A basic pid class. More...

#include <pid.h>

Classes
struct	Gains
	Store gains in a struct to allow easier realtime buffer usage. More...
Public Member Functions
double	computeCommand (double error, ros::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	computeCommand (double error, double error_dot, ros::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.
void	dynamicReconfigCallback (control_toolbox::ParametersConfig &config, uint32_t level)
	Update the PID parameters from dynamics reconfigure.
double	getCurrentCmd ()
	Return current command for this PID controller.
void	getCurrentPIDErrors (double pe, double ie, double *de)
	Return PID error terms for the controller.
void	getGains (double &p, double &i, double &d, double &i_max, double &i_min)
	Get PID gains for the controller.
Gains	getGains ()
	Get PID gains for the controller.
bool	init (const ros::NodeHandle &n)
	Initialize PID with the parameters in a NodeHandle namespace Initializes dynamic reconfigure for PID gains.
void	initDynamicReconfig (ros::NodeHandle &node)
	Start the dynamic reconfigure node and load the default values.
bool	initParam (const std::string &prefix)
	Initialize PID with the parameters in a namespace Initializes dynamic reconfigure for PID gains.
void	initPid (double p, double i, double d, double i_max, double i_min)
	Zeros out Pid values and initialize Pid-gains and integral term limits Does not initialize dynamic reconfigure for PID gains.
void	initPid (double p, double i, double d, double i_max, double i_min, const ros::NodeHandle &node)
	Zeros out Pid values and initialize Pid-gains and integral term limits Initializes dynamic reconfigure for PID gains.
bool	initXml (TiXmlElement *config)
	Initialize PID with the parameters in an XML element Initializes dynamic reconfigure for PID gains.
Pid &	operator= (const Pid &source)
	Custom assignment operator Does not initialize dynamic reconfigure for PID gains.
	Pid (double p=0.0, double i=0.0, double d=0.0, double i_max=0.0, double i_min=-0.0)
	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.
void	printValues ()
	Print to console the current parameters.
void	reset ()
	Reset the state of this PID controller.
void	setCurrentCmd (double cmd)
	Set current command for this PID controller.
void	setGains (double p, double i, double d, double i_max, double i_min)
	Set PID gains for the controller.
void	setGains (const Gains &gains)
	Set PID gains for the controller.
void	updateDynamicReconfig ()
	Set Dynamic Reconfigure's gains to Pid's values.
void	updateDynamicReconfig (Gains gains_config)
void	updateDynamicReconfig (control_toolbox::ParametersConfig config)
ROS_DEPRECATED double	updatePid (double p_error, ros::Duration dt)
	Update the Pid loop with nonuniform time step size.
ROS_DEPRECATED double	updatePid (double error, double error_dot, ros::Duration dt)
	Update the Pid loop with nonuniform time step size. This update call allows the user to pass in a precomputed derivative error.
	~Pid ()
	Destructor of Pid class.
Private Types
typedef dynamic_reconfigure::Server < control_toolbox::ParametersConfig >	DynamicReconfigServer
Private Attributes
double	cmd_
double	d_error_
bool	dynamic_reconfig_initialized_
realtime_tools::RealtimeBuffer < Gains >	gains_buffer_
double	i_term_
double	p_error_
double	p_error_last_
DynamicReconfigServer::CallbackType	param_reconfig_callback_
boost::recursive_mutex	param_reconfig_mutex_
boost::shared_ptr < DynamicReconfigServer >	param_reconfig_server_

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:

$p_{error} = p_{state} - p_{target}$ .

ROS interface

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;
  ...
  ros::Time last_time = ros::Time::now();
  while (true) {
  ros::Time time = ros::Time::now();
  double effort = pid.updatePid(currentPosition() - position_desi_, time - last_time);
  last_time = time;
  }

Definition at line 113 of file pid.h.

Member Typedef Documentation

typedef dynamic_reconfigure::Server<control_toolbox::ParametersConfig> control_toolbox::Pid::DynamicReconfigServer [private]

Definition at line 377 of file pid.h.

Constructor & Destructor Documentation

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`
	)

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.

Definition at line 48 of file pid.cpp.

control_toolbox::Pid::Pid ( const Pid & source )

Copy constructor required for preventing mutexes from being copied.

Parameters:

source - Pid to copy

Definition at line 56 of file pid.cpp.

control_toolbox::Pid::~Pid ( )

Destructor of Pid class.

Definition at line 66 of file pid.cpp.

