US2103661A - Counterbalancing mechanism for lift bridges - Google Patents

Description

De 28, 1937, T. E. BROWN, JR

COUNTERBALANCING MECHANISM FOR LIFT BRIDGES Filed March 14, 1954 3 Sheets-Sheet 2 INVENTOR mama; 55/0 ATTQRNEY T. E. BROWN. JR

GOUNTERBALANCING MECHANISM FOR LIFT BRIDGES Dec. 28, 1937.

Filed March 14, 1934 3 Sheets-Sheet 3 'INVENTOR z hwaff 5 6M ATTORNEY Patented Dec. 28, 1937 UNITED STATES GOUNTERBALANCING MECHANISM FOR LIFT BRIDGES Thomas E. Brown, J12,- Tuxedo, N.'Y. Application March 14, 1934, Serial No. 715,458

6 Claims. (01. 14-42) The invention relates to lift bridges and like structures having a part which is caused to rise and fall by means of power applied thereto, and it relatesmore especially to the counterbalancing means employed in connection therewith.

Various expedients have been proposed for counterbalancing the varying load imposed by the V usual counterweight as utilized in counterbalancing the weight of the span of such structures and which results from weights of the changing lengths of wire ropes, chains or other flexible connections between said usual counterweight and the span. These expedients, which comprise counterbalancing chains, auxiliary ropes with auxiliarycounterweights, etc., are all open to one or more of many objections, such as high cost, inexactness of balance, imposition of horizontal loads on the towers and piers, etc.

The present invention has'for an object the provision of a simpleand effective means for maintaining a substantially exact balance of the entire lift structure in all of its various positions and which means is positive in its action.

.A further object of the invention resides in the provision of balancing means which may be economically installed and whereby imposition of horizontal load components is obviated.

In carrying out the invention, provision is made for a counterweight auxiliary to the main counterweight which acts directly upon the vertical lift span, said main counterweight introducing, as is usual, varying loads on the span in different locations of the latter relative to its associated pair of towers. This auxiliary counterweight is arranged to be connected with the span through a drum rotatably mounted upon a tower and provided with a spiral groove portion, there being provided to this end also a plurality of flexible connections as ropes of wire or fibre connected with said drum, the. auxiliary counterweight and span. Or, sprockets and chains may be utilized instead.

One of said ropes adapted to run in the spiral groove portion of the said drum whereby the moment resulting from a load on this. rope will vary in accordance with the length thereof coiled in said groove, which moment thus may be designed to be proportionate to the unbalancing due I to said main counterweight. The nature of the invention, however, will best be understood when described in connection with the accompanying drawings, in which:

Fig. 1 is a side elevation of a vertical lift bridge equipped with the novel balancing mechanism.

Fig. 2 is an enlarged part side elevation and part vertical section of a drum element constitut ing a member of the'novel mechanism; and Fig.

3 is an end elevation thereof. i

Fig. 4 is a side elevation of a vertical lift bridge illustrating a modification in the application of a the novel balancing mechanism.

Fig. 5 is an enlarged part side elevation and part vertical section of a modified form of a drum element and sheave utilized therein; and. Fig. 6 is an end elevation thereoff I 10 Figs. 7, 8 and 9 are fragmentary side elevations illustrating modifications. V

Referring to the drawings, more particularly Figs. 1 to 3 thereof, Ill and II designate a pair of towersbetween which is mounted to move vertically a span i2, the latter being indicated in full line in its lowermost position and in dotted lines in the raised position. The span is suitably counterweighted, as hereinafter set forth, to move vertically between these towers; and various ar- 20 rangementsof motor and connections may be utilized for effecting the lifting and lowering of the span, these mechanisms being omitted from the drawings for sake of clarity and as they are well known and form no particular part of the 25 present invention.

One or more main counterweights l3 maybe provided for counterweighting the load set up by span l2, as through ropes I l attached, for example, at opposite ends 15 thereof. These ropes 30 are brought in the usual manner over sheaves l6 rotatably mounted in the corresponding towers, preferably a pair at each end of the bridge; and the free ends of the ropes are attached to the respective main co'unterweights. 5

In the particular embodiment illustrated in 3 Figs. 1 to 3, and in accordance with the invention, a tower carries an auxiliary rotatable drum 20. This auxiliary drum supports through a rope 2| attached thereto, as at 22, an auxiliary counterweight 23; and a second rope 24 attached to the drum at 25 is arranged to be connected with the span, in the present embodiment at the point 26 substantially where the ropes M are attached. The'said auxiliary drum, which is mounted 'to 45 rotate upon an axle 21, or by means of trunnions, and supported by a tower, is provided with a spiral cone groove portion 28 and a helical groove portion 29 of constant radius and in which, grooves the respective ropes secured to the drum 50 are adapted to run. For example, in the present embodiment, rope 2! runs in the cone spiral groove portion and the rope 24 in the helical groove portion. 7 Suitable guides 39 and 3'! may be provided along the corresponding towersfor accommodating the respective counterweights i3 and 23 in their reciprocations.

