Shock mounting for a sensor

Abstract

Shock mounting (20) for a sensor (22) with the following features: - a spring element (24) for connecting the sensor (22) to a platform (26), wherein the spring element (24) consists predominantly of a superelastic alloy, wherein the superelastic alloy is composed such that the spring element (24) exhibits pseudoelastic behavior within a specified ambient temperature range in which the spring element (24) is used.

Description

[0001] The invention relates to shock mounting for sensors attached to a platform. In particular, the sensors are located underwater.

[0002] Shock mounting for sensors ensures that the sensors can withstand a shock, i.e., a short-term, large load, such as that caused by an explosion. Devices installed on and attached to submarines or other watercraft are subjected to a characteristic shock load in the event of underwater explosions caused by any type of effector. This shock load is characterized by the submarine experiencing acceleration followed by deceleration within a short period of time. This results in a displacement of the entire submarine, typically on the order of millimeters or a few centimeters.

[0003] The intended damaging effect of the effector is achieved through the high acceleration values ​​that would be introduced into rigidly mounted sensors via the foundation. These high accelerations would lead to high forces in the foundation and in the sensor itself, thus destroying it and potentially also surrounding equipment.

[0004] The aim is therefore to adequately decouple all types of equipment in a watercraft, and especially on submarines, from the structurally load-bearing hull, thus reducing the interface forces between the hull's foundation and the equipment. This can be described as extremely soft mounting (shock mounting) of a comparatively rigid body (then accordingly referred to as a "rigid body"). This measure reduces the accelerations within the equipment itself to the so-called residual shock value.

[0005] Soft mounting can traditionally be achieved using springs, which are described by their stiffness. Since a spring is a linear element, the force it exerts is directly proportional to its elongation. Therefore, a relationship can be established between the static deflection of the device under the influence of gravity and the shock displacement that needs to be compensated for. a0x0=arestxShock→arest=a0x0∗xShock That is, the deflection of the device is x o If the acceleration due to gravity is 5 mm, then the residual acceleration is a rest = 10g when the shock offset is x = 50mm.

[0006] If sensors are to achieve and maintain precise alignment / positioning, the aforementioned concept using only a conventional spring is unsuitable, as the positioning in this case depends on additional factors such as heeling (leading to static deflection of the object being positioned) or wave action (leading to dynamic positional displacement of the object being positioned). The target position can thus be deviated from by up to 100% of the static deflection. Since the static deflection is directly related to the tolerable residual shock, significant positional errors arise. Generally, positional errors at the mounting points of a device also lead to (equally undesirable) alignment errors of the device relative to the target orientation. When this disclosure refers to positional errors, it also includes alignment errors.

[0007] Up to now, a damper has been connected in parallel to the spring, which, depending on the design, either reduces the dynamic deflection (Newtonian damper, rather rare) or completely prevents movement at low acceleration amplitudes (non-Newtonian damper: relative movement is only allowed when a breakaway force is exceeded). This spring-damper element is classically implemented as a wire rope damper.

[0008] While the use of a non-Newtonian damper allows for good positional accuracy during normal operation, in the event of an impact, the intended position is disregarded (the spring damper fulfills its function and limits the device's acceleration to the permissible residual acceleration values), and after a few oscillation cycles, the system comes to rest in a different position than the original intended position. Therefore, this system is unsuitable for sensors and applications with high requirements for positional accuracy relative to the boat hull.

[0009] A solution currently found is, for example, the use of springs in combination with a locking mechanism with a defined detent position, which allows the intended position to be disengaged in the event of an explosion. During the recovery phase after the explosion, the detent position is repeatedly exceeded in each direction and finally reached again, meaning the mechanism "locks" back into place. The intended position can thus be restored. A disadvantage is the mechanically complex and therefore particularly vulnerable design, especially underwater, consisting of several components. This design can corrode (contact corrosion occurs with different materials), become fouled and stuck due to marine growth, or, for example, become blocked by mechanical relative movement during a shock, resulting in undefined lubrication properties. This is also known as cold welding.

