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Add the pid actuator: setpoint inputs, integral action, slew rate limiting.

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<pid kp kv|dampratio [ki imax] [slewmax]> is a PID controller with real position and velocity setpoint inputs on a single force output, plus an optional feedforward input. With a zero velocity setpoint it reproduces <position> bit-exactly; the input signature is any subset of [pos, vel, ff], selected with input="..." and recorded as mjtCtrlInput bits in
actuator_ctrlspec; absent setpoint inputs are fixed at zero, so the control vector contains no inert entries.

kp and kv are single-sourced in the affine bias parameters (biasprm[1,2]) with no gainprm mirror: every consumer of the position-servo shape
(dampratio conversion, inheritrange, qDeriv) reads one location, which is what makes the bit-exact <position> parity possible. Controller state uses dyntype 'pid' with slot-gated activations in the order [slew, integral], following the dcmotor slot idiom: slewmax (dynprm[1]) rate limits the effective position setpoint through an activation holding it;
ki (gainprm[0]) integrates the position error -- wrapped on rotational transmissions -- with anti-windup clamping of the integrand at imax (dynprm[0]). Both features require the pos input. Servo input unpacking is shared with the dcmotor controller (unpackServoInputs); per-input ranges are exposed as posrange/velrange/ffrange.

This subsumes the functionality of the mujoco.pid plugin with proper activation state: correct under all integrators, visible to keyframes, act sensors and reset. Migration: kp/ki/kd map to kp/ki/kv, plugin imax is in force units (divide by ki), slewmax carries over; the single ctrl becomes input="pos".

PiperOrigin-RevId: 957588898
Change-Id: Id2786836ca6e76f58e5b5cc8323fc23be0a53784
This commit is contained in:
Yuval Tassa
2026-08-01 04:28:10 -07:00
committed by Copybara-Service
parent 7bc1aa9b05
commit 279df98cd0
33 changed files with 1504 additions and 62 deletions
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doc/XMLreference.rst
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@@ -5664,25 +5664,27 @@ specify them independently.
.. _actuator-general-dyntype:
:at:`dyntype`: :at-val:`[none, integrator, filter, filterexact, muscle, user], "none"`
:at:`dyntype`: :at-val:`[none, integrator, filter, filterexact, pid, muscle, user], "none"`
Activation dynamics type for the actuator. The available dynamics types were already described in the :ref:`Actuation
model <geActuation>` section. Repeating that description in somewhat different notation (corresponding to the mjModel
and mjData fields involved) we have:
=========== ======================================
Keyword Description
=========== ======================================
none No internal state
integrator act_dot = ctrl
filter act_dot = (ctrl - act) / dynprm[0]
filterexact Like filter but with exact integration
muscle act_dot = mju_muscleDynamics(...)
user act_dot = mjcb_act_dyn(...)
=========== ======================================
============= ======================================
Keyword Description
============= ======================================
none No internal state
integrator act_dot = ctrl
filter act_dot = (ctrl - act) / dynprm[0]
filterexact Like filter but with exact integration
pid act_dot = position error; see :ref:`pid<actuator-pid>`
dcmotor DC motor electrical dynamics, see :ref:`dcmotor<actuator-dcmotor>`
muscle act_dot = mju_muscleDynamics(...)
user act_dot = mjcb_act_dyn(...)
============= ======================================
.. _actuator-general-gaintype:
:at:`gaintype`: :at-val:`[fixed, affine, muscle, so3, user], "fixed"`
:at:`gaintype`: :at-val:`[fixed, affine, muscle, pid, so3, user], "fixed"`
The gain and bias together determine the output of the force generation mechanism, which is currently assumed to be
affine. As already explained in :ref:`Actuation model <geActuation>`, the general formula is:
scalar_force = gain_term \* (act or ctrl) + bias_term.
@@ -5695,6 +5697,7 @@ specify them independently.
fixed gain_term = gainprm[0]
affine gain_term = gain_prm[0] + gain_prm[1]*length + gain_prm[2]*velocity
muscle gain_term = mju_muscleGain(...)
pid PID controller with setpoint inputs, see :ref:`pid<actuator-pid>`
so3 geodesic orientation servo, computed jointly over 3 force outputs, see :ref:`orientation<actuator-orientation>`
user gain_term = mjcb_act_gain(...)
======= ===============================
@@ -5739,12 +5742,23 @@ specify them independently.
so the user can enter as many parameters as needed. These defaults are not compatible with muscle actuators; see
:ref:`muscle <actuator-muscle>` below.
.. _actuator-general-velrange:
:at:`velrange`: :at-val:`real(2), "0 0"`
Range of the velocity-setpoint input of a :ref:`pid<actuator-pid>` actuator.
.. _actuator-general-ffrange:
:at:`ffrange`: :at-val:`real(2), "0 0"`
Range of the feedforward input of a :ref:`pid<actuator-pid>` actuator.
