# validated: 2017-12-13 EN f9bece2ffbf7 edu/wpi/first/wpilibj/PIDController.java
#----------------------------------------------------------------------------
# Copyright (c) FIRST 2008-2016. All Rights Reserved.
# Open Source Software - may be modified and shared by FRC teams. The code
# must be accompanied by the FIRST BSD license file in the root directory of
# the project.
#----------------------------------------------------------------------------
from collections import deque
from itertools import islice
import threading
import warnings
from networktables import NetworkTables
import hal
from .interfaces import PIDSource
from .sendablebase import SendableBase
from .resource import Resource
from .timer import Timer
from .lineardigitalfilter import LinearDigitalFilter
from ._impl.timertask import TimerTask
from ._impl.utils import match_arglist, HasAttribute
__all__ = ["PIDController"]
[docs]class PIDController(SendableBase):
"""Can be used to control devices via a PID Control Loop.
Creates a separate thread which reads the given :class:`.PIDSource` and takes
care of the integral calculations, as well as writing the given
:class:`.PIDOutput`.
This feedback controller runs in discrete time, so time deltas are not used
in the integral and derivative calculations. Therefore, the sample rate affects
the controller's behavior for a given set of PID constants.
"""
kDefaultPeriod = .05
instances = 0
PIDSourceType = PIDSource.PIDSourceType
# Tolerance is the type of tolerance used to specify if the PID controller
# is on target. The various implementations of this such as
# PercentageTolerance and AbsoluteTolerance specify types of tolerance
# specifications to use.
[docs] def PercentageTolerance_onTarget(self, percentage):
return abs(self.getError()) < percentage / 100.0 * self.inputRange
[docs] def AbsoluteTolerance_onTarget(self, value):
return abs(self.getError()) < value
def __init__(self, Kp, Ki, Kd, *args, **kwargs):
"""Allocate a PID object with the given constants for P, I, D, and F
Arguments can be structured as follows:
- Kp, Ki, Kd, Kf, source, output, period
- Kp, Ki, Kd, source, output, period
- Kp, Ki, Kd, source, output
- Kp, Ki, Kd, Kf, source, output
:param Kp: the proportional coefficient
:type Kp: float or int
:param Ki: the integral coefficient
:type Ki: float or int
:param Kd: the derivative coefficient
:type Kd: float or int
:param Kf: the feed forward term
:type Kf: float or int
:param source: Called to get values
:type source: A function, or an object that implements :class:`.PIDSource`
:param output: Receives the output percentage
:type output: A function, or an object that implements :class:`.PIDOutput`
:param period: the loop time for doing calculations. This particularly
effects calculations of the integral and differential terms.
The default is 50ms.
:type period: float or int
"""
super().__init__(False)
f_arg = ("Kf", [float, int])
source_arg = ("source", [HasAttribute("pidGet"), HasAttribute("__call__")])
output_arg = ("output", [HasAttribute("pidWrite"), HasAttribute("__call__")])
period_arg = ("period", [float, int])
templates = [[f_arg, source_arg, output_arg, period_arg],
[source_arg, output_arg, period_arg],
[source_arg, output_arg],
[f_arg, source_arg, output_arg]]
_, results = match_arglist('PIDController.__init__',
args, kwargs, templates)
self.P = Kp # factor for "proportional" control
self.I = Ki # factor for "integral" control
self.D = Kd # factor for "derivative" control
self.F = results.pop("Kf", 0.0) # factor for feedforward term
self.pidOutput = results.pop("output")
self.origSource = results.pop("source")
self.period = results.pop("period", self.kDefaultPeriod)
self.filter = LinearDigitalFilter.movingAverage(self.origSource, 1)
self.pidInput = self.filter
self.pidInput = PIDSource.from_obj_or_callable(self.pidInput)
if hasattr(self.pidOutput, 'pidWrite'):
