Ball transfer unit

A ball deck is disclosed capable of conveying a container having an uneven bottom surface. The ball deck, having an upper surface, houses a plurality of ball transfer units. Each ball transfer unit has a first housing having an upper end terminating adjacent the upper surface of the ball deck. A first load supporting ball, which is preferably hollow, is disposed in an upper section of the housing and has a portion extending above the upper surface of the ball deck. A second load supporting ball, having a lesser diameter than the first ball, supports the first ball. A spring biases the balls axially upward by allowing the first ball to move between an upward position and a downward position when supporting an irregular load surface.

FIELD OF THE INVENTION 
The present invention relates to a transfer system for conveying containers 
such as pallets and the like, and more particularly, to a component of 
such a system sometimes known as a ball transfer unit. 
BACKGROUND OF THE INVENTION 
Ball transfer units (BTUs) are known for facilitating movement of pallets 
or cargo containers from one location to another. Generally, each ball 
transfer unit has a ball or roller, which projects above a "ball deck" and 
which is capable of freely rolling. The ball contacts a portion of the 
bottom surface of the container being conveyed along the deck. The pallet 
or container is conveyed by a person walking along the ball deck and 
pushing the pallet or container. The pallet or container is moveable along 
the ball deck by the reduced friction provided by the BTUs in the ball 
deck. 
Prior art BTUs, when used with aluminum air cargo containers, have several 
operating disadvantages. The prior art BTUs are unable to readily 
accommodate uneven bottom surfaces of air cargo containers, and have been 
susceptible to contamination with dirt and other materials, causing 
increased friction and decreased performance. 
Another disadvantage of known BTUs is that the balls have relatively small 
diameters. Consequently, the balls present relatively small contact areas 
to support a pallet or container, creating very high loads on the areas of 
the pallet or container supported by the BTU. This excessive contact 
stress can damage the containers, which are typically light-weight 
aluminum, and hence are somewhat fragile. This excessive contact stress 
requires the pallets or containers to have structural strength in excess 
of that otherwise necessary to support the loads carried therein, and also 
requires that there be a substantial number of such BTUs to spread the 
contact stress over a larger area. 
A ball transfer unit, as used in a different field of art, i.e., conveying 
slabs of hot milled steel, is disclosed in Belgium Pat. No. 510,684. The 
BTU disclosed in the Belgium patent has two roller balls of the same 
diameter. The unit is useful primarily with slabs or other materials 
having a uniform bottom surface. The ball transfer unit is unable to 
accommodate uneven bottom surfaces of containers or pallets, for example, 
aluminum air cargo containers, which typically have uneven bottom surfaces 
to enhance their structural integrity. Furthermore, the design is 
susceptible to contamination of the ball bearings with dirt and other 
contaminants, which may enter through the top of the housing. Thus the 
contaminants are capable of interfering with the operation of the ball 
bearings, sometimes resulting in BTU failure. 
What is desired, therefore, is a ball transfer unit which minimizes the 
force necessary to move a container, which is capable of accommodating 
uneven bottom surfaces of the container, which reduces the ability of dirt 
and other contaminates to interfere with the operation of the unit. 
Further, such a desirable ball transfer unit should permit the use of 
lighter weight cargo containers, which is of critical importance when the 
container is used in connection with air cargo, where every saved ounce of 
weight will save the airline the cost of the fuel needed to lift that 
weight. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a ball 
transfer unit that minimizes frictional drag in order to enhance movement 
of the container. 
It is another object of the invention to provide a ball transfer unit which 
is capable of moving vertically within a ball field to accommodate uneven 
bottom surfaces of a container. 
It is yet another object of the present invention to provide a ball 
transfer unit which more effectively reduces the ability of contaminants 
to interfere with the operation of the unit. 
It is a further object to provide a ball transfer unit which reduces the 
amount of contact stress on a container, allowing for the use of a 
container which is more light-weight than conventional containers. 
To overcome the deficiencies of the prior art and to achieve the objects 
listed above, a ball deck is disclosed, having an upper surface, and 
having a plurality of ball transfer units disposed within the ball deck 
for conveying containers. Each of the ball transfer units includes: a 
first housing having an upper end terminating adjacent the upper surface 
of the ball deck; a first load supporting ball contained in the first 
housing and projecting above the upper surface of the ball deck for 
conveying a container; a second load supporting ball having a lesser 
diameter than the first ball, for supporting the first ball; and a spring 
for biasing the first and the second balls upward toward the bottom 
surface of the container. 
