US2616768A

US2616768A - Crane supported movable selfleveling scaffold

Info

Publication number: US2616768A
Application number: US7310A
Authority: US
Inventors: Irwin G Stemm
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-02-10
Filing date: 1948-02-10
Publication date: 1952-11-04
Anticipated expiration: 1969-11-04

Description

Nov. 4, 1952 I. G. sTEMivl CRANE SUPPORTED MOVABLE SELF-LEVELING SCAFFOLD Filed Feb. 10, 1948 4 Sheets$heet l 4 Mb mm A TTORNE) Nov. 4, 1952 Filed Feb. 10, 1948 l. G. STEMM CRANE SUPPORTED MOVABLE SELF-LEVELING SCAFFOLD '4 Sheets-Sheet 2 INVENTOR.

I rvz'n 6. fifemm BY ATTORNEY Nov. 4, 1952 G. sfEMM CRANE SUPPORTED MOVABLE $ELF-LEVELING SCAFFOLD Filed Feb. 10, 1948 4 Sheet-Sheet' 3 vs v $3 w.

I Eli Ill INVENTOR. Irwin' G. ST'emm Nov. 4, 1952 I. e. STEMM 2,616,768

CRANE SUPPORTED MOVABLE SELF-LEVELING SCAFFOLD Filed Feb. 10, 1948 4 Sheets-Sheet 4 IN VEN TOR.

Irwin 6.5km m Figure 1 is a view in side elevation Patented Nov. 4, 1952 I UNITED STAT-ES PATENT OFFICE CRANE SUPPORTED MOVABLE SELF- I QLEYELING SCAFFOLD Irwin L G Q Stemm, Leavenworth, Wash. Application February 10, 1948, Serial No. 7,310

3 Claims; (01. 304-9) My invention relates to scaffolds adapted to support laborers while picking fruit from trees,

spraying trees, thinning andpruning trees, rerpairing or painting buildings and the like, and more particularly to scaffolds adapted to *be easily and readily adjusted in position to facilitate the work to bedone. V The main object of my invention is to provide a scaffold consisting of a mast or tower mounted on a four wheeled vehicle, such as an automobile or the like, and supporting one or more seats for men working at a distance above the ground, so that said scaffold may be moved into convenient position for the work to be done. 1

Another object of my invention is to provide a scaffold of the character indicated above, wherein the scaffold comprises a lower mast piv otally mounted on a turntable and an upper-mast pivotally secured to the upper end of the lower mast and supporting the seat for the working man on its upper end.

Afurther object of my invention is to provide a scaffold of the character indicated above, equipped with mechanisms for adjusting the two masts and for holding the seat for the laborer permanently in horizontal position, said mechanisms being adapted to be operated by the laborer from the seat on the upper mast.

Other objects of my invention not specifically mentioned may appear in the following specification. describing my inventionnwith reference to the accompany-ing'drawing illustrating preferred embodiments of my invention. It is, however; to

be understood, that my invention is not to be limited .or restricted to the exact construction and combination of parts described in the specifi cation and shownin the drawing, but that such changes and modifications may. be made which fall within the scope of the claims appended hereto. r I'--- t i In the several figures of the drawingsimilar parts are designated by similar reference characters and j illustrating an apparatus including scaffolds embodying the invention, parts being broken away;

Figure 2 is a fragmentary view in top. plan of the upper portion of a scaffold as comprised in Figure 1; i .Figure 3 is av viewin side elevation of the apparatus including scaffolds constructed in accordance with another embodiment of the inelevation and partly in section of the lower por 2 tion of one of the scaffolds comprised in Figure 3;

Figure 5 is a fragmentary view in top plan of one of the scaffolds as embodied in Figure 3;

Figure 6 is a fragmentary view partly in section and partly in elevation of one ofthe wheel motor units; and

Figure '7 is a diagrammatic view of the oil circuit as herein comprised.

The scaffold forming the subject matter of my invention is supported by a four wheeled vehicle 20 having a rigid frame or chassis 2!, to which a front axle 22 is rigidly secured. The rear axle 23 is secured to said frame 2| so that it is adapted to oscillate freely in a vertical plane, as will be described later, to enable the rear wheels 24 of the scaffold supporting vehicle to pass over obstacles or uneven ground without tilting. A conventional steering wheel 25 is arranged about midway of the frame slightly to one side of the longitudinal center line of said frame and is connected by any preferred conventional means with each of the rear and front wheels 24 and 26 respectively for the purpose of steering the vehicle Zfl. The construction of the front and rear steering mechanism is similar and operates each wheel individually so that each rear wheel 24 follows the exact path of the corresponding front'wheel 26.

