| The PCR1810 COMPENSATOR motor load control,
manufactured by Load Controls Inc, is a very effective unit for
increasing the efficiency of grinders. For an automatic grinding
cycle, it is desirable to quickly bring the grinding wheel into
contact with the work piece without "grinding air" and
wasting production time. Since the size of the grinding wheel is
always changing, it's hard to predict exactly where the wheel is.
The solution is to monitor the spindle power as the wheel
advances toward the work piece. An increase in power means that
the wheel has touched the work piece. A great advantage of doing
this is that the sensor is not located in the work area. To make
this work reliably in practice requires 3 important elements:
1)Eliminate the need for adjustment, 2)High sensitivity, 3)Fast
response. The Compensator senses the machine spindle
power and has two set points, one is used to control the grinding
wheel whilst the other to prevent gross overloads. By measuring
motor power rather than just motor amps, the sensitivity is
greatly increased. For a lightly loaded motor, there is a 10X
improvement in sensitivity over current monitoring systems. The
control also has a compensating feature which will zero out the
baseline power. The machine baseline power changes significantly
as temperatures change, coolant and the lubricant viscosity
change and the mechanical clearances change. During each machine
cycle when the process is in its baseline or idling position a
contact closure is sent to the control from a limit switch (or
from a programmable controller) and the control learns this value
and retains it in memory during the next machine cycle.
The control then looks for an increase above
this baseline value. By zeroing out the inherent machine drift ,
the control is quite precise. A special filtering scheme is used
to insure fast response, it is easy to install since it requires
no machine modifications and is a low cost solution.
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