Abstract: A versatile construction hoist system comprises a hoist trolley having a first pair of connection members, and a work platform having a second pair of connection members. The work platform is releasably connectable to the trolley through interconnection of the first and second pairs of connection members with the work platform in a horizontal position in which the work platform floor is situated at the first level relative the trolley. A transport platform, which has a third pair of connection members, is releasably connectable to the trolley through interconnection of the first and third pairs of connection members with the transport platform in a horizontal position in which its floor is situated at a second level relative the trolley, said second level being below said first level. An adapter enables use of standard transport platform elements.

Abstract: A lifting apparatus to facilitate lifting and maneuvering of a scaffold or the like by a forklift is provided. The lifting apparatus includes two identical portions, each portion including two end structure portions and a backbone portion. The end structure portions removably secure the lifting apparatus to the scaffold. The backbone portion is adapted to accommodate the width of the working platform of a scaffold, to link the end structure portions together, and to provide locations for a forklift to attach to the lifting apparatus. The lifting apparatus is adapted to allow the forklift to align perpendicular or parallel to the length of the scaffold. Furthermore, the lifting apparatus aligns the lifting structure of the scaffold with the center of mass of the scaffold.

Abstract: A self-raising platform assembly (1) comprising at least one mast (3, 5, 113) along which a platform (13) may be moved up or down including the following: a) a base element (9) with a supporting plate (25) connected to a jack (27) and several stabilizer arms (33, 37) incorporating height adjustment. b) modular mast sections (7) made from rectangular sections with openings (63) cut out to form steps and bars (55) to allow adjacent sections to be bolted together. c) hydraulically operated ram lifting mechanism (73, 83, 84) with hooks (77, 79, 81) to engage steps on the mast to raise and lower the platform, d) a plastic lined sleeve (17, 19) on the platform which slides against the mast e) a modular platform which can be lengthened or widened by adding additional modules (101, 103).

Abstract: A scaffold structure accessory is essentially comprised of a elongated, horizontal, laborer's alternate walkway and material support member having a clevis connector at its inboard end and a safety rail receptacle connector at its outboard end, a first vertical support member attached to the laborer's alternate walkway and material support member near its outboard end, a second vertical support member attached to the laborer's alternate walkway and material support member near its inboard end, and a connector on each vertical support member that co-operates with the scaffolding laborer's walkway and material support of a conventional prefabricated lift-type scaffolding module.

Abstract: An elevated location descent apparatus comprising a descending device, a braking device and a power transmitting device; the descending device comprising sprockets positioned in a vertical plane, a suspension chain positioned around the sprockets and a payload-suspending means attached to the suspension chain, the braking device comprising a fluid pump converting the rotational movement of a crankshaft into the reciprocal movement of pistons, which reciprocal movement causes the fluid pump to receive a fluid from an inlet and discharge the fluid through an outlet, a fluid circulating conduit connecting the outlet of the fluid pump with the inlet of the fluid pump wherein the fluid discharged from the fluid pump circulates, a flow-restricting valve adjusting the amount of the fluid passing through the outlet of the fluid pump to generate the fluid resistance, and a rotational governor controlling the flow-restricting valve based on the rotational speed of the sprocket; the power transmitting device comprising

Abstract: A device and methods for supporting a payload, such as a user, at a variable height above the ground and for repositioning the payload in a dynamically stabilized mode of operation. The transporter device has two laterally disposed primary wheels and a payload support that may be used to raise or lower the payload. A torque is applied to the laterally disposed wheels so as to propel the transporter on the basis of a control signal that may include repositioning of the device.

Abstract: A storage lift includes two vertically extending tracks mounted to a wall surface such as a garage wall. The tracks guide associated sliding members through vertical motion up and down adjacent the wall. The sliding members are in turn hinged to a platform that serves in alternative embodiments as a storage platform base or a variable-height work surface, and which may also be folded compactly when not in use or during shipping. A full box framework is provided for most applications, and panels are slidable within framework grooves or brackets to fully enclose the platform. A cover may optionally be provided as required. In the preferred embodiment, an electric motor is provided within the storage platform base for motive power, and a key switch control is provided to safely actuate the motor. The electric motor in the preferred embodiment is attached to the tracks through a combination of cables and pulleys, though other techniques are contemplated.

