Abstract:
A system is disclosed that minimizes the effect of internal pressure upon weight-loss weighing systems. The system can include a flexible gas purge line that pressurizes the system as well as a pressure compensator that negates the adverse effects of internal pressure on weight sensing equipment during normal operation.

Description:
TECHNICAL FIELD 
   This disclosure relates to a weight-loss weigh feeder using pressure compensation. 
   BACKGROUND 
   Weight-loss weigh feeders are used to meter dry and liquid ingredients, at specific feed rates, either on a continuous or batch basis, into a wide range of processes. In many applications, weight-loss weigh feeders can be used to proportion various ingredients that comprise a particular formulation (e.g, foods, plastics, chemicals, pharmaceuticals, etc.). 
   Generally, weight-loss weigh feeders include a vessel (e.g., a hopper or tank appropriately designed and sized for specific ingredients and/or applications) mounted onto a weighing system (e.g., a scale) where product discharge is regulated based on a desired discharge or feed rate (i.e., weight output vs. time). 
   Typically, product is discharged out of the vessel by applying a metering device. The loss of weight, as sensed by the weighing system, can be transmitted to the feeder&#39;s controller and calculated into a feed rate (e.g., pounds or tons per minute or hour). The controller then can compare the calculated rate of discharge to a desired (set) discharge rate and simultaneously modulate the output of the weigh feeder&#39;s metering device to maintain the desired (set) rate. 
   Weight-loss weigh feeders require the weigh vessel be periodically refilled with product. In some applications, the weight-loss weigh feeder also may need to operate under the presence of dry air, or a gas purge (e.g., nitrogen, helium, argon) to prevent the material being handled from being exposed to potentially adverse reactants, such as ambient air. Generally, these applications require internal areas of the weight-loss weigh feeder to operate in the presence of some pressurized inert gas that forces out ambient air from within the feeder, and/or precludes ambient air from entering the feeder. The introduction of internal pressure in the vessel (whether constant or fluctuating), however, can create forces upon the weighing system that adversely affect accurate performance during normal operation. 
   SUMMARY OF THE DISCLOSURE 
   A system is disclosed that minimizes the effect of internal pressure upon weight-loss weighing systems. The system can include a gas inlet flexibly connected to a container and a pressure compensator that negates the adverse effects of internal pressurization (positive or negative) upon the weighing system during normal operation. 
   For example, according to one aspect, a system includes a container attached to a scale, the container having at least one material inlet for adding a material supply (product) and at least one flexible gas impermeable connector connected to the container that is capable of pressurizing the container, and a metering mechanism for removing material supply from the container. 
   In some implementations, the system also can include a pressure compensator attached to the container. The pressure compensator is configured to affect the adverse effects upon weight sensing when either a pressurized gas enters the container or a vacuum condition exists in the container. 
   In another aspect, a method includes providing a material supply or product into a container through at least one material inlet, the at least one material inlet providing a path or passage for the material supply or product entering the container. The method may either pressurize or depressurize the container by passing gas through a flexible gas inlet having a gas-impermeable flexible conduit and allowing the gas to contact a pressure compensator, the pressure compensator reducing an unequal pressurized force in the container, and metering at least a portion of the material supply from the container. 
   According to another aspect, a method includes providing material into a container, the container having a material inlet to provide a path for the material to enter the container and a gas inlet having a gas-impermeable flexible conduit for gas to enter the container. The method includes weighing the material in the container which has attached to it a pressure compensator that has an annular ring for minimizing unequal pressurized force in the container. 
   In some implementations, one or more of the following advantages can be present. For example, the pressure compensator can minimize or eliminate the adverse effects of internal pressure (positive or negative) from affecting accurate weight sensing. This may be particularly advantageous in optimizing system performance and cost effectiveness. 
   Another benefit may relate to container venting. Container venting may be accomplished by using a vent valve which opens and closes. 
   A further benefit may relate to sizing of the system components. The components of the pressure compensator would be sized as needed so that internal pressure in the container is equalized, thereby leaving the system to operate in a normal fashion. 
   An additional benefit may relate to the system&#39;s flexible gas line. The flexible gas line delivers purge gas to the interior of the container and has no positive or negative influence on the scale. The system also utilizes flexible sleeve material that allows free scale movement, but is gas impermeable so the purge gas can be contained in the container and not escape into the surrounding environment. 
   Additional features and advantages will be readily apparent from the following detailed description, the accompanying drawings and the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates an example of a weight-loss weigh feeder system with pressure compensation. 
       FIG. 2  illustrates an example of pressure forces applied to the weight-loss weigh feeder system of  FIG. 1 . 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  discloses an example of a weight-loss weigh feeder system  100  that operates in the presence of internal pressure. The weight-loss weigh feeder system  100  may be installed as part of a contained materials-handling system that can be sealed for dust containment. 
   As shown in the  FIG. 1  example, the system  100  includes a flexible gas purge line  140  that provides gas pressurization of a container (e.g., vessel, hopper, or tank)  110  capable of accommodating product supply. The flexible gas purge line  140  can be located anywhere on an upper portion of the system  100 , the container  110 , or the lower conical portion  122  of the pressure-compensator  121 . The container  110  is affixed to a scale  130 . The system  100  includes a metering mechanism  101  that provides discharge of product from the container  110 . 
   The system  100  includes a pressure-compensator  121  that is affixed to the scale. The pressure-compensator  121  operates to minimize or eliminate the effect of internal pressure in the container  110  on the scale  130  during weight sensing operations. For example, when pressure in the container is present, the pressure-compensator  121  operates to equalize internal pressure forces exerted on the scale  130  and thereby minimizes or eliminates inaccurate weighing of product supply in container  110  that can occur otherwise. 
