Abstract:
A conveyor for clean manufacturing applications. The conveyor comprises interconnected conveyor modules, each of which includes a conveyor belt segment (s). Each conveyor belt segment includes a pair of side rails that are in parallel or substantially in parallel to each other; a pair of autonomous, belt-drives for transporting work pieces or objects carrying work pieces from a proximal end of the belt segment to a distal end of the belt segment; a pair of driving wheels for turning the belt-drives, and a motor for directly or indirectly driving each of the pair of driving wheels. One of the driving wheels is mechanically or magnetically coupled to a magnetic hysteresis clutch that allows the driving wheels to disengage from the drive shaft of the motor if the inertia of the work piece does not permit synchronization of work piece with the drive speed of the motor during acceleration or deceleration.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present utility patent application claims the benefit of priority through U.S. Provisional Patent Application No. 61/125,901 dated Apr. 29, 2008 entitled “Clean, High Density, Soft-Accumulating Conveyor”. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    (Not applicable) 
       BACKGROUND OF THE INVENTION 
       [0003]    In some industrial applications of conveyors there are a number of special performance requirements in addition to common parameters such as speed, weight, and transport capacity. Such applications can be found in the Semiconductor, Pharmaceutical, Solar Cell, Hard Disk Drive, Flat Panel Display, and other manufacturing industries. For these applications and other similar applications, the conveyors used for inter-tool movement of Work In Process (WIP), require “Particulate Free Cleanliness”, “Vibration Free Transport”, “Very High Density WIP Flow”, and “Asynchronous Movements of Pallets with Soft-Accumulation of WIP” (i.e., without collisions or bumping). 
         [0004]    Of the above four requirements, current technology has provided for cleanliness, for asynchronous movement, and for soft-accumulation of WIP, e.g., using precisely guided WIP on rollers, driven by motors coupled to the wheels via magnetic hysteresis. See, e.g., U.S. Pat. Nos. 4,793,262 and 6,047,812. Conventionally, a conveyor transporting mechanism consists of a series of wheels supporting and driving a multiplicity of WIP pallets on each of two parallel sides. A magnetic hysteresis coupling allows the driving wheels under a WIP to disengage from the drive shaft of the motor if the inertia of the WIP does not permit synchronization of WIP pallets with the drive speed during acceleration or deceleration, to avoid the squealing of tires. 
         [0005]    Advantageously, magnetic hysteresis coupling reduces rubbing motion between driving wheels and WIP pallets, which could otherwise generate particulates that would adversely impact the clean transport requirement. Furthermore, magnetic hysteresis coupling, in combination with segmentation of the conveyor, provides soft accumulation, i.e., without bumping, of WIP pallets because the WIP pallets are guided by presence-of-WIP sensors that define the boundaries of segments on a conveyor that can be occupied by one and only one WIP pallet. 
         [0006]    A fundamental drawback of current technology is that the supporting (idling) and driving wheels generate minute vibrations during transport and, therefore, are not able to meet the “vibration-free” requirement. Several physical factors are the cause. First is the near impossibility of manufacturing a large number of wheels to an absolute same diameter and concentricity. Another factor is the practical impossibility of disposing and positioning the wheels to form a straight line, so that any perfectly-planar WIP pallet riding on it would concurrently touch all of the wheels thereunder. 
         [0007]    A further drawback of existing practice is a limitation in achieving very high density WIP flow due to relatively moderate acceleration and deceleration rates of the WIP. High density WIP flow requires a relatively close spacing of pallets that travel at high speed. To achieve this in a collision-free environment and in which pallets may move asynchronously of each other requires relatively high acceleration and deceleration rates in case one pallet, for whatever reason, slows or stops. 
         [0008]    The physical cause of this drawback is the limited surface contact between WIP pallet undersides and driving wheels necessary for frictional adhesion. Indeed, the friction coefficient of soft or deformable materials is surface area dependent, while hard or more rigid surfaces is less so. As a result, low settings to initiate early disengagement of the magnetic hysteresis drive or clutch, would be necessary, to prevent the spinning of the driving wheels under the pallet during an acceleration mode in which the rubber tires of the clutch-driven wheels are in direct contact with the underside of the driven pallet. 
