Electricity: motive power systems – Positional servo systems
Reexamination Certificate
1998-11-06
2001-10-30
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S565000
Reexamination Certificate
active
06310454
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
The present invention relates broadly to bulk material supply systems and, more particularly, to a feed system for bulk solids and its associated controller wherein the controller employs fuzzy logic for rapid reactions to changes in weight.
Bulk solids appear throughout industry and must be handled or processed in a manner which will provide consistent results without waste. Examples of industries which utilize bulk solids include food, lumber, paper, chemical, petroleum refining, rubber, stone, clay, glass, and concrete. The bulk solid materials may include such diverse items as cabbage flakes, bleach, bauxite, baking soda, fiberglass, flour, grass seed, iron ore, starch, sugar, raisins, parsley, noodles, nylon, mineral fiber, mica, lime, and detergent. All of these materials share a common feature in that they are flowable solids. They are fungible materials which may be poured for filling into containers or otherwise metered under flow conditions for processing.
Typically, such processing includes providing a hopper filled with the bulk material with some form of regulator or metering device providing the necessary flow control for processing.
One method of determining how much bulk solid material has been dispensed during any given dispensing operation is by using the so-called loss-in-weight method. There, the hopper containing the bulk material is continually weighed and the reduction in weight is indicative of the material dispensed.
Further, the reduction in weight-per-unit time is indicative of the rate at which a predetermined amount of the bulk material is dispensed. Therefore, by precisely determining the change in weight of the hopper, a precise indication of the amount of material dispensed is realized. This information can be used for controlling the feed process. Furthermore, while the present invention is described for operation with a vibratory feeder, it should be noted that it is equally effective with screw feeders or belt feeders. The focus of the present invention lies in its applicability to loss-in-weight feeders.
A common method which is used to control dispensing of bulk solids is the proportional method used throughout the industry. The setpoint for such control method is a desired rate of change of weight for a supply of the bulk solid. However, because the control variable (the weight change) is the integral of the rate of weight change and not the rate of weight change itself, the proportional control method currently used in the industry, while reliable, is clumsy and lacks a certain amount of precision.
Several methods may be used to control the actual feed of the bulk solid material. Valves may be used which are open proportionally or open for a certain time period. Other methods include the use of a belt feeder or a screw feeder. A vibratory feeder is disclosed in Peschl U.S. Pat. No. 3,973,703. There, a vibrating tray is disclosed containing a number of plates in an angular relationship to one another. According to this method, the bulk material will not flow unless the feeder is vibrated or otherwise agitated in some manner. Such feeders allow for precise flow with the flow rate being based on the amplitude of vibration or agitation. This type of feeder can provide accurate flow characteristics and can respond rapidly to changing inputs from an associated excitation motor. The motor is driven responsive to a control variable. As discussed above, the current proportional controllers are slow to respond to changes in demand or process changes and, therefore, the precision and rapid changing characteristics of any loss in weight type feeders including the vibratory feeder are not fully realized using a proportional controller.
SUMMARY OF THE PRESENT INVENTION
It is accordingly an object of the present invention to provide a feed control system which precisely controls a vibratory feeder and offers rapid response to a change in demand.
Briefly summarized, the method of the present invention includes determining an appropriate change to a regulator that controls an outflow of a flowable material from a supply of the flowable material. The method includes the steps of, for a plurality of small time intervals during the outflow, (a) calculating average values representative of a rate of weight change of the supply of the flowable material; (b) calculating average values representative of a rate error based on the calculated average values for the rate of weight change and based on a setpoint value for the rate of weight change; (c) calculating values representative of the change in the rate error based on the calculated average values for the rate error; and (d) determining a value representative of an appropriate change to the regulator for controlling the outflow by applying fuzzy logic control to the calculated average values representative of the rate error and the calculated values representative of the change in the rate error.
Preferably, the method further comprises weighing the supply of the flowable material during the plurality of small time intervals as well as determining the setpoint value by weighing the outflow of the flowable material.
The apparatus of the present invention precisely controls the feed rate of the feeder and itself includes: (a) a motor operatively connected to the feeder which causes dispensing of a flowable material by the feeder when the motor is driven; (b) a control circuit operatively connected to the motor which provides a voltage supply to the motor for driving the motor when the control circuit is actuated; (c) a counter disposed in communication with the control circuit for actuating the control circuit after a determined time interval; and (d) a fuzzy logic controller disposed in communication with the counter for determining the time interval.
Preferably, the voltage supply is AC voltage and the determined time interval ranges between zero and one-half of a time period of the AC voltage. Furthermore, the apparatus preferably includes a sensor disposed in communication with the fuzzy logic controller for measuring a weight of a supply of flowable material that is dispensed by the feeder.
In a feature of the present invention, the control circuit deactuates at a recurring point in time. Preferably, the recurring point in time is a crossover of a median voltage of the AC voltage supply. Furthermore, the counter preferably restarts at the recurring point in time as well.
The preferred embodiment of the apparatus of the present invention includes: (a) a motor operatively connected to the feeder to cause dispensing of the feeder when the motor is driven; (b) a control circuit for controlling the driving of the motor, the control circuit including a pair of silicon control rectifiers disposed in parallel but reversed to one another with each silicon control rectifier operatively connected to the motor such that, when each silicon control rectifier is fired, an AC voltage is supplied to the motor and the motor is driven, the parallel and reversed disposition of the silicon control rectifiers in the control circuit resulting in each silicon control rectifier being able to supply the AC voltage to the motor during opposite half periods of a time period of the AC voltage; (c) a counter disposed in communication with each of the silicon control rectifiers for actuation thereof when an overflow signal is generated by the counter; (d) a latch controller disposed in communication with the counter for enablement and disablement of the counter with the latch controller disabling the counter when the overflow signal is generated by the counter; (e) a detector connected to the AC voltage for detecting when the AC voltage crosses over a median voltage thereof with the detector being further disposed in communication with the latch controller, with the detector generating a signal to the latch controller for enablement of the counter when the median voltage is detected; (f) a fuzzy logic controller disposed in communication with the counter for generating an output to the counter that l
Flesher James L.
Moran Robert L.
Duda Rina I.
Kennedy Covington Lobdell & Hickman LLP
Moran Robert L.
Nappi Robert E.
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