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					                                                                                                                      COVER STORY
                                                                                                                      COVER STORY




The                                Flying
                                                           Carpet
Engineers from the US National Institute of Standards &
Technology have designed a way of using hoists and ropes
to access awkward spots




F
                  loating on a web of wire       in pitch, roll and yaw.                        ships in dry dock during repair and
                  rope, the Flying Carpet            For the Stewart Platform’s rods, the       conversion operations. Or it could be
                  can reach remote corners       RoboCrane substituted wire rope.               used for more autonomous assembly
                  of large cargo or              Where the Stewart Platform is moved by         applications on construction sites.
                  passenger ships under          rods that push, the RoboCrane’s platform           The Construction Metrology &
                  construction in dry dock.      is moved in a direction by winches pulling     Automation Group at NIST is
                  It is quicker to set up than   on the rope. The Flying Carpet design          instrumenting a RoboCrane platform
                  normal scaffolding and         uses six hoists and a computer to move a       with a three-dimensional, laser-based site
relatively inexpensive – parts cost about        work platform in three dimensions.             measurement system (SMS) for absolute
$60,000, vastly cheaper than a large                 “By attaching the cables to a work         position control in all six degrees-of-
gantry crane. Like a crane, it uses hoists       platform and keeping all cables in             freedom. Follow-on experiments will
for lift, but the resemblance ends there.        tension, the load is kinematically             incorporate registered LADAR (laser
     Electric overhead travelling cranes         constrained, and the work platform             detection and ranging) scans of the work
need a gantry system to move a hoisted           resists perturbing forces and moments          site for task analysis and navigation
load horizontally. Hoists only work on           with equal stiffness to both positive and      planning.
one axis – they pull toward their rope           negative loads,” according to a 1994
                                                                                                                                                    The full-size
drum, or drop a load away from it.               paper written by the developers*. “The
                                                                                                                                                    Flying Carpet
Winches, which pull a load from one side,        result is that the suspended load is
                                                                                                                                                    prototype
still only operate in one dimension.             constrained with a mechanical stiffness
                                                                                                                                                    equipped with
     But the Flying Carpet, like its             determined by the elasticity of the
                                                                                                                                                    welding gear
progenitor, a 1980s design called the            cables, the suspended weight, and the
RoboCrane, moves not in one but six              geometry of the mechanism.”
directions. The RoboCrane was a kind of              The designers have built a full-scale
adaptation of another idea from the              working prototype in a test facility. They
world of robotics, the Stewart Platform          intend to transfer this technology to other
parallel-link manipulator.                       industries and/or government, to study
     Six rods control every movement of a        construction applications and to study
sheet of metal in the centre. Push one,          autonomous navigation of the Flying
and the metal tilts or moves in one              Carpet. They envisage a combined closed-       * Bostelman, R., et al. ‘Applications of the NIST
direction. The Platform has a total of 12        loop system, whereby the Flying Carpet         RoboCrane,’ Proceedings of the 5th
movements – both directions along the x,         can autonomously and rapidly lift, position,   International Symposium on Robotics and
y, and z (vertical) axes, and around them        and fixture heavy, bulky steel plates onto     Manufacturing, Maui, HI, 14-18 August 1994

