DE102014000987B4 - Mounting system for opto-electronic instruments - Google Patents

Abstract

Mounting system for an opto-electronic instrument in a carrier vehicle, wherein the opto-electronic instrument (1, 2) is connected to a rigid module (3) with an inertial navigation system (23) for detecting at least the orientation of the instrument (1, 2) in space, but optionally also for determining the position of the same in a coordinate system, which inertial navigation system (23) is able to resolve periodic movements up to a defined limit frequency, wherein the corresponding data can be linked to the measured values of the opto-electronic instrument (1, 2), for example those of a laser rangefinder or a laser scanner, to form data sets and the module (3) formed from the instrument (1, 2) and the navigation system is connected to the structure of the carrier vehicle via spring/damping elements (24, 26, 29), characterized in that the spring/damping elements (24, 26, 29) together with the mass of the module (3) form a mechanical low-pass filter, which essentially absorbs vibrations of the carrier vehicle which are above the limit frequency of the inertial navigation system (23) and thus stabilizes the module (3) in space, while the module (3) follows lower-frequency movements of the carrier vehicle and provides the data of the respectively changed spatial orientation of the module (3) for linking with the measured values of the instrument (1, 2).

Description

The invention relates to a mounting system for an opto-electronic instrument in a carrier vehicle, wherein the opto-electronic instrument is connected to an inertial navigation system for detecting at least the orientation of the instrument in space, but optionally also for determining its position in a coordinate system to form a rigid module, which inertial navigation system is capable of resolving periodic movements up to a defined limit frequency, wherein the corresponding data can be linked to the measured values of the opto-electronic instrument, for example those of a laser rangefinder or a laser scanner, to form data sets, and the module formed from the instrument and the navigation system is connected to the structure of the carrier vehicle via spring/damping elements.

The carrier vehicles can be land or rail vehicles, watercraft or aircraft such as fixed-wing aircraft or helicopters, on which measurements, photographic recordings or the like are made while they are moving. What all of these carrier vehicles have in common is that they can move around one or more axes during these measurements, recordings or the like. In order to ensure appropriate assignment to the space to be measured or recorded, it is known to combine the optoelectronic instrument with an inertial navigation system (IMU) and to connect it to it as rigidly as possible so that the orientation of the optical axis of the instrument in space can be recorded as data for each measurement, recording or the like. As a rule, such an instrument is also combined with a navigation system, with which its respective position in a higher-level, for example global, coordinate system is determined. Wheel sensors can also be used as such navigation systems for rail and land vehicles, but satellite-based systems (GNNS, e.g. GPS) have proven to be the most effective for all of these applications. These are often combined with an inertial navigation system (IMU) to form an integrated IMU/GNNS system. This provides the exact coordinates for each measuring point in a higher-level coordinate system.

During use, the opto-electronic instruments are not only exposed to the intended movements of the carrier vehicle, but also to shocks, jolts, vibrations, etc. that are transmitted from the structure of the carrier vehicle to the instruments. Such instruments usually contain components that are sensitive to shocks and vibrations and must therefore be connected to the structure of the carrier vehicle with spring/damping elements to protect them.

According to the invention, the spring/damping elements, together with the mass of the module, form a mechanical low-pass filter in a manner known per se, which essentially absorbs vibrations of the carrier vehicle that are above the cut-off frequency of the inertial navigation system and thus stabilizes the module in space, while the module follows lower-frequency movements of the carrier vehicle and provides the data of the respectively changed spatial orientation of the module for linking with the measured values of the instrument.

Mechanical low-pass filters are, as mentioned above, already known and are described, for example, in US Patent No. 6,688, 174-B1 (Pierre Gallon et.al.) and in the German disclosure documents EN 10 2010 062 017 A1 (Robert Bosch GmbH) and DE 2 353 101 A (Fraser-Volpe Corp.). The first publication relates to the vibration-damped suspension of a laser gyro system, the second to the shock and vibration damping of micro-projectors, the third to the vibration-damped suspension of a prism system of a telescope. The mechanical low-pass filters are described in these applications in a completely different context and therefore could not provide any inspiration for the present invention. An alternative active stabilization of a carrier system by means of a device with driven tilt axes is known from the German laid-open specification DE 20 2007 005 801 U1 (Somag AG).

