The torque magnitudes are plotted in  Figure 4  . In the model-based impedance
control they were on the same order of magnitude as in the case with a single
prismatic impedance-controlled joint, i.e., 10  0  …10  −1  Nm for joint 1 and
10  −1  …10  −2  Nm for the subsequent joints although on average the loads on
the joints were on average 38% higher for the proposed architecture. The peak
torques in the joints are summarized in  Table 2  . Importantly, the torque
about joint 2 was 67 × 10  −3  Nm for the proposed architecture with the
prismatic impedance-controlled joint instead of 4 × 10  −2  Nm in the case of
the baseline model-based impedance control. In the pose which the robot had
during the contact (  Figure 3  ), the torque on this joint acted about axis
close to the y-axis of the base, and was significantly contributed to by the
contact force via the long “lever arm” of the whole manipulator. The 40% lower
torque on joint 2 in the case of the proposed impedance controller translated
to a much lower disturbance of the base about the y-axis: 24 × 10  −3  °/s
with the proposed control instead of the −6 × 10  −2  °/s with the baseline
impedance control. The reason for this behavior is the following: in the case
of the baseline controller, where all the joints took part in realizing the
impedance control behavior at the end effector, the masses and inertias of all
the links preceding the end effector needed to be suitably accelerated, while
in the case of the proposed architecture, in principle, just the mass of the
end effector needed to be accelerated to realize the impedance behavior of the
end effector.


**Table 3.** Velocity and angular rates of the center of mass of the satellite
body at the end of simulation.


Line Spacing:


© 1996-2024 MDPI (Basel, Switzerland) unless otherwise stated


##  3\. Simulation


[ xacro macros model not showing up in rviz(noetic) ](/question/379957/xacro-
macros-model-not-showing-up-in-rviznoetic/)


J  S  =  [  I  r  ˜  ees  T  0  I  ]


where finally the Generalized Jacobian Matrix GJM emerges as **J** D


[ ![lockandfire gravatar image](/m/default/media/images/nophoto.png?v=27)
](/users/18746/lockandfire/) [ lockandfire ](/users/18746/lockandfire/) (
2014-07-22 02:52:07 -0500  )  edit


M  m  (  q  p  )  =  N  −  [  D  M  F  M  ]  T  [  A  B  B  T  E  M  ]  −  1
[  D  M  F  M  ]


const std::string& hardware_interface = joint_interfaces.front();


[ Submit to this Journal
](https://susy.mdpi.com/user/manuscripts/upload?form%5Bjournal_id%5D%3D145) [
Review for this Journal ](https://susy.mdpi.com/volunteer/journals/review) [
Propose a Special Issue ](/journalproposal/sendproposalspecialissue/aerospace)


**Figure 4.** Comparison of time histories of the torques in robot joints.
**Left** : model-based full robot impedance control, **right** : impedance
control with single prismatic joint at the end effector.


The virtual trajectory is useful in its generality since it can be defined in
terms of position space, as well as velocity or acceleration spaces and need
not be within the reachable space of the manipulator [  5  ]. In a basic form,
the mechanical impedance is typically described to be composed of elements
which exhibit an inertia-like or mass-like behavior, represented below as
matrix **M** d  , with damping-like behavior described by **D** and elastic-
like behavior described by matrix **E** .


      * [ Palma, P. ](http://doaj.org/search/articles?source=%7B%22query%22%3A%7B%22query_string%22%3A%7B%22query%22%3A%22%5C%22Piotr%20Palma%5C%22%22%2C%22default_operator%22%3A%22AND%22%2C%22default_field%22%3A%22bibjson.author.name%22%7D%7D%7D)
      *       * [ Seweryn, K. ](http://doaj.org/search/articles?source=%7B%22query%22%3A%7B%22query_string%22%3A%7B%22query%22%3A%22%5C%22Karol%20Seweryn%5C%22%22%2C%22default_operator%22%3A%22AND%22%2C%22default_field%22%3A%22bibjson.author.name%22%7D%7D%7D)
      *       * [ Rybus, T. ](http://doaj.org/search/articles?source=%7B%22query%22%3A%7B%22query_string%22%3A%7B%22query%22%3A%22%5C%22Tomasz%20Rybus%5C%22%22%2C%22default_operator%22%3A%22AND%22%2C%22default_field%22%3A%22bibjson.author.name%22%7D%7D%7D)
      *     * on Google Scholar


**Table 2.** Comparison of peak torque loads in robot joints.


**MDPI and ACS Style**


Follow


                case POSITION_PID:
                {
                    double error;
                    switch (joint_types_[j])
                    {
                        case urdf::Joint::REVOLUTE:
                            angles::shortest_angular_distance_with_limits(joint_position_[j],
                                                                          joint_position_command_[j],
                                                                          joint_lower_limits_[j],
                                                                          joint_upper_limits_[j],
                                                                          error);
                            break;
                        case urdf::Joint::CONTINUOUS:
                            error = angles::shortest_angular_distance(joint_position_[j],
                                                                      joint_position_command_[j]);
                            break;
                        default:
                            error = joint_position_command_[j] - joint_position_[j];
                    }


add a comment


* Table of Contents


##  Abstract


[ Descartes package in ROS Kinetic Error ](/question/294176/descartes-package-
in-ros-kinetic-error/)


The success of space missions like capture-and-deorbit or capture-and-service
relies on the ability of the capturing satellite to establish a stable
mechanical connection by its gripping tool with the object being intercepted.
Most of the potential objects of capture missions are not equipped with
dedicated docking ports; hence, the satellite robot intercepting them will
have to provide the mechanical compliance necessary for the safe establishment
of contact between the two structures. Articulated robotic arms with
controlled mechanical impedance are one set of promising solutions for this
challenge. In this study, the authors discuss how the mechanical impedance
realized only along a single axis can be useful for facilitating the contact
between the manipulator arm’s end effector of a free-floating robot and an
uncooperative object in microgravity. By distinguishing a dominant direction
in the final approach and contact establishment maneuver, the need for
impedance control of six degrees of freedom may be relaxed, and a single
prismatic joint with controlled impedance can be used at the end effector.
Such architecture is simulated and compared with the full model-based six-
degree-of-freedom Cartesian impedance control of a free-floating manipulator.
Authors then discuss the limitations and possibilities of such architecture in
a potential practical setting.


* [ indigo ](/questions/scope:all/sort:activity-desc/tags:indigo/page:1/)


                    const joint_limits_interface::PositionJointSaturationHandle
                            sat_handle(joint_handle, limits);
                    pj_sat_interface_.registerHandle(sat_handle);
                }
                    break;
                case VELOCITY:
                {
                    const joint_limits_interface::VelocityJointSaturationHandle
                            sat_handle(joint_handle, limits);
                    vj_sat_interface_.registerHandle(sat_handle);
                }
                    break;
            }
        }
    }


You can make submissions to other journals [ here
](https://susy.mdpi.com/user/manuscripts/upload) .


            // Decide what kind of command interface this actuator/joint has
            hardware_interface::JointHandle joint_handle;
            hardware_interface::PosVelJointHandle jointHandlePosVel;
            if(hardware_interface == "EffortJointInterface" || hardware_interface == "hardware_interface/EffortJointInterface")
            {
                // Create effort joint interface
                joint_control_methods_[j] = EFFORT;
                joint_handle = hardware_interface::JointHandle(js_interface_.getHandle(joint_names_[j]),
                                                               &joint_effort_command_[j]);
                ej_interface_.registerHandle(joint_handle);
            }
            else if(hardware_interface == "PositionJointInterface" || hardware_interface == "hardware_interface/PositionJointInterface")
            {
                // Create position joint interface
                joint_control_methods_[j] = POSITION;
                joint_handle = hardware_interface::JointHandle(js_interface_.getHandle(joint_names_[j]),
                                                               &joint_position_command_[j]);
                pj_interface_.registerHandle(joint_handle);
            }
            else if(hardware_interface == "VelocityJointInterface" || hardware_interface == "hardware_interface/VelocityJointInterface")
            {
                // Create velocity joint interface
                joint_control_methods_[j] = VELOCITY;
                joint_handle = hardware_interface::JointHandle(js_interface_.getHandle(joint_names_[j]),
                                                               &joint_velocity_command_[j]);
                vj_interface_.registerHandle(joint_handle);
            }
            else if(hardware_interface == "PosVelJointInterface" || hardware_interface == "hardware_interface/PosVelJointInterface")
            {
                // Create velocity joint interface
                joint_control_methods_[j] = POS_VEL;


Duplicate with: [
http://answers.gazebosim.org/question/6654/gazeboos-x-109-no-valid-hardware-
interface-element/
](http://answers.gazebosim.org/question/6654/gazeboos-x-109-no-valid-hardware-
interface-element/%3C/p%3E)


**Figure 2.** Various gripping strategies for interception of a space object.
Dominant direction in each case is shown by the arrow.


