WO2023033768A1

WO2023033768A1 - Inertial measurement unit comprising a body with a lattice structure and a sensor block

Info

Publication number: WO2023033768A1
Application number: PCT/TR2022/050915
Authority: WO
Inventors: Caner Gençoğlu; Hasan Baran ÖZMEN
Original assignee: Roketsan Roket Sanayi̇i̇ Ti̇caret A.Ş.
Priority date: 2021-09-03
Filing date: 2022-08-26
Publication date: 2023-03-09

Abstract

The invention relates to inertial sensor technologies. In particular, the invention relates to a system comprising mechanical solutions for a low-mass inertial sensor unit that is resistant to environmental influences such as vibration and thermal shock.

Description

INERTIAL MEASUREMENT UNIT COMPRISING A BODY WITH A LATTICE STRUCTURE AND A SENSOR BLOCK

Technical field of the invention:

State of the Art:

Inertial measurement systems are units that measure accelerations and spins in six directions of freedom of movement and calculate instantaneous location information using these data. In these systems, an accelerometer is used to detect acceleration in three translational directions, and a tachometer is used to detect angular acceleration in three spin directions. These sensors are mounted on a mechanical structure called the sensor block. The resulting complete set powers the sensors, collects the acceleration data as the output of the sensors, is integrated in an outer body with the appropriate geometry, together with the electronic cards that will process them and turn them into a meaningful inertial measurement system output. Vibration and temperature are the environmental effects that affect the measurement accuracy performance of inertial measurement units most. Thermally insulating the sensors inside from the outside world is one of the most important requirements of the inertial measurement unit outer body. In order for the vibration performance of the inertial measurement system to be high, it is essential that the natural frequencies of the sensor block to which the sensors used are mounted are high. While the system performance needs to be protected from these environmental effects, the mass increase must not exceed certain limits. With the point that additive manufacturing methods have reached compared to the past, the way to obtain designs that can provide optimum mechanical properties in different sections instead of conventional mechanical structures is opened.

Contrary to traditional materials, materials created with lattice structure provide the necessary strength for the design, while providing serious weight advantages. Today, especially with the development and spread of the capabilities of 3D printers, the use of lattice materials has increased. It is possible to obtain materials according to the desired weight stiffness ratio with different micro-mechanical structure designs. Since these materials contain cavities, they can also be designed according to thermal insulation requirements. For this reason, in cases where low mass, thermal insulation and high stiffness are required, the use of parts containing lattice structure provides a great advantage.

In the application no "US 2005/0042416 A1” in the state of the art, the thermal advantages offered by the panels in hexagonal geometry and lattice structure are mentioned. In said application, the hexagonal lattice structure is referred to as "honeycomb lattice structure". Instead of a single layer lattice structure, the use of more than one layer with different layouts and the comparison of thermal properties for these different options are shared.

In the application no "US 2017/0023084 A1” in the state of the art, it is mentioned that the desired special damping properties can be achieved with parts with a lattice structure. It has been evaluated that a three-dimensional lattice structure can be obtained by knitting wire-like parts in different materials, and in this way, parts with mechanical properties that cannot be obtained with parts produced with materials readily available in nature.

The application no "W02017070929A1” in the state of the art is about an inertial measurement unit that can be used in an automobile, ship or unmanned aerial vehicle, and more specifically, a mobile device to which the inertial measurement unit is applied. In the mentioned system, there are elements such as a sensor, a heat- conducting and thermally insulating body, many heating sources, and inertial measurement units. The thermally insulating body may be made of a material such as aluminium, magnesium, silver or the like. There is also a circuit board assembly comprising an extension portion from one side of the body portion. The heating source is distributed over two side walls each opposite to each of the thermally insulating bodies and there are recesses to accommodate multiple sensors. There is also a thermally conductive element on the side wall of the main body. However, in the mentioned embodiment, there is no mention of an improvement in reducing the building mass. The application no “CN109827570A” in the state of the art is related to the inertial measurement unit, and more specifically, to the use of microelectromechanical components (MEMS) as inertial sensors. The aim of the invention is to provide a structure that increases resistance to temperature changes, allows higher inertial measurement accuracy and reduces calibration costs significantly. In said design, there is a fin structure on the outside of the outer casing, and this fin structure increases the efficiency of the heat exchange between the temperature control element and the outer part. Acceleration sensor or angular velocity sensor can be used. For example, in flight control or automatic driving, three acceleration sensors, three angular velocity sensors and the like are generally used. In the holes in the structure of the sub layer having hexagonal geometry, the top surface, bottom surface and inner wall of the hexagonal geometry are covered with a copper coating to increase the thermal conductivity of the sub layer. However, there is no information that the outer body can be made of a hexagonal lattice and the sensor block can be made of a triangular prismshaped lattice structure.

In the current system, the use of lattice structure to reduce the effects of environmental factors such as vibration and temperature on the lower parts of inertial measurement units has not been evaluated.

As a result, due to the negativities described above and the inadequacy of the existing solutions on the subject, it was necessary to make a development in the relevant technical field.