Member Function Documentation

double control_toolbox::Pid::computeCommand	(	double	error,
		ros::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

Definition at line 254 of file pid.cpp.

double control_toolbox::Pid::computeCommand	(	double	error,
		double	error_dot,
		ros::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

Definition at line 320 of file pid.cpp.

void control_toolbox::Pid::dynamicReconfigCallback	(	control_toolbox::ParametersConfig &	config,
		uint32_t	level
	)

Update the PID parameters from dynamics reconfigure.

Definition at line 246 of file pid.cpp.

double control_toolbox::Pid::getCurrentCmd ( )

Return current command for this PID controller.

Definition at line 383 of file pid.cpp.

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.

Definition at line 388 of file pid.cpp.

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.

Definition at line 170 of file pid.cpp.

Pid::Gains control_toolbox::Pid::getGains ( )

Get PID gains for the controller.

Returns:: gains A struct of the PID gain values

Definition at line 181 of file pid.cpp.

bool control_toolbox::Pid::init ( const ros::NodeHandle & n )

Initialize PID with the parameters in a NodeHandle namespace Initializes dynamic reconfigure for PID gains.

Parameters:

n	The NodeHandle which should be used to query parameters.

Definition at line 93 of file pid.cpp.

void control_toolbox::Pid::initDynamicReconfig ( ros::NodeHandle & node )

Start the dynamic reconfigure node and load the default values.

Parameters:

node	- a node handle where dynamic reconfigure services will be published

Definition at line 144 of file pid.cpp.

bool control_toolbox::Pid::initParam ( const std::string & prefix )

Initialize PID with the parameters in a namespace Initializes dynamic reconfigure for PID gains.

Parameters:

prefix The namespace prefix.

Definition at line 87 of file pid.cpp.

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

Zeros out Pid values 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.

Definition at line 80 of file pid.cpp.

void control_toolbox::Pid::initPid	(	double	p,
		double	i,
		double	d,
		double	i_max,
		double	i_min,
		const ros::NodeHandle &	node
	)

Zeros out Pid values and initialize Pid-gains and integral term limits Initializes 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.

Definition at line 70 of file pid.cpp.

bool control_toolbox::Pid::initXml ( TiXmlElement * config )

Initialize PID with the parameters in an XML element Initializes dynamic reconfigure for PID gains.

Parameters:

config the XML element

Definition at line 122 of file pid.cpp.

Pid& control_toolbox::Pid::operator= ( const Pid & source ) [inline]

Custom assignment operator Does not initialize dynamic reconfigure for PID gains.

Definition at line 349 of file pid.h.

void control_toolbox::Pid::printValues ( )

Print to console the current parameters.

Definition at line 398 of file pid.cpp.

void control_toolbox::Pid::reset ( )

Reset the state of this PID controller.

Definition at line 161 of file pid.cpp.

void control_toolbox::Pid::setCurrentCmd ( double cmd )

Set current command for this PID controller.

Definition at line 378 of file pid.cpp.

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

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.

Definition at line 186 of file pid.cpp.

void control_toolbox::Pid::setGains ( const Gains & gains )

Set PID gains for the controller.

Parameters:

gains A struct of the PID gain values

Definition at line 193 of file pid.cpp.

void control_toolbox::Pid::updateDynamicReconfig ( )

Set Dynamic Reconfigure's gains to Pid's values.

Definition at line 201 of file pid.cpp.

void control_toolbox::Pid::updateDynamicReconfig ( Gains gains_config )

Definition at line 216 of file pid.cpp.

void control_toolbox::Pid::updateDynamicReconfig ( control_toolbox::ParametersConfig config )

Definition at line 234 of file pid.cpp.

double control_toolbox::Pid::updatePid	(	double	p_error,
		ros::Duration	dt
	)

Update the Pid loop with nonuniform time step size.

Deprecated:: in ROS Hydro. This function assumes p_error = (state - target) which is an unconventional definition of the error. Please use computeCommand instead, which assumes error = (target - state) . Note that calls to computeCommand should not be mixed with calls to updatePid.

Parameters:

p_error	Error since last call (p_state-p_target)
dt	Change in time since last call

Definition at line 287 of file pid.cpp.

double control_toolbox::Pid::updatePid	(	double	error,
		double	error_dot,
		ros::Duration	dt
	)

Update the Pid loop with nonuniform time step size. This update call allows the user to pass in a precomputed derivative error.

Deprecated:: in ROS Hydro. This function assumes p_error = (state - target) which is an unconventional definition of the error. Please use computeCommand instead, which assumes error = (target - state) . Note that calls to computeCommand should not be mixed with calls to updatePid.

Parameters: