Package edu.wpi.first.math.system

Class LinearSystemLoop<States extends Num,Inputs extends Num,Outputs extends Num>

java.lang.Object

edu.wpi.first.math.system.LinearSystemLoop<States,Inputs,Outputs>

public class LinearSystemLoop<States extends Num,Inputs extends Num,Outputs extends Num>
extends Object

Combines a controller, feedforward, and observer for controlling a mechanism with full state feedback.

For everything in this file, "inputs" and "outputs" are defined from the perspective of the plant. This means U is an input and Y is an output (because you give the plant U (powers) and it gives you back a Y (sensor values)). This is the opposite of what they mean from the perspective of the controller (U is an output because that's what goes to the motors and Y is an input because that's what comes back from the sensors).

For more on the underlying math, read https://file.tavsys.net/control/controls-engineering-in-frc.pdf.

Constructor Summary

Constructors

Constructor	Description
LinearSystemLoop(LinearQuadraticRegulator<States,Inputs,Outputs> controller, LinearPlantInversionFeedforward<States,Inputs,Outputs> feedforward, KalmanFilter<States,Inputs,Outputs> observer, double maxVoltageVolts)	Constructs a state-space loop with the given controller, feedforward and observer.
LinearSystemLoop(LinearQuadraticRegulator<States,Inputs,Outputs> controller, LinearPlantInversionFeedforward<States,Inputs,Outputs> feedforward, KalmanFilter<States,Inputs,Outputs> observer, Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction)	Constructs a state-space loop with the given controller, feedforward, and observer.
LinearSystemLoop(LinearSystem<States,Inputs,Outputs> plant, LinearQuadraticRegulator<States,Inputs,Outputs> controller, KalmanFilter<States,Inputs,Outputs> observer, double maxVoltageVolts, double dtSeconds)	Constructs a state-space loop with the given plant, controller, and observer.
LinearSystemLoop(LinearSystem<States,Inputs,Outputs> plant, LinearQuadraticRegulator<States,Inputs,Outputs> controller, KalmanFilter<States,Inputs,Outputs> observer, Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction, double dtSeconds)	Constructs a state-space loop with the given plant, controller, and observer.

Method Summary

Modifier and Type	Method	Description
Matrix<Inputs,N1>	clampInput(Matrix<Inputs,N1> unclampedU)	Clamp the input u to the min and max.
void	correct(Matrix<Outputs,N1> y)	Correct the state estimate x-hat using the measurements in y.
Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>>	getClampFunction()	Get the function used to clamp the input u.
LinearQuadraticRegulator<States,Inputs,Outputs>	getController()	Return the controller used internally.
Matrix<States,N1>	getError()	Returns difference between reference r and current state x-hat.
double	getError(int index)	Returns difference between reference r and current state x-hat.
LinearPlantInversionFeedforward<States,Inputs,Outputs>	getFeedforward()	Return the feedforward used internally.
Matrix<States,N1>	getNextR()	Returns the controller's next reference r.
double	getNextR(int row)	Returns an element of the controller's next reference r.
KalmanFilter<States,Inputs,Outputs>	getObserver()	Return the observer used internally.
Matrix<Inputs,N1>	getU()	Returns the controller's calculated control input u plus the calculated feedforward u_ff.
double	getU(int row)	Returns an element of the controller's calculated control input u.
Matrix<States,N1>	getXHat()	Returns the observer's state estimate x-hat.
double	getXHat(int row)	Returns an element of the observer's state estimate x-hat.
void	predict(double dtSeconds)	Sets new controller output, projects model forward, and runs observer prediction.
void	reset(Matrix<States,N1> initialState)	Zeroes reference r and controller output u.
void	setClampFunction(Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction)	Set the clamping function used to clamp inputs.
void	setNextR(double... nextR)	Set the next reference r.
void	setNextR(Matrix<States,N1> nextR)	Set the next reference r.
void	setXHat(int row, double value)	Set an element of the initial state estimate x-hat.
void	setXHat(Matrix<States,N1> xhat)	Set the initial state estimate x-hat.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LinearSystemLoop

public LinearSystemLoop(LinearSystem<States,Inputs,Outputs> plant, LinearQuadraticRegulator<States,Inputs,Outputs> controller, KalmanFilter<States,Inputs,Outputs> observer, double maxVoltageVolts, double dtSeconds)

Constructs a state-space loop with the given plant, controller, and observer. By default, the initial reference is all zeros. Users should call reset with the initial system state before enabling the loop. This constructor assumes that the input(s) to this system are voltage.

Parameters:

plant - State-space plant.

controller - State-space controller.

observer - State-space observer.

maxVoltageVolts - The maximum voltage that can be applied. Commonly 12.

dtSeconds - The nominal timestep.

LinearSystemLoop

public LinearSystemLoop(LinearSystem<States,Inputs,Outputs> plant, LinearQuadraticRegulator<States,Inputs,Outputs> controller, KalmanFilter<States,Inputs,Outputs> observer, Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction, double dtSeconds)

Constructs a state-space loop with the given plant, controller, and observer. By default, the initial reference is all zeros. Users should call reset with the initial system state before enabling the loop.

