MICRO INERTIAL MEASUREMENT SYSTEM

Abstract

An inertial measurement device includes a sensing module including a support, a flexible circuit board, and a plurality of sensors. The support includes a plurality of external surfaces facing away from one another. Two or more of the plurality of external surfaces each includes a groove engraved thereon. The flexible circuit board substantially covers the plurality of external surfaces of the support and includes a plurality of panels configured to be bent along edges of the support. The plurality of sensors each is arranged at a respective one of the plurality of panels of the flexible circuit board and received in a groove of a corresponding one of the plurality of external surfaces of the support.

Claims

1. An inertial measurement device, comprising: a sensing module including: a support including a plurality of external surfaces facing away from one another, two or more of the plurality of external surfaces each including a groove engraved thereon; a flexible circuit board substantially covering the plurality of external surfaces of the support and including a plurality of panels configured to be bent along edges of the support; and a plurality of sensors each arranged at a respective one of the plurality of panels of the flexible circuit board and received in a groove of a corresponding one of the plurality of external surfaces of the support.

2. The inertial measurement device of claim 1, wherein the plurality of external surfaces are orthogonal to each other.

3. The inertial measurement device of claim 1, wherein measuring axes of the plurality of sensors are orthogonal to each other.

4. The inertial measurement device of claim 1, wherein each of the plurality of panels includes a front surface that supports one or more electrical components and faces an external surface of the plurality of external surfaces of the support.

5. The inertial measurement device of claim 4, wherein each of the plurality of panels further includes a back surface that is opposite to the front surface and faces away from the support, and the back surface does not support any electrical components.

6. The inertial measurement device of claim 1, wherein the plurality of sensors include a gyroscope and an accelerometer.

7. The inertial measure device of claim 6, wherein the support has an inherent frequency that is substantially different from an operating vibration frequency of the gyroscope.

8. The inertial measurement device of claim 1, further comprising: a housing including an upper housing and a lower cover together forming a cavity configured to contain the sensing module.

9. The inertial measurement device of claim 8, further comprising: a plurality of damping units arranged between the sensing module and an inside wall of the housing.

10. The inertial measurement device of claim 9, wherein the plurality of damping units are arranged relative to the sensing module such that an elastic center of the one or more damping units substantially coincides with a centroid of the sensing module.

11. The inertial measure device of claim 9, wherein the support includes a cube-shaped structure with six external surfaces.

12. The inertial measure device of claim 11, wherein the flexible circuit board includes six panels.

13. The inertial measure device of claim 12, wherein the plurality of damping units include six damping units, and each of the damping units is arranged between a respective one of the six panels and the housing.

14. The inertial measure device of claim 1, wherein the flexible circuit board includes an anti-aliasing circuit.

15. The inertial measure device of claim 1, wherein the flexible circuit board includes an A/D switching circuit.

16. The inertial measure device of claim 1, wherein a shape of each of the plurality of panels is congruent to a shape of a corresponding one of the plurality of external surfaces of the support.

17. The inertial measure device of claim 1, wherein the support is manufactured using an integral forming process.

18. An unmanned aerial vehicle (UAV), comprising: a sensing module including: a support including a plurality of external surfaces facing away from one another, two or more of the plurality of external surfaces each including a groove engraved thereon; a flexible circuit board substantially covering the plurality of external surfaces of the support and including a plurality of panels configured to be bent along edges of the support; and a plurality of sensors each arranged at a respective one of the plurality of panels of the flexible circuit board and received in a groove of a corresponding one of the plurality of external surfaces of the support.

19. The UAV of claim 18, wherein: the plurality of sensors include a gyroscope; and the flexible circuit board is configured to generate a signal indicative of a rotation of the UAV using the gyroscope.

