JLG 450AJ Service Manual - Manual (Page 67)

SECTION 2 - PROCEDURES
3120869 – JLG Lift – 2-51
Only green light on and no actuator movement
Action:
1. Adjust trim potentiometers.
2. If problem continues, replace unit.
2.23 DRIVE AND STEER CONTROLLER
Controller Theory & Definitions
This controller is specifically designed and manufactured
to provide a proportional output to a SUNDSTRAND Dual
Coil electro-hydraulic valve. The controller you are about
to calibrate has the following features:
PWM Output (Pulse \Width Modulation)
The SUNDSTRAND valve being driven by this controller
requires an electrical current, between 20 and 130 milli-
amps in order to shift the valve spool from minimum to
maximum flow. Because of the mass of the spool, shifting
it a very small distance would be very difficult to do with-
out overshooting the mark. This overshoot is called hys-
teresis and makes precise control of the function very
difficult. PWM output provides a pulsed current to the
spool which actually vibrates the spool so that it is never
at rest and very easy to shift. This controller pulses the
spool 100 times (cycles) per second and as you move the
handle, the electronics change the time period the pulse
is on within that cycle. As you move the handle away from
center, the on time period or width of the cycle pulse will
increase and as you move the handle back towards the
center, the pulse will decrease. The percentage of on time
to off time of the PWM signal is called the Duty Cycle, if it
is on for 80% we call that an 80% duty cycle.
Current Regulated Output
This controller output is also current regulated. This con-
troller was designed to output from 20 to 130 milliamps
through a 17 Q coil using a 12 volt supply. Ohms Law dic-
tates that the Current is always equal Voltage divided by
Resistance. If the supply voltage or the coil resistance
should change, Ohms Law dictates that the output current
must also change which will affect the speed of the func-
tion accordingly. Because this controller is equipped with
a current regulated output, it senses a change in voltage
or resistance in the circuit and adjusts the duty cycle of
the PWM signal so that the output current remains a con-
stant current. Because the Current is constant and Resis-
tance is machine dependent, the duty cycle will vary in an
attempt to supply the required level of output. This feature
ensures that the function speed the operator wishes to
select always remains the same, within the limits of Ohms
Law.
Dual Range
This controller is capable of providing two, independently
adjustable, maximum output ranges with the same
amount of handle travel. The Hi Range would normally be
adjusted for full flow (maximum function speed) of the
valve at full handle travel. The LO Range would provide
some potion of the Hi Range setting, providing reduced oil
flow to the valve, with the handle at full travel. LO Range
provides the operator with excellent control of the propor-
tional function with increased resolution for precise
maneuverability.
Both outputs are linear between the Threshold setting and
their respective setting. The controller is in the Hi Range
mode when 12 volts is applied to the (R) terminal. As a fail
safe, when system voltage is removed from the (R) termi-
nal, the Lo Range feature is active.
I.R.S (Integrated Ramp System)
This controller is calibrated to provide a maximum ramp
time of 2 seconds. This feature limits the rate of change of
the output, eliminating a jerky response associated with
sudden handle movements. Any change in handle posi-
tion will result in a smooth change in function speed. The
2 seconds is measured between the Threshold and Hi or
LO range setting.