Abstract:
A weigh feeding apparatus has a plurality of compartments to hold a material that is fed into the compartments and a scale for weighing the material held in the compartments. The compartments are configured to revolve about an axis at a substantially constant rate and the scale is configured to produce a signal determined by the weight of the material held in the compartments. The signal is capable of being used to control the rate at which material is fed into the compartments.

Description:
BACKGROUND 
     The invention relates generally to material feeding systems and more particularly to dry solid feeding systems. 
     The precise metering of dry solids is important in many applications, including numerous manufacturing processes in various industries. Usually when material is continuously metered into a process, it must be precisely controlled at a specific feed rate so that the process functions as designed, the product formulation is correct, and the quality of the end product of the process does not suffer. 
     Various kinds of weigh feeders have been used for weighing and feeding dry solids such as sand, gravel, grain, foodstuffs, chemicals, pharmaceuticals, ceramics, etc. In general, material is provided to a weigh feeder continuously or periodically and the weigh feeder discharges the material at a continuous and constant output rate. Different weigh feeders, however, have different capabilities, which depend on the design of the weigh feeder and its principle of operation. Weight-loss, weigh belt, and weigh auger feeders are three types of commonly used weigh feeders. 
     Weigh belt feeders weigh material as the material is transported by a moving belt and require a continuous supply of material, generally from an overhead storage supply. In one functional configuration (e.g. Acrison, Inc., Model 260 Belt Weigher/Feeder), material travels from a storage supply, down a chute and onto a rear portion of the belt, which is not weighed. As the belt moves, the material on the belt passes over a weighing section, and a weight signal is produced that corresponds to the weight of material traveling across the weighing section. The weight signal is processed in conjunction with another signal, representing the speed of the belt, by the weigh feeder&#39;s controller to derive a feed rate signal. The feed rate signal is compared to the feed rate desired by the user, and the weigh feeder&#39;s controller continuously adjusts a variable speed drive powering the belt to maintain the desired feed rate. 
     A weigh belt feeder may also utilize a feeding mechanism to actively feed material onto the belt (e.g. a screw conveyor/feeder, another belt, a vibratory tray device, etc.). Although such active feeding (or prefeeding) is different from the method of gravimetric feeding described above, the material on the belt is weighed in an identical manner. Such active feeding of material onto the weigh belt generally provides a greater degree of physical control over the material being fed. In this mode of operation, the weigh belt moves at a fixed constant speed, and the feed rate of the feeding mechanism is variable. Thus, the weigh feeder&#39;s controller continuously modulates the output of the feeding mechanism that feeds material onto the belt to maintain a selected feed rate of material off the belt. Material is usually provided to the feeding mechanism directly from a storage supply, for example, a hopper or silo. 
     A different type of weigh belt feeder (e.g. Acrison, Inc., Models 203/210) operates by weighing the entire weigh belt assembly, while a pre-feeder (e.g. a screw conveyor/feeder, another belt, or a vibratory type device) meters material onto the weigh belt, which operates at a fixed constant speed. The output of the pre-feeder, which is equipped with a variable speed output drive, is continuously modulated by the weigh feeder&#39;s controller so that the rate at which material passes across the weigh belt accurately matches the selected feed rate. In such a weigh feeder, material is also usually supplied to the pre-feeder directly from a storage supply. 
     A weigh auger feeder (e.g. Acrison, Inc., Model 203B) operates in a manner similar to the weigh belt described immediately above, except that an auger, rather than a belt, is used to weigh and convey the material. 
     A weight-loss feeder (e.g. Acrison, Inc. Model 400 Series) comprises a material supply hopper and a feeding mechanism mounted on a scale. As material is fed out of the scale-mounted metering/supply system, a decreasing weight signal is produced, which is processed by the weigh feeder&#39;s controller in conjunction with a time signal to calculate a feed rate. The feeding mechanism of a weight-loss weigh feeder is equipped with a variable speed drive so that its feed rate output can be continuously modulated by the weigh feeder&#39;s controller in order to maintain the selected feed rate. The supply hopper of a weight-loss weigh feeder can be periodically refilled. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the invention features a weigh feeding apparatus having a plurality of compartments to hold a material that is fed into the compartments and a scale for weighing the material held in the compartments. The compartments are configured to revolve about an axis at a substantially constant rate and the scale is configured to produce a signal determined by the weight of the material held in the compartments. The signal is capable of being used to control the rate at which material is fed into the compartments. 
