Class Pid
Defined in File pid.hpp
Nested Relationships
Nested Types
Class Documentation
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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.
This class also allows for retention of integral term on reset. This is useful for control loops that are enabled/disabled with a constant steady-state external disturbance. Once the integrator cancels out the external disturbance, disabling/resetting/ re-enabling closed-loop control does not require the integrator to wind up again.
In particular, this class implements the standard pid equation:
where:
given:
.
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.initialize(6.0, 1.0, 2.0, 0.3, -0.3); double position_desired = 0.5; ... rclcpp::Time last_time = get_clock()->now(); while (true) { rclcpp::Time time = get_clock()->now(); double effort = pid.compute_command(position_desired - currentPosition(), time - last_time); 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
Public Functions
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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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
- Throws:
An – std::invalid_argument exception is thrown if i_min > i_max
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Pid(const Pid &source)
Copy constructor required for preventing mutexes from being copied.
- Parameters:
source – - Pid to copy
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void initialize(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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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void reset()
Reset the state of this PID controller.
Note
The integral term is not retained and it is reset to zero
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void 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()
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void clear_saved_iterm()
Clear the saved integrator output of this controller.
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void get_gains(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 – Upper integral clamp.
i_min – Lower integral clamp.
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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 – Upper integral clamp.
i_min – Lower integral clamp.
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void get_gains(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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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void set_gains(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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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void set_gains(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
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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
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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
.- Parameters:
error – Error since last call (error = target - state)
dt_s – Change in time since last call in seconds
- Returns:
PID command
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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
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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
.- Parameters:
error – Error since last call (error = target - state)
dt_ns – Change in time since last call, measured in nanoseconds.
- Returns:
PID command
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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
.- Parameters:
error – Error since last call (error = target - state)
dt – Change in time since last call
- Returns:
PID command
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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
.- Parameters:
error – Error since last call (error = target - state)
dt_ns – Change in time since last call
- Returns:
PID command
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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.
- 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
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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/1e9) since last call
dt – Change in time since last call in nanoseconds
- Returns:
PID command
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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.
- 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
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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.
- 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
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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.
- 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
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void set_current_cmd(double cmd)
Set current command for this PID controller.
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void setCurrentCmd(double cmd)
Set current command for this PID controller.
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double get_current_cmd()
Return current command for this PID controller.
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double getCurrentCmd()
Return current command for this PID controller.
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double getDerivativeError()
Return derivative error.
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void get_current_pid_errors(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.
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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.
Protected Attributes
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double p_error_last_
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double p_error_
Save state for derivative state calculation.
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double i_error_
Error.
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double d_error_
Integral of error.
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double cmd_
Derivative of error.
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double error_dot_
Command to send.
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struct Gains
Store gains in a struct to allow easier realtime buffer usage.
Public Functions
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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 – Upper integral clamp.
i_min – Lower integral clamp.
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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 – Upper integral clamp.
i_min – Lower integral clamp.
antiwindup – Antiwindup functionality. When set to true, limits the integral error to prevent windup; otherwise, constrains the integral contribution to the control output. i_max and i_min are applied in both scenarios.
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inline Gains()
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inline Gains(double p, double i, double d, double i_max, double i_min)