         [0009]    However, low-torque clutch settings cancel higher acceleration rates of the motor driving the clutch. Consequently, high speed and high density of the pallet flow is not currently achievable. Instead, it is important to be able to start a pallet from a standing still position quickly and to stop the same pallet traveling in a high-speed transport mode just as quickly, to maintain the high density of flow. 
         [0010]    The need for asynchronous movement of the pallets also necessitates being able to transport each pallet individually if there is space to move the pallet downstream and/or to stop a pallet independently and without bumping if another downstream pallet is obstructing its way. In short, high speed and high density flow, together, require a firm grip on the pallet during its movements. However, individual driving wheels, with the limited surface contact area with the WIP pallet, currently are not able to deliver this performance. 
         [0011]    To address these shortcomings, existing conveyor segments, which are structured and arranged to be slightly larger then a WIP or a WIP pallet, can, instead, be equipped with a dedicated drive belt, riding on top of wheels that are independently driven by the same hysteresis clutch/motor mechanism as before. The high-friction belt, sandwiched between the wheels and the WIP pallets, provides necessary adhesion between the WIP pallet and the driving, return idler, and/or idler wheels, to ensure required high, slip-free acceleration. Furthermore, the belt, which is riding on top of the previously disclosed wheels, reduces vibrations generated by any uneven height differences of sequential wheels. 
         [0012]    Disadvantageously, generic belt-driven conveyors are not inherently clean. Hence, merely adding belt drives may impact a particulate-free environment. As a result, maintaining a high degree of cleanliness in a belt-driven environment requires special wheel and belt designs. 
         [0013]    Accordingly, it would be desirable to provide a high density, high speed, asynchronous belt-driven conveying system that is particulate-free, vibration-free, and that employs soft accumulation. 
       SUMMARY OF THE INVENTION 
       [0014]    A first belt-driven conveyor includes a flat, thin belt in combination with crowned hysteresis driving wheels and flanged idler wheels. Each driving wheel is structured and arranged to drive and center the flat, thin belt while the idler wheels are structured and arranged to laterally confine the work piece or the object carrying the work piece using the flanges on the idler wheels. A magnetic hysteresis clutch or coupling allows the driving wheels for the belt to disengage from the drive shaft of the motor whenever the inertia of a work piece or object carrying a work piece does not permit synchronization of the work piece or the object carrying the work piece with the drive speed during acceleration or deceleration. Indeed, the clutch setting is pre-programmed or keyed so that it does not exceed the friction force between the belt and the work piece or the object carrying the work piece. When the acceleration exceeds this setting, the work piece or the object carrying the work piece is decoupled from the motor. 
         [0015]    A relatively thin belt thickness is desirable because, although idler wheels rotate at the same rate, those portions of the idler wheel closer to the axis of rotation, i.e., at or near the root, rotate more slowly relative to portions of the idler wheel that are disposed farther from the axis of rotation. As a result, any difference in the velocities of two surfaces on the flange that contact the work piece or object carrying the work piece may result in undesirable rubbing and resulting frictional particulation. Consequently, relatively thin, relatively flat belt cross sections are more desirable, to reduce the velocity differential between potential points of contact and to maintain required cleanliness levels. 
         [0016]    In a second system, a relatively thicker belt having a raised edge, i.e., an L-shaped belt, is used to laterally confine the work piece or object carrying the work piece. In this embodiment, each of the driving wheels and the return idler wheels are machined to include crowns on the outer peripheral surface on which the belt travels. The center of the crown radius machined on the driving wheels and on the return idler wheels, however, is slightly offset relative to the centerline of the belt by a distance x. This offset centers the L-shaped belts whose belt dimensions, e.g., the cross-section, are not uniform. 
         [0017]    A third system is effected by eliminating the flanges of the idler wheels altogether. More specifically, a third belt-driven conveyor includes a belt having a rounded or substantially rounded cross-section in combination with hysteresis-clutch driving wheels having negative crowns and idler wheels having negative crowns and guide flanges. 
         [0018]    Each of the three embodiments described above divides the conveyor into modules that include one or more segments. Belt segments are the smallest element of the whole and are dimensioned to handle and to transport a single work piece or object carrying the work piece at a time. Each belt segment includes a sensor(s) that is/are adapted to confirm the presence or absence of a discrete work piece or the object carrying the work piece within the belt segment. Currently, movement of an upstream work piece or an object carrying the work piece is realized only when one or more sequential downstream belt segments is/are completely unoccupied. Hence, forward movement of an upstream work piece or an object carrying the work piece does not begin until downstream segments are totally unoccupied. This, then, defines a velocity-independent minimum distance between work pieces or objects carrying work pieces. 
         [0019]    However, this approach affects work piece density, by delaying the forward movement of an upstream work piece or of the object carrying the work piece until a clear signal is received from a downstream belt segment sensor. This limitation becomes important once higher accelerations and decelerations are implemented. In this manner, the addition of soft belts becomes an enabling technology for higher density, higher speed, asynchronous, bump-free flow of work pieces or objects carrying the work pieces. 
         [0020]    A further improvement to current technology is obtained by sensing the precise location of each of the work pieces or of the objects carrying work pieces during movement by including more sensors or other feedback means along the path(s) of the moving work pieces or objects carrying work pieces. Data signals from more sensors increase the granularity of conveyor segmentation, which then becomes virtually finer than the size of the work piece or the object carrying the work piece. At the extreme, if various technologies are applied to the conveyor to locate moving work pieces or objects carrying the work pieces more precisely, higher work piece density at higher flow speeds can be achieved, while maintaining the asynchronous, bump-free, movement requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention is pointed out with particularity in the appended claims. However, the advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily drawn to scale, and like reference numerals refer to the same parts throughout the different views. 
           [0022]      FIG. 1  shows a conveyor module having plural belt segments in accordance with the invention as claimed; 
           [0023]      FIG. 2  shows a belt segment in accordance with the invention as claimed; 
           [0024]      FIG. 3  shows a driving wheel in accordance with the invention as claimed; 
           [0025]      FIG. 4  shows a segment of a belt-driven conveyor in accordance with the present invention; 
           [0026]      FIG. 5  shows a segment of another belt-driven conveyor in accordance with the present invention; 
           [0027]      FIG. 6A  shows a segment of yet another belt-driven conveyor in accordance with the present invention; and 
           [0028]      FIG. 6B  shows a detail of a driving wheel for the belt segment shown in  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Referring to  FIGS. 1 and 2 , a belt-driven conveying system (“conveyor”) will be described. The conveyor  10  includes a multiplicity of interconnected conveyor modules  15  having at least one belt-driven conveyor segment  25 . The belt segments  25  and conveyor modules  15  can be structured and arranged in a myriad of patterns to satisfy local transportation and plant requirements. Each conveyor module  15  is internally segmented into unit length zones or belt segments  25 , whose size (length and width) is determined by the dimensions of the work piece or by the object carrying a work piece  19 . Indeed, the length of a conveyor module  15  is an integer multiplier of the length of each belt segment  25  within that module  15 . 
         [0030]    For example, if the dimension of the work piece or object carrying the work piece  19  is 0.5 meters in length and the conveyor module  15  is approximately two meters in length, a total of four autonomous, belt-driven conveyor segments  25 , which are each slightly larger than the 0.5 meter length of the work piece or object carrying the work piece  19 , would be needed per conveyor module  15 . Those of ordinary skill in the art can appreciate that the size of the work piece or the object carrying the work piece  19 , the length of the conveyor module  15 , and the length of each belt segment  25  in each module are all variable. 
