Footguards
Footguards are fitted to the outside of the lifting arms to
prevent people from having their toes trapped and
crushed when lowering the hoist. The footguards are
spring mounted so they deflect out of the way if they
are accidentally hit by the operator or vehicle.
Protective covers fitted over the bottom limit switches
also help protect feet as well as protecting the limit
switch from accidental damage or operation. The
footguards must always be fixed in place and kept in
good condition.
Drive covers
A cover is fitted over the vee belt drive on top of each
column to prevent people from accidentally trapping
and cutting off their fingers between the moving vee
belts and the pulleys. The covers must always be fixed
in place and people must not stand or ride on any part
of the hoist when it is being operated.
Brakes
The hoist is fitted with two brakes to stop both sides of
the hoist quickly and consistently so the vehicle is kept
level. The brake shoes rub on the inside of the screw
pulley and are kept permanently engaged under spring
pressure.
The brakes are partially self energizing when lowering
so they work harder when lowering. The brake shoes
are self adjusting for the life of the shoe and if the
shoes are allowed to wear past the allowable limit they
become more self energizing and will eventually
prevent the hoist from lowering. This prevents the hoist
from being used until the brake shoes are replaced.
Dead man controls
The raise and lower buttons are spring loaded so the
hoist is immediately stopped when the buttons are
released.
Height synchronization
The height of the lifting carriages are kept level by a
computer controller. A proximity switch is fitted under
the screw pulley on top of each column. These
switches go on and off as the holes in the pulleys go
past. The computer counts and compares the numbers
of pulses from each switch to check that both lifting
screws have rotated the same number of turns. If one
side gets ahead by more than 2 turns (12 mm) then it is
switched off momentarily until the other side catches up
then it is restarted.
Alarm system
The computer controller checks that the hoist is
operating correctly and it will stop the hoist if it is faulty.
A warning light between the raise and lower buttons
comes on to warn the operator. The hoist cannot be
operated until the fault is found and rectified and the
alarm is reset. The alarm is activated if the lifting
screws get up to 4 turns out of synchronization or if the
proximity switches are not detecting pulses when they
should be. Refer to the fault finding section to identify
and rectify the fault and reset the alarm.
Page 17
To Next Page
Loading...