Abstract: A method for adjusting a first force applied to a movable element in a first position of the movable element by a force applying device, the force applying device applying a second force to the movable element in a second position of the movable element. The method includes connecting the movable element and a base element with a scissors-type linkage; mounting the force applying device to the scissors-type linkage at a first mounting point; mounting the force applying device to the base element at a second mounting point; and moving at least one of the first and the second mounting points along a constant force curve, so that the second force remains constant as the first force is adjusted. A device for adjusting a first force applied to a movable element in a first position is also provided.

Abstract: A scaffolding system for volumes of various shapes that present a bottom and end walls. The system includes at least a first scaffolding structure having a gantry with at least two interconnected vertical poles; guides secured to the bottom of the volume to guide the poles in rectilinear displacement in a longitudinal direction; a horizontal main platform defining at least a working floor, and guides for guiding the main platform in vertical translation along the poles; at least two horizontal auxiliary platforms each defining a working floor mounted to move in horizontal translation relative to the main platform; and structure for displacing each auxiliary platform separately relative to the main platform between a retracted position and an extended position in which the outer edge of the auxiliary platform is substantially in register with the outer edge of the main platform.

Abstract: A tower sleeve for sliding engagement with a tower that defines a tower longitudinal axis includes a main body that defines a body longitudinal axis and a channel longitudinally extending therethrough for slidably and selectively receiving at least part of a longitudinal section of the tower therein with the body axis generally parallel to the tower axis. A closing body connectable to said main body is movable between a first limit position and a second limit position relative to the main body. The closing body at least partially closes off the channel when in the first limit position so as to secure the sleeve in sliding engagement with the tower inside the channel, and opens up the channel when in the second limit position so as to allow the sleeve to engage and disengage from the tower in a direction generally transverse relative to the body axis.

Abstract: A cargo lift for transporting goods between ground level and a raised handling position at the side of a building includes a vertical mast extending between ground level and the handling position alongside the building. A cargo container for carrying the goods is attached to a rolling sleeve carried on the mast. An electric winch raises the cargo container along the mast between ground level and raised handling position.

Abstract: An elevating platform assembly comprises a pair of laterally spaced, generally vertical masts and an elongated working platform extending generally horizontally between the masts. Hoist mechanisms act between the ends of the working platform the masts and are actuable to move the working platform along the masts to different elevations. At least one level sensor is provided on the working platform and detects when the working platform deviates from a generally horizontal orientation. At least one controller is responsive to the at least one level sensor and controls the hoist mechanisms to adjust movement of the working platform when the working platform deviates from the generally horizontal orientation thereby to return the working platform to the generally horizontal orientation.

Abstract: A lifter includes a beam tiltably secured on top of an elevator for supporting an object to be elevated. A base is secured on top of the elevator, and a seat secured to the beam and having one end rotatably secured to the base with a shaft. A bracket and a spring may resiliently support the shaft in the seat. A plate is secured on the seat, a board secured to the beam and rotatably secured on the plate, and a spring biased pin may position the board to the plate at the required angular position. One or more posts and arms may be attached to the beam for supporting the object.

Abstract: An emergency escape veranda apparatus includes a movable veranda member (1) provided so as to form a veranda in a normal state together with a stationary veranda portion (2) projected outside a building. A lowering device (3) makes the movable veranda member (1) descend vertically in an emergency state.

Abstract: An adjustable universal scaffold bracket and walkboard ladder holder that absolutely prevents scaffold collapse or disattachment from a building and absolutely prevents a ladder placed against a walkboard from slipping sideways. A safety scaffold and bracket is provided with a safety walkboard with rails that also contains a positive means of preventing ladder slip. Vertical supports can attach top and bottom to the building or work under construction. Hold brackets that can be raised or lowered slide up and down the vertical supports. A walkway sits on the hold brackets and is positively held in place by pins. The hold brackets can be equipped with vertical arms in the front so that posts can be place on them to form a place to put a guard rail. In addition a ladder can be optionally leaned against the walkway and secured by additional stay bolts into the walkway to prevent horizontal slipping.

Abstract: A locking and securing device including a securing means which is movable between a secured position and an unsecured position by using a force at a substantially center point of the securing means.

Abstract: Scaffold having a locking and securing device for securing a first support to a second support is disclosed where the locking and securing device is movable between a secured position and an unsecured position by using a force at a substantially center point of the securing means.

