Abstract:
A system and method are disclosed that provide a specific volumetric output (e.g., product feed and discharge) of a material. In some implementations, these systems and methods are particularly suited for use with strand-type materials, namely, materials having difficult handling characteristics. For some implementations, a specific pile depth and width of a material is created on a moving belt to provide a specific volumetric output based on the speed of the belt. One or more leveling drums can be used to make the pile depth consistent. Moreover, a weighing system can be provided that is used in combination with the metering mechanism and other components (e.g., a control system) to create a “weight-loss” type weigh feeder.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a metering mechanism for strand-type bulk solid materials. 
       BACKGROUND 
       [0002]    The precise metering of materials (e.g., dry solids) is very important in many applications, particularly in the manufacturing processes of the numerous processing industries. Usually when such materials are continuously metered into such processes, they must be precisely controlled at specific feed rates so that the processes function as designed, that product formulation is correct, and that the quality of the end product does not suffer. Many of these applications are automated, and productivity demands that they proceed without human intervention to the greatest extent possible. 
         [0003]    On a global basis, a number of different types of feeders are utilized for metering the many thousands of different dry solid materials that are regularly used by manufacturers in their various processes. Such materials can be in the form of granules, powders, flakes, chunks, strands, and can be foodstuffs, plastics, chemicals, pharmaceuticals, ceramics, etc., with each possessing its own individual physical handling characteristics. In general, material is provided to a feeder continuously or periodically from storage supply and the feeder discharges the material at a desired output rate. Different feeders, however, have different capabilities, which depend on the design of the individual feeders and their principles of operation. 
         [0004]    Feeding mechanisms, especially when feeding adhesive, cohesive, fibrous, or hygroscopic dry solids materials, sometimes experience problems in handling the material due to the material either sticking to the walls of a supply hopper blocking downward flow, or bridging of the material in the feeding mechanism itself and/or the supply hopper supplying material to the feeder (e.g., compaction due to the adhesive, cohesive and/or compressible nature of the material). 
       SUMMARY 
       [0005]    In an aspect of the invention, a system and method are disclosed that provide a specific volumetric output (e.g., product feed and discharge) of a material. In some implementations, these systems and methods are particularly suited for use with strand-type materials, namely, materials having difficult handling characteristics. For some implementations, a specific pile depth and width of a material is created on a moving belt to provide a specific volumetric output based on the speed of the belt. One or more leveling drums can be used to make the pile depth consistent. Moreover, a weighing system can be provided that is used in combination with the metering mechanism and other components (e.g., a control system) to create a “weight-loss” type weigh feeder. 
         [0006]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Various features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]      FIG. 1A  is a first view of an implementation of a feeding mechanism for strand-type materials with an integral hopper. 
           [0008]      FIG. 1B  is a close up view of the region  250  of  FIG. 1A . 
           [0009]      FIG. 2A  is a second view from the perspective of the region  250  of  FIG. 1A  of an implementation of a feeding mechanism for strand-type materials and an integral supply hopper. 
           [0010]      FIG. 2B  is a close up view of the region  350  of  FIG. 2A . 
       
    
    
       [0011]    The figures are not drawn to scale. 
       DETAILED DESCRIPTION 
       [0012]    The following is a description of preferred implementations, as well as some alternative implementations, of a metering mechanism for materials. 
         [0013]    Users who require feeding “strand”-type materials (e.g., strands, fibrous, or any strand-type material that tends to clump, interlock, attach or otherwise exhibit poor metering and flowability characteristics) into their processes have historically found this to be challenging, whether the requirement is for metering by volume (volumetric metering) or by weight (weigh feeding). For fibrous or strand-type materials, the problem is generally more pronounced when the “strands” have a length of about 0.5 to 1 inch or more, such as those commonly encountered with the requirement to meter certain types of fiberglass. This problem stems from the typically difficult handling characteristics of such materials, making most commercially available dry solids feeding/metering mechanisms ineffective, unreliable and/or inaccurate. 
