control_toolbox::Pid Class Reference

Generic Proportional–Integral–Derivative (PID) controller. More...

#include <pid.hpp>

Collaboration diagram for control_toolbox::Pid:

Classes
struct	Gains
	Store gains in a struct to allow easier realtime box usage. More...

Public Member Functions
	Pid (double p=0.0, double i=0.0, double d=0.0, double u_max=std::numeric_limits< double >::infinity(), double u_min=-std::numeric_limits< double >::infinity(), const AntiWindupStrategy &antiwindup_strat=AntiWindupStrategy())
	Constructor, initialize Pid-gains and term limits.
	Pid (const Pid &source)
	Copy constructor required for preventing mutexes from being copied.
	~Pid ()
	Destructor of Pid class.
bool	initialize (double p, double i, double d, double u_max, double u_min, const AntiWindupStrategy &antiwindup_strat)
	Initialize Pid-gains and term limits.
void	reset ()
	Reset the state of this PID controller.
void	reset (bool save_i_term)
	Reset the state of this PID controller.
void	clear_saved_iterm ()
	Clear the saved integrator output of this controller.
void	get_gains (double &p, double &i, double &d, double &u_max, double &u_min, AntiWindupStrategy &antiwindup_strat)
	Get PID gains for the controller (preferred).
Gains	get_gains ()
	Get PID gains for the controller.
Gains	get_gains_rt ()
	Get PID gains for the controller.
bool	set_gains (double p, double i, double d, double u_max, double u_min, const AntiWindupStrategy &antiwindup_strat)
	Set PID gains for the controller.
bool	set_gains (const Gains &gains)
	Set PID gains for the controller.
double	compute_command (double error, const double &dt_s)
	Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_s.
double	compute_command (double error, const rcl_duration_value_t &dt_ns)
	Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_ns.
double	compute_command (double error, const rclcpp::Duration &dt)
	Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt.
double	compute_command (double error, const std::chrono::nanoseconds &dt_ns)
	Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_ns.
double	compute_command (double error, double error_dot, const double &dt_s)
	Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.
double	compute_command (double error, double error_dot, const rcl_duration_value_t &dt_ns)
	Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.
double	compute_command (double error, double error_dot, const rclcpp::Duration &dt)
	Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.
double	compute_command (double error, double error_dot, const std::chrono::nanoseconds &dt_ns)
	Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.
void	set_current_cmd (double cmd)
	Set current command for this PID controller.
double	get_current_cmd ()
	Return current command for this PID controller.
void	get_current_pid_errors (double &pe, double &ie, double &de)
	Return PID error terms for the controller.
Pid &	operator= (const Pid &source)
	Custom assignment operator Does not initialize dynamic reconfigure for PID gains.

Protected Attributes
Gains	gains_
realtime_tools::RealtimeThreadSafeBox< Gains >	gains_box_ {gains_}
double	p_error_last_ = 0
double	p_error_ = 0
double	d_error_ = 0
double	i_term_ = 0
double	cmd_ = 0
double	cmd_unsat_ = 0

Detailed Description

Generic Proportional–Integral–Derivative (PID) controller.

The PID (Proportional–Integral–Derivative) controller is a widely used feedback controller. This class implements a generic structure that can be used to create a wide range of PID controllers. It can function independently or be subclassed to provide more specific control loops. Integral retention on reset is supported, which prevents re-winding the integrator after temporary disabling in presence of constant disturbances.

PID Equation

The standard PID equation is:

\[ command = p\_term + i\_term + d\_term \]

where:

• \( p\_term = p\_gain \times error \)
• \( i\_term \mathrel{+}= i\_gain \times error \times dt \)
• \( d\_term = d\_gain \times d\_error \) and:
• \( error = desired\_state - measured\_state \)
• \( d\_error = (error - error\_{last}) / dt \)

Parameters

Parameters

p	Proportional gain. Reacts to current error.
i	Integral gain. Accumulates past error to eliminate steady-state error.
d	Derivative gain. Predicts future error to reduce overshoot and settling time.
u_min	Minimum bound for the controller output.
u_max	Maximum bound for the controller output.
tracking_time_constant	Tracking time constant for BACK_CALCULATION anti-windup. If zero, a default is chosen based on gains: \( \sqrt{d\_gain / i\_gain} \) if d_gain ≠ 0 \( p\_gain / i\_gain \) otherwise.
antiwindup_strat	Anti-windup strategy: NONE: no anti-windup (integral always accumulates). BACK_CALCULATION: adjusts i_term based on difference between saturated and unsaturated outputs using tracking_time_constant. CONDITIONAL_INTEGRATION: only integrates when output is not saturated or error drives it away from saturation.

