Abstract: A tower for a material handler includes a housing surrounding an interior space. The tower has an interior mounting system including a base plate through which a plurality of interior mount openings pass. The interior mount openings are located at positions of the base plate that are interior of the housing. In some embodiments, the tower is part of a material handler that also includes two stabilizers located on opposite sides of the tower, a platform located above the tower, and a boom projecting away from the platform.

Abstract: The present invention relates to a crane comprising a main boom and a rearwardly directed derrick boom for bracing the main boom, wherein a suspended ballast is directly or indirectly attached to the derrick head via connecting means, wherein at least one luffable, rearwardly aligned ballast adjusting boom is provided, which acts on the connecting means and influences the suspended ballast radius by its luffing angle.

Abstract: To provide a crane capable of stably traveling a transporter capable of supporting a counterweight in cooperation with slewing of an upper slewing body. The crane has a connecting body connecting the self-propelled transporter and the upper traveling body, a transporter angle detecting unit, and a steering angle setting unit. A transporter connecting portion of the connecting body is rotatably connected to the self-propelled transporter about a rotation center axis, and moves relative to a slewing body connecting portion whereby the relative distance between the self-propelled transporter and the upper slewing body is variable. The steering angle setting unit sets the steering angle of the wheels of the self-propelled transporter according to the transporter angle detected by the transporter angle detecting unit so that the transporter angle approaches 90 degrees.

Abstract: Provided is a crane capable of changing a moment on a counterweight side without changing a total weight of the crane by using a simple method. The crane includes a base, and a swiveling body that is provided above the base so as to swivel about a pivot center, and includes a boom and a counterweight attaching unit. The counterweight attaching unit includes a plurality of attaching positions, and is configured to selectively attach and detach the counterweight to and from any attaching position among the plurality of attaching positions, and the plurality of attaching positions is positions of which distances from the pivot center are different from each other.

Abstract: The present disclosure relates to a work machine, in particular to a hydraulic excavator, having at least one ballast device, wherein the ballast device comprises at least one ballast weight and at least one ballast support. The present disclosure is furthermore directed to a ballast weight for a corresponding work machine.

Abstract: The invention relates to a mobile crane having at least one ballast receiver that is vertically adjustable via one or more ballast cylinders and having a coupling for connecting the ballast cylinder or cylinders to the energy supply of the crane, wherein the energy supply can be releasably connected to the at least one ballast cylinder via at least one coupling part.

Abstract: A counterweight device installed in a rear end portion of a machine body frame includes amounting table having amounted counterweight, a hydraulic cylinder that raises/lowers the mounting table, a connection structure that connects the mounting table and a cylinder rod of the hydraulic cylinder, a support member that supports the hydraulic cylinder on the mounting table via an oscillating spindle, a first coupling mechanism that couples the connection structure and the rear end portion of the machine body frame to each other at a position where an upper end of the rear end portion is lower than an upper end of the connection structure, a second coupling mechanism that couples the support member and the rear end portion of the machine body frame to each other, a first operation unit that operates the first coupling mechanism, and a second operation unit that operates the second coupling mechanism.

Abstract: The present disclosure relates to a mobile work machine, in particular to a crane or to a mobile crane, comprising an undercarriage, a superstructure rotatable with respect to the undercarriage, and a counter ballast carrier plate that can be mounted to the superstructure via a ballast suspension thereof, wherein the counter ballast carrier plate comprises at least one guide pin that can be guided along at least one guide edge of the undercarriage to bring the counter ballast carrier plate into a predefined installation position on the undercarriage.

Abstract: A mower may include a body frame, a mower unit installed to the body frame, a grass collection container optionally installed at a rear portion of the body frame, a front-wheel support arm provided at a front portion of the body frame, a left front wheel and a right front wheel supported by the front-wheel support arm, a counterweight, and a weight bracket. The weight bracket may be provided on the front-wheel support arm and configured to attach the counterweight thereto. The counterweight may include a plurality of weight elements. The weight bracket may include a plurality of attachment portions. The at least one weight element may be attached to each attachment portion.

Abstract: The invention relates to a crane having at least one apparatus for determining the effective counterweight of said crane comprising at least one receiver for receiving at least one counterweight body; at least one coupling that is configured to pivotably couple the receiver with the further structure of the crane; and at least one abutment that is configured to limit the pivot range of the receiver.

Abstract: An apparatus for moving a counterweight includes an attachment fixed to a frame of a machine, a supporting member that includes a supporting face for placing a counterweight thereon when the counterweight is mounted on the machine, and a link mechanism that moves the counterweight. The link mechanism includes an arm and a rotating cylinder that rotates the arm. One end of the arm is pivotally supported by the attachment while the other end of the arm is pivotally supported by the upper inner portion of a recess of the counterweight. One end of the rotating cylinder is pivotally supported by the upper inner portion of the recess of the counterweight. The supporting face is shaped so as to coincide with the arc locus drawn by a contact face arranged on the side of the counterweight, as the counterweight moves. The contact face comes into contact with the supporting face when the counterweight is mounted on the machine.

Abstract: A crane may include a travelable undercarriage, a superstructure rotatably supported thereon with a luffable boom system arranged thereon and a derrick boom, with an auxiliary crane being used as derrick ballast. In The auxiliary crane may be driven onto a ballast base plate attached to the derrick boom for the alignment of the boom system in order to thus form at least a large portion of the counter-weight.

Abstract: A computing device is described that is configured to display a graphic visualization representing a physical work site for conveying whether a member is accessible as a function of parameters. In an implementation, the computing device includes a display device, a memory, and a processor communicatively coupled to the memory and the display device. The computing device includes a module stored in memory and executable by the processor. The module is configured to instruct the processor to receive parameters. The module is configured to cause the processor to determine liftability of at least one member. The module is configured to cause display of a graphic visualization representing a physical work site at the display device. The graphic visualization includes a graphical representation of the member. The graphical representation is displayed in a first hue when the crane can lift the member.

Abstract: The present invention relates to a combined counterweight hitching device and method thereof, and a counterweight mounting structure.

Abstract: A construction machine in which a fuel tank is mounted to enable the machine to work for a long time through one fueling.

Abstract: A ballast system for heavy equipment including a ballast weight configured to be removably mounted, proximate to an end of a portion of the horizontal structure of the heavy equipment, at least one actuator mounted on the horizontal structure of the heavy equipment, operable between a first position and a second position, and oriented to actuate horizontally along at least a portion of the horizontal structure, at least one tension member that connects the ballast weight to the actuator and is configured to move the ballast weight vertically in response to the at least one actuator actuating along at least a portion of the horizontal structure; and a locking mechanism configured to removably attach the ballast weight to the end portion of the horizontal structure.

Abstract: A hydraulic excavator is provided, facilitating access to the lower side inside an engine compartment, allowing a maintenance job to be performed in a reasonable posture. The hydraulic excavator includes a revolving frame, an engine arranged on the revolving frame, and a counterweight arranged on the revolving frame, at the back side of the engine. A recess indented from the bottom face in the upward direction is formed at the counterweight. An opening is formed at the revolving frame for allowing a person to access from the lower side of the revolving frame to the space between the engine and the counterweight. The recess has a section overlapping with the opening, when viewed from the top.

Abstract: A mobile lift crane includes a carbody; a rotating bed; a boom; a moveable counterweight unit; at least one linear actuation device; and at least one arm pivotally connected at a first end to the rotating bed and at a second end to the linear actuation device. The arm and linear actuation device are connected between the rotating bed and the counterweight unit such that extension and retraction of the linear actuation device changes the position of the counterweight unit compared to the rotating bed. In one method of operation, the counterweight unit is never supported by the ground during crane pick, move and set operations other than indirectly by the ground engaging members on the carbody.

Abstract: The present disclosure relates to a crane with a travelling undercarriage, an uppercarriage rotatably mounted on the same with a luffing boom and derrick boom arranged on the same, and a ballast carriage connectable with the uppercarriage via a coupling element, wherein the ballast carriage is a standardized heavy-duty transport device with separate drive and separate drive controller, and wherein this drive controller can be influenced as a result of the movement of the crane.

Abstract: A device for detecting and monitoring an assembled counterweight on a crane includes a turntable steelwork construction comprising a counterweight cylinder; a sensor which is arranged in the region of a connection between the counterweight cylinder and the turntable steelwork construction; and a computational unit (8), wherein the sensor is connected to the computational unit, and the computational unit comprises a logic which determines a weight of a counterweight which can be connected to the turntable steelwork construction from data which are captured by the sensor and transmitted to the computational unit.