The first load supporting ball, which is preferably hollow, is disposed in 
an upper section of the first housing and has a portion extending above 
the upper surface of the ball deck. A substantially frictionless means is 
provided inside the upper section of the housing. The frictionless means 
has an inner diameter bore for retaining the first ball and for limiting 
lateral movement of the first ball, and in one preferred embodiment, had 
bearings to enhance frictionless rotation of the first load supporting 
ball. A retaining member retains the first ball in the sleeve inside the 
housing and prevents the first ball from escaping in the upward direction. 
The second load supporting ball is disposed inside a second housing, the 
second housing being disposed inside the first housing. The second ball is 
supported by a plurality of freely rotating ball bearings housed within a 
ball bearing cup disposed within the second housing. 
The spring, adjacent to the second housing and disposed inside the first 
housing, biases the second housing axially upward, which in turn, biases 
the first and second balls axially upward. As such, the first and second 
ball and the second housing are moveable between an upward position and a 
downward position. 
The first ball is larger than the second ball to shield the second ball 
from contaminants, and a gutter is provided around the second ball to 
collect contaminants. Preferably, the first ball has a diameter which is 
between about 1.8 and about 4 times the diameter of the second ball. Most 
preferably, the first ball has a diameter which is about 63.5 millimeters 
and the second ball has a diameter of about 30 millimeters. 
The invention and its particular features and advantages will become more 
apparent from the following detailed description when considered with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIGS. 1-5 in detail, a ball transfer unit 10 in accordance 
with the invention is shown. In the Figures, the same figure numbers are 
used to identify like elements in the Figure. FIGS. 2 and 3 relate to one 
embodiment and FIGS. 4 and 5 relate to a second preferred embodiment. To 
the extent details of these embodiments are distinct, separate numbers are 
used. As shown in FIG. 1, ball transfer unit 10 is generally inserted into 
ball deck or field 12 and, as shown respectively in FIGS. 2 and 4, 
comprises a housing 14, 114 for housing a first ball 16, a second ball 18 
which supports first ball 16, and a spring 20, 220 for biasing first and 
second balls 16 and 18 upward in housing 14, 114. 
As shown in FIG. 1, a plurality of ball transfer units 10 are inserted into 
ball field 12 to move container 22 along a path P. It should be understood 
that ball field 12 may be inclined (not shown), if desired, to facilitate 
movement of container 22. 
As used herein "container" means any type of container, pallet, or other 
object or workpiece to be conveyed or moved along ball field 12 in any 
direction, such as along path P. Typically, containers 22 will be air 
cargo bins or containers. Containers 22 sometimes have an uneven bottom 
surface 24, the bottom surface 24 having uppermost portion 26 and 
lowermost portion 28. 
The first housing 14, 114 is preferably circular and made of any suitable 
material, such as metal, although any material, including plastic 
materials, may be used which has sufficient structural integrity to 
withstand the forces exerted by containers 22, conveyed along ball field 
12 and workers walking along ball field 12. As shown, for example, in FIG. 
2, the first housing has an upper end 30 terminating adjacent upper 
surface 32 of ball deck 12, and has chamber 34 therein. 
Referring respectively now to FIGS. 2 and 4, first freely rotating load 
supporting ball 16 is located in upper section or portion 36, 136 of 
housing chamber 34, 134. First ball 16 has a portion extending above upper 
surface 32 of ball deck 12, best shown in FIG. 2. First ball 16 can be 
made of any suitable material, such as very hard plastic, but is most 
preferably made of metal. First load supporting ball 16 may be solid or 
hollow, but preferably is hollow, and is most preferably made of two half 
spheres welded securely together. 
Referring now to the embodiment of FIGS. 2 and 3, first housing 14 has a 
substantially circular frictionless sleeve 38 located in upper portion 36 
of chamber 34, as shown in FIGS. 2, 3. Sleeve 38 has inner diameter bore 
40 for retaining first ball 16 such that first ball 16 has limited lateral 
movement. Sleeve 38 may be made of any suitable anti-friction material, 
such as TEFLON.RTM., or any other suitable plastic or other material. 
Sleeve 38 is supported;by retaining ring 42. Retaining ring 42 is 
removably fixed in groove 37 in chamber 34, as shown in FIG. 2. 
Referring now to the preferred embodiment of FIGS. 3 and 4, first housing 
114 has a plurality of bearing elements 137 located around the perimeter 
of first ball 16. bearing elements 137 reduce frictional drag on rotation 
of first ball 16 to reduce the pushing force needed to move a container 
across a ball deck 12. Preferably there are three such bearing elements 
located about 120 degrees apart around the horizontal plane of ball 16. 