**Figure 5.** Contact force between the spheres simulating the end effector
and the target. **Left** : model-based full robot impedance control, **right**
: impedance control with a single prismatic joint at the end effector.


###  MDPI Initiatives


[  P  L  ]  =  H  2  [  v  s  ω  s  ]  \+  H  3  θ  ˙  =  0


Q  =  M  (  q  p  )  q  ˙  v  \+  C  (  q  ˙  p  ,  q  p  )  q  ˙  v


Back to Top  Top


        if (has_soft_limits)
        {
            switch (ctrl_method)
            {
                case EFFORT:
                {
                    const joint_limits_interface::EffortJointSoftLimitsHandle
                            limits_handle(joint_handle, limits, soft_limits);
                    ej_limits_interface_.registerHandle(limits_handle);
                }
                    break;
                case POSITION:
                {
                    const joint_limits_interface::PositionJointSoftLimitsHandle
                            limits_handle(joint_handle, limits, soft_limits);
                    pj_limits_interface_.registerHandle(limits_handle);
                }
                    break;
                case VELOCITY:
                {
                    const joint_limits_interface::VelocityJointSoftLimitsHandle
                            limits_handle(joint_handle, limits, soft_limits);
                    vj_limits_interface_.registerHandle(limits_handle);
                }
                    break;
            }
        }
        else
        {
            switch (ctrl_method)
            {
                case EFFORT:
                {
                    const joint_limits_interface::EffortJointSaturationHandle
                            sat_handle(joint_handle, limits);
                    ej_sat_interface_.registerHandle(sat_handle);
                }
                    break;
                case POSITION:
                {


General robotic manipulator dynamics are modeled by the configuration-
dependent inertia  I  (  θ  )  , configuration- and velocity-dependent
inertial coupling between the links, e.g., Coriolis and centrifugal effects  C
c  (  θ  ,  ω  )  **,** and  V  c  (  θ  )  the velocity-dependent terms,
e.g., the viscous friction. There, static forces  S  (  θ  )  such as
gravitational loads are assumed to be zero, since the application we are
discussing is set in the microgravity context of an on-orbit operation. The
manipulator control torques are denoted as **T act  ** and **T** int  , and
**F** int  are the torques and force due to interaction at the interface.


        if (*joint_type == urdf::Joint::UNKNOWN)
        {
            // Infer the joint type.


**AMA Style**


Feature papers are submitted upon individual invitation or recommendation by
the scientific editors and must receive positive feedback from the reviewers.


* Contact force magnitude;


_Attention:_ answers.gazebosim.org is deprecated as of August the 11th, 2023.
Please visit [ robotics.stackexchange.com ](http://robotics.stackexchange.com)
to ask a new question. This site will remain online in read-only mode during
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the corresponding questions on Robotics Stack Exchange. Additional details are
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gazebo-answers-migration-schedule/2185) .


[ ![](https://pub.mdpi-res.com/img/design/mdpi-pub-logo-black-
small1.svg?da3a8dcae975a41c?1713167732) ](/)


[ ![ROS Answers logo](/m/ros/media/images/logoros.png?v=28) ](/questions/)


##  Cite


##  1\. Introduction


[ __ ](/cdn-cgi/l/email-
protection#17387479733a74707e387b38727a767e7b3a676578637274637e78793427272721202327732621272627202423262026212671227627242622272422762723262f)


* [ gazebo-ros-control ](/questions/scope:all/sort:activity-desc/tags:gazebo-ros-control/page:1/)


The differentiation of the state vector yields the following expression, where
T  Θ  transforms the angular velocities into the time derivatives of the Euler
angles:


##  Conflicts of Interest


|  [ Ask Your Question ](/questions/ask/)
---|---|---|---

6


Using Prismatic Joint in Gazebo


In this section we briefly recall the Cartesian impedance control after [  5
,  31  ] and show how the dynamics model of the free-floating satellite robot
is incorporated into the control law. We, with a slight abuse of the notation,
reuse the symbol  θ  in this section to symbolize a vector of rotational
configuration coordinates of a robot with purely rotational joints, whereas
outside of the description of model-based Cartesian impedance control, this
symbol retains its meaning set in  Section 2.3  .


Position-based approach, where typically the controller’s outer loop gives the
desired position based on the desired impedance parameters and feedback
information about interaction force, and the inner loop tracks the position
simply as a position servo,


Sort by »  [ oldest  ](/question/186681/no-valid-hardware-interface-element-
found-in-joint/?sort=oldest#sort-top) [ newest  ](/question/186681/no-valid-
hardware-interface-element-found-in-joint/?sort=latest#sort-top) [ most voted
](/question/186681/no-valid-hardware-interface-element-found-in-
joint/?sort=votes#sort-top)


[ Download PDF ](/2226-4310/9/8/406/pdf?version=1658994379)
Download PDF with Cover
Download XML
[ Download Epub ](/2226-4310/9/8/406/epub)


[ tags ](/tags/) [ users ](/users/) [ badges ](/badges/)


Disclaimer/Publisher’s Note: The statements, opinions and data contained in
all publications are solely those of the individual author(s) and
contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s)
disclaim responsibility for any injury to people or property resulting from
any ideas, methods, instructions or products referred to in the content.


q  v  =  [  d  r  s  dt  T  Θ  −  1  d  Θ  s  dt  d  θ  dt  ]  =  [  v  s  ω
s  θ  ˙  ]


Having arrived at the kinematic expressions for the velocities, the model of
dynamics of the satellite manipulator system can be formulated.


The scalar parameters for the mechanical impedance of the prismatic joint in
the second simulation were set to be  M  d  =  4  kg  ,  D  =  500  Ns  m  and
E  =  40  N  /  m  with the help of the VIM method proposed in [  5  ]. The
Cartesian controller tracking the virtual trajectory in this case used the
same gain values as in the work [  20  ] with the matrix sizes adjusted
accordingly.


[ Overview ](/about) [ Contact ](/about/contact) [ Careers
](https://careers.mdpi.com) [ News ](/about/announcements) [ Press
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Altmetric  _share_ Share  _announcement_ Help  [ _format_quote_ Cite
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"Discuss in Sciprofiles") _thumb_up_ ...  Endorse  _textsms_ ...  Comment


Karol Seweryn


The simulations of a free-floating space robot concerning both of the proposed
end effector impedance control methods were performed using the simulation
tool developed at the Space Research Centre of the Polish Academy of Sciences
and used in numerous research studies [  11  ,  14  ,  33  ]. The robot arm
configuration used in the simulation of motion and in trajectory planning was
7-DoF for both cases. In case of the configuration with the prismatic
compliant stage, there was an additional prismatic joint providing mechanical
impedance between the joint no. 7 and the end effector. This joint was not
used in trajectory planning and was initialized to its neutral position in
which the actual end effector center coincided with the virtual trajectory
point  x  0  .


#  Impedance Control Using Selected Compliant Prismatic Joint in a Free-
Floating Space Manipulator


[ Article Processing Charges ](/apc) [ Pay an Invoice ](/about/payment) [ Open
Access Policy ](/openaccess) [ Contact MDPI ](/about/contact) [ Jobs at MDPI
](https://careers.mdpi.com)


I can't help you with your actual problem, but might I suggest you change your
question title to something a little more descriptive? Your current title is
rather vague.


