LINK Systems System 1100 Tonnage Monitor - Manual (Page 40)

THEORY OF OPERATION
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3-3
monitor total machine tonnage.
This monitoring method, however, does not determine load
distribution to the two sides of the machine frame due to off
center die forces. Since press manufacturers rate machines with a
uniformly distributed central load, the two "C" shaped side members
of the machine are designed to carry one-half the total machine
load rating (usually a generous overdesign allowance is provided
for short-term overloads). Tooling forces that act to the left or
right of the front vertical centerline of a gap or OBI press
distribute a larger proportion of the load to the left or right
side of the frame, respectively. Thus, it is possible to use dies
that exert forces within the machine rating and still overstress
one side of the machine frame due to off center loading.
Using two strain links, one on each sideframe member of a gap OBI
press, and using a two channel tonnage monitor gives the
distribution of tonnage to each side of the machine frame. Alarm
limits may be set for both sides of the frame to prevent
overloading due to off center loads. The total peak tonnage
exerted by the press is obtained for display by continuously
summing the two channel outputs and storing the maximum value of
the sum each machine cycle.
Similarly, machines with straight side frame configurations (four
corner post or modified four post construction) can be monitored as
to load distribution and total load by using a four channel tonnage
monitor with strain links on each upright between bed and crown.
Such monitoring indicates both eccentric loading from front to back
as well as left to right. A two channel tonnage monitor with
strain links mounted on the two connections of a two point straight
side press can measure left and right load distribution and total
load, but not front to back off center loading.
3.3 Summing Multiple Channel Outputs to Obtain Total Load
When multiple strain links are used to measure load distribution to
machine frame members, the outputs of tonnage monitor channels
associated with each transducer must be added to obtain the total
tonnage exerted by the machine in the production process. Strain
links should be mounted on geometrically symmetrical frame members
that share equal proportions of a centrally located machine load;
i.e., the two side frames on "C" frame machines, uprights on