Patent Document

TECHNICAL FIELD 
     The invention relates generally to the field of casters for movably supporting objects and, in particular, casters that can be locked to prevent the caster wheel from rotating about its running axis (wheel braking) and/or from turning about its swivel axis. 
     BACKGROUND ART 
     A swivel lock for a caster helps to maintain directional control (tracking) of an object that it supports, such as a cart, while the object is being moved. A wheel brake keeps the supported object from rolling unintentionally. Total locking of the caster (wheel brake and swivel lock) is the most stable condition, preventing all rolling and swiveling movement. Examples of both are disclosed in U.S. Pat. No. 4,035,864; U.S. Pat. No. 4,835,815; U.S. Pat. No. 4,205,413; U.S. Pat. No. 3,571,842; U.S. Pat. No. 4,349,937; and U.S. Pat. No. 6,725,501, to name a few. 
     SUMMARY DISCLOSURE OF THE INVENTION 
     The present invention is directed to a unique and improved caster having directional and total locking capabilities. From one perspective, the invention is directed to a lockable caster comprising a mounting member adapted to be connected to a load to be supported by the caster; a yoke, comprising two depending legs interconnected by an upper bight portion, pivotally connected to the mounting member for relative pivotal movement about a swivel axis; a wheel mounted between the legs of the yoke for rotation about a running axis; and a locking structure between the legs of the yoke adjacent the bight portion and fixed relative to the mounting member. The locking structure comprises recesses spaced so as to at least partially surround the swivel axis. A total lock mechanism is carried by the yoke and comprises a movable brake member adapted to engage the wheel to lock it against rotation, and a movable total lock tooth configured to engage any of a plurality of the recesses to lock the yoke against pivotal movement about the swivel axis in any of a plurality of total lock positions. A directional lock mechanism is carried by the yoke and comprises a movable directional lock tooth adapted to engage at least one of the recesses to lock the yoke against pivotal movement about the swivel axis in at least one directional lock (tracking) position while allowing the wheel to rotate. The number of directional lock positions is fewer than the number of total lock positions. 
     In a preferred arrangement, all of the recesses may be coplanar, and all may lie along a circle centered on the swivel axis. For example, the locking structure may comprise a lower ball retainer of a pivot bearing assembly, and the recesses may be located at the periphery of the lower ball retainer. The directional lock tooth preferably is wider than the total lock tooth; at least one of the recesses is a directional lock recess having a width sized to accommodate the directional lock tooth; and the other recesses are equal-width total lock recesses that are equally spaced on either side of the directional lock recess(es) and are sized to accommodate the total lock tooth but not the directional lock tooth. The number of recesses engageable by the directional lock tooth preferably is fewer than the number of recesses engageable by the total lock tooth. Further, the total lock tooth preferably comprises at least two tines spaced such that each tine can engage a total lock recess, the overall width of the plurality of tines being equal to the width of the directional lock tooth so that the total lock tooth can also engage a directional lock recess. Preferably there are two diametrically opposed directional lock recesses. 
     The total lock mechanism preferably comprises a total lock lever pivoted intermediate its ends to the yoke, with the brake member and the total lock tooth at opposite ends of the total lock lever. The directional lock mechanism preferably comprises a directional lock lever pivoted intermediate its ends to the yoke, with the directional lock tooth at one end of the directional lock lever. The total lock lever and the directional lock lever preferably are arranged side-by-side, with both pivoted to the yoke about a common pivot axis. The brake member preferably is canted toward the medial plane of the wheel so as to be engageable with the outer circumference of the wheel. 
     Each of the lock mechanisms preferably is spring-biased away from a locked state and comprises an expanding over-center toggle mechanism pivoted to the yoke for moving the lock mechanism against the spring bias into a locked state. Each toggle mechanism preferably comprises a four-bar linkage, one link of the toggle mechanism being pivoted to its respective lock lever remote from its toothed end and having an extension forming an operating pedal for moving the lock mechanism into a locked state. The operating pedals of the toggle mechanisms preferably are arranged side-by-side, with a common release pedal pivoted to the yoke above the operating pedals and linked to each toggle mechanism for releasing either or both of the lock mechanisms from a locked state. 
     From another perspective, the invention is directed to a lockable caster comprising a mounting member adapted to be connected to a load to be supported by the caster; a yoke, comprising two depending legs interconnected by an upper bight portion, pivotally connected to the mounting member for relative pivotal movement about a swivel axis; a wheel mounted between the legs of the yoke for rotation about a running axis; and a locking structure between the legs of the yoke adjacent the bight portion and fixed relative to the mounting member. The locking structure preferably comprises coplanar recesses spaced along a circle centered on the swivel axis, at least one of the recesses being a directional lock recess, and a greater number of other recesses being total lock recesses, which are configured differently from the directional lock recess. A total lock mechanism carried by the yoke comprises a movable brake member configured to engage the wheel to lock it against rotation, and a movable total lock tooth configured to engage any of the total lock recesses and any of the directional lock recesses to lock the yoke against pivotal movement about the swivel axis in any of a plurality of total lock positions. A directional lock mechanism is carried by the yoke and comprises a movable directional lock tooth configured to engage only the directional lock recesses to lock the yoke against pivotal movement about the swivel axis in at least one directional lock (tracking) position while allowing the wheel to rotate. 
     In a preferred arrangement, the total lock tooth is at one end of a total lock lever, and the directional lock tooth is at one end of a directional lock lever. The two lock levers preferably are arranged side-by-side with their toothed ends adjacent each other. 
     Further features, aspects and advantages of the invention will become apparent from the following detailed description of preferred embodiments, including the best mode for carrying out the invention, when considered together with the accompanying figures of drawing. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of one example of a locking caster according to the invention. 
         FIG. 2  is a front elevational view of the caster of  FIG. 1 . 
         FIG. 3  is a left side elevational view of the caster of  FIG. 1 . 
         FIG. 4  is an exploded view of the caster of  FIG. 1 , showing details of the lock mechanisms. 
         FIG. 5  is a partially exploded perspective view of the caster of  FIG. 1 , with some parts removed, showing how the lock mechanisms interface with the lock recesses. 
         FIG. 6  is a partially exploded perspective view of the lock mechanisms of the caster of  FIG. 1 , from an opposite viewpoint. 
         FIG. 7  is a cross-sectional view taken along line  7 - 7  in  FIG. 2 , with most of the yoke removed, showing the relationship among the total lock mechanism, the lock recesses and the wheel. 
         FIG. 8  is a bottom plan view of the caster of  FIG. 1 , with the wheel removed, showing the relationship of the lock mechanisms to the lock recesses. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , a locking caster  2  according to the invention comprises a mounting member in the form of a plate  4  having four elongated holes  6  through which bolts, screws or other suitable fasteners can be installed to attach the caster to a load to be movably supported. A yoke  8  is connected to the plate  4  for relative pivotal movement about a swivel axis  10  by means of a pivot bearing assembly  12  and a rivet  14  or other suitable fastener. The yoke has depending legs  16  between which a ground-engaging wheel  18  is mounted for rotation about a running axis  20  by means of an axle  22 , which extends through aligned holes in the legs  16  and through bearings in the wheel, secured by a locknut  24 . The legs  16  are interconnected by an upper bight portion  26 . Also visible in these figures are a total lock operating pedal  28 , a directional lock operating pedal  30 , and a common release pedal  32 , all of which are parts of the lock mechanisms described below. 
     Referring to  FIGS. 4-8 , two side-by-side lock mechanisms  40 ,  60  are carried by the yoke  8  and are selectively engageable with various recesses R formed by and between teeth  15  on the lower ball retainer  13  of pivot bearing assembly  12 . Lower ball retainer  13  is fixed relative to plate  4 . Teeth  15  and recesses R thus form a locking structure that is fixed (stationary) in relation to plate  4 . One of the lock mechanisms is a total lock mechanism  40 , which comprises a total lock lever  42  pivoted intermediate its ends to the yoke  8  about a pivot rod  34 , which is secured to the legs  16  through holes  36 . Lever  42  preferably is made of spring steel and has a projecting central tab  44 , which is flanked by curved shoulders  46 . Resilient tab  44  and shoulders  46  embrace pivot rod  34 , with the tip of tab  44  trapped against the underside of bight portion  26  (see  FIG. 7 ) to bias total lock lever  42  toward an unlocked position (counterclockwise as seen in  FIG. 7 ). Although shown passing beneath pivot rod  34 , for easier assembly tab  44  alternatively could be configured to pass above rod  34  and still perform its biasing function. 
     The front (lower) end of lock lever  42  has a brake member  50  that is canted toward the medial plane  38  of the wheel  18  so as to overlie the center of the wheel tread. Brake member  50  has braking elements on its underside in the form of ribs  52  that grip the wheel tread when in a locked condition. Other types of braking elements or surfaces may be employed, depending at least in part on the type of wheel tread used. The opposite (rear) end of total lock lever  42  has a total lock tooth structure  54  in the form of two tines  56  shaped and arranged along an arc that conforms to the arc along which teeth  15  of lower ball retainer  13  are arranged. 
     The other lock mechanism is a directional lock mechanism  60 , which comprises a directional lock lever  62  that is similar in many respects to total lock lever  42 . Directional lock lever  62  also preferably is made of spring steel, is pivoted intermediate its ends to the yoke  8  about pivot rod  34 , and has a projecting central tab  65 , which is flanked by curved shoulders  66 . Resilient tab  65  and shoulders  66  embrace pivot rod  34 , with the tip of tab  65  trapped against the underside of bight portion  26  to bias directional lock lever  62  toward an unlocked position (counterclockwise with reference to  FIG. 7 ). Although shown passing beneath pivot rod  34 , for easier assembly tab  65  alternatively could be configured to pass above rod  34  and still perform its biasing function. The rear end of directional lock lever  62  has a directional lock tooth structure in the form of a single tooth  64  shaped and arranged along an arc that conforms to the arc along which teeth  15  of lower ball retainer  13  are arranged. 
     Referring to  FIG. 8 , the swivel locking relationship that involves recesses R on lower ball retainer  13 , directional lock tooth  64  and total lock tooth  54  (tines  56 ) will now be explained. The recesses R on lower ball retainer  13  are of two different sizes, all formed by teeth  15 : fourteen narrow, equal-width total lock recesses  72 , and two wider, equal-width and diametrically opposed directional lock recesses  74 . All are arranged in a circle centered on swivel axis  10 . Total lock recesses  72  are equally spaced on either side of each of the directional lock recesses  74 . The angular offsets of adjacent teeth  15  are as follows: 
                                                 teeth 15 that form total lock recesses 72:   20 degrees;           teeth 15 that form directional lock recesses 74:   40 degrees.                        
Thus, the space between alternate teeth  15  that form the total lock recesses  72  is equal to the width of each directional lock recess.
 
     Directional lock tooth  64  is sized to fit into (engage) only a directional lock recess  74 ; it is too wide to engage any total lock recess  72 . The tines  56  of total lock tooth  54  are sized and spaced to fit into (engage) any adjacent pair of total lock recesses  72 ; or one tine  56  can engage a single total lock recess  72  adjacent a directional lock recess  74 , with the other tine residing in that directional lock recess  74 . The pair of tines  56  together have an overall width that is equal to the width of the directional lock tooth  64 ; therefore, the total lock tooth  54  can also fit into (engage) either of the directional lock recesses  74 . Accordingly, total locking can be effected in any of eighteen swivel positions, equally spaced by 20 degrees. On the other hand, directional locking in a tracking position can be effected in only two swivel positions (with the directional lock tooth  64  engaging a directional lock recesses  74 ); and because those positions are diametrically opposed, the plane of rotation of the wheel  18  when so locked is the same regardless of which directional lock recess  74  is engaged. 
     Upward (locking) movement of the rear toothed end of each of the lock levers  42 ,  62  to engage recesses R is effected through separate but similar expanding toggle mechanisms, each comprising a four-bar, over-center linkage. Depressing common release pedal  32  (labeled “OFF”) unlocks either or both of the lock mechanisms, i.e., lowers the toothed end(s) of the lock lever(s) out of engagement with recesses R. Both toggle mechanisms are pivotally linked to the legs  16  of the yoke by a common pivot rod  86 , about which common release pedal  32  also pivots. Each toggle mechanism includes its respective lock lever  42 ,  62 , which is pivotally linked by an individual pivot pin  82  held in a pair of upturned ears  84  at the front (lower) end of the lock lever. Each toggle mechanism further includes the rear extension  88  of its respective lock operating pedal  28 ,  30 , and a cam link  90  individually linked to its respective pedal extension by a pivot pin  92  and nestled in a recess  33  in common release pedal  32 . The upper end of cam link  90  is pivoted to the legs  16  by common pivot rod  86 . Thus, the four “bars” of each linkage are: the yoke  8  (leg(s)  16 ); the lock lever ( 42 ,  62 ) from pivot rod  34  to pivot pin  82 ; the rear extension  88  of the lock operating pedal ( 28 ,  30 ) from pivot pin  82  to pivot pin  92 ; and the cam link  90  from pivot pin  92  to pivot rod  86 . 
