JLG 1250AJP Service Manual - Manual (Page 248)

SECTION 4 - BOOM & PLATFORM
4-8 – JLG Lift – 3121171
4.9 ELECTRICAL RETRIEVAL SYSTEM
The Electrical Retrieval System provides a backup means
of retrieving an elevated boom in the event of a failure of
any sensor used in the envelope control system (see Sec-
tion 4.6, Envelope Control System). Although the system
is continuously monitored for its viability, it is not active
until a failure of the envelope control system is detected.
The system uses a load cell pin to attach the tower lift cyl-
inder to the turntable. This pin is instrumented with
gauges allowing the forces in the pin to be monitored. The
control system uses these force readings to select one of
two sequences of retrieving the boom in a manner neces-
sary to maintain the stability and structural integrity of the
machine.
The two sequences of boom retrieval are determined
based on the boom being closest to a position of forward
stability concern or closest to a position of backward sta-
bility concern (See Figure 4-2., Figure 4-3., and Figure 4-
4.). Regardless of the sequence selected by the control
system, the control system must recognize successive
positions of the main and tower booms before continuing
with the sequence.
While operating in this mode, the positions of the booms
are determined by sensors not used by the primary enve-
lope control system. These include the tower length
switch, tower cylinder angle sensor, main boom angle
switch, and main boom length switches.
Operating in this mode will result in reduced function
speeds, BCS warning light illumination, and restriction of
functions. Attempts to operate restricted functions will
flash the BCS light and sound the platform alarm.
NOTE: For more detailed information concerning system
adjustment and operation, refer to Section 6 - JLG
Control System.
4.10 HYDRAULIC RETRIEVAL SYSTEM
The Hydraulic Retrieval System provides a backup means
of retrieving an elevated boom in the event of a recog-
nized failure within the primary hydraulic control system
related to the main lift, tower lift, and tower telescope func-
tions. The control system monitors the primary hydraulic
control system for short and open circuits, unexpected
boom sensor response to command, control valve spool
position faults, internal valve control module faults, and
CAN BUS communication faults.
When a fault is detected, the control system automatically
bypasses the appropriate hydraulic components and
using alternative valves and control logic allows the opera-
tor to return the boom to the ground. In some cases the
boom will be allowed to move only to the extent gravity is
capable of assisting and in other cases the boom will be
powered to allow complete retrieval to the transport posi-
tion.
Although the envelope control system (see Section 4.6,
Envelope Control System) remains active during the
hydraulic retrieval, the tower lift functionality will follow the
tower path (see Section 4.7, Tower Path Control System)
in an approximated fashion. Rather than the normal com-
bined movements of tower lift, tower telescope, and main
lift, the tower lift movements will move in an alternating
sequence between tower lift and tower telescope with the
automatic main lift system (see Section 4.8, Automatic
Main Boom Control System) disabled.
Operating in this mode will result in reduced function
speeds, and restriction of functions. Attempts to operate
restricted functions will flash the BCS light and sound the
platform alarm.
NOTE: For more detailed information concerning system
adjustment and operation, refer to Section 6 - JLG
Control System.
4.11 CONTROLLED BOOM ANGLE SYSTEM
The Controlled Boom Angle System uses the envelope
control sensors to enhance the control of the boom by
minimizing the interaction of swing and drive functions
with the envelope edges. This interaction is due to two
factors. First, the envelope is controlled relative to gravity
regardless of ground slope and second, the turntable/
boom mounting is effected by swing and drive functions
when the ground slope varies. This can cause the boom
position to vary within the envelope or even violate the
envelope edges when swinging or driving without inten-
tionally moving the boom. The controlled boom angle sys-
tem minimizes this effect by automatically introducing
either the tower or main boom lift up or down during swing
and drive commands to maintain a constant boom angle
relative to gravity.
When the tower is below the tower transport angle and the
main boom is 25 degrees above the tower boom, the
angle of the main boom is controlled. When the tower is
above the tower transport angle, the angle of the tower is
controlled regardless of main boom position.
Just as the booms are controlled during swing and drive
functions, the tower angle is also controlled during main
boom lift and main boom telescope functions.
Controlled boom angle is disabled with any envelope vio-
lation or failure.
NOTE: For more detailed information concerning system
adjustment and operation, refer to Section 6 - JLG
Control System.
4.12 SLOW DOWN SYSTEM
To reduce the machine dynamics and improve operator
control, the control system uses the envelope control sen-
sors to automatically slow down the tower lift up, main lift
up, and main lift down function speeds as the minimum
and maximum angles of the working envelope are