ACCELERATION SENSOR

• US 20120227494A1
• Filed: 11/23/2010
• Published: 09/13/2012
• Est. Priority Date: 11/24/2009
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Management Co., Ltd. (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Ibara, Nobuyuki, Ueda, Hideki, Okada, Takeshi, Mori, Takeshi, Suzuki, Yuji, Yosida, Hitoshi, Nomura, Masatosi, Kakimoto, Katumi
• Granted Patent: US 9,261,530 B2
• Time in Patent Office: Days
• US Class Current: 73/514.32
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

An acceleration sensor includes a weight portion having a recess section and a solid section, beam portions, a movable electrode provided on the opposite surface of the weight portion from an open surface of the recess section to extend over the recess section and the solid section, a first fixed electrode arranged at the opposite side of the movable electrode from the recess section, and a second fixed electrode arranged at the opposite side of the movable electrode from the solid section. The acceleration sensor detects acceleration using a change in capacitance between the movable electrode and the fixed electrodes caused by rotation of the weight portion. The beam portions are shifted toward the recess section such that an angle between a perpendicular line extending from a gravity center position of the weight portion to the rotation axis and a surface of the movable electrode becomes equal to 45 degrees.

Claims

1. An acceleration sensor, comprising:

a sensor unit including a weight portion having a recess section with one open surface and a solid section one-piece formed with the recess section, a pair of beam portions configured to rotatably support the weight portion in such a state that the recess section and the solid section are arranged along a rotation direction, a movable electrode provided on the opposite surface of the weight portion from the open surface of the recess section to extend over the recess section and the solid section, a first fixed electrode arranged at the opposite side of the movable electrode from the recess section and a second fixed electrode arranged at the opposite side of the movable electrode from the solid section, the acceleration sensor being configured to detect acceleration based on a change in capacitance between the movable electrode and the fixed electrodes caused by rotation of the weight portion about a rotation axis defined by a straight line interconnecting the beam portions,

wherein the beam portions are shifted toward the recess section such that an angle between a perpendicular line extending from a gravity center position of the weight portion to the rotation axis and a surface of the movable electrode becomes substantially equal to 45 degrees.

2. The acceleration sensor of claim 1, wherein a separate recess section with one open surface is provided in the solid section and an auxiliary weight portion made of a metallic material is embedded in the separate recess section.

3. The acceleration sensor of claim 2, wherein the auxiliary weight portion is made of a metallic material higher in specific gravity than a constituent material of the weight portion.

4. The acceleration sensor of claim 2, wherein the auxiliary weight portion has a weight substantially equal to a weight of a structural body making up an outer wall of the recess section.

5. The acceleration sensor of claim 1, wherein acceleration applied to the weight portion in a first direction and acceleration applied to the weight portion in a second direction orthogonal to the first direction are detected.

6. The acceleration sensor of claim 1, wherein the sensor unit includes a plurality of sensor units formed in a single chip.

7. The acceleration sensor of claim 6, wherein the sensor unit includes two sensor units formed in the single chip, one of the two sensor units rotated 180 degrees on a single plane with respect to the other sensor unit.

8. The acceleration sensor of claim 7, wherein the two sensor units are arranged adjacent to each other.

9. The acceleration sensor of claim 1, wherein the sensor unit includes a frame portion surrounding the weight portion and a pair of detection electrodes formed in the frame portion and electrically connected to the fixed electrodes and wherein gaps are provided between the detection electrodes, between the detection electrodes and the frame portion and between the detection electrodes and the weight portion.

10. The acceleration sensor of claim 1, wherein protrusions are formed on the surfaces of the fixed electrodes facing the movable electrode or on the surface of the movable electrode facing the fixed electrodes.

11. The acceleration sensor of claim 10, wherein the protrusions are formed of a silicon film or a silicon oxide film.

12. The acceleration sensor of claim 10, wherein the protrusions have surface layers made of a carbon material.

13. The acceleration sensor of claim 1, further comprising:

a fixed plate arranged in a spaced-apart relationship with the opposite surface of the weight portion from the fixed electrodes, the fixed plate including an adherence-preventing film for preventing the weight portion from adhering to the fixed plate, the adherence-preventing film formed on the surface of the fixed plate facing the weight portion.

14. The acceleration sensor of claim 13, wherein the adherence-preventing film is made of the same material as the fixed electrodes.

15. The acceleration sensor of claim 13, wherein the change in capacitance between the first and second fixed electrodes and the movable electrode is detected by generating an attraction force between the fixed electrodes and the movable electrode.

