MXPA00011703A - Loss-in-weight feeder control - Google Patents

Abstract

The present invention is related to a method of feeding particulate matter in a process or similar application. The feed control is based on a loss-in-weight measurement scheme. The control signal for the loss-in-weight control system is formed from the sum function of loss-in-weight measurements performed on the weight of a feed unit and a replenishment unit communicating with a plug f low with the former.

Description

FEED LOSS CONTROL IN WEIGHT The present invention relates to a method for feeding fine particulate material in a continuous manner, for example, to different types of manufacturing processes. In the context of the invention, the term particulate material is used in general with reference to any bulk particulate material. In a large number of applications, the material is in granular or powder form, with which its flow qualities can be improved by fluidization, which is implemented through blowing air into the material. A system based on the so-called weight loss gravimetric weighing technique is used to control the feed. The use of weight loss feed for the aforementioned purpose is known in the art from different applications. The control system is implemented using the equipment in which an essential part is formed by the storage medium of suspended material on the weight transducers, which comprises a so-called hopper or weighing hoppers whose weight can be measured in a moment of time wanted. The flow of material is passed from said hopper to a feeder constructed to cooperate intimately with the container, and which has its operation controlled by a measurement signal obtained from the weight loss information of said weigh hopper. A problem in the present arises from the filling of the weigh hopper. The continuous operation of the system presupposes that the filling must be carried out simultaneously with the discharge of the content of the weighing hopper for the feeding, which causes disturbances to the control of the feeder. Consequently, it is desired that the filling phase be more instantaneous, and during this time of uncertainty of weight, it is intended that the control system runs under different types of empirical or co-putational algorithms. However, this period of unavoidable uncertainty of weight control remains a persistent problem. Various solutions to this problem have been proposed, one of which is described in the published German Patent Application No. 37,42,229. The arrangement described here is based on a type of weight loss feeder in which the flow of material to the feeder is passed via two weighing hoppers connected in series. The scale of the first weighing hopper of the series connection is adapted to check periodically the changes in weight of this hopper only, while the scale of the last hopper periodically verifies the changes in weight of the complete system. As a rule, the weight signal of the last hopper scale as such is used in the feeder control except in situations when the first hopper is being filled. In this situation, the control signal is conditioned by subtracting the weight signal of the first scale from the weight signal of the last scale. Superficially, the operation of the system seems unproblematic, despite its simplification procedures that inevitably degrade the control precision. An essential simplification is that, during the transfer of the filling of the material from the first weighing table to the last, the amount of material that falls between the hoppers can be known only computationally, not being under the control of any scale, that of origin to an uncertainty factor in the control system. An arrangement is also known in the art in which two feeders with a weight loss control system are connected in parallel. In this configuration, the weight loss feeders are alternately filled. The feeding of the material is done using the feeder that is not in its filling phase. A control arrangement based on the principle described above is described, for example, in the United States Patent No. 4, 579,252. While this arrangement offers reasonable weight control accuracy, complete accuracy is degraded by weighing errors during the start phases of the feeder. The equipment costs of the system are high. According to the present invention, in the above-described type of feeder control method, of continuous operation, in which the control of material flow is achieved by gravimetric measurement of weight loss of feed speed and speed continuous feeding is maintained by means of alternating filling flows made under the flow measurement of gravimetric material, the precision of the control has been improved by virtue of the provision of filling and feeding phases with weight measurement subsystems operating independently of each other, holding the flow of material passing through the filling and feeding phases to the real-time weight measurement, at least one of the subsystems and performing the control of the feeding speed based on the function of sum of the weight loss signal of filling and the power loss signal in weight. Advantageously, the real-time continuation of the material flow during the filling phase or the feeding phase carried out under the weight control is achieved by arranging the material flow between the filling and the feeding units, so that it occurs as a Gravitational piston type expense in which the material is passed as a continuous flow from the filling unit to the power unit. Advantageously, the feeding continuity is ensured by the completion of the filling of the feeding unit in an alternating manner using a greater number of two of the inter-container filling flows, of parallel operation. In the following, the invention will be described in greater detail when referring to the accompanying drawing in which a modality of an apparatus suitable for the implementation of the invention is shown schematically. The apparatus comprises first two filling hoppers 1 and 2, each connected to its own independent weighing equipment. In the following text, the hoppers are called weighing hoppers. The material to be fed is passed to these filling hoppers via tubes 3 and 4 equipped with closing valves 9 and 10 of the appropriate type. The weighing filling hoppers 1 and 2 are provided with hopper nozzles 5 and 6 for transferring the material to be fed to the weighing hopper 7 comprised of a hopper and a weighing system. The feeder 8 communicates in a fixed manner with the weighing hopper and operates under the control of the weighing system thereof.

