Abstract: A support pad including a body and a washer for supporting a leg is provided. The body includes a bottom and an opposed top defining a top external surface. The body has a central portion defining a spherically shaped pocket formed in the top of the body. The central portion receives a spherically shaped end of the leg and defines a central axis of the body. The body also has a dome shaped intermediate portion extending radially outward from the central portion. The body further has an outer portion extending radially outward from the central portion. The bottom includes a support pad support surface. The dome shaped intermediate portion has a uniform wall thickness. The washer is positioned adjacent the top external surface of the body and has an inner surface defining a central opening in the washer.

Abstract: A support arm having a proximate support arm segment, a distal support arm segment, and a hinge system having a proximate end pivotally connected to the proximate support arm segment at a proximate pivot, and a distal end pivotally connected to the distal support arm segment at a distal pivot. A tensile member having a first end and a second end, has the first end extending into and secured at a termination point on or beyond either the proximate support arm segment or the distal support arm segment, and the second end extending into and secured at a termination point on or beyond either the proximate support arm segment or the distal support arm segment. The tensile member thereby biases one or both of the proximate support arm segment and the distal support arm segment with respect to the hinge system.

Abstract: A novel tolerance ring includes a hollow cylindrical body defining a longitudinal axis that passes axially through its center. The hollow cylindrical body includes first and second longitudinal edges that define a circumferential gap. A plurality of bumps protrude radially from the hollow cylindrical body, and consists of a plurality of gap-adjacent bumps and a plurality of non-gap-adjacent bumps. At least one of the plurality of bumps is circumferentially between the gap and each of the non-gap-adjacent bumps. None of the plurality of bumps is circumferentially between the gap and each of the gap-adjacent bumps. Structure is disclosed to increase an otherwise lower average radial compressive stiffness of the gap-adjacent bumps to become more similar to an average radial stiffness of the non-gap-adjacent bumps.

Abstract: A ball joint assembly may include a housing having a cavity, a friction seat received within the cavity, and a ball stud having a ball that frictionally contacts the friction seat. In one embodiment, a friction control mechanism moves the friction seat within the cavity to adjust the friction between the ball and the friction seat. In another embodiment, both the cavity and an outer surface of the friction seat may be substantially frustoconically shaped.

Abstract: A deformable washer incorporated into a pivot assembly including a support sector and a rotatable sector pivotally mounted to the support sector by aligning apertures in the sectors which receive a widthwise inserting pin. The washer includes a disk shaped body defining an open interior and such that the body is supported by the pin in a desired sandwiching arrangement between the sectors. Protrusions extend from either or both of first and second annular extending faces of the body exhibiting deformable characteristics such that, a laterally applied compressive force associated with the stacking assembly results in collapse of the protrusions without otherwise affecting the structural integrity of the underlying body and allows for variations in material thickness resulting in a lateral gap at the pivot while reducing instances of lateral play.

Abstract: A resettable break-away joint for a pole assembly includes a lower end of an upper pole member and an upper end of a lower pole member. A biasing mechanism urges the lower end of the upper pole member toward engagement with the upper end of the lower pole member to urge the upper pole member toward an upright position until the upper pole member is moved to a collapsed position.

Abstract: A wheelchair includes a pivotable mechanism. The pivotable mechanism allows for a pivoting movement about an axis defined by an interface between adjacent components. These components may be (a) a seat member and a back member, (b) a seat member and a footrest, (c) a foot rest and a footplate support, (d) a baseplate and a footplate, or (e) a back member and a headrest.

Abstract: The present invention discloses a connecting mechanism connecting bicycle auxiliary wheels with a bicycle, which comprises a first rod body, a second rod body, a baffle cover, a spring and a rotary cover. The first rod body comprises first side walls defining a containing space. A first through hole passes through the first side walls, and a first fixing base is disposed between another end of the first rod body and the containing space. One end of the second rod body is contained in the containing space and has a second through hole aligned with the first through hole for the second rod body to pivot around. One end of the spring is fit to the first fixing base and the other one is fit to the second fixing base. The baffle cover is fit to the second rod body and a rotary cover is disposed on the baffle cover.

