Inertial actuator with multiple flexure stacks

• US 7,288,861 B1
• Filed: 10/19/2004
• Issued: 10/30/2007
• Est. Priority Date: 03/06/2004
• Status: Active Grant

• Current Assignee: Motran Industries Inc.
• Original Assignee: Motran Industries Inc.
• Inventors: Pusl, Kenneth E., Van Namen, Frederick T., Willard, Charles L.
• Primary Examiner(s): TAMAI, KARL I
• Application Number:
  US10/967,771
• Time in Patent Office: 1,106 Days
• Field of Search: 310/36, 310/14, 310/15, 188/378, 188/379, 248/550, 267/140.14, 267/140.15, 335/220
• US Class Current: 310/15
• CPC Class Codes: H02K 41/0356 moving along a straight path

Abstract

An inertial actuator for active vibration control utilizes a single cylindrical actuator module of the “voice coil” type. A moving armature assembly, including a soft iron shell with a tubular sleeve coaxially surrounding a core with two permanent magnets and corresponding pole plates, is suspended compliantly by a flexure assembly including a multiple-stack array of shaped flexure strips and a pair of end support flexure plates mounted to a base. Two magnetically charged annular air gaps at the pole plates in the moving armature traverse two corresponding annular coils wound in a tubular bobbin that extends as a heat-sinking mounting column attached to the base. This form of inertial actuator provides cost benefits along with improved performance and reliability due to the stability of the moving parts and uniformity of linear motion.

Claims

1. An inertial actuator for converting electrical energy into mechanical vibration for active control of unwanted vibration in a host apparatus, comprising:

a fixed base mass portion comprising (1) a generally tubular coil bobbin, (2) a primary annular electrical coil wound on said coil bobbin, and (3) a generally horizontal base, supporting said coil bobbin, made and arranged to be firmly attached to a selected region of the host apparatus for deployment therewith;

a moving armature mass portion closely surrounding said primary coil coaxially, made and arranged to produce a primary annular magnetically-charged air gap with magnetic flux path lines of force traversing said primary coil radially, such that, in accordance with rules of physics, an electrical current in said primary coil will produce a force that urges said primary coil to move in an axial direction; and

a flexure structure comprising a plurality of stacks of compliant flexure strips supporting said armature mass portion from the base in a compliant manner such as to allow driven travel of the armature mass portion relative to the base mass portion in an axial direction only, while constraining said armature mass portion against radial displacement, thus enabling said armature mass portion to be vibrated axially, at a resonant frequency determined by mass of the armature mass portion and compliance of the flexure structure, in response to alternating electrical current applied to said primary coil;

a secondary annular electrical coil wound on said coil bobbin, disposed axially displaced from said primary coil toward said base;

a secondary cylindrical permanent magnet, surrounded by said coil bobbin, magnetized to have opposite magnetic poles at first and second flat end thereof, attached coaxially to the primary soft iron circular pole piece at a flat end selected so as to locate two like magnetic poles interfacing opposite sides of the primary soft iron circular pole piece;

a secondary circular soft iron pole plate whose periphery, interfacing an inner wall of the shell, creates a secondary annular magnetically-charged air gap traversing a central region of the secondary coil;

the secondary coil receiving alternating current of amplitude and phase polarity such as to interact with said primary coil in an additive manner so as to further drive said armature mass portion in vibrational travel;

said tubular coil bobbin being configured with an integral tubular portion constituting a support column extending from secondary annular electrical coil to an end configured with an inwardly extending flange by which said tubular coil bobbin is attached to said base in a manner to constitute a heat sink for said coils;

said moving armature mass portion comprising (1) a soft iron shell configured with (1A) a tubular sleeve portion disposed coaxially around the coil bobbin and (1B) a yoke plate attached to the tubular sleeve portion at an end opposite the base; and

(2) a magnetic core having (2A) a primary cylindrical permanent magnet, surrounded coaxially by the coil bobbin, magnetized to have opposite magnetic poles at first and second flat ends thereof, the first flat end being attached coaxially to the yoke plate, (2B) a primary circular soft iron pole plate having a flat surface attached coaxially to the second flat end of said primary permanent magnet, and having a periphery interfacing an inner wall of the shell sleeve in a manner to create the primary annular magnetically-charged air gap traversing said primary coil, (2C) a secondary cylindrical permanent magnet, surrounded coaxially by the coil bobbin, magnetized to have opposite magnetic poles at first and second flat ends thereof, the first flat end being attached coaxially to the primary pole plate; and

(2D) a secondary circular-soft iron pole plate having a flat surface attached coaxially to the second flat end of said secondary permanent magnet, and having a periphery interfacing an inner wall of the shell sleeve in a manner to create the secondary annular magnetically-charged air gap traversing said secondary coil;

said flexure structure comprising (1) a flexure stack array comprising a plurality of stacks of flexure strips disposed uniformly side by side, each stack comprising a plurality of flexure strips each having first and second ends and a central region attached to said armature mass portion via the yoke plate, and (2) a pair of end support flexure members, each comprising at least one flexure plate, disposed at corresponding opposite ends of said stack array, each having a first end attached perpendicularly to corresponding end of said stack array and a second end attached to a corresponding end of said base, made and arranged to support said stack array to said base in a manner to accommodate variations in length of said stack array due to vibrational displacement of the central region thereof;

the flexure strips in said stack array being symmetrically shaped laterally and longitudinally to have a common designated maximum width at both ends and in the mid-region and to have a common reduced width in two opposite intermediate regions between the ends and the mid-region so as to provide desired compliance and optimal stress distribution; and

wherein the plurality of stacks of compliant flexure strips in the flexure stack array of said flexure structure comprises a designated quantity of like side-by-side stacks of flexure strips in a range from 3 to 7, each of said stacks comprising a designated quantity of the flexure strips in a range between 5 and 60.

2. The inertial actuator as defined in claim 1 wherein the flexure stack array comprises five like side-by-side stacks of flexure strips.