Transcript Team-based design and CAD modelling using Lego in first year

ES050 – Introductory Engineering
Design and Innovation Studio
ECE Case Study
Accelerometers in Interface
Design
Prof. Ken McIsaac
2008 11 19
1
Outline
Review of generated concepts
 Design selection
 Accelerometer mathematics
 Accelerometer mechanics
 Accelerometer electrical theory

2
Review of Generated Concepts

Pendulum proposal
d

3
Review of Generated Concepts

Mercury Switch
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Review of Generated Concepts

Motion capture
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Review of Generated Concepts
Accelerometer


“Something to measure acceleration”
Untethered, inertial sensor
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Decision Making
Now, we have a set of concepts. What criteria
would we use to choose between them?
Some thoughts I had:

Infrastructure (ease of installation) #1

Accuracy (How close to reality is the model?) #6

Resolution (How fine motions can we detect?) #3

Form factor (weight/size) #4

Cost #5

Range of motion (What can the user do?) #2
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Decision Making
Evaluating our choices:
Option
Problems
Pendulum
Infrastructure, range
Mercury Sw
Range, resolution
Motion
Infrastructure
Capture
Accelerometer Maybe none, IF we
get the right one
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Accelerometer Mathematics


A transducer is a device that measures a
physical quantity and turns it into an electrical
signal
An accelerometer is a transducer that turns
acceleration into voltage
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Accelerometer Mathematics

We measure V=f(a), then:
a f
1
V 
v   a dt  v0 
p   v dt  p0 
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Accelerometer Mathematics
As it happens, this is inaccurate, but who cares?
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Accelerometer Mechanics
So how do we transduce acceleration?
Stationary
Can we instead transduce
this bending?
Acceleration
One dimensional model
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Accelerometer Theory
New problem: measure bending
L

1.
2.
A
R
L
A
L
R
A
Resistance of a wire varies with length
Length of a bent strut changes
So…the resistance of a wire bonded to the
strut detects the bending.
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Accelerometer Theory
Proposed circuit:
+
R1 (Fixed)
R2 (Variable)
Vin
+
-
Vout
-
R2
Vout 
Vin
R1  R 2
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Accelerometer Theory
Now, some math:
V1 
L

A
L
R1  
A
Vin
Stationary
L  L
A
V2 
Vout
L  L
R1  
A

Accelerating
L
A Vin
V 
L
R1  
A

Assuming L  L
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Accelerometer Theory
This will work, but it is hard to measure, so…
Strain gauges are thin wires
folded and printed onto flexible
foils. They magnify the
deformation effect on
resistance
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Accelerometer Theory
Accelerometer for into plane acceleration or
pitch
Strain gauge
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Wii First Proposal
We can build something like this:
Computer monitors
and integrates
acceleration data
Acc 1
Acc 3
Acc 2
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Design Evaluation
Our design will work, but:

It is too big

It is difficult (= costly) to manufacture
We need a design iteration to resolve these
problems.
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