector with a central bore 15, which allows the thin laser beam 4 to pass through the bore 15, while the reflector 14 directs the relatively larger bundle of reflected rays 4 'through the receiver optics 16 onto the receiver 17. The sender and the

Receiving beams run coaxially and are deflected together by the oscillating mirror. Since the receiving beam 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 beam 4' and the maximum deflection angle of the oscillating mirror 3. The transmitter 12, the transmission optics 13, the deflecting mirror 18 and the

Beam splitters 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 is made between the

Transmitter 12 and the receiver 17 on the one hand and the corresponding electronic circuits on the other hand via a schematically shown, tight plug connections 20. The individual circuits of the

Block diagrams are explained in more detail below together with FIG. 2.

Doi -2 *&gt; Λ

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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 transmission beam 4 and on the incident beam 4 'or also separately for the two

Rays. In the first case, this consists in introducing the correction lens 21 (FIG. 1) into the beam path. Alternatively, the surface of the mirror 3 can be designed to be slightly concave for compensation. A third way of correcting the optical effect of the window 2 is to use the

Use transmitter and / or receiver optics 13 or 16 correction elements. Another, simple compensation for the optical refractive effect of the window 2 consists in already taking this into account when calculating the curvatures and refractive indices of the elements of the optical systems 13 and / or 16. In practice, the window 2 acts as a concave lens which extends the focal length. This effect can be compensated for by using lenses with higher refractive indices in the optics 13 and 16, for example. However, if one takes into account that the lengthening of the focal length is small and is only 2 mm, for example, one can move and adjust the optics 13, 16 or the receiver diode 17 or the laser transmitter or transmitter 12 by a corresponding distance that achieve the necessary compensation. In Fig. 1 are essentially the optical elements of a preferred one

Embodiment shown.

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 from a scanner12

Pat. 320

Controller 23 activated 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 controlled by a

Power supply stage 24 'fed. An output signal of 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 mirror 3, on the other hand, any time

Takes 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 is used. 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 possibly 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 one

Electronics unit 31. The connection to the receiving stage 17 'is 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) gives the distance in the direction of the transmission beam 4 (FIG. 1) and the angle encoder 11, 11 'via the second interface a 2-dimensional Provide information regarding which the distance value in the direction of the laser beam 4 is the third

Dimension results, the microprocessor 28 has all the necessary data, ···· ·· ···· ··

Pat. 320 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 known per se

CAD software is similar and suitable for generating a three-dimensional image, can be used directly or in a modified version to rotate the 3-D image on the screen as required.

Horn, on November 21, 2007

RIEGL

Laser Measurement Systems GmbH

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Pat. 320

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RIEGL

Laser Measurement Systems GmbH. HORN