US3103257A

US3103257A - Elevating apparatus

Info

Publication number: US3103257A
Application number: US102181A
Authority: US
Inventors: Richards Philip
Original assignee: Individual
Current assignee: Individual
Priority date: 1961-04-11
Filing date: 1961-04-11
Publication date: 1963-09-10
Anticipated expiration: 1980-09-10

Description

Sept.v 10, 1963 1 P. RICHARDS 3,103,257

ELEVATING APPARATUS Filed April 11, 1961 4 Sheets-Sheet 1 I n l In PHIL/P RICHARDS IN VE' N 70/? HUEBNER 8 WORRE' L A 7 TORNEKS P. RICHARDS ELEVATING APPARATUS Sept. 10, 1963 $3,103,257

Filed April 11, 1961 4 Sheets-Sheet 2 PHIL/P" RICHARDS IN l E N 70/? /0 M HUEBNER a WORREL ATTORNEYS 4 Sheets-Sheet 3 Filed April 11, 1961 W m m a k S 9 Lo R W R O A E R ,Q Q\ Q m M w R v a m R w QR M 8\ P m Mn 0 a H Q. 8 5 g 9% 3 Q 8 Q Q g mu Q g k w as \1 H \=|.n|\ an Q u N. n d 5 5% m2 QR wQ I w m Q a 8 5 $3 2 Q wQ mm Q porting member to a precise location.

United States Patent 3,103,251 ELEVATING APPARATUS Philip Richards, 5560 Columbia Drive N.,

I Fresno, Calif. Filed Apr. 11, 1961, Ser. No. 102,181 8 Claims. (Cl. 1822) The present invention relates to an elevating apparatus and more particularly to such an apparatus providing an articulated boom for elevationally supporting and motivating a load bearing member through pro-selected paths of travel to selected positions in which the paths can be precisely controlled as to direction, curvature, alignment and distance and desired positions of the load bearing Conventional elevating devices have long provided member can be attained with precision. articulated booms forelevating a load supporting member. Such members are adapted to mount movie cameras, television cameras, suitable platforms for supporting workmen thereon while attending various jobs in elevated positions, and loads which requireelevational positioning. The booms of such devices usually employ separate power members for motivating the individual sections of the boom relative to one another to adjust the load supporting member between its various elevated and retracted positions. With the plurality of. controls necessary for such movement, it is frequently difficult for even experienced operators properly tosynchronize the manipulation of the controls when attempting to position the load sup- The slightest mistake during such positioning is not only hazardous from a safety standpoint but is also time consuming and uneconomical.

It is therefore an object of the present invention to provide ,an elevating apparatus having an articulated boom which is adapted to position a load support member with improved precision.

Another object is to provide an elevating apparatus which is capable of motivating a load supporting member in a substantially straight .path of travel to a precisely predetermined position.

Another object is to provide .an elevating apparatus having a load supporting member movable in a straight path of travel wherein such travel is angularly adjustable during or preliminary .to such travel.

Another object is to provide an elevating apparatus which can be motivated from a retracted position to a predetermined elevated position-by. the actuation of a single control.

Another object is to maintain such a supporting memher in a substantially horizontal position .throughout said elevationa'l movement.

Another object 'is to provide an elevating apparatus which is simply constructed, economically manufactured, dependable in operation, accurately controllable, and of improved safety characteristics.

Other objects and advantages of .the present invention will become more fully apparent in the subsequent description in the specification.

In the drawings:

FIG. 1 is a side elevation of an elevating apparatus embodying the principles of the present invention shown in a retracted position.

FIG. 2 .is a side elevation of the elevating apparatus of FIG. 1 shown in an elevated position.

FIG. 3 is a plan view of the elevating apparatus shown in the retracted position. of FIG; 1.

FIG. 4 is a front elevation of the elevating apparatus shown in the elevated position of FIG. 2 having portions sectioned tor illustrative convenience.

FIG. 5 is a side elevation of the elevating apparatus having the booms angularly adjusted from FIG. 1.

3,103,257 Patented Sept. 10, 1963 FIG. 6 is a side elevation of the elevating apparatus shown extended from the retracted position of FIG. 5.

