Platform Control Station
3.4 CONTROLS & SENSORS Elevation
The elevation sensor is an inductive proximity switch. It must be powered to operate. There is a 1.3k Ohm resistor where it connects to the ground module to produce the proper signal for the ground module. (See electrical sche- matic in Section 9 for details.) If Ferrous material is present, i.e. the mast is fully retracted, it will close. The sensor is calibrated mechanically.
The control system uses a combination of the elevation proximity switch and pothole protection switches to deter- mine if the platform is elevated. If these sensors do not agree a fault is thrown.
Joystick
The joystick is used to "command" both lift and drive. The Lift/Drive switch selects which one is applicable. This command may be modified by the control system based on interlocks and personalities.
On the joystick there are three switches and the control handle. The joystick control handle sensor is not a simple potentiometer. There is a position sensing element, and signal conditioning circuitry in it to generate the position signal. It is powered by 5VDC supplied from the platform controller. When centered it will output approximately 2.5VDC. Fully forward, it will output approximately 1 VDC. Fully backward, it will output approximately 4 VDC. On the handle is the trigger switch that must be depressed in order to operate the vehicle. This prevents unintentional movement. To pass start-up tests the three switches must be open and the joystick must be centered.
Joystick personalities to define the centered position (where command is 0%), minimum and maximum for- ward, as well as minimum and maximum reverse can be accessed. Joystick system Personality settings can be changed via ANALYZER -> PERSONALITIES -> ACCEL- ERATOR as follows:
• FWD MIN - The forward extent of the centered position. Values between this and REV MIN are where 0% is commanded.
• REV MIN - The reverse extent of the centered position. Values between this and FWD MIN are where 0% is commanded.
• FWD MAX - Joystick voltage where 100% will be com- manded.
• REV MAX - Joystick signal voltage where -100% will be commanded.
Tilt
The control system monitors the tilt sensor to determine if the vehicle is tilted excessively. This condition is called "Tilted". In the CE, Australia and Japan markets, if the vehi- cle tilt angle in any direction is greater than or equal to
other markets, the vehicle is considered Tilted if the vehi- cle tilt angle front to back is greater than or equal to 3.0 or tilt left to right is greater than or equal to 1.5.
3.5 TRACTION
The traction, or drive system, moves the vehicle along the ground by electric motors. The Armatures (rotating wind- ings) of the separately-excited drive motors are wired in parallel to the Power Module's M1 and M2 terminals. The M1 Terminal is always at the same voltage as the +B (Bat- tery Voltage when the Line Contactor is closed) and allows the module to measure current with the internal shunt (extremely low impedance). The M2 Terminal is pulled to Ground by the Armature Switch MOSFET's (con- nected to -B Terminal).
To provide variable speed control, the Armature MOSFET transistors switch On and Off at high frequencies (PWM/ pulse-width modulation; 16kHz). The Duty Cycle (On & Off time) is varied to control the voltage applied to the Arma- tures. When the MOSFET's spend 50% of the period On and 50% Off, approximately ½ of the available power will be applied to the Armatures (50% Duty Cycle). Similarly, the MOSFET are On continuously (100% Duty Cycle) to apply all available Battery power to the Armatures (as in Driving at Full Speed).
Instead of permanent magnets, the separately-excited drive motors use electro-magnets (called Field Windings) located in the stator (non-rotating) portion of the motor. Field windings are preferable to permanent magnets because the Power Module can adjust the stator's magne- tism for optimum motor performance. When climbing a grade at low speeds, the Power Module may apply as much as 40A to the field windings for more electro-motive force. On level terrain, the Power Module will apply as little as 14A to the fields for higher rotational speeds and better electrical efficiency.
Figure 3-2. Drive Motors Schematic - 1600346 (SEV- CON) Power Module
Line Contactor 24V +B –B F2 F1 M2 M1 Power Module Left Field Winding
Right Field Winding
Armature Switch Field Switches Shunt 1 3 2 4 Left Armature Right Armature
The Field Windings also provide direction reversal for trac- tion. When driving forward, MOSFET switches 1 and 4 turn On to apply positive potential to F2 and ground potential to F1. In reverse, MOSFET switches 2 and 3 turn On to apply positive potential to F1 and ground potential to F2. Theses switches are pulse-width modulated by the Power Module to maintain a fixed relationship between Field and Armature Current.
Two electrically-released parking brakes are mounted to the rear of the drive motors. The Ground Module ener- gizes the two 24V electro-magnets when appropriate to allow vehicle motion. The parking brakes can be released electrically for emergency vehicle towing.
Personalities
Traction system Personality settings can be changed via ANALYZER -> PERSONALITIES -> DRIVE:
• ACCEL - Time to ramp from 0% to 100% of command • DECEL - Time to ramp from 0% to 100% of command • MINIMUM - Minimum drive speed (Creep)
• MAXIMUM - Maximum drive speed when platform is stowed
• ELEV. MAX - Maximum drive speed when platform is elevated
Interlocks
As the machine travels down an incline the drive power output will be reduced proportionally to avoid overspeed- ing the vehicle. A bad tilt sensor will force the control sys- tem to assume maximum incline and reduce drive power accordingly.
Creep mode (reduced drive speed) will be active if the control system determines the platform is elevated. Drive may be prevented by a different interlock, however. Drive will be prevented if any of the following occur:
• Vehicle is tilted, elevated and ANALYZER -> MACHINE SETUP -> TILT CUTOUT is set to YES.
• Batteries are being charged (0V is applied to ground board J1-29)
• Vehicle is elevated above the calibrated Drive Cutout height and ANALYZER -> MACHINE SETUP -> DRIVE CUTOUT is set to YES.
Figure 3-3. Drive Motors Schematic - 1001092456 (ZAPI) Power Module
+
24V
+
+
+
Line Contactor
Right Field Winding
Left Field Winding Power Module
Left
Armature ArmatureRight