Abstract: A stepping exerciser includes a lower main body and an upper main body. The lower main body includes a bottom board. The bottom board has a lower resilient portion extending upward. The upper main body includes a top board. The top board has an upper resilient portion extending downward. The two ends of the upper resilient portion and the lower resilient portion are pivoted by shaft members to form an oval shape. The user can use one or two stepping exerciser as desired. When in use, the user wears the stepping exerciser to jump and step for exercise or amusement. This is beneficial for promoting gastrointestinal peristalsis and digesting.

Abstract: An exercise device having a selectively adjustable footpad is disclosed. More specifically, the present invention describes a footpad whose angular orientation is adjustable by a cam having at least two support sides. The cam can be positioned between the footpad and a link arm. The cam can be rotatable about an axis with each support side being a different distance from the axis. The angle of the footpad can be adjusted by selectively rotating the cam so that the footpad is resting on different support sides of the cam.

Abstract: An exercise device employing side-by-side pivotally supported moving surfaces. In one example, an exercise device employs a first pivotable treadle assembly including a first moving surface, a first foot platform extending outwardly from a side of the first treadle assembly, and a second pivotable treadle assembly including a second moving surface. In some implementations, the exercise device includes a resistance element operably coupled to at least one of the first treadle assembly or the second treadle assembly to resist movement of the at least one of the first treadle assembly or the second treadle assembly. In some implementations, the exercise device includes an adjustment mechanism for adjusting a slope of at least one of the first treadle assembly or the second treadle assembly.

Abstract: An exercise apparatus includes a pair of step-up apparatuses wearable on feet of a user. Each step-up apparatus is configurable between an expanded configuration and a compressed configuration to simulate a selected motion when the user wearing the pair of step-up apparatuses travels by foot. One of the step-up apparatuses moves towards the expanded configuration while the other step-up apparatus moves towards the compressed configuration.

Abstract: An elliptical exercise device includes a frame supporting guide links which provide for a horizontal component of motion of associated foot support links. A mechanical coupling couples the foot support links to a crank system and intermediate links couple the crank system to the guide links such that a foot receiving area of each foot support link moves in a closed generally elliptical path when the crank system rotates.

Abstract: An elliptical exercise device includes a frame supporting guide links which provide for horizontal motion of associated foot support links. A mechanical coupling couples the foot support links to the crank system and intermediate links connect the crank system to the guide links such that a foot receiving area of each foot support link moves in an elliptical path when the crank system rotates.

Abstract: An improved treadmill includes a pedestal, arm stand, drag wheel, two swinging rods and pedals, a stride regulating mechanism, and two elbow-type drive connecting rods. The arm stand is set vertically onto the pedestal's mounting surface. The drag wheel is pivoted axially onto the pedestal through a vertical framework. A mandrel is set transversely onto the center of the drag wheel. Two swinging rods have the pivotal end pivoted onto the pedestal and located at a spacing on two sides of the drag wheel. Two pedals are separately set onto the swinging ends of two swinging rods. Two elbow-type drive connecting rods are linked separately to the mandrel and two swinging rods of the drag wheel, and the stride regulating mechanism is set between two swinging rods. The treadmill has less driving members, lower manufacturing and assembly cost and better driving performance.

Abstract: An exercise machine includes a base, an axle rotationally supported on the base and two cranks connected to the axle. The cranks are rotational synchronously with the axle. A drive wheel unit includes an active wheel provided on the axle so that the active wheel is rotational synchronously with the cranks. A passive wheel unit includes a load wheel supported on the axle so that the load wheel is rotational relative to the axle and a passive connected to the load wheel so that the passive wheel is rotational synchronously with the load wheel. A step-up device includes a shaft rotationally supported on the base and small and large wheels connected to the shaft so that they are rotational synchronously. The small wheel is connected to the active wheel so that they are rotational together. The large wheel is connected to the passive wheel so that they are rotational together.

Abstract: An up and down restoration treading leisure exercise apparatus comprises a rack body, a rear wheel shaft gear, a braking component, an unidirectional flywheel, a spindle component, a chain wheel, a driving belt and a transmission belt. The spindle component is disposed to the rack body. The shaft core of the spindle component is provided for mounting the unidirectional flywheel and the chain wheel. The driving belt is circularly disposed to the unidirectional flywheel to provide unidirectional transmission force. When a user downwardly treads the braking component, the branch bar of the braking component will pull the driving belt and enable the unidirectional flywheel and the chain wheel at the same axis to synchronously rotate. The chain wheel drives the rear wheel shaft gear and the rear wheel through the transmission belt.