For ease of construction, bearing elements 137 may comprise small circular 
bearings placed in circular insets 139 in the upper wall 141 of housing 
114. In such case, as seen in FIG. 5, the bearing elements are positioned 
so that they face slightly off-center from the centerpoint of ball 16, 
such that only one small portion 143 of the circular bearing is in contact 
with ball 16. This permits unimpeded frictionless rotation of ball 16 in 
any direction around a horizontal axis. 
As shown in FIGS. 1-5, first housing 14, 114 has retaining member 46, 146 
most preferably made of steel and securely fixed to housing 14, 114, for 
retaining first ball 16 in housing 14, 114. In FIG. 2, upper surface 48 of 
retaining member 46 is adjacent to upper surface 32 of ball deck 12. In 
FIG. 4, upper surface 148 of the housing 114 would be adjacent an upper 
surface of a ball deck 12. Retaining member 46 is generally circular in 
shape and has a circular opening having a smaller diameter than first ball 
16 to prevent escape of ball 16 from housing 14. In FIG. 2, member 46 has 
angular lip 47, which follows the curvature of first load supporting ball 
16; that is, lip 47 has a radius of curvature substantially equal to the 
radius of curvature of ball 16. It should be understood that any suitable 
retaining member could be used so long as upward escape of ball 16 is 
prevented while rotational movement of ball 16 is not interfered with. 
It is to be appreciated that any frictional drag caused by the interaction 
of first ball 16 with retaining member 46, 146 will be eliminated when a 
load is passed over the ball transfer unit 10, because the load will cause 
ball 16 to move downwardly away from retaining member 46, 146 so that it 
can rotate without frictional interference with the retaining member 46, 
146. It is possible to increase the frictional drag between first ball 16 
and retaining member 46, when the ball 16 is pressed against member 46, by 
addition of friction materials at the lip 47, if desired to increase 
safety for workers who might otherwise step on a ball 16 and become 
unbalanced and fall. However, in the arrangement of FIGS. 2 and 4 the 
retaining member 46 provides a sufficiently high friction to prevent 
rotation of ball 16 when a load is not present to prevent possible injury. 
Wiper 50, shown in FIGS. 2, 3, extends around upper portion 52 of first 
ball 16, and, as shown in FIG. 2, is generally located adjacent sleeve 38 
and beneath retaining member 46. Wiper 50 has a tapered surface for 
contacting first ball 16. Wiper 50 will typically comprise multiple layers 
of any suitable cloth, such as a durable felt. 
Referring to FIGS. 2-5, freely rotating second load supporting ball 18 is 
disposed in second housing 54, 154 and supports first ball 16. Second 
housing 54, 154, which can be made of any suitable material, preferably 
plastic, houses a plurality of freely rotating ball bearings, such as ball 
bearings 56a, 56b, for supporting second ball 18 to provide substantially 
frictionless rotation thereof. Ball bearings 56a, 56b are housed in ball 
bearing cup 57, which is most preferably a metal hemispherical or 
parabolic housing disposed in second housing 54. Housing 154 of FIG. 4 
extends above second ball 18 and can provide support for ball 16 in case 
of a failure of ball bearings 56a. 
First ball 16 has a diameter which is larger than, and preferably between 
about 1.8 to about 4 times larger than the diameter of the second ball 18. 
Preferably the diameter of first ball 16 is at least twice the diameter of 
second ball 18. First ball 16 most preferably has a diameter which is 
about 63.5 millimeters and the second ball 18 most preferably has a 
diameter of about 30 millimeters. This permits the second ball 18 to be 
shielded by first ball 16 to prevent contamination of second ball 18. 
Spring 20, 120 is located adjacent to second housing 54, 154 and biases 
second housing 54, 154 upward, as shown respectively in FIGS. 2 and 4. As 
such, spring 20, 120 biases first and second load supporting balls 16, 18, 
respectively, to an upward position, and permits balls 16, 18 to be 
movable to a downward position through a distance D. 
The annular spring 20 of FIG. 2 is a Belleville washer, and operates 
against ring 58 and shoulder 60 of second housing 54, and ring 58 
generally acts as a stop means for spring 20. Ring 58 surrounds a chamber 
66. Ring 58 can be made of any suitable material, such as metal plastic or 
other material. 
In contrast, the coil spring 120 of FIG. 4 operates against the shoulder 
160 of second housing 154 and the base 158 of chamber 134. 
Referring respectively to FIGS. 2 and 4, wiper 61, 161 adjacent second ball 
18, is similar to wiper 50 adjacent first ball 16. Wiper 61, 161 contacts 
second ball 18 at a plurality of points and is preferably made of multiple 
layers of durable felt cloth. Wiper 61, 161 removes dirt and other 
contaminants from the outer surface of second load supporting ball 18 to 
reduce the likelihood that contaminants interfere with the rotational 
movement of ball bearings 56a, 56b. 
