2. Description of the Related Art Machinery is required and designed to move in many different directions, e. g., rotational movement and lateral movement. Bearing design has evolved to a point which permits relatively frictionless rotational and lateral movement of machinery, such as, for example, bearings relative to shafts. However, in some applications, a need exists for a piece of machinery (e. g., a load carrying bearing) to move in a lateral direction along a longitudinal axis of a shaft while minimizing rotational movement of the bearing relative to the shaft. Typical bearings used for a lateral movement are incapable of affecting rotational movement relative to the shaft. Thus, a need exists for a device which may be used alone or in conjunction with such a bearing to permit unrestricted lateral motion of a bearing relative to a shaft while restricting rotational motion of the bearing relative to the shaft.

SUMMARY OF THE INVENTION It is an object of the present invention to provide anti-rotation apparatus to restrict or inhibit rotational movement of a load bearing member relative to a shaft or cylinder while allowing unrestricted linear motion of the member along the longitudinal

axis of the shaft or cylinder. The apparatus may advantageously be used in conjunction with linear motion type bearings.

An embodiment of the anti-rotation apparatus in accordance with the present disclosure includes a housing, at least one locking element and a locking element retainer. The housing has a longitudinal bore therethrough for receiving the locking element (s) and the locking element retainer. The locking element retainer defines an inner longitudinal bore configured and dimensioned to receive a shaft. The locking element (s) are disposed adjacent the shaft and, in a preferred embodiment, a plurality of locking elements are symmetrically disposed around a central axis of the shaft within the housing and are pivotally retained about a central portion of each element by the locking element retainer. Preferably, the locking elements and retainer generally combine to form a cam clutch insert within the housing to limit rotational motion of the housing relative to the shaft while permitting linear motion of the housing along the length of the shaft. In a preferred embodiment, each of the individual locking elements are formed in the shape of asymmetrical cam plates.

In an alternative embodiment, two or more retainers containing locking elements are provided within a housing. The locking elements in each of the retainers may have a common orientation or they may alternate.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference is made to the following description of exemplary embodiments thereof, and to the accompanying drawings, wherein: FIG. 1 is a cross-sectional end view of an anti-rotation apparatus in accordance with an embodiment of the present disclosure; FIG. 2 is a side view in cross-section of an anti-rotation apparatus in accordance with another embodiment of the present disclosure; and FIG. 3 is an enlarged view of a single locking element of the anti-rotation apparatus in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to FIG. 1, an anti-rotation apparatus 10 in accordance with the present disclosure is illustrated. Anti-rotation apparatus 10 generally includes a housing 12, a plurality of locking elements 14 and a locking element retainer 16. The entire assembly may be used in conjunction with a linear motion bearing (not shown) such as the linear motion bearing assembly disclosed in U. S. Patent No. 5,558,442 to NG, the entire disclosure of which is incorporated by reference herein. Anti-rotation apparatus 10 may be mounted on a shaft 18, to limit or restrict the rotational movement of apparatus 10 relative to shaft 18 in either direction without limiting linear motion of apparatus 10 along the longitudinal axis of shaft 18. In particular, apparatus 10 is provided to restrict

rotational movement of a bearing associated with apparatus 10 where the rotational force applied to apparatus 10 is substantially less than the prevailing applied longitudinal force.

Housing 12 has a longitudinal bore 13 therethrough for receiving the plurality of locking elements 14 and locking element retainer 16. Housing 12 is illustrated having a substantially square outside configuration in cross-section, corresponding to a cube-shaped housing. However, it is contemplated that housing 12 may also be configured as a cylinder or any other suitable configuration to fit a particular application or other design criteria. It is further contemplated that locking elements 14 can be either individually installed or monolithically formed as a single unitary element.

As shown in FIG. 1, locking element retainer 16 defines an inner longitudinal bore 17 configured and dimensioned to receive shaft 18. Shaft 18 is illustrated having a solid cylindrical shape. However, it is contemplated that a hollow tubular shaped shaft may also be used. It is also contemplated that shaft 18 may be a spline shaft or some other configuration. In such a case, anti-rotation apparatus 10 may be modified accordingly.

Locking elements 14 are disposed around a central axis of shaft 18 within housing 12 and are pivotally retained within retainer 16. Locking elements 14 and retainer 16 combine to form a cam clutch insert within housing 12 to which functions restrict rotational motion of housing 12 relative to shaft 18 while permitting linear motion of housing 12 along the length or longitudinal axis of shaft 18. As illustrated in FIGS. 1 and 3, and as discussed in detail hereinbelow, each of the individual locking elements 14

are formed in the shape of asymmetrical cam plates. Generally, as shaft 18 is subjected to a torque (clockwise or counterclockwise) causing it to rotate, ends of locking elements 14 contact shaft 18 thereby pivoting each element 14 about its central portion and create a friction force between housing 12 and shaft 18. Eventually, the locking element 14 will be rotated to the point where the normal force exerted by the locking elements will become so great that the friction force between shaft 18 and locking elements 14 will exceed the rotational force exerted by the external torque applied to shaft 18, and shaft 18 will not rotate.

Referring for the moment to FIG. 3, one side of the locking element 14 has a larger camming surface than the other. Specifically, in a preferred application, locking element 12 has an overall length OL of approximately 3 to 6 millimeters ("mm") and preferably 4.0 +/-0. 1 mm. Locking element 14 includes a head portion 21 having a preferred length HL of approximately 2.33 mm and a tail portion 23 having a length of TL of approximately 1.75 mm. Generally, the ratio of OL to HL is about 2.3 to 1.0.

However, the ratio may be from about 1.0 to 1.0 up to about 5.0 to 1.0. Head portion 21 and tail portion 23 meet to define a waist W. As shown, retainer 16 contacts W on a first side 25.

An opposite side 27 of waist W has an offset area O which allows element 14 to pivot within a predetermined area within retainer 16. O is preferable approximately 0.31 mm. Head portion 21 has a preferred width HW of about 2.40 +/-0. 03 mm. and tail portion 23 has a preferred width TW of about 1.59 +/-0. 03 mm. The recited dimensions

are for a preferred embodiment. It is contemplated that other sizes of locking elements may be provided depending on particular applications. Additionally, the ratios of the sizes of the locking element portions may be adjusted accordingly.

Head portion 21 includes two radiused surfaces, i. e. a camming surface 29 having a preferred radius RC of about 2.20 mm and a release or clearance surface 30 having a substantially smaller radius RS. Tail portion 23 has a contact portion 31 with a radius RT of about 2.15 mm. A radius RW of approximately 1.22 mm is provided adjacent side 27 of waist W.

With continued reference to FIG. 3, when a shaft is positioned adjacent head portion 21 of a locking element 14 and is rotated in, for example, a counterclockwise direction, the shaft causes locking element 14 to pivot about waist W in a clockwise direction bringing clearance surface 30 adjacent the shaft. Radius RS is sufficiently small so as to allow clearance surface 30 to clear or drag on the shaft and allow the shaft to rotate in the counterclockwise direction. However, should a shaft be rotated in a clockwise direction, it will cause locking element 14 to be rotated about waist W in a counterclockwise direction. As locking element 14 rotates counterclockwise, the larger Radius RC brings camming surface 29 into frictional engagement with the shaft thereby camming the shaft against any further rotation.

In order to inhibit rotation in both directions, it is preferable that each adjacent locking element 14 be placed within locking element retainer 16 in a fashion so

as to alternate the position of the camming surfaces 29, thereby preventing rotation of shaft 18 in both the clockwise and counterclockwise directions.

Locking elements 14 have a surface finish at the contact area which is a maximum of approximately 0.0004 millimeters Center Line Average (CLA) and are preferably formed of 52100 or AISI 1075 material (i. e., bearing steel containing nickel and chromium with high carbon). All radii on locking elements 14 are in the range of approximately 0.05 inches to approximately 0.5 inches, and are preferably 0.2 inches.

In an alternative embodiment, two rings of locking elements 14 may be placed adjacent to each other as illustrated in FIG. 2. In this embodiment, all of the locking elements 14 in a first ring 35 have a common orientation while all of the elements 14 in an adjacent second ring 37 have an orientation 180 opposite than that of the locking elements 14 in the first ring 35. Alternatively, the individual locking elements 14 in each ring may alternate as discussed above and provide for an increased friction force on shaft 18.

With continued reference to FIG. 2, locking elements 14 and retainer 16 are illustrated in the form of a cam clutch type insert assembly which is fitted within housing 12. The cam clutch type insert generally comprises a cylindrical ring 22, two sets of locking elements 14, locking element spacers 24 and a cylindrical locking element retainer 16 for each set of locking elements 14. The insert is secured within housing 12 by locking ring 20 which is fitted within an open end of housing 12. Locking ring 20

may engage housing 12 by an interference fit or it may be affixed thereto by epoxy, welding or any other suitable means known to one having ordinary skill in the art.

Cylindrical ring 22 is configured and dimensioned to fit within the longitudinal bore in housing 12. Three locking element spacers 24 are disposed in the three circumferential grooves formed in an inner surface of cylindrical ring 22 to maintain locking elements 14 in proper alignment about shaft 18. This may assist in elimination of movement or chatter between elements 14 and housing 12 as a bearing moves longitudinally relative to shaft 18.

As discussed above, rotation of housing 12 relative to shaft 18 will cause locking elements 14 to rotate and restrict housing 12 from rotating by virtue of the camming action of elements 14. However, lateral movement of housing 12 along shaft 18 along its longitudinal axis will not be significantly inhibited. Rather, during lateral movement thereof, locking elements 14 will slide or slightly drag relative to shaft 18.

An exemplary application of the anti-rotation apparatus of the present disclosure may be appreciated with regard to material handling applications. In such applications (i. e., pick and place material handling applications), it is desired that the piston rods move laterally along the longitudinal axis of the rods without any rotation of the rods.

Although the non-rotational linear shaft assembly of the present disclosure has been described with reference to an application for restricting rotational motion of a shaft, it is contemplated that it may be utilized in any application having a cylinder or

shaft wherein it is desired that the cylinder or shaft does not rotate while at the same time allowing for lateral motion of the cylinder or shaft. In the cylinder application, however, the locking elements must be rotated 180° from the position illustrated and described above with respect to the shaft application. When the locking elements are rotated 180 °, they will be properly situated to restrict the cylinder, rather than the shaft, from rotating.

Although the illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention.