SEMI-FLEXIBLE PROOF-MASS

• US 20170082519A1
• Filed: 09/12/2016
• Published: 03/23/2017
• Est. Priority Date: 09/22/2015
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Blomqvist, Anssi, RYTK?NEN, Ville-Pekka, LIUKKU, Matii
• Granted Patent: US 10,190,938 B2
• Time in Patent Office: Days
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 3/001 Structures having a reduced contact area, e.g. with bumps or with a textured surface
• CPC Class Codes: B81B 3/0013 Structures dimensioned for mechanical prevention of stiction, e.g. spring with increased stiffness
• CPC Class Codes: B81B 7/0016 Protection against shocks or vibrations, e.g. vibration damping
• CPC Class Codes: B81C 1/00968 Methods for breaking the stiction bond
• CPC Class Codes: G01M 7/08 Shock-testing
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 2015/0874 using means for preventing stiction of the seismic mass to the substrate

Abstract

A microelectromechanical device includes a semi-flexible proof-mass comprising a primary part, a secondary part and a stiff spring suspending the primary part and the secondary part. The spring causes the parts to move as a single entity when the device is in its normal range. A first stopper structure stops the primary part. The proof-mass is configured to deform through deflection of the spring, when the device is subjected to a shock having a force that is beyond the normal operation range. While the shock causes motion of the proof-mass in one direction along an axis of movement, the spring is configured to cause a restoring force causing the secondary part of the proof-mass to be driven into a restoring motion in a direction opposite to motion along an axis caused by the shock. Momentum of the secondary part causes the primary part to dislodge from the first stopper structure.

Claims

1. A microelectromechanical device, comprising:

a substantially planar semi-flexible proof-mass comprising at least one primary part and at least one secondary part, and at least one stiff spring coupling the at least one primary part and the at least one secondary part of the semi-flexible proof-mass, the at least one stiff spring substantially causing the at least one primary part and the at least one secondary part to move as a single, rigid entity when the device is in a normal operation range;

at least one main spring coupled to the at least one secondary part, the main spring coupling the semi-flexible proof-mass to a suspension structure; and

at least one first stopper structure configured to stop the at least one primary part,

wherein the semi-flexible proof-mass is configured to deform through deflection of the at least one stiff spring, when the device is subjected to a shock that impacts the device with a force that is beyond the normal operation range of the device, the shock causing a motion of the semi-flexible proof-mass at least in a direction along an axis of movement, and

wherein the at least one stiff spring further causes a restoring force causing the at least one secondary part of the semi-flexible proof-mass to be driven into a restoring motion in a direction opposite to the motion along the axis of movement caused by the shock, wherein momentum of the at least one secondary part in the restoring motion further causes the at least one primary part to dislodge from the at least one first stopper structure.

2. The microelectromechanical device according to claim 1, wherein

at least one of the at least one primary part of the semi-flexible proof-mass is configured to be stopped by the first stopper structure, when displacement of the semi-flexible proof-mass along the axis of movement due to the shock exceeds a first distance.

3. The microelectromechanical device according to claim 1, further comprising:

at least two first stopper structures disposed on opposite sides of the semi-flexible proof-mass along the axis of movement, wherein the at least two first stopper structures are configured to stop motion of the semi-flexible proof-mass caused by shocks occurring in opposite directions along the axis of movement.

4. The microelectromechanical device according to claim 1, where the at least one secondary part of the semi-flexible proof-mass is configured to continue movement caused by the shock along the axis of movement after the at least one primary part has been stopped, and wherein the continued movement along the axis of movement caused by the shock causes deflection of at least one of the stiff springs, thus deforming the semi-flexible proof-mass.

5. The microelectromechanical device according to claim 1, further comprising:

at least one second stopper structure configured to stop the at least one secondary part,

wherein the at least one secondary part of the semi-flexible proof-mass is configured to be stopped by the second stopper structure, when displacement of the secondary part of the semi-flexible proof-mass along the axis of movement due to the shock exceeds a second distance, wherein the second distance is greater than the first distance.

6. The microelectromechanical device according to claim 5, further comprising:

at least two second stopper structures disposed on opposite sides of the semi-flexible proof-mass along the axis of movement, wherein the at least two second stopper structures are configured to stop motion of the semi-flexible proof-mass caused by shocks occurring in opposite directions along the axis of movement.

7. The microelectromechanical device according to claim 1, wherein the semi-flexible proof-mass is configured to have more than one axes of movement, and the semi-flexible proof-mass is configured to deform in a direction of at least one of the axes of movement.

8. The microelectromechanical device according to claim 1, wherein the semi-flexible proof-mass comprises:

a primary part comprising an essentially rigid, rectangular frame, disposed symmetrically across a symmetry axis of the semi-flexible proof-mass, wherein the symmetry axis is aligned with the direction of the axis of movement; and

two secondary parts each disposed symmetrically across the symmetry axis in an enclosure within the primary part,

wherein each of the secondary parts is coupled to the primary part with two stiff springs placed symmetrically with respect to the symmetry axis of the semi-flexible proof-mass.

9. The microelectromechanical device according to claim 8, wherein fingers of a moving comb electrode are attached to the primary part.

10. The microelectromechanical device according to claim 8, wherein

the primary part carries more than a half of the entire mass of the semi-flexible proof-mass.

11. The microelectromechanical device according to claim 1, wherein the semi-flexible proof-mass comprises:

a secondary part formed as an essentially rigid, rectangular frame disposed symmetrically across a symmetry axis of the semi-flexible proof-mass, the symmetry axis aligned with the direction of the axis of movement,

two primary parts disposed outside the area of the secondary part and disposed symmetrically across the symmetry axis,

wherein each of the two primary parts is coupled to the secondary part with two stiff springs placed in symmetrically with respect to the symmetry axis.

12. The microelectromechanical device according to claim 11, wherein fingers of a moving comb electrode are attached to the secondary part.

13. The microelectromechanical device according to claim 11, wherein

the secondary part carries more than a half of the entire mass of the semi-flexible proof-mass.

14. The microelectromechanical device according to claim 1, wherein the semi-flexible proof-mass comprises:

two primary parts disposed essentially longitudinally in parallel positions on two sides of a symmetry axis of the semi-flexible proof-mass, the symmetry axis aligned with the direction of the axis of movement, each of the primary parts configured to be stopped in direction of the axis of movement by the first stopper structures placed on a first distance away from both ends of each primary part; and

two secondary parts each disposed symmetrically across the symmetry axis, each of the secondary parts configured to be stopped by a respective second stopper structure placed on the second distance away from the side of the respective secondary part that is away from the geometrical center of the device;

wherein the second distance is greater than the first distance.

15. The microelectromechanical device according to claim 14, wherein fingers of a moving comb electrode are attached to the primary parts.

16. The microelectromechanical device according to claim 14, wherein

the secondary parts carry more than 20% of an entire mass of the semi-flexible proof-mass.