Patent Abstract:
A material handling turntable includes a turntable including a top for receiving a load thereon and also a bottom. The turntable further includes a motor and gear set for driving said turntable in circular motion and also includes a low friction disc slidably receiving said bottom of said turntable thereon. Preferably the turntable is assembled from multiple pie sections fastened to each other wherein each pie section including a lattice work type frame with the bottom of each frame member defining a bottom load bearing surfaces making sliding contact with said low friction disc.

Full Description:
This application claims the benefit of Provisional Application No. 60/324,930, filed Sep. 27, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to material handling equipment. It has been developed specifically for the automobile industry for handling parts on a mass production line. However; from what follows, it will be apparent that this has applications in other production areas and is not limited to the production of automobiles or other motor vehicles. 
     BACKGROUND OF THE INVENTION 
     On a production line, such as an automobile parts production line, parts, such as doors, trunk lids, hoods, body panels, etc., are stamped form sheet metal at a press and are produced at the rate, currently, of eight to twenty five per minute. The handling of these parts on the line is largely automated but at the end of the line, the parts are removed manually by crews of workers. The parts are moved into a rack that is mounted on a riser. Usually the parts are placed vertically in slots in a rack and thereafter are moved to a storage location; usually by a fork lift truck for storage before further processing and assembly. 
     The standard procedure is to provide a table onto which the stamped parts discharge from a conveyor. As the parts arrive at the table they are manually removed then placed in a rack. When a rack is filled, it is moved to a location from which it can be carried by forklift to storage. 
     Commonly the racks are placed on turntables at the end of the press line. The turntable can rotate from the loading position to an unloading position at which they are picked up by forklift to be moved to a temporary storage location. Thereafter the turntable is rotated to a position at which empty racks can be positioned and then the table is turned to the loading position once more to repeat the cycle. 
     Currently the turntables are supported by air bearings and are moved to the load, unload and reload rack positions by a mechanical drive. The riser mechanism can be adjusted for height to accommodate the ergonomic requirements of the crew and the geometry of the parts of the plan, but the loads placed on the conveyor are ones, which involve significant and taxing physical effort. While with the air bearing arrangement the loads once moving require little effort but to start these loads and to stop them with accuracy is demanding and inaccurate. Thus it is proposed that the table be mechanically rotated giving accuracy of position and increased speed. The most attractive proposition was using an air motor to assist in turning the table simply because air is abundant and compressors are commonly involved in production line processes. However, simply because compressed air is available, it is not abundant and cheap. Vast amounts are needed to inflate air bearings underneath the bulk of a large table and its load. These applications did not achieve higher index speed and are too expensive to operate and maintain. 
     In order to achieve enough rigidity for turntables supported on air bearings, it is necessary to have a fairly massive structure to tolerate the vertical loading and achieve smooth operation of the turntable. The rigidity and strength requirements results in turntables being considerably heavier than the present invention. The large mass associated with turntables riding on air bearings results in high inertia conditions that require large amounts of horse power in order to accelerate and decelerate the table to a preselected position. 
     In addition, in order to provide for the rigidity and strength that is necessary, the tables tend to be very thick which usually means that the turntable is mounted above the normal floor level. Therefore tow motors and/or tractors cannot simply drive onto the turntable, but must take precautions to ensure that any moving vehicles do not bump into the elevated turntable and that the load is carefully placed onto the turntable from a distal position. 
     It is common to have two or even more turntables receive from a production line with a crew to each turntable. The receiving table being a hexagonal outline with a base receiving from the line, two adjacent sides defining paths to two turntables, two sides facing the turntables and aside opposite the base side which could, conceivably, accommodate a third turntable. The conditions clearly are crowded and, shared by a crew and forklifts are fraught with risk. 
     The turntables are usually elevated and risers are positioned on them to hold the racks so that the turntables are occupying spaces, which are dedicated to them and are useless for other purposes. To this state of the art comes the inventor/engineer with a dramatic new proposal. 
     The inventor proposes a new turntable one or more of which can be placed at the end or intermediate location of a production line and which can be moved between a load, unload and reload positions with precision and can be moved to intermediate positions between the load and unload positions to accommodate a crew requirement with precision and safety. To achieve this the inventor uses a disc depending on a central bearing and housed within a peripheral curbing and drive comprising a motor, a drive gear, a chain, or other flexible element trained around a drive gear and the periphery of the disc. The disc has a generally flat top surface and has an annular flange at or adjacent to its periphery about which the chain is trained. The disc and flange together have a height equal to the thickness of the floor finishing layer so that by removal of that layer to expose the sub flooring the, disc can be located with its top surface flush with the surrounding floor. This provides significant safety advantages over existing arrangements and it permits the space the disc occupies to be used for multiple purposes. 
     With such an arrangement it becomes necessary only to excavate sub floor in a small region to accommodate the drive mechanism. 
     It is desirable to have a turntable which has low total mass which results in a low total inertia which results in a turntable requiring much less power to accelerate and decelerate efficiently and accurately. Additionally such a turntable has a much lower profile and/or overall thickness resulting in a turntable which in most cases can be mounted flush to the existing floor line due to the shallower profile. 
     SUMMARY OF THE INVENTION 
     The present invention a material handling turntable comprises: 
     a) a turntable including a top for receiving a load thereon and a bottom; 
     b) a means for driving said turntable in circular motion; 
     c) a bearing means for supporting vertical loading on said turntable operably adapted to slidably interact with said bottom of said turntable. 
     Preferably wherein said bearing means includes a low friction disc slidably receiving said bottom of said turntable thereon. 
     Preferably wherein said turntable assembled from multiple pie sections fastened to each other. 
     Preferably wherein each pie section including a lattice work type frame with the bottom of each frame member defining a bottom load bearing surfaces making sliding contact with said bearing means. 
     Preferably wherein each frame member including U shaped steel beams laid on their side with one leg of the U shaped channel defining the load bearing surfaces at the bottom. 
     Preferably wherein each pie section attached to a central hub at one end and to adjacent pie sections at the other broad end. 
     Preferably wherein each pie section is attached with one locating pin to the central hub and with one fastener at each side of the broad end of the pie to each adjacent pie section. 
     Preferably wherein each pie section fixed in place at three attachment points. 
     Preferably wherein said drive means including a chain trained around the outer periphery of said turntable which is driven by a sprocket to rotate said table. 
     Preferably wherein said chain is trained onto a frictional element located on the outer periphery of said turntable for holding said chain in place and imparting rotational forces. 
     Preferably wherein said low friction disc comprised of ultra high molecular weight polyethylene pad. 
     Preferably wherein said top including top plates providing for a substantially level loading surface. 
     Preferably wherein the number and size of pie sections is selected for ease of transportation on a flatbed trailer. 
     Preferably wherein said drive means including control means for controlling the rotation and positioning accuracy of said turntable. 
     Preferably wherein said drive means including a feed back drive system with servo motors. 
     Preferably wherein the turntable including a central precision bearing for supporting any radial forces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of the turntable. 
     FIG. 2 is a vertical section through the peripheral region of the turntable taken at detail P in FIG.  4 . 
     FIG. 3 a section on line AA of FIG.  1 . 
     FIG. 4 is a vertical section through the axis of the turntable. 
     FIG. 5 is a schematic partial cut away view of two pie sections of the turntable shown sliding along a low friction disc. 
     FIG. 6 is a schematic perspective view of a single pie section of the turntable showing the frame components and the general construction together with the top plate of a single pie section of the turntable. 
     FIG. 7 is a top plan view of the turntable with the top plates removed showing the frame structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The turntable, generally indicated at  10  is made up of a plurality of triangular plates  12  radiating form a central, circular bearing cover  14 . Secured at the outer edge of each plate are removable inspection/maintenance plates  16  having part circular outer edges, which complete the turntable disc. 
     As can be seen in FIG. 2, detail P in FIG. 4, the turntable has peripheral, downwardly depending flange  18  having a high friction drive surface element  20  about which, as described herein after, the drive chain  38  is trained. As seen in FIG. 3 the radial edges of the plates  12  have C-sectioned connector/reinforcement frame elements  21  which are bolted together at spaced intervals to form a unitary turntable. The lower flanges of the C-section elements ride on a low-friction disc  22 . 
     The turntable is radially loaded by a large diameter precision bearing  24  to which access can be had through removable cover  14 . At its outer periphery the turntable top is overlapping a curbing ring  26  to form a labyrinth to keep out dirt and also for obvious safety reasons. 
     The total height of the turntable and disc  22  is, where feasible, selected to be equal to the thickness of the top layer of the flooring so that once only the top floor is removed; the turntable assembly can be installed to be flush with the surrounding floor. 
     It is necessary to excavate the sub floor at  30  to accommodate a motor  32 . The motor, through a gear box  34  drives a sprocket  36  about which drive chain  38  is trained. The chain extends fully about flange  18  of the turntable and passes between chain tensioning snub sprockets  40 . The snub sprockets are mounted on a moving arm and provide chain tension by an air pressure device  42 . 
     In the alternative the snub sprockets are stationary and the drive base is sliding to provide chain tension by means of an air pressure device  42 . 
     In operation the motor turns to cause the turntable to be rotary indexed through a divisible portion of a circle at which an appropriate component receiving container and/or rack is placed. The motor than advances the turntable with the container and/or rack through a further index. To bring the container and/or rack to a loading position adjacent to the end of a production line at which the components of the line are placed into the container and/or rack after another index the loaded container and/or rack can be removed and the container and/or rack with the components taken to a temporary storage area. 
     As noted above, the turntable has been designed for use with an automobile production line but it will be apparent that it is not limited to that application. 
     Referring now to FIG. 1, the turntable shown generally as  10  is shown constructed of 18 roughly equally sized pie sections  126 . The radial direction  120  of turntable  10  is shown in FIG.  1  and radial forces which are imparted upon turntable  10  are accommodated by a precision bearing  24  which is shown in FIG.  4 . 
     The turntable is rotated via a drive chain  38  which is mounted around the outer periphery  132  of the pie sections  126  of turntable  10  and is driven by a drive assembly  80 . 
     Referring now to FIGS. 2,  3  and  4 , one can see that the turntable  10  is mounted flush with the surrounding flooring and has a very small profile or thickness shown as t in FIG. 2 as  124 . The entire thickness  124  is comprised of top plate  12 , the thickness of C-section frame elements  21  and as well the thickness of low friction disc  22 . Therefore, the entire vertical profile and/or thickness of the turntable  10  depends upon the thickness of top plates  12 , the thickness or the profile of C-section frame elements  21  and the thickness of low friction disc  22 . The mechanical structure of the present invention can provide for much thinner thickness t  124  compared to prior art devices as will be explained below. 
     Referring now to FIG. 4, the drive assembly  80  includes a motor  32  gear box  34 , a main gear or sprocket  36  for driving drive chain  38  and a tensioning system air pressure devices  42  which in practice are preferably air bags for applying tension to chain  38  via a set of snub sprockets  40 . It is possible that the entire gear box/motor arrangement be designed to slide back and forth on a set of rails and/or bearings in order to maintain tension on drive chain  38 . Drive chain  38  is trained around the entire outer periphery  132  of turntable  10  and is mounted onto surface elements  20  which in practice are rubber belting compounds and/or rubber pieces to maintain friction between drive chain  38  and the surface element  20 . Chain  38  then trains through drive assembly  80  which imparts rotational forces onto turntable  10  and also maintains a predetermined amount of tension on drive chain  38 . 
     One will note that the drive assembly  80  requires deeper excavation than the balance of turntable  10  in order to accommodate the larger components, namely the motor  32 , gear box  34 , and the tensioning mechanism. 
     FIG. 2 shows the details of the outer periphery  132  of turntable  10 . Removable inspection plates  16  overlap with a curbing ring  26  and in practise there is a small gap, although not seen in the diagrams between the removable inspection plate  16  and the curbing ring  26 . An overlap is present to ensure that there is a minimum amount of debris entering into the cavity below where the turntable is mounted. 
     Referring now to FIG. 6 depicting a single pie section  126  inverted in order to show the bottom load bearing surfaces  140  which are essentially the bottom portion  84  of C-section frame elements  21 . The bottom  150  of each pie section  126  is comprised of a lattice of C-section frame elements  21  which are welded or by other means joined together to form frame  128  which is a semi flexible contiguous frame component. On the narrow end of pie section  126  is a locating pin  130  which is inserted into a central hub  15  which is mounted onto large diameter precision bearing  24 . Pie section  126  is further attached at the broad end on each side via attachment hole  134  in order to securely fasten pie section  126  to each adjacent pie section on the left and right hand side. Assembling and joining pie sections  126  in this manner, those skilled in the art will see that individual pie sections  126  are more or less free floating in nature in that they are attached to a central hub  15  at one end via a locating pin  130  and are fastened with fasteners  136  to attach the distal outer ends of each pie section to another. Between locating pin  130  and the outer periphery  132  there is no further attachment of one pie section  126  to the adjacent pie section  126  and therefore there is a great deal of freedom of movement and flexibility of each pie section  126  as it rotates as part of turntable  10 . 
     Furthermore, a person skilled in the art will see that a great deal of rigidity is not required for frame  128  in that the load is evenly distributed along the load bearing surfaces  140  which in fact are all the bottom portions  84  of the C-section frame elements  21  which make contact with low friction disc  22  as turntable  10  rotates. 
     Prior art devices utilizing air bearings usually are much thicker than the present device for the same load carrying ability. Turntable  10  can easily be manufactured with much less total thickness due to the use of the low friction disc  22  and the lattice frame structure  128  as shown in FIG. 6 along with the minimal attachment points. 
     Referring now to FIG. 5 which shows two upright pie sections  126  mounted side by side. First of all the pie sections are mounted via locating pins  130  onto a central hub  15  which is mounted onto the large diameter precision bearing  24 . At the other end pie sections  126  are fastened together using fasteners  136 , one at each corner of the broad end of the pie sections  126 . FIG. 5 depicts pie sections  126  from the top  152  rather than from the bottom  150  as shown in FIG.  6 . Each pie section  126  has top plates  12  mounted thereon in order to provide a secure platform. Not shown in FIG. 5 the top is also covered with removable inspection plates  16  proximate the broad end which can be used for maintenance procedures such as replacing and repairing chain  38 . Top plates  12  are mounted onto the top portion  83  of C-section frame elements  21 , whereas the bottom portions  84  of C-section frame elements are acting as bearing surfaces riding on low friction disc  22 . At the outer periphery  132  of each pie section  126  is flange  18  and thereon is mounted a surface element  20  which is normally a rubber type material for receiving drive chain  38 . 
     Referring to FIG. 2 a service flange  82  is also optionally mounted onto flange  18  in order to provide for servicing of the chain when not in a tensioned condition. 
     A person skilled in the art will see that the drawings indicate that this turntable is made in 18 equally dimensioned pie sections, however in practise there is no reason why any number of a different number of pie sections could be used depending upon the size of the turntable the loading requirements and the flexibility requirements of the specific application. 
     In use, drive motor  32  drives a set of gears within gear box  34  which in turn rotates sprocket  36  which in turn drives drive chain  38  which is trained around the entire outer periphery  132  of turntable  10 . Therefore as sprocket  36  rotates, so does turntable  10  as drive chain  38  makes contact with surface elements  20  at outer periphery  132  of turntable  10 . Chain tensioning snub sprockets  40  and air pressure devices  42  which preferably are air bags and/or air cylinders maintain a preselected tension onto drive chain  38 . 
     As a load is placed onto any portion of turntable  10 , the bottom portion or the flanges of the C-section frame elements  21  make contact with the low friction disc  22  which preferably is a ultra high molecular weight polyethylene pad. Other materials exhibiting similar properties may also be used. The contact between the bottom portion  84  of C-section frame elements  21  and the low friction disc  22  ensures that the turntable  10  is moveable in circular fashion and any axial and/or vertical loading in the axial or vertical direction  122  is supported by the low friction disc  22  and any radial forces in the radial direction  120  are supported by the large diameter precision bearing  24 . 
     It is possible to load turntable  10  unevenly and yet be able to support a substantial weight and be able to rotate turntable  10  freely because bearing surfaces  140  extend evenly over most of the entire bottom  150  of turntable  10 . 
     The free floating arrangement of each pie section  126  adjacent to the other is accomplished by minimzing the number of attachment points between each pie section  126 . In the present embodiment one locating pin  130  is used at the narrow end of the pie and two attachment fasteners  136  are used at the broad end of the pie adjacent each pie section  126 . This results in each pie section  126  being able to undulate somewhat up and down depending upon the evenness of the floor which is bearing the weight below the low friction disc  22 . In this manner the ultimate stiffness required by turntable  10  is much reduced since the load is evenly distributed along each frame member  128  which provide evenly spaced load bearing surfaces  140  through out the entire area of turntable  10 . 
     A person skilled in the art will see the advantages of turntable  10  as compared to the prior art. A very low profile and/or thickness  124  can be accomplished because of the large evenly spaced load bearing surfaces  140  which are provided for by frame  128  of each pie section  126  and also due to the free floating attachment of each pie section to the other via locating pins  130  and fasteners  136 . Therefore, the entire weight of turntable  10  is much reduced and the inertia of turntable  10  is also significantly reduced which results in quicker acceleration and deceleration times and also greater accuracy in being able to position the turntable to a given position. In addition the total horsepower requirements are much reduced as compared to the prior art. 
     Furthermore, construction time and transportation of the turntable to the installation site is greatly simplified since it can be transported in pie sections  126  and easily assembled together on site due to the minimal number of attachment points and reduced excavation requirements. 
     Sensors, proximity sensors and location sensors are additionally used at various locations and also around the outer periphery  132  of turntable  10  to sense, locate and control the position of turntable  10  at any given point in time. Thereby a feed back system through drive assembly  80  can be used to very accurately control the rotational position of turntable  10 . 
     In comparison to prior art devices which employ air bearings, the present invention has the advantage of being significantly lighter in weight than turntables employing air bearings. Secondly, the present invention does not require large volumes of compressed air in order to make the table function. Due to the fact that the present invention can be easily disassembled into smaller pieces, shipping is much easier and the total weight that is shipped is also significantly reduced. And finally, turntables using air bearings also inflate and deflate air bearings during each cycle of the movement of the turntable thereby increasing the response time of the table to move from one position to the next. 
     In particular during deceleration of the table, the inertial energy of the rotating table must be dissipated in some manner. With the air bearing supports which offer no friction, all of the energy required to decelerate the table must go through the drive to slow it down. In the present invention the low friction disc  22  suggested provides friction to remove driving power and a quick stop is the result of the presently invented turntable. 
     By the addition of a complete feedback drive system including servo&#39;s, increased stopping accuracy can be obtained by tuning the servo close to the natural stopping of the turntable and thus avoids having to dump excess energy through the drive mechanism of the turntable. 
     It should be apparent to persons skilled in the arts that various modifications and adaptation of this structure described above are possible without departure from the spirit of the invention the scope of which defined in the appended claim.

Technology Classification (CPC): 1