Motive power is provided by a conventional internal combustion engine 2! driving a trans-' This ,trans' fdrive shaft with a rear differential 40, and these two difierentials are connected with the'fiont and

rear axles

22 and 23 respectively. The raf' axle is secured to the frame 2| by means" ii-an upwardly extending pivot plate 4| pivotallybonnected with the rear axle centrally of its ends. The pivot plate is located between twobracket plates 42 rigidly secured to the frame fl.

so that the pivot plate 4| is adapted to pivot in a vertical plane about the pivot pin 43.

The conventional operating and control means commonly used inconnection with automotive vehicles are arranged conveniently near the .A' pivot pin 43 extends through the three plates '3 steering wheel and consist of the engine throttle 44, the gear shift lever 45, the engine clutch control 45, the engine switch 41, the ammeter 48, the oil pressure gauge 49, and the brake lever 56, which controls the two rear Wheels 24 and the two front wheels 26.

A tank 52 supplies the motor 21 with liquid fuel. The steering wheel 25 actu'ates a gear 53 which in turn pivotsarmsg'i l'and in part circles. These two arms areconnected with each other by means of a link 56 and transmit their motion to the front and rear wheels 26 and 24 on both sides of the vehicle by steering rods 5'l,- so thatthe rear wheels always follow the path travelled --,by the front wheels. 4

The frame 2| extends forwardly and rear- Wardly beyond the front andrear axle .22 and 23 respectively and at each end of the frame a tower A for an operator such as a fruit picker in an orchard, or a plasterenor painter or the like is oca ed, o that th mach n i dap d to arry two operators, which can work independentlypi each other. Each towernqconsi-sts of anupper tub ma t 5. 8 and a i one ubularimas 9 which... rez v t ll eon ected wi each thera described in; deta lat r .andreac lowe wmastis pivotally mounted on a turntable fifilp vhioh m unted on aihollowsha t i x en i -downw d y fr t t rntable and :rota ahl asunpo ted :b u table hea ings :63 s u ed-.01 th rameal. :T' n u archrack t 6.3 .arerrisidly m ntedzon ea h-.o rthe tn i ta g esp n t lower end ofil welrmest 5. iisrivotal y mounte between thes :Mack qs :.a .iix horiz ta shei extendin throngh-thexvertml .shankaof sai bra kets. n ther :p vot .s ai 55 exte ds di met icall through :th :lQWQ mast 5 just below i impel end an t e lower end of th pper mas 25.8 s nivotally mounte ;onx.said;;s.ec- Qn rivet haft- An op rat rs seat hav n hack, est 1 3.1 m u e atthe on-end Q .thenrn t hnla mas 5. by m an 7 o a ho izonta zfihafj :68 ifizsed 2 seat b cket pos 16. e t d n .dowmvardl om he seat 66- h hori ontal. shaft 153 adap d to tat v-iree z nhe r ns n r ror de i d. ast darerii en e i ula ifram M is attached to vthe seat BI -and extends iorwardly therefrom at a SQIIlEWhQII lower level than the seat. The frame-fits freely over abo -adapted to receive fruit or thedike. ,Anangularhand lever 12 isrotatably secured to thetoutside ofieach side wall of the frame ll, and'on the lower .end of each hand lever ,lg allmkmlate 13 is secured-so ha e e at m b er n edto eri nd below the. frame .1! which is open .-at ,its ,t ottom end, to support ,a .box injsaid frame, .or may be positioned to release .said box, ,by otatin the angular hand lever.. p

1.1511 movements andicnerationsof .eachrmast-gare controlled by pe al 1. T5, nd 1 resn t ely arranged at -.both sides o th fra e 11 within easy reach -from .the seat .55. The :two Einner pedals 14 and 1.6 iareadapted .to operate remote control valves 58 and 1.9 respectively." These valves. are. adaptedto openand vclose'anl oilrcircuit 8.0 connectingzanlollpump HI lwith a rluid motor 82. Theoil pump 3} i odrivenby tne mot ga by meansof a power take-off .83 .andthepump is pr t o l homea ker; m un edth vehicle frame 2! [The fluid motor has; on 31175 motor shaft/ a sprocket gear .3 The turn table 60 .is provided .with .a..comparative1y .large sprocket .gear -8fl mounted concentrically with the corresponding turntable and located at the provided with a sprocket gear 9|. -.tively.large s p .ocket gear 92 is rotatably mounted 4 same level as the sprocket gear 86. A sprocket chain 88 is trained over the two sprocket gears. In this manner, pressure on the left side pedal 16 transferred togthe remote control valve 19 is adapted to rotate the turn table in clockwise direction through 360 and pressure of the right side pedal 14 orilthe valve 18 causes rotation of the turn table in counter-clockwise direction.

