Triaxial acceleration sensor

Abstract

The present invention provides a three-axis acceleration sensor, comprising a substrate and at least one anchor fixedly arranged on the substrate; the sensor further comprises: a first movable mass, a second movable mass, and a third movable mass. The centers of gravity of the second movable mass and the third movable mass are respectively located on both sides of the anchor. By providing two masses with different center-of-gravity positions, the present invention eliminates the influence of external stress on acceleration detection through the rotation of the masses.

Description

Technical Field

[0001] The present invention relates to the field of MEMS, and in particular, 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, which is not conducive to manufacturing. Using a single mass block to detect accelerations in three axes easily leads to cross-axis detection, and the detection accuracy in the Z direction is relatively low, and it is also 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 and 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 sensor further includes: a first movable mass block connected to the anchor point through a first elastic element, where the first elastic element is a bidirectional elastic element in the X direction and the Y direction and is connected to a beam; a second movable mass block connected to the first movable mass block through a second elastic element, where 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; and a third movable mass block connected to the first movable mass block through a third elastic element, where the third elastic element is a rotating arm with the Y axis as the rotation axis, so that the third movable mass block can rotate around the XZ plane; the centers of gravity of the second movable mass block and the third movable 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 deformed under the influence of an external acceleration.

[0008] Att Figure 6The following is a schematic diagram of the technological progress of the three-axis acceleration sensor with double symmetric mass blocks according to a specific embodiment of the present invention.

[0009] Appendix Figure 7 The following is a schematic diagram of the technological progress of the three-axis acceleration sensor with multiple anchor points according to a specific embodiment of the present invention. Specific Embodiment

[0010] The following will describe in detail the specific embodiments of the three-axis acceleration sensor provided by the present invention with reference to the accompanying drawings.

[0011] Appendix Figure 1 The following is a schematic structural diagram of the three-axis acceleration sensor according to this specific embodiment, including: an outer frame 10 fixed on a substrate, and at least one anchor point 11 fixedly arranged on the substrate; two opposite directions parallel to the surface of the substrate 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 embodiment, taking 4 anchor points as an example for description, the 4 anchor points are symmetrically arranged around the center O point of the three-axis acceleration sensor and are connected to each other by beams.

[0012] A first movable mass block 121, which 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, which 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; and a third movable mass block 123, which is connected to the first movable mass block 121 through a third elastic element 133, and the third elastic element 133 is a rotating arm with the Y axis as the rotation axis, so that the third movable mass block 123 can rotate around the XZ plane; the centers of gravity of the second movable mass block 122 and the third movable mass block 123 are respectively located on both sides of the anchor point in the Y-axis direction.

[0013] In a specific embodiment, in order to detect the deformation generated by the above structure according to the external acceleration, the comb-shaped electrodes shown in the appendix 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 Figure 1 shown. Figure 3As shown in the figure, 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, resulting in a change in the X electrode gap. By detecting the differential capacitance of the X electrode group, the acceleration in the X direction can be detected. Since the second elastic element 132 and the third elastic element 133 have a relatively large stiffness in the X direction, the relative displacements of the second movable mass block 122 and the third movable mass block 123 relative to the first movable mass block 121 are relatively small. The second movable mass block 122 and the third movable mass block 123 provide inertial mass for the X-direction inspection without generating cross-axis noise. Therefore, they can be regarded as being displaced in the X direction integrally with the first movable mass block 121, playing the role of increasing the inertial mass.

[0014] In a specific embodiment, in order to detect the deformation generated by the above structure according to the external acceleration, a Figure 1 comb-shaped electrode as shown in the figure is 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 Figure 4 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, resulting in a change in the Y electrode gap. By detecting the differential capacitance of the Y electrode group, the acceleration in the Y direction can be detected. Since the second elastic element 132 and the third elastic element 133 have a relatively large stiffness in the Y direction, the relative displacements of the second movable mass block 122 and the third movable mass block 123 relative to the first movable mass block 121 are relatively small. The second movable mass block 122 and the third movable mass block 123 provide inertial mass for the Y-direction inspection without generating cross-axis noise. Therefore, they can be regarded as being displaced in the Y direction integrally 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, in this specific embodiment, a Figure 2 electrode arrangement form as shown in the figure is used to set the electrode structure for detecting the acceleration in the Z direction. That is, at least two first Z electrodes composed of metal layers provided on the substrate surface, in this specific embodiment, the negative electrodes ZN1 and ZN2, and the positive electrodes ZP3 and ZP4, are respectively located on both sides of the anchor point, corresponding to the electrodes on the surface of the second movable mass block 122, forming at least one differential capacitance pair; and at least two second Z electrodes composed of metal layers on the substrate, in this specific embodiment, the negative electrodes ZN3 and ZN4, and the positive electrodes ZP1 and ZP2, are located on both sides of the anchor point, corresponding to the electrodes on the surface of the third movable mass block 123, forming at least one differential capacitance pair.

