Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
SlideShare a Scribd company logo

Photo optical devices

•Download as PPTX, PDF•
•
Hemant Aggarwal
Hemant Aggarwal

This document discusses various photo optical techniques used to capture and analyze human movement, including cinematography, video, and optoelectric techniques. It describes cine cameras, their characteristics, types, lenses, and camera positioning. It also discusses other measurement devices like accelerometers, gyroscopes, force platforms, footswitches, and instrumented walkways that are used along with video recordings to measure temporal gait parameters and forces during walking. The analysis of gait cycle and advantages of using video recording for gait analysis are also summarized.

1 of 22
PRESENTED BY :- PRABHAT KUMAR ARYA PIYUSH BHARDWAJ HEMANT AGGARWAL
 THE chinease saying “A PICTURE IS WORTH MORE THAN TEN THOUSAND WORDS” gives a very important message to biomechanics  The imaging measurement techniques give description of human movement in a very purposeful manner i.e. presentation of the position or of the body part in space & time.
INTRODUCTION  Photo optical devices, are the devices which are utilize to capture movement of body from images sensors to triangulate the 3D position of subjects between 2 or cameras calibrated to provide overlaping projections.
THERE ARE 4 TECHNIQUES Cinematography Video Optoelectric techniques
Cinematography  cine cameras these are available in 8mm, super 8 ,16 mm ,35 mm & 70mm  8mm, super 8 are least expensive but the image size is small & also these have become obsolete(out-dated)  35 mm & 70mm cameras offer a large images size but are expensive  16 mm cameras are used for biomechanical research purpose as these a compromise between the cost & the images size
CHARACTERISTICS OF A CINE CAMERA  It must have stabilized frequency. It must provide a range of frequency between 64-200 frames per second .The preferable upper limit is 500 f.P.S.  It should provide time information on the film itself. It should synchronize with another cameras or the other measurement devices eg. dynamometric platform or electrogoniormerters
Types of cine cameras  The are three type of cine cameras Intermittent pin-registered Rotating prism Streak cameras.
 The type of mechanical movement puts constraints of the maximum possible speed of these cameras.  Operate up to 500 frames per sec.  Advantage of these camera is that these produce extremely high resolutions.
• Rotating prism cameras provide a frequency up to 2500 fps with a short exposure time. • The disadvantage of these cameras is the poor resolution than the intermittent cameras
 These are used to study the self-luminous events in the linear motion.  These cameras operates in the range of 20,000 picture per se. to 1 million pictures per sec. For evaluation of technique, usually pin registered cameras are used as these give good resolution as well as the range of camera speed is sufficient for most of the events
LENS  The choice of the lens depends upon the purpose & the filming situations but there are certain other factors:- Distance from the object: usually the distance between the object & camera is kept large to keep the distortion or the perspective error to the minimum.thus, preference goes towards a tele lens.  Recording area : usually zoom lenses are used as with zoom lens desired area can be obtained by keeping the camera & the object distance large
Camera position  For biomechanical evaluation, camera should be placed perpendicular to the plane of motion of the object.  In case it is not possible to position the camera perpendicular to the plane of motion then a necessary correction should be made using trigonometric rules.