[ about ](/about/) |  [ faq ](/faq/) |  [ help ](/help/ "help") |  [ privacy
policy ](/privacy/) |  [ terms of service ](/terms/)


Palma, P.; Seweryn, K.; Rybus, T. Impedance Control Using Selected Compliant
Prismatic Joint in a Free-Floating Space Manipulator. _Aerospace_ **2022** ,
_9_ , 406. https://doi.org/10.3390/aerospace9080406


By using the approach used in the paper [  17  ] and using constrained
Lagrangian formulation, the mass matrix becomes:


            // Get the gazebo joint that corresponds to the robot joint.
            //ROS_DEBUG_STREAM_NAMED("default_robot_hw_sim", "Getting pointer to gazebo joint: "
            //  << joint_names_[j]);
            gazebo::physics::JointPtr joint = parent_model->GetJoint(joint_names_[j]);
            if (!joint)
            {
                ROS_ERROR_STREAM("This robot has a joint named \"" << joint_names_[j]
                                                                   << "\" which is not in the gazebo model.");
                return false;
            }
            sim_joints_.push_back(joint);
            if(!joint_control_methods_[j] != POS_VEL) {
                registerJointLimits(joint_names_[j], joint_handle, joint_control_methods_[j],
                                    joint_limit_nh, urdf_model,
                                    &joint_types_[j], &joint_lower_limits_[j], &joint_upper_limits_[j],
                                    &joint_effort_limits_[j]);
            }
            else {
                registerJointLimits(joint_names_[j], jointHandlePosVel, joint_control_methods_[j],
                                    joint_limit_nh, urdf_model,
                                    &joint_types_[j], &joint_lower_limits_[j], &joint_upper_limits_[j],
                                    &joint_effort_limits_[j]);


##  JSmol Viewer


            std::vector<std::string> joint_interfaces = transmissions[j].joints_[0].hardware_interfaces_;
            if (joint_interfaces.empty() &&
                !(transmissions[j].actuators_.empty()) &&
                !(transmissions[j].actuators_[0].hardware_interfaces_.empty()))
            {
                // TODO: Deprecate HW interface specification in actuators in ROS J
                joint_interfaces = transmissions[j].actuators_[0].hardware_interfaces_;
                ROS_WARN_STREAM_NAMED("default_robot_hw_sim", "The <hardware_interface> element of tranmission " <<
                                                                                transmissions[j].name_ << " should be nested inside the <joint> element, not <actuator>. " <<
                                                                                "The transmission will be properly loaded, but please update " <<
                                                                                "your robot model to remain compatible with future versions of the plugin.");
            }
            if (joint_interfaces.empty())
            {
                ROS_WARN_STREAM_NAMED("default_robot_hw_sim", "Joint " << transmissions[j].joints_[0].name_ <<
                                                                       " of transmission " << transmissions[j].name_ << " does not specify any hardware interface. " <<
                                                                       "Not adding it to the robot hardware simulation.");
                continue;
            }
            else if (joint_interfaces.size() > 1)
            {
                ROS_WARN_STREAM_NAMED("default_robot_hw_sim", "Joint " << transmissions[j].joints_[0].name_ <<
                                                                       " of transmission " << transmissions[j].name_ << " specifies multiple hardware interfaces. " <<
                                                                       "Currently the default robot hardware simulation interface only supports one. Using the first entry!");
                //continue;
            }


[ Versions Notes ](/2226-4310/9/8/406/notes)


##  Share Link


_Arial_ _Georgia_ _Verdana_


Z  (  s  )  =  F  (  s  )  X  ˙  (  s  )


Page


X  r  =  X  −  X  0


namespace gazebo_ros_control
{


        // Initialize the emergency stop code.
        e_stop_active_ = false;
        last_e_stop_active_ = false;


[ __ ](/questions/) |


* [ gazebo ](/questions/scope:all/sort:activity-desc/tags:gazebo/page:1/)


_Aerospace_ **2022** , _9_ (8), 406; [
https://doi.org/10.3390/aerospace9080406
](https://doi.org/10.3390/aerospace9080406)


###  Guidelines


##  Question Tools


Please note: ROS Answers requires javascript to work properly, please enable
javascript in your browser, [ here is how
](https://www.google.com/support/bin/answer.py?answer=23852)


Palma P, Seweryn K, Rybus T. Impedance Control Using Selected Compliant
Prismatic Joint in a Free-Floating Space Manipulator. _Aerospace_ . 2022;
9(8):406. https://doi.org/10.3390/aerospace9080406


##  References


With the advancement of space exploration leaving a substantial amount of
large disused objects in orbit as well as the recently growing interest in
extending the life of existing satellites by in-orbit servicing, the relevance
of satellite robots capable of mechanically manipulating those orbiting
objects is growing. The mitigation of space debris is an important priority of
space exploration agencies [  1  ]. A collision of two objects in space above
the size of approximately 10 cm is going to produce objects capable of causing
further destruction of in-orbit equipment, producing again objects of a size
sufficient to continue this perpetual destruction and littering. The highest
risk is posed by large defunct satellites occupying important and populated
orbits such as the geostationary or low Earth orbits [  2  ]. The successful
interception of large objects in orbit opens possibilities to stop them from
becoming dangerous space debris either by deorbiting them safely or extending
their useful life by providing refueling or maneuverability. In either case,
the success of the capture operation depends on the ability of the robotic arm
to bring its end effector in contact with the object being captured and
establish a mechanical connection between them.


L  =  L  0  \+  r  s  ×  P


##  Stats


Last updated: **Jul 20 '14**


  *[
              2014-07-15 14:39:57 -0500
             ]: 2014-07-15 14:39:57 -0500
  *[
              2014-07-18 13:32:04 -0500
             ]: 2014-07-18 13:32:04 -0500
  *[
             2014-07-15 14:58:07 -0500
            ]: 2014-07-15 14:58:07 -0500
  *[
             2014-07-15 15:31:30 -0500
            ]: 2014-07-15 15:31:30 -0500
  *[
              2014-07-20 13:58:04 -0500
             ]: 2014-07-20 13:58:04 -0500
  *[
              2014-07-20 13:59:30 -0500
             ]: 2014-07-20 13:59:30 -0500
  *[
             2014-07-20 20:22:53 -0500
            ]: 2014-07-20 20:22:53 -0500
  *[
             2014-07-22 02:52:07 -0500
            ]: 2014-07-22 02:52:07 -0500
  *[
             2014-08-02 01:49:18 -0500
            ]: 2014-08-02 01:49:18 -0500
  *[
             2014-08-02 01:50:42 -0500
            ]: 2014-08-02 01:50:42 -0500
  *[
             2015-01-10 18:20:25 -0500
            ]: 2015-01-10 18:20:25 -0500
  *[
        2014-07-15 14:39:57 -0500
       ]: 2014-07-15 14:39:57 -0500
  *[
        2024-04-16 00:59:02 -0500
       ]: 2024-04-16 00:59:02 -0500


During the contact event, the momentum exchange between both the target and
the free-floating robot took place causing the disturbance to the
satellite–robot system. The disturbance was recorded in the form of linear and
angular velocities of the center of mass of the robot’s satellite base. They
are summarized in  Table 3  .


####  2.6. Cartesian Impedance Control


[ Get Support ](/about/contactform)


Seen: **9,457 times**


                case POSITION:
#if GAZEBO_MAJOR_VERSION >= 4
                    sim_joints_[j]->SetPosition(0, joint_position_command_[j]);
#else
                    sim_joints_[j]->SetAngle(0, joint_position_command_[j]);
#endif
                    break;


The impedance parameters selection and optimization could likely lead to
closing the gap between the sets of results eventually. Rather than
elaborating on the impedance parameters selection method, the purpose and
scope of this work was to verify the possibility of replacing the full robot
model-based impedance control with the simplified scheme for the free-floating
robot. The initial expectation was to arrive with the prismatic joint approach
at the same order of magnitude of the joint torques, contact force and base
disturbance as in the full model-based impedance control of the robot. Even
without more accurate impedance parameters selection, the results met that
criteria.


Submission received: 7 June 2022  /  Revised: 12 July 2022  /  Accepted: 20
July 2022  /  Published: 28 July 2022


c  i  j  =  ∑  k  =  1  n  1  2  (  d  d  q  k  m  i  j  \+  d  d  q  j  m  i
k  −  d  d  q  i  m  j  k  )  q  ˙  i


Find support for a specific problem in the support section of our website.


P.P. would like to thank the Space Research Centre for providing resources
necessary to conduct and publish this research.


![](/bundles/mdpisciprofileslink/img/unknown-user.png) Piotr Palma


##  Notice


The text is organized as follows: In  Section 2  , the mathematical model of
the system is elaborated.  Section 2.2  derives the equations of motion of the
space robot and the model-based Cartesian impedance control law for a free-
floating robot. The simplified architecture of a 7-DoF space robot with only
one compliant joint is presented and described in  Section 2.8  . In  Section
3  , the simulation environment for the space robotics platforms is used to
simulate two free-floating impedance-controlled robot architectures: the full
model-based Cartesian impedance control from [  11  ] and the one based on a
single-axis prismatic joint with impedance control. Both share the same GJM.
Section 4  discusses the results obtained with both approaches to impedance
control and compares their performance and implementational complexity.


####  3.3. Results


        if (*joint_type == urdf::Joint::UNKNOWN)
        {
            // Infer the joint type.


            // Create joint state interface for all joints
            js_interface_.registerHandle(hardware_interface::JointStateHandle(
                    joint_names_[j], &joint_position_[j], &joint_velocity_[j], &joint_effort_[j]));


A simple control strategy for a trajectory-following task in Cartesian
coordinates can be realized for a space robot using the GJM. This strategy can
be used to bring the end effector to follow the virtual trajectory required by
the impedance control.


