Proceedings of the ICMT 2003 conference in Taipei, Taiwan, ROC,
December 2-6, 2003.
Measurement of Volumetric Positioning
Accuracy of a 5-axis Machine By Laser Vector Technique Charles Wang and Clark Chung* Optodyne Inc., 1180 Mahalo Place Compton, CA 90220 U. S. A. 310-635-7481 mailto:optodyne@aol.comAbstract For
a 5-axis machine tool, the 3D volumetric tool-tip positioning accuracy is
very important for parts
accuracy and quality
assurance. Just calibrate the 3
linear axes and the
2 rotational axes is not enough.
There are straightness
errors for each of the 3 linear
axes, and squareness errors between the 3
linear axes, misalignment errors
between the linear axes and the
rotary axes. Hence, it is very
important to measure the over
all positioning accuracy by measuring the
tool-tip positioning errors.
Reported here are the measurement of 3D volumetric
positioning accuracy by
the laser vector method; the measurement of the rotary axes angular accuracy by a
dual-beam laser system; and a theoretical
analysis on the tool tip
positioning accuracy measurement by a
single aperture laser system.
The performance of these measurements
is relatively simple,
fast and straight forward. Its
applications in the
calibration and compensation of 5-axis
machines will improve the
parts accuracy and quality without
incurring high costs and long machine down
time. *Currently with Ford Motor Company in Taiwan.
1.Introduction The
world wide
competition demands
higher machining
efficiency and better quality. As 5-axis
machine tool is a high added value work
machine, it is not only
provided with 3 axis of CNC machine
but also has 2
rotary axes to produce blade or
complex parts. 5-axis is
applied in aerospace industries, die
manufacturing, and
other precision
applications. Furthermore, due
to the
needs for
complex components
to be machined, the
usage of 5-axis machining center has been increasing in recent years.
The contouring
accuracy or tool-tip positioning
accuracy is considered to
be one of the most
important features
especially for machining mold
components. For a 5-axis
machine tool, just calibrate the 3 linear
axes, X, Y, Z and the 2 rotational axes, A and B, or A and C, is not enough. There are vertical
and horizontal straightness
errors for each of the 3 linear axes, and squareness errors between the 3 linear
axes, misalignment
errors, such as
skew, non-orthogonal and non-intersection of the
2 rotational axes, and
the non-intersection of the center lines
of the spindle
and the z-axis.
Hence, it is very
important to
calibrate and compensate
the 3D volumetric positioning errors and the
rotational axes angular
errors, and to check
the over all tool-tip
positioning errors.
Reported here are the
measurement of 3D volumetric positioning
errors by the laser vector method and the rotary axes angular errors
by a dual-beam laser
system. The theoretical analysis on
the over all tool-tip positioning
errors measured by a single-aperture
laser system and a spherical target are
presented. 2. Measurement of 3D volumetric
positioning errors
2.1 Basic theory Based on the rigid body motion
assumption , for a 3-axis machine, there are
21 errors, namely 3
displacement errors, 6
straightness errors, 9 angular errors and 3 squareness errors. These 21 rigid body
errors can be expressed as the following
[1]. Linear displacement errors: Dx(x), Dy(y), and
Dz(z) Vertical straightness errors: Dy(x), Dx(y), and
Dx(z) Horizontal straightness errors: Dz(x), Dz(y), and
Dy(z) Roll angular errors: Ax(x),
Ay(y), and Az(z) Pitch
angular errors: Ay(x),Ax(y), and Ax(z)
Yaw angular errors: Az(x), Az(y), and
Ay(z) Squareness errors: Øxy,
Øyz, Øzx,
where, D is the
linear error, subscript is the error
direction and the
position coordinate is inside the
parenthesis, A is the
angular error, subscript is the