In some installations of optoelectronic instruments, these are not mounted directly on the carrier vehicle, but on a stabilized platform arranged on the carrier vehicle. In such a case, according to the invention, at least the module formed from the instrument and the navigation system is mounted on the stabilized platform with the interposition of spring/damping elements, whereby the spring/damping elements together with the mass of the module form a mechanical low-pass filter known per se, which essentially absorbs vibrations of the stabilized platform that are above the cut-off frequency of the inertial navigation system, but transmits low-frequency vibrations to the module.

According to a further feature of the invention, the mounting system comprises a two-stage mechanical decoupling, whereby on the one hand the rigid module is mechanically decoupled from the support structure by means of damping elements in order not to transfer deformations of the same to the module and, on the other hand, the spring/damping elements which, together with the mass of the module and its support structure, form a known mechanical low-pass filter which essentially absorbs vibrations of the carrier vehicle which are above the cut-off frequency, but transfers low-frequency vibrations to the module.

For the most commonly used inertial navigation systems (IMU) and carrier vehicle/instrument configurations, the cutoff frequency is preferably about 25 Hz.

According to a further feature of the invention, the module is suspended or braced so as to be movable in all three coordinate directions.

Preferably, the spring and damping elements at the individual points of application on the module are designed, taking into account their position in relation to the center of gravity of the module, in such a way that both longitudinal and torsional vibrations or deformations can be dampened as far as possible.

According to the invention, the spring/damping elements are designed and positioned on the module in such a way that, relative to the center of gravity of the module, the sum of the moments of those forces that can be transferred to the module is essentially zero.

In applications where the measuring distance is significantly greater than the dimensions of the instrument module, displacements of the module in longitudinal directions have only a very small effect on the measurement results, while the system reacts extremely sensitively to rotational movements of the module. In order to avoid the excitation of such rotational movements or torsional vibrations as far as possible, the spring and damping elements at the individual points of application on the module are designed according to the invention, taking into account their position in relation to the center of gravity of the module, so that torsional vibrations can be dampened as far as possible.

Preferably, the spring/damping elements are designed and positioned on the module in such a way that, relative to the center of gravity of the module, the sum of the moments of those force components that can be transferred to the module and are normal to the optical axis of the optoelectronic instrument is essentially zero. This measure allows longitudinal movements in the direction of the optical axis of the instrument and normal to it, but the excitation of torsional vibrations is suppressed.

In order to avoid having to intervene in the module when installing additional devices such as digital photo or video cameras or navigation devices or their sensors, connectors are provided on the outside of the module for rigidly attaching these additional devices. Since the installation of such additional devices changes the total mass of the module, which affects the tuning of the mechanical low-pass filter formed from the spring/mass system, it is advantageous to initially provide compensation masses on the connectors on the outside of the module, which are then reduced accordingly when additional devices are installed.

Further features of the invention will become apparent from the following description of some embodiments and with reference to the drawing. 1 As an example of an opto-electronic instrument, a laser scanner for airborne applications is shown, partly in section. The 2 shows a ready-to-install instrument in axionometric representation, the 3 and 4 illustrate two different mounting systems for two essentially similar instrument modules.

The Indian 1 The laser scanner for "airborne" applications shown as an example of an optoelectronic instrument essentially comprises a laser rangefinder 1 based on the pulse transit time method and a downstream beam deflection device 2. In the example shown, the beam deflection device comprises a glass wedge prism 11 which rotates at high speed about the optical axis 7 of the laser rangefinder 1.

The instrument is built on a mounting plate 31, which is connected to a plate 33 by four columns 32 and forms a stable and rigid frame with these. A laser source 4 is arranged within this frame 31-33, which reflects a laser beam into the optical axis 7 of the instrument via a mirror system 5, 6. Instead of the mirror system 5, 6, a flexible glass fiber light guide can also be used.