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    void Komodo2RobotHWSim::eStopActive(const bool active)
    {
        e_stop_active_ = active;
    }


This way, the impedance control law does not involve the whole state vector of
the robot, only the prismatic stage. Defining the impedance control law in the
above way is useful for practical applications, e.g., involving an
electromagnetic linear actuator, where the force  F  (  t  )  after scaling by
a motor force constant becomes the immediate input for the actuator’s
quadrature current controller [  32  ].


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Z  (  s  )  =  M  d  s  \+  D  \+  E  /  s


d  V  dt  =  J  M  (  θ  )  d  ω  dt  \+  G  (  θ  ,  ω  )


##  Article Menu


Issue


[ none ](/questions/scope:all/sort:activity-desc/tags:none/page:1/) ×


D  M  =  ∑  i  =  1  n  (  m  i  J  T  i  )


The equation relates the driving torques **T** act  of the joints to the end
effector’s deviation from the virtual trajectory, parametrized by desired
impedance terms, in essence expressing the Cartesian impedance control law for
the robot on a free-floating satellite base.


Since this study did not consider any specific gripper architecture, the
target and end effector were simulated by spheres. The mass of the simulated
target body was 1000 kg had uniform mass distribution. The satellite base mass
was 100 kg and had inertia  I  xx  = 2.8 kgm  2  ,  I  yy  = 6.0 kgm  2  and
I  zz  = 7.4 kgm  2  with zero off-axis components.


* [ gazebo ](/questions/scope:all/sort:activity-desc/tags:gazebo/page:1/)


F  M  =  ∑  i  =  1  n  (  I  i  J  R  i  \+  m  i  r  ˜  i  _  s  J  T  i  )


[ ![Gazebo logo](/upfiles/gazebo_logo_1.png) ](/questions/)


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[ Joints not independent ](/question/16059/joints-not-independent/)


####  2.5. The Impedance Control


case POS_VEL:


##  Author Services


        /*  if (has_soft_limits)
          {
              switch (ctrl_method)
              {
                  case POS_VEL:
                  {
                      const joint_limits_interface::PositionJointSoftLimitsHandle limits_handle(joint_handle., limits, soft_limits);
                      pj_limits_interface_.registerHandle(limits_handle);
                  }
                      break;
              };
          }
          else
          {
              switch (ctrl_method)
              {
                  case EFFORT:
                  {
                      const joint_limits_interface::EffortJointSaturationHandle
                              sat_handle(joint_handle, limits);
                      ej_sat_interface_.registerHandle(sat_handle);
                  }
                      break;
                  case POSITION:
                  {
                      const joint_limits_interface::PositionJointSaturationHandle
                              sat_handle(joint_handle, limits);
                      pj_sat_interface_.registerHandle(sat_handle);
                  }
                      break;
                  case VELOCITY:
                  {
                      const joint_limits_interface::VelocityJointSaturationHandle
                              sat_handle(joint_handle, limits);
                      vj_sat_interface_.registerHandle(sat_handle);
                  }
                      break;
              }
          }*/
    }


v  ee  =  v  s  \+  ω  s  ×  (  r  ee  −  r  s  )  \+  ∑  i  =  1  n  [  k  i
×  (  r  ee  −  r  i  )  ]  θ  ˙  i  \+  k  prism  λ  ˙


**Figure 5.** Contact force between the spheres simulating the end effector
and the target. **Left** : model-based full robot impedance control, **right**
: impedance control with a single prismatic joint at the end effector.


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  28. Angeles, J.  Fundamentals of Robotic Mechanical Systems: Theory, Methods, and Algorithms  ; Springer: New York, NY, USA, 1995. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Fundamentals+of+Robotic+Mechanical+Systems:+Theory,+Methods,+and+Algorithms&author=Angeles,+J.&publication_year=1995) ]
  29. Spong, M.W.; Hutchinson, S.; Vidyasagar, M.  Robot Modeling and Control  ; Wiley: New York, NY, USA, 2020. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Robot+Modeling+and+Control&author=Spong,+M.W.&author=Hutchinson,+S.&author=Vidyasagar,+M.&publication_year=2020) ]
  30. Rybus, T.; Seweryn, K.; Sasiadek, J.Z. Trajectory optimization of space manipulator with non-zero angular momentum during orbital capture maneuver. In Proceedings of the AIAA Guidance, Navigation, and Control Conference, San Diego, CA, USA, 4–8 January 2016; p. 885. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Trajectory+optimization+of+space+manipulator+with+non-zero+angular+momentum+during+orbital+capture+maneuver&conference=Proceedings+of+the+AIAA+Guidance,+Navigation,+and+Control+Conference&author=Rybus,+T.&author=Seweryn,+K.&author=Sasiadek,+J.Z.&publication_year=2016&pages=885) ]
  31. Hogan, N. Impedance control of industrial robots.  Robot. Comput. Manuf.  **1984** ,  1  , 97–113. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Impedance+control+of+industrial+robots&author=Hogan,+N.&publication_year=1984&journal=Robot.+Comput.+Manuf.&volume=1&pages=97%E2%80%93113&doi=10.1016/0736-5845\(84\)90084-X) ] [ [ CrossRef ](https://doi.org/10.1016/0736-5845\(84\)90084-X) ]
  32. Palma, P. Linear Electromagnetic Actuator with Mechanical Impedance Control for Experimental Investigation of Landing and Transient Contact in Low Gravity.  Mech. Mach. Sci.  **2019** ,  73  , 2691–2700. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Linear+Electromagnetic+Actuator+with+Mechanical+Impedance+Control+for+Experimental+Investigation+of+Landing+and+Transient+Contact+in+Low+Gravity&author=Palma,+P.&publication_year=2019&journal=Mech.+Mach.+Sci.&volume=73&pages=2691%E2%80%932700) ]
  33. Basmadji, F.L.; Chmaj, G.; Rybus, T.; Seweryn, K. Microgravity testbed for the development of space robot Conference, control systems and the demonstration of orbital maneuvers.  SPIE  **2019** ,  11176  , 1158–1172. [ [ Google Scholar ](https://scholar.google.com/scholar_lookup?title=Microgravity+testbed+for+the+development+of+space+robot+Conference,+control+systems+and+the+demonstration+of+orbital+maneuvers&author=Basmadji,+F.L.&author=Chmaj,+G.&author=Rybus,+T.&author=Seweryn,+K.&publication_year=2019&journal=SPIE&volume=11176&pages=1158%E2%80%931172) ]


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        if (limits.has_position_limits)
        {
            *lower_limit = limits.min_position;
            *upper_limit = limits.max_position;
        }
        if (limits.has_effort_limits)
            *effort_limit = limits.max_effort;


[ spawn urdf model in gazebo by C++ ](/question/171346/spawn-urdf-model-in-
gazebo-by-c/)


    <xacro:right name="right"/>

    <joint name="dummy_joint_1" type="fixed">
        <parent link="dummy_link_2" />
        <child link="base_link_right" />
        <axis xyz="0 0 1"/>
    </joint>

    <xacro:left name="left"/>

    <joint name="dummy_joint_2" type="fixed">
        <parent link="dummy_link_2" />
        <child link="base_link_left" />
        <axis xyz="0 0 1"/>
    </joint>

    <link name="end_link">
        <mu1>0.2</mu1>
        <mu2>0.1</mu2>
        <visual>
            <geometry>
                <cylinder radius="0.0025" length="0.005" />
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0" />
            <material name="blue">
                <color rgba="0 0 1 1" />
            </material>
        </visual>
        <collision>
            <geometry>
                <cylinder radius="0.0025" length="0.005" />
            </geometry>
            <origin rpy="0 0 0" xyz="0 0 0" />
        </collision>
        <inertial>
            <origin xyz="0.0 0.0 0.0025" rpy="0.0 0.0 0.0" />
            <mass value="2.0" />
            <inertia ixx="5.0" ixy="0.0" ixz="0.0" iyy="5.0" iyz="0.0" izz="5.0" />
        </inertial>


Keywords:


[ **updated 2014-07-18 13:32:04 -0500  ** ](/questions/186681/revisions/)


Editor’s Choice articles are based on recommendations by the scientific
editors of MDPI journals from around the world. Editors select a small number
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The authors declare no conflict of interest.


    bool Komodo2RobotHWSim::initSim(
            const std::string& robot_namespace,
            ros::NodeHandle model_nh,
            gazebo::physics::ModelPtr parent_model,
            const urdf::Model *const urdf_model,
            std::vector<transmission_interface::TransmissionInfo> transmissions)
    {
        // getJointLimits() searches joint_limit_nh for joint limit parameters. The format of each
        // parameter's name is "joint_limits/<joint name>". An example is "joint_limits/axle_joint".
        const ros::NodeHandle joint_limit_nh(model_nh, robot_namespace);


](/topics)


[ **updated 2014-07-20 13:59:30 -0500  ** ](/answers/187192/revisions/)


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Read more about our cookies [ here ](/about/privacy) .


