Upload
jeremy-gaines
View
237
Download
1
Embed Size (px)
Citation preview
Shape Memory Alloys Team:High Torque Rotary Actuator/Motor
Team Members:Uri Desai
Tim GuenthnerJ.C. ReevesBrad Taylor
Tyler Thurston
Gary Nickel NASA JSC MentorDr. Jim Boyd Faculty Mentor
Reid Zevenbergen Graduate Mentor
Outline
Project Goal: Fall 2008
Fundamentals of Shape Memory Alloys
Design Concepts
Heat Transfer Analysis
Comparison and Recommendations
Future Tasks: Spring 2009
Questions
Project Goal: Fall 2008
Research and understand SMAs and their applications Research current conventions: Electric motors Develop concepts for a Rotary Actuator/Motor driven by
SMAs Evaluate concepts Conduct initial analysis of chosen concepts Select a baseline design
Motivation: Design a motor that will have a higher torque per unit volume and less weight than current motors.
What are Shape Memory Alloys?
5
1
2
3
4
Austenite
Deformed Martensite
Self-Accommodated
Martensite
1 2 3
45
Mf Ms AfAsTemperature
Stress
• Converting thermal energy to mechanical work.
Applications of SMAs Aerospace:
Airfoils, Boeing Chevrons, STARSYS
Medical Stints, Instrumentation
Other Eyeglasses frames, Locking mechanisms, Underwires, etc.
Electric Motors Most applications for space utilize electric motors. Electric motors are very dense and therefore there is a
weight penalty Electric motors operate better at higher speeds and lower
torque: For low torque applications, a gear box must be added to the motor, which increases the weight.
Pittman motors have been used, in this case, as an example of electric motors with higher than average torque densities.
Highest torque density from Pittman motor studied: 6.83 oz in
Where: Δθ = angle of rotation (rad)εtrans = transition strainL = length of SMA wireΔx = change in lengthR = respective radii
Modeling Wire Behavior: Angular Displacement
11
11
321 2
3 2
;
trans
trans
x
R
x L
L
R
R
R
2 23 2 1
3 3
23
1 3
trans
R R
R R
LR
R R
Modeling Wire Behavior: Moments and Torque
1
1 1 1 1
1 2
1 1 2 2
1
3 22
1 3
3 3 32
1 3
32
( )
SMA spring SMA
SMA
transSMA
transSMA
transSMA
F F F F F k x
T F R F k x R
T T
F R F R
F k L RF F
R
F k L R RT F R
R
nF k L R RT
R
Where:F = respective forcesR = respective radiik = spring constantFSMA = SMA recovery forceΔx = change in lengthη = efficiency of gear trainn = number of SMA wiresT = torque generated
Modeling Wire Behavior: SMA Analysis
0
2
02
trans elastic A M Ai
M A
SMAi
SMA
trans elastic ASMA M ASMA
M A
E ET T
E E
F
A
d E EF T T
E E
•Substituting above equation into previous moment equation
2
0 1 3
32
2trans elastic A transSMA M A
M A
d E En T T k L R R
E ET
R
Where: εtrans = actuation strainεelastic = elastic strainσi = recovery stress αA: coefficient of thermal expansion for austeniteT -T0: change in temperatureEM: Young’s Modulus for martensiteEA: Young’s Modulus for austenitedSMA = diameter of SMA wiren = number of SMA wires
• Typical actuation stress values: 21,755-29,000 psi
Results
Pittman Motor: Model GM14X02 Torque: 107 oz in Torque Density: 6.83 oz/in2
SMA Wire Application 1 wire with diameter of 5mm or
10 wires with diameter of .02in (equivalent of 5mm)
Torque Density:Max: 1250 oz/in2 @ 5.5° rotationMin: 33.5 oz/in2 @ 115.5 ° rotation
SMA Wires
Company Transformation Temperature
Sizing Strain
Dynalloy Flexinol:: Af: 70° - 100°C
Nitinol:: Af: 80° - 90°C
Flexinol:: 0.001”-0.02”
Nitinol:: 0.004”-0.01”
~4-5%
SMA, Inc. PseudoelasticAf: -25°-125°C
Wire:: 0.012”-0.25”
~4-5%
Small Parts VaryingAf: 70° - 90°C
Wire: 0.006”-0.1”
~3-5%
Mechanism Operation
Drive Shaft
Torque Tubes
Bevel gear attached to drive shaft
Bevel gear attached to torque tube
Torque Tube Analysis
max
Tc
JJG
TL
L
R
Where:T = applied torque J = polar moment of inertiac = radius of beamG = shear modulusL = length of beamφ = angle of twist
Analyzing a shape memory alloy torque tube:
RM
( )
M
M M
M M
elastic trans thermal
RM
elastic transR R
M
elastic MR R
L
R
L
R
TRG
J
Where:γ = shear strainγthermal= 0 (for isotropic material)RM = median radius of tube
M
transMR
M
RGJT
R L
Torque Analysis
γtrans Max Torque (oz-in)
Torque (φ = 8°)(oz-in)
2% 10558.6 3069.4
3% 15837.9 8348.7
4% 21117.2 13627.9
5% 26396.5 18907.3
6% 31675.8 24186.6
This data based upon:G = 152,289.625 psiRM= 0.2 inL = 2 inJ = 0.0053 in4
ηtra
ns =2%
Heat Transfer: Overview
Drives SMA actuation Cp varies between 0.32 and 0.6 during actuation Material Properties (Nitinol)
Wire Properties
Torque Tube Properties
Density Resistivity
Cp Activation
Relaxation
Austenite
6.45 g/cc 76 μΩcm 0.322 J/g°C
78 °C -
Martensite
- 82 μΩcm 0.322 J/g°C
- 42 °C
Trans. - - 0.6 J/g°C 68 °C 52 °C
Radius 1 Radius 2 Length Voltage Power Conv. Coeff.
Tempa
0 cm 0.05 cm 10 cm 0.2 V 0.44 W 0.01 W/cc K 20 °C
Radius 1 Radius 2 Length Exterior Heat Conv. Coeff.
Tempa
0.3 cm 0.5 cm 5 cm 110 W – 70 W 0.1 W/cc K 20 °C
Heat Transfer: Wire
Resistive Heating
4 seconds to heat
Forced Air Cooling
4 seconds to cool
Cycle Time: 8 Seconds
Heat Transfer: Torque Tube
Contact Conductive Heating
8 seconds to heat
Forced Air Cooling
10.5 seconds to cool
Cycle Time: 18.5 Seconds
Compare/Contrast and Future Recommendation
SMA Wire Design SMA Torque Tube Design Simple and feasible Flexibility in altering torque
versus output rotation: Gear Ratios
Less expensive to manufacture Light weight
Modular design Capable of extremely high torque
output Greater complexity Difficult to implement multi-
directional rotation More expensive to manufacture
Recommendation: The SMA Team recommends pursuing the SMA wire application due to its simplicity, feasibility and low cost. This design meets our objective of designing a rotary motor that has high torque per unit volume while maintaining a small weight.
Future Tasks: Spring 2009 Detailed analysis of SMA wire application Detailed design of SMA wire application Build working prototype Test and compare results to theoretical