Abstract: Provided is a mobile counterweight equipment of crawler crane, which includes a main platform, wherein the said mobile counterweight equipment further includes a pair of sliding rails on two sides of the main platform, a slider and counterweight equipment on the sliding rails; the counterweight equipment is connected to the slider, the slider sliding back and forth on the sliding rails. Accordingly, total weight of the counterweight is greatly reduced, the structure is simplified and it is easy to operate and to maintain.

Abstract: Disclosed herein, amongst other things, is a system for providing added safety for workers using rigging systems. In an embodiment, the invention includes a safety device for a roof rigging system including a rigger arm having a proximal end and a distal end; an attachment member disposed on the distal end of the rigger arm, the attachment member defining an aperture, the attachment member configured to engage a rigging line with the aperture; and a blocking member disposed on the distal end of the rigger arm, the blocking member configured to interface with the attachment member to prevent engagement of the attachment member with the rigging line by occluding the aperture when a counterweight is not attached to the roof rigging system.

Abstract: A weight adapter bracket is provided for a drawbar support frame having a cylinder coupling member for coupling to a hydraulic cylinder. The coupling member has a slot for removably receiving an end of the cylinder. The adapter bracket includes a lug which extends from a flange. The lug is removably receivable by the coupling member, and the flange is adapted to engage and support a weight. A coupling bore extends through the lug and bracket bores extend through the coupling member. A coupling pin is insertable through the coupling bore and the bracket bores and to releasably hold the bracket in the coupling member. A pin bore extends vertically through the bracket, and a further coupling pin is removably insertable through the pin bore. The further coupling pin is adapted to engage a weight which is mounted on the bracket.

Abstract: A vehicle (1) for transporting ballast weights (4) which are intended for weighting a crane (2). The vehicle according to the invention is characterised in that the vehicle (1) has a ballast lifting device (5), by which the ballast weights (4) can be moved between a transport position located on the vehicle (1) and a usage position provided for on the crane (2).

Abstract: A counterweight attachment and removal system includes a machine mounting bracket and a link having two spaced apart arms. A proximal end of the link is pivotably coupled with the machine mounting bracket. A rotate cylinder has a proximal end pivotably coupled with the machine mounting bracket and a distal end pivotably coupled with a distal end of the link. A slide cylinder has a proximal end pivotably coupled with the link and a distal end pivotably coupled with a lift pin. The lift pin is positioned through slots defined by the two spaced apart arms. The counterweight attachment and removal system includes a first configuration in which the link is pivoted away from the machine mounting bracket, the rotate cylinder is retracted, the slide cylinder is extended, and the lift pin is positioned through distal portions of the slots.

Abstract: A counterweight loading and unloading device and a movable crane have a freestanding pallet (10) with two ends whose upper end faces are used for holding a counterweight (61). The two ends of the freestanding pallet (10) are both equipped with a cavity, and at least one telescopic oil cylinder (11, 12, 13, and 14) is provided in the cavity. A fixed end of the telescopic oil cylinder is fixed with the freestanding pallet (10), and a telescopic end of the telescopic oil cylinder is coupled with a pallet lifting mechanism for lifting the freestanding pallet. The device is not limited by a planar space of a vehicle frame and a turntable height of the movable crane. An integral dimension of the movable crane is not increased, thus preventing integral dimension of the movable crane from exceeding a road traveling standard. The structure of the device is more compact, and the telescopic oil cylinder plays a role of the counterweight, thus enabling stress of the turntable to be more reasonable.

Abstract: A mobile lift crane includes a carbody, a rotating bed, a boom, a moveable counterweight unit, at least one linear actuation device and at least one arm pivotally connected at a first end to the rotating bed and at a second end to the linear actuation device. The arm and linear actuation device are connected between the rotating bed and the counterweight unit such that extension and retraction of the linear actuation device changes the position of the counterweight unit. In one method of operation, the counterweight is never supported by the ground during crane pick, move and set operations other than indirectly by the ground engaging members on the carbody. One embodiment includes a counterweight movement structure having a rectangular rack with at least first and third pinion gears engaged with teeth on one side and second and fourth pinion gears engaged with teeth on the opposing side.

Abstract: The present disclosure relates to a crane with a travelling undercarriage, an uppercarriage rotatably mounted on the same with a luffing boom and derrick boom arranged on the same, and a ballast carriage connectable with the uppercarriage via a coupling element, wherein the ballast carriage is a standardized heavy-duty transport device with separate drive and separate drive controller, and wherein this drive controller can be influenced as a result of the movement of the crane.

Abstract: Embodiments of the present invention generally relate to a pipelayer and a method for of loading a pipelayer or excavator for transportation. One embodiment includes a method for transporting a pipelayer or excavator from a first work site to a second worksite via a public road. The method includes acts of: raising the pipelayer or excavator off of track shoes of the pipelayer or excavator; removing a first track assembly from the pipelayer or excavator using a boom of the pipelayer or a boom assembly of the excavator; loading the first track assembly onto a first trailer of a first tractor-trailer using the boom of the remaining pipelayer or the boom assembly of the remaining excavator; removing the second track assembly from the pipelayer using the boom of the remaining pipelayer or the boom assembly of the remaining excavator; and loading the second track assembly onto the first trailer using the boom of the remaining pipelayer or the boom assembly of the remaining excavator.

Abstract: A lift crane includes a carbody; a rotating bed comprising a counterweight support frame; a boom; a counterweight unit supported on the counterweight support frame in a moveable relationship with respect to the counterweight support frame; and a counterweight unit movement device connected between the rotating bed and the counterweight unit to move the counterweight unit toward and away from the boom. The crane is configured such that during crane operation, the moment generated by the counterweight unit acts on the rotating bed predominantly through the counterweight support frame. Alternatively, the crane can include a mast. In some embodiments the same basic crane is configured to be set-up with two different counterweight options, i) a counterweight unit directly supported on the counterweight support frame and ii) a counterweight support beam moveably connected to the remainder of the rotating bed and a counterweight unit supported on the counterweight support beam.

Abstract: A counterweight installation device includes: a weight support unit provided on a rear end of a body frame of a construction machine; a weight mounting unit disposed on a counterweight; a pin member for mounting the counterweight adapted to move between a first position at which the weight mounting unit is mounted on the weight support unit and a second position at which the weight mounting unit is dismounted from the weight support unit; and a rod device, one end of which is linked with the pin member and an other end of which extends so as to project to an outside of the counterweight, adapted to move the pin member between the first position and the second position by operation at the other end thereof.

Abstract: The present invention relates to a crane vehicle having a base plate fastenable to its undercarriage to receive ballast and two hoisting means vertically fastened to the part of the superstructure projecting outwardly in the opposite direction to the boom, said hoisting means having first load receiving points which can be moved into cut-outs of connection rods arranged at the base plate and engage there into matched recesses, wherein in accordance with the invention both hoisting means are extended beyond the first load receiving points and are provided at their extended ends with second load receiving points which engage into corresponding shape-matched recesses of the connection rods.

Abstract: An adjustable counterweight for use on construction vehicles that includes a body having a first section, a central section adjacent to the first section and a second section adjacent to the central section, wherein the first section and the second section each define a cavity therein. At least one weight plate, preferably a plurality of weight plates, is mounted in a predetermined position within each of the cavities and secured to the body of the counterweight. Each weight plate is shaped to fit the contour of each cavity, such that the amount of weight contained within each cavity is maximized.

Abstract: The present disclosure relates to a mobile crane comprising an undercarriage and a superstructure arranged in a revolving manner thereon with a device for the reception of ballast. In accordance with the present disclosure, the device for the reception of ballast comprising at least three pulling means which can be moved up and down vertically and which can be connected to a pallet or base plate carrying the ballast and located beneath the total center of gravity of the ballast to pull the pallet or base plate toward the superstructure and to connect it to it or to let it down from it.

Abstract: The embodied mobile cranes have a travelling base structure that allows for travel of the crane over a surface. The cranes have a revolving superstructure mounted on the base structure and a boom and a backmast. The boom and backmast are each hinged about an associated pivot axis to horizontal the superstructure. The crane has a main load hoisting manner associated with the boom for hoisting a load. A superstructure ballast is supported on the superstructure. The cranes have a superlift ballast and associated connection manners to connect the superlift ballast to the backmast while the superlift ballast is resting on the surface and/or suspended from the backmast above the surface. The travelling base structure is provided with superlift ballast support to support the superlift ballast on the base structure so that the superlift ballast is movable along with the mobile crane while being supported by the base structure.