   A product-supply inlet  102  and a vent connection  106  are provided and allow internal pressure in the container to extend out to fixed surfaces  104 ,  108  respectively. Fixed surfaces  104 ,  108  are off the scale. The product-supply inlet  102  is attached to a product-refill mechanism  180  that typically includes an actuator  112  and a product-supply inlet valve  181 . A vent shut-off valve  115  and a vent shut-off valve actuator  114  are located adjacent to the pressure-compensator  121 . Actuator  114  acts to move valve  115  between an open position and a closed position. The product-refill mechanism  180  and vent valve actuator  114  cooperate together to provide for adding product in the container  110  when the product reaches a low level. For example, in one embodiment, when a certain amount of product needs to be added to refill the container  110 , the vent shut-off valve  115  opens to allow venting of gas from the container  110 . The actuator  112  then activates, valve  181  opens, and product is added to the container  110  at inlet  102 . Once a desired amount of material supply or product is loaded into the container  110 , the product-supply inlet valve  181  closes, and then vent shut-off valve  115  closes. Inert or other gas can be added via flexible gas purge line  140  to reestablish purge pressurization of the container  110 . 
   The product-refill mechanism  180  is mounted to a fixed surface  104  and is flexibly connected to the product-supply inlet  102  located on a cover  120  of the container  110  via flexible sleeve  131 . The vent valve actuator  114  and vent shut-off valve  115  are mounted to a fixed surface  108 . The vent connection  106  can be connected to a dust collection or exhaust system. In one implementation, as shown in the  FIG. 1  example, the vent valve actuator  114  is attached to the vent shut-off valve  115 . The vent shut-off valve  115  eliminates any potentially adverse effects of a vacuum draw (negative draw) on the container  110  that can be caused by a dust collection system. 
   The vent connection  106  may be used to extract dust and displaced air from the container  110  when the container  110  is refilled with product through the product-supply inlet  102 . As shown in the  FIG. 1  example, the vent connection  106  extends through the pressure-compensator  121 , which includes a conical lower portion  122  to direct product that may settle out of dust laden displaced air or other gas back into the container  110 . In one implementation, the conical lower portion  122  of the pressure-compensator  121  is independently supported off the container  110 . 
   Once pressurization of the container  110  occurs, equal and opposite forces generated by pressure internal to the container  110  act against internal surfaces of the container  110  uniformly. The upward component of force, which acts uniformly across the face of the container cover  120 , extends through the product-supply inlet  102  and vent connection  106  onto the fixed surfaces  104 ,  108 . Due to the product-supply inlet  102  and vent connection  106  penetrations in the container cover  120 , the surface area of the container cover  120  is not equal to that of the surfaces directly opposite the container cover, e.g., at areas  116 ,  118 . Therefore, the upward component of force acting against the container cover  120  is less than the opposite downward component of force acting on the bottom of container  110 . 
   The pressure-compensator  121  includes an annular compensation ring  124 , sized such that the surface area of the ring is identical to the sum of the cross sectional areas of the system&#39;s product-supply inlet  102  and vent connection  106 . The compensation ring  124  operates to equalize the before-mentioned forces. One advantage of the compensation ring  124  is that it may minimize or negate the adverse effects of internal pressure (positive or negative) from affecting accurate weight sensing and, in turn, system performance. In some implementations, the pressure-compensator  121  is arranged as a pressure-balancing mechanism to ensure accurate weight sensing by scale  130  in the presence of an internal (purge) pressure. 
     FIG. 2  illustrates an example of pressure forces applied to the example weight-loss weigh feeder system of  FIG. 1 . As explained previously, in one implementation, the pressure-compensator  121  is located in the vent connection  106  and has the conical lower portion  122  that directs the return of accumulated product back into the container  110  (i.e., dust that rises upward) while venting during a product refill operation. 
   Example forces acting on the weigh feeder system due to pressurization are illustrated as arrows in  FIG. 2 . Positive forces that add (erroneously) to the weight measurement of product within the container  110  are illustrated with a “+” symbol. Negative forces that subtract from the weight measurement of product are illustrated with a “−” symbol. These negative forces counterbalance the positive forces mentioned previously. Static forces that neither add nor subtract weight have no symbol. 
   The flexible gas purge line  140  provides purge gas to the interior of the container  110 , but itself has no positive or negative influence on the scale  130 . Flexible connectors or sleeves  131 ,  131   a ,  131   b  and  131   c  are provided to allow free movement of the weighing system in response to changes of weight (e.g., material) within the container  110 , and are gas impermeable. Thus, the purge gas contained within the container  110  can not escape into the surrounding atmosphere and the flexible sleeves can create an airtight system when valves  181  and  115  are closed. The compensation ring  124  of the pressure-compensator  121  is attached directly to the container cover  120  of the container  110  by elements  121 . The compensation ring  124  is exposed to the contents of container  110  and may be attached to any location on the container cover  120 . During pressurization, the internal purge pressure imparts an upward force on the compensation ring  124  equal to the downward force on the opposite portions of container  110  at locations  116 ,  117 ,  118  and  119 . Since the compensation ring  124  is mounted to the container  110  of the system  100  by attachment to cover  120 , the upward force on ring  124  is transferred directly to the container  110 . The conical lower portion  122  of the pressure-compensator  121  is supported off the scale  130 . The compensation ring  124  can continuously negate any adverse effects that pressure (internal to the container) would have upon weight sensing, and system performance. 
   Other implementations are within the scope of the following claims.