Abstract: An exercise apparatus links rotation of a crank to generally elliptical motion of a foot supporting member. A foot supporting linkage is movably connected between a rocker and a crank in such a manner that the foot supporting member moves through paths of motion which are fixed, adjustable or variable.

Abstract: An exercise device providing a fore and aft horizontal component of striding motion that is dynamically user-defined, while providing a vertical component of the motion that is maintained on a predetermined vertically reciprocating path in some embodiments. The exercise device guides the user's foot in a pseudo-elliptical stride path, while providing a dynamically variable stride length that allows the user to move with a natural stride length. The exercise device allows tall and short users to extend or curtail the stride length to match their natural stride lengths. The length of the reciprocating path is dynamically adjusted during the exercise operation without equipment adjustments by changes in the length of the stride input by the user at a pair of foot engagement pads disposed on laterally spaced apart foot support members.

Abstract: An athlete training apparatus includes a platform, a force redirecting device that is mounted on the platform, an elastic member, a first user coupler and a second user coupler. The elastic member has a first end and an opposite second end and is engaged with the force redirecting device. The first user coupler is coupled to the first end of the elastic member and is also configured to be worn by a first individual. The second user coupler is coupled to the second end of the elastic member and is configured to be worn by a second individual. When the first individual stands in the standing area and when the second individual applies a force to the elastic member, the force redirecting device redirects a portion of the force to the second user coupler so that a force having a downward vertical component is applied to the first individual.

Abstract: Various exercise machines have foot supporting linkages that move a person's feet through respective left and right paths of motion in respective planes that are skewed relative to one another.

Abstract: An adaptive exercise device includes a frame which supports swing arms which provide for horizontal motion of associated foot links. A crank system provides for vertical motion of the foot links and is movable relative to the frame. The vertical and horizontal motions of the foot links are mechanically decoupled and may be blended to approximate a desired foot path. The movable crank system causes the foot path to correspond to a natural running action.

Abstract: Disclosed is a simple harmonic motion exercise device including: a base having a front stand, a rear stand and an oblique stand; a handle module with a transverse gear; two longitudinal gear linkage rods, each having a longitudinal gear installed at the top; two pedal linkage rods, each having a pedal; two swing linkage rod pivotally coupled to rear ends of the pedal linkage rods; two stretch linkage rods pivotally coupled to top ends of the rear stand, and the other end of the stretch linkage rod being pivotally coupled to the swing linkage rod, and then an elastically stretchable member being installed between the stretch linkage rod and a hinge portion of the swing linkage rod, and a holder being installed at the other end of the elastically stretchable member and mounted onto the oblique stand of the base, so as to achieve an expected simple harmonic motion exercise.

Abstract: An adjustable elliptical trainer has a base, two driving brackets, two handles, two pedal assemblies and an adjustment assembly. The base has a transmission wheel mounted rotatably thereon. The driving brackets are connected respectively to the transmission wheel. The handles are connected pivotally and respectively to the driving brackets. The pedal assemblies are mounted at opposite sides of the transmission wheels. The adjustment assembly is mounted on the front end of the base and has two guiding rods and a guiding bracket. The guiding rods are mounted on the base. The guiding bracket is connected to the transmission wheel and mounted slidably on the guiding rods. The adjustment assembly allows the pedal assemblies to move along two different elliptical motion paths.

Abstract: An exercise apparatus may comprise a frame, and first and second foot support members each comprising a central region mechanically constrained to follow an ovoid path. The exercise apparatus may further comprise first and second foot pads coupled to the respective first and second foot support members, and configured for selective rotation relative to the first and second foot support members. The exercise apparatus may further comprise first and second locking mechanisms positioned and configured to selectively lock the respective first and second foot pads in a first angular position and at least one second angular position relative to the respective first and second foot support members.

