This page contains links to articles related to coordinate measuring
machines and inspection. All articles are provided in PDF format
and can be opened using any PDF viewer.
the biggest question when performing any kind of measurement that has a
tolerance is simply “is it in spec?”. In some cases it is very clear
that the measurement is either inside or outside of tolerance and in
other cases, particularly when the measurand is close to the tolerance
limit, it is not so clear and cannot be stated with any kind of
confidence. Measurements that are close to the tolerance limit can
randomly fall on either side of it due to measurement repeatability.
Measurement uncertainty widens up the grey area around the measurement
tolerance beyond what can easily be seen from measurement repeatability.
This article is about compliance statements and the accepted practice
for expressing compliance to a specification. When expressing an opinion
of compliance from the performance tests on a coordinate measuring
machines following ASME B89.4.10360 or ISO/IEC 10360, it is necessary to
do this with a suitable level of confidence particularly if traceability
is a requirement.
Applying Compensation Map Data
article is written as an example of how to interpret compensation data
from a coordinate measuring machine and create a correction value and
tool coordinate system for any position in the measuring volume. This
information can be used to build a working model for error map
correction and can be useful for developing other utilities to allow
interpretation or correction based on measurement data.
Compensation Error Map Rotation Point
article describes the significance of the position selected for the
compensation error map rotation point for a coordinate measuring
machine. In a perfect world the application of the compensation data
will behave exactly the same as the mechanical error but there is
usually a bit of difference as the compensation methods are often
generic. For physical angular errors the measurable straightness error
is always zero at the point where the mechanical rotation occurs. The
rotation point of the compensation map is a description where rotational
corrections are calculated from, and ideally the same, as the mechanical
Calibration Sphere Form Error
article describes the effect of form error on a sphere when used as a
calibration artifact on a CMM. The purpose of the calibration sphere is
to determine the effective stylus tip diameter and relative probe offset
between multiple probe positions. Multiple probe positions can be from a
fixed head with more than one stylus or a single stylus on an
articulating probe head.
Comparison Between ISO/IEC 10360-2:2009 and
ASME B89.4.1:1997 Performance Standards
document describes the testing method and results from a comparison of
the two major performance testing standards for coordinate measuring
machines; ISO/IEC 10360-2:2009 and ASME B89.4.1:1997. The ASME
B89.4.10360-2:2008 is identical to ISO/IEC 10360-2:2009 therefore the
results apply to both standards.
The Renishaw Machine Checking Gauge is included in the comparison tests
as a point of reference. This gauge is ideal for CMM interim checking
due to its speed and ease of use so therefore a comparative test using
this gauge to established standards seemed appropriate.
CMM Measurement Uncertainty Budget
article describes a generic uncertainty budget when using a CMM for
inspection. The estimation of measurement uncertainty is a requirement
for ISO/IEC 17025.
article describes the reasons for having the environment of a coordinate
measuring machine at the standard reference temperature of 20 ?C and the
effects of using a CMM at a non-standard temperature. This article also
looks at common methods used to compensate for temperature and the types
of materials used in the construction of CMM's that have an impact on
how the machine will perform when temperature changes.
Temperature variation in a lab environment, when using a coordinate
measuring machine, can be a large source of measurement error. Partial
solutions to temperature related problems exist but do not address all
problems and may even introduce collateral problems in the process.
Compensation Map Increments
article is written as a guide for the choice of compensation map
increments used on coordinate measuring machines. Selecting a suitable
increment is important since a step size that is too large or too small
will result in a loss of machine accuracy. Often the actual compensation
map increment is selected based on secondary reasons (i.e. matches the
increment of a step gauge or is simply a round number). In some cases
map increments are selected with the belief that using a very small
increment will improve the performance of the CMM. Most calibrators only
have one opportunity to fully map a machine so comparative tests where
the map increment is adjusted are never performed.
Horizontal Arm Deflection
Arm coordinate measuring machines have a unique problem due to their
cantilever design. As the arm extends the center of gravity changes
resulting in a measurable deflection in the tower of these machines.
This article describes some of the problems related to calibration of
horizontal arm coordinate measuring machines and effects of deflection.
All manufacturers of horizontal arm CMM's have provisions for dealing
with tower deflection as this is a common problem for this type of
CMM Interim Testing
tests are performance checks of a CMM that are done regularly between
calibrations. Interim checks are important as they can proactively
indicate that a problem exists with a machine and can also provide
confidence in the equipment.
This article is written to describe different methods for CMM interim
CMM Kinematic Axis Order
describe the significance of the kinematic axis order of a CMM machine.
The kinematic order defines how the machine axis are interconnected and
is used as part of the machine compensation data to correct for known
errors. An incorrect kinematic order means the software is not capable
of compensating for the known machine errors properly and may actually
increase the measurement error of a CMM.