Rewrite mimic joints

doc/index.rst

@@ -101,35 +101,31 @@ include
 Using mimic joints in simulation
 -----------------------------------------------------------
 
-To use ``mimic`` joints in *gazebo_ros2_control* you should define its parameters to your URDF.
-We should include:
-
-* ``<mimic>`` tag to the mimicked joint `detailed manual <https://wiki.ros.org/urdf/XML/joint>`__
-* ``mimic`` and ``multiplier`` parameters to joint definition in ``<ros2_control>`` tag
+To use ``mimic`` joints in *gazebo_ros2_control* you should define its parameters in your URDF, i.e, set the ``<mimic>`` tag to the mimicked joint (see the `URDF specification <https://wiki.ros.org/urdf/XML/joint>`__)
 
 .. code-block:: xml
 
+  <joint name="right_finger_joint" type="prismatic">
+    <axis xyz="0 1 0"/>
+    <origin xyz="0.0 -0.48 1" rpy="0.0 0.0 0.0"/>
+    <parent link="base"/>
+    <child link="finger_right"/>
+    <limit effort="1000.0" lower="0" upper="0.38" velocity="10"/>
+  </joint>
   <joint name="left_finger_joint" type="prismatic">
-    <mimic joint="right_finger_joint"/>
+    <mimic joint="right_finger_joint" multiplier="1" offset="0"/>
     <axis xyz="0 1 0"/>
     <origin xyz="0.0 0.48 1" rpy="0.0 0.0 3.1415926535"/>
     <parent link="base"/>
     <child link="finger_left"/>
     <limit effort="1000.0" lower="0" upper="0.38" velocity="10"/>
   </joint>
 
+The mimic joint must not have command interfaces configured in the ``<ros2_control>`` tag, but state interfaces can be configured.
 
-.. code-block:: xml
-
-  <joint name="left_finger_joint">
-    <param name="mimic">right_finger_joint</param>
-    <param name="multiplier">1</param>
-    <command_interface name="position"/>
-    <state_interface name="position"/>
-    <state_interface name="velocity"/>
-    <state_interface name="effort"/>
-  </joint>
+.. note::
 
+  Independent of the interface type of the mimicked joint in the ``<ros2_control>`` tag, the mimic joint will use the position interface of the gazebo classic physic engine to follow the position of the mimicked joint.
 
 Add the gazebo_ros2_control plugin
 ==========================================
@@ -250,19 +246,26 @@ When the Gazebo world is launched you can run some of the following commands to
   ros2 run gazebo_ros2_control_demos example_tricycle_drive
 
 
-The following example shows parallel gripper with mimic joint:
+The following example shows a parallel gripper with a mimic joint:
+
+
+.. code-block:: shell
+
+  ros2 launch gazebo_ros2_control_demos gripper_mimic_joint_example_position.launch.py
 
 .. image:: img/gripper.gif
-  :alt: Cart
+  :alt: Gripper
 
+To demonstrate the setup of the initial position and a position-mimicked joint in
+case of an effort command interface of the joint to be mimicked, run
 
 .. code-block:: shell
 
-  ros2 launch gazebo_ros2_control_demos gripper_mimic_joint_example.launch.py
-
+  ros2 launch gazebo_ros2_control_demos gripper_mimic_joint_example_effort.launch.py
 
-Send example commands:
+instead.
 
+Send example commands with
 
 .. code-block:: shell
 

gazebo_ros2_control/src/gazebo_system.cpp

@@ -28,13 +28,6 @@
 #include "hardware_interface/lexical_casts.hpp"
 #include "hardware_interface/types/hardware_interface_type_values.hpp"
 
-struct MimicJoint
-{
-  std::size_t joint_index;
-  std::size_t mimicked_joint_index;
-  double multiplier = 1.0;
-};
-
 class gazebo_ros2_control::GazeboSystemPrivate
 {
 public:
@@ -93,7 +86,7 @@ class gazebo_ros2_control::GazeboSystemPrivate
   /// \brief handles to the FT sensors from within Gazebo
   std::vector<gazebo::sensors::ForceTorqueSensorPtr> sim_ft_sensors_;
 