[0010] However, a change in the sensor's position after deployment can lead to inaccurate measurements. For example, in a sonar system that uses an array of numerous underwater transducers as sensors, it is crucial to know the position of the transducers within the array. This is the only way to perform precise beamforming or to set up a synthetic aperture sonar (SAS).

[0011] The object of the present invention is therefore to create an improved concept for the shock mounting of sensors.

[0012] The problem is solved by the subject matter of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0013] Exemplary embodiments show a shock mounting for a sensor. The shock mounting is a spring element that mechanically connects the sensor to a platform. That is, the sensor is not directly attached to the platform, but indirectly via the spring element. The spring element consists predominantly of a superelastic alloy, the superelastic alloy being formulated such that the spring element exhibits superelastic or pseudoelastic behavior within a predetermined ambient temperature range in which it is used. The superelastic alloy may contain or consist of nitinol. Suitable spring elements include, for example, a bending beam, a leaf spring, or a torsion bar.

[0014] A superelastic alloy is characterized by a non-linear, but continuously monotonic, stiffness profile. Such superelastic alloys allow pseudoelastic strains through the modification of their crystalline structure, strains that are significantly greater than purely elastic strain without any change in the crystalline structure. A well-known alloy with this property is, for example, Nitinol. Nitinol can withstand pseudoelastic (and thus reversible and self-restoring) strains of up to 8% by modifying its lattice. This pseudoelastic effect is also referred to as superelasticity. Nitinol is the intermetallic phase of the nickel-titanium alloy with an ordered cubic crystal structure. Nitinol consists predominantly, particularly between 50% and 60%, preferably between 54% and 57%, of nickel; the remaining proportion is titanium, as well as very small amounts of any impurities.Impurities such as carbon, chromium, oxygen, or helium. Advantageously, the impurities together constitute a maximum of 1%, preferably a maximum of 0.5%.

[0015] The pseudoelastic behavior can be interpreted as meaning that a spring made of such a material, to a certain extent, replicates the aforementioned mechanical spring action, without containing any moving parts. When the linear elastic strain (approximately 1.5% strain for Nitinol) of the microstructure in its initial state is exceeded, a gradual transformation to the stretched microstructure begins, allowing for large deformations (up to 8% strain). If the external load, and thus the deformation, is reduced, the transformation back to the initial microstructure occurs, and no permanent positional deviation remains, unlike, for example, in a non-Newtonian wire rope damper. The initial stiffness (deformation per unit force) in the range of conventional strain without microstructure transformation is high. The stiffness in the microstructure transformation range is very low.

[0016] The optimal design of a spring made of superelastic material would therefore be such that, during normal operation, the material does not transform into its elongated configuration (strains remain below 1.5%). In other words, the spring element is designed so that its elongation during regular operation remains below the threshold of pseudoelasticity. For Nitinol as a superelastic alloy, the threshold of pseudoelasticity is approximately 1.5%. In the event of a shock, the microstructure transformation occurs. The stiffness is low (the system is in the "unlatched" position), and consequently, the resulting residual shock values ​​are also low. Due to this microstructure transformation, the superelastic alloy can tolerate large mechanical strains.

[0017] To utilize the described effect, for example with Nitinol, it is advantageous in this case to set the so-called austenite finish (AF) temperature of the selected superelastic (Nitinol) alloy sufficiently below the intended operating temperature. Otherwise, the return to its original position from the deflected state will only occur once the AF temperature is exceeded. This relationship is commonly referred to as the shape memory effect, but it is not used for the described shock storage.

[0018] Furthermore, a watercraft, in particular a submarine, comprising the shock mounting according to one of the preceding claims is disclosed, wherein the spring element connects the watercraft to the sensor.

[0019] Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. These show: Fig. 1: a schematic stress-strain curve of a spring element made of a superelastic alloy; Fig. 2: An exemplary schematic representation of a shock mounting for a sensor.

