Background of the Present Invention

Dual wheel casters have gained considerable success over the last decade because of their greater load carrying capa¬ city compared to single wheel casters. This greater load carrying capacity permits the caster components to be made from less expensive materials than were required in single wheel caster assemblies. Dual wheel casters have also gained considerable success in supporting costly data processing equipment not primarily as a result of the relatively low cost of the caster, but because of the increased mobility of the equipment that results from the use of the dual wheel caster design.

Because any caster assembly raises the supported article a significant .distance from the floor, there is a possibility that the supported article will tip over when encountering a . rigid obstruction even at relatively low speeds, i.e. less than 3.6 miles per hour. Because the cost of data process¬ ing equipment is of course considerable, it has been found desirable to reduce or eliminate the possibility of the equip- ment tipping over upon encountering rigid obstructions of certain heights. Standard testing has indicated that there is a likelihood of the equipment tipping over when the forward casters encounter a fixed obstruction of 1.181 inch high or one-half- the diameter of the wheel at a speed of 3.6 miles per hour. For this reason an arbitrary "standard" has been set in certain phases of the data processing industry, for the design of caster assemblies that will not tip the support¬ ed equipment when the forward casters strike a 1.181 inch high or one-half the diameter of the wheel high fixed angle iron on the floor at a speed of 3.6 miles per hour.

One such prior caster design for achieving this result includes a "nose" projecting forwardly from the caster that has an upwardly inclined lower surface of approximately 20 degrees. As this "nose" strikes the one and a half inch angle

iron, the lower surface of the nose slides up the angle iron raising the forward casters and the front of the supported article and this limits the forward tipping movement of the rear end of the equipment to approximately one foot and it merely bounces back to the floor.

This prior caster assembly only rides part way up the obstruction and not completely over the obstruction. It is desirable that for certain lower obstructions, that a caster assembly be designed to pass completely over the obstruction and this is the primary object of the present invention.

Summary of the Present Invention

In accordance with the present invention, a dual wheel caster assembly is provided with a forward "nose" having a flat angular slide surface for riding up on relatively large obstructions to reduce tipping of the supported article and also is provided with an integral arcuate projection that engages and guides the caster assembly and supported article completely over relatively smaller obstructions such as door sills. Toward this end the caster assembly includes a central horn that carries an axle supporting wheel assemblies on either side of the horn for free rotational movement. A pintle assembly is mounted in the horn offset from the axis of the wheels to accommodate free swivelling movement of the caster. The pintle assembly includes a ball bearing assembly at its upper end having a hardened steel ball cup to increase the mobility of the caster and it has a straight locking pin re¬ ceived in a recess on the lower end of the pintle to positively prevent the pintle from becoming disengaged from the horn when the caster strikes an obstruction.

The horn has an enlarged integral "nose" projecting in the normal forward direction of movement of the caster that has a lower flat surface extending upwardly away from the wheel assembly at an angle of approximately 22 degrees. This flat

inclined surface is adapted to engage obstructions having a height somewhat less than or greater than the radius of the caster and ride-up on the obstruction a limited distance, depending upon the forward speed of the supported equipment to prevent the supported article from tipping. The "nose" of the pintle also includes an arcuate surface directly adjacent the forward area of the wheels that engages floor obstructions substantially less than the radius of the wheel assembly and rides up and over these obstructions to guide the caster assembly and the supported equipment thereover.

Thus the horn assembly according to the present inventon includes a high ramp for riding up but not over large projec¬ tions to reduce the likelihood of tipping the supported equip¬ ment and includes a second integral arcuate projection to assist the caster in riding up and over somewhat lower pro¬ jections that would otherwise possibly cause tipping of the equipment at sufficient speeds.

Brief Description of the Drawings

Fig. 1 is a perspective view of the present caster assembly;

Fig. 2 is a side view, partly in section, of the caster assembly illustrated in Fig. 1;

Fig. 3 is a front view of the caster assembly illustrated in Fig. 2; Fig. 4 is a top plan view of the caster assembly illus¬ trated in Fig. 2;

Fig. 5 is a rear view of the caster assembly illustrated in Fig. 2; -

Fig. 6 is an enlarged fragmentary section taken generally along line 6-6 of Fig. 4 illustrating the pintle assembly;

Fig. 7 is a fragmentary section taken generally along line 7-7 of Fig. 6;

Fig. 8 is a fragmentary section taken generally along line 8-8 of Fig. 6;

Fig. 9 is a schematic dynamic illustration of the present caster assembly in two positions as it encounters a fixed one and a half inch angle iron; and

Fig. 10 is a schematic dynamic illustration of the pre- sent caster assembly as it encounters a door sill.

Detailed Description of the Preferred Embodiment

Referring to the drawings, and particularly Figs. 1 to 4, the present dual wheel caster assembly 10 is seen to gene¬ rally include an integral horn 11 carrying an axle 12 that rotatably supports wheels 14 and 15 and a pintle assembly 16. Both the horn 11 and the wheels 14 and 15 may be constructed of an impact resistant plastic although in some cases the horn 11 may be die cast of a metal such as zinc.

