421/521 Lab 5
Total Station, Laser Tracker and
Coordinate Measuring Machine CMM
Motivation
• Become familiar with three types of precision 3D
measuring devices
• Not to become experts, but to be aware of their
existence and their potential to solve problems
• To large extent computers make these
instruments useful to the common person
• They can be lifesavers in certain situations
– Total stations and laser trackers can be leased
– Can buy time on a CMM, or contract inspection
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Total station
Read instructions
Go through set up
Measure length of a ruler at end of lab
Measure distance to ruler with tape measure
Does math make sense? Don’t believe any
measurement with a new instrument
Try measuring size of light fixture
– Does the math rectify the shape?
Total Station
More fun with the TS
• Set the TS up outside behind the East Wing
• There is a bench mark in the sidewalk to the
garage
• Measure some features of the buildings visible
• Check that dimensions make sense by
measuring a brick
• Pick a easily identified point and do a reversal
– Do you get the same answer both times?
– This is the classic check of a theodolite or transit
Laser tracker
• Get help from the TA or knowledgeable user
• These are very expensive instruments
• Use the LT to measure some of the same
features measured with the total station
• How do the two sets of measurements compare?
• Which measurements are more precise, axial or
lateral (azimuthal)? Why?
Laser Tracker
• Adopting spherical coordinate
system, R(radius), Θ(Azimuthal
angle), Φ (Elevation angle)
– R: measured by
• IFM: distance measuring laser
interferferometer
• ADM: measuring time taking the
light travel between the tracker
and SMR
– Θ(Azimuthal angle), Φ
(Elevation angle)
• Precision rotary encoder
• Versatile precision measuring
tool in large volumetric target
SMR(Sphere Mounted
Retroreflector)
Lab: Measure OD and ROC of
an optic
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Install and set up Laser Tracker
Home the Laser Tracker using a
given SMR
Sample OD of a given optic(Lens
or Mirror)
Establish coordinate frame
Sample the surface of optic
Query,
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OD of the optic
RoC of the optic
Surface figure
Compare the measured OD and
RoC to the result from Vernier
calipers and 3-ball spherometer
CMM
• Go through start up check list
– Marco made up a nice couple pages on this
– He is out but I will get this on-line asap
• Follow through with the measurement of the
Master ball to establish the machine coordinate
system
• Measure several artifacts and use the software
to see the best fit shape
CMM
• Adopt Cartesian
coordinate, X, Y, Z
– Linear coordinates XYZ are
implemented in a precision
guide way(typically
airbearing)
– Each position is measured
by a precision linear
encoder
– Touch trigger probe (a
switch) trigger the signal to
record position
Lab: Measurement features
• Install the part provided on
CMM
• Establish coordinate frame
• Measure dimensions, write
down the reading and see if
the measured value meet the
tolerance
• Compare the result to the
result from the measurement
using Vernier calipers,
Micrometer and other
mechanical measurement
tools
Drawing
Important
• All the instruments are very expensive
– Little to no money to fix them if broken
– Money earning projects rely on the CMM and LT
• Do not force anything, move slowly and
deliberately. Don’t drop anything
• Think about each step before making a move
• The CMM probe tip is very delicate, move up to
work slowly and gently