# US 5,350,189 A · Capacitance type accelerometer for air bag system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,350,189 A - Document ID: US5350189A - Status: Granted - Kind: A - Application number: 07/918,021 - Filed: 1992-07-24 - Granted: 1994-09-27 - Earliest claimed: 1991-07-24 - Assignees: Hitachi, Ltd. - Inventors: Shigeki Tsuchitani; Seiko Suzuki; Masayuki Miki; Masahiro Matsumoto - Web page: https://patentgrep.com/patent/US5350189A ## CPC - G01P 1/003: {used for damping} - G01P 15/125: by capacitive pick-up - G01P 2015/0828: {the mass being of the paddle type being suspended at one of its longitudinal ends} - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) ## Abstract In a capacitance type accelerometer used for an air bag system etc., a plurality of grooves crossing each other are provided on the surface of a movable electrode which is arranged to face a fixed electrode at a portion having a gap thereinbetween, and end portions of each groove open to an outside space at the portion between the movable electrode and the fixed electrode. The grooves can be provided on surface of the fixed electrodes. Ventilation between inside and outside of the facing portion is improved by opening of the grooves to outside space, and air damping which is caused at operation of the movable electrode at the gap between the electrodes is reduced, and, consequently, response speed of the movable electrode is increased. ## Claims ### Claim 1 A capacitance-accelerometer, comprising: a fixed electrode; and a movable electrode being supported by a cantilever at a portion adjacent to said fixed electrode having a gap thereinbetween; wherein grooves for reducing air damping are provided on a surface of said movable electrode, and said grooves are so arranged that electrode surface areas divided by said grooves are symmetrical with respect to a symmetrical axis parallel to said cantilever. ### Claim 2 (depends on 1) A capacitance type accelerometer as claimed in claim 1, wherein said fixed electrode is arranged so as to respectively face both surfaces of said movable electrode, and said grooves are formed on both surfaces of said movable electrode. ### Claim 3 A capacitance-accelerometer, comprising: a fixed electrode; and a movable electrode being supported by a cantilever at a portion adjacent to said fixed electrode having a gap thereinbetween; wherein grooves having openings which are disposed of at at least one side of said electrodes and are inter-connected with each other, are provided on a surface of said movable electrode, and said grooves are so arranged that electrode surface areas divided by said grooves are symmetrical with respect to a symmetrical axis parallel to said cantilever. ### Claim 4 (depends on 3) A capacitance type accelerometer as claimed in claim 3, wherein said fixed electrode is arranged so as to respectively face both surfaces of said movable electrode, and said grooves are formed on both surfaces of said movable electrode. ### Claim 5 (depends on 2, 4) A capacitance type accelerometer as claimed in either of claims 2 and 4, wherein said grooves are symmetrically formed on both surfaces of said movable electrode. ### Claim 6 A capacitance-accelerometer comprising: a fixed electrode; and a movable electrode being supported by an elastic body and facing said fixed electrode at a portion having a gap thereinbetween; wherein grooves are provided on a surface of said movable electrode to divide said surface into a plurality of electrode surface areas, said grooves are so arranged that said plurality of electrode surface areas divided by said grooves are uniformly balanced, and end portions of said grooves open to four sides of said movable electrode. ### Claim 7 A capacitance-accelerometer, comprising: a movable electrode being supported by an elastic body; and fixed electrodes, said movable electrode being disposed thereinbetween said fixed electrodes and said fixed electrodes facing respective surfaces of said movable electrode at a portion having a gap thereinbetween; wherein a plurality of grooves crossing each other on the surface of said movable electrode, end portions of said grooves open to an outside portion at the portion between said fixed electrodes and said movable electrode through openings, and through-holes leading to both surfaces of said movable electrode are formed at crossing points of said grooves. ### Claim 8 (depends on 1, 2, 3, 4, 5, 6, 7) A capacitance type accelerometer as claimed in any of claims 1, 3, 5, 6, 7, 2 and 4, wherein the movable electrode, either of the cantilever or the elastic body for supporting said movable electrode, and grooves or grooves and through-holes on the movable electrode are formed by anisotropic etching of a silicon substrate. ### Claim 9 (depends on 1, 2, 3, 4, 5, 6, 7) A capacitance type accelerometer as claimed in any of claims 1, 3, 5, 6, 7, 2 and 4, wherein said fixed electrodes are formed on a glass substrate, furthermore, the movable electrode, either of the cantilever or the elastic body for supporting said movable electrode, and grooves or grooves and through-holes on said movable electrode are formed by anisotropic etching of a silicon substrate, and said substrates are adhered by anodic bonding. ### Claim 10 (depends on 1, 2, 3, 4, 5, 6, 7) A capacitance type accelerometer as claimed in any of claims 1, 3, 5, 6, 7, 2 and 4, wherein said fixed electrodes are formed on glass of a silicon/glass laminated substrate, furthermore, the movable electrode, either of the cantilever or the elastic body for supporting said movable electrode, and grooves or grooves and through-holes on said movable electrode are formed by anisotropic etching of a silicon substrate, and said substrates are adhered by anodic bonding. ### Claim 11 (depends on 1, 2, 3, 4, 5, 6, 7) A capacitance type accelerometer as claimed in any of claims 1, 3, 5, 6, 7, 2 and 4, wherein said fixed electrodes are formed on glass of a silicon/glass laminated substrate, furthermore, the movable electrode, either of the cantilever or the elastic body for supporting said movable electrode, and grooves or grooves and through-holes on said movable electrode are formed by anisotropic etching of a silicon substrate, and said substrates are adhered by silicon oxide therebetween.