Two 'fiuid rnbtors 89 and respectively are mounted on each turn table 643 diametrically opposite to each other and the fluid motor 89 is A comparaon the shaft 64 between one of the brackets 63 and the lower mast 59 is firmly connected with said mast :as at 92a. A sprocket chain 93 is .trainedrover thesprocket gears SI and 92 so that rotation of the sprocket gear 9| under power of the-fluid motor 89 pivots the lower mast in a vertical plane through approximately 180. The fiuidmotor 8. 11 co o ed-h theronislde ed l -Q h e ta q t erbox nam t Thi p d l is-p ta l s pported inter ediet its-ends and a remot co t ol val e 9 4 1 he te und r t toe ii a sai red l an 9 i lQ-. control valve -;95 is locatedpnder theheel-portion of said pedal. The toe controlled lvalve efi setathe io -8 -in'c1ock e ro ationand the he l e a e wauses eouniem eokw serotation ,of said motor.

At the side of the n astes, remote :fmmathe e i o bly mou e on :the she-ft 4 comparatively s lls ack ts earwfi A roc i gear 7 is nt d one heahaf fi befi eenth masts '58 and 15.

im e mast a lendthe Sprocket gear- 9,! are firmly. securedeto each other y a :bolt- 98 .or 'the like, and arsprocke :cna n :59 s ed over the sprock t sea s 5 and .95- t er sprocket ea 1 0 is rotatabl mounte on therhorizontal shaft 64 adjacent-to .theip iocket gear 96 with which it ,is seeure ly ponnccted. 0n the :shaf :of :lhe fluid :motor 9.8, ano her prock t gear .:ri id1y m unted and a sp k t chain mus trained rover thez-two ears l 00 and 1L0] tThe-fiuidimotnr 0 iis :.contltolleri :by r ote c n r l valves 21113 and 104 ilocatedgunder the toe and heelwportion respectivelylof'itheronh side pedal 15. sa rangedqatrthe rightside nfcthe box -:frame ;ll aandpivotallysunported, intermedi ate its .rends. When :the :toe controlled Na/1V6 r1103 is.operated,-:the fluidmotormfl iislcaused torrotate in .one direction and when the. h. eel:,contro1led valve Hi4 :is operated, .=said motor is realised etc rotate in :the opposite direction. ;I-n' this mam ner, .the .upper mast iiBiis pivoted =in;either.direction about the pivot .shaft :and by operating theepedals "M, 16 and J1 selectively, thei-operator sitting in the. seat isableito .arrangeand adjust .said .seat to .t-he :best.-a dvantage for the work to be done. At the same time, the operator may. adjust .theseat so ithat ghe is enabled to operate the controls for themotor 12-7 to place the entire machine at any desired place.

The fiuid motors 80 iand-Sl are sup-plied with oil :byfthe oil pump t" through "a rotary connection I05 with 'thehollow shai't 61 ofth mum table at. Suitable provisionzis' made=to 1=eturn the exhausted oil'fr'om ethes'e iinid motors back to the tank 84v To keep the ;seat :56 at all times .parallel with he srounda comparatively small isprocketcgear Hi6 is rigid y :mQnntQd lonzthe :horizontalshaft 68 fixed on the seat post 69. The sprocket-gear 0 is lo a es-inside the liB fi x ii si afifi- Q ithe Pivot mit 5. etectin he tw with by'the'inner races of said bearings.

each "other, two sprockets gears I01 and I08 respectively are rigidly mounted, one of them, I01 inside the upper mast and the other one, I08 inside the lower mast. On the fixed horizontal shaft 64, supported by. the brackets 63, another sprocket gear I09 is rigidly mounted inside the lower mast 59. The four sprockets I06, I01, I08 andI09 are. of equal size and one sprocket chain H is trained over the sprockets I06 and I01 inside the upper mast and another sprocket chain III is .trained over the. other two sprocket gears I08 and I09 inside the lower mast.

