Abstract:
A self-orienting caster for pieces of furniture, comprising a pair of wheels, which are supported so that they can rotate about a horizontal axis by a supporting body, which has a cylindrical recess that has a vertical axis and is open upward and axially offset with respect to the horizontal axis, and in which a pivot for the caster is inserted rotatably, the pivot being insertable in a receptacle of the piece of furniture in which the caster is to be fitted, further comprising a through seat formed in the body, a tubular element that is driven through the seat coaxially to the horizontal axis and has two cylindrical tubular portions that lie on opposite sides of the body in order to rotatably support the wheels, devices for the axial and rotational locking of the tubular element in the seat and devices for retaining the wheels on the tubular portions.

Description:
The present invention relates to a self-orienting caster for pieces of furniture and the like. 
   BACKGROUND OF THE INVENTION 
   Self-orienting casters are known, particularly of the so-called twin type, which are constituted by two wheels that are mounted so they can rotate about a horizontal shaft. The shaft is supported in a seat formed in a supporting structure that is arranged between the wheels. 
   In the supporting structure there is a vertical cylindrical recess, which is open upward, is axially offset with respect to the shaft, and acts as a rotation seat for a vertical pivot for the spontaneous orientation (pivoting) of the wheel, which is intended to be inserted and retained in a receptacle of the piece of furniture on which the caster is to be fitted. 
   Self-orienting casters are also known in which the wheels can rotate about a tubular shaft that protrudes on opposite sides of the central supporting structure. Casters of this type, also known as hubless casters, are disclosed in U.S. Pat. No. 978,161, in US publication 2002/01758539, in British patent 967,915, and in German publication 101 28 099. Swiss patent 477,999, British patent 967,915 and US publication 2002/1178539 describe solutions in which the wheels and the tubular shaft are provided with mutually opposite tracks for the rolling of balls or rollers for rotatably supporting the wheels. Known casters have drawbacks as regards the structure composed of the central support and the tubular shaft, which is unable to combine satisfactorily mechanical strength characteristics, in order to be able to withstand the loads, with the need to obtain a product which, as it is intended for pieces of furniture (chairs, tables, etc.), must meet appreciable aesthetic requirements. 
   SUMMARY OF THE INVENTION 
   The aim of the present invention is to provide a contribution in this regard, by providing a caster that is capable of meeting these requirements, is easy and cheap to manufacture and assemble, and offers new aesthetic standards. 
   Within this aim, an object of the present invention is to provide a caster having a structure suitable to ensure very smooth rolling on surfaces of any kind. 
   Another object of the present invention is to provide a caster that can be provided with a braking device that can be neutralized when necessary. 
   This aim and these and other objects that will become better apparent hereinafter are achieved with a self-orienting caster for pieces of furniture and the like, the characteristics of which are defined in the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages will become better apparent from the following detailed description of some preferred but not exclusive embodiments of the caster according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a self-orienting twin caster according to a first embodiment; 
       FIG. 2  is an exploded view of the caster of  FIG. 1 ; 
       FIG. 3  is a sectional view of the caster of  FIG. 1 , taken along a vertical plane that passes through the horizontal rolling axis; 
       FIG. 4  is a sectional view of the caster of  FIG. 1 , taken along the line IV-IV of  FIG. 3 , and also shows a detail in enlarged scale; 
       FIG. 5  is a perspective view of parts of the caster shown in  FIG. 2 ; 
       FIG. 6  is an exploded view of a self-orienting twin caster according to a second embodiment; 
       FIG. 7  is an exploded view of a self-orienting twin caster according to a third embodiment in which there is a self-braking device; 
       FIG. 8  is a sectional view, taken along a vertical plane, of the caster of  FIG. 7 ; 
       FIG. 9  is a sectional view, taken along the line IX-IX of  FIG. 8 ; 
       FIG. 10  is a view of parts of the caster of  FIG. 7 ; 
       FIG. 11  is a partially sectional perspective view of a different embodiment of the wheel supporting bearing; 
       FIG. 12  is a sectional view of a bearing according to another embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to  FIGS. 1-4 , the reference numeral  1  generally designates a self-orienting caster of the so-called twin type, particularly for pieces of furniture. The caster comprises a body  2  that has a substantially ring-like structure reinforced by radial ridges. The body  2  is provided with a peripheral expansion  3  in which there is a cylindrical recess  4 , which is tangent to the body  2 . 
   The body  2  is provided with a through seat  5  that has a circular cross-section and through which a tubular element or sleeve  6  is arranged; such element comprises two cylindrical portions  7 ,  8 , which protrude coaxially in a cantilever fashion from opposite sides of the body  2 . The portions  7 ,  8  are aligned along a horizontal axis A, which is axially offset and perpendicular with respect to the vertical axis B of the recess  4 , and enclose a cylindrical cavity  9 , which passes through the body  2 . 
   The sleeve  6  is provided with a collar  10  ( FIG. 5 ), which lies around the central region and is composed of two annular ridges  11 ,  12 , between which a channel  13  is formed. The ridges  11 ,  12 , in diametrically opposite positions, are rounded and form two flat surfaces  14 ,  15 , which are tangent to the cylindrical surface of the sleeve  6 . An annular ridge  16  and two diametrically opposite flat surfaces  17 ,  18 , arranged on planes that are parallel to the axis B, are provided within the seat  5  of the body  2 . The diameters of the seat  5  and of the ridges  11 ,  12 , as well as the dimensions of the flat surfaces  17 ,  18  and the width of the channel  13  and of the annular protrusion  16  are chosen so as to allow the sleeve  6  to be inserted by forcing in the seat  5 , thus providing an axial connection of the sleeve  6  to the body  2  by way of the engagement of the annular protrusion  16  in the channel  13 . At the same time, rotary locking is provided by side-fit engagement between the flat regions  14 ,  15  and  17 ,  18 . 
   The forcing action can be facilitated by acting on the configuration of the annular ridges  11 ,  12  and by resorting to a suitable choice of the materials for the sleeve  6  and the body  2 . Advantageously, the sleeve  6  is made of plastic material, whereas for the body  2  it is possible to use plastic material and metal, for example a metallic alloy of zinc, aluminum and magnesium, known by the tradename ZAMA, depending on the load stresses to which the caster is subjected. 
   Respective annular slots  19 ,  20  are formed in the tubular portions  7 ,  8 , proximate to their free ends, and form respective annular lips  21 ,  22 , which are folded outward. 
   Two wheels  25 ,  26  are fitted rotatably on the tubular portions  7 , 8  ( FIG. 3 ) by way of the interposition of bearings  23 ,  24 . The bearings  23 ,  24  are of the rolling type and are constituted by rollers  27  inserted in receptacles  28  of an annular cage  29 . The rollers  27  have a diameter that is larger than the radial thickness of the cage  29 , so that they protrude toward the inside and the outside of the receptacles  28  and can roll on the opposite cylindrical tracks  30 ,  31  of the tubular portions  7 ,  8  and respectively  32 ,  33  of the wheels  25 ,  26 . 
   The wheels  25 ,  26  have, on the side that faces the body  2 , respective grooves  34 ,  35  and, on the opposite side, respective internal collars  36 ,  37 . The internal collars  36 ,  37  are sized so as to engage by elastic forcing in the slots  19 ,  20  of the sleeve  6  and therefore retain axially thereon the wheels  25 ,  26  with minimal friction. At the same time, two annular ridges  38 ,  39  engage in the grooves  34 ,  35 , protrude frontally from the lateral faces of the body  2  and surround the seat  5 , forming a sort of labyrinth-like coupling that prevents foreign particles and dirt from penetrating toward the bearings  23 ,  24  and compromising their correct operation. 
   The caster is fitted to the piece of furniture by means of a pivot  40 , which can rotate in a bush  41  ( FIGS. 2 and 4 ), which acts as an antifriction bearing for the rotation of the caster about the pivot  40 . The bush  41  is shaped like a bushing that has a stud  42  that protrudes from the bottom and an internal collar  43 . The stud  42  acts as a resting point for the pivot  40  on the caster  1 , while the internal collar  43  is used to retain the pivot  40  within the bushing  41  after it has been forced to engage in an annular groove  44  of said pivot. 
   In order to retain the bush  41  in the recess  4 , the inlet of the recess is formed by a protruding rim, which has a groove  45  that divides it into two mutually concentric lips  46 ,  47 . The inner annular lip  46  is suitable to be folded onto the rim of the bush  41 , so as to lock it axially in the recess. Advantageously, the outer rim of the bush  41  is rounded in order to allow the internal lip  46  to be folded over onto it and ensure more effective axial retention of the bush. Likewise, the outer annular lip  47  is folded outward so as to lock any optional ring-like element  48  that is applied so as to cover the expansion  3  and is shaped so as to mate with the contour of the body  2 . 
   During use, the described caster  1  behaves like a known twin caster, but with the considerable advantage that the sleeve  6 , by way of its radial dimensions, provides the caster with the rigidity required to withstand effectively load imbalances on the two wheels and facilitate their smooth rotation. Further, the hollow structure of the sleeve  6  does not encumber, also from an aesthetic standpoint, the caster, whose appearance maintains the requirements of lightness even in the case of large casters. 
   It should be noted that the bush  41  may be omitted. In this embodiment, shown in  FIG. 6 , the pivot  40  of the caster  1  rests directly on the bottom of the recess  4  with the interposition of a ball  49 . The covering element  48  is locked by providing, around the rim of the inlet of the recess  4 , an annular lip  50  suitable to engage in a groove  51  formed inside the ring  52  of the element  48 . 
     FIGS. 7 ,  8 ,  9  and  10  illustrate another embodiment, which relates to a twin caster provided with a self-braking device that ensures wheel locking when the caster is not loaded, for example as required by safety standards if the caster is used in office chairs. 
   In the caster of  FIGS. 7-10 , the seat  5  is formed by two substantially semicylindrical portions  53 ,  54 , which have a radius that is equal to the radius of the portions  7 , 8  of the sleeve  6  but are mutually spaced so that the seat  5  is ovalized. The adjacent ends of the portions  53 ,  54  are connected by the two opposite flat surfaces  17 ,  18 , which as mentioned have a mutual distance that is equal to the distance between the flat surfaces  14 ,  15  of the sleeve  6 . The ridges  38 ,  39  also are constituted by semicylindrical portions that are concentric with respect to the respective portions  53 ,  54 . The ovalization of the seat  5  allows to insert therein the sleeve  6  so that the flat surfaces  14 ,  15  are in sliding contact with the flat surfaces  17 ,  18  of the body  2 , allowing the sleeve  6  to perform vertical movements within the seat  5  while remaining rotationally coupled to the body  2  and being retained axially by the engagement of the annular protrusion  16  in the channel  13 . 
   A through hole  5  is provided centrally through the lower semicylindrical portion  53  and is aligned vertically with a blind seat  56  formed in the upper semicylindrical portion  54 . A spring  57  is inserted in the blind seat  56 , before the sleeve  6  is positioned in the seat  5 , and acts on said sleeve, when said sleeve is inserted, so as to push it towards the lower portion  53 . 
   The spring  57 , once the caster  1  has been fitted to the chair, allows the body  2  to move with respect to the sleeve  42 . In particular, the spring  57  is sized as so as to lift the body  2  with respect to the sleeve  6  when the caster is not loaded and instead allow its lowering when the caster  1  is loaded. In the first manner of use (for example, when the caster  1  is mounted on an office chair on which no one is sitting), locking of the caster is provided by way of the friction effect obtained by means of the contact of sliding blocks  58 ,  59 , which are constituted by protrusions formed above the top of the ridges  38 ,  39 , against the walls of the grooves  34 ,  35  of the wheels  25 ,  26  in which the ridges  38 ,  39  are engaged. In the second manner of use, i.e., when the caster is loaded (for example when a person is sitting on the chair), the ridges  38 ,  39  are perfectly free in the grooves  34 ,  35 , allowing the free gliding of the chair. 
   The spring  57  may also act as a shock absorber. In this case, the sliding blocks  58 ,  59  are omitted in order to avoid a braking effect. 
   The caster of  FIGS. 7-10  can be modified easily in order to make it able to glide freely or glide with friction when necessary. For this purpose, the lower through hole  55  is threaded in order to receive an adjustment screw  60 , which is suitable to act on the sleeve  6 . Actuation of the screw  60  allows the sleeve  6  to be raised so as to move the sliding blocks  58  of the ridges  38 ,  39  into friction-controlled or free engagement against the walls of the grooves  34 ,  35 . 
   In the embodiment shown in  FIG. 11 , the partitions  61  of the bearings  23 ,  24  that mutually separate the receptacles of the rollers  27  have ends that are divided by respective radial slits  62 , which form two flexible prongs  63 . The prongs  63  are provided with teeth  64 , which narrow the access of the rollers  27  in the receptacles  28 . The prongs  63 , by way of their flexibility, allow the insertion of the rollers in the receptacles and their retention by means of the teeth  64 . 
   In the embodiment shown in  FIG. 12 , roller retention is provided by providing a ring  65 , which is associated with the cage  29  by means of an annular flange  66  that protrudes from one of its faces and engages slits  67  formed in the ends of the partitions  61 . 
   In another embodiment, a metal strip is applied, is connected to the metal body  2  and is in sliding contact with the rolling surface of the casters in order to discharge any electrostatic charges to the ground. 
   The disclosures in Italian Patent Application No. BO2004A000352 from which this application claims priority are incorporated herein by reference.