M A E D A Crawler Crane 4.3 MOMENT LIMITER (OVERLOAD PREVENTION DEVICE)
5/2020 CC1908S-1 4-21
MOMENT LIMITER
FUNCTION
DANGER
• Do not remove or disassemble the controller
to conduct repairs. Also, do not reposition
the controller.
• If an object hits the controller or damage is
discovered, be sure to check that the
overload operation functions correctly.
Be sure to repair the detector if the overload
operation does not function correctly.
• The slewing operation does not stop
automatically even when the crane is
overloaded. Do not slew the crane if it is
overloaded.
• When the crane is approaching the stop
position while operating the boom, be sure
to reduce the boom operation speed.
If the boom is operated at a high speed, it
may exceed the predetermined stop position
and the machine may tip over, causing
serious accidents resulting in death or
serious injury.
The moment limiter is a device that is installed to
prevent dropping the hoisted load, damaging the
crane boom, and/or toppling the machine if it is
overloaded.
Before starting crane operations, be sure to
inspect the moment limiter to make sure that it
operates correctly.
MOMENT LIMITER
MECHANISM
The moment limiter knows the current posture
based on the boom angle gauge and boom length
gauge and calculates the "Rated total load" for the
current conditions using the number of falls (input
by the operator).
When the load is actually hoisted, the moment
limiter calculates the "actual load" (hoisted load)
from the pressure value taken from the pressure
sensor on the derricking cylinder. The moment
limiter compares the "Rated total load" calculated
for the current posture against the "Actual load"
(hoisted load) and issues an alarm if the result is
as follows: "Actual load / Rated total load = 90 %
to under 100 %".
If the calculated result is "Actual load / Rated total
load = 100 % or greater", the moment limiter
issues an alarm and automatically stops
operations to move the boom toward danger.
The overload stop accuracy satisfies the stop
accuracy in the following equation by slowly
lowering the boom:
Stop
accuracy =
A − B
× 100 < +10 %
B
Where, A: Total weight of hoisted load + hook +
hoisting accessories (slings, etc.)
B: Rated total load for working radius
(actual measured radius) where the
boom stopped due to overloading
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