WORKPIECE HOLDER

Abstract: A workpiece holder for supporting an annular workpiece (34) such as a tire for a vehicle. The holder (10) includes a plurality of elements (27) movable radially outwardly into engagement with an inner surface of an annular workpiece (34) in response to movement of a cam (32). The gripping force applied to the inner surface of the tire by this arrangement is only slightly greater than that required to support the tire carcass thus overcoming the problem of core breakage.

Description: Description WORKPIECE HOLDER Background of the Invention This invention relates to a workpiece holder for supporting an annular workpiece by engagement between radially extending elements of the workpiece -holder and the inner surface of the workpiece. In one process of making large tires fo'r earth oving vehicles, layers of rubber and wire are .applied to the surface of a toroidal shaped hollow and core which remains within the tire carcass during the construc¬ tion of the tire. The sand core is eventually dissolved as one of the final steps in making the tire. The sand core is somewhat fragile and care must be taken so as not to apply excessive force thereto during the manufac¬ turing operations. Excessive force could crush or otherwise cause the sand core to fail. In the latter steps of the manufacturing process, tire materials, such as uncured rubber, breaker plys and belts are applied to the tire carcass as it is being rotated about its axis. Heretofore, the carcass has been supported during such rotation by an apparatus having shoes which . grip the„outer of the carcass, during application of materials to the sidewalls. Application of tire materials to the crown area of the tire involves other fixturing and a separate carcass handling step. This is both time consuming and adds to the manufacturing cost. Thus it is desirable to support the tire ~ _ ) _ carcass by gripping the inner surface so that tire mate¬ rials can be applied to both the sidewalls and the crown area. One of the problems with gripping the tire carcass from the inside is that the sand core is more prone to _OMPI -2- breakage if excessive force is applied to the inner surface or if the force is applied unequally. Preferab the gripping force applied to the inner surface should only slightly greater than that required to support the 5 tire carcass. However, this creates another problem in that normally-one support apparatus is used for several sizes of sand cores wherein the weight of the carcass _.-_. -varies thereby requiring different gripping forces for each of the several sizes. 10 Summary of the Invention The present invention is directed to overcomi one or more of the problems as set forth above. According to the present invention, this is accomplished by providing a workpiece holder having a 15 plurality of elements slidably maintained by a support structure and which extend radially relative to a longi tudinal axis of the support structure. A cam engages the inner ends of the elements and movable along the longitudinal axis between a first position at which the 20 ■ elements.are retracted and a second position at which t elements are extended into engagement with an inner surface of an annular workpiece.. Brief Description of the Drawings Fig. 1 is a diagrammatic elevational view of 25 workpiece holder embodying the present invention. Fig. 2 is a sectional view taken along the li II-II of .Fig. 1. Detailed Description Referring now to the drawings, a workpiece ho 30 10 includes a support structure 11 having a spindle 12 extending into preferably a hollow member 13 of a mount frame 14. The spindle 12 is rotatably connected to the " BURE OMPI member 13 by a pair of bearings 16, 17. The spindle 12 extends from a hub 18 and has a bore 19 therein extending along a longitudinal axis "X". The bore 19 is concentric with an opens into a bore 21 in hub 18. A plurality of spokes 22 are connected to the hub 18 and extend radially outwardly therefrom. Each of the spokes has a bore 23 therein opening into bore 21 of the hub 18. A bearing 24 is positioned with in each of the bores in the spokes. A plurality of elements, preferably rods 26,- are individually slidably -positioned within the bearings 24 in bores 23 of spokes 22. Each of the rods 26 has an arcuate shoe 27 connected to i ' ts outer end portion with each shoe 27 having a resilient pad 28 on the outer surface. Each of the rods 26 has a roller 29 rotatably connected to the inner end portion thereof. A plurality • of springs 31 are individually connected to the shoes 27 and to the hub18 for resiliently retracting the rods 26 from an extended position shown in the