         [0031]    Each belt segment  25  of each conveyor module  15  includes first and second side rails  12  and  14 . The side rails  12  and  14  are structured and arranged to be mutually in parallel or substantially in parallel. The side rails  12  and  14  can be elevated to any desired height above a planar surface, e.g., a floor or slab, and/or suspended from an overhead structure, e.g., a ceiling or beams. 
         [0032]    The first and second side rails  12  and  14  of each belt segment  25  are fixedly coupled, respectively, to first and second sides rails  12  and  14  of adjacent belt segments  25   a  and  25   b  in the same conveyor module  15 . Furthermore, first and second side rails  12  and  14  of belt segments  25  located at the end of a conveyor module  15  are fixedly coupled, respectively, to first and second sides rails  12  and  14  of end portions of adjacent conveyor modules  15 . 
         [0033]    To alter the direction of flow of work pieces or objects carrying work pieces  19  or to branch the conveyor  10  in another direction(s), corner elements (not shown) are constructed on the basis of the length and width of the work piece or the object carrying the work piece  19 , to allow free network configuration based on such mathematical modularity. Optionally, vertical lifts (not shown) can be outfitted with discrete belt segments  25  and/or conveyor modules  15 , to allow vertical networking between conveyors  10  that are disposed at different elevations. 
         [0034]    Each conveyor module  15  includes at least one lateral brace  13 , which is structurally connected between parallel rails  12  and  14 , to add structural support to the belt segment  25  and to the conveyor module  15 . Although the lateral braces  13  shown in  FIGS. 1 and 2  are disposed orthogonal or substantially orthogonal to each of the side rails  12  and  14 , struts for lateral bracing, instead, could be crossed, e.g., to form an X (not shown). 
         [0035]    Belt segments  25  have modular dimensions that are pre-determined according to the size (length and width) of a work piece and/or of an object carrying a work piece  19 . Moreover, each belt segment  25  is structured and arranged to provide autonomous transport of a work piece and/or of an object carrying a work piece  19 , to transport the work piece and/or the object carrying a work piece  19  from one end of the belt segment  25  to the other end. Accordingly, each belt segment  25  includes its own supporting and conveying means and its own driving means and, more specifically, each belt segment  25  includes a pair of drive belts  20  and belt-supporting wheels, i.e., idler wheels  18 , which physically support and convey the work piece and/or the object carrying the work piece  19 , and a motor  11  and a pair of belt-driving wheels  16   a  and  16   b  that propel the pair of drive belts  20 . 
       Belt Segment 
       [0036]    As mentioned above, each belt segment  25  is structured and arranged to provide autonomous transport of a work piece and/or of an object carrying a work piece  19 , to transport the work piece and/or the object carrying a work piece  19  from one end of the belt segment  25  to the other end. Accordingly, each belt segment  25  includes its own supporting and conveying means as well as its own driving means. The supporting and conveying means provide underlying indirect rolling support to the work pieces and/or to the objects carrying the work piece  19  and transport work pieces or objects carrying work pieces  19 , e.g., pallets, boxes, and the like, from one end of the belt segment  25  to the other. The driving means is adapted to provide the inertial force necessary to drive the supporting and conveying means. 
         [0037]    Referring to  FIGS. 2 and 3 , an illustrative driving means is shown. The driving means can include a drive motor  11  and first and second belt driving mechanisms, each of which includes plural driving wheels  16   a  and  16   b . The driving wheels  16   a  and  16   b  are disposed, respectively, on the first and second side rails  12  and  14 . An extended drive shaft  17  is mechanically coupled to each of the driving wheels  16   a  and  16   b.    
         [0038]    The motor  11  is adapted to directly drive, i.e., rotate, one of the two driving wheels  16   a  and respective belt driving mechanism and to indirectly rotate the other driving wheel  16   b  and belt driving mechanism via the extended drive shaft  17 . The belt-driving mechanisms are synchronized by the connecting drive shaft  17 . Consequently, transported work pieces or objects carrying work pieces  19  rest on and are supported by the drive belts  20 , which are synchronously driven. The connecting drive shaft  17  and its means of attachment to the driving wheels  16   a  and  16   b  must also meet design criteria, which excludes the generation of contaminating particulates. Accordingly, the designs described below are unique, because they allow the first and second conveyor rails  12  and  14  to be slightly out of alignment. As a result, the connecting drive shafts  17  may attach to each of the driving wheels  16   a  and  16   b  in a less than a perfectly orthogonal fashion. 
         [0039]    Indeed, referring to  FIG. 3 , without the disclosed connecting drive shaft  17  and driving wheel  16   a  configuration, were the connecting drive shaft  17  to enter the driving wheels  16   a  and  16   b  at a non-orthogonal angle, rotation would induce strain on the shaft  17  and on the attachment flange, forcing one or both to wear excessively. To circumvent this problem, the ends  42  of the drive shaft  17  can be substantially flattened from the round. The flange attached to the wheel hub  31 , can be structured and arranged to include a centrally positioned slot  35  to accommodate the flat ends  42  of the shaft  17 . The slotted openings  35  in the flange are counter bored and rounded on the shaft entry side, to accommodate a less than orthogonal shaft  17  without strain. Rotating this assembly will then precess the shaft  17  in the slot  35  freely, eliminating or substantially eliminating any undesired material wear. Material selection is also important to minimize incident friction at the point of insertion of each slot  35 . 
         [0040]    Preferably, the motor  11  is coupled to a driving wheel  16  and the connecting drive shaft  17  via a magnetic hysteresis clutch that is integrated internal to the driving wheel  16 . The magnetic hysteresis clutch allows different driving speeds between the drive belt  20  and the motor  11  during acceleration and deceleration. The variable load associated with each belt segment  25 , e.g., fully-loaded, partially-loaded, and empty, affects the inertia of the work piece or object carrying the work piece  19 . 
         [0041]    The hysteresis clutch has an internal, rotary portion and an external clutch housing, which is the driving wheel  16  itself. The magnetic hysteresis clutch is adapted so that the internal, rotary portion is fixedly coupled to, i.e., pressed onto, the rotor or drive shaft of the motor  11  while, due to a magnetic hysteresis effect, the external, clutch housing portion (not shown) is free to rotate asynchronously on the same rotor or drive shaft. In this manner of operation, when desired, the motor  11  can continue to drive the internal, rotary part of the clutch while, at the same time, the external clutch housing portion is arrested from rotating. 
         [0042]    The drive belts  20  are driven by each of the drive wheels  16   a  and  16   b  that are mechanically coupled to the external clutch housing portion. Hence, by engaging and disengaging the external clutch housing portion, the motor-clutch combination can be controlled to deliver limited driving torque to the belts  20  that is independent of speed. For example, if motor torque exceeds the retarding forces on the belts  20  and the external clutch housing portion, the clutch housing portion will de-synchronize from the motor drive shaft turning speed. As a result, the external clutch housing portion will rotate at the retarded speed of the spinning drive belt  20 . Advantageously, while the clutch housing is de-synchronized and rotating at a retarded speed, it continues to exert a pre-established, constant driving torque. 
         [0043]    The supporting and conveying means of each belt segment  25  includes a pair of rails  12  and  14  that are structured and arranged to structurally support the dead load of the driving and conveying means as well as the live load of a work piece and/or of any object carrying a work piece  19 . The work pieces or objects that carry work pieces  19  are in direct contact with and ride directly on the pair of drive belts  20 , which, when rotated by corresponding driving wheels  16   a  and  16   b , move the work pieces or objects carrying work pieces  19  from one end of the belt segment  25  to the other end. The drive belts  20  travel along the idler wheels  18 , which are adapted to rotate freely with the belts  20  without adding additional driving forces. 
         [0044]    Each drive belt  20  is structured and arranged to journey over the freely-rotatable idler wheels  18 . Idler wheels  18  are removably attached to the first and second side rails  12  and  14 , e.g., using bearing combinations, screws, bolts or rivets having low-friction axles, and the like, so that the weight of the work pieces or objects carrying work pieces  19  is transferred to the first and second side rails  12  and  14  via the drive belt  20  and idler wheels  18 . Idler wheels  18  are spaced along the side rails  12  and  14  at critical intervals, which are determined by the belt speed, vibration level, and other design requirements, as will be discussed further, below. 
         [0045]    At one end of each of the first and second side rails  12  and  14  of each belt segment  25 , opposite the driving wheels  16   a  and  16   b , a pair of idler wheels  18   a  and  18   b  serves as a return means for the belt  20 . The diameter of the return wheels  18   a  and  18   b  can be the same or substantially the same as the diameter of the driving wheel  16   a  or  16   b  and/or the idler wheels  18  or may be larger or smaller than both. Driving wheels  16   a  and  16   b  as well as the return idler wheels  18   a  and  18   b  can also be critically shaped to maintain central positioning and tracking of the drive belt  20 . 
         [0046]    Drive belt lengths are determined by the length of a belt segment  25  less the measure or amount of critical stretch of the elastic belt  20  for tensioning purposes. Wheel crown cross-sectional geometry for driving wheels  16  and idler wheels  18  is determined by the belt material, cross-sectional geometry, and the like. Exemplary combinations of various belts and wheel types will be described below. 
         [0047]    Referring to  FIG. 4 , there is shown a clutch-driven primary driving wheel  16   b  that has a relatively smooth, centering-crown machined onto its outer periphery. The centering-crown is adapted to center a relatively flat, relatively thin, elastic belt  20 . The drive belt  20  is returned at one end of the belt segment  25  using a similarly-crowned and similarly-flanged return idler wheel  18   b.    
         [0048]    Between the pair of driving wheels  16   a  and  16   b  and their corresponding return wheels  18   a  and  18   b , the drive belt  20  journeys on smaller idler wheels  18  that include a flange  30 . The flanged idler wheels  18  are structured and arranged to laterally contain the work piece or object carrying the work piece  19 . 
         [0049]    A relatively thin belt thickness is desirable because, although the idler wheels  18  rotate at the same rate, those portions of the idler wheel  18  closer to the axis of rotation. i.e., at or near the root, rotate more slowly relative to portions of the idler wheel  18  that are disposed farther from the axis of rotation. As a result, any difference in the velocities of two surfaces on the flange  30  that contact the work piece or object carrying the work piece  19  may result in undesirable rubbing, which may result in frictional particulation. Consequently, relatively thin, relatively flat drive belt  20  cross sections are more desirable, to reduce the velocity differential between potential points of contact of the work piece or the object carrying the work piece  19  and to maintain required cleanliness levels. 
         [0050]    Referring to  FIG. 5 , there is shown a cross-sectional view of another embodiment of a belt segment  25  for a system  10  as seen from the return idler wheel end of the belt segment  25 . The motor  11  is mechanically coupled to one of the driving wheel  16   a  via a magnetic hysteresis clutch. The driving wheels  16   a  and  16   b  (at the far end of the figure) drive an L-shaped or substantially L-shaped belt  20  that includes a raised edged section  33 . The long leg of the “L” is disposed on and generally in the plane of the peripheral surface of the wheels while the short leg of the “L” is orthogonal or substantially orthogonal thereto. The confining flanges  33  on the L-shaped belt are structured and arranged to laterally confine the work piece or object carrying the work piece  19  therebetween. 
         [0051]    Between the driving wheels  16   a  and  16   b  and respective return idler wheels  18   a  and  18   b  there are plural idler wheels  18  that, optionally, may include a confining flange  36  (shown in phantom). When a flange  36  is included with the idler wheels  18 , the bottom, outside corner of the L-shaped belt  20  is guided by the idler wheels  18  at their root. 
