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Screw Jack with Integral Bevel Gearbox
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Screw
jacks are extensively used to build lifting systems to lift / lower
several tons of load. A lifting system generally consists of 2 to 8
screw jacks driven by a single motor. To divide the power to various
screw jacks, bevel gearboxes are essential to turn the drive through 90
degs. To connect screw jacks and bevel gearboxes, connecting elements
like shafts, flexible couplings, bearing blocks etc are required.
Designers strive to make layouts using minimal connecting elements in
order to reduce space, to reduce cost and to minimise assembly problems
in aligning the shafts.Gears & Gear Drives has developed a
screw
jack with integral bevel gearbox. Their cubical worm gear screw jacks,
models CWJ and MCJ can be fitted with this bevel gearbox to turn input
or inline output through 90 deg. A standard schematic layout in which 4
worm gear screw jacks are driven by two bevel gearboxes and a motor -
shown in Drawing 1.The same arrangement can now be achieved by using
cubical worm gear screw jack with integral bevel gearbox as shown in
new layout, Drawing 2. It is evident that additional connecting shafts
and couplings are avoided. The layout is more compact with less
connecting elements. Some of the possible arrangements are shown in
Drawing. 3 & 4. Other advantage is that, the input or output
from
the bevel gear box can be turned through 90 deg and vertical shafts can
be easily connected. (Ref. Drawing 5)
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End Limit Control Device |
Screw
jacks driven by electric motors, they generally require end limiting
devices, to limit upper and lower end positions so that unwanted over
shoot is avoided. Several end limit control devices are available such
as limit switches, proximity switches, reed switches, mechanical
counting devices to operate limit switches etc. Limit switches and
proximity switches are not normally adjustable at site and have pre
fixed end positions.Gears & Gear Drives has developed end limit
devices using proximity switches and electronic counter. The device is
simple, reliable and easy to adjust over entire range of stroke. The
end limits can be adjusted from almost zero to max stroke length by
simply setting the counter.The device has a proximity switch on non
driving end of input shaft and counts the number of revolutions of the
input shaft or the motor shaft.
The signals from proximity switch are received by an electronic counter. The counter has two display windows, one window is for presetting the number of revolutions required for a given lift. The second window counts the actual number of revolutions from proximity switch. When digits on this counter coincide with preset digits on first counter, the motor stops. The motor cannot be run further in same direction. After 5-10 seconds, the second counter resets to zero and the motor can now be run in opposite direction. Until the digits again coincide with the digits of first counter. The Motor then stops. The presetting counter can be set to any number from 1 to max for the given stroke. Total number of revolutions required for a given stroke can be calculated from ratio of worm / worm wheel and pitch of screw. This data is available in the catalogue or dimension sheet. |
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