Accelerometer with a cantilever beam formed as part of the housing structure

• US 5,627,315 A
• Filed: 04/18/1995
• Issued: 05/06/1997
• Est. Priority Date: 04/18/1995
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Figi, Bruce B., Giuffre, Thomas R.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Kwok, Helen C.
• Application Number:
  US08/423,196
• Time in Patent Office: 749 Days
• Field of Search: 73/514.31, 73/DIG. 3, 73/514.16, 324/207.26, 324/207.21, 324/162
• US Class Current: 73/514.31
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/105 by magnetically sensitive devices
• CPC Class Codes: G01P 2015/0817 for pivoting movement of the mass, e.g. in-plane pendulum
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

An accelerometer is provided in which a magnet structure is encapsulated within a distal end of a cantilever beam that is formed as an integral part of a housing structure. The cantilever beam, the distal end and the housing structure are formed of a nonmagnetic material, such as plastic, during a single injection molding procedure. The magnetic structure within the distal end of the cantilever beam can comprise two magnets associated with a pole piece and disposed within an opening formed in a nonmagnetic bracket. Although many types of magnet structures are possible within the scope of the present invention, a particularly preferred magnet structure comprises two magnets that are arranged in opposite polarity with the opposite poles of the two magnets being located adjacent to each other on opposite sides of a centerline. The magnet structure can be held in place during the injection molding process by the magnetic attraction between the magnet structure and a ferromagnetic portion of the mold. The magnetically sensitive component, which is held in place within a wall of the housing structure, can be a Hall effect element.

Claims

1. An accelerometer comprising:

a housing structure having a cavity formed therein;

a cantilever beam extending inwardly into said cavity from a first wall of said housing structure;

a magnet structure attached to a distal end of said cantilever beam, said distal end being movable along a first path in response to flexure of said cantilever beam; and

a magnetically sensitive component attached to a second wall of said housing structure, said magnetically sensitive component being displaced from said magnet structure by a preselected distance, said magnetically sensitive component having an output signal which is representative of the position of said magnet structure relative to said magnetically sensitive component, said housing structure and said cantilever beam being formed as parts of a single unitary plastic structure which is produced by a single injection molding process.

2. The accelerometer of claim 1, wherein:

said magnet structure comprises two permanent magnets.

3. The accelerometer of claim 2, wherein:

said two permanent magnets are disposed within a nonmagnetic bracket.

4. The accelerometer of claim 3 wherein:

said nonmagnetic bracket is encapsulated within said distal end of said cantilever beam.

5. The accelerometer of claim 4, wherein:

said magnet structure comprises a ferromagnetic pole piece disposed in magnetic flux conducting association with said two permanent magnets.

6. The accelerometer of claim 5, wherein:

means for locating first and second permanent magnets of said two permanent magnets at first and second positions, respectively, which are equally spaced on opposite sides of a centerline, said centerline being disposed at a preselected position relative to said magnetically sensitive component.

7. The accelerometer of claim 6, wherein:

said bracket is made of brass.

8. The accelerometer of claim 7, further comprising:

a lid structure attached to said housing structure.

9. The accelerometer of claim 8, wherein:

said magnetically sensitive component comprises a Hall effect element.

10. An accelerometer comprising:

a housing structure having a cavity formed therein;

a cantilever beam extending inwardly into said cavity from a first wall of said housing structure, said housing structure and said cantilever beam being formed as parts of a unitary structure;

a magnet structure attached to a distal end of said cantilever beam, said distal end being movable along a first path in response to flexure of said cantilever beam;

a magnetically sensitive component attached to a second wall of said housing structure, said magnetically sensitive component being displaced from said magnet structure by a preselected distance, said magnetically sensitive component having an output signal which is representative of the position of said magnet structure relative to said magnetically sensitive component, said magnet structure comprising two permanent magnets, said two permanent magnets being disposed within a nonmagnetic bracket, said nonmagnetic bracket being encapsulated within said distal end of said cantilever beam, said magnet structure comprising a ferromagnetic pole piece disposed in magnetic flux conducting association with said two permanent magnets;

means for locating first and second permanent magnets of said two permanent magnets at first and second positions, respectively, which are equally spaced on opposite sides of a centerline, said centerline being disposed at a preselected position relative to said magnetically sensitive component, said bracket being made of brass and said housing structure and said cantilever beam being made of plastic, said housing structure and said cantilever beam being formed as parts of a single plastic structure which is produced by a single injection molding process; and

a lid structure attached to said housing structure, said magnetically sensitive component comprising a Hall effect element.