A cylinder 8 is provided under the laser rangefinder 1, which is mounted in bearings 9 so that it can rotate around the optical axis 7 of the laser rangefinder 1 and is driven by an electric motor 10 at high speed. The glass wedge prism 11, through which the transmitted laser beams are deflected, is mounted in this cylinder. When the wedge prism 11 rotates, these laser beams 12 form a beam cone in their entirety, which scans a flat area lying under the laser scanner in a circular arc. The laser beams are reflected by the area and the area present on it. objects, vegetation, etc. A small part of this radiation reaches the laser scanner again, is aligned parallel to the optical axis 7 by the wedge prism 11 and is imaged by the receiver optics 14 onto the light-sensitive cell of the receiver 15. In the receiver 15, the incoming optical pulses are converted into electrical signals. The electrical pulses are possibly digitized in an evaluation device (not shown), which can also be arranged externally and connected to the laser scanner with a cable. The distance from the laser scanner is determined from the time period from the transmission of the laser pulses to the arrival of the received pulses. An angle decoder (not shown) is attached to the rotating cylinder 8 or the drive motor 10. The data from this decoder determines the respective direction of the laser beam 12 in an instrument-related coordinate system. Digital photo cameras 17 and/or video cameras 18 can be arranged on the stationary instrument base 16. These cameras and the laser scanner are protected against environmental influences by an exit window 19. The distance data supplied by the evaluation device are linked to the instrument-related coordinates derived from the angle decoder and stored together with the data from any digital cameras 17, 18 as a data set.

In order to be able to transform the instrument-related data into a higher-level, for example global, coordinate system, it is necessary on the one hand to determine the orientation of the instrument 1, 2 in space and to link this with data derived from a navigation system. An inertial navigation system (IMU), 23 is used to determine the position of the instrument in space. The navigation system used to determine the position is usually based on a satellite-based system (GNNS, e.g. GPS). When arranging this navigation system 23 on the instrument 1, 2, it is of crucial importance that the inertial navigation unit (IMU), 23 is completely rigidly connected to the instrument, in this case to the laser scanner 1, 2, to form a module 3. This module 3 comprises a platform 20 on which the instrument base 16 with the rotating wedge prism 11 is arranged on the one hand, and on the other hand the platform 20 carries the receiver optics 14 with the receiver unit 15, as well as four columns 21 which are welded to a plate 22. The inertial navigation unit (IMU) 23 is rigidly attached to this plate 22.

The laser source 4 is also connected to this frame 21, 22. The module 3, which consists of the laser scanner 1, 2 and the inertial navigation unit IMU, 23, is connected to the mounting plate 31 and the plate 33 with damping elements 24. These elements 24 primarily serve to prevent deformations of the external structure 31-33 of the instrument, which can result, for example, from being transferred to the module 3.

The opto-electronic instruments installed in carrier vehicles, for example in fixed-wing aircraft and helicopters, are exposed to vibrations and a wide range of oscillations and shocks caused by drive motors and also external influences. The same applies to water, land and rail vehicles. If the instruments are exposed to these forces, many of these opto-electronic instruments react relatively insensitively to displacements in the direction of the optical axis 7 and normal to it. However, it is critical if these forces excite torsional vibrations of the instruments about axes that run normal to the optical axis. As a rule, the measuring distance is orders of magnitude larger than the instrument, so that even with small torsional vibration amplitudes, significant displacements of the measuring points result. In the case of low-frequency vibrations, this can be compensated for by the inertial navigation system (IMU), 23 measuring the changes in the orientation of the instrument and assigning modified instrument-related coordinates to the measured values. However, unacceptable measurement errors occur with higher frequency vibrations that the IMU cannot follow. This problem occurs not only with laser scanners, but also with digital photo and video cameras and many other instruments with a wide variety of opto-electronic sensors. According to one feature of the invention, this problem can be solved by selecting the mounting points of the instrument in the carrier vehicle in such a way that the forces introduced into the system are directed towards the instrument's center of gravity, or the moments of these forces related to the instrument's center of gravity compensate each other.

