A two-masted lifting apparatus particularly adapted to lift a weighty object such as a vehicle or the like to a desired height and then incline it at a desired angle in either direction. The two-masted lifting apparatus comprises two opposing upright masts on each of which a carriage for supporting the object is slidably mounted and a height-difference detecting means. Both carriages are independently hoisted up or down along the respective masts by separate driving means, and the height-difference detecting means is adapted to detect the height-difference between the two carriages and restrict the further ascent or descent of one of the two carriages when the height difference between them has reached a predetermined limit.

The present invention generally relates to two-masted lifting apparatus for 
lifting a weighty object such as a vehicle or the like, and more 
particularly relates to a two-masted lifting apparatus of the kind in 
which it is possible to lift up a vehicle or the like to a desired height 
with its original posture maintained and then incline it at a desired 
angle in either direction; whereby inspecting, repairing or cleaning works 
upon the underside of the vehicle or the like can be carried out with much 
ease and safety. 
There have heretofore been proposed various kinds of two-masted lifting 
apparatus. One of the typical two-masted lifting apparatus is one which is 
capable of inclining a vehicle or the like at a desired angle after 
lifting it up to a certain height, thereby enabling persons to work easily 
and safely under the vehicle for inspecting or repairing. The lifting 
apparatus of this prior art comprises two opposing upright masts on each 
of which a carriage having a pair of supporting means is slidably mounted. 
Both carriages, each independently driven by separate driving means, are 
associatively connected with each other by a chain so that the actuation 
of one of the two driving means effects the synchronous lifting of both 
carriages while the actuation of the other administers only the lifting of 
one of the two carriages to incline the horizontallylifted vehicle. 
One of the difficulties in this prior art, though advantageous at least 
over other lifting apparatus of the similar type, is that it is not 
possible to incline the vehicle in both directions: i.e., the inclining 
direction of the vehicle is restricted to only one direction. Accordingly, 
in order to incline it in the opposite direction, the vehicle has to be 
dismounted from the lifting apparatus to change its front and then the 
whole operation has to be started again. 
Another difficulty of the prior art is that there is not provided a safety 
means -- if any, the structure will be very complicated -- for controlling 
the maximum admissible inclination angle of such weighty objects to 
prevent their possible slippage from the apparatus. 
The present invention therefore aims at overcoming the above and other 
difficulties of the prior art by providing a new and improved two-masted 
lifting apparatus, simple and reliable in structure and cheap in 
manufacturing cost, which is adapted not only to lift up a weighty object 
such as a vehicle or the like to a desired height but also to incline it 
at a desired angle in either direction. 
According to one aspect of the two-masted lifting apparatus of the 
invention, there are provided separate driving means adapted to hoist up 
or down two carriages independently of each other along the respective 
upright masts and a height-difference detecting means adapted to detect 
the height difference between the two carriages and, according to the 
detected value, restrict the further ascent of one carriage which is 
higher than the other or restrict the further descent of one carriage 
which is lower than the other so as to prevent a lifted object from 
slipping off. 
The height-difference detecting means comprises a pair of pulleys each 
suspended by a tension spring at the upper portion of each mast, a pair of 
limit switches each secured to the mast slightly below the pulley, an 
endless wire extending around the two pulleys via suitable guide pulleys 
rotatably mounted on the lower portion of the masts, and two stoppers 
secured to the wire. The endless wire is partly secured to the carriage 
mounted on one of the two masts, and the two stoppers are firmly but 
removably attached to one of vertically extending portions of the wire so 
as to get into contact with the upper or lower surface of the carriage 
mounted on the other mast when a predetermined height difference arises 
between the two carriages.

Referring first to FIGS. 1 to 3, there is shown a base 2 having forewardly 
and rearwardly projecting supporting wings 1. A pair of upright masts 3 
and 3' of substantially channel section are vertically disposed on the 
base 2 in such a manner that the connected portions of channel-shaped 
masts 3 and 3' face each other. On each mast 3 or 3', a carriage 4 or 4' 
or channel section is slidably mounted such that its opened portion faces 
innerward. Each carriage 4(4') is provided with two horizontal rollers 
5(5') and 6(6') at its upper outer portion and lower inner portion 
respectively. These rollers 5(5') and 6(6'), rolling over the side 
surfaces of each mast 3(3'), facilitates the smooth sliding up or down of 
the carriage 4(4') along the mast. 
As is best shown in FIG. 4, a cantilever plate 7 or 7' of substantially 
L-shape is secured at its bottom end to the inner surface of one of the 
lateral walls of each carriage 4(4'). The cantilever palte 7(7'), the free 
portion of which protrudes into the open space defined by walls of the 
mast 3(3') along one of the lateral walls of the mast, is provided with 
two longitudinally extending bores 8(8'). 
With particular reference to FIG. 3 showing the left-hand part of the 
apparatus of the invention, the carriage 4'(4) is provided on its both 
lateral walls with two brackets 9'(9), to each of which a hollow sleeve 
10'(10) of square section is firmly secured at a right angle with respect 
to the bracket 9'(9). A supporting arm 11'(11) is slidably inserted into 
each of the hollow sleeves 10 and 10'. A step 12'(12), comprising a base 
portion 12b'(12b) and a side wall 12a'(12a) making an obtuse angle with 
the base portion 12b'(12b), is pivotally supported on the upper surface of 
the inner end portion of the supporting arm 11'(11) through a pin-coupling 
13'(13). Removably installed between the inner ends of the two opposing 
arms 11 and 11' is a chain 14, so that the distance between the two 
opposing arms is always kept constant even when the two carriages 4 and 4' 
have been hoisted to a different height. 
According to this invention, the hoisting up or down of each carriage 4(4') 
is effected by a piston-cylinder device of the fluid pressure type 15(15') 
which is disposed on the base 2 and extends upwardly through the open 
space in each mast 3(3'). As can be seen in FIG. 1, a piston 17(17') 
adapted to reciprocate within a cylinder 16(16') of the piston-cylinder 
device 15(15') has on the top thereof a bifurcate bearing member 18(18') 
on which a pulley 20(20') is rotatably supported by a horizontal pin 
19(19'). Extended around each pulley 20(20') is a chain 21 (21'), whose 
one end is fixed to the almost central portion of the mast 3(3') and whose 
other end is anchored at the carriage 4(4') by a pin 22(22'). 
Thus, it will readily be understood that each carriage 4(4') can be hoisted 
up or down independently along the mast by reciprocal motions of the 
piston 17(17') through the chain 21(21'). 
There is further provided, according to this invention, a control means for 
controlling the actuation of the aforementioned piston-cylinder devices 15 
and 15', the means comprising height-difference detecting means 23 and a 
pair of height-restricting means 24. The detecting means 23 is adapted to 
detect the height difference between the two carriages 4 and 4' and, 
according to the detected value, restrict the further ascent of one 
carriage which is higher than the other or restrict the further descent of 
one carriage which is lower than the other. 
On the other hand, the pair of height-restricting means 24, each disposed 
on the upper portion of mast 3 or 3', are adapted to detect whether the 
carriage 4 or 4' has climbed up to a desired position and restrict the 
further ascent thereof from that position independently of the above 
detecting means 23. 
As can best be seen in FIG. 5, the height-difference detecting means 23 
comprises a pair of pulleys 26 and 26'suspended by tension springs 25 and 
25', a pair of limit switches 27 and 27' secured to the upper portion of 
the masts 3 and 3'slightly below the pulleys 26 and 26', two pairs of 
guide pulleys 28, 28', 29 and 29' each rotatably mounted on the lower 
portion of the mast, an endless wire 30 extending around these pulleys 26, 
26', 28, 28', 29 and 29' and penetrating the cantilever plate 7 and 7' 
through bores 8 and 8', and two stoppers 31 and 32 both attached to one of 
the vertically-extending portions of the endless wire 30. As shown in FIG. 
5, both of stoppers 31 and 32 are attached in a spaced-relationship to a 
vertically extending portions of the wire 30 where the wire penetrates 
through the inner bore 8 of the right-hand cantilever plate 7, whilst the 
wire 30 is secured to the left-hand cantilever 7' at its outer bore 8'. 
With the foregoing descriptions in mind, attention will now be directed to 
the operation of the two-masted lifting apparatus of this invention, and 
in particular how the height-difference detecting means 23 works will be 
explained in detail with reference to FIG. 5. 
As has been described immediately above, since the endless wire 30 is 
partly secured to the cantilever plate 7' of the left-hand carriage 4', it 
travels around pulleys together with the upward or downward movements of 
the carriage 4'. The two stoppers 31 and 32 are attached to the right-hand 
part of the wire 30 in such a manner that when both carriages 4 and 4' are 
same in height the right-hand carriage 4 can be located exactly at the mid 
point of the distance between the two stoppers 31 and 32. Accordingly, in 
so far as both carriages 4 and 4' are hoisted up or down by 
piston-cylinder devices 15 and 15' at the same time and same speed, the 
location of the right-hand carriage 4 is maintained at the mid point of 
the two stoppers. 
In case a height difference arises between two carriages 4 and 4'; for 
instance, in case the left carriage 4' is hoisted up higher than the right 
carriage 4, a vertical portion of the wire 30 where two stoppers 31 and 32 
are installed moves upward by the amount equal to the height difference 
between the two carriages 4 and 4'. In other words, the displacement 
amount of both stoppers 31 and 32 is always equal to the ascending amount 
of the left-hand carriage 4'. After the lower stopper 32 has moved up into 
contact with the lower portion of the right-hand carriage 4, the further 
ascent of the left-hand carriage 4' along the mast 3' is substantially 
prevented by the stopper 32. However, the hoisting operation of the left 
carriage 4' by a piston-cylinder 15' is further continued until the right 
pulley 26 suspended by a tension spring 25 is pulled downward by the wire 
30 and gets into contact with a limit switch 27 secured to the mast 3 to 
actuate the latter. In this case, it should be noted that, in the strict 
sense of the word, the left carriage 4' does not stop ascending the 
instant the stopper 32 moves up to contact with the right carriage 4. It 
continues to move up slightly until the pulley 26 comes down into contact 
with the limit switch 27. 
This limit switch 27, when actuated, is adapted to halt instantly the 
further ascent of the left carriage 4' and the further descent of the 
right carriage 4 as well, so as to prevent the left carriage 4' from 
ascending beyond a predetermined height difference with respect to the 
right carriage 4. 
On the other hand, another limit switch 27 fixed to the left mast 3' has a 
similar function, being adapted to immediately halt the further descent of 
the left carriage 4' and the further ascent of the right carriage 4 to 
prevent the left carriage 4' from descending beyond a predetermined height 
difference when the upper stopper 31 contacts the upper portion of the 
right carriage 4. 
It will thus be understood that the height difference between the two 
carriages 4 and 4' is always restricted within a predetermined range by 
the height-difference detecting means 23, and fear can totally be 
eliminated of a lifted vehicle's slippage from steps 12 mounted on 
supporting arms 11 even if it is inclined. It is of course feasible to 
adjust a maximum height difference between the two carriages by changing 
the installation position of stoppers as desired. 
In the meantime, each of the pair of height-restricting means 24 comprises 
a limit switch 33 or 33', which, being secured to the upper portion of the 
respective 3 or 3', is adapted to stop at once the supply of fluid 
pressure to the piston-cylinder device 15 or 15' when the carriage 4 to 4' 
touches the limit switch 33 or 33'; thereby restricting the further ascent 
of each carriage independently of the aforementioned height-difference 
detecting means 23. 
From the above descriptions thus far made, it will be seen that each 
carriage 4 or 4' is hoisted up or down independently of each other by the 
piston-cylinder device 15 or 15' within a range defined by the 
height-difference detecting means 23 and height-restricting means 24, and 
that it therefore becomes possible to incline at a desired angle a vehicle 
or the like, which has been horizontally lifted up to a desired height, 
with no fear of slipping accidents. 
In FIG. 6, similar to FIG. 1, showing an alternative embodiment of the 
present invention, reference numerals are indicative of the same members 
as in FIGS. 1 to 5 if same. According to the alternative embodiment, a 
carriage 4(4') of channel section is secured to each mast 3(3') such that 
its opened portion faces innerward. A horizontal bar 40, comprising a 
lateral portion 40a traversing the open space of the mast and a base 
portion 40b, is secured to the inner surface of the carriage's outer wall. 
The lateral portion 40a of the bar 40 has a threaded bore 41 excavated at 
an almost central part thereof and two smaller bores 8, similar to those 
in FIG. 4, through which a wire 30 of a height-difference detecting means 
23 penetrates. From this it will be understood that the horizontal bar 40 
performs the same function as that of the cantilever plate 7(7') shown in 
FIG. 4. 
According to this alternative embodiment of the invention, the hoisting up 
or down of each carriage 4 or 4' is effected by a threaded rod 42 or 42' 
vertically mounted within each mast 3 or 3'. This threaded rod 42(42'), 
being adapted to threadably fit in with the threaded bore 41(41') of the 
bar 40(40'), is rotatably supported at its lower end on the base 2 and at 
its upper end by a bearing plate 43(43') secured to the upper portion of 
the mast 3(3'). Each of the threaded rods 42 and 42' is provided at its 
lower portion with a bevel gear 44(44'), which is engageable with another 
bevel gear 45(45') extending from a reversible motor 46(46') via a rotary 
shaft 47(47'). A turning force from the motor 46(46') in either direction 
is transmitted through the shaft 47(47') and two bevel gears 44(44') and 
45(45') to the threaded rod 42(42'), by which each carriage 4 or 4' can be 
hoisted up or down independently. 
Similarly to the first embodiment of the invention, the inclining of a 
horizontally lifted-vehicle A or the like at a desired angle is controlled 
by a height-difference detecting means 23 having two limit switches 27 and 
27', and the prevention of each carriage from the further ascending or 
descending beyond a predetermined limit is effected by two limit switches 
48(48') and 49(49') fixed to upper and lower portions of each mast 
respectively. 
Thus, it will clearly be understood that the two-masted lifting apparatus 
of the present invention, whose structure is simple and reliable, is most 
suited to inspecting, repairing or cleaning works of a vehicle's underside 
or the like.