control_toolbox::Pid Class Reference

A basic pid class. More...

#include <pid.hpp>

Collaboration diagram for control_toolbox::Pid:

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

Public Member Functions
	Pid (double p=0.0, double i=0.0, double d=0.0, double i_max=0.0, double i_min=-0.0, bool antiwindup=false)
	Constructor, zeros out Pid values when created and initialize Pid-gains and integral term limits. Does not initialize dynamic reconfigure for PID gains.
	Pid (const Pid &source)
	Copy constructor required for preventing mutexes from being copied.
	~Pid ()
	Destructor of Pid class.
void	initPid (double p, double i, double d, double i_max, double i_min, bool antiwindup=false)
	Zeros out Pid values and initialize Pid-gains and integral term limits Does not initialize the node's parameter interface for PID gains.
void	reset ()
	Reset the state of this PID controller.
void	getGains (double &p, double &i, double &d, double &i_max, double &i_min)
	Get PID gains for the controller.
void	getGains (double &p, double &i, double &d, double &i_max, double &i_min, bool &antiwindup)
	Get PID gains for the controller.
Gains	getGains ()
	Get PID gains for the controller.
void	setGains (double p, double i, double d, double i_max, double i_min, bool antiwindup=false)
	Set PID gains for the controller.
void	setGains (const Gains &gains)
	Set PID gains for the controller.
double	computeCommand (double error, uint64_t 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	computeCommand (double error, double error_dot, uint64_t 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.
void	setCurrentCmd (double cmd)
	Set current command for this PID controller.
double	getCurrentCmd ()
	Return current command for this PID controller.
double	getDerivativeError ()
	Return derivative error.
void	getCurrentPIDErrors (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
realtime_tools::RealtimeBuffer< Gains >	gains_buffer_
double	p_error_last_
double	p_error_
double	i_error_
double	d_error_
double	cmd_
double	error_dot_

Detailed Description

A basic pid class.

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 controls based on a particular control loop.

In particular, this class implements the standard pid equation:

\(command = p_{term} + i_{term} + d_{term} \)

where:

• \( p_{term} = p_{gain} * p_{error} \)
• \( i_{term} = i_{term} + \int{i_{gain} * p_{error} * dt} \)
• \( d_{term} = d_{gain} * d_{error} \)
• \( d_{error} = (p_{error} - p_{error last}) / dt \)

given:

• \( p_{error} = p_{desired} - p_{state} \).

Parameters

p	Proportional gain
d	Derivative gain
i	Integral gain
i_clamp	Min/max bounds for the integral windup, the clamp is applied to the \(i_{term}\)

Usage

To use the Pid class, you should first call some version of init() (in non-realtime) and then call updatePid() at every update step. For example:

control_toolbox::Pid pid;
pid.initPid(6.0, 1.0, 2.0, 0.3, -0.3);
double position_desi_ = 0.5;
...
rclcpp::Time last_time = get_clock()->now();
while (true) {
rclcpp::Time time = get_clock()->now();
double effort = pid.computeCommand(position_desi_ - currentPosition(), (time - last_time).nanoseconds());
last_time = time;
}

Constructor & Destructor Documentation

Pid() [1/2]

control_toolbox::Pid::Pid	(	double	p = 0.0,
		double	i = 0.0,
		double	d = 0.0,
		double	i_max = 0.0,
		double	i_min = -0.0,
		bool	antiwindup = false
	)

Constructor, zeros out Pid values when created and initialize Pid-gains and integral term limits. Does not initialize dynamic reconfigure for PID gains.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
i_max	The max integral windup.
i_min	The min integral windup.
antiwindup	If true, antiwindup is enabled and i_max/i_min are enforced

Exceptions

An	std::invalid_argument exception is thrown if i_min > i_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

computeCommand() [1/2]

double control_toolbox::Pid::computeCommand	(	double	error,
		double	error_dot,
		uint64_t	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 in nanoseconds

Returns

PID command

computeCommand() [2/2]

double control_toolbox::Pid::computeCommand	(	double	error,
		uint64_t	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 in nanoseconds

Returns

PID command

getCurrentPIDErrors()

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

Return PID error terms for the controller.

Parameters

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

getGains() [1/3]

Pid::Gains control_toolbox::Pid::getGains

(

)

Get PID gains for the controller.

Returns

gains A struct of the PID gain values

getGains() [2/3]

void control_toolbox::Pid::getGains	(	double &	p,
		double &	i,
		double &	d,
		double &	i_max,
		double &	i_min
	)

Get PID gains for the controller.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
i_max	The max integral windup.
i_min	The min integral windup.

getGains() [3/3]

void control_toolbox::Pid::getGains	(	double &	p,
		double &	i,
		double &	d,
		double &	i_max,
		double &	i_min,
		bool &	antiwindup
	)

Get PID gains for the controller.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
i_max	The max integral windup.
i_min	The min integral windup.
antiwindup	If true, antiwindup is enabled and i_max/i_min are enforced

initPid()

void control_toolbox::Pid::initPid	(	double	p,
		double	i,
		double	d,
		double	i_max,
		double	i_min,
		bool	antiwindup = false
	)

Zeros out Pid values and initialize Pid-gains and integral term limits Does not initialize the node's parameter interface for PID gains.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
i_max	The max integral windup.
i_min	The min integral windup.
antiwindup	If true, antiwindup is enabled and i_max/i_min are enforced

Note

New gains are not applied if i_min_ > i_max_

setGains() [1/2]

void control_toolbox::Pid::setGains

(

const Gains &

gains

)

Set PID gains for the controller.

Parameters

gains

A struct of the PID gain values

Note

New gains are not applied if gains.i_min_ > gains.i_max_

setGains() [2/2]

void control_toolbox::Pid::setGains	(	double	p,
		double	i,
		double	d,
		double	i_max,
		double	i_min,
		bool	antiwindup = false
	)

Set PID gains for the controller.

Parameters

p	The proportional gain.
i	The integral gain.
d	The derivative gain.
i_max	The max integral windup.
i_min	The min integral windup.
antiwindup	If true, antiwindup is enabled and i_max/i_min are enforced

Note

New gains are not applied if i_min > i_max

Member Data Documentation

cmd_

double control_toolbox::Pid::cmd_

protected

Command to send.

d_error_

double control_toolbox::Pid::d_error_

protected

Derivative of position error.

error_dot_

double control_toolbox::Pid::error_dot_

protected

Derivative error

i_error_

double control_toolbox::Pid::i_error_

protected

Integral of position error.

p_error_

double control_toolbox::Pid::p_error_

protected

Position error.

p_error_last_

double control_toolbox::Pid::p_error_last_

protected

_Save position state for derivative state calculation.

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

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