US3108656A

US3108656A - Lifting apparatus for electric-line construction or maintenance workers

Info

Publication number: US3108656A
Application number: US833347A
Authority: US
Inventors: Asplundh Lester
Original assignee: Asplundh Tree Expert Co
Current assignee: Asplundh Tree Expert Co
Priority date: 1959-08-12
Filing date: 1959-08-12
Publication date: 1963-10-29
Anticipated expiration: 1980-10-29

Description

L. AsPLuNnH 3&1 08,656

4 Sheets-Sheet l Odi. -29, 1963 LIFTING APPARATUS FOR ELECTRIC-LINE CONSTRUCTIQ 0R MAINTENANCE WORKERS Filed Aug..12, 1959 Y l ENToR ATTQRNEYS '3,108,656 TRUCTION oct. 29', 1963 L. ASPLUNDH LIFTING APPARATUS FOR ELECTRIC-LINE CONS 0R MAINTENANCE -WORKERS 4 Sheets-Sheet 2 Filed Aug. 12, 1959 ATTORNEYS Oct. 29, 1963 L. AsPLUNDH 3,108,556

LIFTING APPARATUS Foa ELEc'rRIc-LINE CONSTRUCTION OR MAINTENANCE WORKERS Filed Aug. 12, 1959 A 4 Sheets-Sheet 5;

ll ATTORNEYS v Oct. 29, 1963 L. AsPLuNDH 3,108,656

' LIETINC APPARATUS FCR ELECTRIC-LINE CONSTRUCTION 0R MAINTENANCE woRKERs Filed Aug. 12, 1959 Y 4 Sheets-Sheet 4 v I ENT R Yfw ATTORN EY5 United States Patent O 3 108,656 LIFTING APPARATUSFOR ELECTRIC-LINE CGN- STRUCTIGN GR MAINTENANCE WORKERS Lester Asplundh, Bryn Athyu, Pa., assigner, by mesme assignments, to Asplundh Tree Expert Co., Jenkintown,

Pa., a corporation of Pennsylvania Filed Aug. 12, 1959, Ser. No. 833,347 15 Claims. (Cl. 182-2) y'l'his invention relates to lifting apparatus and par-ticularly to equipment which is suitable for raising a workman to a position where he has convenient access to electrical lines either for the purpose of construction or maintenance of the line itself or for trimmingthe branches of trees which may be interfering with the line. As is well known workmen who perform these duties are often subjected to danger especially when servicing lines which carry high voltages or heavy current loads. Beyond this, the truck or base upon which the lifting equipment is mounted is often a potential danger to those who may be working on or around it on the ground because a short circuit through the equipment may seriously injure or even kill a man who touches the appartus while in contact with the ground. To use an expression which is [familiar to the industry a truck which is carrying a short circuit to the ground is known as a hot truck.

The primary object of the present invention is to construct equipment or apparatus of the character described which will completely protect either the workman who is elevated above the ground or a man on or in circuit with the ground from all danger due to shorting of charged wires. At the same time it is an object of my invention to provide for such safety in equipment of this kind without in any way interfering with its mobility or maneuverability.

It is also an object of my invention to provide means whereby the workman who is supported above the ground can maneuver himself into whatever position is most convenient for the work in hand and also by means of which someone standing on the ground or located in the truck can also maneuver the workmans platform to whatever position may be desired, and both of these without danger of injury from short circuits or structural deliciencies.

-A still further object is to provide the required insulation through use of structural, load-carrying members or parts which are constructed of electrically non-conducting material as distinguished from the use of structural parts which in themselves are not non-conducting and are only surfaced or covered with insulating material. The latter type of equipment is known in the art and has many times proved to be unsatisfactory because it is relatively easy to so seriously damage the insulating covering as to endanger the workmen. Such dangerous conditions can be developed under normal service conditions or through careless handling of the equipment and may result from scraping, bumping or breaking -the insulating surfaces, and this without knowledge of those involved and often without discovery even upon careful inspection.

Still another object of the invention is to provide suitable raising and lowering equipment as well as platform leveling equipment which is also thoroughly insulated in order to prevent short circuiting from the wires to the ground.

How the foregoing objects together with such other objects as may appear hereinafter or are incident to my invention are attained is illustrated in preferred form in the accompanying drawings wherein FIGURE 1 is a somewhat diagrammatic elevational view of my improved lifting apparatus mounted upon a 3,108,656 Patented Oct. 29, 1963 p ICC truck with a portion of the upper boom used in the apparatus broken out to show `the platform leveling cables with their insulating means;

FIGURE 2 is an enlarged plan section taken on the line 2 2 of FIGURE Il;

FIGURE 3 is an enlarged fragmentary section taken as indicated by the line 3 3 of FIGURE 4;

FIGURE 4 is a vertical section through the supporting mast or pylon and through the lower portion of the lower boom which is pivotally mounted thereon;

FIGURE 5 is a plan section on the line 5 5 of FIG- URE 4;

FIGURE 6 is a sectional elevation of portions of the lower and upper booms including the point where they are articulated together;

FIGURE 7 is an exploded view of the mast or pylon structure;

FIGURE 8 is a view taken on the line 8 8 of FIG- URE 9 showing the upper boom and the workmans platform or basket which is pivoted at the outer end thereof;

FIGURE 9 is a plan section on the line 9 9 of FIG- URE 8;

FIGURE 10 is an enlarged fragmentary sectional elevational view of the lower portion of the mast or pylon and the so-called pylon box;

FIGURE 1l is an enlarged fragmentary section on the line Il l of FIGURE 8; and

FIGURE 12 is a section on the line 12 12 of FIG- URE 6.

`By referring to the drawings, it will be seen that I have mounted my improved lifting apparatus upon a truck T so as to provide for a high degree of mobility. Preferably the mounting point is on the chassis 13 directly in back of the cab 14 because this is a location which provides for the highest degree of stability. A mast or pylon box 15 is arranged at the back of the cab as shown in FIGURE l, which box is constructed to provide suitable bearing means for the vertical mast or pylon 16 as will appear below. It also houses the horizontally disposed hydraulic cylinder and piston mechanism 17 18 which rotates the mast together with certain of the hydraulic valve controlling mechanisms and fluid lines. An outrigger 19 is provided at each side of the pylon box which is adapted to engage the ground to ensure stability when the appartus is in use. These outriggers, however, form no part of the present invention.

With my invention I prefer to construct the vertical mast or pylon I6 of three principal parts, namely a stuk mast or section 2d at the bottom, an upper mast portior or section 2l and an intermediate load-carrying mas member or section 22 which latter is constructed entirely of a suitable electrically non-conductive material of suffi cient structural strength to carry the loads and resist tht stresses incident to operation of the lifting apparatus. Thi: intermediate section is mounted on the stub mast to ro tate therewith and project upwardly therefrom and tht upper mast section is mounted on the intermediate sec tion also to rotate therewith, so that the whole mas structure constitutes a rotatable pylon for supporting tht booms to be described below.

Preferably the

sections

20, 2l and 22 of the'mast o pylon are tubular in form with their adjacent ends ar ranged to telescope. I provide for this telescoping bj making the stub section and the upper section of slightlj larger diameter than the adjacent end portions of the in termediate insulating section so that they will embrace th adjacent ends of the intermediate section as indicated it` best advantage in FIGURES 1 `and 7. Furthermore, th

intermediate non-conducting section 22 is provided wit an annular shoulder 23 of substantial extent longitudina ly of the section, against the vupper face of which shou der the bottom end of section 21 abuts and against the under face of which shoulder the upper end of the stub section 20 abuts when the parts are in assembled relation. rIihe stub section 20 and the upper section 21 are preferably composed of suitable metal but it will be obvious that no electrical path from the upper section 21 to the lower section 20 exists because the intermediate section 22 with its shoulder .-23 prevents contact of the upper section with the lower section. Furthermore, the width of the shoulder 23 is designed to resist jumping of current from the upper section to the lower section up to voltages as high as will be encountered in the service for which the lifting apparatus is intended. In some instances `this may be as much as 100,000 volts,

My preference, insofar as material from which to construct the insulating section 22 is concerned, is Fibreglas in which the fibres are spun to the shape :desired and bonded `with suitable bonding material, because I have found that a unit constructed in this way is fully non-conductive and of outstanding strength from a structural standpoint. At the same time it can be made within very practical and reasonable limits insofar as size is concerned.

The three sections of the mast are fitted and secured together so that they rotate as a unit, the bottom section 20 being mounted on the horizontal wall 24 near the bottom of the pylon box in a suitable bearing 25. The upper end of the section 20' passes through the upper wall 26 of the pylon box `where it is provided with another bearing 27.

Ata point between the

bearings

25 and 27 and preferably near the upper bearing 27 as shown in FIGURE 10, the stub section 20 of the mast is provided with a pulley surface 2S and adjacent thereto is the horizontal hydraulic cylinder 17 with its piston 1S already referred to. The piston is double acting and projects from both ends of the cylinder and on each end of the piston is a pulley 29.

A cable 30 `for rotating the mast leads from the upper bracket 31 on the cylinder 17 to the lower pulley 29 (las viewed in FIGURE then to the pulley surface 2S which is secured to the section 20' and around this pulley 2S one turn and finally up to and around the upper pulley 29 and then down to the lower bracket 32 on the cylinder 17 (still viewed as in FIGURE 5). This cable 30 is secured at a central anchor 33 on the pulley 28.

High pressure hydraulic operating fluid comes in through the supply pipe 34 (FIGURE l0) .which delivers it to the valve housing 35 in which is located a series of control valves the details of which are not illustrated because, per se, they `form no part of the present invention. Suflice it to say at this point that an upper valve chamber 36 controls the fluid which operates the piston 1S in the cylinder 17, the -iiuid circulating and returning through the lines 37. A lever 33 is provided in the pylon box within easy reach of a workman on the ground by means of which, if desired, he can cause rotation of the mast.

The Khandle 38 for actuating the valve which controls the operation of the cylinder and piston I7-18 can also be operated by the workman up on the platform or basket 66. To this end a valve actuating cylinder and piston mechanism 39 is provided -which is under the control of the low pressure hydraulic lines 40 leading up to a low pressure valve control mechanism in the basket within convenient reach of the workman `as will further appear.

A lower boom 41 is suitably pivoted for up and down swinging movement in a forked member 42 secured to the top of the upper mast section 21 (see FIGURES 1 and 3). Swinging motion of the boom `411. takes place around an axis shaft 43 which, for convenience, will be referred to as lthe pylon shaft. This pylon shaft is fixed against rotation in the forked member 42 and the boom 41 swings thereon through the medium of suitable bearing construction shown in FIGURE 3 but 4which will not be described in detail since in and of itself it forms no part of the pres- :nt invention. For a purpose which will appear hereinafter, the shaft 43 also carries a sheave 44 which is fixed to the shaft 43. The sheave 44, therefore, never rotates at all because it is fixed on the shaft 43y and the shaft 43 is fixed in the forked member 42 as described.

Still referring to FIGURE 3 it will be seen that a boom operating sheave 45 is `also mounted on the shaft 43 Iwhich sheave is free to rotate on the shaft. The cable 46 which raises and lowers the upper boom 47 passes around this sheave 45 as will further appear.

