Rotator Assembly; Theory Of Operation - JLG 400S Service And Maintenance Manual

4.9

ROTATOR ASSEMBLY

Theory of Operation

The rotary actuator is a simple mechanism that uses the slid-
ing spline operating concept to convert axial piston motion
into powerful shaft rotation. Each actuator is composed of a
housing with integrated gear ring (1) and only two moving
parts: the central shaft with integrated bearing tube and
mounting flange (2), and the annular piston sleeve (3). Helical
spline teeth machined on the shaft engage matching splines
on the inside diameter of the piston. The outside diameter of
the piston carries a second set of splines, of opposite hand,
which engage with matching splines in the housing. As
hydraulic pressure is applied, the piston is displaced axially
within the housing similar to the operation of a hydraulic cyl-
inder while the splines cause the shaft to rotate. When the
control valve is closed, oil is trapped inside the housing, pre-
venting piston movement and locking the shaft in position.
1
2
Bars indicate starting positions of piston and
shaft. Arrows indicate direction they will rotate.
The housing with integral ring gear remains sta-
tionary.
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3
SECTION 4 - BOOM & PLATFORM
The shaft is supported radially by the large main radial bearing
and the lower radial bearing. Axially, the shaft is separated
from the housing by the main and lower thrust washers. The
end cap is adjusted for axial clearance and locked in position
by set screws or pins.
The actuators are equipped with factory installed counterbal-
ance valves, which performs four major functions.
• Protects the actuator in the event of overload.
• Enables the actuator to hold position without drifting
when external loads are applied.
• Reduces hydraulic backlash by pressuring the hydraulic
fluid.
Provides a constant controlled rate of rotation in over-center
load conditions.
Applying fluid pressure will displace the piston axially
while the helical gearing causes the piston and shaft
to rotate simultaneously.
The double helix design compounds rotation: shaft
rotation is about twice that of the piston. Applying
pressure to the opposite port will return the piston
and shaft
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