LINK Systems System 1100 Tonnage Monitor - Manual (Page 41)

THEORY OF OPERATION
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3-4
Figure 6.
straight side machines, or, in certain applications, on the
multiple connections between crankshaft and slide on machines that
develop slide motion mechanically. Under these conditions of
geometric symmetry, a central machine load should be divided
equally to each strain link. Each channel of a two channel tonnage
monitor should read 1/2 and each channel of a four channel unit
should read 1/4 of a central load.
To obtain the peak total tonnage exerted by complex tooling in a
machine cycle with staggered forces that are not centrally located,
System 1100 tonnage monitors do not add the peak tonnages on each
channel. Rather, the instantaneous sum of all channel outputs is
taken, and a separate peak hold circuit stores the peak total
signal for display. On complex tooling, the total peak tonnage is
not usually the sum of the displayed tonnages on each channel! To
illustrate this principle, consider a die with two staggered
punches of equal cross-sectional area and that are equally sharp.
The longer punch is located on the left side of the die, and the
shorter punch is on the right side of the die as shown in Figure 5.
Assume the die is located in the
center of an OBI press bed and
that two holes are to be pierced
in a sheet metal blank. A two
channel tonnage monitor is used
with strain gauge transducers
located on both sides of the
press frame, and the load signal
for both left and right channels
is observed on an oscilloscope
to be that shown in Figure 6.
The oscilloscope trace shows
that the longer left punch
contacts the blank first and
exerts a peak total force of 100
tons at time t1, with 60 tons distributed to the left side of the
frame (since the punch exerts its force to the left of the press
centerline) and 40 tons distributed to the right side of the frame.
A moment after the left punch breaks through the blank, the right
punch contacts the blank and builds up to a total peak tonnage of
100 tons at time t2, with 60 tons distributed to the right side and
40 tons to the left side of the press frame.