PID Class Reference

#include <pid.h>

Inheritance diagram for PID:

Public Types
enum	ERROR_TYPE

Public Member Functions
	PID (double kp, double ki, double kd, double deadband, double on_target_time, ERROR_TYPE error_method=PID::LINEAR)
	Create the PID object.
void	init (double start_pt, double set_pt) override
double	update (double sensor_val) override
double	update (double sensor_val, double v_setpt)
double	get_sensor_val () const
	gets the sensor value that we were last updated with
double	get () override
	Gets the current PID out value, from when update() was last run.
void	set_limits (double lower, double upper) override
bool	is_on_target () override
void	reset ()
	Reset the PID loop by resetting time since 0 and accumulated error.
double	get_error ()
	Get the delta between the current sensor data and the target.
double	get_output ()
	Get the delta between the current sensor data and the target.
double	get_target () const
void	set_target (double target)
	Set the target for the PID loop, where the robot is trying to end up.

Public Attributes
double	kp
	Proportional coeffecient; p * error().
double	ki
	Integral coefficient; i * integral(error).
double	kd
	Derivative coefficient; d * derivative(error).
double	deadband
	A deadband that determines the threshold for what counts as finished.
double	on_target_time
	The time, in seconds, that we have to be in the threshold in order to be considered on target.
ERROR_TYPE	error_method
	Determines whether error is performed as a simple subtraction (LINEAR) or wrapping (ANGULAR).

Detailed Description

PID Class

Defines a standard feedback loop using the constants kP, kI, kD, deadband, and on_target_time. The formula is:

out = kP*error + kI*integral(d Error) + kD*(dError/dt)

The PID object will determine it is "on target" when the error is within the deadband, for a duration of on_target_time

Author

Ryan McGee

Date

4/3/2020

Member Enumeration Documentation

ERROR_TYPE

enum PID::ERROR_TYPE

An enum to distinguish between a linear and angular caluclation of PID error.

Constructor & Destructor Documentation

PID()

PID::PID	(	double	kp,
		double	ki,
		double	kd,
		double	deadband,
		double	on_target_time,
		PID::ERROR_TYPE	error_method = PID::LINEAR )

Create the PID object.

Create the PID object

Parameters

kp	Coefficient double p. Direct error to voltage.
ki	Coefficient double i. Integral of error to voltage. Helps get the motor "unstuck" if P is not enough to drive the motor.
kd	Coefficient double d. Derivative of error to voltage. Helps prevent overshooting.
deadband	Double. Acceptable margin of error.
on_target_time	Double. How long the reading must be within the deadband to consider robot "aligned."
error_method	ERROR_TYPE struct. Can be either LINEAR or ANGULAR. Determines how we want the PID to enact, on position or rotation for example.

Member Function Documentation

get()

double PID::get ( )

overridevirtual

Gets the current PID out value, from when update() was last run.

Gets the current PID out value, from when update() was last run

Returns

the Out value of the controller (voltage, RPM, whatever the PID controller is controlling)

Implements Feedback.

get_error()

double PID::get_error

(

)

Get the delta between the current sensor data and the target.

Get the delta between the current sensor data and the target

Returns

the error calculated. how it is calculated depends on error_method

get_output()

double PID::get_output

(

)

Get the delta between the current sensor data and the target.

Get the output calculated from the P, I, D and Error values

Returns

the output calculated from the pid controller

get_sensor_val()

double PID::get_sensor_val

(

)

const

gets the sensor value that we were last updated with

Returns

sensor_val

get_target()

double PID::get_target

(

)

const

Get the PID's target

Returns

the target the PID controller is trying to achieve

init()

void PID::init ( double start_pt, double set_pt )

overridevirtual

Inherited from Feedback for interoperability. Update the setpoint and reset integral accumulation

start_pt can be safely ignored in this feedback controller

Parameters

start_pt	commpletely ignored for PID. necessary to satisfy Feedback base
set_pt	sets the target of the PID controller
start_vel	completely ignored for PID. necessary to satisfy Feedback base
end_vel	sets the target end velocity of the PID controller

Implements Feedback.

is_on_target()

bool PID::is_on_target ( )

overridevirtual

Checks if the PID controller is on target.

Returns

true if the loop is within [deadband] for [on_target_time] seconds

Returns true if the loop is within [deadband] for [on_target_time] seconds

Implements Feedback.

set_limits()

void PID::set_limits ( double lower, double upper )

overridevirtual

Set the limits on the PID out. The PID out will "clip" itself to be between the limits.

Parameters

lower	the lower limit. the PID controller will never command the output go below lower
upper	the upper limit. the PID controller will never command the output go higher than upper

Set the limits on the PID out. The PID out will "clip" itself to be between the limits.

Implements Feedback.

set_target()

void PID::set_target

(

double

target

)

Set the target for the PID loop, where the robot is trying to end up.

Set the target for the PID loop, where the robot is trying to end up

Parameters

target

the sensor reading we would like to achieve

update() [1/2]

double PID::update ( double sensor_val )

overridevirtual

Update the PID loop by taking the time difference from last update, and running the PID formula with the new sensor data

Parameters

sensor_val

the distance, angle, encoder position or whatever it is we are measuring

Returns

the new output. What would be returned by PID::get()

Implements Feedback.

update() [2/2]

double PID::update	(	double	sensor_val,
		double	v_setpt )

Update the PID loop by taking the time difference from last update, and running the PID formula with the new sensor data

Parameters

sensor_val	the distance, angle, encoder position or whatever it is we are measuring
v_setpt	Expected velocity setpoint, to subtract from the D term (for velocity control)

Returns

the new output. What would be returned by PID::get()

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

• pid.h
• pid.cpp