Control system and method for machine or process having dead time

Claim 1

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of sampling the output at discrete time intervals which are less than the dead time, deriving a signal indicative of the error between the sampled output and a set point for the output, in response to the error signal initiating control for the machine or process, providing a model of the machine or process, coupling to said model a signal indicative of the control action for the machine or process, and modifying the response of said model with the magnitude of the error signal to determine the magnitude of the control for the machine or process, said model response having characteristics such that subsequent transient and steady state errors between the output and the setpoint in response to the control action are fully corrected at time intervals which are less than the dead time.

Claim 2

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of sampling the output at discrete time intervals which are less than the dead time, deriving a signal indicative of the error between the sampled output and a set point for the output, in response to the error signal initiating control for the machine or process, providing a model of the machine or process, coupling to said model a signal indicative of the control action for the machine or process, and modifying the response of said model with the magnitude of the error signal to determine the magnitude of the control for the machine or process, said model response having characteristics such that subsequent transient and steady state errors between the output and the setpoint in response to the control action are fully corrected at time intervals which are less than the dead time.

Claim 3

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of sampling the output at discrete time intervals which are less than the dead time, deriving an error between the sampled output and a set point for the output, in response to the error actuating the control to fully correct the error at time intervals which are less than the dead time, providing a model of the machine or process, said model producing an output which includes first and second components respectively simulating the steady state and transient responses of the machine or process, and comparing the sampled output with the response of said model to actuate the control.

Claim 4

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of sampling the output at discrete time intervals which are less than the dead time, deriving an error between the sampled output and a set point for the output, in response to the error actuating the control to fully correct the error at time intervals which are less than the dead time, providing a model of the machine or process, said model producing an output which includes first and second components respectively simulating the steady state and transient responses of the machine or process, and comparing the sampled output with the response of said model to actuate the control.

Claim 7

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of averaging the output for a discrete time interval less than the dead time, deriving, at the end of each interval, an indication of the error between the set point for the output and the average of the output over the interval, providing a modeled response of the machine or process, the modeled response including a model of the dead time, and in response to each of the indications initiating the control action to fully correct the error for transient and steady state responses at time intervals shorter than the dead time by modifying the error by an amount indicative of the modeled response.

Claim 8

A method of controlling an output of a machine or process having a dead time between the time a control action affecting the output is taken and the time the output is affected by the control action, comprising the steps of averaging the output for a discrete time interval less than the dead time, deriving, at the end of each interval, an indication of the error between the set point for the output and the average of the output over the interval, providing a modeled response of the machine or process, the modeled response including a model of the dead time, and in response to each of the indications initiating the control action to fully correct the error for transient and steady state responses at time intervals shorter than the dead time by modifying the error by an amount indicative of the modeled response.

Claim 12

A method of controlling a property of a sheet formed by a machine having a transportation lag between a location where a control for the property is performed and the location of a gauge for the property comprising scanning the gauge in a direction between the sheet edges to monitor the sheet property, averaging the gauge response after the gauge has traversed, at least, a portion of the sheet and for a time interval less than the transportation lag, deriving, at the end of the interval, an indication of the error between a set point for the output and the average of the response over the interval, providing a modeled response of the machine or process, the modeled response including a model of the dead time, and in response to each indication initiating the control action to fully correct the error for transient and steady responses at intervals shorter than the time required for the transportation lag by modifying the error by an amount indicative of the modeled response.

Claim 13

A method of controlling a property of a sheet formed by a machine having a transportation lag between a location where a control for the property is performed and the location of a gauge for the property comprising scanning the gauge in a direction between the sheet edges to monitor the sheet property, averaging the gauge response after the gauge has traversed, at least, a portion of the sheet and for a time interval less than the transportation lag, deriving, at the end of the interval, an indication of the error between a set point for the output and the average of the response over the interval, providing a modeled response of the machine or process, the modeled response including a model of the dead time, and in response to each indication initiating the control action to fully correct the error for transient and steady responses at intervals shorter than the time required for the transportation lag by modifying the error by an amount indicative of the modeled response.

Claim 18

A method of controlling a plurality of interacting outputs of a machine or process having a dead time between the time a control for each output is taken and the time the output is affected by the control comprising modeling the response of the machine including the dead time for each output, coupling the modeled response for one output to an input of the modeled response for another of the outputs, and in response to a comparison of each modeled response with each output actuating the controls at time intervals less than the dead time.

