screwmpcpy 0.4.1

Dual Quaternion based MPC generating screw motion for n-DOF robot arm.

screwmpcpy

Generate smooth motions for a n-DOF robot arm end effector using Dual Quaternions while enforcing velocity-, acceleration- and jerk constraints. The package includes a base optimization scheme and a base motion generator, which can be easily extended for custom robot arms. A motion generator for the Franka Emika Panda robot is included.

Install

The package is available in PyPI, you can install it via pip:

pip install screwmpcpy

Getting started

The motion generators yield velocity commands for an n-DoF robot arm. For the basic usage have a look at examples/motiongenerator.py. You can also use the dual quaternions to generate waypoints. Check it out the example for the panda robot at examples/panda_screwmotion_ik.py. To install the required package dependencies execute pip install screwmpcpy[examples]. You can find advanced usage examples here. We include two generators for the panda robot:
The basic screw motion generator and a modified variant, which includes manipulability maximization from [1].

Extending the available robots

You can easily extend the base class by adding your custom robot arm. Ensure the forward kinematics of your robot are available.
Create a new file your_robot_mg.py in folder src/screwmpc.py.

Custom robot example

from dqrobotics import DQ
from .basemg import BaseMotionGenerator
from .screwmpc import BOUND


class YourRobotMotionGenerator(BaseMotionGenerator):

    def __init__(
                self,
                n_p: int,
                n_c: int,
                q_mpc: float,
                r_mpc: float,
                lu_bound_vel: BOUND,
                lu_bound_acc: BOUND,
                lu_bound_jerk: BOUND,
                ) -> None:
        super().__init__(
            n_p, n_c, q_mpc, r_mpc, lu_bound_vel, lu_bound_acc, lu_bound_jerk
        )
        # custom attributes here
        self._kin = YourRobotKinematics()

    def step(self, q_robot: np.ndarray, goal: DQ) -> np.ndarray:

        # Initialize Dual Quaternion with 6D pose
        x_current = DQ(self._kin.your_forward_kinematics(q_robot))
        error, smooth_traj = super()._step(x_current, goal)
        # calculate commanded dq here
        ...
        return dq

References

[1] Haviland, J., & Corke, P. (2020). A Purely-Reactive Manipulability-Maximising Motion Controller. ArXiv. /abs/2002.11901