Referring in greater particularity to the drawings, a mobileframe generally indicated at 10 typifies one of the many mounting arrangements which can be provided for the subject invention. It will be understood that the invention is adaptable for mounting on various mobile vehicles such as tractors, trucks, railway cars and the like, not shown. It is further evident that the present invention has utility in stationary installations not requiring mobility. The mobile frame 10 includes a substantially square base 11 having a pair of angularly related legs 12 mounted thereon in transversely spaced substantially parallel relation. The legs-individually mount a pair of opposite forward wheels 14 and a pair of opposite rearward wheels 15.

As best shown in FIG. 4, the base 11 rigidly mounts an upwardly extended kingpin 18 centrally thereof and an upwardly opening cup member 20 having an outer calibrated peripheral azimuth '21 in circumscribing concentric relation to the kingpin. A turntable 22 is received within in the cup member 20 and provides a bore slidably receiving the kingpin 18 for rotation of the turntable relative to the kingpin and to the cup member 20. The extended end of the kingpin includes suitable threads for receiving a locknut 23 which is operative to adjust the compression of a spring 25 positioned between the locknut and the turntable. A pair of vertical posts 27 provide lower ends rigidly secured, as by welding, to the turntable in spaced diametrically opposed relation to the kingpin 18. The posts are rigidly upwardly extended from the turntable in transversely spaced substantially parallel relation to each other. The posts provide upper ends which include suitably aligned bores for rotatably receiving a main elongated pivot pin 28 therethrough.

A main sheave 30 having a grooved outer periphery 31 is concentrically rigidly mounted on the main pivot pin 28 between the upper ends of the vertical posts 27. An arcuate calibrated scale 32 is provided on one side of the sheave 30 for reasons soon to: be described. A main boom 35 provides a pair of elongated transversely spaced substantially parallel arms 36 having 'inner ends rotatably journaled on the main pivot pin 28 immediately outwardly of the vertical posts 27. A pointer member 37 is rigidly connected to the inner end of the arm 36 in upwardly extended relation adjacent to the calibrated scale 32 on the sheave 30. The arms 36 include outwardly extended ends which rotatably receive a transverse hinge pin 38. The arms 36 are held in their spaced parallel relation by apair of longitudinally spaced connecting

bars

39 and 40 intermediate the ends of the arms. The bar 40 provides an extended end 41 which projects outwardly of the main boom 35.

A pair of

arms

42 and 43 having inner ends rigidly secured to opposite sides of the main sheave 30 act as spacer members between the sheave and their respective upper ends of the vertical posts 27. As shown in FIG. 1, the arm 42 provides an angularly downwardly directed extended end 44. A hydraulic lifit jack 4 6 includes a cylinder 47 rotatably mounted at its lower end on the extended end 44 of the arm 42. The cylinder further includes a piston rod 48 adapted for reciprocation therein which is rotatably mounted on the outwardly extended portion 41 of the connecting bar 40. 1 The arm 43 also provides a rearwardly extended end portion 50 which rigidly mounts an angularly upwardly.

a a p rearwardly extends therefrom to connect to the extended end of the bracket 51 by a non-riotatable pin 56 extended therethrough. A second arcuate segment 57 providing a calibrated scale is disposed concentrically about the main pivot pin 28 between the sheave 53 and the arm 36 of the boom 35 and includes a lower end secured to the arms 27 by a bolt 58.

A pointer 59 rigidly secured to the sheave 53 is disposed adjacent to the scale on the arcuate segment 57 for reading purposes. A lower support arm fillineludes a forward end which is rigidly connected, as by Welding,

connected to the pin 56 on the bracket 51.

Thus, it is evident that upon actuation of the hydraulic lift jack 46 the main boom 3 5 is caused to swing in a vertical are about the main pivot pin 28 relative to the main sheave 30. At this time the hydraulic tilt jack 65 remains in a retracted position to prevent rotation of the main sheave 30 and its associated

lever arms

42 and 43. The degree of such movement is indicated by the pointer member 3-7 associated with the calibrated scale 32 on the sheave 30. With actuation of the jack 65, however, the entire assembly'this far described is tilted or pivoted on the main pivot pin 2 8'including the main boom 35, the lift jack 46, the main sheave Sil and the levers 4-2 and 43. The degree of tilting movement is d terminable by the pointer 59 associated with the calibrated scale on the arcuate segment 57. I

. A second boom 70 providesa pair of transversely spaced substantially parallel arms'72 having inner end 73 pivotally mounted upon the pin 38 between the extended end of the main boom arms 36. An auxiliary sheave 74 is rigidly secured between the inner ends '73 of the arms 72 for rotation therewith about the pivot pin38. The sheave further includes a grooved outer periphery 75 which is half the diameter of the main sheave 30*. The arms 72 of the second boom provide outer ends 76 each of which rigidly mounts an outwardly extending coaxial stub shaft-77. The stub shafts 77 individually rigidly mount at their outer ends a pair of forwardly extended arms 78 in obtusely angularly extended relation from the arms 72. The outer ends of the arms 73 provide aligned bores 79 which are. outwardly spaced in straddling aligned relation with the main pivot pin 23 when the

booms

35 and 70 are in the retracted position of FIG. 1. -As best shown in FIGS. 2" and 3, a U-shaped bracket 80 includes a pair of arms '81 which are individually pivotally mounted on a pair of pins 83 extended through the bores 79 of the arms 78. Aspacer bar 85 rigidly interconnects the arms 81 at their outer ends and rigidly mountsa load supporting member 90 thereon in outwardly extended relation. In the present environment, the supporting member 910* is preferably hinged intermediate its ends to provide anouter section 92 which can (be swung relative to the support member by retraction of a hydraulic jack 94 connected therebetween.

A cable 100 is trained about the grooved peripheries of the main sheave 30 and the auxiliary sheave 74. The cable is connected to each so that during swinging movement of the first boom 35, such movement is transmitted to the second boom-70.- With the diameter of the main sheave 30 being twice that of the auxiliary sheave 74, such transmission of movement is multiplied to the second boom so that the-rate of movement of the second boom is twice that of the first boom.

. 4 I11 order to maintain the load supporting member in a substantially horizontal position throughout said vertical swinging movement of the arms, a. secondary pulley or sheave and cable arrangement is provided. This arrangement includesa sheave which is rotatably mounted on the main pivot pin '28.. A bracket 106, rigidly mounted on the vertical post 27, engages the periphery of the sheave -16=5to preclude rotation thereof but permits rotation of the pin 28 within the sheave. A second coplanar sheave 108 of the same diameter as the sheave 105 is rigidly mounted on the pin 38 in the outer end of the first boom 35. A third sheave 110 of the same diameter of the sheaves 10 5 and 108 is rotatably mounted on the pivot pin 79 associated with the load supporting bracket 80. A cable 111 is rigidly connected eccentrically of the

sheaves

110 and 105 to a pin 1 12' on the arm 81 and to the bracket 11% andis trained about their outer peripheries by way of the sheave 108 so that during downward collapsing movement of the booms such action will tend to shorten the cable 111 and pivot the load supporting member in an are opposite to the are being described by the'second boom '70 to maintain the load support member in a level position. During upward movement of the boom arms the load supporting member has sufiicient weight to maintain the proper ten sion on the cable 111 for the same purposes.

A directional indicating mechanism is provided to indicate the angular straight path of travel of the load supporting member when the hydraulic jack 65' is actuated alone to adjust the angular positions of the booms. Such arrangement includes a grooved wheel or sheave 115 rigidly mounted on the pivot pin 38 opposite to the end mounting the sheave 108. The indicator arrangement further includes a sheave or wheel 117 on the same diameter rigidly mounted on the pin '79 on the arm 78- opposite to the sheave 110. The sheave 117 rigidly mounts an indicator or pointer rod 113 which preferably employs a spot light 119 aligned with the pointer as a night time direct ing aid. The cable 120 interconnects the

sheaves

117, 115 and 53- which co-act in a manner similar to the leveling sheaves to maintain the pointer in a direct line with the path of travel described by the load transporting member. Since the sheave 117 is not of sufiicient weight to maintain the cable 121i under tension a spring 121 is preferably provided about the outer periphery of the sheave for this purpose. Duringelevational positioning of the booms by the lift jack 46, the indicator member automatically corrects its angular relation to the arms 7 8 in the identical manner of the previously. described load member leveling arrangement.