[0016] When there is an acceleration in the Z direction, the deformation of the above structure is as Figure 5As shown. The second elastic element 132 will deform, and the second movable mass 122 will rotate. Its main motion form is that the second movable mass 122 rotates around the Y-axis. Due to the arrangement of the negative electrodes ZN1 and ZN2, and the positive electrodes ZP3 and ZP4, a differential capacitance will be generated, thereby detecting the acceleration in the Z direction. The third elastic element 133 will also deform, and the third movable mass 123 will rotate around the Y-axis. Its main motion form is that the third movable mass 123 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.

[0017] Two masses are provided, and the center of gravity position of the third movable mass 123 is opposite to that of the second movable mass 122, which can cancel out the systematic error caused by the anchor tilt. The schematic diagram of the above setting is as Figure 6 shown. The left side is the case of a single mass, and the right side is the case of a double mass. The double mass can be a symmetric or asymmetric structure. The upper part is the case of being subjected to acceleration in the Z direction, and the lower part is the case of anchor offset. It can be seen that when subjected to acceleration in the Z direction, for a single mass, the tilting situation reflects the acceleration situation; for a double mass, by arranging the first Z electrode and the second Z electrode to cross on both sides of the anchor, when the metal electrode corresponding to the second movable mass 122 is the positive electrode of the differential capacitance on one side, the metal electrode corresponding to the third movable mass 123 on the same side is the negative electrode of the differential capacitance. Therefore, through the reverse setting of the capacitance, the contributions of the two masses with opposite offsets to the capacitance value are the same. When the anchor is offset, for the left case, the anchor tilt directly causes a change in the capacitance value, resulting in a zero offset of the accelerometer, and it is impossible to distinguish whether the mass tilt is caused by stress causing the anchor tilt or acceleration; for the right case, since the first Z electrode and the second Z electrode are arranged to cross on both sides of the anchor, when the metal electrode corresponding to the second movable mass 122 is the positive electrode of the differential capacitance on one side, the metal electrode corresponding to the third movable mass 123 on the same side is the negative electrode of the differential capacitance. Therefore, the contributions of the two substrates with the same tilting direction to the capacitance are opposite. The differential capacitance generated between the second movable mass 122 and the first Z electrode and the differential capacitance generated between the third movable mass 123 and the second Z electrode are in the same direction, and finally the total differential capacitance cancels each other out to 0, thereby eliminating the influence of external stress on acceleration detection. Further, setting the above two masses to have the same moment about the anchor can better accurately zero the differential capacitance.

[0018] Setting multiple anchors, such as the four anchors distributed at the four corners of a rectangle in the above specific embodiment, can cancel out the systematic error caused by the anchor tilt. The schematic diagram of the above setting is as Figure 7As shown. For the case of an anchor point, when the anchor point tilts, it will cause the tilt of the mass block. However, when there are two anchor points at two distances in the corresponding tilt direction, the influence caused by the tilt of the mass block can be greatly reduced. Since the above situation may occur in both the X and Y directions, two anchor points should be provided corresponding to both the X and Y directions, that is, the four anchor points distributed at the four corners of the 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 in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A three-axis acceleration sensor, comprising a substrate and 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, and the plane where they are located is the XY plane, and the direction perpendicular to the XY plane is the Z direction; characterized in that, The sensor further includes: A first movable mass block, connected to the anchor point through a first elastic element, where the first elastic element is a bidirectional elastic element in the X and Y directions and is connected to the beam; A second movable mass block, connected to the first movable mass block through a second elastic element, where 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; and A third movable mass block, connected to the first movable mass block through a third elastic element, where the third elastic element is a rotating arm with the Y-axis as the rotation axis, enabling the third movable mass block to rotate around the XZ plane; The centers of gravity of the second and third movable mass blocks are respectively located on both sides of the anchor point in the Y-axis direction, and the torques relative to the anchor point are the same; It further includes: 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 second 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 third movable mass block, forming at least one differential capacitance pair; The first Z electrodes and the second Z electrodes are arranged crosswise on both sides of the anchor point. When the metal electrode corresponding to the second movable mass block on one side is the positive electrode of the differential capacitance, the metal electrode corresponding to the third movable mass block on the same side is the negative electrode of the differential capacitance.

2. The triaxial acceleration sensor according to claim 1, wherein There are four 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 and Y directions is a right-angle folding spring.

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