Retaining member 62, 162 adjacent second ball 18, operates similarly to 
retaining member 46. Retaining member 62 operates to prevent undesired 
escape of second ball 18 from second housing 54. 
In use, first ball 16 of ball transfer unit 10, when not operated upon by 
outside forces, is naturally biased to an upward position as shown in 
FIGS. 2 and 4, respectively, by springs 20, 120. As such, the upper 
surface of first ball 16 is maximally displaced above upper surface 32 of 
ball deck 12. 
In operation, container 22 is placed on ball field 12 and is generally 
pushed by worker 64 along path P, as depicted in FIG. 1. As container 22 
moves across individual ball transfer units 10, lower portion 28 of bottom 
surface 24 of container 22 contacts upper portion 52 of first load 
supporting ball 16, causing first load supporting ball 16 to rotate. 
Downward force from container 22 causes first load supporting ball 16 to 
move downwardly from an up position (shown in FIG. 2) to a down position. 
First and second load supporting balls 16, 18 are maintained in downward 
positions so long as a sufficient force is exerted downward onto first 
load supporting ball 16 to overcome the biasing of spring 20, 120. 
As first load supporting ball 16 rotates due to movement of container 22, 
second load supporting ball 18 and ball bearings 56a, 56b also rotate. As 
first load supporting ball 16 rotates, wiper 50 brushes against outer 
surface of first ball 16 and wiper 61, 161 brushes against outer surface 
of second ball 18, wiping off dirt and other contaminants. While wiper 50 
reduces the amount of the contaminants which may fall toward second load 
supporting ball 18, first ball 16 shields second ball 18 from contaminants 
by virtue of its larger size. As such, contaminants which fall downwardly 
do not contact second ball 18 or ball bearings 56a, 56b. Contaminants 
generally accumulate in annular channel 69, defined in FIG. 2 by the 
surface 68 of ring 58, the inner wall of housing 14, and the shoulder 60 
of second housing 54, and in FIG. 4 by the housing 114 and upper end of 
second housing 154. Thus failure of ball transfer unit 10 due to excessive 
contamination in ball bearings 56a, 56b, is reduced or eliminated because 
contaminants can collect in a channel away from the ball bearings. 
After lowermost portion 28 of bottom surface 24 of container 22 moves 
across ball transfer unit 10, uppermost portion 26 of bottom surface 24 
passes across unit 10. Spring 20, 120 biases second housing 54, 154 
upward, moving first ball 16 from a down position to an up position, until 
first ball 16 contacts surface 26 of container 22 or until housing 54 is 
maximally displaced a distance D. 
Applicant's comparative data reveals that a ball transfer unit which does 
not use a spring requires substantially more force to convey container 22 
having an uneven bottom surface, than does a ball transfer unit 10 which 
has spring 20 capable of biasing first load supporting ball 16 upward. For 
example, the ball transfer unit of FIGS. 2 and 3, where spring 20 is 
omitted, requires 585 pounds of force to move a 10,000 pound container. 
However, with spring 20 included in the ball transfer unit of FIGS. 2-3, 
only 400 pounds of force are needed to move the same 10,000 pound 
container. 
Although the operation of only one ball transfer unit 10 was described in 
operation of movement of container 22, it should be understood that 
multiple such units 10 will be used in a ball deck to contact and support 
container 22. 
Although the invention was described as operating in a particular direction 
along path P, it should be understood that the invention is equally 
operable for conveying container 22 in any direction. 
The ball transfer unit 10 of the invention may be manufactured for 
installation in as new ball deck 12, or it may be retrofitted into an 
existing ball deck 12. 
An advantage of the invention is that first supporting balls 16 are used 
that are larger than the roller balls in prior art BTUs, so each such ball 
16 provides a larger surface area to support container 22. Therefore fewer 
ball transfer units 10 are needed for a given area of ball deck 12. And 
because a larger ball 16 with a larger supporting area reduces the point 
contact stress on container 22, less durable containers can be used. For 
example, containers can be made of thinner, lighter weight materials. 
Light weight containers 22, particularly when used in connection with air 
cargo, provide substantial fuel economy and cost savings because of the 
reduced excess weight that must be carried into the sky with each flight. 
The use of lighter containers 22 also reduces the amount of human energy 
necessary to convey the containers. Thus, the use of ball transfer units 
10 provide substantial opportunities to increase efficiency and economy in 
baggage handling. 
It should be understood by those skilled in the art that obvious 
modifications can be made without departing from the spirit of the 
invention. Accordingly, reference should be made primarily to the 
accompanying claims, rather than the foregoing specification, to determine 
the scope of the invention.