The robot_model library is a wrapper for the Pinocchio library, used
to compute dynamics model of a robot.
It is specifically designed to work seamlessly with the state_representation library, offering conversion functions
between the states and input/output needed for pinocchio.
The library offers a single class Model that encapsulates most of the functionalities from pinocchio, as well
as extra functions.
A Model is defined by a robot name, and initialized from a URDF description file of the robot.
robot_model::Model model("myrobot", "path/to/urdf/myrobot.urdf")At creation, it uses the parser from pinocchio to read the URDF file and fill the needed parameters for computation.
Most common robotics functionalities are implemented such forward_kinematics, inverse_kinematics,
forward_velocity, inverse_velocity`, ...
// forward kinematics: pose of end-effector frame from the robot joint positions
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
state_representation::CartesianPose pose = model.forward_kinematics(jp);
// inverse kinematics: joint positions from end-effector pose
state_representation::CartesianPose cp = state_representation::CartesianPose::Random("eef");
state_representation::JointPositions jp = model.inverse_kinematics(cp);
// forward velocity kinematics: twist of end-effector frame from the robot joint velocities and positions
state_representation::JointState js = state_representation::JointState::Random("myrobot", 7);
state_representation::CartesianTwist twist = model.forward_velocity(js);
// inverse velocity kinematics: joint velocities from end-effector twist and current state of the robot
state_representation::CartesianTwist ct = state_representation::CartesianTwist::Random("eef");
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
state_representation::JointVelocities jv = model.inverse_velocity(ct, jp);All of those functions check for inconsistencies between the model and the inputs (incompatibility of joints, frame non existent in the robot model, ...). Thus, they can be called on other frames than the end-effector (which is the default value), or even vector of frames for bulk operations.
// pose of multiple robot frames from the robot joint positions
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
auto poses = model.forward_kinematics(jp, std::vector<std::string>{"joint2", "eef_link"});The Jacobian of the robot can also be computed and stored in the state_representation::Jacobian wrapper:
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
state_representation::Jacobian = model.compute_jacobian(jp);It can also be computed on lower frames than the end-effector, returning then a subset of the matrix, where non used joints are filled with 0 values.
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
state_representation::Jacobian = model.compute_jacobian(jp, "joint3");Dynamic modeling of the robot is available within pinocchio and allows the computation of the gravity, coriolis, and
inertia torques as well as their matrix counterpart.
// inertia matrix from joint positions
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
Eigen::MatrixXd inertia = model.compute_inertia_matrix(jp);
// inertia torques, equivalent to inertia multiplied by joint accelerations. The joint positions part of the state
// is used to compute the inertia matrix
state_representation::JointState js = state_representation::JointState::Random("myrobot", 7);
state_representation::JointTorques inertia_t = model.compute_inertia_torques(js);
// coriolis matrix from joint positions and velocities
state_representation::JointState js = state_representation::JointState::Random("myrobot", 7);
Eigen::MatrixXd coriolis = model.compute_coriolis_matrix(js);
// coriolis torques, equivalent to coriolis multiplied by joint velocities. The joint positions part of the state
// is used to compute the coriolis matrix
state_representation::JointState js = state_representation::JointState::Random("myrobot", 7);
state_representation::JointTorques coriolis_t = model.compute_coriolis_torques(js);
// gravity torques from joint positions
state_representation::JointPositions jp = state_representation::JointPositions::Random("myrobot", 7);
state_representation::JointTorques gravity_t = model.compute_gravity_torques(jp);