Brief Description and Aims of the Invention

The most important aim of the invention is to provide an inertial measurement unit in which the environmental effects (temperature change, temperature change slope, etc.) that will impair performance and the total mass are reduced by using a lattice structure having holes.

Another aim of the invention is to provide an inertial measurement unit in which thermal insulation is provided by using a lattice structure with hexagonal geometry in which more than one hollow hexagonal geometry surfaces in the outer body are formed in such a way that each edge is adjacent to the edge of the other. For this purpose, a lattice structure with hexagonal geometry is used, which provides thermal insulation due to the large space it has.

Another aim of the invention is to provide a system in which a triangular prism shaped lattice structure formed in a way each side of surfaces of more than one hollow triangular geometry being adjacent to one another is used to achieve low mass and high stiffness in the sensor block.

Another aim of the invention is to provide an inertial measurement unit in which thermal insulation is provided by using a hexagonal (honeycomb) lattice wall with high thermal insulation between the electronic boards and the sensor block so that the sensors in the sensor block are not affected by the temperature change and temperature change slope.

FIGURE 1 ; is the drawing that gives the lattice structure with hexagonal geometry in the outer body of the system that is the subject of the invention.

FIGURE-2; is the drawing that gives the triangular prism lattice structure in the sensor block in the system that is the subject of the invention.

FIGURE-3; is the drawing that gives the design of the body and sensor block containing the lattice structure for the inertial measurement unit that is the subject of the invention.

FIGURE-4; is the drawing that gives the view of the lattice structure with hexagonal geometry in the inertial measurement unit that is the subject of the invention.

FIGURE-5; is the drawing that gives the view of the triangular prism lattice structure in the inertial measurement unit that is the subject of the invention.

Definition of Elements/Parts Composing the Invention

To better explain the design of the body and sensor block containing the lattice structure for the inertial measurement unit developed with the present invention, the parts and elements in the figures are numbered, and the equivalent of each number is given below:

1. Lattice structure with hexagonal geometry

2. Triangular prism lattice structure

3. Outer body

4. Sensor block

5. Mounting feet

6. Wall

7. Body Cavity

8. Panel

Detailed Description of the Invention

The invention relates to inertial sensor technologies. In particular, the invention relates to a system comprising mechanical design solutions for a low-mass inertial sensor unit that is resistant to environmental influences such as vibration and thermal shock.

In the system developed with the invention, there is an outer body (3) and a sensor block (4) in an inertial measurement unit, in which the environmental effects that will impair performance and the total mass are minimized.

With the invention, a sensor block (4) with high performance for vibration is designed in which thermal insulation is ensured between the outside world and electronic boards. The sensors in the sensor block (4) are the sensors in the inertial measurement unit. As a result, the performance of the sensors, which are insulated from environmental effects, has been increased despite the low mass of the sub-parts, and thus a low-mass, high-performance inertial measurement unit has been obtained.

The outer body (3) and the sensor block (4) have a lattice inner structure. Preferring the lattice structure, a very serious decrease in mass is obtained compared to the solid pieces produced by the classical method. The mass reduction that can be achieved with the lattice structure varies with the wall/beam thicknesses of the lattice structure. In this way, system performance has been increased to a higher level. While the hexagonal lattice structure (1 ), which provides the best thermal insulation property, is used in the outer body (3), the triangular prism lattice structure (2) is used in the sensor block (4) to obtain the highest stiffness.

The triangular prism lattice structure (2) is such that the edge of each of the surfaces with more than one hollow triangular geometry is adjacent to another one. Due to the fact that it consists of hollow triangular geometries, a significant weight reduction has been achieved compared to the classical solid wall structures used in the current system. The outer part of the triangular prism lattice structure (2) is covered with the panel (8). The aforementioned triangular prism lattice structure (2) is shown in Figure- 2.

The lattice structure (1 ) with hexagonal geometry, on the other hand, is configured in such a way that one edge of each of the surfaces with more than one hollow hexagonal geometry is adjacent to the edge of another one. Due to the fact that it consists of hollow hexagonal geometries, a significant weight reduction has been achieved compared to the classical solid wall structures used in the current system. The outer part of the hexagonal lattice structure (1 ) is covered with the panel (8). The lattice structure (1 ) with the mentioned hexagonal geometry is shown in Figure-1.

The outer body (3) contains two body cavities (7). Said body cavities (7) are shown in Figure-3.

The accelerometer and tachometer sensors used in the inertial measurement unit are placed on the sensor block (4) positioned inside the outer body (3) by using mounting feet (5) mounted on the sensor block (4). In the other body cavity (7) inside the outer body (3), the sensor performs power feeds. The electronic board assembly located in the body cavity (7) collects the sensor output data, processes this data and turns it into meaningful inertial measurement unit outputs.

