Patent Application
20070290008
Referring to
Hopper 12 contains material 22 that is to be distributed from feeder 14. Hopper 12 may be in communication with a source of material 22 such as an external hopper 23 (e.g., prefeeder, another bin, etc.), that periodically refills or reloads material 22 to hopper 12. To facilitate a continuous and uniform flow of material 22 from hopper 12 into feeder 14, an agitation mechanism or agitator may be provided to aid the flow of material and to condition the material to a constant density. For example, in systems employing flexible hoppers (e.g., vinyl, silicone, rubber, elastomer, etc.), massaging paddles or rods are driven by a motor 21 and are disposed to undulate against the sides of the hopper, agitating the material within it. These high amplitude, relatively low frequency vibrations are intended to condition the material into a uniform bulk density above the metering screw, and tend to prevent arching or bridging of the material across the hopper discharge that inhibits or prevents further flow. Examples of suitable commercially available feeders are AccuRate dry material feeders marketed by the assignee of the present application. In alternative embodiments, the hopper is a rigid structure that may have an internal agitator.
Hopper 12 tapers downwardly and inwardly to form a laterally extending duct or trough 28 at the bottom of hopper 12. The trough 28 is generally cylindrical and top opening and in communication with feeder 14. Feeder 14 receives material 22 flowing from hopper 12. Feeder 14 comprises a driven conveyer (shown as an auger 24) mounted at least partially within a hollow member (e.g., tube, extension piece, hollow cylinder, etc. and generally referred to herein as a passageway or nozzle 30). Auger 24 urges (e.g., feeds, transports, flows, pushes, moves, etc.) material 22 received from hopper 12 through nozzle 30 to a discharge port or outlet 32. Outlet 32 is shown as an opening in nozzle 30 centered on the longitudinal axis of nozzle 30—in other words, the end of nozzle is open. According to alternative embodiments, the discharge outlet may be a slot, aperture, or other opening in the wall of the nozzle (e.g., facing downwardly below the feeder) and the end of the nozzle may be closed. Material 22 existing outlet 32 may be discharged to (or into) packaging or process equipment in which the material is being used or to be further processed, mixed, or the like. According to an exemplary embodiment, the auger and agitation device are driven by one or more electric motors. Alternatively, the motor may be powered by pneumatic, hydraulic or the like. According to alternative embodiments, the hopper, feeder, and auger may have any of a variety of configurations, shapes, sizes, or the like.
Scale 16 is preferably a mechanically counterbalanced flexure type scale, and comprises a frame 33 supported on a pivot or fulcrum. Frame 33 may comprise one or more members such as beams, arms, linkage, or the like. The pivot may be any of a variety of frictionless or friction pivot devices that allow pivoting or counterbalancing of hopper 12.
Controller 18 is configured to receive signals from weight measurement system 20, store data, analyze performance, and generate appropriate control signals to ensure that the weight of material discharged by feeder 14 is maintained in accordance with operator-input parameters or program specifying the desired feed rate/quantity. The controller compares signals representative of the actual feed rate to the set point feed rate and adjusts the speed of the motor 31 to adjust the speed of auger 24. According to an exemplary embodiment, controller 18 comprises a computing device, a display, a user interface, and/or one or more signal converters. The computing device may comprise a computer, a processor, or the like. The user interface may be a keyboard, keypad, or the like. The signal converters may be analog to digital converters, digital to analog converters, or the like. Controller 18 is shown schematically coupled (in communication with) motor 31, motor 21, and load cell 40 in
According to an exemplary embodiment, weight measurement system 20 is configured to measure or detect the weight of material 22 being dispensed by feeder 14. Weight measurement system 20 comprises one or more sensors (e.g., a load cell, strain gauge, transducer, or the like, and shown generally schematically as load cell 40). In the schematically illustrated embodiment, scale 16 is counterbalanced by a counterbalance force, preferably provided by a “dead” weight load, to counterbalance or offset the weight of hopper 12, so that the sensor output signal is representative of the weight of material 22 in hopper 12. As such, output of the sensor is thus zeroed to the tare weight of hopper 12. Control is effected in accordance with differences in the weight, rather than absolute weight, and non-zero signals indicative of the tare weights may thus be accommodated. The dead weight may be provided by any of a variety of weighted structures, such as functional devices and non-functional “dead” weight, that offsets or balances the weight of the material in hopper 12. The description of a gravimetric dispenser is illustrative only; according to alternative embodiments, the dispensing system may be any of a variety of dispensing systems, including volumetric, continuous, or the like.
According to a preferred embodiment, auger 24 is particularly advantageously used to accurately and precisely convey material, particularly material having high cohesive properties (e.g., an angle of repose of 30 degrees or more), at relatively low feed rates, although the auger may be used to feed a wide variety of materials. Examples of such materials include calcium carbonate, lactose, magnesium stearate, cellulose, starch, wheat protein, or diatomaous earth, or the like. Possible applications for such dispensing include, for example, ingredients in pharmaceuticals, chemical compositions, or biological or dietary applications. An auger, as described herein, “inefficiently” moves the material by being “centerless” and having a relatively large diameter helix made from conveying members with relatively small cross-sectional dimensions and rotated at a relatively high revolution speed compared to prior art augers or metering screws that have been typically used for such applications. Such a configuration allows the material to be slowly moved toward the discharge outlet and to tumble upon itself and upon the conveying members through the open space in the center of the centerless auger 24.
Referring to
Driven hub 50 (e.g., base, quill, etc.) is coupled to a motor 41 and is configured to transfer rotation to the one or more conveying members 52, 54. Driven hub 50 may be coupled to or supported by a bearing in trough 28 and/or nozzle 30 to help maintain an axial alignment of auger 24 within nozzle 30 and reduce friction against rotation of auger 24. The rotation of auger 24 is preferably at a relatively high rate, e.g., revolutions per minute (rpm), compared to rotational speeds that have previously been used for materials with an angle of repose of 30 degrees or more, or for feed rates of less than 200 grams per hour. For example, auger 24 is rotated at higher revolutions than conventional augers of the same outer diameter for the same type of application. The relatively higher rotation speed of auger 24 reduces the pulsations that tend to occur when known screws are rotated slowly to provide low feed rates. According to an exemplary embodiment, auger 24 is rotated at least 1 rpm, particularly for material that has an angle of repose of 30 degrees or more. According to a preferred embodiment, auger 24 is rotated between about 3 rpm and about 200 rpm for such materials. The higher revolution speed of the auger 24 reduces the pulsations normally seen with slow turning helixes used for low rates. According to alternative embodiments, other rotational speeds by be used that provide the desired material handling.
The one or more conveying members 52, 54 (e.g., rods, flights, blades, etc.) are configured to engage and urge material 22 from hopper 12 toward discharge outlet 32. As shown in
Each one or more conveying member 52, 54 includes a first end 60 coupled (e.g., fastened, welded, etc.) to driven hub 50 and a second end 62 coupled (e.g., fastened, welded, etc.) to discharge hub 56. The one or more conveying members 52, 54 are preferably rods with a circular cross-section that have been formed into or provided a helical curvature. The one or more conveying members 52 or 54 have or provide an outer circumference or diameter OD. The size of the outer diameter OD is intended to allow material 22 to fall from conveying member 52, 54 more easily. According to exemplary embodiments, the one or more conveying members 52, 54 provide a uniform outer diameter OD of at least ½ inch for materials with an angle of repose of 30 degrees or more. According to a preferred embodiment, the outer diameter OD is between about ¾ inch and about 2¼ inches for such materials. The larger diameter allows material to fall into the one or more conveying members more easily and the small surface presented to the material is less likely to bind or stick to the one or more conveying members. According to exemplary embodiments, the outer diameter may be any of a variety of dimensions depending on the desired feed rate performance, size of the dispensing system, size of the material being dispensed, or the like.
According to an exemplary embodiment, the outer surface of the one or more conveying members 52, 54 contact the inner wall surface of nozzle 30 so that material is not trapped between the one or more conveying members 52, 54 and nozzle 30, i.e., scrapes the wall 70 of nozzle 30. According to a preferred embodiment, the outside diameter OD of the conveying members 52, 54 is slightly smaller than the inside diameter ID of the nozzle 30 to provide a gap or space between the conveying members and the wall of the nozzle (e.g., a clearance fit). According to a particularly preferred embodiment, the gap between the conveying members and the wall of the nozzle is approximately 0.060 inches on the radius (i.e., approximately 0.120 inch difference between the outside diameter OD of the conveying members 52, 54 is slightly smaller than the inside diameter ID of the nozzle 30). According to an alternative embodiment, the outer diameter OD of the one or more conveying members 52, 54 (measured before being mounted within nozzle 30) is slightly larger than the inside diameter ID of nozzle 30 (e.g., an interference or force fit). As such, the one or more conveying members 52, 54 are in a biased condition when mounted in nozzle 30 and are ensured to be in contact with the wall 70 of nozzle 30.