         [0052]    In this second embodiment, each of the pair of driving wheels  16   a  and  16   b  and the pair of return wheels  18   a  and  18   b  are machined to include belt-centering crowns on an outer peripheral surface on which the belt  20  travels. Because the cross-section of the L-shaped belt  20  is not uniform, the centers of the crown radius  34  machined on the driving wheels  16   a  and  16   b  and on the return idler wheels  18   a  and  18   b  are slightly offset relative to the centerline  37  of the drive belt  20  by a distance x, to center the drive belt  20  properly. The dimension of the offset x is determined by the material of the belt, the belt thickness, and so forth. 
         [0053]    Referring to  FIG. 6A  and  FIG. 6B , there is shown a belt segment  25  having relatively thin, rounded or substantially rounded, elastic drive belts  20  that are tightly stretched between driving wheels  16   a  and  16   b , which are disposed at one end of the belt segment  25 , and corresponding return idler wheels  18   a  and  18   b , which are disposed at the other end of the belt segment  25 . A first driving wheel  16   a  is directly propelled by a motor  11  via an internal hysteresis clutch. A second driving wheel  16   b  is indirectly propelled by a motor  11  coupled thereto by the internal hysteresis clutch and via the drive shaft  17 . Between the pair of driving wheels  16   a  and  16   b  and respective pair of return idler wheels  18   a  and  18   b  are disposed plural idler wheels  18  for guiding the drive belt  20  and for supporting the weight of the work piece or object carrying the work piece  19 . 
         [0054]    All of the wheels are machined to include a relatively smooth, reverse or negative crown  38  in their outer peripheries. The negative crown  38  is adapted to center and retain the rounded or substantially rounded belt  20  cleanly, owing to the crown radius  39 . Preferably, the radius  39  is larger then the radius of the drive belt  20 , to minimize cross motion of belt and wheel surfaces, which ensures particulate-free motion. 
       Controller 
       [0055]    Control of the asynchronous movement and flow of the work piece or object carrying the work piece  19  can be achieved by embedding a microcontroller or a network of microcontrollers in the conveyor body. The controller  50  ( FIG. 5 ) includes hardware or software applications to execute fundamental transport logic, such as asynchronous flow and soft accumulation, i.e., without bumping, linear drive and speed regulation, acceleration and deceleration of the work piece or object carrying the work piece  19 , logic controlling the branching into and merging from plural flow, as well as for tracking the work piece or object carrying the work piece  19  from a source or point of entry to a destination or exit point. Asynchronous flow on the internally segmented conveyor  10  follows the embedded logic where each belt segment  25  is capable of sensing the presence of a work piece or of an object carrying a work piece  19  and allows work piece or object carrying the work piece  19  entry from a direction of upstream flow if, and only if, that belt segment  25  is confirmed to be vacant and available, which is to say empty of any work piece or object carrying the work piece  19 . Such logic inherently promotes linear movements and soft accumulation of work pieces or objects carrying the work pieces  19 . 
         [0056]    An even further improvement on the above control logic includes the preferential movement of work pieces or objects carrying work pieces  19  towards belts segments  25  that are in the process of evacuating a respective work piece or object carrying a work piece  19 . The improved logic allows higher throughput by increasing flow density on the conveyor  10  and, further, includes time and distance calculation of physical positions of discrete work pieces or objects carrying the work pieces  19 . Such an improved algorithm can be enhanced by the addition of additional sensors  60  ( FIG. 2 ) on each belt segment  25  of the conveyor  10 , which enables more precise location of discrete work pieces or objects carrying work pieces  19 , than the original segments would allow. 
         [0057]    A further improvement towards higher density and higher throughput would be the mechanical reduction of the belt segment  25  size. The reduction would mean zone segment size less than that of work pieces or objects carrying the work pieces  19 , but still an integral fraction of it. 
         [0058]    Many changes in the details, materials, and arrangement of parts and steps, herein described and illustrated, can be made by those skilled in the art in light of teachings contained hereinabove. Accordingly, it will be understood that the following claims are not to be limited to the embodiments disclosed herein and can include practices other than those specifically described, and are to be interpreted as broadly as allowed under the law.