The lower boom 41 is raised and lowered around its pivot on shaft 43 by means of a hydraulic cyl-inder and piston mechanism 48-49, the lower end of the cylinder 48 being suitably pivoted on the upper section 21 of the mast and the outer end of the piston 49 being suitably pivoted to the boom 41 at a point just above the shaft 43. By so placing the cylinder and piston 48-49 it cannot act as a short circuit to the ground because its points of connection are above Ithe insulating mid section 22--23 of the mast or pylon. The high pressure hydraulic fluid for actuating the cylinder land piston mechanism 48-49 and so raising and lowering the lower boom 41 is delivered and returned through lthe h-igh pressure hydraulic lines 50 under the control of a suitable valve in the box 51 (see FIGURE 10). An actuating lever 51a is provided for moving the valve in box 51 and, as in the case of lever 38, it may be actuated by a workman on the ground as well as by the workman up in the basket through the medium of low pressure fluid lines 51b and an operating cylinder 51e.

The upper boom 47 is pivoted on the upper end of the lower boom 4I by means of the following construction (see particularly FIGURES 1, 2, 6 and 12). At its lower :end the upper boom 47 is provided with an end member 52 which is bolted to an extended hub portion 53 of an `operating sheave 54 (see FIGURE 2). The sheave 54 with its extended hub 53 rotates in bearings in a fixture 56 which latter is attached to the upper end of the lower boom 41. In turn the sheave 54 supports, in suitable bearings, a hollow shaft 55 which latter extends from a point within the upper boom end member 52 outwardly through sheave 54 to the inside of the upper end of the lower boom 41. The bearings for the shaft 55 are shown to best advantage in FIGURE 2. On the end of .the shaft 55 within ythe member 52 there is fixed a leveling pulley 57 and. at the opposite end of the shaft 55 there is fixed another leveling pulley 58. Both of these leveling pulleys therefore can turn with the shaft 55 during leveling lof the basket as will further appear.

In order to swing the upper hoorn 47 upwardly and downwardly a high pressure, fiuid-actuated cylinder and piston mechanism 59-60 is provided, the cylinder being mounted on the lower boom 41 as shown in FIGURES l and 6. The sheave 54 is a double sheave `as shown in FIGURE 2 and the operating cables are `anchored to this sheave at the points 62 and 63 (see FIGURE 6). The anchor 63 is the anchor for the right hand run 46a of the cable which run is in the sheave groove closest to the observer in FIGURE 6. In other words, the right hand cable run in FIGURE 6 leads upwardly from the piston rod 60 into and around the front groove in the sheave 54, then over the sheave for approximately 3A of a turn to the anchor 63 near the bottom of the sheave as viewed in FIGURE 6. The left hand run 4611 of the cable leads from the connection 61 at the bottom of the cylinder 59 to and around the lower sheave 45 and then up yto `the other groove of the upper double sheave 54 (as viewed in FIGURE 6) and then approximately I/a turn to the right `around the said sheave 54 to the anchor 62. Therefore, when the hydraulic operating fiuid is circulated to and from the cylinder 59 the cable runs 46a and 46b will rotate the sheave 54, the hub S3 of which is connected to the lower end of the upper boom 47 so that said upper boom may be swung upwardly and downwardly in its bearings in x-ture 56. Here again the mechanism just described, namely 4the cylinder and piston mechanism 59-60 with the cable 46 cannot create a short circuit to the ground because of the fact that they are located entirely above the insulating section 22.-23 of the pylon.

High pressure iluid for operating the cylinder and piston mechanism 59-60 is delivered through the conduits 64 under the control of the valve in box 65 (FIGURE lever 65a and low pressure actuating cylinder 65C and low pressure lines 65b which latter lines as before run up to the operating platform or basket at the top of the upper boom.

At this point I wish to call particular attention to the fact that the hydraulic flu-id lines 40, Slb, 50, 64 and 65h are made entirely of suitable electrically non-conductive material such as nylon or rubber so that none of them can possibly act as conductors for carrying `a short circuit from the electric line above to the ground below. The hydraulic fluid lines 37 need not be made of nonconductive material because they extend only to -tlhe cylinder and piston mechanism 17-18 and are located within the pylon box at a point below the insulating section 22-23.

The platform which takes the form of a suitable basket 66 is pivoted on the outer end of the upper boom in the following manner (see particularly FIGURES 8, 9 and l1). At 'one side near the top, a shaft 67 is welded or otherwise securely fastened to `the basket so that the shaft and the basket move together. This shaft 67 projects outwardly through the upper end tting 68 of the upper boom 47 and is mounted in suitable bearings 69. Fastened to the shaft 67 is a leveling pulley 7d. As the booms are raised and lowered the basket also must be swung either to the right or to the left in order to maintain it substantially level at all times. This is accomplished by means of the leveling sheaves 44, 57, 58 and 70 already referred to and the leveling

cables

71, 72, 73 and 74 which are reeved thereon. Each of

cables

71 and 72 is secured by a suitable `anchoring means 75 on the upper portion of the sheave 44 (see FIGURE 3). 'Ilhe llower end of each

cable

71 and 72, therefore, passes roughly three quarters of `a turn 'around the leveling pulley 44. Similarly, on the sheave 5S at the upper end of the lower boom the ends of the leveling

cables

71 and 72 are passed approximately three quarters of a turn around the sheave rand then anchored at a point in the lower portion of the sheave. A similar arrangement exists for the leveling

cables

73 and 74, their low-er ends being passed three quarters of a turn around the sheave 57 in opposite directions and then anchored to the sheave. Finally, the basket ends of the leveling

cables

73 and 74 pass around the basket sheave 70v to a suitable anchor 7 6 near the bottom of this sheave.

Since the bottom leveling sheave or pulley 44 is firmly xed and never rotates at all it is obvious that when the lower boom swings upwardly or downwardly on its pivot the leveling

cables

71 and 72 will be wrapped around or unwrapped from the leveling pulley 44. For example, when the lower boom 41 swings downwardly toward the right on its pivot from the position shown in FIGURE 1 the left hand leveling cable 71 will be wrapped on the fixed pulley 44 to effect counterolockwise rotation of the sheave 58, shaft 55 and sheave 57. This causes the cable 74 to rotate the basket sheave 7@ in a counterclockwise direction so as to swing the basket to the right and thereby maintain it in level position as the lower boom is swung downwardly. It is obvious, of course, that the reverse action takes place when the lower boom is swung upwardly back to the position of FIGURE 1 and also when it is swung downwardly toward the left from the position of FIGURE l, i.e., the sheave 5S, shaft 55, sheave 57 and sheave 70 are rotated in a clockwise direction so as to swing the basket to the left and thereby again maintain it in level position. An entirely analogous or similar action takes place when the upper boom is swung on the lowerV 6 boom because at such times the leveling pulleys in the joint which connects the two booms will be held in iixed position by the leveling cables in the lower boom. Of course, it will be obvious that a composite result of such motions will be effected where both booms are being swung simultaneously.

I now wish to refer to other important insulating features of my improved apparatus. The upper boom 47 has the major portion of its shank constructed completely of some suitable, structural, electrically non-conducting material such as Fiberglas spun and bonded together. As in the case lof the pylon section 22f-23 I prefer Fiberglas for this purpose because of its absolute insulating qualities and its great structural strength. Indeed, I have determined by extensive tests that a boom constructed in this way will resist, for very long periods, all destructive effects of the forces created during operation of the apparatus.

It will be seen, therefore, that, insofar as the upper boom is concerned, I have in the present disclosure, shown it as involving a pair of spaced end members or ttings which are interconnected by a long tubular section or shank of spun glass fibres bonded together into a rigid, load-carrying structural member lthrough which it is absolutely impossible for any current to pass in case the upper end of the boom structure or the basket itself should come into contact with a live wire. The workman in the basket, therefore, is completely protected against any possible injury unless he should himself :grasp two high tension lines, one with each hand.