In Figures 3 to 7, a modified form of the scaffold according to my invention is illustrated and in this modified form two towers B are mounted on. the rigid frame II2. of an automotive vehicle H3, having a front axle H4 and a rear. axle II5. One axle is secured rigidly to the vehicle frame and the other is connected thereto, so that it is adapted to pivot in a vertical planeas described above regarding the rear axle 23. In the longitudinal center of the framel I2 and slightly to one side of the machine, a conventional steering wheel H6 is arranged, which is connected by means of any preferred well known meansto each of the two front wheels H1 and to each of the two rear wheels vI'I8,,individually and said wheels are steered so that the rear wheels follow the'exact path over which the front wheels travel.

Motive power is provided by an engine unit I,I92.consisting of a motor, a fuel tank and the necessary gauges and controls.j Said motor is connected by any preferred conventional means with an oil pump I20, which in turn is connected,

as shown best in thediagram oi the oil circuit.

illustrated in Figure 7 with an oil reservoir I2I and with the four wheel motor units I22, I23, I24 and I25. Each of these units comprises a fluid motor I26 provided with a gear I21 meshing with the speed reducing gear I28 driving the shaft I29, to which the wheel I30 is secured by means of bolts I3I. This entire assembly is pivotally secured by means of a conventional spindle bolt I32 to the endof the corresponding axle.

The frame II2 extends beyond the front and rear axles H4 and H respectivelyand one of the towers B is arranged on the front end portionand the otherone on the rear end portion of the frame. Each tower B comprises a turn table-I33, in the center of which a hole I34 is provided. A tubular shaft I35 is arranged in this hole, welded to the turn table and extends downwardly therefrom. To each end of the vehicle frame II2, a short section of heavy steel tubing I36 is'welded and is provided in its top and bottom portions with a counterbore I31; to receive the outer: races of bearings I 38. The tubular shaft extends through and is supported The lower end'of thetubular shaft I35 is connected with the oil pump I20 b'ymeans of a swivel connection I 3.9" screwed into the lower end portion of the tubular shaft and a hose I40 connected with said swivel connection. A comparatively large 7 spur gearI4I is rigidly mounted on each steel tubing I36 adjacent its upper end and a fluid motor I42 is secured on each turn table I33 ad-- jacent its periphery. The shaft I43 of each fluid motor I42 extends downwardly through the corresponding turn table I33, and on the lower end portion of each motor shaft I43 a spur gear I44 is rigidly mounted and meshes with the comparativelv large gearI4I, so that the turn table rotates about its axis-when the fluid motor I42 is-set into motion, as'will be described later.

Two heavy bracket plates I45 are firmly secured on top of each turn table, so that they'extend-upwardly therefrom and parallel to each other at equal distances from the center of the turn .table. Each plate I45 is braced on its outside by a pair of brace plates I45. Centrally of each plate I45 and adjacent its upper edge, a hole' I41 is provided so that the holes in each pair of plates are coaxial. A pivot pin I48 .ex-

tends through. each pair of coaxial holes and is secured to the plates I45. A sprocket gear I49 is rigidly. mounted on the pivot pin I48 adjacent one. of the bracket plates I45 and the central portion of the pivot pin is equipped with a bronze bushing I50. A heavy tubing I5I surrounds the bushing rotatably and extends through'a pair of coaxial holes'I52 provided centrally in and intermediate, the ends of two pivot plates I53, the upper end portions of which are set into cut outs I54 arranged in the lower end portion of a tubularmast I55 forming the lower part of each tower B. The upper end portions of these pivot plates I53 are welded to the lower tubular'mast I55 and are braced by brace plates I50 secured to the heavy tubing I51 and the pivotjplate's'.

The lower end portions ofthe pivot plates-extend beyond the tubing I5I between the bracket plates I45. The upper end portion of each lower tubular mast I55 is provided with two cut outs I58, in which joint'xplates I59 are set. These plates extend parallel to each other upwardly beyond the lower tubular mast and are firmly secured to said mast. A diametrical notch I60 is cut into the upperend of the lower mast and extends parallel tothe joint plates. In each pair of joint plates two coaxial bearings I6I are arranged ad jacent the upper edges of the plates and a pivot shaft I62 extends through and is pivotally supported in said bearings. A double sprocket gear I53 is rotatably mounted on the pivot shaft adjacent the outside surface of one of the joint plates I59 so that sprocket chain I64 may be trained over the sprocket gear I49 on the pivot pin I48 and the outer set of teeth of the double sprocket gear I63. A second pair of pivot plates I65 is pivotally mounted with their lower end portions on the pivot shaft I62, so that each one of these second pivot plates is located adjacent one of the joint plates I59. The upper ends of the pivot plates I55 extend into slots I66 provided in the lower end portion of a tubular upper mast I61, and the pivot plates I65 are welded to said mast. A comparatively large sprocket gear I68 is rigidly mounted on "the pivot shaft I62 be tween the two pivot plates I65 and extends through the notch I 60 in the lower mast I55 and the connected slots I66 in the upper mast I61. The gear I69 is firmly connected with the upper mast I61 by a pin 168a or the like. A somewhat smaller sprocket gear I69 is rotatably mounted in and extends diametrically through the lower mast, andanother sprocket chain I19 is trained over the two sprocketgears I69 and I68.