The nozzles 5 and 6 are connected downstream via a flexible connector to ensure the independent function of the weighing hoppers 1 and 7, respectively connected in series, respectively 2 and 7. In the design and sizing of the nozzles, it should be taken in account that a disturbance free operation of the system requires a continuous piston-type expense in such a way that the material levels in the weighing hopper 7 and in the filling and weighing hoppers 1, 2 respectively connected to it, by the continuous piston type expense, can be considered to have a content of contiguous material. The nozzles 5 and 6 are provided in a similar manner with closing valves 11 and 12 of appropriate type. The weighing feed hopper 7 is fixed to the feeder 8 which in the embodiment illustrated is implemented using a screw type feeder. The drive machinery 13 of the feeder is provided with a suitable control that allows adjustment of the rotational speed of the feed screw to achieve the proper feeding speed. According to the invention, the feed rate control signal is obtained from the summation function of the weight loss signal of the weighing feed container and the weight loss signal from the weighing container 1 6 2 that communicates concurrently with this one. The weight loss measurement of the weighing hoppers 1 and 2 is used to control the feed rate only when the effective filling hopper has a free flow connection with the weighing hopper 7 and, respectively, the Weight loss measurement of a weighing hopper must be included in the control function over the moments when the filling hopper is in a free flow connection with the weighing hopper. Here, the measurement must be taken to ensure that the flow connection to the weighing hopper is cut so that the weighing hopper is refilled. In the implementation of the invention, the feeder described herein can be replaced by any type of controllable, equivalent feeder, such as a band feeder, a bin feeder, a plate feeder, a vibration feeder, etc. The embodiment of the invention is operated starting from the following initial situation. The feeder 8 is stopped and the material to be fed is flowed for example via the filling nozzle 3 to the weighing hopper 1. The discharge valve 11 of the weighing hopper 1 is opened, thus allowing the material to flow towards the weighing hopper 1 in order to fill it. When the weighing hopper 1 is filled with material, the flow of filling into the container is cut off. During this filling phase of the filling hopper 1, the discharge valve 12 of the weighing hopper 2 is kept closed. After these initial steps, the system is ready to be used. Then, the feeder 8 is started and its operation is controlled by the summing function of the weight loss signals obtained from the hoppers 1 and 7 connected to their respective weighing systems. As a supplementary function, the filling of the weighing hopper 2 is carried out. After the weighing hopper 1 is empty or almost completely empty, the discharge valve 11 thereof is closed, and, respectively, the discharge valve 12 of the second weighing container 2 is opened. Simultaneously with the change of the discharge valves to the open / closed states, the input signal of the weight loss measurement to the feed control system is switched from the weighing hopper 1 to the filling hopper of weighing 2, whereby also the control of the feeder 8 is continuously based on the summing function of the weight loss signals of the hoppers 2 and 7. Immediately afterwards the discharge valve 12 of the weighing hopper 1 is closed, the next fill to the weighing hopper 1 can be started. The arrangement described above makes it possible to eliminate the uncertain period of weight control almost completely, since the material that is transferred as a piston-like expense from the weighing hoppers 1 and 2, respectively, to the weighing hoppers 7 is during the complete phase of transfer of material under the control of the scale of the weighing hopper 1 (or 2, respectively) and the weighing hopper 7, and virtually no material flow can occur in the state of loose fall. The only instantaneous moment for the slightly uncontrolled flow of material to occur is during the change or commutation of the flow of filler material from hopper 1 to hopper 2, and vice versa. With an adequate equipment arrangement also this uncertain period of weight control can be eliminated up to an insignificant factor. The described control arrangement presupposes that the weighing feed container 7 is kept continuously full. The novel arrangement also reduces the risk of uncontrolled deflection flow through the feeder 8, and decreases the effect of variations in the quality of the material being fed, on the accuracy of the control.

Claims (3)

1. Method for feeding particulate material in a continuous manner, in which method the control of the flow of material feed is achieved by means of the gravimetric measurement of weight loss of the feeding speed, and the continuous feeding speed is maintained by means of the flows alternating filling made under the gravimetric measurement of the material flow, characterized in that the filling and feeding phases are provided with subsystems of weight measurement operating independently of each other, so that the flow of material passes through the filling phases and power is subject to real-time measurements by at least one of the subsystems, and because the control of the feed rate is achieved based on the summation function of the fill loss signal and the loss signal in weight of food.

2. Method according to claim 1, characterized in that the flow of material between the filling and feeding phases is maintained as a gravitational piston-type expense.

3. Method according to claim 1 or 2, characterized in that the filling of the feeding unit is carried out in an alternating manner using a greater number of two of the filling flows.