60/062,957, filed October 10,1997.

FIELD OF THE INVENTION The present invention relates to a swivel device that together with one or more wheels defines a caster for attachment to the base of a structure such as a cart or piece of furniture. The invention has particular application to casters for attachment to the bottom of meal and beverage carts used on airplanes.

BACKGROUND OF THE INVENTION Casters are often used on the bottom of carts, trolleys, furniture, or other objects to make them easier to move. One common use of casters involves meal and beverage carts from which airline attendants serve refreshments to passengers aboard airplanes or other aircraft. The casters comprise swivel devices and attached wheels that are placed on the bottom of these carts so the attendants can roll them up and down the aisles of the aircraft.

Naturally, it is important that casters be durable and low in cost and also, that they enable the user to both easily roll or swivel the cart and brake the cart when needed. It also is desirable that the casters require little or no maintenance, have high shock-absorbency on varied surfaces, and particularly for airline applications, be low in weight. Indeed, it is estimated that a reduction of approximately one-kilogram in weight aboard an aircraft could over the course of one year result in savings to an airline company of up to hundreds of thousands of dollars. Collection of debris within

the casters, or conversely the soiling of carpets or other surfaces from the lubrication of the casters, is a further concern.

Typically swivels for the casters (and, in particular, casters for use on airline meal and beverage carts), have been fabricated with zinc-plated carbon steel and lubricated steel ball bearings, as the industry involved in making casters for airline use has considered steel to have the greatest durability relative to its weight. The swivels are typically permanently secured or swedged together during the manufacturing or assembly process, and they even may be permanently lubricated. Permanent securing of the swivel parts has been considered desirable to address durability and maintenance concerns. When the swivels become damaged, the wheels are removed and the swivels replaced.

For example, Figures IA and 1B show a front view and a cross-sectional side view, respectively, of a previous caster 10 used for airline meal and beverage carts.

Referring to Figure 1A, the caster 10 comprises a set of wheels 12 and a swivel 14.

The wheels are secured by a wheel nut 16 and wheel bolt 18 to the swivel 14. While the swivel is comprised of a number of component parts (shown in Figure 1B), the swivel is swedged together to form one integral unit 14, permanently secured together.

Therefore, the user cannot disassemble the parts of the swivel without destroying the device.

Figure 1B shows a cross-sectional side view taken along the line B-B of Figure IA. As can be seen, this swivel 14 is comprised of about seven interconnected parts, not including the wheel 12, wheel nut 16, and bolt 18, which together with the swivel 14 form the caster 10. The swivel 14 comprises a brake pin 20, brake disc 22, and brake nut 24. A spring 26 surrounds the brake pin 20 adjacent the top of the swivel

for biasing the brake disc 22 against the wheel 12 when the top of the brake pin 20 is depressed. The brake pin 20 must be movably disposed within the swivel for biasing against the wheel 12, and a central rivet 28 is used to permanently secure the parts of the swivel together.

The parts of the caster secured together with the rivet 28 further include a fork 30 for attaching the wheels to the swivel (shown more fully in Fig. IA), a plurality of steel ball bearings 32a, 32b (only two are shown in light of the side view), a ball bearing cup 34, and one or more flanges or collars 35,36. The collars 35,36, together with the cup 34 define a raceway for tracking of the ball bearings. An upper plate 38 is disposed over the raceway. The ball bearing cup 34 or flanges 35,36, may be integrally molded or fixedly secured to the fork or plate 38. In any case, the ball bearings are traditionally disposed within a circular raceway, and since they are typically fabricated from steel, as are the remaining parts of the swivel, the bearings must be lubricated to reduce friction and allow for ease of swiveling of the fork 30 and wheel 12 relative to the upper plate 38. Such swivels as traditionally manufactured with zinc-plated steel and as designed for airline use can weigh approximately 750 grams.

Other caster devices are known and shown, for example, in U. S. Pat. No.

1,753,431 to Herold, issued April 8,1930 ; U. S. Pat. No. 1,796,068 to Van Der Meer, issued March 10,1931; U. S. Pat. No. 2,034,315 to Skelton, issued March 17,1936 ; U. S. Pat. No. 2,750,619, to Kramcsak, issued June 19,1956; U. S. Pat. No. 3,964,124 <BR> <BR> <BR> <BR> to Crawford, issued June 22,1976; U. S. Pat. No. 4,494,271 to Perlin et al., issued Jan. 22,1985, and U. S. Pat. No. 4,777,697 to Berndt, issued Oct. 18,1988, all of which are incorporated herein by reference.

The swivels described in these patents contain some or all of the drawbacks described above, such as the use of complicated parts that are difficult to clean, the need to use lubrication, and parts that are swedged or otherwise permanently attached together and therefore difficult to dissassemble. For example, the caster of Van Der Meer has parts that are sealed together by plugging or otherwise sealing pin holes (page 2, lines 26-28,55-65), and lubrication is required (page 2, lines 50-55). The caster of Berndt requires two separate raceways and two sets of bearings, along with a grease fitting for lubrication. (Berndt, col. 5, lines 8-11.) Kramcsak shows a caster involving a swedged center pin and numerous interconnected parts, including an outer snap-ring for holding the ball bearing unit in place and an encased inner race member held in place by an inner disk-like sleeve. Complicated caster structures involving numerous interacting parts are also disclosed in Herold (#1,753,431), Skelton (#2,034,315), Crawford (#3,964,124), and Perlin (#4,494,271). Perlin, for example, uses two separate raceways, two sets of ball bearings, and two top plates. Also, in Perlin, the neck of the caster is integrally formed with the fork which may make cleaning cumbersome to perform.

Applicants have discovered a configuration for a swivel device that advantageously addresses concerns described above relating to durability, ease of use, weight, collection of debris, maintenance, and so forth. Further advantages may appear more fully upon considering the description given below.

SUMMARY OF THE INVENTION Summarily described, the invention embraces a swivel comprising a base, a fork, and a plug, preferably fabricated from milled aluminum, which may be assembled and disassembled without causing destruction of the device. The fork, base, and plug

may be detachable pieces nestled together and secured with a removable joining piece, such as one or more screws. The fork has two downwardly-extending prongs for attachment to the wheel, a bridge surface joining the prongs, and a promontory disposed on the bridge surface opposite the prongs. The plug has a ridge with a bottom diameter smaller than the top diameter, and it is placed on top of the promontory. The base has a bore with an inner side surface. The bore is sized to nestle over the plug and the promontory of the fork so that surfaces of the plug and promontory together with the inner side surface of the bore define a raceway for tracking a plurality of ball bearings. The raceway may be substantially rhombus, and the ball bearings are preferably fabricated with a plastic material, which is more preferably acetal and even more preferably polyamide-imide, so that no lubrication is required for the ball bearings to freely roll within the raceway.

BRIEF DESCRIPTION OF THE DRA WINGS For a better understanding of the invention, an exemplary embodiment is described below, considered together with the accompanying drawings, in which: FIG. IA is a front view of a previous swivel device used for airline meal and beverage carts; FIG. 1B is a cross-sectional side view of a previous swivel device taken along the line B-B of Figure 1 A; FIG. 2 is a three-dimensional perspective view of a caster comprising the inventive swivel device and attached wheels ; FIG. 3 is a cross-sectional side view of the inventive swivel device in an assembled configuration and attached to a wheel; FIG. 4 is a top view of the swivel device and attached wheel;

FIG. 5 is a cross-sectional side view of the fork, base, and plug of the inventive swivel device partially disassembled to show assembly of the parts; FIG. 6 is a cross-sectional side view of the plug; FIG. 7 is a cross-sectional side view of the base; FIGS. 8A and 8B are cross-sectional side views of the fork; and FIG. 9 is a perspective view of a disassembled caster comprising the inventive swivel device showing all parts of the caster.

It is to be understood that these drawings are for the purposes of illustrating the concepts of the invention and are not to scale.

DETAILED DESCRIPTION OF THE INVENTION Applicants have discovered that difficulties associated with swivel devices and particularly swivels used for airline meal and beverage carts can be addressed by using a swivel comprised primarily of three detachable parts, namely, a fork, base, and plug, preferably milled from extruded aluminum block and used with plastic ball bearings.

Previously, it had been considered desirable to use stamped, zinc-plated steel for the swivel components with steel ball bearings to achieve the needed durability, as discussed above. However, applicants have discovered that the milled aluminum swivel as preferably used herein is lighter, simpler, easier to assemble, stronger, and more corrosive-resistant than known steel devices, such as described above with reference to FIGS. IA and IB. Also, the inventive swivel as described herein uses fewer parts as compared with previous devices and is easier to manufacture.

Further, all the parts of the inventive swivel may be detachable without any special equipment, unlike prior devices which have parts permanently secured together, and yet, the durability of the device is not adversely affecte but instead is improved.

The detachability of the parts makes the inventive swivel easy to maintain and, if necessary, repair, because a user need not purchase or replace an entire swivel when one part becomes damaged. The detachability of the parts also makes the manufacturing and assembling of the device more simple. The inventive device configured with milled aluminum and detachable parts is durable not only due to the use of the milled aluminum, but also because it has been discovered that the swedged inner plug of previous devices presented a stress point at which cracks form, and the present device does not require use of the swedge technique to fasten the parts together.

Additionally, applicants have discovered that no lubrication is necessary with the present invention, particularly when the spheres or ball bearings are fabricated with plastic and rotated within a milled aluminum raceway (as defined by the fork, plug, and base of the swivel). With the inventive swivel, the profile of the raceway allows for greater ease and continuous rotation of the fork with respect to the base, even when no lubrication is used. The ability to avoid the use of lubrication provides a clean device which is less likely to soil surfaces or to collect debris, thus maintaining a freely rotating swivel.

More particularly with reference to the Figures, FIG. 2 shows a perspective view of a caster 50, comprising the inventive swivel 52, and attached wheels 54a, 54b.

The wheels 54a, 54b may be attached to the swivel with a wheel nut (hidden from view) and bolt 53, as previously described. The swivel 52 comprises a base 56, a fork 57, and a plug 58 (which is substantially hidden from view by the fork 57, with only the underside of the plug 58 shown in this figure). The base 56, fork 57, and plug 58 are preferably fabricated with milled aluminum, and more preferably aluminum grade

6082T6, which is a grade of aluminum that is known and available in the industry; they may be removably secured together with four blocking screws 59a, 59b, 59c, 59d, which traverse each of the base 56, fork 57, and plug 58. However, other numbers of screws or means of releasably attaching the base, fork and plug are contemplated. The fork and plug may be integrally formed but preferably are separate detachable parts.

Referring to FIG. 3, the internal alignment of the base 56, fork 57, and plug 58 can be seen with a side, cross-sectional view, wherein hatched lines are used to distinguish the parts. (In FIGS. 3 through 9, the same character references are used to refer to the corresponding parts of the swivel and caster device.) The downwardly extending prong portions of the fork 57 for attachment to the wheel are here substantially hidden from view by the wheel 54. However, as can be seen in FIG. 3 (and FIGS. 8A and 8B), the fork has an upwardly extending promontory 63, with a face surface at least a portion of which is angular to define an angled face surface 64.

A bridge surface 100 joins the two prongs to the fork (FIG. 8B). The angled face surface 64, together with surfaces on the base 56 and plug 58, define a raceway 65 for tracking of the ball bearings. That is, the plug 58 has a ridge portion 66, and at least part of the surface of the ridge portion 66 is angular to define an angled ridge surface 67. The base 56 has an inner bore with an inner groove 68, so that when the base 56, fork 57, and plug 58 are nestled together, a raceway 65 is defined by the angled face surface 64 of the fork, the angled ridge surface 67 of the plug, and the groove 68 of the base.

Preferably, the angled surfaces 64,67, may be plane surfaces disposed at a substantially forty-five degree angle relative to a horizontal plane X, and the groove 68

comprises two such plane surfaces so that the raceway 65 has a substantially rhombus- like shape, as shown in FIG. 3. However, other geometric shapes for the raceway are contemplated, which can be varied with changes in the dimensions of the inner groove 58 and angled surfaces 64,67. Within the raceway 65, there is disposed a plurality of ball bearings, with one ball bearing 70 shown in FIG. 3. Preferably, about fifteen to twenty-five ball bearings are used. Advantageously, a raceway with a rhombus-like profile is used with spherical ball bearings having a substantially smooth outer circumference. The use of a raceway having a shape that does not conform to the shape of the ball bearings aids in the smooth operation of the device. This reduces the friction points between the ball bearings and the raceway, and further, it provides gap points at which debris may accumulate without interfering with the rotation of the ball bearings. To illustrate, when a raceway with a rhombus-like profile is used with spherical ball bearings, debris may collect in the four corners defined by the rhombus with little or no impact upon the interface between the ball bearings and the raceway.

The ball bearings are advantageously fabricated with a plastic material, more preferably an acetal material which is commonly sold under the tradename DELRINID and even more preferably a polyamide-imide material commonly sold under the tradename TORLON, depending also upon cost constraints. Nylon is less preferred than the acetal and polyamide-imide materials because it is more likely to exhibit thermal expansion, and the temperature of the ball bearings may rise during use or from changed environmental conditions. Expansion of the ball bearings could cause them be become lodged in, or otherwise reduce the ease with which they rotate within, the raceway.