In the 2 Such an arrangement is shown. The laser scanner 1, 2 is opposite the one in 1 shown, particularly with regard to the arrangement of the damping elements 24 and their support on the outer frame and the instrument module 3. A further plate 25 is provided under the mounting plate 31 of the laser scanner 1, 2, to which four so-called wire rope springs 26 are attached.

The other side of these springs 26 is connected to the platform 27, which can be attached to the structure of the carrier vehicle with screws (not shown). The springs are connected to the Mass of the instrument module 3 is adjusted so that together with it they form a mechanical low-pass filter. The cut-off frequency is selected so that only vibrations that can still be measured by the IMU 23 can reach the instrument module 3. The plate 25 is positioned on the instrument so that the plane of its underside, via which forces excited by the carrier vehicle are introduced into the system, contains the center of gravity 28 of the instrument including the plate 25. This largely suppresses torsional vibrations of the instrument about axes that run normal to the optical axis.

The spring arrangement 25 to 27 represents an integral part of the instrument, which is specially adapted to the system and is installed or removed from the carrier vehicle together with it. In the example shown, a two-stage mechanical decoupling is implemented. A first, 24, which prevents the transmission of deformations to the module and a second, 25 to 27, which minimizes the effects of vibrations, oscillations and forces introduced into the system by the carrier vehicle.

In the 3 Another example of the assembly of an opto-electronic instrument is shown, which is intended for use in a carrier vehicle, whereby the rigid frame structure attached to the carrier vehicle has been omitted for reasons of better clarity. The module 3, consisting of laser scanner 1, 2 and IMU 23, is supported on the one hand by the plate 31 and three spring/damping elements 29 and with the IMU housing via a single, similar spring/damping element 29 on this frame structure. Oscillations, vibrations, etc. of the carrier vehicle act via the frame structure on the three spring/damping elements 29 attached to the mounting plate 31, as well as the individual element 29 attached to the IMU housing. In this example, the center of gravity 28 of the module 3 is on the instrument axis 7 at a distance a from this individual element 29. The distance of the center of gravity 28 from the three elements 29 on the mounting plate 31 is _b, where a is equal to 3xb. This balances out the moments of the introduced force components directed normal to the optical axis 7 and prevents the excitation of a torsional vibration of the module.

The 4 shows an alternative arrangement of the spring / damping elements 29. These are arranged in the corners of a virtual cube and aligned with the center of the cube. The elements 29 are supported on the other side analogously to 3 on a frame construction (not shown) connected to the structure of the carrier vehicle. The center of the virtual cube essentially coincides with the center of gravity 28 of module 3, so that no torsional vibrations of module 3 are excited by the forces introduced. The elements 29 are coordinated as a whole with the mass of module 3 and represent a spring/mass system that acts as a mechanical low-pass filter and only transmits forces in a frequency range to the module that excite movements of module 3 that can be measured by the IMU 23.

Instead of arranging the spring/damping elements 29 at the corner points of a virtual cube, they can also be arranged at the corner points of other regular bodies, for example at the corner points of a regular virtual tetrahedron.

In contrast to the 2 shown instrument with a two-stage mechanical decoupling, the ones in the 3 and 4 The systems shown have a single-stage mechanical decoupling.

Claims (12)