Abstract: A lifting apparatus for high-place work which includes a moving supporting leg having a guiding case with opposite open ends and plural walls, guiding grooves attached to said walls, plural elastic strips, a plurality of connecting pieces transversely attached to said elastic strips with the connecting pieces having a proportional number composed of shorter and longer lengths with the longer connecting pieces having fitting grooves on ends thereof, which matingly engage the ends of the shorter connecting pieces. The elastic strips are rotatably wound about respective winding drums disposed on the loading box of a vehicle and driven a driving force originating from the power source of the vehicle such that by unwinding the respective elastic strips an integrated column is formed at a desired elevated high location.

Abstract: An elevating platform assembly includes a generally vertical mast having a generally vertical rack mounted thereon. A first trolley is coupled to the mast and is moveable therealong. A drive mechanism is carried by the first trolley and includes at least one pinion in mating engagement with the rack. An elongated elevating platform extends from the mast and has a second trolley mounted adjacent one end thereof. The second trolley couples the elevating platform to the mast and is moveable along the mast. The first trolley is coupled to at least one of the second trolley and elevating platform in a manner to maintain alignment of the at least one pinion and rack when loads are placed on the elevating platform that create moments at the mast.

Abstract: The present invention is directed to a drilling rig base and a lower mast section that are collapsible into a compact transportable position. The base is expandable in the field to support a drilling platform and all necessary equipment, and the telescoping mast is also expanable for supporting the crown block and cables of the drawworks. More specifically, the rig of the present invention has a base having a plurality of beams, the outer beams being collapsible to a transportable position for placing on a single truck or trailer, and the A-frame lower mast section which is collapsible to a transportable position for placing on a single truck or trailer.

Abstract: A carrying track for a building, which includes a building including a plurality of floors, a track extending from a lower floor of the building to a floor above the lower floor, the track structurally forming part of the floors and part of an outside surface of the building, wherein the track includes two vertical halves with a gap formed between, the gap being exposed to the outside surface of the building and extending inwards from the outside surface.

Abstract: Apparatus for lifting and transporting drywall panels on a lift platform has a pair of panel-supporting legs of square metal tubing attachable to side rails of a lift platform. Each of the legs is connected to the rails by an upper clamp at the top of the leg and a lower clamp at a middle location. A panel-receiving U-shaped channel is located on the opposite side of the leg, away from the rails. The lower clamp has a standoff member included in its connection to the leg, which serves to project the bottom of the legs outward at an angle. Rollers at the top and bottom of the legs provide low-friction rolling contact for weight bearing surfaces, and other rollers are placed to keep panels away from contacting the legs or other surfaces.

Abstract: Scaffolding (10) having safety features for coupling scaffolding structural members so as to prevent equipment damage and worker injury from inadvertent disassembly, while permitting quick assembly and disassembly when desired. The scaffolding (10) incorporating the safety features broadly comprises legs (12); beams (14); a platform (16); coupling braces (18); platform pins (20); and platform clips (22). The first safety feature is a rounded, spring-biased, rotation-limited G-pin for adjustably coupling the beams (14) with the legs (12). The G-pin's rounded shape and a perpendicularly projecting stop (51) minimize risks of inadvertent removal. The second feature is a lockable pin (44) operable to independently couple structural members (12,14) in the event the G-pin is inadvertently removed. The third and fourth features are platform pins (20) and spring-biased platform clips (22) operable to prevent, respectively, undesirable horizontal and vertical movement of the platform (16).

Abstract: A lift apparatus having a pair of support members and a carriage movable along the support members. The carriage includes a pair of rotating members, a band extending between and around the rotating members and a plurality of lift members carried by the band and engageable with support surfaces on the support members. The invention also relates to a support member and a carriage useable with the lift apparatus.

Abstract: A self locking basket assembly has a basket extending from a base platform, and a gate system for releaseably securing a worker within the cage. The gate system includes a gate operatively mounted on a pivotable locking mechanism. The locking mechanism is opened by moving the gate in a rearward direction at an angle to a plane defined by the base platform and thereafter pivoting the gate about a hinge mechanism to an open position.

Abstract: Scaffolding (10) having safety features for coupling scaffolding structural members so as to prevent equipment damage and worker injury from inadvertent disassembly, while permitting quick assembly and disassembly when desired. The scaffolding (10) incorporating the safety features broadly comprises legs (12); beams (14); a platform (16); coupling braces (18); platform pins (20); and platform clips (22). The first safety feature is a rounded, spring-biased, rotation-limited G-pin for adjustably coupling the beams (14) with the legs (12). The G-pin's rounded shape and a perpendicularly projecting stop (51) minimize risks of inadvertent removal. The second feature is a lockable pin (44) operable to independently couple structural members (12,14) in the event the G-pin is inadvertently removed. The third and fourth features are platform pins (20) and spring-biased platform clips (22) operable to prevent, respectively, undesirable horizontal and vertical movement of the platform (16).

Abstract: The present invention provides a transformable linked structure, a deployable diagonal structure, a plane stowage-type deployable truss and a line stowage-type deployable truss with high rigidity and reliability constituted by the above-described transformable linked structure and the above-described deployable diagonal structure, and also provides a plane/line stowage truss structure extremely approximated to a spherical surface using the two types of deployable trusses. The present invention discloses a module linked structure for linking deployable trusses securely and a holding/releasing mechanism for realizing reliable holding and release. Further, the present invention provides a modular deployable antenna with high precision even if it is large-sized which is realized by spreading mesh on the plane/line stowage truss structure.

Abstract: A reconfigurable work platform for an aerial work platform system includes at least one outwardly tiltable portion on which an occupant of the work platform can lean so as to extend his or her lateral reach. This is useful when the work platform itself cannot be moved closer to a desired location. An aerial work platform system using such a reconfigurable work platform, and a method for reconfiguring a work platform are also contemplated.

Abstract: A boom arrangement for a rock drilling apparatus includes at least one boom and an actuator, e.g., a passenger cage, arranged at a free end of the boom. The boom also includes at least two boom parts articulated pivotably with respect to each other. The first boom part is articulated by a first articulation pivotable substantially in a horizontal direction. The second boom part in turn is arranged at an end of the first boom part, and the second boom part can be turned both vertically and horizontally with respect to the first boom part.

Abstract: Aerial work platform apparatus comprising a vehicle, a work platform, a lift on the vehicle for elevating and lowering the work platform, and a stabilizer for inhibiting tipping over of the apparatus when the work platform is elevated. The stabilizer is mounted on the vehicle for movement between a raised retracted position and a lowered position for engagement with the surface traversed by the vehicle should the apparatus start tipping. A mechanism moves the stabilizer between its raised and lowered positions.

Abstract: A mobile human life unit includes an elevatable platform supported by a ladder mounted on a wheeled vehicle. A first embodiment of the mobile human lift unit utilizes a winch with a winch cable reeved over a pulley carried by a support having at least three legs which are held in fixed positions on the platform. A second embodiment of the mobile human lift unit has an overhead crane with a track which swings about a vertical pivot axis and carries a trolley with a winch.

Abstract: A stabilizing system includes at least one outrigger assembly. Each outrigger assembly has a pivotable first leg operably connected to a second leg. At least one locking mechanism is operatively mounted to the pivotable first leg and the second leg. At least one sensing mechanism is connected to the first leg for detecting when the first and second legs are in a stabilized position.

Abstract: A mobile lift having extendable axes that is capable of switching between front-wheel steer, rear-wheel steer, all-wheel steer, and crab steer without resulting in undesirable tire scrubbing or unfavorable steering geometry. One embodiment provides a mobile personnel lift having a chassis supported by steerable front and rear wheel sets. The steerable wheel sets are mounted on axles that are extendable and retractable. A double-acting hydraulic cylinder is pivotally coupled between each steerable wheel and its corresponding axle for turning the wheel. A microprocessor controls the flow of hydraulic fluid to the hydraulic cylinders. Sensors positioned adjacent to each wheel measure the angular position of each wheel relative to the chassis, and transmit this information to the microprocessor to synchronize the wheels as required to provide the optimum steering geometry for the selected mode.

Abstract: An accommodation assembly for use as a temporary studio in outside broadcasting comprises a plurality of support legs (2) erectable to upstand from ground level, structural elements (7 to 9) erectable into an accommodation structure (6), and means, such as an electric hoist motor (10) and a chain (11′), arranged to cause the accommodation structure (6), when erected, to self-climb the erected support legs (2) from ground level to an elevation thereabove.