Abstract: There is provided a frame assembly for a backpack for carrying small children and comprising a back frame and a U-shaped support stand. The support stand is connected with the back frame at both ends through an articulated joint each. The articulated joints each comprise two housing members adapted to be placed in relatively angled positions and have to end positions each between which the articulated joints can be flexed. One of said articulated joints has disposed between said end positions resistance means that can be overcome independently from both end positions. The other articulated joint comprises resistance means that can be overcome independently from the first end position but from the second end position by an externally acting force only.

Abstract: A resettable break-away joint for a pole assembly includes a lower end of an upper pole member and an upper end of a lower pole member. A biasing mechanism urges the lower end of the upper pole member toward engagement with the upper end of the lower pole member to urge the upper pole member toward an upright position until the upper pole member is moved to a collapsed position.

Abstract: A cleaning apparatus includes an elongate rod defined by a proximal end portion having a first linkage member and an opposed distal end portion. The first linkage member is pivotally coupled to a second linkage member of a cleaning head. There is a biasing assembly that is coupled to the elongate rod and to the cleaning head, which tensions the cleaning head to a maximum pivotal excursion relative to the cleaning rod.

Abstract: An exemplary rotatable joint (100) used for a mechanical device includes a socket (10), a rotatable arm (20), a supporting shaft (13), a fastening member (15), an adjusting member (16), and a resilient module (18). A pivot hole (212) is defined in the rotatable arm. The supporting shaft includes a first shaft portion (130) and a second shaft portion (132). A threaded hole (131) is defined in the first shaft portion and the first shaft portion extends through the pivot hole. The second shaft portion is fixed to the socket. The fastening member includes a threaded portion (152) for engaging in the threaded hole of the supporting shaft. The adjusting member is disposed at the threaded portion of the fastening member. The resilient module is disposed between the rotatable arm and the adjusting member for providing an axial resilient force. The axial resilient force is fine tuned by moving the adjusting member.

Abstract: A ball joint, in particular for the wheel suspension systems of motor vehicles, an external, essentially cylindrical housing, an internal joint piece with a pin supporting a ball section and a bearing race surrounding the ball section, is retained in the cylindrical housing and has annular seals on both sides of the pin ends. In order to achieve a hydraulic damping function, annular gaps are provided about the pin adjacent to the ball section, filled directly or indirectly with a damping fluid.

Abstract: The invention relates to a rotatable link, which may be incorporated in an upright. The upright may be used in connection with a support for a card terminal. The rotatable link may be characterized as a rotary friction link. Compressive forces caused by a mechanical tension in a pipe are transferred via two first objects to a second object clamped between them. The two first objects are secured and partly built into the pipe, and the second object is rotatable relative to the pipe. The second object constitutes a rotatable link part on which a plate may be welded to provide an upright.

Abstract: An improved ball joint for use in a motor vehicle steering or suspension system comprises a ball joint having a shank portion and a ball portion disposed in a socket shell. A ball joint retention member is provided having a first end operatively secured to the socket shell and a second end operatively secured to the shank portion.

Abstract: A linear guide, in particular for a device for electrochemical metal machining, that guides a linear movement of a quill that is moved periodically in a machine frame in order to periodically modify a working gap between a cathode situated on the quill and a workpiece in the direction of the longitudinal axis of the quill, the quill being connected to the machine frame by a plurality of connecting rods, the connecting rods being situated, in the no-load, non-deflected state, essentially parallel to the longitudinal axis of the quill , and the connecting rods having at the point of connection to the quill, as well as at the point of connection to the machine frame, a notch hinge in order to enable, via the hinge, the periodic linear movement of the quill, and the flexibilities of these notch hinges being based on elasticities in their structures formed by targeted thinning of the material.

Abstract: A ball joint assembly includes a housing (12) defining a socket chamber (18) and having an opening (32); a composite ball joint bearing (20) disposed within the socket chamber; a ball stud (24) supported by the composite ball joint bearing and having a shank portion (30) which projects through the opening of the housing; and a seal assembly (40) adapted to seal the opening between the ball stud and the socket chamber. The composite ball joint bearing is formed from a first plastic material (20A) and a second magnetostrictive alloy material (20B) which is adapted to change its shape when in the presence of a magnetic field to thereby change the rotational and oscillation properties of the ball joint assembly.

Abstract: Novel tie rod ends and ball joint combinations that are especially useful in racing vehicles in which high performance is desired. The devices provide a reduction in friction such that the required steering effort with regard to both the rotation and misalignment of tie rods can be managed to enhance the steering.

Abstract: A ball-and-socket joint (1) is provided with a housing (2) closed by a cover (3), with a bearing shell (5, 6) and a joint ball (4) accommodated therein rotatably and tiltably with a ball pivot. The bearing shell (6) provided with projections and offsets on its outside as well as an entropy-elastic, pretensioned spring element (7) are fixed by the cover (3) in the housing (2). The bearing shell is formed by lower and upper bearing shells (5, 6), both of which are closed, and the lower bearing shell (5) extending partially over the upper bearing shell (6) is provided on its overarching inside (5b) and the upper bearing shell (6) is provided on its outside (6a) with the projections and offsets (20, 21; 11, 12) with which the entropy-elastic spring element (7) cooperates in a positive-locking and/or non-positive manner under the action of the cover (3) in its closed position and nonrotatably couples the two bearing shells (5, 6) with one another.

Abstract: A joint for rotatably connecting a distal part to a proximal part of a testing and training target the joint including a first member attachable to one of the distal part and the proximal part of the target, a second member attachable to the other of the distal part and the proximal part of the target with the first and second members being rotatable relative to each other and engageable with each other such that the first member may be rotated with respect to the second member between first and second positions and upon the application of a predetermined force rotated past the second position to a third position. A detent communicates with one or both of the first and second members preventing movement of the members past the second position to the third position until at least the first predetermined force is applied to one or both of the members.

Abstract: A pivot socket of the present invention incorporates a stud shaft component having a partially spherical head portion disposed within a housing cavity, and an axial pin extension extending upward into the cavity therefrom. The partially spherical head portion seats against a partial spherical bearing surface disposed within the housing cavity, and the axial pin extension is enclosed within a resilient cushion. A Belleville washer is interposed between the resilient cushion and the partial spherical bearing surface. During use, lateral and axial loads imparted on the stud shaft are transformed into radial and axial component forces at the bearing surfaces. The radial force components are distributed to the interior walls of the housing cavity, while the axial force components are transferred axially through the resilient cushion to the end closure components secured to the housing.

Abstract: A constant velocity fixed ball joint in the form of a counter track joint, having an outer joint part with outer tracks, an inner joint part with inner tracks, torque transmitting balls received in pairs of tracks formed of outer tracks and inner tracks, and a ball cage with cage windows in which the balls are held in a common plane and guided on to the angle-bisecting plane when the joint is articulated. First outer tracks, together with first inner tracks, form first pairs of tracks whose control angles open in a first axial direction. Second outer tracks, together with second inner tracks, form second pairs of tracks whose control angles open in a second axial direction, with the control angles being defined as angles between the tangents at the ball contact points in the tracks when the joint is in the aligned condition. The outer joint part forms a first stop-and-guiding face for a spherical outer face of the ball cage.

Abstract: A mounting structure of a change lever in a vehicle constructed and arranged to absorb an allowance between a housing and a ball rotatively pivoting a lower end of the change lever to rule out generation of noise and to prevent leakage of lubricant coated on a frictional part located therebetween, thereby improving a lever-shifting feeling, the change lever having a change lever knob thereon and a ball thereunder and accommodated in a housing forming a spherical inner space therein for rotation, the structure comprising a support member integrally formed at a lower end of the change lever with a cylindrical upper body unit inserted into a change lever and a spherical inner lower body unit having its diameter expanded at a lower part of the upper body unit and its upper surface adhered to a lower surface of the ball and its lower surface adhered to an inner surface of the housing.

Abstract: A rocker device for an openable motor vehicle roof, with support element (14), rocker element (12) and spring (30) has the rocker element (12) connected to pivot relative to the support element (14) via an axle (10). The spring (30) is located between the rocker element and support element such that it applies a pre-stressing force to the rocker element (12) with respect to the direction of pivoting motion. Furthermore, the spring is a helical spring arranged and formed such that it provides pre-stressing force between the rocker element and support element in an axial direction. The axle is stationary with respect to one element and is guided in the other element through a corresponding axial opening (16).

Abstract: An adjustable articulated positioning device is disclosed which utilizes at least two air-controlled clutch hinges that may be simultaneously unlocked to allow rotation of the articulating members about each hinge.

Abstract: A connection tightness and swing angle adjustable pivot includes a rotary shaft, a stationary shaft having a slit end rotatably received in an end of the rotary shaft, and an adjusting bolt. The adjusting bolt is screwed into the slit end of the stationary shaft with a head portion located in the rotary shaft but accessible with a hand tool via openings formed on the rotary shaft. The adjusting bolt has a tapered portion contacting with another tapered surface around inner wall of the stationary shaft. When the adjusting bolt is turned at the head portion via the openings on the rotary shaft so that it is screwed further into the stationary shaft, its tapered surface tightly presses against the tapered surface in the stationary shaft to expand the slit end of the stationary shaft, so that the stationary shaft more tightly contacts with inner wall of the rotary shaft.

Abstract: An articulated conduit joint (8) includes first and second arms (10, 12), defining first and second passages (106), pivotally coupled by a main clutched joint (14) for movement of the arms about a joint pin (78) defining a first axis (20). The main clutched joint includes a generally open central portion (70) located between first and second end portions (72, 74). Clutch plates (82, 84) in the first end portion are alternately keyed to the first end portion and the joint pin. A compression spring (100) within the second end portion biases the joint pin along the first axis and forces the clutch plates against one another. The first and second end portions are integral with the first and second arms so that relative pivotal movement of the arms about the first axis is frictionally resisted by the clutch plates sliding against one another. One or both of the arms may include a hollow arm extension (22) housed within an arm body (16) for movement about a second axis (24) passing along the passage within the arm.

Abstract: A joint for deploying and locking a solar panel or a reflector has a fork which is pivotable through 180.degree. about a common pivot axis with a fixed bearing support. A disk mounted on the fixed bearing support has a sliding curve that terminates in a groove. A latching fork mounted rotatably on pivotable fork has a latching bolt and sliding roller which runs on the sliding curve when the pivotable fork deploys, and together with a latching bolt, engages the groove. A leg spring engages the latching bolt. The sliding curve has a shape such that during the first half of a deployment angle of the fork that is pivoted by the force of a coil spring, a decreasing portion of the coil spring moment is stored in leg spring. In the second half of the deployment angle, a moment 16 stored in leg spring 9 is again added increasingly to the movement, so that during deployment, an approximately constant corrected deployment moment is provided.

Abstract: A computer includes a base unit and an upper unit which encloses all electronic components of the computer, such as an LCD display, system board, various drives, sound card, speakers, and modem. The base unit has dimensions of only about 11 inches by 7 inches and can easily be placed in small areas. Unlike a typical desk-top computer which has external cords or cables connecting the display to a main casing, the computer only requires a single power cable and a telephone cord and has a light weight which permits the computer to be easily transported to different locations. The upper unit can pivot relative to the base unit by simply pulling or pushing the upper unit with one hand to the desired angle and then releasing the upper unit. The base unit frictionally engages the upper unit to maintain the upper unit at the desired angle.

Abstract: An articulated conduit joint (8) includes first and second arms (10, 12), defining first and second passages (106), pivotally coupled by a main clutched joint (14) for movement of the arms about a joint pin (78) defining a first axis (20). The main clutched joint includes a generally open central portion (70) located between first and second end portions (72, 74). Clutch plates (82, 84) in the first end portion are alternately keyed to the first end portion and the joint pin. A compression spring (100) within the second end portion biases the joint pin along the first axis and forces the clutch plates against one another. The first and second end portions are integral with the first and second arms so that relative pivotal movement of the arms about the first axis is frictionally resisted by the clutch plates sliding against one another. One or both of the arms may include a hollow arm extension (22) housed within an arm body (16) for movement about a second axis (24) passing along the passage within the arm.

Abstract: A self-adjusting bearing assembly comprising a ball member, a connector member, and a bearing seat component having at least two seat members arranged to receive the ball member therebetween. The ball member has a shaped segment providing an outer bearing surface, and the seat members include correspondly shaped inner bearing surfaces for engaging the outer bearing surface of the ball member. A slack removal mechanism is provided to urge a movable one of the seat members toward the ball member and may comprise a pressure chamber having a wall formed by a resilient diaphram positioned adjacent a pressure surface of the movable seat member, and a fitting for pressurizing this chamber with a fluid. The assembly may include a second fitting for feeding lubricant from the pressure chamber to the bearing surfaces. Optionally, a screw member may be provided for exerting an adjustable mechanical force to urge the movable seat member against the ball member.

