FIELD OF THE INVENTION
The present invention relates generally to a linrjit switch and, more particularly, to a modified
pindle type limit switch for crane hoists and other similar rotating equipments that has plural
novable contacts interposed between respective pairs of fixed contacts with an actuator
upported in a head mounted on the switch casing for moving the respective movable contacts
)etween two positions which is easily maintainable and less costly compared to the conventional
)ne and which has a very fine precision in Hs set-reset mechanism.
!. DESCRIPTION OF THE RELATED ART
Generally, the limit switches are designed to control the movement of a mechanical part.
Jmit switches are widely used in various fields of engineering, especially for automatic and semi-
jutomatic control purposes. Limit switches are widely used in industry to achieve automatic
)peration of equipments. It is used to limit movement of machine / equipment in either direction
3S per requirement whether it is rotational or transverse. It is also used as safety devices in many
jiaces. There are many types of limit switches, viz., lever type, wheel type, micro limit switches,
ever type, cam type, striker type, spindle type, proximity type. These limit switches are used
lepending upon the requirement and provision made by the supplier for different machines.
In integrated siteel plant cranes, rope-transfer, chain-transfers are widely used for different
jurposes. Here rotation of rope drum is more than one revolution, i.e., 360°. For example,
otation of hoist rope drum in a crane may be 25 to 50 revolutions depending upon the height of
he crane and diameter of the rope drum. Similarly, in rope and chain transfer it depends on the
inear distance travel by the dogs. Dogs transfer plates in a plate mill. Spindle type limit switches
are used in chargir«g car of l)last furnaces. Rotation of limit switch spindle finally connected to an
slectrical contact that in turn disconnect or connects power thereby either stop or start depending
Dn the command given to it or adjustment done on it.
Examples of such devices are disclosed in U.S. Pat. Nos. 3,275,764 and 4,406,933.
Additional switching devices similar character are disclosed in U.S. Pat. Nos. 3,317,687;
3,370,138; 3,539,738; 3,721,782; and, 3,882,290.
US Pat. No. 3,721,780 dated 1973-03-20 to Kelly and Ward discloses a limit switch assembly
including rotatable cam with longitudinally guided indexing nut and cam longitudinal displacement
means.
CN 2056542U dated 1990-04-25 to Xiangtan Electromechanical TRA talks about a limit
switch for tower crane. KR 9504740Y dated 1995-06-14 to Posco reveals a limit switch weight for
crane hoist.
US Pat. No. 5,405,027 dated 04/11/1995 to Plass teaches a crane hoist system having a
hoist drum, a drum drive motor and control and power circuit limit switches. The said invention
involves a first trip t)ar coupled to the power circuit limit switch and a second trip bar coupled to
the control circuit limit switch. The l>ars are vertically aligned arxl both are pivot mounted at their
corresponding ends. The second trip bar is mourrted for movement independently of the first trip
bar. If the control circuit limit switch fails to function as the second bar is moved a suitable
distance upward, such bar contacts and lifts the first bar which, in turn, trips the power limit
switch. In one emiMXliment, both tjars are straight and elongate and in another, the second bar is
"U" shaped.
US Pat. No. 5,362,029 dated 11/08/1994 to Kallenbenger describes a limit device for
preventing travel of a hoist lift rope load atKJve a predetermined height. The said limit device
includes an actuator mounted at a reference position adjacent the hoist lifting rope as it is raised
and lowered by a prime mover. A switch is connected in a control circuit for the prime mover to
place the prime miover in either a raise-lower m/i) Conventional limit switches use complicated mechanism in its set reset system.
Therefore, the working principle is not easy to understand by common people.
\/ii) Dust deposited on the mechanism of set reset system of conventional limit switches
affects adversely operation as well as perfonmance of the limit switch,
viii) Very fine adjustment is very difficult to achieve in the conventional limit switches,
ix) Highly skilled personnel are required for maintenance of these conventional limit
switches,
x) Wear and tear plays an important role in the operation of spindle type limit switches.