Claim 19

A method of controlling a plurality of interacting outputs of a machine or process having a dead time between the time a control for each output is taken and the time the output is affected by the control comprising modeling the response of the machine including the dead time for each output, coupling the modeled response for one output to an input of the modeled response for another of the outputs, and in response to a comparison of each modeled response with each output actuating the controls at time intervals less than the dead time.

Claim 23

A system for controlling, in rEsponse to an input signal, a machine having a dead time, T, said machine having a transfer function, including the dead time, represented by: GM(s)e sT where: s is the LaPlace operator, e is the base of natural logarithms, and GM is dependent upon the machine response, comprising means for periodically sampling the input signal at a frequency greater than 1/T; first feedback means responsive to the sampled signal, said first fedback means including: a controller for feeding a control signal to the machine, a negative feedback loop responsive to the controller, said negative feedback loop including means having a transfer function indicative of the steady state response of the machine, GM(0), another feedback loop responsive to the controller having a transfer function indicative of the transfer function of the machine, GM(s)e sT; and a further feedback loop having a polarity opposite to that of the another feedback loop responsive to a property of the machine; said feedback loop and loop means being completed substantially simultaneously with sampling of the input signal.

Claim 24

A system for controlling, in rEsponse to an input signal, a machine having a dead time, T, said machine having a transfer function, including the dead time, represented by: GM(s)e sT where: s is the LaPlace operator, e is the base of natural logarithms, and GM is dependent upon the machine response, comprising means for periodically sampling the input signal at a frequency greater than 1/T; first feedback means responsive to the sampled signal, said first fedback means including: a controller for feeding a control signal to the machine, a negative feedback loop responsive to the controller, said negative feedback loop including means having a transfer function indicative of the steady state response of the machine, GM(0), another feedback loop responsive to the controller having a transfer function indicative of the transfer function of the machine, GM(s)e sT; and a further feedback loop having a polarity opposite to that of the another feedback loop responsive to a property of the machine; said feedback loop and loop means being completed substantially simultaneously with sampling of the input signal.

Claim 27

A system for controlling, in response to an input signal, a machine having a dead time, T, said machine having a transfer function, including the deadband time, represented by: GM(s)e sT where: s is the LaPlace operator, e is the base of natural logarithms, and GM is dependent upon the machine response, comprising first feedback means responsive to the input signal, said first feedback means including: a controller for feeding a control signal to the machine, a negative feedback loop responsive to the controller, said loop including means having a transfer function indicative solely of the steady state response of the machine, GM(0), another feedback loop responsive to the controller having a transfer function indicative of the transfer function of the machine, GM(s)e sT; and a further feedback loop having a polarity opposite to that of the another feedback loop responsive to a property of the machine.

Claim 28

A system for controlling, in response to an input signal, a machine having a dead time, T, said machine having a transfer function, including the deadband time, represented by: GM(s)e sT where: s is the LaPlace operator, e is the base of natural logarithms, and GM is dependent upon the machine response, comprising first feedback means responsive to the input signal, said first feedback means including: a controller for feeding a control signal to the machine, a negative feedback loop responsive to the controller, said loop including means having a transfer function indicative solely of the steady state response of the machine, GM(0), another feedback loop responsive to the controller having a transfer function indicative of the transfer function of the machine, GM(s)e sT; and a further feedback loop having a polarity opposite to that of the another feedback loop responsive to a property of the machine.

Claim 31

A system for controlling a machine having a dead time between the time a control action is taken on a plurality of controlled variables thereof and the time output signals indicative of the variables are derived, said variables interacting with each other, said machine being responsive to input signals indicative of desired values of the variables, comprising means for modeling the steady state and transient response of the machine to control actions affecting each of said variables, means for establishing a negative feedback loop between each of said input signals and said modeled steady state responses, means for establishing opposite polarity feedback loops between each of said output signals and said modeled transient responses of the machine, the modeled transient responses including the dead time, and means for cross coupling a response between models of the variables included in the feedback loops.

Claim 32

A system for controlling a machine having a dead time between the time a control action is taken on a plurality of controlled variables thereof and the time output signals indicative of the variables are derived, said variables interacting with each other, said machine being responsive to input signals indicative of desired values of the variables, comprising means for modeling the steady state and transient response of the machine to control actions affecting each of said variables, means for establishing a negative feedback loop between each of said input signals and said modeled steady state responses, means for establishing opposite polarity feedback loops between each of said output signals and said modeled transient responses of the machine, the modeled transient responses including the dead time, and means for cross coupling a response between models of the variables included in the feedback loops.