Abstract: An exercise apparatus includes a frame, two crank units, two reciprocating members, two swing arms, two linkages and two carrying arms. A predetermined portion oriented between the top and bottom ends of each linkage is pivotally coupled to the corresponding crank unit and is moved along a circular path. The top end of each linkage is pivotally coupled to the corresponding reciprocating member and is moved along a curved path between two retracing points. The front end of each carrying arm is pivotally coupled to the bottom end of the corresponding linkage and is moved along a first closed path which is elliptical-like shaped. A predetermined portion oriented between the front and rear ends of each carrying arm is pivotally coupled to the bottom of the corresponding swing arm. The rear end of the carrying arm supports user's foot and is moved along a second closed path.

Abstract: Described herein are embodiments of stationary exercise machines having reciprocating foot and/or hand members, such as foot pedals that move in a closed loop path. Some embodiments can include reciprocating foot pedals that cause a user's feet to move along a closed loop path that is substantially inclined, such that the foot motion simulates a climbing motion more than a flat walking or running motion. Some embodiments can further include reciprocating handles that are configured to move in coordination with the foot via a linkage to a crank wheel also coupled to the foot pedals. Variable resistance can be provided via a rotating air-resistance based mechanism, via a magnetism based mechanism, and/or via other mechanisms, one or more of which can be rapidly adjustable while the user is using the machine.

Abstract: An exercise assembly has a frame, a pair of elongated foot pedal members, a pair of elongated coupler arms, a pair of crank members, a pair of elongated rocker arms, and a front cross-shaft. The pair of foot pedal members are each movable along user-defined paths of different dimensions. Each crank member is rotatable in a circular path and is freely rotatable along the circular path in a first direction and restrained from rotation along the circular path in a second, opposite direction.

Abstract: An exercise assembly comprises a frame and elongated foot pedal members that are each movable along user-defined paths of differing dimensions. Each foot pedal member has a from portion and a rear portion. Footpads are disposed on the rear portion of one of the pair of foot pedal members. Elongated coupler arms have a lower portion and an upper portion that is pivotally connected to the frame. Crank members have a first portion that is pivotally connected to the front portion of one of the pan of foot pedal members and have a second portion that is pivotally connected to the lower portion of one of the pair of coupler arms, such that each crank member is rotatable in a circular path. Elongated rocker arms have a lower portion that is pivotally connected to one of the pair of foot pedal members in between the foot pad and the crank member and have an upper portion that is pivotally connected to the frame.

Abstract: An exercise assembly comprises elongated first and second rocker arms that pivot with respect to each other in a scissors-like motion about a first pivot axis. A slider has a slider body that slides along a linear axis extending through and perpendicular to the first pivot axis. A linkage pivotally couples the first and second rocker arms to the slider body. Pivoting the first and second rocker arms with respect to each other causes the slider body to slide in a first direction along the linear axis. Opposite pivoting of the first and second rocker arms with respect to each other causes the slider body to slide in an opposite, second direction along the linear axis.

Abstract: An elliptical trainer with a variable track is disclosed. The elliptical trainer has a base, a left and a right linkage, a transmission and a left and a right adjusting assembly. The linkages are connected to an upright posts extending upward from the base, respectively. Each of the linkages includes a pedal set configured to slide with respect to the linkage. The transmission deposited on the upright post drives the pedal sets to perform reciprocal elliptical motions. The adjusting assemblies are pivotally connected to the upright post, respectively, and serve to change an elliptical track along which the pedals move. Thereby, the elliptical track varies by expanding or retracting along only a major axis thereof. When using the elliptical trainer, a user will not need to step higher as the elliptical track expands. This design is more ergonomic and adaptive to users with various body heights and habitus.

Abstract: The present invention relates to a standup exercise apparatus that simulates walking and jogging with arm exercise. More particularly, the present invention relates to an exercise machine having separately supported pedals for the feet and arm exercise coordinated with the motion of the feet where the pedal stride length is determined by the movements of an operator. Crank arms are positioned on the framework forward the operator at a height comparable to the pedals. Easy starting occurs in the default mode.

Abstract: A device (1) for a user to secure a workpiece (2) that is positioned on a substrate (3) during the processing of the workpiece (2) with a hand-held power tool. A stepping element (4) has a stepping surface (10) via which the user applies a holding force, and that also has a placement surface (11) for placing the device (1) onto the workpiece (2).