I should also like to point to certain features of construction which are important. One of these is involved in the fact that the booms and the mas-t are all of hollow tubular construction and that `the leveling cables are completely housed therein. This in itself is a great protection insofar as short circruiting is concerned, but in addition I provide long sections 73a and 74a for the

upper leveling cables

73 and 74 which sections are constructed of suitable, electrically non-conducting material such as nylon so that in the event of damage to any portion of the upper boom or its associated structure it would` not be possible for current to pass down through the leveling cables to the lower portions of the apparatus.

I also wish to mention certain details with respect to the means whereby the operator in the basket 66 can maneuver himself into the best possible position for the work he is doing. At the side of the basket within easy reach of the operator are a plurality of levers (in this case three levers) 76, 77 and 78, which levers control valves for the low pressure hydraulic system, the fluid for which passes upwardly and downwardly through the low pressure lines 4t), 51b and 65:5 already described. By manipulating the

handles

76, 77 and 73 the operator can move the valve levers 38, 51a and 65a which, respectively, cause rotation of the mast, raising and lowering of the lower boom or raising and lowering the upper boom. Furthermore, all of the low pressure hydraulic lines just mentioned are arranged together in a bundle 82 and passed along the inside of the booms and the mast so `that they are at all times well housed and well protected against damage. At the basket this bundle of low pressure hydraulic tubes i: coupled in the forim of a tlexible coil preferably of rubber material 79 which surrounds the shaft 67, one end of the coil being secured to the basket at 8G and the other en( to the boom, At the joint between the booms this bundlf of low pressure hydraulic tubes passes through the hollov center of the pivot shaft 55 and then into the shield mem ber 81 and from thence into the .interior of the lowei boom. At the bottom of the lower boom it passes arounc the hub of the sheave 45 as indicated at 82a in FIGURE 4. After passing the sheave hub 45 the bundle passe down through the interior of the mast or pylon and out a the bottom in the lower space 15a of the plyon box ani then upwardly to the valve operating cylinders and piston as shown in FIGURE l0.

Since the improvements described eliminate all possibli arcanes ,a7 pathways or conductors along which current might iiow from the wires to the ground it will be seen that 'workmen either in the rbasket or on the ground are fully protected against injury. Furthermore, the :basket can be maneuvered to proper position either by a rnan in the basket or by a lman on the truck or on the ground and `the several motion producing devices by which the position of the backet is adjusted are controlled from the basket by controlling connections which are inherently non-conducting. In other words by the present invention all wires or other possible electrical pathways between the lines and the ground are eliminated.

I claim:

l. A structure for supporting a lifting boom or the like, comprising a base, a stub mast rotatably mounted on the base, a load-carrying mast member constructed entirely of electrically non-conductive material mounted on the stub mast to rotate therewith and project upwardly therefrom, and an upper mast section mounted on the non-conductive mast member to rotate therewith, the lifting boom being pivoted on said upper mast section.

2. Apparatus according to claim l wherein the load carrying, electrically non-conductive mast member is formed of glass fibers bonded into the form of a tube and wherein a hydraulic cylinder and piston device for raising and lowering the boom is provided, said device reacting between the boom and the upper mast section, and still further wherein electrically non-conductive tubing is provided for carrying the hydraulic uid to and from the cylinder.

3. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, boom supporting means on the truck, said boom supporting means being rotatable in a horizontal plane, a boom articulated to said supporting means for vertical swinging movement, and a workmans platform articulated to the boom and supported for vertical swinging movement upon a horizontal pivot; the combination therewith of the improvement for reducing the workmansl hazards which includes an extended length of boom being constructed entirely of dielectric material formed as a hollow structural member adapted to carry the platform load and resist the stresses developed during use of the apparatus.

4. An apparatus according to claim 3 wherein said boom supporting means includes an upright mast of which an extended section is also constructed entirely of dielectric material adapted to carry the boom and its load and resist the stresses developed during use of the apparatus.

5. An apparatus according to claim 3 wherein the dielectric material in the boom consists of glass fibers bonded together to form the hollow structural member.

6. Lifting apparatus comprising a base, a tubular pylon rotatably mounted on the base, said pylon including a tubular load-carrying mast member constructed of electrically non-conductive material, a tubular `first or lower boom pivoted for up and down swinging movement on said electrically non-conductive mast member, a tubular second or upper boom pivoted for up and down swinging movement on the outer end of said lower boom, said upper boom having the major portion of its length formed of a load-carrying, electrically non-conductive material, a workmans platform pivoted on the outer end of said upper boom, and leveling cable for .the platform extending through the interior of said tubular booms, said cable where it traverses the interior of the upper boom including a major length of electrically non-conducting material.

7. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, an upright mast mounted on the truck, a boom mounted for vertical pivoting upon said mast, a workmans platform articulated to the boom and supported for vertical swinging movement upon a horizontal pivot, a hydraulic cylinder and piston device for raising and lowering the boom and uid pressure supply conduits for the cylinder and piston device; the combination therewith of the improvements for reducing the workmans hazards which include the upright mast being constructed with a lower stub section rotatably mounted on the truck, an upper section upon which the boom is pivoted and an intermediate section formed entirely of electrical insulating material of suflicient strength to carry the boom and its load and resist the stresses developed during use of the apparatus, the hydraulic cylinder and piston device being arranged to react between the boom and said upper mast section and said fluid pressure supply conduits being formed of electric insulating material.

8. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, an upright mast mounted on the truck, a boom mounted for vertical pivoting upon said mast, and a workmans platform articulated to the boom and supported for vertical swinging movement upon a horizontal pivot; the combination therewith of the improvements for reducing the workmans hazards which include an extended length of the boom being constructed entirely of dielectric material of sulicient strength to carry the platform load and resist the stresses developed during use of the apparatus, and with the upright mast being constructed with a lower stub mast section rotatably mounted on the truck, an upper mast section upon which the boom is pivoted and an intermediate mast section formed entirely of electrical insulating material of sucient strength to carry the boom and its load and resist the stresses developed during use of the apparatus, said intermediate and said upper mast sections rotating with said lower stub section to provide for horizontal rotation of the boom around the axis of the mast.

9. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work around electrically charged overhead Wires, said apparatus comprising a truck, hollow upper and lower booms pivotally interconnected, a vertical mast structure including a rotatable mounting carried by the truck by means of which said booms may be supported and moved in a horizontal plane, a Workmans platform swingably secured to the outer end of the upper boom upon a horizontal pivot, platform leveling cable housed in the booms, iiuid pressure motor means for adjusting the inclination of each boom and fluid pressure supply conduits for said motor means; the combination therewith of the upper boom having an extended section thereof formed entirely of electric insulating material consisting of glass iibers bonded together to form a structural member of sufhcient strength to carry the platform load, together with a supporting insert in said vertical mast constructed entirely of electric insulating material of suiiicient structural strength to carry the booms and their load, said leveling cable in the upper boom including extended sections consisting entirely of electric insulating material and said uid pressure supply conduits being formed entirely of electric insulating material.

l0. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, a hollow upright mast carried by the truck, a hollow boom mounted for vertical pivoting upon said mast, a workmans platform swingably secured to the outer end of the boom upon a horizontal pivot, platform leveling cable housed in the booma fluid pressure actuated motor means for adjusting the inclination of the boom, and iluid pressure supply conduits housed in the mast; the combination therewith of the improvements for reducing the workmans hazards, which include an extended portion of the length of the boom being constructed entirely of electric insulating material of suiiicient structural strength to carry the platform load, an extended portion of the length of said mast also being constructed entirely of electric insulating material of suicient structural strength to carry the boom and its load, an extended section of said leveling cable also being formed entirely of electric insulating material, and, still further, said iluid pressure supply conduits being formed of electric insulating material.

11. In apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, boom supporting means on the truck, said boom supporting means including a horizontally rotatable mounting on the truck and a mast-like, boom-supporting member projecting from said rotatable support, a boom pivoted on said mast-like member for vertical swinging movement, and a workmans platform articulated to the boom and supported for vertical swinging movement upon a horizontal pivot; the combination therewith of the improvements for reducing the Workmans hazards which include an extended section of boom being constructed entirely of electric insulating material of suiiicient structural strength to carry the platform load and an extended section of said mast-like member being constructed entirely of electric insulating material of suiiicient structural strength to carry the boom and its load.

12. An apparatus according to claim 11 wherein said electric insulating sections consist of glass fibers bonded together in the form of hollow structural members.

13. An apparatus according to claim 11 wherein the boom is hollow and wherein platform leveling cable runs between and is reeved around said pivots and is housed in the boom with each run of the leveling cable including an extended section formed entirely of electric insulating material.

14. ln apparatus for elevating a man and supporting him from a position on the ground in an elevated location for work on and around electrically charged overhead wires, said apparatus comprising a truck, boom supporting means on the truck, said boom supporting means being rotatable in a horizontal plane, upper and lower booms pivotally interconnected and with the lower end of the lower boom being pivoted on said supporting means for vertical swinging movement, and a workmans platform supported for vertical swinging movement upon a horizontal pivot at the outer end of the upper boom; the combination therewith of the improvement for reducing the workmans hazards which includes an extended length of boom being constructed entirely of dielectric material adapted to carry the platform load and resist the stresses developed during use of the apparatus.

15. An apparatus according to claim 14 wherein said boom supporting means on the truck includes an upright mast to which the boom is articulated and further wherein an extended section of said mast is constructed entirely of electrical insulating material of suicient structural strength to carry the boom and its load.

References Cited in the le of this patent UNITED STATES PATENTS 433,001 Hall July 29, 1890 1,786,631 Roe Dec. 30, 1930 2,091,852 Hinds Aug. 31, 1937 2,616,768 Stemm Nov. 4, 1952 2,666,417 Harsch Jan. 19, 1954 2,798,623 Girardi July 9, 1957 2,825,752 Kuntz Mar. 4, 1958 2,881,030 Troche Apr. 7, 1959 2,915,137 Troche Dec. 1, 1959 2,936,848 Hall May 17, 1960 2,940,539 Richey lune 14, 1960 OTHER REFERENCES Aerial Platform, from the publication Electrical World, vol. 151, No. 26, page 133.

Claims

3. IN APPARATUS FOR ELEVATING A MAN AND SUPPORTING HIM FROM A POSITION ON THE GROUND IN AN ELEVATED LOCATION FOR WORK ON AND AROUND ELECTRICALLY CHARGED OVERHEAD WIRES, SAID APPARATUS COMPRISING A TRUCK, BOOM SUPPORTING MEANS ON THE TRUCK, SAID BOOM SUPPORTING MEANS BEING ROTATABLE IN A HORIZONTAL PLANE, A BOOM ARTICULATED TO SAID SUPPORTING MEANS FOR VERTICAL SWINGING MOVEMENT, AND A WORKMAN''S PLATFORM ARTICULATED TO THE BOOM AND SUPPORTED FOR VERTICAL SWINGING MOVEMENT UPON A HORIZONTAL PIVOT; THE COMBINATION THEREWITH OF THE IMPROVEMENT FOR REDUCING THE WORKMAN''S HAZARDS WHICH INCLUDES AN EXTENDED LENGTH OF BOOM BEING CONSTRUCTED ENTIRELY OF DIELECTRIC MATERIAL FORMED AS A HOLLOW STRUCTURAL MEMBER ADAPTED TO CARRY THE PLATFORM LOAD AND RESIST THE STRESSES DEVELOPED DURING USE OF THE APPARATUS.