Inverse Kinematics

Inverse Kinematics and Dynamics

Inverse Kinematics

Given marker information, Toolkit is able to perform inverse kinematics to estimate the joint angle. An set of example files can be found in examples/jumping. To load the Lua model and the marker file into rbdl-toolkit, the command is rbdl-toolkit --model model_deLeva_reduced_meshes_updated.lua --motionmarker pendulum.csv.

To perform IK, the model file must contain a set of model marker data, which tells rbdl where the markers are expected to be, denoted as the marker parameter in this example.

  name   = "Shank_R",
  parent = "Thigh_R",
  visuals = {{
    src  = "meshes/shank.obj",
    dimensions  =    { 0.09620384090780759, 0.09620384090780759, 0.5772230454468454,},
    mesh_center =    { 0.0, 0.0, -0.24050960226951895,},
    color       =    { 0.2, 0.7, 0.3,},
    },},
  joint_frame = {
    r =    { 0.0, 0.0, -0.49261621870323574,},
    E = 
      {{ 1.0, 0.0, 0.0,},
       { 0.0, 1.0, 0.0,},
       { 0.0, 0.0, 1.0,},},
  },
  body = {
    mass = 3.8835180205509205,
    com =    { 0.0, 0.0, -0.21140794039490715,},
    inertia = 
      {{ 0.05661057932661182, 0.0, 0.0,},
       { 0.0, 0.054377641918846385, 0.0,},
       { 0.0, 0.0, 0.009348684422692806,},},
  },
  markers = {
    R_FAX =  { 0.0, -0.051740928075740725, -0.047799526307102866,},
    R_TTC =  { 0.044597633995881035, 0.0, -0.10467188566080729,},
    R_FAL =  { 0.0, -0.04605324082023483, -0.4766302737782796,},
    R_TAM =  { 0.0, 0.04605324082023483, -0.46825823322041826,},
  },

RBDL uses Levenberg Marquardt least squares to perform this fit, and require the adjustment of the IK lambda (damping factor on the fit), max_step (max number of iteration per frame), and tol (step tolerance per iteration)