Abstract: The present invention relates to a spherical joint for transmitting rotating and rocking motions between an inner member and an outer member in sliding contact with each other, and provides a spherical joint which is excellent in the mechanical strength and capable of achieving smooth rocking or rotating motions, and a process for manufacturing the spherical joint. In order to achieve this object, according to the present invention, there is provided a spherical joint comprising: an internal member having a convex-spherical surface; an outer member cast by using the inner member as a core and so connected to the inner member as to rock and rotate relative to the inner member; and a bushing sandwiched between the inner member and the outer member and having a concave-spherical surface for sliding contact with the convex-spherical surface of the inner member. When the outer member is to be cast, the bushing made of a thin metal is partially fused to and rigidly unified with the cast outer member.

Abstract: A linear device includes a housing supporting a central hydraulic or pneumatic cylinder and a pair of support shafts on either side of the central cylinder. The cylinder includes a longitudinally-moveable piston rod which is attached at its distal end to a tooling plate. An alignment coupler is received within a cavity in the tooling plate, and interconnects the cylinder piston rod and the tooling plate. The alignment coupler includes an annular bearing pad with an inner planar surface disposed adjacent an inner endwall of the cavity, and an outer convex curved surface facing away from the inner endwall. A T-shaped operating rod is disposed within the cavity having an annular shoulder flange with a concave curved inner surface adjacent to the curved surface of the bearing pad, and a convex curved outer surface.

Abstract: An artificial knee having a dual flexion action during locomotion is disclosed. The knee comprises a femur part and a tibia part capable of rolling over each other in two different ways depending on whether or not the artificial leg is loaded. Pressure exerted on a cam surface of the femur part flattens the curvature of the cam surface, limiting the angle of rotation of the artificial knee when the knee is loaded. The parts are connected by elastic ties which are fixedly connected to the femur part and movably connected to the tibia part. When the knee is loaded, depending arms from the femur part contact the movable tibia connection and increase the elongation of the elastic ties, thereby additionally resisting rotation.

Abstract: The coupling is provided for linking and supporting conduits hanging above the ground and is adjustable by means of a hand-operatable nut modifying the contact friction between flat and circular edges of two hollow casings. The nut is in mesh with an axle extending through both casings and urges a spring against an axial bearing that rests on one of the casings.

Abstract: A handlebar including a shank, a ring formed integral in the shank, a number of teeth formed in the ring, a rod slidably engaged in the ring, a number of teeth formed on the rod for engagement with the teeth of the ring so as to prevent the rod from rotating relative to the shank, a disc fixed to one end of the rod and a tube coupled to the other end of the rod, and a spring biased between the ring and the disc for cushioning shocks transmitted to the handlebar.

Abstract: A shaft slide-locking apparatus comprises a stationary shaft housing, a rotary main shaft extending through the shaft housing and rotatably disposed in the shaft housing; a movable cam axially movable on the rotary main shaft; an elastic member disposed between the movable cam and the shaft housing; and a control cam opposing the movable cam and fixed to the rotary main shaft and pushing the movable cam on the side of the shaft housing to press the elastic member towards the shaft housing and the rotary main shaft when the rotary main shaft is rotated.

Abstract: The end of the lever (2b) ends in a fork that receives the lever (5b) between its tines (6a, 6b). Each time (6a, 6b) has a recess (9) made on its inner face. This recess (9) is parallel to this inner face and extends longitudinally of this tine, thus opening out at its end to make a passage for receiving a pivot (10). This open space (9) does not extend through the full thickness of the tines (6a, 6b), thus preserving axial stop faces for retaining the pivot (10). The end of the lever (5b) has a lateral recess (11) intended to engage the pivot (10). A draw spring (13) has one end solid with the lever (2b), while the other is caught in a groove (12) that is concentric with the axis of the pivot (10) and is made at the end of the lever (5b) opposite the side face in which the recess (11) opens.

Abstract: A pivot arm for apparatus, particularly medical apparatus has two mounting supports and a connecting cross-member. One mounting support is to be mounted on a stationary support and the other is to be attached to the apparatus to be moved. A first coupling hingedly connects one of the mounting supports to a connecting rod housed within the cross-member, and the other end of the connecting rod is connected to the other mounting support. A helical spring is supported concentrically with respect to the connecting rod within the cross-member. The cross-member is formed as a single hollow, essentially completely closed, primarily tubular spring housing and a second coupling is provided between a spring support that is near the end of the rod and is stationary relative thereto, and the adjacent mounting support, so that both couplings are always arranged parallel to each other in the housing. The ends of the housing are sealed with caps to prevent the escape of undesirable matter, such as dust, dirt, or lubricants.