In the operation of the mechanism hereinbefore described, it will be appreciated that, as span l2 rises, the descent of the counterweights l3 and 23 will cause rotation respectively of the sheave l6 and drum 26, This, in the case of the drum, will cause rope 2i not only to unwind from the drum but in so doing will cause its contacting portion to bear in the groove of the drum at a different radius or distance from the axle 27 due to the spiral character of this groove. The moment applied by the auxiliary counterweight 23 through this radius upon the drum as'a whole will therefore vary accordingly, and a difierent lifting effort will be applied from the auxiliary counterweight to the span-decreasing as the span rises, and being at a minimum when the span is in its uppermost position, as indicated by the dotted line position, Fig. 1 of the drawings.

This effectively counteracts the increasing load developed by the main counterweight it, due to the increasing length of rope Hi on the counterweight side of the sheave, the curve of the groove 28 being so proportioned with respect to the weight of counterweight 53, its ropes M and counterweight 23 as to cause the change in the upward force during any motion of the span to equal the unbalance caused by the movement of the rope it over. the sheave it.

The upward stresses at points 26 are also affected by the weights of ropes 2i and 2 3 as they wind and unwind from drum 28. If the weights of these ropes be sumcient to materially afiect the required power to operate the span, compensation for their effect may be had by modification of the curve of groove 28.

To determine the required lever arms through which the ropes 2i act for the various positions of the span, I first choose such proportions for the extreme positions as will satisfy the conditions of balance in these two positions, i. e., if'

m and H equal respectively the weights per unit of length of ropes 2i and 26, H the height of rise of span l2, and H and H equal respectively the total lengths of the ropes 24 and 2! that are respectively wound up on and unwound from drums it during the complete motion of the span, then H=H; and the proportions must meet the conditions of balance expressed by the for-' mula (2p+n)H=% (W1Wl-mHl) 2pH= (1 1")(nH+ f where W represents the weight of the auxiliary counterweight 23; p the weight per unit length of ropes M; r the radius of the groove 29 about the axis of rotation of the drum and i, i l" the various lever arms, about said axis, of the center line of rope H as it unwinds from the conical groove 28l being the lever arm corresponding to the lowered position of the span, l the lever arm corresponding to the fully raised position of the span, and i the lever arm corresponding to an intermediate position.

It will readily be seen that the stress in rope 2 caused by the said weight 23 acting through rope 2i and drum 2% is W times its lever arm divided by r. This stress is communicated to the span by rope 2 3 and produces an upward force on the span at point of attachment 2%. As the span rises and rope 2i unwinds from groove aioaeei 28, the lever arm i changes causing a change in this upward force. The curve of groove 28 is to be so proportioned with respect to the weight of counterweight 23 as to cause the change in this upward force during any motion of the span, to equal the unbalance caused by the movement of the ropes i in passing over the sheaves iii.

The proportions having been chosen to meet the aforesaid requirements for the extreme positions of the span, the curve of groove 28 is determined by finding the required lever arms for various intermediate positions, as follows:

If h be any rise of the span 62 from its closed position, and h be the amount of rope 2i unwound from drum by such rise, then the required lever arm l to maintain the balance is If the weights of the auxiliary ropes 2| and 2% be so inconsiderable that they may be neglected, then the proportions to satisfy the extreme conditions become W 2pH= -(1-1),

and the lever arm for any intermediate position Many various combinations and mechanical arrangements can be made with my device.

In Figs. i to 6, a modification is illustrated in connection with the arrangement of the ropes and the auxiliary drum. The main counterweight 33 is connected over the sheave to the span as in the previously described embodiment; and it is guided in its travel by the guide member 33. Thus, the cone spiral-groove portion having the grooves 35 is in this instance adapted to receive the rope 35 which is attached to the span as at 3?, while the helical groove portion having the grooves 38 of equal radius receives the rope 39 attached to the auxiliary counterweight. The auxiliary counterweight ii! will therefore move vertically in straight lines, being guided by the guide member it; and because of the varying radius of the grooves 35, the ropes 36 will have a varying angle to the vertical in accordance with the position of the span. Depending upon the proportions chosen, a rope 36 may be made to reach or to pass through the vertical position, indicated by the dotted line position, Fig. 5; but it is preferred to so choose the dimensions that a said rope will be vertical or nearly so when the span is in its extreme elevated position.

This angle of deviation from the vertical will, of course, affect the vertical component of the pull of a rope on the span, which effect may be readily computed and compensated for, but in the majority of cases the effect thereof will be inconsiderable.

It will be understood, furthermore, that for any given set of conditions the smallest radius of both grooves of an auxiliary drum may be increased by constructing both of the sets of grooves of the drum of a spiral character, thereby permitting the use of a larger size of ropes.

