Loss-in-weight feeder system

• US 5,260,880 A
• Filed: 07/26/1991
• Issued: 11/09/1993
• Est. Priority Date: 08/04/1987
• Status: Expired due to Term

• Current Assignee: Schenck Process LLC (Schenck Process Holding GmbH)
• Original Assignee: Accurate, Inc.
• Inventors: Tump, Ronald S.
• Primary Examiner(s): RUGGIERO, JOSEPH F
• Application Number:
  US07/736,681
• Time in Patent Office: 837 Days
• Field of Search: 364/479, 364/478, 364/567, 364/571.04, 364/571.08, 177/50, 177/105, 177/59, 177/60, 177/63, 177/65, 177/66, 177/71, 177/114, 177/119, 177/121, 177/122, 177/123, 222/56, 222/58-59
• US Class Current: 700/240
• CPC Class Codes: G01G 11/086 of the loss-in-weight feeding type
• CPC Class Codes: G05D 7/0611 characterised by the set value given to the control element

Abstract

A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge member, including a closed loop controller configured to compare the actual rate at which material is discharged from the reservoir to a desired discharge rate. During operation, a racheting process is used to avoid the use of spurious weight signals to determine the material weight in the feeder for purposes of properly controlling the discharge rate.

Claims

1. A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge arrangement, comprising:

a reservoir for holding a material;

means for developing a weight signal representative of the instantaneous weight of the material within the reservoir;

means for sampling the weight signal to produce a sample value at each of a plurality of times during each of a series of time periods and averaging the sample values for each time period to produce an average weight value;

means for storing a first array of M number of average weight values as M-array values, where each average weight value is compared to the previous M-array value stored in the first array such that the average weight value is stored as an M-array value if the previous M-array value is greater than the average weight value, and the previous M-array value is stored as the M-array value if the average weight value is less than the previous M-array value;

means for calculating a first weighted weight value based upon the M-array values;

computing means for generating and applying a control signal to a controllable discharge arrangement operatively associated with the reservoir, the control signal being indicative of the desired rate of discharge of the material therefrom;

first input means for entering a first signal into the computing means, the first signal being representative of the desired rate of discharge of the material;

means for developing a correction signal based on the weighted weight value, and the first signal; and

means for adjusting the control signal in accordance with the correction signal.

2. The feeder of claim 1, wherein:

the controllable discharge member comprises a metering screw and an electric motor; and

the computing means comprises means for applying the control signal to the electric motor.

3. The feeder of claim 1, further comprising

means for storing a second array of N number of average weight values as N-array values, where each average weight value is compared to the previous N-array value stored in the second array such that the average weight value is stored as an N-array value if the previous N-array value is greater than the average weight value, and the previous N-array value is stored as the N-array value if the average weight value is less than the previous N-array value;

and

means for calculating a second weighted weight value based upon the N-array values.

4. A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge arrangement, comprising:

a scale configured to develop a weight signal representative of the instantaneous weight of a material within a reservoir;

means for taking a plurality of samples of the weight signal during each of a plurality of successive sample intervals of regular, predetermined duration;

means for averaging the samples to produce an average weight value for each of the intervals;

means for storing a first array of M number of average weight values as M-array values, where each average weight value is compared to the previous M-array value stored in the first array such that the average weight value is stored as an M-array value if the previous M-array value is greater than the average weight value, and the previous M-array value is stored as the M-array value if the average weight value is less than the previous M-array value;

means for calculating a first weighted weight value based upon the M-array values;

computing means for developing a first weighted weight value based upon the M-array values;

computing means for developing, in accordance with the weighted weight values, an actual feed rate signal Q representative of the rate at which the material is being discharged through a controllable discharge member operatively associated with the reservoir;

first input means for entering a first signal SP, representative of desired feed rate, into the computing means;

second input means for entering a signal MCMXACC, representative of a desired threshold acceleration, into the computing means;

third input means for entering a third signal GAIN/INC, representative of a preselected incremental change in the actual feed rate, into the computing means;

wherein, for each sample interval, the computing means is configured to generate;

an error signal E representative of the difference between the actual feed rate signal and the first signal;

a proportionating signal PF representative of a desired gain;

a correction factor signal CF determined as a function of E and PF; and

an acceleration signal ACC representative of the time rate of change of Q;

wherein, for each sample interval,

space="preserve" listing-type="equation">CF=PF×

E

if ACC is less than MCXACC; and

space="preserve" listing-type="equation">CF=(PF/ACC)×

E

if ACC is greater than MCXACC;

fourth input means for entering a fourth signal, representative of a predetermined maximum allowable value of the correction factor signal, into the computing means; and

means for applying the fourth signal to the discharge member if the value of the correction factor signal exceeds the value of the fourth signal.