Claim 33

A system for controlling a machine forming a fibrous sheet having: a headbox responsive to a slurry of fiber and water fed thereto and feeding the slurry to a moving draiNage means on which the sheet is formed; a dryer for the sheet downstream of the drainage means; said system comprising gauge means monitoring the moisture and weight of the sheet downstream of the dryer for deriving first and second signals respectively indicative of the sheet moisture and weight, means for deriving a third signal indicative of the total mass flow rate of the slurry fed to the headbox, means for establishing set points for the sheet weight and moisture at the site of the gauge means, means responsive to the set points and the third signal for simulating the moisture and weight responses of the sheet at the gauge site, and means combining the simulated moisture and weight responses with the first and second signals and the set points for deriving control signals for the drying rate of the dryer and the amount of fiber fed to the headbox.

Claim 34

A system for controlling a machine forming a fibrous sheet having: a headbox responsive to a slurry of fiber and water fed thereto and feeding the slurry to a moving draiNage means on which the sheet is formed; a dryer for the sheet downstream of the drainage means; said system comprising gauge means monitoring the moisture and weight of the sheet downstream of the dryer for deriving first and second signals respectively indicative of the sheet moisture and weight, means for deriving a third signal indicative of the total mass flow rate of the slurry fed to the headbox, means for establishing set points for the sheet weight and moisture at the site of the gauge means, means responsive to the set points and the third signal for simulating the moisture and weight responses of the sheet at the gauge site, and means combining the simulated moisture and weight responses with the first and second signals and the set points for deriving control signals for the drying rate of the dryer and the amount of fiber fed to the headbox.

Claim 45

A method of controlling a machine forming a fibrous sheet having: a headbox responsive to a slurry of fiber and water fed thereto and feeding the slurry to a moving drainage means on which the sheet is formed; a dryer for the sheet downstream of the drainage means; said method comprising monitoring the moisture and weight of the sheet downstream of the dryer, deriving an indication of the mass flow rate of the slurry fed to the headbox, establishing set points for the sheet weight and moisture at the site of the gauge means, in response to the set points and the mass flow rate indication, simulating the moisture and weight responses of the sheet at the gauge site, and in response to comparisons of the simulated moisTure and weight and the set points for sheet moisture and weight controlling the amount of fiber fed to the headbox and the dryer drying rate.

Claim 46

A method of controlling a machine forming a fibrous sheet having: a headbox responsive to a slurry of fiber and water fed thereto and feeding the slurry to a moving drainage means on which the sheet is formed; a dryer for the sheet downstream of the drainage means; said method comprising monitoring the moisture and weight of the sheet downstream of the dryer, deriving an indication of the mass flow rate of the slurry fed to the headbox, establishing set points for the sheet weight and moisture at the site of the gauge means, in response to the set points and the mass flow rate indication, simulating the moisture and weight responses of the sheet at the gauge site, and in response to comparisons of the simulated moisTure and weight and the set points for sheet moisture and weight controlling the amount of fiber fed to the headbox and the dryer drying rate.

Claim 69

A method of controlling a machine or process in response to an input control signal, the machine or process having a dead time between the time a control is applied to the machine or process and the time the control is reflected in an output of the machine or process, the machine or process having a steady response and a transient response, comprising comparing the output of the machine or process with the input control signal to derive an error signal, supplying an error signal to a controller, deriving a first output signal from the controller, applying the first output signal to the machine or process, responding to the first output signal to derive a first indication for the expected steady state Response of the process or machine to the first output signal and a second indication of the expected transient response of the process or machine to the first output signal, said first indication being derived substantially immediately after the first output signal is derived, said second indication being derived following the derivation of the first output signal by a time interval substantially equal to the dead time, and modifying the error signal derived by the comparison step by the first and second indications so that the modified error signal is supplied to the controller.

Claim 70

A method of controlling a machine or process in response to an input control signal, the machine or process having a dead time between the time a control is applied to the machine or process and the time the control is reflected in an output of the machine or process, the machine or process having a steady response and a transient response, comprising comparing the output of the machine or process with the input control signal to derive an error signal, supplying an error signal to a controller, deriving a first output signal from the controller, applying the first output signal to the machine or process, responding to the first output signal to derive a first indication for the expected steady state Response of the process or machine to the first output signal and a second indication of the expected transient response of the process or machine to the first output signal, said first indication being derived substantially immediately after the first output signal is derived, said second indication being derived following the derivation of the first output signal by a time interval substantially equal to the dead time, and modifying the error signal derived by the comparison step by the first and second indications so that the modified error signal is supplied to the controller.