20. The UAV of claim 19, further comprising: a control computer operably coupled to the flexible circuit board and configured to receive and process the signal to determine the rotation of the UAV.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 is a structure diagram for a strapdown inertial measurement system of a small-sized UAV in the prior art;

[0024] FIG. 2 is a structure diagram for a sensing support in the inertial measurement system of FIG. 1;

[0025] FIG. 3 is a schematic diagram for an equivalent model of a damper in the inertial measurement system of FIG. 1;

[0026] FIG. 4 illustrates the distribution of internal damping units of a damper in one embodiment of the present invention; wherein the S in the figure stands for an upper, a lower, a left and a right inside wall of a housing;

[0027] FIG. 5 is a schematic diagram for a sensing support in a preferred embodiment of the present invention;

[0028] FIG. 6 is an outline view for a flexible measuring and controlling circuit board and an arrangement diagram for components on the flexible measuring and controlling circuit board; wherein the flexible measuring and controlling circuit board cooperates with the sensing support in the FIG. 5;

[0029] FIG. 7 is a schematic diagram for the composition of a sensing module in a preferred embodiment of the present invention;

[0030] FIG. 8 is a structure diagram for a housing that cooperates with the sensing module in the FIG. 7;

[0031] FIG. 9 illustrates the position relation between an internal damping unit and a sensing module that are employed in a preferred embodiment of the present invention;

[0032] FIG. 10 is an assemblage diagrammatic sketch for a micro inertial measurement system in a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0033] During operation, in the mechanical environment for a strapdown inertial navigation system, the violent random vibration may often present. The vibration may induce instability of the system and damage to electronic components, which will impact on the system stability greatly. In order to reduce such impact produced by the violent random vibration of a carrier, which may damage electronic components or make an inertial measurement unit unstable, except that the connection stiffness between respective sensor circuit boards is strengthened, the inertial measurement unit is elastically connected to the carrier using a damper as a damping medium, so as to realize a desired damping effect.

[0034] Since the selection of a damping mode influences both damping performance and measurement precision of the inertial navigation system, it is always an important link in its structure design. In various aspects of the present invention, an improved design of sensing support and a rational damping mechanical structure may be operable to improve the performance of the micro inertial measurement system.

[0035] The sensing support is a key component for mounting a gyroscope, a measuring and controlling circuit board and a connecting wire. The sensing support may suffer a variety of violent vibration during operation, in which case a mounting surface for the gyroscope has the relative maximum amplitude. Therefore, dynamic properties for the structure of the mounting surface will definitely impact on the operating reliability and accuracy of the gyroscope. To minimize such impact, it is required to possess a certain static strength, anti-vibration strength and fatigue life. With respect to process, the support is required to be easy to mount and manufacture. Besides, the structure for the support is designed rationally as well as its rigidity and damping performance are improved, so that its inherent frequency is definitely significantly distinguished from the operating vibration frequency of a shaker of the gyroscope and the relative amplitude for the mounting surface of the gyroscope is minimized. In the prior art, a traditional method for optimizing the support is shown as follows: wall thickness is greatly increased to enhance the rigidity and increase the inherent frequency of the corresponding structure. In the present invention, the structural design is improved by optimizing material, shape and joint surface, instead of increasing thickness unilaterally, so as to enhance the structural rigidity and damping performance of the support. In addition, the conditionality between the support and a damping device should be resolved on the whole. The mounting position and the line route of the measuring and controlling circuit board on the support are also in the consideration.

[0036] It can be seen from the above description that, in order to overcome the above mentioned technical drawbacks for the inertial measurement system in the prior art, the following technical measures is taken in the present invention: a micro inertial measurement system is provided based on the concept of improving its mechanical structure, wherein the system has a greatly reduced volume and includes a damping structure with three-dimensional equal rigidity; the micro inertial r:ieasurement system is provided in such a way that harmful effects of various drawbacks including three-dimensional unequal rigidity, resonance excitation and torsional vibration on the strapdown inertial navigation system are overcome.

[0037] A preferred embodiment of the present invention is shown in FIGS. 4-10. Such micro inertial measurement system comprises a sensing module 12, a damping unit, an upper housing 16 and a lower cover 18.