' Operation The operation of the described embodiment of the present invention is believed clearly apparent and is briefly summarized at this point. Assuming that the

booms

35 and 70 are in the retracted position of FIG. 1, the support frame 12 is motivated by suitable means, not shown, to a location at which it is desired to elevate a load such as elevationally to position a television or movie camera. I

In the retracted position of FIG. 1, the load supporting member 90 is positioned in substantially horizontal parallel relation to the frame and the turntable, isrotated to the desired azimuth. Upon actuation of the lift jack 46, the b ooms are swung in opposite vertical arcs above I the main pivot pin 28 and the auxiliary pivot pin 38,

operative to maintain the directional indicator member in a substantially vertical upright position indicating the path of travel of the load supporting member 90. It is also to be noted that the entire elevating apparatus can be rotated about the kingpin 18 and the azimuth 2.1 on the turntable 22 to provide a 360 sweep of the load supporting member.

When it is desired to lower the load supporting memher from its elevated position, the hydraulic jack 46 is retracted at which time the cables 111 and 120 in effect are shortened by the collapsing movement of the boom arms to maintain the load supporting member 90 in its level position and the directional indicator member 118 in a substantially vertical position. The straight path of travel described by the load supporting member when motivated from the retracted position of FIG. 1 to the elevated position of FIG. 2 can beangularly adjusted from the vertical path of travel previously described to a substantially horizontal path of travel as when motivated from the retracted position shown in FIG. 5 to the extended position of FIG. 6.

Initially the

booms

35 and 70 are swung as a unit through a vertical arcuate path from the retracted position of FIG. 1 to the substantially vertical position shown in FIG. 5 by actuation of the tilt jack 65. It is to be noted that the jack is operative to position the booms in any angular relationship between the retracted substantially horizontal position and the vertical position. During such movement the directional indicator member 118 is swung in the same arcuate path of travel accurately to indicate the direction of subsequent movement Which the load supporting member will describe upon actuation of the lift jack 46. Such condition is shown in FIG. 6 wherein the jack '46 is actuated to swing the booms through .opposite arcuate paths of travel which function, as before,

to motivate the load supporting member in a substantially straight path of travel. In this instance, such straight path of travel is substantially horizontal in corresponding relation to the preceding adjustment of the booms by the tilt jack 65.

From the foregoing it is evident that the elevating apparatus of the present invention is effective for positioning a load supporting member in a substantially straight path of travel to any pre-selected elevational position. Such straight path of travel can be angularly adjusted prior to the elevational movement of the load supporting member so that only a single control need be actuated to accurately position the load support member to said pre-selected elevational position. As will be obvious, combined actuation of the

jacks

46, 65 and 94 can achieve any desired positioning and course of travel of the load support member 90 that is desired.

Although the'invention has been herein shown and tures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

Having described my invention, What I claim as new and desire to secure by Letters Patent is:

1. An elevating apparatus comprising a base, a first boom pivotally mounted on the base for elevational swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the first boom for elevational swinging movement and having an extended end, a first sheave rigidly mounted concentrically of the pivotal mounting of the first boom on the base whereby relative movement occurs between the first sheave and the first boom upon elevational movement of the latter, a second sheave rigidly mounted on the second b'oom concentrically of the pivotal mounting of the second boom on the first boom, powered means connected to the first boom for pivotally raising and lowering same and means interconnecting said sheaves eccentrically of their respective boom mountings for pivoting said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave being of a diameter twice that of said second sheave whereby the extended end of the second boom defines a substantially straight path of travel during said elevational swinging movement of the booms.

2. An elevating apparatus comprising a base, a first boom pivotally mounted on the base for elevational swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the first boom for elevational swinging movement and having an extended end, a first sheave rigidly mounted concentrically of the pivotal mounting of the first boom on the base whereby relative movement occurs between the first sheave and the first boom upon elevational movement of the latter, a second sheave rigidly'mounted on the second boom concentrically of the pivotal mounting of the second boom on the first boom, first powered means connected to the first boom for pivotally raising and lowering the sa1ne,.means interconnecting said sheaves eccentrically of their respective boom mountings for pivoting said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave being of a diameter twice that of said second sheave whereby the extended end of the second boom defines a substantially straight path of travel during said elevational swinging movement of the booms, and second powered means connected to said first sheave for pivoting the booms, the sheaves and the first powered means as a unit relative to the base for angularly adjusting said straight path of travel of the extended end of said second boom.