Each conveying member 52, 54 have a cross-sectional dimension D; for example, a diameter or gauge when the one or more conveying members are made from wire or rods with a circular cross-section. The cross-sectional dimension D of the one or more conveying members 52, 54 is relatively small compared to the dimension or size of flights that would typically be used for conveying material with an angle of repose of 30 degrees or more at low feed rates. The relatively small cross-sectional dimension D of the one or more conveying members 52, 54 is intended to provide or present a smaller surface area that engages material 22 so that less material is conveyed and the material is less likely to bind or stick to the one or more conveying members 52, 54. According to exemplary embodiments, the diameter D of the wire used for the one or more conveying members is more than 1/32 inch for material with an angle of repose of 30 degrees or more. According to a preferred embodiment, the diameter is between about 1/16 inch and about ¼ inch for such materials. Preferably but not necessary, the conveying members 52, 54 have the same cross-sectional dimension. According to alternative embodiments, the cross-sectional dimension of one or both of the conveying members 52, 54 may be any of a variety of dimensions configured to provide the desired material handling.
Referring to
Discharge hub 56 is configured to provide structural support for conveying members 52 and/or 54. Discharge hub 56 may be coupled to nozzle 30 by a bearing to help maintain axial alignment of auger 24 within nozzle 30 and reduce friction against rotation of auger 24.
According to an exemplary embodiment, one or more supplemental discharge members 74 is coupled to discharge hub 56 and is configured to stir or agitate material prior to or assist the material as it is being discharged, to reduce pulsations that normally occurs with slow moving screws that are used for low feed rates, and to generally create a more uniform material flow. The one or more discharge members 74 are also configured to provide for additional discharges of material per revolution than conventional screws without discharge members 74 extending from discharge hubs 56. Each discharge member 74 provides for an additional discharge per revolution. For example, two discharge members 74 provide for two additional discharges per revolution. The additional discharges are intended to provide improved discharge constancy (i.e., more constant discharge) at the same rotational speed. Referring to
In operation, the motor 41 rotates auger 24 by a rotational force applied to driven hub 50. Rotation of auger 24 causes material 22 being received from hopper 12 and falling into trough 28 to be driven (e.g., moved, transferred, urged, etc.) from the trough 28 through nozzle 30, and out discharge outlet 32. The one or more conveying members 52, 54 present a large diameter OD in the throat of trough 28 to agitate and move material horizontally. The relatively large pitch P and relatively small cross-sectional dimension D of the one or more conveying members 52, 54 pushes a small amount of material 22 through nozzle 30. The relatively large pitch P and relatively small cross-sectional dimension of the conveying members 52, 54 moves material in partially filled nozzle 30 to the discharge outlet 32.
A test has been conducted to compare the feed rate and accuracy of an auger according to an exemplary embodiment to two conventional or known augers. The conveying apparatuses used for the test are shown in
The test results indicate that feed rates can be attained for a low feed rate application (e.g., around 20 grams per hour or g/hr) using the exemplary centerless helix 90 and with a known centerless helix 98. However, the larger diameter of the exemplary centerless helix 90 allowed the material to more easily fall into the trough at the bottom of the hopper, allowed for a more total clean out of the hopper since stirring rods are not needed. Stirring rods are intended to increase the effective trough diameter to ¾ inch on the exemplary centerless helix that provides for a “dead space” for material to build up and provide a more gentle agitation of the material.
Performance accuracy is preferably calculated as two standard of deviations (percentage) of the mean feed rate. The lower the standard of deviation, the more accurate the dispensing. The graphs below are based on the data above and are intended to illustrate the improvement in performance of the exemplary auger. The exemplary auger provides better accuracy, less deviation, and more consistent material dispensing. The conventional screw provides one discharge of material per revolution, which results in accuracy that is quite poor. The exemplary centerless helix 90 with discharge members 92 allow for four pulses per revolution, which results in improved discharge constancy.
Additionally, the build-up on the exemplary auger was minimal compared to the known conveying apparatuses. The build-up on the conventional screw was noticeable and substantially more than the exemplary centerless helix. Below are charts illustrating the test data for the exemplary auger according to an exemplary embodiment compared to performance of a conventional screw.
According to an exemplary embodiment shown in
While the components of the disclosed embodiments will be illustrated as a loss-in-weight dispensing system, the features of the disclosed embodiments have a much wider applicability. For example, long-pitch centerless helix design is adaptable for other dispensing systems. Further, the size of the various components and the size of the containers can be widely varied. Also, one or more stirring members or rods, such as those shown in
Also, the particular materials or products that may be dispensed are also illustrative. For example, the dispensing system may be used for any of a variety of dispensed products, including liquid, fine powder, or larger bulk solid.
Further, it is important to note that the term “hopper,” “feeder,” “helix,” and “conveying members” are intended to be broad terms and not terms of limitation. These components may be used with any of a variety of products or arrangements and are not intended to be limited to use with loss-in-weight dispensing applications.
It is also important to note that the construction and arrangement of the elements of the long pitch auger as shown in the preferred and other exemplary embodiments are illustrative only. Although only a few embodiments of the present invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and/or omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present invention as expressed in the appended claims.