         [0014]    In addition, users who require that “strand-type” materials be accurately metered into their processes also require that the discharging feed stream be relatively smooth which, due to the nature of such materials, presents an additional challenge. Generally, such materials do not flow very well because of the tendency to interlock and/or form clumps that make metering difficult and sporadic, especially when product flow is channeled through converging or restrictive orifices or outlets, typical of various types of metering devices, especially when metering at feed rates below 50 or 100 pounds per hour. For example, in the case of fibrous or “strand-type” materials, strands tend to interlock with each other that make accurate metering and smoothness of flow difficult at best. 
         [0015]    Overview 
         [0016]    An implementation of a feeding mechanism suited for feeding strand-type materials operates on the principle of volumetric displacement, achieved by maintaining a specific pile depth and width of material on a variable speed belt, thereby providing a specific volumetric output (e.g., product discharge) over a given period of time, based on the speed of the belt. Producing a consistent, non-agglomerated material pile depth on the belt can result in good volumetric metering performance and operational dependability. Weigh feeder performance can be obtained by, e.g., utilizing such a device as the metering mechanism of a weigh feeder (e.g., an Acrison, Inc. “Weight-Loss” Weigh Feeder). 
         [0017]    Various implementations can be used, for example, to handle fibrous or strand-type materials having strand lengths of less than 0.125 inches to 1.5 inches or more. 
         [0018]    Such a metering mechanism can be made in various sizes to accommodate a wide range of feed rates. For example, a feeder with a belt having a useable width of approximately 12 inches can produce feed rates as low as about 20 pounds per hour upwards to about 2000 pounds per hour. Narrower or wider belts can result in correspondingly smaller or larger feed rates, respectively. Some implementations create a specific pile depth and width of material by using one or more rotating drums. In those implementations, it is sometimes preferred that the useable width of the belt is about the same as the effective width of one or more of the rotating drums. In practice, this can result in the belt and drum having about the same overall width. 
         [0019]    Implementations of a Feeder Mechanism 
         [0020]      FIG. 1A  is a view of a metering mechanism  101  with its supply hopper  102  for feeding strand-type materials. Material supply to the metering belt  201  is stored in hopper  102  mounted above the rear end of the metering belt  201  (e.g., an endless belt). The angle at which the hopper  102  tapers is chosen, in some implementations, to avoid bridging of the material. The hopper  102  and metering belt  201  are kept in substantially operational alignment by, among other things, support frame  203  and chassis  202 . The metering belt  201  is powered by a variable speed belt gearmotor (see  FIGS. 2A and 2B , item  306 ). In some implementations, the belt gearmotor operates at a very slow speed. Note that the gearmotors mentioned throughout this disclosure can be AC or DC, induction or synchronous, commutated or brushless, and/or could take the form of a stepper motor. Moreover, they may include reduction gear assemblies (e.g., to increase applied torque) or may be direct-driven. The gearmotors may be driven or controlled by, e.g., a variable speed motor controller such as the Acrison, Inc. 060 or 040 SCR/DC motor controllers, or by commercially available DC or AC variable speed motor controllers. 
         [0021]    A hopper discharge spout  205  directs material flow out of the feeder&#39;s integral supply hopper  102  and onto the back end of the metering belt  201 . The top half of the metering belt  201  travels from left to right, i.e., the rear pulley  210  rotates in a clockwise direction (the front pulley is not visible in this view (see  FIGS. 2A and 2B , item  311 ), but it rotates in the same direction as the rear pulley  210 ). Note, however, that the feeder  101  can be reconfigured such that material from the hopper  102  is discharged onto the metering belt  201  and moves from right to left. This reconfiguration could involve, e.g., reverse-mounting the feeder  101  relative to other elements of a system. 