3. In an elevating apparatus comprising a base, a first boom pivotally mounted on the base for elevational swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the first boom for elevational swinging movement and having an extended end, a load supporting member pivotally mounted on the extended end of said second boom, a first sheave having a periphery mounted concentrically of the pivotal mounting of the first boom on the base, a second sheave rigidly mounted on the second boom and having a periphery disposed concentrically of the pivotalmounting of the second boom on the first boom, powered means connected to the first boom for pivotally raising and lowering the same, and means rigidly mounted on the peripheries of said sheaves fin interconnecting relation therebetween for pivoting said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave'being of a diameter twice that of said second sheave whereby the load supporting member defines a substantial- =ly straight path of travel during said elevational swinging movement of the booms.

4. In. an elevating apai'atus comprising a base, a first boom pivotally mounted on the base -for elevational swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the first boom for elevational swinging movement and having an extend ed end, load supporting member pivotally mounted on the extended end of said second boom, a first sheave having a periphery mounted concentrically of the pivotal mounting of the fi-r-st boom on the base, means normally restraining said sheave from rotation relative to the base and permitting rotation relative to the first boom, a second sheave rigidly mounted on the second boom and having a pcriphery disposed concentrically of the pivotal mounting of the second boom on the first boom, first powered means connected to the first boom for pivotally raising and lowering the same, means rigidly mounted and trained over the peripheries of said sheaves in interconnecting relation therebetween for positioning said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave being of a iliameter g twice that of said second sheave whereby the load supporting member defines a substantially straight path of travel during said elevational swinging movement of the booms, and second powered means connected to said first sheave for pivoting the booms, the sheaves, the first powered 1 means, and the load supporting member as a unit relative to the base for angul-arly adjusting said straight path of travel of the load supporting member.

5. In an elevating apparatus comprising a base, a first boom pivotally mounted on the base for elevational swinging movement and having an extended end, a second boom pivotally mounted on theextended end of the first boom 'for elevational-swingingmovement and having and extended end, a load supporting member pivotally mounted on i the extended end of said second boom, a first sheave having a periphery mounted concentrically of the pivotal mounting of the first boom on the base, a second sheave rigidly mounted on the second boom and having a periphery dis- I posed concentrically of the pivotal mounting of the-second boom on the first boom, first powered means connected to the first boom for pivotally raising and lowering the same, means rigidly mounted on and trained over the peripheries of said sheaves in interconnecting relation therebetween for positioning said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave being of a diameter twice that of said second sheave whereby the load supporting member defines a substantially straight path of travel during said elevational swinging movement of the booms,

second powered means connected to said first sheave for pivoting the booms, the sheaves, the first powered means,

and the load supporting member as a unit relative to the boom pivotally mounted on the base for elevational V swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the.

first boom for elevational'swinging movement and having an extended end, a substantially horizontally disposed load supporting member pivotally connected to the extended end of said second boom, a first sheave mounted concentrically of the pivotal mounting of the first boom Ion the base, a second sheave rigidly mounted on the.

second boom concentrically of the pivotal mounting of the second boom on the first boom, first powered means connected ,to the first boom for pivotally raising and lowering the same, a cable having ends rigidly mounted on said sheaves eccentrically of their respective boom mountings in interconnecting relation therebetween for ing an extended end, a substantially horizontally disposed load supporting member pivotally mounted on the extended end of said second boom, a first sheave having a periphery mounted concentrically of the pivotal mounting of the first boom on the base, a second sheave rigidly mounted on the second boom and having a periphery disposed concentrically of the pivotal mounting of the second boom on the first boom, first powered means connected to the first boom for pivotally raising'and lowering the same, a cable having ends rigidly mounted on and trained over the peripheries of said sheaves in interconnecting relation therebetween tor positioning said second boom relative to the first boom during said elevational swinging movement of thefirst boom, said'first sheave being of a diameter twice that of said second load supporting member, and means mounted eccentri cally of said pivotal mounting of the first boom being disposed equally eccentrically about said pivotal connection of the second boom and connected to said load sup- 1 porting member at a position equally eccentrically of its pivotal connection with the second boom whereby said load supporting member is maintained substantially horizontal during said elevational swinging movement of the booms. 1

8. in an elevating apparatus comprising a base, a first boom pivotally mounted on the base for elevational swinging movement and having an extended end, a second boom pivotally mounted on the extended end of the first boom for elevational swinging movement and having an extended end, a substantially horizontally disposed load supporting member having a wheel connected thereto providing a grooved periphery pivotally mounted on the extended end of said second boom, a first sheave having a periphery mounted concentricallyof the pivotal mounting of the first boom on the base, a second sheave rigidly mounted on the second boom and having a periph- I cry disposed concentrically of the-pivotal mounting of the second boom on the first boom, first powered means connected to the first boom for pivotally raising and lowering the same, a cable having endsrigidly mounted tional swinging movement'of the first boom, said first positioning said second boom relative to the first boom during said elevational swinging movement of the first boom, said first sheave being of a diameter twice that of said second sheave whereby the load supporting member defines a substantially straight path of travel during said elevational swinging movement of the booms, and means mounted eccentrically of said pivotal mounting of the first boom being disposed equally eccentrically sheave being of a diameter approximately twice that of said second sheave whereby the load supporting member defines a substantially straight path of travel during said elevational swinging movement of the booms, second powered means connected to said first sheave for pivoting the booms, the sheaves, the first powered means, and the load supporting member as a unit relative .tothe base for angularly adjusting said straight path of travel of the load supporting member, a second wheel having a grooved periphery concentrically mounted adjacent said pivotal mounting of the first boom, a third wheel having a grooved periphery concentrically mounted adjacent to said pivotal mounting of the second boom, and a cable having ends rigidlyconnected eccentrically of the peripheries of said first and second wheels trained over the periphery of said third Wheel whereby said load supporting member is maintained substantially horizontal during said elevational swinging movement of the booms, a pluralityof pulleys individually, concentrically mounted on each of said pivotal boom mountings, a pointer member rigidly mounted on one of said pulleys, and means interconnecting said pulleys whereby said pointer member in- 9 10 dicates the directional line of said straight path of travel 2,724,620 Johnson Nov. 22, 1955 of the load supporting member. 2,815,250 Trump Dec. 3, 1957 2,881,030 Troche Apr. 7, 1959 References Cited in the file of this patent 3,009,546 Anderson Nov. 21, 1961 T D PA E 5 1965 689 ovfan STATES T iuly 10 1934 FOREIGN PATENTS 434,384 Germany Sept. 23, 1926 2,616,768 Stemm Nov. 4, 1952

Claims

1. AN ELEVATING APPARATUS COMPRISING A BASE, A FIRST BOOM PIVOTALLY MOUNTED ON THE BASE FOR ELEVATIONAL SWINGING MOVEMENT AND HAVING AN EXTENDED END, A SECOND BOOM PIVOTALLY MOUNTED ON THE EXTENDED END OF THE FIRST BOOM FOR ELEVATIONAL SWINGING MOVEMENT AND HAVING AN EXTENDED END, A FIRST SHEAVE RIGIDLY MOUNTED CONCENTRICALLY OF THE PIVOTAL MOUNTING OF THE FIRST BOOM ON THE BASE WHEREBY RELATIVE MOVEMENT OCCURS BETWEEN THE FIRST SHEAVE AND THE FIRST BOOM UPON ELEVATIONAL MOVEMENT OF THE LATTER, A SECOND SHEAVE RIGIDLY MOUNTED ON THE SECOND BOOM CONCENTRICALLY OF THE PIVOTAL MOUNTING OF THE SECOND BOOM ON THE FIRST BOOM, POWERED MEANS CONNECTED TO THE FIRST BOOM FOR PIVOTALLY RAISING AND LOWERING SAME AND MEANS INTERCONNECTING SAID SHEAVES ECCENTRICALLY OF THEIR RESPECTIVE BOOM MOUNTINGS FOR PIVOTING SAID SECOND BOOM RELATIVE TO THE FIRST BOOM DURING SAID ELEVATIONAL SWINGING MOVEMENT OF THE FIRST BOOM, SAID FIRST SHEAVE BEING OF A DIAMETER TWICE THAT OF SAID SECOND SHEAVE WHEREBY THE EXTENDED END OF THE SECOND BOOM DEFINES A SUBSTANTIALLY STRAIGHT PATH OF TRAVEL DURING SAID ELEVATIONAL SWINGING MOVEMENT OF THE BOOMS.