Wear and tear for these conventional spindle type limit switches are more as these use
fibre / teflon in set reset system.
xi) Conventional limit switches viz., tyf)e 62 SNE 411 have only 62 threads. So it can only be
used for a very specific purpose.
;xii) Indirect actuation of limit contacts reduces its reliability for conventional switches.
|xiii) Conventional limit switches require frequent lubrication for its bushes and springs.
According to other heretofore known devices the angular movement of the spindle is
transmitted through clutch, slotted disc and lodcing lever etc to the square shaft which when
rotated to strike the limit contact block ased for cut off electrical power. Therefore, energy is
transferred, in conventional spindle type limit switches, in two stages:
(i)from spindle to square shaft, and
(ii) from square shaft to the contact block.
This reduces the reliability of the said conventional limit switches.
The present invention seeks to mitigate or at least alleviate such inconveniences against
users by providing a modified spindle type) limit iswitch for crane hoists and other similar rotating
equipments.
While the various types of limit switches in existence today have operated successfully,
manufacturers of such products are constantly looking for improvements that will increase the
versatility of the mechanisms, and at the same time can be manufactured at reduced costs.
3. SUMMARY AND OBJECTS OF THE INVENTION
Accordingly, the present invention is directed to propose a new design and construction for a
modified spindle type limit switch for crane hoists and other similar rotating equipments.
An object of the present invention is to provkle a modified spindle type limit switch for crane
hoists and other similar rotating equipments that obviate the disadvantages of the conventional
arts.
Another object of the present invention is to provide a modified spindle type limit switch for
(i ane hoists and other similar rotating equipments that are used as a stopping device against the
(1 ve.
Another further object of the present invention is to provide a modified spindle type limit switch
tc ¦ crane hoists and other similar rotating ei^uipments that is used as a safety device for crane
ai d for the workers working in the vicinity of the said crane.
Yet another further object of the present invention is to provide a modified spindle type limit
s.\ 'itch for crane hoisis and other similar rotating equipments that are reliable.
Still another object of the present invention is to provide a modified spindle type limit switch for
CI 3ne hoists and other similar rotating equipments by which very fine adjustment can be achieved
vv/ len attached to a crane hoist and / or other similar rotating equipmerrts.
Still another further object of the present invention is to provide a modified spindle type limit
SI 'itch for crane hoists and other similar rotating equipments in which wear and tear are
si inificantly low in set reset system of the said limit !5witch.
The various features of novelty that characterise the invention are pointed out with particularity
i) the claims annexed to and forming a part of this disclosure. For a better understanding of the
i 1 'ention, its operating advantages and specific ot)jects attained by its uses, reference is made to
tti; accompanying drawings and descriptive matter in which preferred embodiments of the
in 'enfion are illustrated.
To achieve these and other advantages and in accordance with the purpose of the present
i 1 mention, as embodied and ttroadly descritied, the modified spindle type limit switch for crane
h( ists and other similar rotating equipments includes:
a casing made from a 6 mm thick M.S. plate on t)earings-end and 4 mm thick M.S. plates on
3ther three sides;
a jpindle / shaft and a plurality of threads having suitable pitch in the middle portion of the said
jpindle shaft;
l» arings fitted on the both end of the said casing to hokJ the said spindle shaft;
t.^ D rectangular nuts fitted on the said spindle in which the material of the rectangular nuts are
chosen in such a manner that chances of wearing out of spindle thread are reduced;
Cii e guide rod fixed over two fixing amns to facilitate the movement of the said nuts, the design of
he said two nuts being in a manner that one end of a nut is inserted inside the said guide rod;
U 0 L'-shaped fibre actuators fixedly fitted to the said nuts, the said actuators being fastened to
he said nuts with screws and suitat)le degrees of slopes are made at the edges of the actuator
or a smooth ride over the moving contact, i.e., to avoid jerks while actuafing;
tv 3 thin metal sheets fitted to each end of the said fit>re actuator by an actuator screw;
a suitably cut and fabricated metallic sheet rigidly fixed below the said actuator to avoid chances
3f wearing out of fibre actuator;
01 e flat iron, inverted 'U', L'-shaped fixed at ttoth end in downward direction, with a plurality of
hreaded holes fitted inside the said casing, the height of the said flat iron being adjustable
hrough slotted hole situated at both the end of the said casing and the said flat iron being fixed
igidly with bolt at the ttoth ends thereby fixing the said flat iron in the said casing;
U D contact block fixtures 'H' shaped fitted with a contact block and screwed to the said flat iron,
he said two contact blocks being adjustat)ly fitted at different locations of the said flat iron
lepending upon requirements, and the said fit>re actuator strikes directly the said contact block
hat is fixed horizontally in a separate frame;
1:! fel of contact tips being adjustat>ie in such a manner that the said fibre actuator first passes
hrough the bend fwrtion of the said contact tips, the said contact tips being detachable from
he said contact block fixture during operation due to lever action;
al least three adjustable-slotted foundation facilitating fixing of the said modified limit switch;
CII e key way cut at one end of the shaft to facilitate fixing of any coupling or pinion as per
equirement;
U 0 bearing cups fittesd to the said casing to fix bearings;
al least four nuts with bolts fixed to the said two txjaring cups' end to ensure no-play of the said
shaft;
a Plurality of surclips fitted on the shaft near the said bearings to arrest any movement of the said
rearing over the said shaft; and
4
Dur threaded blocks welded to four comer of the casing to fix the cover of limit switch;
' therein the said limit of the said limit switch can be adjusted by rotating the nuts over the spindle
after detaching it from the guide rod and removing the fibre actuator and precision adjustment
of the upper limit of the said limit switch is made to prevent the said crane hook from hitting the
said structure of the said crane thereby ceasing the said limit's work.
The said modified spindle type limit switch in which the said limit switch assembly is fixed on
1 ie foundation near to rope drum and one pinion of required teeth is fitted to the limit switch
( xtension shaft near the hoist-gear box to suitably match the output pinion of the hoist rope drum
; haft with that of limit switch and required circuit a)nnections are ensured to the contact blocks of
I le limit switch.
The said modified spindle type limit switch in which the said pinion of the said limit switch
I states and the said fibre actuator moves inside the said casing when the drive is operated
The said modifie(J spindle type limit switch wherein during hoisting the pinion of the said limit
! witch rotates thereby rotating the said spindle of the said limit switch.
The said modified spindle type limit switch in which the said two rectangular nuts move from
( ne end to the other as both the said nuts are connected to the said spindle, and the said
f lovement is passed on to the fibre actuator thereby converting the angular movement of the
! pindle to linear movement of the actuator
The said modified spindle type limit switch in which the said contact blocks are adjusted In
! jch a manner that during the operation of the hoist as well as the said limit switch, the fibre
i ctuator strikes the said contact Wock fixture thereby opening the fixed contact due to spring
i ction inside the contact block arid thus disconnecting the entire circuit resulting in stoppage of
t le said crane hoist.
The said modified spindle type limit switch wherein lowering the other fibre actuator actuates
t le other set of contact block and the said crane hoist stops thereby preventing hitting of the hook
[ f the said hoist, in both directions (either hoisting or lowering), by adjusting the said limit switch
t locks.
The said modified spindle type limit switch in which the said limits of the said limit switch can
t 8 adjusted by rotating the nuts over the spindle after detaching it from the guide rod and
f jmoving the fibre actuator.
The said modified spindle type limit switch in which the said limit of the said limit switch can be
I jjusted by displacing the contact block.
The said modified spindle type limit switch in which the said limit of the said limit switch can be
: jjusted by rotating the spindle after removing the limit switch from the foundation.
The said modified spindle type limit switch wherein by adjusting the limit switch, opening of
c Dntact tips in the contact block is ensured when the fibre actuator touches over the said contact
i: ock.
The said modified spindle type limit switch in which minor adjustments are done by displacing
'.: ightly the said fibre actuator after loosenirvg the sc^rews tightened on it.
The said modified spindle type limit switch in which the said limit switch works as a stopping
embly through a lever (16). The mechanism follows
detachment from the spring (15) of the locking lever (16) thereby rotating the square shaft (20) by
90°. This rotates the cam (17) and the limit swrtc^h contacts are actuated. The said contacts are
connected to an electrical circuit that disconnects power supply to the driver of the limit switch
thereby stopping the drive. Further rotation of limit switch shaft (2) is not possible thereafter
However, there is no change in status of limit contact even if the shaft (2) is rotated by 15
revolutions.
When the driver of limit switch illustrated in Fig. 1 rotates in other direction, both the teflon
gears (12, 23) get engaged and the slotted discs; (24, 13) start rotating in reverse direction. This
resets the limit switch clutch assembly (14) and the square shaft (20) rotates in opposite direction
and the cams (17) strike the limit contacts. Hence the contacts get closed. This process of
resetting the limit switch is most importaitt t)ecause the drive is now ready for use in both the
directions as all contact blocks (18) are closed in this condition. Further rotation in this direction
causes the opening of contacts at the ene done by displacing slightly the said fibre actuator (114) after loosening the
:i ;rews (115) tightened on it.
When the limit switch is used in crane hoist it is most important to adjust the upper limit of the
I nit switch. Here more accuracy is required because the crane hook may hit the structure of the
: ane thereby ceasing the limit's work. Therefore, the limit switch works in two folds:
(i)as a stopping device against the drive, and
(ii) as a safety device for crane and for the workers working in the vicinity of the said
crane.
The unique feature of the modified limit switch, according to the present invention, is the
: esign of direct striking system. As a whole, the unkjue features of the present invention are as
I )llows:
() angular movement of the spindle (112) is converted to linear movement of the actuator (114);
(i) fibre actuator (114) strikes directly the contact Wock (121) that is fixed horizontally in a
! sparate frame;
(ii) chances of wearing out of fibre actuator (114) are avoided by fixing a suitably cut and
I ibricated metallic sheet below the sakl actuator (114);
( v) for a smooth ride over the moving contact, i.e., to avokj jerks while actuating, slope is made
i t the edges of the actuator (114);
(f) chances of wearing out of spindle thread are reduced as suitable materials are used in
I octangular nuts (113).
While the principles of this invention have been described in connection with specific
( mbodiment, it should be understood cleariy that these descriptions are made only by way of
I xample and are not intended to limit the scope of the invention.
We Claim:
. A modified spindle type limrt switch for crane hoists and other similar rotating equipments
( omprising;
; casing (111) made from a 6 mm thick MS pJate on bearings-end and 4 mm thick M.S plates
on other three sides;
; spindle / shaft (112) and a pluralrty of threads having suitable pitch in the middle portion of the
said spindle shaft (112);
I earings (125) fitted on the both end of the jiaid casing (111) to hold the said spindle shaft (112);
t vo rectangular nuts (113) fitted on the said spindle (112) in which the material of the rectangular
nuts (113) are chosen in such a manner that chances of wearing out of spindle thread are
reduced;
' ne guide rod (118) fixed over two fixing amns (117) to facilitate the movement of the said nuts
(113), the design of the said two nuts (113) being in a manner that one end of a nut (113) is
inserted inside the said guide rod (118);
/vo 'L'-shaped fibre actuators (114) fixedly fitted to the said nuts (113), the said actuators (114)
being fastened to the said nuts (113) with screws (115) and suitable degrees of slopes are
made at the edges of the actuator (114) for a smiooth ride over the moving contact, i.e., to avoid
jerks while actuating;
NO thin metal sheets fitted to each end of the said fibre actuator (114) by an actuator screw
(113);
I suitably cut and fabricated metallic sheet rigidly fixed below the said actuator (114) to avoid
chances of wearing out of fibre actuator (114);
me flat iron (129), inverted 'U', L'-shaped fixed at txjth end in downward direction, with a plurality
of threaded holes (120) fitted inside the said casing (111), the height of the said flat iron (129)
being adjustable through slotted hole situated at both the end of the said casing (111) and the
said flat iron (129) t>eing fixed rigidly with tx)lt (122) at the txrth ends thereby fixing the said flat
iron (129) in the said casing (111);
wo contact block fixtures (119) 'H' shaped fitted with a contact block (121) and screwed to the
said flat iron (129), the said tw) contact blocks (121) t)eing adjustably fitted at different
locations of the said flat iron (129) depending upon requirements, and the said fibre actuator
(114) strikes direc^tly the said contact block (121) that is fixed horizontally in a separate frame;
evel of contact tips (110) l)eing adjustable in such a manner that the said fibre actuator (114) first
passes through the bend portion of the said contact tips (110), the said contact tips (110) being
detachable from the said contact block fixture (119) during operation due to lever action;
jt least three adjustable-slotted foundation (128) facititating fixing of the said modified limit switch;
)ne key way (127) cut at one end of the shaft (112) to facilitate fixing of any coupling or pinion as
per requirement;
wo bearing cups (126) fitted to the said casing (111) to fix t)earings (125);
3t least four nuts with bolts (116) fixed to the said two tiearing cups' (126) end to ensure no-play
ofthe said shaft (112);
a plurality of surclipts fitted on the shaft (112) near the said bearings (125) to arrest any movement
of the said bearing (115) over the said shaft (112); and
our threaded blocks (124) wekied to four comer of the casing (111) to fix the cover of limit switch;
wherein the said limit of the said limit swHc^h can be adjusted by rotating the nuts (113) over the
spindle (112) after detaching it from the guide rod (118) and removing the fibre actuator (114)
and precision adjustment of the upper limit of the said limit switch is made to prevent the said
crane hook from hitting the said structure of the said crane thereby ceasing the said limit's
work.
2 A modified spindle type limit switch as claimed in claim 1, wherein the said limit switch
assembly is fixed on the foundation near to rope drum and one pinion of required teeth is fitted to
the limit switch extension shaft (112) near the hoist-gear Ixjx to suitably match the output pinion
of the hoist rope; drum shaft with that of limit switch and required circuit connections are ensured
to the contact blocks (119) ofthe limit switch.
3. A modified spindle type limit switch as daimed in daim 2, wherein the said pinion of the said
limit switch rotates and the said fibre actuator (114) moves inside the said casing (111) when the
drive is operated.

This invention relates to a modified spindle type limit switch for crane hoists and other similar
rotating equipments comprising a casing (111) made from a 6 mm thick MS. plate on bearings-
end and 4 mm thick MS. plates on other three skies, a spindle I shaft (112) and a plurality of
threads having suitable pitch in the middle portion of the said spindle shaft (112). bearings (125)
fited on the both end of the said casing (111) to hold the said spindle shaft (112), two rectangular
nuts (113) fitted on the said spindle (112) in which the material of the rectangular nuts (113) am
chosen in such a manner that chances of wearing out of spindle thread are reduced, one guide
rod (118) fixed over two fixing arms (117) to facilitate the movement of the said nuts (113), the
design of the said two nuts (113) being in a manner that one end of a nut (113) is inserted inside
the said guide rod (118), two "L-shaped fibre actuators (114) fixedly fitted to the said nuts (113).
the said actuators (114) being fastened to the said nuts (113) with screws (115) and suitable
degrees of slopes are made at the edges of the aduator (114) for a smooth ride over the moving
contact, i.e.. to avoid jerks while actuating, two thin metal sheets fitted to each end of the said
fibre actuator (114) by an actuator screw (113). a suitably cut and fabricated metallic sheet rigidly
fixed below the said aduator (114) to avoid chances of wearing out of fibre actuator (114), one
flat iron (129), inverted 'U', L-shaped fixed at both end in downward direction, with a plurality of