In Figs. 4 to 6, a sheave 3 1 for the main counterweight and a drum for the auxiliary counterweights have been indicated as rotatable about the same axis; while in Fig. 7 they are arranged one behind the other whereby the rope t! from the auxiliarydrum 62 may be attached to the main counterweight 43 which in turn is attached by rope st to the span 45. Theeffect of the auxiliary counterweight =36 is thereby transmitted to the main counterweight 43 by means of the ropes 4i and 47, instead of directly to the span es. With this arrangement, the effects of the two counterweights are opposed and the auxiliary counterweight effects an increasing lift on the main counterweight as the latter falls with the rise of the span. Also, but a single connection is required to the span from each set of balancing means comprising a main and an auxiliary counterweight. The latter are guided in their movement by the respective guide members 48 and 49. If the sheaves and drums of a set be so constructed, for example, as set forth in Fig. 8 of the drawings, as to have identical angular rotation for all movement of the span, a single rope v be may also be utilized for attachment to the span 55, as at 52. In this embodiment, a sheave 53 for the main counterweight 54, guided in guide member 54 and a drum'55 for the auxiliary counterweight 58, guided in guide member 58,

may be made integral with each other or secured together, or their axles may be integrally united. This arrangement admits, also, of positioning the auxiliary counterweight 60, Fig. 9, on the span side of its tower 6 l, with the main counterweight 62 acting on the opposite side of the tower as in the previously described embodiment. The two said counterweights 6i) and 62 are guided respectively in the guide members 63 and 64. I

' I claim:

1. In vertical liftapparatus: the combination acting in conjunction with the main counterweight for substantially counterbalancing said span in all of its difierent vertical positions, and comprising an auxiliary counterweight carried by the said supporting means, a drum mounted on the sheave supporting means and provided with a spiral groove of substantial lever arm throughout its operable portion, and a plurality of flexible connections interconnecting the said counterweights, drum and vertical lift member and in all positions of the span substantially vertically disposed, one of which connections runs in the spiral groove of said drum whereby vary-1 ing loads developed by the main counterweight flexible connection in the diiferent positions of the vertical lift member are counterbalanced by the changing effective moment of the one drum connection as said connection wraps around said drum in the spiral groove thereof.

2. In vertical lift apparatus: the combination with a pair of vertical supporting means, a vertical lift member movable'relatively thereto between the same, a main counterweight for the lift member, and a sheave carried'by one of the vertical supporting means for supporting said main counterweight; of supplementary means acting in conjunction with the main counterweight for substantially counterbalancing said span in all of its different vertical positions,and

comprising an auxiliary counterweight carried and. ropes connecting the main counterweight with said drum, the respective connections in all positions of the vertical lift member being substantially vertically disposed and such as to effect opposing turning moments on the drum and one of the connecting ropes being wrappediaround the spiral. of .said drum. L

3. In vertical lift apparatus: the combination with a pair of vertical supporting means, a vertical lift member movable relatively thereto between the same, a main counterweight for. the lift member, and a sheave carried by one of the vertical supporting means for supporting. said main counterweight; of supplementary means acting. in conjunction with the main counterweight for substantially counterbalancing said span in all of its different vertical positions, and comprising an auxiliary counterweight carried by the said supporting means, a drum mounted on the sheave supporting means and provided with a spiral groove of substantial lever arm throughout its operable portion, a rope connecting said auxiliary counterweight with the drum, and ropes connecting the main counterweight'with said drum,the respective connections in all posi-- tions of the vertical lift member being substantially vertically disposed and such as .to effect opposing turning moments on the drum, and

the rope from the auxiliary counterweight being wrapped around the spiral of said drum.

4. In vertical lift apparatus: the combination with a pair of vertical supporting means,'a vertween the same, a main counterweight for the lift member, and a sheave carried by one of the vertical supporting means for supporting said main counterweight; of supplementary means acting in conjunction with the main counterweight for substantially counterbalancing said span in all of its different vertical positions, and

comprising an auxiliary counterweight carried by the said supporting means, a drum mounted on the sheave supporting means, coaxial with said sheave and connected therewith for like angular movement, said drum being provided with a spiral groove of substantial lever arm throughout its operable portion, and a plurality of flexible connections interconnecting the said counterweights, drum and vertical lift member and in all positions of the span substantially vertically disposed, one of which connections runs in the spiral groove of said drum whereby varying loads developed by the main counterweight flexible connection in the different positions of the vertical lift member are counterbalanced by the changing effective moment of the one drum connection as said connection wraps around said drum in the spiral groove thereof.

5. In vertical lift apparatus: the combination with a pair of vertical supporting means, a vertical lift member movable relatively thereto between the same, a main counterweight for the lift member, and a'sheave carried by one of the vertical supporting means for supporting said main counterweight; of supplementary means acting in conjunction with the main counterweight for substantially counterbalancing said span in all of its different vertical positions, and comprising an auxiliary counterweight carried by the said supporting means, a drum mounted on the sheave supporting means, coaxial with said sheave and connected therewith for like angular movement, said drum being provided with a spiral groove of substantial lever arm throughout its operable portion, a rope connecting the sheave tical lift member movable relatively thereto bethe sheave and the drum and in all positions of the rising part substantially vertically disposed, an axle supporting said drum, a spiral groove provided in said drum, said groove having a substantial varying lever arm about said axle throughout its operable portion, one of said flexible connections running in said groove, and said counterweights being so proportioned in relation to the lever arms of said groove as to maintain a substantially exact balance of said rising part, 3;

said counterweights and said flexible connections in all their positions.

THOMAS E. BROWN, JR.

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