Laser Based Diagnostics in Engineering Flashcards
Describe the distance measurement method of triangulation for HEIGHT MEASUREMENT.
Use a laser range finder - uses laser triangulation
Sensor calculates single point height by imaging the reflected light off a target and onto a 1D pixelised array detector. Changes in object height casue a corresponding change on the detector.
Trade off between range and resolution.
Describe the distance measurement method of triangulation for SURFACE MAPPING
Traingulation sensor alone can measure relative height and change of height at a single point or along a strip.
Sensor can be integrated with a precision xyz movement stage and a control system with rapid data acquisition and data processing/display software.
Sensitive to changes in surface condition due to it being an optical technique.
Black painted surface will read different to a white painted surface.
Sensor should be used as a relative not absolute distance measurement device
Describe the distance measurement method of triangulation for PROFILE SCANNING
Use a cylindrical or power lens
A laser beam is enlarged to form a static laser line and is projected oonto the target surface
Optical system projects the diffusly reflected light of this laser line onto a highly sensitive matrix array (2D)
Camera can also calculate x position so 3D data is possible to obtain.
Describe the distance measurement method of time fo flight
Send a laser pulse towards an object and measuring the time taken for the pulse to be reflected backoff teh target.
What is LIDAR?
Precise and rapid component surface characterisation by laser scanning and digitisation techniques
Sequential single point range measurements form 3D images
Used in automobiles
What are the basics of 3D laser scanning?
3D laser scanner uses fast repetition rate pulse laser
Rapid anglular deflection of the laser beam or line scanning is achieved by a rotating polygon mirror wheel
This is combined with slow scanning (frame scanning) rotation of the complete optical head.
Fast signal processing and high speed data interface are required to stitch together position and multiple views to complete image
What are the advntages and disadvantages of triangulation?
adv:
Relatively high accuracy of distance measurement (order of tens of micrometers)
disadvantage:
Limited range (approximalty a metre)
What are the advntages and disadvantages of “time of flight”?
adv:
capable of operation over very long distances, suitable for scanning large structures
disadvantage:
Relatively low accuracy of distance, difficulty in precise timing of the light round- trip.
What are further limitations of distance measurements?
Accuracy can be lost when single pulse hits the edge of an object
High resolution scans increasre the chances of the beam hitting an edgeand data will show noise just behind edges of objects.
Any motion in the subject or the scanner will distort the collected data so vibration must be minimised
