stormbots

Class MiniPID

java.lang.Object

stormbots.MiniPID

public class MiniPID
extends Object

Small, easy to use PID implementation with advanced controller capability.
Minimal usage:
MiniPID pid = new MiniPID(p,i,d);
...looping code...{
output= pid.getOutput(sensorvalue,target);
}

See Also:

http://brettbeauregard.com/blog/2011/04/improving-the-beginners-pid-direction/improving-the-beginners-pid-introduction

Constructor Summary

Constructors

Constructor and Description
MiniPID(double p, double i, double d) Create a MiniPID class object.
MiniPID(double p, double i, double d, double f) Create a MiniPID class object.

Method Summary

Modifier and Type	Method and Description
double	getOutput() Calculate the output value for the current PID cycle.
double	getOutput(double actual) Calculate the output value for the current PID cycle.
double	getOutput(double actual, double setpoint) Calculate the output value for the current PID cycle.
void	reset() Resets the controller.
void	setD(double d) Changes the D parameter This has two primary effects: Adds a "startup kick" and speeds up system response during setpoint changes Adds "drag" and slows the system when moving toward the target A small D value can be useful for both improving response times, and preventing overshoot.
void	setDirection(boolean reversed) Set the operating direction of the PID controller
void	setF(double f) Configure the FeedForward parameter.
void	setI(double i) Changes the I parameter This is used for overcoming disturbances, and ensuring that the controller always gets to the control mode.
void	setMaxIOutput(double maximum) Set the maximum output value contributed by the I component of the system This can be used to prevent large windup issues and make tuning simpler
void	setOutputFilter(double strength) Set a filter on the output to reduce sharp oscillations.
void	setOutputLimits(double output) Specify a maximum output range.
void	setOutputLimits(double minimum, double maximum) Specify a maximum output.
void	setOutputRampRate(double rate) Set the maximum rate the output can increase per cycle.
void	setP(double p) Configure the Proportional gain parameter.
void	setPID(double p, double i, double d) Configure the PID object.
void	setPID(double p, double i, double d, double f) Configure the PID object.
void	setSetpoint(double setpoint) Configure setpoint for the PID calculations This represents the target for the PID system's, such as a position, velocity, or angle.
void	setSetpointRange(double range) Set a limit on how far the setpoint can be from the current position Can simplify tuning by helping tuning over a small range applies to a much larger range.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MiniPID

public MiniPID(double p,
               double i,
               double d)

Create a MiniPID class object. See setP, setI, setD methods for more detailed parameters.

Parameters:

p - Proportional gain. Large if large difference between setpoint and target.

i - Integral gain. Becomes large if setpoint cannot reach target quickly.

d - Derivative gain. Responds quickly to large changes in error. Small values prevents P and I terms from causing overshoot.

MiniPID

public MiniPID(double p,
               double i,
               double d,
               double f)

Create a MiniPID class object. See setP, setI, setD, setF methods for more detailed parameters.

Parameters:

p - Proportional gain. Large if large difference between setpoint and target.

i - Integral gain. Becomes large if setpoint cannot reach target quickly.

d - Derivative gain. Responds quickly to large changes in error. Small values prevents P and I terms from causing overshoot.

f - Feed-forward gain. Open loop "best guess" for the output should be. Only useful if setpoint represents a rate.

Method Detail

setP

public void setP(double p)

Configure the Proportional gain parameter.
This responds quickly to changes in setpoint, and provides most of the initial driving force to make corrections.
Some systems can be used with only a P gain, and many can be operated with only PI.
For position based controllers, this is the first parameter to tune, with I second.
For rate controlled systems, this is often the second after F.

Parameters:

p - Proportional gain. Affects output according to output+=P*(setpoint-current_value)

setI

public void setI(double i)

Changes the I parameter
This is used for overcoming disturbances, and ensuring that the controller always gets to the control mode. Typically tuned second for "Position" based modes, and third for "Rate" or continuous based modes.
Affects output through output+=previous_errors*Igain ;previous_errors+=current_error

Parameters:

i - New gain value for the Integral term

See Also:

#setMaxIOutput(double) setMaxIOutput} for how to restrict

setD

public void setD(double d)

Changes the D parameter
This has two primary effects:

Adds a "startup kick" and speeds up system response during setpoint changes Adds "drag" and slows the system when moving toward the target A small D value can be useful for both improving response times, and preventing overshoot. However, in many systems a large D value will cause significant instability, particularly for large setpoint changes.
Affects output through output += -D*(current_input_value - last_input_value)

Parameters:

d - New gain value for the Derivative term

setF

public void setF(double f)

Configure the FeedForward parameter.
This is excellent for velocity, rate, and other continuous control modes where you can expect a rough output value based solely on the setpoint.
Should not be used in "position" based control modes.
Affects output according to output+=F*Setpoint. Note, that a F-only system is actually open loop.