Abstract: An elliptical exercise machine includes a base support structure adapted to be positioned on a support surface. The machine includes first and second reciprocating foot supports, each foot support being movably linked to the base support structure. Additionally, a ramp assembly is situated on the base support structure, the ramp assembly having first and second guide rails for guiding the respective second ends of the first and second foot supports such that the foot supports move in an elliptical path when the elliptical exercise machine is operating. Moreover, a first support member is linked to the base support structure, wherein the first support member is pivotably linked to the ramp assembly at a point above the base support structure. Furthermore, a lift mechanism is linked on a first end to the base support structure and pivotably linked on a second end to the ramp assembly above the base support structure.

Abstract: A pedal correction mechanism used in an elliptical trainer is disclosed to include a pedal link having a coupling portion at the inner side thereof, and a pedal bracket carrying a pedal and having a shaft pivotally inserted into the coupling portion of the pedal link for allowing the pedal bracket to be biased leftwards and rightwards on the axis of the shaft relative to the pedal link to eliminate cumulative tolerances among component parts, preventing derailment and reducing noises.

Abstract: An exercise apparatus links rotation of a crank to generally elliptical motion of a foot supporting member. A foot supporting linkage is movably connected between a rocker and a crank in such a manner that the foot supporting member moves through paths of motion which are fixed, adjustable or variable.

Abstract: An oblong orbital exercising machine includes a main frame, an upright post mounted on the main frame, two swinging handles connected with the upright post, a cycle movement mechanism mounted on the main frame, two shafts secured on the cycle movement mechanism, two adjusting units mounted on the shafts, two links connected with the swinging handles and the adjusting units, and two pedals mounted on the links. Each of the adjusting units includes a fixing member mounted on the respective shaft and having a plurality of adjusting holes, an adjusting member juxtaposed to the fixing member, and a positioning member mounted on the adjusting member and locked in one of the adjusting holes. Thus, the adjusting member is rotated relative to the fixing member, so that each of the links is driven to change its position and to adjust its movement trace.

Abstract: An elliptical trainer includes a base, a pair of foot-oriented elliptical mechanisms, and a pair of hand-oriented elliptical mechanisms. The base is anteriorly provided with a frame having a first axle and a second axle. The first and second axles are parallel and spaced apart by a distance. The foot-oriented elliptical mechanisms flank the frame and include a revolving assembly pivotally disposed at the first axle and adapted to enable the foot-oriented elliptical mechanisms to revolve relative to the first axle. The hand-oriented elliptical mechanisms flank the frame and include a reversing assembly pivotally disposed at the second axle. The revolving assembly and the reversing assembly revolve in opposite directions. The hand-oriented and foot-oriented elliptical mechanisms enable a user's hands and feet to revolve in the same direction and follow closed paths, respectively. Hence, the user can exercise ergonomically and work different muscle groups.

Abstract: This invention provides a lower-limb off-axis movement training apparatus, which is mounted on the movement part of a sagittal plane exercise machine and allows the user to perform off-axis movement training during sagittal plane functional movements. The said apparatus for the lower limb off-axis training consists of a base, an off-axis movement generating part mounted on the base, and a foot container supported by the off-axis movement generating part. The said off-axis movement generating part comprising at least one of the following two: (1) off-axis pivoting generating part, which generates the pivoting movement of the foot container; (2) off-axis sliding generating part, which generates the sliding movement of the foot container. A feedback training system including the said training apparatus is provided. While the user performs sagittal plane movements of the lower limbs, the said system provides off-axis movement training integrated with the sagittal plane movements.

Abstract: Stationary exercise machines having adjustable incline systems are disclosed herein. In one embodiment, for example, an elliptical exercise machine includes a system for adjusting the inclination of foot support guide tracks. The incline adjustment system can include a lift member that operates between the guide tracks and the floor on which the exercise machine is placed.

Abstract: An improved energy conversion system for propelling a manually powered vehicle is disclosed. The energy conversion system converts the linear kinetic energy applied by an operator to rotational kinetic energy to propel a vehicle. The energy conversion system includes a mechanical stroke multiplier to increase the distance over which the operator may apply a force to the vehicle.

Abstract: A pedal motion path adjustable elliptical trainer includes a base frame , a support mechanism including a rail holder pivoted to the base frame, a support member and two sliding rails, a rotating mechanism set mounted at the left and right sides of the base frame and movable along a respective closed-loop motion path with a respective support link thereof respectively slidably coupled to one respective sliding rail, a linkage mechanism set mounted at the left and right sides of the base frame, and a sliding mechanism mounted at the rail holder and including a transmission member, two follower members respectively mounted on two opposite ends of the transmission member and movable relative to each other. Thus, the elliptical trainer allows the user to change forward-backward pedal motion paths or left-right pedal motion paths, achieving training of different groups of the muscles of the legs.