Referring to FIG. 4, there is shown a top view of the swivel in the assembled configuration, wherein the base 56, plug 58, and a portion of the fork 57 can be seen.

The base may have base holes 72,72b, etc., for securing it to a structure or piece of furniture. Screws 59a, 59b, may be used to secure the plug to the fork, and the base is secured on the fork by the ball bearings in the raceway. In FIG. 5, a side view showing the base 56, fork 57, and plug 58, together illustrates their assembly, and each of these parts are shown individually in FIGS. 6-8, i. e., FIG. 6 shows the plug at boxed region 6-6 of FIG. 5; FIG. 7 shows the base at boxed region 7-7 of FIG. 5; and FIG. 8 shows the fork at boxed region 8-8 of FIG. 5. Hatched lines are used to show in greater detail surface dimensions of the parts.

In FIGS. 5 and 6, the plug 58 is shown with the ridge portion 66, having the angled ridge surface 67, and a projection 76, with screw holes 79a, 79b, extending through the ridge portion 66, for screws 59a, 59b. The plug 58 also has an inner brake-pin channel 80 for insertion of a brake pin 81 (shown in FIG. 9). In FIGS. 5,8A and 8B, the fork 57 is shown with the promontory 63 and angled face surface 64. Also disposed within the fork and extending through the promontory 63 may be a plurality of screw holes 74a, 74b, for removably attaching the plug to the fork via screws 59a, 59b, which extend through the screw holes of both the plug (79a, 79b), and the fork (74a, 74b). The fork 57 has an inner plug hole 75 for insertion of the projection 76 of the plug 66. Thus, the inner dimensions of the plug hole 75 should be slightly larger than the outer dimensions of the projection 76. However, the ridge portion 66 of the plug rests on the promontory 63. The base 56, shown in FIGS. 5 and 7, has an inner bore 77 which fits over the promontory 63 of the fork 57 and also receives both the projection 76 and ridge portions 66 of the plug.

In any case, referring now to FIGS. 3 and 5, the base 56 is placed over the promontory 63 of the fork 57; a plurality of ball bearings (e. g., 70), may be placed within the channel defined by the groove 68 and angled face surface 64 of the promontory; the projection 76 of the plug 58 is inserted into the plug hole 75, so that the ball bearings may be retained in a raceway 65 defined by the angled face surface 64, groove 68, and angled ridge surface 67; and the fork 57 and plug 58 may besecured together with the plurality of screws 59a, 59b, inserted through the screw holes 74a, 79a, and 74b, 79b. Although two screws and screw holes are shown in these side views, preferably four are used. The ball bearings 70 allow the base 56 to rotate about the fork 57 and plug 58, as the base 56 is configured so that a small gap 82 is disposed between the base 56 relative to the fork and plug. The base may be secured to the bottom of a cart or piece of furniture, such as a meal and beverage cart used on an airplane, with screws inserted through the base holes 72a, 72b, and to the bottom of the cart. When plastic ball bearings are used and the base 56, fork 57, and plug 58 are fabricated with milled aluminum, no lubrication is necessary to allow for the base to freely rotate about the fork and plug.

Referring to FIG. 9, there is shown a perspective view of the components of the swivel 52, together with the wheels and brake unit, which define the inventive caster 50, depicted in a disassembled configuration. As can be seen, all the parts can be readily removed and replaced with the use of simple tools, such as a screwdriver, allowing for easy repair and replacement. FIG. 5 shows the components of the swivel device, as previously described, as well as a brake unit and wheels 54a, 54b. The brake unit comprises a brake pin 81, a brake spring 84, a brake disc 86, and a brake nut 88. As can be seen in FIG. 5, the brake pin 81 may be inserted into the brake hole

80 traversing the plug. When the projection 76 of the plug 58 is inserted into the plug hole 75 of the fork 57, the brake pin 81 extends to the underside of the fork 57, at which point the brake disc 86 and brake nut 88 are applied to the pin 81. The brake spring 84 surrounds the brake pin 81 adjacent the top of the swivel for biasing the brake disc 86 against the wheels 54a, 54b when the top of the brake pin 81 is depressed. The wheels 54a, 54b, may be attached to the fork 57 with the wheel bolt 53 and nut 53a.

A swivel as configured and fabricated according to the foregoing description with milled aluminum and sized for use on airline meal and beverage carts can weigh approximately 250 grams, resulting in a substantial reduction in weight.

It is understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the above description and appended claim.