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1.5.2 FUNCTIONS OF MOMENT LIMITER
• Do not remove or disassemble, or repair any detectors, such as the boom angle gauge,
boom length gauge, or pressure sensor. Never reposition the detector from the
original location to another.
• When an object hits the detector or damage is found on it, be sure to check the
operating condition of the automatic stop.
If an abnormality occurs during automatic stop operation due to a failed detector, be
sure to repair it.
• Do not set the override switch to the “ON” (reset)
position except in case of an abnormality, or during
a load test. Setting the override switch to the “ON”
(cancel) position will disable the moment limiter
functions. Any crane operation in such conditions
will result in dropping of hoisted load, breakage of
crane boom, and/or crane tipping due to over load,
and may cause a serious accident resulting in
death or serious injury.
If the emergency stop cancel switch is set to the
“ON” (release) position, an alarm buzzer sounds
intermittently.
• The crane slewing operation does not stop automatically when the crane is
overloaded. When overloaded, the crane must not be slewed.
• When the boom is approaching the stop position while in operation, be sure to lower
the operation speed of the boom.
Operating the boom at high speeds may result in a serious accident, such as death or
serious injury. The boom may fail to stop at the predetermined position, causing the
machine to overturn.
The moment limiter is a safety device for preventing accidents arising from overload, such as
dropping of a suspended load, damage to the boom or an overturning accident of the machine.
Before starting crane operations, be sure to inspect operation of the moment limiter to make sure
that there is no abnormality.
[1] MECHANISM OF MOMENT LIMITER
The moment limiter calculates the Rated Total Load in the
current condition by (1) detecting the current boom position
from the boom angle and the boom angle gauges, (2)
detecting the outrigger extension state with the outrigger
position detection switch, and further (3) obtaining the
number of wires falls (specified by an operator).
When a load is actually hoisted at this time, the pressure
sensor for the derrick cylinder section causes the Actual
Load (i.e., a hoisting load) to be output to the moment
limiter.
The moment limiter makes a comparison and calculation
on the “Actual Load” (hoisting load) and the “Rated Total
Load” that was calculated based on the current boom
position. Then, an alarm goes off if the result is as follows:
“Actual Load/Rated Total Load = 90 to 100 %”.
If the result is as follows: Actual Load/Rated Total Load ≥
100%, then the moment limiter generates an alarm and
automatically stops the ongoing boom operation.
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