Anti-Windup Strategies

Without anti-windup, clamping causes integral windup, leading to overshoot and sluggish recovery. This class provides two strategies:

• BACK_CALCULATION

  \[ i\_term \mathrel{+}= dt \times \Bigl(i\_gain \times error + \frac{1}{trk\_tc}\,(command_{sat} - command)\Bigr) \]

  Prevents excessive accumulation by correcting i_term toward the saturation limit.
• CONDITIONAL_INTEGRATION Integrates only if

  \[ (command - command_{sat} = 0)\quad\lor\quad(error \times command \le 0) \]

  Freezes integration when saturated and error drives further saturation.

Usage Example

Initialize and compute at each control step:

control_toolbox::Pid pid;
pid.initialize(6.0, 1.0, 2.0, 5.0, -5.0,
               control_toolbox::AntiWindupStrategy::BACK_CALCULATION);
rclcpp::Time last = get_clock()->now();
while (running) {
  rclcpp::Time now = get_clock()->now();
  double effort = pid.compute_command(setpoint - current(), now - last);
  last = now;
}

Constructor & Destructor Documentation

Pid() [1/2]

control_toolbox::Pid::Pid	(	double	p = 0.0,
		double	i = 0.0,
		double	d = 0.0,
		double	u_max = std::numeric_limits<double>::infinity(),
		double	u_min = -std::numeric_limits<double>::infinity(),
		const AntiWindupStrategy &	antiwindup_strat = AntiWindupStrategy()
	)

Constructor, initialize Pid-gains and term limits.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
u_max	Upper output clamp.
u_min	Lower output clamp.
antiwindup_strat	Specifies the anti-windup strategy. Options: 'back_calculation', 'conditional_integration', or 'none'. Note that the 'back_calculation' strategy use the tracking_time_constant parameter to tune the anti-windup behavior.

Exceptions

An	std::invalid_argument exception is thrown if u_min > u_max.

Pid() [2/2]

control_toolbox::Pid::Pid

(

const Pid &

source

)

Copy constructor required for preventing mutexes from being copied.

Parameters

source

- Pid to copy

Member Function Documentation

compute_command() [1/8]

double control_toolbox::Pid::compute_command	(	double	error,
		const double &	dt_s
	)

Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_s.

Parameters

error	Error since last call (error = target - state)
dt_s	Change in time since last call in seconds.

Returns

PID command

compute_command() [2/8]

double control_toolbox::Pid::compute_command	(	double	error,
		const rcl_duration_value_t &	dt_ns
	)

Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_ns.

Parameters

error	Error since last call (error = target - state)
dt_ns	Change in time since last call, measured in nanoseconds.

Returns

PID command

compute_command() [3/8]

double control_toolbox::Pid::compute_command	(	double	error,
		const rclcpp::Duration &	dt
	)

Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt.

Parameters

error	Error since last call (error = target - state)
dt	Change in time since last call

Returns

PID command

compute_command() [4/8]

double control_toolbox::Pid::compute_command	(	double	error,
		const std::chrono::nanoseconds &	dt_ns
	)

Set the PID error and compute the PID command with nonuniform time step size. The derivative error is computed from the change in the error and the timestep dt_ns.

Parameters

error	Error since last call (error = target - state)
dt_ns	Change in time since last call

Returns

PID command

compute_command() [5/8]

double control_toolbox::Pid::compute_command	(	double	error,
		double	error_dot,
		const double &	dt_s
	)

Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.

Parameters

error	Error since last call (error = target - state)
error_dot	d(Error)/dt_s since last call
dt_s	Change in time since last call in seconds

Returns

PID command

compute_command() [6/8]

double control_toolbox::Pid::compute_command	(	double	error,
		double	error_dot,
		const rcl_duration_value_t &	dt_ns
	)

Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.

Parameters

error	Error since last call (error = target - state)
error_dot	d(Error)/dt_ns since last call
dt_ns	Change in time since last call, measured in nanoseconds.

Returns

PID command

compute_command() [7/8]

double control_toolbox::Pid::compute_command	(	double	error,
		double	error_dot,
		const rclcpp::Duration &	dt
	)

Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.

Parameters

error	Error since last call (error = target - state)
error_dot	d(Error)/dt since last call
dt	Change in time since last call

Returns

PID command

compute_command() [8/8]

double control_toolbox::Pid::compute_command	(	double	error,
		double	error_dot,
		const std::chrono::nanoseconds &	dt_ns
	)

Set the PID error and compute the PID command with nonuniform time step size. This also allows the user to pass in a precomputed derivative error.