[0020] Before exemplary embodiments of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0021] Fig. Figure 1 shows a schematic representation of the stress-strain relationship of a spring element made of a superelastic alloy. Stress denotes the internal stress in the spring element, which, under tension, scales approximately proportionally with the external force. Strain describes the corresponding relative change in length of the deformed spring element. Furthermore, the limits of linear strain without microstructural transformation (40, 1.5% chosen as an example) and the strained microstructure (42, approximately 8% limit for Nitinol) are shown. It is noticeable that, even after further deformation, the internal stress of the spring element increases only slightly when the linear strain is exceeded. This can be described as a strongly degressive stiffness of the material. It is also evident that the recovery occurs at a lower stress level than the initial deformation, which corresponds to energy dissipation.This results in a nonlinear, yet reversible, stress-strain relationship. The observed energy dissipation causes a mechanically oscillating system, primarily containing such a spring as its elastic element, to exhibit a highly damped oscillation and settle within a few cycles. This relationship is of great benefit in the aforementioned application.

[0022] Fig.Figure 2 shows a schematic side view of a shock mount 20 for a sensor 22. The shock mount 20 includes a spring element 24 for connecting the sensor 22 to a platform 26, in particular a watercraft such as an underwater vehicle, especially a submarine. The spring element 24 is shown by way of example as a bending beam. The spring element 24 consists predominantly or exclusively of a superelastic alloy. The superelastic alloy is composed such that the spring element 24 exhibits pseudoelastic behavior within a specified ambient temperature range in which the spring element is used.

[0023] The disclosed (water) sound transducers are designed for underwater use, particularly in the sea. The transducers can convert underwater sound into an electrical signal (e.g., voltage or current) corresponding to the sound pressure, the underwater sound signal. Furthermore, it is possible for the transducers to convert an applied electrical voltage into underwater sound. The transducers can therefore be used as underwater sound receivers and / or underwater sound transmitters. The transducer material can be a piezoelectric material, for example, a piezoceramic. The transducers can be used for (active and / or passive) sonar (sound navigation and ranging). The transducers are preferably not suitable for, or are not used for, medical applications.

[0024] Besides its application for underwater transducers, shock mounting can also be used for other devices, such as those mounted above the waterline of normal surface ships or submarines, or on the conning tower of a submarine. Radio antennas and cameras can also benefit from such mounting, as precise alignment is crucial for them, unlike, for example, a signal horn or a flagpole.

[0025] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device.

[0026] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments. Reference symbol list: 20 Shock positioning 22 Sensor 24 spring element 26 platform 40 Limit of linear elongation 42 Limit of the stretched microstructure

Claims

[1] Shock mounting (20) for a sensor (22) with the following features: - a spring element (24) for connecting the sensor (22) to a platform (26), wherein the spring element (24) consists predominantly of a superelastic alloy, wherein the superelastic alloy is composed such that the spring element (24) exhibits pseudoelastic behavior within a specified ambient temperature range in which the spring element (24) is used. [2] Shock mounting (20) according to claim 1, wherein the superelastic alloy comprises a nickel-titanium alloy. [3] Shock mounting (20) according to one of the preceding claims, wherein the spring element (24) is designed such that the elongation of the spring element (24) during regular operation remains below the limit of pseudoelasticity, in particular below a maximum elongation of approximately 1.5% when using Nitinol as a superelastic alloy. [4] Shock mounting (20) according to one of the preceding claims, wherein the spring element (24) is designed such that the elongation of the spring element (24) remains below 8% in the event of a shock. [5] Shock bearing (20) according to one of the preceding claims, wherein the austenite finish temperature of the superelastic alloy is below the intended operating temperature. [6] Watercraft (26) comprising the shock mounting (20) according to one of the preceding claims, wherein the spring element (24) connects the watercraft (26) to the sensor (22).

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