FGActuator Class Reference

Detailed Description

Encapsulates an Actuator component for the flight control system.

The actuator can be modeled as a "perfect actuator", with the Output being set directly to the input. The actuator can be made more "real" by specifying any/all of the following additional effects that can be applied to the actuator. In order of application to the input signal, these are:

• System lag (input lag, really)
• Rate limiting
• Deadband
• Hysteresis (mechanical hysteresis)
• Bias (mechanical bias)
• Position limiting ("hard stops")

There are also several malfunctions that can be applied to the actuator by setting a property to true or false (or 1 or 0).

Rate limits can be specified either as a single number or property. If a single <rate_limit> is supplied (with no "sense" attribute) then the actuator is rate limited at +/- the specified rate limit. If the <rate_limit> element is supplied with a "sense" attribute of either "incr[easing]" or "decr[easing]" then the actuator is limited to the provided numeric or property value) exactly as provided.

Lag filter's numerical integration assumes that the lag parameter is constant. So a continuously varying parameter via a property will introduce a non negligible error that will accumulate as the simulation progresses.

Syntax:

<actuator name="name">
  <input> {[-]property} </input>
  <lag> {property name | value} </lag>
  [<rate_limit> {property name | value} </rate_limit>]
  [<rate_limit sense="incr"> {property name | value} </rate_limit>
   <rate_limit sense="decr"> {property name | value} </rate_limit>]
  <bias> number </bias>
  <deadband_width> number </deadband_width>
  <hysteresis_width> number </hysteresis_width>
  [<clipto>
    <min> {property name | value} </min>
    <max> {property name | value} </max>
   </clipto>]
  [<output> {property} </output>]
</actuator>

Example:

<actuator name="fcs/gimbal_pitch_position_radians">
  <input> fcs/gimbal_pitch_command </input>
  <lag> 60 </lag>
  <rate_limit> 0.085 </rate_limit> <!-- 0.085 radians/sec -->
  <bias> 0.002 </bias>
  <deadband_width> 0.002 </deadband_width>
  <hysteresis_width> 0.05 </hysteresis_width>
  <clipto> <!-- +/- 0.17 radians -->
    <min> -0.17 </min>
    <max>  0.17 </max>
   </clipto>
</actuator>

Author

Jon S. Berndt

Version

Revision

1.20

Definition at line 127 of file FGActuator.h.

#include <FGActuator.h>

Inheritance diagram for FGActuator:

Collaboration diagram for FGActuator:

Public Member Functions
	FGActuator (FGFCS *fcs, Element *element)
	Constructor.
	~FGActuator ()
	Destructor.
bool	GetFailHardover (void) const
bool	GetFailStuck (void) const
bool	GetFailZero (void) const
bool	IsSaturated (void) const
void	ResetPastStates (void) override
bool	Run (void) override
	This function processes the input.
void	SetFailHardover (bool set)
void	SetFailStuck (bool set)
void	SetFailZero (bool set)
	This function fails the actuator to zero.
Public Member Functions inherited from FGFCSComponent
	FGFCSComponent (FGFCS *fcs, Element *el)
	Constructor.
virtual	~FGFCSComponent ()
	Destructor.
std::string	GetName (void) const
double	GetOutput (void) const
virtual double	GetOutputPct (void) const
std::string	GetType (void) const
virtual void	SetOutput (void)
Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.
virtual	~FGJSBBase ()
	Destructor for FGJSBBase.
void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers. More...
Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static constexpr double	sign (double num)
Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text
static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text
static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text
static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties
static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text
static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off
static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text
static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text
static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text
static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text
static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text
static short	debug_lvl = 1
Protected Member Functions inherited from FGFCSComponent
void	CheckInputNodes (size_t MinNodes, size_t MaxNodes, Element *el)
void	Clip (void)
void	Delay (void)
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGFCSComponent
bool	clip
FGParameter_ptr	ClipMax
FGParameter_ptr	ClipMin
bool	cyclic_clip
unsigned int	delay
double	delay_time
double	dt
FGFCS *	fcs
int	index
std::vector< FGPropertyValue_ptr >	InitNodes
double	Input
std::vector< FGPropertyValue_ptr >	InputNodes
std::string	Name
double	Output
std::vector< double >	output_array
std::vector< FGPropertyNode_ptr >	OutputNodes
std::string	Type
Static Protected Attributes inherited from FGJSBBase
static constexpr double	radtodeg = 180. / M_PI
static constexpr double	degtorad = M_PI / 180.
static constexpr double	hptoftlbssec = 550.0
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	fttom = 0.3048
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inhgtopa = 3386.38
static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff.
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static const std::string	needed_cfg_version = "2.0"
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

Constructor & Destructor Documentation

FGActuator()

FGActuator	(	FGFCS *	fcs,
		Element *	element
	)

Constructor.

Definition at line 53 of file FGActuator.cpp.

