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Effective tool condition detection on a multi-spindle head is possible with the right controller, using MEMS
vibration-sensing technology in combination with true power monitoring that derives data from seven additional
linear axes.
FIGURE 3
tracing the entire profile
of a tapping operation at
speeds up to 27,000 rpm.
True power monitoring
is not effective in such an
application because most of
the power that is supplied
to the motor is actually
consumed in the motor
under those conditions,
making it extremely
difficult to differentiate the
power that is consumed by
the tap.
Multi-spindle heads
are another specialized
situation that often require
different monitoring tech-
nologies. In practical terms,
true power monitoring of
the spindle motor can be
effective in detecting tool
condition or breakage on
a multi-spindle head using
up to four identical tools
(see Figure 3). Anything
beyond that will prob-
ably require an alternative
technology. In those cases, acoustic monitoring is the most
common choice. As long as the tool diameter does not vary
by more than 20 percent, an acoustic monitor can detect
breakage in a multi-spindle head with many more than four
tools. If the diameter varies by more than 20 percent, mul-
tiple monitors may be necessary.
(PROCESS
FIELD BUS
It is also possible to instrument individual toolholders
with strain gauge technology. Unlike piezoelectric sensors,
strain gauges can be loaded for extended periods of time
without drifting. This makes them an excellent solution for
gun drilling and tapping applications. For example, there are
toolholder-mounted strain gauge units capable of