     Implementations of the invention may include one or more of the following. The compartments may include at least two vanes that radiate from an axle. The compartments may be configured to move from a first position to a second position, where the compartments are capable of receiving material fed into the compartments when the compartments are in the first position and are capable of discharging material when the compartments are in the second position. The signal may be capable of being used to control the rate which material is material is fed into the compartments, such that the weight of the material in the plurality of compartments is held substantially constant as the material is discharged from the compartments in the second position. The compartments may be configured to discharge material at a substantially constant discharge rate. 
     In an additional implementation, the invention may include a pre-feeder to feed material into the compartments, where the pre-feeder is capable of receiving the signal from the scale. The pre-feeder may be configured to feed material into the compartments at a rate determined by the signal from the scale. The compartments of the rotatable compartmented mechanism may be configured to move from a first position to a second position, and the compartments may be capable of receiving material fed into the compartments from the pre-feeder when the compartments are in the first position and may be capable of discharging material when the compartments are in the second position. The signal may be capable of being used to control the feed rate of the pre-feeder, such that the weight of the material in the plurality of compartments is held substantially constant as the material is discharged from compartments in the second position while the material is discharged from the rotatable compartmented mechanism at a substantially constant discharge rate. 
     In a second aspect, the invention features a method for providing a material at a substantially constant rate by feeding the material from a pre-feeder into a plurality of compartments for holding the material, as the compartments revolve about an axis at a substantially constant speed; weighing the material held in the plurality of compartments; providing a signal determined by the weight of the material held in the plurality of compartments; and using the signal to adjust the feed rate of the pre-feeder. 
     Implementations of the invention may include one or more of the following. The signal may be an electrical, mechanical, or optical signal. The material may be a solid or a liquid. The compartments may include at least two vanes that radiate from an axle and at least two endplates. As the compartments revolve, each of the compartments may move from a first position to a second position, and material may be fed into each of the compartments when the compartment is in the first position and may be discharged from each of the compartments when the compartments are in the second position. The rate at which the feeder feeds the material into the compartments may be adjusted, such that the weight of the material in the plurality of compartments is held substantially constant as the compartments revolve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  and FIG. 1 b  are schematic side elevations of a weigh feeder. 
     FIG. 2 a  and FIG. 2 b  are schematic side elevations of a weigh feeder. 
     FIG. 3 is a schematic side elevation of a rotary vane weighing apparatus of a weigh feeder. 
     FIG. 4 is a schematic side elevation of a scale. 
     FIG. 5 is a schematic diagram of a feedback system. 
    
    
     DESCRIPTION 
     FIG. 1 a  schematically illustrates a weigh feeder  10 , including a weighing chamber  100  housing a rotatable compartmented mechanism  102 . Weigh feeder may be operably connected to a pre-feeder  14  and a supply hopper  12 . The supply hopper  12  contains material to be fed and is mechanically connected at an inlet port  13  of pre-feeder  14 . Pre-feeder  14  is equipped with a variable speed drive in order to feed material into weigh feeder  10  at a controlled rate, based on signals from the weigh feeder. FIG. 1 a  shows a rotary vane type pre-feeder  14  and FIG. 1 b  shows an auger type pre-feeder  14 , both of which may move material into weigh feeder  10  at a controllable rate. The invention may also be practiced in combination with other pre-feeders that move material into weigh feeder at a controllable rate. 
     Supply hopper  12  may have a conical profile to facilitate gravitational discharge of material into the pre-feeder  14 . Material also may be actively moved by an active mechanical mechanism, to ensure positive flow of material out of supply hopper  12 , through inlet port  13  and into pre-feeder  14 . 
