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BMEG 230 > BMEG 230 MT2 > Flashcards

BMEG 230 MT2 Flashcards

1
Q

3D tracking methods

A

Passive relective markers
Active Markers
Markerless

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2
Q

Pros and Cons of Passive Reflective Markers

A

Pros:
* Accurate
* Capable of large frame rates
* Complex 3D motions
* No wires
Cons:
* Need multiple cameras
* Manual marker identification or need software
* Mis-identified markers
* Usually constrained to a lab setting, struggles
in uncontrolled lighting

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3
Q

Pros and Cons of Active Marker

A

Pros:
* Accurate (especially in uncontrolled lighting)
* High resolution
* Greater capture volume
* Complex 3D motions
* No need to identify markers
* Less likely to loss sight of marker
Cons:
* Wires can be intrusive
* May need multiple cameras
* Complex to setup
* “bit of a pain” – Pawel

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4
Q

Pros and Cons to Markerless tracking

A

Pros:
* Cheap and easy
* Unconstrained motion
* In the field data collection
* Can have various modalities of video
Cons:
* Not very accurate (yet)
* Mostly still in the research phase
* Usually need large training data sets
(i.e. machine learning)
* Can be constrained to single-plane and
simple motions
* Takes time/computing power to
process data

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5
Q

What do force plates measure?

A

GRFs - Fx,Fy,Fz
CoP
momets of forces
impulse

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6
Q

how do they measure this

A
  • Convert energy from one form to another
  • In our case: mechanical to electrical
  • We cannot “measure” force, but we can measure strain as a
    change in electrical resistance
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7
Q

Strain Gauge

A
  • change their resistance as they are stretched or compressed
  • to measure a desired change, there is a velocity drop acroos the strain gauge for a given level of force.
  • uses differing sensors in different locations to determine CoP
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8
Q

Pizoelectric in force plates

A

*Deformation to cause charge is very
small (usually a few microns)
* High frequency response
* Can not measure static loads
* Excellent for dynamic and impact loads

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9
Q

CoP

A

All ground reaction forces
can be replaced by a single force acting
at a single point. This point is called
the center of pressure.

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10
Q

how is voltage used to determine CoP in force plates

A

the force plates outputs the voltages proportional to forces, then coverted while accounting for amplifier gains and plate sensitivites. The forces are then used to calculate where the CoP is

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11
Q

Degree of Freedom

A

an expression that describes the ability of an object to move in space.

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12
Q

How many degrees of freedom are there for:
human finger
human shoulder

A

2
3

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13
Q

why are degrees of freedom important

A
  1. Understanding Movement: Knowing the degrees of freedom helps us understand how joints and bodily systems move and what
    limitations they may have.

2.Modeling and Simulation: In computational biomechanics, degrees of freedom are essential parameters for creating accurate
models of human movement.

3.Injury Prevention: By understanding the limitations of a joint’s degrees of freedom, healthcare professionals can better prescribe
treatments or preventative measures for potential injuries.

4.Prosthesis Design: Engineers use the concept to design more efficient and functional prosthetic limbs that mimic the natural degrees of freedom as closely as possible.

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14
Q

Global vs Local coordinate system

A
  • For global the rotation is performed concerning the global coordinate system whilst local concerns the local.
  • in global, the axes of rotation are fixed and do not change as the object rotates, in local the axes is fixed to the object.
  • A global Z-axis rotation means that no matter the current orientation of the object, the rotation will be around the fixed global Z-axis. In local it will rotate around its own z axis

.

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15
Q

Definition of Inertia

A

the tendency of an object to maintain its state of rest or uniform motion, the resistance to change in motion of an object. The more mass the more inertia, the more resistance

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16
Q

moment of inertia

A

depends not only on the masses, but also on how far they are from the axis of rotation

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17
Q

Parallel axis theorem

A

if the mass moment of inertia about an axis passing through the center of gravity is known, the moment of inertia about a second, parallel axis is given by

I_pat = I_cg +M_t(R_cg)^2

I_cg = MOI about axis through cg
m_t = total mass of the object
R_cg = perpendicular distance between the axes