Abstract: A free positioning tilt unit for use in portable computer or the like, comprises of main frame, mounting bracket element, sleeve, display unit and bushing, in which the opening, closing and positioning of the display unit is achieved by means of the revolving and positioning of the bushing in the sleeve; the bushing is secured to the display unit by means of the engagement of relative tangent planes so as to follow the display unit to move; a central through-hole is formed, when all the component parts are respectively connected together, for insert therethrough of electric wires.

Abstract: An electric starter comprising a dc motor; an output rotary shaft which is rotated by an armature shaft; an overrunning clutch fitted on the output rotary shaft so that the clutch is slidable in the axial direction thereof; a splined tube coupled to outer member of the clutch and engaged with the helical splines of the output rotary shaft so as to transmit the torque of the shaft to the outer member. A shift lever is engaged at the lower end thereof with the peripheral portion of the tube and at the upper end with the actuator of an electromagnetic switch provided at the peripheral portion of the dc motor, so that the lever is swingable about the fulcrum thereof, wherein the fulcrum is shaped as a cylindrical body, the bottom of the inside of which is shaped as an arc.

Abstract: Two pin joints, each mounted at a respective end of a coupling rod, each comprise an outer joint head including a cavity which is open at least in one axial direction as well as a diametral bore and an inner joint head disposed in the cavity and likewise including a diametral bore. A pin extends through both bores and is locked at the outer joint head by a pin retaining device. To accomplish that, the pin has two ends projecting radially out of the outer joint head and each formed with a notch transversely of the longitudinal direction of the pin. The pin retaining device is embodied by a helical spring supported at its one end in the two notches of the pin and at its other end on a shoulder. The shoulder preferably is formed at a sliding ring seal which seals the outer joint head against a housing member.

Abstract: A camera supporting tripod is described with a hip to which legs are attached. The legs are adjustable as to length. In addition, the tripod includes a center shaft mounted to the hip for tilting movement. The center shaft is also adjustable as to length. Manually actuated hydraulic mechanisms are provided for releasably holding the legs as to length, for releasably locking the center shaft to the hip to prevent relative tilting, and for releasably holding the shaft at the length to which it is adjusted. An instrument supporting head on the tripod includes friction brake panning and tilting mechanisms designed to apply a variable drag to these motions and also for smooth operation.

Abstract: In a spring-loaded missile projecting device such as a bow including a center holding part with outwardly projecting support portions having bow members pivotally mounted thereto with a string extending between the free outer ends of the bow members, elbow linkages are arranged between the support portions and the bow members such that the elbows are slightly bent away from the string when the string is straight and the elbow linkages are spring-loaded so as to be forced toward the string for tensioning the string, so as to provide for a relatively large initial string tensioning force which does not appreciably increase by pulling out of the string thereby generating a relatively constant arrow-accelerating force and requiring a relatively low holding force.

Abstract: A hinged butt joint for connecting struts to multijoint fittings used in space structures is disclosed as two end fittings pivoted together, one of which is bifurcated and the other having a cammed butt end extending between the bifurcation with a pivot pin through aligned openings so that the fittings are rotatable to a desired angular position. Nominal manufacturing tolerances are used throughout. A wedge is forcibly fitted into the base of the bifurcation when the fittings are colinear, and bonded to the base in that position during manufacture or assembly, to preclude freeplay in the joint under alternating compression and tension leads and to create a solid mechanical path though which load is transmitted and heat and electricity conducted.

Abstract: Dredge ladder shock mounting arrangements for two or more part dredge ladders with a main dredge ladder part pivotally connected at a dredge platform and a secondary dredge ladder part adjustably connected to the main ladder part. The interconnecting systems for connecting the two ladder parts includes a pivot pin for accommodating changes in the angular inclination of the two ladder parts with respect to one another as well as locking members for pivotally locking the ladder parts in predetermined adjusting working positions. Shock mounting devices are interposed between the pivot pin and the two ladder parts so that relative movement of the ladder parts in a direction radially of the pivot pin axis against the shock absorbing forces is permitted.