The schematic of the manipulator and target initial positions is depicted in
Figure 3  . The robot pose was initialized with the end effector in a position
at the beginning of the final approach as shown in  Figure 2  , which in this
case was 5 mm away from the target. Both the end effector center and the
target body center lay on a straight line which was then followed during the
approach to contact. This line defined the dominant direction and coincided
with the axis of the prismatic stage.


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      * [ For Conference Organizers ](/conference_organizers)


with


                case VELOCITY_PID:
                    double error;
                    if (e_stop_active_)
                        error = -joint_velocity_[j];
                    else
                        error = joint_velocity_command_[j] - joint_velocity_[j];
                    const double effort_limit = joint_effort_limits_[j];
                    const double effort = clamp(pid_controllers_[j].computeCommand(error, period),
                                                -effort_limit, effort_limit);
                    sim_joints_[j]->SetForce(0, effort);
                    break;


[ ![Logo](../../../../_static/logo_ros-controls.png) ](../../../../index.html)
  * [ Getting Started ](../../../getting_started/getting_started.html)
  * [ ros2_control ](../../../ros2_control/doc/index.html)
  * [ ros2_controllers ](../../doc/controllers_index.html)
    * [ Guidelines and Best Practices ](../../doc/controllers_index.html#guidelines-and-best-practices)
    * [ Controllers for Mobile Robots ](../../doc/controllers_index.html#controllers-for-mobile-robots)
    * [ Controllers for Manipulators and Other Robots ](../../doc/controllers_index.html#controllers-for-manipulators-and-other-robots)
      * [ Admittance Controller ](../../admittance_controller/doc/userdoc.html)
      * [ Effort Controllers ](../../effort_controllers/doc/userdoc.html)
      * [ Forward Command Controller ](../../forward_command_controller/doc/userdoc.html)
      * [ Gripper Controller ](../../gripper_controllers/doc/userdoc.html)
      * Joint Trajectory Controller
        * Hardware interface types
        * Other features
        * Using Joint Trajectory Controller(s)
          * Preemption policy
          * Description of controller’s interfaces
            * References
            * States
            * Commands
            * Actions
            * Subscriber
            * Publishers
            * Services
        * Further information
          * [ Trajectory Representation ](trajectory.html)
          * [ Trajectory Replacement ](trajectory.html#trajectory-replacement)
          * [ joint_trajectory_controller Parameters ](parameters.html)
          * [ rqt_joint_trajectory_controller ](../../rqt_joint_trajectory_controller/doc/userdoc.html)
      * [ Position Controllers ](../../position_controllers/doc/userdoc.html)
      * [ Velocity Controllers ](../../velocity_controllers/doc/userdoc.html)
    * [ Broadcasters ](../../doc/controllers_index.html#broadcasters)
  * [ Demos ](../../../ros2_control_demos/doc/index.html)
  * [ Command Line Interface ](../../../ros2_control/ros2controlcli/doc/userdoc.html)
  * [ Simulator Integrations ](../../../simulators/simulators.html)
  * [ Differences to ros_control (ROS1) ](../../../differences_to_ros1/differences_to_ros1.html)
  * [ Migration Guide to ros2_control ](../../../differences_to_ros1/differences_to_ros1.html#migration-guide-to-ros2-control)
  * [ Supported Robots ](../../../supported_robots/supported_robots.html)
  * [ Resources ](../../../resources/resources.html)
  * [ Contributing ](../../../contributing/contributing.html)


B  =  (  m  s  \+  ∑  i  =  1  n  (  m  i  )  )  r  ˜  s  _  q


####  2.4. Dynamics of the Space Robot


J  M  =  [  ρ  R  ,  1  k  1  ×  (  r  ee  −  r  1  )  …  ρ  R  ,  n  k  n  ×
(  r  ee  −  r  n  )  ρ  T  ,  1  k  1  …  ρ  T  ,  n  k  n  ]  ,  ρ  R  ,  i
=  1  for  rotational  joint  ,  0  otherwise  .  ρ  T  ,  i  =  1  for
translational  joint  ,  0  otherwise  .


T  =  G  θ  ˙  (  J  D  −  1  G  ee  e  p  −  θ  ˙  )


                jointHandlePosVel = hardware_interface::PosVelJointHandle(js_interface_.getHandle(joint_names_[j]), &joint_position_command_[j], &joint_velocity_command_[j]);
                pvj_interface_.registerHandle(jointHandlePosVel);
            }
            else
            {
                ROS_FATAL_STREAM_NAMED("default_robot_hw_sim","No matching hardware interface found for '"
                        << hardware_interface );
                return false;
            }


[ Skeleton_tracker working with kinect v2 ](/question/216752/skeleton_tracker-
working-with-kinect-v2/)


[ Give Feedback ](/feedback/send)


                case VELOCITY:
                    sim_joints_[j]->SetVelocity(0, e_stop_active_ ? 0 : joint_velocity_command_[j]);
                    break;


The impedance parameters,  M  d  ,  D  and  E  , do not need to be constants.
Their values may be varied over the course of the maneuver to the required
values. A useful case for varying the impedance is the following: during the
initial approach phase when the chaser satellite is closing in on the target
and moving the manipulator arm into the position of readiness to start the
final approach, the end effector’s inertia experienced by the rest of the
manipulator and base should be minimized. This would be achieved by fully
retracting the prismatic stage, e.g., by keeping **x** 0  at a value
corresponding to a fully retracted state, and setting the  M  d  ,  D  and  E
to very high impedance. The prismatic stage should then be extended by setting
new  x  0  and thus  λ  0  , to prepare it for being compressed after coming
into contact with the target. Shortly before the end effector comes into
contact with the target, the impedance parameters,  M  d  ,  D  and  E  ,
should be set to values suitable for the given target, e.g., using the virtual
mass impedance matching (VIM) method for mechanical impedance matching [  17
] or other methods, e.g., [  9  ]. Finally, once the positive gripping is
confirmed, the impedance can be further changed to meet the requirements of
post-capture activities, e.g., rigidizing it to bring the target and chaser
relative velocity to zero [  19  ], detumbling or docking.


The symbol **v** s  is the satellite base velocity,  ω  s  is its angular
velocity,  θ  ˙  is the vector of angular rates of the joint angles. The
position vector of the end effector in the inertial frame is determined by the
sum of positions of the links of the robot manipulator and the satellite
position:


Title / Keyword


θ  =  [  θ  1  …  θ  n  λ  ]  T  ,


M  d  =  [  19.25  0  0  0  0  0  0  0  19.25  0  0  0  0  0  0  0  19.25  0
0  0  0  0  0  0  10  0  0  0  0  0  0  0  10  0  0  0  0  0  0  0  10  0  0
0  0  0  0  0  10  ]


Font Type:


      * [ Palma, P. ](https://scholar.google.com/scholar?q=Piotr%20Palma)
      *       * [ Seweryn, K. ](https://scholar.google.com/scholar?q=Karol%20Seweryn)
      *       * [ Rybus, T. ](https://scholar.google.com/scholar?q=Tomasz%20Rybus)
      *     * on PubMed


[ [UUV Simulator] Including robot into a Gazebo world ](/question/19326/uuv-
simulator-including-robot-into-a-gazebo-world/)


>           - position
>
>         state_interfaces:
>           - position
>           - velocity
>
>         state_publish_rate: 50.0
>         action_monitor_rate: 20.0
>
>         allow_partial_joints_goal: false
>         open_loop_control: true
>         constraints:
>           stopped_velocity_tolerance: 0.01
>           goal_time: 0.0
>           joint1:
>             trajectory: 0.05
>             goal: 0.03
>
###  Preemption policy  [  1  ]  
Only one action goal can be active at any moment, or none if the topic
interface is used. Path and goal tolerances are checked only for the
trajectory segments of the active goal.
When an active action goal is preempted by another command coming from the
action interface, the goal is canceled and the client is notified. The
trajectory is replaced in a defined way, see [ trajectory replacement
](trajectory.html#joint-trajectory-controller-trajectory-replacement) .
Sending an empty trajectory message from the topic interface (not the action
interface) will override the current action goal and not abort the action.
###  Description of controller’s interfaces  
####  References  
(the controller is not yet implemented as chainable controller)
####  States  
The state interfaces are defined with ` joints  ` and ` state_interfaces  `
parameters as follows: ` <joint>/<state_interface> ` .
Legal combinations of state interfaces are given in section  Hardware
Interface Types  .
####  Commands  
There are two mechanisms for sending trajectories to the controller:
  * via action, see  actions
  * via topic, see  subscriber


                case EFFORT:
                {
                    const double effort = e_stop_active_ ? 0 : joint_effort_command_[j];
                    sim_joints_[j]->SetForce(0, effort);
                }
                    break;