As seen in Figs. 2, 4 and 5, the horn 11 has an arcuate segment 17 extending between the wheels 14 and 15, having a radius slightly greater, than the radius of the outer diameter of the wheels. ^• The arcuate segment 17 includes a relatively wide outer rim 18 having an end 19 spaced from the floor that connects with an ^' equal width lower rim 20 extending horizon- tally forwardly from rim 18. The rims 18 and 20 are supported by a relatively narrow web portion 22 that connects to a ver¬ tical shoulder 23 on the main body portion of the horn. The horn 11 has a U-shaped lug portion 26 having a width slightly less than the width of the rim 18 with a bore 27 therethrough that receives the axle 12. The axle 12 has a splined central portion (not shown in the drawings) that non-ro a ably mounts the axle in bore 27.

As seen in Figs. 6, 7 and 8, the pintle assembly 16 in¬ cludes a vertical pintle 28 rotatably mounted in a stepped bore 29 on the upper surface of the horn 11 by an annular array of ball bearings 30. Pintle 28 includes an annular thrust flange 31 having a lower surface 32 that engages ball bearings 30 to absorb the axial thrust transmitted between the supported

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article and the caster while at the same time permitting free swivelling movement of the caster in horn 11 with respect to the pintle 28. Ball bearings 30 are mounted in a hardened steel cup 32a to significantly increase the load carrying ca- pacity and mobility of the entire caster assembly.

Pintle 28 has a lower stem 33 with an annular semi- toroidal recess 34 that receives a straight removable lock¬ ing pin 35 that positively locks the pintle 28 within the horn 11. Pin 35 as seen in Fig. 8 is mounted in a through bore 37 in the horn (also see Fig. 2). The pin 35 prevents the horn 11 from separating from the pintle 28 particularly when the supported article abruptly strikes an obstruction and the supported equipment bounces off the floor.

The vertical axis of the pintle assembly 16 is spaced laterally from the axis of the axle 12 as viewed in Fig. 2 so that the normal forward direction of the caster assembly would be to the right as viewed in Fig. 2.

As seen most clearly in Figs. 1 to 4, the horn member 11 has a forwardly projecting integral projection or "nose" 38 having a flat horizontal upper surface 39, a semi-cylin¬ drical forward surface 40, a flat upwardly extending slide surface 41, and parallel side surfaces 43 and 44. Each of the side surfaces 43 and 44 has large recesses 46 and 47 in the sides thereof separated by centrally disposed integral webs 48 and 49 as seen in Figs. 1, 2 and 4.

The slide surface 41 extends at an angle of 22 degrees with respect to a horizontal plane and extends vertically a distance of approximately one-third the radius of the wheels 14 and 15 both below the axis of axle 12 and above the axis of axle 12. If wheels 14 and 15 have a diameter of 60 millimeters, for example, this relationship of surface 41 will result in a one and a half inch angle iron (see Fig. 9) striking the slide surface 41 a short distance below its upper or forwardly most end. As explained below the slide

surface 41 serves to raise the forward caster assemblies 10 (assuming the article is supported by four casters) and the forward end of the supported article upwardly a short distance when striking relatively high fixed obstructions to prevent the supported article from tipping over.

The lower surface of the projection or "nose" 38 has an arcuate projection 50, having a radius ■approximately equal to the radius of the wheels 14 and 15 about an axis 51, immedia¬ tely below and adjacent to the connected surface 41 at its forward end, and connected to a flat lower horizontal surface 52 on the horn 11 at its other end.

Fig. 9 illustrates the manner of operation of the caster 10 in encountering a high fixed obstruction, namely a fixed one and one-half inch angle iron 60 bolted to the floor. The one and one-half inch angle iron is used as part of a standard anti-tipping test procedure ^* adopted by some data processing equipment manufacturers. A conventional caster will cause complete forward tipping of the supported article when striking a one and one-half inch angle iron at three miles per hour. It should be understood that the casters illustrated are posi¬ tioned in pairs at the front and rear of a supported piece of equipment 61 with the casters illustrated in Fig. 9 being the forward casters as they encounter the obstruction or angle iron 60. The solid line position of the caster 10 in Fig. 9 occurs at the point of initial impact of the slide surface

41 with the top of the angle iron 60. The supported article travels toward the angle iron at a standard test speed of three miles per hour. After impact, the caster 10 and parti¬ cularly surface 41 slides upwardly and forwardly on the upper surface of the angle iron 60, causing the entire caster and the supported article 61 to raise up approximately one inch (less at lower forward speeds) . This causes a deceleration of the supported article 61 at a lower rate than conventional casters and prevents the entire piece of equipment 61 from tipping over in a forward or clockwise direct-ion in Fig. 9.

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The rear end of the article 61 merely bounces up in the air a short distance and then returns to the floor.

Fig. 10 illustrates the manner of operation of the caster 10 when encountering an obstruction significantly less than the radius of the wheels 14 and 15, such as a door sill 63 having tapered side surfaces 64 and 65. The solid line position of the caster 10 shown in Fig. 10 is at the point of impact of the horn 11 and particularly arcuate "bumper" projection's 50 engagement with surface 64 on the door sill 63. After impact the surface 50 rides upwardly and forwardly on the sill 63 causing the wheels 14 and 15 along with the entire caster and supported article to be raised upwardly prior to the time the wheels 14 and 15 engage the sill 63, so that the wheels only have to ride over a smaller portion of the vertical height of sill 63. The wheels 14 and 15 climb the remaining portion of the sill 63 after engagement by rolling motion and the caster can thereby easily pass over the sill 63 without any tipping of the supported equipment 61.