Self Aligning Magnetic Locking Device for Module Swivel Caster Assembly

The device consists of two ceramic magnets (2 .times. 7/8 .times. 3/8 inches thick) installed on the underside of the top swivel caster bearing plates, one on each side (180.degree. apart); and one ceramic magnet (2 .times. 7/8 .times. 3/16 inches thick) installed on the top of the caster fork bracket. The top two magnets are of one polarity and the bottom magnet is of opposite polarity. The three magnets are glued onto the base metal with contact cement adhesive. The same procedure is repeated on the second swivel caster wheel.

Both swivel casters are free to swivel while the module is on the floor (manual force for pushing the module is much greater than the pull of the two magnets). As soon as the module is lifted off the floor, onto a car, attracting force between the two magnets of opposite polarity pulls the swivel, floppy wheel inward, toward and inside the module base (within the overall bumper dimensions) and automatically locks the caster in line with the travel of the car.

This self-aligning feature helps prevent damage to the car's body and prevents interference with lift door openings caused by the swivel wheels flopping back and forth while riding on the car.

Patents showing mechanical wheel positioners are: U.S. Pat. Nos. 2,714,255; 2,687,546; 2,654,112; 2,799,514; 3,353,218; 3,518,714.

It is an object of the invention to provide an improved caster wheel for a vehicle.

Another object of the invention is to provide a caster wheel which is simple in construction, economical to manufacture and simple and efficient to use.

With the above and other objects in view, the present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawing and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.

FIG. 1 is a side view of the vehicle according to the invention.

FIG. 2 is a view of the caster taken on line 2--2 of FIG. 1.

FIG. 3 is a cross-sectional view taken on line 3--3 of FIG. 1.

FIG. 4 is a cross-sectional view taken on line 4--4 of FIG. 1.

FIG. 5 is a cross-sectional schematic view showing the magnetic circuit.

FIG. 6 is a diagramatic view of the magnetic field of the magnets.

Now, with more particular reference to the drawing, the vehicle generally indicated at 10 has caster wheels 11 which are supported on caster forks 12. Caster forks 12 have spaced legs 13 and 14 connected together by fork bracket 15, and axle 17 extends through suitable openings in the lower end of the legs. Axle 17 is held in place by suitable nuts connecting said legs and rotatably receiving the wheels 11. The fork 12 is pivotally connected at 18 by a suitable pivotal member, familiar to those skilled in the art, connecting the fork bracket top 15 to the top bearing plate 16. A first permanent magnet 19 is fixed to the fork bracket top 15 at a position spaced from the pivot member 18, and a second permanent magnet 20 is fixed to the bearing plate 16 at positions spaced from the pivot means. A third permanent magnet 21 is fixed to the bearing plate 16 on the side of the pivot 18, opposite the magnet 20. The magnets 20 and 21 are so oriented that their fields project a field, FIGS. 1 and 2, downward, and the field (FIG. 6) of magnet 19 is disposed in the influence of this field and is urged to align itself in desired position when the vehicle is lifted from the floor, as when it is being carried by another vehicle.

The magnets are preferably of the barium ferrite type or other ceramic magnets may be used. However, metallic magnets such as Alnico mgnets could be used in this invention. The bearing plate 16, being made of iron, acts as an armature for magnets 20 and 21, since the magnet 19 is in the external field between magnet elements 20 and 21. Magnet 19 is urged toward the magnet having the opposite external polarity, in this case being magnet 20 or 21. This magnetic force on magnet 19 is sufficient to swing the caster wheel about its pivot when it is lifted off the floor. However, when the vehicle is lowered back to the floor, the caster wheel will follow the direction of driving force exerted on the vehicle. Therefore, the magnets disclosed herein do not interfere with the normal operation of the vehicle.

The magnets 19 are attached to the frame 10 and the magnets 20 and 21 are attached to the fork bracket 15 by sheets of foam plastic material 24, the foam plastic material having adhesive on each side. The sheets of foam material may be, e.g, 1/32 inches thick and may have a suitable darometer, tensile strength and sheer strength suitable to hold the magnets in position when they are adjacent each other; the sheer strength sufficient to withstand the force exerted by the magnets on each other to rotate the caster about its axis.

The foam material darometer will be such that it will compensate for any stress between the magnets and the member on which it is supported to prevent the brittle ceramic material from being broken.

When the magnets are in position, one over the other, they are spaced from each other a substantial distance, which may be e.g. approximately 1/8.

Since the magnetic force of permanent magnets increases rapidly as the magnets approach each other, by spacing the magnets from each other, a considerably better action between the caster and its frame results than if the magnets came into contact with each other when in their home position.

The foregoing specification sets forth the invention in its preferred, practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention which is to be understood is broadly novel as is commensurate with the appended claims.