     The sectional view of  FIG. 7  shows in broken lines the locked positions of the components of one of the lock mechanisms. When the lock operating pedal ( 28 ,  30 ) is depressed, the rear extension  88  of the lock operating pedal and the cam link  90  expand the distance between pivot rod  86  and pivot pin  82 , forcing the front end of the lock lever ( 42 ,  62 ) downwardly so that the lock lever pivots about pivot rod  34 , raising the opposite (rear) end of the lock lever toward the lower ball retainer  13  and its recesses R. The lock operating pedal rear extension  88  and the cam link  90  are dimensioned such that an over-center latching effect is achieved, whereby the lock operating pedal ( 28 ,  30 ) snaps downwardly near the end of its travel and remains there. At the same time, a front extension  94  on cam link  90  raises common release pedal  32 . When the common release pedal  32  is in this position and is depressed, it forces the cam link  90  to rotate downwardly, raising the front end of the lock lever ( 42 ,  62 ), lowering the opposite (rear) end away from the lower ball retainer  13  and its recesses R, and raising the lock operating pedal ( 28 ,  30 ). 
     When the total lock operating pedal  28  is depressed, if the tines  56  of resilient total lock lever  42  are not aligned with any of the recesses  72 ,  74 , slight pivoting of the yoke and wheel (less than 20 degrees) about the swivel axis  10  will allow them to snap into engagement with one or more nearby recesses to effect total locking. When the directional lock operating pedal  30  is depressed, if the tooth  64  of the resilient directional lock lever  62  is not aligned with a directional lock recess  74 , pivoting of the yoke and wheel by less than 180 degrees about the swivel axis  10  will allow tooth  64  to snap into engagement with one of the directional lock recesses  74  to effect directional locking. Of course, if the yoke and wheel are pivoted in a direction that moves the tooth  64  toward the nearer directional lock recess  74 , locking will be accomplished by swiveling the yoke and wheel less than 90 degrees. 
     The above-described arrangement of recesses R on stationary lower ball retainer  13  is exemplary only, and it is envisioned that the invention may encompass many variants. For example, it may be desirable to be able to lock the wheel directionally in one of two (or even more) planes of rotation (tracking positions), in which case an additional pair of diametrically opposed directional lock recesses  74  may be formed on lower ball retainer  13 , e.g., displaced 90 degrees from the first pair. Alternatively, instead of forming the directional lock recesses in diametrically opposed pairs, individual directional lock recesses  74  may be formed at positions on lower ball retainer  13  that are not diametrically opposed to one another. Further, a different number of total lock recesses  72  may be formed on lower ball retainer  13 , depending on the size of the caster and/or the requirements of the particular caster application, the sizes of the recesses and the lock teeth being adjusted accordingly. In a further variant, the recesses may be formed on a stationary plate fixed below and coaxial with lower ball retainer  13 , instead of on the lower ball retainer. In almost any variant, the recesses themselves may be formed as depressions or holes rather than being defined by the square shoulders of teeth such as those on lower ball retainer  13 . Of course, in that case, the lock teeth  54 ,  64  would have to be configured appropriately to engage such recesses. 
     It is also possible, within the scope of the invention, to deviate from the exclusively coplanar arrangement of recesses R described above. For example, two sets of recesses in spaced parallel planes may be employed: one set (e.g., the total lock recesses) formed at the periphery of stationary lower ball retainer  13 , and the other set (the directional lock recess(es)) formed along a circle on a stationary plate fixed below and coaxial with lower ball retainer  13 , or along a smaller circle on lower ball retainer  13 . With such arrangements, the directional lock lever would be differently configured so as to reach the differently placed directional lock recess(es) and clear the total lock recesses. The locations of the different sets of recesses could be reversed, in which case the total lock lever would be differently configured for reach and clearance. Those skilled in the art will recognize that further variations are within the scope of the invention, which is defined by the appended claims. 
     As to material selection, it is preferred that most of the parts of the caster of the invention be made of steel (e.g., stainless) for strength and durability. Possible exceptions are the pedals  28 ,  30 ,  32  and the cam links  90 , which preferably are molded of a stiff and durable plastic, such as HDPE. The wheel and its bearings may be made of any materials suitable for the particular application. Of course, material selection for any of the parts of the caster will be governed at least in part by particular load, environmental and regulatory requirements of the application. 
     INDUSTRIAL APPLICABILITY 
     It will be readily apparent that selectively lockable casters embodying the invention can be employed to movably support a wide variety of objects and structures used in many fields, such as food service carts, equipment carts, utility carts, dollies, and patient beds, to name just a few.

Technology Category: 4