Abstract:
A conveyor system is provided, in which the drive chain which drives products along the conveyor has features that permit control of the threshold driving force that will be reached before the chain&#39;s carrier rollers begin to rotate to permit accumulation of product on the conveyor. The threshold driving force is controlled by friction members which are located between split portions of the carrier rollers and by the angle of the outer surface of the carrier rollers. The steeper the angle, the greater the threshold force.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to conveyor chains for accumulating conveyors. Accumulating conveyor chains are known. These chains generally include a roller which carries a product, and, when the products begin to back up on the conveyor, the rollers begin to rotate, allowing the products to sit on top of the chain while the chain continues to run, without creating a large back line pressure on the products. A problem that can be encountered with such chains is that, if a substantial driving force is needed to move the products, the rollers may begin to rotate too soon, so that the products are not moved by the conveyor. Prior art accumulating conveyors generally do not allow control or adjustment of the threshold force at which the rollers begin to rotate. 
     SUMMARY OF THE INVENTION 
     The present invention provides a chain design in which the threshold force at which the rollers begin to rotate is controlled. In the design of the present invention, the central carrier roller that carries the product is made in two pieces, and a friction member is mounted between the two roller pieces so as to restrict rotation of the roller pieces until a threshold force is reached. Also, in the preferred embodiment, the central carrier roller pieces may be tapered at various angles, in order to control the amount of friction force exerted on the roller pieces by the friction member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view through a conveyor using a chain made in accordance with the present invention; 
     FIG. 2 is a top view of the chain of FIG. 1; 
     FIG. 3 is a side view of the chain of FIG. 1; 
     FIG. 4 is an exploded perspective view of a portion of the chain of FIG. 1; and 
     FIG. 5 is an enlarged front sectional view of the chain of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-5 show an example of a chain 10 made in accordance with the present invention. FIG. 1 shows the chain 10 mounted on an extruded support frame 12, and driving a carriage 14. The weight of the carriage 14 is carried on the support frame 12 by rollers 13, which roll along the support frame 12. The carriage 14 includes a spring-biased drive member 16, the bottom surface 18 of which has an inverted V-shape. The contour of the inverted V-shaped bottom surface 18 of the drive member 16 is the same as the contour 34 of the carrier rollers 20 of the chain 10. As will be explained later, the slope of the V-shaped contour affects the drive force with which the chain 10 drives products being carried on the chain, and different slopes can be used, as needed. The carrier roller 20 is made in two pieces 20a, 20b, and a friction member 22 is mounted between and in friction contact with the pieces 20a, 20b. The friction member 22 is recessed below the outer drive surface 34 of the carrier roller 20 and does not extend above that drive surface 34. The friction member 22 prevents the carrier roller 20 from rotating until some threshold force is reached. This means that the chain 10 will drive the carriages 14 until the threshold force is reached. Once the threshold force is reached, the carrier rollers 20 will rotate so that the carriages 14 remain stationary as the chain 10 passes under the carriages 14. 
     FIG. 1 also shows that, in addition to the carrier roller 20 and the friction member 22, the chain 10 includes chain pins 24, inner sidebars 26, outer sidebars 28, and support rollers 30. At intervals along the chain 10 are pairs of outer guiding sidebars 28a, which project downwardly to help guide the chain 10 between the rails 29 of the frame 12. As shown in FIGS. 2 and 3, the carrier rollers 20 are mounted on every odd-numbered chain pin 24a, while the even-numbered chain pins 24b do not carry a carrier roller 20. (The use of the terms even-numbered and odd-numbered is arbitrary. The odd-numbered pins 24a may also be referred to herein as forward pins, and the even-numbered pins 24b may be referred to as rear pins.) All the chain pins 24a, 24b carry left and right support rollers 30, which roll along the frame 12 as the chain 10 is driven. The mechanism for driving the chain 10 is not shown in these drawings but includes a drive sprocket, as is well known in the art. The friction members 22 are mounted on the odd-numbered chain pins 24a but also partially encircle the even-numbered chain pins 24b, which prevents the friction members 22 from rotating relative to the chain 10. It would be possible to use other known methods to prevent the friction members 22 from rotating relative to the chain 10, such as keying the friction members 22 to the pins 24 or to the bushings 42 or press fitting them onto the chain 10, but this embodiment is preferred. Each of the friction members 22 includes horizontally-projecting wings 32, which cover a space in the chain 10, preventing dirt and debris from getting into the chain 10. 
     FIG. 4 is an exploded perspective view of the chain 10, showing the odd-numbered pins 24a, the even-numbered pins 24b, the friction members 22 with wings 32, the carrier roller halves 20a, 20b, each having a tapered outer edge surface, so that, when they are put together, they form an inverted V-shaped drive surface 34, which contacts the complementary-shaped bottom surface 18 of the drive member 16. FIG. 4 also shows the inner sidebars 26, outer sidebars 28, support rollers 30, and snap-rings 36, which fit into ring-shaped grooves 38 in the pins 24 (shown in FIG. 5). 
     FIG. 5 is the same sectional view of the chain 10 as shown in the top portion of FIG. 1, but it is enlarged to show more detail. It can be seen that there is a bushing 42, pressed onto the odd-numbered pins 24a, on which the split carrier roller 20 is mounted. As shown in this view, there is an angle α between the drive surface 34 of the carrier roller portions 20a, 20b and the horizontal (shown in phantom). The axis 40 of the pin 24 defines the horizontal direction. In this preferred embodiment, the angle α is 15°. The angle α may vary, depending upon the desired threshold friction force. The greater the angle α, the greater the threshold friction force, because, as the angle α increases, the spring force on the drive member 16 exerts a greater horizontal force on the carrier roller halves 20a, 20b, pushing them toward each other and against the friction member 22 with greater force. The greater the horizontal force against the friction member 22, the greater the friction force between the friction member 22 and the carrier roller halves 20a, 20b, and the greater the threshold force required to cause rotation of the carrier rollers 20 relative to the chain 10, meaning that the chain 10 will exert a greater drive force on the products being driven before the carrier rollers 20 begin to rotate relative to the chain 10. 
     The threshold force of the chain may also be varied by varying the materials used to make the chain. The higher the coefficient of friction between the carrier roller portions 20a, 20b and the friction member 22, the greater the threshold force. 
     So, the present invention provides an arrangement whereby the threshold force of the chain may be controlled, to ensure that the products are driven up to the threshold force before the chain goes into an idling or accumulation mode, in which the carrier rollers rotate as the chain passes under the stationary products. 
     It will be obvious to those skilled in the art that modifications may be made to the embodiment described above without departing from the scope of the present invention.