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Chapter 13 Coordinate Measuring Machines


Each carriage has a fitted positioning transducer record the displacement of ... Gantry type: extreme large work pieces. 5 variation types ... – PowerPoint PPT presentation

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Title: Chapter 13 Coordinate Measuring Machines

Chapter 13 Coordinate Measuring Machines
  • Overview
  • The role of CMMs
  • Types of CMMs
  • Types of probes
  • Probe calibration
  • Machine programming
  • Modes of operations
  • Metrological features

The Role of CMMs
  • Reduce inspection time (80-90)
  • Widely use in manufacturing
  • Short runs
  • Apply for Multiple features
  • Flexibility
  • Avoid Production interruption

Structure of a CMM
  • 3 Axes XYZ
  • Carriage on each axis the 1st carriage travels
    ?guide the 2nd one ?3rd travels along its axis
  • Each carriage has a fitted positioning transducer
    ?record the displacement of them ? computer or
  • The 3rd carriage ? probe ? contact ? all
  • Envelope limits of travel in all three axes (not
    limit size of work pieces)

Types of CMMs
  • 10 standard types
  • 5 common types
  • Cantilever type large envelop
  • Bridge type rigidity
  • Column type rigidity, accuracy
  • Horizontal arm type large work pieces
  • Gantry type extreme large work pieces
  • 5 variation types
  • Special type rotating work table or probe
    spindles (column type) speed up inspection

Five Basic Types of CMMs
Five Variations of Basic CMM Types
Types of Probes
  • Hard contact make contact manually
  • Soft contact (electronic probes) probe head,
    probe, stylus
  • Can record movement directions 4-way, 5-way,
    6-way probes
  • Use soft probes compare as zero point
    standard null process, standard built-in scale
  • Non-contact type probes Avoid deforming objects
    by stylus
  • Light beam stylus
  • Microscope
  • Optical probes

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The Ball Styli, Multiple Styli Probe, Joints and
Probes Calibration
  • Probe calibration remove the deflection problem
    of probe

Machine Programming
  • Benefitsaccuracy, speed, precision
  • Functions
  • Resolution selection
  • Measurement units conversion
  • Conversion of rectangular coordinates to polar
  • Axis scaling
  • Datum selection and reset
  • Circle center and diameter solution
  • Bolt-circle center and diameter
  • Save and recall previous datum (datum reference
    ? data)
  • Nominal and tolerance entry
  • Out-of-tolerance computation
  • Statistical process analysis and control (contour
  • Use of subroutines for repetitive inspection
    work ? reduce operator errors caused by fatigue

Typical Useful Subroutines
Modes of Operations
  • Manual mode CMMs obtain measurement data and the
    program provides the measurements in the required
    form of user
  • Automatic mode the computer provides the
    measurements in the proper sequence, then uses
    the data to compute the results
  • Programming mode self-teach ? record sequence
    or add off-line instructions
  • Statistical analysis mode use the batch mode
    for large number of similar parts ? trends that
    may lead to out-of-control conditions, CMMs use
    for complex parts with many features

Metrological Features
  • Repeatability 2.54?m (?when size of CMM?)
  • Accuracy 10.16?m (?when size of CMM?)
  • CMMs can reduce computational errors, systematic
    errors (check before measure)
  • CMMs do not diminish thermal error,
  • User must be careful about normalization of the
    machine, vibration
  • CMMs have the alignment built-in function (line
    of measurement//the axis of standard)
  • Avoid the misinterpretation the source of error
    in angle measurement
  • Easy control the distortion of the workpiece with
  • High reliability check itself.