drawings toward the longitudinal axis "X". A circular cam 32 is slidabl positioned within the bore 21 and has a convex cam surface 33 in engagement with the rollers 29. The cam 32 is movable along the longitudinal axis "X" between a first position at which the rods 26 are at a retracted position and a second position at which the rods 26 are extended into engagement with an inner surface of a workpiece indicated at 34. The convex cam surface 33 is defined as a surface of revolution in which a curved line is revolved about the axis "X". In the present instance, the curved line is an arc having a radius "R". A means 38 is operatively connected to the cam 32 for moving the cam between the first and second posi¬ tions. The means 38 can be, for example, a fluid cylinder 39 and a spring 41. The cylinder 39 is connected "BUREA OMPI fa WIPO to the hollow member 13 and has a.piston rod 42 extendin into the bore 19. The piston rod 42 is screwthreadably connected to one end of a rod 43 which has its other en connected to the cam 32 by a pair or .bearings 44. The bearings 44 provide for relative rotation between, the c 32 and rod 43. The spring 41 is preferably a constant rate spring and exerts a force on the piston rod 42 and rod 43 for urging the cam 32 toward its second position Selective introduction of fluid into a chamber 46 of th cylinder moves the piston rod 42 and hence the cam 32 t its first position. A means 47 for rotating the support structure 11 relative to the mounting frame 14 includes a motor means 48, a drive sprocket 49 connected to the motor means, a sprocket 51 on the spindle 12 and a chain 52 entrained around the sprockets. A plurality of arms 53 are pivotally connecte to * brackets 54 of the mounting fr'ame 14. Each of the arms 53 is movable from a first position at which a dis end portion 56 is at a position for ' locating the workpi 34 relative to the shoes ' 27 as shown by the solid lines the drawings and a second position at which the distal end portion 56 is free of contact with the workpiece, as shown by the phantom line in Fig. 1. In use, fluid is introduced into the chamber - to retract the piston rod 42 of the cylinder 39 against the bias of spring 41. This in turn moves the cam to i first position at which the rods 26 are retracted by th springs 31. With the arms 53 at their first position, the workpiece 34 is positioned so that the inner surfce encircles the shoes 27. The fluid is then vented from the chamber 46 so that the spring 41 exerts a force against the piston rod 42 which in turn moves the cam 3 toward its second position. This movement of the cam causes the rollers 29 to follow the convex cam surface of the cam thereby extending all the rods 26 simultaneous¬ ly so that the shoes 27 engage the inner surface of the workpiece and center the workpiece 34 relative to the axis "X". The relative position of rods 26 on the convex cam surface 33 and the available force of the spring 41 at the instantaneous position of cam 32 determines the amount of radial force being exerted against the work- piece. Specifically, the convex cam surface functions as a variable angle ramp such that the ramp angle decreases as the cam moves toward the second position. The increase in radial force caused by the decrease in ramp angle more ' than offsets the decrease in radial force caused by the decrease in the available force of the spring 41 as it expands with the net result being that the force exerted by the rods increases as the rods are extended in response to the cam moving to its second position. Thus, the force exerted against the workpiece increases as the diameter of the inner surface of the workpiece increases. Since the diameter of the inner surface is generally indicative of the size and weight of the workpiece, a greater force is automatically exerted against a larger and heavier workpiece while a lesser force is exerted against a smaller and lighter workpiece. Prior to rotating the support structure 11 and hence the workpiece 34, the arms 53 are moved to their second position. To remove the workpiece 34 from workpiece holder 10, .fluid is again introduced into chamber 46 for moving cam 32 to its first position. In view of the foregoing, it ~" Ts " readily apparent that the structure of the present invention provides an improved workpiece holder for supporting an annular workpiece. The rods are moved radially outwardly in unison by the cam so that the force exerted by the rods is uniformly distributed against the inner surface of the workpiece. Further, since the amount of radial force exerted against the inner surface by the rods increases as the rods are extended, a greater force is automatically exerted against a larger heavier workpiece than is exerted against a smaller lighter workpiece. Thus, the workpiece holder can suitably support any of several sizes of workpieces without any modification or adjust¬ ment thereto during changing of workpiece sizes. Other aspects, objects and advantages of this invention can be " obtained from a study of the drawings, the disclosure and the appended claims. l-ΛJREΛ

Claims: Claims 1. A workpiece holder for supporting an annular workpiece (34) having an inner surface characterized by a support structure (11) having a longitudinal axis "X"; a plurality of elements (26) having inner and outer end portions and being slidably maintained by said support structure; a cam (32) engaging said inner end portions of said elements and being movable along the longitudinal axis between a first position at which the elements are at a retracted position and a second position at which the elements are extended into engagement with said inner surface of the workpiece; means (38) for moving the cam ' between said first and second positions; and a bearing (44) rotatably connecting said cam moving means (38)to said cam (32). 2. The workpiece holder of claim 1 wherein said cam (32) has a convex camming surface (33) , said inne end portions of the elements being in contact with the • convex cam surface, and wherein, preferably, said cam moving means (38) includes means for exerting a force against the cam for moving the cam from the first position to the second position. 3. The workpiece holder of claim 2 wherein said force exerting means includes a constant rate spring (41) , said cam moving mean ' s includes a fluid cylinder (39) connected to said cam for moving the cam from the second position to the first position. 4. The workpiece holder of claim 1 wherein said support structure (11) includes a bore (21) concentric with said axis, said cam (32) being slidably positioned within said bore, and wherein, preferably, said support structure includes a plurality of spokes (22) each having a bore (23) extending radially relative to said axis, said elements being rods (26) slidably positioned within the bores in the spokes . 5. The workpiece holder of claim 1 wherein the outer end portions of the elements each include an arcuate shoe (27) , . " wherein, preferably, the inner end portions of the elements each include a roller (29) rotatably connected to the element and rollably engaging said cam, and wherein, preferably, resilient means (31) are connected to the elements for moving the elements to the retracted position in response to the cam being moved to said first position. 6. The workpiece holder of claim 1 includin mounting frame (14) , means for rotatably σonnecting th support structuie to the mounting frame, and means (48) for rotating the support structure relative to the mounting frame. 7. The workpiece holder of any of claims 1-6 including a plurality of arms (53) pivotally connected to said frame and having distal end portions, said arms being movable between a first position at which said ddstal end portions are positioned for engagement with said workpiece and a second position a which the distal ends are at a position free of contac with the workpiece. 8. The workpiece holder as claimed in claim 2 wherein said convex cam surface (33) functions as a variable angle ramp such that the ramp angle decreases the cam moves from a first positon towards a second pos 9. The workpiece holder as claimed in claim 1, wherein said support structure (11) comprises a spindle (12) extending into a hollow member (13) of a mounting frame (14) , said spindle is rotatably connected to said member by bearing means (16, 17) , extends from a hub (18) , and has a first bore (19) therein β.tending along said longitudinal axis, said bore (19) being concentric with and opens into a second bore (21) in said hub, said plu¬ rality of elements, preferably rods (26) , are individually slidably positioned within bearings (24) and are indi¬ vidually associated with a plurality of springs (31) for resiliently retracting the rods (26) from an extended position toward said longitudinal axis, and a fluid cylinder (39) . is connected to the hollow member and has a piston rod (42) extending into said first bore (19) , * said piston rod being connected to one end of a rod (43) which has its other end connected to said cam by said bearing (44) . 10. A tire carcass holder, characterized by - the features of one or more of the preceding claims.

Inventors: DENNIS R
Applicants: CATERPILLAR TRACTOR CO
Application year: 1979
Main classification: B23Q3
IPC codes: B23B31, B23Q3, B60B30