Class Pid

Nested Relationships

Nested Types

Class Documentation

class Pid

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:

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

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;
}
Param p:

Proportional gain

Param d:

Derivative gain

Param i:

Integral gain

Param i_clamp:

Min/max bounds for the integral windup, the clamp is applied to the \(i_{term}\)

Public 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.

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

Throws:

An – std::invalid_argument exception is thrown if i_min > i_max

Pid(const Pid &source)

Copy constructor required for preventing mutexes from being copied.

Parameters:

source – - Pid to copy

~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.

Note

New gains are not applied if i_min_ > i_max_

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

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.

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.

void 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

Gains getGains()

Get PID gains for the controller.

Returns:

gains A struct of the PID gain values

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

Set PID gains for the controller.

Note

New gains are not applied if i_min > i_max

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

void setGains(const Gains &gains)

Set PID gains for the controller.

Note

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

Parameters:

gains – A struct of the PID gain values

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.

Parameters:

  • error – Error since last call (error = target - state)

  • dt – Change in time since last call in nanoseconds

Returns:

PID command

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.

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

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.

Parameters:

  • pe – The proportional error.

  • ie – The integral error.

  • de – The derivative error.

inline 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_

_Save position state for derivative state calculation.

double p_error_

Position error.

double i_error_

Integral of position error.

double d_error_

Derivative of position error.

double cmd_

Command to send.

double error_dot_

Derivative error

struct Gains

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

Public Functions

inline Gains(double p, double i, double d, double i_max, double i_min)

Optional constructor for passing in values without antiwindup.

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.

Throws:

An – std::invalid_argument exception is thrown if i_min > i_max

inline Gains(double p, double i, double d, double i_max, double i_min, bool antiwindup)

Optional constructor for passing in values.

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

Throws:

An – std::invalid_argument exception is thrown if i_min > i_max

inline Gains()

Public Members

double p_gain_

Proportional gain.

double i_gain_

Integral gain.

double d_gain_

Derivative gain.

double i_max_

Maximum allowable integral term.

double i_min_

Minimum allowable integral term.

bool antiwindup_

Antiwindup.