16. An acceleration sensor, comprising:

a sensor unit including a weight portion having a recess section with one open surface and a solid section one-piece formed with the recess section, a pair of beam portions configured to rotatably support the weight portion in such a state that the recess section and the solid section are arranged along a rotation direction, a movable electrode provided on the opposite surface of the weight portion from the open surface of the recess section to extend over the recess section and the solid section, a first fixed electrode arranged at the opposite side of the movable electrode from the recess section and a second fixed electrode arranged at the opposite side of the movable electrode from the solid section, the acceleration sensor being configured to detect acceleration based on a change in capacitance between the movable electrode and the fixed electrodes caused by rotation of the weight portion about a rotation axis defined by a straight line interconnecting the beam portions; and

a first fixed plate arranged in a spaced-apart relationship with the surface of the weight portion facing the fixed electrodes, the fixed electrodes provided on one surface of the first fixed plate,

wherein protrusions are formed on the surface of the movable electrode facing the fixed electrodes and wherein engraving sections are formed in the areas of the fixed electrodes facing the protrusions by digging out one surface of the first fixed plate.

17. The acceleration sensor of claim 16, wherein surface irregularities are provided in the areas of the first fixed plate corresponding to the engraving sections.

18. The acceleration sensor of claim 16, wherein a thin film made of a material higher in hardness than a constituent material of the protrusions is provided on a surface of each of the protrusions.

19. The acceleration sensor of claim 16, further comprising:

a second fixed plate arranged in a spaced-apart relationship with the opposite surface of the weight portion from the fixed electrodes, the second fixed plate including an adherence-preventing film for preventing the weight portion from adhering to the second fixed plate, the adherence-preventing film formed on the surface of the second fixed plate facing the weight portion.

20. The acceleration sensor of claim 16, wherein the sensor unit includes a frame portion surrounding the weight portion and a pair of detection electrodes formed in the frame portion and electrically connected to the fixed electrodes and wherein gaps are provided between the detection electrodes, between the detection electrodes and the frame portion and between the detection electrodes and the weight portion.

21. An acceleration sensor, comprising:

a sensor unit including a weight portion having a recess section with one open surface and a solid section one-piece formed with the recess section, a pair of beam portions configured to rotatably support the weight portion in such a state that the recess section and the solid section are arranged along a rotation direction, a movable electrode provided on the opposite surface of the weight portion from the open surface of the recess section to extend over the recess section and the solid section, a first fixed electrode arranged at the opposite side of the movable electrode from the first recess section and a second fixed electrode arranged at the opposite side of the movable electrode from the solid section, the acceleration sensor being configured to detect acceleration based on a change in capacitance between the movable electrode and the fixed electrodes caused by rotation of the weight portion about a rotation axis defined by a straight line interconnecting the beam portions,

wherein protrusions are formed on the surfaces of the fixed electrodes facing the movable electrode.

22. An acceleration sensor, comprising:

a sensor unit including a weight portion having a recess section with one open surface and a solid section one-piece formed with the recess section, a pair of beam portions configured to rotatably support the weight portion in such a state that the recess section and the solid section are arranged along a rotation direction, a movable electrode provided on the opposite surface of the weight portion from the open surface of the recess section to extend over the recess section and the solid section, a first fixed electrode arranged at the opposite side of the movable electrode from the recess section, a second fixed electrode arranged at the opposite side of the movable electrode from the solid section and a pair of electrode portions having detection electrodes electrically connected to the fixed electrodes, the acceleration sensor being configured to detect acceleration based on a change in capacitance between the movable electrode and the fixed electrodes caused by rotation of the weight portion about a rotation axis defined by a straight line interconnecting the beam portions,

wherein the sensor unit includes two sensor units formed in a single chip, the electrode portions are arranged along one direction to divide the chip into two halves, the weight portions of the two sensor units are arranged in point symmetry with respect to a center of an array of the electrode portions, and the beam portions are arranged such that a straight line interconnecting the beam portions extends in a direction orthogonal to the arranging direction of the electrode portions.

23. The acceleration sensor of claim 22, further comprising:

a fixed plate arranged in a spaced-apart relationship with the opposite surface of the weight portion from the fixed electrodes, the fixed plate including an adherence-preventing film for preventing the weight portion from adhering to the fixed plate, the adherence-preventing film formed on the surface of the fixed plate facing the weight portion.

24. The acceleration sensor of claim 23, wherein the adherence-preventing film is made of the same material as the fixed electrodes.