Shock resistant accelerometer for implantable medical device

• US 5,885,471 A
• Filed: 07/31/1997
• Issued: 03/23/1999
• Est. Priority Date: 03/08/1995
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Messer, Ronald F., O'Gara, Joan A., Inman, Roy, Larson, Larry R., Molinari, Louis A., Ruben, David A., Henschel, Mark E.
• Primary Examiner(s): POWELL, WILLIAM A
• Application Number:
  US08/904,142
• Time in Patent Office: 600 Days
• Field of Search: 216/2, 216/33, 216/52, 607/19, 607/17, 607/18, 607/20-26, 128/782, 128/419 PG, 73/514.33, 73/517 R
• US Class Current: 216/33
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration
• CPC Class Codes: B81B 3/0051 For defining the movement, i.e. structures that guide or limit the movement of an element mechanical arrangements for preventing or damping vibration or shock H01H3/60
• CPC Class Codes: G01P 1/02 Housings
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

The present invention relates to accelerometer assemblies for implantable medical devices such as pacemakers, IPGs, PCDs, defibrillators, ICDs and the like. The accelerometer assembly of the present invention comprises a beam that deflects in response to being subjected to an externally provided force. Deflection of the beam generates a voltage in a piezoelectric material disposed in the assembly. At least one stop is provided to limit the vertical range of motion through which the beam may deflect to prevent failure, fracturing or breakage of the beam resulting from excessive deflection of the beam that might otherwise occur were the stop not present.

Claims

1. An implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient'"'"'s level of activity, and control means responsive to the accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising:

at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface;

a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;

at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and

at least one stop disposed at a location above or below the second end of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam.

2. The stimulator of claim 1, wherein the sheet assumes a generally rectangular structural configuration.

3. The stimulator of claim 1, wherein the sheet has first and second generally parallel cuts disposed through the sheet, each cut extending in a longitudinal direction from the second end towards the first end and defining an edge of the beam.

4. The stimulator of claim 1, wherein the stop forms a rail disposed on at least one of the upper surface and the lower surface, respectively, of the upper housing member and the lower housing member, the stop further being disposed in a direction parallel to the imaginary longitudinal axis.

5. The stimulator of claim 4, wherein the rail is centrally disposed along the upper surface or the lower surface, respectively, of the upper or lower housing members.

6. The stimulator of claim 4, wherein the rail is a wide rail.

7. The stimulator of claim 1, wherein the stop forms a post or protrusion protruding from and disposed on one of the upper surface and the lower surface, respectively, of the upper housing member and the lower housing member.

8. The stimulator of claim 1, wherein the stop forms a rail disposed on at least one of the upper surface and the lower surface, respectively, of the upper housing member and the lower housing member, the stop further being disposed in a direction perpendicular to the imaginary longitudinal axis.

9. The stimulator of claim 1, wherein the stop forms a T-shaped rail disposed on at least one of the upper surface and the lower surface, respectively, of the upper housing member and the lower housing member.

10. The stimulator of claim 1, wherein the stop forms a dab or blob of silicone disposed on at least one of the upper surface and the lower surface, respectively, of the upper housing member and the lower housing member.

11. The stimulator of claim 1, wherein the upper and lower members are formed of a material selected from the group consisting of a nickel-cobalt-iron alloy, copper, brass, aluminum, nickel, a noble metal, a carbon composite, a ceramic composition and a plastic.

12. The stimulator of claim 1, wherein the upper and lower members are plated with an electrically conductive metal or alloy.

13. The stimulator of claim 1, wherein the sheet of piezoelectric material is formed from at least one of lead zirconate titanate, quartz, lithium niobate, and lithium titanate.

14. The stimulator of claim 1, wherein the upper or lower housing members are attached to sheet of piezoelectric material by at least one of electrically conductive thermoplastic, epoxy and glue.

15. An implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient'"'"'s level of activity, and control means responsive to said accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising:

at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface;

a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;

at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and

at least one stop disposed on at least one of the upper surface of the beam and the lower surface of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam.

16. The stimulator of claim 15, wherein the stop is formed of foam tape.

17. An implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient'"'"'s level of activity, and control means responsive to said accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising:

at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface, the downwardly facing bottom surface and upwardly facing top surface defining at least portions of an internal cavity;

a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;

at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and

a stop comprising a visco-elastic damping fluid or gel disposed within the internal cavity, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam.

18. The stimulator of claim 17, wherein the accelerometer assembly further comprises front and rear ends and correspondingly configured front and rear covers disposed on and in sealing engagement with the front and rear ends, the front and rear covers retaining the damping fluid or gel within the internal cavity.

19. A method of making an implantable stimulator comprising a pulse generator, an accelerometer assembly mounted within the stimulator for providing a signal indicative of a patient'"'"'s level of activity, and control means responsive to the accelerometer signal for controlling operation of said pulse generator, the accelerometer assembly comprising at least one of an upper housing member and a lower housing member, the upper member having at least one downwardly facing bottom surface, the lower member having at least one upwardly facing top surface;

a sheet of piezoelectric material disposed generally within an imaginary plane defined by two major substantially horizontal orthogonal axes, the sheet having upper and lower surfaces, the sheet having formed therein a beam disposed along an imaginary longitudinal axis extending between the first and second ends, laterally extending outer members being formed in the sheet and adjacent at least the first end, the second end of the beam being deflectable along an imaginary vertical axis oriented substantially perpendicular to the plane;

at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet being attached to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and at least one stop disposed at a location above or below the second end of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure, breakage or fracturing of the beam, the method comprising the steps of;

(a) providing at least one of the upper housing member and the lower housing member;

(b) providing the sheet of piezoelectric material;

(c) forming the beam by cutting first and second notches in the sheet, the notches defining the lateral edges of the beam separating the beam from the laterally extending outer members;

(d) attaching at least portions of the lower or upper surfaces of the first end of the sheet and optionally at least portions of the upper or lower surfaces of the laterally extending outer members of the sheet to at least one of the upper surface of the lower housing member and the lower surface of the upper housing member, and

(e) providing at least one stop at a location above or below the second end of the beam, the stop limiting the vertical range of motion through which the beam may deflect along the imaginary vertical axis to prevent failure or fracturing of the beam.