JLG 1250AJP Service Manual - Manual (Page 335)

SECTION 4 - BOOM & PLATFORM
3121171 – JLG Lift – 4-95
4.29 ELECTRONIC PLATFORM LEVELING
NOTE: For more detailed information concerning system
adjustment and operation, refer to Section 6 - JLG
Control System.
Description
Electronic platform leveling replaces the conventional
hydraulic method of platform leveling.
To control electronic platform leveling the platform is
equipped with a pair of tilt sensors, one primary and one
secondary, mounted to the non-rotating portion of the
platform rotator. The tilt sensors are monitored regularly
and the platform level up and down valves are automati-
cally controlled to maintain set point as the machine is
operated.
PRIMARY AND SECONDARY TILT SENSOR INTERAC-
TION
The secondary tilt sensor is used as a backup to the pri-
mary tilt sensor. Any time a tilt set point is reset, a value
from each sensor shall be set.
If a fault occurs with the primary sensor, control will revert
to the secondary sensor. (This is discussed in more detail
in the error response section.)
Because of the mounting orientation of the tilt sensors, the
primary tilt sensor will output ascending voltage values
with increases in positive platform tilt angle. The backup
or secondary tilt sensor will output descending voltage
values with increases in positive platform angle.
PLATFORM VALVES
The platform specific valves are located in a manifold at
the platform.
There are individual proportional control valves that con-
trol each of the four platform functions; Platform Level,
Platform Rotate, Jib Lift, and Jib Swing.
There is also a Platform Dump Valve, located in the plat-
form valve manifold, which is used to hydraulically isolate
the control valves and to improve hydraulic response.
The Ground Module controls this valve to provide manual
platform leveling in the event that the Platform Module is
inoperable.
In ground mode, the platform dump valve is turned on
whenever any platform or jib valve output is turned on.
Whenever all platform and jib valves are turned off, the
platform dump valve is turned off.
In platform mode, the platform dump valve is turned on
whenever the footswitch is depressed.
Normal Operation
AUTOMATIC LEVELING
Two tilt sensors, mounted on either side of the platform
support, are used to measure the incline of the platform
with respect to gravity and control the automatic leveling
function, one is used as the primary sensor and one as a
secondary back up sensor.
The level system shall assume a new fixed set point
(fixed incline of the platform with respect to gravity) each
time the control system is powered up (cycling of the
EMS).
Automatic platform leveling only functions while operating
drive, telescope, lift or swing. It does not operate while
operating any other function (e.g. rotate, jib, or steer).
The proportional control for these valves varies. This is
dependant on the tilt variance from target as well as on the
impact coil temperature is having on the current to the
valves.
If a command from the Platform Level Up and Down tog-
gle switch on either the platform or the ground is received,
automatic platform leveling will cease and the appropriate
output will be commanded to turn on.
When the toggle switch is released, after ¼ second, the
current filtered value of tilt angle will be taken as the new
set point.