operated safety interlock control are in the operating positions. With the crane running, release
any, either or both of the foot switches or the safety interlock. All crane motions should stop. It
will be necessary to release both foot switches as well as the safety interlock and the joystick
master before motion can be resumed. With the foot switches and the safety interlock in
operating position, place the joystick control in the full or hoisting direction. The platform
should decelerate from full speed to slow speed and automatically stop at the upper limit.
Reverse the direction and check the lower limit. With the foot switches and the safety interlock
in operating position, place the joystick control in full forward position. The crane should
decelerate and stop at the end of the aisle. Reverse the direction and check the reverse aisle limit
16.3 INSPECTION OF THE BRIDGE
The bridge is that part of the crane consisting of the lower truck, hoist drive system, hoist
drum, and aisle drive.
Determine that the floor mounted guide rail is free of debris. Check all lower guide rollers for
worn or damaged wheels, bearings or shaft pins. (See Figure 16-6). Inspect the wheels for
cracks or chipping. Inspect the wheels for flat spots and any unusual wear patterns or markings.
Check the wheel bearings for adequate lubrication. Inspect the wheels for excessive float.
Wheel float is the amount the wheel can move across the rail. The allowable wheel float is
approximately 1/8 inch. If any of these conditions exist, the wheels must be repaired or replaced.
16.3.3 Hoist Drive System
Check the brake linings for wear, and the air gap for proper spacing. Check the mounting
bolts to insure they are tight. Check the hoist drive system (See Figure 16-7). The hoist drive
system consists of a motor, gear case, holding brake, load brake and hoist drum. The hoist drive
system serves to raise and lower the carriage by wire ropes. Hoisting power is provided by an
AC wound rotor type motor driving the rope drum through a reduction gear box. A magnetorque
load brake is employed to help control the speed of the hoist motor. A spring-set shoe type
motor brake is used to stop the motor. This motor brake holds the hoist system in position until
power is reapplied. Check the motor bearings for proper lubrication and vibration due to wear.
Check motor brushes for adjustment or replacement and the slip ring for reconditioning. Check
the gear case for proper oil level, using the visual oil level indicator.