-  /// \brief An array per FT sensor for 3D force and torquee
+  /// \brief An array per FT sensor for 3D force and torque
   std::vector<std::array<double, 6>> ft_sensor_data_;
 
   /// \brief state interfaces that will be exported to the Resource Manager
@@ -102,9 +95,6 @@ class gazebo_ros2_control::GazeboSystemPrivate
   /// \brief command interfaces that will be exported to the Resource Manager
   std::vector<hardware_interface::CommandInterface> command_interfaces_;
 
-  /// \brief mapping of mimicked joints to index of joint they mimic
-  std::vector<MimicJoint> mimic_joints_;
-
   // Should hold the joints if no control_mode is active
   bool hold_joints_ = true;
 };
@@ -199,36 +189,20 @@ void GazeboSystem::registerJoints(
     // Accept this joint and continue configuration
     RCLCPP_INFO_STREAM(this->nh_->get_logger(), "Loading joint: " << joint_name);
 
-    std::string suffix = "";
-
     // check if joint is mimicked
-    if (joint_info.parameters.find("mimic") != joint_info.parameters.end()) {
-      const auto mimicked_joint = joint_info.parameters.at("mimic");
-      const auto mimicked_joint_it = std::find_if(
-        hardware_info.joints.begin(), hardware_info.joints.end(),
-        [&mimicked_joint](const hardware_interface::ComponentInfo & info) {
-          return info.name == mimicked_joint;
-        });
-      if (mimicked_joint_it == hardware_info.joints.end()) {
-        throw std::runtime_error(
-                std::string("Mimicked joint '") + mimicked_joint + "' not found");
-      }
-      MimicJoint mimic_joint;
-      mimic_joint.joint_index = j;
-      mimic_joint.mimicked_joint_index = std::distance(
-        hardware_info.joints.begin(), mimicked_joint_it);
-      auto param_it = joint_info.parameters.find("multiplier");
-      if (param_it != joint_info.parameters.end()) {
-        mimic_joint.multiplier = hardware_interface::stod(joint_info.parameters.at("multiplier"));
-      } else {
-        mimic_joint.multiplier = 1.0;
-      }
+    auto it = std::find_if(
+      hardware_info.mimic_joints.begin(),
+      hardware_info.mimic_joints.end(),
+      [j](const hardware_interface::MimicJoint & mj) {
+        return mj.joint_index == j;
+      });
+
+    if (it != hardware_info.mimic_joints.end()) {
       RCLCPP_INFO_STREAM(
         this->nh_->get_logger(),
-        "Joint '" << joint_name << "'is mimicking joint '" << mimicked_joint <<
-          "' with multiplier: " << mimic_joint.multiplier);
-      this->dataPtr->mimic_joints_.push_back(mimic_joint);
-      suffix = "_mimic";
+        "Joint '" << joint_name << "' is mimicking joint '" <<
+          this->dataPtr->joint_names_.at(it->mimicked_joint_index) <<
+          "' with multiplier: " << it->multiplier << " and offset: " << it->offset);
     }
 
     RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\tState:");
@@ -263,7 +237,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.state_interfaces[i].name == "position") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t position");
         this->dataPtr->state_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_POSITION,
           &this->dataPtr->joint_position_[j]);
         initial_position = get_initial_value(joint_info.state_interfaces[i]);
@@ -272,7 +246,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.state_interfaces[i].name == "velocity") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t velocity");
         this->dataPtr->state_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_VELOCITY,
           &this->dataPtr->joint_velocity_[j]);
         initial_velocity = get_initial_value(joint_info.state_interfaces[i]);
@@ -281,7 +255,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.state_interfaces[i].name == "effort") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t effort");
         this->dataPtr->state_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_EFFORT,
           &this->dataPtr->joint_effort_[j]);
         initial_effort = get_initial_value(joint_info.state_interfaces[i]);
@@ -296,7 +270,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.command_interfaces[i].name == "position") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t position");
         this->dataPtr->command_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_POSITION,
           &this->dataPtr->joint_position_cmd_[j]);
         if (!std::isnan(initial_position)) {
@@ -310,7 +284,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.command_interfaces[i].name == "velocity") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t velocity");
         this->dataPtr->command_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_VELOCITY,
           &this->dataPtr->joint_velocity_cmd_[j]);
         if (!std::isnan(initial_velocity)) {
@@ -324,7 +298,7 @@ void GazeboSystem::registerJoints(
       if (joint_info.command_interfaces[i].name == "effort") {
         RCLCPP_INFO_STREAM(this->nh_->get_logger(), "\t\t effort");
         this->dataPtr->command_interfaces_.emplace_back(
-          joint_name + suffix,
+          joint_name,
           hardware_interface::HW_IF_EFFORT,
           &this->dataPtr->joint_effort_cmd_[j]);
         if (!std::isnan(initial_effort)) {
@@ -340,6 +314,15 @@ void GazeboSystem::registerJoints(
     // check if joint is actuated (has command interfaces) or passive
     this->dataPtr->is_joint_actuated_[j] = (joint_info.command_interfaces.size() > 0);
   }
+
+  // set initial position for mimic joints
+  for (const auto & mimic_joint : hardware_info.mimic_joints) {
+    this->dataPtr->sim_joints_[mimic_joint.joint_index]->SetPosition(
+      0,
+      mimic_joint.offset + (mimic_joint.multiplier *
+      this->dataPtr->joint_position_[mimic_joint.mimicked_joint_index]),
+      true);
+  }
 }
 
 void GazeboSystem::registerSensors(
@@ -551,10 +534,10 @@ GazeboSystem::perform_command_mode_switch(
     }
   }
 
-  // mimic joint has the same control mode as mimicked joint
-  for (const auto & mimic_joint : this->dataPtr->mimic_joints_) {
+  // mimic joint has always position control mode
+  for (const auto & mimic_joint : this->info_.mimic_joints) {
     this->dataPtr->joint_control_methods_[mimic_joint.joint_index] =
-      this->dataPtr->joint_control_methods_[mimic_joint.mimicked_joint_index];
+      static_cast<ControlMethod>(POSITION);
   }
   return hardware_interface::return_type::OK;
 }
@@ -610,25 +593,10 @@ hardware_interface::return_type GazeboSystem::write(
   rclcpp::Duration sim_period = sim_time_ros - this->dataPtr->last_update_sim_time_ros_;
 
   // set values of all mimic joints with respect to mimicked joint
-  for (const auto & mimic_joint : this->dataPtr->mimic_joints_) {
-    if (this->dataPtr->joint_control_methods_[mimic_joint.joint_index] & POSITION &&
-      this->dataPtr->joint_control_methods_[mimic_joint.mimicked_joint_index] & POSITION)
-    {
-      this->dataPtr->joint_position_cmd_[mimic_joint.joint_index] =
-        mimic_joint.multiplier *
-        this->dataPtr->joint_position_cmd_[mimic_joint.mimicked_joint_index];
-    } else if (this->dataPtr->joint_control_methods_[mimic_joint.joint_index] & VELOCITY && // NOLINT
-      this->dataPtr->joint_control_methods_[mimic_joint.mimicked_joint_index] & VELOCITY)
-    {
-      this->dataPtr->joint_velocity_cmd_[mimic_joint.joint_index] =
-        mimic_joint.multiplier *
-        this->dataPtr->joint_velocity_cmd_[mimic_joint.mimicked_joint_index];
-    } else if (this->dataPtr->joint_control_methods_[mimic_joint.joint_index] & EFFORT && // NOLINT
-      this->dataPtr->joint_control_methods_[mimic_joint.mimicked_joint_index] & EFFORT)
-    {
-      this->dataPtr->joint_effort_cmd_[mimic_joint.joint_index] =
-        mimic_joint.multiplier * this->dataPtr->joint_effort_cmd_[mimic_joint.mimicked_joint_index];
-    }
+  for (const auto & mimic_joint : this->info_.mimic_joints) {
+    this->dataPtr->joint_position_cmd_[mimic_joint.joint_index] =
+      mimic_joint.offset + mimic_joint.multiplier *
+      this->dataPtr->joint_position_[mimic_joint.mimicked_joint_index];
   }
 