Accelerometers  Accelerometers, measure acceleration.  The type of accelerometer used in gait analysis is usually very small, weighing only a few grams.  It normally only measures acceleration in one direction, but more than one may be grouped together for two- or three-dimensional measurements.  Typically, accelerometers have been used for gait analysis in one of two ways:  1. either to measure transient events  2.to measure the motion of the limbs.
GYROSCOPES  A gyroscope is a device used for measuring or maintaining orientation and angular velocity
FORCE PLATFORMS  The force platform, which is also known as a ‘forceplate’, is used to measure the ground reaction force as a subject walks across it .  a ‘typical’ design being about 100 mm high, with a flat rectangular upper surface measuring 400mm by 600 mm  Within the platform, a number of transducers are used to measure tiny displacements of the upper surface, in all three axes, when force is applied to it. 
Cont…  a force platform should be mounted below floor level, the upper surface being flush with the floor.  If this is not possible, it is usual to build a slightly raised walkway, to accommodate the thickness of the platform.
Uses in gait analysis:  Methods of gait analysis- 1. visual gait analysis:- Simplest form of gait analysis made by unaided human eyes 2.using video recording :- high technology gait analysis photo optical devices
Advantages:  It helps to overcome two of the limitations of visual gait analysis:  the lack of a permanent record  the difficulty of observing high-speed events. 1. It reduces the number of walks a subject needs to do during gait analysis 2. It makes it possible to show the subject exactly how they are walking gait analysis 3. It makes it easier to teach visual gait analysis to someone else.
Analysis of gait cycle through photo optical devies  A number of systems have been described which perform the automatic measurement of the timing of the gait cycle, sometimes called the temporal gait parameters.  Such systems may be divided into two main classes: 1.footswitches 2. instrumented walkways
Fooswitches:  Footswitches are used to record the timing of gait  If one switch is fixed beneath the heel  and one beneath the forefoot,  it is possible to measure the timing of initial contact, foot flat, heel rise and toe off, and the duration of the stance phase  If switches are mounted on both feet, the single and double support times can also be measured  The footswitches are usually connected through a trailing wire to a computer, although alternatively either a radio transmitter or a portable recording device may be used to collect the data and transfer them to the measuring equipment.
Instrumented walkways  used to measure the timing of foot contact, the position of the foot on the ground, or both  A conductive walkway is a gait analysis walkway which is covered with an electrically conductive substance, such as sheet metal, metal mesh or conductive rubber  The speed needs to be determined independently, typically by having the body of the subject interrupt the beams of two photoelectric cells, one at each end of the walkway, again connected to the computer
Cont…  An alternative arrangement is to have the walkway itself contain a large number of switch contacts, which detect the position of the foot, as well as the timing of heel contact and toe off.  This has the advantage that no trailing wires are required and the walkway can be used to measure both step lengths and the stride length.