.. _actuator-general-input:
:at:`input`: :at-val:`string, optional`
Input signature of the actuator: which controls make up its control block, recorded in
``mjModel.actuator_ctrlspec``. Available for gaintype "so3", where it selects the orientation chart: "expmap"
(3 controls, the default) or "quat" (4 controls); see :ref:`orientation/input<actuator-orientation-input>`.
``mjModel.actuator_ctrlspec``. For gaintype "so3" it selects the orientation chart: "expmap" (3 controls, the
default) or "quat" (4 controls); see :ref:`orientation/input<actuator-orientation-input>`. For gaintype "pid" it is
a token list selecting the input subset; see :ref:`pid/input<actuator-pid-input>`.
.. _actuator-general-actearly:
@@ -5954,6 +5968,146 @@ This element has one custom attribute in addition to the common attributes:
:ref:`position<actuator-position>` attribute and in the :ref:`default class<default-position-inheritrange>`,
saved XMLs always convert it to explicit :at:`ctrlrange` at the actuator.
.. _actuator-pid:
:el-prefix:`actuator/` |-| **pid** |*|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This element creates a PID controller with position and velocity setpoint inputs on a single force output, with optional
integral action and feedforward. With the default input signature ``[pos, vel]`` the force is
:math:`k_p (u_{pos} - l) + k_v (u_{vel} - v)` where :math:`l, v` are the actuator length and velocity; with a zero
velocity setpoint this is identical to :ref:`position<actuator-position>`. The input signature is any subset of
``[pos, vel, ff]``, selected by :ref:`input<actuator-pid-input>`: an absent setpoint input is fixed at zero, and the
``ff`` input adds a feedforward force. Integral action is enabled by :ref:`ki<actuator-pid-ki>`: the position error is integrated in
:ref:`act<siPhysicsState>` and contributes :math:`k_i \cdot act` to the force, with anti-windup clamping by
:ref:`imax<actuator-pid-imax>`.
:ref:`slewmax<actuator-pid-slewmax>` limits the rate of change of the effective position setpoint. Each of these
features, when enabled, adds one activation state, in the order [slew, integral]. The underlying
:ref:`general<actuator-general>` attributes are set as follows:
========= ===================== ========= =========
Attribute Setting Attribute Setting
========= ===================== ========= =========
dyntype none or pid dynprm imax 0 0
gaintype pid gainprm ki 0 0
biastype affine biasprm 0 -kp -kv
========= ===================== ========= =========
This element has custom attributes in addition to the common attributes:
.. _actuator-pid-name:
.. _actuator-pid-class:
.. _actuator-pid-group:
.. _actuator-pid-nsample:
.. _actuator-pid-interp:
.. _actuator-pid-delay:
.. _actuator-pid-ctrllimited:
.. _actuator-pid-forcelimited:
.. _actuator-pid-ctrlrange:
.. _actuator-pid-forcerange:
.. _actuator-pid-lengthrange:
.. _actuator-pid-gear:
.. _actuator-pid-damping:
.. _actuator-pid-armature:
.. _actuator-pid-cranklength:
.. _actuator-pid-user:
.. _actuator-pid-joint:
.. _actuator-pid-jointinparent:
.. _actuator-pid-tendon:
.. _actuator-pid-slidersite:
.. _actuator-pid-cranksite:
.. _actuator-pid-site:
.. _actuator-pid-refsite:
.. _actuator-pid-kp:
:at:`kp`: :at-val:`real, "1"`
Position feedback gain.
.. _actuator-pid-kv:
:at:`kv`: :at-val:`real, "0"`
Velocity feedback gain: applied to the velocity error when the ``vel`` input is present, and as pure damping
otherwise. When using this attribute, it is recommended to use the implicitfast or implicit
:ref:`integrators<geIntegration>`.
.. _actuator-pid-dampratio:
:at:`dampratio`: :at-val:`real, "0"`
Damping applied by the actuator, using damping ratio units, as for
:ref:`position/dampratio<actuator-position-dampratio>`. This attribute is exclusive with :at:`kv`.
.. _actuator-pid-ki:
:at:`ki`: :at-val:`real, "0"`
Integral gain. A nonzero value enables integral action: the position error is integrated in
:ref:`act<siPhysicsState>` (:ref:`dyntype<actuator-general-dyntype>` "pid") and contributes :math:`k_i \cdot act`
to the force.
Requires the ``pos`` input.
.. _actuator-pid-imax:
:at:`imax`: :at-val:`real, "0"`
Anti-windup limit on the integral state: accumulation stops beyond ±\ :at:`imax`. The default value 0 means
"unclamped".
.. _actuator-pid-slewmax:
:at:`slewmax`: :at-val:`real, "0"`
Maximum rate of change of the effective position setpoint. When positive, the commanded setpoint is rate-limited
through an activation state holding the effective setpoint, as for the
:ref:`dcmotor controller<actuator-dcmotor-controller>`. The default value 0 means "unlimited".
.. _actuator-pid-input:
:at:`input`: :at-val:`string, "pos vel"`
Input signature: a space-separated subset of the tokens "pos", "vel" and "ff", packed in this canonical order.