   for (unsigned int j = 0; j < this->dataPtr->joint_names_.size(); j++) {

gazebo_ros2_control_demos/config/gripper_controller_effort.yaml

@@ -0,0 +1,15 @@
+controller_manager:
+  ros__parameters:
+    update_rate: 100  # Hz
+
+    gripper_controller:
+      type: forward_command_controller/ForwardCommandController
+
+    joint_state_broadcaster:
+      type: joint_state_broadcaster/JointStateBroadcaster
+
+gripper_controller:
+  ros__parameters:
+    joints:
+      - right_finger_joint
+    interface_name: effort

gazebo_ros2_control_demos/launch/gripper_mimic_joint_example.launch.py → gazebo_ros2_control_demos/launch/gripper_mimic_joint_example_effort.launch.py

@@ -33,7 +33,7 @@ def generate_launch_description():
                 [FindPackageShare(
                     'gazebo_ros2_control_demos'),
                     'urdf',
-                    'test_gripper_mimic_joint.xacro.urdf']
+                    'test_gripper_mimic_joint_effort.xacro.urdf']
             ),
         ]
     )

gazebo_ros2_control_demos/launch/gripper_mimic_joint_example_position.launch.py

@@ -0,0 +1,88 @@
+# Copyright 2022 Stogl Robotics Consulting UG (haftungsbeschränkt)
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# Author: Denis Stogl
+
+from launch import LaunchDescription
+from launch.actions import ExecuteProcess, IncludeLaunchDescription, RegisterEventHandler
+from launch.event_handlers import OnProcessExit
+from launch.launch_description_sources import PythonLaunchDescriptionSource
+from launch.substitutions import Command, FindExecutable, PathJoinSubstitution
+from launch_ros.actions import Node
+from launch_ros.substitutions import FindPackageShare
+
+
+def generate_launch_description():
+
+    robot_description_content = Command(
+        [
+            PathJoinSubstitution([FindExecutable(name='xacro')]),
+            " ",
+            PathJoinSubstitution(
+                [FindPackageShare(
+                    'gazebo_ros2_control_demos'),
+                    'urdf',
+                    'test_gripper_mimic_joint_position.xacro.urdf']
+            ),
+        ]
+    )
+    robot_description = {"robot_description": robot_description_content}
+
+    node_robot_state_publisher = Node(
+        package='robot_state_publisher',
+        executable='robot_state_publisher',
+        output='screen',
+        parameters=[robot_description]
+    )
+
+    gazebo = IncludeLaunchDescription(
+        PythonLaunchDescriptionSource(
+            [FindPackageShare("gazebo_ros"), "/launch", "/gazebo.launch.py"]
+        ),
+    )
+
+    spawn_entity = Node(package='gazebo_ros', executable='spawn_entity.py',
+                        arguments=['-topic', 'robot_description',
+                                   '-entity', 'gripper'],
+                        output='screen')
+
+    load_joint_state_controller = ExecuteProcess(
+        cmd=['ros2', 'control', 'load_controller', '--set-state', 'active',
+             'joint_state_broadcaster'],
+        output='screen'
+    )
+
+    load_gripper_controller = ExecuteProcess(
+        cmd=['ros2', 'control', 'load_controller', '--set-state', 'active',
+             'gripper_controller'],
+        output='screen'
+    )
+
+    return LaunchDescription([
+        RegisterEventHandler(
+          event_handler=OnProcessExit(
+                target_action=spawn_entity,
+                on_exit=[load_joint_state_controller],
+            )
+        ),
+        RegisterEventHandler(
+            event_handler=OnProcessExit(
+                target_action=load_joint_state_controller,
+                on_exit=[load_gripper_controller],
+            )
+        ),
+        gazebo,
+        node_robot_state_publisher,
+        spawn_entity,
+    ])