Parameters:

f - Feed forward gain.

setPID

public void setPID(double p,
                   double i,
                   double d)

Configure the PID object. See setP, setI, setD methods for more detailed parameters.

Parameters:

p - Proportional gain. Large if large difference between setpoint and target.

i - Integral gain. Becomes large if setpoint cannot reach target quickly.

d - Derivative gain. Responds quickly to large changes in error. Small values prevents P and I terms from causing overshoot.

setPID

public void setPID(double p,
                   double i,
                   double d,
                   double f)

Configure the PID object. See setP, setI, setD, setF methods for more detailed parameters.

Parameters:

p - Proportional gain. Large if large difference between setpoint and target.

i - Integral gain. Becomes large if setpoint cannot reach target quickly.

d - Derivative gain. Responds quickly to large changes in error. Small values prevents P and I terms from causing overshoot.

f - Feed-forward gain. Open loop "best guess" for the output should be. Only useful if setpoint represents a rate.

setMaxIOutput

public void setMaxIOutput(double maximum)

Set the maximum output value contributed by the I component of the system This can be used to prevent large windup issues and make tuning simpler

Parameters:

maximum. - Units are the same as the expected output value

setOutputLimits

public void setOutputLimits(double output)

Specify a maximum output range.
When one input is specified, output range is configured to [-output, output]

Parameters:

output -

setOutputLimits

public void setOutputLimits(double minimum,
                            double maximum)

Specify a maximum output. When two inputs specified, output range is configured to [minimum, maximum]

Parameters:

minimum - possible output value

maximum - possible output value

setDirection

public void setDirection(boolean reversed)

Set the operating direction of the PID controller

Parameters:

reversed - Set true to reverse PID output

setSetpoint

public void setSetpoint(double setpoint)

Configure setpoint for the PID calculations
This represents the target for the PID system's, such as a position, velocity, or angle.

Parameters:

setpoint -

See Also:




getOutput

public double getOutput(double actual,
                        double setpoint)

Calculate the output value for the current PID cycle.

Parameters:

actual - The monitored value, typically as a sensor input.

setpoint - The target value for the system

Returns:

calculated output value for driving the system

getOutput

public double getOutput()

Calculate the output value for the current PID cycle.
In no-parameter mode, this uses the last sensor value, and last setpoint value.
Not typically useful, and use of parameter modes is suggested.

Returns:

calculated output value for driving the system

getOutput

public double getOutput(double actual)

Calculate the output value for the current PID cycle.
In one parameter mode, the last configured setpoint will be used.

Parameters:

actual - The monitored value, typically as a sensor input.

setpoint - The target value for the system

Returns:

calculated output value for driving the system

See Also:

MiniPID#setSetpoint()

reset

public void reset()

Resets the controller. This erases the I term buildup, and removes D gain on the next loop.
This should be used any time the PID is disabled or inactive for extended duration, and the controlled portion of the system may have changed due to external forces.

setOutputRampRate

public void setOutputRampRate(double rate)

Set the maximum rate the output can increase per cycle.
This can prevent sharp jumps in output when changing setpoints or enabling a PID system, which might cause stress on physical or electrical systems.
Can be very useful for fast-reacting control loops, such as ones with large P or D values and feed-forward systems.

Parameters:

rate, - with units being the same as the output

setSetpointRange

public void setSetpointRange(double range)

Set a limit on how far the setpoint can be from the current position
Can simplify tuning by helping tuning over a small range applies to a much larger range.
This limits the reactivity of P term, and restricts impact of large D term during large setpoint adjustments. Increases lag and I term if range is too small.

Parameters:

range, - with units being the same as the expected sensor range.

setOutputFilter

public void setOutputFilter(double strength)

Set a filter on the output to reduce sharp oscillations.
0.1 is likely a sane starting value. Larger values use historical data more heavily, with low values weigh newer data. 0 will disable, filtering, and use only the most recent value.
Increasing the filter strength will P and D oscillations, but force larger I values and increase I term overshoot.
Uses an exponential wieghted rolling sum filter, according to a simple

output*(1-strength)*sum(0..n){output*strength^n}

algorithm.

Parameters:

output - valid between [0..1), meaning [current output only.. historical output only)