Parameters:

plant - State-space plant.

controller - State-space controller.

observer - State-space observer.

clampFunction - The function used to clamp the input U.

dtSeconds - The nominal timestep.

LinearSystemLoop

public LinearSystemLoop(LinearQuadraticRegulator<States,Inputs,Outputs> controller, LinearPlantInversionFeedforward<States,Inputs,Outputs> feedforward, KalmanFilter<States,Inputs,Outputs> observer, double maxVoltageVolts)

Constructs a state-space loop with the given controller, feedforward and observer. By default, the initial reference is all zeros. Users should call reset with the initial system state before enabling the loop.

Parameters:

controller - State-space controller.

feedforward - Plant inversion feedforward.

observer - State-space observer.

maxVoltageVolts - The maximum voltage that can be applied. Assumes that the inputs are voltages.

LinearSystemLoop

public LinearSystemLoop(LinearQuadraticRegulator<States,Inputs,Outputs> controller, LinearPlantInversionFeedforward<States,Inputs,Outputs> feedforward, KalmanFilter<States,Inputs,Outputs> observer, Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction)

Constructs a state-space loop with the given controller, feedforward, and observer. By default, the initial reference is all zeros. Users should call reset with the initial system state before enabling the loop.

Parameters:

controller - State-space controller.

feedforward - Plant inversion feedforward.

observer - State-space observer.

clampFunction - The function used to clamp the input U.

Method Details

getXHat

public Matrix<States,N1> getXHat()

Returns the observer's state estimate x-hat.

Returns:

the observer's state estimate x-hat.

getXHat

public double getXHat(int row)

Returns an element of the observer's state estimate x-hat.

Parameters:

row - Row of x-hat.

Returns:

the i-th element of the observer's state estimate x-hat.

setXHat

public void setXHat(Matrix<States,N1> xhat)

Set the initial state estimate x-hat.

Parameters:

xhat - The initial state estimate x-hat.

setXHat

public void setXHat(int row, double value)

Set an element of the initial state estimate x-hat.

Parameters:

row - Row of x-hat.

value - Value for element of x-hat.

getNextR

public double getNextR(int row)

Returns an element of the controller's next reference r.

Parameters:

row - Row of r.

Returns:

the element i of the controller's next reference r.

getNextR

public Matrix<States,N1> getNextR()

Returns the controller's next reference r.

Returns:

the controller's next reference r.

setNextR

public void setNextR(Matrix<States,N1> nextR)

Set the next reference r.

Parameters:

nextR - Next reference.

setNextR

public void setNextR(double... nextR)

Set the next reference r.

Parameters:

nextR - Next reference.

getU

public Matrix<Inputs,N1> getU()

Returns the controller's calculated control input u plus the calculated feedforward u_ff.

Returns:

the calculated control input u.

getU

public double getU(int row)

Returns an element of the controller's calculated control input u.

Parameters:

row - Row of u.

Returns:

the calculated control input u at the row i.

getController

public LinearQuadraticRegulator<States,Inputs,Outputs> getController()

Return the controller used internally.

Returns:

the controller used internally.

getFeedforward

public LinearPlantInversionFeedforward<States,Inputs,Outputs> getFeedforward()

Return the feedforward used internally.

Returns:

the feedforward used internally.

getObserver

public KalmanFilter<States,Inputs,Outputs> getObserver()

Return the observer used internally.

Returns:

the observer used internally.

reset

public void reset(Matrix<States,N1> initialState)

Zeroes reference r and controller output u. The previous reference of the PlantInversionFeedforward and the initial state estimate of the KalmanFilter are set to the initial state provided.

Parameters:

initialState - The initial state.

getError

public Matrix<States,N1> getError()

Returns difference between reference r and current state x-hat.

Returns:

The state error matrix.

getError

public double getError(int index)

Returns difference between reference r and current state x-hat.

Parameters:

index - The index of the error matrix to return.

Returns:

The error at that index.

getClampFunction

public Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> getClampFunction()

Get the function used to clamp the input u.

Returns:

The clamping function.

setClampFunction

public void setClampFunction(Function<Matrix<Inputs,N1>,Matrix<Inputs,N1>> clampFunction)

Set the clamping function used to clamp inputs.

Parameters:

clampFunction - The clamping function.

correct

public void correct(Matrix<Outputs,N1> y)

Correct the state estimate x-hat using the measurements in y.

Parameters:

y - Measurement vector.

predict

public void predict(double dtSeconds)

Sets new controller output, projects model forward, and runs observer prediction.

After calling this, the user should send the elements of u to the actuators.

Parameters:

dtSeconds - Timestep for model update.

clampInput

public Matrix<Inputs,N1> clampInput(Matrix<Inputs,N1> unclampedU)

Clamp the input u to the min and max.

Parameters:

unclampedU - The input to clamp.

Returns:

The clamped input.