[ Hi there! Please sign in ](/account/signin/?next=/question/29263/using-
prismatic-joint-in-gazebo/) [ help ](/help/ "help")


      * [ Palma, P. ](http://www.pubmed.gov/?cmd=Search&term=Piotr%20Palma)
      *       * [ Seweryn, K. ](http://www.pubmed.gov/?cmd=Search&term=Karol%20Seweryn)
      *       * [ Rybus, T. ](http://www.pubmed.gov/?cmd=Search&term=Tomasz%20Rybus)
      *
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For more information on the journal statistics, click [ here
](/journal/aerospace/stats) .


Impedance control [  4  ,  5  ,  6  ,  7  ,  8  ,  11  ,  22  ,  31  ] is a
paradigm which aims to achieve desired characteristics of the interaction
between the robot and its environment. It draws from the long-recognized
analogies between electrical and mechanical building blocks of dynamic systems
and became an important toolbox for modeling robotics interacting with
environments and humans, cooperative robotics, exoskeletons, etcetera.
Impedance describes the dynamic behavior of the system at its interaction port
with the environment which is the end effector in the case of most robotic
manipulators.


z: -0.5


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nsec: 250000000


No, it does not produce relative increments.


  return CallbackReturn::SUCCESS;
}


  // set flag, otherwise tolerances will be checked with success_trajectory_point too
  rt_is_holding_.writeFromNonRT(true);


The controller types are placed into namespaces according to their command
types for the hardware (see [ general introduction into controllers
](../../index.rst) ).


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gz sim -v 4 -r example.sdf


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</  joint  >


>
>  Similar thing with the efforts.
>  When looking at the /joint_states/effort[] values, they seem to be
> correctly clamped to the effort limit as specified in the URDF.
>  However, using only one revolute joint (the others fixed) this effort
> sometimes is already used up just to keep the joint at velocity 0.
>


</  axis  >


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  // Update new trajectory
  {
    preempt_active_goal();
    auto traj_msg =
      std::make_shared<trajectory_msgs::msg::JointTrajectory>(goal_handle->get_goal()->trajectory);


Jul 3, 2014, 2:56:00 PM  7/3/14


controller_interface::InterfaceConfiguration
JointTrajectoryController::command_interface_configuration() const
{
  controller_interface::InterfaceConfiguration conf;
  conf.type = controller_interface::interface_configuration_type::INDIVIDUAL;
  if (dof_ == 0)
  {
    fprintf(
      stderr,
      "During ros2_control interface configuration, degrees of freedom is not valid;"
      " it should be positive. Actual DOF is %zu\n",
      dof_);
    std::exit(EXIT_FAILURE);
  }
  conf.names.reserve(dof_ * params_.command_interfaces.size());
  for (const auto & joint_name : command_joint_names_)
  {
    for (const auto & interface_type : params_.command_interfaces)
    {
      conf.names.push_back(joint_name + "/" + interface_type);
    }
  }
  return conf;
}


Default values for tolerances if no explicit values are states in
JointTrajectory message.


Message data type: ` Double ` .


  traj_external_point_ptr_ = std::make_shared<Trajectory>();
  traj_msg_external_point_ptr_.writeFromNonRT(
    std::shared_ptr<trajectory_msgs::msg::JointTrajectory>());


  // Check that cancel request refers to currently active goal (if any)
  const auto active_goal = *rt_active_goal_.readFromNonRT();
  if (active_goal && active_goal->gh_ == goal_handle)
  {
    RCLCPP_INFO(
      get_node()->get_logger(), "Canceling active action goal because cancel callback received.");


< ixx  >0.0003358</  ixx  >


Report message


</  inertial  >


name: "j1"


</  model  >


      // have we reached the end, are not holding position, and is a timeout configured?
      // Check independently of other tolerances
      if (
        !before_last_point && *(rt_is_holding_.readFromRT()) == false && cmd_timeout_ > 0.0 &&
        time_difference > cmd_timeout_)
      {
        RCLCPP_WARN(get_node()->get_logger(), "Aborted due to command timeout");


< attenuation  >


Delete


Copy link


void JointTrajectoryController::compute_error_for_joint(
  JointTrajectoryPoint & error, const size_t index, const JointTrajectoryPoint & current,
  const JointTrajectoryPoint & desired) const
{
  // error defined as the difference between current and desired
  if (joints_angle_wraparound_[index])
  {
    // if desired, the shortest_angular_distance is calculated, i.e., the error is
    //  normalized between -pi<error<pi
    error.positions[index] =
      angles::shortest_angular_distance(current.positions[index], desired.positions[index]);
  }
  else
  {
    error.positions[index] = desired.positions[index] - current.positions[index];
  }
  if (
    has_velocity_state_interface_ &&
    (has_velocity_command_interface_ || has_effort_command_interface_))
  {
    error.velocities[index] = desired.velocities[index] - current.velocities[index];
  }
  if (has_acceleration_state_interface_ && has_acceleration_command_interface_)
  {
    error.accelerations[index] = desired.accelerations[index] - current.accelerations[index];
  }
}


< range  >1000</  range  >


< size  >0.25 0.1 0.05</  size  >


< collision  name  =  "RR_position_control_link1_collision_1"  >


< diffuse  >0.8 0 0 1</  diffuse  >


</  dynamics  >


</  plugin  >


position: 0.99999991907580654


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< child  > base_link  </  child  >


On Wed, Jul 2, 2014 at 10:18 PM,  < [ mfr...@vt.edu ]() > wrote:


  // action server configuration
  if (params_.allow_partial_joints_goal)
  {
    RCLCPP_INFO(logger, "Goals with partial set of joints are allowed");
  }


4) Now let's add the Gazebo JointController plugin to the SDF file. Add the
following line to your file just before the tag ` </model> ` .


< inertia  >


< direction  >-1 -1 -1</  direction  >


  for (size_t i = 0; i < trajectory.joint_names.size(); ++i)
  {
    const std::string & incoming_joint_name = trajectory.joint_names[i];


constraints.stopped_velocity_tolerance (double)


controller_interface::CallbackReturn JointTrajectoryController::on_deactivate(
  const rclcpp_lifecycle::State &)
{
  const auto active_goal = *rt_active_goal_.readFromNonRT();
  if (active_goal)
  {
    rt_has_pending_goal_.writeFromNonRT(false);
    auto action_res = std::make_shared<FollowJTrajAction::Result>();
    action_res->set__error_code(FollowJTrajAction::Result::INVALID_GOAL);
    action_res->set__error_string("Current goal cancelled during deactivate transition.");
    active_goal->setCanceled(action_res);
    rt_active_goal_.writeFromNonRT(RealtimeGoalHandlePtr());
  }


nsec: 750000000


< radius  >0.025</  radius  >


#  Gazebo Sim


unread,


Forward


< dynamics  >


< pose  >0.0 0.0 0.1 0 0 0</  pose  >


###  Adolfo Rodríguez Tsouroukdissian


< ambient  >0.5 0 0 1</  ambient  >


Message data type: ` Double `


< radius  >0.01</  radius  >


Sorry for the late response Adolfo,

First of all thanks for the feedback. I guess what my main concern is how can
I extract the velocity data being sent through the trajectory msg? I started
digging around and came to the conclusion that I dont fully understand the
difference between "effort_controllers/JointTrajectoryController" and
"position_controllers/JointTrajectoryController".

At first I thought "effort_controllers/JointTrajectoryController" was giving
me the relative position to which my joint should move to. It did this by
connecting and registering a "hardware_interface::EffortJointInterface
jnt_pos_interface" object to a array named cmd[ ] (This is all from this
tutorial). The cmd array had only one value for each joint, that being the
relative position. Adolfo am I correct in assuming that? Or is the value being
sent something different?

If I am correct in my assumption from above what is
"position_controllers/JointTrajectoryController" for (I havent tried to use
this controller yet)?