         [0022]    Material from the feeder&#39;s supply hopper  102  is deposited onto the metering belt  201  in a manner that substantially avoids spilling material off the back and/or sides of the metering belt  201 . In this implementation, the terminus of the hopper discharge spout  205  is disposed in close proximity to the metering belt  201 . This small gap aids in keeping the material contained. Although not visible in this view, the back end of the hopper discharge spout  205  (i.e., the left side in this view of this implementation) is substantially solid to prevent spillage whereas the front end of the hopper discharge spout  205  (i.e., the right side in this view of this implementation) is substantially open to allow unrestricted flow of the material in the hopper  102  onto the metering belt  201 . Possible cross-sections for the hopper discharge spout include a half-circle (e.g., “C” shaped) or an open triangle (e.g., “V” shaped). Also, mounted on the chassis are side guides (see  FIGS. 2A and 2B , item  301 ) that maintain the desired width of material on the belt  201  and prevent material from flowing off either side of the metering belt  201 . 
         [0023]    Mounted on the feeder chassis  202 , directly above the metering belt  201 , are two pile depth (spiked) leveling drums (front  206  and rear  207 ). As shown, the drums  206  and  207  are spaced apart disposed above and oriented across and parallel to the upper surface of the belt  201 . In some implementations, front and rear drums  206  and  207  are mechanically connected together and driven by a single gearmotor  208 . In some implementations, the gearmotor  208  rotates drums  206  and  207  at a speed proportional to the speed of the metering belt  201 . Although it may vary depending upon the implementation, from this perspective, rear drum  207  and front drum  206  rotate in the same clockwise direction. As material flows out of the supply hopper  102  and onto the belt, the solid diameter of the rotating rear leveling drum  207  controls the pile depth of material that is conveyed forward (i.e., rightward in this view of this implementation). The rear leveling drum  207  also controls material that it catches in the leveling spikes  209  and partially directs it backward toward the hopper discharge spout  205 . Put another way, excess material is contained and maintained within the reservoir (e.g., the shaded area  211 ) of the hopper discharge spout  205  by the rotational action of the “spiked” rear leveling drum  207 , which also partially restricts forward movement of excess material on the metering belt  201 . The action of the front leveling drum  206  further levels the height of material being conveyed forward by the belt  201 , such that as the material reaches the discharge point of the belt, its pile depth across the width of the belt  201  is substantially consistent and uniform. Some implementations may omit the front leveling drum  206 . 
         [0024]    The leveling drums  206  and  207  include “spikes”  209  distributed on their outside diameters that, in conjunction with the leveling drums, assist in controlling the height of material on the belt  201 , but also, substantially eliminate the possibility of interlocking and/or clumping of material on the belt  201  as it is conveyed forward and off the belt. The leveling spikes  209  may be disposed in a variety of patterns and at different densities depending on, e.g., the characteristics of the material(s) to be processed. The leveling spikes  209  typically have a preselected length, but each leveling spike  209  need not have the same length, and can vary in length depending upon application parameters and material physical characteristics. One possible material for constricting the spikes  209  is stainless steel. Ceramics, mild steel, and plastics are usable as well in some implementations. 
         [0025]    Generally, the amount of material that the leveling drums  206  and  207  and their spikes  209  handle and control depends on how close they (and their spikes  209 ) are to the surface of the metering belt  201 , the rotational speed of the leveling drums  206  and  207 , and the speed of belt  201 . In some implementations, it is the distance between the upper surface of the belt and the drum (and more particularly, the distance between the upper surface of the belt and the closest line tangent to the diameter of the drum) that substantially determines the maximum height of material that will be allowed to pass. In some implementations, the distance from the upper surface of the belt to the outermost portion (end tip) of a spike which is substantially perpendicular to and adjacent to the upper surface of the belt aids in maintaining the depth of material on the belt. At any given time, more than one spike may be substantially perpendicular and adjacent to the upper surface of the belt. It is also possible at any given time for there to be no spikes that are substantially perpendicular and adjacent to the upper surface of the belt. “Adjacent” may be used to distinguish between spikes that are nearer to the belt as compared to those that are on opposite sides of the circumference of the drum (e.g.,  206  and  207 ). 