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18
Q

Momentum

A

tendency to resist changes in the existing state of motion, only applies to moving ibjects, while inertia applies to moving and stationary

force is a change in momentum and time

p=mv
L=Iw

19
Q

impulse momentum principle

A

F * delta(t) = delta(p)

20
Q

Energy

A

kinetic = (1/2)mv^2
potential = mgh

21
Q

work energy principle

A

SUM(Fd)=(1/2)mv^2b-(1/2)mv^2a

22
Q

What is the instantaneous centre of zero velocity

A

when a body is moving there is a point where its velocity is zero for a moment, that point is not always attached to the body, seems to spin about that point

23
Q

how to find IC

A

velocity mag is proportional to relative distance, therefore we can use velocity being perp to relative distance. Draw lines perp to velocity, where they intersect is the IC.

v_a/r_a,ic = v_b/r_b,ic

24
Q

Instrumented Treadmills

A
  • Force Platforms are built either into (AMTI) or under (Bertec) the treadmill
  • Use strain gage platforms
  • Measure Plate Forces and Moments (Center of Pressure and Free Moment computed
    from output)
24
Q

types of force plates

A

Strain Gage:
* AMTI
* Bertec
* Kyowa-Dengyo

Piezo-Electric:
* Kistler

25
Q

Standing Balance Control

A
  1. Muscle Stretch Reflex
    • Role in balance
    • Muscle tension adjustment

2.Vestibular System
- Location and function
- Orientation in space
3. Proprioceptive Feedback
- Sources (muscles, tendons, joints)
- Role in balance and posture

4.Teleceptive Inputs - Vision
- Vision in spatial navigation
- Environmental perception

26
Q

Kinetic energy equation for rotation

A

E = (1/2)mv^2 + (1/2)Iw^2

27
Q

rigid body force equations

A

F = ma
sum(Fx) = ma_x
sum(Fy) = ma_y

sum(Fn) = (w^2r)m
sum(Ft) = (alphar)m

28
Q

angular momentum about the COM

A

sum(M)=I(alpha)

29
Q

a body’s trajectory can be determined if

A

the applied forces and moments are known

30
Q

if the moments is taken about a point different to COM

A

apply parallel axis theorem (I//) to determine the new I

31
Q

If COM is accelerating

A

sum(M_newpoint) = I//alpha +m(R_new/com x a_com)

32
Q

Definition of Dynamics

A

the study of how forces affect motion

33
Q

Definition of Kinematics

A

the study of motion in isolation

34
Q

2D planar video adavntages and disadvantages

A

Pros:
* Cheap and easy
* Various speeds
* Can see the video after

Cons:
* Only in one plane
* Can take a long time to process data
* Hard to align properly and distortion
correction is often required

35
Q

Distance Callibration

A

s = actual length / digitized length

36
Q

frame rate

A
  • Fast Movements (e.g., running, jumping): Use a high frame rate, typically 120 fps or higher. This ensures fine-grained detail, reducing motion blur
  • Slower Movements (e.g., walking, stretching): A lower frame rate like 60 fps may suffice, but higher frame rates provide more detailed data
37
Q

Data triangulation

A

Enhanced Accuracy and Validation

Minimization of Occlusion and Blind Spots

Improved Depth of Analysis through Multidimensional Data

Enhanced Reliability and Reproducibility

Broader Context and Environmental Factors

Reduction of Measurement Bias and Artifacts

38
Q

2D marker placement

A

3 DOFs

X, Y of the COM and one angle describing its orientation

39
Q

3D marker placement

A

6 DOFs

X, Y, Z of COM and 3 angles describing its orientation

40
Q

equations for attached bodies

A

R_b = R_a + R_b/a
V_b = V_a + W_ab x R_b/a
A_b = A_a + alpha_ab x R_b/a - W^2*R_b/a

41
Q

unit vector

A

<R_k/a = R_k/a divided by |R_k/a|

42
Q

Acceleration

A

A_b = A_a + A_b/a
A_b = A_a + (A_b/a)t + (A_b/a)n

43
Q

when would V_a = 0

A

when there is rolling without slipping

BMEG 230 (1 decks)

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