Lever Action Caster With Shock Absorbing Spring

1. Field of the Invention

This invention relates generally to caster wheels for support of cabinets, carts, dollies and the like.

2. Description of the Prior Art

Casters have been used for a great many years to support furniture and other items in a way whereby they can be conveniently moved. In the use of casters, it has been found desirable in some instances, to use springs in the casters to support the loads in a somewhat resilient manner. This can make it easier to move the item supported by the caster and to accommodate irregularities in the surface on which the item is supported or along which it is moved. In addition, the use of springs enables less jostling of the item supported on the casters.

There are situations in which a caster which employs metal springs can be caused to oscillate undesirably. An example is where a set of casters supports a cart or cabinet or furniture that is being transported on or in a vehicle. To address one or more of these problems, various efforts have been made and some have resulted in issuance of patents employing various types of vibration damping systems. Examples are as follows:

These efforts notwithstanding, there has remained the need for a caster assembly having the spring and shock absorbing features, well adapted to high volume production, easily adjusted to provide the desired pre-loading for capacity, and wherein the springs can be easily replaced if and when needed. The present invention is directed to meeting these needs.

Described briefly, according to a typical embodiment of the invention, the caster assembly mounts a beam to the lower portion of a leg extending downward from the part by which the caster assembly is connected to a cart or whatever it is intended to support. A wheel is mounted to the rear end of the beam. An elastomeric spring is associated with the front end of the beam and the leg, the beam being pivotally mounted to the leg between the wheel rotational axis and the spring. An adjustable fastener is used to connect the spring to the leg and the beam and, being adjustable, enables pre-loading the spring as desired.

FIG. 1 is a pictorial view of the caster assembly.

FIG. 2 is a top plan view.

FIG. 3 is a bottom plan view.

FIG. 4 is a rear elevational view.

FIG. 5 is a side elevational view.

FIG. 6 is a front elevational view of the caster assembly but with the urethane springs shown in vertical section.

FIG. 7 is a side elevational view showing the horn fragmentarily and the spring base and anchor shaft in section to illustrate in more detail, the connection of the spring fastener to the anchor rod.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring to the drawings in detail, the caster assembly includes a mounting plate 11 with four holes for attachment by bolts or the like to the bottom of a piece of furniture, a utility cart or the like. The mounting plate has a downwardly opening groove serving as an upper race for a series of bearing balls 12 in circular array around a swivel axis 13, with the cup 14 providing the lower bearing race. The mounting plate and cup 14 may be secured together by a rivet 16 to provide a permanent bearing assembly for which a grease fitting 17 is provided. Two downwardly projecting legs 18 affixed by welding, staking or otherwise to the cup 14 cooperate therewith to provide a swiveling caster horn assembly.

A horizontally extending plate 19 is pivotally mounted to the bottom of each of the legs 18 by a rivet 21 passing through both the plate and the horn leg 18, each rivet having permanently upset heads at the outside of the plate 19 and inside of the leg 18, as shown in FIG. 3, but fitted loose enough to serve as a pivot pin. The pivot axes of the two rivets 21 are along a line 22 that is in front of the rotational axis 13 of the swivel bearing assembly. The mounting bolt 23 for the caster wheel 24 is behind the swivel axis and extends across the space between the two plates 19 and receives a spanner sleeve (not shown) thereon. The wheel bearing is mounted on the spanner sleeve and is centered by the spacers 26 between each side of the wheel bearing and the side plates 19.

An anchor bolt 28 whose axis is parallel to those of the rivets and wheel axle bolt 23 is mounted through apertures near the front ends of the plates 19. This bolt likewise has a spanner 29 received on it and which receives the collars 31 on it. Each of these collars has a threaded aperture 30 (FIG. 7) which extends radially outward from the spanner-receiving central aperture of the collar. For each collar 31, its aperture 30 is aligned with an aperture through a bar 32 which can be staked or preferably welded to the front portions of the two horns 18. This bar 32 provides shelf which serves as a seat for a pair of urethane spring cylinders 33 through each of which a cold-formed "D" headed bolt 35 extends. A cap plate 34 rests on top of the spring cylinders and has a pair of square holes in which the part-rectangular "D" portion 36 on each of the boltheads, resides. In FIG. 2 a portion of the swivel assembly is broken out and the flanged top portion of the boltheads is omitted, showing the two corners of the head portion blending into the round shaft portion of the "D". The two corners fitting in the square hole prevent the bolt 35 from rotating in the cap plate 34. The lower end of the bolt is threaded to receive the threaded transverse aperture 30 of the collar thereon. Thus, the collar serves as a nut. Before the anchor bolt and spanner sleeve 28, 29 are installed, the bolts 35, cap plate 34 and spring cylinders 33 are assembled, and the spring cylinders are mounted on shelf 32 already welded to horn legs 18. Then the collars are screwed onto the lower ends of the bolts 35 to the upper end of the bolt thread, i.e. to where the thread stops, whereupon the collar stops. During this operation, the collars engage the bar 32 and begin to compress the springs. The length of the bolt from head flange to upper end of thread, the thickness of the cap plate 34 and the thickness of the shelf 32 and the length of spring are predetermined so that when the collar stops at the upper end of the bolt thread, the bearing of the collars on the bottom of shelf 32 provides a certain minimum desired factory pre-load on the springs. An example is 300 pounds. Thus, each such caster assembly is able to resiliently resist loading on the springs during use in a range of 300 to 1200 pounds, for example.

The shock absorbing springs employed according to the present invention are typically made of solid urethane material. As stated above, the initial pre-load desired is achieved by screwing the collars onto the bolts to where the bolt threads stop. This is near enough to the lower ends of the bolts, and the depth of the radial threaded apertures 30 in the collars is great enough that the collar will stop before the end of the bolt 35 enters the central aperture of the collar. The collars can be backed off 1/2 turn or less if needed to align their sleeve receiving apertures for installation of the spanner sleeve 29 and anchor bolt 28. This construction makes it possible to readily change, during mass production, from one pre-load and/or spring rate for one run of casters to a different pre-load and/or spring rate for another run of casters, by simply using different cap plate thickness, bolt head-to-thread length, or different sizes or compositions of the springs, whichever is easiest. Also, if a spring becomes damaged during use, it can be removed and replaced easily.

The plates 19 serve as beams whereby the invention uses lever action to apply the caster load from the horn fulcrum rivets to the wheel behind the fulcrum and to the spring in front of it. The spacing from the beam pivot axis to the wheel axle and to the anchor bolt 28 can be identical, but will usually be slightly greater from the pivot axis to the wheel axis, depending on desired wheel diameter and clearance.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.