Inverse dynamics

Computation of the system inverse dynamics. It computes the required forces and torques in the actuated joints to follow a given motion. For more information, see Robotran theoretical framework.

Code sample

For running the inverse dynamics, in the current configuration, insert the following code in your main script and adapt it to your need:

mbs_data.process = 6
mbs_invdyn = MBsysPy.MbsInvdyn(mbs_data)
mbs_invdyn.set_options(motion = "oneshot")
mbs_invdyn.run()

You can compute the inverse dynamics for a time-define trajectory by providing the trajectory files as follow:

# Set all driven joint as independent
mbs_data.set_qu(mbs_data.qc[1:].tolist())

mbs_data.process = 6
mbs_invdyn = MBsysPy.MbsInvdyn(mbs_data)

# Set the motion to be solved as a trajectory
mbs_invdyn.set_options(motion = "trajectory")

# Provide the trajectory files to use
mbs_invdyn.set_options(trajectoryqname = "../resultsR/inverse_kinematics_q.res",
                       trajectoryqdname = "../resultsR/inverse_kinematics_qd.res",
                       trajectoryqddname = "../resultsR/inverse_kinematics_qdd.res")

# Provide the time interval and time step to solve the inverse dynamics.
mbs_invdyn.set_options(t0 = 0.0, tf = 6.0, dt = 1e-3)
# The final time "tf' must be less than the last time of the trajectory files.

mbs_invdyn.run()

In all cases the analysis requires actuated joint, see next section to set them.

Use

The inverse dynamics computation is requires an instance of MbsInvdyn. Then the analysis is performed by calling the function MbsInvdyn.run().

The options of the module are set with the function MbsInvdyn.set_options().

The force and torques are computed on the actuated joints (see Robotran theoretical framework). A joint is (de)selected as actuated with the function MbsData.set_qa() (resp. MbsData.unset_qa()).

Requirements on the system

The system either:

• contains independent joints:

  • The driven joints cannot be actuated;

  • The independent and dependent joint can be actuated;

  • The number of actuated joint must be equal or greather (over-actuated) than the number of independent joints.

• does not contain any independent joints:

  • The driven joints must be actuated;

  • The dependent joints cannot be actuated