Abstract:
A belt conveyor having clutch-driven flights for extremely low-torque operation. The flights have pivot members that rotate about an axis over a limited range of angles. A clutch mechanism includes a spring pushing a clutch wheel against a pivot member. The clutch wheel is arranged to rotate as the conveyor belt advances. Frictional contact between the rotating wheel and the pivot member imparts a moment on the flight to raise it to an extended position. When the flight is encumbered even by a light load, the low-torque mechanism automatically slips to prevent the flight from rising to the extended position.

Description:
BACKGROUND 
       [0001]    The invention relates generally to power-driven conveyors and, more particularly, to modular belt conveyors having retractable flight members. 
         [0002]    Many conveying applications require that conveyed articles be spaced apart on a conveyor belt. For example, merging two or more flows of articles into a single file without collisions is a common requirement. One conveyor used to accomplish this without slowing the belt or using complex sensors and external spacing bars is described in co-pending U.S. patent application Ser. No. 11/610,737, filed on Dec. 14, 2006, by the applicant of this application. The disclosure of that application is incorporated herein by reference. The conveyor includes a conveyor belt, belt rollers, and flights. Lower surfaces on the rollers engage a roller-engagement surface below the belt. Upper surfaces of the rollers define a plane above the belt. As the belt advances, the rollers roll on the roller-engagement surface and rotate to move an article supported on the rollers forward along the plane. The flights, which are spaced apart along the length of the belt, include cams that engage a cam surface below the belt to impart a moment on the flight and projections that respond to the moment by rotating from a retracted position to an extended position blocking the further advance of an article propelled forward. The cam-actuated flights, in conjunction with the article-accelerating rollers, cause conveyed articles to be staged at known locations on the belt for proper merging. The flights assume a retracted position as they return from the returnway before they encounter the cam surface. A conveyed article resting atop a retracted flight before it is raised to the extended position prevents the flight from popping up by cam action until the article is pushed clear of the flight by the rollers. Then the cam pops the unencumbered flight up to the extended position. When a flight is weighted down, its cam merely slides along the cam surface. 
         [0003]    This device works well in most applications. But, in the case of lightweight articles, such as envelopes, for example, the cam-actuated flights have enough torque to rotate the retracted flight with a lightweight article atop it to the extended position. The lightweight article may be left stranded, leaning from the top of the flight without enough frictional contact with the belt rollers to clear the article from the flight. Consequently, the regular positioning of articles atop the belt for reliable merging or other applications requiring uniform product spacing is disrupted. 
       SUMMARY 
       [0004]    This shortcoming is overcome by a conveyor embodying features of the invention. The conveyor comprises a conveyor belt arranged to advance in a direction of belt travel. A flight having a pivot member and a projection is coupled to the conveyor belt. The pivot member is rotatable over a limited angular range about an axis that is transverse to the direction of belt travel. The projection rotates from a retracted position generally parallel to the upper outer surface of the belt to an extended position upstanding from the upper outer surface by rotation of the pivot member. A clutch mechanism is mechanically coupled to the flight. The clutch mechanism rotates by contact with the engagement surface as the conveyor belt advances in the direction of belt travel. The rotation induces a moment on the flight about the axis. The moment is directed to rotate the projection about the axis from the retracted position to the extended position. 
         [0005]    In another aspect of the invention, a conveyor belt embodying features of the invention comprises a flight rotatably coupled to the conveyor belt and a clutch mechanism rotatably coupled to the conveyor belt. As the clutch mechanism is rotated by contact with an engagement surface external to the belt as it advances in a direction of belt travel, a driving face of the rotating clutch mechanism biased in contact with a driven face of the flight rotates the flight from a first position to a second position. 
         [0006]    In yet another aspect of the invention, a modular conveyor belt embodying features of the invention comprises a series of rows of belt modules linked end to end by hinge rods through interleaved hinge elements of consecutive rows into an endless belt. The belt has an outer surface and an opposite inner surface. Openings extend from the inner surface to the outer surface. One or more flights are rotatably attached to the modular conveyor belt in the openings. The flights are adapted to be rotated from a retracted position resting atop the outer surface of the belt to an extended position upstanding from the belt. One or more wheels are rotatably attached to the belt in the openings. Salient portions of the wheels extend from the opening past the inner surface of the belt. Pivot members on the flights have driven faces. The wheels have driving faces. The driving faces are biased against the driven faces to form a clutch that allows the driving faces of the wheel, when rotating, to apply a moment directed to rotate the flights from the retracted position to the extended position when the flights are unencumbered and to slip on the driven faces of the pivot members when the flights are encumbered. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These features and aspects of the invention, as well as its advantages, are better understood by referring to the following description, appended claims, and accompanying drawings, in which: 
           [0008]      FIG. 1  is an axonometric view of a portion of a conveyor embodying features of the invention, including a clutch-driven flight in an extended position; 
           [0009]      FIG. 2  is an axonometric view of the conveyor in  FIG. 1  from a slightly different perspective showing the flight in a retracted position; 
           [0010]      FIG. 3A  is a side elevation view of the conveyor of  FIG. 1 ;  FIG. 3B  is a side elevation view of the conveyor of  FIG. 2 ; and 
           [0011]      FIG. 4  is a partly exploded view of the clutch-driven flight in the conveyor belt in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    A portion of a conveyor embodying features of the invention is shown in  FIGS. 1 ,  2 ,  3 A, and  3 B. The conveyor  10  comprises a conveyor belt  12  driven in a direction of belt travel  14  along a carryway that includes a support plate  16  having an upper engagement surface  17 . The conveyor belt may be a flat belt, but is preferably a modular plastic conveyor belt constructed of a series of rows  18  of one or more side-by-side injection-molded thermoplastic modules  20  linked together by hinge rods  22  through interleaved hinge elements  24  along leading and trailing ends of each row. The belt extends in thickness from a top outer surface  26  to an opposite inner surface  27 . 
         [0013]    Some of the hinge elements along one end of some of the belt modules are missing to provide openings  28  for article-accelerating rollers  30  or clutch wheels  32 . The support plate  16  supports the conveyor belt on the carryway and provides an engagement surface  17  on which the article-accelerating rollers can roll as the conveyor belt advances. Articles  34  supported atop the rollers  30  are accelerated forward along the belt by rotation of the rollers until the articles contact the flight  36  in an extended position blocking their further advance, as in  FIGS. 1 and 3A . The positions of the flights on the belt define relative registered positions along the length of the belt that can be used to set precise spacings between consecutive conveyed articles, such as for a pre-merge conveyor used to prevent collisions between merging articles. 
         [0014]    The flight  36  rotates from a retracted position as shown in  FIGS. 2 and 3B , to an extended position ( FIGS. 1 and 3A ). In the retracted position, the flight rests atop the outer conveying surface  26  of the belt, generally parallel to the direction of belt travel  14 . In this non-blocking position, articles are propelled forward by rotation of the belt rollers  30  rolling on the engagement surface  17 . In the extended position, the flight stands up from the outer belt surface in an article-blocking position with a rear edge  40  of the flight serving as a registration surface. Intermediate structure  42  in the belt module forms a stop past which the flight cannot rotate. In this example, the flight can rotate over a limited angular range of about 90° between the retracted and extended positions. But, in other applications, the intermediate structure and the flight could be structured to allow the flight to rotate through a range of less than 90° or a range up to as much as 180°. 
         [0015]    Details of the flight are shown in more detail in  FIG. 4 . The flight  36  comprises four pivot members  44  having aligned bores  46 . A projection  48  extends outward from the flight to a top edge  50 . The projection is shown as a thin, generally rectangular structure whose rear edge  40  defines a registration position on the belt. The flight is preferably made of a lightweight material such as plastic. The pivot members are grouped in two pairs on opposite lateral halves of the flight. A gap  52  is formed between the pivot members of each pair. A bushing, or sleeve  54 , preferably made of stainless steel, is inserted into the bore of the outside pivot member, through a bore  56  in one of the wheels  32 , through the center of a coil spring  58 , through the bore of another wheel, and into the bore of the inside pivot member. The outer diameter of the sleeve is slightly greater than the nominal inside diameter of the bores in the pivot members so that the sleeve is retained firmly at each end in the pivot members in a press fit. The inside diameter of the bores in the wheels is slightly greater than the outside diameter of the sleeve so that they can rotate on the sleeve. The coil spring serves as one means for biasing the wheels against corresponding pivot members. An axle, in this example, one of the belt&#39;s hinge rods  22 , is received in the sleeve and defines an axis of rotation  60  transverse, preferably perpendicular, to the direction of belt travel. The pivot members, the wheels, and the coil spring are all coaxially aligned along that axis. 
         [0016]    The spring-loaded wheels engage the pivot members in a clutch arrangement. The wheels have flat driving faces  62  on the sides of the wheels opposite the spring. The driving faces are pushed against driven faces  64  on corresponding confronting sides of the pivot members. As the belt advances on the carryway, rotation of the wheels  65  rubbing against the pivot members imparts a moment  66  about the axis of rotation on the pivot members that rotates a flight unencumbered by a conveyed article or the stop  42  to the extended position. When the flight is weighted down by a conveyed article or reaches the stop and is hindered from rotating, the driving faces of the clutch wheels slip on the driven faces of the pivot members. The total friction between the wheels and the pivot members can be increased or decreased by adjusting the tension in the spring, changing the contact area between the driving and the driven faces, or changing the materials out of which the wheels and the flight are made to adjust the coefficient of friction. 
         [0017]    In a preferred mode of operation, as the flights return to the carryway around an idle sprocket (not shown), they are gravitationally returned to their retracted state while running upside down along the returnway. Until the clutch wheels  32  reach the engagement surface  17 , the flights remain retracted. If an article  34 , even a lightweight article, is atop a flight above the engagement surface, the flight does not pop up because the low torque produced by the clutch mechanism is insufficient to overcome the load and rotate the flight. (Of course, as already mentioned, the amount of torque may be set to a predetermined level to meet other operating requirements.) The wheels slip on the pivot members of the flight until the article is propelled forward past the flight by contact with the rotating rollers  30  and the clutch wheels  32 . Windows  68  are provided in the flight projections to clear the belt rollers when the flight is retracted. The diameter of the clutch wheels and the rollers is preferably equal so that their salient portions extending above and below the belt define common planes—an article-supporting plane  70  on top and a plane containing the engagement surface  17  along the carryway—parallel to the conveying surface of the belt. And the diameter of the clutch wheels exceeds the diameter of the pivot members so that the wheels extend above the level of the retracted flight into position to accelerate conveyed articles. Thus, both the rollers and the clutch wheels can be activated by contact with the same engagement surface and can also be used to propel conveyed articles forward. 
         [0018]    Although the invention has been described in detail with respect to a preferred version, other versions are possible. For example, both the clutch wheels and the belt rollers are shown rotating on hinge rods. But they could rotate on other axles in the belt not serving as hinge rods. As another example, the flight could be rotated through an angular range other than 90° between retracted and extended positions. And the clutch-driven flights may serve different purposes and be shaped differently from those described. Furthermore, the clutch-driven flight works on belts without article-accelerating rollers. So, as these few examples suggest, the scope of the claims is not to be limited to the preferred versions.