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imposed by a rigid connection, an interface plate was
suspended by four chains approximately 300mm long.
As long as the CG of the load is between the chains it
will maintain a vertical attitude. In addition, as long as
lateral accelerations are limited the load will maintain its
attitude. A drawing of the transporter side interface plate
is shown in Figure 6. An isometric drawing of the
GRAWDE and transporter is shown below in Figure 7.
Figure 7 - GRAWDE and transporter
The effect of the chains while safely maintaining a
vertical attitude is to effectively change the load from a
long pendulum, to a 300mm pendulum with the same
mass, thereby raising the natural frequency. This
configuration however also creates a torsional
pendulum. This can result in rotational oscillations if
excited by sudden the slewing of the mast. To eliminate
these oscillations, three hydraulic dampers were added
between the chains.
Figure 8 - Transporter receptacle plate on GRAWDE
The interface itself consists of four 80 mm mushroom
shaped plungers attached to the interface plate. The
receptacle on the GRAWDE consists of a plate with four
holes to accept the plungers. On the bottom side of the
receptacle plate, there are two keyhole plates. Each of
these has two keyhole shaped cutouts with a lever
mechanism to move them. The mechanism is actuated
manually from a handle on the outside of the GRAWDE.
Detents on the keyhole plates eliminate any possibility of
the plates sliding while under load.
To aid in aligning the transporter to the GRAWDE a
laser crosshair generator is affixed to the interface plate
on the transporter and a cross hair target on the
GRAWDE. The target is fixed to the GRAWDE at about
eye level and rotated about 40 degrees with respect to
the floor to aid in visibility. This allows both rotational
and translational alignment.
There is minimal communication between the GRAWDE
and the transporter. The interface plate on the
transporter has three proximity and four mechanical
switches. The mechanical switches determine whether
the keyhole plates are in the locked, indeterminant or
unlocked position. The proximity switches on the crane
determine that the GRAWDE is present. This is
important as the transporter is also designed to move
the other equipment.
Because the GRAWDE always faces the wing surface
that it’s drilling, it needs to be rotated approximately 180
degrees between beds. To accomplish this, the stacking
transporter is fitted with slewing capabilities.
THE GRAWDE-BED INTERFACE
Figure 9 - The X-Sled
As previously mentioned, the GRAWDE resembles a
five-axis post mill. To make it portable, a means of
separating it from the precision X-axis bearing rails was
necessary. To accomplish this, each bed is fitted with a
100 mm thick base plate permanently fixed to the bed
via bearing cars – also referred to as the X-sled. The Xsled
is shown in Figure 9. The X-sled is fitted with
various features to precisely locate the GRAWDE as
well as clamp it to the X-sled. The X-axis drive motors
and scale are attached to the X-sled.
Machine Pads
Figure 10 - Machine Pad
There are four pads to locate the GRAWDE in the
vertical direction. See Figure 10. Though three pads
would prevent an over constrained condition, four pads
lend stiffness. The X-sled is fitted with 8 bearing cars,
two at each corner of the sled. The machine pads are
located above each pair of bearing cars on the X-sled.
There is a mating set of pads fixed to the GRAWDE.
Each of these is also hardened and precision ground to
create a mating plane perpendicular to the Y-axis rails.
Perpendicularity is measured with a laser tracker.
In order to prevent swarf and dust from contaminating
the mating surface and effecting alignment, the pads are
fitted with automatic covers. Both the GRAWDE and the
sled have covers, and each has a cam and roller to push
the other open as the interfaces approach. Each cover
is spring-loaded in the closed position.
Lateral and Rotational Alignment
To accomplish constraint in the remaining degrees of
freedom, the X-sled is fitted with three pins and the
GRAWDE with three receptacles. The pins are
precision ground 100 mm case hardened steel. Only
two pins are required to constrain the remaining degrees
of freedom, but geometry and visibility prevent ideal
positioning of the pins. One pin is the master, the other
a rough locator, the third is a precision locator. The
precision locator is shorter than the other two and out of
sight from the operator. The master locator and the
　
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