421/521 Lab 5 Total Station, Laser Tracker and Coordinate Measuring Machine CMM
Motivation • Become familiar with three types of precision 3 D 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
• • • 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 • • • 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, – OD of the optic – Ro. C of the optic – Surface figure • Compare the measured OD and Ro. C to the result from Vernier calipers and 3 -ball spherometer
CMM • Go through start up check list – Written by Marco Favela and Todd Horne • 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
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