fix(franka_gazebo): fix tau_ext internal controller bug

This commit makes sure that internal controller forces are not
used while calculating the external torque when a joint is in its
joint limits.

Author: rickstaa

franka_gazebo/include/franka_gazebo/joint.h

@@ -67,6 +67,11 @@ struct Joint {
   /// be controlled.
   ControlMethod control_method = POSITION;
 
+  /// The currently CLAMPED applied command from the controller acting on this joint either in \f$N\f$ or
+  /// \f$Nm\f$ without gravity.
+  /// NOTE: Clamped to zero when the joint is in its limits.
+  double clamped_command = 0;
+
   /// The currently acting gravity force or torque acting on this joint in \f$N\f$ or \f$Nm\f$
   double gravity = 0;
 

franka_gazebo/src/franka_hw_sim.cpp

@@ -585,7 +585,9 @@ void FrankaHWSim::updateRobotState(ros::Time time) {
     }
 
     if (this->robot_initialized_) {
-      double tau_ext = joint->effort - joint->command + joint->gravity;
+      // NOTE: Here we use the clamped command to filter out the internal controller
+      // force when the joint is in its limits.
+      double tau_ext = joint->effort - joint->clamped_command + joint->gravity;
 
       // Exponential moving average filter from tau_ext -> tau_ext_hat_filtered
       this->robot_state_.tau_ext_hat_filtered[i] =

franka_gazebo/src/joint.cpp

@@ -50,6 +50,13 @@ void Joint::update(const ros::Duration& dt) {
   }
   this->jerk = (this->acceleration - this->lastAcceleration) / dt.toSec();
   this->lastAcceleration = this->acceleration;
+
+  // Store the clamped command
+  // NOTE: Clamped to zero when joint is in its joint limits.
+  this->clamped_command =
+      (this->position > this->limits.min_position && this->position < this->limits.max_position)
+          ? this->command
+          : 0.0;
 }
 
 double Joint::getLinkMass() const {
@@ -64,10 +71,10 @@ double Joint::getLinkMass() const {
 }
 
 bool Joint::isInCollision() const {
-  return std::abs(this->effort - this->command) > this->collision_threshold;
+  return std::abs(this->effort - this->clamped_command + this->gravity) > this->collision_threshold;
 }
 
 bool Joint::isInContact() const {
-  return std::abs(this->effort - this->command) > this->contact_threshold;
+  return std::abs(this->effort - this->clamped_command + this->gravity) > this->contact_threshold;
 }
 }  // namespace franka_gazebo