The present invention provides a device for determining the dynamics of a tool
sited in a CNC machine, as encapsulated by the Frequency Response Function. The
device uses an actively controlled electromagnet to excite forces on the tool.
The force is excited in a non-contact manner, allowing the force to be applied
to both a stationary and a rotating tool. The displacement is measured by standard
means, such as accelerometers, optical displacement or capacitance sensors. The
ratio of the force and the displacement in the frequency domain is the Frequency
Response Function. The force may be applied as a pure sine wave, providing the
Frequency Response Function at the frequency of the sine wave. Varying the frequency
of the sine wave provides the Frequency Response Function over the range of frequencies
of interest. The control of the force profile is handled entirely by the automated
controls and requires no special skills, training or manual interaction by the
user. No separate force sensor is required, since the electromagnetic force on
the tool may be accurately determined from the design of the electromagnet and
the tool position, geometry and material.