Mounting system for an opto-electronic instrument in a carrier vehicle, wherein the opto-electronic instrument (1, 2) is connected to a rigid module (3) with an inertial navigation system (23) for detecting at least the orientation of the instrument (1, 2) in space, but optionally also for determining the position of the same in a coordinate system, which inertial navigation system (23) is capable of resolving periodic movements up to a defined limit frequency, wherein the corresponding data can be linked to the measured values of the opto-electronic instrument (1, 2), for example those of a laser rangefinder or a laser scanner, to form data sets, and the module (3) formed from the instrument (1, 2) and the navigation system is connected to the structure of the carrier vehicle via spring/damping elements (24, 26, 29), characterized in that the spring/damping elements (24, 26, 29) together with the mass of the module (3) form a mechanical low-pass filter, which essentially absorbs vibrations of the carrier vehicle which are above the limit frequency of the inertial navigation system (23) and thus stabilizes the module (3) in space, while the module (3) follows lower-frequency movements of the carrier vehicle and provides the data of the respectively changed spatial orientation of the module (3) for linking with the measured values of the instrument (1, 2). Mounting system for an opto-electronic instrument according to Patent claim 1 , with a stabilized platform (20) provided on the carrier vehicle, characterized in that at least the module (3) formed from the instrument (1, 2) and the navigation system (23) is mounted on the stabilized platform (20) with the interposition of spring/damping elements (24, 26, 29), wherein the spring/damping elements (24, 26, 29) together with the mass of the module (3) form a mechanical low-pass filter which essentially absorbs vibrations of the stabilized platform (20) which are above the cut-off frequency of the inertial navigation system (23), but transmits low-frequency vibrations to the module (3). Mounting system for an opto-electronic instrument in a carrier vehicle according to Claim 1 or 2 , characterized in that the mounting system comprises a two-stage mechanical decoupling, wherein on the one hand the rigid module (3) is mechanically decoupled from the support structure by means of first damping elements (24) in order not to transmit deformations of the same to the module (3), and on the other hand second spring/damping elements (26) together with the mass of the module (3) and its support structure form a mechanical low-pass filter which essentially absorbs vibrations of the carrier vehicle which are above the cut-off frequency, but transmits low-frequency vibrations to the module (3). Mounting system for an opto-electronic instrument according to one of the Patent claims 1 until 3 , characterized in that the cutoff frequency is approximately 25 Hz. Mounting system for an opto-electronic instrument according to one of the Patent claims 1 until 4 , characterized in that the module (3) is suspended or braced so as to be movable in all three coordinate directions. Mounting system for an opto-electronic instrument according to one of the Patent claims 1 until 5 , characterized in that the spring and damping elements (24, 26, 29) at the individual points of application on the module (3) are designed, taking into account their position with respect to the center of gravity (28) of the module (3), in such a way that both longitudinal and torsional vibrations or deformations can be dampened as far as possible. Mounting system for an opto-electronic instrument according to Patent claim 6 , characterized in that the spring / damping elements (24, 26, 29) are designed and positioned on the module (3) such that, relative to the center of gravity (28) of the module (3), the sum of the moments of those forces which can be transferred to the module (3) is substantially zero. Mounting system for an opto-electronic instrument according to one of the Patent claims 1 until 5 , characterized in that the spring and damping elements (24, 26,29) at the individual points of application on the module (3) are designed, taking into account their position with respect to the center of gravity (28) of the module (3), so that torsional vibrations can be dampened as far as possible. Mounting system for an opto-electronic instrument according to Patent claim 8 , characterized in that the spring / damping elements (24, 26, 27) are designed and positioned on the module (3) such that, relative to the center of gravity (28) of the module (3), the sum of the moments of those force components which can be transferred to the module (3) and which run normal to the optical axis (7) of the opto-electronic instrument (1, 2) is essentially zero. Mounting system for an optoelectronic instrument according to one of the preceding claims, characterized in that connecting pieces for the rigid fastening of video (18) and/or photo cameras (17) and/or navigation systems (23) or their sensors and, if appropriate, compensation masses are provided on the module (3). Opto-electronic instrument with a mounting system according to one of the preceding claims, characterized in that the instrument (1, 2) comprises a platform (27) or the like which can be rigidly connected to the structure of the carrier vehicle and that spring/damping elements (26) are provided between the module (3) and the platform (27). Opto-electronic instrument according to Patent claim 11 , characterized in that the housing of the module (3) has a flange (25) or the like and spring / damping elements (26) are arranged between this flange (25) and the platform (27) and the center of gravity (28) of the module (3) lies substantially in the plane of the flange (25).

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