  : FGFCSComponent(fcs, element)
{
  // inputs are read from the base class constructor
 
  PreviousOutput = 0.0;
  PreviousHystOutput = 0.0;
  PreviousRateLimOutput = 0.0;
  PreviousLagInput = PreviousLagOutput = 0.0;
  bias = hysteresis_width = deadband_width = 0.0;
  lag = nullptr;
  rate_limit_incr = rate_limit_decr = 0; // no limit
  fail_zero = fail_hardover = fail_stuck = false;
  ca = cb = 0.0;
  initialized = 0;
  saturated = false;
 
  CheckInputNodes(1, 1, element);
 
  if ( element->FindElement("deadband_width") ) {
    deadband_width = element->FindElementValueAsNumber("deadband_width");
  }
  if ( element->FindElement("hysteresis_width") ) {
    hysteresis_width = element->FindElementValueAsNumber("hysteresis_width");
  }
 
  // There can be a single rate limit specified, or increasing and
  // decreasing rate limits specified, and rate limits can be numeric, or
  // a property.
  auto PropertyManager = fcs->GetPropertyManager();
  Element* ratelim_el = element->FindElement("rate_limit");
  while ( ratelim_el ) {
    string rate_limit_str = ratelim_el->GetDataLine();
    FGParameter* rate_limit = new FGParameterValue(rate_limit_str,
                                                   PropertyManager, ratelim_el);
 
    if (ratelim_el->HasAttribute("sense")) {
      string sense = ratelim_el->GetAttributeValue("sense");
      if (sense.substr(0,4) == "incr")
        rate_limit_incr = rate_limit;
      else if (sense.substr(0,4) == "decr")
        rate_limit_decr = rate_limit;
    } else {
      rate_limit_incr = rate_limit;
      rate_limit_decr = rate_limit;
    }
    ratelim_el = element->FindNextElement("rate_limit");
  }
 
  if ( element->FindElement("bias") ) {
    bias = element->FindElementValueAsNumber("bias");
  }
 
  // Lag if specified can be numeric or a property
  Element* lag_el = element->FindElement("lag");
  if ( lag_el ) {
    string lag_str = lag_el->GetDataLine();
    lag = new FGParameterValue(lag_str, PropertyManager, lag_el);
    InitializeLagCoefficients();
  }
 
  bind(element, PropertyManager.get());
 
  Debug(0);
}

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~FGActuator()

~FGActuator

(

)

Destructor.

Definition at line 121 of file FGActuator.cpp.

{
  delete rate_limit_incr;
  if (rate_limit_decr != rate_limit_incr)
    delete rate_limit_decr;
 
  delete lag;
 
  Debug(1);
}

Member Function Documentation

GetFailHardover()

bool GetFailHardover ( void  ) const

inline

Definition at line 150 of file FGActuator.h.

{return fail_hardover;}

GetFailStuck()

bool GetFailStuck ( void  ) const

inline

Definition at line 151 of file FGActuator.h.

{return fail_stuck;}

GetFailZero()

bool GetFailZero ( void  ) const

inline

Definition at line 149 of file FGActuator.h.

{return fail_zero;}

IsSaturated()

bool IsSaturated ( void  ) const

inline

Definition at line 152 of file FGActuator.h.

{return saturated;}

ResetPastStates()

void ResetPastStates ( void  )

overridevirtual

Reimplemented from FGFCSComponent.

Definition at line 134 of file FGActuator.cpp.

{
  FGFCSComponent::ResetPastStates();
 
  PreviousOutput = PreviousHystOutput = PreviousRateLimOutput
    = PreviousLagInput = PreviousLagOutput = Output = 0.0;
}

Run()

bool Run ( void  )

overridevirtual

This function processes the input.

It calls private functions if needed to perform the hysteresis, lag, limiting, etc. functions.

Reimplemented from FGFCSComponent.

Definition at line 144 of file FGActuator.cpp.

{
  Input = InputNodes[0]->getDoubleValue();
 
  if( fcs->GetTrimStatus() ) initialized = 0;
 
  if (fail_zero) Input = 0;
  if (fail_hardover) Input = Input < 0.0 ? ClipMin->GetValue() : ClipMax->GetValue();
 
  Output = Input; // Perfect actuator. At this point, if no failures are present
                  // and no subsequent lag, limiting, etc. is done, the output
                  // is simply the input. If any further processing is done
                  // (below) such as lag, rate limiting, hysteresis, etc., then
                  // the Input will be further processed and the eventual Output
                  // will be overwritten from this perfect value.
 
  if (fail_stuck) {
    Output = PreviousOutput;
  } else {
    if (lag)                Lag();        // models actuator lag
    if (rate_limit_incr != 0 || rate_limit_decr != 0) RateLimit();  // limit the actuator rate
    if (deadband_width != 0.0)   Deadband();
    if (hysteresis_width != 0.0) Hysteresis();
    if (bias != 0.0)             Bias();       // models a finite bias
    if (delay != 0)              Delay();      // Model transport latency
  }
 
  PreviousOutput = Output; // previous value needed for "stuck" malfunction
 
  initialized = 1;
 
  Clip();
 
  if (clip) {
    double clipmax = ClipMax->GetValue();
    saturated = false;
 
    if (Output >= clipmax && clipmax != 0)
      saturated = true;
    else{
      double clipmin = ClipMin->GetValue();
      if (Output <= clipmin && clipmin != 0)
        saturated = true;
    }
  }
 
  SetOutput();
 
  return true;
}

SetFailHardover()

void SetFailHardover ( bool  set )

inline

Definition at line 146 of file FGActuator.h.

{fail_hardover = set;}

SetFailStuck()

void SetFailStuck ( bool  set )

inline

Definition at line 147 of file FGActuator.h.

{fail_stuck = set;}

SetFailZero()

void SetFailZero ( bool  set )

inline

This function fails the actuator to zero.

The motion to zero will flow through the lag, hysteresis, and rate limiting functions if those are activated.

Definition at line 145 of file FGActuator.h.

{fail_zero = set;}

---

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

• FGActuator.h
• FGActuator.cpp