     A discharge port  15  of pre-feeder  14  is coupled to one end of a separately supported isolation inlet port  18  of weigh feeder  10  with a connector  30  that may be flexible or rigid (a flexible connector is shown). Isolation inlet port  18  is supported by a flange  19  so that it is mechanically isolated from weigh feeder  10 . The opposite end of inlet port  18  is coupled to the inlet  115  of weighing chamber  100  with a flexible connector  31  that may be a dust-tight flexible sleeve. The sleeve may be made of cloth, rubber, a combination of both cloth and rubber, or some other type of material that allows a flexible dust-tight mechanical connection, yet which mechanically isolates inlet port  18  from weigh feeder  10 . A similar flexible connector  32  couples the outlet  117  of weighing chamber  100  to an isolation outlet port  20 , which is separately supported by a flange  21  to mechanically isolate outlet port  20  from weigh feeder  10 . Isolation inlet port  18  and isolation outlet port  20  may be included with weighing chamber  100 , so that a user of weigh feeder  10  need not make connections directly to the inlet  115  and outlet  117  of the scale-mounted weighing chamber  100 . It preferable for the user to make connections to ports that are mechanically isolated from the weigh feeder so that the sensitivity of the scale mounted weighing chamber  100  is not disturbed. 
     Pre-feeder  14  feeds material through isolation inlet port  18  to the weighing chamber  100 , which houses a rotatable compartmented mechanism  102 . The rotatable compartmented mechanism  102  comprises a series of compartments  130 , defined by vanes  120  that revolve about an axle  122  on the central axis of weighing chamber  100 . The entire chamber is mounted on a precision scale  20  (not shown) and counterbalanced so that only the material actually fed into weighing chamber  100  by pre-feeder  14  is weighed. A signal directly related to the weight of the material in weighing chamber  100  provides feedback to control the output rate of material from the weigh feeder  10  in a way described below. First, however, weighing chamber  100  is described. 
     Referring to FIGS. 2 a  and  2   b , an end view (FIG. 2 a ) and a side view (FIG. 2 b ) of the weighing chamber  100  are illustrated. Weighing chamber  100  is formed from generally cylindrical sidewalls  110  and flat endwalls  113 . An entrance opening  118  and an exit opening  119  exist in weighing chamber  100  for material to enter and exit. Inside weighing chamber  100 , multiple vanes  120  extend out from a central axle  122 . Two flat disk-shaped endplates  114  are attached to axle  122  and are connected to the longitudinal ends of multiple vanes  120 , forming multiple approximately pie-wedge-shaped compartments  130  of the weighing chamber. The invention may also be practiced without endplates  114 , in which case the longitudinal ends of vanes  120  extend close to, but do not touch, flat endwalls  113 . When endplates are not used, compartments  130  are formed by central axle  122 , vanes  120 , and flat endwalls  113 . 
     The invention may be practiced using two or more compartments, but generally 6-20 compartments are used. Because of the finite diameter of the axle  122 , the compartments  130  are not exactly pie-wedge-shaped because the vanes  120  do not touch each other where they contact the axle  122 . Rather, the vanes  120  meet the axle at different azimuthal positions around the axle, and therefore the shape of the compartments is more precisely described as pie-wedge-shaped portion minus a portion of the tip of the wedge. 
     The clearance between the outer ends of the vanes  120  and the inside wall  110  of weighing chamber  100  is small, such that only insignificant amounts of material, if any material at all, can pass between the radial ends of vanes  120  and cylindrical sidewall  110 . If endplates  114  are not used to form compartments  130 , the clearance between the longitudinal ends of vanes  120  and end flatwalls  113  is similarly small. The exact dimension of the clearance depends on the type of material fed into the weigh feeder  10 , its particle size, and the temperature of the weigh feeder. Typically, a smaller clearance is required if fine powder is used in weigh feeder  10  than if large grains are used in it. The radial and/or longitudinal ends of the vanes  120  may be fitted with a flexible material, such as a rubber wiper, that makes contact with the cylindrical sidewall  110  and/or flat endwalls  113 , so that there is nominally no gap between revolving vanes  120  and inside wall  110  and or flat endwalls  113  of the weighing chamber  100 . Material cannot leak past the ends of vanes  120  either because of the small clearance between the ends of vanes  120  and endwalls  113  or because the flat disk-shaped plates  114  may form the ends of, and rotate with, compartments  130 . 
     Central axle  122  is coupled to a synchronous drive gearmotor  140 , located outside the weighing chamber  100 , either directly, through a coupling, or with a chain. Drive gearmotor  140  turns the central axle  122  and the vanes  120  of the rotatable compartmented mechanism  102 . As vanes  120  revolve around the axle  122 , the compartments  130  defined by the vanes also revolve around the central axis  122  of weighing chamber  100 . Axle  122  rotates at a constant speed, driven by synchronous drive gearmotor  140 . Generally, the rotation speed of axle  122  and rotatable compartmented mechanism  102  is approximately 3-30 rotations per minute (RPM) and is determined based on application parameters. Once this speed has been set, however, it generally remains constant for a given application. 
     Further referring to FIG. 2, while rotatable compartmented mechanism  102  rotates within weighing chamber  100 , material is fed through entrance opening  118  into compartments  130  from pre-feeder  14  (not shown) located directly above weighing chamber  100 . Material falls into a compartment  130  when compartment  130  is in a first position (horizontal striped shaded area in FIG. 2 a ), located in the upper part of mechanism  102  and revolves within the compartment  130  until the compartment  130  is in a second position (vertical striped shaded area in FIG. 2 a ), in the lower portion of the mechanism  102 . In the second position, the material in the compartment  130  passes over exit opening  119  of weighing chamber  100 , where the material is discharged from weighing chamber  100  by the force of gravity. For example, as rotatable compartmented mechanism  102  rotates, material may fall from pre-feeder  14  (not shown) through input  115  and be deposited in compartments  130  in positions a and/or b, located under inlet  115 . As rotatable compartmented mechanism  102  rotates, the deposited material is moved with the compartments as they revolve around axle  122  until the compartments reach positions e and f, at which point the material falls out the compartments and weighing chamber  100  through outlet  117  under the force of gravity. Compartments  130  generally are filled from 5 percent to 80 percent of their volume capacity when the weigh feeder is operating. Operation at less than 100 percent capacity is generally necessary when feeding dry materials into weigh feeder due to their tendency to “pile-up,” rather than spread out to fill all available capacity of a compartment. 
     Referring to FIG. 3, the profile of weighing chamber  100  may be constructed such that in the bottom portion of its body, the distance from axle  122  to sidewall  110  is significantly greater than the length of the vanes  120 , so that the vanes  120  do not confine material when the material reaches this larger portion of the body. 
     Because compartments  130  of the rotatable compartmented mechanism  102  revolve at a constant rate, if material is fed into weighing chamber  100  at a constant rate, it also falls out of weighing chamber  100  at a constant rate. 
     Because of the closed configuration of weighing chamber  100 , weigh feeder  10  is substantially dust-tight, unlike weigh belt feeders in which a large portion of the functional mechanism is exposed to dust accumulation. Additionally, because weighing chamber  100  has relatively few moving parts, weigh feeder  10  is mechanically relatively simple. 
     Referring to FIGS. 2 a ,  2   b , and  4 , the entire weighing chamber  100 , and all components thereof, including drive gearmotor  140  and the material contained within weighing chamber  100 , are weighed by scale  20 , which may be a beam balance type weighing mechanism. Weighing chamber  100  is suspended by a principal lever beam  210 , which may split into a Y-shaped yoke to hold weighing chamber  100  at its two ends. Principal lever beam  210  is attached to a main support structure  211  with primary flextures  212  and to a structure supporting the weighing chamber  100  with secondary flextures  213 . A stabilizer linkage assembly  214  connects the lower portion of the structure supporting weighing chamber  100  to main support structure  211 . Stabilizer linkage assembly  214  is attached to the main support structure and to the structure supporting the weighing chamber  100  with linkage flextures  215 . 