A seat unit S consists of a seat I'll and a back the upper mast ipivotally with each other and extends ltoward one :side beyond the correspondinglug. A sprocket gear 116 is rigidly mounted on the pivot pin H5, which firmly connected with the lugs 114. :A sprocket Lchain H1 is trainedover the sprocket gear I16 and the inner set of :teeth of the double sprocket gear I63.

Each tower B is controlled from the seat III by means of a plurality of pedals, :pivota'lly 1'88- cur'ed to small :platforms I I8 located "on the'outside of each 0f the "angle'irons I13. The operator may rest his feet on said platformsand on each of these :platforms an outer .ipedal H9 is pivotally mounted, which is remotely connected by any conventional operating means to a cantrolvalve 18 0. Each of the valves I80 is connected with the oil'pump I2Ilan'd the fluid motor I42, .as indicated in :Figure 7, so that said motor isactuated to rotate the turn table I33 and the tower =-B mounted-thereon in clockwise direction, whenone'of the outerfpedals I19 is operated and to rotate these members in counterclockwise direction, when the "other outer pedal I19 used. On the inside of'each outerpedal an innerpedal I84 plvotally mounted on the platforms I18.

The inner pedal 'IBI on theright hand platform is pivoted intermediate its ends and operates a control valve I82 by means of a cable I83. The valve I82 is connected with the oil .pump I20 and a cylinder 'IM .pivotally mounted intermediate its ends between the bracket plates I on the turn table I33. -A piston I85 is reciprocally mounted in said cylinder and is equipped with a lpus'h rod I 85, the outer "end portion of which is;pivotally connected by a pivot pin I81 to the pivot..=plates I53. By depressing the toe or front portion of the pedal I8I, the valve 182 is set so that the piston I85 is forced outwlairdlt of the cylinder] M-andthe push rod I86 pivots thelower mast I to a lower-position about the pivot pin I8'I. When the heelportion of the pedal I8I is depressed, the valve 182 is set'so that the piston I85 operates in the opposite direction and the mast I55 is raised. The inner :pedal I88 on the left handplatform I13 is pivotally mounted "intermediate its "ends on said platform and operates a'control valve I89 by-means of a cable I90 or the like. This valve'isconnectedwith the'oil pump In and with a cylinder I9I secured to the lower mast I55 in any preferred conventionalmanner. -In the 'cylinder -I9l,'a-piston I92 is 'reciprocally arranged, which has a push rod I93, the outer end of which isrigidly'connected with thesprocket chain 119. Whenthetoe end of the pedal I88 is depressed, the valve I89 is set to cause the piston I92 to move in one direction and when the heel end of the 'saidpedal is depressed the valve is arranged to cause the piston 'to move inthe opposite direction. 'Themovement of the piston is transmitted through the :push rod I93, the sprocketnchain I and the sprocket gear I 68 to the upper'mast-I 61.

The several va-lves 1-80, 182 and I89 are con nected with oil pump I20 by means of feed pipes I94 and with the oil reservoir by means of return pipes I95. The feed pipes 1-94areals0connected with a control valve I96 controlling the wheel motors I2-2'and I23 of thelefthand wheels and with another control valve I91 controlling the wheel motors -I-24and I25 -of the right hand wheels, an'dthese valves' are connected also with the-return pipeS IQB. V

The above description shows clearly that the operator is able to operate'the tower'B, on which theseat which he occupies is located, and that 8 the sprocket and chain connections iI49, IBM-1B3, I'll and I'll; will keep rthesea'tll'll in. horizontal position, when either one of'the masts israised or lowered.

A box or crate adapted to receive fruit or the like may be placed 'on'the horizontal legs of the angle irons H3, the vertical legs of which will serve as'guides and guardians for such crate or box. Underneath the front edge of theiseat III., a movable hook-like member I98 is "arranged adapted to engage the inner end of 1a crate located on the angle irons to prevent accidental removal of said crate.