                                                                                                                      JUNE/JULY 2003 HOIST                     11
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       The Project
       The         Manufacturing       Engineering
       Laboratory of the National Institute of                                                                    Two cables
       Standards and Technology (NIST) teamed                                                                     terminate at each
       with Atlantic Marine, Inc. in Mobile,                                                                      corner of the
       Alabama to study efficient methods to                                                                      Flying Carpet.
       repair ships in dry dock or along a pier.                                                                  Cable runs start at
       The concept developed in this project,                                                                     the hoist’s rope
       called the Flying Carpet, combines two                                                                     drum, then travel
       main technologies: the NIST RoboCrane                                                                      through pulleys
       and commercially available suspended                                                                       located near the
       scaffolding to produce an effective concept                                                                anchor point, loop
       for worker access to ships, submarines,                                                                    around a snatch
       buildings, and other large objects.                                                                        block, and then
           While RoboCrane can lift large, heavy                                                                  fastens to the
       and awkward loads, its stability and                                                                       Flying Carpet
       maneuverability        allow       advanced                                                                through an S-
       programming techniques more analogous                                                                      shaped load cell
       to robots than cranes. The RoboCrane
       combines sensors, a computer, a platform
       and tensioned cables to perform heavy
       manufacturing and construction tasks,
       such as: lifting and positioning heavy loads
       and manipulation of workers, tools and
       parts. The RoboCrane manipulator can
       improve worker accessibility to ships and
       buildings for performing tasks such as:
       assembly, fixturing, welding, cutting,
       grinding, machining, surface finishing and
       inspection.
           Recent research has yielded the
       Flying Carpet concept as a movable                                                     Operator uses a joystick to manoeuvre
       scaffolding and worker positioning                                                     the Flying Carpet. The joystick mimics
       system that enables workers to                                                         some of its movements: push the
       maneuver themselves, parts, and tools                                                  joystick forward and back and side to
       throughout a large work volume for                                                     side to move along the Y and X axes.
       tasks such as ship repair and aircraft                                                 Twist the joystick to move up and down
       paint removal with expected 20-times                                                   (marked Z). The odd one out: yaw. To
       improved efficiency. This efficiency is                                                pivot along the vertical axis, operators
                                                                                              press and hold a thumb button (not
       based on a comparison of scaffold set-up
                                                                                              visible) and twist. The control also
       time observed at the shipyard (at least
                                                                                              includes a red emergency stop button
       64 man-hours) versus expected Flying                                                   and a hoist set-up dial
       Carpet deployment time extrapolated
       from NIST RoboCrane experiments (3
       man-hours). The Flying Carpet is a
       cable-supported platform that uses
       single-axis jog-, velocity- and force-
       control modes.



        Specifications
        Overall system dimensions: 31m (100ft) wide by
        12m (40ft) deep
        Work platform dimensions: 18m (60ft) wide by
        maximum 6m (20 ft) deep
        Wire rope cable length: 46m (150ft)
        Maximum yaw rotation: +/- 25o
        Working height: up to 24m (80ft)
        Platform weight: 2.5t (2.8 US tons)
        Estimated total cost to build: $60,000, including
        $40,000 on winches and pulleys, $11,200 on
        structure and $7,800 on electronics in 2003 prices
        Suggested winch: 2.2kW three-phase Jeamar NLT                 A computer simulation of the Flying Carpet’s range of motion,
        2800, fourth layer (minimum) working load limit               rendered in a 3D object. The picture plots the maximum extent of
        rope pull of 972kg with 10mm wire rope                        the platform’s centre of gravity, rendered into a 3D object. (That
        Figures apply to a full-size Flying Carpet installed at the   means that the ends of the platform can actually reach much
        facilities of collaborator Atlantic Marine.                   farther to either side). Because it can move backward as well as
        The NIST does not endorse products; winch model chosen        side to side, the Carpet can track the bow from top to bottom
        only for purpose of price estimate



 12   HOIST JUNE/JULY 2003
                                                                     COVER STORY
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               Control system including servo
               controls, power amplifiers, computer
               and circuit breakers




      Six winches control the     Rigid support structure resists
      Flying Carpet motion.       forces caused by six hoist ropes
      Most of them must           pulling in all directions
      operate to move the
      Flying Carpet in any
      single direction




         An extra dimension on a suspended work platform:
 Six computer-controlled winches enable the Flying Carpet to move
in the direction of, and around, all three axes. On each side, a set of
three cables (each in different colours) hold the Flying Carpet stable

                                                                     JUNE/JULY 2003 HOIST   13
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 Because the
 Flying Carpet
 can move in
 three
 dimensions,
 it can
 manoeuvre
 around any
 complex
 object, such as
 a submarine
 (near right) or
 a dam in
 operation
 (right)