     Principal lever beam  210  pivots about primary flexures  212 . Without any material in weighing chamber  100 , scale  20  is in equilibrium at its “null” position. This is known as the scale&#39;s “zero point,” which provides a reference for feed rate calibration. As material is added into weighing chamber  100 , lever beams  210  pivots slightly about primary flexures  212  in response to the weight of the material. A sensor  220  measures the displacement of principal lever beam  210 . The sensor may be a mechanical, electromechanical, strain gauge, piezo-electric, LVDT, a displacement measurement, or similar transducer of some type. Because the measured displacement is directly proportional to the weight of the material in the weighing chamber  100 , the sensor  220  provides a precise signal directly and linearly related to the weight of the material in the weighing chamber  100 . 
     Principal lever beam  210  is also equipped with one or more dashpots  222  to dampen motion of the lever arms due to sudden deviations from equilibrium in the weighing system, typically produced by vibration or by the manner in which material enters the weighing chamber  100 . Although a beam balance type lever mechanism scale is described above as the scale used in the invention, it is understood that the invention may also be practiced using other types of scales equipped with other types of weight sensors. 
     Referring to FIG. 5, a weight signal  300  generated by scale  20  and proportional to the weight of material in weigh feeder  10  is used in a comparator  310  to compare the actual output rate of material from weigh feeder  10  to the desired output rate of material from weight feeder  10 . Comparator  310  is generally a computer, but mechanical, electrical, or other comparators may also be used to practice the invention. 
     A user determines the desired output rate, and the user, in effect, sets the value of a signal  320  related to the desired output rate, which is fed into comparator  310 . A signal  330  related to the rotation rate of rotatable compartmented mechanism  102  is also fed into comparator  310 . Combined with weight signal  300 , signal  330  permits a calculation of the actual output rate of material from the weigh feeder  10 . Since signal  300  is related to the weight of material in weighing chamber  100 , and signal  330  is related to the rate at which material is discharged from weighing chamber  100 , a simple mathematical algorithm, in which signals  300  and  310  are parameters, gives a signal related to the actual output rate of material from weigh feeder  10 . 
     The signal related to the actual output rate is compared in comparator  310  to the signal  320  related to the desired output rate. If the actual output rate is lower than the desired output rate, a feedback signal  340  is sent from comparator  310  to pre-feeder  14  instructing it to feed material into weigh feeder  10  at a faster rate. If the actual output rate is higher than the desired output rate, a feedback signal  340  is sent from comparator  310  to pre-feeder  14  instructing it to feed material into weigh feeder  10  at a slower rate. Feedback signal  340  ensures that the actual output rate of material from weigh feeder  10  is equal to the desired output feed rate. 
     The accuracy of the signal corresponding to the actual output rate depends not only on the accuracy of the weight and rotation rate measurements, but also on the validity of the assumption that all the material that enters weighing chamber  100  exits the chamber. If all the material that enters weighing chamber  100  exits it, then the laden weight of the weighing chamber minus the unladen weight is equal to the weight of material that is moved through the weighing chamber in a certain amount of time. 
     If, however, some material adheres to weighing chamber  100  or to any components of it, then somewhat less material moves through weigh feeder in the same amount of time. Feedback signal  330  effectively operates to maintain a certain weight of material in weighing chamber  100 , and if material sticks to weighing chamber  100  rather than discharging from it, then the actual output rate from weigh feeder  10  will be less than the desired output rate. This is because the material adhering to internal surfaces of weighing chamber  100  causes an upward shift in the “zero point” of the weighing system, causing a lesser amount of material to be fed. Weigh feeder  10  is optimized for dry non-sticky types of materials that easily pass though the weighing chamber  100  and its rotatable compartmented mechanism  102  without adhesion. 
     Vanes  120 , endplates  114 , sidewalls  110 , and central axle  122  that form compartmented weighing mechanism  102  may be made of any durable, non-reactive material. Stainless steel is a material that meets these requirements. The materials of which weighing chamber  100  and its rotatable compartmented mechanism  102  are made may be provided with a material “release” type coating, such as a Teflon® coating, to assist in preventing material adhesion as well as promoting its release if it begins to adhere. Additionally, if some material does stick to components of weighing chamber  100 , signal  300  from scale  20  may be “re-zeroed” in comparator  310  to account for the material that adheres to surfaces of weighing chamber  100 . Re-zeroing signal  300  effectively relates it again only to the weight of material that passes through weighing chamber  100  and weigh feeder  10 .