Abstract: A structure of mounting a weight in a forklift truck which has a frame and the weight that is to be connected and fixed to the frame by a bolt and a nut includes a first hole, a second hole, a first fitting part and a second fitting part. The first hole is formed through the frame. The second hole is formed through the weight in such a manner that the first hole and the second hole correspond to each other. The first fitting part is formed on the frame. The second fitting part is formed on the weight in such a manner that the first fitting part and the second fitting part fit to each other and that the first hole and the second hole are aligned with each other when the frame and the weight are combined together.

Abstract: In a counterweight attaching and detaching apparatus for a crane, the length of a suspension member is adjusted by an extendable member and links because the distance provided between the peak of a gantry and an upper surface of each of weights when the gantry is suspending the weight at a respective mounting position varies depending on the mounting position. In order to complement the adjustment of the length, different amounts of protrusion of rings from the upper surfaces of the weights are set so that the protrusion amount in the forefront weight is the largest and the protrusion amount in the rearmost weight is the smallest. This reduces the number of types of necessary links used in the suspension member to attach and detach the weights, and the number of operations of connecting and removing the links, and improves operation efficiency.

Abstract: The device combines ballast blocks (3) that can be stacked onto a base frame of the crane, and a gripper (2) for handling these blocks, the gripper being designed to be connected, during use, to a handling means. This device comprises means of nonpermanent connection, by hooking, between the gripper (2) and a ballast block (3) and means (34, 37, 38) for centering the stacked ballast blocks (3) relative to one another. The aforementioned connection means are constituted by two opposed gripping hooks (15, 16) mounted pivotably at the ends of a lifting beam (4) of the gripper (2) and interacting with transverse pins (35) of a block (3). The rear part of each hook (15, 16) is attached to a sling (27, 28), and a lock (21, 22) is assigned to it. The invention applies in particular to the ballasting of tower cranes.

Abstract: A crane vehicle is provided with a carrier and a rotating deck pivotable around a vertical axis thereon on which a boom swivellable around a horizontal axis is supported. Pallets are mounted at the projecting outer end of the rotating desk at both sides to receive counterweight slabs stacked on top of one another. To produce a greater balancing counter-moment to the boom and the load suspended thereon without putting on additional counterweight slabs, a frame can be attached to the outer end of the rotating deck, said frame being provided with accommodations or couplings at least for the respective rear suspension points of the pallets.

Abstract: The invention relates to the mounting of the revolving part of a tower crane, at the top of the mast. A first assembly, formed by the counterjib (8), its tie rod (19) and a rear part (22) of the jib bearer (5), made in two separable parts, is pre-built on the ground, then lifted up and assembled by pinning (at 18) on the revolving pivot or the mast-cab (10) and is held temporarily in place by retaining link rods (48). Another assembly, formed by the jib (6), its tie rods (13, 14) and the front part (21) of the jib bearer, is also pre-built on the ground, then lifted up and assembled by pinning (at 77) on the revolving pivot or the mast-cab (10). The respective tops (28, 47) of the front part (21) and of the rear part (22) of the jib bearer (5) are then joined together by temporary pinning along an axis (78), followed by definitive pinning along an axis (79).

Abstract: A crane vehicle is provided with a carrier and a rotating deck pivotable around a vertical axis thereon on which a boom swivellable around a horizontal axis is supported. Pallets are mounted at the projecting outer end of the rotating desk at both sides to receive counterweight slabs stacked on top of one another. To produce a greater balancing counter-moment to the boom and the load suspended thereon without putting on additional counterweight slabs, a frame can be attached to the outer end of the rotating deck, said frame being provided with accommodations or couplings at least for the respective rear suspension points of the pallets.

Abstract: A counterweight for a monorail hoist. The monorail hoist includes a single support beam and a suspended hoist assembly which is supported for movement along the support beam. The hoist assembly includes a support member which is transverse to the support beam. The counterweight is mounted on the support member. The counterweight is slidable along the support member to optimally balance the overall weight distribution of the hoist assembly. Once the counterweight is properly positioned to balance the hoist assembly, a locking device locks the counterweight to the support member to prevent any further movement of the counterweight along the support member. The locking device is also releasable to allow the counterweight to be moved to or removed from any location along the support member in order to accommodate any changes which may occur to the overall weight distribution of the hoist assembly. Preferably, a plurality of counterweights and cooperating locking devices are provided.