Also I was wondering does "effort_controllers/JointTrajectoryController" use
joint_position_controller.cpp located in
ros_controllers/effort_controllers/src directory? If so does the cmd [ ]
(mentioned above) use the setCommand() function to get its target position
data?

Finally I just wanted to know if I could use
"effort_controllers/JointTrajectoryController" and some how grab the velocity
values coming from the trajectory msg from moveit using it?

Mike


Action server for commanding the controller.


</  joint  >


to ros-sig-ro...@googlegroups.com, felixm...@gmail.com, mfr...@vt.edu,
adolfo.r...@pal-robotics.com


      // Check state/goal tolerance
      for (size_t index = 0; index < dof_; ++index)
      {
        compute_error_for_joint(state_error_, index, state_current_, state_desired_);


< geometry  >


##  Other features  


< mass  >0.1</  mass  >


Either email addresses are anonymous for this group or you need the view
member email addresses permission to view the original message


void JointTrajectoryController::query_state_service(
  const std::shared_ptr<control_msgs::srv::QueryTrajectoryState::Request> request,
  std::shared_ptr<control_msgs::srv::QueryTrajectoryState::Response> response)
{
  const auto logger = get_node()->get_logger();
  // Preconditions
  if (get_state().id() != lifecycle_msgs::msg::State::PRIMARY_STATE_ACTIVE)
  {
    RCLCPP_ERROR(logger, "Can't sample trajectory. Controller is not active.");
    response->success = false;
    return;
  }
  const auto active_goal = *rt_active_goal_.readFromRT();
  response->name = params_.joints;
  trajectory_msgs::msg::JointTrajectoryPoint state_requested = state_current_;
  if (has_active_trajectory())
  {
    TrajectoryPointConstIter start_segment_itr, end_segment_itr;
    response->success = traj_external_point_ptr_->sample(
      static_cast<rclcpp::Time>(request->time), interpolation_method_, state_requested,
      start_segment_itr, end_segment_itr);
    // If the requested sample time precedes the trajectory finish time respond as failure
    if (response->success)
    {
      if (end_segment_itr == traj_external_point_ptr_->end())
      {
        RCLCPP_ERROR(logger, "Requested sample time precedes the current trajectory end time.");
        response->success = false;
      }
    }
    else
    {
      RCLCPP_ERROR(
        logger, "Requested sample time is earlier than the current trajectory start time.");
    }
  }
  else
  {
    RCLCPP_ERROR(logger, "Currently there is no valid trajectory instance.");
    response->success = false;


< size  >0.5 0.5 0.01</  size  >


![@christophfroehlich](https://avatars.githubusercontent.com/u/3367244?s=80&u=98db36351213b952b1c6ce663c1fde4108272539&v=4)
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###
**[ christophfroehlich ](/christophfroehlich) ** commented  Aug 24, 2023
Do you use the topic or action interface? In case of the latter, do you get a
success action result?

---

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**[ christophfroehlich ](/christophfroehlich) ** commented  Aug 29, 2023
[ @BarisYazici ](https://github.com/BarisYazici) do you have a public repo
with which I could try your setup?

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###
**[ BarisYazici ](/BarisYazici) ** commented  Aug 29, 2023  •
edited
yes, here is the launch file I used to try JTC - [
https://github.com/frankaemika/franka_ros2/blob/humble/franka_moveit_config/launch/moveit.launch.py
](https://github.com/frankaemika/franka_ros2/blob/humble/franka_moveit_config/launch/moveit.launch.py)
. All settings are default. I removed the old JTC in our repo and added the
one in humble branch from ros2_controllers. Devcontainer in the repo should
reflect my setup.


Sign in to reply to author


The initial velocity is set to 1.0 rad/s.


Delete


unread,


orientation {


Report message


xyz {


< position_i_max  >1</  position_i_max  >


sec: 0


</  plugin  >


[ Conversations  ](./g/ros-sig-robot-control)


Replace the velocity mode plugin mentioned above with the following lines in
the SDF file for force mode.


bool JointTrajectoryController::validate_trajectory_point_field(
  size_t joint_names_size, const std::vector<double> & vector_field,
  const std::string & string_for_vector_field, size_t i, bool allow_empty) const
{
  if (allow_empty && vector_field.empty())
  {
    return true;
  }
  if (joint_names_size != vector_field.size())
  {
    RCLCPP_ERROR(
      get_node()->get_logger(),
      "Mismatch between joint_names size (%zu) and %s (%zu) at point #%zu.", joint_names_size,
      string_for_vector_field.c_str(), vector_field.size(), i);
    return false;
  }
  return true;
}


< inertial  >


![](JointPositionController.gif)


< specular  >0.8 0.8 0.8 1</  specular  >


Sign in to forward


Allow joint goals defining trajectory for only some joints.


1) Replace the JointController plugin with the JointPositionController plugin
in SDF file.


</  geometry  >


  for (const auto & pid : pids_)
  {
    if (pid)
    {
      pid->reset();
    }
  }


< child  > RR_position_control_link0  </  child  >


[ Previous ](../../forward_command_controller/doc/userdoc.html
"forward_command_controller") [ Next
](../../position_controllers/doc/userdoc.html "position_controllers")


  if (!params_.allow_nonzero_velocity_at_trajectory_end)
  {
    for (size_t i = 0; i < trajectory.points.back().velocities.size(); ++i)
    {
      if (fabs(trajectory.points.back().velocities.at(i)) > std::numeric_limits<float>::epsilon())
      {
        RCLCPP_ERROR(
          get_node()->get_logger(),
          "Velocity of last trajectory point of joint %s is not zero: %.15f",
          trajectory.joint_names.at(i).c_str(), trajectory.points.back().velocities.at(i));
        return false;
      }
    }
  }


            traj_msg_external_point_ptr_.reset();
            traj_msg_external_point_ptr_.initRT(set_success_trajectory_point());
          }
          else if (!within_goal_time)
          {
            const std::string error_string = "Aborted due to goal_time_tolerance exceeding by " +
                                             std::to_string(time_difference) + " seconds";


##  Trajectory representation  


Delete


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Topic for commanding the controller.


Publish-rate of the controller’s “state” topic.


filename  =  "gz-sim-joint-position-controller-system"


child: "rotor"


< cast_shadows  > true  </  cast_shadows  >


[ About  ](./g/ros-sig-robot-control/about)


<?  xml  version  =  "1.0"


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  // order all joints in the storage
  for (const auto & interface : params_.command_interfaces)
  {
    auto it =
      std::find(allowed_interface_types_.begin(), allowed_interface_types_.end(), interface);
    auto index = std::distance(allowed_interface_types_.begin(), it);
    if (!controller_interface::get_ordered_interfaces(
          command_interfaces_, command_joint_names_, interface, joint_command_interface_[index]))
    {
      RCLCPP_ERROR(
        get_node()->get_logger(), "Expected %zu '%s' command interfaces, got %zu.", dof_,
        interface.c_str(), joint_command_interface_[index].size());
      return CallbackReturn::ERROR;
    }
  }
  for (const auto & interface : params_.state_interfaces)
  {
    auto it =
      std::find(allowed_interface_types_.begin(), allowed_interface_types_.end(), interface);
    auto index = std::distance(allowed_interface_types_.begin(), it);
    if (!controller_interface::get_ordered_interfaces(
          state_interfaces_, params_.joints, interface, joint_state_interface_[index]))
    {
      RCLCPP_ERROR(
        get_node()->get_logger(), "Expected %zu '%s' state interfaces, got %zu.", dof_,
        interface.c_str(), joint_state_interface_[index].size());
      return CallbackReturn::ERROR;
    }
  }


All the parameters related to this controller can be found [ here
](classgz_1_1sim_1_1systems_1_1JointPositionController.html) .


