Lecture 10 - Measurement & Instrumentation

Question 1

Who was Eadweard Muybridge?

Answer 1

“Father of Biomechanics,” pioneer in photographic studies of movement. Used sequence of photographs in bet about horse

Question 2

What is parallax?

Answer 2

When things look different depending on where you stand

Question 3

How can you measure motion?

Answer 3

Using optical motion analysis, electrogoniometers, footswitches, accelerometers, and gyroscopes

Question 4

How can you measure force?

Answer 4

Strain gauge, load cell, force platform

Question 5

What are the three types of optical motion analysis?

Answer 5

Digital video, optical motion tracker, and markerless tracking

Question 6

What type of optical motion analysis are standard or specialized video cameras?

Answer 6

Digital video

Question 7

What type of optical motion analysis are infrared omitting and detecting cameras?

Answer 7

Optical motion trackers

Question 8

What type of optical motion analysis are image recognition algorithms?

Answer 8

Markerless tracking

Question 9

What type of equipment can you use to conduct video motion analysis?

Answer 9

Inexpensive software and standard miniDV cameras or specialized digital cameras using automatic or manual tracking

Question 10

How should cameras be set up for 2D video motion analysis?

Answer 10

Perpendicular to plane of motion with entire motion fitting in view of camera.
Far away and zoomed in to reduce parallax with fast sampling rate.

Question 11

What are optical systems?

Answer 11

A type of optical motion capture system that emits and reads infrared light

Question 12

What is an Optotrak?

Answer 12

A type of optical motion capture system that uses 3 cameras set at a fixed distance that use active markers that emit infrared light

Question 13

What is a GaitRite/GaitMat?

Answer 13

A type of markerless tracking system that tracks where stepped and measures stride length and step rate

Question 14

What is a Tekscan?

Answer 14

A type of markerless tracking system that uses pressure sensors in someone’s shoe to gather force information

Question 15

What is an electrogoniometer?

Answer 15

A type of markerless tracking system that uses change in electrical resistance to sense amount of bend at joints

Question 16

What is a footswitch?

Answer 16

A type of markerless tracking system that goes on the bottom of the shoe or food that uses electrical capacitance to sense contact and indicate each time foot hits ground

Question 17

What is an accelerometer?

Answer 17

A type of markerless tracking system that measures acceleration using mass-spring damper system

Question 18

What are some limitations of accelerometers?

Answer 18

When integrates twice, can create a large error

Question 19

What is a gyroscope?

Answer 19

A type or markerless tracking system that measures three dimensional rotations (orientation) in three directions - roll, pitch, and yaw

Question 20

What is a strain gauge?

Answer 20

A type of force transducer that measures how much a material bends to determine force. Usually uses a Wheatston bridge

Question 21

How does a Wheatson bridge work?

Answer 21

Deforming the bridge causes a change in the resistance of the circuit

Question 22

What is a load cell?

Answer 22

A type of force transducer that measures force in 1-3 directions along 1-3 axes using a strain gauge or piezoelectic sensor

Question 23

How does a piezoelectric sensor work?

Answer 23

Uses quartz. Emits a static charge when compressed. Charge is related to force applied.

Question 24

What is a force platform?

Answer 24

Type of force transducer used to measure gait. Uses 4 piezoelectric or strain gauge load cells.

Question 25

What are some limitations to force sensors?

Answer 25

Fragile, expensive, trades range of forces for sensitivity