JLG 24RS Service Manual - Manual (Page 101)

SECTION 4 - BOOM & PLATFORM
3121287 – JLG Lift – 4-1
SECTION 4. BOOM & PLATFORM
4.1 PLATFORM CONTROL ENABLE SYSTEM
The platform controls use a time dependent
enable circuit to limit the time availability of
“live” or enabled controls. When the footswitch
is depressed, the controls are enabled and the
operator has 7 seconds to operate any control.
The controls will remain enabled as long as the operator con-
tinues to use any function and will remain enabled 7 seconds
after the last function has been used. While the controls are
“live”, the enabled light will be illuminated in the platform dis-
play panel. When the time limit has been reached, the
enabled light will turn off and the controls will be disabled. To
continue use of the machine the controls must be re-enabled
to start the timer system over again. This is done by releasing
all functions, then releasing and re-depressing the footswitch.
4.2 FUNCTION SPEED CONTROL SYSTEM
The platform controls for the telescope and
platform rotate functions are controlled
through a common variable speed control
knob. This knob provides a common control
signal allowing a smooth ramp up, controlled
maximum output speed, and ramp down.
Each function has its own personality settings
allowing the characteristics of each function to be modified
using the standard analyzer. Not all functions will respond the
same to the changes in the function speed knob position.
4.3 TRANSPORT POSITION SENSING SYSTEM
This system is used to control the following systems:
• Above Elevation - Drive Speed Cutback System
• Drive/Steer – Boom Function Cutout System
The transport position sensing system uses a tower boom
angle switch mounted on the turntable side sheet and the
telescope switch mounted to the side of the base boom to
sense when the boom is in the position associated with high
speed travel. Both of these switches are normally closed and
positively open in the safe state. Above transport angle is rec-
ognized when the main boom travels from the stowed posi-
tion to 9° ± 2.5° above (it resets at 5.1° ± 2.5° above horizontal)
Out of transport position is also considered when the main
boom is telescoped out more than 16in. This is indicated by a
proximity switch on the side of the base boom.
4.4 BOOM TELESCOPE SPEED
The machine is equipped with a dual acting 2-stage cylinder
which performs the boom telescope function. The cylinder is 2
sections that equal a total stroke of approximately 8922mm
(351 in).
Extend Function
During operation of the telescope extend function the boom
will extend with multiple speeds. When the boom is fully
retracted and the telescope function is actuated, the boom
will provide fluid to the extend side of the cylinder causing the
boom to move at approximately 4.5 in/sec. After approxi-
mately 4440mm (175 in) of cylinder stroke the first stage will
bottom out and flow will be directed to the second stage. The
flow of hydraulic fluid stays the same and results in an increase
in cylinder speed due to the decrease in cylinder area. The cyl-
inder will continue to extend at approximately 9 in/sec for the
remainder of the 8922 mm (351 in) of stroke.
Retract Function
During the telescope retract function the boom also retracts
with multiple speeds. When the telescope retract function is
actuated flow will be directed to the 2nd stage of the cylinder
first causing the boom to retract at approximately 9 in/sec.
After approximately 4482mm (176 in) of cylinder stroke the
2nd stage will bottom out and the 1st stage will start to move.
It is not until the 2nd stage piston crosses over ports within the
cylinder that the 1st stage will start to retract. The 1st stage
will retract at approximately 4.5 in/sec for the remaining
amount of stroke.
4.5 BEYOND TRANSPORT POSITION - DRIVE SPEED
CUTBACK SYSTEM
When boom is positioned beyond the Transport Position as
described under Transport Position Sensing System, the drive
pump is automatically restricted to limit the drive system to a
speed of approximately 0.75 mph. See Drive System in Section
3 for more detail on the drive speeds, and see 3.10, Chassis Tilt
Indicator System for interaction with the tilt sensor.
4.6 DRIVE/STEER – BOOM FUNCTION CUTOUT
SYSTEM (OPTIONAL)
The Drive/Steer – Boom Function Interlock System uses the
Transport Position Sensing System to sense when the boom is
out of the transport position. Drive and Boom functions are
simultaneously functional when the booms are within the
transport position, as on the standard machine. When the
boom is beyond the transport position, the control functions
are interlocked to prevent simultaneous operation of any
boom function with drive/steer functions. The first function
set to be operated in this mode, becomes the master function
set. In other words, while operating drive/steer functions the
boom functions are inoperable and if operating boom func-
tions drive/steer functions are inoperable.