SC_PID Class Reference

#include <SC_PID.h>

Public Types
Enumerated Types and Constants.
enum	mode_t { AUTO , USER , OFF }
enum	control_t { DIRECT , REVERSE }

Public Member Functions
Class constructor and destructor.
	SC_PID (int16_t *cv, int16_t *co, int16_t *sp, float Kp, float Ki, float Kd, float pOn=1.0, control_t controller=DIRECT)
	~SC_PID (void)
Methods for core object control.
bool	compute (void)
void	reset (void)
void	setPIDPeriod (uint32_t newPeriod)
void	setMode (mode_t newMode)
void	setOutputLimits (int16_t min, int16_t max)
void	setTuning (float Kp, float Ki, float Kd, float pOn)
void	setTuning (float Kp, float Ki, float Kd)
Utility Functions.
void	setControlType (control_t cType)
int16_t	getError (void)
float	getKp (void)
float	getKi (void)
float	getKd (void)
uint32_t	getPIDPeriod (void)
mode_t	getMode (void)
control_t	getControlType (void)

Detailed Description

Core object for the SC_PID class Implements PID control algorithm DC motor control, as a hybrid fixed-point and floating-point PID controller

Member Enumeration Documentation

control_t

enum SC_PID::control_t

Different ways the controller can operate

Enumerator
DIRECT	An increase in the control output increases the controlled variable.
REVERSE	An increase in the control output decreases the controlled variable.

mode_t

enum SC_PID::mode_t

Different possible modes for the controller execution

Enumerator
AUTO	The controller will keep track of time and execute one PID iteration when time expires.
USER	The user is responsible for calling the PID computation when the calculation time interval expires.
OFF	The controlled variable is controlled manually (ie, no PID control).

Constructor & Destructor Documentation

SC_PID()

SC_PID::SC_PID	(	int16_t *	cv,
		int16_t *	co,
		int16_t *	sp,
		float	Kp,
		float	Ki,
		float	Kd,
		float	pOn = 1.0,
		control_t	controller = DIRECT
	)

Class Constructor.

Instantiate a new instance of the class.

The main function for the core object is to reset the internal shared variables and timers to default values.

See also

setTuning(), setMode()

Parameters

cv	Pointer to the current value for the controlled variable.
co	Pointer to the control output for the controlled variable.
sp	Pointer to the setpoint for the controlled variable.
Kp	Proportional coefficient for the PID algorithm.
Ki	Integral coefficient for the PID algorithm.
Kd	Derivative coefficient for the PID algorithm.
pOn	Factor for combining errors (proportional on Error or Measurement).
controller	The type of controller (one of the controller_t values).

~SC_PID()

SC_PID::~SC_PID

(

void

)

Class Destructor.

Release any allocated memory and clean up anything else.

Member Function Documentation

compute()

bool SC_PID::compute

(

void

)

Perform PID calculation.

Perform the next step in the PID calculation. How this occurs will depend on the current controller mode (AUTO, USER, OFF) and the time period set.

In AUTO mode the method should be called frequently (ideally every time through loop()) and the return value will inform the application when the calculation actually happened.

In USER mode, the method will run when it is invoked under the assumption that the time elapsed between steps is the currently set PID calculation period.

In OFF mode (default) the calculation is never executed.

The current value, setpoint and new control output used are located by the pointers passed to the constructor.

See also

setMode(), setPIDPeriod(), setOutputLimits()

Returns

true if the calculation was completed, false otherwise.

getControlType()

control_t SC_PID::getControlType

(

void

)

Return the current controller type.

Returns

The controller type (one of the controller_t values).

getError()

int16_t SC_PID::getError

(

void

)

Return the current PID error value.

Returns

The error value resulting from the last PID calculation step.

getKd()

float SC_PID::getKd

(

void

)

Return the current Kd value.

Returns

The Kd coefficient for PID calculation.

getKi()

float SC_PID::getKi

(

void

)

Return the current Ki value.

Returns

The Ki coefficient for PID calculation.

getKp()

float SC_PID::getKp

(

void

)

Return the current Kp value.

Returns

The Kp coefficient for PID calculation.

getMode()

mode_t SC_PID::getMode

(

void

)

Return the current controller mode.

Returns

The controller mode (one of the mode_t values).

getPIDPeriod()

uint32_t SC_PID::getPIDPeriod

(

void

)

Return the current PID calculation period.

Returns

The calculation period in milliseconds.

reset()

void SC_PID::reset

(

void

)

Reset the PID calculation.

Reset the PID calculation. The library will ensure a bumpless transition between current and reset state.

Not generally required but available.

setControlType()

void SC_PID::setControlType

(

control_t

cType

)

Set the controller type.

Sets the controller type. This is already set in the constructor and is unlikely to change for a given control application.

For DIRECT controllers an increase in the output causes an increase in the input. The opposite is true for REVERSE controllers.

Parameters

cType

The new control type (one of control_t).

setMode()

void SC_PID::setMode

(

mode_t

newMode

)

Set the controller mode.

Sets the controller mode to one of the mode_t values

In AUTO mode the library tracks time and executes the PID calculation when the correct period has expired.

In USER mode, the library does not track time and the PID calculation will be run whenever it is invoked.

In OFF mode (default) the PID calculation is never executed.

See also

compute()

Parameters

newMode

The new mode for the controller (default OFF).

setOutputLimits()

void SC_PID::setOutputLimits	(	int16_t	min,
		int16_t	max
	)

Set the PID control limits

Sets the upper and lower values for the control output. The value will always be clamped to this range. The default is [0, 255], which suits an Arduino PWM output.

Parameters

min	The low value of the permissible range (default 0).
max	The high value for the permissible range (=default 255).

setPIDPeriod()

void SC_PID::setPIDPeriod

(

uint32_t

newPeriod

)

Reset the PID calculation period.

Reset the PID calculation period. Really only applies in AUTO mode.

Not generally required but available.

See also

setMode()

Parameters

newPeriod

the new calculation interval in milliseconds.

setTuning() [1/2]

void SC_PID::setTuning	(	float	Kp,
		float	Ki,
		float	Kd
	)

Set the PID coefficients only.

This overload of the method allows the PID coefficients to be changed during run time. These will replace the current coefficients, including those supplied with the constructor.

This method can be used to implement adaptive control or during tuning of the PID control loop.

Parameters

Kp	The new Proportional coefficient.
Ki	The new Integral coefficient.
Kd	The new Derivative coefficient.

setTuning() [2/2]

void SC_PID::setTuning	(	float	Kp,
		float	Ki,
		float	Kd,
		float	pOn
	)

Set the PID coefficients and Proportional on Error.

Allows the PID coefficients and proportional on error factor to be changed during run time. These will replace the current coefficients, including those with the constructor.

This method can be used to implement adaptive control or during tuning of the PID control loop.

The is the Proportional on Error weighting value is expressed as a number between 0.0 and 1.0. This controls the mix of Proportional on Error (PonE) and Proportional on Measurement (PonM) that's used in the compute algorithm. Note that POn controls the PonE amount, whereas the remainder (1-PonE) is the PonM amount.

Parameters

Kp	The new Proportional coefficient.
Ki	The new Integral coefficient.
Kd	The new Derivative coefficient.
pOn	The new proportional on Error coefficient (default 1.0).

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

• src/SC_PID.h
• src/SC_PID.cpp