Abstract: A crane having an upper works rotatably mounted on a lower works and a boom pivotally mounted on the upper works, wherein the crane further comprises an apparatus and method for lifting, positioning, and assembling a counter weight to the upper works. The apparatus and method includes pivotally connecting a counter weight pivot frame between the counter weight and the upper works and lifting the counter weight into position with the hydraulic boom hoist cylinder. The crane further comprises a boom parking device.

Abstract: A counter-jib on which ballast can be hung and a hydraulic ram which can swivel said counter-jib both being falcrumed on a supporting frame. The frame is bolted at at least two connecting points to the rotating deck in such a way that after the creation of the bolt connection located in the area of the fulcrum part, the other connecting point of the bolt connection can be swivelled at its bolting position on the rotating deck by luffing up the retracted jib. The mobile crane in accordance with the invention possesses as an additional piece of equipment a counter-jib whose installation allows said mobile crane to be converted into a derrick crane with a very much higher lifting capacity.

Abstract: A convertible crane with a movable sheave assembly which is operable in two distinct positions. In the first position, the sheave is adjacent the body of a crane to enable it to operate in relatively restricted space without interference from obstacles adjacent the rear end of the base. In the second position, the sheave extends away from the body of a crane where it may be attached to an auxiliary counterweight to enable a crane to lift larger loads. The movable sheave assembly enables a crane to be easily and rapidly converted between normal and enhanced lifting modes.

Abstract: A ring-supported lift crane is provided with a counterweight handling system to facilitate repositioning of the crane. The ring-supported crane includes a ring, a crane upper works and a crane lower works, a boom supported on rollers on the ring and a counterweight assembly also supported on rollers on the ring. The counterweight assembly preferably includes a counterweight carrier on which at least one stack of counterweight boxes or units are placed. A counterweight holder is interposed between the at least one stack of counterweight units and the counterweight carrier with a friction reduction device, such as rollers or slider pads, interposed between the counterweight holder and the counterweight carrier. When the ring-supported crane is to be repositioned for a second lift at a construction site, the counterweight holder with the stack of counterweight units is moved off of the counterweight carrier onto a separate counterweight support member, which may be mobile or stationary.

Abstract: The invention provides a self-mounting counterweight device which is mounted to one end of the chassis frame of the vehicle. The counterweight is U-shaped having two vertical sides and an outward wall defining an internal enclosure. The counterweight includes a rod mounted to the top of the counterweight for suspending it from a boom and includes lateral threaded bolts to releasably mount the counterweight to blocks on the chassis frame. The lifting boom has an inward end journalled to the frame and an outward end with tackle for releasably connecting the boom outward end to the counterweight suspending rod. A hydraulic cylinder provides mechanical lift with an inward end journalled to the frame and an outward end pivotally connected to the boom. The combination of the boom and lift provides a scissor-like lever for selectively raising and lowering the counterweight between a lowered and mounted position.

Abstract: A counterweight installation and removal apparatus for a truck-mounted crane includes a counterweight having a bottom surface, a plurality of rollers attached to either the bottom surface of the counterweight or to a crane carrier deck, and at least one inclined surface positioned on the other of the bottom surface of the counterweight or the crane carrier deck to engage the plurality of rollers when the counterweight is installed and removed.

Abstract: A lift crane having enhanced lifting capability includes a self-installing counterweight system which utilizes actuators forming part of a counterweight assembly for raising the counterweight to an operative position with respect to the rear of the crane. A pair of slidable counterweight beams are slidably supported within main frame members forming part of the upper works of the crane and have their outer ends attached to the counterweight. Fluid pressure operated actuators within the frame members extend and retract the beams in order to move the counterweight rearwardly with respect to the rear of the crane. The upperworks also includes spaced-apart, parallel frame members each having a pair of spaced-apart vertical side plates with integral flange sections extending upwardly. The flanged sections include mounting locations for hoist machinery which utilize pins for easily mounting and dismounting the equipment.

Abstract: A lifting apparatus mountable on a rotatable platform for transferring counterweights. The lifting apparatus includes a lifting element having an upper, stationary cage, and a lower cage rotatable relative to the upper cage, each being composed of a tube having a rectangular cross-section. A ball bearing slewing gear connects the lower cage to the upper cage, and has an upper part forming a base plate of the upper cage rigidly connectable to the rotatable platform. A vertically-extendable double-acting counterweight-lifting cylinder is positioned within the upper and the lower cages. A rectangular bar guide is secured to an upper end of the counterweight-lifting cylinder, and is slidingly guided within the upper and the lower cages.