self.pidOutput = self.pidOutput.pidWrite
self.maximumOutput = 1.0 # |maximum output|
self.minimumOutput = -1.0 # |minimum output|
self.maximumInput = 0.0 # maximum input - limit setpoint to this
self.minimumInput = 0.0 # minimum input - limit setpoint to this
self.inputRange = 0.0 # input range - difference between maximum and minimum
self.continuous = False # do the endpoints wrap around? eg. Absolute encoder
self.enabled = False # is the pid controller enabled
self.prevError = 0.0 # the prior error (used to compute velocity)
self.totalError = 0.0 #the sum of the errors for use in the integral calc
self.setpoint = 0.0
self.prevSetpoint = 0.0
self.error = 0.0
self.result = 0.0
self.mutex = threading.RLock()
self.pidWriteMutex = threading.RLock()
self.pid_task = TimerTask('PIDTask%d' % PIDController.instances, self.period, self._calculate)
self.pid_task.start()
self.setpointTimer = Timer()
self.setpointTimer.start()
# Need this to free on unit test wpilib reset
Resource._add_global_resource(self)
PIDController.instances += 1
hal.report(hal.UsageReporting.kResourceType_PIDController,
PIDController.instances)
self.setName("PIDController", PIDController.instances)
[docs] def free(self):
"""Free the PID object"""
super().free()
# TODO: is this useful in Python? Should make TableListener weakref.
self.pid_task.cancel()
with self.mutex:
self.pidInput = None
self.pidOutput = None
def _calculate(self):
"""Read the input, calculate the output accordingly, and write to the
output. This should only be called by the PIDTask and is created
during initialization."""
if self.origSource is None or self.pidOutput is None:
return
with self.mutex:
enabled = self.enabled # take snapshot of these values...
if enabled:
feedForward = self.calculateFeedForward()
with self.mutex:
input = self.pidInput.pidGet()
pidSourceType = self.pidInput.getPIDSourceType()
P = self.P
I = self.I
D = self.D
minimumOutput = self.minimumOutput
maximumOutput = self.maximumOutput
prevError = self.prevError
error = self.getContinuousError(self.setpoint - input)
totalError = self.totalError
# start
if pidSourceType == self.PIDSourceType.kRate:
if P != 0:
totalError = self.clamp(
totalError + error,
minimumOutput / P,
maximumOutput / P)
result = P * totalError + D * error + feedForward
else:
if I != 0:
totalError = self.clamp(
totalError + error,
minimumOutput / I,
maximumOutput / I)
result = P * error + I * totalError + D * (error - prevError) + \
feedForward
result = self.clamp(result, minimumOutput, maximumOutput)
with self.pidWriteMutex:
with self.mutex:
enabled = self.enabled
if enabled:
self.pidOutput(result)
with self.mutex:
self.prevError = error
self.error = error
self.totalError = totalError
self.result = result
[docs] def calculateFeedForward(self):
"""Calculate the feed forward term
Both of the provided feed forward calculations are velocity feed forwards.
If a different feed forward calculation is desired, the user can override
this function and provide his or her own. This function does no
synchronization because the PIDController class only calls it in
synchronized code, so be careful if calling it oneself.
If a velocity PID controller is being used, the F term should be set to 1
over the maximum setpoint for the output. If a position PID controller is
being used, the F term should be set to 1 over the maximum speed for the
output measured in setpoint units per this controller's update period (see
the default period in this class's constructor).
"""
if self.pidInput.getPIDSourceType() == self.PIDSourceType.kRate:
return self.F * self.getSetpoint()
else:
temp = self.F * self.getDeltaSetpoint()
self.prevSetpoint = self.setpoint
self.setpointTimer.reset()
return temp
[docs] def setPID(self, p, i, d, f=0.0):
"""Set the PID Controller gain parameters.
Set the proportional, integral, and differential coefficients.
:param p: Proportional coefficient
:param i: Integral coefficient
:param d: Differential coefficient
:param f: Feed forward coefficient (optional, default is 0.0)
"""
with self.mutex:
self.P = p
self.I = i
self.D = d
self.F = f
[docs] def getP(self):
"""Get the Proportional coefficient.
:returns: proportional coefficient
"""
with self.mutex:
return self.P
[docs] def getI(self):
"""Get the Integral coefficient
:returns: integral coefficient
"""
with self.mutex:
return self.I
[docs] def getD(self):
"""Get the Differential coefficient.
:returns: differential coefficient
"""
with self.mutex:
return self.D
[docs] def getF(self):
"""Get the Feed forward coefficient.
:returns: feed forward coefficient
"""
with self.mutex:
return self.F
[docs] def get(self):
"""Return the current PID result.
This is always centered on zero and constrained the the max and min
outs.
:returns: the latest calculated output
"""
with self.mutex:
return self.result
[docs] def setContinuous(self, continuous=True):
"""Set the PID controller to consider the input to be continuous.
Rather then using the max and min in as constraints, it considers them
to be the same point and automatically calculates the shortest route
to the setpoint.
:param continuous: Set to True turns on continuous, False turns off
continuous
"""
with self.mutex:
self.continuous = continuous
[docs] def setOutputRange(self, minimumOutput, maximumOutput):
"""Sets the minimum and maximum values to write.
:param minimumOutput: the minimum percentage to write to the output
:param maximumOutput: the maximum percentage to write to the output
"""
with self.mutex:
if minimumOutput > maximumOutput:
raise ValueError("Lower bound is greater than upper bound")
self.minimumOutput = minimumOutput
self.maximumOutput = maximumOutput
[docs] def setSetpoint(self, setpoint):
"""Set the setpoint for the PIDController.
:param setpoint: the desired setpoint
"""
with self.mutex:
if self.maximumInput > self.minimumInput:
if setpoint > self.maximumInput:
newsetpoint = self.maximumInput
elif setpoint < self.minimumInput:
newsetpoint = self.minimumInput
else:
newsetpoint = setpoint
else:
newsetpoint = setpoint
self.setpoint = newsetpoint
[docs] def getSetpoint(self):
"""Returns the current setpoint of the PIDController.
:returns: the current setpoint
"""
with self.mutex:
return self.setpoint
[docs] def getDeltaSetpoint(self):
"""Returns the change in setpoint over time of the PIDController
:returns: the change in setpoint over time
"""
with self.mutex:
t = self.setpointTimer.get()
# During testing/simulation it is possible to get a divide by zero because
# the threads' calls aren't strictly aligned with the master clock.
if t:
return (self.setpoint - self.prevSetpoint) / t
else:
return 0.0
[docs] def getError(self):
"""Returns the current difference of the input from the setpoint.
:return: the current error
"""
with self.mutex:
return self.getContinuousError(self.getSetpoint() - self.pidInput.pidGet())
[docs] def getAvgError(self):
"""
Returns the current difference of the error over the past few iterations. You can specify the
number of iterations to average with setToleranceBuffer() (defaults to 1). getAvgError() is
used for the onTarget() function.
.. deprecated :: 2018.0.0
Use getError(), which is now already filtered.
:returns: the current average of the error
"""
warnings.warn("use getRate instead", DeprecationWarning)
with self.mutex:
return self.getError()
[docs] def setPIDSourceType(self, pidSourceType):
"""Sets what type of input the PID controller will use
:param pidSourceType: the type of input
"""
self.pidInput.setPIDSourceType(pidSourceType)
[docs] def getPIDSourceType(self):
"""Returns the type of input the PID controller is using
:returns: the PID controller input type
"""
return self.pidInput.getPIDSourceType()
[docs] def setAbsoluteTolerance(self, absvalue):
"""Set the absolute error which is considered tolerable for use with
:func:`onTarget`.
:param absvalue: absolute error which is tolerable in the units of the
input object
"""
with self.mutex:
self.onTarget = lambda: \
self.AbsoluteTolerance_onTarget(absvalue)
[docs] def setPercentTolerance(self, percentage):
"""Set the percentage error which is considered tolerable for use with
:func:`onTarget`. (Input of 15.0 = 15 percent)
:param percentage: percent error which is tolerable
"""
with self.mutex:
self.onTarget = lambda: \
self.PercentageTolerance_onTarget(percentage)
[docs] def setToleranceBuffer(self, bufLength):
"""Set the number of previous error samples to average for tolerancing. When
determining whether a mechanism is on target, the user may want to use a
rolling average of previous measurements instead of a precise position or
velocity. This is useful for noisy sensors which return a few erroneous
measurements when the mechanism is on target. However, the mechanism will
not register as on target for at least the specified bufLength cycles.
:param bufLength: Number of previous cycles to average.
:type bufLength: int
.. deprecated:: 2018.0.0
Use a LinearDigitalFilter as the input
"""
with self.mutex:
self.filter = LinearDigitalFilter.movingAverage(self.origSource, bufLength)
self.pidInput = self.filter
[docs] def onTarget(self):
"""Return True if the error is within the percentage of the total input
range, determined by setTolerance. This assumes that the maximum and
minimum input were set using :func:`setInput`.
:returns: True if the error is less than the tolerance
"""
with self.mutex:
return self.tolerance.onTarget()
[docs] def enable(self):
"""Begin running the PIDController."""
with self.mutex:
self.enabled = True
[docs] def disable(self):
"""Stop running the PIDController, this sets the output to zero before
stopping."""
with self.pidWriteMutex:
with self.mutex:
self.enabled = False
self.pidOutput(0)
[docs] def isEnabled(self):
"""Return True if PIDController is enabled."""
with self.mutex:
return self.enabled
[docs] def reset(self):
"""Reset the previous error, the integral term, and disable the
controller."""
with self.mutex:
self.disable()
self.prevError = 0
self.totalError = 0
self.result = 0
[docs] def setP(self, p):
"""
Set the Proportional coefficient of the PID controller gain.
:param p: Proportional coefficient
"""
with self.mutex:
self.P = p
[docs] def setI(self, i):
"""
Set the Integral coefficient of the PID controller gain.
:param i: Integral coefficient
"""
with self.mutex:
self.I = i
[docs] def setD(self, d):
"""
Set the Differential coefficient of the PID controller gain.
:param d: differential coefficient
"""
with self.mutex:
self.D = d
[docs] def setF(self, f):
"""
Set the Feed forward coefficient of the PID controller gain.
:param f: feed forward coefficient
"""
with self.mutex:
self.F = f
[docs] def setEnabled(self, enable):
"""Set the enabled state of the PIDController."""
if enable:
self.enable()
else:
self.disable()
[docs] def initSendable(self, builder):
builder.setSmartDashboardType("PIDController")
builder.setSafeState(self.reset)
builder.addDoubleProperty("p", self.getP, self.setP)
builder.addDoubleProperty("i", self.getI, self.setI)
builder.addDoubleProperty("d", self.getD, self.setD)
builder.addDoubleProperty("f", self.getF, self.setF)
builder.addDoubleProperty("setpoint", self.getSetpoint, self.setSetpoint)
builder.addBooleanProperty("enabled", self.isEnabled, self.setEnabled)
[docs] def getContinuousError(self, error):
"""
Wraps error around for continuous inputs. The original error is
returned if continuous mode is disabled. This is an unsynchronized
function.
:param error: The current error of the PID controller.
:return: Error for continuous inputs.
"""
if self.continuous:
error %= self.inputRange
if abs(error) > self.inputRange / 2:
if error > 0:
return error - self.inputRange
else:
return error + self.inputRange
return error
[docs] def clamp(self, value, low, high):
return max(low, min(value, high))