Abstract: A lifting apparatus for mounting to a vehicle includes a base assembly that is adapted to cooperate with the vehicle. Extending from a base of the base assembly is a plurality of columns. The base assembly further includes a connecting mechanism that securely attaches the base assembly to a bed of the vehicle. The lifting apparatus further includes a platform assembly having a platform and a plurality of outer column receivers extending from the platform. The outer column receivers cooperatively engage with the columns of the base assembly to allow sliding engagement therebetween. Cooperating with the platform assembly is a driving mechanism that is adapted to elevate the platform assembly relative to the base assembly. The driving mechanism includes a lifting chain, a motor assembly, and a gear assembly. The lifting chain has a first end attached to the base assembly and a second end attached to the platform assembly.

Abstract: A movable safety tunnel rides on parapets within a bridge. The safety tunnel is locked in place in a respective section of the bridge while maintenance or other operations are performed on that section of the bridge. This allows the traffic to flow through the safety tunnel and along the bridge, and the safety tunnel shields the traffic from any dust or debris. When the maintenance on that respective section of the bridge has been completed, the safety tunnel is unlocked and pushed (and/or pulled) by suitable equipment to the next adjacent section of the bridge; and the safety tunnel is again locked in place as the maintenance is performed. This procedure continues, progressively, along the bridge. In one embodiment, the safety tunnel has a trolley system riding on respective rails constructed on top of the parapets.

Abstract: A mobile device for releasably and adjustably supporting structures of varying dimensions that are capable of elevating a user above a supporting surface. The mobile device includes a plurality of wheels releasably and adjustably attached to the mobile device. The wheels include at least one driven wheel. The mobile device includes a driver for driving the at least one driven wheel. The driver is controllable by the user.

Abstract: A raising system for scaffolding, elevator cabins and the like which comprises a vertical stationary beam member from one side of which equally vertically spaced similar rack teeth are protruding, each tooth having a substantially horizontal straight top face, a framework guided for up and down movement along said beam member, a power driven shaft rotatably supported by said framework and carrying spaced radial supports, a series of parallel idle shafts extending between the supports, equally spaced from one another and radially equally spaced from the driven shaft, and a plurality of cylindrical roller assemblies rotatably mounted on the idle shafts and adapted to come in successive rolling engagement with the top faces of said teeth during upward or downward movement of said framework. Each roller assembly includes several rollers disposed side by side.

Abstract: A scaffold mountable hoist platform for conveying of materials to different levels of a scaffold. The scaffold mountable hoist platform includes a frame having a rear frame member, a deck support member. The deck support member is orthogonally extending from the rear frame member is for supporting a deck. A plurality of rear vertical guides are positioned proximate the frame. A plurality of stanchion guide assemblies are mounted to the frame such that the stanchion guide assemblies are adapted for releasably engaging the stanchions. Each of the stanchion guide assemblies have a bearing plate and a plurality of bearings. The bearing plate has a plurality of apertures therethrough. The bearings are coupled to the bearing plate such that the bearings extend through the apertures for rollably engaging the stanchions. A lifting assembly is coupled to the frame for raising and lowering the frame along the stanchions of the scaffold.

Abstract: An ergonomically adjustable machine operator platform includes a worker support surface which includes a top surface and a bottom, a plurality of support legs disposed on a floor, wherein each support leg includes an external threaded surface portion, a drive member operably connected to each support leg and having an inner threaded bored surface therethrough which is configured to be complimentary threaded to the external threaded surface portion in a manner to permit axial movement along the support leg and wherein the drive member includes a bearing support surface disposed adjacent the bottom. The drive member further includes an exterior sprocket surface extending generally radially from the drive member, and a rotating device connected to the external sprocket surface for rotating the drive member to cause axial movement along the support leg to vertically move the worker support surface.

Abstract: The invention relates to an elevating work platform having a working platform (16) which can move vertically upwards on at least two parallel masts (3, 4), and which has a carriage (14, 15) for each mast (3, 4). The carriage (14, 15) is guided on the respective mast (3, 4) and has a driving unit. The working platform (16) is supported on the carriage (14, 15) by means of joining elements (40), and power transmission between the mast (3, 4) and the carriage (14, 15) takes place by positive locking. The invention seeks by simple means to compensate the movement of the working platform (16) in relation to the masts (3, 4). This is necessary due to the load to which the working platform (16) is subjected and due to construction tolerances, and so as to prevent high levels of tension in the devating work platform.