'1. A scaffold to support an operator comprising a turntable mounted for swinging movement on an upright axis, a tower .consisting'of a lower mast mounted for verticalrswinging movement on said turntable and an upper mast mounted for vertical swinging movement on the upper end portion of said lower mast, a level seat secured to the top end portion of said tower, means for elevating the seat and means for securing the seat in level :positionwhile 'it is being elevated, the last named means comprising sprocket and chain idrives interconnecting the two masts 'and the turn table with each other, and "consisting :of a'stationary "pivot pin located in brackets rigidly secured to the turn table, a sprocket gear rigidly mounted on the pivot pin to which-said lower mast portion of the tower is :pivotally mounted, another pivot pinin the upper end of the lower mast,:said upper vmas't por'tion of the'tower pivo'tally mounted 'on the second pivot pin, a pivot shaft rigidly secured to'the seat and pivotallv mounted in the upper end portion of the upper mast, a s rocket chain trained :over the first named sprocket gear and a gear rotatably mounted on the second pivot pin, another sprocket gear rigidly mounted on the pivot shaft and a second sprocket chain trained over the l'ast n'amed gear and a gear rotatably mounted on the second pivot pin;

2. In apparatus ofthe "class described, frame means; upright pivot means supporting 'said frame means for pivotal movement; frame moving means connected'with-saidframe means for pivotally moving the same; a lower *mastj 1a. =horizontal pivot-means connecting one end portion of said lower mast with said frame means; an upper mast; horizontal :pivot means pivotally connecting the lower end portion of said upper mast with the upper :end portion 'of 'said' lower mast; a scafiold platform; horizontal pivot means pivotally connecting said scaffold platform with the outer end portion of :said upper mast, said three horizontal 'pivot'means "being parallel; two independentrpower devices operable to swingingly-move theresp'ective masts on their ho'r izontalipivot means; a:non rotatablesprocket wheel positioned co-axially of the pivot mean's which connects the lower "end 0f the lower mast with the *frameme'ans; two -rigidly attached together sprocket wheels rotatively mounted coaxially of the pivot means which pivotally connects the two masts; another sprocket wheel positioned c'o-axially of the pivot means which mounts the scaffold platform-on the upper end of the upper mast and rigidly attached to said scaffold platform; and two ehdl'ess link'beltsrespectively connecting the two rigidly attached together sprocket wheels with the sprocket wheel at :"the lower "end of the lower mast and the sprocket wheel at the upper 'end of the upper mast, whereby said scaffold platform is -m'ain=.

tained substantially horizontal irrespective of vertical swinging movement of said masts.

3. In apparatus of the class described, a wheel supported frame; a swinging frame; upright pivot means mounting said swinging frame on said wheel supported frame; power operated frame moving means connected with said swinging frame to angularly move the same about said upright pivot means; a lower mast; a horizontal pivot member connecting the lower end portion of said lower mast with said swinging frame; an upper mast; a horizontal pivot member pivotally connecting the lower end portion of said upper mast with the upper end portion of said lower mast; a scaffold platform; a. horizontal pivot member pivotally connecting said scaffold platform with the upper end portion of said upper mast, said three horizontal members being parallel; mast supporting and mast moving means connected with said lower mast, whereby said lower mast is swingingly moved vertically and is supported in difierent inclined positions; sprocket wheels provided on said three horizontal pivot members; endless link belts operatively disposed on said sprocket wheels, whereby said scaffold platform is maintained substantially horizontal irrespective of the vertical swinging movement of said two masts; another sprocket wheel supported on the horizontal pivot member 10 which connects said two masts and non-rotatively secured to the upper mast; and power ac tuated endless link belt means engaging said other sprocket wheel, whereby said upper mast can be swingingly adjusted and fixedly held in selected adjusted positions by said power actuated link belt means.

IRWIN G. STEMM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,410,190 Kaiser Mar. 21, 1922 1,728,854 Carr Sept. 17, 1929 1,761,726 Havens June 3, 1930 2,099,998 Berg Nov. 23, 1937 2,335,584 Couse Nov. 30, 1943 2,410,030 Horni Oct. 29, 1946 2,450,152 Miller Sept. 28, 1948 2,450,812 Ray Oct. 5, 1948 2,500,815 Gerli Mar. 14, 1950 FOREIGN PATENTS Number Country Date 238,065 Great Britain Aug. 13, 1925