LINK Systems 5100-8 Tonnage & Analog Signal Monitor - Manual (Page 11)

Doc #: L-802-1110 Page 9 Rev. 02
machine frame was 60 tons, that the maximum tonnage measured on the right side of the machine frame
was 60 tons, and that the maximum total tonnage exerted on the machine frame was 100 tons.
2.1.3 Reverse Tonnage
In addition to monitoring the “forward” tonnages for a press, the tonnage monitor also measures and
monitors the “reverse” tonnage. A press frame acts as a kind of stiff spring. When exerting tonnage in
the down part of the cycle, portions of the press frame stretch proportionally to the tonnage exerted. In
the case of a punch, for example, the tooling comes down and contacts the material. The press frame
starts stretching, and this generates tonnage exerted on the material. Finally the tonnage exerted is
sufficient for the punch to “break through” the material, and when it does the press frame tries to “spring
back” to its original shape. Just like a regular spring, the press will overshoot its original resting
position due to inertia and will actually compress instead of stretch. The tonnage registered on the frame
during this “rebound” is the reverse tonnage. Reverse tonnages are typically much harder on the press
than forward tonnages. As a result, press manufactures usually allow much less reverse tonnage on a
machine than forward tonnage. For instance, a 500 ton machine may only be rated for 50 tons of reverse
load.
2.2 Data Windows
Peak tonnage monitors capture the maximum tonnage seen by each strain gage over the stroke. This
maximum tonnage is compared to setpoints to determine if an alarm should be generated to stop the
production process. While this is adequate for most applications, complex tooling can produce multiple
peaks resulting in only the highest peak being checked against setpoints. Where closer monitoring is
desired in these applications, the tonnage monitor provides up to four “Data Windows” to monitor
additional peaks other than the absolute maximum peak tonnage. These additional peaks are referred to
as “local” peaks. Each data window consists of a separate high and low limit that are used from a given
start angle to a given end angle.
The tonnage graph in Figure 3A is for a two station
die. The first station (between 165 and 170 degrees)
cuts out the part (local peak), and the second station
(at 180 degrees) stamps a logo onto the part (absolute
peak).
Since the tonnage required to coin the logo is greater
than the tonnage required to cut the part, the local
peak is not checked using a normal peak tonnage
monitor. The local peak could completely disappear
and a normal peak tonnage monitor would not detect
any anomaly in the process since the absolute peak
limits are still being satisfied. This is exactly what
would happen if the material did not feed between
strokes as shown in Figure 3B. Using a single data window, however, places a separate high and low
limit on the local peak.
DW1
B.
A.
LOCAL
PEAK ABSOLUTE
PEAK
165 170 180
DW1
B.
A.
LOCAL
PEAK ABSOLUTE
PEAK
165 170 180
Figure 3: Example Data Window