 The Flying
 Carpet can be
 rigged
 differently for
 navigating flat
 surfaces, such
 as buildings or
 the sides of
 ships.
 Right: a scale
 model of the
 Flying Carpet
 in the ship       The Concept                                    equipment can mount to the Flying             maintenance.
 side-access       Small and full scale static physical models,   Carpet. The platform allows rapid                  The Flying Carpet can be reconfigured
 configuration     a computer model for studying system           fixturing of tools, equipment, or cargo to    from ship bow and stern access as
                   work volume and a full-scale working           provide direct worker access to the           discussed above to a thin, ship side-access
                   prototype demonstrate the advanced             equipment as needed at the site.              configuration as shown in Figure 3. Yaw
                   functionality of the Flying Carpet as a tool       An on-board supply hoist can also         motion is limited to approximately 5° due
                   for ship repair and other uses. Its basic      attach to the platform to bring tools,        to the reduced front-back depth and
                   geometry includes four upper support           workers, and supplies up to the work site     reduced rear platform depth. The
                   points, instead of three as used for           while the platform is parked in position.     platform in this configuration includes
                   RoboCrane, to match the rectangular dry        The Flying Carpet cable configuration         similar rigidity characteristics as in the
                   dock configuration. The four points            provides a constrained and easily             bow and stern access configuration. For
                   connect to three work-platform points          maneuvered work platform as compared          platform heights above the dry dock wing
                   with six cables in a unique configuration      to conventional worker-access systems         wall, the cables are at smaller angles with
                   creating a relatively rigid system.            typically used for ship repair, thereby       the horizontal axis and therefore provide
                       The four upper support points can be       aiding ship repair and inspection tasks.      the lateral stiffness necessary for upper
                   attached to towers mounted to a dry                The platform provides minimized           ship side-access, at a cost of increased
                   dock, ground, or along a pier, to a gantry,    sway and rotation, and can exert forces       cable tension and some reduced vertical
                   ceiling, walls, or other superstructures.      and torques with full six degree-of-          stiffness. Two front cables can be crossed
                   Two front cable pairs provide platform lift    freedom       control. The       operator     for additional rigidity and the towers
                   while two rear cables mount lower to           commands through the tethered joystick,       (support points) can be separated by 30m
                   pull back on the platform creating a rigid     either worn by the operator or mounted        or more to provide a large, side-to-side
                   system. Cables can be multi-part lines for     to the platform.With the platform, an on-     range of motion. Along the wing wall,
                   added safety factor and lift capacity. By      board or remotely-located operator can        similar platform rigidity can be
                   suspending the platform from above, the        manipulate and hold attached materials,       accomplished by pushing against the dry
                   RoboCrane improves operating efficiency        such as heavy steel plates, or tools, such    dock wall with outriggers.
                   by “flying” over ground-clutter or             as welders, grinders, robots and other             The US Office of Naval Research
                   landscaping that typically hinders wheeled     cargo dependent upon the platform rated       sponsored this research.                 H
                   vehicles at the work site.                     capacity.Tension sensors in-line with each
                       Hoists that control each cable’s length    cable can prevent hoist or platform           Adapted from:
                   can mount on the support structure or          overloading or sense slack cables.            Bostelman, R., Shackleford, W., Proctor, F.,
                   the work platform. The total hoist rigging         The Flying Carpet moves in Cartesian      Albus, J., Lytle A.,‘The Flying Carpet: A Tool to
                   capacity of the prototype, which uses two-     and joint modes. Cartesian control            Improve Ship Repair Efficiency,’ Proceedings
                   part wire ropes, totals 8,200kg (18,000 lb).   allows the worker to intuitively move the     of the American Society of Naval Engineers
                   In the prototyped configuration, the Flying    platform front-to-back, side-to-side, up-     Symposium on Manufacturing Technology for
                   Carpet carries its hoist motors, providing     and-down, and yaw about the vertical axis     Ship Construction and Repair, Bremerton,
                   maximum platform flexibility as well as        all while maintaining platform level. Joint   WA, 10-12 September 2002.
                   providing a counterweight.                     mode allows single-hoist motion for           Further information from:
                       Welders, paint sprayers, or other          setup or cable replacement for normal         www.isd.mel.nist.gov/projects/robocrane

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