Report message


</  collision  >


pose {


---

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](/firesurfer) [ firesurfer ](/firesurfer) mentioned this pull request  Aug
29, 2023
[ [JTC] set_hold_position results into not exactly reaching desired target
#759  ](/ros-controls/ros2_controllers/issues/759)
Closed
[ christophfroehlich ](/christophfroehlich) added a commit to
christophfroehlich/ros2_controllers that referenced this pull request  Aug 31,
2023
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` [ [JTC] Explicitly set hold position (
](/christophfroehlich/ros2_controllers/commit/f5f8d27c11722a0bd5e94f98f0c2b64c2cce0323
"\[JTC\] Explicitly set hold position \(#558\)") [ ros-controls#558
](https://github.com/ros-controls/ros2_controllers/pull/558) [ )
](/christophfroehlich/ros2_controllers/commit/f5f8d27c11722a0bd5e94f98f0c2b64c2cce0323
"\[JTC\] Explicitly set hold position \(#558\)") `
` [ f5f8d27
](/christophfroehlich/ros2_controllers/commit/f5f8d27c11722a0bd5e94f98f0c2b64c2cce0323)
`
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**[ christophfroehlich ](/christophfroehlich) ** commented  Aug 31, 2023
> yes, here is the launch file I used to try JTC - [
> https://github.com/frankaemika/franka_ros2/blob/humble/franka_moveit_config/launch/moveit.launch.py
> ](https://github.com/frankaemika/franka_ros2/blob/humble/franka_moveit_config/launch/moveit.launch.py)
> . All settings are default. I removed the old JTC in our repo and added the
> one in humble branch from ros2_controllers. Devcontainer in the repo should
> reflect my setup.
This PR hasn't been backported to humble yet, which means you were still


Training


![Felix Meßmer's profile photo](//lh3.googleusercontent.com/a-/ALV-UjXo2aXfAk-
du0bo7Rk6_qcY5MZE8BRzAtLvSi33j1VJUTXvhQ=s40-c)


For this let's use the previously discussed SDF file.


< parent  > world  </  parent  >


> To unsubscribe from this group and stop receiving emails from it, send an
> email to [ ros-sig-robot-co...@googlegroups.com ]() .


</  plane  >


joint {


###  Example usage:


Sign in to report message


< diffuse  >0.8 0.8 0.8 1</  diffuse  >


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< sdf  version  =  "1.6"  >


Yes, it's a single-joint controller.


  RCLCPP_INFO(
    logger, "Action status changes will be monitored at %.2f Hz.", params_.action_monitor_rate);
  action_monitor_period_ = rclcpp::Duration::from_seconds(1.0 / params_.action_monitor_rate);


points {


3) Checking joint state.


![mfr...@vt.edu's profile photo](//lh3.googleusercontent.com/a-/ALV-
UjXLZw18gFzZHa2C4A0mrLpZ13blWBOpMeCRZ4tYXUaxAYg45w=s40-c)


Supporting velocity-controlled joints implies implementing a new
specialization for the HardwareInterfaceAdapter class. Only this file needs to
be touched:

[ https://github.com/ros-controls/ros_controllers/blob/indigo-
devel/joint_trajectory_controller/include/joint_trajectory_controller/hardware_interface_adapter.h
](https://github.com/ros-controls/ros_controllers/blob/indigo-
devel/joint_trajectory_controller/include/joint_trajectory_controller/hardware_interface_adapter.h)


Report message


> How exactly is the effort value calculated?
>


>
>  At first I thought "effort_controllers/JointTrajectoryController" was
> giving me the relative position to which my joint should move to.


< sphere  >


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Jump to bottom
#  [JTC] Explicitly set hold position  #558
Merged
[ bmagyar ](/bmagyar) merged 65 commits into  [ ros-controls  :  master
](/ros-controls/ros2_controllers/tree/master "ros-
controls/ros2_controllers:master") from  [ christophfroehlich  :
jtc_hold_position
](/christophfroehlich/ros2_controllers/tree/jtc_hold_position
"christophfroehlich/ros2_controllers:jtc_hold_position") Aug 15, 2023
Merged
#  [JTC] Explicitly set hold position  #558
[ bmagyar ](/bmagyar) merged 65 commits into  [ ros-controls  :  master


< initial_position  >-1.5708</  initial_position  >


< i_gain  >0.01</  i_gain  >


Reply to author


No, "effort_controllers/JointTrajectoryController" does not depend on the
"effort_controllers" package. What lead you to believe this?. You can verify
dependencies of a package by using rospack:

rospack depends joint_trajectory_controller | grep effort_controllers #
returns an empty list


  // Set smartpointer to expire for create_wall_timer to delete previous entry from timer list
  goal_handle_timer_.reset();


positions: -0.7854


< visual  name  =  "RR_position_control_link0_visual_0"  >


< position_cmd_max  >10</  position_cmd_max  >


z: -0.5


</  visual  >


  // Assign values from the hardware
  // Position states always exist
  assign_point_from_interface(state.positions, joint_state_interface_[0]);
  // velocity and acceleration states are optional
  if (has_velocity_state_interface_)
  {
    assign_point_from_interface(state.velocities, joint_state_interface_[1]);
    // Acceleration is used only in combination with velocity
    if (has_acceleration_state_interface_)
    {
      assign_point_from_interface(state.accelerations, joint_state_interface_[2]);
    }
    else
    {
      // Make empty so the property is ignored during interpolation
      state.accelerations.clear();
    }
  }
  else
  {
    // Make empty so the property is ignored during interpolation
    state.velocities.clear();
    state.accelerations.clear();
  }
}


JointTrajectoryController letsâs user specify the required position,
velocity, and effort with respect to time. For velocity and position, this
controller uses a PID controller.


          if (default_tolerances_.goal_time_tolerance != 0.0)
          {
            if (time_difference > default_tolerances_.goal_time_tolerance)
            {
              within_goal_time = false;
              // print once, goal will be aborted afterwards
              check_state_tolerance_per_joint(
                state_error_, index, default_tolerances_.goal_state_tolerance[index],
                true /* show_errors */);
            }
          }
        }
      }


Delete


Jul 14, 2014, 4:01:10 PM  7/14/14


orientation {


< geometry  >


      // set values for next hardware write() if tolerance is met
      if (!tolerance_violated_while_moving && within_goal_time)
      {
        if (use_closed_loop_pid_adapter_)
        {
          // Update PIDs
          for (auto i = 0ul; i < dof_; ++i)
          {
            tmp_command_[i] = (state_desired_.velocities[i] * ff_velocity_scale_[i]) +
                              pids_[i]->computeCommand(
                                state_error_.positions[i], state_error_.velocities[i],
                                (uint64_t)period.nanoseconds());
          }
        }


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</  attenuation  >


###  Example usage:


controller_interface::CallbackReturn JointTrajectoryController::on_error(
  const rclcpp_lifecycle::State &)
{
  if (!reset())
  {
    return CallbackReturn::ERROR;
  }
  return CallbackReturn::SUCCESS;
}


to ros-sig-ro...@googlegroups.com, mfr...@vt.edu


</  inertia  >


Jul 3, 2014, 4:18:02 AM  7/3/14


< constant  >0.9</  constant  >


    // Mark the current goal as canceled
    rt_has_pending_goal_.writeFromNonRT(false);
    auto action_res = std::make_shared<FollowJTrajAction::Result>();
    active_goal->setCanceled(action_res);
    rt_active_goal_.writeFromNonRT(RealtimeGoalHandlePtr());


  query_state_srv_ = get_node()->create_service<control_msgs::srv::QueryTrajectoryState>(
    std::string(get_node()->get_name()) + "/query_state",
    std::bind(&JointTrajectoryController::query_state_service, this, _1, _2));


> Any counter-arguments against removing this tag from the URDF?
>


gz topic -e -t "/model/RR_position_control/joint_trajectory_progress"


4,776 views


      if (active_goal)
      {
        // send feedback
        auto feedback = std::make_shared<FollowJTrajAction::Feedback>();
        feedback->header.stamp = time;
        feedback->joint_names = params_.joints;


< ixy  >0</  ixy  >


The commanded velocity(cmd_vel) can be published or subscribed at the topic: `
/model/<model_name>/joint/<joint_name>/cmd_vel ` by default.


  return has_values;
}


  if (!validate_trajectory_msg(goal->trajectory))
  {
    return rclcpp_action::GoalResponse::REJECT;
  }


mkdir gz_tutorial


command_interface (list(string)):


< specular  >0.8 0 0 1</  specular  >


###  Example usage


An example where p_gain was set to 2.0 and the joint controller failed to
reach the desired velocity and behaved absurdly due to improper gains is shown
below.


###  Adolfo Rodríguez Tsouroukdissian


< link  name  =  "RR_position_control_link0"  >


< topic  > topic_name  </  topic  >


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</  link  >


name: "j1"


  auto assign_point_from_interface =
    [&](std::vector<double> & trajectory_point_interface, const auto & joint_interface)
  {
    for (size_t index = 0; index < dof_; ++index)
    {
      trajectory_point_interface[index] = joint_interface[index].get().get_value();
    }
  };


parent: "base_link"


Copy link


< ixy  >0</  ixy  >


< box  >


The generic version of Joint Trajectory controller is implemented in this
package. A yaml file for using it could be:


  if (params_.command_interfaces.empty())
  {
    RCLCPP_ERROR(logger, "'command_interfaces' parameter is empty.");
    return CallbackReturn::FAILURE;
  }


<!-- Illumination -->