         [0026]    The heights of the front and rear leveling drums  206  and  207  (and their spikes  209 ) relative to the metering belt  201  are adjusted by the drum height adjustment mechanism  204 . The adjustment mechanism  204  can take the form of a rotating threaded shaft (e.g., a screw) as shown. Rotation of the threaded shafts  204  causes the drums  206  and  207  (and spikes  209 ) to become closer or further away from the metering belt  201 . The height of the front and rear drums  206  and  207  relative to the metering belt  201  may be the same or may differ. The closer that the leveling drums  206  and  207  and their spikes  209  are to the metering belt  201 , the lower the maximum volumetric flow rate will be, due to lower material height on the metering belt  201  and its related volumetric capacity. The further leveling drums  206  and  207  and their spikes  209  are from the metering belt  201 , the greater the maximum volumetric flow rate, due to a higher material height on the belt  201 . Depending upon the implementation, the distance the spikes  209  and/or drums  206  and  207  are above the metering belt  201  is determined by product characteristics and feed rate requirements. In some implementations, such adjustment would allow the leveling spikes  209  to be anywhere between (and including) about 0.12 to 1.5 inches above the metering belt  201 . This height can be adjusted manually, e.g., by having an operator adjust threaded shafts  204 . 
         [0027]    As mentioned, the height of the drums  206  and  207  is related to the maximum volumetric flow rate. The drums  206  and  207  create a certain pile depth of material, and moreover, the material will maintain a certain width on the belt  201  (see  FIG. 2A , items  308  and  309 ) based on the distance established by belt side guides  301 . The volumetric flow rate is related to the speed of the metering belt  201  combined with the width of the material on the belt  201 , controlled by side belt guides  301 . To control the volumetric flow rate, the speed of the metering belt  201  is varied, along with the speed of the leveling drums  206  and  206 , which speed may be electrically slaved to the speed of the metering belt  201 . A sensor  214 , which can take the form of a tachometer integral to either the belt gearmotor drive  208  or belt pulley (e.g.,  210 ), can monitor the speed of the metering belt. Alternatively, the back EMF of the motor that drives the belt (e.g., item  306  of  FIGS. 2A and 2B ) can be detected (e.g., by reading the voltage generated by the motor between voltage pulses of a pulse-driven motor). 
         [0028]    By using the combination of the front and rear pile depth spiked leveling drums ( 206  and  207 , respectively), a substantially consistent pile depth on the metering belt  201  can be achieved. In some implementations, the front pile depth spiked leveling drum  206  would normally rotate at a faster speed (e.g., 2 to 3 times faster) than the rear pile depth leveling drum  207 . Both the front and rear drums  206  and  207 , respectively, are in some implementations designed and operated at speeds that will not degrade the material being metered. For example, excessive drum speed may damage certain materials and certain drum materials may react with or otherwise damage certain materials. Also, the drums  206  or  207  can themselves be damaged by abrasive materials. Accordingly, one possible drum and spike material is stainless steel. Ceramics, mild steel, aluminum and plastics are usable as well. 
         [0029]      FIG. 1B  is a close-up view of the region generally identified by item  250  in  FIG. 1A . 
         [0030]      FIG. 2A  depicts an alternate view of the feeding mechanism  101 , wherein the mechanism  101  is viewed from the perspective  350  of  FIG. 1A . Visible in this orientation are side guides  301  that maintain the desired width of material on the metering belt  201  and prevent material from spilling off the sides of the metering belt  201 . Material on the belt  201  flows substantially directly against the side guides  301 , which in conjunction with the depth of material on the belt  201 , produces a given volumetric output based on the speed of the belt  201 . Thus, both the minimum and maximum volumetric flow rates are directly related to the width of the belt  201 , material depth on the belt, and belt speed. Although not visible in this view, the width of drums  206  and  207  is preferred, in most implementations, to be at least about as wide as the dimension  309 , i.e., the dimension between both side guides  301  in order to ensure that the volumetric displacement parameter associated with the width of material on the belt  201  is satisfied. 
         [0031]    The metering belt  201  is driven by belt gearmotor  306 . The belt gearmotor  306  is preferred, in some implementations, to be a variable speed drive. Thus, varying the speed of the belt gearmotor  306  at a fixed pile depth and width allows varying the volumetric flow rate. Note, of course, that the pile depth is adjustable (see, e.g.,  FIGS. 1A and 1B , item  204 ). 