The performance of the sensors used in the inertial measurement unit is dependent on the temperature change and the rate of change of the temperature change with respect to time. The temperature change varies from product to product. This variation is between -40°C and +60°C. To achieve high inertial measurement unit performance, the sensors must be thermally insulated. For this reason, the electronic boards producing heat in the inertial measurement unit and the sensor block (4) are thermally insulated from each other by a wall (6) located between them. In this wall (6), a lattice structure (1 ) with hexagonal geometry is used for high thermal insulation.

The inertial measurement unit calculates the position of the entire system by using the translation and angular acceleration information detected by the sensors in it. For this reason, the mechanical parts to which the sensors that detect the acceleration are connected must be rigid so that the sensors move the same amount as the mounting surfaces of the inertial measurement unit. In addition, in order for the vibration performance to be high, the natural frequencies of the mechanical parts to which the sensors are connected should be increased to a high level. For these reasons, the resistance of the sensor block (4) must be high. Since high stiffness values are obtained with low mass, the inner structure that best responds to such needs is the triangular prism lattice structure (2). For this reason, a triangular prism lattice structure (2) is used in the sensor block (4). The outside of the triangular prism lattice structure (2) is covered with a thin flat panel (8).

There are mounting feet (5) on the sensor block (4) in order to mount the sensors at the required positions. The mounting feet (5) are subjected to post-processing after additive manufacturing in order to provide the sensitivity values of the sensor. For this part, the sensor connection surfaces are manufactured to provide perpendicularity and flatness with appropriate tolerance. If the body structure is to be produced from a non- metallic material with a 3D printer, the metal connection slots for the mounting feet (5) should be embedded and these mounting feet (5) should be precisely machined according to the appropriate perpendicularity and flatness tolerances after the body is printed with the 3D printer.

In order for the sensors and thus the inertial measurement unit to have a high performance, it is necessary to isolate the sensors as much as possible from thermal effects. The lattice structure (1 ) with the hexagonal geometry with the largest space inside is one of the most suitable options for thermal insulation with low mass. For this reason, a hexagonal lattice structure (1 ) is used inside all outer body walls and base for thermal insulation of the sensor block (4) from electronic boards and the outside world. As with the sensor block (4), the outer body walls and the outside of the base are also covered with thin flat panels (8). The system developed with the invention made it possible to design different micromechanical structures in the lattice materials used. Thus, in Ashby diagrams, where the properties of stiffness, strength, thermal conductivity, etc., are compared according to the densities of different types of materials, areas that cannot be reached with materials found in nature can be reached. Ashby diagrams are diagrams used to compare prepared comparative material properties to contribute to material selection.

By making different internal structure designs in lattice materials, the lowest weight structure design suitable for the desired mechanical or thermal properties is obtained and designs that are not possible with traditional materials can be realized. The system developed with the invention can be produced from metal or non-metal materials with a three-dimensional printer in one go. Here, 17-4PH stainless steel or titanium alloys suitable for use in 3D printers can be preferred as metal materials. Carbon fibre reinforced plastic or composite fibres can be preferred for non-metallic materials. Appropriate body material should be selected according to the mechanical vibration, shock, operating temperature range, weight and performance requirements of the system. The sensor block (4) is connected to and the mounting feet (5) are made on the hollow structure to be printed in a three-dimensional printer in one go, and these parts are then processed.

Claims

CLAIMS An inertial measurement unit that measures accelerations and spins in six directions of freedom of movement and calculates instantaneous location information using this data, resistant to environmental effects such as vibration and thermal shock, comprising:

■ the outer body (3), consisting of a hexagonal lattice structure (1 ) and a panel (8) covering the outer part of adjacent hexagonal surfaces formed in such a way one edge of each of the surfaces having more than one hollow hexagonal geometry in its structure being adjacent to the edge of another one to provide thermal insulation and to reduce weight by increasing the gaps in the inertial measurement unit and in one of the two body cavities (7) inside of which is placed the sensor block (4) and in the other body cavity (7) is placed the electronic board assembly where the sensor power feeds are carried out;

■ the sensor block (4), positioned inside the outer body (3), and consisting of a triangular prism mesh structure (2) formed to be adjacent to each edge of surfaces with more than one hollow triangular geometry, and a panel (8) covering the outer part of adjacent triangular surfaces in its body in order to increase stiffness and reduce weight by increasing the gaps in the inertial measurement unit;

■ the wall (6) positioned between the heat generating electronic boards and the sensor block (4) to thermally isolate the sensors in the sensor block (4). Inertial measurement unit according to Claim 1 , comprising mounting feet (5) that enable the accelerometer and tachometer sensors used in the inertial measurement unit to be mounted on the sensor block (4) positioned inside the outer body (3). Inertial measurement unit according to Claim 1 , comprising the wall (6) containing the hexagonal geometry lattice structure (1 ) to provide thermal insulation between the heat-generating electronic boards and the sensor block (4). Inertial measurement unit according to Claim 1 , comprising the electronic board assembly, in which the data received from the sensor block (4) are collected and processed and transformed into inertial measurement unit outputs, enabling the sensor power feeds to be realized and positioned in the body cavity (7) inside the outer body (3).

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