5. A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge arrangement, comprising:

a scale configured to develop a weight signal representative of the instantaneous weight of a material within a reservoir;

means for taking a plurality of samples of the weight signal during each of a plurality of successive sample intervals of regular, predetermined duration;

means for averaging the samples to produce an average weight value for each of the intervals;

means for storing a first array of M number of average weight values as M-array values, where each average weight value is compared to the previous M-array value stored in the first array such that the average weight value is stored as an M-array value if the previous M-array value is greater than the average weight value, and the previous M-array value is stored as the M-array value is the average weight value is less than the previous M-array value;

means for calculating a first weighted weight value based upon the M-array values;

computing means for developing a first weighted weight value based upon the M-array values;

computing means for developing, in accordance with the weighted weight values, an actual feed rate signal Q representative of the rate at which the material is being discharged through a controllable discharge member operatively associated with the reservoir;

first input means for entering a first signal SP, representative of desired feed rate, into the computing means;

second input means for entering a signal MCXACC, representative of a desired threshold acceleration, into the computing means;

third input means for entering a third signal GAIN/INC, representative of a preselected incremental change in the actual feed rate, into the computing means;

wherein, for each sample interval, the computing means, is configured to generate;

an error signal E representative of the difference between the actual feed rate signal and the first signal;

a proportionating signal PF representative of a desired gain;

a correction factor signal CF determined as a function of E and PF; and

an acceleration signal ACC representative of the time rate of change of Q;

wherein, for each sample interval,

space="preserve" listing-type="equation">CF=PF×

E

if ACC is less than MCXACC; and

space="preserve" listing-type="equation">CF=(PF/ACC)×

E

if ACC is greater than MCXACC;

fifth input means for applying a fifth signal, representative of a minimum speed change value, into the computing means; and

means for applying the fifth signal to the discharge member if the value of the fifth signal exceeds the value of the correction factor signal and the value of the acceleration signal exceeds the value of the second signal.

6. The feeder of claim 5, further comprising:

means for storing a second array of N number of average weight values as N-array values, where each average weight value is compared to the previous N-array value stored in the second array such that the average weight value is stored as an N-array value if the previous N-array value is greater than the average weight value, and the previous N-array value is stored as the N-array value if the average weight value is less than the previous N-array value, wherein the processor circuit produces a second weighted weight value based upon the N-array values.

7. A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge arrangement, comprising:

a scale configured to develop a weight signal representative of the instantaneous weight of a material within a reservoir;

means for taking a plurality of samples of the weight signal during each of a plurality of successive sample intervals of regular, predetermined duration;

means for averaging the samples to produce an average weight value for each of the intervals;

means for storing a first array of M number of average weight values as M-array values, where each average weight value is compared to the previous M-array value stored in the first array such that the average weight value is stored as an M-array value if the previous M-array value is greater than the average weight value, and the previous M-array value is stored as the M-array value if the average weight value is less than the previous M-array value;

means for calculating a first weighted weight value based upon the M-array values;

computing means for developing a first weighted weight value based upon the M-array values;

computing means for developing, in accordance with the weighted weight values, an actual feed rate signal Q representative of the rate at which the material is being discharged through a controllable discharge member operatively associated with the reservoir;

first input means for entering a first signal SP, representative of desired feed rate, into the computing means;

second input means for entering a signal MCXACC, representative of a desired threshold acceleration, into the computing means;

third input means for entering a third signal GAIN/INC, representative of a preselected incremental range in the actual feed rate, into the computing means;

wherein, for each sample interval, the computing means is configured to generate;

an error signal E representative of the difference between the actual feed rate signal and the first signal;

a proportionating signal PF representative of a desired gain;

a correction factor signal CF determined as a function of E and PF; and

an acceleration signal ACC representative of the time rate of change of Q;

wherein, for each sample interval,

space="preserve" listing-type="equation">CF=PF×

E

if ACC is less than MCXACC; and

space="preserve" listing-type="equation">CF=(PF/ACC)×

E

if ACC is greater than MXCACC;

wherein the correction factor signal comprises a digital correction factor signal, and wherein the controllable discharge arrangement further comprises;

a metering screw;

an electric motor configured to drive the metering screw such that the actual feed rate is substantially linearly proportional to the speed of the motor;

converting means for converting the digital correction factor signal to an analog output signal representative of the speed of the motor; and

means for applying the analog output signal to the motor.

8. A loss-in-weight feeder for discharging a flowable material from a reservoir through a controllable discharge arrangement, comprising:

a reservoir for holding a material;

a sensor disposed to produce a weight signal representative of the instantaneous weight of the material within the reservoir;

a circuit coupled to the sensor to sample the weight signal to produce a sample value at each of a plurality of times during each of a series of time periods and average the sample values for each time period to produce an average weight value;

a memory coupled to the circuit to store a first array of M number of the average weight values as M-array values, where each average weight value is compared to the previous M-array value stored in the first array such that the average weight value is stored as an M-array value if the previous M-array value is greater than the average weight value, and the previous M-array value is stored as the M-array value if the average weight value is less than the previous M-array value;

a processor circuit coupled to the memory to produce a first weighted weight value based upon the M-array values, and to generate and apply a control signal to a controllable discharge arrangement operatively associated with the reservoir, the control signal being indicative of the desired rate of discharge of the material therefrom; and

a first user input device coupled to the processor circuit to enter a first signal into the processor circuit, the first signal being representative of the desired rate of discharge of the material, wherein the processor circuit produces a correction signal based on the weighted weight value, and the first signal, and adjusts the control signal in accordance with the correction signal.

9. The feeder of claim 8, wherein:

the controllable discharge member comprises a metering screw and an electric motor; and

the processor circuit is configured to apply the control signal to the electric motor.