UniCarriers FRSB14-8 - How the Lift Truck Works

HOW THE LIFT TRUCK WORKS?HOW THE LIFT TRUCK WORKS?
1-151-15
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HOW TRUCK BALANCE IS MAINTAINEDHOW TRUCK BALANCE IS MAINTAINED
Truck’s center of gravityTruck’s center of gravity
TrailingTrailing
wheelwheel
Load’s center of gravityLoad’s center of gravity
FulcrumFulcrum
Reach trucks have load handling equipment,Reach trucks have load handling equipment,
including a mast assembly, which travels back andincluding a mast assembly, which travels back and
forth along the outriggers. The trailing wheels of theforth along the outriggers. The trailing wheels of the
truck work as a fulcrum to achieve balance betweentruck work as a fulcrum to achieve balance between
the truck's center of gravity and the load's center ofthe truck's center of gravity and the load's center of
gravity. The relationship between the locations ofgravity. The relationship between the locations of
those two centers of gravity is vitally important forthose two centers of gravity is vitally important for
safety. The stability of the reach truck is maintainedsafety. The stability of the reach truck is maintained
best when the mast assembly is best when the mast assembly is fully retracted.fully retracted.
■■KNOW THE CENTER OF GRAVITY OFKNOW THE CENTER OF GRAVITY OF
YOUR LOADYOUR LOAD
Load center (from fork root) mmLoad center (from fork root) mm
Load’s centerLoad’s center
of gravityof gravity
DistanceDistance
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ll
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ww
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Weight x distance =Weight x distance =
moment (constant)moment (constant)
Basic load centerBasic load center
Materials of various shapes such as boxes or at orMaterials of various shapes such as boxes or at or
cylindrical items may be loaded on the lift truck. Incylindrical items may be loaded on the lift truck. In
order to accurately judge the stability of the truck,order to accurately judge the stability of the truck,
it is vitally important for the operator to know theit is vitally important for the operator to know the
location of the center of gravity for each type of load.location of the center of gravity for each type of load.
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HOW THE CENTER OF GRAVITY SHIFTSHOW THE CENTER OF GRAVITY SHIFTS
The stability of the lift truck is determined by theThe stability of the lift truck is determined by the
combined center of gravity, which is the product ofcombined center of gravity, which is the product of
the centers of gravity of the truck and the load.the centers of gravity of the truck and the load.
When the truck is empty, this point is the same asWhen the truck is empty, this point is the same as
the center of gravity for the truck, and when it isthe center of gravity for the truck, and when it is
loaded it shifts according to the center of gravityloaded it shifts according to the center of gravity
of the load. Since the center of gravity of the loadof the load. Since the center of gravity of the load
changes whenever the mast assembly is advancedchanges whenever the mast assembly is advanced
or retracted along the outriggers or the forks areor retracted along the outriggers or the forks are
raised or lowered, the combined center of gravityraised or lowered, the combined center of gravity
also changes. The center of gravity is also governedalso changes. The center of gravity is also governed
by the following factors:by the following factors:
••
 Size, weight Size, weight and shape and shape of the of the loadload
••
 Acceleration, deceleration Acceleration, deceleration and turning and turning radiusradius
••
 Loading Loading or or unloading unloading heightheight
••
 Surface condition Surface condition and gradient and gradient of the of the roadroad
•• Tilt Tilt angle of angle of the forksthe forks
•• Type Type of of attachment usedattachment used
•• Tire Tire materialmaterial
Rear view of the truck with loadRear view of the truck with load
The higherThe higher
the load, thethe load, the
higher thehigher the
combinedcombined
center ofcenter of
gravitygravity
CombinedCombined
center of gravitycenter of gravity
with truck tiltedwith truck tilted
Center of loadCenter of load
CombinedCombined
center ofcenter of
gravitygravity
Truck’s centerTruck’s center
of gravityof gravity
Center of loadCenter of load
Combined centerCombined center
of gravityof gravity
Center of the truckCenter of the truck
■■THE TRUCK TIPS WHEN THE CENTERTHE TRUCK TIPS WHEN THE CENTER
OF GRAVITY IS OUTSIDE THEOF GRAVITY IS OUTSIDE THE
STABILITY TRIANGLESTABILITY TRIANGLE
For a reach truck to remain stable, the combinedFor a reach truck to remain stable, the combined
center of gravity must be inside the triangle formedcenter of gravity must be inside the triangle formed
by the ground contact points of the left and rightby the ground contact points of the left and right
trailing wheels and the ground contact point of thetrailing wheels and the ground contact point of the
drive wheel. This is called the stability triangle.drive wheel. This is called the stability triangle.
If the combined center of gravity moves back furtherIf the combined center of gravity moves back further
than the trailing wheels, the truck will tip overthan the trailing wheels, the truck will tip over
backward with the trailing wheels as the fulcrum. Ifbackward with the trailing wheels as the fulcrum. If
the combined center of gravity moves outside thethe combined center of gravity moves outside the
stability triangle to the left or the right, the truck willstability triangle to the left or the right, the truck will
fall over to that side.fall over to that side.
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