[0038] Wherein, the sensing module 12 comprises a sensing support 121, an inertial sensor 122 and a flexible measuring and controlling circuit board 123. In this embodiment, the sensing support 121 is a rigid and cube-shaped support satisfying certain requirements of specific gravity and rigidity. And the sensing support 121 is engraved with a groove on its respective surface.

[0039] The inertial sensor 122 comprises a gyroscope and an accelerometer. In particular, it comprises three gyroscopes and one accelerometer, all of which are welded onto the flexible measuring and controlling circuit board 123.

[0040] The flexible measuring and controlling circuit board 123 should have a function of preprocessing sensor signals. For this purpose, such flexible measuring and controlling circuit board 123 should comprise at least an anti-aliasing circuit and an A/D switching circuit. On one hand, a circuit board and connecting wire are made of flexible material to withstand the bending of 90°. On the other hand, the shape of the flexible measuring and controlling circuit board should be congruent to that of the developed plane of the sensing support, so that they can cover each surface of the sensing support completely and smoothly after they are bent by an angle of 90° along the edges of the sensing support.

[0041] In certain implementation, six circuit modules composed of the anti-aliasing circuit, the A/D switching circuit, the three gyroscopes and the one accelerometer are arranged on six flexible measuring and controlling circuit boards, respectively. Moreover, the circuit components on each flexible measuring and controlling circuit board are respectively embedded in the groove on its corresponding surfaces of the sensing support.

[0042] An inner cavity that is formed by the upper housing 16 and the lower cover 18 should have a shape similar to the configuration of the sensing module 12, and the volume of the inner cavity is relatively larger than that of the sensing module 12. As a result, respective space formed between each inside wall of the housing and the corresponding plane of the sensing module is approximately the same to each other, in which is installed an internal damping units 14.

[0043] The internal damper is composed of a number of internal damping units {K.sub.i, c.sub.i} 14 with appropriate damping properties. Such internal damping units are mounted between the inside wall S of the upper housing 16 and the six planes of the sensing module 12. The number of the internal damping units is determined depending on the vibration characteristics of different carriers, the maximum of which is 6. The sensing module is hung at the centre of the inner cavity of the housing. In this arrangement, the respective force axis of deformation for each internal damping unit is orthogonal to each other, and the elastic centre P of the damper coincides with the centroidal m of the sensing module, so that the forced vibration from the carrier is absorbed and consumed uniformly. In specific implementation, the damping unit is made of elastic matter with certain damping effect. Such elastic matter may be selected from but not limited to spring, rubber blanket, silica gel, sponge or any other damping matter.

[0044] In a preferred embodiment of the present invention, the sensing support 121 in the shape of a cube is made of metal material or non-metal material with a certain gravity and rigidity and manufactured using an integral forming process. The integral forming instead of assembling for a sensing support 121 is employed to ensure that rigidity of the. support itself is enough to reduce measurement error caused by insufficient rigidity and anisotropy (referring to FIG. 5).

[0045] FIG. 6 is a schematic diagram illustrating the developed plane of a flexible measuring and controlling circuit board 123 and an arrangement for components thereon, according to a preferred embodiment of the present invention. The circuit substrate and the connecting wire of the flexible measuring and controlling circuit board 123 are both made of flexible material to withstand bending of 90°. Besides, its shape is designed to be congruent to that of the developed outer plane of the sensing support, such that the flexible measuring and controlling circuit board has six developed planes. Sensors and any other electronic components are respectively welded in appropriate positions on the front side of the six developed planes.

[0046] FIG. 7 is a schematic diagram illustrating the structure of a sensing module in a preferred embodiment of the present invention. An inertial sensor 122 and any other electronic components are welded on the front side of the flexible measuring and controlling circuit board 123. The front side of the flexible measuring and controlling circuit board 123 is attached to the sensing support 121 and bends by an angle of 90° along the edges of the sensing support 121. Then each sensor or electronic component is embedded into the groove on each surface of the sensing support 121. After that, the back side of the whole flexible measuring and controlling circuit board 123 directs outward. Such that, the flexible measuring and controlling circuit board 123 can enclose the sensing support 121 together with the sensing component and electronic component therein, as well as cover each surface of the sensing support 121 completely and smoothly.

