project #3: design of a mems vertical actuator
DESCRIPTION
Project #3: Design of a MEMS Vertical Actuator. Jianwei Heng Alvin Tai ME128 Spring 2005. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Project #3:Design of a MEMS Vertical
ActuatorJianwei Heng
Alvin Tai
ME128 Spring 2005
IntroductionThe MEMS vertical actuator described in
this project consists of a center mass with a flat surface and is supported by simple flexures arranged symmetrically around the center mass. The device uses electrostatic comb structures to displace the flat surface.
IntroductionDesign constraints
Active Constraints Minimum width of structure 5m Minimum gap 5m Thickness of the device 50m Minimum diameter of center mass 200m E =160 GPa =2.33 gm/cm3
Maximum DC input voltage = 30 V Maximum die area, Ad 10mm2
gNtVF
20
IntroductionDesign Constraints
Inactive Constraints Minimum displacement under max voltage: 20 m Maximum DC acceleration survival, amax 2,000g Maximum stress in suspension, max 1.6 GPa Bandwidth of the device 1 kHz (resonance
frequency)
Approach to ProblemObservations
To fully maximize mass displacement, it is desirable to design a system with: Minimum spring constant, k
By using a circular center mass, we can maximize the spring length/constant
Maximum amount of combs, N Maximum overlapping comb distance, t
Approach to ProblemFrom the force equation, We can
easily observe that it is a function of N and t: F = f(N,t)
With our area constraint active, there is a direct effect on one variable when the other is modified (as t is decreased, N can be increased and vice versa). Therefore, a compromise must be realized.
gNtVF
20
Approach to ProblemRelationship of N and t
Overlap distance, t
Num
ber o
f com
bs, N
If t is designed too large, the combs may deflect. Conversely, if t is too small, the gaps between the combs become significant and limits the number of combs in our system.
t 200 m >> 5 m
t>>5m
t 5m
Approach to Problem1. Used MATLAB to get a preliminary analysis of
the design
Calculated k using Euler-Bernoulli Beam Theory (guided/fixed beam)
Optimized comb overlap, t Calculated displacement
2. Built the model in Solidworks to verify that it satisfies all constraints
Used static and frequency analysis to check constraints
Approach to ProblemFormation of final design
We initially set the thickness = 50 m as an active constraint, but that resulted either in deflections that are too small, or resonant frequencies that are too small.
Since actuating a maximum of 20 m requires the thickness to be 30 m (to allow for significant comb overlap when fully displaced), we changed the thickness constraint from active to inactive!
Then we redesigned the actuator with thickness = 30 m
Final Design
Final Design of the Actuator
Final Design
Final Design of the Substrate
Final Design
Spring and Center mass Combs design
Final Design
Deflection when 30V force applied
>20um
Min DC displacement underMax DC voltage
SATISFIED
Final Design
Max Stress when 30V force applied
>150MPa<1.6GPa
Max Stress in suspensionMin Deformation stress (Part B)
SATISFIED
Final Design
Max Stress points
Final Design
Max Stress when 30V force applied
Max DC acceleration survival
SATISFIED
<1.6GPa
Final Design
Resonant Frequencies for Modes I to V
Approach to Problem Although the resonant frequency requirement fails in
Mode I, the actuator is unlikely to exhibit this characteristic motion due to the forces applied.
Hence we can rule out Mode I.
Approach to Problem More importantly, Mode II resonant frequency =
1244.2Hz > 1kHz. Since the motion in Mode II is the most likely one,
we can conclude that the actuator will fulfill the resonant frequency requirement stipulated.
Resonant Frequency Requirement
SATISFIED
Final DesignFEM constraints
Displacement (satisfied) Maximum acceleration shock test (satisfied) Maximum Stress (satisfied) Minimum Deformation Stress, Part B (satisfied) Resonant Frequency (satisfied)
Concerns Base structure analysis: instability issues
involving comb contact