Three-axis acceleration sensor

Abstract

The present invention provides a three-axis acceleration sensor, comprising: a substrate, at least one anchor fixedly arranged on the substrate, two directions parallel to the surface of the substrate and perpendicular to each other are defined as the X direction and the Y direction, the plane where they are located is the XY plane, and the direction perpendicular to the XY plane is the Z direction. The three-axis acceleration sensor further comprises: a first movable mass block connected to the anchor through a first elastic element, wherein the first elastic element is a bidirectional elastic element in the X direction and the Y direction; a second movable mass block connected to the first movable mass block through a second elastic element, wherein the second elastic element is a rotating arm with the Y axis as the rotation axis, so that the second movable mass block can rotate around the XZ plane; the centers of gravity of the first mass block and the second mass block are respectively located on both sides of the anchor in the Y-axis direction. By arranging two mass blocks with different center-of-gravity positions, the present invention eliminates the influence of external stress on acceleration detection through the rotation of the mass blocks.

Description

Technical Field

[0001] The present invention relates to the field of MEMS, and particularly to a triaxial acceleration sensor. Background Art

[0002] For triaxial acceleration sensors, in the prior art, multiple independent mass blocks are usually used to sense accelerations in different axial directions. The disadvantages are that the volume is large and the structure is complex, so it is not conducive to manufacturing. While using a single mass block to detect accelerations in three axes is prone to cross-axis detection, and the detection accuracy in the Z direction is relatively low, and it is easily affected by external stress. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a triaxial acceleration sensor that can improve the detection accuracy.

[0004] To solve the above problems, the present invention provides a triaxial acceleration sensor, including: a substrate, at least one anchor point fixedly arranged on the substrate, two directions parallel to the surface of the substrate and perpendicular to each other are defined as the X direction and the Y direction, and the plane where they are located is the XY plane, and the direction perpendicular to the XY plane is the Z direction. The triaxial acceleration sensor further includes: a first movable mass block connected to the anchor point through a first elastic element, and the first elastic element is a bidirectional elastic element in the X direction and the Y direction; a second movable mass block connected to the first movable mass block through a second elastic element, and the second elastic element is a rotating arm with the Y axis as the rotation axis, so that the second movable mass block can rotate around the XZ plane; the centers of gravity of the first mass block and the second mass block are respectively located on both sides of the anchor point in the Y-axis direction.

[0005] The present invention eliminates the influence of external stress on acceleration detection by setting two mass blocks with different center-of-gravity positions and rotating the mass blocks. Brief Description of the Drawings

[0006] Att Figure 1 and Att Figure 2 Shown is a schematic structural diagram of the triaxial acceleration sensor according to a specific embodiment of the present invention.

[0007] Att Figure 3 to Att Figure 5 Shown is a schematic structural diagram of the triaxial acceleration sensor according to a specific embodiment of the present invention when it is deformed under the influence of an external acceleration.

[0008] Att Figure 6 Shown is a schematic diagram of the technical progress principle of setting double symmetric mass blocks in the triaxial acceleration sensor according to a specific embodiment of the present invention.

[0009] Att Figure 7 Shown is a schematic diagram of the technical progress principle of setting multiple anchor points in the triaxial acceleration sensor according to a specific embodiment of the present invention. Detailed implementation manners

[0010] The following will make a detailed description of the specific implementation manners of the triaxial acceleration sensor provided by the present invention with reference to the accompanying drawings.

[0011] Accompanying Figure 1 Shown is a structural schematic diagram of the triaxial acceleration sensor described in this specific implementation manner, including: an outer frame 10 fixed on a substrate, and at least one anchor point 11 fixedly arranged on the substrate; two directions parallel to the substrate surface and perpendicular to each other are defined as the X direction and the Y direction, and the plane where they are located is the XY plane, and the direction perpendicular to the XY plane is the Z direction. In this specific implementation manner, taking 4 anchor points as an example for description, the 4 anchor points are symmetrically arranged with respect to the center O point of the triaxial acceleration sensor and are connected to each other through beams.

[0012] A first movable mass block 121 is connected to the anchor point 11 through a first elastic element 131, and the first elastic element is a bidirectional elastic element in the X direction and the Y direction and is connected to the beam; a second movable mass block 122 is connected to the first movable mass block 121 through a second elastic element 132, and the second elastic element is a rotating arm with the Y axis as the rotation axis, so that the second movable mass block 122 can rotate around the XZ plane; the centers of gravity of the first movable mass block 121 and the second movable mass block 122 are respectively located on both sides of the anchor point in the Y-axis direction.

[0013] In a specific implementation manner, in order to detect the deformation generated by the above structure according to the external acceleration, the comb electrodes shown in the accompanying Figure 1 are used to detect the acceleration in the XY plane. When there is an acceleration in the X direction, the deformation of the above structure is as shown in Figure 3 shown, and its working principle is as follows: when there is an acceleration in the X direction, the first elastic element 131 will generate a deformation along the X direction, and the first movable mass block 121 will generate a displacement in the X direction, thereby causing a change in the X electrode gap, checking the differential capacitance of the X electrode group, and thus detecting the acceleration in the X direction. Since the second elastic element 132 has a relatively large stiffness in the X direction, the relative displacement of the second movable mass block 122 relative to the first movable mass block 121 is relatively small. The second movable mass block 122 only provides inertial mass for the X direction detection and does not generate cross-axis noise. Therefore, it can be regarded as being displaced in the X direction together with the first movable mass block 121, playing the role of increasing the inertial mass.

[0014] In a specific implementation manner, in order to detect the deformation generated by the above structure according to the external acceleration, the comb electrodes shown in the accompanying Figure 1 are used to detect the acceleration in the XY plane. When there is an acceleration in the Y direction, the deformation of the above structure is as shown in Figure 4As shown in the figure, its working principle is as follows: When there is an acceleration in the Y direction, the first elastic element 131 will generate a deformation along the Y direction, and the first movable mass block 121 will generate a displacement in the Y direction, thereby causing a change in the Y electrode gap, checking the differential capacitance of the Y electrode group, and thus detecting the acceleration in the Y direction. Since the second elastic element 132 has a relatively large stiffness in the Y direction, the relative displacement of the second movable mass block 122 relative to the first movable mass block 121 is relatively small. The second movable mass block 122 only provides an inertial mass for the Y direction inspection without generating cross-axis noise. Therefore, it can be regarded as being displaced in the Y direction together with the first movable mass block 121, playing the role of increasing the inertial mass.

[0015] In order to more accurately detect the acceleration in the Z direction, the electrode structure is set in the form of the electrode arrangement shown in the figure to detect the acceleration in the Z direction. That is, at least two first Z electrodes composed of metal layers provided on the substrate surface, which are the negative electrodes ZN1 and ZN2 and the positive electrodes ZP3 and ZP4 in this specific embodiment, are respectively located on both sides of the anchor point and correspond to the electrodes on the surface of the first movable mass block 121, forming at least one differential capacitance pair; and at least two second Z electrodes composed of metal layers on the substrate, which are the negative electrodes ZN3 and ZN4 and the positive electrodes ZP1 and ZP2 in this specific embodiment, are located on both sides of the anchor point and correspond to the electrodes on the surface of the second movable mass block 122, forming at least one differential capacitance pair. Figure 2 As shown in the figure, its working principle is as follows: When there is an acceleration in the Y direction, the first elastic element 131 will generate a deformation along the Y direction, and the first movable mass block 121 will generate a displacement in the Y direction, thereby causing a change in the Y electrode gap, checking the differential capacitance of the Y electrode group, and thus detecting the acceleration in the Y direction. Since the second elastic element 132 has a relatively large stiffness in the Y direction, the relative displacement of the second movable mass block 122 relative to the first movable mass block 121 is relatively small. The second movable mass block 122 only provides an inertial mass for the Y direction inspection without generating cross-axis noise. Therefore, it can be regarded as being displaced in the Y direction together with the first movable mass block 121, playing the role of increasing the inertial mass.