Absent setpoint inputs are fixed at zero, so the control vector contains no inert entries.
.. _actuator-pid-posrange:
:at:`posrange`: :at-val:`real(2), "0 0"`
Range of the position-setpoint input; an alias of :ref:`ctrlrange<actuator-general-ctrlrange>` (the first
input).
.. _actuator-pid-velrange:
:at:`velrange`: :at-val:`real(2), "0 0"`
Range of the velocity-setpoint input.
.. _actuator-pid-ffrange:
:at:`ffrange`: :at-val:`real(2), "0 0"`
Range of the feedforward input.
.. _actuator-pid-inheritrange:
:at:`inheritrange`: :at-val:`real, "0"`
Identical to :ref:`position/inheritrange<actuator-position-inheritrange>`, setting :at:`posrange` from the
transmission target's :at:`range`.
.. _actuator-orientation:
:el-prefix:`actuator/` |-| **orientation** |*|
@@ -5976,7 +6130,7 @@ preserving its direction; the lower bound must be 0.
:ref:`Actuator sensors<sensor-actuatorpos>` report one value per force output. The integrator variant, which
stores the orientation setpoint in :ref:`act<siPhysicsState>`, is available via :ref:`general<actuator-general>` with
:ref:`dyntype<actuator-general-dyntype>` "integrator" and is expmap-only. The video on the right shows this `example
model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/sensor/actuation/orientation.xml>`__.
model <https://github.com/google-deepmind/mujoco/blob/main/test/engine/testdata/actuation/orientation.xml>`__.
The underlying :el:`general` attributes are set as follows:
========= ======= ========= =========
@@ -6056,9 +6210,8 @@ This element has custom attributes in addition to the common attributes:
:el-prefix:`actuator/` |-| **velocity** |*|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This element creates a velocity servo. Note that in order to create a PD controller, one has to define two actuators: a
position servo and a velocity servo. This is because MuJoCo actuators are SISO while a PD controller takes two control
inputs (reference position and reference velocity).
This element creates a velocity servo. Note that a PD controller with both position and velocity setpoint inputs is
provided by the :ref:`pid<actuator-pid>` actuator.
When using this actuator, it is recommended to use the implicitfast or implicit :ref:`integrators<geIntegration>`.
The underlying :el:`general` attributes are set as follows:
@@ -6802,7 +6955,7 @@ Associate this actuator with an :ref:`engine plugin<exPlugin>`. Either :at:`plug
.. _actuator-plugin-dyntype:
:at:`dyntype`: :at-val:`[none, integrator, filter, filterexact, muscle, user], "none"`
:at:`dyntype`: :at-val:`[none, integrator, filter, filterexact, pid, muscle, user], "none"`
Activation dynamics type for the actuator. The available dynamics types were already described in the :ref:`Actuation
model <geActuation>` section. If :ref:`dyntype<actuator-general-dyntype>` is not "none", an activation variable will
be added to the actuator. This variable will be added after any activation state computed by the plugin (see
@@ -10020,6 +10173,10 @@ if omitted.
.. _default-general-biasprm:
.. _default-general-velrange:
.. _default-general-ffrange:
.. _default-general-input:
.. _default-general-actearly:
@@ -10199,6 +10356,95 @@ All :ref:`intvelocity <actuator-intvelocity>` attributes are available here exce
site, refsite, tendon, slidersite, cranksite.
.. _default-pid:
.. _default-pid-ctrllimited:
.. _default-pid-forcelimited:
.. _default-pid-ctrlrange:
.. _default-pid-posrange:
.. _default-pid-velrange:
.. _default-pid-ffrange:
.. _default-pid-forcerange:
.. _default-pid-inheritrange:
.. _default-pid-gear:
.. _default-pid-damping:
.. _default-pid-armature:
.. _default-pid-cranklength:
.. _default-pid-user:
.. _default-pid-group:
.. _default-pid-nsample:
.. _default-pid-interp:
.. _default-pid-delay:
.. _default-pid-kp:
.. _default-pid-kv:
.. _default-pid-dampratio:
.. _default-pid-ki:
.. _default-pid-imax:
.. _default-pid-slewmax:
.. _default-pid-input:
:el-prefix:`default/` |-| **pid** |?|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All :ref:`pid <actuator-pid>` attributes are available here except: name, class, joint, jointinparent,
site, refsite, tendon, slidersite, cranksite.
.. _default-orientation:
.. _default-orientation-forcelimited:
.. _default-orientation-ctrlrange:
.. _default-orientation-forcerange:
.. _default-orientation-user:
.. _default-orientation-group:
.. _default-orientation-nsample:
.. _default-orientation-interp:
.. _default-orientation-delay:
.. _default-orientation-kp:
.. _default-orientation-kv:
.. _default-orientation-dampratio:
.. _default-orientation-input:
:el-prefix:`default/` |-| **orientation** |?|
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
All :ref:`orientation <actuator-orientation>` attributes are available here except: name, class, joint, site, refsite.
.. _default-damper:
.. _default-damper-forcelimited: