Transcript www.eecs.umich.edu

icro
Electro
echanical
Systems
MEMS
Accelerometers
Ben Wang
Frederick Wirth
Meredith Ostrowski
https://learn.sparkfun.com/tutorials/accelerometer-basics
1
MEMS: Microelectromechanical Systems
•
•
•
Micrometer scale
o 1-1000 micrometers
o Human hair: 17-180µm
Convert between electrical
and mechanical energy
forms
Used in accelerometers,
gyroscopes, inkjet printers,
displays (eg. DLP), microscale energy harvesters
http://www.memsnet.org/mems/what_is.html
2
Michigan and MEMS
The Lurie Nanofabrication
Facility attached to the
EECS building is one of
the leading laboratory in
MEMS research and
fabrication.
http://www.nnin.org/researchsupport/nnin-sites/universitymichigan
3
What are accelerometers?
● Accelerometers measure static acceleration (gravity)
and dynamic acceleration (starts and stops) along as
many as 3 axes (x, y, and z).
z-axis
x-axis
y-axis
engineerguy.com
engineerguy.com
4
Why use accelerometers?
•
•
Systems responding to acceleration
Examples:
www.digital-digest.com
http://www.bosch-presse.de/presseforum/details.htm?txtID=5620&locale=en
5
What are MEMS accelerometers?
Accelerometers built
with tiny mechanical
structures that
convert physical
acceleration to an
electronic signal.
https://www.sparkfun.com/p
roducts/9652
6
Practical acceleration
http://www.techwallpapers.com/wpcontent/uploads/wallpapers/Cool/Sony-Xperia-Z-SmartphoneOn-Table-Hd-Screen-Background.jpg
1g
7
Practical acceleration
6.7g
http://www.themotorreport.com.au/content/image/d/u/dut_ra
cing_world_record_electric_car_01-1003-m:610x450.jpg
1g
8
Acceleration Examples
www.sparkfun.com
Earth’s gravity
1g
Passenger car in corner
2g
Bumps in road
2g
IndyCar driver in corner
3g
Bobsled rider in corner
5g
Space shuttle
10g
http://www2.usfirst.org/2005comp/Manuals/Acceler1.pdf
9
What is the acceleration on the 3 axes?
Accelerometer
Accelerometer moves at
constant speed in a
circle. What acceleration
does it experience on the
x-, y-, and z-axes?
10
What is the acceleration on the 3 axes?
x:
y:
z:
11
What is the acceleration on the 3 axes?
x:
y:
z:
12
What is the acceleration on the 3 axes?
x:
y:
z:
13
Do’s and Dont’s
● Sense movement/shaking/impact
○
But do not get actual quantity for movement
● Find direction of motion
○
But do not find the speed/location
● Sense orientation relative to gravity
○
But only if you’re holding it still
14
Accelerometer Considerations
Number Axes
1, 2, or 3 (x-axis, y-axis, z-axis)
Range
g (not grams!)
Sensitivity & Resolution
mV/g
Interface
Analog, PWM, SPI, I2C
Power Consumption
Order of 100’s of μW
Additional Features
Freefall, tap, sleep, self-test, etc
15
Accelerometer from lab
MMA7361 Accelerometer & Breakout Board
https://www.sparkfun.com/products/9652
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Triple Axis Accelerometer Breakout - MMA7361
17
MMA7361: Datasheet - Pin Layout & Interface
Sleep Mode (Pin 7):
● High for output on, Low for sleep mode
0g-detect (Pin 9):
● Outputs 1 (high) when all 3 axes sense 0g
● Connect to interrupt or a polled-line
g-select (Pin 10):
● 0: 1.5g range, 800mV/g (also lower power
consumption)
● 1: 6g range, 206mV/g
Self-Test (Pin 13):
● Hold accelerometer upside-down (-1g on z-axis)
● Electrostatic force applied to accelerometer (xand y-axis deflected slightly, z-axis deflected 1g)
18
MMA7361: Datasheet - Orientation
19
Breakout Board Orientation
20
MMA7361: Range & Sensitivity Tradeoffs
+/- 1.5g Range
+/- 6g Range
Pros
❖ Lower power consumption
❖ Higher resolution (800mV/g)*
❖ Increased detection acceleration
range
Cons
❖ Lower acceleration detection
range
❖ Lower resolution (206mV/g)*
* Note: Actual resolution depends on the ADC used with the accelerometer.
21
MMA7361: Datasheet - Operating Characteristics
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MMA7361: Datasheet - Operating Characteristics
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MMA7361: Datasheet - Operating Characteristics
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MMA7361: Analog Output
+/- 1.5g Range:
-1.5g
0g
1.5g
0V
3.3V
.45 V
+/- 6g Range:
-6g
1.65 V
2.85 V
0g
6g
0V
3.3V
.45 V
1.65 V
2.85 V
25
MMA7361: Datasheet - Functional Block Diagram
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MMA7361: Datasheet - Functional Block Diagram
http://www.engineerguy.com/
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MMA7361: Datasheet - Functional Block Diagram
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MMA7361: Datasheet - Functional Block Diagram
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MMA7361: Datasheet - Functional Block Diagram
30
References
Bosch Sensortec: https://www.boschsensortec.com/en/homepage/05_technologies/glossary/glossary
MEMSnet: http://www.memsnet.org/mems/what_is.html
Silicon Designs, Inc.
http://www.silicondesigns.com/tech.html
Sparkfun: https://learn.sparkfun.com/tutorials/accelerometer-basics
Stanford University: http://large.stanford.edu/courses/2007/ph210/noriega1/
Tadigadapa and Najafi: http://www.mems-issys.com/pdf/issystech12.pdf
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Questions?