         [0032]    To smooth-out and produce a more uniform flow of material as it begins to flow off the metering belt  201 , a rotating flow smoothing picker  302  is mounted onto the chassis  202  at the discharge end of the metering belt  201  (i.e., at about the rightmost end of the metering belt  201  in  FIG. 1A  and as shown in  FIG. 2A ). The flow smoothing picker  302  includes a rotating shaft (e.g., a type of rotating drum). From the perspective of  FIG. 1A  or  1 B, the picker  302  rotates in a counter-clockwise direction. This, however, may vary depending upon the implementation. In some implementations, the smoothing picker  302  operates independently at a constant speed, powered by its own gearmotor  307 . In other implementations, the picker  302  can be driven by another gearmotor (e.g., via a belt or chain). The pickers  310  of the flow smoothing picker  302  create a more uniform flow of material off of the belt  201  by “picking” (or dispersing/breaking up) the material just as it reaches the very end of the metering belt  201  and begins to fall off the belt, i.e., just as the portion of the belt beneath the material begins to travel around the front pulley  311 . 
         [0033]    Depending on the implementation, the pickers  310  of the flow smoothing picker  302  rotate relatively close to the metering belt  201 , e.g., about and including between 0.125 and 0.5 inches from the surface of the belt. This height may be adjusted by picker height adjusters  312  and  313 . These adjusters  312  and  313  include a threaded shaft (as shown), that as it is rotated, adjusts the height of the flow smoothing picker  302 . 
         [0034]    In some implementations, the configuration and construction of the pickers  310  is similar to that of the leveling spikes  209  of leveling drums  206  and  207 . In other implementations, the pickers  310  of the flow smoothing picker  302  may be in a spiraling configuration directed toward the center of the metering belt  201 . In some implementations, the distribution of pickers  310  is uniform about the rotating shaft of the picker  302 . The distribution of pickers  310  may vary depending on the material type. 
         [0035]    Also, mounted beneath the metering belt  201 , near the discharge end, is a wiper assembly  303 , which in some implementations comprises three flexible synthetic wiper blades that make gentle contact with the surface of the belt  201 . The wiper assembly  303  is mounted to the chassis  202 , and rotates against the metering belt  201  to remove any residual material that may remain thereon. From the perspective of  FIG. 1A , the wiper  303  rotates clockwise. This may vary depending upon the implementation, e.g., the wiper  303  may rotate counterclockwise. The wiper  303  may just barely touch the metering belt  201 , or it may be oriented such that it applies somewhat more pressure to the metering belt  201 . The amount of pressure can depend on the implementation and how the material may tend to cling/adhere to the metering belt  201  (note that in some implementations, the metering belt  201  is designed such that it resists material adherence-possible belt materials could include, e.g., neoprene, Teflon, polyethylene, and/or polyester). The wiper assembly  303  may be driven independently by a gearmotor  305 . Alternatively, the wiper assembly  303  may share a motor with another element of the device, e.g., driven via a belt or chain. Depending on the implementation, the wiper assembly may be rotated at a constant, but relatively slow speed, generally in the range of 30 to 100 RPM. 
         [0036]      FIG. 2B  is a close-up view of the region generally identified by item  350  in  FIG. 2A . 
         [0037]    Means for creating a substantially predetermined height and width of material may comprise items  208 ,  209 ,  301  and one or both of  206  and  207 . 
         [0038]    Various features of the system may be implemented in hardware, software, or a combination of hardware and software. For example, some features of the system may be implemented in computer programs executing on programmable computers. Each program may be implemented in a high level procedural or object-oriented programming language to communicate with a computer system or other machine. Furthermore, each such computer program may be stored on a storage medium such as read-only-memory (ROM) readable by a general or special purpose programmable computer or processor, for configuring and operating the computer to perform the functions described above. Moreover, various implementations of the metering mechanism may be employed with a weighing mechanism to construct a weight-loss feeder. Such implementations enable a user to determine the precise amount of material metered and/or fed through the apparatus. 
         [0039]    A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.