Abstract: A lift apparatus having a pair of support members and a carriage movable along the support members. The carriage includes a pair of rotating members, a band extending between and around the rotating members and a plurality of lift members carried by the band and engageable with support surfaces on the support members. The invention also relates to a support member and a carriage useable with the lift apparatus.

Abstract: An apparatus for cleaning bridges or other elevated structures includes a base element and an upper element that is vertically movable with respect to the base element. The upper element supports workmen for cleaning the structure. The floor of the upper element is made of a grid or grating such that debris falls through the floor and is collected in the base element. The base forms a collection hopper and includes a conveyor running along the center for carrying the debris to one end of the base for discharge of the debris. Hydraulic cylinders control the vertical position of the upper element so that the upper element may be placed at the desired elevation. The base element includes wheels and a hitch for allowing the apparatus to be towed on the highway to the structure to be cleaned or repaired.

Abstract: Each of a plurality of cargo holds of a bulk carrier vessel has a self-contained staging system lowered into it, from the platform track of which workers operate semi-automatic blasting machines that are mounted onto the platform. The set-up for each vessel also includes, for each hold, a ventilation unit provided on a hatch plug, and a transporter for the staging system. Groups of staging systems are served by on-deck air compressors. Staging systems actually engaging in blasting are served by recycling shot blast units which recycle and supply steel shot. Following blast cleaning, the cleaned surfaces are painted from the platforms.

Abstract: A lift apparatus having a pair of support members and a carriage movable along the support members. The carriage includes a pair of rotating members, a band extending between and around the rotating members and a plurality of lift members carried by the band and engageable with support surfaces on the support members. The invention also relates to a support member and a carriage useable with the lift apparatus.

Abstract: A movable safety tunnel rides on parapets within a bridge. The safety tunnel is locked in place in a respective section of the bridge while maintenance or other operations are performed on that section of the bridge. This allows the traffic to flow through the safety tunnel and along the bridge, and the safety tunnel shields the traffic from any dust or debris. When the maintenance on that respective section of the bridge has been completed, the safety tunnel is unlocked and pushed (and/or pulled) by suitable equipment to the next adjacent section of the bridge; and the safety tunnel is again locked in place as the maintenance is performed. This procedure continues, progressively, along the bridge. In one embodiment, the safety tunnel has a trolley system riding on respective rails constructed on top of the parapets.

Abstract: A scaffolding system that includes a pair of tower portions, with each tower portion having a proximal section that is held in working relation with a bearing surface and each tower portion having a distal section, a platform, the platform supported by the distal section of each tower portion and the platform selectively movable both toward and away from the bearing surface, and a conveyor, the conveyor positioned on the platform between the pair of tower portions.

Abstract: A work platform for use with a lift truck. The work platform has a pair of wing platforms that are pivotally hinged to a center platform. The work platform has a wing-extended position in which the wing platforms are extended from the center platform so as to provide an extended-length work platform, and further has a transport position in which the wing platforms are pivoted about their respective vertical hinges so as to provide a reduced-width work platform for transport along a highway while loaded on the bed of a transport truck. A removable guard fence is provided for safety around the perimeter of the work platform. Hold-down latches secure the guard fence to the work platform, and latches secure the wing platforms in the transport position and in the wing-extended position.

Abstract: Each of a plurality of cargo holds of a bulk carrier vessel has a self-contained staging system lowered into it, from the platform track of which workers operate semi-automatic blasting machines that are mounted onto the platform. The set-up for each vessel also includes, for each hold, a ventilation unit provided on a hatch plug, and a transporter for the staging system. Groups of staging systems are served by on-deck air compressors. Staging systems actually engaging in blasting are served by recycling shot blast units which recycle and supply steel shot. Following blast cleaning, the cleaned surfaces are painted from the platforms.

Abstract: In a scaffolding at least one tower anchor to secure the tower to a wall, a sleeve surrounding the tower and guided for up and down movement along the same, a support frame releasably secured to the sleeve in vertical position and normal to the wall, a shiftable frame moveably supported by and parallel to the support frame, replace ("the wall supported by the sleeve not ",) by and releasably secured to the shiftable frame at one end a work platform parallel to for horizontal shifting movement transversely of the tower towards and away from the wall and an actuator carried by the support frame and acting on the work platform through the intermediary of the shiftable frame to effect said shifting movement.