[0016] When there is an acceleration in the Z direction, the deformation of the above structure is as shown in the figure. Figure 5 As shown in the figure. The first elastic element 131 will not generate deformation, and the first movable mass block 121 will not generate rotation. Therefore, the capacitance values between the negative electrodes ZN1 and ZN2 and the positive electrodes ZP3 and ZP4 remain unchanged. However, the second elastic element 132 will generate deformation, and the second movable mass block 122 will generate rotation around the Y axis. Its main motion form is that the second movable mass block 122 rotates around the Y axis. Due to the arrangement of the negative electrodes ZN3 and ZN4 and the positive electrodes ZP1 and ZP2, a differential capacitance will be generated, thereby detecting the acceleration in the Z direction. The first mass block has a relatively large stiffness in the Z direction and can be considered not to be affected by the acceleration in the Z direction.

[0017] By setting two mass blocks, with the first movable mass block 121 being stationary relative to the Z direction and the second movable mass block 122 being movable, the systematic error caused by the tilt of the anchor point can be offset. The schematic diagram of the above setting is as shown in the figure. Figure 6As shown, the left side shows the case of a single mass block, and the right side shows the case of a double mass block. The upper part shows the case of being subjected to an acceleration in the Z direction, and the lower part shows the case of anchor point offset. It can be seen that when subjected to an acceleration in the Z direction, for the single mass block, the tilting situation reflects the acceleration situation; while for the double mass block, the signal of the first Z electrode does not change, but the signal of the second Z electrode changes. When the anchor point is offset, for the left case, the tilting of the anchor point directly causes a change in the capacitance value, resulting in a zero offset of the accelerometer, and it is impossible to distinguish whether the tilting of the mass block is caused by stress leading to the tilting of the anchor point or by acceleration; while for the right case, the signals of both the first Z electrode and the second Z electrode change. Therefore, by using the signal of the first Z electrode as the background signal and performing an operation with the signal of the second Z electrode, the influence of external stress on acceleration detection can be eliminated.

[0018] Setting multiple anchor points, such as the four anchor points distributed at the four corners of a rectangle in the above specific embodiment, can offset the systematic error caused by the tilting of the anchor points. The schematic diagram of the above setting is as Figure 7 shown. For the case of a single anchor point, when the anchor point tilts, it will cause the tilting of the mass block. While when there are two anchor points at a certain distance in the corresponding tilting direction, the influence caused by the tilting of the mass block can be greatly reduced. Since the above situation may occur in both the X and Y directions, two anchor points are required corresponding to both the X and Y directions, that is, the four anchor points distributed at the four corners of a rectangle in the above specific embodiment.

[0019] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A triaxial acceleration sensor, comprising a substrate, at least one anchor fixedly arranged on the substrate, two directions parallel to the surface of the substrate and perpendicular to each other are defined as the X direction and the Y direction, the plane where they are located is the XY plane, and the direction perpendicular to the XY plane is the Z direction, and it is characterized in that, Further comprising: A first movable mass block, connected to the anchor point through a first elastic element, and the first elastic element is a bidirectional elastic element in the X direction and the Y direction; A second movable mass block, connected to the first movable mass block through a second elastic element, and the second elastic element is a rotating arm with the Y-axis as the rotation axis, enabling the second movable mass block to rotate around the XZ plane; At least two first Z electrodes composed of metal layers provided on the substrate surface, located on both sides of the anchor point, corresponding to the electrodes on the surface of the first movable mass block, forming at least one differential capacitance pair; At least two second Z electrodes composed of metal layers provided on the substrate surface, located on both sides of the anchor point, corresponding to the electrodes on the surface of the second movable mass block, forming at least one differential capacitance pair; The first movable mass block is stationary relative to the Z direction, and the second movable mass block is movable relative to the Z direction.

2. The triaxial acceleration sensor according to claim 1, characterized in that, There are four of the anchor points, symmetrically arranged around the center of the triaxial acceleration sensor, and connected to each other through beams.

3. The triaxial acceleration sensor according to claim 1, characterized in that, The bidirectional elastic element in the X direction and the Y direction is a right-angle folding spring.

4. The triaxial acceleration sensor according to claim 1, wherein The first Z electrode and the second Z electrode are cross-arranged on both sides of the elastic unit. When the metal electrode corresponding to the second movable mass block is the positive electrode of the differential capacitance on one side, the metal electrode corresponding to the first mass block on the same side is the negative electrode of the differential capacitance.

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