More Related Content

Photo optical devices

  • 1. PRESENTED BY :- PRABHAT KUMAR ARYA PIYUSH BHARDWAJ HEMANT AGGARWAL
  • 2.  THE chinease saying “A PICTURE IS WORTH MORE THAN TEN THOUSAND WORDS” gives a very important message to biomechanics  The imaging measurement techniques give description of human movement in a very purposeful manner i.e. presentation of the position or of the body part in space & time.
  • 3. INTRODUCTION  Photo optical devices, are the devices which are utilize to capture movement of body from images sensors to triangulate the 3D position of subjects between 2 or cameras calibrated to provide overlaping projections.
  • 4. THERE ARE 4 TECHNIQUES Cinematography Video Optoelectric techniques
  • 5. Cinematography  cine cameras these are available in 8mm, super 8 ,16 mm ,35 mm & 70mm  8mm, super 8 are least expensive but the image size is small & also these have become obsolete(out-dated)  35 mm & 70mm cameras offer a large images size but are expensive  16 mm cameras are used for biomechanical research purpose as these a compromise between the cost & the images size
  • 6. CHARACTERISTICS OF A CINE CAMERA  It must have stabilized frequency. It must provide a range of frequency between 64-200 frames per second .The preferable upper limit is 500 f.P.S.  It should provide time information on the film itself. It should synchronize with another cameras or the other measurement devices eg. dynamometric platform or electrogoniormerters
  • 7. Types of cine cameras  The are three type of cine cameras Intermittent pin-registered Rotating prism Streak cameras.
  • 8.  The type of mechanical movement puts constraints of the maximum possible speed of these cameras.  Operate up to 500 frames per sec.  Advantage of these camera is that these produce extremely high resolutions.
  • 9. • Rotating prism cameras provide a frequency up to 2500 fps with a short exposure time. • The disadvantage of these cameras is the poor resolution than the intermittent cameras
  • 10.  These are used to study the self-luminous events in the linear motion.  These cameras operates in the range of 20,000 picture per se. to 1 million pictures per sec. For evaluation of technique, usually pin registered cameras are used as these give good resolution as well as the range of camera speed is sufficient for most of the events
  • 11. LENS  The choice of the lens depends upon the purpose & the filming situations but there are certain other factors:- Distance from the object: usually the distance between the object & camera is kept large to keep the distortion or the perspective error to the minimum.thus, preference goes towards a tele lens.  Recording area : usually zoom lenses are used as with zoom lens desired area can be obtained by keeping the camera & the object distance large
  • 12. Camera position  For biomechanical evaluation, camera should be placed perpendicular to the plane of motion of the object.  In case it is not possible to position the camera perpendicular to the plane of motion then a necessary correction should be made using trigonometric rules.
  • 13. Accelerometers  Accelerometers, measure acceleration.  The type of accelerometer used in gait analysis is usually very small, weighing only a few grams.  It normally only measures acceleration in one direction, but more than one may be grouped together for two- or three-dimensional measurements.  Typically, accelerometers have been used for gait analysis in one of two ways:  1. either to measure transient events  2.to measure the motion of the limbs.
  • 14. GYROSCOPES  A gyroscope is a device used for measuring or maintaining orientation and angular velocity
  • 15. FORCE PLATFORMS  The force platform, which is also known as a ‘forceplate’, is used to measure the ground reaction force as a subject walks across it .  a ‘typical’ design being about 100 mm high, with a flat rectangular upper surface measuring 400mm by 600 mm  Within the platform, a number of transducers are used to measure tiny displacements of the upper surface, in all three axes, when force is applied to it. 
  • 16. Cont…  a force platform should be mounted below floor level, the upper surface being flush with the floor.  If this is not possible, it is usual to build a slightly raised walkway, to accommodate the thickness of the platform.
  • 17. Uses in gait analysis:  Methods of gait analysis- 1. visual gait analysis:- Simplest form of gait analysis made by unaided human eyes 2.using video recording :- high technology gait analysis photo optical devices
  • 18. Advantages:  It helps to overcome two of the limitations of visual gait analysis:  the lack of a permanent record  the difficulty of observing high-speed events. 1. It reduces the number of walks a subject needs to do during gait analysis 2. It makes it possible to show the subject exactly how they are walking gait analysis 3. It makes it easier to teach visual gait analysis to someone else.
  • 19. Analysis of gait cycle through photo optical devies  A number of systems have been described which perform the automatic measurement of the timing of the gait cycle, sometimes called the temporal gait parameters.  Such systems may be divided into two main classes: 1.footswitches 2. instrumented walkways
  • 20. Fooswitches:  Footswitches are used to record the timing of gait  If one switch is fixed beneath the heel  and one beneath the forefoot,  it is possible to measure the timing of initial contact, foot flat, heel rise and toe off, and the duration of the stance phase  If switches are mounted on both feet, the single and double support times can also be measured  The footswitches are usually connected through a trailing wire to a computer, although alternatively either a radio transmitter or a portable recording device may be used to collect the data and transfer them to the measuring equipment.
  • 21. Instrumented walkways  used to measure the timing of foot contact, the position of the foot on the ground, or both  A conductive walkway is a gait analysis walkway which is covered with an electrically conductive substance, such as sheet metal, metal mesh or conductive rubber  The speed needs to be determined independently, typically by having the body of the subject interrupt the beams of two photoelectric cells, one at each end of the walkway, again connected to the computer
  • 22. Cont…  An alternative arrangement is to have the walkway itself contain a large number of switch contacts, which detect the position of the foot, as well as the timing of heel contact and toe off.  This has the advantage that no trailing wires are required and the walkway can be used to measure both step lengths and the stride length.