Parameters

error	Error since last call (error = target - state)
error_dot	d(Error)/(dt_ns/1e9) since last call
dt_ns	Change in time since last call, measured in nanoseconds.

Returns

PID command

get_current_pid_errors()

void control_toolbox::Pid::get_current_pid_errors	(	double &	pe,
		double &	ie,
		double &	de
	)

Return PID error terms for the controller.

Parameters

pe	The proportional error.
ie	The weighted integral error.
de	The derivative error.

get_gains() [1/2]

Pid::Gains control_toolbox::Pid::get_gains

(

)

Get PID gains for the controller.

Returns

gains A struct of the PID gain values

Note

This method is not RT safe

get_gains() [2/2]

void control_toolbox::Pid::get_gains	(	double &	p,
		double &	i,
		double &	d,
		double &	u_max,
		double &	u_min,
		AntiWindupStrategy &	antiwindup_strat
	)

Get PID gains for the controller (preferred).

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
u_max	Upper output clamp.
u_min	Lower output clamp.
antiwindup_strat	Specifies the anti-windup strategy. Options: 'back_calculation', 'conditional_integration', or 'none'. Note that the 'back_calculation' strategy use the tracking_time_constant parameter to tune the anti-windup behavior.

Note

This method is not RT safe

get_gains_rt()

Gains control_toolbox::Pid::get_gains_rt ( )

inline

Get PID gains for the controller.

Returns

gains A struct of the PID gain values

Note

This method can be called from the RT loop

initialize()

bool control_toolbox::Pid::initialize	(	double	p,
		double	i,
		double	d,
		double	u_max,
		double	u_min,
		const AntiWindupStrategy &	antiwindup_strat
	)

Initialize Pid-gains and term limits.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
u_max	Upper output clamp.
u_min	Lower output clamp.
antiwindup_strat	Specifies the anti-windup strategy. Options: 'back_calculation', 'conditional_integration', or 'none'. Note that the 'back_calculation' strategy use the tracking_time_constant parameter to tune the anti-windup behavior.

Returns

True if all parameters are successfully set, False otherwise.

Note

New gains are not applied if antiwindup_strat.i_min > antiwindup_strat.i_max or u_min > u_max.

reset() [1/2]

void control_toolbox::Pid::reset

(

)

Reset the state of this PID controller.

Note

The integral term is not retained and it is reset to zero

reset() [2/2]

void control_toolbox::Pid::reset

(

bool

save_i_term

)

Reset the state of this PID controller.

Parameters

save_i_term

boolean indicating if integral term is retained on reset()

set_gains() [1/2]

bool control_toolbox::Pid::set_gains

(

const Gains &

gains

)

Set PID gains for the controller.

Parameters

gains

A struct of the PID gain values.

Returns

True if all parameters are successfully set, False otherwise.

Note

New gains are not applied if gains.i_min_ > gains.i_max_ or gains.u_min_ > gains.u_max_

This method is not RT safe.

set_gains() [2/2]

bool control_toolbox::Pid::set_gains	(	double	p,
		double	i,
		double	d,
		double	u_max,
		double	u_min,
		const AntiWindupStrategy &	antiwindup_strat
	)

Set PID gains for the controller.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
u_max	Upper output clamp.
u_min	Lower output clamp.
antiwindup_strat	Specifies the anti-windup strategy. Options: 'back_calculation', 'conditional_integration', or 'none'. Note that the 'back_calculation' strategy use the tracking_time_constant parameter to tune the anti-windup behavior.

Returns

True if all parameters are successfully set, False otherwise.

Note

New gains are not applied if antiwindup_strat.i_min > antiwindup_strat.i_max or u_min > u_max.

This method is not RT safe

Member Data Documentation

cmd_

double control_toolbox::Pid::cmd_ = 0

protected

Integrator state.

cmd_unsat_

double control_toolbox::Pid::cmd_unsat_ = 0

protected

Command to send.

d_error_

double control_toolbox::Pid::d_error_ = 0

protected

Error.

gains_

Gains control_toolbox::Pid::gains_

protected

Initial value:

{
    0.0,
    0.0,
    0.0,
    std::numeric_limits<double>::infinity(),
    -std::numeric_limits<double>::infinity(),
    AntiWindupStrategy()}

i_term_

double control_toolbox::Pid::i_term_ = 0

protected

Derivative of error.

p_error_

double control_toolbox::Pid::p_error_ = 0

protected

Save state for derivative state calculation.

---

The documentation for this class was generated from the following files:

• control_toolbox/control_toolbox/include/control_toolbox/pid.hpp
• control_toolbox/control_toolbox/src/pid.cpp