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PIDController feed forward term can now be calculated by the end user

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The current feed forward calculation is only useful for velocity PID controllers where F, the feed forward constant, is 1 over the maximum setpoint for the output. For motion profiles which use position PID controllers, the appropriate calculation for velocity and acceleration feed forwards is different. This change allows the user to provide their own feed forward implementation without having to rewrite the entire Calculate() function.

Both default feed forward calculations are velocity feed forwards. Suggestions for sensible feed forward constants are included in the inline comments.

Change-Id: Id175786f26bd342de52a1fae89595cbeba5dfc93
This commit is contained in:
Tyler Veness
2015-08-26 03:19:35 -07:00
parent 3cd1253977
commit e3ce991f18
4 changed files with 190 additions and 66 deletions
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9
wpilibc/shared/include/PIDController.h
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@@ -14,6 +14,7 @@
#include "PIDSource.h"
#include "Notifier.h"
#include "HAL/cpp/priority_mutex.h"
#include "Timer.h"
#include <memory>
@@ -55,6 +56,7 @@ class PIDController : public LiveWindowSendable,
virtual void SetSetpoint(float setpoint) override;
virtual double GetSetpoint() const override;
double GetDeltaSetpoint() const;
virtual float GetError() const;
virtual float GetAvgError() const;
@@ -82,6 +84,7 @@ class PIDController : public LiveWindowSendable,
std::shared_ptr<ITable> m_table;
virtual void Calculate();
virtual double CalculateFeedForward();
private:
float m_P; // factor for "proportional" control
@@ -94,7 +97,7 @@ class PIDController : public LiveWindowSendable,
float m_minimumInput = 0; // minimum input - limit setpoint to this
bool m_continuous = false; // do the endpoints wrap around? eg. Absolute encoder
bool m_enabled = false; // is the pid controller enabled
float m_prevInput = 0; // the prior sensor input (used to compute velocity)
float m_prevError = 0; // the prior error (used to compute velocity)
double m_totalError = 0; // the sum of the errors for use in the integral calc
enum {
kAbsoluteTolerance,
@@ -105,6 +108,7 @@ class PIDController : public LiveWindowSendable,
// the percetage or absolute error that is considered on target.
float m_tolerance = 0.05;
float m_setpoint = 0;
float m_prevSetpoint = 0;
float m_error = 0;
float m_result = 0;
float m_period;
@@ -114,9 +118,10 @@ class PIDController : public LiveWindowSendable,
std::queue<double> m_buf;
double m_bufTotal = 0;
mutable priority_mutex m_mutex;
mutable priority_recursive_mutex m_mutex;
std::unique_ptr<Notifier> m_controlLoop;
Timer m_setpointTimer;
void Initialize(float p, float i, float d, float f, PIDSource *source,
PIDOutput *output, float period = 0.05);