Abstract: A fitness apparatus includes a chassis, two linkages, two handlebars, two cranks and two joint bars. Each of the linkage includes a first linking-up part and second linking-up part transversally. The first linking-up parts are pivotably attached to the cranks for revolution of the cranks relatively to the chassis. Each of the handlebars includes a lower portion pivotably attached to the second linking-up portion, and an upper portion which can be held by the user to move along a closed elliptical trajectory. Each of the joint bars includes a rear and portion pivotably attached between the upper portions and the lower portions, and a front end portion pivotably attached to the chassis. In this way, the user's arms can take exercise effectively along an elliptical trajectory to further prevent the user from suffering sports injury resulting from incorrect posture.

Abstract: A workout device with a foot-oriented elliptical loop is provided and bilaterally equipped with a transmission rod, a first link rod, a driving rod, a second link rod, a swing arm, and a supporting rod. The transmission portions are pivotally coupled to cranks to enable the cranks to undergo revolution. The supporting rods each have a supporting portion to support a user's feet. The aforesaid rods interact with each other. The supporting portions of the supporting rods move along a closed elliptical loop with segmental junctions spaced apart by a relatively short distance, such that the user's treading process is prevented from undergoing abrupt descents, un smooth transitions, and thus jolts.

Abstract: A pedal motion path adjustable elliptical trainer includes a base frame, a rotating mechanism assembly, a lifting mechanism, a sliding mechanism and a control mechanism. The lifting mechanism is biasable relative to the base frame, including a rail holder, a support member and two sliding rails. The rotating mechanism assembly includes two cranks coaxially pivoted with one ends thereof to the base frame, and a support link set pivotally coupled between the other ends of the cranks and slidably coupled to the sliding rails. The control mechanism is mounted between the base frame and the rail holder to control the angle of deflection of the lifting mechanism. The sliding mechanism is pivotally coupled between the control mechanism and the rail holder. Thus, the invention allows quick adjustment of the pedal motion paths, training different muscles of the legs.

Abstract: An adjustable stepping structure for aerobic exercise is disclosed having a platform and a plurality of support elements. The support elements include a downwardly arcuate notch or channel for receiving a sidewall or endwall of the platform, allowing the platform to be arranged in multiple angled orientations.

Abstract: The present invention relates to a stair exercise device for simulating stair climbing, the device having a plurality of steps which are activated by the weight of a person walking up them. A stationary platform at the base of the stair exercise device sends a signal to a controller to bring the exercise device to a controlled stop when an operator steps onto the platform. The steps of the exercise device stop in a predetermined location when the exercise device comes to a controlled stop, ensuring proper step location to allow the operator to easily enter and exit the exercise device. Steps have a step platform of a different color than the risers between steps to aid in foot placement.

Abstract: A method and/or a device may limit a distance traveled by a treadle assembly in an exercise device. For example, the distance traveled by the treadle assembly may be limited by limiting a distance that a resistance element operably coupled to the treadle assembly may travel. An exercise apparatus may include a travel-limiting device or capability.

Abstract: An exercise apparatus includes a substantially flat, rigid platform for supporting a user during exercise. An inflatable tubular support having an upper portion with a first radial outside diameter, and a lower portion with a second radial outside diameter that is greater than the first radial outside diameter, is coupled to the platform by a fastener. The tubular support defines a central opening that communicates between the platform and a support surface. The platform includes a venting structure for releasing air from the central opening during use. The inflatable support includes an intermediate portion between the upper portion and the lower portion of the tubular support, the intermediate portion including a support feature to restrain the intermediate portion from radial expansion induced by an air pressure internal to the integral inflatable support.

Abstract: An elliptical exercise apparatus includes a base frame with two supporting frames, two swing sleeves each pivotally connected with one supporting frame, two sliding arms each having a top portion slidably inserted through one swing sleeve and a bottom portion extending transversely inwardly and coupled with a treadle, two swing arms each having an end pivotally coupled with the base frame, and two sliding sleeves each axially slidably sleeved onto one swing arm and pivotally connected with the bottom portion of one sliding arm through a pivot. A rotational shaft is transversely and rotationally coupled with the base frame. Two links each have an end vertically coupled with one of two ends of the rotational shaft, and an opposite end pivotally connected with a lower portion of one of the sliding sleeves.

Abstract: An adaptive exercise device provides for a foot motion in which the vertical component of the path of foot travel is mechanically decoupled from the fore-aft component of the path of foot travel so that a user may selectably control the ratio of these two components during the use of the device. The adaptive exercise device includes foot links which are supported on a track for motion therealong. The links are mechanically interconnected so that when a first link moves in a first direction along the track, the second link moves in an equal and opposite direction. The apparatus further includes a vertical motion control system which raises and lowers portions of each of the foot links along a vertical path of travel independent of their position along the track.

Abstract: The present invention relates to a standup exercise apparatus that simulates walking and jogging with arm exercise. More particularly, the present invention relates to an exercise machine having separately supported pedals for the feet and arm exercise coordinated with the motion of the feet where the pedal stride length is determined by the movements of an operator. Crank arms are positioned on the framework forward the operator at a height comparable to the pedals. Compound guides are used to achieve elliptical curve pedal paths.

Abstract: An exercise device employing side-by-side pivotally supported moving surfaces. In one particular example, an exercise device employs a first belt deployed about a front roller and a rear roller and an adjacent second belt deployed about a front roller and a rear roller. The rear of the belts in the area of the rear rollers are pivotally secured and the front of the belts in the area of the front roller are adapted to reciprocate in an up and down motion during use. In some implementations, the moving surfaces include an interconnection structure such that a generally downward movement of one surface is coordinated with a generally upward movement of the other surface. In other implementations, the moving surfaces are operably associated with one or more resistance elements that effect the amount of force required to pivot or actuate the moving surfaces.

Abstract: An exercise device includes a first treadle assembly supporting a first moving surface and a second treadle assembly supporting a second moving surface. The exercise device further includes an upper body exercise assembly operably associated with the exercise device. The first treadle assembly is pivotally coupled with the frame structure, and the second treadle assembly is pivotally coupled with the frame structure. In another form, an exercise device includes a frame structure, a first treadle assembly having a first endless belt in rotatable engagement with a first roller, a second treadle assembly having a second endless belt in rotatable engagement with a second roller, and a flywheel operably coupled with the first endless belt and the second endless belt.

Abstract: Stationary exercise machines having adjustable incline systems are disclosed herein. In one embodiment, for example, an elliptical exercise machine includes a system for adjusting the inclination of foot support guide tracks. The incline adjustment system can include a lift member that operates between the guide tracks and the floor on which the exercise machine is placed.

Abstract: A treading exerciser includes a base, and a first rotary unit and a second rotary unit are respectively connected to the base. The first rotary unit and the second rotary unit are connected to a first link unit and a second link unit respectively. The first link unit and the second link unit are connected to each other by a first connection portion. A pedal is connected adjacent to the first connection portion and drives the first and second link units. The first link unit is pivoted about the first pivot to form up-and-down action. The second link unit is pivoted about the second pivot to form back-and-forth action.

Abstract: The invention relates to a fitness device for exercising the lower limbs, characterized in that the pedals (112), the frame (12) and the various means (13) for articulation, pressure resistance and pedal-restoring, are designed as a single component, consisting of at least one single plate (1) in an elastic material in a V shape with a rounded apex or a U shape with parallel or flared branches, one of the branches (11) thereof being provided with an opening (111) opening up at the base of the “V” or the “U”, for forming the two pedals (112), the other branch (12) thereof forming the frame for the two pedals, and each rounded apex (13) thereof that connects each pedal (112) to the frame (12) forming, as a single component, the means for articulation, pressure-resistance and restoring each pedal.

Abstract: An elliptical exercise machine includes a base support structure, first and second reciprocating foot supports movably linked to the base support structure, first and second guide rails, and first and second rollers. The guide rails guide respective first and second foot supports to provide reciprocal movement of the foot supports. The guide rails each include a track surface having first and second end portions and at least first and second arch portions, respectively. The first arch portion is positioned at a location between the first and second end portions and having a first radius of curvature. The second arch portion is positioned at one of the first and second end portions and has a second radius of curvature that is less than the first radius of curvature. The first and second rollers are movable along the track surface of the guide rails.