[0047] In the present invention, the primary consideration for designing the strapdown inertial navigation damping system is how to avoid or reduce coupled vibration. If the mechanical structure of such system is irrational, the respective vibration in its six degrees of freedom will be coupled to each other, so as to produce a cross excitation of a linear vibration and an angular vibration. As a result, the detected data of the inertial measurement system would contain cross excitation information of its own, consequently a pseudo movement signal would be introduced into the system, which may significantly impact the measurement precision of the inertial navigation system. In order to reduce the interference produced by the damper during the measurement of angular motion of the system, the angular vibration frequency of the damping system should be significantly distinguished from the measuring bandwidth of the inertial navigation system. In the circumstances of broad-band random vibration, the lower the damping frequency is, the higher the damping efficiency is.

[0048] FIG. 8 is a schematic diagram illustrating a housing 16 in a preferred embodiment of the present invention; wherein the housing 16 forms an inner cavity in the shape of cube together with a lower cover 18 (not shown in the figure for clarity). The inner cavity is used for holding the sensing module 12 and the damping units 14. In this case, compared with the shape of the sensing module 12, the inner cavity of the housing formed as mentioned above is designed to have the same shape, i.e. in the shape of cube, and have a relative larger volume. Upon such design, the respective space formed between each of the six inside walls of the housing and the corresponding one of the six outer surfaces of the sensing module has a nearly same shape and size to each other; wherein, the six inside walls of the housing are formed by the upper housing 16 and the lower cover 18. When the damping units 14 with approximately the same shape respectively are mounted in the space, an assembly of internal damper is completed, so as to provide relatively excellent damping effect.

[0049] FIG. 9 illustrates a position relation between an internal damper composed of all internal damping units 14 and a sensing module according to a preferred embodiment of the present invention. In the embodiment, in order to effectuate an effective attenuation or a complete absorption of the forced vibration on the sensing module 12 in the six degrees of freedom comprising front and back, right and left, and up and down degrees of freedom, six internal damping units 14, i.e., six damping pads of the same shape are mounted between the inside wall of the upper housing 16 and the sensing module 12; besides, the sensing module is hung at the centre of the inner cavity of the housing, and the respective force axis of deformation for each internal damping unit is orthogonal to each other, so that the forced vibration from the carrier is absorbed and consumed uniformly.

[0050] FIG. 10 is an assemblage diagrammatic sketch for a micro inertial measurement system 2.1 in a preferred embodiment of the present invention. Due to a series of technical measures mentioned above, it is ensured that all of the inherent frequency, damping coefficient, damping efficiency and mechanical strength of the damper can meet the requirement of impact and vibration resistance. Such that, in the three coordinate systems of the micro inertial measurement system, i.e. an elastic coordinate system, an inertial coordinate system and a solution coordinate system, their respective corresponding coordinate axes are in parallel with each other, and the centroidal of the measurement system is coincident with the elastic centre of the damping device. In such optimal state, significant decoupling effect is achieved among vibrations in each degree of freedom, and the respective inherent frequency is approximate to each other to implement a technical effect of narrow frequency distribution.

[0051] The micro inertial measurement system of the present invention can be applied for UAVs, automatic driving aircraft, watercraft and underwater automatic detection equipment or various cars and robots and so on. Apart from the embodiments above, there are some other implementations for the present invention. For example, (1) the housing is not limited to be formed by the coordination between the upper housing and the lower cover; instead, it can be formed by the coordination between a lower housing and an upper cover or between a middle housing and an upper cover as well as a lower cover; (2) integrated processing can be performed on all or portions of the six functional modules of the flexible measuring and controlling circuit board, so that the number of the flexible measuring and controlling circuit board can be reduced to be less than six, and the number of the groove on the surface of the sensing support can be correspondingly reduced as well; (3) the support can be in the shape of cuboid and the structure of the circuit board is adjusted accordingly at this moment. It can be seen that all relevant and equivalent alternative technical solution should be within the scope of protection claimed by the present invention.